Microfabrication in Space Papers: Prof.
Glenn H.
Chapman
This page contains the paper abstracts and full PDF versions of
publications
on the Microfabrication in Space concept. Click on the link to
download
pdf version. Papers here are listed in the order of
publication
Refereed Conference Proceedings
G.H. Chapman, "Space: the Ideal Place to
Manufacture
Microchips", Proc. of Inter. Space Development Conf. '91, San
Antonio,
Texas, 25-32 (1991).
sdc-91w.pdf 97KB
The electronics industry is dependent on the production of
microchips;
high value, low mass, devices well suited to production in orbit.
Microchip
fabrication procedures inherently involve what are, by earth
standards,
extreme cleanliness of facilities, processes that intrinsically
require
good vacuums, and substantial control over contaminates. In
addition,
on
earth the exposure of materials to the atmosphere between processes
steps
creates complications that require additional procedures to remove
thin
oxide layers. The controlled environment, and common vacuum of
extratressestrial
facilities helps control the cleanliness, allows for simpler
processing
equipment, diminishes the contamination problem, and reduces the
oxidation
of materials between process steps. However, some complications are
introduced
by steps that currently work best with gravity. This paper surveys
the
advantages and problems for extraterrestrial processing of
microchips.
G. H. Chapman N. Pfeiffer, J. S. Johnson,
"Synergy of Combining Microfabrication Technologies in Orbit”,
Proceedings
Spacebound 2000, CD version 13 pages, June 2000. sb00Chapman.pdf
409KB
The free vacuum in orbit makes it an ideal place for many
microfabrication
processes. Much current research has concentrated on orbital
fabrication
of single high vacuum processes, such as Wakeshield's silicon
epitaxial
growth. Yet, even the simplest semiconductor devices require
the
combination of many microfabrication steps, such as thin film
deposition,
patterning (photolithography), and etching. Fortunately, with
the
right choice of processes, the advantage of the native vacuum
greatly
reduces
the number of microfabrication process steps, and equipment
complexity,
mass and power requirements. The key to this synergy is the
modification
of the processes that use abundant earth based resources (water,
power),
to those better suited to the vacuum and microgravity space
environment.
We have investigated a wide range of microfabrication processes for
orbital
environmental compatabilty. Many types of deposition (plasma
sputtering,
CVD, ion implant) and etching processes (Plasma, RIE) require base
vacuum
levels >10-7 torr, above that of LEO. Compared to earth
operations,
removal
of the vacuum systems from orbital equipment leads to reductions
estimated
for each process in equipment mass (48-72%), volume (37-59%),
process
consumable
supplies, and equipment life cycle maintenance. To create true
structures,
an important simplifying step is the introduction of a vacuum based
process
inorganic resist for photolithographic patterning of films. Since
the
orbital
vacuum also removes earth based contamination from the wafer
environment,
the elimination of organic resists almost eliminates local
contamination
thus reducing interprocess cleaning steps, which consume large
quanities
of water, acids and organic solvents. It also increases
throughput
and improves film/etching quality. The adding vacuum based
plasma/ion
cleaning processes further eliminates liquid consumables. The result
is
a synergistic orbital based methodology for deposition, patterning,
and
etching that is capable of building microfabricated
structures.
This
is leading to studies of an orbital microfabrication satellite.
N.
Pfeiffer, G.H. Chapman, "Silicon Wafer Transport in a High Vacuum,
Microgravity
Environment, Proceedings Spacebound 2000, CD version 23 pages, June
2000.
sb00Pfeiffer.pdf
2229KB
Semiconductor fabrication processes are best tested in the high
vacuum
environment of space using silicon wafer substrates. Handling
of
these 37 g, 200 mm diameter by 0.5 mm thick disks cannot be
accomplished
in a high vacuum environment with the vacuum suction method used on
earth.
Mechanical grips cause damage and scatter particulates that are
detrimental
to the fabrication processes. We are studying a system based
upon
magnetic levitation for the transport and fixturing of wafers in the
orbital
environment. A system has been modeled in which non-contact
forces
are exerted on the wafer in six degrees of freedom through magnetic
levitation.
In this system, the wafer is produced with a series of circular eddy
current
circuits formed on one side using refractory metals or
silicides.
Time varying eddy currents are induced in these circuits by external
solenoids
and the resulting magnetic fields are manipulated to provide the
desired
forces on the wafer. A circular array of external solenoids is
found
to be capable of exerting an average force of 0.058 N (1.6 m/s2)
perpendicular
to the plane of the wafer at a distance of 1 mm at a power
consumption
of 26 W. A rectilinear array of external solenoids, each
individually
controllable, is found to be capable of exerting average forces of
0.020
N (0.55 m/s2) perpendicular to the plane of the wafer and 0.0015 N
(0.041
m/s2) parallel to the plane of the wafer at a power consumption of
6.7
W. The results of the modeling indicate that the
circular
solenoid
array system can be used to provide wafer fixturing and is well
suited
for use on an end effector, and that the rectilinear array system
can
be
used to provide both wafer transport between fabrication processes
and
wafer fixturing within a process.
J.
S. Johnson, G.H. Chapman, N. Pfeiffer, "
Feasibility of Commercial Space Based Microship Fabrication
", Proceedings AIAA Space 2000, CD version 11 pages,
Sept.
2000
aiaa00f.pdf
111KB
Microchips are high value per mass products whose fabrication
requires
the vacuum levels available in low Earth orbit. However
standard
terrestrial fabrication techniques are difficult to transfer into
the
microgravity
and vacuum environment of space. They are optimized for using
in-situ
resources: water, power, air pressure and gravity that are plentiful
on
Earth. An alternative microfabrication process has been
developed
using the native vacuum environment which could replace wet
terrestrial
based microfabrication, with significant savings in equipment size,
mass
and consumables, while reducing cycle time. More importantly
these
dry space processes remove significant sources of contaminants thus
eliminating
many manufacturing steps. Computer models have been developed
which
compare the standard Earth-based process consumables, power and
fabrication
time with space-oriented processes and also assess alternative space
transportation
architectures, resulting in a process flow that is optimized for
orbital
facilities. The outcome is a synergistic orbital-based
methodology
for microfabrication capable of building and delivering commercially
marketable
microfabricated structures. Analysis suggests that commercial
space-based
microchip fabrication may be feasible at current launch prices,
which
will
only become more competitive with terrestrial fabrication in the
future
as launch costs decline.
G.H.
Chapman, N. Pfeiffer, W. Esser, "A Comparison of Microfabrication
and
Wakeshield's
processing Requirements", Proceedings AIAA ISS Utilization
2001,
CD version, 11 pages Orlando, FL 2001.
issu01p.pdf
822KB
Using orbital vacuum for enhanced semiconductor fabrication was
pioneered
in the Wake Shield project which produced ultra-high vacuums for
epitaxial
growth of high quality GaAs like materials. A proposed alternative
uses
the native Low Earth Orbit vacuum levels to achieve the silicon
microfabrication
processes needed for manufacturing silicon microchips. Space
microfabrication
combines many processes that are easier to achieve in LEO,
potentially
producing a flexible range of Microchips (high value per mass
products).
However standard terrestrial fabrication techniques are difficult to
transfer
into the microgravity and vacuum environment of space. They
are
optimized
for using in-situ resources: water, power, air pressure and gravity
that
are plentiful on Earth. An alternative microfabrication
process
has
been developed using the native vacuum environment which could
replace
wet terrestrial based microfabrication, with significant savings in
equipment
size, mass and consumables, while reducing cycle time. Computer
models
have been developed which compare the standard Earth-based process
consumables,
power and fabrication time with space-oriented processes resulting
in a
process flow that is optimized for orbital facilities. ISS based
microfabrication
testing is possible before developing an integrated orbital
microchip
facility:
FabSat .- a synergistic orbital-based system for microfabrication
capable
of building and delivering commercially marketable microfabricated
structures
and devices
Microfabrication in Space Thesis
Nicholas
Pfeiffer, “Process Development for Fabrication of Silicon
Semiconductor
Devices in a Low Gravity, High Vacuum, Space Environment”, Master of
Applied
Science Thesis, Simon Fraser University, Burnaby, B.C., Canada,
2000
MScPfeiffer00.pdf
1304KB
Semiconductor microchips are high value per mass products whose
fabrication
requires many of the resources available in low-Earth orbit. It is
hypothesized
that orbital fabrication of silicon microchip devices may be more
economically
attractive than traditional Earth-based fabrication based upon the
inherent
advantages of the space environment: vacuum, cleanliness, and
microgravity.
This thesis examines the feasibility of fabricating semiconductor
devices
in near-Earth orbit through the use of process and economic
models. The
semiconductor fabrication processes are represented in a detailed,
step-by-step,
numerical model which uses mass flow, thermodynamics and other
operational
calculations to create models of important process operational
parameters.
Wherever possible, these calculations are verified either with
measurements
or published literature data on existing systems. Advantages
of
this
approach are the ability to easily add new processes and to
determine
energy,
consumable, time, and equipment requirements for each process
step.
As a confirmation of accuracy, the process flow for a standard 12
level
CMOS device is modeled and the generated results are comparable to
published
literature values.
Handling of 37 gram, 200 mm diameter by 0.5 mm thick silicon
wafers
cannot be accomplished in a high vacuum environment with the
vacuum
suction
method used on Earth. A system for the transport and
fixturing of
wafers in the orbital environment, in which non-contact forces are
exerted
on the wafer in six degrees of freedom through magnetic
levitation, is
modeled in this thesis.
It is found that by developing new, dry processes that are vacuum
compatible,
fabricating semiconductor devices in orbit is both technically and
economically
feasible. The outcome is a synergistic, orbital-based
methodology
for micro-fabrication capable of building and delivering
commercially
marketable
microfabricated structures. The base case modeled,
production of
5,000 ASIC wafers per month, indicates that orbital fabrication is
103%
more expensive than existing commercial facilities. However,
optimization
of process parameters and consumable requirements is shown to
decrease
the cost of orbital fabrication dramatically. Modeling
indicates
that the cost of orbital fabrication can be decreased to 58% that
of an
advanced, future Earth-based facility when trends of increasing
process
equipment costs and decreasing orbital transport costs are
considered.