U.S. patent application number 13/682479 was filed with the patent office on 2013-03-28 for apparatus for forming energy storage and photovoltaic devices in a linear system.
The applicant listed for this patent is Mahesh Arcot, Vikas Gujar, Dieter Haas, Omkaram Nalamasu, Pravin K. Narwankar, VICTOR L. PUSHPARAJ, Bipin Thakur. Invention is credited to Mahesh Arcot, Vikas Gujar, Dieter Haas, Omkaram Nalamasu, Pravin K. Narwankar, VICTOR L. PUSHPARAJ, Bipin Thakur.
Application Number | 20130074771 13/682479 |
Document ID | / |
Family ID | 43759290 |
Filed Date | 2013-03-28 |
United States Patent
Application |
20130074771 |
Kind Code |
A1 |
PUSHPARAJ; VICTOR L. ; et
al. |
March 28, 2013 |
APPARATUS FOR FORMING ENERGY STORAGE AND PHOTOVOLTAIC DEVICES IN A
LINEAR SYSTEM
Abstract
A method and apparatus are provided for formation of a composite
material on a substrate. The composite material includes carbon
nanotubes and/or nanofibers, and composite intrinsic and doped
silicon structures. In one embodiment, the substrates are in the
form of an elongated sheet or web of material, and the apparatus
includes supply and take-up rolls to support the web prior to and
after formation of the composite materials. The web is guided
through various processing chambers to form the composite
materials. In another embodiment, the large scale substrates
comprise discrete substrates. The discrete substrates are supported
on a conveyor system or, alternatively, are handled by robots that
route the substrates through the processing chambers to form the
composite materials on the substrates. The composite materials are
useful in the formation of energy storage devices and/or
photovoltaic devices.
Inventors: |
PUSHPARAJ; VICTOR L.;
(Sunnyvale, CA) ; Narwankar; Pravin K.;
(Sunnyvale, CA) ; Haas; Dieter; (San Jose, CA)
; Thakur; Bipin; (Mumbai, IN) ; Arcot; Mahesh;
(Thane, IN) ; Gujar; Vikas; (Thane, IN) ;
Nalamasu; Omkaram; (San Jose, CA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
PUSHPARAJ; VICTOR L.
Narwankar; Pravin K.
Haas; Dieter
Thakur; Bipin
Arcot; Mahesh
Gujar; Vikas
Nalamasu; Omkaram |
Sunnyvale
Sunnyvale
San Jose
Mumbai
Thane
Thane
San Jose |
CA
CA
CA
CA |
US
US
US
IN
IN
IN
US |
|
|
Family ID: |
43759290 |
Appl. No.: |
13/682479 |
Filed: |
November 20, 2012 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
12885139 |
Sep 17, 2010 |
8334017 |
|
|
13682479 |
|
|
|
|
61243813 |
Sep 18, 2009 |
|
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|
Current U.S.
Class: |
118/719 ;
977/891 |
Current CPC
Class: |
C23C 16/545 20130101;
Y02P 70/521 20151101; H01L 31/1876 20130101; H01L 31/206 20130101;
Y02E 10/548 20130101; Y02E 10/549 20130101; H01L 31/035227
20130101; H01L 51/4213 20130101; H01L 51/0048 20130101; B82Y 10/00
20130101; H01L 31/075 20130101; B82Y 40/00 20130101; Y02P 70/50
20151101 |
Class at
Publication: |
118/719 ;
977/891 |
International
Class: |
C23C 16/54 20060101
C23C016/54 |
Claims
1. An apparatus for forming a composite material, comprising: a
first end; a second end; at least one web of material extending
from the first end to the second end; a support system to support
the at least one web of material from the first end to the second
end; and a plurality of chambers disposed between the first and the
second end, the plurality of chambers being adapted and configured
to form the composite material on the substrate, wherein the at
least one web of material extends through the plurality of
chambers.
2. The apparatus of claim 1, wherein the plurality of chambers
comprises: a first chamber having a source that is configured to
deliver a catalytic precursor to a surface of the substrate; and a
second chamber having a heating element that is adapted to heat a
deposited catalyst material to form catalyst particles on the
substrate.
3. The apparatus of claim 1, wherein the plurality of chambers
comprises: a first chamber that has a source that is configured to
form graphitic nanofilaments on the substrate using a thermal
chemical vapor deposition (CVD) process, a plasma enhanced CVD
process or a hot wire CVD process; and a second chamber that is
configured to form an amorphous silicon layer over the graphitic
nanofilaments using a hot wire CVD process.
4. The apparatus of claim 3, wherein the plurality of chambers
further comprises: a third chamber that is configured to form a
polymeric material over the amorphous silicon layer using an
initiated CVD process; and a fourth chamber that is configured to
form a cathodic material on the polymeric material using a hot wire
CVD process or a physical vapor deposition process.
5. The apparatus of claim 1, further comprising: a supply roll at
the first end for supplying the continuous web of material to the
plurality of chambers; and a take-up roll at the second end for
receiving the continuous web of material with the composite
material formed thereon.
6. The apparatus of claim 1, wherein the plurality of chambers
comprises: a first chamber for deposition of intrinsic silicon on
one of the first or second sides of the large scale substrates; and
a second chamber for deposition of doped silicon on the intrinsic
silicon.
7. The apparatus of claim 6, further comprising return means
between the second chamber and the second end of the apparatus, the
return means adapted and configured to flip the plurality of
discrete large scale silicon substrates and return them to the
first chamber for deposition of the intrinsic silicon on the other
of the first and second sides of the large scale substrates and to
the second chamber for deposition of a doped silicon on the
intrinsic silicon.
8. The apparatus of claim 7, further comprising inverting means
between the second chamber and the second end of the apparatus, the
inverting means adapted and configured to flip the plurality of
discrete large scale silicon substrates.
9. The apparatus of claim 6, wherein the plurality of chambers
comprises a third chamber for deposition of intrinsic silicon on
the other of the first or second sides of the large scale
substrates.
10. The apparatus of claim 9, wherein the plurality of chambers
comprises a fourth chamber for deposition of doped silicon on the
intrinsic silicon deposited on the other of the first or second
sides of the large scale substrates.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This is a divisional application of U.S. patent application
Ser. No. 12/885,139, filed Sep. 17, 2010, which claims benefit of
U.S. provisional patent application Ser. No. 61/243,813, filed Sep.
18, 2009, which is herein incorporated by reference.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] Embodiments of the present invention generally relate to the
formation of a composite material on a surface of a substrate. More
specifically, embodiments of the invention relate to an apparatus
and methods used to form composite materials that form part of an
energy storage device and/or a photovoltaic device.
[0004] 2. Description of the Related Art
[0005] Composite materials that may be formed using the apparatus
and methods described herein include energy storage components and
photovoltaic (PV) devices. Composite materials useful in energy
storage components include nanotubes (and nanofibers) that are
further coated to produce highly electrically conductive
components, such as electrodes. Composite materials useful for
forming PV devices, include intrinsic amorphous silicon (a-Si),
n-type doped silicon (Si) and/or p-type doped silicon.
[0006] Carbon nanotubes and nanofibers possess many interesting and
unique properties which make carbon nanotubes and nanofibers
attractive for use in many potential applications, such as cold
field emission, electrochemical energy storage, high-capacity
hydrogen storage media, and composite material reinforcement, to
name just a few. Some of the unique and interesting properties of
carbon nanotubes include great strength, high electrical and
thermal conductivity, large surface area-to-volume ratios, and
thermal and chemical stability. The structures of carbon nanotubes
and nanofibers give rise to many of their properties.
[0007] Carbon nanotubes and nanofibers are graphitic nanofilaments
with diameters ranging from about 0.4 nanometers to about 500
nanometers and lengths which typically range from a few micrometers
to a few millimeters. Graphitic nanofilaments may be categorized
according to at least four distinct structural types, namely,
tubular, herringbone, platelet, and ribbon. The term "nanotube" may
be used to describe the tubular structure whereas "nanofiber" may
describe the non-tubular forms.
[0008] Carbon nanotubes are generally classified as single-walled
carbon nanotubes and multi-walled carbon nanotubes. FIG. 1A is a
schematic view of a single-walled carbon nanotube (SWCNT). The
SWCNT 100 is a graphitic nanofilament which comprises a cylindrical
carbon molecule that may be conceptualized as a one-atom thick
sheet of graphite called graphene rolled into a seamless graphene
tube 104 of diameter "d" and filament length "L." The graphene tube
104 forms a cylindrical wall which is parallel to the filament axis
direction. One or more of the nanotube ends 102 may be capped (see
FIG. 2A) by additional carbon atoms. The diameter "d" may range
from about 0.4 nanometers to a few nanometers and the filament
length "L" may range from a few micrometers to a few
millimeters.
[0009] The rolled graphene layer or sheet of the SWCNT 100
comprises six-member hexagonal rings of carbon atoms held together
by covalent sp.sup.2 bonds. These bonds combined with the tubular
graphene structure impart extraordinary strength (tensile strength)
and stiffness (elastic modulus) to carbon nanotubes. The SWCNT 100,
for example, may have an average tensile strength of about 30 GPa
and an elastic modulus of about 1 TPa compared to stainless steel
which may have a tensile strength of about 1 GPa and an elastic
modulus of about 0.2 TPa. Carbon nanotubes also have a fairly low
density for a solid (about 1.3 g/cm.sup.3 for SWCNT's 100), and
their strength-to-weight ratio is among the highest of known
materials. The electrical conductivity of the SWCNT 100 may be
semiconducting or metallic depending upon how the graphene sheet is
rolled to form the graphene tube 104, and metallic-type carbon
nanotubes can carry electrical current densities orders of
magnitude larger than those carried by the best conducting
metals.
[0010] FIG. 1B is a schematic view of a multi-walled carbon
nanotube (MWCNT). The MWCNT 110 may be conceptualized as one or
more graphene tubes 104 of filament length "L" coaxially arranged
about the SWCNT 100 of diameter "d." The graphene tubes 104 form
cylindrical walls which are parallel to the filament axis direction
"A" and the walls are separated from each other by an interlayer
spacing 116 of about 0.34 nm which approximates the distance
between graphene layers in graphite. The number of tubes (three are
shown) or cylindrical walls within the MWCNT 110 may range from two
to fifty, or more. An outer nanotube 112 has a filament diameter
"d.sub.o" which may range from a few nanometers to several hundred
nanometers or more depending upon the number of walls within the
MWCNT 110.
[0011] The term "carbon nanotube" is typically used to describe a
nanofilament which comprises one or more graphene layers or sheets
which are parallel to the filament axis and which form tubular
structures. The term "carbon nanofiber," on the other hand,
typically describes a nanofilament which comprises graphene layers
which may or may not be parallel to the filament axis and which do
not form tubular structures, although the structures may be formed
so that the nanofibers are substantially round or polygonal in
cross-section. Examples of nanofiber structures include
herringbone, platelet, ribbon, stacked-cone, and other carbon
nanofiber structures known in the art. Some nanofibers may have a
hollow core or central hole along the filament axis of each
nanofiber, while other nanofibers may have solid cores. While the
term "carbon nanotube" is used herein, it should be understood that
this term may refer to a carbon nanotube and/or carbon nanofiber.
The carbon nanotubes may have overall shapes which include but are
not limited to straight, branched, twisted, spiral, and
helical.
[0012] The tubular structure of carbon nanotubes have some unique
properties which are not shared by carbon nanofibers. Carbon
nanofibers are more closely related to graphite which consists of
graphene layers held together by interlayer van der Waals forces
which are much weaker than the intra-layer bonding forces within
each graphene layer. The properties of carbon nanofibers are
determined by the combination of the strong intra-layer bonds and
the weaker interlayer bonds of the graphene structures, whereas the
properties of carbon nanotubes are determined more by the strong
intra-layer bonds in the tubular graphene structures. As a result,
some of the properties of carbon nanofibers may be characterized as
being intermediate to the properties of carbon nanotubes and
graphite.
[0013] The properties of carbon nanotubes and nanofibers make their
potential use in various applications desirable. The low density,
high mechanical strength, electrical conductivity, and thermal
conductivity of carbon nanotubes make them attractive for potential
use in composite material applications. Carbon nanofibers also have
fairly low densities and may be used to improve the mechanical
strength and electrical conductivity of composite materials,
although carbon nanofibers typically possess much less strength
than carbon nanotubes.
[0014] Carbon nanotubes and nanofibers are also attractive for
potential use in energy storage applications, such as electrodes
for lithium-ion batteries, supercapacitors, or fuel cells. The
large surface areas of carbon nanotubes and nanofibers can form
large surface areas which may provide improved charge storage
capabilities for electrodes. Carbon nanofibers, in particular, have
many interlayer spacings through which small ions may enter and
intercalate between the graphene layers, and this property makes
carbon nanofibers attractive for electrode applications. It may
also be desirable to deposit additional materials, such as metals,
for example, onto the carbon nanotubes or nanofibers to enhance or
modify various properties (e.g., electrical conductivity, strength,
stiffness, thermal expansion, density) of the composite
material.
[0015] Carbon nanotubes are typically formed using laser ablation,
arc discharge, or chemical vapor deposition (CVD). The techniques
of laser ablation and arc discharge typically use higher processing
temperatures than CVD and the higher temperatures facilitate the
formation of nanotubes. However, laser ablation and arc discharge
form nanotubes separately (i.e., not directly on substrates) and
require post-production processing (e.g., recovery, sorting,
purification) of the nanotubes before they can be applied to
substrates. In contrast, CVD methods allow the formation of carbon
nanotubes and nanofibers directly onto substrates. Additionally,
CVD methods can produce nanotubes and nanofibers at lower
temperatures while providing control over the types and sizes of
carbon nanotubes and nanofibers produced. Thus, CVD may provide a
cost effective means for forming carbon nanotubes or nanofibers on
large area substrates.
[0016] The use of various types of substrates on which the
composite materials are formed may increase the range of
applications for the composite materials. The substrates may
include wafers, panels, sheets, webs, and fibers, for example.
Thus, it is desirable to provide a cost effective means for forming
carbon nanotubes and nanofibers on a substrate that that can be
used to form part of an electrode used in a battery,
supercapacitor, or fuel cell. Additionally, it is desirable to
provide a cost effective means for the metallization of carbon
nanotubes and nanofibers formed on large area substrates used in
composite materials.
[0017] One method of forming a PV cell is by depositing intrinsic
silicon (i-Si) and doped silicon layers on a substrate. As the need
for cost effective energy sources rises, it becomes more desirable
to develop methods and apparatus for forming larger PV cells. In
order to do so, the ability to deposit these composite materials on
ever larger substrates, also has become more desirable.
[0018] Therefore, a need exists for a cost effective method and
apparatus for the formation of composite materials on various types
of substrates.
SUMMARY OF THE INVENTION
[0019] Embodiments of the present invention include methods and
apparatus for the formation of composite materials, which include
metallized graphitic nanofilaments and intrinsic and doped silicon
on various types of large area substrates, as well as the composite
materials formed using these methods and apparatus.
[0020] In one embodiment, the invention is a method for forming
composite materials on substrates. The method includes depositing a
catalytic layer on a surface of a substrate in a first processing
chamber, processing the catalytic layer to form a plurality of
nanoislands, forming a plurality of graphitic nanofilaments over
the nanoislands in a second processing chamber, wherein the second
processing chamber is coupled to the first processing chamber,
depositing a silicon containing layer over the graphitic
nanofilaments in a third processing chamber which is coupled to the
second processing chamber and depositing a polymer layer over the
graphitic nanofilaments and silicon containing layer in a fourth
processing chamber which is coupled to the third processing
chamber.
[0021] In another embodiment, the invention is a method of forming
composite materials on a substrate in a substrate processing
system. The method includes depositing a catalytic layer on a
surface of a substrate in a first processing chamber by delivering
a catalytic precursor from a first source, processing the catalytic
layer to form a plurality of nanoislands while the substrate is
disposed in the first processing chamber, forming a plurality of
graphitic nanofilaments over the nanoislands in the first
processing chamber by delivering a carbon containing gas from a
first source, depositing a silicon containing layer over the
graphitic nanofilaments in a second processing chamber which is
coupled to the first processing chamber and depositing a polymer
layer over the graphitic nanofilaments and silicon containing layer
in a third processing chamber which is coupled to the second
processing chamber.
[0022] In a further embodiment, the invention is an apparatus for
forming composite materials on a substrate. The apparatus includes
a first end, a second end, at least one web of material extending
from the first end to the second end, a support system to support
the at least one web of material from the first end to the second
end and a plurality of chambers disposed between the first and the
second end, the plurality of chambers being adapted and configured
to form the composite material on the substrate, wherein the at
least one web of material extends through the plurality of
chambers.
[0023] In another embodiment, the invention is an apparatus for
forming composite materials on a substrate. The apparatus includes
a first end, a second end, a first chamber disposed between the
first and the second end, a second chamber disposed between the
first and the second end, a third chamber disposed between the
first and the second end, a fourth chamber disposed between the
first and the second end and a support system that is configured to
transfer a substrate through the first, second, third and fourth
chambers. The first chamber has a target having a surface in
contact with a processing region, wherein the target includes a
catalytic material and a power supply adapted to deliver energy to
the target so that atoms from the surface of the target are
deposited on a surface of a substrate disposed in the processing
region. The second chamber has a heater configured to transfer heat
to the surface of the substrate disposed in the processing region
of the second chamber. The third chamber includes a first heated
filament disposed within a processing region of the third chamber
and a first source that is configured to deliver a carbon
containing gas past the first heated filament and to a surface of a
substrate that is disposed in the processing region of the third
chamber. The fourth chamber has a second heated filament disposed
within a processing region of the fourth chamber and a second
source that is configured to deliver a carbon containing gas past
the second heated filament and to a surface of a substrate that is
disposed in the processing region of the third chamber.
[0024] In yet a further embodiment, the invention is a composite
material including a substrate, a plurality of graphitic
nanofilaments disposed on the substrate, a silicon containing layer
disposed on the plurality of graphitic nanofilaments, a layer of
polymeric material disposed on the layer of silicon and a layer of
cathodic material disposed on the layer of polymeric material.
BRIEF DESCRIPTION OF THE DRAWINGS
[0025] So that the manner in which the above recited features of
the present invention can be understood in detail, a more
particular description of the invention, briefly summarized above,
may be had by reference to embodiments, some of which are
illustrated in the appended drawings. It is to be noted, however,
that the appended drawings illustrate only typical embodiments of
this invention and are therefore not to be considered limiting of
its scope, for the invention may admit to other equally effective
embodiments.
[0026] FIG. 1A is a schematic view of a single-walled carbon
nanotube.
[0027] FIG. 1B is schematic view of a multi-walled carbon
nanotube.
[0028] FIG. 2A is a schematic view of nanotubes and nanofibers
formed by two catalytic CVD growth processes which use a catalyst
support substrate.
[0029] FIG. 2B is a schematic view of a catalyst film on a catalyst
support.
[0030] FIG. 2C is a schematic view of catalyst particles formed
from the catalyst film shown in FIG. 2B.
[0031] FIG. 3 is a schematic side view of one embodiment of an
apparatus for forming composite materials on large area substrates
in the form of discrete substrates, showing the various chambers
for forming the composite materials.
[0032] FIG. 4A is a schematic side view of one embodiment of an
apparatus for forming composite materials on large area substrates
in the form of a continuous web, showing the various chambers for
forming the composite materials.
[0033] FIGS. 4B-4D show several embodiments of substrate transfer
ports.
[0034] FIG. 5A is a schematic side view of one embodiment of a
chamber for depositing catalyst material on substrates.
[0035] FIG. 5B is a schematic side view of another embodiment of a
chamber for depositing catalyst material on substrates.
[0036] FIG. 6 is a schematic side view of one embodiment of a
chamber for heating the catalyst material to form nanoislands of
catalyst material on substrates.
[0037] FIG. 7 is a schematic side view of one embodiment of a
chamber for forming nanotubes on substrates.
[0038] FIG. 8 is a schematic side view of one embodiment of a
combination chamber for depositing and heating catalyst material to
form nanoislands of catalyst material on substrates and for forming
nanotubes on substrates.
[0039] FIG. 9 is a schematic side view of one embodiment of a
chamber for depositing amorphous silicon on the nanotubes.
[0040] FIG. 10 is a schematic side view of one embodiment of a
chamber for depositing polymeric material on the nanotubes.
[0041] FIG. 11 is a schematic side view of one embodiment of a
chamber for depositing cathodic material on the nanotubes.
[0042] FIG. 12 is a schematic side view of one embodiment of a
chamber for depositing intrinsic silicon on substrates.
[0043] FIG. 13 is a schematic side view of one embodiment of a
chamber for depositing doped silicon on substrates.
[0044] FIG. 14 is a schematic plan view of another embodiment of an
apparatus for forming composite materials on large area
substrates.
[0045] FIG. 14A is a schematic plan view of another embodiment of
an apparatus for forming composite materials on a substrate.
[0046] FIG. 14B is a cross-section of the apparatus of FIG. 14A
taken through section line 14B-14B.
[0047] FIG. 14C is a schematic side view of the apparatus of FIG.
14A.
[0048] FIGS. 15A-15G are schematic side views showing the various
stages of forming carbon nanotube based composite materials
according to embodiments of the invention.
[0049] FIGS. 16A-16F are schematic side views showing the various
stages of forming silicon based composite materials according to
embodiments of the invention.
[0050] FIGS. 17A-17C are top views of composite materials according
to embodiments of the invention.
[0051] FIG. 18 is a process flow chart summarizing a method for
forming a composite layer on a substrate according to one
embodiment of the invention.
[0052] FIG. 19 is a process flow chart summarizing a method for
forming a portion of a solar cell device according to one
embodiment of the invention.
[0053] FIGS. 20A-20D are schematic isometric views showing the
various stages of forming carbon nanotube based composite materials
according to further embodiments of the invention
[0054] FIG. 21 is a schematic plan view of a further embodiment of
an apparatus for forming composite materials on large area
substrates in the form of discrete substrates, showing the various
chambers for forming the composite materials.
[0055] FIG. 22 is a schematic side view of a further embodiment of
an apparatus for forming composite materials on large area
substrates in the form of a continuous web, showing the various
chambers for forming the composite materials.
[0056] FIG. 23 is a process flow chart summarizing a method for
forming a composite layer on a substrate according to a further
embodiment of the invention.
[0057] To facilitate understanding, identical reference numerals
have been used, where possible, to designate identical elements
that are common to the figures. It is contemplated that features of
one embodiment may be incorporated in other embodiments without
further recitation.
DETAILED DESCRIPTION
[0058] Embodiments of the present invention generally provide a
cost effective method and apparatus for forming graphitic
nanofilaments (i.e., carbon nanotubes and/or nanofibers) on various
types of substrates and then coating the graphitic nanofilaments
with other types of materials to form a composite material, which
can be used to form part of an electrode that may used in a
battery, supercapacitor, or fuel cell. The substrates may comprise
various materials and structural forms such as fibers, sheets of
woven fibers, glass or metal plates, metal foils, polycrystalline
silicon substrates, semiconductor wafers, oxidized metal containing
substrate, oxidized semiconductor substrate, or other similar
substrate material, for example.
[0059] The composite material containing graphitic nanofilaments
may be used for various applications, such as a large surface area
electrode or current collector in an electrochemical storage
device, for example. The electrochemical storage device (e.g.,
battery, supercapacitor, fuel cell) may be formed by depositing
additional material layers onto the metallized graphitic
nanofilaments of the composite material. In one embodiment,
portions of the resulting electrochemical storage device may be
integrated into a woven sheet, panel, or other flexible structure
depending upon the type of substrate used to form the composite
material.
CVD Growth Processes for Graphitic Nanofilaments
[0060] In one embodiment, the composite material containing
graphitic nanofilaments may be formed using different deposition
and processing techniques. One desirable processing technique that
can be used to form the graphitic nanofilaments is a chemical vapor
deposition (CVD) process. The chemical vapor deposition (CVD)
techniques used to form graphitic nanofilaments may be generally
categorized into two types: catalytic and non-catalytic. The
methods which use catalyst materials to facilitate and help control
the growth of graphitic nanofilaments are referred to as catalytic
CVD methods. The methods which use no catalyst materials for
graphitic nanofilament growth are referred to as non-catalytic or
pyrolytic CVD methods since only heating, and not catalysis,
typically drives nanofilament growth. The catalytic CVD methods
often provide greater control over graphitic nanofilament growth
than non-catalytic methods. Various methods of graphitic
nanofilament growth are described by K. Teo et al., in "Catalytic
Synthesis of Carbon Nanotubes and Nanofibers," Encyclopedia of
Nanoscience and Nanotechnology, Volume X, pg. 1-22, American
Scientific Publishers, 2003.
[0061] The use of substrates for the catalytic CVD growth of
graphitic nanofilaments provides some advantages over "floating"
catalytic methods which do not require substrates or supporting
surfaces for the catalyst materials. First, in some applications,
it may be desirable to form graphitic nanofilaments directly on a
surface which forms part of a functional structure. For example, it
may be desirable to deposit graphitic nanofilaments at the bottom
of a small aperture on a substrate to form a field emission
electron source, and space limitations may make direct growth of
the graphitic nanofilaments on a surface of the aperture the only
practical means to achieve the deposition. Second, the use of a
substrate makes it possible to anchor catalyst nanoparticles to a
surface in order to control the size of the catalyst nanoparticles.
At typical CVD nanofilament growth temperatures (e.g., 500.degree.
C. to 900.degree. C.), the catalyst nanoparticles (typically metal)
have sufficient mobility and cohesive forces to coalesce into
larger particles. The anchoring of the catalyst nanoparticles can
prevent such coalescence and help control the diameters of the
graphitic nanofilaments. Third, the use of a substrate can
facilitate the alignment of the graphitic nanofilaments.
[0062] FIG. 2A is a schematic view of graphitic nanofilaments
formed by two catalytic CVD growth processes that use a catalyst
support 205, which comprises a substrate that is discussed above.
The CVD growth of carbon nanotubes involves heating catalyst
particles 202 to a high temperature and flowing a carbon source
gas, such as a hydrocarbon (C.sub.nH.sub.m), carbon monoxide, or
other carbon-containing gas over the catalyst particles 202 for a
period of time. The catalyst particles 202 reside on a support
surface 206 of the catalyst support 205. The catalyst particles 202
are typically nanometer scale in size, and the diameters or widths
of the graphitic nanofilaments are often closely related to the
sizes of the catalyst particles 202.
[0063] The catalyst particles 202 comprise any suitable catalyst
materials for graphitic nanofilament growth, but preferred
materials are the transition metals and transition metal oxides.
The catalyst materials may include but are not limited to iron
(Fe), cobalt (Co), nickel (Ni), copper (Cu), silver (Ag), magnesium
(Mg), ruthenium (Ru), rhodium (Rh), iridium (In), platinum (Pt),
palladium (Pd), molybdenum (Mo), tungsten (W), chromium (Cr), and
alloys, oxides, and combinations thereof. Combinations or mixtures
of catalyst materials which may be used include but are not limited
to iron-nickel, iron-molybdenum, iron-cobalt, cobalt-nickel, and
cobalt-molybdenum. Preferred catalysts include iron (Fe), cobalt
(Co), nickel (Ni) and alloys thereof.
[0064] The catalytic CVD growth of graphitic nanofilaments
typically involves the catalytic dissociation of a hydrocarbon
source gas into carbon and hydrogen at the surfaces of a transition
metal particle which acts as a catalyst. Not wishing to be bound by
theory, it is believed that, at high temperatures, the carbon has
solubility in the transition metal particle and the carbon
dissolves into and diffuses through the metal to form a carbon
saturated metal-carbon solution. The carbon precipitates from the
saturated solution at one or more surfaces of the metal particle to
grow a graphitic nanofilament with a diameter substantially equal
to the diameter of the metal particle.
[0065] Referring to FIG. 2A, the catalytic growth of graphitic
nanofilaments may proceed by a tip-growth or base-growth process.
If the interaction between the catalyst particle 202 and the
catalyst support 205 is strong, the precipitation of carbon atoms
may produce a base-growth nanotube 200A with tubular nanofilament
walls 203 that grow up around the catalyst particle 202 which
remains attached to the catalyst support 205 at the base of the
nanotube. The base-growth nanotube 200A typically forms a
hemispherical cap 204 of carbon atoms opposite the base of the
nanotube. Alternately, if the interaction between the catalyst
particle 202 and the catalyst support 205 is weak, the nanotube may
grow so as to lift the catalyst particle 202 away from the catalyst
support 205 and form a tip-growth nanotube 200B with the catalyst
particle 202 located at the tip of the nanotube. The nanotubes
shown in FIG. 2A are single-walled, but multi-walled structures may
be formed by similar growth processes. The graphitic nanofilament
grows in the filament axis direction "A" as carbon precipitates
from one or more surfaces of the catalyst particle 202 for both the
tip-growth and base-growth processes.
[0066] Carbon nanofibers may also grow by a tip-growth or
base-growth process depending upon the strength of interaction
between the catalyst particle 202 and catalyst support 205. A
carbon nanofiber may form when the catalyst particle 202 has one or
more faceted or planar surfaces 211, whereas the catalyst particle
202 may be more spherical in shape for the formation of a carbon
nanotube. A tip-growth nanofiber 200C of the herringbone-type may
be formed when the catalyst particle 202 has two planar surfaces
211 at an angle to each other. Carbon precipitates at the planar
surfaces 211 to form graphene sheets 121 parallel to the planar
surfaces 211 and at an angle to the filament axis direction. The
edges of the graphene sheets 121 form nanofilament walls 203 for
the tip-growth nanofiber 200C.
[0067] In one embodiment, the catalyst support 205 comprises a
support material 212 covered with an optional buffer layer 213. The
support material 212 may comprise aluminum oxide, silicon oxide,
silicon, glass, metals or other materials which are stable in the
range of temperatures used for graphitic nanofilament growth. In
one embodiment, the support material 212 is the substrate, which,
as discussed above, may comprise structural elements that are
formed into sheets of woven fibers, glass plates, metal plates,
metal foils, polycrystalline silicon substrates, semiconductor
wafers, oxidized metal containing substrate, oxidized semiconductor
substrate, or other similar structure. The buffer layer 213
comprises a buffer material (e.g., titanium nitride, silicon
dioxide) which prevents the catalyst particles 202 from reacting or
alloying with the support material 212 at the nanofilament growth
temperature. Such reacting or alloying of the catalyst particles
202 with the support material 212 may be undesirable since it can
effectively reduce or consume the catalyst particles 202 and
thereby reduce the growth yield of graphitic nanofilaments. The
buffer layer 213 may also act as a diffusion barrier to prevent the
catalyst particles 202 from diffusing into the support material
212.
[0068] In one embodiment, the catalyst support 205 comprises a
buffer layer 213 which is patterned to cover some areas of the
support material 212 and not cover other areas of the support
material 212. In one embodiment, the buffer layer 213 is suitably
adapted to allow limited reaction between the catalyst particles
202 and support material 212. In another embodiment, the catalyst
support 205 comprises the support material 212 without the buffer
layer 213.
Catalyst Preparation
[0069] Various methods may be used to prepare the catalysts and the
catalyst supporting surfaces used for graphitic nanofilament
growth. The catalyst particles 202 may be deposited onto the
catalyst support 205 using wet or dry deposition techniques. Dry
deposition techniques include, but are not limited to, physical
vapor deposition processes (or sputtering), thermal evaporation,
and CVD. Wet deposition techniques include, but are not limited to,
the techniques of wet catalyst, colloidal catalyst solutions,
sol-gel, electrochemical plating, and electroless plating.
[0070] One method for forming catalyst particles 202 on a catalyst
support 205 begins by depositing a thin layer or film of catalyst
material on the catalyst support 205 using a dry deposition process
technique. FIG. 2B is a schematic view of a catalyst film 210 on a
catalyst support 205. The catalyst film 210 may be deposited by
sputtering, thermal evaporation, atomic layer deposition (ALD), CVD
or other dry deposition techniques. The catalyst film 210 may
comprise one or more layers of different catalyst materials, such
as a layer of molybdenum over a layer of iron, for example,
although any number of layers and materials may be used.
Alternately, the catalyst film 210 may comprise layers of catalyst
materials overlying layers of non-catalyst materials. The
non-catalyst layers may be used to control the surface properties
of the catalyst layers and the growth yield of graphitic
nanofilaments. The catalyst film 210 has a film thickness "t.sub.f"
which may range from 1 nanometer (nm) to several tens of nanometers
or more.
[0071] FIG. 2C is a schematic view of catalyst particles 202 formed
by further processing the catalyst film 210 shown in FIG. 2B. In
one embodiment, the catalyst film 210 may be sufficiently heated so
that the metallic catalyst film 210 breaks up and coalesces into
catalyst particles 202. The heated catalyst film 210 may form
particles due to the surface mobility and strong cohesive forces of
the metal atoms. In some cases, the metallic catalyst film 210 may
be said to "de-wet", and coalesce on the surface of the support
material 212 or the buffer layer 213, which are part of the
catalyst support 205. The catalyst particles 202 may then catalyze
the growth of base-growth (base-growth nanotubes 200A are shown) or
tip-growth graphitic nanofilaments. The heating or annealing of the
catalyst film 210 to form the catalyst particles 202 may occur
before or during the growth process. In one embodiment, the step of
forming the catalyst particles 202 includes heating the metallic
catalyst film 210 and catalyst support 205 to a temperature between
about 20.degree. C. and about 1000.degree. C. in an inert, ammonia
containing or hydrogen containing environment at a pressure of
between about 50 Torr and about 500 Torr. In further embodiments,
the temperature range may be between about 20.degree. C. to about
300.degree. C., and the pressure range may be between about 100-400
Torr. In general, for embodiments with a catalyst film that is
greater than 10 nm thick, temperatures above about 400.degree. C.
may be required to form the particles 202, while for embodiments
wherein the film is less than 10 nm thick, temperatures below
400.degree. C. may be sufficient to form the particles 202.
[0072] The sizes of the catalyst particles 202 may be controlled by
controlling the parameters of film thickness "t.sub.f",
temperature, and the annealing time of the catalyst film 210,
although the particle sizes may follow a distribution since the
coalescence process tends to be random in nature. The
aforementioned parameters are typically controlled so that the
catalyst particles 202 are nanometer-scale in size. Larger catalyst
particles 202 may result by increasing the film thickness
"t.sub.f", temperature, and annealing time of the catalyst film 210
due to increased surface mobility, migration, and availability of
metal catalyst atoms. The catalyst film 210 may be patterned on a
surface of the catalyst support 205 using various masking,
lithography, etching, or other techniques to form lines, dots,
rectangles, or other patterns for the catalyst film 210, and such
patterning may facilitate the controlled formation of the catalyst
particles 202.
[0073] The catalyst particles 202 shown in FIG. 2C may also be
formed by roughening the surface of a thick catalyst film 210. The
surface roughening may be accomplished through mechanical (e.g.,
abrasion, plasma etching, ion bombardment) and/or electrochemical
(e.g., wet etching) means to generate the catalyst particles 202.
Alternately, no catalyst film 210 may be used and the catalyst
particles 202 may also be formed by roughening the support surface
206 of a catalyst support 205 which comprises a catalyst material.
In another method, the metal surface of the catalyst film 210 or
catalyst support 205 is oxidized by heating or other means to form
a porous metal oxide surface and then the metal oxide is reduced
using a reducing gas (e.g., hydrogen) to form metal catalyst
particles 202. The reduction of the metal oxide may occur before or
during the nanofilament growth process.
[0074] Graphitic nanofilaments may also be formed using the
"floating catalyst" method in which catalyst-containing materials
are injected directly into a graphitic nanofilament growth chamber.
The catalyst-containing materials may be injected before, during,
or after the injection of a carbon source gas. The
catalyst-containing materials may comprise the catalyst particles
202 or catalyst precursors from which the catalyst particles 202
are formed.
[0075] The catalyst precursors may comprise liquid catalyst
mixtures, organometallic catalyst compounds, or other materials
which contain catalysts. The liquid catalyst mixtures may comprise
solutions, suspensions, or colloids of catalyst materials. The
organometallic catalyst compounds may include but are not limited
to iron pentacarbonyl, iron (II) phthalocyanine, ferrocene,
nickelocene, cobaltocene, and other metallocenes. The catalyst
precursors may be injected in either the gas, liquid, or solid
phase using atomizers, syringe pumps, showerheads or other
injecting means. After injection, the catalyst precursors may be
converted into catalyst particles 202 by various means such as
heating, reducing, decomposing, vaporizing, condensing, and
sublimating, for example.
[0076] In the floating catalyst method, graphitic nanofilaments
(e.g., reference numeral 200A in FIGS. 2A and 2C) may grow from the
catalyst particle 202 as the particle falls from the top to the
bottom of the growth chamber or after the catalyst particle 202 has
come to rest upon a surface within the chamber. If a substrate is
included within the growth chamber, many catalyst particles 202 may
come to rest upon the surface of the substrate and graphitic
nanofilaments may form on the substrate surface. The floating
catalyst method may, under certain conditions, be used to form many
densely packed and aligned graphitic nanofilaments on the surface
of a substrate.
CVD Growth Parameters for Graphitic Nanofilaments
[0077] The graphitic nanofilament type (nanotube or nanofiber),
structure (single-walled, multi-walled, herringbone, etc.),
diameter, length and alignment may be controlled by controlling the
CVD growth parameters. The growth parameters include, but are not
limited to, carbon source gas, carrier gas, growth temperature,
growth pressure, and growth time. For catalytic CVD growth,
additional growth parameters may include catalyst parameters such
as catalyst size, shape, composition, surface composition, and
catalyst precursors. The parameter ranges and options for catalytic
CVD growth, excluding catalyst parameters, may, in general, be
applicable to the non-catalytic CVD growth of graphitic
nanofilaments, although higher temperatures may be used for the
non-catalytic CVD methods.
[0078] Generally, the temperatures for the catalytic CVD growth of
graphitic nanofilaments may range from about 300.degree. C. to
about 3000.degree. C., but preferably from about 500.degree. C. to
about 800.degree. C., although temperatures lower than 600.degree.
C. may be used, especially if the CVD growth is plasma enhanced.
The growth pressures may range from about 0.1 Torr to about 1
atmosphere, but more preferably from about 50 Torr to about 500
Torr, with a better growth rate of the nanotubes occurring between
about 200 to about 400 Torr. In some cases, a lower or higher
process pressure may be used without deviating from the scope of
the invention described herein. In another embodiment, the growth
pressures are above atmospheric pressure, and may range from about
1 atmosphere to about 10 atmospheres. The temperatures and
pressures used during the nanotube formation process can depend in
part on the type of process used to form the nanotubes. For example
in embodiments where thermal CVD is used such as CVD with banks of
halogen or infrared lamps, substrate temperatures may be about
800.degree. C., while in embodiments where HWCVD is used having
filament (e.g., tungsten wire) temperatures between about
1400.degree. C. and about 1800.degree. C., the substrate
temperature is less than about 500.degree. C. In one embodiment, a
HWCVD process includes delivering the precursor gas(es) (e.g.,
carbon containing source) across a filament having a temperature
between about 1400.degree. C. and about 1800.degree. C. in a
processing environment that is at a pressure between about 50 Torr
to about 500 Torr, and the substrate is maintained at a temperature
of about 300.degree. C. In some simplified configurations of a
HWCVD chamber, the substrate is primarily heated by the heat
delivered from the HWCVD filament(s), thus greatly simplifying the
chamber design and complexity. Another consideration of substrate
temperature, is the desired diameter of the formed nanotubes. In
one embodiment, it is desirable to control the temperature to the
lower end of the range (e.g., <500.degree. C.) since it has been
found that lower substrate temperatures result in smaller diameter
tubes, which provide a greater surface area to volume ratio, which
is attractive in many applications. The growth time or "residence
time" depends in part on the desired graphitic nanofilament length,
with longer growth times producing longer lengths. The growth time
may range from about ten seconds to many hours, but more typically
from about ten minutes to several hours.
[0079] The carbon containing source gas used for graphitic
nanofilament growth may include a compound selected from a group
consisting of alkanes, alkenes alkynes, aromatic hydrocarbons,
oxygenated hydrocarbons, low-molecular-weight hydrocarbons, or
combinations thereof. For example, the carbon containing source gas
may include, but is not limited to ethylene, xylene, propylene,
acetylene, benzene, toluene, ethane, methane, butane, propane,
hexane, methanol, ethanol, propanol, isopropanol, carbon monoxide,
or acetone. In general, the carbon source gas may comprise any
carbon-containing gas or gases, and the carbon source gas may be
obtained from liquid or solid precursors for the carbon-containing
gas or gases. An auxiliary gas may be used with the carbon source
gas to facilitate the growth process. The auxiliary gas may
comprise one or more gases, such as carrier gases, inert gases,
reducing gases (e.g., hydrogen, ammonia), dilution gases, or
combinations thereof, for example. The term "carrier gas" is
sometimes used in the art to denote inert gases, reducing gases,
and combinations thereof. Some examples of carrier gases are
hydrogen, nitrogen, argon, and ammonia.
Composite Material Formation Apparatus
[0080] FIG. 3 is a schematic side view of one embodiment of an
apparatus 300 for forming composite materials on discrete
substrates 301, wherein the apparatus 300 has various chambers 302,
304, 306, 308, 310 and 312 that are used to form the composite
materials on the substrates 301. The apparatus 300 has a first end
314 where substrates 301 enter the apparatus 300, and a second end
316 where substrates 303 with composite materials deposited
thereon, exit the apparatus 300. At the first end 314 an input
conveyor 318 supports and guides substrates 301 into the first
chamber 302. At the second end 316, an exit conveyor 320 receives
substrates 303 from the final chamber 312. A series of substrate
transfer ports 324 are provided at the entrance and exit of the
apparatus and between each of the chambers 302, 304, 306, 308, 310
and 312 to allow the substrates to pass between chambers, while
maintaining the required environment within each chamber during
processing. Details of the ports 324 are described below with
reference to chamber 302. A series of intermediate conveyors 322
support and guide the substrates through the various chambers.
While the conveyor system has been shown with a number of
individual conveyors 318, 320 and 322, a single conveyor with a
continuous web of material may be used. In one configuration, the
conveyors include support rollers 326 that support and drive the
web(s) of material. When individual conveyors 318, 320 and 322 are
used, the rollers 326 may be mechanically driven by a common drive
system (not shown) such that they are moved in unison, or
individually. The various drives for the rollers 326, ports 324 and
other system actuators are provided by control signals from a
system controller 305. While in the embodiment illustrated in FIG.
3, has six chambers, this is not intended to be limiting as to the
scope of the invention, since any number of chambers may be
provided depending on the number of processes and the required
equipment for each process. In one embodiment, the apparatus 300
also contains at least one additional chamber (not shown) at either
end 314, 316 of the system that acts as a load lock to provide a
buffer between the environment external to the apparatus 300 and
the processing regions of the chambers 302-312.
[0081] The controller 305, used to control the various components
in the apparatus 300, generally has a memory 307, a central
processing unit (CPU) 309 and support circuits 311. The controller
305 is utilized to control the process sequence of the chambers,
regulating the gas flows from gas sources and power application
from power sources into the chambers. The CPU 309 may be of any
form of a general purpose computer processor that can be used in an
industrial setting. The software routines can be stored in the
memory 307, such as random access memory, read only memory, floppy
or hard disk drive, or other form of digital storage. The support
circuits 311 are conventionally coupled to the CPU 309 and may
comprise cache, clock circuits, input/output subsystems, power
supplies, and the like. The software routines, when executed by the
CPU 309, transform the CPU into a specific purpose computer
(controller) 305 that controls the process chambers such that the
processes are performed in accordance with the present invention.
The software routines may also be stored and/or executed by a
second controller (not shown) that is located remotely from the
apparatus 300.
[0082] FIG. 4A is a schematic side view of one embodiment of an
apparatus 400 for forming composite materials on large area
substrates. The substrate(s) in FIG. 4A is in the form of a
continuous web 401 of material. As with apparatus 300, apparatus
400 includes various chambers 402, 404, 406, 408, 410 and 412, for
forming the composite materials. The apparatus 400 has a first end
414 where a supply roll 418 stores the unprocessed substrate(s),
web 401, and feeds the web 401 into the first chamber 402. The
apparatus 400 has a second end 416 where a take-up roll 430
receives and stores the processed substrate(s), web 403, with
composite materials deposited thereon. At the first end 414 a first
diverter roller 420 receives web 401 from the supply roll 418, and
diverts the web 401 into the first chamber 402. At the second end
416, a second diverter roller 422 receives the processed web 403
from the final chamber 412 and diverts it to the take-up roll 430.
In some embodiments, a roll 432 of a protective web of material 434
may be routed unto take-up roll 430. The web of protective material
434 isolates adjacent layers of processed web 403, to thereby
protect the web 403 while it is stored and or transported on roll
430.
[0083] A series of substrate transfer ports 424 are provided at the
entrance and exit of the apparatus 400 and between each of the
chambers 402, 404, 406, 408, 410 and 412 to allow the substrates to
pass between chambers, while maintaining the required environment
within each chamber during processing. Details of the ports 424 are
described below with reference to FIGS. 4B-4D. A series of rollers
426 supports the web 401 of material as it is guided through the
various chambers. In some embodiments, a drive belt 428 may be
included to form a conveyor to provide additional support to the
web 401 between the rollers 426. The rollers 426 may be
mechanically driven by a common drive system (not shown) such that
they are controlled in unison, thereby avoiding wrinkling or
stretching of the web 401. While in the embodiment of FIG. 4A, six
chambers are shown, more or fewer chambers may be provided
depending on the number of processes and the required equipment for
each process. In one embodiment, the apparatus 400 also contains at
least one additional chamber (not shown) at either end 414, 416 of
the system that act as a load lock to provide a buffer between the
environment external to the apparatus 400 and the processing
regions of the chambers 402-412. The various drives for the supply
roll 418, take-up roll 430, rollers 426, ports 424 and other system
actuators are provided by control signals from a system controller
405. The controller 405 has a memory 407, a central processing unit
(CPU) 409 and support circuits 411 that are coupled to the
apparatus 400. The controller 405 is utilized to control the
process sequence of the chambers, regulating the gas flows from gas
sources and power application from power sources into the chambers.
The CPU 409 may be of any form of a general purpose computer
processor that can be used in an industrial setting. The software
routines can be stored in the memory 407, such as random access
memory, read only memory, floppy or hard disk drive, or other form
of digital storage. The support circuits 411 are conventionally
coupled to the CPU 409 and may comprise cache, clock circuits,
input/output subsystems, power supplies, and the like. The software
routines, when executed by the CPU 409, transform the CPU into a
specific purpose computer (controller) 405 that controls the
process chambers such that the processes are performed in
accordance with the present invention. The software routines may
also be stored and/or executed by a second controller (not shown)
that is located remotely from the apparatus 400.
[0084] FIGS. 4B-4D show several embodiments of the substrate
transfer ports 424 that may provided between the various chambers
402, 404, 406, 408, 410 and 412 and/or at the entrance and exit of
the apparatus 400. In a first embodiment, as shown in FIG. 4B, the
substrate transfer port 424 is closeable and is mounted on the
chamber wall 440. A closeable door 442 is sealed with the wall and
captures the web 401 between the door 442 and a support roller 426.
The end of the door 442 that contacts the web 401 may include an
elastomeric strip 446 or other similar compliant element that will
reduce damage to the web 401 and to provide an effective seal. An
actuator 444, extends and retracts the door 442, based on commands
from a system controller 405. When the door 442 is in the closed
position as shown in FIG. 4B, a sealed chamber is formed between
the chamber walls 440, the top of the chamber (e.g., reference
numeral 502 shown and described below), and the web 401, which
forms the bottom of the chamber, in some embodiments. After the
process associated with the chamber is performed, the door 442 is
opened and the web 401 is advanced for the length of the chamber.
The door 442 can then be reclosed and the process performed on
another length of the web 401.
[0085] Another embodiment of the substrate transfer ports 424 is
shown in FIG. 4C. In this embodiment, the bottom of the wall 440 of
the chamber includes two longitudinal extensions 448. The
extensions 448 form a gap G between themselves and the web 401. The
gap G extends for a length L as shown in FIG. 4C. The height of the
gap G and the length L of the gap are chosen based on relative
pressure and temperature differences between adjacent chambers and
are thus chosen according to these specifications. In general, a
large length to height ratio allows the gap G to function as a
restriction, reducing the transfer of processing gases into and out
of the chambers. In a further embodiment, as shown in FIG. 4D, a
number of vacuum ports 450 are provided, proximate to the center of
the bottom of wall 440. A vacuum line 452 routes vacuum ports 450
to a source of vacuum 454 via valve 456. Valve 456 is controlled by
signals received from the support circuits 411 (FIG. 4A) of the
system controller 405. The vacuum ports 450 evacuate any gases in
the gap region by providing airflow as shown by the arrows labeled
"Gas" in FIG. 4D. By removing the gases in the gap region, the
transfer of gases between chambers is reduced. It should be noted
that one advantage of the embodiments of the transfer ports 424 as
shown in FIGS. 4C and 4D, over embodiments requiring a door, such
as the one shown in FIG. 4B, is that the processes in each chamber
can be performed continuously (i.e., web 401 is fed continuously
through the system). There are many types of chamber isolation
systems in use in deposition processes, and the particular
isolation system used should not be considered limiting with
respect to the present invention.
[0086] FIG. 21 depicts a schematic diagram of a further embodiment
of a substrate processing system (e.g., cluster tool 2100) used to
deposit a composite material on a substrate. The cluster tool 2100
includes a vacuum-tight processing platform 2101, a factory
interface 2102, and a system controller 2136. The platform 2101
comprises a plurality of chambers 2108, 2110, 2112, 2114, 2116,
2118 and at least one load-lock chamber (a load-lock chamber 2120
is shown), which are coupled to vacuum substrate transfer chambers
2103, 2104. The factory interface 2102 is coupled to the transfer
chamber 2104 by the load lock chamber 2120.
[0087] In one embodiment, the factory interface 2102 comprises at
least one docking station 2126, at least one substrate transfer
robot 2138, at least one substrate transfer platform 2140, at least
one precleaning chamber 2124, and a precleaning robot 2122. In one
embodiment, the docking station 2126 is configured to accept at
least one front opening unified pod (FOUP). Two FOUPs 2128A, 2128B
are shown in the embodiment of FIG. 1, but any number of FOUPs may
be provided within the physical limits of the docking station 2126.
The substrate transfer robot 2138 is configured to transfer the
substrate from the factory interface 2102 to the precleaning
chamber 2124 wherein a precleaning process may be performed. The
precleaning robot 2122 is configured to transfer the substrate from
the precleaning chamber 2124 to the loadlock chamber 2120.
Alternatively, the substrate may be transferred from the factory
interface 2102 directly to the loadlock chamber 2120, by-passing
the precleaning chamber 2124.
[0088] The loadlock chamber 2120 has a first port coupled to the
factory interface 2102 and a second port coupled to a first
transfer chamber 2104. The loadlock chamber 2120 is coupled to a
pressure control system (not shown) which pumps down and vents the
chamber 2120 as needed to facilitate passing the substrate between
the vacuum environment of the transfer chamber 2104 and the
substantially ambient (e.g., atmospheric) environment of the
factory interface 2102.
[0089] The first transfer chamber 2104 has a first robot 2107
disposed therein. The first robot 2107 transfers substrates between
the loadlock chamber 2120, the processing modules 2116 and 2118,
and two substrate transfer platforms 2106A and 2106B. The second
transfer chamber 2103 has a second robot 2105 disposed therein. The
second robot 2105 transfers substrates between the two substrate
transfer platforms 2106A and 2106B and the chambers 2108, 2110,
2112 and 2114. The two substrate transfer platforms 2106A, 2106B
are disposed between the transfer chamber 2104 and the transfer
chamber 2103 to facilitate transfer of the substrate between the
robot 2105 and the robot 2107. The platforms 2106A, 2106B can
either be open to the transfer chambers 2103, 2104 or be
selectively isolated (i.e., sealed) from the transfer chambers
2103, 2104 to allow different operational pressures to be
maintained in each of the transfer chambers 2103, 2104.
[0090] In one embodiment, the processing chambers coupled to the
first transfer chamber 2104 may be a physical vapor deposition
(PVD) chamber 2118 and a chemical vapor deposition (CVD) chamber
2116, for performing a CVD process such as hot-wire CVD (HWCVD).
The processing chambers coupled to the second transfer chamber 2103
may be a second PVD chamber 2114, a HWCVD chamber 2110, a third PVD
chamber 2108, and a degas chamber 2112. Suitable CVD, PVD, HWCVD
and degas processing chambers are available from Applied Materials,
Inc., located in Santa Clara, Calif.
[0091] The system controller 2136, which may be similar to the
system controller 305 described above, is coupled to the integrated
cluster tool 2100. The system controller 2136 controls the
operation of the cluster tool 2100 using a direct control of the
process chambers of the cluster tool 2100 or alternatively, by
controlling the computers (or controllers) associated with the
process chambers and cluster tool 2100. In operation, the system
controller 2136 enables data collection and feedback from the
respective chambers and system to optimize performance of the
cluster tool 2100. The software routines, such as an electrode
deposition process 2300 described below with reference to FIG. 23,
when executed by the CPU 309, transform the CPU into a specific
purpose computer (controller) 2136. The software routines may also
be stored and/or executed by a second controller (not shown) that
is located remotely from the cluster tool 2100.
[0092] FIG. 22 is a schematic side view of a further embodiment of
an apparatus 2200 for forming composite materials on large area
substrates. The substrate(s) in FIG. 22 is in the form of a
continuous web 2201 of material. As with apparatus 300 and 400, the
apparatus 2200 includes various chambers 2202, 2204, 2206 and 2208,
that are used to form the composite materials on the continuous web
2201. The apparatus 2200 has a supply cabinet 2214 with a supply
roll 2218 that stores the unprocessed substrate(s), or web 2201.
The apparatus 2200 has a take-up cabinet 2216 with a take-up roll
2230 that receives and stores the processed substrate(s), or web
2203, that has the composite materials deposited thereon. The
supply roll 2218 feeds the web 2201 to a first diverter roller 2220
which diverts the web 2201 onto a rotating drum 2228. The
un-processed web 2201 is then supported and transferred through the
various chambers 2202, 2204, 2206 and 2208 by use of the rotating
drum 2228. In this configuration, the rotating drum 2228 is used to
deposit or process portions of the web 2201 as they pass through
each respective chamber 2202, 2204, 2206 and 2208. As the processed
web 2203 leaves the rotating drum 2228, a second diverter roller
2222 receives the processed web 2203 and diverts it to the take-up
roll 2230. In some embodiments, a roll of a protective web of
material may be routed unto take-up roll 2230, as shown with
respect to apparatus 400. The web of protective material isolates
adjacent layers of processed web 2203, to thereby protect the web
2203 while it is stored and or transported on roll 2230.
[0093] In addition to diverting the substrate, web 2201, 2203, the
first diverter roller 2220 and the second diverter roller 2222,
hold the web against the rotating drum 2228, as the web is fed
through the chambers 2202, 2204, 2206 and 2208. The rotating drum
2228 provides support to the web as it undergoes processing in the
chambers of apparatus 2200. The drum 2228 may, in one embodiment,
provide temperature control to at least a portion of the web. For
example the drum 2228 may be chilled to reduce or maintain the
temperature of the web, or may be heated to increase or maintain
the temperature of the web. To provide the temperature control,
cooling or heating fluid may be circulated within the drum 2228 or
through passages (not shown) internal to the drum 2228.
[0094] A series of substrate transfer ports 2224 are provided at
the entrance of the chamber 2202 and the exit of the chamber 2208
and between each of the chambers 2202, 2204, 2206 and 2208 to allow
the web to pass between chambers, while maintaining the required
environment within each chamber during processing. Details of some
embodiments of the ports 2224 are described above with reference to
ports 424 in FIGS. 4B-4D. It should be understood that the
longitudinal extensions 448 of the embodiments of ports 424 shown
in FIGS. 4C and 4D, may be curved to conform to the curvature of
drum 2228, when used in the apparatus 2200. The supply roll 2218,
the take-up roll 2230, the diverter rollers 2220 and 2222, as well
as drum 2228 may be mechanically driven by a common drive system
(not shown) such that their movement is in unison, thereby avoiding
wrinkling or stretching of the web 2201.
[0095] While in the embodiment of FIG. 22, four chambers are shown,
more or fewer chambers may be provided depending on the number of
processes and the required equipment for each process. In one
embodiment, the chamber 2202 is a PVD chamber, the chamber 2204 is
an anneal chamber and the chambers 2206 and 2208 are HWCVD
chambers. In one embodiment, one or more of the chambers 2202-2208
are similar to the chambers 302-312 discussed above. Further in
some embodiments, the apparatus 2200 also contains at least one
additional chamber (not shown) at either end of the system that act
as a load lock to provide a buffer between the environment external
to the chambers 2202-2208 and the processing regions of the
chambers 2202-2208. To control the pressure in one or more of the
chambers 2202-2208, each chamber may be separately connected to one
or more vacuum sources 2234 through a flow control valve 2232. For
example, as shown in FIG. 22, the chambers 2206 and 2208 are
connected to a single vacuum source 2234.
[0096] The various drives for the supply roll 2218, take-up roll
2230, rollers 2220 and 2222, drum 2228, ports 2224 and other system
actuators are provided control signals from a system controller
2205. The controller 2205, which may be similar to the controller
305 discussed above, may contain a memory 307, a central processing
unit (CPU) 309 and support circuits 311 that are coupled to the
apparatus 2200. The controller 2205 is utilized to control the
process sequence of the chambers, regulating the gas flows from gas
sources and power application from power sources into the chambers.
The software routines, when executed by the CPU 309, transform the
CPU into a specific purpose computer (controller) 2205 that
controls the process chambers such that the processes are performed
in accordance with the present invention. The software routines may
also be stored and/or executed by a second controller (not shown)
that is located remotely from the apparatus 2200.
[0097] With respect to the above apparatus 300, 400, 2100 and 2200,
it should be understood that the various components of the chambers
of each of these apparatus are useable within the chambers of the
other apparatus. The components shown in FIGS. 5A-11 and described
below with respect to chambers 302, 302', 304, 306, 800, 308, 310
and 312, are also capable of being incorporated into the chambers
of apparatus 400, 2100 and 2200. Likewise, the components shown in
FIGS. 12 and 13 and described below with respect to chambers 1200
and 1300, are also capable of being incorporated into the chambers
of apparatus 300, 2100 and 2200. The different composite materials
and methods of making these materials can each be formed or
performed in any of the above described apparatus 300, 400, 2100
and 2200. Further, the formation of these composite materials may
also be accomplished by performing some steps in one type of
apparatus, while performing other steps in another type of
apparatus.
[0098] FIG. 5A shows a schematic side view of one embodiment of a
chamber 302 for depositing catalyst material on a substrate S. In
this embodiment, the chamber 302 includes a first wall 540 facing
the first end 314 of apparatus 300 and a second wall 540' between
chamber 302 and chamber 304 (see FIG. 3). While second wall 540' is
shown as a shared wall between chambers 302 and 304, double walls
may be used to provide greater insulation between chambers. Chamber
302 also includes a top 502, that may be a common one-piece top for
all of the chambers as shown, or each chamber could be provided
with a separate top. FIG. 5A also illustrates a further embodiment
of substrate transfer ports 324 that are positioned on the walls
540 and 540'. Walls 540 and 540' include a lower portion 506 that
connects to the chamber bottom 504, below the substrate transfer
ports 324. As with the top 502, chamber bottom 504 may be a common
one-piece bottom for all of the chambers as shown, or each chamber
could be provided with a separate bottom.
[0099] Each of the substrate transfer ports 324 as shown in FIG.
5A, is generally closeable and is mounted on the chamber wall. A
closeable door 542 is sealed with the wall and contacts an
elastomeric strip 546 on top of the lower portion 506 of the wall
to seal the substrate transfer port 324. An actuator 544, extends
and retracts the door 542, based on commands received from the
support circuits 311 (FIG. 3) of the system controller 305. When
the door 542 is in the closed position as shown on the left in FIG.
5A, the chamber 302 is sealed so that regions on either side of the
door 542 are isolated from each other. In one embodiment, the door
542 is a conventional gate valve that is configured to prevent gas
leakage through the substrate transfer port 324. During processing
the doors 542 are closed so that a processing region 548 is formed
between the chamber walls 540, the top 502 of the chamber, and the
chamber bottom 504 and doors 542 so that one or more substrate
processing steps may be performed therein. After the process
associated with each chamber is performed, the doors 542 of each
chamber are opened as shown on the right side of FIG. 5A. The
conveyors 322 (as well as the input conveyor 318 and the exit
conveyor 320) advance the substrates "S" in the direction "T" into
the subsequent chamber, based on commands received by a drive
mechanism 514 from the support circuits 311 (FIG. 3) of the system
controller 305, as shown for example by substrate S'. The doors 542
can then be reclosed and the appropriate processes performed on the
substrates S. It should be noted that other embodiments of
substrate transfer ports, such as those shown in FIGS. 4C and 4D
may also be used in conjunction with chamber 302 or any of the
other chambers of apparatus 300, 400 or 2200.
[0100] In one embodiment, a pumping device 530 is coupled to the
processing region 548 to evacuate and control the pressure therein.
The pumping device 530 may be a conventional rough pump, roots
blower, turbo pump or other similar device that is adapted control
the pressure in the processing region 548. In one embodiment, the
pressure level of the processing region 548 of the chamber 302 may
be maintained at less than about 760 Torr. In one embodiment, the
pressure level of the processing region 548 of the chamber 304 may
be maintained at about 1 Torr or less. In another embodiment, the
pressure level within the chamber 302 may be maintained at about
10.sup.-3 Torr or less. In yet another embodiment, the pressure
level within the chamber 302 may be maintained at about 10.sup.-3
Torr to about 10.sup.-7 Torr.
[0101] FIGS. 15A-15G are schematic side views showing the various
stages of one embodiment of a method for forming graphitic
nanofilament based composite materials. FIG. 18 illustrates a
process sequence 1800 used to form the composite materials on a
substrate S. The sequence found in FIG. 18 corresponds to the
stages depicted in FIGS. 15A-15G, which are discussed herein. The
composite materials may be formed on a number of discrete
substrates S as shown in FIG. 5A, or a web 401, 2201 as shown in
FIGS. 4A and 22, respectively. Such a substrate S is shown in FIG.
15A. The substrate S can be made of, but is not limited to, glass,
silicon (Si) or metal such as aluminum (Al), stainless steel, or
copper (Cu). The substrate S may be relatively non-flexible when
provided as individual substrates, but is relatively flexible when
supplied as a web 401 or 2201 (for example, aluminum, stainless
steel, or copper foil).
[0102] At step 1802, as shown in FIGS. 5A-5B, 15B and 18, a
substrate S is positioned in the processing chamber 302 and a layer
1502 of catalytic material is deposited on the substrate S. The
layer 1502 of catalytic material can be formed of, but is not
limited to, iron (Fe); cobalt (Co); nickel (Ni); alloys of Fe, Co
and Ni; Fe polymer; Co polymer; and Ni polymer. The layer 1502 of
catalytic material may be deposited on the substrate S using a
number of methods including a physical vapor deposition (PVD)
method such as sputtering, or a chemical vapor deposition (CVD)
method, as described above. In one embodiment, the layer 1502 of
catalytic material is deposited to a thickness of about 0.2 nm to
about 20 nm. In one embodiment, the layer 1502 of catalytic
material is deposited to a thickness of less than about 20 nm.
[0103] In one embodiment, a chamber 302 of FIG. 5A, is configured
and adapted to deposit the layer 1502 of catalyst material on a
substrate S during step 1802, using a sputtering deposition
process. A target 508 of the catalyst material is provided in the
chamber 302. A power source 510 is connected to the target 508 so
that a cathodic DC and/or RF bias can be applied to the target 508
so that the catalytic material can be deposited on the surface of
the substrate S. The plasma generated by the bias applied to the
target 508 causes atoms from the target surface to be removed, and
be deposited on the exposed surfaces of the substrate S. In
embodiments requiring heating of the substrates, one or more
heating elements 512 may be provided. The heating elements 512 may
comprise resistive heating elements, induction coils, or other
heating means. In batch-type systems, once the layer 1502 of
catalytic material is deposited on the substrate S, (and the other
chambers' processes are complete as described below), the doors 542
of the chambers are opened and the substrates are advanced to the
next chamber in the fabrication process. In continuous systems, the
speed of the conveyors 322 are maintained to provide the correct
residence time within the chamber 302, to deposit the required
thickness of layer 1502, such as about 0.2 nm to about 20 nm, as
described above. Some examples of the materials used to form the
catalytic layer include iron (Fe), nickel (Ni), cobalt (Co), iron
nickel alloys (FeNi) and iron cobalt alloys (FeCo). Suitable
precursors include ferrocene, nickelocene and cobaltocene. The
catalyst may be deposited using PVD sputtering, evaporation, vapor
phase CVD or sol gel methods.
[0104] In another embodiment, during step 1802, a chamber 302' of
FIG. 5B is used to deposit catalyst material on the substrates S
using a chemical vapor deposition (CVD) process. One will note that
the components found in chamber 302' (and the other chambers as
described below) are generally similar to the components founds in
chamber 302 in FIG. 5A, and thus have the same reference
designators, and are not described with reference to FIG. 5B. In
chamber 302', process gases are provided to a showerhead 516 from
one or more gas sources 518, 520 via valves 522, 524, respectively.
Valves 522, 524 are controlled by signals received from the support
circuits 311 of the system controller 305. The process gases
provided to the showerhead 516 include gases used to form the
catalytic material, such as metal organic precursors. While in this
embodiment, two gas sources 518, 520 are shown, a single gas source
or a plurality of gas sources may be provided depending on the
number and combination of gases used. To improve the film quality,
increase the deposition rate and/or film uniformity, the CVD
process may be enhanced by applying a bias to the showerhead 516
and/or substrate S. In one embodiment, a power supply 526 is
configured to RF bias the showerhead 516 based on signals received
from the support circuits 311 of the system controller 305. The
applied voltage may be RF, DC or AC depending on system
requirements. In another embodiment, an inductively coupled plasma
may also be formed in the processing region 548 by use of the power
supply 526 and one or more coils (not shown) which are positioned
to generate a plasma therein.
[0105] Next, during step 1804, as illustrated in FIGS. 15C and 18,
the deposited catalyst material layer 1502 is further processed to
form nanoislands 1504 of catalyst material on the substrate S. In
one embodiment, the processing step(s) used to form the nanoislands
1504 includes heating the substrate S to a desired temperature for
a desired period of time. In one embodiment, as shown in FIG. 6, a
chamber 304 is configured and adapted to heat the catalyst material
to form nanoislands 1504 of catalyst material on a substrate S. To
assist in heating, chamber 304 may include the additional heaters
604 in addition to the heater elements 512 that are similarly
configured as shown in FIG. 5A. The additional heaters 604 may
comprise resistive heating elements or radiant heat lamps that are
positioned to uniformly heat the substrate S disposed in the
processing region 549 formed in the chamber 304. A heater power
supply 602 receives control signals from the support circuits 311
of the system controller 305, to control the amount of heat
delivered from one or more of the heaters 604. The temperature in
chamber 304 may be constant or may be increased over time.
Temperatures in chamber 304 for forming the nanoislands may be
between about 300.degree. C. and about 1000.degree. C. It should be
noted that the processes performed in chamber 304 could also be
performed in chamber 302 or chamber 306. However, the use of a
separate chamber may reduce the total processing time needed in
each chamber, thus increasing substrate throughput.
[0106] Next, during step 1806, as illustrated in FIGS. 15D and 18,
graphitic nanofilaments 1506 are formed on the substrate S. By
supplying a carbon containing precursor to the surface of the
substrate S that contains the nanoislands 1504, graphitic
nanofilaments 1506 can be formed on a surface of the substrate S
disposed in the processing region 550. In one embodiment, the
graphitic nanofilaments 1506 comprise carbon nanotubes or
nanofibers that are single-walled or multi-walled. In chamber 306,
process gases are provided to a showerhead 716 from one or more gas
sources 718, 720 via valves 722, 724, respectively. Valves 722, 724
are controlled by signals received from the support circuits 311 of
the system controller 305. The process gases provided to the
showerhead 516 include carbon source gases used to form the
nanotubes. Gases for the carbon source include, but are not limited
to, xylene, ethylene, propylene, acetylene, benzene, toluene,
ethane, methane, butane, propane, hexane, methanol, ethanol,
propanol, isopropanol, carbon monoxide, acetone, oxygenated
hydrocarbons, low-molecular-weight hydrocarbons, or combinations
thereof. In some embodiments, the process to form the graphitic
nanofilaments 1506 may be a plasma enhanced chemical vapor
deposition (PECVD) process. To improve the film quality, increase
the deposition rate and/or film uniformity, the CVD process may be
enhanced by applying a bias to the showerhead 716 and/or substrate
S. In one embodiment, a power supply 702 is configured to RF bias
the showerhead 716 based on signals received from the support
circuits 311 of the system controller 305. The applied voltage may
be RF, DC or AC depending on the processing requirements. In
another embodiment, an inductively coupled plasma may also be
formed in the processing region 550 by use of the power supply 702
and one or coils (not shown) which are positioned to generate a
plasma therein. In further embodiments, the process to form the
graphitic nanofilaments 1506 may be a hot-wire chemical vapor
deposition process (HWCVD), as described below with respect to FIG.
9.
[0107] In another embodiment, a combination chamber 800 of FIG. 8
is configured and adapted to perform the functions of chambers 302,
304 and 306, so that depositing and heating the catalyst material
layer 1502 to form the nanoislands 1504 of catalyst material on the
substrates S and then forming the graphitic nanofilaments 1506 on
the substrates S can be performed in the processing region 551 of a
single chamber. In this configuration, the processing steps
1802-1806 are all performed in the combination chamber 800. To
perform these combined functions, chamber 800 includes a showerhead
816 that receives process gases from one or more gas sources 818,
820 via valves 822, 824, respectively. The valves 822, 824 are
controlled by signals received from the support circuits 311 of the
system controller 305. The gases for forming the catalyst material
on the substrate and the gases for forming the graphitic
nanofilaments may be sequentially supplied, or may be
simultaneously provided (co-flowed). By first providing the gases
required to form the catalyst, then heating the catalyst to form
the nanoislands, and following with the gases to form the graphitic
nanofilaments, graphitic nanofilaments that are relatively free of
catalyst particles can be formed. When the gases for forming the
catalyst and the graphitic nanofilaments are simultaneously
provided, some amount of catalyst particles may be present on the
graphitic nanofilaments. In some applications, a small amount of
contamination is acceptable. Thus, the increased substrate
throughput of a co-flowed method may be desirable. To provide the
necessary heat for forming the nanoislands and graphitic
nanofilaments, a heater power supply 802 receives control signals
from the support circuits 311 of the system controller 305, to
supply power to one or more of the heaters 804 (e.g., radiant heat
lamps or resistive heaters). In one embodiment of a plasma enhanced
deposition process, a plasma may be generated by delivering power
from a power source 826 to the showerhead 816 based on signals
received from the support circuits 311 of the system controller
305. In HWCVD embodiments, chamber 800 includes a hot-wire, as
described below with respect to FIG. 9.
[0108] Next, during step 1808, as illustrated in FIGS. 15E and 18,
a silicon containing layer is deposited over the graphitic
nanofilaments 1506 formed during step 1806. In one embodiment, the
silicon containing layer is an amorphous silicon layer that is
between about 0.5 nm and about 10 nm thick. In one embodiment, an
amorphous silicon layer is formed over the graphitic nanofilaments
1506 using a hot wire chemical vapor deposition (HWCVD) process. In
one embodiment, as shown in FIG. 9, a chamber 308 is configured and
adapted to deposit the amorphous silicon on the graphitic
nanofilaments using a HWCVD process. The HWCVD process generally
uses a hot filament (usually tungsten or tantalum) to "crack" the
reactive gas components (e.g., silane and hydrogen) into atomic
radicals. The hot filament is typically maintained at a surface
temperature significantly higher than 1500.degree. C. The reactive
species, after passing across the surface of the hot filament, are
transported through a processing region 552 to the substrate in a
low pressure ambient which enables a high deposition rate without
gas-phase particle formation. In one example, as shown in FIG. 15E,
a layer of amorphous silicon 1508 is deposited and conformably
coats the graphitic nanofilaments 1506. To accomplish this, the
chamber 308 includes a showerhead 916 that receives process gases
from one or more gas sources 918, 920 via valves 922, 924,
respectively. The valves 922, 924 are controlled by signals
received from the support circuits 311 of the system controller
305. The gases supplied by the shower head 916, for forming
amorphous silicon on the graphitic nanofilaments include, for
example, hydrogen (H.sub.2), silane (SiH.sub.4), disilane
(Si.sub.2H.sub.6), silicon tetrafluoride (SiF.sub.4), silicon
tetrachloride (SiCl.sub.4), and/or dichlorosilane
(SiH.sub.2Cl.sub.2). To assist in the CVD process, a resistive wire
928 is placed in close proximity to the substrate S. Electrical
current is supplied to the wire 928 by a power supply 926, based on
signals received from the support circuits 311 of the system
controller 305. The electrical current heats the wire 928 to form
the amorphous silicon 1508 on the graphitic nanofilaments 1506.
[0109] Next, during step 1810, as illustrated in FIGS. 15F and 18,
a polymeric layer is deposited over the silicon containing layer
formed during step 1808. In one embodiment, after the amorphous
silicon 1508 is deposited on the surface of the substrate, a
polymeric material 1510, such as a polytetrafluoroethylene (PTFE),
is deposited thereon. The polymeric material 1510 is generally used
to provide a dielectric barrier and/or encapsulate both the
graphitic nanofilaments 1506 and the amorphous silicon 1508. In one
embodiment, the formed layer of polymeric material 1510 is porous.
In one embodiment, chamber 310 of FIG. 10 is configured and adapted
to deposit polymeric material 1510 on the amorphous silicon 1508
and graphitic nanofilaments 1506 using an initiated chemical vapor
deposition (iCVD) process. The iCVD process generally involves the
vapor phase delivery of both initiator species and monomers into a
processing region 553 of the processing chamber 310 that is
maintained in a vacuum state. In one embodiment, the polymeric
material 1510 is formed on the surface of the substrate by use of a
hot wire chemical vapor deposition (HWCVD) process. In one
embodiment, the chamber 310 is configured to deposit the polymeric
material 1510 using a low temperature HWCVD process in which the
filament temperature is maintained at a temperature between about
1000.degree. C. and 2100.degree. C. while the substrate temperature
is maintained between about 300.degree. C. and 450.degree. C., such
as about 400.degree. C. In the chamber 310, a showerhead 1016
receives process gases from one or more gas sources 1018, 1020 via
valves 1022, 1024, respectively. The valves 1022, 1024 are
controlled by signals received from the support circuits 311 of the
system controller 305. One of the gas sources may include the
initiator species. Such gases include, but are not limited to,
perfluorooctane solfonyl fluoride, triethylamine, tert-butyl
peroxide, 2,2' azobis (2-methylpropane) and benzophenone. Another
of the gas sources may provide the monomer. Such gases include but
are not limited to fluoropolymer type material.
[0110] During step 1810, as illustrated in FIGS. 15G and 18, a
cathodic layer 1512 of material is deposited on top of the
polymeric material 1510, to form a cathode and complete the
composite material structure. In one embodiment, the cathodic layer
1512 is a lithium (Li) based material, such as lithium transition
metal oxides, such as LiMn.sub.2O.sub.4, LiCoO.sub.2, and/or
combinations of Ni, Fe and/or Li oxides. In one embodiment, the
cathodic material includes a series of layers which include a
lithium containing layer and a metal layer. In one example, the
metal layer includes but is not limited to include aluminum,
stainless steel, and nickel. In one embodiment, chamber 312 of FIG.
11 is configured and adapted to deposit cathodic material on the
polymeric material, using either a PVD, PECVD, CVD, iCVD or HWCVD
process. In one example, the chamber 312 is similarly configured
like chamber 302, shown in FIG. 5A, to perform a PVD process that
is able to deposit the cathodic layer of material on the surface of
the substrate. In another example, chamber 312 is configured to
deposit the cathodic layer using a CVD process. In this
configuration, a showerhead 1116 delivers the process gases to the
processing region 554 from one or more gas sources 1118, 1120 via
valves 1122, 1124, respectively. The valves 1122, 1124 are
controlled by signals received from the support circuits 311 of the
system controller 305. Such gases include, but are not limited to,
metal organic precursors, carrier gases, or other similar gases. In
HWCVD processes, the chamber 312 may include a resistive wire 1128
that is positioned in close proximity to the substrate S to help
improve the reactivity of the process gas species. Electrical
current is supplied to the wire 1128 by a power supply 1126, based
on signals received from the support circuits 311 of the system
controller 305. The electrical current heats the wire 1128 to
assist in the formation of the cathodic material layer 1512 on the
polymeric material 1510. Some examples of cathode materials include
LiCoO.sub.2, LiMn.sub.2O.sub.4, LiFePO.sub.4 and
Li.sub.2FePO.sub.4. The wire 1128 or filament temperature, in one
embodiment, is maintained between about 300.degree. C. to
1600.degree. C., while the substrate temperature is maintained
between about 100.degree. C. to about 700.degree. C. In some
embodiments the operating pressures vary from about 1 mTorr to
about 10 Torr. Once the cathodic material 1512 is deposited on the
polymeric material 1510, door 542 (on the right side of the chamber
312) is opened and the conveyor 322 directs the completed substrate
S (303 in FIG. 3) through the door 542 and onto exit conveyor
320.
[0111] In one embodiment, the process sequence 1800 further
comprises separating the composite material layers formed during
steps 1802-1812 from the support material 212 (substrate) so that
the support material 212 can be reused in the processing system. In
one configuration, it is desirable to use a sacrificial layer, such
as a buffer layer 213 (FIG. 2A) between the deposited composite
material layers and the support material 212, so that the composite
material layers can be easily separated from the support material
212.
Alternate Deposition Processes
[0112] In addition to the graphitic nanofilament based composite
materials described above, apparatus 300, 400, 2100 or 2200 may
also be used to form portions of a photovoltaic (PV) device, or
solar cell. FIG. 19 illustrates a process sequence 1900 used to
form the composite materials on a surface of a substrate S to form
one or more regions of a solar cell device. The sequence found in
FIG. 19 corresponds to the stages depicted in FIGS. 16A-16F, which
are discussed herein. The substrate S, which is illustrated in FIG.
16A, may be a discrete substrate such as substrates 301 and 303 in
FIG. 3, or substrate S may be in the form of a web 401 of material
in FIG. 4A or 2201 in FIG. 22.
[0113] At step 1902, as shown in FIGS. 12, 16B and 19, a substrate
S is positioned in the processing chamber 1200 and a layer of
intrinsic silicon layer 1602 deposited on the substrate S. In one
embodiment, chamber 1200 is configured to deposit an intrinsic
silicon layer on the substrate using a showerhead 1216 that
delivers the process gases to a processing region 555 from one or
more gas sources 1218, 1220 via valves 1222, 1224, respectively.
The valves 1222, 1224 are controlled by signals received from the
support circuits 311 of the system controller 305. The gases
supplied by the shower head 1216, for forming intrinsic silicon on
the substrates include hydrogen (H.sub.2), silane (SiH.sub.4),
disilane (Si.sub.2H.sub.6), silicon tetrafluoride (SiF.sub.4),
silicon tetrachloride (SiCl.sub.4), and/or dichlorosilane
(SiH.sub.2Cl.sub.2). In one embodiment, a HWCVD process is
performed that uses a resistive wire 1228 to deliver energy to the
reactive gases to improve the deposition process speed and film
properties. The resistive wire 1228 is heated by delivering an
electrical current through the wire by use of a power supply 1226,
based on signals received from the support circuits 311 of the
system controller 305. The electrical current heats the wire 1228
to assist in forming the intrinsic silicon layer 1602 on the
substrate S. After deposition of the intrinsic silicon, the door
542 (on the right side of the chamber 1200) is opened and the
conveyor 322 directs the substrate S through the door 542 and into
the chamber 1300. It should be noted that while FIG. 12 shows
chamber 1200 to the right of an adjacent chamber, chamber 1200 may
be configured as the first chamber (302 or 402) of the apparatus
300 or 400 and receives substrate(s) from the input conveyor 318 or
the supply roll 418.
[0114] Next, during step 1904, as illustrated in FIGS. 16C and 19,
a doped silicon layer 1604 is disposed over the intrinsic silicon
layer 1602. In one embodiment, the chamber 1300 of FIG. 13 is
configured and adapted to deposit doped silicon on the intrinsic
silicon layer disposed on the substrate S. The chamber 1300
includes a showerhead 1316 that delivers the process gases to a
processing region 556 from one or more gas sources 1318, 1320 via
valves 1322, 1324, respectively. The valves 1322, 1324 are
controlled by signals received from the support circuits 311 of the
system controller 305. The gases supplied by the shower head 1316,
for forming doped silicon may include, but are not limited to
hydrogen (H.sub.2), silane (SiH.sub.4), disilane (Si.sub.2H.sub.6),
silicon tetrafluoride (SiF.sub.4), silicon tetrachloride
(SiCl.sub.4), dichlorosilane (SiH.sub.2Cl.sub.2), trimethylboron
(TMB (or B(CH.sub.3).sub.3)), diborane (B.sub.2H.sub.6), BF.sub.3,
B(C.sub.2H.sub.5).sub.3, and phoshine (PH.sub.3). To assist in the
CVD process, a resistive wire 1328 is placed in close proximity to
the substrate S. Electrical current is supplied to the wire 1328 by
a power supply 1326, based on signals received from the support
circuits 311 of the system controller 305. The electrical current
heats the wire 1328 to assist in forming the doped silicon layer
1604 on the intrinsic silicon layer 1602. After deposition of the
doped silicon, the door 542 (on the right side of the chamber 1200)
is opened and the conveyor 322 directs the substrate S through the
door 542 and out of chamber 1300.
[0115] In FIG. 14 another embodiment of an apparatus 1400 for
forming composite materials on a substrate is shown. Apparatus 1400
is generally similar to apparatus 300 as shown in FIG. 3, but
further includes a robot 1402. The apparatus 1400 generally
includes chambers 1200 and 1300 as described above. In one
embodiment, the apparatus 1400 also includes additional chambers
1200' and 1300'. The robot 1402 includes a pair of blades 1404
attached to an end effector 1406. The blades are moveable relative
to each other, to allow the robot 1402 to grasp and release a
substrate S. The end effector 1406 is mounted to a rod 1408 that is
supported by a robot carriage 1410. The rod 1408 is mounted to the
robot carriage such that it can be rotated about its central axis,
and can be retracted into the carriage and moved up and down
relative to the carriage. After deposition of the doped silicon in
step 1904, the substrate S is conveyed out of chamber 1300, and
onto conveyor 322 of FIG. 14. During step 1906 (FIG. 16D) the
substrate S is flipped over, by rotating the grasped substrate by
rotating the rod 1408 until the unprocessed bottom of the substrate
S is face-up. As shown in FIG. 16D, the substrate S is thus in an
inverted position with the unprocessed bottom of the substrate S
face-up and the doped silicon layer 1604 and the intrinsic silicon
layer 1602 in a face-down orientation. The flipped substrate is
then lowered onto the conveyor 322 for transport into chamber
1200'.
[0116] Next, during step 1908, as illustrated in FIGS. 16E and 19,
a second layer of silicon, or second layer 1606 is then deposited
onto the substrate S using the components found in chamber 1200, or
chamber 1200', as described above with reference to FIG. 12. The
substrate is then conveyed into chamber 1300 or 1300' and a second
layer of doped silicon, or second doped layer 1608 is then
deposited onto the second layer 1606 using the components in
chamber 1300, or chamber 1300', as described above with reference
to FIG. 13. The completed silicon-based composite material is then
conveyed to output conveyor 320 or conveyor 322.
[0117] In one embodiment of the apparatus 1400, the system
comprises only two chambers 1200 and 1300. In this configuration,
the robot may be further adapted to reposition the substrate for
loading into chamber 1200 after the flipping step has been
performed (step 1906). In one embodiment, the robot 1402 may
further include a track 1412 that is adapted to translate the robot
between the output of chamber 1300 and the input of chamber 1200.
Thus, after lifting the substrate and retracting the rod 1408 into
the carriage 1410, the robot 1402 travels down the track 1412 and
lowers the substrate S onto input conveyor 318. The robot also
rotates rod 1408 until the unprocessed bottom of the substrate S is
face-up during this process. The substrate S is then ready for
transport back into chamber 1200.
[0118] In FIGS. 14A-14C another embodiment of an apparatus 1450 for
forming composite materials on a substrate S is shown. The
apparatus 1450 includes a carrier 1452 with an open central portion
1458. A lip 1454 extends around the inside perimeter of carrier
1452 and supports a substrate thereon. The lip 1454 has an inner
surface 1456 such that the open central portion 1458 is smaller in
dimension than the substrate S to support the substrate S thereon.
In one case the open central portion 1458 and lip 1454 is
configured so that both the top surface S.sub.Top and most of its
bottom surface S.sub.Bottom of the substrate S remain exposed. In
FIG. 14C a top deposition apparatus 1460 and a bottom deposition
apparatus 1462 are shown. The top deposition apparatus 1460
deposits material on the top surface S.sub.Top of the substrate S,
while the bottom deposition apparatus 1462 deposits material on the
bottom surface S.sub.Bottom of the substrate S. The deposition
apparatus 1460, 1462, in one embodiment, comprise one of the
deposition apparatuses shown with respect to chambers 1200 and
1300, which are discussed above. In one embodiment, one type of
chamber 1200 and 1300 is used to deposit the intrinsic and doped
silicon layers on both sides of the substrate as shown and
described with respect to FIG. 16F above. Thus, in this
configuration, the additional deposition chambers 1200' and 1300'
as well as robot 1402 in FIG. 14 are not required in the apparatus
of 1450. It should be noted that while only one open central
portion 1458 is shown with respect to apparatus 1450, several open
portions may be provided such that a plurality of substrates can be
supported while they are disposed in a larger version of the
carrier 1452. In addition, while open central portion 1458 is shown
as square in shape, other shapes are contemplated to support
substrates. Furthermore, while the open central portion 1458 is
shown in a carrier 1452, such an open central portion could be
provided in the belt of a continuous type apparatus which support
the substrates S.
[0119] In addition to the graphitic nanofilament based composite
materials described above, apparatus 300, 400, 2100 or 2200 may
also be used to form a different type of graphitic nanotube based
composite material, such as a porous Si--CNT electrode structure.
FIG. 23 illustrates a process sequence 2300 used to form the
composite material on a surface of a substrate S. The sequence
found in FIG. 23 corresponds to the stages depicted in FIGS.
20A-20D, which are discussed herein. The substrate S, which is
illustrated in FIG. 20A, may be a discrete substrate such as
substrates 301 and 303 in FIG. 3, or substrate S may be in the form
of a web 401 of material in FIG. 4A or 2201 in FIG. 22.
[0120] At step 2302, as shown in FIGS. 20B and 23, a substrate S is
positioned in a chamber and a layer 2002 of a silicon (Si) matrix
2004 with an Aluminum (Al) phase 2006 segregated therein is
deposited on the substrate S. In one embodiment, the chamber used
to deposit layer 2002 is a PVD chamber such as the chamber 302 in
FIG. 5A, the chambers 2108, 2114 or 2118 in FIG. 21, the chamber
2202 in FIG. 22, or any chamber configured to deposit layer 2002.
In some embodiments layer 2002 is sputter deposited, as will now be
described with respect to chamber 302 in FIG. 5A. In one
embodiment, the chamber 302 of FIG. 5A, is configured and adapted
to deposit the layer 2002 on a substrate S during step 2302, using
a sputtering deposition process. A target 508 of Al.sub.56Si.sub.44
is provided in the chamber 302. A power source 510 is connected to
the target 508 so that a cathodic DC and/or RF bias can be applied
to the target 508 so that the layer 2002 can be deposited on the
surface of the substrate S. The plasma generated by the bias
applied to the target 508 causes atoms from the target surface to
be removed, and be deposited on the exposed surfaces of the
substrate S. In one embodiment, the power supplied by the power
source is between about 100 W and about 200 W. In embodiments
requiring heating of the substrates, one or more heating elements
512 may be provided. The heating elements 512 may comprise
resistive heating elements, induction coils, or other heating
means. In one embodiment, the heating elements 512 maintain a
substrate temperature of between about 20.degree. C. and about
300.degree. C. (preferably below 150.degree. C.) in an inert
environment. As layer 2002 is sputtered onto the substrate S, the
aluminum phase 2006 is segregated in the silicon matrix 2004.
[0121] After the formation of layer 2002 on the substrate S,
process 2300 proceeds to step 2304. In step 2304, the aluminum is
etched out of the silicon matrix. In one embodiment, the etching of
the aluminum is performed using a wet etch process, such as a
process using a sodium hydroxide (NaOH) solution. The etch process
may be performed in the chamber 2204 of apparatus 2200, or in any
of the chambers of apparatus 300, 400 or 2100 that are configured
for etching. Suitable etching chambers are available from Applied
Materials, Inc., located in Santa Clara, Calif. The etching process
may be a dry etch process using an etching gas that contains
Cl.sub.2 or H.sub.2 in an RF inductively or capacitively coupled
plasma processing chamber. After the aluminum has been etched out
of the silicon matrix, the resulting structure is as is shown in
FIG. 20C. The substrate S includes a porous silicon layer 2008
disposed thereon. The porous silicon layer 2008 is formed by the
silicon matrix 2004 with the aluminum 2006 removed to form a
plurality of pores 2010.
[0122] Next, during step 2306, as illustrated in FIGS. 20D and 23,
carbon nanotubes (CNT) 2012 are deposited in the pores 2010 of
silicon matrix 2004. In one embodiment, the chamber 2206 of
apparatus 2200 in FIG. 22 is configured and adapted to deposit the
CNT's 2012 in the porous silicon matrix 2004 using a CVD process.
One such CVD chamber suitable for the growth of CNT's is the
chamber 800 of FIG. 8. The CNT's can be grown in the porous silicon
matrix 2004 by first depositing and heating catalyst material to
form nanoislands of catalyst material in the pores of silicon
matrix 2004 in the processing region 551 of the chamber 800. To
perform these functions, chamber 800 includes a showerhead 816 that
receives process gases from one or more gas sources 818, 820 via
valves 822, 824, respectively. The valves 822, 824 are controlled
by signals received from the support circuits 311 of the system
controller 305. The gases for forming the catalyst material on the
substrate and the gases for forming the CNT's may be sequentially
supplied, or may be simultaneously provided (co-flowed). By first
providing the gases required to form the catalyst, then heating the
catalyst to form the nanoislands, and following with the gases to
form the CNT's, CNT's that are relatively free of catalyst
particles can be formed. When the gases for forming the catalyst
and the CNT's are simultaneously provided, some amount of catalyst
particles may be present on the resulting CNT's. In some
applications, a small amount of contamination is acceptable. Thus,
the increased substrate throughput of a co-flowed method may be
desirable. To provide the necessary heat for forming the
nanoislands and CNT's, a heater power supply 802 receives control
signals from the support circuits 311 of the system controller 305,
to supply power to one or more of the heaters 804 (e.g., radiant
heat lamps or resistive heaters). In one embodiment of a plasma
enhanced deposition process, a plasma may be generated by
delivering power from a power source 826 to the showerhead 816
based on signals received from the support circuits 311 of the
system controller 305. In HWCVD embodiments, chamber 800 includes a
hot-wire, as described above with respect to FIG. 9.
[0123] After the deposition of CNT's in the silicon matrix, in some
embodiments, additional silicon is deposited at step 2308 of
process 2300, on the structure shown in FIG. 20D. The additional Si
may be deposited using HWCVD or other suitable processes in the
chamber 2208 of apparatus 2200, or in any other HWCVD enabled
chamber such as chambers 308, 312, 1200 or 1300, described above.
In one embodiment, the silicon containing layer is an amorphous
silicon layer that is between about 5 nm and about 200 nm thick. In
a further embodiment, the amorphous silicon layer is between about
13 nm and about 15 nm thick for a 15.mu. long tube. Referring to
FIG. 9, the chamber 308 is configured and adapted to deposit the
amorphous silicon on the Si/CNT matrix (2004 and 2012 of FIG. 20D)
using a HWCVD process. The HWCVD process generally uses a hot
filament (usually tungsten or tantalum) to "crack" the reactive gas
components (e.g., silane and hydrogen) into atomic radicals. The
hot filament is typically maintained at a surface temperature
significantly higher than 1500.degree. C. The reactive species,
after passing across the surface of the hot filament, are
transported through a processing region 552 to the substrate in a
low pressure ambient which enables a high deposition rate without
gas-phase particle formation. The chamber 308 includes a showerhead
916 that receives process gases from one or more gas sources 918,
920 via valves 922, 924, respectively. The valves 922, 924 are
controlled by signals received from the support circuits 311 of the
system controller 305. The gases supplied by the shower head 916,
for forming amorphous silicon on the Si/CNT matrix include, for
example, hydrogen (H.sub.2), silane (SiH.sub.4), disilane
(Si.sub.2H.sub.6), silicon tetrafluoride (SiF.sub.4), silicon
tetrachloride (SiCl.sub.4), and/or dichlorosilane
(SiH.sub.2Cl.sub.2). To assist in the CVD process, a resistive wire
928 is placed in close proximity to the substrate S. Electrical
current is supplied to the wire 928 by a power supply 926, based on
signals received from the support circuits 311 of the system
controller 305. The electrical current heats the wire 928 to form
the amorphous silicon on the Si/CNT matrix.
[0124] The structure shown in FIG. 20D is advantageously used in
the formation of an electrode structure for energy storage devices.
The Si--CNT nanocomposite formed by depositing a plurality of
nanotubes 2012 in the pores 2010 of the silicon matrix 2004,
provides several advantages. On such advantage is that the partial
exposure of the porous silicon allows for higher current capacity
with a charge capacity per weight of the resulting energy storage
device being in excess of 3600 mAh/g, or even 4200 mAh/g. Another
advantage is the ability of the structure to accommodate volume
expansion (such as thermal expansion) through the presence of the
pores 2010. In addition, the nature of the CNT's when incorporated
in the inventive structure provide for prolonged cycle life,
excellent structural integrity and excellent electronic conduction
pathways. The scalability of these nanostructures will also reduce
costs of the final products in both electric vehicle (EV) and
consumer electronic markets.
[0125] In FIGS. 17A-17C top views of composite material structures
are shown to illustrate exemplary shapes of the structures. In FIG.
17A, the composite material structure 1700 is shown to have a
rectangular shape, and in particular a square shape. In FIG. 17B,
the composite material structure 1702 is shown to have a elliptical
shape, and in particular a circular shape. In FIG. 17C, the
composite material structure 1704 is shown to have the shape of a
regular hexagon. It should be understood that these shapes are only
presented as examples, and the composite material structures may be
provided in any shape desired. In one embodiment, the shapes can be
formed by cutting the substrate(s) (such as web 401 in FIG. 4A)
into the desired shape after the deposition process. In other
embodiments, discrete substrates (such as 301 in FIG. 3) may be
provided in the desired shape prior to processing. In some
embodiments, the structures 1700, 1702 and 1704 have a large area
on the order of 5 m.sup.2 or greater. As described above, the
composite material structures 1700, 1702 and 1704 may be graphitic
nanofilament-based structures useful in forming electrical storage
devices, or they may be silicon-based structures for forming
photovoltaic (PV) devices, according to embodiments of the
invention.
[0126] While the foregoing is directed to embodiments of the
present invention, other and further embodiments of the invention
may be devised without departing from the basic scope thereof, and
the scope thereof is determined by the claims that follow.
* * * * *