U.S. patent application number 11/626388 was filed with the patent office on 2008-07-24 for method, system, and apparatus for the growth of sic and related or similar material, by chemical vapor deposition, using precursors in modified cold-wall reactor.
Invention is credited to Yuri Makarov, Michael Spencer.
Application Number | 20080173239 11/626388 |
Document ID | / |
Family ID | 39640034 |
Filed Date | 2008-07-24 |
United States Patent
Application |
20080173239 |
Kind Code |
A1 |
Makarov; Yuri ; et
al. |
July 24, 2008 |
Method, system, and apparatus for the growth of SiC and related or
similar material, by chemical vapor deposition, using precursors in
modified cold-wall reactor
Abstract
An approach for the growth of high-quality epitaxial silicon
carbide (SiC) films and boules, using the Chemical Vapor Deposition
(CVD) technique is described here. The method comprises
modifications in the design of the typical cold-wall CVD reactors,
providing a better temperature uniformity in the reactor bulk and a
low temperature gradient in the vicinity of the substrate, and an
approach to increase the silicon carbide growth rate and to improve
the quality of the growing layers, using halogenated
carbon-containing precursors (carbon tetrachloride CCl.sub.4 or
halogenated hydrocarbons, CHCl.sub.3, CH.sub.2Cl.sub.2, CH.sub.3Cl,
etc.), or introducing other chlorine-containing species in the gas
phase in the growth chamber. The etching effect, proper ranges, and
high temperature growth are also examined.
Inventors: |
Makarov; Yuri; (Richmond,
VA) ; Spencer; Michael; (Ithaca, NY) |
Correspondence
Address: |
MAXVALUEIP CONSULTING
11204 ALBERMYRTLE ROAD
POTOMAC
MD
20854
US
|
Family ID: |
39640034 |
Appl. No.: |
11/626388 |
Filed: |
January 24, 2007 |
Current U.S.
Class: |
118/724 ;
118/728 |
Current CPC
Class: |
C30B 25/02 20130101;
C30B 25/08 20130101; C23C 16/32 20130101; C23C 16/4405 20130101;
C23C 16/4411 20130101; C30B 29/36 20130101 |
Class at
Publication: |
118/724 ;
118/728 |
International
Class: |
C23C 16/00 20060101
C23C016/00 |
Claims
1. A chemical vapor deposition system, said system comprising: an
enclosure with walls; a substrate holder; and an inlet for one or
more gasses, wherein said system uses or produces one or more of
the followings: halogenated carbon, carbon tetrachloride,
halogenated hydrocarbon, CHCl.sub.3, CH.sub.2Cl.sub.2, or
CH.sub.3Cl.
2. A system as recited in claim 1, wherein said halogenated carbon
comprises one or more of the followings: F, Cl, Br, I, or At.
3. A system as recited in claim 1, wherein said halogenated
hydrocarbon comprises one or more of the followings: F, Cl, Br, I,
or At.
4. A system as recited in claim 1, wherein said system uses or
produces a gas comprising Si, H, C, and Cl species.
5. A system as recited in claim 1, wherein said system is used for
the growth of SiC.
6. A system as recited in claim 1, wherein said system comprises a
heating element.
7. A system as recited in claim 1, wherein said system comprises a
water cooling unit.
8. A system as recited in claim 1, wherein said system produces or
uses one or more of the followings: SiH.sub.2, SiH, Si, CCl.sub.3,
or CCl.sub.2.
9. A system as recited in claim 1, wherein said system produces or
uses one or more of the followings: HCl, CH.sub.3Cl, CH.sub.4, or
SiH.sub.2Cl.sub.2.
10. A system as recited in claim 1, wherein said system produces or
uses one or more of the followings: SiCl.sub.2, CH.sub.4, or
HCl.
11. A system as recited in claim 1, wherein said system produces an
etching agent.
12. A system as recited in claim 1, wherein said substrate holder
holds a wafer or substrate of at least 3 inch in diameter.
13. A system as recited in claim 1, wherein said system comprises
one or more of the following materials, or their alloys or
mixtures: graphite, SiC-coated graphite, graphite coated with
carbides of refractory metals, carbides of refractory metals,
quartz, quartz coated with refractory metals, or pure refractory
metals.
14. A system as recited in claim 1, wherein said system comprises
at least a refractory metal.
15. A system as recited in claim 14, wherein said at least a
refractory metal is made of one or more of the following materials,
or their alloys or mixtures: tantalum, niobium, titanium, tungsten,
molybdenum, zirconium, or hafnium.
16. A system as recited in claim 1, wherein said system is a
cold-wall CVD reactor.
17. A system as recited in claim 1, wherein said system has a
relatively uniform temperature distribution around said substrate
holder.
18. A system as recited in claim 1, wherein said system is used for
the growth of semiconductor materials.
19. A system as recited in claim 1, wherein said system is used for
the growth of epitaxial materials.
20. A system as recited in claim 1, wherein said system uses a
specific ratio of the number of Si to C atoms in input gas
mixture.
21. A system as recited in claim 1, wherein said system uses a
specific ratio of the number of Si to Cl atoms in input gas
mixture.
22. A system as recited in claim 1, wherein said system uses an
input gas mixture with a value in the range of 0.02 to 1.5 for the
ratio of the number of Si to Cl atoms in said input gas
mixture.
23. A system as recited in claim 1, wherein said system uses an
input gas mixture with a value in the range of 0.7 to 1.3 for the
ratio of the number of Si to C atoms in said input gas mixture.
24. A system as recited in claim 1, wherein said system uses an
input gas mixture with a value close to the range of 0.02 to 1.5
for the ratio of the number of Si to Cl atoms in said input gas
mixture.
25. A system as recited in claim 1, wherein said system uses an
input gas mixture with a value close to the range of 0.7 to 1.3 for
the ratio of the number of Si to C atoms in said input gas
mixture.
26. A system as recited in claim 1, wherein said system uses a
relatively low growth temperature.
27. A system as recited in claim 1, wherein said system produces a
relatively high growth rate.
28. A system as recited in claim 1, wherein said system accepts
multiple substrates on said substrate holder.
29. A system as recited in claim 1, wherein said system suppresses
parasitic deposits inside said system.
30. A system as recited in claim 1, wherein said system uses a Si
substrate coated with a thin film of monocrystalline SiC.
31. A system as recited in claim 1, wherein said system produces or
uses one or more of the CH.sub.iCl.sub.j or SiH.sub.mCl.sub.n
species, wherein i, j, m, and n are non-negative integers.
32. A system as recited in claim 1, wherein said system uses a
growth temperature in the range of 1000 to 1800 centigrade.
33. A system as recited in claim 1, wherein said system reduces the
consumption of the source materials.
34. A system as recited in claim 1, wherein said system uses a
growth temperature in the range of 1500 to 1800 centigrade.
35. A system as recited in claim 1, wherein said system uses a
relatively high growth temperature.
Description
CROSS-REFERENCE TO A RELATED APPLICATION
[0001] This application is related to another co-pending U.S.
application filed on the same day, with same title, inventors, and
assignee.
BACKGROUND
[0002] A novel approach for the growth of high-quality epitaxial
silicon carbide (SiC) films and boules using the Chemical Vapor
Deposition (CVD) technique is described here, as one embodiment.
The method comprises: [0003] modifications in the design of the
typical cold-wall CVD reactors, providing a better temperature
uniformity in the reactor bulk and a low temperature gradient in
the vicinity of the substrate; [0004] an approach to increase the
silicon carbide growth rate and to improve the quality of the
growing layers, using halogenated carbon-containing precursors
(carbon tetrachloride CCl.sub.4 or halogenated hydrocarbons,
CHCl.sub.3, CH.sub.2Cl.sub.2, CH.sub.3Cl, etc.), or introducing
other chlorine-containing species in the gas phase in the growth
chamber.
[0005] Some of the prior art dealing with this or similar
technology are listed here (US patent number and its title):
[0006] U.S. Pat. No. 7,061,073, Diamondoid-containing
capacitors,
[0007] U.S. Pat. No. 6,989,428, Methods of preparing
polysilynes,
[0008] U.S. Pat. No. 6,984,591, Precursor source mixtures,
[0009] U.S. Pat. No. 6,982,230, Deposition of hafnium oxide and/or
zirconium oxide, and fabrication of passivated electronic
structures,
[0010] U.S. Pat. No. 6,958,253, Process for deposition of
semiconductor films,
[0011] U.S. Pat. No. 6,878,628, In-situ reduction of copper oxide
prior to silicon carbide deposition,
[0012] U.S. Pat. No. 6,849,109, Inorganic dopants, inks, and
related nanotechnology,
[0013] U.S. Pat. No. 6,830,822, Inorganic colors and related
nanotechnology,
[0014] U.S. Pat. No. 6,821,825, Process for deposition of
semiconductor films,
[0015] U.S. Pat. No. 6,800,552, Deposition of transition metal
carbides,
[0016] U.S. Pat. No. 6,783,589, Diamondoid-containing materials in
microelectronics,
[0017] U.S. Pat. No. 6,733,830, Processes for depositing low
dielectric constant materials,
[0018] U.S. Pat. No. 6,482,262, Deposition of transition metal
carbides,
[0019] U.S. Pat. No. 5,851,942, Preparation of boron-doped silicon
carbide fibers,
[0020] U.S. Pat. No. 5,792,416, Preparation of boron-doped silicon
carbide fibers,
[0021] U.S. Pat. No. 5,789,024, Subnanoscale composite,
N2-permselective membrane for the separation of volatile organic
compounds,
[0022] U.S. Pat. No. 5,593,783, Photochemically modified diamond
surfaces, and method of making the same,
[0023] U.S. Pat. No. 5,536,323, Apparatus for flash vaporization
delivery of reagents,
[0024] U.S. Pat. No. 5,322,913, Polysilazanes and related
compositions, processes, and uses,
[0025] U.S. Pat. No. 5,204,314, Method for delivering an involatile
reagent in vapor form to a CVD reactor,
[0026] U.S. Pat. No. 5,055,431, Polysilazanes and related
compositions, processes, and uses,
[0027] U.S. Pat. No. 5,008,422, Polysilazanes and related
compositions, processes, and uses,
[0028] U.S. Pat. No. 4,952,715, Polysilazanes and related
compositions, processes, and uses, and
[0029] U.S. Pat. No. 4,228,142, Process for producing diamond-like
carbon.
[0030] Other prior results are summarized in the following
references: [0031] Y. Gao, J. H. Edgar, J. Chaudhari, S. N. Cheema,
M. V. Sidorov, D. N. Braski, Journ. Cryst. Growth 191, 439 (1988).
[0032] J. Chaudhari, K. Ignatiev, J. H. Edgar, Z. Y. Xie, Y. Gao,
Z. Rek, Mater. Sci. Eng. B76, 217, (2000). [0033] S. Jonas, C.
Paluszkiewicz, W. S. Ptak, W. Sadowski, J. Molec. Structure 349, 72
(1995). [0034] F. Loumagne, F. Langlais, R. Naslain, J. Cryst.
Growth 155, 205, (1995). [0035] C.-F. Wang, D.-S. Tsai, Materials
Chemistry and Physics 63, 196, (2000). [0036] H. Sone, T. Kaneko,
N. Miyakawa, Journ. Cryst. Growth 219, 245 (2000). [0037] Y.-P. Wu
and Y.-S. Won, Combustion and Flame 122, 312 (2000).
[0038] However, none of the prior art teaches the features of the
current invention.
SUMMARY
[0039] In this invention, we present the following:
[0040] 1. An apparatus for the improvement of temperature
distributions in the typical commercial cold-wall CVD reactors,
which comprises:
[0041] an addition of the refractory insert in the reactor, to get
more uniform temperature distribution and to decrease the
temperature gradient in the vicinity of the substrate. Possible
materials for such an insert are graphite, SiC-coated graphite,
graphite coated with carbides of refractory metals (tantalum,
niobium, titanium, tungsten, molybdenum, zirconium, hafnium, etc.),
carbides of the refractory metals listed above, quartz or quartz
coated with refractory metals (molybdenum, tungsten, niobium,
etc.), or pure refractory metals listed above; and
[0042] an addition of the showerhead unit near the inlet of the
typical commercial cold-wall reactor, which increases the
temperature in the inlet region and improves the flow patterns in
the reactor. The construction materials for this unit are the same
as for the insert, described in the paragraph above.
[0043] 2. A method of SiC layer CVD growth, wherein the increase in
silicon carbide growth rate and in the epilayer quality are
achieved by using input gas mixture containing silicon and carbon
species, along with chlorine-containing components with optimal
silicon-to-carbon and silicon-to-chlorine ratios. This approach can
be realized using halogenated carbon precursors (carbon
tetrachloride CCl.sub.4 or halogenated hydrocarbons, CHCl.sub.3,
CH.sub.2Cl.sub.2, CH.sub.3Cl, etc.), or introducing other
chlorine-containing species in the gas phase of the growth
chamber.
[0044] Increase in SiC growth rate, along with the improvement of
the growing layer quality, are achieved under the following
silicon-to-carbon and silicon-to-chlorine ratios (range of
values):
x.sup.(int)(Si)/x.sup.(int)(C)=0.7-1.3,
x.sup.(int)(Si)/x.sup.(int)(Cl)=0.02-1.5,
[0045] where x.sup.(int)(Si), x.sup.(int)(C), x.sup.(int)(Cl) are
the number of silicon, carbon, and chlorine atoms in the input gas
mixture, respectively.
[0046] Note that for all the discussions in this patent
application, the ranges (such as those mentioned above) are
approximate ranges/values, and any value close to those ranges (but
outside those ranges) would also be considered included and
protected under this current patent. That is, for the numbers
outside the ranges, but in close proximity (e.g. in the same order
of magnitudes, or relatively similar values), the system may not
work in optimum conditions, but still produces excellent results.
In other words, the boundaries of the ranges are not sharply
defined, as absolute cut-off values or thresholds. Instead, they
are gradually changed, and they are meant to be as guidelines for
focusing on the optimum values, and, still, for other outside
close-by values, ranges, or regions, the system is producing good
or excellent material and results, as well. (This above discussion
applies to all ranges mentioned in the current patent
application.)
[0047] An etching effect, decreasing the net SiC growth rate, can
be expected at x.sup.(int)(Si)/x.sup.(int)(Cl)<0.66.
[0048] In contrast to the conventional SiC growth from silane
(SiH.sub.4) and propane (C.sub.3H.sub.8), some basic mechanisms of
the process are changed, as a result of presence of chlorine atoms
in the gas phase in a certain optimal amount. First, SiCl.sub.2
becomes the major source providing Si for SiC growth, instead of
SiH.sub.2 and Si in the conventional approach. Second, the
formation of silicon clusters and particles in the gas phase is
suppressed by chlorine-containing species under the above process
conditions. These effects give rise to an increase in the net
growth rate, and improve the quality of the grown layers.
[0049] 3. A method for reducing the growth temperatures from the
existing >1500.degree. C. to below 1500.degree. C. (in the range
1000 to 1500.degree. C.). The lower growth temperature is achieved
by the addition of halogenated carbon precursors or other
chlorine-containing additions, to provide the above mentioned
chlorine-to-silicon and silicon-to-carbon ratios:
x.sup.(int)(Si)/x.sup.(int)(C)=0.7-1.3,
x.sup.(int)(Si)/x.sup.(int)(Cl)=0.02-1.5.
[0050] It is well-known that silicon carbide growth rate decreases
with the temperature decrease for the growth conditions (total
pressure range, input precursor flow rates, reactor geometry, etc.)
typical for the process. However, epitaxial layers grown at low
temperatures (see e.g. A. Itoh and H. Matsunami, IEEE Electron
Device Lett. 16, 280, (1995)) (describing SiC epilayer growth at
temperatures below 1200.degree. C.) are characterized by perfect
epilayer quality. So, there is a need to increase SiC growth rate
at low temperatures to produce perfect SiC epilayers, effectively.
The above mentioned addition of chlorine-containing species
increases the net SiC growth rate due to mechanisms described here.
As a result, the process temperature can be significantly
decreased.
[0051] The capability to grow SiC epitaxial layers below
1500.degree. C. allows the growth of Silicon Carbide epitaxial
layers on composite substrates that may comprise of Silicon
substrates, coated with a thin film of monocrystalline SiC.
[0052] 4. A method of suppressing parasitic deposits on the
susceptor, reactor walls, and injector system. Parasitic deposits
forming at the reactor units during SiC growth are known to be one
of the main technical problems in the process. Indeed, silicon,
carbon, SiC, or mixed Si--SiC/C--SiC solid phases can be generated
on the walls of the injector unit, susceptor and susceptor holder,
reactor walls, etc. This negative effect leads to the losses in the
source material for SiC growth, deviations in the gas composition
and flow characteristics during the process, and/or changes in the
injector geometry. In turn, it results in the variations in SiC
growth rate, stoichiometry, and the quality of the growing layers.
Due to its etching effect, chlorine addition in the system at the
following silicon-to-carbon and silicon-to-chlorine ratios will
suppress parasitic deposits formation:
x.sup.(int)(Si)/x.sup.(int)(C)=0.7-1.3,
x.sup.(int)(Si)/x.sup.(int)(Cl)=0.02-1.5,
[0053] This follows from the fact that chlorine interaction with
the above listed deposit phases, in hydrogen ambience, results in
the formation of volatile CH.sub.iCl.sub.j and SiH.sub.iCl.sub.j
species. Hence, parasitic deposits will be effectively etched, and
volatile products of this etching will return silicon and carbon as
source materials for SiC growth.
[0054] 5. In some applications, to get high quality material, we
have used high temperatures, in the range of 1500-1800 Centigrade,
with an excellent material characteristics.
BRIEF DESCRIPTION OF THE DRAWINGS
[0055] FIG. 1. (a) A typical design of the commercial cold-wall CVD
reactors; and (b) the modified reactor design with the heat
shielding insert and graphite showerhead.
[0056] FIG. 2. One possible geometry/example of the graphite insert
with the showerhead for the cold-wall reactor.
[0057] FIG. 3. The improvement of the uniformity in the temperature
distributions as a result of the design modifications in the
reactor.
[0058] FIG. 4. The decrease in the silicon cluster density near the
substrate, with hydrochloric acid input flow rate estimated for a
typical reactor, e.g. at T.sub.substrate of 1600.degree. C., total
pressure of 200 Torr, silane flow rate=65 cc (10% in hydrogen),
propane flow rate=96.8 cc (2% in hydrogen), rotation rate=1000 rpm,
main hydrogen flow rate=12500 cc, reactant push flow rate=1500 cc,
and pyrometer opening purge=550 cc.
[0059] FIG. 5. The comparison of the general mechanisms of the
gas-phase chemistry during SiC growth for the conventional approach
(growth from silane and propane) (shown in part (a), as
conventional method), versus the method of growth in Si--C--H--Cl
ambience, as shown in part (b), as our method.
[0060] FIG. 6. SiC growth rate in the typical reactor with propane
(C.sub.3H.sub.8) and halogenated carbon precursors from the group
CCl.sub.4, CH.sub.3C.sub.1, C.sub.2Cl.sub.2, and CHCl.sub.3.
Operating conditions: T.sub.substrate=1600.degree. C.; total
pressure=200 Torr; silane flow rate=65 cc (10% in hydrogen);
rotation rate=1000 rpm; main hydrogen flow rate=12500 cc; reactant
push flow rate=1500 cc; and pyrometer opening purge=550 cc. Propane
flow rate was 96.8 cc (2% in hydrogen), and the halogenated carbon
precursors input flow rate was taken to maintain the same Si/C
input ratio (e.g. it was 290.4 cc for CCl.sub.4 (2% in
hydrogen)).
[0061] FIG. 7. Silicon carbide growth rates versus silane input
flow rate, in a modified reactor at: T.sub.substrate=1600.degree.
C.; total pressure=200 Torr; silane flow rate=65 cc (10% in
hydrogen); rotation rate=1000 rpm; main hydrogen flow rate=12500
cc; reactant push flow rate=1500 cc; and pyrometer opening
purge=550 cc. Silane flow rate was varied from 20 to 65 cc (10% in
hydrogen), and the halogenated carbon precursors input flow rate
was taken to maintain the Si/C input ratio of 1.12.
[0062] FIG. 8. A modified reactor design, as an example.
[0063] FIG. 9. Simulation of the temperature profile of our reactor
before (left profile) and after (right profile) insertion of a
"screen" and "shower head".
[0064] FIG. 10. Temperature distribution in the reactor with 3''
wafer placed on the susceptor.
[0065] FIG. 11. Illustration of screen system introduction
significantly improving the temperature distributions in a
"GaNzilla" reactor.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0066] The superior properties of silicon carbide as compared with
silicon make it a perspective material for high power and
high-temperature electronics (high-power transistors, thyristors,
and rectifiers). Due to an extremely high thermal conductivity (3
W/cm*K for SiC vs. 1.3 for Si) and high breakdown voltage (1 MV/cm
for SiC vs. 0.3 MV/cm for Si), the SiC-based device structures are
capable to operate at much higher voltage and power. The wide
bandgap of SiC (2.3 eV for SiC vs. 1.1 eV for Si) provides a low
leakage current of the p-n junction, even at high temperatures. In
addition, SiC exhibits a remarkable mechanical and chemical
stability.
[0067] Despite the obvious advantages, wide-scale application of
SiC in the device industry is currently hindered by essential
technological difficulties arising in manufacturing of SiC-based
structures of the required high quality and by their high costs.
Among the tasks, the improvement of the quality of the growing
epitaxial layers seems to be most important at the moment. This
task includes the achievement of a good surface morphology, high
thickness uniformity, an accurate stoichiometry, and a low defect
density of the epilayers.
[0068] Chemical vapor deposition is conventionally used to grow the
epitaxial SiC films. Among the devices used in this technique,
cold-wall CVD reactors provide the low-cost and effective process
of SiC growth, as compared with other systems. The typical design
of a cold-wall CVD reactor includes a single heater or some heater
system, to achieve the uniform high temperature at the susceptor
and in the vicinity of it, and the injector system, reactor walls,
and outlet unit are usually kept at a low temperature. Generally,
the reactor geometry varies by a wide range--horizontal, vertical,
barrel, shower-head pyramid, etc. (see, for example, the
information on the commercial AIXTRON or Veeco cold-wall CVD
reactors for more details, by their respective manufacturers).
[0069] However, some technical problems are typical for these
systems. First, the high temperature gradient in the vicinity of
the substrate is inevitable in this technique. This leads to the
decrease in the quality of the growing film, due to the strain
produced by a thermal expansion mismatch between the substrate and
the growing epilayer, which is known to be the general source for
defect generation in the growing layer. As a result, the silicon
carbide layer would be low quality. The effective way to minimize
this mismatch, and to improve the film quality, is to decrease the
growth temperature, but this will significantly decrease the SiC
growth rate, making the process less effective and more
expensive.
[0070] The increase in the input precursor flow rates (silane and
propane or acetylene typically used in the CVD of SiC) can be
suggested as a way to increase the growth rate. Unfortunately, this
will increase the partial pressures of silicon-containing species
in the reactor. In turn, this effect gives rise to the formation of
silicon clusters in the gas phase. As known from experiments,
silicon particles in the gas phase lead to the decrease in the
epilayer quality, due to the boulders or wavy effect on the surface
(particles on the surface can be also observed). In addition,
silicon nucleation leads to the losses in the source material for
silicon carbide growth, which decreases the net SiC growth rate and
distorts the stoichiometry of the growing layer.
[0071] Silicon nucleation can be partially suppressed via the
decrease in the percentage of silicon-containing species in the
reactor, using the increased flow rates of the carrier gas (usually
hydrogen). Another approach is to decrease the total pressure in
the reactor, in order to minimize the partial pressures of
silicon-containing species. Unfortunately, these methods lead to
the high gas flows that require more expensive pumps and manifolds.
In addition, etching by hydrogen is significant at high hydrogen
concentrations. As a result, the decrease in SiC growth rate and
the destruction of the construction materials (due to the
interactions with hydrogen) can be expected.
[0072] Another problem typical for cold-wall CVD reactors is poor
temperature uniformity in the growth chamber. As is well-known, the
main sources for the SiC growth are the products of thermal
decomposition of the initial precursors (silane and propane or
acetylene), which occurs at temperatures above 800-850.degree. C.
The region with such a temperature in a cold-wall reactors is
localized near the substrate. It is relatively small, as compared
with the whole reactor volume. So, the significant part of the
initial precursors can remain un-decomposed. Obviously, this effect
will manifest itself at increased input precursor flow rates. In
turn, this will also decrease the silicon carbide growth rate.
[0073] Attempts to reduce silicon nucleation and to improve the SiC
layer quality using the chlorine-containing silicon precursors
(chlorosilanes) or adding a chlorine-containing etching agent (e.g.
HCl) in the gas were carried repeatedly. The above approach was
suggested in the disclosure for U.S. patent application
20040222501, Serial No. 431819, by O. Kordina. However, HCl is a
fairly reactive compound, and its addition requires a special
separate manifold line. These modifications are rather expensive.
In addition, chlorosilanes decomposition requires temperatures
above 800-950.degree. C., and even higher temperatures are
necessary to provide the suppression of silicon nucleation by
chlorine-containing species. So, the application of the above
approach in the cold-wall CVD reactors is strictly limited by the
fact that the "hot zone" in these reactors is rather small.
[0074] Our method differs from the above patents/prior art with
respect to the following terms and parameters:
[0075] (i) The specific range of silicon-to-carbon and
chlorine-to-silicon ratios:
x.sup.(int)(Si)/x.sup.(int)(C)=0.7-1.3,
x.sup.(int)(Si)/x.sup.(int)(Cl)=0.02-1.5;
[0076] (ii) Halogenated carbon precursors (carbon tetrachloride
CCl.sub.4 or halogenated hydrocarbons, CHCl.sub.3,
CH.sub.2Cl.sub.2, CH.sub.3Cl, etc.) are primarily considered as
chlorine-containing species, forming the gas composition mentioned
above;
[0077] (iii) Suppression of parasitic deposits due to the etching
by chlorine-containing species is considered as one of the
mechanisms providing the increase in SiC growth rate and layer
quality;
[0078] (iv) Modifications in the reactor design are suggested,
which makes the chlorine addition really effective in the cold-wall
reactors;
[0079] (v) Effective SiC growth process at temperatures as low as
1000.degree. C. is possible;
[0080] (vi) SiC growth on on-axis surfaces is provided, due to the
effective etching of silicon clusters at Si/Cl ratios of <0.66,
which are known as a main source of undesirable cubic SiC phase,
typical for the on-axis growth in the conventional approach.
[0081] Accordingly, a need exists to increase the temperature
uniformity, to minimize the temperature gradient near the substrate
in the commercial cold-wall reactors, and to suppress silicon
nucleation, to get high SiC growth rates at higher precursor input
flow rates and lower carrier gas flow, maintaining high crystal
quality.
[0082] Typical commercial cold-wall CVD reactors are characterized
by rather non-uniform temperature distributions in the growth
chamber. The "hot zone" with the temperatures above 800.degree. C.
(necessary for an onset of silane and propane thermal
decomposition) is localized near the substrate, and is rather
small, as compared with the whole reactor bulk. A graphite or
SiC-coated graphite insert arranged near the cold walls of the
upper part of the reactor (that acts as a temperature shield) (see
the design modifications in FIG. 1) is an effective way to improve
the temperature distribution in those types of reactors. Some
alternative construction materials can be also used for such an
insert. For example, they are: graphite coated with carbides of
refractory metals (tantalum, niobium, titanium, tungsten,
molybdenum, zirconium, hafnium, etc.); carbides of the refractory
metals listed above; quartz or quartz coated with above refractory
metals or their carbides; pure refractory metals listed above; or
any other material, alloy, or mixture having same or similar
properties.
[0083] The insert walls in such a design are heated by the
radiation flux from the heated substrate. The high thermal
conductivity of the graphite provides the effective and uniform
heating of the whole insert. A special design of the insert
fixation gives the opportunity to minimize the contact area between
the insert and the water-cooled reactor units, and to vary the gap
between the insert and the top flange of the reactor. In doing so,
the cooling effect of the reactor units on the temperature of the
insert walls is minimized. Since the temperature of the insert wall
in such a modified reactor became quite higher than the temperature
of the water-cooled units, the temperature of the gas in the
reactor bulk is increased.
[0084] However, the above modifications in the reactor design can
be insufficient for some operating regimes, due to the effect of
the cooled inlet. So, the showerhead, made from the refractory
materials listed above, can be optionally added to increase the
temperature near the reactor inlet. Note that this unit also
provides an additional improvement of the flow patterns in the
reactor and more uniform species delivery. The scheme of the
suggested modifications in the typical design of cold-wall CVD
reactors is depicted in FIG. 1. FIG. 1 is (a) a typical design of
the commercial cold-wall CVD reactors, and (b) the modified reactor
design, with the heat shielding insert and graphite showerhead.
[0085] As an example, FIG. 2 demonstrates the geometry of the
graphite insert with the showerhead applied in the cold-wall
reactor. The described modifications in the reactor design result
in significant improvement of the temperature distributions in the
reactor. For example, typical cold-wall reactor with and without
modifications was tested in the following basic regime of SiC CVD:
substrate temperature=1600.degree. C.; total pressure=200 Torr;
rotation rate=1000 rpm; main hydrogen flow rate=12500 sccm;
reactant push flow rate=1500 sccm; pyrometer opening purge=550
sccm; and silane and propane diluted in hydrogen input flow rates
were varied during the runs (the typical values of the input flows
were hundreds cc). FIG. 3 illustrates the general changes in the
temperature distributions obtained as a result of the modifications
in the reactor design. As seen from the figure, temperature
distributions in a modified reactor are more uniform. We emphasize
that the "hot zone" with the temperature of .about.800.degree. C.
is significantly enlarged in the modified reactor. The increase in
the average inlet temperature here can be estimated as being more
than 350-400.degree. C. As a result, thermal decomposition of the
precursors used for SiC CVD takes place in the whole reactor
volume, providing the optimal utilization of the source materials
in the process. This gives an opportunity to increase the SiC
growth rate in a modified reactor at the same or even lower
precursor input flow rates. Thus, the effectiveness of the process
can be increased.
[0086] The temperature gradient near the substrate decreases from
7.2*10.sup.4 K/m for the initial cold wall design to 4*10.sup.4 K/m
in the modified geometry. Further optimization of the operating
conditions gives the opportunity to get this value to about
1.7-2*10.sup.4 K/m. Obviously, such a significant decrease in the
temperature gradient will decrease the strain produced by a thermal
expansion mismatch between the substrate and the growing epilayer,
which is known to be the main source for defect generation in a
growing SiC layer. So, we believe that the suggested modifications
will improve the quality of the epitaxial SiC layers, due to the
minimization of the defects generation in the growing layer and
increase the growth rate via the optimal utilization of the source
materials.
[0087] FIG. 3 shows the improvement of the uniformity in the
temperature distributions, as a result of the design modifications
in the reactor. As it follows from the other research data, the
addition of the chlorine-containing species in the gas phase during
SiC CVD can suppress or completely eliminate silicon nucleation.
Two approaches were suggested: HCl addition in the input gas flow
and the use of chlorosilanes (chloromethylsilanes) as precursors.
Our experiments support these data.
[0088] As an example, FIG. 4 demonstrates the relative decrease in
the silicon cluster mass density in the region near the substrate,
estimated for the typical reactor under the following operating
conditions: substrate temperature=1600.degree. C.; total
pressure=200 Torr; silane flow rate=65 sccm (10% in hydrogen);
propane flow rate=96.8 sccm (2% in hydrogen); rotation rate=1000
rpm; main hydrogen flow rate=12500 sccm; reactant push flow
rate=1500 sccm; and pyrometer opening purge=550 sccm. One can see
that the chlorine effect manifests itself immediately upon the HCl
addition. Small amounts of HCl provide the sharp decrease in the
mass density of silicon clusters. The silicon cluster density is
expected to be less than 15-20% of the initial value, when the
integral molar percentage of silicon-containing species is
approximately the same as that of chlorine-containing species.
However, the complete elimination of silicon clusters became
possible at rather high HCl input flow rates. As a result of
silicon nucleation suppression, the SiC growth rate increased from
.about.2-2.2 to 5-6 microns/hour.
[0089] However, the addition of HCl in the input flow requires a
separate input pipeline, so the input system became more
complicated and expensive. In addition, the compound is fairly
reactive. For this reason, the use of halogenated carbon precursors
(carbon tetrachloride CCl.sub.4 or halogenated hydrocarbons,
CHCl.sub.3, CH.sub.2Cl.sub.2, CH.sub.3Cl, etc.) is a reasonable
alternative to HCl addition. As it was shown above, the significant
suppression of silicon nucleation is observed, even at low chlorine
percentage in the gas.
[0090] FIG. 5 illustrates the mechanisms of silicon nucleation
suppression in Si--C--H--Cl gas. (FIG. 5 shows the comparison of
the general mechanisms of the gas-phase chemistry during SiC growth
for the conventional approach (growth from silane and propane),
versus our method of growth, in Si--C--H--Cl ambience.) It compares
the general schemes of precursor decomposition in the conventional
CVD of SiC from silane and propane versus our approach. As seen
from the figure, silicon is one of the main decomposition species
generated due to the silane thermal decomposition. Due to local
supersaturation, gaseous silicon forms silicon clusters. As a
result, there is significant loss of the source material for
silicon carbide growth. The addition of the chlorine-containing
agent in the gas under the process conditions discussed above (i.e.
the following silicon-to-carbon and silicon-to-chlorine ratios)
leads to a set of interaction reactions between the precursor
decomposition products:
x.sup.(int)(Si)/x.sup.(int)(C)=0.7-1.3,
x.sup.(int)(Si)/x.sup.(int)(Cl)=0.02-1-5
[0091] Three basic results of such interactions under the suggested
process conditions are: [0092] Silicon dichloride (SiCl.sub.2),
instead of silicon, is the main source of silicon for SiC growth.
So, the silicon percentage is significantly lower than that in the
conventional approach. As a result, silicon supersaturation is
eliminated and nucleation is suppressed. [0093] Gaseous
hydrochloric acid is generated and its content can be quite high,
as compared with the percentage of silicon- and carbon-containing
species. Being a strong etching agent, HCl reacts with the gaseous
silicon and silicon clusters forming volatile chlorides. As a
result, an additional suppression of silicon nucleation is
observed. [0094] Parasitic deposits at the susceptor, injector, and
reactor walls (pure carbon, silicon, silicon carbide, Si--SiC and
C--SiC phases) are effectively etched, as a result of formation of
volatile CH.sub.iCl.sub.j and SiH.sub.iCl.sub.j species. Such
parasitic deposits suppression increases the stability of the
process and decreases the losses in the source material.
[0095] Since the typical silicon-to-carbon input ratio in SiC CVD
technologies is .about.1, the integral percentages of silicon- and
chlorine-containing species are comparable in the SiC CVD from
silane and halogenated carbon precursors. A low temperature of the
onset of thermal decomposition is an additional advantage of the
suggested method (since it provides optimal precursor
utilization).
[0096] FIG. 6 illustrates the comparison of the SiC growth rates
obtained for a typical reactor using propane and carbon
tetrachloride, as carbon-containing precursors, under the similar
growth conditions. The only exception was the carbon-containing
precursor input flow rate: For CCl.sub.4, it was taken to provide
the same silicon-to-carbon input ratio as for propane
(Si/C=1.12).
[0097] FIG. 6 shows SiC growth rate in the typical reactor with
propane (C.sub.3H.sub.8) and halogenated carbon precursors from the
group CCl.sub.4, CH.sub.3C.sub.1, C.sub.2Cl.sub.2, and CHCl.sub.3.
Operating conditions are: T.sub.substrate=1600.degree. C.; total
pressure=200 Torr; silane flow rate=65 cc (10% in hydrogen);
rotation rate=1000 rpm; main hydrogen flow rate=12500 cc; reactant
push flow rate=1500 cc; and pyrometer opening purge=550 cc. Propane
flow rate was 96.8 cc (2% in hydrogen) and the halogenated carbon
precursors input flow rate was taken to maintain the same Si/C
input ratio (e.g. it was 290.4 cc for CCl.sub.4 (2% in
hydrogen)).
[0098] As seen from the figure, the SiC growth rate increased more
than twice. This effect can be attributed to the significant
suppression of silicon nucleation. Indeed, the estimated mass
density of silicon clusters near the substrate decreases from
.about.3*10.sup.-5 kg/m.sup.3 for the regime with propane to
.about.4*10.sup.-7 kg/m.sup.3 for CCl.sub.4 (as a carbon-containing
precursor). The same effect was observed for all halogenated carbon
precursors tested. The slight difference in SiC growth rate is due
to the peculiarities of the gas chemistry.
[0099] Thus, the possibility of the significant suppression of the
silicon nucleation by using halogenated carbon precursors is
proven. In turn, this gives the opportunity to use such advantages
of the modified cold-wall reactors, as high temperature uniformity
and low temperature gradient near the substrate at elevated input
precursor flow rates. We believe that this method increases the SiC
growth rate significantly, while maintaining the high quality of
the grown layers.
[0100] FIG. 7 shows silicon carbide growth rates vs. silane input
flow rate in a modified reactor at: T.sub.substrate=1600.degree.
C.; total pressure=200 Torr; silane flow rate=65 cc (10% in
hydrogen); rotation rate=1000 rpm; main hydrogen flow rate=12500
cc; reactant push flow rate=1500 cc; and pyrometer opening
purge=550 cc. Silane flow rate was varied from 20 to 65 cc (10% in
hydrogen) and the halogenated carbon precursors input flow rate was
taken to maintain the Si/C input ratio of 1.12.
[0101] Comparing the data from FIG. 7 with the growth rates typical
for the regime with a low silane input flow rate of 65 cc (10% in
hydrogen), as shown in FIG. 6, one can see a significant increase
in the silicon carbide growth rate.
[0102] In addition, in some applications, to get high quality
material, we have used high temperatures, in the range of 1500-1800
Centigrade, with an excellent material characteristics.
An Example: Scale-up to 3 Inch Wafers It is well known from the
reference data that the strains produced by temperature mismatch
between the substrate and the growing epilayer are the main sources
of wafer bow. Obviously, a decrease in the temperature gradient in
the wafer region is an effective way to improve the layer quality.
One approach to minimize the gradient is to decrease the growth
temperature. However, this will significantly decrease the SiC
growth rate. Another method is to improve temperature uniformity in
the reactor, increasing wall and inlet temperatures. An additional
advantage of such a method is the optimal precursor utilization.
Indeed, thermal decomposition of silane, propane, and halogenated
carbon precursors were shown to occur in a narrow hot zone near the
wafer. An increase of this hot zone will provide the possibility of
more effective precursor decomposition. In turn, this will lead to
an additional increase in SiC growth rate.
[0103] The modified reactor design, as seen for example in FIG. 8,
helps to increase the temperature uniformity, and to decrease
temperature gradients near the wafer. It includes a spool-like
graphite insert that replaces the water-cooled unit of a typical
reactor. A shower head is also added near the inlet region. The gap
between the reactor top flange and the insert, as well as the gap
between the shower head and the insert's inner walls, are
additional dimensions that can be adjusted for further optimization
of the design, based on the specific gas and gas flow.
[0104] The effect of the reactor design modifications on the
temperature distributions in the reactor bulk is demonstrated in
FIG. 9. One can see that the typical cold wall reactor is
characterized by a hot zone localized in the vicinity of the
susceptor (as shown in FIG. 9, left picture). The addition of the
graphite insert with the shower head in the inlet region gives an
opportunity to make the temperature distributions more uniform (see
FIG. 9, right side (after insertion of a "screen" and "shower
head")). Note that the temperature scale in the figure is limited
by 700.degree. C., to clarify the sharp temperature gradient.
[0105] Proper transfer of the growth recipe to 3 inch wafers (FIG.
10) requires a careful tuning of all main growth parameters. Within
this task, modeling is used to find the optimal flow rate and
rotation rate, providing the stable, recirculation-free growth
conditions in the reactor. The special attention should be paid to
suppression of the recirculation near the reactor side walls that
may spoil the uniformity in case of growth on large-diameter
wafers.
[0106] The distribution of silicon and carbon precursors between
the injection zones is adjusted, in order to ensure the necessary
growth rate uniformity and preserve a high efficiency process.
[0107] Modification of the flow profile allows for the required
doping and thickness uniformity, while modification of the
temperature gradient potentially improves the wafer bow. FIG. 10
shows the temperature distribution in the reactor with 3'' wafer
placed on the susceptor. Of course, this technology can be applied
to any size wafer.
An Example: Modification of Veeco's "GaNzilla" Reactor The
modifications in our cold-wall Veeco Ganzilla reactor provide the
optimization of the temperature distributions, due to the
introduction of the screen system, making the existing reactor
close to hot-wall devices. As a result, the SiC growth rate will be
increased, maintaining the high layer quality. We have applied the
approach tested above for the Veeco Instruments reactor. It was
shown that temperature distributions can be significantly improved
in the modified geometry. The temperature gradient near the wafer
is estimated as 15-20 K/mm. Note that these values can be further
decreased during the optimization of the process parameters for a
specific situation.
[0108] A point of essential interest in our modified "GaNZilla"
reactor is a possibility to realize the regime with decreased input
hydrogen flow. Obviously, this can be an important step to get an
effective and low-cost process. A set of regimes was computed for
the modified GaNZilla reactor. The regimes with the hydrogen flows
decreased to 30 slm. Veeco's GaNzilla reactor is modified to
accomodate 8.times.3'' SiC wafers for thick epitaxial layer
growth.
[0109] The effect of the screen system introduction was preliminary
computed for GaNzilla reactor (FIG. 10). FIG. 11 illustrates the
effect of these modifications for the regime with substrate
temperature of 1400.degree. C. As seen from the figure, the hot
zone in such modified reactor is significantly enlarged. (Screen
system introduction significantly improves the temperature
distributions in GaNzilla reactor.) Thus, this invention
helps/improves temperature uniformity, suppress phase nucleation,
reducing Si clusters, reducing total flow rate, reducing defects,
reducing mismatch and bow effect, improving morphology, improving
deposition condition, improving quality, application for larger
diameter wafers, and reducing depositions on graphite, among other
results.
[0110] The system also accepts multiple substrates on the substrate
holder.
[0111] The embodiments above are just for the purpose of
clarification (as examples). However, the inserts/additions to the
walls/setup/shower-head can be any shape, angled, orientations,
size, any material, and at any position, as long as they can stand
the environment inside chamber. The precursors can be any other
chemical compound, element, or mixture, as long as the ratio,
amount, or percentage of the decomposed species stay substantially
the same or similar. In addition, the temperatures, flow rates,
dimensions, and other design and growth parameters can be varied,
as long as the main objectives of the invention, mentioned above,
are more or less satisfied. It can also be applied to
semiconductors other than SiC and its related compounds.
[0112] Any variations of the teachings above are also included and
meant to be protected by the current patent application.
* * * * *