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All 102561 PUBLICATIONS 298

Welser, Sidney/Study of the feasibility QC100 U56 NO.86-3410 1986 V19 C.1 NBS-P Study of the Feasibility of

Introducing Automation into

Critical Manufacturing Processes

for Producing Mercury Cadmium

Telluride Detector Arrays

Sidney Weiser, Chief

U.S. DEPARTMENT OF COMMERCE

National Bureau of Standards

Engineering Design Group

Fabrication Technology Division

Gaithersburg, MD 20899

U.S. Army

Director-Night Vision and Electro Optics Laboratory

n: DELNV-R-FP

OC foir, VA 22060-5077

100 >• 25209

. U 5 6

86-3410

1986

Final Report

May 1986

Prepared for

NBSIR 86-3410

STUDY OF THE FEASIBILITY OF

INTRODUCING AUTOMATION INTO

CRITICAL MANUFACTURING PROCESSES

FOR PRODUCING MERCURY CADMIUM

TELLURIDE DETECTOR ARRAYS

NBS

RESEARCH

information CENTER N&yR

-M

Sidney Weiser, Chief

U.S. DEPARTMENT OF COMMERCE

National Bureau of Standards

Engineering Design Group

Fabrication Technology Division

Gaithersburg, MD 20899

Final Report

May 1986

Prepared for U.S. Army

Director— Night Vision and Electro Optics Laboratory

Attention: DELNV-R-FP

Fort Belvoir, VA 22060-5077

MIPR No. 25209

U.S. DEPARTMENT OF COMMERCE, Malcolm Baldrige, Secretary

NATIONAL BUREAU OF STANDARDS, Ernest Ambler. Director

TABLE OF CONTENTS

Page

Abstract. 1 Disclaimer. 2

Phase I —Automation Study o-f the Process

I. Overview o-f This Study........ 3

II. General Discussion 4

III. Technical Approach. 5 A. Feasibility Study Report.............................. 5 B. Analysis o-f the HgCdTe Fabrication Process............ 5 C. Recommendations . 25

D. Detailed Description o-f Recommended Options 29

Option 1 —Automation at a Laboratory Level 29

Option 2—Automation o-f Several Steps in an

Existing Production Line 50

Option 3—Setting Up a New Automated Production

Li ne 52

Phase II —Implementation o-f Near Term Demonstration o-f Automation

Development o-f a Laser Scanner to Determine

Crystal Axis 'Orientation

I. Statement o-f the Problem 54

II. General Discussion 54

III. Technical Approach..... 56

IV. Results. 74

V. Recommendations 74

Appendix 1 —Bibliography. 75

Appendix 2 —Field Trips and Conferences 77

Appendix 3—Detailed Process -for Fabricating HgCdTe IR

Detector Arrays 79

1
List of Figures

Page

1 Light Duty Robot 13

2 Robot -for Etching Process...... 14

3 Robot Gripper for Cassette. 16

4a Etching Process with Multiple Robots. 17

4b Etching Process with Single Robot on Rail 17

5a Basic Computer Integrated Manuf actur i ng (CIM) System and

Various Module Components...... 18

5b CIM System Phased Implementation into Existing or New

Fabrication Areas.... 18

6 Illustration of Robotic Vehicle with Robotic Arm and on

Board Storage. 19

7 Five Axis Robot (Medium Dexterity) 21 7a Array Measurements Being Made with a High Power

Microscope. 23

7b High Power Microscope with Vertical Camera Port Mounted

Under Laser Scanner 24

S Block Diagram of Generic Process for Fabrication of HgCdTe

Detector Arrays 27

9 Block Diagram of HgCdTe Fabrication Process with Automation

Projects Recommended for Option 1 30

10 Mul ti -f uncti on Robot End Effector 33

11 Automated Plasma Cleaning Station 35

12 Automated Washing Station 36

13 Fourier Transform Infrared Spectrometer for Transmission

and Reflectance 38

14 Surface Analysis Instrument 39

15 Automated Coater and Baker 40

16 Automated Optical Inspection Using Laser Scanner with

Microscope. . 42

ii
17 A Typical Configuration for a Laser Flying Spot Scanner

with Microscope 43

18 One Detector Array (There are several arrays on each

substrate) 46

19 Automated Array Slicing Saw with Optical Inspection

Station. 47

20 Automated Array Slicing Station and Inspection Station

Shown in a Clean Room 48

21 Measurement of Reflection Pattern from Scanning a Single

Crystal 57

22a Oscilloscope Trace of Reflected Pattern at 50 Degrees 58

22b Oscilloscope Trace of Reflected Pattern at 60 Degrees...... 58

23 Oscilloscope Trace of Reflected Pattern at 67.5 Degrees.... 59

23b Oscilloscope Trace of Reflected Pattern at 70 Degrees 59

24 Oscilloscope Trace of First Derivative of Reflected

Pattern at 67. 5 Degrees. 60

24a Laser Scanner for Counting Bacteria Colonies 61

25a Laser Scanner for Crystal Axis Orientation 62

25b Signal to Noise Enhancement. 62

25c Dynamic Spiral Conical Toroidal Laser Scanner... 62

26a Typical Crystal Structure for the End of a Boule or a Wafer

of CdTe 64

26b Mapping Display for Round Wafer or End of Boule 65

26c Surface of Boule 65

27 Side View of Toroidal Laser Scanner.. 66

28 Front View of Toroidal Laser Scanner 67

29 Top View of Toroidal Laser Scanner 68

30 Typical Geometric Patterns Produced by Scanning Crystal

with Laser 69

31 Schematic of Clock Circuitry for Laser Scanner 70
Schematic of Signal Amplifier Digitizer for Laser Scanner.. 71 Schematic of Pattern Recognition Circuitry for Laser

Scanner. . . ......... s ...... „ 72

Schematic of LED Readouts for Laser Scanner 73

%

IV
Abstract

The task was divided into two phases.

Phase I was a systems study of the existing process and

recommendation o-f a plan -for automation. Since this process is

complex, with over 100 steps, three options were proposed -For

i mpl ementati on

:

Option 1 Automation o-F eight critical subprocesses at a Laboratory level.

Option 2 Automation of five critical subprocesses in an

existing production line.

Option 3 Automation of the complete process in a new

f aci 1 i ty

.

Approximate costs were prepared for each of these options as

required by the contract.

Phase II was to implement a near term demonstration of

automation in infrared fabrication. This was directed to the

development of a more efficient way for the measurement of the

crystal axis orientation of cadmium telluride substrates. A

breadboard model of a toroidal laser scanner with pattern

recognition was developed. This instrument will reduce the

mapping time for a substrate from 4 hours to 4 minutes. The

scanner can identify three different crystal orientations and

characterize four others in a fraction of a second. This can

improve the yield by 300 A goniometric mount controlled by a dedicated computer is planned for fully automating this

inspection process.

Key Words: Automation; Clean Room Applications; Crystal Axis

Measurement; Fabrication Processes; Infrared Sensor Arrays;

Laser Scanner, Mercury Cadmium Telluride Detectors; Robotics.

1
DISCLAIMER

The use o-f trade names and commercially available equipment in

this report does not constitute an endorsement by the National

Bureau o-f Standards (NBS). Manufacturers specifications and

performance data have not been verified by NBS. Therefore, it

should not be construed that NBS guarantees the performance of

the referenced products. This report may not be used to

support advertising or sales efforts for referenced equipment.

The references to typical products or equipment have been used

to estimate the magnitude of a problem and to help determine

approximate costs of overall systems.

2
FINAL REPORT ON STUDY OF

AUTOMATION OF HgCdTe ARRAY

FABRICATION PROCESS

Phase I-—Automation Study of the Process

I Overview of thi. s Study

This study was initiated to explore the feasibility of

introducing automation into the manufacture of mercury cadmium

telluride (HgCdTe) arrays for detecting infrared radiation. The

present fabrication technology is changing very rapidly, driven

by the need for larger arrays, smaller detectors and lower costs.

Due to the critical nature of the present fabrication process and

its similarity to semi conductor processing, much of this work is

conducted in a clean room environment. The continuing problems of

reduced yields in this processing have been attributed in part to

particle contamination.

Recent advances in the use of robotics and other automation in

the clean room have resulted in notable reductions in particle

counts. This study was intended to explore and define the

manufacturing processes which would be most suitable for

automation and provide the greatest return in improved yield and

reduced time and labor.

The goal of this program was to study the feasibility- * of

introducing automated concepts into the material growth and

fabrication processes necessary to produce I.R. detector arrays.

In addition the program was to develop the following:

A. A conceptual block diagram of the major elements of an

automated infrared material and array fabrication line.

B. A listing of non—contact , automated inspection procedures

which detect visual material flaws and evaluate electrical

par ameter s

C. A recommendat i on of available robotic technology which can be

incorporated into infrared processing, and recommendat i on of

specific technology which requires further development.

D. An estimate of the cost and time schedule for implementation

of an automated infrared fabrication process.

E. An implementation of a near term demonstr at i on of automation

in infrared detector fabrication.

The program was initiated January 13, 1985 to run until September

30, 1985. An extension to December 31, 1985 was granted for the

final report.

3
I I . General Discussion.

The -first step in implementing this study was to acquire a thorough background in the process -for manufacturing HgCdTe

infrared detectors. This includes the technology -for bulk grown

HgCdTe (-first generation) as well as the epitaxial layer

detectors grown on cadmium telluride substrates (second

generation) . Since some o-f these techniques are still under

development, and the technology is rapidly changing, it was

necessary to acquire this background as quickly as possible.

This was done by visits to the Night Vision Laboratory at Fort

Bel voir Va. , to vendors presently engaged in the development and

production of these detectors, and to technical conferences with

scientists working in this field at NBS. New techniques for nondestructive testing and evaluation were explored and

instrumentation for spectral measurements was reviewed.

The processes for Liquid Phase Epitaxy (LF'E) , Vapor Phase Epitaxy

(VF'E) and Molecular Beam Epitaxy (MBE) were discussed and the

equipment for performing these processes was examined for

suitability to automation.

The nature of the defects which reduce yields was examined and

reviewed. Discussions were held with scientists at NBS on the

feasiblity of relating defects to the performance of these

detectors using the following types of measurements:

XF'S

UPS

SIMS

TPD

LEED

ISS

AES

FT IPX-ray Photo Emission Spectroscopy

Ultra Violet Photo Emission Spectroscopy

Secondary Ion Mass Spectroscopy

Temperature Programmed Desorption

Low Energy Electron Diffraction

Low Energy Ion Spectroscopy

Auger Electron Spectroscopy

Spectrophotometry

Automated Spectroscop i c Ellipsometry

Ultrasonic Non-Destructive Testing

Ultrasonic Surface Imaging of Elastic Moduli and Near

Surface Defects.

Utrasonic Tomographic Imaging of Internal Crystal

Structure.

4
While some o-f these scientific techniques are already being

investigated at the Night Vision Laboratory, the conferences,

exposure to this equipment, and expertise o-f the NBS scientific

staff have been very valuable in identifying new testing

techniques which may be applicable to this project.

III. Technical Approach^

A. Feasibility Study Report

This phase was implemented by reviewing of R and D reports in

this field furnished by the Night Vision Laboratory,

References 1, 2, 3, 9, 10, 11, and 12. These reports

supplemented by visits and field trips from January 19S5 to

November 1985 (Appendix 2) provided basic familiarization

with infrared detector fabrication technology and the

applicable clean room robotics technology.

B. Anal_ysi.s of the HgCdTe Fabrication Process

1 • Histgry of HgCdTe Sensor Techngiggy

Early infrared detector technology used large HgCdTe

detectors cooled in liquid nitrogen to get usable D*

values (signal to noise ratio). The detectors were

usually used to sense radiation levels in

spectrophotometr i c i nstrumentai on . With the need for

infrared sensors for imaging, a technology for spatial

scanning was developed to get two-dimensional

information. These systems were implemented by using

two-dimensional mechanical scanning techniques with

relatively large I.R. detectors.

For this reason, early I.R. scanners were bulky and

limited in resolution capability. With the need for

higher resolution it became necessary to reduce the size

of the HgCdTe detectors.

As the size was reduced the area was reduced. This

resulted in a reduction in the signal level. Fortunately

the noise is also proportional to the area so that the

signal to noise ratio is maintained in the smaller I.R.

detectors

A further reduction in the size of these scanners is now

feasible using detector arrays with a single optomechanical system to provide the second coordinate. With

this history it is easy to understand why a size

reduction of appr ox i matel y 250 times in individual sensor

dimensions presents such a challenge to technology.

5
a) First Generation I.R. Detectors

The original detectors were generally -fabricated -from

bulk grown HgCdTe crystals. This type o-f detector is

generally considered as -first generation technology.

More advanced configurations -for these I.R.

detectors have been in development -for several years.

In general they have consisted o-f an epitaxial layer

o-f HgCdTe grown on a CdTe single crystal substrate.

The new technology has generally been referred to as

second generation technology.

Since it is still early in development, the present

epitaxial layer I.R. detectors are sometimes ref erred

to as early second generation (1 1/2 generation)

detectors. These new infrared detectors have many

-features which make them very suitable -for arrays.

This study addressed improvements in processing which

can be applied to 1—1/2 generation detectors.

Application to -future technology is sel-f evident.

b. Iyei£=!!. Early Second Generation Fabrication Process

Techniques -for -fabrication o-f HgCdTe infrared

detectors are in the process o-f very rapid

development. Techniques which are appropriate in the

laboratory are being carried over into limited

production. In some cases the equipment used is

identical, con-firming the need to improve portions o-f the process. The epitaxial layer is presently grown

by liquid phase epitaxy in the laboratory.

Experimental work is concurrently being done in vapor

phase epitaxy, molecular beam epitaxy, and metal

organic chemical vapor deposition. This study

considered liquid phase epitaxy and molecular beam

epitaxy since the automation and material handling

elements -for these two technologies are similar.

A sequential (si mpl i -f i ed ) description o-f the process

has been prepared to identi-fy areas -for potential

automation. Automating all parts o-f the process at

once may be extremely di-f-ficult at this time, due to

the limits in dexterity available in robotics and the

state o-f the art o-f vision systems. Therefore an attempt was made to prioritize the selection of areas

which have automation potential.

It is recognized that cont ami nat i on of the material

used in fabricating these detectors is a prime factor

in reducing yield. This cont ami nat i on may be due to

the operators handling the components and assemblies,

the atmosphere, or other production factors. It is

also recognized that the materials used in these

detectors have some toxic properties. In addition,

many of the fabrication and assembly operations are

6
already performed in clean rooms. The use of

robotics to replace the human operator, where

possible, within the clean room is now well

recognized. A brief description of the process is

given in the next section.

2.

Generalized Processes

This is shown in six subprocesses in Figure 8. A

brief summary of these is given below.

Subprocess 1 ) Prepare, grow single crystal

slice CdTe wafer substrates.

material

Subprocess 2) Grow epitaxial layer on substrate

test

and

Subprocess 3) Prepare arrays by photo etching,

metal deposition processes.

and

Subprocess 4) Saw arrays to size and

inspect

optical 1

y

Subprocess 5) Bond leads

Subprocess 6) Final test.

In order to evaluate the potential for applying robotics

and automation to- these generalized processes, they must

be expanded to include detailed fabrication and inspection

steps. The following process chart has been prepared in

greater detail for only Subprocess 1.

Subgrocess 1_)_ Pr egar

x GrgwA and Sl_i_ce CdTe Substrates

a. Material Growth

1. Refine Cd and Te materials

2. Divide into small pieces suitable for precision

al 1 oyi ng

3. Alloy and grow single crystal in vertical

Bridgman furnace or equivalent.

4. Zone, refine and anneal crystal boule.

b. Substrate Preparation

1. Sandblast boule

2. Determine 1,1,1 crystal axis plane

3. Orient and slice boule into wafers

7
4. Polish wa-fers mechanically and chemically and then

cl ean

5. Dice wafers into substrates 12 x 20 mm.

c. Substrate evaluation and testing

1 . FI atness

2. Resistivity

3. Etch pit density

4. Te precipitates

5. Orientation

6 . Dimensions

The above process is further expanded in Appendix 3 to

include a more detailed description. This process

may vary in industry from vendor to vendor. However,

certain areas of the fabrication process are

particularly suitable to automation. These are

considered to have the highest priority.

d. Define areas of this fabrication technology which are

suitable to automation.

In order to evaluate these areas a typical process

chart is included in Appendix 3. Even this process

chart is abbreviated since listing of all the detailed

steps would be prohibitive; however, it is typical for

the fabrication of an LPE epitaxial layer array. The

steps which lend themselves to automation are

indicated with an asterisk (*) in Appendix 3.

1 ) Automation of the Fabricatign Process

The design of an automated system to perform this

fabrication process is extremely difficult since

the process is changing rapidly. It is presently

highly dependent upon the human skills of manual

dexterity and visual sensing. A glossary of terms

for robotics is given in Reference 13. In order

to initiate an automation effort it is necessary

to establish a set of principles which can be

followed. These are:

a) The elimination of operators from clean room

areas to reduce particulate counts.

8
b) Operator assisted automation will be

acceptable where it can afford a saving in

production cost.

c) Partial automation will be an acceptable goal

provided it can be accomplished at a reasonable

cost

d) The use o-f several smaller clean rooms in

place of one large clean room will be acceptable

since this allows the progressive introduction o-f automation with minimum disruption o-f production.

e) The use o-f robots in production will be

acceptable where they can economically perform the

work equivalent to a human operator. The

operations may be tailored to the robot's

capability, if required.

f) The use of fixtures or carriers to simplify

material handling is an acceptable technique so

long as the technical process, the costs and the

production rate justify this approach.

Examination of the typical array fabrication

process in Appendix 3 indicates the large number

of detailed operations performed by human

operators. In many of them the manual skill

requirements are very high. In some of these

operations visual sensing is required in addition

to the manual skills. These operations are more

difficult to automate.

Due to the complexity of this process and the fact

that it is rapidly changing, it is necessary to

define an approach which can be immediately

applied but which has potential for future

enhancement. This can be done by analyzing the

fabrication processes and defining all the typical

processes which exist. In that way when a process

is successfully automated, it can be used in more

than one production operation.

It is also desirable to classify the operations

and the types of automation so that applications

of technique where feasible can be applied across

the entire fabrication process. This approach can

be aided by considering the process with regard to

the following parameters.

1) Type of Operation - Active (much manipulation)

or Passive (little manipulation)

a) Fabrication

9
b) Assembly

c) Testing or Calibration

2) Dexterity Required

a) High

b) Medium

c ) Low

3. Part Handling

a) Single

b) Multiple

4) Speed of Process

a) Fast

b) Slow

5) Sensors Required

a) None - Open Loop

b) One - Closed Loop ( vi si on

c

More

Test

than one - Instruments)closed loop (Vision and

6)

Human Interaction Required

a) Possible

b) Not Possible

In considering the type of automation, active

pertains to an operator performing a task which

modifies the product while passive pertains to

measuring and recording a char act erst l c of the

product. In the fabrication process, most of the

operations are active. This also applies to the

assembly operations. Testing may be passive while

calibration may be either active or passive.

The dexterity requirement together with process

speed really determines the type of automation

required. Where the speed is low and dexterity is

low it may be possible to use a programmed robot

to perform the operation. This may be single part

or multiple part handling dependent on the

10
production rate required. Multiple handling is

more difficult unless the multiple parts are

fastened together (not cut apart) or mounted in a magazine or on a holder.

Generally this type of automation is less flexible

and more difficult to modify when the process is

changed. An example of this is etching a number

of subtrates on a single carrier. This is

particularly suitable where the process requires

appreciable time for completion.

Where the dexterity requirement is high, it may be

difficult to use a robot without adding sensors

for vision and touch. However, it may be possible

to divide this operation to allow a robot to

perform part and a human operator to perform the

remainder of the operation.

At the present time robots cannot achieve the

production rate of human operators in highly

dextrous operations. A robot, however, can

perform repetitive operations and reliably count

occurrences with a lower error rate than human

operators. Robots can also perform tasks which

require greater strength than the human operator.

Therefore, in analyzing the typical HgCdTe

fabrication process, the operations can be broken

down as follows:

o Manual positioning - (loading, unloading,

carry i ng

)

— Low dexterity — robot — Medium dexterity - robot or robot

assisted operation — High dexterity - human operator

o Process control - computer

o Cleaning - low dexterity - robot

o Polishing - low dexterity - robot

o Etching - low dexterity - robot

o Sandblasting — medium dexterity - robot to

turn part while in process

o Cutoff ends of boule — medium dexterity — robot with vision sensor and interactive

f eedbac k

.

11
o Slice wafers — low dexterity - robot

o Dice waters - medium dexterity - robot with

vision sensor and interactive feedback

o Furnace loading and unloading - high

dexterity - robot or human operator depending

upon analysis o-f specific operation

o Contact formation - high dexterity - robot or

human operator depending upon analysis of

specific operation

The types of automation which can be applied to

this technology will depend upon the specific

process, the production rate required, the system

flexibility needed and the capital cost. Since the

HgCdTe fabrication process is presently in an

evolutionary state, the automation selected should

be capable of modification. This type of

automation should utilize medium dexterity robots

programmed by a computer and capable of being

reprogrammed if required. Several of these robots

could be programmed to perform multiple operations

in a synchronized manner.

One of these robots is shown in Figure 1. This is

a light duty robot. Generally this type of

automation is more costly than fixed automation.

Its advantage however is that it can be modified

and reprogrammed to conform with process changes.

A light duty robot with programming control can

cost from $30,000 to $40,000 without any special

tooling. Light duty robots of this type can move

rapidly but cannot carry a heavy payload (one

pound to three pound capacity). Vision systems to

improve the robot capability are often carried on

the robot arm. Light duty robots usually cannot

carry the weight of a robot vision system which

may weigh 2 to 3 pounds.

A robot vision system is an optical system which

can acquire the work piece, and redirect the

control system of the robot to locate the work

piece position and orientation. The vision system

then translates this information to the robot wrist

to orient the grippers to reliably pick up the wort'

piece. Without a vision system the work piece will

have to be preoriented before it is picked up by a light duty robot unless a simplified lighter weight

optical sensor can be adapted to this application.

A larger robot is shown in Figure 2 carrying a cassette of wafers through a series of etching

solutions. This type of robot has been

12
Figure 1 Light Duty Robot

13
Figure 2 Robot for Etching Process

14
successf ul 1 y used in clean room applications. The

gripper on the end of the robot arm can be adapted

to pick up and manipulate single waters or

cassettes holding a number of waters. An example

ot the type ot grippers used to pick up the

cassette is shown in Figure 3. These robots may

carry payloads as heavy as 5 pounds.

Where the etching and cleaning process is set up in

a linear contiguration, which is too long tor the

reach ot a single robot, a series ot robots can be

operated trom a single computer controller. An

example ot this is shown in Figure 4a. Each

rotating arm is capable ot transterring a cassette

trom one bath to the next.

Fixed automation such as pick and place systems ot

limited dexterity and tlexibility are usually

designed tor a specific application and can cost

from *10, 000 to *20,000.

An alternate method for accompl i shi ng this is to

translate the robot on an additional longitudinal

axis along the length of the process. This may

affect the processing rate since a single arm must

service several stations as shown in Figure 4b.

This automation method requires accurate

positioning of the robot in front of each station.

It is not difficult to accomplish this positioning

with a precision translation system and appropriate

sensors. • •

Where the length of the etching process is much

greater, it may be necessary to have a number of

etching lines. Automating this type of process

requires some type of transfer device to move the

work piece or cassette from one line to another.

This may be fixed automation at the end of a line,

or a simple pick and place robot or it may be a more versatile robot dedicated to this operation.

Where the process is extensive as shown in Figure

5, a robotic vehicle may be used to transfer

cassettes from one etching bath to the next. One

robotic vehicle of this type is shown in Figure 6.

This automation system has increased versatility

since the robot vehicle may carry the work piece or

pieces on to the next fabrication process.

However, this system requires additional sensors

and location devices for aligning the vehicle

precisely with each work station. These vehicles

are generally called mobile transfer units or

MTU's. These units generally require an "on board"

power source, such as storage batteries, to

eliminate trailing umbilical cables. These mobile

15
Figure 3

Robot Gripper for Cassette

16
Figure 4a Etching Process with Multiple Robots

17
Basic CIM System

Service a Combined Total of Up to 10 Production Tools and WIP Stations

Vmtu

rati

SECS Interlace

Figure 5a Basic CIM System and various module components.

Semiconductor Fab Area with MTU

Figure 5b CIM System phased imDlementation into existing or new

fab areas.

18

oooooooooh
FIGURE 6 Illustration of robotic vehicle with robotic arm and

on-board storage.
transfer units are usually used in Computer

Integrated Manufacturing Systems (CIM) where more

than one vehicle is required per system. Traffic

control must be implemented to minimize the chance

of collision. Figure 5 shows several robotic

vehicles operating together with a number of human

operators in the same clean room area. The safety

problems must be carefully reviewed for this type

of operation. Normally, these systems are designed

to operate within the clean room area so that the

low particulate count within the area can be

mai ntai ned

When the process requires a high level of dexterity

the robot may require as many as six degrees of

freedom. This may be improved by the addition of

one or more sensors of various types to the end of

the robot arm. However these sensors carried on

the end of the arm reduce the actual payload which

the robot can carry. A robot with five axes,

having medium dexterity is shown in Figure 7. A

high dexterity robot usually has six axes to allow

it to manipulate a work piece almost as well as the

human operator.

2) Automation of the Inspection Process

Inspection and testing can be very similiar to

manual positioning, depending upon the dexterity

needed to access and load the test equipment.

This may be done by a robot or a human operator.

However the success of this automation application

may be dependent upon the ingenuity applied to

selecting or developing the test equipment so that

it requires low levels of dexterity to load and

unload. If production quantities are high it may

be feasible to not only develop the test

equipment, but to develop a simplified pick and

place robotic system for loading and unloading.

This type of system can operate at higher cycle

rates than general purpose robots. It may also be

necessary to design the test instrumentation to do

multiple product testing in order to increase the

throughput

One example of special test equipment designed to

improve production is the substrate crystal axis

mapping goniometer described in Phase II of this

report. Other examples are the Hall Effect Test

Equipment, and the FTIR interf erometer

spectrometer for mapping cutoff wavelength and

expitaxial layer thickness.

Inspection instrumentation is generally similar to

test instrumentation. However inspection

20
Figure 7 Five Axis Robot (Medium Dexterity)

21
i nstrumentat i on may depend more upon the visual

sensing supplied by a human operator -for judging

the quality of the product. This type of

i nstrumentat i on is much more difficult to automate

since the measurement parameters are hard to

quanti f y

One example of this type of inspection instrument

is the microscope station used to count etch pits

on substrates. The automation of this type of

station is dependent upon substituting a suitable

optical scanner with a pattern recognition system

for the human operator. Since the human operator

is very knowledgeable in detecting subtle

differences in small patterns, it is difficult to

achieve the sensitivity from automated scanners.

In addition it is difficult to program an

automated scanner with a detection algorithm which

is equal to the human data reduction capability.

Consequently the inspection equipment and scanning

algorithm may have to utilize techniques for

increasing the contrast of artifacts to insure the

quality of the inspection process. One of these

techniques is to use level slicing or thresholding

of the gray scale in the image. This is a commonly utilized technique in video image

manipulation. The automated scanner, however, is

far superior to the human operator for counting

defects and reliably recording this data.

Examples of this type of inspection instrument are

given in References 7 and 8. This system was

developed at NBS for testing micro circuitry in

the semi -conductor field. The principles used in

this system are pertinent to inspection operations

in the HgCdTe detector fabrication process. The

basic laser scanner and computer programming

system is adaptable to many microscope inspection

systems which have a vertical camera port. An

example of a microscope inspection station of this

type is shown in Figure 7A. The vertical camera

port in this figure contains an eye-piece to

protect the optics. The basic 1 aser scanner can

fit over this microscope as shown in Figure 7B to

project the scanning 1 aser beam through the

optical system. The advantage of this system is

that the work is illuminated by coherent light

which increases the contrast of the artifacts in

the field. The modification to complete this

1 aser flying spot scanner is to replace the

vertical illuminator lamp with an optical sensor.

This approach is well documented in References 7

and 8.

22
Vertical

Camera

Port

23

Figure

7a

Array

Measurements

Being

Made

With

A

High-Power

Microscope
Figure 7b High Power Microscope with vertical camera port mounted under laser scanner

X

24
The coherent illumination can be varied in

wavelength by using a tuneable dye laser. The

references describe a raster scanning system -for

the laser. The same laser has been used with a polar scan in Phase II o-f this project. It is

readily apparent that a diametral scan can also be

easily introduced. This would enable the computer

to initiate a suitable inspection algorithm to

detects using existing

already in place in the

A typical algorithm -for

detects in the intrared

to align the array

perpendicular to the raster scan and to look tor

detectors which are not periodic. The repetition

rate can then be programmed in microseconds and

synchronized with the pattern, to count detectors.

Any artitacts which do not appear at the

repetition rate are detects. This is a very

elementary algorithm tor this type ot

More elaborate algorithms are used

processing ot biological materials,

the algorithm to the particular

process, this automated system can be

several applications.

count and record

microscopic equipment

production process,

recognizing random

detector array is

detect i on

.

in video

By adapting

inspection

utilized in

For these reasons this tabrication process must be carefully

analyzed for access, feasibility, production rate, traffic

patterns, potential changes and costs before it is implemented.

A comparison of costs is usually made between partial and full

automation to obtain the best return on capital investment.

Where overiding factors such as contamination or particle count

are present, it may be necessay to select a system which is not

the most cost effective. The cost of robots with six degrees of

freedom is much greater than those with three or four degrees of

freedom. Sensors and robot vision systems also add to the cost.

For complex computer controlled systems the one time programming

costs may also be relatively high. It is also necessary to tool

the end of the robot arm for holding and storing work pieces.

These costs must also be considered part of the capital cost in

automating a process. In some cases the process equipment must

be altered to make it compatible with the robotic systems. This

may reduce the reliability of the process equipment unless the

changes are carefully planned and engineered.

C. Recommendat i ons

The purpose of this study was to explore the feasibility of

introducing automation into the manufacturing of HgCdTe

detectors. The broader goals were to increase yields and reduce

costs. The addition of robots to the clean room operations should

also reduce the particulate count (Reference 9 and 10). This

alone should result in an additional improvement in yield.

25
In considering this process -for automation, it is very important

to establish an order of priority which will optimize the

bene-f its. Therefore the following criteria should be used to

determine the order of priority.

o Potential for cost reduction

o Simplicity of the application

o Probability of success

o Potential for multiple applications

There are approximately 102 stations in the fabrication process

described in Appendix 3 and each of these stations may have more

than one step. Of these 102 stations approx i matel y 69 are

suitable for automation. These are marked with asterisks in

Appendix 3. The projects selected for automation should be

suitable for implementation at a laboratory level with provision

for expansion to adapt to the production process.

A block diagram of the generic process for fabrication of HgCdTe

detector arrays is shown in Figure 8. Many of the steps in this

process are still under development to improve yields and reduce

labor. Therefore some processes are being carried on at both the

laboratory and the production levels simultaneously. For this

reason there are a number of options available in planning the

automation of this fabrication process. These will be listed

below and then described in some detail so that the magnitude of

these options can be evaluated.

Option 1 —Automate several key steps in the process at

laboratory l_evel_ where evaluation can be performed without

interfering with existing production. The steps selected

should be typical so that they may be applied at several

positions in the process. They should also be suitable for

transfer from the laboratory to the production process.

Option 2—Automate some of the subprocesses on an ex^st^ng

ECQductign line to reduce the number of assembly and

fabrication operators located in the clean room

environment. The purpose is to reduce particulate counts

and improve the yield of the production process.

Option 3—Set up and implement a new production line

for the purpose of fabricating HgCdTe detector arrays using

the latest automated equipment commercially available and

designing robotic stations where needed. This option

i nc 1 udes site and building location, impl ement i ng the

design and installation of the clean room facility and

specifying processing equipment and automation to eliminate

human operators. This option also requires that the

process and the production rate be studied to determine the

optimum throughput and that operation times be equalized by

either duplication of process steps and equipment or by

automated buffer storage systems. This option may also

include the design of automation equipment and inspection

instrumentation where not commercially available.

26
Figure

HgCdTe Fabrication Process

Sub Process I Substrate Preparation

Crystal Growth

Orientation, Si ic

i

n g and Polishing CdTe

Sub Process 2 ] f Epitaxial Layer Growth

on CdTe Substrate

Sub Process 3 1

'

Array Fabrication

sure

c t ion.

Photo Resist, Expos

Etching, Cleaning,

Implantation, Inspe

Metal 1 ization

Sub Process 4 '

'

Array Dicing and Assy

I nspe c t i on

Su b Process 5

Lead Bonding

I nspe c t i on

Sub Process 6 1

Final Testing

Inspecting

8 Block Diagram of Generic Process for

Fabrication of HgCdTe Detector Arrays

27
General, Di_scussi_on of Q^tfons

Automating a complex process is done to reduce labor,

increase output, or improve safety or quality. Normally the

process should be well defined so that there are no marginal

steps which have high rejection rates. In addition the

individual steps in the process should be matched to the

output rate. Where necessary, multiple operations are used to

maintain the output rate. The automation process therefore is

based upon valid manufacturing, inspection and testing

procedures which already provide a good quality product

through the manual fabrication process. In order to

sat i sf actor i 1 y resolve the production problems which arise

from automation, it may be necessary to modify some step in

the process. This must be done with great care since these

mod i f i cat i ons may affect performance or throughput. While

these modifications are expected during automation, they

should be kept to a minimum in order to insure the quality of

the product and to keep within the time schedule.

In automating a process which is in the developmental stage it

is necessary to carefully select the steps which are to be

automated since it would be uneconomical to automate a process

which will be changed. Therefore emphasis should be placed

upon automating those processes for which there is a reasonable certainty of continued use. The processes which

are subject to change should be scheduled last and reasonable

alternatives should be planned for backup if technical

problems are encountered.

It should be recognized that there is an element of risk which

exists in automating a complex process. Some allowance in the

time and cost is made for this risk in planning an automated

process.

o Qgtfgn Automate several steps at a laboratory level.

This plan has the least element of risk since automation

can be carried out without affecting production. In

addition measurements of quality, defects, and particulate

count can be made to determine the benefits of automation

and robotics in the clean room environment.

o QQti.on 2._ Automate several significant steps in

operating production environment.

an

This plan will require the study of an existing fabrication

process for the HgCdTe detector arrays to determine those

process steps which can be automated. The fabrication

process selected should be well defined technically and

have a reasonable throughput so that improvement in

performance resulting from automation can be measured.

Implementing an existing fabrication process with even one

automated step introduces intangibles which will probably

affect production rate. Therefore allowance should be made

28
to carry out the automation "off line" until performance

can be assured. The automated process steps can then be

incorporated into the production line one at a time with

appropriate measurements to determine improvement.

Allowance -for these measurement costs must be made in the

automation plan.

o Option 3._ Set up a new automated production line.

Setting up of a new automated production line -for

-fabricating HgCdTe detector arrays is both a challenge and

a risk. Since the technology is not mature at this time,

it would be necessary to select a suitable technical

approach to the complex -fabrication process with the

understanding that some portions o-f the process may have

to be changed. The portions o-f the process which can be

performed using commercially available automated systems,

will be integrated into the design. It would be logical to

divide the facility into several clean room areas so that

servicing of equipment or solving production problems will

not shut down the entire process. This introduces the

requirement for a suitable buffer storage area for both

input and output ends of each clean room.

A typical clean room may be large enough to have more than

one production line in order to conserve floor space and

cost. However, the lines must be planned so that the flow

of materials is not impeded and that access is available

for trouble shooting production problems and for service

and repair of equipment.

In designing a facility having several clean rooms, it is

necessary to consider entrance and exit locks to preserve

the dust free environment. In addition it is necessary to

carry the work pieces in suitable dust tight containers or

equivalent when transferring from one clean room to the

next

.

This option therefore requires an overal 1 systems design in

order to optimize its implementation.

D. Detailed Description of Recommended Options

QE£i.on The projects which are recommended for

implementation under this option are at the laboratory

process level. These are described in greater detail in

this section. A plan for automating significant steps in

this process is shown in Figure 9 adjacent to each of the

six sub processes. The proposed automation is based upon

the production labor required, yield or other pertinent

factors which can reduce the cost of fabrication. The

eight resulting candidates for automation projects under

Option 1 are described as follows:

29
HgCdTe Fabr i cat i

n Pr o c e s s Au t o ma t i o n Re c o mme n d a t i o n s

Sub Process I

Real Time Measure me n't and

Mapp i ng of 1,1,1 Cr ys 1 a I Ax is Orientation

Robotic Automation of Single

Chip Cleaning Process in

Clean Ro o m Automate Epitaxial Layer Thickness Mapping with

FT I R Spectrometer

Robotic Automation of

Multiple Chips In Cassette

Mu I t I Ba th Etching Process

Automated Optical Inspection

of Etch Pit Defects

Su bstrate Preparation

Cr ys t a I Gr owt h

Orientation, Si icing and Polishing CdTe

Sub Process 2 f

Epitaxial Layer Growth

on CdTe Substrate

Sub Process 3

PROJECT

PROJECT 2

PROJECT 3

Array Fabrication

Photo Resist, Exposure

Etching, Cl ean i ng. Implantation, Inspection,

Metal I ization

PROJECT 4

PROJECT 5

Sub Process 4

Array Dicing and Assy

1 nspec t i on

PROJECT 6 Automated Array Dicing

Saw with Optical Inspection

St at Ion

Sub Process 5

PROJECT 7 Automated Indium Bump Method

of Lead Attachment Using

Optical Inspection Techniques

Lead Bond i ng

Inspect i on

Sub Process 6

PROJECT 0 Au t o ma t e Op tical Inspection

of Arrays for Defects and

Co n t a c t s

Figure 0 Block Diagram of HgCdTe Fabrication Process

with Automation Reco mme ndat ions for Op t i o n I

Final Testing

I nspec t i on

30
Project #j--Real.-Ti_me d§§surement and Mapping jj_ jj_ jj_ Cdje

Cryst aj Axis Quien tat jon^

This is part o-f subprocess (1) Figure 9. This measurement

is now performed by an X-ray (Laue Pattern) technique on

CdTe wafers which have already been sliced -from a boule.

This measurement technique requires exposure o-f -film -for 15

to 20 minutes per test location (1mm diameter) with an

average testing time o-f 4 hours per wafer. The yield o-f 1,1,1 material per wafer using this method is indeterminate

since it depends entirely upon the e-f-ficiency o-f the

crystal growing process. There may be very little 1,1,1,

oriented material on a wafer. The wafers are too thin to

provide enough material to try to use crystals which occur

in other axial orientations. I-f the wafers were sliced

thicker, some o-f the other crystal orientations could be

converted to the 1,1,1 axis. This however would be

i nef -f i c i ent since more 1,1,1 oriented material would be

wasted

.

It therefore would be a great advantage to determine the

crystal 1 ogr aph i c orientation o-f the material prior to

slicing the boule. The boule could then be cut to optimize

the yield o-f 1,1,1 material. In addition, i denti -f i cat i on

o-f 1,0,0, and 1,1,0 crystal axes in the boule would provide

additional useable material since these sections could then

be reoriented to the 1,1,1 axis.

The development o-f a breadboard model o-f an instrument to

rapidly identi-fy crystal axes using laser technology has

been done under Phase II o-f this project. Feasibility was

demonstrated on October 24, 1985 to representatives o-f the

Night Vision Laboratory. This instrument is being -finished

to a prototype level so that it can be delivered on this

contract. This prototype has a hard wired pattern

recognition system to identi-fy seven di-f-ferent

crystal 1 ographi c orientations. Three o-f these orientations

are the 1,1,1 the 1,0,0 and the 1,1,0 axes. The remaining

four are patterns which appear frequently on one of the

sample boules supplied by the Night Vision Laboratory. The

hard wired pattern recognition system uses 960 shift

registers which can be rewired, if required to identify

other crystal orientations. However, this hard wired

system does not have sufficient capability for recognizing

more complex geometric patterns which may be encountered in

further applications of this system.

Further work is needed under Project #1 to program

instrument to operate with a host computer , which will

enhanced software pattern recognition capability,

will allow much more sophisticated pattern recogni

routines to be easily programmed to expand the capabi

of this instrument. Further research is suggested

"rocking curves" for the goniometric crystal mount

improve the accuracy of cr ystal 1 ogr aph i c orientation,

this

have

Th i s

t i on

1 i t y

on

to

and

31
for mapping techniques. A more detailed description o-f this instrument is given in Phase II o-f this report.

Project #2--Robgti_c ^ytgmati_on of Si_ngl_e Chfg Ql9*QiQ9

Process fn Cl.ean Room^

This is part o-f subprocess (2) Figure 9. This operation

was selected since it is an example o-f a medium dexterity

application which is typical o-f many steps in this process.

The single chip handling capability will require the design

of appropriate grippers to handle the substrates without

chipping, stress damage or contamination. The manipulation

of the unmounted chip will require the programming of

intricate motions which are applicable to other processing

steps as well as inspection and testing. The use of this

robot in a clean room environment will require the solution

of problems of material supply, finished part delivery, and

robot particulate generation. Many clean room robots use

shrouded members to contain any particles produced in the

mechanism. In addition an evacuation system inside the

robot is used to remove particles generated by the

mechanism and carry them outside the clean room

environment. This is done by keeping a negative pressure

inside the robot mechanism. Experience has shown that

particulate levels can be reduced from class 1000 to class

10 providing there are no operators inside the clean room.

The robot should be able to perform a complex operation

reliably and continuously' to give consistent parts and an

increased yield.

This project would employ a commercial robot such as shown

in Figure 2 with modifications of the wrist mechanism and

grippers to increase the dexterity. The grippers would

probably use a vacuum system to hold the CdTe substrate.

Special trays or magazines must be designed to facilitate

the input and output of substrates. If the substrates are

irregular in shape and size it will be necessary to use a sensor or vision system to help the robot locate each

individual substrate. This vision system may be on the

robot arm or it may be mounted above the station in a fixed

position. If the cleaning process is a liquid dip or flush

it may not be possible to use a vacuum pickup since the

vacuum will aspirate the solutions. Therefore it may be

necessary to have both vacuum and mechanical grippers

built on the end of the robot arm so that the appropriate

end effector can be selected. An example of this is shown

in Figure 10. This single end effector has three modes

of operation. It can pick up single pieces by vacuum,

single pieces by mechanical jaws and it can pick up

cassettes mechani cal 1 y . If the substrate is cleaned

by the plasma method it would be appropriate to use a vacuum gripper. However the plasma cleaning system will

also have to be automated with racks for loading, doors

for closing the vacuum chamber and controls -for

automatically cycling the time, the vacuum, the R. F.

32
connection to jaw servo

MULT

FIGURE 10

-FUNCTION ROBOT END-EFFECTOR

33
excitation, and the oxygen bleed. A typical configuration

for the operation is shown in Figure 11.

For some materials, plasma cleaning may adversely affect

the surface or the subsurface character i st i cs. With

cadmium telluride substrates, surface anomalies can be

cleaned with a bromine etch after plasma cleaning. The

robot should therefore have appropriate grippers to enable

it to carry the substrate through this process. If a vacuum pickup is used for a wet process, such as etching,

the substrate may be delivered to a dry carrier which then

feeds into an automated etching system. The substrate is

then etched and dried and then delivered to an output

station where the robot can again pick it up and take it to

the next operation. Grippers which use vacuum to pick up

parts must be made of materials which do not deteriorate,

contaminate, or mechanically damage the substrates.

Therefore, one or more elements of compliance must be built

into the vacuum gripper. The gripper must be designed to

pick up and to put down the substrate reliably, quickl

and in a pr edetermi ned position. It is assumed that th

finished item from one stage in the subprocess will be

reliably fed to the next stage in the process.

An alternate method of cleaning the substrate would mafe

use of semi automated wafer cleaning stations such as the

unit shown in Figure 12. This cleaning station uses a vacuum chuck to hold the substrate while solutions are

sprayed and brushed across the surface to remove greases

and particulate material. The robot shown in Figure 11 can

be used to load and unload the vacuum chuck of this

cleaning station.

Other steps in this process can be automated in the clean

room by using a similar robot to load and unload the

processing station.

Project #3——Automate Epi_taxi_al_ Layer Thickness Magging wi_th

FTIR Spectrometer

This instrument must measure the spectral transmi t tance of

the chip in the infrared spectrum from 400 to 4000 wave

numbers. The application of this instrument is to measure

the thickness of the epitaxial layer to determine the

potential sources of defects which reduce the yield. These

defects may affect only one detector in the array.

Therefore the exploring spot must be small enough to be

able to measure the epitaxial film thickness of a single

pixel having a sice of 25 microns by 37 microns.

The spectral tr ansmi t t ance curve will also provide

information on the cutoff wavelength. This instrument

requires an automated "X", "Y" positioning system such that

the substrate can be translated by small increments to map

a selected area and record the data. The data storage

34

>

<n
eo

•r*

(0+>0

01

35

Cleaning

Station
Figure 12 Automated Washing Station

36
requirement is very large in order to store a spectral

transmission curve tor each pixel on the 1/2" x 1

substrate. If this substrate is mapped in 25 micron steps

this will require storing 500,000 transmission curves. In

order to reduce the data storage, a set of data reduction

algorithms can be used to calculate the cutoff wavelength

and the epitaxial layer thickness for each point so that

only this information is stored.

Specifications on this instrument were prepared by NBS and

it was procured for this application. This instrument is

presently being programmed with the data reduction

algorithms for cutoff wavelength and expitaxial layer

thickness. It is then scheduled for delivery to the U.S.

Army Night Vision Laboratory (Figure 13).

Further research should be done on the mounting of sample

substrates and the mapping techniques needed to locate and

identify the surface morphology and the defects which

affect the IR performance of these detector arrays. The

identification of defect composition and substrate

condition will require using one or more of the following

nondestructive testing procedures for surface analysis. An

instrument to perform theses tests is shown in Figure 14.

XPS—X—ray photo emission spectroscopy

UPS—Ultra violet photo emission spectroscopy

SIMS—Secondary ion mass spectroscopy (this may be

destructive)

TPD—Temperature programmed desorption

LEED—Low energy electron diffraction

ISS—Low energy ion spectroscopy

#4-—Robotic Automation gf Etching of Mul_ti.gl_e

Substrates in a Cassette^

This project requires designing a special cassette for

holding 1/2" X 1" substrates with minimum edges masking.

The number of substrates in the cassette should be

determined to give a throughput compatible with the overal

1

process throughput. The robot may be similar to the unit

shown in Figure 2. The etching process is usually

associated with the photo resist, baking and mask transfer

processes. Good automation systems incorporate the

principle that once a part has been oriented it should not

be released. It would therefore be advantageous to

incorporate as much of the above processing as possible

into the same automated line. Using this technical

approach a number of suitable systems are commercially

available. They may however have to be modified to fit the

substrate size. One of these systems is shown in Figure

15. This system takes its input from a cassette and

carries the substrates through the process on an air

bearing transport device to minimize damage to the surface.

It will however be necessary to investigate the affect of

37
Infrared

Microscope

Head

38
X-Ray Monochromator Spherical Sector Analyser

Analysis Preparation Fast Entry

Lock

Figure 14 - Surface Analysis Instrument

_

39
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40
the air bearing transfer device on the distribution o-f the

particulate count in the clean room. The substrates are

taken -from the -feed cassette and delivered to a spinner

where they are coated with the photo resist and then go to

a hotplate -for baking. The substrates are then returned to

a second cassette where they are accumulated until the

cassette is -filled. The input and output cassettes are

located adjacent to each other so that the robot can

transfer the -finished cassettes to the next stage o-f the

process. This may be a mask printer to expose the photo

resist. The throughput o-f this station is typically 80

wafers per hour allowing ample time -for the robot to

transfer the waters. The mask printer may be cassette fed

with the robot loading and unloading the printer. A more

integrated layout of the clean room will be required to

determine the optimum method for transferring the cassettes

to the next stage in the process. This may be chemical

etching or ion beam milling, dependent upon the specific

process selected.

Project #5--Automate Optical, Inspection of Etch Fit Defects

This project concerns the development of a general purpose

scanning system which can be adapted not only to etch pit

counting, but to other optical inspection operations. The

use of coherent light to improve the resolution of a conventional inspection microscope is well recognized. In

addition the inspection operation will need to be automated

with signal enhancement, pattern recognition and special

scan patterns. To perform this function, a laser flying

spot scanner can be adapted to the inspection station.

The laser flying spot scanner can consist of the basic

toroidal laser scanner from Phase II adapted to the

microscope inspection station. This is shown in Figure 17.

The inspection station is mounted on the adjustable height

platform and aligned under the laser scanner so that the

1 aser beam sweeps the full projection eyepiece. This

conf iguration is illustrated in simplified form in Figure

16 with a conventional microscope. The 1 aser beam is

scanned in a circular pattern by exciting both the "X" and

the "Y" gal vanometer s with a sinusoidal signal of the same

amplitude having a 90 degree difference in phase between

galvanometer signals. The resulting 1 aser scan will then

fill the eyepiece and be reimaged through the objective at

a reduction ratio determined by the product of the powers

of these optical elements. The excitation voltage to the

gal vanometer s can be reduced during a discrete time

interval so that the circle is gradually reduced to a point. This results in a spiral scan of the 1 aser beam in

the object plane of the microscope. Since this is also the

substrate surface it will be scanned by a very small 1 aser

spot which will also describe a spiral. Any light which is

reflected from the substrate surface will re-enter the

objective and be reflected by the vertical illuminator beam

41
El ipsoid
Figure 17 - A Typical Configuration 1 for a Laser Flying Spot Scanner with Microscope

43
splitter to a detector mounted in place of a normal

vertical illuminator light source. This signal will be

synchronized with the galvanometer excitation signals to

produce a polar coordinate scan. The detector signal will

be used to intensity modulate the pattern displayed on a CRT. This will give an image o-f the substrate on the

microscope stage. It can easily be seen that the scanning

pattern can be changed to a two coordinate X, Y scan or a diametral scan of constant angle or variable angle. These

techniques of scanning may be used i nterchangeab 1 y and can

be programmed from the display console.

A pattern recognition system can be adapted to identify

shape, size, and number of artifacts identified in the

field. Reliable number counts can be obtained if

programmed properly using a diametral scan with a motorized

X, Y stage on the microscope. This system can eliminate

the tedious counting operation now carried out by human

operators.

The height of the microscope can be adjusted

the height of the mounting plate shown in

Algorithms for image enhancement and pattern

can be added to this system to further enhance

the inspection process.

by changing

Figure 16.

r ecogn i t i on

its uses in

This system can also be

transmission mode and to

wavelengths to be used; see

1 . The laser flying spot

the near infrared with

objectives and detectors.

adapted to operate in the

allow lasers of •different

references 7 and 8 in Appendix

scanner can also be adapted to

appropriate reflecting type

This project includes the design and fabrication of a full

defect counting system with a suitable microscope station

and a computer driven mechanical stage, using a helium neon

laser scanner (wavelength 6328 angstroms). The output

image will be displayed on a monitor screen. Simplified

controls for changing scan modes will be required. A

tunable die laser, not included in this study, may be

substituted for the helium neon 1 aser to explore the

improvement in detection which can be obtained by spectral

filtering.

Project #6-—Automat ed Array S^i_cjng Saw w i_t h Ogti^

lQ!=E>?£tjqn Station

This project concerns inspecting

after the epitaxial 1 ayer has been

have been processed through the

baking, exposure and developing,

determining the best yield of 60,

detector arrays from the substrate.

the finished substrates

formed and the arrays

photo resist spinner,

This inspection is (or

120, and 150 element

The inspection is tor

44
defects in the array as well as inclusions and other

artifacts which limit array length. After the good arrays

on the substrate have been located, an automated counting

system will check length and determine how to cut for best

yield of longest arrays or whatever other rationale is

selected to meet the immediate production needs.

The substrate should be mounted on a carrier which will

also be compatible with the " cutoff" saw. The substrate

will be approx i matel y 1/2" X 1" with a number of arrays

located on its surface. The arrays will have sufficient

space between them to allow for cutting and separating

without damaging the detectors. A typical array is shown

in Figure IS after it has been cut from the substrate.

A number of carriers can be mounted in a cassette so that

the operation may proceed with a minimum amount of human

intervention. The input to this station will therefore be

one or more cassettes. Since the substrate is mounted on a carrier, the output of this station can also be a cassette.

The very small arrays which have been cut from the

substrate will still be held in place on the carrier by a suitable cement.

The station can consist of an input buffer containing a number of magazines, a robot to unload and transfer the

substrates to the laser scanner, a cutoff saw with magnetic

or vacuum chuck for the carriers, a washing station and an

output buffer for magazines. The robot must have enough

reach to also transfer the carriers from the laser scanner

to the "cutoff" saw. The data on the array lengths and

defects will be fed to a computer which determines the

cutting pattern and records it. This information is

processed and used to determine the cutoff saw adjustments

so that they can be made automat i cal 1 y . The finished

carriers with cut substrates are processed through a washer

before being transferred to the output cassette. A

tentative floor plan for this station is shown in Figure

19. It is apparent that these operations must be carried

out in a clean room area. Therefore the r ear r angemen t of

these operations within a clean room is shown in Figure 20.

This station should be controlled by a computer which is

programmed for this specific operation. The computer

should be located outside of the clean room area to allow

convenient access for programming. Ideally this clean room

area should have glass partitions so that the work modules

can be observed during operation. The clean room

facilities for this station can have one of two

configurations. Either a clean room can be built

individually for this operation or this operation may be

located in part of a larger clean room area. The

particulate generating quality of a cutoff operation would

45
Figure 18 - One Detector Array (There will be several arrays on each substrate)

46
Input

Cassette

Figure 19 - Automated Array Slicing Saw with Optical Inspection Station

47
Clean Room

Operator

Figure 20 - Automated Array Slicing Station and Inspection Station Shown in a Clean i

48
normally -favor a separate room. The diffusion o-f particulate matter may be minimized by building a suitable

shield around the cutoff saw and using a cutting liquid

which does not contaminate the substrate.

The cost o-f installed clean rooms varies -from $350 to $800

per square -foot depending on particle count and

accessories. Therefore, the clean room area assigned to

each operation should be minimized.

Project #7--Aut ornate I.ndi_um Bump Method of Lead Attachment

Using 0gt gcaf Inspection Technggues^

This project may consist o-f evaluating the -features o-f already developed equipment -for attaching leads to the

HgCdTe detection array by the Indium Bump method. This

equipment uses an infrared microscope to look through the

detector array and the mask. These are displayed on a T.V.

screen. The matching o-f -fiducial marks is now accomplished

by manual translation o-f the stage in X and Y coordinates.

The stage should be converted to a motorized stage with

stepping motors and suitable power supplies so that it can

be driven by a computer.

This equipment should be examined to see whether there is

an available optical port through which the laser scanner

described in Project #6 can be used to -find the -fiducial

marks. The dedicated computer can be programmed with a search algorithm to direct the laser scanner to locate the

-fiducial . marks and measure their location with regard to a convenient datum point. This in-formation can be matched

with the -fiducial marks -from the infrared microscope and

suitable difference signals can be generated. These

signals can drive the X and Y translation motors to align

the detector with the mask. The computer may also contain

a program -for automating the remaining steps in the lead

attachment process.

The -functions o-f loading the detector into this equipment

and unloading the completed detector should be examined -for

suitability to automation. The detector arrays are very

small and may have to be mounted on a subplate to be

handled by a robot. This subplate must not interfere with

the other steps in this operation, therefore it must

transmit the infrared radiation used in the microscope

system. This project should be a feasibility study with

the implementation to be carried out on a best efforts

basi s

.

S^zz^ytomate the Opt jcaf Inspection of Arrays for

Defects and the Ex§<mjnati_on of Contacts^

This project would utilize' the laser scanning equipment

described in Project #6 with a suitable high power

microscope. The configuration for this equipment is shown

49
in Figure 17. This project must explore the combination of

raster polar and diametral scan techniques to determine the

best combination to use in developing an algorithm for

determining the quality of the overal 1 detector array and

contact structure. Pattern recognition techniques can be

utilized with appropriate image enhancement to devise a method for automating this process. This inspection

represents one of the highest skill levels which is

performed by the operator. Therefore it is anticipated

that the experimental nature of this project would make it

appropriate to undertake it on a best efforts basis.

While it is difficult to estimate the cost of developmental

projects in advance the following very rough estimates

have been prepared for determining overall program

magni tude.

Option 1 Budgetary Estimate

Project #1 *250 000

Pro ject #2 300 000

Project #3 200 000

Pro ject #4 350 000

Pro ject #5 250 000

Project #6 450 000

Project #7 350 000

Project #S 250j.000

*2 , 400 000

This will be approx i matel y a 2.4 million dollar effort over

a period of two years. It is estimated that a team of 15

scientists and engineers would be required. The

implementation of these projects could take place in the

existing clean room facilities at the Night Vision

Laboratory at Fort Bel voir, VA.

Option XX. This option considers the automation of

critical processes in an actual production line fabricating

HgCdTe detector arrays (for profit). The difficulty, which

can be immediately seen, is that any delay in production

caused by this automation will cause scheduling problems

and therefore losses. While there is no good way of

avoiding some delays these can be minimized by developing

the automated process "off line". The process can then be

installed at the production facility with minimum downtime.

Since this automation will be done in a clean room

environment it will involve a duplication of facilities and

efforts which add to the cost. A typical program for

automating each operation is as fallows:

o On site study of the selected process at the plant

o Design of the automated process at the laboratory

o Fabrication and purchase of equipment for the process

o Selection of a suitable laboratory "off line" clean room

installation site

50
o Installation at laboratory "off line" site

o Trouble shooting process at laboratory site

o Disassembly of equipment and shipment to production plant

o Installation of equipment at production plant

o Trouble shooting process at production plant

The duplication o-f effort involved in setting up the

process twice has the advantage o-f showing up potential

problem areas. The selection o-f the process to be

automated at a production plant must be done with

consi derat i on o-f the probability o-f success since this type

o-f task does not -fit into a best efforts category.

Consequently it is not logical to select the most di-f-ficult

and intangible process -for automation in a plant production

line. The process must also be mature enough so that it is

not changed during the period that the automation task is

being carried out. These consi derat i ons point to the

difficulty of automating a process which is already

operating in a manufacturing plant. One additional

consideration which past experience has disclosed is that

the level of cooperation from the plant personnel is better

when this automation is carried out by plant personnel.

This often makes the difference between success and

failure.

Considering these factors the cost of automating a process

of mean complexity such as the "Automated Array Dicing Saw

and Optical Inspection Station" similar to Option 1,

Project 6, can be 8 to 10 times the cost of automating at a laboratory level. Nevertheless the following five

subprocesses are listed for automation at a plant. They are

identified with their estimated levels of complexity.

Subgrocess Level_ of Complexity

o Automated Optical Inspection

of Etch Pit Defects

o Automated Loading and Unloading

of CdTe in Horizontal Bridgman

Furnace for Growing Single

Cr ystal

s

o Automated Loading and Unloading

of Liquid Phase Epitaxial Layer

Growing Process

o Automated Array Dicing Saw with

Optical Inspection Station

o Automated Indium Bump Method of

Lead Attachment using Optical

Inspection Technique

Medium to high

Very high

Very high

Mean

High

The approximate cost of automating a mean complexity

process at plant level is between 2 and 3 million dollars.

The cost of automating a high complexity process cannot be

estimated in this report since a detailed estimate from a mature process must be used as a guide. However, it will

51
be generally much higher than a process of mean complexity.

A program to automate the -five processes in Option II at

production plant level is estimated to cost -from 10 to 20

million dollars and success o-f the high complexity

processes cannot be guaranteed.

QetiQD III" Automate complete HgCdTe detector array

process at a manufacturing plant level. Using the process

in Appendix 3 as a guide, with direction -from the Night

Vision Laboratory project monitor, 69 o-f the 102 processes

were to be considered -for automation. However, if the

manufacturing plant is to be considered operational it must

have all processes performed at a reasonable throughput

rate.

Since Option III is a considerable task, the site, building

and clean room facilities should be adequate to perform the

entire process. Using this principle as a guide it is

possible to estimate the approximate area needed for the

average sub-process steps and to allow for access areas.

T.he parameters developed here are considered to be

tentative since it will require a detailed engineering

design to establish firm requirements.

The average floor space needed per operation with room for

equipment, robots, and access area, excluding aisles can be

estimated as 6 ft.X 10 ft. or 60 square feet. This should

be doubled to allow for aisles and buffer storage.

Therefore at 120 square feet per subprocess, 102

subprocesses will require 12,240 square feet of clean room

facility. Using the''cost of $800 per square foot gives a cost of $9,792,000 for the clean room area. The support

facilities for this type of manufacturing will require

approximately 8000 square feet so that a total building of

20,000 square feet would be required. This can probably be

built at a cost of $100 per square foot or a total cost of

$2 , 000 , 000 . The average cost of each automated operation can be

estimated at $2.5 million while manual operations can be

estimated at $600,000 each. Therfore if this plant

contains 69 automated operations and 33 manual operations

it is possible to get an overall estimate of installation

costs

.

20,000 square foot building

at 1 00 , 000 per sq . ft.

12,240 square foot clean room

installation at $800.00 per sq . ft.

69 automated operations at 2.5 million

33 manual operations at $600,000

Total

n 000

,

000

.

00

792, ooo . 00

172, 500

,

000

.

00

1

CM 800

,

ooo . 00

$194 , 092, 000

.

00

This cost does not include the trouble shooting required by

scientists, engineers, and technicians to get the facility

52
operational. It is estimated that a team of 30 people will

be required -for a period o-f 4 years to carry out this work.

With travel costs this can be estimated at approximately

$5,000,000 per year for 4 years or $20,000,000. There will

be many other -factors not covered in these estimates

including building site, partitions, power lines, office

equipment, waste disposal and other facilities necessary to

a manufacturing plant of this type.

It is therefore apparent that a more refined estimate is

needed. It is also apparent that the clean room area

should be minimized to accommodate the detailed operations.

Some consideration has been given to developing a better

operating clean room configuration to minimize cost.

However, the principal costs are for the automated

operat i ons.

The total cost for this four year program is estimated

215 million dollars. The estimates for Option I, II and

have been prepared from information

industrial sources. The costs are based

chart in Appendix 3. If changes in

introduced, it will be necessary to

est i mates

.

at

1 1

1

gathered from

upon the process

the process are

modify the cost

53
Phase II — Implementation of a Near Term Demonstration

of Automation. The Development of a Laser Scanner

to Determine Crystal Axis Orientation

I Statement of the F'robfem

The determination o-f the orientation o-f the crystal axis o-f the

cadmium telluride substrate material has been one o-f the most

time consuming operations in this process. This axis must be

located within 0.5 degrees in order to optimize the performance

o-f the detector. The subsequent processes o-f epitaxial 1 ayer

growth and implantation are affected by errors in the alignment

of the 1,1,1 crystal axis. The current method for determining

the location of this axis is a Laue pattern using X-ray

radiation. The X—ray beam is directed through a photographic

film to a point on the cadmium telluride crystal . The X-rays

are reflected back from the lattice planes of this crystal to

give a pattern of dots. This requires an exposure of 15 to 20

minutes per print. The resulting pattern is then examined for

threefold symmetry which indicates the 1,1,1 plane. The errors

in angular position of the dots must be correlated with the

error in the 1,1,1 axis. Therefore, this is not a real-time

techn i que nor is it direct readi ng. Since the crystal growi ng

process for cadmium telluride is not as mature as for silicon,

the wafers may have several different crystal orientations over

the surface. It is, therefore, necessary to take a number of

Laue patterns over the surface of the wafer to locate the

desired 1,1,1 crystal orientation. The areas which will have

this orientation are unpredictable and with present crystal

growing techniques it may take as long as 4 hours to completely

explore a one inch wafer.

The objective of Phase II was to explore the techniques for the

determi nat i on of the crystal axis orientation and seek a faster

method which could be used for mapping the surface of the

cadmium telluride wafer. A laser technique was demonstrated at

the Night Vision Laboratory to illustrate an alternative

method

.

The goal was to develop, design and build a breadboard model of

this instrumentation to demonstrate the feasibility of

automating this process. The demonstration was to show that the

measurement could be accomplished more rapidly and the yields

of 1,1,1 material increased.

I I . Genera^ Di_scuss_i oq

The cadmium telluride crystal must have a polished surface in

order to get a good Laue pattern for crystal axis

determi nat i on . The X-rays are diffracted from the atoms in the

lattice planes of the crystal giving the charac t er i st i c pattern

which can identify the crystal axis orientation. This

54
technique is essentially a surface technique since the X-rays

penetrate only 100 to 1000 lattice planes dependent upon the

absorption constants of the crystal. The actual depth of

penetration is very small.

Using an optical technique to measure the crystal orientation

requires a different surface preparation from the X-ray

technique. This technique requires a selectively etched surface

where the etch pits follow the lattice plane boundaries and the

etch pit density is high. Since selective etches for cadmium

telluride have not had extensive development, it has been found

that sandblasting the crystal with 15 micron silicon carbide

abrasive gives a high population of etch pit related surfaces.

These result from cleavage along lattice plane boundaries.

Reflecting a coherent laser beam from a sandblasted surface of

a crystal, therefore, can give a character i sti c pattern. This

is described in greater detail in the ASTM Standards,

References 5 and 6. The laser technique is therefore also a surface technique but it uses much deeper surface morphology

than the X-ray technique.

The pattern produced by a laser reflecting from a 1,1,1

oriented surface of a cadmium telluride single crystal has

threefold symmetry. Therefore, if a real time system can be

devised to detect this symmetry, the crystal axis determi nat i on

can be automated.

The laser pattern from the 1,1,1 plane of cadmium telluride is

reflected at a very wide angle and does not have good

definition. This is due to the diffuse reflection which comes

from surface features unrelated to the crystal lattice planes.

The difficulty of this problem was recognized only after a number of crystal samples were tested with a laser beam in the

laboratory. These samples were supplied in the form of wafers

and boules of crystalline cadmium telluride. Since the crystal

growing techniques for this material are not yet mature, these

wafers and boules contained multiple crystals.

Methods for exploring the

beam were investigated,

were reviewed with regar

Laser scanning

this problem,

determined in

these crystals

techn i ques

If the

the boule,

in addition

surface of the crystal with a laser

The problems of signal to noise ratio

d to improvement of this parameter,

were also analyzed for application to

orientation of the crystals can be

then it may be possible to recover

to the 1,1,1 orientation.

From these inputs, the principles for the 1 aser scanner were

derived. The advantage of a laser scanner over a fixed 1 aser

beam is that it can generate much more information from the

reflected patterns providing there is a means for correlating

the 1 aser beam position with the reflected energy. The proposed

technical approach was developed from these principles.

55
III. Techn Aggroach

The 1,1,1 cadmium telluride crystal was explored with a 1 aser

beam normal to the surface as shown in Figure 21. A photo

sensor was mounted on an angle sector so that it could be

rotated 360 degrees through angle W around the laser axis. The

angle of reflection, theta, was also adjustable. This allowed

the photo sensor to measure the polar reflection from the

crystal at a number of angular settings of theta. The angle

theta was varied from 50 degrees to 70 degrees giving cone apex

angles of 100 degrees to 140 degrees. Correlating this

information in osc i 1 1 ogr aph i c patterns in Figures 22a, 22b, 23a

and 23b it was found that the maximum signal reflected from

1,1,1 cadmium telluride occurred at an angle of reflection of

67.5 degrees. This is equivalent to a cone angle of 2 X 67.5

degrees or 135 degrees. The three lobed pattern was clearly

detected. This signal was differentiated in Figure 24 and

showed a signal to noise ratio which was good enough to be

used in an automated system. It was inferred that other

crystals would have different peak reflection angles. This was

corroborated with a selectively etched 1,1,1 silicon crystal

whose peak angle of reflectance was approximately 35 degrees

giving a solid cone angle of 70 degrees.

A review of existing commercial laser scanners identified a bacteria colony counter having some features which were

applicable to this requirement. This instrument is made by

Exotech Inc. It uses a helium-neon laser beam in a circular

scanning pattern to measure the transmission of light through a bacteria culture in a petri dish. This instrument is shown in

Figure 24A. The 1 aser beam deflection is accomplished by two

galvonometer driven mirrors excited by two sine waves of the

same frequency but 90 degrees out of phase. The radius of the

circular scan is determined by the amplitude of the sine waves.

This instrument was adapted to scan a point from all azimuth

angles by using an ellipsoidal reflector to converge the

circular scan. Using the exit pupil of the optical system at

one focus of the ellipsoid, the second focus was then imaged

directly on the crystal surface. This is shown in Figure 25a.

In this manner the crystal was illuminated by a 1 aser beam

rotating 360 degrees about its axis at a rate of 125

revolutions per second. A detector in the center of the

scanner , located close to the crystal , was used to detect the

light reflected from the 1,1,1 crystal surfaces. The principle

for enhancement in signal to noise ratio obtainable from this

scanner is shown in Figure 25b. This enhancement is due to the

fact that most of the light from the diffuse reflection

surface does not reach the detector. The signal reflected from

the facets of the crystal however is picked up by the detector.

The diameter of the 1 aser scan on the ellipsoidal mirror is

changed to change the angle of incidence of the 1 aser beam as

shown in Figure 25c. This system, therefore, provided a rotating beam which is incident on a 1mm diameter spot on the

crystal and whose apparent origin moves around in a toroidal

conical path at the rate of 125 revolutions per second.

56
ILuTEN'brvX VS. KmGUG ^\s*SULfc£tAevrrs>

Figure 21 - Measurement of Reflection Pattern from Scanning a Single Crystal

57
XKJTE k\S l*T Y VS ANa ^ fc O 0 A 0 - 'SO

0

Figure 22a - Oscilloscope Trace of Reflected Pattern at 0= 50°

X ITY u) © - (oO

Rotation Angle is time base

Figure 22b - Oscilloscope Trace of Reflected Pattern at 0= 60° * ^HOTOS ExVOSXb A*;! ^ ^ t£vtLo?K.E«oT T><At ' c- e ~

AX '5 - SVolts

b\Y
v< KMGr Us Vo®- @ - yt .*5

X-AXIS 5 5Volts

l,6<0

o Rotation Angle is time base

Figure 23a - Oscilloscope Trace of Reflected Pattern at 67.

5

C

VTY NfS. 0 -- 10°

5Volts

* PhdtoS AT "S -

*5.(o T\tA£ -- 59

*
Vo/

/s

Figure 24 - Oscilloscope Trace of First Derivative of Reflected Pattern at 67.5

-at of O c.x^C/.'Ev. At A ^ ^ ^ Lcf t’ T\ t\t - 3*

^

60

Laser Beam

Elipsoid

Focus *1

Entrance

Pupil

X” Galvanometer Mirror

T" Galvanometer Mirror '

llipsoidal Mirror

Conical Laser Scan

Incident Scanning Laser Beam

Signal to Detector

Diffuse Reflectance;

Between Pits "X

c Single Crystal • y Selectively Etched

Surface with Pits

that Follow Crysta’

Lattice

i Figure 25 b Signal to Noise Enhancement

Scanning Laser Beam

. . , . . « / Cn<r..i\ Minimum Cone Angle

Toroidal Conical (Spiral) r

Path of Scanning Laser Beam Maximum Cone Anglt

\ \

• (

Signal to Detector

; Apex of Cone is

Single Crystal ' Stationary on Cryst.

Figure 25c Dynamic Spiral Conical

Toroidal Laser Scan

Test Crystal

Detector

Apex of Conical Laser Scan

Ellipsoid Focus #2

Figure 25 a Laser Scanner for Crystal Axis Orientation

62
Synchronizing this signal with an oscilloscope sweep yields a time based display o-f this pattern. The driving signals -For

the galvanometers can also be used to drive the "X" and "Y"

axes o-f the oscilloscope to get a polar pattern. Connecting

the detector output to the " Z " axis o-f this oscilloscope

displays the spatial patterns o-f the reflected light -from the

crystal surface.

The design of this instrument included a goniometric stage to

mount the crystal so that it can be mapped for orientation

over its entire surface. This may be accomplished by a simple

polar translation for wafers. However, since it would also be

desirable to map the surface of the boule to improve the yield,

a system for translating and rotating the goniometer stage in

cylindrical coordinates was devised. Sample mapping display

techniques were explored to facilitate analysis of this

information. A typical crystal distribution for a boule is

shown in Figure 26a. A r epr esen tat i on of the cylindrical map

of the surface of the boule is shown in Figures 26b and 26c.

A goniometric mount having two rotational axes and one

translation axis with the appropriate power supplies was used

to map the crystal suf ace. The goniometer is controlled by

signals received on either an RS-232 serial or an IEEE 483

parallel data bus.

The design of the 1 aser scanner is shown in Figures 27, 28, and

29. A vertical adjustment table was designed to mount the

goniometer so that it can be focused on both the end and the

circumference of the boule. This adjustment is manual but it

can be automated in- the future.

A hardware version of a simplified pattern recognition

algorithm was designed and built using 960 shift registers to

count 360 degrees. This gives a potential accuracy of

approx i matel y 0.3 degrees for location of the lobes of the

reflected pattern. The algorithm selected for the three lobed

pattern was to "and gate" the signals every 120 degrees using

the clock frequency of the laser scanner to synchronize the

clock of the pattern recognition system. Detection of these

patterns shown in Figure 30 is indicated by lighting a diode.

This scheme was easily extended to the 1,0,0 plane which has a four lobed pattern and to the 1,1,0 plane which has a two lobed

pattern. The schematics for this pattern recognition system

and associated circuitry are contained in Figures 31, 32, 33,

and 34.

This scanner was demonstrated to the Project Monitor as a breadboard model on October 24, 1985 with a 1,1,1 cadmium

tel luride crystal and a 1,1,1 silicon crystal . The signal to

noise ratio of this scanner is so good that it can pick up the

reflection from silicon far outside of the optimum reflection

angle for this material, where it cannot even be seen by the

human eye.

63
COl4)(rt

CdTe Cry STOwl Bougie

4 * Kctuo.1 S’\^e of Top V\ew

Figure 26a Typical Crystal Structure for the end of a Boule or a Wafer of CdTe

"Fwe 2.€*ro rer\ ue po\ni"

64
Length

0—3

lnoh«s

Y—

C^ordinatfl

Orientation of Points

TOP SUFFAGE

X—Coordinate

igure 26b Mapping Display for Round Wafer or End of Boule

Orientati on of Points

2

2.S

2.e

2.4

2.2

2

i .e

i .e

1 .4

1 .2

1 O.S

o.e

0.4

0.2

o

-0.2 0.2 0.6 1 1.4 IS 2.2 2.6 2

PERIPHERAL SURFACE

Ancle O—3&D Dec|re>=s

Figure 26c Mapping Display for Cylindrical Surface of a Boule

65
Laser Scanner

Scanning Laser Beam

Detector Mounting Plate 1

Ellipsoidal Reflector

Test Boule

Mounting Adapter

Motorized Rotation Stage -

Motorized Rotation Stage

Motorized Translation Stage-

-i r If W’ 1

1 . T i

i i

Vertical Adjustment Handwheel

Vertical Adjustment Platform

Base

Lead Screw Synchronizing Sprockets

Figure 27 - Side View of Toroidal Laser Scanner

66
Laser Scanner

Scan Switch

Crystal Axis Indicators

Power Switch

* l^ L“T

Mounting Adapter

Motorized Rotation Stage

—Scanning Laser Beam

Detector Mounting Plate

Ellipsoidal Reflector

Test Boule

Motorized Rotation Stage

Motorized Translation Stage

Vertical Adjustment Platform

Figure 28 - Front View of Toroidal Laser Scanner

67
Three

Synchronized

Lead

Screws

for

Elevation

Travel

68

Lead

Screw

Synchronizing

Sprockets
Cadmium Tel luride Silicon

Figure 30 Typical Geometric Patterns Produced by Scanning Crystal

69
rw 3: *

• VI n _2 - vj O

fM

V*o

VJ

70

Figure

31

Schematic

of

Clock

Circuit

ry

for

Laser

Scanne
+

12V

71

Figure

32

Schematic

of

Signal

Amplifier

Digitizer

for.

Laser

Scanner
72

Figure

33

Schematic

of

Pattern

Recognition

Circuitry

tor

Laser

Scanner
+

12V

OSrv

*0od

^

g -Os 5

-05

-o=

it AVV—

Wr^

D

— —

0

IrJ

o

&•

I04

•0~

I 1~

73

Figure

34

Schematic

of

LED

Readouts

for

Laser

Scanner
Since there were no samples o-f 1,0,0 cadmium telluride

available, much time was spent mapping the sample boules using

X-ray techniques to locate other crystal orientations to test

the scanner. A selectively etched crystal o-f 1,0,0 silicon was

however, obtained -from the NBS Center -for Electronics and

Electrical Engineering. This crystal was immediately

identi-fied by the laser scanner pattern recognition system as

having a -four lobed pattern.

This breadboard has been upgraded to a prototype model by

automating the scanning circuitry, extending the pattern

recognition to seven di-f-ferent crystal orientations and

packaging the circuitry and the displays inside the instrument.

This instrument has been developed -far beyond the breadboard

model called tor contractually. The goniometric mount has also

been completed and assembled to the scanner.

The Night Vision Laboratory has

this scanner. This has not

expiration o-f -funding.

provided a yet beencomputer to

i nterf aced

automat

e

due to

IV. Results

The -feasibility o-f this scanner has been successfully

demonstrated using a number o-f crystalline samples. The

potential accuracy is good since the sensitivity is doubled by

reflecting the laser beam -from opposite sides o-f the sample.

In addition the very favorable signal to noise ratio of this

scanning system improves its sensitivity to small angular

def 1 ecti ons.

While further development should be done on

presently usable for experimental work,

telluride and silicon have been tested

patterns have been identified in real

gallium arsenide have also been tried and

pattern indications.

this scanner it is

Crystals of cadmium

and char ac t er i st l

c

time. Crystals of

show some favorable

V. Recommendations

The successful demonstration of this laser scanner for crystal

axis orientation shows a great reduction in testing time:

mapping a one inch wafer in 3 to 4 minutes instead of 4 hours.

In addition the automated pattern recognition of the 1,0,0 and

1,1,0 planes as well as the 1,1,1 plane give a 300 percent

potential improvement in yield. The mapping of the boules can

therefore help to provide lower cost material. This toroidal

1 aser scanner also has the potential for higher angular

accuracy due to its high signal to noise ratio.

It is recommended that work on this scanner be continued to

include more advanced software algorithms for pattern

recognition, automating of the coordinate mapping program and

automating the logging of data and the printing of maps.

74
Appendix I Bi bl i ography

1. Photoconductor Liquid Phase Epitaxy MCT Processing Guide,

prepared by Night Vision and Electro-Optics Laboratory,

Fort Belvoir, VA, March 10, 1984 (official use only).

2. Preliminary Benefits Analysis for Enforced Yield of

HgCdTe Dector Arrays, by Santa Barbara Research Center,

Hughes Aircraft Co., January 1985 (official use only)

3. Infrared Detector Array Fabrication PV Diode by

William Garrett, February 1985.

4. Inclusions in Cadmium Telluride Estimates for Damage

Thresholds by H.S. Bennett NBS and C.D. Cantrell

University of California, Los Alamos Scientific

Laboratory, Journal of Applied Physics Vol . 48,

No. 2, dated February 1977.

5. Standard Methods for Determining the Orientation of a Semi conduct i ve Single Crystal, ASTM Designation

F26-84.

6. Standard Methods for Determining the Orientation of a

Metal Crystal, ASTM Designation E 82-63 (Reapproved

1984).

7. Laser Scanning of Active Semi conductor Devices by

David E. Sawyer and David W. Berning, U.S. Department

of Commerce, National Bureau of Standards, NBS Special

Publication 400—27, issued February 1976.

8. A Laser Scanner for Semi conductor Devices by David E.

Sawyer and David W. Berning, U.S. Department of

Commerce, National Bureau of Standards, NBS Special

Publication 400—24, February 1977.

9. "Remote Monitoring and Control of Semiconductor Processing,

by Wesley H. Higaki, Page 30, Hewlett-Packard Journal

,

July 1985.

10. "Computer Management of Wafer Fabrication Process," SIS

Industry-Technology, Copyright 1984, Dataquest Incorporated

July 30 Edition.

11. Produci bi 1 i ty Demonstration Manufacturing Methods and

Technology Program. Contract No. DAAK20-83—C-0433.

HgCdTe LPE for Common Module Detector Arrays, Texas

Instruments Incorporated, Central Research Labor at or i es

,

November 19, 1985.

75
Production Capability Demonstrat i on -for Common Module

Detectors Using Liquid Phase Epitaxial HgCdTe. Contract

DAAK 20—03—C—0432. Hughes Aircraft Company, Santa

Barbara Research Center, November 21, 1985.

A Glossary of Terms for Robotics by Smith, Albus, and

Barbera, U. S. Department of Commerce, National Bureau

of Standards. Prepared for the U.S. Air Force Materials

Laboratory, Integrated Computer Aided Manufacturing Program.

NBSIR 81-2340, October 1981.

76
Appendix 2

Field Trips and Conferences

Date

January 14, 1935 Conference at Night Vision Laboratory Fort

Bel voir , VA and Visit to Laboratory

Facilities to Observe HgCdTe Fabricating

Processes

.

January 24, 1935 Conference at NBS on Ellipsometry of Thin Films

January 29, 1935 Conference at NBS on Non Destructive Testing

Applied to HgCdTe InfraRed Detectors

February 5, 1935 Conference at Night Vision Laboratory Fort

Bel voir, VA on Materials Growth and

Fabrication for HgCdTe Infrared Detectors.

March 7, 1935 SME Workshop on Machine Vision in Baltimore, MD

March 19-20, 1985 SME/RE Seminar on Robotics in the Clean Room,

San Jose, Calif.

March 21, 1985 Conference Santa Barbara Research Division

Hughes Aircraft Company, Santa Barbara, Calif.

April 17, 1935 Conference at NBS on Non Destructive Testing

of HgCdTe

April 19, 1985 Conference at NBS on Crystal Axis Measurement

on Cd Te substrates.

May 1, 1985 Presentation of Progress at Night Vision

Laboratory, Fort Belvoir, Va.

May 13, 1985 Pr esentat i ons of Program status at Night

Vision Laboratory Fort Belvoir, VA.

July 10, 1985 Presentation by GMF on Robots for Night Vision

Laboratory at NBS.

August 1 , 1985 Conference at NBS on Automated Inspection of

Cd Te Substrate Crystals and Substrates,

Dr. Santos Mayo.

August 9, 1985 Conference with Dr. Mayo on Photogr aph i ng Cd

Te Substrate Crystals.

August 21, 1985 Presentation of Status of Project at Night

Vision Laboratory to William Garrett and

Raymond Balcerak, Fort Belvoir, VA.

October 24, 1985 Demonstration of NBS Breadboard Model of Laser

Scanner-Gon i ometer for Substrate Crystal Axis

77
November

November

Determination Under Phase II of Contract to

William Garrett and Raymond Balcerak.

19, 1985 Conference at Texas Instruments on Status of

Work on HgCdTe Contract. Dallas, Tx.

21, 1985 Conference at Santa Barbara Research Division

of Hughes Aircraft Corp. on HgCdTe Contract at

Santa Barbara, CA.

78
Appendix 3

* Process Suitable -for Automation

Detailed Process -for Fabricating

HgCdTe IR Detectors Arrays

1. Prepare Cd Te Substrate

A. Material Growth

1) Refine Cd and Te into ingots

*2) Divide Cd and Te into small pieces or granules

suitable for precision alloying

3) Weigh each material for proper alloying

4) Make quartz ampule

5) Carbon coat (or other non stick method) interior

of quartz ampule

6) Load ampule with seed and Cd and Te, evacuate and

seal . *7) Load ampule into vertical Bridgman furnace, melt

alloy and grow crystal boule (14 days) or equivalent

process.

8) Zone refine and anneal boule

9) Break quartz ampule and remove boule.

B. Substrate Preparation

1) Cut off ends of boule and cut into several

cyl i nders

2) Sandblast ends and outside of cylinder.

*3) Map cylinder to find 1,1,1 axis and others if

possi bl

e

*4) Cut cylinders to recover 1,1,1 cyrstals

(additional yield may be derived from 1,0,0 and 1,1,0

axes)

*5) Recheck 1,1,1 orientation

*6) Slice wafer on 1,1,1 axis

*7) Polish wafers mechanically

*8) Palish wafers chemically

*9) Clean wafers

*10) Dice wafers into 1/2" x 1" substrates

C. Substrate Evaluation and Testing

*1 ) FI atness

*2) Resistivity

*3) Etch pit density

*4) Te precipitates

*5) Orientation

6) Hall effect measurement

*7) IR transmission measurements

79
Grow Epitaxial Layer on Substrate (LF'E)

*A. Clean Substrate

1 ) Remove grease

2) Etch

*B. Furnace Loading

Co LF'E layer growth, anneal and cool

D„ Furnace unloading

*E. FTIR—Spectrophotometer Mapping

*1) Cutoff wavelength

*2) Epitaxial layer thickness

*F„ Detect Counting

G. Hall effect measurement

*H„ Surface roughness

*1. Mi nor i ty-carr i er lifetimes

*J. Other Measurements

*1) Etch pit density

Array Photo Lithography

*A„ Optical Inspection (material defects, pits,

scratches)

*B„ Mount chip on carrier

C. Plasma clean

*D= Etch (general clean up)

*E. Deposit zinc sulfide

*F. Apply photo resist

*G. Bake

*H. Expose

*1. Develop

*J o Rinse in DI water

*K. Optical Inspection (check for sharpness of pattern

underdeveloped areas)

Lo Plasma strip

*M. Etch (to take off ZnS)

burr s

,

80
*N„ Etch (to clean sur-face)

*0. Implantation

*P. Plasma strip

*Q. Remove photo resist

*R. Etch (remove remaining ZnS)

*S. Remove chip from carrier

*T. Plasma strip (chip and carrier)

*U. Anneal

Remount chip

*W. Etch (clean the surface)

*X. Etch (neutralize the surface)

*Y. Deposit ZnS

*2. Apply photo resist

*aa. Expose

*ab . Soak* in chlorobenzene

*ac . Develop

*ad. Rinse in DI water

*ae. Optical inspection (mask alignment, underdeveloped areas)

*af . Etch (remove zinc)

*ag. Metallization (zinc metal)

*ah . Lift Off

*ai . Optical Inspection (check to see if metal is removed from

undesired areas)

*aj. Apply photo resist

*ak. Expose

*al . Soak in chlorobenzene and bake

*am. Develop

*an. Rinse in DI water

81
*ao. Optical inspection

underdeveloped areas)

(check al ignment o-f masks

*ap. Metallization (bonding pads)

*aq . Lift Off

*ar. Optical inspection (check i -f metal was removed -from

undesired areas)

*as. Bonding

*at. Testing

4. Hybrid Array Assembly and Test

A. Dicing

B. Silicon readout hybridization

C. Wa-fer char acter i zat i on

D. Current — voltage test

*E. Spectral response

F. Active area

G. Radiometric tests

5. Bond Leads

6. Final Test

A. Nominal area

B. Applied voltage

C. Noise bandwidth

D. Individual element tests—electrical

E. Individual element tests—spectral

F. Individual element tests—conversion status

Go Test summary

82
U.S. DEPT. OF COMM.

BIBLIOGRAPHIC DATA

1. PUBLICATION OR

REPORT NO.

2. Performing Organ. Report No. 3. Publ ication D ate

SHEET (See instructions) NBSIR 86-3410 JULY 1986

4. TITLE AND SUBTITLE

"Study of the Feasibility of Introducing Automation into Critical Manufacturing

Processes for Producing Mercury Cadmium Telluride Detector Arrays."

5. AUTHOR(S)

Sidney Weiser

6. PERFORMING ORGANIZATION (If joint or other than NBS, see instructions)

NATIONAL BUREAU OF STANDARDS

DEPARTMENT OF COMMERCE

WASHINGTON, D.C. 20234

7. Contract/Grant No. MIPR No. 25209

8. Type of Report & Period Covered

NBSIR

12-4-84 to 12-31-85

9.

SPONSORING ORGANIZATION NAME AND COMPLETE ADDRESS (Street, City, Store, ZIP)

U.S. Army Night Vision and Electro Optics Laboratory

Attention DELMV-R-FP

Fort Belvoir, Va. 22060-5677

10.

SUPPLEMENTARY NOTES

| | Document describes a computer program; SF-185, FIPS Software Summary, is attached.

11.

ABSTRACT (A 200-word or less factual summary of most significant information. If document includes a significant

bi bliography or literature survey, mention it here)

The task was divided into two phases.

Phase I was a systems study of the existing process and recommendation of a plan for

automation. Since this process is complex, with over 100 steps, three options were

proposed for implementation:

Option 1 Automation of eight critical subprocesses at a Laboratory level.

Option 2 Automation of five critical subprocesses in an existing production line.

Option 3 Automation of the complete process in a new facility.

Approximate costs were prepared for each of these options as required by the contract.

Phase II was^to implement a near term demonstration of automation in infrared fabrication. This was directed to the development of a more efficient way for the measurement

of the crystal axis orientation of cadmium telluride substrates used in this infrared

detector. A breadboard model of a toroidal laser scanner, with pattern recognition

was developed. This instrument will reduce the mapping time for a substrate from 4

hours to 4 minutes. The scanner can identify three different crystal orientations and

characterize four others in a fraction of a second which can improve the yield by 300%.

A goniometric mount controlled by a dedicated computer is planned for fully automating

this inspection process. (Bibliography consists of twelve references)

12.

KEY WORDS (Six to twelve entries; alphabetical order; capitalize only proper names; and separate key words by semicolons)

Automation; Clean Room Applications; Crystal Axis Measurement; Fabrication processes;

Infrared Sensor Arrays; Laser Scanner, Mercury Cadmium Telluride Detectors; Robotics

13.

AVAILABILITY

( 1 Uni imite*d

[_XJ For Official Distribution. Do Not Release to NTIS

Q Order From Superintendent of Documents, U.S. Government Printing Office, Washington, D C

20402. Qj Order From National Technical Information Service (NTIS), Springfield, VA. 22161

14. NO. OF

PRINTED PAGES

15. Pr

USCOMM-DC S043-P80
.

)J