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OCR for page 25
Report of the
Research Briefing Panel on
Chemical Processing of Materials and
Devices for Information Storage
and! Handling
OCR for page 26
Research Beefing Panel on
Chemical Processing of Materials and
Devices for Information Storage
and Handling
Larry F. Thompson (Chairman), Head,
Organic Materials and Chemical
Engineering, AT&T Bell Laboratories
Lee L. Blyler, Supervisor, Plastics Applied
Research, Properties, and Processing,
AT&T Bell Laboratories
lames Economy, Manager, Polymer Science
and Technology, IBM Almaden Research
Center
Dennis W. Hess, Professor of Chemical
Engineering, University of California,
Berkeley
Richard Pollard, Professor of Chemical
Engineering, University of Houston
T. W. Fraser Russell, Professor of Chemical
Engineering, University of Delaware
Michael Sheptak, Senior Staff Engineer,
Magnetic Tape Division, Ampex
Corporation
26
Staff
Robert M. Simon, Project Director, Board on
Chemical Sciences and Technology
AlIan R. Hoffman, Executive Director,
Committee on Science, Engineering, and
Public Policy
OCR for page 27
Report of the
Research Bneftug Panel on
Chemical Processing of Materials and
Devices for Information Storage
and! Handlling
INTRODUCTION
Almost every aspect of our lives-at work,
at home, and in recreation has been affected
by the information revolution. Today, infor-
mation is collected, processed, displayed,
stored, retrieved, and transmitted through
the use of an array of powerful technologies
that rely on electronic microcircuits,
lightwave communication systems, mag-
netic and optical data storage and recording,
and electrical interconnections. Materials
and devices for these technologies are manu-
factured using sophisticated chemical pro-
cesses. The United States is now engaged in
a fierce international competition to achieve
and maintain supremacy in the design and
manufacture of materials and crevices for in-
formation storage and processing. The eco-
nomic stakes are large (see Table I); national
productivity and security interests dictate
that we make the strongest possible efforts to
stay ahead in processing science and tech-
nology for this area.
This briefing explores the chemical pro-
cessing required in three of these key tech-
nologies: electronic microcircuits, lightwave
communication systems, and magnetic re-
cording media. This briefing also explores
27
briefly some potential needs for advanced
chemical processing that may be required to
realize more fully the promise of supercon-
ducting metal oxides.
In high-technology manufacturing of com-
ponents for information systems, there has
been a long-term trend away from mechani-
cal production and toward production using
chemical processes. In several of these in-
dustries, chemists and chemical engineers
have become increasingly involved in re-
search and process development. WorId-
wide, though, many high-technology indus-
tries, such as the microelectronics industry,
still have surprisingly little strength in chem-
ical processing and engineering. The United
States has a special advantage over its inter-
national competitors its chemical engineer-
ing research community leads the world in
size and sophistication. The United States is
in a position to exploit its strong competence
in chemical processing to (1) regain leader-
ship in areas in which the initiative in manu-
facturing technology has passed to Japan,
and (2) maintain or increase leadership in ar-
eas of U. S. technological strength.
To achieve their potential contribution
fully, it is of paramount importance that
chemical engineers strongly interact with
OCR for page 28
TABLE 1 Total Estimated Worldwide
Market for Materials and Devices for
Information Storage and Handling (billions
of 1986 dollars)
Year
Technology
Electronic semicon
cluctors
1985 1990
1995
25
Lightwaves
Recording
materials 720
Interconnections 1021
Photovoltaics 0.30.S
Total Electronics 397550
60160
3
55
58
3
(n. a)
Source: AT&T Bell Laboratories.
Compiled from various published sources.
other disciplines in high-technology indus-
tries and have the ability to communicate
across clisciplinary lines. The technologies
discussed in this report cross over disci-
plines such as solid-state physics and chem-
istry, surface ancT interracial science, electri-
cal engineering, and materials science.
Materials and devices for information stor-
age and handling are exceedingly cliverse,
yet they have many characteristics in com-
mon: the products are high in value; they re-
quire relatively small amounts of energy or
materials to manufacture; they have short
commercial life cycles; anc! their markets are
fiercely competitive consequently, these
products experience rapid price erosion. The
manufacturing methods used to produce in-
tegrated circuits, optical fiber, and recording
media also have common characteristics.
Each of these products is manufactured us-
ing a sequence of individual, complex steps,
most of which entail the chemical moclifica-
tion or synthesis of materials. The inclividual
processes are designed as discrete unit or
batch operations and, to date, there has been
little effort to integrate the overall manufac-
turing process. Because chemical reactions
and processes are used in the manufacture of
this broad array of materials and devices,
28
chemical engineers could play a significant
role in improving manufacturing processes
and techniques, and investments in chemi-
cal processing science and engineering re-
search represent a potentially high-leverage
approach to improving our competitive posi-
tion.
CURRENT CHEMICAL
MANUFACTURING PROCESSES
MICROCIRCUITS
The use of chemical reactions and pro-
cesses in the manufacture of microcircuits
begins with the basic material for integrated
circuits, high-purity (less than 150 parts per
trillion of impurities) polycrystalline silicon.
This ultrapure silicon is produced from met-
allurgical grade (98 percent pure) silicon, by
(~) reaction at high temperature with hydro-
gen chIoricle to form a complex mixture con-
taining trichIorosilane; (2) separation and
purification of trichIorosilane by absorption
and distillation; and (3) reduction of ultra-
pure trichlorosilane to polycrystalline silicon
by reaction with hydrogen at Il00-1200°C.
To prepare single-crystal silicon ingots suit-
able for use as materials in semiconductors,
polycrystalline silicon is melted in a crucible
at 1400-1500 °C under an argon atmosphere.
Tiny quantities of dopants compounds of
phosphorus, arsenic, or boron are then
added to the melt to achieve the desired elec-
trical properties of the finished single-crystal
wafers. A tiny seed crystal of silicon with the
proper crystalline orientation is inserted into
the melt and slowly rotated and withdrawn
at a precisely controlled rate, forming a large
(15 cm x I.3 m) cylindrical single crystalwith
the desired crystalline orientation and com-
position. Crystal growth kinetics, heat and
mass transfer relationships, and chemical re-
actions all play important roles in this
process of controlled growth. The resulting
single-crystal ingots are sawed into wafers
that are polished to a flatness in the range of
from ~ to 10,um.
OCR for page 29
CHEMICAL PROCESSING OF MATERIALS AND DEVICES
The next steps in device fabrication are the
sequential deposition and patterning of thin
dielectric and conducting films. The pol-
ishecl silicon wafer is first oxidized in a fur-
nace at 1000-1200°C. The resultant silicon di-
oxide film is a few hundred nanometers thick
and extremely uniform. The wafer is then
coated with an organic photosensitive mate-
rial, termed a resist, and is exposed to light
through the appropriate photomask. The
purpose of the photolithographic process is
to transfer the mask pattern to the thin film
on the wafer surface. The exposed organic
film is developed with a solvent that re-
moves unwanted portions, and the resulting
pattern serves as a mask for chemically etch-
ing the pattern into the silicon dioxide film.
The resist is then removed with an oxidizing
agent such as a sulfuric acid-hydrogen per-
oxide mixture, then the wafer is chemically
cleaner! and is ready for other steps in the
fabrication process.
The patterned wafer might next be placed
in a diffusion furnace, where a first eloping
step is performed to deposit phosphorus or
boron into the holes in the oxide. A new ox-
ide film can then be grown and the photore-
sist process repeated. As many as 12 layers of
conductor, semiconductor, anct dielectric
materials are deposited, etched, and/or
doped to build the three-ctimensional struc-
ture of the microcircuit. Thus a semiconcluc-
tor device is a series of electrically intercon-
nected films, the successful growth and
manipulation of which depends heavily on
proper reactor design, the choice of chemical
reagents, separation and purification steps,
and the design and operation of sophisti-
cated control systems.
LIGHTWAVE MEDIA AND DEVICES
Optical fibers are also made by chemical
processes. The critical feature of an optical fi-
ber that allows it to propagate light down its
length is a core of high refractive index sur-
rounded by a cladding of Tower index. The
higher index core is procluced by doping sil
29
ice with oxides of phosphorus, germanium,
and/or aluminum. The cladding is either
pure silica or silica doped with fluorides or
boron oxide.
Four processes are principally used to
manufacture the glass body that is drawn
into today's optical fiber. "Outside" pro-
cesses, such as outside vapor-phase oxida-
tion and vertical axial deposition, produce
layered deposits of doped silica by varying
the concentration of SiCl4 and dopants pass-
ing through a torch. The resulting "soot" of
doped silica is deposited and partially sin-
tered to form a porous silica boule. In a sec-
ond step, the boule is sintered to a pore-free
glass rod of exquisite purity and transpar-
ency. "Inside" processes, such as modified
chemical vapor deposition (MCVD) and
plasma chemical vapor deposition (PCVD),
deposit doped silica on the interior surface of
a fused silica tube. in MCVD, the oxidation
of the halide reactants is initiated by a flame
that heats the outside of the tube. In PCVD,
the reaction is initiated by a microwave
plasma. Over a hundred different layers
with different refractive indexes (a function
of glass composition) may be deposited by
either process before the tube is collapsed to
form a glass rod.
In current manufacturing plants for glass
fiber, the glass rods formed by all of the
abovementioned processes are then carried
to another facility where they are drawn into
a thin fiber and immediately coated with a
polymer. The polymer coating is important;
it protects the fiber surface from microscopic
scratches, which can seriously degrade the
glass fiber's strength.
Current manufacturing technologies for
optical fiber are relatively expensive, com-
pared to the low cost of commodity glass.
U.S. economic competitiveness in optical
technologies would be greatly enhanced if
low-cost means were found for producing
waveguide-quality silica glass. The manu-
facture of glass lends itself to a fully inte-
grated and automated process (i.e., a contin-
uous process). One can envision a fiber
OCR for page 30
manufacturing plant that starts with the
purification of chemical reagents, which is
then followed by a series of chemical reac-
tions, glass-forming operations, and finally
fiber-drawing steps. in such a plant, inter-
mediate products would never be removed
from the "production line." Sol-gel and re-
lated processes are attractive canctidates for
such a manufacturing process, which would
start with inexpensive ingredients anct pro-
ceed from a so! to a gel, to a porous silica
body, to a dried and sintered glass rod, and
finally to drawn and coated fibers. Such a
process could reduce the cost of glass fiber by
as much as a factor of 10, a step that would
greatly increase the scope, availability, and
competitiveness of lightwave technologies.
At present the chemical steps involvec! in
sol-ge} processes are poorly understood.
Methods are being sought to manipulate
these processes to produce precisely layered
structures in a reliable and reproducible
way.
RECORDING MEDIA
Recording media come in a variety of for-
mats (e.g., magnetic tape, magnetic clisks, or
optical disks) and are made using a variety of
materials anc! processes (e.g., evaporated
thin films or deposited magnetic particles in
polymer matrixes). To illustrate the chemical
reactions and processes in the manufacture
of recording media, this section focuses on
magnetic particle technology, an economi-
cally important part of the market for which
the processing challenges are easy to dis-
cuss. Chemical reactions and processes are
equally relevant to emerging technologies
and materials in recording.
The manufacture of magnetic recording
media depends heavily on chemical process-
ing. The density at which information can be
recorded is determined by the chemical and
physical properties of the magnetic particles
or thin films coated on a disk or tape. Para-
mount among these properties are the
shape, size, and size distribution of the mag-
netic particles. An extremely narrow range
30
in the size of magnetic particles themselves
only a few tenths of a micron in size must
be achieved in a reliable and economic man-
ner. These particles must be deposited in a
highly oriented fashion, so that high record-
ing densities can be achieved by having the
magnetic particles lie as closely together as
possible. Accomplishing this requires the so-
lution of a variety of challenging problems in
the chemistry and chemical engineering of
barium ferrite anc! the oxides of chromium,
cobalt, and iron (e.g., the synthesis and pro-
cessing of micron-sized materials with spe-
cific geometric shapes).
The manufacture of magnetic tape illus-
trates an interesting sequence of chemical
processing challenges. A carefully prepared
dispersion of needIe-like magnetic particles
is coated onto a fast-moving (150-300
miming polyester film base that is 0.0066- to
0.08-mm thick. The ability to coat thin,
smooth layers of uniform thickness is cru-
cial. The coated particles are oriented in a de-
sired direction either magnetically or me-
chanically during the coating process. After
drying, the tape is calendared squeezed be-
tween microsmooth steel and polymer rolls
that rotate at different rates, providing a
"microslip" action that polishes the tape
surface. These manufacturing steps (i.e.,
materials synthesis, preparation anct han-
dling of uniform dispersions, coating, dry-
ing, and calendaring) are chemical processes
and/or unit operations that are familiar terri-
tory to chemical engineering analysis and
clesign.
INTERNATIONAL COMPETITIVE
ASSESSMENT
INTRODUCTION
In each of the technologies described in the
preceding section, U.S. leadership in both
fundamental research and manufacturing is
severely challenged, and in some cases the
United States has been judged to lag behind
foreign competitors such as Japan.
OCR for page 31
CHEMICAL PROCESSING OF MATERIALS AND DEVICES
MICROCIRCUITS
A recent report of the National Research
Council* has assessed the comparative posi-
tion of the United States and Japan in ad-
vanced processing of electronic materials.
The report, which focuses heavily on evaTu-
ating Japanese research on specific process
steps in the manufacture of electronic mate-
rials, provides significant background for
the following observations.
· The U. S. electronics industry appears to
be ahead of, or on a par with, Japanese in-
dustry in most areas of current techniques
for the deposition and processing of thin
films chemical vapor deposition (CVD),
metalorganic chemical vapor deposition
(MOCVD), and molecular beam epitaxy
(MBE). There are differences in some areas,
though, that may be crucial to future tech-
nologies. For example, the Japanese effort in
low-pressure microwave plasma research is
impressive and surpasses the U.S. effort in
some respects. The Japanese are ahead of
their U.S. counterparts in the design and
manufacture of deposition equipment, as
well.
· Japanese industry has a very substantial
commitment to advancing high-resolution
lithography at the fastest possible pace. Two
Japanese companies, Nikon and Canon,
have made significant inroads at the cutting
edge of optical lithography equipment. In
the fields of x-ray and electron-bean~ lithog-
raphy, it appears that U.S. equipment man-
ufacturers have lost the initiative to Japan for
the development of commercial equipment.
· Japanese researchers are ahead of their
U.S. counterparts in the application of laser
and electron beams and solid-phase epitaxy
for the fabrication of silicon-on-insulator
structures.
* Panel on Materials Science, National Materials Ad-
visory Board. Advanced Processing of Electronic Ma-
terials in the United States and Japan. Washington,
D.C.: National Academy Press, 1986.
· The Unitecl States leads in basic research
related to implantation processes and in the
development of equipment for conventional
applications of ion implantation. Japan ap-
pears to have the initiative in the develop-
ment of equipment for ion microbeam tech-
nologies.
Neither the United States nor Japan has
satisfactorily solved the problems of process
integration in microcircuit manufacture. As
the previous comparisons indicate, much ef-
fort is being expended on equipment design
for specific processing steps, but a parallel ef-
fort to integrate the processing of these ma-
terials across the many individual steps has
received less attention in both countries. Yet
the latter effort might have significant pay-
offs in improved process reliability and effi-
ciency that is, in "manufacturability." The
United States has the capability to take a sig-
nificant lead in this area.
LIGHTWAVE TECHNOLOGY
The Japanese are our prime competitors in
the development of lightwave technology.
They are not dominant in the manufacture of
optical fiber thanks in part to a strong overlay
of patents on basic manufacturing processes
by U.S. companies. In fact, a major Japanese
company manufactures optical fiber in
North Carolina for shipment to Japan. This is
the only example to date of Japan importing
a high-technology product from a U. S. sub-
sidiary. Nonetheless, the Japanese are mak-
ing strong efforts to surpass the United
States, and are reaching a par with the
United States in many areas.
The United States still significantly leads
Japan in producing special purpose and
high-strength fibers, in preparing cables
from groups of fibers, and in research on her-
metic coatings for fibers.
RECORDING MEDIA
Japan is the United States' principal tech-
nological competitor in the manufacture of
31
OCR for page 32
magnetic media, anct Korean firms are be-
ginning to make significant inroads at the
Tow end of the market for magnetic tape.
U.S. companies producing magnetic tape
use manufacturing processes that achieve
higher integration through combined unit
operations, but Japanese companies have a
higher degree of automation in these sepa-
rate operations. U. S. companies are ahead of
the Japanese in the use of newer thermoplas-
tics in caTendar-compliant roll materials. la-
pan used to surpass the United States in the
product uniformity of magnetic tape for pro-
fessional applications; U.S. firms have
closed this gap in recent years, and are now
capturing worldwide market share from the
Japanese, even in Japan.
The most significant development in Japan
is the entry of photographic film companies
(i.e., Fuji and Konishuroku) into the manu-
facture of magnetic media. They are having a
large impact because the heart of the manu-
facturing process is the deposition of thin
layers, and chemical processing technology
from the photographic film business can be
used to improve the quality and yield of
magnetic tape.
The United States still lags behind Japan in
the treatment and manufacture of magnetic
particles (except possibly for 3M, which
manufactures its particles internally). There
are disturbing signs that the Japanese maybe
aheact of the United States in the next gener-
ation of film base, especially the film base for
vapor-deposition magnetic media. The situ-
ation is not entirely clear, because 3M and
Kodak make their own proprietary film.
Other U.S. magnetic meclia companies,
though, maybe buying their film technology
from Japan in the future.
GENERAL OBSERVATIONS
AS noted previously, the industries that
manufacture high-technology materials and
components for information processing and
storage are characterized by short product
life cycles, enormous competition, and rapid
erosion of product value. These industries
also need rapid technology transfer from the
research laboratory onto the production line.
Many of their products cannot be protected by
patents, except for minor features. The key
to their competitive success is thoroughly
characterized and integrated manufacturing
processes, supported by process innovations.
in the past, much of the process technology
on which these industries depend has been
developed empirically. If the United States is
to maintain a competitive position in these
industries, it is essential that we develop the
fundamental knowledge necessary to stimu-
late further improvement of, anc! innovation
in, processes involving chemical reactions
that must be precisely controlled in a manu-
facturing environment. In the next section
the principal technical challenges are set
forth.
GENERIC RESEARCH ISSUES
INTRODUCTION
A variety of important research issues are
ripe for a substantially increased effort to en-
able U.S. companies to establish and main-
tain dominance in information storage and
handling technologies. These research is-
sues are quite broad and cut across the spec-
trum of materials and crevices.
PROCESS TNTEGRATION
Process integration is the key challenge in
the design of efficient and cost-effective
manufacturing processes for electronic,
photonic, and recording materials anc! de-
vices. Currently, these products are manu-
facturecl by a series of individual, isolated
steps. If the United States is to retain a posi-
tion of leadership, it is crucial that the overall
manufacturing methodology be examined
and integrated manufacturing approaches
be implemented. Historically, all industries
have benefited both economically and in the
quality and yield of products by the use of in
32
OCR for page 33
CHEMICAL PROCESSING OF MATERIALS AND DEVICES
tegrated manufacturing methods. As indi-
vidual process steps become more complex
anc! precise, the final results of manufactur-
ing (e.g., yield, throughput, and reliability)
often depend critically on the interactions
among the various steps. Thus, it becomes
increasingly important to automate and inte-
grate individual process steps into an overall
manufacturing process.
The concepts of chemical engineering are
easily applied in meeting the challenge of
process integration, particularly because
many of the key process steps involve chemi-
cal reactions. For example, in the manufac-
ture of microcircuits, chemical engineers can
provide mathematical models and control al-
gorithms for the transient and steady-state
operation of individual chemical process
steps (e.g., lithography, etching, film depo-
sition, diffusion, and oxidation), as well as
models and associated control algorithms for
the interactions between one process step
and another, and ultimately between pro-
cessing and the characteristics of the final de-
vice. As another example, in microcircuit
manufacture, chemical engineers can pro-
vide needed simulations of the dynamics of
material movement through the plant, and
thus optimize the flow of crevices (or wafers)
through a fabrication line.
REACTOR ENGINEERING AND DESIGN
Closely related to challenges in process in-
tegration are research challenges in reactor
engineering and design. Research in this
area is important if we are to automate man-
ufacturing processes for higher yields and
improved product quality. Contributions
from chemical engineers are needed to meet
this challenge processes such as CVD, epi-
taxy, plasma-enhanced CVD, plasma-en-
hanced etching, reactive sputtering, and oxi-
dation all take place in chemical reactors. At
present, these processes and reactors are
generally developed and optimized by trial
and error. .4~ basic understanding of funda-
mental phenomena and reactor design in
33
these areas would facilitate process design,
control, anc! reliability. Because each of these
processes involves reaction kinetics, mass
transfer, and fluid flow, chemical engineers
can bring a rich background to the study and
improvement of these processes.
An important consideration in reactor de-
sign and engineering is the ultraclean stor-
age and transfer of chemicals. This is not a
trivial problem; generally, the containers
and transfer media are the primary sources
of contamination in manufacturing. Meth-
ods are neecled for storing gases and liquids,
for purifying them (see the next section), and
for delivering them to the equipment where
they will be used all the while maintaining
impurity levels below ~ part per billion. This
purity requirement puts severe constraints
on the types of materials that can be used in
handling chemicals. For example, materials
in reactor construction that might be chosen
primarily on the basis of safety often cannot
be used. Designs are needed that will meet
the multiple objectives of high purity, safety,
and low cost.
The ultimate limit to the size of microelec-
tronic devices is that of molecular climen-
sions. The ability to "tailor" films at the mo-
lecular level to deposit a film and control its
properties by altering or forming the struc-
ture, atomic layer by atomic layer opens ex-
citing possibilities for new types of devices
and structures. The fabrication of these mul-
tilayer, multimaterial structures will require
more sophisticated deposition methods,
such as MBE and MOCVD. Depositing uni-
form films by these methods over large
dimensions will require reactors with a dif-
ferent design than those currently used, es-
pecially for epitaxial growth processes. The
challenge is to be able to control the flow of
reactants to build layered structures tens of
atoms thick (e.g., superIattices). To achieve
economic automated processes, the reactor
design has to allow for the acquisition of de-
tailed real-time information on the surface
processes taking place, fed back into an ex-
quisite control system and reagent delivery
OCR for page 34
system. This problem gives rise to an excit-
ing series of basic research topics.
ULTRAPURIFICATION
A third research challenge that is generic to
electronic, photonic, and recording materi-
als and devices stems from the need for start-
ing materials that meet purity levels once
thought to be unattainable.
This need is particularly acute for semicon-
ductor materials and optical fibers. For semi-
conductor materials, the challenge is to fin ct
new, Tower cost routes to ultrapure silicon
and gallium arsenide, and to purify other re-
agents used in the manufacturing process so
that they do not introduce particulate con-
tamination or other defects into the device
being manufactured. For optical fibers, pre-
cursor materials of high purity are also
needed. For example, the SiCi4 currently
used in optical fiber manufacture must have
a total of less than 5 parts per million of hy-
drogen-containing compounds and less
than 2 parts per billion of metal compounds.
Either impurity will result in strong light ab-
sorption in the glass fiber. For magnetic me-
dia, the challenge is to separate and purify
submicron-sized magnetic particles to very
exacting size and shape tolerances.
A variety of separation research topics
have a bearing on these needs. These include
generating improved selectivity in separa-
tions by tailoring the chemical and steric in-
teractions of separating agents, understand-
ing and exploiting interracial phenomena in
separations, improving the rate and capacity
of separations, and finding improved pro-
cess configurations for separations. These
are all research issues central to chemical
. .
engineering.
CHEMICAE SYNTHESIS AND PROCESSING OF
CERAMIC MATERIAES
The traditional approach to creating and
processing ceramics has been through the
grinding, mixing, and sintering of powders.
34
Although still useful in some applications,
this technology is being replaced by ap-
proaches that rely on chemical reactions to
create a uniform microstructure. Among the
typical examples of such an approach would
be sol-ye! and related processes. A tremen-
dous opportunity exists for chemists and
chemical engineers to apply their detailed
knowledge of funciamental chemical pro-
cesses in developing new chemical routes to
high-performance ceramics for electronic
and photonic applications.
Deeper involvement of chemical engi-
neers in manufacturing processes for ce-
ramics may be particularly important in the
eventual commercialization of metal oxide
superconductors. The current generation of
such superconductors consist of structures
that are formed during a conventional ce-
ramic synthesis. It is by no means clear that
the structures that may produce optimal per-
formance in such superconducting ceramics
(e.g., room-temperature superconductivity,
capacity for high current density are accessi-
ble by these techniques. Rational synthesis
of structured ceramics by chemical process-
ing may be crucial to further improvements
in superconducting properties and in afford-
ing efficient large-scare production.
DEPOSITION OF THIN FILMS
Precise and reproducible deposition of
thin films is another area of great importance
in the chemical processing of materials and
devices for the information age.
In microelectronic devices, there is a
steady trend toward decreasing pattern
sizes, and by the end of this decade the
smallest pattern size on production circuits
will be less than ~ ,um. Although the litho-
graphic tools to print such patterns exist, the
exposure step is only one of a number of pro-
cesses that must be performed sequentially
in a mass production environment without
creating defects. Precise and uniform depo-
sition of materials as very thin films onto
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CHEMICAL PROCESSING OF MATERIALS AND DEVICES
substrates 15 cm or more in diameter must be
performed in a reactor, usually at reduced
pressure. Particulate defects larger than 0.!
,um in these films must be virtually nonexis-
tent. Low-temperature methods of film dep-
osition will be needed so that defects are not
generated in previous or neighboring films
by unwanted diffusion of dopants.
For optical fibers, improved control over
the structure of the thin films in the preform
will lead to fibers with improved radial gradi-
ents of refractive index. A particular chal-
lenge might be to achieve this sort of control
in preforms created using sol-gel or related
processes.
Another challenge in depositing thin films
on optical fibers occurs in the final coating
step. improved coating materials that can be
cured very rapidly, for example, by ultravio-
let radiation, are neecled for high-speed
~ > 10 mist fiber-drawing processes. Both
glassy and elastomeric polymers with Tow
glass transition temperatures are needed for
use over temperatures ranging from-60 to
85°C or higher. Hermetic coatings are re-
quired to avoid water-induced stress corro-
sion of silica glasses, which proceeds by slow
crack growth. Materials under study inclucle
silicon carbide anct titanium carbide applied
by chemical vapor deposition, as well as
metals such as aluminum. A lO-foIcl increase
in the rate at which such coatings can be ap-
plied to silica fiber during drawing is needed
for commercial success. These coatings must
be pinhole-free, have low residual stress,
and adhere well. Hermetic coatings will also
be needed to protect the moisture-sensitive
halide and chaTcogenide glasses that may
find use in optical fibers of the future because
of their compatibility with transmission at
longer wavelengths.
Considerable progress in the science and
technology of depositing thin films is
neecled if the U.S. recording media industry
is to remain competitive with foreign manu-
facturers. New, fully automated coating pro-
cesses that will generate high-quality, Tow-
defect media are needed. Not only must con
35
siderable effort be mounted in designing
hardware and production equipment, but it
is also necessary to develop complex mathe-
matical models to gain an understanding of
the kinetic and thermodynamic properties of
film coating, as well as the effect of non-
Newtonian flow and polymer and fluid rhe-
ology. A better understanding of dispersion
stability during drying, as well as of diffu-
sion mechanisms that result in intermixing
of sequential layers of macromolecules, is
important.
MODELING AND THE STUDY OF CHEMICAE
DYNAMIC S
A challenge related to the problems of re-
actor design and engineering is the model-
ing and study of the fundamental chemistry
occurring in manufacturing processes for
semiconductors, optical fibers, and mag-
netic media. For example, mathematical
models originally developed for continu-
ously stirred tank reactors and plug-flow re-
actors are applicable to the reactors used for
thin-fiIm processing, and can be modified to
elucidate ways in which thin-film reactors
can be improved. Enabling these models to
reach their full descriptive potential will re-
quire cletailed studies of the fundamental
chemical reactions occurring on surfaces and
in the gas phase. For example, etching rates,
etching selectivity, line profiles, deposited
film structure, film bonding, ancT film prop-
erties are determined by a host of variables,
including the promotion of surface reactions
by ion, electron, or photon bombardment.
The fundamental chemistry of these surface
reactions is poorly understood, anct accurate
rate expressions are particularly needed for
electron-impact reactions (i.e., dissociation,
ionization, or excitation), ion-ion reactions,
neutral-neutral reactions, and ion-neutral
reactions. The scale and scope of the effort
devoted in recent years to understanding
catalytic processes needs to be given to re-
search related to film deposition and plasma
etching. Until a basic understanding is
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achieved of chemical reactions occurring at
the surface and in the gas phase, it will be dif-
ficult to clevelop new etching systems.
Research related to this area has had a de-
monstrable impact on recent innovations in
plasma processing. Five years ago, it was
well known that a fluorine-containing
plasma etches silicon at a rate significantly
greater than the rate for SiO2, thus offering
significant advantages for fabricating inte-
grated circuits. However, well-controlled
processes could not be developed that
would perform in a production environ-
ment. The work of chemical engineers in eTu-
cidating the relevant chemical reactions and
their kinetics was crucial to the identification
of the important chemical species in the etch-
ing process, their reaction pathways, and, in
addition, to the discovery that the organic
polymer photoresist contributed to plasma
chemistry and selectivity in important ways.
These studies led to new, improved plasma
processes that are currently being usec! in
production.
For magnetic media, mathematical models
could enhance our fundamental under-
standing of the manufacturing processes
used to make uniform high-purity magnetic
particles. Models for the kinetics and mecha-
nisms of reactions and an improved uncler-
standing of the thermodynamics of produc-
ing inorganic salts are required.
ENVIRONMENT AND SAFETY
Safety and environmental protection are
extremely important concerns in all of the
high-technology areas already discussed.
They present demanding intellectual chal-
lenges. The manufacture of materials and
devices for information handling and stor-
age involves substantial quantities of toxic,
corrosive, or pyrophoric chemicals (e.g., hy-
drides and halides of arsenic, boron, phos-
phorus, and silicon; hydrocarbons and or-
ganic chlorides, some of which are cancer
suspect agents; and inorganic acids). Unfor-
tunately, the industries involved in manu
36
factoring these materials and devices have
only recently begun to employ significant
numbers of chemical professionals, and
have suffered from a lack of expertise in the
safe handling and disposal of dangerous
chemicals. Recent studies in California indi-
cate that the semiconductor industry has an
occupational illness rate 3 times that of gener-
al manufacturing industries. Nearly half of
these illnesses involve systemic poisoning
from exposure to toxic materials. Problems
with groundwater contamination in Santa
Clara County, California, have also raised
concerns about how well the semiconductor
industry is equipped to handle waste man-
agement and disposal. If the semiconductor
and other advanced material industries are
to continue to prosper in the United States, it
is important that the expertise of chemical
engineers be applied to every aspect of
chemical handling in manufacturing, from
procurement through use to disposal.
RECOMMENDATIONS
Pursuing the research frontiers discussed
in the preceding section will significantly
benefit our national standard of living, de-
fense, education, and trade balance. How
can we best use resources to foster work in
these areas, and to foster communication
and collaboration among researchers in in-
dustrial, academic, and federal laboratories?
The following goals should be set for im-
proving national research capabilities that
will result in improved manufacturing pro-
cesses for electronic, photonic, and record-
ing materials and devices.
· Federal agencies involved in the support
of basic materials research (for example, the
National Science Foundation tNSF], the
U.S. Department of Energy, and the U.S.
Department of Defense) should consider un-
dertaking new initiatives in the support of
fundamental research addressing the ge-
neric intellectual issues in the chemical pro
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CHEMICAL PROCESSING OF MATERIALS AND DEVICES
cessing of electronic, photonic, and record-
ing materials and crevices (see the preceding
section).
· It is particularly important to involve
chemists and chemical engineers in research
related to ceramic synthesis and processing.
Researchers trained in traditional ap-
proaches to ceramic materials may not have
the optimal background to pursue the new
challenges in the molecular clesign, synthe-
sis, and engineering of ceramics.
· Fundamental research and training to
meet the needs of industry for chemical
process engineers and scientists should be
broadly based in many academic institu-
tions, for two reasons. First, many of the re-
search areas mentioned in the preceding sec-
tion lend themselves to research groups led
by single principal investigators or by small
teams of two or three coprincipal investiga-
tors. The magnitude of support given to
such research groups should be enhanced to
provide access to the sophisticated instru-
mentation neecled to pursue effective re-
search on fundamental phenomena impor-
tant to research areas such as separations,
processing, and reactor design. Second, the
demand from the electronics industry alone
for personnel with chemical backgrounds is
sufficiently large that the founding of a few
large centers is not likely to meet the need.
Some chemical engineering clepartments,
for example, are reporting that up to a quar-
ter of their baccalaureate graduates are being
hired by electronics firms.
· University research, particularly in engi-
neering, should be effectively coupled to in-
dustry through collaborative mechanisms.
industry has been the prime mover in ad-
vancing technology in materials and compo-
nents for information storage and handling,
and will remain so for the foreseeable future.
It is important, then, for university research
groups to develop and maintain good com-
munication with counterpart research groups
in industry. The NSF Engineering Research
Centers program and Tndustry-University
Cooperative Research program are two effec
37
five means to stimulate such communication
and collaboration.
· A few of the existing NSF Engineering
Research Centers are addressing research is-
sues that touch on the topics covered in this
briefing. Where appropriate, these centers
should be encouraged to seek broader partic-
ipation in their programs from chemical sci-
entists and engineers.
· The current undergraduate curriculum in
chemical engineering, although it provides
an excellent conceptual base for graduates
who move into the electronics industries,
could be improved by the introduction of in-
structional material and example problems
relevant to the challenges outlined in this
briefing. This would not require the creation
of new courses, but the provision of material
to enrich existing ones. Seminal texts often
serve to redefine the boundaries of a clisci-
pline and to direct teaching and research to-
ward new frontiers. The NSF should create
incentives for select researchers at the cutting
edge of chemical engineering to write the
next generation of textbooks for their field.
The existing network of programs in fund-
ing agencies do not address some important
problems in the generation and transfer of
expertise and ideas from the research labora-
tory to the production line. For the technolo-
gies cliscussed in this report, a key role in
generating new process concepts and equip-
ment is played by a large number of rela-
tively small firms. These firms are generally
not in a position to make financial contribu-
tions to Engineering Research Centers or to
retain academic consultants, yet face impor-
tant research problems in fundamental sci-
ence and engineering that would benefit
markedly from the insights of academic re-
searchers. The United States could signifi-
cantly boost its competitive position in the
technologies discussed in this report by facil-
itating information transfer between aca-
clemia and this segment of industry. The
problem for funding agencies with an inter-
est in promoting U. S. capabilities in this area
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is how to create incentives for academic re
searchers to seek out and forge links to the
small firms that stand at the crucial step be-
tween laboratory research and production
processes. Examples of two possible mecha-
nisms that provide these incentives follow.
· Agencies such as the NSF could create a
new sabbatical award for academic research-
ers to spend up to a year in the laboratory of a
small process technology firm. The rationale
for such a program would be both to provide
a critical sector of U.S. advanced process
technology firms with the latest insights
from university research, and to provide
university researchers with insights into the
ways in which fundamental science and en-
gineering can contribute to the practice
problems of high-technology processing of
materials and devices.
· A limited number of "incubator re-
search programs," providing state-of-the-
art facilities cohabited by researchers from
1
38
advanced process technology firms and re-
searchers in process engineering associated
with universities, could be set up in close
proximity to academic research campuses.
Key to these programs would be the contri-
bution by industry of high-quality research
personnel, in lieu of providing financial sup-
port for academic research conducted under
these programs. The government might pro-
vide a significant portion of the facility costs
to those university applicants that could as-
semble a critical mass of researchers from
their own departments and from high-tech-
nology firms. The concept of "incubators" is
not novel, and past attempts to translate
such a concept into reality have met with
success on some occasions and failure on
others. The panel believes that a solicitation
of proposals emphasizing interactions be-
tween academia and the small process tech-
nology companies that are capital-poor but
problem-rich would prove a worthwhile ex-
periment with a good chance of success.
/
Representative terms from entire chapter:
chemical engineers
