EFER

NBS TECHNICAL NOTE 717

U.S.

fPARTMENT

OF

OMMERCE

National

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Methods of

Measurement for

Semiconductor

Materials, Process

Control, and Devices

Quarterly Report

July 1 to September 30, 1971
NATIONAL BUREAU OF STANDARDS

The National Bureau of Standards1 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 measure- ment 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 Center 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—Heat—Mechanics—Optical Physics—Linac

Radiation2—Nuclear Radiation2—Applied Radiation2—Quantum Electronics3—

Electromagnetics3—Time and Frequency3—Laboratory Astrophysics3—Cryogenics3

. THE INSTITUTE FOR MATERIALS RESEARCH conducts materials research lead- ing 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 pro- mote 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 also monitors NBS engineering standards activities and

provides liaison between NBS and national and international engineering standards

bodies. The Institute consists of the following divisions and offices: Engineering Standards Services—Weights and Measures—Invention and

Innovation—Product Evaluation Technology—Building Research—Electronic Technology—Technical Analysis—Measurement Engineering—Office of Fire Programs.

THE CENTER FOR COMPUTER SCIENCES AND TECHNOLOGY conducts re- search and provides technical services designed to aid Government agencies in improving cost effectiveness 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 Center

consists of the following offices and divisions: Information Processing Standards—Computer Information—Computer Services —Systems Development—Information Processing 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,

and directs the public information activities of the Bureau. The Office consists of the following organizational units: Office of Standard Reference Data—Office of Technical Information and

Publications—Library—Office of International Relations.

1 Headquarters and Laboratories at Gaithersburg, Maryland, unless otherwise noted; mailing address Washington, D.C. 20234.

2 Part of the Center for Radiation Research.

3 Located at Boulder, Colorado 80302.
NAL BUREAU OF STANDARDS

( 1 6 1972

Methods of Measurement for

Semiconductor Materials,

717

no- Process Control, and Devices

Quarterly Report, July 1 to September 30, 1971

W. Murray Bullis, Editor

Electronic Technology Division

Institute for Applied Technology

National Bureau of Standards

Washington, D.C. 20234

Jointly Supported by:

The National Bureau of Standards,

The Defense Nuclear Agency,

The U.S. Navy Strategic Systems Project Office, The U.S. Navy Electronic Systems Command,

The Air Force Weapons Laboratory,

The Air Force Cambridge Research Laboratories,

The Advanced Research Projects Agency,

The Atomic Energy Commission, and

The National Aeronautics and Space Administration.

Vau <* **

U.S. DEPARTMENT OF COMMERCE, Peter G. Peterson, Secretary

U.S. NATIONAL BUREAU OF STANDARDS, Lewis M. Branscomb, Director,

Issued April 1972 ^TecYiY> \ Ca\ <^Ve \VO . "7
National Bureau of Standards Technical Note 717

Nat. Bur. Stand. (U.S.), Tech. Note 717, 52 pages (Apr. 1972) CODEN: NBTNAE

Issued April 1972

For sale by the Superintendent of Documents, U.S. Government Printing Office Washintgon, D.C. 20402 (Order by SD Catalog No. C 13.46:717). Price 55 cents.
CONTENTS

PAGE

Foreword vi

1. Introduction 1

2. Highlights 3

3. Methods of Measurement for Semiconductor Materials

3.1. Resistivity 6

3.2. Gold-Doped Silicon 10

3.3. Infrared Methods 13

3.4. Specification of Germanium 17

3.5. References 18

4. Methods of Measurement for Process Control

4.1. Die Attachment Evaluation 19

4.2. Wire Bond Evaluation 22

4.3. References 30

5. Methods of Measurement for Semiconductor Devices

5.1. Thermal Properties of Devices 31

5.2. Thermographic Measurements .... 32

5.3. Microwave Device Measurements 34

5.4. Carrier Transport in Junction Devices 36

5.5. Silicon Nuclear Radiation Detectors 40

5.6. References 42

Appendix A. Joint Program Staff 43

Appendix B. Committee Activities 44

Appendix C. Solid-State Technology & Fabrication Services ... 46

Appendix D. Joint Program Publications 47

in
LIST OF FIGURES

PAGE

1. Typical reverse current-voltage characteristic for a 0.5-mm diameter silicon diode prepared for capacitancevoltage measurements 8

2. Resistivity as a function of gold concentration in

initially n-type silicon 11

3. Infrared response spectra of two lithium-drifted,

germanium gamma-ray detectors 14

4. Comparison of the digital form of an infrared response

spectrum as displayed on the oscilloscope of a multichannel analyzer system with a directly obtained strip

chart recording of the same spectrum 15

5. Infrared response spectrum of a lithium-drifted, silicon

detector after neutron irradiation 16

6. Percent increase in average junction-to-case temperature

difference of diodes with voids over that of their respective controls measured under steady-state and transient

conditions as a function of percent void area in the diode

die attachment 21

7. Schematic representation of device structure assumed in

calculation of wire-bond flexure 23

8. Wire-bond flexure as a function of power dissipation

for triangular and semicircular loops with several

values of initial height 25

9. SEM photomicrograph of a rectangular wire-feed hole in an ultrasonic bonding tool 26

10. Most desirable placement position for capacitor microphone

used in study of variations in vibration amplitudes of the

bonding tool at the fundamental driving frequency and its

harmonics during bonding 27

11. A relatively stable waveshape observed 5 to 10 ms after the

start of bonding showing individual differences in the

harmonic content from peak to peak

12. Measured pull strength as a function of bond angle (0) .... 29

IV
PAGE

13. Common-base circuit for measuring thermal resistance

of transistors using the collector-base voltage as the

temperature sensitive parameter 32

14. Equivalent circuit used to model a transistor for

analysis of delay-time measurements 38

LIST OF TABLES

1. Transitions in Neutron-Irradiated, Lithium-Drifted

Silicon Detector 17

2. Summary of Results of Junction-to-Case Temperature

Difference Measurements 20

v
FOREWORD

The Joint Program on Methods of Measurement for Semiconductor Materials, Process Control, and Devices was undertaken in 1968 to focus NBS efforts to enhance the performance, interchangeability , and reliability of

discrete semiconductor devices and integrated circuits through improvements in methods of measurement for use in specifying materials and devices and in control of device fabrication processes. These improvements

are intended to lead to a set of measurement methods which have been carefully evaluated for technical adequacy, which are acceptable to both

users and suppliers, which can provide a common basis for the purchase

specifications of government agencies, and which will lead to greater

economy in government procurement. In addition, such methods will provide

a basis for controlled improvements in essential device characteristics,

such as uniformity of response to radiation effects.

The Program is supported by the National Bureau of Standards,* the

Defense Atomic Support Agency, T the U.S. Navy Strategic Systems Project

Office, the U.S. Navy Electronics Systems Command,'*' the Air Force Weapons

Laboratory ,^ the Air Force Cambridge Research Laboratories," the Advanced

Research Projects Agency, x the Atomic Energy Commission,** and the National

Aeronautics and Space Administration. lT Although there is not a one-toone correspondence between the tasks described in this report and the

cost centers through which the Program is supported, the concern of certair

sponsors with specific parts of the program is reflected in planning and

conduct of the work.

tt

Through Research and Technical Services Cost Centers 4251126, 4252128, and

4254115.

Through Order EA071-801. (NBS Cost Center 4259522).

Administered by U.S. Naval Ammunition Depot, Crane, Indiana through Project

Order PO-2-0023. (NBS Cost Center 4259533).

Through Project Order PO-2-1034. (NBS Cost Center 4252534).

Through Delivery Order F29601-71-F-0002 . (NBS Cost Center 4252535).

Through Project Order Y71-906. (NBS Cost Center 4251535).

ARPA Order 1889 Monitored by Space and Missile Systems Organization under

MIPR FY76167100331. (NBS Cost Center 4254422).

Division of Biology and Medicine. (NBS Cost Center 4259425).

Through Order S-70003-G, Goddard Space Flight Center. (NBS Cost Center 4254429),

vi
METHODS OF MEASUREMENT FOR

SEMICONDUCTOR MATERIALS, PROCESS CONTROL, AND DEVICES

Quarterly Report

July 1 to September 30, 1971

ABSTRACT

This quarterly progress report, thirteenth of a series,

describes NBS activities directed toward the development of

methods of measurement for semiconductor materials, process

control, and devices. Significant accomplishments during this

reporting period include the disclosure of substantial differences in measurements of transistor delay time, a device characteristic frequently used as a screen in radiation hardness

assurance tests, as measured with two different instruments;

successful application of the infrared response technique to

the study of radiation-damaged, lithium-drifted silicon detectors; and identification of a condition that minimizes wire

flexure and reduces the failure rate of wire bonds in transistors and integrated circuits under slow thermal cycling

conditions. Work is continuing on measurement of resistivity

of semiconductor crystals; study of gold-doped silicon; specification of germanium for gamma-ray detectors; evaluation of

wire bonds and die attachment; measurement of thermal properties of semiconductor devices, delay time and related carrier

transport properties in junction devices, and noise properties

of microwave diodes; and characterization of silicon nuclear

radiation detectors. Supplementary data concerning staff,

standards committee activities, technical services, and publications are included as appendixes.

Key Words: Alpha-particle detectors; aluminum wire ; base

transit time; carrier lifetime; die attachment; electrical

properties; epitaxial silicon; gamma-ray detectors; germanium; gold-doped silicon; infrared response; methods of measurement; microelectronics; microwave diodes; nuclear radiation

detectors; probe techniques (a-c) ; resistivity; semiconductor

devices; semiconductor materials; semiconductor process control; silicon; thermal resistance; thermographic measurements;

ultrasonic bonding; wire bonds.

1. INTRODUCTION

This is the thirteenth quarterly report to the sponsors of the Joint

Program on Methods of Measurement for Semiconductor Materials, Process

Control, and Devices. It summarizes work on a wide variety of measurement
INTRODUCTION

methods that are being studied at the National Bureau of Standards. Since

the Program is a continuing one, the results and conclusions reported here are subject to modification and refinement.

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 report is subdivided according to these

tasks. Highlights of activity during the quarter are given in Section 2.

Section 3 deals with tasks on methods of measurement for materials;

Section 4, with those on methods of measurement for process control; and

Section 5, with those on methods of measurement for devices. References

for each section are listed in a separate subsection at the end of that

section.

The report of each task includes the long-term objective, a narrative description of progress made during this reporting period, and a listing of plans for the immediate future. Additional information concerning the material reported may be obtained directly from individual

staff members connected with the task as indicated throughout the report.

The organization of the Joint Program staff and telephone numbers are

listed in Appendix A.

An important part of the work that frequently goes beyond the task

structure is participation in the activities of various technical standardizing committees. The list of personnel involved with this work givei

in Appendix B suggests the extent of this participation. Additional details of current efforts in this area are given in Section 2.

Background material on the Program and individual tasks may be found

in earlier reports in this series as listed in Appendix D. From time to

time, publications that describe some aspect of the program in greater

detail are prepared. Current publications are also listed in Appendix D.

..
2. HIGHLIGHTS

Significant accomplishments during this reporting period include

successful application of the infrared response technique to the study of

radiation-damaged, lithium-drifted silicon detectors J identification of a

I

condition that minimizes wire flexure and reduces the failure rate of

transistors under slow-thermal cycling conditions; and completion of

initial intercomparison measurements of transistor delay time made with

two different circuits. Highlights of these and other technical activities are presented in this section; details are given in subsequent

sections of the report. This section concludes with a summary of standardization activities being carried out by program staff members.

Resistivity — Measurements of the current and probe-force dependence

of four-probe measurements on lapped specimens were completed. Compared

tfith the mechanical and chem-mechanically polished surfaces of the same

wafers previously measured, lapped surfaces exhibit resistivity values

several tenths of a percent higher than chem-mechanically polished surfaces, and several tenths of a percent lower than mechanically polished

surfaces. General current and pressure dependences are the same for all

surfaces. A modification of the collaborative reference program is under

consideration as an appropriate mechanism for providing resistivity standards to the industry. Attempts to locate the source of low yield of

diodes used in the study of the capacitance-voltage method indicated that

none of the steps in the mechanical processing of in-house diodes affected diode yield if they were followed by chem-mechanical polish prior to

diffusion. Work on detailed study of the relationship between the fourprobe and capacitance-voltage measures of resistivity continued.

Gold-Doped Silicon — Resistivity measurements on gold-doped n-type

silicon wafers and diffusions of gold into p-type silicon wafers were

made as scheduled and analyzed. Several short-time diffusions and annealing treatments were made to study effects due to interstitial gold and

precipitation of gold, respectively. Additional preliminary measurements

of carrier lifetime in gold-diffused wafers were made by the surface

photovoltage method.

Infrared Methods — The infrared response (IRR) technique was used to

study nine germanium diodes; the presence of lithium precipitate clusters

was tentatively identified in two diodes. Initial IRR measurements on

three lithium-drifted silicon detectors, two of which had been subjected

to radiation damage, revealed features at energies associated with divacancies , vacancy-oxygen pairs, and lithium precipitates. A second cryostat has been constructed for use with this technique, and the system for

converting the analog output of the IRR system into digital form was put

into use.

Die Attachment Evaluation — Measurements of steady-state thermal re- sponse and transient thermal response for heating-power pulse widths
HIGHLIGHTS

ranging from 5 to 100 ms were made on several additional groups of diodes

bonded to TO-5 headers with dimples ultrasonically machined into the bonding surface to provide voids of known size. The spread in thermal re- sponse of the group of devices with 20-percent void areas was significantly improved over the spread reported previously for devices which had the same 20-percent dimple area in the header in accord with the finding that some of the previously bonded devices had void areas larger than the dimple. For the various groups of devices the percent increase in sensitivity to voids of transient thermal response over the steady-state thermal

response measurements varied from 123 percent to 333 percent. The in- crease in average steady-state thermal response of the devices with 10

percent void areas over that of their controls was of the same order as the sample standard deviation of the controls for these groups and therefore does not yield a useful indication of the presence of voids. A theoretical study was undertaken to ascertain the limitations of thermal re- sponse techniques for detecting poor die adhesion in the devices under

investigation.

Wire Bond Evaluation — Additional calculations have been carried out

to examine the problem of thermal-expansion-induced wire bond-loop flexing in more detail. Application of a minimum loop-height specification

based on the results of these calculations to a production run of transistors has resulted in a dramatic decrease in failure due to slow thermal

cycling. Progress was made in adapting ribbon-wire bonding techniques to

a production environment. Work was resumed on the study of bonding tool

motion during bonding by means of a capacitor microphone. This work is

directed toward the eventual development of an in-process control technique for the evaluation of bonds. Work on evaluation of the destructive,

double-bond, pull test has resumed with the continuation of experiments

to test the effects on the measured pull strength of single-level bond

pairs of variation in pull rate, pull angle, and hook position. Results

of a second series of tests to determine the effect of variations in bond

angle on the measured pull strength of single-level bond pairs pulled

vertically at the center of the loop did not agree with the results obtained previously.

Thermal Properties of Devices — The common-base thermal resistance

measuring circuit using the transistor emitter-base voltage as the temperature sensitive parameter, was modified so that the collector-base voltage

could also be used as the temperature sensitive parameter to measure

thermal resistance. A single test unit with as much common circuitry as possible was built to facilitate the comparison of these methods with the

common-emitter, base-and-collector switching technique using the transistor base-emitter voltage as the temperature sensitive parameter.

Microwave Device Measurements — A group of 1N23 diodes was measured

for insertion loss to obtain detailed reproducibility data on the waveguide system. The system was then modified by the introduction of new,

rigid base plates and clamping-type supports. The rotary-vane attenuator

i
HIGHLIGHTS

was modified by the addition of two lockable vernier micrometer heads.

Visits were made to two major suppliers of microwave mixer diodes in order

to discuss measurement requirements for mixer diodes and to obtain information and guidance for the planning of future activities in the mixer

diode area.

Carrier Transport in Junction Devices — Preliminary intercomparison

measurements of transistor delay time have been made on the Sandia bridge

and vector voltmeter. Under some conditions of measurement, significantly

different values were obtained for this characteristic that is frequently

used as a screen in radiation hardness assurance tests. Both S-parameter

systems have been assembled and familiarization tests begun. Additional

study has been completed on the problem of high frequency electrical probing of semiconductor devices at the wafer stage. An analysis was completed which relates delay time as measured by the Sandia bridge and the vector voltmeter to internal device time constants.

Standardization Activities — Many of the standardization activities

undertaken by program staff are broader than the technical tasks described in the following sections. These activities involve general staff

support in committees, coordination of efforts which may encompass a variety of tasks, and participation in areas where no direct in-house technical effort is underway. Standardization activities directly related to

particular task areas are reported with the appropriate tasks.

Seven program staff members attended the regular fall meeting of

ASTM Committee F-l on Electronics, in Boston. The new section on Bonding

continued to show considerable vitality with an attendance of nearly 30.

Program staff members accepted responsibility for preparing a number of new and revised methods including measurement of carrier lifetime by the

surface photovoltage method, measuring resistivity profiles by the spreading resistance method, and three leak detection methods. Two documents

were edited at the committee level and four at the subcommittee level by

program staff members.

Activity in connection with JEDEC committees of the Electronic Industries Association was hampered by the cancellation of several meetings

of committees and task groups during the quarter.

Two program staff members attended meetings of SAE Subcommittee A-2N

on Radiation Hardness and Nuclear Survivability and of ASTM Subcommittee

E-10.07 on Radiation Effects on Electronic Materials held in July in

connection with the IEEE Annual Conference on Nuclear and Space Radiation

Effects.
3. METHODS OF MEASUREMENT FOR SEMICONDUCTOR MATERIALS

3.1. RESISTIVITY

Objective : To develop methods suitable for use throughout the electronics industry for measuring resistivity of bulk, epitaxial, and diffused silicon wafers.

Progress : Measurements of the current and probe-force dependence of

four-probe measurements on lapped specimens were completed. Compared

with the mechanical and chem-mechanically polished surfaces of the same wafers previously measured, lapped surfaces exhibit resistivity values

several tenths of a percent higher than chem-mechanically polished surfaces, and several tenths of a percent lower than mechanically polished

surfaces. General current and pressure dependences are the same for all

surfaces. A modification of the collaborative reference program is under

consideration as an appropriate mechanism for providing resistivity standards to the industry. Attempts to locate the source of low yield of

diodes used in the study of the capacitance-voltage method indicated that none of the steps in the mechanical processing of in-house diodes affected

diode yield if they were followed by a chem-mechanical polish prior to

diffusion. Work on detailed study of the relationship between the fourprobe and capacitance-voltage measures of resistivity continued.

Four-Pvobe Method — Measurement of the current and probe-force dependence of resistivity by the four-probe method continued. Measurements

were made on lapped surfaces of the same wafers used previously with

other surface conditions. Each wafer exhibited the same general dependence on current and probe force that had been observed on mechanically

and chem-mechanically polished surfaces of the same specimens. In all

cases wafer surfaces mechanically polished with 0.3 ym diamond grit yield

the highest measured resistivity values. Lapped surfaces yield values a few tenths to perhaps 1 percent lower, and chem-mechanically polished surfaces yield values a few tenths of a percent lower still. In most cases

the sample standard deviation associated with measurements made under a given set of conditions was of the order of 0.5 percent or less. It has

been found that the apparent current dependence of some wafers was due to

order of current sampling as well as to current level but the two effects

have not yet been separated.

These results and those obtained from measurements made on lapped

surfaces at the beginning of this experiment cannot be compared satisfactorily. Although the precision of measurements made under the same current and probe-force conditions shows very little variation between the

two sets of data, considerably greater variation of the measured average

resistivity value on current and probe force was found in the earlier

data. These large variations in the earlier data were erratic functions L of current and probe force and apparently resulted in part from inadequate

teJ
RESISTIVITY

control of unsuspected variables in the experiment. The tighter experimental control initiated after the original set of data was completed is

probably responsible for the reduction of this erratic variability in the

present results. (D. R. Ricks and J. R. Ehrstein)

No further work has been done on the study of subsurface damage in

silicon slices as a result of various steps of wafer preparation. Previous work using an infrared photovoltage technique pointed out the need

for a infrared detector with better sensitivity than that being used. An

improved detector has been installed and the system is again operational.

(W. R. Thurber and W. E. Phillips)

Standardization Activities — Further study was made of the results

of the partially completed round robin on four -probe measurement of re- sistivity of silicon epitaxial layers deposited on substrates of opposite

conductivity being conducted in cooperation with the Resistivity Section

of ASTM Committee F-l on Electronics. The conclusion was reached that

the results to date are not adequate to support a precision statement in

the test method. Plans for resuming the round robin were prepared and

presented at the September meeting of the Committee.

(J. R. Ehrstein and F. H. Brewer)

Proposed methods for providing resistivity standards to the semiconductor device industry (NBS Tech. Note 560, pp. 10-11) were also discussed

at the September meeting of the Committee. As a result of the discussion

'a modified collaborative reference program has been given primary consideration as the most useful vehicle for providing standards. In such a program a consensus definition of standard values is arrived at through

a multipass exchange of material between NBS and the other participants.

The consensus is biased in the direction of the NBS data by virtue of the

fact that NBS measures the circulated specimens immediately before each

shipment to another participant. In addition, if feasible, replicate

specimens are to be provided to each participating laboratory during the

program. Such replicates would provide each laboratory with a link to

the consensus specimens at times when those specimens are in circulation

elsewhere.

A program of this sort would be expected to provide information on

the extent of deterioration of standards samples with use and an understanding of typical "between/within" measurement errors [1] to be experienced in using resistivity standards, as well as to identify changes in

neasurement conditions that might be desirable. It is anticipated that

this means of achieving resistivity standards would be succeeded by a Less cumbersome one, such as one involving the use of standard reference

naterials with certified resistivity values, at some later date. At present, consideration is being given to detailed experimental design, various

experimental safeguards, possible cost to participants, and the general

-ogistics of such a program. (J. R. Ehrstein)

K
RESISTIVITY

Figure 1. Typical reverse currentvoltage characteristic for a 0.5-mm

diameter silicon diode prepared for

capacitance-voltage measurements. (The

wafer was diffused for 63 min at 1038°C

with an oxidized boron nitride source

and an ambient of 99 percent nitrogen,

1 percent oxygen with a flow rate of

about 2500 cur /min. The wafer was initially doped with phosphorous at a ' level of about 3 x 10* k cm

-3

. The

junction depth was 1.05 ym and the

boron surface concentration was 5 x 10 20 cm" 3 .)

Capacitance-Voltage Method — The search continued to discover the

origin of the linear defects observed on low quality diodes (NBS Tech.

Note 702, p. 8). A l.S-^-cm n-type silicon wafer, fully sliced and polished by the manufacturer, was used to fabricate an array of p-n junctions. More than 90 percent of the diodes in the finished array exhibited

reverse breakdown voltages of 50 to 70 V. This suggested that the oxidation, photolithography, and diffusion processes were not the cause of the

previously observed linear defects.

A second group of similar, sliced and polished, 1.8-fl*cm n-type silicon wafers was then subjected to various mechanical treatments to investigate the effect of in-house preparation on final diode yield. These

treatments included lapping, mechanical polishing, and chem-mechanical

polishing. Following these treatments diode arrays were fabricated as before. Wafers which were mechanically polished or lapped and mechanically polished but which had no final chem-mechanical polish treatment

exhibited an average breakdown voltage of about 12 V. The wafer which

had been chem-mechanically polished after lapping exhibited an average

breakdown voltage of 42 V. A current-voltage characteristic typical of

diodes from this wafer is shown in figure 1. Leakage currents to the

point of breakdown in these diodes are usually less than 2 nA at room

temperature. In addition, a diode array that exhibited an average breakdown voltage of 71 V was fabricated on a 2.9-fi'cm n-type silicon wafer

which had been sawed as well as polished in-house. Therefore, it could

be concluded that lapping and mechanical polishing introduced defects

which could then be removed by chem-mechanical polishing.

Since the 12-fi*cm n-type wafers upon which the linear defects were

originally observed had also been chem-mechanically polished in-house,

the origin of the defects in these wafers is still unidentified. An ex- periment to see if the linear defects were inherent in the 12-fi*cm material is currently in progress on a third group of specimens. A wafer of

the 12-fi*cm n-type silicon in which the defects were first observed, a wafer of the 2.9-fi*cm n-type silicon discussed above, and a wafer of

8
RESISTIVITY

1.4-fi»cm n- type silicon are being processed from sawing to diffusion in

preparation for observation and electrical measurements.

(R. L. Mattis, T. F. Leedy, and M. Cosman)

Attention was given to factors which may be used to correct

capacitance-voltage data for fringing around the edge of the diode, diffusion tails into the region being profiled, and back depletion into the

diffused layer. Some of the things considered included a published edge

correction applicable to Schottky barrier diodes [2], the error in com- puted doping density that results from error in the measurement of capacitance, voltage, or diode area of an ideal abrupt junction, and the effect

of making the measurement in a junction which is not abrupt but which can be approximated by an exponential doping distribution over the region of

interest. When the edge correction was applied to existing C-V data the

result was often a flattening of the doping density versus depth profiles.

An edge correction would therefore appear to be suitable, and one applicable to diffused diodes is being sought. (R. L. Mattis)

Difficulties have been experienced in the past getting a high degree

of agreement between resistivity values of bulk silicon slices as measured

by the four-probe technique and as derived from capacitance voltage measurements. Therefore, five sets of ft-type silicon wafers with radial re- sistivity gradient of 5 percent or less at half radius were obtained for

detailed comparison of the capacitance-voltage and four-probe methods for

measuring resistivity. Sets of 20 or more lapped wafers with nominal re- sistivity of 0.2, 0.3, 1.5, 4, and 8-fi'cm are being processed. Three wafers from each set have been visually inspected, profiled along perpendicular diameters by the four-probe method, and chem-mechanically polished

on one side prior to fabrication of diode arrays.

(R. L. Mattis and D. R. Ricks)

Spreading Resistance Methods — A study of probe damage on silicon

wafers with the scanning electron microscope continued. Because of general past difficulties with bulk silicon specimens both with and without

gold coatings, an epitaxial specimen was tried instead. A p-type epitax-

| ial layer of about 0.1-fi* cm on about a 10-fl*cm ft-type substrate was used;

/ electrical contact was made to the epitaxial layer. Moderate resolution

| photographs of 5000 X were obtained, less than the best magnification yet

obtained with bulk silicon, but better than results generally experienced

with bulk silicon. In general, the epitaxial specimen allowed the identification of the probe damage locations with greater ease than was generally true on bulk specimens. Difficulties with apparent surface contamination build-up were not eliminated, however. (J. R. Ehrstein)

Plans ; The study of current and probe-force dependence of four-probe

resistivity will continue on wafers previously measured after the surfaces

are vapor etched. The detailed analysis of results to date will continue,

and an attempt to sort out the current level dependence from the dependence on the order of current level sampling will be made. Work will be

resumed on the use of the surface photovoltage effect in an attempt to
RESISTIVITY

relate surface treatment procedures to changes in subsurface damage and

in measured resistivity.

The round robin on measurement of resistivity of epitaxial layers by

the four-probe method will be resumed. Details related to the establishment of a functional program for providing silicon resistivity standards

to the industry will be investigated.

The experiment currently in progress to identify the source of the

observed linear defects in a wafer used to fabricate diode arrays for C-V

measurements will be completed. Capacitance-voltage and four-probe resistivity values will be compared for slices from the five sets of n-type

silicon wafers. Consideration will be given to the suitability of shallow

diffusions, Schottky barriers, and metal-oxide-semiconductor structures

for measuring doping density in thin layers by C-V methods.

3.2. GOLD-DOPED SILICON

Objective ; To characterize n- and p-type silicon doped with gold

and to develop a model for the energy-level structure of gold-doped silicon which is suitable for use in predicting its characteristics.

Progress ; Resistivity measurements on gold-doped n-type silicon

wafers and diffusions of gold into p-type silicon wafers were made as scheduled and analyzed. Several short-time diffusions and annealing treatments were made to study effects due to interstitial gold and precipitation

of gold, respectively. Additional preliminary measurements of carrier

lifetime in gold-diffused wafers were made by the surface photovoltage

method.

Resistivity Measurements — Resistivity and Hall effect measurements

were made at room temperature (25 ± 1°C) on Hall bars cut from 5-, 80-,

and 400-ft'cm n-type wafers that had been diffused with gold at 850, 950,

1050, 1150, and 1250°C and from 2200-fi'cm n-type wafers diffused at 950,

1050, 1150, and 1250°C. In all cases except the 5-fi'cm wafer diffused at

850°C, the gold concentration exceeds the shallow donor concentration.

As the gold concentration is increased, the resistivity is expected to

reach a maximum and then decrease. Shortly before the maximum the specimens become p-type. At large values of gold concentration the resistivity

should approach a constant value characteristic only of the gold impurity.

The resistivity maximum should occur at the intrinsic value where the product of electron concentration and mobility is equal to the product of

hole concentration and mobility and, except for possible differences in

mobility, be independent of the resistivity of the wafer before gold is

added.

10
GOLD-DOPED SILICON —1

1 1 1 1 1 1

1

1 -i—i—i i

1

1 1—i—i i i 1 1

1

1

-

-""°\ - /'" "

10

5

if

A'- N * Sf \

s / \ % • *

if 2

* »». ^ » i - O N» \» 1 -

i

" N\

_4 n p ^ 10 5 A -cm o* \

~~z 80 XI cm a a x£ •. — 400X1 -cm oa Vx 1 -

\ » 1 2200 XX -cm o* " \ 1 - s

io3 —i i i

' i 1

1 il 1.1 1 1 1 1 1 1 1 1 I 1

1

10" 10* 10" 10' GOLD CONCENTRATION (atoms/cm*)

Figure 2. Resistivity as a function of gold concentration in

initially n-type silicon. (Resistivity of the specimens prior

to gold doping is given. Open

symbols represent specimens

which remained n-type after gold

diffusion; solid symbols, specimens which were converted to ptype by the addition of gold.

The dashed curves indicate the

form of the relationship between resistivity and gold con- centration required by the existence of a common maximum as discussed in the text. Error

bars are not indicated. The

standard deviation of the gold

determination is estimated to

be about 10 percent. Resistivity values are reproducible

within about 10 percent.)

The measured resistivity, shown in figure 2, is generally consistent

with theoretical expectations although it does not agree in a number of

important details. The dashed lines associated with the data points suggest the form the resistivity-concentration curves would have to take in

order to reach a common resistivity maximum near the value of about

3.5 x 10 5 ft*cm calculated for a temperature of 25°C (intrinsic carrier

concentration 1.10 * 10 10 cm

-3

, electron mobility of 1300 cm2 /V*s, and

hole mobility of 500 cm2 /V # s). The differences in shapes of these curves,

the poor fit of the data for the 400-fl*cm specimens, and the n-type nature

of the 5-fl'cm specimen diffused at 1150°C (which appears at the maximum)

all are indicative of either experimental or interpretative difficulties.

The experimental data were taken with a newly fabricated specimen holder

designed to provide improved means for controlling and measuring the specimen temperature which is a most important consideration when measuring

specimens with near-intrinsic resistivity, but this does not preclude the

existence of other experimental problems.

Perhaps even more significant is the fact that the resistivity at the

largest gold concentrations approaches a value lower by at least an order

of magnitude from that predicted by any model examined to date. The value

approached is consistent with the resistivity measured on p-type wafers

which had about the same value of resistivity at a gold concentration of

10 17 atoms per cubic centimeter (NBS Tech. Note 702, pp. 9-10). Evidently

the same mechanism is affecting the resistivity in both types of specimens,

(W. R. Thurber, A. W. Stallings , and W. M. Bullis)

Specimen Preparation — Gold diffusions were completed on sets of

p-type wafers with initial resistivity of 0.5, 1000, and 2000 fi*cm.

Gold concentrations were determined by neutron activation analysis at the

11
GOLD-DOPED SILICON

NBS reactor facility on portions of the wafers diffused at 850, 950, and

1050°C. Wafers diffused at 1150 and 1250°C have been lapped and cut in

preparation for analysis. Four 10-ft»cm p-type wafers were diffused at

1250 °C for times of 8, 16, 32, and 64 hours to determine if foreign

impurities are introduced during the high temperature diffusions.

To examine the effect of interstitial gold on the electrical properties of silicon, diffusions of short duration were done at 950 and 1150°C

in both n- and p-type 2000-fl»cm wafers. A study of possible gold precipitation was begun in which two slices, previously diffused, were lapped

and their rims sandblasted to remove regions of high gold concentration.

One slice was annealed at a higher temperature than the original diffusion and one at a lower temperature.

(W. R. Thurber, A. W. S tailings, J. Krawczyk , and M. Cosman)

Carrier Lifetime Measurements — Measurements of carrier diffusion

length by the surface photovoltage method on the etched surface of a Hall bar cut from a 10-ft* cm p-type wafer with a gold concentration of

4.9 x 10 ltf atoms per cubic centimeter gave a diffusion length of 10 ym.

The value of about 30 ns calculated for the minority carrier lifetime is

consistent with the capture cross section of electrons on the positively

charged gold donor center reported by Fairfield and Gokhale [1] . Preliminary measurements were also made on a portion of a 10-fi»cm p-type

wafer with a gold concentration of 2.9 x 10 16 atoms per cubic centimeter.

Although a diffusion length of about 1 ym was obtained, additional measurements are needed to confirm this value as the degree of reproducibility that can be achieved in measuring such short diffusion lengths has

not been established. The calculated lifetime for a 1 ym diffusion

length is 0.3 ns, somewhat shorter than would be obtained from published

values of capture cross-sections.

(W. R. Thurber, W. E. Phillips, and W. M. Bullis)

Plans ; Electrical measurements will be made on Hall bars cut from

the 0.5-, 10-, 1000- , and 2000-fi*cm gold-diffused p-type wafers. Data

will also be obtained on the wafers which have been diffused to study

interstitial and precipitated gold. Additional material will be selected

for diffusion.

Study of the application of the surface photovoltage methods to the

measurement of short carrier lifetimes will continue. Additional carrier

diffusion length measurements will be made by the surface photovoltage

method on many of the Hall bars used for electrical measurements. The

apparatus will be further improved and studies of the reproducibility

that can be obtained will be undertaken.

Models for the recombination of carriers through the gold centers

will be studied, and available information on capture cross sections

will be examined further. Search for a suitable model to explain the

electrical behavior of heavily gold-doped silicon will continue.

12
3.3. INFRARED METHODS

Objective : To study infrared methods for detecting and counting impurity and defect centers in semiconductors, and, in particular, to evaluate the suitability of the infrared response technique for this purpose.

Progress : The infrared response (IRR) technique was used to study

nine germanium diodes; the presence of lithium precipitate clusters was tentatively identified in two diodes. Initial IRR measurements on three

lithium-drifted silicon detectors, two of which had been subjected to

radiation damage, revealed features at energies associated with divacancies , the vacancy-oxygen pairs, and lithium precipitates. A second cryostat has been constructed for use with this technique, and the system for

converting the analog output of the IRR system into digital form was put

into use.

Infrared Response Measurements on Germanium — The infrared response

(IRR) of nine lithium-drifted germanium diodes was measured during this

quarter. One diode that was of special interest was NBS 83-6, fabricated

from a specimen of the same crystal as were NBS 83-3 and NBS 83-4 (NBS

Tech. Note 598, pp. 14-15). This specimen had been thermally-diffused with

lithium at 390°C for 15 min (depth ^750 ym) and was stored at room temperature for several months prior to lithium drifting. The finished detector

exhibited such severe carrier trapping that no peaks were observed in a

50 Co gamma-ray spectrum (1173.2- and 1332.5-keV gamma rays) despite the

fact that an electric field of several hundred volts per centimeter could

be applied to the device. In figure 3 the IRR spectrum obtained from

NBS-83-6 is compared with that obtained from NBS-83-3 which is considered

to be an example of good-quality germanium. It has been suggested by

Armantrout [1] that the formation of lithium precipitate clusters can introduce bands of energy levels below the conduction band due to the strain

induced in the crystal lattice. Based on results of previous lithium precipitation measurements [2], it is quite likely that considerable lithium

precipitation occurred because of the prolonged storage at room temperature of NBS-83-6 prior to drifting. The bands of levels mentioned above

might then account for the "smearing" of the spectrum of NBS-83-6 relative

to that of NBS-83-3 shown in figure 3. That lithium precipitates have a large trapping cross-section for holes [1] might also account for the

, severe degradation in charge collection observed in NBS-83-6. It is to

be noted that the IRR spectrum of NBS-83-6 bears some resemblance to that

of NBS-113, a specimen of high-purity germanium doped with approximately

10 11 gold atoms per cubic centimeter (NBS Tech. Note 702, pp. 12-13);

however, the maximum in the spectrum at 0.66 eV does not appear in the

spectrum for NBS-83-6.

Subsequently, another specimen, NBS-74, one of the 85 crystals of

various origins collected for the study of germanium problems, was found

to exhibit an IRR spectrum similar to that of NBS-83-6. This specimen

showed poor charge collection as a Ge(Li) detector, both at this and the

originating laboratory; the IRR response suggests that the reason for poor

|] detector quality is the formation of lithium precipitate clusters.

13
INFRARED METHODS

Figure 3. Infrared response spectra of

two lithium-drifted, germanium gamma-ray

detectors.

MBS-83-3

0.50 0.60

ENERGY (eV)

0.70

Two other diodes, NBS-302 and NBS-303, that were characterized by

electron trapping at the originating laboratory were observed to have a strong IRR peak at 0.50 eV indicative of the lithium-defect trap. This

trap was shown previously to be preferential for electrons [1]

(A. H. Sher, W. J. Keery, and H. E. Dyson)

To aid in the intercomparison of IRR spectra from diodes of different sensitive volumes, the first of a series of experiments was performed

on specimen NBS-83-12. The IRR was measured after an initial drifting

period and then measured again after further lithium-drifting. Using a 1-mm thick germanium filter window, an increase in the IRR signal of approximately 30 percent was observed for a 20 percent increase in sensitive volume. (E. A. Simmons)

The construction of a second cryostat for use in IRR measurements has

been completed. This cryostat has the same features as the one currently

in use (see NBS Tech. Note 555, p. 17) but has both a larger charge of

molecular sieve and a larger dewar to increase the holding time of diodes

under study. With the new cryostat an increased number of diodes of the same type can be studied; further, the amount of time required to -prepare

a cryostat for use with diode configurations that require special mounts

is reduced. (W. J. Keery and G. P. Spurlock)

14
INFRARED METHODS

Figure 4. Comparison of the digital form

of an infrared response spectrum as displayed on the oscilloscope of a multichannel analyzer system (top) with a directly obtained strip chart recording

of the same spectrum (bottom).

In figure 4 the digital form of an IRR spectrum photographed from

the oscilloscope display of the multichannel analyzer obtained using the

equipment previously described (NBS Tech. Note 702, pp. 12-13) is compared

with an analog strip chart recording of the same data. The digital information faithfully reproduces the analog form as can be seen from the noise

spikes indicated by arrows. Once stored in the multichannel analyzer, the

spectrum can be printed out in hard copy form, punched onto paper tape for

computer analysis or storage, plotted out by x-y point plotter, or displayed on the oscilloscope. (W. J. Keery)

Several specimens from germanium crystal NBS-83 have been prepared

for neutron irradiation and subsequent IRR measurement. Some specimens were untreated, some were lithium-diffused, and others were compensated

by lithium drifting. (A. H. Sher and Y. M. Liu)

The nearly completed initial phase of the IRR study of germanium

crystals has shown that the improved IRR technique can be used to obtain

information on the energy levels of known defects and impurities introduced into germanium. This phase included measurements of the infrared

response and iron-doped copper-, gold-germanium, and of specimens known

to contain thermally-generated acceptors, lithium-defect centers, and

lithium precipitates. IRR measurements on neutron-irradiated germanium

specimens remain to be done to complete this initial phase.

The second phase, which has been carried on concurrently to some extent with the initial phase in order to gain some understanding of the

15
INFRARED METHODS

Figure 5. Infrared response spectrum of a lithium-drifted, silicon

detector after neutron irradiation.

00

1

NBS- 2S

1 " 1 1 T

ro

1

1— oi Ol - o

1 o1 .

>- c ex. en 1 1 s o

-

(-

1 "Z Ol a? r^ li

«t — o• CO

LU /y

o

z 1 /

D-oo i^

UJ

q: © - o 1 UJ

en 1 <t

a.

LL. z:

1 i 1 1 '

l 1 0.65 0.75 0.85 ENERGY (eV)

0.95 1.05

experimental results obtained thus far, consists of a detailed study of

the literature on photoconductivity measurements on germanium and silicon

containing known impurities and defects and experimental investigation of

the effects of infrared quenching, crystal surface condition, and filter

bandwidth on photoconductivity. This phase of the study is intended to

provide a deeper understanding of the measurement method in order that some general conclusions can be drawn regarding the causes of poor quality

in semiconductor crystals used in the fabrication of nuclear radiation detectors. (A. H. Sher)

Infrared Response Measurements on Silicon — Measurements of IRR on lithium-drifted silicon nuclear radiation detectors of commercial origin

were begun this quarter. These detectors are mounted in metal annular

rings so that unlike the case for the germanium detectors, infrared radiation must be directed through the thin gold contact to the p-type region.

Thus, in addition to the effects of this thin gold electrode that is about

15 nm thick, the applied bias on the detector should have a considerable

effect on the observed IRR spectrum because of its effect on the thickness

of the insensitive, undepleted region behind the p-contact. Such effects

have been observed on a pair of detectors fabricated from the same crystal,

one electron-damaged and the other unirradiated. Work is proceeding on

the interpretation of these effects. The IRR spectrum of NBS-2S, a lithium-drifted detector subjected to neutron irradiation at a fluence of

about 10 11 cm

-2

, taken at 100 K with a 0.14-mm thick silicon filter window

on the cryostat is shown in figure 5. The bandedge peak in silicon was

found to be at 1.17 eV. Features whose energies are identified in figure

5 can be tentatively linked to the defects listed in table 1. A peak at

approximately 0.59 eV (corresponding to one-half the bandgap energy) is

also observed as in the case of germanium (NBS Tech. Note 555, p. 25).

(A. H. Sher, W. J. Keery, and Y. M. Liu)

16
INFRARED METHODS

Table 1 — Features in Neutron- Irradiated,

Lithium-Drifted Silicon Detector

Feature Defect State Origin

0.99 eV E

c

- 0.17 eV vacancy-oxygen paira

0.93 eV E

y + 0.24 eV divacancyb

0.90 eV E v + 0.27 eV lithium precipitate

0.79 eV E c- 0.38 eV divacancyb

0.71 eV E

v + 0.45 eV lithium precipitate

Corbett, J. W. , Electron Radiation Damage in Semiconductors and Metals, Suppl. 7, Solid-State Physics,

(Academic Press, New York, 1966).

Konozenko, I. D. , Semenyak, A. K. , and Khivrich, V. I.,

Radiation Defects Created by Co 50 y-Rays in p~ and

n-Type Silicon of High Purity, Phys. Stat. Sol. 35,

1043-1052 (1969).

Smirnova, I. V., Chapnin, V. A., and Vavilov, V. S.,

Radiation Defects in Lithium-Doped Silicon, Sov. Phys. —

Solid State 4_, 2469-2474 (1962-63).

Plans : An intensive review of photoconductivity literature for germanium and silicon will be begun. The study of the IRR of diodes fabricated from the collection of 85 germanium crystals now on hand will continue

at an increased rate, and the results will be correlated with measured

detector characteristics. The study of the IRR of silicon detectors will

also proceed. Efforts to extend the use of the IRR technique to transistors and diodes will resume.

3.4. SPECIFICATION OF GERMANIUM

Objective : To measure the properties of germanium crystals and to

correlate these properties with the performance of germanium gamma-ray

detectors in order to develop methods for the early identification of

crystals suitable for fabrication into lithium-compensated gamma-ray detectors.

Progress : Principal effort during this quarter was directed toward

the continuing study of the infrared response (IRR) technique. This work

is reported in the section on infrared methods (see Section 3.3). The

operating characteristics of several Ge(Li) detectors were measured in

conjunction with the infrared response study in order to obtain information to aid in the interpretation of the IRR method. Work has resumed on

17
SPECIFICATION OF GERMANIUM

collection of the bibliography of publications relating to Ge(Li) detector

technology that have appeared since January 1, 1969.

(A, H. Sher, W. J. Keery, and H. E. Dyson)

Plans : The Ge(Li) detector bibliography will be completed and preparations will be instituted for its publication. Work on Ge(Li) detectors will be carried out in cooperation with the Germanium Section of

ASTM Committee F-l on Electronics; the exact nature of this effort has

not yet been decided upon by the Section. The results of the study of

infrared response will continue to be applied to the measurement of germanium quality.

3.5. REFERENCES

3.1. Resistivity

1. Mandel, J., Repeatability and Reproducibility, Materials Research and Standards 11, No. 8, 8-15, 52 (1971).

2. Copeland, J. A., Diode Edge Effect on Doping-Profile Measurements, IEEE Trans. Electron Devices ED-17, 404-407 (1970).

3.2. Gold-Doped Silicon

1. Fairfield, J. M. , and Gokhale, B. V., Gold as a Recombination Centre in Silicon,

Solid-State Electronics _8, 685-691 (1965).

3.3. Infrared Methods

1. Armantrout, G. A., Infrared Evaluation Techniques for Ge(Li) Detectors,

IEEE Trans. Nucl. Sci. NS-1? No. 2, 16-23 (1970).

2. Sher, A. H. , Croll, W. K. , and Thurber, W. R. , Determination of Oxygen in Germanium Below 20 Parts per Billion by Measurements of Lithium Mobility and Precipitation, Anal. Chem. 43_, 1831-1834 (1971).

18
4. METHODS OF MEASUREMENT FOR PROCESS CONTROL

4.1. DIE ATTACHMENT EVALUATION

Objective : To evaluate methods for detecting poor die attachment in

semiconductor devices with initial emphasis on the determination of the

applicability of thermal measurements to this problem.

Progress : Work reported previously (NBS Tech. Notes 598, pp. 18-20,

and 702, pp. 15-17) indicated that a measurement of transient thermal re- sponse of a semiconductor diode, using a pre-determined heating power

pulse width, is more sensitive to the presence of voids in the die attachment material between the semiconductor chip and header than is a measurement of the thermal resistance or steady-state thermal response of the

diode. The results reported showed that a 10-percent circular void in the

chip bonding area is the lower limit in void size that can be detected by

using the transient thermal response technique in the particular device

structure studied. It was also found that the spread in thermal response

of a group of devices with 20-percent void areas was significantly larger

than in that of devices with 40-percent and 10-percent void areas.

Measurements of steady-state thermal response and transient thermal

response for heating-power pulse widths ranging from 5 to 100 ms were made

on several groups of diodes bonded to T0-5 headers with dimples ultrasonically machined into the bonding surface to provide voids of known size.

Group K devices consisted of diode chips bonded to T0-5 headers with offcenter 15-mil (0.37-mm) diameter dimples. Group L and M devices consisted

of bare silicon and gold backed diode chips, respectively, bonded to T0-5

headers with 20-mil (0.51-mm) diameter dimples. Ten control devices without voids were bonded with each group of devices with the various size

voids. The spread in thermal response of the Group L devices with the

20-percent void areas was significantly improved over the spread reported

previously for Group H devices which had the same 20-percent dimple area

in the header (NBS Tech. Note 702, pp. 15-16). This result is in accord

with the previous finding that the Group H devices were not properly bonded and that some had void areas larger than the dimple.

The results obtained on the most recently prepared groups as well as on two earlier groups are summarized in table 2. The first group of entries gives the junction-to-case temperature difference measured under

steady-state conditions for the control diodes [AT (controls)] and the

diodes with voids [AT

( (voids)]. A heating current of 300 mA was used.

The third line is the increase in the average junction-to-case temperature

difference of the voided devices over that of their controls expressed

as a percentage of the latter. The range given is one sample standard

deviation. The second group of entries gives the junction-to-case temperature difference measured after a 10-ms long power pulse for the control diodes [AT (controls)] and the diodes with voids [AT (voids)].

19
DIE ATTACHMENT EVALUATION

TABLE 2 — Summary of Results of Junction-to-Case

Temperature Difference Measurements

Lot No. J K a

L M I d

AT (controls) ( •o 1 5. 53±0. 73 15.0o±0.37 15.58±0.48 16.04±0 39 15.02±0. 52 AT

SS (voids) ( 8 C) 15.91±0.57 15.71±0.40b 16.93±0.35c 18.06±0 62

c 16.69±0 59

c

% increase 2.4 ±6.0 4.3 ±3.6 8.7 ±3.8 12.6 ±4 6 11.1 ±5 3

AT

t (controls) CO 12.01±0.90 12. 62±0.72 1 1 . 74±0. 49 14.62±0 67 11.33±0. 55 AT

t (voids) (°C) 13.26+1 . 1

13.83±0.73b 15.66±0.63 c 18.98±1 19° 15.22±0 63c

% increase 10.4±12.3 9.6 ±8.2 33.4 ±7.0 29.8 ±9 5 34.3 ±7 6

% difference (t-s: 333 123 284 137 209

Lot J 15-mil (o 37-mm) diameter (10%) void area

Lot K 15-mil (0 37-mm) diameter (10%) void area, off-center

Lot L 20-Tnil (0 51-mm) diame"ter (20%) void area

Lot M 20-mil (0 51-mm) diameter (20%) void area, gold-backed

Lot I 29-mil (0 74-mm) diameter (40%) void area

a

t = 30 ps me as. 13 diodes

9 diodes

power-pulse width = 9 ms

A heating current of 800 mA was used. The third line of this group is

the increase in the average junction-to-case temperature difference of

the voided devices over that of their controls expressed as a percentage

of the latter. Again, the range given is one sample standard deviation.

The last line of the table gives the difference between the percent in- crease obtained for transient response measurement and that obtained for

steady-state response measurements expressed as a percentage of the latter,

This quantity represents the percent increase in sensitivity to voids of

transient response over that of steady-state response. Except where

otherwise noted each sample group consisted of 10 diodes and the thermal

response was measured 50 us after the termination of the power pulse.

The percent increase in sensitivity to voids of transient thermal

response over the steady-state thermal response measurements varied from

123 percent to 333 percent. It should also be noted that in the case of

the devices with the 10 percent void areas (Columns J and K) , the increase

in average steady-state thermal response of the devices with voids over

that of their controls ranged from 2.4 to 4.3 percent. This increase is

of the same order as the sample standard deviation of the controls for

these groups and therefore does not yield a useful indication of the presence of voids. For the transient thermal response measurements it was

20
DIE ATTACHMENT EVALUATION

l

1 1

1

TRANSIENT RESPONSE

STEADY -STATE RESPONSE

20 30 PERCENT VOID AREA

40

Figure 6. Percent increase in

average junction-to-csse temperature difference of diodes with

voids over that of their respective controls measured under

steady-state and transient conditions as a function of percent

void area in the dioc'e die

attachment. (Error bars indicate one sample standard deviation) .

found that for half of the diodes with voids, the measured junction-tocase temperature difference fell within the scatter obtained on the controls, while the other half showed significantly larger values.

The average percent increase in steady-state and transient thermal

response of the devices with voids over their respective controls is

shown in figure 6 as a function of percent void area. For void areas of

20 and 40 percent, the increase in both steady-state and transient thermal response of the devices with voids over their respective controls is

nearly the same, although the percent increase in transient thermal re- sponse over the controls is three times that of the steady-state thermal

response. This implies that a given increase in electrically measured

thermal response may be indicative of a wide range of void sizes. Also,

the data presented indicate that, at least for this particular device,

measuring steady-state thermal response (or thermal resistance) would not

be an acceptable industrial screening technique to cull out devices with

various size voids due to the low sensitivity of the technique, while

measuring the transient thermal response for a particular heating power

pulse would. Although a 10 percent increase in thermal resistance might

appear to be acceptable from a thermal standpoint, a 20- to 40-percent

void area might be totally unacceptable from a thermal fatigue or thermal

shock viewpoint.

A study was undertaken to determine whether increasing the low level

measuring current would decrease the non-thermal switching effects such

that the temperature sensitive parameter could be measured sooner, thus

increase its sensitivity to voids. The low level measuring current is

that current which is applied after the termination of the heating power

pulse and during which time the temperature sensitive parameter is meas-~~

ured. It was found that by increasing the measuring current from 1 mA to

5 mA, the temperature sensitive parameter could be measured 25 ys after

the termination of the heating power pulse instead of 50 ys . Measurements

made on the group M, gold-backed silicon chip devices, at both 25 and 50 ys

indicated that no general increase in sensitivity was gained by decreasing

the delay time in measuring the temperature sensitive, parameter; in fact,

21
DIE ATTACHMENT EVALUATION

the average sensitivity decreased slightly. The reason for this decrease

in sensitivity appears to be the slow rate of cooling of these devices

between 10 and 50 us combined with the wide variation in the rate of cooling of the devices with voids. (F. F. Oettinger and R. L. Gladhill)

A theoretical study was undertaken to ascertain the limitations of

thermal response techniques for detecting poor die adhesion in the devices

under investigation. A tool that is being considered for use in this

study is the TRUMP [1] thermal analysis program. This program is expected

to allow both transient and steady-state temperature distributions to be

calculated for multidimensional systems.

(W. E. Phillips and F. F. Oettinger)

Plans : Measurements of steady-state and transient thermal response

on diodes with two controlled voids, having a total void area of 20 percent will be made to investigate the dependence of thermal response on

the details of the void geometry. Measurements will also be made on diode chips bonded to solid-steel T0-5 headers. These measurements are intended to test the assumption that the transient thermal response for a given chip size and power dissipation, measured under conditions such that

the heating power pulse width is less than the case time constant, is relatively independent of the case thermal resistance. A study will be un- dertaken to determine to what extent the transient thermal response measurement procedure can be simplified and made less time consuming for use

as an industrial screen. The theoretical study to determine the limitations of thermal response techniques for detecting poor die adhesion in

the devices under investigation will continue. Experiments to apply the

transient thermal response technique to include transistors with poor die

adhesion will be initiated.

4.2. WIRE BOND EVALUATION

Objective : To survey and evaluate methods for characterizing wire

bond systems in semiconductor devices and where necessary to improve

existing methods or develop new methods in order to detect more reliably

those bonds which eventually will fail.

Progress : Additional calculations have been carried out to examine

the problem of thermal-expansion-induced wire bond-loop flexing in more

detail. Application of a minimum loop-height specification based on the

results of these calculations to a production run of transistors has re- sulted in a dramatic decrease in failure due to slow thermal cycling.

Progress was made in adapting ribbon-wire bonding techniques to a production environment. Work was resumed on the study of bonding tool motion

during bonding by means of a capacitor microphone. This work is directed

toward the eventual development of an in-process control technique for

22
WIRE BOND EVALUATION

Figure 7. Schematic representation of

device structure assumed in calculation

of wire-bond flexure.

SILICON D IE 1 0.125 mm

I mm

the evaluation of bonds. Work on evaluation of the destructive, doublebond, pull test has resumed with the continuation of experiments to test

the effects on the measured pull strength of single-level bond pairs of

variation in pull rate, pull angle, and hook position. Results of a second series of tests to determine the effect of variations in bond angle

on the measured pull strength of single-level bond pairs pulled vertically

at the center of the loop did not agree with the results obtained previously.

Bond Failure from Slow Thermal Cycling — Transistor failure under

conditions of thermal cycling at slow rates has been traced to wire fatigue resulting from repeated thermal-expansion- induced wire flexing as discussed previously (NBS Tech. Note 598, pp. 24-25). Additional calculations of wire flexure have been carried out to examine this problem in

greater detail.

The analysis was made specifically for the 1-mil (25-um) diameter

post-to-die aluminum wire interconnection in a 500-mW, 50-mA silicon

transistor in a TO-18 can with post and header of the usual iron-nickelcobalt alloy, but it is generally applicable to other devices with similar

current and power ratings. The device under study is shown schematically

in figure 7. It was assumed that all heat was generated as a result of

power dissipation in the device; Joule (I 2 R) heating in the wire was as- sumed to be insignificant at the relatively low current levels in the

device. Based on manufacturer's specifications and empirical data and

for an ambient temperature of 23°C the junction temperature was taken as

T = 23 + 0.314 P; the temperature under the die, as T = T - 0.012 P;

and the case temperature, as T = 23 + P 0,7 where the power dissipation,

P, is in milliwatts.

Thermal expansion was assumed to be linear over the test range and

the expansion coefficients were taken as 2, 5, and 24 x 10~6 /°C for silicon, iron-nickel-cobalt alloy, and aluminum, respectively. The header

expansion was assumed to be due only to the change in case temperature;

local heating under the die only increases internal header stress. Die

expansion was calculated on the basis of a uniform temperature taken to

be the arithmetical average of the top and bottom temperatures. The

23
WIRE BOND EVALUATION

change in length of the various elements is then:

X(P) = X

Q

[1 + a(T - 23)],

where X_ is the length of the element at ambient temperature, a is the

thermal expansion coefficient of the material, and T is the temperature

of the element, a function of the power dissipation, P. The wire is attached at points on the post and the die. The bond-to-bond distance, L,

is given by

L = [d 2 + (Y - Z) 2

] 1 / 2

,

where d is the bond-to-bond distance in the plane of the header, Y is

the post height and Z is the die height.

The temperature distribution along the wire was accounted for with

i a

c

the assumption that the temperature decreased exponentially from T to

T with a characteristic length, X:

T(x) = T

c + (Tj - T

c

) exp (-x/X)

where x is the coordinate along the wire in the direction from the die

to the post. If X = S n /2, the length of the wire is:

S = S Q

[1 + aA1 (0-57T

c + 0.43^ - 23)].

The prefactors for T and T are changed if other values of X are selectj

dL J

The flexure can be defined as the change in loop height

AH

L

-

H

L

" H

L0- £

The functional relationship between loop height and the lengths S and L

depends on the shape of the wire loop. Calculations were made for two

cases; bending moments in the wire were neglected. If the wire loop is

in the form of an arc of a circle, the loop height is given approximately

by:

H = [3(3S + 5L) (S - L)] l/2 /8,

If the loop is assumed to retain its circular shape during flexing, this

expression is appropriate for calculations before and after flexing. The

calculation is made by selecting a value for IL _ and computing S„ to obtain the initial condition. Then S, L, and AHT are computed for various

values of P to obtain the flexure as a function of power dissipation.

The results for H _ = 50, 100, and 250 ym are identified by semicircular

symbols in figure 8.

24

^B
WIRE BOND EVALUATION

Tj co

55 85

1000

Figure 8. Wire-bond flexure

(AH ) as a function of power

dissipation (?

n

) fox-1 triangular1 (A) and semicircular (Q) loops

with several values of initial

height (H

Q

).

Pn (mW)

If the wire loop is in the form of a triangle, the loop height is

given by

H = 2[s (s - a) (s - b) (s - L)] x / 2 /L,

Ju where a + b = S and s = (a + b + L)/2. This formulation allows the dift _ference in expansion of the die and post ends of the wire, which results

from the temperature distribution along the wire

count

to be taken into actelj

Results for the case where a„ = b_ = S n /2 are identified by triangular symbols in figure 8.

From these plots, it can be seen that regardless of the details of

the model the flexure is approximately proportional to power dissipated

and approximately inversely proportional to initial loop height. Increasing loop height would be expected to reduce failures from this cause. A

group of transistors fabricated with a loop height of 300 to 375 urn sur- vived more than 70,000 slow thermal cycles without a failure whereas in

earlier groups failures began to occur from a few hundred to a few thousand cycles. (W. E. Phillips)

Ribbon-Wire Bonding — Problems encountered in setting up the ribbon

wire bonding machine were discussed last quarter (NBS Tech. Note 702,

p. 19). The most serious problem was a jumping and bouncing motion of

|the bonding tool immediately after the first bond is made. Although com- plete correction of this undesired motion can be accomplished only by re- designing the transducer-motion cam, considerable reduction of the undesired motion was achieved by regrinding the appropriate surfaces of the

existing cam by hand.

25
WIRE BOND EVALUATION

Figure 9. SEM photomicrograph of a rec- tangular wire-feed hole in an ultrasonic

bonding tool. (There is a slight build

up of aluminum in the upper left corner

of the hole.. Magnification: about

750 X.)

The variability of bond tail-length, observed last quarter, was re- duced by a factor of two by improving the wire feed mechanism. This taillength variation, which is only of cosmetic concern to bonding on a laboratory basis, must be controlled before the machine can be used in production since long wire tails may cause short circuits. The remaining

tail-length variation now appears to result entirely from the non-uniform

dimensions of the available ribbon wire also observed last quarter. This

non-uniformity prevents the machine wire cut-off characteristics from being further optimized for a specific wire thickness. For the conditions

used, a flatter wire has a shorter tail; a more nearly square wire has a longer tail.

As yet a solution to the control of wire size has not been reached.

Contact has been made with several manufacturers. A contract has been

let to one supplier to furnish aluminum wire in a variety of sizes and

in two different alloys (1 percent silicon or 1 percent magnesium) so that

optimum sizes and alloy can be selected.

For bonding with ribbon-wire, the wire feed and clamp mechanism must

be modified so that the clamps are horizontal instead of vertical, as is

normal with round-wire bonding machines. Two bonding machine manufacturers have developed wire feed and clamp mechanisms; a third has a mechanism

under development. Ribbon-wire bonding feasibility, from an economic

point of view, would be enhanced if suitable retrofit ribbon-wire clamping

mechanisms are made available. Then device manufacturers would not have

to invest in new bonders in order to bond devices with ribbon-wire.

Some modification of bonding tools may also be desirable for use in

ribbon-wire bonding. At present, a variety of shapes for the bonding

face are being studied. Since some of the shapes to be studied are not

commercially available, it has been necessary to develop techniques for

regrinding tools to the desired shape. The technique for repolishing flat

tools (NBS Tech. Note 702, p. 20) is being used to obtain flat surfaces

26
WIRE BOND EVALUATION

TAPER. ,

ol I I 1 I I

Figure 10. Most desirable placement position for capacitor microphone used in

study of variations in vibration amplitudes

of the bonding tool at the fundamental

driving frequency and its harmonics during

bending.' (Measurements may also be made

at the upper node, but with somewhat different results.

)

VIBRATION AMPLITUDE (RELATIVE VALUES)

which are then modified to a convex or concave shape with or without

grooves.

A second modification to the bonding tool that is desirable but not

essential is the introduction of a rectangular wire-feed hole. The tools

now being used in the experimental work were obtained commercially. An

SEM photomicrograph of the rectangular feed hole in one of these tools is

shown in figure 9. A different manufacturer has agreed to make such tools

if NBS supplies the tungsten ribbon-wire required in the electricaldischarge-machining operation. Although a commercial source of small size

tungsten ribbon-wire could not be located, it was a relatively simple

process to flatten 0.001-in (25-um) and 0.002-in. (50-um) diameter round

wire by placing the tungsten wire in a press between glass plates, and

applying a load of 6.5 to 11 ksi (45 to 76 MN/m2

) for 0.001-in (25-um)

diameter wire, or 15 to 21 ksi (103 to 145 MN/m2 ), for 0.002-in (50-um)

diameter wire, to flatten it. The resulting ribbon was not generally uniform, but pieces could be selected for the desired sizes of rectangular

holes. (H. K. Kessler and G. G. Harman)

In-Proaess Bond Quality Determination — Work was resumed on the study

of bonding tool motion during bonding (NBS Tech. Notes 592, pp. 39-41,

and 598, p. 27). The object of this study is to analyze the ultrasonic

vibration amplitudes at various points along the bonding tool during the

process of making a bond. The detector used in this study is a capacitor

microphone that responds to frequencies up to approximately 200 kHz. Information gained from this study is expected to increase the understanding

of the ultrasonic bonding process and may lead to an in-process control

technique for evaluation of bonds.

Present studies have indicated that the most sensitive and desirable

microphone pickup point is at a node of the fundamental frequency on the

27
WIRE BOND EVALUATION

Figure 11. A relatively stable waveshape

observed 5 to 10 ms after the start of

bonding showing individual differences in

the harmonic content from peak to peak.

(This was obtained with the microphone

placed at a node as shown in figure 10.

Vertical axis: 20 millivolts per division. Horizontal axis: 20 microseconds

per division.

M nil i & i iji sii

ill jy 'ti q 1} jy ij fy a

tool as shown in figure 10. This position has the advantage that the

60-kHz fundamental is essentially cancelled out. Since higher harmonics

do not share a common node with the fundamental, their relative amplitude

is enhanced. For this application, a hole in the microphone taper (NBS

Tech. Note 520, pp. 63-66) of approximately 0.020-in. (0.5-mm) diameter is

most suitable since it straddles the node. Under loaded conditions when

the tool is transmitting ultrasonic energy into the bond, the node associated with the fundamental shifts by as much as 0.007 in. (0.18 mm) (NBS

Tech. Note 520, p. 39). As a result the amplitude of the fundamental in- creases by about a factor of two, but the amplitudes of various harmonics

increase even more.

A typical ultrasonic bond with 0.001-in. (25-um) diameter aluminum

wire is made within 3000 to 6000 cycles of the vibrating bonding tool

(50 to 100 ms) . The continually changing amplitude, measured at the node,

can be described as follows: During the first 10 to 20 cycles the amplitude is small and erratically distorted; the wave shape is primarily the

60-kHz fundamental. Little or no ultrasonic energy appears to be being

transmitted into the wire or bonding pad. The amplitude grows rapidly

for the next 10 to 20 cycles; the wave shape remains essentially 60-kHz.

After 300 to 600 cycles (5 to 10 ms) the amplitude becomes relatively

stable; higher harmonics are clearly evident in the waveshape as shown in

figure 11. During the next 30 to 40 ms as the bond is made the amplitude

increases slowly and the leading peak becomes more prominent.

(G. G. Harman)

Pull Test Evaluation — Work on evaluation of the destructive, doublebond, pull test was resumed. An extensive series of experiments has been

initiated to test the effects on the measured pull strength of singlelevel bond pairs of variation in pull rate, pull angle, and position of

the hook along the loop.

A second series of tests was conducted to determine the effect of

variations in bond angle (or ratio of loop height to bond-to-bond spacing)

on the measured pull strength of single-level bond pairs pulled at the

center of the loop in a direction perpendicular to the plane of the pads.

Eight groups of 20 single-level bond pairs were made with different loop

28

E^BHBOHH
WIRE BOND EVALUATION

140 Figure 12. Measured pull strength as

a function of bond angle (0). (The

solid line is calculated from the

resolution of forces; the numerical

factor is twice the breaking force

in the wire.

)

7.0 i r i r

25 30 35 40 45

6 (degrees)

a. Unannealed.

50 55

b. Annealed.

heights and spacings. The bond angle varied from 25.7 to 50.3 deg. Ten

of the bond pairs in each group were pulled in the unannealed condition;

1 all broke at the heel of the first bond. The remaining groups of 10 were

| annealed at 500° C for 20 min and then pulled; essentially all broke in

the wire span.

Results of the experiment are shown in figure 12. The mean measured

pull strength and 95 percent confidence intervals for the mean are plotted

for each group against the bond angle; bond angles for the annealed wire

have been adjusted to account for the elongation of about 8 percent that

occurred before breakage (NBS Tech. Note 592, p. 36). The solid curves

I are calculated from the resolution-of-forces equation (NBS Tech. Note 555,

| pp. 31-35) for the symmetrical case under study:

T = 2T sin 0, w where T is the measured pull strength, T is the force in the wire, and

is the bond angle. In the unannealed case, where the break occurs at

the heel of the first bond, the calculated pull strength agrees with the

, measured value, but for annealed bonds, where the break occurs in the

' wire span, the measured pull strength is much less dependent on bond

j angle. These results are not in agreement with earlier experiments (NBS

Tech. Notes 571, pp. 24-26, and 592, pp. 36-37); the origin of the differences has not yet been established. (K. 0. Leedy and C. A. Main)

29
WIRE BOND EVALUATION

Bibliography and Critical Review — Preparation of an annotated bibliography of limited distribution reports concerned with degradation and

testing of wire bonds was begun. The bibliography of the open literature

[1] was prepared for printing. Work on the final draft of the critical

survey paper continued, and editorial procedures for publication clearance

were initiated. (H. A. SchafftO

Plans : Evaluation of ribbon wire for ultrasonic bonding will contin-j

ue. Further theoretical and experimental work on electronic mixing of

bonding tool ultrasonic signals with local oscillators will continue in

the effort to better understand and control bonding. Experimental and

statistical analysis of significant factors in the wire bond pull test

will continue.

The preparation of the bibliography of the open literature will be

completed and sent to the printer. The critical survey paper will be

prepared for publication clearance. A draft of the bibliography of limite

distribution reports will be prepared.

4.3. REFERENCES

4.1. Die Attachment Evaluation

1. Edwards, A. L. , TRUMP: A Computer Program for Transient and Steady-State Temperature Distributions in Multidimensional Systems, Lawrence Radiation Laboratory, Univ. of California, Livermore, California, UCRL-14754 Rev. I., 1 May

1968. Available from the National Technical Information Service, Springfield

Virginia 22151.

4.2. Wire Bond Evaluation

1. Schafft, H. A., Wire Bond Electrical Connections- Testing, Fabrication and Degradation- A Bibliography 1957-1971, NBS Tech. Note 593, January, 1972.

:

il

2:

30
5. METHODS OF MEASUREMENT FOR SEMICONDUCTOR DEVICES

5.1. THERMAL PROPERTIES OF DEVICES

Objective : To evaluate and, if necessary, improve electrical meas- urement techniques for determining the thermal characteristics of semiconductor devices.

Progress : The preliminary round robin on thermal resistance being

conducted in cooperation with JEDEC Committee JC-25 on Power Transistors

jas continued. The 14 test specimens are being measured under specified

levice operating conditions with thermal resistance test equipment that

jxists in each participating organization. The temperature sensitive

>arameter is to be measured 10, 20, 50, and 100 us after the termination

)f the heating power pulse. The devices are now in the hands of the

:hird participant.

The literature search and work on the bibliography on thermal resis-

:ance and transient thermal response measurements were resumed.

(F. F. Oettinger)

The study was continued to compare other frequently used thermal resistance measuring methods with the common-emitter base-and-collector

switching technique. In this technique the base-emitter voltage, V

,

Is used as the temperature sensitive parameter, TSP. The common-base

:hermal resistance measuring circuit in which the emitter-base voltage,

/ , is used as the TSP was modified so that the collector-base voltage

could also be used as the TSP. This circuit, shown in figure 13, is generated from the earlier circuit (NBS Tech. Note 702, pp. 23-24) by disconnecting both the sample-and-hold unit and the negative lead of the V

neasuring current supply from the emitter terminal of the transistor

jnder test and reconnecting them to the collector terminal. The new cir-

:uit functions in the same manner as the previously described unmodified

circuit. In order to facilitate the comparison of the three techniques

for measuring thermal resistance a single test unit which incorporates

as much common circuitry as possible was fabricated.

1 Initial measurements made on a triple-diffused power transistor indicated that the difference in thermal resistance when measured using V

and V as the TSP was less than 10 percent of the average value, while

for measurements made on a wide-base, single-diffused power transistor

the difference was less than 5 percent. In both cases, using Vr as the

TSP gave lower values of thermal resistance than using V . It xs not yet

apparent whether this difference is real or due in part to effects of

ion-thermal switching transients.

At one time during the quarter it was found that the difference between thermal resistance as measured by the V and V methods increased

trom the 2 or 3 percent reported previously (NBS Tech. Note 702, pp. 25-

16) to approximately 10 percent. The cause of this deviation was traced

31
THERMAL PROPERTIES OF DEVICES

Figure 13. Common-base circuit

for measuring thermal resistance

of transistors using the collectorbase voltage as the temperature

sensitive parameter.

to excessive leakage through the biased-off collector switching transistor, Ql. This observation- showed the importance of using a very lowleakage device in this position in the measuring circuit.

(S. Rubin and F. F. Oettinger)

Plans : The literature search and work on the bibliography on thermal

resistance and transient thermal response measurements will continue.

The comparison of thermal resistance measurements using VT iture sensitive paramete:

made on a variety of device types

BE'

V

EB'

and V

CB

as temperature sensitive parameters will continue; measurements will be

5.2, THERMOGRAPHIC MEASUREMENTS

Objective : To evaluate the utility of thermographic techniques for

the detection of hot spots and measurement of temperature distribution in

semiconductor devices.

Progress : Initial attempts were made to coat various devices with

phosphors by the slurry-settling technique (NBS Tech. Note 702, p. 28).

It does not appear possible at this time to coat each device with an opaque, uniform, and controlled thickness of phosphor because of difficulties associated with the device surface contour, header construction, device position on the header, lead size, and lead location. As a result,

it is not possible to eliminate the necessity of calibrating each point

on a phosphor-coated device at which it is desired to know the temperature.

The calibration is accomplished by maintaining the device in an unpowered

state at a known temperature and measuring the fluorescent intensity of

the phosphor at each point of interest for a constant intensity of ultraviolet radiation. The temperature of the device during calibration is

varied to span the entire expected temperature range of the surface when

the device is operated.

Further studies were made of both microcopy resolution charts (NBS

Tech. Note 592, p. 56) and metallization patterns on silicon and silicon

dioxide to determine their suitability for measuring the spatial resolution

32
THERMOGRAPHIC MEASUREMENTS

of the 50-ym fiber-optic probe. Neither had a sharp enough transition

from the white, highly reflecting to the black, poorly reflecting surfaces

to be suitable for this purpose. The information to date indicates that

the distance over which the apparent intensity as measured with the fiber

optic probe varies from 10 to 90 percent of the total intensity change at a step boundary is no more than 35 urn.

Measurements were made to compare the relative uniformity of phosphor

coatings deposited by the slurry-settling technique and the water-flotation

technique. The 50-ym fiber-optic probe was scanned over a 1-mm long re- gion of the coated wafer. The scans were made on a wafer coated with a phosphor with a temperature sensitive range of 120 to 280°C for six different temperatures within the temperature range. For each of the temperatures, the standard deviation about the average phosphor intensity for

the water-flotation technique was about ±10 percent (approximately equal

to ±2°C) and for the slurry settling technique about ±3 percent (±0.6°C).

The difference is a result of the thicker coating one can obtain using the

slurry-settling technique (about 50 urn in this instance) compared to the

water-flotation technique (generally about 10-15 urn thick).

i Preliminary experiments have been performed to establish if it is

feasible to use the photomultiplier tube and present optical equipment to

measure the transient response of the phosphors to a heat pulse. The

measurements were performed on a transistor chip coated with a phosphor

that covers the range from room temperature to 80° C. It was found that

noise on the output of the photomultiplier tube was great enough that

quantitative measurements would be very difficult without cooling the

tube. Recent work by Blanks [1] indicates that the best response time

one can achieve with the phosphors of the type being used is 200 ys . This

is hardly fast enough to be of much value as a transient thermographic

technique for device studies. Blanks [1] does mention a phosphor with a response time of 35 ys , but the thermal sensitivity (2 percent change in

intensity per degree Celsius) is probably too small to make it of use as

a thermographic tool.

A survey of the literature concerned with thermographic techniques

pother than thermographic phosphors is being conducted. The technique

which is now of greatest value for thermographic device studies is infrared microscopy. Scanning electron microscopy and holographic micoscopic

•interferometry are two other methods which are of potential value for

, thermographic device studies. (D. L. Blackburn and L. R. Williams)

Plans : To conclude the evaluation phase of the thermographic phosphor study, experiments will be designed to determine the spatialtemperature resolution of the phosphors and to establish the accuracy with

which the temperature of a hot spot can be measured with the phosphors.

These experiments will require an independent measurement of the temperature distribution of the devices under study. An infrared microradiometer

will be obtained for this independent measurement; experimental work will

not begin until April, 1972.

33
5.3. MICROWAVE DEVICE MEASUREMENTS

Objective : To study the problems and uncertainties associated with

the measurement of microwave devices, and to improve the techniques of

these measurements.

Progress : Lack of rigidity in the waveguide system has been reported as a limitation on the precision that can be achieved in making conversion loss measurements (NBS Tech. Note 702, p. 30). To obtain detailed

reproducibility data on the original waveguide system, the supporting

jacks were adjusted to give the most stable and uniform support, and 16

type 1N23 (and equivalent) diodes of assorted makes and suffix letters

(mostly WE's, with some E's and D's) were measured for insertion loss

(conversion loss without i.f. mismatch correction) using the incremental

modulation method described last quarter (NBS Tech. Note 702, pp. 29-30).

Each diode was measured twice after insertion in the holder; it was then

removed from the holder and immediately reinserted with the same angular

orientation and again measured twice before removal. An identical run was made the following day, after the local oscillator power had been re- adjusted with a bolometer substituted for the mixer. Two diodes appeared

to be unstable, as evidenced by large loss differences. Excluding these

unstable devices it was found that differences between pairs of readings

taken on the same diode after removal and reinsertion were, on the average, about twice as large as differences between pairs of readings taken

at the same time without removing the diode between readings . It was

also found that, excluding the two unstable devices, differences between

pairs of readings from the two runs conducted on successive days were on

the average about three times as large as differences between pairs of

readings taken at the same time without removing the diode between readings. It has not yet been determined how much of this additional variation was due to waveguide motion, how much to lack of reproducibility at

the diode contact and waveguide flange, and how much to local oscillator

and voltmeter drift.

To prevent power changes due to waveguide motion, a clamping-type

support system has been designed and constructed. The support system

consists of the following: A lower base plate of %-in. thick aluminum

alloy covering the bench top supports an upper base plate of the same size

and material. The upper base plate is divided into two sections, one of

which supports that part of the waveguide structure that will be sent to

NBS-Boulder for noise calibration. The upper base plate sections were

drilled and tapped at 1-in. intervals over their surfaces to accept

threaded brass rods used in clamping the waveguide. The threaded rods

pass through aluminum alloy waveguide support blocks to which they are rigidly locked by nuts. The waveguide is held down against each support

block by an aluminum alloy top plate which is drilled to clear the rods

and secured with even pressure by means of wing nuts.

In order to facilitate clamping of the waveguide to the base plate,

and to accomodate the lesser but more critical power requirements of a new type of synchronizer used to phase-lock the klystron, the waveguide

34
MICROWAVE DEVICE MEASUREMENTS

system between the klystron and the modulation attenuator was rebuilt.

Most of the changes were mechanical, to eliminate elevation of some com- ponents over other components. Minor electrical changes include the substitution of a 20 dB directional coupler to connect the leveling loop de-

. tector for the 10 dB coupler previously used (NBS Tech. Note 598, pp. 36-

38) , the addition of a level-set attenuator next to the phase-lock (synchronizer) coupling in order to reduce the power to an optimum level, and

the return to the use of a hybrid tee (NBS Tech. Note 560, p. 43) in place

of the 20 dB directional coupler used to divide power between the phaselock (synchronizer) and the wavemeter. The resulting power increase to

the wavemeter allows the making of klystron adjustments with a passive

D' Arsonval-Weston type microammeter instead of with the more sluggish and

less stable electronic galvanometer.

The rotary-vane type precision attenuator, used to set the power

incremental in the incremental modulation method of measuring mixer con- version loss, was modified by the addition of two lockable 0- to 1-in.

vernier micrometer heads that engage round-headed fixed stops screwed to

opposite assembly flanges of the rotating drum holding the center vane.

In order to use this attenuator to set precisely two independent power

increments (one above and the other below the local oscillator level) an attempt is currently being made to add a third stop to be used to estabI lish the upper increment, from local oscillator level to modulation peak.

The micrometer head for this stop is mounted on a hinged platform so that

I it may be swung clear to allow use of the other stop on the same side of

1 the rotating drum. This second stop is used to establish the more critij cal and more frequently required peak-to-trough bilateral increment. Both

t of these increments also depend upon the stop on the opposite side of the

I rotating drum. By keeping this stop at the zero vane angle position its

uncertainty contribution is minimized. These modifications not only greatly increase the accuracy that can be achieved, but allow the attenuator to

be used directly as the modulator, instead of using it to calibrate the

i electrical (leveling loop) modulator, should the latter prove to be insufficiently repeatable.

Visits were made to two major suppliers of microwave mixer diodes in

order to discuss measurement requirements for these devices and to obtain

information and guidance for the planning of future activities in this

< area. These discussions indicated that the fixed-tuned MIL-standard holdi ers (diode mounts) for the various frequency bands may not be sufficiently

! reproducible, although there was disagreement between manufacturers as to

which bands presented the most serious problems. It appears, that the

holder problem may have to be studied at an earlier phase in the program

than had been anticipated. (J. M. Kenney)

Plans : The first meeting of the IEEE Task Group concerned with mixer

diodes and video detector diodes will be held at NBS early next quarter.

This group is a part of the IEEE-GED Standards Committee for Electron Devices. The main item to be discussed at this meeting is IEC document

35
MICROWAVE DEVICE MEASUREMENTS

47(Central Office)376. The subject of this document is general principles

of measuring methods for mixer diodes used at microwave frequencies.

Fabrication of the third attenuator stop and installation of the

clamping-type waveguide support system will be completed. Additional con- version loss measurements will be taken to estimate the repeatability

that can be achieved with the modified system. The precision modulation

attenuator and the bolometers used for power measurement will be calibrated at NBS-Boulder.

5.4. CARRIER TRANSPORT IN JUNCTION DEVICES

Objective ; To improve methods of measurement for charge carrier

transport and related properties of junction semiconductor devices.

Progress : Preliminary intercomparison measurements of transistor

delay time have been made on the Sandia bridge [1] and vector voltmeter.

Under some conditions of measurement, significantly different values were

obtained for this characteristic that is frequently used as a screen in

radiation hardness assurance tests. Both S-parameter systems have been

assembled and familiarization tests begun. Additional study has been

completed on the problem of high-frequency electrical probing of semiconductor devices at the wafer stage. An analysis was completed which relates

delay time as measured by the Sandia bridge and the vector voltmeter to

internal device time constants.

Experimental — Intercomparison measurements of transistor delay time

have been started on the two completed measurement systems. In describing

the initial results, one of these systems is designated as system A and

the other as system B. Measurements were made on three transistor types:

2N2219, 2N2222, and 2N2907A. These are all low power (less than one watt)

silicon units. The first two types are n-p-n and the last is a p-n-p

Measurements of delay time were made on each system for various frequencies between 3 and 30 MHz and at various emitter currents up to about

50 mA. The collector-base junction had a constant reverse bias of 5 V. In some cases, the transistors oscillated initially, but this was cured

by threading ferrite beads onto the collector leads.

For a given transistor and measurement frequency, the measured delay

time decreased with emitter current in the manner expected, and asymptotically reached its minimum value at a current between 30 and 50 mA, for

both systems. For 2N2219 transistors, as measured with system A, the

shapes of the curves of delay-time as a function of emitter current were

similar; for frequencies between about 3 and 10 MHz, the curves were displaced significantly one from the other, but for measurements made between

10 and 30 MHz the curves were within about 5 percent of one another. For

all devices, system A consistently produced larger delay-time readings

than system B. Typically, as compared with system B under the same con- ditions of measurement frequency, transistor, and bias condition, system

36
CARRIER TRANSPORT IN JUNCTION DEVICES

A yielded an asymptotic value of delay time that was higher for a 2N2219

by 29 percent; for a 2N2222, by 37 percent; and for a 2N2907, by 17 percent. (F. R. Kelly and D. E. Sawyer)

The components for the two S-parameter measurement systems were re- ceived, checked for performance, and assembled. Devices were measured to

check the performance of these systems and to familiarize personnel with

their operation. (G. J. Rogers)

Probing Studies — Additional study was conducted of the problem of

electrical probing of semiconductor devices while they are at the wafer

stage of preparation. This study, based both on a survey of the literature and past experiences, included consideration of various instruments

javailable to make probe-type measurements at frequencies up to a few

gigahertz, of both reversible and non-reversible effects of probe pressure

on device parameters, and of the influence of contact resistance and stray

capacitances on the measurements. An informal letter report that summarizes the results of this investigation is being prepared for the sponsor.

(D. E. Sawyer)

Analytical — The analysis relating delay time as measured by the

Sandia bridge and vector voltmeter circuit to the various time constants

and delay times within the device has been completed. These measurement

circuits have the common characteristic that the a-c signal voltage between the transistor collector and base terminals is zero when the delay

time is measured. This is accomplished in the Sandia bridge with the use

of a "bucking" or "nulling" signal from a phase-splitter and electrical

delay circuit and, more simply, in the vector voltmeter setup by bypassing

Uthe transistor collector to the base (ground). Because of this common

'operating characteristic, it is appropriate that both be analyzed in the same way; it turns out that the resulting expressions for measured delay

time are generically similar. Although this analysis is based on simplified models for the measuring circuits, the methodology employed may be

extended to other, more complex, models or circuits.

A surprising result of this analysis is that neither circuit measures

the sum of the propagation delays between the emitter and collector leads,

'as one might expect. On the contrary, certain time constants may diminish

the delay time measured. This is because the measurement yields the

phase, rather than the group delay time. The phase delay is the delay of

the carrier frequency, to, while the group delay represents the delay of

the envelope of the input signal or the propagation delay of the information contained in the input signal. The quantity measured, the phase defray, may differ from the (true) propagation delay if certain RC time constants exist.

The analysis, which is reported in greater detail elsewhere [2], is

sased on the widely used transistor model shown in figure 14. This

aquivalent circuit is expected to represent mesa devices quite well. This

37
CARRIER TRANSPORT IN JUNCTION DEVICES

Figure 14. Equivalent circuit used to model a transistor for analysis of delay-time measurements. E •-

* B

-• C

5= i,l| re

aii© "

C<

circuit is perhaps the simplest transistor representation for the analysis

of delay-time measurements. Other types of transistors might require

the addition of other passive elements, such as an additional capacitor

between the top of the current generator and "B", the base terminal, to

represent the base-collector overlap diode capacitance of a planar transistor or a resistor in series with "C", the collector terminal, to represent the collector series resistance.

In figure 14, C and C are the transition-region capacitances of

the emitter-base and base-collector junctions, respectively, r represents

the base resistance, and r represents the dynamic resistance of the

(forward-biased) emitter junction. For forward emitter currents much

larger than the emitter-base diode saturation current,

r

e = kT/qIE

, (1)

where k is Boltzmann's constant, T the absolute temperature, q the electronic charge, and I F the dc emitter current. At room temperature,

r = 26/1 ohms if I is given in milliamperes . Only i.. , the current

through r , is effective in producing transistor action. The current

source in the collector circuit represents the active portion of the transistor operation and is specified as the product of i, and a, the smallsignal base-transport coefficient. In general, a is complex and varies

with frequency. It can always be written a = |a(w)| exp(-ju)i ), where

|a(w)| is an even function of frequency and i is the delay time associated with the transit of minority carries across the base region and across

the collector junction. The quantity t may itself be a function of frequency. It is convenient to define the time constants t = r C and

t CDC= r, C . From eq (1) it is clear that t varies inversely wxth emitter

6

current and that it can be made negligibly small if sufficiently large

emitter currents are used.

In the vector voltmeter circuit the quantity read is the phase shift

38
CARRIER TRANSPORT IN JUNCTION DEVICES

between the transistor emitter and collector currents. The emittercollector phase delay time, x, in seconds, is related to the measured

phase shift by

T = e/w,

where 8 is the phase angle in radians and to is the signal angular frequency.* If, as is usually tt delay times defined above by

quency. If, as is usually the case, got << 1, then t, is related to the

t = t + t - x /hr , (2) a e c fe' v '

where h

f

is the small-signal common-emitter current gain (as usually defined) . Note that h

f

, rather than h

f

, , appears in eq (2), even though

the transistor base is the common element in the measurement circuit.

Equation (2) states that the delay time, as determined from the

measured emitter-collector current phase angle, is the sum of t and t

oi e diminished by the collector-base RC time constant divided by the common- emitter current-gain. For most good-quality transistors, h

f is sufficiently large, and t sufficiently small, so that this t /h term may

be neglected, and so the delay time measured will be simply the sum of

t and t . However, following irradiation, h f is expected to drop and

t to increase (as a result of an increase in r, ). Then it is possible

that the t /hf term may affect the delay time measured.

To analyze the idealized Sandia bridge, it is necessary to include

in the equivalent circuit an impedance, R , in series with both the emitter and collector of the transistor. This impedance is the sum of the

load and source impedances for the delay lines. In the present case R

is 100 ft, twice the characteristic impedance of the delay lines. With

these additions and the assumption that cox << 1, the measured delay time

is given by

is For 9 in degrees and the frequency, f, in hertz, the expression for i in seconds

is

T = 9 /(360 f).

A particularly useful form of this equation expresses the delay time in nanoseconds

in terms of the frequency in megahertz and the phase angle in degrees:

T (ns)

= (2 - 7a/fmz ) per deSree - A one degree phase shift at 27.8 MHz would indicate a delay time of 0.1 ns, for

example.

39
CARRIER TRANSPORT IN JUNCTION DEVICES

T =

1 - ia(u) i rb

R +r +r,

z e b

T + 1 - - /

P- T a | R +r +r, | e

z e d -ft) (3)

Note that if R -*• », then this delay time expression for the idealized

Sandia bridge becomes identical with eq (2) , the delay time expression

for the vector voltmeter. The quantities r , r, , and |a(w)| can all be

determined and so the correction factors multiplying the delay time com- ponents—the factors in the parentheses—can be computed. The same general

comments about the term t /h_ made above in connection with the vector

c re voltmeter also apply.

Another result of this analysis is the finding that the delay time

of RC elements suitably combined on transistor headers can be calculated.

Thus, they can be expected to provide a means to check the overall operation of delay-time instruments and make a convenient means to spot-check

their calibration. (D. E. Sawyer)

Plans : Passive networks will be made for making comparison measurements on the several measurement systems. The results of the S-parameter

measurements will be related to the physics of the devices under test.

Now that the required accessories have been received the vector voltmeter

will be calibrated against passive networks. Transistor intercomparison

delay-time measurements will be continued; attempts will be made to re- solve the differences between systems.

5.5. SILICON NUCLEAR RADIATION DETECTORS

Objective : To conduct a program of research, development, and device

evaluation in the field of silicon nuclear radiation detectors with em- phasis on the improvement of detector technology, and to provide consultation and specialized device fabrication services to the sponsor.

Progress : Study of 2-MeV proton radiation damage effects in lithiumdrifted silicon detectors has been completed. Ambient exposure tests were delayed because of the appearance of anomalous effects.

Radiation Damage — The experimental portion of the study of proton

radiation damage effects has been completed with the irradiation of two,

2-mm thick, lithium-drifted silicon detectors by protons of approximately

2-MeV energy. Both detectors were reverse biased at 400 V during the irradiation which was carried out at room temperature; one detector was irradiated through the front (p-contact) and the other through the rear

(n-contact)

40
SILICON NUCLEAR RADIATION DETECTORS

For the detector irradiated through the p-contact, a rapid increase

of leakage current and noise was observed with increased proton fluence

above 3 x 10 11 cm-2

. After irradiation at a fluence of 2 x 10 12 cm

-2

, the leakage current was 3.5 uA, measured at room temperature, and the

noise was 80 keV, compared with 1.5 uA and 15 keV, respectively, before

irradiation. A dead layer was observed at the irradiated contact, but

the detector exhibited little change in capacitance throughout the irradiation. Protons of the energy used have a range of approximately 45 um

in silicon and thus introduce defects into a volume small relative to the

total space charge region.

The degradation of detector performance observed for the device irradiated through the n-contact occurred at a much lower rate than that

'for the front-contact irradiation. No change in charge collection efficiency was observed at fluences up to approximately 10 cm

-2

. The fabrication process for lithium-drifted detectors results in a dead region at

i the n-contact. This detector had a dead layer of about 50 um; therefore,

proton- induced defects would be localized mainly in the n-contact outside

the sensitive depletion region. The only significant changes that were

observed were increases in contact noise (from 17 to 17 to 27 keV) and

leakage current (from 1.5 to 2.3 uA) after irradiation at a fluence up to

ilO 14 cm" 2

.

Both detectors exhibited annealing effects in leakage current and

detector noise when they were kept under reverse bias of 400 V at room

I temperature. For the detector irradiated through the p-contact, the current decreased to 2 uA and the noise to 35 keV after 3 days. For the

other detector, the current decreased almost to its pre-irradiation level

after 1 day, and the noise decreased to 20 keV after 2 days.

Measurements were begun using the infrared response technique on lithium-drifted silicon detectors which had been irradiated with neutrons

or electrons (see Section 3.3). (Y. M. Liu)

Ambient Exposure Tests — Anomalous effects observed during the operation of the test chamber did not permit dry ammonia measurements to be

concluded on three silicon surface barrier detectors. The origin of

these effects, whether due to contamination in the vacuum system or behavior of this type of detector at low pressures, is not understood at

the present time. (W. K. Croll)

P lans : Further neutron irradiation will be performed to gain additional information on the long-term stability of lithium-drifted and

surface-barrier silicon nuclear radiation detectors. Results obtained

thus far in the study of nuclear radiation damage effects in lithiumdrifted silicon detectors will be analyzed in preparation for possible

publication. Measurements of infrared response on lithium-drifted silicon detectors, before and after neutron irradiation will continue. The

study of the effects on detector performance of dry ammonia and hydrogen,

41
SILICON NUCLEAR RADIATION DETECTORS

the main reaction products of the hydrazine used in spacecraft thrusters,

will continue once the source of the anomalous observations has been as- certained and corrected.

5.6. REFERENCES

5.2. Thermographic Measurements

1. Blanks, H. S., The Transient Behaviour of ZnS-Type Phosphors used in Thermography, Proa. I.E.E.E. (Aust) 31, 397-405 (1970).

5.4. Carrier Transport in Junction Devices

1. Sullivan, W. H. , A New Technique for the Direct Measurement of Minority Carrier

Base Transit Time in the Junction Transistor, Sandia Laboratories Report

SC-DR-69-419, September, 1969. Available from the National Technical Information Service, Springfield, Va. 22151

2. Sawyer, D. E. , A Simple Analysis of Idealized Delay-Time Measurement Circuits,

NBS Technical Note (in preparation).

42
Appendix A

JOINT PROGRAM STAFF

Coordinator: J. C. French

Consultant: C. P. Marsden

Semiconductor Characterization Section

(301) 921-3625

Dr. W. M. Bullis, Chief

F. H. Brewer

M. Cosman

Dr. J. R. Ehrstein

R. L. Mattis

Dr. W. E. Phillips

Miss D. R. Ricks

H. A. Schafft

Miss K. E. Smith"1"

A. W. Stallings

Mrs. M. L. Stream"*"

W. R. Thurber

H. A. Briscoe

W. K. Croll

Mrs. S. A. Davis+

H. E. Dyson*

G. G. Harman

D. L. Blackburn

Mrs. C. F. Bolton"1"

I Miss B. S. Hope+

R. L. Gladhill

F. R. KellylF

Semiconductor Processing Section

(301) 921-3541

Dr. A. H. Sher, Acting Chief*

W. J. Keery

H. K. Kessler

J. Krawczyk

T. F. Leedy

Electron Devices Section

(301) 921-3622

J. C. French, Chief

J . M. Kenney

Mrs. K. 0. Leedy

§

Miss C. A. Main§

F. F. Oettinger

*

Y. M. Liu

Mrs. J. M. Guy ton

Mrs. E. A. Simmons

L. M. Smith

G. P. Spurlock

M. K. Phillips

G. J. Rogers

S. Rubin

D. E. Sawyer

L. R. Williams

Part Time

Secretary

Summer

Dr. J. A. Coleman is on temporary assignment to Office of Associate

Director for Programs.

Telephone: (301) 921-3625

43

l
Appendix B

COMMITTEE ACTIVITIES

ASTM Committee F-l on Electronics

C. F. Bolton, Committee Assistant Secretary

W. M. Bullis, Editor, Subcommittee 4, Semiconductor Crystals, and

Subcommittee 7, Hybrid Microelectronics; Leaks, Resistivity,

Mobility, Dielectrics, and Compound Semiconductors Sections

J. A. Coleman, Secretary, Subcommittee 5, Semiconductor Processing

Materials

J. R. Ehrstein, Chairman, Resistivity Section, Epitaxial Resistivity.

and Epitaxial Thickness Sections

J. C. French, Committee Editor

G. G. Harman, Interconnection Bonding Section

K. 0. Leedy, Chairman, Interconnection Bonding Section

T. F. Leedy, Photoresist Section

C. P. Marsden, Committee Secretary

R. L. Mattis, Lifetime Section

W. E. Phillips, Chairman, Lifetime Section; Secretary, Subcommittee

4, Semiconductor Crystals; Crystal Perfection, Encapsulation,

Thin Films, and Thick Films Sections

A. H. Sher , Germanium Section

W. R. Thurber, Mobility, Germanium, Compound Semiconductors, and

Impurities in Semiconductors Sections

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

Electronic Industries Association: Solid State Products Division, Joint

Electron Device Engineering Council (JEDEC)

J. M. Kenney, Microwave Diode Measurements, Committee JC-21 on UHF

and Microwave Diodes

F. F. Oettinger, Chairman, Task Group JC-11.3-1 on Thermal Considerations for Microelectronic Devices, Committee JC-11 on Mechanical Standardization; Technical Advisor, Thermal Resistance

Measurements, Committees JC-22 on Rectifier Diodes and

Thyristors, JC-20 on Signal Diodes, JC-25 on Power Transistors, and JC-30 on Hybrid Integrated Circuits

S. Rubin, Chairman, Council Task Group on Galvanomagnetic Devices

H. A. Schafft, Technical Advisor, Second Breakdown and Related

Specifications, Committee JC-25 on Power Transistors

IEEE Electron Devices Group:

J. C. French, Standards Committee

J. M. Kenney, Chairman, Standards Committee Task Force on Microwave

Solid-State Devices II (Mixer and Video Detector Diodes)

44
APPENDIX B

H. A. Schafft, Chairman, Standards Committee Task Force on Second

Breakdown Measurement Standards

IEEE Nuclear Science Group:

J. A. Coleman; Administrative Committee; Nuclear Instruments and

Detectors Committee; Editorial Board, Transaction on Nuclear

Science

IEEE Magnetics Group

S. Rubin, Chairman, Galvanomagnetic Standards Subcommittee

IEEE Parts , Hybrids , and Packaging Group

W. M. Bullis , New Technology Subcommittee, Technical Committee on Hybrid Microelectronics

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

IEC TC47, Semiconductor Devices and Integrated Circuits:

S. Rubin, Technical Expert, Galvanomagnetic Devices; U.S. Specialist

for Working Group 5 on Hall Devices and Magnetroresistive Devices

NMAB ad hoc Committee on Materials and Processes for Electron Devices

W. M. Bullis

NMAB ad hoc Committee on Materials for Radiation Detection Devices

D. E. Sawyer

45
Appendix C

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 services that cannot be obtained

through normal commercial channels. Such services provided during the

last quarter are listed below and indicate the kinds of technology available to the program.

1. Failure Analysis (W. J. Keery)

Material from an aircraft air conditioning unit was inspected for the Naval Weapons Engineering Support Activity

using the scanning electron microscope and x-ray energy

analysis for the presence of foreign particles.

2. Radiation Detectors (W. K. Croll)

An ion- implanted silicon nuclear radiation detector was mounted and connections attached so that it could be used

at liquid helium temperatures for the Nuclear Spectroscopy

Section.

3. Silicon Weight (M. Cosman and W. K. Croll)

A weight to be used in the determination of vacuum pump

fluid density was fabricated from a single crystal of silicon for the Pressure and Vacuum Section.

4. Electrical Burnout Studies (H. A. Schafft, K. 0. Leedy, and

W. J. Keery)

Electrical tests and visual and scanning electron microscope examinations were conducted on 17 devices (transistor

pairs and transistors) for the Harry Diamond Laboratories

to assist in establishing degradation and failure modes.

46
Appendix D

JOINT PROGRAM PUBLICATIONS

Prior Reports :

A review of the early work leading to this Program is given in

Bullis, 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 since July 1, 1968, have been

issued under the title Methods of Measurement for Semiconductor Materials,

Process Control, and Devices. These reports may be obtained from the

Superintendent of Documents (Catalog Number C. 13. 46: XXX) where XXX is the

appropriate technical note number. Microfiche copies are available from

the National Technical Information Service (NTIS) , Springfield, Virginia

22151.

Quarter Ending NBS Tech. Note Date Issued NTIS Accession

i September 30, 1963 472 December, 1968 AD 681330

December 31, 1969 475 February, 1969 AD 683808

March 31, 1969 488 July, 1969 AD 692232

June 30, 1969 1 * 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

I

1

Erenner, D. J.. , A Technique for Measuring the Surface Temperature of

ransistors by Means of Fluorescent Phosphor, NBS Tech. Note 591, July,

971.

i

Current Publications:

>her, A. H. , and Thurber, W. R. , Minority Carrier and Lithium-Ion Drift

lobilities and Oxygen Concentration in p-Type Germanium, J. Appl. Phys.

>2, 4508-4509 (October, 1971).

, her, A. H. , Croll, W. K. , and Thurber, W. R. , Determination of Oxygen in

ermanium Below 20 Parts per Billion by Measurements of Lithium Mobility

nd Precipitation, Anal. Chem. 43, 1831-1834 (November, 1971).

NBS Measurement Engineering Division

47
APPENDIX D

Harman, G. G. , Ultrasonic Systems and Mechanisms of Bonding, presented at

the Advanced Microelectronics Techniques Conference, Los Angeles, Calif,,

September 30, 1971.

Sher , A. H. , Keery , W. J., and Dyson, H. E., Improved Infrared Response

Measurements in Semiconductor Nuclear Radiation Detectors, presented at

the 1971 Nuclear Science Symposium, San Francisco, November 5, 1971, IEEE

Trans. Nual. Soi. NS-19 , No. 1, 341-344 (February, 1972).

Schafft, H. A., Wire-Bond Electrical Connections: Testing, Fabrication,

and Degradation, A Bibliography — 1957-1971, NBS Technical Note 593 (January, 1972).

Sher, A. H. , and Keery, W. J., Improved Infrared-Response Technique for

Determining Impurity and Defect Levels in Semiconductors, Appl. Phys . Lett.

jU, 120-122 (1 February 1972).

Marsden, C. P., Tabulation of Data on Semiconductor Amplifiers and Oscillators at Microwave Frequencies, NBS Technical Note 597 (December, 1971).

48
FORM NBS-114A (1-71) U.S. DEPT. OF COMM. BIBLiOGRAPHIC DATA

SHEET

1. PUBLICATION OR REPORT NO. NBS-TN-7172. Gov t Accession No.

3. Recipient's Accession No.

4. TITLE AND SUBTITLE Methods of Measurement for Semiconductor Materials, Process

Control, and Devices. Quarterly Report, July 1 to September

30, 1971.

5. Publication Date April 1972

6. Performing Organization Code

7. AUTHOR(S)

W. Murray Bullis , Editor

8. Performing Organization

10. Project/Task/Work Unit No. See Item 15

9. PERFORMING ORGANIZATION NAME AND ADDRESS

NATIONAL BUREAU OF STANDARDS

DEPARTMENT OF COMMERCE

WASHINGTON, D.C. 20234

11. Contract/Grant No.

See Item 12

12. Sponsoring Organization Name and Address NBS , DASA (EA071-801) , Navy

Strategic Systems Project Office, NAD, Crane, Indiana

(PO-2-0023), NAVELEX (PO-2-1034) , AFWL (F29601-71-F-0002) , AFCRL

(Y71-906), ARPA (MIPR FY76167100331) , AEC, NASA (S-70003-G).

13. Type of Report & Period Covered -r . • T t n Interim July 1 to September 30, 1971

14. Sponsoring Agency Code

15. supplementary NOTES ^ZillZb, 4252128, 4254115, 4259522, 4259533, 4252534, 4252535,

4251536, 4254422, 4259425, 4254429.

16. ABSTRACT (A 200-word or less factual summary of most significant information. If document includes a significant bibliography or literature survey, mention it here.) This quarterly progress report, thirteenth of a series, describes NBS activities

directed toward the development of methods of measurement for semiconductor materials,

process control, and devices. Significant accomplishments during this reporting period

include the disclosure of substantial differences in measurements of transistor delay

time, a device characteristic frequently used as a screen in radiation hardness assurance

tests, as measured with two different instruments; successful application of the infrared

response technique to the study of radiation-damaged, lithium-drifted silicon detectors;

and identification of a condition that minimizes wire flexure and reduces the failure

rate of transistors under slow thermal cycling conditions. Work is continuing on measurement of resistivity of semiconductor crystals; study of gold-doped silicon; specification of germanium for gamma-ray detectors; evaluation of wire bonds and die attachment;

neasurement of thermal properties of semiconductor devices; noise properties of microwave

diodes; and characterization of silicon nuclear radiation detectors. Supplementary data

concerning staff, standards committee activities, technical services, and publications

are included as appendixes.

<.ey Words (cont . ) : measurement; microelectronics; microwave diodes; nuclear radiation

detectors: probe techniques (a-c) ; resistivity; semiconductor devices; semiconductor

naterials, semiconductor process control; silicon; thermal resistance; thermographic

measurements ; ultrasonic bonder: wire bonds.

17. key WORDS (Alphabetical order, separated by semicolons) Alpha-particle detectors; aluminum wire; base

transit time- carrier lifetime; die attachment; electrical properties; epitaxial silicon;

gamma-ray detectors; germanium: gold-doped silicon; infrared response; methods of

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