1

NISTIR 6850

Nanomanufacturing of Atom-Based

Dimensional Standards

A Final Project Report of the

National Advanced Manufacturing Testbed

T.V. Vorburger, R.H. Allen, B. Damazo, J. Fu, D. Monk,

M. Osti, J. Pellegrino, R. Rhorer, R. Russell, R. Silver,

R. Sriram, K. Stouffer, D.A. Swyt, E.C. Teague,

T. Wheatley, D. Wilmering

U.S. DEPARTMENT OF COMMERCE

Technology Administration

National Institute of Standards

and Technology

Precision Engineering Division

Gaithersburg, MD 20899

January 2002
2

Nanomanufacturing of Atom-Based 

Dimensional Standards

A Final Project Report of the

National Advanced Manufacturing Testbed

T.V. Vorburger1, R.H. Allen2, B. Damazo3, J. Fu1,

D. Monk4, M. Osti5, J. Pellegrino4, R. Rhorer5, R. Russell6,

R. Silver1, R. Sriram2, K. Stouffer6, D.A. Swyt1, 

E.C. Teague1,3, T. Wheatley6, D. Wilmering5

ABSTRACT

This report describes the accomplishments of the Nanomanufacturing of Atom-based

Dimensional Standards Project, which operated as part of the National Advanced Manufacturing

Testbed (NAMT), a program to research a wide range of leading edge technologies for

manufacturing. As part of the NAMT vision, the Nanomanufacturing of Atom-based

Dimensional Standards Project researched the techniques to manufacture and use dimensional

standards at subnanometer levels of uncertainty. Its main area of application is the

microelectronics and data storage industries where in the future, the critical dimensions of

manufactured devices will grow continually smaller and where we anticipate that environments

in which certain components are manufactured and used will become more specialized and

exotic. This report discusses developments in atom-based step height standards, atom-based

linewidth standards, a vacuum-based artifact transport system, a portable data logger, design and

communication processes, and telerobotics.

Keywords: artifact transport; atom-based; collaborative design; data logger; dimensional

standards; linewidth; nanomanufacturing; step height; telerobotics 

1

Precision Engineering Division, MEL

2

Manufacturing Systems Integration Division, MEL

3

Manufacturing Metrology Division, MEL

4

Semiconductor Electronics Division, EEEL

5

Fabrication Technology Division, MEL

6

Intelligent Systems Division, MEL
3

Table of Contents

Page

1. Introduction 4

2. Basic Concepts of NAMT 4

2.1 The NAMT Program and Projects 4

2.2 The Overall Themes of NAMT 5

2.3 The NAMT Nanomanufacturing of Atom-based 6

Dimensional Standards Project and NAMT Themes

3. Description of the Nanomanufacturing of Atom-based 6

Dimensional Standards Project 

3.1 Motivation for the Project 6

3.2 Atom-based Artifacts 8

3.3 Results 9

3.4 Project Team and Partners 9

4. Project Accomplishments 10

4.1 Atom-based Standards 10

4.1.1 Goals 10

4.1.2 Step Height 11

4.1.3 Linewidth 15

4.2 Artifact Transport System 21

4.2.1 Current Design and Results 21

4.2.2 A Second ATS Concept 23

4.2.3 Observations 25

4.3 Artifact Transport System Data Logger 26

4.3.1 Introduction 26

4.3.2 System Design Overview 26

4.3.3 System Design Specifics 27

4.3.4 Internet Access 30

4.3.5 Results 30

4.4 Enhanced Design and Communication Processes 32

4.4.1 Computer Visualizations 32

4.4.2 Collaborative Design (Engineering Tools) 36

4.4.3 Design Repository 38

4.5 Telerobotics 39

4.5.1 Control and Image Standards 40

4.5.2 Remote Diagnostics Testbed 40

4.5.3 Recommendations 41

5. Conclusions and Future Work 42

6. Acknowledgments 42

7. References 43
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1. Introduction

This report describes the accomplishments of the Nanomanufacturing of Atom-based

Dimensional Standards Project, which operated as part of the National Advanced Manufacturing

Testbed (NAMT) in the Manufacturing Engineering Laboratory (MEL) at the National Institute

of Standards and Technology (NIST). Formally operating from fiscal year (FY) 1996 to FY

2000, the NAMT was an ambitious program to research a wide range of leading edge

technologies for manufacturing. As part of the NAMT vision, the Nanomanufacturing of Atombased Dimensional Standards Project researched the techniques to manufacture and use

dimensional standards at subnanometer levels of uncertainty. Its main area of application is the

microelectronics and data storage industries where in the future, the critical dimensions of

manufactured devices will grow continually smaller and where we anticipate that environments

in which certain components are manufactured and used will become more specialized and

exotic. We pursue these ideas further in Section 2 of this report as we describe the basic

concepts of NAMT. In Section 3, we provide a description of the Nanomanufacturing of Atombased Dimensional Standards Project itself. In Section 4, we give a final report of the

accomplishments of the project, and in Section 5, we discuss future directions in research arising

from this project.

2. Basic Concepts of NAMT

2.1 The NAMT Program and Projects

To support the development of solutions to the standards and metrology issues of modern

information technology (IT)-based manufacturing, the NIST MEL has carried out a research and

development (R&D) program called the National Advanced Manufacturing Testbed

(NAMT) [1-3]. The NAMT was developed to be a showcase for the future of manufacturing,

demonstrating how machines, software and people can be networked together to achieve

interoperability at all levels of a manufacturing enterprise. One feature of the NAMT is a stateof-the-art computer/conferencing laboratory [1]. At this facility, scientists and engineers from

industry, NIST, academia, and other government agencies work together on measurement and

standards issues in information-based manufacturing and on test methods for industry that are

part of NIST's mission. 

The projects of the NAMT have been characterized by: (1) collaborative industrial partners,

(2) leading edge technologies, (3) development and use of advanced measurement technologies,

(4) development of standards for manufacturing applications, (5) use of IT, and (6) tasks and

processes at multiple sites on-line. The results of the NAMT are metrology techniques, interface

standards, and infrastructural technologies and standards. 

The NAMT program developed components of an information infrastructure for manufacturing,

extending the capabilities of advanced computing, communications, and control technologies to

multiple manufacturing applications and domains. The program also leveraged pools of

manufacturing resources, including physical facilities, equipment, expertise, and software. 
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The NAMT program began in FY96 with four five-year projects:

• The Nanomanufacturing of Atom-Based Dimensional Standards project, led by the

Precision Engineering Division (MEL), focused on the distributed design, fabrication,

and use of nanometer-scale dimensional artifacts. 

• The Framework for Discrete Part Manufacturing project, led by the Manufacturing

Systems Integration Division (MEL), aimed at developing a consensus-based framework

for the interoperability of distributed manufacturing systems. 

• The Development of Machine Tool Performance Models and Machine Data Repositories

project, led by the Manufacturing Metrology Division (MEL), created a virtual

manufacturing and inspection model and data repository to reduce the need for physical

prototyping. 

• The Characterization, Remote Access, and Simulation of Hexapod Machines project, led

by the Intelligent Systems Division (MEL), aimed at measuring and extending the

capability limits of parallel machines, and developing and evaluating techniques for open

architecture control interface standards. 

Subsequently twelve additional projects were added to the NAMT program [3], and these

projects were led technically by NIST laboratories other than MEL. The projects focused on

real-time construction site metrology, telepresence microscopy and microanalysis, virtual die

design for information-based metal forming, radioactive seeds, internet commerce, a virtual

cybernetic building testbed, tele-calibration of gas flow meters, remote calibration of electrical

standards, next generation internet and intelligent collaboration and visualization technologies,

IT solutions for small and medium size manufacturing enterprises, interface standards for arc

welding, and internet-based calibration for radiation processing industries. In varied ways, these

projects exploited the capabilities of high performance networking and advanced computing.

2.2 The Overall Themes of NAMT

Within the context of IT-based manufacturing, the unifying technical focus of the NAMT

projects was development and demonstration of distributed and virtual manufacturing.

• By distributed manufacturing, we mean the cooperation in the overall manufacturing

process among functionally specialized facilities at a variety of geographically separated

sites by means of modern computer and communications systems. 

• By virtual manufacturing, we mean both: 

- real manufacturing by virtual enterprises, which come together by means of

computer communications to produce a product or aspect thereof; and 
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- virtual manufacturing by means of comprehensive and realistically predictive

simulation of designs, processes and resulting products by means of quantitative

modeling and qualitative animation.

2.3 The NAMT Nanomanufacturing of Atom-Based Dimensional Standards Project

 and NAMT Themes

As with each of the other three MEL-led NAMT projects, the Nanomanufacturing of Atombased Dimensional Standards Project was designed to jointly support:

• the overall NAMT program objective of support to IT-based distributed and virtual

manufacturing; and

• the Precision Engineering Division's lead mission objective to provide, realize, and

disseminate the international standard of length through length-measurement research

and services.

As a result, the project used or supported the technologies of: 

• distributed fabrication and use of nanometer-scale dimensional artifacts,

• computer modeling and simulation of mechanical systems and components,

• remote tele-operation of scanned probe microscopes (SPMs),

• all linked by means of advanced computers and communications for high-speed video,

voice, and data transmission among collaborators.

These topics are described below.

3. Description of the Nanomanufacturing of Atom-based Dimensional

 Standards Project

This section is divided into four parts: motivation, atom-based artifacts, principal results, and

the project team and partners.

3.1 Motivation for the Project

Two major trends in industry were driving forces for this project. First is the ever decreasing

dimensions and tolerances posed by the semiconductor and data-storage industries. The

International Technology Roadmap for Semiconductors 1999 projected that by 2005, the 3σ

resolution requirement for metrology of circuit critical dimensions (CDs) will be as small as

1.2 nm [4], only a few silicon (Si) lattice constants. However, imperfections in linewidth

standards limit the CD measurement accuracy. For example, the line from NIST Standard

Reference Material (SRM) 473 [5], shown in Fig. 1a, is among the best calibration artifacts that

industry and NIST can now produce in reasonable quantities.
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The imperfections in the line, its

edge roughness and out of

straightness, and irregular wall

geometry, produce calibration

uncertainties which are typically

much greater than that of NIST’s

and industry’s measurement

instrumentation. This in turn results

in limiting NIST’s ability to meet

the pressing needs of industry. 

One of the project goals was to

fabricate artifacts with feature

geometries which are limited only

by the atomic structure of matter and whose dimensions are determined by atomic diameters and

lattice constants, such as the one shown schematically in Fig. 1b. By collaborating with industry

NIST hopes to develop such physical standards and to develop and put in place documentary

standards to support their development. With these standards NIST will be in a much better

position to meet the future needs of industry.

The second major trend in industry is the demand (resulting principally from the first trend) for

ever cleaner and highly controlled manufacturing environments. These trends have been

manifested in the move from clean rooms to mini-environments [6] and the use of standard

mechanical interface, or SMIF, pods [7] for transferring materials between the manufacturing

tools.

In advanced technologies such as extreme ultra-violet lithography [8], facilities for the various

manufacturing and inspection steps may typically not be co-located with one another. The cost

to bring expert staff, facilities, and materials to a common site is very expensive.

Based on this trend and the awareness that certain atom-based artifacts may live most of their

lives in ultra-high vacuum (UHV) or at least highly controlled environments, Fig. 2 illustrates a

vision of future distributed nanomanufacturing for an increasing number of specialized products

such as x-ray photomasks [9] for advanced lithography which may require repair by a user in a

separate laboratory from the manufacturing facility. This vision can be thought of as part of the

larger vision of electronic (e)-manufacturing for semi-conductors [10] discussed elsewhere.

Figure 2 shows component fabrication, inspection, and control performed at three separate sites.

Both the inspection and fabrication might take place in clean microenvironments. Such facilities

might evolve further into UHV system environments with an artifact-transport system for

transporting materials between the various manufacturing and inspection tools and geographical

sites.

Figure 1 Properties of Linewidth Measurement

Standards
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Figure 2 Vision of Future Distributed Nano-manufacturing in Microelectronics

 and Data-storage Industries.

The second major project goal was to develop a standard artifact-transport system along with

standard mechanisms and artifact carriers for transferring artifacts between UHV systems. Such

systems will enable the use of geographically-distributed facilities as shown in Fig. 2 and might

require the development of a database dealing with the impact of various environmental

conditions on the stability of atom-based feature geometry and dimensions. This database might

also be needed for determining the final design of the artifact-transport system.

An additional activity of this project was to explore user and controller interfaces for telerobotic

operation of scanned probe microscopes (SPMs), scanning electron microscopes (SEMs), and

other scientific instrumentation that would be used for nanofabrication or inspection of atombased dimensional standards or devices. This is an area of great interest in the academic

community for providing access to a remote scientific instrument and in the industrial

community for remote diagnostics of instrumentation (e-diagnostics) [10] and remote operation

of instrumentation across clean room boundaries. However, there are currently no documentary

standards for operator or controller interfaces for most scientific instrumentation. It seems that

the combined efforts of industry, government agencies and academia are needed to develop the

technology and standards in this area.

3.2 Atom-based Artifacts

What do we mean by atom-based artifacts and how do we propose making them? The basic idea

is to let the intrinsic atomic spacings of matter provide the scale for length related parameters of

the artifacts.
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As shown in the scanning runneling

microscope (STM) images of an

Indium Antimonide (InSb) surface in

Fig. 3, highly structured features on

single crystal surfaces could serve as

atom-based dimensional standards -

step height from the steps, roughness

and line spacing from the stripe-like

features, and linewidth as discussed

before.

The current need is for feature sizes having linewidths on the scale of 10’s to 100’s of

nanometers. For these features we must develop processes that do not result in excessively

rough edges such as those shown in Fig. 3. The real challenge is then to make 100 nm scale

features that result in straight and vertical edges and that are stable and transferable between

NIST and industry.

Figure 4 shows some processes that

may be used to produce atomicallydetermined features: electric-field

evaporation, SPM transport of

atomic or molecular species,

molecular beam epitaxy (MBE), and

thermal transport, perhaps with the

application of electric-field

gradients. In our initial efforts we

have used MBE, field evaporation,

and another process called selective

dry etching.

3.3 Results

The results of the project include atom-based step height artifacts, prototypes for atom-based

linewidth artifacts, the UHV artifact transfer system (ATS), a portable data logger for both real

time and web-based monitoring of the ATS, and enhancements in design and simulation

processes. Research questions still remaining include the need for standardizing mechanical

interfaces, transfer mechanisms, and specimen carriers for UHV systems, and development of a

standard controller and user interfaces for telerobotic operation of SPMs and other scientific

instrumentation.

3.4. Project Team and Partners

The project team was composed of 16 people from the NIST MEL and the NIST Electronics and

Electrical Engineering Laboratory (EEEL). In addition, colleagues at the University of

Figure 3 Concept of Atom-Based Artifacts

Figure 4 Nanomanufacturing Processes
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Maryland, Thermo Microscopes, Texas Instruments, Veeco Metrology, and SEMATECH also

contributed as partners.

4. Project Accomplishments

We now turn to accomplishments in the five principal areas of the project.

4.1 Atom-Based Standards

4.1.1 Goals

This component of the project had as its main goal:

• To develop and fabricate standards for step height and linewidth, whose dimensions and

geometries are inherent in their structure and are tied to fundamental properties of matter,

such as material lattice constants or atomic dimensions. The uncertainty arising from

non-uniformity in the properties of such specimens should be significantly smaller than

the uncertainties in instruments measuring them. Therefore, the uncertainties in their

measured properties will not be limited by the specimens themselves.

Two other important goals follow from the one above:

• To develop specimen structures that may be exchanged between NIST and its

collaborators. This implies either that the specimens themselves are robust and stable or

that they are housed and moved in environmental support systems that avoid degradation

of the specimens' dimensional properties. The environmental capability is important. The

requirements of U.S. industry are such that NIST measurements may be required to

demonstrate traceability of an artifact. If the structures are not sufficiently robust for them

to be exchanged between NIST as the source of calibration and an industrial concern as

the receiver, then the traceability of the calibrated atom-based structures might be

compromised.

• To work with industrial collaborators in developing appropriate documentary standards to

support efficient use of such artifact standards. This activity proceeds naturally from the

successful development of the specimens themselves, but is not a trivial task. Standard

algorithms for achieving closure between measurements taken by different laboratories

have become more difficult to define as the amount of data generated by measurement

systems has increased, owing to the increased speed of computers.

These goals proceed from the observation that the uncertainty that limits many types of

precision measurements arises from the imperfection of the calibration artifacts that often

serve as the sources of calibration for those measurements. When a highly accurate

calibration system is used to measure a transfer artifact that is then used to calibrate another

measurement system, the imperfection in the artifact itself often limits the accuracy of the
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calibration. On the other hand, some precision measurements rely on artifacts whose

dimensional properties are based on the fundamental structure of condensed matter itself,

either on its symmetry properties or its lattice spacings. A crystal lattice spacing is a quantity

that is both small and precise. Smallness is important because the artifact can then serve as

the source of calibration for other small quantities that require measurement; precision is

important because it enables these calibrations to be done at high relative accuracy. The

precision arises from the basic invariability of the properties of the crystal lattice itself.

The following discusses how such artifacts could be developed for precision step height and

linewidth calibration.

4.1.2 Step Height

Precise specimens for calibrating

step height are produced

commercially*

 using optical

lithography in Si. These

standards are available with

heights ranging down to 8 nm.

The uncertainty for these

specimens ranges from about

0.5 % (k=2) for steps on the order

of 1 μm to about 7.5 % for an

8 nm step. An important source

of the uncertainty for small steps

is the uniformity of the step itself

as a function of position on its

surface, which in turn depends on

the surface roughness of the bare

Si and on the uniformity of the

oxide growth process. This

uniformity could be improved significantly with a step fabrication process under which the

fabricated step height is determined by the lattice constant of the material from which it is

made. If, in addition, the surface roughness is at the atomic level, then a value for the step

height can be obtained with an uncertainty that is less than 0.1 nm (k=2). Williams et al. and

others have shown that single atom step heights may be obtained on the (111) face of a Si

single crystal by heating the specimen in vacuum [11]. The step height structure remains on

the surface even after the Si specimen has been removed from the vacuum and the native

oxide has formed. An image of three of these steps measured with NIST's calibrated atomic

force microscope (C-AFM) is shown in Fig. 5. In principle, the step height is strictly related

 

* Certain commercial equipment, instruments, or materials are identified in this paper to specify

adequately the experimental procedure. Such identification does not imply recommendation or

endorsement by the National Institute of Standards and Technology, nor does it imply that the

materials or equipment identified are necessarily the best available for the purpose.

Figure 5 Image of 3 Si Steps Obtained

with the C-AFM.
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to the lattice constant of Si [12] and is equal to 313.560 137(9) pm, where the "(9)" indicates

standard uncertainty in the last decimal place. Such an artifact can be used to calibrate a

precise measuring instrument that is then used to measure another surface or another standard.

During the present project, we fabricated a number of Si(111) single-atom step height

standards through a collaboration with the Materials Research Science and Engineering

Center at the University of Maryland and later in a UHV system at NIST.

We then independently measured the value of the step height by using the Calibrated Atomic

Force Microscope (C-AFM) [13,14]**, whose displacements in all three axes of motion are

calibrated in terms of the wavelength of a helium neon (HeNe) laser. The value obtained for

the Si(111) step height using the C-AFM is 304 ± 4 pm (k=1), which gives us two

independent values of the step height value differing by only 10 pm or 3.2%, thus imparting a

higher integrity to the calibration artifact.

A third value of 312 pm ± 7 pm (k=1) has been obtained from low energy electron

diffraction [15] of the stepped Si(111) surface. A fourth value of 340 pm ± 30 pm (k=1) has

been obtained from grazing x-ray diffraction [16] of the stepped Si(111) surface. Using these

independent results, we estimate a recommended value of the Si(111) step for use as a physical

step height standard. The value predicted from the bulk lattice constant is many times more

precise than the other values. If we were to weight the results as 2 1/ c u , where uc is the standard

uncertainty for each, the weighted value would be determined entirely by the bulk lattice value

and would have an extremely small calculated uncertainty. In our opinion, this is unrealistic.

The value obtained from the bulk lattice constant may not represent the actual surface step

height. By contrast, the other three values were obtained from measurements actually made on

the surface of Si(111). 

We obtain a recommended value for the step height using an approach based on methods

explored by Kacker [14]. The first step is to develop a model of the probability distribution for

the value of the step height. We take 313.56 pm as the most probable value of the step height.

Hence, the model distribution is peaked at 313.56 pm. In the absence of detailed knowledge of

the distribution, we represent the state of knowledge by an asymmetric triangular distribution.

To determine the lower endpoint of the triangle, we take the C-AFM result and subtract the

expanded uncertainty (k=2) from it. This leads to a value of 296 pm. To determine the upper

endpoint, we take the low energy electron diffraction (LEED) result and add the expanded

uncertainty (k=2) to it. This leads to a value of 326 pm. We have thus interpreted the C-AFM

result as indicating negligible probability that the true value lies below 296 pm, and the LEED

result as indicating negligible probability that the true value lies above 326 pm. This is the basis

for the selection of 296 pm and 326 pm as endpoints of the distribution. Because of its large

uncertainty, the grazing x-ray result did not figure into our analysis. Using this model

distribution, we obtain a mean and standard deviation of 312 pm and 6 pm, respectively. This

 

** The references shown in bold are publications of the Nanomanufacturing of Atom-Based

Dimensional Standards Project.
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leads to an “accepted” value and expanded uncertainty of 312 pm ± 12 pm (k=2). This

represents a relative expanded uncertainty of about 4 % in the “accepted” value.

In continuing work we formed a working group whose purpose is to evaluate the usefulness

of these step height specimens as calibration standards. The participants provided

measurements of the Si(111) specimens to enable an estimation of the reproducibility of the

step height measurements. Those providing information and measurements are shown in

Table I.

Table I: Participants in the Laboratory Comparison

Participant Organization

Debra Cook

Hal Edwards

Joseph Fu

Ralph Nyffenegger

Paul West

Veeco Metrology

Texas Instruments

NIST, Precision Engineering Division

Park Scientific, now TM Microscopes

Topometrix, now TM Microscopes 

Each participant received his/her own specimen to test. We then received and analyzed

altogether 36 topographic images from the five participants. Each instrument was calibrated

independently according to the operator's customary procedure. Therefore, the absolute values

of the measured step height results are not as important here as the fractional reproducibility of

the step height results for each instrument.
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Typical results are shown in Fig. 6. Each

topographic image consisted of several

steps, six in this illustration. A step height

measurement was then taken in several

small areas where the data look to the

operator as being free from noise and

other measurement errors. The average

step height value for the image was then

calculated from the set of positions and

the average step height value and standard

deviation were calculated for the several

images from each participant. The

algorithm for calculating the step height

value was a single-sided straight line fit as

shown in Fig. 7. The results are shown in

Table II. The order of the participants

shown in Table II is not correlated with

that of Table I.

Figure 7 Illustration of the step height calculation for a single profile.

nm

100 200 300 400 500

50

100

150

200

250

300

350

400

450

500

-2.5

-2

-1.5

-1

-0.5

0

0.5

1

1.5

2

Figure 6 Topographic image of the stepped

surface of Si(111) measured by one of the

participants. The rectangles indicate typical

areas used for determining the step height

value.
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Table II: Results for the Si Single-Atom Step Height Measurements.

The order of participants here is not correlated with that of Table I.

Participant

Number of

Topographic

Images Used

(NI)

Average

Number of

Steps in

Each

Image

Total Number of

Rectangular

Step Areas

Measured for

Each Participant

Average

Step

Height

Value

(pm)

One

Standard

Deviation

for the NI

Values

(pm)

A 7 6 268 325 12

B 9 4 90 302 8

C 10 7 100 317 4

D 4 6 180 306 3

E 6 6 60 311 3

The results are very encouraging. The standard deviation for each set of measured images is

6 pm on the average for results altogether. This suggests that with measurements from a single

image of Si(111) step heights, one can obtain a calibration value reproducible to about 2% (one

standard deviation (1σ)).

A similar effort has taken place in Japan where a community of users of atomic force

microscopes working under a committee of the Ultra Clean Society developed a standard

procedure to use the Si single atom steps as a source of calibration for AFMs in the vertical

direction [17,18]. Their results illustrate the variability of results that are possible with AFMs

without such a standard. Their procedure uses a histogram analysis to determine the step height.

The histogram analysis is more widely available in commercial software than the fitted straight

line method. However, in our experience [19], the straight line method provides a more stable

result.

4.1.3 Linewidth

Linewidth specimens serve as comparison standards for measurements of the smallest width

features (critical dimensions, or CDs) on integrated circuits. Because the speed and density of

integrated circuits improve as the size decreases, the CDs are manufactured to be as small as

possible, thus challenging the capabilities for measuring them.

Linewidth measuring standards are currently available from NIST [5] and the National

Physical Laboratory [20] in the U.K. for use as standards for optical instruments used to

measure linewidth. However, the accuracy of the NIST specimens, and probably the U.K.

specimens as well, is limited in large part by the quality of the edges on the lines themselves

(see Fig. 1a). For example, the lines of the NIST specimens are produced with significant

edge roughness leaving them with a variable width along the line length. In addition, the

side-walls of these lines are not perpendicular to the substrate thus creating ambiguity as to

where on the side-wall the lines should be calibrated and measured. The size of these effects

imparts an uncertainty of approximately 40 nm (k=2) to a linewidth specimen with nominal

width of 500 nm.
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In this project, we explored the use of Si and Gallium Arsenide (GaAs) as counted atom

linewidth standards [21]. These specimens would have linewidth features created by

anisotropic etching such that the sides would be determined by the lattice planes of the crystal

and would be perpendicular to the substrate. These lines would be heated in vacuum to

remove the oxide, thus exposing the nearly perfect Si or GaAs lattice. The atoms in the lattice

across the top width would be counted using a SPM or a transmission electron microscope

(TEM) as the imaging system. The number of counted atoms across the top would then give

us a measurement of the top width in terms of the lattice constant of silicon, which is known

to a high accuracy. If the quality of the artifact can be preserved by maintaining it in vacuum

with intermittent periods of gentle cleaning, it could be used as source of calibration for

linewidth measurements made in UHV systems. It could also be used as a calibration artifact

in atmospheric conditions at a slightly higher uncertainty.

Atom Counting Methods

Measuring linewidths accurately at very small feature dimensions is difficult as evidenced by the

lack of industry standard artifacts. To analyze a line profile measured by an instrument requires

advanced modeling methods to determine the linewidth because the chosen edge locations, upon

which the linewidth value is based, depend on the response of the measurement system probe to

the material. SEMs and optical microscopes have different responses to the edge of an etched

feature. The SEM exhibits blooming and other edge related effects, and the optical microscopes

show diffraction limited resolution. Both effects obscure the physical edge within the data.

Currently the physical models for either type of reflection mode system are not sufficiently

accurate for standard samples to be accurately calibrated and disseminated to industry.

However, efforts are underway to develop sophisticated models. These efforts require a

thorough evaluation and verification process. The development of models is advancing in

parallel with efforts like ours to produce artifacts which are measured and characterized on the

atomic scale, whose metric is then based on the crystal lattice. These atomically characterized

samples can then be used in different ways to calibrate linewidth measurement tools as discussed

next.

In the effort to develop a sample for accurate linewidth calibration, it has been proposed that a

well defined linewidth structure whose dimensions could be measured with near to atomic

accuracy would be useful. The structure or sample does not need to be the same as that

measured in an industry measurement, on a product wafer for instance, if the calibration can be

transferred to another artifact which can be measured in the industrial setting. On the other hand,

products of some process levels are perhaps measurable atomically and are more directly

transferable. At the root of both of these implementations is the idea of counting the atoms

across a well defined structure and relating the number of atoms to the linewidth. This function

requires a well defined sidewall or at least a well characterized sidewall close to vertical. The

measurement uncertainty will be affected by variations in the sidewall geometry.

The sample we are developing, in part within this project, has therefore two primary capabilities

based on the atomic measurement concept [21]. First, the metric for the measurement can be
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based on the silicon crystal lattice. Second, the geometry of the edges can be measured or

analyzed using the actual atoms that make up the edges.

Although both Si surfaces and GaAs surfaces form a native oxide, which is a few nanometer

thick, the underlying crystal lattice has a well defined stable structure. The native oxide in Si is

ordinarily disordered which is to say that the top 5 or 6 atomic layers of bound Si and oxygen,

forming SiO2, are randomly ordered. Beneath this oxide there is a transition to a well ordered

crystal whose orientation is dependent on the initial cut of the crystal; typically 200 mm wafers

for semiconductor manufacturing have a (100) surface orientation. This oxide, however,

maintains the topography of the underlying surface, as evidenced by the step and terrace

structure persisting after exposure to atmosphere. A series of high temperature processing steps

in UHV can remove the oxide and yield an atomically ordered surface. These surfaces at the

crystal/vacuum interface, however, do not reflect necessarily the underlying crystal structure, but

rather form a surface reconstruction more energetically favorable than the bulk crystal lattice

because of the asymmetry of forces on the interfacial layer. The surface atoms have strong

bonding forces on the crystal side and usually dangling bonds on the vacuum side, a condition

that tends to restructure these surface atoms to relieve the stress. These Si reconstructions

depend on the crystal orientation and processing, although there are several well established and

understood reconstructions. An important fact is that the surface reconstructed atoms are

commensurate with the underlying crystal lattice.

An outline of the overall process flow for atom counting in Si follows. The first steps are to take

a Si wafer and etch an array of features using ordinary photolithographic techniques. Caution is

necessary in removing excess photoresist and cleaning the etched wafer because contamination

is a problem at the elevated process temperatures. Atomic surface reconstructions usually

require the Si to be heated to 1250o

C at a vacuum background pressure of less than 2.5×10-7 Pa

at temperature. Once the wafer is cleaned, it is diced and mounted on a quartz sample holder for

loadlock into the UHV system. Currently, the die is cleaved rather than cut to avoid

contamination from metals during the cutting process. The sample is then thermally processed

and, after cooling to room temperature, transferred into the STM chamber. A feature is located

and then measured with the STM. We navigate on the sample with piezo elements and a 200X

telescope, which is capable of resolving the linewidth features of current interest. The STM,

capable of lateral and vertical atomic resolution, then captures atomic resolution images across

the linewidth feature which can be later analyzed with a variety of methods to count the number

of atomic spacings across a feature. One method might utilize a template which is computer

generated and laid over the image, or the atoms could be counted in a more pedestrian but

automated fashion by counting the individual features.

Although we have just outlined the major steps in obtaining atomically resolvable silicon

features, the process is not limited to Si and in fact GaAs offers some appealing alternatives,

which address some of the problems associated with high temperature Si processing. Whether

using Si or GaAs, underlying the entire process is the critical choice of crystalline orientation for

the wafer as this affects the surface reconstructions and sidewall geometries.

Given the goal of fabricating lines in single-crystal silicon with countable atoms across the top

surface, the choice of line geometry is constrained by the physics and chemistry of Si and
18

existing etch technology and is dictated in part by the existence of certain energetically preferred

stable faces of Si. The Si(100) face is one example. Miscuts near (100) result in (100) terraces

of varying widths separated by steps. The nonperiodic nature of the steps would complicate the

counting of atoms across the surface. While perfect alignment is not possible, alignment close to

a stable face results in larger terraces. Therefore, the first requirement is to orient the upper face

of the line as near as possible to one of the stable faces of Si.

Another factor is the expected arrangement of atoms on the upper surface of the line. The

surface atoms reconstruct in a pattern commensurate with, but not identical to, the underlying

bulk structure. The ideal candidate structure would have only a single possible reconstruction.

Otherwise, if we encounter domains of various possible reconstructions, this increases the

difficulty of the measurement. The well-known Si(100)-2×1 reconstruction has an advantage for

atom-counting measurement because it is easier to resolve the resulting dimer rows (containing

two atoms) from each other than it is to resolve atoms within a row. There are, thus, easy-count

and difficult-count directions respectively perpendicular to and parallel to the dimer rows. The

easy-count direction would be oriented across the line to be measured. 

After selection of a crystal structure and its expected surface reconstruction, the samples are

prepared and analyzed in the UHV environment. Subsequent to the UHV work, it is necessary to

transfer the samples to other measurement systems. This commonly requires transfer of the

artifact through air and therefore requires a stabilized surface, which will not compromise the

dimensional integrity of the sample. One option is to simply allow the native oxide to form on

the sample surface. Other options are the growth of oxide at elevated temperatures in varying

pressures within the controlled environment of the UHV preparation facility. This may

eventually result in more stable or smoother surfaces. We and others [11] have performed

measurements on the Si(100) and (111) surfaces with the AFM in air after UHV preparation.

The step and terrace structure with the subnanometer step heights remain clearly visible in the

data for an extended period of time. These steps have been observed at least as long as six

months after preparation, thus indicating that the topography remains stable enough for the

atomic step heights to be observed with an AFM. This implies that, although there is no longer

any observed lateral atomic order, there is enough quasi-order for the vertical steps to remain.

This is important for using SEM analysis on previously measured, atomically ordered samples. 

A problem for NIST and other national measurement institutes is finding a practical method for

making traceable wafer linewidth measurements with uncertainties small enough to be useful in

semiconductor applications. An atom-based linewidth standard might furnish part of the

solution to this problem by taking an important place in the traceability chain between the

definition of the meter and an optical or SEM measurement of a product specimen. We describe

the following links in the chain: 

1. Bulk Si lattice spacings are traced to the meter by measurements that combine x-ray

diffraction with optical interferometry.

2. Surface lattice spacings on the atomically ordered linewidth artifact can be determined from

the bulk Si lattice spacings. 
19

3. An STM measurement of the artifact uses the lattice spacing to define an intrinsic "ruler" for

distance measurements, and locates the edges of the line in terms of the atomic corrugation,

thereby determining its width. 

4. The artifact is passivated so it can be used in an ambient or near-ambient environment with a

minimum change to its width. Two alternatives are also possible. First, a materialsindependent SPM measurement could be used to transfer the width from the atom-based

primary standard to a stable secondary standard. Second, if required by the user, it may be

feasible to transfer the specimen in its pristine condition under UHV to a second

measurement system for an atom recount. Providing this capability is the subject of research

described in Section 4.2.

5. Passivated or stable secondary standards are made available to manufacturers as SRMs. The

manufacturer uses an SPM to compare the widths of the SRM and a representative product

sample. The product sample thereby becomes an in-house standard with composition and

geometry close to other product wafers. 

6. Large numbers of measurements on product wafers are performed rapidly using optical or

SEM intercomparison with the calibrated product wafer. Although the product wafer may not

be stable for long periods of time, new ones can be made as required. The stable secondary

standard would be used to determine the dimensional stability of the product standard, so a

suitable schedule for generating new ones could be determined.

In general, each step in the above chain has an associated uncertainty which must be assessed in

order for the final measurement to be traceable. For example, Step 2 is rendered easier by the

fact that any surface reconstruction must be commensurate with the bulk, but lattice relaxation

over a few atomic layers nearest the sidewalls would need to be taken into account. It is

necessary to characterize any changes in width arising from the passivation at Step 4. The use of

product wafers at Step 6 minimizes differences between the unknown and the calibrated product

standard during SEM and optical comparisons, but manufacturing process variations will cause

residual differences between them to occur. 

In related work, Si specimens have been produced and are being measured in an intercomparison of electrical, SPM, and SEM methods for linewidth measurement. The first set of

experiments has produced excellent agreement [22]. Similar specimens will be prepared in UHV

for measurements using the counted atom approach, a technique that in principle is limited by

uncertainty components at the atomic level.

Field Ion Field Emission Microscope 

When using the STM as a metrology tool to make measurements both on the atomic scale and on

features with dimensions of a few hundred nanometers, detailed information about the tip shape

is needed. In much of the previous STM work where the tip shape was taken into consideration,

the tip shape was usually idealized as conical, spherical, or parabolic. The size of the tip can be

accurately measured, as described below, with a field ion microscope (FIM). In previous work,
20

the shape was most commonly modeled with a spherical end form, which gives good agreement

for blunt tips. The tip radius can then be calculated based on this assumption.

The field ion field emission microscope (FIFEM) is an instrument which allows atomic

characterization and cleaning of STM tips. We use it to measure the geometry of our STM

probes on an atomic scale. The FIM is located in an adjacent UHV chamber to our UHV STM,

and tips can be moved through UHV to the FIM before or after their use in the STM. The FIM

was first developed in the 1950’s [23] and until the development of the STM in 1982, nearly all

FIM work was performed on tips with radii of several hundred nanometers. In an FIM image of

a blunt tip it is possible to identify many crystallographic planes, although in an FIM image of a

sharp tip there are typically only a few planes visible. As a result, blunt tips can yield significant

information when studying grain boundaries, various types of dislocations, field desorption, and

adsorption of other atoms. FIM analysis was also carried out to characterize sharp tips [24] for

use in STM. This work was primarily intended to elucidate the tip preparation requirements

focusing on the end of the tip for obtaining atomic resolution using STM. A more complete

understanding of the actual tip shape was not of immediate interest, even though the overall tip

dimensions and shape were recognized as important for understanding the tip robustness. 

The current instrument has two modes of imaging and tip preparation. In the FIM, an imaging

gas is bled into the chamber at about 1.3×10-3 Pa and the tip is cooled to near 77 K. The gas is

ionized at the tip and accelerated towards a set of channel plates which generate an image on a

phosphor screen. This image is digitally captured with a high resolution CCD camera and stored

for further analysis and record keeping on a personal computer (PC). These images allow

determination of the tip dimension before and after use, which aids in determination of damage

to the tip during STM imaging. Although the details of dimensional image analysis are

presented elsewhere [25], the basic idea is that known crystal planes are observed and the

number of lattice steps between each crystal plane enables the determination of tip radius.

During this process, the tip is cleaned but potentially dulled as well if the imaging voltage is

increased beyond the minimum voltage required. Not all the atoms on a crystal plane are

observed; only those near the edges where the fields are high are observed because this is where

the imaging gas is first ionized. The second mode of this tool is the field emission mode (FEM).

In this mode, the imaging bias voltage is reversed and electrons are emitted from the sample

surface and impinge the phosphor. This method does not give detailed information about the tip

geometry, although it does allow a calibration of the imaging voltage and geometry to give an

estimate of tip sharpness. The primary advantage of this method is that by reverse biasing the tip

we can clean the tip and remove the native oxide without dulling the tip. Additionally the tip is

not cooled, so it only takes moments to prepare and analyze a tip. After cleaning and a

determination of the tip sharpness, if the tip is measured to be sharp enough for atomic imaging,

it is then placed into the STM and used.

In applying this method, we have found that for very sharp tips the spherical approximation used

to explain the FIM measurement does not represent the tip shape accurately. As part of the

NAMT effort we have developed a more complex model of STM tips using more complex

geometries, which more closely match the physical tip shapes [25].
21

4.2 Artifact Transport System

To make use of a counted atom linewidth specimen with atomic scale accuracy, it will be

necessary to maintain the surface in its original state where the atoms on the surface are

observable with an SPM. That implies that such a specimen must be held in UHV so that any

growth of oxide or other adsorbate is minimized. However, in order to be useful as a transfer

standard with atomic scale accuracy, the specimen must be transferable between measurement

systems at geographically different sites. An artifact transport system (ATS) has been developed

to perform such transfers in UHV. The goal here is a system that would preserve the integrity of

the standard, thus allowing the counted atom approach to be used at more than one location.

Any contamination or build-up on the standards could bias the measurement of the dimensions.

The scope of the ATS task was to design, build or acquire, and test all necessary equipment to

allow atom-based standard artifacts to be transferred: (a) between artifact manufacturers and

artifact measuring systems, and (b) between either manufacturing or measuring systems and final

users of the artifacts. Degradation of artifacts during transport was, therefore, a primary concern

to this project. The convenience, reliability, and cost of the transport systems were also

concerns.

Different types of transfer systems with different levels of vacuum were considered. UHV

transport devices are needed for the most delicate specimens, because even in the high vacuum

range (about 10-4 Pa) a monolayer of gas could be absorbed on the artifact surface in seconds.

When attempting to establish dimensional standards with uncertainties in the nanometer range,

the effect of one monolayer may be significant. We anticipate a need for transferring artifacts

with systems that maintain UHV in the range of 10-7 Pa or better to prevent the formation of a

monolayer of contamination during expected transfer times of about 30 min. Such a system

would require on-board pumping, such as an ion pump and metal-sealed flanges.

To accommodate these requirements, a UHV system was designed specifically to transport

artifacts between the MBE System in the Technology Building at NIST and the STM facility in

the basement of the Metrology Building at NIST. A vital part of the ATS is the internal

mechanisms or manipulators that actually handle the artifact inside the vacuum chamber and

move it between the ATS and host system. For UHV systems, these mechanisms had to be

carefully designed to avoid affecting the vacuum quality.

4.2.1 Current Design and Results

We studied the means of transferring artifacts while maintaining a UHV environment around the

artifact at all times. We developed the ATS, which provides one solution to this challenge. In

the UHV range it is necessary to provide continuous pumping for the chamber carrying the

artifact because even a perfect leak-tight system will not maintain this level for more than a few

seconds. Therefore, the ATS contains an ion pump, an associated battery power supply, and all

other equipment on a portable cart. Although we have colloquially called the ATS a “vacuum

suitcase” it is certainly not something that an individual can pick up and carry around. The

design (Fig. 8) is based around the use of standard 150 mm vacuum flanges for the main transfer

chambers. This size allows the operator to reach inside while the system is open to air.
22

Figure 8 Schematic diagram of the artifact transport system (ATS) and the

host system housing a standard sample ready to be transferred.

The ATS is conceptually similar to other types of transferring systems where an “air-lock”

concept is used [26]. Before opening a valve or door into a host system the appropriate

environment around that opening needs to be ensured. In the case of systems designed to

prevent particulate contamination, such as SMIF [7] pods in the semiconductor manufacturing

industry, an ultra-clean environment is maintained inside a module and only transfer devices of

the same level of cleanliness can be attached for transferring parts. A similar concept has been

used for the ATS. The transfer chamber is connected to the host chamber only when there is a

UHV level pressure in the transition section of the ATS.

The ATS attaches to a port of a fabrication or diagnostic system (called the host system) by a

standard conflat vacuum flange/seal. The host system must have a valve near this connecting

flange. The ATS has a short pipe section (called the transition section) between the artifact

chamber and the flange connection to the host system. There is a valve (Valve 2) between the

artifact chamber and this transition region. The valve in the host system, and Valve 2 are not

opened until the transition region is pumped to an adequate vacuum to ensure no significant

increase in pressure in either the host or the artifact chamber. The artifact chamber is always

maintained at UHV pressure.

After the vacuum joint is made, proper pressures are achieved, Valve 1 is closed, and Valve 2

and the Host Value opened, the sample holder (not shown) on the rod assembly is moved axially
23

into position next to the sample. The sample holder then latches to the sample and is pulled back

into the ATS specimen chamber. After the transfer is made, the valves can be closed and then

the transition region of the ATS can be vented and the ATS can be disconnected from the host

system. If the ATS artifact chamber has received the artifact from the host system, the ATS is

then moved to a second host system. The vacuum flange is connected to the second host system,

and the sequence of pumping and opening valves is repeated. The artifact can then be placed

into the second host system with the manipulator. The artifact handling mechanism for our ATS

was designed using standard vacuum feed-throughs and manipulators. Special hardware was

designed and built to fit our particular artifacts and holders. 

The ATS has successfully transferred an artifact from the UHV STM to the UHV MBE system

about 300 m away. During transfer of the artifact from the UHV STM into the ATS chamber,

the vacuum rose to approximately 3 × 10-7 Pa, then quickly settled to 9 × 10-8 Pa and remained

there as the ATS traveled to the MBE laboratory where the artifact was transferred into the MBE

system. This demonstration verified that an artifact can be handled in such a manner that it

never sees a pressure environment greater than 5 × 10-7 Pa while being transferred between the

two UHV systems. The pressure during a transfer was documented along with other parameters

by a data logging system that was built as part of the PED-NAMT project. Details of this system

are included in Section 4.3. A videotape of the transfer may be viewed on the internet [27].

4.2.2 A Second ATS Concept

A prototype lightweight and portable vacuum suitcase has been designed (Fig. 9) and partially

constructed (Fig. 10). All components here were based on commercially available 70 mm UHV

flanges rather than 150 mm flanges as in the original ATS. The system (Fig. 9) consists of two

six-way crosses with a metal gate valve to divide two UHV compatible regions, an inner

chamber and an outer chamber. Two ion pumps, 60l /s and s 40l / , are used to pump the

system. A portable power supply is capable of providing the power for the ion pumps and an ion

gauge during transporting.
24

Figure 9 CADKEY diagram of a design for a small vacuum suitcase with 70 mm flanges.

Figure 10 Photograph of partially constructed vacuum suitcase.

The novel design of the internal mechanism follows. A pair of transfer rods, mounted

orthogonal to each other, allow transfer of the sample from stage to stage. The sample holder is

shaped like a double yo-yo as shown in Fig. 11. The manipulators are two-pronged forks, which

slide into different slots in the sample holder as a handoff is made. The design of Fig. 9 shows

two stages of sample transfer in the suitcase itself. Due to the design of the sample holder, a

fork-like grabber must also be installed in the host system prior to transferring the sample in or

out of it.
25

Figure 11 Sample holder for the small vacuum suitcase.

4.2.3 Observations

The basic concept of the ATS — producing an appropriate vacuum in a transition region prior to

opening a host system — can be considered for other applications. One such future application

may be handling wafers during part of the fabrication and inspection in the semiconductor

industry. Such handling in a UHV environment is currently not being considered, but there may

be a logical progression in some processes to better and cleaner environments. When a transfer

of a standard or a production part is needed in the UHV range, the concept demonstrated by the

ATS will be beneficial. 

All the vacuum flanges and valves needed for this type of system are available as standard items

from suppliers of vacuum equipment. The actual mechanisms for manipulating and handling the

standards, or perhaps wafers in the future, need to be designed and built for particular situations.

The handling mechanisms present challenges already encountered by robotic applications as well

as the constraints of working in a UHV environment. These types of concerns have been

addressed by others [28].

The NAMT project demonstrated the possibility of transferring a sample in the UHV

environment between two locations. It is important to note that, whereas UHV chamber

technology is standardized around conflat flanges, sample holders and manipulators are not

standardized. Hence, for example, the 150 mm size ATS uses different sample manipulators

than the 70 mm size. Before UHV transfers become widely used, the standardization of sample

holders and manipulators will likely need to be addressed. The weight of the system is also an
26

issue. If aluminum UHV hardware were used rather than stainless steel, a 50% weight reduction

would be possible.

4.3 Artifact Transport System Data Logger

4.3.1 Introduction

During the artifact transportation process, researchers are interested in the stability of the

vacuum levels and the environmental conditions that may have affected the transport system

(e.g., vibration levels, power failures, and equipment failures). A data logger has been

developed and implemented to monitor the ATS, and in this section we discuss the system

design and present results taken during the transport process described previously.

4.3.2 System Design Overview

The data logger uses an event-based algorithm to detect changes in the system and logs to the

hard disk only these changes as a function of time. While this method of data acquisition

continuously samples the system, it minimizes the amount of data stored and facilitates quicker

analysis of data. One has to set a range over which the data may change without storing this as

an event. The vacuum levels on the ATS are obtained using three different vacuum pumps (ion,

sublimation and roughing), and the levels are read using two vacuum ionization gauges located

in the artifact chamber (chamber one) and the transition section (chamber two). In addition,

three accelerometers measure the real-time vibration levels seen by the chambers. The

accelerometer levels are shown on real-time display charts on the data logger’s front panel in

Fig. 12. The X direction accelerometer measures positive values with forward motion of the

ATS, the Y direction accelerometer measures side to side motion, and the Z direction

accelerometer measures positive values in the upward vertical direction.
27

Figure 12 Data logger front panel is updated in real-time and is

programmed in LabView. The X-direction accelerometer signal is at the top.

The Z-direction accelerometer signal is at the bottom.

The data logger application software was developed in LabView on a laptop computer, which is

mounted on the ATS with vibration isolation pads to minimize damage to the hard disk. In order

to industrially harden the data logger, a PC104 format computer with a solid-state-disk (hard

disk composed of solid-state memory) would be an alternative over the more delicate laptop

used. In the event of a power failure, the laptop’s batteries allow the data logger to continue

operating for up to 1.5 hours.

A PCMCIA data acquisition card with 16-bit resolution and with a maximum 20 kHz sampling

rate is used to sample the analog signals. An eight channel sample-and-hold interface board

connects the differential analog signals to the data acquisition card. Otherwise the data

acquisition card samples the individual analog signals one after the other - not simultaneously.

The ion pump controller and ionization gauge controller are interfaced to the laptop through the

RS-232 communications port. The power for these instruments is from an uninterruptible power

supply (battery powered).

4.3.3 System Design Specifics

Details related to the individual subsystems of the data logger are discussed in the following

section.
28

Accelerometer Levels

Three accelerometers are mounted on the ATS to measure the vibration (shock) seen during the

transportation process. Three corresponding real-time charts show measured values in Fig. 12.

Note that the third chart has a steady state value near 10 volts due to the gravity vector effect on

the Z-axis accelerometer. The charts are set up for automatic vertical scaling and have a

sampling rate of 1 kHz. The data acquisition card includes an oscilloscope that stores values to

disk when a certain trigger level is exceeded. The values need to be post-processed to convert

from the units of voltage to units of acceleration.

Pump Status

The three vacuum pumps draw their AC power from a custom made power strip. Mounted

within the power strip are three current sensors that measure the current draw of the pumps.

Three differential channels on the data acquistion card are used to read the current sensors.

From the LabView front panel, indicator lights show red for no pump operation and green for

pump operation as shown in Fig. 13. By setting the value for “Percentage Change to Record,”

the application will save to disk events due to changes in current draw of the pumps. In the

event of equipment failure during the transport process, this information will help to determe if

power was lost to the pumps, an individual pump failed, or the pump controller failed.

Figure 13 Vacuum pump status indicates the presence of a working pump.

Ion Pump Current Draw and Ionization Gauge

Both the ion pump controller and the ionization gauge controller are interfaced to the data logger

via an RS-232 interface. Laptop computers typically only have one RS-232 port and in this

application, an RS-232 switch was used to communicate with both controllers. The application

software selects which controller to communicate with by sending control codes to the switching

device. The current drawn by the ion pump controller is an indication of the vacuum level

within the chamber and is shown in Fig. 14. This value is read continuously and stored to disk

with a time stamp, when changes occur. The same is true for the ionization gauges.
29

Figure 14 Current draw from the ion pump and ionization gauge values.

For chamber two, the indicator shows that the ion gauge is turned off. The

pressure indication in chamber one, shown here as 8.7 × 10-10 Torr is

approximately equal to 1.2 × 10-7 Pa.

Battery Voltage Level

During transport, the ATS is powered by an uninterruptible power supply, where the voltage of

the battery is read using a channel on the data acquisition card. Changes in battery voltage are

stored to disk with a time stamp and the voltage is displayed on the front panel as shown in

Fig. 15. Based on a trend of increasing voltage (when unit is plugged into the wall) or

decreasing voltage (during transport), the indicator represents a charging or discharging state of

the battery. When the battery voltage drops below a threshold, an audible alarm sounds and the

alarm indicator on the front panel lights.

Figure 15 Battery status representation.

Status and Execution

Since an event-based algorithm is used to determine when to store changes in the physical

system, a time stamp must also be stored. The status panel reads the laptop system clock and

displays the information for the user. Internal to the LabView application is a high resolution

counter programmable in ms that sets the sampling times of the accelerometers. In LabView, the

start of an application is effected by clicking the run button. To stop or exit the data logger, the

exit button shown in Fig. 16 is used. The indicator with the number "40" is used to determine

how full the memory buffer is. Once the buffer is full, the contents are saved to disk. This

indicator was only used in the software development process.
30

Figure 16 Status, controls and alarm representation.

4.3.4 Internet Access

This application includes the LabView 5.0 Internet Toolkit, which features the ability to view the

data logger front panel status with an Internet browser. When the ATS was parked in the STM

lab, the data logger was connected to the internal network and had its own internet protocol (IP)

address. With the data logger running, snap shots of the front panel can be viewed and updated

using the reload feature of a browser for a remote location. Also implemented is the ability to

upload data files, collected during transport, to a server using a file transfer protocol (FTP).

4.3.5 Results

On July 27, 2000, a GaAs sample was moved into the ATS and transported from the UHV STM

in the NIST Metrology Building to the MBE lab in the NIST Technology Building. The sample

was successfully deposited in the MBE machine. The vacuum levels remained stable as shown

in Fig. 17. The single spike in recorded vacuum level likely occurred when crossing over an

expansion joint in the floor or moving into and out of an elevator.

Ionization Gauge On Main Chamber for transport on 7/27/00

7.00E-10

7.20E-10

7.40E-10

7.60E-10

7.80E-10

8.00E-10

8.20E-10

8.40E-10

8.60E-10

8.80E-10

9.00E-10

4:12:00 4:19:12 4:26:24 4:33:36 4:40:48

Time (h:min:s)

Vacuum Level (Torr)

Ion Gauge

Figure 17 Ionization gauge plot showing trend in vacuum level during the

transport. One Torr is approximately equal to 133 Pa.
31

During the transport, the ion pump current draw fluctuated as shown in Fig. 18. The current

draw is proportional to the vacuum level and the average for the move was 0.12 μA, equivalent

to a vacuum of about 2 × 10-8 Pa, with a standard deviation of 0.055 μamps.

Ion Pump Current Draw from transport on 7/27/00

0.00

0.05

0.10

0.15

0.20

0.25

0.30

4:12:00 4:19:12 4:26:24 4:33:36 4:40:48

Time (h:min:s)

Current Draw (

μamps)

Ion Pump

Figure 18 The ion pump current draw is an indication of vacuum level. The

above data were taken during the move between buildings.

Figure 19 shows a plot of acceleration levels read from the X- and Y-axis accelerometers that

were mounted on the ATS. The data represents the noise floor. Due to a malfunction, the Z-axis

data were not available at this time.

Acceleration Levels for 7/27/00, 

4:15:58 transport

-0.04

-0.02

0

0.02

0.04

0 0.1 0.2 0.3

Time (seconds)

Acceleration (g)

X-axis

Y-axis

Figure 19 For the time period listed, the plot shows the acceleration levels

for the X- and Y-axis. This represents the noise floor.
32

Overall, the data logger performed reliably and indicated stable operation of the ATS and

excellent vacuum. New generation linewidth standards may need to be transported under UHV

to insure that no contamination or exposure to air degrades them. The data logger will provide

researchers with information on vacuum level stability and environmental conditions impacting

the transport systems to study the effects on the standards.

4.4 Enhanced Design and Communication Processes

In this section, we discuss work to enhance the design and communication processes of the ATS.

Specifically, we discuss how simulations were used to aid in visualizing function and assembly,

how collaborative software tools were used to reduce design time and improve communication,

and how the design and the basis for the design are encapsulated in a design repository. Further

details of this work are given elsewhere [29-33].

4.4.1 Computer Visualizations

We performed four types of modeling and simulation tasks in support of this project: simulating

the internal mechanism of the ATS, representing its overall geometry, simulating its assembly

sequence, and modeling the STM tips used for probing surface geometry.

Simulating the internal mechanism of the ATS was important to describing and understanding

the transfer procedure so that mishaps could be avoided during the transfer. The components of

the internal mechanisms, which have distinct, precise linear motion and rotary motion, were

designed in ProEngineer and I-DEAS. These are the mechanisms for moving specimens from

the MBE system and placing them in the STM, or vice versa. Realistic simulation of the

assembly was achieved by exporting the ProEngineer and I-DEAS models to Alias

PowerAnimator — a flexible animation tool developed for SGI workstations — via the Initial

Graphic Exchange Specification (IGES). Figures 20 and 21 show snapshots from the simulation.

artifact

support

plate

artifact

support

plate

Figure 20 Picking the artifact from

MBE system, before redesign

Figure 21 Placing the artifact in

the STM, before redesign
33

Because this simulation was developed on a computer workstation, this particular evaluation was

conducted in a face-to-face meeting in NIST’s NAMT Lab [29]. This laboratory was developed,

in part, to enhance synchronous communications, such as meetings and conference calls. Part of

that enhancement is a linked videowall, which can project images from any of the workstations

in the lab (and other sites around NIST) via a high-performance network. 

When the simulation was displayed in the NAMT Laboratory during the meeting, one physicist

identified a problem with the mechanism. As depicted in Figs. 20 and 21, for example, the initial

configuration had a support plate that could slip when placed in a vertical orientation, taking the

artifact along with it. Since the same mechanism is being used to unload the artifact in STM, as

shown in Fig. 21, the same slipping problem occurs. Along with other suggestions, this

ultimately resulted in the engineers modifying the mechanism. This again was developed into a

simulation that was reviewed and approved, and now is available as a demonstration model. 

Representing the ATS geometry was our next task to enhancing collaboration. The assembled

designs of the ATS were presented to the team members so that each could evaluate details of

the design. In this effort, we chose an asynchronous approach so that the team members could

perform their evaluations at different times and places. We chose Virtual Reality Modeling

Language (VRML) and the Internet as communication media because they support our aim by

allowing team members to view graphic files at their convenience.

We used CADKEY and ProEngineer converters to export the assembly models to VRML

models. These models were made available through the Internet and thereby accessible to the

entire team at one time. We then edited these VRML files to complete the ATS system

assembly, which is shown in Fig. 22. 

Because VRML objects can be manipulated without losing their representations as solid models,

the final assembly still retained the computer aided design (CAD) model rendering to help

engineers to visualize space constraints, such as whether the UHV system fits into the cart or not.

VRML also provided the team members the feel of virtual reality, which means that one can

obtain a sense of the VRML model using a walk-through of the simulation supported by VRML

browsers.
34

Figure 22 Assembly of cart and UHV system as a unified VRML model.

Simulating the assembly sequence for the ATS, our third effort, was aimed at improving the

design process. Digital mock up of this assembly sequence was crucial to identifying problems

of assembling components, and to saving time and effort by avoiding these problems during

actual assembly. The engineers needed information on UHV system assembly procedures from

the physicists. 

Following the success of the second effort, we used VRML animation for asynchronous

visualization of the assembly sequence. Similar to our earlier efforts, we used CADKEY

converters to export the assembly models that the engineers developed to IGES models, which

we imported into ProEngineer. We edited these VRML files to complete the cart and UHV

system animation. Figure 23 shows a sample VRML snapshot of the simulation, an exploded

view of the UHV system and the cart at the beginning of the animation. 

Ultimately, the team used the animation sequence synchronously to agree on the optimal

assembly sequence. This animation also proved quite useful in revealing problems that

previously had gone unnoticed. 
35

Figure 23 An exploded view of the ATS at the start of the assembly sequence.

Computer modeling of the FIM of STM tips enabled us to understand the structure and quality of

the STM tips. Gray-scale images obtained from SPMs are functions of both the geometrical

properties of the emitting tip and the electronic properties of the surface. Creating accurate

models of SPM tips is important in the area of dimensional metrology because features such as

lines and surface profiles obtained with an SPM, for the purpose of measuring linewidth, are

strongly dependent on the tip geometry. The modeling of an SPM tip involves surface

reconstruction of the atomic structure of the tip from a FIM image using image processing

techniques. This modeling required both a reasonably good understanding of single crystal
36

properties and crystallography, as well as the basic principles of operation of an FIM. Our

results are discussed elsewhere [25]. An example of our results for a (111) Tungsten (W) tip is

shown in Figure 24.

In future work, we intend to simulate the dynamic response

characteristics of scanning probes. In all SPMs, the signal

obtained is a strong function of the spacing between a

mechanical tip and a test surface. In a STM, this signal is

the quantum mechanical tunneling current, which is

produced by a small electrical bias voltage between the tip

and the surface. Here the tunneling current is an

exponential function of the tip-surface spacing, such that a

change of tip-surface spacing of one atomic diameter

produces approximately a factor of ten change in the

tunneling current. In an AFM, the signal is proportional to

the net atomic force between atoms on the SPM tip and

those nearby on the test surface.

Both types of microscopes and other similar microscopes produce a gray scale representation of

the test surface topography by electromechanically servoing the tip to maintain a fixed spacing

from the surface. By recording the servo-control signal as a function of the tip (x,y) position as

it is scanned across the surface one may obtain a profile of the test surface. Repeated parallel

scans are used to build up a gray-scale image. We plan to develop and demonstrate a model to

simulate the response of the SPM to varying step heights or other sharp variations in surface

topography. The response of the instrument to both external acoustic and/or seismic

perturbations will also be carried out. We will also provide visualizations of the varying

response characteristics of the SPM to changes in the resonance frequencies of the mechanical

structure of the SPM, to varying bandwidths of the servo control loop, and to different values of

noise in the servo control loop. Such modeling would be of great value to the SPM community

and to SPM manufacturers.

Simulations of fabrication processes such as MBE, thermal and field evaporation, and STM pickup and transport of atoms and molecules may also be carried out. Here the challenge of

obtaining adequate scientific models of the processes would be of greater interest than executing

the simulations.

The use of web-enabled tools for modeling and simulation aids significantly in carrying out the

above mentioned tasks. 

4.4.2 Collaborative Design (Engineering Tools)

To share the different types of information associated with the ATS design among the team

members, we implemented a collaborative workbench (CW) that was designed specifically for

platform-independent design and manufacturing collaboration. The CW consisted of two

principal parts: an Internet-accessible portion and a platform-specific collaboration notebook.

The Internet-accessible portion ran on a local server and consisted of a Project Area, containing

Figure 24 Atomic model of a W

STM tip with (111) orientation.
37

project-specific information such as drawings, specifications, and schedules, and a Document

Vault, which stored files of any type that could be uploaded via client World Wide Web

browsers. The collaboration notebook is software local to each team member’s workstation, and

was primarily used as a whiteboard for pasting comments on existing documents and drawings.

Figure 25 Using the collaboration notebook, this figure captures a sample

asynchronous interaction between team members Dave Monk and Manfred

Osti over the ATS internal mechanism shown in Figs. 20 and 21.

Based on the specifications for the ATS, designers created and represented ATS components and

assemblies on their respective CAD systems. The designers published their designs on the CW

and informed project team members of the newly available CAD drawings via automatic email.

Team members then commented directly on the CW representations of the CAD drawings

(example shown in Fig. 25), and those comments were republished with the drawings. This

process continued until team members reached a consensus, or until face-to-face meetings helped

resolve conflicting issues. Similar processes occurred with documents such as reports and

schedules and with digitized photographs of manufactured components. Environments like the

CW can be effective in helping teams overcome the problems associated with diverse computing

environments and heterogeneous data formats, and they can be effective in facilitating
38

consensus-based decisions among several collaborators. This technology improved the design

and manufacturing processes for the ATS in specific instances. 

4.4.3 Design Repository

In an effort to preserve the design documentation for the ATS, we encapsulated the form,

function, behavior and rationale of each ATS component in a NIST-developed design repository

(DR). The DR captures form, function and behavior of each component within a design and

maps it onto the data elements such as objects, classes and relations. As an example, the

pumping system takes ambient air inside the chamber and reduces it with a turbo pump to a high

vacuum, which in turn gets pumped down with an ion pump to UHV. Schematically, we can

represent the pump down system as a single artifact, having an input state characterized by

ambient air, and an output state (destination) characterized by UHV. However, the functions of

this system's two-fold vacuum pumping are intertwined. The turbo pump produces an

intermediate, high vacuum in the ion pump chamber by taking air and decreasing pressure in a

controlled way. The turbo pump is then valved off and the ion pump completes the process to

achieve UHV in the chamber.

To populate the design repository, we represented engineering geometry, function, and

associated behavior, as well as taxonomies of generic functions and flows of the transport

system. We modeled geometry with digital photographs and VRML images of actual CAD

drawings. We represented function with linked textual descriptions, and we captured behavior

with mathematical expressions. Through an evolving user interface, shown in Fig. 26, this

representation serves to capture the more than 50 parts and systems of the ATS in such a way

that the information relating to form, function and behavior is accessible and browsable to

subsequent designers and other interested parties.
39

Figure 26 A sample user interface. The graphic screen depicts one VRML

view of the overall system. The lower screen describes the system, its basic

function and its subartifacts. The system hierarchy is defined on the left.

4.5 Telerobotics 

In our vision of future microelectronics manufacture, a variety of micro-, nano-, and

quantum-electronic devices with tightly controlled dimensional features could be fabricated

under high vacuum in systems located in clean room environments at geographically distributed

sites. Each site could specialize in one or more functions in the overall manufacture of the mask

or device such as R&D, design, fabrication, inspection, processing, or repair. Within this

distributed nanomanufacturing system, partially processed devices, mask and device design data,

and real-time diagnostic information need to be moved rapidly and efficiently among different

geographical sites.

With the requirement for device fabrication in clean room environments increasing, there is a

growing need for automated control of processes and robotic manipulation of wafers and

carriers. Remote, “through the clean room wall,” teleoperation of SPMs used for inspection of

fabricated microstructures and remote “from a vendor’s firm” teleoperation of such SPMs for

instrument troubleshooting (e-diagnostics [10]) may become commonplace and necessary. 

Traditional teleoperation usually involves a close physical and visual interaction with the

mechanism, typically moving a single joint at a time to achieve the desired motion. It can
40

become tedious, for repetitive motions such as scanning, as well as prone to error due to operator

inattentiveness. Any robotic mechanism requires continual updates to its motors, even when

stationary, due to the effects of gravity. This data is required to be deterministic, that is, arriving

on a regular basis much like the individual frames of a movie, to ensure smooth operation. Lowlevel teleoperation over long distances can be difficult, if not impossible, due to inherent network

delays encountered with propagation, protocol, and routing choice [34].

Fully automated robotics relieves the tedium of single-joint motions and allows the system to run

unattended. It allows the operator to interact at a high level with the system and, therefore, is a

good candidate for long distance interactions. However, full automation can require significant

programming time and is often not practical for research or diagnostic operations. 

The term ‘telerobotics' [35] is derived from the merging of teleoperation (intensive human

interaction moving one joint at time) and fully automated robotics (repetitive motions without

any human interactions). It allows the operator to define the level between full automation and

teleoperation on an operation by operation basis. A short teleoperated operation might be a test

of the Z-axis to ensure engagement of the surface or perhaps the taking of a single scan line of

data. After such an initial check, the operator could define a full image to be taken under robotic

control. The tradeoff between the two modes of interaction depends on the desired task at hand

and the distances involved. 

4.5.1 Control and Image Standards 

Telerobotics requires the development of standard interfaces between the controller and the user

program. This takes the form of both control interfaces for the physical motion and image

standards for feedback to the operator and analysis of the scanned surface. A meeting was

convened in conjunction with the 4th Workshop on Industrial Applications of Scanned Probe

Microscopy held at NIST in May, 1997, to explore these standards issues.

The workshop was attended by representatives from the major SPM vendors at the time and

several NIST staff members. The NAMT Nanomanufacturing project was first presented to give

the telerobotic project task some context for the vendors. Detailed discussions centered on the

issues of remote control, diagnostics, and image standardization. A lively discussion was held

on the pros and cons of remote operation. In general, while vendors acknowledged the

usefulness of remote diagnostics, many were uncomfortable with the idea of remote operation

stating safety and sample preparation concerns. The discussion of a potential image standard

garnered more support for simple X-Y scans, but stalled when the discussion turned to more

complex images and techniques such as force curves. The general feeling was that the industry

was still in a formative stage and not ready for an image standard that could cover all current and

future image possibilities.

4.5.2 Remote Diagnostics Testbed 

Another task was the development of a testbed to demonstrate remote diagnostic operation of a

SPM and to identify standard interface needs. Based on the feedback of the workshop, this work

focused on only high-level diagnostic operations and not complete low-level remote operations. 
41

The effort was carried out in collaboration with the University of North Carolina at Chapel Hill.

Researchers there had worked closely with TopoMetrix Inc. [36] to define a low-level interface

into the control system of the TopoMetrix SPM. This interface allowed the researchers to set

gains, define simple trajectories for the microscope to perform, and in general, control the

microscope in the same manner as an operator at the console. Real-time access to the control

system and the image allowed a closed loop system called the Nanomanipulator [37,38] to be

developed. 

The Nanomanipulator system is capable of both low-level operations, such as moving a

component along a single axis, as well as higher-level operations such as scanning images. The

system is coupled with a high-speed graphic display and a haptic device to let the researcher

‘feel’ the surface under study. It has proven to be an excellent testbed for determining the

tradeoffs involved between user access, network delays, and appropriate level of telerobotic

operation for remote operation of SPMs. 

We performed experiments on the Nanomanipulator system using a number of different control

and network interfaces. The networks under consideration used either the industry standard

transmission control protocol / internet protocol (TCP/IP) or the emerging Asynchronous

Transfer Mode (ATM) protocol. ATM was developed to deliver data packets in a deterministic

manner, which is often needed for the demands of networked multimedia data. TCP/IP ensures

delivery of all data packets, but in a non-deterministic manner. These experiments confirmed the

importance of a smooth, uninterrupted data stream to and from the SPM when performing lowlevel operations or very high-speed image transfers. This was achieved by TCP/IP over short

distances on a lightly loaded network, or by ATM under most conditions. 

4.5.3 Recommendations

The time is right for the SPM community to develop image and high-level control standards.

The laboratory systems developed in the early and mid 1990s have given rise to the production

systems of today. As the SPM finds its way out of the individual researcher’s lab and onto the

factory floor, the need for control and image standards increases. An image standard will not

only allow free interchange of data between researchers; it will also allow third party vendors to

supply image analysis packages and other add-on packages for inclusion on the factory floor.

Although true remote operation may only make sense for laboratory experimentation, remote

diagnostics will rise in importance as more SPMs are placed in factory settings. 
42

5. Conclusions and Future Work

In the atom-based standards field, we will continue to develop Si(111) specimens as single-atom

step height standards. The work to determine the average step height is completed, and the

manufacture of these specimens is practical. The specimens are now commercially available. In

future projects, we will pursue standardization work to develop a user friendly measurement

procedure that employs the standard to calibrate profiling instruments operating at the highest

levels of resolution.

We will also continue to work on the critical problem of fabricating counted atom linewidth

standards. This will involve developing a procedure for fabrication of clearly defined linewidth

structures, then cleaning and annealing them to produce crystalline surfaces whose atoms can be

measured and counted without degrading or melting their overall linewidth shapes in the process.

The use of mobile UHV environments may be further off. On one hand, UHV systems could

become crucial for semiconductor manufacturing as functional thin films such as gate oxides

approach atomic size thicknesses. Surface contamination before or after the fabrication of such

thin layers could change their properties significantly. In addition, the need for delicate

standards that must remain in UHV their entire lives may become greater if there is no other way

to maintain highly perfect nanometer size dimensional standards. On the other hand, it may not

be necessary to handle an artifact entirely in UHV. Other types of controlled environments may

be acceptable, such as high vacuum, rough vacuum, clean gas, or clean atmospheric conditions.

Atmospheric clean environments may suffice for housing many types of devices and standards,

or centralized systems with all the UHV fabrication tools integrated into them may preclude the

need for sample handoff between manipulators. Even so, the UHV community in general may

profit greatly by developing standardized sample holders and manipulators that allow handoff of

samples between them. 

If there is a long-range need for distributed UHV systems allowing the atom-based dimensional

artifacts to be used by many different users, arriving at some standards for both the transport

container interfaces and the internal mechanisms will be necessary. This work will need to be

closely coordinated with industrial partners such as vacuum equipment suppliers and end users

of artifacts.

6. Acknowledgments

The authors are grateful to C. Jensen for designs and fabrication of a number of elements of the

ATS, to E. Williams, V.W. Tsai, and Z. Hui at the University of Maryland for fabrication of the

Si step height specimens and other technical contributions, to R. Fejol for work on the

development of the design repository for the ATS and its elements, to N.G. Orji and R. Dixson

for analysis of the round robin data for the Si(111) single-atom step height specimens, to B.

Young for creation of the Vacuum Suitcase videotape and website, to Michael Lin and Alice

Ling for their assistance in developing the ATS data logger, and to V.S. Gagne for preparation of

the text and graphics. The work was supported in part by the MEL NAMT Program and in part

by the NIST Office of Microelectronics Programs. 
43

7. References

Note: The references shown in bold are publications of the Nanomanufacturing of AtomBased Dimensional Standards project.

[1] Bello, M.A.; Densock, R.J.; Swyt, D.A.; Land, J.L.; Stieren, D.C.; Wavering, A.J.;

Donmez, M.A.; Christopher, N.B.; Carver, G.P., NIST: Toward 21st Century

Information-Based Manufacturing, NIST Special Publication 913, Gaithersburg, MD,

September 1997.

[2] Stieren, D.C.; Densock, R.J.; Luce, M.E., National Advanced Manufacturing Testbed,

NISTIR 6383 (National Institute of Standards and Technology, Gaithersburg, MD;

August 1999). 25 pp.

[3] Stieren, D.C.; Luce, M.E., Information-Based Manufacturing Program Summary and

Accomplishments, NISTIR 6490 (National Institute of Standards and Technology,

Gaithersburg, MD; March 2000). 52 pp.

[4] International Technology Roadmap for Semiconductors: 1999 (Semiconductor Industry

Association, Austin, TX, 1999).

[5] Vezzetti, C.F.; Varner, R.N.; Potzick, J.E., Antireflecting-Chromium Linewidth

Standard, SRM 473, for Calibration of Optical Microscope Linewidth Measuring

Systems, NIST Special Publication 260-119 (National Institute of Standards and

Technology, Gaithersburg, MD; September 1992). 36 pp.

[6 ] Granneman, E.H.A., Trends in Contamination Control in IC Production Tools, Solid

State Technology 40(7):225, July 1997.

[7] Parikh, M.; Kaempf, U., SMIF - A Technology for Wafer Cassette Transfer in VLSI

Manufacturing, Solid State Technology 27 (7): 111-115; 1984.

[8] Stulen, R.H.; Sweeney, D.W., Extreme Ultraviolet Lithography, IEEE J. Quantum

Elect. 35: 694-699; 1999.

[9] Hawryluk, A.M., Characterization and Possible Repair of Defects in SXPL Masks, OSA

Proc. on Soft X-Ray Projection Lithography 18: 43-46; 1993.

[10] Singer, P.E., Diagnostics: Monitoring Tool Performance, Semiconductor International

24 (3): 27; 2001.
44

[11] See, for example, Tsai, V.W.; Wang, X.-S.; Williams, E.D.; Schneir, J.; Dixson, R.D.,

Conformal Oxides on Silicon Surfaces, Appl. Phys. Lett. 71 (11): 1495; 1997, and

references contained therein.

[12] See: Mohr, P.J.; Taylor, B.N., CODATA Recommended Values of the Fundamental

Physical Constants: 1998, Journal of Physical and Chemical Reference Data 28 (6);

1999; and Reviews of Modern Physics 72 (2): 351-495; 2000.

[13] Tsai, V.W.; Vorburger, T.V.; Dixson, R.; Fu, J.; Köning, R.; Silver, R.; Williams,

E.D., The Study of Silicon Stepped Surfaces as Atomic Force Microscope

Calibration Standards with a Calibrated AFM at NIST, in Characterization and

Metrology for ULSI Technology: 1998 International Conference, D.G. Seiler, et al.,

eds. (AIP Press, 1998), pp. 839-842.

[14] Dixson, R.; Orji, N.G.; Fu, J.; Tsai, V.W.; Williams, E.D.; Kacker, R.; Vorburger,

T.V.; Edwards, H.; Cook, D.; West, P.; Nyffenegger, R., Silicon Single Atom Steps

as AFM Height Standards, Proc. SPIE 4344: 157-168; 2001.

[15] Phaneuf, R.J.; Williams, E.D., Surface Phase Separation of Vicinal Si (111), Phys. Rev.

Lett. 58: 2563; 1987.

[16] Noh, D.Y.; Blum, K.I.; Ramstad, M.J.;. Birgeneau, R.J., Long-range Coherence of

Macroscopic Phase Separation of Steps on Vicinal Si(111), Phys. Rev. B 44: 10969;

1991.

[17] Suzuki, M.; Aoyama, S.; Futatsuki, T.; Kelly, A.J.; Osada, T.; Nakano, A.; Sakasibara,

Y.; Suzuki, Y.; Takami, H.; Takenobu, I.; Yasutake, M., Standardized Procedure for

Calibrating Height Scales in Atomic Force Microscopy on the Order of 1 nm, J. Vac.

Sci. Technol. A 14 (3): 1228-1232; 1996.

[18] UC Standard, One-Nanometer-Order Z-Axis Calibration of AFM (Ultraclean Society,

Tokyo, 1995).

[19] Fu, J.; Tsai, V.W.; Köning, R.; Dixson, R.; Vorburger, T.V., Algorithms for

Calculating Single Atom Step Heights, Nanotechnology 10: 428-433; 1999.

[20] Photomask Linewidth Standards, Micrometrology Section, National Physical Laboratory

Queens Road, Teddington, Middlesex, TW11 0LW, England.

[21] Silver, R.M.; Jensen, C.P.; Tsai, V.; Fu, J.; Villarrubia, J.; Teague, E.C.,

Developing a Method to Determine Linewidth Based on Counting the AtomSpacings Across a Line, Proc. SPIE 3332: 441-460; 1998.
45

[22] Villarrubia, J.S.; Dixson, R.; Jones, S.; Lowney, J.R.; Postek, M.R.; Allen, R.A.;

Cresswell, M.W., Intercomparison of SEM, AFM, and Electrical Linewidths, Proc.

SPIE 3677: 587-598; 1999.

[23] Müller, E.W., Field-Ion Microscopy and the Electronic Structure of Metal Surfaces,

Quarterly Reviews XXIII (2) (The Chemical Society, London, 1969), pp 177-186.

[24] Fink, H.W., Mono-atomic Tips for Scanning Tunneling Microscopy, IBM J. Res

Develop. 30 (5): 460-465; 1986.

[25] Rao, P.V.M.; Jensen, C.P.; and Silver, R.M., A Generic Model for STM Tip

Geometry Measured with FIM (submitted to Ultramicroscopy).

[26] Hobson, J.P.; Kornelsen, E.V., UHV Technique for Intervacuum Sample Transfer, J.

Vac. Sci. Technol. 16 (2): 701-710; 1979.

[27] Young, B., Vacuum Suitcase, http://www.mel.nist.gov/gallery/vcase/vscase1.htm ,

Last updated June 8, 2001.

[28] Korczynski, E., Design Challenges in Vacuum Robotics, Solid State Technology,

October 1996.

[29] Nidamarthi, S.; Allen, R.H.; Sriram, R.D., Observations from Supplementing the

Traditional Design Process via Internet-based Collaboration Tools, International

Journal of Computer-Integrated Manufacturing 14 (1): 95-107; 2001.

[30] Allen, R. H.; Fijol, R. J.; Szykman, S.; Sriram, R.D., Representing an Artifact

System in a Design Repository: A Case Study, Proc. DETC'00/CIE, D. E. Lee, ed.

(American Society of Mechanical Engineers, New York, September 2000); Paper

No. CIE 14608, 8 pp.

[31] Allen, R.H.; Nidamarthi, S.; Regalla, S.P.; Sriram, R.D., Enhancing Collaboration

Using an Internet-Integrated Workbench, Proc. DETC'99, M. Gartner et al., eds.

(American Society of Mechanical Engineers, New York, September 1999); Paper

No. DAC 8573, 12 pp.

[32] Nidamarthi, S.; Allen, R.H.; Prakash, S.R.; Sriram, R.D., Observations from

Multidisciplinary, Internet-based Collaboration on a Practical Design Project,

International Conference on Engineering Design, ICED99 2: 709-714; August 1999.

[33] Allen, R.H.; Nidamarthi, S.; Rao, P.V.M.; Rhorer, R.; Sriram, R.D.; Teague, E.C.,

Collaborating on the Design and Manufacture of an Artifact Transport System: A

Case Study in VRML as a Visualization Tool for Consensus Building, Proc.

DETC'98, M. Gartner et al., eds. (American Society of Mechanical Engineers, New

York, September 1998, Paper No. DAC 5600, 12 pp.
46

[34] Clark, M.; Jeffray, K., Application-Level Measurements of Performance on the vBNS,

IEEE Intl. Conference on Multimedia Computing and Systems, June 1999, Florence,

Italy.

[35] Lumia, R.; Michaloski, J.; Russell, R.; Wheatley, T.; Backe, P.; Lee, S.; Steele, R.;

Unified Telerobotic Architecture Project (UTAP) Standard Interface Environment (SIE),

NISTIR 5658; National Institute of Standards and Technology, Gaithersburg, MD, May

1995.

[36] TopoMetrix has merged with Park Scientific and is now called TM Microscopes.

[37] Taylor, R.M., The Nanomanipulator: A Virtual-Reality Interface to a Scanning

Tunneling Microscope, Ph.D. Dissertation, University of North Carolina, Chapel Hill,

TR94-030, May 1994.

[38] Falvo, M.; Superfine, R.; Washburn, S.; Finch, M.; Taylor, R.M.; Chi, V.L.; Brooks Jr.,

F.P., The Nanomanipulator: A Teleoperator for Manipulating Materials at the

Nanometer Scale, Proceedings of the International Symposium on the Science and

Technology of Atomically Engineered Materials, (Richmond, VA, Oct 30 - Nov 4, 1995).

World Scientific Publishing 1996. pp. 579-586.