U.S. patent application number 12/373145 was filed with the patent office on 2010-01-14 for method of manufacturing substrates having improved carrier lifetimes.
Invention is credited to Gilyong Chung, Mark Loboda.
Application Number | 20100006859 12/373145 |
Document ID | / |
Family ID | 38666791 |
Filed Date | 2010-01-14 |
United States Patent
Application |
20100006859 |
Kind Code |
A1 |
Chung; Gilyong ; et
al. |
January 14, 2010 |
Method of Manufacturing Substrates Having Improved Carrier
Lifetimes
Abstract
This invention relates to a method for depositing silicon
carbide material onto a substrate such that the resulting substrate
has a carrier lifetime of 0.5-1000 microseconds, the method
comprising a. introducing a gas mixture comprising a chlorosilane
gas, a carbon-containing gas, and hydrogen gas into a reaction
chamber containing a substrate; and b. heating the substrate to a
temperature of greater than 1000.degree. C. but less than
2000.degree. C.; with the proviso that the pressure within the
reaction chamber is maintained in the range of 0.1 to 760 torr.
This invention also relates to a method for depositing silicon
carbide material onto a substrate such that the resulting substrate
has a carrier lifetime of 0.5-1000 microseconds, the method
comprising a. introducing a gas mixture comprising a
non-chlorinated silicon-containing gas, hydrogen chloride, a
carbon-containing gas, and hydrogen gas into a reaction chamber
containing a substrate; and b. heating the substrate to a
temperature of greater than 1000.degree. C. but less than
2000.degree. C.; with the proviso that the pressure within the
reaction chamber is maintained in the range of 0.1 to 760 torr.
Inventors: |
Chung; Gilyong; (Midland,
MI) ; Loboda; Mark; (Bay City, MI) |
Correspondence
Address: |
DOW CORNING CORPORATION CO1232
2200 W. SALZBURG ROAD, P.O. BOX 994
MIDLAND
MI
48686-0994
US
|
Family ID: |
38666791 |
Appl. No.: |
12/373145 |
Filed: |
July 17, 2007 |
PCT Filed: |
July 17, 2007 |
PCT NO: |
PCT/US07/16192 |
371 Date: |
January 9, 2009 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
60831839 |
Jul 19, 2006 |
|
|
|
Current U.S.
Class: |
257/77 ;
257/E21.09; 257/E29.104; 438/478 |
Current CPC
Class: |
C30B 25/02 20130101;
H01L 21/02378 20130101; H01L 21/02433 20130101; H01L 21/02529
20130101; C30B 29/36 20130101; H01L 21/0262 20130101; C23C 16/325
20130101; H01L 21/02579 20130101; H01L 21/02576 20130101 |
Class at
Publication: |
257/77 ; 438/478;
257/E21.09; 257/E29.104 |
International
Class: |
H01L 29/24 20060101
H01L029/24; H01L 21/20 20060101 H01L021/20 |
Goverment Interests
[0002] This invention was made with United States Government
support under Contract No. N00014-05-C-0324 awarded by the Office
of Naval Research. The United States Government may have certain
rights in the invention.
Claims
1. A method for depositing silicon carbide coating onto a substrate
such that the resulting coating has a carrier lifetime of 0.5-1000
microseconds, the method comprising a. introducing a gas mixture
comprising a chlorosilane gas, wherein the chlorosilane gas is
dichlorosilane gas, methylhydrogendichlorosilane gas,
dimethyldichlorosilane gas, or mixtures thereof, a
carbon-containing gas, and hydrogen gas into a reaction chamber
containing a single crystal silicon carbide substrate; b. heating
the substrate to a temperature of greater than 1000.degree. C. but
less than 2000.degree. C.; with the proviso that the pressure
within the reaction chamber is maintained in the range of 0.1 to
760 torr.
2. A method according to claim 1 wherein the gas mixture further
comprises a doping gas.
3. A method according to claim 2 wherein the doping gas is nitrogen
gas, phosphine gas, or trimethylaluminum gas.
4. (canceled)
5. A method according to claim 1, wherein the carbon-containing gas
has the formula H.sub.aC.sub.bCl.sub.c, where a and b are greater
than zero, and c is greater than or equal to zero.
6. A method according to claim 1 wherein the carbon-containing gas
is C.sub.3H.sub.8 gas, C.sub.2H.sub.6 gas, CH.sub.3Cl gas, or
CH.sub.3CH.sub.2CH.sub.2Cl gas.
7. A product produced in accordance with the method of claim 1.
8. (canceled)
9. (canceled)
10. (canceled)
11. (canceled)
12. (canceled)
13. (canceled)
14. (canceled)
15. (canceled)
16. (canceled)
17. (canceled)
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application claims the benefit of U.S. Provisional
Patent Application Ser. No. 60/831,839, filed on 19 Jul. 2006,
under 35 U.S.C. .sctn. 119(e). U.S. Provisional Patent Application
Ser. No. 60/831,839 is hereby incorporated by reference.
BACKGROUND OF THE INVENTION
[0003] The present invention relates to the growth of silicon
carbide epitaxial layers. As a semiconductor material, silicon
carbide is particularly superior for high power, high frequency,
and high temperature electronic devices. Silicon carbide has an
extremely high thermal conductivity, and can withstand both high
electric fields and high current densities before breakdown.
Silicon carbide's wide band gap results in low leakage currents
even at high temperatures. For these and other reasons, silicon
carbide is a quite desirable semiconductor material for power
devices; i.e., those designed to operate at relatively high
voltages.
[0004] Silicon carbide is, however, a difficult material to work
with. Growth processes must be carried out at relatively high
temperatures, above at least about 1400.degree. C. for epitaxial
growth and approximately 2000.degree. C. for sublimation growth.
Additionally, silicon carbide can form over 150 polytypes, many of
which are separated by small thermodynamic differences. As a
result, single crystal growth of silicon carbide, either by
epitaxial layer or bulk crystal, is a challenging process. Finally,
silicon carbide's extreme hardness (it is most often industrially
used as an abrasive material) contributes to the difficulty in
handling it and forming it into appropriate semiconductor
devices.
[0005] Nevertheless, over the last decade much progress has been
made in growth techniques for silicon carbide and are reflected,
for example, in U.S. Pat. Nos. 4,912,063; 4,912,064; Re. Pat.
No.34,861; U.S. Pat. Nos. 4,981,551; 5,200,022; 5,459,107; and
6,063,186.
[0006] One particular growth technique is referred to as "chemical
vapor deposition" or "CVD." In this technique, source gases (such
as silane SiH.sub.4 and propane C.sub.3H.sub.8 for silicon carbide)
are introduced into a heated reaction chamber that also includes a
substrate surface upon which the source gases react to form the
epitaxial layer. In order to help control the rate of the growth
reaction, the source gases are typically introduced with a carrier
gas, with the carrier gas forming the largest volume of the gas
flow.
[0007] Chemical vapor deposition (CVD) growth processes for silicon
carbide have been refined in terms of temperature profiles, gas
velocities, gas concentrations, chemistry, and pressure. The
selection of conditions used to produce particular epilayers is
often a compromise among factors such as desired growth rate,
reaction temperature, cycle time, gas volume, equipment cost,
doping uniformity, and layer thicknesses.
[0008] Silicon carbide is a wide band gap semiconductor material
with theoretical properties that offer promise to build high
performance diodes and transistors. Compared to materials like
silicon, these semiconductor devices would be capable of operating
at higher power and switching speeds.
[0009] Power electronics applications often prefer to build
circuits with a transistor or diode design, one class of these
devices are known as minority carrier or bipolar devices. The
operating characteristics of these types of devices depend on the
generation rate and recombination rate of electron hole pairs. The
inverse of the rate is called the lifetime. Specific bipolar
devices include PiN diodes, insulated gate bipolar transistors
(IGBT), thyristors, and bipolar junction transistors.
[0010] A key material parameter which must be optimized to
theoretical levels for semiconductor power device performance is
the carrier recombination lifetime. In silicon, lifetimes are
limited by impurities like iron. In silicon carbide, less is known
than silicon, but the best knowledge to date indicates that the
lifetime of silicon carbide is degraded by the presence of
vacancies and antisites in the crystal lattice. Vacancies are
locations where a silicon or carbon atom is absent. An antisite is
a location where the wrong atom is located.
[0011] Semiconductor silicon carbide is typically grown by physical
vapor transport methods (also known as sublimation) from solid
mixtures which could contain silicon, carbon, silicon carbide, or
by chemical vapor deposition (CVD) from gas mixtures of silanes and
hydrocarbons. Silicon carbide materials grown by these methods have
lifetime's less than 500 ns, too small to realize theoretical
device behavior in silicon carbide diodes and transistors.
Epitaxial layers of semiconductor silicon carbide often exhibit
lifetime values much less than 2 microseconds which is low compared
to materials like silicon and low compared to the expected
theoretical values for silicon carbide.
BRIEF SUMMARY OF THE INVENTION
[0012] In a first embodiment this invention relates to a method for
depositing silicon carbide coating onto a substrate such that the
resulting coating has a carrier lifetime of 0.5-1000 microseconds,
the method comprising a. introducing a gas mixture comprising a
chlorosilane gas, a carbon-containing gas, and hydrogen gas into a
reaction chamber containing a substrate; and b. heating the
substrate to a temperature of greater than 1000.degree. C. but less
than 2000.degree. C.; with the proviso that the pressure within the
reaction chamber is maintained in the range of 0.1 to 760 torr.
[0013] In a second embodiment, this invention relates to a method
for depositing silicon carbide coating onto a substrate such that
the resulting coating has a carrier lifetime of 0.5-1000
microseconds, the method comprising a. introducing a gas mixture
comprising a non-chlorinated silicon-containing gas, hydrogen
chloride, a carbon-containing gas, and hydrogen gas into a reaction
chamber containing a substrate; and b. heating the substrate to a
temperature of greater than 1000.degree. C. but less than
2000.degree. C.; with the proviso that the pressure within the
reaction chamber is maintained in the range of 0.1 to 760 torr.
DETAILED DESCRIPTION OF THE INVENTION
[0014] In the first embodiment of this invention the gas mixture
can further comprise a doping gas. The doping gas is exemplified by
nitrogen gas, phosphine gas, or trimethylaluminum gas. The
chlorosilane gas typically has the formula
R.sub.wH.sub.xSi.sub.yCl.sub.z, where y and z are greater than
zero, w and x are greater than or equal to zero, and R denotes a
hydrocarbon group. The hydrocarbon group is exemplified by
hydrocarbon groups containing from 1-3 carbon atoms illustrated by
alkyl radicals such as the methyl, ethyl, or propyl, alkenyl
radicals such as the vinyl or allyl, halohydrocarbon radicals such
as 3-chloropropyl. The R group can be identical or different as
desired. R is illustrated by monovalent hydrocarbon radicals having
from 1 to 3 carbon atoms such as methyl, ethyl, or propyl The value
of w is typically from 0 to 3, the value of x is typically from 0
to 3, and the value of y is typically from 1 to 3, and the value of
z is typically from 1 to 3. The chlorosilane gas is illustrated by
dichlorosilane gas, trichlorosilane gas, trimethylchlorosilane gas,
methylhydrogendichlorosilane gas, dimethylhydrogenchlorosilane gas,
dimethyldichlorosilane gas, methyltrichlorosilane gas, or mixtures
thereof.
[0015] The carbon-containing gas in the first embodiment of this
invention typically has the formula H.sub.aC.sub.bCl.sub.c, where a
and b are greater than zero, and c is greater than or equal to
zero. The carbon-containing gas is exemplified by C.sub.3H.sub.8
gas, C.sub.2H.sub.6 gas, CH.sub.3Cl gas, or
CH.sub.3CH.sub.2CH.sub.2Cl gas.
[0016] In the first embodiment of this invention, the substrate is
typically heated to a temperature of from 1200.degree. C. to
1800.degree. C. The substrate can be heated using any conventional
means available or the reaction chamber itself can be heated to a
temperature sufficient to raise the temperature of the substrate to
the desired level. The substrate typically comprises a single
crystal silicon carbide substrate or a single crystal silicon
wafer. Such substrates are commercially available.
[0017] The total pressure of the gases in the reaction chamber in
the first embodiment can be varied over a wide range from 0.1 to
760 torr and is generally controlled to a level which provides a
reasonable rate of epitaxial growth. The pressure within the
reaction chamber is typically from 10 to 250 torr, alternatively,
pressures in the range of about 80 to 200 torr can be used.
[0018] The amount of chemical vapor introduced into the reaction
chamber in the first embodiment of this invention should be that
which allows for a desirable silicon carbide epitaxial layer growth
rate, growth uniformity and, doping gas incorporation. Total gas
flow rates are typically in the 1-150 liters per minute range,
depending on the size of the reaction chamber and the temperature
profile. The combined flow rates of the carbon and silicon
containing gases are typically in the range of 0.1 to 30% of the
total flow rate. Flow rates of doping gases are typically much less
than 1% of the total flow rate. The ratio of the flow rates of the
carbon containing gas to the silicon containing gas will typically
range 0.3 to 3 and are adjusted based on the desired doping gas
incorporation efficiency and surface morphology, the ratio is
strongly influenced by the reaction chamber design (size,
temperature profile, etc.). Under these conditions, growth rates in
the range of about 1-100 micrometers/hr may generally be achieved.
Those of skill in the art should appreciate that specific
parameters such as gas flow, pressure and wafer temperature can
vary greatly from embodiment to embodiment still obtain a like or
similar result without departing from the spirit and scope of the
invention.
[0019] The first embodiment of the invention can be conducted under
static conditions, but it is usually preferred to continuously
introduce a controlled amount of the gas mixture into one portion
of a chamber while drawing a vacuum from another site in the
chamber so as to cause flow of the vapor to be uniform over the
area of the substrate.
[0020] The reaction chamber used in the process of the invention
can be any chamber which facilitates the growth of films by a
chemical vapor deposition process. Examples of such chambers are
described by Nordell et al., Journal Electrochemical Soc., Vol.
143, No. 9, 1996 (page 2910) or Steckl and Li, IEEE Transactions on
Electronic Devices, Vol. 39, No. 1, January 1992.
[0021] The resultant product of the first embodiment is a
crystalline 3C, 4H, or 6H silicon carbide coated substrate. The
coating can be grown in a wide variety of thicknesses such as from
about 1 nm up to 25 cm. The coating can be separated from the
substrate and be used as a new substrate if desired.
[0022] In the second embodiment of this invention the gas mixture
can further comprise a doping gas. The doping gas is as described
above for the first embodiment of this invention.
[0023] The non-chlorinated silicon-containing gas in the second
embodiment of this invention has the formula
R.sub.wH.sub.xSi.sub.y, where y is greater than zero, w and x are
greater than or equal to zero, and R denotes a hydrocarbon group.
The hydrocarbon group is as described above. The non-chlorinated
silicon-containing gas is illustrated by trimethylhydrogensilane
gas, dimethyldihydrogensilane gas, methyltrihydrogensilane gas, or
mixtures thereof. The carbon-containing gas in the second
embodiment has the formula H.sub.aC.sub.bCl.sub.c, where a and b
are greater than zero, and c is greater than or equal to zero. The
carbon-containing gas is illustrated by C.sub.3H.sub.8 gas,
C.sub.2H.sub.6 gas, CH.sub.3Cl gas, or CH.sub.3CH.sub.2CH.sub.2Cl
gas. It is typical that at least one gas in the gas mixture will
contain a chlorine atom.
[0024] In the second embodiment of this invention, the substrate is
typically heated to a temperature of from 1200.degree. C. to
1800.degree. C. The substrate in the second embodiment of this
invention is as described above for the first embodiment.
[0025] The total pressure of the gases in the reaction chamber in
the second embodiment can be varied over a wide range from 0.1 to
760 torr and is generally controlled to a level which provides a
reasonable rate of epitaxial growth. The pressure within the
reaction chamber is typically from 10 to 250 torr, alternatively,
pressures in the range of about 80 to 200 torr can be used.
[0026] The amount of chemical vapor introduced into the reaction
chamber in the second embodiment of this invention should be that
which allows for a desirable silicon carbide epitaxial layer growth
rate, growth uniformity and, doping gas incorporation. Total gas
flow rates are typically in the 1-150 liters per minute range,
depending on the size of the reaction chamber and the temperature
profile. The combined flow rates of the carbon-containing and
non-chlorinated silicon-containing gases are typically in the range
of 0.1 to 30% of the total flow rate. Flow rates of doping gases
are typically much less than 1% of the total flow rate. The ratio
of the flow rates of the carbon-containing gas to the
non-chlorinated silicon-containing gas will typically range 0.3 to
3 and are adjusted based on the desired doping gas incorporation
efficiency and surface morphology, the ratio is strongly influenced
by the reaction chamber design (size, temperature profile, etc.).
Under these conditions, growth rates in the range of about 1-100
micrometers/hr may generally be achieved. Those of skill in the art
should appreciate that specific parameters such as gas flow,
pressure and wafer temperature can vary greatly from embodiment to
embodiment still obtain a like or similar result without departing
from the spirit and scope of the invention.
[0027] The second embodiment of the invention can be conducted
under static conditions, but it is usually preferred to
continuously introduce a controlled amount of the gas mixture into
one portion of a chamber while drawing a vacuum from another site
in the chamber so as to cause flow of the vapor to be uniform over
the area of the substrate.
[0028] The reaction chamber used in the second embodiment of the
invention is as described above for the first embodiment.
[0029] The resultant product from the second embodiment is a
crystalline 3C, 4H, or 6H silicon carbide coated substrate. The
coating can be grown in a wide variety of thicknesses such as from
about 1 nm up to 25 cm. The coating can be separated from the
substrate and be used as a new substrate if desired.
[0030] The products of the methods in the above embodiments of this
invention are useful in semiconductor devices. The product can
serve as a single substrate containing a coating or the coating can
be separated from the substrate and converted to several
substrates. The product can be processed into transistors or diodes
or integrated semiconductor devices. Thus this invention also
relates to a semiconductor device comprising (i) at least one
semiconductor device component and (ii) a substrate comprising a
silicon carbide region having a carrier lifetime of 0.5-1000
microseconds. The semiconductor device component is illustrated by
transistors and diodes such as PiN diodes, insulated gate bipolar
transistors (IGBT), thyristors, and bipolar junction transistors.
The substrate is as described above in the two embodiments of this
invention.
EXAMPLES
[0031] The following examples are included to demonstrate preferred
embodiments of the invention. It should be appreciated by those of
skill in the art that the techniques disclosed in the examples
which follow represent techniques discovered by the inventor to
function well in the practice of the invention, and thus can be
considered to constitute preferred modes for its practice. However,
those of skill in the art should, in light of the present
disclosure, appreciate that many changes can be made in the
specific embodiments which are disclosed and still obtain a like or
similar result without departing from the spirit and scope of the
invention.
[0032] Measurements of the carrier lifetime were performed using
microwave photoconductive decay. The lifetime value extracted from
this technique is a combination of surface recombination rates and
bulk recombination rates or lifetimes.
Example 1
[0033] Five silicon carbide wafers (4H n+SiC, 76 mm diameter, 8
degrees tilted to <1120>) were placed into a reaction chamber
and heated to approximately 1570-1600.degree. C. The pressure in
the reaction chamber was maintained at 95 torr. A gas mixture
containing hydrogen gas, propane gas, dichlorosilane gas and
nitrogen gas was introduced into the reaction chamber while the
above pressure was maintained. The resulting products were 5
silicon carbide wafers, each wafer containing a 30 um 4H SiC
epitaxial layer. The n-type doping achieved with the nitrogen flow
corresponds to a net carrier concentration of about
6.times.10.sup.14/cm.sup.3. Recombination lifetime measurements
were performed using the microwave photoconductive decay technique.
The individual median lifetimes measured on the five wafers ranged
1.0-6.0 microseconds. The individual mean lifetimes measured on the
five wafers ranged 1.2-12.0 microseconds.
Example 2
[0034] One of the silicon carbide wafers (4H n+SiC, 76 mm diameter,
8 degrees tilted to <1120>) from Example 1 was individually
tested using time resolved photoluminescence spectroscopy and the
lifetime was determined from the decay of the photoluminescence
signal. The lifetime was evaluated by scanning the material along
both the x axis and y axis diameters. When measured by microwave
photoconductive decay the sample had a lifetime value range of 5-12
microseconds, when measured by time resolved photoluminescence
spectroscopy the lifetime value range was 24 microseconds.
Example 3
[0035] Five silicon carbide wafers (4H n+SiC, 76 mm diameter, 8
degrees tilted to <1120>) were placed in a reaction chamber
and heated to approximately 1570-1600.degree. C. The pressure in
the reaction chamber was maintained at 95 torr. A gas mixture
containing hydrogen gas, propane gas, trichlorosilane gas and
nitrogen gas was introduced into the reaction chamber while the
above pressure was maintained. The resulting products were 5
silicon carbide wafers, each wafer containing a 30 um 4H SiC
epitaxial layer. The n-type doping achieved with the nitrogen flow
corresponds to a net carrier concentration of about
5.times.10'.sup.5/cm.sup.3. Recombination lifetime measurements
were performed using the microwave photoconductive decay technique.
The individual median lifetimes measured on the five wafers ranged
0.9-1.2 microseconds. The individual mean lifetimes measured on the
five wafers ranged 0.9-1.6 microseconds.
[0036] Thus the methods of this invention minimize lifetime
limiting defects in single crystal silicon carbide materials. This
invention describes methods to grow silicon carbide with
recombination lifetime values more closely approaching theoretical
silicon carbide values than other methods currently known in the
art of growing silicon carbide.
* * * * *