U.S. patent application number 12/572245 was filed with the patent office on 2010-04-08 for vapor phase epitaxy system.
This patent application is currently assigned to VEECO COMPOUND SEMICONDUCTOR, INC.. Invention is credited to Eric Armour, Joshua Mangum, William E. Quinn.
Application Number | 20100086703 12/572245 |
Document ID | / |
Family ID | 41429649 |
Filed Date | 2010-04-08 |
United States Patent
Application |
20100086703 |
Kind Code |
A1 |
Mangum; Joshua ; et
al. |
April 8, 2010 |
Vapor Phase Epitaxy System
Abstract
A vapor phase epitaxy system includes a platen that supports
substrates for vapor phase epitaxy and a gas injector. The gas
injector injects a first precursor gas into a first region and
injects a second precursor gas into a second region. At least one
electrode is positioned in the first region so that first precursor
gas molecules flow proximate to the electrode. The at least one
electrode is positioned to be substantially isolated from a flow of
the second precursor gas. A power supply is electrically connected
to the at least one electrode. The power supply generates a current
that heats the at least one electrode so as to thermally activate
at least some of the first precursor gas molecules flowing
proximate to the at least one electrode.
Inventors: |
Mangum; Joshua; (Baskin
Ridge, NJ) ; Quinn; William E.; (Whitehouse, NJ)
; Armour; Eric; (Pennington, NJ) |
Correspondence
Address: |
RAUSCHENBACH PATENT LAW GROUP, LLC
P.O. BOX 387
BEDFORD
MA
01730
US
|
Assignee: |
VEECO COMPOUND SEMICONDUCTOR,
INC.
Somerset
NJ
|
Family ID: |
41429649 |
Appl. No.: |
12/572245 |
Filed: |
October 1, 2009 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
61195093 |
Oct 3, 2008 |
|
|
|
Current U.S.
Class: |
427/569 ;
118/723E |
Current CPC
Class: |
C23C 16/483 20130101;
C23C 16/45551 20130101; C30B 29/406 20130101; C30B 25/105 20130101;
C23C 16/303 20130101; C23C 16/511 20130101; C30B 29/403
20130101 |
Class at
Publication: |
427/569 ;
118/723.E |
International
Class: |
C23C 16/50 20060101
C23C016/50; C23C 16/00 20060101 C23C016/00; H05H 1/24 20060101
H05H001/24 |
Claims
1. A vapor phase epitaxy system comprising: a. a platen that
supports substrates for vapor phase epitaxy; b. a gas injector
comprising a first region that is coupled to a first precursor gas
source and a second region that is coupled to a second precursor
gas source, the gas injector injecting the first precursor gas into
the first region and injecting the second precursor gas into the
second region; c. at least one electrode that is positioned in the
first region so that first precursor gas molecules flow proximate
to the at least one electrode and positioned to be substantially
isolated from a flow of the second precursor gas; and d. a power
supply having an output that is electrically connected to the at
least one electrode, the power supply generating a current that
heats the at least one electrode so as to thermally activate at
least some of the first precursor gas molecules flowing proximate
to the at least one electrode.
2. The system of claim 1 wherein the gas injector comprises liquid
cooling channels to control a temperature of the gas injector.
3. The system of claim 1 wherein the first and second regions in
the gas injector comprise a plurality of first and second regions
that alternate across at least a portion of the gas injector.
4. The system of claim 1 wherein at least one of the first and
second precursor gases flows through the gas injector in a
direction that is perpendicular to the platen that supports the
substrates.
5. The system of claim 1 wherein at least one of the first and
second precursor gases flows through the gas injector in a
direction that is parallel to the platen that supports the
substrates.
6. The system of claim 1 wherein one of the first and second
precursor gases flow through the gas injector in a direction that
is substantially parallel to the platen that supports the
substrates and the other of the first and second precursor gases
flow through the gas injector in a direction that is substantially
perpendicular to the platen that supports the substrates.
7. The system of claim 1 wherein the gas injector flows the first
and second precursor gases over the platen with a laminar flow.
8. The system of claim 1 wherein the gas injector flows the first
and second precursor gas over the platen with a non-laminar
flow.
9. The system of claim 1 wherein the gas injector further comprises
a baffle that physically separates the first and the second
regions.
10. The system of claim 9 wherein the baffle is shaped to preserve
laminar flow of the first and second precursor gases across the
platen that supports the substrates.
11. The system of claim 9 wherein the baffle is formed of a
non-thermally conductive material.
12. The system of claim 1 wherein the at least one electrode is
formed of a catalytic material.
13. The system of claim 12 wherein the catalytic material comprises
at least one of tungsten, rhenium, and molybdenum.
14. The system of claim 1 further comprising a catalytic electrode
positioned proximate to the platen.
15. The system of claim 1 wherein the electrode is formed in a
non-linear structure.
16. The system of claim 1 wherein the electrode is oriented in a
plane of the gas injector.
17. The system of claim 1 wherein the electrode is oriented in a
plane that is perpendicular to the gas injector.
18. The system of claim 1 wherein the electrode is positioned
proximate to the platen.
19. A method of vapor phase epitaxy, the method comprising: a.
injecting a first precursor gas for vapor phase epitaxy in a first
region proximate to a platen supporting substrates; b. injecting a
second precursor gas for vapor phase epitaxy in a second region
proximate to the platen supporting substrates; c. positioning an
electrode in a flow of the injected first precursor gas; d.
isolating the electrode from a flow of the injected second
precursor gas; and e. activating the first precursor gas with the
electrode.
20. The method of claim 19 wherein the activating the first
precursor gas generates first precursor gas radicals.
21. The method of claim 19 wherein the activating the first
precursor gas comprises energizing the electrode to thermally
activate the first precursor gas.
22. The method of claim 19 wherein the activating the first
precursor gas comprises catalytically activating the first
precursor gas with a catalytic electrode material.
23. The method of claim 19 wherein the injecting the first
precursor gas comprises injecting a hydride precursor gas and the
injecting the second precursor gas comprises injecting an
organometalic precursor gas.
24. The method of claim 23 further comprising injecting a halide
precursor gas.
25. The method of claim 19 wherein the injecting the first
precursor gas for vapor phase epitaxy comprises injecting a hydride
precursor gas and the injecting the second precursor gas for vapor
phase epitaxy comprises injecting an metal halide precursor
gas.
26. The method of claim 19 wherein the injecting the first and
second precursor gases for vapor phase epitaxy comprise injecting
the first and second precursor gases parallel to the platen
supporting substrates.
27. The method of claim 19 wherein the injecting the first and
second precursor gases for vapor phase epitaxy comprise injecting
the first and second precursor gases perpendicular to the platen
supporting substrates.
28. The method of claim 19 wherein the injecting the first and
second precursor gases for vapor phase epitaxy comprise injecting
one of the first and second precursor gases perpendicular to the
platen supporting substrates and injecting the other of the first
and second precursor gases parallel to the platen supporting
substrates.
29. The method of claim 19 wherein the injecting the first and
second precursor gases comprise injecting the first and second
precursor gases in a plurality of alternating first and second
regions wherein the first precursor gas is injected in the first
regions and the second precursor gas is injected in the second
regions of the plurality of alternating first and second
regions.
30. The method of claim 19 wherein the isolating the electrode from
a flow of the injected second precursor gas comprises baffling the
electrode.
31. The method of claim 30 wherein the baffling preserves laminar
flow over the platen supporting substrates.
32. A vapor phase epitaxy system comprising: a. a means for
injecting a first precursor gas for vapor phase epitaxy in a first
region proximate to a platen supporting substrates; b. a means for
injecting a second precursor gas for vapor phase epitaxy in a
second region proximate to the platen supporting substrates; c. an
electrode positioned in a flow of the injected first precursor gas;
d. a means for isolating the electrode from a flow of the injected
second precursor gas; and e. a means for activating the first
precursor gas with the electrode.
33. The system of claim 32 wherein the means for activating the
first precursor gas with the electrode comprises energizing the
electrode.
34. The system of claim 32 wherein the means for activating the
first precursor gas with the electrode comprises forming a
catalytic reaction with the electrode.
35. The system of claim 32 wherein the means for isolating the
electrode from a flow of the injected second precursor gas
comprises baffling the electrode.
36. A method of vapor phase epitaxy, the method comprising: a.
injecting a first precursor gas comprising H.sub.2 and N.sub.2 for
vapor phase epitaxy in a first region proximate to a platen
supporting substrates; b. injecting a second precursor gas for
vapor phase epitaxy in a second region proximate to the platen
supporting substrates; c. positioning a catalytic electrode in a
flow of the injected first precursor gas; d. isolating the
electrode from a flow of the injected second precursor gas; and e.
energizing the catalytic electrode to activate the first precursor
gas to generate at least one of NH.sub.2 and NH.
37. The method of claim 36 further comprising positioning a second
catalytic electrode in thermal communication with the platen
supporting substrates that is not energized.
Description
RELATED APPLICATION SECTION
[0001] This application claims priority to U.S. Provisional Patent
Application Ser. No. 61/195,093 filed Oct. 3, 2008, entitled
"Chemical Vapor Deposition with Energy Input," the entire
application of which is incorporated herein by reference.
[0002] The section headings used herein are for organizational
purposes only and should not to be construed as limiting the
subject matter described in the present application in any way.
INTRODUCTION
[0003] Vapor phase epitaxy (VPE) is a type of chemical vapor
deposition (CVD) which involves directing one or more gases
containing chemical species onto a surface of a substrate so that
the reactive species react and form a film on the surface of the
substrate. For example, VPE can be used to grow compound
semiconductor material on a substrate. The substrate is typically a
crystalline material in the form of a disc, which is commonly
referred to as a "wafer." Materials are typically grown by
injecting at least a first and a second precursor gas into a
process chamber containing the crystalline substrate.
[0004] Compound semiconductors, such as III-V semiconductors, can
be formed by growing various layers of semiconductor materials on a
substrate using a hydride precursor gas and an organometalic
precursor gas. Metalorganic vapor phase epitaxy (MOVPE) is a vapor
deposition method that is commonly used to grow compound
semiconductors using a surface reaction of metalorganics and metal
hydrides containing the required chemical elements. For example,
indium phosphide could be grown in a reactor on a substrate by
introducing trimethylindium and phosphine. Alternative names for
MOVPE used in the art include organometallic vapor phase epitaxy
(OMVPE), metalorganic chemical vapor deposition (MOCVD), and
organometallic chemical vapor deposition (OMCVD). In these
processes, the gases are reacted with one another at the surface of
a substrate, such as a sapphire, Si, GaAs, InP, InAs or GaP
substrate, to form a III-V compound of the general formula
In.sub.XGa.sub.YAl.sub.ZN.sub.AAs.sub.BP.sub.CSb.sub.D, where X+Y+Z
equals approximately one, and A+B+C+D equals approximately one, and
each of X, Y, Z, A, B, C, and D can be between zero and one. In
some instances, bismuth may be used in place of some or all of the
other Group III metals.
[0005] Compound semiconductors, such as III-V semiconductors, can
also be formed by growing various layers of semiconductor materials
on a substrate using a hydride or a halide precursor gas process.
In one halide vapor phase epitaxy (HVPE) process, Group III
nitrides (e.g., GaN, AN) are formed by reacting hot gaseous metal
chlorides (e.g., GaCl or AlCl) with ammonia gas (NH.sub.3). The
metal chlorides are generated by passing hot HCl gas over the hot
Group III metals. All reactions are done in a temperature
controlled quartz furnace. One feature of HVPE is that it can have
a very high growth rate, up to 100 .mu.m per hour for some
state-of-the-art processes. Another feature of HVPE is that it can
be used to deposit relatively high quality films because films are
grown in a carbon free environment and because the hot HCl gas
provides a self-cleaning effect.
[0006] In these processes, the substrate is maintained at an
elevated temperature within a reaction chamber. The precursor gases
are typically mixed with inert carrier gases and are then directed
into the reaction chamber. Typically, the gases are at a relatively
low temperature when they are introduced into the reaction chamber.
As the gases reach the hot substrate, their temperature, and hence
their available energy for reaction, increases. Formation of the
epitaxial layer occurs by final pyrolysis of the constituent
chemicals at the substrate surface. Crystals are formed by a
chemical reaction and not by physical deposition processes. Growth
occurs in the gas phase at moderate pressures. Consequently VPE is
a desirable growth technique for thermodynamically metastable
alloys. Currently, VPE is commonly used for manufacturing laser
diodes, solar cells, and LEDs.
BRIEF DESCRIPTION OF THE DRAWINGS
[0007] The present teaching, in accordance with preferred and
exemplary embodiments, together with further advantages thereof, is
more particularly described in the following detailed description,
taken in conjunction with the accompanying drawings. The skilled
person in the art will understand that the drawings, described
below, are for illustration purposes only. The drawings are not
necessarily to scale, emphasis instead generally being placed upon
illustrating principles of the teaching. The drawings are not
intended to limit the scope of the Applicant's teaching in any
way.
[0008] FIG. 1 illustrates a known vapor phase epitaxy system used
to form compound semiconductors.
[0009] FIG. 2 illustrates a vapor phase epitaxy system according to
the present teachings that includes at least one electrode
positioned in a flow of a first precursor gas and being
substantially isolated from a flow of a second precursor gas.
[0010] FIG. 3 illustrates a top-view of one embodiment of a
disk-shaped gas injector according to the present teaching that
includes a first region that is positioned in quadrants of the gas
injector and a second region extending radially through the
quadrants.
[0011] FIG. 4A illustrates a cross-section of one embodiment of a
disk-shaped gas injector according to the present teaching that
includes a plurality of first and second regions which alternates
across the gas injector.
[0012] FIG. 4B illustrates an expanded view of the disk-shaped gas
injector illustrating mechanical or chemical barriers that isolate
the electrodes from the second precursor gas.
[0013] FIG. 5 illustrates a perspective top-view of a vapor phase
epitaxy system according to the present teachings that includes a
horizontal flow gas injector.
[0014] FIG. 6 illustrates a foil-shaped electrode positioned close
to the surface of the platen for thermally activating a precursor
gas in a vapor phase epitaxy system according to the present
teaching.
DESCRIPTION OF VARIOUS EMBODIMENTS
[0015] Reference in the specification to "one embodiment" or "an
embodiment" means that a particular feature, structure, or
characteristic described in connection with the embodiment is
included in at least one embodiment of the teaching. The
appearances of the phrase "in one embodiment" in various places in
the specification are not necessarily all referring to the same
embodiment.
[0016] It should be understood that the individual steps of the
methods of the present teachings may be performed in any order
and/or simultaneously as long as the teaching remains operable.
Furthermore, it should be understood that the apparatus and methods
of the present teachings can include any number or all of the
described embodiments as long as the teaching remains operable.
[0017] The present teaching will now be described in more detail
with reference to exemplary embodiments thereof as shown in the
accompanying drawings. While the present teachings are described in
conjunction with various embodiments and examples, it is not
intended that the present teachings be limited to such embodiments.
On the contrary, the present teachings encompass various
alternatives, modifications and equivalents, as will be appreciated
by those of skill in the art. Those of ordinary skill in the art
having access to the teaching herein will recognize additional
implementations, modifications, and embodiments, as well as other
fields of use, which are within the scope of the present disclosure
as described herein.
[0018] The term "available energy" as used in the present
disclosure refers to the chemical potential of a reactant species
that is used in a chemical reaction. The chemical potential is a
term commonly used in thermodynamics, physics, and chemistry to
describe the energy of a system (particle, molecule, vibrational or
electronic states, reaction equilibrium, etc.). However, more
specific substitutions for the term chemical potential may be used
in various academic disciplines, including Gibbs free energy
(thermodynamics) and Fermi level (solid state physics), etc. Unless
otherwise specified, references to the available energy should be
understood as referring to the chemical potential of the specified
material.
[0019] FIG. 1 illustrates a known VPE system 100 used to form
compound semiconductors. This system 100 includes a reaction
chamber 101 having a spindle 102 mounted therein. The spindle 102
is rotatable about an axis 104 by a rotary drive mechanism 106. The
axis 104 extends in an upstream direction U and a downstream
direction D as shown in FIG. 1. A platen 108, which in many systems
is a disc-like substrate carrier, is mounted on the spindle 102 for
rotation therewith. Typically, the platen 108 and spindle 102
rotate at rotation rates that are in the range of about 100-2,000
revolutions per minute. The platen 108 is adapted to hold a
plurality of disc-like substrates 110 so that surfaces 112 of the
substrates 110 are in a plane perpendicular to axis 104 and face in
the upstream direction U.
[0020] A heater 114, such as a resistance heating element, is
positioned within the reaction chamber 101 proximate to the platen
108. The heater 114 heats the substrate carrier to the desired
processing temperature. A gas injector 116, which is sometimes
known in the art as a flow inlet element, is mounted upstream of
the platen 108 and spindle 102. The gas injector 116 is connected
to process gas sources 118, 120, and 122. The gas injector 116
directs streams of various process gases into the reaction chamber
101. A fluid coolant supply 117 is coupled to liquid cooling
channels in the flow injector 116 to circulate the cooling fluid in
order to control the temperature of the gas injector 116.
[0021] In operation, streams of process gases from the process gas
sources 118, 120, and 122 flow generally downstream toward the
platen 108 and substrates 110 in a region of the reaction chamber
101 between the gas injector 116 and the platen 108, that is
referred to herein as the "flow region 124." In known systems, this
downward flow does not result in substantial mixing between
separate streams of downwardly flowing gas. It is typically
desirable to design and operate the system 100 so that there is
laminar flow in the flow region 124. In normal operation, the
platen 108 is rotated rapidly about the axis 104 with the rotary
drive 106 so that the surface of the platen 108 and the surfaces of
the substrates 110 are moving rapidly. The rapid motion of the
platen 108 and substrates 110 entrains the gases into rotational
motion about axis 104. Consequently, the process gases flow
radially away from axis 104, thereby causing the process gases in
the various streams to mix with one another within a boundary layer
that is schematically indicated in boundary layer region 126.
[0022] In practice, there is a gradual transition between the
generally downstream gas flow indicated by arrows 128 in the flow
region 124 and the rapid rotational flow and mixing in the boundary
layer 126. Nevertheless, the boundary layer 126 is generally
regarded as a region in which the gas flow is substantially
parallel to the surfaces of the substrates 110. In some methods of
operation, the thickness of the boundary layer 126 is on order of
about 1 cm and the distance from the downstream face of gas
injector 116 to the surfaces 112 of the substrates 110 is about 5-8
cm. Thus, the flow region 124 occupies the major portion of the
space between the gas injector 116 and the platen 108. The
rotational motion of the platen 108 pumps the gases outwardly
around the peripheral edges of the platen 108, and hence the gases
pass downstream to an exhaust system 130. In many methods of
operation, the reaction chamber 101 is maintained under an absolute
pressure from about 25-1,000 Ton. Many processes operate at an
absolute pressure of about 50-760 Torr.
[0023] The gas injector 116 is maintained at a relatively low
temperature, which is typically about 60.degree. C. or less,
although higher temperatures are sometimes used. In Halide VPE
systems, the Group III halide is maintained at an elevated
temperature to prevent condensation. This elevated temperature is
below the temperature of the substrates 110 where deposition
occurs. The relatively low temperature is chosen to inhibit
decomposition of reactants and/or to inhibit the formation of
undesired reactions of the reactants in the gas injector 116 and in
the flow region 124. Also, in many processes, the walls 101' of
reaction chamber 101 are cooled to about 25.degree. C. in order to
minimize the rate of any reactions of the process gases in the flow
region 124 remote from the platen 108.
[0024] It is desirable to promote rapid reactions between the gases
in the boundary layer 126 at the surfaces of the substrates 110
because the residence time of the gases in the boundary layer 126
is relatively brief. In a conventional VPE system, the reaction
energy is provided primarily by heat from the platen 108 and
substrates 110. For example, in some processes, the reaction energy
is the energy required to dissociate a Group V hydride, such as
NH.sub.3, to form reactive intermediates, such as NH.sub.2 and NH.
However, increasing the temperature of the platen 108 and
substrates 110 also tends to increase dissociation of the deposited
compound semiconductors. For example, increasing the temperature of
the platen 108 and substrates 110 can result in a loss of nitrogen
from the semiconductor especially when growing Indium-rich
compounds such as InGaN and InN.
[0025] In one aspect of the present teachings, VPE systems include
one or more electrically active electrodes that are used to add
additional energy to a process gas in order to increase the
reaction rate or to modify the reaction chemistry. One skilled in
the art will appreciate that any type of electrically active
electrode can be used, such as wires and filaments in any shape,
which are exposed to a process gas in the process chamber 101.
[0026] In many embodiments of the present teachings, it is
desirable to supply energy to one of the process gases without
supplying significant energy to other process gases. For example,
in many Group III-V deposition processes, it is desirable to apply
additional energy to the Group V hydride precursor gases, which for
example, can be ammonia (NH3) without supplying significant energy
to the Group III metal precursor gases. One skilled in the art will
appreciate that selective application of energy to one or more of
process gases can be accomplished in numerous ways. For example,
the one or more electrically active electrodes can be physically
isolated from a precursor gas that will react in the presence of
the elevated temperatures. Physical isolation can be achieved by
introducing the gases separately in different regions of the
reactor and by using baffles and/or gas curtains as described
herein. One feature of the present teachings is that gases can be
introduced separately, but at the same distance from the substrates
110 in order to maintain laminar flow over the surfaces of the
substrates 110.
[0027] FIG. 2 illustrates a vapor phase epitaxy system 200
according to the present teachings that includes at least one
electrode positioned in a flow of a first precursor gas and being
substantially isolated from a flow of a second precursor gas. The
VPE system 200 is similar to the VPE system described in connection
with FIG. 1. The VPE system 200 includes a process chamber 201 for
containing process gasses. In addition, the VPE system 200 includes
a platen 202, which is a disk-shaped substrate carrier that
supports substrates 204 for vapor phase epitaxy.
[0028] The VPE system 200 includes a gas injector 206 comprising
multiple regions that are separated by physical barriers and/or
chemical barriers. For example, the VPE system 200 can include a
first region 208 that is coupled to a first precursor gas source
210 and a second region 212 that is coupled to a second precursor
gas source 214. Any type of precursor gas can be used in the VPE
system according to the present teachings. In various other
embodiments, the gas injector 206 can include additional regions
that are separated by physical barriers and/or chemical barriers
that may or may not be coupled to additional precursor and/or inert
gas sources 211.
[0029] As described herein, there are many possible gas injector
designs that inject different precursor gases into different
regions of the process chamber 201. For example, in one embodiment
that is described in connection with FIG. 3, the first region 208
in the gas injector 206 is positioned in quadrants of a disk and a
second region 212 extends radially through the quadrants. In
another embodiment that is described in connection with FIG. 4A,
the first and second regions 208, 212 in the gas injector 206
include a plurality of first and second regions that alternate
across at least a portion of the gas injector 206. In many
practical embodiments, the gas injector 206 comprises liquid
cooling channels to control a temperature of the gas injector 206.
A fluid coolant supply 216 is coupled to liquid cooling channels in
the flow injector 206 to circulate the cooling fluid in order to
control the temperature of the gas injector 206.
[0030] In various embodiments, the gas injector 206 is designed to
flow the first and second precursor gases over the platen 202 that
supports the substrates 204 with either a laminar flow or a
non-laminar flow. Also, in various embodiments, the gas injector
206 flows the first and second precursor gases in various
directions relative to the platen 202 that supports the substrates
204. For example, in some VPE systems according to the present
invention, the gas injector 206 flows at least one of the first and
second precursor gases in a direction that is perpendicular to the
surface of platen 202 that supports the substrates 204. Also, in
some VPE systems, the gas injector 206 flows at least one of the
first and second precursor gases in a direction that is parallel to
the platen 202 that supports the substrates 204. In one particular,
VPE system, the gas injector 206 flows one of the first and second
precursor gases in a direction that is substantially parallel to
the platen 202 that supports the substrates 204 and the other of
the first and second precursor gases through the gas injector 206
in a direction that is substantially perpendicular to the platen
202 that supports the substrates 204.
[0031] Electrodes 218, 219 are positioned in the first region 212
so that first precursor gas flows in contact with or in close
proximity to the electrodes 218, 219. In addition, the electrodes
218, 219 are positioned so that they are substantially isolated
from the flow of the second precursor gas. The electrodes 218, 219
can be oriented in numerous ways. For example, the electrodes 218,
219 can be oriented in a plane of the gas injector 206 (e.g.
electrode 218). The electrodes 218, 219 can also be oriented
perpendicular to the plane of the gas injector 206 (e.g. electrode
219). In addition, the electrodes 218, 219 can be positioned
anywhere between the gas injector 206 and the platen 202 that
supports the substrates 204 including in close proximity to the gas
injector 206 and in close proximity to the platen 202 that supports
the substrates 204.
[0032] In various embodiments, the electrodes 218, 219 can be
formed of any type of electrode material. However, the electrodes
218, 219 are typically formed of a material that is resistant to
corrosion so that they do not introduce any contamination into the
VPE system 200. Also, in various embodiments, any type of electrode
configuration can be used including any number of electrodes, which
can include only one electrode. In addition, in various
embodiments, the electrodes 218, 219 can be formed in any shape.
For example, the VPE system 200 shows two different types of
electrodes, a linear (straight) electrode 218 and a non-linear
electrode 219, such as a coiled electrode or other structure that
increases or maximizes the surface area of the electrode that is
exposed to the first precursor gas. In many systems, the same type
of electrode is used, but in some systems two or more different
types of electrodes are used.
[0033] The electrodes 218, 219 are electrically active. In the
embodiment shown in FIG. 2, the electrodes 218, 219 are at a
floating potential when not powered. An output of a power supply
220 is electrically connected to the electrodes 218, 219. The power
supply 220 generates a current that heats the electrodes 218, 219
so as to thermally activate at least some of the first precursor
gas molecules flowing in contact with or proximate to the
electrodes 218, 219.
[0034] One skilled in the art will appreciate that there are
numerous ways of isolating the electrodes 218, 219 so that they are
substantially isolated from the flow of the second precursor gas.
For example, in one embodiment, the gas injector 206 includes one
or more baffles 222 or other types of physical structure that
physically separates the first region 208 from the second region
212 so as to isolate the electrodes 218, 219 from the flow of the
second precursor gas. In many embodiments, the one or more baffles
222 are formed of non-thermally conductive materials so that the
thermal profile in the process chamber 201 does not significantly
change from thermal radiation emitted by the baffles 222. In one
embodiment, the one or more baffles 222 are shaped to preserve
laminar flow of at least one of the first and second precursor
gases across the platen 202 that supports the substrates 204.
[0035] In one embodiment, the electrodes 218, 219 are formed of a
catalytic material. A heater can be positioned in thermal
communication with the catalytic material so as to increase a
reaction rate of the catalytic material. One skilled in the art
will appreciate that numerous types of catalytic materials can be
used. For example, in some embodiments, the electrodes 218, 219 are
formed of a catalytic material including at least one of rhenium,
tungsten, niobium, tantalum, and molybdenum. In various
embodiments, the electrodes 218, 219 can be formed of refractory
and/or transition metals.
[0036] A method of operating a vapor phase epitaxy system according
to the present teachings includes injecting a first precursor gas
for vapor phase epitaxy in the first region 208 proximate to a
platen 202 supporting substrates 204 and injecting a second
precursor gas for vapor phase epitaxy in a second region 212
proximate to the platen 202 supporting substrates. In one method,
the first and second precursor gases are injected in a plurality of
respective alternating first and second regions as described in
connection with FIG. 4A.
[0037] Any type of VPE precursor gases can be used. For example,
the first precursor gas can be a hydride precursor gas, such as
NH.sub.3 and the second precursor gas can be an organometalic
precursor gas, such as trimethyl gallium, that is used to grow GaN
by VPE. Also, the first precursor gas can be a hydride precursor
gas, such as NH.sub.3 and the second precursor gas can be a metal
halide precursor gas, such as gallium chloride, that is used to
grow GaN by VPE. In some methods, three precursor gases are used.
For example in these methods, the first precursor gas can be a
hydride precursor gas, such as NH.sub.3, and the second precursor
gas can be an organometalic precursor gas, such as trimethyl
gallium. The third precursor gas can be a halide precursor gas,
such as HCl. With these three precursor gases, the halide precursor
gas and the organometallic precursor gas react to form a metal
halide. In methods using three precursor gases, the gas injector
206 can include a third region for injecting the third precursor
gas. Alternatively, the third precursor gas can be injected in the
either the first or the second regions 208, 212.
[0038] The first and second precursor gases can be injected at any
angle including perpendicular and parallel to the platen 202
supporting substrates 204. The angle of injection for the second
precursor gas can be the same as or different from the angle of
injection of the first precursor gas. First precursor gas molecules
flow in contact with or in close proximity to the electrodes 218,
219. However, the electrodes 218, 219 are at least partially
isolated from the flow of the injected second precursor gas. The
electrodes 218, 219 are then electrically activated. In some
methods, the electrodes 218, 219 are isolated from a flow of the
injected second precursor gas with physical baffles 222. The
baffles 222 can be performed so as to preserves laminar flow over
the platen 202 supporting substrates 204 as described in connection
with FIG. 6.
[0039] In methods using gas curtains, inert gases are injected in
regions that isolate the electrodes 218, 219 from a flow of the
second precursor gas. The term "inert gas" as used herein refers to
a gas which does not substantially participate in the growth
reactions. Inert gases are often mixed with the precursor gases.
Such inert gases are referred to in the art as "carrier gases." For
example, when growing III-V semiconductor materials, gases, such as
N2, H2, He or mixtures thereof, are commonly used as carrier gases
for precursor gases.
[0040] The power supply 220 generates a current that flows through
the electrodes 218, 219 so that the electrodes 218, 219 generates
heat that thermally activates the first precursor gas molecules
without activating a substantial amount of second precursor gas
molecules. The heated electrodes 218, 219 transfer energy to the
first precursor gas molecules by various mechanisms including
thermionic emission of electrons and interaction of the electrons
with the reactant species. In some methods according to the present
teachings, the electrons do not have sufficient energy to ionize
the reactant species. One example where the electrons do not have
sufficient energy to ionize the reactant species is ionizing
NH.sub.3. In methods that ionize NH.sub.3, the electrons interact
with the reactant species so as to promote the species to a higher
energy state.
[0041] In some VPE systems according to the present teachings, the
electrodes 218, 219 are catalytic electrodes, which are formed of a
catalytic material capable of catalyzing the first precursor gas if
conditions are favorable. The catalytic electrode can be heated
with a separate heater to enhance the catalytic reaction. In some
methods, such a catalytic electrode is useful to decompose NH.sub.3
close to the gas injector 206 surface because it is far from the
platen 202 supporting the substrate 204 and, therefore, may not
have enough thermal energy for decomposition. Using a catalytic
electrode lowers the activation energy for decomposition and,
therefore, increases the probability of NH.sub.3 decomposition even
in regions of the process chamber 201 that have relatively low
temperatures (i.e. regions close to the gas injector 206 away from
the substrate). The catalytic electrode allows the reaction to
proceed or, if the reaction was inclined to occur, to proceed more
rapidly by lowering the activation energy of the reaction or having
the reaction proceed through a different reaction pathway. In one
VPE system according to the present teachings, the catalytic
electrode is positioned proximate to the boundary layer region 126
(FIG. 1) so that the first precursor gas mixes with the second
precursor gas shortly after the first precursor gas interacts with
the catalytic electrode.
[0042] Other VPE systems according to the present teachings include
a catalytic electrode that is not energized. This is a catalytic
electrode that is not powered by a power supply and that uses only
the catalytic material and ambient heat to enhance the catalytic
reaction. In various VPE systems according to the present
teachings, a catalytic electrode can be positioned anywhere in the
process chamber 201. In some of these VPE systems, the catalytic
electrode is positioned proximate to the platen 202. Catalytic
electrodes positioned proximate to the platen 202 can reach
effective catalytic activity through secondary heating from the
platen 202 alone.
[0043] Slab-like streams of thermally activated first precursor gas
molecules flow generally downstream toward the platen 202 and
substrates 204 in a flow region 224 of the reaction chamber 201
between the gas injector 206 and the platen 202. In many methods
according to the present teachings, the downward flow does not
result in substantial mixing between separate streams of downwardly
flowing gas. It is sometimes desirable to design and operate the
system 200 so that there is laminar flow in the flow region 224.
The platen 202 is rotated rapidly about the axis 104 with the
rotary drive 106 so that the surface of the platen 202 and the
surfaces of the substrates 204 are moving rapidly. The rapid motion
of the platen 202 and substrates 204 entrains the gases into
rotational motion about axis 104. Consequently, the process gases
flow radially away from axis 104, thereby causing the process gases
in the various streams to mix with one another within a boundary
layer that is schematically indicated in boundary layer region 126.
The activated first precursor gas molecules and the second
precursor gas molecules in the mixture within the boundary layer
flow over the surface of the substrates 204, thereby reacting to
form a VPE film.
[0044] In conventional VPE systems, precursor gasses are introduced
into the process chamber 201 at a relatively low temperature, and
hence have low available energy, typically well below the energy
required to induce rapid reaction of the reactants on the surface
of the substrate 204. In conventional methods of VPE, there may be
some heating of the reactants by radiant heat transfer as the
reactants pass downstream from the inlet towards the boundary layer
region 126. However, most of the heating, and hence most of the
increase in available energy of the reactants, occurs within the
boundary layer region 126. In these conventional VPE systems,
substantially all of the heating depends upon the temperature of
the substrate 204 and platen 202.
[0045] In VPE systems according to the present teachings,
substantial energy is supplied to at least one precursor gas other
than energy applied by heat transfer from the substrate, platen,
and chamber walls. The location where the energy is applied can be
controlled. For example, by applying the energy to the first
precursor gas near the transition between the flow region 124 (FIG.
1) and the boundary layer region 126, the time between the moment
when a given portion of a first precursor gas reaches a high
available energy and the time when that portion encounters the
substrate surface can be minimized. Such control can help to
minimize undesired side reactions. For example, ammonia having high
available energy may spontaneously decompose into species such as
NH.sub.2 and NH, and then these species in turn may decompose to
monatomic nitrogen, which very rapidly forms N.sub.2. Nitrogen is
essentially unavailable for reaction with a metal organic. By
applying the energy to the ammonia just before or just as the
ammonia enters the boundary layer, the desired reactions which
deposit the semiconductor at the surface, such as reaction of the
excited NH.sub.3 with the metal organic or reaction of NH.sub.2 or
NH species with the metal organic at the substrate surface can be
enhanced, whereas the undesirable side reaction can be
suppressed.
[0046] Thus, one feature of the present teachings is that by using
the electrodes according to the present invention, the operator has
the ability to control the available energy of at least one
precursor gas independently of the temperature of the substrates
204. Thus, the available energy of at least one precursor gas in
the boundary layer region 126 (FIG. 1) can be increased without
increasing the temperature of the substrates 204 and the platen
202. Conversely, the substrates 204 and the platen 202 can be
maintained at a lower temperature while still maintaining an
acceptable level of available energy.
[0047] FIG. 3 illustrates a top-view of one embodiment of a
disk-shaped gas injector 300 according to the present teaching
which includes a first region 302 that is positioned in quadrants
of the gas injector 300 and a second region 304 extending radially
through the quadrants. The top-view shown in FIG. 3 is presented
looking upstream toward the precursor gas inlets in the gas
injector 300. The disk-shaped gas injector 300 includes mechanical
or chemical barriers 305 that isolate the first and second regions
302, 304. As described herein, the mechanical or chemical barriers
305 can be physical structures, such as baffles and/or gas curtains
that inject inert gases to isolate the first and second regions
302, 304.
[0048] FIG. 3 shows electrodes 306, 308 in two quadrants for
clarity. In many VPE systems according to the present invention,
electrodes 306, 308 are positioned in each of the quadrants of the
first region 302. In some embodiments, each of the electrodes 306,
308 is suspended with an insulating support structure so that the
electrodes 306, 308 are electrically floating and easily connected
to the power supply 220 (FIG. 2). In various embodiments, the
electrodes can be linear (straight) electrodes or non-linear
electrodes, such as coiled electrodes or other structures that
increases or maximizes the surface area of the electrodes 306, 308
that are exposed to the first precursor gas.
[0049] In many systems, the same type of electrode is used
throughout the first region 302, but in some systems two or more
different types of electrodes are used in different positions in
the first region 302. For example, the type of electrode near the
second region 304 (at the edges of the first region 302) can be
different from the type of electrode in the middle of the first
region 302. For the purpose of illustrating the positioning of
different types of electrodes, FIG. 3 shows a first type of
electrode 306, which can be either linear or non-linear, positioned
in the plane of the first precursor gas flow. In addition, FIG. 3
shows a second type of electrode 308 positioned in the plane of the
gas injector 300. FIG. 3 shows the second type of electrode 308 in
a linear pattern. However, it should be understood that the second
type of electrode can also be formed in a non-linear pattern, such
as a coil.
[0050] The electrodes 306, 308 are positioned far enough from the
second region 304 so that the chemical potential of the second
precursor is not changed based on its proximity to the electrodes
306, 308. In other words, the electrodes 306, 308 have essentially
no interaction with the second precursor gas. One feature of the
VPE system of the present teachings is that the first and second
precursor gases can be injected at the same distance from the
substrate 204 (FIG. 2). In other words, the second precursor gas
does not have to be injected below the first precursor gas in the
process chamber 201 to avoid activation. Injecting both the first
and the second precursor gases at the same level in the process
chamber 201 is important in many VPE processes because such
injection can achieve laminar flow over large areas in vertical
flow VPE process chambers. Laminar flow is desirable for many VPE
processes because it improves uniformity.
[0051] Methods of operating VPE systems comprising the gas injector
300 of FIG. 3 include injecting the first precursor gas in the
quadrants of the first region 302 so that first precursor gas
molecules contact the electrodes 306, 308. The electrodes 306, 308
are powered with power supply 220 (FIG. 2) so that they thermally
activate the first precursor gas molecules. For example, the first
precursor gas can be a hydride precursor gas precursor gas
admixture with a carrier gas. The second precursor gas is injected
in the second region 304 adjacent to the electrodes 306, 308. For
example, the second precursor gas can be an organometallic
admixture with a carrier gas such as nitrogen. Process conditions
are chosen so that the second precursor gas does not flow close
enough to the electrodes 306, 308 to be thermally activated by heat
generated by the electrodes. The activated first precursor gas
molecules and the second precursor gas molecules then flow over the
surface of the substrates 204 (FIG. 2), thereby reacting to form a
VPE film.
[0052] FIG. 4A illustrates a cross-section of one embodiment of a
disk-shaped gas injector 400 according to the present teaching that
includes a plurality of first and second regions 402, 404 which
alternates across the gas injector 400. The top-view shown in FIG.
4A is presented looking upstream toward the precursor gas inlets in
the gas injector 400. The plurality of first regions 402 includes
gas inlets for injecting hydride or halide precursor gases with a
carrier gas. The plurality of second regions 404 includes gas
inlets for injecting organometallic gases with a carrier gas.
[0053] In many VPE systems according to the present teachings, the
area of the first regions 402 is larger than the area of the second
regions 404. The flow rates of the first and second precursor gases
and of the carrier gases during operation can be adjusted for the
particular dimensions of the first and the second regions 402, 404
so that the desired volumes and concentrations of precursor gases
flow across the substrates 204 (FIG. 2) being processed.
[0054] The gas injector 400 includes a plurality of electrodes 406,
408 positioned in the plurality of first regions 402. In many VPE
systems according to the present invention, the plurality of
electrodes 406, 408 are positioned in the first region 402 or as
far from the flow of the second precursor gas as possible so as to
minimize the activation of second precursor gas molecules with the
electrodes 406, 408. FIG. 4A illustrates electrodes 406, 408 in two
different orientations. Electrodes are only shown in a few sections
of the plurality of first regions 402 for clarity. In many VPE
systems according to the present teachings, electrodes 406, 408 are
positioned in each of the plurality of the first regions 402. In
some embodiments, each of the electrodes 406, 408 is suspended with
an insulating support structure so that the electrodes 406, 408 are
electrically floating and easily connected to the power supply 220
(FIG. 2). In various embodiments, the electrodes 406, 408 can be
linear (straight) electrodes or non-linear electrodes, such as
coiled electrodes or other structures that increases or maximizes
the surface area of the electrodes 406, 408 that are exposed to the
first precursor gas.
[0055] In many systems, the same type of electrode is used
throughout the first region 402, but in some systems two or more
different types of electrodes are used in different positions in
the first region 402. For the purpose of illustrating the
positioning of different types of electrodes, FIG. 4A shows a first
type of electrode 406, which can be either linear or non-linear,
positioned in the plane of the first precursor gas flow. In
addition, FIG. 4A shows a second type of electrode 408 positioned
in the plane of the gas injector 400. FIG. 4A shows the second type
of electrode 408 as a non-linear electrode that can also be coiled.
However, it should be understood that the second type of electrode
408 can also be a linear electrode.
[0056] FIG. 4B illustrates an expanded view of the disk-shaped gas
injector 400 illustrating mechanical or chemical barriers 405 that
isolate the electrodes 406 (FIG. 4A), 408 from the second precursor
gas. The mechanical or chemical barriers 405 isolate the electrodes
406, 408 in first region 402 from the precursor gas flowing in the
second region 404. As described herein, the barriers 405 can be a
physical structure, such as baffle. In addition, the barriers 405
can be a gas curtains that inject inert gases between the first and
second regions 402, 404 as described herein.
[0057] Methods of operating VPE systems comprising the gas injector
400 of FIGS. 4A and 4B include injecting the first precursor gas in
the plurality of first regions 402 so that first precursor gas
molecules contact the electrodes 406, 408. The electrodes 406, 408
are powered with the power supply 220 (FIG. 2) so that they
thermally activate the first precursor gas molecules. For example,
the first precursor gas can be a hydride precursor gas admixture
with a carrier gas that is thermally activated when it flows in
contact with the electrodes 406, 408. The second precursor gas is
injected in the plurality of second regions 404. For example, the
second precursor gas can be an organometallic admixture with a
carrier gas. Process conditions are chosen so that the second
precursor gas does not flow close enough to the electrodes 406, 408
to be thermally activated by heat generated by the electrodes 406,
408. The activated first precursor gas molecules and the second
precursor gas molecules then flow over the surface of the
substrates 204 (FIG. 2), thereby reacting to form a VPE film.
[0058] FIG. 5 illustrates a perspective top-view of a VPE system
500 according to the present teachings that includes a horizontal
flow gas injector 502. The VPE system 500 is similar to the VPE
system 200 that was described in connection with FIG. 2. However,
the VPE system 500 includes circular gas injectors 504, 506, and
508 that inject precursor gases and inert gases in the plane of the
platen 510 (i.e. horizontal flow into the process chamber).
[0059] In the embodiment shown in FIG. 5, the first circular gas
injector 504 is coupled to a first precursor gas source 512. The
second circular gas injector 506 is coupled to an inert gas source
514. The third circular gas injector 508 is coupled to a second
precursor gas source 516. In some VPE systems according to the
present teachings, the first and third circular gas injectors 504,
508 are also coupled to a carrier gas source. The first circular
gas injector 504 injects the first precursor gas in a first
horizontal region 518. The third circular gas injector 508 injects
the second precursor gas in a second horizontal region 520.
[0060] A circular electrode 522 is positioned in the first
horizontal region 518 so that first precursor gas molecules flow in
contact with or proximate to the circular electrode 522. A physical
or chemical barrier can be positioned between the first and the
second horizontal regions 518, 520 in order to isolate the circular
electrode 522 from the flow of the second precursor gas molecules.
In some systems according to the present teachings, a baffle is
positioned above the circular electrode 522 to substantially
prevent the first precursor gas molecules from being thermally
activated by the electrode 522 as they flow to the platen 510.
[0061] In some systems according to the present teachings, a gas
curtain is used to separate the first and the second horizontal
regions 518 and 520. In these systems, the second circular gas
injector 506 injects inert gas between the first and the second
horizontal regions 518, 520 in a pattern that substantially
prevents the second precursor gas molecules from being activated by
the circular electrode 522.
[0062] Methods of operating the VPE system 500 of FIG. 5 include
injecting the first precursor gas with the first circular gas
injectors 504 and injecting the second precursor gas with the third
circular gas injectors 508. An inert gas is injected between the
first and the second horizontal regions 518, 520 with the second
circular gas injectors 506 to form a chemical barrier that prevents
the second precursor gas molecules from being activated by the
circular electrode 522. When the circular electrode 522 is powered
by a power supply 220 (FIG. 2), the circular electrode 522
thermally activates first precursor gas molecules injected by the
first circular gas injector 504 that flow in contact with or in
close proximity to the circular electrode 522. The activated first
precursor gas molecules and the second precursor gas molecules then
flow over the surface of the substrates 524, thereby reacting to
form a VPE film.
[0063] FIG. 6 illustrates a foil-shaped electrode 600 positioned
close to the surface of the platen 602 for thermally activating a
precursor gas in a VPE system according to the present teaching.
The electrode 600 is positioned close to the surface of the platen
602 and substrate 604 being processed. The electrode 600 shown in
FIG. 6 is shaped as an airfoil in order to provide a laminar or
near laminar flow of precursor gases across the surface of the
substrate 604. In addition, in embodiments where the electrode 600
is formed of a catalytic material, the electrode 600 can be shaped
to provide a relatively large surface area for the catalytic
reaction.
EQUIVALENTS
[0064] While the applicant's teaching are described in conjunction
with various embodiments, it is not intended that the applicant's
teaching be limited to such embodiments. On the contrary, the
applicant's teaching encompass various alternatives, modifications,
and equivalents, as will be appreciated by those of skill in the
art, which may be made therein without departing from the spirit
and scope of the teaching.
* * * * *