Rational Bureau of Standards

Library, E-01 Admin. Bldg.

MAY 1 5 1970

NBS TECHNICAL NOTE 527

Methods of

Measurement for

Semiconductor

Materials, Process

Control, and Devices

Quarterly Report

October 1 to December 31, 1969
NATIONAL BUREAU OF STANDARDS

The National Bureau of Standards ' was established by an act of Congress March 3, 1901. Today,

in addition to serving as the Nation's central measurement laboratory, the Bureau is a principal

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standards, (3) technological measurements and standards, and (4) transfer of technology.

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UNITED STATES DEPARTMENT OF COMMERCE

Maurice H. Stans, Secretary

NATIONAL BUREAU OF STANDARDS • Lewis M. Branscomb, Director

NBS TECHNICAL NOTE 527

ISSUED MAY 1970

Nat. Bur. Stand. (U.S.), Tech. Note 527, 60 pages (May 1970)

CODEN: NBTNA

Methods of Measurement for Semiconductor

Materials, Process Control, and Devices

Quarterly Report

October 1 to December 31, 1969

Edited by W. Murray Bullis

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, 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. CI 3.46:527). Price 60 cents.

CONTENTS

PAGE

1. Introduction and Highlights 1

2. Methods of Measurement for Semiconductor Materials

2.1 Resistivity 6 2.2 Carrier Lifetime 9

2.3 Inhomogeneities 11

2.4 Infrared Methods 15

2.5 Hall Effect 16

2.6 Gold-Doped Silicon 16

2.7 Specification of Germanium 17

2.8 References 21

3. Methods of Measurement for Semiconductor Process Control

3.1 Metallization Evaluation 23

3.2 Processing Facility 28

3.3 Die Attachment Evaluation 31

3.4 Wire Bond Evaluation 31

3.5 References 46

4. Methods of Measurement for Semiconductor Devices

4.1 Thermal Properties of Devices ^8

4.2 Thermographic Measurements 51

4.3 Microwave Device Measurements 51

4.4 Silicon Nuclear Radiation Detectors 52

4.5 References 54

Appendix A. Joint Program Staff 55

Appendix B. Standards Committee Activities

Appendix C. Solid-State Technology and Fabrication Services .

Appendix D. Joint Program Publications

56

57

58

in
LIST OF FIGURES

PAGE

1. Resistivity profiles along a diameter of an rt-type germanium, thin, circular

wafer obtained by the four-probe and photovoltaic methods 1"+

2. Resistivity profiles along a diameter of a p-type germanium, thin, circular

wafer obtained by the two-probe, four-probe, and photovoltaic methods 14

3. Nomograph relating the time t, temperature T, applied bias V, and drifted

depth W 18

4. Gamma-ray peak shapes for 137Cs 18

5. Scratch test apparatus 24

6. Test data for the determination of threshold adhesion failure obtained from a set of typical scratch test measurements 26

7. SEM photomicrophotographs of stylus tips 27

8. The sequence of producing a mask set 30

9. A section of the diode array produced by the mask set 30

10. Mechanical resonance curves taken on the same transducer driven by three

different ultrasonic power supplies 32

11. Vibration amplitude of an ultrasonic bonding tool 32

12. Modification of transducer horn to reduce the mechanical Q 34

13. Response of the bonding tool vibration amplitude to frequency modulation of

the power supply oscillator 36

14. Wire marks in the coating of a spool left by 0.00 1-in. diameter .. aluminum bonding wire 38

15. Pull strength in grams as a function of bonder power setting for oxidized

substrate, aluminum sintered at 550°C 38

16. SEM photomicrographs (575 X) of aluminum ultrasonic wire bonds showing heel

crack and clamp marks 40

17. SEM photomicrographs (460 X) of bond adhesion (lift-off) patterns for first

bonds made at different time settings and constant power setting 42

18. SEM photomicrograph (800 X) of bond adhesion (lift-off) pattern for a strong

first bond 44

19. SEM photomicrographs (600 X) of bond adhesion (lift-off) patterns for two second

bonds made consecutively at identical time and power settings 44

20. Block diagram of apparatus used to generate and plot curves of the temperature

difference between the device junction and the case as a function of collectoremitter voltage with the collector current held constant 49

LIST OF TABLES

1. Doping mixture flow rates 30
METHODS OF MEASUREMENT FOR

SEMICONDUCTOR MATERIALS, PROCESS CONTROL, AND DEVICES

Quarterly Report

October 1 to December 31, 1969

ABSTRACT

This quarterly progress report, sixth of a series,

describes NBS activities directed toward the development

of methods of measurement for semiconductor materials,

process control, and devices. Principal emphasis is

placed on measurement of resistivity, carrier lifetime,

and electrical inhomogeneities in semiconductor crystals;

evaluation of wire bonds, metallization adhesion, and die

attachment; and measurement of thermal properties of semiconductor devices and electrical properties of microwave

devices. Work on related projects on silicon nuclear

radiation detectors and specification of germanium for

gamma-ray detectors is also described. Supplementary

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

Key Words: Alpha detectors; aluminum wire; carrier lifetime; die attachment; electrical properties; epitaxial

silicon; gamma detectors; germanium; gold-doped silicon;

metallization; methods of measurement; microelectronics;

microwave devices; nuclear radiation detectors; resistivity;

semiconductor devices; semiconductor materials; semiconductor process control; silicon thermal resistance; thermographic measurements; ultrasonic bonder; wire bonds.

1. INTRODUCTION AND HIGHLIGHTS

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

Program on Methods of Measurement for Semiconductor Materials, Process

Control, and Devices. The report is subdivided according to tasks which

have been identified as parts of the Program. Section 2 deals with

methods of measurement for materials; section 3, with methods of measurement for process control; and section 4, with methods of measurement for

devices. Contrary to previous practice, references for a particular

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

Resistivity — Two new round-robin experiments involving the fourprobe method for measuring resistivity are being coordinated at the re- quest of ASTM Committee F-l. In the study of the dependence of four-probe
INTRODUCTION AND HIGHLIGHTS resistivity on current, probe force, and surface finish it was necessary

to repeat some of the measurements on specimens with lapped surfaces before beginning work on specimens with polished surfaces. New equipment

was designed and built for both the spreading resistance and capacitancevoltage methods in order to permit more detailed study of these methods.

Carrier Lifetime — Emphasis in the carrier lifetime task was placed

on the study of methods for measuring carrier lifetime in epitaxial

layers. Work is underway on both the metal-oxide-semiconductor capacitance and surface photovoltage methods for this measurement. Emphasis

on measurement of carrier lifetime in diode structures has been shifted

back to the study of the abrupt p-n junction in order to resolve the

discrepancy between minority carrier lifetime values as measured by the

voltage decay and reverse recovery techniques.

Irihomogeneities — The analysis of the photovoltaic method for measuring radial resistivity gradients in germanium and silicon circular

wafers has been extended to include measurements made with knife-edge

pressure contacts. Use of these contacts makes the application of the

method to production monitoring much more attractive. Preliminary re- sults suggest that the use of these contacts will be possible despite

the fact that some difficulty has been encountered in measuring the

photoconductivity near the contacts. A further advantage of this technique is that it permits the van der Pauw technique to be used to determine the average resistivity of the wafer, and the expression relating

the resistivity gradient to the photovoltage has been modified to take

this into account. The interest of the industry in the application of

this method is being sought.

Other Measurement Methods for Materials — Work on the development of

infrared methods is drawing to a close. A summary report has been prepared to describe the work on oxygen determination by infrared absorption,

An informal report on the use of low temperature photoconductivity for

identifying and determining the concentration of deep-lying impurities

in silicon and germanium is being prepared.

During this quarter no work was carried out on either the high field

effects task or the deep- level studies task. Work on the former has been

suspended indefinitely in order that the staff originally assigned part

time to it may devote all their efforts to the wire bond evaluation task.

Work on the latter will be completed before the end of this fiscal year.

Metallization Evaluation — Studies of the scratch test for determining adhesion strength of aluminum films has led to the development of

a new concept, threshold adhesion failure, as a criterion for evaluating

the result of the test. This concept involves the identification of the

load at which any removal of the film can be detected rather than com- plete removal as required by the previous critical load criterion. The
INTRODUCTION AND HIGHLIGHTS

importance of the nature of the stylus tip to this test has led to detailed study of the topography of the tip both by shadowgraph techniques

and with the scanning electron microscope.

Wire Bond Evaluation — Further progress was made in the characterization of the ultrasonic bonding system by means of the capacitor microphone technique. Mechanical resonance curves were measured on the same transducer-tool combination, driven successively by three different

commercial ultrasonic power supplies . As predicted from earlier measurements made with special laboratory amplifiers, the mechanical Q was

lowest in the case of constant current drive and highest in the case of

constant voltage drive. Further experiments demonstrated that the me- chanical Q of a system driven by a constant-power source can be reduced

by drilling an array of holes in the transducer horn. A low-Q system

is desirable because the detuning effects of thermal environmental

changes and instabilities in the oscillator are reduced.

Another way of minimizing the effect of resonant frequency shifts

is with the use of swept-frequency operation. Detailed studies of such

operation were made for a constant-power source swept by various modulation voltage wave forms

These studies of bonder characteristics are an essential feature of

the development of a process which will yield the reproducible bonds

necessary for evaluation of the pull and other tests for bond strength.

They also yield information of immediate value to suppliers and to users

of the equipment, such as those producing devices for one of the sponsors of the Joint Program. During this quarter, considerable effort was directed toward identification of problems encountered on operational

lines

Extensive use was made of the scanning electron microscope for

studying bonds made both on commercial lines and in-house. Detailed

studies were made on the bonding pattern by observing the bonding pad

after the bond had been peeled off.

Preparation of both the bibliography and critical review survey

paper on wire bond evaluation is continuing.

Other Measurement Methods for Process Control — Work is continuing

on development of the processing facility and in the study of die attachment evaluation. Additional assistance was given ASTM Committee F-l in

the development of standard procedures for leak testing. The correlation

of NASA test methods , ASTM test methods , and the requirements of NASA

line certification was initiated. This work has taken on broader significance since the NASA line certification requirements are cited in the

General Specification for Microcircuits , MIL-M-38510. Their use is man- datory for class A microcircuits.
INTRODUCTION AND HIGHLIGHTS Measurement Methods for Devices — Further measurements of d-c

current gain as a function of collector-emitter voltage were made on a variety of transistor structures in the investigation of the applicability

of this measurement as a screen for devices susceptible to hot-spot formation. The apparatus for measuring thermal resistance by the emitterbase voltage technique as a function of collector-emitter voltage has

been partially automated.

In the area of second breakdown measurement, continuing assistance

is being given to JEDEC Committee JS-6 on Power Transistors in regard to

definitions of second breakdown and the writing of "Users Guide to Power

Transistors."

Work on microwave device measurements was expanded significantly

with the addition of a full-time senior staff member on this task. Assembly of experimental equipment for measurement of mixer diode noise

parameters at X band was begun.

Symposia — Arrangements for the Symposium on Silicon Device Processing to be held in June, 1970, under the joint sponsorship of ASTM

Committee F-l and the National Bureau of Standards are continuing as planned. Final selection of the papers to be presented in the various

sessions is to be made early in 1970. At the request of one of the

sponsors , organization of a limited-attendance information exchange on problems associated with ultrasonic wire bonds is being considered.

History and Sponsorship — The Joint Program was undertaken last year

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

reliability of discrete semiconductor devices and integrated circuits

through improvements in methods of measurement for use in specifying

materials and devices and in control of device fabrication processes.

These improvements are intended to lead to a set of measurement methods

which have been carefully evaluated for technical adequacy, which are acceptable to both users and suppliers, and which can provide a common basis for the purchase specifications of government agencies. 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 National Aeronautics and Space Administration, 4

* the Defense Atomic Support Agency, x and the U. S. Navy Strategic Systems Project Office. § Because of the cooperative nature of the Program, there is

+ Through Research and Technical Services Projects 4251120, 4251123,

4251126, 4252128, 4254111, 4254112, and 4254115.

* Through Order ER-22448, Electronics Research Center. (NBS Project

4251523)

x Through Project Order 808-70. (NBS Project 4259522)

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

Project Orders PO-0-0036 and PO-0-0055. (NBS Project 4259533)
INTRODUCTION AND HIGHLIGHTS not a one-to-one correspondence between the tasks described in this re- port 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 taken into consideration in planning.

Additional background information on the Program and individual

tasks may be found in earlier reports in this series (see Appendix D).

Besides the tasks sponsored under the Joint Program, this report contains

descriptions of activity on related projects supported by NBS or other

agencies. Although the specific objectives of these projects are different from those of the Joint Program, much of the activity undertaken in

these projects will be of interest to Joint Program sponsors. The sponsor of each of these related projects is identified in the description

of the project.
2. METHODS OF MEASUREMENT FOR SEMICONDUCTOR MATERIALS

2.1 RESISTIVITY

Objective: To develop improved methods, suitable for use throughout

the electronics industry, for measuring resistivity of bulk, epitaxial,

and diffused silicon wafers.

Progress : Work has continued on programs to improve understanding

and control of the factors which limit the precision and accuracy of the

four-probe resistivity measurement technique and to extend its range of

applicability to specimens with higher resistivity, polished surfaces, or thin layers. Two alternative techniques, spreading resistance and

capacitance-voltage, which are particularly useful for measuring resistivity and resistivity profiles on thin-layer structures are being

studied to determine the parameters which limit their effectiveness and

intercomparability.

Four-Probe Method — Two round-robin experiments are being coordinated in conjunction with ASTM Committee F-l. The first is to establish

the precision which can be expected from the four-probe method [1] when

it is used to measure silicon wafers with room temperature resistivity

up to 10,000 fi-cm. Detailed resistivity profiles were taken of the material available for this round robin, both to select the most uniform

slices for consideration and to have more detailed information with which

to correlate any anomalies which may occur in the round robin results.

Measurements made indicated that enough satisfactory wafers were available, and selected wafers were mailed to the first participant. In

addition, single laboratory precision figures were obtained at the slice

centers for the slices considered. The relative sample standard deviation was ±1.5 percent or less of the average value for each slice measured. During the course of these measurements it was found that electrical guarding of the potential-measurement leads resulted in considerable reduction of background noise and, hence, improvement in short-term

stability [2].

In the other round robin, the four-probe method is used to measure

the resistivity of silicon epitaxial layers deposited on substrates of

the opposite conductivity type. Material to be included in this round

robin has been measured according to a draft procedure derived from the

standard method for making four-probe resistivity measurements on wafers

[1]. Three of the epitaxial slices, although showing no severe measurement difficulty, did have enough surface damage that they could not be

used for the round robin.

The study of the dependence of four-probe resistivity measurement on current, probe force, and surface finish has continued. Because of inconsistencies in the data collected to date, the silicon wafers under
RESISTIVITY

study, which cover each decade in the resistivity range 0.001 to 100 Q-cm , were remeasured. The surfaces were freshly lapped with 5-um alumina and

thoroughly washed prior to remeasurement . Measurements with probe loading of 150 g,have been completed for a two-decade current range about

the recommended value [l] for these wafers. The wafers in general show

a nearly flat current dependence; all but two wafers show less than a 1-percent change in resistivity between the lowest and highest currents

used. A slightly higher resistivity value at the lowest current is a general feature. This study is being continued with determination of

the current dependence of the resistivity of these wafers at lower probe

loadings on the same 5-um lapped surfaces.

(F. H. Brewer, J. R. Ehrstein, and D. R. Ricks)

Spreading Resistance Methods — This technique is widely used for

depth profiling of both diffused and epitaxial structures and can also

be used for radial profiling of both wafers and thin layers because of

its applicability to regions of either conductivity type over a seven- decade range of doping densities. Lack of correlation of results among

several variants of the technique appears to be due to lack of a full

understanding of the degree of control required for the experimental

variables. This was evidenced by the results of a preliminary round

robin which was undertaken by ASTM Committee F-l.

As part of a study of the effect of various parameters on this meas- urement a new probe holder was designed and built. The design of this

holder allows control of the probe position on the wafer surface, re- peatability of probe loading to within better than 0.25 g in the total

load range from 10 to 50 g, and regulation of the probe impact velocity

to values as low as 0.1 mm/s. These features allow the attainment of

reproducible contact between the probe and the wafer. Further efforts

were made to reduce the electrical noise in the measurement circuit. At

present, measurements can be made with 10-uV sensitivity for silicon in

all resistivity ranges and with somewhat improved sensitivity for silicon

with resistivity less than 1 Q-cm. (J. R. Ehrstein)

Capaoitanoe-Voltage Method — This method utilizes the measurement of

capacitance as a function of bias voltage applied to a junction in a semiconductor wafer or epitaxial layer to yield a measure of the doping

density as a function of depth into the wafer. It has a primary position

among impurity density and hence resistivity measurements, in that it is

the only technique applicable to thin layers on conducting substrates

which does not rely on a transfer calibration from some other measurement.

With the aid of a digital computer, the data are fitted to a theory based

on an approximate model for the junction to obtain values of carrier

density versus diode depletion depth. Although the method is relatively

more time consuming than either the spreading resistance and four-probe

methods and has definite limitations with regard to the range of layer

thickness which can be probed, it is of great importance as a reference
RESISTIVITY method with which to compare the results of other resistivity measurements on thin layers. This method is being studied to gain a better un- derstanding of the conditions which affect its precision and limitations

both to make it useful as a technique with which to compare the results

of four-probe and spreading resistance measurements, also under study,

and to provide measurement capability useful to other in-house programs.

A semiautomated data taking system has been assembled to expedite

the measurement of capacitance as a function of bias voltage on these

diodes. Interface circuitry was designed and built so the outputs of

direct-reading capacitance and voltage meters can be recorded by an operational data acquisition system which consists of a scanner, digital

voltmeter, and card-punch. At present bias voltages must be selected

manually. However a fully automatic sequencing system for this bias

voltage has been designed and is being built. The investigation of planar

diodes with this technique has been slowed by difficulties in diode fabrication which have now been resolved. (G. N. Stenbakken)

Plans ; The investigation of the current and probe-force dependence

of resistivity as measured by the four-probe method on lapped wafer

surfaces will be completed and studies of wafers with mechanically and

chemically polished surfaces will begin.

Three new specimens for the four-probe epitaxial silicon resistivity

round robin will be obtained, and the set will be sent to the first participant. Data will be reduced and tabulated as received from participants in this and the four-probe high resistivity silicon wafer round

robin.

In the next phase of the spreading resistance investigation, the

measurement will be studied at various values of current and probe force.

To minimize the number of variables to be controlled, measurements will

be made with a single spreading resistance contact on wafers with a large area back contact. Initial measurements will be on silicon wafers in the

resistivity range 0.1 to 10 JJ-cm. Wafers with both lapped and mechanically polished surfaces will be studied. Osmium and tungsten carbide

will be used as probe tips.

Capacitance-voltage measurements will be made on both planar and

mesa diodes fabricated on bulk silicon wafers. These measurements will

be used to identify and study the important factors which affect the precision and accuracy of this method.
2.2 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 alternate methods for measuring

minority carrier lifetime in germanium and silicon which are more precise,

more convenient, or more meaningful in the specification of material for

device purposes.

Progress : Effort on the carrier lifetime task has continued in the

four areas established last quarter (NBS Tech. Note 520, pp. 13-16).

In the area of bulk crystal measurements, the study designed to establish

the single-laboratory precision to be expected from the revised photoconductive decay (PCD) method has been initiated, and additional surface

photovoltage (SPV) measurements have been made on the specimens in the

intercomparison study. Study of both the metal-oxide-semiconductor (MOS)

capacitance and SPV methods for measurement of carrier lifetime in epitaxial layers is continuing. Emphasis in the diode area has been shifted

back to the study of the abrupt p-n junction diode in order to resolve

the discrepency between minority carrier lifetime values as measured by

the voltage decay and reverse recovery techniques. The study of methods

for measuring minority carrier lifetimes in transistor structure, still

in its preliminary stages, did not progress significantly.

Bulk Crystals — The experiment to establish a multi-operator, singlelaboratory precision for the revised procedure for carrier lifetime measurement by the PCD method was begun. The first operator has completed

measurements on five specimens. It has become evident that, in addition

to its primary purpose, this experiment will also yield suggestions from

the various operators that will assist in improving the form of the re- vised procedure. (R. L. Mattis and F. R. Kelly)

Carrier lifetime was measured by the SPV method on six silicon and

two germanium specimens which had been previously measured by the PCD

method. In several cases there was substantial disagreement between the

SPV and PCD values. It is not yet clear whether these differences are real or if they result from problems with the SPV measurement. The SPV

measurement is being repeated on some specimens on which the surface re- combination velocity has been reduced in an effort to resolve the question. (H. A. Gitelson and W. E. Phillips)

Epitaxial Layers — The review of the published literature on MOS

capacitance measurements was completed. Several ways were found to deduce the minority carrier lifetime from the transient change in MOS

capacitance which follows a change in the applied voltage. Jund and

Poirier [1] derive the lifetime in epitaxial layers from the transient

increase in capacitance following the application of a voltage step with

the assumption that this transient is exponential. Heiman [2] is able

to deduce the lifetime from a non- exponential capacitance change. Zerbst

[3] obtains a straight line when he plots the time derivative of the
CARRIER LIFETIME square of the reciprocal capacitance against the reciprocal capacitance.

The slope of this line is proportional to the lifetime and the intercept

on the ordinate is proportional to the surface recombination velocity.

Tomanek [4] describes a method in which an MOS capacitor is biased into

inversion after which pulses of opposite polarity and variable duration

are applied. The values of capacitance measured just as the pulse is

terminated for various duration times are used to determine the carrier

lifetime.

To proceed further it is necessary to demonstrate the equivalence of

these various approaches either theoretically, experimentally, or both or

to confirm the validity of one or more nonequivalent approaches. Before

starting this relatively complex study, a survey to determine the extent

of use of MOS capacitance measurements of lifetime in the industry has

been initiated. (R. L. Mattis)

The theoretical analysis of the SPV response when the condition that

the diffusion length be less than the thickness of the specimen is violated indicated that a plot of photon intensity against penetration

depth, or reciprocal absorption coefficient, should yield a straight line

for penetration depths greater than the surface depletion depth. This

finding is in accord with experimental results reported last quarter.

However, the intercept of this line extrapolated to zero photon intensity

was found to be dependent on the thickness of the specimen as well as the

diffusion length. This result may be also applied to interpret SPV measurements in thin epitaxial layers since the SPV response in such layers

can be treated in the same manner as a thin specimen with very large

surface recombination velocity on the back surface. Further analysis is

underway to determine whether or not the value of diffusion length can

be extracted from SPV measurements on relatively thin layers of known

thickness. (W. E. Phillips)

Diodes — Emphasis in this area has been shifted back to the study of

the abrupt p-n junction diode with the aim of resolving the discrepancy

between the values of minority carrier lifetime measured by means of the

voltage decay and reverse recovery techniques. Theoretical study re- vealed no basis for this difference. Examination of the experimental

conditions used in previous measurements has shown that these measurements

were made at substantially different current levels. Both the voltage

decay and reverse recovery circuits are being modified so that these

measurements can be repeated at the same current levels.

An experiment to determine the reproducibility to be expected from

the reverse recovery measurement on a single-operator basis has been

conducted over a six-month period. The reverse recovery time of seven

commercial diodes was measured at intervals throughout the course of the

experiment. Equal forward and reverse currents of 4 mA were employed.

The diodes were driven by a square wave generator at a frequency of 1 kHz.

10
CARRIER LIFETIME.

The effective lifetime was calculated as 4.4 times the measured recoverytime (the time between the current zero and the beginning of current decay, see NBS Tech. Note 475, pp. 6-7). Standard deviations ranging from

4 to 13 percent were observed. (A. J. Baroody)

Transistors — Study of literature on methods for measuring minority

carrier lifetime in transistor structures was deferred pending completion

of the analysis of SPV response. (W. E. Phillips)

Plans : Work on the PCD method will continue with emphasis on the

establishment of the s ingle- laboratory , multi-operator precision. A

number of SPV measurements will be repeated as part of the intercomparison study between the SPV and PCD methods.

Guided by the extent of industry usage, a decision will be made con- cerning the continuation of the study of the MOS capacitance technique

for measuring minority carrier lifetime. If the study is continued, the

various approaches referenced above will be examined both theoretically

and experimentally to determine the extent of their equivalance. Analysis

of the SPV method will continue in order to determine the suitability for

measurement of minority carrier lifetime in thin epitaxial layers.

After modifications to the voltage decay and reverse recovery circuits are completed, experimental work will resume on the study of the

dependence of carrier lifetime on current level and frequency. The limits

of applicability of the two techniques will be studied on commercial

diodes which have been characterized by the capacitance-voltage technique

to insure that they have abrupt junctions.

Review and study of methods for measuring carrier lifetime in transistor structures will resume.

2.3 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 sili- con circular wafers.

Progress: The evaluation of the relationship between photovoltage

and radial resistivity gradients in germanium and silicon circular wafers

was extended to include photovoltaic measurements made with knife-edge

contacts rather than the specially prepared, semicircular, soldered con- tacts which have been used previously. A new specimen holder was designed and constructed to allow four knife-edge contacts to be made at

11
INHOMOGENEITIES the ends of two orthogonal diameters of the specimen. In addition to

permitting inhomogeneity measurements to be made along perpendicular

diameters, this configuration also allows the measurement of the average

resistivity of the specimen by the van der Pauw method [1, 2],

Use of the knife-edge contacts makes the application of the method

to production monitoring much more attractive. Preliminary results indicate that it is possible to make the photovoltaic measurement, but some difficulty has been encountered in measuring the photoinduced change in

resistance which must also be determined in order to evaluate the degree

of inhomogeneity. With the knife-edge contacts, the measured value of

the photoinduced change in resistance depends somewhat on the polarity

of the current through the specimen; this dependence increases as the

light probe approaches a contact. The difficulty is particularly pronounced in silicon wafers.

The derivation of the equation relating the photovoltage to the

resistivity gradient along the diameter of the circular wafer was re- examined because it appeared that discrepancies between the resistivity

profile obtained from photovoltaic and four-probe measurements were too

large to be accounted for by the errors present in the methods.^ It was found that a factor of 2 had been omitted in the previous derivation

so that the resistivity gradient is actually twice as large as heretofore

thought. At the same time the relation was modified to permit use of

average resistivity as determined by the van der Pauw technique instead

of the specimen resistance measured between contacts of known dimensions

at the ends of the measurement diameter. The corrected and modified

expression for the resistivity gradient, dp/dx, is as follows:

2 x £

dx 2tt l-(y/r) 2 rt AR

dp 3 B p

z V —— = X X - X —

where:

B=^_(ltb),

q = charge of the majority carrier (C),

k = Boltzmann's constant (J/K),

T = absolute temperature (K),

b = ratio of the mobility of the majority carrier to the mobility

of the minority carrier,

y = distance of light spot from specimen center (cm),

r = specimen radius (cm),

This work was carried out with the assistance of Dr. L. J. Swartzendruber of the NBS Alloy Physics Section.

12
INHOMOGENEITIES

t = specimen thickness (cm),

p = average resistivity of the specimen (ft-cm),

V = photovoltage (V), and

AR = photoinduced change in resistance of the wafer (ft).

Use of the corrected equation has, in all cases, improved the agreement between the resistivity profiles determined from photovoltaic and

four-probe measurements. Examples of the degree of agreement which can now be achieved are shown in Figs. 1 and 2. Significant differences

still appear near the edge of the wafer, particularly in specimens such

as the p-type germanium wafer shown in Fig. 2. Some of the differences

in shape between the four-probe profile and the other two profiles of

Fig. 2 arise because the spatial resolution of the four-probe method is

limited by a characteristic distance somewhat larger than the 1.6-mm

probe spacing used for both the two- and four-probe measurements . The

resolution of the photovoltaic method is limited by the light probe diameter and the minority carrier diffusion length. For the above specimens,

the volume sampled is approximately equal to that sampled by the twoprobe method. Probe measurements were made every 1.25 mm. Photovoltage

and photoconductivity data were averaged over 0.625-mm intervals and

summed to obtain the resistivity as a function of position.

Expressions of interest in use of the photovoltaic method to determine radial resistivity variations were sought from a number of silicon

and germanium suppliers through telephone contacts. Each contacted ex- pressed positive interest particularly in the possible use of the method

for measuring higher resistivity material intended for non-epitaxial,

high-voltage devices and low-resistivity material intended for voltagereference diodes. The potential of the method for making precise, con- tinuous, contactless measurement of the resistivity gradient elicited

particular attention. At present, radial resistivity gradients are meas- ured almost exclusively by the four-probe method. To varying degrees the

problems of each supplier with this method center around the lack of

sufficient precision and the specimen damage which results from contacting

the regions being measured.

Two additional applications arose as a result of the measurement

needs expressed by the suppliers contacted. It was suggested that the

contactless feature of the method could be exploited in the characterization and identification of polished specimens without the risk of degrading the surface. Currently this presents a serious measurement problem not only to the vendor but also to the user who wishes to determine

that specimens conform to his specifications. Two suppliers were particularly interested in the possibility of using the method to measure

longitudinal resistivity variations in as-grown semiconductor crystals.

This is made difficult by the necessity for the light probe to generate

electron-hole pairs uniformly throughout a narrow slice of the crystal;

penetration depths from 2 to 8 cm are required.

(D. L. Blackburn and H. A. Schafft)

13
RESISTIVITY

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FOUR POINT PROBE • PHOTOVOLTAIC

2 2 DISTANCE (mm)

10

Fig. 1 Resistivity profiles along a diameter of an n-type germanium, thin, circular wafer obtained by

the four-probe and photovoltaic methods. The diameter of the specimen was 22.4 mnu

7.6

7.4 -

1 T

7.2

7.0

«•«

<36.6 >-^6.4

8"

'6.0

5.8

5.6

5.4 2 2 4 DISTANCE (m)

Fig. 2 Resistivity profiles along a diameter of a p-type germanium, thin, circular wafer obtained by

the two-probe, four-probe, and photovoltaic methods. The two-probe resistivity profile was

obtained on <* narrow, bar-shaped specimen cut from the wafer as shown in the inset. The diameter of the circular wafer was 22.9 mm. 14
INHOMOGENEITIES

Plans ; The relationship between photovoltage and radial resistivity

gradient will be evaluated experimentally by determining how well resistivity profiles generated by this relationship, using data obtained both

with special, relatively large area, contacts and with knife-edge con- tacts , compare both in shape and magnitude with profiles obtained with

the two-probe method. Several specimens will be examined which exhibit

the different but typical resistivity profile shapes that have been en- countered. These specimens have already been chosen on the basis of the

profiles obtained with four-probe measurements. Photovoltaic measurements

will be made on at least one polished specimen to determine the feasibility of applying this method to such specimens.

Inquiry into the interest of semiconductor suppliers and users in

the application of this method will continue.

2.4 INFRARED METHODS

Objective : To evaluate impurity photoconductivity as a method for

detecting low concentrations of deep-lying impurities such as copper,

gold, iron, and nickel in silicon and germanium, and to assist ASTM

Committee F-l in extending the applicability of infrared absorption as a method for detecting impurities such as oxygen and carbon in silicon and

germanium.

Progress ; A draft of the summary report [1] describing work com- pleted on the determination of oxygen in silicon and germanium by infrared absorption methods has been written. An important part of this report

is a comparison of the oxygen concentration deduced from absorption meas- urements made by various techniques on silicon specimens. In addition,

results of measurements on both silicon and germanium at room temperature,

80 K, and 20 K are compared.

Assistance to ASTM Committee F-l on the work on infrared absorption

measurement methods was completed with a detailed review of the draft

documents [2] submitted for committee letter ballot after the September

meeting. Additional measurements at low temperatures have been made in

conjunction with round-robin tests which are still being conducted by the

committee.

Work continued on an informal report on the use of low-temperature

photoconductivity (LTPC) for identifying deep-lying impurities and determining their concentration in silicon and germanium. The facility for

making LTPC measurements has been modified so that infrared response (IRR)

measurements on lithium-drifted germanium diodes (see Section 2.7) can also be made. (W. R. Thurber)

15
INFRARED METHODS Plans : Work on oxygen determination by infrared absorption will be

concluded with the publication of the summary report.

LTPC and IRR measurements will be made in connection with the task

on Specification of Germanium and will be reported there. On completion

of the informal report on LTPC measurements, the task on Infrared Methods

will be terminated.

2.5 HALL EFFECT

Objective : To establish a facility for making measurements of Hall

coefficient as a function of temperature between 4 and 350 K and to

improve methods for collecting and interpreting Hall effect data.

Progress : Tests were made on the modified Hall effect apparatus

which enables measurements to be made on high-resistivity specimens with

the automatic data acquisition system. Preliminary observations indicated that the objectives of impedance matching and reduction of measurement time were realized. Minor changes were made to eliminate the effect

of electrical leakage in the scanner circuit of the data acquisition

system. (W. R. Thurber)

Work on the report concerning Hall effect measurements and their

interpretation was deferred.

Plans : Detailed tests will be made with high-resistance resistors

to determine how accurately specimens with resistance greater than 1 Mft can be measured. Time constants associated with such measurements will

also be determined.

Work will resume on the report concerning Hall effect measurements

and their interpretation.

2.6 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 sili- con which is suitable for use in predicting its characteristics.

Progress : Initial electrical measurements were completed on 10 ft-cm

boron-doped silicon wafers which had been diffused with gold at temperatures of 850, 950, 1050, 1150, and 1250°C. It was found that the room

temperature resistivity increased monotonically as the gold concentration,

determined by neutron activation analysis, increased. This is contrary

16
GOLD-DOPED SILICON

to previous experimental observations but is in accord with theoretical

calculations completed in the last quarter (NBS Tech. Note 520, p. 23).

This suggests that the previously observed maximum in resistivity with

increasing gold concentration may be an experimental artifact.

The gold concentration measured by neutron activation analysis

techniques was in general lower than the solid solubility limit at the

temperature of diffusion. To establish that this did not arise because

of too short a diffusion time, two sets of 10 fi-cm boron-doped silicon

wafers were diffused with gold for various times. Times ranging from

30 min to 810 min were used for diffusion at 850°C while times from 15

min to 120 min were used at 1250°C. A section was cut from each wafer

and lapped so that the gold concentration in the interior of the wafer

can be determined by neutron activation analysis.

Slices from 0.1 and 1.0 ft-cm n- and p-type silicon crystals have

been cut in anticipation of additional gold diffusions. Further diffusions have been defered, however, until the discrepancy noted above is

resolved. (W. M. Bullis and W. R. Thurber)

Plans: Gold diffusions and electrical measurements on the 1.0 and

0.1 ft-cm wafers will be made after the discrepancy in gold concentration

has been resolved.

2.7 SPECIFICATION OF GERMANIUM1

"

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 : Construction of the series of six nomographs relating to

Ge(Li) detector technology has been completed, and the characterization

of p-type, germanium single-crystals by observation of etch-pit distributions has begun. Gamma-ray pulse-height spectra have been obtained as a function of Ge(Li) detector bias in order to study empirically the change

in peak shape with increased trapping of charge carriers. Various theoretical models which seek to predict peak shapes on the basis of trapping

parameters were evaluated against experimental data.

Supported by the Division of Biology and Medicine, U. S. Atomic

Energy Commission. (NBS Project 4259425)

17
SPECIFICATION OF GERMANIUM

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SPECIFICATION OF GERMANIUM Nomographs for Ge(Li) Detector Technology — Preparation of the series

of nomographs relating to the fabrication and testing of Ge(Li) detectors

has been completed with the development of a nomograph relating the area,

drifted depth, and capacitance for right-circular cylindrical, doubleopen-ended, true coaxial Ge(Li) detectors. The nomograph for determining

the drifted depth as a function of time, temperature, and applied bias

during drift has been revised by combining the two charts previously

required into a single alignment chart with five parallel scales as shown

in Fig. 3. The relationship between oxygen concentration, acceptor impurity concentration, and lithium-ion drift mobility and the range of

interest of these parameters makes it difficult to construct a single

alignment chart such that the resulting scale calibrations are usuable

over the range of interest. Therefore, the figure relating the above

parameters will be retained in its present concurrency nomograph form

(NBS Tech. Note 488, p. 17). Work has begun on text material containing

directions for use, comments, and examples to accompany the series of

six nomographs.

The equation used in constructing the nomograph relating the

capacitance C (pF), junction area A (cm2 ), and drifted depth W (cm) for

planar Ge(Li) detectors was C = 1.41 (A/W). For true coaxial Ge(Li)

detectors, the capacitance C (pF) is related to the detector length L

(cm) and ratio of outer and inner radii R2/R1 (such that R2 - Ri is the

drifted depth) by C = 1.41 (2ttL) [ln(R2 /Ri )]

-1

. The prefactor 1.41 pF/cm

is the product of £q> the electrical permittivity of vacuum, and k , the

dielectric constant of germanium. Previously published values of the

prefactor eqk erroneously give a value of 1.44 pF/cm [l, 2],

(A. H. Sher)

Characterization of Germanium — Approximately two-thirds of the

crystals which had been assembled for characterization have been etched

[3] to develop etch-pit patterns on the (ill) faces. The crystals ha\e

been sorted with respect to the type of pattern found, such' as star,

ring, or propellor, for comparison with the results of infrared response

(IRR) measurements on Ge(Li) structures [4]. Further testing of the lownoise preamplifier constructed for use with the IRR measurements was suspended when it was found that a commercial low-noise detector preamplifier was suitable for use in the measurement system.

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

Work has resumed on the paper comparing the measurement of oxygen

concentration in germanium by the methods of lithium mobility, lithium

precipitation, and infrared absorption. This paper includes a discussion

of the range of applicability of each method as well as correlations

between them. (A. H. Sher, W. K. Croll, ,and W. R. Thurber)

Ge(Li) Detector Measurements — Within the framework of the study of

gamma-ray peak shapes obtained from pulse-height spectra using Ge(Li)

19
SPECIFICATION OF GERMANIUM detectors, several theoretical models from which peak shapes can be predicted on the basis of carrier trapping parameters have been evaluated

against experimental data. Figure 4a shows the change in peak shape

of the 137Cs, 662-keV gamma-ray spectrum as a function of applied bias

for Ge(Li) detector 213.

Figure 4b shows peaks calculated from the model proposed by Trammel

and Walter [5] for a gamma-ray of 662-keV energy, a detector of 8.5 mm

drifted depth, and a fixed hole trapping length, Xp

, of 200 cm. The

electron trapping length, A n

, was varied from 90 to 5 cm to simulate

increased electron trapping in the detector as the applied bias is re- duced, but there is no direct correspondence between the variation in

applied bias in the experimental case of Fig. 4a and the variation in

A in Fig. 4b. However, it is interesting to note that the model does

predict a small shift downward in energy with increased carrier trapping

as observed in the experimental case. The tailing observed on the low

energy side of the peaks, however, does not grow from the base of the

peak as seen in Fig. 4a, but from near the top of the peak. The ratio

of the height of the peak to the height at the point at which the tail

intersects the peak is also much smaller than observed in the experimental data.

One problem with this model as the authors themselves point out

[5], is that the calculations are restricted to the case where there

is a uniform probability of carrier trapping throughout the sensitive

volume of the detector. This has been shown to be inconsistent with

experimental results [6, 7], Thus, while the model does predict relatively small shifts to lower energy of gamma-ray pulse-height peaks wixh increasing trapping of charge carriers as well as the magnitude of increase

in peak width at half the maximum peak-height, it is not accurate enough

for use in quantitative evaluation of trapping parameters from experimental data. Similar results are also obtained from a model proposed earlier

by Chartrand and Malm [6],

The series of experimental spectra which is currently being obtained from Ge(Li) detector 213 as a function of applied bias are part

of an empirical study of the variation in peak shape with increased

carrier trapping being carried out in order to specify the characteristics

of a theoretical model which would accurately reflect changes in the ex- perimental data. (A. H. Sher and W. J. Keery)

Plans : Lithium mobility studies, Ge(Li) detector performance measurements, and the investigation of the relationship between etch-pit

distributions on p-type germanium crystals and the characteristics of

Ge(Li) detectors fabricated from the crystals will be continued. Impurity photoconductivity measurements will be made on germanium crystals

which show a high degree of carrier trapping; measurements of infrared

response will also be made at 77 K on Ge(Li) structures fabricated from

this material.

20
2.8 REFERENCES

2.1 Resistivity

1. "Method of Test for Resistivity of Silicon Slices Using Four Pointed

Probes" (ASTM Designation: F84-68T), 1969 Book of ASTM Standards,

Part 8, November, 1969. This document covers the range 0.05 to

120 ft-cm ; a revision covers the range 0.001 to 2000 J}- cm.

2. A similar conclusion was reached on somewhat lower resistivity

material by J. K. Hargreaves and D. Millard, "The Accuracy of FourProbe Resistivity Measurements on Sil? on," Brit. J. Appl. Phys.

13, 231-234 (1962).

2.2 Carrier Lifetime

1. C. Jund and R. Poirier, "Carrier Concentration and Minority Carrier

Lifetime Measurement in Semiconductor Epitaxial Layers by the MOS

Capacitance Method," Solid-State Electronics _9, 315-319 (1966).

2. F. P. Heiman, "On the Determination of Minority Carrier Lifetime

From the Transient Response of an MOS Capacitor," IEEE Trans. Electron

Devices ED-14 , 781-784 (1967).

3. M. Zerbst, "Relaxationseffekte an Halbleiter-Isolator-Grenzflachen,"

Z. Angew. Phys. 22, 30-33 (1966).

4. P. Tomanek, "Measuring the Lifetime of Minority Carriers in MIS

Structures," Solid-State Electronics 12, 301-303 (1969).

2.3 Inhomogeneities

1. Standard Method for Measuring Hall Mobility in Extrinsic Semiconductor

Single Crystals (ASTM Designation: F76-68), 1969 Book of ASTM

Standards3 Part 8, November, 1969.

2. L. J. van der Pauw, "A Method of Measuring Specific Resistivity and

Hall Effect of Discs of Arbitrary Shape," Philips Research Reports

13, 1-9 (1958).

2.4 Infrared Methods

1. W. R. Thurber, "Determination of Oxygen in Silicon and Germanium by

Infrared Absorption," NBS Tech. Note (in preparation).

2. Recommended Practices for Infrared Absorption Analysis of Impurities

in Single Crystal Semiconductor Materials; Method of Test for Interstitial Oxygen Content of Silicon by Infrared Absorption; Method of

Test for Interstitial Oxygen Content of Germanium by Infrared

21
REFERENCES

Absorption; Method of Test for Substitutional Carbon Content of

Silicon by Infrared Absorption.

2.7 Specification of Germanium

1. G. A. Armantrout, "A Fabrication Technique for Significantly Reducing

the Capacitance of Large-Volume Ge LID Detectors," IEEE Trans. Nucl.

Sci. NS-13, No. 3, 328-335 (1966).

2. D. Camp, "Application and Optimization of the Lithium-Drifted Germanium Detector System," UCRL-50156 (March 1, 1967), p. 10.

(Available from the Clearinghouse for Federal Scientific and Technical Information (CFSTI), Springfield, Va. 22151)

3. W. L. Hansen, R. H. Pehl, E. J. Rivet, and F. S. Goulding, "Selection

of Germanium for Lithium-Drifted Radiation Detectors by Observation

of Etch-Pit Distributions," UCRL-19326 (October, 1969); to be published in Nucl. Instr. & Meth.

4. G. A. Armantrout, "A Highly Sensitive Photoresponse Technique for

Determining Impurity and Defect Energies and Concentration in Germanium," presented at Third International Conference on Photoconductivity, Palo Alto, (August, 1969); UCRL-71625. (Available from

CFSTI)

5. R. Trammel and F. J. Walter, "The Effects of Carrier Trapping in

Semiconductor Gamma-Ray Spectrometers," Nucl. Instr. & Meth. 76 , 317-321 (1969).

6. M. G. Chartrand and H. L. Malm, "Variation of the Gamma-Ray Resolution of Ge(Li) Detectors with the Position of Irradiation," AECL2764 (June, 1967). (Available from Scientific Document Distribution

Office, AECL, Chalk River, Ontario, Canada)

7. P. P. Webb, H. L. Malm, M. G. Chartrand, R. M. Green, E. Sakai, and

I. L. Fowler, "Use of Collimated Gamma-Ray Beams in the Study of

Ge(Li) Detectors," Nucl. Instr. & Meth. 63, 125-135 (1968).

22
3. METHODS OF MEASUREMENT FOR SEMICONDUCTOR PROCESSING

3.1 METALLIZATION EVALUATION

Objective : To improve methods for measuring the properties of thin

film metal films with initial emphasis on adhesion of aluminum metallization deposited on various substrates.

Progress : As previously reported (NBS Tech. Note 520, pp. 27-29),

familiarization studies had been made on the aluminum-quartz system using

a rudimentary scratch test apparatus. This work, which broadly followed

the method of Karnowsky and Estill [l], verified the suitability of this

system for further detailed experiment. These efforts have been con- centrated on evaluation of the test procedures and investigation of the

topography of the stylus tips employed in the study.

Evaluation of the Scratch Test — A new scratch test apparatus was designed and built. This apparatus employs a balanced lever system as shown in Fig. 5. A commercial triple-beam balance is used to hold the

specimen and supply a controlled stylus force (load) when balanced. The

scribing stylus is held in a vertically adjustable jig so that it may

contact the specimen while the beam apparatus is balanced. This jig is

mounted on a heavy-duty stage which provides two orthogonal horizontal

movements. With one movement the stylus is drawn across the specimen,

while with the second the stylus is indexed laterally for subsequent

scratches. The stylus track is observed through a microscope to detect

film failure by transmitted light. The stylus load is continuously

variable within the limits of the balance (0-1600 g) with a resolution of

0.1 g.

The criterion for adhesion failure has generally been considered to

be complete removal of the film over a specified length (usually 1 cm)

[1-4]. The stylus load required to do this is called the critical load.

It was found in the familiarization studies that complete removal of the

films over a 1 cm path is relatively infrequent. Moreover, private

communications with earlier workers in this field revealed that under

only the best experimental circumstances was complete removal "generally"

achieved. Critical load determination, then, is often a matter of

weighted judgement.

Because of the ambiguity of this criterion, the following operational

definition was tentatively adopted for use in the present study:

threshold adhesion failure occurs if, within the boundaries of a scratch and over its 1 cm path, removal of the film from its

substrate can be detected by transmitted light wi'th a microscope [magnification = 40 X] at even one spot no matter how small.

In addition, the following test conditions have been adopted:

(a) Aluminum film thickness: 0.5 um,

(b) Substrate: fused quartz,

23
METALLIZATION EVALUATION

a: Schematic.

b: Photograph.

1. Specimen under test.

2. Stylus (in holder).

3. Triple-beam balance.

4. Vertical adjustment for stylus.

5. x-movement drive for scratching.

6. y-movement drive for indexing.

7. Fibre optic light source.

8. Viewing microscope.

Fig. 5 Scratch test apparatus.

24
(c) Stylus material: tungsten carbide or diamond,

(d) Stylus shape: right circular cone, 60-deg included angle,

50-um nominal tip radius.

Initial tests with the new apparatus were conducted with a single

tungsten carbide stylus . Films were prepared by vacuum evaporating

aluminum of 99.999 percent purity on 75 mm by 25 mm by 1.5 mm transparent

fused quartz sheets which had been cleaned and heat treated in air to remove adsorbed water [5] prior to the deposition of the film.

Three groups of measurements , one group in the central area and

one group close to each end, were made on each of several films. For

any group of test data, stylus load is plotted against scratch position.

If threshold adhesion failure (response) is observed, it is plotted as

V; if no failure (non-response), as o. Only one scratch is made at any

stylus position; a second piece of meaningful data cannot be obtained by

scribing over an existing scratch.

This type of data can be statistically analyzed conveniently if the

up-and-down design [6] is used for the experiment. In this design the

test is started at a level where about half of the scratches are expected

to show threshold adhesion failure. The load is increased one increment

after each non-response and decreased one increment after each response.

Ideally, the load increment should be nearly equal to the standard

deviation. For the initial tests, the load increment was taken as 0.1 g,

the resolution of the balance.

A plot of a set of typical scratch test measurements on a freshlydeposited aluminum film in which the concept of threshold adhesion

failure was applied is shown in Fig. 6. This and other measurements

demonstrate that the scratch test can discriminate between loads 0.1 g

apart. The precision of the test is limited by the resolution of the

balance; statistical analysis [6] of the data suggests that the standard

deviation in these measurements is actually somewhat smaller. In another

experiment thirteen scratches were made with successively increasing

(and then decreasing) loads to obtain complete removal of the film. At

a load of 200 g complete removal was obtained on only one scratch. All

scratches at lower ("massive") loads showed partial film removal in

varying amounts, not necessarily in relative proportion to the applied

load. On the basis of all experimental data gathered thus far, the

ambiguity of the complete removal criterion and critical failure load is

confirmed, and the concept of threshold adhesion failure from which a mean threshold failure load can be calculated statistically, appears

sufficiently valid to investigate and develop in depth.

Stylus Tip Characteristics — A modified shadowgraph technique is

currently being used to measure the overall radius of curvature of the

stylus tips. A photomicrograph of the tip profile is made with a

25
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METALLIZATION EVALUATION

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• mm J3 O T3 CU k, ^ 4-1 4-1 C 4-1 CO •H CO

<4-4 m O Z O CJ

CO

0) -H M T3 o cO .H

CO C

•H to o

f- 4J U

CO -H

01 01 > u

c a M co o o 0) u-i

cu

CO T3 XI 0) O > S2 Q_ 4-1 O

01 UCO cu T3 4J CO CO 01 3 XI X

0) CO J3 o

cu o

4-i a) 1* 4-1 3 O h- n a

o o •H < <4-l V4

<4-l

CO CO

M-l CO cr

CO 4J T3 o CO 0) 13 C

CJ 0) en

•H

4J CO XI 3 3 r*

CO 4J •H

01 X 4J CO H O CO IM

V43

00

•H

Ptl

CVJ

c\j

c©

cvi (sujdj6) M'avcn

26
METALLIZATION EVALUATION

2 *"->*-'--

1

' 'JrABjMb_, .

;

r 2-HfS ^BL^«^j«t *

. -tit . *

-

1 -*'*" im

Si. ? Wfl -^'*~ ; *

' ^Wl''' »> /" .

Tip of a typical tungsten carbide stylus

with a nominal radius of 50 ym before use.

Tip of a tungsten carbide stylus with a nominal radius of 50 vim which was used

for scratching an aluminum film. Note the agglutination of aluminum at the tip (1) and the single tungsten car- bide granule (2) showing through.

The tip of a good commercial diamond stylus with a nominal radius of 20 \im. Notice the exceptional

smoothness of this stylus as compared to tungsten

carbide.

Fig. 7 SEM photomicrophotographs of stylus tips,

black line represents a distance of 10 um. In each case the

27
METALLIZATION EVALUATION

magnification somewhat in excess of 100 X. A reticle-type comparator is

then used to match semicircles of known radius to the photograph of the

tip profile. Matching can be done within 0.5 mm so that with 130 X magnification a determination of the nominal tip radius within approximately ±4 urn is obtained.

More detailed information about the surface features of the tip of

the stylus, which does the actual scratching, can be obtained with the

scanning electron microscope (SEM). The tip of a tungsten carbide stylus

is shown in Fig. 7a. With higher magnification, the individual grains of

tungsten carbide are clearly evident, the smaller ones being about 0.6 ym

in size. The tip of the stylus actually used in these experiments is

shown in Fig. 7b. Aluminum from the scratched films can be seen on the

surface of the tip area. From this photograph it also appears probable

that a single granule was responsible for all the cutting. Further en- largements of this area show that the two clearly exposed edges of this

granule are about 1.2 urn long and the radius of the included tip is

about 0.18 ym. Relative to a metal film thickness of 0.5 ym, this granule represents a fairly sharp cutting edge. The tip of a commercial

diamond stylus with a nominal radius of 20 ym is shown in Fig. 7c. From

this it can be seen that diamond styli considerably smoother than

tungsten carbide styli can be obtained. (J. Oroshnik and W. K. Croll)

Plans : In order to make a comparative behavior study, additional

adhesion measurements by the scratch method will be made on the same aluminum-silica system. Measurements will be made with at least one more

tungsten carbide stylus and two diamond styli, all having the same nominal 50 ym tip radius of curvature. The measurement precision of the

two stylus materials will then be compared; if statistically significant

differences are noted the better material will be selected for further

testing.

The interferometric method for determining the radius of curvature

of this tip will be studied further. The literature search on adhesion

testing will be continued as planned. Work on the orthogonal pull test

will be deferred until the scratch test has been evaluated more fully.

3.2 PROCESSING FACILITY

Objective : To establish a microelectronics fabrication laboratory

consisting of the facilities necessary for the production of specialized

silicon devices for use in research on measurement methods.

Progress : The major effort during the last quarter was expended in

the improvement and characterization of the existing processes, with

emphasis on the production of sets of photomasks and the improvement of

28
PROCESSING FACILITY

control of diffusion processes. These operations are two of the most

critical operations encountered in semiconductor device production.

To assure consistent results in the production of sets of emulsion

photomasks , a set of procedures was written describing each operation in

detail. Incorporated in the procedures is a method for obtaining alignment keys or reference marks to facilitate the registration of the

various masks of a set. Masks were made for oxide-passivated, n

+-p

junction diodes for use in the study of voids in die bonding (see Section

3.3). Various stages in the making of this mask set are shown in Fig. 8.

A section from the wafer which includes several of these diodes is shown

in Fig. 9. A die bonder [2] was obtained with which these diodes can be

eutectically bonded to gold-plated TO-5 headers. Voids incorporated into

the surface of the header in a controlled way simulate a defective diebond.

During the past quarter, difficulty was experienced with the adhesion of the photoresist to the silicon dioxide during etching. This

resulted in undercutting of the resist and a severe degradation of the

pattern being etched. This was found to be caused by insufficient

buffering of the etching solution. The problem was solved by lowering

the hydrofluoric acid concentration of the etch, and etched patterns in

1-um thick oxides with no undercutting visible at 400 X magnification

can now be obtained.

Diffusion schedules [l] were adopted for both p- and n-type furnaces.

The operating procedures which had been used previously yielded diffused

wafers with sheet resistances only marginally reproducible (approximately

±20 percent at 20 ft/square for p-type diffusions and ±10 percent at

7 ft/square for n-type diffusions _ both junction depths were 2 urn in

1 °,-cm silicon of the opposite type). The flow rates for dopant gas

mixtures in the p- and n-type diffusion furnaces were increased from

1600 cm 3 /rain to 4500 cm 3 /min and 3500 cm 3 /min respectively. Increasing

the flow has improved both the uniformity of the doped oxide and the

reproducibility of the sheet resistance. In addition, better thermal

transient characteristics of the furnaces were obtained. The compositions of the doping mixtures presently used are listed in Table 1. The

p-type furnace is operated at 1050 ± 1°C; the n-type furnace, at 1100 ± 1°C. (T. F. Leedy and J. Krawczyk)

Work was begun on obtaining an operational SCEPTRE computer program

at NBS. SCEPTRE [3] provides the circuit analyst with a tool for com- puting the transient responses of electrical networks. The program is

capable of performing d-c steady state and transient -analysis. Transient

analysis may be performed with initial conditions either specified by

the user or calculated from a previous part of the computation.

(T. F. Leedy)

29
PROCESSING FACILITY

UUUUUUUUUUUUUUUUL

DnnnnnnnnnDDnnDnc c3DDnnannnannnnnnE

nnnannnnaannnnanc: nunnanannpnannniic DDnnDDDDDnnnnnDnc

annnnannnnnnnnnnc: DnaDnnnnc annDnannnnnnnnnnc

DDDnnnnannnDnnnnc

nannnaDnnnnnnnnnn

DnnnannnnnnnnnnnD

. nnDGannniinnBDnnnn

Fig. 8 The sequence of producing a mask set.

a: The original artwork (250 times the final size),

b: The first reduction on an 8 in. by 10 in. glass

photographic plate,

c: The contact print of the first reduction,

d: The final set of three masks after the second

reduction.

nnnnnnnDsnnnDnnDD

nnnnnnnnnnnDnnnnn

nnDnnnnnnnnnnnnnn

nnDDDDDnaDnnnnnnn

DnnnnnnnnnDnnnnnn oddd DDD

nnnannnnnannnannn a^aannannnnnnnniEa -annnnDCD

nnnannnnnnnnnnnnn

annnnnGnnnnnnnana

C nrunnnnnnnnnnnnnn

B 1

H1 -':-. HH

Table 1. Doping mixture flow rates

Gas

Fl ow rate

p-type n-type

cm 3 /min cm 3 /min

Nitrogen 4330 3265

Oxygen 150 35

Diborane3 18

Phosphine 200

Fig. 9 A section of the diode array produced by

the mask set. Final die size is 0.050 in. by 0.050 in. 1 -percent mixture of dopant in nitrogen or

argon.

30
PROCESSING FACILITY Plans : The die bonding machine will be put into operation and

procedures for attaching dice to headers will be established. Preliminaryinvestigations of methods for incorporating voids under dice will start.

A test structure will be developed to evaluate further the currently

used processing techniques. This structure will include three diffused

resistors, a diode, and a transistor. The objective of such a structure

is to determine the compatability of the photomasking and diffusion processes and to provide active devices for electrical measurements.

3.3 DIE ATTACHMENT EVALUATION

Objective : To evaluate methods of detecting poor die attachment

in semiconductor devices with initial emphasis on the determination of

the applicability of thermal measurements to this problem.

Progress : Thermal resistance measurements are presently used to

evaluate the quality of the semiconductor device die attachment with

varying degrees of success. Present practices for measuring thermal

resistance, Rfi , frequently yield results of questionable accuracy and

poor reproducibility. Furthermore, when the thermal resistance of the

chip-to-header bonding area is small compared to the overall thermal

resistance of the device, it may be possible to detect only large voids

by means of the thermal resistance technique. The transient thermal

response of devices is expected to be more sensitive to voids than the

R

Q

measurement. For this reason, it was decided to measure transient

thermal response in addition to R in the study of diodes with controlled

voids

.

The processing of diode chips to be used in the void detection

studies was continued (see Section 3.2). Further radiographic studies were conducted to establish procedures and techniques for taking X rays

of semiconductor devices. (F. F. Oettinger)

Plans : The processing of the diode chips to be used in the void

detection studies will be completed. The design and fabrication of

equipment which will be used to measure thermal resistance and transient

thermal response of the diodes with controlled voids will be initiated.

3.4 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.

31
WIRE BOND EVALUATION

16

14

<

_lUJK- 10

UJQ

3

Q_<z

o

I-<

CO

8

Af = 870-f/ Af=2 Q«70 / Q

a /

-°* O'

/

59 60 62 63

0.8 —

0.6

zo

Z

I

o0.4

0.2

FREQUENCY { kHz)

Fig. 10

I 'I I I I

Mechanical resonance curves taken on

the same transducer driven by three

different ultrasonic power supplies.

In each case the tool extension is 0.555 in.

a: Constant current source.

b: Constant voltage source.

c: Constant power source. (The sweep range indicated is that

provided with this supply, see

Fig. 13d.)

8 6 4 2 VIBRATION AMPLITUDE (RELATIVE VALUES)

11 Vibration amplitude of an ultrasonic

bonding tool. The tool extension is 0.555 in. below the horn. The tool exten- sion above the horn is close to a half

wavelength and thus the vibration amplitude is much larger than that of the bottom portion of the tool.

32
WIRE BOND EVALUATION

Progress: To make wire bonds with reproducible pull strengths^ in

part for the development of a meaningful method for bond evaluation, tiie

characterization of ultrasonic wire bonding systems used for attaching

leads to integrated circuits has continued. The techniques for using a capacitor microphone to study the parameters which affect the motion of

bonding tool tips have been improved, and procedures for fabricating

bonding pads on both oxidized and unoxidized silicon wafers have been

developed. Direct assistance has been given one of the sponsors of the

Joint Program. Detailed investigations of wire bonds with the scanning

electron microscope has led to the identification of problems associated

with the bonding machine used on operational production lines and provided information concerning the pattern of bond formation. An apparatus

to evaluate the uniformity of deformation of bonding wire after indentation has been designed. Work on the bibliography and critical review

survey paper is continuing.

Characterization of Ultrasonic Bonding Systems — Previous work has

shown that slight changes in the power supply impedance can have a significant effect on the mechanical Q of the wire bond system (NBS Tech.

Note 495, pp. 26-28). These measurements were made with special laboratory amplifiers in which the current and voltage were individually con- trolled. Similar measurements have since been made with three commercially available ultrasonic wire bonding power supplies which were used

to drive the same transducer-tool combination. The vibration amplitude

was measured with a capacitor microphone positioned near the tip of the

bonding tool. Mechanical resonance curves obtained with these three

power supplies are shown in Fig. 10. As would be expected from the

earlier results, it was found that the mechanical Q of the system was lowest when driven with a constant current source (curve a), intermediate

when driven with a constant power source (curve c), and highest when

driven with a constant voltage source (curve b). For these tests, a 0.828-in. long bonding tool was used with an extension which is commonly

used on some bonders, 0.555 in. below the horn.

Investigation of the vibration amplitude along the entire tool

length has shown that the tool extension above the horn can significantly

affect the resonant frequency and other characteristics of the transducertool system. The data shown in Fig. 11 were taken from the same tool

driven under the same conditions as were used to obtain the data for

curve c of Fig. 10. In this case the residual extension above the top of

the horn is approximately a resonant length. Under similar conditions,

different bonding tools have been observed to have amplitude maxima above

the horn greater than ten times those below the horn. Since the normal

tool tolerance is ±0.015 in. and since only the tool extension below the

horn is measured when mounting a new tool, it is possible that the re- sidual extension above the horn can vary as much as 0.03 in. from tool

to tool. When the measurement was repeated with a different tool, 0.013

in. longer than the one used in the measurement shown in Fig. 11, the

33
WIRE BOND EVALUATION

o

c • <u a

8 -h

• CD I c o o

co 00

i-H i-H O

ta a • o o

<u c

x; x: Q

111 W T) e o c

0)

• o

<D CM

nj -u u o M

co P0 <u

.H u cj o

c

iJ CO

CD C S O

cO en

CD

3

•o

CO CD C iH

CO CO U

u-i .-I •H CO T3 iJ O C e o

N ,-v CM T-l >

O 1-1 -H O -a

CU EC —

> -^ N w as 3o • O

w m

CD CD CN O CJ C 3

CO T3 C CO CD O C iH

CD CO CO

CD M CJ 13 Pd -ul CO pd -U CO H Kao

fa

34
WIRE BOND EVALUATION

amplitude of the top portion was similar to that of the bottom. The

changes in system resonant frequency and mechanical Q which result from

large resonances of the top of the tool require significant adjustment

of the ultrasonic power supply power control setting to reestablish the

original bonding tool motion. It was also observed that, when the maxima

above the horn were as much as ten times those below, these parameters

become critically dependent on the tightening torque applied to the

bonding tool set screw.

Since mechanical resonance curves measured with a capacitor microphone have been very useful in characterizing ultrasonic wire bonders, a simple system of generating them was constructed. A small, variable

capacitor with a linear potentiometer attached to its shaft is connected

across the oscillator coil of the ultrasonic power supply. The potentiometer is used to control the voltage which is applied to the horizontal

input of an oscilloscope. When the capacitor is manually tuned, a com- plete resonance curve is generated, picked up by the microphone, and

displayed on the oscilloscope. Such a system permits the rapid comparison of resonant curves taken under different conditions.

In order to lower its mechanical Q a series of holes was drilled in

the horn of an older transducer as shown in Fig. 12a. The resonance

curve with the unmodified transducer obtained with the above system is

shown in Fig. 12b. The initial Q of this particular transducer-toolpower supply combination was 165. After the modification, the Q dropped

to 125 as shown in Fig. 12c, a decrease of approximately 25 percent. The

mechanical resonance frequency decreased only 2.6 kHz. For both measurements the same bonding tool and power supply were used and the bonding

tool extension and power supply settings were reproduced as accurately

as possible. Thus it can be seen that by means of a simple modification

the mechanical Q of an existing transducer can be lowered significantly

while the frequency and amplitude remain essentially unchanged. The

broader resonance peak obtained in this way reduces the detuning effects

of thermal environmental changes and instabilities in the oscillator.

Frequency modulation of the power supply oscillator is another

technique which is often used to reduce the problems associated with

thermal and oscillator instabilities. The characteristic motion of the

tool tip which results from frequency modulation of the 60-kHz power

supply oscillator of a bonding machine transducer was studied in some detail by means of the capacitor microphone. The response of the tool

tip vibration amplitude to a square-wave modulation voltage is shown in

Fig. 13a. The rise time (10 to 90 percent) was 1 ms whereas the rise

time of the modulating pulse was much shorter. The mechanical Q calculated from the time required for the amplitude to decay to one half its

equilibrium value agrees very well with the measured static Q of the

system (curve c, Fig. 10).

35
WIRE BOND EVALUATION

a: Square-wave modulation. b: Triangular-wave modulation.

c: Saw-tooth modulation (decreasing frequency). d: Modulation wave-form supplied with power supply.

Top curve: Vibration amplitude of the tool tip as measured

with a capacitor microphone.

(Vertical scale — 0.5 mV/div) Bottom curve: Modulation voltage applied to oscillator.

(Vertical scale — a: 0.5 V/div;

b, c: 1 V/div;

d: 0.1 V/div) Center curve (a only): Power supply oscillator output voltage.

(Vertical scale - 2 V/div)

(Horizontal scale — a, d: 1 ms/div;

b, c: 5 ras/div)

Fig. 13 Response of the bonding tool vibration amplitude to frequency

modulation of the power supply oscillator

36
WIRE BOND EVALUATION

A linear frequency drive was introduced into the power supply

oscillator by means of a triangular-wave modulation voltage with the re- sult shown in Fig. 13b. The frequency changed linearly with voltage,

but the vibration amplitude envelopes for increasing and decreasing frequency were not the same. The decreasing frequency envelope resembled a normal resonance curve; however, the increasing frequency envelope was compressed toward the high frequency end. This effect is presumed to

result from the slow mechanical rise time of the system. In the increasing frequency case, not only the tool tip amplitude but also the

frequency is increasing. Thus the net acceleration of the motion is

significantly higher, equivalent to frequency modulation at a considerably higher sweep rate. Conversely, by sweeping toward lower frequencies,

a lower mechanical acceleration is applied to the system, and a more

nearly quasi-static sweep results.

If the slow mechanical response of the system is taken into account,

it is possible, by adjusting the sweep rate, amplitude, and center frequency and by using a saw-tooth modulation voltage, to obtain a symmetrical system response curve that is closely related to the static resonance

curve c of Fig. 10. The result shown in Fig. 13c was obtained on the same transducer-tool system with the same tool extension and the same power supply as were used to obtain the static resonance curve.

Studies of the frequency modulation in some commercial power supplies

have revealed that the frequency may not always be swept through the en- tire static resonance peak. In a typical case the sweep starts from the

lower frequency side, barely goes over the resonance peak, and then returns toward lower frequencies. The result shown in Fig. 13d was obtained when the transducer system was tuned by the method recommended by

the manufacturer. The sweep range for this case is shown in Fig. 10. A

possible result of such a partial sweep technique is that the resonance

frequency detuning due to the temperature sensitivity of the transducer

may be effectively increased if the resonance peak shifts in such a way

that the modulating voltage is not large enough to reach the new maximum.

Extensive assistance was given one of the sponsors in connection with

with wire bonding problems encountered on production lines. A detailed

procedure for trouble shooting and tuning bonding machines and determining their mechanical stability with the capacitor microphone is being

prepared for issuance as a NBS Technical Note. Several potential problem

areas in addition to those discussed above were also identified. Many

marks and scratches were found on the anodized aluminum spools that are used for holding the 0.001-in. aluminum bonding wire. In some instances

clear impressions left by the wire on the spool as depicted in Fig. 14 were observed. It is possible that some of the spool material can stick

to the wire and be carried along the wire feed path or onto the semiconductor die. In an investigation of possible contamination along the

wire feed path, a large accumulation of white particles was observed in

37
WIRE BOND EVALUATION

Fig. 14 Wire marks (2) in the coating of a spool

left by 0.001-in. diameter aluminum

bonding wire. Other marks shown (1) are tooling marks. Magnification: 60 X.

12.0

CO| 10.

O 8.0

Z

Id

<zh3

Q.

6.0

4.0

_ <

1 1 1

1 * ?

' t

i I

<

i i

- t I -

—

i i i i i 6.0 7.0

POWER SETTING

8.0

Fig. 15 Pull strength in grams as a function of bonder power setting for oxidized substrate,

aluminum sintered at 550°C. Intervals shown

are 95 percent confidence levels for the mean.

38
WIRE BOND EVALUATION

a relatively new transducer wire feed hole through which less than two

spools of wire had been passed.

The mechanical stability of the bonding machine was checked by means

of a capacitor microphone and a laser beam reflected from a mirror on the cam housing onto a distant wall. Relatively low frequency mechanical

vibrations were observed between the top portion of the machine that

houses the transducer cam and motor and the base that clamps the semiconductor die. This motion was attributed to the cantilever type of

support provided for the transducer housing. The motion was very noticeable when the cam motor was turning. This vibration may cause the displacement of wire during bonding which has been observed in some cases with the scanning electron microscope (see Fig. 17d, p. 43).

Temperature characteristics of an ultrasonic transducer system were measured last quarter (NBS Tech. 520, pp. 40-41). One commercially

available bonding machine used in this study is supplied with a largearea, high-intensity lighting system which is capable of heating the

general bonding area between 5 and 10°C above the ambient temperature.

As the entire unit warms up, the resonant frequency drifts downward 100

to 200 Hz. To obtain reproducible bonding conditions with this machine,

it was necessary to preheat the transducer by turning the lights on for

several hours prior to bonding or to put a heat absorbing filter in front

of the lamps.

The fixture used on this machine to hold the transistor or integrated

circuit is designed to be rotated manually; the operator's hand normally

contacts it during the bonding operation. Measurements made with the

capacitor microphone revealed that slight motion of the hand could move

the fixture as much as 0.001 in. Such motion of the fixture can cause undesirable skidding of the wire across the pad during bonding.

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

An improvement in the taper tip used to increase the resolution of

the capacitor microphone (NBS Tech. Note 520, pp. 63-66) was achieved

with the fabrication of precision, stainless-steel taper tips. The performance of these tips is similar to ones made of aluminum foil; however

the steel tips are considerably more rugged and therefore more practical

for frequent tuning of bonding machines as might be required on a production line. (L. M. Smith)

Fabrication of Bonding Pads — The bonding pads that were used for

the work reported here are fabricated on 0.01-in. thick, 1-in. diameter

silicon wafers, coated with 0.5 urn of steam-grown silicon dioxide and 0.5

to 1 um of evaporated aluminum. The aluminum is etched to leave 0.005-in.

square bonding pads by means of standard photolithographic techniques.

The photomasks for these patterns were made from readily available Ronche

rulings which can be obtained from optical suppliers. When two-level

39
WIRE BOND EVALUATION

a: Normal configuration.

b: Wire has twisted after being clamped and before bonding.

Fig. 16 SEM "photomicrographs (575 x) of aluminum ultrasonic wire bonds showing heel crack (1) and clamp marks (2). The clamp marks appear on both sides of the wire.

40
WIRE BOND EVALUATION bonding is desired, strips are cut from similar wafers and epoxied to

multi-level substrates. Finally the entire wafer is bonded with epoxy

to a steel holder so that hundreds of bonds can be made without changing

wafer or other bonding conditions.

This procedure was selected as a result of an evaluation which was made of substrates prepared with different sintering temperatures in

order to establish conditions which yielded reproducible bond strengths

as determined by a pull test. Silicon wafers were prepared in pairs.

One wafer of each pair had a 0.75-um thick layer of thermally-grown

oxide while the other did not. A 0.5-um thick aluminum film was evaporated on each wafer. After the array of square bonding pads was etched,

pairs were sintered for 15 min at 425, 500, 550, and 577°C in a helium

atmosphere.

Ultrasonic bonds were made on each specimen with 0.001- in. diameter

aluminum wire at various power settings of the ultrasonic wire bonder.

The single-loop wire bond strength was measured by a pull test with a simple hook at the center of the loop. By means of a one-sided t-test at

a 95 percent confidence level [l], it was found that the oxidized specimens sintered at 500 and 550°C were statistically similar and that they

both yielded higher pull strength than the oxidized specimens sintered at

either 425 or 577°C. As an example, the curve for the 550°C specimen is

shown in Fig. 15. The two-sided 95 percent confidence level for the mean

is indicated for each point plotted. For the unoxidized specimens, the curves were uneven and the results were inconclusive.

(K. 0. Leedy, J. K. Madello, and J. Krawczyk)

Scanning Electron Microscopy — Bonds from several devices selected

from the output of operational production lines were examined with

the scanning electron microscope (SEM). The bonding machine used on these lines has a tool motion such that the vibrating tool is inclined

forward 4 deg from the normal for the first bond and is perpendicular to

the die surface for the second bond. The crack in the wire at the heel

of the bond as shown in Fig. 16 is a feature of all first bonds made by

this machine. In addition, deep indentations, also shown in Fig. 16, were observed on the sides of the wire. It has been determined by additional SEM photographs that these marks are produced by the jaws of the

clamping system through which the wire is fed from the spool to the

bonding tool. In addition to marring the surface finish, these imprints

could work-harden the wire and thus affect bonding conditions. Occasionally the wire twists after passing through the clamping system, and the

indented portion then becomes a part of the actual bond interface as shown in Fig. 16b. Of particular concern is the possibility of contamination from the clamp becoming embedded in the wire and directly interfering with the bonding process. Since the twists, such as those depicted in Fig. 16b, occur only occasionally and since not all of these

need be significantly contaminated, the possibility should be considered

that this may be a cause of occasional, otherwise unexplained weak bonds.

41
WIRF ROND EVALUATION

/

•'4

m

% \

b

\

mm

Fig. 17 SEM photomicrographs (460 X) of bond adhesion (lift-off) patterns for first bonds

made at different time settings and constant power setting. The time is longest

for case a and is decreased to the shortest value for case d. Settings used in case a result in a bond which will adhere to the pad; the shorter time settings

do not produce an adherent bond. Note that the scratches on the bonding pads

(which result from a cleaning process no longer in use) are polished out by the ultrasonic motion of the compressed wire even before appreciable bonding occurs. Note also the apparent movement during bonding exhibited in case d. This is thought to result from mechanical vibration in the bonding machine.

42
WIRE BOND EVALUATION By studying the bonding pad after a bond has been intentionally

lifted or peeled off, the pattern of bond formation can be seen. The

threshold of welding can be observed by decreasing either the power or time in the bonding schedule to a point where essentially no bonding has

taken place. This experiment was performed for a number of first and

second bonds. An example is shown in Fig. 17.

In all cases, bonding begins at localized points and then, as the

power or time is increased, the weld extends to other areas, usually the

toe or the heel or both. The next areas to weld are the sides; the cen- ter is the last portion to weld. Even in some very strong bonds, the

center area generally remains unbonded. This is illustrated in Fig. 18

which shows the pad under a strong bond which has been peeled off with

a force of 8 g.

Although there are general characteristics of bond patterns which

can be observed, it is premature to draw firm conclusions about the bonding process from these initial studies. However certain facts are evident. From cases in which very low power or short time was used, such as that shown in Fig. 17d, it appears that most of the deformation of the

wire occurs before welding begins. The unwelded area under the wire becomes polished as a result of the ultrasonic motion of the compressed

wire. When welding begins, it starts at tiny, isolated points which are seldom located in the same positions for successive bonds. Occasionally

the weld will start in entirely different sections of the bond. An ex- ample of two consecutive first bonds made with the same bonding conditions

is shown in Fig. 19. One possible explanation for these observations is

that the hard silicon precipitates in the 1-percent-silicon doped wire

are necessary, or at least help, to start the substrate abrasion which

leads to welding. This suggests the need for further studies in which

the lifted off wire is observed with an electron microprobe in order to

determine the presence or absence of silicon precipitates at the initiating points.

Another problem which is apparent in the lift-off patterns is that

of bonding machine movement during the bonding which was discussed ear*

lier. An example of such movement can be seen in Fig. 17d.

f/ire Evaluation — Additional evaluation of ribbon wire has been delayed because it has not been possible to obtain ribbon wire of higher

tensile strength in the desired size. (K. 0. Leedy)

A wire tester has been designed for determining the uniformity of

the deformation of aluminum bonding wire. The wire is indented automatically at regular intervals and the extent of the deformation is detected by a displacement sensor. The results of this test are affected

by variations in both diameter and hardness of the wire. Measurements

of the uniformity of deformation are expected to be of value in the

43
WIRE BOND EVALUATION

Fig. 18 SEM photomicrograph (800 x) of bond adhesion (lift-off)

pattern for a strong first bond.

Fig. 19 SEM photomicrographs (600 x) of bond adhesion (lift-off) patterns for two second bonds

made consecutively at identical time and power settings.

44
WIRE BOND EVALUATION

selection of wire to be used in the evaluation of the pull test and

other tests for wire bond quality.

Pull Test Evaluation — A low-duty cycle, high-current pulser and

probe system, originally designed and constructed to evaluate the highcurrent pulse method for testing bond quality has been adapted for the

purpose of cutting the loop between two bonds without otherwise damaging

the bonds. Since normal bonding machines make two bonds with a loop

between, it is necessary to cut the loop without pulling or damaging

either the wires or the bonds in order to test each bond separately.

Then the hot-melt glue bond puller (NBS Tech. Note 488, pp. 22-24) can be

used to determine the individual bond strengths. The new technique for

cutting the loop represents an improvement over previously used, mechanical procedures. (H. K. Kessler)

Bibliography and Critical Review — The collection of papers for the

bibliography is essentially complete. Although earlier work has been

obtained either from reference citations or from the bibliographic search

prepared by the Defense Documentation Center (DDC), which included re- ports published as early as 1953, major emphasis has been given to the

collection of papers and reports which have appeared in the period 1965

to 1969, inclusive. Each issue of about 30 journals published during

this period was scanned. Because the report file from which the DDC

search was prepared does not contain all NASA documents, issues of Scientific and Technical Aerospace Reports published during this period were

also scanned. More than 80 articles and reports that are considered significant have been assigned key words for their inclusion in the bibliography. (H. A. Schafft and E. C. Cohen)

The first draft of the introduction and much of the section on the

evaluation of wire bond systems has been written for the critical review

survey paper.

In general, the evaluation methods that have been found in this

survey are used to perform one or more of the following three functions:

to optimize bonding procedures, to determine if the bonding procedures

remain controlled, and to determine the quality of the wire bond system.

Detailed analyses of three commonly used methods (visual inspection,

double bond pull tests, and centrifuge tests) were undertaken.

(H. A. Schafft)

Plans: Evaluation of ultrasonic bonding machines will continue.

This will include further consideration of problems encountered on production lines. A simple milliwatt laser interferometer will be con- structed for use in conjunction with the capacitor microphone to study

tool and transducer motion during the bonding process.

45
WIRE BOND EVALUATION Experiments for the purpose of evaluating the importance of variable

parameters of the bonder, such as power and bonding time, with respect to

the pull test will be designed. A bonding tool design most appropriate

for making bonds for these experiments will be selected. Work on the

modification to the bond puller will resume. The modified puller will

also have the capability of varying the pull rate and of prestressing

bonds to a fixed-force level in addition to providing a means of re- cording the force at which the bond failed.

The scanning electron microscope will be used for studying bonding

wire. Sections of bonding wire with which good bonds could not be made

will be studied in an effort to evaluate the effect of inhomogeneities

in the wire which might be responsible for its poor performance. Study

of lift-off patterns will continue.

Work on ribbon bonding wire will resume. The wire testing machine

will be assembled and tested.

The first draft of the critical review survey paper and the assignment of key words to all the papers to be included in the bibliography

will be completed.

3.5 REFERENCES

3.1 Metallization Evaluation

1. M. M. Karnowsky and W. B. Estill, "Scratch Test for Measuring

Adherence of Thin Films to Oxide Substrates," Rev. Sci. Instrum. 35 , 1324-1326 (1964). A standard method based on similar principles

is being developed by ASTM Committee F-l.

2. 0. S. Heavens, "Some Factors Influencing the Adhesion of Films Produced by Vacuum Evaporation," J. Phys. Rad. 11, 355-360 (1950).

3. P. Benjamin and C. Weaver, "Measurement of Adhesion of Thin Films,"

Proa. Roy. Soc. (London) 254-A , 163-176 (1960).

4. L. E. Collins, J. G. Perkins, and P. T. Stroud, "Effect of Ion Bombardment on the Adhesion of Aluminum Films on Glass," Thin Solid

Films 4_, No. 1, 41-45 (1969).

5. M. L. Hair and A. M. Filbert, "Surface Chemistry of Glass," Research/

Development 20, No. 10, 34-38 (1969).

6. M. G. Natrella, Experimental Statistics, NBS Handbook 91, August 1,

1963, pp. 10-22 to 10-23.

46
REFERENCES

3.2 Processing Facility

1. R. M. McLouski, "Diffusion of Impurities into Silicon from Gaseous

Sources," NASA CR-524 (November, 1966). (Available from the

Clearinghouse for Federal Scientific and Technical Information

(CFSTI), Springfield, Va. 22151, N56/39891)

2. R. J. Anstead, "Semiconductor Wafer Bonder," TM-66-4 (April, 1966).

(Available from CFSTI, AD 634030)

3. S. R. Sedore, "SCEPTRE: A Program for Automatic Network Analysis,"

IBM Journal 11, 627-637 (1967).

3.4 Wire Bond Evaluation

1. M. G. Natrella, Experimental Statistics^ NBS Handbook 91, August 1,

1963, p. 3-34. The NBS Omnitab Computer Program was used in the

statistical evaluation for this experiment.

47
4. METHODS OF MEASUREMENT FOR SEMICONDUCTOR DEVICES

1.1 THERMAL PROPERTIES OF DEVICES

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

Progress: The literature search and the review of the methods of

measurement of thermal resistance and transient thermal response of semiconductor devices were continued. The writing of the first draft of the

section of the review paper on steady-state thermal resistance measurements was continued. The identification of key words for the bibliography was initiated. (M. Sigman and F. F. Oettinger)

Last quarter the measurement of d-c current gain, hpE

, versus collector-emitter voltage, VpF

, was automated. Initial measurements made

on a limited number of transistors showed an abrupt decrease in hpE as the device went into a current-constricted operating mode. It was also

found that the re-trace of the h

pF versus VqE curve did not follow the

original trace, but that a hysteresis effect was in evidence (NBS Tech.

Note 520, pp. 49-52).

Preliminary measurements of hpE versus VpE were made for several

transistors representing a variety of production techniques, geometries,

and manufacturers. The devices were interdigitated, planar, triplediffused or epitaxial-diffused power transistors. Initial results indicated that although a decrease in hpE did occur at the onset of lateral

thermal instability it was not always an abrupt change. It was found

that the shape of the hpE curve as well as the associated hysteresis

effect was dependent on the collector current level as well as on the

severity of the current constriction.

Because of the quantity of data required for each device in this

study it was decided to determine how best to automate the measurement of

thermal resistance, R , versus V

p

. The existing equipment has been

partially automated for AT measurements and plans are underway to determine the feasibility of using a sample-and-hold technique to automate

the measurements completely. Then Rg would be obtained by dividing

the transistor power dissipation into the temperature difference between the device junction and the case, ATj_c

, which is accomplished

with an analog divider.

The block diagram of the apparatus now being used to generate and

plot AT as a function of VCE for constant collector current, I c

, is

shown in Fig. 20. The device under test, DUT , is operated in a common- emitter configuration with a variable, current regulated source driving

the base. An operational amplifier (Ig SERVO) adjusts Ig to keep Iq

48
THERMAL PROPERTIES OF DEVICES

> y

-o CO

4-1 QJ CO J= c

4-1 O

CJ c

CU T3

(1) .-I 3 <U

4-" 43

<U ,Q 4-1

a o

a)

CU r-t u <-< o o

4-1 O

a)u cu

cu x: I"CU XI

4J CU

14-4 CD O 4-1

co' o

cu > >

l-l s-< 3 CU

CJ 4-1

T3 O

a 4J

CU

u o

cuC M-i

cu o M

a o o a o

cu a

en 3

3 m

a)

CO CO U

eg cu a ca a co

CO CJ

n) t3 n a

60 CO CO •H C

•a oH

Ai 4-1 o o

o c H 3

DO

T-l

49
THERMAL PROPERTIES OF DEVICES constant as Vqjt is varied. Thermal resistance is measured using Vg£ as the temperature indicator by interrupting the collector voltage supply

and simultaneously reducing the base drive to the required low- level

metering current. This is accomplished at a repetition rate of from 2 to 20 Hz. The low-level metering portion of the cycle is less than 0.1

percent of the total. An x-y recorder is used to display ATj_c as a function of Vpp. The d-c comparison voltage of a high gain differential

comparator plug- in oscilloscope unit, which is made equal to the forward

voltage of the emitter-base junction, VBE> at a specified time after interrupting the collector supply voltage, is subtracted from a reference

potential equal to Vg£ for a junction temperature of 25°C by means of a differential amplifier. The temperature coefficient of Vg£ is used to

convert the output voltage of this differential amplifier to ATj_q by means of a suitable voltage divider. The output of this voltage divider

is fed into the y-input of the recorder. The plot of ATj_£ versus VqE

is

generated by first increasing V^g , which moves the pen of the recorder

parallel to the x axis, and then adjusting the d-c comparison voltage to

obtain a value of VgE appropriate to the value of Vq£. This procedure is

continued until the trace is completed. The trace generated is a series

of steps from which the curve of ATj_q is derived by connecting the end

"points after each step increase.

(S. Rubin, R. L. Gladhill, and F. F. Oettinger)

Plans : The literature search will continue. The identification of

key words for the bibliography will be completed and their assignment to

relevant articles initiated. The first draft of the section of the re- view paper on steady-state thermal resistance measurements will be com- pleted, and work on a second, independent section on transient thermal

response will be started.

The merits of fully automating the Rq measuring system by replacing

the manually-operated comparator plug- in unit and oscilloscope by a sample-and-hold unit will be studied. If it is found to be both feasible

and warranted, the required circuit modifications will be made.

Consideration will be given to a test circuit similar to the Vgjr

measuring apparatus which will measure Rq using the collector-base

voltage, Vq£, as the temperature sensitive parameter. This will allow

a study of the reason for the higher measured temperature of the emitter

junction over the collector junction [l], even though it is assumed that

the power is being dissipated at the collector junction.

Further measurements of Rq and hpE as a function of Vpp will be made

on transistors representing a variety of production techniques and geometries and an attempt will be made to correlate the results from the

thermographic phosphor study (see Section 4.2).

50
4.2 THERMOGRAPHIC MEASUREMENTS

Objective : To evaluate the utility of thermographic techniques for

detection of hot spots and measurement of temperature distribution in

semiconductor devices.

Progress : The photometric equipment was modified to facilitate the

study of hot-spot formation and the heat exchanger was improved to permit

better control of transistor case temperature. A test fixture for the

study of the temperature sensitivity and spatial resolution of the phosphors was fabricated. Studies of the extent and temperature of hot spots

as a function of collector-emitter voltage were begun, but data are too

limited to draw any conclusions at this time.

Time was spent in becoming familiar with the operation of an infrared microradiometer which was loaned to us by one of the Joint Program

sponsors. A device test fixture and heat sink for use with the automatic stage of this instrument was designed and fabricated.

(G. J. Rogers, F. F. Oettinger, and L. R. Williams, Jr.)

Plans: Studies of hot spots and their relationship to the electrically determined thermal characteristics of transistors will be con- tinued. Experiments will also be carried out to determine if coating

thickness or the material under the coating has an effect on temperature

resolution of the phosphors and to determine the effect of coating thickness on spatial resolution.

The infrared microradiometer will be used to assist in evaluating

the relative merits of the phosphor and infrared techniques.

4.3 MICROWAVE DEVICE MEASUREMENTS

Objective: To study the problems and uncertainties associated

with measurement of microwave device properties and to improve the

methods of measurement for related characteristics.

Progress: Continuing discussions have been held with representatives

of the Electronic Industries Association, the Naval Electronic Systems

Command, the Naval Applied Science Laboratory, and others to determine

the work which is to be undertaken on microwave diode and transistors.

Work was continued on the error analysis for transistor scattering

parameter measurements in cooperation with JEDEC Committee JS-9 on Low

Power Transistors Task Group on Transistor "S" Parameter Measurements.

A survey was made of manufacturers of measurement equipment for microwave transistor "S" parameters to collect existing error analyses of

51
MICROWAVE DEVICE MEASUREMENTS commercial equipment. Very little data exists on the errors inherent in

these instruments at the low signal levels required for linear transistor

measurements.

Some of the apparatus which is required for the measurement of

mixer diode noise parameters at X band is on hand and has been assembled.

The set up can not be completed until more equipment is obtained.

(R. C. Powell and J. M. Kenney)

Plans: Transistor scattering parameter measurement evaluation will

continue. Assembly of the mixer diode noise apparatus will continue as equipment becomes available. A survey of mixer diode noise measurement

techniques will start.

4.4 SILICON NUCLEAR RADIATION DETECTORS1

"

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 : Silicon detectors obtained for use on earth-oriented

satellites and sounding rockets were tested and evaluated with respect

to performance specifications and stability. Special lithium-compensated

silicon detectors for use in future satellite experiments were fabricated

and tested. The performance degradation of surface-barrier detectors by

the radiation damage effects of low-energy protons was studied. Assembly

of the system for the automated testing of large numbers of detectors has

progressed slowly because key parts were not available. Further characterization of large-diameter, dislocation-free silicon for use in

lithium-compensated detectors has been deferred for six months because of

the heavy work load in other areas requested by the sponsor.

Testing and Evaluation — Totally depleted surface-barrier detectors,

with nominal area and thickness of 50 mm2 and 100 urn, respectively,

were extensively tested prior to incorporation into the very low-energy

radiation detection system for the IMP-I satellite. The temperature of

detectors in the spacecraft is expected to be within the range between

-10 and 40°C. The reverse current, noise, and alpha-particle resolution

of each detector was measured as a function of applied reverse bias at

operating temperatures of -10, 23, and 40°C. Capacitance and bias for

' Supported by Goddard Space Flight Center, National' Aeronautics and

Space Administration. (NBS Project 4254429) Irradiations were

carried out at Goddard Space Flight Center.

52
SILICON NUCLEAR RADIATION DETECTORS total depletion were also determined but only at 23°C. In general, the

detector current and noise decreased with temperature as expected while

there was little change in the alpha particle energy resolution. Operation of surface-barrier detectors at temperatures only a few degrees

below room temperature can result in significantly reduced current and

noise levels primarily because the thermal generation of carriers de- creases exponentially with temperature. Critical requirements for the

use of detectors on satellites are that the detector noise remain within

acceptable bounds and that bias across the detector always be large

enough to insure total depletion of the device over the expected range of

operating temperatures

A series of five special Si(Li) detectors in the form of cubes,

3-mm on a side, were fabricated and tested for use as proton detectors

on future TIROS and IMP satellites. The resolution of these devices

operating at room temperature and at 300 V reverse bias for the 972-keV

conversion electrons from 207Bi was in the range of 15 to 23 keV (FWHM).

(B. H. Audet and D. M. Skopik)

The evaluation of silicon avalanche-type detectors for counting lowenergy electrons and protons continued with an investigation of the temperature dependence of the leakage current, noise, and avalanche voltage

of two typical units. At the operating bias (a few volts below the

avalanche bias of about 200 V) the current remained constant when the

detector temperature was between 23 and 30°C. Above 30°C, the current

increased gradually; at 50°C its value was four times the value at 30°C.

The noise increased only slightly over this temperature range. This may

indicate that the principal source of noise in the avalanche detectors is

not due to fluctuations in the thermally-generated carriers in the normal

sense. Noise analysis in avalanche- type devices has been considered by

Haitz and Smits [1] who showed that two noise sources in avalanche detectors can be related to the multiplication process.

The temperature coefficient of the avalanche bias for these two

detectors was observed to be 0.1 percent/deg C for an operating temperature between 23 and 50°C. This variation of bias is acceptable for

operation of these detectors in a spacecraft.

Radiation Damage — The effect of damage of 15-keV and 22-KeV protons

on the current, capacitance, noise, and alpha-particle resolution of

100 urn thick, totally-depleted, surface-barrier detectors (Au-n-Si-Al)

operating at room temperature was studied. Four different detectors with

similar initial electrical and geometrical characteristics were irradiated, one detector for each combination of front- or rear-contact irradiation with 15- or 22-keV protons. Irradiation of the front (Au) contact

at each energy produced damage effects similar to those observed in previous studies which used higher energy protons (50- to 800-keV). The

current and noise increased with fluence, with a sharp increase in noise

occurring at fluences of about 5 x 10 13 protons/cm2

. The detector

53
SILICON NUCLEAR RADIATION DETECTORS

capacitance increased with fluence for a reverse bias of less than a few

volta, but was essentially unchanged with increasing fluence at the

normal operating bias of 50 V. The degradation of energy resolution for

monoenergetic alpha particles, incident on the front or rear contacts,

was primarily due to the noise induced by damage to the front contact.

Irradiation of the rear (Al) contact at each energy produced only

minor changes in the detector current, noise, capacitance, or energyresolution of alpha particles incident on the front (Au) contact, even for fluences of 1 x 10 16 protons/cm2

. However, in this case, the detector

energy resolution for alpha particles incident on the rear contact degraded with fluence and the spectral peak position decreased slightly

whereas the noise remained essentially unchanged. This suggests that a dead layer was formed as a result of the proton damage at the rear con- tact, thus causing degraded energy resolution due to the poor collection

of charge produced by alpha particles in that "dead" region. The presence

of a relatively large electric field associated with the surface barrier

at the front contact and the lower magnitude of fluence (by a factor of

500) may be the reasons why the dead layer effect was not observed for

the front-contact irradiations. (J. A. Coleman and Y. M. Liu)

Plans: Detectors for use in space vehicles will be tested and evaluated. Evaluation of avalanche-type detectors for use in satellites and

sounding rockets will continue with emphasis on the criterion of high

detection efficiency for low-energy protons and electrons. Low-energy

electron (<600 keV) damage effects in surface-barrier detectors will be

studied if the accelerator is available.

4.5 REFERENCES

4.1 Thermal Properties of Devices

1. M. R. P. Young and D. A. Peterman, "Reliability Engineering,"

Microelectronics and Reliability 7, 91-103 (1968).

4.4 Silicon Nuclear Radiation Detectors

1. R. H. Haitz and F. M. Smits , "Nose Analysis for a Silicon Particle

Detector with Internal Multiplication," IEEE Trans. Nucl. Sci.

NS-13 , No. 3, 198-207 (1966).

2. J. A. Coleman, D. P. Love, J. H. Trainor and D. J. Williams, "LowEnergy Proton Damage Effects in Silicon Surface-Barrier Detectors,"

IEEE Trans. Nucl, Sci. NS-15 , No. 1, 482-490 (1968); "Effects of

Damage by . 8 MeV — 5.0 MeV Protons in Silicon Surface-Barrier

Detectors," IEEE Trans. Nucl. Sci. NS-15, No. 3, 363-372 (1968).

54
Appendix A

JOINT PROGRAM STAFF

Coordinator: J. C. .French Consultant: C. P. Marsden

Semiconductor Characterization Section

Dr. W. M. Bullis, Chief

Mrs. K. 0. Leedy

Mrs. J. K. Madello"1

R. L. Mattis

Dr. W. E. Phillips

Miss T. A. Poole"1"

Miss D. R. Ricks

H. A. Schafft

A. W. Stallings

G. N. Stenbakken

H. K. Kessler W. R. Thurber

Semiconductor Processing Section

Dr. J. A. Coleman, Chief

A. J. Baroody, Jr.

D. L. Blackburn

F. H. Brewer

Mrs. E. C. Cohen*

M. Cosman

Dr J . R. Ehrstein

G. G. Harman

Mrs

.

R. E. Joel+

F. R. Kelly

B. H. Audet

H. A. Briscoe

W. K. Croll

Mrs. S. A. Davis"1"

H. E. Dyson'

-

H. A. Gitelson*

W. J. Keery

E. I. Klein

Electron Devices Section

J. C. French, Chief

Mrs. C. F. Bolton

Mrs. R. Y. Cowan

Miss B. S. Hope+

R. L Gladhill

J. M Kenney

F. F Oettinger

Part Time

Secretary

J. Krawczyk

T. F. Leedy

Y. M. Liu

Miss J. M. Morrison

J. Oroshnik

D. M. Skopik

Dr . A . H. Sher

L. M. Smith

G. P. Spurlock

M. K. Phillips

R. C. Powell*

G. J. Rogers

S. Rubin

M. Sigman

L. Williams

55
F. H W. M

J. A

J. R

J. C

APPENDIX B

STANDARDS COMMITTEE ACTIVITIES

ASTM Committee F-l; Materials for Electron Devices and Microelectronics

Brewer, Resistivity Section

Bullis , Editor, Subcommittee IV, Semiconductor Crystals

Coleman, Secretary, Subcommittee V, Semiconductor Processing Materials

Ehrstein, Epitaxial Resistivity and Epitaxial Thickness Sections

French, Chairman, Subcommittee VIII, Editorial

T. F. Leedy, Photomasking Section

J. Oroshnik, Thin Films, Thick Films, and Photomasking Sections

W. E. Phillips, Crystal Perfection, Encapsulation, Thin Films, and Thick Films Sections;

Chairman, Lifetime Section

A. H. Sher, Germanium Section

M. Sigman, Editor, Subcommittee V, Semiconductor Processing Materials

W. R. Thurber, Germanium and Impurities in Semiconductors Sections

Electronic Industries Association:

F. F. Oettinger, Associate Member, MED 32, Active Digital Circuits; TG 41.6, Thermal

Considerations, MED tl, Physical Characterization Requirements

Joint Electron Device Engineering Councils (EIA-NEMA):

J. M. Kenney, Microwave Diode Measurements, JS-3, UHF and Microwave Diodes

F. F. Oettinger, Technical Advisor on Thermal Resistance Measurements, JS-9, Low Power Transistors; Technical Advisor, JS-14, Thyristors

R. C. Powell, Microwave Diode Measurement, JS-3, UHF and Microwave Diodes; Task Group

on Transistor Scattering Parameter Measurement Standards, JS-9, Low Power Transistors.

H. A. Schafft, Consultant on Second Breakdown Specifications, JS-6, Power Transistors

IEEE Electron Devices Group:

J. M. Kenney, Chairman, Standards Committee Task Group on Microwave Solid State Devices

II (Mixer and Video Detector Diodes)

IEEE Nuclear Science Group:

J. A. Coleman, Administrative Committee; Nuclear Instruments and Detectors Committee;

Editorial Board, Transactions on Nuclear Science; Chairman, 1970 Nuclear Science

Symposium

IEEE Magnetics Group:

S. Rubin, Chairman, Galvanomagnetic Standards Subcommittee

IEC TC47, Semiconductor Devices and Integrated Circuits:

F. F. Oettinger, U. S. Experts Advisory Committee

S. Rubin, Technical Expert, Galvanomagnetic Devices

NAS-NRC Ad Hoc Panel on Radiation Detectors and Associated Circuitry:

J . A . Coleman

56
Appendix C

SOLID-STATE TECHNOLOGY AND 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. Quartz and glass fabrication — (E. I. Klein)

a. Five He-Ne gas laser tubes were rebuilt and one new tube

was constructed for the Laboratory Astrophysics Division

b. A 50-um inside diameter, thick-walled capillary discharge

tube was fabricated for the Radiation Thermometry Section.

c. Two methane adsorption cells for use with lasers were

made from quartz for the Engineering Metrology Section.

The quartz end-windows for these cells had to be aligned

and attached as precisely as those for a gas laser tube.

d. Various jobs which required special fabrication and repair

were carried out for the Instrument Shops Division and

the Engineering Metrology Section.

2. Thin films - (W. K. Croll)

A special pattern of aluminum metallization was deposited

by vacuum evaporation on plastic sheet for the Instrumentation Applications Section.

3. Radiation detectors — (B. H. Audet and A. H. Sher)

Assistance with reprocessing, testing and mounting semiconductor nuclear radiation detectors was provided for the

Nuclear Spectroscopy Section and Photonuclear Physics

Section.

4. Semiconductor crystal fabrication — (M. Cosman)

a. A silicon internal reflection element was made for the

Vacuum Measurements Section

b. A silicon crystal was cut for the Mass and Volume Section

57
Appendix D

JOINT PROGRAM PUBLICATIONS

Prior Reports :

"Methods of Measurement for Semiconductor Materials, Process Control, and Devices, Quarterly Report, July 1 to September 30, 1968," NBS

Tech. Note 472, December, 1968. (AD 681330)

^Methods of Measurement for Semiconductor Materials, Process Control, and Devices, Quarterly Report, October 1 to December 31, 1968,"

NBS Tech. Note 475, February, 1969. (AD 683808)

"Methods of Measurement for Semiconductor Materials , Process Control, and Devices, Quarterly Report, January 1 to March 31, 1969," NBS

Tech. Note 488, July, 1969. (AD 692232)

"Methods of Measurement for Semiconductor Materials, Process Control, and Devices, Quarterly Report, April 1 to June 30, 1969." NBS

Tech. Note 495, September, 1969. (AD 695820)

"Methods of Measurement for Semiconductor Materials, Process Control, and Devices, Quarterly Report, July 1 to September 30, 1969."

NBS Tech. Note 520, March, 1970.

Current Publications

A. H. Sher and W. J. Keery, "Variation of the Effective Fano Factor in

a Ge(Li) Detector," ^o appear in IEEE Trans. Nuol. Sci. 3 February, 1970.

J. L. Scales and W. M. Bullis , "Investigation of the Residual Defect in

Indium Antimonide," to be presented at American Physical Society Meeting,

Dallas, March, 1970, Bull. APS II, 15_, 280 (1970).

A. H. Sher and J. A. Coleman, "Lithium Driftability in Detector Grade

Germanium," accepted for presentation at 12th Scintillation and Semiconductor Counter Symposium, Washington, March, 1970; to appear in

IEEE Trans. Nuol. Sci. , June, 1970.

J. A. Coleman, "Material Limitations on the Performance of Semiconductor

Nuclear Radiation Detectors," accepted for presentation at 12th Scintillation and Semiconductor Counter Symposium, Washington, March, 1970; to

appear in IEEE Trans. Nuol. Sci. 3 June, 1970.

R. C. Powell, "Precision Coaxial Connectors," a chapter to be published

in Advances in Microwaves (Academic Press).

C. P. Marsden and R. Y. Cowan, "Tabulation of Data on Semiconductor

Amplifiers and Oscillators at Microwave Frequencies," NBS Tech. Note

518, February, 1970.

58


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