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STATES IENTOF ERCE

JATION NBS TECHNICAL NOTE 598

U.S.

VRTMENT

OF

IMMERCE

National

Bureau

of

andards

Methods of

Measurement for

Semiconductor

Materials, Process

Control, and Devices

Quarterly Report

January 1 to March 31, 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 t6 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 technical divisions and offices: Engineering Standards Services—Weights and Measures—Flammable Fabrics

Invention and Innovation—Vehicle Systems Research—Product Evaluation

Technology—Building Research—Electronic Technology—Technical Analysis

Measurement Engineering.

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 Public Information—Office of International

Relations.

1 Headquarters and Laboratories at Gaithersburg, Maryland, unless otherwise noted; mailing address Washing-
UNITED STATES DEPARTMENT OF COMMERCE

Maurice H. Stans, Secretary

NATIONAL BUREAU OF STANDARDS • Lewis M. Branscomb, Director

NBS TECHNICAL NOTE 598

ISSUED OCTOBER 1971

Nat. Bur. Stand. (U.S.), Tech. Note 598, 54 pages (Oct. 1971)

CODEN: NBTNA

Methods of Measurement for Semiconductor

Materials, Process Control, and Devices

Quarterly Report

January 1 to March 31, 1971

Edited by W. Murray Bui lis

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 Atomic Support Agency, the U.S. Navy

Strategic Systems Project Office, the U.S. Navy Electronic Systems

Command, the Air Force Weapons Laboratory,

the Atomic Energy Commission, and the National Aeronautics

and Space Administration

NBS Technical Notes are designed to supplement the Bureau's regular publications program. They provide a means for making available scientific data that are of transient or limited interest. Technical Notes may be

listed or referred to in the open literature.

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

(Order by SD Catalog No. C 13.46:598). Price 55 cents.

CONTENTS

PAGE

Foreword vi

1. Introduction 1

2. Highlights 3

3. Methods of Measurement for Semiconductor Materials

3.1. Resistivity 7 3.2. Carrier Lifetime 9

3.3. Inhomogeneities 10

3.4. Gold-Doped Silicon 12

3.5. Specification of Germanium 13

3.6. References 17

4. Methods of Measurement for Process Control

4.1. Die Attachment Evaluation 18

4.2. Wire Bond Evaluation 20

4.3. Processing Facility 28

4.4; References 29

5Methods of Measurement for Semiconductor Devices

5.1. Thermal Properties of Devices 30

5.2. Thermographic Measurements 35

5.3. Microwave Device Measurements 36

5.4. Carrier Transport in Junction Devices 39

5.5. Silicon Nuclear Radiation Detectors 41

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. Four-probe and photovoltaic resistivity profiles along

a diameter of a p-type silicon wafer showing effect of

uncertainty in the probe location on the four-probe

profile 10

2. Four-probe and photovoltaic resistivity profiles along a diameter of a p-type silicon wafer showing the effect of

contact quality on the photovoltaic profile 11

3. Four independently made photovoltaic resistivity profiles

along the diameter of an n-type silicon wafer showing the

degree of reproducibility that can be achieved 12

4. Infrared response spectra of four lithium-drifted germanium

diodes . 15

5. Junction-to-case temperature difference as a function of

diode heating current for steady-state heating and for

5- and 10-ms wide heating-power pulses 19

6. Measured bond pull strength for a first bond as a function

of machine power setting 22

7. Measured bond pull strength for a second bond as a function

of machine power setting 22

8. SEM photomicrograph of a well made ribbon wire bond 23

9. Fixture used in measurement of bonding force 23

10. Recorder traces of impressions made in three different

specimens of 1-mil (25-um) diameter aluminum (1% silicon)

bonding wire 24-

11. Comparison of dynamic and d-c calibration of a 25-W,

silicon n-p-n transistor 31

12. Base-emitter voltage of a 35-W, triple-diffused, silicon

transistor measured as a function of applied power for

collector currents of 0.1, 0.2, 0.4-, and 1.0 A, at times

10, 20, 50, and 100 ys after removal of power 32

13. Normalized thermal resistance of a 35-W, triple-diffused,

silicon transistor measured as a function of delay time

for both current constricted and normal (non-constricted)

operating conditions 32

IV
14-. Modified r-f section of microwave mixer measurement

system 37

LIST OF TABLES

1. Results of Repetitive Junction-tO-Case Temperature

Difference Measurements to Demonstrate Reproducibility

of Method 18

2. Results of Junction-to-Case Temperature Difference

Measurements on Control Diodes 20

3. Comparison of Thermal Resistance Measured using

Collector-and-Base Switching and Collector-Only

Switching 34
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 care- fully 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, ^ the U. S. Navy Strategic Systems Project

Office,^ the U. S. Navy. Electronics Systems Command,-1" the Air Force

Weapons Laboratory,^ the Atomic Energy Commission, # and the National

Aeronautics and Space Administration. x There is not a one-to-one cor- respondence between the tasks described in this report and the projects

by which the Program is supported. Although all sponsors subscribe to

the need for the entire basic program for improvement of measurement

methods for semiconductor materials, process control, and devices, the

concern of certain sponsors with specific parts of the Program is re- flected in planning and conduct of the work.

* Through Research and Technical Services Projects 4251120, 4251123, 4251126, 4252114,

4252119, 4252128, 4254111, 4254112, and 4254115.

+ Through Order EA071-801. (NBS Project 4259522).

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

PO-1-0030, PO-1-0041, and PO-1-0067 and Naval Avionics Facility through Work Request

WR-1-1038! (NBS Projects 4259533 and 4254432)

+ Through Project Order PO-1-1057. (NBS Froject 4252534)

11 Through Delivery Order F29601-71-F-0002. (NBS Froject 4252535)

# Division of Biology and Medicine. (NBS Project 4259425)

x Through Orders S-70003-G, Goddard Space Flight Center, and H-76553A, Marshall Space

Flight Center. (NBS Projects 4254429 and 4251449)

VI
METHODS OF MEASUREMENT FOR

SEMICONDUCTOR MATERIALS, PROCESS CONTROL, AND DEVICES

Quarterly Report

January 1 to March 31, 1971

ABSTRACT

This quarterly progress report, eleventh 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 re- porting period include application of tuning and other related

procedures for ultrasonic wire bonders in an industrial environment with a reported reduction of rejection rate at visual inspection by more than a factor of two, more complete evaluation

of the photovoltaic method for determining radial resistivity

profiles of circular semiconductor wafers, and identification of

test conditions in which a d-c calibration curve may properly be

used in measurements of thermal resistance. Work is continuing

on measurement of resistivity, carrier lifetime, and electrical

inhomogeneities in semiconductor crystals; specification of

germanium for gamma-ray detectors; evaluation of wire bonds

and die attachment; measurement of thermal properties of semiconductor devices, transit-time and related carrier transport

properties in junction devices, and electrical properties of

microwave devices; 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; methods of measurement; microelectronics;

microwave devices ; nuclear radiation detectors ; probe techniques (a-c); resistivity; semiconductor devices; semiconductor

materials, semiconductor process control; silicon; thermal resistance; thermographic measurements; ultrasonic bonder; wire

bonds

1 . INTRODUCTION

This is the eleventh 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 methods that are being studied at the National Bureau of Standards,
INTRODUCTION

Since the Program is a continuing one, the results and conclusions re- ported here are subject to modification and refinement.

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

directed toward 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 con- cerning 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

given 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.

H
2. HIGHLIGHTS

Significant accomplishments during this reporting period include

successful application of tuning and other related procedures for ultrasonic wire bonding machines in an industrial environment with a reported

reduction in rejection rate at visual inspection by more than a factor

of two, more complete evaluation of the photovoltaic method for determining radial resistivity profiles of circular semiconductor wafers, and

identification of test conditions in which a d-c calibration curve may

properly be used in measurements of thermal resistance. 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 — Principal emphasis was placed on continuation of the

study of current and probe-force dependence of resistivity as measured bv

the four-probe method. Measurements completed on mechanically polished

wafers with revised experimental procedures are being evaluated. The

wafers were chem-mechanically polished, and measurements on the chemmechanically polished surfaces were begun. Coordination of two round

robins on the four-probe method being conducted in cooperation with ASTM

Committee F-l on Electronics continued. Measurements were made in con- nection with a round robin on the metal-oxide-semiconductor capacitancevoltage method also conducted by Committee F-l. Experimental work on the

diode capacitance-voltage method and further consideration of silicon

wafer resistivity standards were deferred. Effort on spreading resistance methods was devoted to further study of procedures for preparing

silicon wafers for examination by the scanning electron microscope and

initial study of probe impact with a force transducer.

Cawiev Lifetime — The level of effort in this area was decreased

significantly during the quarter. Additional experiments were conducted

in an effort to define appropriate conditions for the measurement of car- rier lifetime in bulk crystals by the photoconductive decay (PCD) method.

Measurements were made on bulk crystals to compare results obtained by

the PCD and surface photovoltage (SPV) methods. The draft of the paper

describing the application of the SPV method to measurement of carrier

lifetime in epitaxial layers was completed. An experiment on measurement of carrier lifetime by the' metal-oxide-semiconductor capacitance

method was completed.

Irihomogeneities — Various aspects of the application of the photovoltaic method as a means for measuring radial resistivity profiles in

circular semiconductor wafers without contacting the flat surfaces of the

wafers were evaluated. Some problems in comparing profiles made by photovoltaic and four-probe methods were traced to the effects of uncertainty in the probe location in a four-probe measurement. It was shown

that abrading the wafer rim improved the quality of the rim contacts and

permitted measurements to be made closer to the edge of the wafer. An
HIGHLIGHTS

experiment conducted to obtain an indication of the reproducibility of

the photovoltaic method yielded a maximum difference between four independent readings of less than 2 percent.

Gold-Doped Silicon — Work continued in preparing and evaluating

gold-doped silicon wafers in the extensive series outlined previously. A

preliminary study to determine if the retrograde behavior of the resistivity of heavily gold-doped, p-type silicon could be explained by a var- iation of the ionization energy of the gold donor level with gold con- centration yielded negative results. The study of the lateral uniformity

of diffused gold as determined by x-ray fluorescence with the scanning

electron microscope continued.

Specification of Germanium — Standards pertaining to the measurement

of lithium-ion drift mobility and lithium-drifted germanium detector

characterization are being developed in cooperation with ASTM Committee

F-l and IEEE Nuclear Instruments and Detectors Committee respectively.

Additional semiconductor diodes, including a heat-treated germanium specimen, a diode fabricated from a crystal of high-purity germanium, and a lithium-drifted silicon diode, have been examined by the improved infrared response technique. Preliminary studies of the infrared response

measurement system have been directed toward determination of specimen

temperature during the measurement and of the effects of changing the

magnitude of applied bias to the diode on the spectral response.

Die Attachment Evaluation — Experiments' were completed which demonstrated that the procedures and equipment used to make thermal response

measurements result in adequate reproducibility and that the spread in

the measured thermal response of diodes without voids is small compared

to the change introduced by the presence of voids. Both these conditions

had to be met in order to compare the relative sensitivity to the presence of voids in the die attachment material of transient thermal res- ponse measurements and steady-state thermal resistance measurements . It was found that transient thermal response measurements were significantly

more sensitive to the presence of voids than steady-state thermal resistance measurements

.

Wire Bond Evaluation — At the request of a sponsor capacitor microphones and magnetic pickups were distributed to four semiconductor device manufacturers together with instructions for their use in setting

up and tuning ultrasonic wire bonding machines. In one case, use of this

equipment and associated technology for process control resulted in a reduction in rejection rate due to faulty bonds at visual inspection by more than a factor of two. A study of wire -bond failures due to slowpower-cycling of transistors indicated that use of a large loop height

minimizes such failures. Two new ultrasonic wire bonding machines, one for bonding round wire and the other for bonding ribbon wire, were set

up. Extensive modifications were necessary to correct faults in the

machines as delivered. Detailed procedures for setting up bonding
HIGHLIGHTS

machines were developed. The wire tester was completed; initial tests

showed distinct differences in uniformity of three different wire samples. An apparatus to measure bonding force was designed for the purpose of reducing variability between measurements made by different operators. Initial studies of ultrasonic bonding that may eventually lead

to an in-process method for determination of bond quality were made with

a self-tuning ultrasonic power supply and transducer.

Thermal Properties of Devices — Conditions under which d-c calibration procedures yield correct values in making thermal resistance measurements have been identified. It was found that the thermal resistance

can be calculated from differences in temperature and power between two

different power levels on the linear portion of the base-emittervoltage — transistor-power curve. Preliminary measurements of the reproducibility which can be achieved by the thermal resistance measuring

equipment were undertaken. A procedure for electrically measuring junction temperature during the current-constricted operating mode was investigated. A comparative study of several different techniques for

measuring thermal resistance was begun in order to determine the general

applicability of the various techniques for use as industrial standards

Microwave Device Measurements — The r-f portion of the X-band mixer

measurement system was extensively rebuilt to permit active stabilization

of the local oscillator power and improve other aspects of the circuit.

Carrier Transport in Junction Devices — Evaluation of the Sandiatype delay-time bridge continued. Preliminary delay-time measurements

were made as a function of emitter current on a silicon n-p-n transistor

with fa of about 350 MHz. A theoretical analysis of a delay-time error

that might be introduced during rebalancing of the bridge was completed.

From a survey of noise properties of semiconductor devices that was com- pleted, it was concluded that the use of noise spectrum measurements

should enable one to measure separately device phenomena which otherwise

are almost always measured by their sum effect.

Silicon Nuclear Radiation Detectors — Pre-flight bench testing of

lithium-drifted silicon radiation detectors continued. A test chamber

for carrying out measurements of the effects of ambients that may affect

the performance characteristics of semiconductor detectors was constructed and evaluated. Radiation damage measurements on lithium-drifted

silicon detectors using 1.5 MeV electrons were begun.

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 under way. Standardization activities directly

related to particular task areas are reported with the appropriate tasks
HIGHLIGHTS

Six program staff members attended the regular winter meeting of

ASTM Committee F-l. W. E. Phillips was appointed secretary of Subcommittee 4 on Semiconductor Crystals in addition to his other assignment as chairman of the Carrier Lifetime Section. W. M. Bullis acted as temporary chairman of the Resistivity and Conductivity Type Sections. He also

reported on the completion of a revised portion of the general information guide for members of ASTM Committee F-l. A broadened scope of the

committee to include device as well as material measurement methods was approved by the ASTM Board of Directors. J. C. French and W. M. Bullis

proposed activities that might be undertaken in response to this broadened scope to several committee officers. Subcommittee 7 on Hybrid

Microelectronics is taking the lead in developing new areas of effort.

Considerable interest exists both in the evaluation of wire and die bonds

and in the characterization of chips destined for use in hybrid microcircuits. Other areas of interest are radiation effects on and thermal

properties of semiconductor devices and integrated circuits.

J. C. French and W. M. Bullis attended meetings of the sections of

ASTM Committee E-10 that are concerned with radiation effects on electronic components. Reviews of Committee F-l and Joint Program activities were presented. This committee has a significant interest in definitions and test methods appropriate to the study of response of devices

to radiation. Program staff members are providing a communication link

between Committee F-l, oriented toward electronics and Committee E-10,

oriented toward radiation effects.

Activity in connection with JEDEC committees of the Electronic

Industries Association was concentrated in the thermal measurements and

second breakdown areas. F. F. Oettinger was recently named to a task

group on thermal measurements for the newly organized Committee JC-30 on Hybrid Integrated Circuits and was instrumental in the preparation of

JEDEC Engineering Bulletin No. 18, Thermal Parameters of Microelectronic

Devices, issued through Committee JC-11 on Mechanical Standardization.

D. E. Sawyer was appointed liaison representative to the National

Materials Advisory Board ad hoc Committee on Materials for Radiation Detection Devices. W. M. Bullis continued his work in connection with the

NMAB ad hoc Committee on Materials and Processes for Electron Devices.

In this connection he organized a symposium of experts on metal-insulatorsemiconductor structures to provide input to the committee report.

Activity in various IEEE committees increased. J. C. French, H. A.

Schafft, and J. M. Kenney continued work with the Standards Committee of

the Group in Electron Devices particularly with respect to thermal properties and microwave diode characteristics. W. M. Bullis was appointed

to the New Technology Subcommittee of the Technical Committee on Hybrid

Microelectronics of the Group on Parts, Hybrids, and Packaging. This

committee is beginning to undertake development of a terms glossary and

test methodology appropriate to hybrid microcircuits
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 : Principal emphasis was placed on continuation of the

study of current and probe force dependence of resistivity as measured

by the four-probe method. Measurements, made with revised experimental

procedures , were completed on mechanically polished wafers . The wafers

were then chem-mechanically polished, and measurements on the chemmechanically polished surfaces were begun. Standardization activity this

quarter consisted of continued coordination of two round robins on the

four-probe method and participation in a third on the metal-oxidesemiconductor capacitance-voltage method, all in cooperation with ASTM

Committee F-l on Electronics. Experimental work on the capacitancevoltage method and further consideration of silicon wafer resistivity

standards were deferred. Effort on spreading resistance methods was devoted to further study of procedures for preparing silicon wafers for

examination by the scanning electron microscope (SEM) and initial study

of probe impact with a force transducer.

Four-Probe Method — Mechanically polished bulk silicon wafers were

measured using new experimental procedures in the study of current and

probe force dependence of resistivity as measured by the four-probe method. The new procedures require that at each of twelve orientations of

the wafer under the probe head, data for all current levels be taken before raising the probe to sample a new orientation. Further, by interchanging probe springs, data for all values of probe loading can be taken

in order of increasing load before a slice is replaced by another specimen. In this way, and using a recently constructed slice centering

apparatus that rapidly positions a slice such that its center is within

2 mils (50 ym) of the center of the four-probe array, it is possible to

make all measurements at the same location at the center of the slice and

vary all relevant parameters before there has been any significant change

in the surface cleanliness. In addition, probe impressions were recorded

at each value of probe loading immediately after measurement on each

slice to assure that the probe itself remained essentially unchanged during the data taking.

The results appeared to show greater consistency of trend with cur- rent and probe force for each slice resistivity than had been observed

heretofore. In general the relative sample standard deviation for the

twelve measurements taken on a specimen at each current, probe-force com- bination was less than 0.35 percent and often was less than 0.2 percent.

Exceptions to this were the two specimens in the 100 ft •cm range where

measurements made with low current (10 yA) and probe loading (25 and
RESISTIVITY sometimes 50 g) yielded relative sample deviations that were as high as

1 percent. At the other extreme of the resistivity range (0.001 fi-cra),

measurements made with low current (10-30 mA) yielded relative sample

standard deviations that were as high as 0.7 percent but were generally

independent of loading. The source of difficulty at high resistivities

was mainly due to the large noise susceptibility of the high impedance

(up to 1 MQ) voltage contacts. At the low end of the resistivity scale,

scatter in the data was due predominantly to low signal level (as low as

20 yV).

On completion of the measurements on mechanically polished surfaces,

the wafers were chem-mechanically polished and a new sequence of measurements was begun. (J. R. Ehrstein and D. R. Ricks)

Standardization Activities — Data has now been returned from all

participants in the round robin on four-probe measurement of ultra-high

resistivity silicon that is being run in conjunction with ASTM Committee

F-l. The results are being tabulated for presentation to the committee.

No further measurement data have been received in the Committee F-l

round robin to measure four-probe resistivity of epitaxial layers with

opposite conductivity-type substrates. (J. R. Ehrstein and D. R. Ricks)

A series of measurements was made as part of a Committee F-l round

robin in the metal-oxide-semiconductor capacitance-voltage method for

measuring resistivity. (G. N. Stenbakken)

Spreading Resistance Methods — Work on definition of proper specimen

preparation in order to obtain high-quality SEM photomicrographs of the

contact damage made by spreading resistance probes continued. Although

pictures of favorable quality were obtained from some wafers, the procedures tested to date do not give consistent results

.

(W. J. Keery and J. R. Ehrstein)

A piezoelectric transducer of lead zirconate-lead titanate capped

with an anvil of tungsten carbide has been acquired in an -attempt to

measure the force of a spreading resistance probe impacting a silicon

wafer surface as a function of time. Because the transient response of

the transducer structure to a fast event such as probe impact has not yet

been determined it has not been possible to separate the probe impact

signal from transducer generated "noise" such as ringing or reflection of

pressure waves. (J. R. Ehrstein)

Plans: Study of the probe force and current dependence of fourprobe resistivity measurements will continue with completion of data collection on chem-mechanically polished wafer surfaces and beginning of re- measurement of lapped wafer surfaces. Efforts to locate a suitable epitaxial reactor so that the wafer surfaces can be vapor etched will continue. Complete results of the round robin on four-probe measurements
RESISTIVITY

on ultra-high resistivity silicon and a status report on the round robin

on four-probe measurement of resistivity of epitaxial wafers will be presented to ASTM Committee F-l at its June meeting. Further work will be

undertaken on clarifying the conditions necessary to take high-quality

SEM photomicrographs of probe damage to the silicon surface and on characterization of the piezoelectric transducer intended for use in measuring the impact momentum of spreading resistance probes. Work on the

capacitance-voltage method will resume with measurement on 15 fi»cm n- type wafers diffused with boron.

3.2. CARRIER LIFETIME

Objective : To determine the fundamental limitations on the precision and applicability of the photoconductive decay method for measuring

minority carrier lifetime and to develop alternative methods for measuring minority carrier lifetime in germanium and silicon which are more

precise, more convenient, or more meaningful in the specification of

materials for device purposes.

Progress: Reprogramming led to a significant decrease in the level

of effort in this area. The experiment to study the effect of specimen

current on specimen heating during photoconductive decay (PCD) measurements was completed. It was found that the current required to increase

the surface temperature of the specimen by 0.5°C depended on both the

resistivity and shape of the specimen but no universally applicable relationship could be developed. Analysis of this result and the results of

previously conducted experiments (NBS Tech. Note 592, pp. 15-16) to establish specifications for specimen current and signal level was not com- pleted. The experiment to compare the time mark and null methods for

determining the voltage decay time was terminated prior to completion.

(R. L. Mattis and A. J. Baroody)

Several measurements were made on bulk crystals to compare the PCD

and surface photovoltage (SPV) methods. Measurements made by the two methods on one specimen gave similar values while for another specimen the

SPV value was only l/40th the PCD value. The significance of these results cannot be determined until additional measurements are made.

The draft of the paper describing the application of the SPV method

to measurement of carrier lifetime in epitaxial layers was completed.

(W. E. Phillips)

Experimental work on a preliminary study of measurement of carrier

lifetime by the metal-oxide-capacitance method was completed. Details

of this work are reported elsewhere [1]. (R. L. Mattis)
CARRIER LIFETIME

Plans : Work in this area, with the exception of investigation of

the applicability of the SPV method to measurements of carrier lifetime

in gold-doped silicon, will be suspended temporarily. Results of the

SPV study will be reported as part of the task on gold-doped silicon.

3.3. INHOMOGENEITIES

Objective: To develop improved methods for measuring inhomogeneities

responsible for reducing performance and reliability of germanium and

silicon devices and, in particular, to evaluate a photovoltaic method as

a means for measuring radial resistivity gradients in germanium and silicon circular wafers without contacting the flat surfaces of the wafers.

Progress : Study of the effect of uncertainty in the probe location

on radial resistivity profiles determined by the four-probe method was completed. The asymmetry that results from applying off-center correction factors [l] to measurements on a mis-centered wafer as though it had

been centered has been reported previously (NBS Tech. Note 520, pp. 8-9).

Similar asymmetry was noted in several four-probe profiles made in con- nection with the present study. It was found that shifting the position

variable a small amount improved both the symmetry of the four-probe profile and the agreement between the four-probe and photovoltaic profiles.

In the example shown in figure 1, the original four-probe profile on a p-type silicon wafer was corrected by a shift in position variable 0.3 mm

to the right and reapplication of the off-center correction factors . The

photovoltaic profile along the same diameter is also shown for comparison.

The influence of the electrical quality of the measurement contact

on the measurement of photovoltaic profiles was also studied. Photovoltaic profiles were measured along the same diameter of the p-type

Figure 1. Four-probe and photovoltaic

resistivity profiles along a diameter

of a p-type silicon wafer showing

effect of uncertainty in the probe

location on the four-probe profile.

I 43.0

cs

t42.2 >

FOUR-PROBE (ORIGINAL) FOUR-PROBE (CORRECTED)

PHOTOVOLTAIC

\

2 2 4 DISTANCE (mm)

10
INHOMOGENEITIES

1 I 1 I I T Figure 2. Four-probe and photovoltaic resistivity profiles

along a diameter of a p-type

silicon wafer showing the effect

of contact quality on the photovoltaic profile.

2 2 4 DISTANCE (mm)

silicon wafer with knife-edge contacts pressed into the as-grown wafer

rim and into an abraded wafer rim. The former contacts were apparently

less ohmic in nature than the latter as can be seen from the profiles in

figure 2. The anomalously large resistivity gradient to the left of the

wafer center indicated by the photovoltaic measurements made with the as- grown rim is a result of the barrier photovoltage generated by carriers

which diffuse to the large barrier present at the measurement contact.

A similar, but smaller, effect can be seen to the right of the wafer center, but only beyond about a half a wafer radius. This indicates that

while both contacts were very nonohmic, the contact on the left was much

less ohmic than the one on the right. In the measurements made with the

abraded rim, the barrier photovoltage is significantly smaller; again the

contact on the left appears to be somewhat less ohmic than the one on the

right. The asymmetry of the four-probe profile may be due to slight miscentering of the wafer as noted above.

To obtain an indication of the reproducibility of the photovoltaic

method, four resistivity profiles were made by the photovoltaic method

along the same diameter of an n-type silicon wafer. The maximum difference between any of the four profiles, as shown in figure 3, was less

than 2 percent of the average specimen resistivity. Since the wafer had

a large non-radial gradient along the chosen measurement diameter and

since the apparent resistivity profile of the wafer varied considerably

as the measurement diameter was changed slightly, the reproducibility is

considered to be indicative of that which would be obtained under less

than ideal conditions.

A summary of the work to date on the photovoltaic method is being

prepared for presentation [2], (D. L. Blackburn)

11
INHOMOGENEITIES

Figure 3. Four independently made photovoltaic resistivity profiles along the

diameter of an n-type silicon wafer

showing the degree of reproducibility

that can be achieved.

I 69

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:

1

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I i i I i i i i i i i 2 2 4 DISTANCE (mm)

Plans : Next effort in this area will be directed toward determination, in cooperation with ASTM Committee F-l, of the suitability of this

technique as an alternative to the existing standard four-probe method

for measuring resistivity variation. Because of the close relationship

with resistivity measurements, results of future work will be included

in the report of the resistivity task.

3.4. 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 : Gold was diffused into additional 10- and 20-Q»cm $ borondoped silicon wafers to complete the range of gold concentrations for

these resistivities. Also 90-A«cm, p-type wafers were diffused in an oxygen atmosphere at temperatures from 850 to 1250°C. After diffusion,

0.12 mm was lapped from each side of the wafers. A part of each slice

was reserved for the determination of gold concentration by activation

analysis and a Hall bar for electrical measurements was cut from the re- mainder.

Sets of n-type silicon wafers with resistivities of 5, 80, M-00, and

2200 ft* cm were prepared for gold diffusion at five temperatures from 850

to 1250°C. The present procedure is to clean the slices and evaporate

40 nm of gold on each side just prior to inserting them in the furnace.

Control wafers without gold are also being included at two temperatures

to determine if the heat treatment alone affects the electrical properties. (W. R. Thurber, T. F. Leedy, and W. M. Bullis)

12
GOLD-DOPED SILICON

To determine if the retrograde behavior of the resistivity in borondoped material (NBS Tech. Note 592, p. 21) could be explained by a variation with gold concentration of the ionization energy of the gold donor

level, Hall effect and resistivity measurements were made as a function

of temperatute on two 20-ft»cm, boron-doped specimens which had gold con- centrations of 3.1 and 9.9 x 10 16 atoms per cubic centimeter. The speci- men with the higher gold concentration had the slightly larger ionization

energy, but the difference was not considered significant. To serve as an explanation for the retrograde behavior of the resistivity, the speci- men with the lower gold concentration should have had the larger ionization energy. (W. R. Thurber)

Work continued on study of the lateral uniformity of the diffused

gold as determined by x-ray fluorescence with the scanning electron microscope. A Hall bar was cut from a diffused wafer to use in this study.

The complex shape of the Hall bar facilitates examination of the various

regions of the specimen after successive surface treatments. Aqua regia

was used to remove any excess gold on the surface. Examination of the

Hall bar in four areas showed it to be farily uniform except for occa- sional small clusters of gold 2 to 5 urn in diameter on the surface. A

layer 5-um thick has been removed from the surface of the bar preparatory

to making x-ray fluorescence measurements at the locations previously ex- amined to determine if the gold clusters seen on the surface extend into

the bulk of the material. (W. J. Keery and W. R. Thurber)

Plans: After the gold diffusions are completed, a portion of each

wafer will be sent for activation analysis and a Hall bar will be cut

from the adjacent material. Hall coefficient and resistivity measurements will be made at room temperature on each of the bars. The investigation of the lateral uniformity of the gold diffusion process in the

Hall bar specimen will continue

3.5. 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 : Standards pertaining to the measurement of lithium-ion

drift mobility and Ge(Li) detector characterization are being developed

in cooperations with ASTM Committee F-l and IEEE Nuclear Instruments and

Detectors Committee respectively. Additional semiconductor diodes were

examined by the improved infrared response (IRR) technique. Response

spectra were obtained for a heat-treated germanium specimen and a diode

fabricated from a crystal of high-purity germanium. The infrared response

13
SPECIFICATION OF GERMANIUM

of a lithium-drifted silicon diode was measured. Thermocouples were added to the IRR cryostat and preliminary measurements performed to

determine the specimen temperature. The effects of the magnitude of

applied bias on the IRR of germanium diodes were studied.

Standardization Activities — In cooperation with the Germanium Section of Committee F-l, two specimens from each of two different germanium

crystals are being prepared according to a procedure outlined for the

second round robin on carrier trapping measurements . The measurement of

lithium-ion drift mobilities of these four specimens has been completed,

and the diodes are undergoing further drifting prior to the detector

trapping measurements. (H. E. Dyson and A. H. Sher)

Standard test procedures for characterizing germanium gamma-ray detectors have been approved by the members of the Nuclear Instruments and

Detectors Committee [1] and have been submitted to ANSI Committee N*42

for approval as an American National Standard.

(A. H. Sher and J. A. Coleman)

Ge(Li) Detector Measurements —Work on the development and evaluation

of an improved infrared response (IRR) technique has proceeded on two

fronts. Measurements have been continued on different types of semiconductor diodes in order to further the qualitative understanding of details

observed in the IRR spectra. Work has also begun on the study to determine the effects of various factors such as specimen temperature and applied bias on the results obtained. This is intended to aid in determining the capability of the method for obtaining quantitative information

about the concentration of defect or impurity levels in the semiconductor

specimens examined.

The IRR of a Ge(Li) diode fabricated from a p-type germanium crystal

which had been heated to 800°C for 15 min and then cooled rapidly to room

temperature has been measured. The spectrum of this diode, Ge(Li) 83-4,

is shown in figure 4 together with spectra from three diodes previously

discussed (NBS Tech. Note 592, pp. 22-25). Diode Ge(Li) 83-3 was fabricated from a specimen of the same germanium crystal as Ge(Li) 83-4 but

was subjected only to the typical lithium-drifted detector fabrication

process. Diodes Ge(Li) 13 and Ge(Li) 13Cu were fabricated from two specimens of another p-type crystal that had more than 10,000 dislocations per

square centimeter; diode Ge(Li) 13Cu also contained approximately 10 llf copper atoms per cubic centimeter. The spectra were taken with the speci- mens at a temperature of about 100 K. A 1-mm thick germanium filter was placed in the radiation path. For higher energies, to the right of the

vertical dashed line in figure 4, a 640-line per millimeter grating was used in the monochromator . For lower energies to the left of the dashed

line, a 240-line per millimeter grating was used.

In a study of thermally-induced acceptors in germanium, Logan [2]

found from Hall effect data that the levels introduced into p-type

14
SPECIFICATION OF GERMANIUM

300

100

Figure 4. Infrared response spectra of four lithium-drifted germanium diodes.

0.010.30 0.40 0.50 ENERGY (eV)

0.60 0.70

crystals by heat treatment and subsequent quenching to room temperature

were indistinguishable from those of copper. For a temperature of 800°C,

the concentration of added acceptors was found to be about 10 11+ cm-3. Miles [3] has studied acceptors arising from edge dislocations in plastically deformed germanium. Using measurements of specimen photoconductivity, he interpreted the observed photoresponse in terms of a band

of dislocation acceptor states extending in energy from about 0.62 eV to

0.38 eV with a peak response at approximately 0.58 eV. The observed IRR

spectrum of diode Ge(Li) 83-4 as shown in figure 4 is consistent with

these models. A "knee" is observed at 0.58 eV on the broad response that

extends to below 0.40 eV. Features observed at 0.38 and 0.49 eV that are similar to but less intense than those observed in the copper-doped speci- men are attributed to the copper levels at Ev

+ 0.33 eV and E c

- 0.22 eV.

No special precautions were taken to exclude copper from the furnace during the heat treatment of Ge(Li) 83-4; therefore, it is possible that

some contamination might have occurred.

Measurements of IRR were also obtained from a diode fabricated from

a specimen of high-purity germanium which initially contained a net donor

concentration of approximately 7 x 10 10 cm

-3

. This diode was prepared at

another laboratory" with the use of an indium-gallium regrowth technique

for the p

+-contact and a lithium diffusion for the n+-contact. Such a diode can be depleted to a depth of several millimeters. The IRR spectra

obtained were similar to those of lithium-drifted germanium diodes of high

A"Supplied by R. D. Baertsch, Semiconductor Branch, General Electric Company, Research

and Development Center, Schenectady, N. Y. 12301.

15
SPECIFICATION OF GERMANIUM

quality such as Ge(Li) 83-4 except that the level at about 0.50 eV attributed to the lithium-defect interaction was not observed. This is

consistent with the fact that lithium-drifting was not used to obtain

the compensated or depleted region that is the only portion of the diode

sensitive to either optical or nuclear radiation.

Preliminary IRR measurements were also made on a germanium alloy

transistor and a lithium-drifted silicon diode. A special right-angle

mount for the IRR cryostat cold finger was designed and fabricated for

use with the transistor. Because of the small size of the device and the

resultant low signal level, only the band-edge peak could be observed in

the IRR spectrum. The signal-to-noise ratio was further degraded by the

high leakage current characteristic of this type of device at 100 K.

Suitable large area devices with low leakage current are required to continue further measurements of this type. The IRR spectrum of the silicon

diode at approximately 100 K exhibited a band-edge peak at approximately

1.15 eV and a broad IRR distribution, peaked near 1.00 eV. On the low

energy side of the band-edge peak, a shelf-like response was observed at

approximately 1.12 eV, similar to that observed in the germanium diodes

(NBS Tech. Note 555, pp. 16-21).

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

The IRR cryostat was modified to accept two chromel-constantan thermocouples. One thermocouple, mounted in the end of the cold finger above

the point where the semiconductor diode is mounted, is to be used to monitor the temperature in all subsequent IRR measurements. The second

thermocouple, mounted in a hole ultrasonically machined into a block of

germanium of the same approximate dimensions as typical test specimens,

is being used in the study of the temperature characteristics of the system. Preliminary measurements indicate that, as expected, the temperatures measured by the thermocouples depend upon the quality of the vacuum maintained in the cryostat. Typically, equilibrium temperatures about

95 K are obtained. In some instances, the germanium crystal was found

to be as much as 4 K warmer than the cold finger. (W. J. Keery)

A series of measurements was made on several devices in order to as- certain the effects of the magnitude of applied reverse bias on the IRR

spectral distribution. In general; it was observed that only the magnitude of the output signal depends on the magnitude of the applied bias.

The same spectral features are observed when no external voltage is applied to the device as when a potential of several hundred volts is applied. Typically, the largest increase in output signal occurred for

voltages ranging from to perhaps 20 V, whereas from 20 to 200 V the

increase was much smaller. In one germanium device, however, an approximately linear increase of signal with applied bias was observed over the

range of to 200 V. (W. J. Keery and A. H. Sher)

16
SPECIFICATION OF GERMANIUM

Plans: The interpretation of results obtained using the improved

IRR technique on semiconductor diodes will be emphasized. This will en- tail the continuing examination of different types of radiation-damaged

or specially doped crystals. Measurements will be carried out to study

the effects of the germanium filter window on the energy of the spectral

features observed as well as the effects of specimen temperature. Further IRR studies will be carried out on diodes fabricated from high-purity

germanium. One such diode that will be investigated was intentionally

doped with approximately 10 11 gold atoms per cubic centimeter.

3.6. REFERENCES

3.2. Carrier Lifetime

1. Mattis, R. L. , Carrier Lifetime Measurement by the MOS Capacitance Method,

Thesis submitted to the University of Maryland, in partial fulfillment of

the requirement for the degree Master of Science, May, 1971 (unpublished).

3.3. Inhomogeneities

1. Swart zendruber, L. J., Correction Factor Tables for Four-Point Probe Resistivity Measurements on Thin Circular Semiconductor Samples, NBS Tech. Note

199 (April, 1964).

2. Blackburn, D. L. , Nondestructive Photovoltaic Resistivity Gradient Measurements of Circular Semiconductor Wafers, Recent News Paper, Electrochemical

Society Meeting, Washington, D. C, May, 1971.

3.5. Specification of Germanium

1. IEEE Test Procedure, Germanium Gamma-Ray Detectors, IEEE No. 325 (1971).

2. Logan, R. A., Thermally Induced Acceptors in Germanium, Phys. Rev. 101 , 1455-1459 (1956).

3. Miles, M. H. , Extrinsic Photoconductivity from Edge Dislocations in Germanium, J. Appl. Phys. 40, 2720-2724 (1969).

17
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. Note 555, pp. 25-27)

indicated that a measurement of transient thermal response of a semiconductor diode is, in principle, 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 temperature rise. In order that a valid comparison can be made, it is necessary

to satisfy two conditions: 1) the procedures and equipment used to make

the measurements must give reproducible results and 2) the spread in the

measured thermal response of diodes without voids must be small compared

to the change introduced by the presence of voids. The experiments re- proted herein indicate that both these conditions have been met.

Long-term, single-operator measurements were made to check the re- producibility of the die attachment evaluation equipment. Measurements

both of steady-state temperature rise and transient thermal response with

a heating power pulse width of 5 ms , were made on commercial silicon mesa

diode chips bonded to TO-5 headers. Over a six-week period, 25 measurements of forward voltage drop were made at times, tmeas < , 15 and 50 ys

after removal of the heating power on each of four diodes . The temperature difference between the diode junction and case was calculated from

the forward voltage temperature coefficient generated for each of the

four diodes

.

The average values and sample standard deviations of the junctionto-case temperature, listed in table 1, indicate a degree of reproducibility that was adequate, but not as great as was desired. Several ways

to improve the reproducibility were considered. The reproducibility of

the data for a given diode appeared to be limited by the meter used to

Table 1 -Results of Repetitive Junction-to-Case Temperature

Difference Measurements to Demonstrate Reproducibility of Method

Steady State, I p = 0.3A Pulse Width = 5ms, Ip = 0.6A

Device " No - W.^5 W50" s W.^5 ^eas.^5

1 17.4 ± 0.41°C 16.9 ± 0.53°C 10.6 ± 0.37°C 9.4 ± 0.42°C

2 16.9 ± 0.55 16.4 ± 0.64 9.6 ± 0.44 8.2 ± 0.53

3 17.9 ± 0.54 17.6 ± 0.69 10.6 ± 0.40 9.5 ± 0.46

4 16.1 ± 0.47 15.8 ± 0.69 8.4 ± 0.47 7.2 ± 0.54

18
DIE ATTACHMENT EVALUATION

o

BU I I I ' » ' !*

|-L? < 70 - /

111 (0<

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* 5rIS / o

K 50 — — o

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Li! KK 30 - -

u.o / S*

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Q_

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n

JrI 1 1

I 1 1

Figure 5. Junction-to-case temperature difference as a function of diode heating current for

steady-state heating and for 5- and 10-ms wide

heating-power pulses.

400 600 800 FORWARD CURRENT- I, ImW

measure the forward voltage drop. Increasing the sensitivity of the meter

would be expected to reduce the observed sample standard deviation. Increasing the magnitude of the observed temperature difference would also

be expected to permit greater reproducibility. Measurements of junctionto-case temperature difference, ATjq, were made as a function of diode

heating current for steady-state heating and for 5- and 10-ms wide heating power pulses. The forward voltage of the diode was measured 15 ys

after switching to the 1-mA measuring current. Case temperature was held

at 25°C. Typically, as depicted in figure 5, it was found that doubling

the diode heating current at least doubles ATjcTo compare the magnitude of the spread in thermal response of diodes

without voids with the change in thermal response introduced by the presence of voids, measurements were made on groups of diodes bonded to TO-5

headers with 0-, 20-, and 40-percent void areas. The 20- and 40-percent

void areas were produced by 20- and 29-mil (0.51- and 0.74-mm) diameter

dimples ultrasonically machined into the bonding surface of gold-plated

T0-5 headers (NBS Tech. Note 560, pp. 27-29). Ten control devices without voids were bonded with each group of 10 to 15 devices with voids.

Average values and sample standard deviations of junction-to-case temperature difference for the two groups of control devices used in this

experiment are summarized in table 2. Group H controls were associated

with the diodes with 20-percent void area; group I controls, with diodes

with 40-percent void area. Measurement of steady-state temperature rise

and transient thermal response with heating-power pulse widths of 5 , 7

,

and 9 ms were made 50 ys after removal of the heating power. In view of

the previous experiment, the heating current pulses were increased to

800 mA for the measurement of transient thermal response. The observed

sample standard deviations in these measurements made under a given set

of conditions on a group of devices are not much greater than those previously observed in measurements on a single device made over an extended

period of time.

19
DIE ATTACHMENT EVALUATION

Table 2 — Results of Junction-to-Case Temperature

Difference Measurements on Control Diodes

Current

Pulse Width Group H Grou P !

300mA steady state 14.09±0.52°C 15.0±0.52°C

800 5ms 8.7 ±G.44 9.2±0.58

800 7 9.9 ±0.50 10.4*0.49

800 9 10.08*0.53 11.3*0.55

Measurements were also made under the same conditions on the devices

with voids and the results were compared with the appropriate results on control devices. The percent increase in ATjq of the devices with voids over the average ATjq of the controls for the various heating power pulse

widths (including steady-state temperature rise) was, in every case,

greatest when measuring the transient thermal response as opposed to the

steady-state temperature rise measurement. The percent increase in sen- sitivity to voids of the transient thermal response measured for power

pulses of 7 and 9 ms over that of the steady-state thermal response ranged

from 30 to 700 percent. For all but two of the devices measured the percent increase in sensitivity to voids was above 90 percent for the readings made with power pulses 7- and 9-ms wide.

The measurements thus far indicate that a heating power pulse width

between 7 and 10 ms should be used for maximum sensitivity to voids. It was also found that although the spread in ATjq was small for the devices

with no intentional voids, this was not the case with the intentionally

voided devices. No conclusions regarding the relationship between void

size and the change in ATjq can be drawn from these data until the actual

void sizes are determined by direct measurement.

(F. F. Oettinger and R. L. Gladhill)

Plans: Measurements of thermal response on diodes with controlled

voids of various diameters will continue. The effect of introducing a more sensitive meter into the measuring circuit will be studied.

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 : Two new ultrasonic wire bonding machines were recieved

during the quarter. The first was for bonding round wire and is presently being set up for statistical analysis of bonding parameters. The

20
WIRE BOND EVALUATION

set-up procedure, and typical bond pull strength data are given in this

report. The second machine was designed to handle ribbon wire. Initial

modifications and set-up procedures have been carried out. The wire tester was completed; initial tests showed distinct differences in uniformity of three different wire samples. A special bonding-force measuring

apparatus is described that gives reproducible non-operator-dependent

results. The self-tuning ultrasonic power supply and transducer were

received and initial studies of the ultrasonic bonding process were made

with this equipment.

At the request of a sponsor, a study was made of wire bond failures

in transistors subjected to cyclical applications of power. A calculation indicated that use of as large a loop height as is permitted by

device and package geometry minimizes such failures.

Four different semiconductor manufacturers and one Government laboratory were visited at the request of sponsors. Capacitor microphones

and magnetic pickups were distributed to the four manufacturers together

with instructions for their use. In one case, use of this equipment and

associated technology for process control developed as a part of this

task resulted in a reduction in rejection rate due to faulty bonds at

visual inspection by more than a factor of two.

Initial Set-up Procedures for Ultrasonic Bonding Machines — A new

ultrasonic bonding machine, designed to bond round wire, was acquired to

replace the borrowed machine that had been used previously for the statistical .analysis of various bonding parameters. The new machine was delivered with a. number of problems involving the motor speed control,

the wire clamps, the wire feed system, and the loop height control.

These problems had not been completely solved at the end of this reporting period.

Initial experiments were performed to establish the optimum operating parameters for the new machine. These are the values of force, time,

and ultrasonic power which yield the most repeatable pull strengths for

a group of consecutively made bonds. The results of this initial work

are reported primarily to indicate the methods that are presently used to

set up the bonding machine. From previous experience, acceptable force

values for 1-mil (25-ym) diameter aluminum wire lie between 20 and 30 gf

(196 and 294 mN). Initial experiments included four such values: 21,

24, 27, and 30 gf (206, 235, 264, and 294 mN). At each of these force

settings, four values of time were selected: 47, 75, 100, and 130 ms

For each of the combinations of force and time, bonds were made at five or six different power settings, from the lowest to the highest power setting that is possible to make a bond. At a power level that is too low,

the wire does not stick to the pad. At too high a power level, the bond

is so greatly deformed that it is severed at the heel during bonding. The

The reported data lie within these two extremes.

21
WIRE BOND EVALUATION

Bonds were made in groups of 10 at each of the different combinations

of force, time, and power for the first bond and then repeated separately

for the second bond. Bonds were tested by pulling to destruction. In

order that the first bond be tested independently of the second, epoxy

was placed over the second bonds of the bond loop to prevent breakage at

that point. The first bonds were similarly epoxied when testing the sec- ond bonds. In all, 186 groups of 10 bonds each were tested.

Typical results for first and second bonds are shown in figures 6

and 7, respectively. In each case the bonding force was 27 gf (264- mN);

the bonding time was 4-7 ms for the first bond and 100 ms for the second

bond. Each point on the graph represents the average pull strength for

10 bonds made on a single level with a ratio of bond separation to loop

height, d/h, equal to 2.5. The measured pull strength should be multiplied by approximately 0.8 to give the actual force in the wire at breakage. In general, the shape of the curves for the first and second bonds

differed, particularly in the low-power regions. The pull strength of

the second bond drops to a lower value before lift off occurs than is the case for the first bond. In the high-power region, however, the pull

strength for the first bond falls off more rapidly than that of the sec- ond bond. The reasons for this behavior are not fully understood but may

be related to the crack that exists in the heel of the first bond. The

error bars in both figures, which represent the 95 percent confidence

interval for the mean, are at least twice as large as desired, apparently

resulting from the problems with the wire clamp and loop height control

mentioned earlier.

The next step in the optimizing procedure is to select a specific

force setting and choose reduced power and time ranges based on the data

obtained. The experiment is then repeated and further reduced ranges are

6 7 POWER SETTING Figure 6. Measured bond pull strength for a first bond as a function of machine power

setting.

T 1

r I

8.0 .. f t ;

: : X

I

'

;

D) -k- ^^ i

X 6.0 - - 1-

(9Z

UJ

fc 4.0

f

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t = 100ms

_J

_l

z>°- 2.0

; c

i i , 4 5 6 POWER SETTING Figure 7. Measured bond pull strength for a second bond as a function cf machine power

setting.

22
WIRE BOND EVALUATION

Figure 8. SEM photomicrograph of a well made Figure 9. Fixture used in measurement of bondribbon wire bond. (Magnification 530 Jt) ing force.

selected until the single best operating point is obtained. This procedure is expected to yield sample standard deviations small enough (^ 1 gf)

to perform the desired experiments. (K. 0. Leedy and C. A. Main)

Ribbon Wire — A new ultrasonic bonding machine designed to bond ribbon wire was received during the quarter. Considerable effort was re- quired to put the machine in working order. This included suppressing

electrical transients, polishing the wire clamps, modifying the transducermotion cam, and designing a new work holder. Since more changes are an- ticipated, this bonder has not been through the extensive set-up procedure

described above. Nevertheless, for a series of single level bonds made

with a d/h ratio of 2.5 (tensile force in the wire approximately 0.8

times the measured pull strength) the average measured pull strength was

10.1 gf (99 mN) with a standard deviation of 0.6 gf (5.9 mN). The ribbon

wire used for the test had a cross sectional area of approximately 1.5

by 0.5 mil (38 by 13 urn), equivalent to 1-mil (25-um) diameter round

wire, and had a tensile strength of approximately 10 gf (98 mN). Figure

8 shows an SEM photomicrograph of a well made ribbon wire bond. Very

little deformation is evident. (H. K. Kessler)

Bonding Foree Measurement — The bonding force is the most critical

parameter in an ultrasonic bonding schedule. Small changes in the value

of the bonding force can markedly affect the nature of the bond. Yet the

bonding force is measured on most bonding machines by a hand-held gage

,

and the force value obtained may depend greatly on the skill of the person making the measurement. Therefore, the special force-gage mounting

future shown in figure 9 was designed to clamp onto the bonding machine

work-stage. In use, the unit is moved against the transducer until the

bonding tool rises 5 mils (125 ym) as shown by comparison with a 5-mil

thick shim placed on the work-stage next to the tool, and the indicated

force is read. (H. K. Kessler and A. W. Stallings)

Wire Tester — Evaluation of the wire indentation tester described

previously (NBS Tech. Note 592, pp. M^-M-M-) has revealed several problems

associated with the high sensitivity inherent in its application. These

23
WIRE BOND EVALUATION

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a. Wire rejected by a device manufacturer.

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b. Wire not specified

as ultrasonic bonding

quality.

c. Wire specified as high-quality for ultrasonic bonding.

Figure 10. Recorder traces of impressions made in three different specimens of 1-mil

(25-pm) diameter aluminum (1% silicon) bonding wire.

include slow drift of the tester assembly due to temperature changes

,

drift of the recorder and other instruments, and insufficient dust shielding. Thus far no method has been devised for calibrating the depth of

impression on an absolute basis to within the desired 5 yin (0.13 um).

Therefore, the data must be compared on a relative basis. A series of

impressions made on three different grades of 1-mil (25-ym) diameter aluminum (1% silicon) wire is shown in figure 10. Each line represents one impression. Impressions were made each \ in . (6.3 mm) for a distance of

about 12 in. (0.3 m). The differences in uniformity can be clearly seen by the variations at the top of the repeated traces. The higher the

trace, the smaller the impression and the harder the wire. Further ex- periments must be conducted to establish the optimum depth of impression

to produce the maximum resolution. No correlation was found between var- iability of the wire impressions and the average tensile strength of the

wire as measured with the hot-melt-glue puller (NBS Tech. Note 488,

pp. 22-24). The wire specified as high-quality for ultrasonic bonding

exhibited considerably less variability in the hot-melt-glue -puller meas- urement than the other two samples which showed about the same variability

when measured with the puller. Additional development is necessary before the wire tester can be used to evaluate bonding wire quantitatively.

(H. K. Kessler)

Transistor Failure Resulting from Slow-Thermal Cycling — In some applications, such as telemetering, transistors are operated within their

24
WIRE BOND EVALUATION

power ratings but are subjected to cyclical applications of power. Manytransistors .have been observed to fail under such conditions of thermal

cycling at slow rates (2 or more minutes per cycle). This failure has

been traced to aluminum interconnection wire fatigue resulting from re- peated thermal-expansion-induced wire flexing [1, 2], A study was made

of the wire bond flexure resulting from such cycling of 500-mW, 50-mA

transistors. This low current does' not produce significant Joule heating

of the lead wires. However, the die may reach 180°C and cause considerable thermal expansion. For the thermal expansion calculation, the die was assumed to be the sole source of heat. The analysis was made specifically for the 1-mil (25-um) diameter post-to-die aluminum wire interconnection in a particular transistor in a TO-18 can, but it is generally

applicable to other devices with similar current and power ratings.

It was found that the changes in loop height and the angle of the

wire at the bond heel were approximately proportional to the dissipated

power and inversely proportional to the equilibrium loop height. Since

wire flexing is reduced as the loop height is increased, failures due to

wire flexing are minimized if the largest loop height permitted by device

and package geometry is used. For discrete transistors in TO-18 cans, a loop height of 5 to 10 mils (0.13 to 0.25 mm) is recommended when these

devices are subjected to thermal cycling during operation.

An alternative solution to using aluminum wire with large loop

heights is to use gold bonding wire. The basis for the above flexure

calculation is the differential coefficient of expansion between the wire

and the iron-nickel-cobalt alloy header. This differential is significantly smaller for gold wire than for aluminum wire. The use of gold

wire with the same loop height as aluminum reduces the wire flexing in

the device by about one half. In addition, gold wire has a much higher

resistance to flexure fatigue. To realize the advantages of gold wire,

consideration must be given to the voids that form with intermetallic

compounds if the gold wire is attached directly to aluminum films and is

subjected to too high a temperature during testing or operation.

In an earlier analysis [3] of lead wire flexing due to heating, the

expansion due to self heating by high current pulses was considered in

addition to that induced by chip heating. Although the details of this

calculation differ from the present one, the conclusion that the greater

the loop height the less pronounced is the wire movement was also reached.

(W< E. Phillips)

Putt-Strength Acceptance Criterion — Most wire-bond acceptance criteria do not take account of the degradation of the bond during thermal

cycling. Available data [2] suggest that failures due to thermal cycling

occur principally near the bond to the semiconductor die. This suggests

that a bond pull-strength criterion that is dependent upon the quality of

the metallurgical weld, the bond deformation, and strain or cracking in

the bond heel Is essential. One possible criterion (often termed bond

25
WIRE BOND EVALUATION

efficiency [4, 5]) that may satisfy the above requirements is based upon

the ratio of the actual breaking force in the wire, T-g, to the tensile

strength of the wire, Trp, Determination of the minimum value of Tg/T^

for which satisfactory metallurgical welding and bond deformation are indicated and minimum cracking or strain has occurred in the heel region

would be valuable in specifying bond quality in terms of actual bond

characteristics

.

For example, consider a typical 1-mil (25-um) diameter aluminum

wire with a tensile strength of 18 gf (176 mN). If the minimum acceptable value of T /T be chosen as 0.4, a bond to be acceptable must break

with a force not less than 7.2 gf (70 mN) in the wire. To translate this

into acceptable measured pull strength it is necessary to consider the

geometry (NBS Tech. Note 555, pp. 31-35). For a typical bond pair on a device in a TO-18 can with a chip thickness of 0.125 mm, a post height

of 0.25 mm, a bond separation of 1 mm, and a loop height of 0.1 mm pulled

vertically halfway between the bonds 9 a "minimum bond pull strength of

3.3 gf (32 mN) would be required. If the wire tensile strength were re- duced to 13 gf (127 mN), as might occur as a result of annealing during

heat-sealing or testing the device, a minimum bond pull strength of

2.4 gf (24 mN) would be required. If, on the other hand, a value of

T /T of 0.7 be required for acceptance, then bond pull strengths of

5.7 or 4.1 gf (56 or 40 nM) would be required for the wire with tensile

strength of 18 or 13 gf, respectively.

Although determination and verification of an appropriate value for

Tg/T^ is, at present, beyond the scope of this task, such a criterion

based upon actual bond parameters is of sufficient importance to be

brought to the attention of persons interested in this field. Ratios of

Tg/T.p from 0.8 to 0.9 have been achieved using wires of very different

tensile strengths when proper -bonding machine parameters were chosen [5].

Bonds made at NBS typically show Tg/T^ ratios of 0.8 or more, and bonds

made on certain high-reliability device production lines show Tg/T^

ratios consistently greater than 0.7. Ratios for bonds made on typical

commercial lines might be expected to be lower. (G. G. Harman)

Consultations — At the request of a sponsor, a comparison was made

between two slow-thermal-cycle test systems, one at a semiconductor manu- facturing plant and the other at the sponsor's laboratory. Two informal

reports were submitted to the sponsor covering aspects of the comparison.

(G. G. Harman)

Four visits were made to semiconductor device producers at the re- quest of sponsors. Calibrated microphones and magnetic pickups were distributed along with preliminary copies of instructions for their use [6],

Measurements were made of the ultrasonic vibration amplitude of the bonding machines at each site. All had identical equipment. Significant

variations in tool tip vibration amplitude and bonding time were found;

these were more characteristic of the particular producer than of the

26
WIRE BOND EVALUATION

packages being bonded. In one case, a factor of two variation in power

supply power dial settings was observed to produce the same tool tip vibration amplitude from one bonding machine to the next . Twenty-five

percent variations were common. This is attributed to variations in

transducer conversion efficiency rather than to properties of the power

supply. In one case, involving the least efficient transducer, the technician had apparently been unwilling to increase the power dial setting

sufficiently to compensate for the transducer inefficiency; instead he

increased the bonding time in order to establish good bonding. As it

turned out, that machine produced the most reliable bonds on that assembly

line so that it would appear that an optimum bonding schedule had been

achieved. Although the intuition of a good technician is valuable in setting up a bonding machine, only by actual measurement of the tool vibration amplitude is it possible to set up a known bonding schedule on a number of apparently identical bonding machines

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

In-Prooess Bond Quality Determination — A system of studying ultrasonic bonding by listening to an audible beat frequency of the vibration

bonding tool has been described (NBS Tech. Note 592, pp. 39-41). This

early work was performed with two fixed- frequency power supply-transducer

combinations. This quarter, initial studies of the ultrasonic bonding

process were made with a new self-tuning transducer-power supply system

that the experiment was originally designed to use. During normal bonding, the fundamental frequency was observed to shift by several hundred

hertz. This frequency shift was very easily distinguished when the operator listened to the audible beat frequency of the second (120 kHz) or third (180 kHz) harmonic. Qualitative experiments were performed under

a number of conditions and on different substrates. For instance when

the wire was intentionally placed near the edge of the bonding tool the

sound was characteristic of the wire being squeezed out from under the

tool when the ultrasonic energy was applied. Different sounds were heard

when the bonding took place on a normal aluminum bonding pad, to silicon

oxide, or only half on the pad. Many variables were encountered. The

most sensitive response was obtained when the local oscillator was on the

low side of the particular harmonic chosen (generally the second harmonic

was preferred), but in some cases the reverse was true. Identification

and control of the important parameters of this measurement system are still under investigation. (G. G. Harman)

Bibliography and Critical Review — The draft of the bibliography

was completed and work on the final draft of the critical review survey

paper was continued. (H. A. Schafft)

Plans : Experimental and statistical analysis of significant factors

in the wire bond pull test will continue. Evaluation of ribbon wire for

ultrasonic bonding will continue. Work on the wire indentation tester

will continue. Further assistance will be given to sponsors in connection with problems encountered on device production lines. Calculations

27
WIRE BOND EVALUATION

of the wire flexing due to heating of the device during thermal cycling

will be refined. Further work on electronic mixing of bonding tool ultrasonic signals with local oscillators will continue in an effort to better

understand and control bonding. The bibliography will be submitted for

publication as an NBS Technical Note and work on the final draft of the

critical review survey paper will be continued.

4.3. PROCESSING FACILITY

Objective : To establish a microelectronic fabrication laboratory

with the facilities and procedures necessary for the production of specialized silicon devices and for use in research in measurement methods.

Progress : Considerable effort was spent In attempts to improve the

electron beam evaporation system (NBS Tech. Note 592, p. 45). The initial experience with the unit demonstrated that aluminum evaporation

rates greater than 5 nm/s could be achieved on silicon substrates. With

the use of the planetary substrate holder it was found that the variation of thickness of deposited aluminum was less than 1 percent across

the surface of any one substrate and less than 2 percent from substrate

to substrate in a given run. All thickness measurements were performed

with a multibeam interferometer. Typical deposition thicknesses were in

the range of 0.6 um to 1.0 urn.

However, during the initial testing period, excessive pressure in- creases were noted during the time the electron beam current was energized. The pressures further increased as the system was run. Typically

the pressure within the chamber increased from 5 x 10 ' to 5 x 10 5 Torr

when the beam was established. The latter pressure is too high for the

production of high quality films because residual gasses are entrapped

in the film. The result is oxidized aluminum having a milky appearance,

poor electrical conductivity, and poor etching characteristics. At this

time the reason for the pressure increase in uncertain, but it is sus- pected that secondary electrons, released from the aluminum charge as the

primary beam strikes it, outgas the surface of the chamber providing the

pump with an excessive gas load. In an attempt to provide a greater

throughput of gas, all vacuum components were disassembled, cleaned,

and re-installed. The diffusion pump was charged with a lighter molecular weight oil than used previously.

Installation of a new three-tube diffusion furnace was begun. The

necessary electrical power was made available for its operation and some minor defects in the temperature controllers and overheat systems were

corrected. Delays in the fabrication of the quartzware and procurement

of the flow meters made it impossible to complete the furnace installation. (T. F. Leedy and J. Krawczyk)

28
PROCESSING FACILITY

Plans : Work will continue on both the completion of the diffusion

furnace installation and the improvement of the electron beam evaporation system. The rebuilt vacuum system will be tested to determine if

the gas pressure can be reduced during evaporation. If necessary, other

measures, such as the installation of a larger diffusion pump' or cryogenic pumping of the chamber during evaporation, will be considered.

Either of the measures would involve extensive modification of the

system.

4.4. REFERENCES

4.2. Wire Bond Evaluation

1. Gaffney, J., Internal Lead Fatigue Through Expansion in Semiconductor Devices,

IEEE Trans. Electron Devices ED-15 , 617 (1968).

2. Villella, F. , and Nowakowski, M. F., Investigation of Fatigue Problem in OneMil Diameter Thermocompression and Ultrasonic Bonding of Aluminum Wire, NASA

Technical Memorandum TM-X-64566, November 30, 1970. Available from National

Technical Information Service, Springfield, Va. 22151 (Accession No. N71-

16494).

3. Gaffney, J., Bottaro, D., and Root, C. D., Internal Lead Fatigue in Semiconductor Devices Through Thermal Expansion, Presented at the Seventh Annual

Reliabiltiy Physics Symposium, Washington, D. C, December 3, 1968.

4. Riben, A. R._, Sherman, S. L. , Land, W. V., and Geisler, R., Microbonds for

Hybrid Microcircuits , Physics of Failure in Electronics vol. 5, Eds. T. S. Shillday and J. Vaccaro, pp. 534-556 (Rome Air Development Center, 1967).

5. Cox, W. P., Anderson, E. E., and Anderson, J. H., Jr., Ultrasonic Aluminum

Wire Bonding for Microelectronic Applications, Annals of Assurance Sciences 3_, No. 1, 228-236 (1970).

6. Harman, G. G., and Kessler, H. K. , Applications of Capacitor Microphones and

Magnetic Pickups to the Tuning and Trouble Shooting of Microelectronic Ultrasonic Bonding Equipment, NBS Tech. Note 573 (April, 1971).

29
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 : Work on the literature search and compilation of articles

for the bibliography on methods for measurement of thermal resistance

and transient thermal response of semiconductor devices were postponed.

After reviewing a portion of the first draft of the survey paper on electrical methods for these measurements it was decided to utilize the re- levant portions as an introduction in an appropriate report on the results

of the semiconductor device thermal studies now in progress rather than

publish an independent survey.

Work on the implementation of a preliminary thermal resistance round

robin being conducted by JEDEC Committee JC-25 on Power Transistors was continued. Completed questionnaires on the capabilities of the available

on-line thermal resistance measuring equipment have been received from

7 of the 10 members of Committee JC-25. (F. F. Oettinger)

Both the d-c and dynamic procedures for calibrating base-emitter

voltage, Vg£, as a function of case temperature have been reported previously (NBS Tech Note 571, pp. 35-37). It was noted that at low power

levels the d-c calibration procedure could give erroneous values of com- puted thermal resistance due to the presence of non-thermal switching

transients, but that a reasonably good correction for such low level distortions could be effected by using the appropriate dynamic calibration

procedure

.

Measurements were made on a variety of transistors rated at 20 to

35 W to compare the dynamic calibration procedure with the d-c procedure

using various measuring or calibration currents. In the dynamic procedure, V-d E was measured 10, 20, 50 and 100 ys after the transistor under

test was switched from an operating condition of collector-emitter voltage of 1 V and collector current of 1 .A to the test condition. In both

procedures, the base current was controlled at 6.5 mA during measurement

of VBE . It was found that for the transistors tested, the measuring base

current was small enough to avoid significant heating of the base-emitter

junction and large enough to reduce the non-thermal switching transients

to manageable proportions. Typical plots of Vg£ as a function of case temperature for the various conditions, shown in figure 11, are essen- tially parallel straight lines. Although the lines are separated as a result of both a cooling of the junction and the decay of the electrical

component of the base switching transient, the slopes are essentially

the same. Therefore, if the thermal resistance is calculated from a difference in temperature and power between two different power levels , the

30
THERMAL PROPERTIES OF DEVICES

520 540 560 580 600 BASE -EMITTER VOLTAGE - VBE (mV) Figure 11. Comparison of dynamic and d-c calibration of a 25-W, silicon

n-p-n transistor.

dynamic calibration does not afford any advantage provided that the measurement is not made at very low power levels where Vgg is not a linear

function of power (NBS Tech. Note 592, pp. 52-53).

Long-term, single-operator measurements were undertaken to check the

reproducibility of the equipment for measuring thermal resistance of power

transistors. Ten measurements of Vgfj were made both 10 and 20 ys after

the termination of the heating power pulse over a period of three weeks on three transistors of the same type under conditions that would not stress

the transistors. From these data the junction temperature was determined

with the use of appropriate calibration curves. It was assumed that any

significant change in the parameters of the transistors would not occur simultaneously in more than one unit at the same time and in the same

way. During this period, the electrical characteristics of one of the

transistors changed so it was dropped from the experiment. If the data

for the remaining transistors are assumed to be normally distributed, it can be asserted with 95 percent confidence that the standard deviation

of the junction temperature is less than 0.51°C. Other measurements suggest that over a workable range this standard deviation does not depend

significantly on the magnitude of the junction temperature. Therefore,

the relative standard deviation can be reduced by increasing the heating

power.

In a continuation of the study in which it was found that for the

three transistor types tested, for collector currents of 100 and 200 mA

and for collector-emitter voltage levels below those at which current

constriction occurred the thermal resistance, Rq , was essentially constant (NBS Tech. Note 571, p. 37), R0 was measured as a function of power

for collector current levels up to 1 A. The measurements at both the

higher and lower current levels showed similar results although as the

collector current was increased the devices with low gain or relatively

high saturation voltage levels showed increased non-thermal switching

31
THERMAL PROPERTIES OF DEVICES

J 1 1 1 1 1 ^•^--I.OA

l 1 1

1 1 1 1 1

x— 0.IA.0.2A.0.4A

tmeas. = 'O^S -^

- -—^^*— I.OA ^-O.IA

tmeos 320/^

*-0.2A ^"^

V-04A

^-O.IA,0.2A,0.4A ^

Figure 12. Base-emitter voltage of a 35-W, triple-diffused, silicon

transistor measured as a function of applied power for collector currents of 0.1, 0.2, 0.A, and 1.0 A, at times 10, 20, 50, and 100 us after

removal of power

.

Figure 13. Normalized thermal resistance of a 35-W, triple-diffused, silicon transistor measured as a function of delay time for both current constricted and normal (non-constricted)

operating conditions.

20 40 60 BO 100 DELAY TIME BEFORE MEASUREMENT

0F v«- 'mm </»>

32
THERMAL PROPERTIES OF DEVICES

transient effects at low and, in some cases, intermediate power levels

when Vg£ was measured 10 ys after the termination of power pulse. Increasing the time between the termination of power pulse and the measurement of Vgg decreased the effects of these non-thermal transients.

The curves depicted in figure 12 are plots of Vg-o measured as a function of power dissipation for various collector currents and measurement delay times on a 35-W, triple-diffused, silicon transistor. The

measuring base current was 6.5 mA and the case was held at 25°C. The

thermal resistance was calculated from the raw data by dividing the slope

of the linear portion of the (VgE

) meas — power curve by the slope of the

d-c calibration curve

, BE s , BE .

= K AW meas

l AT 'd-c calib'

As previously reported (NBS Tech. Note 571, p. 37), if thermal

hysteresis occurs when a hot spot is formed, the hot spot remains during

the measurement of Rq even though the power to the device under test is

interrupted for periods of time up to 120 ys. The data in figure 12 for

a collector current of 0.1 A also indicate that while the current is con- stricted, the measured thermal resistance is apparently constant. Further studies are needed to determine how closely junction temperatures

calculated from the slope of the (V-nrO meas — power curve during the

current-constricted operating mode approximate the actual hot-spot temperature. This depends in part on the distribution of the measuring cur- rent when the device is operating in the current-constricted mode. Fig- ure 13 shows the effect of delaying the measurement of V-gg in both the

normal (non-constricted) and constricted operating conditions based on the 0.1-A curves of figure 12. As expected, the curves indicate that

the larger the temperature difference involved, the greater is the error

in delaying the measuring of Vgg.

To determine the general applicability of various techniques for use

as industrial standards , a study was begun to compare other widely used

methods for measuring thermal resistance to the common-emitter, base-andcollector-switching technique . This technique , in which both the base

and collector of the transistor under test are momentarily opened and a constant current of a given magnitude is applied to the base , was com- pared to a collector-only-switching method, in which the constant base

drive that is applied during the heating cycle is continued when the collector is momentarily opened for test purposes. The measurement of thermal resistance by the collector-only-switching method is usually made by

applying a given collector voltage and collector current during the heating cycle and computing the dissipation. The value of Vgg measured during the collector-off period is then used to determine junction temperature from a calibration curve of Vg-g as a function of case temperature

33
THERMAL PROPERTIES OF DEVICES

(assumed equal to the junction temperature during calibration) for the same magnitude of base drive used during the transistor heating period.

Measurements indicated that erroneous values of thermal resistance could

be obtained if measurements were made only at zero power and at a specified higher power level. Error can be minimized by using a procedure

similar to that developed for the base-and-collector-switching method.

Measurements were made using the same collector current at two different

levels of collector voltage, Vq^, in the linear portion of the Vg£ —

power curve. The thermal resistance was calculated by taking the difference in junction temperature, as determined from the appropriate d-c calibration curve relating Vgr- to case temperature , and dividing it by the

difference in power between the two voltage levels used. It should be

noted that since the collector current was kept constant for the two different collector voltage measurements, two different base current drives

and therefore two different calibration curves had to be used. Measurements of Rq by this technique are valid only if the two calibration

curves have essentially the same slope. Measurements of thermal resistance determined by both methods on a 35-W, triple-diffused, silicon

transistor are given in table 3. Measurements of Vgg were made 10, 20,

50, and 100 ys after the termination of the heating power pulse. Power

levels of 10 and 20 W at a collector current of 1 A were employed. The

difference between the measured thermal resistance using the two methods

in all cases is less than 3 percent. The data also show the cooling effect due to increased delay times when measuring Vg£.

The 35-W, triple-diffused, silicon transistor was also used in a study to compare the electrically measured thermal resistance with measurements by an infrared microradiometer. The electrical measurements

were made at Vqj? values of 10 and 20 V with a collector current of 500 mA.

Infrared measurements of the chip surface temperature made at a Vqe of

20 V indicated that a significant temperature gradient existed with a low

temperature around the edges of the chip, a relatively constant intermediate temperature over the greater portion of the interior of the chip,

and a higher temperature on the chip in the vicinity of the emitter lead.

The computed thermal resistance was 1.88°C/W in the interior area of the

chip and 2.68°C/W in the hottest portion of the chip near the emitter

Table 3 - Comparison of Thermal Resistance Measured using

Collector-and-Base Switching and Collector-Only Switching

tmeas CollectorSwitch

anding Base Collector-Only

Switching

10viS 2.16°C/W 2.10°C/W

20 2.01 2.00

50 1.92 1.88

100 1.85 1.83

34
THERMAL PROPERTIES OF DEVICES

lead. Thermal resistance measured electrically 10 ys after the termination of the heating power pulse was 2.08°C/W, higher than the value meas- ured with the infrared microradiometer in the major portion of the chip

interior, but less than that in the elevated temperature region. It

should be pointed out that these measurements were made under operating

conditions well below those that cause severe current constriction or hot-spot formation. Further studies are needed to determine to what extent the electrically measured thermal resistance is increased by properly extrapolating Vgg to zero time delay after the termination of the

heating power pulse. (S. Rubin and F. F. Oettinger)

Plans : Data collection for the Committee JC-25 preliminary thermal

resistance round robin will be started. A common -base circuit for measuring Rq, wherein both the collector and emitter of the transistor under

test can be" switched, will be designed and fabricated. ' Measurements of

thermal resistance and d-c current gain of power transistors under various operating conditions will continue. Infrared microradiometer measurements will be made on the same devices to continue the investigation

of relationships which may exist between the peak temperature and the

electrically measured temperature.

5.2. THERMOGRAPHIC MEASUREMENTS

Objective : To evaluate the utility of thermographic techniques for

detection of hot spots and measurement of temperature distribution in

semiconductor devices.

Progress : Although the work on the characterization of the phosphors is far from complete, it is possible to estimate some of the capabilities of the phosphors and equipment. By illuminating the specimen

with minature ultraviolet lamps and detecting the radiation with the

photometric microscope, temperature sensitivities (change in brightness)

between 5 and 7 %/°C have been obtained on the four phosphors that cover

the range between room temperature and 400°C. In two of the phosphors

this is less than the sensitivity specified by the phosphor manufacturer,

but it is still sufficient to permit measurement of temperature changes

of 2°C. The low sensitivity may be due to the thinness of the phosphor

coating, approximately one particle thick, obtained by the flotation

technique (NBS Tech. Note 488, p. 31).

Spatial resolution is limited by the capabilities of the photometric

microscope and 50-um fiber optic probe to about 35 urn. For comparison,

the spatial resolution was estimated to be 20 ym when the light output

of the phosphor was recorded photographically [1], and the spatial re- solution using the infrared microscope at a comparable working distance

was found to be 35-um. Since maximum phosphor particle size is about

25-um, particle size does not limit the spatial resolution at present.

(G. J. Rogers)

35
THERMOGRAPHIC MEASUREMENTS

Plans : Fabrication of a new heat sink with better temperature con- trol for testing silicon wafers will begin. Test specimens with surfaces

of silicon dioxide, polished silicon, aluminum, chromium, and gold will

be fabricated. These surfaces will be coated with phosphor by the s lurry- settling technique and characterized.

5.3. MICROWAVE DEVICE MEASUREMENTS

Objective : To study the problems and uncertainties associated with

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

these measurements.

Progress : The r-f portion of the X-band mixer measurement system

was extensively rebuilt to permit active stabilization (leveling) of the

local oscillator power and to improve certain other aspects of the circuit. The new circuit, shown schematically in figure 14, incorporates

the following changes from the previously reported circuit (NBS Tech.

Note 560, p. 43):

1. A heat sink has been added next to the klystron. This is a 10-in. (25-cm) long waveguide section, machined from a 4-in. (10-cm)

diameter copper bar. The bar was sliced in half lengthwise, the waveguide opening and cooling fins milled, and the .halves silver-soldered

together using plugs to maintain the correct waveguide width. This design avoids the thermal resistance that would have been added by the use of separately attached waveguide flanges or cooling fins. With heatconducting silicone grease between the klystron and the heat sink and

with the blower off, the temperature rise of the klystron at a point opposite the waveguide flange was only about half as much as it was before

the heat sink was installed. The heat sink is expected to improve the

life and stability of the klystron without the complexity of water cooling. It also adds considerable mechanical stability to the klystron and

adjacent components.

2. A 20 dB directional coupler was substituted for the 10 dB cou- pler, previously used to extract power to frequency stabilize (phaselock) the klystron in order to reduce the power loss. To obtain sufficient phase-lock power, the hybrid tee previously used for initial

klystron adjustments was replaced by another 20 dB directional coupler.

A diode detector is now used for these adjustments in place of the bolometer because of the much lower power level.

3. The PIN modulator is now permanently in the local- oscillator

(l-o) line. This eliminates loss and leakage of the coaxial cable previously used to connect the modulator. Leveling is achieved by a negative-feedback loop using a 10 dB directional coupler and a diode

detector to sample the l-o power. The detector output is fed to an

36
MICROWAVE DEVICE MEASUREMENTS

OSCILLATOR

PHASE-LOCK

WG.-

COAX

120 Dl

ABSORPTION

WAVEMETER

LEVEL-SET ATTENUATOR

DETECTOR

DIR. COUPLER

PHASE-LOCK LOOP

KLYSTRON

OSCILLATOR

HEAT

SINK LOWPASS

FILTER

20DBJ

ELECTRONIC

GALVANOMETER

DIR. COUPLER

LEVEL-SET ATTEN £

DIR. COUPLER

PRECISION VARIABLE

ATTENUATOR

10DB

PIN MODULATOR

LEVELING LOOP

BANDPASS

FILTER o

MODULATION

VOLTAGE

LEVEL-SET ATTENUATOR

TUNABLE

DETECTOR

TO AUXILIARY REFLECTOMETER

OR FREQUENCY COUNTER, ETC.

DIGITAL VOLTMETER

TO DC/IF

CIRCUIT

MIXER

Figure 14. Modified r-f section of microwave mixer measurement system.

37
MICROWAVE DEVICE MEASUREMENTS

operational amplifier which provides a large open-loop gain .for precise

leveling and whose output is capable of directly driving the PIN modulator. A stable r-f attenuator controlling the sampled power is used in

setting the l-o power available to the mixer. This attenuator setting

and the tuning adjustment on the detector can be locked. Stable modulation of the l-o power, used to produce a test signal, is easily achieved

by applying the modulation voltage to the otherwise unused input terminal

of the operational amplifier. The peak-to-trough ratio of this modulation, from which the equivalent single-frequency signal is calculated, is

measured by using a precision variable attenuator following the leveling

loop in a substitution method (NBS Tech. Note 571, p. 44).

4. An auxiliary l-o source for braodband tuning with a 30 MHz i-f

can be introduced through the transfer switch that is normally set so that it powers the auxiliary reflectometer that is used in obtaining a line-matched source for the mixer, in setting and checking the l-o frequency on a counter, and for experimental purposes. The level-set attenuator at the auxiliary source port is primarily intended to reduce

the reflection from this port of power leading through the isolator and

circulator when the auxiliary reflectometer is is use. This minimizes

the change in mixer-source match as the transfer switch is thrown.

5

.

The low-pass filter used to remove out-of-band power from the

noise source has been moved into the l-o line where it will also remove harmonics that may possibly be generated in the PIN modulator. The new

location also affords better mechanical stability by shortening the noise- source arm, and it properly spaces the circulator from the hybrid tee

isolator so that these magnetic components do not interact.

6. The waveguide loop used for the reflectometer was rearranged

completely to make it more compact and rigid, with shorter paths and fewer bends. The 10 dB directional coupler formerly used in the reflectometer nulling circuit was replaced by a 20 dB coupler.

7. The hybrid tee formerly used to separate reflected from incident

l-o power, for the reflectometer, has been replaced by a circulator,

thereby saving 2 to '2 1/2 dB of loss each for both the incident power and

the reflected power. This change reduces the l-o power requirement and

increases the reflectometer senstivity.

8. Power monitoring, that had previously utilized the half of the

l-o power lost in the hybrid tee now replaced by the circulator, is now

accomplished with a switch following the circulator and the tuner. This

switch allows the relative amplitude of the l-o power to be ascertained

by measuring the output voltage of either a diode or a film thermocouple

with a high-precision digital voltmeter. The relative stability of these

two types of detectors has yet to be determined.

38
MICROWAVE DEVICE MEASUREMENTS

9. Since it may be desirable, for reproducible measurements, to

avoid reflecting harmonics of the l-o frequency generated by the mixer

diode back to the mixer, a well-matched pad has been constructed to absorb

a moderate amount of power at all frequencies (including, unfortunately,

the l-o and signal frequencies). This pad consists of an 11-in.. (28-cm)

long section of waveguide containing a dielectric element with 5-in.

(13-cm) long tapers on both ends. At the center, the dielectric com- pletely fills the waveguide, thereby providing attenuation for all modes

of propagation. Two types of pads were made: one with a nylon element

which exhibited a loss of only 2 dB, the other with an unfired steatite

element with a loss of 7 dB. The higher loss can be tolerated for the

low i-f measurements, but may be too high for the 30 MHz i-f measurements

using the gas-discharge noise source.

10. The guillotine -type waveguide gate formerly used to reflect the

incident power has been replaced with a transfer switch and a movable

non-contacting, choke-type short. The switch is more reproducible in its

action than the gate, and the movable short is less lossy and thereby

provides a more nearly perfect reflection. (J. M. Kenney)

Plans : Methods for improving the precision of measurement of mixer

output voltage will be sought by reducing non-random interference , modulation drift, and power drift.

5.4. CARRIER TRANSPORT IN JUNCTION DEVICES

Objective : To improve methods of measurement for charge carrrier

transport and related properties of junction semiconductor devices.

Progress : Most of the laboratory effort this quarter was concentrated on the Sandia-type delay-time bridge [1]. Prior to the insertion

of the transistor bias networks within the attenuator and phase-splitter

box and prior to connecting a transistor socket at the bridge -summing

(null) point, interchannel (emitter and collector delay line) isolation,

constancy of delay-time zero setting with frequency, and incremental delay ratio were measured for signal frequencies in the operating range of

the bridge between 3 and 30 MHz. The interchannel isolation was found

to be greater than 50 dB at all frequencies. This means that the maxi- mum amplitude error introduced into the test channel from the reference

channel will be less than 0.5 percent. The variation in the "zero set"

delay-time reference value was found to be less than 2.5 x 10~ 10 s, which

is felt to be an acceptably small value: large values of shift in the

reference value of delay time could be a nuisance if one wished to make

rapid measurements at a variety of frequencies. Incremental delay ratio

measurements were made by measuring the delay required to be added to

the test channel, for null, when known time delays were inserted in the

reference channel. Ideally the ratio of these two should be unity,

39
CARRIER TRANSPORT IN JUNCTION DEVICES

independent of frequency. The desired 1:1 incremental delay time ratio

was approached closely for frequencies between 3 and 30 MHz, and for delay time increments between a few tens of picoseconds and 10 ms . A loglog plot showed a straight-line behavior over this delay-time range with

deviations of only a few picoseconds at the lower end. :

Following these measurements, bias networks were inserted into the

emitter and collector (ground) returns within the attenuator and phasesplitter box, and a TO-18 transistor socket and collector-voltagemonitoring circuit and jack were connected to the radio receiver end of

the emitter and collector delay lines . Preliminary delay-time measurements were made as a function of emitter current on a silicon n-p-n transistor with fa of about 350 MHz as a functional check of the operation of

the bridge. (D. E. Sawyer and G. J. Rogers)

The delay-time error that might be introduced by moving the primary

loop in the attenuator and phase-splitter box relative to the two se- condary loops was analyzed theoretically. Such relative motion could be

the result of rebalancing the bridge, during a measurement sequence, to

accomodate a change in the common-base current gain due to changes in

biasing conditions such as a change in emitter current. (C. Hoer*)

A survey of noise in semiconductor devices was completed this

quarter [2]. One of the conclusions reached is that with noise-spectrum

measurements one should be able to measure separately device phenomena

which otherwise are almost always measured by their sum effect . One ex- ample is the prediction that one might be able to separate the true base

delay time in a transistor from the delay time associated with the car- riers interacting with the collector junction electric field following

their passage across the base.

Additional references have been compiled on the utilization of various probing techniques for the determination of transistor device parameters while the devices are in the wafer stage of preparation.

(D. E. Sawyer)

Plans : The equivalent circuit of a transistor in the Sandia-type

bridge will be analyzed to relate the measured delay time to the various

times within the device, such as the emitter RC charging time and the

base-collector delay time. A second delay-time measurement circuit will

be constructed after the arrival of the vector voltmeter. A third system, based on the measurement of S -parameters will be assembled following

the ordering and arrival of necessary additional parts. Intensive device

measurements will be begun following the construction of the system based

on the vector voltmeter, since two different systems will then be available for intercomparison measurements. The analysis of delay-time error

will be evaluated within the context of the measurement procedure.

"NBS Electromagnetics Division.

40
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

emphasis on the improvement of detector technology, and to provide con- sultation and specialized device fabrication services to the sponsor.

Progress : Pre-flight bench-testing of lithium-drifted silicon radiation detectors continued. A test chamber for carrying out measurements of the effects of ambients that may affect the performance characteristics of semiconductor detectors was constructed and evaluated.

Radiation damage measurements on lithium-drifted silicon detectors using

1.5-MeV electrons were begun.

Testing and Evaluation — Commercial lithium-drifted silicon detectors

were give'n extensive bench-tests as part of a continuing program of detector evaluation and acceptance for the sponsor. These measurements,

for the IMP-H and Pioneer-F programs, were performed at the NASA-GSFC

site. (A. J. Baroody)

Radiation Damage — A commercial, 2-mm thick, lithium-drifted silicon

detector was irradiated with 1.5-MeV electrons at fluences between 10 12

and 10 ^ cm

-2 on a 20-mm2 spot on the particle-entrance window (p-contact),

The irradiation was carried out at room temperature with the detector reverse biased at 400 V. The detector reverse leakage current, noise, and

capacitance were observed to increase with increasing fluence with a sharp increase in noise above a fluence of approximately 3 x 10 13 cm

-2

. After the irradiation at 10 14 electrons per square centimeter, the current

and noise had increased by more than an order of magnitude over the initial values, and the charge collection efficiency for charged particles

incident on the irradiated contact was much degraded.

The effect of room temperature annealing on the detector characteristics was monitored continuously with the detector kept under 4-00-V reverse bias. After approximately four days, the current and noise had

almost completely returned to their pre-irradiation levels , while the ca- pacitance and charge collection efficiency exhibited only a small percentage recovery. The collection efficiency and energy resolution re- mained relatively unchanged from pre-irradiation levels, however, for

particles incident on the n- contact following irradiation and annealing.

This observation might be explained by the fact that radiation-induced

defect centers act as traps only for electrons. However, it is also possible that the irradiation produced a dead layer near the i-p junction

due to precipitation of lithium on the radiation-induced defects. The

characteristics of the irradiated detector continued to deteriorate when

the applied bias was removed.

A second detector was irradiated under the same conditions as above,

except that the detector was under a reverse bias of 200 V. The in- crease of current and noise with increasing fluence was alower than in

41
SILICON NUCLEAR RADIATION DETECTORS

the 400-V case, whereas the increase of capacitance and reduction in

charge collection efficiency was accelerated. (Y. M. Liu)

Ambient Exposure Tests — The construction of the new all-metal vacuum

system was completed. Preliminary tests were completed to check out the

performance of the system. The ultimate pressure attained was approximately 3 x 10" 5 Torr, and the system was found capable of returning to

its ultimate pressure after exposure to dry ammonia gas at pressure up

to 1 Torr.

Electronic equipment in accordance with standard procedures [1] was assembled and tested for the measurement of noise of detectors exposed

to ambients such as ammonia, methanol, and a commercial leak-detection

fluid. (E. I. Klein, W. K. Croll, and B. H. Audet)

Plans: Pre-flight bench-testing of detectors will continue as re- quired by the sponsor. The radiation damage study of lithium-drifted

silicon detectors will continue with irradiation with 600-keV electrons

and fast neutrons. The pressure of gas at which measurable effects on detector noise and leakage current are observed will be determined as well as the duration of such effects once the gas is removed from the

system.

5.6. REFERENCES

5.2. Thermographic Measurements

1. Brenner, D. J., A Technique for Measuring the Surface Temperature of Transistors

by Means of Fluorescent Phosphor, NBS Tech. Note 591 (July, 1971).

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., Noise in Semiconductor Devices, Its Determination and Significance,

NBS Electron Devices Section Report 9"21, January, 1971. This unpublished internal

-report, written under the guidance of Prof. H. P. D. Lanyon of the Worcester Polytechnic Institute, is intended to provide preliminary information for discussion

purposes.

5.5. Silicon Nuclear Radiation Detectors

1. USA Standard. and IEEE Test Procedure for Semiconductor Radiation Detectors (for

Ionizing Radiation), USAS N42.1/IEEE No. 300/(1969), pp. 5-6.

42
Appendix A

JOINT PROGRAM STAFF

Coordinator: J. C. French

Consultant : C . P . Marsden

Semiconductor Characterization Section

(301) 921-3625

A. J. Baroody, Jr.

D . L . Blackburn

F. H. Brewer

t

M. Cosman

Dr. J. R. Ehrstein

G

.

G . Harman

Dr. W. M. Bullis, Chief

Mrs. R. E. Joel+

H. K. Kessler

Mrs. K. 0. Leedy

Miss C. A. Main

R. L. Mattis

Dr. W. E. Phillips

Miss D. R. Ricks

H. A. Schafft

Mrs. T. A. Schultz+

A. W. Stallings

G. N. Stenbakken § W. R. Thurber

Semiconductor Processing Section

(301) 921-3541

Dr. A. H. Sher, Acting Chief x

B. H. Audet

H. A. Briscoe

W. K. Croll

Mrs. S. A. Davis"1"

H. E. Dyson*'

W. J. Keery

J. Krawczyk

T. F. Leedy

Y. M. Liu

Miss J. M. Morrison

L. M. Smith

G. P. Spurlock

Mrs. C. F. Bolton+

R. L. Gladhill

Miss B. S. Hope"1"

Electron Devices Section

(301) 921-3622

J. C. French, Chief

J . M . Kenney

F. F. Oettinger

M. K. Phillips

G. J. Rogers

S. Rubin

D. E. Sawyer

L. R. Williams

* Part Time

t On Leave

+ Secretary

§ On Temporary Detail to Mechanics Division

x Dr. J. A. Coleman is on temporary assignment to Office of Associate

Director for Programs.

43
Appendix B

COMMITTEE ACTIVITIES

ASTM Committee F-l on Electronics

A. J. Baroody, Lifetime Section

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, Resistivity, Epitaxial Resistivity, and Epitaxial

Thickness Sections

J. C. French, Committee Editor

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 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 Micorwave

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, Transactions 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

IEC TCM-7, Semiconductor Devices and Integrated Circuits:

S. Rubin, Technical Expert, Galvanomagnetic Devices; U. S. Specialist

for Working Group 5 on Hall Devices and Magnetoresistive 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 6 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. Carrier Lifetime Measurements (W. E. Phillips)

Carrier lifetime was measured in three silicon solar cell

blanks by the surface photovoltage method for NASA Lewis

Research Center.

2. Infrared Absorption Measurements (W. R. Thurber)

Thirteen silicon solar cell blanks were examined for oxygen

content by the infrared absorption method for NASA Lewis

Research Center to discriminate between Czochralski-grown

and float-zoned crystals.

3. Thin-Film Deposition (T. F. Leedy)

Reticles were fabricated for the Microwave and Mechanical

Instrumentation Section using vacuum evaporation of chromium

onto glass plates.

4. Radiation Detectors (B. H. Audet)

Four silicon nuclear radiation detectors were reprocessed

for the Photonuclear Physics Section.

5. Sectioning and Plating (H. A. Briscoe)

Transistors were sectioned, polished, and stained to reveal

cross-sectional geometries, small piece parts were gold or nickel plated, and silver films were vacuum evaporated on several types of plastics for other groups in the Electronic

Technology Division.

6. Thermographic Studies of Semiconductor Devices (F. F. Oettinger)

Thermal studies were performed on transistors and integrated

circuits using an infrared microradiometer for the Naval

Ammunition Depot, Crane, Indiana.

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,

Va. 22151.

Quarter Ending

September 30, 1968

December 31, 1968

March 31, 1969

June 30, 1969

September 30, 1969

December 31, 1969

March 31, 1970

June 30, 1970

September 30, 1970

December 31, 1970

Current Publications

NBS Tech. Note Date Issued NTIS Accessioi

472 December, 1968 AD 681330

475 February, 1969 AD 683808

488 July, 1969 AD 692232

495 September, 1969 AD 695820

520 March, 1970 AD 702833

527 May, 1970 AD 710906

555 September, 1970 AD 718534

560 November, 1970 AD 719976

571 April, 1971 AD 723671

592 August, 1971

Sher, A. H. , Carrier Trapping in Ge(Li) Detectors, IEEE Trans. Nual. Sei.

NS-18, No. 1, 175-183 (February, 1971).

Liu, Y. M. , and Coleman, J. A. , Electron Radiation Damage Effects in

Silicon Surface-Barrier Detectors, IEEE Trans. Nuel. Soi. NS-18 , No. 1,

192-199 (February, 1971).

Rubin, S., and Oettinger, F. F. , Thermal Hysteresis and its Possible

Effect on Restriction of the Hot-Spot Free Operating Range of Some Power

Transistors, IEEE Trans. Electron Devices ED-18 , 393-394 (June, 1971).

Thurber, W. R. , Determination of Deep Impurities in Silicon and Germanium

by Infrared Photoconductivity, NBS Tech. Note 570 (March, 1971).

Harman, G. G. , and Kessler, H. K. , Application of Capacitor Microphones

and Magnetic Pickups to the Tuning and Trouble Shooting of Microelectronic

Ultrasonic Bonding Equipment, NBS Tech. Note 573 (April, 1971).

47
APPENDIX D

Sher, A. H. , and Thurber, W. R. , Minority Carrier and Lithium-Ion Drift

Mobilities and Oxygen Concentration in p-Type Germanium, submitted to

J. Appl. Phys.

Sher, A. H. , Croll, W. K. , and Thurber, W. R. , Determination of Oxygen in

Germanium Below 20 ppb by Measurements of Lithium Mobility and Precipitation, submitted to Anal. Chem.

Blackburn, D. L. , Nondestructive Photovoltaic Resistivity Gradient Measurements of Circular Semiconductor Wafers, Recent News Paper, Electrochemical Society Meeting, Washington, D. C. (May, 1971).

48
FORM NBS-114A (1-71) 2. Gov t Accession No.

U.S. DEPT. OF COMM. BIBLIOGRAPHIC DATA

SHEET

1. PUBLICATION OR REPORT NO.

NBS-TN-598

3. Recipient's Accession No.

4. TITLE AND SUBTITLE

Methods of Measurement for Semiconductor Materials , Process

Control, and Devices. Quarterly Report, January 1 to March

31, 1971.

5. Publication Date October 1971

6. Performing Organization Code

7. AUTHOR(S) 8. Performing Organization W. Murray Bullis, Editor

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 NB g ^ DAgA (EA071-801) , Navy

SSPO, NAD (Crane) (PO-1-0030, P0- 1-0041. PO-1-0067) and NAFI

(WR- 1-1038), NESC (PO-1-1057), AFWL (F29601-71-F-0002)

and NASA (S-70003-G and H-76553A).

AEC.

13. Type of Report & Period Covered _ , Interxm

Jan. 1 to March 31, 1971

14. Sponsoring Agency Code

15. SIIPPI FMFNTARY NOTFS 4251120 ^ 4 251123, 4251126, 4252114, 4252119, 4252128, 4254111.

4254112, 4254115, 4259522, 4259533, 4254432, 4252534, 4252535, 4259425, 4254429,

4251449.

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, eleventh 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 application of tuning and other related procedures for ultrasonic wire bonders

in an industrial environment with a reported reduction of rejection rate at visual inspection by more than a factor of two, more complete evaluation of the photovoltaic

method for determining radial resistivity profiles of circular semiconductor wafers

,

and identification of test conditions' in which a d-c calibration curve may properly

be used in measurements of thermal resistance. Work is continuing on measurement of

resistivity, carrier lifetime, and electrical inhomogeneities in semiconductor crystals:

specification of germanium for gamma-ray detectors ; evaluation of wire bonds and die

attachment; measurement of thermal properties of semiconductor devices, transit-time

and related carrier transport properties in junction devices, and electrical properties

of microwave devices; and characterization of silicon nuclear radiation detectors.

Supplementary data concerning staff, standards committee activities, technical services,

and publications are included as appendixes

.

Key Words (cont.): microelectronics; microwave devices; nuclear radiation detectors;

probe techniques (a-c); resistivity; semiconductor devices; semiconductor materials;

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; methods of measurement;

18. AVAILABILITY STATEMENT

fx] UNLIMITED.

I I FOR OFFICIAL DISTRIBUTION. DO NOT RELEASE

TO NTIS.

19. SECURITY CLASS

(THIS REPORT)

UNCLASSIFIED

20. SECURITY CLASS

(THIS PAGE)

UNCLASSIFIED

21. NO. OF PAGES

54

22. Price

55 cents

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Monographs. Major contributions to the technical

literature on various subjects related to the Bureau's

scientific and technical activities.

National Standard Reference Data Series.

NSRDS provides quantitative data on the physical

and chemical properties of materials, compiled from

the world's literature and critically evaluated.

Product Standards. Provide requirements for sizes, types, quality, and methods for testing various industrial products. These standards are developed co- operatively with interested Government and industry

groups and provide the basis for common understanding of product characteristics for both buyers and

sellers. Their use is voluntary.

Technical Notes. This series consists of communications and reports (covering both other agency and

NBS-sponsored work) of limited or transitory interest.

Federal Information Processing Standards

Publications. This series is the official publication

within the Federal Government for information on

standards adopted and promulgated under the Public

Law 89—306, and Bureau of the Budget Circular A—86

entitled, Standardization of Data Elements and Codes

in Data Systems.

TECHNICAL NEWS BULLETIN

The best single source of information concerning the Bureau's research, developmental, cooperative, and

publication activities, this monthly publication is designed for the industry-oriented individual whose

daily work involves intimate contact with science and

technology

for engineers, chemists, physicists, re- search managers, product-development managers, and

company executives. Annual subscription: Domestic,

$3.00; $1.00 additional for foreign mailing.

Consumer Information Series. Practical information, based on NBS research and experience, covering

areas of interest to the consumer. Easily understandable language and illustrations provide useful background knowledge for shopping in today's technological marketplace.

NBS Special Publication 305, Supplement 1, Publications of the NBS, 1968-1969. When ordering, include Catalog No. C13.10:305. Price $4.50;

$1.25 additional for foreign mailing.

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National Bureau of Standards

Washington, D.C. 20234

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