U.S. patent application number 11/133308 was filed with the patent office on 2005-09-22 for silicon carbide single crystal and method and apparatus for producing the same.
This patent application is currently assigned to BRIDGESTONE CORPORATION. Invention is credited to Endo, Shigeki, Maruyama, Takayuki.
Application Number | 20050205003 11/133308 |
Document ID | / |
Family ID | 26607195 |
Filed Date | 2005-09-22 |
United States Patent
Application |
20050205003 |
Kind Code |
A1 |
Maruyama, Takayuki ; et
al. |
September 22, 2005 |
Silicon carbide single crystal and method and apparatus for
producing the same
Abstract
A method of producing a silicon carbide single crystal in which
a sublimation raw material 40 is accommodated at the side of vessel
body 12 in a graphite crucible 10, placing a seed crystal of a
silicon carbide single crystal at the side of cover body 11 of the
graphite crucible 10, the sublimation raw material 40 is sublimated
by a first induction heating coil 21 placed at the side of
sublimation raw material 40, a re-crystallization atmosphere is
form by a second induction heating coil 20 placed at the side of
cover body 11 so that the sublimation raw material 40 sublimated by
the first induction heating coil 21 is re-crystallizable only in
the vicinity of the seed crystal of a silicon carbide single
crystal, and the sublimation raw material 40 is re-crystallized on
the seed crystal of a silicon carbide single crystal, and a silicon
carbide single crystal 60 is grown while keeping the whole surface
of its growth surface in convex shape through the all growth
processes. A high quality silicon carbide single crystal with large
diameter excellent in dielectric breakdown property, heat
resistance, radiation resistance and the like, suitable for
electronic and optical devices and the like, and showing no
contamination of polycrystals and polymorphs, no defect of
micropipes and the like can be produced efficiently without
cracking and the like.
Inventors: |
Maruyama, Takayuki; (Tokyo,
JP) ; Endo, Shigeki; (Tokorozawa-shi, JP) |
Correspondence
Address: |
SUGHRUE MION, PLLC
2100 PENNSYLVANIA AVENUE, N.W.
SUITE 800
WASHINGTON
DC
20037
US
|
Assignee: |
BRIDGESTONE CORPORATION
|
Family ID: |
26607195 |
Appl. No.: |
11/133308 |
Filed: |
May 20, 2005 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
11133308 |
May 20, 2005 |
|
|
|
10450151 |
Jun 11, 2003 |
|
|
|
10450151 |
Jun 11, 2003 |
|
|
|
PCT/JP01/11270 |
Dec 21, 2001 |
|
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Current U.S.
Class: |
117/84 |
Current CPC
Class: |
C30B 23/00 20130101;
C30B 23/00 20130101; C30B 29/36 20130101; C30B 29/36 20130101 |
Class at
Publication: |
117/084 |
International
Class: |
C30B 023/00; C30B
025/00; C30B 028/12; C30B 028/14 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 28, 2000 |
JP |
P2000-402730 |
Apr 10, 2001 |
JP |
P2001-111374 |
Claims
1-30. (canceled)
31. An apparatus for generating a silicon carbide single crystal in
which a sublimation raw material being sublimated is
re-crystallized to grow a silicon carbide single crystal,
comprising: a crucible provided with a vessel body to accommodate a
sublimation raw material and a cover body attachable to and
detachable from the vessel body and, when the cover body is
installed on the vessel body and, when the cover body is installed
on the vessel body, a seed crystal of a silicon carbide single
crystal can be arranged at a surface facing the inside of the
vessel body; a first induction heating coil wound around the outer
periphery of a part or the crucible when the sublimation raw
material is accommodated, so as to form a sublimation atmosphere to
enable sublimation of the sublimation raw material; a second
induction heating coil wound around the outer periphery of a part
of a crucible where the seed crystal is placed, so as to form a
re-crystallization atmosphere so that the sublimation raw material
being sublimate by the first induction heating coil is
re-crystallize only in the vicinity of the seed crystal of a
silicon carbide single crystal, and re-crystallizing the
sublimation raw material on the seed crystal of a silicon carbide
single crystal; and an interference preventing coli for providing
the induction current and preventing Interference between the first
heating coil and the second heating oil, placed between the first
heating coil and the second heating oil.
32. The apparatus of claim 1, wherein the interference preventing
coil is a coil through which cooling water can flow.
33. The apparatus of claim 1, wherein the crucible includes a lower
end and an upper end.
34. The apparatus of claim 1, further comprising a quartz tube
wherein the vessel is placed in the quartz tube.
35. The apparatus of claim 1, wherein an induction current flows
through the Interference preventing coil, and the Interference
preventing coil minimizes and prevents Interference between the
first heating coil and the second heating coil, when an Induction
heating is conducted by the first heating coil and the second
heating coil simultaneously.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to a silicon carbide single
crystal particularly suitable as an electronic device, optical
device or the like, and a method and an apparatus which can produce
this silicon carbide single crystal efficiently.
[0003] 2. Description of the Related Art
[0004] Silicon carbide shows a larger band gap and is excellent in
dielectric breakdown property, heat resistance, radiation
resistance and the like as compared with silicon. Therefore,
silicon carbide has been noticed as an electronic device material
for small-size high output semiconductors and the like, or as an
optical device material owing to its excellent optical property. Of
such silicon carbide crystals, silicon carbide single crystals have
a merit that, when applied to devices such as a wafer and the like,
uniformity of properties in a wafer is particularly excellent as
compared with a silicon carbide polycrystals.
[0005] Though there are some conventionally suggested methods of
producing the above-mentioned silicon carbide single crystal, each
of them have a problem that the resulting silicon carbide single
crystal shows contamination of a polycrystal or polymorphs and
crystal defects in the form of hollow pipe (so-called,
micropipe).
[0006] Then, as the method of producing a silicon carbide single
crystal solving such a problem, for example, a method employing an
apparatus for generating a silicon carbide single crystal as shown
in FIG. 8 is generally known. This silicon carbide single crystal
production apparatus 80 comprises a graphite crucible 10 having a
vessel body 12 which can accommodate a sublimation raw material 40
and having a cover body 11 which can be attached to and detached
from the vessel body 12 and, when installed on the vessel body 12,
can arrange a seed crystal 50 of a silicon carbide single crystal
at approximately the center of a surface facing the sublimation raw
material 40 accommodated in the vessel body 12; a supporting rod 31
fixing the graphite crucible 10 to the inside of a quartz tube 30;
and an induction heating coil 25 placed, being wound in spiral form
and at an equal interval, at a part around the outer periphery of
the quartz tube 30 and at which part the graphite crucible 10 is
situated. In the silicon carbide single crystal production
apparatus 80, when the induction heating coil 25 is energized to be
heated, the sublimation raw material 40 is heated by this heat. The
sublimation raw material 40 sublimates when heated to given
temperature. The sublimated raw material 40 does not re-crystallize
until cooled to the re-crystallization temperature. Here, an
atmosphere at the side of the cover body 11 has temperature lower
than that in the side of the sublimation raw material 40 and the
sublimation raw material 40 being sublimated can re-crystallize in
this atmosphere, therefore, silicon carbide re-crystallizes on the
seed crystal 50 of a silicon carbide single crystal, and the
crystal of silicon carbide grows.
[0007] Under this condition, a silicon carbide single crystal 60
re-crystallizes and grows on the seed crystal 50 of a silicon
carbide single crystal, and a silicon carbide polycrystal 70
re-crystallizes and grows on the peripheral part of the seed
crystal 50 of a silicon carbide single crystal. Finally, as shown
in FIG. 8, a concave portion 71 sinking toward the cover body 11 is
shaped in the form of a ring, and the part around this concave
portion 71 through at the peripheral side of the cover body 11 are
in condition wherein extraneous substances, polycrystals and
polymorphs are mixed and present in a large amount. At the cover
body 11, the whole surface at the side facing to the inside of the
vessel body 12 is covered by crystals of silicon carbide, and on
the peripheral part of the cover body 11, a silicon carbide
polycrystal 70 grows contacting with the inner peripheral surface
of the vessel body 12. Under this condition, when cooled to room
temperature, stress based on the thermal expansion difference
concentrates on the side of the silicon carbide single crystal 60
from the side of the silicon carbide polycrystal 70, leading to
breakage such as cracking and the like on the silicon carbide
single crystal 60, as shown in FIG. 9, contamination of
polycrystals and polymorphs or defects such as micropipes and the
like, in some cases. At recentness wherein production of a silicon
carbide single crystal of large diameter is required, this
phenomenon is an important problem which should be overcome.
[0008] That is, a high quality silicon carbide single crystal
showing no such breakages as cracking and the like, no
contamination of polycrystals and polymorphs and having no defect
such as micropipes, and a method and an apparatus which can
efficiently and easily produce such a high quality silicon carbide
single crystal with large diameter, are not provided yet, and these
are needed to be provided, under the present situation.
SUMMARY OF THE INVENTION
[0009] The subject of the present invention is to solve the
above-mentioned conventional various problems and to attain the
following object, responding to the above-mentioned
requirement.
[0010] An object of the present invention is to provide a high
quality silicon carbide single crystal excellent in dielectric
breakdown property, heat resistance, radiation resistance and the
like, particularly suitable for electronic devices such as
semiconductor wafers and the like and optical devices such as
emitting diodes and the like, and having no contamination of
polycrystals and polymorphs and no defects such as micropipes and
the like, and a method and an apparatus which can efficiently and
easily produce the above-mentioned high quality silicon carbide
single crystal with large diameter, under condition including no
breakages such as cracking and the like.
[0011] Means for attaining the above-mentioned object are as
described below.
[0012] <1> A method of producing a silicon carbide single
crystal in which a sublimation raw material being sublimated is
re-crystallized to grow a silicon carbide single crystal,
comprising
[0013] growing the silicon carbide single crystal while maintaining
the whole growing surface in a convex shape throughout all growth
processes.
[0014] <2> The method of producing a silicon carbide single
crystal according to <1>,
[0015] wherein a crystal of silicon carbide containing a silicon
carbide single crystal is grown approximately in a protruded
shape.
[0016] <3> The method of producing a silicon carbide single
crystal according to <1> or <2>, comprising
[0017] growing the crystal of silicon carbide containing a silicon
carbide single crystal while maintaining the approximate protruded
shape and,
[0018] wherein the diameter of the crystal of silicon carbide
decreases gradually toward the sublimation raw material throughout
all the growth processes.
[0019] <4> The method of producing a silicon carbide single
crystal according to any of <1> to <3>, further
comprising
[0020] accommodating the sublimation raw material in a reaction
vessel,
[0021] placing a seed crystal of a silicon carbide single crystal
at an end approximately facing the sublimation raw material in the
reaction vessel, and
[0022] conducting the growth of the crystal of silicon carbide
containing a silicon carbide single crystal only in a region
excluding a part adjacent to, a peripheral side surface part in the
reaction vessel.
[0023] <5> A method of producing a silicon carbide single
crystal in which a sublimation raw material being sublimated is
re-crystallized to grow a silicon carbide single crystal,
comprising
[0024] accommodating the sublimation raw material in a reaction
vessel,
[0025] placing the seed crystal of a silicon carbide single crystal
at the end approximately facing the sublimation raw material in the
reaction vessel, and
[0026] growing the crystal of silicon carbide containing a silicon
carbide single crystal only in a region excluding the part adjacent
to the peripheral side surface part in the reaction vessel at the
end.
[0027] <6> The method of producing a silicon carbide single
crystal according to any of <2> to <5>,
[0028] wherein the crystal of silicon carbide containing a silicon
carbide single crystal is composed only of a silicon carbide single
crystal.
[0029] <7> The method of producing a silicon carbide single
crystal according to any of <1> to <6>, further
comprising
[0030] accommodating a sublimation raw material at one end side in
a reaction vessel, and placing a seed crystal of a silicon carbide
single crystal at another end side in the reaction vessel;
[0031] forming a sublimation atmosphere by a first heating means
placed at the one end side so as to enable sublimation of the
sublimation raw material;
[0032] forming a re-crystallization atmosphere by a second heating
means placed at another end side so that the sublimation raw
material being sublimate by the first heating means is
re-crystallizable only in the vicinity of the seed crystal of a
silicon carbide single crystal, and the sublimation raw material is
re-crystallized on the seed crystal of a silicon carbide single
crystal.
[0033] <8> The method of producing a silicon carbide single
crystal according to <7>,
[0034] wherein the temperature of the re-crystallization atmosphere
is lower than the temperature of the sublimation atmosphere by 30
to 300.degree. C., in the reaction vessel.
[0035] <9> The method of producing a silicon carbide single
crystal according to <7> or <8>,
[0036] wherein the first heating means and the second heating means
are an induction-heatable coil.
[0037] <10> The method of producing a silicon carbide single
crystal according to <9>,
[0038] wherein the current value of the induction heating current
in the first heating means is larger than the current value of the
induction heating current in the second heating means.
[0039] <11> The method of producing a silicon carbide single
crystal according to <9> or <10>,
[0040] wherein the current value of the induction heating current
in the second heating means is decreased continuously or gradually
with the increase of the diameter of a growing silicon carbide
single crystal.
[0041] <12> The method of producing a silicon carbide single
crystal according to any of <7> to <11>,
[0042] wherein if the temperature at one end side accommodating a
sublimation raw material is represented by T.sub.1 and the
temperature at another end side at which a seed crystal of a
silicon carbide single crystal is placed is represented by T.sub.2,
in the reaction vessel, and the temperature of the part adjacent to
the inner peripheral side surface part of the reaction vessel at
said another end side is represented by T.sub.3, then,
T.sub.3-T.sub.2 and T.sub.1-T.sub.2 increase continuously or
gradually.
[0043] <13> The method of producing a silicon carbide single
crystal according to any of <9> to <12>,
[0044] wherein an interference preventing means capable of flowing
the induction current and preventing interference between the first
heating means and the second heating means by flowing the induction
current is placed between the first heating means and the second
heating means.
[0045] <14> The method of producing a silicon carbide single
crystal according to <13>, wherein the interference
preventing means is a coil through which cooling water can
flow.
[0046] <15> The method of producing a silicon carbide single
crystal according to any of <7> to <14>, wherein the
one end is a lower end and another end is an upper end.
[0047] <16> The method of producing a silicon carbide single
crystal according to any of <7> to <15>, wherein the
reaction vessel is a crucible placed in a quartz tube.
[0048] <17> The method of producing a silicon carbide single
crystal according to any of <7> to <16>,
[0049] wherein a first region in which a silicon carbide single
crystal is grown and a second region situated at the outer
periphery of the first region and adjacent to the inner peripheral
side surface part of the reaction vessel, at another end, are
formed from different members, and one end of the member forming
the first region in which a silicon carbide single crystal is grown
is exposed to the inside of the reaction vessel and another end
thereof is exposed to the outside of the reaction vessel.
[0050] <18> The method of producing a silicon carbide single
crystal according to any of <5> to <17>, wherein the
surface of the part adjacent to the peripheral side surface part in
the reaction vessel at another end is made of glassy carbon.
[0051] <19> The method of producing a silicon carbide single
crystal according to any of <1> to <18>, wherein the
sublimation raw material is a silicon carbide powder obtained
by
[0052] using as a silicon source at least one compound selected
from high purity alkoxysilanes and alkoxysilane polymers, as a
carbon source a high purity organic compound generating carbon by
heating;
[0053] uniformly mixing the silicon source and the carbon source to
obtain a mixture; and
[0054] calcinating the resulted mixture by heating under a
non-oxidizing atmosphere.
[0055] <20> The method of producing a silicon carbide single
crystal according to any of <1> to <18>, wherein the
sublimation raw material is a silicon carbide powder obtained
by
[0056] using as a silicon source a high purity alkoxysilane, as a
carbon source a high purity organic compound generating carbon by
heating;
[0057] uniformly mixing the silicon source and the carbon source to
obtain a mixture; and
[0058] calcinating the resulted mixture by heating under a
non-oxidizing atmosphere.
[0059] <21> The method of producing a silicon carbide single
crystal according to any of <1> to <18>, wherein the
sublimation raw material is a silicon carbide powder obtained
by
[0060] using as a silicon source at least one of a high purity
alkoxysilane and a polymer of a high purity alkoxysilane, as a
carbon source a high purity organic compound generating carbon by
heating;
[0061] uniformly mixing the silicon source and the carbon source to
obtain a mixture; and
[0062] calcinating the resulted mixture by heating under a
non-oxidizing atmosphere.
[0063] <22> The method of producing a silicon carbide single
crystal according to any of <1> to <18>, wherein the
sublimation raw material is a silicon carbide powder obtained
by
[0064] using as a silicon source at least one compound selected
from the group consisting of high purity methoxysilane, high purity
ethoxysilane, high purity propoxysilane and high purity
butoxysilane, as a carbon source a high purity organic compound
generating carbon by heating;
[0065] uniformly mixing the silicon source and the carbon source to
obtain a mixture; and
[0066] calcinating the resulted mixture by heating under a
non-oxidizing atmosphere.
[0067] <23> The method of producing a silicon carbide single
crystal according to any of <1> to <18>, wherein the
sublimation raw material is a silicon carbide powder obtained
by
[0068] using as a silicon source at least one compound selected
from the group consisting of high purity methoxysilane, high purity
ethoxysilane, high purity propoxysilane and high purity
butoxysilane, and a polymer of them having a polymerization degree
of 2 to 15, as a carbon source a high purity organic compound
generating carbon by heating;
[0069] uniformly mixing the silicon source and the carbon source to
obtain a mixture, and calcinating the resulted mixture by heating
under a non-oxidizing atmosphere.
[0070] <24> The method of producing a silicon carbide single
crystal according to any of <1> to <18>, wherein the
sublimation raw material is a silicon carbide powder obtained
by
[0071] using as a silicon source at least one of compound selected
from the group consisting of high purity monoalkoxysilanes, high
purity dialkoxysilanes, high purity trialkoxysilanes and high
purity tetraalkoxysilanes, and a polymer of them having a
polymerization degree of 2 to 15, as a carbon source a high purity
organic compound generating carbon by heating;
[0072] uniformly mixing the silicon source and the carbon source to
obtain a mixture; and
[0073] calcinating the resulted mixture by heating under a
non-oxidizing atmosphere.
[0074] <25> The method of producing a silicon carbide single
crystal according to any of <19> to <24>, wherein the
silicon source is a tetraalkoxysilane polymer and the carbon source
is a phenol resin.
[0075] <26> The method of producing a silicon carbide single
crystal according to any of <19> to <25>, wherein each
content of impurity elements in the silicon carbide powder is 0.5
ppm or less.
[0076] <27> A silicon carbide single crystal produced by the
method of producing a silicon carbide single crystal according to
any of <1> to <26>.
[0077] <28> The silicon carbide single crystal according to
<27>, wherein the crystal defect in the form of hollow pipe
of which image is optically detected is 100/cm.sup.2 or less.
[0078] <29> The silicon carbide single crystal according to
<27> or <28>, wherein the total content of impurity
elements is 10 ppm or less.
[0079] <30> An apparatus for generating a silicon carbide
single crystal in which a sublimation raw material being sublimated
is re-crystallized to grow a silicon carbide single crystal,
comprising
[0080] a crucible provided with a vessel body to accommodate a
sublimation raw material and a cover body attachable to and
detachable from the vessel body and, when the cover body is
installed on the vessel body, a seed crystal of a silicon carbide
single crystal can be arranged at a surface facing the inside of
the vessel body;
[0081] a first induction heating coil placed in the state wound
around the outer periphery of a part or the crucible when the
sublimation raw material is accommodated, and forming a sublimation
atmosphere so as to enable sublimation of the sublimation raw
material; and
[0082] a second induction heating coil placed in the state wound
around the outer periphery of a part of a crucible where the seed
crystal is placed, forming a re-crystallization atmosphere so that
the sublimation raw material being sublimate by the first induction
heating coil is re-crystallizable only in the vicinity of the seed
crystal of a silicon carbide single crystal, and re-crystallizing
the sublimation raw material on the seed crystal of a silicon
carbide single crystal.
[0083] The above-described method of producing a silicon carbide
single crystal described in <1> is a method in which a
sublimation raw material being sublimated is re-crystallized to
grow a silicon carbide single crystal, wherein the above-mentioned
silicon carbide single crystal is grown while maintaining the whole
growing surface in a convex shape throughout the all growth
processes. In this method of producing a silicon carbide single
crystal, the above-mentioned concave portion sunk toward the
reverse direction to the growth direction is not shaped in the form
of ring at the whole surface of the growth surface of the growing
silicon carbide single crystal. Therefore, a high quality silicon
carbide single crystal is produced having no conventional various
problems described above, namely, showing no breakages such as
cracking and the like and having no contamination of polycrystals
and polymorphs and no crystal defects present such as micropipes
and the like.
[0084] In the above-mentioned methods of generating a silicon
carbide single crystal described in <2> and <3>, a
crystal of silicon carbide containing a silicon carbide single
crystal is grown approximately in shape in <1>, consequently,
the above-mentioned concave portion sunk toward the reverse
direction to its growth direction is not present at all, in the
growing silicon carbide single crystal. Therefore, a high quality
silicon carbide single crystal is produced having no conventional
various problems described above, namely, showing no breakages such
as cracking and the like and having no contamination of
polycrystals and polymorphs and no crystal defects present such as
micropipes and the like.
[0085] In the above-mentioned method of producing a silicon carbide
single crystal described in <4>, the above-mentioned
sublimation raw material is accommodated in a reaction vessel,
placing a seed crystal of a silicon carbide single crystal at the
end approximately facing the sublimation raw material in the
reaction vessel, and growth of the above-mentioned crystal of
silicon carbide containing a silicon carbide single crystal is
conducted only in a region excluding the part adjacent to the
peripheral side surface part in the reaction vessel, at the
above-mentioned end, in any of <1> to <3>. Therefore,
the above-mentioned concave portion sunk toward the reverse
direction to the growth direction of the silicon carbide single
crystal is not shaped in the form of ring, in the growing silicon
carbide single crystal, further, the silicon carbide single crystal
does not grow contacting with the peripheral surface part in the
reaction vessel. Therefore, stress based on the thermal expansion
difference does not concentrate on the silicon carbide single
crystal side from the silicon carbide polycrystal side when a grown
silicon carbide single crystal is cooled to room temperature, and
defects such as cracking and the like do not occur on the resulting
silicon carbide single crystal. As a result, a high quality silicon
carbide single crystal is efficiently and securely produced having
no conventional various problems described above, namely, showing
no breakages such as cracking and the like and having no
contamination of polycrystals and polymorphs and no crystal defects
present such as micropipes and the like.
[0086] The method of producing a silicon carbide single crystal
described in <5> is a method of producing a silicon carbide
single crystal in which a sublimation raw material being sublimated
is re-crystallized to grow a silicon carbide single crystal,
wherein the above-mentioned sublimation raw material is
accommodated in a reaction vessel, the above-mentioned seed crystal
of a silicon carbide single crystal is placed at the end
approximately facing the sublimation raw material in the reaction
vessel, and the above-mentioned crystal of silicon carbide
containing a silicon carbide single crystal is grown only in, a
region excluding the part adjacent to the peripheral surface part
in the reaction vessel, at the above-mentioned end. Therefore, the
above-mentioned silicon carbide single crystal does not grow
contacting with the peripheral surface part in the reaction vessel,
at the above-mentioned end. Stress based on thermal expansion
difference on the silicon carbide single crystal side from the
silicon carbide polycrystal side when a grown silicon carbide
single crystal is cooled to room temperature, and defects such as
cracking and the like do not occur on the resulting silicon carbide
single crystal. As a result, a high quality silicon carbide single
crystal is produced having no conventional various problems
described above, namely, showing no breakages such as cracking and
the like and having no crystal defects present such as
contamination of polycrystals and polymorphs and micropipes and the
like.
[0087] In the method of producing a silicon carbide single crystal
described in <6>, the above-mentioned crystal of silicon
carbide containing a silicon carbide single crystal is composed
only of a silicon carbide single crystal, in any of <2> to
<5>. Therefore, a silicon carbide single crystal having a
larger diameter is obtained, and it is not necessary to separate
the silicon carbide single crystal from a silicon carbide
polycrystal and the like.
[0088] In the method of producing a silicon carbide single crystal
described in <7>, the above-mentioned sublimation raw
material is accommodated at one end side in the above-mentioned
reaction vessel, and the above-mentioned seed crystal of a silicon
carbide single crystal is placed at another end side in the
reaction vessel, a sublimation atmosphere is formed by a first
heating means placed at the above-mentioned one end side so as to
enable sublimation of the sublimation raw material, a
re-crystallization atmosphere is formed by a second heating means
placed at the above-mentioned another end side so that the
above-mentioned sublimation raw material being sublimated by the
above-mentioned first heating means is re-crystallizable only in
the vicinity of the above-mentioned seed crystal of a silicon
carbide single crystal, and the sublimation raw material is
re-crystallized on the above-mentioned seed crystal of a silicon
carbide single crystal, in any of <1> to <6>.
[0089] In this method of producing a silicon carbide single
crystal, heating for formation of a sublimation atmosphere so as to
enable sublimation of the above-mentioned sublimation raw material
is conducted by the above-mentioned first heating means, formation
of a re-crystallization atmosphere so as to enable
re-crystallization only on the above-mentioned seed crystal of a
silicon carbide single crystal is conducted by the above-mentioned
second heating means, as a result, re-crystallization can be
conducted selectively only on the above-mentioned seed crystal of a
silicon carbide single crystal and the part in the vicinity of
this, and the above-mentioned silicon carbide polycrystal does not
grow contacting with the peripheral side surface part in the
reaction vessel, at the above-mentioned end. And, stress based on
thermal expansion difference on the silicon carbide single crystal
side from the silicon carbide polycrystal side when a grown silicon
carbide single crystal is cooled to room temperature, and defects
such as cracking and the like do not occur on the resulting silicon
carbide single crystal. As a result, a high quality silicon carbide
single crystal is produced having no conventional various problems
described above, namely, showing no breakages such as cracking and
the like and having no crystal defects present such as
contamination of polycrystals and polymorphs and micropipes and the
like.
[0090] In the method of producing a silicon carbide single crystal
described in <8>, the temperature of the re-crystallization
atmosphere is lower than the temperature of the sublimation
atmosphere by 30 to 300.degree. C., in the above-mentioned reaction
vessel, in <7>.
[0091] In the method of producing a silicon carbide single crystal
described in <9>, the above-mentioned first heating means and
the above-mentioned second heating means are an induction-heatable
coil, in <7> or <8>. Therefore, control of the
temperature of the above-mentioned first heating means for forming
the above-mentioned sublimation atmosphere and control of the
temperature of the above-mentioned second heating means for forming
the above-mentioned re-crystallization atmosphere can be conducted
easily and securely, by induction heating by this coil.
[0092] In the method of producing a silicon carbide single crystal
described in <10>, the current value of the induction heating
current in the first heating means is larger than the current value
of the induction heating current in the second heating means, in
any of <7> to <9>. Therefore, the temperature of the
re-crystallization atmosphere in the vicinity of on the
above-mentioned seed crystal is maintained lower than the
temperature of the above-mentioned sublimation atmosphere, and
re-crystallization is conducted easily.
[0093] In the method of producing a silicon carbide single crystal
described in <11>, the current value of the induction heating
current in the above-mentioned second heating means is decreased
continuously or gradually with the increase of the diameter of a
growing silicon carbide single crystal, in any of <7> to
<10>. By this constitution, the heating quantity by the
above-mentioned second heating means is controlled to be smaller
with the growth of the above-mentioned silicon carbide single
crystal, therefore, re-crystallization is conducted only in the
vicinity of the above-mentioned silicon carbide single crystal
keeping on growing, and a polycrystal is not formed around the
silicon carbide single crystal.
[0094] In the method of producing a silicon carbide single crystal
described in <12>, if the temperature at one end side
accommodating a sublimation raw material is represented by T.sub.1
and the temperature at another end side at which a seed crystal of
a silicon carbide single crystal is arranged is represented by
T.sub.2, in the reaction vessel, and the temperature of the part
adjacent to the inner peripheral side surface part of the reaction
vessel, at another end side, is represented by T.sub.3, then,
T.sub.3-T.sub.2 and T.sub.1-T.sub.2 increase continuously or
gradually, in any of <7> to <11>. When T.sub.1-T.sub.2
increases continuously or gradually, even if a silicon carbide
single crystal keeps on growing toward the above-mentioned one end
side, with the lapse of time, the crystal growth peak side of the
silicon carbide single crystal is always maintained at the
condition susceptible to re-crystallization. On the other hand,
when T.sub.3-T.sub.2 increases continuously or gradually, even if a
silicon carbide single crystal keeps on growing toward the
peripheral direction at the above-mentioned another end side, with
the lapse of time, the crystal growth peripheral end side of the
silicon carbide single crystal is always maintained at the
condition susceptible to re-crystallization. As a result,
production of a silicon carbide single crystal is effectively
suppressed, and the silicon carbide single crystal keeps on growing
toward a direction along which its thickness increases and its
diameter enlarges, and finally, a silicon carbide single crystal of
a larger diameter is obtained under condition without contamination
of a silicon carbide polycrystal and the like.
[0095] In the method of producing a silicon carbide single crystal
described in <13>, an interference preventing means capable
of flowing the induction current and preventing interference
between the first heating means and the second heating means by
flowing the induction current is placed between the first heating
means and the second heating means, in any of <9> to
<12>. Owing to this constitution, when induction heating by
the above-mentioned first heating means and induction heating by
the above-mentioned second heating means are conducted
simultaneously, induction current flows through the interference
preventing means and the interference preventing means minimizes
and prevents interference between them.
[0096] In the method of producing a silicon carbide single crystal
described in <14>, the interference preventing means is a
coolable coil, in <13>. Since this coil is cooled even if
induction current flows in the coil to heat the coil, this coil
does not heat the above-mentioned reaction vessel. Namely, control
of the temperature of the above-mentioned reaction vessel is
easy.
[0097] In the method of producing a silicon carbide single crystal
described in <15>, the above-mentioned one end is a lower end
and the above-mentioned another end is an upper end, in any of
<7> to <14>. Therefore, the above-mentioned sublimation
raw material is accommodated in the lower portion of the
above-mentioned reaction vessel, and sublimation of the sublimation
raw material is conducted smoothly, and the above-mentioned silicon
carbide single crystal grows toward lower direction, namely, grows
under condition without an excess load toward the gravity
direction.
[0098] In the method of producing a silicon carbide single crystal
described in <16>, the reaction vessel is a crucible placed
in a quartz tube, in any of <7> to <15>. Namely, since
sublimation and re-crystallization of the above-mentioned
sublimation raw material, and growth of the above-mentioned silicon
carbide single crystal are conducted in the sealed system in the
quartz tube, the control of them is easy.
[0099] In the method of producing a silicon carbide single crystal
described in <17>, a region in which the silicon carbide
single crystal is grown and a region situated at the outer
periphery of the above-mentioned region and adjacent to the inner
peripheral side surface part of the above-mentioned reaction
vessel, are formed from different members, and one end of the
member forming the region in which the silicon carbide single
crystal is grown is exposed to the inside of the reaction vessel
and another end thereof is exposed to the outside of the reaction
vessel, in any of <7> to <16>. Since the region in
which the silicon carbide single crystal is grown (inside region)
and the region situated at the outer periphery of the
above-mentioned region and adjacent to the inner peripheral side
surface part of the above-mentioned reaction vessel (outside
region) are formed from different members, when heating is
conducted by the above-mentioned second heating means, the
above-mentioned outside region situated at the second heating means
side is heated easily, however, the inside region is not heated
easily by the difference of contact resistance with the outside
region. Therefore, even if heating is conducted by the
above-mentioned second heating means, a difference in temperature
occurs between the above-mentioned outside region and the
above-mentioned inside region, and since the above-mentioned inside
region is not heated easily than the above-mentioned outside
region, temperature is maintained low and the above-mentioned
re-crystallization of silicon carbide is conducted easily. Further,
since the opposite side to the inside of the above-mentioned
reaction vessel in the member forming the above-mentioned inside
region is exposed to the outside of the reaction vessel and
consequently heat is easily discharged out of the reaction vessel,
when heating is conducted by the above-mentioned second heating
means, the above-mentioned inside region is not heated easily than
the above-mentioned outside region, a difference in temperature
occurs between the above-mentioned outside region and the
above-mentioned inside region, the temperature of the
above-mentioned inside region is maintained lower than the
temperature of the above-mentioned outside region, consequently,
the above-mentioned re-crystallization of silicon carbide is
conducted easily. As a result, a silicon carbide single crystal
does not grow easily in the above-mentioned outside region, and a
silicon carbide single crystal re-crystallizes and grows
selectively only in the inside region.
[0100] In the method of producing a silicon carbide single crystal
described in <18>, the surface of the part adjacent to the
inner peripheral side surface part of the reaction vessel is made
of glassy carbon, in any of <5> to <17>. Therefore, the
part adjacent to the inner peripheral side surface part of the
reaction vessel does not easily cause re-crystallization than
regions other than the above-mentioned adjacent part. As a result,
a crystal of silicon carbide does not grow at the above-mentioned
adjacent part, at the above-mentioned another end, and a silicon
carbide single crystal re-crystallizes and grows selectively only
in regions other than the above-mentioned adjacent part.
[0101] In the methods of generating a silicon carbide single
crystal described in <19> to <24>, the above-mentioned
sublimation raw material is a silicon carbide powder obtained by
using as a silicon source at least one compound selected from high
purity alkoxysilanes and alkoxysilane polymers, using as a carbon
source a high purity organic compound generating carbon by heating,
uniformly mixing the silicon source and the carbon source to obtain
a mixture, and calcinating the resulted mixture by heating under a
non-oxidizing atmosphere, in any of <1> to <18>. Since
the sublimation raw material is a high purity silicon carbide
powder, contamination of polycrystals and polymorphs into a silicon
carbide single crystal does not occur when growing a silicon
carbide single crystal, and a silicon carbide single crystal grows
smoothly and the resulted silicon carbide single crystal contains
no defects such as micropipes and the like.
[0102] In the method of producing a silicon carbide single crystal
described in <25>, the above-mentioned silicon source is a
tetraalkoxysilane polymer and the above-mentioned carbon source is
a phenol resin, in any of <19> to <24>. Therefore, the
above-mentioned sublimation raw material is obtained easily at low
cost.
[0103] In the method of producing a silicon carbide single crystal
described in <26>, each content of impurity elements in the
above-mentioned silicon carbide powder is 0.5 ppm or less, in any
of <19> to <25>. Therefore, the above-mentioned
sublimation raw material has extremely high purity, and
contamination of polycrystals and polymorphs into the
above-mentioned silicon carbide single crystal and generation of
crystal defects are effectively suppressed.
[0104] The silicon carbide single crystal described in <27>
is produced by the method of producing a silicon carbide single
crystal described in any of <1> to <26>. Therefore, the
resulting silicon carbide single crystal shows no breakages such as
cracking and the like and has no crystal defects such as
contamination of polycrystals and polymorphs and micropipes and the
like present, namely, has extremely high quality and excellent in
dielectric breakdown property, heat resistance, radiation
resistance and the like and suitable particularly for electronic
devices such as semiconductor wafers and the like, optical devices
such as light emitting diodes and the like.
[0105] In the silicon carbide single crystal described in
<28>, the crystal defects in the form of hollow pipe of which
image is 100/cm.sup.2 or less, in <27>. Therefore, the
silicon carbide single crystal has extremely high quality,
particularly excellent in dielectric breakdown property, heat
resistance, radiation resistance and the like, and suitable
particularly for electronic devices such as semiconductor wafers
and the like, optical devices such as light emitting diodes and the
like.
[0106] In the silicon carbide single crystal described in
<29>, the total content of the above-mentioned impurity
elements is 10 ppm or less, in <27> or <28>. Therefore,
the silicon carbide single crystal has very high quality.
[0107] An apparatus for generating a silicon carbide single crystal
described in <30> is an apparatus for generating a silicon
carbide single crystal wherein a sublimation raw material being
sublimated is re-crystallized to grow a silicon carbide single
crystal.
[0108] This silicon carbide single crystal production apparatus
comprises at least a crucible having a vessel body and a cover
body, a first induction heating coil and a second induction heating
coil.
[0109] In the above-mentioned crucible, the above-mentioned vessel
body accommodates the above-mentioned sublimation raw material. The
above-mentioned cover body can be attached to and detached from the
above-mentioned vessel body. When the cover body is installed to
the above-mentioned vessel body, placing a seed crystal of a
silicon carbide single crystal on a surface facing the inside of
the vessel body. The above-mentioned first induction heating coil
is placed, being wound, at the outer periphery of the part
accommodating the above-mentioned sublimation raw material, in the
above-mentioned crucible, and this forms a sublimation atmosphere
so as to enable sublimation of the sublimation raw material, to
sublimate the sublimation raw material. The above-mentioned second
induction heating coil is placed, being wound, at the outer
periphery of the part at which the above-mentioned seed crystal is
placed, in the above-mentioned crucible, and this forms a
re-crystallization atmosphere so that the above-mentioned
sublimation raw material being sublimate by the above-mentioned
first induction heating coil is re-crystallizable only in the
vicinity of the above-mentioned seed crystal of a silicon carbide
single crystal, and re-crystallizes the sublimation raw material on
the above-mentioned seed crystal of a silicon carbide single
crystal. Owing to this constitution, a silicon carbide single
crystal is grown while maintaining the whole growing surface in a
convex shape throughout the all growth processes, a concave portion
sunk toward the reverse direction to the growth direction is not
shaped in the form of ring, further, a silicon carbide single
crystal does not grow contacting with the peripheral side surface
part in the vessel body. Consequently, stress based on thermal
expansion difference on the silicon carbide single crystal side
from the silicon carbide polycrystal side when a grown silicon
carbide single crystal is cooled to room temperature, and defects
such as cracking and the like do not occur on the resulting silicon
carbide single crystal. As a result, a high quality silicon carbide
single crystal is efficiently and securely produced showing no
breakages such as cracking and the like and having no crystal
defects present such as contamination of polycrystals and
polymorphis and micropipes and the like.
[0110] This application claims benefit of priority based on
Japanese Patent Application previously filed by this applicant,
namely, No. 2000-402730 (filing date Dec. 28, 2000) and No.
2001-111374 (filing date Apr. 10, 2001), the specifications of
which are incorporated by reference herein.
BRIEF EXPLANATION OF THE DRAWINGS
[0111] Other objects, features, and advantages of the invention
will become apparent from the following description taken together
with the drawings, in which:
[0112] FIG. 1 is a schematic view for illustrating the initial
condition in the method of producing a silicon carbide single
crystal of the present invention.
[0113] FIG. 2 is a schematic view for illustrating a condition in
which a silicon carbide single crystal is being produced by the
method of producing a silicon carbide single crystal of the present
invention.
[0114] FIG. 3 is a schematic view of the silicon carbide single
crystal of the present invention produced by the method of
producing a silicon carbide single crystal of the present
invention.
[0115] FIG. 4 is a schematic illustration view showing one example
of the crucible used in the method of producing a silicon carbide
single crystal of the present invention.
[0116] FIG. 5 is a schematic illustration view showing another
example of the crucible used in the method of producing a silicon
carbide single crystal of the present invention.
[0117] FIG. 6 is a schematic view of the silicon carbide single
crystal of the present invention produced by the method of
producing a silicon carbide single crystal of the present
invention.
[0118] FIG. 7 is a schematic view of the silicon carbide single
crystal of the present invention produced by the method of
producing a silicon carbide single crystal of the present
invention.
[0119] FIG. 8 is a schematic view for illustrating a condition in
which a silicon carbide single crystal is being produced by a
conventional method of producing a silicon carbide single
crystal.
[0120] FIG. 9 is a schematic view of a silicon carbide single
crystal-produced by a conventional method of producing a silicon
carbide single crystal.
EXPLANATION OF MARKS
[0121] 1: Apparatus for generating a silicon carbide single
crystal
[0122] 10: Graphite crucible
[0123] 11: Cover body
[0124] 12: Vessel body
[0125] 13: Peripheral side surface part
[0126] 15: Inside region forming part
[0127] 20: Second induction heating coil
[0128] 21: First induction heating coil
[0129] 22: Interference preventing coil
[0130] 25: Induction heating coil
[0131] 30: Quartz tube
[0132] 31: Supporting rod
[0133] 40: Sublimation raw material
[0134] 50: Seed crystal of silicon carbide single crystal
[0135] 60: Silicon carbide single crystal
[0136] 70: Silicon carbide polycrystal
[0137] 71: Concave portion
[0138] 80: Conventional apparatus for generating a silicon carbide
single crystal
DETAILED DESCRIPTION OF THE INVENTION
[0139] (Method of Generating Silicon Carbide Single Crystal)
[0140] The method of producing a silicon carbide single crystal of
the present invention will be described below.
[0141] The method of producing a silicon carbide single crystal of
the present invention is a method of producing a silicon carbide
single crystal in which a sublimation raw material being sublimated
is re-crystallized on a seed crystal of a silicon carbide single
crystal to grow a silicon carbide single crystal.
[0142] In the method of producing a silicon carbide single crystal
of the present invention, the following first to third embodiments
are listed, and among them, the third embodiment is a preferable
embodiment having a content combining the first embodiment and the
second embodiment.
[0143] In the first embodiment, the above-mentioned silicon carbide
single crystal is grown while maintaining the whole growing surface
in a convex shape throughout the all growth processes.
[0144] In the second embodiment, the above-mentioned sublimation
raw material is accommodated in a reaction vessel, placing a seed
crystal of a silicon carbide single crystal at the end
approximately facing the sublimation raw material in the reaction
vessel, and the above-mentioned silicon carbide single crystal is
grown only in regions excluding the part adjacent to the peripheral
side surface part in the reaction vessel, at the above-mentioned
end.
[0145] In the third embodiment, the above-mentioned sublimation raw
material is accommodated in a reaction vessel, placing a seed
crystal of a silicon carbide single crystal at the end
approximately facing the sublimation raw material in the reaction
vessel, and the above-mentioned silicon carbide single crystal is
grown while maintaining the whole growing surface in a convex shape
throughout the all growth processes and only in a regions (inside
part) excluding the part (outside pate) adjacent to the peripheral
side surface part in the reaction vessel, at the above-mentioned
end.
[0146] --Reaction Vessel--
[0147] The reaction vessel is not particularly restricted and can
be appropriately selected depending on its object, and it is
preferable that it can contain the above-mentioned sublimation raw
material inside and it has an end on which the above-mentioned seed
crystal of a silicon carbide single crystal can be placed, at a
position approximately facing the sublimation raw material.
[0148] The form of the above-mentioned end is not particularly
restricted and preferably in the form of approximate flat, for
example.
[0149] The site accommodating the above-mentioned sublimation raw
material is not particularly restricted, and preferably an end
approximately facing one end at which the above-mentioned seed
crystal of a silicon carbide single crystal can be placed. In this
case, the inside of the above-mentioned reaction vessel is in the
form of cylinder, and the axis of this cylindrical form may be
linear or curved, and the form of a section vertical to the axis
direction of this cylindrical form may be circle or polygon.
Suitably listed as the preferable example of the circular form are
those having a linear axis and having a section vertical to the
axis direction, in the form of circle.
[0150] When two ends are present in the above-mentioned reaction
vessel, the above-mentioned sublimation raw material is
accommodated in one end side and the above-mentioned seed crystal
of a silicon carbide single crystal is placed in another end side.
Hereinafter, the above-mentioned one end may be referred to as
"sublimation raw material accommodating part", and the
above-mentioned another end may be referred to as "seed crystal
placing part".
[0151] The form of the above-mentioned one end (sublimation raw
material accommodating part) is not particularly restricted, and
may be in the flat form, or a structure for promoting soaking (for
example, convex portion and the like) may be appropriately
provided.
[0152] In the above-mentioned reaction vessel, it is preferable
that the above-mentioned another end (seed crystal placing part) is
designed so as to enable attachment and detachment. In this case,
it is advantageous in that a grown silicon carbide single crystal
can be easily separated from the reaction vessel only by removing
another end (seed crystal placing part).
[0153] Suitably listed such a reaction vessel is, for example, a
reaction vessel comprising a vessel body which can accommodate a
sublimation raw material and a cover body which can be attached to
and detached from the vessel body and, when installed on the vessel
body, can carry a seed crystal of a silicon carbide single crystal
placed at approximately the center of a surface facing the
above-mentioned sublimation raw material accommodated in the
reaction vessel, and other vessels.
[0154] The positional relation between the above-mentioned one end
(sublimation raw material accommodating part) and the
above-mentioned another end (seed crystal placing part) is not
particularly restricted and can be appropriately selected depending
on its object, and it is preferable that the above-mentioned one
end (sublimation raw material accommodating part) is a lower end
and the above-mentioned another end (seed crystal placing part) is
an upper end, namely, that the above-mentioned one end (sublimation
raw material accommodating part) and the above-mentioned another
end (seed crystal placing part) are situated along the gravity
direction. This case is preferable in that sublimation of the
above-mentioned sublimation raw material is conducted smoothly, and
growth of the above-mentioned silicon carbide single crystal is
conducted toward lower direction, namely, conducted under condition
without an excess load toward the gravity direction.
[0155] At the above-mentioned one end (sublimation raw material
accommodating part), a member formed of a material excellent in
heat conductivity, for example, may be placed for the purpose of
conducting sublimation of the above-mentioned sublimation raw
material efficiently.
[0156] Suitably listed as this member are, for example, members in
the form of reverse cone or reverse truncated cone of which outer
periphery can closely contact with the peripheral side surface part
in the above-mentioned reaction vessel and of which inner diameter
gradually increases when approaching the above-mentioned another
end (seed crystal placing part), and other members.
[0157] On the portion exposed to the outside of the above-mentioned
reaction vessel, threading, concave portion for measuring
temperature, and the like may be provided, depending on the object,
and the concave portion for measuring temperature is preferably
provided at at least one of the above-mentioned one end side and
the above-mentioned another end side.
[0158] The material of the above-mentioned reaction vessel is not
particularly restricted and can be appropriately selected depending
on the object, and it is preferable that the reaction vessel is
formed of a material excellent in durability, heat resistance, heat
conductivity and the like, and particularly preferable is graphite
in that contamination of polycrystals and polymorphs due to
generation of impurities is little and control of sublimation and
re-crystallization of the above-mentioned sublimation raw material
is easy, and the like, in addition to the above-mentioned
properties.
[0159] The above-mentioned reaction vessel may be formed from a
single member, or two or more members, and members can be
appropriately selected depending on the object. When formed from
two or more members, it is preferable that the above-mentioned
another end (seed crystal placing part) is formed from two or more
members, and it is more preferable that the center part and its
peripheral part of the above-mentioned another end (seed crystal
placing part) are formed from different members since the
temperature difference or temperature gradient can be formed.
Specifically, it is particularly preferable in the above-mentioned
reaction vessel that a region in which a silicon carbide single
crystal is grown (inside region) as the center part and a region
situated at the outer periphery of the above-mentioned inside
region and adjacent to the inner peripheral side surface part of
the reaction vessel (outside region) as the peripheral part are
formed from different members, and one end of a member forming the
inside region is exposed to the inside of the reaction vessel and
another end thereof is exposed to the outside of the reaction
vessel.
[0160] In this case, when the above-mentioned another end (seed
crystal placing part) is heated from its outside, the
above-mentioned outside region is heated easily, however, the
above-mentioned inside region is not easily heated due to contact
resistance with the outside region. Therefore, a difference in
temperature occurs between the above-mentioned outside region and
the above-mentioned inside region, the temperature of the inside
region is maintained slightly lower than the temperature of the
outside region, and silicon carbide can be re-crystallized more
easily in the inside region than in the outside region. Further,
since the above-mentioned another end of a member forming the
above-mentioned inside region is exposed to the outside of the
above-mentioned reaction vessel, the inside region easily
discharges heat to the outside of the above-mentioned reaction
vessel, consequently, silicon carbide is re-crystallized more
easily in the inside region than in the outside region.
[0161] Here, the embodiment in which the above-mentioned another
end of a member forming the above-mentioned inside region is
exposed to the outside of the above-mentioned reaction vessel is
not particularly restricted, and shapes having the inside region as
the bottom surface and having a diameter varying (increasing or
decreasing) continuously or discontinuously toward the outside of
the above-mentioned reaction vessel, and the like are listed.
[0162] Specifically listed as such a form are pillar forms having
the inside region as the bottom surface (cylinder, prism and the
like are listed, and cylinder is preferable), truncated pyramidal
forms (truncated cone, truncated pyramid, reverse truncated cone,
reverse truncated pyramid and the like are listed, and reverse
truncated cone is preferable), and the like.
[0163] It is preferable in the above-mentioned reaction vessel that
the surface of a region (outside region) situated at the outer
periphery of the above-mentioned region (inside region) in which a
silicon carbide single crystal is grown and adjacent to the inner
peripheral side surface part of the reaction vessel, at the
above-mentioned another end (seed crystal placing part), is made of
glassy carbon or amorphous carbon. In this case, the
above-mentioned outside region is preferable in that
re-crystallization does not occur easily as compared with the
above-mentioned inside region.
[0164] It is preferable that the above-mentioned reaction vessel is
surrounded by a heat insulating material and the like. In this
case, it is preferable that the above-mentioned heat insulating
material and the like are not provided at approximately the center
of the above-mentioned one end (sublimation raw material
accommodating part) and the above-mentioned another end (seed
crystal placing part) in the above-mentioned reaction vessel, for
the purpose of forming a temperature measuring window. When the
above-mentioned temperature measuring window is provided at
approximately the center of the above-mentioned one end
(sublimation raw material accommodating part), it is preferable
that a graphite cover member and the like are further provided for
preventing falling the above-mentioned heat insulating material
powder and the like.
[0165] It is preferable that the above-mentioned reaction vessel is
placed in a quartz tube. This is preferable in that loss of heat
energy for sublimation and re-crystallization of the
above-mentioned sublimation raw material is small.
[0166] A high purity quartz tube is available, and use of the high
purity product is advantageous in that contamination of metal
impurities is small.
[0167] --Sublimation Raw Material--
[0168] Regarding the above-mentioned sublimation raw material, the
polymorphs of a crystal, use amount, purity, its production method
and the like are not particularly restricted as long as the
material is made of silicon carbide, and can be appropriately
selected depending on the object.
[0169] As the polymorphs of a crystal of the above-mentioned
sublimation raw material, for example, 4H, 6H, 15R, 3C and the like
listed, and among them, 6H and the like are suitably listed. These
are preferably used alone, however, two or more of them may be used
in combination.
[0170] The use amount of the above-mentioned sublimation raw
material can be appropriately selected depending on the size of a
silicon carbide single crystal produced, the size of the
above-mentioned reaction vessel, and the like.
[0171] The purity of the above-mentioned sublimation raw material
is preferably higher from the standpoint of preventing
contamination of polycrystals and polymorphs into a silicon carbide
single crystal produced as much as possible, and specifically, it
is preferable that the content of each impurity element is 0.5 ppm
or less.
[0172] Here, the content of the above-mentioned impurity elements
is impurity content by chemical analysis, and only means a
reference values, and practically, evaluation differs depending on
whether the above-mentioned impurity elements are uniformly
distributed in the above-mentioned silicon carbide single crystal
or not, or whether they are localized or not. Here, "impurity
element" means elements belonging to Groups I to XVII in the
Periodic Table according to 1989, IUPAC Inorganic Chemical
Nomenclature Revision and at the same time having an atomic number
of 3 or more (excluding carbon atom, oxygen atom and silicon atom).
When dopant elements such as nitrogen, aluminum and the like are
added by intention for imparting n-type or p-type conductivity to a
silicon carbide single crystal to be grown, these elements are also
excluded.
[0173] A silicon carbide powder as the above-mentioned sublimation
raw material is obtained, for example, by dissolving at least one
silicon compound as a silicon source, at least one organic compound
generating carbon by heating as a carbon source, and a
polymerization catalyst or cross-linking catalyst in a solvent and
drying the resulted solution to give a powder, and calcinating the
resulted powder under a non-oxidaing atmosphere.
[0174] As the above-mentioned silicon compound, liquid compounds
and solid compounds can be used together, however, at least one
compound is selected from liquid compounds.
[0175] As the above-mentioned liquid compound, alkoxysilanes and
alkoxysilane polymers are suitably used.
[0176] As the above-mentioned alkoxysilane, for example,
methoxysilane, ethoxysilane, propoxysilane, butoxysilane and the
like are listed, and among them, ethoxysilane is preferable from
the standpoint of handling.
[0177] The above-mentioned alkoxysilane may be any of
monoalkoxysilanes, dialkoxysilane, trialkoxysilane and
tetraalkoxysilane, and tetraalkoxysilanes are preferable.
[0178] As the above-mentioned alkoxysilane polymer, lower molecular
weight polymers (oligomers) having a degree of polymerization of
from about 2 to 15 and silicic acid polymers are listed. For
example, a tetraethoxysilane oligomer is mentioned.
[0179] As the above-mentioned solid compound, silicon oxides such
as SiO, silica sol (colloidal ultrafine silica-containing liquid,
having an OH group and alkoxyl group inside), silicon dioxides
(silica gel, fine silica, quartz powder) and the like are
listed.
[0180] The above-mentioned silicon compounds may be used alone or
in combination of two or more.
[0181] Among the above-mentioned silicon compounds, a
tetraethoxysilane oligomer, a mixture of a tetraethoxysilane
oligomer and fine powdery silica, and the like are preferable from
the standpoint of excellent uniformity and handling property.
[0182] The above-mentioned silicon compound preferably has high
purity, and the content of each impurity at the initial period is
preferably 20 ppm or less, more preferably 5 ppm or less.
[0183] As the above-mentioned organic compound generating carbon by
heating, a liquid organic compound may be used alone and a liquid
organic compound and a solid organic compound may be used
together.
[0184] As the above-mentioned organic compound generating carbon by
heating, organic compounds manifesting high carbon-remaining ratio
and being polymerized or crosslinked by a catalyst or heat are
preferable, and for example, monomers and prepolymers of phenol
resins, furan resins, resins such as polyimides, polyurethanes,
polyvinyl alcohol and the like, are preferable, and additionally,
liquid substances such as cellulose, sucrose, pitch, tar and the
like are mentioned. Among them, those of high purity are
preferable, phenol resins are more preferable, and resol type
phenol resins are particularly preferable.
[0185] The above-mentioned organic compound generating carbon by
heating may be used alone dr in combination of two or more.
[0186] The purity of the above-mentioned organic compound
generating carbon by heating can be appropriately selected
depending on the object, and when a high purity silicon carbide
powder is necessary, it is preferable to use organic compounds in
which the content of each metal is not 5 ppm or more.
[0187] The above-mentioned polymerization catalyst and crosslinking
catalyst can be appropriately selected depending on the
above-mentioned organic compound generating carbon by heating, and
when the above-mentioned organic compound generating carbon by
heating is a phenol resin or furan resin, acids such as
toluenesulfonic acid, toluenecarboxylic acid, acetic acid, oxalic
acid, maleic acid, sulfuric acid and the like are preferable, and
maleic acid is particularly preferable.
[0188] The ratio of carbon contained in the above-mentioned organic
compound generating carbon by heating to silicon contained in the
above-mentioned silicon compound (hereinafter, abbreviated as C/Si
ratio) is defined by element-analyzing a carbide intermediate
obtained by carbonizing a mixture of them at 1000.degree. C.
Stoichiometrically, the content of free carbon in a silicon carbide
powder obtained when the above-mentioned C/Si ratio is 3.0 should
be 0%, however, free carbon generates at lower C/Si ratio by
vaporization of a simultaneously produced SiO gas, actually. It is
preferable to previously determine the compounding ratio so that
the amount of free carbon in the resulted silicon carbide powder is
suitable amount. Usually, by calcinations at 1600.degree. C. or
higher at around 1 atm, free carbon can be controlled when the
above-mentioned C/Si ratio is 2.0 to 2.5. When the above-mentioned
C/Si ratio is over 2.5, the above-mentioned free carbon increases
remarkably. However, when calcinations is conducted at lower
atmosphere pressure or higher atmosphere pressure, the C/Si ratio
for obtaining a pure silicon carbide powder varies, therefore, the
ratio is not necessarily limited in the above-mentioned C/Si range,
in this case.
[0189] The above-mentioned silicon carbide powder is obtained also
by hardening a mixture of the above-mentioned silicon compound and
the above-mentioned organic compound generating carbon by heating,
for example.
[0190] As the above-mentioned hardening method, a method of
hardening by heating, a method of hardening by a hardening
catalyst, methods using electronic beam and radiation, and the like
are listed.
[0191] The above-mentioned hardening catalyst can be appropriately
selected depending on the kind of the above-mentioned organic
compound generating carbon by heating, and the like, and in the
case of a phenol resin or furan resin, acids such as
toluenesulfonic acid, toluenecarboxylic acid, acetic acid, oxalic
acid, hydrochloric acid, sulfuric acid, maleic acid and the like,
amic acids such as hexamine, and the like are suitably listed. When
these hardening catalysts are used, the hardening catalyst is
dissolved or dispersed in a solvent. As the above-mentioned
catalyst, lower alcohols (for example, ethyl alcohol and the like),
ethyl ether, acetone and the like are listed.
[0192] A silicon carbide powder obtained as described above is
calcinated in a non-oxidizing atmosphere such as nitrogen, argon
and the like at 800 to 1000.degree. C. for 30 to 120 minutes.
[0193] By the above-mentioned calcinations, the above-mentioned
silicon carbide powder becomes a carbide, and by calcinating this
carbide in a non-oxidizing atmosphere such as argon and the like at
1350 to 2000.degree. C., a silicon carbide powder is produced.
[0194] The temperature and time of the above-mentioned calcinations
can be appropriately selected depending on the granular size of a
silicon carbide powder to be obtained, and the above-mentioned
temperature is preferably from 1600 to 1900.degree. C. from the
standpoint of more effective production of a silicon carbide
powder.
[0195] For the purpose of removing impurities and obtaining a high
purity silicon carbide powder, after the above-mentioned
calcinations, it is preferable to conduct heat treatment at 2000 to
2400.degree. C. for 3 to 8 hours.
[0196] Since the silicon carbide powder obtained as described above
has non-uniform size, given particle size can be obtained by powder
destruction, classification and the like.
[0197] The average particle size of the above-mentioned silicon
carbide powder is preferably from 10 to 700 .mu.m, more preferably
from 100 to 400 .mu.m.
[0198] When the above-mentioned average particle size is less than
10 .mu.m, sintering occurs quickly at the sublimation temperature
(1800 to 2700.degree. C.) of silicon carbide for growing a silicon
carbide single crystal, therefore, sublimation surface area
decreases and growth of a silicon carbide single crystal delays, in
some cases, and when a silicon carbide powder is accommodated in
the above-mentioned reaction vessel and when the pressure of a
re-crystallization atmosphere is changed for control of the growth
speed, a silicon carbide powder is splashed easily. On the other
hand, when the above-mentioned average particle size is over 500
.mu.m, the specific surface area of a silicon carbide powder itself
decreases, therefore, growth of a silicon carbide single crystal
may delay also in this case.
[0199] As the above-mentioned silicon carbide powder, any of 4H,
6H, 15R, 3C and mixtures of them may be used. The grade of the
above-mentioned 3C silicon carbide powder is not particularly
restricted, and those generally marketed may be permissible,
however, those of high purity are preferable.
[0200] Further, nitrogen or aluminum and the like can be introduced
into a silicon carbide single crystal grown using the
above-mentioned silicon carbide powder for the purpose of giving n
type or p type conductivity, and when nitrogen or aluminum is
introduced in generating the above-mentioned silicon carbide
powder, it is recommendable that, first, the above-mentioned
silicon source, the above-mentioned carbon source, an organic
substance composed of a nitrogen source or aluminum source, the
above-mentioned polymerization catalyst or crosslinking catalyst
are uniformly mixed. In this case, it is preferable that, for
example, when a carbon source such as phenol resins and the like,
an organic substance composed of a nitrogen source such as
hexamethylenetetramine and the like and a polymerization or
crosslinking catalyst such as maleic acid and the like are
dissolved in a solvent such as ethanol and the like, they are mixed
sufficiently with a silicon source such as a tetraethoxysilane
oligomer and the like.
[0201] As the above-mentioned organic substance composed of a
nitrogen source, substances generating nitrogen by heating are
preferable, and listed are, for example, polymer compounds
(specifically, polyimide resins, nylon resins and the like),
various amines such as organic amines (specifically,
hexamethylenetetramine, ammonia, triethylamine, and the like, and
compounds and salts of them). Of them, hexamethylenetetramine is
preferable. A phenol resin synthesized using hexamine as a catalyst
and containing nitrogen derived from this synthesis process in an
amount of 2.0 mmol or more based on 1 g of the resin can also be
suitably used as the organic substance composed of a nitrogen
source. These organic substances composed of a nitrogen source may
be used alone or in combination of two or more. The above-mentioned
organic substance composed of an aluminum source is not
particularly restricted and can be appropriately selected depending
on the object.
[0202] Regarding the addition amount of the above-mentioned organic
substance composed of a nitrogen source, when the above-mentioned
silicon source and the above-mentioned carbon source are added
simultaneously, nitrogen is contained in an amount of preferably 1
mmol or more based on 1 g of the above-mentioned silicon source,
and the organic substance is added in an amount of 80 to 1000 .mu.g
based on 1 g of the above-mentioned silicon source.
[0203] --Sublimation--
[0204] It is preferable to conduct sublimation of the
above-mentioned sublimation raw material by using a separate
heating means from a heating means for effecting heating necessary
for re-crystallization, from the standpoints of precise control and
independent control of the heating means and prevention of
interference and the like. In this embodiment, the number of
heating means is two or more, and two heating means are preferably
used in the present invention.
[0205] In the preferable embodiment in which two of the
above-mentioned heating means are used, a heating means for forming
a sublimation atmosphere enabling sublimation of the
above-mentioned sublimation raw material is a first heating means
and a heating means for forming the above-mentioned
re-crystallization atmosphere enabling re-crystallization of the
above-mentioned sublimation raw material being sublimate only
around the above-mentioned seed crystal of a silicon carbide single
crystal is a second heating means.
[0206] The above-mentioned first heating means is placed at the one
end (sublimation raw material accommodating part) side of the
above-mentioned reaction vessel, forms a sublimation atmosphere so
as to enable sublimation of the above-mentioned sublimation raw
material, and heats the above-mentioned sublimation raw material to
cause sublimation.
[0207] The above-mentioned first heating means is not particularly
restricted and can be appropriately selected depending on the
object, and for example, induction heating means, resistance
heating means and the like are listed, and the induction heating
means are preferable since temperature control is easy, and among
the induction heating means, induction-heatable coils are
preferable.
[0208] When the above-mentioned first heating means is an
induction-heatable coil, the number of winding is not particularly
restricted and can be determined so that heating efficiency and
temperature efficiency are optimum depending on the distance from
the above-mentioned second heating means, the material of the
above-mentioned reaction vessel, and the like.
[0209] --Growth of Silicon Carbide Single Crystal--
[0210] Growth of the above-mentioned silicon carbide single crystal
is conducted on a seed crystal of a silicon carbide single crystal
placed on the above-mentioned another end (seed crystal placing
part) of the above-mentioned reaction vessel.
[0211] Regarding the above-mentioned seed crystal of a silicon
carbide single crystal, the polymorphs, size and the like of the
crystal can be appropriately selected depending on the object, and
as the polymorphs of the crystal, the same polymorph as that of a
silicon carbide single crystal to be obtained is selected,
usually.
[0212] For re-crystallizing and growing the above-mentioned silicon
carbide single crystal on the above-mentioned seed crystal, it is
preferable to form a re-crystallization atmosphere having
temperature lower than the temperature for sublimation of the
above-mentioned sublimation raw material and enabling
re-crystallization of the above-mentioned sublimation raw material
being sublimate only around the above-mentioned seed crystal (in
other words, temperature distribution and atmosphere so that
temperature becomes lower when approximating the center part
(center of the inside region), along the diameter direction of a
surface on which the above-mentioned seed crystal is placed).
[0213] Formation of the above-mentioned re-crystallization
atmosphere can be more suitably conducted by the above-mentioned
second heating means. Such a second heating means is placed at
another end (seed crystal placing part) side of the above-mentioned
reaction vessel and forms a re-crystallization atmosphere so as to
enable re-crystallization of the above-mentioned sublimation raw
material being sublimate by the above-mentioned first heating means
only around the seed crystal of a silicon carbide single crystal,
and causes re-crystallization of the sublimation raw material on
the above-mentioned seed crystal of a silicon carbide single
crystal.
[0214] The above-mentioned second heating means is not particularly
restricted and can be appropriately selected depending on the
object. For example, induction heating means, resistance heating
means and the like are listed, and the induction heating means are
preferable since temperature control is easy, and among the
induction heating means, induction-heatable coils are
preferable.
[0215] When the above-mentioned second heating means is an
induction-heatable coil, the number of winding is not particularly
restricted and can be determined so that heating efficiency and
temperature efficiency are optimum depending on the distance from
the above-mentioned first heating means, the material of the
above-mentioned reaction vessel, and the like.
[0216] The quantity of induction heating current flowing through
the above-mentioned second heating means can be appropriately
determined depending on relation with the quantity of induction
heating current flowing through the above-mentioned first heating
means, and regarding the relation of them, it is preferable that
the current value of induction heating current in the
above-mentioned first heating means is larger than the current
value of induction heating current in the above-mentioned second
heating means. This case is advantage in that the temperature of a
re-crystallization atmosphere around on the above-mentioned seed
crystal is maintained lower than the temperature of an atmosphere
in which the above-mentioned sublimation raw material sublimates,
and re-crystallization is conducted easily.
[0217] It is preferable to control the current value of induction
heating current in the above-mentioned second heating means so that
it decreases continuously or gradually when the diameter of a
silicon carbide single crystal to be grown increases. In this case,
the heating quantity by the above-mentioned second heating means is
controlled small when the above-mentioned silicon carbide single
crystal grows, consequently, re-crystallization is conducted only
around the above-mentioned silicon carbide single crystal keeping
growing, and formation of polycrystals around the silicon carbide
single crystal is effectively suppressed, advantageously.
[0218] A preferable tendency is obtained when the current value of
induction heating current in the above-mentioned second heating
means is controlled small when the diameter of the above-mentioned
seed crystal of a silicon carbide single crystal is large and
controlled large when the above-mentioned diameter is small.
[0219] In the present invention, the above-mentioned second heating
means can be controlled independently from the above-mentioned
first heating means, therefore, preferable growth speed can be
maintained through the all growth processes of a silicon carbide
single crystal by appropriately controlling the heating quantity of
the second heating means depending on the growth speed of a silicon
carbide single crystal.
[0220] The temperature of a re-crystallization atmosphere formed by
the above-mentioned second heating means is lower than the
temperature of the above-mentioned sublimation atmosphere formed by
the above-mentioned first heating means by preferably 30 to
300.degree. C., more preferably 30 to 150.degree. C.
[0221] The pressure of a re-crystallization atmosphere formed by
the above-mentioned second heating means is preferably from 10 to
100 Torr (1330 to 13300 Pa). When this pressure condition is
applied, it is preferable that pressure reduction is not effected
at ambient temperature, and after heating to given temperature,
pressure reduction is effected to control pressure condition so as
to fall within the above-mentioned given numerical value range.
[0222] It is preferable that the above-mentioned re-crystallization
atmosphere is an inert gas atmosphere composed of an argon gas and
the like.
[0223] In the present invention, it is preferable from the
standpoint of obtaining a silicon carbide single crystal having
large diameter that temperature at one end (sublimation raw
material accommodating part) side accommodating a sublimation raw
material, in the above-mentioned reaction vessel, controlled by the
above-mentioned first heating means, temperature of the center part
at another end (seed crystal placing part) side carrying the
above-mentioned seed of a silicon carbide single crystal placed, in
the above-mentioned reaction vessel, controlled by the
above-mentioned second heating means, and temperature of parts
situated at the outside of the center part and adjacent to the
inner peripheral surface part of the reaction vessel are controlled
in a relation described below. Namely, it is preferable to conduct
control so that, if the temperature at one end side accommodating a
sublimation raw material is represented by T.sub.1, the temperature
at another end side at which a seed crystal of a silicon carbide
single crystal is placed is represented by T.sub.2, and the
temperature of parts adjacent to the inner peripheral surface part
of the reaction vessel, at another end side, is represented by
T.sub.3, then, T.sub.3-T.sub.2 and T.sub.1-T.sub.2 increase
continuously or gradually.
[0224] In this case, since T.sub.1-T.sub.2 increases continuously
or gradually, even if a silicon carbide single crystal keeps on
growing toward the above-mentioned one end side with the lapse of
time, the peak side of crystal growth of the silicon carbide single
crystal is usually maintained at condition liable to cause
re-crystallization. On the other hand, since T.sub.3-T.sub.2
increases continuously or gradually, even if a silicon carbide
single crystal keeps on growing toward the outer peripheral
direction at above-mentioned another end side with the lapse of
time, the outer peripheral end side of crystal growth of the
silicon carbide single crystal is usually maintained at condition
liable to cause re-crystallization. As a result, production of a
silicon carbide single crystal is effectively suppressed, and the
silicon carbide single crystal keeps on growing toward the
direction of increasing its thickness while enlarging its diameter,
finally, a silicon carbide single crystal having large diameter is
obtained without contamination of a silicon carbide polycrystal and
the like, advantageously.
[0225] In the present invention, the above-mentioned silicon
carbide single crystal re-crystallizes and grows according to the
above-mentioned first to third embodiments.
[0226] In the above-mentioned first embodiment, the above-mentioned
silicon carbide single crystal is allowed to grow while keeping the
whole surface of its growth surface in convex shape through the all
growth processes. In this case, a concave portion sunk toward the
above-mentioned another end (seed crystal placing part) side is not
shaped in the form of ring, at the whole surface of the growth
surface of the silicon carbide single crystal.
[0227] In the above-mentioned second embodiment, growth of the
above-mentioned silicon carbide single crystal is conducted only in
the region excepting parts adjacent to the peripheral surface part
in the reaction vessel (inside region), at the above-mentioned end
of the above-mentioned reaction vessel. In this case, a silicon
carbide polycrystal does not grow contacting with the peripheral
surface part in the reaction vessel, at the above-mentioned another
end (seed crystal placing part). Therefore, when a silicon carbide
single crystal grown is cooled to room temperature, stress based on
a difference in thermal expansion does not concentrate from the
silicon carbide polycrystal side to the silicon carbide single
crystal side, and breakages such as cracking and the like do not
occur on the resulted silicon carbide single crystal.
[0228] In the above-mentioned third embodiment, the above-mentioned
silicon carbide single crystal is grown only at the region
excepting parts adjacent to the peripheral surface part of in the
reaction vessel (inside region), at the above-mentioned end of the
above-mentioned reaction vessel, while keeping the whole surface of
its growth surface in convex shape through the all growth
processes.
[0229] In this case, a concave portion sunk toward to the
above-mentioned another end (seed crystal placing part) side of the
above-mentioned reaction vessel is not shaped in the form of ring
at the whole surface of its growth surface of the above-mentioned
silicon carbide single crystal, and a silicon carbide single
crystal does not grow contacting with the peripheral surface part
in the reaction vessel, at the above-mentioned another end (seed
crystal placing part). Therefore, when a silicon carbide single
crystal grown is cooled to room temperature, stress based on a
difference in thermal expansion does not concentrate from the
silicon carbide polycrystal side to the silicon carbide single
crystal side, and breakages such as cracking and the like do not
occur on the resulted silicon carbide single crystal.
[0230] Regarding the form of the above-mentioned silicon carbide
single crystal to be grown, it is preferable that the whole surface
of its growth surface is in convex form toward its growth direction
side, and when the above-mentioned one end (sublimation raw
material accommodating part) faces the above-mentioned another end
(seed crystal placing part), it is preferable that the whole
surface of its growth surface is in convex form toward the
above-mentioned sublimation raw material side, namely, toward the
above-mentioned one end (sublimation raw material accommodating
part) side.
[0231] This case is preferable in that a concave portion sunk
toward the above-mentioned another end (seed crystal placing part)
side is not present, on which contamination of polycrystals and
polymorphs is significant and concentration of stress based on a
difference in thermal expansion is believed to be easy.
[0232] Regarding the form of the above-mentioned silicon carbide
single crystal to be grown, it may not in the above-mentioned
convex form or a flat portion may be partially contained, providing
the whole surface of its growth surface does not contain a part
sunk toward the reverse side to its growth direction side.
[0233] The form of a silicon carbide crystal containing a silicon
carbide single crystal is preferably in angle form toward the
above-mentioned sublimation raw material side, namely, toward the
above-mentioned one end side, and an approximate protruded shape
having diameter decreasing gradually is more preferable. In other
words, it is preferable that a silicon carbide crystal containing a
silicon carbide single crystal is allowed to grow while keeping
approximate protruded shape having diameter decreasing gradually
when approximating the sublimation raw material side, through the
all growth processes.
[0234] In skirt parts of a silicon carbide crystal in the form of
the above-mentioned approximate protruded shape, namely, at outer
peripheral parts, silicon carbide polycrystals and polymosphism may
be mixed, however, generation of this mixing can be prevented by
combination of the thickness, size, form and the like of the
above-mentioned seed crystal with the heating quantity by the
above-mentioned second heating means. Prevention of the
contamination of silicon carbide polycrystals and polymorphs is
preferable since then the above-mentioned silicon carbide crystal
containing silicon carbide can be made only of a silicon carbide
single crystal.
[0235] In the present invention, a plate member in the form of ring
may also be fixed and placed on the peripheral surface part in the
above-mentioned reaction vessel, approximately in parallel to the
above-mentioned another end (seed crystal placing part). In this
case, when the above-mentioned silicon carbide single crystal is
re-crystallized and grown on the above-mentioned seed crystal, only
the above-mentioned silicon carbide single crystal can be
re-crystallized and grown on the above-mentioned seed crystal, and
a silicon carbide polycrystal is not allowed to grow or can be
deposited selectively on the above-mentioned plate member in the
form of ring. In this case, the diameter of the resulting silicon
carbide single crystal is constrained corresponding to the size of
the above-mentioned plate member in the form of ring.
[0236] In the present invention, it is preferable, for the purpose
of effecting efficient growth of the above-mentioned silicon
carbide single crystal, to use an interference preventing means for
preventing interference between the above-mentioned first heating
means and the above-mentioned second heating means.
[0237] The above-mentioned interference preventing means is not
particularly restricted and can be appropriately selected depending
on the kind of the above-mentioned first heating means and the
above-mentioned second heating means, and the like, and for
example, interference preventing coils, interference preventing
plates and the like are listed, and when the above-mentioned first
heating means and the above-mentioned second heating means are the
above-mentioned induction-heatable coil, interference preventing
coils and the like are suitably listed.
[0238] The above-mentioned interference preventing coil (simply
called as "coil" in some cases) is preferably a coil through which
induction current flows and having a function of preventing
interference between the above-mentioned first heating means and
the above-mentioned second heating means by flowing induction
current.
[0239] The above-mentioned interference preventing coil is
preferably placed between the above-mentioned first heating means
and the above-mentioned second heating means. This case is
preferable in that, when induction heating is conducted by the
above-mentioned first heating means and the above-mentioned second
heating means simultaneously, induction current flow through the
interference preventing coil, and the interference preventing coil
can minimize and prevent interference between them.
[0240] The above-mentioned interference preventing coil is
preferably designed so that it is not heated by induction current
flowing through itself, a self-coolable coil is more preferable,
and a coil through which a cooling medium such as water and the
like can flow is particularly preferable. This case is preferable
in that, even if induction current in the above-mentioned first
heating means and the above-mentioned second heating means flows
through the interference preventing coil, the interference
preventing coil is not heated, therefore, the above-mentioned
reaction vessel is also not heated.
[0241] The number of winding of the above-mentioned wound
interference preventing coil is not particularly restricted and
differs depending on the kind of the above-mentioned first heating
means and the above-mentioned second heating means and the amount
of current flowing through them, and the like and can not be
limited to a constant range, namely, even a single coil is
sufficient.
[0242] As described above, according to the method of producing a
silicon carbide single crystal of the present invention, the
silicon carbide single crystal of the present invention having high
quality can be easily produced efficiently and in condition showing
no breakages such as cracking and the like.
[0243] (Silicon Carbide Single Crystal)
[0244] The silicon carbide single crystal of the present invention
is produced by the method of producing a silicon carbide single
crystal of the present invention described above.
[0245] In the silicon carbide single crystal of the present
invention, the crystal defects (pipe defect) of which image is
optically detected non-destructively is preferably 100/cm.sup.2 or
less, more preferably 50/cm.sup.2 or less, particularly preferably
10/cm.sup.2 or less.
[0246] The above-mentioned crystal defect can be detected, for
example, by the following manner. Namely, illumination prepared by
adding suitable amount of transmission illumination to reflection
illumination is allowed to irradiate the silicon carbide single
crystal, and the focus of a microscope is adjusted to an opening of
crystal defect (pipe defect) on the surface of the silicon carbide
single crystal, then, portions continuing to the inside of the pipe
defect can be observed as shadow weaker than an image of the
opening, connected to the opening. Under such conditions, the whole
surface of the silicon carbide single crystal is scanned to obtain
a microscope image, then, this microscope image is image-treated,
and only forms characteristic to the pipe defect are extracted and
the number of them are counted. Thus, the pipe defect can be
detected.
[0247] According to the above-mentioned detection, only the
above-mentioned pipe defect can be correctly detected, from a
mixture of defects other than the above-mentioned pipe defect, such
as extraneous substances adhered to the surface of the
above-mentioned silicon carbide single crystal, polishing flaw,
void defect and the like, further, even fine pipe defects of about
0.35 .mu.m can be detected correctly. On the other hand, there is
conventionally conducted a method in which the above-mentioned pipe
defect parts are selectively etched, and detected in magnification,
however, this method has a problem that, adjacent pipe defects
described above join mutually, and resultantly, smaller number of
defects than the real number of the pipe defects is detected.
[0248] The total content of the above-mentioned impurity elements
in the above-mentioned silicon carbide single crystal is preferably
10 ppm or less.
[0249] The silicon carbide single crystal of the present invention
contains no crystal defects such as contamination of polycrystals
and polymorphs and micropipes and the like and has extremely high
quality: therefore, it is excellent in dielectric breakdown
property, heat resistance, radiation resistance and the like and
particularly suitable for electronic devices such as semiconductor
wafers and the like and optical devices such as light emitting
diodes and the like.
[0250] (Silicon Carbide Single Crystal Production Apparatus)
[0251] With the apparatus for generating a silicon carbide single
crystal of the present invention, the above-mentioned sublimation
raw material being sublimate is re-crystallized to grow a silicon
carbide single crystal, generating the silicon carbide single
crystal of the present invention.
[0252] The above-mentioned apparatus for generating a silicon
carbide single crystal comprises at least a crucible, a first
induction heating coil and a second induction heating coil, and if
necessary, other members appropriately selected, and the like.
[0253] The above-mentioned crucible is not particularly restricted
and can be appropriately selected from known products, and in
general, comprises a vessel body and a cover body.
[0254] The material of the above-mentioned crucible is not
particularly restricted and can be appropriately selected from
known materials, and graphite is particularly preferable.
[0255] The above-mentioned vessel body is not particularly
restricted providing it has a function capable of accommodating the
above-mentioned sublimation raw material, and known products can be
adopted.
[0256] The above-mentioned cover body is preferably attachable to
and detachable from the above-mentioned vessel body, and known
products can be adopted. The above-mentioned vessel body and the
above-mentioned cover body may be designed so that attachable and
detachable by any of engagement, spiral fitting and the like, and
spiral fitting is preferable.
[0257] In the above-mentioned apparatus for generating a silicon
carbide single crystal, usually, when the above-mentioned cover
body is installed to the above-mentioned vessel body, a seed
crystal of the above-mentioned silicon carbide single crystal is
placed at approximately the center of a surface facing the
above-mentioned sublimation raw material accommodated in the vessel
body.
[0258] The above-mentioned first induction heating coil is not
particularly restricted providing it generates heat by flow of
current and can form a sublimation atmosphere so as to enable
sublimation of the above-mentioned sublimation raw material, and
induction heatable coils and the like are suitably listed.
[0259] The above-mentioned first induction heating coil is placed
in condition wound around the outer periphery of a part
accommodating the above-mentioned sublimation raw material, in the
above-mentioned crucible.
[0260] The above-mentioned second induction heating coil is not
particularly restricted providing it can form a re-crystallization
atmosphere so that the above-mentioned sublimation raw material
being sublimate by the above-mentioned first induction heating coil
can re-crystallize only around the above-mentioned seed crystal of
silicon carbide, to re-crystallize the sublimation raw material on
the above-mentioned seed crystal of silicon carbide, and
induction-heatable coils and the like are listed.
[0261] The above-mentioned second induction heating coil is placed
in condition wound around the outer periphery of a part on which
the above-mentioned seed crystal of silicon carbide is placed, in
the above-mentioned crucible.
[0262] In the above-mentioned silicon carbide single crystal
production apparatus, the above-mentioned first induction heating
coil forms a sublimation atmosphere so as to enable sublimation of
the above-mentioned sublimation raw material, to sublimate the
above-mentioned sublimation raw material. The above-mentioned
second induction heating coil forms a re-crystallization atmosphere
so that the above-mentioned sublimation raw material being
sublimate by the above-mentioned first induction heating coil can
be re-crystallized only around the above-mentioned seed crystal, to
re-crystallize the sublimation raw material on the above-mentioned
seed crystal. Therefore, the whole surface of its growth surface of
a silicon carbide single crystal to be grown is maintained in
convex form toward its growth direction in the all growth
processes, a concave portion sunk toward the above-mentioned cover
body is not shaped in the form of ring, and silicon carbide
polycrystal does not grow contacting the peripheral surface part in
the above-mentioned vessel body. Therefore, when a silicon carbide
single crystal grown is cooled to room temperature, stress based on
a difference in thermal expansion does not concentrate from the
silicon carbide polycrystal side to the silicon carbide single
crystal side, and breakages such as cracking and the like do not
occur on the resulted silicon carbide single crystal. As a result,
a high quality silicon carbide single crystal can be efficiently
and securely produced having no conventional various problems
described above, namely, having no breakages such as cracking and
the like and crystal defects such as contamination of polycrystals
and polymorphs and micropipes and the like present.
[0263] As described above, according to the silicon carbide single
crystal production apparatus for the present invention, the silicon
carbide single crystal of the present invention having high quality
can be produced efficiently and easily without breakages such as
cracking and the like.
EXAMPLES
[0264] The following examples will described the present invention,
but do not limit the scope of the invention at all.
Example 1
[0265] Using a silicon carbide single crystal production apparatus
1 shown in FIG. 1, a silicon carbide single crystal was produced.
Use of the silicon carbide single crystal production apparatus 1
leads to execution of the silicon carbide single crystal production
method of the present invention.
[0266] The silicon carbide single crystal production apparatus 1
comprises a graphite crucible 10 having a vessel body 12 capable of
accommodating a sublimation raw material 40 and a cover body 11
which can be attached to and detached from the vessel body 12 by
spiral fitting, and in which, when installed on the vessel body 12,
a seed crystal 50 of a silicon carbide single crystal can be placed
approximately at the center of a surface facing the sublimation raw
material 40 accommodated in the vessel body 12; a supporting rod 31
fixing the graphite crucible 10 to inside of a quartz tube 30; a
first induction heating coil 21 placed at a part which is on the
outer periphery of the quartz tube and in which the sublimation raw
material 40 is accommodated, in the graphite crucible 10; and a
second induction heating coil 20 placed at a part which is on the
outer periphery of the quartz tube 30 and on which the cover body
11 is situated, in the graphite crucible 10. The graphite crucible
10 is covered with an insulation material (not shown).
[0267] The sublimation raw material 40 is a silicon carbide powder
(6H (partially containing 3C), average particle size: 200 .mu.m)
obtained by using a high purity tetraethoxysilane polymer described
above as a silicon source, a resol type phenol resin as a carbon
source, and mixing them uniformly to obtain a mixture, calcinating
the mixture by heating under an argon atmosphere, and the seed
crystal 50 of a silicon carbide single crystal is a Rayleigh
crystal of 6H.
[0268] In the silicon carbide single crystal production apparatus
1, electric current was allowed to flow through the first induction
heating coil 21. By this heat, the sublimation raw material 40 was
heated (after heating to 2500.degree. C., pressure was maintained
at 50 Torr (6645 Pa) by an argon gas atmosphere). The sublimation
raw material 40 was heated up to given temperature (2500.degree.
C.) to show sublimation: The sublimation raw material 40 sublimated
does not re-crystallize unless cooled to the re-crystallization
temperature. Here, the cover body 11 side was heated by the second
induction heating coil 20 and had temperature lower than the
sublimation raw material 40 side (temperature of seed crystal is
2400.degree. C.), and maintained in a re-crystallization atmosphere
(pressure is 50 Torr (6645 Pa)) in which the sublimation raw
material 40 sublimated can re-crystallize, therefore, silicon
carbide re-crystallized only around on the seed crystal 50 of a
silicon carbide single crystal, and a crystal of silicon carbide
grew.
[0269] Here, a silicon carbide single crystal 60 re-crystallizes
and grows on the seed crystal 50 of a silicon carbide single
crystal, and a silicon carbide polycrystal 70 re-crystallizes and
grows on the outer periphery on the seed crystal 50 of a silicon
carbide single crystal, as shown in FIG. 2. In growth of the
silicon carbide single crystal 60, a convex form was maintained
toward the sublimation raw material 40 side in the all growth
processes, and a concave portion sunk toward the cover body 11 side
was no shaped in the form of ring, and the silicon carbide single
crystal 70 did not grow contacting the peripheral surface part 13
in the vessel body 12.
[0270] As a result, when the silicon carbide single crystal 60
grown was cooled to room temperature, stress based on a difference
in thermal expansion was no applied in concentration from the
silicon carbide polycrystal 70 side to the silicon carbide single
crystal 60 side, and breakages such as cracking and the like did
not occur on the resulted silicon carbide single crystal 60, as
shown in FIG. 3.
[0271] When the resulted silicon carbide single crystal 60 was
evaluated, contamination of polycrystals and polymorphs crystals
was not found, and crystal defect of micropipes was as scarce as
4/cm.sup.2, meaning extremely high quality.
[0272] The above-mentioned crystal defect of micropipes was
detected as described below, after cutting the resulted silicon
carbide single crystal 60 into a thickness of 0.4 mm, mirror
polishing to give a wafer having a surface roughness of 0.4 nm, and
removing extraneous substances on the surface as much as possible
by alkali washing. Namely, illumination prepared by adding suitable
amount of transmission illumination to reflection illumination was
allowed to irradiate the above-mentioned wafer after alkali
washing, the focus of a microscope was adjusted to an opening of
micropipes on the wafer surface, then, portions continuing to the
inside of the micropipe could be observed as shadow weaker than an
image of the opening, connected to the opening. Under such
conditions, the whole surface of the above-mentioned wafer was
scanned to obtain a microscope image, then, this microscope image
was image-treated, and only forms characteristic to the micropipe
are extracted and the number of them were counted. Thus, the
micropipes were detected. In this detection, even fine micropipes
of about 0.35 .mu.m were detected correctly without breakage.
Example 2
[0273] The same procedure as in Example 1 was conducted except that
the graphite crucible 10 was changed to a graphite crucible 10
shown in FIG. 4 in Example 1. As a result, the same result as in
Example 1 was obtained. The graphite crucible 10 shown in FIG. 4
differs from the graphite crucible 10 shown in FIG. 1 used in
Example 1 only in that an inside region forming part 15 is provided
in the cover body 11. The inside region forming part 15 is, as
shown in FIG. 4, a cylinder having the above-mentioned inside
region on which a seed crystal of a silicon carbide single crystal
is placed as the bottom surface, and one end of which is exposed to
outside of the graphite crucible 10. The material of inside region
forming part 15 had a heat conductivity of 117 J/m/s/.degree. C.
(W/m.multidot.K), and the material of the cover body 11 other than
inside region forming part 15 had a heat conductivity of 129
J/m/s/.degree. C. (W/m.multidot.K).
[0274] In the case of Example 2, since the above-mentioned inside
region is formed of a different member (inside region forming part
15) from that in the above-mentioned outside region, heating is
difficult by a difference in contact resistance, and one end of the
inside region forming part 15 is exposed to outside, heat is
discharged to outside easily, therefore, re-crystallization of
silicon carbide was conducted easily.
Example 3
[0275] The same procedure as in Example 1 was conducted except that
the graphite crucible 10 was changed to a graphite crucible 10
shown in FIG. 5 in Example 1. As a result, the same result as in
Example 1 was obtained. The graphite crucible 10 shown in FIG. 5
differs from the graphite crucible 10 shown in FIG. 1 used in
Example 1 only in that an inside region forming part 15 is provided
in the cover body 11. The inside region forming part 15 has, as
shown in FIG. 5, a form having the above-mentioned inside region on
which a seed crystal of a silicon carbide single crystal is placed
as the bottom surface, of which diameter increases discontinuously
in two stages toward the above-mentioned outside, and one end of
which is exposed to outside. The material of inside region forming
part 15 had a heat conductivity of 117 J/m/s/.degree. C.
(W/m.multidot.K), and the material of the cover body 11 other than
inside region forming part 15 had a heat conductivity of 129
J/m/s/.degree. C. (W/m.multidot.K).
[0276] In the case of Example 3 since the above-mentioned inside
region is formed of a different member from that in the
above-mentioned outside region, heating is difficult by a
difference in contact resistance, and one end of the inside region
forming part 15 is exposed to outside, heat is discharged to
outside easily, therefore, re-crystallization of silicon carbide
was conducted easily.
Example 4
[0277] The same procedure as in Example 1 was conducted except the
following point in Example 1. Namely, the resulted silicon carbide
powder had 6H and an average particle size of 300 .mu.m, and the
seed crystal 50 of a silicon carbide single crystal is a 15R wafer
(diameter: 40 mm, thickness 0.5 mm) obtained by cutting the bulk
silicon carbide single crystal obtained in Example 1 and
mirror-polishing the whole surface.
[0278] Current of 20 kHz was flown through a first induction
heating coil 21 to heat, and current of 40 kHz was flown through a
second induction heating coil 20 to heat to increase the
temperature. The lower part of the graphite crucible 10 (part
accommodating the sublimation raw material 40) was heated to
2312.degree. C., and the upper part of the graphite crucible 10
(place on which the seed crystal 50 of a silicon carbide single
crystal is placed in the cover body 11) was heated to 2290.degree.
C., respectively. In this operation, the feeding powder to the
first induction heating coil 21 was 10.3 kW, and the induction
heating current (feeding current to LC circuit) was 260 A, and the
feeding power to the second induction heating coil 20 was 4.6 kW,
and the induction heating current was 98 A. The pressure was
reduced to 20 Torr (2658 Pa) from normal pressure over 1 hour, and
maintained for 20 hours, to obtain a silicon carbide single crystal
60 of which convex form was maintained toward the sublimation raw
material 40 side as shown in FIG. 6. In this situation, the height
to the peak of the convex form in the silicon carbide single
crystal 60 was 12 mm, and the diameter of a grown crystal of
silicon carbide containing the silicon carbide single crystal 60
and a silicon carbide polycrystal formed around this was 87 mm. In
the silicon carbide single crystal 60, a concave portion sunk
toward the cover body 11 was not shaped in the form of ring. The
silicon carbide single crystal 60 did not grow contacting the
peripheral surface part 13 of the vessel body 12 of the graphite
crucible 10. Further, a silicon carbide single crystal 70 generated
only slightly around the silicon carbide single crystal 60.
Example 5
[0279] The same procedure as in Example 1 was conducted except the
following point in Example 4. Namely, the procedure was as in
Example 4 except that the seed crystal 50 of a silicon carbide
single crystal had a diameter of 20 mm and a thickness of 0.5 mm,
the lower part of the graphite crucible 10 (part accommodating the
sublimation raw material 40) was heated to 2349.degree. C., and
heating temperature of the upper part of the graphite crucible 10
(place on which the seed crystal 50 of a silicon carbide single
crystal is placed in the cover body 11) was 2317.degree. C., and
under these conditions, the feeding powder to the second induction
heating coil 20 was 5.5 kW, the induction heating current was 118
A, and the diameter of a grown crystal of silicon carbide
containing the silicon carbide single crystal 60 and a silicon
carbide polycrystal formed around this was 60 mm, and the same
excellent results were obtained as in Example 4.
Example 6
[0280] The same procedure as in Example 1 was conducted except the
following point in Example 6. Namely, an interference preventing
coil 22 was used in which water flows and which can be cooled. The
resulted silicon carbide powder had 6H and an average particle size
of 250 .mu.m, and the seed crystal 50 of a silicon carbide single
crystal is a wafer (6H) having a diameter of 25 mm and a thickness
of 2 mm obtained by cutting the bulk silicon carbide single crystal
obtained in Example 4 and mirror-polishing the whole surface.
[0281] Current of 20 kHz was flown through a first induction
heating coil 21 to heat, and current of 40 kHz was flown through a
second induction heating coil 20 to heat. The lower part of the
graphite crucible 10 (part accommodating the sublimation raw
material 40) and the upper part of the graphite crucible 10 (place
on which the seed crystal 50 of a silicon carbide single crystal is
placed in the cover body 11) were heated to 2510.degree. C.,
respectively, and heated for 1 hour. While maintaining the lower
part of the graphite crucible 10 at the same temperature (T.sub.1),
the feeding power to the second induction heating coil 20 was
gradually lowered (from 5.8 kW, 120 A, to 4.2 kW, 90 A), to lower
the temperature of the seed crystal placing part of the cover body
11 of the graphite crucible 10 down to 2350.degree. C. (T.sub.2)
over 20 hours and to lower the temperature of the outer peripheral
part of the seed crystal placing part of the cover body 11 down to
a calculated estimated temperature of 2480.degree. C. (T.sub.3),
respectively. In this operation, the pressure was decreased
simultaneously from normal pressure to 20 Torr (2658 Pa) over 1
hour, as a result, a silicon carbide single crystal 60 of which
convex portion was maintained toward the sublimation raw material
40 side was obtained, as shown in FIG. 7. In this situation, the
height to the peak of the convex form in the silicon carbide single
crystal 60 was 18 mm. In the silicon carbide single crystal 60, a
concave portion sunk toward the cover body 11 was not shaped in the
form of ring. The silicon carbide single crystal 60 did not grow
contacting the peripheral surface part 13 of the vessel body 12 of
the graphite crucible 10. Further, a silicon carbide single crystal
70 did not generate or grow adjacent to and around the silicon
carbide single crystal 60.
Example 7
[0282] The same procedure as in Example 1 was conducted except the
following point in Example 1. Namely, the second induction heating
coil 20 and the first induction heating coil 21 were substituted by
an induction heating coil 25 in a conventional silicon carbide
single crystal production apparatus 80 shown in FIG. 8, and only on
outside regions of a circle having a radius of 60 mm from the
center, of surfaces (surfaces on which growth of silicon carbide
single crystal is conducted) facing the inside of the vessel body
12, on the cover body 11 of the graphite crucible, a carbon thin
membrane which is judged to be glassy or amorphous by X ray
diffraction was formed by the following method to give a thickness
of 1 to 10 .mu.m. Its was placed in a vacuum chamber while exposing
only the above-mentioned outside regions on the cover body 11, and
under a benzene atmosphere, the pressure in the chamber was
controlled to 0.23 Pa. Then, the cover body 11 was kept at a
negative potential of 2.5 kV, and by decomposing benzene by ark
discharge plasma generated at a facing part of a filament ard an
anode, positive ions generated in plasma were allowed to collide
against the above-mentioned outer regions on the cover body 11 at
high speed, to effect membrane formation.
[0283] In Example 7, a crystal of silicon carbide did not grow on a
part on which membrane formation of glassy carbon or amorphous
carbon was effected, on a surface of the side facing to the inside
of the vessel body 12 in the cover body 11, and only on the center
part (circular part having a diameter of 60 mm) on which membrane
formation was not effected, a silicon carbide single crystal 60
grew of which whole surface of its growth surface was maintained in
convex form toward the sublimation raw material 40 side. Therefore,
the silicon carbide single crystal 60 did not grow contacting the
peripheral surface part 13 of the vessel body 12 in the graphite
crucible 10, and when cooled to room temperature, breakages such as
cracking and the like did not occur.
Comparative Example 1
[0284] A silicon carbide single crystal was produced in the same
manner as in Example 1 except that a silicon carbide single crystal
production apparatus 80 shown in FIG. 6 was used.
[0285] Specifically, the same procedure was conducted as in Example
1 except that the first induction heating coil 21 and the second
induction heating coil 20 placed at a pat which is situated at the
outer periphery of the quartz tube 30 and on which the cover body
11 in the graphite crucible 10 is situated were substituted by
induction heating coils 25 placed under condition wound in spiral
form at approximately the same interval at a part which is situated
at the outer periphery of the quartz tube 30 and on which the
graphite crucible 10 is situated, and the interference preventing
coil 22 was not used.
[0286] In Comparative Example 1, the whole surface of the side
facing the inside of the vessel body 12, in the cover body 11, was,
covered with a crystal of silicon carbide, and a silicon carbide
single crystal 70 grew on the outer periphery of the cover body 11
contacting the inner peripheral surface of the vessel body 12, as
shown in FIG. 8. When cooling was conducted to room temperature
under this condition, stress based on a difference in thermal
expansion is applied in concentration from the silicon carbide
polycrystal 70 side to the silicon carbide single crystal 60 side,
and defects such as cracking and the like occurred on the silicon
carbide single crystal 60, as shown in FIG. 8.
[0287] It will be understood by those skilled in the art that the
examples described above are preferable embodiments of the present
invention, and a lot of variations and modifications can be carried
out without violating the spirit and range of this invention.
[0288] According to the present invention, a high quality silicon
carbide single crystal excellent in dielectric breakdown property,
heat resistance, radiation resistance and the like, particularly
suitably for electronic devices such as semiconductor wafers and
the like and optical devices such as light emitting diodes and the
like, and showing no defects such as contamination of polycrystals
and polymorphs and micropipes and the like, and a method and an
apparatus capable of generating the above-mentioned high quality
silicon carbide single crystal with large diameter efficiently and
easily without breakages such as cracking and the like, can be
provided.
* * * * *