U.S. patent application number 09/750157 was filed with the patent office on 2001-05-10 for method of making sic single crystal and apparatus for making sic single crystal.
Invention is credited to Nishino, Shigehiro, Shiomi, Hiromu.
Application Number | 20010000864 09/750157 |
Document ID | / |
Family ID | 26341856 |
Filed Date | 2001-05-10 |
United States Patent
Application |
20010000864 |
Kind Code |
A1 |
Shiomi, Hiromu ; et
al. |
May 10, 2001 |
Method of making SiC single crystal and apparatus for making SiC
single crystal
Abstract
An apparatus comprises an Si-disposing section in which solid Si
is disposed; a seed-crystal-disposing section in which a seed
crystal of SiC is disposed; a synthesis vessel adapted to
accommodate the Si-disposing section, the seed-crystal-disposing
section, and carbon; heating means adapted to heat the Si-disposing
section and the seed-crystal-disposing section; and a control
section for transmitting to the heating means a command for heating
the Si to an evaporation temperature of Si or higher and heating
the seed crystal to a temperature higher than that of Si; wherein
the Si evaporated by the heating means is adapted to reach the
seed-crystal-disposing section.
Inventors: |
Shiomi, Hiromu; (Itami-shi,
JP) ; Nishino, Shigehiro; (Kyoto-shi, JP) |
Correspondence
Address: |
SMITH GAMBRELL & RUSSELL, L.L.P.,
The Beveridge DeGrandi Weilacher & Young
Intellectual Property Group
1850 M Street, N.W., Suite 800
Washington
DC
20036
US
|
Family ID: |
26341856 |
Appl. No.: |
09/750157 |
Filed: |
December 29, 2000 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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09750157 |
Dec 29, 2000 |
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09231628 |
Jan 15, 1999 |
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6193797 |
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Current U.S.
Class: |
117/84 |
Current CPC
Class: |
Y10S 117/906 20130101;
C30B 23/002 20130101; C30B 29/36 20130101; C30B 23/00 20130101;
Y10T 117/10 20150115; C30B 23/00 20130101; C30B 29/36 20130101 |
Class at
Publication: |
117/84 |
International
Class: |
C30B 023/00 |
Foreign Application Data
Date |
Code |
Application Number |
Jan 19, 1998 |
JP |
007537/1998 |
Jan 26, 1998 |
JP |
012646/1998 |
Claims
1. A method of making an SiC single crystal comprising: a disposing
step of disposing solid Si within a first temperature area T.sub.1
and disposing a seed crystal of SiC within a second temperature
area T.sub.2 that is higher than said first temperature area
T.sub.1; an Si-evaporating step of evaporating Si from said first
temperature area T.sub.1; an SiC-forming-gas-generating step of
generating an SiC-forming gas by reacting said evaporated Si and
carbon; and a single-crystal-forming step of causing said
SiC-forming gas to reach said seed crystal so as to form said SiC
single crystal.
2. A method of making an SiC single crystal according to claim 1,
wherein: solid carbon is disposed in a third temperature area
T.sub.3 at a temperature higher than that in said second
temperature area T.sub.2 in said disposing step; said Si-forming
gas is formed by causing Si evaporated in said Si-evaporating step
to pass through said third temperature area T.sub.3 and react with
said carbon in said SiC-forming-gas-generating step; and said
SiC-forming gas is caused to reach said seed crystal in said
single-crystal-forming step to form said SiC single crystal.
3. A method of making an SiC single crystal according to claim 2,
wherein a shield made of carbon, quartz, or SiC is disposed at a
boundary between Si in a liquid phase and Si in a vapor phase in
said first temperature area T.sub.1, said shield controlling the
vapor pressure of said Si.
4. A method of making an SiC single crystal according to claim 3,
wherein said shield and solid carbon in said third temperature area
T.sub.3 are mechanically connected to each other, such that, as
said shield changes a position thereof along with a decrease in the
amount of Si caused by evaporation of Si in said first temperature
area T.sub.1, said carbon migrates so that the distance between the
formed SiC single crystal and said carbon is kept substantially
constant.
5. A method of making an SiC single crystal according to claim 2,
wherein said solid carbon in said third temperature area T.sub.3 is
formed with a through hole through which said evaporated Si can
pass.
6. A method of making an SiC single crystal according to claim 2,
wherein said seed crystal is a substrate of SiC single crystal.
7. A method of making an SiC single crystal according to claim 1,
wherein: said Si and said seed crystal of SiC are disposed in a gas
containing carbon in said disposing step; said evaporated Si is
reacted with a carbon component in said gas to form the SiC-forming
gas in said SiC-forming-gas-generating step; and said SiC-forming
gas is caused to reach said seed crystal in said
single-crystal-forming step, so as to form said SiC single
crystal.
8. A method of making an SiC single crystal according to claim 7,
wherein a shield made of carbon, quartz, or SiC is disposed at a
boundary between Si in a liquid phase and Si in a vapor phase in
said first temperature area T.sub.1, said shield controlling the
vapor pressure of said Si.
9. A method of making an SiC single crystal according to claim 1,
wherein an argon gas is used as a carrier gas of said Si evaporated
from said first temperature area T.sub.1.
10. A method of making an SiC single crystal according to claim 1,
wherein said seed crystal is rotated at 100 rpm or over.
11. A method of making an SiC single crystal according to claim 1,
wherein said seed crystal is a substrate of SiC single crystal.
12. A substrate of SiC single crystal formed by the method of
making an SiC single crystal according to claim 2.
13. A substrate of SiC single crystal formed by the method of
making an SiC single crystal according to claim 7.
14. An apparatus for making an SiC single crystal in which the SiC
single crystal is formed, said apparatus comprising: an
Si-disposing section in which solid Si is disposed; a
seed-crystal-disposing section in which a seed crystal of SiC is
disposed; a synthesis vessel adapted to accommodate said
Si-disposing section, said seed-crystal-disposing section, and
carbon; heating means adapted to heat said Si-disposing section and
said seed-crystal-disposing section; and a control section for
transmitting to said heating means a command for heating said Si to
an evaporation temperature of Si or higher and heating said seed
crystal to a temperature higher than that of said Si; wherein said
Si evaporated by said heating means is adapted to reach said
seed-crystal-disposing section.
15. An apparatus for making an SiC single crystal according to
claim 14, wherein: solid carbon is disposed between said
Si-disposing section and seed-crystal-disposing section in said
synthesis vessel; said control section controls said heating means
such that the temperature of said solid carbon becomes higher than
that of said seed crystal; and said Si evaporated by said heating
means is adapted to reach said seed crystal by way of said solid
carbon.
16. An apparatus for making an SiC single crystal according to
claim 15, wherein, at an upper face of said Si disposed in said
Si-disposing section,a shield made of carbon, quartz, or SiC having
passage holes that allow said Si evaporated by said heating means
to pass therethrough is disposed.
17. An apparatus for making an SiC single crystal according to
claim 16, further comprising connecting means for mechanically
connecting said shield and said solid carbon to each other,
wherein, as said shield changes a position thereof along with a
decrease in said Si caused by evaporation in said Si-disposing
section, said carbon migrates so that the distance between the SiC
single crystal formed on said seed crystal and said carbon is kept
substantially constant.
18. An apparatus for making an SiC single crystal according to
claim 15, wherein said solid carbon is formed with a through hole
through which said evaporated Si can pass.
19. An apparatus for making an SiC single crystal according to
claim 15, wherein an inner face of said synthesis vessel comprises
diamond-like carbon or glass-like carbon.
20. An apparatus for making an SiC single crystal according to
claim 15, wherein a heat shield made of graphite is disposed
outside said synthesis vessel.
21. An apparatus for making an SiC single crystal according to
claim 20, wherein said heat shield is made of a plurality of
rectangular graphite sheets disposed close to each other with a gap
therebetween, such as to yield substantially a cylindrical form as
a whole.
22. An apparatus for making an SiC single crystal according to
claim 20, wherein a plurality of said heat shields are disposed
radially of said synthesis vessel.
23. An apparatus for making an SiC single crystal according to
claim 14, wherein said synthesis vessel is adapted to accommodate a
gas containing carbon; said Si evaporated by said heating means
generating the SiC-forming gas by reacting with carbon in a carbon
component in said gas, said SiC-forming gas being adapted to reach
said seed crystal.
24. An apparatus for making an SiC single crystal according to
claim 22, wherein, at an upper face of said Si disposed in said
Si-disposing section, a shield made of carbon, quartz, or SiC
having passage holes that allow said Si evaporated by said heating
means to pass therethrough is disposed.
25. An apparatus for making an SiC single crystal according to
claim 23, wherein an inner face of said synthesis vessel comprises
diamond-like carbon or glass-like carbon.
26. An apparatus for making an SiC single crystal according to
claim 23, wherein a heat shield made of graphite is disposed
outside said synthesis vessel.
27. An apparatus for making an SiC single crystal according to
claim 26, wherein said heat shield is made of a plurality of
rectangular graphite sheets disposed close to each other with a gap
therebetween, such as to yield substantially a cylindrical form as
a whole.
28. An apparatus for making an SiC single crystal according to
claim 26, wherein a plurality of said heat shields are disposed
radially of said synthesis vessel.
Description
BACKGROUND OF THE INVENTION
1. 1. Field of the Invention
2. The present invention relates to a method of making an SiC
single crystal and apparatus for making an SiC single crystal in
which high-quality SiC suitable for semiconductor electronic
components is grown.
3. 2. Related Background Art
4. Being a material excellent in resistance to chemicals such as
acids and alkalis, less likely to be damaged by high energy
radiation, and yielding a high durability, SiC has been used as a
semiconductor material.
5. In order for SiC to be used as a semiconductor material, it is
necessary to obtain a high-quality single crystal thereof having a
certain order of dimensions. Conventionally utilized as a method of
growing an SiC single crystal of the aimed scale is Acheson method
employing a chemical reaction or Lely method employing
sublimation/recrystallization technique.
6. In particular, as a method of growing a bulk of SiC single
crystal, Japanese Patent Publication No. 59-48792, for example,
discloses so-called modified Lely method in which, in a crucible
made of graphite, an SiC single crystal of appropriate dimensions
is used as a seed crystal, and material SiC powder is sublimed in
an atmosphere under a reduced pressure, so as to be recrystallized
on the seed crystal, whereby an SiC single crystal of the aimed
scale is grown.
SUMMARY OF THE INVENTION
7. Of the above-mentioned conventional methods, the Acheson method
heats a mixture of silica and coke in an electric furnace and
deposits the crystal due to naturally occurring nucleation, thus
yielding a large amount of impurities and making it difficult to
control the form of resulting crystal and crystal faces, whereby it
is hard to produce high-quality SiC single crystals.
8. Also, in the case where an SiC single crystal is made by the
Lely method, since the crystal is grown due to naturally occurring
nucleation, it is difficult to control the form of crystal and
crystal faces.
9. On the other hand, an SiC single crystal having a considerably
good quality can be obtained in accordance with the invention
disclosed in the above-mentioned Japanese Patent Publication No.
59-48792, which belongs to the modified Lely method. When the SiC
single crystal is obtained by this method, however, SiC crystals
naturally occur from the graphite crucible during the crystal
growth period. Using these SiC crystals as nuclei, crystals rapidly
grow and inhibit the crystal growth from the seed crystal, thus
making it difficult to yield a crystal with a high homogeneity.
10. Further, there is a problem that, under the influence of heat
radiation, the temperature of the upper face of the material
becomes higher than that within the material, whereby the amount of
sublimation is large at the early stage of growth and gradually
decreases as the surface is graphitized. In order to overcome this
problem, Japanese Patent Application Laid-Open No. 5-105596
proposes to make a material contain carbon and further form a
surface portion of the material with a layer containing carbon,
thereby preventing heat radiation from occurring from the upper
part of the crucible. Even in this method, however, it is difficult
to effect such control that the material consistently reaches the
seed crystal under the same vapor pressure during the synthesis,
whereby the production of a high-quality SiC single crystal cannot
be expected.
11. Also, the area where the material is sublimed upon heating by
the heat conduction or heat radiation from the crucible gradually
expands from the material in the vicinity of the part in contact
with the side face or bottom face of the crucible to the material
located at the center part. Since the part of material in the
vicinity of the side face or bottom face of the crucible sublimed
in the early stage changes into highly heat-insulating soot-like
powder as the sublimation area expands, however, the heat
conduction and heat radiation to the material at the center part
would decrease drastically, whereby the sublimation of the material
at the center part may diminish suddenly or fail to occur. In
particular, for synthesizing a single crystal having a large area,
the crucible for charging the material is required to have a large
diameter as well, whereby the radial alteration of material would
be a severe problem. Though the growth apparatus disclosed in
Japanese Patent Application Laid-Open No. 5-58774 aims at uniformly
heating the material by installing a heat conductor within the
crucible, it cannot restrain the SiC material from subliming so as
to change into soot-like powder, thus failing to keep crystallizing
speed from changing over time in principle, whereby the manufacture
of high-quality SiC single crystal cannot be expected in this
apparatus, either.
12. FIG. 5 is a graph showing vapor pressure curves of carbon (C)
and SiC, in which the ordinate (on a logarithmic scale) and the
abscissa indicate pressure (Pa) and temperature (.degree. C.),
respectively. As shown in FIG. 5, the vapor pressure of Si is
higher than that of SiC.sub.2 or Si.sub.2C occurring during the
generation of SiC by one digit. For enhancing the SiC-forming
speed, it is necessary to supply a sufficient amount of Si and C to
the seed crystal. In this case, however, there is a problem that,
if the material temperature is raised so as to increase the partial
pressures of SiC.sub.2 and Si.sub.2C, which have low vapor
pressures, in order to sufficiently supply C, the partial pressure
of the Si system will be so high that the stoichiometry
(stoichiometric composition) of the material and synthesized
crystal may shift.
13. WO9713013A discloses an epitaxial growth method in which a
high-speed jet of silane gas is sprayed onto an SiC substrate
within high-temperature hot walls. The SiC single crystal can be
grown at a high speed in this technique. Since Si is supplied by a
gas, however, there occurs a problem that hydrogen etches SiC
within the high-temperature hot walls. Also, the silane gas may
form particles in the vapor phase, thus contaminating the inside of
the apparatus and degrading the SiC single crystal.
14. FIG. 6 shows the temperature dependence of Si partial pressure
in a major reaction in which SiC grows in thermal CVD of SiC. From
this graph, it can be seen that, as the hydrogen partial pressure
rises, the reverse reaction for SiC growth proceeds, whereby SiC is
etched. Namely, when the hydrogen partial pressure is high, it
becomes difficult to form a high-quality SiC single crystal.
15. In view of such conventional problems, it is an object of the
present invention to provide a method of making an SiC single
crystal and an apparatus for making an SiC single crystal in which
a high-quality SiC single crystal can be obtained.
16. In order to overcome the above-mentioned problems, the present
invention provides a method of making an SiC single crystal, the
method comprising a disposing step of disposing solid Si with in a
first temperature area T.sub.1 and disposing a seed crystal of SiC
within a second temperature area T.sub.2 that is higher than the
first temperature area T.sub.1; an Si-evaporating step of
evaporating Si from the first temperature area T.sub.1; an
SiC-forming-gas-generating step of generating an SiC-forming gas by
reacting thus evaporated Si and carbon; and a
single-crystal-forming step of causing the SiC-forming gas to reach
the seed crystal so as to form the SiC single crystal.
17. First, in the method of making an SiC single crystal in
accordance with the present invention, solid Si is evaporated as
being heated by the first temperature area T.sub.1. Here, as the
temperature of the first temperature area T.sub.1 is regulated, the
partial pressure of Si can be adjusted. Subsequently, thus
evaporated Si is reacted with carbon, whereby an SiC-forming gas is
generated. As the SiC-forming gas reaches the seed crystal of SiC,
the SiC single crystal is formed. Here, if the partial pressure of
carbon to combine with the evaporated Si is made substantially the
same as the partial pressure of Si determined by the temperature of
the first temperature area T.sub.1, a high-quality SiC single
crystal can be obtained.
18. Also, since a solid source of Si is used, the partial pressure
of hydrogen in the atmosphere decreases, thereby eliminating the
problem that the SiC single crystal is etched. Further, since
unstable gases such as silane are not used as the SiC source, there
would be no problem of particles being formed upon decomposition of
the gases in the vapor phase. As a consequence, Si can sufficiently
be supplied, so as to enable high-speed growth and make it possible
to prevent the SiC single crystal from degrading due to the
particles.
19. Here, it can be seen from FIG. 6 that, as the hydrogen partial
pressure decreases, the reaction proceeds in the direction causing
SiC to grow. Since the flux amount (cm.sup.-1s.sup.-1) of SiC can
be calculated from its partial pressure, assuming that all of the
flux contributes to growth, it can be seen that a growth rate as
high as several hundred .mu.m/h is expectable.
20. Preferably, in the method of making an SiC single crystal in
accordance with the present invention, solid carbon is disposed in
a third temperature area T.sub.3 at a temperature higher than that
in the second temperature area T.sub.2 in the disposing step; the
Si-forming gas is formed by causing the Si evaporated in the
Si-evaporating step to pass through the third temperature area
T.sub.3 and react with carbon in the SiC-forming-gas-generating
step; and the SiC-forming gas is caused to reach the seed crystal
in the single-crystal-forming step to form the SiC single
crystal.
21. Namely, in this case, the partial pressure of Si can be
adjusted by regulating the temperature of the first temperature
area T.sub.1, and the partial pressure of carbon can be made
substantially the same as that of Si by regulating the temperature
of the third temperature area T.sub.3. In general, in order for the
partial pressure of carbon and the partial pressure of Si to become
identical to each other, it is necessary for carbon to have a
temperature higher than that of Si. Here, since the temperatures of
Si and carbon are raised independently of each other, a sufficient
amount of carbon can be supplied to the seed crystal while
suppressing the amount of evaporation of Si. As the seed crystal, a
single crystal substrate of SiC may also be used.
22. FIG. 7 is a graph showing the respective vapor pressure curves
of Si and C, in which the ordinate (on a logarithmic scale) and the
abscissa indicate pressure (Pa) and temperature (.degree. C.),
respectively. As can be seen from FIG. 7, as Si which can yield a
sufficient vapor pressure at 1400.degree. C. and over is caused to
pass through the area of C (graphite) heated to 2000.degree. C. or
higher, the SiC single crystal can be synthesized with a favorable
controllability.
23. Also, highly pure materials are inexpensively available for
solid Si and C (graphite), which are raw materials, respectively.
Therefore, the concentration of impurities in the SiC single
crystal being synthesized can greatly be lowered. Further, since
each of material Si and C is a single element, unlike the case
using SiC powder, no composition changes would occur during
synthesis, whereby the synthesizing condition becomes stable, thus
allowing a high-quality SiC single crystal to be obtained. Also,
since the materials at the time of filling are not in the form of
powder but solid (bulk) of Si and graphite, the filling ratio is so
high that a large, elongated SiC single crystal can be
synthesized.
24. Silicon Carbide-1973, p.135 (Proceedings of the Third
International Conference on Silicon Carbide held at Miami Beach,
Fla., on Sep. 17-20 1973) discloses that an SiC single crystal with
a good quality was obtained when the temperature of molten Si was
2200.degree. C. in the state where the growth chamber in which SiC
was formed had a temperature of 2500.degree. C. The heater used in
the growth apparatus disclosed in this literature, however, had
only one zone, and the temperature of molten Si was not forcibly
adjusted to but only turned out to be 2200.degree. C., thus being
greatly different from the present invention in this regard.
25. Preferably, in the present invention, a shield made of carbon,
quartz, or SiC is disposed at a boundary between Si in a liquid
phase and Si in a vapor phase in the first temperature area
T.sub.1, so as to control the vapor pressure of Si. Here, as
carbon, glass-like carbon (glassy carbon) is suitable in
particular, which forms an excellent shield without reacting with
Si even at a high temperature.
26. Preferably, the above-mentioned shield and solid carbon in the
third temperature area T.sub.3 are mechanically connected to each
other, such that, as the shield changes its position along with a
decrease in the amount of Si caused by evaporation of Si in the
first temperature area T.sub.1, carbon migrates so that the
distance between the formed SiC single crystal and carbon is kept
substantially constant. Employing such a configuration enables an
SiC single crystal to be formed stably for a long period of
time.
27. Preferably, solid carbon in the third temperature area T.sub.3
is formed with a through hole through which evaporated Si can pass.
Using carbon formed with a through hole such as capillary or slit
would increase the area at which evaporated Si comes into contact
with carbon, thus allowing Si and carbon to react with each other
efficiently.
28. Preferably, in the method of making an SiC single crystal in
accordance with the present invention, Si and the seed crystal of
SiC are disposed in a gas containing carbon in the disposing step,
the evaporated Si is reacted with a carbon component in the gas to
form the SiC-forming gas in the SiC-forming-gas-generating step;
and the SiC-forming gas is caused to reach the seed crystal in the
single-crystal-forming step, so as to form the SiC single
crystal.
29. Namely, in this case, the partial pressure of Si can be
adjusted by regulating the temperature of the first temperature
area T.sub.1, and the partial pressure of carbon can be made
substantially the same as that of Si by regulating the amount of
supply of the gas containing carbon, whereby a high-quality SiC
single crystal substrate can be obtained. Here, as the seed
crystal, a substrate of single crystal SiC may be used.
30. Preferably, a shield made of carbon, quartz, or SiC is disposed
at the boundary between Si in the liquid phase and Si in the vapor
phase in the first temperature area T.sub.1, so as to control the
vapor pressure of Si. Here, as carbon, glass-like carbon (glassy
carbon) is suitable in particular, which forms an excellent shield
without reacting with Si even at a high temperature.
31. Preferably, an argon gas is used as a carrier gas of the Si
evaporated from the first temperature area T.sub.1. Using the argon
gas as the carrier gas can prevent by-products from being
generated.
32. Preferably, in the single-crystal-forming step, the seed
crystal is rotated at 100 rpm or over. Thus rotating the seed
crystal at a high speed can minimize the film thickness
distribution and further enables high-speed growth. It is due to
the fact that the rotation would thin the diffusion layer of the
substrate surface, thereby increasing the driving force for
diffusion. As a consequence, the growth rate can be increased
without using a proximity method such as sandwich technique.
33. The apparatus for making an SiC single crystal in accordance
with the present invention comprises an Si-disposing section in
which solid Si is disposed; a seed-crystal-disposing section in
which a seed crystal of SiC is disposed; a synthesis vessel adapted
to accommodate the Si-disposing section, the seed-crystal-disposing
section, and carbon; heating means adapted to heat the Si-disposing
section and the seed-crystal-disposing section; and a control
section for transmitting to the heating means a command for heating
the Si to an evaporation temperature of Si or higher and heating
the seed crystal to a temperature higher than that of the Si,
wherein the Si evaporated by the heating means is adapted to reach
the seed-crystal-disposing section.
34. In the apparatus for making an SiC single crystal in accordance
with the present invention, Si is evaporated by the heating means
receiving the command from the control section. Here, as the
heating temperature of Si is regulated, the partial pressure of Si
can be adjusted. Subsequently, thus evaporated Si is reacted with
carbon, whereby an SiC-forming gas is generated. Then, as the
SiC-forming gas reaches the seed crystal disposed in the
seed-crystal-disposing section, the SiC single crystal is formed.
Here, if the partial pressure of carbon is made substantially the
same as the partial pressure of Si, then a high-quality SiC single
crystal can be obtained.
35. Preferably, in the apparatus for making an SiC single crystal
in accordance with the present invention, solid carbon is disposed
between the Si-disposing section and seed-crystal-disposing section
in the synthesis vessel, the control section controls the heating
means such that the temperature of solid carbon becomes higher than
that of the seed crystal, and the Si evaporated by the heating
means is adapted to reach the seed crystal by way of the solid
carbon.
36. When such a configuration is employed, the partial pressure of
Si can be adjusted by regulating the heating temperature of Si, and
the partial pressure of carbon can be made substantially the same
as that of Si by regulating the heating temperature of carbon,
whereby a high-quality SiC single crystal substrate can be
obtained.
37. Preferably, the apparatus for making an SiC single crystal in
accordance with the present invention is configured such that the
synthesis vessel is adapted to accommodate a gas containing carbon,
the Si evaporated by the heating means reacts with carbon in a
carbon component in the gas so as to generate the SiC-forming gas,
and the SiC-forming gas is adapted to reach the seed crystal.
38. When such a configuration is employed, the partial pressure of
Si can be adjusted by regulating the heating temperature of Si, and
the partial pressure of carbon can be made substantially the same
as that of Si by regulating the amount of supply of the gas
containing carbon to the synthesis vessel, whereby a high-quality
SiC single crystal substrate can be obtained.
39. Preferably, in the apparatus for making an SiC single crystal
in accordance with the present invention, an inner face of the
synthesis vessel is formed from diamond-like carbon or glass-like
carbon. This can suppress natural nucleation in the inner face of
the synthesis vessel, thus allowing a high-quality SiC single
crystal to be synthesized.
40. Preferably, a heat shield made of graphite is disposed outside
the synthesis vessel. This can suppress the heat dissipation caused
by heat radiation.
41. Preferably, the heat shield is made of a plurality of
rectangular graphite sheets disposed close to each other with a gap
therebetween, such as to yield substantially a cylindrical form as
a whole. This can suppress the induced current caused by
high-frequency heating. Further, if a plurality of such heat
shields are disposed radially of the synthesis vessel, then the
heat dissipation and induced current can further be suppressed.
42. The present invention will become more fully understood from
the detailed description given hereinbelow and the accompanying
drawings which are given by way of illustration only, and thus are
not to be considered as limiting the present invention.
43. Further scope of applicability of the present invention will
become apparent from the detailed description given hereinafter.
However, it should be understood that the detailed description and
specific examples, while indicating preferred embodiments of the
invention, are given by way of illustration only, since various
changes and modifications within the spirit and scope of the
invention will become apparent to those skilled in the art from
this detailed description.
BRIEF DESCRIPTION OF THE DRAWINGS
44. FIG. 1 is a schematic configurational view showing the
apparatus for making an SiC single crystal in accordance with a
first embodiment of the present invention;
45. FIG. 2 is a sectional view of the apparatus for making an SiC
single crystal taken along the II-II direction;
46. FIG. 3 is a schematic configurational view showing the
apparatus for making an SiC single crystal in accordance with a
second embodiment of the present invention;
47. FIG. 4 is a sectional view of the apparatus for making an SiC
single crystal taken along the IV-IV direction;
48. FIG. 5 is a graph showing vapor pressure curves of C and
SiC;
49. FIG. 6 is a graph showing the temperature dependence of Si
partial pressure in a major reaction in which SiC grows in thermal
CVD of SiC; and
50. FIG. 7 is a graph showing vapor pressure curves of C and
SiC.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
51. In the following, preferred embodiments of the method of making
an SiC single crystal and apparatus for making an SiC single
crystal in accordance with the present invention will be explained
in detail.
52. (First Embodiment)
53. FIG. 1 is a view showing an apparatus for making an SiC single
crystal 101, whereas FIG. 2 is a sectional view of the apparatus
101 shown in FIG. 1 taken along the II-II direction. In the
apparatus 101, a crucible 1, which is a cylindrical synthesis
vessel made of graphite, is constituted by an upper crucible 1a and
a lower crucible 1b each having a cylindrical form. The upper end
of the upper crucible 1a is closed with a disk-shaped lid 2. Inside
the lower crucible 1b, on the other hand, a cylindrical Si-holding
crucible 3 made of graphite is inserted so as to be axially movable
with a slight gap from the lower crucible 1b. The lower part of the
Si-holding crucible 3 is fixedly attached to the upper face of a
disk-shaped crucible support 4, whereas the lower side face of the
Si-holding crucible 3 is provided with a plurality of through holes
3a communicating with the above-mentioned gap. Here, the
Si-supporting crucible 3 and the crucible support 4 constitute an
Si-disposing section. Fixedly attached to the center part of the
lower face of the crucible support 4 is a cylindrical support shaft
5 connected to a drive source which is not shown. Namely, as the
support shaft 5 moves up and down, the Si-supporting crucible 3 can
move axially. Also, since the support shaft 5 has a hollow
cylindrical form, the temperature of the bottom face of the
Si-holding crucible 3 can be measured with a two-temperature
pyrometer.
54. The inner peripheral faces of the crucible 1 and Si-holding
crucible 3 are formed from diamond-like carbon or glass-like carbon
(glassy carbon) having a high smoothness. Preferably, the inner
peripheral faces of the crucible 1 and Si-holding crucible 3 have a
surface roughness of R.sub.max<10 .mu.m.
55. Outside the crucible 1, three pieces of heat shields 6 are
disposed concentrically, aligning in radial directions of the
crucible 1. As shown in FIG. 2, each heat shield 6 is formed by a
plurality of substantially rectangular (strip-shaped) graphite
sheets 6a disposed close to each other with a gap therebetween,
such as to yield substantially a cylindrical form as a whole,
whereas the neighboring heat shields 6 are disposed such that their
gaps would not overlap radially. Since the heat shields 6 are not
formed from carbon fiber or porous graphite which is often used in
general and causes impurity contamination, there is no fear of
impurity contamination. Further, as shown in FIG. 1, the upper end
of these heat shields 6 is closed with a disk-shaped lid 7 formed
from the same material.
56. Outside the outermost heat shield 6, a cylindrical quartz tube
8 made of quartz is disposed concentrically with the heat shields
6. A coolant such as water is allowed to flow through the quartz
tube 8, thus protecting the latter. Outside the quartz tube 8, RF
work coils 17a, 17b, 17c, which function as heating means, are
successively disposed from the upper side so as to enable
high-frequency heating of the crucible 1, Si-holding crucible 3,
and the like. Also, a control section 18 for effecting temperature
adjustment of the work coils 17a to 17c is connected thereto.
57. Into the crucible 1, at the upper part thereof, a cylindrical
seed-crystal-supporting rod 9 penetrating through the center parts
of the lid 7 and lid 2 is inserted so as to be axially movable. To
the lower end of the seed-crystal-supporting rod 9, a disk-shaped
seed crystal holder 10 is fixedly attached such as to close the
lower end opening thereof. To the lower face of the seed crystal
holder 10, which functions as a seed-crystal-disposing section, a
seed crystal 11 of SiC is fixedly attached with a paste made of
glucose which has been melted at a high temperature. Since the
seed-crystal-supporting rod 9 has a hollow cylindrical form, the
temperature of the seed crystal 11 can be measured with a
two-temperature pyrometer. Also, the seed-crystal-supporting rod 9
is disposed such as to be axially rotatable at a speed as high as
200 rpm. The seed-crystal-supporting rod 9 is constituted such as
to be able to attain a vacuum state as a whole, together with the
crucible 1, crucible support 4, and support shaft 5, within the
range surrounded by the inner wall of the quartz tube 8. As the
seed crystal, a substrate of SiC single crystal may be disposed in
the seed crystal holder 10.
58. On the other hand, an Si source 12 in a cylindrical bulk is
accommodated within the Si-holding crucible 3. On the upper face of
the Si source 12, a disk-shaped shield 13 for regulating Si vapor
pressure made of carbon, quartz, or SiC is mounted. The shield 13
for regulating Si vapor pressure is formed with a plurality of
passage holes 13a axially penetrating therethrough such as to allow
Si vapor to pass therethrough. To the upper face of the shield 13
for regulating Si vapor pressure, at the center part thereof, an
auxiliary shield 14 for regulating Si vapor pressure formed from
the same material as the shield 13 for regulating Si vapor pressure
is fixedly attached. The auxiliary shield 14 for regulating Si
vapor pressure is constituted by a center shaft, and two disks
disposed near the shield 13 for regulating Si vapor pressure. For
regulating the vapor pressure from the Si source 12, the shield 13
for regulating Si vapor pressure and the auxiliary shield 14 for
regulating Si vapor pressure can control the area of the boundary
between Si in the liquid phase melted at a high temperature and Si
in the vapor phase and control the diffusion of Si in the vapor
phase, respectively.
59. To the upper end part of the auxiliary shield 14 for regulating
Si vapor pressure, a carbon supply source (graphite) 15 in a
cylindrical bulk form is fixedly attached. The carbon supply source
15 is formed with passage holes 15a axially penetrating
therethrough, thus allowing Si vapor to pass therethrough. While
passing through the passage holes 15a, Si reacts with graphite,
thereby yielding an SiC-forming gas which is an active species for
forming SiC. The descending movement of the carbon supply source 15
is restricted by a drop stopper 16 fixedly disposed at the lower
inner peripheral face of the upper crucible 1a even when the
Si-holding crucible 3 falls down.
60. In thus configured apparatus 101, according to the command from
the control section 18, heating control can be effected such that
the temperature of the Si source 12 is set to 1300.degree. C. to
1600.degree. C. by the work coil 17c, the temperature of the seed
crystal 11 is set to 2000.degree. C. to 2400.degree. C. by the work
coil 17a, and the temperature of the carbon supply source 15 is set
to 2300.degree. C. to 3000.degree. C. by the work coil 17b. Namely,
this apparatus 101 is configured such that three areas consisting
of a low-temperature area (first temperature area) T.sub.1 for the
Si source 12, a medium-temperature area (second temperature area)
T.sub.2 for the seed crystal 11, and a high-temperature area (third
temperature area) T.sub.3 for the carbon supply source 15 can be
formed within the crucible 1.
61. In this apparatus 101, the through holes 3a of the Si-holding
crucible 3 are configured such that the Si source 12 is melted due
to a high temperature so as to partially flow out from the through
holes 3a and block them as being solidified at the gap to the lower
crucible 1b, whereby Si vapor is efficiently guided upward.
62. With reference to FIG. 1, a method of making an SiC single
crystal by using thus configured apparatus 101 for making an SiC
single crystal will now be explained.
63. First, after the seed crystal 11, the Si source 12, the carbon
supply source 15, and the like were set to their predetermined
positions, the seed-crystal-supporting rod 9 was moved up to lift
the seed crystal 11, the Si source 12 was moved down together with
the Si-supporting crucible 3, and then evacuation was effected for
an hour in the space formed inside the inner wall of the quartz
tube 8. Subsequently, an Ar gas was caused to flow into the
apparatus 101 such as to yield a normal pressure (760 Torr) and,
with coolant flowing through the quartz tube 8, the crucible 1 was
set to 2800.degree. C. and baked for an hour, so as to effect
degassing. Here, graphite in the carbon supply source 15 can be
baked at the same time since it remains within the crucible 1 due
to the drop stopper 16 of the carbon supply source 15.
64. Subsequently, the Si source 12 was moved up together with the
Si-holding crucible 3 so as to attain the state shown in FIG. 1,
the seed-crystal-supporting rod 9 and the seed crystal 11 were
moved down to a predetermined position, and then, with the
seed-crystal-supporting rod 9 being rotated at 100 rpm, the control
section 18 was operated to adjust the work coils 17a to 17c such
that the seed crystal 11, graphite in the carbon supply source 15,
and the Si source 12 attained temperatures of about 2300.degree.
C., about 2500.degree. C., and about 1600.degree. C., respectively.
As the temperature setting is thus effected at the normal pressure,
crystals with inferior crystallinity can be prevented from growing.
Also, as the temperatures of the Si source 12 and carbon supply
source 15 are thus set, the partial pressure of Si and the partial
pressure of carbon in the apparatus 101 can be made substantially
identical to each other.
65. Thereafter, the pressure inside the inner wall of the quartz
tube 8 was lowered to 5 Torr in the Ar gas atmosphere, and this
state was maintained, so as to cause Si vapor to pass through the
passage holes 13a of the shield 13 for regulating Si vapor pressure
and further through the passage holes 15a of the carbon supply
source 15, thus making an SiC-forming gas. As the SiC-forming gas
reached the seed crystal 11, an SiC single crystal grew on the
surface of the seed crystal 11 at a rate of 1 to 2 mm/h, whereby a
bulk of SiC single crystal having a diameter of 2 inches in
accordance with this embodiment was finally formed.
66. In this embodiment, since the partial pressure of Si and the
partial pressure of carbon are made substantially identical to each
other, a high-quality SiC single crystal can be obtained. Also,
since the inner peripheral surfaces of the crucible 1 and
Si-holding crucible 3 are formed from diamond-like carbon or
glass-like carbon as mentioned above, they can restrain natural
nucleation from occurring in the inner face of the upper crucible
1a, whereby the high-quality SiC single crystal can be formed.
67. Also, since a solid source of Si is used, the partial pressure
of hydrogen within the crucible 1 decreases, whereby there is
substantially no problem of the SiC single crystal being etched.
Further, since no unstable gases such as silane are used as the Si
source, there would be no problems of particles caused by
decomposition of the gases in the vapor phase. As a consequence, a
sufficient amount of Si can be supplied, so as to enable high-speed
growth, and the SiC single crystal can be prevented from degrading
due to the particles.
68. Also, since the heat shields 6 made of graphite are disposed
outside the crucible 1, the heat dissipation caused by heat
radiation can be suppressed. Further, since the heat shield 6
comprises a plurality of graphite sheets 6a disposed with a gap
therebetween, so as to yield substantially a cylindrical form as a
whole, it can suppress the induced current caused by high-frequency
heating. Also, since a plurality of such heat shields 6 are
disposed radially of the crucible 1, the heat dissipation and
induced current can further be suppressed.
69. Further, since the carbon supply source 15 is formed with the
passage holes 15a, the area at which evaporated Si comes into
contact with carbon increases, thus allowing Si and carbon to react
with each other efficiently. Further, since the shield 13 for
regulating Si vapor pressure and the carbon supply source 15 are
mechanically connected to each other, the carbon supply source 15
moves down as the Si source 12 decreases, so that the distance
between the synthesized SiC single crystal and the carbon supply
source 15 is kept substantially constant, whereby the formation of
SiC single crystal can be effected stably for a long period of
time.
70. When investigating the photoluminescence characteristic of thus
obtained SiC single crystal, its peak wavelength was found to be
about 490 nm, thereby indicating it to be a 6H-type SiC single
crystal.
71. Upon Hall measurement, electric characteristics were found to
be such that a high-resistance, low-carrier-density SiC single
crystal having a resistivity of 8 .OMEGA.cm, a carrier density of
about 3.times.10.sup.16 cm.sup.-3, and n-type conduction could be
synthesized.
72. Further, this bulk of SiC single crystal was sliced into a
wafer having a thickness of 400 .mu.m, which was then polished with
diamond grindstone such that both sides were mirror-finished. As a
result, it was found to be homogenous in the whole surface of 2
inches upon visual observation, and polycrystallization from edges
and light transmissibility of the crystal were found to be
favorable at a wavelength of 2 to 5 .mu.m, thus indicating this
crystal to be a good crystal which did not take a large amount of
impurities therein.
73. In this embodiment, as mentioned above, since the respective
temperatures of the Si source 12 and carbon supply source 15 are
separately raised, and their vapor pressures are regulated at their
corresponding optimal temperatures so as to effect synthesis, a
high temperature can be set in the high-temperature area T.sub.3
independently of the amount of supply of Si, whereby the SiC single
crystal can efficiently be synthesized. Also, the Si source 12 and
the carbon supply source 15 can be made of highly pure materials
which are inexpensively available as a bulk, can greatly reduce the
concentration of impurities, and can synthesize a large-size,
elongated SiC single crystal. Further, since each of the Si source
12 and graphite of the carbon supply source 15 is a single element,
the synthesizing condition becomes stable, whereby a high-quality
SiC single crystal can be obtained. Also, since the
seed-crystal-supporting rod 9 can be rotated at a speed as high as
200 rpm, the in-plane homogeneity can be enhanced, and diffusion
can be accelerated, so as to raise the growth rate.
74. Though the method of making an SiC single crystal and apparatus
for making an SiC single crystal in accordance with the present
invention are explained in detail with reference to the
above-mentioned embodiment in the foregoing, the present invention
should not be restricted to the above-mentioned embodiment. For
example, as the means for heating the synthesis vessel such as
crucible, resistance heating or the like may be used in place of
the RF work coils. Also, it is not necessary for the passage holes
for Si vapor formed in the carbon supply source to have a circular
cross section, and solid carbon may be formed with a slit as
well.
75. (Second Embodiment)
76. FIG. 3 is a view showing an apparatus 102 for making an SiC
single crystal in accordance with this embodiment, whereas FIG. 4
is a sectional view of the apparatus shown in FIG. 3 taken along
the IV-IV direction.
77. In this apparatus 102, a hot wall 21, which is a cylindrical
synthesis vessel made of graphite, is constituted by an upper hot
wall 21a and a lower hot wall 21b each having a cylindrical form.
The upper end of the upper hot wall 21a is closed with a
disk-shaped lid 22. On the other hand, the lower hot wall 21b has a
double structure in which two cylinders radially align with each
other with a slight gap therebetween. Each of the inner peripheral
faces of the upper hot wall 21a and lower hot wall 21b is formed
from diamond-like carbon or glass-like carbon (glassy carbon)
having a high smoothness. Preferably, the inner peripheral faces of
the upper hot wall 21a and lower hot wall 21b have a surface
roughness of R.sub.max<10 .mu.m.
78. Inside the lower hot wall 21b, an Si-accommodating crucible
(Si-disposing section) 23, having a bottomed cylinder form made of
graphite, is inserted so as to be axially movable with a gap from
the lower hot wall 21b. The lower part of the Si-accommodating
crucible 23 is fixedly attached to the upper face of a disk-shaped
crucible support 24 which is slidable along the inner peripheral
face of the lower hot wall 21b, whereas a cylindrical support shaft
25 connected to a drive source not shown is fixedly attached to the
center part of the lower face of crucible support 24. Namely, as
the support shaft 25 moves up and down, the Si-accommodating
crucible 23 can move axially. Also, since the support shaft 25 has
a hollow cylindrical form, the temperature of the bottom face of
the Si-accommodating crucible 23 can be measured with a
two-temperature pyrometer.
79. The center parts of the support shaft 25, crucible support 24,
and crucible 23 are provided with an Ar gas supply pipe 26 for
supplying an Ar gas as a carrier gas. Also, the outer periphery of
the crucible support 24 is provided with a plurality of hydrocarbon
supply holes 27 for supplying hydrocarbon as a gas containing
carbon which axially penetrate therethrough.
80. Within the crucible 23, a solid Si source 28 is accommodated.
On the upper face of the Si source 28, a disk-shaped shield 29 for
regulating Si vapor pressure made of carbon, quartz, or SiC is
mounted. The shield 29 for regulating Si vapor pressure is formed
with a plurality of passage holes 29a axially penetrating
therethrough so as to allow Si vapor to pass therethrough. This
shield 29 is used for regulating the area of the boundary between
Si in the melted liquid phase and Si in the vapor phase, in order
to control the vapor pressure from the Si source 28.
81. To the upper part of the crucible 23, a disk-shaped control
plate 30 for uniformly supplying Si vapor is fixedly attached. This
control plate 30 is made of the same material as the shield 29,
such that the upper end of a cylinder vertically disposed on the
crucible 23 is provided with a disk, which is formed with a
plurality of passage holes 30a axially penetrating
therethrough.
82. On the other hand, into the hot wall 21 at the upper part
thereof, a cylindrical substrate-holder-supporting rod 31
penetrating through the center part of the lid 22 is inserted so as
to be axially movable. To the lower end of the
substrate-holder-supporting rod 31, a disk-shaped substrate holder
(seed-crystal-disposing section) 32 is fixedly attached such as to
close the lower end opening thereof. To the lower face of the
substrate holder 32, a substrate 33 of SiC single crystal, which is
a seed crystal, is fixedly attached with a paste made of glucose
which has been melted at a high temperature. Since the
support-holding rod 31 has a hollow cylindrical form, the
temperature of the substrate 33 can be measured with a
two-temperature pyrometer. Also, the substrate-holding rod 31 is
disposed such as to be axially rotatable at a speed as high as 1500
rpm. The outer periphery of the lid 22 is provided with a plurality
of gas exhaust holes 34, axially penetrating therethrough, for
exhausting gases.
83. Outside the hot wall 21, as shown in FIG. 4, three pieces of
heat shields 35 are disposed concentrically, aligning in radial
directions of the hot wall 21. Each heat shield 35 is formed by a
plurality of strip-shaped graphite sheets 35a disposed close to
each other with a gap therebetween, such as to yield substantially
a cylindrical form as a whole, whereas the neighboring heat shields
35 are disposed such that their gaps would not overlap radially.
Since the heat shields 35 are not formed from carbon fiber or
porous graphite which is often used in general and causes impurity
contamination, there is no fear of impurity contamination.
84. Outside the outermost heat shield 35, a cylindrical quartz tube
36 made of quartz is disposed concentrically with the heat shields
35. A coolant such as water is allowed to flow through the quartz
tube 36, thus protecting the latter. Outside the quartz tube 36, RF
work coils 37a, 37b, which function as heating means, are
successively disposed from the upper side so as to enable
high-frequency heating of the hot wall 21 and the like. Also, a
control section 38 for effecting temperature adjustment of the work
coils 37a, 37b is connected thereto.
85. Here, the hot wall 21, heat shields 35, and so forth are
configured such as to be able to attain a vacuum state as a whole
within the range surrounded by the inner wall of the quartz tube
36.
86. In thus configured apparatus 102, according to the command of
the control section 38, heating control can be effected such that
the temperature of the Si source 28 is set to 1300.degree. C. to
1600.degree. C. by the work coil 37b and the temperature of the
substrate 33 is set to 1500.degree. C. to 2200.degree. C. by the
work coil 37a. Namely, this apparatus 102 is configured such that
two areas consisting of a low-temperature area (first temperature
area) T.sub.1 for the Si source 28 and a high-temperature area
(second temperature area) T.sub.2 for the substrate 33 can be
formed within the hot wall 21.
87. With reference to FIG. 3, a method of making an SiC single
crystal by using thus configured apparatus 102 for making an SiC
single crystal will now be explained.
88. First, after the Si source 28, the substrate 33 of SiC single
crystal, and the like were set to their predetermined positions,
the substrate-holder-supporting rod 31 was moved up to lift the
substrate 33, the Si source 28 was moved down together with the
crucible 23, and then evacuation was effected for an hour in the
space formed inside the inner wall of the quartz tube 36.
Subsequently, an Ar gas was caused to flow into the apparatus 101
such as to yield a normal pressure (760 Torr) and, with coolant
flowing through the quartz tube 36, the hot wall 21 was set to
2800.degree. C. and baked for an hour, so as to effect
degassing.
89. Subsequently, the Si source 28 was moved up together with the
crucible 23 so as to attain the state shown in FIG. 3, the
substrate-holder-suppor- ting rod 31 and the substrate 33 were
moved down to their predetermined positions, and then, with the
substrate-holder-supporting rod 31 being rotated at 1000 rpm, the
control section 38 was operated to adjust the work coils 37a, 37b
such that the substrate 33 and the Si source 28 attained
temperatures of about 2300.degree. C. and about 1450.degree. C.,
respectively. As the temperature setting is effected at such a
normal pressure, crystals with inferior crystallinity can be
prevented from growing.
90. Thereafter, the pressure inside the inner wall of the quartz
tube 16 was lowered to 5 Torr in the Ar gas atmosphere and, with
this state being maintained, the Ar gas as the carrier gas was
caused to flow from the Ar gas supply pipe 26, thereby causing Si
vapor to pass through the passage holes 29a of the shield 29 and
further through the passage holes 30a of the control plate 30.
Thereafter, Si vapor was reacted with hydrocarbon supplied from the
hydrocarbon supply hole 27 in the vicinity of the substrate 33.
Then, the SiC-forming gas generated by the reaction between Si and
the carbon component contained in hydrocarbon was caused to reach
the substrate 33, so as to grow an SiC single crystal on the
surface of the substrate 33 at a rate of 100 .mu.m/h, whereby an
epitaxial film of SiC single crystal having a diameter of 2 inches
and a thickness of 0.5 mm in accordance with this embodiment was
finally formed.
91. In this embodiment, by adjusting the amount of hydrocarbon
supplied from the hydrocarbon supply hole 27, the partial pressure
of evaporated Si determined by the heating temperature of the work
coil 37a and the partial pressure of carbon contained in
hydrocarbon can be made substantially identical to each other. As a
consequence, a high-quality SiC single crystal can be obtained.
92. Further, since the inner peripheral surfaces of the upper hot
wall 21a and lower hot wall 21b are formed from diamond-like carbon
or glass-like carbon as mentioned above, they can restrain natural
nucleation from occurring in the inner face of the hot wall 21,
whereby a high-quality SiC single crystal can be formed.
93. Also, since a solid source of Si is used, the partial pressure
of hydrogen within the hot wall 21 decreases, whereby there is
substantially no problem of the SiC single crystal being etched.
Further, since no unstable gases such as silane are used as the Si
source, there would be no problems of particles caused by
decomposition of the gases in the vapor phase. As a consequence, a
sufficient amount of Si can be supplied, so as to enable high-speed
growth, and the SiC single crystal can be prevented from degrading
due to the particles.
94. Also, since the heat shields 35 made of graphite are disposed
outside the hot wall 21, the heat dissipation caused by heat
radiation can be suppressed. Further, since the heat shield 35
comprises a plurality of graphite sheets 35a disposed with a gap
therebetween, so as to yield substantially a cylindrical form as a
whole, it can suppress the induced current caused by high-frequency
heating. Also, since a plurality of such heat shields 35 are
disposed radially of the hot wall 21, the heat dissipation and
induced current can further be suppressed.
95. Also, Si, hydrocarbon, and the like can be made of highly pure
materials which are inexpensively available, and can greatly reduce
the concentration of impurities in the epitaxially grown film.
Further, since the substrate-holder-supporting rod 31 and the
substrate 33 are rotated at 100 rpm or over, the film thickness
distribution can be made uniform, so as to allow the in-plane
homogeneity to enhance, and diffusion can be accelerated, so as to
raise the growth rate.
96. When investigating the photoluminescence characteristic of thus
obtained epitaxial film, its peak wavelength was found to be about
490 nm, thereby indicating it to be a 6H-type SiC epitaxial film.
Also, upon Hall measurement, electric characteristics were found to
be such that a high-resistance, low-carrier-density epitaxial film
having a resistivity of 1000 .OMEGA.cm, a carrier density of about
3.times.10.sup.14 cm.sup.-3, and n-type conduction could be
synthesized. Further, when the substrate on the rear side was
shaved off so as to investigate the light transmissibility of this
epitaxial film, it was found to be favorable at a wavelength of 2
to 5 .mu.m, thus indicating this epitaxial film to be a good
crystal which did not take a large amount of impurities
therein.
97. As explained in the foregoing, in the method of making an SiC
single crystal and apparatus for making an SiC single crystal in
accordance with the present invention, since the temperature of
solid Si is raised independently of the temperature of carbon, the
partial pressure of Si and the partial pressure of carbon can be
made substantially identical to each other, whereby a high-quality
SiC single crystal can be obtained.
98. From the invention thus described, it will be obvious that the
invention may be varied in many ways. Such variations are not to be
regarded as a departure from the spirit and scope of the invention,
and all such modifications as would be obvious to one skilled in
the art are intended for inclusion within the scope of the
following claims.
* * * * *