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A11103 DflVMMl

NBS SPECIAL PUBLICATION 400-24

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

National Bureau of Standards

Library, E-01 Admin, Bidg.

OCT 1 1981

131027

r Measu t Techno

A Laser Scanner for

Semiconductor Devices
NATIONAL BUREAU OF STANDARDS

The National Bureau of Standards^ was established by an act of Congress March 3, 1901. The Bureau's overall goal is to strengthen and advance the Nation's science and technology and facilitate their effective application for public benefit. To this end, the Bureau conducts research and provides: (1) a basis for the Nation's physical measurement system, (2) scientific and

technological services for industry and government, (3) a technical basis for equity in trade, and (4) technical services to pro- mote public safety. The Bureau consists of the Institute for Basic Standards, the Institute for Materials Research, the Institute for Applied Technology, the Institute for Computer Sciences and Technology, the Office for Information Programs, and the

Office of Experimental Technology Incentives Program.

THE INSTITUTE FOR BASIC STANDARDS provides the central basis within the United States of a complete and consist- ent system of physical measurement; coordinates that system with measurement systems of other nations; and furnishes essential services leading to accurate and uniform physical measurements throughout the Nation's scientific community, industry,

and commerce. The Institute consists of the Office of Measurement Services, and the following center and divisions: Applied Mathematics — Electricity — Mechanics — Heat — Optical Physics — Center for Radiation Research — Laboratory Astrophysics' — Cryogenics* — Electromagnetics' — Time and Frequency'.

THE INSTITUTE FOR MATERIALS RESEARCH conducts materials research leading to improved methods of measurement, standards, and data on the properties of well-characterized materials needed by industry, commerce, educational insti- tutions, and Government; provides advisory and research services to other Government agencies; and develops, produces, and

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and Water Measurement, and the following divisions:

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THE INSTITUTE FOR COMPUTER SCIENCES AND TECHNOLOGY conducts research and provides technical services designed to aid Government agencies in improving cost effectiveness in the conduct of their programs through the selection, acquisition, and effective utilization of automatic data processing equipment; and serves as the principal focus wthin the executive branch for the development of Federal standards for automatic data processing equipment, techniques, and computer

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THE OFFICE OF EXPERIMENTAL TECHNOLOGY INCENTIVES PROGRAM seeks to affect public policy and process

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

> Located at Boulder, Colorado 80302.
' Semiconductor Measurement Technology:

A Laser Scanner for Semiconductor Devices

David E. Sawyer and

David W. Berning

Electronic Technology Division

Institute for Applied Technology

National Bureau of Standards

Washington, D.C. 20234

Jointly supported by; The Defense Advanced Research Projects Agency

and The National Bureau of Standards

U.S. DEPARTMENT OF COMMERCE, Juanita M. Kreps, Secretary

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

\j NATIONAL BUREAU OF STANDARDS, Ernest Ambler, Acting Director

t «• Issued February 1977
Library of Congress Cataloging in Publication Data

Sawyer, David E. A laser scanner for semiconductor devices. (Semiconductor measurement technology) (National Bureau of Standards special publication ; 400-24)

Supt. ofDocs. no.: C 13.10:400-24

1. Optical scanners. 2. Lasers. 3. Semiconductors-Testing. L

Beming, David W., joint author. IL Title. IIL Series. IV. Series: United States. National Bureau of Standards. Special publication ; 400-24. QC100.U57 no. 400-24 [TK7882.S3] 602Ms [621.3815'48] 76-608408

National Bureau of Standards Special Publication 400-24

Nat. Bur. Stand. (U.S.), Spec. Publ. 400-24, 72 pages (Feb. 1977) CODEN: XNBSAV

U.S. GOVERNMENT PRINTING OFFICE

WASHINGTON: 1977

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

(Order by SD Catalog No. C13. 10:400-24). Stock No. 003-003-01739-6 Price 1.35 (Add 25 percent additional for other than U.S. mailing).
CONTENTS

Page

1. Introduction - Purpose of the Laser Scanner 2

2. Operating Mechanism at the Device Level 3

3. Principles of Operation

3.1 Optical and Mechanical Operation 4

3.2 Electrical Operation ^

4. Using the Laser Scanner

4.1 Operation of the Electronics 9

4.2 Specimen Connection 14

4.3 Magnification and Achievement of Optimum

Definition 14

4.4 Optimizing Scanning Rates 15

4.5 Getting the Picture - A Quick Guide I6

5. Optical Alinement ..... 17

6. Accessories

6.1 Radio Receiver 18

6.2 Laser Modulator 19

6.3 High Impedance Probe 19

7. Specifications 19

8. References 21

Appendix A - Commercial Equipment Used 22

Appendix B - Reimaging Lens System 23

Appendix C - Mechanical Construction 24

Appendix D - Color Monitor 27

Appendix E - Circuit Schematics 29

Appendix F - Resolution - How it is Defined 31

iii

List of Figures

Page

1. The light and signal paths of the dual-laser scanner. ... 32

2. A block diagram of the electrical interconnections for the

scanner 33

3. Mixer controls 3/^^

4. Pre-ampl i fier controls 35

5. Using the electronics to extract a small signal from a large

one. The offset control on the pre-ampl ifier is set so that

only specimen signal voltages that fall in the B region are amplified 35

6. Typical hookup of specimen to electronics ... yj

7. Hookup of specimen to electronics when an external power

supply is used 33

8. Connection of a typical integrated circuit specimen to the

scanner's electronics 3(^

9. Hookup of an integrated circuit specimen when the circuit

requires two power supplies 40

10. Specimen connection to both radio receiver and scanner's

electronics

B-1. Reimaging lens system LI 1^2

C-1. Mechanical drawing of the support frame. Dimensions are given in millimeters 1^0^

C-2. The holder for the horizontal scanning mirror H. Dimensions are given in millimeters

C-3. The holder for the two lenses making up the LI system.

Dimensions are given in millimeters 45

C-4. The holder for the vertical scanning mirror V. Dimensions

are given in millimeters 46

C-5. The bracket for holding mirror Ml. Dimensions are given

in millimeters 46

V
Page

C-6. The movable slide which holds mirrors M3 and M4. The

small item in the upper left is one of two identical mirror

mounts which are held inside the slide with thumb screws. Dimensions are given in millimeters 47

C-7. The holder for the half wave plate. The dimensions are given in millimeters i^q

C-8. The plexiglas dust cover. Dimensions are given in

millimeters

C-9. Overall view of the laser scanner ^0

C-10. Top view of the scanner showing the relative position of

most of the optical components and assemblies

C-U. Closeup of the optical deflection system. Note that the

microscope camera tube extends through a hole in the support frame ^1

C-12. Rear view of the support frame top

C-13. End view of the top of the scanner as seen from the left. . ^2

C-14. The base of the microscope with the scanner support frame.

The adjustment screws for moving the frame are visible. . . 52

C-15. Rear view of the scanner 53

C-16. Closeup of the reflected light circuit components 53

C-17. The half silvered mirror in the microscope vertical illuminator port

D-1. Schematic diagram for one of two deflection amplifiers with

power supply for the color monitor 55

D-2. Simplified schematic of high voltage portion of color

monitor 55

D-3. Schematic diagram of the video and blanking circuits for

the color monitor

E-1. Block diagram of mixer chassis

E-2. Schematic diagram of the mixer chassis 59

E-3. Block diagram of pre-ampl i fier chassis 50

vi
Page

E-4. Schematic diagram of the pre-ampl i fier 6l

E-5. Schematic diagram of the attenuator-magnifier 62

E-6. Schematic diagram of the reflected light amplifier including the germanium photodetector 62

E-7. Schematic diagram for the laser modulator 63

E-8. Schematic diagram for the high impedance probe 64

F-1. Graphical explanation of the meaning of resolution figures

quoted in the specifications section of this report 5/^

vii

A Laser Scanner for Semiconductor Devices

by

David E. Sawyer

and

David W. Berning

Abstract: This is a construction guide and

operators manual for a laser scanner built for

semiconductor device studies. A very brief discussion

of the theory of operation of the scanner is given.

The scanner's operation from a systems point of view

is described in detail with emphasis on block diagrams.

The scanner is described from a hardware point of view

with a detailed description of the function of the

various controls on the electronic equipment that was built for the laser scanner. A quick guide for the use of the scanner is given so that a person unfamiliar with

the instrument can use it effectively. Specifications

relating to the scanner's data gathering ability are also given. Mechanical drawings and circuit schematics

are given to enable others to build a similar scanner. The optics and their alignment are discussed. Various

display modes including color are discussed to enhance

operator viewing.

Key Words: Electronic reliability, electronics;

laser scanner; measurement method; mixer; optics;

pre-amplifier; radio receiver; semiconductor device

studies.

1
1. INTRODUCTION - PURPOSE OF THE LASER SCANNER

The National Bureau of Standards laser scanner is a versatile

apparatus which can be used to study photo-responsive materials and

devices on a point by point basis. The scanner is intended for specimens

that have a physical size such that they can be viewed under a typical

optical microscope and would require magnifications that are typically

achieved by such microscopes. The scanning system, by its very nature,

produces an output which is an electrical signal that can be displayed

in real time on a cathode ray tube (CRT) or which might be processed

electronically in some other manner. Specifically, the National

Bureau of Standards laser scanner was assembled to determine the usefulness and versatility of such an approach for studying semiconductor

devices such as transistors and integrated circuits, and the materials

from which these devices were made. The laser scanner is an apparatus

that is able to nondestructively map photosensitive semiconductor devices

and materials by scanning them with low power lasers. In general, the

specimen being scanned is its own detector. The scanning operation is

intended to reveal information which can be used to gain insight as to

how well a particular semiconductor device is working on a point by

point basis. The scanner can be used to locate weak points and stress

points in functioning devices, as well as failure locations on failed

devices. The scanner might also be valuable for checking semiconductor

materials for quality (1).

The scanner, like the scanning electron microscope (SEM), requires

interpretation of the displays generated. Unlike the SEM, the scanner

is completely non-destructive to the device being studied. Several

aspects of the usefulness of the scanner described in this report have

been reported in the literature. These include mapping high and low

frequency signal characteristics of transistors j spatially pin-pointing

nonuniformi ties in thermal characteristics and linearity characteristics

of transistors, revealing logic states in MOS and bipolar integrated circuits, and changing the logical state of elements in an IC (2,3,4,5,6).

Of course, an important requirement for optical scanning is that the

active areas in the device must be accessible by light and not totally

covered by metal. The trend, however, in modern device design is toward

interdigitated structures and polysilicon gates, so it is easier to obtain

scanning results now than it has been previously. In certain types of

devices, it is also possible to scan the device from the back side, thus

eliminating any problem connected with top metal coverage.

In interpreting the display, the total operation of the specimen

must be considered. For example, the information gathered by scanning

an integrated circuit is obtained by monitoring changes in power supply

current to the device, and so all the effects of photogenerating a current in a particular transistor within the IC may need to be fully

taken into account. In scanning the transistor, only a small increase

in collector current and thus power supply current would be produced

if the device were electrically isolated. However, if the scanned

transistor serves as a signal source for others, then the supply bus
signal will be a composite of the various device currents. In some

cases, the effect of scanning a portion of a device is to reduce the bus

quiescent current, and this produces a darkened region on the display

screen. While these considerations are important in explaining apparent

photoresponse signal strength and polarity, only the elements that give

a photoresponse will show in the display; so the situation is not as complicated as it may seem. Furthermore, specimens having a large

number of transistors are usually digital and small changes in current

passing through a given transistor influence few others. Even if the

scanned IC were linear rather than digital, some degree of response

isolation may be achieved automatically. For example, many linear

circuits contain negative feedback loops, and these may compensate

for perturbations introduced inside the loops.

In hopes that semiconductor device manufacturers and users would

find it desirable to have a laser scanner similar to the one developed

at the Bureau, this publication has been prepared to serve as both a construction guide and an operator's manual. Highlights in this publication include mechanical and electronic schematics, examples of uses,

and a guide to the operation of the scanner.

2. OPERATING MECHANISM AT THE DEVICE LEVEL

A moving light spot, generated by a mechanically deflected laser

beam, has the effect of generating current carriers in the semiconductor

material. In the simplest case, this can cause a current in an unbiased

junction if the light spot falls sufficiently close to the junction.

This current can be measured in an external circuit connected to the

device being scanned. As the light spot is swept across the device

being scanned, the amplitude of this current will vary as the composition

of the semiconductor device changes. This current variation is the

information that is used to present a photoresponse map of the device

being scanned. The current variations are simply amplified and fed to

a cathode ray display which is driven in synchronism with the laser scan. The information is obtained by interpreting the map produced.

The system works equally well for mapping reversed-biased junctions.

In this case the light spot, in generating carriers, causes the reverse

current to increase. This change of current can be produced in the same manner as for the non-biased junction. If a transistor biased in the

active mode is observed using the laser scanner, a change in basecollector junction current may be amplified by the transistor being

scanned to give an enhanced photoresponse map.

Another category of studies that can lend itself to observation

on the scanner is that of resistivity. In particular, a resistor in an integrated circuit can show a photoresponse when the circuit is

scanned. Again, the light spot creates carriers in the semiconductor

material, but in this case the semiconductor becomes more conductive and

the current passing through the resistor increases. For the resistor to

3
be detected on a photoresponse map of the device being scanned, the

resistor must be carrying a current. The scanner can be used to tell

how uniform a resistive area is. If the resistor is in the base circuit

of a transistor biased in its active region, this current can be amplified!

to give an enhanced photoresponse.

In FET transistors and integrated circuits the light spot can cause

an increase in the current in the channel. With proper interpretation

one can tell which transistors in MOS arrays are on and which are off.

3. PRINCIPLES OF OPERATION

3.1 Optical and Mechanical Operation

The laser scanner incorporates two low-power, continuous wave

helium-neon lasers. One of the lasers operates at a wavelength of

0.633 ym in the visible portion of the spectrum, and the other at a wavelength of 1.15 m in the near infrared. A movable slide in the

optical paths of the lasers allows the user to select which of the lasers

is to be used for a particular experiment. The chosen laser is sequentially reflected from two nodding scanning mirrors which oscillate in

orthogonal directions. The moving light spot forms a raster on the

specimen upon being directed through the camera tube of an optical

microscope (see Appendix A for a description of the microscope). The

specimen is electrically connected to a cathode ray display which is

deflected in synchronism with the scanning mirrors.

Let us examine the system in more detail. Figure 1 is a pictorial

diagram of the light and signal paths of the dual-laser scanner. The

beam from the 1.15 ym laser is deflected from M, through a half wave

plate onto Mp. The half wave plate is used to rotate the polarization

angle of the 1.15 ym radiation to maximize the intensity of the radiation

at the specimen and, more importantly, at the reflected light photodiode

(see Appendix A). The mirrors and fold the optical path to make

the scanner more compact and rugged. Mirror M2 directs the 1.15 ym laser

beam toward the first deflection mirror labeled V. The beam of the other

laser, which operates at 0.533 ym, passes through a polarizer-analyzer,

and is deflected from mirror M4 onto mirror M3. The analyzer can be

used to attenuate the beam when desired. Mirrors M4 and M3 are located

on a movable slide. When this slide is moved to the right, the beam

is reflected from M3 onto the first deflection mirror V. When the slide

is in this position the beam from the 1.15 ym laser is blocked. When

the slide is moved to the left, the 1.15 ym radiation is allowed to fail on deflection mirror V and mirrors M4 and M3 no longer direct the 0.633

beam onto V. The first deflection mirror V generates the vertical com- ponent of the scanning raster. This mirror is a commercially available

galvanometer device. This mirror is driven with a triangle waveform

through a suitable power amplifier. After the light leaves the vertical

deflection mirror V it passes through a lens system designated Li which

has the effect of focusing the vertical deflection from V onto trie

4
horizontal deflection mirror H(7,8) (see Appendix B for a complete description of the lens system represented by L^). Refocusing the vertical

deflection onto mirror H allows H to be small so that faster scanning

rates can be used. Mirror H is located at the exit-pupil point of the

microscope camera tube. The beam diverges from the horizontal mirror H to form the scanning raster. The raster is focused onto the specimen

by the microscope optics. The scan raster can cover all of the field

of view that can be seen with the eye when the microscope is used in its

usual manner. Additional details of the mechanical construction are given

in Appendix C.

The laser scanner incorporates a reflected light circuit to enable

one to obtain a map of the topography of the specimen being scanned.

This circuit makes use of a half-silvered mirror that is built into the

microscope for vertical illumination purposes when the microscope is

used in a normal manner. Some of the laser light that is reflected from

the specimen as it is scanned is collected by the microscope's objective

and subsequently reflected from the half-silvered mirror in the microscope. This light passes out of the microscope through the vertical

illuminator. In order that the microscope could retain its vertical

illumination capability, a second half-silvered mirror (not shown in

figure 1) was placed in the vertical illuminator tube (see figure C 17

in Appendix C) to direct the reflected light out of the tube and through

a lens I2 and onto a germanium photodiode. The second half-silvered

nirror makes it possible to use either the vertical illumination or the

reflected light circuit without changing any parts. The lens L2 focuses

the raster of the reflected light to a point on the photodiode. Refocusing to a point is necessary so that irregularities in the photodiode

do not distort the electrical signal obtained from that device when

the scanning mirrors V and H are driven to fairly high excursions. A

germanium photodiode was chosen over a silicon photodiode because the

germanium responds to both the 1.15 ym laser and the 0.633 ym laser.

The photocell provides an electrical signal which can be used to

obtain a spatial map of the refleatanae of the specimen being scanned

by the laser radiation. Another electrical signal can be obtained from

the specimen at the same time, and this signal is extracted by simple

electrical connections to the device being scanned. This is the photoresponse signal, and it can be used to display spatially the electrical

response of the specimen to the laser radiation. This photoresponse

signal is generally of greater importance in studying semiconductor

devices than the reflected light signal, the reflected light signal

being mainly used to identify areas on the specimen that give a photoresponse signal. Both the response signal and the reflected light

signal are generated at the same time and are thus synchronized.

3.2 Electrical Operation

Electrical signals generated within the specimen as a result of the

laser scanning the device, as well as the electrical signal developed by

the reflected light photodiode, are amplified and modulate the electron

5
beam of a cathode ray display. The electron beam of the display is , deflected horizontally and vertically at the same rates, and in synchronism to, the deflection of the scanning mirrors. A point-to-point ' correspondence is thus established between the position of the laser spot ] on the specimen and the position of the electron beam on the display. ; As the light spot and the electron beam move, the electrical signals from : the device and/or reflected-light photodiode, in modulating the electron ' beam, produce a picture of the response of the specimen on the display

screen. I

Figure 2 is a block diagram showing the important elements in the

j electrical section of the system. The mixer is the heart of the electrical system. Its signal processing capabilities include signal amplif- ; ication from up to three sources, addition and subtraction of these

' signals (mixing), and superimposing the signals onto the vertical

deflection waveform driving the display for the vertical deflection

type presentation. The mixer allows signals from the specimen and the j. reflected light photodiode to be mixed in any desired proportions so

' that a display of the specimen's photoresponse, for example, can be [ superimposed on a topological display generated by the photodiode.

Any signal, or combination of signals from the specimen can be mixed , with the deflection waveform that is used for vertical deflection of , the electron beam on the display screen. This is a display technique

which provides a picture which appears to have a three-dimensional

quality. An advantage of this presentation mode is that it allows

quantification of the specimen's photoresponse, since the deflection of [ the spot on the cathode ray tube display, as compared to a change in

spot intensity, can more easily be measured. With the mixer, either the

j conventional spot intensity modulation, or the vertical deflection modu- }' lation, or both, can be used. The mixer provides separate outputs for l each of the three channels, and each channel has a voltage gain of up to |; 50. These outputs can be used for separate processing of the signals

derived from the specimen and the reflected light circuits. For example, |l when a color display is used instead of a monochromatic display (see I Appendix D for details) different signals from the device under investi- [ gation can be displayed at the same time without losing their identity [ of origin. Even with the monocromatic display, two of these signals

can be separated by using intensity modulation for one signal, and ver- 4

tical modulation for the other. The mixer has provisions for specimen j} bias, so that a separate power supply for the specimen is often not needed,

however the pre-amplifier (shown in figure 4) has the same provision and

is usually used for this purpose. If the specimen signal is very strong

the pre-amplifier is not needed and the specimen can be connected direct- J ly to the mixer. The schematic diagrams for both the mixer and the pre- ii| amplifier are included in Appendix E along with a more detailed description of the internal circuitry.

The pre-amplifier has two channels which allow monitoring of two

different signals that might be generated by the specimen. For example, t if the specimen requires two power supplies, variations in both of these \ supplies can be displayed at the same time. The pre-amplifier has a 0

6
to 20 V power supply and a 0 to -20 V supply for specimen excitation.

There is also a selection of load resistors for each supply. The preamplifier has a variable-cutoff high-pass filter which can be used

when the specimen is noisy or has a tendency to drift. All of the circuits in both the mixer and pre-ampl ifier are dc coupled so that slow

scanning rates can be used when the specimen requires a long recovery time

from the scanning light spot. One of the channels in the pre-ampl if ier

is a special FET amplifier circuit with no loop feedback. This circuit

features very fast recovery from transients and severe overload conditions.

This feature allows an accurate observation of weak signals when strong

ones are present.

The reflected light amplifier is a very simple one which amplifies

the signal developed by the reflected light photodiode. The circuit

for this amplifier is given in Appendix E.

Two signal generators are used for the laser scanner. One generator,

designated horizontal signal generator in figure 2, provides both a square wave and a sine wave. It is used at frequencies between 10 Hz

and 1.2 kHz. This generator determines the horizontal sweep rate.

The other generator, designated vertical signal generator^ provides

both a square wave and a triangle wave, and is used at frequencies

between 0.01 Hz and 100 Hz for the frame rate. The square waves of both

generators provide the blanking signals, and are fed into the mixer

where a composite blanking signal is developed. This composite signal

is then fed to the blanking input on the display. The sinusoidal

waveform from the horizontal generator is fed directly to the horizontal

deflection amplifier in the display. This waveform is also fed to the

horizontal scanning mirror through an attenuator which serves as a picture magnifier, and thence to the scan power amplifier which drives

the mirror galvanometer assembly. Operation of the magnifier will be

discussed in section 4.3. The triangular waveform from the vertical

generator is fed to the vertical deflection amplifier in the display;

however, before it goes to the display, it first goes through the mixer

where specimen signals can be added to the vertical deflection as discussed earlier. The composite signal, consisting of the triangular

waveform, and the specimen modulation signal if any, is then fed to the

vertical deflection amplifier in the display. The triangular waveform

from this generator is also fed to the scanning mirror through a second

channel of the attenuator and its scan power amplifier.

The scanning mirrors have a resonant frequency of approximately

1 kHz and do not respond to frequencies much higher. Furthermore,

there is a substantial phase shift between the electrical signal driving

the mirror and the actual mirror movement at even 100 Hz. It is desirable

to use the fastest scanning rates possible for most specimens, simply

for viewing ease. If operation at the resonant frequency were used,

then obviously some kind of phase shift network would be needed to cause the mirror to move in step with the spot on the cathode ray

display. A convenient solution to this problem has been found, and

it is to operate the mirror slightly above resonance so as to cause

7
a 180 degree phase shift between the electrical driving signal and

the movement of the mirror. Maximum spatial linearity of the presentation is achieved either with an in-phase, or a completely out-of -phase

relationship. The picture is reversed by operating at 180 degrees

out of phase, however, the picture is linear, and the picture can be

restored to its proper perspective by simply interchanging the leads

to the scanning mirror. The 180 deg. point can be found by scanning

anything that has regularly spaced elements or markings, and using the

reflected light circuit to tune the horizontal frequency for a linear

picture. The horizontal sweep frequency is about 1.2 kHz, for the

scanning mirrors used, when the scanner is operated under these conditions.

The galvanometer responds only to the fundamental frequency when driven

at resonance, and so the horizontal generator need only furnish a simple

sinusoidal signal. A 3-or 4-Hz frame rate usually yields adequate

definition with the 1.2 kHz sweep rate. This combination gives a 300

to 400 line scan. A triangular waveform can be used for the vertical

scan because the vertical deflection galvanometer can follow this waveform at the rather slow frame frequencies. Much slower scan rates must

be used if the specimen cannot recover quickly from the photo-generated

signal. For these situations both the horizontal and vertical frequencies are dropped by one or two orders of magnitude. The vernier

frequency adjustment on the horizontal generator is usually not disturbed because of the rather critical adjustment needed for the 180

deg. phase shift at 1.2 kHz. Unfortunately, when the scanning mirror

is switched out of its 180 deg. phase shift mode to a lower frequency

operation, the display not only reverses, but the amplitude of the laser

deflection changes by approximately a factor of two. Both of these

effects are easily correctable. A switch was added to the display

to make it possible to reverse the deflection signals fed to the CRT,

thus reversing the display, and a separate attenuator in the signal path

between the horizontal generator and the main attenuator shown in figure

2 allows an amplitude correction to be made.

The attenuator shown in figure 2 serves as a display magnifier. This

attenuator simply changes the amplitude of the drive signal going to the

scanning mirrors, and thus causes a change in the raster size incident

on the specimen without changing the raster size on the display. The

display sweep signals are kept at constant amplitude. As the area on the

specimen scanned by the light spot is reduced, a magnification of the area that is being scanned occurs. The attenuator controls both the

vertical and the horizontal mirror excursions at the same time, and is ac- tuated by a rotary switch arrangement with a 2-5-10 sequence.

The scan power amplifiers shown in figure 2 are commercially available

units and were purchased with the scanning mirrors. These amplifiers are essentially audio amplifiers with dc coupling, and are capable of

delivering 5 watts into a 5 to 10 load.

8
4. USING THE LASER SCANNER

In this section the operation of the scanner will be described with

particular emphasis on the operation of the electronics that were designed

for the scanner. The mixer and pre-ampl if ier are described in detail,

however, descriptions pertaining to the operation of purchased equipment

are omitted, as these are assumed to be well known.

For many applications, the electronics of the scanner are capable

of performing all of the desired measurements on a particular device or

I specimen. Power supplies, both negative and positive, are built into

I the scanner's electronics, as well as a choice of load resistors. When

j higher voltage or current is needed to energize a particular specimen,

! external power supplies can be easily interfaced with the scanner elec-

] tronics.

4.1 Operation of the Electronics

I As pointed out previously, the mixer is the heart of the electronic

! portion of the scanner. The mixer can be used with or without the preamplifier; it will be described as if it is to be used by itself. The

j front panel of the mixer is shown in figure 3. The mixer can be divided

I into four separate sections as shown by the dashed lines in the figure.

1 The first section starting from the left, designated channel 1, contains

I the controls necessary to energize a specimen, extract the signals

i generated by the device when the laser spot is swept over it, and amplify

these signals so that they can be displayed. This channel is for specimens

I that require positive voltages for excitation when the specimen is energized with the built-in supply. The supply that is built in does not have

I to be used and this channel can simply be used as an amplifier. The

next section designated channel 2, is identical to channel 1 except that

i it contains a negative voltage supply for specimens that require a negI ative supply. Channel 3 is to the right of channel 2 and contains no power supplies. It is intended for use as just an amplifier. Signals

developed by the photodiode and amplified by the reflected light

amplifier are usually fed into this channel, although they could

, equally well go into either of the other two channels. The fourth section,

I which is on the right-hand side of the chassis, is the mixing section.

This can be subdivided into two sections. The four controls on the top

1 mix signals from the three channels with the vertical waveform used for

deflection on the cathode ray display. The use of these controls allows

the user to obtain quantitative information from the scanner, as the

specimen's response can be made to appear as a vertical displacement which

can be measured, whereas it is much more difficult to assign numbers to a

. change in spot intensity on the face of the cathode ray display. The

three controls on the bottom mix the signals from the three channels so that they can be displayed in the desired proportion by intensity modulation of the beam on the cathode ray display.

! It is useful to specifically identify the controls and describe

their function. In figure 3, the controls are labeled for the first

9
channel. The specimen is connected to the INPUT, usually by its lead

which normally receives power when the specimen is used in a circuit in

its normal function. The LOAD switch provides a choice of resistors from

330 a to 10 KQ across which the specimen signals are developed by

the scanning light spot incident on the specimen. A voltage, which is

set by the SPECIMEN SUPPLY VOLTAGE switch is fed through the chosen

load switch resistor to the specimen. This arrangement furnishes power

to the specimen as well as provides for signal detection. In addition to

providing load resistors, the load switch can be used to disconnect the

supply from the specimen if the channel is to be used as an amplifier

only. The switch is set to the OPEN position for this function. The

load switch can also connect the specimen directly to the power supply.

This function is useful if the specimen requires two supplies and obtains

all of its power by using both channel 1 and channel 2. By using two

channels on the mixer, specimen current variations caused by the light

spot can be monitored on both power supply connections to the device.

Under these conditions, it may be useful to connect one supply directly

to the specimen while the other is monitored. The load switch position

which allows this to be done is designated DIR, and in this position the

mixer is capable of furnishing about 300 mA to the specimen. When the

load resistors are used, experimentation is often the best course to

follow in determining which resistor is the best for a particular device

specimen. In general, specimens that require a greater amount of power

need a smaller load resistor in order to keep the dc voltage drop across

the resistor as small as possible. Unfortunately, a small resistor does

[ not allow much signal voltage to be developed by the specimen when the

light spot scans it. Specimens that have a strong photoresponse can

' easily produce enough signal for a good display; however, if the response

is weak, a larger load resistor may be required. The specimen i supply voltage switch may have to be reset to maintain the specimen

at its proper operating voltage if the dc drop across the load resistor ' is too high. It may be useful to monitor the specimen voltage with a

' meter (the pre-ampl ifier has this provision built in). The specimen

' voltage switch provides a choice of five voltages from 0 to 15 volts.

These voltages are approximate and should not be used to calibrate the

system. The two controls in the preceding description determine in part

' the operation of the specimen. Neither of these controls is needed if ' an external power supply is used to power the specimen. If an external J supply is used, an external load resistor will also be needed in most

applications. It is interesting to note that the load-switch setting ^ actually determines the input impedance to the amplifier and can be used

as an attenuator, if the source impedance is not too low, when the channel

is used as just an amplifier.

The remaining controls in channel 1 which are labeled in figure 3

control the operation of the amplifier portion of the channel. The

OFFSET control and the OFFSET INDICATORS are used to guide the signal

through the amplifier. The offset control compensates for the relatively

large dc voltage that is present on the specimen so that small ac signals can be amplified. The offset indicator lamps monitor the state

of the output of the amplifier and light if the amplifier is saturated

10
by either the dc or the signal. If the amplifier is being saturated

by the signal, both lamps will light, usually blinking alternately.

The lighting of only one lamp indicates that the amplifier is being

saturated by dc. If the dc level at the input is within 20 volts of

ground, either plus or minus, the offset control can be used to compensate. Compensation of the dc level, and indication that the input

signal is within acceptable limits, is shown when neither lamp is lit.

The GAIN control can be used to reduce or boost the signal level, and

should be set, along with the offset control, so that neither offset

indicator light is lit. It is still possible to overload the input

stages of the amplifier with the gain control turned all of the way down,

and so an attenuator before the specimen and the amplifier may have to be

used under certain conditions. The INVERT switch inverts the polarity

of the signal. The output of channel 1 of the mixer is available in the rear of the equipment and is designated Z, out. The output of this

channel is also fed to the mixing portion of the mixer for further

processing. The outputs of channels 2 and 3 are also available separately as well as being fed to the mixing section.

As mentioned previously, the mixing section of the mixer has two

parts. The three controls on the bottom row, labeled Z AXIS MIX-1;

Z AXIS MIX-2; and Z AXIS MIX-3, provide a means by which the outputs

from the various channels can be combined in any desired proportion and

fed to a single output jack. This output is designated MIXED Z OUT,

and is the source which modulates the intensity of the electron beam in

the display. By the use of these controls it is possible to superimpose

a reflected light image of the specimen on its own photoresponse. The

controls for unused channels should be rotated full counter clockwise

so that dc offset voltages and noise from those channels is not introduced

into the display. The four controls on the top row allow the outputs

from the three channels to be mixed with the vertical deflection waveform. The first three controls (from the left) are for the three channels

respectively, and the fourth control adds the vertical deflection waveform which is fed to the Y FUNCTION IN jack on the rear panel. This

fourth control is designated Y AXIS MIX-Y, and it can be used to adjust

the raster size in the vertical direction on the display. When no signal

vertical deflection is desired on the display, but intensity modulation

only, the first three controls labeled Y AXIS MIX-1; Y AXIS MIX-2; and

Y AXIS MIX-3, are all rotated fully counter clockwise and the fourth

control is set to some level which gives a suitable vertical height to

the raster on the display. This group of controls enables the user to

obtain quantitative information from the scanner because the signal output

from the channel or channels being used can be displayed as a vertical

deflection of the horizontal scanning lines on the display, and can

thus be measured. The output from this portion of the mixer is fed to

the Y FUNCTION OUT jack on the rear panel, and from there it goes to the

vertical input on the display. The two sections of the mixer part of

the mixer chassis are independent, and one channel's signal output can

be displayed using intensity modulation of the display screen, while

another channel's output can be displayed using the vertical modulation

technique. The identity of two separate signals from the specimen can

11
be maintained by taking advantage of the two different display present- 5 ation techniques. The identity of three separate signals from the specimen \ can be maintained by connecting the individual outputs from the three : channels to a color cathode ray display (see Appendix D) so that the ( output from each channel is presented in a different color. The pictures ! obtained from this tri-color display mode can be quite dramatic and \ revealing of specimen behavior. i

Before concluding the mixer chassis description, a few other items 1 should be discussed. The mixer incorporates the circuit for developing i the blanking signal for the display. Even though the waveforms for both 11! the vertical and the horizontal scans are symmetric, it is necessary 1 to blank the retraces for both. A small amount of phase shift between

the travel of the laser scanning mirrors and the motion of the electron i beam in the display shows up as a significant error in position of the | spot on display screen. If the screen is not blanked during retrace, then 3 two images are produced, and the result is poor definition and a confusing \ display. For the blanking function to be performed, square-wave outputs

from both the vertical and horizontal generators are fed to the HORZ IN and s VERT IN jacks on the rear of the mixer. The composite blanking signal 5 for the display is available at the BLANK OUT jack, and this is connected i to the blanking input on the display screen. A couple of voltage out- I puts are also available on the mixer. These outputs include a 12-V

output for the reflected light photo-diode and its amplifier, and plus ' and minus 25-V outputs for a high-impedance probe. i

The pre-ampl if ier is really simply an extension of the mixer with a few added features to make it suitable for lower signal level extraction. ' The pre-ampl if ier ' s features include two channels, a high-pass filter,

metered specimen supplies, continuously variable supply voltages, and a choice of FET or bipolar amplification. '

The front panel of the pre-ampl if ier is shown in figure 4. The

' pre-ampl if ier can be divided into three sections as shown by the dashed i lines. Channel 1 is used for specimen connections that use a positive

power supply in much the same manner as channel 1 on the mixer can be | used. Channel 2 is identical except that negative voltages are available. ^ The pre-ampl if ier rather than the mixer is almost always used for specimen ^ excitation and signal pick-up because the pre-ampl ifier has certain ' features that the mixer does not have. The mixer, however, is always I used as an amplifier in the system. The outputs from the pre-ampl if ier

| channels are usually fed into the inputs on the mixer and the specimen " supplies on the mixer are not used when the pre-ampl ifier is in the

system. On the pre-ampl if ier, the specimen supply voltage controls

are continuously variable instead of having fixed positions as they do ^ on the mixer. The pre-ampl if ier is also equipped with a VOLTAGE INDI- ' CATOR METER and a METER FUNCTION SWITCH for each channel, which allow ^ the voltage on either side of the specimen load resistor to be read with ' the meter. One can determine the voltage drop (the difference between ' the two meter readings) across the load resistor and calculate the specimen ^ current. This can be done easily when the FILTER switch is in some '

12
position other than dc, as the amplifier input stages draw some current

from the specimen supply when the switch is in the dc position. When

the filter switch is in the dc position, specimen current can still be

measured, but the current drawn by the input stages must be subtracted

from the total current indicated by the meter when the specimen is connected. A determination of the current drawn by the input stages can

be made by disconnecting the specimen and using the meter function switch

and the meter to determine the IR drop across the load resistor as if a specimen current was being calculated. The LOAD, OFFSET, OFFSET INDICATORS, and GAIN controls all have the same function that they ao on the mixer.

A FILTER switch is provided which affects both channels at the same time and limits the response of the pre-ampl if ier at low frequencies.

Normally, it is desirable to have the video amplification dc-coupled

since it yields a more accurate display. Furthermore, the dc coupling

is a necessity when slow scanning rates are used. However, many specimens

drift substantially, or produce large amounts of noise at low frequencies,

and it is desirable to filter this out. Another interesting feature

that the preamplifier has is an FET-BIPOLAR SELECT switch. The preamplifier has both an FET amplifier and a bipolar amplifier, so that the

type of amplifier with the most desirable characteristics for a particular

application can be used. The switch has the effect of placing the FET

amplifier on channel 1 and the bipolar amplifier on channel 2 when the

left-hand button is pushed, and placing the bipolar amplifier on channel

1 and the FET amplifier on channel 2 when the right-hand button is depressed. The maximum voltage gain of the FET amplifier is 400 while that of

the bipolar is 100.

The FET amplifier was designed primarily as a fast recovery amplifier.

It uses no negative loop feedback except when the filter is used, and then

only dc feedback. This design approach allows the amplifier to be used

in certain applications where it is driven into saturation by large

signals which obscure more important small signals. By using the offset

control it is possible to extract the desirable information by setting

a window on either the most positive or most negative part of the waveform developed by the specimen. Figure 5 helps illustrate this method

of signal extraction. The window, which is labeled B, is moved vertically by the offset control, and the width of the window is set by the

gain control. Increasing the gain has the effect of narrowing the window.

For the particular waveform illustrated, the amplifier is driven into

saturation by relatively high positive voltages in the region designated

A in the figure. If the waveform were to protrude into the region

labeled C, the amplifier would saturate there as well. Only the portions

of the waveform in the window region will be amplified. For viewing

ease, the invert switch on the mixer will be set so that the portion

of the waveform in region A will appear on the display screen as dark,

and only areas on the specimen that cause the signal to go into the B region will be displayed. For this condition of display, one of the

offset-indicator lamps will be lit or blinking on the pre-ampl if ier. It

is important that the mixer amplifier not be driven into saturation because

13
it is a conventional bipolar transistor design with negative feedback,

and it cannot recover fast enough to preserve the accuracy of the desired

portion of the signal. An output attenuator is provided on the rear

panel of the pre-ampl if ier to make it possible to reduce the amplitude

of the signal fed into the mixer. This should be used together with gain

control on the mixer because as mentioned previously, the input stages

on the mixer can be overloaded, even with the gain turned all of the

way down.

j For normal signal conditions, that is, when the pre-ampl if ier is

not driven into saturation, the FET amplifier and the bipolar amplifier

are very similar in performance. The bipolar amplifier has a slightly

better signal to noise ratio, and its lower gain is often an advantage.

4.2 Specimen Connection

It is useful to look at some examples of how specimens are connected

to the electronics. Figure 6 shows one way that a transistor can be

connected to either the pre-ampl if ier or the mixer. A simplified portion

of the electronics that is built into both the mixer and the pre-ampl ifier

is shown so that it can be seen how the specimen obtains power and how I the signal is picked off of the power supply line. It is usually

desirable to vary the bias on the device under observation, and this may

be accomplished with an external power supply. The specimen must be I placed under the scanning light spot so that it is as level as possible

to obtain uniform focus on the chip area. Many specimens are sensitive

to room light, and the lights should be kept dim, particularly if they are of the fluorescent type, as the line frequency modulation of the room light is readily transformed into a modulation of the specimen signal

by the specimen. Figure 7 shows a typical connection when it is desirable i to power the device under observation entirely with external supplies.

For this application the load switch should be set to the highest load

position or to the " open " position on the mixer. If the external supply

used is a high-voltage unit, the specimen signal voltage entering the ] mixer or pre-ampl ifier should be blocked with a capacitor or divided

with a resistive network to keep high voltages out of the pre-amplifier

or mixer. Alternatively, for the example shown in figure 7, the specimen

signal can be picked off across the emitter resistor. Figure 8 shows a typical scheme for energizing and scanning an integrated circuit. The ^ power supply lead for the device is connected to the pre-amplifier and " powered by it. The inputs and outputs on the integrated circuit are ' connected as necessary to make the circuit function in its normal manner.

A typical specimen connection for a device requiring dual power supplies

is shown in figure 9. It is often desirable to terminate the inputs to

a high-gain 1 inear device with low resistances, otherwise a very large ? signal is obtained from the input transistors.

4.3 Magnification and Achievement of Optimum Definition ^

The optimum definition, that is, the maximum number of distinct ' objects that can be seen on the display, is obtained by setting the '

14
attenuator that controls the scanning mirror excursion so that the mirrors

have the largest excursion without the light raster being vignetted by

the microscope optics. These conditions are best satisfied by setting the

attenuator on 1000 ym regardless of which microscope objective is used.

This 1000 ym position is calibrated so that the raster size on the specimen

will be 1000 ym x 1000 ym when the 8X objective is used in the microscope.

By switching the attenuator to the 500 ym position, the magnification

is doubled. The picture definition is degraded however because of the non-zero spot size. The preferred method for changing the magnification

is to change microscope objectives. It is important to remember that the

markings on the attenuator are referenced to the 8X objective, and if a 16X objective is substituted for the 8X objective, and the attenuator is

set on the 1000 ym position, then the raster size on the specimen will be

500 ym x 500 ym. The attenuator is of course very useful for electronically

magnifying a portion of the specimen and measuring particular portions. An

additional item that must be noted is that the markings on the attenuator

are valid for the normal, 1.2 kHz horizontal and 3 to 4 Hz vertical

scanning rates because, as previously described, the horizontal scanning

mirror is operated slightly beyond resonance so that decreasing the scanning rate changes the amplitude of the excursion of that mirror.

4.4 Optimizing Scanning Rates

In general it may be best to use the fastest scanning rates that the

scanning mirrors will allow because it is important that a picture of the

specimen is produced in the shortest possible time. This reduces the

effects of drift in the specimen or electronics and is particularly

appropriate when the display is being photographed. The fast scanning

rates also make it easier to view the display in real time, especially

the color display because fast-decay phosphors are used.

Many specimens have carrier storage effects which make it necessary

to use slower scanning rates to maintain resolution. Situations where

these storage problems occur are usual ly made apparent by blurring of

vertical lines in the image. Solar cells are particularly susceptible

to these storage problems. On certain specimens there is a strong

dependence on the storage time and bias. Increases in reverse bias

voltage on the specimen usually shorten this storage time. As mentioned

in the section of this report dealing with the principle of operation

of the scanner, the horizontal scanning mirror normally is operated

beyond resonance at 1.2 kHz. It was also stated that reducing

the horizontal scanning rates not only changes the magnification in the

horizontal direction, but also reverses the picture in such a way that

the left-hand side of the picture becomes the right-hand side and vice

versa. It must also be remembered that the 1.2 kHz is the frequency

where picture linearity is obtained by virtue of 180 deg. out of phase

operation between the mirror movement and the electron beam movement in

the display. When the scanning rates are changed to slower ones, usually

only the frequency multiplier knob on the horizontal generator is

disturbed because of the rather fine tuning required to find the 180

deg. phase shift needed for picture linearity. Thus sweep rates of 1.2

15
kHz, 120 Hz, or 12 Hz are usually used. The vertical generator for the

frame rate can be set to any frequency.

4.5 Getting the Picture - A Quick Guide

Presented below is a list of the steps that can be taken to obtain

a monocromatic picture of a particular specimen as quickly as possible.

1. Energize scanner with main power switch.

2. Set knobs on the MIXER, from the left-hand side of the unit, as follows:

a. Channel 1 OFFSET - any position

b. INVERT switch - either up or down

c. GAIN - 9 o'clock

d. VOLTAGE switch - GND

e. LOAD - 10k

f. Channel 2 controls - same as channel 1 controls

g. Channel 3 (reflected light) GAIN - 3 o'clock

h. INVERT - up

i. OFFSET - so that both offset indicator lights are extinguished

j. Y-AXIS MIX 1, 2, and 3 - full counter-clockwise

k. Y-AXIS MIX-Y - 2 o'clock

1. Z-AXIS MIX 1,2, and 3 - full counter-clockwise

3. Set knobs on the PRE-AMPLIFIER, from the left-hand side of the unit,

as follows:

a. METER - SUP

b. OFFSET - any position

c. +SUPPLY - full counter-clockwise

d. LOAD - 3.3k

e. GAIN - 9 o'clock

f. CUT OFF - 10 Hz

g. FET - BIPOLAR select switch - either position

h. Channel 2 controls - same as channel 1 controls

i. Attenuator controls on rear of unit - 12 o'clock

4. Set brightness on display so that a dim raster can be seen.

5. Set Magnifier/Attenuator on 1000 ym

6. Install 8X objective in microscope.

7. Place specimen on microscope stage.

8. Use figures 6 through 9 in this report as a guide and connect the

specimen to the input of the pre-ampl if ier - use channel 1 for those

devices that require a positive supply, and channel 2 for those devices

that require a negative supply.

9. Connect the output of channel 1 of the pre-ampl if ier to the input

of channel 1 on the mixer. Do the same for channel 2 of both units.

10. Set the movable slide in the microscope so that the laser is blocked

and the eyepiece is activated, energize the lamp in the vertical

illuminator, and focus the microscope onto the specimen.

11. Reset the prism slide so that it allows the laser to impinge on the specimen, and turn off the illuminator.

12. See that the scanner is working by using the reflected light signal.

Rotate the Z AXIS MIX-3 control clockwise to obtain a reflected

light image of the specimen. Adjust the offset control to extinguish

the offset indicators to compensate for drift if necessary.

16
13. Set the SUPPLY voltage control on the channel being used to the

desired operating voltage for the specimen.

14. The METER switch can be set on SAM so that the actual voltage on the specimen is monitored. If the specimen is a transistor, changing

the bias (figure 6) will cause this voltage to change. If the

specimen is an integrated circuit, it may be desirable to change

the load switch to select a smaller resistor so that there is less

voltage drop across the load. It may also be desirable to increase

the voltage to compensate for the drop.

15. Adjust the OFFSET control on the pre-ampl if ier of the channel being

used so that both offset lamps are extinguished. If both lamps cannot be extinguished, reduce the gain so that both lamps can be

extinguished with the offset control.

16. Adjust the OFFSET control on the mixer for the channel being used.

Follow the same procedure as above. It may be necessary to reduce

the gain on the pre-ampl if ier further to avoid overloading the

input stages of the mixer.

17. Rotate the Z-AXIS MIX l(or 2 if channel 2 is used) clockwise to

obtain a display of the photo response of the specimen. It may

be necessary to increase the gain on one or both of the units.

Remember that there are also attenuators on the rear of the preampl if ier.

18. The photo-response image can be superimposed on the reflected

light picture by using the Z-AXIS MIX knobs as desired. The YAXIS MIX controls can be used to obtain the vertical deflection

type display.

If the color display is to be used, the OFFSET on each of the three

channels controls the level of the three primary colors, red, blue,

and green. The Z-AXIS MIX and the Y-AXIS MIX controls are not used.

5. OPTICAL ALINEMENT

Optical alinement should be performed to some extent when the scanner is moved, when a laser is changed, or when the scanner is

subjected to excessive vibration. The following is a complete listing

of the steps for alinement of a new instrument; many of these steps

can be omitted for realinement purposes.

*CAUTION: Care must be exercised to avoid having either the infrared

laser radiation or the visible laser light reflected into

the eye . 1. All power to the scanner should be off. Set the mirrors, both the

stationary ones and the scanning mirrors, to their approximate

positions needed to cause the laser radiation from the infrared

laser to be deflected down the camera tube of the microscope. Use

figure 1 as a guide to the deflection sequence.

2. Energize only the vertical illuminator lamp in the microscope.

Adjust the four screws at the base of the scanner which set the

height of the scanner mainframe relative to the microscope and

microscope stand. The screws should be adjusted so that the camera

tube passes through the center of the hole in the top of the scanner

frame. The screws must also be adjusted so that the light from

17
the vertical illuminator comes to a point on the scanning mirror

directly above the camera tube. The prism in the microscope must

be set so that the light passes through the camera tube and not to

the eyepieces.

3. Turn off the vertical illuminator lamp and energize the infrared

laser. Using an IR phosphor card, guide the infrared laser radiation through the optical system and through the microscope by

adjustment of the mirrors. Aim the radiation down the center of the camera tube. Slightly adjust the screws at the base of the scanner

so that the radiation passes through the center of the microscope

optics onto the stage.

4. Activate the visible laser and move the slide which changes the

laser sources to the position that blocks the infrared laser. Adjust

the position of the two mirrors on this slide so that the visible

light beam follows the same path as the infrared light beam from the

scanning mirrors and through the microscope. Do not disturb any other

adjustments. By switching back and forth between the two lasers, make

the spot from the two lasers hit the microscope stage at the same point.

5. Turn on the generators and the scanning mirror drivers. Set the

magnifier so that the scanning mirrors have large enough excursions

so that the raster formed on the microscope stage by either laser

has some of its corners cut off. Adjust the screws at the base

of the scanner so that all four corners of the raster are equally

cut off - that is, center the raster. Lock the adjustment screws

at the base of the scanner.

6. Adjust the half-silvered mirror and lens in the reflected-1 ight

circuit so that the raster degenerates to a point on the active

area of the photo diode.

7. Energize the remainder of the electronics and adjust the x/2 plate

to maximize the output from the reflected light circuit when the

infrared laser is used.

6. ACCESSORIES

6.1 Radio Receiver

A specimen's response to VHP and UHF frequencies can be conveniently studied with the use of a radio receiver in place of one preamplifier channel in the scanning system \^)\^K The lasers are self

modulated due to their basic principles of operation, and the visible

laser used in the NBS system has useful modulation components at 0.5

GHz and 1.0 GHz, while the near infrared laser has useful components

at 385 MHz and 770 MHz. The laser spot effectively embeds a signal

generator in the specimen which has both a dc component and a highfrequency component. The dc component gives the conventional display

results; however, when a radio receiver is connected to the specimen,

a map of the response of the device at the laser modulation frequency

may be obtained. The radio receiver is tuned to either of the two

useful modulation frequencies for the laser being used. Figure 10

shows a typical hook up for a specimen so that both the video information and the high frequency information can be contracted at the
same time. The output from the radio receiver is fed into an unused

channel in the mixer for display.

6.2 Laser Modulator

As an extension to the radio receiver concept, a dc to 100 kHz

laser modulator was added to the system. The modulator is capable

of at least a 10% depth of modulation. The modulator permits the

response of the specimen to be studied at frequencies up to 100 kHz;

however, much longer scanning times must be used as the signal bandwidth is limited. A lock-in amplifier can be substituted for the

radio receiver to detect the desired signal (l^^). The circuit for the

modulator is given in Appendix E.

6.3 High Impedance Probe

Certain applications in optical scanning require the use of a high-impedance probe to minimize disturbance of the scanned specimen.

Such a probe is shown schematically in Appendix E. The probe features

dc coupling and can pass signals riding on dc voltages when these dc

voltages are as high as 20 V and as low as -20 V. The probe loads

the circuit being measured with 3.1 pF at 1 MHz and 22 Mfi at dc. The

probe obtains its operating power from the mixer.

7. SPECIFICATIONS

1. Optical radiation sources

a. 0.6328 ym He-Ne laser

3 mW power output at 0.6328 ym, polarized

Lowest axial mode modulation frequency: 500 MHz

External modulator: dc to 100 kHz at 10% depth of modulation

b. 1.15 ym He-Ne laser:

2 mW power output at 1.15 ym, polarized

Lowest axial mode modulation frequency: 385 MHz

2. Optical power at the specimen (approximate)

a. 0.6328 ym laser, referenced to 3 mW

with 4x objective, 0.3 mW; NA = 0.1

with 8x objective, 0.36 mW; NA = 0.2

with 16x objective, 0.16 mW; NA = 0.35

with 40x objective, 0.15 mW; NA = 0.6

b. 1.15 ym laser, referenced to 2 mW

with 4x objective, 0.12 mW

with 8x objective, 0.15 mW

with 16x objective, 0.15 mW

with 40x objective, 0.10 mW

3. Resolution (This is a measure of the system's ability to separate

closely-spaced features and it varies both with the laser wavelength and microscope objective chosen. Appendix F describes in

detail how the following resolution values were obtained and defined).

A = 0.6328 ym; 40 x objective;

2 ym spaced lines yield 30% resolution.

19
A = 1.15 ym; 40 X objective;

2 ym spaced lines yield 18% resolution.

X = 0.6328 ym; 16 x objective;

3.12 ym spaced lines yield 30% resolution.

X = 1.15 ym; 16 x objective;

4 ym spaced lines yield 13% resolution.

A = 0.6328 ym; 8 x objective;

4 ym spaced lines yield 13% resolution.

A = 1.15 ym; 8 X objective;

8 ym spaced lines yield 10% resolution.

A = 0.6328 ym; 4 X objective;

16 ym spaced lines yield 50% resolution.

A = 1.15 ym; 4 X objective;

16 ym spaced lines yield 13% resolution.

4. Scanning rates

a. horizontal

3 mHz to 100 Hz without incurring significant distortion, and

1.2 kHz

b. vertical

3 mHz to 100 Hz

5. Mixer specifications

dc to 2 MHz frequency response

up to 34 dB gain on each channel

0, 3, 5, 12, 15 V specimen bias

0, -3, -5, -12, -15 V specimen bias

0 fi, 330 1 kfi, 3.3 kn, 10 kft specimen loads

+_ 20 V offset compensation

input impedance 100 kn maximum

output impedance <250 on all signal outputs

6. Pre-ampl ifier specifications

dc to 2 MHz frequency response

up to 52 dB gain FET fast recovery channel

up to 40 dB gain channel

0 to 20 V specimen bias

0 to -20 V specimen bias

0 n, 330 fi, 1 k^, 3.3 kfi loads for specimen

+ 12 V offset compensation at full gain setting (compensation

range increases from this as gain is reduced)

input impedance 3.3 kn maximum

output impedance 3.5 k^^ maximum

20
8. REFERENCES

1. DiStefano, T. H. , Photoemission and Photovoltaic Imaging of Semiconductor Surfaces, in Semioonduatov Measurement Teahnology : ARPA/NBS

Workshop IV. Surface Analysis for Silicon Devices, A. G. Lieberman,

ed., NBS Special Publication 400-23 (March 1976) pp. 197-209.

2. Sawyer, D. E., and Berning, D. W. , Laser Scanning of Active Semiconductor Devices, Technical Digest, 1975 International Electron Devices

Meeting, Washington, D.C., December 1-3, 1975, pp. 111-114.

3. Sawyer, D. E. , and Berning, D. W. , Laser Scanning of MOS IC's Reveals

Internal Logic States Nondestructi vely , Proa. IEEE 64, 393-394 March

(1976).

4. Sawyer^ D, E. , and Berning, D. W. , Mapping Nonl ineari ties Over the

Active Regions of Semiconductor Devices, Fvoa. IEEE 64, 1635-1637

November (1976)

.

5. Sawyer, D. E. , and Berning, D. W. , Thermal Mapping of Transistors With

a Laser Scanner, Pvoa. IEEE 6^, 1634-1635 November (1976).

6. Sawyer, D. E., and Berning, D. W. , Semiaonduotor Measurement Technology:

Laser Scanning of Active Semiconductor Devices: Videotape Script, NBS

Special Publication 400-27 (February 1976).

7. Beiser, L. , Laser Beam Scan Enhancement through Periodic Aperture

Transfer, Applied Optics 7_, 647-650 (1968).

8. Langberg, E. , Lincoln Laboratory, MIT, (private communication). The

operation of a Scanner Employing the Refocusing Technique has been

described by R. E. McMahon: Laser Tests IC's with light touch,

Electronics 44, 92-95 (1971).

9. Potter, C. N., and Sawyer, D. E. , A Flying-Spot Scanner, Bev. Sci.

Instrum. 39, 180-183 (1968).

10. Levy, M. E., Imaging LSI Microcircuits with Optical Spot Scanners,

Report No. P76-39, prepared for the National Aeronautics and Space

Administration under Contract No. NA58-31239 by Hughes Aircraft Co.,

January 1976.

21
APPENDIX A

Commercial Equipment Used

This section contains a list of the commercial equipment that

was used to build the scanner. The equipment was selected with the

aim that the scanner should be extremely versatile.

1. Microscope Equipment

a. Binocular microscope suitable for use with polarized

light; including camera tube, vertical illuminator port,

and prism slide to change optical paths between specimen

and camera tube. The microscope has a large stage travel

and a large working distance.

b. 12. 5X eyepiece oculars.

c. 4X(NA=0.1), 8X(NA=0.2), 16X(NA=0. 35) , and 40X(NA=0.6)

objectives.

d. lOX camera tube ocular.

2. Signal Generators

a. Waveforms: Sine, square, and triangle, ramp, and sync

pulse, available simultaneously.

b. Frequency: 0.005 Hz to 1 MHz.

c. Output impedance: 600 u or lower.

3. Lasers

a. 0.633 ym, 3 mW cw HeNe, noise less than 2%.

b. 0.633 ym, 5 mW cw HeNe, noise less than 2%, mirrors changed

to cause it to operate at 1.15 ym.

4. Analyzer

Rotatable polarizing optical component.

5. Half-Wave Plate

Mica-between-glass type for 1.15 ym radiation.

6. Monochromatic Display

a. Bandwidth: dc to 20 MHz on X, Y, and Z inputs.

b. Digital dc blanking, blanked +5 V, unblanked -5 V.

7. Scanning Mirrors and Amplifier Systems

a. Gal vanometric type nodding mirrors.

b. Frequency response dc to 1 kHz.

22
APPENDIX B

Reimaging Lens System

The reimaging lens system which is placed between the vertical and

horizontal scanning mirrors must refocus the laser beam deflection

from the vertical scanning mirror to a point on the horizontal scanning

mirror. This is done so that this mirror can be made small for relatively fast scanning rates. As the laser radiation leaves the horizontal

scanning mirror, it emerges as a beam deflected in both the vertical and

horizontal directions. An additional requirement of the lens system

is that the laser radiation impinging on the second scanning mirror

must consist of parallel light rays. To satisfy these requirements

two lenses back-to-back are used between the vertical and horizontal

deflection mirrors^'''^) to form the composite lens system LI. The

distance between the vertical deflection mirror and the first principal plane of the first lens is made equal to the focal length fi,

and the distance between the first principal plane of the second Tens

and the horizontal deflection mirror is made equal to f2, the focal

length of the second lens. The separation between the second principal

planes of the two lenses is set equal to f^ + f2. The characteristics

of the lenses used were:

f;^ = 50 mm

f number = 2

and

f2 = 25 mm

f number = 1.4

Both are TV camera lenses. Figure Bl shows the two lenses

and the scanning mirrors. The vertical scanning mirror is on the left.

23
APPENDIX C

Mechanical Construction

The scanner is designed to be compact, rugged and portable. All

equipment required to operate the scanner in any of its services is

easily contained on a 2 by 1 meter work bench. It was not found necessary to shock-mount the scanner, or choose a special location to ensure

freedom from perturbing influences such as building vibration. The

purpose of this appendix is to present enough information on the

mechanical design and construction of the scanner so that others may

also build scanners with these desirable attributes.

A heavy-duty microscope stand serves as the mounting support for

all the mechanical items. Most of the scanner components are attached

to a rigid, reinforced frame bolted to the stand. With this construction,

the entire apparatus tends to move in unison in response to outside

mechanical influences, and this minimizes blurring of the scanner images

by unwanted deflection of the laser spot on the scanned specimen.

In the figures which follow, all dimensions are in millimeters

and, unless noted otherwise, the construction material is aluminum.

Figures CI - C8 are mechanical drawings of the scanner and the location

of the items to be described subsequently can be inferred from the

photos in figures C9 - C17.

Figure CI shows the support frame. The vertical dimension indicated as 435 mm is tailored to the particular microscope used so that

the axis of the horizontal scanning mirror is at the exit pupil point

of the microscope camera tube. In general, the mounting holes will vary

with the particular choice of the vendor selected to provide items

such as lenses and galvanometer deflectors. These choices will also

influence the dimensions shown for the mounting hardware in the following figures.

Figure C2 shows the holder for the horizontal scanning galvanometer

mirror. It is designed to allow rotation of the galvanometer around the

axis of its mirror during alinement of the system.

Figure C3 shows the holder for the two lenses making up the system

described in the main text and in Appendix B. The clamps allow the

center-to-center spacing of the lenses to be varied, and the oval holes

allow the assembly to be moved for system alignment.

Figure C4 shows the holder for the vertical scanning galvanometer mirror.

Figure C5 shows the bracket in which is mounted the holder for

mirror Ml.

Figure C6 is an assembly view of the moveable slide which changes

the scanning service from one laser to the other. Two small, rectangular

24
i mirrors are alined within the assembly. The small item in the upper

i left is one of the two identical mirror mounts. Each is glued to an

I edge of its associated mirror, and the mirrors are locked in position

! with thumbscrews.

I Figure C7 shows the holder for the 1.15 ym half-wave plate. The

plate is first mounted in a metal ring which may then be rotated within

the cut-out portion of the holder during system alinement and then

locked with a thumbscrew.

i Figure C8 is an assembly view of the clear plastic cover. The

I projections on the bottom fit the support frame top surface. The cover

! protects the alinement adjustments and it also prevents dust from set1 tling on the optical surfaces thus relaxing the cleanliness requirements

I on the room in which the scanner is located.

Figure C9 is an overall view of the apparatus showing the proportions

and the spatial relations of the various items comprising the scanner.

Figure CIO is a top view which includes all the items used to

deflect the laser beams in the raster patterns. Also shown are the

locations of the assemblies which are drawn in figures C-2 through C-7.

The terminal strip in the upper left is used to anchor the electrical

loads to the galvanometer.

Figure Cll is a closeup of the deflection system between the vertical

deflection scanning mirror and the microscope camera tube. The latter

I extends through a hole in the support frame.

'i

, Figure C12 is a rear view of the support frame top. The half-

^ wave plate is in the foreground, and mirror M2 is on its right.

Figure C13 is an end view from the left of the support frame top.

The slide assembly is in the center, and the vertical mirror galvanometer

and lens assembly LI are in-line on the right. The circular item below

the slide assembly is the holder for the rotatable analyzer used to

I adjust the intensity of the 0.6328 ym scan.

i! Figure C14 shows the clamps locking the microscope to the base

plate, and the base itself (both supplied by the microscope manufacturer).

! Also shown is the screw arrangement used at all four corners of the support

frame which allows precise alinement to be made of the scanning system

as described in the main text.

Figure C15 is a rear view of the scanner apparatus. It shows most

clearly the position of mirror Ml. The reflected light circuit lens L2

and photodetector amplifier can be seen attached to the support frame

to the right of the microscope.

Figure C16 is a closeup of the items used for the reflected light

circuit. The 5 cm focal length lens L2 focuses the reflected light

25
to a pinpoint on the germanium photodiode mounted in the center of the 5

by 9 centimeter box which contains an amplifier for the photodiode. The BNC

signal output cable was disconnected for photographic clarity.

Figure C17 is a view into the vertical illuminator port with the

illuminator removed. A half-silvered mirror was mounted in a metal

frame which fits snugly in a slot intended for an optical filter in the

illuminator port. The mirror can be adjusted and locked into position

with a thumbscrew. The frame on which the half-silvered mirror is mounted

can also be rotated. The mirror is adjusted so that light reflected

from the specimen during scanning is directed to a germanium photodiode

where it is focused to a point. With proper adjustment of the 5 cm

lens in this light path, the point is stationary on the photodiode

during scanning of the specimen.

as
APPENDIX D

Color Monitor

' The color monitor was made by rebuilding an inexpensive color TV

set. The TV set served as a convenient source of parts rather than

serving as equipment to be modified. None of the original circuits

in the TV were used, however, in starting with a TV, the advantage of

having a color CRT mounted in a cabinet complete with degaussing coil,

purity yoke, deflection yoke, convergence yoke, and radiation shielding

is realized. The TV used for the project was a small -screen tube-type

set with in-line guns in the picture tube. The in-line guns simplify

color convergence. Three basic circuits are needed to make the color

monitor. These include the deflection amplifiers, the video amplifiers,

and the high voltage power supply for the anode of the CRT.

The deflection amplifiers were built on a separate chassis, and the

remainder of the circuits were built in the cabinet that contains the

CRT. The identical vertical and horizontal deflection amplifiers are essentially class B audio power amplifiers with current sensing rather

I than the usual voltage sensing for feedback control. Figure Dl is the

' schematic for a deflection amplifier and its associated power supply.

I The deflection yoke is almost totally an inductive load so some

special considerations had to be taken into account when designing these

amplifiers. The most important consideration is that the beam deflection

be proportional to the current passing through the yoke and not the

i voltage across it. Therefore, the amplifier should be a voltage to

\ current converter. A low value resistor in series with the yoke provides

j a negative feedback signal that causes the high gain amplifier to

I perform the conversion. Since the yokes made for the various makes

II and models of TV sets are all different in terms of dc resistance,

number of turns, and voltage required to achieve a given beam deflection,

certain parameters of the amplifier given in figure Dl may need to be

i adjusted to match it to a particular yoke. It was experimentally

determined what current was needed to provide about a 50% overscan at

dc or low frequencies, and what voltage was needed to provide a similar

overscan at the highest scanning frequency that would be used. When

the yoke was connected to a dc power supply, a 2 A current was needed

j to deflect the spot on the CRT from the center to the edge of the screen.

i It was concluded that the amplifier should therefore have current limiting

' at plus or minus 3 A.

An audio power amplifier was used to determine the ac requirements

! of the yoke at 1.2 kHz which is the highest operating frequencies of

' the scanning mirrors. It was found that with a 1.2 kHz sine wave about

14 V peak-to-peak was needed to give a full screen deflection. It was

ll concluded that 21 V peak-to-peak would provide enough overscan. An

overall supply voltage of about 24 V should allow for circuit losses,

so that plus and minus 12 V supplies were made to operate the amplifiers.

I The dc resistance of the horizontal winding of the particular yoke used

27
was 1.6 and the resistance of the vertical winding was 2 The

lower frequency frame rate is used on the vertical winding, so that the

current-deflection measurement should be done using this winding.

Similarly, the higher frequency measurement should be performed on the

horizontal winding. The 0.2 n emitter resistors for the output transistors set the current limiting point. If these are increased in value,

the amplifier will current limit at lower current values. The maximum

voltage that can be delivered across the yoke is limited by the power

supply. The circuit should work equally well with higher supply voltages.

However, all resistors except those to the left of the diode bias string

in figure Dl should be increased in value as the supply voltage is

increased. For the particular set that was rebuilt to make the monitor,

the horizontal deflection winding and a winding on the color convergence

yoke were connected in series. This connection was not disturbed, and

the deflection amplifier output goes through both yokes.

The high-voltage supply for the CRT used has to supply approximately

18 kV for the anode and 680 V for the focus element. The horizontal

output stage for most black and white large screen TV sets made during

the last fifteen years generates these voltages. An easy approach to

obtaining such a supply is to use the parts from such a TV, since such

a supply uses many special inductors and high voltage parts. Figure

D2 shows a simplified schematic of such a circuit. Also shown in the

figure is the power supply for the high-voltage circuit and the other

circuits in the monitor. An inductor must be connected to the highvoltage transformer in the place where the deflection yoke is normally

connected, as this is a tuned circuit. Due to the high voltage and

current demands on the inductor, the deflection yoke from the black

and white TV was actually used. The part was mounted as far away as possible from the CRT so that it would not deflect the electron beam in

the CRT. The yoke must be mounted in such a manner that there are no conducting materials in the hole where the CRT normally goes. The power

transformer also generates fields that can deflect the electron beam

or cause color purity problems, so this part should also be mounted as far away as possible from the CRT.

The schematic for the video amplifiers and blanking circuit is

given in figure D3. The dual -gate MOS transistors are depletion devices

and are of the type that have integral protection diodes. A negative

voltage bias is required for the input gate of the blanking circuit.

The grid of the horizontal output tube conveniently provides a source

for this bias. The 12 Vac required for the CRT heater must be provided

from a separate winding on the power transformer (or a separate transformer) because the heater should be at a dc potential close to that

of the cathode.

28
APPENDIX E

Circuit Schematics

The electronic circuits for the scanner were designed to handle

a wide variety of specimen-measurement situations. All of the circuits

feature dc coupling with temperature-drift compensation with the exception of the single-stage photodiode amplifier which does not have drift

compensation. All of the circuits utilize regulated power supplies.

These features make it possible to achieve a high degree of display

accuracy even when slow scanning rates are used. Both the mixer and

the preamplifier feature a wide dc offset nulling capability with

indicator lamps to enable fast and accurate compensation for the dc

voltages present on the specimen. The wide offset range and indicator

lamps have been found to be indispensable.

Figure El is the block diagram and figure E2 is the schematic

diagram of the mixer. High-voltage video-amplifier transistors are used

extensively throughout the mixer. One reason for using such transistors

is that the immunity to high-voltage transients accidentally applied

i to the input is improved. The particular transistors used are fast

enough so that the amplifier has a flat response to about 2 MHz, but

slow enough so that high frequency instabilities do not occur.

Figure E3 is the block diagram and figure E4 is the schematic

diagram of the preamplifier. The preamplifier uses a tightly-regulated

power supply for improved performance at low signal voltage levels.

Actually, three voltage regulators are used for each voltage polarity.

The first regulator for each voltage polarity is a pre-regulator which

provides the other two regulators with a relatively clean, constant

voltage. The second regulator provides a very clean voltage to operate

the amplifier circuits and also provides a voltage reference for the

third regulator. The third regulator supplies the specimen with the

required operating power and can be adjusted anywhere between 0 and

20 V for the positive-polarity regulator, and 0 and -20 V for the

negative-polarity regulator. A high-pass filter is included in the

preamplifier. This filter is a double-pole type which inserts a coupling

capacitor in the input circuit as well as inserts a capacitor in the

feedback loop. A switch is also included in the preamplifier which

allows the type of amplifier to be changed without disconnecting the

specimen or disturbing the specimen voltage settings. Either a conventional bipolar transistor amplifier or a fast recovery FET amplifier

with no loop ac feedback can be used. There are two sections on this

switch and the section which switches the input signal is located

physically toward the front of the chassis and the section which switches

the output is located toward the rear of the chassis. A long connecting

rod operates the two sections in unison. The physical separation

ensures freedom from oscillation. Output attenuators are located on the rear of the preamplifier chassis. The gain-bandwidth product of

the circuits in both the preamplifier and the mixer is quite large, and

construction should be attempted only by persons familiar with such circuits.

29
The attenuator-magnifier schematic for the electronic magnification

of the specimen is shown in figure E5.

Figure E6 is the schematic for the reflected-1 ight amplifier with

the germanium photodetector. This circuit obtains its operating power

from the mixer.

The schematic for the dc to 100 kHz laser modulator is shown in

figure E7. A novel approach to high voltage control is used in the

modulator. The screen of a tube designed for horizontal output service

in television sets is driven with direct-coupled circuitry to yield a reliable high voltage switch. The grid and cathode are connected

together in this scheme. As a result, the common failure mode of grid

to cathode short, which is the real voltage limiting factor in such

devices, is eliminated, and the voltages commonly used in gas lasers

can easily be switched.

Figure E8 is the schematic for the high impedance probe which

can be used in applications where device loading is important. The

probe obtains its operating power from the mixer.

30
APPENDIX F

Resolution - How It Is Defined

In the specifications section of this report the resolution figures

are specified as percentages. Figure Fl helps explain the meaning

of these numbers in terms of measurable quantities. Figure Fla shows

the detector output as a function of laser spot position on a resolution

test target if the resolution were perfect. The test target contains

both widely spaced bars which serve as a reference, and closely spaced

bars with a separation d. The distance d is the test pattern line

spacing to which the resolution is referenced in the specifications.

Figure Fib shows a typical output which is obtained from the detector

due to the finite resolution of the system. The resolution given in

the specifications is defined as

31
32
UNMIXED SIGNAL

OUTPUTS FOR

OPTIONAL COLOR

SYSTEM

PHOTODIODE

SIGNAL

VERTICAL

SIGNAL

GENERATOR

VERTICAL

SCANNING

MIRROR

Figure 2. A block diagram of the electrical interconnections for the scanner.

33
A - SPECIMEN SUPPLY VOLTAGE

B - OFFSET

C - OFFSET INDICATORS

0 - INPUT

E - INVERT

F - GAIN

G - LOAD

H - CHANNEL 1 CONTROLS

FOR POSITIVE SPECIMEN

SUPPLY VOLTAGES

I - CHANNEL 2 CONTROLS

FOR NEGATIVE SPECIMEN

SUPPLY VOLTAGES

J

- CHANNEL 3 CONTROLS

FOR REFLECTED LIGHT

0 I »IMNM»

\

M

K - MIX 3 CHANNELS AND VERTICAL WAVEFORM

L - POWER AND INDICATOR

M MIX 3 CHANNELS INTO COMPOSITE Z OUT

Figure 3. Mixer controls.

34
A - VOLTAGE INDICATORS

B - OFFSET INDICATORS

C - OFFSET

D - LOAD

E - CHANNEL 1 CONTROLS

FOR POSITIVE SPECIMEN

SUPPLY VOLTAGES

F ~ CONTROLS COMMON TO BOTH CHANNELS

G - CHANNEL 2 CONTROLS

FOR NEGATIVE SPECIMEN

SUPPLY VOLTAGES

\ B C D E F I \ K\|//, i

N M J

H - POWER AND INDICATOR

I - FILTER

J

- FET BIPOLAR SELECT

K - METER FUNCTION

L - INPUT

M - GAIN

N - SPECIMEN SUPPLY VOLTAGE

Figure 4. Pre-ampl ifier controls.

35
o

LU

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36
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38
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40
SPECIMEN

< . \\ Q TO RADin

/I RECEIVER

)bead

: 47il

) VIDEO SIGNAL

AND SPECIMEN

SUPPLY

(TO MIXER OR

PRE-AMPLIFIER INPUT)

Figure 10. Specimen connection to both radio receiver and scanner's

electronics.

41
42
Figure C-1. Mechanical drawing of the support frame. Dimensions are given in millimeters.

43
Q 12

in

^

• CD

50

38

I

I—-

ICVJ

25 ^1

ASSEMBLY A

Figure C-2. The holder for the horizontal scanning mirror H. Dimensions are given in millimeters.

44
ASSEMBLY B

Figure C-3. The holder for the two lenses making up the LI system.

Dimensions are given in millimeters.

45
T

00

CM

00

..A

79

12.7

Figure C-4.

ASSEMBLY C

The holder for the vertical scanning mirror V are given in millimeters.

Dimensions

12 50 — 160

ASSEMBLY D

10- 00

ro O

in

12.7

Figure C-5. The bracket for holding mirror Ml. Dimensions are given

in millimeters.

h6
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49
Figure C-9. Overall view of the laser scanner.

ASSEMBLY E ASSEMBLY F

-x\2 PLATt

/ oV.

^

ASSEMBLY

" .t

ASSEMBLY D

ASSEMBLY C

ASSEMBLY 6

Figure C-10. Top view of the scanner showing the relative position of

most of the optical components and assemblies.

50
Figure C-11. Closeup of the optical deflection system. Note that the

microscope camera tube extends through a hole in the support frame.
AHALYZER

Figure C-13. End view of the top of the scanner as seen from the left.

Figure C-14. The base of the microscope with the scanner support frame.

The adjustment screws for moving the fr^ame are visible.

52
53
Figure C-17. The half silvered mirror in the microscope vertical illuminator port.

54
HORIZONTAL AMPLIFIER SHOWN-VERTiCAL AMPLIFIER

IS IDENTICAL-POWER SUPPLY COMS^ON TO BOTH AMPLIFIERS.

Figure D-1. Schematic diagram for one of two deflection amplifiers with

power supply for the color monitor.

55
3A3

HV RECT

IN 4007 40-350

2A

inv.

DEGAUSS COIL " -L- " i—^ »l ^ T

T IN 4007 -!J- 117V

IN 40U7

50 low ] 4 • Vs/V

N 4007 ^150-200

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] •

IN 4005 tr

68-2W —vs/v—

:200 |iK

1 ,„ '^^r^2N 3439 4^ 13Vlf^lO

4

.01

12

Figure D-2. Simplified schematic of high voltage portion of color monitor.

56
DUAL GATE MOS FET WITH INTEGRAL GATE PROTECTION DIODES

RED in 10K O WV15K 2W

GREEN In 10K O —WVr- 1.5K

I) WAr15K 2W

IM ^820

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280

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680

{2.5M

280

P680I

.01 280

880

J2.5M

280

Figure D-3. Schematic diagram of the video and blanking circuits for the

color monitor.

57
INPUT 1

FROM

PREAMPLIFIER

OR SPECIMEN

INPUT 2

FROM

PREAMPLIFIER

OR SPECIMEN

INPUT 3

FROM

PHOTODIODE

AMPLIFIER

UNMIXED OUTPUTS

FOR OPTIONAL COLOR

DISPLAY i i i

SPECIMEN LOAD I- SPECIMEN BIAS

SPECIMEN LOAD - SPECIMEN BIAS

MIX 1, 2, 3

u u u

MIX 1, 2, 3, Y

VERTICAL HORIZONTAL VERTICAL DEFLECTION BLANKING BLANKING

MIXED SIGNALS

FOR INTENSITY

MODULATION OF DISPLAY

VERTICAL DEFLECTION PLUS SIGNAL DEFLECTION

COMPOSITE

BLANKING

SIGNAL

Figure E-1. Block diagram of mixer chassis.

58
59

61
Figure E-5. Schematic diagram of the attenuator-magnifier.

3.3K

OTO CHANNEI

3 ON MIXER

3-4 VOLTS WITH

NO LIGHT INTO PHOTODIODE AND NO ATTENUATOR CONNECTED

Figure E-6. Schematic diagram of the reflected light amplifier includ

ing the germanium photodetector.

62
63
25

RCA TYPE 40673 WITH

INTEGRAL PROTECTION DIODES

OUTPUT

Figure E-8. Schematic diagram for the high impedance probe

LASER SPOT POSITION ON TEST TARGET

oco

b

LASER SPOT POSITION ON TEST TARGET

Figure F-1. Graphical explanation of the meaning of resolution figures

quoted in the specifications section of this report.

64
JS-114A <REV. 7-73)

U.S. DEPT. OF COMM. BIBLIOGRAPHIC DATA

SHEET

1. PUBLICATION OR REPORT NO. NBS SP 400-24

2. Gov't Accession

No.

3. Recipient's Accession No.

TITLE AND SUBTITLE

Semiconductor Measurement Technology: A Laser Scanner for

Semiconductor Devices

5. Publication Date February 1977

6. Performing Organization Code

, J. AUTHOR(S)

Dav id E. Sawyer and David W. Berning

8. Performing Organ. Report No.

PERFORMING ORGANIZATION NAME AND ADDRESS

NATIONAL BUREAU OF STANDARDS

DEPARTMENT OF COMMERCE

WASHINGTON, D.C. 20234

10. Project/Task/Work Unit No.

11. Contract/ Grant No. ARPA Order 2397

Program Hode 6D10

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

NBS — Washington, D. C. 20234

ARPA — 1400 Wilson Boulevard, Arlington, Virginia 22209

13. Type of Report & Period Covered Final

14. Sponsoring Agency Code

5. SUPPLEMENTARY NOTES

Library of Congress Catalog Card ^famber: 76-6O84O8

6. ABSTRACT (A 200-word or less factual summary almost si^iiicant information. If document includes a significant

bibliography or literature survey, mention it here.)

This is a construction guide and operators manual for a laser scanner built for

semiconductor device studies. A very brief discussion of the theory of operation

of the scanner is given. The scanner's operation from a systems point of view is

described in detail with emphasis on block diagrams. The scanner is described from

a hardware point of view with a detailed description of the function of the various

controls on the electronic equipment that was built for the laser scanner. A quick

guide for the use of the scanner is given so that a person unfamiliar with the instrument can use it effectively. Specifications relating to the scanner's data

gathering ability are also given. Mechanical drawings and circuit schematics are

given to enable others to build a similar scanner. The optics and their alignment

are discussed. Various display modes including color are discussed to enhance

operator viewing.

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)

Electronic reliability, electronics; laser scanner; measurement method; mixer;

optics; pre-ampl ifier; radio receiver; semiconductor device studies.

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UNCL ASSIFIED

21. NO. OF PAGES

72

20. SECURITY CLASS

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$1.35

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<l U .S . GOVERNMENT PRINTING OFFICE: 19 7 7-2 40-848/16
'1 i11
Announcement of New Publications on Semiconductor Measurement Technology

Superintendent of Documents,

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Dear Sir:

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