U.S. patent application number 10/414787 was filed with the patent office on 2006-09-28 for methods for controlling formation of deposits in a deposition system and deposition methods including the same.
Invention is credited to Michael John O'Loughlin, Michael James Paisley, Joseph John Sumakeris.
Application Number | 20060216416 10/414787 |
Document ID | / |
Family ID | 34375145 |
Filed Date | 2006-09-28 |
United States Patent
Application |
20060216416 |
Kind Code |
A1 |
Sumakeris; Joseph John ; et
al. |
September 28, 2006 |
METHODS FOR CONTROLLING FORMATION OF DEPOSITS IN A DEPOSITION
SYSTEM AND DEPOSITION METHODS INCLUDING THE SAME
Abstract
A method for controlling parasitic deposits in a deposition
system for depositing a film on a substrate, the deposition system
defining a reaction chamber for receiving the substrate and
including a process gas in the reaction chamber and an interior
surface contiguous with the reaction chamber, includes flowing a
buffer gas between the interior surface and at least a portion of
the process gas to form a gas barrier layer such that the gas
barrier layer inhibits contact between the interior surface and
components of the process gas.
Inventors: |
Sumakeris; Joseph John;
(Apex, NC) ; Paisley; Michael James; (Garner,
NC) ; O'Loughlin; Michael John; (Chapel Hill,
NC) |
Correspondence
Address: |
MYERS BIGEL SIBLEY & SAJOVEC
PO BOX 37428
RALEIGH
NC
27627
US
|
Family ID: |
34375145 |
Appl. No.: |
10/414787 |
Filed: |
April 16, 2003 |
Current U.S.
Class: |
427/248.1 ;
118/715 |
Current CPC
Class: |
C23C 16/455 20130101;
C23C 16/4401 20130101; C23C 16/45519 20130101; C23C 16/488
20130101 |
Class at
Publication: |
427/248.1 ;
118/715 |
International
Class: |
C23C 16/00 20060101
C23C016/00 |
Goverment Interests
STATEMENT OF GOVERNMENT SUPPORT
[0001] The present invention was made, at least in part, with
government support under Office of Naval Research Contract No.
N00014-02-C-0302. The United States government may have certain
rights to this invention.
Claims
1. A method for controlling parasitic deposits in a deposition
system for depositing a film on a substrate, the deposition system
defining a reaction chamber for receiving the substrate and
including a process gas in the reaction chamber and an interior
surface contiguous with the reaction chamber, the method
comprising: providing a buffer gas to the reaction chamber at a
temperature greater than a temperature of the process gas in the
reaction chamber; and flowing the buffer gas to form a flowing gas
barrier layer between the interior surface and at least a portion
of the process gas, such that the flowing gas barrier layer
inhibits contact between the interior surface and components of the
process gas.
2. The method of claim 1 wherein the step of flowing the buffer gas
includes flowing the buffer gas along and in contact with the
interior surface.
3. The method of claim 1 including flowing the process gas through
the reaction chamber in a flow direction, and wherein the step of
flowing the buffer gas includes flowing the buffer gas through the
reaction chamber in the flow direction.
4. The method of claim 3 wherein the step of flowing the buffer gas
includes flowing the buffer gas through the reaction chamber at
substantially the same velocity as the process gas.
5. The method of claim 3 including introducing both the buffer gas
and the process gas into the reaction chamber at substantially the
same location along the flow direction so as to inhibit turbulence
in and mixing between their respective flows.
6. The method of claim 1 including flowing the process gas into the
reaction chamber through a process gas inlet, and wherein: the
process gas inlet has a smaller cross-sectional area than a
cross-sectional area of the reaction chamber so as to define a
buffer gas region in the reaction chamber; and the step of flowing
the buffer gas includes flowing the buffer gas into the buffer gas
region.
7. The method of claim 1 wherein the step of flowing the buffer gas
includes providing a substantially laminar flow of the buffer gas
along the interior surface.
8. The method of claim 1 wherein the interior surface overlies the
substrate.
9. (canceled)
10. The method of claim 1 including heating the buffer gas before
introducing the buffer gas into the reaction chamber.
11. The method of claim 1 including heating the buffer gas as the
buffer gas flows along the interior surface.
12. The method of claim 1 including heating the interior surface to
a temperature sufficient to promote sublimation of parasitic
deposits from the process gas that deposit on the interior
surface.
13. The method of claim 1 including inductively heating a susceptor
member adjacent the interior surface to thereby heat the interior
surface.
14. The method of claim 1 wherein the step of flowing the buffer
gas includes flowing the buffer gas through the reaction chamber at
a velocity of at least about 1 m/s.
15. The method of claim 14 wherein the step of flowing the buffer
gas includes flowing the buffer gas through the reaction chamber at
a velocity of between about 5 and 100 m/s.
16. The method of claim 1 wherein the buffer gas comprises a noble
gas.
17. The method of claim 16 wherein the noble gas is selected from
the group consisting of argon, helium, neon, krypton, radon, and
xenon.
18. The method of claim 1 wherein the buffer gas comprises H.sub.2,
N.sub.2, NH.sub.3 and/or air.
19. The method of claim 1 wherein the buffer gas includes an active
material capable of chemically inhibiting the deposition of
parasitic deposits on the interior surface and/or removing
parasitic deposits from the interior surface.
20. The method of claim 19 wherein the active material includes an
etchant.
21. The method of claim 20 wherein the etchant includes at least
one of HCl, Cl.sub.2 and a carbon-containing gas.
22. The method of claim 1 wherein the deposition system is a
chemical vapor deposition (CVD) system.
23. The method of claim 22 wherein the deposition system is a
hotwall CVD system.
24. The method of claim 1 wherein the substrate is a semiconductor
substrate.
25. The method of claim 24 wherein the substrate comprises a
material selected from the group consisting of SiC, sapphire, a
Group III nitride, silicon, germanium, and III-V and II-VI
compounds and interalloys.
26. The method of claim 1 wherein the process gas comprises a
reagent selected from the group consisting of SiH.sub.4,
C.sub.3H.sub.8, C.sub.2H.sub.4, Si.sub.2H.sub.6, SiCl.sub.4,
SiH.sub.2Cl.sub.2, SiCl.sub.3(CH.sub.3), NH.sub.3, trimethyl
gallium, and trimethyl aluminum.
27. The method of claim 1 wherein the process gas is adapted to
deposit onto the substrate a layer of material selected from the
group consisting of SiC, a Group III nitride, silicon, germanium,
and III-V and II-VI compounds and interalloys.
28-63. (canceled)
64. The method of claim 1 wherein the average temperature of the
buffer gas is at least 10.degree. C. hotter than the average
temperature of the process gas in the reaction chamber.
65. A method for controlling parasitic deposits in a deposition
system for depositing a film on a substrate, the deposition system
defining a reaction chamber for receiving the substrate and
including a process gas in the reaction chamber and an interior
surface contiguous with the reaction chamber, the method
comprising: flowing the process gas through the reaction chamber in
a flow directions wherein the flow direction is substantially
horizontal; and flowing a buffer gas through the reaction chamber
in the flow direction to form a flowing gas barrier layer between
the interior surface and at least a portion of the process gas,
such that the flowing gas barrier layer inhibits contact between
the interior surface and components of the process gas; wherein the
step of flowing the buffer gas includes flowing the buffer gas
through the reaction chamber at substantially the same velocity as
the process gas; and wherein the step of flowing the buffer gas
includes providing a substantially laminar flow of the buffer gas
along the interior surface to at least a location downstream of the
substrate.
66. The method of claim 65 including introducing both the buffer
gas and the process gas into the reaction chamber at substantially
the same location along the flow direction so as to inhibit
turbulence in and mixing between their respective flows.
67. The method of claim 65 including flowing the process gas into
the reaction chamber through a process gas inlet, and wherein: the
process gas inlet has a smaller cross-sectional area than a
cross-sectional area of the reaction chamber so as to define a
buffer gas region in the reaction chamber; and the step of flowing
the buffer gas includes flowing the buffer gas into the buffer gas
region.
68. (canceled)
69. A method for controlling parasitic deposits in a deposition
system for depositing a film on a substrate, the deposition system
defining a reaction chamber for receiving the substrate and
including a process gas in the reaction chamber and an interior
surface contiguous with the reaction chamber, the method
comprising: flowing a buffer gas to form a flowing gas barrier
layer between the interior surface and at least a portion of the
process gas, such that the flowing gas barrier layer inhibits
contact between the interior surface and components of the process
gas; and heating the interior surface to a temperature sufficient
to promote sublimation of parasitic deposits from the process gas
that deposit on the interior surface.
70. The method of claim 69 including flowing the process gas
through the reaction chamber in a flow direction, and wherein the
step of flowing the buffer gas includes flowing the buffer gas
through the reaction chamber in the flow direction.
71. The method of claim 69 including chemically inhibiting the
deposition of parasitic deposits on the interior surface and/or
removing parasitic deposits from the interior surface using an
active material included in the buffer gas.
72. The method of claim 71 wherein the active material includes an
etchant.
73. The method of claim 72 wherein the etchant includes at least
one of HCl, Cl.sub.2 and a carbon-containing gas.
74. (canceled)
75. The method of claim 65 wherein the substrate is a wafer having
an exposed surface, the method including positioning the wafer in
the reaction chamber such that the exposed surface is disposed
horizontally and parallel to the flow direction.
76. The method of claim 69 wherein the substrate is a semiconductor
wafer.
77. The method of claim 76 wherein the wafer comprises a material
selected from the group consisting of SiC, sapphire, a Group III
nitride, silicon, germanium, and III-V and II-VI compounds and
interalloys.
78. The method of claim 69 wherein the process gas comprises a
reagent selected from the group consisting of SiH.sub.4,
C.sub.3H.sub.8, C.sub.2H.sub.4, Si.sub.2H.sub.6, SiCl.sub.4,
SiH.sub.2Cl.sub.2, SiCl.sub.3(CH.sub.3), NH.sub.3, trimethyl
gallium, and trimethyl aluminum.
79. The method of claim 69 wherein the process gas is adapted to
deposit onto the wafer a layer of material selected from the group
consisting of SiC, a Group III nitride, silicon, germanium, and
III-V and II-VI compounds and interalloys.
Description
FIELD OF THE INVENTION
[0002] The present invention relates to deposition processes and
apparatus and, more particularly, to methods and apparatus for
depositing a film on a substrate.
BACKGROUND OF THE INVENTION
[0003] Deposition systems and methods are commonly used to form
layers such as relatively thin films on substrates. For example, a
chemical vapor deposition (CVD) reactor system and process may be
used to form a layer of semiconductor material such as silicon
carbide (SiC) on a substrate. CVD processes may be particularly
effective for forming layers with controlled properties,
thicknesses, and/or arrangements such as epitaxial layers.
Typically, in a deposition system, such as a CVD system, the
substrate is placed in a chamber and a process gas including
reagents or reactants to be deposited on the substrate is
introduced into the chamber adjacent the substrate. The process gas
may be flowed through the reaction chamber in order to provide a
uniform or controlled concentration of the reagents or reactants to
the substrate. Undesirably, the reagents or reactants may tend to
deposit on interior surfaces of the reaction chamber as well. Such
deposits may be referred to as "parasitic" deposits because they
remove reagents or reactants from the process.
[0004] With reference to FIG. 5, an exemplary conventional
deposition system 40 is shown therein and illustrates the process
by which deposits may be formed on unintended surfaces of a
reaction chamber. The system 40 is, for example, a flow through,
hot wall, CVD reactor. The system 40 has a top susceptor member 42
and a bottom susceptor member 44. The system 40 also has a top
liner 43 and a bottom liner 45 defining a reaction chamber 47
therebetween. A substrate 20, such as a wafer, is positioned in the
reaction chamber 47 and may be situated on an interior surface of a
platter (which may rotate), for example. A process gas is
introduced to the reaction chamber 47 at one end, flowed through
the reaction chamber 47 past the substrate 20, and finally
exhausted from the reaction chamber 47 at the opposite end. As
indicated by the arrows in the reaction chamber 47 as shown in FIG.
5, as the process gas flows through the reaction chamber 47 a
portion of the process gas may contact the substrate 20 as intended
and thereby deposit the reagents or reactants on the substrate 20
to form a layer thereon. However, as indicated by the arrows, a
portion of the process gas also contacts an interior surface or
ceiling 46 of the top liner 43 as well as interior surfaces of the
bottom liner 45 and side walls. As a result, parasitic deposits 50
and 52 of the reagents or reactants from the process gas tend to
form on the ceiling 46 and the bottom liner 45, respectively, as
well as on the sidewalls. The parasitic deposits on the ceiling 46
may be particularly harmful because they may dislodge and fall onto
the substrate 20 during processing, reducing the quality of the
formed layer. Moreover, the changing amount of the parasitic
deposits may introduce undesirable variations in temperature and
gas flow dynamics, thereby influencing the growth of the layer on
the substrate 20. Depletion of the process gas because of the
formation of the parasitic deposits may tend to waste reactants,
thereby reducing efficiency and growth rate.
[0005] Typically, the deposition process is managed to accommodate
the formation of parasitic deposits. The cumulative growth time may
be limited to reduce the impact of parasitic deposits on product
material. After a set time, the susceptor may be cleaned and
reconditioned before more production growth runs are attempted.
This procedure may limit both the possible length of any single
growth run and the number of runs of shorter duration between
cleaning cycles. Despite such efforts, parasitic deposits may
nonetheless negatively impact product material due to particle
formation, process variability and reduced reactant utilization
efficiency.
SUMMARY OF THE INVENTION
[0006] According to embodiments of the present invention, parasitic
deposits are controlled in a deposition system for depositing a
film on a substrate, the deposition system of the type defining a
reaction chamber for receiving the substrate and including a
process gas in the reaction chamber and an interior surface
contiguous with the reaction chamber. Such control is provided by
flowing a buffer gas to form a gas barrier layer between the
interior surface and at least a portion of the process gas such
that the gas barrier layer inhibits contact between the interior
surface and components of the process gas.
[0007] According to further embodiments of the present invention, a
deposition system for depositing a film on a substrate using a
process gas includes a reaction chamber adapted to receive the
substrate and the process gas. The system further includes an
interior surface contiguous with the reaction chamber. A buffer gas
supply system is adapted to supply a flow of a buffer gas between
the interior surface and at least a portion of the process gas such
that the flow of the buffer gas forms a gas barrier layer to
inhibit contact between the interior surface and components of the
process gas when the process gas is disposed in the reaction
chamber.
[0008] According to yet further embodiments of the present
invention, a deposition control system is provided for controlling
parasitic deposits in a deposition system for depositing a film on
a substrate, the deposition system of the type defining a reaction
chamber for holding the substrate and including a process gas in
the reaction chamber and an interior surface contiguous with the
reaction chamber. The deposition control system includes a buffer
gas supply system adapted to provide a flow of a buffer gas between
the interior surface and at least a portion of the process gas such
that the flow of the buffer gas forms a gas barrier layer to
inhibit contact between the interior surface and components of the
process gas.
[0009] According to further embodiments of the present invention, a
deposition system for depositing a film on a substrate includes a
reaction chamber adapted to receive the substrate and an interior
surface contiguous with the reaction chamber. A process gas is
disposed within the reaction chamber. A flow of a buffer gas is
disposed between the interior surface and at least a portion of the
process gas. The flow of the buffer gas forms a gas barrier layer
to inhibit contact between the interior surface and components of
the process gas.
[0010] According to further embodiments of the present invention, a
susceptor assembly for depositing a film on a substrate using a
process gas and a buffer gas each flowed in a flow direction
includes at least one susceptor member. The at least one susceptor
member defines a reaction chamber, a process gas inlet and a buffer
gas inlet. The reaction chamber is adapted to receive the substrate
and has a buffer gas region to receive the buffer gas. The reaction
chamber has a first cross-sectional area perpendicular to the flow
direction. The process gas inlet has a second cross-sectional area
perpendicular to the flow direction. The second cross-sectional
area is less than the first cross-sectional area. The buffer gas
inlet is adjacent the process gas inlet and is adapted to direct
the buffer gas into the buffer gas region of the reaction
chamber.
BRIEF DESCRIPTION OF THE DRAWINGS
[0011] FIG. 1 is a schematic view of a deposition system according
to embodiments of the present invention;
[0012] FIG. 2 is a perspective view of a susceptor assembly forming
a part of the deposition system of FIG. 1;
[0013] FIG. 3 is a cross-sectional view of the susceptor assembly
of FIG. 2 taken along the line 3-3 of FIG. 2, wherein a buffer gas
supply line, a substrate, a flow of buffer gas and a flow of
process gas are also shown;
[0014] FIG. 4 is a rear end elevational view of the susceptor
assembly of FIG. 2 and the substrate; and
[0015] FIG. 5 is a schematic view of a conventional deposition
system.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0016] The present invention now will be described more fully
hereinafter with reference to the accompanying drawings, in which
embodiments of the invention are shown. This invention may,
however, be embodied in many different forms and should not be
construed as limited to the embodiments set forth herein. Rather,
these embodiments are provided so that this disclosure will be
thorough and complete, and will fully convey the scope of the
invention to those skilled in the art. In the drawings, the
relative sizes of regions or layers may be exaggerated for clarity.
It will be understood that when an element such as a layer, region
or substrate is referred to as being "on" another element, it can
be directly on the other element or intervening elements may also
be present. In contrast, when an element is referred to as being
"directly on" another element, there are no intervening elements
present.
[0017] With reference to FIG. 1, a deposition system 101 according
to embodiments of the present invention is schematically shown
therein. The deposition system 101 may be a horizontal, hot wall,
flow through, CVD system as shown including a susceptor assembly
100, a quartz tube 180 defining a through passage 180A, an
electromagnetic frequency (EMF) generator 182 (for example,
including a power supply and an RF coil surrounding the tube 180)
and a process gas supply system 161. An insulative cover may be
provided about the susceptor assembly 100 in addition to or in
place of the quartz tube 180. The deposition system 101 further
includes a buffer gas supply system 171 in accordance with the
present invention. The deposition system 101 may be used to form a
layer or film on a substrate 20 (FIG. 3). While only a single
substrate 20 is illustrated in FIGS. 3 and 4, the system 101 may be
adapted to form films concurrently on multiple substrates 20.
[0018] The substrate 20 may be a wafer or other structure formed of
the same or a different material than that of the layer to be
deposited. The substrate 20 may be formed of, for example, SiC,
sapphire, a Group III nitride, silicon, germanium, and/or a III-V
or II-VI compound or interalloy, or the like. The substrate surface
upon which the film is deposited may be a base substrate or a first
or subsequent layer superimposed on a base substrate. For example,
the surface of the substrate 20 for receiving the deposited film
may be a layer previously deposited using the deposition system 101
or an alternative apparatus. As will be appreciated by those of
skill in the art in light of the present disclosure, embodiments of
the present invention may be advantageously utilized with
semiconductor materials other than those specifically mentioned
herein. As used herein, the term "Group III nitride" refers to
those semiconducting compounds formed between nitrogen and the
elements in Group IIIA of the periodic table, usually aluminum
(Al), gallium (Ga), and/or indium (In). The term also refers to
ternary and quaternary compounds such as AlGaN and AlInGaN. As is
well understood by those in this art, the Group III elements can
combine with nitrogen to form binary (e.g., GaN), ternary (e.g.,
AlGaN, AlInN), and quaternary (e.g., AlInGaN) compounds. These
compounds all have empirical formulas in which one mole of nitrogen
is combined with a total of one mole of the Group III elements.
Accordingly, formulas such as Al.sub.xGa.sub.1-xN where
0.ltoreq.x.ltoreq.1 are often used to describe them.
[0019] Generally, the process gas supply system 161 supplies a
process gas into and through the susceptor assembly 100 as
discussed below. The EMF generator 182 inductively heats the
susceptor assembly 100 to provide a hot zone in the susceptor
assembly 100 where deposition reactions take place. The process gas
continues through and out of the susceptor assembly 100 as an
exhaust gas which may include remaining components of the process
gas as well as reaction by-products, for example. Embodiments of
the present invention may be used in types of deposition systems
other than hot wall CVD systems. Other modifications to the systems
and methods of the present invention will be apparent to those of
ordinary skill in the art upon reading the description herein.
[0020] The process gas supply system 161 includes a supply 160 of
the process gas. The process gas includes one or more components
such as reagents, reactants, species, carriers and the like. One or
more of these components may be capable, alone or in combination
with one or more other components (which may also be present in the
process gas), of forming deposits on a surface such as the ceiling
or interior surface 120 (FIG. 3). Exemplary components that may
form or assist in forming deposits upon contacting the ceiling
surface 120 include SiH.sub.4, C.sub.3H.sub.8, C.sub.2H.sub.4,
Si.sub.2H.sub.6, SiCl.sub.4, SiH.sub.2Cl.sub.2,
SiCl.sub.3(CH.sub.3), NH.sub.3, trimethyl gallium, and trimethyl
aluminum. Where it is desired to form a SiC layer on a substrate,
the process gas may include precursor gases such as silane
(SiH.sub.4) and propane (C.sub.3H.sub.8) along with a carrier gas
such as purified hydrogen gas (H.sub.2). The process gas supply 160
may be provided from one or more pressurized containers of the
gases with flow control and/or metering devices as needed. The
process gas may be adapted to deposit a layer of SiC, a Group III
nitride, silicon, germanium, and/or a III-V and/or II-VI compound
or interalloy on the substrate 20.
[0021] The buffer gas supply system 171 includes a supply 170 of a
buffer gas fluidly connected to the susceptor assembly 100 by a
line 172. The buffer gas supply 170 may be provided from one or
more pressurized canisters of the gas or gases with flow control
and/or metering devices as needed. A heater 174 may be provided
along the line 172, in or at the susceptor assembly 100, or at the
buffer gas supply 160 for preheating the buffer gas.
[0022] The buffer gas may be any suitable gas. According to some
embodiments, the buffer gas is a gas having relatively low
diffusion rates for many or selected ones of the species or
components present in the process gas. According to some
embodiments, the buffer gas is a noble gas. The noble gas may
include argon, helium, neon, krypton, radon, or xenon. Other
suitable gases include H.sub.2, N.sub.2, NH.sub.3 or air. The
buffer gas may include or be substantially composed of a species
capable of chemically assisting in removing or inhibiting deposits
of reactants from the process gas. For example, in accordance with
some embodiments and particularly in the case of a process for
growing a layer of SiC on a substrate, the buffer gas includes an
etchant such as HCl, Cl.sub.2 and/or a carbon-containing gas such
as propane.
[0023] Turning to the susceptor assembly 100 in greater detail and
with reference to FIGS. 2 to 4 the susceptor assembly 100 includes
a top member 110, a pair of side members 130, and a bottom member
140. The susceptor assembly 100 extends from an entrance end 100A
to an exit end 100B. The members 110, 130, 140 define an entrance
opening 102 (at the end 100A) and an exit opening 104 (at the end
100B). The members 110, 130, 140 also define a reaction chamber 106
extending from a process gas inlet 102B to the opening 104.
According to some embodiments, the reaction chamber 106 has a
length of between about 0.1 and 1 meter, a width of between about
0.05 and 0.5 meter, and a height of between about 1 and 10 cm.
[0024] The top member 110 includes a core or susceptor body 112
covered (and preferably substantially fully surrounded) by a layer
114. The layer 114 includes the ceiling or interior surface 120
facing and contiguous with the reaction chamber 106.
[0025] The core 112 is preferably formed of a susceptor material
suitable to generate heat responsive to eddy currents generated
therein by the EMF generator 182, such materials and inductive
heating arrangements being well known to those of skill in the art.
The core 112 may be formed of graphite, and more preferably of high
purity graphite.
[0026] The layer 114 may be formed of a material having high purity
and which is able to withstand the process temperatures (typically
in the range of 1500 to 1800.degree. C. for SiC deposition). The
layer 114 may be formed of, for example, SiC or a refractory metal
carbide such as TaC, NbC and/or TiC. The layer 114 may be applied
to the core 112 by any suitable method. Preferably, the layer 114
is a dense, impervious coating and has a thickness of at least
about 10 .mu.m, and more preferably, between about 20 .mu.m and 100
.mu.m.
[0027] The top member 110 further includes a downwardly stepped
portion 116 adjacent the opening 102. The stepped portion 116 and
the underlying portion of the liner 152 define the process gas
inlet 102B and a process gas inlet passage 102A extending from the
opening 102 to the process gas inlet 102B. The step portion 116
also defines a buffer gas region 106A (FIG. 3) in the upper portion
of the reaction chamber 106.
[0028] A plurality of passages 117 (one shown in FIG. 3) extend
through the top member 110 and terminate at a respective port 176
(see FIGS. 3 and 4). A common feed inlet 117A (FIGS. 2 and 3) is
provided for connecting the buffer gas line 172 to the passages 117
which may be interconnected in a manifold arrangement by a lateral
passage 117B (FIG. 3). Alternatively, separate lines and/or inlets
may be provided for some or each of the ports 176. The passages
117, the inlet 117A and the ports 176 may be formed in the top
member 110 by any suitable method such as drilling or molding.
[0029] The bottom member 140 includes a core 142 covered by a
coating or layer 144. Suitable materials and methods for forming
the core 142 and the layer 144 are as described above for the core
112 and the layer 114. The side members 130 similarly include
respective cores (not shown) and covering layers which may be
formed of the same materials and using the same methods as
described above for the core 112 and the layer 114.
[0030] A liner or liners 152 may overlie the bottom member 140 as
shown in FIGS. 3 and 4. The liner 152 may be formed of SiC or SiC
coated graphite, for example, as disclosed in U.S. patent
application Ser. No. 10/017,492, filed Oct. 20, 2001, the
disclosure of which is incorporated herein by reference.
[0031] A platter 154 or the like may be situated between the bottom
member 140 and the substrate 20 to support the substrate 20.
According to some embodiments, the platter 154 may be rotatively
driven by a suitable mechanism (not shown). For example, the system
may include a gas-driven rotation system as described in
Applicant's U.S. application Ser. No. 09/756,548, titled Gas Driven
Rotation Apparatus and Method for Forming Silicon Carbide Layers,
filed Jan. 8, 2001, and/or as described in Applicant's U.S.
application Ser. No. 10/117,858, titled Gas Driven Planetary
Rotation Apparatus and Methods for Forming Silicon Carbide Layers,
filed Apr. 8, 2002, the disclosures of which are hereby
incorporated herein by reference in their entireties.
Alternatively, the platter 154 may be stationary. The platter 154
may be adapted to hold one or multiple substrates 20. The platter
154 may be formed of any suitable material such as SiC coated
graphite, solid SiC or solid SiC alloy. The platter 154 may be
omitted such that the substrate rests on the bottom member 140, the
liner 152, or other suitable support.
[0032] In use, the process gas supply system 161 supplies a flow of
the process gas to the reaction chamber 106 through the inlet
opening 102. The process gas P flows generally in a flow direction
R (FIG. 3). The arrows labeled P in FIG. 3 indicate the general
flow path of the process gas and the reagents therein. As shown,
the process gas and the reagents therein contact the substrate 20
to form the desired layer (e.g., an epilayer) on the exposed
surface of the substrate 20.
[0033] Concurrently, the buffer gas supply system 171 supplies or
inserts a flow of the buffer gas into the buffer gas region 106A of
the reaction chamber 106 through the ports 176 such that the buffer
gas B flows through the reaction chamber 106 generally in the flow
direction R. The arrows labeled B in FIG. 3 indicate the general
flow path of the flow of buffer gas. The buffer gas B flows in the
buffer gas region 106A along the ceiling or interior surface 120 so
as to form a barrier layer 178 of flowing buffer gas extending
upwardly from the dashed line of FIG. 3 to the ceiling surface
120.
[0034] The barrier layer 178 serves to inhibit or impede the
movement of the process gas P and components thereof from moving
into contact with the ceiling surface 120 where reagents or
reactants of the process gas P might otherwise form deposits. Below
the barrier layer 178, the process gas P is permitted to flow in
the normal manner to, over and beyond the substrate 20. In this
manner, the process gas P and the deposition system 101 form the
desired layer(s) on the exposed surface(s) of the substrate 20. The
flow of buffer gas B may also serve to push the reactant stream of
the process gas P toward the substrate 20, thereby accelerating the
growth rate.
[0035] As discussed in more detail below, according to some
embodiments, the buffer gas B flow is maintained as a substantially
laminar flow. As long as the flow of the buffer gas B is laminar,
the only way reagents or other components from the process gas P
can reach the ceiling surface is by diffusing from the process gas
P flow and through the barrier gas B flow. In general, the distance
S a diffusing species will traverse during time span of t follows
the relationship S.apprxeq. {square root over (Dt)}, where D is the
diffusion rate. In the present case, t is the transit time of
species through the reaction chamber 106. The transit distance of
concern will depend on to what lengthwise extent the operator or
designer desires to inhibit deposits downstream of the process gas
inlet 102B. In most cases, it will be deemed sufficient to inhibit
or prevent the formation of deposits on the ceiling surface 120 up
to the downstream edge of the substrate 20. In the susceptor
assembly 100 illustrated in FIG. 3, this transit distance is
indicated by the distance L. The transit time can generally be
determined as follows: t .apprxeq. L ( M .rho. .times. .times. A )
##EQU1## Where: L=Length of susceptor M=Mass flow rate
.rho.=Average density of gas within susceptor, determined by
pressure, temperature and gas composition. A=Cross sectional area
of susceptor opening. In order for the barrier layer 178 to prevent
all diffusion of the components of the process gas P, the thickness
S of the barrier layer 178 (which may correspond generally to the
height I of the step portion 116) should satisfy: S .gtoreq. Dt =
DL ( M .rho. .times. .times. A ) ##EQU2##
[0036] It will be appreciated by those of ordinary skill in the art
upon reading the description herein that, in accordance with the
present invention, it is not necessary to completely prevent all
components of the process gas P from contacting the ceiling surface
120 as may be accomplished by providing fully laminar flow of the
buffer gas B and a barrier layer 178 having a thickness S
satisfying the foregoing criteria. Rather, the system 101 may be
designed to allow some turbulence and/or have a barrier layer
thickness S less than that necessary to preclude all deposits. In
this manner, for example, the system 101 may provide a significant
reduction in parasitic deposits while allowing some deposits to
occur. According to some embodiments, the rate of formation of
parasitic deposits on the ceiling surface 120 is preferably no more
than one half the growth rate on the substrate 20 and more
preferably no more than one quarter the growth rate on the
substrate 20.
[0037] The barrier layer thickness S may be increased to provide an
additional margin of protection for the ceiling surface 120 or to
compensate for turbulence in the buffer gas flow B. The height of
the buffer gas region 106A may be greater than, less than, or the
same as the optimal thickness S of the barrier layer 178.
[0038] Further, various process parameters may be considered in
determining the degree of laminarity of the buffer gas B flow and
the distance S needed to obtain the desired reduction or prevention
of deposits on the ceiling surface 120. For example, at typical SiC
epilayer growth temperatures (i.e., in the range of about 1500 to
1800.degree. C.), simultaneous etch and deposition processes may
take place. Therefore, for a given growth condition, there may
exist a critical minimum reagent supply rate necessary to stabilize
the surface (in this case, the ceiling surface 120). A reagent
supply rate above critical will result in growth of parasitic
deposits on the ceiling surface 120 while a supply rate below
critical will result in etching of parasitic deposits from the
ceiling surface 120. Accordingly, even if the reagent flux to the
ceiling were only reduced to the critical supply rate, then
essentially no net deposition would occur on the ceiling.
[0039] Preferably, the deposition system 101 is adapted to maintain
the flow of the buffer gas B and the flow of the process gas P as a
laminar flow to at least a location downstream of the substrate 20,
and more preferably, throughout the reaction chamber 106, to reduce
or prevent mixing or turbulence between the flows that may promote
transport of the process gas P through the barrier layer 178.
[0040] The relative dimensions and configurations of the reaction
chamber 106, the process gas inlet 102B, and the buffer gas ports
176 may be selected to promote laminar flow. According to some
embodiments and as illustrated (see FIGS. 3 and 4), the process gas
inlet 102B is smaller in cross-section (i.e., generally
perpendicular to the flow direction R of the gases, and as shown in
FIG. 4) than the reaction chamber 106 so that a remaining space
(i.e., the buffer gas region 106A) is available in the reaction
chamber 106 for insertion of the buffer gas B into the reaction
chamber 106 without inserting the buffer gas B into the process gas
or into the unmodified flow path of the process gas P.
[0041] In the illustrated embodiment, the provision of the stepped
portion 116 may facilitate laminar flow. According to some
embodiments of the present invention, the sum of the height G of
the opening 102 and the height I of the step portion 116 is
substantially the same as the full height H of the reaction chamber
106 (see FIG. 3). Preferably, the widths of the process gas inlet
102B, the step portion 116, and the reaction chamber 106 are
substantially the same so that the cross-sectional area (i.e.,
generally perpendicular to the flow direction R of the gases, and
as shown in FIG. 4) of the reaction chamber 106 is substantially
the same as the combined cross-sectional area of the process gas
inlet 102B and the step portion 116. In this manner, the flow of
the process gas P and the flow of the buffer gas B enter the
reaction chamber 106, in parallel, at substantially the same axial
location in the reaction chamber 106 along the direction of flow R
of the gases P, B. Because the buffer gas region 106A is provided
above the natural flow path of the process gas P, the buffer gas B
can be inserted into the reaction chamber 106 without substantially
displacing the process gas P. As a result, turbulence and mixing of
the gas flows that might otherwise be created by initially
introducing the buffer gas B into the path of the process gas P may
be avoided. The height I of the step portion 116 is preferably
between about 5 and 25% of the height H of the reaction chamber
106.
[0042] According to some embodiments and as illustrated, the
reaction chamber 106 has a substantially uniform height H along
substantially its full length. In this case, the reaction chamber
106 may have a substantially uniform cross-sectional area along its
full length. This configuration may serve to promote the integrity
of the boundary layer between the flow of the process gas P and the
flow of the buffer gas B. The height H of the reaction chamber 106
is preferably between about 0.5 and 5 cm. According to further
embodiments, the height H is not uniform, but rather the ceiling is
tilted or curved in either direction to improve uniformity or
efficiency of the process. In this case, the cross-sectional area
of the reaction chamber 106 may vary, uniformly or
non-uniformly.
[0043] While a step portion 116 and ports 176 are shown and
described, other features and geometries may be used to control the
flow of the buffer gas B so as to control turbulence in the flow of
the buffer gas B. The configurations of the process gas inlet
passage 102A, the process gas inlet 102B, the inlet opening 102,
the buffer gas passages 117, and/or the buffer gas inlets 176 may
be adapted to promote laminar flow of and between the process gas P
and the buffer gas B. The axial length K (FIG. 3) of the process
gas inlet passage 102A may be extended to reduce turbulence in the
process gas P entering through the inlet 102 before the process gas
P enters the reaction chamber 106 through the process gas inlet
102B. However, because the passage 102A is within the susceptor
assembly 100 and is thus heated, reactions may occur which tend to
form deposits or the ceiling surface of the passage 102A. For this
reason, it may be desirable to minimize the length of the passage
102A. The buffer gas ports 176 may be replaced with one or more
suitably configured slots.
[0044] According to some embodiments, the velocity of the process
gas P and the velocity of the buffer gas B through the reaction
chamber 106 are substantially the same. For SiC epitaxy, in
accordance with some embodiments of the present invention where the
length of the reaction chamber 106 is between about 0.1 and 1 m,
the velocity of the gases P, B is at least about 1 m/s, and
preferably between about 5 and 100 m/s to limit the time for
diffusion of the process gas P through the barrier layer 178.
[0045] In order to further promote the integrity of the barrier
layer 178 and thereby inhibit diffusion of the process gas P
therethrough, the buffer gas B may be provided at a temperature
greater than the temperature of the adjacent process gas P. The
hotter buffer gas B will naturally segregate from the relatively
cooler process gas P along the ceiling surface 120 because of the
relative buoyancy of the hotter gas. According to some embodiments,
the average temperature of the buffer gas B is at least 10.degree.
C. hotter than the average temperature of the process gas in the
reaction chamber 106.
[0046] The buffer gas B may be heated using the heater 174.
Additionally or alternatively, the buffer gas B may be heated by
heating the ceiling surface 120 to a temperature greater than the
temperature or temperatures of the lower surfaces contiguous with
the reaction chamber 106 which the process gas P contacts, i.e., by
providing a temperature differential between the ceiling surface
120 and the floor, the platter 154 and/or other surfaces contacting
the process gas P. That is, the temperature profile in the reaction
chamber 106 may be deliberately and selectively maintained as
spatially non-uniform (e.g., as a gradient) extending from the
ceiling surface 120 to the lower and/or other surfaces contiguous
with the reaction chamber 106. This may be accomplished, for
example, by providing greater thermal insulation between the core
142 and the surfaces of the liner 152, the platter 154 and the
substrate 20 contacting the process gas P than is provided between
the core 112 and the ceiling surface 120. For example, the liner
152 and the layer 114 may be suitably relatively constructed (e.g.,
by selection of material and thickness) to provide desired relative
insulative effects. Because the top member 110 and the bottom
member 140 are inductively heated, primarily by the resistivity of
their graphite cores 112, 142, the temperatures of the surfaces of
the liner 152, the platter 154 and the substrate 20 contacting the
process gas P are thereby reduced as compared to the temperature of
the ceiling surface 120. The buffer gas B is thus heated at a
faster rate than the process gas P. To promote conduction of heat
from the core 112 to the ceiling surface 120, the layer 114 may be
directly coated on the core 112 to form a relatively monolithic or
unitary top member 110.
[0047] Alternatively or additionally, a temperature differential
can be created or increased between the ceiling surface 120 and the
other surfaces such as the liner 152 or other lower surfaces by
forming the layer 114 (and thus the ceiling surface 120) from a
material having a lower emissivity than the material of the layer
144 and/or of the liner 152 or other surfaces contacting the
process gas P stream. For example, the layer 114 may be formed of
TaC (which has an emissivity of about 0.4) and the liner 152 and
the platter 154 may be formed of SiC (which has an emissivity of
about 0.9). As a result, the layer 114, and therefore the ceiling
surface 120, will lose comparatively less heat from radiation,
resulting in a higher temperature at the ceiling surface 120.
Moreover, parasitic deposits may tend to adhere less well to TaC or
other metal carbides than to SiC. As a further advantage, in many
applications, a TaC coating will typically be more durable than a
SiC coating, which may serve to prolong the service life of the
part.
[0048] In addition to the barrier effect, the ceiling surface 120
can be heated, for example, in one or more of the manners described
above, such that it is sufficiently hotter than the other
components in the reaction chamber 106 to induce etching or
sublimation of deposits on the ceiling surface 120. That is,
deposits on the relatively hot ceiling surface 120 will tend to
etch away or sublime and return to the buffer gas B or the process
gas P rather than remaining on the ceiling surface 120.
[0049] As discussed above, the buffer gas B may consist of or
include HCl or other active gas to chemically impede the formation
of parasitic deposits on the ceiling surface 120 and/or to remove
such deposits.
[0050] Because the growth of parasitic deposits on the ceiling
surface 120 is inhibited or suppressed, greater volumes of process
gas P can be flowed through the reaction chamber 106 before
cleaning or the like is required. Deposition systems and methods in
accordance with the present invention may greatly extend the
permissible growth time and layer thickness while improving
repeatability and efficiency. Moreover, the reduction in the rate
of deposit formation may allow the use of lower ceiling heights,
which allows for more efficient use of the process gas and improved
thermal uniformity.
[0051] While the foregoing deposition system 101 and methods are
described as relating to a horizontal, hot wall, CVD, flow through
deposition process, various aspects of the present invention may be
used in other types of deposition systems and processes. While
particular embodiments have been described with reference to "top",
"bottom" and the like, other orientations and configurations may be
employed in accordance with the invention. For example, the
deposition system and process may be a cold wall and/or
non-horizontal flow through system and process. The deposition
system and process may be a vapor phase epitaxy (VPE), liquid phase
epitaxy (LPE), or plasma enhanced CVD (PECVD) deposition system and
process rather than a CVD system or process. The present invention
is not limited to providing a barrier layer for a ceiling surface
of a reaction chamber. The buffer gas supply system may be modified
to provide a buffer gas flow along one or more surfaces in addition
to or instead of the ceiling surface. For example, the buffer gas
supply system may be employed to inhibit parasitic deposits from
forming on a lower liner or other surfaces upstream from the
substrate 20, or in other locations where parasitic deposits are
problematic.
[0052] While the systems and methods have been described in
relation to processes for depositing layers on substrates such as
semiconductor wafers, the present invention may be employed in
processes for depositing layers or the like on other types of
substrates. The systems and methods of the present invention may be
particularly useful in processes for forming an epitaxial layer on
a substrate.
[0053] Various other modifications may be made in accordance with
the invention. For example, the reaction chamber may be closed at
one or both ends rather than providing a through passage. Heating
systems may be used other than or in addition to inductive
heating.
[0054] As used herein a "system" may include one or multiple
elements or features. In the claims that follow, the "deposition
system", the "deposition control system", the "buffer gas supply
system", the "process gas supply system" and the like are not
limited to systems including all of the components, aspects,
elements or features discussed above or corresponding components,
aspects, elements or features.
[0055] The foregoing is illustrative of the present invention and
is not to be construed as limiting thereof. Although a few
exemplary embodiments of this invention have been described, those
skilled in the art will readily appreciate that many modifications
are possible in the exemplary embodiments without materially
departing from the novel teachings and advantages of this
invention. Accordingly, all such modifications are intended to be
included within the scope of this invention. Therefore, it is to be
understood that the foregoing is illustrative of the present
invention and is not to be construed as limited to the specific
embodiments disclosed, and that modifications to the disclosed
embodiments, as well as other embodiments, are intended to be
included within the scope of the invention.
* * * * *