U.S. patent application number 14/806370 was filed with the patent office on 2016-01-28 for uv light emitting devices and systems and methods for production.
The applicant listed for this patent is RayVio Corporation. Invention is credited to Doug COLLINS, Yitao LIAO, Robert WALKER.
Application Number | 20160027962 14/806370 |
Document ID | / |
Family ID | 55163715 |
Filed Date | 2016-01-28 |
United States Patent
Application |
20160027962 |
Kind Code |
A1 |
LIAO; Yitao ; et
al. |
January 28, 2016 |
UV LIGHT EMITTING DEVICES AND SYSTEMS AND METHODS FOR
PRODUCTION
Abstract
A method of fabricating an ultraviolet (UV) light emitting
device includes receiving a UV transmissive substrate, forming a
first UV transmissive layer comprising aluminum nitride upon the UV
transmissive substrate using a first deposition technique at a
temperature less than about 800 degrees Celsius or greater than
about 1200 degrees Celsius, forming a second UV transmissive layer
comprising aluminum nitride upon the first UV transmissive layer
comprising aluminum nitride using a second deposition technique
that is different from the first deposition technique, at a
temperature within a range of about 800 degrees Celsius to about
1200 degrees Celsius, forming an n-type layer comprising aluminum
gallium nitride layer upon the second UV transmissive layer,
forming one or more quantum well structures comprising aluminum
gallium nitride upon the n-type layer, and forming a p-type nitride
layer upon the one or more quantum well structures.
Inventors: |
LIAO; Yitao; (Hayward,
CA) ; WALKER; Robert; (Hayward, CA) ; COLLINS;
Doug; (Hayward, CA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
RayVio Corporation |
Hayward |
CA |
US |
|
|
Family ID: |
55163715 |
Appl. No.: |
14/806370 |
Filed: |
July 22, 2015 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
62028256 |
Jul 23, 2014 |
|
|
|
Current U.S.
Class: |
257/13 ; 118/719;
204/298.02; 438/47 |
Current CPC
Class: |
C23C 14/568 20130101;
C23C 16/303 20130101; H01L 33/16 20130101; H01L 33/06 20130101;
H01L 21/0254 20130101; C23C 16/54 20130101; C23C 16/481 20130101;
H01L 21/02458 20130101; H01L 33/32 20130101; C23C 16/18 20130101;
H01L 33/0025 20130101; H01L 21/0243 20130101; H01L 33/007 20130101;
C23C 14/0617 20130101; C23C 14/0641 20130101; H01L 33/0062
20130101; H01L 33/18 20130101; H01L 21/02505 20130101; H01L 21/0262
20130101; H01L 33/0075 20130101; C23C 14/0036 20130101; H01L
2933/0091 20130101 |
International
Class: |
H01L 33/06 20060101
H01L033/06; C23C 14/00 20060101 C23C014/00; C23C 14/06 20060101
C23C014/06; C23C 16/18 20060101 C23C016/18; H01L 33/00 20060101
H01L033/00; H01L 33/32 20060101 H01L033/32 |
Claims
1. A method of fabricating an ultraviolet (UV) light emitting
device comprising: receiving a UV transmissive substrate; forming a
UV transmissive layer upon the UV transmissive substrate,
comprising: forming a first UV transmissive layer comprising
aluminum nitride upon the UV transmissive substrate using a first
deposition technique at a temperature less than about 800 degrees
Celsius or greater than about 1200 degrees Celsius; and forming a
second UV transmissive layer comprising aluminum nitride upon the
first UV transmissive layer comprising aluminum nitride using a
second deposition technique that is different from the first
deposition technique, at a temperature within a range of about 800
degrees Celsius to about 1200 degrees Celsius; and forming a UV
light emitting layer structure on the UV transmissive layer,
comprising: forming an n-type layer comprising aluminum gallium
nitride layer upon the UV transmissive layer; forming one or more
quantum well structures comprising aluminum gallium nitride upon
the n-type layer; and forming a p-type nitride layer upon the one
or more quantum well structures.
2. The method of claim 1 wherein the UV transmissive layer has a
thickness within a range of about 10 nm to about 3 microns.
3. The method of claim 1 wherein the UV transmissive layer has a
thickness of about 3 microns to 10 microns.
4. The method of claim 1 wherein the UV transmissive layer has
transmissivity in the UV wavelength range within a transmissivity
range of about 50% to about 99%.
5. The method of claim 1 wherein the method of forming the first UV
transmissive layer uses a deposition process selected from a group
consisting of: hydride vapor phase epitaxy, atomic layer
deposition, liquid phase epitaxy, physical vapor deposition,
sputtering, solid source solution epitaxy.
6. The method of claim 1 wherein the method of forming the second
UV transmissive layer uses a deposition process selected from a
group consisting of: metalorganic chemical vapor deposition,
metalorganic vapor phase epitaxy, molecular beam epitaxy, chemical
beam epitaxy.
7. The method of claim 1 wherein the first UV transmissive layer
comprises polycrystalline aluminum nitride; and wherein the second
UV transmissive layer comprises single crystal aluminum
nitride.
8. The method of claim 1 wherein the receiving the UV transmissive
substrate comprises receiving a substrate selected from a group
consisting of: a quartz substrate, a sapphire substrate, and a free
standing single crystal aluminum nitride substrate.
9. An ultraviolet (UV) light emitting device comprising: a UV
transmissive substrate; a UV transmissive layer disposed upon the
UV transmissive substrate, the UV transmissive layer comprising: a
first UV transmissive layer comprising aluminum nitride disposed
upon the UV transmissive substrate at a temperature less than about
800 degrees Celsius or greater than about 1200 degrees Celsius; and
a second UV transmissive layer comprising aluminum nitride disposed
upon the first UV transmissive aluminum nitride material at a
temperature within a range of about 800 degrees Celsius to about
1200 degrees Celsius; and a UV light emitting structure disposed
upon the UV transmissive layer, the UV light emitting layer
structure comprising: an n-type layer comprising aluminum gallium
nitride disposed upon the UV transmissive layer; one or more
quantum well structures disposed upon the n-type layer; and a
p-type layer comprising nitride material disposed upon the one or
more quantum well structures.
10. The UV device of claim 9 wherein the UV transmissive layer has
a thickness within a range within about 10 nm to about 3
microns.
11. The UV device of claim 9 wherein the UV transmissive layer has
a thickness within a range within about 3 microns to about 10
microns.
12. The UV device of claim 9 wherein the UV transmissive layer has
transmissivity in the UV wavelength range within a transmissivity
range of about 50% to about 99%.
13. The UV device of claim 9 wherein the first UV transmissive
layer comprises polycrystalline aluminum nitride; and wherein the
second UV transmissive layer comprises single crystal aluminum
nitride.
14. The UV device of claim 9 wherein the UV transmissive substrate
comprises a plurality of patterns that scatter strongly with short
wavelength UV light.
15. The UV device of claim 14 wherein the patterns comprises
geometric features within a height range of about 50 nm to about
500 nm.
16. The UV device of claim 9, wherein UV transmissive substrate is
selected from a group consisting of: quartz, sapphire, and free
standing single crystal aluminum nitride.
17. A multi-chambered deposition system comprising: a first chamber
for depositing a first UV transmissive layer comprising aluminum
nitride at temperature less than about 800 degrees Celsius or
greater than about 1200 degrees Celsius; and a second chamber for
depositing a second UV transmissive layer comprising aluminum
nitride at a temperature within a range of about 800 degrees
Celsius to about 1200 degrees Celsius upon the first UV
transmissive layer comprising aluminum nitride.
18. The system of claim 17 further comprising a third chamber for
depositing an n-type layer comprising aluminum gallium nitride
material upon the second UV transmissive layer.
19. The system of claim 18 wherein the third chamber is the second
chamber.
20. The system of claim 17 wherein the first chamber comprises a
chamber adapted to perform: hydride vapor phase epitaxy, atomic
layer deposition, liquid phase epitaxy, physical vapor deposition,
sputtering, or solid source solution growth.
21. The system of claim 17 wherein the second chamber comprises a
chamber adapted to perform: metalorganic chemical vapor deposition,
metalorganic vapour phase epitaxy, molecular beam epitaxy, or
chemical beam epitaxy.
22. The system of claim 18 wherein the third chamber is also for
depositing one or more quantum well structures comprising aluminum
gallium nitride upon the n-type layer.
23. The system of claim 22 wherein the third chamber is also for
depositing a p-type nitride layer upon the one or more quantum well
structures.
24. The system of claim 22 further comprising a fourth chamber for
depositing a p-type nitride layer upon the one or more quantum well
structures.
25. The system of claim 18 further comprising a fourth chamber for
depositing one or more quantum well structures comprising aluminum
gallium nitride upon the n-type layer.
26. The system of claim 25 wherein the fourth chamber is also for
depositing a p-type nitride layer upon the one or more quantum well
structures.
27. The system of claim 25 further comprising a fifth chamber for
depositing a p-type nitride layer upon the one or more quantum well
structures.
28. The system of claim 17 further comprising a wafer handling
portion coupled to the first chamber and the second chamber,
wherein the wafer handling portion is configured to transfer the
wafer between the first chamber and the second chamber under
control of a processor.
29. The system of claim 17 further comprising a vacuum chamber
coupled to the first chamber and the second chamber, wherein the
vacuum chamber is configured to maintain the wafer under a vacuum
when the wafer is transferred between the first chamber and the
second chamber.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] The present application is a non-provisional of provisional
App. No. 62/028,256 filed Jul. 23, 2014. The present application is
also related to co-pending U.S. patent application Ser. No.
13/646,038 filed Oct. 5, 2012 and U.S. patent application Ser. No.
14/194,425 filed Feb. 28, 2014. The above references are
incorporated by reference herein, for all purposes
BACKGROUND
[0002] The present invention relates to UV light emitting devices.
Additionally, embodiments of the present invention relate to UV
light emitting devices, fabrication techniques and equipment for
fabricating UV light emitting devices.
[0003] As illustrated and disclosed in U.S. Pat. No. 8,409,895
issued Apr. 2, 2013, U.S. patent application Ser. No. 11/404,516,
filed on Apr. 14, 2006, and Ser. No. 11/429,022, filed on May 5,
2006, various techniques and systems have been previously proposed
to form a buffer layer for visible light LEDs. However, because UV
light has significantly higher wavelengths, buffer layers suitable
for visible light LED can be unsuitable for UV light emitting
devices. More specifically, the inventors of the present invention
recognize that UV light emitting devices based upon (AlxGa(1-x))N,
require higher quality buffer layers that are not disclosed or
provided by the above prior art.
[0004] What is desired are improved methods and apparatus for
forming buffer layers for UV light emitting devices, with reduced
drawbacks.
SUMMARY
[0005] In the fabrication of typical semiconductor devices, there
is an emphasis for reducing the number of fabrication steps to
reduce costs and reduce errors. The reduction is steps may include
eliminating formation of a layer, eliminating a masking layer, and
reducing alignment tolerances. The reduced number of fabrication
steps almost always directly correlates to lower fabrication
costs.
[0006] The inventor of the present invention have recognized that
various embodiments of the present invention are costly in terms of
additional fabrication steps and increased hardware requirements,
however these embodiments provide surprising benefits.
[0007] One example of the present invention includes replacing a
single buffer layer comprising aluminum nitride deposited in a
growth chamber/single process with a minimum of two layers
comprising aluminum nitride deposited in two different growth
processes in one or two chambers. Aluminum nitride layers deposited
in two different chambers exhibits different material properties as
a result of different crystal grow techniques leading to faster
cycle time, or simpler growth condition and process requirements,
reduced impurity concentration, or superior performance.
[0008] In some examples, the first category of growth chamber for
the first layer comprising aluminum nitride can include, but not
limited to: hydride vapor phase epitaxy, atomic layer deposition,
liquid phase epitaxy, physical vapor deposition, sputtering, solid
source solution epitaxy. Further, in some examples, the first
category of growth chamber for the first layer comprising aluminum
nitride can have the following characteristics, but not limited to
growth temperature of the layer comprising aluminum nitride is in
the temperature that is lower than 800 degrees Celsius or higher
than 1200 degrees Celsius.
[0009] In some examples, the second category of growth chamber for
the second layer comprising aluminum nitride can include, but not
limited to: metalorganic chemical vapor deposition, metalorganic
vapor phase epitaxy, molecular beam epitaxy, or chemical beam
epitaxy. Further, in some examples, the second category of growth
chamber for the second layer comprising aluminum nitride can have
the following characteristics, but not limited to growth
temperature of the layer comprising aluminum nitride is in the
temperature that is equal or higher than 800 degrees Celsius and
equal or lower than 1200 degrees Celsius.
[0010] In some embodiments, instead of a single composition
aluminum nitride buffer layer as a foundation for a UV light
emitting source, embodiments detail a dual layer aluminum nitride
material having a quick growth low quality aluminum nitride
material followed by a high quality crystalline aluminum nitride
material in separate growth chambers. The quality of the aluminum
nitride materials specified in a dual layer growth method can be
characterized and differentiated by, including, but not limited to,
the following characteristics: polycrystalline or single
crystalline, dislocation density, point defects, optical
transparency, or the like. In various embodiments, the inventors
recognize that the quick growth, low quality aluminum nitride
material should still maintain a defect density lower than 1e10
cm-2 so UV light is not excessively scattered or absorbed within
the buffer layer. Additionally, the quick growth, low quality
aluminum nitride material should have a background contamination,
of oxygen, carbon, etc. less than about 1e18 cm-3, and of hydrogen
of less than about 1e20 cm-3 so that UV light is not excessively
scattered or absorbed within the buffer layer. The latter factors
may be facilitated through the use of higher purity source gasses,
higher purity elemental sources, higher quality cleanings, higher
quality vacuums, and the like.
[0011] The inventors believe that a single aluminum nitride buffer
layer based upon HVPE or PVD or the like is insufficient to provide
a high quality growth surface necessary for formation of a UV light
emitting source. This is because of the higher frequencies of light
provided by a UV light source compared to a conventional visible
light LED. More succinctly, the inventors do not believe that a UV
light source could be effectively paired with a polycrystalline
aluminum nitride buffer layer. Additionally, the inventors believe
that a single aluminum nitride buffer layer based upon MOCVD, MBE,
or the like is too time consuming. More specifically, the growth of
a sufficiently thick single crystal aluminum nitride layer is slow.
Accordingly, benefits provided by embodiments of the present
invention provide lower fabrication times, but still provide a high
quality growth surface required by UV light sources.
[0012] With various embodiments of the present invention, the
inventors believe that using the first category of growth chambers
such as PVD or HVPE to grow the first layer comprising aluminum
nitride can lead to reduced growth time required by the second
category of growth chambers such as MOCVD or MBE, leading to
reduction of the overall cycle time for a complete UV LED
structure, as described in the present invention. Further, in order
to reduce contamination by exposure to atmosphere environments, it
is necessary to transfer the wafer after completion of growth of
the first layer comprising aluminum nitride in the first growth
chamber to the second growth chamber for the growth of the second
layer comprising aluminum nitride under vacuum, preferably using a
robotic arm to move the wafer from the first chamber to the second
chamber. The same concept applies to a multiple chamber epitaxy
growth system comprising more than two chambers as well.
[0013] Various embodiments of the present invention include a UV
transparent substrate that is patterned with UV diffusive
structures, e.g. gratings, or the like. A buffer layer is formed
upon the UV transparent substrate that includes a minimum of two
layers. The first layer adjacent to the substrate is primarily a
poly crystalline material including aluminum and nitrogen, e.g.
aluminum nitride. The second layer on top of the first layer is
primarily a crystalline material including aluminum and nitrogen,
e.g. aluminum nitride. The buffer layer serves as a foundation for
a stack of aluminum, gallium and nitrogen-based material (e.g. a UV
light emitting device).
[0014] In various embodiment, the stack of material includes an
n-type material having aluminum, gallium, and nitrogen, e.g.
AlxGa(1-x)N on top of the buffer layer; one or more quantum well
material having aluminum, gallium and nitrogen, e.g. AlyGa(1-y)N on
top of the n-doped material; and a p-type material having aluminum,
gallium, and nitrogen, e.g. AlzGa(1-z)N. In other embodiments, the
stack includes a semiconductor structure such as a transistor, a
high electronic mobility transistor comprising aluminum gallium
nitride; the stack includes a semiconductor structure such as a
laser comprising aluminum gallium nitride; the stack includes a
semiconductor structure such as a MEMS devices with piezoelectric
effects induced by material comprising aluminum gallium nitride; or
the like.
[0015] Various embodiments of the present invention include methods
for fabricating a UV light emitting device. Fabrication steps may
include formation of a two-part buffer layer upon a UV transparent
substrate. In various embodiments, the term buffer layer refers to
not only a buffer layer that comprises low quality, very thin (a
few nanometer, or a few tens of nanometer) polycrystalline layer
for subsequent growth of high quality mostly single-crystalline
layer, but also refers to a general purpose template layer than
comprises a low quality layer and a high quality layer which can
amount to a total thickness of a few microns.
[0016] In some embodiments, a material of the first part of the
buffer layer includes aluminum and nitrogen, and is formed using
one of the following processes: hydride vapor phase epitaxy, atomic
layer deposition, liquid phase epitaxy, physical vapor deposition,
sputtering, and solid source solution epitaxy, or combination
thereof. A material of the second part of the buffer layer includes
aluminum and nitrogen, and is formed using one of the following
processes: metalorganic chemical vapor deposition, metalorganic
vapor phase epitaxy, molecular beam epitaxy, and chemical beam
epitaxy, or combination thereof. The processes for forming the
first part of the buffer layer are different from forming the
second part of the buffer layer. Subsequently, a process includes
depositing a stack of material that forms a UV light source. In
some embodiments, the process includes depositing an n-doped
material having aluminum, gallium and nitrogen; depositing one or
more a quantum well structures having aluminum, gallium and
nitrogen, and depositing a p-doped material having aluminum,
gallium and nitrogen. The processes for forming the UV light source
may include one or more of the following processes: metalorganic
chemical vapor deposition, metalorganic vapor phase epitaxy,
molecular beam epitaxy, and chemical beam epitaxy. In some
examples, the process in the first chamber may include a
nitridation step where the substrate is subjected to a flux of
active nitrogen, or a flow of ammonia.
[0017] Various embodiments of the present invention include a
multi-chambered process for forming a UV light emitting device. A
first chamber is adapted to form a first part of a buffer layer
with aluminum and nitrogen in a low temperature process, e.g.
<800 C or a high temperature process, e.g. >1200 C. A second
chamber is for forming a second part of a buffer layer with
aluminum and nitrogen in a medium temperature process, e.g. between
about 800 C and about 1200 C. The second chamber or one or more
additional chambers may also be used for forming a stack of
materials that form UV light source above the buffer layer. This
includes formation of an n-doped material having aluminum, gallium
and nitrogen, formation of one or more quantum well material having
aluminum, gallium and nitrogen, and formation of an p-doped
material having aluminum, gallium and nitrogen. The second or one
or more additional chambers may be suitable for one of the
following processes: metalorganic chemical vapor deposition,
metalorganic vapor phase epitaxy, molecular beam epitaxy, and
chemical beam epitaxy. In various embodiments, a wafer handling
tool is directed by one or more programs running upon a
microprocessor to move a wafer to the first chamber, from the first
chamber to the second chamber, and from the second chamber to
additional chambers, or the like. In some embodiments, when
transferring the wafer from the first chamber to the second, the
wafer may be under a controlled atmosphere, a vacuum, or the
like
[0018] According to one aspect of the invention, a method of
fabricating an ultraviolet (UV) light emitting device is disclosed.
A technique may include receiving a UV transmissive substrate, and
forming a UV transmissive layer upon the UV transmissive substrate,
that includes forming a first UV transmissive layer comprising
aluminum nitride upon the UV transmissive substrate using a first
deposition technique at a temperature less than about 800 degrees
Celsius or greater than about 1200 degrees Celsius; and forming a
second UV transmissive layer comprising aluminum nitride upon the
first UV transmissive layer comprising aluminum nitride using a
second deposition technique that is different from the first
deposition technique, at a temperature within a range of about 800
degrees Celsius to about 1200 degrees Celsius. A process may
include forming a UV light emitting layer structure on the UV
transmissive layer, including forming an n-type layer comprising
aluminum gallium nitride layer upon the UV transmissive layer,
forming one or more quantum well structures comprising aluminum
gallium nitride upon the n-type layer, and forming a p-type nitride
layer upon the one or more quantum well structures.
[0019] According to another aspect of the invention, an ultraviolet
(UV) light emitting device is disclosed. One device includes a UV
transmissive substrate, and a UV transmissive layer disposed upon
the UV transmissive substrate. In some embodiments, the UV
transmissive layer may include a first UV transmissive layer
comprising aluminum nitride disposed upon the UV transmissive
substrate at a temperature less than about 800 degrees Celsius or
greater than about 1200 degrees Celsius, and a second UV
transmissive layer comprising aluminum nitride disposed upon the
first UV transmissive aluminum nitride material at a temperature
within a range of about 800 degrees Celsius to about 1200 degrees
Celsius. One device includes a UV light emitting structure disposed
upon the UV transmissive layer. In some embodiments, the UV light
emitting layer structure includes an n-type layer comprising
aluminum gallium nitride disposed upon the UV transmissive layer,
one or more quantum well structures disposed upon the n-type layer,
and a p-type layer comprising nitride material disposed upon the
one or more quantum well structures.
BRIEF DESCRIPTION OF THE DRAWINGS
[0020] FIG. 1 illustrates a UV light emitting structure including a
two layer aluminum nitride buffer layer on a UV transmissive
substrate.
[0021] FIG. 2A illustrates an example of a multiple chamber tool
for growth of a multi-layer aluminum nitride buffer having and
aluminum, gallium and nitrogen based UV light emitting source with
a transfer chamber system.
[0022] FIG. 2B illustrates a UV light-emitting device structure in
accordance with an embodiment of the present invention.
[0023] FIG. 3 is a flowchart representing operations in a method of
fabricating an aluminum gallium nitride-based UV light emitting
device with a two part aluminum nitride buffer layer, in accordance
with an embodiment of the present invention.
[0024] FIG. 4 is a schematic cross-sectional view of a chamber
suitable for the fabrication of fabrication of materials, in
accordance with an embodiment of the present invention.
[0025] FIG. 5 is a schematic cross-sectional view of a chamber
suitable for the fabrication of materials, in accordance with an
embodiment of the present invention.
DETAILED DESCRIPTION
[0026] The fabrication of aluminum gallium nitride-based UV light
emitting devices with an aluminum nitride buffer layers is
described. In the following description, numerous specific details
are set forth, such as process chamber configurations and material
regimes, in order to provide a thorough understanding of
embodiments of the present invention. It will be apparent to one
skilled in the art that embodiments of the present invention may be
practiced without these specific details. In other instances,
well-known features, such as specific diode configurations, are not
described in detail in order to not unnecessarily obscure
embodiments of the present invention. Furthermore, it is to be
understood that the various embodiments shown in the Figures are
illustrative representations and are not necessarily drawn to
scale. Additionally, other arrangements and configurations may not
be explicitly disclosed in embodiments herein, but are still
considered to be within the spirit and scope of the invention.
[0027] A UV light emitting device method of fabrication can include
the formation of a buffer layer of aluminum nitride between a
substrate and a device layer of un-doped and/or doped aluminum
gallium nitride. In embodiments described herein, a multi-layer
aluminum nitride buffer layer is used in between the substrate and
the device layer of un-doped and doped aluminum gallium nitride.
For the purposes herein "aluminum gallium nitride" or "AlGaN"
refers generally to materials having aluminum, gallium and
nitrogen, having the stoichiometric ratio of
(Al.sub.xGa.sub.(1-x))N, where 0<x<1. The multi-layer
aluminum nitride layer may have a first layer formed by sputter
deposition in a PVD process, and a second layer formed by a
metal-organic vapor deposition (MOCVD) chamber or a molecular beam
epitaxy (MBE) chamber. In other embodiments, the first layer may be
formed by non-reactive sputtering from an aluminum nitride target
housed in the PVD chamber or, alternatively, may be formed by
reactive sputtering from an aluminum target housed in the PVD
chamber and reacted with a nitrogen-based gas or plasma, or the
like.
[0028] One or more of the embodiments described herein may enable
higher throughput in a multi-chamber fabrication tool used for UV
light emitting device fabrication. Additionally, the overall
thermal budget of UV light emitting device fabrication may be
reduced since the first layer of aluminum nitride layer may be
formed at temperatures below about 800 degrees Celsius. By
contrast, a typical aluminum gallium nitride buffer layer is formed
between 800-1200 degrees Celsius. One or more of the embodiments
described herein may enable faster deposition rates, e.g. two times
the growth rate, for materials such as un-doped and/or n-type doped
aluminum gallium nitride. Faster rates may be achieved since, in
some embodiments, the un-doped and/or n-type doped aluminum gallium
nitride layers are formed on a second layer of the aluminum nitride
(AlN) buffer layer which is crystalline and may provide a correct
crystal orientation and morphological relationship for growing
un-doped and/or n-type doped aluminum gallium nitride layers
thereon. The inventors have discovered that for UV light emitting
devices, it is especially important to have the layer of material
upon which the un-doped and/or n-type doped aluminum gallium
nitride layers be crystalline. Further, forming such aluminum
gallium nitride layers upon a polycrystalline aluminum nitride
buffer layer fails to provide acceptable results. One or more of
the embodiments described herein may enable elimination of oxide
removal operations since many of the described operations are
performed in-situ (within a vacuum) in a cluster tool. One or more
of the embodiments described herein may enable an improvement of
aluminum gallium nitride crystalline quality by forming the
aluminum gallium nitride on a second layer of an aluminum nitride
buffer layer.
[0029] Described in association with one or more embodiments herein
are systems for the fabrication of aluminum gallium nitride-based
UV light emitting devices with a first PVD-formed aluminum nitride
buffer layer and a second MOCVD formed aluminum nitride buffer
layer. In one embodiment, a multi-chamber system includes a PVD
chamber, or the like having a target composed of a metallic or
compound of aluminum to deposit a poly-crystalline aluminum nitride
first layer. The multi-chamber system also includes chambers
adapted to deposit a crystalline aluminum nitride on top of the
first layer, chambers adapted to deposit un-doped or n-type
aluminum gallium nitride, or both, and for other device layers such
as multiple quantum well layers and p-type doped aluminum gallium
nitride layers.
[0030] Also described in association with one or more embodiments
herein are methods of fabricating aluminum gallium nitride-based UV
light emitting devices with a multi-layer aluminum nitride buffer
layers, including a quick-growth, low-temperature (e.g. PVD), or
high temperature (e.g. HVPE) aluminum nitride buffer layer and a
slow-growth, medium-temperature aluminum nitride buffer layer (e.g.
MOCVD). In one embodiment, a method of fabricating a UV light
emitting device includes forming a first aluminum nitride layer
above a substrate in a PVD chamber of a multi-chamber system, and
forming a second aluminum nitride layer above the first aluminum
nitride layer in a MOCVD chamber of a multi chamber system. The
method may also include forming an un-doped or n-type aluminum
gallium nitride layer on the aluminum nitride layer in a second
chamber of the multi-chamber system.
[0031] FIG. 1 illustrates a UV light emitting device 100 according
to various embodiments of the present invention. In FIG. 1, a
substrate 110 is illustrated. Substrate 110 is typically
transmissive to UV light within different UV light regions,
including the UV-C light region. In various embodiments, substrate
110 is considered transmissive if substrate 110 is transmissive of
at least 50% of incident UV light; in other embodiments, the
percentage may be higher, e.g. 70%, 90%, or the like.
[0032] As shown in the example in FIG. 1, substrate 110 may include
interior geometric features 170 and/or exterior geometric features
180. In various embodiments, the geometric features 170 and/or 180
are used to facilitate light extraction from a UV light emitting
device 185 and output of UV light 190. In various embodiments,
geometric features 170 and/or 180 are of sufficient geometric scale
so as to effectively scatter light within the UV frequency band. In
particular, geometric features 170 and/or 180 may have a height on
the order of a few hundred nanometers with a lateral spacing on the
order of 0.1 to 5 microns. In some embodiments, only geometric
features 170 or 180 or both are present upon substrate 110. Further
shapes of geometric features 170 and 180 may be different from that
illustrated, depending upon routine engineering considerations.
Further details may be found in the patent application incorporated
by reference, above.
[0033] In various embodiments, a first aluminum nitride layer 120
(buffer layer) is deposited upon substrate 110. The first AlN layer
is quickly grown and includes a relatively high amount of defects.
This quick growth may cause the first AlN layer to include high
amounts of polycrystalline growth. As discussed above, the defects
should remain below about 1e10 cm-2, with background contamination,
i.e., oxygen, carbon less than about 1e18 cm-3 and hydrogen less
than about 1e20 cm-3. A second aluminum nitride layer 130 (buffer
layer) is then deposed upon the first AlN layer 120. The second AlN
130 layer grown at a slower rate and includes a relatively low
amount of defects. This causes second AlN layer 130 to include high
amounts of crystalline growth. The total thickness of the first and
second layers comprising aluminum nitride may be in the range of a
few nanometers to a few microns.
[0034] On top of buffer layers 120 and 130 is a UV light emitting
structure 185. In various embodiments, UV light emitting source 185
includes a n-doped aluminum, gallium and nitrogen compound 140; one
or more quantum wells 150, also formed from aluminum, gallium and
nitrogen compound; and a p-doped aluminum, gallium and nitrogen
compound 160. In various embodiments, the relative amount of
aluminum, gallium, and nitrogen in layers 140, 150 and 160 may be
the same or different with respect to each other. As an example,
compound 140 may be AlxGa(1-x) N, compound 150 may be AlyGa(1-y)N,
and compound 160 may be AlzGa(1-x)N, or the like. The values of x,
y, and z depend upon the desired wavelengths of UV light provided
by UV light emitting source 185. Optionally the p-AlGaN layer may
be p-GaN without aluminum content. Further details with regards to
UV light emitting source 185 are found in the patent application
incorporated by reference, above.
[0035] FIG. 2A illustrates a cluster tool schematic for UV light
emitting device structure fabrication, in accordance with an
embodiment of the present invention. FIG. 2B illustrates an UV
light emitting device structure along with a corresponding
time-to-deposition plot, in accordance with an embodiment of the
present invention.
[0036] Referring to FIG. 2A, a multiple chamber tool 200 includes
an aluminum nitride deposition chamber 202 (e.g. PVD AlN), an
aluminum nitride MOCVD reaction chamber 203, an un-doped and/or
n-type aluminum gallium nitride MOCVD reaction chamber 204 (MOCVD1:
u-AlGaN/n-AlGaN), a multiple quantum well (MQW) MOCVD reaction
chamber 206 (MOCVD2: MQW), and a p-type aluminum gallium nitride
MOCVD reaction chamber 208 (MOCVD3: p-AlGaN). The cluster tool 200
may also include a load lock 210, a carrier cassette 212, and a
transfer chamber 214, all of which are depicted in FIG. 2A.
[0037] In various embodiments described herein, chamber 202 may
include a chamber adapted to perform: hydride vapor phase epitaxy,
atomic layer deposition, liquid phase epitaxy, physical vapor
deposition, sputtering, solid source solution epitaxy, or the like.
Although embodiments herein refer to chamber 202 as a PVD chamber,
it should be understood that chamber 202 may be adapted for any or
all of these formation processes. Further, in various embodiments,
chambers 203, 204, 206 and 208 may include one or more chambers
adapted to perform: metalorganic chemical vapor deposition,
metalorganic vapor phase epitaxy, molecular beam epitaxy, chemical
beam epitaxy, or the like. Although embodiments herein refer to
these chambers as MOCVD chambers, it should be understood that
chambers 203, 204, 206, and 208 may be adapted for any or all of
these formation processes.
[0038] In other embodiments, reaction chambers 202, 203, 204, 206
and 208 may be distinct individual chambers. In other embodiments,
reaction chamber 203 may also be used as reaction chambers 204, 206
and/or 208; reaction chamber 204 may also be used as reaction
chambers 206 and/or 208; reaction chamber 206 may also be used as
reaction chamber 208; and the like. Separation of chambers 202,
203, 204, 206, and 208 may be desirable in some embodiments to
reduce any potential cross-contamination between reactants within
the respective chambers. However, as mentioned above, multiple
deposition processes described herein may be performed within the
same physical reaction chamber or within a smaller number of unique
reaction chambers to reduce hardware costs. In some embodiments,
reaction chamber 202 performs the initial aluminum nitride buffer
layer; a single chamber takes the place of chambers 203, 204 and
206 for forming the second aluminum nitride buffer layer, forming
the n-doped aluminum gallium nitride material, as well as the
multiple quantum well structures; and a reaction chamber 208 forms
the p-doped material. These three chambers may be disposed about a
transfer chamber similar to that disclosed in FIG. 2A. In some
embodiments, the reaction chambers may be organized in other
arrangements, such as along a linear transfer mechanism, or the
like.
[0039] Thus, in accordance with an embodiment of the present
invention, a multi-chamber system includes a PVD chamber having a
target of metallic or compound aluminum, and a chamber adapted to
deposit a crystalline aluminum nitride, or both. In one embodiment,
the target of the PVD chamber is composed of aluminum nitride. In
such an embodiment, reactive sputtering need not be used since the
target is composed of the same material desired for deposition.
However, in an alternative embodiment, a target composed of
aluminum is used, and aluminum nitride is reactively sputtered from
the aluminum target by or in the presence of a nitrogen source. In
one embodiment, the chamber adapted to deposit a crystalline
aluminum nitride e is a MOCVD chamber, as depicted in FIG. 2A.
However, in an alternative embodiment, the chamber adapted to
deposit a crystalline aluminum nitride is a hydride vapor phase
epitaxy (HVPE) chamber. In one embodiment, the PVD chamber and the
chamber adapted to deposit a crystalline aluminum nitride are
included in a cluster tool arrangement, as depicted in FIG. 2A.
However, in an alternative embodiment, the PVD chamber and the
chamber adapted to deposit a crystalline aluminum nitride are
included in an in-line tool arrangement. Deposition processes based
on PVD, as described herein, may be performed at temperatures
approximating standard room temperature, or may be performed at
higher temperatures.
[0040] Referring to FIG. 2B, a UV light emitting device structure
220 includes a stack of various material layers, many of which
include III-V materials. For example, the UV light emitting device
structure 220 includes a UV transmissive substrate 222 (Substrate:
sapphire, quartz, free standing aluminum nitride, etc.) and a first
aluminum nitride layer 224 (AlN) with a thickness approximately in
the range of 10-200 nanometers. The aluminum nitride layer 224 is
formed by sputter deposition in the PVD aluminum nitride sputter
chamber 202 of cluster tool 200. An estimate process time for wafer
handling, and depositing layer 224 is on the order of about 2
hours. The UV light emitting structure 220 also includes an
approximately 1 microns thick of aluminum nitride 225, and
approximately 2 microns thick of un-doped/n-type aluminum gallium
nitride combination or n-type aluminum gallium nitride-only layer
226 (n-AlGaN). The un-doped/n-type aluminum gallium nitride
combination or n-type aluminum gallium nitride-only layer 226 may
be formed in un-doped and/or n-type aluminum gallium nitride MOCVD
reaction chamber 204 or 203 of cluster tool 200. The LED structure
220 also includes an MQW structure 228 with a thickness in the
range of 30-300 nanometers. The MQW structure 228 is formed in MQW
MOCVD reaction chamber 206 or 203 or 204 of cluster tool 200. In
one embodiment, the MQW structure 228 is composed of one or a
plurality of field pairs of AlGaN well/AlGaN barrier material
layers. In various embodiments, it is estimated that formation of
layers 225, 226 and 228 may take on the order of about 4 hours. The
LED structure 220 also includes an approximately 20 to 200
nanometers thick p-type aluminum gallium aluminum nitride layer 230
(e.g. p-AlGaN, or p-GaN, or p-AlN) with a thickness in the range of
50-200 nanometers. The p-type nitride layer 230 is typically formed
in p-type nitride MOCVD reaction chamber 208 of cluster tool 200.
This process is expected to take on the order of an hour. It is to
be understood that the above thicknesses or thickness ranges are
exemplary embodiments, and that other suitable thicknesses or
thickness ranges are also considered within the spirit and scope of
embodiments of the present invention.
[0041] In addition to the throughput improvement for cluster tool
200, there may be additional benefits to a PVD chamber plus one to
four MOCVD chambers tool arrangement. For example, cost savings may
be achieved since less reaction gas may need to be delivered to the
first MOCVD chamber. In the case that the above process enables a
reduced thickness for the n-doped aluminum, gallium and nitrogen
portion of device layer 220, simpler down-the-line etch-back
processes may be performed. This may also enable the saving of
material and operation cost while reducing cycle time. Also, by
using a multiple aluminum nitride buffer layer in place of a single
aluminum nitride buffer layer, faster growth of the buffer layer is
enabled while maintaining a high quality buffer layer, thereby
reduced defectivity in the active layers of a device, such as a UV
light emitting device, may be achieved.
[0042] Thus, in accordance with an embodiment of the present
invention, a multi-chamber system includes a PVD chamber, or the
like having an aluminum nitride target to deposit a high
growth-rate aluminum nitride layer, a first MOCVD chamber to
deposit a high quality aluminum nitride layer, and a second MOCVD
chamber to deposit un-doped or n-type aluminum gallium nitride. The
multi-chamber system also includes third MOCVD chamber to deposit a
multiple quantum well (MQW) structure, and a fourth MOCVD chamber
to deposit p-type aluminum gallium nitride or p-type aluminum
gallium nitride, or both. In one embodiment, the PVD chamber having
the aluminum nitride target is for non-reactive sputtering of
aluminum nitride. In a specific such embodiment, the PVD chamber is
for non-reactive sputtering of aluminum nitride at a low or
slightly elevated temperature approximately in the range of 20-200
degrees Celsius. In another specific such embodiment, the PVD
chamber is for non-reactive sputtering of aluminum nitride at a
high temperature approximately in the range of less than about 800
degrees or greater than 1200 degrees Celsius in the case of a HVPE
chamber.
[0043] In another aspect of the present invention, methods of
fabricating aluminum gallium nitride-based UV light emitting device
with multiple aluminum nitride buffer layers are provided. For
example, FIG. 3 is a Flowchart 300 representing operations in a
method of fabricating an aluminum gallium nitride-based light UV
light source with a multiple process-formed aluminum nitride buffer
layer, in accordance with an embodiment of the present
invention.
[0044] Referring to operation 302 of Flowchart 300, a method
includes forming a first aluminum nitride layer above a substrate
in a PVD chamber, or the like. For example, an aluminum nitride
layer may be formed in a chamber such as chamber 202 of cluster
tool 200. In one embodiment, forming the aluminum nitride layer
includes sputtering from an aluminum nitride target housed in the
PVD chamber. In one embodiment, forming the aluminum nitride layer
includes performing the forming at a low to slightly elevated
substrate temperature approximately in the range of 20-200 degrees
Celsius. In one embodiment, forming the aluminum nitride layer
includes performing the forming at a high substrate temperature
approximately in the range of 200-800 degrees Celsius. In some
embodiments, the temperature may be below 800 degrees Celsius or
above 1200 degrees Celsius. In various embodiments, this step
enables a relatively quick growth of an aluminum nitride layer,
however the material may be relatively polycrystalline in
nature.
[0045] Referring to operation 303 of Flowchart 300, the method
includes forming a second aluminum nitride layer above the first
aluminum nitride layer. For example, an aluminum nitride layer may
be formed in a chamber such as chamber 203 of cluster tool 200. In
one embodiment, forming the aluminum nitride buffer layer includes
performing the forming in a MOCVD chamber. In one embodiment,
forming the aluminum nitride layer includes performing the forming
in a HVPE chamber. In some embodiments, the chamber temperature may
be between about 300 to 800 degrees Celsius to about 1200 degrees
Celsius. In various embodiments, this step enables a high quality
(relatively large single crystal) crystalline growth of an aluminum
nitride layer, however the material may be relatively slow to form.
Referring to operation 304 of Flowchart 300, the method includes
forming an un-doped or n-type aluminum gallium nitride layer on the
high quality aluminum nitride buffer layer. For example, an
un-doped or n-type aluminum gallium nitride layer may be formed in
a chamber such as chamber 204 of cluster tool 200. In one
embodiment, forming the un-doped or n-type aluminum gallium nitride
layer includes performing the forming in a MOCVD chamber. In one
embodiment, forming the un-doped or n-type aluminum gallium nitride
layer includes performing the forming in a HVPE chamber.
[0046] Referring to operation 306 of Flowchart 300, the method also
includes forming a MQW structure above the un-doped or n-type
aluminum gallium nitride layer. For example, a MQW structure may be
formed in a chamber such as chamber 206 of cluster tool 200. In one
embodiment, the MQW structure is composed of one or a plurality of
field pairs of AlGaN well/AlGaN barrier material layers.
[0047] Referring to operation 308 of Flowchart 300, the method
further includes forming a p-type aluminum gallium nitride or
p-type gallium nitride layer above the MQW structure. In some
embodiments, an undoped or p-type doped aluminum nitride layer may
be used prior to the growth of the p-type aluminum gallium nitride
or p-type gallium nitride layers. For example, the p-type aluminum
gallium nitride or p-type aluminum gallium nitride layer may be
formed in a chamber such as chamber 208 of cluster tool 200.
[0048] As discussed above, the amount of aluminum versus gallium
used within the chambers may be different in steps 304 to 308. The
proportions are selected, based upon desired range of output UV
light desired.
[0049] Exemplary embodiments of tool platforms suitable for housing
a PVD chamber along with three MOCVD chambers include an Opus.TM.
AdvantEdge.TM. system or a Centura.TM. system, both commercially
available from Applied Materials, Inc. of Santa Clara, Calif.
Embodiments of the present invention further include an integrated
metrology (IM) chamber as a component of the multi-chambered
processing platform. The IM chamber may provide control signals to
allow adaptive control of integrated deposition process, such as
the multiple segmented sputter or epitaxial growth processes
described above in association with FIG. 3. The IM chamber may
include a metrology apparatus suitable to measure various film
properties, such as thickness, roughness, composition, and may
further be capable of characterizing grating parameters such as
critical dimensions (CD), sidewall angle (SWA), feature height (HT)
under vacuum in an automated manner. Examples include, but are not
limited to, optical techniques like reflectometry and
scatterometry. In particularly advantageous embodiments, in-vacuo
optical CD (OCD) techniques are employed where the attributes of a
grating formed in a starting material are monitored as the sputter
and/or epitaxial growth proceeds. In other embodiments, metrology
operations are performed in a process chamber, e.g., in-situ in the
process chamber, rather than in a separate IM chamber.
[0050] A multi-chambered processing platform, such as cluster tool
200 may further include an optional substrate aligner chamber, as
well as load lock chambers holding cassettes, coupled to a transfer
chamber including a robotic handler. In one embodiment of the
present invention, adaptive control of the multi-chambered
processing platform 200 is provided by a controller. The controller
may be one of any form of general-purpose data processing system
that can be used in an industrial setting for controlling the
various subprocessors and subcontrollers. Generally, the controller
includes a central processing unit (CPU) in communication with a
memory and an input/output (I/O) circuitry, among other common
components. As an example, the controller may perform or otherwise
initiate one or more of the operations of any of the
methods/processes described herein, including the method described
in association with Flowchart 300. Any computer program code that
performs and/or initiates such operations may be embodied as a
computer program product. Each computer program product described
herein may be carried by a medium readable by a computer (e.g., a
floppy disc, a compact disc, a DVD, a hard drive, a random access
memory, etc.).
[0051] Suitable PVD chambers for the processes and tool
configurations contemplated herein may include the Endura PVD
system, commercially available from Applied Materials, Inc. of
Santa Clara, Calif. The Endura PVD system provides superior
electromigration resistance and surface morphology as well as low
cost of ownership and high system reliability. PVD processes
performed therein may be done so at requisite pressures and
suitable target-to-wafer distance which creates directional flux of
deposited species in the process cavity. Chambers compatible with
in-line systems such as the ARISTO chamber, also commercially
available from Applied Materials, Inc. of Santa Clara, Calif.,
provides automated loading and unloading capabilities, as well as a
magnetic carrier transport system, permitting significantly reduced
cycle times. The AKT-PiVot 55 KV PVD system, also commercially
available from Applied Materials, Inc. of Santa Clara, Calif., has
a vertical platform for sputtering deposition. The AKT-PiVot
system's module architecture delivers significantly faster cycle
time and enables a large variety of configurations to maximize
production efficiency. Unlike traditional in-line systems, the
AKT-PiVot's parallel processing capability eliminates bottlenecks
caused by different process times for each film layer. The system's
cluster-like arrangement also allows continuous operation during
individual module maintenance. The included rotary cathode
technology enables nearly 3.times.higher target utilization as
compared with conventional systems. The PiVot system's deposition
modules feature a pre-sputter unit that enables target conditioning
using only one substrate, rather than up to 50 substrates that are
needed with other systems to achieve the same results.
[0052] An example of an MOCVD deposition chamber which may be
suitable for use as one or more of MOCVD chambers 203, 204, 206, or
208, described above, is illustrated and described with respect to
FIG. 4. FIG. 4 is a schematic cross-sectional view of an MOCVD
chamber according to an embodiment of the invention. Exemplary
systems and chambers that may be adapted to practice the present
invention are described in U.S. patent application Ser. No.
11/404,516, filed on Apr. 14, 2006, and Ser. No. 11/429,022, filed
on May 5, 2006, both of which are incorporated by reference in
their entireties.
[0053] The apparatus 4100 shown in FIG. 4 includes a chamber 4102,
a gas delivery system 4125, a remote plasma source 4126, and a
vacuum system 4112. The chamber 4102 includes a chamber body 4103
that encloses a processing volume 4108. A showerhead assembly 4104
is disposed at one end of the processing volume 4108, and a
substrate carrier 4114 is disposed at the other end of the
processing volume 4108. A lower dome 4119 is disposed at one end of
a lower volume 4110, and the substrate carrier 4114 is disposed at
the other end of the lower volume 4110. The substrate carrier 4114
is shown in process position, but may be moved to a lower position
where, for example, the substrates 4140 may be loaded or unloaded.
An exhaust ring 4120 may be disposed around the periphery of the
substrate carrier 4114 to help prevent deposition from occurring in
the lower volume 4110 and also help direct exhaust gases from the
chamber 4102 to exhaust ports 4109. The lower dome 4119 may be made
of transparent material, such as high-purity quartz, to allow light
to pass through for radiant heating of the substrates 4140. The
radiant heating may be provided by a plurality of inner lamps 4121A
and outer lamps 4121B disposed below the lower dome 4119, and
reflectors 4166 may be used to help control chamber 4102 exposure
to the radiant energy provided by inner and outer lamps 4121A,
4121B. Additional rings of lamps may also be used for finer
temperature control of the substrate 4140.
[0054] The substrate carrier 4114 may include one or more recesses
4116 within which one or more substrates 4140 may be disposed
during processing. The substrate carrier 4114 may carry six or more
substrates 4140. In one embodiment, the substrate carrier 4114
carries eight substrates 4140. It is to be understood that more or
less substrates 4140 may be carried on the substrate carrier 4114.
Typical substrates 4140 may include sapphire or quartz. It is to be
understood that other types of UV transmissive substrates 4140,
such as glass substrates 4140, may be processed. Substrate 4140
size may range from 50 mm-100 mm in diameter or larger. The
substrate carrier 4114 size may range from 200 mm-750 mm. The
substrate carrier 4114 may be formed from a variety of materials,
including SiC or SiC-coated graphite. It is to be understood that
substrates 4140 of other sizes may be processed within the chamber
4102 and according to the processes described herein. The
showerhead assembly 4104 may allow for more uniform deposition
across a greater number of substrates 4140 and/or larger substrates
4140 than in traditional MOCVD chambers, thereby increasing
throughput and reducing processing cost per substrate 4140.
[0055] The substrate carrier 4114 may rotate about an axis during
processing. In one embodiment, the substrate carrier 4114 may be
rotated at about 2 RPM to about 100 RPM. In another embodiment, the
substrate carrier 4114 may be rotated at about 30 RPM. Rotating the
substrate carrier 4114 aids in providing uniform heating of the
substrates 4140 and uniform exposure of the processing gases to
each substrate 4140.
[0056] The plurality of inner and outer lamps 4121A, 4121B may be
arranged in concentric circles or zones (not shown), and each lamp
zone may be separately powered. In one embodiment, one or more
temperature sensors, such as pyrometers (not shown), may be
disposed within the showerhead assembly 4104 to measure substrate
4140 and substrate carrier 4114 temperatures, and the temperature
data may be sent to a controller (not shown) which can adjust power
to separate lamp zones to maintain a predetermined temperature
profile across the substrate carrier 4114. In another embodiment,
the power to separate lamp zones may be adjusted to compensate for
precursor flow or precursor concentration non-uniformity. For
example, if the precursor concentration is lower in a substrate
carrier 4114 region near an outer lamp zone, the power to the outer
lamp zone may be adjusted to help compensate for the precursor
depletion in this region.
[0057] The inner and outer lamps 4121A, 4121B may heat the
substrates 4140 to a temperature of about 400 degrees Celsius to
about 1200 degrees Celsius. It is to be understood that the
invention is not restricted to the use of arrays of inner and outer
lamps 4121A, 4121B. Any suitable heating source may be utilized to
ensure that the proper temperature is adequately applied to the
chamber 4102 and substrates 4140 therein. For example, in another
embodiment, the heating source may include resistive heating
elements (not shown) which are in thermal contact with the
substrate carrier 4114.
[0058] A gas delivery system 4125 may include multiple gas sources,
or, depending on the process being run, some of the sources may be
liquid sources rather than gases, in which case the gas delivery
system may include a liquid injection system or other means (e.g.,
a bubbler) to vaporize the liquid. The vapor may then be mixed with
a carrier gas prior to delivery to the chamber 4102. Different
gases, such as precursor gases, carrier gases, purge gases,
cleaning/etching gases or others may be supplied from the gas
delivery system 4125 to separate supply lines 4131, 4132, and 4133
to the showerhead assembly 4104. The supply lines 4131, 4132, and
4133 may include shut-off valves and mass flow controllers or other
types of controllers to monitor and regulate or shut off the flow
of gas in each line.
[0059] A conduit 4129 may receive cleaning/etching gases from a
remote plasma source 4126. The remote plasma source 4126 may
receive gases from the gas delivery system 4125 via supply line
4124, and a valve 4130 may be disposed between the showerhead
assembly 4104 and remote plasma source 4126. The valve 4130 may be
opened to allow a cleaning and/or etching gas or plasma to flow
into the showerhead assembly 4104 via supply line 4133 which may be
adapted to function as a conduit for a plasma. In another
embodiment, apparatus 4100 may not include remote plasma source
4126 and cleaning/etching gases may be delivered from gas delivery
system 4125 for non-plasma cleaning and/or etching using alternate
supply line configurations to shower head assembly 4104.
[0060] The remote plasma source 4126 may be a radio frequency or
microwave plasma source adapted for chamber 4102 cleaning and/or
substrate 4140 etching. Cleaning and/or etching gas may be supplied
to the remote plasma source 4126 via supply line 4124 to produce
plasma species which may be sent via conduit 4129 and supply line
4133 for dispersion through showerhead assembly 4104 into chamber
4102. Gases for a cleaning application may include fluorine,
chlorine or other reactive elements.
[0061] In another embodiment, the gas delivery system 4125 and
remote plasma source 4126 may be suitably adapted so that precursor
gases may be supplied to the remote plasma source 4126 to produce
plasma species which may be sent through showerhead assembly 4104
to deposit CVD layers, such as III-V films, for example, on
substrates 4140.
[0062] A purge gas (e.g., nitrogen) may be delivered into the
chamber 4102 from the showerhead assembly 4104 and/or from inlet
ports or tubes (not shown) disposed below the substrate carrier
4114 and near the bottom of the chamber body 4103. The purge gas
enters the lower volume 4110 of the chamber 4102 and flows upwards
past the substrate carrier 4114 and exhaust ring 4120 and into
multiple exhaust ports 4109 which are disposed around an annular
exhaust channel 4105. An exhaust conduit 4106 connects the annular
exhaust channel 4105 to a vacuum system 4112 which includes a
vacuum pump (not shown). The chamber 4102 pressure may be
controlled using a valve system 4107 which controls the rate at
which the exhaust gases are drawn from the annular exhaust channel
4105.
[0063] An example of a HVPE deposition chamber which may be
suitable for use as the HVPE chamber 204 of alternative embodiments
of chamber 204, described above, is illustrated and described with
respect to FIG. 5. FIG. 5 is a schematic cross-sectional view of a
HVPE chamber 500 suitable for the fabrication of group III-nitride
materials, in accordance with an embodiment of the present
invention.
[0064] The apparatus 500 includes a chamber 502 enclosed by a lid
504. Processing gas from a first gas source 510 is delivered to the
chamber 502 through a gas distribution showerhead 506. In one
embodiment, the gas source 510 includes a nitrogen containing
compound. In another embodiment, the gas source 510 includes
ammonia. In one embodiment, an inert gas such as helium or diatomic
nitrogen is introduced as well either through the gas distribution
showerhead 506 or through the walls 508 of the chamber 502. An
energy source 512 may be disposed between the gas source 510 and
the gas distribution showerhead 506. In one embodiment, the energy
source 512 includes a heater. The energy source 512 may break up
the gas from the gas source 510, such as ammonia, so that the
nitrogen from the nitrogen containing gas is more reactive.
[0065] To react with the gas from the first source 510, precursor
material may be delivered from one or more second sources 518. The
precursor may be delivered to the chamber 502 by flowing a reactive
gas over and/or through the precursor in the precursor source 518.
In one embodiment, the reactive gas includes a chlorine containing
gas such as diatomic chlorine. The chlorine containing gas may
react with the precursor source to form a chloride. In order to
increase the effectiveness of the chlorine containing gas to react
with the precursor, the chlorine containing gas may snake through
the boat area in the chamber 532 and be heated with the resistive
heater 520. By increasing the residence time that the chlorine
containing gas is snaked through the chamber 532, the temperature
of the chlorine containing gas may be controlled. By increasing the
temperature of the chlorine containing gas, the chlorine may react
with the precursor faster. In other words, the temperature is a
catalyst to the reaction between the chlorine and the
precursor.
[0066] In order to increase the reactivity of the precursor, the
precursor may be heated by a resistive heater 520 within the second
chamber 532 in a boat. The chloride reaction product may then be
delivered to the chamber 502. The reactive chloride product first
enters a tube 522 where it evenly distributes within the tube 522.
The tube 522 is connected to another tube 524. The chloride
reaction product enters the second tube 524 after it has been
evenly distributed within the first tube 522. The chloride reaction
product then enters into the chamber 502 where it mixes with the
nitrogen containing gas to form a nitride layer on a substrate 516
that is disposed on a susceptor 514. In one embodiment, the
susceptor 514 includes silicon carbide. The nitride layer may
include n-type aluminum gallium nitride for example. The other
reaction products, such as nitrogen and chlorine, are exhausted
through an exhaust 526.
[0067] Some embodiments of the present invention relate to forming
UV light emitting devices using aluminum gallium nitride (AlGaN)
layers in a dedicated chamber of a fabrication tool, such as in a
dedicated MOCVD, or MOVPE, or MBE, or CBE chamber. In at least some
embodiments, the group III-nitride material layers are formed
epitaxially. They may be formed directly on a substrate or on a
buffers layer disposed on a substrate. Other contemplated
embodiments include p-type doped aluminum gallium nitride layers
deposited directly on PVD-formed buffer layers, e.g., PVD-formed
aluminum nitride.
[0068] It is to be understood that embodiments of the present
invention are not limited to formation of layers on the select
substrates described above. Other embodiments may include the use
of any suitable non-patterned or patterned single crystalline
substrate upon which a high quality aluminum nitride layer may be
sputter-deposited, e.g., in a non-reactive PVD approach. The
substrate may be one such as, but not limited to, a sapphire
(Al.sub.2O.sub.3) substrate, a silicon (Si) substrate, a silicon
carbide (SiC) substrate, a silicon on diamond (SOD) substrate, a
quartz (SiO.sub.2) substrate, a glass substrate, a zinc oxide (ZnO)
substrate, a magnesium oxide (MgO) substrate, and a lithium
aluminum oxide (LiAlO.sub.2) substrate. Any well know method, such
as masking and etching may be utilized to form features, such as
posts, from a planar substrate to create a patterned substrate. In
a specific embodiment, however, a patterned sapphire substrate
(PSS) is used with a (0001) orientation. Patterned sapphire
substrates may be ideal for use in the manufacturing of LEDs
because they increase the light extraction efficiency which is
extremely useful in the fabrication of a new generation of solid
state lighting devices. Substrate selection criteria may include
lattice matching to mitigate defect formation and coefficient of
thermal expansion (CTE) matching to mitigate thermal stresses.
[0069] As described above, the group III-nitride films can be
doped. The group III-nitride films can be p-typed doped using any
p-type dopant such as but not limited Mg, Be, Ca, Sr, or any Group
I or Group II element have two valence electrons. The group
III-nitride films can be p-type doped to a conductivity level of
between 1.times.10.sup.16 to 1.times.10.sup.20 atoms/cm.sup.3. The
group III-nitride films can be n-typed doped using any n-type
dopant such as but not limited silicon or oxygen, or any suitable
Group IV or Group VI element. The group III-nitride films can be
n-type doped to a conductivity level of between 1.times.10.sup.16
to 1.times.10.sup.20 atoms/cm.sup.3.
[0070] It is to be understood that the above processes may be
performed in a dedicated chamber within a cluster tool, or other
tool with more than one chamber, e.g. an in-line tool arranged to
have a dedicated chamber for fabricating layers of a UV light
emitting device. It is also to be understood that embodiments of
the present invention need not be limited to the fabrication of UV
light emitting devices. For example, in another embodiment, devices
other than UV light emitting devices may be fabricated by
approaches described herein, such as but not limited to
field-effect transistor (FET) devices. In such embodiments, there
may not be a need for a p-type material on top of a structure of
layers. Instead, an n-type or un-doped material may be used in
place of the p-type layer. It is also to be understood that
multiple operations, such as various combinations of depositing
and/or thermal annealing, may be performed in a single process
chamber.
[0071] Thus, fabrication of aluminum gallium nitride-based UV light
emitting devices with a multi-layer aluminum nitride buffer layers
has been disclosed. In accordance with an embodiment of the present
invention, a multi-chamber system includes a PVD chamber having a
target composed of a material including aluminum to quickly deposit
a base aluminum nitride material. A chamber adapted to deposit a
high quality aluminum nitride material. A chamber adapted to
deposit un-doped or n-type aluminum gallium nitride, or both, is
also included in the multi-chamber system. In one embodiment, the
target of the PVD chamber is composed of aluminum nitride. In one
embodiment, the chamber adapted to deposit the higher quality
aluminum nitride material or the un-doped or n-type aluminum
gallium nitride is a MOCVD chamber. In one embodiment, the PVD
chamber and the chamber adapted to deposit un-doped or n-type
aluminum gallium nitride are included in a cluster or an in-line
tool arrangement.
[0072] Representative claim enabled herein include:
[0073] 1. A method of fabricating an ultraviolet (UV) light
emitting device comprising:
[0074] receiving a UV transmissive substrate;
[0075] forming a UV transmissive layer comprising aluminum nitride
upon the UV transmissive substrate, the UV transmissive layer
comprising: [0076] forming a first UV transmissive layer comprising
aluminum nitride upon the UV transmissive substrate using a first
deposition technique at a temperature less than about 800 degrees
Celsius or greater than about 1200 degrees Celsius; and [0077]
forming a second UV transmissive layer comprising aluminum nitride
upon the first UV transmissive layer comprising aluminum nitride
using a second deposition technique that is different from the
first technique, at a temperature within a range of about 800
degrees Celsius to about 1200 degrees Celsius; and
[0078] forming a UV light emitting layer structure on the UV
transmissive layer, the UV light emitting layer structure
comprising: [0079] forming an n-type layer comprising aluminum
gallium nitride layer upon the UV transmissive layer; [0080]
forming one or more quantum well structures comprising aluminum
gallium nitride upon the n-type layer; and [0081] forming a p-type
nitride layer upon the one or more quantum well structures.
[0082] 2. The method of claim 1 wherein the UV transmissive layer
comprising aluminum nitride has a thickness within a range of about
100 nm to about 3 microns.
[0083] 3. The method of claim 1 wherein the UV transmissive layer
comprising aluminum nitride has a thickness of about 2 microns.
[0084] 4. The method of claim 1 wherein the UV transmissive layer
comprising aluminum nitride has a transmissivity in the UV
wavelength range within a range of about 50% to about 99%.
[0085] 5. The method of claim 1 wherein the method of forming the
first UV transmissive layer uses a deposition process selected from
a group consisting of: hydride vapor phase epitaxy, atomic layer
deposition, liquid phase epitaxy, physical vapor deposition,
sputtering, solid source solution epitaxy.
[0086] 6. The method of claim 1 wherein the method of forming the
second UV transmissive layer uses a deposition process selected
from a group consisting of: metalorganic chemical vapor deposition,
metalorganic vapor phase epitaxy, molecular beam epitaxy, chemical
beam epitaxy.
[0087] 7. The method of claim 1
[0088] wherein the first UV transmissive layer comprises
polycrystalline aluminum nitride; and
[0089] wherein the second UV transmissive layer comprises single
crystal aluminum nitride.
[0090] 8. The method of claim 1 wherein the substrate is selected
from a group consisting of: quartz, sapphire and aluminum
nitride.
[0091] 9. The method of claim 1
[0092] wherein the n-type layer comprises AlxGa(1-x)N;
[0093] wherein the p-type layer comprises AlyGa(1-y)N; and
[0094] wherein x is dissimilar to y.
[0095] 10. The method of claim 9 wherein
[0096] wherein the one or more quantum well structures comprises
AlzGa(1-z)N;
[0097] wherein z is dissimilar to x.
[0098] 11. An ultraviolet (UV) light emitting device
comprising:
[0099] a UV transmissive substrate;
[0100] a UV transmissive layer comprising aluminum nitride layer
disposed upon the UV transmissive substrate, the UV transmissive
layer comprising: [0101] a first UV transmissive layer comprising
aluminum nitride disposed upon the UV transmissive substrate at a
temperature less than about 800 degrees Celsius or greater than
about 1200 degrees Celsius; and [0102] a second UV transmissive
layer aluminum nitride disposed upon the first UV transmissive
aluminum nitride material at a temperature within a range of about
800 degrees Celsius to about 1200 degrees Celsius; and
[0103] a UV light emitting structure disposed upon the UV
transmissive layer, the UV light emitting layer structure
comprising: [0104] an n-type layer comprising aluminum gallium
nitride disposed upon the UV transmissive layer; [0105] one or more
quantum well structures disposed upon the n-type layer; and [0106]
a p-type layer comprising nitride material disposed upon the one or
more quantum well structures.
[0107] 12. The UV device of claim 11 wherein the UV transmissive
layer comprising aluminum nitride has a thickness within a range
within about 100 nm to about 3 microns.
[0108] 13. The UV device of claim 11 wherein the UV transmissive
layer comprising aluminum nitride has a thickness of about 2
microns.
[0109] 14. The UV device of claim 11 wherein the UV transmissive
layer comprising aluminum nitride has a transmissivity in the UV
wavelength range within a range of about 50% to about 99%.
[0110] 15. The UV device of claim 11
[0111] wherein the first UV transmissive layer comprises
polycrystalline aluminum nitride; and
[0112] wherein the second UV transmissive layer comprises single
crystal aluminum nitride.
[0113] 16. The UV device of claim 1 wherein the UV transmissive
substrate comprises a plurality of patterns that scatter strongly
with short wavelength UV light.
[0114] 17. The UV device of claim 16 wherein the UV-scattering
patterns comprises patterns within a height range of about 100 nm
to about 500 nm.
[0115] 18. The UV device of claim 11 wherein the UV transmissive
substrate is selected from a group consisting of: quartz, sapphire
and aluminum nitride.
[0116] 19. The UV device of claim 11
[0117] wherein the n-type layer comprises AlxGa(1-x)N;
[0118] wherein the p-type layer comprises AlyGa(1-y)N; and
[0119] wherein x is dissimilar to y.
[0120] 20. The UV device of claim 19 wherein
[0121] wherein the one or more quantum well structures comprises
AlzGa(1-z)N;
[0122] wherein z is dissimilar to x.
[0123] 21. A multi-chambered deposition system comprising:
[0124] a first chamber for depositing a first UV transmissive layer
comprising aluminum nitride at temperature less than about 800
degrees Celsius or greater than about 1200 degrees Celsius
[0125] a second chamber for depositing a second UV transmissive
layer comprising aluminum nitride at a temperature within a range
of about 800 degrees Celsius to about 1200 degrees Celsius; upon
the first UV transmissive layer comprising aluminum nitride;
[0126] and depositing an n-type layer comprising aluminum gallium
nitride material upon the second UV transmissive layer; and
[0127] depositing one or more quantum well structures comprising
aluminum gallium nitride upon the n-type layer; and
[0128] depositing a p-type nitride layer upon the one or more
quantum well structures.
[0129] 22. The system of claim 21 wherein the first chamber
comprises a chamber adapted to perform a hydride vapor phase
epitaxy, atomic layer deposition, liquid phase epitaxy, physical
vapor deposition, sputtering, or solid source solution growth.
[0130] 23. The system of claim 21 wherein the second chamber
comprises a chamber adapted to perform metalorganic chemical vapor
deposition, metalorganic vapor phase epitaxy, molecular beam
epitaxy, or chemical beam epitaxy.
[0131] 24. The system of claim 21 wherein the wafer transfer
between the first chamber and the second chamber is automated.
[0132] 25. The system of claim 21 wherein the wafer transfer
between the first chamber and the second chamber is performed under
vacuum.
[0133] 26. A multi-chambered deposition system comprising:
[0134] a first chamber for depositing a first UV transmissive layer
comprising aluminum nitride at temperature less than about 800
degrees Celsius or greater than about 1200 degrees Celsius
[0135] a second chamber for depositing a second UV transmissive
layer comprising aluminum nitride at a temperature within a range
of about 800 degrees Celsius to about 1200 degrees Celsius; upon
the first UV transmissive layer comprising aluminum nitride
[0136] a third chamber for depositing an n-type layer comprising
aluminum gallium nitride material upon the second UV transmissive
layer; and
[0137] depositing one or more quantum well structures comprising
aluminum gallium nitride upon the n-type layer; and
[0138] depositing a p-type nitride layer upon the one or more
quantum well structures.
[0139] 27. The system of claim 26 wherein the first chamber
comprises a chamber adapted to perform a hydride vapor phase
epitaxy, atomic layer deposition, liquid phase epitaxy, physical
vapor deposition, sputtering, solid source solution growth.
[0140] 28. The system of claim 26 wherein the second and third
chamber comprise a chamber adapted to perform metalorganic chemical
vapor deposition, metalorganic vapor phase epitaxy, molecular beam
epitaxy, or chemical beam epitaxy.
[0141] 29. The system of claim 26 wherein the wafer transfer among
the first, second and third chamber is automated.
[0142] 30. The system of claim 26 wherein the wafer transfer among
the first, second and third chamber is performed under vacuum.
[0143] 31. A multi-chambered deposition system comprising:
[0144] a first chamber for depositing a first UV transmissive layer
comprising aluminum nitride at temperature less than about 800
degrees Celsius or greater than about 1200 degrees Celsius
[0145] a second chamber for depositing a second UV transmissive
layer comprising aluminum nitride at a temperature within a range
of about 800 degrees Celsius to about 1200 degrees Celsius; upon
the first UV transmissive layer comprising aluminum nitride
[0146] a third chamber for depositing an n-type layer comprising
aluminum gallium nitride material upon the second UV transmissive
layer; and
[0147] depositing one or more quantum well structures comprising
aluminum gallium nitride upon the n-type layer; and
[0148] a fourth chamber for depositing a p-type nitride layer upon
the one or more quantum well structures.
[0149] 32. The system of claim 31 wherein the first chamber
comprises a chamber adapted to perform a hydride vapor phase
epitaxy, atomic layer deposition, liquid phase epitaxy, physical
vapor deposition, sputtering, solid source solution growth.
[0150] 33. The system of claim 31 wherein the second, third and
fourth chamber comprise a chamber adapted to perform metalorganic
chemical vapor deposition, metalorganic vapor phase epitaxy,
molecular beam epitaxy, or chemical beam epitaxy.
[0151] 34. The system of claim 31 wherein the wafer transfer among
the first, second, third, and fourth chamber is automated.
[0152] 35. The system of claim 31 wherein the wafer transfer among
the first, second, third, and fourth chamber is performed under
vacuum.
[0153] 36. A multi-chambered deposition system comprising:
[0154] a first chamber for depositing a first UV transmissive layer
comprising aluminum nitride at temperature less than about 800
degrees Celsius or greater than about 1200 degrees Celsius
[0155] a second chamber for depositing a second UV transmissive
layer comprising aluminum nitride at a temperature within a range
of about 800 degrees Celsius to about 1200 degrees Celsius; upon
the first UV transmissive layer comprising aluminum nitride
[0156] a third chamber for depositing an n-type layer comprising
aluminum gallium nitride material upon the second UV transmissive
layer; and
[0157] a fourth chamber for depositing one or more quantum well
structures comprising aluminum gallium nitride upon the n-type
layer; and
[0158] a fifth chamber for depositing a p-type nitride layer upon
the one or more quantum well structures.
[0159] 37. The system of claim 36 wherein the first chamber
comprises a chamber adapted to perform a hydride vapor phase
epitaxy, atomic layer deposition, liquid phase epitaxy, physical
vapor deposition, sputtering, solid source solution growth.
[0160] 38. The system of claim 36 wherein the second, third, fourth
and fifth chamber comprise a chamber adapted to perform
metalorganic chemical vapor deposition, Metalorganic vapor phase
epitaxy, molecular beam epitaxy, or chemical beam epitaxy.
[0161] 39. The system of claim 36 wherein the wafer transfer among
the first, second, third, fourth and fifth chamber is
automated.
[0162] 40. The system of claim 36 wherein the wafer transfer among
the first, second, third, fourth and fifth chamber is performed
under vacuum.
* * * * *