J

NBS SPECIAL PUBLICATION 400-12

U.S. DEPARTMENT OF COMMERCE / National Bureau of Standards

v

Measurement Technology

Quarterly Report

July 1 to September 30, 1974
NATIONAL BUREAU OF STANDARDS

The National Bureau of Standards' was established by an act of Congress March 3, 1901. The Bureau's overall goal is to strengthen and advance the Nation's science and technology

and facilitate their effective application for public benefit. To this end, the Bureau conducts

research and provides: (1) a basis for the Nation's physical measurement system, (2) scientific and technological services for industry and government, (3 ) a technical basis for equity in trade, and (4) technical services to promote public safety. The Bureau consists of the Institute for Basic Standards, the Institute for Materials Research, the Institute for Applied Technology,

the Institute for Computer Sciences and Technology, and the Office for Information Programs.

THE INSTITUTE FOR BASIC STANDARDS provides the central basis within the United

States of a complete and consistent system of physical measurement; coordinates that system

with measurement systems of other nations; and furnishes essential services leading to accurate and uniform physical measurements throughout the Nation's scientific community, industry, and commerce. The Institute consists of a Center for Radiation Research, an Office of Measurement Services and the following divisions: Applied Mathematics — Electricity — Mechanics — Heat — Optical Physics — Nuclear

Sciences " — Applied Radiation " — Quantum Electronics " — Electromagnetics " — Time

and Frequency " — Laboratory Astrophysics " — Cryogenics \

THE INSTITUTE FOR MATERIALS RESEARCH conducts materials research leading to improved methods of measurement, standards, and data on the properties of well-characterized

materials needed by industry, commerce, educational institutions, and Government; provides

advisory and research services to other Government agencies; and develops, produces, and

distributes standard reference materials. The Institute consists of the Office of Standard Reference Materials and the following divisions: Analytical Chemistry — Polymers -— Metallurgy — Inorganic Materials — Reactor

Radiation — Physical Chemistry.

THE INSTITUTE FOR APPLIED TECHNOLOGY provides technical services to promote

the use of available technology and to facilitate technological innovation in industry and

Government; cooperates with public and private organizations leading to the development of

technological standards (including mandatory safety standards), codes and methods of test; and provides technical advice and services to Government agencies upon request. The Institute consists of a Center for Building Technology and the following divisions and offices: Engineering and Product Standards — Weights and Measures — Invention and Innovation — Product Evaluation Technology — Electronic Technology — Technical Analysis — Measurement Engineering — Structures, Materials, and Life Safety * — Building

Environment * —• Technical Evaluation and Application ' — Fire Technology.

THE INSTITUTE FOR COMPUTER SCIENCES AND TECHNOLOGY conducts research and provides technical services designed to aid Government agencies in improving cost effec- tiveness in the conduct of their programs through the selection, acquisition, and effective

utilization of automatic data processing equipment; and serves as the principal focus within

the executive branch for the development of Federal standards for automatic data processing

equipment, techniques, and computer languages. The Institute consists of the following

divisions: Computer Services — Systems and Software — Computer Systems Engineering — Information Technology.

THE OFFICE FOR INFORMATION PROGRAMS promotes optimum dissemination and

accessibility of scientific information generated within NBS and other agencies of the Federal Government; promotes the development of the National Standard Reference Data System and

a system of information analysis centers dealing with the broader aspects of the National Measurement System; provides appropriate services to ensure that the NBS staff has optimum

accessibility to the scientific information of the world. The Office consists of the following

organizational units: Office of Standard Reference Data — Office of Information Activities — Office of Technical

Publications — Library — Office of International Relations.

1 Headquarters and Laboratories at Gaithersburg, Washington, D.C. 20234.

^ Part of the Center for Radiation Research.

» Located at Boulder, Colorado 80302.

Part of the Center for Building Technology.

Maryland, unless otherwise noted; mailing address
'

'' ' Semiconductor Measurement Technology

^> Quarterly Report, July 1 to September 30, 1974

r

W. Murray Bullis, Editor

Electronic Technology Division

Institute for Applied Technology

,S ) National Bureau of Standards

Washington, D.C. 20234

Jointly Supported by:

The National Bureau of Standards,

The Defense Nuclear Agency,

The Defense Advanced Research Projects Agency, and The Navy Strategic Systems Project Office

I"

U.S. DEPARTMENT OF COMMERCE

NATIONAL BUREAU OF STANDARDS, Richard W. Roberts, Direcfor

Issued May 1 975
National Bureau of Standards Special Publication 400-12

Nat. Bur. Stand. (U.S.), Spec. Publ. 400-12, 59 pages (May 1975)

CODEN: XNBSAV

1

U.S. GOVERNMENT PRINTING OFFICE

WASHINGTON: 1975

For sale by the Superintendent of Documents, U.S. Government Printing Office, Washington, D.C. 20402

(Order by SD Catalog No. C13.10 :400-12) . Price $1.15 cents (Add 25 percent additional for other than U.S. mailing).
TABLE OF CONTENTS

SEMICONDUCTOR MEASUREMENT TECHNOLOGY

PAGE

I Preface vi

1 1. Introduction 1

2. Highlights 3

^3. Resistivity; Dopant Profiles 6 l|3.1. Incremental Sheet Resistance 6 3.2. Mathematical Models of Dopant Profiles 6

4. Crystal Defects and Contaminants = 8 4.1. Thermally Stimulated Current and Capacitance Measurements 8 4.2. Energy Level Model for Gold in Silicon 11

5. Oxide Film Characterization 15

5.1. X-Ray Photoelectron Spectroscopy 15

5.2. Comparative Study of Surface Analysis Techniques 17

6. Test Patterns 19

6.1. Test Pattern for Resistivity-Dopant Density Evaluation 19

6.2. Charge-Coupled Device Test Pattern 22

7. Epitaxial Layer Thickness 26

7.1. Cleave and Stain Measurements 26

7.2. Metal-Photoresist-Semiconductor Capacitors 26

8. Wafer Inspection and Test 27

8.1. Flying-Spot Scanner Development ... 27

8.2. Automated Scanning Low Energy Electron Probe 28

9. Interconnection Bonding 29

|9.1. In-Process Bond Monitor 29

9.2. Beam- Lead Bonding Force Measurement 30

9.3. Non-Destructive Test for Beam-Lead Bonds 31

jjlO. Hermeticity 33

' 10.1. Helium Mass Spectrometer Method for Leak Detection 33

,11. Thermal Properties of Devices 35

j|ll.l. Thermal Resistance Methods — Darlington Pairs 35

:|11.2. Transient Thermal Response 37

i)l2. References 41

1 Appendix A. Semiconductor Technology Program Staff 44

I Appendix B. Semiconductor Technology Program Publications 45

,.|Appendix C. Workshop and Symposium Schedule 47

I' yAppendix D. Standards Committee Activities 48

(Appendix E. Solid-State Technology & Fabrication Services 50

Index 51

i iii
LIST OF FIGURES

PAG

1. Cross sectional view of holder designed for the determination of dopant density

profiles by the incremental sheet resistance method 6'

2. Electron density on gold acceptors in the space-charge region of a silicon \ p'^n junction g3. Schematic representation of the distribution of charge throughout the ^ space-charge region of a p'^n junction during the discharge of electrons from

uniformly distributed acceptor defects 9 4. Calculated reduced thermally stimulated current, (p'^'n) /qAW N^, from gold j acceptor defects in a silicon p'^'n junction as a function of temperature for

B = 10 K/s, = 0, and several values of the ratio N^/N^ lO' 5. Calculated reduced thermally stimulated current, Ij (p''"n) /qAW N^, from gold

acceptor defects in a silicon p'^n junction as a function of temperature for

W, = 0, N,/N = 100, and several values of 6 id

b d t 6. Calculated reduced thermally stimulated current, l2(p^n)/qAW N^, from gold

acceptor defects in a silicon p'^n junction as a function of temperature for j 6 = 10 K/s, N^/Nj. = 100, and several values of g 10!

7. Emission temperature of the phase I current response of gold acceptor defects i in n-type silicon as a function of heating rate for various conditions 10

8. Hall effect activation energy plot for the gold donor in initially n-type

silicon converted to p-type by diffusion with gold '. 11

9. Experimental data and theoretical curves for determining the energy level | of the gold acceptor in initially n-type silicon converted to p-type by

diffusion with gold 13

10. X-ray photoelectron spectra of carbon, silicon, and oxygen from an air-stabilized silicon specimen 15

11. Relative areas of x-ray photoelectron spectral peaks as a function of . electron emission angle 16

12. Ratios of the relative areas of the x-ray photoelectron peaks due to carbon and silicon as a function of electron emission angle 16

13. Relative areas of x-ray photoelectron spectral peaks of cleaned silicon

surface heated in an ultralow pressure of oxygen as a function of heater

current and ratio of relative areas of the peaks due to carbon 16

,

14. Test pattern, NBS-3, for characterizing the resistivity-dopant density

relation in silicon 20;

I.' 15. A topographic view and cross section of an n-channel, three-phase, f aluminum-gate CCD 22 i 16. High-frequency capacitance-voltage characteristics of a p-MOS capacitor t and an n— channel, 32—bit CCD connected as an MOS capacitor 24 i 17. Pulse height of a "one" preceded by 9 zeros as a function of the number

of transfers around a 32-bit circular CCD operating at 125 kHz ... 24

18. Fractional charge loss per transfer from a "one" preceded by N zeros

and transferred 336 times around a 32-bit circular CCD operating at 125 kHz ... 24

19. Fractional charge loss from a "one" preceded by N zeros as a function

of the number of transfers around a 32-bit circular^8cD operating at 125 kHz . . 24 j 20. Electron beam induced current response and unmodulated 0.633-Mm laser beam

induced current response of a 0.76-mm square, unbiased, silicon p-n

junction diode 27

j

! iv
LIST OF FIGURES

PAGE

'21. Measured and calculated normalized vibration amplitudes of ultrasonic bonding

tools mounted in inverted positions 29

1 22. Beam-lead force indicator as supplied with the beam-lead bonder 30

23. Modified beam-lead force gauge assembly 31

*24. Block diagram of acoustic emission test system 32

25. Indicated leak rate for sealed-off borosilicate glass capsules of same outer dimensions as test leak capsules as a function of time after pressuri-

't zation at 75 psia for 20 h in helium 33

I 26. Commercially available Darlington circuits 35

0 27. Circuit diagram of emitter-only switching circuit for measuring thermal

resistance modified to allow use of a variety of junction voltages as temperature sensitive parameters 35

[|j28. Model used for simulating the way in which the emitter-base voltage

1 averages the junction temperature 38

1 29. Temperature and relative measurement current density along a diagonal of

( a 0.51-mm square heat source on a 2.54-mm square silicon chip 38

||30. The computed ratio of the average junction temperature to the peak

(j junction temperature as a function of heat source size for a 2.54-mm

j square silicon chip corrected to account for the increased measurement

I current density compared to the calibration current density 39

I

LIST OF TABLES

' PAGE

1. Properties of Gold-Doped Silicon Specimens 13

2. Specimens for the Comparative Study of Surface Analysis Techniques 17

3. Planar Test Structures on Test Pattern NBS-3 21

4. Epitaxial Layer Thickness by Three Methods 26

5. Bonding Tool Material Properties 30

6. Thermal Resistance of a Type d Darlington Device 36

7. Peak Temperature Determination 39

V
PREFACE

The Semiconductor Technology Program serves

to focus NBS efforts to enhance the performance, interchangeability, and reliability

of discrete semiconductor devices and integrated circuits through improvements in measurement technology for use in specifying

materials and devices in national and international commerce and for use by industry in

controlling device fabrication processes.

Its major thrusts are the development of

carefully evaluated and well documented test

procedures and associated technology and the

dissemination of such information to the

electronics community. Application of the

output by industry will contribute to higher

yields, lower cost, and higher reliability

of semiconductor devices. The output provides a common basis for the purchase specifications of government agencies which will

lead to greater economy in government procurement. In addition, improved measurement

technology will provide a basis for con- trolled improvements in fabrication processes and in essential device characteristics.

The Program receives direct financial support principally from three major sponsors:

the Defense Advanced Research Projects Agency (ARPA) , the Defense Nuclear Agency

(DNA),^ and the National Bureau of Standards

(NBS). In addition, the Program receives

support from the U.S. Navy Strategic Systems

§ Project Office. The ARPA-supported portion

of the Program, Advancement of Reliability,

Processing, and Automation for Integrated

Circuits with the National Bureau of Standards (ARPA/IC/NBS) , addresses critical Defense Department problems in the yield, re- liability, and availability of integrated

circuits. The DNA-supported portion of the

Program emphasizes aspects of the work whicl

relate to radiation response of electron de- vices for use in military systems. There is considerable overlap between the interests

of DNA and ARPA. Measurement oriented activity appropriate to the mission of NBS is a critical element in the achievement of th< objectives of both other agencies. \

Essential assistance to the Program is also i received from the semiconductor industry

through cooperative experiments and technical exchanges. NBS interacts with industrial users and suppliers of semiconductor de- - vices through participation in standardizing

organizations; through direct consultations

with device and material suppliers , government agencies, and other users; and through

periodically scheduled symposia and workshops. In addition, progress reports, such

as this one, are regularly prepared for is- suance in the NBS Special Publication 400

sub-series. More detailed reports such as state-of-the-art reviews, literature compilations, and summaries of technical efforts

conducted within the Program are issued as these activities are completed. Reports of

this type which are published by NBS also

appear in the Special Publication 400 subseries. Announcements of availability of

all publications in this sub-series are sent

by the Government Printing Office to those

who have requested this service. A request

form for this purpose may be found at the

end of this report.

Through ARPA Order 2397, Program Code 5D10

(NBS Cost Center 4259555).

Through Inter-Agency Cost Reimbursement

Order 75-816 (NBS Cost Center U259522).

Through Scientific and Technical Research

Services Cost Centers 4251126, 4252128,

and 4254115.

Code SP-23, Administered by Naval Ammunition Depot, Crane, Indiana, through project order N0016475P070030 (NBS Cost Center

4251533) and Code SP-27, through IPR SP6-

75-4 (NBS Cost Center 4251547).

vi
SEMICONDUCTOR MEASUREMENT TECHNOLOGY

QUARTERLY REPORT

July 1 to September 30, 1974

Abstract: This quarterly progress report describes NBS

activities directed toward the development of methods of measurement for semiconductor materials, process control, and devices. The emphasis is on silicon device technologies. Principal accomplishments during this reporting period include

(1) completion of Hall effect measurements to determine activation energies of the gold donor and acceptor levels in silicon; (2) successful direct measurement of fast interface state

density with the circular CCD test structure; and (3) demonstration of the feasibility of the use of acoustic emission as a non-destructive means for testing individual beam-lead bonds.

Results are also reported on a holder for semi-automated sheet

resistance measurements, progress on development of mathematical

models of dopant profiles, analysis of thermally stimulated

current and capacitance measurements on junction diodes, X-ray

photoelectron spectroscopy, a comparative study of surface

analysis techniques, design and fabrication of a test pattern

for resistivity-dopant density evaluation, epitaxial layer

thickness measurement', use of the flying-spot scanner, initial

work on the scanning low energy electron probe, mathematical

modeling of ultrasonic bonding, an improved method for force

adjustment and measurement on beam-lead bonders, helium mass spectrometry for leak testing, thermal resistance measurements

on Darlington pairs, and transistor thermal response measurements. Supplementary data concerning staff, publications,

workshops and symposia, standards committee activities, and

technical services are also included as appendices.

Key Words: Acoustic emission; beam-lead bonds; boron

redistribution; Darlington pairs; dopant profiles; electrical

properties; electronics; epitaxial layer thickness; flyingspot scanner; gold-doped silicon; hermeticity; incremental

sheet resistance; measurement methods; microelectronics;

micrometrology ; MOS devices; oxide films; resistivity; scan- ning low energy electron probe; semiconductor devices; semiconductor materials; semiconductor process control; silicon;

test patterns; thermal resistance; thermal response; thermally

stimulated current; ultrasonic bonding; wire bonds; x-ray

photoelectron spectroscopy.

1 . INTRODUCTION

This is a report to the sponsors of the

Semiconductor Technology Program on work

during the twenty-fifth quarter of the Program. It summarizes work on a wide variety

of measurement methods for semiconductor materials, process control, and devices that

are being studied at the National Bureau of

Standards. The Program, VNl.ich emphasizes

silicon-based device technologies, is a con- tinuing one, and the results and conclusions

reported here are subject to modification

and refinement.

1
INTRODUCTION

The work of the Program is divided into a number of tasks, each directed toward the

study of a particular material or device

property or measurement technique. This re- port is subdivided according to these tasks.

Highlights of activity during the quarter

are given in section 2. Subsequent sections

deal with each specific task area. References cited are listed in the final section

of the report.

The report of each task includes a narrative

description of progress made during this re- porting period. Additional information con- cerning the material reported may be obtained directly from individual staff

members identified with the task in the report. The organization of the Program staff

and telephone numbers are listed in Appendix

A.

Background material on the Program and individual tasks may be found in earlier quarterly reports as listed in Appendix B. From

time to time, publications are prepared that

describe some aspect of the program in

greater detail. Current publications of

this type are also listed in Appendix B. Reprints or copies of such publications are usually available on request to the author.

Communication with the electronics community

is a critical aspect both as input for guid ance in planning future program activities ' and in disseminating the results of the wor

to potential users. Formal channels for

j such communication occur in the form of

workshops and symposia sponsored or co- sponsored by NBS. Currently scheduled semi nars and workshops are listed in Appendix C In addition, the availability of proceeding

from past workshops and seminars is indi- j cated in the appendix. '[

An important part of the work that frequent'

ly goes beyond the task structure is partic ' ipation in the activities of various techni

cal standardizing committees. The list of

personnel involved with this work given in

Appendix D suggests the extent of this participation. In most cases, details of

standardization efforts are reported in con nection with the work of a particular task.

Technical services in areas of competence \ are provided to other NBS activities and

other government agencies as they are re- quested. Usually these are short-term,

specialized services that cannot be obtained

through normal commercial channels. To in-,

dicate the kinds of technology available to the Program, such services provided during

j the period covered by this report are listeij

in Appendix E. 1

2
2 . HIGHLIGHTS

I Particularly significant accomplishments

I during this reporting period include (1)

completion of Hall effect measurements to

j determine activation energies of the gold

I donor and acceptor levels in silicon; (2)

,: successful direct measurement of fast inter-

^1 face state density with the circular CCD

"'j test structure; and (3) demonstration of the

^1 feasibility of the use of acoustic emission

! as a non-destructive means for testing individual beam-lead bonds. Highlights of progI ress in these and other technical task areas

"i are listed below.

;i

^1 Resistivity; Dopant Profiles — A plastic

specimen holder was designed and fabricated

1 to facilitate measurement of doping profiles

'i by the incremental sheet resistance method.

The holder is intended for semi-automated

'i measurements on a van der Pauw resistor test

' structure to obtain data for use in the rei evaluation of Irvin's curves which relate

! resistivity and dopant density for n- and pI type silicon. In addition, the development

j of mathematical models for dopant profiles,

^ especially for the redistribution of boron

1 during oxidation, has taken a more fruitful

approach based on a finite difference

' algorithm.

' Crystal Defeats and Contaminants — Analysis

of the thermally stimulated current and ca- pacitance response of mid-gap acceptor-type

defects in a p^n junction identified the

heating rate, the ratio of donor density to defect density, and the spatial fraction of

the space charge region in which the defects

are initially charged as the three parameters which influence the shape of the dynajj thermal current response curve.

I Activation energies of both the gold acceptor and gold donor were found from Hall effect measurements on initially n-type silicon wafers converted to p-type by the

addition of gold. The more precise value

found for the gold donor is in good agreement with the published values of others.

To obtain an accurate value for the gold

,| acceptor, it is necessary to determine the

j temperature variation of the energy of the

acceptor level with respect to the band

edges; this in turn requires improved formulas for calculating carrier mobilities in

the presence of charged impurity centers.

These are being sought in connection with

the reevaluation of Irvin's curves, discussed previously; further work on the

energy level model for gold will be deferred

so that the mobility problem can be

attacked.

Oxide Film Charaaverization — Study of x- ray photoelectron spectra from the surface

of air-stabilized silicon demonstrated the

usefulness of the angular dependence of the

intensity of spectral peaks in qualitatively

locating the depth of surface impurities and

determining the thickness of surface films.

Other experiments on low-carbon silicon suggested that the previously observed carbon

film arises from external sources and not

from the surface or bulk of the silicon.

A series of measurements was initiated to compare various electron, ion, and photon

beam measurement technologies for determination of impurities in silicon and silicon

dioxide. In these preliminary measurements,

ion implanted specimens are being used to provide a reasonably well known density of

impurity at a reasonably well defined location. Boron and zinc implanted silicon and

aluminum and sodium implanted silicon dioxide are being measured by ion microprobe

mass analysis, ion scattering mass analysis.

Auger electron spectroscopy, and other techniques in laboratories associated with the

manufacturer of an instrument or in laboratories associated with semiconductor analysis or device production.

The fourth ARPA/NBS Workshop on Surface

Analysis for Silicon Devices is being organized to determine the present qualitative

and quantitative capabilities and future

prospects of modern analytical beam techniques as applied to the analysis of silicon, and associated insulator films and device structures. Of particular interest are determinations of impurity profiles, surface contamination, and interface characteristics. Techniques utilizing impinging

electron, ion, neutral, or photon beams will

be considered. The workshop, scheduled for

April 23 and 24 at NBS, Gaithersburg , is intended to foster discussions among analysts,

users of their results, and instrument

manufacturers.

Test Patterns — Test patterns were the subject of the third ARPA/NBS Workshop held in

Scottsdale following the September meeting

of ASTM Committee F-1 on Electronics. About

70 scientists and engineers, representing 38

organizations, attended the workshop. Seven

speakers from industry and government addressed various aspects of test pattern analysis and use. The Workshop was particularly

3
HIGHLIGHTS significant in disclosing the value of

test patterns in manufacturing for rapid

start up of new processes and control of ongoing processes and, in the market place,

for evaluation of incoming materials for

processing, for device-vendor intercomparisons, and for device specifications. There was general agreement that full utilization

of test patterns will require both increased

understanding of the interpretation of the

measurement results and improved data acquisition, analysis, and display systems.

An initial fabrication run of the new test

pattern, NBS-3, was completed. Preliminary

experiments were conducted on the collector

resistor and incremental sheet resistance

(van der Pauw) test structures.

The CCD test pattern being developed by the

Naval Electronics Laboratory Center with

ARPA funding has been fabricated and the

correlation of its test structures begun.

The CCD can be connected and satisfactorily

operated as an MOS capacitor, but some ex- traneous capacitance is observed in the inversion region of the CCD C-V characteristics. Threshold voltages and channel

mobilities of the CCD structure connected as an MOS transistor agree reasonably well with

those of an ordinary MOS transistor. Most

importantly, the effectiveness of the circular CCD structure was demonstrated in con- nection with the direct determination of interface state density by the double-pulse

method because the number of transfers is

The system is built around an oscilloscope

in which the displayed waveform can be divided into 512 channels in the horizontal

direction. In an associated memory each

channel is represented by a 10-bit word

which, together with the scale factor information for the oscilloscope, input, defines the amplitude of the signal within

that channel. Each 10-bit word can be

stored in 6.5 ps, so that a waveform com- posed of 512 data points can be stored in

less than 3.5 ms. An associated minicomputer, which has a 24,000 bit memory and

computes with four significant figures, is

. able to process the stored waveforms as necessary. BASIC commands are available

to activate and control programmable voltage and current supplies. A digital temperature indicator can also be interfaced

with the system. Peripheral equipment includes a CRT display terminal, a hard copy

unit which can copy whatever is displayed

on the CRT, and a paper tape reader/punch.

not limited by the number of elements in the" structure.

i A computer-controlled data acquisition and

analysis system was received from the ven- | dor in July. Following preliminary checkout^

and familiarization tests, the system was , set up together with an automatic wafer \ prober to obtain real time wafer maps of

' base sheet resistance using the appropriate i, test structure on test pattern NBS-2. In I addition the system has been used to acquire;

capacitance-voltage (C-V) data from a gated ,1 p-n junction and calculate and plot the dop-s

ant density profile employing peripheral and]

diffused layer corrections; acquire C-V data

from an MOS capacitor and calculate dopant

density, flat-band voltage, and oxide charge

density; and generate a curve of capacitance

as a function of time for an MOS capacitor

fabricated on an epitaxial specimen, fit the

portions of the curve which represent relax-j

ation in the substrate and relaxation in the i, epitaxial layer, and calculate the layer J thickness from the intersection of the two 1

fits. J

Pho toli thography Work in the task which |l has been initiated to develop procedures for]'

primary line width measurement calibrations,!

to provide calibrated line width measurement

artifacts for use with optical microscopes, > and to develop improved theory and experi- iJ mental verification for accurate measure- I ments with optical systems is currently be- J ing concentrated on construction of I essential measurement equipment. A two di- | rectional interferometer is being designed a and built for use in improving the line i center to line center distance measurement

between two parallel lines. A modified Ben-ji

nett polarizing interferometer, which mea- 3 sures the movement of a mirror mounted on

the stage of a scanning electron microscope j (SEM) relative to a fiducial mirror by mea- 3 suring the angle of polarization of the j light produced by the relative movement of |i the two mirrors is being constructed for j prototype in situ measurements. In addition, measurements are being made both on a j gold-nickel thin-line laminate designed for [ use in calibrating the magnification of an ; SEM and on commercially produced patterns ofi

chromium lines on glass with both filar and n image shearing attachments to a convent ional[;

microscope. This task was undertaken in re

sponse to particularly strong statements

which have been received from the integrated 1, circuits industry emphasizing the critical

need for the development of NBS line width

standards in the 1 pm range to assist the

4
HIGHLIGHTS

J industry in meeting the micrometrology rejquirements associated with high resolution

photomasks.

The state-of-the-art review of available

j technologies for automated photomask inspection was completed [1], and detailed

analyses of the identified specific technolI ogies identified were begun.

i

'. Epitaxial Layer Thickness — Cleave-andI stain measurements were made of thickness of

- several epitaxial layers previously measured

i by the step-relaxation method. The agree-

"iment, although somewhat better than achieved

H between other methods and the step-

' relaxation method, was not fully satisfactory. A technique was developed for making

-: aluminum-photoresist-silicon capacitors for

- use with the step-relaxation and rampvoltage methods. These capacitors are made

without subjecting the specimen to high tem-

: perature processing steps.

Wafer Inspeation and Test — The characteristics of the laser flying spot scanner were

measured and preliminary scans were made on

a group of devices which were also investii gated in the scanning electron microscope

operating in the electron beam induced cur-

' rent mode. A survey was initiated to deter-

• mine the state of activity within the semiconductor device industry in the areas of

application of laser scanning for wafer

testing and other purposes, application of

the SEM to topological inspection and electrical testing of silicon wafers, and study

of SEM-induced damage during inspection or

test in order to establish directions of

future NBS work in these areas.

Work was begun at the Naval Research Laboratory on the development of an automated

scanning low energy electron probe as a noncontacting non-damaging wafer test technique; this work was initiated with the

design and construction of the electron gun

and initiation of procurement of the control

computer

Interoonneation Bonding — Experimental verification of the uniform beam model for

analysis of the vibration of an ultrasonic

bonding tool continued with study of tools

mounted in an inverted position so that the cross section of the vibrating portion was

uniform.

' An improved mechanism was designed and constructed to measure and control the force

applied during beam-lead bonding.

Initial studies of a non-destructive acoustic emission test to determine the bond

quality of beam-lead, flip-chip, or other

gang bonded devices demonstrated the feasibility of this approach. Well bonded beamlead devices gave little or no noise while

devices with one or two beams bonded to areas rendered intentionally defective gave

noise bursts at applied test forces low

enough not to deform the beams.

Two new bond test methods based on work carried out at NBS, a hot-melt-glue destructive

pull test for beam-lead bonds and a non- destructive wire bond pull test, were prepared for ASTM Committee F-1 on Electronics.

An intercomparison of the double-bond destructive pull test between NBS and another

laboratory was conducted in preparation for

a complete interlaboratory evaluation of

this method.

Eermeticity — Progress in conducting the

interlaboratory evaluation of the helium

mass spectrometer method for leak testing

semiconductor devices and integrated circuits was delayed by difficulties encountered in the back pressurization phase.

These difficulties were traced to outgassing

of helium which diffused into the glass

walls of the test leaks during pressurization and procedures for reducing this effect were developed.

The interlaboratory evaluation of the radioisotope method for leak testing semiconductor devices is proceeding as scheduled.

Thermal Properties of Devices — A modified

emitter-only-switching thermal resistance

test circuit was successfully used to separate thermal effects of the input and output

transistors of a monolithic Darlington circuit. This simple two-transistor circuit is an elemental integrated circuit in that

leads to all regions of each device are not

available at the exterior terminals so that

it is not possible to measure all desired

junction voltages independently; hence localization of effects to a particular device

must be inferred from the results of several

measurements made under different conditions

A method was developed for estimating peak

junction temperature from the electrically

generated heating and cooling response of

medium power transistors. Results obtained

on several transistors showed good agreement

with peak junction temperatures measured by

an infrared microradiometer
3. RESISTIVITY; DOPANT PROFILES

3.1. Incremental Sheet Resistance

A specimen holder was fabricated to facilitate the measurement of dopant profiles by

the Incremental sheet resistance method [2]. It was designed so that the repeated se- quence of anodic oxidation, oxide stripping

with hydrofluoric acid, and sheet resistance

measurement can be done without removing the

specimen from the holder. A cross sectional

view of the holder, which is an adaptation

of existing designs [3, A], is shown in figure 1. The critical aspect of the design

and fabrication is the achievement of a liquid-tight seal around the area to be anodized. In the apparatus shown the seal is

made by pressing the specimen against a TFE

fluorocarbon lip (L) by means of pressure

applied by a spring (S) in the bottom of the

A Socket

C Test structure die

H TO-5 header

L TFE fluorocarbon lip

0 0-ring seal

P Platinum cathode

S Spring

Figure 1. Cross sectional view of holder

designed for the determination of dopant

density profiles by the incremental sheet

resistance method.

holder. The holder is intended for use with' test structure 30 of Test Pattern NBS-3 (see sec. 6.1.). This structure is a van der

Pauw [5] sheet resistor with a diameter of * 0.76 mm and symmetrically placed contact ' arms which extend to contact pads at each j corner of the square chip, 2.54 mm (100 mil)* on a side. The test structure die (C) is ^ mounted on a TO-5 header (H) , which is

placed in the holder beneath a 1.25 mm diam-^

eter opening in the lip. The 0.4 mm wide ' seal between the lip and the die protects ! the contact pads, the bonded lead wires ' which connect the pads to posts on the head-i

er, and the header from the electrolyte used

for anodic oxidation.

In the course of overcoming various design

and fabrication difficulties, certain precautions became evident. One is the importance of precisely machining the sealing lip

to obtain a smooth, scratch-free surface and

then handling the piece carefully so that it

does not acquire scratches and dents during

use. To aid in putting the holder together

without damaging the sealing lip, it has

been extremely helpful to use a ring around

the holder to center the top piece as it

makes contact with the bottom section.

All external parts of the holder are made of

TFE fluorocarbon so that the entire apparatus may be immersed in the electrolyte.

Alternatively, the electrolyte acid can be | confined to the top reservoir. For removal

of the oxide layer, hydrofluoric acid can be

poured into the reservoir only. There is a tendency for an air bubble to be trapped

just above the specimen when liquids are introduced into the reservoir so it is often

necessary to use a small brush to clear away

the bubble. Not shown in figure 1 are the

wires going to the socket (A) and the plastic tubing and elbows through which the ^ wires run. The holder can be varied for use'

in either a vertical or horizontal position

by appropriate elbow and tubing changes.

The apparatus has been tested numerous times

with an ethylene glycol mixture as the electrolyte and found to be adequate. However,

much more experience in actual profiling is

needed before the design can be considered

to be fully satisfactory.

(W. R. Thurber and L. M. Smith)

3.2. Mathematical Models of Dopant Profiles

Work continued in the project to develop a mathematical model which can be solved for

6
RESISTIVITY; DOPANT PROFILES

the redistribution of boron in silicon during thermal oxidation and diffusion. A com- putational scheme described previously (NBS

Spec. Publ. 400-8, p. 14) was based on the

numerical solution of a system of integral

equations (NBS Spec. Publ. 400-4, pp. 9-11).

Study of this scheme has revealed the need

to add several additional quadrature subroutines in order to resolve various numerical

difficulties. Since the program is already

long and complex and hence very difficult to check, work was shifted to a shorter and

more promising finite difference algorithm.

Using this algorithm [6], a computer program

has been written for the moving boundary

value problem (NBS Spec. Publ. 400-1, pp. 9-

11). In order to solve the two diffusion

equations, one in the oxide and one in the

silicon, and to satisfy the segregation and

conservation of mass boundary conditions,

the double sweep method [7] was used. Results of several computer runs are being

studied with regard to their convergence to the closed form solution of Grove et at,

[8]. (S. R. Kraft''> and M. G. Buehler)

NBS Mathematical Analysis Section, Applied

Mathematics Division.

7
1^ . CRYSTAL DEFECTS AND CONTAfllNANTS

4.1. Thermany Stimulated Current and

Capacitance Measurements

Analysis of thermally stimulated current and

capacitance measurements continued with em- phasis on the thermally stimulated current

response of mid-gap acceptor-type defects in

a p^n junction. The parameters which influence the response of a particular defect

center have been identified as the heating

rate, B; the ratio of the donor density to the defect density, N,/N ; and the spatial

d t fraction of the space-charge region over which defects are initially charged, g.

Recall that the experiment is conducted by

cooling the junction to a low temperature

with a small bias which corresponds to a space-charge width W^, then reverse biasing

the junction to increase the space-charge

width to W_j^, and then observing the current

as the junction is warmed up [9]. The temperature dependence of the electron density

on the defects in the space-charge regions

can be found by solving numerically eqs (7a)

and (7c) of reference [9]. As an example

consider the gold acceptor in silicon for

which the electron and hole emission rates,

in inverse seconds, are [10]

e^ = 1.97 X 10^T2exp(-6348/T)

and

Bp = 5.82 X 106T2exp(-6847/T)

,

respectively, where T is the absolute temperature in kelvin. The results are illustrated in figure 2 and discussed in the following paragraphs.

In equilibrium, the electron and hole emission rates govern the electron density on

the defects in the space-charge region ac- cording to the relation

n^^ = e N^/(e + e ) tf p t n p where n^^ is the isothermal, steady-state

electron density. The ratio '^^.f/N^ is the

lowest curve in the figure. If the spacecharge region is cooled from high temperatures at a finite rate, the actual electron

density, n , will be larger than n , as depicted in the figure for two typical cooling

rates. Nevertheless, electrons occupy only , a very small fraction of the defects and in j this portion of the space-charge region, the: defects are essentially uncharged. Once

* * I cooled to the desired temperature, n^(= n^.^)'

remains essentially unchanged until the warn

up period is begun.

In the neutral region, essentially all the

defects are occupied by electrons since the

Fermi energy is well above the defect enerj gy. When the space-charge region is in- ; creased from W, to W. at low temperature the

b i electron density on the defect centers in

this portion, n^, does not change, so the

defects are initially essentially fully

charged (n^^ = N^) . i

The initial distribution of charge in both

portions of the space-charge region Is shown'

by the dotted line in figure 3. During warm'

up the electron density on the defects in ' the initially uncharged portion between 0

* ! and W^, n^, follows the appropriate cool- , down curve (see fig. 2) until it reaches the' value n^j. The electron density in the ini-!

tlally charged portion between W, and W.

,

D 1 n^, remains essentially constant until it

begins to fall rapidly toward the value n^^

at a temperature which depends on the heating rate as shown by the upper curves in

TEMPERATURE |K|

Figure 2. Electron density (normalized to the gold density) on gold acceptors in the

space-charge region of a silicon p'^n junction (A: n^^/N^; B: n*/N^; C: n^/N^)

8
CRYSTAL DEFECTS AND CONTAMINANTS

figure 2. Referring to figure 3, the charge

I distribution in the space-charge region

(which contracts as the defects discharge)

shown by the solid line is for an intermedij ate temperature where n^ is changing rapid-

[ ly, and the final distribution occurs at

j high temperature where n^ = n^ = n^^.

During the discharging of the defects there

is a reverse current from the space-charge

region which is composed of two parts, namely, the conduction current and the displacement current [11]. For a constant applied

bias during warm up and for uniformly distributed defect centers, the current is

I(p\) = ^ [A^(W - W^)2 + A*(2WW^ - W2)

- e 2WW, - e p 2W(W - W, )] (1) p t D p t b

I' where n = e p - en, n = e p - en, t nt t pt nt

= N - n . p= N - n , t' t f

A *

P'

q is the elect t tronic charge, W is the space charge width,

and A is the junction area. The sum of the

applied and built-in junction voltages is

related to the width of the space-charge region and the charge densities by the

relation

s + (N^ - n^)(w2 - W2)], (2)

where e is the dielectric constant of silis con. These equations are applicable to both

isothermal and dynathermal measurements [8].

Two limiting cases lead to simplified ex- pressions for the current. First consider

that all defects in the space-charge region

are charged; that is, W, = 0. In this case

b a reduced form of eq (1) is

Il(p n)

qAW N

o t

-1/2

e n^ + e p^ n t p t 2N.

(3)

where W = (2e V_/qN,)^/2 g^d the reduced

o s T ^ d current is in inverse seconds. Plots of re- duced current as a function of temperature

for several values of the ratio N,/N , shown

d t in figure 4, demonstrate that the temperature of the current peak is only weakly dependent on this ratio. The small shift

which occurs for small values of the ratio

is related to the contraction of the spacecharge region as the defect centers discharge. When >> , the motion of the

edge of the space-charge region during

discharge is not significant and the current

response is insensitive to the exact value

of the ratio N,/N . Plots of reduced curd t rent for various heating rates, shown in

figure 5, demonstrate that the temperature

of the current peak shifts toward higher

temperatures for faster heating rates. The

heating rate is the most significant parameter to affect the temperature of the current peak.

p'- SILICON n • SILICON WITH ACCEPTOR DEFECTS

Nd-ntf Nd-it

Nd-nti

N,8(0)lINITIAL III INTERMEOIATE

FIN«l |f|

Wb Wf W W|

DISTANCE

Figure 3. Schematic representation of the

distribution of charge throughout the spacecharge region of a p'^n junction during the

discharge of electrons from uniformly distributed acceptor defects.

The second case, which occurs for >> N^,

facilitates study of the effect of charging

the defects only in a portion of the spacecharge region. In this case, one finds from

eq (2) that W = W^, a constant, consistent

with the lack of motion of the edge of the

space-charge region during discharge of the

defects, and that g = (W - W, )/W . With

o b o these substitutions in eq (1) , the reduced

current becomes

l2(P n) -1 * * = i^TT [en (1 - g2) + e p (1 - g)^

qAW N 2N n t p t o t t

+ e^n^g2 + epP^(2g - g^)] (4)

Plots of this reduced current are shown in

9
0.40

CRYSTAL DEFECTS AND CONTAMINANTS 0.4

180 200 220 240 260

TEMPERATURE (K) 280

Figure 4. Calculated reduced thermally

stimulated current, Ij (p'^'n) /qAW N^, from

gold acceptor defects in a silicon p'^'n junction as a function of temperature for 3 = 10 K/s, W, = 0, and several values of the

ratio N^/R^« [See eq (3).]

0

180 200 220 240 260 280

TEMPERATURE |K| Figure 6. Calculated reduced thermally

stimulated current, 1 2 (p"''n) /qAW^N^ , from 1 gold acceptor defects in a silicon p'^n junc

tion as a function of temperature for 6 = 10 K/s, N,/N = 100, a,nd several values of

d t g0.4

0.3

0.2

0.1 -

1 1 1

i

1

- /3 = iOK/s-^/\ i

/ M / /

1 180 200 220 240 260 280

TEMPERATURE (K] Figure 5. Calculated reduced thermally

stimulated current, Ij (p'''n) /qAW N , from

gold acceptor defects in a silicon p'^n junction as a function of temperature for =

0, N,/N = 100, and several values of 3. [See%q^(3).]

240

1.0 HEATING RATE |K/sj

10.0

Figure 7. Emission temperature of the phase

I current response of gold acceptor defects'

in n-type silicon as a function of heating

rate for various conditions. [Calculated:

A: N /N = 5, g = 1; B: N /N = 100, g =

1; C: N 7n = 100, g = 0.8. Experimental:

O: p?''"n junction (Device 2107.1, N. g = 0. 803) ; 2107.7, N /N = 25, g = 0.833).]

d^^t

= n-MOS capacitor (Device

10
CRYSTAL DEFECTS AND CONTAMINANTS

figure 6 for various values of g. The significance of this figure lies in the possibility of confusion when identifying defects

j

I according to the shape of the current reI sponse. One must be aware that this shape

] is intrinsically tied to the value of g. It should be noted that it is not possible in

practice to achieve g = 1 (W^ = 0) for this

requires that junctions be heavily forward

biased. This in turn results in significant

injection of minority carriers and attendant

1 alteration of the initial values of n and

i *

, The results presented in figures 4, 5, and 6 are summarized in figure 7 in which the

emission temperature, the temperature at

; which the peak of the current occurs during warm up, is plotted against heating rate for

several conditions. Experimental values are

also shown for both a gold doped p^n junction (NBS Tech. Note 806, p. 15) and an n-MOS capacitor (NBS Spec. Publ. 400-1, p.

I 17). This model for the current response of

'I a p'^n junction is also applicable to the

! phase I response of an n-MOS capacitor (NBS

' Spec. Publ. 400-1, pp. 16-19) provided that

g 0. A thorough discussion of the n-MOS

capacitor current response will be presented

at a later date.

(W, E. Phillips and M. G. Buehler)

a plot of R^t3/2 against 1/T. Instead it

is necessary to use a two carrier analysis

to fit the Hall effect data as a function of

temperature and arrive at an activation en- ergy based on the fit of the calculated

curves to the experimental data.

The gold donor was studied on wafer 80N1250-

8 which was processed from a 1.1 mm thick

wafer with an initial room temperature re- sistivity of 75 fi'cm. Gold was evaporated

on both sides of the silicon wafer and diffused at 1250°C for 8 h; then both wafer

faces were lapped to a depth of 125 ym to remove excess surface gold before ultrasonically cutting a six-contact bridge-type

specimen [14] for Hall effect and resistivity measurements. After diffusion, the room

temperature resistivity was 1.7 x 10^ fi'cm and the conductivity type had changed from n

to p. A gold density of 1.05 x 10^'' cm'^ was determined by neutron activation analysis on a specimen from the same wafer as the

Hall bar.

The activation energy of the gold donor was

computed from the data shown in figure 8 by means of a least squares analysis [15] for

the slope. The data points included in the

analysis are shown by circles; the points

excluded because of their deviation from

linearity are shown as squares. The calculated energy of 0.3616 ± .0002 eV represents

4.2. Energy Level Model for Gold in Silicon

ji The Hall effect measurement phase of a con-

! tinning effort to obtain parameters for an energy level model for gold in silicon [12]

I, was concluded with the determination of acI tivation energies of the gold donor and gold

[' acceptor from measurements of the Hall coef-

' ficient as a function of temperature on initially phosphorus-doped specimens diffused

with sufficient gold to convert the conductivity type from n to p. Depending on the

I amount of gold added, either the gold donor

Ij level or gold acceptor level will dominate

i [13]. If the gold density greatly exceeds

the phosphorus density, gold-coupled shallow

acceptors are introduced (NBS Tech. Note

788, pp. 18-24) and the gold donor level

dominates. The gold acceptor level domi-

! nates when the gold density exceeds the

phosphorus density by a smaller amount so

I that there is weak p-type conduction. Cont sequent ly the specimens for which the deep

acceptor level can be observed are nearly

: intrinsic and the activation energy cannot

be accurately determined from the slope of

T (K)

ioVt (k"' ] Figure 8. Hall effect activation energy

plot for the gold donor in initially n-type

silicon converted to p-type by diffusion

with gold. (Specimen 80N1250-8.)

11
CRYSTAL DEFECTS AND CONTAMINANTS

the value at zero kelvin of the energy difference between the valence band edge and

the gold donor level with the assumption

that this difference is a linear function of

temperature. The uncertainty in the energy

is the square root of the estimated variance

of the slope and does not take into account

systematic errors which might be present.

The energy difference obtained from this

specimen of initially phosphorus-doped silicon is in excellent agreement with an average activation energy of 0.3617 ± 0.0011 eV

measured previously on four initially borondoped specimens diffused with gold (NBS

Tech. Note 754, pp. 14-15).

In obtaining the above values, the Hall co- efficient, R^, was multiplied by the threehalves power of the absolute temperature, T, to correct for the principal temperature dependence of the density of states. However

the hole effective mass, m^, is also temperature dependent and consequently this affects the values obtained for the activation

energy. To account for the temperature dependence of m^, the quantity R^T^/^ was multiplied by (m^)^/^ using a polynomial equak tion for m^ which was derived previously

(NBS Spec. Publ. 400-4, pp. 15-23). With

this correction a value for the activation

energy of 0.3555 ± .0002 eV was calculated

for the set of points shown in figure 8. The values previously reported for borondoped silicon would also be reduced by the same amount when the temperature dependence

* of m^ is included in the analysis.

A second small correction is required to account for the temperature dependence of the

scattering factor, which relates the Hall

coefficient to the carrier density. If this

factor is assumed to vary as T~°*^^, as re- ported for high purity silicon [16], the

value of the activation energy is further

reduced to 0.3511 ± 0.0002 eV.

The more precise energy level value for the

gold donor from this work is in good agreement with both the early results of Collins

et al. [13] and the more recent data of

Briickner [17]. It is reasonable to conclude

that the activation energy for this level is

well known and a good value is available for use in a model.

The gold acceptor was studied on three

1.1-mm thick wafers with properties listed

in table 1. Except for the time and temper

ature of the gold diffusion, the procedure

followed in preparing these specimens was

the same as that described above. The results of the Hall measurements on these

specimens are plotted in figure 9.

Theoretical curves of R^T^/^ as a function

of reciprocal temperature were generated fo

three values of the gold acceptor level for

each of the three specimens using the

charge-balance equation and a model for the

energy levels in gold-doped silicon as discussed previously (NBS Tech. Note 788, pp.

18-24) but changes were made in the values

of some of the parameters. For the temperature dependence of the energy band gap,

E - E , the electron effective mass, m , c V e and the hole effective mass, m , the polyn nomial fits published earlier (NBS Spec.

Publ. 400-4, pp. 15-23) were used. The lat

tice and impurity mobilities, calculated as given in Tech. Note 788, were combined by

the sine and cosine integral method [18] to

obtain carrier mobility for use in the ex- pression for the Hall coefficient in the

mixed conduction case [19]. The scattering

factor for electrons was taken as 1.2 [20]

while the factor for holes was taken to be

0.87 [21], the temperature dependence of

these quantities was neglected. Based on experimental results as reported above, the

energy of the gold donor with respect to th

valence band was taken as 0.355 eV.

Three values of the energy of the gold ac- ceptor were selected. Two values, 0.58 and

0.60 eV above the valence band edge, were

chosen to correspond approximately with mea

sured slopes of the linear regions of the

plots of R^t3/2 against 1/T. The third

value, 0.535 eV below the conduction band

edge, is based on measurements of the gold

acceptor energy with respect to the conduction band (NBS Spec. Publ. 400-1, p. 19)

corrected for the previously neglected temperature dependence of the electron effective mass. The value for the density, N^,

of each specimen was adjusted to obtain a calculated Hall coefficient which agreed

with the experimental one at room temperature. Since heat treatments, such as those;

employed in the diffusion process, have beef observed to result in significant changes o| resistivity of lightly doped silicon, differences between these values of N^ and thei initial phosphorus density may be due to changes in net dopant density. Although th

12
CRYSTAL DEFECTS AND CONTAMINANTS

Table 1 — Properties of Gold-Doped Silicon Specimens

Specimen Number 2200N950-144 400N950-144 80N1050-72

Initial resistivity, Q-cm 2300 380 75

Initial phosphorous density, cm-3 2.0 x 10^2 i.2 x 10^3 6.3 x 10^3

Diffusion time, hr 144 144 72

Diffusion temperature, °C 950 950 1050

Resistivity after diffusion, fi-cm 6.4 x 10'+ 2.2 x 10^ 1.6 x lo^

Gold density, cm'^ 4.4 x lO^s 2.6 x iQis i.o x iQie

T (K] 400 350 300 250

T (Kl 400 350 300 250

T (K) 400 350 300 250

107T (K

a. Specimen 2200N950-144

Ec - = 0.535 eV, = 0.580 eV, = 1

x 10^

10VT [K-'l

b. Specimen 400N950-144.

A: Ec - = 0.535 eV, =

1 2 X 10^3 cm~3; B: Ea - Ey = c. Specimen 80N1050-72

- Ey = 0.600 eV, =

:se!

::e

:t3.'

4 X I0l2 B; _ = « , 0.580 eV, Njj = 2 X ±0^^ cm-3; 3.5 x lO^^ cm-^. Solid data

C: E^ - Ey = 0.600 eV, = points correspond to negative

1 X I0l2 cm~3. values of Hall coefficient.

... _^ E^ = 0.535 eV, =

4 X I0l3 cm-3; B: E^ - Ey = 0.580 eV, Njj = 3 X 10^3 cm'^;

C: - Ey = 0.600 eV, = 1.25 X 10^* cm-3

Figure 9. Experimental data and theoretical curves for determining the energy level of

the gold acceptor in initially n-type silicon converted to p-type by diffusion with gold,

13
CRYSTAL DEFECTS AND CONTAMINANTS

gold density could have been adjusted to match the calculated and measured Hall coefficients, it was found that the gold density

changes needed to accomplish this were some- what larger than the estimated uncertainty

of the gold density determinations.

The fit of the calculated curve to the ex- perimental data at higher and lower temperatures was examined for different values of

the gold acceptor energy to determine which

value gave the best fit. The data at the

low temperature end, where the resistivity

is very high, were not given much weight in

selecting the best value for the gold acceptor energy. It is thought that surface con- duction or other experimental problems

caused the data points to deviate downward

from the true bulk values. Data from measurements on different days on these and

other high resistivity specimens often

showed shifts where the magnitude of the

change increased as the resistivity increased or as the temperature decreased.

The points plotted for each specimen are the

highest set of values obtained as they are considered to be most representative of the

bulk values. In each case, it is evident

that the experimental results fit the shape

of the curve calculated with the acceptor

level 0.535 eV below the conduction band

edge better than they fit either of the

other two curves. Although it is clear that

fixing the acceptor to the valence band edge

does not give a satisfactory fit, it is possible that allowing the acceptor level to maintain its same relative position in the

forbidden gap as the temperature changed

might give as good or better fits.

Numerous values of the activation energy of

the gold acceptor have been reported in the

literature. Tasch and Sah [22] and Sah et

at. [10] concluded from emission rate data

as a function of temperature that the level

is 0.59 eV above the valence band. Parillo

and Johnson [23], also from emission rate

measurements, concluded that the level is

0.72 ± 0.01 eV above the valence band.

Collins et at. [13] concluded from Hall and

resistivity data that the level is 0.62 ± 0.02 eV above the valence band. Detailed

agreement with the present work depends on

the temperature variation of the acceptor

level with respect to the band edges. To

establish the temperature variation, an improved model for carrier mobility is re- quired so that more accurate fits can be

made to the data near the Hall inversion.

Further analysis of the Hall effect data is

being deferred pending investigation of procedures for calculating electron and hole

mobilities. (W. R. Thurber)

i

It

!

ll

14
5. OXIDE FILM CHARACTERIZATION

5.1. X-Ray Photoelectron Spectroscopy

The angular dependence of x-ray photoelectron spectra (NBS Spec. Publ. 400-4, p. 42) was investigated to study its applicability

to the determination of depth distributions

of surface impurities and thicknesses of

thin surface films. A wide spectral survey

scan of air stabilized silicon (which has a protective oxide coating resulting from room

temperature aging in air) revealed three

significant elements: silicon, oxygen and

carbon. The spectra associated with these

elements are shown in figure 10.

The relative area of each peak as a function

of electron emission angle, 0, is shown in

figure 11. The similar responses of the

lower kinetic energy silicon peak, labeled

Si02» and the oxygen peak supports the association of the SiO? peak with an oxide of

silicon. The smaller carbon peak, labeled

Cj, displays the same behavior and may be

due to carbon bonded to oxygen in the silicon oxide layer. The essentially flat angular dependence of these peaks also suggests

that the oxide layer is thicker than the

electron escape depth. The higher energy

carbon peak, C^^, has maximum intensity for

electron emission parallel to the surface.

This behavior may be expected of a thin

superficial carbon layer. In contrast, the

higher energy silicon peak, which is associated with elemental silicon is largest for

electron emission perpendicular to the surface. This is typical of a substance

covered by a material which attenuates electron emission from below.

These conclusions can be confirmed from an examination of the relative peak magnitudes.

The ratios of the relative areas of the two carbon peaks and the two silicon peaks are drawn in figure 12 as functions of the electron emission angle. This figure emphasizes

the usefulness of angular studies for determining the relative depths of the surface

constituents. In this case, one notes that

the elemental silicon is covered by its

oxide and that carbon appears in two forms

with C^^ exterior to C^.

Earlier, ultralow-pressure oxidation in the

spectrometer vacuum chamber of a silicon

surface cleaned by Ar"*^ bombardment resulted

in the introduction of a carbon film, presumably as silicon carbide, on the specimen.

This experiment was repeated using a silicon

specimen having an exceptionally low carbon

content. The specimen was fixed at a given

angle and heated by an adjacent tantalum

strip through which current was passed. The

current in the tantalum heater was varied

from 0 to 22 A; at 35 A the silicon glows

dull red, corresponding to a temperature of

750°C.

As recorded in figure 13, the area of the

total carbon peak was observed to drop 60

percent over the heating range, while the

oxygen and silicon peaks together increased

by this same amount. The C^^/C^ ratio was

KINETIC ENERGY |eV| KINETIC ENERGY |eV| KINETIC ENERGY leV|

a. Carbon Is. b. Silicon 2p. c. Oxygen Is,

Figure 10. X-ray photoelectron spectra of carbon, silicon, and oxygen from an airstabilized silicon specimen.

15
OXIDE FILM CHARACTERIZATION

i

20 0 20 40 60 80 100

ELECTRON EMISSION ANGLE (degj

TOO

LU 80

<

60

UJ

Q.UJ 40 >

1 20

UJoe 0

T I r

SPECTROMETER

X-RAY SOURCE

. B/'

SPECIMEN

-20 0 20 40 60 80 100

ELECTRON EMISSION ANGLE (deg|

Figure 11. Relative areas of x-ray photoelectron spectral peaks as a function of electron

emission angle. (•: oxygen; : total silicon; : total carbon; : Si; o: Si02;

0: The inset depicts the geometrical arrangement and the electron emission angle, 9.)

0.8 -

-20 0 20 40 60 80 100

ELECTRON EMISSION ANGLE (deg)

Figure 12. Ratios of the relative areas of

the x-ray photoelectron peaks due to carbon

and silicon as a function of electron emission angle. (•: C /C ; o: Si02/Si.)

8 12 16 CURRENT |A)

Figure 13. Relative areas of x-ray photoelectron spectral peaks of cleaned silicon

surface heated in an ultralow pressure of

oxygen as a function of heater current and

ratio of relative areas of the peaks due to carbon. (•: total carbon; O: oxygen;

0: total silicon; : Si; a: SiO?; :

l!

I

^ii/c^.)

16
OXIDE FILM

I also observed to rise. A mass spectrometer

monitored the vacuum chamber gases during

; heating. At low temperatures the primary

! gas constituent was hydrogen, but as the

j temperature was raised the carbon monoxide

! content began to increase. At the highest

j temperatures, the mass spectrum became exj tremely complex.

I The drop in the total carbon photoelectron

signal is interpreted as a loss of this element from the specimen surface. The near

constancy of the elemental silicon to the

SIO? signal ratio indicates that practically

i no additional oxide was formed or removed

i! from the specimen surface. The oxygen inI tensity variation is more puzzling. The

kinetic energies and, correspondingly, the mean free paths for the oxygen electrons are

, less than for the silicon electrons. Therei fore, the removal of a surface contamination

\ layer should have a more pronounced effect

' upon the oxygen photoelectron emission. If all the oxygen were associated with the

Si02, then the oxygen peak should increase

to a greater degree than the silicon peak.

; Since this was not the case, some of the

' oxygen may have been removed with the carbon, which suggests that not all the oxygen

is associated with the silicon dioxide.

The C/0 ratio of the monitored off-gassed

material was in the order of 3:1. This ratio is rather low for typical diffusion pump

oils, which probably suggests that some of

the off-gassed oxygen was present as adsorbed water. At the highest heating cur-

(I rents used, a plateau appears in the silicon

NBS Surface Processes and Catalysis Section, Physical Chemistry Division.

CHARACTERIZATION

and oxygen photoemission intensities.

Whether all the excess (non-Si02) oxygen was

removed is not known, but it does seem clear

that at least some fraction of the oxygencontaining adlayer has been removed.

In view of the above off-gassing data, one might wonder whether the angular distribution of photoelectrons from non-Si02 oxygen

and Si02 silicon should actually track one another as in figure 11. The explanation

may lie with the orientation of the adsorbed

molecules. The oxygen end of the molecule

is certain to be more polar than the hydrogen fraction and probably rests against the

Si02 layer. These two oxygen signals would

then contribute to a single oxygen signal,

similar to that in figure 10b, which would

track the Si02 angular variation.

(N. Erickson", J. T. Yates, Jr.", T. E. Madey", and A. G. Lieberman)

5.2. Comparative Study of Surface Analysis

Techniques

A series of measurements has been initiated

to compare various electron, ion and photon

beam technologies for the determination of

the depth profiles of impurities in silicon

and silicon dioxide. In these preliminary

measurements, specimens of boron and zinc

implanted silicon and of aluminum and sodium

implanted silicon dioxide are being used to provide, in most cases, a reasonably well

known density of impurity at a reasonably

well defined location. The specimens were

selected from materials contributed by various semiconductor processing houses. The

properties of the specimens are summarized

in table 2. For each specimen the implantation angle (measured between the incident

beam and the normal to the specimen surface)

,

Table 2 — Specimens for the Comparative Study of Surface Analysis Techniques

Implanted Ion B Zn Al Na Host Si Si 85 nm Si02 on Si 300 nm SiO- on Si Implantation Angle, deg 0 0 80 0 Implantation Energy, keV 150 30 40 50

Total Dose, cm"^ 2.8 X IQis 5 X 1016 1.7 X 1013 1 X 101"*

Peak Density, cm"^ 1 X 1020 3.5 X 1022 3.1 X 1019

Projected Range, nm 570.6 22.6 7.8

Projected Standard Deviation, nm 113.0 5.7 2.3

17
OXIDE FILM CHARACTERIZATION

the implantation energy, and the total dose were reported by the laboratory which supplied the implants; the peak density was calculated from the work of Mayer et at. [24]; and the projected range and standard

deviation were based on calculations of

Johnson and Gibbons [25].

Samples of these specimens are being subjected to secondary ion mass analysis (SIMS)

[26], low and high energy ion scattering

spectrometry (ISS [27] and RBS [28], re- spectively) , Auger electron spectroscopy

(AES) [29], x-ray photoemission spectroscopy

(XPS or ESCA^) [30] and other techniques in

laboratories associated with instrument

manufacture, semiconductor analysis, or semiconductor device production. The specimens are expected to exercise the capabilities of the various measurement techniques

and to provide illustrations of their different realms of applicability. Some characteristics of the results can be anticipated on the basis of the physical processes

involved.

For detecting boron in a silicon matrix, it

is expected that SIMS will demonstrate certain advantages over other techniques. The

sensitivity of SIMS to small quantities of

material and the virtual impossibility that

a molecular ion having almost the boron mass may form during sputtering together imply

that the density profile of boron in the

boron implanted silicon specimen should be

easily measured, even with a low resolution

SIMS instrument. On the other hand, the low

atomic mass of boron relative to silicon

makes boron a difficult element to detect by

an ion scattering technique at any energy.

In addition, due to the low atomic number of

boron, the cruss-sections for x-ray photoemission and Auger electron emission are both very small, even though the Auger process is considerably more probable than the occurance of x-ray photoemission.

The zinc implanted silicon specimen presents

some interesting challenges to the measurement technologies under consideration. Zinc

has twice the atomic mass of silicon and, in

contrast to boron, should be readily detectable by ion scattering. Zinc, also possesses

a reasonable cross section for XPS and AES

processes. However, while the sputter yield

for SIMS may be high, the enormous peak density of zinc atoms is nearly equal to the

density of silicon atoms in the crystal and severe matrix effects should be anticipated

in the SIMS measurement. Chemical shifts in

the XPS and AES spectra may also arise near

the depth of maximum implantation.

Any measurement technique resulting in localized heating or charging of the sodium implanted silicon dioxide specimen is capable

of displacing the sodium distribution [31]

This is true to varying degrees for all the

techniques being discussed. Furthermore,

the sensitivities of XPS and AES to sodium

are low, and the mass ratio of sodium to silicon or silicon dioxide is unfavorable

for ion scattering to be useful. Channeling

cannot be used to enhance the Rutherford ion

backscattering spectrum because the Si02

film is amorphous.

From the measurements viewpoint, the alumi- num implanted silicon dioxide specimen is

interesting because aluminum neighbors on silicon in the periodic table and interferences may be expected in some cases. For

example, even under optimum conditions the mass resolution M/AM is no better than 30

for ISS measurements [27]. In addition, the

very shallow depth of the aluminum implantation provides a test for the depth resolution of the various techniques.

A trade off exists with respect to the intensity of the analyzing beam and the measurement time for a given signal strength.

By reducing the beam intensity and integrating the signal over a longer period of time,

the presence of elusive elements on a surface can often be detected by less sensitive

techniques. The duration of a measurement

is limited by the degree of sample destruction that can be tolerated during an analysis and by the patience of the investigator.

Thus while the sensitivity of photoemission.

Auger emission and ion scattering techniques

may not be as great as that of SIMS, these

techniques are far less destructive to the

specimen surface and the detection limit can

be enhanced by prolonging the measurement

interval. (A. G. Lieberman)

Rutherford Backscattering Spectrometry

Electron Spectroscopy for Chemical

Analysis

18
6 . TEST PATTERNS

6.1. Test Pattern for Resistivity-Dopant

Density Evaluation

Test pattern NBS-3 was designed primarily

for evaluation of the relationship between

resistivity and dopant density in both n- and p-type silicon. Other purposes include

the evaluation of test structures for use

as process control tools and the development

of new and improved test structures. The

test pattern, shown in the photomicrograph

in figure 14, is composed of various test

structures including MOS capacitors, p-n

junctions, bipolar and MOS transistors, diffused and metal resistors, alignment markers, and etch-control and resolution structures contained in a square silicon chip

200 mils (5.08 mm) on a side. The pattern

requires four mask levels (Base, Emitter,

Contact, Metal) for its fabrication. In addition, there is provision in the design of

the test structures for a fifth (Passivation) mask. As shown in figure 14, the chip

is conposed of an array of 33 test structures. In designing these structures the

following design rules were observed:

1. Minimum stripe width: 0.25 mil

(6. 4 pm)

2. Minimum base to channel stop separation: 0.50 mil (12.7 ym)

3. Minimum emitter to base separation:

0.50 mil (12.7 ym)

4. Minimum contact to base (or emitter) separation: 0.50 mil

(12.7 ym).

5. Metal overlap at contacts:

0.25 mil (6.4 um) [0.50 mil

(12.7 ym) where a passivation layer

is opened].

6. Minimum field plate overlap at diffusions: 0.50 mil (12.7 ym)

7. Minimum metal separation: 0.50 mil

(12.7 ym).

8. Exposed bonding pad width when a passivation layer is used:

4.00 mil (101.6 ym)

9. Minimum passivation overlap at metal: 0.25 mil (6.4 ym)

10. Scribe grid width: 4.00 mil

,(101.6 ym).

11. Expanded metallization contacts:

avoided where possible by extending diffusions under contacts.

12. Top side contacts: provided whenever possible.

13. The lines on each mask level:

uniquely located so that they do

not coincide with the lines on another mask level.

These rules were chosen to minimize problems

encountered in bonding, probing, mask alignment, and pinhole shorting. For instance,

a misalignment of ± 0.25 mil (6.4 ym) between either the Contact or Metal mask and

the Diffusion mask is tolerable. Eliminating expanded metal contacts reduces shorting

problems associated with expanded metal contacts. Unique location of lines on each

mask level simplifies inspection procedures.

These design rules eliminate certain fabrication faults and thereby improve the

chances that a test structure will function

properly.

The test structures shown in figure 14 are listed in table 3. Most of these structures

are adaptations of commonly used configurations. Some of the structures on test pattern NBS-2 (NBS Tech. Note 788, pp. 15-17)

[32] were included in the present pattern.

It should be noted that the Hall effect device (26) is functional only after it has

been scribed from the wafer. To accomodate

this device, the scribe grid was omitted

from the Base and Emitter masks and included

on only the Contact mask. Special care must

be taken when scribing to assure proper chip

separation.

The devices specifically designed for the

resistivity-dopant density evaluation are indicated by an asterisk in table 3. Bulk

dopant density values can be found from the

following structures: MOS capacitor over collector (8) , base-collector diode (10)

,

and Hall effect device (26). In obtaining

values, difficulties can be encountered with

the MOS capacitor (8) in that it measures

at the surface of the silicon where the dopant density may be altered by the oxidation

process. Values obtained from the Hall effect device (26) rely on a knowledge of the

scattering factor which is not well established. The best chance for obtaining unam- biguous values appears to lie with the basecollector diode (10)

Bulk resistivity values can be found from

the collector resistors (1, 7, 12, 17, and

18) and the Hall effect device (26). Collector resistors (1, 7, 12, and 18) are intended

19
TEST PATTERNS

32B 32C 32M

Figure 14. Test pattern, NBS-3, for characterizing the resistivity-dopant density relatioti' in silicon. (The 33 test structures are identified in table 3. The overall pattern is '< 200 mils (5.08 mm) on a side.)

to operate with current passing from the top

of the chip to the backside contact. In this mode, backside contact resistance and

geometrical factors must be determined.

Collector resistors (12) and (18) are ex- pected to yield information about the backside contact resistance, and collector resistor (7) was designed to have a readily

calculable geometrical factor. The collector four-probe resistor (17) is a conceptually simple structure but it is difficult to

fabricate; it is expected to yield reliable

values provided that it can be satisfactorily fabricated. The Hall effect device (26) can yield reliable values but, as noted

above, cannot be used on an unscrilSed wafer.

Resistivity and dopant density values can b^ obtained from base profiles by combining the results of two test structures. The base

dopant density profile can be obtained from

the emitter-base diode (9) , and the base

20
TEST PATTERNS

Table 3 — Planar Test Structures on Test Pattern NBS-3

Test Important Mask

^ Number Structure^ Dimension, mil (mm)

1 * Collector resistor (FP, CS) D = 17 (0.43)

2 MOS capacitor over base D = 15 (0.38)

3 MOS capacitor over emitter D = 15 (0.38)

4 Alignment marker

5 Logo

6 * Tetrode transistor D = 23.5 (0.60)

7 * Collector resistor (DGR) D = 15 (0.38)

8 * MOS capacitor over collector D = 15 (0.38)

9 * Emitter-base diode (FP, CS) D = 17 (0.43)

10 * Base-collector diode (FP, CS) D = 17 (0.43)

n Base sheet resistor (VDP, FP, CS) D = 17 (0.43)

12 * Collector spreading resistor D = 5 (0.13)

13 Bipolar transistor D = 5.5 (0.14)

14 Base-collector diode (FP, CS) D = 5 (0.13)

15 MOSFET (circular, W/L = 18.2) L = 3.5 (0.089)

16 MOSFET (W/L =4) L = 0.5 (0.013)

17 * Collector four-probe resistor S = 2.25 (0.057)

18 * Collector spreading resistor D = 15 (0.38)

19 MOS capacitor over collector D = 15 (0.38)

20 Metal sheet resistor S = 1.5 (0.038)

21 Emitter sheet resistor (VDP) S = 1.5 (0.038)

22 Base sheet resistor (VDP) S = 1.5 (0.038)

23 Metal-to-emitter contact resistor S = 1.0 (0.025)

24 Metal-to-base contact resistor S = 1.0 (0.025)

25 MOS capacitor over collector S = 4 (0.10)

26 Hall effect device S = 100 (2.54)

27 Emitter sheet resistor (B, W/L = 0.25) L = 6 (0.15)

28 Base sheet resistor (B, W/L = 0.25) L = 6 (0.15)

29 Surface profile structure

30 Incremental base sheet resistor (VDP) D = 30 (0.76)

31 Etch-control structures^

32 Resolution structures^

33 Metal step-coverage resistor

B = bridge, CS = channel stop; DGR = diffused guard ring; FP - field plate;

L = length along current path; VDP = van der Pauw, W = width of current path;

* = structures designed for resistivity-dopant density evaluation.

D = diameter; L = length along current path; S = side of a square.

B = base mask; C = collector mask, E = emitter mask; M = metal mask.

21
TEST PATTERNS

resistivity profile can be obtained from the

tetrode transistor (6) . Use of these structures should allow one to establish resistivity values continuously over several decades in dopant density.

Many of the remaining test structures are in

support of the above described devices.

They are intended to assure that proper fabrication steps have been followed and to aid

in diagnosing problems. (M. G. Buehler)

6.2. Charge-Coupled Device Test Pattern

This study was undertaken to investigate the

applicability of the charge-coupled device

(CCD) as a test structure for use in semiconductor process control. Prior to using

the CCD as a process control tool, the parameters measured from the CCD must be cor- related with those measured on other better

known devices such as MOS capacitors and MOS

transistors. The initial phase of the electrical evaluation has begun with the operation of the CCD in three modes: (1) as an MOS capacitor; (2) as an MOS transistor; and

(3) in the charge transfer mode.

Various simplified views of the particular

linear CCD structures used in this study are shown in figure 15 with typical input and

output stages. The circular CCD's have a slightly different configuration; the input

and output stages are rotated 90 deg and are located on opposite sides of the circle.

The test structures were fabricated on 1.5

to 3 ohm-cm p-type silicon wafers with (100)

surfaces. The test pattern and the various

test structures have been listed previously

(NBS Spec. Publ. 400-8, pp. 26-27). The

interelectrode gap for the CCD structures is

0.1 mil (2.5 ym) and the net gate area of

each electrode is 0.36 mil^ (232 ym^) . The

"phase three" electrodes (V^.) are connected

by an aluminum interconnection, and the

"phase one" (V,J and "phase two" (V,^)

<pl

_^

(j)2 electrodes are connected by n diffused interconnections. The field oxide is about

1000 nm thick and is located outside the

contact and gate regions.

The MOS C-V characteristics for 32-bit circular CCD (device 2 on the CCD test pattern)

are compared to those for the MOS capacitor

(device 20) in figure 16. These characteristics were measured in the dark, at room

temperature, with a 1-MHz, 15-mV(rms) signal. An analysis of the MOS capacitor data

yields a flat-band voltage V^^^ = -1.05 V, a work function difference A = -0.90 V, an

ms acceptor substrate dopant density N = 2.2 x

Vid

Vsub •0

|-*-«0.5 mil 113/im)

m p+ CHANNEL STOP

^ n"^ SOURCE/DRAIN/INTERCONNECT

13 CONTACT

METAL

Figure 15. A topographic view and

cross section of an n-channel, threephase, aluminum-gate CCD.

22
TEST PATTERNS

10^^ cin~^, a gate oxide thickness X =

o 116 nm, and a surface charge density com- posed of fixed oxide charge density, Q ^,

and fast interface charge density, N , , of

FS Qss ^^FS- = 2.7 X 10 10 cm-2, The slight

distortion observed in the C—V curve near inversion is attributed to fast interface

states with charge density of about

IQlO cin-2.

The MOS C-V characteristics were obtained

from the circular CCD by treating the phase

three electrodes as the gate while grounding

the phase one and phase two electrodes.

This effectively eliminates the interelectrode capacitances (between the phase three

and the phase one or phase two metallization) , the phase three cross-over capacitances (between the phase three metallization and the n" interconnections under

thick, field oxide), and the junction capacitances (between the interconnects and

the p substrate) from the measurement, but

the capacitances between the phase three

metallization and the channel stop under

the thin, gate oxide, the p^ channel stop

under the thick field oxide, and the psubstrate under the thick, field oxide re- main in parallel with the phase three gate

capacitance. In the inversion region, these

parallel capacitances add to the phase three

gate capacitance, as is evident in the CCD

inversion characteristics shown in figure

16. More comprehensive analysis is planned

for the coming quarter in order to extract

the physical parameters.

The 32-bit circular CCD was given a bias

temperature stress test at 250°C for 15 min

with a field of 10^ V/cm applied across the

phase electrodes. Under these conditions

the room temperature C-V curves did not

shift more than 0.05 V which indicates that

this device is reasonably free of mobile ion

contaminants (density <. lO^'' cm"^) .

MOS transistor characteristics as measured

on the 32-bit circular CCD agree quantitatively with those for the MOS transistor

(device 28). The latter device was measured

in both the linear and saturation regions.

For V << (V - V ) in the linear region,

the drain current, 1^^, is [33]

/p e \ W

I = ( - (V - V ) V , D \ X ) L G T-^ D'

where W is the channel width, L Is the channel length, y is the channel electron mon bility, is the dielectric constant of the

oxide, X is the oxide thickness, is the

o ' G

gate voltage, is the threshold voltage.

and Vj^ is the drain voltage. The channel

conductance gj^, determined as V^^ approaches

zero, is

91

^D

= 8V n o' V=const

L <^G (5)

In the saturation region, if is much less

than 1 V (where = X ^ (e q N ) /e ^ q is

o s a o the electronic charge, is the dielectric

constant of silicon, and is the acceptor

dopant density) , the drain current is

'y e 1 n o D sat 2L (^G - ^T'>'' (6)

In the analysis of the MOS transistor, X

o was taken as 116 nm from the measurements on device 20. Rather than assuming the nominal

value of W/L (= 1) , a value of W/L =1.56

was obtained from a conducting-paper analog

of the device taking into account both

fringe currents and channel narrowing due to the source and drain lateral diffusion. For

this device, is about 0.41 V. From the

intercept and slope of a plot of g^ as a function of V [eq (5)], it was found that

G

= 0.20 V and y^ = 1070 cm^/V-s. From the

intercept and slope of a plot of /l^ as

a function of V [eq (6)], it was found that

V^, = 0.17 V and y^ = 1040 cm^/V-s. These

values are in agreement with those given

elsewhere [34] if boron redistribution during oxide growth is taken into account.

The MOS transistor characteristics for the

32-bit circular CCD were obtained by treating the input diode, V^^, as a drain; the

input gate, V^^, as a gate; and the three

phase electrodes, the output gate, V^g» ^'^'^

the preset gate, V , (heavily inverted at ps + 40 V) as the source which was accessed

23
TEST PATTERNS

1.0

0.8

^0.6

u

hO.4

I

0.2 -

°3

^

1

'

-— Wa\ "

-—

1 1 1 L 1

1 -2 -1 0

GATE VOLTAGE [Vj

+1

Figure 16. High-frequency capacitancevoltage characteristics of a p-MOS

capacitor (Cq = 60.3 pF) (A) and an n- channel, 32-bit CCD connected as an MOS

capacitor (B) . (The flat band capacitance, C fb' is 0.79 C ). o

</? 10.0

eaCO

0.1

NFs=2.3x10'°(cm%V)"l

0 5 10 15 20x|0-<

FRACTIONAL LOSS PER TRANSFER

Figure 18. Fractional charge loss per

transfer from a "one" preceded by ^zero

zeros and transferred 336 times around a 32-bit circular CCD operating at 125 kHz.

(The slope yields Npg, and the intercept

yields F; see eq (7).)

NUMBER OF TRANSFERS NUMBER OF TRANSFERS

Figure 17. Pulse height of a "one"

preceded by 9 zeros as a function of

the number of transfers around a 32-bit

circular CCD operating at 125 kHz.

(The intercept yields Pq, the unattenuated pulse height.)

Figure 19. Fractional charge loss

from a "one" preceded by N^gy^ zeros as

a function of the number of transfers

around a 32-bit circular CCD operating

at 125 kHz.

24
TEST PATTERNS

through the terminal, V ^. Note that in ref

the circular CCD there are two parallel

paths between source and drain. In this

I mode of operation the source acts as part of

I the channel with W/L = 0.034. In the linear

region = 0.34 V and = 1140 (cm^/Vs)

and in the saturation region V^, = 0.25 V

and y = 520 (cm^/V-s). In the linear ren gion the mobility is in agreement with the

values found for the MOS transistor. In the

saturation region the decrease in mobility

is consistent with the reduction in mobility

with increased electric field in the

' channel.

The 32-bit circular CCD was operated in a charge transfer mode in order to measure the

fast interface state density per unit energy, N , by the double-pulse method [35].

I Typically potentials on the three phase

j electrodes were varied between 0 V and +15 V

1 with respect to a grounded substrate at a

I frequency of 125 kHz. The input and output

J gates were held at +15 V when injecting or

i extracting charge from the channel; otherwise they were held at zero bias. In addij tion, the input diode was slightly forward

i biased with respect to the input gate when

the latter was at + 15 V, V ^ = + 15 V, and

ref

1 V = + 17 V. Using the double-pulse methps

od, a pair of "ones" followed by N zeros

' zero followed by a second pair of "ones" were

circulated around the CCD accumulating

tran

transfers. As N increased, the pulse

tran

height P of the first "one" in the second

I pair of "ones" is attenuated as shown in

j figure 17 where the unattenuated pulse

height, Pq, is found from the intercept,

i The fractional charge loss per transfer, a,

I is given by

a = (Po - P)/(Po X \^^^).

This quantity is related to the fast state

density per unit energy, N^g, by [35]

In N = (N . /kTN^^) a + In F (7) zero sig FS

where k is Boltzmann's constant (eV/k) , T is the temperature (K) , N^^^ is the unattenuated signal charge density (cm~^) , and F is

the fraction of time available from each

period during which charge can be transferred. This fraction can be determined

graphically as shown in figure 18. For the

three-phase CCD used here one would anticipate F ~ 1/3. The value determined experimentally, F = 0.29, is not unreasonable;

the exact value depends on the details of

the phase voltage rise and fall times and

the interelectrode gap fringing fields. The

value = 1.2 x iQlO (cm^-eV)"! follows

r o from the slope of the plot in figure 18;

this value was calculated for room temperature, kT = 0.025 eV, and N . = 5 x

' sig

10^^ cm~^ as derived from the electrical

characteristics of the output inverter

stage.

The power of the circular CCD configuration

is illustrated in figure 19 where the data

from figures 17 and 18 are rep lotted. The

circular CCD allows the accumulation of a very large number of transfers which allows

the pulses to decay to detectable levels.

In a linear CCD, the number of transfers is

fixed by the number of bits and cannot be

changed. In addition, the double-pulse

method establishes a number for N^g which is more difficult to obtain from high-frequency

MOS C-V characteristics.

(I. Lagnado''" and M. G. Buehler)

t

The factor F is not explicitly included in

reference [35] but is implicit in the

derivation

Naval Electronics Laboratory Center, San

Diego, California 92152.

25
7 . EP I TAX I AL LAYER THICKNESS

7.1. Cleave-and-Stain Measurements

An attempt was made to stain the regions of

the five specimens which had been anglelapped and probed by a spreading resistance

probe as reported previously (NBS Spec.

Publ. 400-8, pp. 32-33). By observing the

stain, a measurement [36] was to be made of

epitaxial thickness on each of the five

slices. It was found, however, that the

bevel angle, rather than having a welldefined apex, was rounded owing to preferential polishing at the apex during angle lapping. This would have caused the spreading

resistance measurement and the lap-and-stain

measurement, had it been made, to give erroneously large values of epitaxial thickness.

An alternative approach was taken. The segment from each slice on which spreading re- sistance and step relaxation measurements

had been made was cleaved at a 90 deg angle,

stained, and photographed using a scanning

electron microscope (SEM) . The epitaxial

thickness was then determined from the SEM

photographs. The results of these measurements together with previously reported

thickness determinations on these wafer segments are given in table 4. Although the

cleave-and-stain measurements appear to be

in somewhat better agreement with the stepHi-Rel Laboratories, San Marino, California 21108.

Table 4 — Epitaxial Layer

Thickness by Three Methods

Layer Thickness, ym

Wafer Step- Spreading Cleave-andNo. Relaxation Resistance Stain Method

Method Method

2302 2 80 3.3 2 72

2351 1 49 4.6 2 55

2352 1 47 —a 2 6 2203 5 03 6.6 6 3 2204 5 17 5.4 4 6

The constant level of spreading resistance

characterizing the substrate was not

reached abruptly in this wafer making the

thickness determination obscure.

relaxation measurements than the spreading

resistance measurements, the agreement is

still only fair.

(J. R. Devaney" and R. L. Mattis) '

7.2. Metal -Photoresi st-Semi conductor

Capacitors

In order to apply the principles of the MOS

capacitance methods (NBS Spec. Publ. 400-4,

pp. 51-53) for epitaxial thickness measurement in a manner that is non-destructive and

involves no high temperature processes and

resultant impurity redistribution such as occurs during thermal oxidation, an effort

was directed toward the use of photoresist

as the dielectric in place of the oxide and,

further, toward use of a photolithographed

metal pattern which would provide a known

and uniform device area. The specimen preparation which has been developed involves

(1) spin-on application of negative photoresist to a clean epitaxial wafer, (2) bake

to form a dielectric layer 0.3 to 0.7 ym

thick, (3) evaporation of aluminum over the

dielectric layer, (4) spin-on application of

positive photoresist, (5) bake of the positive photoresist and its subsequent exposure

through the metal mask of test pattern NBS-3

(see sec. 6.1.), (6) development of the

positive photoresist, and (7) etching away

the aluminum which is not a part of the desired metal pattern. The result is an array

of metal dots which form metal-photoresistsemiconductor [M(PR)S] capacitors analogous

to the MOS capacitors which employ oxide as the dielectric. Epitaxial specimen 2213 was prepared by the above process and the transient capacitance characteristics of five

M(PR)S capacitors along a slice diameter were recorded. The resulting values of

layer thickness ranged from 5.24 to 6.04 ym.

These values are consistent with the layer

thicknesses of other epitaxial wafers from

the same lot (see wafers 2203 and 2204 in

table 4)

Improvements are still needed in the processing by which M(PR)S specimens are prepared in order to obtain thinner and more

reproducible dielectric layers, but the feasibility of using such structures for thickness measurement has been demonstrated.

(J. Krawczyk and R. L. Mattis)

26
8. WA.FER INSPECTION AND TEST

8.1. Flying-Spot Scanner Development

Several additions were made to the optical

flying-spot scanner in order to extend its

usefulness. A superheterodjrne receiver was

added to allow one to obtain the scanned re- sponse of structures to 0.633 pm light modulated at 385 and 770 MHz, mode-beat frequencies internally generated within the particular laser used. The scanner has been operated also with 1.15 ym light; operation can

be shifted from 0.633 ym to 1.15 ym and back

by changing the laser mirrors . The control

chassis, incorporating wide-band dc coupled

circuits for signal processing and blanking

and deflection circuits, was completed.

The scanner was used to view several devices

which had been scanned in the electron beam

induced current (EBIC) mode with a scanning

electron microscope (SEM) . These devices,

obtained from an industry source, were arrays of nine silicon p-n junction diodes,

each 0.76 mm (30 mils) on a side. The junction depths were 0.5 ym and all diodes in an array shared a common 1 to 3 Q'cm n-type

substrate about 0. 25 mm thick bonded to a gold-plated header. For the tests, only one

of the nine diodes was electrically connected to the header leads. For the array which

will be discussed the central diode was the one connected.

The SEM EBIC scan for the device without applied bias and the corresponding zero-bias

video (unmodulated) 0.633 ym response are shown in figure 20. The SEM was operated

with an electron beam current of 2 nA and an accelerating voltage of 30 kV. It appears

that most, if not all, of the features seen with the SEM can also be seen with the optical scanner. Presumably, the lines are striations in the silicon and the dark spots

are swirls [37]

With the diode bias increased to yield a dark current of 1 or 2 yA, discrete spots of

enhanced photoresponse to the unmodulated

0.633 ym light could be seen at the junction

periphery. The spots, which increased in

brightness as the diode bias was further

raised, are regions where the junction field

at the surface is large enough to cause electrical breakdown with concomitant multiplication of the photoinduced charge carriers. However, observation of the 385- and

770-MHz 0.633 ym photoresponse with the

junction voltage raised to produce currents more than twenty times larger showed no such

discrete photoresponse, or enhancement, at

the periphery. Since ionic processes would

not be expected to follow 385 MHz modulation, it is likely that the surface breakdown was ionic, rather than electronic, in

nature.

Figure 20. Electron beam induced current response (a) and unmodulated 0.633-ym laser beam

induced current response (b) of a 0.76-mm square, unbiased, silicon p-n junction diode.

(Scanning electron micrograph, EBIC mode, by K. 0. Leedy.)

27
WAFER INSPECTION AND TEST

When the detected modulating frequency was

changed from 385 to 770 MHz, the optical

photoresponse shrank and fell off more rapidly with distance from the connected bonding pad. This is because p-n junctions with

contact areas less than junction areas lose

their lumped R-C nature and increasingly become distributed networks as the signal frequency is raised. Applied to the present

case, this has the consequence that the signal from charge carriers photogenerated and

collected by the junction beyond the contact area is increasingly attenuated with distance from the contact. With the total

junction capacitance known from independent

low-frequency measurements, it should be

possible to determ.ine the sheet resistance,

and perhaps local variations in the sheet

resistance, of the p-diffused skin by interpreting the spatial and frequency dependence

of the scanning photoresponse.

The response of the device to 1.15 pm light

is quite different from the 0.633 \im response. Almost all of the response features were different, except of course for the

shadows of the pads and lead wire. Although

only the central diode of the array was electrically connected, the lead wire could

be followed across the entire die by observing its shadow; even portions of the die not

connected electrically yielded an apparent

photoresponse. The shadows of the bonding

pads on the other eight array diodes were

also seen, and the die portions not covered

by pads showed structure. It is likely that

these phenomena are due to internal reflection within the silicon die and that the

structure observed is due to irregularities

in the die bond. Preliminary observations

on a device with a known die bond void tend

to confirm this hypothesis.

(D. E. Sawyer and D. W. Berning)

8.2. Automated Scanning Low Energy Electron

Probe

The scanning low energy electron probe

(SLEEP) [38] is an electron beam probing

technique in which an electron beam is first

accelerated (to provide beam definition) and

then decelerated by a grid placed in front

of the specimen to be probed. The SLEEP

technique is inherently simple, involving a low energy (800 to 900 V) gun structure and

Naval Research Laboratory, Washington,

D. C. 20375.

a standard vidicon electromagnetic beam focusing and deflection system. The specimen

under investigation is scanned by the electron beam in the retarding field region.

Only those electrons are collected whose

energies are sufficient to overcome the local potential barrier at the specimen surface. This collected current is measured

in the specimen-cathode circuit. Similarly,

electrons with insufficient energy to overcome the local surface potential are re- flected from the specimen and may be collected to form the mirror-mode operation.

Thus, either the directly collected currertt or reflected current provides a surface potential map of the specimen. In the current program, which is intended to develop

an automated SLEEP as a versatile diagnostic

tool for determination of semiconductor resistivity, defect density, and oxide uniformity as well as a means to test complex

integrated circuits, only the collectedcurrent mode is being investigated. A

single crystal target, adjacent to the specimen under test, is used to provide absolute

voltage measurements.

SLEEP can be used on-line for separate or combined measurements of wafer resistivity,

wafer surface defect density, uniformity of

the ratio of dielectric constant to thickness for oxide films, and for programmable

"contactless" production oriented, functional testing and exercising of complicated

LSI. Since the specimen is at, or near,

ground potential, SLEEP provides significant

advantages over a standard mirror microscope. In the latter use, the specimen must

be at, or near, the cathode potential up to 20 kV below ground. Similarly, the ionization damage due to soft x-rays in high voltage systems is not a major problem with

SLEEP. The SLEEP technique can also be used

in an off-line mode in which it may be interfaced with other complementary diagnostic

techniques.

Initial efforts have concentrated on the design of the electron gun and acquisition of

the computer control system. The design of

the gun is similar to that of a commercial

vidicon tube. The electrons from the cathode are accelerated by the grids and directed onto a cap at one end of the drift tube

where the beam size is defined by an aperture 8 ym in diameter. The specimen being

probed is mounted 2 mm from the other end

of the drift tube and the aperture is imaged

on the surface of the specimen by magnetic

focus and deflection as in a standard

vidicon. (W. C. Jenkins* and G. P. Nelson*)

28
|| 9 . I N T E R C 0 N N

! 9.1. In-Process Bond Monitor

Further experimental verification was undertaken of the uniform beam model for the

ultrasonic bonding tool (NBS Spec. Publ.

400-8, pp. 37-39) in order to determine more accurately the value of the physical constant q at 60 kHz for both tungsten carbide

and tantalum carbide. Bonding tools of each

material were mounted in Inverted positions

in a transducer horn. The length of the inverted. tools was set at three different values below the transducer horn and the vibrational amplitude along the tool was measured

by means of a capacitor microphone. The am- plitude data were then normalized in terms

of the amplitude of vibration at the transj ducer horn. Further, the distance along the

' tool was written in terms of the fractional

length along the tool. These normalized

'! data were then compared with the previously

determined theoretical result.

Since the capacitor microphone picks up

i sound waves emitted over a finite distance

\ along the length of the Inverted tool and

! since the microphone cannot probe the tool

in the neighborhood of the transducer horn,

I there are small errors in: 1) the exact

length, £, of the Inverted tool below the

horn, 2) the vibrational amplitude at the

tip of the tool, and 3) the vibrational am- plitude, a, of the inverted tool at the

transducer horn. The small errors in the

j determination of a and I give rise to small

I errors in both the normalized vibration amC T I 0 N B 0 N D I N n

plitude, Y(N), and the fractional length

along the tool, N.

Another difficulty which was encountered

during the course of these experiments arose from the presence of torsional modes of vibration. For a uniformly clamped beam, the

effects of torsional motion would be negligible. However, for a beam held in the

transducer horn by means of a screw clamp,

these modes may be of more significance.

Although torsional modes have been observed

to be negligible when the tools are mounted

with the design extension in the normal con- figuration, torsional modes of significant

amplitude were found in most of the inverted

configurations studied. The presence of

these modes, which could be observed by

sweeping the capacitor microphone across the

vibrating tool, severely hampered the interpretation of the data according to the previous theoretical analysis which obtains for

only transverse modes. Only those data

taken on the one length for each tool material composition which showed little presence of torsional modes were compared with

the theory. Furthermore, in light of these

difficulties, the comparisons of the experimental and theoretical results were based on

the location of the tool nodes.

The results of these comparisons are presented in figure 21. For each tool, the

value of q£ which resulted in the best

agreement was determined and combined with

i to calculate q, listed in table 5. These

0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 N

a. Tungsten carbide tool with

0.488 in. (12.40 mm) extension. Solid

curve: measured; dashed curve: calculated for a uniform beam for which

qi = 5.4.

1.2

1.0

0.8 ^0.6

0.4

0.2

0

- 1 1 1 1 1 1 1 1 1

+ \\ // // - N> ij- \ \ - \ A \ \ /' \ A

\ / A /

A / V // \i V /

\ll

1 1 iW 1 1

1 1 1 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0

b. Titanium carbide tool with

0.579 in. (14.71 mm) extension. Solid

curve: measured, dashed curve: calculated for a uniform beam for which

qS, = 5.8.

Figure 21. Measured and calculated normalized vibration amplitudes of ultrasonic bonding

tools mounted in Inverted positions.

29
Table 5

INTERCONNECTION BONDING — Bonding Tool Material Properties i

Material Length (mm) q£ q (mm"^)

Tungsten carbide 12,40 5.4 0.44

Titanium carbide 14.71 5.8 0.39

values of q are somewhat larger than previously reported for the conventionally mounted tools but maintain the same trends (NBS

Spec. Publ. 400-8, table 7). Because the

tool as mounted in the inverted position has

a uniform cross section, the present values

of q are expected to be more accurate than

those previously reported. (J. H. Albers)

9.2. Beam-Lead Bonding Force Measurement

The bonding force is a critical parameter

in beam-lead bonding. Changes in bonding

force can markedly affect the strength and

integrity of the beam lead bonds. In order

to determine the bonding force with most

conventionally designed beam-lead bonding

machines such as the one pictured in figure

22, a calibration curve must be prepared.

In this procedure, the measured force at the

bonding head is plotted against the reading

of a dial setting (A) . It should be noted

that the dial setting is not a direct reading of the bonding force as the mechanism

used is not that of a force gauge.

In attempting to calibrate the force mechanism while setting up a beam-lead bonder,

several problems were encountered with the

bonding force assembly as supplied by the

manufacturer. First, a non-linear relation

was found between the measured bonding force

and the dial setting. Second, the bonding

force could not be adjusted in the range below about 500 gf (4.9 N) because of mechanical inertia of the spring (B) in the force

adjusting assembly. Within this range only

a single force of about 130 -gf (1.3 N)

,

which corresponds to the sum of the weight

of the bonding tripod assembly and the tension of the tripod spring, could be applied.

Third, for the range where the force could

be calibrated it was found that differences

in substrate heights change the force calibration so that an individual calibration

must be performed for each substrate height.

Fourth, any change in the tension of the

spring in the force adjusting assembly is

not reflected in the dial setting and,

hence, any such changes and the subsequent

bond force changes would go unnoticed. Such

problems appear to be common to most wobbletool beam-lead bonding machines.

In light of the above, a modified force as- sembly was developed to give a linear bonding force read out and hence eliminate these

problems. This assembly is shown in figure

23. When the bonding tool (K) is lowered to contact with the beam-lead device (L) , the

uppermost rod (F) of the tripod assembly (H)

presses against the lever arm (D) . As the

distance between this point of contact and

the pivot point (E) is the same as that of

the between the pivot point and the compensating spring (C), the force due to the tension of the compensating spring (which is

A Bonding force indicator dial

B Bonding force spring

Figure 22. Beam-lead force indicator

as supplied with the beam-lead bonder.

30
INTERCONNECTION BONDING

a. Front view.

b. Schematic diagram.

A Force gauge holder

B Lever arm of force gauge

C Force compensating spring

D Lever arm

E Pivot

F Rod

G Tripod spring

H Tripod

J Heater

K Bonding tool

L Beam- lead device

M Substrate holder

N Bonder base

P Bonding position

Q Reset position

Figure 23. Modified beam-lead force gauge

assembly

directly read f rom the force gage) is added

to the weight of the tripod assembly (H) and

the tension of the tripod spring (J) to give

the total bonding force. These latter con- tributions to the force may be measured by

disconnecting the compensating spring (C)

from the lever arm (D) and then lifting the

tripod assembly (H) from below at the tip of

the bonding tool (K) with a force gauge until the rod (F) makes contact with the lever arm (D) . The force gauge reading at this

point is the weight of the tripod assembly

plus the tension of the tripod spring. The

compensating spring is then reinstalled on

the lever arm.

The contribution to the force arising from

the compensating spring may be varied by

loosening the force gage holder (A) from the

rod assembly and then raising the force gage

mounting to increase the force or lowering

the force gage mounting to decrease the

force. The range of the gage may be extended by a factor of 2 or 4 by mounting the

compensating spring at position 2 or A located a distance of 1/2 or 1/4 the length

of the lever arm of the force gage (B) . To obtain an accurate reading on the force

gage, its lever arm (B) must be adjusted so that it is perpendicular to the rod (F)

This is accomplished by pivoting the force

gage holder (A)

It should be noted that this remedy of the

beam-lead bonding force measurement problem

can be used for all wobble-tool beam-lead

bonders, but that the implementation of this

technique for a particular beam-lead bonding

machine depends upon the details of the design of the machine.

(H. K. Kessler and J. H. Albers

)

9.3. Non-Destructive Test for Beam-Lead

Bonds

When bonds between metals, ceramics, plastics, etc. are broken, a white acoustic

noise spectrum is emitted which contains

frequency components extending into the

megahertz range. In recent studies, such

acoustic emissions have been observed from

the break up of sea ice [39], broken epoxy

bonds [40], and damaged ceramic hybrid substrates [41]. A study was initiated to utilize this phenomenon as a non-destructive

test to reveal one or several poorly welded

beams in a bonded multibeam device.

The object of the experiment was to stress

the device mechanically in such a way that
INTERCONNECTION BONDING

a force of 10 mN (1 gf) or more was applied

to each of the beams in the peel direction

by pushing the die downward with sufficient

force. The block diagram of the system used

for this purpose is shown in figure 24.

Two test series have been carried out thus

far. The first was a feasibility test in

which 10 to 20 beam-leaded devices were

stressed by pushing, probing, and pulling.

Individual beams were peeled back and acoustic emission noise counts were taken. It was determined that the acoustic emission

apparatus had sufficient sensitivity to detect the breaking or peeling of a single

bonded beam and that the probing system did

not itself produce any measurable acoustic

emission.

The second test series was conducted on 72,

14-beam devices which, except for 10 wellbonded control devices, had one or two of

their beams bonded to areas rendered intentionally defective. These defective or contaminated areas included thinned substrate metallization, oxidized surface

layers of chromium, graphite on the surface,

or a fluorocarbon grease-stop on the gold

bonding pads.

The output of the sensing equipment was read

as noise counts. The background was typically only three to five counts. The wellbonded control devices either gave no signal

above background or a burst of 10 to 20

counts at the point of complete beam collapse. For these particular devices this

typically occurred when a force of about 450

to 550 mN (45 to 55 gf) was applied to the

device. The majority of those devices with

one or more beams bonded onto defective substrates produced a series of two to five

acoustic bursts in the 20 to 40 count range

with some bursts as high as 100 counts. For

the most weakly bonded beams , such noise

counts appeared at an applied force of about

100 mN (10 gf), the minimum force available

from the test apparatus. Surprisingly the

devices bonded over the fluorocarbon greasestop gave little or no noise counts with applied force. Later examination revealed

FORCE

EMISSION DETECTOR

LOW NOISE PREAMPLIFIER

AMPLIFIER AND

A TO D CONVERTER

DIGITAL COUNTER

RECORDER

Figure 24. Block diagram of acoustic

emission test system.

that these beams were well bonded despite

the contamination. One other device that was thought to be well bonded nevertheless

gave several high noise counts (about 27 to

30 counts) with an applied force in the

range 100 to 200 mN (10 to 20 gf ) . In this

case post-mortem examination revealed that

the beam anchors on the device were poorly

adherent.

The above studies are considered very preliminary. A subsequent test produced more

ambiguous results. Therefore, much more verification and technique development are j needed before this can be used as a practical test method. If successful, the measure- ment method should also prove useful as a non-destructive test for flip-chip and other

gang bonding techniques. (G. G. Harman

The experiments were performed with the

help of Dr. M. Linzer, of the Inorganic

Materials Division at NBS, where acoustic

emission studies have been carried out on both brittle and ductile materials for

many years

32
10 . HERFIETI C I TY

10.1. Helium Mass Spectrometer Method for

Leak Detection

Anomalous results were obtained from the

second stage of the interlaboratory evaluation of the helium mass spectrometer method

[42] for testing fine capillary leaks in

large volume ("^ 1.5 cm^) containers being

conducted in cooperation with ASTM Committee

F-1 on Electronics (NBS Spec. Publ. 400-4,

p. 67). This stage of the experiment was intended primarily to check the Howl and

Mann theory [43] for relating measured to actual leak rate. Following stage one, which consisted of the direct measurement of

the 50 borosilicate glass capillary leaks in

open tubulated capsules, the tubulations were sealed off at NBS and tested by the

participants by the back pressurization

technique [42]. Pressurization of the capsules was at 75 psia (5.2 x 10^ Pa) for 20 h

in helium. Measured leak rates on the re- sultant "packages" were found to be orders

of magnitude greater than anticipated and of

approximately identical value independent of

true leak rate as measured in stage one.

All 50 leaks were returned to NBS for diagnosis of the problem. For the diagnosis, 20

of the capsules were pressurized and measured as prescribed. Again, uniformly high

and approximately identical threshold values

of 10"^ atm'cm^/s (10"^ Pa-mVs) were measured. Measurements, however, were then

continued on the leaks over a four-day period. Leak rates declined, but the smallest

indicated leak rate at the end of this period was still of the order of 10"^ atm'cm^/s

(10~^ Pa*m^/s) . Measurements were then made

on 10 capsules which had been pressurized

and measured one month previously. Leak

rates were about 5 x 10~^° atm*cm^/s (5 x 10-11 Pa-mVs).

Such values as found are obviously outside

the prediction from the Howl and Mann theory

and must be due to surface effects. To isolate the surface effects, ten sealed-off

capsules were constructed with approximately

the same dimensions as the test leak capsules. These were then pressurized and measured in the same way as the test leaks.

The measured leak rates were of the same order of magnitude as those of the test

leaks and also were tightly grouped in value. The resultant data as measured over a period of time are shown graphically in fig- ure 25. The measured leak rates were plotted on a logarithmic scale against time on both a linear scale and a logarithmic scale

in order to discriminate between the gas

emission mechanisms. Surface desorption

Figure 25. Indicated leak rate for sealed-off borosilicate glass capsules of same outer

dimensions as test leak capsules as a function of time after pressurization at 75 psia

(5.2 X 10^ Pa) for 20 h in helium.

33
HERMETICITY

with a constant residence time is a first

order rate process which would evidence a linear relationship of log leak rate as a function of time [44]. Since the plot in

figure 25a is not linear, one can conclude

that surface desorption is not the primary

emission mechanism. Outgassing of helium

from the glass walls by diffusion would show

a reciprocal square root of time dependence

of the measured leak rate for short times

after pressurization and a t~-^'^e~^*^ dependence at longer times [44,45]. Thus, a linear relationship of log leak rate as a function of log time would be evidenced for

a short time after pressurization followed

by a drop off due to the exponential factor.

The plot in figure 25b follows this behavior

so one can conclude that helium outgassing

is responsible for the anomalously high apparent leak rates. The helium diffuses into

the glass walls during the pressurization

cycle. Were the helium at uniform concen- tration within the glass after removal from

the pressure vessel, the initial slope of

the outgassing curve of figure 25b would be

-0.5. Here it is about -0.7. Presumably,

this deviation from -0. 5 is due to the large

concentration gradient still evidenced at the surface after 20 h of pressurization.

Calculations show that the contribution due

to helium pressure buildup within the actual

leaks due to permeation through the glass

walls would not be significant relative to the outgassing of helium from the walls

themselves.

As a further test, four of the leaks and

four sealed capsules were repressurized and

measured over a period of several hours.

Again, both the test leaks and the sealed

capsules evidenced high values with small

dispersion, with values from capsules and

leaks being comparable. Removal of the S metal shields from the leaks caused no sig- ". nif leant change. One capsule was measured : after being broken open; no significant dif-1

ference occurred from the unbroken capsules.,]

Finally, emission from the interior only of : the test leaks was attempted by holding the * tip of the leak into the 0-ring of the i quick-connect of the leak detector. The ef-. feet of outgassing was then limited to the

wall area around the capillary leak; only

one-sixteenth to one-tenth of the total wall: area was exposed to the detector. From the

data of figure 25b it is possible to estimate the apparent leak rate due to outgassing from the walls at the time of measurement to be between 4 and 7 x 10~^ atm*cm^/s

(4 and 7 x 10"^ Pa-m-^/s). From the theory

of Howl and Mann [43] and the directly measured leak rate it is possible to calculate

the leak rate which should be measured in

the absence of outgassing. Two of the three

leaks tested had measured leak rates within

a factor of 2 of the calculated sum of the

contributions from the leak itself and from

the exposed walls. The measured leak rate

of the third was 5 to 10 times the calculated sum.

In order to benefit further from the interlaboratory evaluation, a new fixture was devised to allow exposure only of the tip area

of the leak to the helium leak detector for use in repeating the second stage.

(S. Ruthberg)

34
11. THERMAL PROPERTIES OF DEVICES

11.1 Thermal Resistance Methods —

Darlington Pairs

Considerable progress has been made in the

investigation of methods for the measurement

of thermal resistance of monolithic and hybrid Darlington transistors. The available

configurations can be grouped into four distinct types, of which only one type has the common point of the input emitter and output

base accessible for measurement (NBS Spec.

Publ. AOO-8, pp. 46-47). Diagrams of the

four circuit types are repeated in figure

26. All four types are measurable as a unit

using the standard emitter-only switching

-oC

<2

a. Four-terminal stripped Darlington.

h°—1£

-oC

E2

b. Three-terminal stripped Darlington.

-oC

AAA^-*-AAAr

Rl R2

c. Three-terminal Darlington with

integrated resistors and input diode,

K D2cC

-AAiVd. Three-terminal Darlington with

integrated resistors and output diode.

Figure 26. Commercially available

Darlington circuits.

circuit [46], but only the type with the common point brought out is amenable to direct measurement of the input and the output

transistor with the standard circuit. The

other types are also amenable to separate,

but indirect, measurement of both input and

output transistors, but require modification

in the basic test circuit to accommodate all

the available configurations.

The modified test circuit is shown in figure

27. Although a type d Darlington is shown

in the figure, the test circuit will accom- modate any of the four types. As shown

(with switches S2 and St^ closed, switch Si open, and switch S3 set at E) the test circuit is electrically identical to the standard emitter-only circuit. With this circuit, the temperature sensitive parameter

(TSP) is the series combination of emitterbase voltages of both the input and output

transistors, V„_, + V__„, provided that, for

Eel sldZ the case of type c and d devices, the measuring current is large enough to assure

that both transistors are turned on during

the measurement. If a very small measuring

current is used, such that the output transistor remains off during the measurement,

the TSP is the emitter-base voltage of the

input transistor, V--, , only. To accomplish

this, the ratio of the bias resistors,

R1/R2, must be large enough so that the current required to cause a sufficient potential across Rj to turn transistor Qj on will

not cause a sufficient drop across R2 to turn transistor Q2 on. This condition must

Figure 27. Circuit diagram of emitteronly switching circuit for measuring

thermal resistance modified to allow

use of a variety of junction voltages

as temperature sensitive parameters.

(Components shown with dashed connections are added to the basic circuit.)

35
THERMAL PROPERTIES OF DEVICES

Table 6 — Thermal Resistance of a Type d Darlington Device

TSP Method Switch^

deg C/W

V'eb(i+2;

EBl

'CBl 'CB2

High current, emitter-only Open Closed E Closed 0 .9 Low current, emitter-only Open Closed E Closed 0 .5 Grounded-base, emitter-and-col lector Open Closed C Open 0 .5 Grounded-emitter , emitter-and-col lector Closed Open C Open 1 .1 Calculated R^j^^ [eq (8)] 1 .3 Infrared microradiometry (hottest spot) 1 .6

See circuit diagram, figure 27,

be satisfied following heating of transistor

Q2 when Vgg2 drop to a few hundred millivolts. The measured voltage also includes

the constant drop across R2. Because there are no bias resistors, this low current measurement cannot be made on device types a and b. For the former, of course, the individual emitter-base voltages can be measured

independently.

The collector-base voltage of the input

transistor, V^^^, can be used as the TSP

with switches and open, switch S2

closed, and switch S3 set at C. In this

configuration, the measuring current is fed

to the collector terminal and an emitterand-collector switching mode (NBS Tech.

Note 743, pp. 34-35) is employed. The TSP

is V , because the combination of the tranCBl

sistor Q and the diode D causes the emitter of the output transistor to be open

during the measuring period. When measuring

type c and d devices, the shunting effect of

the bias resistors could allow some current

in alternative parallel paths such as Ri and

the collector-base junction of transistor

Q2, or Ri , R2 and the diode (for type d

devices), but if the test current is sufficiently large (6 mA, for example) these

shunting effects should be negligible.

The collector-base voltage of the output

transistor, V , (in parallel with the outCdZ

put diode voltage for type d devices) can be

used as the TSP with switch Si closed,

switches S2 and Si^ open, and switch S3 set

to C. In this configuration the measuring

circuit is changed to a quasi grounded-base

circuit during heating and a quasi groundedemitter circuit during measurement. The

diode D„ is needed to keep the input tranB sistor (Qi) from turning on during measurement while it is conducting during the heating period so that the degenerative stabilizing effects of emitter drive are obtained

and the instabilities frequently encountered

with a conventional grounded-emitter circuit

are avoided. For type c devices, the path

of the measuring current, I^, is through the

collector-base junction of the output transistor (Q2) and R2 in series and its magnitude is determined by the magnitude of R2.

If L, is too large then the collector-base

M

junction of Qi will turn on. For type d devices, the measuring current splits between

the diode D2 and the series combination of

R2 and the collector-base junction of Q2.

A set of four measurements was made on a type d Darlington transistor using each of

the four methods described above with a collector current of 3.5 A and a collector

voltage of 20 V. Values of junction-to-case

thermal resistance, R^^n* obtained by linear

extrapolation to zero time (see ref 46,

Appendix C)s are listed in table 6. The

36
THERMAL PROPERTIES OF DEVICES

values derived for the Input transistor using

both the low current V method and V_,_,

EJi± CBl

method give the same result. This Is not

unreasonable for a small driver transistor

operating at a relatively small overall temperature rise despite earlier contrary results on higher power transistors (NBS Tech.

Note 806, pp. 45-47; NBS Spec. Publ. 400-8,

pp. 43-45). These earlier results would

suggest that the thermal resistance of the

output transistor measured with V „ as the

TSP would be significantly below the true

thermal resistance. The problem then is to extract the thermal resistance of the output

transistor from the combined thermal resistance of both Input and output transistors

which was obtained using the high measuring

current. As a first approximation, one can assume that the calibration coefficient for

this method can be divided equally between

the two devices. If this Is done, one finds

that

ejC2

= 2 ^ejc(i + 2) ^ejci (8)

where ^/^o is the unknown thermal reslstance of the output transistor, ^^^qj^^ + 2) Is the combined Input and output thermal re- sistance obtained using the high current V^^

method, and Rq Is the thermal resistance

of the input transistor measured using the

low current V_„ method with the same heating

EB power as was used for the high current measurement. For the device studied, it can be seen from table 6 that the value of ^qjq2

calculated from eq (8) is significantly

higher than the value measured with '^^^2 the TSP. To check the electrically measured

values of Rqjq2» temperature rise of the

hottest area which was located near the output emitter lead and toward the center of

the chip was measured using an infrared

microradiometer . The thermal resistance

calculated from this temperature rise is also listed in table 6. The agreement between

this value and the calculated Rqj(-2 '^

as good as has been obtained on discrete devices which do not have severe current

crowding (NBS Tech. Note 773, pp. 28-30),

but the calculation represents a significant

improvement over the direct measurement with

V-_„ as the TSP vjhich has been the method

CB2

generally used for thermal resistance measurements on Darlington devices.

It should be emphasized that the measurements discussed above are measurements on a specific transistor type under a given set

of conditions and thus do not serve as a basis for other device types or measuring

conditions. The results of these measurements indicate that it may be possible to extract all the needed information to allow

an approximation to the temperature rises of

the individual transistors forming the Darlington pair by using a modified emitteronly switching measuring system. This re- quires an individual tailoring of the

measuring current magnitudes for each transistor type and may not be possible for devices in which the output bias resistor is

too large with respect to the input bias re- sistor to allow a measuring current selection which will turn on the input transistor

while keeping the output transistor off. It should also be pointed out that while the

Individual transistor temperatures are measured, the Darlington device is being operated with normal conditions. (S. Rubin)

11.2. Transient Thermal Response

It has been shown that an effective area of

power generation at steady state can be determined for power transistors by observing

the electrically measured cooling response

of these devices [47]. Because the peak

steady-state junction temperature of a device is a function of the area in which

power is generated, and because it is the

peak junction temperature which limits the

safe operating region of a device, work was begun to attempt to derive a quantitative

relationship between the peak steady-state

junction temperature of a power transistor,

the electrically determined area of power

generation at steady state, and the electrically measured average steady-state junction

temperature. Such a relationship should be

valuable for aiding in the thermal rating of

power devices since all of the presently

used electrical Indicators of device junction temperature average the junction temperature in some generally unknown way.

A simple model was developed for use in simulating the manner in which the measured

emitter-base voltage of a power transistor

averages the junction temperature. The

model consists of N parallel resistor-diode

series combinations with each parallel leg

assigned a temperature, T^ (in kelvins) , an

area, A (in square centimetres), and a ren slstance, R^ (in ohms) , as indicated in

37
THERf^L PROPERTIES OF DEVICES

E

B

Figure 28. Model used for simulating

the way in which the emitter-base voltage averages the junction temperature.

figure 28. The surfaces E and B are assumed

to be equipotential surfaces and the total

measuring current, I^^^ (in amperes), is maintained constant. The voltage that is measured and used to determine the average

i unction temperature is V., = V_ - V„ (in

, . M E B volts)

The temperature distribution was calculated

from a model of Linstead and Surty [48] for

the case of a square heat source centered on

the top surface of a square chip, the bottom

surface of which was assumed uniform in

temperature.

Once the temperature of each element of the

model is set and the measurement current defined, the current density, (in amperes

per square centimetre) , in each element can

be calculated from the n equations

J = CT3 exp(- E /kT ) n n g n

X [exp(V,, -JAR )/mkT ) - 1] M n n n n

subject to the constraint

n n M

n = 1

In these equations C is taken as a constant

(3.1 X 10^ A/cm^.K^), E^ is the zero kelvin

band gap of silicon (1.1 eV) , k is Boltzmann's constant (8.6173 x 10"^ eV/K) , m is a constant (assumed unity) , and the other symbols have been defined previously. The con- stant C is a function of the minority carrier diffusion coefficient and lifetime and

the dopant density; it was assumed that the

temperature and current density dependence

of these quantities can be neglected. It was also assumed that any leakage current

due to the application of a collector-base

voltage (such as the voltage applied in the

emitter-only switching technique for measuring junction temperature [46]) can be

neglected

These equations are satisfied by a single

value of V,, which corresponds to the

M

electrically-measured emitter-base voltage

for the given temperature distribution. A

calibration curve is generated by finding V^^ as a function of temperature with the as- sumption that for each point all the T^ have

the same value. The electrically deter- v mined, average junction temperature is the

temperature on this curve appropriate to the

V,, calculated for a particular temperature M

distribution.

The model indicates that all of the measuring current goes through the actual area of

power generation at steady state. This is

illustrated in figure 29 where the surface

temperature along a diagonal is plotted for

an 0.51 mm (20 mil) square heat source, in

which 5 W is uniformly dissipated, on a square chip 2.54 mm (100 mil) on a side,

0.25 mm (10 mil) thick. Also plotted is the

relative measurement current density, J /J , •' ' n o along the same diagonal where is the current density at the center of the heat

DIAGONAL POSITION |mm|

Figure 29. Temperature and relative

measurement current density along a diagonal of a 0.51-mm (20-mil) square

heat source on a 2.54-mm (100-mil)

square silicon chip.

38
THERMAL PROPERTIES OF DEVICES

source area. Note that beyond the corner of

the heat source the measurement current density is effectively zero.

Because the measurement current is confined

to the area of power generation while the

calibration current is distributed throughout the entire active area of the device,

the measurement current density is greater

than the calibration current density, and

the calibration curve must be shifted to account for this difference (NBS Spec. Publ.

400-8, pp. 43-45).

A simple correction is made for this assuming all the measurement current exists uniformly throughout the area of power generation. The shift in temperature for a given

value of V„ is, if the slope of the calibra- M

tion curve,

current density,

(AV^^/ATj^^) , is independent of

6T = 8. 62x10-2(1+273. 15)£n (9)

0.5 1.0 15 20

LENGTH OF HEAT SOURCE SIDE |mml

Figure 30. The computed ratio of the

average junction temperature to the

peak junction temperature as a function

of heat source size for a 2.54-mm

(100-mil) square silicon chip corrected

to account for the increased measurement current density compared to the

calibration current density.

where the slope is in millivolts per degree

Celsius, T is the junction t-emperature in

degrees Celsius (approximated by the uncorrected electrically measured junction temperature, extrapolated to zero time after

cessation of the power pulse) , is the

total active area of the device, and A is m

the area of power generation.

The ratio of the average junction temperature to the peak junction temperature was computed according to the above model (including the correction of eq (9)) for various sizes of square heat sources on a square

chip 2.54 mm on a side, 0.25 mm thick. The

results, which are plotted in figure 30,

show that the ratio is nearly constant for

heat sources 1.5 mm on a side or less.

Table 7 — Peak Temperature Determination

Average

Total Area of Junction Calculated Measured

Device Collector Collector Active Power Temperature Peak Peak

No. Current, Voltage, Area, Generation, (extrapolated). Temperature, Temperature,

A V cm2 cm^ deg C deg C deg C

1 1 30 0.022 0.018 114 9 130 3 134

1 0.5 40 0.022 0.019 79 6 89 6 91

2 0.2 110 0.027 0.006 152 5 202 8 225

2 0.6 50 0.027 0.016 127 0 149 7 159

3 2 12. 5 0.054 0.040 110 0 121 2 119

4 2 57 5 0.105 0.081 160 7 173 4 185

39
THERMAL PROPERTIES OF DEVICES

The area of power generation at steady state

for various operating conditions has been

determined from the cooling response for

several different devices. In addition, the

average junction temperature was determined

by extrapolating the cooling response back

to zero time (NBS Spec. Publ. 400-8, pp. 49-

51). For these same devices, the heating

response was also determined. Because it is

relatively independent of operating conditions, the heating response was used to determine the total active area of the device

by assuming one-dimensional transient heat

flow for the first few milliseconds of

heating. This was used to calculate 6T witt

eq (9) and together with the data of figure

30 to calculate the peak temperature. The

peak temperature was also measured with the

infrared microradiometer . The results of

these experiments are summarized in table 7. The close agreement between the calculated

and measured peak junction temperatures indicates the feasibility of estimating the

peak junction temperature by this method.

(D. L. Blackburn;

40
12 . REFERENCES

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Novotny, D. B. , Automated Inspection of

IC Photomasks, Photofabrication Imagery

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Photo-Optical Instrumentation Engineers,

P.O. Box 1146, Palos Verdes Estates,

California 90274.)

2. Donovan, R. P., and Evans, R. A., In- cremental Sheet Resistance Technique

for Determining Diffusion Profiles,

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123-131 (November 1970).

3. Crowder, B. L., and Fairfield, J. M.,

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4. Ryssel, H., Schmid, K., and Muller, H.,

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7. Godunorv, S., and Ryabenki, V., An In-

' troduotion to the Theory of Difference

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Publishing Company, Amsterdam, 1964).

8. Grove, A., Leistiko, 0., Jr., and Sah,

C. T. , Redistribution of Acceptor and

Donor Impurities during Thermal Oxida-

, tion of Silicon, J. Appl. Phys. 35_,

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i 9. Buehler, M. G., Thermally Stimulated

Measurements: The Characterization of

Defects in Silicon p-n Junctions, Semiconductor Silicon/1973, H. R. Huff and

R. R. Burgess, eds. , pp. 549-560

(Electrochemical Society, Princeton,

N. J., 1973).

10. Sah, C. T., Forbes, L., Rosier, L. I.,

Tasch, A. F., Jr., and Tole, A. B.

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Thermal Emission Rates of Carriers At Gold Denters in Silicon, Appl. Phys.

Letters 15, 145-148 (1969).

11. Buehler, M. G. , Impurity Centers in p-n

Junctions Determined from Shifts in the

Thermally Stimulated Curr ent and Capacitance Response with Heating Rate,

Solid-State Electronics 15_, 69-79

(1972).

12. Thurber, W. R,, Lewis, D. C, and

Bullis, W. M., Resistivity and Carrier

Lifetime in Gold-Doped Silicon, AFCRL

Report AFCRL-TR-73-0107, January 31,

1973, pp. 14-23. (Available from the

National Technical Information Service,

Springfield, Virginia 22151, Accession

No. AD 760150.)

13. Collins, C. B., Carlson, R. 0., and

Gallagher, C. J., Properties of GoldDoped Silicon, Phys. Rev. 105, 1168-

1173 (1957).

14. Standard Method for Measuring Hall Mobility and Hall Coefficient in Extrinsic Semiconductor Single Crystals, ASTM

Designation F 76, Annual Book of ASTM

Standards, Part 43 (November 1974)

(Available as a separate reprint from

American Society for Testing and Materials, 1916 Race Street, Philadelphia,

Pennsylvania 19103.)

15. Natrella, M. G., Experimental Statistics, NBS Handbook 91 (August 1, 1963),

115-5.1.3.

16. Messier, J., and Flores , J. M. , Temperature Dependence of Hall Mobility and

Pj^/mq for Si, J. Phys. Chem. Solids 24 , 1539-1542 (1963).

17. Bruckner, B., Electrical Properties of

Gold-Doped Silicon, Phys. Status Solidi

A 4, 685-692 (1971)

18. Debye, P. P., and Conwell, E. M. , Electrical Properties of N-Type Germanium,

Phys. Rev. 9_3, 693-706 (1974).

19. Smith, R. A., Semiconductors, p. 124

(University Press, Cambridge, 1961).

20. Norton, P., Braggins , T., and Levinstein, H., Impurity and Lattice Scattering Parameters as Determined from

Hall and Mobility Analysis in n-Type

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Silicon, Phys. Rev, B8, 5632-5653

(1973).

21. Runyan, W. R., Silicon Semioonduator

Technology, p. 180 (McGraw-Hill, New

York, 1965).

22. Tasch, A. F. , Jr., and Sah, C. T.,

Recombination-Generation and Optical

Properties of Gold Acceptor in Silicon,

Fhys. Rev. Bl, 800-809 (1970).

23. Parrillo, L. C., and Johnson, W. C.,

Acceptor State of Gold in Silicon —

Resolution of an Anomaly, Aip'pl. Phys.

Lett. 20, 104-106 (1972).

24. Mayer, J. W., Erickson, L., and Davis,

J. A., Ion Implantation, p. 36 (Academic Press, New York, 1970); see eq (29).

25. Johnson, W. S., and Gibbons, J. F.,

Projected Range Statistics in Semiconductors (1969) . Distributed by Stanford University Bookstore, Stanford,

California 94305.

26. McCrea, J. M. , Mass Spectrometry, Chapter 21, Characterization of Solid Surfaces, Kane, P. F., and Larrabee, G. R., Eds., pp. 606-615 (Plenum Press,

New York, 1974) .

27. Honig, R. E., and Harrington, W. L.,

Ion Scattering Spectrometry Below

10 keV, Thin Solid Films 19, 46-56

(1973).

28. Nicolet, M. A., Mayer, J. W. , and

Mitchell, I. v., Microanalysis of Materials by Backscattering Spectrometry,

Science 177, 841-849 (1972).

29. Chang, C. C, Analytical Auger ElectroSpectroscopy, Chapter 20, Characterization of Solfd Surfaces, Kane, P. F.,

and Larrabee, G. R. , Eds., pp. 509-576

(Plenum Press, New York, 1974).

30. Hercules, S. H. , and Hercules, D. M.

,

Surface Characterization by Electron

Spectroscopy for Chemical Analysis

(ESCA) , Chapter 13, Characterization of

Solid Surfaces, Kane, P. F., and Larrabee, G. R., Eds., pp. 30'7-335 (Plenum

Press, New York, 1974).

31. Kushner, R. A., McCaughan, D. V.,

Murphy, V. T., and Hellig, J. A., Mobilization of Sodium in Si02 Films by

Ion Bombardment, Phys. Rev. BIO , 2632-

2641 (1974).

32. Buehler, M. G., Semiconductor Measurement Technology : Microelectronic Test

Patterns: An Overview, NBS Spec. Publ.

400-6 (August 1974) pp. 4-6, 12-19.

33. Sze, S. M., Physics of Semiconductor

Devices, pp. 515-524 (John Wiley and

Sons, Inc., New York, 1969).

34. Sah, C. T., and Pao, H. C, The Effects of Fixed Bulk Charge on the

Characteristics of Metal-OxideSemiconductor Transistors, IEEE Trans, on Electron Devices ED-13 , 393-409

(1966).

35. Games, J. E., and Kosonocky, W. F.,

Fast-Interface-State Losses in ChargeCoupled Devices, Appl. Phys. Letters

20, 261-263 (1972).

j 36. Standard Method of Test for Thickness

of Epitaxial or Diffused Layers in Silicon by the Angle Lapping and Staining

Technique, ASTM Designation F 110,

Annual Book of ASTM Standards, Part 43

(November 1974) . (Available as a sepa-^

rate reprint from American Society for : Testing and Materials, 1916 Race

Street, Philadelphia, Pennsylvania

19103.)

37. Ravi, K. V., and Varker, C. J., Comj ments on the Distinction between "Striations" and "Swirls" in Silicon, Appl.

Phys. Lett. 25_, 69-71 (1974).

38. Haas, G. E. , and Thomas, R. E., Electron Beam Scanning Technique for Measuring Surface Work Function Variations, Surface Science 4^, 64-88 (1966).

39. Hanagud, S., Craig, J. I., and

Deadwyler, R., Acoustic Emission in Sea! Ice, Proc. 1972 IEEE Ultrasonic Conference, Boston, Mass., October 4-7, 1974,

pp. 4-7.

40. Stephens, R. W. B., and Pollack, A. A.,

Waveforms and Frequency of Acoustic

Emission, J. Acoustical Soo. Am. 50 , 904-910 (1971).

41. Vahaviolos, S. J., Real Time Detection

of Microcracks in Brittle Materials

using Stress Wave Emission, Proa. 1974

IEEE Electronics Components Conference,

Washington, D. C, May 14-16, 1974,

pp. 34-42. I
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42. Tentative Reconmiended Practices for Determining Hermeticity of Electron Devices with a Helium Mass Spectrometer

Leak Detector, ASTM Designation F 134,

Annual Book of ASTM Standards^ Part 43

(November 1974) . (Available as a separate reprint from American Society for

Testing and Materials, 1916 Race

Street, Philadelphia, Pennsylvania

19103.)

43. Howl, D. A., and Mann, C. A., The

Back-Pressurization Technique of LeakTesting, Vaouim 15, 347-352 (1965)

44. Santeler, D. J., Holkeboer, D. H.,

Jones, D. W. , and Pagano, F., Vaauum

Technology and Space Simulation^ pp.

184-191, NASA SP-105 (1966). (Available from U.S. Government Printing Office, Washington, D. C. 20402.)

45. Barrer, R. M., Diffusion In and Through

Solids^ Chapter 1 (University Press,

Cambridge, 1951).

46. Thermal Resistance Measurements of Conduction Cooled Power Transistors, JEDEC

Publication No. 91, August 1974.

(Available from Engineering Department,

Electronic Industries Association, 2001

Eye Street, N.W., Washington, D. C. 20006.)

47. Blackburn, D. L., and Gettinger, F. F.,

Transient Thermal Response Measurements

of Power Transistors, PESO 1974 Record,

IEEE Power Electronics Specialists Conference, Murray Hill, New Jersey, June

10-12, 1974, pp. 140-148. (Available

from IEEE Publication Sales Dept., 345

E. 47th Street, New York, New York

10017, Catalog No. 74CH0863-1-AES .

)

48. Linstead, R. D., and Surty, R. J.,

Steady State Junction Temperatures of

Semiconductor Chips, IEEE Trans. Elect.

Dev. ED-19 , 41-44 (1972).

43
APPENDIX A

SEMICONDUCTOR TECHNOLOGY PROGRAM STAFF

Coordinator: J. C. French

Secretary: Miss B. S. Hope

Consultant: C. P. Marsden'

F. H. Brewer

Miss F. C. Butler"*" M. Cosman

Mrs. K. E. Dodson^

Dr. J. R. Ehrstein

Semiconductor Characterization Section

(301) 921-3625

Dr. W. M. Bullis, Chief

Dr. M. G. Buehler, Asst. Chief

Dr. R. Y. Koyama

Dr. A. G. Lieberman

R. L. Mattis

Dr. S. Mayo

Dr. W. E. Phillips

Miss D. R. Ricks

L. M. Smith

Mrs. M. L. Stream

W. R. Thurber

Dr. J. H. Albers

Mrs. C. A. Cannon

W. A. Cullins

G . G . Harman

Semiconductor Processing Section

(301) 921-3541

Dr. A. H. Sher, Chief

S. Ruthberg, Asst. Chief — Assembly

H. A. Schafft, Asst. Chief — Processing

Miss D. L. Hines"*"

H. K. Kessler

J . Krawczyk

T. F. Leedy

Y. M. Liu

Dr. D. B. Novotny

R. L. Raybold

1. Szabo

Mrs. E. Y. Trager"*

D. L. Blackburn

D. W. Berning

H. E. Dyson

Dr. K. F. Galloway

Mrs. A. D. Glover^

Electron Devices Section

(301) 921-3622

F. F. Oettinger, Acting Chief

W. J. Keery

Mrs. K. 0, Leedy

Dr. D. C. Lewis

Mrs. B. A. Oravec

M. K. Phillips

M. C. Rhodes"

G. J. Rogers

S. Rubin

D. E. Sawyer

L. R. Williams

IF Part Time + Secretary

* Telephone: (301) 921-3357

t Telephone

(301) 921-3621

44
APPENDIX B SEMICONDUCTOR TECHNOLOGY PROGRAM PUBLICATIONS

B.l. Prior Reports

A review of the early work leading to this Program Is given in Bullls, W. M., Measurement

Methods for the Semiconductor Device Industry — A Review of NBS Activity, NBS Tech. Note

511, December, 1969.

Quarterly reports covering the period July 1, 1968, through June 30, 1973, were published

as NBS Technical Notes with the title. Methods of Measurement for Semiconductor Materials,

Process Control, and Devices:

Quarter Ending NBS Tech. Note Date Issued NTIS Accession

September 30, 1968 472 December 1968 AD 681330

December 31, 1968 475 February 1969 AD 683808

AAA July lyoy AD oyz/jz

June 30, 1969 495 September 1969 AD 695820

September 30, 1969 520 March 1970 AD 702833

December 31, 1969 527 May 1970 AD 710906

March 31, 1970 555 September 1970 AD 718534

June 30, 1970 560 November 1970 AD 719976

September 30, 1970 571 April 1971 AD 723671

December 31, 1970 592 August 1971 AD 728611

March 31, 1971 598 October 1971 AD 732553

June 30, 1971 702 November 1971 AD 734427

September 30, 1971 717 April 1972 AD 740674

December 31, 1971 727 June 1972 AD 744946

March 31, 1972 733 September 1972 AD 748640

June 30, 1972 743 December 1972 AD 753642

September 30, 1972 754 March 1973 AD 757244

December 31, 1972 773 May 1973 AD 762840

March 31, 1973 788 August 1973 AD 766918

June 30, 1973 806 November 1973 AD 771018

After July 1, 1973 quarterly reports were issued in the NBS Special Publication 400 subse

with the title. Semiconductor Measurement Technology:

Quarter Ending NBS Spec. Publ. Date Issued NTIS Accession

September 30, 1973 400-1 March 1974 AD 775919

December 31, 1973

400-4 November 1974 March 31, 1974 J June 30, 1974 400-8 February 1975

B.2. Current Publications

As various phases of the work are completed, publications are prepared to summarize the

results or to describe the work in greater detail. Publications of this kind which have

been issued recently are listed below:

Buehler, M. G., Semioonduator Measurement Technology: Microelectronic Test Patterns: An Overview, NBS Spec. Publ. 400-6 (August 1974).

Bullis, W. M., Standard Measurements of the Resistivity of Silicon by the Four-Probe Method,

NBSIR 74-496 (August 1974). (Supersedes NBS Report 9666, NTIS Accession No. N68-18067.)

45
APPENDIX B

Ciarlo, D. R. , Schultz, P. A., and Novotny, D. B., Automated Inspection of IC Photomasks,

Teahnologiaal Advances in Mioro and Sub-Miaro Photofabrication Imagery^ Society of PhotoOptical Instrumentation Engineers, San Diego, California, August 21-23, 1974, to appear.

Sher, A. H., Semiconductor Nuclear Radiation Detector Studies — A Final Report,

NBSIR 74-626 (September 1974).

Marsden, C. P., Tabulation of Published Data on Electron Devices in the U.S.S.R. Through

December 1973, NBS Technical Note 835 (November 1974). (Supersedes NBS Technical Note 715.)

Ehrstein, J. R. , Ed., Semiconductor Measurement Technology: Spreading Resistance Symposium,

NBS Spec. Publ. 400-10 (December 1974).

Schafft, H. A., Semiconductor Measurement Technology: ARPA/NBS Workshop II. Hermeticity

Testing for Integrated Circuits, NBS Spec. Publ. 400-9 (December 1974).

Ehrstein, J. R., Improved Surface Preparation for Spreading Resistance Measurements on p-Type

Silicon, Semiconductor Measurement Technology: Spreading Resistance Symposium, J. R. Ehrstein,

Ed., NBS Spec. Publ. 400-10 (December 1974), pp. 249-255.

Rogers, G. J., Sawyer, D. E., and Jesch, R. L., Semiconductor Measurement Technology:

Measurement of Transistor Scattering Parameters, NBS Spec. Publ. 400-5 (January 1975).

Sher, A. H. , Semiconductor Measurement Technology: Improved Infrared Response Technique for

Detecting Defects and Impurities in Germanium and Silicon p-i-n Diodes, NBS Spec. Publ. 400-13

(February 1975)

Lewis, D. C, On the Determination of the Minority Carrier Lifetime from the Reverse Recovery

Transient of pnR Diodes, Solid-State Electronics 18, 87-91 (1975).

B.3. Availability of Publications

In most cases reprints of articles in technical journals may be obtained on request to the

author. NBS Technical Notes and Special Publications are available from the Superintendent

of Documents, U.S. Government Printing Office, Washington, D. C. 20402, or the National

Technical Information Service, Springfield, Virginia 22161, or both. Current information

regarding availability of all •publications issued by the Program is provided in the latest

edition of NBS List of Publications No. 72 which can be obtained on request to Mrs. K. 0. Leedy, Room B3t6, Technology Building, National Bureau of Standards, Washington, D. C. 20234.

B.4. Videotapes

Color videotape cassette presentation on improvements in semiconductor measurement technology

are being prepared for the purpose of more effectively disseminating the results of the work

to the semiconductor industry. These videotapes are available for distribution on loan

without charge on< request to H. A. Schafft, Room A317, Technology Building, National Bureau

of Standards, Washington, D. C. 20234. Copies of these videotapes may be made and retained

by requestors. The first videotape, titled "Defects in PN Junctions and MOS Capacitors Observed Using Thermally Stimulated Current and Capacitance Measurements," by M. G. Buehler

has been completed and released for distribution. As an added feature, arrangements can be

made for the author to be available for a telephone conference call to answer questions and

provide more detailed information, following a prearranged showing of the videotape.

46
APPENDIX C WORKSHOP AND SYMPOSIUM SCHEDULE

C.l. Proceedings or Reports of Past Events:

Symposium on Silicon Device Processing, Gaithersburg, Maryland, June 2-3, 1970.

(Cosponsored by ASTM Committee F-1 and NBS) . Proceedings: NBS Spec. Publ. 337

(November 1970)

ARPA/NBS Workshop I. Measurement Problems in Integrated Circuit Processing and Assembly,

Palo Alto, California, September 7, 1973. Report: NBS Spec. Publ. 400-3

(January 1974).

ARPA/NBS Workshop II. Hermeticity Testing for Integrated Circuits, Gaithersburg,

Maryland, March 29, 1974. Report: NBS Spec. Publ. 400-9 (December 1974).

Spreading Resistance Symposium, Gaithersburg, Maryland, June 13-14, 1974. (Cosponsored

by ASTM Committee F-1 and NBS). Proceedings: NBS Spec. Publ. 400-10

(December 1974)

ARPA/NBS Workshop III. Test Patterns, Scottsdale, Arizona, September 6, 1974. Report:

NBS Spec. Publ. 400-15 (to appear).

C.2. Calendar of Future Events : ARPA/NBS Workshop IV. Surface Analysis for Silicon Devices, Gaithersburg, Maryland,

April 23-24, 1975.

47
APPENDIX D STANDARDS COMMITTEE ACTIVITIES

ASTM Committee F-1 on Electronics

J. H. Albers, Secretary, Packaging Subcommittee; Hybrid Microelectronics Subcommittee i M. G. Buehler, Chairman, Task Force on Test Patterns, Process Controls Section;

Semiconductor Crystals and Semiconductor Measurements Subcommittees , W. M. Bullis, Secretary; Editor, Semiconductor Crystals Subcommittee

C. A. Cannon, Arrangements Committee

J. R. Ehrstein, Chairman, Resistivity Section; Semiconductor Crystals and Semiconductor

Measurements Subcommittees

J. C. French, Chairman, Editorial Subcommittee; Secretary, Advisory Committee; Awards

Committee

G. G. Harman, Secretary, Interconnection Bonding Section; Hybrid Microelectronics

Subcommittee

B. S. Hope, Assistant Secretary '

K. 0. Leedy, Chairman, Packaging Subcommittee; Chairman, Interconnection Bonding

Section; Hybrid Microelectronics and Quality and Hardness Assurance Subcommittees :

D. C. Lewis, Semiconductor Measurements and Quality and Hardness Assurance Subcommittee:

C. P. Marsden, Honorary Chairman; Chairman, Arrangements Committee

R. L. Mattis, Editor, Semiconductor Measurements Subcommittee; Semiconductor Crystals

Subcommittee

J. F. Mayo-Wells, Editorial Subcommittee

D. B. Novotny, Editor, Semiconductor Processing Materials Subcommittee

W. E. Phillips, Chairman, Lifetime Section; Secretary, Semiconductor Crystals Subcommittee; Semiconductor Processing Materials, Semiconductor Measurements, and Hybrid!

Microelectronics Subcommittees 1

G. J. Rogers, Quality and Hardness Assurance Subcommittee

S. Ruthberg, Chairman, Hermeticity Section; Semiconductor Processing Materials, Hybrid

Microelectronics, and Quality and Hardness Assurance Subcommittees

H. A. Schafft, Chairman, Publicity Committee

A. H. Sher, Semiconductor Crystals, Semiconductor Processing Materials, and Hybrid

Microelectronics Subcommittees

W. R. Thurber, Semiconductor Crystals and Semiconductor Measurements Subcommittees

ASTM Committee E-10 on Radioisotopes and Radiation Effects

W. M. Bullis, Subcommittee 7, Radiation Effects on Electronic Materials

J. C. French, Subcommittee 7, Radiation Effects on Electronic Materials

D. C. Lewis, Subcommittee 7, Radiation Effects on Electronic Materials

Electronic Industries Association: Solid State Products Division, Joint Electron Device

Engineering Council (JEDEC)

F. F. Oettinger, Chairman, Task Group JC-11.3-1 on Thermal Considerations for Microelectronic Devices, Committee JC-11.3 on Mechanical Standardization for Microelectronic Devices; Chairman, Task Group JC-25-5 on Thermal Characterization of

Power Transistors, Committee JC-25 on Power" Transistors; Technical Advisor,

48
APPENDIX D

Thermal Properties of Devices, Committees JC-22 on Rectifier Diodes and Thyristors,

JC-20 on Signal and Regulator Diodes, and JC-30 on Hybrid Integrated Circuits

S. Rubin, Chairman, Council Task Group on Galvanomagnetic Devices

D. E. Sawyer, Task Group JC-24-5 on Transistor Scattering Parameter Measurement Standard,

Committee JC-24 on Low Power Transistors

H. A. Schafft, Technical Advisor, Second Breakdown and Related Specifications Committee

JC-25 on Power Transistors

Electronic Industries Association: Government Products Division

F.-F. Oettinger, Chairman, Task Group G-12-08-74 on Recommendations for Military Usage

of Proposed Standards and Test Methods for Thermal Resistance, Coiranittee G-12 on Solid State Devices

IEEE Electron Devices Group

J. C. French, Standards Committee

H. A. Schafft, Standards Committee Task Force on Second Breakdown Measurement Standards

IEEE Magnetics Group

S. Rubin, Chairman, Galvanomagnetic Standards Subcommittee

Society of Automotive Engineers

J. C. French, Subcommittee A-2N on Radiation Hardness and Nuclear Survivability

W. M. Bullis, Planning Subcommittee of Committee H on Electronic Materials and Processes

lEC TC47, Semiconductor Devices and Integrated Circuits

S. Rubin, Technical Expert, Galvanomagnetic Devices; U.S. Specialist for Working Group

5 on Hall Devices and Magnetoresistive Devices

49
APPENDIX E SOLID-STATE TECHNOLOGY & FABRICATION SERVICES

Technical services in areas of competence are provided to other NBS activities and other ^ government agencies as they are requested. Usually these are short-term, specialized service^

that cannot be obtained through normal conmiercial channels. Such services provided during

the last quarter, which are listed below, indicate the kinds of technology available to the

program.

E.l. Thin Metal Films (J. Krawczyk)

Thin films of aluminum and gold were evaporated onto the front and back sides, respectively,

of silicon wafers intended for MOS device production for the Harry Diamond Laboratories.

E.2. Semiconductor Device Assembly (J . Krawczyk)

Silicon wafers containing arrays of transistors were scribed, the resulting dice attached

to TO-5 headers, and the devices bonded with gold wire leads for the Harry Diamond

Laboratories.

E.3. Scanning Electron Microscopy (W. J. Keery)

Scanning electron micrographs of microporous glass specimens were taken for the NBS Inorganic

Glass Section.

i

i

:

i!

50
INDEX

acoustic emission 31-32

anodic oxidation 6 ARPA/NBS Workshop on Surface Analysis for

Silicon Devices 3 ARPA/NBS Workshop on Test Patterns 3-4

ASTM Method F 110 26

I ASTM Recommended Practice F 134 33-34

I Auger electron spectroscopy 18

beam-lead bonding 30-31, 31-32

bond pull tests 5

b boron redistribution 6-7

carbon contamination 15-17

charge-coupled device test pattern 22-25

' cleave-and-stain method 26

Darlington pairs 35-37

dopant profiles 6-7

double-pulse method 25

electron beam induced current mode 27

I electron spectroscopy for chemical analysis

15-17, 18

j emitter-only switching method 35-37

epitaxial layer thickness 26

'l flying-spot scanner 27-28

' gold-doped silicon 8-11, 11-14

'! Hall effect 11-14

' helium mass spectrometer leak test 33-34

I hermeticity 33-34

j incremental sheet resistance 6

interface state density 25

ion scattering spectrometry 18

line-width standards 4-5

metal-photoresist-semiconductor capacitor 26

MOS capacitance-voltage 22-24

MOS capacitor 11, 22-24

MOS transistor 23, 25

NBS-3 test pattern 19-22

peak junction temperature 37-40

photolithography 4-5

photomask inspection 5 p-n junction 8-11

radioisotope leak test 5 Rutherford backscattering spectrom'='tr 18

scanning electron microscopy 27 scanning low energy electron probe 28

secondary ion mass spectrometry 18

step-relaxation method 26

test patterns 19-22, 22-25

thermal resistance 35-37

thermal response 37-40

thermally stimulated current 8-11

titanium carbide 29-30

tungsten carbide 29-30

ultrasonic bonding 29-30

uniform beam model 29-30

x-ray photoelectron spectroscopy 15-17, 18

51
SHEET J NBS Spec. Publ. 400-12

4. TITLE AND SUBTITLE

Semiconductor Measurement Technology: Quarterly Report

July 1 to September 30, 1974.

5. Publication Date May 1975

6. Performing Organization Ci

7. AUTHOR(S)

W. Murray Bullis, Editor

8. Performing Organ. Report

9. PERFORMING ORGANIZATION NAME AND ADDRESS

NATIONAL BUREAU OF STANDARDS

DEPARTMENT OF COMMERCE

WASHINGTON, D.C. 20234

10. Project/Task/Work Unit ^ See Item 15

11. Contract/Grant No. ARPA Order 2397, Pgm Code DNA lACRO 75-816; SSPO Ord N0016475PO70030. IPR SP6-y

12. Sponsoring Organization Name and Complete Address (Street, City, State, ZIP)

NBS — Washington, D. C. 20234

\ARPA — 1400 Wilson Boulevard, Arlington, Va. 22209

DNA — Washington, D. C. 20305

SSPO — Washington, D. C. 20376

13. Type of Report & Period Covered Interim Jul;

to September 30, 19

14. Sponsoring Agency Code

15. SUPPLEMENTARY NOTES 4251126, 4251533, 4251547, 4252128, 4254115, 4259522, 4259555

16. ABSTRACT (A 200-word or less factual summary of most si^ificant information. If document includes a significant

bibliography or literature survey, mention it here.) ThiS quarterly prOgreSS report describes NBS aC

ities directed toward the development of methods of measurement for semiconductor mat

als, process control, and devices. The emphasis is on silicon device technologies.

Principal accomplishments during this reporting period include (1) completion of Hall

feet measurements to determine activation energies of the gold donor and acceptor lev

in silicon; (2) successful direct measurement of fast interface state density with th

circular CCD test structure; and (3) demonstration of the feasibility of the use of , acoustic emission as a non-destructive means for testing individual beam-lead bonds. ' suits are also reported on a holder for semi-automated sheet resistance measurements,

progress on development of mathematical models of dopant profiles, analysis of therma

stimulated current and capacitance measurements on junction diodes. X-ray photoelectr

spectroscopy, a comparative study of surface analysis techniques, design and fabricat

of a test pattern for resistivity-dopant density evaluation, epitaxial layer thicknes

measurement, use of the flying-spot scanner, initial work on the scanning low energy

electron probe, mathematical modeling of ultrasonic bonding, an improved method for f

adjustment and measurement on beam lead bonders, helium mass spectrometry for leak te

ing, thermal resistance measurements on Darlington pairs, and transistor thermal resp

measurements. Supplementary data concerning staff, publications, workshops and sjnmpo

standards committee activities, and technical services are also included as appendice

17. KEY WORDS (six to twelve entries; alphabetical order; capitalize only the first letter of the first key word unless a proper name; separated by semicolons) Acoustic emission; beam-lead bonds; boron redistribution;

Darlington pairs; dopant profiles; electrical properties , trl'i;!:,i^t'ynica;' epitaxial laye

thickness; flying-spot scanner; gold-doped silicon; hermeticity; incremental sheet

resistance; measurement methods; microelectronics; mlcrometrology ; MOS devices; oxide

films; resistivity; scanning low energy electron probe; semiconductor devices; semicoi

iuctor materials; semiconductor process control; silicon; test patterns; thermal resi;

tance; thermal response; thermally stimulated current; ultrasonic bonding; wire bon

x-ray photoelectron spectroscopy.

18. AVAILABILITY Unlimited

I

' For Official Distribution. Do Not Release to NTIS

I X I Order From Sup. of Doc, U.S. Government Printing Office Washington, D.C. 20402, SD Cat. No. CI 3 . 10 : 400-12

I

I Order From National Technical Informat,ion Service (N

Springfield, Virginia 22151 (Microf XChe only)

TIS)

19. SECURITY CLASS

(THISREPORT)

UNCLASSIFIED

20. SECURITY CLASS

(THIS PAGE)

UNCLASSIFIED

21. NO. OF PA(

59

22. P/ice ,^1.

USCOMM-DC 2904 *U.S.r,nVERNMENT PRINTING OFFICE; 1975-583-0
Announcement of New Publications on Semiconductor Measurement Technology

Superintendent of Documents,

Government Printing Office,

Washington, D.C. 20402

Dear Sir:

Please add my name to the announcement list of new publications to be issued in the series: National Bureau of Standards Special Publication 400-.

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Address

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(Notification Key N-413)

NBS TECHNICAL PUBLICATIONS

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of Standards research and development in physics,

mathematics, and chemistry. It is published in two sections, available separately:

• Physics and Chemistry (Section A)

Papers of interest primarily to scientists working in these fields. This section covers a broad range of physical and chemical research, with major emphasis on

standards of physical measurement, fundamental constaftts, and properties of matter. Issued six times a

year. Annual subscription: Domestic, $17.00; Foreign,

$21.25. • Mathematical Sciences (Section B)

Studies and compilations designed mainly for the mathematician and theoretical physicist. Topics in mathematical statistics, theory of experiment design, numerical analysis, theoretical physics and chemistry, logical design and programming of computers and computer

systems. Short numerical tables. Issued quarterly. Annual subscription: Domestic, $9.00; Foreign, $11.25. DIMENSIONS/NBS (formerly Technical News Bulletin) —This monthly magazine is published to inform

scientists, engineers, businessmen, industry, teachers,

students, and consumers of the latest advances in science and technology, with primary emphasis on the work at NBS. The magazine highlights and reviews such

issues as energy research, fire protection, building tech- nology, metric conversion, pollution abatement, health and safety, and consumer product performance. In addition, it reports the results of Bureau programs in measurement standards and techniques, properties of matter and materials, engineering standards and services, instrumentation, and automatic data processing. Annual subscription: Domestic, $9.45; Foreign, $11.85.

NONPERIODICALS

Monographs—Major contributions to the technical liter- ature on various subjects related to the Bureau's scientific and technical activities. Handbooks—Recommended codes of engineering and

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Special Publications—Include proceedings of confer- ences sponsored by NBS, NBS annual reports, and other

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as wall charts, pocket cards, and bibliographies.

Applied Mathematics Series—Mathematical tables, manuals, and studies of special interest to physicists, engineers, chemists, biologists, mathematicians, computer programmers, and others engaged in scientific and technical work.

National Standard Reference Data Series—Provides

quantitative data on the physical and chemical properties of materials, compiled from the world's literature and critically evaluated. Developed under a world-wide

program coordinated by NBS. Program under authority

of National Standard Data Act (Public Law 90-396). NOTE: At present the principal publication outlet for these data is the Journal of Physical and Chemical

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Technical Notes—Studies or reports which are complete

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subject. Analogous to monographs but not so comprehensive in scope or definitive in treatment of the subject area. Often serve as a vehicle for final reports of work performed at NBS under the sponsorship of other government agencies.

Voluntary Product Standards—Developed under pro- cedures published by the Department of Commerce in Part 10, Title 15, of the Code of Federal Regulations. The purpose of the standards is to establish nationally

recognized requirements for products, and to provide

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administers this program as a supplement to the activities of the private sector standardizing organizations.

Federal Information Processing Standards Publications (FIPS PUBS)—Publications in this series collectively constitute the Federal Information Processing Standards Register. Register serves as the official source of information in the Federal Government regarding stand- ards issued by NBS pursuant to the Federal Property and Administrative Services Act of 1949 as amended,

Public Law 89-306 (79 Stat. 1127), and as implemented

by Executive Order 11717 (38 FR 12315, dated May 11, 1973) and Part 6 of Title 15 CFR (Code of Federal

Regulations). Consumer Information Series—Practical information, based on NBS research and experience, covering areas

of interest to the consumer. Easily understandable language and illustrations provide useful background

knowledge for shopping in today's technological

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NBS Interagency Reports (NBSIR)—A special series of interim or final reports on work performed by NBS for

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D.C. 20402. BIBLIOGRAPHIC SUBSCRIPTION SERVICES

The following current-awareness and literature-survey

bibliographies are issued periodically by the Bureau:

Cryogenic Data Center Current Awareness Service A literature survey issued biweekly. Annual subscription: Domestic, $20.00; foreign, $25.00.

(..iquefied Natural Gas. A literature survey issued quarterly. Annual subscription: $20.00. Superconducting Devices and Materials. A literature

survey issued quarterly. Annual subscription: $20.00. Send subscription orders and remittances for the pre- ceding bibliographic services to National Technical Information Service, Springfield, Va. 22161.

Electromagnetic Metrology Current Awareness Service Issued monthly. Annual subscription: $100.00 (Special rates for multi-subscriptions). Send subscription order and remittance to Electromagnetics Division, National Bureau of Standards, Boulder, Colo. 80302.
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