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OCR for page 37
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38
_ MOST EVERY ASPECT of our lives at
_. work, at home, and in recreation has
been affected by the information rev-
olution. Today, information is collected, proc-
essed, displayed, stored, retrieved, and trans-
mitted by an array of powerful technologies that
rely on electronic microcircuits, light wave
communication systems, magnetic and optical
data storage and recording, and electrical inter-
connections. Materials and devices for these
technologies, along with photovoltaic materials
and devices, are manufactured by sophisticated
chemical processes. The United States is now
engaged in fierce international competition to
achieve and maintain leadership in the design
and manufacture of these materials and devices.
The economic stakes are large (see Table 4.11;
national productivity and security interests dic-
tate that we make the strongest possible effort
to stay ahead in processing science and tech-
nology for this area.
In the manufacturing of components for in-
formation and photovoltaic systems, there has
been a long-term trend away from mechanical
production and toward production by chemical
processes. Chemists and chemical engineers
have become increasingly involved in several
areas of research and process development.
Worldwide, however, many high-technology in-
dustries, such as microelectronics, still have
surprisingly little strength in chemical process-
ing and engineering. The United States has a
particular advantage over its international com-
petitors in that its chemical engineering research
TABLE 4.1 Worldwide Market for Materials
and Devices for Information Storage and
Handling (billions of 1986 dollars)
Year
Technology
1985 1990a 1995a
Electronic semiconductors
Light wave fiber and devices
Recording materials
Interconnections
Photovoltaics
Total electronics
25 60 160
5.5
55
58
20
10 21
0.8
550
a Market projection.
SOURCE: AT&T Bell Laboratones. Compiled from var-
ious published sources.
FRONTIERS IN CHE^~AL ENGINEERING
community leads the world in size and sophis-
tication. The United States is in a position to
exploit its strong competence in chemical pro-
cessing to regain leadership in areas where the
initiative in manufacturing technology has passed
to Japan and to maintain or increase leadership
in areas of U.S. technological strength.
Table 4.2 illustrates some of the ways in
which chemical engineering can contribute to
research on information and photovoltaic ma-
terials and devices. To fully achieve its potential
contribution, though, the field of chemical en-
gineering must strongly interact with other dis-
ciplines in these industries. Chemical engineers
must be able to communicate across disciplinary
lines, as the technologies discussed in this
chapter involve solid-state physics and chem-
istry, electrical engineering, and materials sci
ence.
Electronic, photonic, and recording materials
and devices may seem to be an exceedingly
diverse class of materials, but they have many
characteristics in common: their products are
high in value; they require relatively small
amounts of energy or materials to manufacture;
they have short commercial life cycles; and
their markets are fiercely competitive-conse-
quently, these products experience rapid price
erosion. The manufacturing methods used to
produce integrated circuits, interconnections,
optical fibers, recording media, and photovol-
taics also share characteristics. All involve a
sequence of individual, complex steps, most of
which entail the chemical modification or syn-
thesis of materials. The individual steps are
designed as discrete unit or batch operations
and, to date, there has been little effort to
integrate the overall manufacturing process.
Chemical engineers can play a significant role
in improving manufacturing processes and tech-
niques, and investments in chemical processing
science and engineering research represent a
potentially high-leverage approach to enhancing
our competitive position.
n.a. CURRENT CHEMICAL MANUFACTURING
PROCESSES
Before the invention of the transistor in 1948,
the electronics industry was based on vacuum
OCR for page 39
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tube technology, and most electronic gear was
assembled on a metal chassis with mechanical
attachment, soldering, and hand wiring. All the
components of pretransistor electronic prod-
ucts-vacuum tubes, capacitors, inductors, and
resistors were manufactured by mechanical
processes.
A rapid evolution occurred in the electronics
industry after the invention of the transistor and
the monolithic integrated circuit:
· Today's electronic equipment is filled with
integrated circuits, interconnection boards, and
other devices that are all manufactured by
chemical processes.
· The medium used for the transmission of
information and data over distances has evolved
from copper wire to optical fiber. It is quite
likely that no wire-based information transmis-
sion systems will be installed in the future. The
manufacture of optical fibers, like that of mi-
crocircuits~ is almost entirely a chemical cro
cess.
· Early data storage memory was based on
ferrite core coils containing a reed switch that
mechanically held bits of information in either
an on or off state. Today, most data is perma-
nently stored through the use of magnetic ma-
terials and devices, and the next generation of
data storage devices, based on optoelectronic
materials and devices, is beginning to enter the
marketplace. Ferrite cores were manufactured
by winding coils and mechanically mounting the
individual memory cells in large arrays. Mag-
netic and optical storage media are manufac-
tured almost entirely by chemical processes.
The importance and sophistication of current
chemical manufacturing processes for elec-
tronic, photonic, and recording materials and
devices are not widely appreciated. A more
detailed description serves to highlight their
central role in these technologies.
Microcircuits
A semiconductor microcircuit is a series of
electrically interconnected films that are laid
down by chemical reactions. The successful
growth and manipulation of these films depend
heavily on proper design of the chemical reac
· ~ ~ _ . _ ~ ~ ~ ~ _ ^\ :~ A ;1 ~ 4 = ~ ~ ~ ~ ^: ~ ~ ~ Al tip
tors in which they are laid down, the choice of
chemical reagents, separation and purification
steps, and the design and operation of sophis-
ticated control systems. Microelectronics based
on microcircuits are commonly used in such
consumer items as calculators, digital watches,
personal computers, and microwave ovens and
in information processing units that are used in
communication, defense, space exploration,
medicine, and education.
Microcircuitry has been made possible by our
ability to use chemical reactions and processes
to fabricate millions of electronic components
or elements simultaneously on a single sub-
strate, usually silicon. For example, a 1-million-
bit dynamic random access memory device
(Figure 4.1) contains 1.4 million transistors and
1 million capacitors, with some chemically etched
features on the chip being as small as 1.1 ~m.
This stunning achievement is just one step in a
long-term trend toward the design and produc-
tion of integrated circuits of increasing com-
plexity and capability. There is still considerable
room for further increases in component density
in silicon-based microelectronics (Figure 4.2),
not to mention possible advances in component
density that would result from alternative meth
F1GURE 4.! Chemical reactions are used to achieve the
fine structures seen in modern integrated circuits. This
electron micrograph shows a transistor in a '~cell" of a I-
megabit dynamic random access memory chip. The distance
between features is about ~ Am. Courtesy, AT&T Bell
Laboratories.
OCR for page 41
7, PHOTON`C, AV~ RE£~15iG MATER47~S ii.~D DE-~S
109
1o8
I
~ 106
CL
Oh
z
z
o
o
107
105
104
103
1 o2 - ^
1 960
SILICON CHIPS IN
PRODUCTION
\
PHYSICAL LIMIT
Galas
CHIPS UNDER
~ DEVELOPMENT
1970
YEAR
1 980
1 990
FIGURE 4.2 The chemical processes used for the manufacture of microcircuits
have become progressively more sophisticated. This development is respon-
sible for the large increases in the number of components that can be placed
on a single chip. Trends in increasing component density are shown from
1960 for silicon chips (top line) and from 1975 for developmental chips based
on gallium arsenide (bottom line). The rates of growth shown have been
remarkable. From 1962 to 1972, silicon component density increased a
thousandfold and from 1972 to 1982, a hundredfold. From 1975 to 1985,
component density in developmental gallium arsenide devices grew by a factor
of 40,000. Courtesy, AT&T Bell Labortories.
oafs of storing and transferring information (e.g.,
three-dimensional circuits and Josephson (quan-
tum) or optical devices).
Chemical reactions and processes in the man-
ufacture of microcircuits (Figure 4.3) begin with
the basic material for integrated circuits, high-
purity (less than lSO parts per trillion of impur-
ities) polycrystalline silicon. This ultrapure sil-
icon is produced from metallurgical grade (98
percent pure) silicon by the following steps
(Figure 4.41:
· reaction at high temperature with hydrogen
chloride to form a complex mixture containing
trichlorosilane;
· separation and purification of of trichloro-
silane by absorption and distillation; and
· reduction of ultrapure trichlorosilane to
polycrystalline silicon by reaction with hydro-
gen at 1,100-1,200°C.
To prepare single-crystal silicon ingots suit-
able for use as materials in semiconductors,
polycrystalline silicon is melted in a crucible at
1,400-1,500°C under an argon at
mosphere. Tiny quantities of dop
ants compounds of phospho
rus, arsenic, or boron are then
added to the melt to achieve the
desired electrical properties of
the finished single-crystal waf
ers. A tiny seed crystal of silicon
with the proper crystalline ori
entation is inserted into the melt
and slowly rotated and with
drawn at a precisely controlled
rate, forming a large cylindrical
single crystal 6 inches (14 cm) in
diameter and about as tall as an
adult human being (1.8 m) with
the desired crystalline orienta
tion and composition. Crystal
growth kinetics, heat and mass
transfer relationships, and chem
ical reactions all play important
roles in this process of controlled
growth. The resulting single
crystal ingots are sawed into waf
ers that are polished to a flatness
in the range of from 1 to 10 ~m.
The next steps in device fab
rication are the sequential deposition and pat
terning of thin dielectric and conducting films
(Figure 4.51. The polished silicon wafer is first
oxidized in a furnace at 1,000-1,200°C. The
resultant silicon dioxide film is a few hundred
nanometers thick and extremely uniform. The
wafer is then coated with a photosensitive
polymeric material, termed a resist, and is
exposed to light through the appropriate pho
tomask. 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
removes unwanted portions, and the resulting
pattern serves as a mask for chemically etching
the pattern into the silicon dioxide film. The
resist is then removed with an oxidizing agent
such as a sulfuric acid-hydrogen peroxide mix
ture, and the wafer is chemically cleaned and
ready for other steps in the fabrication process.
The patterned wafer might next be placed in
a diffusion furnace, where a first doping step is
performed to deposit phosphorus or boron into
OCR for page 42
~2
the holes in the oxide. A new oxide film can
then be grown and the photoresist process
repeated. As many as 12 layers of conductor,
semiconductor, and dielectric materials are de-
posited, etched, and/or doped to build the three-
dimensional structure of the microcircuit.
Light Wave Media and Devices
Photonics involves the transmission of optical
signals through a guiding medium generally a
FRONTIERS IN CHEMICAL ENGINEERI~G
FIGURE 4.3 The manufacture of integrated circuits requires both expertise
in electronic design and chemical processing. Chemical process steps are
important to the preparation of silicon materials, to the steps from oxidation
of silicon wafers through establishment of bonding pads, and to the final
assembly of chips in individual packages. Excerpted by special permission
from Chemical Engineering, June 10, 1985. Copyright 1985 by McGraw-Hill,
Inc., New York, NY 10020.
glass fiber for purposes that include telecom-
munications, data and image transmission, en-
ergy transmission, sensing, display, and signal
processing. Optical fiber technology is less than
14 years old and only became a commercial
reality in the early 1980s. It is now a $1 billion
per year industry. The data-transmitting capac-
ity of optical fiber systems has doubled every
year since 1976 (Figure 4.61. In fact, optical
fiber systems planned on the basis of the pre-
vailing technology at that time are often obsolete
OCR for page 43
ELECTRONIC, PHOTONIC, AND RECORDING MATERIALS AND DEVICES
Si + HCI · SiHCI3 +
SkHyClz
[2] SiHC13 + H2
Distillation
1,100°C
HCI + SiXHyClz
Metallurgical silicon ~,~ ~, ~_
SixHyClz
FIGURE 4.4 The production of polycrystalline silicon for the electronics
industry involves several chemical steps aimed at the reduction of impurities.
These include (1) reaction of metallurigcal grade silicon to produce a mixture
of chlorosilanes, (2) distillation of trichorosilane, and (3) reduction of trichloro-
silane to polycrystalline silicon. Excerpted by special permission from Chem-
ical Engineering, June 10, 1985. Copyright 1985 by McGraw-Hill, Inc., New
York, NY 10020.
by the time they are implemented. Typically, a
given light wave technology is supplanted by
an improved technology after one year.
Other applications for light guides, such as
optical fiber sensors and transducers, are re-
ceiving a great deal of attention. Image trans-
mission (e.g., endoscopes), energy transmission
(e.g., light pipes), and display (e.g., decorative
signs) are growing commercial areas.
Light wave media and devices include the
guiding medium (optical fibers), sending and
receiving devices, and associated electronics
and circuitry. The transmission of light signals
through optical fibers must occur at wavelengths
where the absorption of light by the fiber is at
a minimum. Typically, for SiO2/GeO2 glass, the
best transmission windows are at 1.3 or 1.5 Am
(Figure 4.71.
Optical signal processing for integrated optics
and optical computing is in a rudimentary state
but is certain to be an important area for future
technological development. The processing in-
volved in making optoelectronic devices is very
similar to that used in microcircuit manufacture,
but with considerable utilization of Group III-
V compound semiconductors, lithium niobate,
and a variety of polymeric materials. Devel-
opmental manufacturing processes for optoelec
~3
SiHCI3
[3] Polycrystalline silicon
tropics emphasize reactive ion etching, epitaxy
(e.g., metalorganic chemical vapor deposition
(MOCKED), vapor-phase epitaxy, and molecu-
lar-beam epitaxy (MBE)), and photochemical
and beam processing techniques for writing
circuit configurations. All these processes are
based on chemical reactions that require precise
process control to produce useful devices.
Optical fibers are made by chemical process-
es. The critical feature of an optical fiber that
allows it to propagate light down its length is a
core of high refractive index surrounded by a
cladding of lower index. The higher index core
is produced by doping silica with oxides of
phosphorus, germanium, and/or aluminum. The
cladding is either pure silica or silica doped with
fluorides or boron oxide.
There are four principal processes that may
be used to manufacture the glass body that is
drawn into today's optical fiber. "Outside"
processes-outside vapor-phase oxidation and
vertical axial deposition-produce layered de-
posits of doped silica by varying the concentra-
tion of SiCl4 and dopants passing through a
torch. The resulting "soot" of doped silica is
deposited and partially sintered to form a porous
silica boule. Next, the boule is sintered to a
pore-free glass rod of exquisite purity and trans
OCR for page 44
~(
SILICON
INGOT
¢' SILICON WAFER
-i\// Inky\\:
-A Mask
Pnsitiv~ / \ Negative
\,~
Develop
tCh
~ Strip
FIGURE 4.5 Chemical steps in photolithography. A sim-
plified series of steps in photolithography is shown. A
silicon wafer, taken from a single-crystal silicon ingot, is
coated with a polymer resist that is sensitive to light. A
mask is placed over the wafer and the resist is thus
selectively exposed to light. Depending on the type of
polymer coating used, two things can happen. If the polymer
is a positive resist, exposure to light makes the polymer
easier to dissolve in a solution during the development step.
After the development step, a protective film is left on the
wafer that is the image of the mask used. If the polymer is
a negative resist, exposure to light makes the polymer more
difficult to dissolve during the development step. After-
wards, a protective film is left on the wafer that is the
opposite of the image on the mask used. A corrosive gas
or liquid is then used to etch away those parts of the wafer
unprotected by the resist film. The resist film is removed
after etching in preparation for other process steps. Ex-
cerpted by special permission from Chemical Engineering,
June 10, 1985. Copyright 1985 by McGraw-Hill, Inc., New
York, NY 10020.
FRONTIERS iN CHEMICAL ~,YGI^~EER`~N'6
F 107
By
e. 1 o6
-
c~ 105 _
id
'09 104 _
103
lot 1 1 1 1
1 975
[PHYSICAL
LIIIIIT 109tl I'm'
9: tOUBlES
O ~ O ElERY YEAR
. ~ ._
1 980 1 985 1 g90
YEAR
FIGURE 4.6 Since 1975, both the capacity of optical fiber
and the distance a signal can be carried on optical fiber
have steadily increased. Courtesy, AT&T Bell Laborato-
r~es.
parency. "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 (Figure 4.8~. In PCVD,
the reaction is initiated by a microwave plasma.
More than a hundred different layers with dif-
ferent refractive indexes (a function of glass
composition) may be deposited by either pro-
cess before the tube is collapsed to form a glass
rod.
In current manufacturing plants for glass fiber,
the glass rods formed by all the above processes
are carried to another facility where they are
E _
In 1
a)
o
0.~
0.1 _
\
. 1250nm 1390nm 1600nrr
Sl-OH COMB Sl-OH P-OH
SHARP SHARP BROAD
POOH
` ~ADDED
RAYLEIGH SCATTERI NG \-4
1 , 1 1 1 1 1 ~ 1
0.8 1.0 1.2 1.4 1.6
WAVELENGTH (~1 m)
FIGURE 4.7 Transmission losses in glass fibers carrying
optical signals are due to the interaction of light with
chemical bonds. From 1.2 am to 1.6 am, losses due to
Rayleigh scattering in the fiber are minimized, but trans-
mission losses from Si-OH and P-OH bonds become large.
The lowest transmission losses occur at wavelengths of 1.3
and 1.5 ~m. Courtesy, AT&T Bell Laboratories.
OCR for page 45
ELECTR0~G, PHOT0~C, AND RECORDING MATERIALS AND DEVICES
FLOW METERS,
MASS-FLOW CONTROLLERS
O2 AND MANIFOLD
~5
r FUSED SILICATUBE
026], 02, 1 : ~1__O2
POCQ3 | GeCQ4
~7 V ;;;;;;'; Cal
MULTIBURNER ~ DEPOSITED LAYER
TORCH ~OFCOREG~SS
1 O2
H2
I L BC]3 SiF4
SiC]A SF6 Ct FREON
~ /
BUBBLERS
drawn into a thin fiber and immediately coated
with a polymer. The polymer coating is impor-
tant; it protects the fiber surface from micro-
scopic scratches, which can seriously degrade
the glass fiber's strength.
Current manufacturing technologies for op-
tical fiber are expensive compared with the low
cost of commodity glass. U.S. economic com-
petitiveness in optical technologies would be
greatly enhanced if low-cost means were found
for producing wave guide-quality silica glass.
The manufacture of glass lends itself to a fully
integrated and automated (i.e., continuous)
process. One can envision a fiber manufacturing
plant that moves from purification of chemical
reagents to a series of chemical reactions, glass-
forming operations, and, finally, fiber-drawing
steps. Intermediate products would never be
removed from the production line. Sol-gel and
related processes (see Chapter 5) are attractive
candidates for such a manufacturing technology,
which would start with inexpensive ingredients
and proceed from a sol to a gel, to a porous
silica body, to a dried and sintered glass rod,
to drawn and coated fibers. Such a process
TRANSLATION
FIGURE 4.8 Modified chemical. vapor deposition (MCVD) is one of the
principal processes used to manufacture optical fiber. In MCVD, a mixture
of gases (O', POCK, SiCl4, GeCl4, BC13, SiF4, SF6, Cal, and freon) pass down
the interior of a hollow silica tube that is being externally heated by a moving
flame. The gases react to form a fine layer of silica glass doped with constituents
of the gaseous mixture. Many layers can be deposited before the silica tube
is collapsed and drawn into optical fiber. Courtesy, AT&T Bell Laboratories.
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 competi-
tiveness of light wave technologies.
At present the chemical steps involved in sol-
gel 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-n~-mb-er of formats
(e.g., magnetic tape, magnetic disks, or optical
disks) and are made by a variety of materials
and processes (e.g., evaporated thin films or
deposited magnetic particles in polymer ma-
trixes). The next generation of recording media
will be based on optical storage of data (Figure
4.91. Already, read-only optical disks (or CD-
ROMsJ are on the market for applications such
as search and retrieval of information from large
data bases. And optically based compact disks
(CDs) are available in every record store. The
possibility of creating optically based recording
OCR for page 46
~6
media for read-write storage of information has
generated a tremendous amount of industrial
research but, so far, no commercially viable
products.
Since a practical read-write optical disk has
not yet been invented, it is hard to describe the
processing challenges involved in making it.
Thus, the remainder of this section examines
the most challenging (from a processing stand-
point) of the remaining forms of recording me-
dia: magnetic disks and tape. Magnetic media
are still an economically important part of the
recording market and have a rich array of
processing challenges with which chemical en-
gineers have been involved. These challenges
are relevant to the emerging technologies and
materials in recording.
In the manufacture of magnetic recording
media, the chemical and physical properties of
the magnetic particles or thin films coated on a
1o1o
109
-
.~
y 1 o8
in
._
~5
o
.~
~ 10
co
a)
1o6
Optical disks _ ~
-
-
over halide|
~Limit
Demonstrated Magnetic disk
/ Product density
/ ~ Low estimate of __
/ / current optical
/ / density
/ 3370
~ 3350
/ 3033-11
~/3033
C IBM 2314
05
1965 1 970
^.~0
1980 1990 2000
FIGURE 4.9 The density at which information can be
written on optical disks (measured in bits/in) was demon-
strated in the early 1980s to be 10 times greater than the
current highest performance magnetic disk. The gap be-
tween optical and magnetic storage capabilities is projected
to increase over the next 20 years. Reprinted with permis-
s~on from Electronic Design, August 18, 1983, 141.
.~NTIERS IN CHEMICAL ENGINEERING
disk or tape are very important, for they deter-
mine the density at which information can be
recorded. Paramount among these properties
are the shape, size, and distribution of the
magnetic particles. An extremely narrow size
range of magnetic particles themselves only a
few tenths of a micrometer in diameter must
be achieved in a reliable and economic manner.
Furthermore, the particles must be deposited
in a highly oriented fashion and lie as closely
together as possible, so that high recording
densities can be achieved. To accomplish this,
a variety of challenging problems must be solved
in the chemistry and chemical engineering of
barium ferrite and the oxides of chromium,
cobalt, and iron (e.g., the synthesis and pro-
cessing of micrometer-sized materials with spe-
cific geometric shapes).
The manufacture of magnetic tape illustrates
an interesting sequence of chemical processing
challenges (Figure 4.101. A carefully prepared
dispersion of needle-like magnetic particles is
coated onto a fast-moving (150-300 m/min) poly-
ester film base 0.0066-0.08 mm thick. The ability
to coat thin, smooth layers of uniform thickness
is crucial. The particles, after being coated onto
the film, are oriented in a desired direction
either magnetically or mechanically during the
coating process. After drying, the tape is cal-
endered (squeezed between 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 and handling
of uniform dispersions, coating, drying, and
calendering) are chemical processes and/or unit
operations that are familiar territory to chemical
engineering analysis and design.
Materials and Devices for Interconnection
and Packaging
Interconnection and packaging allow elec-
tronic devices to be usefully incorporated into
products. The manufacture of complex elec-
tronic systems requires that hundreds of thou-
sands of electronic components be efficiently
connected with one another in an extremely
small space. In the past, this was accomplished
by hand wiring discrete components on a chassis
OCR for page 47
ELECTRONIC, PHOTONIC, AND RECORDING MATERIALS A.~D DEVICES
(4)
(2) Drying oven
air flotation
(1) Coating head air flotation (5)
Coating ~reverse roll (shown) (shown) Calender
mix ~gravure knife ~l
/1 ~ | (3) Ferrite magnets \\
Sandmill Dispersing If ~ ~ J ~
Coating head
reverse roll (shown) (shown)
gravure knife
l
it'
Mix In: _
Enlargement of
sandmill dispersing
chamber
Rotating
Blades
\; Media
FIGURE 4.10 The manufacture of magnetic tape involves a series of steps
including (1) forming a uniform dispersion of coating mix, (2) applying this
coating to the film base, (3) orienting the magnetic particles, (4) drying the
magnetic coat in an air-flotation oven, and (5) calendering and final wind-up
on spools. Chemical processes are central to several of these steps. Excerpted
by special permission from Encyclopedia of Chemical Technology, 3rd ea.,
Vol. 14, p. 745. Copyright 1978 by McGraw-Hill, Inc., New York, NY 10020.
assembly. Today, interconnection technology
is based on high-density printed wiring boards,
often with as many as 30 parallel layers of
interconnection. The board insulation substrate
may be either polymer or ceramic, with appro-
priate metal conductors.
~7
an\
T electro magnets
Unwind Base film
Breakaway of
base film to
~_ / show air slots
;~ co: her
Base
\-
Enlargement of
alr-flotatlon oven
creating sinusoidal
wave form of base film
-
The dielectric and the conductors are selected
to maximize data transmission speed while min-
imizing signal loss. In addition, dissipating heat
generated by the microcircuits is rapidly becom-
ing an important consideration. If too much
heat builds up in the microelectronic device,
OCR for page 50
FRONTIERS IN AWAY ENGI1VEERING
of the United States and Japan in advanced
processing of electronic materials. The report,
which focuses heavily on evaluating Japanese
research on specific process steps in the man-
ufacture of electronic materials, provides sig-
nificant background for the following observa-
tions:
· The U.S. electronics industry appears to
be ahead of, or on a par with, Japanese industry
in most areas of current techniques for the
deposition and processing of thin films chem-
ical vapor deposition (CVD), MOCVD, and
MBE. There are differences in some areas,
though, that may be crucial to future technol-
ogies. For example, the Japanese effort in low-
pressure microwave plasma research is impres-
sive 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 li-
thography 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-beam lithography, it appears
that U.S. equipment manufacturers 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.
· The United States leads in basic research
related to implantation processes and in the
development of equipment for conventional ap-
plications of ion implantation. Japan appears to
have the initiative in the development of equip-
ment for ion microbeam technologies.
There is a penalty to be paid for falling behind
foreign competitors in process equipment design
and engineering. Early access to new prototypes
of equipment allows a manufacturing firm to
concurrently troubleshoot the equipment and
integrate it into its existing process line. When
the state-of-the-art processing equipment comes
from overseas, companies in the country of
origin gain a competitive advantage stemming
from this early access. A look at the installation
record for JEOL focused ion beam instruments
(which are the best in the world) illustrates this
phenomenon (Table 4.31.
Much remains to be done, in both the United
States and Japan, to solve the problems of
process integration in microcircuit manufacture.
Effort is being expended on equipment design
for specific processing steps, but a parallel effort
to integrate the processing of semiconductor
materials and devices across the many individ-
ual steps has received less attention in both
countries. Yet the latter effort may have signif-
icant payoffs in improved process reliability and
efficiency- that is, in "manufacturability." The
United States, with the strongest chemical en-
gineering research community in the world, has
the capability to take a significant lead in this
area.
Light Wave Media and Devices
The Japanese are our prime competitors in
the development of light wave 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. com-
panies. 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 prod-
uct from a U.S. subsidiary. Nonetheless, the
Japanese are making strong efforts to surpass
the United States and are reaching a par with
us 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 hermetic coatings
for fibers.
Recording Media
Japan is the America's principal technological
competitor in the manufacture of magnetic me-
dia, and Korean firms are beginning to make
significant inroads at the low end of the magnetic
tape market. U.S. companies producing mag-
netic tape use manufacturing processes that
OCR for page 51
ELECTRONIC, PHOTONIC, AND RECORDIATO i'~ATERIALS AND DEVICES
TABLE 4.3 Installation Record for Focused Ion Beam Instruments
Made by JEOL Semiconductor Equipment Division
Instrument Instrument Year
Number Customer Country Type Installed
8
10
12
13
14
16
18
19
20
21
22
23
24
25
1 The Institute of Physical and Japan JIBL-34 1982
Chemical Research
2 The Institute of Physical and Japan JIBL-100 1983
Chemical Research
3 Optoelectronics Joint Japan JIBL-100 1983
Laboratory
4 LSI R&D Lab, Mitsubishi Japan JIBL-100 1983
Electric Corporation
5 Fujitsu Laboratories Ltd.- Japan JIBL-1OOA 1984
AtSugl
Optoelectronics Joint
Laboratory
Institute of Laser Engineering,
Osaka University
The Institute of Physical and
Chemical Research
NTT Musashino Electrical
Communication Laboratories
Institute of Industrial Science
,
Tokyo University
Fujitsu Laboratories Ltd.
Atsugi
Dainippon Screen
Fujitsu Laboratories Ltd.
Atsugi
NTT Atsugi Electrical
Communication Laboratories
Tsukuba Research Center,
Sanyo Electric Co., Ltd.
NEC Corporation
LSI R&D Lab, Mitsubishi
Electric Corporation
Optoelectronics Joint
Laboratory
Institute of Industrial Science,
Tokyo University
Matsushita Laboratory
Nihon Denso
Sony
Denka
Max Planck Institute
IBM
Japan
Japan
Japan
Japan
Japan
Japan
Japan
Japan
Japan
Japan
Japan
Japan
Japan
Japan
Japan
Japan
Japan
Japan
Germany
U.S.A.
JIBL-1OOA
JIBL-30
JIBL-200
JIBL-100
JIBL-100
JIBL-GP1
JIBL-100
JIBL-100
JIBL-100
1984
1984
1984
1984
1984
1984
1984
1984
1984
JIBL-1OOA 1984
JIBL- 140
JIBL- 140
IPMA-10
IPMA-10
JIBL-106
JIBL-106
JIBL-GPI
JIBL-100
JIBL-1OOA
JIBL- 106
1984
1984
1984
1986
1986
?
?
?
?
1988
SOURCE: AT&T Bell Laboratories and JEOL.
achieve higher integration through combined
unit operations, but Japanese companies have
a higher degree of automation in these separate
operations. U.S. companies lead the Japanese
in the use of newer thermoplastics in calender-
compliant roll materials. Japan used to surpass
the United States in the product uniformity of
magnetic tape for professional applications; U.S.
51
firms have closed this gap in recent years and
are now capturing worldwide market shares
from the Japanese, even in Japan.
The most significant development in Japan 1S
the entry of photographic film companies (Fuji
and Konishuroku) into the manufacture of mag-
netic media. They are having a large impact
because the heart of the manufacturing process
OCR for page 52
52
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 and disks.
The United States still lags behind Japan in
the treatment and manufacture of magnetic
particles (except possibly for 3M, which man-
ufactures its particles internally). There are
disturbing signs that the Japanese may be ahead
of the United States in the next generation of
film base, especially for vapor-deposition mag-
netic media. The situation is not entirely clear,
because 3M and Kodak make their own pro-
prietary film. Other U.S. magnetic media com-
panies, though, may be buying their film tech-
nology from Japan in the future.
Optical recording media for read-write appli-
cations are still in the research stage. U.S.
companies are roughly on par with European
and Japanese companies in such research. Read-
only applications (e.g., CD-ROM disks and
compact audio disks) are largely dominated by
manufacturing technology from overseas.
Interconnection and Packaging
The United States leads its competitors in the
design of central processing unit packaging for
large computers. Companies such as IBM, Cray,
and Amdahl are on the cutting edge of inter-
connection design and manufacturing. Japanese
companies are ahead in some interconnection
technologies found in mid-sized and smaller
computers (e.g., phenolic paper boards and
epoxy-resin boards).
Photovoltaics
The U.S. photovoltaics industry serves more
than 100 different countries. Major competition
comes from Japan and, to a limited extent, from
Europe. U.S. firms have a dominant position
in the power module market (devices with
photovoltaic areas greater than 0.5 m2) while
Japanese firms have dominated the consumer
market for small-photovoltaic goods (e.g., cal-
culators, watches, and radios).
Superconductors
A recent report on high-temperature super-
conductivity' characterizes international com
FEgATIERS i^~\ CHEMICAL ENGINEERI.\G
petition as intense, but the U.S. competitive
position in science as good. Japan, China, a
number of European countries, and the USSR
are putting in place significant scientific and
technological efforts. In Japan, industrial con-
sortia are being organized by the government
to begin initial development activities. The re-
port concludes, "Japan offers perhaps the
strongest long-range competitive threat to the
U.S. position."
General Observations
The industries that manufacture materials and
components for information applications are
characterized by products that are rapidly
superseded in the market by improved ones.
This rapid turnover stems from the intense
competition among these industries and results
in rapid price erosion for products, once intro-
duced. These industries also require rapid tech-
nology transfer from the research laboratory
onto the production line. Many of theirproducts
cannot be protected by patents, except for minor
features. Therefore, the key to their competitive
success is thoroughly characterized and inte-
grated 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 po-
sition in these industries, it is essential that it
develop the fundamental knowledge necessary
to stimulate further improvement of, and in-
novation in, processes involving chemical re-
actions that must be precisely controlled in a
manufacturing environment. In the next section,
the principal technical challenges are set forth.
INTELLECTUAL FRONTIERS
A variety of important research issues require
much more work if U. S. companies are to
establish and maintain dominance in information
storage and handling technologies. These issues
are quite broad and cut across the spectrum of
materials and devices.
Process Integration
Process integration is the key challenge in the
design of efficient and cost-effective manufac
OCR for page 53
ELECTRONIC, PHOTONIC, AND RECORDING MATERIALS AND DEVICES
luring processes for electronic, photonic, and
recording materials and devices. Except for
magnetic tape, these products are currently
manufactured through a series of individual,
isolated steps. If the United States is to retain
a position of leadership, it is crucial that its
overall manufacturing methodology be exam-
ined and that integrated manufacturing ap-
proaches be implemented. Historically, all in-
dustries have benefited both economically and
in the quality and yield of products by the use
of integrated manufacturing methods. As indi-
vidual process steps become more complex and
precise, the final results of manufacturing (e.g.,
yield, throughput, and reliability) often depend
critically on the interactions among the various
steps. Thus, it becomes increasingly important
to automate and integrate individual process
steps into an overall manufacturing process.
The concepts of chemical engineering are
easily applied in meeting the challenge of pro-
cess integration, particularly because many of
the key process steps involve chemical reac
,
WAFER _ LASER
ENTRY ~ READER
Let i.
1 1
_ ~_ __ _ ~__ J
RESIST PATTERN DEVELOP
COAT & ~ TRANSFER ~ ETCH ~ TEST
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1
1
53
lions. For example, in the manufacture of mi-
crocircuits, chemical engineers can provide
mathematical models and control algorithms for
the transient and steady-state operation of in-
dividual chemical process steps (e.g., lithogra-
phy, etching, film deposition, diffusion, and
oxidation), as well as interactions between pro-
cess steps and ultimately between processing
and the characteristics of the final device. As
another example, in microcircuit manufacture,
chemical engineers can provide needed simu-
lations of the dynamics of material movement
through the plant and thus optimize the flow of
devices (or wafers) through a fabrication line
(Figure 4.12~. The continuous production of
photovoltaic devices will require similar studies
with even more emphasis on automation.
Reactor Engineering and Design
Closely related to challenges in process in-
tegration are those in reactor engineering and
design. Research in this area is important if we
MICROPROCESSOR
CONTROL UNIT
~ _ ION IMPLANT
_ , &
THERMAL
DRIVE
....
:
.
, , ~,
|PRODUCT| I REJECT| I
1
FIGURE 4.12 The integrated semiconductor processing line of the future will
be a fully automated series of chemical processing steps. Chemical engineers
will be needed to integrate individual process steps into a manufacturing line
that can be operated free from human handling, and possible contamination,
of the devices. Courtesy, AT&T Bell Laboratories.
FILM
DEPOSITION
(SPUTTER,
MBE, CVD
EVAPORATE)
l
t~ T
WAFER TRANSPORT
ELECTRONIC CONTROL
RF-ENTRY PATH
EXIT PATH
OCR for page 54
54.
are to automate manufacturing processes for
higher yields and improved product quality.
Processes such as CVD, epitaxy, plasma-en-
hanced CVD, plasma-enhanced etching, reac-
tive sputtering, and oxidation all take place in
chemical reactors. At present, processes and
reactors are generally developed and refined by
trial and error. A basic understanding of fun-
damental phenomena and reactor design would
facilitate process design, control, and reliability.
Because all these processes involve reaction
kinetics, mass transfer, and fluid flow, chemical
engineers bring a rich background to their study
and improvement. For example, high-yield,
continuous processes for film deposition and
packaging are required if photovoltaic devices
are to be manufactured at costs that are com-
petitive with other energy technologies. New
reactors and a better understanding of chemical
dynamics in reactors are central to achieving
this.
An important consideration in reactor design
and engineering is the ultraclean storage and
transfer of chemicals. This is not a trivial prob-
lem; generally, the containers and transfer me-
dia are the primary sources of contamination in
manufacturing. Methods are needed 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 1 part
per billion. This requirement puts severe con-
straints on the types of materials that can be
used in handling chemicals. For example, ma-
terials 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 of molecular dimensions. The
ability to "tailor" films at the molecular level-
to deposit a film and control its properties by
altering or forming the structure, atomic layer
by atomic layer opens exciting possibilities for
new types of devices and structures. The fab-
rication of these multilayer, multimaterial struc-
tures will require deposition methods such as
MBE and MOCVD. Depositing uniform films
by these methods over large dimensions will
FRONT`tERS 4~N CHEMICAL ElYrGINEERI^~!G
require reactors with a different design from
those currently used, especially 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., superlat-
tices). To achieve economic automated pro-
cesses, the reactor design must allow for the
acquisition of detailed real-time information on
the surface processes taking place, fed back
into an exquisite control system and reagent
delivery system. This problem gives rise to an
exciting series of basic research topics.
Ultrapurification
A third research challenge that is generic to
electronic, photonic, and recording materials
and devices stems from the need for starting
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 find
new, lower cost routes to ultrapure silicon and
gallium arsenide and to purify other reagents
used in the manufacturing process so that they
do not introduce particulate contamination or
other defects into the device being manufac-
tured. For optical fibers, precursor materials of
high purity are also needed. For example, the
SiCl4 currently used in optical fiber manufacture
must have a total of less than 4 parts per million
of hydrogen-containing compounds and less
than 2 parts per billion of metal compounds
(Figure 4.131. Either impurity will result in
strong light absorption in the glass fiber. For
magnetic media, the challenge is to separate
and purify submicrometer-sized magnetic par-
ticles to very exacting size and shape toler
ances.
A variety of separation research topics bear
on these needs, such as generation of improved
selectivity in separations by tailoring the chem-
ical and steric interactions of separating agents,
understanding and exploiting interracial phe-
nomena in separations, improving the rate and
capacity of separations, and finding improved
process configurations for separations. These
are all research issues central to chemical en
. .
glneerlng.
OCR for page 55
ELECTRONIC, PHOTONIC, AND RECORDING MATERIALS AND DEVICES
Irene
N2/Ct 2
C
A'
~ FEED ~
-
h~ N2
~Wi ~
' ' 1~
ES PRoDUCT
FIGURE 4.13 Schematic diagram for a purification plant for producing "optical
fiber grade" SiCl4. The feed material is passed through a reactor (1) where
chlorination takes place. Excess HCl generated in the reactor is removed (2)
and the product stream is passed through two distillation columns (3,4) where
contaminants are removed. On-line IR spectroscopy (5) is used to monitor
final product purity. Plants built using this design currently produce about 27
kg/in of ultrapure SiCl4. Contaminants (e.g., compounds containing R-H,
compounds containing C-H, and Fe) are reduced to below the limits of
detection. Courtesy, AT&T Bell Laboratories.
Chemical Synthesis and Processing of
Polymeric Materials
Although chemical engineering challenges re-
lated to polymeric materials are discussed in
Chapter 5, the special challenges for polymers
in materials and devices for information storage
and handling deserve some mention here.
For the processing of microcircuits and in-
terconnecting devices, improved radiation-sen-
sitive polymers are needed for the formulation
of better photoresists. Resists must be highly
sensitive to the radiation used for exposure, but
not to the microwave radiation used after de-
velopment for other process steps such as plasma
etching. Chemical engineering studies of poly-
mer behavior during development steps are also
needed. Details of the dissolution of the exposed
(or unexposed) regions of the resist are at
present poorly understood. There is a need for
fundamental studies and modeling of the for-
mation of a swollen gel layer at the solvent/
polymer interface and the subsequent diffusion
of polymer chains into solution.
Light wave technologies provide a number of
special challenges for polymeric materials. Poly-
mer fibers offer the best potential for optical
Scommunications in local area
network (LAN) applications, be-
cause their large core size makes
it relatively cheap to attach con-
nectors to them. There is a need
for polymer fibers that have low
losses and that can transmit the
bandwidths needed for LAN ap-
plications; the acrylate and meth-
acrylate polymers now under
study have poor loss and band-
width performance. Research on
monomer purification, polymer-
ization to precise molecular-size
distributions, and well-con-
trolled drawing processes is rel-
evant here. There is also a need
for precision plastic molding
processes for mass production of
optical fiber connectors and splice
hardware. A tenfold reduction in
the cost of fiber and related de-
vices is necessary to make the
utilization of optical fiber and related devices
economical for local area networks and the
telecommunications loop.
Another challenge for polymer research in
light wave applications is in the use of active
coatings on optical fibers as transducers for
sensors. Such coatings may have magnetostric-
tive or piezoelectric properties. These coatings,
or the fiber itself, may also incorporate dyes
that would respond to chemicals, light, radia-
tion, or other stimuli to produce transmission
loss changes in the fiber. Such systems have
enormous potential as sensors that would be
ultrasensitive, capable of distributed sensing,
able to operate in harsh environments, and
unaffected by electromagnetic interference.
Specialty fibers such as polarization-maintain-
ing fibers, which have an asymmetric core and
can double the bandwidth by transmitting two
modes at once, may also play an important role
in sensor technology.
Techniques for fabricating low-cost optical
components such as graded index lenses, mi-
crolenses, couplers, splitters, and polarizers are
needed to support optical fiber technology.
Traditionally, amorphous inorganic materials
have been used, but there are tremendous
OCR for page 56
56
opportunities for innovation with polymers,
which offer manufacturing versatility that is not
available with glass. For example, photoselec-
tive polymerization techniques can be used to
make branching wave guide circuits such as
splitters and couplers. Photopolymerization and
copolymerization of multiple monomer systems
have been used to make radial, axial, and
spherical graded-index lenses with a high degree
of perfection (e.g., freedom from aberration).
Large-scale, well-controlled chemical proc-
esses will be needed to fabricate these struc-
tures.
For recording applications, new approaches
to high-quality polymeric film substrates are
needed. Improved automation and control of
thin-film coating are also important.
For interconnection and packaging technol-
ogies, an important goal is to achieve high-
purity molding and dielectric materials. Epoxy-
Novolac prepolymers with ionic impurity levels
below 20 ppm offer one approach. There is a
further need for low-viscosity molding com-
pounds to minimize the development of flow
stresses during processing. Continued devel-
opment of thermally stable polymers with low
dielectric constants (such as the polyimides) is
also necessary. Advances in our fundamental
understanding of polymer chemistry and rheol-
ogy are crucial for all these areas (see Chapter
51.
Chemical Synthesis and Processing of
Ceramic Materials
Challenges for chemical engineering related
to ceramic materials are also discussed in Chap-
ter 5, but the potential contribution of chemical
engineers to this area cannot be emphasized too
strongly. A tremendous opportunity exists for
chemical engineers to apply their detailed
knowledge of fundamental chemical processes
in the development of new chemical routes to
high-performance ceramics for electronic and
photonic applications. The traditional approach
to creating and processing ceramics has been
through the grinding, mixing, and sintering of
powders. Although still useful in many appli-
cations, this technology is being replaced by
approaches that rely on chemical reactions to
HERS IN CHEMICAL ENGINEERING
create a uniform microstructure. Chemical routes
to better ceramics have the advantage of being
more amenable to continuous and automated
processing. Among the typical examples of such
approaches are sol-gel and related processes.
(See Chapter 5 for a more detailed treatment of
sol-gel processing.)
Deeper involvement of chemical engineers in
manufacturing processes for ceramics may be
particularly important to the eventual commer-
cialization of metal oxide superconductors. The
current generation of such superconductors
consists of planar structures formed during a
conventional ceramic synthesis. The ability to
precisely control complex phase structure and
phase boundaries seems critical. It is by no
means clear that the formulations and structures
that may produce optimal performance in su-
perconducting ceramics (e.g., room-tempera-
ture superconductivity, capacity for high-cur-
rent density) are accessible by these techniques.
Rational synthesis of structured ceramics by
chemical processing may be crucial to further
improvements in superconducting properties
and to efficient large-scale 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 much less than
1 Am (Figure 4.141. Although the lithographic
tools to print such patterns exist, the exposure
step is only one of a number of processes that
must be performed sequentially in a mass pro-
duction environment without creating defects.
Precise and uniform deposition of materials as
very thin films onto substrates 14 cm or more
in diameter must be performed in a reactor,
usually at reduced pressure. Particulate defects
larger than 0.1 Am must be virtually nonexistent.
Low-temperature methods of film deposition
will be needed so that defects are not generated
in previous or neighboring films by unwanted
diffusion of dopants.
OCR for page 57
ELECTRONIC, PHOTONIC, AND RECORDING MATERIALS A.~D DEVICES
10
8
6
, -O
7 _ o
E 4 _
r-~ 3 _
J
I
_
2 _
1 1 1
o
o
o
o
o
1 1 1 1 1 1 1 1 1 1 1
'74 '76 '78 '80
YEAR
'82 '84 '86
FIGURE 4.14 Feature size on microelectronic devices has steadily declined
over the years as improved chemical etching processes have been developed.
This graph shows feature size as a function of the year in which the device
with the smallest feature size was first produced. Courtesy, AT&T Bell
Laboratories.
For optical fibers, improved control over the
structure of the thin films in the preform will
lead to fibers with improved radial gradients of
refractive index. A particular challenge is to
achieve this sort of control in preforms created
by 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 ultraviolet radia-
tion, are needed for high-speed (>10 m/s) fiber-
drawing processes. Both glassy and elastomeric
polymers are needed for use over temperatures
ranging from - 60 to 84°C or higher. Hermetic
coatings are required to avoid water-induced
stress corrosion of silica glasses, which pro-
ceeds by slow crack growth. Materials under
study include silicon carbide and titanium car-
bide applied by chemical vapor deposition, as
well as metals such as aluminum. A tenfold
increase in the rate at which such coatings can
be applied to silica fiber during drawing is
needed for commercial success. Coatings must
be free of pinholes, have low residual stress,
and adhere well. Hermetic coatings will also be
needed to protect the moisture-sensitive halide
57
and chalcogenide glasses that may
find use in optical fibers of the
future because of their compati-
bility with transmission at longer
wavelengths.
Considerable progress in the
science and technology of de-
positing thin films is necessary if
the U.S. recording media indus-
try is to remain competitive with
foreign manufacturers. New, fully
automated coating processes that
will generate high-quality, low-
defect media are needed. Not
only must considerable effort be
mounted in designing hardware
and production equipment, but
complex mathematical models
must be developed to study the
kinetic and thermodynamic
properties of film coating and the
effect of non-Newtonian flow and
polymer and fluid rheology. A
better understanding of dispersion
stability during drying, as well as of diffusion
mechanisms that result in intermixing of se-
quential layers of macromolecules, is important.
Thin films are also critical to the performance
of electrical interconnection devices (Figure
4.15) Better methods for depositing thin films
conformably (for good sidewall coverage) and
for achieving high-aspect-ratio trenches are
needed for the interconnection of electronic
devices for the high-frequency transmission of
data. New processing strategies and device
structures are required that use compatible
layers of materials to minimize undesirable
phenomena such as contact resistance; elec-
tromigration; leakage currents; delamination;
and stress-related defects such as cracks, voids,
and pinholes.
~ , it,
Modeling and the Study of Chemical
Dynamics
A challenge related to the problems of reactor
design and engineering is the modeling and study
of the fundamental chemistry occurring in man-
ufacturing processes for semiconductors, opti-
cal fibers, magnetic media, and interconnection.
OCR for page 58
~8
For example, mathematical
models originally developed for
continuously stirred tank reac-
tors and plug-flow reactors are
applicable to the reactors used
for thin-film processing and can
be modified to elucidate ways to
improve these reactors. For these
models to reach their full descrip-
tive potential, detailed studies of
the fundamental chemical reac-
tions occurring on surfaces and
in the gas phase are required.
For example, etching rates, etch-
ing selectivity, line profiles, de-
posited film structure, film bond-
ing, and film properties are
determined by a host of varia-
bles, including the promotion of
surface reactions by ion, elec-
tron, or photon bombardment.
The fundamental chemistry of
these surface reactions is poorly
understood, and accurate rate
expressions are particularly
needed for electron-impact reactions (i.e., dis-
sociation, ionization, and excitation), ion-ion
reactions, neutral-neutral reactions, and ion-
neutral reactions. The scale and scope of effort
devoted in recent years to understanding cata-
lytic processes need to be given to research on
film deposition and plasma etching. Until we
have a basic understanding of chemical reac-
tions occurring at the surface and in the gas
phase, it will be difficult to develop new etching
systems.
Research in this area has had a demonstrable
impact on recent innovations in plasma process-
ing. 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 fabri-
cating integrated circuits. However, well-con-
trolled processes could not be developed that
would perform in a production environment.
The work of chemists and chemical engineers
in elucidating the relevant chemical reactions
and their kinetics was crucial to the identifica-
tion of the important chemical species in the
FRONTIERS IN CHE.~CAL E~GINEERING
Pb-Sn ~ Cu-Sn intermetallic
solder pad ~ / Phased Cr-Cu
75~< Cal 3.8 rum SiO2
:///////////~ 2.4 ,um SiO2
i ·4 Am ~-4% Cu ~7~:
//////////////////// ~ 7 ~ 1
Si3N4 /' Thermal SiO2' PtSi ~
0.15 ,Um Cr-CrxOy
FIGURE 4.15 Cross-section of multilevel interconnections for advanced bi-
polar devices. Fourteen separate layers are laid down in the fabrication of
interconnections such as the one shown. The precise orientation and com-
position of these layers are controlled by chemical process steps. Copyright
1982 by the International Business Machines Corporation. Reprinted with
. .
permission.
etching process and their reaction pathways. In
addition, this work led to the discovery that the
organic polymer photoresist contributed to
plasma chemistry and selectivity in important
ways. This in turn led to new, improved plasma
processes that are currently being used in pro-
duction.
For magnetic media, mathematical models
could enhance our fundamental understanding
of the manufacturing processes used to make
uniform high-purity magnetic particles. Models
for the kinetics and mechanisms of reactions
and an improved understanding of the thermo-
dynamics of producing inorganic salts are re-
quired.
Modeling to describe the flows of viscous
fluids could lead to better packaging of inte-
grated circuits by assisting in the development
of molding compounds and processes that will
provide for lower thermal shrinkage stresses,
lower permeability, and lower thermal conduc-
tivity. Such modeling could also contribute to
the development of packaging materials and
processes amenable to automation.
OCR for page 59
ELECTRONIC, PHOTONIC, A^~D RECORDING IS Aims DEVICES
Engineering for Environmental Protection
and Process Safety
Safety and environmental protection are ex-
tremely important concerns that present de-
manding intellectual challenges. The manufac-
ture of materials and devices for information
handling and storage involves substantial quan-
tities of toxic, corrosive, or pyrophoric chemi-
cals (e.g., hydrides and halides of arsenic,
boron, phosphorus, and silicon; hydrocarbons
and organic chlorides, some of which are sus-
pected carcinogens; and inorganic acids). The
expertise of chemical engineers in the safe
handling and disposal of highly reactive mate-
rials is much needed in the electronics industry.
Recent studies in California indicate that the
semiconductor industry has an occupational
illness rate three times that of general manufac-
turing industries. Nearly half of these illnesses
involve systemic poisoning from exposure to
toxic materials. Problems with groundwater
contamination in Santa Clara County, Califor-
nia, have also raised concerns about how well
the semiconductor industry is equipped to han-
dle waste management and disposal. If the
semiconductor and other advanced materials
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.
IMPLICATIONS OF RESEARCH
FRONTIERS
Industry has been the prime mover in ad-
vancing technology in electronic, photonic, and
recording materials and devices. It will remain
so for the foreseeable future. University re-
search groups need to develop and maintain
good communication with counterpart research
groups in industry. Collaborative mechanisms
are needed to promote academic-industrial cou-
pling.
This coupling will become even more im-
portant as the electronics industry hires ever
greater numbers of chemical engineers. Since
59
TABLE 4.4 Employment of Chemical
Engineers in the Electronics Industry,
1977-1 986
Year
Number of
Chemical Engineers
1977
1980
1983
1986
700
960
1,648
2,100
a Employment figures for Standard Industrial
Classification code 367, "Electronic components
and accessories."
SOURCE: National Science Foundation.3
1977, the number of chemical engineers em-
ployed by the industry has tripled (Table 4.4J.
Up to 25 percent of the recent graduating classes
of several leading chemical engineering depart-
ments have been employed by the electronics
industries. The increasing demand of these in-
dustries for chemical engineers is one factor to
consider in planning for the support of the field.
Any new mechanisms proposed must address
this need.
In the electronics industry, a large number of
relatively small firms play a key role in gener-
ating new process concepts and equipment.
These firms face important research problems
in fundamental science and engineering that
would benefit markedly from the insights of
academic chemical engineering researchers. Ac-
ademic researchers should seek out and forge
links to these small firms that stand at the
crucial step between laboratory research and
production processes. Potential mechanisms for
accomplishing this are described in Chapter 10.
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 instructional
material and example problems relevant to the
challenges outlined in this chapter. This would
not require the creation of new courses, but
rather the provision of material to enrich existing
ones. This theme is echoed, more broadly, in
Chapter 10.
OCR for page 60
6a
NOTES
1. National Research Council, National Materials
Advisory Board. State of the Art Reviews: Ad-
vanced Processing of Electronic Materials in the
United States and Japan. Washington, D.C.:
National Academy Press, 1986.
2. National Academy of Sciences-National Academy
of Engineering- Institute of Medicine, Committee
on Science, Engineering, and Public Policy. "Re-
search Briefing on High-Temperature Supercon-
ductivity," in Research Briefings 1987. Washing-
ton, D.C.: National Academy Press, 1987.
3. (a) National Science Foundation, Division of Sci-
ence Resources Studies. Employment of Sci-
entists, Engineers, and Technicians in Man-
ufacturing Industries: 1977 (NSF 80-3061.
Washington, D.C.: U.S. Government Printing
Office, 1980.
(b) National Science Foundation, Division of Sci-
ence Resources Studies. Scientists, Engi-
neers, and Technicians in Manufacturing and
Non-Manufacturing Industries: 1980-81 (NSF
83-324~. Washington, D.C.: U.S. Government
Printing Office, 1983.
(c) National Science Foundation, Division of Sci-
ence Resources Studies. Scientists, Engineers,
and Technicians in Manufacturing Industries:
1983 (NSF 85-328~. Washington, D.C.: U.S.
Government Printing Office, 1985.
FRONTIERS IN CHEMICAL ENGINEERING
(d) Preliminary data from the 1986 survey of
manufacturing industries provided by the NSF
Division of Science Resources Studies.
SUGGESTED READING
M. Bohrer, J. Amelse, P. Narasimham, B. Tariyal,
J. Turnipseed, R. Gill, W. Moebuis, and J. Bo-
deker. "A Process for Recovering Germanium
from Effluents of Optical Fiber Manufacturing."
J. Lightwave Tech., LT-3 (3), 1984, 699.
T. Li, ed. Optical Fiber Communications, Vol.
Orlando, Fla.: Academic Press, 1984.
P. D. Maycock and E. N. Striewalt. A Guide to the
Photovoltaic Revolution: Sunlight to Electricity in
One Step. Emmaus, Pa.: Rodale Press, 1984.
R. H. Perry and A. A. Nishimura. "Magnetic Tape
Production," in Kirk-Othmer Encyclopedia of
Chemical Technology, 3rd ea., Vol. 14, p. 744.
New York: Wiley-Interscience, 1979.
Solar Engineering Research Institute. Basic Photo-
voltaic Principles and Methods (FT-290-14481.
Washington, D.C.: U.S. Government Printing Of-
fice, 1982.
S. M. Sze. Semiconductor Devices: Physics and
Technology. New York: John Wiley & Sons, 1984.
W. Thomas, ed. SPSE Handbook of Photographic
Science and Engineering. New York: Wiley-Inter-
science, 1973.
L. F. Thompson, C. G. Willson, and M. J. Bowden.
Introduction to Microlithography (ACS Sympo-
sium Series No. 2191. Washington, D.C.: American
Chemical Society, 1983.
Representative terms from entire chapter:
electronics industry
