i

Materials Science and

Engineering Laboratory

FY 2004 Programs and

Accomplishments

MSEL Materials

for Micro- and

Optoelectronics

Eric K. Lin

Leader, Electronics Materials Group

Polymers Division

NISTIR 7129

January 2005

National Institute of

Standards and Technology

Arden L. Bement, Jr.

Director

Technology

Administration

Phillip J. Bond

Undersecretary of

Commerce for Technology

U.S. Department

of Commerce

Donald L. Evans

Secretary
ii

Certain commercial entities, equipment, or materials may be identified in this document

in order to describe an experimental procedure or concept adequately. Such identification

is not intended to imply recommendation or endorsement by the National Institute of

Standards and Technology, nor is it intended to imply that the entities, materials,

or equipment are necessarily the best available for the purpose.
iii

Table of Contents

Table of Contents

Executive Summary ............................................................................................... 1

Technical Highlights .............................................................................................. 3

First-Principles Studies of Technologically Important Dielectric Materials ...................... 4

Anomalous Elastic Behavior for SrTiO3 Thin Films

Grown on Si(001) Observed by X-ray Diffraction ........................................................ 6

Profiling the Photoresist-Liquid Interface: Fundamentals

for Immersion Lithography and Polymer Dissolution ..................................................... 8

On-Chip Interconnects: Extending Performance of Sub-100 nm Lines ....................... 10

Dielectric Metrology and Test Methods Supporting

Embedded Passive Device Technology ...................................................................... 12

Friction Scaling Artifact ............................................................................................ 14

Grand Challenges in Nanomagnetics: High Coercivity FePt

Alloys for Future Perpendicular Magnetic Data Storage ............................................. 16

Breakthroughs in Magnetic Refrigeration ................................................................... 18

Quantitative Nanomechanical Properties ................................................................... 20

Data and Standards Resources ................................................................................ 22

Projects in Materials for Micro- and Optoelectronics ...........................................25

Microelectronics

Combinatorial Tools for Materials Science ................................................................. 26

Spectroscopy, Diffraction, and Imaging of Electronic Materials ................................... 27

Phase Equilibria and Properties of Dielectric Ceramics .............................................. 28

Theory and Modeling of Dielectric Materials ............................................................. 29

Polymer Photoresists for Next-Generation Nanolithography ........................................ 30

Nanoimprint Lithography ......................................................................................... 31

Characterization of Porous Low-k Dielectric Constant Thin Films ............................... 32

Physical Properties of Thin Films and Nanostructures:

Nanoporous Low-k Dielectric Films .......................................................................... 33

Micrometer-Scale Reliability: Chip-Level Interconnects .............................................. 34

Electrical Properties of On-Chip Interconnections ...................................................... 35

Electronic Packaging and Components: Packaging Reliability .................................... 36

Electronic Packaging and Components: Acoustic Characterization ............................. 37

Lead-Free Surface Finishes: Sn Whisker Growth .................................................... 38

Lead-Free Solders and Solderability ........................................................................ 39

Micrometer-Scale Reliability: Solder Reliability .......................................................... 40

Micrometer-Scale Reliability: Mechanical Behavior of Thin Films ............................... 41

Physical Properties of Thin Films and Nanostructures:

Grain Size Effects on Actuator Fatigue ...................................................................... 42
iv

Table of Contents

Experimental and Theoretical Influence of Thin Film Texture

on Ferroelectric Hysteresis ....................................................................................... 43

Organic Electronics .................................................................................................. 44

Optoelectronics

Combinatorial/Phase Diagram Approach for

Metallization to Wide-Band-Gap Semiconductors ..................................................... 45

Metrology and Standards for Optoelectronic Materials ............................................... 46

Magnetic Materials

Nanomagnetodynamics ............................................................................................ 47

Electrodeposited Pt1–x (Fe,Co,Ni)x Alloys ................................................................. 48

Novel Magnetic Materials for Sensors and Ultra-High Density Data Storage ............... 49

Discovery of Spin Density Waves in a Ferromagnet: Fe-Al ........................................ 50

Micrometer-Scale Reliability: Dynamic Imaging of Magnetic Domain Walls ................. 51

Nanotribology and Surface Properties ....................................................................... 52

Related and Cross-Cutting Projects

Nanoscale Characterization by Electron Microscopy ................................................... 53

Metrology for Nanoscale Properties: X-ray Methods ................................................. 54

Metrology for Nanoscale Properties: Brillouin Light Scattering .................................. 55

Nanostructure Fabrication Processes: Thin Film Stress Measurements ...................... 56

Nanomechanics: Coupling Modeling with Experiments .............................................. 57

Physical Properties of Thin Films and Nanostructures:

Green’s-Function Methods ....................................................................................... 58

Micrometer-Scale Reliability: Bridging Length Scales ................................................ 59

Micrometer-Scale Reliability: Molecular Dynamics ..................................................... 60

Mechanical Metrology for Small-Scale Structures ...................................................... 61

Nanoindentation Methods and Standards ................................................................. 62

Nanostructure Fabrication Processes:

Patterned Electrodeposition by Surfactant-Mediated Growth ..................................... 63

Chemistry and Structure of Nanomaterials ................................................................ 64

Thermochemistry and Metrology of Interfacial Interactions ......................................... 65

Phase Relations of High Tc Superconductors ............................................................. 66

NIST Combinatorial Methods Center (NCMC)

Pioneer and Partner in Accelerated Materials Research ............................................. 67

Organizational Charts ..........................................................................................68
1

Executive Summary

Executive Summary

Introduction

The U.S. electronics industry faces strong

international competition in the manufacture of

smaller, faster, more functional, and more reliable

products. Many critical challenges facing the industry

require the continual development of advanced

materials and processes. The NIST Materials Science

and Engineering Laboratory (MSEL) works closely

with U.S. industry covering a broad spectrum of

sectors including semiconductor manufacturing, device

components, packaging, data storage, and assembly,

as well as complementary and emerging areas such as

optoelectronics and organic electronics.

MSEL has a multidivisional approach, committed to

addressing the most critical materials measurement and

standards issues for electronic materials. Our vision is

to be the key resource within the Federal Government

for materials metrology development for commercial

microelectronics manufacturing and will be realized

through the following objectives:

■ Develop and deliver standard measurements and

data;

■ Develop advanced measurement methods needed

by industry to address new problems that arise with

the development of new materials;

■ Develop and apply in situ as well as real-time,

factory floor measurements, for materials and devices

having micrometer- to nanometer-scale dimensions;

■ Develop combinatorial material methodologies for

the rapid optimization of industrially important

electronic materials;

■ Quantify and provide the fundamental understanding

of the divergence of thin film and nanoscale material

properties from their bulk values;

■ Provide the fundamental understanding of materials

needed for future nanoelectronic devices, including

first principles modeling of such materials.

The NIST/MSEL program consists of projects led

by the Metallurgy, Polymers, Materials Reliability,

and Ceramics Divisions. These projects are

conducted in collaboration with partners from

industrial consortia (e.g., International SEMATECH),

individual companies, academia, and other government

agencies. The program is strongly coupled with other

microelectronics programs within the government such

as the National Semiconductor Metrology Program

(NSMP). Materials metrology needs are also identified

through the International Technology Roadmap for

Semiconductors (ITRS), the IPC Lead-free Solder

Roadmap, the National Electronics Manufacturing

Initiative (NEMI) Roadmap, the Opto-electronics

Industry Development Association (OIDA) Roadmap,

IPC (the International Packaging Consortium), and

the National [Magnetic Data] Storage Industry

Consortium (NSIC) Roadmap.

The present report describes the major technical

activities and accomplishments in the area of Materials

for Micro- and Optoelectronics within MSEL in

FY2004 (October 2003 through September 2004).

In this report, we have tried to provide insight into

how MSEL research programs meet the needs of our

customers, how MSEL capabilities are being used to

solve problems important to the national economy and

the materials metrology infrastructure, and how MSEL

interacts with its customers to establish new priorities

and programs. Feedback and suggestions on how

we can better serve the needs of our customers

and encourage increasing collaboration to this end

are welcomed.

Mission

Our mission is to provide critical leadership in the

development of measurement methods and standards,

as well as fundamental understanding of materials

behavior needed by the U.S. microelectronics and

optoelectronics industries to remain competitive in

the changing global marketplace. As an essential

part of this mission, we are responsible not only for

developing new measurement methods with broad

applicability across micro- and optoelectronics

classes and industries, but also for working with

individual industry groups to develop and integrate

measurements, standards, software tools, and

evaluated data for specific, technologically

important applications.

Establishing Priorities

In the development of this technical program, a

wide range of research opportunities is first examined.

Choices for the research portfolio are based on

several criteria: the match to the NIST mission,

the magnitude and immediacy of industrial need,

the degree to which NIST’s contribution is critical

for success, the anticipated impact relative to the

investment, ability to respond in a timely fashion with

high-quality output, and the opportunity to advance

mission-oriented science. This requires that MSEL

establish its research priorities through extensive

consultation and collaboration with customers in U.S.

industry and with counterparts in the international

metrology community using a variety of methods
2

Executive Summary

including workshops, technical meetings, standards

committee participation, and individual consultation

with our customers. Materials metrology needs are

also identified through industry groups and roadmaps,

including the International Technology Roadmap for

Semiconductors (ITRS), the IPC Lead-free Solder

Roadmap, the National Electronics Manufacturing

Initiative (NEMI) Roadmap, the Optoelectronics

Industry Development Association (OIDA)

roadmaps, and the Information Storage Industry

Consortium (INSIC).

This program deals almost exclusively with rapidly

evolving technologies, where advances in measurement

science are needed to understand the limitations on

system behavior. MSEL focuses its efforts to address

these needs in order to have the best chance to have

an impact on the course of technology.

Research Portfolio

Although there is increasing integration within various

branches of microelectronics and optoelectronics, the

field can be considered to consist of three main areas.

The first, microelectronics, includes needs ranging

from integrated circuit fabrication to component

packaging to final assembly. MSEL programs address

materials metrology needs in each of these areas

including, for example, polymer photoresists for

next-generation lithography and electrodeposition of

interconnects; electrical, mechanical, and physical

property measurement of dielectrics (interlevel,

packaging, and wireless applications); and packaging

and assembly processes (lead-free solders, solder

interconnect design, and thermal stress analysis).

New areas this year include advanced gate dielectric

materials (pp. 4–7, p. 26), nanoimprint lithography

(p. 31) methods to quantify nanomechanical properties

(pp. 20–21), and organic electronics (p. 44).

The second major area is optoelectronics, which

includes work that often crosses over into electronic

and wireless applications. Projects currently

address residual stress measurement in optoelectronic

films, performance of III–V optical materials, and

wide bandgap semiconductors. In particular, the wide

bandgap program has grown as a collaboration with the

NIST Electronic and Electrical Engineering Laboratory

(EEEL). Building on the existing projects on metal

interconnects for GaN (Metallurgy Division) and

on interface and bulk defects in GaN (Ceramics

Division), the EEEL/MSEL program is developing

a comprehensive suite of measurement methods,

including an integrated, phase-diagram combinatorial

approach for characterizing and optimizing interface

and bulk defects limiting the application of GaN and

related materials.

A third, complementary area is magnetic data storage,

where the market potential is vast and growing, and

the technical challenges extreme. INSIC plans to

demonstrate a recording density of 1 terabit per square

inch — 40 times today’s level — by 2006. To reach

these goals, new materials are needed that have smaller

grain structures, can be produced as thin films,

and can be deposited uniformly and economically.

New lubricants are needed to prevent wear as spacing

between the disk and head becomes smaller than the

mean free path of air molecules. Some measurements

require calibration of magnetometers using certified

magnetic standards in several different shapes and

magnetic strengths, and with a wide range in magnetic

character. These standards are now being produced

under this program. MSEL is working with the

magnetic recording industry to develop measurement

tools, modeling software, and standards to help achieve

these goals. Staff expertise at MSEL spans all fields

relevant to magnetic data storage, including materials

science, electrical engineering, physics, mathematics

and modeling, manufacturing engineering, chemistry,

metrology, and computer science, with the Materials

Science and Engineering Laboratory, the Electronics

and Electrical Engineering Laboratory, the Physics

Laboratory, the Information Technology Laboratory,

and the Manufacturing Engineering Laboratory

working as partners in this effort.

Project Output

An integral part of our research programs is the

dissemination of our technical accomplishments.

Project output exists in a variety of forms, ranging

from a fundamental understanding of micro- and

optoelectronics behavior to new measurement

techniques required for anticipated developments in

materials use or design. These outputs are conveyed

through the scientific literature and oral presentations,

workshops, standard reference materials, standard

test method development, evaluated data and online

databases, software tools, and sensors for online

process control.
3

Technical Highlights

The following Technical Highlights section includes

expanded descriptions of research projects that have

broad applicability and impact. These projects generally

continue for several years. The results are the product

of the efforts of several individuals. The Technical

Highlights include:

■ First-Principles Studies of Technologically Important

Dielectric Materials

■ Anomalous Elastic Behavior for SrTiO3 Thin Films

Grown on Si(001) Observed by X-ray Diffraction

■ Profiling the Photoresist-Liquid Interface:

Fundamentals for Immersion Lithography and

Polymer Dissolution

■ On-Chip Interconnects: Extending Performance

of Sub-100 nm Lines

■ Dielectric Metrology and Test Methods Supporting

Embedded Passive Device Technology

■ Friction Scaling Artifact

■ Grand Challenges in Nanomagnetics: High Coercivity

FePt Alloys for Future Perpendicular Magnetic

Data Storage

■ Breakthroughs in Magnetic Refrigeration

■ Quantitative Nanomechanical Properties

■ Data and Standards Resources

Technical Highlights
4

Technical Highlights

Dielectric materials are needed for diverse

applications ranging from gate dielectrics to

microwave resonator materials to transducer

and actuator materials. The specific materials

requirements depend on the application.

First-principles theoretical studies on dielectric

materials are revealing the roles of chemical

order and internal electric fields in controlling

the properties of these materials.

Eric Cockayne and Benjamin P. Burton

Current semiconductor technology uses amorphous

SiO2 as a gate dielectric material. As size has

decreased, however, the leakage current of SiO2 has

become a limiting factor. Finding an alternative gate

dielectric material is a “grand challenge” in the industry.

Alternative materials must have higher dielectric

constants than SiO2 to yield equivalent performance

with reduced leakage current. Hf-containing oxides

are a promising set of materials.

First-Principles Studies of Technologically Important

Dielectric Materials

Figure 1: HfO2 structure (Hf green, O blue).

Figure 2: First-principles-derived model for the dielectric

constant of (CaAl1/2Nb1/2O3)

1–x-(CaTiO3)x shows nonlinear

composition dependence, in agreement with experiment.

and temperature stability. In general, temperature stability

is achieved by forming solid solutions between end

member compounds with opposite signs of temperature

coefficient, for example, between CaAl1/2Nb1/2O3 (CAN)

and CaTiO3 (CT). We have used the FP-based model to

calculate the dielectric constant of arbitrary solid solutions

of -CaAl1/2Nb1/2O3-CaTiO3. The model is based on

cluster expansions of the interatomic forces and ionic

charges, which control the dielectric properties.

The model reproduces the experimentally measured

composition dependence of the dielectric constant of

CT-CAN very well (Figure 2).

Figure 3: Combined first-principles/empirical model for the

Raman spectrum of CaZrO3 shows semiquantitative agreement

with experiment.

Dielectric constants are related to the effective charges

of ions and to phonon-frequencies. First-principles (FP)

calculations show that the effective charge of Hf in HfO2

(Figure 1) is higher than the effective charge of Si in

SiO2, providing an explanation why Hf-containing oxides

should have, in general, higher dielectric constants than

silicates. By comparing the effective charge of Hf in the

experimental structure with that in hypothetical structures,

it was found that the effective charge of Hf depends on

its environment. Because amorphous gate dielectrics

are desirable, knowledge of how crystal environments

dictate effective ion-charges provides a basis for designing

gate dielectric materials.

Microwave resonator and filter materials typically

require a moderate dielectric constant, low dielectric loss,
5

Technical Highlights

Dielectric properties, and, therefore, the Raman

spectra, of solid solutions depend on chemical ordering

of ions as well as composition. To understand the

connection between local structure, composition,

dielectric properties, and spectroscopy, we are working

on computing Raman spectra directly from FP. The

idea is to create a spectroscopic/computational tool for

measuring short- and long-range chemical order via

Raman spectroscopy. Experiments have shown that

Raman spectra are sensitive to short- and long-range

order, but little is known quantitatively about the

relationship between Raman spectra and chemical order.

We have created a model, based on FP results, for the

Raman spectra of solids, and are applying it to study

the CAN-CT and CaZrO3-CaTiO3 (CZ-CT) solid

solution systems. Figure 3 shows that the Raman

spectrum of CZ is reproduced reasonably well

with only a few parameters. Both long-range

electrostatics and short-range covalent bonding

contribute to the Raman spectra, but not equally to

all peaks. This provides a natural explanation for

the experimental observation that different Raman

peaks can have different sensitivities to the amount

of long-range order. Evidence is also found that

small Ti or Zr concentrations create local vibrations

that produce significant, but broad, peaks in the

Raman spectrum.

Relaxor behavior is desirable, because it implies

high-dielectric constants and piezoelectric coefficients

over a broad temperature range, but it poses a

theoretical challenge because these properties are

sensitive to structural/chemical heterogeneities at many

length-scales. For example, PbSc1/2Nb1/2O3 (PSN)

exhibits normal ferroelectric behavior as a function of

temperature (e.g., a sharp dielectric peak) when Sc3+

and Nb5+ are ordered. However, when there is only

short-range order, such as nanoscale chemically

ordered domains in a disordered matrix, PSN exhibits

relaxor ferroelectric behavior (e.g., a broadened,

frequency-dependent dielectric peak). Similar changes

in dielectric properties are caused by the introduction

of Pb- and O-vacancies. We have constructed a

computational model for PSN, which allows these

structure–property issues to be explored in detail.

FP calculations show that Pb atoms move off their

ideal crystallographic positions, and that the dielectric

and piezoelectric response in PSN is dominated by the

dynamics of Pb-displacements. At low temperature,

Pb–Pb interactions favor coherent alignments

of Pb-displacements, but local electric fields, caused

by the charge difference between Sc3+ and Nb5+,

randomly bias individual Pb-displacements. Electric

fields generated by Pb- and O-vacancies are also

included in this model. Molecular dynamics simulations

on a 320,000 atom supercell yield a sharp dielectric

peak for ordered PSN, and successive broadening as

chemically ordered nanodomains and/or Pb vacancies

are added, in agreement with experiment.

The wide band-gap semiconductor system

AlN-GaN is used to make light emitting diodes, and

the wavelength of emitted light is adjusted by alloying.

First-principles phase diagram calculations for this

system predict the expected miscibility gap when

the excess vibrational entropy is excluded; but when

it is included, an ordered phase based on AlGaN2

stoichiometry is predicted. To our knowledge, this

is the first prediction of vibrational-entropy induced

atomic ordering, and it suggests a novel way to affect

band gaps: via ordering and alloying rather than

alloying alone.

For More Information on this Topic

E. Cockayne, B.P. Burton (Ceramics Division, NIST)

E. Cockayne, “First-principles Calculations of the

Dielectric Properties of Perovskite-Type Materials,”

J. Eur. Ceram. Soc. 23, 2375–2379 (2003).

U.V. Waghmare, E. Cockayne, and B.P. Burton,

“Ferroelectric Phase Transitions in Nano-scale

Chemically Ordered PbSc0.5Nb0.5O3 using a

First-principles Model Hamiltonian,” Ferroelectrics

291, 187–196 (2003).

Figure 4: Simulated dielectric constant of PbSc1/2Nb1/2O3

as a function of temperature and type of Sc-Nb ordering.

The broadening of the dielectric peak that occurs in the case of

ordered nanodomains is one characteristic of relaxor behavior.

Transducers used for sonar and medical imaging

applications typically require extremely high dielectric

and piezoelectric coefficients. Very large piezoelectric

coefficients are observed in Pb[Mg;Zn]1/3Nb2/3O3–

PbTiO3 solid solutions, based on the relaxor

ferroelectrics PbMg1/3Nb2/3O3 and PbZn1/3Nb2/3O3.
6

A major driving force of the semiconductor

industry is the integration of transition-metal

oxides with Si transistor technology. Much of

this effort has focused on the development of

SrTiO3 thin-film growth on Si(001). These films

have served successfully as the gate-oxide layer

for metal-oxide field-effect transistors and as

the buffer layer for III–V on Si semiconductor

technology. In addition, ferroelectric thin

films show promise for quantum computing

applications. However, these perovskite films

exhibit unusual features, and it is imperative

for future advances that the fundamental aspects

of the thin-film epitaxy be understood from

both an experimental and a theoretical view.

To address this issue, we are studying SrTiO3

as a model material representative of the

larger class of candidate oxides with the

perovskite structure.

Joseph C. Woicik

We have performed high resolution x-ray diffraction

measurements at the UNICAT beamline facility

at the Advanced Photon Source on a series of SrTiO3

thin films grown on Si(001) by Motorola. Figure 1

Anomalous Elastic Behavior for SrTiO3 Thin Films

Grown on Si(001) Observed by X-ray Diffraction

shows the results of our glancing-incidence x-ray

diffraction experiment performed around the

SrTiO3(220) diffraction for the in-plane and the

SrTiO3(002) diffraction for the out-of-plane SrTiO3

lattice parameters.

Because the crystal structure of SrTiO3 is simple

cubic (Figure 2), whereas the crystal structure of

Si is face-centered cubic, SrTiO3 films grow on

the Si(001) surface with their unit cell rotated 45°

around the Si(001) surface-normal direction.

Consequently, this choice of SrTiO3 reflections

determines accurately the SrTiO3 unit cell dimensions

relative to the underlying Si lattice and hence the

thin film epitaxy.

Our diffraction measurements find that all of the

thin films studied are under in-plane tensile strain.

This finding is counter to what is expected from the

bulk lattice constants of SrTiO3 and Si that predict

in-plane compressive strain for coherent SrTiO3

thin-film growth on Si(001). The observed

expansion of the in-plane SrTiO3 lattice constant

must therefore result from the much larger thermal

expansion coefficient of SrTiO3, compared to Si,

coupled with incoherent growth at the elevated

growth temperature.

Figure 1: In-plane and out-of-plane SrTiO3 lattice constants for

40 Å, 60 Å, 80 Å, and 200 Å SrTiO3 thin films grown on Si(001).

The horizontal lines show the bulk cubic lattice constants of

SrTiO3 and bulk Si.

Figure 2: Crystal structure of SrTiO3.

Technical Highlights
7

Even more surprising is the result that the SrTiO3

out-of-plane lattice constant increases with decreasing

film thickness, indicating a large negative Poisson’s

ratio for the thinnest films; i.e., the out-of-plane

lattice constant of the SrTiO3 is expanded more

than its in-plane lattice constant.

 To understand both the nature and driving

force of this anomaly, we performed polarization

dependent x-ray absorption fine-structure (XAFS)

measurements on the same samples. Together,

XAFS and x-ray diffraction determine uniquely the

degree of epitaxy and the local atomic distortions

that result.

Our XAFS measurements find significant p-d

hybridization for the thinner films. This hybridization

is allowed only for a non-centrosymmetric distortion

of the SrTiO3 unit cell. Polarization-dependent

measurements of the Ti-O bond lengths find one

Ti-O distance parallel to the SrTiO3 interface

and two Ti-O distances perpendicular to it.

The Ti-O radial splitting is ≈ 0.22 Å. The elastic

anomaly observed by diffraction is, therefore,

likely driven by the interfacial polarization of the

SrTiO3 layers.

To test this hypothesis, first-principles

density-functional calculations were performed

on periodic SrTiO3 supercells containing √2 x √2 x N

unit cells. The calculations were performed at the

Naval Research Laboratory Center for Computational

Materials Science. Figure 3 shows the results of

the calculations as a function of N, the number of

SrTiO3 layers. The in-plane lattice constant of the

supercells was constrained to equal the average

in-plane lattice constant of the SrTiO3 films as

determined by x-ray diffraction. To mimic the

polarization of the interface as determined by XAFS,

a single Ti-O layer was polarized in the normal

direction by constraining its z-coordinates to lie

0.22 Å apart. All other coordinates were

fully relaxed.

Remarkably, the out-of-plane lattice constant of

the supercells is found to expand in agreement with

Figure 3: Calculated out-of-plane SrTiO3 lattice constant as a

function of the number of SrTiO3 layers.

the measurement of the out-of-plane lattice constant

of the films. These results suggest that this behavior

may be common for hetero-epitaxial growth of

materials that possess an ionic polarizability; it arises

simply from the inequivalent perpendicular heights

of the anions and cations at the film/substrate

interface which drives the polarization of the film.

Additional calculations are being performed to

understand the role of Si diffusion and O vacancies,

and experiments are planned to study both the epitaxy

and interfacial structure of films grown under

different growth conditions.

For More Information on this Topic

F.S. Aguirre–Tostado, A. Herrera–Gomez

(CINVESTAV); R. Droopad, Z. Yu (Motorola);

D.G. Schlom (Pennsylvania State University);

P. Zschack, E. Karapetrova (UNICAT);

C.S. Hellberg (NRL)

Technical Highlights
8

Technical Highlights

Profiling the Photoresist-Liquid Interface: Fundamentals

for Immersion Lithography and Polymer Dissolution

Recent advancements in the semiconductor

industry have resulted in new problems involving

the photoresist-liquid interface. For immersion

lithography, the water profile within a resist film

impacts pattern quality from changes in photoacid

generator diffusion or optical transparency.

For the development step, where a latent image

is realized into the final structure, an improved

understanding of photoresist swelling and

dissolution mechanisms is needed to address

stringent line-edge roughness requirements.

Data from neutron reflectivity measurements

provide critical insight needed to understand

and optimize next-generation photoresists and

process strategies.

Bryan D. Vogt and Vivek M. Prabhu

Introduction

Polymer thin film photoresists comprise the materials

foundation for the production of semiconductor

devices with nanoscale dimensions. The extension of

optical methods has been problematic due to challenges

arising from the implementation of shorter exposure

wavelengths. The past focus of the semiconductor

industry has been the development of sufficiently

transparent photoresist materials for future exposure

sources. However, future progress requires depth

profile information at the photoresist–liquid interface,

due to the emergence of immersion lithography and

the increased influence of the photoresist development

process on lithographic performance.

Using neutron reflectivity (NR), NIST successfully

quantified the profile of water and aqueous base

counterions in model photoresist films. NR provides

structural information regarding the composition

profile normal to the thin-film surface with isotopic

selectivity between protons and deuterium. Selective

deuteration of components in the system allows for

the quantification of water or counterion distribution

within photoresist films despite the negligible

differences in physical density. This data provide

critical insight needed to refine models for immersion

lithography and polymer dissolution.

Immersion Lithography: Water Profile

Recently, immersion lithography has emerged

as the key strategy to extend existing optical tools.

A liquid, such as water, is placed between the lens

and photoresist thin film to enhance resolution.

The industry anticipates using immersion lithography

for production in 2007 at the 65 nm node. The role of

liquids in contact with photoresist films is important;

not only for component leaching and contamination,

but also due to the detrimental influence of trace levels

of water on the reaction and diffusion of photoacid

generators. Additionally, a non-uniform water profile

within thin films leads to incorrect assumptions

regarding the transmission and reflection at the

photoresist–anti-reflective coating interface.

Figure 1 shows the measured volume fraction

profile of water versus the distance from a

trimethylsilane-primed silicon oxide interface.

Far from the substrate, the 248 nm photoresist,

poly(4-tert-butoxycarbonlyoxystyrene) (PBOCSt),

shows bulk water absorption near 2.5 %. However,

significant deviations occur near the interface.

An excess of water, up to 17 %, extends 40 Å from

the substrate. This enriched interfacial water was

previously unknown and unaccounted for.

In contrast, a depletion of water was observed for

poly(4-hydroxystyrene) (PHOSt), the developer soluble

resist, even though the bulk of the film absorbs 25 %.

This depletion indicates the interface cannot accommodate

excess water. It appears that the relative hydrophobicity

between polymer and substrate controls the amount of

interfacial water.

Figure 1: Volume fraction of water distributed near the

PBOCSt/HMDS treated substrate during immersion, as

determined by neutron reflectivity. The excess of water at the

substrate reaches a maximum concentration of 17 % by volume.

Inset: Dependence of initial film thickness on the total film

swelling for two model photoresists in thin and ultrathin films.
9

Technical Highlights

The total film swelling is also observed to be a

function of the initial thickness and interfacial water.

For thinner resist films the interfacial water dominates

the swelling as shown in the inset to Figure 1 for

PBOCSt and PHOSt. For these different resists, the

swelling becomes similar for ultrathin films with

thickness less than 200 Å. The data are consistent with

an interfacial water thickness and content for each film

thickness. The interfacial concentration is strongly

dependent upon the surface chemistry, but relatively

independent of the photoresist material or film thickness.

Dissolution Effects: Aqueous Base Profile

The development step of a latent image in an

aqueous base contributes significantly to undesirable

line-edge roughness (LER). There is a strong need

for improved dissolution models incorporating

photoresist-developer interactions. A key component

is the depth profile of the aqueous base counterion

through a photoresist film because it controls the

dissolution mechanisms that lead to unacceptable

LER. We provided the first direct measurement of

the aqueous base distribution (tetramethylammonium

hydroxide) (TMAH) within the film. These

measurements quantify the extent of developer

penetration and the influence of ionization on the

response of the photoresist to the developer solution.

We used a zero-average contrast (ZAC) experiment

where the neutron scattering length density of a thin

film of poly(norbornene hexafluoroisopropanol)

(PNBHFA), a model 157 nm photoresist, is matched

to the developer solution with a D2O/H2O mixture.

As shown in the schematic of Figure 2, the contrast

matched film and solvent (equal color) eliminates

neutron contrast at this interface. However, when base

(d12–TMAH) enters the film, the reflectivity contrast

is enhanced. These changes allow quantification of

both film swelling and the base profile through the film.

throughout the entire film rather than gradually through

the film. In addition, a depletion of base was observed

at the substrate. The film-solution interfacial width

increases with higher base concentration. These

measurements show that ionization-induced swelling

occurs at the dissolution front. At even higher base

concentrations, the photoresist film dissolves quickly.

Understanding the transition from swelling to rapid

dissolution with base concentration will provide

guidance into developer-induced roughness.

Figure 2: Schematic of the zero-average neutron reflectivity

experiment. The contrast between the film and solvent are equal,

only the enrichment of deuterated aqueous base within the film

provided the reflectivity enhancement.

Figure 3: Volume fraction profiles of d12-TMA+ within the

PNBHFA film. The aqueous base profile illustrates the enhanced

swelling and content within the thin film with higher equilibrating

base concentration.

These base profilometry experiments were followed

by a deswelling step by rinsing with pure water. The

rinse kinetically traps base within the film where it could

contaminate other processes during device fabrication.

NR measurements provide new information about

the liquid–photoresist interface needed to improve

current models of dissolution. In future work, we will

examine the effects of liquid–photoresist interactions

on surface roughness with atomic force microscopy

measurements of surface features.

For More Information on this Topic

C. Soles, M. Wang, C. Wang, R. Jones, W. Wu,

E. Lin (Polymers Division, NIST); S. Satija

(NIST Center for Neutron Research); D. Goldfarb,

M. Angelopoulos (IBM T.J. Watson Research Center);

H. Ito (IBM Almaden Research Center)

B.D. Vogt, et al., “Water immersion of model

photoresists: Interfacial influences on water concentration

and surface morphology,” J. Microlithography,

Microfabrication, and Microsystems, in press.

The volume fraction of d12–TMA+ is plotted

versus distance from the substrate in Figure 3 for

four different equilibrating concentrations of base.

The change in the counterion profile illustrates the

advancement of the swollen solid front. A key finding

was that the film expansion proceeds via base transport
10

Technical Highlights

Conductors in on-chip metallizations are now

reaching dimensions so small that defective

seed layers are impacting manufacturing yields,

and electron scattering on surfaces and grain

boundaries is reducing electrical transport in

the buried wires. Our goal is to provide tools

to overcome these barriers. Recent efforts have

quantified sources of the increased resistivity in

wires made of silver, the most conductive of all

metals, demonstrated seedless processing routes

for copper wires, and improved understanding

and modeling of the superfill fabrication process.

Daniel Josell and Thomas P. Moffat

The steady reduction of transistor dimensions in

integrated circuits has been accompanied by similar

size reductions of the on-chip interconnects that carry

electrical signals, pushing the industrial technology for

copper seed deposition close to its limit for defect-free

sidewall coverage. Defects in seed layers, which

arise from limitations in existing sputter technology,

lead to voiding during electrodeposition of the

copper metallization.

Additionally, with the dimensions of the copper

wires in these metallizations now approaching the

intrinsic mean-free-path length of the conduction

electrons, scattering on the wire surfaces has begun

to significantly reduce electron transport and, thus,

the associated electrical conductance of the wires.

With grains in these conductors similarly sized, a

reduction is also to be expected from grain boundary

scattering. While the penalty for both effects is

increased power dissipation and reduced clock speed,

the appropriate approach for mitigation requires

quantitative determination of the relative sizes of

the contributions.

On-Chip Interconnects:

Extending Performance of Sub-100 nm Lines

Technical Details

A tri-layer titanium, palladium and silver seed

(Figure 1) was shown to yield smooth, conductive

surfaces for the electrodeposition of silver wires for

the electrical properties study. The poor seed coverage

that is visible toward the bottom of the smallest

trench (Figure 1c) is a technical challenge noted in the

International Technology Roadmap for Semiconductors.

Such seed defects motivated the “seedless” ruthenium

barrier-based process detailed in last year’s report and

continued by this year’s demonstration of seedless

copper superfill in trenches with ruthenium or iridium

barriers (Figure 2) deposited by perfectly conformal

atomic layer deposition (ALD).

Figure 1: Ti/Pd/Ag seed layer in sub-100 nm deep trenches.

Figure 2: Trenches containing copper that was electrodeposited

directly on an ALD iridium barrier (thin bright layer).

Figure 3: Cross-section views of silver wires fabricated by

electrodeposition in the seeded trenches followed by removal of the

metal from the field (transmission electron microscope).
11

Technical Highlights

Figure 4: Electrical resistivities of 300 nm tall silver wires

compared to predictions that account for surface scattering with

varying amounts of grain boundary scattering. Resistivities for

wires less than 100 nm wide are impacted by defects.

For the electrical studies, silver wires (Figure 3) were

fabricated by silver electrodeposition on the tri-layer seeds

(Figure 1), using a superfill process developed in the

Metallurgy Division, followed by removal of the metal

in the field adjacent to the wires through chemical–

mechanical planarization and ion polishing.

The wires were studied in a standard four-point probe

geometry that permitted measurement of wire resistances.

Resistivities, obtained from the resistances using measured

wire dimensions, increased significantly with decreasing

wire width (Figure 4). To assess the origin of the resistivity

increase, the Fuchs–Sondheimer analysis for diffuse

scattering of electrons on surfaces was extended to

permit analysis in the presence of both specular and

diffuse scattering. The resulting equations, along with

a previously published equation for grain boundary

scattering, permitted quantitative evaluation of the

experimental data. Significantly, modeling of the data

showed that the increase of resistivity with decrease

of wire size arises as much from scattering on grain

boundaries as from scattering on the wire surfaces.

This indicates that efforts to mitigate size effects must

increase grain size as well as surface specularity if

they expect to be more than modestly successful.

The continuing industrial need for predictive

simulation of feature filling spurred experiment and

modeling of the superfill process itself. Consumption

of adsorbed accelerator, a detrimental deviation from

the surface segregation behavior that is responsible for

the superfill process, was measured. Inclusion of such

consumption in our Curvature Enhanced Accelerator

Coverage (CEAC) model and computer code have made

the filling predictions even more accurate.

This research has continued to impact industry,

indicated by requests for our superfill code from Intel,

Applied Materials, ST Microelectronics, and ATMI;

an invited article on superfill in the IBM Journal of

Research and Development; and invited presentations

given at Cookson–Enthone, in addition to publications

and presentations at conferences.

Selected Project Publications

for FY2004

T.P. Moffat, D. Wheeler, M. Edelstein and D. Josell,

“Superconformal Film Growth: Mechanism and

Quantification,” IBM J. Res. and Dev., in press.

D. Josell, C. Burkhard, Y. Li, Y.-W. Cheng, R.R.

Keller, C.A. Witt, D. Kelley, J.E. Bonevich, B.C. Baker,

T.P. Moffat, “Electrical Properties of Superfilled

Sub-Micrometer Silver Metallizations,” J. Appl. Phys.

96 (1), 759–768, (2004).

D. Wheeler, T.P. Moffat, G.B. McFadden, S. Coriell

and D. Josell, “Influence of Catalytic Surfactant

on Roughness Evolution During Film Growth,”

J. Electrochem. Soc. 151 (8), C538–C544, (2004).

T.P. Moffat, D. Wheeler, and D. Josell,

“Electrodeposition of Copper in the SPS-PEG-Cl Additive

System: I. Kinetic Measurements: Influence of SPS,”

J. Electrochem. Soc. 151 (4), C262–C271, (2004).

W.J. Evans, D.G. Giarikos, D. Josell, and J.W. Ziller,

“Synthesis and Structure of Polymeric Networks of

Silver Hexafluoroacetylacetonate Complexes of THF,

Toluene, and Vinyltrimethylsilane,” Inorg. Chem. 42,

8255–8261, (2003).

For More Information on this Topic

D. Josell, T.P. Moffat (Metallurgy Division, NIST);

G. McFadden (Mathematical and Computational Sciences

Division, NIST); R.R. Keller, Y.-W. Cheng (Materials

Reliability Division, NIST); C. Witt (Cookson–Enthone);

C. Burkhard, Y. Li (Clarkson University); D. Wheeler

(University of Maryland); T.K. Aaltonen, M. Ritala,

M. Leskelä (University of Helsinki, Finland)

Figure 5: Simulations of superconformal feature filling now

account for consumption (incorporation) of adsorbed catalyst.
12

Technical Highlights

Embedded passive devices require high dielectric

constant hybrid materials consisting of filled

polymers to advance miniaturization and

functional performance of high-speed electronics.

New metrology methods were developed to address

the needs of the electronics industry. Two test

methods, a Test Method for Dielectric Permittivity

and Loss Tangent of Embedded Passive Materials

from 100 MHz to 12 GHz and a Test Method for

Dielectric Withstanding Voltage were completed and

have received wide acceptance by industry as new

test methods to accelerate the development of

embedded passive device technology.

Jan Obrzut

Introduction

Continuous reductions in the electrical charge

required to drive logic gates and storage cells

have resulted in tremendous progress in miniaturization

and density of integrated circuits. However, enhanced

functional performance increasingly depends on

passive components such as capacitors, resistors,

and inductors, where the dielectric permittivity and

impedance characteristics of the material control spatial

dimensions, time scale, speed, shapes and amplitude

of electronic signals. Passive devices have not shrunk

in size as rapidly as active devices and occupy an

increasingly larger area and mass fraction of electronic

subassemblies.

Dielectric Metrology and Test Methods Supporting

Embedded Passive Device Technology

Significant advantages arise if passive devices are

integrated directly into the circuit board as embedded

passive devices rather than discretely attached with

automated assembly. These include much thinner and

sleeker electronics such as cell phones, decreased

manufacturing costs, better electrical performance,

and enhanced design flexibility. Companies including

Gould, Shipley, Ohmega, MacDermid, DuPont, Motorola,

Oak-Mitsui, 3M, and Sanmia have devoted millions

of dollars to advance this technology in an effort that

represents a huge transition for the electronics industry.

High dielectric constant hybrid materials

consisting of filled polymers are essential for advancing

miniaturization and functional performance. There

are significant challenges in developing new thin-film

materials that require enhanced electrical performance

characteristics, such as impedance and high dielectric

constant (high-k), in order to operate at higher

microwave frequencies and at increased voltage

strengths. Consequently, new metrology and test

methods are needed to address the specific behavior

of thin film specimens and to better understand the

relation between functional performance and the

structural attributes of the materials.

The materials and testing requirements for

Embedded Passives Technology are outlined in

the National Electronics Manufacturing Initiative

(NEMI) 2004 Roadmap. A need for new standard test

methods for embedded materials was identified by the

Association Connecting Electronic Industries (IPC),

Roadmap 2005 Outlook Update, IPC Embedded Passive

Device Standard Committee D-39. In partnership with

industry, NIST chaired a test methods task group to

communicate and collaborate with industrial partners.

This year, two new test methods were accepted and

will be used extensively by industry to accelerate

implementation of this new technology.

Dielectric Permittivity and Loss Tangent

The development of new thin-film materials that

exhibit enhanced electrical performance characteristics,

such as impedance and high dielectric constant (high-k),

requires a broadband measurement technique for

measuring permittivity at microwave frequencies

(100 MHz to 12 GHz). Instead of expensive, single-test

microwave strip test structures, NIST forwarded a

general measurement strategy of incorporating a thin

passive film material into a device that is comprised

of a capacitive or resistive termination in a transmission

line. The technique is based on the observation and

theoretical analysis of the fundamental mode propagating

at high frequencies in thin film dielectrics that terminate a

coaxial air-filled transmission line. The development of

the method involved nearly 50 active industrial partners

and was reviewed by more than 300 other parties.
13

Technical Highlights

An example measurement of the dielectric constant

for a high-k material obtained from DuPont is shown

in Figure 1. We guided the design of the test protocol

and made arrangements with co-sponsoring member

companies for round robin evaluation of the measurement

method. The work resulted in a test document “Test

Method for Dielectric Permittivity and Loss Tangent

of Embedded Passive Materials from 100 MHz to

12 GHz,” which has received wide industrial acceptance

and recommendation as a new standard test method.

This new capability to measure the dielectric

properties at high frequencies for a wide range of

dielectric permittivity values is also used to quantify

dispersion, alignment, and structure in hybrid materials.

For example, we demonstrated that composites of

organic polymer resins filled with ferroelectric ceramics

exhibit a dominant intrinsic high-frequency relaxation

behavior. Such dielectric properties are beneficial in

enhancing performance of processors and logic devices.

Dielectric Withstanding Voltage

The dielectric breakdown of thin film materials is also

a significant issue in embedded passive devices. Due to a

thin film configuration, nonlinear effects may be activated

at moderate bias levels and contribute to the dielectric

breakdown. A non-linear dielectric measurement

methodology was developed and applied for testing

passive materials at high electric fields and voltages.

NIST-developed experimental set-up and

testing procedures demonstrated the unambiguous

determination of the dielectric withstanding voltage

of embedded passive materials. In contrast to

conventional procedures, the specimen voltage and

current are determined as complex quantities from the

corresponding time-resolved voltage waves. The new

testing procedure represents an extension compatible

with the existing standard test method, but is better

suited for capacitive and resistive thin film materials.

The specimen impedance and the loss tangent of

the material can be determined by performing complex

algebra calculations. It was found that thin-film

materials for embedded passives do not exhibit a

flat impedance characteristic, as is the case for

conventional dielectrics, but the impedance sharply

decreases with increasing voltage. The voltage

withstanding condition may be attributed to a voltage

range where the impedance characteristic remains

insignificantly affected by the applied voltage. An

equivalent impedance comparison indicates that high-k

organic composites can withstand only a small fraction

of the conventional dielectric withstanding voltage.

The NIST-developed procedure of recording and

analyzing waveforms also allows the evaluation of

specific characteristics of materials that cannot be

readily evaluated with conventional techniques.

This measurement procedure is especially suitable

for detecting and analyzing non-linear dielectric effects

that can result from polarization reversal and rectifying

barriers. Such effects may appear at relatively low

voltages in nano-sized interfaces, composites, and

sub-micron thin dielectric films that are of interest

to emerging technologies.

For More Information on This Topic

A. Anopchenko, K. Kano (Polymers Division,

NIST); D. McGregor, G.S. Cox, J. Felten (DuPont);

D. Fritz (MacDermid); T. Bergstresser (Gould

Electronics); K. Fjeldsted (Electro Scientific Industries);

R. Crosswell (Motorola); C. Vanderpan (UL);

R. Whitehouse (Sanmina-SCI)

J. Obrzut and A. Anopchenko, “Input Impedance

of a Coaxial Line Terminated with a Complex Gap

Capacitance — Numerical and Experimental Analysis,”

IEEE Transactions on Instrumentation and

Measurement, 53 (4), August (2004).

J. Obrzut and K. Kano, “Measurement of Complex

Impedance at High AC Voltages using Waveforms,”

IEEE, IMTC/2004 3, 1994–1997 (2004).

J. Obrzut, A. Anopchenko, K. Kano, and H. Wang,

“High Frequency Loss Mechanism in Polymers Filled

with Dielectric Modifiers,” Mat Res. Symp. Proc. 783,

B3.5-8 (2003).

J. Obrzut and A. Anopchenko, “High frequency

input impedance characterization of dielectric films

for power-ground planes,” IEEE Transactions on

Instrumentation and Measurement 52, 1120–1124 (2003).

Figure 1: Dielectric constant of high-k polyimide-based composite

films determined according to the Standard Test Method. (HK10 is

a 25 μm thick composite; HK11 is a 14 μm thick composite).
14

Technical Highlights

Nanofrictional forces are an important factor

in the design of nanodevices and assemblies of

nanoparticles. Literature data on nanofriction,

however, exhibit many discrepancies and

have a wide range of scatter. In a series of

well-controlled experiments, we have discovered

that a significant portion of this discrepancy may

actually be attributed to an unintended scratching

of the surface by the sharp tips used in making

the measurements themselves. Deviation of tip

shape from the “ideal” spherical shape is another

contributor to the disagreements found among the

literature data. This work sheds important insight

into the nature of nanoscale friction measurement.

Z. Charles Ying and Stephen M. Hsu

Accurate measurement of nanofriction is emerging

 as one of the critical issues in nanotechnology.

Manipulation of molecules, clusters, and nanoparticles

across surfaces to form a functional entity relies on the

ability to overcome the resistance of the particles to

motion across the surface. Further, reliable operation

of micro- and nano-devices often depends on an

accurate estimate of lateral loading. Literature data

on nanofriction, however, have shown wide ranges

of values depending on the length scale of the device.

Silicon friction, e.g., shows an order of magnitude

variation from 0.03 to 0.25. Such results have led to

speculations that there might be an intrinsic scaling

effect such that different friction levels would occur

across the nano-, micro-, and macro-scales. If proven

true, well established friction laws would be invalidated

for nanomaterials.

Given the broad technological significance of this

issue, we have undertaken a detailed investigation of

the nature of this discrepancy. Friction measurements

between non-adhering surfaces were carried out in both

elastic and plastic deformation regions. Diamond tips

of various sizes were used to measure nanofriction

forces on well-characterized substrates such as single

crystal silicon, silicon dioxide, and calcium fluoride.

Experiments were performed using a specially designed

multiscale friction tester developed jointly by NIST and

Hysitron Incorporated based on a capacitance probe

force transducer. In each experiment, the environment

was carefully controlled, and the tip penetration into the

substrate during sliding was continuously measured.

The size and shape of each tip were characterized

using a newly developed “replica technique.” Tips

were imprinted into a soft material, and the imprints

were scanned by AFM and digitally inverted to

Friction Scaling Artifact

Figure 1: 3D profiles, obtained using the replica technique, of the

tips used in the friction measurements.

“reconstruct” the tip in three-dimensional details.

Figure 1 shows images of two of the diamond tips

used in the experiments. The tip shown in Figure 1(a)

is spherical in shape with a 1.2 μm tip radius while

Figure 1(b) shows an ellipsoidal shape with nominal

radius of 4 μm. The detailed dimensional data are

crucial in determining the apparent contact areas and

isolating the influence of surface forces.

Figure 2: Coefficient of friction between Si (100) surface and a

diamond tip with radius R = 1.2 μm, as a function of mechanical

loading force.

Figure 2 shows the coefficient of friction (COF)

between a Si (100) surface and a diamond tip with tip

radius R = 1.2 μm.
15

Technical Highlights

path. Numerical integration of actual tip size and shape

over the sliding path is required. For the hypothesis of

“elastic plowing,” the calculation shows that the friction

force in this regime should be proportional to the projected

cross-sectional area in the direction of sliding. Figure 5

confirms this hypothesis for all three tips.

Figure 3: Image of the silicon surface after friction

measurements, showing scratches at 2.5 mN and higher load.

Figure 4: Coefficient of friction between Si (100) surface and

three diamond tips used in the experiments, as a function of mean

contact pressure.

Figure 5: Friction force as a function of projected cross-section

area in the direction of tip sliding.

Two distinct regions can be seen. Initially, the COF

is constant up to a load of 2.0 mN. For loads above

2.5 mN, the COF increases with load. This friction

transition is contrary to Amoton’s law. Subsequent

investigation revealed that this change in COF is caused

by unintended plowing of the tip into the substrate.

Atomic force microscopy, using a sharp tip on the

surface, suggests that the COF increase coincides with

the first appearance of plastic grooving. In the case

of silicon, a groove 5 Å deep and 2000 Å wide was

detected on the surface at a load of 2.5 mN (Figure 3).

This observation was repeated for different tips and

different substrates. At higher loads, deeper and wider

grooves were observed. These results suggested that

unintended scratching of the surfaces by the sharp tips

used in the friction measurements contributed to the

discrepancies among friction data in the literature.

The initiation of plastic grooving can be quantified in

terms of contact pressure. By determining the apparent

contact area using the digitally inverted tip method, the

transition contact pressures could be calculated for all

of the observed cases. All the results corresponded to

12 GPa which is approximately the hardness of silicon.

Elastic Plowing

Figure 4 shows the friction data for three tips in the

elastic region (no plastic grooving). The data for the two

spherical tips with radii R = 0.5 μm and 1.2 μm exhibit a

common value for the COF. However, a higher friction

value was observed for the 4 μm radius tip.

To explain this discrepancy, we tested the various

contact mechanics models which require the accurate

determination of the real contact areas. Considering a tip

plowing through an elastic substrate, the real area of

contact is the projected cross-section area of the tip in

the direction of sliding. This can be determined from the

tip geometry and “penetration depths” across the sliding

This work shows clearly that nanoscale friction, in

practice, is a complex result of both elastic and inelastic

strains and deformations, and accurate nanofriction

measurement will require careful accounting of all the

forces contributing to the phenomenon. The methodology

established in this work provides a substantial step towards

the data and understanding needed by industry.

For More Information on this Topic

Z.C. Ying, S.M. Hsu (Ceramics Division, NIST)
16

Technical Highlights

The magnetic data storage industry is seeking

to sustain the 30-year trend of exponentially

increasing storage density. This must be achieved

at the same time as maintaining the stability of the

recorded data. The Metallurgy Division at NIST

is collaborating with Seagate Technology to

develop the processes required to produce

patterned media of high-magnetic coercivity

that will meet this challenge.

Jonathan J. Mallett, Thomas P. Moffat, and

William F. Egelhoff, Jr.

Conventional magnetic data storage media are based

on granular films in which many fine grains are

used to define each magnetic bit. The minimum

number of grains per bit is limited by the irregularity

of the shape and spacing of the grains, which produces

irregular boundaries between bits. This irregularity

results in noise in the read signal and can only be

constrained at an acceptable level by maintaining a

fixed minimum number of grains per bit. The natural

approach to increasing data storage density has been

to reduce the grain size, while maintaining the same

number of grains per bit. The limit to this approach

occurs when the magnetic energy barrier to the reversal

of magnetization of each grain approaches the energy of

random thermal fluctuations. At this point, the medium

is no longer stable against spontaneous magnetization

reversal and consequential data loss.

The grain size at which this limit occurs depends

on the magnetocrystalline anisotropy energy of the

Grand Challenges in Nanomagnetics: High Coercivity FePt

Alloys for Future Perpendicular Magnetic Data Storage

magnetic material. FePt in its L10 phase has a

sufficiently large anisotropy energy to allow

magnetically stable grains of 5 nm diameter (Figure 1).

Furthermore, FePt deposited by a variety of means

typically forms grains approaching this size.

Unfortunately, the annealing treatment required to

transform the as-deposited A1-structured FePt to

the desirable L10 phase is widely found to result

in an increase in grain size to 100 nm. Current

efforts at NIST focus on developing a method of

electrochemically depositing FePt into a regular

patterned template, circumventing the problem of grain

growth. Simultaneously, the imposed regularity of the

magnetic cells opens the possibility of addressing single

cells (i.e., of using one “grain” per bit). The estimated

achievable density from such an approach is 7 Tbits

per square inch, which is 100 times higher than current

storage densities. Electrodeposition is an obvious

choice for deposition into high aspect ratio templates,

since it does not suffer from the shadowing effect

that characterizes vacuum deposition techniques.

Figure 2: The double cell, designed to minimize the concentration

of Fe3+ and dissolved O2 in the FePt plating solution.

Figure 1: The dependence of storage density on magnetocrystalline

anisotropy energy. The most promising materials are FePt

and CoPt.

Electrodeposition of FePt from aqueous solutions

presents many challenges. The double cell shown in

Figure 2 has been developed to address the problem of

the instability of Fe2+ solutions, which readily oxidize

to produce insoluble Fe(OH)3. The plating solution,

containing FeCl2 and PtCl4 (left) is separated from the

anode by a cation selective membrane, preventing the

oxidation of Fe2+ to Fe3+ that would otherwise occur

at the anode. Fe3+ formation by oxidation with air is

also minimized by blanketing the cell in nitrogen, and

residual Fe3+ is reduced to Fe2+ by an auxiliary

platinum grid electrode.
17

Technical Highlights

The alloy composition of 300 nm thick films

deposited from this solution was found to depend

mainly on the applied potential and to be insensitive

to the concentration of the solution components.

A thermodynamic regular solution model was used

to describe the dependence of film composition on

applied potential. The comparison of theory to

experimental data can be seen in Figure 3.

The deposited films were found to be remarkably

smooth, with RMS roughness values less than 5 nm

for micron-thick deposits. This was surprising given

the large platinum overpotential (supersaturation),

which usually results in growth instabilities and

consequent roughening.

The control of crystal orientation is an essential

consideration for high-density recording applications.

A transition in the recording industry is currently in

progress to perpendicular media, in which the bits are

magnetized perpendicular to the plane of the medium.

Maximum advantage can be derived from L10 FePt as a

perpendicular medium when it is correctly aligned with

its magnetic easy-axis perpendicular to the substrate

plane. A careful choice of substrate and annealing

parameters is required to recrystallize the as-deposited

random fcc alloy to appropriately oriented L10.

Figure 3: The theoretical and experimental dependence of

composition on the applied potential.

FePt electrodeposited onto a Cu (001) substrate

has recently shown great promise. X-ray diffraction

revealed the transition to L10 upon annealing, and X-ray

pole figures indicated favorable orientations. Figure 4

shows FePt L10 (001) and (110) pole figures. The

(001) figure indicates perpendicular orientation of the

magnetic easy-axis (the c-axis), while the (110) figure

indicates an in-plane texture. The in-plane texture is an

added advantage, as it results in a narrower switching

field distribution.

Copper additions to the alloy have been found to

lower the A1/L10 phase transition temperature by up

to 90 oC. It may be speculated that interdiffusion of

copper from the substrate during the anneal allowed the

recrystallization to proceed from the interface with the

substrate. It is likely that this would allow the film to

replicate the orientation of the substrate.

Figure 4: X-ray pole figures showing favorably oriented FePt L10 .

Figure 5: Magnetic hysteresis measurements showing a 10 kOe

coercivity.

Magnetic hysteresis measurements performed

using a Kerr magnetometer are shown in Figure 5.

The magnetic coercivity of 10 kOe is comparable to

figures quoted in the literature for vacuum-deposited

FePt. It is believed to be the highest value reported

for an electrodeposited film.

Current efforts focus on controlling the

interdiffusion between substrate and film to minimize

loss of magnetization in the alloy, and on moving

from planar films to through-mask deposited arrays

of FePt pillars.

For More Information on this Topic

W.F. Egelhoff, Jr. (Metallurgy Division, NIST);

E.B. Svedberg (Seagate Research, Pittsburgh)
18

Technical Highlights

Breakthroughs in Magnetic Refrigeration

In the past 10 to 15 years, there has been a

substantial effort to find alternative cooling

technologies to vapor compression systems.

This has been driven largely by the need to

reduce the high energy costs of present systems

along with their use of harmful CFC refrigerants.

Magnetic refrigeration technology is one such

alternative. In principal, because it is a reversible

process, magnetic cooling should be more efficient

than the competing irreversible vapor compression

systems. However, magnetic cooling technology

has historically been relegated to cryogenic,

high-magnetic field applications since efficiency

was so poor at higher temperatures. In 2004, we

made progress in identifying materials with greatly

improved performance close to room temperature.

For U.S. industry to take advantage of these new

materials, their behavior needs to be understood

and methods of proper measurement determined.

We are providing the metrology to do that.

Robert Shull, Virgil Provenzano, and

Alexander Shapiro

I

n 1997 a large (“giant”) magnetocaloric effect was

reported in the Gd5Ge2Si2 compound between 270 K

and 300 K, thereby generating a great deal of interest as

a potential near-room temperature magnetic refrigerant.

Unfortunately, large hysteretic losses occur in the same

temperature range where this compound exhibits its

large magnetocaloric effect, making the magnetic

refrigeration with the material inefficient.

In Nature [Vol. 429, p. 853 (2004)], we reported

on the discovery of an effective and straightforward

method for greatly reducing (by more than 90 percent)

the large hysteresis losses in Gd5Ge2Si2. This is

accomplished by alloying the compound with a small

amount of iron, which has the additional benefit of

shifting the magnetic entropy change (∆Sm) peak

to higher temperature, from 275 K to 305 K, and

broadening its width. Although the addition of Fe yields

comparable refrigerant capacity (RC) values, a greater

resultant value is obtained for the Fe-containing alloy

when the hysteresis losses are subtracted. The

Fe-containing alloy is clearly better for near-room

temperature magnetic refrigeration applications.

Figure 1 shows the magnetization (M) vs. applied

magnetic field (H) data measured in the important

temperature range of peak magnetocaloric effects

for the Gd5Ge2Si2 compound. In this material, the

enhanced values of the magnetocaloric effect have

been ascribed to the existence of a field-induced

crystallographic phase change in the material from

a low-field paramagnetic structure to a high-field

ferromagnetic crystal structure. As a consequence of

this field-induced phase change, there is hysteresis in

its transformation, shown by the shaded areas enclosed

within the field cycles, corresponding to the cost in

energy to make one cycle. The magnitude must be

assessed when determining whether a particular

refrigerant is useful in a given application.

Figure 2: Magnetic hysteresis measurements showing no

field-induced ferromagnetic transition and nearly zero hysteresis

in the Gd5Ge1.9Si2Fe0.1 alloy.

Figure 1: Magnetic hysteresis measurements showing a

field-induced ferromagnetic transition and large hysteresis in

the “giant magnetocaloric effect” Gd5Ge2Si2 compound.

We have found that by adding a small amount of

Fe to the Gd5Ge2Si2 compound, the hysteresis may

be significantly reduced. This effect is shown in the

M vs. H data for this alloy in the important temperature

range of potential use in Figure 2, where the shaded

hysteresis regions are nearly zero.
19

Technical Highlights

A magnetic field is alternately applied and removed

from a refrigerant during a single cooling cycle in a

magnetic refrigerator, thus any magnetic hysteresis

will reduce the usefulness of a material. Figure 3

shows exactly how much of a difference in hysteresis

there is between the Gd5Ge2Si2 and Gd5Ge1.9Si2Fe0.1

alloys.

The reduced hysteresis in the quaternary alloy is due

to a lack of field-induced paramagnetic-to-ferromagnetic

crystallographic phase change. This change in behavior

is caused by the Fe combining with primarily the Si in

the ternary compound to form an Fe-rich secondary

phase, thereby reducing the Si content in the majority

Gd-Ge-Si phase. As a consequence, the thermodynamics

of the Gd-Ge-Si alloy were changed from that of the

precursor Gd5Ge2Si2 compound.

The magnetic entropy change (∆Sm) for a 5 T

applied field as a function of temperature for both

alloys is shown in Figure 4. The computed refrigerant

capacities (RC) are indicated on the figures and shown

by the shaded areas. Compared to Gd5Ge2Si2, the

iron-containing compound exhibits a smaller, but

broader ∆Sm peak, and a ∆Sm peak at a higher

temperature. Purely on this basis, Gd5Ge2Si2 is the

superior material, but the Fe-containing alloy might be

attractive for higher temperature applications due to

its higher temperature peak.

One method to account for the hysteresis losses of

each alloy is to simply subtract it from the corresponding

refrigerant capacity value. Subtraction of the average

hysteresis in the temperature range of the ∆Sm peak

for each alloy (~ 65 J/kg and ~ 4 J/kg, respectively,

for the ternary and quaternary alloys) from the

corresponding refrigerant capacity values yielded

approximate values of 240 J/kg for the Fe-free alloy

and 355 J/kg for the Fe-containing alloy. Consequently,

when the hysteresis losses are taken into account,

it is clear that the Gd5Ge1.9Si2Fe0.1 alloy is a much

better magnetic refrigerant than the Gd5Ge2Si2

compound despite its lower ∆Sm peak value.

Most prior evaluations of magnetic refrigerants have

disregarded the material hysteresis losses, and in

some materials these losses can be quite large; this

example shows the weakness in that approach.

“The results are pretty amazing,” states Michael

DiPirro [Science News 165, 405 (2004)], a cryogenic

engineer at the NASA Goddard Space Flight Center

in Greenbelt, Maryland.

For More Information on this Topic

Virgil Provenzano, Robert D. Shull, and

Alexander J. Shapiro, “Reduction of hysteresis

losses in the magnetic refrigerant Gd5Ge2Si2 by

the addition of Iron,” Nature 429, 853 (2004).

Figure 3: Hysteresis energy loss as a function of temperature

for the Gd5Ge2Si2 and Gd5Ge1.9Si2Fe0.1 alloys.

Figure 4: Computed ∆Sm [for ∆H = 3980 kA/m (5 T)],

normalized with respect to sample mass, of the Gd5Ge2Si2

compound (top) and of the Gd5Ge1.9Si2Fe0.1 alloy (bottom),

plotted as a function of temperature showing the presence of

peaks centered near 270 K and 305 K respectively for Gd5Ge2Si2

and Gd5Ge1.9 Si2Fe0.1.
20

Technical Highlights

We are developing AFM-based metrology for

rapid, nondestructive measurement of mechanical

properties with true nanoscale spatial resolution.

Atomic force acoustic microscopy methods enable

elastic-modulus measurements at either a single

point or as a map of local property variations.

Complementary information obtained with

scanning electron microscopy provides insight

into structure-property relations and helps to

interpret nanoscale contact-mechanics behavior.

The information obtained furthers our understanding

of the nanomechanical properties of surfaces,

thin films, and nanoscale structures.

Donna C. Hurley

New measurement solutions are required to address

the rapidly burgeoning field of nanotechnology.

In particular, information about mechanical properties on

the nanoscale is needed. Knowledge of properties like

elastic modulus and interfacial quality (defects, strain,

adhesion, etc.) is critical to successful development of

new films and nanoscale assemblies. Such information

could also assess integrity or reliability in applications

from microelectronics to biotechnology. Existing

methods for mechanical-property measurements have

drawbacks: they are destructive, limited to specialized

test specimens, or not quantitative. Instrumented or

“nano-” indentation (NI), a current industry workhorse,

will have limited value as scales shrink well below

1 μm, and softer materials are more frequently used.

To meet this need, we are developing tools that

exploit the spatial resolution of atomic force microscopy

(AFM). Our approach, called atomic force acoustic

microscopy (AFAM), involves the vibrational resonance

of an AFM cantilever when its tip is in contact with a

sample. By comparing the cantilever’s contact-resonance

frequencies for an unknown material to those for a

reference sample with known properties, the indentation

modulus M of the unknown material can be determined.

[For an isotropic material M = E/(1–ν2), where E is

Young’s modulus and ν is Poisson’s ratio.] The small

tip radius (~5–50 nm) means that we can obtain in-situ

elastic stiffness images with nanoscale spatial resolution.

In FY04, we extended our quantitative AFAM

techniques in a variety of ways. In one effort, the

effect of film thickness on measurement accuracy

was investigated. We measured M for three nickel

(Ni) films approximately 50, 200 and 800 nm thick.

The values of M ranged from 220 GPa to 223 GPa,

significantly lower than that expected for bulk

Quantitative Nanomechanical Properties

polycrystalline Ni. Scanning electron microscopy (SEM)

revealed that the films were nanocrystalline (grain diameter

< 30 nm). The observed reduction in M may be attributed

to an increased volume fraction of grain boundaries in the

nanocrystalline films. More importantly, the average values

of M for all three films were the same within measurement

uncertainty (~10 %). Thus the AFAM results were not

influenced by the elastic properties of the silicon substrate,

even for a 50 nm film. This behavior is due to the fact

that the AFAM stress field extends less than 100 nm into

the sample and decreases rapidly with depth due to the

small applied static loads (0.3–3 μN) and small radius of

contact (5–25 nm). Our result contrasts sharply with

nanoindentation, in which substrate properties must be

included to accurately measure submicrometer films.

The elastic properties of the 800 nm Ni film were also

measured using NI, microtensile testing, and surface

acoustic wave spectroscopy (SAWS). Both AFAM and

NI measure the film’s out-of-plane indentation modulus.

The results were in excellent agreement, validating AFAM

as a quantitative method in spite of its relative newness.

Microtensile testing values for the in-plane Young’s

modulus of the film were not consistent with the AFAM

and NI results if the film was assumed to be elastically

isotropic. The apparently contradictory results were

reconciled by use of a transversely anisotropic model for

the film’s elastic properties. This model is consistent with

the strong <111> film texture observed by x-ray diffraction.

When analyzed with the same model, the SAWS results

indicated that the film density was only slightly lower

(< 5 %) than the bulk value. These results illustrate a

relatively straightforward way to interpret mechanicalproperty measurements of thin films that is based on a

more physically realistic model than the simple assumption

of elastic isotropy.

Another effort investigated the effects of relative

humidity (RH) on AFAM measurements. AFAM contact

Figure 1: a) AFM tapping-mode topography and b) AFAM

relative-stiffness images of Si with n-octyldimethylchlorosilane SAM.
21

Technical Highlights

stiffness measurements may be affected by a variable

water layer between the tip and sample, at least in some

cases. By refining our data analysis methods to include

the effects of such a layer, apparent correlations between

the measured values of M and the ambient RH were

eliminated. This year we also developed a RH-controlled

AFM chamber in order to systematically study

these effects. Samples for the experiments were

provided by the Polymers Division and consisted

of patterned self-assembled monolayers (SAM) of

n-octyldimethylchloro-silane on Si substrates.

Through controlled ultraviolet-ozone exposure, the

relative hydrophobic/hydrophilic nature of the SAM

was adjusted in different sample regions. Figure 1

shows an AFM topography image and an AFAM

relative-stiffness image for a SAM/Si sample. The

SAM stripes are virtually invisible in the topography

image, even at very high resolution (10 nm full scale

height). However, the AFAM image clearly reveals the

hydrophobic SAM stripes. The regions covered by the

SAM appear more compliant (lower contact stiffness)

due to AFAM’s sensitivity to local variations in the

tip-sample adhesion. We are currently performing

further experiments on similar samples in order to

quantify how humidity and adhesion effects can be

distinguished from true mechanical-property variations.

measurements were done at relatively low static loads;

the load was then successively increased up to several

micronewtons to try to break and/or plastically deform

the tip. High-magnification SEM images were obtained

before and after each AFAM measurement. As can be

seen in Figure 2, R increased with use, indicating tip

wear. Values of R measured from the SEM images

were compared to the values obtained from AFAM

data using a Hertzian contact-mechanics model.

The AFAM values of R were consistently smaller than

the SEM values. Further data analysis and additional

experiments are planned to clarify this issue. The

knowledge gained in this way will help us to refine

our understanding of AFAM contact mechanics,

beyond the Hertz approximation, in order to improve

measurement accuracy and repeatability.

In related work, we are performing finite-element

studies of the AFM cantilever. The finite-element mesh

is based on actual cantilever dimensions from SEM

images and includes elastic anisotropy. The predicted

free-space resonant frequencies are in excellent

agreement with those observed experimentally.

Work is underway to predict the vibrational behavior

in contact. These results will allow us to refine

our data analysis models and thus improve

measurement accuracy.

The research described above involves either

quantitative single-point measurements, or qualitative

imaging of relative stiffness. In FY04, we worked to

realize our ultimate goal of quantitative nanomechanical

mapping. Critical to our success is a new frequency

tracking circuit that can determine the contact-resonance

frequencies at each image pixel. The circuit is based on

digital signal processing architecture that enables rapid

data acquisition (typically < 30 min. for a 256 × 256

image). We have begun to obtain resonance-frequency

images for a variety of materials. Recent enhancements

to our AFM mean that we can acquire images from not

only the flexural modes, but also the torsional modes of

the cantilever. By combining information from flexural

and torsional images, it may be possible to determine

simultaneously both Young’s modulus and Poisson’s

ratio for an isotropic material. Work in upcoming

months will focus on issues related to quantitative

image interpretation such as calibration procedures,

cantilever selection, tip wear, and choice of

contact-mechanics model. Each of these elements

plays a role in attaining our goal of truly quantitative

nanomechanical imaging.

For More Information on this Topic

D.C. Hurley (Materials Reliability Division, NIST)

Figure 2: SEM images of AFM cantilever tip a) before use and

b) after repeated AFAM contact experiments. The circled regions

indicate the tip wear that occurred through use.

 AFAM contact-resonance frequencies depend not

only on elastic properties, but also on the value of the

tip radius R. Thus knowledge of R and how it changes

over time is essential for accurate measurements of

elastic properties. To address this issue, we performed

AFAM experiments with different AFM cantilevers

on a sample with known elastic properties. The first
22

Data and Standards Resources

Advances in technology and the vitality of basic

research have an unequivocal dependence on

reliable data. Indeed, the technology transfer

between research and application is facilitated

and sometimes enabled by the development and

accessibility of carefully designed and evaluated

databases. The MSEL Ceramics Division has

excelled in its leadership in data resources for

crystallography, phase equilibria diagrams, and

materials property data.

Ronald G. Munro, Terrell A. Vanderah, and

Vicky L. Karen

The issue of reliable data has been examined vigorously

in numerous studies over the last three decades.

Early assessments, such as Critical Surveys of Data

Sources (NBS SP 396-1, 1978), voiced concerns over the

availability of data, while other studies, such as Economic

Effects of Corrosion (NBS SP 511-1&2, 1978), noted the

influential role that data can perform as a component of

a sound economy. More recently, defense and security

concerns, Materials Research to Meet 21st Century

Defense Needs (NMAB-498, 2002), have continued to

stress the need for reliable data.

The Ceramics Division has made a substantial effort

to address the multiple needs for materials data, the

scientific fundamentals for data evaluation methodology,

and the technological issues involved in optimizing the

utility of the data resources. Programmatically, Figure 1,

the data and standards technology projects are well

attuned to NIST’s core mission and its strategic

focus efforts, and there is abundant evidence that our

objectives are being met with considerable success.

There are several technology transfer mechanisms

that can be used for data and standards work, including

traditional publications, internet distribution, software

products for personal computers, and standard reference

materials. The Division’s most readily visible mechanism

for data technology transfer is provided by the Ceramics

WebBook that is featured on the Division’s internet

Figure 1: Programmatic contributions of the Data and Standards

Technology Group to the NIST mission.

Figure 2: Activity seen by the Ceramics Division’s homepage,

showing the substantial attraction to property data.

Figure 3: The relative distribution of users downloading data

from the Ceramics WebBook.

website. This site provides evaluated data for the physical,

mechanical, and thermal properties of advanced

ceramics, particularly structural ceramics (NIST Standard

Reference Database Number 30) and high-temperature

superconductors (NIST Standard Reference Database

Number 62). The activity on this site, Figure 2, is a clear

indicator of both the strong interest and the persistent

need for materials data. The site attracts more than 11,000

page requests per month of which approximately 78 %

are data downloads (nearly 9000 data tables).

The distribution of users, Figure 3, shows that all

sectors of the ceramics community have a keen interest

in the evaluated data provided by NIST.

Another very important mechanism for technology

transfer is provided by the Standard Reference Data Act

(Public Law 90-3960, 1968). Under the SRD Act, NIST

can pursue technology transfer through partnerships that

broadly serve the public interest. These partnerships

Technical Highlights
23

Technical Highlights

typically involve costs in excess of our Congressionally

funded base operations and consequently result in

small charges for the data products. Two prominent

collaborations of this type between the Ceramics Division

and private sector nonprofit organizations have brought

considerable credit and recognition to NIST.

The ACerS–NIST database began with the publication

of 178 diagrams in 1933. Since then, the collection has

evolved, Figure 5, to contain nearly 20,000 diagrams.

Originally, the diagrams were distributed in printed

volumes, now amounting to thirteen regular book

volumes, four topical volumes, and three annual volumes

that serve as supplements to the regular volumes.

Today, both printed and computerized versions are

provided and are made available through ACerS.

The newest addition to the series, Figure 6, is the

special topical volume, Phase Diagrams for Electronic

Ceramics I, edited by Robert S. Roth. This collection

concentrates on the technically important oxides of

titanium, niobium, and tantalum. Additionally, a newly

updated Cumulative Index 2003 was published this year

providing comprehensive coverage of all the ACerS–NIST

content published to date. All of the new diagrams and

Figure 4: commentaries are included in the CD-ROM database. Phase Equilibria Diagrams CD-ROM Database

Version 3.0 (NIST Standard Reference Database Number 31),

released in March 2004, provides comprehensive coverage of

all diagrams and commentaries published to date in the twenty

printed volumes of the series.

Figure 5: Evolution of the compilation of phase diagrams in the

ACerS–NIST collaborative database.

The longstanding NIST collaboration with the American

Ceramic Society (ACerS) on phase diagrams provides a

clear example of the remarkable productivity that can result

from these partnerships. Now led by Dr. Terrell Vanderah,

the ACerS–NIST collaboration achieved one of its most

anticipated goals this year, Figure 4, the development of a

new computerized version of NIST Standard Reference

Database Number 31, Phase Equilibria Diagrams.

Phase equilibria diagrams are used throughout

the ceramics industry to understand and control the

complex phenomena which increasingly underlie

advanced processing and materials performance.

These diagrams provide maps of the equilibrium

chemical and structural behaviors exhibited by materials

and provide critical starting information for the rational

design of materials processing schemes, for quality

assurance efforts, and for the optimization of the

physical and chemical properties of advanced materials.

Figure 6: Recent ACerS–NIST printed data products include a

topical volume on electronic ceramics and an updated cumulative

index for all content published to date.

The mutual commitment of ACerS and NIST to

this collaboration was reaffirmed in May of this year

with the signing of a new five-year agreement.

The ability to develop partnerships in the public

interest also has enabled a successful collaboration,

led by Dr. Vicky Karen, between NIST and

Fachinformationszentrum Karlsruhe Gesellschaft

fur wissenshaftlich-techmische Information mbH

(FIZ). This collaboration, Figure 7, has resulted

in the development of NIST Standard Reference

Database Number 84, the comprehensive FIZ–NIST

Inorganic Crystal Structure Database.

Crystallographic information is critical to efforts

to visualize, explain, and predict behaviors of

chemicals and materials, as well as to establish

the identity of materials in forensic investigations.

Literally tens of thousands of structures have been

reported. Those reports, however, have varying

degrees of reliability and completeness. Consequently,

researchers and instrument manufacturers have a
24

Technical Highlights

critical need for evaluated data and the mathematical

tools capable of distinguishing good structures from

bad structures and compatible data from incompatible

data. Through NIST’s efforts, the use of standard

crystallographic cells, unique reduced cells, and

the powerful mathematical matrix methods for

the application of group theory have become

fundamental to the analysis and identification of

crystal structures.

Figure 8: NIST Recommended

Practice Guide, SP 960-11,

examines pivotal issues in

data evaluation.

Additional technology transfer has been achieved

through the distribution of NIST Recommended

Practice Guide, SP 960-11, Data Evaluation Theory

and Practice for Materials Properties, Figure 8.

This Guide presents a unique view of data evaluation

as a scientific discipline. A theoretical foundation is

developed from the formal underpinnings of materials

metrology, and an extensive collection of examples

is used to examine the issues of accessibility,

reproducibility, consistency, and predictability with

distinctions being made among definitive relations,

correlations, derived and semiempirical relations,

heuristic theories, and value estimates. Critical

discussions include the use of properties as parameters

in models, the interpretation of ad hoc parameters,

and the treatments of procedural properties, response

dependent properties, and system dependent data.

Completed in FY2003 and printed in June 2003,

more than 1200 hard copies have been issued to

interested individuals, and an electronic version in

pdf format, available since January 2004, has resulted

in the distribution of another 1600 copies.

For a greater appreciation of the full range of data

and standards activities in the Ceramics Division, see

the tabulation of our products in the section, Databases

and Standards, later in this report.

For More Information on this Topic

P. Schenck, J. Harris, C. Sturrock (Ceramics

Division, NIST); A. Belsky (SRD, NIST Technology

Services); R. Roth, J. Hastie, M. Harne, A. Mighell

(Research Associates, Ceramics Division, NIST);

D. Watson (Cambridge Crystallographic DB);

M. Mecklenborg, J. You, C. Cedeno, E. Farabaugh,

K. Hill, N. Swanson, X.M. Wang (American

Ceramic Society); P. Luksch (FIZ); K. Rajan,

X. Li, A. Rajagopalan (RPI)

Figure 7: The FIZ–NIST Inorganic Crystal Structure Database

contains approximately 70,000 entries providing full structural,

three-dimensional crystallographic parameters.

The FIZ–NIST collaboration provides a

comprehensive compilation of three-dimensional

crystallographic data. The components of a typical

entry include data on the conventional cell, the reduced

cell, lattice type, space group, lattice parameters,

atomic coordinates, d-spacings, chemical name,

chemical formula, material class indicators, and

literature reference citations.

The collaboration is built on shared and

complementary responsibilities. NIST is responsible

for the essential scientific and informatic aspects

of the work, while FIZ provides data abstracting

and related interactions with the International Union

of Crystallography, particularly for bibliographic

information. Data evaluation is done jointly.

The latest version of the database, released this

year, contains more than 70,000 critically evaluated

data entries. The database is licensed to research

facilities, instrument manufacturers, educational

institutions, and individuals. Distributor license

agreements with instrument manufacturers are

propagated subsequently as user licenses to the

instrument buyers. As a result, these data are used

every day in defense, aerospace, electronic, petroleum,

chemical, and homeland defense related industries,

as well as in government and academic research

facilities worldwide.
25
26

Microelectronics

Combinatorial materials science has rapidly

become a new paradigm for the acceleration

of materials research. It is a fast and efficient

methodology for materials optimization and

discovery, characterized by high throughput,

parallel experiments, automated analysis, and

massive data sets. NIST’s industrial stakeholders

are identifying it as the only viable technique for

understanding complex materials science systems

in a competitive timeframe. Its application to

a critical materials science problem in the Si

microelectronics industry, the replacement of the

gate stack, is expected to drive an inorganic

combinatorial materials science program at NIST.

Martin L. Green

NIST/MSEL is poised to play several important roles

in developing combinatorial materials methodologies,

especially as they pertain to industrially important, advanced

inorganic materials. Included in this class are materials

such as thermoelectrics, dielectric and metal layers

for advanced Si CMOS gate stacks, multiferroics,

magnetic semiconductors for spintronics, transparent

semiconductors, and fuel cell and H2 storage materials.

NIST/MSEL has an opportunity to take a lead position

in the use of combinatorial methodologies for:

■ New, combinatorially-friendly (rapid, local,

microscopic measurements) metrologies;

■ Materials optimization and development;

■ Means of experimentally verifying computed

materials properties;

■ Tools for determining phase diagrams and other

property data; and

■ “Data on demand,” or “just-in-time-data.”

The advanced gate stack application for Si CMOS

is a good example. International Sematech (ISMT) is

currently faced with major materials challenges to further

miniaturization. Figure 1 schematically illustrates a metal

oxide-semiconductor field effect transistor (MOSFET),

showing the advanced gate stack which consists of the

high-κ (κ = dielectric constant) gate dielectric and the

metal gate electrode. To enable further device scaling,

the capacitive equivalent thickness (CET) of the gate stack

thickness must be 0.5 nm to 1.0 nm. This will not be

achievable with existing SiO2/polycrystalline Si gate stacks.

Given the large number of possible choices for these

new layers, the only feasible approach to understanding

the complex materials interactions that result at the

gate dielectric/substrate and gate dielectric/metal gate

electrode interfaces is through the application of

combinatorial methodologies.

The acquisition of a state-of-the-art combinatorial

synthesis tool is expected be one of the cornerstones

of the NIST/MSEL effort. In addition, we plan to

acquire combinatorially-friendly tools such as a

micro-x-ray diffractometer, and to develop new

metrologies such as nanocalorimetry for the

detection of phase transformations in thin films.

Figure 1: MOSFET device with advanced gate stack.

Figure 2: Combinatorial ternary and binary film libraries.

Combinatorial Tools for Materials Science

The new combinatorial synthesis tool will be capable

of depositing entire ternary and binary libraries in areas

as small as 6.5 cm2 (1 in2), as is shown in Figure 2.

Contributors and Collaborators

L. Cook, W. Wong-Ng, P. Schenck (Ceramics

Division, NIST); L. Bendersky, A. Davydov (Metallurgy

Division, NIST); S. Semancik (CSTL, NIST);

J. Suehle, E. Vogel (EEEL, NIST); T. Chikyow

(NIMS, Japan); B. Murto (International Sematech);

I. Takeuchi (U. of Maryland)
27

Microelectronics

Modern electronic devices have reached the point

where fundamental materials properties now limit

continued improvement in device performance.

Consequently, new materials, their synthesis, their

properties, and their interactions with established

materials and technologies are in continuous need

of development and investigation. The Ceramics

Division operates a suite of synchrotron beamlines,

at the Advanced Photon Source and at the National

Synchrotron Light Source, designed to address

critical issues focused on these next-generation

materials, including the electronic and structural

properties of materials used in advanced

electronic applications.

Joseph C. Woicik

The electronics industry is seeking to increase device

performance by increasing carrier mobility in silicon

by introducing a small tensile strain into the silicon

lattice. This is accomplished by the epitaxial growth

of a thin silicon layer on a virtual crystalline substrate

of relaxed Si1–xGex with x typically between 10 % and

50 %. A critical aspect of this process is the control of

defects in the SiGe-alloy layer and the propagation of

these defects into the strained-Si film.

Spectroscopy, Diffraction, and Imaging of Electronic Materials

Figure 1: Radial diffraction scan for a strained-Si/SixGe1–x /Si(001)

semiconductor layered structure.

We have utilized x-ray diffraction and x-ray

topography at the UNICAT beamline facility at the

Advanced Photon Source to image defects in the SiGe

film and to study how these defects propagate into the

strained-Si overlayer. Figure 1 shows a high-resolution

x-ray diffraction scan around the Si(004) Bragg

condition from a 500 Å Si film grown on a relaxed

3 μm thick SiGe film with a Ge content of 20 %.

The relaxed SiGe film was grown on top of a SiGe

layer that was grown on a Si(001) substrate and

graded in composition from 0 % to 20 % Ge content

over a thickness of 2 μm.

The diffraction from the SiGe is seen near

2θ = 60.4°; it appears as a doublet due to a slight

composition variation due to the intermediate

planarization process. Diffraction from the grade

is also apparent. The sharp peak near 2θ = 60.9° is

diffraction from the Si substrate, and the much weaker

peak near 2θ = 61.3° is diffraction from the strained-Si

film. The Si film has a smaller perpendicular lattice

constant than the crystalline Si substrate because it is

under in-plane tensile strain due to its epitaxy with the

SiGe layer that possesses a larger cubic lattice constant.

The differences in lattice constants between the

strained-Si film, SiGe layer, and Si substrate make it

possible to image the diffraction from each component

separately. Figure 2 shows the (113) x-ray topographs

recorded with an x-ray energy of ≈ 8.9 keV. This

diffraction geometry was chosen because it is within

Si total external reflection and, therefore, limits the

x-ray penetration depth into the sample.

The microstructure of the substrate and film are

nearly identical, demonstrating that the misfit-dislocation

structure responsible for the relaxation of the SiGe

layer acts as a template for the microstructure of the

strained-Si film. The crystallographic nature of these

defects and their contribution to the ultimate relaxation

of the strained-Si film are currently under investigation.

Contributors and Collaborators

D. Black, I. Levin (Ceramics Division, NIST);

M. Erdtmann, T.A. Langdo (AmberWave)

Figure 2: (113) x-ray topographs of the SiGe film and the

strained-Si overlayer.
28

Microelectronics

Ceramic compounds with exploitable dielectric

properties are widely used in technical applications

such as actuators, transducers, capacitors, and

resonators or filters for microwave communications.

Phase equilibria determination integrated with

systematic chemistry–structure-property studies

contribute toward the fundamental understanding

and rational design of these technologically

important materials with improved properties

and/or reduced processing costs.

Terrell A. Vanderah, Igor Levin, and

Michael W. Lufaso

Cost and performance are the primary and secondary

drivers, respectively, for today’s commercial needs

in the area of dielectric ceramics. For example, component

suppliers and builders of 2 GHz cellular infrastructure are

critically impacted by the high cost of tantalum-containing

ceramics needed for dielectric resonators: only a single

ceramic material, perovskite-like Ba3ZnTa2O9 (BZT),

is available with the needed properties. Interest is keen

to reduce its processing costs or to find an alternative,

less-expensive substitute. The results of an experimental

phase equilibria study of the system (Figure 1) revealed

that BZT ceramics must be processed so that ZnO

volatilization occurs along the two-phase join between

BZT and Ba8ZnTa6O24 (8L) to prevent the formation of

deleterious air-sensitive compounds high in BaO content,

or dielectrically poor “TTB” type phases.

Phase Equilibria and Properties of Dielectric Ceramics

Figure 1: Phase equilibria diagram determined for the system

containing the important commercial ceramic Ba3ZnTa2O9 (BZT).

Figure 2: Phase equilibria diagram determined for the system

containing Ba3ZnNb2O9 (BZN), a possible BZT alternative.

A potential replacement for BZT is the analogous

compound with less costly niobium, Ba3ZnNb2O9.

The phase equilibrium diagram determined for this

system (Figure 2) provides processing information

for this ceramic and clearly indicates that its dielectric

loss cannot be improved by liquid-phase sintering in

the presence of low-melting, electrically acceptable

ZnNb2O6, because the two compounds do not occur

in equilibrium with each other. Such mixtures, instead,

will form dielectrically poor impurity phases.

Systematic studies of the Ba3MNb2–xSbxO9

(M =Mg,Ni,Zn), system were carried out to manipulate

the crystal chemistry and high-frequency (> 2 GHz)

dielectric properties by progressive substitution of Sb5+

(d10) for Nb5+ (d0). The results showed that control of

permittivity and tuning of the temperature coefficient to

zero was possible with appropriate substitution. Optimal

dielectric losses were obtained for specimens with low

x-values and 2:1-type ordered perovskite structures.

Figure 3: HRTEM image of 50:50 LaMg1/2Ti1/2O6-La2/3TiO3.

Dark crosses denote La vacancies, deduced from image simulations

(insert). Short-range order of La vacancies is revealed as pairs

of dark crosses in both the [001] and [100] directions and causes

diffuse superlattice reflections in the diffraction pattern.

Detailed structural studies of the LaMg1/2Ti1/2O6-

La2/3TiO3 solid solution were carried out to elucidate

the origin of the anomalous changes in permittivity and

temperature coefficient near 50:50. The results showed

that the abrupt changes in properties were accompanied

by the disappearance of one octahedral tilting mode and

the onset of short-range ordering of La vacancies.

Contributors and Collaborators

W. Wong-Ng, R.S. Roth, B. Burton, E. Cockayne

(Ceramics Division, NIST); J.E. Maslar (Process

Measurements Division, NIST); R. Geyer

(Radio Frequency Technology Division, NIST);

S. Bell (TCI Ceramics)
29

Microelectronics

Dielectric ceramics are widely used in applications

such as semiconductor gate dielectrics, actuators,

capacitors, and resonators or filters for microwave

communications. For simple systems, first-principles

(FP) methods allow direct calculations of

low-temperature dielectric constants. For complex

systems, and for rational new materials design,

larger scale modeling is required. Multiscale

effective Hamiltonian (EH) models derived from

FP calculations retain high accuracy and allow

phenomena caused by chemical ordering, defects,

and changes in temperature to be explored. The EH

provides a bridge from FP calculations (≤ 100

atoms) to the needed computations with hundreds

of thousands of atoms. We are developing a

methodology to enable automatic EH generation

for real three-dimensional systems.

Eric Cockayne and Benjamin P. Burton

Materials that are optimized for industrial

applications are generally solid solutions in which

the configuration of ions on mixed ion sites strongly

affects the physical properties. To model these

phenomena, detailed FP calculations are performed

on a variety of perfectly ordered systems. For example,

PbMg1/3Nb2/3O3 (PMN) is the main component of

recently discovered materials with ultrahigh piezoelectric

constants. PMN presents a singular challenge, because

the details of Mg-Nb ordering are not fully known.

To better understand PMN, we studied various

PMN composition supercells with 15 to 30 atoms.

A comparison of fully relaxed structures predicts a

ground state ordering different from that previously

assumed. The two lowest-energy structures found are

most compatible with the “random site model” of PMN

deduced from experiment. Calculated infrared spectra

(directly related to the dielectric function) also show

that the two lowest energy structures are most similar

to experiment.

For the (CaAl1/2Nb1/2O3)1–x–(CaTiO3)x (CAN-CT)

system of microwave dielectric interest, a cluster

expansion EH model for the low temperature dielectric

constant was developed to calculate the dielectric

constant for an arbitrary CAN-CT configuration as

a function of x and Ti-Al-Nb ordering. Work is in

progress to parameterize similar models for other solid

solution systems.

Temperature dependent dielectric properties can

be modeled with Monte Carlo and molecular dynamics

simulations based on EHs. The EH for a heterovalent

solid solution includes the random local electric fields

Theory and Modeling of Dielectric Materials

Figure 1: Predicted ground-state ordering of Mg (red) and

Nb (blue) in PbMg1/3Nb2/3O3.

generated by mixing differently charged ions in an

alloy. We compiled a catalog of the possible local field

directions in the nearest-neighbor approximation.

By including local fields in an EH for PbSc1/2Nb1/2O3

(PSN), we can reproduce the experimental observation

that the dielectric peak of PSN, as a function of

temperature, is broadened when nanoscale ordered

domains are present.

Defects also affect physical properties. We computed

the dipole moment of a Pb-O divacancy in PbTiO3

from FP. Its moment is 2.28 e times the distance between

the original Pb and O sites. The large electric fields

produced by such defects have been incorporated into

our EH for PSN.

Effective Hamiltonians for dielectrics and ferroelectrics

are based on an efficient “lattice Wannier function” (LWF)

description of the lattice dynamics of these systems. We

have found a principle for automatically generating LWF

and have demonstrated that it works on one-dimensional

model systems. The method works equally well for

chemically ordered systems, disordered systems, and

systems with defects. This is a highly promising step

towards automatic generation of effective Hamiltonians

for real three-dimensional systems, which will make

these EH methods accessible to non-experts.

Contributors and Collaborators

I. Levin, M. Lufaso, S. Tinte (Ceramics Division,

NIST); P. Gehrig (NIST Center for Neutron Research,

NIST); A. van de Walle (Northwestern U.); S.A.

Prosandeev (Rostov State U.); U.V. Waghmare (JNCASR)
30

Microelectronics

Photolithography, the process used to fabricate

integrated circuits, is the key enabler and driver

for the microelectronics industry. As lithographic

feature sizes decrease to the sub-100 nm length

scale, significant challenges arise because both

the image resolution and the thickness of the

imaging layer approach the macromolecular

dimensions characteristic of the polymers used

in the photoresist film. Unique high-spatial

resolution measurements are developed to

reveal limits on materials and processes that

challenge the development of photoresists for

next-generation sub-100 nm lithography.

Vivek M. Prabhu

Photolithography is the driving technology used by

the microelectronics industry to fabricate integrated

circuits with ever decreasing sizes. In addition,

this fabrication technology is rapidly being adopted

in emerging areas such as optoelectronics and

biotechnology requiring the rapid creation of nanoscale

structures. In this process, a designed pattern is

transferred to the silicon substrate by altering the

solubility of areas of a polymer-based photoresist

thin film through an acid catalyzed deprotection

reaction after exposure to radiation through a mask.

To fabricate smaller features, next generation

photolithography will be processed with shorter

wavelengths of light requiring photoresist films

less than 100 nm thick and dimensional control to

within 2 nm.

To advance this key fabrication technology, we

work closely with industrial collaborators to develop

and apply high-spatial resolution and chemically specific

measurements to understand changes in material

properties, interfacial behavior, and process kinetics

at nanometer scales that can significantly affect the

patterning process.

This year, we have continued to apply and

advance unique measurement methods to provide

structural measurement of fabricated nanoscale

structures and new insight and detail into the complex

physico–chemical processes used in advanced

chemically amplified photoresists. These methods

include x-ray and neutron reflectivity (XR, NR), small

angle x-ray and neutron scattering (SAXS, SANS),

near-edge x-ray absorption fine structure spectroscopy

(NEXAFS), combinatorial methods, solid state nuclear

magnetic resonance (NMR), quartz crystal microbalance

(QCM), fluorescence correlation spectroscopy (FCS),

and atomic force microscopy (AFM).

Polymer Photoresists for Next-Generation Nanolithography

Accomplishments for this past year include:

advancement of photoresist–liquid interfaces for

immersion lithography and developer distribution in

ultrathin films (see highlight); photoresist component

segregation (see Figure 1); quantification of the

post-exposure bake time on the reaction–diffusion of

photoacid 3D deprotection volume; first measurement

of immersion and exposure dependence of the surface

composition of base additives in 193 nm resist films;

identification of key anti-reflective coating (ARC)

components responsible for profile control problems

and residual layer formation at the ARC-resist interface;

quantification of environmental sensitivity by in-situ

processing using NEXAFS; and quantification of the

effects of developer and additives on the final resolution

of lithographic features using a model reaction–front

bilayer geometry.

International SEMATECH has selected NIST in

an effort to apply these fundamental measurements

to identify materials sources of the fabrication limits

of advanced photoresists.

Contributors and Collaborators

B. Vogt, E. Jablonski, C. Soles, W. Wu, C. Wang,

R. Jones, T. Hu, M. Wang, D. VanderHart, C. Chiang,

E. Lin (Polymers Division, NIST); D. Fischer,

S. Sambasivan (Ceramics Division, NIST); S. Satija

(NCNR, NIST); D. Goldfarb, A. Mahorowala,

M. Angelopoulos (IBM T.J. Watson Research Center);

H. Ito (IBM Almaden Research Center); C. Willson

(University of Texas at Austin); R. Puligadda,

C. Devadoss (Brewer Science); R. Dammel,

F. Houlihan (Clariant Corporation)

Figure 1: NEXAFS instrument and spectra illustrating a

homopolymer enrichment at the film surface for a model 157 nm

photoresist blend. The mismatch in surface versus bulk composition

illustrate interfacial limitations for sub 100 nm structures.
31

Microelectronics

Nanoimprint Lithography

Nanoimprint lithography (NIL) has emerged as

a viable next generation lithography (NGL)

capable of transferring physical patterns smaller

than 5 nm into a polymeric film.[1] The production

of nanoscale structures enabled by NIL raises new

metrology challenges, as the ability to pattern now

exceeds the ability to measure and/or evaluate

material properties. The objective of this project

is to develop high-resolution metrologies that

facilitate the development of NIL.

Christopher L. Soles and Ronald L. Jones

NIL has recently emerged as one of the leading

NGL candidates for the semiconductor industry.

The 2003 update of the ITRS Semiconductor Roadmap

identifies NIL as a strong candidate lithography for the

45 nm technology node. Silicon Strategies included

Molecular Imprints, Inc. (Austin, TX) and Nanonex

(Princeton, NJ), two major NIL tool companies, in their

“60 Emerging Start-ups” list for 2004. Going beyond

CMOS, MIT’s Technology Review selected NIL as one

of the “10 Emerging Technologies That Will Change

the World.”[2] The cost efficient and high-resolution

nanopattering of NIL will also be beneficial in emerging

technologies such as optical communications, data

storage, bio devices, nano-electromechanical systems

(NEMS), micro-electromechanical systems (MEMS),

and sensors, by enabling low-cost nanofabrication.

The NIL concept is elegantly simple. A master pattern

with sub-100 nm features is fabricated into a hard material

(Si, quartz, Ni, etc.) using high-resolution (but slow)

patterning, such as e-beam lithography. The patterns are

then transferred into a resist by stamping the hard master

mold into a softer polymer or monomer film. The pattern

is “set” into the resist film with either heat, to facilitate

flow into the mold features, or by using a monomeric

(liquid-like) film that cross-links in the mold. These imprints

can be repeated multiple times using a single master, greatly

reducing the cost of ownership.

One of the greatest challenges facing NIL is to quantify

the fidelity of pattern transfer; traditional shape metrologies

struggle when feature sizes approach 5 nm. We are

developing critical dimension small angle X-ray scattering

(CD-SAXS) to quantify 3-D pattern shape, with sub-nm

resolution. Since CD-SAXS uses high-energy X-rays that

penetrate Si and most mold materials, we can quantify

pattern shape in the master mold, on the mold in contact

with the resist, and in the final pattern (i.e., fidelity of

pattern transfer), as depicted in Figure 1.

Figure 2: CD-SAXS data (intensity versus scattering vector) for

parallel lines and spaces imprinted into a PMMA film.

Figure 1: CD-SAXS quantification of the nanoimprint process.

Figure 2 illustrates CD-SAXS data for parallel lines

and spaces imprinted into a poly(methyl methacrylate)

(PMMA) film. The data are in black, while the red line

is a fit to a trapezoidal cross section. By tilting the

sample and fitting several data sets, we determine that

the pattern pitch is (253 ± 1) nm, the average line

width is (146 ± 1) nm, the trapezoid side-wall angle is

(4.2 ± 0.5) °, and line height is (180 ± 1) nm.

By providing such accurate structural information, we

enable the quantitative evaluation and improvement of

imprint processes. Furthermore, we are also developing

complementary mechanical and physical property

measurements for imprinted polymeric nanostructures.

Understanding the unique properties that arise in these

nanostructures is crucial to engineering functional

and robust polymeric devices at the nanoscale.

References

1. M.D. Austin, et al., Appl. Phys. Lett. 84, 5299 (2004).

2. Technology Review, Feb, 42–44 (2003).

Contributors and Collaborators

W. Wu, T. Hu (Polymers Division, NIST);

S. Hooker, C. Flannery (Materials Reliability Division,

NIST); S. Pang (University of Michigan); C.G. Willson

(UT Austin); L. Koecher (Nanonex); D. Resnick,

K. Nordquist (Motorola)
32

Microelectronics

NIST provides the semiconductor industry with

unique on-wafer measurements of the physical

and structural properties of nanoporous thin films.

Several complementary experimental techniques

are used to measure the pore and matrix

morphology of candidate materials. The data

are used by industry to select candidate low-k

materials. Measurement methods that may be

transferred to industrial laboratories, such as

x-ray porosimetry, are developed. New methods

are being developed to measure patterned low-k

samples and to assess the extent of porous

structure modification caused by plasma etch.

Eric K. Lin and Wen-li Wu

The future generation of integrated circuits requires

porous low-k interlayer dielectric materials to

address issues with power consumption, signal

propagation delays, and crosstalk that decrease device

performance. The introduction of nanometer scale

pores into a solid film lowers its effective dielectric

constant. However, increasing porosity adversely

affects other important quantities such as physical

strength and barrier properties. These effects pose

severe challenges to the integration of porous

dielectrics into the device structure.

There is a need for nondestructive, on-wafer

characterization of nanoporous thin films. Parameters

such as the pore size distribution, wall density, porosity,

film uniformity, elemental composition, coefficient of

thermal expansion, and film density are needed to evaluate

candidate low-k materials. NIST continues to develop

low-k characterization methods using a combination of

complementary measurement methods including small

angle neutron and x-ray scattering (SANS, SAXS), high

resolution x-ray reflectivity (HRXR), x-ray porosimetry

(XRP), SANS porosimetry, and ion scattering. To facilitate

the transfer of measurement expertise, a recommended

practice guide for XRP was completed and will be available

for industrial customers.

In collaboration with industrial and university partners,

we have applied existing methods to new low-k materials

and developed new methods to address upcoming

integration challenges. A materials database developed

in collaboration with International SEMATECH is used

extensively by SEMATECH and its member companies to

help select candidate materials and to optimize integration

processing conditions. This year, we also addressed the

effects of the ashing/plasma etch process on the low-k

material during pattern transfer. Often, surfaces exposed

to ashing/plasma densify and lose terminal groups

(hydrogen or organic moiety) resulting in increased

Characterization of Porous Low-k Dielectric Constant Thin Films

moisture adsorption and, thus, increased dielectric

constant. HRXR measurements enable quantification of

the surface densification or pore collapse in ashing-treated

and/or plasma-treated blanket films.

Figure 1: SAXS data of a test line grating created in a porous

low-k film. Experimental data — solid symbol; model fit — red

line. The top data was fit with a uniform cross-section whereas

the bottom data was fit with a dense skin layer. Regions outlined

by blue circle highlight the difference between these two models.

A new method using SAXS was also developed to

investigate the effect of plasma etch on patterned low-k

films. Any densification of the sidewall may be observable

by x-ray scattering from the cross-section of a patterned

nanostructure. Preliminary SAXS work was carried

out at Argonne National Laboratory using line gratings

of low-k material. The feasibility of this approach is

shown in Figure 1 where a surface layer densification

is needed to fit the SAXS data.

Contributors and Collaborators

H. Lee, C. Soles, R. Hedden, M. Silverstein, T. Hu,

R. Jones, D. Liu, B. Vogt, B. Bauer (Polymers Division,

NIST); C. Glinka (NIST Center for Neutron Research);

Y. Liu (International SEMATECH); Q. Lin, A. Grill,

H. Kim (IBM); M. Ko (LG Chem.); H. Fu (Novellus);

J. Quintana, D. Casa (Argonne National Laboratory);

K. Char, D. Yoon (Seoul National University);

J. Watkins (University of Massachusetts — Amherst)
33

Nanoporous low-dielectric-constant (low-κ) films

present considerable implementation challenges for

the microelectronics industry and also raise new

scientific questions. We apply optical methods to

these films to evaluate such critical properties as

density/porosity, Young’s modulus, and Poisson’s

ratio. Our techniques allow measurement of

properties that are otherwise difficult to determine

and shed light on how the mechanical properties

depend on porosity.

Colm Flannery and Donna C. Hurley

Current miniaturization trends in microelectronics

require faster device switching. This need can be at

least partially met by lowering the resistance-capacitance

factor of the dielectric materials. One promising solution

is to introduce nanometer-sized pores that reduce the

dielectric constant κ. Unfortunately, introduction of

porosity may lead to a drastic reduction in stiffness

(Young’s modulus), adversely affecting the material’s

chances of surviving the fabrication process. In addition

to predicting and ensuring process reliability, accurate

values of a film’s mechanical properties are needed

to model the mechanical behavior of the resulting

microelectronics device. New tools are needed to

characterize these relevant thin-film properties

(e.g., Young’s modulus and Poisson’s ratio ν), as

well as to better define their dependence on porosity.

In FY04, we evaluated Poisson’s ratio ν in

methylsilsesquioxane (MSSQ) polymer films of varying

porosity with Brillouin light scattering. In this technique,

a Fabry–Perot interferometer detects frequency-shifted

photons scattered by ambient thermal phonons in

the material. The frequency shift of the photons is

characteristic of the acoustic phonon modes in the film.

Values of ν were determined from measurements of both

longitudinal and surface acoustic wave modes. Figure 1

reveals that ν decreases as porosity increases. The results

Physical Properties of Thin Films and Nanostructures:

Nanoporous Low-κ Dielectric Films

Figure 1: Measured Poisson’s ratio vs. porosity for MSSQ films.

Figure 2: Predicted dependence of Poisson’s ratio on porosity.

of an existing finite-element model, shown in Figure 2,

predict that ν will either decrease or increase depending

on the initial ν of the matrix material. In addition, ν tends

towards a constant value of 0.2 for all materials at high

porosity. Our measurements are consistent with the

model. However, they show a much larger rate of decrease

in ν, probably because a percolation threshold had

been reached. Quantitative results like these will prove

valuable for modeling of structures involving low-κ

films. The results also yield insight into the porosity

dependence of ν, about which very little is known.

A second method to determine thin-film properties

involves the frequency-dependent dispersion of lasergenerated surface acoustic waves (SAWs). In FY04,

efforts concentrated mainly on the development of a

standard SAW data analysis procedure. With careful

signal processing that minimizes sensitivity to noise and

maximizes the frequency range of the measured signals,

we can extend the frequency range of our measurements

by 20 %. The result is a significant reduction in the

uncertainty of the extracted film properties. The method

lends itself to automatation and has allowed us to inspect

films less than 300 nm thick. (Previously, films less than

500 nm thick were challenging.)

The improved measurement procedure, combined

with new multilayer Green’s function analysis software,

has allowed us to inspect multilayer structures.

With these capabilities, we have extracted properties

of thin (50–100 nm) capping layers of stiffer materials

on top of more compliant functional films. In addition,

the Young’s modulus, density, and thickness of

the underlying dielectric films were evaluated.

Contributors and Collaborators

S. Kim, V. Tewary (Materials Reliability Division,

NIST); Y. Liu (International Sematech); J. Wetzel

(Tokyo Electron America)

Microelectronics
34

Semiconductor manufacturers require increasingly

demanding thermal and electrical performance from

chip-level interconnects, as feature sizes continue

to shrink. Reliability of such small structures then

becomes compromised by failure modes unseen

by earlier generation interconnect systems.

Our studies address thermal and electrical behaviors

of interconnects under conditions of extreme

stressing. In particular, we concentrate on the

roles of localized stress and variations in micro

nanostructure in limiting interconnect performance

and lifetime. We performed basic studies on

aluminum-based structures undergoing AC stressing

at high current density (> 10 MA/cm2) as well as

measurements of electrical behavior in advanced

sub-100 nm copper and silver wires.

Robert R. Keller, Roy H. Geiss, and

Yi-Wen Cheng

A C stressing at high-current density and low frequencies

 is used to simulate the thermomechanical fatigue that

can occur during a microelectronic device’s operational

lifetime, due for example to power cycling, energy saving

modes, and to application-specific thermal fluctuations.

Cyclic Joule heating takes place, leading to differential

thermal expansion between metallic interconnects and

surrounding substrates or passivation layers. The resulting

damage is due to fatigue mechanisms known to operate

in bulk metals, but with the constraints associated with

thin films imposed. This year, we performed detailed

transmission electron microscope (TEM) studies of the

deformation mechanisms, supplementing last year’s

electron backscatter diffraction studies.

Figure 1 shows a pair of TEM images, bright field

(above) and weak beam dark field (below), taken from

the same region of a cross section of a severely stressed

aluminum interconnect. The image shows a high density

of dislocation loops, as indicated by arrows. Analysis of

diffraction contrast suggests these to be prismatic loops,

where the Burgers vector lies normal to the plane of the

loop. Such dislocations can be formed by the coalescence

of lattice vacancies into a platelike arrangement. Probable

sources of vacancies in thermomechanically deformed

metal films include grown-in vacancies or those formed

during cross-cutting of screw dislocations.

The existence of prismatic loops suggests a possible

means for estimating the local temperature rise during a

heating cycle. Such loops are known to disappear after

prolonged exposure to high temperatures, as vacancies

Figure 1: TEM images showing dislocations induced during

high-current density AC stressing in aluminum.

Micrometer-Scale Reliability:

Chip-Level Interconnects

diffuse out of the film. The observation of these loops

after two hours of testing suggests that there was little

sustained exposure above approximately 150 °C, which

is consistent with our estimates based on electrical

resistance measurements. Both a conference proceedings

and an archival manuscript are in progress.

We also completed, in collaboration with Metallurgy

Division, a study of linewidth effects on resistivity in

narrow (< 50 nm) silver interconnects fabricated by

patterned electrodeposition. We found that resistivity

increases could be attributed to electron scattering from

interconnect surfaces. More details are provided in the

Metallurgy Division Annual Report for fiscal year

2004. A manuscript is now in press for Journal of

Applied Physics.

Contributors and Collaborators

D. Josell (Metallurgy Division, NIST); C. Burkhard

(Clarkson University); C. Witt (Cookson Electronics–

Enthone)

Microelectronics
35

Microelectronics

Copper wiring in on-chip electrical conductors

has reached dimensions so small that electrical

resistivity is no longer constant. The higher

resistivity induces greater power dissipation,

aggravating chip cooling problems. We have

quantified the microstructural factors behind this

increase for silver wires, where silver has the

highest electrical conductivity of any metal.

Daniel Josell and Thomas P. Moffat

As dimensions of transistors in integrated circuits

 shrink, the dimensions of the metal wires

connecting them shrink as well. Dimensions of the

wires, and internal grains, are now at approximately

100 nm, similar to the intrinsic mean-free-path lengths

of the conduction electrons. Scattering from wire

surfaces and grain boundaries is significantly reducing

electrical conductivity in such small conductors.

Upcoming dimensional requirements, as specified

in the International Technology Roadmap for

Semiconductors, require determination of the origin

and magnitude of the resistivity increase in order to

direct research that might mitigate these size effects.

To address these issues, we have measured

size-dependent resistivity of silver wires 100 nm to

300 nm tall for widths ranging from approximately

50 nm to 840 nm, produced by electrodeposition on

patterned wafers followed by a combined chemical

mechanical planarization and oblique ion-polishing

process. Silver was selected because of its high

electrical conductivity and our recent development

of a bottom-up “superfill” process for creating

void-free and seam-free wires (Figure 1).

Electrical Properties of On-Chip Interconnections

Figure 1: Transmission electron microscope images of silver

wires cross-sectioned after electrical measurement. The higher

aspect ratio (height/width) wires contain multiple grains while

the lower aspect ratio wires contain only twin boundaries.

To interpret the resistivity data, the Fuchs–Sondheimer

formalism (diffuse scattering of electrons on the wire

surfaces) was extended to permit a nonzero specular

component for surface scattering. The analysis used an

existing formalism to account for grain boundary scattering.

The resulting equations permit quantitative comparison

to experiment (Figure 2).

Significantly, the analysis shows that surface

scattering alone is not capable of explaining the

observed behavior. Grain boundary scattering is found

to contribute a similar, or larger, amount to the overall

increase. As a result, the potential payoff of increasing

the grain size to decrease grain boundary scattering is

recognized to be at least as large as that which might be

obtained by smoothing surfaces to increase specularity.

Contributors and Collaborators

G. McFadden (Mathematical and Computational

Sciences Division, NIST); R.R. Keller, Y.-W. Cheng

(Materials Reliability Division, NIST); C. Witt (Cookson–

Enthone); C. Burkhard, Y. Li (Clarkson University)

Figure 2: Electrical properties of 300 nm tall silver wires as a

function of the wire width. Curves are the result of calculations

including intrinsic, surface and grain boundary scattering of

electrons. The sharp increase at ≈ 100 nm is associated with defects.
36

Microelectronics

We are developing methods to examine materials and

interfaces in electronic packaging applications and

elucidate the damage mechanisms. Our current focus

is on advanced packaging structure, embedded

passive materials, and thin metal films by use of

thermal microscopy to measure heat flow and thermal

properties on increasingly smaller size scales.

Andrew J. Slifka

Technical Description

The microelectronics industry is moving toward

components of higher density and smaller size

that use less expensive materials. One result of this is

that reliability becomes an increasing concern due to

coefficient of thermal expansion (CTE) mismatch and

increased heat flow. As size decreases and functionality

increases, thermomechanical fatigue becomes a factor

in more areas of the microelectronics industry,

including lead-free solders and interconnects.

We are investigating the structural damage induced

from CTE mismatches between the various component

materials in electronic packages to determine initiation

of damage and the ultimate failure mechanisms.

Thermal microscopy is used to measure changes in

interfacial thermal resistance in order to detect the onset

and continuation of thermomechanical damage, leading

to electrical failure at interfaces.

We are developing new measurement methods

using scanned-probe microscopy (SPM) in order to

characterize packages and measure thermal conductivity

of thin films at increasingly smaller size scales.

Accomplishments

We have completed measurements on industrial

embedded resistors (see Figure 1), making comparative

measurements between the SPM thermal system and

the IR microscope.

We have made measurements of films by use

of thermal SPM in a mode that uses the probe tip

simultaneously as a point-source heater and a resistive

element in a Wheatstone bridge circuit. For example,

we have made preliminary measurements using various

thicknesses of gold films on different substrates,

and have compared a new theory, developed by our

collaborators, to our measurements. Figure 2 shows data

from a suite of these measurements. We will add interfacial

modifications to the samples and to the theory in order to

Electronic Packaging and Components:

Packaging Reliability

make the measurement method applicable to films used in

industry. In addition, we have been using this measurement

method on diamond-like-carbon (DLC) films. These

industrial films are made from a polymer precursor,

which allows easy and inexpensive coating onto various

substrates. The thermal conductivity of these films, and

how they compare to conventionally processed DLC films,

is being investigated.

Finally, we are also measuring thermal conductivity

of lead-free solder balls and interfacial thermal

resistance between alloys and intermetallics.

Contributors and Collaborators

J. Felten (DuPont Technologies, Research Triangle

Park, NC); R. Snogren (SAS Circuits, Inc., Littleton,

CO); K. Cole (University of Nebraska, Lincoln, NE);

S. Joray (Cenymer Corp., Longmont, CO); F. Hua

(Intel Corp., Santa Clara, CA)

Figure 1: Results of thermal SPM measurements on embedded

resistor materials.

Figure 2: Thermal SPM measurement results on various

thicknesses of gold films on glass substrates.
37

Microelectronics

Bulk acoustic techniques have been developed

and applied to the characterization of a variety of

materials, with particular emphasis on piezoelectric

crystals for electronic oscillator and filter

applications. The research includes metrology of

mode-selective noncontacting resonant spectroscopy,

characterization of physical mechanisms that

degrade performance of piezoelectric compounds

with the structure of langasite, and determination

of elastic constants of body-centered-cubic Ti

and the shape-memory alloy NiTi.

Ward Johnson, Sudook Kim, and

Carlos Martino

Over the past several decades, the Materials

Reliability Division has established special

capabilities in a variety of resonant acoustic techniques,

including resonant ultrasound spectroscopy (RUS), timedomain resonance methods, noncontacting transduction,

Marx-oscillator measurements, and torsional-pendulum

measurements. The combined capability of these

resonance systems enables elastic constants and anelastic

damping to be measured from 4 K to 1100 K. The division

also has implemented several conventional pulse-echo

systems, including immersion scanning. During FY04,

research was focused primarily on noncontacting mode

selective metrology, analysis of anelastic damping in

piezoelectrics, measurements of the temperature

dependence of elastic constants of a shape-memory

alloy, and determination of elastic constants of Ti in

its high-temperature body-centered-cubic phase.

Langasite (La3Ga5SiO14) and several of its isomorphs,

including langatate (La3Ga5.5Ta0.5O14), have attracted

significant attention in recent years as piezoelectric

materials for improved electronic oscillators and filters.

Research in our lab over the past year has sought to identify

the dominant anelastic mechanisms that degrade the

performance of these materials. An algorithm has been

developed for fitting the measured temperature and

frequency dependences of the mechanical Q to a

superposition of loss mechanisms. For langasite, three

point-defect relaxations are shown to be superimposed

on a contribution that increased monotonically with

temperature. In langatate, very similar anelastic effects

appear, with distributions of activation energies that

apparently arise from variations in residual stress.

To enable robust measurement of elastic constants

of trigonal piezoelectric crystals, such as langasite,

Electronic Packaging and Components:

Acoustic Characterization

methods of selectively measuring and analyzing resonant

frequencies of modes with specified symmetry have

been developed. This approach overcomes errors in

analysis that can arise from misidentification of modes.

The research has included measurements and analysis

of quartz cylinders and sapphire disks. Noncontacting

piezoelectric coupling with switchable electrode

configurations and Ritz inversion algorithms including

full symmetry information have been developed.

In collaboration with Los Alamos National Lab,

analysis of resonance measurements on polycrystalline

Ti at 1270 K were performed. Polycrystalline elastic

constants were determined using the Ritz method. Then,

the Kröner model was used to estimate monocrystalline

constants from these polycrystalline constants.

Measurements of the temperature dependence of

the elastic constants of the shape-memory alloy NiTi

have been pursued in collaboration with the Mechanical

Engineering Department of the University of Colorado.

This study determined the effects of metallurgical

treatments on the martensitic transition temperature and

elastic constants. Pulse-echo measurements of elastic

constants were performed on cold-drawn and hot-rolled

specimens from 155 K to 300 K. Large Poisson ratios (> 0.4)

reflect the material’s superelasticity. Information was

obtained on the hysteresis in elastic constants arising from

the phase transition, which is a subject of controversy.

Contributors and Collaborators

P. Heyliger (Colorado State Univ.); M. Dunn,

K. Gall (Univ. of Colorado, Mechanical Engineering

Dept.); H. Ogi (Osaka Univ., Japan); H. Ledbetter

(Los Alamos National Lab); A.Teklu (Univ. of

Mississippi, Oxford)

Figure 1: Vibrational mode of a sapphire disk.
38

Microelectronics

As the microelectronics industry moves towards

Pb-free assemblies, reliability has become a major

concern. Pb-free coatings of nearly pure tin,

used as a protective layer to maintain solderability

on Cu leadframes and connectors, tend to grow

“whiskers” which can cause shorts across

component leads. Copper additions to the Sn

protective layer have been considered by industry

since the Sn-Cu-Ag is likely to be the Pb-free

bulk solder of choice for industrial applications.

However, measurements made at NIST indicate

that the addition of Cu tends to promote whisker

growth. Our goal is to better understand how

copper and other solutes impact the growth

of whiskers on electrodeposited Sn.

Gery R. Stafford, William J. Boettinger,

and Kil-Won Moon

Whiskers are generally believed to grow to

relieve residual stress in tin and other coatings.

However, the origin of this stress has not been

definitively determined. The addition of certain solutes,

such as Bi and Pb, are known to retard whisker growth

in electrodeposited tin coatings, while solutes, such as

Zn are known to promote growth. Previous work

at NIST has shown that low levels of Pb reduce the

residual compressive stress in Sn-Pb electrodeposits,

while the addition of Cu increases the residual

compressive stress. Current research focuses on the

influence of solute type and concentration on residual

film stress, stress relaxation, and whisker formation.

Metallographic analysis of Sn-Cu electrodeposits

indicates that the Cu is present as the Cu6Sn5 intermetallic

compound (IMC) which is observed both in the grains

and along the grain boundaries. It is unlikely that significant

amounts of this complex IMC are formed directly during

deposition. Rather, we believe that the as-deposited

alloy is a supersaturated solid solution of Cu in Sn that

transforms to an equilibrium mixture of Sn and Cu6Sn5

either during or soon after deposition.

In solid solution, Cu is presumed to occupy interstitial

sites within relatively large square channels that exist in

the body-centered tetragonal (bct) Sn structure. This

gives rise to the anomalously fast diffusion of Cu in the

c-direction of the Sn lattice. In this configuration, it is

assumed that the Cu does not alter the lattice volume of

the Sn. It is further presumed that as Cu6Sn5 precipitates

within the deposit, the Cu exits the interstitial sites in the

Sn phase and occupies volume more typical of its atomic

size; thus, the volume of the entire deposit increases.

We estimate the volumetric strain for Cu6Sn5 precipitation

from a 1 % Cu solid solution to be about +0.004. The

resultant stress generated in the electrodeposit as a result

of the IMC precipitation is then on the order of –95 MPa

(compressive). This, of course, assumes that Cu6Sn5

forms from the solid solution after the deposit has

been formed.

Lead-Free Surface Finishes: Sn Whisker Growth

Figure 1 shows a series of x-ray diffraction patterns

that were taken at the Advanced Photon Source, using

synchrotron radiation, during and after the deposition

of a Sn-Cu alloy onto a tungsten substrate. The inset

pattern was taken during the 2-minute deposition while

the remaining patterns were taken 3 minutes apart after

deposition was complete. The data show that although

a small amount of Cu6Sn5 is present when deposition

is stopped (inset), the bulk of the IMC forms in the

45 minutes following deposition. Although the Sn

reflections decrease as the IMC forms, the peaks do

not change position indicating that the lattice volume of

the Sn is constant. This supports the assumption that

interstitial Cu does not alter the lattice volume of bct Sn.

These results indicate that IMC formation occurs after

deposition is complete and is a likely cause of the higher

compressive stress observed in Sn-Cu alloy deposits.

Contributors and Collaborators

J.E. Guyer, C.E. Johnson, M.E. Williams

(Metallurgy Division, NIST); M.D. Vaudin (Ceramics

Division, NIST); D.R. Robinson, D. Wermeille

(Advanced Photon Source, ANL)

Figure 1: In situ x-ray diffraction (λ = 0.127 Å) showing growth

of the Cu6Sn5 110 reflection in the 45 minutes following deposition

of bright Sn-Cu alloy from commercial methanesulfonate electrolyte.
39

Lead-Free Solders and Solderability

Microelectronics

Solders and solderability are increasingly tenuous

links in the assembly of microelectronics as a

consequence of ever-shrinking chip and package

dimensions and the international movement toward

environmentally friendly lead-free solders. In

collaboration with the NEMI Pb-Free Assembly

Project, we are providing the microelectronics

industry with measurement tools, data, and

analyses that address national needs in the

implementation of lead-free solders.

Ursula Kattner and Carol Handwerker

Since 1999, NIST has served a major role in National

Electronics Manufacturing Initiative (NEMI)

projects to assist the microelectronics industry implement

Pb-free solders. NEMI is an industry-led consortium

of approximately 65 electronics manufacturers,

suppliers and related organizations brought together to

facilitate leadership of the North American electronics

manufacturing supply chain. This move toward Pb-free

solders is a direct result of the European Union ban, starting

in 2006, on Pb-containing solders in electronic products.

NEMI and NIST have worked together to respond

to the identified needs by:

1) Identifying and providing the most important

lead-free solder data for the microelectronics

community (including the definitive database

on thermodynamic properties of Pb-free alloys),

providing an analysis of the mechanical behavior of

Sn-Ag-Cu alloys, and disseminating such data on the

NIST website (see “Delivery of Thermodynamics

and Kinetic Data” in this volume).

2) Developing and widely disseminating a Recommended

Practice Guide on Test Procedures for Developing

Solder Data.

3) Providing a list of literature references on alloys,

processing, reliability, environmental issues, and

components for the implementation of lead-free solders.

4) Completing the microstructure-based failure analysis

on all thermally cycled assemblies as part of the

NEMI project’s full-scale reliability trials.

5) Providing chapters on the materials science of

Pb-free solder alloys for inclusion in four separate

books on Pb-free solder implementation.

Although the NEMI Pb-Free Assembly Project ended

in 2003, in 2004 we continued to serve as an information

resource to the microelectronics industry on issues related

to the effects of alloy composition, reflow temperature

and furnace profiles for best melting and solidification

behavior of solders when circuit boards are assembled,

and to the effects of Pb contamination on alloy melting

and assembly reliability. This activity culminated in a

Circuits Assembly article by Alan Rae, VP of Technology

for Cookson Electronics, and Carol Handwerker of NIST

on the range of acceptable alloy compositions in the

Sn-Ag-Cu system. The following excerpt gives the

NEMI position, and effectively the U.S. position, on

the acceptable composition ranges for the new international

standard Pb-free alloy and allows both the U.S. and the

Japanese preferred alloy compositions based on analyses

of NIST thermodynamic data:

Although the composition of some of the alloys

being commercialized varies slightly from the NEMI

composition, the NEMI alloy is representative of

the acceptable range of lead-free solders. Tin–silver–

copper formulations with silver content between

3.0 [mass] % and 4.1% and copper between 0.5%

and 1.0% are virtually indistinguishable in terms of

melting point and process features. The NEMI alloy

provides a model system for industry that is well

characterized, and several NEMI members currently

are using the alloy in production. The focus on

a single lead-free alloy has helped to accelerate

industry convergence on standard solder

formulations, manufacturing processes and,

ultimately, the timely and cost-effective

conversion to lead-free assembly.

“The NIST group performed a significant service to

industry by being the focal point for development of a

reliable technology base to support the choice of a new

lead-free alloy. They also led the way for further work

on issues such as tin whiskers, which emerged from

the initial lead-free work. NIST provided not only a

strong technical basis but, by verifying reliability and

comparing alternatives, enabled industry to choose

an alloy based on extensive investigation.”

Dr. Robert C. Pfahl, Jr., Director

International and Environmental R&D,

Motorola, (retired), and Vice President

Operations, NEMI, (current)

Contributors and Collaborators

W.J. Boettinger, K.W. Moon, T. Siewert,

D. McCowan, L.C. Smith, S.W. Claggett, M.E. Williams

(NIST); J.P. Clech (EPSI, Inc.); J. Bath (Solectron);

R. Gedney (NEMI); E. Bradley (Motorola); J.E. Sohn

(NEMI, formerly Lucent); A. Rau (Cookson Electronics);

E. Benedetto (HP); R. Charbonneau (StorageTek)
40

The electronics industry is replacing lead–tin eutectic

solders with lead-free solders because of the

environmental hazards of lead. In doing so, they

have created a need for material property data of

the new lead-free solder compositions. A test method

has been developed to measure the mechanical

properties using specimens on the same size scale

as the solder structures used in industry.

Timothy P. Quinn

Background

I

ndustry groups have pointed out the need for material

property data for the new lead-free compositions of

solder; this includes pooling the data that already exist

and filling the critical holes in the data, especially at

low-strain rates.

Most of the data that are available for all solders come

from specimens that are very large (on the order of

millimeters) compared to the solder structures themselves

(on the order of hundreds of micrometers). As the solder

structures (solder balls for flip chip packages, for example)

become smaller (~ 150 μm), their dimensions approach

the dimensions of the phases in the solder itself. The

assumption of a homogeneous material used to analyze

the stresses in the structure is challenged. We have

therefore started testing samples that are on the same size

scale as current solder structures to study this interaction.

Accomplishments

A test method that used “miniature” specimens was

developed to mimic the size of typical soldered joints.

The purpose was to examine the effects of the size of

the specimens (and hence the typical structures found

in industry) and to fill in the gaps in the data for the

lead-free solders. Solder was cast in a Ti mold between

two copper blocks, and 300 μm specimens were cut

from the blocks. The usable gauge length of the

specimens was about 300 μm. We can consistently

make specimens with a known thermal cycle and

maintain well-defined microstructure. Because the

samples were sliced off a relatively large “loaf,” a large

number of samples could be made in a short time.

After determining the geometry of the gage section

using an optical microscope, the specimens were

imaged in an ultrasonic microscope with a beam diameter

of 45 μm at an operating frequency of 100 MHz.

Micrometer-Scale Reliability:

Solder Reliability

Measuring the time-of-flight from the front to the rear

of the sample allowed us to calculate Young’s modulus

knowing the density and Poisson’s ratio (Figure 1).

Figure 2: The measured stress–strain curve for a Sn-3.8Ag-0.7Cu

solder.

Figure 1: An ultrasound scan of a solder tensile specimen.

The image was made by mapping the amplitude of the reflection

off the front interface (white = larger amplitude).

The samples were then tested in uniaxial tension using

pin-style grips. The specimens were first painted white,

and then a dark line was painted on the specimen over the

gauge section. A video-microscope recorded images of

the gauge section at about 0.75 μm/pixel. The edges of

the gauge section were then tracked with an automated

algorithm and used to calculate strain. The stress–strain

curve was then plotted (for example see Figure 2). Note

that because of the small displacements in the elastic

region, the camera does not have enough resolution to

adequately predict Young’s modulus. The ultimate tensile

strength, yield strength and percent elongation were all

obtained using the camera data. Tests have been conducted

using Sn-3.8Ag-0.7Cu, Sn-3.7Ag, Sn-0.7Cu, Sn-5Sb,

and Sn-37Pb.

Contributors and Collaborators

I. Makover, T.P. Quinn, K.R. Waters (Materials

Reliability Division, NIST); Y. Rosenthal (Ben-Gurion

University, Israel)

Microelectronics
41

Measurement methods and materials data are

needed for the design of interconnect structures

in high-performance integrated circuits. These

micro- and nanometer-scale thin films are formed

by physical vapor deposition; their microstructures,

and hence their mechanical properties, are quite

different from those of bulk materials of the same

chemical composition. The ultimate goals of this

project are to characterize the exact materials

used in IC fabrication, at their proper size scale,

and to understand the relevant deformation and

failure mechanisms.

David T. Read

I

nterconnect structures in advanced integrated circuits

carry power, signals, and heat from the transistors to

the outside environment. These structures consist of

multiple layers of thin films of conductors and dielectrics

with barrier and adhesive layers. These thin films are an

essential component of all advanced electronic devices,

and similar materials are used in a variety of other

applications, such as reflective coatings. Industry is

aggressively pressing new materials into service, reducing

the size of the structures, and requiring more functionality,

including mechanical functionality, from all components

of their structures. Design of reliable structures relies on

quantitative numerical modeling, which requires accurate

material property data. Because the films are formed by

physical vapor deposition, their microstructures, and hence

their mechanical properties, are quite different from those

of bulk materials of the same chemical composition.

The objectives of this project are:

■ To develop experimental techniques to measure the

mechanical properties of thin films, in specimens

fabricated and sized like materials used in actual

commercial devices;

■ To relate thin-film mechanical behavior to

microstructure;

■ To extend test techniques from their present level

(1 μm thick, 10 μm wide) to smaller specimens that

are similar in size to the conductive traces used in

contemporary VLSI circuits (widths of 0.1 to 1 μm).

In previous years we reported properties of aluminum,

polyimide, and polysilicon films at room temperature.

We have now measured the tensile properties of aluminum

films from a commercial source, and lab-made

electrodeposited copper films from room temperatures

Micrometer-Scale Reliability:

Mechanical Behavior of Thin Films

Figure 1: TEM of fractured tether of aluminum contact metal

microtensile specimen. The dark lines on the left are dislocations;

note their absence toward the right, near the fracture edge.

up to 150 oC. The mechanical properties decline only

slightly with increasing temperature, in a pattern normal

for face-centered-cubic metals.

Microtensile Young’s (elastic) modulus data for nickel

were contributed to a comparison study. The microtensile

value was 177 ± 8 GPa (most probable uncertainty). Details

are given elsewhere, but the conclusion from the full set

of measurements is that both the modulus and the density

of this sputtered nickel film are lower than bulk values.

Microtensile modulus measurements, in particular, have

been suspect because the results are often lower, by

10 % or more, than bulk values. See the Molecular

Dynamics page of this report for more on this.

The transmission electron microscope (TEM)

micrograph in Figure 1 shows two different deformation

mechanisms for a thin aluminum film. Prismatic vacancy

loops, seen as circular features about 20 nm in diameter

on the right, are formed in the absence of dislocations in

the thinner part of the deformation zone near the fracture

edge (far right, lower). Dislocations are seen only in the

thicker regions, at the left in the image. The size and

density of the loops seems to be dependent on the speed

of the deformation, with smaller loops 5–10nm in diameter

seen in more slowly deformed material.

Contributors and Collaborators

Y-W. Cheng, J.D. McColskey, R.R. Keller, R. Geiss,

J. Wright (Materials Reliability Division, NIST);

MOSIS Service (specimen fabrication)

Microelectronics
42

Microelectronics

Several materials are now produced commercially

with particle sizes on the order of 10–100 nm.

The availability of ceramic materials in this size

classification is particularly important for the

electronic component industry. Nanopowders

can enable significant decreases in internal layer

thickness (for multilayer devices), minimize the

size and prevalence of processing defects, and

boost the overall performance of components

ranging from capacitors to resistive gas sensors.

Quantifying these performance enhancements

and their dependence on microstructure is a key

objective in the Materials Reliability Division.

Stephanie A. Hooker

Many multilayer ceramic devices can benefit from

the use of ultra-fine powders, including passive

electronic components, gas sensors, and miniature

actuators. However, fabrication issues associated

with processing these high-surface-area powders

have hindered their commercialization. Key challenges

have included nanopowder reproducibility, optimization

of processing slurries, and control of sintering

profiles to produce the desired micro/nanostructure

characteristics. Moreover, in many cases, predicting

the optimum microstructure features for maximum

performance is quite difficult, and extensive

experimentation remains necessary.

One specific component that can benefit from the

use of nanopowders is the multilayer piezoelectric

actuator. These devices generate precise, controlled

motion for translating optics, damping vibrations,

redirecting air flow, and dispensing fluids. Each

component consists of many active layers, the

thickness of which determines the device’s power

requirements. Layer thickness is typically on the

order of several hundred microns for conventional

actuators and is driven by the need for many individual

piezoelectric grains to span the active layer, thereby

reducing the chance for electrical failure. Reducing

grain sizes from micrometer to submicrometer scales

enables dramatic decreases in layer thickness, reducing

power needs and increasing applicability.

However, at issue is the piezoelectric response and,

in particular, the long-term fatigue resistance. Fatigue is

the change in polarization or displacement over time and

is a recognized problem for state-of-the-art actuators.

Because processing-induced defects tend to be on the

scale of the starting powder, nanopowders can improve

mechanical durability. However, a corresponding

Physical Properties of Thin Films and Nanostructures:

Grain Size Effects on Actuator Fatigue

decrease in ferroelectric response is also anticipated

as grain size reduces. Fatigue is affected by both

the mechanical and electrical responses, making its

prediction quite difficult for fine-grained components.

In FY04, we investigated the fatigue behavior of

14 microstructures obtained by controlled sintering

of 80-nm PZT-5A powders. The devices tested were

1206-sized (0.30 cm × 0.15 cm, or 0.12′′ × 0.06′′)

chips, each with 10 active layers (50 μm thick).

Characterization included dielectric, impedance, and

ferroelectric properties, as well as short- (< 1 million

cycles) and long-term (1–100 million cycles) degradation

under combined electrical and mechanical influences.

Figure 1: Effect of sintering temperature on ferroelectric fatigue.

The results clearly demonstrate the dependence of

fatigue on microstructure. Figure 1 compares changes

in remanent (i.e., permanent) polarization over time

when devices were cycled using a 35 Hz sinusoidal

wave with an amplitude of +/–75 V. The average

decrease in polarization for the finest-grained materials

(sintered at 1175 °C) was less than 20 % after

0.5 million cycles, compared to nearly 50 % for

larger-grained components.

In FY05, we will expand on this work and examine

the corresponding effects on displacement and domain

reorientation for devices with even thinner internal

layers. The resulting data will then be used to validate

the suitability of these components for biomedical and

smart structures applications, both of which demand

high performance and long operational lifetimes.

Contributors and Collaborators

R. Geiss (Materials Reliability Division, NIST);

C. Kostelecky, D. Deininger, K. Womer (Synkera

Technologies)
43

Microelectronics

Commercial ferroelectric thin film devices are rapidly

approaching the same nanoscale dimensions as

individual grains, yet little is known about the

influence of grain boundaries and local texture

on ferroelectric properties. Accordingly, several

complementary experimental and theoretical

techniques are being developed to assess

the local ferroelectric response. By combining

quantitative piezoelectric force microscopy (PFM),

electron backscattering diffraction (EBSD), and

two-dimensional object oriented finite-element

modeling (OOF), various individual crystallographic

distributions with either beneficial or detrimental

effects can be identified and eventually predicted.

Bryan D. Huey, R. Edwin García and

John E. Blendell

Crystallographic orientation can now be determined

with nanometer scale lateral resolution using the

newly installed electron backscattering diffraction system

(EBSD), allowing the orientation of individual ferroelectric

grains to be mapped as indicated in Figure 1a.

Experimental and Theoretical Influence

of Thin Film Texture on Ferroelectric Hysteresis

Figure 1: (a) Measured surface orientation of PZT thin film and

(b) predicted strain normal to the surface for the same grains

when biased with an electrode as indicated. Bar = 20 μm.

Figure 2: Measured piezoelectric hysteresis areas of several

grains/boundaries.

Recent advances in two-dimensional (2-d) object

oriented finite element modeling (OOF) have made it

possible to predict the piezoelectric response of a

polycrystalline thin film with full consideration of the

sample texture as determined by EBSD. Figure 1b

demonstrates the strain normal to the surface for an

applied bias of 1 V across a 100 nm thick film using

a 100 nm diameter electrode, where the electrode

is positioned across multiple grains of differing

orientations. The local response is strongly dependent

on texture, in some cases oppositely oriented.

Piezoelectric force microscopy (PFM) was

employed to determine experimentally the ferroelectric

properties of the same grain and grain boundary regions

considered by EBSD and OOF. This AFM-based

technique is widely used, but can be significantly

hindered by several instrumental artifacts that were

identified and overcome during this work. The area

of piezoelectric hysteresis loops determined using the

newly developed quantitative methods is indicated in

Figure 2 for several distinct grains and boundaries. The

measured hysteresis variations correlate with grains and

grain boundaries of differing misorientation as measured

by EBSD and correlates with strains calculated by OOF.

Key accomplishments and conclusions include:

1) Novel methods for identifying and overcoming artifacts

in piezoelectric force microscopy to allow quantitative

local piezoelectric hysteresis measurements;

2) Unique 2-d simulations of converse-piezo actuation

with complete incorporation of true thin-film texture;

3) The importance of uniform texture for optimal

ferroelectric properties when device dimensions

approach the lateral grain size; and

4) The likelihood of domain pinning or even crack

initiation at certain grain boundaries and intersections

as a result of local orientation.

Results from this work were presented at the SPIE

Ferroelectrics conference, American Ceramic Society

annual meeting, European Congress on Nanoscale

Materials (Nano-04), IEEE Ferroelectrics and Ultrasonics

joint meeting, and several invited seminars at NIST and

various universities. Publications in the Journal of the

American Ceramic Society, Journal of Electroceramics,

and Journal of Applied Physics are under review.

Contributors and Collaborators

M.D. Vaudin, E.R. Fuller, Jr. (Ceramics Division,

NIST); S. Hong (Samsung)
44

Microelectronics

The field of organic electronics has dramatically

emerged in recent years as an increasingly important

technology encompassing a wide array of devices

and applications including embedded passive

devices, flexible displays, and sensors. Device

performance, stability, and function critically

depend upon charge transport and material

interaction at the interfaces of disparate

materials. We develop and apply non-destructive

measurement methods to characterize the electronic

and interfacial structure of organic electronics

materials with respect to processing methods,

processing variables, and materials characteristics.

Eric K. Lin and Jan Obrzut

Organic electronic devices are projected to

revolutionize integrated circuits through new

applications that take advantage of low-cost, highvolume manufacturing, nontraditional substrates, and

designed functionality. The current state of organic

electronics is analogous to the early stages of the silicon

electronics industry with the concurrent development

of multiple material platforms and processes, and a lack

of measurement standardization between laboratories.

A critical need exists for new diagnostic probes, tools,

and methods to address new technological challenges.

Organic electronics presents fundamentally

different measurement challenges from those identified

for inorganic devices. The adoption of this technology

will be advanced by the development of an integrated

suite of metrologies to correlate device performance

with the structure, properties, and chemistry of

materials and interfaces. We are developing

measurement methods to provide the data and insight

needed for the rational and directed development

of emerging materials and processes.

This year, we have addressed three areas covering

a spectrum of active organic electronic materials:

dielectric measurements for embedded passive devices,

Figure 1: Schematic diagrams of the local structure of

poly 3-hexylthiophene, an organic semiconductor, near an

interface (left) and the architecture for an organic transistor (right).

Organic Electronics

measurements of moisture permeation rates through

barrier films for organic light-emitting diode displays,

and measurements of the orientation and structure of

organic semiconductors for transistor applications.

To meet the metrology needs for embedded

passive devices, two new measurement methods were

successfully developed and will find widespread use

within industry (see Highlight). A NIST-developed Test

Method for Dielectric Permittivity and Loss Tangent of

Embedded Passive Materials from 100 MHz to 12 GHz

was accepted and recommended as a standard test

method. In addition, a new test was developed and

applied for testing passive materials at high electric

fields and voltages.

For organic light-emitting diode displays, a key

measurement challenge is the quantification of the

moisture permeation rates through a barrier coating.

Any moisture able to penetrate the coating compromises

the performance of the device. There is a need

to measure moisture permeation rates as low as

10–6 g/m2 d. In collaboration with Vitex Systems, Inc.,

neutron and x-ray reflectivity measurements demonstrated

the capability of measuring these low permeation rates

in addition to providing spatial detail about the transport

of water within the barrier material itself.

Finally, near-edge x-ray absorption fine structure

(NEXAFS) spectroscopy was applied to several classes

of organic electronics materials to investigate the

electronic structure, chemistry, and orientation of

these molecules near a supporting substrate. NEXAFS

provides a powerful and sensitive method to probe the

interfacial structure that is critical to the performance of

these devices. For example, it was found that several

organic semiconductor molecules preferentially align

“edge-on” rather than “face-down” on solid substrates.

Contributors and Collaborators

D. DeLongchamp, O. Anopchenko, K. Kano, B. Vogt,

H. Lee, E. Jablonski, W. Wu (Polymers Division, NIST);

S. Sambasivan, D. Fischer (Ceramics Division, NIST);

L. Richter (CSTL); C. Richter, E. Vogel (EEEL);

D. McGregor, G.S. Cox, J. Felten (DuPont); D. Fritz

(MacDermid); T. Bergstresser (Gould Electronics);

K. Fjeldsted (Electro Scientific Industries); R. Crosswell

(Motorola); C. Vanderpan (UL); R. Whitehouse (SanminaSCI); L. Moro, N. Rutherford (Vitex); V. Subramanian

(U.C. Berkeley); Z. Bao (Stanford University);

B. Ong (Xerox); A. Afzali (IBM); G. Jabbour (Arizona

State University); R. Pilston (Plextronics); Y. Jung,

D. Yoon (Seoul National University)
45

Optoelectronics

The development of wide-band-gap semiconductor

optoelectronic and electronic devices is hindered

by poor electrical contact performance. Reliability

issues for contacts include the requirements to

be low-resistance, morphologically smooth and

thermally stable. This project develops a strategy to

improve electrical and morphological characteristics

of Ohmic contacts to GaN thin films by optimizing

metallization schemes using an integrated phase

diagram/combinatorial approach.

Albert V. Davydov and William J. Boettinger

Ti/Al/Ti/Au metallizations are the most commonly

used electrical contact to n-type GaN-based

device structures. However, the overall composition

(i.e., thickness ratios) and the thermal processing

of metal layers are not yet optimized. A rationale for

designing the optimum metallization scheme also has

not been developed. This work demonstrates that the

phase diagram approach, along with a combinatorial

experimentation method, is a useful tool in the design

and optimization of electrical contacts to GaN and

other wide-band-gap semiconductors.

A combinatorial library of Ti/Al/Ti/Au metallization

was prepared and characterized electrically and

microstructurally in order to establish optimum

composition and processing parameters for the realization

of high-quality Ohmic contacts. An array of metallic

elements with varying Ti/Al/Ti/Au thicknesses was

deposited by combinatorial ion-beam sputtering (CIBS)

on n-GaN/c-sapphire substrate followed by rapid-thermal

annealing (RTA) in the 600 oC to 900 oC temperature

range. The library design of metal compositions and RTA

temperatures was guided using the Al-Au-Ti phase diagram

so that various Ti/Al/Ti/Au contact compositions

represented different regions on the phase diagram.

Four-probe transmission-line-method and Hall electrical

measurements were used to assess contact resistivity

and GaN sheet resistance. X-ray diffraction, white-light

interferometric microscopy, atomic-force microscopy,

field-emission scanning-electron-microscopy, and

transmission-electron-microscopy were used to evaluate

the microstructure and morphology of contacts and

the metal/GaN interfaces. The most Au-rich/Ti-poor

metallization (E in Figure 1a), Ti(20 nm)/Al(85 nm)/

Ti(15 nm)/Au(150 nm) with an RTA of 800 oC/30 s

in argon, produced the lowest (ρ = 1.3 × 10–5 Ω × cm2)

contact resistivity with reasonable (rms < 150 nm) surface

morphology. However, the most Al-rich metallization

(D in Figure 1a), Ti(20 nm)/Al(170 nm)/Ti(5 nm)/

Au(50 nm) with RTA of 750 oC/30 s in argon, produced

superior surface morphology (rms = 20 nm) and

comparable resistivity of ρ = 2.2× 10–5 Ω × cm2. It is

suggested that scheme (E) with the Au-rich contact can

be used for operating in oxidizing environments, where

thick Au top layer will serve as a protective cap layer,

while scheme (D) can be suitable for applications where

contact surface roughness is critical. According to XRD

results, the superior surface morphology of contacts

in the D-series correlates with the absence of phase

transformations in the 600 oC to 900 oC temperature

interval after the initial formation of Al2Au and Al3Ti

phases in metal films.

The advanced metallizations developed in the project

will be validated in industrial high-electron mobility

transistors (HEMTs) at Northrop–Grumman Corporation.

Contributors and Collaborators

L.A. Bendersky, D. Josell, U.R. Kattner, A.J. Shapiro

(Metallurgy Division, NIST); J.E. Blendell, R.S. Gates,

P.K. Schenck, M.D. Vaudin (Ceramics Division, NIST);

T. Zheleva (Army Research Laboratory); H.G. Henry

(Northrop–Grumman); Q.Z. Xue (Intematix Corp.);

A. Motayed (Howard University); I. Takeuchi (Univ. of

Maryland)

Combinatorial/Phase Diagram Approach for

Metallization to Wide-Band-Gap Semiconductors

Figure 1: a) 36-element combinatorial library of annealed

Ti/Al/Ti/Au contacts on n-GaN: metal compositions change

along the x-axis from A to F, annealing temperature changes

from 600 oC to 900 oC along the y-axis; “X”s mark the library

elements with the lowest resistivity and smoothest morphology;

b) map of surface roughness of the combinatorial array:

yellow-shaded area represents the contacts with the smoothest

(rms < 60 nm) morphology; c) map of electrical resistivity of the

combinatorial array: red-shaded area represents the contacts

with the lowest (ρ < 3 × 10–5 Ω × cm2) resistivity.
46

Optoelectronics

The optoelectronics industry needs measurement

techniques and accurate materials property data

to calibrate their deposition processes and to

evaluate both prototype and finished devices.

Recent work has focused on the electronic band

structure of InGaAsN films (for infrared detectors

and solar cells) and calibration of strain in

ultrathin AlxGa1–xAs films and optical properties

of GaN and ZnO nanowire structures.

Albert J. Paul and Lawrence H. Robins

I

nyGa1–yAs1–xNx semiconductor alloy films show

promise for infrared optoelectronic devices.

Data on the electronic band structure are needed to

facilitate device design and simulation. We examined

Si-doped InyGa1–yAs1–xNx films with x < 0.012 and

0.052 < y < 0.075 by photoreflectance (PR) spectroscopy,

supplemented by secondary ion mass spectroscopy

(SIMS) and energy dispersive x-ray spectroscopy (EDS,

for composition), XRD (strain), and Hall effect (electrical

properties). The composition and carrier concentration

dependence of the critical point energies, designated

E– (fundamental gap), E–+∆SO (split-off valence band

to conduction band), and E+ (valence band to nitrogen

impurity band) was successfully explained by a band

anti-crossing and free-carrier band-filling model with a

small number of adjustable parameters.

Metrology and Standards for Optoelectronic Materials

Figure 1: PR critical-point energies: data and modeling.

The measured critical-point energies (symbols)

and the best-fit model (dashed curves) are plotted as

functions of N mole fraction (x) in Figure 1(a), and Hall

carrier concentration (ne) in Figure 1(b).

We are continuing to develop methods for

quantifying optical measurements of stress and strain

in III–V semiconductors. By calibrating the shift of

the Raman and PL peaks with known applied stress

in a load cell, we are able to measure stresses due to

differential thermal expansion, film-substrate lattice

mismatch, and device packaging. As an example,

the stress induced by bonding of a 10 mm × 10 mm

Al0.2Ga0.8As-on-GaAs sample (grown as a composition

SRM) to a stainless steel disk was measured by this

technique. Results from selected locations on the

bonded sample and, for comparison, an unbonded

piece cut from the same wafer, are shown in Figure 2.

A large tensile stress is seen to occur near the center

of the bonded piece, but not in the unbonded piece.

Stress measurements of ultrathin (5 nm to 30 nm)

AlGaAs films have been initiated to compare spatially

resolved measurements of stress near the edges of

ultrathin films with the quantitative predictions of

Object-Oriented Finite Element (OOF) modeling.

Contributors and Collaborators

E. Fuller, Y.-S. Kang, G. White (Ceramics Division,

NIST); K.A. Bertness, N.A. Sanford (Optoelectronics

Division, NIST); A.V. Davydov, A.J. Shapiro (Metallurgy

Division, NIST); D. Chandler–Horowitz (Semiconductor

Electronics, NIST); M.M.E. Fahmi, S.N. Mohammad

(Howard University)

Figure 2: Tensile stress distributions in two Al0.2Ga0.8As

structures, obtained from calibrated PL measurements.
47

Magnetic Materials

In order to pursue the rapid development path

set out for hard drives and magnetic memory,

industry needs the ability to measure and control

magnetization on nanometer length scales and

nanosecond time scales. This project focuses

on the metrology of dynamics and damping in

magnetic thin films, especially on the effects

of nano-scale dimensions and defects in

ferromagnetic resonance measurements.

Robert D. McMichael

We are developing ferromagnetic resonance (FMR)

techniques to measure the static and dynamic

properties of thin films and patterned arrays of

technologically important ferromagnetic metals and their

interfaces with normal metals. The primary results

include measurements of surface anisotropy, which

becomes increasingly important for nanoscale damping,

which governs behavior on the sub-nanosecond time

scale, and assessment of the magnetic homogeneity

of thin films or patterned arrays of magnetic bits.

These results are communicated to the magnetic data

storage industry through conference presentations,

journal articles and site visits.

For nanostructured materials, surface effects

and interfacial effects are important. For example,

micromagnetic calculations show that switching

behavior of magnetic memory cells will be affected by

surface anisotropy on the edges of the lithographically

patterned elements, an effect that has not been

appreciated until recently. Measuring the anisotropy

of films of varying thickness with ferromagnetic

resonance enables the determination of surface

anisotropy values for Permalloy that will be used

in the micromagnetic design of MRAM cells.

A continuing thrust of this project has been the

development of models that describe broadening of the

FMR linewidth by defects. These models, which are

specifically designed for thin films, account for both

inhomogeneity and magnetic interactions. Our earlier

models were restricted to “local” defects such as

anisotropy. One important application of these models

is as a method for measurement of anisotropy variations

and axis alignment in perpendicular recording media.

This year, we have capped off the model development

with a model for the non-local effects of film roughness.

Nanomagnetodynamics

Figure 1: Surface anisotropy measurements for Permalloy films

with different normal metal over/underlayers. The slopes of the fit

lines correspond to surface anisotropy.

Testing of the roughness-linewidth model involved

making variable roughness substrates, characterizing

the roughness by atomic force microscopy (AFM),

and measuring nearly conformal Permalloy overlayers

in FMR. Using only the AFM microstructural data

and the known properties of Permalloy, and assuming

conformal roughness, the model predictions agreed

extremely well with the measurements. Allowing

one free parameter describing thickness variations,

the agreement with the experiment is nearly perfect.

Validation of this model is the first example of

linewidth modeling based entirely on the measured

microstructure.

Contributors and Collaborators

J.O. Rantschler, B.B. Maranville, J. Mallett,

T. Moffat, W.F. Egelhoff, Jr., A.P. Chen (Metallurgy

Division, NIST); J.A. Borchers, S.K. Satija (NIST

Center for Neutron Research); W. Bailey (Columbia U.);

A. Arrott (Virginia State University)

Figure 2: FMR line broadening measured in a Permalloy film

and calculated almost entirely from the microstructure of the

underlayer shown in the inset.

–0.60

–0.65

–0.70

–0.75

–0.80

–0.85

–0.90

Effective anisotropy (T)

0 0.1 0.2 0.3 0.4 0.5 0.6

Inverse permalloy thickness (nm–1)

Ag / Ni80Fe20 / Ag

Cu / Ni80Fe20 / Cu

Ta / Ni80Fe20 / Ta
48

Magnetic Materials

Platinum-iron group alloys have at least two

important potential applications: as a medium for

magnetic recording and as CO tolerant catalysts

in fuel cells. Alloy formation by electrodeposition

presents a convenient and inexpensive alternative

to conventional vacuum methods. A simple

thermodynamic model has been used to account

for the observed dependence of alloy composition

on the deposition potential.

Jonathan J. Mallett, William F. Egelhoff, Jr.,

and Thomas P. Moffat

Perhaps the most exciting application of iron-group

Pt alloys involves their high magnetic coercivity and

anisotropy in the L10 phase. This makes them ideal

candidates for future magnetic storage media, which

will require high coercivity material to sustain the

reductions in bit size needed to increase storage density.

Controlled alloy composition and microstructure are

essential for achieving the L10 phase, which requires

close to a 50:50 composition.

Iron-group Pt alloys may also find application

as poison-resistant hydrogen fuel cell catalysts.

A primary concern is the lifetime and efficiency of

the catalyst used to oxidize hydrogen gas in the cell.

Recent research suggests that replacing the traditional

Pt catalyst with a Pt alloy containing up to 15 %

of an Fe-group element can dramatically improve

the resistance of the catalyst to CO poisoning.

An inexpensive, reliable process for producing such

alloys is, therefore, likely to be of considerable utility

to fuel cell development.

An electrodeposition method has been developed

that allows smooth (< 5 nm RMS roughness) alloy

films to be deposited to a thickness of between 20 nm

and 3000 nm. Deposition takes place from a bath

containing 3 mM PtCl4 and 0.1 M of the reactive

metal ions (Fe2+, Ni2+, or Co2+). The deposition

potentials were chosen such that deposition of the

reactive metal in its bulk form would have been

energetically impossible. Platinum on the other hand

readily deposits at all of the chosen potentials. The

incorporation of the reactive metal occurs due to the

highly negative enthalpy of mixing of the alloy. This

reduces the activity of the reactive element in the alloy

and allows its deposition to occur at more positive

potentials than would be possible for the pure element.

The reactive ions are in much higher concentration than

the noble complexed platinum ions, which allows the

former to be reduced in a kinetically facile way that

enables equilibrium alloy compositions to be achieved.

Under these conditions, the alloy composition and

morphology was found to remain remarkably invariant

to significant perturbations in constituent concentrations.

The strong dependence of composition on potential is

shown in Figure 1 for three alloys.

Electrodeposited Pt1–x (Fe,Co,Ni)x Alloys

Figure 1: The theoretical (curves) and experimental (data points)

dependence of composition on potential.

Figure 2: The increase in coercivity on annealing.

Figure 2 shows the effect of annealing an FePt film

grown on a Cu(001) substrate. The transformation

to the L10 phase results in a dramatic increase in

magnetic coercivity. The 10 kOe coercivity produced

by the 650 oC anneal is suitable for next-generation

magnetic media.

Current activities are focused on extending

the investigation to ternary alloys and expanding

the available deposited structures to include

nanoparticles (useful as catalysts) and template-formed

nanostructures (for future magnetic recording media).

Contributors and Collaborators

E.B. Svedberg (Seagate Technology)
49

Magnetic Materials

Magnetic sensors play a central role in many

important technologies ranging from health care to

homeland security. A common need among these

technologies is greater sensitivity and smaller size.

In ultra-high density data storage, one of the most

pressing needs is for nano-structured media that store

data at ever-increasing densities. Improved methods

for the magnetic isolation of grains in ultra-thin films

are a key need; we have initiated research programs

in both areas.

William F. Egelhoff, Jr.

NIST’s Magnetic Engineering Research Facility

(MERF) is one of the most versatile facilities in the

world for the fabrication and analysis of novel magnetic

thin films. Two new areas of research, magnetic

sensors and magnetic media, illustrate this versatility.

The common link is that both require novel magnetic

thin films.

the correct composition for complex ultra-thin films.

MERF will soon become the only deposition system in

the world equipped for ultra-thin film deposition by IBSD,

AC and DC magnetron sputtering, and molecular beam

epitaxy. Such versatility will allow MERF to continue

to play a leading role in magnetic thin-film research.

In the area of novel magnetic media we have been

collaborating closely with Seagate. Seagate is the

world’s leading manufacturer of hard-disk drives, and

for the past two years, they have been sending a Ph.D.

physicist from their research labs to work with us,

first on ballistic magnetoresistance, and now on novel

magnetic media.

Novel Magnetic Materials for Sensors and

Ultra-High Density Data Storage

Figure 1: The Magnetic Engineering Research Facility (MERF).

It appears that ultra-sensitive magnetic sensors will

require the use of thin films of ultra-soft magnetic alloys.

These alloys often have a very complex composition such

as Fe73.5Si13.5B9Nb3Cu1 and require a very specific

annealing process. These materials are well-known in

bulk form but have never been produced in thin-film form.

The project goal is to carry out the metrology needed

to produce these materials as ultra-thin films.

We are presently modifying the MERF to add the

capability of ion-beam sputter deposition (IBSD). IBSD,

which is based on sputtering a target of the desired

composition, is the only reliable method for maintaining

Recent work determined a novel method for

magnetically decoupling grains in CoPd media. CoPd

multilayers are one of the leading candidates for the

next generation of magnetic media. We have found that

if a Au film is deposited on top of the CoPd and anneal

in air, two unexpected phenomena occur as a result of

rapid diffusion of atoms along grain boundaries. One is

that Co atoms diffuse to the surface, react with oxygen,

and remain at the surface. The other is that Au atoms

diffuse into the grain boundaries replacing Co. The net

effect is that the grain boundaries are demagnetized, and

each grain can magnetically switch independently of its

neighbors. This method provides the best magnetic

isolation of grains yet found.

Contributors and Collaborators

E.B. Svedberg, D. Weller (Seagate); R.D. McMichael,

T.P. Moffat, J. Mallett (Metallurgy Division, NIST);

D.P. Pappas (Electromagnetics Division, NIST)

Figure 2: Close collaborations with Seagate have contributed to

the success of this project.
50

Magnetic Materials

Magnetism is endemic to our society. Ferromagnets

are the basis for information storage in computers

and recording devices; they are found in all motors,

transformers, and generators; and they are used in

a host of other products like credit cards, cellular

telephones, radios, and televisions. However, the

magnetic characteristics of the ferromagnet used

in each of these applications varies with the

product. Consequently, industry needs to know

the interconnection between material characteristics

and magnetic properties, and how to control them.

A critical element in such an understanding is

knowledge of the fundamentals of spin interaction,

and how to measure it. NIST provides the metrology

needed by industry to do this.

Robert D. Shull and Jeffrey W. Lynn (NCNR)

I

n 1962, a new type of interaction between magnetic

 spins was predicted — a band structure effect caused

by an instability in the conduction electron gas near the

Fermi surface. The instability creates a new low-energy

state in which the magnetic spin orientations form a

standing wave, called a spin density wave (SDW).

Similarly, a wave of charge, called a charge density

wave (CDW), was also predicted. Charge density waves

have since been found experimentally, and the SDW

concept has been successfully used to explain the unusual

incommensurate antiferromagnetism in Cr. However,

evidence for SDWs in a ferromagnet has proven elusive.

Using neutron diffraction measurements at NIST,

we recently discovered a SDW in a single crystal of

Fe60Al40, a material with ferromagnetically interacting

spins. This was shown (Figure 1) by the presence of

scattering intensity at locations where there was no

atomic reciprocal lattice vector (i.e., at places where

there would normally be no coherent atomic scattering).

In fact, the data showed there are several SDWs in

the material with wave vectors near (110) directions

(shown in Figure 2). No such waves were found

along either (100) or (111) directions.

Discovery of Spin Density Waves in a Ferromagnet: Fe-Al

Figure 1: Neutron scattering intensity for a) polycrystalline

Fe60Al40 at 120 K and 1.7 K with their difference in the inset and

b) single crystal Fe60Al40 at 12 K shown as contours about the

(1/7, 1/7, 1/7) peak.

Figure 2: The reciprocal lattice spots in Fe60Al40, showing the

SDW wave vectors (black arrows). (Physical Review Letters 91,

217201-1 (2004).)

The presence of SDWs shows the exchange

interactions between magnetic spins in Fe-Al is a band

structure (i.e., non-local) effect and explains the large

magnetism in these materials containing a large content

of “non-magnetic” atoms. This discovery should be as

important to the understanding of magnetism in metals as

the SDWs in Cr. In Cr, the SDW wave vector, close to a

(100) direction, makes moments of nearest neighbors in

the bcc structure almost oppositely aligned.

Contributors and Collaborators

A.S. Arrott, D.R. Noakes, M.G. Belk (Virginia

State University); S.C. Deevi (Phillip Morris Co.);

D. Wu (Dartmouth College)
51

The purpose is the development of high-sensitivity,

low-noise magnetic sensors for use as metrological

tools in health care, homeland security and general

information technology. In health care, non-invasive

sensors are needed for medical evaluation in the

areas of magneto-cardiography and magnetic bead

tracking of blood flow and stem cells. In homeland

security, sensors are needed to detect low levels of

pathogens. In IT, sensors are needed for ND failure

analysis and magnetic data storage, among others.

Roy H. Geiss

The goal is to develop multi-level magnetic sensors

with a sensitivity better than 1 p-tesla/√Hz at 1 Hz

noise level that operate at room temperature and can

be easily integrated with standard silicon electronics.

This involves a many-faceted program that includes

materials development, sensor fabrication, sensor

characterization, modeling and nanomagnetodynamic

imaging. The component being studied here concerns

the dynamic observation of magnetic domain walls

using Lorentz microscopy in the transmission electron

microscope (TEM). Imaging of static magnetic domain

walls in the TEM is not new, but our focus is to study

the dynamics of domain wall-defect interactions and

changes in spin distributions associated with defects or

other discontinuities in nanodevices. The ultimate goal

is to associate the dynamical interactions with electrical

noise measurements in the same sensor.

The effort to image magnetic domain walls has just

started. A 200 kV TEM was obtained in 2003. A highresolution, high-speed CCD camera was installed, and highresolution, dynamic-magnetic imaging was successfully

demonstrated. A sample holder with multiple current feed

throughs was designed that allows the application of

magnetic fields for in-situ testing. Thus far, we have

obtained high-resolution images of domain walls at frame

rates up to 15 s–1. In particular, we have filmed the

formation and movement of Bloch lines and points in

cross-tie walls in Ni80Fe20 films 50 nm thick, and have

observed the pinning of cross-tie walls at small defects

in a noncrystalline CoFeNiSiB alloy film provided by

a U.S. magnetic sensor company. Both these dynamic

experiments were performed by slowly varying the small

local magnetic field in the neighborhood of the specimens

in the TEM. Movement of domain walls was possible

since the coercivity of both films was very small,

on the order of a few oersteds.

The observation of pinning of the domain walls

by small defects in the CoFeNiSiB film demonstrated

Micrometer-Scale Reliability:

Dynamic Imaging of Magnetic Domain Walls

Figure 1: Images a to d are from a video sequence showing

domain wall pinning. The cross-tie wall seen at the left-hand side

in a slowly moves to the right under the application of a small

magnetic field in b through d. In b the wall is pinned by defect 1.

With continued applied field, the wall breaks free from defect 1

and moves to defect 2, where it is again pinned, as suggested in c

and definitely in d. Defects 1 and 2 are 4 μm apart.

Figure 2: Images of the individual defects 1 and 2.

our capability to view interactions in real time.

Further, with frame-by-frame analysis of the video,

we determined which defects interacted with the

domain walls. A few frames from a video sequence

containing domain wall pinning are shown in Figure 1.

High magnification images of the noncrystalline defects

are given in Figure 2.

An abstract involving this work has been submitted to

the “2004 Magnetism and Magnetic Materials” conference.

Studies on smaller structures are the next phase.

Contributors and Collaborators

S. Russek, B. Rippard, D. Pappas (Magnetic

Technology Division, NIST)

Magnetic Materials
52

Magnetic Materials

Accurate adhesion and friction measurements

at the nanoscale are emerging as critical issues

in device industries and nanotechnology.

Measurements characterizing nanometer-thick

molecular assemblies and surface textures to

control surface properties and to ensure reliability

and durability are also needed. Working with

device and magnetic storage industries and other

agencies, we have designed and built instruments

to meet these needs. These instruments are housed

in NIST’s new Advanced Measurement Laboratory.

The facility features vibration isolation, class 1000

clean room standards, and temperature control.

Stephen M. Hsu

The nanotribology and surface properties project

was initiated as a part of the MSEL Nanotechnology

Initiative. The project aims to develop measurement

capability for adhesion, friction, and surface forces

at the nanoscale. We interact extensively with many

industries and research centers in the U.S. and around

the world to promote advances in measurement

science and seek consensus standard harmonization

in three areas: nanocontacts, nanolubrication, and

surface texturing.

Nanocontacts

Adhesion and friction measurements at nanocontacts

require accurate detection of normal and lateral forces

at nanonewton levels. Scanning probe microscopes

use sensitive cantilevers and laser diodes to detect these

forces, but this approach introduces rotation of the tips

and crosstalk among the xyz planes. To understand

the influence of surface forces, many of which are

functions of contact area, attention must be focused

on determining the real area of contact.

To resolve some of the instrumental challenges,

we have engaged instrument makers, such as

Hysitron, Veeco, and others, to solicit their inputs and

collaborations. At the same time, we have established

our own capability in tip fabrication, cantilever spring

constant calibration, and tip characterization. Three

new instruments were successfully installed as a result

of these collaborations: the NIST–Hysitron multiscale

friction tester, the NIST nanoadhesion apparatus, and

the first prototype of an interferometer microscope

from Veeco. We are continuing to work with our

partners to develop next-generation instruments as

suggested by the Nanometrology Grand Challenges

Workshop (NIST, January 2004).

Nanotribology and Surface Properties

The overall objective of the nanocontacts activity

is to develop the constitutive equation of adhesion

and friction including the various components

of surface forces. With our new adhesion and

nanofriction apparatus, we are quantifying the effects

of plowing and electrostatic charge on measurements.

We continue to work with our external academic

partners (UC Berkeley, UC Davis, and Ohio State U)

under the Nanotechnology Extramural Initiative to

develop friction measurement via three approaches:

friction measuring MEMS devices, AFM methods,

and ultrahigh vacuum friction measurement. These

efforts have been successful, and we have gained

considerable understanding of how meniscus forces

and electrostatic forces can exert significant effects on

nanofriction measurements. A NIST special publication

summarizing these findings is under preparation.

Nanolubrication

Molecular assemblies can be organized to impart

hydrophobicity, anti-adhesion, and friction control

characteristics on device surfaces. Supported by other

agencies and the magnetic storage industry, this activity

focuses on how to measure the effects of controlled

composition and spacing on properties of nanometerthick films. An ultrahigh vacuum scanning tunneling

microscope-atomic force microscope was installed in

May 2004 to provide imaging capability at the molecular

level. A micro-tribometer was also developed to measure

the durability of these films. The synchrotron facility

operated by the Division’s Characterization Methods

Group at Brookhaven National Laboratory continues to

be vital in characterizing these complex molecular mixtures.

Surface Texturing

Surface texture increasingly is being considered as

a tool to control surface energy, polarity, adhesion, and

friction. Supported by other agencies and industries,

we are pioneering the use of specific surface features

such as dimples, triangles, and ellipses at microand nanoscale dimensions to supplement molecular

assemblies to control surface properties of surfaces.

An international cooperative study under the auspices

of International Energy Agency (IEA) is underway.

Contributors and Collaborators

C. Ying, R. Gates, J. Chuang, J. Larson–Basse,

L. Ives, D. Fischer (Ceramics Division, NIST); B. Bhushan

(Ohio State U.); K. Komoupoulas (UC Berkeley);

G. Liu (UC Davis); Y.T. Hsia (Seagate); J. Sengers

(U. of Maryland); O. Warren (Hysitron); C. Su (Veeco)
53

Related and Cross-Cutting Projects

Electron microscopy is used to characterize the

structure and composition of materials at the

nanometer scale to better understand and improve

their properties. New measurement techniques in

electron microscopy are being developed and

applied to materials science research. The MSEL

Electron Microscopy Facility primarily serves the

Metallurgy, Ceramics, and Polymers Divisions as

well as other NIST staff and outside collaborative

research efforts.

John E. Bonevich

Atomic-scale structure and compositional

 characterization of materials can lend crucial

insights to the control of their properties. For instance,

direct observation of local structures by transmission

electron microscopy (TEM) provides important

feedback to the optimization of crystal growth and

processing techniques. Various characteristics may be

observed such as crystal structure and orientation, grain

size and morphology, defects such as stacking faults,

twins, grain boundaries and second phase particles.

Structure, composition and internal defect structures,

as well as the atomic structure of surfaces and

interfaces, can provide powerful knowledge for

engineering and understanding materials.

The MSEL Electron Microscopy Facility consists of

two transmission electron microscopes, three scanning

electron microscopes, a specimen preparation laboratory,

and an image analysis/computational laboratory. The

JEM3010 TEM can resolve atomic structures and employs

an energy selecting imaging filter (IF) and X-ray detector

(EDS) for analytical characterization of thin foil specimens.

The S-4700-II FE-SEM employs electron backscattered

diffraction/phase identification (EBSD) and EDS systems

to characterize the crystallographic texture and

composition of materials.

Nanoscale Characterization by Electron Microscopy

Figure 1: MgO cubes with surfaces decorated by small gold

particles. These particle ensembles are used in model studies of

3D chemical imaging at the nanoscale (electron tomography).

Figure 2: Confined Si single electron transistor device.

Highlights from the EM Facility for FY2004 include:

■ A new, high-sensitivity EBSD CCD camera

which acquires in excess of 70 patterns/second,

was installed on the FE-SEM.

■ 3D Chemical Imaging at the Nanoscale, a collaborative

project with CSTL and PL on tomographic

characterization of materials, was initiated (Figure 1).

■ Research collaboration with the Semiconductor

Electronics and Electricity Divisions (EEEL) has

characterized quantum effects in confined Si devices

(Figure 2).

■ Sub-100 nm Ag interconnects formed by

superconformal electrochemical deposition was

characterized.

Contributors and Collaborators

D. Josell, T. Moffat, L. Bendersky (Metallurgy

Division, NIST); I. Levin, B. Hockey (Ceramics Division,

NIST); J.H.J. Scott (Surfaces & Microanalysis

Science Division, NIST); Z. Levine (Optoelectronics

Division, NIST); E. Vogel (Semiconductor Electronics

Division, NIST)
54

Related and Cross-Cutting Projects

Metrology for Nanoscale Properties: X-ray Methods

Texture has a large influence on many properties

of thin films. XRD was the primary method for the

characterization of texture for many years. Recently,

alternative local techniques have been developed to

bring the measurements to the nanoscale. This year,

we compared measurements taken with conventional

XRD and EBSD on two thin films: sputtered aluminum

and electroplated copper. Both films had a thickness

of about 1 μm and were grown on [100] silicon

wafers. The inverse pole figures for both samples and

techniques are shown in Figure 1. It is obvious that

the agreement between XRD and EBSD in case of

aluminum film is very good, whereas it is rather poor

for copper film. This is a consequence of different

penetration depths of electrons and x-rays; while the

aluminum sample is homogeneous through the film

thickness, copper film is not. After sample preparation,

electroplated copper is likely to undergo self-annealing

at room temperature. This well-known phenomenon

yields a difference in grain size and orientation

between the surface and the bulk of the sample.

Contributors and Collaborators

A. Lita, J. Müller, R.H. Geiss, D.T. Read,

M. Kopycinska–Müller, R. Keller (Materials Reliability

Division, NIST); L. Kaatz, A. Chaudhuri (University

of Denver)

Figure 1: EBSD (left) and XRD (right) inverse pole figures of

aluminum (top) and copper (bottom) thin films.

of the {321} lattice spacings (sin2ψ method) yielded the

total residual stress at ambient temperature. The values

obtained are about 0.7 GPa and higher, where the bulk

of the stress is due to the intrinsic (growth) component.

Macroscopic properties of technologically

interesting materials originate from their

underlying micro-structure. To design and

understand improved materials, it is necessary

to characterize the microstructure and correlate

its changes to the macroscopic properties of

interest. We especially focus on x-ray diffraction

studies of biomedical, ferroelectric, optoelectronic,

photovoltaic, semi-conducting, and other materials

relevant to the health and microelectronics

industries. In particular, studies of microstructural

properties, such as strain and stress, crystalline

defects, and texture, complement the information

obtained by other techniques.

Thomas A. Siewert and Davor Balzar

I

n this report, we focus on two topics: the studies of

superconducting tungsten thin films and comparison

of the thin-film texture, as obtained by Electron Back

Scatter Diffraction (EBSD) and x-ray diffraction

(XRD). Tungsten superconducting transition-edge

sensors (TES) are used in different astrophysics and

astronomy applications, and as single-photon detectors

for the quantum computing experiments. Such

detectors comprise thin tungsten films and operate at

temperatures close to absolute zero and to the critical

superconducting transition temperature (Tc) of

tungsten. Thin films, in general, contain both hightemperature α-W phase (with Tc = 15 mK) and β-W

(A15 cubic structure with Tc = 1–4 K). Close to the

Tc, very small thermal changes, such as the absorption

of a single photon, increase the film electrical

resistance. The result is the production of an electrical

output signal that corresponds directly to the detection

of the absorbed photon energy. In general, residual

stress can influence the Tc of the thin film both directly

and by inducing the β→α phase transformation. Thus,

in order to control the Tc, it is necessary to measure

and control both the phase composition and residual

stresses. Residual stresses in films depend on the

preparation conditions, the thickness of the film, and

the difference in thermal expansion coefficient between

the film and the substrate. The total residual stress

results from both the intrinsic (growth) stress and

thermal stress. We measured the stress by XRD

at both ambient and cryogenic temperatures.

The sample was held in a continuous flow cryostat

that was capable of achieving temperatures as low

as 8 K. The cryostat was mounted on a goniometer

to enable the angle-dispersive XRD measurements.

The shift of the α-W {110} Bragg reflection was used

to estimate stress at 8 K, and directional measurement
55

Related and Cross-Cutting Projects

Brillouin light scattering is being employed to

provide information on acoustic and magnetic

waves at gigahertz frequencies in thin-film

materials. Measurements and modeling in FY04

have focused primarily on interactions of spin

waves in ferromagnetic films, elastic constants of

nanoporous low-κ dielectrics, and propagation

of acoustic waves in nanopatterned polymers.

Ward Johnson, Sudook Kim, and

Colm Flannery

Technical Description

Brillouin light scattering (BLS) is an experimental

technique that measures the intensity of spectral

components of light that is inelastically scattered

by vibrational waves (phonons) or spin waves

(magnons) in a material. Fabry–Perot interferometric

techniques are used to acquire accumulated spectra

through repeated mechanical sweeping of the

etalon spacing.

BLS is the only laboratory technique that is

currently available for detecting magnons of finite

wavenumber. Because of this capability and because

of innovations in interferometric techniques, BLS has

been increasingly applied to problems in magnetics

over the past couple of decades.

For characterization of phonons in thin films,

BLS offers several advantages over other techniques.

Since it detects phonons in the gigahertz range, elastic

constants can be determined in films of submicron

thickness without the complication of vibrational

energy penetrating significantly into the substrate.

Modes localized in submicron structures can be

characterized. Spatial variations in elastic properties

and vibrational patterns can be measured with a lateral

resolution equal to the size of the laser focal spot on

the specimen (typically, ~50 micrometers).

In this division, techniques are being developed

for characterizing interactions of magnons in metallic

ferromagnetic thin films. Such interactions limit

the speed of magnetic-storage devices, spin-valve

sensors, and other thin-film magnetic devices.

BLS measurements and modeling of vibrational

modes are being pursued in several thin-film systems,

including nanoporous low-dielectric-constant (low-κ)

dielectrics, nanopatterned polymers, and arrays of

molecular rotors.

Metrology for Nanoscale Properties: Brillouin Light Scattering

Accomplishments

During FY04, we developed and applied methods

for measuring magnons that arise directly or indirectly

from microwave pumping of metallic ferromagnetic

films in a static magnetic field (Figure 1). BLS

spectra were studied as a function of scattering

angle, microwave power, and laser power to provide

information on magnon–magnon interactions in

Ni81Fe19. The results demonstrate, for the first time,

detection of nonzero-wavevector magnons arising

from the decay of pumped uniform-precession

magnons in metallic thin films.

Young’s modulus and Poisson’s ratio in

nanoporous low-κ dielectric films were measured

using conventional backscattering techniques. This

research is described elsewhere in this annual report.

Measurements and modeling of vibrational modes in

nanoimprinted polymers were pursued in collaboration

with the University of Akron and the NIST Polymers

Division. In addition to bulk and surface modes,

low-frequency modes were detected and found to

be consistent with vibrational localization in the

imprinted lines. This result suggests the possibility

of characterizing elastic properties on a scale of

tens of nanometers.

Contributors and Collaborators

P. Kabos (Radio-Frequency Technology Division,

NIST); S. Russek (Magnetic Technology Division,

NIST); A. Slavin (Oakland Univ.); J. Michl (Univ.

of Colorado, Chemistry Dept.); R. Horansky (Univ. of

Colorado, Physics Dept.); C. Soles (Polymers Division,

NIST); R.H. Hartschuh, A. Kisliuk, A. Sokolov

(Univ. of Akron)

Figure 1: Scattering of light off waves in a thin film.
56

Related and Cross-Cutting Projects

The microelectronics community uses

electrodeposition to produce solderable surface

finishes, magnetic recording media, and copper

interconnections in printed circuit boards and

integrated circuits. These films tend to develop

sizable mechanical stresses that can lead to loss of

adhesion and the generation of bulk and surface

defects. This project focuses on the measurement

of these stresses which should enable the

development of effective mitigation strategies.

Gery R. Stafford and Ole Kongstein

Electrodeposited films tend to develop sizable

mechanical stresses during deposition due to the

nucleation and growth process or solution additives and

alloying elements. We have established an optical bench

dedicated to the in situ measurement of growth and

residual stress during electrodeposition using the wafer

curvature method. In one approach, a substrate of

borosilicate glass is evaporated with 250 nm of gold.

The force exerted on the cantilever by the electrodeposit

causes curvature of the cantilever, which is monitored

during electrodeposition. Forces on the order of

0.03 N/m can be resolved during film deposition.

negative deposition potentials. As the deposit thickens,

the average film stress decreases and becomes

compressive in deposits formed at small deposition

overpotentials. In the physical vapor deposition literature,

this compressive stress has been attributed to the

non-equilibrium concentration of mobile ad-atoms on

the surface that are driven into the grain boundaries.

Nanostructure Fabrication Processes:

Thin Film Stress Measurements

Figure 1: Average film stress during copper deposition.

Figure 1 shows the average in-plane stress associated

with the deposition of copper from an additive-free sulfate

electrolyte. The rapid rise in tensile stress (within the

first 20 nm) and its dependence on deposition potential

are consistent with nuclei coalescence and grain boundary

formation. The highest tensile stresses are associated

with high nucleation densities which are obtained at more

Figure 2: Force/ width exerted on the cantilever during the

electrochemical processing of Sn on Cu.

We have also examined the force exerted onto a copper

cantilever electrode during the deposition of matte tin (Sn),

Figure 2. This is a particularly important system since

the growth of tin whiskers, known to produce electrical

short circuits and device failure, has been attributed to

both the residual stress in the electrodeposit as well as

that generated from intermetallic formation at the Sn-Cu

interface. The force curves show the following features:

a tensile to compressive transition during deposition, a

significant tensile relaxation when plating is discontinued,

the development of tensile stress while the deposit is at

open circuit, and a residual tensile stress after the deposit

is electrochemically dissolved. The two latter features

are attributed to the formation of the Cu6Sn5 intermetallic

(IMC) at the Sn-Cu interface. A tensile stress is generated

since the IMC has approximately 6 % smaller volume than

a rule of mixture combination of the Sn and Cu reactants.

Calculating the IMC thickness from the difference in Sn

deposited and stripped, a nominal stress in the intermetallic

was estimated to be 1.2 GPa after only one hour. Future

work will focus on determining to what degree this

increases the compressive stress in the Sn electrodeposit.

Contributors and Collaborators

W. Boettinger, U. Bertocci (Metallurgy Division, NIST)
57

Related and Cross-Cutting Projects

Knowledge of mechanical behavior is critical

when designing for device performance and

reliability, even for “non-mechanical” systems.

However, nanoscale mechanical behavior

(including failure) is inherently difficult to measure

accurately, and existing modeling tools are only

qualitative at best. We are developing modeling

techniques that provide quantitative predictions

and are validating these results experimentally.

Lyle E. Levine and Anne M. Chaka (838)

Mechanics at the nanoscale is inherently difficult to

model accurately. Finite element modeling (FEM)

can effectively capture the elastic behavior of macroscopic

structures but includes no accurate failure criteria

since this depends upon atomic-scale behavior.

Classical atomistic simulations can handle enough atoms

(millions to billions) to model such events, but these

potentials become inaccurate for large strains and they

cannot effectively handle chemistry. Quantum-mechanicsbased simulations using density functional theory (DFT)

are extremely accurate and handle the chemistry exactly,

but such simulations are so CPU intensive that they

can handle only a few hundred atoms. A combination

of all three modeling techniques is required to

accurately model device behavior at the nanoscale.

the predicted elastic displacement fields to generate

boundary conditions and initial atom positions for

an atomistic simulation using classical potentials.

The use of classical potentials in a large simulation cell

allows the correct propagation of the long-range stresses

to the critical regions where bond distortions are large or

where chemistry effects need to be explored. In these

critical regions, the techniques embed a DFT simulation.

Iteratively, the critical region is relaxed using DFT, and

the classical cell is relaxed using a Monte-Carlo algorithm.

The first application of this hybrid technique was to

determine the vacancy formation energy in aluminum as

a function of distance (at a fixed angle) away from an

edge dislocation. The simulation geometry is shown in

Figure 2. The boundary conditions and initial atomic

positions were calculated from the known elastic

displacement field of an edge dislocation.

Nanomechanics: Coupling Modeling with Experiments

Figure 1: FEM model of a rigid 100 nm diameter sphere

indenting an Al sample to a depth of 10 nm.

Over the past year, we have developed techniques

to handle such multiscale modeling for quasistatic

applications. At the macroscale, FEM is used to simulate

the elastic behavior of a nanomechanical system. Figure 1

shows an example in which an Al sample is being indented

by a rigid 100 nm diameter sphere. The indenter and

three of the sample quadrants have been removed to

highlight the resulting Von Mises stress distribution after

indenting 10 nm. The FEM mesh is fine enough to use

Figure 2: Diagram of a hybrid simulation for obtaining the

vacancy formation energy at different positions relative to an

edge dislocation. The large box represents the EAM cell in

which the DFT region containing the vacancy was embedded.

After an initial dislocation nucleation event,

nanoindentation progresses through the complex

evolution of dislocation structures. For example,

the raised lip around the indent is produced by large

numbers of dislocations exiting the surface. We are

working on modeling the early stages of this process

using 3D dislocation dynamics and assuming a random

distribution of dislocation sources in the sample.

Finally, connection to experimental measurements

requires careful force calibration of the indenter and

calibrated atomic force microscopy measurements (AFM)

of the indenter tip. These calibrations are mostly complete,

and the AFM data will be used to generate a FEM mesh

for the simulations. Bulk single-crystal copper samples

are being cut and polished using non-contact chemical

methods to minimize the dislocation density.

Contributors and Collaborators

S.M. Khan, G. Levi, L. Ma, F. Tavazza (Metallurgy

Division, NIST); B. Hockey, R. Machado, D. Smith,

R. Wagner, D. Xiang (Ceramics Division, NIST)
58

Related and Cross-Cutting Projects

In the continuum model, we simulate free surfaces

and interfaces by applying the usual boundary conditions.

Accomplishments

We have carried out a detailed analysis of SAW

measurements in a thin TiN film on Si, calculated

stresses in a wide range of solids, and modeled Ge

clusters in Si containing a free surface and a vacancy.

The work is reported in six papers. A library of GFs

is available at www.ctcms.nist.gov/gf, which contains

downloadable teaching and tutorial material on

GFs and computer codes for calculation of GFs.

A GF group of about 50 international users has been

formed at CTCMS.

Contributors and Collaborators

D. Hurley, D.T. Read (Materials Reliability

Division, NIST); L. Bartlolo (Kent State University);

A. Powell (M.I.T.)

Precise knowledge of atomistic configuration

and strains in nanomaterials is needed for their

characterization and development of new devices.

We have developed computationally efficient

Green’s-function methods for calculation of lattice

distortion, elastic strains and displacements in

a variety of material systems. Our work is useful

for interpretation of data obtained by AFAM,

nanoindentation, and SAW experiments.

Vinod K. Tewary and Bo Yang

Technical Description

Green’s function (GF) provides a computationally

efficient tool for interpretation of data obtained by

nanoindentation and atomic force acoustic microscopy

(AFAM) which is useful for elastic characterization of

nanomaterials. The dynamic GF is used for modeling

propagation of surface acoustic waves (SAWs) in

solids and their phonon properties. The GF accounts

for interfaces and free surfaces in the solid and its

elastic anisotropy, which play relatively important roles

in the elastic response of nanomaterials as compared

to ordinary solids. We use GF to calculate the elastic

displacement fields, interaction energy between the

embedded nanostructure and other defects and free

surfaces. The displacement field, due to a force at

the surface, is used for interpretation of AFAM and

nanoindentation measurements. The interaction

energy of the nanostructures is an important factor

in the stability and growth of the nanostructure.

We have developed GF methods both at the discrete

atomistic and macro continuum scales. For a lattice

model containing N atoms, the GF is given by:

G = Φ–1

where G and Φ are 3N × 3N matrices of GF and

force constants respectively. The matrix inversion

is carried out by using the discrete Fourier transform

for a perfect lattice or numerically by computer

simulation for a model crystallite as in molecular

dynamics.

In order to model an embedded nanostructure

in a host solid, or a thin film on a substrate, we

define an initial GF for the host and the final GF.

The final GF is related to the initial GF through the

Dyson equation.

Physical Properties of Thin Films and Nanostructures:

Green’s-Function Methods

Figure 1: Stress distribution in Si due to a surface load.

Figure 2: Interaction energy of a cluster of 147 Ge atoms

with a vacancy and free surface in Si.
59

Related and Cross-Cutting Projects

We have developed a multiscale model for

nanostructures in solids. The model relates the

physical processes at the interatomic level to

measurable lattice distortions at the nanometer

level and macroscopic stresses and strains.

The model links the subnano (interatomic),

nano (nanostructures), and macro length scales

by integrating the powerful techniques of

molecular dynamics, lattice-statics Green’s

functions, and continuum Green’s functions.

David T. Read and Vinod K. Tewary

Technical Description

Mathematical modeling is a very important tool

for understanding the mechanical behavior of

nanomaterials and for research and design of devices

based upon nanostructures. A nanostructure needs to

be modeled at the following scales: (i) the core region

of the nanostructure (subnanometer), where the

nonlinear effects may be significant; (ii) the region of

the host solid around the nanostructure (nanometer);

and (iii) free surfaces and interfaces in the host solid

(macro). A nanostructure causes lattice distortion in the

host solid that manifests as strain throughout the solid.

The strain is essentially a continuum-model parameter,

whereas the lattice distortions are discrete variables that

must be calculated by use of a discrete lattice theory.

Hence, one needs a multiscale model that relates the

discrete lattice distortions at the microscopic scale to

a measurable macroscopic parameter such as strain.

Conventional models of nanostructures are based

upon either the continuum theory, which is not valid

close to the defect, or molecular dynamics (MD) which

is CPU intensive and usually limited to small crystallites,

which may introduce spurious size effects. We need a

computationally efficient multiscale model that links the

length scales from subnano to macro and that can be

used on an ordinary desktop. Such a model will be a

valuable tool for research and engineering designs.

 Our model is based upon the lattice-statics Green’s

function (LSGF) G that reduces asymptotically to the

continuum Green’s function (CGF). The displacement

field in this model containing N atoms is given by:

u(l) = (1/N) ΣkG(k) F(k) exp(ik.l),

where l is a lattice site, k is a reciprocal space vector,

and F(k) is the Kanzaki force, which is calculated by

using MD without making the linear approximation.

For small k, G(k) reduces to CGF. Thus, for large l,

the equation reduces to macroscopic continuum

theory while the discrete lattice effects are retained

in F(k). Thus our model is truly multiscale since it

seamlessly links the discrete atomistic effects in F(k)

to macroscopic scales through the GF. Even for a

million atom model, the calculation of GF takes only

a few CPU seconds on a standard 3 GHz desktop.

Accomplishments

Initial conference presentations and a journal paper

on this new approach, first reported at the end of

FY 2003 and during FY 2004, have been well received.

Figure 1: Section through Ge quantum dot in Si matrix after

partial relaxation. The red circles indicate the original positions

of the Si lattice sites; the atom in red is the center of the QD.

This year, we set out to apply the approach to a more

timely, but also more challenging, physical system, namely,

a germanium “quantum dot” (QD) in a silicon matrix.

On the GF side, the challenge was to treat the more

complex diamond-cubic lattice structure; on the MD

side, the more complex modified embedded atom model

potential, needed for silicon and germanium, had to be

coded and tested. As of this writing, the first iteration of

the Si-Ge quantum dot is in progress. The figure shows

the initial distortions of the diamond cubic lattice around a

QD with 281 Ge atoms; the method is capable of handling

much larger QD, even with a desktop computer.

Contributors and Collaborators

R.R. Keller, B. Yang (Materials Reliability Division,

NIST); E. Pan (Akron University)

Micrometer-Scale Reliability:

Bridging Length Scales
60

Related and Cross-Cutting Projects

It is widely anticipated that applications of

nanomaterials will enable major advances

in technology in a variety of fields, including

sensors, high-strength materials, medicine, and

others. Computer simulations seem to offer a path

to quantitative understanding of the behavior of

nanoscale materials. The form and parameters of

the interatomic forces may turn out to be the most

concise and useful representation of materials

measurement results. Atomistic simulations are

widely used in interpreting nanoscale phenomena

at the boundary between mechanics and chemistry

and to support the plausibility of proposed

devices. We are developing the capability to

use molecular-dynamics simulations to interpret

our own measurements, and to assess the

accuracy of proposed interatomic potentials.

David T. Read

Various approaches to simulating atomic interactions

have been reported. The first-principles approach

uses quantum mechanical models of nuclei and electrons.

Even though this approach typically includes only the

valence electrons, it can handle only a few tens of atoms.

Recently, in an innovative study, the first principles

approach was used to search for new superalloys.

The molecular-mechanics approach, widely used

for organic molecules such as proteins, requires explicit

assumptions about atomic bonding, specifically, a list

of which atoms are bonded to which other atoms.

The bonds are represented by force laws, and the

configuration of complex molecules can be studied.

Different force laws may be used for certain types

of atoms, depending on the chemical environment.

For instance, the carbon–carbon force law in diamond

may be different from that in graphite, because of

the difference in local chemistry.

Molecular dynamics (MD) treats atoms or

molecules as particles that follow Newton’s laws of

mechanics. The particles interact with a prescribed

force law, which depends only on the chemical identity

of the interacting atoms. The force laws are derived

empirically, and the parameters are selected by fitting to

measured properties, such as the elastic constants, the

vacancy energy, the energy of sublimation, the phonon

frequencies, and others. This approach can treat solids,

liquids, or gases, and can model melting temperatures

and equilibrium crystal structures.

Micrometer-Scale Reliability:

Molecular Dynamics

Molecular-dynamics results obtained in the current

fiscal year may indicate a mechanism for the recurring

reports that the Young’s (elastic) modulus values of thin

films are lower than those of the corresponding (perfect)

bulk material by 10 % or more. Last year’s report showed

a high-resolution SEM micrograph of electrodeposited

copper with a morphology of agglomerated spheres.

Its Young’s modulus was over 40 % lower than the bulk

value. This year, the elastic behavior of a simplified model

of such a solid was simulated by molecular dynamics.

Caution is in order. The size scale (number of atoms

per sphere) and time scale of the simulation were much

less than for the actual specimen. The results, averaged

over a random set of crystal directions for the spheres,

and for two sizes of spheres, produced a Young’s modulus

35 % below the bulk value. This was surprising because

continuum-mechanics calculations of the modulus

decrease produced by defects of like porosity show values

proportional to the volume loss. The present MD results

are much more dramatic because after the model was

brought to equilibrium, it had a density of about 95 %

of the bulk value.

Contributors and Collaborators

J. Rifkin (University of Connecticut, author of MD

program used)

Figure 1: Cross-section from the center of an array of spheres

(AS) model. Atoms shown in color have local fcc symmetry.

Atoms shown as black have a lower local symmetry. Because of

the periodic boundary conditions, this cell is effectively replicated

indefinitely in all 3 dimensions.
61

Related and Cross-Cutting Projects

Myriad industrial and biological systems are

composed of small-scale structures for which the

mechanical behavior is not accurately known.

Optimizing the performance and reliability of

these systems requires either mechanical property

measurements on specimens of these structures

harvested from the appropriate phases or

interfaces of the system, or the ability to test these

structures in situ. We are developing standardized

testing configurations and methodologies for

localized measurements of strength and fracture

toughness of materials and interfaces at the

micro- to nanometer-length scale.

Edwin R. Fuller, Jr. and George D. Quinn

This project aims to: (1) measure mechanical

properties of microstructures for myriad industrial

and biological systems that cannot be fabricated in bulk

samples; (2) study small-scale phenomena that may

be controlled by surface effects, e.g., the influence of

surface stresses on crack nucleation and extension; and

(3) obtain quantitative mechanical property data of materials

and interfaces for designing small-scale structures and

components and for assessing their mechanical reliability.

To address these goals, well-characterized testing

configurations must be developed for small-scale

measurements of strength and crack extension. We are

pursuing four tasks: (1) configuration design and finite

element analysis; (2) specimen fabrication; (3) mechanical

testing and fracture analysis (fractography); and (4) length

and force metrology. Work in the Ceramics Division

this year has focused on the first and third areas. Two

collaborations were established in the fabrication task:

one with James A. Beall of the Quantum Electrical

Metrology Division (817) in NIST Boulder, and one with

Northwestern University. Work in the fourth task will

Mechanical Metrology for Small-Scale Structures

come in subsequent years, most likely in collaboration

with the Manufacturing Engineering Laboratory.

Significant progress has been made in the design of a

compressively loaded test configuration with a welldefined, tensile gage section. Such a specimen can be

loaded using a depth-sensing nanoindenter as a universal

testing machine, thereby giving a record of both applied

load and load-point displacement. One of these specimens,

fabricated by James Beall from a silicon wafer by

deep reactive ion etching, is shown in the right-side of

Figure 1. The configuration is similar to a theta specimen,

except that the geometry is hexagonal. When a load

(per unit thickness) is applied to the top beam, a uniform

uniaxial tensile stress results in the middle gage section.

Finite element analysis gives (horizontal) gage section

stresses on the order of 1.25 GPa for 50 mN/μm of applied

load. For a 2 N applied load, these 100 mm-thick

specimens generate 500 MPa of tensile stress in the gage

section. The left-side of Figure 1 shows a reconstructed

failed specimen. The insert shows the fracture surface

of the gage section, and the two [111] cleavage facets

that were formed. Alternate geometries, including a

round theta specimen, are also being considered.

Figure 1: Prototype specimen design.

To extend this technique to a wide variety of

materials and systems, general fabrication procedures

need to be developed. Towards this objective, focusedion-beam (FIB) milling is being explored in collaboration

with Northwestern University. Figure 2 shows our first

attempt at producing a hexagonal theta specimen by

FIBing. It has been scaled-down by about a factor

of 10, and is fabricated from a lamellar directionally

solidified eutectic of Ni0.5Co0.5O and ZrO2.

Contributors and Collaborators

D. Xiang, D.T. Smith (Ceramics Division, NIST);

A. Jillavenkatesa (Standards Services Division, NIST);

J.A. Beall (Quantum Electrical Metrology Division,

NIST); N. Alem, V.P. Dravid (Northwestern University)

Figure 2: Hexagonal theta specimen by FIBing.
62

Related and Cross-Cutting Projects

Nanoindentation has rapidly become the method of

choice for quantitative determination of mechanical

properties of thin films and small volumes of material,

but standardization efforts have lagged far

behind the application of the technique in industrial

research and development. Over 1000 commercial

nanoindentation instruments from a variety of

manufacturers are currently in use, with no traceable

force calibration and an extremely limited choice of

standardized test methods. We work with standards

groups and National Measurement Institutes around

the world to develop standard reference materials

(SRMs), traceable calibration transducers, and

robust, reliable methods for obtaining and analyzing

nanoindentation data, so that nanoindentation

results can be used with confidence in product design

and specification.

Douglas T. Smith

Nanoindentation is the most commonly used method

for determining hardness and elastic properties of

small volumes of materials. In this technique, a diamond

indenter is pushed into a specimen surface, and the force

on and displacement into the surface are recorded. The

technique is capable of providing information on the elastic

and plastic deformation of a specimen for indentations as

shallow as 5 nm to 10 nm, and requires minimal specimen

preparation effort. It is routinely used to measure the

mechanical properties of thin films. However, there

are only a very limited number of accepted test methods

available, and no means to traceably calibrate or verify

the performance of nanoindentation instruments.

This leads to large interlaboratory variations in results,

particularly for hard, high modulus materials, and prevents

the use of nanoindentation in thin film or coating

product specifications.

In many mechanical test methods, including

nanoindentation, a force is applied to a specimen, and

some displacement is measured. Traceable displacement

measurement by interferometry is well established. Force

measurement is more problematic, however, because the

SI unit for force is still based on an artifact kilogram mass.

The Microforce Competence Program at NIST has

developed a primary realization of force, traceable to

electronic and length SI units, for force calibration in

the range 1 mN to 10 nN. As part of this program,

transfer force cells are being developed that will allow

force calibration, traceable to NIST, for commercial

nanomechanical test equipment such as nanoindentation

machines and atomic force microscopes. One such

Figure 1: The error in the force applied to a specimen by a

commercial nanoindentation instrument, as referenced to a

traceably calibrated NIST force cell.

Nanoindentation Methods and Standards

transfer force cell was calibrated against the NIST primary

force balance to an uncertainty less than 0.5 % for forces

in the range 0.05 mN to 5.0 mN. That cell was then

mounted, as if it were a specimen, in a popular commercial

nanoindentation instrument that had been recently

calibrated by its manufacturer using their recommended

force calibration procedure. The figure shows the error

in the nanoindentation force recorded by the instrument,

relative to the traceable force cell reading. For forces

above 2 mN, the recorded force is within the 1 %

uncertainty required by most draft standards for

nanoindentation machines. However, for lower applied

force, the error increases dramatically, and at 0.05 mN,

the recorded force is almost 18 % below the actual

applied force.

We are also working with both ASTM (E28.06.11)

and ISO (TC 164/SC 3) on a wide range of standard

test methods for nanoindentation, and an ISO document

for the one method has now been approved (ISO

14577). In addition, the Ceramics and Materials

Reliability Divisions at NIST are working with the

Bundesanstalt für Materialforschung und–prüfung

(BAM) in Germany to develop joint thin film SRMs

(CRMs, or Certified Reference Materials, in Europe)

for use in nanoindentation machine verification.

Contributors and Collaborators

D. Xiang, B. Hockey, G. Quinn (Ceramics Division,

NIST); R. Machado (INMETRO, Brazil); J. Pratt

(Manufacturing Engineering Laboratory, NIST);

D. Hurley (Materials Reliability Division, NIST);

U. Beck (BAM, Germany)
63

Related and Cross-Cutting Projects

Novel structures and devices can be formed

through template electrodeposition. The ultimate

pattern resolution is determined by the size and

packing of molecules that comprise the template

and their ability to inhibit or catalyze various

electrochemical reactions. In the past year, the

effect of molecular functionality on the metal

deposition process has been explored.

Thomas P. Moffat and Michael J. Fasolka

Over the last decade, electrochemical processing

 has been undergoing a renaissance with the

fabrication of new materials and novel microstructures.

The development of new measurement techniques and

metrological tools for studying controlled growth at

fine length scales is the primary objective of this effort.

2. The role of molecular functionality of the surfactant

and robust design rules; and

3. The anisotropy induced in the electrocrystallization

reaction rate for a given surfactant.

As an example, an alkanethiol monolayer film can

either block or accelerate metal deposition depending

on the molecular functionality of its terminal group.

A dynamic range spanning several orders of magnitude

is possible depending on the system in question

(Figures 1 and 2). Based on these measurements,

selective metal deposition may be obtained by

patterning a substrate with the appropriate molecule.

Nanostructure Fabrication Processes:

Patterned Electrodeposition by Surfactant-Mediated Growth

Figure 1: Influence of small changes in molecular structure,

i.e., SO3

– vs. CH3, on the rate of copper deposition.

Figure 3: Spatially patterned monolayer films used to control

nucleation and anisotropic growth of copper crystals.

Through contact printing, higher resolution patterning

is possible, along with some interesting opportunities for

high-throughput combinatorial research. By varying

the surface chemistry, growth of isotropic or faceted

crystals has been shown to be possible (Figure 3).

Contributors and Collaborators

D. Josell, J. Mallett, W.F. Egelhoff (Metallurgy

Division, NIST); M. Walker, L. Richter (CSTL, NIST)

Figure 2: Copper deposition on an alknethiol derivatized gold

substrate only occurs in regions bearing –SO3

– terminated

molecules.

The three key metrology issues addressed are:

1. The rate differentiation accessible via surfactant

mediated metal film growth;
64

Related and Cross-Cutting Projects

Chemistry and Structure of Nanomaterials

Successful nanoscale materials fabrication is

empowered by a detailed knowledge of the chemistry

and structure of surface bound molecules; e.g.,

the optimization of self-assembled monolayers,

molecular templates, micro-electro-mechanical

system lubricants, and functionalized nanotubes.

Near-Edge X-ray Absorption Fine Structure

(NEXAFS) spectroscopy is ideally suited to measure

non-destructively chemical bond concentration,

rehybrization, and orientation with sub-monolayer

molecular sensitivity in diverse nanoscale materials.

Furthermore, NEXAFS can distinguish chemical

bonding in the light elements, measure the orientation

of interfacial molecules, and separately measure

surface versus bulk chemistry simultaneously.

Daniel A. Fischer

Materials having low energy surfaces are used in

many applications, for example, in non-wetting

surfaces or fouling resistant marine coatings. We have

produced a photo-responsive polymer surface by

combining the reversible photo-switching nature of

azobenzene with the self-assembly nature and low

surface energy properties of semi-fluorinated segments,

to create a fluoroazobenzene molecule surface.

Upon UV exposure, this surface reorients between

hydrophobic and less hydrophobic states, as shown

in Figure 1 (left upper and lower panels). For such

surfaces, one could imagine applications ranging from

low cost surface patterning to polymer surfaces that

would adsorb biological macromolecules on cue.

Figure 1: UV light reorients fluorobenzene semi-fluorinated

segments (green) downwards, i.e., to a less hydrophobic state.

We have utilized NEXAFS to observe, verify, and

quantify the reversible cis-trans molecular conformation

transformation from hydrophobic to less hydrophobic

states. The right panels of Figure 1 (upper and lower)

show polarization dependent NEXAFS anisotropy

behavior of the C–F and C–C peaks which reverse with

in situ UV light exposure highlighting the reorientation

of the semi-fluorinated segments.

Figure 2: Carbon NEXAFS of oxidized/functionalized nanotubes.

Figure 3: Model of peroxide functionalization of nanotubes.

Application of NEXAFS spectroscopy to the study of

electronic structure and chemical composition is illustrated

in Figure 2 for various chemically functionalized, singlewalled, carbon nanotubes. Upon peroxide functionalization,

the C= C ring resonance is greatly diminished on extensive

sidewall functionalization indicating loss of extended

conjugation and disruption of nanotube electronic

structure. The C= O peak intensity is greatest for peroxide

chemistry. NEXAFS spectroscopy supports a model

of peroxide funtionalization, shown in Figure 3.

Contributors and Collaborators

S. Samabasivan (Ceramics Division, NIST);

X. Li, C.K. Ober (Cornell); A. Hexemer, E.J. Kramer

(UCSB); S. Banerjee, T. Benny, S.S. Wong (SUSB);

J.A. Misewich (BNL)
65

Related and Cross-Cutting Projects

Reactions occurring at interfaces during the

high-temperature processing of complex electronic

materials involve diverse chemical compositions.

To optimize the design and control of these

interfaces, we are developing a generic

thermodynamic/kinetic model for interfacial

interactions. The model includes modification

of bulk reaction and mass transport parameters

to accommodate nanoscale observations.

Lawrence P. Cook, Winnie Wong-Ng,

and Igor Levin

State-of-the-art electronic devices contain complex

materials with chemical constituents ranging widely

over the periodic table; furthermore, new materials are

continually being added. Many electronic packaging

materials consist of metals, ceramics, and semiconductors,

with bi-phasic interfaces of several types. Processing

temperatures may extend up to 900 oC where diffusion

and reaction can be significant. Two principal

problems arise in the treatment of such interactions:

1) the application of equilibrium thermodynamic data

to the non-equilibrium growth of interfacial reaction

zones, and 2) the transition from micro-scale (bulk

dominated), to nanoscale (surface dominated) phenomena.

To address these issues, we have instituted a combined

thermodynamic/kinetic approach to investigate the model

system Ag-Bi2O3-Nb2O5-O, as outlined in Figure 1.

Thermochemistry and Metrology of Interfacial Interactions

Progress includes determination of a preliminary

phase diagram at 850 oC, and development of a

provisional thermodynamic model. Subsequent

construction of a chemical potential diagram has

allowed us to predict alternative diffusion and reaction

paths. Observations on Ag/BiNb5O14 reaction couples

(Figure 2) confirm the relatively high thermodynamic

mobility of Ag. Thermogravimetric data on the

interfacial reaction require more than a simple parabolic

rate law, due to the rapid initial spread of Ag along

reaction site surfaces. By comparison with particulate

interfacial systems, a two-step reaction model is

proposed, for which rate constants can be obtained.

Data for the model system are of direct interest

to the electronics community because Ag is an

important metallization component in many dielectric

ceramics. It is anticipated that continued work

on Ag-Bi2O3-Nb2O5-O will lead to the goal of a

comprehensive thermodynamic/kinetic model.

The model will be tested, iteratively refined, and

extended to other systems.

Contributors and Collaborators

M.D. Vaudin, P.K. Schenck, T. Vanderah, M. Green

(Ceramics Division, NIST); W. Luecke (Metallurgy

Division, NIST); C. Randall, M. Lanagan (Center for

Dielectric Studies, Pennsylvania State University)

Figure 2: Ag Lα X-ray map of Ag/BiNb5O14 reaction zone

(≈ 80 μm wide) produced by annealing in air for 10 h at 850 oC,

with an applied uniaxial compression of ≈ 1 MPa.

Figure 1: Flow chart for development of interfacial model based

on Ag-Bi2O3-Nb2O5-O.
66

Related and Cross-Cutting Projects

Phase equilibria data are needed for quality control,

cost reductions, performance enhancements, and

optimal processing in high Tc technology. These

needs are being addressed through studies of the

phase equilibria and kinetics of Ba2YCu3O6+x

formation from barium fluoride amorphous

precursor films, determination of Ba2RCu3O6+x

(R=Dy,Yb) phase diagrams, and investigations

of superconductor/buffer layer interactions:

all play critical roles in the development of

RABiTS/IBAD coated conductor technology.

Winnie Wong-Ng, Lawrence P. Cook,

and Igor Levin

Phase diagrams serve as “blue prints” for successful

processing of high Tc superconductor materials.

In the past year, as an integral part of the DOE intensive

R&D program on high Tc wire and cable applications, we

have continued to provide critical data for the development

of practical superconductors. Our research was related

to two groups of superconductors: (1) Ba2RCu3O7

(R=Dy, Yb) coated conductors produced by rolling

assisted biaxially textured substrate/ion beam assisted

deposition (RABiTS/IBAD); and (2) MgB2.

Our main effort has been focused on the determination

of BaO-R2O3-CuOx phase relations as a function of oxygen

pressure, pO2, and choice of lanthanides. These studies

were completed under carbonate-free conditions, to match

better the processing conditions of RABiTS/IBAD

conductors. This year we have completed the study of

the two systems with R = Dy and Yb. A trend in phase

formation and tie-line Ba2RCu3O7 relationships was

observed in the present work which provides a general

correlation for R = Nd, Sm, Eu, Gd, Dy, Ho, Y, Er, and Yb

with respect to the size of the lanthanides. In collaboration

with Brookhaven National Laboratory and California

Institute of Technology, an understanding of the effect of

strain on the trend of the orthorhombic to tetragonal phase

transition temperature of Ba2RCu3O7 was obtained

through modeling. By mixing the smaller lanthanides

R ́ with the larger R in the Ba2–x(R1+x–yR ́y)Cu3O6+z

superconductor, both flux-pinning and melting properties

can be tailored and optimized. A trend in solid solution

extent as related to the size of R was observed in

Ba2–x(R1+x–yYy)Cu3Oz (R = Sm, Eu and Gd).

The “BaF2 ex-situ” process is a promising method

for production of Ba2YCu3O7 superconducting wire

and cable. Previously, using a controlled-atmosphere

apparatus, we determined the presence of low-temperature

liquids in the multicomponent reciprocal Ba-Y-Cu//O,F

system. This year, we identified YOF (Figure 1) as an

Figure 1: Schematic of the YOF rhombohedral structure (left,

showing layers of [OY4 ] and [FY4 ] tetrahedra) and the cubic

fluorite structure (right).

Phase Relations of High Tc Superconductors

important intermediate phase in the system with a low

temperature reversible order–disorder phase transition near

the initial melting of fluoride-rich melts. These more

detailed studies have allowed better definition of the region

of low-temperature melting. Also, phase diagrams of

the pertinent subsystems of BaO-Y2O3-CeO2-CuOx

representing the interaction of product Ba2YCu3O7

with the CeO2 buffer layer were determined.

To control film properties, it is important to

understand the details of Ba2YCu3O7 formation from

“BaF2” films. High temperature x-ray diffraction and

transmission electron microscopy have been applied

to compare the detailed conversion mechanism of

films prepared with different precursors on SrTiO3

substrates and on RABiTS substrates (both provided

by ORNL). A phase with a Ba(OxFy)-based superlattice

has been found to be involved as an intermediate

product. Its presence may prove to be an important

factor influencing the kinetics of Ba2YCu3O7 formation.

Studies on MgB2 also continued with measurements

of the enthalpy of formation (by solution calorimetry) and

vapor pressure (by thermogravimetric effusion). Attention

was focused on the significant sources of variability in

these properties. These data are essential for reproducible

processing of MgB2 films, wire and cable.

Contributors and Collaborators

Q. Huang (NIST Center for Neutron Research);

M. Vaudin, P. Schenck (Ceramics Division, NIST);

R. Shull (Metallurgy Division, NIST); R. Klein

(Biotechnology Division, NIST); R. Feenstra, A. Goyal

(ORNL); T. Holesinger (LANL); M. Rupich (ASC);

J. Kaduk (BP-Amoco); T. Haugan (U.S. Air Force);

P. Canfield (Ames Lab); R. Meng (U. of Houston);

D. Welch (BNL), H.B. Su (Caltech)
67

Related and Cross-Cutting Projects

NIST Combinatorial Methods Center (NCMC)

Pioneer and Partner in Accelerated Materials Research

Combinatorial and high-throughput (C&HT)

techniques hold great potential for making

materials research more productive, more

thorough, and less wasteful. However, significant

barriers prevent the widespread adoption of

these revolutionary methods. Through creative,

cost-effective measurement solutions, and with

an eye towards fruitful collaboration, the NIST

Combinatorial Methods Center (NCMC) strives

to ease the acquisition of C&HT techniques by

the materials research community.

Cher H. Davis and Michael J. Fasolka

Now in its third year, the NIST Combinatorial Methods

Center continues to be a sought after partner among

industry, government laboratories, and academics

interested in acquiring C&HT research capabilities for

materials research. Indeed, the NCMC consortium

currently includes 22 member institutions (see table)

representing a broad cross-section of the materials

research sector.

The NCMC is successful because it serves the

combinatorial materials research community on several

levels. Our foundation is the extensive suite of NCMC

technologies, which provide measurement solutions to

parties interested in acquiring C&HT capabilities. Many

of these methods are described elsewhere in this report,

as identified by the NCMC symbol (see top right corner).

Technology transfer efforts complement our methods

foundation, as evidenced by the many institutions that

have adopted NCMC techniques. For example, Air

Products, Rhodia, National Starch (ICI), Dow, Procter

and Gamble, and Eastman, plus many universities, have

replicated NCMC devices in their laboratories. In this

respect, NCMC Focused Projects are a new paradigm for

NIST/industry partnership, which are extremely effective

for both methods development and technology transfer.

with Procter and Gamble and National Starch (ICI) to

produce HT microfluidic measurements of interfacial

tension. The second Focused Project, sponsored by Intel

and National Starch (ICI), will produce C&HT methods

that gauge the performance of epoxy adhesives for flip

chip electronics applications. Several other Focused

Projects are in development.

New scientific endeavors (such as C&HT materials

research) gain momentum when stake-holding parties are

brought together. Accordingly, to advance the field, the

NCMC invests itself in community forming activities aimed

at information transfer and goal consolidation among

institutions interested in C&HT research. Industry

workshops play a major role in this endeavor, and in

FY04 we hosted the 4th and 5th additions to the NCMC

workshop series, focused on Polymer Formulations

and Processing and Characterization, respectively.

Under a Focused Project, NIST scientists and 2–3 member

companies collaborate to develop a particular C&HT

measurement solution. While the research is co-funded

by industry members, we avoid the study of proprietary

materials and all results are published; this allows the

research to have the broadest impact. Currently, there

are two Focused Projects. In the first, NIST is working

“The focused project approach is particularly effective since it

allows active collaboration with industry, allowing real needs

to be addressed, and resulting technology transferred. The

[NCMC] is at the leading edge of combi-based material science

discovery, and this reflects both the quality of the research program

and of the people.” — Dr. J. Carroll, ICI/National Starch,

Strategic Technology Group

“The NCMC provides a unique platform to exchange information and ideas with other member companies who form a part of

this consortium.”— D. Bhattacharya, Global Coatings Application

Development, Eastman Chemical Co.

Moreover, we have been very active in organizing

symposia at national conferences. In FY04 alone,

NCMC staff developed and organized multi-day

symposia on C&HT methods for the Materials Research

Society, the American Chemical Society, the Adhesion

Society, and the Knowledge Foundation.

For more information on the NCMC, C&HT

technologies, or post-doctoral research opportunities,

see our website at http://www.nist.gov/combi.

“I have heard nothing but praise from all who attended the

recent NCMC conference. . .NIST did a superb job organizing

the symposia, selecting thought-provoking topics, and leading

good general discussions.” — Personal observation of J. Dias,

ExxonMobil; Chair ACS PMSE

Contributors and Collaborators

K.L. Beers, C.M. Stafford, A. Karim, E.J. Amis,

The Multivariant Measurement Methods Group

(Polymers Division, NIST)

NCMC Members (*New in FY2004):

3M Honeywell International

Accelrys* Hysitron International*

Air Force Research Lab Intel*

Air Products & Chemicals ICI/National Starch & Chemicals

Akzo Nobel Michelin

Atofina Chemicals* PPG Industries

BP* Procter & Gamble

BASF Rhodia

Bayer Polymers Sealed Air Corp*

Dow Chemical Company Symyx*

Eastman Chemical* Univ. of Southern Mississippi

ExxonMobil Research Veeco/Digital Instruments*
68

Organizational Charts

Organizational Charts

Materials Science and Engineering Laboratory

Polymers

E.J. Amis, Chief

C.R. Snyder, Deputy

Metallurgy

C.A. Handwerker, Chief

F.W. Gayle, Deputy

Ceramics

D.L. Kaiser, Chief

R.G. Munro, Deputy

Materials Reliability

A.F. Clark, Chief

T.A. Siewert, Deputy

NIST Center for

Neutron Research

P.D. Gallagher, Director

Director

Deputy Director

National Institute of Standards and Technology

Director

Boulder Laboratories

Baldrige National Quality

Program

Director for

Administration

& Chief Financial

Officer

Technology

Services

Advanced

Technology

Program

Manufacturing

Extension

Partnership

Manufacturing

Engineering

Laboratory

Chemical Science

and Technology

Laboratory

Materials Science

and Engineering

Laboratory

Electronics and

Electrical Engineering

Laboratory

Information

Technology

Laboratory

Physics

Laboratory

Building and

Fire Research

Laboratory

L.E. Smith, Director

S.W. Freiman, Deputy Director