U.S. patent number 10,385,473 [Application Number 15/564,080] was granted by the patent office on 2019-08-20 for seed crystal holder for pulling up single crystal and method of manufacturing silicon single crystal using the same.
This patent grant is currently assigned to SUMCO CORPORATION. The grantee listed for this patent is SUMCO CORPORATION. Invention is credited to Eiichi Kawasaki.
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United States Patent |
10,385,473 |
Kawasaki |
August 20, 2019 |
Seed crystal holder for pulling up single crystal and method of
manufacturing silicon single crystal using the same
Abstract
A seed crystal holder for pulling up a single crystal is made of
a carbon fiber-reinforced carbon composite material, and has a
substantially cylindrical shape with a hollow space having a shape
matching an outer shape of a substantially rod-shaped seed crystal.
A direction of carbon fibers at a part in contact with at least an
outer peripheral surface of the seed crystal has isotropy as viewed
from a central axis of the hollow space.
Inventors: |
Kawasaki; Eiichi (Tokyo,
JP) |
Applicant: |
Name |
City |
State |
Country |
Type |
SUMCO CORPORATION |
Tokyo |
N/A |
JP |
|
|
Assignee: |
SUMCO CORPORATION (Tokyo,
JP)
|
Family
ID: |
57072606 |
Appl.
No.: |
15/564,080 |
Filed: |
February 18, 2016 |
PCT
Filed: |
February 18, 2016 |
PCT No.: |
PCT/JP2016/054653 |
371(c)(1),(2),(4) Date: |
October 03, 2017 |
PCT
Pub. No.: |
WO2016/163161 |
PCT
Pub. Date: |
October 13, 2016 |
Prior Publication Data
|
|
|
|
Document
Identifier |
Publication Date |
|
US 20180135201 A1 |
May 17, 2018 |
|
Foreign Application Priority Data
|
|
|
|
|
Apr 9, 2015 [JP] |
|
|
2015-079864 |
|
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
C30B
29/06 (20130101); C30B 15/32 (20130101); C04B
35/83 (20130101); B32B 18/00 (20130101); C30B
15/007 (20130101); C04B 2237/765 (20130101); C04B
2237/84 (20130101); C04B 2237/385 (20130101); C04B
2235/5268 (20130101) |
Current International
Class: |
C30B
15/32 (20060101); B32B 18/00 (20060101); C30B
15/00 (20060101); C30B 29/06 (20060101); C04B
35/83 (20060101) |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
|
|
|
|
|
|
|
09295889 |
|
Nov 1997 |
|
JP |
|
H09-295889 |
|
Nov 1997 |
|
JP |
|
H09-315883 |
|
Dec 1997 |
|
JP |
|
H11-116378 |
|
Apr 1999 |
|
JP |
|
H11-292689 |
|
Oct 1999 |
|
JP |
|
Other References
Search Report issued in International Bureau of WIPO Patent
Application No. PCT/JP2016/054653, dated Mar. 29, 2016. cited by
applicant.
|
Primary Examiner: Qi; Hua
Attorney, Agent or Firm: Greenblum & Bernstein,
P.L.C.
Claims
What is claimed is:
1. A seed crystal holder for pulling up a single crystal that is
made of a carbon fiber-reinforced carbon composite material and
that has a substantially cylindrical shape with a hollow space
having a shape matching the outer shape of a substantially
rod-shaped seed crystal, including a core part in which a direction
of carbon fibers has isotropy as viewed from a center axis of the
hollow space; and a clad part in which the direction of the carbon
fibers has anisotropy as viewed from the center axis of the hollow
space, wherein the core part is provided at least at a part
contacting an outer peripheral surface of the seed crystal.
2. The seed crystal holder as claimed in claim 1, wherein the
direction of the carbon fibers constituting the core part has a
circumferential direction component.
3. The seed crystal holder as claimed in claim 2, wherein the
direction of the carbon fibers constituting the core part has a
component parallel to the center axis.
4. The seed crystal holder as claimed in claim 1, comprising: a
cylindrical upper section having a first hole diameter, a
cylindrical intermediate section positioned below the cylindrical
upper section and being gradually reduced in diameter from the
first hole diameter to a second hole diameter, and a cylindrical
lower section positioned below the cylindrical intermediate section
and having the second hole diameter, wherein the core part is
provided at least in an inner peripheral side region of the
cylindrical intermediate section, and the clad part is provided in
a region other than a formation region of the core part.
5. The seed crystal holder as claimed in claim 4, wherein the core
part is provided in the cylindrical intermediate section and
cylindrical lower section, and the clad part is provided in the
cylindrical upper section.
6. The seed crystal holder as claimed in claim 4, wherein the core
part is provided in the inner peripheral side regions of the
respective cylindrical upper section, cylindrical intermediate
section, and cylindrical lower section, and the clad part is
provided in the outer peripheral side regions of the respective
cylindrical upper section, cylindrical intermediate section, and
cylindrical lower section.
7. The seed crystal holder as claimed in claim 1, wherein the core
part is removable from the clad part.
Description
TECHNICAL FIELD
The present invention relates to a seed crystal holder for
pulling-up a single crystal, and more particularly to a seed
crystal holder for pulling-up a single crystal used in
manufacturing a silicon single crystal by the Czochralski method
(hereinafter, referred to as CZ method). The present invention also
relates to a method of manufacturing a silicon single crystal using
such a seed crystal holder.
BACKGROUND ART
Most of the silicon single crystals as materials for silicon wafers
are manufactured by the CZ method. In the CZ method, a seed crystal
is dipped into a silicon melt contained in a quartz crucible and
slowly pulled up while rotating the seed crystal and quartz
crucible to grow a silicon single crystal having the same crystal
orientation as that of the seed crystal at a lower end of the seed
crystal.
Recently, along with an increase in the size of the silicon single
crystal being pulled up, the strength of a graphite seed crystal
holder (seed chuck) for holding a seed crystal has become a
problem. When the strength of the seed crystal holder is
insufficient, the holder itself may not withstand the heavy weight
of the silicon single crystal and thus may finally break, causing
the silicon single crystal to fall off.
To increase the strength of the seed crystal holder, Patent
Document 1 proposes a carbon fiber cloth reinforced graphite seed
crystal holder. This seed crystal holder has a structure in which
carbon fibers are wound in the peripheral direction at least at its
lower peripheral portion and arranged in the vertical direction at
the remaining portion thereof. Further, Patent Documents 2 and 3
propose a method of holding a seed crystal while keeping it
unbroken by interposing a cushioning material between the tapered
portion of the seed crystal and the surface of the seed crystal
holder. Further, Patent Document 4 discloses a method of
suppressing SiC reaction by forming a coating of pyrolytic carbon
on the surface of the seed crystal holder formed of a carbon
fiber-reinforced composite material to improve durability of the
seed crystal holder.
CITATION LIST
[Patent Document]
[Patent Document 1] Japanese Patent Application Laid-Open No.
H09-315883
[Patent Document 2] Japanese Patent Application Laid-Open No.
H11-116378
[Patent Document 3] Japanese Patent Application Laid-Open No.
H11-292689
[Patent Document 4] Japanese Patent Application Laid-Open No.
H09-295889
SUMMARY OF THE INVENTION
Problems to be Solved by the Invention
However, in the conventional seed crystal holder described in
Patent Document 1, the direction of the carbon fibers in the
horizontal cross section is straight in one direction. Thus, as
illustrated in FIG. 9, at portions A and C where the inner
peripheral surface S.sub.1 of a seed crystal holder 8 is parallel
to the direction of carbon fibers 8f, an inner peripheral surface
S.sub.1 is likely to be deform, and compression stress to be
applied to the outer peripheral surface of the seed crystal is
small; while at portions B and D where the inner peripheral surface
S.sub.1 of the seed crystal holder 8 is substantially perpendicular
to the direction of the carbon fibers 8f, an inner peripheral
surface S.sub.1 is unlikely to deform, and compression stress to be
applied to the outer peripheral surface of the seed crystal is
large. Thus, when the stress that the outer peripheral surface of
the seed crystal receives from the inner peripheral surface of the
seed crystal holder differs between the part parallel to the fiber
direction (X-direction) and the part perpendicular to the fiber
direction (Y-direction), the stress may concentrate on a specific
part of the seed crystal to break the seed crystal. Further, the
method described in Patent Documents 2 and 3 must separately
prepare the cushioning material, so that not only extra mounting
work is required, but also effects brought about by the cushioning
material are insufficient.
The breakage of the seed crystal due to the stress concentration is
a new problem emerged in the pulling-up of the silicon single
crystal having a diameter of 450 mm. In pulling-up of the silicon
single crystal having a diameter of 300 mm whose crystal weight is
not as heavy as that, the seed crystal is hardly broken at a part
contacting the seed crystal holder. However, in the pulling-up of
the silicon single crystal having a diameter of 450 mm, the crystal
weight sometimes exceeds 1000 kg, which is so heavy as highlighting
the above problem, and hence, early resolution of the problem is
desired.
Means for Solving the Problems
It is therefore an object of the present invention to provide a
seed crystal holder for pulling up a single crystal capable of
preventing stress concentration on a specific part of the seed
crystal and enhancing the strength thereof in the vertical
direction. Another object of the present invention is to provide a
safe and highly reliable silicon single crystal manufacturing
method using the seed crystal holder.
To solve the above problems, a seed crystal holder for pulling up a
single crystal according to a first aspect of the present invention
is made of a carbon fiber-reinforced carbon composite material and
has a substantially cylindrical shape with a hollow space having a
shape matching an outer shape of a substantially rod-shaped seed
crystal, wherein at least the direction of carbon fibers at a part
contacting at least an outer peripheral surface of the seed crystal
has isotropy as viewed from the center axis of the hollow
space.
According to the present invention, it is possible to prevent
stress concentration on a specific part of the outer peripheral
surface of the seed crystal that contacts the seed crystal
holder.
In the present invention, the direction of the carbon fibers at the
part contacting the outer peripheral surface of the seed crystal
has preferably a circumferential direction component. With this
configuration, the entire inner peripheral surface of the hollow
space of the seed crystal holder is parallel to the direction of
the carbon fibers in a horizontal cross section, so that the fiber
structure of the carbon fibers can be made isotropic.
In the present invention, the direction of the carbon fibers at the
part contacting the outer peripheral surface of the seed crystal
preferably further has a component parallel to the center axis.
With this configuration, when, for example, the carbon fibers are
obliquely wound in a crisscrossed form, the carbon fibers include a
fiber component parallel to the axial direction, so that the
tensile strength of the seed crystal holder in the axial direction
can be enhanced.
In the present invention, it is preferable that the seed crystal
has a tapered section having a gradually reduced diameter, that the
hollow space has an inner peripheral surface brought into surface
contact with the tapered section, and that the direction of the
carbon fibers at a part constituting the inner peripheral surface
has isotropy as viewed from the center axis of the hollow space.
When the direction of the carbon fibers included in a part of the
inner peripheral surface of the hollow space that is brought into
surface contact with the tapered surface of the seed crystal has
isotropy as viewed from the center axis of the hollow space as
described above, it is possible to prevent stress concentration on
a specific part of the outer peripheral surface of the seed crystal
that contacts the seed crystal holder.
In the present invention, the direction of the carbon fibers
constituting the entire seed crystal holder preferably has isotropy
as viewed from the center axis of the hollow space. This
configuration, which is simple in structure, can facilitate the
manufacture of the seed crystal holder.
In the present invention, the direction of the carbon fibers at a
part other than that contacts the outer peripheral surface of the
seed crystal preferably has anisotropy as viewed from the center
axis of the hollow space. With this configuration, it is possible
to enhance tensile strength in the axial direction and thus to
improve mechanical strength of the seed crystal holder.
A seed crystal holder for pulling up a single crystal according to
a second aspect of the present invention is made of a carbon
fiber-reinforced carbon composite material and has a substantially
cylindrical shape with a hollow space having a shape matching an
outer shape of a substantially rod-shaped seed crystal, the seed
crystal holder includes a core part in which the direction of
carbon fibers has isotropy as viewed from the center axis of the
hollow space and a clad part in which the direction of the carbon
fibers has anisotropy as viewed from the center axis of the hollow
space, wherein the core part is provided at least at a part
contacting an outer peripheral surface of the seed crystal.
According to the present invention, it is possible to prevent
stress concentration on a specific part of the outer peripheral
surface of the seed crystal that contacts the seed crystal
holder.
In the present invention, the direction of the carbon fibers
constituting the core part preferably has a circumferential
direction component. With this configuration, the entire inner
peripheral surface of the hollow space of the seed crystal holder
is parallel to the direction of the carbon fibers in a horizontal
cross section, so that the fiber structure of the carbon fibers can
be made isotropic.
In the present invention, the direction of the carbon fibers
constituting the core part preferably has a component parallel to
the center axis. With this configuration, the carbon fibers include
a fiber component parallel to the axial direction, so that tensile
strength of the seed crystal holder in the axial direction can be
enhanced.
The seed crystal holder according to the present invention
preferably includes a cylindrical upper section having a first hole
diameter, a cylindrical intermediate section positioned below the
cylindrical upper section and being gradually reduced in diameter
from the first hole diameter to a second hole diameter, and a
cylindrical lower section positioned below the cylindrical
intermediate section and having the second hole diameter. The core
part is preferably provided at least in an inner peripheral side
region of the cylindrical intermediate section. The clad part is
preferably provided in a region other than the formation region of
the core part. When the core part is provided at least in the inner
peripheral side region of the cylindrical intermediate section as
described above, it is possible to prevent stress concentration on
a specific part of the outer peripheral surface of the seed crystal
that contacts the seed crystal holder.
In the present invention, it is preferable that the core part is
provided in the cylindrical intermediate section and cylindrical
lower section, and the clad part is provided in the cylindrical
upper section. With this configuration, separately molded core part
and clad part can be integrated with each other through
carbonization or can mechanically be connected using a pin or a
bolt. This facilitates the manufacture of the seed crystal holder
and can lead to a reduction in manufacturing cost and improvement
in processing accuracy.
In the present invention, it is preferable that the core part is
provided in the inner peripheral side regions of the respective
cylindrical upper section, cylindrical intermediate section, and
cylindrical lower section, and the clad part is provided in the
outer peripheral side regions of the respective cylindrical upper
section, cylindrical intermediate section, and cylindrical lower
section. With this configuration, the clad part can be formed by
winding carbon fiber cloth around a molded product of the
cylindrical core part, thereby facilitating the processing. Thus,
it is possible to achieve a reduction in manufacturing cost and
improvement in processing accuracy.
In the present invention, the core part is preferably removable
from the clad part. With this configuration, the core part and clad
part can be separately manufactured, making a manufacturing process
very simple. Further, the core part and clad part can be separately
replaced with new ones, thereby achieving a reduction in component
cost.
A seed crystal holder for pulling up a single crystal according to
a third aspect of the present invention is made of a carbon
fiber-reinforced carbon composite material and has a substantially
cylindrical shape with a hollow space having a shape matching an
outer shape of a substantially rod-shaped seed crystal, the seed
crystal holder includes a core part in which the direction of
carbon fibers has isotropy as viewed from the center axis of the
hollow space and a clad part in which the direction of the carbon
fibers has isotropy as viewed from the center axis of the hollow
space, wherein the direction of the carbon fibers constituting the
core part has a circumferential direction component, the direction
of the carbon fibers constituting the clad part has both a
circumferential direction component and a component parallel to the
center axis, the core part is provided at least at a part
contacting the outer peripheral surface of the seed crystal, and
the clad part is provided in a region other than the formation
region of the core part.
According to the present invention, it is possible to prevent
stress concentration on a specific part of the outer peripheral
surface of the seed crystal that contacts the seed crystal
holder.
A method of manufacturing silicon single crystal according to the
present invention is characterized in that it pulls up a silicon
single crystal having a diameter of 450 mm or more by CZ method
using the above-mentioned seed crystal holder of the present
invention.
Advantages of the Invention
According to the present invention, it is possible to provide a
seed crystal holder capable of preventing stress concentration on
the seed crystal and enhancing strength in the vertical direction.
Further, according to the present invention, it is possible to
provide a safe and highly reliable silicon single crystal
manufacturing method.
BRIEF DESCRIPTION OF DRAWINGS
FIGS. 1A and 1B are views each illustrating a structure of a seed
crystal holder for pulling-up a single crystal according to a first
embodiment of the present invention, wherein FIG. 1A is a vertical
cross-sectional view, and FIG. 1B is a horizontal cross-sectional
view taken along line A-A' of FIG. 1A;
FIGS. 2A and 2B are views each illustrating a structure of a seed
crystal holder for pulling-up a single crystal according to a
second embodiment of the present invention, wherein FIG. 2A is a
vertical cross-sectional view, and FIG. 2B is a horizontal
cross-sectional view taken along line A-A' of FIG. 2A;
FIGS. 3A and 3B are views each illustrating a structure of a seed
crystal holder for pulling-up a single crystal according to a third
embodiment of the present invention, wherein FIG. 3A is a vertical
cross-sectional view, and FIG. 3B is a horizontal cross-sectional
view taken along line A-A' of FIG. 3A;
FIGS. 4A and 4B are views each illustrating a structure of a seed
crystal holder for pulling-up a single crystal according to a
fourth embodiment of the present invention, wherein FIG. 4A is a
vertical cross-sectional view, and FIG. 4B is a horizontal
cross-sectional view taken along line A-A' of FIG. 4A;
FIGS. 5A and 5B are views each illustrating a structure of a seed
crystal holder for pulling-up a single crystal according to a fifth
embodiment of the present invention, wherein FIG. 5A is a vertical
cross-sectional view, and FIG. 5B is a horizontal cross-sectional
view taken along line A-A' of FIG. 5A;
FIGS. 6A and 6B are views each illustrating a structure of a seed
crystal holder for pulling-up a single crystal according to a sixth
embodiment of the present invention, wherein FIG. 6A is a vertical
cross-sectional view, and FIG. 6B is a horizontal cross-sectional
view taken along line A-A' of FIG. 6A;
FIGS. 7A and 7B are views each illustrating a structure of a seed
crystal holder for pulling-up a single crystal according to a
seventh embodiment of the present invention, wherein FIG. 7A is a
vertical cross-sectional view, and FIG. 7B is a horizontal
cross-sectional view taken along line A-A' of FIG. 7A;
FIG. 8 is a cross-sectional view illustrating an example of the
structure of a silicon single crystal pulling-up apparatus and
FIG. 9. is a schematic horizontal cross-sectional view illustrating
a structure of a conventional seed crystal holder for pulling-up
single crystal.
DETAILED DESCRIPTION OF THE EMBODIMENTS
Preferred embodiments of the present invention will be described in
detail below with reference to the accompanying drawings.
FIGS. 1A and 1B are views each illustrating a structure of a seed
crystal holder for pulling-up a single crystal according to a first
embodiment of the present invention. FIG. 1A is a vertical
cross-sectional view, and FIG. 1B is a horizontal cross-sectional
view taken along line A-A' of FIG. 1A.
As illustrated in FIGS. 1A and 1B, a seed crystal holder 1 is a
substantially cylindrical member made of a carbon fiber-reinforced
carbon composite material (C/C composite), and a seed crystal 9 is
inserted into a hollow space 10h to be held. A lower end section 9d
of the seed crystal 9 held by the seed crystal holder 1 protrudes
downward from the lower end of the seed crystal holder 1, and the
seed crystal 9 is pulled up while the lower end section 9d is
dipped in a silicon melt, whereby a silicon single crystal is
grown. The vertical direction of the seed crystal holder 1 is
defined according to a normal use state.
The seed crystal 9 is formed into an elongated rod shape
(substantially columnar shape) and has an upper section 9a having a
relatively large diameter R.sub.1, a tapered section 9b having a
gradually reduced diameter, and a lower section 9c having a
relatively small diameter R.sub.2 (R.sub.2<R.sub.1). The
diameters of the respective upper section 9a and lower section 9c
are constant. The lower section 9c of the seed crystal 9 has a
length long enough to protrude from the lower end of the seed
crystal holder 1. It is possible to safely pull up a large-diameter
and large-weight silicon single crystal 9 for, e.g., 450 mm wafer
by using as thick a seed crystal 9 as possible. In case of
pulling-up a large-weight silicon single crystal, the effect of the
present invention is remarkable because the influence of stress
concentration that the seed crystal 9 receives from the seed
crystal holder 1 is large.
The seed crystal holder 1 has a cylindrical upper section 10a
having a larger hole diameter than the diameter R.sub.1 of the
upper section 9a of the seed crystal 9, a cylindrical intermediate
section 10b having a gradually reduced hole diameter, and a
cylindrical lower section 10c having a hole diameter smaller than
the diameter R.sub.1 of the upper section 9a of the seed crystal 9
and larger than the diameter R.sub.2 of the lower section 9c. The
hollow space 10h has a shape matching the outer shape of the seed
crystal 9 and extends in the vertical direction to penetrate the
seed crystal holder 1. A thread groove 10d is formed in the inner
peripheral surface of the seed crystal holder 1 at the upper end
portion of the cylindrical upper section 10a, and the distal end
portion of a pulling-up shaft of a silicon single crystal
pulling-up apparatus can be screwed to the thread groove 10d.
The inner peripheral surface of the cylindrical intermediate
section 10b has a tapered surface corresponding to the inclined
angle of the tapered section 9b of the seed crystal 9. By making
the taper angle of the cylindrical intermediate section 10b
substantially the same as the taper angle of the tapered section 9b
of the seed crystal 9, the outer peripheral surface of the seed
crystal 9 can be brought into surface contact with the inner
peripheral surface of the hollow space 10h of the seed crystal
holder 1, thereby widening a contact range between the seed crystal
9 and the seed crystal holder 1. The larger the weight of a single
crystal to be crystallized at the lower end of the seed crystal 9
is, the larger the pressure that the tapered section 9b receives
from the inner peripheral surface of the seed crystal holder 1
becomes; however, by widening the surface contact range, stress to
be applied to the seed crystal 9 can be widely dispersed to thereby
avoid stress concentration on a specific part.
The inner peripheral tapered surface of the cylindrical
intermediate section 10b is more preferably a curved surface
slightly bulging inward. By thus gently curving the inner
peripheral surface of the cylindrical intermediate section 10b, it
is possible to surely bring the inner peripheral surface of the
cylindrical intermediate section 10b contact with the tapered
section 9b of the seed crystal 9 and thus to reliably support the
seed crystal 9.
A carbon fiber-reinforced carbon composite material is used for the
seed crystal holder 1. The carbon fiber-reinforced carbon composite
material is obtained by applying carbonization (graphitization)
treatment to a matrix in which carbon fibers are impregnated with
resin or pitch and can improve mechanical strength while assuming
the characteristics of graphite.
As illustrated in FIG. 1B, carbon fibers 10f of the seed crystal
holder 1 is oriented in the circumferential direction in a
horizontal cross section perpendicular to a center axis Z and has
isotropy as viewed from the center axis Z. As illustrated in FIG.
9, when the direction of the carbon fibers in the horizontal cross
section is straight in one direction, of the outer peripheral
surface (tapered surface) of the seed crystal 9 contacting the
inner peripheral surface of the hollow space 10h of seed crystal
holder, surfaces (portions B and D) perpendicular to the fiber
direction experience larger stress concentration than surfaces
(portions A and C) parallel to the fiber direction do, so that the
seed crystal 9 may be broken therefrom. However, the inner
peripheral surface of the hollow space 10h of the seed crystal
holder 1 according to the present embodiment is parallel to the
direction of the carbon fibers 10f over the entire circumference
thereof, so that it is possible to prevent excessive stress
concentration on a specific part of the outer peripheral surface of
the seed crystal 9.
The seed crystal holder 1 according to the present embodiment can
be molded by a filament winding method (FW method) or a sheet
winding method (SW method). In the filament winding method, a die
(mandrel) having the same shape as the hollow space 10h is
prepared, and a molded product is obtained by winding an array of a
plurality of carbon fibers impregnated with resin or pitch around
the die. In the sheet winding method, a molded product is obtained
by winding carbon fiber cloth impregnated with resin or pitch
around the die. Thereafter, the obtained molded product is heated
at high temperatures in an inert gas atmosphere until it is
carbonized (graphitized). The dipping in the resin or the like of
the molded product and the carbonizing step may be repeated several
times. Then, the carbonized molded product is shaped, followed by
finishing such as polishing, whereby the seed crystal holder 1 is
completed.
In the filament winding method, the carbon fibers are preferably
wound such that the winding angle thereof with respect to a winding
core axis is as small as possible. By winding the carbon fibers in
this way, the number of fiber components in the lengthwise
direction can be increased, and tensile strength in the axial
direction can be enhanced. Further, in the sheet winding method, it
is preferable to enhance tensile strength in the axial direction by
using carbon fiber cloth including a lengthwise fiber
component.
As described above, the seed crystal holder 1 according the present
embodiment is a cylindrical member made of a carbon
fiber-reinforced carbon composite material and having a hollow
space. The carbon fibers 10f extends in the circumferential
direction in the horizontal cross section perpendicular to the
center axis of the seed crystal holder 1 and has isotropy, thereby
making it possible to prevent stress concentration from the seed
crystal holder 1 to the seed crystal 9. Thus, breakage of the seed
crystal 9 can be prevented.
FIGS. 2A and 2B are views each illustrating a structure of a seed
crystal holder for pulling-up a single crystal according to a
second embodiment of the present invention. FIG. 2A is a vertical
cross-sectional view, and FIG. 2B is a horizontal cross-sectional
view taken along line A-A' of FIG. 2A.
As illustrated in FIGS. 2A and 2B, a seed crystal holder 2 is
featured in that it is formed using a carbon fiber cloth including
a fiber component parallel to the center axis Z. That is, the
carbon fiber cloth has both a fiber component 10f.sub.1 in the
circumferential direction intersecting the axial direction and a
fiber component 10f.sub.2 parallel to the axial direction. Other
configurations are the same as those in the first embodiment.
The seed crystal holder 2 according to the present embodiment can
be formed using the sheet winding method. More specifically, in
this method, a molded product is obtained by winding a carbon fiber
cloth impregnated with resin or the like around a die such that the
direction of the fiber component included in the carbon fiber cloth
is parallel to the axial direction. According to the present
embodiment, the carbon fiber cloth includes the fiber component
10f.sub.1 in the circumferential direction intersecting the axial
direction, so that it is possible to prevent stress concentration
from the seed crystal holder 2 to the seed crystal 9 as in the
first embodiment. In addition, according to the present embodiment,
the carbon fiber cloth includes the fiber component 10f.sub.2
parallel to the axial direction, so that it is possible to enhance
tensile strength of the seed crystal holder 2 in the axial
direction.
FIGS. 3A and 3B are views each illustrating a structure of a seed
crystal holder for pulling-up a single crystal according to a third
embodiment of the present invention. FIG. 3A is a vertical
cross-sectional view, and FIG. 3B is a horizontal cross-sectional
view taken along line A-A' of FIG. 3A.
As illustrated in FIGS. 3A and 3B, a seed crystal holder 3 is
featured in that only a part of the seed crystal holder 3 that
contacts the outer peripheral surface of the tapered section 9b of
the seed crystal 9 has an isotropic fiber structure, while the
remaining part has an anisotropic fiber structure. That is, the
seed crystal holder 3 according to the present embodiment includes
a combination of a core part 11 having an isotropic fiber structure
and a clad part 12 having an anisotropic fiber structure, and the
core part 11 is mainly provided in the inner peripheral side region
of the cylindrical intermediate section 10b. Carbon fibers 11f of
the core part 11 is oriented in the circumferential direction in
the horizontal cross section perpendicular to the center axis Z and
has isotropy as viewed from the center axis Z. On the other hand,
carbon fibers 12f of the clad part 12 is aligned straight in one
direction in the horizontal cross section and has anisotropy as
viewed from the center axis Z. Other configurations are the same as
those in the first embodiment.
The core part 11 only needs to be provided at least in the inner
peripheral side region of the cylindrical intermediate section 10b
so as to contact the seed crystal 9 and may extend up to the
cylindrical upper section 10a or cylindrical lower section 10c.
Thus, as illustrated, a configuration may be adopted, in which a
part of the core part 11 extends up to the cylindrical upper
section 10a or cylindrical lower section 10c. Further, the core
part 11 may extend in the entire radial direction of the
cylindrical intermediate section 10b from the inner peripheral side
region of the cylindrical intermediate section 10b to the outer
peripheral side region thereof.
In the present embodiment, the core part 11 is integrally molded
with the clad part 12. The clad part 12 is made of carbon fiber
cloth, in which planar carbon fiber cloth is multilayered. The
plane of the carbon fiber cloth is parallel to the center axis Z
and is oriented in a specific direction in a horizontal cross
section. The carbon fiber cloth preferably has not only the fiber
component intersecting the center axis Z, but also the fiber
component parallel to the center axis Z. This makes it possible to
enhance the tensile strength of the entire holder in the axial
direction.
In the present embodiment, the thread groove 10d for screwing the
pulling-up shaft is provided on the clad part 12 side. When the
thread groove 10d is formed in the clad part 12 having an
anisotropic fabric structure, the strength of the thread groove 10d
can be further enhanced.
The core part 11 can be molded by the filament winding method (FW
method) or sheet winding method (SW method). Further, the clad part
12 can be molded by, e.g., a hand lay-up molding method. In the
hand lay-up molding method, a carbon fiber cloth molded using a
shaping mold is impregnated with resin or the like and laminated to
a predetermined thickness while being subjected to deforming using
a brush or roller, whereby a molded product is obtained. Then, the
molded product of the clad part 12 and molded product of the core
part 11 are carbonized together, whereby both molded products can
be integrated. Thereafter, the carbonized, integrated molded
product is shaped, followed by finishing such as polishing, whereby
the seed crystal holder 3 is completed.
In the seed crystal holder 3 according to the present embodiment,
the fiber structure at a part contacting the seed crystal 9 has
isotropy, so that it is possible to prevent stress concentration
from the seed crystal holder 3 to the seed crystal 9, thereby
making it possible to prevent breakage of the seed crystal 9.
Further, the fiber structure of the clad part 12 has anisotropy and
has a fiber component parallel to the center axis Z, so that it is
possible to enhance tensile strength in the axial direction and
thus to improve mechanical strength of the seed crystal holder.
FIGS. 4A and 4B are views each illustrating a structure of a seed
crystal holder for pulling-up a single crystal according to a
fourth embodiment of the present invention. FIG. 4A is a vertical
cross-sectional view, and FIG. 4B is a horizontal cross-sectional
view taken along line A-A' of FIG. 4A.
As illustrated in FIGS. 4A and 4B, a seed crystal holder 4 is
featured in that the lower half thereof is formed as the core part
11 and the upper half thereof as the clad part 12. That is, the
core part 11 is mainly provided in the cylindrical intermediate
section 10b and the cylindrical lower section 10c, and the clad
part 12 is provided in the cylindrical upper section 10a. A part of
the core part 11 extends up to the cylindrical upper section 10a,
and the boundary surface between the core part 11 and clad part 12
in the vertical direction is formed in a concavo-convex surface, so
that vertical connection strength between the core part 11 and the
clad part 12 can be enhanced. Other configurations are the same as
those of the third embodiment.
In the seed crystal holder 4 according to the present embodiment as
well, the fiber structure of the core part 11 constituting the
contact surface with the seed crystal 9 has isotropy, so that it is
possible to prevent stress concentration from the seed crystal
holder 4 to the seed crystal 9, thereby making it possible to
prevent breakage of the seed crystal 9. Further, the fiber
structure of the clad part 12 has anisotropy and has a fiber
component parallel to the center axis Z, so that it is possible to
enhance tensile strength in the axial direction and thus to improve
mechanical strength of the seed crystal holder. Further, according
to the present embodiment, the separately molded core part 11 and
clad part 12 can be integrated with each other through
carbonization or can mechanically be connected using a pin or a
bolt. This facilitates the manufacture of the seed crystal holder 4
and can lead to a reduction in manufacturing cost and improvement
in processing accuracy.
FIGS. 5A and 5B are views each illustrating a structure of a seed
crystal holder for pulling-up a single crystal according to a fifth
embodiment of the present invention. FIG. 5A is a vertical
cross-sectional view, and FIG. 5B is a horizontal cross-sectional
view taken along line A-A' of FIG. 5A.
As illustrated in FIGS. 5A and 5B, a seed crystal holder 5 is
featured in that the inner peripheral side regions of the
respective cylindrical upper section 10a, cylindrical intermediate
section 10b, and cylindrical lower section 10c are formed as the
core part 11 and outer peripheral sides thereof as the clad part
12. The entire inner peripheral surface of the hollow space 10h of
the seed crystal holder 5 is formed as the core part 11 and,
accordingly, the thread groove 10d for screwing the pulling-up
shaft is provided on the core part 11 side. Other configurations
are the same as those of the third embodiment.
In the seed crystal holder 5 according to the present embodiment as
well, the fiber structure of the core part 11 constituting the
contact surface with the seed crystal 9 has isotropy, so that it is
possible to prevent stress concentration from the seed crystal
holder 5 to the seed crystal 9, thereby making it possible to
prevent breakage of the seed crystal 9. Further, the fiber
structure of the clad part 12 has anisotropy and has a fiber
component parallel to the center axis Z, so that it is possible to
enhance tensile strength in the axial direction and thus to improve
the mechanical strength of the seed crystal holder. Further, the
seed crystal holder 5 according to the present embodiment is easier
to process than the seed crystal holder 3 according to the third
embodiment, thereby making it possible to achieve a reduction in
manufacturing cost and improvement in processing accuracy.
FIGS. 6A and 6B are views each illustrating a structure of a seed
crystal holder for pulling-up a single crystal according to a sixth
embodiment of the present invention. FIG. 6A is a vertical
cross-sectional view, and FIG. 6B is a horizontal cross-sectional
view taken along line A-A' of FIG. 6A.
As illustrated in FIGS. 6A and 6B, a seed crystal holder 6 is
featured in that the core part 11 and clad part 12 are formed as
separate members and that it has a socket structure where the core
part 11 is housed in the cylindrical clad part 12. As in the third
embodiment, the core part 11 contacting the outer peripheral
surface of the tapered section 9b of the seed crystal 9 has an
isotropic fiber structure, and the clad part 12 positioned outside
of the core part 11 has an anisotropic fiber structure.
The core part 11 is removable from the clad part 12. The outer
peripheral surface of the core part 11 is formed into a tapered
surface, and this tapered surface is brought into surface contact
with the tapered inner peripheral surface of the clad part 12,
whereby the core part 11 is fixed in the clad part 12. The core
part 11 may be set in the clad part 12 after the seed crystal 9 is
set in the clad part 12 or before the setting of the seed crystal
9.
According to the present embodiment, in addition to the effects
obtained by the third embodiment, another effect is obtained.
Specifically, a manufacturing process is made very simple since the
core part 11 and clad part 12 can be separately manufactured.
Further, the core part 11 and clad part 12 can be separately
replaced with new ones, thereby achieving a reduction in component
cost.
FIGS. 7A and 7B are views each illustrating a structure of a seed
crystal holder for pulling-up a single crystal according to a
seventh embodiment of the present invention. FIG. 7A is a vertical
cross-sectional view, and FIG. 7B is a horizontal cross-sectional
view taken along line A-A' of FIG. 7A.
As illustrated in FIGS. 7A and 7B, a seed crystal holder 7 is
featured in that the inner peripheral side regions of the
respective cylindrical upper section 10a, cylindrical intermediate
section 10b, and cylindrical lower section 10c are formed as the
core part 11 and outer peripheral sides thereof as the clad part 12
and that the core part 11 has an isotropic fiber structure molded
using the filament winding method (FW method), while the clad part
12 has an isotropic fiber structure molded using the sheet winding
method (SW method). In particular, a carbon fiber cloth is used to
form the clad part 12. The carbon fiber cloth has both a fiber
component 12f.sub.1 in the circumferential direction intersecting
the axial direction and a fiber component 12f.sub.2 parallel to the
axial direction. The entire inner peripheral surface of the hollow
space 10h of the seed crystal holder 7 is formed as the core part
11 and, accordingly, the thread groove 10d for screwing the
pulling-up shaft is provided on the core part 11 side.
The seed crystal holder 7 according to the present embodiment can
be formed by combining the filament winding method (FW method) and
sheet winding method (SW method). That is, first, a molded product
of the core part 11 is prepared by the filament winding method, and
then a carbon fiber cloth impregnated with resin or the like is
wound outside the molded product of the core part 11 to form the
clad part 12. At this time, it is necessary to wind the carbon
fiber cloth in such a way that the orientation direction of the
fiber component 12f.sub.2 included in the carbon fiber cloth is
parallel to the axial direction. Then, the obtained molded product
is heated at high temperatures in an inert gas atmosphere until it
is carbonized (graphitized). Thereafter, the carbonized molded
product is shaped, followed by finishing such as polishing, whereby
the seed crystal holder 7 is completed.
In the seed crystal holder 7 according to the present embodiment,
not only the fiber structure of the core part 11 constituting the
contact surface with the seed crystal 9, but also the fiber
structure of the clad part 12 has an isotropy, so that it is
possible to prevent stress concentration from the seed crystal
holder 7 to the seed crystal 9, thereby making it possible to
prevent breakage of the seed crystal 9. Further, the carbon fiber
cloth constituting the clad part 12 has a fiber component 12f.sub.2
parallel to the center axis Z, so that it is possible to enhance
tensile strength in the axial direction and thus to improve
mechanical strength of the seed crystal holder. Further, the seed
crystal holder 7 according to the present embodiment is easier in
processing than the seed crystal holder 5 according to the fifth
embodiment, thereby making it possible to achieve a reduction in
manufacturing cost and improvement in processing accuracy.
Next, a method of manufacturing a silicon single crystal by the CZ
method using the above-described seed crystal holder will be
described.
FIG. 8 is a cross-sectional view illustrating an example of the
structure of a silicon single crystal pulling-up apparatus.
As illustrated in FIG. 8, a silicon single crystal pulling-up
apparatus 20 includes a chamber 21, a heat insulating material 22
disposed inside the chamber 21, a quartz crucible 23 installed in
the chamber 21, a susceptor 24 supporting the quartz crucible 23, a
rotation support shaft 25 vertically movably supporting the
susceptor 24, a heater 26 disposed so as to surround the susceptor
24, a substantially inverted truncated cone-shaped thermal shield
27 disposed above the quartz crucible 23, a single crystal
pulling-up wire 28 (pulling-up shaft) disposed above the quartz
crucible 23 and coaxially with the rotation support shaft 25, and a
wire winding mechanism 29 disposed above the chamber 21.
The wire 28 extends straight downward from the wire winding
mechanism 29 disposed above the chamber 21 up to near the quartz
crucible 23. The distal end portion of the wire 28 is attached with
a seed crystal holder 30, and the seed crystal holder 30 holds the
seed crystal. As the seed crystal holder 30, any of the above seed
crystal holders 1 to 7 according to the respective first to seventh
embodiments can be used.
First, in the pulling-up process of the silicon single crystal, the
quartz crucible 23 is set inside the susceptor 24, polycrystalline
silicon raw material is filled in the quartz crucible 23, and a
seed crystal is set in the seed crystal holder 30. Then, the
silicon raw material is heated by the heater 26 to generate a
silicon melt 31, and the seed crystal is lowered to contact the
silicon melt 31. Thereafter, the seed crystal is slowly pulled up
while rotating the seed crystal and quartz crucible 23 to thereby
grow a substantially columnar-shaped silicon single crystal 32.
FIG. 1 illustrates a state where the silicon single crystal 32
during growing is suspended to the wire 28 through the seed crystal
holder 30.
The diameter of the silicon single crystal 32 is controlled by
controlling the pulling-up speed and the power of the heater 26. In
the growing process of the silicon single crystal 32, a neck
section in which the crystal diameter is narrowed is formed, and
then the crystal diameter is gradually increased to form a shoulder
section. Then, a pulling-up condition is changed when the diameter
reaches a prescribed value (e.g., equal to or more than 450 mm) to
form a body section having a constant diameter. Further, at the end
of the pulling-up, the diameter is narrowed to forma tail section,
and, finally, the silicon single crystal 32 is separated from the
liquid surface. Thus, a silicon single crystal ingot is
completed.
While preferred embodiments of the present invention have been
explained above, the present invention is not limited thereto.
Various modifications can be made to the embodiments without
departing from the scope of the present invention and it is
needless to say that such modifications are also embraced within
the scope of the invention.
For example, in the above embodiments, the seed crystal holder has
been described as a seed crystal holder for pulling up the silicon
single crystal; however, the seed crystal holder according to the
present invention is not limited to this, and may be used for
pulling up various single crystals. Further, in the above
embodiments, although the angle of the tapered surface of the
hollow space 10h of the seed crystal holder is made equal to the
angle of the tapered surface of the seed crystal 9, it may be made
larger than the angle of the tapered surface of the seed crystal 9.
Further, the above embodiments can be arbitrarily combined as
necessary.
REFERENCE SIGNS LIST
1-8 seed crystal holder 8f carbon fibers 9 seed crystal 9a upper
section 9b tapered section 9c lower section 10a cylindrical upper
section 10b cylindrical intermediate section 10c cylindrical lower
section 10d thread groove 10f carbon fibers 10f.sub.1 fiber
component in the circumferential direction 10f.sub.2 fiber
component parallel to the axial direction 10h hollow space 11 core
part 11f carbon fibers 12 clad part 12f carbon fibers 12f.sub.1
fiber component in the circumferential direction 12f.sub.2 fiber
component parallel to the axial direction 20 silicon single crystal
pulling-up apparatus 21 chamber 22 heat insulating material 23
quartz crucible 24 susceptor 25 rotation support shaft 26 heater 27
thermal shield 28 single crystal pulling-up wire 29 wire winding
mechanism 30 seed crystal holder 31 silicon melt 32 silicon single
crystal
* * * * *