NBS TECHNICAL NOTE

475

Methods of Measurement for Semiconductor

Materials, Process Control, and Devices

Quarterly Report

October 1 to December 31, 1968

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U.S DEPARTMENT OF COMMERCE

National Bureau of Standards

UNITED STATES DEPARTMENT OF COMMERCE

Maurice H. Stans, Secretary

NATIONAL BUREAU OF STANDARDS • A. V. Astin, Director

NBS TECHNICAL NOTE 475

ISSUED FEBRUARY 1969

Methods of Measurement for Semiconductor

Materials, Process Control, and Devices

Quarterly Report

October 1 to December 31, 1968

Edited by W. Murray Bullis

Electronic Technology Division

Institute for Applied Technology

National Bureau of Standards

Washington, D.C. 20234

Jointly Supported by

National Bureau of Standards

Defense Atomic Support Agency

U.S. Naval Ammunition Depot, Crane, Ind. and

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, Government Printing Office

Washington, D.C, 20402 - Price 45 cents

CONTENTS

PAGE

1. Introduction 1

2. Resistivity 3

3. Carrier Lifetime 5

4. Inhomogeneities 8

5. Infrared Methods 10

6. Hall Effect 11

7. Deep-Level Studies 12

8. High Field Effects 14

9. Specification of Germaniumt 15

10. Processing Facility 17

11. Metallization Evaluation 19

12. Wire Bond Evaluation 20

13. Die Attachment Evaluation 23

14. NASA Measurement Methods 24

15. Second Breakdown 25

16. Thermal Properties of Devices 26

17. Thermographic Measurements 27

18. Microwave Diode Measurements . . . * . . . . 29

19. Silicon Nuclear Radiation Detectorst 30

Appendix A. Joint Program Staff 32

Appendix B. Committee Activities 33

Appendix C. Solid-State Technology and Fabrication Services ... 34

Appendix D. Joint Program Publications 35

t Related Projects

iii
ABSTRACT

This second quarterly progress report in this series

describes NBS activities relating to: measurement of

resistivity, carrier lifetime, inhomogeneities , and Hall

effect in semiconductor crystals ; study of infrared measurement methods, properties of deep-lying impurities (in InSb),

and high field effects; establishment of a processing facility;

evaluation of aluminum metallization , wire bonds, and wafer die

attachment; review of NASA measurement methods; and measurement of second breakdown in transistors, thermal properties of

devices, and noise in microwave diodes. Projects on silicon

nuclear radiation detectors and specification of germanium are also described. Supplementary data concerning staff, committee

activities, technical services, and publications are included

as appendixes

Key Words:, carrier lifetime; die attachment; electrical

properties; germanium; metallization; methods of measurement;

microelectronics; resistivity; semiconductor devices; semiconductor materials ; semiconductor process control; silicon;

thermal resistance; thermographic measurements; wire bonds.

IV
METHODS OF MEASUREMENT FOR

SEMICONDUCTOR MATERIALS, PROCESS CONTROL, AND DEVICES

Quarterly Report

October 1 to December 31, 1968

1. INTRODUCTION

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

Program on Methods of Measurement for Semiconductor Materials, Process

Control, and Devices which is supported jointly by the National Bureau

of Standards [1], the National Aeronautics and Space Administration [2],

the Defense Atomic Support Agency [3], and the U. S. Naval Ammunition

Depot, Crane, Indiana [4]. The Joint Program was undertaken earlier

this 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 com- mon 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

This report is subdivided according to tasks which have been identified as parts of the Program. Sections 2 through 9 deal with methods

of measurement for materials; sections 10 through 14, with methods of

measurement for process control; and sections 15 through 19, with methods

of measurement for devices. Because of the cooperative nature of the

Program, there is not a one-to-one correspondence between these tasks

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 program planning.

In the first report of this series [5] background information was given for the Program and for 15 of the tasks . In this quarter work was begun on three new tasks. One of these, the task on Metallization Evaluation, had been identified during the April 1968 program review. The

other two tasks , Die Attachment Evaluation and Thermographic Measurements , evolved from the task on Thermal Properties of Devices

The objective of the task on Infrared Methods has been broadened to

include work on detection of certain impurities in silicon and germanium

by infrared absorption. This work is in support of American Society for

Testing and Materials Committee F-l on Materials for Electron Devices and

Microelectronics which is developing standards for such measurements.
Efforts on the task on Wire Bond Evaluation have been substantially

increased during this quarter. The tasks on Metallization Evaluation

and Die Attachment Evaluation were established, in part, because of the

importance of the overall bond failure problem. Program staff members

participated in several briefings related to various aspects of this

problem and Dr. J. A. Coleman attended the Fact-Finding Conference on Radiation Effects in Semiconductor Devices (sponsored by the Defense

Electronics Supply Center) at General Electric, Syracuse, New York, on November 19, 1968 and the Symposium on Transient Radiation Effects and

Techniques for Circuit Hardening (sponsored by the Defense Atomic Support Agency) at the Naval Research Laboratory, Washington, D. C, on December 9-13, 1968.

Considerable committee work was carried on during this period in

addition to items specifically mentioned in connection with various

tasks. Although there were no meetings of ASTM Committee F-l, four

documents were reviewed editorially for the committee, six were reviewed

editorially for various subcommittees, and four were reviewed informally.

Revisions were prepared for both methods for determining crystallographic

perfection of silicon by etching to extend the method to larger diameter

crystals. A manuscript on "Measurement Standards for Integrated Circuit

Processing" was prepared together with the chairman of ASTM Committee

F-l for submission to a special issue of the Proceedings of the IEEE.

At the November meeting of the Nuclear Instruments and Detectors Committee of the IEEE Nuclear Science Group a revised standard for testing

Geiger-Mueller tubes was reviewed in detail.

In addition to tasks sponsored under the Joint Program, this report

contains descriptions of activity in 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.

1. Through RTS (Research and Technical Services) Projects 4251120,

4251123, 4251126, 4252128, 4254111, 4254112, and 4254115.

2. Through Order ER- 11897, Electronics Research Center. (NBS Project

4259523)

3. Through Inter-Agency Cost Reimbursement Order 808-69. (NBS Project

4259522)

4. Through Cost Reimbursement Order P09-0016. (NBS Project 4259533)

5. "Methods of Measurement for Semiconductor Materials, Process Control,

and Devices, Quarterly Report, July 1 to September 30, 1968," NBS

Tech. Note 472, December 1968.
2. RESISTIVITY

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

Progress : The round robin based on the ASTM four-probe method [1],

which is being conducted in cooperation with ASTM Committee F-l on Materials for Electron Devices and Microelectronics, has not been com- pleted because of delays encountered at several participating organizations. Six of the nine participants in the round robin have completed

the measurements

Measurements for an F-l sponsored round robin based on a proposed

two-probe method [2] for measuring the resistivity of cylindrical silicon crystals are being made. It is necessary to take 120 measurements on each of eight crystals. A calculator program has been prepared to speed

processing of the data. About half the crystals have been measured.

(F. H. Brewer)

Preliminary results have been obtained in the study of the dependence of resistivity of silicon wafers as measured by the four-probe

method on different currents. Pronounced, though not fully consistent,

variations have been observed when the current is changed in the range

between 0.1 and 10 times the current recommended in the standard method.

Specimens with resistivity greater than 100 fi-cm showed decreasing re- sistivity with increasing current, while specimens of less than 100 fl-cm

resistivity usually showed decreasing resistivity with decreasing current.

Although there was a tendency to exhibit a constant resistivity as cur- rent was increased in the range 5 to 10 times the recommended value, a 100 °,-cm n-type specimen exhibited increasing resistivity with increasing

current in this range. A digital voltmeter has been ordered so that data

for this study can be taken more rapidly.

(F. H. Brewer and W. M. Bullis)

A series of measurements was made to try to determine how the

"forming" of the metal-semiconductor contact influences the measurement

of resistivity of epitaxial layers by the voltage-breakdown method. Results so far are inconclusive. The observation by another laboratory

that the value of resistivity measured depends on the precise details

of forming and that forming should therefore be avoided is generally

substantiated by the measurements. However on some specimens, particularly those of resistivity between 1 and 5 fi-cm, no definite breakdown

could be observed until the contact had been formed to some extent. The

reason for this necessity to form contacts in these cases is not understood.

The relation of pulse length to voltage breakdown levels was also

investigated. Indications at present are that triangular voltage pulses

should be limited to about 100 ys because of the onset of forming and the

possibility of probe and wafer deterioration at the high power levels

which accompany longer pulses.

3
An existing probe holder was modified to enable it to be used for

measurements at various points on the specimen surface, with all other

contacts remaining fixed. This probe holder also allows interchanging

high quality probes of various radii in order to evaluate the effect of

probe radius on observed breakdown voltage. Problems with mechanical

vibration of the probe at breakdown have been encountered when using

this holder and so satisfactory measurements have not yet been made.

Some measurements have been made with available pieces of silicon

carbide as breakdown probe material. It has been reported that much

more reproducible voltage breakdown values can be obtained with this

material than with most other materials [3], Available material has not

yielded satisfactory results. (J. R. Ehrstein)

Plans: After work on the two-probe resistivity round robin is

completed the study of the effect of various parameters on four-probe

resistivity values will be extended by measurements at various probe

pressures with the range of current values already used. The four-probe

measuring system will be modified to include the new digital voltmeter.

It is expected that tabulation and analysis of the data from the

four-probe round robin will be completed before the June meeting of

ASTM Committee F-l.

The experiments on the voltage-breakdown method will be continued.

Additional efforts will be made to eliminate the mechanical vibration of

the modified holder at breakdown. The availability of silicon carbide

of suitable and reproducible form and doping level for voltage breakdown

work will be investigated.

Because measurement of spreading resistance is an important and re- lated alternative to the voltage-breakdown method for measuring resistivity of epitaxial layers , the feasibility of obtaining a measurement

system for this technique will be investigated. It is expected that

such a system would be compatible with the requirements of the draft

method for measurement of resistivity by means of spreading resistance

which is now being developed by ASTM Committee F-l.

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

Probes" (ASTM Designation: F84-68T), 1968 Book of ASTM Standards,

Part 8, November 1968.

2. For a general description of the two-probe method see "Method of Test

for Resistivity of Semiconductor Materials" (ASTM Designation: F43-

67T), ibid.

3. P. A. Schumann, Jr., and A. Dupnock, "An Evaluation of Point Material for the Three-Point Probe," Electroehem. Teoh. 6, 218-219 (1968).
3. 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 meas- uring 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 : Experimental work on the determination of bulk lifetime

from filament lifetime as measured by the photoconductive decay (PCD)

method [1] was continued. A 22 ft-cm, p-type germanium specimen with

lapped surfaces was measured at its initial size of 1.0 by 1.0 by

2.15 cm. The specimen cross section was reduced and the decay time

remeasured. It was found that if the diffusion coefficient was chosen

as 101.7 cm2 /s, the computed bulk lifetime values agreed within 7 per

cent for three specimen sizes. Earlier difficulties in a similar experiment on a 4 fi-cm p-type silicon specimen are attributed to inhomogeneities within the specimen.

A mathematical analysis was made of the effect of bulk inhomogeneities on lifetime measurement by the PCD method. The specimen was first

assumed to be divided into incremental lengths with uniform lifetime

within each increment. The measured lifetime was found by averaging

over the specimen length. Second, the specimen was assumed to be com- posed of constant-lifetime parallel filaments. In both cases, the

analysis revealed that in the presence of inhomogeneities the use of

chopped light in which a steady-state non-equilibrium carrier distribution is set up prior to decay should always produce a longer measured

lifetime than the' use of light pulses which have duration smaller than

the carrier lifetime

A study of recombination models was made in the hope that PCD meas- urements could be used to identify a particular specimen with a particular model. It would be helpful for instance to be able to estimate the

density of trapping (as opposed to recombination) centers in a specimen.

It appears that this and similar information can be obtained only by

combining PCD measurements with other lifetime measurements.

A summary of the results to date is being prepared. This summary

considers the problems associated with the PCD method in three groups:

(1) effects of the surface, (2) effects of inhomogeneities, and (3) the

dependence of lifetime on excess carrier density. (R. L. Mattis)

Construction and testing of the circuitry for making voltage decay

carrier lifetime measurements on diodes was completed. A series of

measurements was made on germanium and silicon switching and zener diodes

with lifetimes in the range 5 to 80 us to compare results of carrier

lifetime measurements by the reverse recovery and voltage decay methods.

Although both are expected to yield the same result, lower values for

carrier lifetime were obtained from the voltage decay measurements. The

circuitry is being modified in an effort to eliminate the problem.
With balanced forward and reverse currents at 4.0 mA with a 1 kHz

square wave input , the reverse recovery method was shown to be capable

of measuring lifetimes as low as 1 ps, while the voltage decay method

using 10 V, 20 us pulses at a repetition rate of 4000 pulses per second

is capable of measuring lifetimes as low as 0.1 us. Other reverse re- covery circuitry now being studied is able to measure values of carrier

lifetime below 10 ns

One area of difficulty encountered during these tests was the interpretation of the graphical output of the reverse recovery measurement. A typical reverse recovery curve is shown in Fig. 1. The plateau

is used to determine the carrier lifetime. Experiments showed that the

most consistent results were obtained when the width of the plateau was taken as the time between the current zero (point A in Fig. 1) and the

beginning of the current decay (point B). (A. J. Baroody)

Low temperature steady-state photomagnetoelectric and photoconductivity (PME-PC) measurements on indium antimonide specimens revealed inconsistencies which measurements of the specimen resistance in situ

showed were due to failure of the specimen to follow the temperature

variations of the copper holder. The cause of this failure was traced

to the 0.12 mm- thick glass slide which provided electrical insulation

between specimen and holder. After the slide was replaced with a sapphire wafer the temperature differential between the specimen and holder

was reduced to a value less than the uncertainty in the temperature as measured by a thermocouple imbedded in the copper holder. Following

this modification of the apparatus, several runs were successfully com- pleted (see Section 7).

(W. E. Phillips, J. L. Scales, and A. W. Stallings)

Plans : The summary of work on the problems associated with the PCD

method will be completed.

Instrumentation modifications for the voltage decay method will be

tested. After the problems have been resolved, measurements on p-i-n

and surface barrier diodes will be started. Modifications will be made

in the circuitry used for reverse recovery measurements so that the ratio

of forward to reverse current can be varied continuously between 0.01 and

100. The dependence of the measured response time upon the frequency and

amplitude of the input square wave will also be studied.

The PME-PC equipment will be physically rearranged for convenience

in operation and consolidated with the surface photovoltage (SPV) equipment. Following this, measurements by the SPV method will be resumed.

1. "Method for Measuring the Minority-Carrier Lifetime in Bulk

Germanium and Silicon" (ASTM Designation: F28-66), 1968 Book of

ASTM Standards^ Part 8, November 1968.
Ir

Fig. 1 Typical current vs time curve for the reverse recoverymethod.
4. INHOMOGENEITIES

Objective : To develop improved methods for measuring inhomogeneities responsible for reduced performance and reliability of silicon devices and, in particular, to evaluate a photovoltaic method as a means

to accomplish this.

Progress : While a number of resistivity profile measurements made

on p-type germanium and n- and p-type silicon specimens with the photovoltaic technique did give results which agreed to within less than 1

per cent with the corresponding two-probe resistivity profile measurements, there were other cases where apparent surface effects prevented

such precision. In particular, the photovoltage in these cases changed

magnitude and sometimes even polarity with time (hours to days) and with

surface preparation. These effects produced significant changes in the

calculated resistivity profile. Attention has therefore been shifted

toward a study of the effects of surface conditions on the photovoltage

rather than methods for preparing the surface to minimize the surface

recombination velocity and thereby maximize the photoresponse from the

specimen.

Preliminary measurements on 60 fl-cm n-type silicon indicate that

at least for high resistivity material it may be possible to obtain a sufficiently large photoresponse to determine resistivity profiles

without having to etch or otherwise treat the surface of the specimens

after lapping with 5 ym alumina.

Resistivity measurements on a p-type silicon rectangular bar with

significant variations in resistivity perpendicular to its long axis

(along the width of the specimen) served to underscore the limitation of

the photovoltaic technique for such a case. Here the photovoltaic

resistivity profile along the length of the specimen differed by as much

as 3 per cent from an average of three two-point resistivity profiles

measured along three different lines on one face of the specimen.

Work on the theory of a photovoltaic method for measuring resistivity gradients along the diameter of a circular specimen was begun. The

method makes use of an ohmic contact at each end of a diameter to be

probed. These contacts are used to measure the photovoltage generated

by resistivity gradients along the diameter when probing with a small

circular spot of light.

The effect of geometry on the photovoltage as it is measured at

the ohmic contacts was calculated. In the calculation it was assumed

that a constant voltage dipole could be used to simulate the action of

the light probe in a specimen which has a constant resistivity gradient

along the measurement diameter. The solution for the photovoltage con- sists of two factors . One factor represents the potential difference

which appears at the contacts when the light probe is at the center of

the wafer. This factor is a function of the voltage dipole and therefore

is implicitly dependent on such parameters as the resistivity gradient
and the excess electron-hole pair concentration introduced by the light

probe. The other factor is a form factor in that it is essentially

dependent on the position of the light probe along the measurement diameter. This factor shows how the photovoltage , simulated by the dipole

is modified by the geometry of the specimen.

(H. A. Schafft, D. L. Blackburn, and L. J. Swart zendruber)

Plans : Measurements on p-type germanium and n- and p-type silicon

bar specimens will be continued to improve the technique. Special

emphasis will be placed on overcoming the apparent surface-induced

problems which have caused inconsistent resistivity profile measurements.

Work on the theory of a photovoltaic method for measuring resistivity gradients in circular specimens will be continued. Determination

of the resistivity gradient along the measurement diameter from photovoltage measurements will require the derivation of an expression for

the center position factor which will involve, explicitly, the resistivity gradient and the excess electron-hole pair concentration or photoconductivity. As a first approach the photovoltage generated by a resistivity gradient (non-zero only along the measurement diameter)

will be considered for the case when the light probe is located at the

center of the wafer. Because a separate measurement of the photoconductivity of the specimen will be needed, a form factor to take into ac- count the position of the light probe must be calculated theoretically

or obtained with the use of an electro-mechanical analog. One such

analog which has been considered is a metal disk with a means of altering

the resistance at points along a diameter to simulate the photoconductive

effect of the light probe. As in the semiconductor wafer, the total

resistance is determined from the potential drop between the ends of the same diameter.

The results of these calculations will be used to determine the

kind of preliminary quantitative measurements that will be made on circular specimens. If appropriate, measurements on rectangular bar

specimens where the light probe does not extend completely across the

width of the specimen, postponed this quarter, will be undertaken.
5. 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 liquid helium cryostat for the impurity photoconductivity work was received from a commercial supplier. Additional gratings

and filters to extend the wavelength range of the monochrometer system to

40 ym were ordered.

Tests were made to determine if the signal-to-noise ratio of the

double-beam spectrophotometer used for absorption measurements could be

improved by using a lock-in amplifier in place of the corresponding electronics in the spectrophotometer. No significant improvement was obtained.

The limit of detection for oxygen in germanium was determined for

the differential absorption method. In this, the most sensitive of the

various absorption procedures which can be used, the test specimen is

placed in the sample beam of the spectrophotometer, a specimen of the same thickness but without the impurity is placed in the reference beam,

and the difference in transmission (absorption) is read directly by the

instrument. A detection limit of 8 x 10 lt+ cm

-3 at room temperature and

2 x 10 lt+ cm

-3 at 20 K was found when 10-mm slices were used.

Absorption measurements were made at 78 and 300 K on three silicon

specimens containing oxygen in conjunction with a round robin being

conducted by ASTM Committee F-l. In addition to the air reference method called for in the round robin, oxygen concentration was determined by

using the procedures specified in the existing standard method [1] and

by using the differential absorption technique. (W. R. Thurber)

Plans : The equipment for low temperature photoconductivity measurements will be assembled and preliminary measurements made on germanium

specimens diffused with copper or gold. Several impurity concentrations,

verified by neutron activation analysis or other means, will be used in

these experiments.

The absorption data obtained by the various measurement methods

from the three silicon specimens described above will be analyzed. In

addition results obtained previously will be examined and the need for more work on the various methods will be considered. A value for the

ratio of the 9 ym absorption coefficient due to oxygen in silicon at 80 K

to that at 300 K will be obtained.

"Method of Test for Oxygen Content in Silicon" (ASTM Designation

F45-64T), 1968 Book of ASTM Standards,, Part 8, November 1968.

10
6. 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 : The automatic temperature control system for the Hall

effect experiment was completed, and it is now possible to measure the

Hall coefficient and resistivity of a specimen at 48 different temperatures without an operator. The output data are punched on cards which

are processed at the NBS computer facility. Programs have been written

which enable the computer to prepare a magnetic tape from which the re- sults can be machine plotted. Many plots have been made in connection

with the Deep-Level Studies (see Section 7).

(W. R. Thurber, J. L. Scales, and R. L. Gladhill)

A draft of the report which describes the coupling between the Hall

experiment and the time-shared computer system has been written in cooperation with Computer Center personnel [1],

Work on a report concerning Hall measurements and their interpretation is continuing., Emphasis has been on the relationship between

Hall coefficient and carrier concentration in gallium arsenide, silicon,

germanium, and indium antimonide. (W. R. Thurber and W. M. Bullis)

Plans : Material related to measurement and interpretation of the

Hall effect in gallium arsenide will be discussed at the January meeting

of the Optoelectronics Task Force of ASTM Committee F-l.

Experimental tests will be conducted to determine if it is practical to increase the input impedance of the automatic system by using an electrometer input. Hall coefficient and resistivity measurements will

be made on high-purity germanium specimens which have very high resistance below room temperature (see Section 9).

The two reports now being prepared will be completed.

1. W. M. Bullis, A. L. Koenig, T. N. Pyke , Jr., W. R. Thurber, and

F. H. Ulmer, "Use of a Time-Shared Computer System to Control a Hall Effect Experiment," NBS Tech. Note (in preparation).

11
7. DEEP-LEVEL STUDIES

Objective : To determine the nature and origin of the deep-lying

centers in high-resistivity indium antimonide.

Progress : Lithium diffusion experiments were performed on speci- mens of high resistivity p-type indium antimonide. The specimens became

n-type after diffusion, passed through a precipitation phase lasting

from two to three weeks, and then became p-type again as shown in Fig.

2. Analysis of Hall data gave clear indication that the untreated sam- ples had had a deep-lying donor impurity in a concentration from . 8 to

1.2 x 10 lt+ cm -3 . After lithium treatment, similar Hall measurements

showed complete absence of the donor level.

PME-PC lifetime measurements (see Section 3) were performed on both

treated and untreated specimens. With the same magnetic flux density,

sample dimensions, and light intensity in the two sets of measurements,

the electron lifetime was found to be increased by four orders of magnitude in the lithium-treated material. This was further confirmation of

the idea that lithium had neutralized the donor impurities that had been

acting as recombination centers. The lifetime of holes was increased

slightly by the lithium treatment, but the principal change was in the

variation with temperature. In untreated material, the hole lifetime

showed a pronounced decrease around 125 K. This dip was absent in the

data on treated material. (J. L. Scales)

Plans : Additional lifetime measurements will be made on treated and

untreated material. The problem of calibration of the light source will

be given further consideration. At the conclusion of these experiments

the work will be prepared for publication.

12
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precipitation. Initially and after 21 days the Hall coefficient

is negative at higher temperatures and positive below the transition point. After 1,

temperatures

and 9 days it was negative at all

13
8. HIGH FIELD EFFECTS

Objective : To study the physical characteristics of hot-carrier

semiconductor structures and relate these to performance of devices

Progress : Many silicon specimens were prepared and tested for os- cillation. These were first oxide masked and then had boron or phosphorous diffused into the contact ends. Specimens of different resistivity, carrier type, and length were prepared, each with the long axis

oriented 22° from a <100> direction on a {100} surface. Both ohmic and

junction specimens of 1 and 100 £!-cm were tested at 77 K. None oscillated. The 10 fi-cm junction specimens did oscillate at about 30 MHz,

but the amplitude of the oscillation was only 2 to 3 per cent of the d-c

current level. The orientations of several of these specimens, determined by a precision X-ray technique, were compared with the known

orientations of several specimens which had previously been shown to have

amplitudes about 10 per cent of the d-c current level. All were found

to be very close to the desired 22° so there is no obvious reason for the

variation in oscillation amplitude.

Oxide passivated specimens displayed no current change with increasing magnetic field. Therefore previously observed current changes

can be attributed to surface recombination. The oscillation threshold

and frequency did change as on the unpassivated specimens. These

changes appear to be fundamental to the oscillation phenomenon.

(G. G. Harman)

Plans : Measurements v/ill be completed on the newly prepared specimens. The effect of strong magnetic fields will be investigated, and

the exact temperature dependence of the oscillation will be studied.

14
9. SPECIFICATION OF GERMANIUM

Objective : To measure the properties of germanium crystals and

to correlate these properties with the performance of germanium gammaray detectors in order to develop methods for the early identification

of crystals suitable for fabrication into lithium-compensated gamma-ray

detectors

Progress : The data on the 50 ingots presently being examined in

this study has been transferred to punched cards. Single-crystal, ptype germanium for nuclear radiation detectors obtained from nine domestic and foreign suppliers are represented among the 50 crystals. The

summary includes data on resistivity, lifetime, dislocation density,

method of crystal growth, dopant, electron drift mobility, Hall (hole)

mobility, lithium drift mobility, oxygen concentration (as determined by

measurements of infrared absorption, lithium precipitation, and lithium

mobility), and measured characteristics of Ge(Li) detectors fabricated

from the test crystals. (A. H. Sher and H. E. Dyson)

A manuscript entitled "Lithium Ion Drift-Mobility in Germanium" was completed and submitted for publication to the Journal of Apylied Physios.

Studies of the change in capacitance of a drifting germanium p-i-n diode

as a function of time revealed a third distinct field region at the

junction which occurred at the beginning of the drifting process in addition to the linear-graded junction field normally found at early stages

in the drifting process and the uniform field normally found after charge

compensation. (A. H. Sher)

Hall coefficient and resistivity measurements were made as a function of temperature using the automated data acquisition system on two

high-purity germanium specimens grown by R. N. Hall [1]. The results

obtained from one specimen were in good agreement with those of Hall's

group. The other specimen exhibited very high contact resistance re- sulting in loading by the digital voltmeter. (W. R. Thurber)

Sufficient data has been obtained on the measurement of oxygen impurity concentration in germanium by infrared absorption, lithium precipitation, and lithium mobility [2,3] so that the range of applicability

and expected degree of agreement among the three methods can be examined.

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

The construction of a collimator capable of producing a narrow beam

of gamma-rays was completed, and the apparatus was put into use in the

testing of Ge(Li) detectors. A 15 mCi source of 137Cs (662-keV gammarays) was encased in a lead housing which acts as personnel shielding and

provides the primary collimation of the monoenergetic gamma-ray beam.

A secondary collimator produces a beam 1 mm in diameter at the aperture.

The collimator is adjustable in two perpendicular axes by means of calibrated micrometer screws so that both horizontal and vertical scans of

a Ge(Li) detector can be made. Measurements of the beam spread as a function of the distance from the aperture using dental X-ray film,

15
showed that the beam width at the center of the active region of the

detector is between 1.2 and 1.3 mm. Detector characteristics which can

be determined using such a collimator [4] include the dimensions of the

active region of the detector, hole or electron trapping lifetime, and

identification of the type of carrier, if any, being preferentially

trapped.

A Ge(Li) detector of 2 cm 3 active volume (NBS-83-2) was fabricated

for use as a reference detector for collimation measurements. Gammaray pulse height spectra have been obtained as a function of both the

applied collection field and the position of the gamma-ray beam between

the n

+-i and i-p junction boundaries, using the collimated 662-keV beam

on this detector. The data are being evaluated to determine if the

measurement of the Fano factor in germanium at 77 K is affected by the

collection of either electrons or holes separately [5]. The Fano factor

is a characteristic of the charge production process only; the results

of a measurement, however, also include trapping effects which occur during the collection of the radiation-induced charge. Therefore, this

study seeks to determine the effects of unequal charge collection on the

measurement process. (A. H. Sher and W. J. Keery)

Plans: Infrared absorption studies, impurity photoconductivity

measurements, lithium mobility studies (including effects of surface

type), and detector performance measurements with emphasis on carrier

trapping utilizing a collimated gamma-ray beam and subsequent analysis

of the peak shape will be continued. Additional Hall measurements are planned after modifications to the Hall effect system are made (see

Section 6). Manuscripts describing the results of the oxygen determination and the Fano factor studies will be prepared.

t Supported in part by the Division of .Biology and Medicine, U. S.

Atomic Energy Commission. (NBS Project 4259425)

1. AEC Contract AT (30-1) 3870, High Purity Germanium for Gamma Detectors, with General Electric Research and Development Laboratory.

2. E. M. Pell, "Study of Li-0 Interactions in Si by Ion Drift," J.

Appl. Phys. _3_!> 1048-1051 (1961).

3. R. J. Fox, "Lithium Drift Rates and Oxygen Contamination in Germanium," IEEE Trans. Nucl. Soi. NS-13 , No. 3, 367-369 (1966).

4. P. P. Webb, et. al. , "Use of Collimated Gamma-Ray Beams in the Study

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

5. A. H. Sher and B. D. Pate, "Determination of the Fano Factor in Germanium at 77 K," (Submitted to Nucl. Instr. Meth. ).

16
10. PROCESSING FACILITY

Objective : To establish a microelectronics fabrication laboratory

consisting of oxidation, diffusion, photomask ing , and contacting facilities capable of producing specialized silicon devices for use in re- search on measurement methods.

Progress : The second diffusion furnace was placed into operation

and preliminary data were obtained using a phosphine source. The end- zone temperatures were further adjusted to improve the uniformity over

the entire lengths of both diffusion furnaces. To enable the observation of any long-term trends in the tube temperature with acceptable re- solution, a digital voltmeter with a precision of 2 yV (corresponding to

a temperature uncertainty of about 0.2 degree) was set up to measure the

thermocouple voltages. This voltmeter is coupled to a card punch so that

all three temperature zones of a furnace are sampled and recorded in

rapid succession.

The thermal oxidation facility is being modified so that oxidation

may be carried out with wet or dry oxygen, or steam with a nitrogen or argon carrier gas. In wet oxygen, about four hours will be required to

grow a 1-um thick silicon oxide layer.

The deionized water distribution system was designed but estimates

of installation cost exceeded expectations . Alternate methods for obtaining high-purity water are being investigated.

(J. Oroshnik and T. F. Leedy)

A substrate heater for the vacuum evaporation station has been

built and installed. The heater operates from room temperature to some- what in excess of 600°C. Aluminum films in the range 0.3 to 1.1 urn have

been deposited on silicon at substrate temperatures of approximately

300°C. A quartz crystal thickness monitor was used to control the thickness .

A new multiple-beam interferometer has been set up in the microscopy area. This instrument is capable of measuring film thickness from

M- nm to 2 ym as well as surface roughness . A very sharp interference

pattern is obtained (see Fig. 3) and film thicknesses can be measured

with considerably greater precision than with a two-beam interferometer.

In addition the quartz crystal thickness deposition monitor can now be

calibrated periodically. Arrangements were made to obtain ellipsometric

measurements of index of refraction of silicon dioxide layers.

Sputtering activities were hampered by problems with leaks inherent

in the design of the commercially-obtained system. These problems have

been eliminated by installing a heat exchanger and redesigned flexible

tubing for the cooling system. (T. F. Leedy and W. K. Croll)

Plans : Development of diffusion techniques with diborane and phosphine will continue, with the immediate objective of reproducible

17
surface carrier concentrations and junction depths. For the present,

junction depths will be determined by the angle lapping and staining

technique. Using the junctions depths so measured, approximate surface

concentrations will be determined from sheet resistivity measurements in

conjunction with Irvin's curves [1].

Aluminum evaporations will be made on silicon and silicon dioxide

substrates in order to establish standard evaporation techniques.

Modifications will be made on the substrate heater so as to provide more

accurate temperature measurement and control.

Work will continue on establishing controlled sputtering techniques

for depositing aluminum and silicon dioxide films.

Fig. 3 Interference pattern of a 1.7 ym-thick

aluminum stripe as observed on multiplebeam interferometer.

J. C. Irvin , "Resistivity of Bulk Silicon and of Diffused Layers in

Silicon," Bell System Tech. J. 41, 387-410 (1962).

18
11. METALLIZATION EVALUATION

Objective : To improve methods for measuring the properties of thin

metal films with initial emphasis on adhesion of aluminum metallization

deposited on various substrates.

Background : The only two methods presently in use throughout the

thin film field for measuring film adherence to a substrate are the

peel (pressure sensitive tape) test, and the scratch test. Neither test

yields a well defined value for the adhesive forces between a thin film

and its substrate. It is well established that one of the more important of the many failure areas in the wire bonding system is adherence

failure of the aluminum thin film to the silicon dioxide substrate. A

clear and tangible knowledge of these adhesive forces obtained by way of

a suitable adhesion measurement should prove to be an invaluable asset

in pursuing the problem of wire bond evaluation, since connections to

semiconductor chips are all made on thin metal films

Plans: Efforts will be made to devise a scheme for measuring the

adhesive strength of thin metallic films. The object is to contrive a simple test that will yield unambiguous information, in contradistinction to the peel and scratch tests currently in use. Attention will

be focused on the adhesion of thin aluminum films deposited by vacuum evaporation or sputtering on silicon or silicon dioxide.

19
12. WIRE BOND EVALUATION

Objective : To survey and evaluate methods for characterizing wire

bond systems in semiconductor devices and, where necessary, to improve

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

those bonds which eventually will fail.

Progress : The wire bond system includes all parts of the device

which comprise the connection between the semiconductor chip and the post

or pin which leads to the outside of the package. Among the many materials involved are the semiconductor itself, oxide films, metal films,

bonding wire, and the post or pin with its plating or coating. Preliminary criteria have been established to aid in selecting reports and

papers from the vast literature which exists on the various aspects of

the system for the bibliography and review on wire bonding. Primary

emphasis is being placed on documents which describe methods for evaluating the quality of the wire bond system and for monitoring the bonding

procedure

Special efforts are being directed toward finding documents which

contain correlations between evaluation data and field or laboratory

failures to obtain information on the effectiveness of particular methods

in detecting bond systems that eventually fail. Unfortunately, however,

little such information has been found, either in documents collected or

on visits made to date. Documents with descriptions of bond evaluation

procedures, comparisons between different evaluation procedures, and

correlation between evaluation data and bonding procedures are also of

great interest.

In addition, material is being collected on procedures and techniques for making wire bonds. For the purposes of the bibliography, information relevant to all types of wire bonds (such as thermocompression

and ultrasonic) and various wire and pad materials will be sought.

The 170 papers collected during the previous quarter have been

examined and many have been discarded on the basis of the above criteria.

Other papers obtained this quarter have been added to the collection

which now numbers about 100.

An increased effort has been made to locate pertinent contract

reports where much of the latest information on the problem is believed

to reside. To this end, the bibliographic search capabilities of NASA,

the Defense Documentation Center (DDC), and the Clearinghouse for Federal

Scientific and Technical Information (CFSTI) were investigated. CFSTI

provides listings of reports based on a key word selected from a limited

number of possibilities. The term "integrated circuits" was the available key word most closely related to the wire bond problem. A listing

of reports issued since 1963 based on this key word was requested. Although a long list of documents was received, only a few were relevant

to the bond problem. A list of the unclassified work units relating to

the making and testing of wire bonds in semiconductor integrated circuits

was requested from the DoD Work Unit Data Bank maintained by DDC. NASA

20
search capabilities which were found did not appear to be more useful

for obtaining material for the bibliography than a direct search of the

cumulative subject indexes of Scientific and Technical Aerospace Reports.

The search functions of this task have been combined with those of

Die Attach Evaluation (see Section 13) in order to avoid duplication of

effort. (H. A. Schafft, K. 0. Leedy , and M. Sigman)

Visits to two organizations were made to discuss the wire bond system problem. This brings the total of such visits to twelve. The evaluation of information obtained is continuing. (H s A. Schafft)

A motor-driven bond puller has been designed and is being assembled. This puller is mounted on a bonder platform and uses the bonder

micropositioner. A mechanical dynamometer is used as the indicator.

Initially a simple hook is used to catch the bond wire, but consideration is being given to grasping the wire by other means so that the direction of pull can be controlled. Assembly of equipment and construction of test circuits for conducting burn-in screen tests based on method 1015 of MIL-STD-833 [1] have been initiated.

Aluminum has been vacuum deposited and sintered into several silicon substrates for use in connection with the study of conditions which

will produce good or bad bonds. It was decided to limit this study initially to aluminum- aluminum ultrasonic bonds because of the importance

of this bonding system in radiation-resistant devices.

Equipment for vibration tests of small devices by methods 2005 and

2007 of MIL-STD-883 [1] has been assembled and placed into operation.

This facility may be useful in detecting bonds with poor electrical con- tacts .

Further consideration has been given to the 100 per cent, non- destructive pull test incorporated directly into the bonding machine. A

possible approach to this type of test would be to mount a small counterbalanced magnetic chuck between the capillary and the wire spool.

After the bond is made , the chuck would hold the wire during a programmed ascent of the tool. When the chuck deflected a preset amount,

equivalent to 1 or 2 grams tension, electrical contact would be broken

and the chuck would release. Weak bonds would fail prior to release.

In addition, any severe defects in the wire would result in rupture.

(G. G. Harman, H. K. Kessler, and K. 0. Leedy)

Plans: About 10 more visits to government and industrial laboratories will be scheduled for next quarter as part of the field review

of the current status of wire bonding and wire bond system evaluation

procedures. Collection and review of documents for the bibliography

will continue, and the listing of work units will be examined after it

is received to locate contracts which might bear on the bond problem.

It is expected that the bibliography will be completed during the next

two quarters. Work will begin on analyzing and summarizing the information obtained from the visits made and documents collected. When this

21
is completed, a critical review of the status of the wire bond problem

will be prepared.

Assembly of the facilities for pull testing and burn-in will be

completed. Aluminum- aluminum ultrasonic bonds will be made under a variety of conditions and tested with these facilities . Facilities for

a high-current, pulse method for nondestructive bond testing will be as- sembled and preliminary tests of the method will begin. The use of aluminum wire ribbon in ultrasonic bonding will be investigated [2]. Special tungsten carbide bonding tools for ribbon wire will be designed.

1. "Test Methods and Procedures for Microelectronics," MIL-STD-883,

1 May 1968.

2. Previous experience with gold ribbon indicates that such wire produces bonds that are stronger at the heel, are more flexible in the

direction of greatest movement, and can absorb torque that would

otherwise be transmitted to the bond.

22
13. DIE ATTACHMENT EVALUATION

Objective : To evaluate methods for the detection of poor die

attachment in semiconductor devices with initial emphasis on the determination of the applicability of thermal measurements to this problem.

Background : Voids or other faults in the die attachment are a significant cause of failure in high-reliability semiconductor devices.

These faults usually increase the thermal resistance of the path between

the active area of the device and the case. Thermal resistance measurements as well as thermographic, radiographic, and metallographic techniques are presently used, in varying degrees, for the detection of poor

die attachment. The measurement of thermal resistance and the use of

radiographic techniques lend themselves to 100 per cent testing by both

supplier and user. These techniques are not extensively used but merit

further study to evaluate their applicability and reproducibility for

various types of semiconductor devices (see Section 16).

Progress : A literature search on the techniques utilized in evaluating the uniformity and quality of semiconductor device die attachment

was initiated. This search is being carried out in conjunction with the

Wire Bond Evaluation search (see Section 12).

(F. F. Oettinger and M. Sigman)

Plans: The literature search on the techniques utilized in evaluating the uniformity and quality of semiconductor device die attachment

will continue. A study of the feasibility of fabricating semiconductor

diodes with known voids will be undertaken.

23
14. NASA MEASUREMENT METHODS

Objective : To review existing semiconductor test method standards

for materials and process control measurements and to prepare interim

test methods in a standard format as may be appropriate.

Progress : Early returns of the questionnaire circulated by ASTM

Committee F-l on use and adequacy of ASTM standards for microcircuit

processing and of other test methods in the NASA compilation [1] have

been tabulated and studied. On the basis of this small sample (25) it

appears that there are several test methods which are widely accepted

and used but which have not been standardized. These include measurements of oxide thickness and stability and of photoresist processes.

The responses also tentatively identify some unsatisfactory methods on which further work is needed. These include temperature measurements of

wafers during epitaxial deposition and diffusion processes.

An interim method for measuring oxide thickness on silicon wafers

by interference measurements on a metallized step formed after etching

away part of the oxide layer is being prepared in a standard format.

This method was selected because, although it is destructive, it is

widely used and the procedures appear to be satisfactory.

(W. E. Phillips)

Plans: Analysis of the questionnaire returns will continue. Preparation of the interim method for measuring oxide thickness will be

completed.

"Test Standards for Microcircuits ," Draft of NASA-STD-XX-3 , December

1, 1968

24
15. SECOND BREAKDOWN

Objective : To maintain an awareness of progress in the field of

second breakdown and to assist both manufacturers and users of semiconductor junction devices in the development and use of meaningful specifications for maximum operating conditions free from second breakdown.

Progress : An invited paper titled "Second Breakdown in Transistors" was presented at the Second Symposium on Reliability in Electronics which was held in Budapest, Hungary, in October. In addition, the

author led a round table discussion on the same subject. (H. A. Schafft)

Plans: A first draft of a manuscript on "Failure Modes" will be

written. This will be a section in the chapter titled "Users Guide for

Power Transistors" of "Recommended Standards for Power Transistors"

which is being prepared by the JEDEC Committee JS-6 on Power Transistors,

25
16. THERMAL PROPERTIES OF DEVICES

Objective : To evaluate and, if necessary, improve measurement

techniques for determining the thermal characteristics of semiconductor

devices

Progress : The literature search and review of the -methods of meas- urement of thermal impedance of semiconductor devices were continued.

(F. F. Oettinger and M. Sigman)

The system for determining thermal resistance from measurements of

pulsed and steady-state hpE was built and is being debugged. Initial

measurements utilizing methods based on hpg and V-^g for measuring thermal

resistance indicated that further work is needed to improve the precision of the test procedures. The original temperature-controlled test

fixture is limited to an upper temperature of 75°C, making it necessary

to design a new test fixture which is capable of operating up to a temperature of 275°C in order to enable calibration of the temperature

sensitive parameter at hot-spot temperatures.

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

Plans: The literature search and review of the methods of measurement of thermal impedance of semiconductor devices will continue.

Additional modifications will be made on the hp£ and Vgg thermal

resistance measuring circuits to improve the precision of the measurement as well as to increase the maximum temperature capabilities of the

system. Transistors with selected geometries, lead configurations, and

power handling capabilities will be utilized as test specimens for both

the thermal resistance and thermographic measurements (see Section 17).

26
17. THERMOGRAPHIC MEASUREMENTS

Objective : To evaluate the utility of thermographic techniques for

detection of hot spots and measurement of temperature distribution in

semiconductor devices.

Background : The use of phosphors to display two-dimensional

temperature distributions was first reported by Urback, Nail, and

Pearlman [1]. The utility of these phosphors to determine the current or power dissipation distribution by means of the associated temperature

distribution in discrete semiconductor devices and in integrated circuits has been largely overlooked by the electronics industry. Some work

has been reported in their use as a screening tool for passive components

[2,3] as well as for making qualitative determinations of the current

distribution prior to and after the initiation of second breakdown in

transistors [2,4]. However, no serious attempts have been reported in

the literature to develop the technology for using these phosphors to

make quantitative measurements over areas comparable with those of the

active regions of semiconductor devices

To obtain a two-dimensional temperature distribution, a thin layer

of the phosphor powder is applied to the surface to be studied. The

temperature-dependent luminescence of the phosphor, which is in the

visible range, is excited by near ultra-violet radiation. The phosphors

have the property that the intensity of the luminescence will decrease

and finally quench as the temperature of the phosphors is increased.

Four phosphors are commercially available which cover a temperature range

from room temperature to about 400°C [5]. The temperature range over which a phosphor can be used can be shifted somewhat by changing the

intensity of the exciting radiation. Increasing the intensity shifts

the range to a higher temperature

With refinement in the technology for using these phosphors, the

detection of temperature differences of about 1 degree would be expected.

The average diameter of the phosphor particles is 9 um. With the

ability to apply a thin, uniform layer of phosphor it should be possible

to observe temperature distributions with a spatial resolution of 25 ym.

These two capabilities are significant especially when the relative

simplicity and low cost of the method and the advantages of measuring a visible display are all taken into consideration.

Progress : Measurements of transistor hot-spot temperature made

with thermographic phosphors have demonstrated that quantitative measurements can be made with this technique although some problems remain

to be solved. Hot spots are clearly revealed, but the intensity of the

luminescence over the metallization differs from that over the oxide

as can be seen in Fig. 4. For quantitative measurements the illuminated

phosphor was photographed on a 35-mm film strip and the density was measured point by point with a microdensitometer . The film strip was calibrated by photographing the device at various elevated temperatures

27
without power. This process is both cumbersome and time consuming, and

so it would not be suitable for routine scanning purposes.

(D. B. Brenner," G. J. Rogers, and F. F. Oettinger)

Plans : Improved methods of applying the temperature sensitive

phosphors and measuring their light output will be studied. Suitable

light intensity measuring equipment will be ordered and construction of

a test fixture initiated.

Fig. 4 A 20-watt planar transistor without its cap is shown

covered with a thin semitransparent layer of a temperature sensitive phosphor to display the temperature

distribution for different operating conditions

(a) V =20 V, I =800 mA, P=16 W

(b) V^=40 V, 1^=400 mA, P = 16 W

(c) V^= 60 V, Ip = 255 mA, P=15.3 W

The heat sink temperature is 35°C. The semiconductor

chip is approximately 1.5 mm on a side. The peak temperature in (a) is about 180°C and in (c) is about

190°C. The dark area adjacent to the chip is a scratch

in the phosphor used for orientation purposes.

* NBS Measurement Engineering Division

1. F. Urback, N. R. Nail, and D. Pearlman, "The Observation of Temperature Distributions and of Thermal Radiation by Means of Non-linear

Phosphors ," J. Opt. Soc. Am. 39_, 1011-1019 (1949).

2. H. D. Frazier, "Temperature Dependent Flourescent Paints—A Graphic

Display of Temperature Distribution," IEEE Wescon Convention Record

7_, part 3.1, 1-5 (1963).

3. J. W. Ballard, "Detection and Prediction of Malfunction of Electronic Components by Contact Thermography," Proa. National Aerospace

Electronics Conference (1964), pp. 154-163.

4. H. A. Schafft and J. C. French, "Second Breakdown and Current Distributions in Transistors," Solid-State Electronics, 9_, 681-688

(1966).

5. W. H. Byler and F. R. Hays, "Fluorescence Thermography," Nondestructive Testing 19, 177-181 (1961).

28
18. MICROWAVE DIODE MEASUREMENTS

Objective : To determine if NBS can be of service to industry and

the military in defining and resolving some of the problems associated

with measurement of the characteristics of microwave mixer diodes

Progress : Representatives of the Navy and NBS met at NBS to review

the status of microwave diode measurements. It was concluded that the

measurement of noise figure appears to require immediate attention and

that there was a misunderstanding in industry of what services are available from NBS.

At a subsequent meeting of representatives of EIA, the Naval

Applied Science Laboratory, and NBS the history of the mixer diode noise

figure measurement problem was discussed, calibration services required

and available were outlined, and measurement facilities used by industry

were examined. It was concluded that many of the needs for calibration

of gas-tube noise standards can be met by existing or soon to be available services at the NBS Boulder Laboratories , and that NBS can be of

service in three ways:

1. Continue to provide and expand measurement services for

noise sources and other basic standards,

2Thoroughly study and evaluate methods and equipment used

for testing diodes , and

3. Establish and maintain a measurement service for standard

reference diodes.

The Naval Applied Science Laboratory was visited to discuss apparatus and techniques used for noise measurement there. It was concluded

that it would be most practical for NBS with existing relevant capabilities and experience to supply the above listed services

At a meeting of JEDEC Committee JS-3 on UHF and Microwave Diodes

these conclusions were outlined and material was distributed describing

measurement services already available from NBS . The Committee con- curred with the conclusions.

A study was begun to determine the theoretical limits of the un- certainties in diode noise figure determinations made by different

laboratories with a finite number of measurements. Recent developments

in explaining uncertainties in frequency measurements appear to be applicable to measurements of noise in non-linear devices where a broad

band of frequencies is present. (R. C. Powell and G. J. Rogers)

Plans : The objectives of the present task have been met. If it is

determined that the scope of the effort should be expanded, apparatus

will be assembled for an experimental investigation of problems involved

in mixer noise measurement, the theoretical study of uncertainties will

continue, and other problems associated with measurement of mixer

characteristics will be considered.

29
19. SILICON NUCLEAR RADIATION DETECTORSt

Objective : To conduct a continuing 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 consultation and specialized device fabrication services to

the sponsor.

Progress : A platform and shroud for mounting silicon detectors

in vacuum (<10~ 9 torr) during life testing has been designed so that the

temperature of the detectors can be cycled between -20 and +50°C or be

held constant to within a few tenths of a degree within this range.

This system is being established so that static electrical parameters

and counting performance can be determined for each detector over ex- tended periods of time in order to provide a basis for predicting the

long-term stability of semiconductor detectors in space.

Two ingots of silicon with diameters of approximately 67 mm are being evaluated for use in large-area Si (Li) detectors. The resistivity of each ingot varied between 60 and 100 fi-cm over a distance of

^6 cm. Determination of carrier lifetime by the photoconductive decay

method showed two components , a short-time value of ^200 ys and a longtime value of ^2000 ys . The short-time value is typical of a normal re- combination lifetime, whereas the long-time value is an indication of

either single or multiple trapping of carriers. (B. H. Audet)

A 1.0-mm thick, silicon, surface-barrier, transmission detector was irradiated with 600-keV electrons incident on the front contact at

fluences of 10 12 to 10 16 electrons/cm2

. The detector leakage current

and capacitance, as shown in Fig. 5, and the noise and counting characteristics were determined after each increment of fluence . The counting response to alpha particles from ^^Am incident on the front con- tact decreased with increasing fluence , and the ability to detect alpha

particles through the front contact was lost after a fluence of between

1.5 x 10 13 and 1.2 x 10 lt+ electrons/cm2

. In contrast to this, the

response to alpha particles incident on the rear contact improved with

fluence until noise due to damage began to degrade the energy resolution.

(J. A. Coleman)

Plans : Construction of the detector mount and shroud for high- vacuum life testing will begin. The radial resistivity profile, oxygen

content, lithium mobility, and detector performance characteristics of

the 67-mm diameter silicon will be measured. A second 1.0-mm thick

silicon, surface-barrier, transmission detector will be irradiated with

600-keV electrons incident on the rear contact. The effects of radiation damage on the detector performance for this exposure will be com- pared with those observed for the irradiation of the front contact.

Supported by Goddard Space Flight Center, National Aeronautics and

Space Administration. (NBS Project 4254-429) Irradiations were

carried out at Goddard Space Flight Center.

30
10

<

Z

UJ

cccc3

o

i.o :-

DETECTOR 6-798

1000 /Am

1 | i 1

i i

i i J

600-keV ELECTRON FLUENCE (cm"2

) -|

(3) 1.0 XIO

16

12 HOURS ANNEAL _

(2) 1.2 XIO 14

(I) BEFORE IRRADIATION

0.1 J I L

i I I I i I L

i—

Q. o2.O

<

<

10

1.0

-2\ 600-keV ELECTRON FLUENCE (cm'") _

J I J_

(4) 17 DAYS ANNEAL

(2) 1.2 XIO 14

(I) BEFORE IRRA- _ DIATION

(3) I.0XI0 16

J L

1.0 10 io' APPLIED REVERSE BIAS (V)

io J

Fig. 5 Leakage current and capacitance of a silicon, surfacebarrier, transmission detector (1) before irradiation,

(2, 3) after irradiation with fluences as marked, and

(4) after annealing in one atmosphere of dry nitrogen

at room temperature. Normal operating bias is 150 V.

Data taken after irradiation with a fluence of about

10 12 electrons/cm2 deviated only slightly from data

taken before irradiation. Although both of these parameters tend to improve with annealing following irradiation,

the counting characteristics did not recover so rapidly.

31
Appendix A

JOINT PROGRAM STAFF

Coordinator: J. C. French

Semiconductor Characterization Semiconductor Processing Section

Section

Dr. W. M. Bullis, Chief

A. J. Baroody, Jr.

DL . Blackburn

F. H. Brewer

M. Cosman

Dr. J. R. Ehrstein

R. L. Gladhill

GG . Harman

H. K. Kessler

Mrs. K. 0. Leedy

R. L. Mattis

Dr. W. E. Phillips

J. L. Scalest

H. A. Schafft

A. W. Stallings

Dr. L. J. Swartzendruber

W. R. Thurber

Secretaries

Miss T. A. Poole

Miss R. E. Young

Dr. J. A, Coleman, Chief

* Part Time

t Guest Worker

B. H. Audet

H. A. Briscoe

W. K. Croll

H. E. Dyson*

W . J . Keery

E. I. Klein

J . Krawczyk

T. F. Leedy

J. Oroshnik

Dr. A. H. Sher

L. M. Smith

G. P. Spurlock

Secretary:

Mrs. S. W. Davis

Electron Devices Section

J. C. French, Chief

Mrs. J. K. Moffitt

F. F. Oettinger

M. K. Phillips

R. C. Powell-*

G. J. Rogers

S. Rubin

M. Sigman

L. R. Williams

Secretaries

Mrs. C. F. Bolton*

Miss B. S. Hope

32
Appendix B

COMMITTEE ACTIVITIES

ASTM Committee F-l:

F. H. Brewer, Task Force on Resistivityt

W. M. Bullis , Editor, Subcommittee IV, Semiconductor Crystals

J. A. Coleman, Secretary, Subcommittee V, Semiconductor Processing

Materials

J. R. Ehrstein, Task Forces on Epitaxial Resistivity, Epitaxial

Thickness, etc.

J. C. French, Chairman, Subcommittee VIII, Editorial

W. E. Phillips, Task Forces on Crystal Perfection, Encapsulation,

Thin and Thick Films, etc.

A. H. Sher, Task Force on Germanium

M. Sigman, Editor, Subcommittee V, Semiconductor Processing Materials

L. J. Swart zendruber, Task Force on Resistivity

W. R. Thurber, Task Forces on Conductivity Type, Impurities in

Semiconductorst , Optoelectronic Materials, etc.

Electronic Industries Association:

MED 32, Active Digital Circuits: F. F. Oettinger, TG 32.5, Thermal

Resistance Test Methods

Joint Electron Device Engineering Council (EIA-NEMA):

JS-3, UHF and Microwave Diodes: R. C. Powell, Microwave Diode

Specification Problems

JS-6, Power Transistors: H. A. Schafft , Consultant on Second

Breakdown Specifications

JS-9, Industrial Signal Transistors: F. F. Oettinger, Panel Discussion on Thermal Time Constants

JS-1M-, Thyristors: F. F. Oettinger, Thermal Resistance of SCR's

IEEE:

Nuclear Science Group, J. A. Coleman:

Administrative Committee

Nuclear Instruments and Detectors Committee

Magnetics Group, S. Rubin: Galvanomagnetic Standards Subcommittee

IEC:TC47:

S. Rubin, Galvanomagnetic Devices

NAS-NRC Semiconductor Detector Panel:

J. A. Coleman

t Participated in Round-Robin Experiments this Quarter

33
Appendix C

SOLID-STATE TECHNOLOGY £ FABRICATION SERVICES

Technology 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. Solid-state technology - (B. H. Audet)

Several Al-p-Si surface-barrier detectors are being developed and tested for use at very low temperatures by the

Nuclear Spectroscopy Section. The principal difficulty

with these detectors has been the poor adherence of con- tacts at temperatures near 4 K.

2. Quartz and glass fabrication - (E. I. Klein)

a. A graded-glass seal and semi-ball joint was added to a PbS

cell for the Radiation Thermometry Section.

b. A glass manifold was constructed and repairs were made to

several vacuum systems for the Vacuum Measurements Section.

c. Repairs were made to a variety of equipment for the Building Research Division.

d. Glass-to-kovar seals were fabricated for the Supply Division.

3. Ultrasonic fabrication - (J. Krawczyk)

Additional elements for piezoelectric device arrays were

made for the Naval Ship Research and Development Center

An attempt to produce thin-film piezoelectric elements will

be made during the next reporting period.*

NBS Project 4254431

34
Appendix D

JOINT PROGRAM PUBLICATIONS

L. J. Swart zendruber, F. H. Ulmer, and J. A. Coleman, "Direct Reading

Instrument for Silicon and Germanium Resistivity Measurements," Rev.

Sci. Instr. _39, 1858-1863 (1968).

H. A. Schafft, "Second Breakdown in Transistors," Proa. Second Symposium

on Reliability in Electronics, Budapest, (1968), pp. 225-1 to 225-14.

W. M. Bullis , "Measurement Problems in Microcircuit Processing," 1968

Government Microcircuits Applications Conference3 Digest of Papers,

pp. 215-217.

rU. S. GOVERNMENT PRINTING OFFICE : 1969 —3^1 -02i»/l05 35

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charts.

Published in three sections, available separately:

V

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'apers of interest primarily to scientists working in

"these fields. This section covers a broad range of physical and chemical research, with major emphasis

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Constants, and properties of matter. Issued six times

a year. Annual subscription: Domestic, $6.00; for- eign, $7.25*. . Mathematical Sciences

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and the applied scientist. This section includes many

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data processing, and development of test methods.

It will also cover some of the work in acoustics,

applied mechanics, building research, and cryogenic

engineering. Issued quarterly. Annual subscription:

Domestic, $2.75; foreign, $3.50*.

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