U.S. patent application number 14/233289 was filed with the patent office on 2014-05-29 for sic epitaxial wafer and method for producing same, and device for producing sic epitaxial wafer.
This patent application is currently assigned to SHOWA DENKO K.K.. The applicant listed for this patent is Yoshiaki Kageshima, Yoshihiko Miyasaka, Kenji Momose, Daisuke Muto. Invention is credited to Yoshiaki Kageshima, Yoshihiko Miyasaka, Kenji Momose, Daisuke Muto.
Application Number | 20140145214 14/233289 |
Document ID | / |
Family ID | 47558101 |
Filed Date | 2014-05-29 |
United States Patent
Application |
20140145214 |
Kind Code |
A1 |
Kageshima; Yoshiaki ; et
al. |
May 29, 2014 |
SIC EPITAXIAL WAFER AND METHOD FOR PRODUCING SAME, AND DEVICE FOR
PRODUCING SIC EPITAXIAL WAFER
Abstract
A SiC epitaxial wafer manufacturing method of the present
invention includes: manufacturing a SiC epitaxial wafer including a
SiC epitaxial layer on a surface of a SiC single crystal wafer
while supplying a raw material gas into a chamber using a SIC
epitaxial wafer manufacturing apparatus; and manufacturing a
subsequent SiC epitaxial wafer after measuring a surface density of
triangular defects originating from a material piece of an internal
member of the chamber on the SiC epitaxial layer of the previously
manufactured SiC epitaxial wafer.
Inventors: |
Kageshima; Yoshiaki;
(Chichibu-shi, JP) ; Muto; Daisuke; (Chichibu-shi,
JP) ; Momose; Kenji; (Chichibu-shi, JP) ;
Miyasaka; Yoshihiko; (Sanmu-shi, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Kageshima; Yoshiaki
Muto; Daisuke
Momose; Kenji
Miyasaka; Yoshihiko |
Chichibu-shi
Chichibu-shi
Chichibu-shi
Sanmu-shi |
|
JP
JP
JP
JP |
|
|
Assignee: |
SHOWA DENKO K.K.
Minato-ku, Tokyo
JP
|
Family ID: |
47558101 |
Appl. No.: |
14/233289 |
Filed: |
July 12, 2012 |
PCT Filed: |
July 12, 2012 |
PCT NO: |
PCT/JP2012/067841 |
371 Date: |
January 16, 2014 |
Current U.S.
Class: |
257/77 ; 117/85;
118/728 |
Current CPC
Class: |
C30B 25/12 20130101;
H01L 21/0262 20130101; H01L 21/02576 20130101; C23C 16/52 20130101;
H01L 21/02529 20130101; H01L 29/1608 20130101; H01L 21/681
20130101; H01L 21/02378 20130101; C30B 25/02 20130101; C30B 29/36
20130101; C30B 25/16 20130101; H01L 21/02433 20130101; H01L 29/34
20130101; C23C 16/325 20130101; C23C 16/4401 20130101 |
Class at
Publication: |
257/77 ; 117/85;
118/728 |
International
Class: |
C30B 25/16 20060101
C30B025/16; H01L 29/16 20060101 H01L029/16; C30B 25/12 20060101
C30B025/12; H01L 29/34 20060101 H01L029/34 |
Foreign Application Data
Date |
Code |
Application Number |
Jul 19, 2011 |
JP |
2011-157918 |
Claims
1. A SiC epitaxial wafer comprising: a SiC epitaxial layer formed
on a SiC single crystal substrate with an off-angle, wherein a
surface density of triangular defects, which is present in the SiC
epitaxial layer and has a material piece of an internal member of a
chamber as a starting point, is 0.5 pieces/cm.sup.2 or less.
2. The SiC epitaxial wafer according to claim 1, wherein the
material piece, which becomes the starting point, is formed of
carbon or silicon carbide.
3. A SiC epitaxial wafer manufacturing method comprising:
manufacturing a SiC epitaxial wafer including a SiC epitaxial layer
on a surface of a SiC single crystal wafer while supplying a raw
material gas into a chamber using a SiC epitaxial wafer
manufacturing apparatus; and manufacturing a subsequent SiC
epitaxial wafer after measuring a surface density of triangular
defects having a material piece of an internal member of the
chamber as a starting point on the SiC epitaxial layer of the
previously manufactured SiC epitaxial wafer, wherein the SiC
epitaxial wafer manufacturing apparatus includes a susceptor that
includes a wafer placement unit on which the wafer is placed, a top
plate that is disposed to face an upper surface of the susceptor so
that a reaction space is formed between the susceptor and the top
plate, and a shielding plate that is disposed to be close to a
lower surface of the top plate to such an extent that a deposit is
prevented from being attached to the lower surface of the top
plate, and the shielding plate is formed of silicon carbide or a
surface of the shielding plate facing the susceptor is covered with
a silicon carbide film or a pyrolytic carbon film.
4. The SiC epitaxial wafer manufacturing method according to claim
3, wherein the shielding plate is replaced and the subsequent SiC
epitaxial wafer is manufactured when the surface density of the
triangular defects having the material piece of the internal member
of the chamber as the starting point is greater than a
predetermined density as a result of the measurement.
5. A SiC epitaxial wafer manufacturing method comprising:
manufacturing a SiC epitaxial wafer including a SiC epitaxial layer
on a surface of a SiC single crystal wafer while supplying a raw
material gas into a chamber using a SiC epitaxial wafer
manufacturing apparatus; and manufacturing a subsequent SiC
epitaxial wafer after measuring a surface density of triangular
defects having a material piece of an internal member of the
chamber as a starting point on the SiC epitaxial layer of the
previously manufactured SiC epitaxial wafer, wherein the SiC
epitaxial wafer manufacturing apparatus includes a susceptor that
includes a wafer placement unit on which the wafer is placed and a
top plate that is disposed to face an upper surface of the
susceptor so that a reaction space is formed between the susceptor
and the top plate, and the top plate is formed of silicon carbide
or a surface of the top plate facing the susceptor is covered with
a silicon carbide film or a pyrolytic carbon film.
6. The SiC epitaxial wafer manufacturing method according to claim
5, wherein the top plate is replaced and the subsequent SiC
epitaxial wafer is manufactured when the surface density of the
triangular defects having the material piece of the internal member
of the chamber as the starting point is greater than a
predetermined density as a result of the measurement.
7. A SiC epitaxial wafer manufactured using the SiC epitaxial wafer
manufacturing method according to claim 3.
8. A SiC epitaxial wafer manufacturing apparatus comprising: a
susceptor that includes a wafer placement unit on which a wafer is
placed; a top plate that is disposed to face an upper surface of
the susceptor so that a reaction space is formed between the
susceptor and the top plate; and a shielding plate that is disposed
to be close to a lower surface of the top plate to such an extent
that a deposit is prevented from being attached to the lower
surface of the top plate, wherein the shielding plate is formed of
silicon carbide or a surface of the shielding plate facing the
susceptor is covered with a silicon carbide film or a pyrolytic
carbon film, and an epitaxial layer is formed on a surface of the
wafer while a raw material gas is supplied into a chamber.
9. A SiC epitaxial wafer manufacturing apparatus comprising: a
susceptor that includes a wafer placement unit on which a wafer is
placed; and a top plate that is disposed to face an upper surface
of the susceptor so that a reaction space is formed between the
susceptor and the top plate, wherein the top plate is formed of
silicon carbide or a surface of the top plate facing the susceptor
is covered with a silicon carbide film or a pyrolytic carbon film,
and an epitaxial layer is formed on a surface of the wafer while a
raw material gas is supplied into a chamber.
10. The epitaxial wafer manufacturing apparatus according to claim
8, wherein a film thickness of the silicon carbide film or the
pyrolytic carbon film is within the range of 20 .mu.m to 100
.mu.m.
11. The epitaxial wafer manufacturing apparatus according to claim
8, further comprising: a heating device that is disposed on a lower
surface side of the susceptor and/or an upper surface side of the
top plate.
Description
TECHNICAL FIELD
[0001] The present invention relates to a SiC epitaxial wafer, a
SiC epitaxial wafer manufacturing method, and a SiC epitaxial wafer
manufacturing apparatus.
[0002] Priority is claimed on Japanese Patent Application No.
2011-157918, filed Jul. 19, 2011, the content of which is
incorporated herein by reference.
BACKGROUND ART
[0003] Silicon carbide (SiC) has characteristics in which a
breakdown electric field is larger by a single digit, a band gap is
three times larger, and thermal conductivity is about three times
larger than silicon (Si). Accordingly, silicon carbide (SiC) is
expected to be applied to power devices, high-frequency devices,
high-temperature operation devices, and the like. A SiC epitaxial
wafer is manufactured by growing a SiC epitaxial layer serving as
an active region of a SiC semiconductor device on a SiC single
crystal wafer processed from bulk single crystal of SiC produced by
a sublimation method or the like according to chemical vapor
deposition (CVD). The foregoing SiC single crystal wafer is used as
a substrate in which a SiC epitaxial layer is formed.
[0004] As a cause of deterioration in the quality of a SiC
epitaxial layer, a defect with a triangular shape (hereinafter
referred to as a "triangular defect") is known. A triangular defect
is formed in a direction in which the apex of a triangle and its
opposite side (base) are lined up sequentially in a step-flow
growth direction (Non Patent Literature 3). That is, the opposite
side (base) of the triangular defect is disposed in a direction
perpendicular to the <11-20> direction. A plurality of causes
of the triangular defect can be considered. Examples of the causes
include damage such as a polishing flaw remaining on the surface of
a substrate (wafer) (Patent Literature 1), a 2-dimensional nucleus
formed in a terrace during step-flow growth (Patent Literature 2),
a different kind of polytype of crystal nucleus formed in an
interface between a substrate and an epitaxial layer at the time of
an oversaturated state of an early growth stage (Non Patent
Literature 1), and a minute broken piece of a SiC film to be
described below. The triangular defect grows as the SiC epitaxial
layer grows. That is, the triangular defect grows so that its area
is increased while a shape substantially similar to a triangle
using its starting point as the apex of the triangle is maintained
(see the schematic diagram of FIG. 2). Accordingly, the size of the
starting point is larger as the triangular occurs in the earlier
growth stage of the SiC epitaxial layer, and the depth of the
starting point in the layer can be estimated from the size of the
triangular defect.
[0005] In order to improve a yield at the time of mass production
of the SiC epitaxial wafer, reduction in the triangular defects is
indispensable and Patent Literature 1 and Patent Literature 2 have
suggested countermeasures against the cause for the reduction in
the triangular defects.
[0006] In addition to the foregoing triangular defect, a minute
broken piece (hereinafter referred to as a "downfall") of a SiC
film falling on a SiC single crystal wafer or a SiC epitaxial layer
is also a cause of deterioration in the quality of the SiC
epitaxial layer. The downfall is peeled off from the SiC layer
deposited on a sealing (top plate) disposed on the upper side of an
apparatus so as to face the upper surface of a susceptor including
a wafer replacing unit. This downfall can also be a starting point
of the triangular defect.
[0007] Here, when the SiC epitaxial layer grows, it is necessary to
heat the SiC single crystal wafer which is a substrate at a high
temperature and maintain the temperature. A method of performing
heating using a heating device disposed on the lower surface side
of the susceptor and/or the upper surface side of the sealing is
mainly used as a heating maintaining method, (see Patent Literature
3 and Non Patent Literatures 2 and 3). When the sealing is heated,
a heating method of performing heating by high-frequency induction
heating using an induction coil is generally used and a heating
device formed of carbon suitable for the high-frequency induction
heating is normally used.
[0008] While the SiC epitaxial layer is formed, SiC may be
deposited not only on the SiC single crystal wafer but also on the
sealing. When the layer is repeatedly formed, an amount of SiC
deposited on the sealing also increases. Therefore, the problem of
the downfall also becomes notable particularly in mass
production.
[0009] In order to improve a yield in mass production of the SiC
epitaxial wafer, reduction in the downfall is also indispensable.
In order to reduce the downfall, Patent Literature 4 discloses a
configuration in which a cover plate covering a wafer is disposed
on a SiC single crystal wafer so that the downfall can be inhibited
from falling on the SiC single crystal wafer or the SiC epitaxial
layer.
CITATION LIST
Patent Literature
[Patent Literature 1]
[0010] Japanese Patent No. 4581081
[Patent Literature 2]
[0010] [0011] Japanese Unexamined Patent Application, First
Publication No. 2009-256138
[Patent Literature 3]
[0011] [0012] Published Japanese Translation No. 2004-507897 of the
PCT International Publication
[Patent Literature 4]
[0012] [0013] Japanese Unexamined Patent Application, First
Publication No. 2009-164162
[Patent Literature 5]
[0013] [0014] Japanese Unexamined Patent Application, First
Publication No. 2011-49496
Non Patent Literature
[Non Patent Literature 1]
[0014] [0015] Journal of Applied Physics 105 (2009) 074513
[Non Patent Literature 2]
[0015] [0016] Materials Science Forum Vols. 483 to 485 (2005) pp
141 to 146
[Non Patent Literature 3]
[0016] [0017] Materials Science Forum Vols. 556 and 557 (2007) pp
57 to 60
SUMMARY OF INVENTION
Technical Problem
[0018] However, although the methods disclosed in Patent
Literatures 1 and 2 are used, a triangular defect density is not
sufficiently reduced in practice. One of the reasons is existence
of a triangular defect of which a cause is not well known.
[0019] Also, according to the method disclosed in Patent Literature
4, the downfall can be inhibited from falling from the sealing to
the SiC single crystal wafer or the SiC epitaxial layer growing on
the SiC single crystal wafer, but the depositing of SiC (or growth
of a SIC film) on the sealing which is a cause of the downfall may
not be inhibited. For this reason, it is necessary to clean the
sealing. In this case, a problem that an apparatus operation rate
is reduced may occur. Also, SiC is also deposited on the lower
surface of the cover plate. Therefore, when the layer is repeatedly
formed, a problem that the downfall occurs from the cover plate may
occur.
[0020] The present invention is completed in light of the
above-mentioned circumstances, and an object of the present
invention is to provide a SiC epitaxial wafer, a SiC epitaxial
wafer manufacturing method, and a SiC epitaxial wafer manufacturing
apparatus with a low surface density of triangular defects having a
material piece of an internal member of a chamber as a starting
point.
Solution to Problem
[0021] The present inventors have first found a triangular defect
having a material piece of an internal member of a chamber as a
starting point. That is, the present inventors have found a new
type of triangular defect, i.e., have found that a material piece
of an internal member of a chamber falls on a SiC single crystal
wafer or a SiC epitaxial layer during growth due to a certain cause
and a triangular defect having the material piece as a starting
point grows. In the related art, as described above, a polishing
flaw remaining on the surface of a substrate (wafer), a different
kind of polytype of crystal nucleus occurring in a step, or the
like has been known as the starting point of a triangular defect.
However, this found triangular defect is a triangular defect having
a material piece of an internal member of a chamber as a starting
point. The present inventors have found the new type of triangular
defect and have carried out a thorough examination to reduce this
triangular defect and have thus completed the present
invention.
[0022] FIG. 1A shows a typical optical microscope image of a
triangular defect having a material piece of an internal member of
a chamber as a starting point. MX51 manufactured by Olympus
Corporation is used as an optical microscope.
[0023] Hot Wall SiC CVD (VP 2400 HW) manufactured by AIXTRON
corporation, which is an epitaxial wafer manufacturing apparatus of
a (self-revolution) type having plurality of susceptors for mass
production, is used and a sealing formed of graphite is used
without using a shielding plate. A SiC epitaxial layer of 10 .mu.m
is formed in a 4H-SiC single crystal substrate with an off-angle of
4.degree.. A SiC epitaxial wafer of the 80.sup.th production lot
(that is, after a film corresponding to a SiC epitaxial layer of
800 .mu.m is formed within the chamber) is examined using an
optical microscope.
[0024] When the SiC epitaxial wafer is examined using the optical
microscope, normally, a defect present on a surface is examined
focusing on the surface of the epitaxial layer. FIG. 1B is a
diagram illustrating an optical microscope image in which the same
triangular defect is examined focusing on the surface of the
epitaxial layer normally.
[0025] On the other hand, the present inventors have found a
foreign material (a black point ("starting point of a triangular
defect") shown in the middle of a circle mark) shown black in the
front (a direction distant from the opposite side) of the apex of
the triangular defect by shifting the focus normally taken on the
surface and focusing on an interface between a SiC single crystal
substrate and an epitaxial layer. By analyzing the black point in
detail and identifying the origin (a material piece of an internal
member of a chamber) of the foreign material, a new type of
previously unknown triangular defect having a material piece of an
internal member of a chamber as a starting point has been
found.
[0026] FIG. 2 is a diagram illustrating a transmission electron
microscope (TEM) image obtained from the same SiC epitaxial wafer.
A transmission electron microscope (HF-2200 manufactured by Hitachi
High-technologies Corporation) is used.
[0027] The drawing depicted on the right side of the TEM image in
FIG. 2 schematically indicates the starting point of the triangular
defect and the triangular defect growing from the starting point of
the triangular defect. A portion surrounded by a rectangle
indicates a range shown on the TEM image and the TEM image is an
examined image near the starting point of the triangular defect.
The drawing depicted on the lower side of FIG. 2 schematically
indicates a cross-section near the triangular defect.
[0028] The foreign material, which becomes the starting point of
the triangular defect, is present in the front separate by about 7
.mu.m from the apex of the triangle in the horizontal direction and
a horizontal distance from the starting point to the opposite side
of the triangle is about 143 .mu.m.
[0029] FIG. 3 is a diagram illustrating a transmission electron
microscope (TEM) image near the starting point (foreign material)
of the triangular defect of the SiC epitaxial wafer manufactured
under the same conditions as the manufacturing conditions in which
the foregoing SiC epitaxial wafer is manufactured except that a
shielding plate in which a graphite substrate is covered with a
tantalum carbide (TaC) film is used on the lower surface of the
sealing.
[0030] A portion of the triangular defect having the foreign
material as a starting point is formed from 3C-SiC single crystal
and a portion epitaxially grown normally near the triangular defect
is formed from 4H-SiC single crystal.
[0031] FIG. 4A is a diagram illustrating a result obtained by
performing composition analysis on the foreign material which is
the starting point of the triangular defect illustrated in FIG. 3
according to an energy dispersive X-ray spectroscopy method
(EDX).
[0032] In FIG. 4A, the peaks of 1.711 keV and 8.150 keV indicate
tantalum (Ta). Since a member formed of a material containing
tantalum (Ta) is not present within the chamber other than the
shielding plate, it can be concluded that these peaks are
originated from tantalum (Ta) of tantalum carbide (TaC) which is
the material covering the shielding plate.
[0033] FIG. 4B is a diagram illustrating an EDX analysis result of
the sample holder of the EDX. It can be understood that the peaks
of Zn, Cu, and the like illustrated in FIG. 4A originate from the
material of the EDX holder.
[0034] As described above, the present inventors have found a new
type of triangular defect having a foreign material (material
piece) coming from a material of an internal member of a chamber (a
shielding plate in the case of FIG. 3) as a starting point in the
front of the apex of the triangular defect (in a direction distant
from the opposite side).
[0035] When the triangular defect is observed using an optical
microscope or an optical surface inspection apparatus (for example,
Candela manufactured by KLA-Tencor Corporation) that uses a laser
beam, clear starting points and unclear starting points of the
triangular defects are observed. In the related art, the fact that
normal step-flow growth does not progress due to unsuitable growth
conditions (for example, a considerably low growth temperature) and
a different kind of polytype of crystal nucleus becomes a starting
point has been analyzed as a cause of the triangular defect with
the unclear starting point in many cases. On the other hand, the
present inventors have found that an origin of a material piece of
an internal member of a chamber is present in a triangular defect
with an unclear starting point. At the moment, it may not be
concluded that all of the triangular defects with unclear starting
points come from material pieces of an internal member of a
chamber. As will be described below, however, almost all of the
triangular defects with unclear starting points have successfully
been removed by reducing the triangular defects coming from the
material pieces of the internal member of the chamber. Accordingly,
most of the triangular defects with the unclear starting points are
considered to come from the material pieces of the internal member
of the chamber.
[0036] Whether a triangular defect with an unclear starting point
is the triangular defect having the material piece of the internal
member of the chamber as the starting point can be identified
according to, for example, a method of shifting focus from a
surface in a depth direction using an optical microscope, as
described above. Therefore, a surface density of the triangular
defects having the material piece of the internal member of the
chamber as the starting point can be obtained.
[0037] Deterioration in the internal member of the chamber
progresses as films are repeatedly formed (a production lot number
increases), and thus the amount of falling material piece
increases. Therefore, the surface density of the triangular defects
having the material piece of the internal member of the chamber as
the starting point increases. Here, as a specific example of the
deterioration in the internal member of the chamber, since a
coefficient of thermal expansion is different between a tantalum
film and a graphite substrate in the case of a sealing in which the
graphite substrate is covered with the tantalum carbide (TaC) film,
stress is applied to a tantalum carbide film and the tantalum
carbide film is peeled off due to an increase and a decrease in
temperature by the repetition of the forming of the films. As other
examples, the tantalum carbide film is cracked and dust emission
from the crack occurs in the graphite substrate, and the material
of the sealing is sublimated due to mutual interaction between a
gas within the chamber and the surface of the sealing. Also, when
SiC is deposited on the sealing and a SiC film grows, a difference
in the coefficient of thermal expansion between the SiC film and
the tantalum carbide film causes deterioration in the tantalum
carbide film. Thus, the surface density of the triangular defects
having the material piece of the internal member of the chamber as
the starting point highly depends on the number of times the film
is formed (or a production lot number). Also, when the number of
times the film is formed exceeds a predetermined number of times
(depending on a manufacturing condition), deterioration in the
internal member of the chamber progresses at once and the surface
density of the triangular defects having the material piece of the
internal member of the chamber as the starting point sharply
increases.
[0038] On the other hand, a triangular defect having damage, such
as a polishing flaw of a surface of a substrate (wafer), as a
starting point or a triangular defect having a different kind of
polytype of crystal nucleus formed due to unsuitable growth
conditions as a starting point does not depend on the number of
times the film is formed. That is, a triangular defect caused by a
substrate or a triangular defect caused due to a growth condition
does not depend on the number of times the film is formed.
[0039] On the other hand, a triangular defect having a downfall as
a starting point also depends on the number of times the film is
formed. The downfall falls from the sealing when the shielding
plate is not used. The downfall falls from the shielding plate when
the shielding plate is used. When the film is repeatedly formed,
the SiC film formed on the sealing or the shielding plate is
thicker, and thus is easily peeled off. When the shielding plate is
used, as will be described below, the lower surface of the
shielding plate is preferably formed of a material with a higher
attachment property of the SiC film than that of the sealing.
Accordingly, the downfall can be reduced compared to the case in
which the shielding plate is not used.
[0040] Accordingly, examples of the triangular defect increasing by
the repetition of the forming of the film include not only the
triangular defect having the material piece of the internal member
of the chamber as the starting point but also the triangular defect
having the downfall as the starting point. The triangular defect
having the material piece of the internal member of the chamber as
the starting point has characteristics in which the starting point
is unclear in an optical microscope image or an image (hereinafter
referred to as a candela image) produced by an optical surface
inspection apparatus using a laser beam, whereas a starting point
is clear for the triangular defect having the downfall as the
starting point. Accordingly, each triangular defect can normally be
identified from an optical microscope image, a candela image, or
the like. Even when a defect coming from a cause other than the
downfall is included in the triangular defect with an unclear
starting point, the surface density of the triangular defects with
the unclear starting point can be considered to be the upper limit
of the surface density of the triangular defects having the
material piece of the internal member of the chamber as the
starting point. Accordingly, by managing the surface density, it is
possible to manage the upper limit of the surface density of the
triangular defects having the material piece of the internal member
of the chamber as the starting point. By managing an increase in
the surface density of the triangular defects with the unclear
starting point due to the repetition of the forming of the film, it
is possible to manufacture a SiC epitaxial wafer in which the
surface density of the triangular defects having the material piece
of the internal member of the chamber as the starting point is
low.
[0041] When the density of the triangular defects having the
material piece of the internal member of the chamber as the
starting point is desired to be more precisely measured and
managed, the precise measurement can be taken by performing
composition analysis of a foreign material present in the front of
the triangular defect using energy dispersive X-ray spectroscopy or
the like.
[0042] In the SIC epitaxial wafer manufacturing apparatus, the
internal member of the chamber deteriorates due to the repetition
of the forming of the film and is peeled off from the surface of
the like, and thus a minute lump occurs. When the minute lump falls
on the wafer or the SiC epitaxial layer during growth, a material
piece of the internal member of the chamber, which becomes a
starting point of a triangular defect, is considered to occur. The
internal member of the chamber which causes the material piece
serving as the starting point of the triangular defect is mainly a
member disposed on the upper side of the wafer. An amount of
material piece falling on the wafer from other wall surfaces of the
chamber or other members within the chamber is estimated to be
negligible.
[0043] Accordingly, to reduce the triangular defect having the
material piece of the internal member of the chamber as the
starting point, the present inventors have contrived a technique
for covering a member disposed on the upper side of a wafer to face
the wafer with a material by which dust emission or sublimation is
small, a technique for measuring the surface density of the
triangular defects having a material piece of an internal member of
a chamber as a starting point regularly (for each production lot,
every plurality of production lots, or the like) or irregularly and
managing the value of the surface density, and a technique for
manufacturing a subsequent SiC epitaxial wafer after the member is
replaced when the surface density is greater than a predetermined
value. Thus, the present inventors have found that a SIC epitaxial
wafer with a low surface density of the triangular defects having a
material piece of an internal member of a chamber as a starting
point can be manufactured.
[0044] As described above, the present inventors have consequently
been contrived the present invention including the following means
by finding the existence of a new type of triangular defect having
a material piece of an internal member of a chamber as a starting
point and executing a thorough study on a task of reduction in the
triangular defect.
[0045] The present inventors provide the following invention to
resolve the above-mentioned problems.
(1) A SiC epitaxial wafer including:
[0046] a SiC epitaxial layer formed on a SiC single crystal
substrate with an off-angle, wherein
[0047] a surface density of triangular defects, which is present in
the SiC epitaxial layer and has a material piece of an internal
member of a chamber as a starting point, is 0.5 pieces/cm.sup.2 or
less.
[0048] In the present invention, the SIC single crystal substrate
means a SiC single crystal wafer.
(2) The SiC epitaxial wafer according to (1), wherein the material
piece, which becomes a starting point, is formed of carbon or
silicon carbide. (3) A SiC epitaxial wafer manufacturing method
including:
[0049] manufacturing a SiC epitaxial wafer including a SiC
epitaxial layer on a surface of a SiC single crystal wafer while
supplying a raw material gas into a chamber using a SiC epitaxial
wafer manufacturing apparatus; and
[0050] manufacturing a subsequent SiC epitaxial wafer after
measuring a surface density of triangular defects having a material
piece of an internal member of the chamber as a starting point on
the SiC epitaxial layer of the previously manufactured SiC
epitaxial wafer, wherein
[0051] the SiC epitaxial wafer manufacturing apparatus includes a
susceptor that includes a wafer placement unit on which the wafer
is placed, a top plate that is disposed to face an upper surface of
the susceptor so that a reaction space is formed between the
susceptor and the top plate, and a shielding plate that is disposed
to be close to a lower surface of the top plate to such an extent
that a deposit is prevented from being attached to the lower
surface of the top plate, and
[0052] the shielding plate is formed of silicon carbide or a
surface of the shielding plate facing the susceptor is covered with
a silicon carbide film or a pyrolytic carbon film.
(4) The SiC epitaxial wafer manufacturing method according to (3),
wherein the shielding plate is replaced and the subsequent SiC
epitaxial wafer is manufactured when the surface density of the
triangular defects having the material piece of the internal member
of the chamber as the starting point is greater than a
predetermined density as a result of the measurement. (5) A SIC
epitaxial wafer manufacturing method including:
[0053] manufacturing a SiC epitaxial wafer including a SiC
epitaxial layer on a surface of a SiC single crystal wafer while
supplying a raw material gas into a chamber using a SiC epitaxial
wafer manufacturing apparatus; and
[0054] manufacturing a subsequent SiC epitaxial wafer after
measuring a surface density of triangular defects having a material
piece of an internal member of the chamber as a starting point on
the SiC epitaxial layer of the previously manufactured SiC
epitaxial wafer, wherein
[0055] the SiC epitaxial wafer manufacturing apparatus includes a
susceptor that includes a wafer placement unit on which the wafer
is placed and a top plate that is disposed to face an upper surface
of the susceptor so that a reaction space is formed between the
susceptor and the top plate, and
[0056] the top plate is formed of silicon carbide or a surface of
the top plate facing the susceptor is covered with a silicon
carbide film or a pyrolytic carbon film.
(6) The SiC epitaxial wafer manufacturing method according to (5),
wherein the top plate is replaced and the subsequent SiC epitaxial
wafer is manufactured when the surface density of the triangular
defects having the material piece of the internal member of the
chamber as the starting point is greater than a predetermined
density as a result of the measurement. (7) A SiC epitaxial wafer
manufactured using the SiC epitaxial wafer manufacturing method
according to any one of (3) to (6). (8) A SIC epitaxial wafer
manufacturing apparatus including:
[0057] a susceptor that includes a wafer placement unit on which a
wafer is placed;
[0058] a top plate that is disposed to face an upper surface of the
susceptor so that a reaction space is formed between the susceptor
and the top plate; and
[0059] a shielding plate that is disposed to be close to a lower
surface of the top plate to such an extent that a deposit is
prevented from being attached to the lower surface of the top
plate, wherein
[0060] the shielding plate is formed of silicon carbide or a
surface of the shielding plate facing the susceptor is covered with
a silicon carbide film or a pyrolytic carbon film, and
[0061] an epitaxial layer is formed on a surface of the wafer while
a raw material gas is supplied into a chamber.
(9) A SiC epitaxial wafer manufacturing apparatus including:
[0062] a susceptor that includes a wafer placement unit on which a
wafer is placed; and
[0063] a top plate that is disposed to face an upper surface of the
susceptor so that a reaction space is formed between the susceptor
and the top plate, wherein
[0064] the top plate is formed of silicon carbide or a surface of
the top plate facing the susceptor is covered with a silicon
carbide film or a pyrolytic carbon film, and
[0065] an epitaxial layer is formed on a surface of the wafer while
a raw material gas is supplied into a chamber.
(10) The epitaxial wafer manufacturing apparatus according to (8)
or (9), wherein a film thickness of the silicon carbide film or the
pyrolytic carbon film is within the range of 20 .mu.m to 100 .mu.m.
(11) The epitaxial wafer manufacturing apparatus according to any
one of (8) to (10), further including: a heating device that is
disposed on a lower surface side of the susceptor and/or an upper
surface side of the top plate.
Advantageous Effects of Invention
[0066] In the SiC epitaxial wafer of the present invention, the
surface density of the triangular defects having the material piece
of the internal member of the chamber as the starting point, which
results from a previously unknown cause and thus may not be
reduced, is low as 0.5 pieces/cm.sup.2 or less. Therefore, a larger
number of devices than in the related art can be obtained from one
SiC epitaxial wafer.
[0067] The SiC epitaxial wafer manufacturing method of the present
invention includes the manufacturing of the subsequent SiC
epitaxial wafer after measuring the surface density of the
triangular defects having the material piece of the internal member
of the chamber as the starting point on the SIC epitaxial layer of
the previously manufactured SiC epitaxial wafer by using the SiC
epitaxial wafer including the shielding plate. Therefore, it is
possible to manufacture the SiC epitaxial wafer for which the
triangular defect having the material piece of the internal member
of the chamber as the starting point is small in the SiC epitaxial
layer. Also, the shielding plate is formed of silicon carbide or
the surface of the shielding plate facing the susceptor is covered
with the silicon carbide film or the pyrolytic carbon film.
Therefore, the deterioration in the shielding plate hardly
progresses, the material pieces falling from the shielding plate to
the wafer are reduced, and thus the shielding plate can be used
longer. When the shielding plate covered with the silicon carbide
film and formed of silicon carbide is used, the SiC film deposited
on the shielding plate is the same as the covered film or the
material is the same, there is no difference in the coefficient of
thermal expansion, and therefore the deterioration hardly
progresses. Also, when the shielding plate covered with the
pyrolytic carbon film is used, the shielding plate formed of a
carbon material substrate is used. Since a difference in the
coefficient of thermal expansion is small between the carbon
material substrate and the pyrolytic carbon film, the deterioration
in the shielding plate hardly progresses.
[0068] According to the SiC epitaxial wafer manufacturing method of
the present invention, when the surface density of the triangular
defects having the material piece of the internal member of the
chamber as the starting point is greater than the predetermined
density as the result of the foregoing measurement, the shielding
plate is replaced and a subsequent SiC epitaxial wafer is
configured to be manufactured. Therefore, it is possible to
manufacture the SiC epitaxial wafer in which the surface density of
the triangular defects having the material piece of the internal
member of the chamber as the starting point is equal to or less
than the predetermined surface density.
[0069] The SiC epitaxial wafer manufacturing method of the present
invention includes the manufacturing of the subsequent SiC
epitaxial wafer after measuring the surface density of the
triangular defects having the material piece of the internal member
of the chamber as the starting point on the SiC epitaxial layer of
the previously manufactured SiC epitaxial wafer. Therefore, it is
possible to manufacture the SIC epitaxial wafer in which the
triangular defect having the material piece of the internal member
of the chamber as the starting point is small in the SiC epitaxial
layer. Also, the top plate is formed of silicon carbide or the
surface of the top plate facing the susceptor is covered with the
silicon carbide film or the pyrolytic carbon film. Therefore, the
deterioration in the top plate hardly progresses, the material
pieces falling from the top plate to the wafer are reduced, and
thus the top plate can be used longer. When the top plate covered
with the silicon carbide film and formed of silicon carbide is
used, the SiC film deposited on the top plate is the same as the
covered film of the top plate or the material is the same, there is
no difference in the coefficient of thermal expansion, and
therefore the deterioration hardly progresses. Also, when the top
plate covered with the pyrolytic carbon film is used, the top plate
of a carbon material substrate is used. Since a difference in the
coefficient of thermal expansion is small between the carbon
material substrate and the pyrolytic carbon film, the deterioration
in the top plate hardly progresses.
[0070] According to the SiC epitaxial wafer manufacturing method of
the present invention, the top plate is replaced and the subsequent
SiC epitaxial wafer is manufactured when the surface density of the
triangular defects having the material piece of the internal member
of the chamber as the starting point is greater than the
predetermined density as the result of the foregoing measurement.
Therefore, it is possible to manufacture the SiC epitaxial wafer in
which the surface density of the triangular defects having the
material piece of the internal member of the chamber as the
starting point is equal to or less than the predetermined surface
density.
[0071] The SiC epitaxial wafer manufacturing apparatus of the
present invention includes the shielding plate that is disposed to
be close to the lower surface of the top plate so that a deposit is
prevented from being attached to the lower surface of the top plate
and dust emitted from the lower surface of the top plate is
received. Since the shielding plate is formed of silicon carbide or
the surface of the shielding plate facing the susceptor is covered
with the silicon carbide film or the pyrolytic carbon film, the
material pieces falling from the shielding plate to the wafer are
reduced. Accordingly, it is possible to manufacture the SiC
epitaxial wafer with the low surface density of the triangular
defects having the material piece of the internal member of the
chamber as the starting point.
[0072] In the SiC epitaxial wafer manufacturing apparatus of the
present invention, the top plate is formed of silicon carbide or
the surface of the top plate facing the susceptor is covered with
the silicon carbide film or the pyrolytic carbon film. Therefore,
the material pieces falling from the top plate to the wafer are
reduced. Accordingly, it is possible to manufacture the SiC
epitaxial wafer with the low surface density of the triangular
defects having the material piece of the internal member of the
chamber as the starting point.
BRIEF DESCRIPTION OF DRAWINGS
[0073] FIG. 1A is a diagram illustrating an optical microscope
image of a triangular defect having a material piece of an internal
member of a typical chamber as a starting point and examined
focusing on a foreign material.
[0074] FIG. 1B is a diagram illustrating an optical microscope
image of a triangular defect having a material piece of an internal
member of a typical chamber as a starting point and examined
focusing on the surface of an epitaxial layer.
[0075] FIG. 2 is a diagram illustrating a transmission electron
microscope (TEM) image of the same SiC epitaxial wafer as those of
FIGS. 1A and 1B.
[0076] FIG. 3 is a diagram illustrating a transmission electron
microscope (TEM) image of a SiC epitaxial wafer manufactured using
a shielding plate formed of graphite covered with a tantalum
carbide film.
[0077] FIG. 4A is a diagram illustrating a measurement result
according to energy dispersive X-ray spectroscopy of the same SiC
epitaxial wafer as that of FIG. 3 and a result obtained by
measuring a foreign material.
[0078] FIG. 4B is a diagram illustrating a measurement result
according to energy dispersive X-ray spectroscopy of the same SiC
epitaxial wafer as that of FIG. 3 and a result obtained by
measuring a sample holder.
[0079] FIG. 5 is a schematic sectional view illustrating an
epitaxial wafer manufacturing apparatus used in an embodiment of
the present invention.
[0080] FIG. 6 is a perspective view illustrating a lower side of
the epitaxial wafer manufacturing apparatus taken along the line
A-A' of FIG. 5.
[0081] FIG. 7 is a schematic expanded view of the periphery of a
shielding plate shown in FIG. 5.
[0082] FIG. 8A is a diagram illustrating a candela image of an
example.
[0083] FIG. 8B is a diagram illustrating a candela image of an
example.
[0084] FIG. 8C is a diagram illustrating a candela image of an
example.
[0085] FIG. 9A is a diagram illustrating a candela image of a first
comparative example.
[0086] FIG. 9B is a diagram illustrating a candela image of a
second comparative example.
DESCRIPTION OF EMBODIMENTS
[0087] Hereinafter, a SiC epitaxial wafer, a SiC epitaxial wafer
manufacturing method, and an epitaxial wafer manufacturing
apparatus to which the present invention is applied will be
described in detail with reference to the drawings.
[0088] In the drawings used for the following description,
characteristic portions are expanded to facilitate the
understanding of the characteristics in some cases, and thus
dimension scales and the like of respective constituent elements
are different from the actual scales and the like in some cases.
Materials, dimensions, and the like exemplified in the following
description are examples, and thus the present invention is not
limited thereto and may be appropriately modified within the scope
of the present invention without departing from the gist of the
present invention.
[SiC Epitaxial Wafer]
[0089] A SiC epitaxial wafer to which the present invention is
applied is a SiC epitaxial wafer that includes a SiC epitaxial
layer on a SIC single crystal substrate having an off-angle and is
characterized in that a surface density of triangular defects
having a material piece of an internal member of a chamber as a
starting point is 0.5 pieces/cm.sup.2.
[0090] Since the triangular defect having the material piece of the
internal member of the chamber as the starting point is not a
triangular defect caused by a substrate, the substrate is not
particularly limited to a SiC single crystal substrate.
[0091] Since any polytype can be used as the SiC single crystal
substrate, 4H-SiC mainly used to manufacture a practical SIC device
can be used. A SiC single crystal substrate processed from a bulk
crystal produced by a sublimation method or the like is used as a
substrate of the SiC device. Typically, a SiC epitaxial layer
serving as an active region of the SiC device is formed on the SiC
single crystal substrate according to chemical vapor deposition
(CVD).
[0092] Any off-angle may be used as the off-angle of the SiC single
crystal substrate. Although the off-angle is not limited, a small
off-angle of, for example, 0.4.degree. to 5.degree. is preferable
from the viewpoint of cost reduction. The angle of 0.4.degree. is
the lower limit of the off-angle at which step-flow growth can be
realized.
[0093] When the SiC single crystal substrate has a size up to about
2 inches, 8.degree. has mainly been used as the off-angle of the
SiC single crystal substrate. At this off-angle, a terrace width of
the wafer surface is small and the step-flow growth can easily be
realized. However, the number of wafers obtained from a SiC ingot
decreases as the off-angle increases. Therefore, an off-angle of
about 4.degree. is mainly used in a SiC substrate of 3 inches or
more.
[0094] As the off-angle decreases, the terrace width of the surface
of the SiC single crystal substrate increases. Therefore, a speed
at which migration atoms are taken at a step end, that is, a growth
speed of the step end, may easily become irregular. As a result,
step bunching may easily occur since a step of a fast growth speed
catches up with a step of a slow growth speed to be coalesced. For
example, in a substrate of the off-angle of 0.4.degree., the
terrace width is 10 times the terrace width of the substrate of the
off-angle of 4.degree., and thus a length of the step-flow growth
is increased by a single digit. Accordingly, it is necessary to
notice that the condition of the step-flow growth used in the
substrate of the off-angle of 4.degree. is required to be
adjusted.
[0095] A SiC single crystal substrate in which the growth surface
of the SiC epitaxial layer is processed with a convex shape can be
used.
[0096] When the SiC epitaxial wafer is manufactured (the SiC
epitaxial layer is formed (grows)), the rear surface of the SiC
single crystal substrate is heated directly from a heated
susceptor. However, the front surface (the surface on which the SiC
epitaxial layer is formed) is exposed to a vacuum space, and thus
is not heated directly. Also, since hydrogen which is a carrier gas
flows on the front surface, the heat is carried away. From this
circumstance, the temperature of the front surface is lower than
that of the rear surface at the time of epitaxial growth. Due to a
difference in the temperature, the magnitude of thermal expansion
of the front surface is lower than that of the rear surface, and
the front surface of the SiC single crystal substrate is deformed
to become concave at the time of epitaxial growth. Accordingly, by
using the SiC single crystal substrate in which the growth surface
of the SiC epitaxial layer is processed with a convex shape, the
epitaxial growth can be performed in a state in which the
concaveness (warping) of the substrate at the time of the epitaxial
growth is resolved.
[0097] The thickness of the SiC epitaxial layer is not particularly
limited. However, for example, when the layer is formed in 2.5
hours at a typical growth speed of 4 .mu.m/h, the thickness of the
SiC epitaxial layer becomes 10 .mu.m.
[SiC Epitaxial Wafer Manufacturing Apparatus (First
Embodiment)]
[0098] FIG. 5 is a schematic sectional view illustrating a part of
an epitaxial wafer manufacturing apparatus to which the present
invention is applied. FIG. 6 is a perspective view illustrating a
lower side of the epitaxial wafer manufacturing apparatus taken
along the line A-A' of FIG. 5. FIG. 7 is a schematic expanded view
of the periphery of a shielding plate shown in FIG. 5.
[0099] An epitaxial wafer manufacturing apparatus 100 according to
an embodiment herein is, for example, a CVD apparatus 100
illustrated in FIG. 5. Specifically, the epitaxial wafer
manufacturing apparatus 100 includes a plurality of placement units
2b on which a wafer is placed, a susceptor 2 for which the
plurality of placement units 2b are arranged in tandem in a
circumferential direction, a sealing (top plate) 3 disposed to face
the upper surface of the susceptor 2 so that a reaction space 4 is
formed in a space between the susceptor 2 and the sealing 3, and a
shielding plate 10 disposed to be close to the lower surface of the
sealing 3 to the extent that deposits in a gaseous phase are
prevented from being deposited on the lower surface of the sealing
3. The shielding plate 10 is formed of silicon carbide or the
surface of the shielding plate 10 facing the susceptor 2 is covered
with a silicon carbide film or a pyrolytic carbon film. The
epitaxial wafer manufacturing apparatus 100 forms an epitaxial
layer on a surface of a wafer while supplying a raw material gas
into a chamber 1.
[0100] As the raw material gas, for example, a gas in which silane
(SiH.sub.4) included in a Si source or propane (C.sub.3H.sub.8)
included in a C source can be used. Also, a gas containing hydrogen
(H.sub.2) can be used as a carrier gas.
[0101] The epitaxial wafer manufacturing apparatus 100 according to
the embodiment includes heating devices 6 and 7 that are disposed
on the lower surface side of the susceptor 2 and on the upper
surface side of the sealing and heat wafers places on the placement
units 2b, and includes a gas introduction pipe 5 that has a gas
introduction port through which a raw material gas is introduced
from the middle portion of the upper surface of the sealing 3 to
the reaction space 4 and supplies the raw material gas discharged
from the gas introduction from the inside of the reaction space 4
to the outside thereof.
[0102] The heating devices 6 and 7, which are induction coils, can
heat the sealing 3 through high-frequency induction heating of the
induction coils, heat the shielding plate 10 through radiation heat
from the heated sealing 3, and heat the wafers through radiation
heat from the shielding plate 10.
[0103] In the embodiment, a wafer is configured to be heated using
the heating devices disposed on the lower surface side of the
susceptor 2 and on the upper surface side of the sealing, but the
heating devices may be configured to be disposed only on the lower
surface side of the susceptor 2.
[0104] The heating device of a SiC single crystal substrate is not
limited to the above-described high-frequency induction heating,
but heating devices of resistance heating or the like may be
used.
[0105] The sealing 3 includes a protrusion portion 12 that is
installed in the middle portion of the lower surface to protrude
and be located inside an opening 10b of the shielding plate 10. The
sealing 3 is held by holding members 13 fixed to the gas
introduction pipe 5 via the protrusion portion 12. Due to the
protrusion portion 12, the gas hardly flows toward the gap between
the shielding plate 10 and the sealing 3 from the inner
circumferential side of the shielding plate 10.
[0106] A sealing formed of a carbon material such as graphite or
silicon carbide or a sealing formed such that a substrate of a
carbon material is covered with a film of SiC, pyrolytic carbon,
TaC, or the like can be used as the sealing 3. The sealing 3 is
preferably formed of a material which is hardly sublimated by dust
emission under a high temperature or mutual interaction with the
gas within the chamber.
[0107] The shielding plate 10 is configured to be detachably
mounted within the chamber. In the embodiment, the outer
circumference portion 10a is placed on a holding unit 11 installed
on the inner wall surface of the chamber.
[0108] The shielding plate 10 can be detachably mounted within the
chamber, while avoiding contact between the gas introduction pipe 5
which is at a low temperature to introduce the raw material gas in
a non-resolved state and the inner circumferential portion (the
middle portion in which the opening is formed) of the shielding
plate 10 by holding only the outer circumferential portion of the
shielding plate 10, compared to the shielding plate 10 which is
heated by heating devices at a high temperature.
[0109] The shielding plate 10 is preferably divided into a
plurality of portions. The shielding plate 10 according to the
embodiment is formed by one pair of members 10A and 10B divided as
two portions along the middle line, as illustrated in FIG. 6. In
this case, each of one pair of members 10A and 10B can be placed on
the holding unit 11. At the time of exchange, the members may be
detached one by one from the holding unit 11. Accordingly,
operability is good and a damage risk is reduced at the time of
placement, exchange, and maintenance.
[0110] Also, when the shielding plate 10 is divided into a
plurality of portions, heat stress is alleviated, and thus a curved
state or deformation occurrence is suppressed.
[0111] The shielding plate 10 normally prevents dust (graphite)
occurring from the lower surface of the sealing 3 formed of
graphite from falling to the wafer, thereby reducing a surface
density of triangular defects having a material piece of the
sealing as a starting point. However, when a material piece of the
shielding plate 10 falls to the wafer, a triangular defect having
the material piece of the shielding plate 10 as a starting point is
formed. To suppress the material piece from falling, the shielding
plate 10 is required to be formed of a material which is hardly
sublimated by dust emission under a higher temperature than the
material of the sealing 3 or mutual interaction with the gas within
the chamber. For this reason, a shielding plate formed of silicon
carbide or a shielding plate in which a graphite substrate is
covered with a silicon carbide film or a pyrolytic carbon film is
used as the shielding plate 10.
[0112] The film thickness of the silicon carbide film or the
pyrolytic carbon film is preferably 20 .mu.m or more from the
viewpoint of the suppression of deterioration. Also, the film
thickness is preferably 100 .mu.m or less from the viewpoint of
reduction in stress based on a difference in a coefficient of
thermal expansion with the graphite substrate.
[0113] To reduce an amount of downfall falling on a SiC single
crystal wafer or a SiC epitaxial layer since a SiC film in a
gaseous phase is deposited and the deposited SiC film is peeled
off, at least the lower surface of the shielding plate 10 is
preferably formed of a material with high attachment of the SiC
film. An example of this material includes silicon carbide. Also,
the lower surface of the shielding plate 10 may be covered with a
silicon carbide film.
[0114] In the embodiment, since the shielding plate 10 is required
to receive heat radiation from the sealing 3, be heated, emit the
radiation heat, and heat the wafer, the material of the shielding
plate 10 preferably has high thermal conductivity.
[0115] When the shielding plate 10 is formed of silicon carbide,
the shielding plate 10 can be manufactured by a chemical vapor
deposition (CVD) method, sintering, or the like. However, when a
CVD method is used, a shielding plate formed of a high-purity
material can be manufactured. Since the surface of the shielding
plate 10 on which silicon carbide is deposited has high attachment
of silicon carbide, the surface thereof is preferably roughened by
polishing or the like.
[0116] The thickness of the shielding plate 10 is preferably within
the range of 2 mm to 6 mm from the viewpoint of prevention of
cracking. This is because the shielding plate 10 is easily cracked.
That is, when the thickness is thinner than 2 mm, the shielding
plate 10 is too flexible (bent) and is cracked. When the thickness
is thicker than 6 mm, the shielding plate 10 is also cracked.
[0117] When the sealing is formed of silicon carbide, even the same
material can be resistant to thermal strain by thinning the
thickness of the shielding plate 10 to be thinner than the sealing,
and thus the cracking hardly occurs.
[0118] The plurality of placement units 2b are arranged in tandem
in the circumferential direction on the disk-like susceptor 2 so as
to surround the middle portion of the susceptor 2. A rotary shaft
2a for revolution is mounted in the middle portion of the lower
surface of the susceptor 2. The rotary shaft 2a for revolution is
disposed immediately below the gas introduction pipe 5. A rotary
shaft (not illustrated) for rotation is mounted on each placement
unit 2b.
[0119] In such a configuration, the susceptor 2 resolves each SiC
single crystal wafer by using the gas introduction pipe 5 as a
central axis, and each SiC single crystal wafer itself is rotated
along with each placement unit 2b using the center of the SiC
single crystal wafer as an axis.
[0120] In the SiC epitaxial wafer manufacturing apparatus, since a
cool gas is introduced from the gas introduction pipe 5 disposed at
the middle portion and the induction heat is rarely added to the
middle portion of the susceptor 2, the temperature of the susceptor
2 is generally lower at a portion closer to the middle portion. Due
to this effect, the temperature of the outer circumferential
portion of the rotating placement unit 2b, i.e., the temperature of
the outer circumferential portion of the SiC single crystal wafer
installed on the placement unit 2b, is lowered. For this reason, in
a general susceptor-type epitaxial growth apparatus, the installed
SiC single crystal wafer has a temperature gradient in which the
temperature of the wafer middle portion is the highest and the
temperature decreases toward the wafer outer circumferential
portion. The temperature gradient of the SiC single crystal wafer
causes compressible stress in the middle portion of the SiC single
crystal wafer during epitaxial growth.
[0121] A flange portion 5a protruding in a diameter expansion
direction is installed in a front end portion (lower end portion)
of the gas introduction pipe 5. The flange portion 5a is configured
to flow a raw material gas G discharged vertically downward from
the lower end portion of the gas introduction pipe 5 radially in
the horizontal direction in a space with the facing susceptor
2.
[0122] In the CVD apparatus 100, the raw material gas G can be
supplied in parallel to the in-plane of the SiC single crystal
substrate by flowing the raw material gas G discharged from the gas
introduction pipe 5 radially outward from the inside of the
reaction space 4. Also, the gas unnecessary within the chamber can
be discharged from a discharge port (not illustrated) installed in
a wall of the chamber to the outside of the chamber.
[0123] Here, the sealing 3 is heated at a high temperature by the
foregoing induction coils 7, but the inner circumferential portion
(the middle portion in which the opening 10b is formed) does not
come in contact with the gas introduction pipe 5 which is at a low
temperature to introduce the raw material gas G. Also, the sealing
3 is held in the upward vertical direction since the inner
circumferential portion thereof is placed on the holding member 13
attached to the outer circumferential portion of the gas
introduction pipe 5. The sealing 3 can be moved vertically.
[0124] The temperature gradient of the SiC single crystal wafer
varies due to a flow rate of the gas to be introduced or a change
in the positions of the induction heating coils. In the embodiment,
the flow rate of the gas to be introduced or the positions of the
induction heating coils are preferably adjusted such that the SiC
single crystal wafer has the temperature gradient in which the
temperature is the lowest in the wafer middle portion and the
temperature increases toward the wafer outer circumferential
portion.
[0125] A distance d.sub.1 between the upper surface of the
shielding plate 10 and the lower surface of the sealing 3 is
preferably set within the range of 0.5 mm to 1 mm. This is because
deposits of SiC are prevented from being deposited on the lower
surface of the sealing 3 by the shielding plate 10.
[0126] The shielding plate 10 is disposed to be separate from an
inner wall 1a of the chamber 1, and a separation distance d.sub.2
between an outer circumferential side surface 10c of the shielding
plate 10 and the inner wall 1a of the chamber 1 in the horizontal
direction is preferably within the range of 1.0 mm to 3.0 mm. This
is to prevent the shielding plate 10 from coming into contact with
the wall surface 1a due to thermal expansion at the time of
heating.
[0127] For example, when the shielding plate is formed of silicon
carbide, the separation distance is preferably within the range of
1.0 mm to 2.0 mm.
[0128] A distance d.sub.3 between an inner wall 10d of the opening
10b of the shielding plate 10 and the outer wall of the protrusion
portion 12 is preferably set within the range of 0.5 mm to 1 mm.
This is so that the shielding plate 10 is prevented from coming
into contact with the protrusion portion 12 due to the thermal
expansion at the time of heating and the gas is rarely flowed
toward the space between the shielding plate 10 and the sealing 3
from the inner circumferential side of the shielding plate 10.
[0129] A distance d4 between the inner circumferential surface of
the sealing 3 and the outer circumferential surface of the gas
introduction pipe 5 is preferably set within the range of 0.5 mm or
less. This is so that the gas introduction pipe 5 which is at a low
temperature to introduce the raw material gas G is affected by the
radiation heat from the sealing 3 which is heated at a high
temperature by the foregoing induction coils 7 as little as
possible.
[0130] In the embodiment, as illustrated in FIG. 7, the sealing 3
includes the protrusion portion 12 which is formed from the inner
circumferential portion 3d of the lower surface 3c of the sealing 3
and between the inner wall 10d of the opening 10b of the shielding
plate 10 and an outer wall 5b of the gas introduction pipe 5. The
protrusion portion 12 may be formed integrally with the sealing 3
or may be a member separate from the sealing 3. The protrusion
portion 12 is preferably disposed along the inner wall 10d in the
opening 10b of the shielding plate 10. Only the cross-section of a
part of the protrusion portion is illustrated in FIGS. 5 and 7.
[0131] The protrusion portion 12 can prevent the gas of the film
material in a gaseous phase from penetrating from a gap between the
inner wall 10d in the opening 10b of the shielding plate 10 and the
outer wall 5b of the gas introduction pipe 5 to be deposited on the
sealing 3.
[0132] In the embodiment, the protrusion portion 12 is provided,
but may not be provided.
[0133] The epitaxial wafer manufacturing apparatus 100 according to
the embodiment includes the shielding plate 10. Therefore, even
when a material piece of the sealing 3 falls, the material piece
can be received by the shielding plate 10, and thus can be
prevented from falling on the wafer or the epitaxial layer.
Accordingly, it is possible to reduce a surface density a
triangular defects having the material piece of the sealing 3 as a
starting point in the epitaxial layer. Also, since the lower
surface of the shielding plate 10 is covered with the silicon
carbide film or the pyrolytic carbon film or the shielding plate 10
is formed of silicon carbide, an amount of material pieces falling
from the shielding plate 10 is less compared to the sealing.
[0134] Accordingly, when the epitaxial wafer manufacturing
apparatus is used, it is possible to manufacture the SiC epitaxial
wafer with a lower surface density of triangular defects having a
material piece of an internal member of the chamber as a starting
point compared to a case in which an epitaxial wafer manufacturing
apparatus of the related art is used.
[SiC Epitaxial Wafer Manufacturing Apparatus (Second
Embodiment)]
[0135] An epitaxial wafer manufacturing apparatus according to an
embodiment herein includes a susceptor that includes a wafer
placement unit on which a wafer is placed and a sealing (top plate)
that is disposed to face the upper surface of the susceptor so that
a reaction space is formed between the sealing and the susceptor.
The sealing is formed of silicon carbide or the surface of the
sealing facing the susceptor is covered with a silicon carbide film
or a pyrolytic carbon film, and an epitaxial layer is formed on a
surface of the wafer while a raw material gas is supplied into a
chamber. The epitaxial wafer manufacturing apparatus is different
from the epitaxial wafer manufacturing apparatus according to the
first embodiment in that a shielding plate is not provided.
[0136] In the epitaxial wafer manufacturing apparatus, since
material pieces falling on the wafer from the sealing are reduced,
it is possible to manufacture a SiC epitaxial wafer with a low
surface density of triangular defects having a material piece of an
internal member of the chamber as a starting point.
[0137] In the epitaxial wafer manufacturing apparatus of the
present invention, since the surface of a member (a shielding plate
when a shielding plate is provided, and a sealing when no shielding
plate is provided) facing the susceptor is formed of a silicon
carbide film or a pyrolytic carbon film, a triangular defect having
a material piece of an internal member of the chamber as a starting
point can be reduced. However, other internal members of the
chamber are preferably formed of the material.
[SiC Epitaxial Wafer Manufacturing Method (First Embodiment)]
[0138] An epitaxial wafer manufacturing method according to an
embodiment herein includes a process of manufacturing a SiC
epitaxial wafer using the epitaxial wafer manufacturing apparatus
according to the first embodiment and a process of manufacturing a
subsequent SiC epitaxial wafer after measuring a surface density of
triangular defects having a material piece of an internal member of
a chamber as a starting point in a SiC epitaxial layer of the
previously manufactured SiC epitaxial wafer.
[0139] Since the method includes the process of manufacturing the
surface density of the triangular defects, it is possible to manage
the surface density of the triangular defects having the material
piece of the internal member of the chamber as the starting point
on the SiC epitaxial layer.
<Polishing Process>
[0140] In the polishing process, the 4H-SiC single crystal
substrate remaining on the surface of the wafer in a slice process
is polished until the thickness of a lattice disturbance layer on
the surface of the wafer is 3 nm or less.
[0141] The "lattice disturbance layer" refers to a layer in which a
part of a striped structure or a stripe thereof corresponding to an
atomic layer (lattice) of the SiC single crystal substrate is not
clear in a lattice image (an image in which a crystal lattice can
be confirmed) of a TEM (see Patent Literature 5).
[0142] The polishing process normally includes a plurality of
polishing processes such as rough polishing called lap, precise
polishing called polish, and chemical mechanical polishing
(hereinafter referred to as CMP) which is more precise polishing.
By setting a processing pressure in mechanical polishing before the
CMP to 350 g/cm.sup.2 or less and performing the polishing using
sharpening particles with a diameter of 5 .mu.m or less, the
thickness of a damage layer (not only a damage detectable as the
"lattice disturbance layer" by the TEM but also a portion in which
distortion or the like of the lattice undetectable by the TEM
exists more deeply) is preferably suppressed to 50 nm. Further, a
polishing slurry containing polishing material particles with an
average particle diameter of 10 nm to 150 nm and inorganic acid is
used in the CMP. Here, pH of the polishing slurry at 20.degree. C.
is preferably 2 or less. The polishing material particles are
silica and 1 mass % to 30 mass % thereof is preferably contained.
The inorganic acid is more preferably at least one kind of acid
among hydrochloric acid, nitric acid, phosphoric acid, and sulfuric
acid.
<Cleaning (Gas Etching) Process>
[0143] In the cleaning process, the substrate after the polishing
and convex processing is heated at 1400.degree. C. to 1800.degree.
C. under a hydrogen atmosphere so that the surface is subjected to
cleaning (gas etching).
[0144] The gas etching is performed for 5 minutes to 30 minutes at
a flow rate of a hydrogen gas of 40 slm to 120 slm and at a
pressure of 100 mbar to 250 mbar by maintaining the SiC single
crystal substrate at 1400.degree. C. to 1800.degree. C.
[0145] After the polished SiC single crystal substrate is cleaned,
the substrate is set in an epitaxial growth apparatus, for example,
a plurality of planetary type CVD apparatuses for mass production.
After the hydrogen gas is introduced into the apparatus, the
pressure is adjusted to 100 mbar to 250 mbar. Thereafter, the
temperature of the apparatus is raised so that the substrate
temperature is within the range of 1400.degree. C. to 1600.degree.
C. and is preferably set to be equal to or greater than
1480.degree. C. and equal to or less than 1600.degree. C., and the
gas etching is performed on the surface of the substrate using the
hydrogen gas for 1 minute to 30 minutes. When the gas etching is
performed using the hydrogen gas under the same conditions, an
etching amount is about 0.05 .mu.m to 0.4 .mu.m.
[0146] SiH.sub.4 gas and/or C.sub.3H.sub.8 gas can be added to the
hydrogen gas. In a shallow pit caused in spiral dislocation, short
step bunching incidentally occurs in some cases. By adding
SiH.sub.4 gas with concentration less than 0.009 mol % to the
hydrogen gas and performing the gas etching, Si becomes rich in the
environment of a reactor and the depth of the shallow pit can be
made shallow, thereby suppressing occurrence of the short step
bunching incidental on the shallow pit.
[0147] When the SiH.sub.4 gas and/or the C.sub.3H.sub.8 gas is
added to the hydrogen gas, a hydrogen gas atmosphere is preferably
formed by performing discharging at once before a film forming
(epitaxial growth) process.
<Film Forming (Epitaxial Growth) Process>
[0148] In the film forming (epitaxial growth) process, the SiC film
is allowed to epitaxially grow by supplying the surface of the
substrate after the foregoing cleaning with an amount of
carbon-containing gas and an amount of silicon-containing gas
necessary for the epitaxial growth of silicon carbide at a
predetermined concentration ratio.
[0149] When the temperature of the growth of the epitaxial layer is
higher than the temperature of the cleaning (gas etching), the film
forming process is performed after an increase in the temperature
from the cleaning process. Also, an example of a combination of the
carbon-containing gas and the silicon-containing gas at the
predetermined concentration ratio includes a combination of the
C.sub.3H.sub.8 gas and the SiH.sub.4 gas at a concentration ratio
C/Si of 0.7 to 1.2.
[0150] The carbon-containing gas and the silicon-containing gas are
preferably supplied simultaneously. This is so that the step
bunching is considerably reduced.
[0151] Here, the "simultaneous supply" means that the gases may not
necessarily be supplied at exactly the same time but a difference
between timings of the supply of the gases is within several
seconds.
[0152] The respective flow rates, the pressures, the substrate
temperatures, and the growth temperatures of the SiH.sub.4 gas and
the C.sub.3H.sub.8 gas are 15 sccm to 150 sccm, 3.5 sccm to 60
sccm, 80 mbar to 250 mbar, and greater than 1600.degree. C. and
equal to or less than 1800.degree. C. The growth speed of the SiC
film is within the range of 1 .mu.m to 20 .mu.m per hour. The
uniformity of the off-angle, the film thickness, and the carrier
concentration is determined while the growth speed is controlled.
By introducing nitrogen gas as a doping gas simultaneously with the
start of the forming of the film, the carrier concentration in the
epitaxial layer can be controlled. A method of lowering the
concentration ratio C/Si of the supplied raw material gases and
increasing migration of Si atoms on the growing surface is known as
a method of suppressing the step bunching during the growth. In the
present invention, however, the concentration ratio C/Si is within
the range of 0.7 to 1.2. Normally, the growing epitaxial layer has
a film thickness of about 5 .mu.m to about 20 .mu.m and the carrier
concentration is the range of about 2 to 15.times.10.sup.15
cm.sup.-3.
[0153] The growth temperature is within the range of 1400.degree.
C. to 1800.degree. C., but the lower limit of the growth
temperature is preferably 1600.degree. C. in order to reduce a
stacking fault. Also, the growth speed is preferably faster as the
growth temperature is higher. When the growth temperature is the
same, the growth speed is preferably faster as the off-angle of the
SiC single crystal substrate is larger.
[0154] For example,
[0155] (1) when a 4H-SiC single crystal substrate with an off-angle
of 0.4.degree. to 2.degree. is used, the growth temperature and the
grow speed are preferably adjusted as follows.
[0156] When the growth temperature at which the silicon carbide
film is allowed to epitaxially grow is set within the range of
1600.degree. C. to 1640.degree. C., the growth speed is set within
the range of 1 .mu.m/h to 3 .mu.m/h.
[0157] When the growth temperature is set within the range of
1640.degree. C. to 1700.degree. C., the growth speed is set within
the range of 3 .mu.m/h to 4 .mu.m/h.
[0158] When the growth temperature is set within the range of
1700.degree. C. to 1800.degree. C., the growth speed is set within
the range of 4 .mu.m/h to 10 .mu.m/h.
[0159] (2) When a 4H-SiC single crystal substrate with an off-angle
of 2.degree. to 5.degree. is used, the growth temperature and the
growth speed are preferably adjusted as follows.
[0160] When the growth temperature at which the silicon carbide
film is allowed to epitaxially grow is set within the range of
1600.degree. C. to 1640.degree. C., the growth speed is set within
the range of 2 .mu.m/h to 4 .mu.m/h.
[0161] When the growth temperature is set within the range of
1640.degree. C. to 1700.degree. C., the growth speed is set within
the range of 4 .mu.m/h to 10 .mu.m/h.
[0162] When the growth temperature is set within the range of
1700.degree. C. to 1800.degree. C., the growth speed is set within
the range of 10 .mu.m/h to 20 .mu.m/h.
<Temperature Dropping Process>
[0163] In a temperature dropping process, the supply of the
carbon-containing gas and the silicon-containing gas (for example,
a SiH.sub.4 gas and a C.sub.3H.sub.8 gas) is preferably stopped
simultaneously. This is so that degradation in morphology is
efficiently suppressed. After the stop, the substrate temperature
is maintained until the carbon-containing gas and the
silicon-containing gas are discharged. Thereafter, the temperature
is dropped.
<Processes of Measuring Surface Density of Triangular Defect and
Replacing Member>
[0164] Regularly (for each production lot, every plurality of
production lots, or the like) or irregularly, the surface density
of the triangular defects having the material piece of the internal
member of the chamber as the starting point on the SiC epitaxial
layer of the SiC epitaxial wafer is measured. After the
measurement, a subsequent SiC epitaxial wafer is manufactured.
[0165] The surface density of the triangular defects having the
material piece of the internal member of the chamber as the
starting point can be obtained, for example, by shifting the
position of focus from the surface of the epitaxial layer of the
SiC epitaxial wafer to an interface side (film depth direction)
between the epitaxial layer and the SiC single crystal substrate,
finding the triangular defect having the material piece of the
internal member of the chamber as the starting point, and measuring
the triangular defect using an optical microscope. In the
embodiment, kinds (types) of triangular defects increasing due to
the repetition of the forming of the film can be considered to be
only the triangular defect having the material piece of the
internal member of the chamber as the starting point and the
triangular defect having the downfall as the starting point.
Normally, the starting point of the triangular defect having the
downfall as the starting point is clear, but the starting point of
the triangular defect having the material piece of the internal
member of the chamber as the starting point is unclear. By
identifying the triangular defect having the downfall as the
starting point and managing an increase in its surface density
based on the characteristics, it is possible to manufacture the SiC
epitaxial wafer with a low surface density of the triangular
defects having the material piece of the internal member of the
chamber as the starting point. When the density of the triangular
defects having the material piece of the internal member of the
chamber as the starting point is desired to be measured and managed
more precisely, the composition of a foreign material present in
the front of the triangular defect is analyzed using energy
dispersive X-ray spectroscopy or the like.
[0166] When the surface density of the triangular defects having
the material piece of the internal member of the chamber as the
starting point is greater than a predetermined density as the
result of the foregoing measurement, it is desirable to replace the
shielding plate 10 and manufacture a subsequent SiC epitaxial
wafer. For example, when the surface density of the triangular
defects in the previously manufactured SiC epitaxial wafer is about
0.25 pieces/cm.sup.2, the SiC epitaxial wafer of which the surface
density of the triangular defects is reliably equal to or less than
0.5 pieces/cm.sup.2 can be manufactured by replacing the shielding
plate 10 and manufacturing the subsequent SiC epitaxial wafer.
[SiC Epitaxial Wafer Manufacturing Method (Second Embodiment)]
[0167] An epitaxial wafer manufacturing method according to an
embodiment herein includes a process of manufacturing a SiC
epitaxial wafer using the epitaxial wafer manufacturing apparatus
according to the second embodiment and a process of manufacturing a
subsequent SiC epitaxial wafer after measuring a surface density of
triangular defects having a material piece of a internal member of
a chamber as a starting point in a SiC epitaxial layer of the
previously manufactured SiC epitaxial wafer.
[0168] Since the method includes the process of measuring the
surface density of the triangular defects, it is possible to manage
the surface density of the triangular defects having the material
piece of the internal member of the chamber as the starting point
on the SiC epitaxial layer.
[0169] In the epitaxial wafer manufacturing method according to the
embodiment, it is also possible to manufacture each SiC epitaxial
wafer, as in the first embodiment.
[0170] Also, the process of measuring the surface density of the
triangular defects can also be performed as in the first
embodiment.
[0171] When the surface density of the triangular defects having
the material piece of the internal member of the chamber as the
starting point is greater than a predetermined density as the
result of the foregoing measurement, it is desirable to replace the
sealing 3 and manufacture a subsequent SiC epitaxial wafer. For
example, when the surface density of the triangular defects in the
previously manufactured SiC epitaxial wafer is about 0.25
pieces/cm.sup.2, the SiC epitaxial wafer of which the surface
density of the triangular defects is reliably equal to or less than
0.5 pieces/cm.sup.2 can be manufactured by replacing the sealing 3
and manufacturing the subsequent SiC epitaxial wafer.
EXAMPLES
[0172] Hereinafter, the advantageous effects of the present
invention will be described specifically according to examples. The
present invention is not limited to these examples.
Example
[0173] In an example herein, the SiC epitaxial wafer manufacturing
apparatus and the SiC epitaxial wafer manufacturing method
according to the first embodiment were realized.
[0174] In the SiC epitaxial wafer manufacturing apparatus
illustrated in FIG. 5, the sealing formed of graphite and the
shielding plate (with a diameter of 371 mm and a thickness of 4 mm)
which was divided into two portions illustrated in FIG. 6 and in
which a graphite substrate was covered with a silicon carbide film
were used. The shielding plate was disposed to be a distance
(d.sub.1) of 0.5 mm from the sealing.
[0175] A SiC single crystal wafer which had a Si surface in which
the c surface ((0001) surface) was inclined at 4.degree. in the
<11-20> direction as a main surface, a diameter of 3 inches
(76.2 mm), and a thickness of 350 .mu.m was used as the 4H-SiC
single crystal wafer.
[0176] Next, as preprocessing, organic solvent cleaning, acid and
alkali cleaning, and sufficient water washing were performed on the
SiC single crystal wafer.
[0177] The SiC single crystal wafer was placed on the wafer
placement unit, vacuum discharging was performed, and then hydrogen
gas was introduced so that an atmosphere was adjusted to a
reduced-pressure atmosphere of 200 mbar. Thereafter, a temperature
was raised up to 1570.degree. C., growth was performed at a growth
speed of 5 .mu.m/h for 1 hour, and a SiC epitaxial layer with a
thickness of 5 .mu.m was formed to manufacture the SIC epitaxial
wafer.
[0178] Hydrogen was used as the carrier gas, a mixed gas of
SiH.sub.4 and C.sub.3H.sub.8 was used as the raw material gas, and
N.sub.2 was supplied as a dopant.
[0179] The SiC epitaxial wafer was repeatedly manufactured under
the above conditions without replacing the internal member of the
chamber. FIGS. 8A and 8B are diagrams illustrating a candela image
of the 2.sup.nd production lot and a candela image of the 80.sup.th
production lot. Dots shown with a black spot shape indicate the
triangular defects.
[0180] The number of all of the kinds of triangular defects was
measured from the candela images and the surface densities of all
of the kinds of triangular defects were obtained. By a method of
performing observation by shifting the focus using an optical
microscope, the number of triangular defects having the material
piece of the internal member of the chamber as the starting point
was measured and the surface density of the triangular defects was
obtained.
[0181] The surface density of the triangular defects of the SiC
epitaxial wafer of the 2.sup.nd production lot was 0.5
pieces/cm.sup.2 and the surface density of the triangular defects
having the material piece of the internal member of the chamber as
the starting point was 0 pieces/cm.sup.2 in this surface
density.
[0182] The surface density of the triangular defects of the SiC
epitaxial wafer of the 80.sup.th production lot was 2
pieces/cm.sup.2 and the surface density of the triangular defects
having the material piece of the internal member of the chamber as
the starting point was 0.5 pieces/cm.sup.2 in this surface
density.
[0183] The surface density of the triangular defects of the SiC
epitaxial wafer of the 20.sup.th production lot was 1
piece/cm.sup.2 and the surface density of the triangular defects
having the material piece of the internal member of the chamber as
the starting point was 0 pieces/cm.sup.2 in this surface
density.
[0184] FIG. 8C is a diagram illustrating a candela image of the
production lot manufactured immediately after the placement of the
shielding plate with a new shielding plate after the 80.sup.th SiC
epitaxial wafer is manufactured. The surface density of the
triangular defects was 0.5 pieces/cm.sup.2 and the surface density
of the triangular defects having the material piece of the internal
member of the chamber as the starting point was 0 pieces/cm.sup.2
in this surface density.
[0185] From this result, it can be confirmed that the surface
density of the triangular defects having the material piece of the
internal member of the chamber as the starting point can be reduced
by replacing the shielding plate with a new shielding plate.
Comparative Example 1
[0186] A first comparative example was different from the example
in that a shielding plate in which the graphite substrate was
covered with a tantalum carbide film was used in the SiC epitaxial
wafer manufacturing apparatus used in the example and the other
manufacturing conditions were the same.
[0187] The SiC epitaxial wafer was repeatedly manufactured under
the condition without replacing the internal member of the chamber.
FIG. 9A is a diagram illustrating a candela image of the 20.sup.th
production lot.
[0188] The surface density of all of the kinds of triangular
defects of the SiC epitaxial wafer was 2 pieces/cm.sup.2 and the
surface density of the triangular defects having the material piece
of the internal member of the chamber as the starting point was 1
piece/cm.sup.2 in this surface density.
[0189] Although the number of repetitions of the manufacturing the
SiC epitaxial wafer is the same as that of the case of the example,
both of the surface density of all of the kinds of triangular
defects and the surface density of the triangular defects having
the material piece of the internal member of the chamber as the
starting point were higher than those of the example.
[0190] From this result, it can be understood that the surface
density of all of the kinds of triangular defects and the surface
density of the triangular defects having the material piece of the
internal member of the chamber as the starting point can be reduced
using the plate in which the graphite substrate is covered with the
silicon carbide film as the shielding plate compared to when the
plate in which the graphite substrate is covered with the tantalum
carbide film is used.
Comparative Example 2
[0191] A second comparative example was different from the example
in that a shielding plate in which the shielding plate was not used
in the SiC epitaxial wafer manufacturing apparatus used in the
example and the other manufacturing conditions were the same.
[0192] The SiC epitaxial wafer was repeatedly manufactured under
the condition without replacing the internal member of the chamber.
FIG. 9B is a diagram illustrating a candela image of the 20.sup.th
production lot.
[0193] The surface density of all of the kinds of triangular
defects of the SiC epitaxial wafer was 100 pieces/cm.sup.2 and the
surface density of the triangular defects having the material piece
of the internal member of the chamber as the starting point was 90
pieces/cm.sup.2 in this surface density.
[0194] Although the number of repetitions of the manufacturing the
SiC epitaxial wafer is the same as that of the case of the example,
both of the surface density of all of the kinds of triangular
defects and the surface density of the triangular defects having
the material piece of the internal member of the chamber as the
starting point were considerably higher than those of the
example.
[0195] From this result, it can be understood that the surface
density of all of the kinds of triangular defects and the surface
density of the triangular defects having the material piece of the
internal member of the chamber as the starting point can be
considerably reduced using the shielding plate.
INDUSTRIAL APPLICABILITY
[0196] A SiC epitaxial wafer, a SiC epitaxial wafer manufacturing
method, and a SiC epitaxial wafer manufacturing apparatus according
to the present invention can be used to manufacture a SiC epitaxial
wafer with a low surface density of triangular defects having a
material piece of a internal member of a chamber as a starting
point.
REFERENCE SIGNS LIST
[0197] 1 Chamber [0198] 1a Inner wall [0199] 2 Susceptor [0200] 2b
Placement unit [0201] 3 Sealing (top plate) [0202] 4 Reaction space
[0203] 6, 7 Induction coil (a heating device) [0204] 10 Shielding
plate [0205] 10a Outer circumferential portion [0206] 10A, 10B
Shielding plate [0207] 11 Holding unit [0208] 100 CVD apparatus
(epitaxial wafer manufacturing apparatus)
* * * * *