A111Q3 Qfi74S^

A1 11 03087459

Buehler, Martin G/Defects in PN junction QC100 .U57 NO.400-26, 1976 C.2 NBS-PUB-C

V) J

NBS SPECIAL PUBLICATION 400-26

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

:Sem icondiiclor Me.murempiil Technology:

Defects in PN Junctions

and MOS Capacitors Observed

ing Thermally Stimulated Current

ind Capacitance Measurements

.400-26

75 Videotape Script
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Semiconductor Measurement Technology:

APR 2 0

Defects in PN Junctions and MOS Capacitors Observed - ^^^'^

Using Thermally Stimulated Current and Capacitance

Measurements-Videotape Script

Martin G. Buehler

Electronic Technology Division

Institute for Applied Technology

National Bureau of Standards

Washington, D.C. 20234

no, t^OO-Q^k

This activity was supported by

The Defense Advanced Research Projects Agency and

The National Bureau of Standards

V AU.S. DEPARTMENT OF COMMERCE, Elliot L. Richardson, Secreiory

James A. Baker, III, Under Secretary

Dr. Betsy Ancker-Johnson, Assistant Secretary for Science and Technology

(J, 5 ^NATIONAL BUREAU OF STANDARDS, Ernest Ambler, Ac/mg D/recfor

Issued April 1976
Library of Congress Cataloging in Publication Data

Buehler, Martin G. Defects in PN junctions and MOS capacitors observed using

thermally stimulated current and capacitance measurements,

videotape script. (Seriiiconductor measurement technology) (NBS special publi cation ; 400-26)

Supt. of Docs, no.: 013.10:400-26

1. Semiconductors—Junctions—Defects. 2. Condensers

(Electricity)— Defects. 3. Cryostat. 4. Electric measurements.

I. Title. II. Series. III. Series: United States. National Bureau of Standards. Special publication ; 400-26. QC100.U57 no. 400-26 [TK7871.85] 602'.1 s [621 .381 5'28] 76-608059

National Bureau of Standards Special Publication 400-26

Nat. Bur. Stand. (U.S.), Spec. Publ. 400-26, 20 pages (Apr. 1976) CODEN: XNBSAV

U.S. GOVERNMENT PRINTING OFFICE

WASHINGTON: 1976

For sale by the Superintendent of Documents. U.S. Government Printing Office, Washington, D.C. 20402 (Order by SD Catalog No. C13.10:400-26). Price '.s cents. (Add 25 percent additional for other than U.S. mailing).
PREFACE

This is the script for the first in a series of videotape presentations being distributed on loan without charge in order to disseminate more effectively to the semiconductor community the measurement technology improvements developed under the Semiconductor Technology Program in the Electronic Technology Division of the National Bureau

of Standards (NBS)

.

The Semiconductor Technology Program serves to focus NBS efforts to enhance the performance, interchangeability , and reliability of discrete semiconductor devices and integrated circuits through improvements in measurement technology for use in specifying

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output by industry will contribute to higher yields, lower cost, and higher reliability

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improvements in fabrication processes and in essential device characteristics.

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iii

Semiconductor Measurement Technology:

Defects in PN Junctions and MOS Capacitors

Observed Using Thermally Stimulated Current and Capacitance Measurements

Videotape Script

by

Martin G. Buehler

T\<ro measurement methods are described which detect and characterize

defects which can control such device characteristics as lifetime and

junction leakage. The methods can be used as diagnostic tools in the

fabrication of bipolar and MOS devices. The number of different kinds

of defects and their densities may be obtained with little effort and

simple apparatus. Positive identification of these defects may be obtained with more effort and more sophisticated apparatus. Of more importance, the measurements characterize defects in an environment which

is identical to that of the finished product. Thus, the answers derived

are directly applicable to process control and device design.

These methods involve thermally stimulated capacitance and current

measurem.ents which utilize the ability of defects in the vicinity of a p-n junction or in an MOS capacitor to trap holes or electrons and emit

fi them after receiving sufficient thermal energy. Values for defect den-

! sities, energy levels, and emission rates can be derived from these

measurements. The limit of detectability can be as low as 10-^'' defects/cm^. These values provide sufficient information to positively

identify the defects.

Three vehicles are used to illustrate the methods: a gold doped

n'^-p diode, a p^-n diode with a process-induced defect center, and a gold doped n-type MOS capacitor. Two cryostats are described which

have a maximum heating rate of 10 K/s.

Key Words: Cryostat; defects; gold-doped silicon; measurement methods;

microelectronics; MOS capacitor; p-n junctions; semiconductors; silicon; thermally stimulated capacitance; thermally stimulated current.

The class of measurements that will be presented are known as thermally stimulated (000)*

^current and capacitance measurements. These measurements detect defects in the space

|icharge region of p-n junctions and MOS capacitors. The defects may be intentionally in-

[itroduced, such as gold, or they may be processed induced defects or radiation induced dejlfects. The introduction of these defects has the effect of either changing the resistivity

of silicon or of lowering its lifetime and thereby increasing the leakage currents in

junctions. The thermally stimulated current and capacitance measurements are very sensitive to the presence of defect centers, for they are able to detect as little as one defect center in a trillion silicon atoms.

The measurements presented here are for defect centers observed in silicon; however,

j.defects have been observed by these measurements in other semiconductors. Compared to

pother methods, these measurements are the most sensitive and the analysis is rapid.

In this presentation the physics of the m.easurement is discussed first, followed by

Tape counter setting

1
various practical examples, and finally the measurement apparatus is described.

The key features of the thermally stimulated current and capacitance measurements ar shown in this energy band diagram. [Figure 1] In this p-type semiconductor, acceptors

have an electron and are negatively charged. For conceptional purposes these donor defects may be thought of as the gold donor defect in p-type silicon. These defects have

an energy level, E^, close to the valence band. Defects communicate with the valence

band and conduction band through either electron capture, electron emission, hole capture, or hole emission [indicated by arrows, in Figure 1, from left to right]. Donor

defects are either positive, when a hole resides at the center, or neutral, when an electron resides at the center.

In the space-charge region the emission rates govern the charge state of the defect

center. From energy considerations the hole emission rate is much faster than the electron emission rate. Thus, the defect has no charge in the space-charge region under

steady state conditions. In the neutral region the charge state is governed by the

Fermi energy level, E^, which dictates that the defect be positively charged.

In order to detect defect centers, there must be a change in charge states between

centers in the space-charge region and those in the neutral region. This point will be

amplified later. _ • - •

Et (±) (!) g

, (Al

V o o o^o O^O^O O qO o^o o o

o o o o o" o o o

Figure 1. Emission and capture processes at a defect center

in the energy gap of a semiconductor.

The emission rate for the holes and

electrons depends on the defect energy

level. The mathematical relationship is

shown next. [Figure 2] This expression

pertains to holes or electrons depending

on whether the subscript x is p or n. The

expression indicates that the emission

rate depends on a pre-exponential B-coefficient, times the temperature T squared,

times the negative exponential of the en- ergy needed by a hole or electron to escape to its respective band edge normalized

EMISSION RATE

2

e XX= B T exp (-AE /kT) X HOLE EMISSION (x = p)

ELECTRON EMISSION (x = n)

Figure 2. Emission rate expressions
© (5 (5 (5 <i) * ©o

& Q 6 6 6 *<3o

||- P-TYPE(DONOR DEFECTS)-|

t N"^-TYPE

Figure 3. Charge state of defect centers in

n'^-p junction.

by kT, where k is the Boltzmann constant.

The nature of the measurement is illustrated next [Figure 3] by this schematic

representation of an n'^-p junction with two donor defects on the lightly doped p-type

side of the junction [defect indicated by

a star] . With zero bias applied to the

junction, the space-charge region is very

small, extending from the junction to the

dashed line [Figure 3A] . The region is

assumed to be so heavily doped that the

space-charge penetration into this region

may be neglected. In the neutral region,

the negative charge on the acceptor atoms

is neutralized by valence-band holes, and

the positive charge on the donor defects

is neutralized by conduction-band electrons.

Under zero bias the junction is now

lowered to liquid nitrogen temperature.

Now, at this temperature, a reverse bias

is applied to the junction which widens

the space-charge region as illustrated here [Figure 3B] . Valence-band holes and conduction-band electrons are removed from the space-charge region. At this temperature the

hole remains on both defect centers: the one in the space-charge region and the one in

the neutral region.

As the temperature of the junction is increased, a critical temperature is reached,

called the emission temperature, at which the hole on the defect in the space-charge

region receives sufficient thermal energy to be released to the valence band. Through

this process the defect center has changed charge state from positive to neutral and

the release of the hole constitutes a current which can be measured in an external circuit. The change in charge state means that the space-charge region must shrink so as

to maintain charge balance [indicated in Figure 3C]. This motion of the space-charge

region constitutes a change in the junction capacitance which can also be measured in

an external circuit. This example illustrates the case of the gold donor in a silicon

ri^-p junction.

Experimental results for such a junction will be shown next [with use of Figure 4]

.

The junction was first cooled to liquid nitrogen temperature. The donors were charged

with holes by zero biasing the junction. After a reverse bias of 22.5 volts was applied,

the junction was heated slowly at 0.61 kelvin per second and the current measured [Figure 4A]. The junction was again cooled to liquid nitrogen temperature and defects

charged, but this time the junction was heated at 5 kelvin per second.

(95)
KpA)

1

0

1

I 11^5.0 K/s

/ 1/0.61

100 125 150

T(K)

Figure 4. Response of a gold doped n'^-p junction.

These dynathermal or dynamic-temperature measurements indicate that hole emission

from the gold donor is heating-rate dependent, for at the slower heating rate the peak

occurs at 125 kelvin and at the higher heating rate it occurs at 134 kelvin. Because

the current response is governed by the rate at which holes are emitted per unit time,

the sensitivity of this measurement depends on the heating rate. For a high heating

rate of 10 kelvin per second it is possible with our equipment to detect 10^'^ defects/cm^

or one defect center in a trillion silicon atoms.

Next [Figure 4B] is shown the dynathermal capacitance response of the gold donor.

This step in the capacitance response is directly related to the number of gold atoms

which in this case is about 10-^ ^/cm^. Because the capacitance response is governed by

the number of the holes emitted, the magnitude of the capacitance step is not heating

rate dependent. For our equipment, defect centers are detectable if their density is

greater than one defect in five hundred background dopant atoms.

For the non mid-g'^ap defect shown here, the capacitance measurement is by far the

easier in terms of the experimental apparatus and theoretical interpretation. For

example, simple cryostats may be used, for icing is not a problem and low heating rates

may be used. However, as will be shown, the dynathermal current measurements are su- perior when evaluating mid-gap defect centers which are the source of junction leakage.

The next example is a process-induced defect center in a silicon p'^-n junction.

This defect was unintentionally introduced into the junction. It resulted from the

fabrication process. The dynathermal current and capacitance response for this defect

[Figure 5] indicates that this center has two energy levels, as indicated by the emission

processes at 150 and 225 kelvin. This example allows a comparison between the dynathermal

response of a non-mid-gap energy level and a mid-gap energy level. The non-mid-gap energy

level is initially completely full of electrons and finally completely emptied of electrons. The mid-gap energy level is initially completely full of electrons but after

the electrons have begun to be emitted, this level begins to generate both electrons
C (pF

2.92

2.84

Figure 5. Response of a p'^-n junction with

process-induced defect centers.

and holes. It is the leakage source for

the junction as indicated by the rapid rise

in the current with temperature. This

shoulder response of the dynathermal current is a key to its rapid identification.

As will be shown this response is quite

different from the gold acceptor response.

Before this center is discussed further, a limitation of the measurements is

discussed [with the use of Figure 6] . The

ability of these measurements to detect defects depends on whether the defects change

charge state. This in turn depends on the

position of the defect energy level in the

energy gap. As an example, consider an n-type semiconductor [Figure 6A] with an acceptor

defect center whose energy level is located well below mid-gap. In the neutral region,

denoted by electrons in the conduction band, the center is negatively charged. In the

space-charge region, denoted by the absence of electrons in the conduction band, the

electron sticks on the center for at reasonable temperatures the electron cannot receive

enough thermal energy to be excited to the conduction band. This defect center does not

change charge state and is therefore not detectable by these measurements.

For an energy level at mid-gap, the center is initially charged with an electron

but in its final state it acts as a generation site emitting holes and electrons [Figure

6B] . Its final charge state is governed by these emission rates which dictate its detectability

.

For an energy level above mid-gap, centers are initially fully charged with electrons

and finally fully discharged [Figure 6C]. These centers have optimum detection conditions

In summary [Figure 6D], the ability to detect defects in n-type silicon depends on

the position of the energy level of the defect center. If the energy level lies in the

lower half of the gap, then no measurement is possible (M=0) . If the level is in the

upper half of the energy gap then the measurement has the best chance of succeeding (M=l)

.

(222)

(?) (?)

Ev

INITIAL FINAL

Ef —

INITIAL FINAL INITIAL FINAL

Ec

M

A B - C D Figure 6. Measurement detectability of acceptor defect centers located at different

energy levels

.

5
If the level lies above the Fermi level, E^, detectability is poor because the center is (26

initially not charged with electrons.

The three kinds of measurement methods used to characterize defects are discussed now with respect to the process-induced defect in a silicon p'^-n junction [Figure 5].

The measurements shown here are dynathermal measurements. The emission temperature and

the heating rate are initial clues to the atomic identity of the defect center. The

emission temperature is defined by the current peak or the maximum capacitance slope.

A more definitive analysis of the emission rate, which involves the energy level determination, follows from isothermal capacitance measurements. In this measurement, made

at a fixed temperature, the capacitance time constant is determined as the capacitance

goes from its initial state to its final state. Measurements are taken at various tem- peratures and from the analysis comes both the energy level and the pre-exponentlal B- coefficient. Such measurements were used to evaluate the electron emission rate for the

150 kelvin emission process.

The emission process at 225 kelvin is a mixture of both electron and hole emission.

To evaluate these emission rates both isothermal capacitance and steady state leakage

measurements are needed. The results of such evaluations are shown next [Figure 7] for

the two emission processes. The non-mid-gap electron emission observed at 150 K is

characterized by this emission rate, [e^ = 4.1 x 10^ T^ exp (-0.23/kT)], and its energy

level is in the middle of the upper half of the energy gap. The emission process observed at 225 K is given by these electron and hole emission rates, [e^ = 3.5 x 10^ T^ exp

(-0.61/kT) and e^ = 3.4 x 10^ T^ exp (-0.55/kT)], and their energy level is near mid-gap.

The defect density, N^, for the two levels is the same within experimental error since

both emission processes are coupled to the same defect center.

T = 150 K for 3 =7.5 K/s

e e e^ = 4.1 X 103 t2 exp (-0.23/kT)

= 3.0 X 10^2 cm-3

T = 225 K for g = 4.2 K/s

e e e^ = 3.5 X 10^ T^ exp (-0.61/kT)

e^ = 3.4 X 10^ t2 exp (-0.55/kT)

= 2.9 x 10^2 cm-3

Figure 7. Emission rate expressions and defect density for the process-induced center

shown in Figure 5

.

i

I

6
200 250 300

T(K)

^ A

c

200 250 300

T(K)

B Figure 8. Response of a gold doped p'^-n junction.

The shoulder shape of the dynathermal current response is a unique signature for (311)

the process-induced defect center [Figure 5]. This shape is distinctly different from

the dynathermal current response for the gold acceptor defect in a silicon p'^-n junction

shown next [Figure 8A] . This response shows a peak and valley before it goes into steady

state leakage. This dramatically demonstrates how dynathermal current measurements can

be used to identify mid-gap defect centers. The currents shown here were measured at various heating rates. If the heating rate is slow enough, [0.17 K/s], electron emission

is difficult to detect and the current response is essentially the steady state leakage

response. The capacitance response is shown next [Figure 8B] for various heating rates.

From -this shift in characteristics the gold density was found to be about 3 percent of

the background donor density.

7
200 250 300

T(K)

c

200 250 300

T(K)

Figure 9. Response of a gold doped n-type

MOS capacitor.

The current and capacitance response for a gold doped silicon p'^-n junction is (330)

identical to the initial response of a gold doped n-type MOS capacitor. The dynathermal current response of such an MOS capacitor is shown next [Figure 9A] for various

heating rates. The phase I response has a peak and valley characteristic indicative

of the gold acceptor. This response, which is dominated by electron emission, is

scaled according to the left hand axis. In addition to phase I there is a second

phase. The phase II response, which is dominated by hole emission, is scaled according to the right hand axis. Notice that once equilibrium has been reached [at high

temperatures], no current flows through the MOS capacitor.

The phase I capacitance response is shown next [Figure 9B] and from this step in the

8
response the gold density was found to be about 4 percent of the background donor density. (345)

Once the gold center begins to act as a generation site, the capacitance begins to change

rapidly. By rescaling the capacitance response, the overall response is shown next [Fig- ure 9C] where phase I response is no longer visible. The phase II response is clearly

evident. Once the capacitance reaches equilibrium inversion, no further change is

noted. This point corresponds to cessation of current flow through the capacitor.

The physics of this measurement is ex14J 1 1<§ a &\&*<^,&*

I 6 § © o

I k<S) 6 © <S (5 ©

I

D

B

plained in the following schematic diagram

of an MOS capacitor [Figure 10] . A bias

has been applied to the metal gate so as

to invert the oxide-silicon interface represented by the hole [at the oxide-silicon

interface, Figure lOA] . A space-charge region exists free of conduction-band electrons and 'valence-band holes [from the interface to the dashed line] . This region

is followed by a neutral region. Acceptor

defects are located at three positions [indicated by stars]. This condition is established at room temperature and then the MOS

capacitor is cooled to liquid nitrogen temperature. At this low temperature the applied bias is changed so that the spacecharge region is increased [Figure lOB]

.

This gold center [middle one] has been effectively charged with an electron which

sticks since at this low temperature it

does not receive enough thermal energy to be released.

As the temperature is increased, the

electron is emitted and the space-charge

region shrinks ever so slightly in order

to maintain charge balance [Figure IOC]

.

This is the phase I response, which is dominated by electron emission.

As the temperature continues to rise, these gold defects act as generation sites

emitting electrons and holes. Emitted electrons are swept by the electric field to the

neutral region; whereas, emitted holes are swept to the oxide-silicon interface where

they increase the hole density. This is the phase II response which is dominated by hole

emission. As holes appear at the oxide-silicon interface, the space-charge region shrinks

so as to maintain charge balance. The space-charge region continues to shrink until equilibrium inversion conditions are established [Figure lOD]

.

A

I^N-TYPE (ACCEPTOR DEFECTS) -i —OXIDE

METAL

Figure 10. The charge state of defect centers

in an n-type MOS capacitor.
A brief review of the MOS capacitor dynathermal response is presented next [Figure 11]. (396)

This current response [Figure llA] illustrates the turn-on of phase I, the phase I emission temperature [T^-^], the phase II emission temperature [T^-j-j] , and final equilibrium

[zero current]. These four critical temperatures [indicated by the dashed lines] are related to the capacitance response as shown here [Figure IIB] . The phase I turn-on, the

transition between phases, and final equilibrium are related to the MOS capacitance gate

voltage characteristics [Figure IIC] . The room temperature, high frequency characteristics

are shown by the heavy line. Recalling the

measurement sequence, gate bias V^^ is first

applied at room temperature and then the

capacitor is lowered to liquid nitrogen

temperature. Gate bias V^^ then biases

the MOS capacitor into deep depletion.

With applied, the temperature is increased and during phase I, electrons are

emitted. As the temperature continues to rise, holes are pumped into the oxide-sillcon interface until the equilibrium inversion condition is achieved.

The dynathermal measurements show

great promise in being able to identify

the atomic nature of defects found in the

space-charge region of p-n junctions and

MOS capacitors. A catalog of defects might

take the following form [Figure 12]. Here

the defect energy level relative to the

appropriate band edge has been plotted with

respect to its phase I emission temperature

for a heating rate of 1 kelvin per second.

The dashed lines are related to the emission rate B-coef f icient and the heating rate. For example, the gold donor [hole emission] has an emission temperature of 128 kelvin

for a heating rate of 1 K/s; whereas, for a heating rate of 10 K/s it has a 136 kelvin

emission temperature. In addition to the process-induced defect centers and the gold

centers, radiation-induced defect centers are also shown. These centers were generated

by electron irradiation or by neutron irradiation. Some centers have the same energy

level but different B-coef ficients and thus have different emission temperatures. Other

centers have the same emission temperatures but different energy levels. If they are non-mid-gap centers, they can be identified by determining their energy levels from

isothermal capacitance measurements. If they are mid-gap centers, then the shape of

the dynathermal current response can be used to establish their identity. For example

Figure 11. A schematic representation of the

MOS capacitor response shown in Figure 9.

10
0.6

0.4

0.2

PROCESS /

:'GOLD /V.///^^

RADIATIOM /// //y^^y^

_RADIATIOP^^^^^// PROCESS

,^A^^o HOLE EMISSION (x p) ^ • ELECTRON EMISSION (x n)

100 200 300

Te,<K

Figure 12. Emission temperatures of various defect centers

in silicon for a heating rate of 1 K/s

.

recall that the process-induced defect had a shoulder response [Figure 5] whereas the

gold acceptor defect had a peak and valley response [Figure 8A]

.

The experimental apparatus used in these experiments is capable of measuring currents one hundred times less than a picoampere and of measuring capacitance changes one hundred times smaller than a picofarad at heating rates as high as 10 kelvin per second.

This is achieved in part by mounting p-n junctions or KOS capacitors on a TO-5 header.

The unit under test is m^ounted on a ceramic slab as shown here [Figure 13] . The ceramic slab is gold coated on both sides which allows easy alloying. On its top side the

gold coating is broken so that a temperature sensing diode mounted here is electrically

isolated from the unit under test. The temperature sensing diode is forward biased at

10 microamperes, and its forward voltage is proportional to the temperature.

(436)

Ceramic Slab

Temperature

Sensing Diode

nit under Test

Figure 13. Sample mounting scheme in a 10-pin TO-5 header.

11
Two experimental systems are in current use in our laboratory. The first system (A53}

[Figure 14] is capable of both dynathermal and isothermal measurements. It consists of

a liquid nitrogen reservoir with a needle valve at the bottom of the reservoir which allows the liquid nitrogen to flow around a copper thermal transfer block and out of the

cryostat. Within the copper block is a 150 watt heater. Under test conditions the TO-5

header is mounted in the hole in the copper block. The chamber is evacuated using a roughing pump. This procedure prevents icing problems. Dynathermal measurements consist

of cooling the unit under test to liquid nitrogen temperature, charging the defects

using a proper bias sequence, shutting off the liquid nitrogen, heating the copper block,

and recording the current or capacitance response.

The second and simpler system that has only dynathermal capabilities is shown here

[Figure 15]. It consists of a funnel which directs liquid nitrogen into the bellows area where the TO-5 header is mounted. The cap is raised into position and the chamber is

evacuated. The capacitance meter is located close to the apparatus to minimize lead

length. A closer view [Figure 16] reveals the TO-5 header positioned into the base of

a copper thermal transfer block. The header looks directly into the end of a 150 watt

heater which is silver soldered into the copper block. The heater leads are taken out of

the funnel and thereby shielded from the TO-5 header. This cryostat features quick loading and unloading capabilities. A dynathermal measurement can be performed in well under

10 minutes

.

In conclusion, this class of measurements reveals defects in the space-charge

region of p-n junctions and MOS capacitors if the defects can be charged and discharged.

This means that defects must lie in the mid to upper half of the energy gap in n-type

silicon, and must lie in the mid to lower half of the gap in p-type silicon. However,

this is not a handicap in that these measurements can detect mid-gap leakage centers

12
Figure -15. Close up view of cryostat number 2.

13
in both n- and p-type silicon. The detectability of the defects is one defect in a (4

trillion silicon atoms when measuring current, and when measuring capacitance it is one defect in five hundred dopant atoms. These estimates are conservative for ultimate detectable limits may be lower. Dynathermal measurements are useful in providing a quick thermal scan which reveal the variety of emission processes present and

the density of each. From a defect catalog the atomic nature can be tentatively identified. Mid-gap leakage centers that have a unique dynathermal current signature can

be readily identified. For non mid-gap centers, isothermal capacitance measurements

can be used to determine its energy level. Using a defect catalog leads to positive

identification.

In our laboratory, work is currently under way to catalog more defect centers by

intentionally doping silicon with various defect centers. In addition, work is directed

toward enhancing the usefulness of these measurements. For example, the measurements

as described here are limited in that chips must be mounted on TO-5 headers. A hot and

cold stage is under development that will allow these measurements to be made in wafer

form providing rapid feedback for process control.

The material presented here is available in various written forms. Two journal

articles [1], [2], have been published and a third is in preparation [3]. Many of the

details have been published in the NBS quarterly reports issued by the Electronic Technology Division. For these or other technical information, please contact me, Martin

Buehler, National Bureau of Standards, Building 225, Room B-346, Washington, D. C. 20234.

CREDITS

Jointly Supported by: Defense Advanced Research Projects Agency and

the National Bureau of Standards

Technical Advisors: Harry Schafft, Willie Phillips, and Kathryn Leedy

Graphics: Ray Gates and Ralph Perry

Producer: Jane Wheeler

Recorded at: HQ USAF Television Studio, June 1974.

REFERENCES

[1] Buehler, M. G., Impurity Centers in PN Junctions Determined from Shifts in the

Thermally Stimulated Current and Capacitance Response with Heating Rate, SolidState Electronios, 15, pp. 69-79, 1972.

[2] Buehler, M. G., Thermally Stimulated Measurements: The Characterization of Defects

in Silicon p-n Junctions, Semiconductor Silicon/1973 , H. R. Huff and R. R. Burgess,

Eds., (Electrochemical Society, Princeton, New Jersey 1973).

[3] Buehler, M. G., and Phillips, W. E., Gold Acceptor Observed in a Silicon p^-n Junction and a n-type MOS Capacitor by Dynathermal Capacitance and Current Measurements,

accepted for publication in Solid-State Electronics.

14
NBS-1 14A (REV. 7-73)

U.S. DEPT. OF COMM. 1. PUMLICATION OR RHPORT NO. 2. Gov't Accession BIBLIOGRAPHIC DATA ..„„ „„ ,„„ No. SHEET NBS SP 400-26

3. Recipient's Accession No.

A TITI IT 4Mr^ CI 1 n "P 11^ I I,' 4. 1 1 1 L h A N U oU o 1 1 I r. Semiaonductop Measurement Technology; Defects in PN Junctions and MOS Capacitors Observed Using Thermally

Stimulated Current and Capacitance Measurements - Videotape Script

5. Publication Date April 1976

6. Performing Organization Code

7. AUTHOR(S) .« J- • n ui Martin G. Buehler

8. Performing Organ. Report No.

9. PERFORMING ORGANIZATION NAME AND ADDRESS

NATIONAL BUREAU OF STANDARDS

DEPARTMENT OF COMMERCE

WAbnINOlUN, D.C-. 2U/o4

10. Project/Task/Work Unit No.

11. Contract/Grant No. ARPA Order 2397,

Program Code 6D10

12. Sponsoring Organization Name and Complete Address (Street, City, State, ZIP)

Defense Advanced Research Projects Agency

1400 Wilson Blvd., Arlington, VA 22209

National Bureau of Standards

Washington, DC 20234

13. Type of Report 8d Period Covered

14. Sponsoring Agency Code

15. SUPPLEMENTARY NOTES

Library of Congress Catalog Card Number: 76- 608059

16. ABSTRACT (A 200-word or less factual summary of most sigriificant information. If document includes a significant bibliography or literature survey, mention it here.) Two measurement methods are described which detect and characterize defects which

can control such device characteristics as lifetime and junction leakage. The' methods

can be used as diagnostic tools in the fabrication of bipolar and MOS devices. The

number of different kinds of defects and their densities may be obtained with little

effort and simple apparatus. Positive identification of these defects may be obtained

with more effort and more sophisticated apparatus. Of more importance, the measurements characterize defects in an environment which i§ identical to that of the finished

product. Thus, the answers derived are directly applicable to process control and

device design.

These methods involve thermally stimulated capacitance and current measurements

which utilize the ability of defects in the vicinity of a p-n junction or in an MOS

capacitor to trap holes or electrons and emit them after receiving sufficient thermal

energy. Values for defect densities, energy levels, and emission rates can be derived

from these measurements. The limit of detectabil ity can be as low as lO^o defects/cm^.

These values provide sufficient information to positively identify the defects.

Three vehicles are used to illustrate the r^'^t'^oHs: a gold doped n+-p diode, a p+-n diode with a process-induced defect center, and a gold doped n-type MOS capacitor.

Two cryostats are described which have a maximum heating rate of 10 K/s.

17. KEY WORDS (six to twelve entries; alphabetical order; capitalize only the first letter of the first key word unless a proper name; separated by semicolons) ^ i , , , .

.

Cryostat; defects; gold-doped silicon; measurement methods;

microelectronics; MOS capacitor; p-n junctions; semiconductors; silicon; thermally

stimulated capacitance; thermally stimulated current.

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I ! For Official Di stribution. Do Not Release to NTIS

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