Miniaturization Technologies

November 1991

OTA-TCT-514

NTIS order #PB92-150325
Recommended Citation:

U.S. Congress, Office of Technology Assessment, Miniaturization Technologies, OTA-TCT514 (Washington, DC: U.S. Government Printing Office, November 1991).

For sale by the U.S. Government Printing Office

Superintendent of Documents, Mail Stop: SSOP, Washington, DC 20402-9328

ISBN O-16-035983–X
Advances in miniaturization technologies have had dramatic impacts on our lives. Radios, computers, and telephones that once occupied large volumes now fit in the palm of a hand. Dozens of sensors are sent on spacecraft to the planets and on instruments into the human body. Electronic brains

are in everything from bombs to washing machines.

This report analyzes various technologies that may be important for future advances in miniaturization. Current research in the United States and other nations is pushing the limits of miniaturization

to the point that structures only hundreds of atoms thick will be commonly manufactured. Researchers

studying atomic and molecular interactions are continuing to push the frontiers, creating knowledge

needed to continue progress in miniaturization. Scientists and engineers are creating microscopic mechanical structures and biological sensors that will have novel and diverse applications.

OTA characterizes U.S. research and development in miniaturization technologies as the best in

the world. Despite the growing prowess of foreign research, American researchers continue to innovate

and push the frontiers of miniaturization. The more elusive challenge is to translate success in the laboratory to success in the global marketplace.

OTA gratefully acknowledges the contributions of the workshop participants, contractors, reviewers, and contributors who provided information, advice, and assistance. OTA, of course, bears sole

responsibility for the contents of this report.

(JJOHN H. GI BBONS

Director

. . . 111
Miniaturization of Electronic and Mechanical Devices Workshop, Feb. 19, 1991

Karl Hess, Chairman

Professor of Electrical Engineering

Fernand Bedard

Research Physicist

National Security Agency

T.H. Phillip Chang

IBM T.J. Watson Research Center

Harold Craighead

Director

National Nanofabrication Facility

Cornell University

Eric Drexler

Visiting Scholar

Beckman Institute -

University of Illinois

Wen Hsiung Ko

Professor of Electrical Engineering

Professor of Biomedical Engineering

Member of the Electronics Design Center

Case Western Reserve University

Carl Kukkonen

Director

Center for Space Microelectronics Technology

Jet Propulsion Laboratory

Richard S. Muller

Department of Electrical Engineering/

Computer Science

University of California at Berkeley

Stanford Computer Science Department

Stanford University

.

David K. Ferry

Regents Professor

Department of Electrical Engineering

Arizona State University

Kaigham Gabriel

AT&T Bell Labs

Stephen Jacobsen

Director

Center of Engineering Design

University of Utah

James S. Murday

Superintendent of Chemistry

Naval Research Laboratory

Richard Potember

Johns Hopkins Applied Physics Lab

Arati Prabhakar

Director

Microelectronics Technology Office

DARPA

George Sai-Halasz

Research Staff Member

IBM T.J. Watson Research Center

NOTE: OTA appreciates and is grateful for the valuable assistance and thoughtful critiques provided by the workshop participants. The

workshop participants do not, however, necessarily approve, disapprove, or endorse this report. OTA assumes full responsibility

for the report and the accuracy of its contents.
Miniaturization Technologies Project Staff

John Andelin, Assistant Director, OTA

Science, Information, and Natural Resources Division

James W. Curlin, Program Manager

Telecommunication and Computing Technologies Program

Project Staff

Sunil Paul, Project Director

Contractor Staff

Harold Craighead, Cornell University

Michael Skvarla, Cornell University

Clayton Teague, National Institute of Standards and Technology

Administrative Staff

Liz Emanuel, Office Administrator

Jo Anne Young, Secretary

Karolyn St. Clair, PC Specialist
Miniaturization Technologies

Reviewers

John Alic

Industry, Technology and

Employment Program

Office of Technology Assessment

Samuel Baldwin

Energy and Materials Program

Office of Technology Assessment

Robert Bate

Texas Instruments

Fernand Bedard

National Security Agency

Robert Birge

Center for Molecular Electronics

Syracuse University

Frederico Capasso

AT&T Bell Labs

Kenneth Davis

Electronics Division

Office of Naval Research

Bob Dennard

IBM

Eric Drexler

Stanford Computer Science

Department

Stanford University

Larry Dworsky

Motorola, Inc.

David K. Ferry

Arizona State University

Kaigham Gabriel

AT&T Bell Labs

Joseph Giachino

Ford Motor Co.

L Val Giddings

U.S. Department of Agriculture

Lance Glasser

DARPA

Henry Guckel

University of WisconsinMadison

George Hazelrigg

Electrical and Communications

Systems Division

National Science Foundation

Karl Hess

University of Illinois

Stephen Jacobsen

Center of Engineering Design

University of Utah

Wen Hsiung Ko

Electrical Engineering and

Applied Physics

Case Western Reserve University

Carl Kukkonen

Center for Space Microelectronics

Technology

Jet Propulsion Laboratory

Rolf Landauer

IBM

Ralph Merkle

Xerox Palo Alto Research Center

Lester W. Milbrath

State University of New York

at Buffalo

Richard S. Muller

Department of Electrical

Engineering/Computer Science

University of California at Berkeley

James S. Murday

Naval Research Laboratory

Robyn Nishimi

Biological Applications Program

Office of Technology Assessment

Wally Parce

Molecular Devices

Carl Pilcher

Office of Space Science

and Applications

National Aeronautics and

Space Administration

Richard Potember

Johns Hopkins Applied Physics Lab

Arati Prabhakar

DARPA

George Sai-Halasz

IBM T.J. Watson Research Center

Charles Shanley

Motorola, Inc.

Clayton Teague

NIST

William Trimmer

Princeton University

William Troutman

AT&T

Matthew Weinberg

Energy and Materials Program

Office of Technology Assessment

Sheryl Winston

Biological Applications Program

Office of Technology Assessment

Ken D. Wise

The University of Michigan

NOTE: OTA appreciates and is grateful for the valuable assistance and thoughtful critiques provided by the reviewers. The

reviewers do not, however, necessarily approve, disapprove, or endorse this report. OTA assumes full responsibility for the

report and the accuracy of its contents.

vi
Contents

Page

Chapter 1. Introduction and Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1

FINDINGS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . “ 1

WHY IS MINIATURIZATION IMPORTANT? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. ... ... ......4

COMPETITIVENESS OF U.S. MINIATURIZATION TECHNOLOGIES . . . . . . . . . . . . . . . . . . . . . . . . 5

Semiconductors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

Quantum Effect Devices . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

Molecular and Biological Computing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. ... ... .......7

Packaging and Interconnection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8

Biosensors and Chemical Sensors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8

Micro-Mechanical Systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8

Fabrication Technology Research and Development . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10

Chapter 2. Technology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13

INTEGRATED CIRCUITS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ......... 13

Physical Limits to Transistor Miniaturization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13

Continuing the Trend in Miniaturization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15

Fabrication Technologies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17

COMPUTING SYSTEMS TECHNOLOGIES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19

Display Technology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ...... 23

Data Storage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23

Interconnection and Packaging . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23

SENSORS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ... ......27

Charge Coupled Devices . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27

Chemical and Biological Sensors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28

Micromachined Silicon Sensors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30

ACTUATORS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32

Micro-Electro-Mechanical Actuators . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32

Integrating Actuators, Sensors, and Electronics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33

Appendix A. Fabrication Technology for Miniaturization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35

Appendix B. Glossary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43

Boxes

Box Page

2-A Molecular Machines . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20

2-B Bedside Analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29

2-C A New Way To Machine . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32

Figures

Figure Page

1-1 How Small Is Small? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2

1-2 Cost of a New Memory Fabrication Facility . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

1-3 Price History of Electronic Logic . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

1-4 Use of Surface Mount Technologies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6

1-5 Semiconductor R&D Spending-Top Four Merchant Companies in the U.S. and Japan 6

2-1 TransistorTrends . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

. . . . . . . . . . .

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14

2-2 Microprocessor Clock Speeds . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15

2-3 The Photolithographic Process . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18

2-4 Three Approaches to Electronics Miniaturization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22

2-5 Relative Cost of a Chip at Different Levels of Interconnection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25

2-6 Relationship of Die Size and Yield . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26

2-7 Impact of Surface Mount Technologies on Calculator Thickness . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27

2-8 Cut-away View ofa Silicon Pressure Sensor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30

2-B-1 Bedside Analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29

2-C-1 Surface Micromachining . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32

A-1 Fabrication Sequence for a Metal-Oxide-Semiconductor (MOS) Circuit . . . . . . . . . . . . . . . . . . . . . . . . . 36

A-2 Ion Implantation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39

vii
Chapter 1

Introduction and Summary

“Small is Beautiful.” The truth of that statement is debated in economic and sociological

circles, but when it comes to technology, there is

no debate; small is beautiful because small is fast,

small is cheap, and small is profitable. The revolution begun by electronics miniaturization during World War II is continuing to change the

world and has spawned a revolution in miniaturized sensors and micromechanical devices.

Miniaturization plays a major role in the technical and economic rivalry between the United

States and its competitors. It translates to market

share and competitive advantage for many commercial and scientific products. Those companies and nations that can successfully develop

and capitalize on miniaturization developments

will reap handsome rewards. Personal computers, portable radios, and camcorders are examples of products that created massive new markets through miniaturization: they added billions

of dollars to the GNP of countries where they

were designed and built.

FINDINGS

The United States remains strong in miniaturization technologies research and development

(R&D), although the lead over other nations is

less substantial than it has been in the past.

U.S. researchers continue to innovate and produce world-leading research despite strong research programs in Japan and Europe. There are

some areas where Japanese or European research surpasses the United States in quantity

and in a few cases in quality as well. But on the

whole, U.S. researchers lead in miniaturization

technology R&D. The danger is that U.S. companies will lag other nations in implementing

advanced technologies, especially when new

technology is driven by a product or market dominated by another nation’s industry.

The trends in silicon electronics miniaturization show no signs of slowing in the near future.

The current pace of miniaturization will produce memory chips (dynamic random access

memory, DRAM) with a billion transistors and

the capacity to store 1 billion bits (1 gigabit) of information around the year 2000.1 Transistors will

continue to shrink until the smallest feature is

around 0.1 micron (1 micrometer or one millionth

of a meter). By comparison, today’s most advanced mass-produced integrated circuits have

features as small as 0.8 microns. A human hair is

50 to 100 microns in width (see figure l-l).

Achieving such tiny features will require a huge

engineering and research effort. New fabrication

equipment and processing techniques must be

developed, pushing the cost of chip fabrication

plants to over $1 billion, compared to hundreds of

millions for a current state-of-the-art plant (see

figure 1-2). It is likely that despite the high costs,

chips having features around 0.1 micron will be

manufactured; progress beyond the era of O.l-micron transistors is uncertain.

The technology of semiconductor manufacturing is being applied to other fields to create new

capabilities. Sensors created with semiconductor manufacturing technology hold the promise

of widespread applications over the next 10

years.

Micromechanical sensors for pressure and acceleration have used semiconductor manufacturing technology for several decades now, but recent innovations allow further miniaturization,

greater flexibility, and compatibility with microelectronics. A wider range of sensors can now be

fabricated using micromechanical structures.

l~i~ ~omPre~ t. t~ay~s ~mt dense memoy chip, which have about 4 million transistors and hold 4 million bits (4 megabits) ofinformation.

-1-
2 ● Miniaturization Technologies

Figure 1-1 -How Small Is Small?

Human hand

 m wide

Grain of sand

 mm

Human hair

50-100 microns

wide

Smoke particle

 microns

DNA nm wide

Atoms 1-4 

100m

1 foot

0.3m

1 0-1m

1 inch

25.4 mm

10-2m.

1 0- 3m .

l o- 4

m .

 -

1 0-

lOrn-

– 1 meter (m)

—

 0.1 m Printed circuit board

100 mm 0.05-1 m wide

– 0.01 m

10 mm

1 centimeter

- 1 millimeter

(mm)

- 0.1 mm

100 microns

- 0.01 mm

10 microns

- 1 micrometer

1 micron

- 0.1 micron

100 nm

- 0.01 micron

10 nm

- 1 nanometer (rim)

10A

. 0.1 mm

Integrated circuit chip (die)

 mm wide

Micromechanical

components

10-1000 microns wide

Transistor on integrated circuit

2-20 microns wide

(smallest feature -O.8 micron)

Quantum electronics structures

 wide

Atomic lettering using

scanning tunneling microscope

65A high 1 angstrom 

Each increment on the vertical scale indicates change in scale bye factor of 10. On the right of the scale are examples of miniaturization

technologies. For comparison, several objects of similar scale are shown on the left.

SOURCES: of Technology Assessment, 1991. Data from Philip Morrison, (San Francisco, CA: American

Books, 1982); David Michael Valley, CA: Jones and 1987), p. 183;

Douglas M. cd., Van Scientific Encyclopedia (New NY: Van Nostrand Reinhold Co., 1983).
Chapter l–Introduction and Summary ● 3

$1,800

$1,600

$1,400

$1,200

Figure 1-2–Coat of a New Memory Fabrication Facility (DRAM Fab)

 0’

 $1,000 //, 

–

$600 –

$400 –

$200 –

I I I I I

64K 256K 1Mb 4Mb 16Mb 64Mb 256Mb

1979 1982 1985 1988 1991 1994 1997

SOURCE: Dataquest (August 1991) and Graydon Texas Instruments, personal 

 Sept. 18, 1991.

Biosensors and chemical sensors that can sense

gases and chemicals are being perfected using integrated circuit manufacturing techniques and

will be used in medical, food processing, and

chemical processing applications. The economics

of microelectronics fabrication will result in these

new sensors becoming cheap and ubiquitous

since hundreds or thousands can be created on a

single wafer. Integrating sensors with electronics

promises to increase the versatility of sensors for

consumer, medicine, automotive, aerospace,

and robotics markets.

Materials and surface science research is critical to further advancement of all miniaturization technologies.

In every miniaturization technology-from silicon microelectronics to quantum electronics, to

micromechanics and biosensors—better understanding of materials and surface interactions

will be a critical part of further technology advances. Better characterization of manufacturing

processes will be necessary to make future generations of miniaturized semiconductors. Making

practical miniaturized biosensors and chemical

sensors will require better understanding of how

to bond molecules to surfaces. Progress in micromechanics will depend on how well the mechanical and surface properties of materials like silicon

are understood. Resolving problems in quantum

electronics and molecular computing—the frontier of electronics miniaturization-are highly

dependent on improved understanding and control of materials and surfaces. Basic research on

material properties and surface interactions—especially in semiconductor processing and manufacturing-will be necessary for further miniaturization in many technology areas.
4 ● Miniaturization Technologies

Packaging is playing an increasingly larger

role in miniaturization of electronics.

Trends in miniaturization are creating pressure

in the electronics industry to improve packaging:

1.

2.

3.

The proliferation of electronics into portable devices, consumer electronics, automobiles, and industrial applications is forcing

more compact and ruggedized packaging;

The miniaturization of transistors causes

them to operate faster and is forcing attention to better packaging because fast electronics must be packed close together to

avoid delay in sending signals from chip to

chip; and

As the costs of integrating more and more

transistors onto the same piece of silicon

increase, alternative ways to integrate transistors into a single package, such as multichip modules and surface mount technologies, are becoming more attractive.

10

0.001

n 

WHY IS MINIATURIZATION

IMPORTANT?

Miniaturization has inherent advantages,

among them higher speed, lower cost, and greater

density. Smaller electronics devices are generally

faster because the signals do not have to travel as

far within the device. Packing more functionality

into a smaller or same-sized device reduces the

cost of electronics. For example, a l-megabit

DRAM chip has four times the memory capacity

of a 256-kilobit DRAM, but costs only about

twice as much and occupies the same space as the

lower capacity chip. Since the number of components (e.g., chips) on a circuit board largely determines the cost of the system, every l-megabit

DRAM used instead of four 256-kilobit DRAM

reduces the number of memory chips on a board

and reduces cost. Similarly, decreasing transistor

size and greater integration has caused the price

of logic devices to decline (see figure 1-3).

Miniaturization is important because it can

create new markets by enabling new applications.

Development of the microprocessor-a tiny comFigure 1-3-Price History of Electronic Logic

I Discrete d\\

transistors

r scale \ \

I

Largescale

integration —

1 I I I I

1955 1960 1965 1970 1975 1980 1985 1990 1995

The price per gate-a circuit that performs a simple Iogic function -has continued on a steep downward

trend since the introduction of the integrated circuit.

SOURCE: John S. Mayo, “The Microelectronics in Communications, 

 (San Francisco, CA: Freeman & Co., 1977), p. 106. Copyright(c) 1977 Scientific

American, Inc. All rights reserved. Additional data from Graydon Texas

Instruments, personal communication, Sept. 30, 1991.
Chapter l–Introduction and Summary ● 5

puter on an integrated circuit—in 1970 led to a

still expanding personal computer market currently valued at $70 billion per year. Flat panel

displays and improved chip packaging have led to

battery-powered portable personal computers

the size of notebooks (and some even smaller—

the size of a checkbook), one of the newest markets created by miniaturization. Personal communications is a developing major consumer

market created by miniaturization. With the

simultaneous reduction in the size of personal

computers and cellular telephones, the two are

merging into a cordless appliance that can communicate with the rest of the world through a network. Nippon Electric Co. (NEC) already offers a

laptop computer with a built in cellular phone for

sale in Japan; similar products are under development by American companies.

COMPETITIVENESS OF U.S.

MINIATURIZATION

TECHNOLOGIES

The competitive position of U.S. R&Din miniaturization technology remains strong, although

competition from Japanese and European industry and governments has increased. As a result,

the U.S. lead is less substantial than it was in the

past. The rejuvenation of postwar Japanese and

European economies has resulted in greater

quality and quantity of research in those nations.

There are now many more sources of competition

in research worldwide.

Although U.S. R&D strength is still sound,

U.S. industry has a mixed record in the implementation of miniaturization technology. Many

miniaturization technologies that are crucial to

the success of consumer electronics, for example,

were embraced by Japanese industry more quickly than by U.S. industry. Surface mount technology, which allows more electronic chips to be

placed on a circuit board, has had greater penetration into Japanese industry than U.S. industry

(see figure 1-4). Concerned with packing more

electronics into portable consumer products, e.g.,

cameras, calculators, and stereo receivers, Japanese consumer electronics companies were eager

to reduce the size of their products. U.S. companies that produce computers, industrial controls,

and other large systems serve markets that are

not as concerned with size and portability.

Semiconductor

Shrinking the size of transistors and their interconnections is being pursued vigorously by U.S.

industry, government, and universities. The

mainstream approaches to transistor miniaturization use silicon with designs similar to those of

past devices. In many respects, the United States

leads world research on smaller transistors. Design of miniaturized transistors draws heavily on

basic sciences and computer modeling, areas in

which the United States remains strong. Implementing smaller transistors in products, however,

is a strength of Japanese industry. DRAM chips

have historically been the first commercial products produced with each new generation of semiconductor manufacturing equipment. Since

DRAM chips are made primarily by Japanese

companies, they are the leaders in implementing

small transistors in products.

R&D in semiconductor technology is done primarily by industry in both the United States and

Japan. The Federal Government spends about

$0.5 billion per year on semiconductor R&D.2

Japanese merchant semiconductor firms, companies that sell chips to other companies, have

been outspending U.S. merchant firms on R&D

(see figure 1-5). Total U.S. and Japanese industry

R&D spending is roughly equal; $3.7 billion is

spent in the United States and $4 billion in

Japan. 3

@ffice of Management and Budget estimates for fiscal year 1990.

3Dataquest estimates for 1990”
6 ● Miniaturization Technologies

Figure 1-4-Use of Surface Mount Technologies

100%

o% Japan W. U.S. Japan W. U.S. Japan W. U.S.

Europe Europe Europe

1985 1991 1995

Use of surface mount technologies (SMT), which can reduce the thickness and volume of electronic products, has

lagged in the United States compared to other nations. This graph shows past, current, and projected estimates of

SMT use on printed circuit boards for Japan, Western Europe and the United States. - -

SOURCE: Office of Assess 1991. Data from VLSI R Inc. (Fall 

Figure 1-5-Semiconductor R&D Spending-Top Four Merchant Companies in the

United States and Japan

$3

Top four

Japanese merchant

companies

$2 — (then-yr. conversion) ~@@

-00 ----

#&~

 ---------

- ‘Top four Japanese

merchant companies

o (avg. conversion)

m

$1

● U.S. merchant

companies

1985 1986 1987 1988 1989 1990

U.S. semiconductor merchant companies are outspent in R&D by Japanese merchant firms. There are two

curves for Japanese spending. The more dramatic increase results from converting yen to dollars at annual

conversion rates. The other curve accounts for changes in the exchange rate by using a single conversion rate

averaged over 5 years.

SOURCE: Office of Technology Assessment, 1991. Data from Dataquest.
Chapter l–Introduction and Summary ● 7

Quantum Effect Devices

Significant momentum is left in the current

trend in silicon miniaturization. But what happens when today’s silicon designs hit physical

limits in further miniaturization, as many experts

expect will happen in about 10 years? One option

will be to change the way switching devices (used

to make computer logic) are made. Several alternative approaches are being pursued by the

United States, Japan, and Europe. One approach—quantum effect electronics—is still aresearch topic, but is receiving worldwide support.

In the United States, about $8 million are spent

annually by the Federal Government in this area.

Most of the research is being sponsored by the

Defense Advanced Research Project Agency

(DARPA), with significant efforts at other DoD

research agencies and the National Science Foundation (NSF). Industry support for this basic research is sparse; AT&T Bell Laboratories and

Texas Instruments both have research activities

in the area. IBM has a small research effort as

well. Most of the research in the United States is

being conducted at universities supported by

government agencies.

The United States leads in research related to

quantum effect devices, but this lead competes

with other nations’ efforts. Japanese efforts are

significant and are beginning to make an impact;

the Japanese involvement at recent conferences

has grown. The United States can expect to maintain its lead in research, but, as the research

moves toward development and implementation,

the competition with Japanese researchers and

corporations grows more fierce. Japanese industries have the advantage of being the world leaders in semiconductor processing technology and

optoelectronics technology.4 U.S. companies

have the advantage of proximity to the world’s

leading researchers in the field. The Japanese

Government will spend less than $3 million in fiscal year 1991 on quantum effect device research.

With two new projects initiated in 1991 and 1992,

funding will increase to about $6 million per year

over the next 5 years. Japanese industry is actively

pursuing quantum effect device research. Fujitsu

and NTT have the two largest research efforts.

Estimates of Japanese industrial investment in

the field are difficult to confirm, but the sum may

be more than double the government investment.

The Ministry of International Trade and Industry

(MITI) 1992 Large Scale Program, “Angstrom

Technologies,” will also fund research in quantum

electronics. The program will spend 25 billion yen

($183 million) over ten years to conduct research

on technologies at the scale of angstroms. It is not

known, however, how much funding will go to

quantum electronics.

Molecular and Biological Computing

One proposed way to continue the miniaturization of computers is to use individual molecules

as switching devices in place of today’s semiconductor transistors. U.S. investment in research

related to molecule-based computing has diminished substantially since a period of intense interest in the early 1980s. NSF was the principal funding source for much of the original research.

NSF’s current funding for molecule-based computing is a few hundred thousand dollars and

may end next year. Funding from U.S. industry is

limited to a few venture capital firms and Digital

Equipment Corp. Much of the effort in the

United States has turned to development of molecular or biologically derived materials for applications in computing-related areas. For example,

films of molecules rather than individual molecules 5 are being considered for use in optical

disks and other data storage technologies.

Japanese and European governments continue

to fund molecular computing research. However, differences in terminology complicate

comparisons of programs between countries.

Portions of one of the Japanese Exploratory Research for Advanced Technology (ERATO) projects are designed to pursue molecule-based comqMany ~ument app]imtions for suFr]attius—a structure used to create quantum effect detius-invoke oPto electronics.

!$Films of bactenorh~owin, a light ~nsitfie biologi~] molecule, are being prepared by re~archers at syracu~ university, Mitsubishi, and a

few American companies.
8. Miniaturization Technologies

puting6 and the Ministry of International Trade

and Industry (MITI) Basic Technologies for

Future Industries Program spends about 300 million yen ($4 million) on research for biological

molecular computing.

Packaging and Interconnection

As electronics become more ubiquitous, faster,

and denser, the pressure on improving electronic

packaging technology will increase. Federal funding has not addressed the issue of packaging as a

whole, but many different programs fund research on packaging. Technologies such as surface mount technologies (SMT) and multichip

module (MCM) technology can place more semiconductor chips into a system than traditional

packaging. SMT is maturing and is seeing widespread application. Over 50 companies and research institutions worldwide are now pursuing

MCM or related technology.7 One focus of the

Microelectronics and Computing Technology

Consortium (MCC)–a consortium of U.S. companies—is packaging and interconnection technology, including MCM technology. A National

Research Council report in 199@ found that the

American and Japanese industries are about

equally matched in printed wiring boards, multichip modules, and other interconnection technology. The report also found that U.S. industry was

dependent on Japanese suppliers for materials

required for several packaging technologies.

Biosensors and Chemical Sensors

There is intense worldwide interest in developing biosensors and chemical sensors, particularly

in Japan. Biosensors can detect the presence of

chemicals or molecules such as glucose, urea, and

oxygen. Diverse applications are seen in medical

diagnosis, industrial process monitoring and control, fermentation process control, and food quality monitoring. Most of the R&D is being done by

industry. Within the Federal Government, the

Department of Defense (DOD) is a primary supporter of biosensor R&D with the National Institutes of Health supporting some development.

According to a 1989 Japanese Technology and

Evaluation Center (JTEC) Panel report, the U.S.

efforts in chemical and biological sensors trail

those of Japan.9 The panel report rated Japanese

efforts more advanced in commercialization,

product development and quantity of basic research. In quality of research, the U.S. and Japanese efforts were considered equal. OTA interviews in the biosensor industry indicate the

situation has not changed much since the JTEC

report. According to the report, in 1985 there

were more Japanese publications and patents for

biosensors than U.S. publications and patents.10

A consortia has been established by 35 Japanese

companies to conduct R&Din biological sensors.

The annual budget for the consortia is about $2

million from industry matched by funds from the

Ministry of Agriculture, Forestry and Fisheries.ll

In addition, a large number of Japanese companies are funding independent development of biosensors.

12

Micro-Mechanical Systems

Development of new manufacturing techniques by researchers at American universities

during the 1980s has led to an expansion of interest in micromechanics around the world. Build6Kunitake molecuiar architecture project (1987-92).

TDenni~ Hemel and HasSan Hashemi, “Hybrid wafer Scale Integration, “ MCC Ikchnical Report P/I-329-89, 1989.

8National Re=arch Council, commission on Engineering and Ikchnical Systems, National Materials Advisov Board, Matefia~~or Hi@-

Density Electronic Packuging and Interconnection (Wshington, DC: National Materials AdvisogI Board, March 1990).

9u.s. Depa~ment of Commerw, C4JTECH (Japanese lkchnology Evaluation Program) Panel Report on Advanced Sensom in Japan,” JanUaV

1989, p. 184.

IofibliMtions: 59 Japan, 35 United States; patents: 74 Japan, 9 United States.

llHi& Tec~olo~ Business, September-October 1989, p. 29.

12National science Foundation, JaPnew ~ChnoloW and Evaluation Center (~c), Viewgraphs for “~c Workshop on Bioprocess Engineering in Japan” (Washington, DC: National Science Foundation, May 21, 1991); and U.S. Congress, Office of Technology Assessment, Biotechnology in a Global Economy, OTA-BA-494 (Washington, DC: U.S. Government Printing OffIce, October 1991).
Chapter l–Introduction and Summary ● 9

ing upon established semiconductor processing

techniques, researchers have been able to fabricate elaborate mechanical structures: motors and

turbines as wide as a hair (see photograph), cantilevers capable of measuring acceleration, and

gear assemblies smaller than a fleck of dust.

These new techniques are closely related to techniques traditionally used to create mechanical

structures for use as pressure sensors. The first

applications with sizeable markets for the new

technology are in sensors and instrumentation.

Future applications may involve micromechanical actuators or systems of actuators and sensors.

Some niche applications are already using micromechanical actuators made with conventional

milling and extrusion techniques (non-microelectronics techniques).

Researchers at U.S. universities are the acknowledged leaders in micromechanical sensor

research. The European nations, especially Germany, have a strong technology base in sensor

technology and are supported with extensive government funding. Germany’s Karlsruhe Nuclear

Research Center and Fraunhofer Institute codeveloped a new lithographic process for making

relatively thick (hundreds of microns) micromechanical structures, called LIGA. Although their

industrial research in pressure and acceleration

sensors is impressive, the Japanese trail the

United States and Europe in R&D.

Although still relatively modest in scale, in the

last few years funding for micromechanics has

been increasing rapidly. In the United States, research in the field is sponsored by several different agencies, including DOD, NSF, the National

Institutes of Health (NIH), the National Aeronautics and Space Administration (NASA), and

the Department of Energy (DOE). Total Federal

spending in the field is planned to be over $15 million in 1991-from under $6 million in 1990 and

1991. DOD and NSF were early supporters of the

technology. DARPA has been spending about $2

million per year, and plans to spend about $3 million per year in 1992. NSF has been funding much

of the research at universities since 1983 at about

$2 million per year. Efforts at the DOE have been

mostly at Sandia and Lawrence Livermore National Laboratories. Starting in 1991, DOE will

spend about $16 million over 3 years at Louisiana

Technical University (LTU) as directed by Congress. Other State governments including California and Louisiana have shown interest in promoting micromechanics research.

On the whole, U.S. industry is playing "wait

and see” while trying to sort out what commercial

applications the technology might have. Sensor

and instrumentation companies, however, see

clearer potential for applications and are pushing

forward more aggressively. Analog Devices, Inc.,

for example, has developed the first commercial

product that uses the new manufacturing technique—an acceleration sensor targeted for automobile airbag deployment applications. Other

companies are abandoning micromechanics. A

pioneer in the field, AT&T Bell Laboratories, terminated its efforts in micromechanics. U.S. industry spent over $20 million in fiscal year 1991

on micromechanics R&D.

In Europe the largest and most advanced research efforts are being pursued by Germany. In

1990, the Germany Federal Ministry for Research

and Technology initiated a 4-year program that

will spend 400 million marks ($230 million) on research. The German Government recently announced it will extend the program for at least

another year. The Karlsruhe Nuclear Research

Center and the Fraunhofer Institute are conduct-
10. Miniaturization Technologies

ing leading research in micromechanics. The

Fraunhofer Institute is designed to encourage

participation from industry and receives about 50

percent of its funding for micromechanics from

industry. A consortium of German companies

has licensed technology from Karlsruhe and is

developing industrial applications based on the

technology. Germany companies are interested in

applications of the technology. Bosch has the

largest effort, and Siemens and Messerschmidt

also have significant R&D efforts in the field.

Other European nations and industries are

also pursuing micromechanics research. The

most notable research efforts besides Germany

are in Switzerland and the Netherlands. The Institute of Microelectronics in Neuchatel, Switzerland, is developing solid-state sensors and is active in the field of micromechanics research. The

University of Twente and the University of Delft

in the Netherlands are active in the field, with a

new institute formed at the University of

Twente—the Micro-Electromechanical Sensors

and Actuators (MESA) Institute. Almost every

nation in Europe has research activity in micromechanics—much of which is at universities.

Perceiving themselves as behind in micromechanics research, Japanese researchers are vigorously pursuing the technology with a new MITI

program that will spend 25 billion yen ($183 million) over the next 10 years. The program, initiated in April of 1991, aims to develop microrobots for health and industrial applications.

Micromechanical systems will be a major part of

the program’s research, although portions of the

program will bean extension of a previous MITI

program to develop miniature robots. Fiscal year

1991 funding for the program is only about $3 million, but that will increase to over $20 million annually as the program accelerates to full speed.

Japanese industry typically adds its own investment of labor and equipment to work sponsored

by MITI, so the total research effort associated

with this program is substantially larger than the

government investment. In addition to the MITI

program, the Japanese Science and Technology

Agency (STA) funds research at several universities in Japan, including the University of Tokyo,13

at a total of about $1 million per year. Japanese

industry is pursuing research in the field, with

1991 expenditures estimated at over $20 million.

One of the largest industrial research efforts is at

Toyota’s central R&D facility in Nagoya. Other

industrial research is underway at NTT, NEC

Corp., Ricoh Corp., IBM-Tokyo, and Matsushita

Central Research. The MITI project has increased the interest of industry in micromechanics, and R&D can be expected to increase over

the next several years.

Fabrication Technology Research

and Development

Making miniaturized electronics, sensors, and

micromechanics requires increasingly sophisticated manufacturing equipment as each generation of miniaturized components demands greater precision in fabrication.

Lithography—the technique used to etch features into integrated circuits—is one of the most

challenging hurdles for future miniaturization of

integrated circuits. The size of a transistor, the

lines connecting transistors, and other devices in

a circuit can only be made as small as the resolution of the tools used to make them. As the size of

transistors become smaller, making tools of adequate resolution becomes increasingly difficult

and more expensive. The current approach to increasing the resolution of lithography has been to

reduce the wavelength of the light source, progressing from visible wavelengths, to ultraviolet,

to deep ultraviolet. Now many experts are predicting that the trend will continue to x-ray lithography, but the outcome is far from certain. Some

experts predict ultra-violet lithography will be

useful in creating features as small as those possible with x-ray lithography. Using a technique

called phase–shifting, this approach would require very sophisticated masks and computer

software to be successful. Other lithographic aplsothem include ~hoku University, University of Osaka Prefecture, and K..shu university.
Chapter 1-–Introduction and Summary ● 11

preaches such as electron-beam and ion-beam

are considered viable options.

The debate surrounding x-ray lithography has

been well documented.14 The governments and

industries of the United States, Japan, and European nations are all investing heavily in R&D for

the next generation of lithography tools. Congress

allocated $60 million to DARPA in fiscal year

1991 to develop x-ray lithography technology, including research on mask development and laser

x-ray sources. There are a total of five synchrotrons currently in the United States for lithography research. Two more will come on line by 1993

in Baton Rouge, Louisiana and Upton, New York.

Industrial support for x-ray lithography using

synchrotrons consists primarily of IBM and Motorola. AT&T is focusing on x-ray lithography using laser sources instead of synchrotrons. In Japan and Germany, government and industry are

taking an aggressive approach to x-ray lithography development. There are nine synchrotrons in

Japan and two synchrotrons in Berlin for lithography research.

laFor enmp]e, we Mark Crawford, “The Silicon Chip Race Advances Into X-rays,” Science, VO1. 246, Dec. 15, 1989, pp. 1382-1383; U.S.

Congress, Congressional Budget Office, UsingR&l) Consom”a for Cornmmiallnnovahon: SEM4TECH, X-ray h”thography, and High-Resolution

Systems (Washington, DC: Congressional Budget Office, July 1990), pp. 69-87; U.S. Congress, Senate Committee on Commerce, Science, and

‘llansportation, Subcommittee on Science, lkchnology, and Space, Sem”conductozs and the Electronics Zndustry, Serial No. 101-771, May 17,

1990; and John Markoff, “Etching the Chips of the Future,” New Mrk Times, June 20, 1990, p. D1.
Chapter 2

Technology

INTEGRATED CIRCUITS

Since World War II, system designers have

tried to create smaller electronics. Reduction in

the size of vacuum tubes progressed slowly as

practical limits were encountered. Replacement

of vacuum tubes with transistors in the 1960s was

a breakthrough in miniaturization. Transistors

became smaller, but each transistor was packaged individually, thus mounting large numbers

of transistors on a circuit board still resulted in

large assembly units. Invention of the integrated

circuit overcame that problem by embedding

many transistors on a single silicon chip that

could be then connected to other components on

a circuit board. Integrated circuits accelerated

the drive toward transistor miniaturization because, unlike discrete transistors, the connections

between transistors could shrink with the transistor. The smaller the transistor and its interconnections, the greater the transistor density (the

number of transistors in a given chip area). As

chip designers were able to pack more and more

transistors onto a single silicon chip, the number

of transistors per chip increased nearly a

hundred fold each decade (see figure 2-l). As the

size of a transistor shrinks it operates faster, leading to faster computation (see figure 2-2).

If this trend continues, sometime after 2000 the

smallest feature on an integrated circuit will be

about 0.1 micron (1 micron is 1 micrometer or one

millionth of a meter). For comparison, today’s

dynamic random access memory (DRAM) transistor has a smallest feature of about 0.8 micron.

The equivalent capacity of a DRAM1 chip will be

over 1 billion bits (1 gigabit). With O.1-micron

transistors, microprocessors will contain over 400

million transistors. Industry experts believe that

such densities are possible and that there are no

fundamental physical limits to prevent achieving

them.

The time needed to overcoming engineering

and manufacturing problems to reach these high

densities is uncertain. Several problems must be

overcome to develop high-density chips, including: 1) higher resistance of the minute connections between transistors and within transistors;

2) the tendency of very small transistors (about

0.1 micron) to “leak,” rendering them useless; and

3) lack of high-volume manufacturing equipment

capable of creating very small features.

Fabrication technologies, especially lithography, have paced the miniaturization of transistors in the past and may ultimately determine the

practical economic limits of transistor miniaturization. Fabrication equipment used to make

circuits at 0.1 microns must be affordable and

capable of sustaining reliable, high-volume production. Electron-beam lithography can now produce features much smaller than 0.1 micron, but

is unable to manufacture a sufficient volume of

chips to be economical.2 X-ray lithography and

phase-shifted masks (another lithography technique using visible light) are the two most likely

contenders for achieving manufacturable O.l-micron transistors. Other prospects include projection electron beam, and projection focused ion

beam.

Physical Limits to Transistor Miniaturization

What are the prospects for increasing densities

of transistor based integrated circuits beyond 1

gigabit DRAM and 400 million transistor microprocessors? On this question, experts’ opinions

ID~is the ~nmay means ofstonng information in a computer system temporanlywhile the computer is working on the info~ation. Mass

storage (e.g., hard disk) is used for permanent storage.

zElectron.beam lithography is Currentb used in production of masks and may be useful in some production applimtion% e.g., manufacturing

chips for high-performance computers.

-13-
14 ● Miniaturization Technologies

Figure 2-1 –Transistor Trends

Decreasing transistor size. . .

100

10

1

0.1

0.01

I

1970 1980 1990

and increasing die (chip) size. . .

1 

64 MA/ n’

❑

I I I I n 10

1970

 of Technology Assessment,

Texas Instruments.

1980 1990

is resulting in rapid growth in the number of transistors per chip.

10,OOO

100 I

10

I

I I 1 I

1970 1980 1990

Data from Intel David Ferry, Arizona State and Graydon
18. Miniaturization Technologies

Figure 2-3-The Photolithographic Process

Silicon dioxide

Photoresist

Ultraviolet radiation

Hardened

photoresist

Photolithography is the process by which a microscopic pattern is transferred from a photomask to a layer of material in a circuit. In this

illustration a pattern is shown being etched into a silicon dioxide layer (shaded) on the surface of a silicon wafer. The oxidized wafer (1) is first

coated with a layer of a light-sensitive material called photoresist (2) and then exposed to ultraviolet light through the photomask (3). The

exposure renders the photoresist insoluble in a developer solution; hence a pattern of the photoresist is Ieft wherever the mask is opaque (4).

The wafer is next immersed in a solution of hydrofluoric acid, which selectively attacks the silicon dioxide, leaving the photoresist pattern and

the silicon substrate unaffected (5). In the final step the photoresist pattern is removed by means of another chemical treatment (6). There

are variations on this process such as use of photoresists that become soluble instead of insoluble (4), and use of reactive gases instead of

liquid acid solutions for etching (5).

SOURCE: Adapted from William G. “The Fabrication of Microelectronic Circuits,” (San Francisco, CA: 

Freeman & Co., 1977), p. 47. Copyright (c) 1977 Scientific American Inc.–George Kelvin.

most common current technology uses visible or The current state-of-the-art photolithography

ultraviolet wavelengths of light for the photolitho- uses ultraviolet light, typically with a wavelength

graphic process. of less than 400 nanometers. Use of excimer laser
Chapter 2-–Technology .19

sources could achieve wavelengths less than 200

nanometers. By improving mask technology, optics, and resists, ultraviolet systems may be usable to 0.25- or 0.2-micron minimum feature

size—dimensions that are expected to be needed

in the mid-1990s. There are several lithography

technologies that can create features smaller than

0.25 or 0.2 microns. The likely candidates for the

next generation of lithography tools are x-ray lithographies, optical lithographies using phase

shift masks, electron-beam lithographies, and

ion-beam lithographies. Combinations of the

techniques are also possible. (For a more detailed

description of the photolithographic process, see

app. A.)

Materials and the principles of surface

sciences are fundamental to advancing miniaturization of transistors and electronics. Improvements in semiconductor manufacturing rely on

understanding how materials react to processing

and fabrication techniques. Physical phenomena

underlying the critical fabrication steps are not

well understood; knowledge has developed mostly from experience, not derivation from physical

laws. Better understanding of the physical laws

affecting small-scale structures would accelerate

advances in miniaturization.

There are more speculative ideas for future

fabrication technologies that would require even

more rigorous understanding of surface interactions. Some exploratory work is currently underway to use proximal probes to fabricate integrated circuits. Using a scanning tunneling

microscope (STM) or some variation of an STM,

scientists are beginning to fashion crude structures from individual atoms and clusters of

atoms. Researchers have been able to move or

deposit atoms on or below surfaces to “draw”

figures, maps, and company logos (see photograph). Even if these techniques do not result in

usable manufacturing tools, they will increase our

understanding of surface interactions of atoms,

leading to better understanding of traditional

semiconductor manufacturing. Even more speculative is the prospect of creating molecular-sized

robots and machines that could be programmed

Photo credit: IBM

Scientists at IBM’s Almaden Research Center used a scanning

tunneling microscope (STM) to move xenon atoms around on a

nickel surface and spell out the company name. The distance

between each atom of xenon is about 13 angstroms.

to manufacture virtually any molecular structure

(see box 2-A).

COMPUTING SYSTEMS

TECHNOLOGIES

Computer systems have shrunk dramatically

during the last 30 years. Mainframe computers

once filled large rooms and required air conditioning to dissipate the heat generated by vacuum

tubes and early transistors. Computers have become so small that laptops and notebook computers are more powerful than mainframe computers of 10 years ago. Equivalent power will soon

be available in a checkbook-size package. Past

miniaturization of electronics has played the major role in bringing this capability about and future miniaturization advances will be driven primarily by electronics (see figure 2-4). Other

components in addition to integrated circuits

also had to shrink in size to accommodate today’s

notebook-sized computers. Increased mass

memory density, greater circuit board density,

and thinner flat panel displays have improved

computer system performance and allowed

downsizing. Trends toward smallness are expected to continue as customers demand higher

quality, higher performance, and portability from

smaller boxes.
Chapter 2–Technology .17

The technical problems associated with making practical memory or logic systems from molecular devices are substantial and are not likely

to be solved in this decade. The most vexing problem is the interface (connection) between the molecule and the circuit itself, a problem common to

many forms of miniature transistors. At 0.1 micron, transistors begin to experience problems

with high resistance, but a molecular transistor

would be smaller still—0.001 microns or less. In

order to avoid the electrical interface problem,

some researchers are exploring optical interfaces.

The diameter of an optical interface, however, is

limited by the wavelength of light. The stability of

the molecules is also a problem. To be useful for

computation, a molecule must remain in a specific configuration until changed by an external signal. Individual molecules sometimes change configurations unexpectedly. Using clusters of

molecules makes them easier to connect to circuits and reduces the errors in the stored data,

but makes the computing device larger.

Related research is underway in the use of

biologically derived or organic material for storing information or computing. These approaches

minimize the interface and stability problems of

individual molecule computation. A few U.S.

companies are working on organic materials for

optical disks and at least one Japanese firm, Mitsubishi, is working on an optical disk that will use

bacteriorhodopsin as the storage material.5 Few

materials have suitable properties for computing;

this has been a major stumbling block for molecular computing. U.S. research is directed at better understanding materials that might serve as

the basis of future molecule-based computers.

The more immediate results may be faster data

storage, but proponents of molecule-based computing hope that the experience gained will lead

to true molecule-based computing and processing systems in the future.

Fabrication Technologies

There are several manufacturing technologies

that are important in making semiconductor devices. The most critical manufacturing technology by many accounts, is lithography–the techniques used to pattern and etch transistors and

their interconnections on a substrate like silicon

or GaAs.

There are several different lithographic technologies including photolithography, electronbeam lithography, ion-beam lithography, and xray lithography. In addition, there are several

novel technologies still in early stages of development—e.g., scanned photolithography, combined patterning and growth, and proximal probe

fabrication.

One of the most critical steps in lithography is

exposing the resist—usually an organic compound layered on top of the semiconductor wafer–to an energy source (see figure 2-3). The

energy source can be optical, ultraviolet, or x-ray.

It can also be a beam of charged electrons or a

beam of charged atoms (ions). Some of the resist

is exposed to the energy source and some is not,

depending on whether the resist lies under a

transparent or opaque portion of the mask. In the

places exposed to the energy source, the resist is

modified so that certain chemicals can dissolve

it.6 Exposing the wafer with a series of etching

chemicals removes the resist and a layer of material (usually silicon dioxide) underneath. The remaining resist is then removed by another chemical that does not affect the semiconductor

material. A layer of material is typically deposited again and the process is repeated—as many

as 12 or more times—to make an integrated circuit. The minimum feature size that can be

formed is determined primarily by the precision

that the energy source can be focused to discriminate between the areas of the resist that are exposed to the energy and those that are not.7 The

5Robefi Birg~, Syacuw University, personal communication, Ju& 29) 1991-

%ere are different types of resists. Exposure to radiation causes some types to become susceptible to the subsequent etching step, and causes

others to become resistant to etching.

TOther key factom are the ability to align subsequent layers of masks to create the proper vertical geometxy and the ability to control the rate

and direction of etching.
18. Miniaturization Technologies

Figure 2-3-The Photolithographic Process

Silicon dioxide

/ Photoresist / /

Ultraviolet radiation

Hardened

photoresist

Photolithography is the process by which a microscopic pattern is transferred from a photomask to a layer of material in a circuit. In this

illustration a pattern is shown being etched into a silicon dioxide layer (shaded) on the surface of a silicon wafer. The oxidized wafer (1) is first

coated with a layer of a light-sensitive material called photoresist (2) and then exposed to ultraviolet light through the photomask (3). The

exposure renders the photoresist insoluble in a developer solution; hence a pattern of the photoresist is Ieft wherever the mask is opaque (4).

The wafer is next immersed in a solution of hydrofluoric acid, which selectively attacks the silicon dioxide, leaving the photoresist pattern and

the silicon substrate unaffected (5). In the final step the photoresist pattern is removed by means of another chemical treatment (6). There

are variations on this process such as use of photoresists that become soluble instead of insoluble (4), and use of reactive gases instead of

liquid acid solutions for etching (5).

SOURCE: Adapted from William G. Oldham, “The Fabrication of Microelectronic Circuits,” Microekctronics (San Francisco, CA: W.H.

Freeman & Co., 1977), p. 47. Copyright (c) 1977 Scientific American Inc.–George V. Kelvin.

most common current technology uses visible or The current state-of-the-art photolithography

ultraviolet wavelengths of light for the photolitho- uses ultraviolet light, typically with a wavelength

graphic process. of less than 400 nanometers. Use of excimer laser
Chapter 2-–Technology .19

sources could achieve wavelengths less than 200

nanometers. By improving mask technology, optics, and resists, ultraviolet systems may be usable to 0.25- or 0.2-micron minimum feature

size—dimensions that are expected to be needed

in the mid-1990s. There are several lithography

technologies that can create features smaller than

0.25 or 0.2 microns. The likely candidates for the

next generation of lithography tools are x-ray lithographies, optical lithographies using phase

shift masks, electron-beam lithographies, and

ion-beam lithographies. Combinations of the

techniques are also possible. (For a more detailed

description of the photolithographic process, see

app. A.)

Materials and the principles of surface

sciences are fundamental to advancing miniaturization of transistors and electronics. Improvements in semiconductor manufacturing rely on

understanding how materials react to processing

and fabrication techniques. Physical phenomena

underlying the critical fabrication steps are not

well understood; knowledge has developed mostly from experience, not derivation from physical

laws. Better understanding of the physical laws

affecting small-scale structures would accelerate

advances in miniaturization.

There are more speculative ideas for future

fabrication technologies that would require even

more rigorous understanding of surface interactions. Some exploratory work is currently underway to use proximal probes to fabricate integrated circuits. Using a scanning tunneling

microscope (STM) or some variation of an STM,

scientists are beginning to fashion crude structures from individual atoms and clusters of

atoms. Researchers have been able to move or

deposit atoms on or below surfaces to “draw”

figures, maps, and company logos (see photograph). Even if these techniques do not result in

usable manufacturing tools, they will increase our

understanding of surface interactions of atoms,

leading to better understanding of traditional

semiconductor manufacturing. Even more speculative is the prospect of creating molecular-sized

robots and machines that could be programmed

Photo credit: IBM

Scientists at IBM’s Almaden Research Center used a scanning

tunneling microscope (STM) to move xenon atoms around on a

nickel surface and spell out the company name. The distance

between each atom of xenon is about 13 angstroms.

to manufacture virtually any molecular structure

(see box 2-A).

COMPUTING SYSTEMS

TECHNOLOGIES

Computer systems have shrunk dramatically

during the last 30 years. Mainframe computers

once filled large rooms and required air conditioning to dissipate the heat generated by vacuum

tubes and early transistors. Computers have become so small that laptops and notebook computers are more powerful than mainframe computers of 10 years ago. Equivalent power will soon

be available in a checkbook-size package. Past

miniaturization of electronics has played the major role in bringing this capability about and future miniaturization advances will be driven primarily by electronics (see figure 2-4). Other

components in addition to integrated circuits

also had to shrink in size to accommodate today’s

notebook-sized computers. Increased mass

memory density, greater circuit board density,

and thinner flat panel displays have improved

computer system performance and allowed

downsizing. Trends toward smallness are expected to continue as customers demand higher

quality, higher performance, and portability from

smaller boxes.
20 ● Miniaturization Technologies

Box 2-A—Molecular Machines

With electronics continuing to shrink and advances in the ability to make tiny mechanical devices,

one wonders if there is a limit to the ability to manipulate small structures. Some theorists speculate that

humans could control individual molecules precisely enough to build molecule-sized machines and robots. These machines would be so small that millions would fit in one of the micromotors described elsewhere in this report. Various terms have been used to describe the concepts;l here they will be referred to

as “molecular machines.”

The process of DNA replication and protein generation demonstrates that molecules can store information and use it to fabricate complex molecular structures. Molecular machine theorists claim humans will be able to create molecular machines to perform similar functions.2 These molecular robots

could be programmed to manufacture virtually any molecule-based structure Possible--everything from

hamburgers to spaceships. According to proponents, such technology could control pollutants, create

flawless materials, and provide almost limitless computing power. But they warn that there are potentially dangerous applications such as weapons more powerful than nuclear bombs, or machines that replicate uncontrollably, reducing the earth to a “gray goo.”

Significant barriers prevent the immediate implementation of molecular machine concepts. The

only tools that can directly manipulate molecules are proximal probes, e.g. the scanning tunneling microscope (STM). Proximal probes allow imaging and manipulation of atoms on a surface. Although STM

technology is advancing rapidly, manipulating molecules and atoms is awkward and time consuming-a

simple molecule has yet to be fabricated.3 Problems with reliability of molecular-sized systems might

make them impractical or delay their development. Because of their extremely small size, molecular

machines are especially susceptible to influences such as thermal noise and radiation damage. Molecular

machine system designers must compensate for these damaging effects. In many molecular machine

application concepts, e.g., random access memory (RAM) or gene sequencing, molecular scale systems

must interface with larger scale systems. In addition, molecular machines must interface with the outside

world in order to be “programmed.” The problems of interfacing molecules to larger scale systems hamper the ability to miniaturize many devices,4 including many of those proposed by molecular machine

designers.

Should Policymakers Be Concerned?

Because of the tremendous impact molecular machine technology might have, there are calls for

government to monitor progress in the field and fund research toward its realization.5 OTA attempted to

determine the importance of molecular machine ideas to policymakers by assessing the basis of the molecular machine concepts and prospects for their development.

lot~er le~ ~cment~ and in the past include “nanotechnolo~,” “Feynman machines,” “eutaxic control,” “=mblem,”

and “narmbots.” The term “nanotechnol@’ is particularly confusing because it is also used to refer to sub-micron electronics,

micro-sensors, quantum electronics, and micromechanics. As a result, molecular machine concepts are often portrayed in the same

light as those other technologies that are very different in size, technology base, and time to realization.

ZFor more ~e~iled d~riptions of molemdar machine concepts, see ~~ Drexler, En@s of c~~n(N~wyork ~: ‘Chor

Books, 1986) or references 7 and 8.

sDonald Eider, IBM ~~den R_ch Center, personal communication, May 1991. Fabrication of a simPle molecule a

reasonable near-term expectation.

Xsec t~ dc~ptions Of transistor miniaturization in this chapter for details.

Sb Sumn G. Hadden et a#.,A.r$&g j##o~ec~~ and Atomic Scale Technologies (MAST) (Austin, ~: Universiq of ~ms at

Austin Board of Regents, 1989); and Chris Peterson, “Molecular Manufacturing for Space,” Forsight Updlzte, No. 12, p. 8.

Conflmmd on next page
Chapter 2–Technology ● 21

Despite the skepticism of many researchers contacted by OTAand the evident controversial nature

of their ideas, there has been little written criticism of molecular machine Concepts.6 The two seminal

articles on the topic of molecular machines were written by Richard Feynman7 and Eric Drexler.8 The

arguments for and against molecular machines tend to be conceptual and not refined to the point of

discussing architectures or systems the debate so far seems to center on whether such devices are possible within bounds of natural law. Written criticism tends to focus on more specific suggestions and architectures in the related field of molecule-based electronics rather than molecular machine concepts. The

scarcity of criticism maybe due to the reluctance of scientists to denounce new concepts in publications.9

There are many concepts of what impossible within the bounds of natural law--e.g., steam-powered

computers and interstellar travel-but they do not exist as technologies. While science can determine

whether a concept is feasible, technology development is influenced by unpredictable economic and social factors. As a technology, molecular machines are non-existent; the only work to date has been conceptual and computational modeling.

When will molecular machine technology be developed? Estimates from the proponents of the concepts are 10 to 30 years, while others predict from centuries to “never.” One of the basic components of a

molecular machine technology base would be a protoassembler, a molecular machine capable of fabricating other molecular machines, The earliest prediction for development of protoassemblers is 5 to 10

years.

l0

Is There a Government Role?

To date, no proposal for research on molecular machine development has been received by a Federal agency. Basic scientific and engineering research in the fields of materials science, chemistry, molecular biology, advanced electronics, molecular modeling, and surface science are being funded by many

Federal agencies and would be necessary precursors to the realizationof molecular machines. It is impossible to estimate the level of funding, however, since there is no exact definition of precursor technologies. There are a few small research efforts explicitly addressing molecular machines concepts in U.S.

academia and industry and Japanese government.ll

Development of a framework for government regulation and oversight of molecular machine technologies has been suggested by several analysts, driven by fears of abuse or accidents associated with the

development of these technologies. The communities of researchers working on these precursor technologies is rather small and the concern over accidents or misuse of the technology is well known among

them. Government regulation at this stage would be premature, might hamper emerging research efforts, and have uncertain advantages. The question of regulation and oversight should be revisited and

analyzed in greater depth if developments in the field bring the technology closer to reality. The development of the first protoassembler might bean appropriate milestone to reconsider government regulatory

involvement.

%YEAccmducted alittxature seamhof articles that reference the two articles and analyzed them for critical and supporting arguxnents.

TR, FWnn, ~~erc~~ p~enw of Room at the ~ttom,}> Mi.niazurizution, A. Gilbert (cd.) (New York, NY: Reinhold, 196~), PP.

282-2%.

8KR ~re~er, “Molecular Engineer@: ArI Approach to the Development of General Capabilities for Molecular Manipulation: Proceedings of the NationulAcademy of Science USA, vol. 78, No. 9, September 1981, pp. 5275-5278.

gRolf Lan&uer, ‘*Poor Signal to Noise Ratio in Science,” f?Y~ “c Patterns in Compkx Systems, J.A.S. KeIso, A.J. Mandell, M.F.

$$hlesinger (eds.) (Singapore: World Scientific, 1988), pp. 388-394.

IQwC Dr~yder, For~i@t Institute, personal communication, March 1991.

~l~n tie Unitd Statm, one researcher is Performing mohcular modeling at Xerox Palo ~fo Research center. A ~@wrofit Owanization, Institute for Molecular Manufacturing, in Palo AJto, Gliforniawas formed this year and plans to qxmwr research in the

fi.Iture. No projects in .lapan or Europe are explicitly directed at xnolecular machine development, although the ~otani Molecuh

Dynamics project sponsored under the Japanese Iilx#oratory Research for Advanwd %chnology (E-) program addressed

molecular machine concepts in addition to its regular line of scientific investigation.

297-927 0 - 91 -- 3 : (IL 3
22 ● Miniaturization Technologies

Smaller transistor size

allows more transistors

per area

Figure 24–Three Approaches to Electronics Miniaturization

Make Transistors Smaller

❑

❑ 

Make Die Larger

Larger area allows more

transistors per die (chip)

Multi-chip modules

and

multi-chip packages

Three basic strategies are used to miniaturize electronics systems. By making each transistor smaller (l), more can be placed on an integrated circuit, incorporating the functions of other chips. Increasing the size of the chip (2) has a similar effect by increasing the available

area for transistors and their interconnections. These first two approaches have been the driving force behind electronics miniaturization for

at Ieast the past two decades. Improved packaging (3) is a way to improve use of space on a printed circuit board. Atypical printed circuit

board has only a small fraction of its space covered with integrated circuits; the rest is primarily packaging and interconnection.

SOURCE: Office of Technology Assessment, 1991.
Chapter 2–Technology ● 23

Display Technology

The size of a typical cathode ray tube (CRT)

desktop computer display is about a cubic foot.

New technologies, e.g., as liquid crystal display

(LCD) and electroluminescence displays, have

allowed the development of flat panel displays

that occupy a tenth of the volume. Flat panel

display technologies are discussed in detail in the

OTA report The Big Picture: HDTV & High Resolution Systems. New technologies required to advance high-resolution video technology are many

of the same that are required for advanced electronics and more powerful computer systems.8

Japanese producers of flat panel displays favor

LCD technology and are increasingly adapting it

to larger screens, but current fabrication techniques are limiting screen size to about 15 inches.

Further increases in screen size await improved

lithography.

Data Storage

“Mass Storage” refers to storage technologies

with large capacities, including optical and magnetic media that retain data when the power is off.

These devices encode data on a surface that can

change its magnetic or optical characteristics. By

moving the surface under a device that can sense

and change the characteristics of the surface—a

read/write head—data is stored and retrieved.

Semiconductor memory storage increases capacity as constraints on transistor miniaturization can be overcome, but mass storage operates

on different physical principles and therefore has

different limitations. There are two major types

of mass storage technologies—magnetic and optical. The trends in magnetic storage show no sign

of slowing as they approach densities that will put

1 billion bits onto 1 square inch. Researchers at

IBM’s Almaden Research Center have demonstrated such densities.9 Today’s storage densities

are about 50 to 100 million bits per square inch in

high-end storage systems. Optical storage technology uses lasers to write and read data from an

optical disk and is limited by the size of the laser

beam spot on the disk. The spot size, in turn, is

limited by the wavelength of the laser source.

Most optical disks today use a red (wavelength of

800 nanometers) laser to write and read data.

Efforts are underway now to develop blue lasers

(wavelength of 400 to 500 nanometers) that would

have smaller spot sizes and be able to increase the

capacity of optical disks by four times.

Another technique that promises much higher

densities uses STM1O to write and read data. The

STM and related instruments use sharp tips in

close proximity to a surface to create an atom-byatom image of the surface. These tools also have

the capability to physically modify surfaces by

either etching away or building up a few hundred

atoms at a time. Such techniques could result in

massive data density-more than 1,000 billion

bits (1 terabit) per square centimeter. The major

problem with STM and related approaches to

data storage is that the data access speed is painfully slOW.

ll There is research currently underway

at a few labs to combine many tips in parallel,

increasing the speed of writing and reading.

These approaches remain speculative, but might

yield useful technology in the long term.

Interconnection and Packaging

The basic packaging component of most computer systems is one or more circuit boards. Various components are placed on the circuit board

and interconnected with strips of metal. Due to

manufacturing costs, the number of components

8~e techniques ~wd t. make ~D displays are many of the same that are used to make integrated Circuits. For more information see OTA’s

Background Paper, The Big Picture: HDTV& High-Resolution Systems, OTA-BP-CIT-64 (Washington, DC: U.S. Government Printing Office,

June 1990}

gRobefi M. ~ite, “Peripherals,” IEEE Spectrum, February 1990, pp. 28-30.

IOSee app. A for details on the STM.

none ~stimate is that 32 ~entunes would be required t. ~te one ~uare centimeter with one profirna] probe. see James S. Murday and

Richard J. Colton, “Proximal Probes: lkchniques for Measuring at the Nanometer Scale,” in ChemiszryandPhysics of Solid Surfaces, R. Vanelow

and R. Howe (eds.) (New York, NY: Spnnger-Verlang, 1990), p. 347.
24 ● Miniaturization Technologies

is the greatest contributor to the overall cost of an

electronics system (see figure 2-5). System designers seek to reduce the number of components on a

board to improve reliability as well. The interconnecting strips of metal on a board and connections between boards are more likely to break

than connections elsewhere in the system. Ever

since the invention of the integrated circuit, the

best way to reduce costs and increase reliability is

by putting more transistors on integrated circuits, hence reducing the number of circuit board

components. By decreasing the size of each transistor and their interconnections, more transistors have been crammed onto integrated circuits.

While the density of circuits on a chip have

been increasing, the size of the chip has been

increasing as well. The first microprocessor in

1971 was on a 19,000 square mil (1 mil = onethousandth of an inch) chip. For the next 20 years,

chip size increased by about 14 percent per year.

Current microprocessors are on chips of about

260,000 square roils. Chip size may rise even faster over the next few years, yielding a chip size of

625,000 square roils in production by 1994.12

Since the probability that a chip is defective increases with its size, chip size is limited by the

number of defects on a wafer (see figure 2-6).

If the increase in chip size is taken to its limit,

an entire wafer can become one large circuit.

Since a typical wafer produces about a hundred

chips, a huge number of transistors could be put

on one wafer. But there are significant problems

with such an approach. There are defects in every

wafer (primarily caused by particulate from the

manufacturing equipment), so a wafer-scale circuit is virtually guaranteed to have defects. With

the high defect rate, strategies for routing connections around defective components must be considered in circuit design. Another problem is that

the complexity of interconnecting wafer-scale circuits increases the number of processing steps.

Finally, the fine lines of metal used to link the

imbedded transistors together are not suited for

the relatively long interconnections needed for

wafer-scale integrated systems. There are some

specialized applications that could use waferscale integration such as image processing and

large memory storage,

13 but unless fabrication

problems are solved, it will likely not be an important technology. Applications that have regular

designs —e.g., memory is essentially the same circuit pattern repeated over and over—have

achieved marginal success with wafer-scale integration because errors in the circuit are relatively

easy to detect and correct or bypass.

Hybrid wafer-scale integration—known as

multichip module (MCM)—is another approach

to increasing circuit density. MCMs take several

chips, place them on a substrate (usually silicon

or a ceramic), and connect them with thin films of

conducting metal using techniques like those

used in integrated circuits. Multichip modules

place chips closer together than is possible using

single chip packages —an important advantage as

chip speeds increase. The distance a signal can

travel in one clock cycle—the “heartbeat” of a

computer system—shrinks as cycle times shorten. Machines with clock cycles of 2 nanoseconds

will soon be available,14 which corresponds to 500

megahertz. (The fastest of today’s personal computers operate at about 33 to 50 megahertz.) Reliability is also enhanced because the number of

printed circuit board connections and board-toboard connections are reduced.

MCMs have been successfully used in the IBM

3090 and the NEC SX-AP; high manufacturing

costs, however, keep them from being used in

mass production items like personal computers

and workstations.15 The Microelectronics &

Computer Technology Corp. (MCC)–-a private

consortium of electronics companies—has developed a MCM technology capable of producing

lzJe~ Sulllvan, c’~e Nem Generation of Electronics Design Automation Technology for Systems in Silicon,” MCC l’kchnical Repofl No.

CAD-043-90, Jan. 24, 1990.

13’(A Dream Remembered,” The EconomisI, Nov. 17, 1990, p. 12.

IdDennis He~ell and HasSan Hashemi, “Hybrid Wafer Scale Integration,” MCC llchnieal Report P/I-329-89, 1989.

IsIbid.
Chapter 2–Technology ● 25

Figure 2-5–Relative Cost of a Chip at Different Levels of Interconnection

Chip in wafer, untested

Testing and yield

per good chip

Package, packaging

and testing

Space on printedcircuit board

Share of back panel and wiring

Share of cabinet and

power supply

Total

Average

cost

$0.55

$0.15

$1.00

$0.35

$2.63

Space on the printed circuit board is one of the most expensive commodities in a system design. By integrating more functions onto a chip,

system designers can reduce the number of chips on board, lowering overall system cost. The illustration shows the steps that a chip goes

through on its way to becoming part of a computer system and the relative cost per chip for each stage.

SOURCE: Adapted from Ivan E. Sutherland and A. Mead, “Microelectronics and Computer Science,” (San

Francisco, CA: Freeman &Co., 1977), p. 113. Copyright(c) 1977 by Scientific American, Inc. All rights reserved. Data from

Graydon Texas Instruments, personal communications, Sept. 20, 1991.
26 ● Miniaturization Technologies

Full wafer

Figure 2-6- Relationship of Die Size and Yield

■ Defects

Yield = O

Large die

Yield = 25%

Small die

Yield = 71%

Smaller die (chip) size means higher yield (percentage of good chips) for a given density of defects.

SOURCE: Adapted from Sand, Systems, Howard K. (cd.) (Scottsdale, AZ: DM Data Inc.,

1986), p. 7-12.

computers that are fast (3 nanosecond cycle time,

or 333 megahertz), use 10 million gates, and cost

$5,000. Costs must be reduced further for the

technology to be affordable for workstations and

personal computers.

A major obstacle to widespread use of MCMs

is the lack of standardized interfaces for the hardware and software needed to design the modules.

For the last 30 years the electronics industry has

been building an infrastructure that is focused on

the same objective: improving the performance of

the integrated circuit. All the manufacturing

equipment and computer software is geared for

designing and optimizing a single chip. It is difficult to obtain “naked” chips (dice) outside their

package from semiconductor vendors. Computer-aided design and testing are all difficult

with MCMs.

Dissipating the heat generated by dense circuitry is a major problem facing circuit designers.

This becomes more difficult as the number of

transistors in a chip increases. The simplest approach to accomplish this in a computer system is

to flow air over the circuits. In high-performance

systems (supercomputers and some mainframes), however, where speed is critical, other

means for cooling are often used. Some supercomputers flow inert fluids, e.g., freon, directly

over the circuitry. Sometimes fluid distribution

systems attached directly to the chip package are

used to dissipate heat, a scheme used in several

mainframe computers.

Many options for increasing the density of electronic circuits now being investigated operate

best at very low temperatures and require external refrigeration units. Advancements in refrigeration and heat dissipation technology are important to pushing the miniaturization of electronics

devices. This is because as the cross-section of a

conductor decreases, the resistance to current

flow rises. Greater resistance means greater heat

generation because the same current flowing

through a high resistance material creates more

heat than in a low resistance material.

The need for better interconnection is greatest

in two areas: 1) consumer electronics and 2) highperformance computers. Consumer electronics

must combine low costs with high dependability.

High-performance computers demand ultra-fast

computing speeds and extensive interconnection;

while the field is highly competitive, cost is less a

factor than performance. In high-performance

computing, the need for better interconnection

results from the short distance that an electronic

signal can travel before another clock cycle starts.

Supercomputers push clock cycles to the limit, so

designers must devise ways to minimize interconnection distance. The Cray supercomputers have

an unconventional circular shape in order to keep

components close together and reduce the time
Chapter 2-–Technology .27

needed to communicate among components.

Massively parallel computers face an even more

serious interconnection problem because many

more components (processors) must be connected. A conventional serial (von Neumann architecture) mainframe has only one central processing unit (CPU) that is centrally located so

that other components can be closely connected

to the CPU. A massively parallel computer may

have over 1,000 CPUs that must be interconnected.

In consumer electronics, a major objective is to

make the product smaller, lighter, cheaper, and

more reliable. Each of these objectives demand

better interconnection and packaging. Japanese

industry, with its emphasis on consumer electronics, tends to adopt packaging innovations to meet

the demands of the market. The impact can be

seen in the many consumer products around us

(see figure 2-7).

SENSORS

Sensors are devices that can monitor and

translate observed conditions—light level, acceleration, pressure, or temperature—into a signal.

The signal can then be transmitted, processed

through a system or stored as data. A mercury

thermometer, for example, responds to an environmental condition—temperature—and translates to a visual readout indicated by the level of

mercury gauged against a calibrated scale. An

electrical temperature sensor might sense the

change in temperature by measuring the change

in voltage across a material. The resulting electrical signal can be manipulated and displayed for

read-out.

There are a wide variety of sensors; each can be

classified as imaging or non-imaging. 16 Imaging

sensors take many measurements of radiated energy from the imaged target. Camcorders, for

example, use a charge coupled device (CCD) as

an imaging sensor to convert a visible light image

to an electrical signal that can be recorded on a

Figure 2-7–impact of Surface Mount Technologies

on Calculator Thickness

1969

1973

1975

1976

1977

1978

1979

26mm

9mm

7mm

5mm

1.6mm

Implementing surface mount technologies in calculators had a

dramatic impact on thickness. Surface mount technologies include surface mounted packages as well as surface mounted keyboards and displays.

SOURCE: VLSI Research.

VCR tape. Non-imaging sensors act at a single

point, typically in contact with the object being

sensed. Sensors can be made to sense different

substances and energies: electromagnetic radiation, temperature, pressure, acceleration, chemicals, and biological materials. Of the many sensor technologies, a few are key to miniaturizing

systems: CCDs, chemical and biological sensors,

and micromechanical sensors.

Charge Coupled Devices

CCDs are solid-state image sensors that detect

light. They are used in cameras—from camcorders to professional cameras to astronomical cam-

 t. this include some tactile sensors that detect sensations of touch an of 
28. Miniaturization Technologies

eras on satellites. The resolution of a CCD is

determined by the number of picture elements

(pixels) on a CCD. The devices are a special kind

of integrated circuit with problems similar to other integrated circuit manufacturing. Reducing

the size of each pixel improves the pixel density

and the image resolution. Increasing the size of

the CCD can increase the number of pixels, but

defects in the circuit cause yield to plummet as

the CCD size increases. Manufacture of CCDs is

dominated by Japanese industry. More than 20

Japanese companies manufacture CCD chips

and they are the leaders in small pixel size, and

innovative design.

17 In the United States, Tektronix, Texas Instruments, and Kodak produce

CCDs designed for military, industrial and space

applications. The majority of the image-sensing

market is in consumer electronics.18

Imaging sensors are particularly important to

the Department of Defense (DOD). DOD relies

on imaging data for things like aiming missiles,

detecting rocket launches, and enhancing nightvision. Most DOD applications sense areas of the

electromagnetic spectrum that are unique to military needs.

Chemical and Biological Sensors

By combining information technologies with

biotechnologies, researchers are developing new

sensors that are cheaper, faster, more versatile,

and more efficient than previous generations.

These sensors, known as biosensors, can detect

gases, chemicals, and biological molecules. The

first biosensor was invented in 1%2 by Leland C.

Clark Jr., but it was not until the 1970s that biosensors came into practical use. The early biological and chemical sensors were relatively large;

Clark’s first glucose sensor was about a centimeter in diameter.19 There are many ways to make

biological and chemical sensors; some can be

made using techniques borrowed from integrated

circuit manufacturing. By applying this technology, it is now possible to make sensors that are only

a few thousandths of a centimeter wide.

Smaller biosensors have two advantages: 1)

they can be placed in areas that were previously

inaccessible, and 2) they are fast since the measurement can be done in the field instead of at a

central lab. Because they offer similar economies

of production as microelectronics, biosensors

will become cheap and widely available. Biosensors will be useful in portable systems. A market

analysis by Arthur D. Little, Inc. in 1991 predicted that portable biosensors sales would reach

$1 billion by 2000.20 With sensors for substances

like glucose, urea, and carbon monoxide available

in an inexpensive and small package, portable

diagnostic kits could be made available (see box

2-B). The industrial food processing industry is

expected to make use of portable biological sensors to determine the freshness of food. Because

biosensors are small enough to be placed on the

tip of a hypodermic needle, blood chemistry

could be monitored continuously by placing several biosensors onto a chip inserted on a catheter

tip into the patient during surgery. The capability

to measure chemicals concentrations will be useful for process industries such as biotechnology

and chemical production.

Miniaturization of biosensors and chemical

sensors relies on a device called a chemical field

effect transistor (ChemFET).21 ChemFETs are

similar to the field effect transistors (FET) that

are used in normal microelectronics. A microelectronics FET conducts electricity (turns on)

when a voltage is applied to one of it inputs (gate),

creating an electric field in the FET. A ChemFET

ITu.s. Depafiment of Commerce, ‘TI’E(X-I (Japanese Technology Evaluation Program) Panel Report on Advanced Sensors in Jwm” JanUary 1989, p. 40.

181bid., p. 44.

lgJerome S. Schulz, “Biosenmrs,” Scientific 4UriC~, August 1991, pp. 64-69.

z@Strong Gro~h for Biosensors,” New Technolo~ Week, Feb. 19, 1991, P. 8.

21~w knom as ion ~nsitjve fje]d effect transistor (ISF~. “CHEMF~” js usually used to refer to sensors that use whole mOleCUleS, while

“lSFET” refers to sensors designed with ions (charged atoms or molecules).
Chapter 2–Technology 29

 Box 2-B--Bedside Analysis1

A hand-held analyzer currently under evaluation at the Hospital of the

University of Pennsylvania demonstrates how biosensors might find

their way into clinical use. It simultaneously makes six commonly requested chemical measurements on a

patient’s blood-sodium, potassium,

chloride, urea nitrogen, glucose, and

hematocrit-producing results in less

than 2 minutes. The bedside tests cost

more than ones performed in a central laboratory, but their immediacy

may make them more effective.

The device achieves accuracy comparable to that of laboratory equipment by using a disposable cartridge

containing six biosensors and a calibration sample. A medical worker

places 60 microliters of blood in the

cartridge; the analyzer then measures

both the calibration sample and the

patient sample. It displays test results

and also stores them, keyed to time

and the patient’s identification number, for later analysis: The cartridgebased design adopted by manufacturers will make it possible to perform a

different set of tests once the appropriate sensors have been developed.

 from Schultz, 

 1991, pp. 64-69.

Figure 2-B-1 -Bedside Analysis

Display

Sample

Calibration

solution

Cartridge

Sample inlet

Sensors

SOURCE: Adapted from Jerome S. Schultz, Scientific American, 

 1991, pp. 64-69. Copyright (c) 1977 American, Inc. All

rights reserved.

uses a FET that is specially coated with a chemi- testosterone, the male hormone, to produce a

cal or molecules that will create an electric field

when the sensor is exposed to a specific chemical,

gas, or molecule.

Fiber-optics technology aids biosensor and

chemical sensor development and miniaturization. Certain chemical and biological molecules

will change their optical properties (either give off

or absorb light differently) when exposed to other

chemicals or molecules. For example, the enzymes dehydrogenase and luciferase react with

secondary chemical that gives off light (fluoresces). A fiber-optic-based glucose sensor might

one day serve as the basis of an implantable artifi- 22 In the meantime, glucose sensors cial pancreas.

are being incorporated into the latest generation

blood sugar monitors for diabetics. These devices

are portable, take measurements in seconds compared to hours with earlier monitors, and some

function without drawing blood by measuring

absorption of light through skin.23

 footnote 18”

 6, 1991, p. 4.
30 ● Miniaturization Technologies

New generations of biosensors and chemical

sensors will take advantage of theircommon heritage within formation technology to integrate logic functions into the same package with biosensors. Integrating logic with sensors can result in

more useful devices. For example, a glucose sensor with integrated logic might respond differently to blood sugar levels at different times of day.

Integrated circuit fabrication holds promise for

high integration by placing biosensors and electronics on the same chip. It also promises reduction in prices because large numbers of sensors

can be fabricated at one time. Major challenges

remain, however, such as isolating the microelectronics from the environment while allowing the

sensor access to the environment.

Researchers are actively pursuing refinements

to the fabrication processes that will make widespread use of biosensors possible. The yield and

uniformity of the manufacturing process needs to

be improved before large scale production is

practical. Shelf life is a problem with biosensors;

compared to microelectronics and fiber optics,

biosensors are perishable. Biomolecules that

must be affixed to a chip or optical fiber are not

stable outside their cellular environments. As a

result, biosensors can only be stored for weeks or

months—sometimes years. This limitation prohibits some applications, but for some industries

short lifetime products are normal and expected.

In medicine, for example, instruments are often

discarded after use to avoid risk of contamination. The price and capabilities of biosensors in

other applications (e.g., detecting explosive gases

or critical chemicals in a process) are valuable

enough that users are willing to accommodate

limited lifetimes.

Micromachined Silicon Sensors

A significant field for future sensor developments will be mechanical sensors—devices that

rely on the mechanical properties of a material to

sense energy of their surroundings. Since 1958,

silicon has been used in pressure sensors. By

fabricating a covered cavity, changes in ambient

conditions can be detected by monitoring the

resistance across resistors on a membrane covering the cavity (figure 2-8). Improvements in silicon processing technology have reduced the size

and cost of silicon pressure sensors, with major

gains made during the 1980s. Cost has gone from

about $1,000 per sensor in the 1960s to a few

dollars per sensor today. The 1958 silicon pressure sensor that was half an inch wide is now one

hundredth of an inch wide. Growth in the 1980s

was very strong; silicon pressure sensors are 60

percent of the pressure sensor market—up from

40 percent in 1985 and 16 percent in 1980.24

Silicon mechanical sensors are also used to

detect acceleration. Accelerometers are made

with a mechanical silicon structure that places a

mass of material—the “proof mass’’—on the end

of a thin “arm” of silicon. Acceleration makes the

Figure 2-8-Cut-away View of a Silicon

Pressure Sensor

Top entry

pressure

Implanted

strain gages

Silicon frame

Electrostatic

glass-silicon

bond

Silicon diaphragm

Glass

Bottom

entry

pressure

SOURCE: Adapted from et al., Sensors

and Microstructure (Fremont, CA: NovaSensor),

1990, p. 7.3.

 CA: NovaSensor, June p. 
Chapter 2–Technology ● 31

silicon arm bend; the degree of bending determines the acceleration. Accelerometers are finding applications in automobiles for airbag deployment and automatic suspension systems.

Analog Devices, Inc., for example, is using a surface-micromachined cantilever as the basis for a

accelerometer. The separation between the cantilever and the chip surface changes with acceleration, changing the voltage. The voltage change

can be translated into an acceleration measurement.

The miniaturization of silicon sensors resulted

from developments in micromachining–a technique to precisely shape the surface of a material

such as silicon. Silicon in its crystalline form has

different orientations in the crystal that can be

specified for a particular silicon wafer. Chemicals

used to etch silicon “eat away” crystalline silicon

at different rates depending on orientation of the

crystal to the surface. This process is called preferential etching. By combining preferential etching with special chemicals that stop short the

etching process, complex structures can be

created in silicon. This technique is known as

“bulk micromachining,” and has been used since

the 1960s.

Use of “sacrificial layers’’—technique developed during the 1980s--can create more intricate

structures. Sacrificial layers are thin films (usually less than 10 microns) that are removed by etching chemicals to release movable parts from the

substrate (see box 2-C). The process of using

multiple layers of sacrificial layers to create complex structures is called surface micromachining.

Using surface micromachining, researchers at

the University of California at Berkeley and at

AT&T Bell Labs fabricated a working motor

about the width of a hair (100 microns) in 1988

(see photograph). That achievement set off a

flurry of research activities. Laboratories around

the world were soon duplicating and improving

upon the original work. Work at the Massachusetts Institute of Technology (MIT) improved the

sacrificial layer technique, making it more compatible with traditional silicon electronics processing. The Karlsruhe Nuclear Research Center

in Germany developed a variation on the surfacemicromachining technique known as “LIGA.” It

uses x-ray lithography technologies to fabricate

microcomponents from other materials including

plastic and metal.

The new complex structures have created a

need for better understanding and characterization of the materials used in the structures. Silicon is a well known material, but not enough is

understood of its mechanical properties. Structures that are released from the substrate, for

example, can warp due to strains in the material.

In microelectronics these strains are not important because structures remain connected to the

substrate, but for surface micromachining, these

strains can ruin a component. Wear and friction

are not well understood at such small scales, and

researchers need to understand these properties

to improve the reliability of micromotors and

other movable parts. Characteristics of surface

interactions, flow of fluids, and air flow are not

well understood at such small scales. UnderPhoto credit: Analog Devices, Inc.

An acceleration sensor (accelerometer) made by Analog Devices, Inc. will be the first commercial product that uses surface

micromachining, a new processing technique that uses sacrificial

material Iayers to free structures from a substrate. The microstructure, similar to ones fabricated at the Berkeley Sensor and Actuator Center, can be seen in the center of this microphotograph of

the sensor chip. The sensor is surrounded by electronics that

provide calibration and signal conditioning.
32. Miniaturization Technologies

Box 2-C--A New Way To Machine 

l. The pattern of the gear is transferred to the

substrate by shining ultra-violet or x-ray light

through a stencil-like mask.

2. This sequence is repeated several times to

achieve a structure that has alternating layers of

silicon and “sacrificial layers." (See the description of fabrication technologies in this chapter

and app. A for details.)

3. The sacrificial layers can be dissolved in a

chemical that doesn’t disturb the silicon. After

the sacrificial layer is removed, the gear is free

to rotate. A restraining hub prevents it from flying off the surface of the chip.

Figure 2-C-1 -Surface Micromachining

SOURCE: Sharon , “Welcome to Newsweek, vol.

117, No. r. 15, 1991, pp. 60-61. Jared

pyright (c) 1991, k, Inc. All

rights 

standing fluid flow at such small scales will be

important if the technology is used for chemical

and biological processing applications.

Future progress in micromachined sensors are

in three areas of improvement:

1.

2.

3.

design and fabrication processes will improve performance and expand applicability;

manufacturing technology will become

more important as sensors become commodities; and

packaging of the sensor is the third challenge, since reduction in packaging costs

has a significant impact on cost of the final

product.

Manufacturing technologies and procedures

have received insufficient attention in the past.25

This could hold particular peril for U.S. industry

if it is not remedied as it competes with Japanese

companies attuned to the value of robust manufacturing methods.

ACTUATORS

Actuators translate a signal to motion or force.

A solenoid valve is a common type of actuator

that relies on electromagnetic forces to move a

plunger arm to open and close a valve. Electrostatic actuators are promising small-scale actuators because electrostatic fields can easily be

created in micro-structures and are relatively

powerful at small scales. Recent developments

indicate electromagnetic actuators are promising

as well. Small actuators have also been made

from piezo-electric material26 and shape memory

alloys.27

Micro-Electro-Mechanical Actuators

Surface micromachining techniques are used

to fabricate micro-structures with moving parts.

 p. 2.18.

 contract or expand when a voltage applied.

 change shape with a change in 
Chapter 2–Technology .33

Researchers at the University of California at

Berkeley and AT&T Bell Labs fabricated motors

in 1988 using these new techniques. These motors

are typically about 100 microns in diameter (the

width of a hair) and about 3 microns deep. Minuscule motors have also been fabricated at University of Utah and AT&T Bell Labs using more

traditional machining techniques that are as

small as 500 microns in diameter. These motors

produce more power than the smaller motors

produced by surface micromachining and might

be useful in applications such as microsurgery or

drug delivery. 29 Small actuators could also be

used in consumer items, (e.g., cameras, cassette

players, video recorders, and toys) robotics and

defense applications.

Tiny levers, gears, and other mechanical assemblies can be etched from silicon with the same

surface micromachining techniques used to make

motors. Gears, levers, and the like might be useful

for transmitting motion and force. At such small

scales, these mechanisms might be useful formanipulating light, low-mass objects. There are

many potential applications in optics; several materials that can transmit, emit, or reflect light can

also be used in the construction of microactuators. Tiny mirrors on movable levers or gears

could serve as optical switches or light modulators by moving from one position to another.

Moving chemicals, fluids, and cells is currently

the object of much research. Electric fields and

ultrasonic waves are demonstrated techniques

that are being refined through research and development at university and industrial laboratories. Hewlett-Packard and Canon use bulk-micromachined devices to dispense ink for their

thermal ink jet printers.30

Integrating Actuator, Sensors,

and Electronics

One of the most exciting aspects of making tiny

structures in silicon and other materials is the

prospect of combining sensors, actuators, and

electronics into integrated systems on a single

chip. The greatest prospect for near term applications is probably science and engineering instrumentation.

Chemical and biological applications also appear promising: small tweezers might be useful to

hold specimens (e.g., cells) in place while they are

manipulated by other devices, such as injection

needles. Drug delivery systems might be made

small enough to be worn by patients, or even

inserted into the body. Chemical processing that

often uses complex lab equipment might be performed on a chip or wafer in a portable system.

Biotechnology procedures normally performed in

a batch process could be done on a cell-by-cell

basis with greater control over the results.

At Lawrence Livermore Labs in California,

researchers are working on spectrometers that

could be used to monitor environmental hazardous materials. Lawrence Livermore is also developing a DNA sequencer on a chip. At least one

major U.S. company is developing a gas chromatography system on a chip. Hitachi announced in

1989 that it had a prototype cell fusion system31

that fused as many as 60 percent of cells compared with about 2 percent using conventional

techniques.

Looking even further into the future, “microrobots” might be fashioned from micromechanical

components. These tiny robots could perform a

variety of functions. One of the objectives of the

MITI micromechanics program is to develop microrobots that would be capable of inspecting

inaccessible or hazardous locations such as in jet

engines, nuclear plants, and the human body.

Here in the United States, similar research is

being conducted at NASA's Jet Propulsion Laboratory and a few universities. The objective of the

NASA program is to make microrobots and microrovers useful for exploration of other planets

and the moon.

281~~chniqua include ~~mion, diamond-point machining, and EDM (electro-di=harge rnaChin@”

~small moto~ of this @ arc already being used for drug delive~ for livestock.

sophillip Wrth, Hewlett Packard, personal communication, May 29, 1991.

31cell fusion is a technique Uwd t. create ~1~ ~Pble of producing large quantities of monoclinal antibodies.
Appendix A

Fabrication Technology for Miniaturization

Many of

advances in

INTRODUCTION

the technologies that have enabled

miniaturization were first developed

for microelectronics and allow both lateral and

thickness control in the creation of structures.

Although the early techniques and tools were

directed at silicon, recent years have seen increased attention to materials other than silicon:

compound semiconductors, superconductors,

metals, and insulators. Furthermore, they are being applied to more diverse areas: micromechanical structures, biosensors, and chemical sensors.

The same processes that have allowed for decreases in size also allow parallel production of

many devices. Thousands or millions of transistors or other devices can refashioned simultaneously on one chip the size of a thumbnail, and

many chips preprocessed at the same time on one

wafer. The key steps in the process of creating

these structures are:

● lithography,

● pattern transfer, and

● characterization.

LITHOGRAPHY

Integrated circuit fabrication techniques all

rely on lithography, an ancient technique first

used for artistic endeavors. The basic process

involves covering an object with a thin layer of

material (ancient artisans sometimes used wax)

that can be patterned but will resist subsequent

processing and protect the material underneath.

Industrial lithographers use a hydrocarbon polymer, appropriately called “resist.” A pattern is

produced in the resist—usually by exposure to

visible light or ultraviolet (UV) radiation —exposing selected areas of the material below. The exposed areas can then be modified in some way.

Successive applications of this basic process produce a multilevel structure with millions of individual transistors in a square centimeter as described in figure A-1.

Photolithography is the most widely used form

of lithography and is likely to continue to be so for

the near future. UV light, usually with a wavelength less than 400 nanometers, is used to create

patterns resist layers on flat surfaces. Diffraction

of light—the interference of light waves with one

another—limits the resolution or minimum reproducible feature size. Diffraction is minimized

by reducing the wavelength of the exposing radiation. Mercury vapor lamps are routinely used as

a source of 436 nanometer (G-line) and 365 nanometer (I-line) light. Shorter wavelength excimer

laser sources are a new source of UV light with

operation possible at 248 nanometers and in the

future 193 nanometers and other wavelengths. By

combining shorter wavelengths with improved

mask technology (including phase shifted

masks2

), better optics, and more sophisticated

resist chemistries, it is likely that photolithography will be usable to 0.25-microns minimum feature sizes and possibly below 0.2 microns.

The longevity of UV lithography is a subject of

debate in the semiconductor industry. Many experts argue the limits of diffraction and depth of

focus will prevent use of UV photolithography

below 0.2 microns and that x-ray lithography,

which uses substantially shorter wavelength radiation, will be the successor to UV lithography.

X-ray lithography is a candidate for high volume

production of integrated circuits with line widths

below 0.5 microns. The most studied and developed form of x-ray use is “proximity printing,”

IH.G. Craighead and M. Skvarla, “Micro and Nanofabrication lkchnology, Applications & Impact,” contractor repofi prepared for the OffIce

of lkchnology Assessment, April 1990; and Tlm Studt, “Thin Films Get Thinner as Research Heats Up,’’ R&D Magazine, March 1990, pp.70-80.

Zphase shift masks function by Careful& controlling light diffraction, using the constructive and destructive interference to help create the

circuit pattern. Phase shift masks hold greatest promise for manufacturing memory and other ICS with regular, repeated patterns.

-35-
36 ● Miniaturization Technologies

Figure A-1 -Fabrication Sequence for a Metal-Oxide-Semiconductor (MOS) Circuit

Silicon nitride Silicon dioxide

1

First polysilicon

p-Type silicon

Insulating

oxide film

Contact “window”

Aluminum

Fabricating this MOS circuit element (a two-level n-channel-negative charge carrier- polysilicon-gate metal-oxide-semiconductor) requires six masking steps. The first few process steps involve the selective oxidation of silicon with the aid of a film of silicon nitride, which acts as the oxidation mask. A thin film of silicon dioxide is grown over the entire wafer, and a Iayer of silicon nitride is deposited from a chemical (l).

The layer is selectively removed in a conventional photolithographic step in accordance with the pattern on the first mask (2). A p-type

dopant (e.g., boron) is implanted using the silicon nitride as a mask, followed by an oxidation step, resulting in a thick layer of silicon dioxide

in the unmasked-(3). The silicon nitride is then removed in selective etchant that does not attack either the silicon or silicon dioxide (4).

Since silicon is consumed in the oxidation process, the thick oxide layer is partly recessed” into the silicon substrate. The first layer of poly- crystalline silicon is then deposited and patterned in the second masking step (5). A second insulating film of oxide is grown or deposited,

followed by the deposition of the second polysilicon layer, which is in turn patterned in the third masking step (6). A short etch in the hydrofluoric acid at this stage exposes certain regions to an implantation or diffusion of n-type dopant. A thin layer of silicon dioxide is deposited

next, and contact “windows” are opened with the fourth mask (7). Finally a layer of aluminum is deposited and patterned in the fifth masking

operation (8). The wafer will also receive a protective overcoating of silicon dioxide or silicon nitride (not shown); the fact that openings must

be provided in this overcoating at the bonding pads accounts for 6 masking steps. Vertical dimensions are exaggerated for clarity.

SOURCE: William G. ‘The Fabrication of Microelectronic Circuits,” (San Francisco, CA: Freeman & Co.,

1977), p. 48. Copyright (c) 1977 by Scientific American, Inc.–George Kelvin.
AppendixA-Fabrication Technology for Miniaturization .37

where the mask is placed on the substrate material and its pattern is reproduced by exposure to

x-rays, resulting in a substrate pattern the same

size as the mask. Practical problems that must be

addressed include complexity of mask technologies, difficulty in alignment of multiple layers,

economical x-ray sources, and resolution limitations. X-ray lithography operates similarly to UV

photolithography, but with much shorter wavelengths–around 5 nanometers. Proximity printing requires a bright source of x-rays. Synchrotron sources are the highest intensity sources of

x-rays but they are very expensive. Most experts

feel it is unlikely that proximity printing with

x-rays will be practical below 0.2 microns, while

others hold that the technology will be usable to

0.1 microns.

More recent exploratory work in x-rays involves “reduction projection lithography.” X-rays

are focused through a mask that is kept away

from the substrate. The principal advantages of

this approach are cheaper x-ray sources (a synchrotron is not required) and improved resolution. In this country, AT&T Bell Laboratories

and other laboratories are investigating this technology. One of the greatest challenges to making

projection x-ray lithography useful for manufacturing is the optics used in the process; they are

complex, involving the creation of multiple-layer

films with precisely controlled thickness.

Another way to get beyond the diffraction limit

of radiation-based lithography is to use electrons

or atoms to expose the resist. Diffraction does not

limit the resolution of electron-beam lithography

because the quantum mechanical wavelengths of

high energy electrons are exceedingly small. Electrons scatter quickly in solids, limiting practical

resolution to dimensions greater than 10 nanometers—significantly greater than current demands

of any practical technology. Electron-beam lithography has demonstrated resolution as small as

2 nanometers (0.02 microns) in a few materials.

Electron beam technology, however, is limited in

usefulness because an electron beam must be

scanned across the entire wafer. Electron-beam

lithography tools are in use in universities, in

laboratories, and in industry for mask-making

and small manufacturing production runs.

There are approaches still in research that may

yield a more versatile lithography tool. A possible

alternative is to use photolithography for large

feature definition and reserve the scanned electron beam for the critical dimensions. A varietyof

approaches for parallel exposure, rather than

serial scanned exposure, of electron-beams have

been studied for years. There is currently active

research in electron beams reduction projection

using masks at AT&T Bell Laboratories, and in

multiple source systems and proximity printing at

IBM. These approaches would exploit the resolution and alignment possibilities of electron

beams with the speed of parallel exposure techniques.

Ion beam lithography is in many ways similar

to electron beam lithography with beams of

charged atoms (ions) taking the place of electrons. Recent advances in ion sources have increased the utility of scanned focused ion beams.

Compared to photons (x-rays and light) or electrons, ions chemically react with the substrate,

allowing a greater variety of modifications. Some

scattering effects are also reduced compared to

electrons and, as with electrons, diffraction limits

of ion beams are negligible. The fundamental

resolution limits for charged particle lithographies are below 1(M) nanometers. Ion beam lithography suffers the same draw back as electron

beam systems; it relies on a serially scanned

beam. That limits its applications to products

that do not require high throughput—e.g., masks

and small batches of electronics. Research efforts

are underway to develop parallel projection and

multiple source ion beam lithographic equipment

that might overcome the limitations of serially

scanned ion beam lithography.

Scanned probe modification of surfaces, using

recently developed scanning tunneling microscopy (STM) methods, is being done by researchers

in many research laboratories. Since STMs can

manipulate individual atoms, such approaches

have theoretical resolution limits of single atoms.

This approach is still in early phases of research

and is focusing on basic physics measurements
38• Miniaturization Technologies

and better understanding of the behavior of surfaces. The lack of stability of STM tips and slow

speed, however, make it far from a practical technology for manufacturing in the foreseeable future.

PATTERN TRANSFER

The various lithography systems produce relief

patterns in resists, and a subsequent pattern

transfer step is necessary to fabricate the structure. There are a number of options available and

each involves some engineering tradeoffs. Once

the resist pattern is in place, and selected areas of

the underlayer are exposed, there are three possible next steps: 1) add to, 2) remove, or 3) modify

the exposed areas.

Adding to the exposed area involves either deposition or growth of a material on the exposed

areas. Growth is different from deposition because it involves consumption of the surface (usually combining with some introduced chemical)

to create the new substance. The most common

example is a silicon surface being consumed in

the process of forming silicon dioxide. It involves

heating the silicon wafer in the presence of oxygen, causing the growth of silicon dioxide from

the exposed silicon. A number of materials are

grown in this way, since the consumption of the

surface results in excellent adhesion, better electrical and mechanical properties, and improvements in other materials properties. This specific

reaction has been exhaustively investigated and

perfected and now can be used to grow oxide

films whose thickness, and even lateral dimensions, can be measured in atomic layers (a few

angstroms).

Deposition creates new layers of material on

the exposed area. These techniques usually involve evaporating or sputtering a piece of material-the target-so its atoms or molecules fly off

and land on the sample. Deposition techniques

include:

● spin-on,

● thermal evaporators,

● sputtering,

. laser ablation deposition,

● chemical vapor deposition; and

● molecular beam epitaxy such as organometallic chemical vapor deposition.

Spin-on deposition is the simplest deposition

technique. It involves spinning the sample while a

liquid is poured onto it; the spinning action distributes the liquid evenly. Subsequent heating

bakes the liquid into a solid thin film.

Thermal evaporators use a heated filament or

an electron beam to vaporize material. The material passes through a vacuum to impinge on the

sample, building up a film. Evaporators emit material from a point source, resulting in “shadowing” and sometimes causing problems with very

small structures.

Sputter deposition systems erode atoms from a

broad target that then travel to the sample. This

results in better line width control and uniformity, especially with high aspect ratio (height/width)

structures. Refinements of these processes, e.g.,

in situ cleaning with an ion gun, or using electron

cyclotron resonance to confine and densify a

plasma, result in better adhesion, higher quality

films, and more versatility. Using lasers or particle beams in conjunction with deposition presents the possibility of defining patterns on the

sample in a single step.

Laser ablation deposition uses intense laser

radiation to erode a target and deposit the material onto a substrate. This technique is particularly useful in dealing with compounds of different

elements —e.g., yttrium-barium-copper oxide superconductor films.

Chemical vapor deposition (CVD) deposits

thin films by passing reactive gases over the sample. The substrate is heated to accelerate deposition. CVD is used extensively in the semiconductor industry and has played an important role in

past transistor miniaturization by making it possible to deposit very thin films of silicon. Most

CVD is performed in vacuum, but new techniques allow operation without vacuums. Radio

frequency (RF) or photon radiation can be used
Appendix A--Fabrication Technologyfor Miniaturization .39

to enhance the process and is known as plasma

enhanced CVD (PECVD).

Some deposition techniques are so precise that

material can be built up literally atom by atom

with the crystal structure of the new material

exactly matching that of the underlying layer. In

molecular beam epitaxy (MBE), the sample is

placed in an ultra high vacuum in the path of

streams of atoms from heated cells that contain

targets of various types. These atomic streams

impinge on the surface, creating layers whose

structure is controlled by the crystal structure of

the surface, the thermodynamics of the constituents and the sample temperature. Organo-metallic chemical vapor deposition (OMVPE, or sometimes MOCVD) relies on the flow of gases

(hydrides like arsine and phospine or organometallics like tri methyl gallium and tri methyl aluminum) past samples placed in the stream.

Again, the sample surface and thermodynamics

of the processes determine the compounds deposited. Both MBE and OMVPE provide thickness control within one atomic layer (a few angstroms) and are especially useful in creating

compound semiconductors and exploiting quantum effects and band-gap engineering. This

structural control enables researchers to exploit

optical transitions in some materials, producing

lasers, detectors, and other optical elements.

Materials modification processes are used

mainly to vary the electrical conductivity in the

appropriate areas. In the past, dopants (atoms

that can either contribute or subtract electrons

from silicon atoms) were diffused into the substrate thermally; now they are implanted as high

energy ions (see figure A-2). Implantation offers

the advantage of being able to place any ion at any

depth in the sample, independent of the thermodynamics of diffusion and problems with solid

volubility and precipitation. Ion implantation,

originally developed for high energy physics, is

now an indispensable part of semiconductor

manufacturing. Ion beams produce crystal damage in addition to the chemical or electronic effect

of the dopants. Since crystal damage reduces

electrical conductivity, this effect can be exploited to electrically isolate devices from one

another. Ion beams can implant enough material

to actually form new materials--e.g., oxides and

nitrides-some of which show improved wear

and strength characteristics.

Subtractive processes—the removal of material-are also vital to the field. Some of the steps

are still done the same way they were centuries

Figure A-2–ion Implantation

Accelerated boron ions

p-Type- silicon Thick oxide

Polysilicon

/

gate

Ion implantation is employed to place a precisely controlled amount of dopant (in this ease boron ions) below the gate oxide of a MOS

transistor. By choosing a suitable acceleration voltage the ions can be made to just penetrate the gate oxide but not the thicker oxide (left).

After the boron ions are implanted polycrystalline silicon is deposited and patterned to form the gate regions of the transistor. A thin layer of

the oxide is then removed and the source and drain regions of the transistor are formed by the diffusion n - of an n-type impurity (right).

SOURCE: William G. “The Fabrication of (San CA: Freeman Co.,

1977), p. 50. Copyright (c) 1977 by -George V. Kelvin.
40 ● Miniaturization Technologies

ago. The object, with its lithographically defined

areas exposed and the remainder protected by

the “resist,” is dipped into a chemical bath and a

reaction or dissolution is allowed to take place.

Unfortunately, liquid chemicals usually have no

sense of direction and will dissolve at an equal

rate on all sides. As device geometries shrink, it

becomes important to control directionality.

Most modern etching is done in vacuum without

contact with liquids.

Ion milling uses the sputtering process to bombard the substrate with accelerated ions. The

sputtering process relies on a physical mechanism whereby energy is transferred to a surface

by impinging ions. This energy is enough that

some atoms break free of the surface. This mechanism erodes all materials, with small differences

in rate between any two. Selectivity is poor, and

any masking material (resist) will disappear as

fast as the underlayer, limiting the (relief) depth.

Reactive ion etching (RIE) can be highly selective because it is a chemical reaction between ions

(radicals) formed in a plasma and atoms on the

sample surface, and can be highly selective. RIE

has excellent lateral control because the electric

fields produced by the plasma cause ions to diffuse directionally. Straight parallel trenches a micron or more deep can be etched without affecting a rather fragile resist mask; minimum feature

sizes of a few nanometers are possible. RIE is

highly selective in its etching: oxygen etches hydrocarbons (resists), fluorine compounds are

useful in working with silicon systems, and many

materials are susceptible to chlorine etch, especially the compound semiconductors like gallium

arsenide. A great deal of work is directed at discovering the etching characteristics of other compounds.

The combination of physical and chemical

etching is achieved in a process called chemically

assisted ion beam etching (CAIBE). The combined effects of ion sputtering and chemical reaction with reactive ions results in a faster etch rate

than that due to either mechanism alone. CAIBE

is of particular interest to research groups investigating new materials, since it can be exploited to

uncover ways to etch new and exotic materials.

Unlike ancient lithographs, modern semiconductors must undergo many processing steps.

The mask must remain intact until the substrate

etch is complete, without changing feature size or

shape or surface characteristics (morphology).

Multiple operations are often required because of

the processing limitations of materials. For example, to grow a thin layer of silicon dioxide at

1,000°C, a resist is used to pattern a silicon nitride layer which is then capable of surviving the

high temperature during the oxide growth. Multiple layers are often processed in succession to

better allow a straightedge to be carried through

a thick stack of material.

CHARACTERIZATION

Characterization has become an indispensable

tool in the art and science of fabrication. The

designer needs information about device performance, the experimenter needs to know composition and concentration, and the process engineer must have immediate confirmation of the

electrical, mechanical, optical, or chemical properties of a thin film. In fact characterization, or

failure analysis, is in some cases as difficult and

extensive as the original experiment. The most

common questions addressed by characterization concern the shape and size of the structure.

Optical and electron microscopes provide this

information over size ranges from hundreds of

microns to fractions of a nanometer (near-atomic

dimensions).

Instruments also exist to measure a range of

materials properties, including the thickness, refractive index, and electrical resistivity. While

these techniques involve the measurement of thin

film properties over large distances, microcharacterization can determine composition or structure on a size scale comparable to the mean free

path of an electron and some techniques have an

ultimate resolution on the order of a few atomic

diameters.
Appendix A--Fabrication Technology for Miniaturization .41

There are a wide range of techniques usually

identified by acronyms, and some of the more

useful are listed here:

SCANNED BEAM TECHNIQUES

AES –

RBS –

SEM – Scanning electron microscope:

creates image of a surface by

measuring the reflection from a

beam of electrons.

TEM – Transmission electron microscope: determines crystal structure by measuring transmission

of electrons through a thin sample; has high resolution.

Auger electron microscopy: identifies constituents in the surface

layer by measuring energy of electrons emitted due to “Auger transitions.”

Rutherford backscattering spectroscopy: identifies constituents

by measuring the spectrum of

scattered ions off a sample.

SIMS – Secondary ion mass spectroscopy: analyzes composition of material removed by ion bombardment.

XRF – X-ray fluorescence: identifies

composition from photon emission due to x-rays.

EDS (EDX)— Energy dispersive x-ray spectroscopy: identifies composition from

dispersion of x-rays.

IMMA –

EELS –

ED –

LEED –

RHEED –

Ion microprobe mass analysis:

high resolution secondary ion

mass spectroscopy (SIMS).

Electron energy loss spectroscopy: identifies composition by

measuring energy loss of electrons during electron interaction.

Electron diffraction: measures

crystal structure by diffraction of

electrons.

Low energy electron diffraction:

measures surface structure by

diffraction of electrons.

Reflection high energy electron

diffraction: measures surface

structure; particularly useful for

epitaxial film growth.

SCANNED PROBE TECHNIQUES

STM – Scanning tunneling microscopy:

creates image of surface using

electron tunneling between the

surface and a sharp tip near the

surface; very high resolution.

AFM – Atomic force microscopy: creates

image of surface using repulsion

of electron charge distributions

between surface and a tip; nearatomic resolution is possible.

SxM – Other developing scanned probe

microcopies: create images of

surface characteristics for magnetic force, electrochemical measurement, etc., using the principle

of the STM.
Appendix B

Glossary

Actuator: Causes mechanical force or motion in

response to an electrical signal.

Analog: Refers to electrical signals that can vary

continuously over a range, as compared to

digital signals, which are restricted to a pair

of nominally discrete values.

Angstrom: One tenth of a nanometer, 10-10

meters.

Architecture: The overall logic structure of a

computer or computer-based system.

Capacitor: Passive circuit element that stores

electrical charge, creating a voltage differential. Capacitors can be fabricated within integrated circuits, as well as in the form of discrete components.

Charge-Coupled Devices (CCD): A type of solidstate electronic device used as a sensor in

some types of cameras.

Circuit Board: A card or board of insulating

material on which components such as semiconductor devices, capacitors, and switches

are installed.

Clock An electronic circuit, often an integrated

circuit, that produces high-frequency timing

signals. A common application is synchronization of the operations performed by a computer or microprocessor-based system. Typical clock rates in microprocessor circuits are

in the megahertz range, 1 megahertz equaling

106 cycles per second.

Compact Disk (CD): An optical storage medium

used for music and for computer data, among

others.

Deposition: An operation by which a film is

placed on a surface.

Die Bonder: Assembly equipment that bonds the

back side of an integrated circuit die to various materials. A die is a small piece of silicon

wafer that contains the complete circuit being

manufactured.

Doping: Adding to a semiconducting material

small amounts of other elements (dopants) to

change its electronic properties.

Dynamic Random Access Memory (DRAM): The

most common type of computer memory.

DRAM architecture usually uses one transistor and a capacitor to represent a bit, which is

a memory cell in a computer.

Electron Cyclotron Resonance (ECR): A technology that uses a high-frequency microwave energy source to create a plasma in a confined

region using a magnetic field for the purpose

of etching and deposition.

Etching: A process in which chemicals are used

to remove previously defined portions of the

silicon oxide layer covering the wafer to expose the silicon underneath.

Flat Panel Displays: A thin display screen that

uses any of a number of technologies, such as

liquid crystal display. Flat panel displays are

used in laptop computers in order to keep the

overall size and weight of the machine to a

minimum.

Gallium Arsenide (GaAs): A compound semiconductor with properties necessary for very

high-frequency microwave (analog) devices

and optoelectronics.

Gate: A simple electronic circuit that can implement a specified logical operation. In essence,

gates act like switches. Computer processing

units depend on large assemblies of gates, as

do integrated circuit memory chips.

Integrated Circuit (IC): Electronic circuits, including transistors, resistors, capacitors, and ‘

their interconnections, fabricated on a single

small piece of semiconductor material (chip).

Categories of ICs such as LSI and VLSI refer

to the level of integration, which denotes the

number of transistors on a chip. ICs may be

digital (logic chips, memory chips, or microprocessors) or analog.

-43-
44. Miniaturization Technologies

Ion Implantation: A process in which silicon is

bombarded with high-voltage ions in order to

implant them in specific locations and provide the appropriate electronic characteristics.

Liquid Crystal Display (LCD): A liquid crystal

display is a technique that uses a transistor

for each monochrome or each red, green and

blue dot. It provides sharp contrast and

speeds screen refresh. LCD technology is

commonly used in digital watches and laptop

computers.

Lithography A process in which the desired circuit pattern is projected onto a photoresist

coating covering a silicon wafer. When developed, portions of the resist can be selectively

removed with a solvent, exposing parts of the

wafer for etching and diffusion.

Logic Chips: ICs that manipulate digital data.

LSI: Large-scale integration. Typically involving

between 2,000 and 64,000 transistors.

Mainframe Computer: A system, normally intended for general-purpose data processing,

characterized by high performance and versatility. Mainframes have grown steadily in

capability as smaller and less expensive machines have progressed.

Mask: Stencil-like grid used in creating lithographic patterns on semiconductor chips.

Mass Storage: Refers to peripheral equipment

for computer memory suitable for large

amounts of data or for archival storage. Typical mass storage devices are disk and tape

drives.

Memory Chips: Devices for storing information

in the form of electronic signals.

Microcomputer: Refers to integrated circuits

that contain a microprocessing unit plus

memory, as well as to computers designed

around microprocessors or single-chip microcomputers.

Micrometer: One-millionth of a meter.

Micron: One-millionth of a meter.

Microprocessor: A computer central processing

unit on a single chip.

Nanometer: One-billionth of a meter.

Optical Disks: Recording media including CDs

that store information in patterns of microscopic pits on the surface of the disk, which

can then be detected by a solid state laser and

detector system and reproduced as sound,

images, or data.

Optoelectronic Devices: Devices that convert

light signals to electronic signals and vice

versa.

RAM (Random Access Memory): Most commonly, an integrated circuit that stores data in

such form that it can be read, erased, and

rewritten under the control of a computer

processor. Any memory location in a RAM

can be addressed directly (random access) as

opposed to sequentially or serially.

Resist, Photoresist: Chemicals used in lithographic processing of integrated circuits

which, much like photographic emulsions,

can be exposed by light, X-rays, or other radiation to form patterns.

Semiconductors: Materials, e.g., silicon, that

have four electrons in their outer electron

shells and have electrical conductivities that

are lower than good conductors such as metals but higher than insulators such as glass.

Other semiconductors include germanium,

gallium arsenide (GaAs), iridium phosphide

(InP), mercury telluride(HgTe), cadmium telluride (CdTe), and alloys of these compound

semiconductors.

Sensor: Converts a pressure, temperature, or other physical parameter into an electrical signal, often for use in a control system. A digital

speedometer for an automobile transforms

the output of a sensor into a miles-per-hour

reading, as does an airplane’s air speed indicator. In the case of the automobile speedometer, rotary motion is converted into an electrical signal, while an air speed indicator

depends on the pressure created by the motion of the airplane.
Appendix B-Glossary .45

Silicon: One of the most common elements found

in nature and the basic material used to make

the majority of semiconductor wafers.

Stepper: A sophisticated piece of equipment

used to transfer an integrated circuit pattern

from a mask onto a wafer.

Substrate: A piece of material, typically a semiconductor, on which layers of materials are

deposited and etched to fabricate a device or

a circuit.

Transistor: An electronic device that can be used

to switch or amplify electronic signals.

VLSI: Very large-scale integration. Typically involving more than 64,000 transistors.

Wafer: A thin disk, cut from silicon or other semiconductor material. The wafer is the base

material on which integrated circuits are fabricated. It is typically 4 to 8 inches in diameter.

Yield: In the production of microelectronic devices, the fraction that survive all tests and

inspection, function correctly, and can be

sold or incorporated into the manufacturer’s

own end products. Production costs depend

heavily on yields, which themselves depend

on circuit design, fabrication equipment, and

control of the manufacturing process.
Index

Accelerometer, 1,30-31

Analog Devices, Inc., 9,31

Angstrom technology, 7

Arthur D. Little, Inc., 28

Assemblers, 20,21

AT&T Bell Laboratories, 7,9, 11,31,33,37

Automobiles, 3,4,9

Biosensors, 3,8,28-30

Blood analysis, 29

Bosch, 10

Bulk micromachining, 31

California, 9

Canon, 33

Cellular automata, 16

cellular phone, 5

Characterization, 3,35,40-41

Charge coupled device, 27-28

Chemical field effect transistor, 28

Chemical sensors, 3,8,28-30

Chemical vapor deposition, 38

Chemically assisted ion beam etching, 40

chip size, 14,22,24

Clark, Leland C., 28

Clock cycle, 4, 15,24

Communications, 5, 16

Consumer electronics, 4,5, 16,26,27,28,33

Defense Advanced Research Project Agency, 7,9, 11

Department of Defense, 7,8,9,28

Department of Energy, 9

Digital Equipment Corp., 7

Display technology, 5,23

Doping, 39

Drexler, Eric, 21

Dynamic random access memory, 1,4,5,13,15

Electron-beam lithography, 11,13, 17,37

Etching, 39-40

Eutaxic control, 20

Feynman machines, 20

Feynman, Richard, 21

Fiber-optics, 29

Flat panel display, 5,23

Fluid flow, 31,33

Food processing, 28

Fraunhofer Institute, 9, 10

Fujitsu, 7

Gallium arsenide, 16, 17

German Federal Ministry for Research and Technology, 9

German Karlsruhe Nuclear Research Center, 9, 10,31

Glucose sensor, 28,29-30

Hewlett-Packard, 33

High electron mobility transistor, 16

High-performance computers, 15,26

Hitachi, 33

Hybrid wafer-scale integration, 24

Interconnection, 8, 13, 15, 17,21,23-27

International Business Machines, 7, 10, 11,23,24,37

Ion-beam lithography, 11, 17,37

Ion implantation, 39

Ion milling, 40

Japanese Basic Technologies for the Future Industries Program,

7

Japanese Exploratory Research for Advanced Technology, 7

Japanese Large Scale Program, 7

Japanese Ministry of Agriculture, Forestry and Fisheries, 8

Japanese Ministry of International Trade and Industry, 7,33

Japanese Science and Technology Agency, 10

Japanese Technology and Evaluation Center, 8

Jet Propulsion Laboratory, 33

Kodak, 28

Laptop computer, 5,19

Lasers, 16, 18,23,38

Lawrence Livermore National Laboratory, 9,33

LIGA, 31

Lithography, 10-11, 13, 17-19,23,31,32,35-38

Louisiana, 9, 11

Louisiana Technical University, 9

Magnetic storage, 23

Mainframe computer, 19

Manufacturing, 3, 13,30,32

Manufacturing costs, 1,3, 13

Mass storage, 17,23

Massachusetts Institute of Technology, 31

Materials science, 3, 16, 19,31,4041

Matsushita Central Research, 10

Mechanical properties, 31

Medical applications, 16,28-30,33

Messerschmidt, 10

Micro-Electromechanical Sensors and Actuators Institute, 10

Microelectronics and Computing Technology Consortium, 8,24

Micromachining, 30

Micromechanics, 1,3,8,9,20,30-34

Micromotors, 32-33

Microprocessor, 4

Microrobots, 10,33

Military applications, 16

Mitsubishi, 17

Molecular beam epitaxy, 16,38,39

Molecular electronics, 3,7, 16, 17

Molecular machines, 20-21

Motorola, 11

Multi-chip modules and packages, 4,8,24,25

Nanobots, 20

Nanotechnology, 20

-47 –
48 . Miniaturization Technologies

National Aeronautics and Space Administration, 9,33

National Institutes of Health, 9

National Research Council, 8

National Science Foundation, 7,9

Netherlands, 10

New York, 11

Nippon Electric Co., 5, 10,24

Nippon Telephone & Telegraph, 7, 10

Noise, 15

Optical storage, 17,23

Optics, 16,33,39

Optoelectronics, 7,39

Organo-metallic chemical vapor deposition, 39

Packaging, 4,5,23-27,32

Phase-shift lithography, 10, 19,35

Pressure sensor, 30

Quantum electronics, 3,7,15,16

Reactive ion milling, 40

Refrigeration, 15, 19,26

Ricoh, 10

Sacrificial layer, 31-32

Sandia National Laboratory, 9

scaling laws, 15

Scanning tunneling microscope, 19,20,23,37,41

Semiconductor manufacture“ g equipment, 1,3,4,9, 10-11,

17-19,30,31-32,35-41

Siemens, 10

Space applications, 16

Spin on, 38

Sputtering, 38

Surface micro-machining, 31-32

Surface mount technologies, 4,6,8

Surface science, 3, 19,31,38,40-41

Switzerland, 10

Tektronix, 28

Texas Instruments, 7,28

Thermal evaporation, 38

Toyota, 10

Traditional machining, 33

U.S. Congress, 9, 11

Ultraviolet lithography, 10, 17,31,35,37

University of California at Berkeley, 31,33

University of Delft, 10

University of Pennsylvania, 29

University of Tokyo, 10

University of Twente, 10

University of Utah, 33

von Neumann architecture, 16, 27

X-ray lithography, 10, 11, 13, 17,31,32,35,37

US GOVERNMENT PRINTING OFFICE : 1991 0 - 297-927 : QL 3