U.S. patent application number 13/095425 was filed with the patent office on 2012-11-01 for apparatus for manufacturing vitreous silica crucible.
This patent application is currently assigned to JAPAN SUPER QUARTZ CORPORATION. Invention is credited to Takeshi FUJITA, Toshiaki SUDO.
Application Number | 20120272682 13/095425 |
Document ID | / |
Family ID | 46964136 |
Filed Date | 2012-11-01 |
United States Patent
Application |
20120272682 |
Kind Code |
A1 |
SUDO; Toshiaki ; et
al. |
November 1, 2012 |
APPARATUS FOR MANUFACTURING VITREOUS SILICA CRUCIBLE
Abstract
During fabrication of a vitreous silica crucible, contamination
of the vitreous silica crucible due to wear particles and debris of
components of an apparatus for manufacturing a vitreous silica
crucible is reduced by preventing damage and wear of the components
of the apparatus due to silica fume. The apparatus for
manufacturing a vitreous silica crucible is divided into a lower
section for accommodating a mold and a mold driving system and an
upper section for accommodating an arc electrode driving system,
wherein a sectioning member including one or more communication
paths for allowing penetration of arc electrodes, thereby the air
flow is controlled so as to reduce exchange between gas in the
upper section and gas in the lower section.
Inventors: |
SUDO; Toshiaki; (Akita-shi,
JP) ; FUJITA; Takeshi; (Akita-shi, JP) |
Assignee: |
JAPAN SUPER QUARTZ
CORPORATION
Akita-shi
JP
|
Family ID: |
46964136 |
Appl. No.: |
13/095425 |
Filed: |
April 27, 2011 |
Current U.S.
Class: |
65/17.3 ;
65/144 |
Current CPC
Class: |
C03B 19/095 20130101;
Y02P 40/57 20151101 |
Class at
Publication: |
65/17.3 ;
65/144 |
International
Class: |
C03B 19/09 20060101
C03B019/09; C03B 19/01 20060101 C03B019/01 |
Claims
1. An apparatus for manufacturing a vitreous silica crucible,
comprising: a mold having an inner surface having a bottom and a
cylindrical shape; a mold driving unit for rotating the mold; at
least two arc electrodes for generating an arc discharge; and an
electrode driving unit for driving the arc electrodes, and fusing
and vitrifying a powder molded body formed of silica powder
deposited on the inner surface of the mold through a discharge by
the arc electrodes, the apparatus further comprising: a lower
section for accommodating the mold; an upper section for
accommodating the electrode driving unit; and a sectioning member
for isolating the upper section and the lower section, the
sectioning member having at least one communication path, wherein
the communication path is structured for allowing penetration of
the arc electrodes; and an air flow controlling unit for
controlling air flow in the communication path such that exchange
between gas inside the upper section and gas inside the lower
section is suppressed, wherein the sectioning member comprises
first and second barrier walls having space therebetween, the space
being disposed to separate the upper section and the lower section,
the communication path is provided in the first and second barrier
walls, and the air flow controlling unit comprises an exhaust
device for exhausting gas in the space between the first barrier
wall and the second barrier wall and an air supply device for
supplying gas to the space between the first barrier wall and the
second barrier wall.
2. The apparatus of claim 1, wherein the air flow controlling unit
comprises an exhaust device capable of exhausting gas inside the
communication path.
3. The apparatus of claim 1, wherein the air flow controlling unit
comprises an air supply device capable of supplying gas into the
communication path.
4-5. (canceled)
6. The apparatus of claim 1, wherein the air flow controlling unit
comprises an exhaust device for exhausting gas from the lower
section.
7. The apparatus of claim 1, wherein the air flow controlling unit
comprises an air supply device for supplying gas to the lower
section.
8-12. (canceled)
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to an apparatus and method for
manufacturing a vitreous silica crucible, which is capable of
improving a yield of a crucible by reducing contamination generated
during fabrication of a vitreous silica crucible, while enabling
stable operation for a long time by protecting a main body of an
apparatus.
[0003] 2. Description of Related Art
[0004] Currently, growing of silicon single crystal constituting a
raw material of a semiconductor wafer is mainly performed by using
a Czochralski (CZ) method. In the Czochralski method, a seed
crystal is dipped in a silicon melt accommodated in a crucible, and
the seed crystal is pulled up while being rotated, thereby growing
a single crystal from below the seed crystal.
[0005] In the growing of the silicon single crystal, a vitreous
silica crucible is generally used so as to avoid impurities being
mixed with the silicon melt. Specifically, in order to grow a high
purity semiconductor crystal, or to precisely control concentration
of a dopant added to a semiconductor, it is required to precisely
control purity of an inner surface of a vitreous silica crucible,
which contacts the silicon melt. Also, in order to improve a yield
of silicon single crystal growth by continuously pulling up a
plurality of single crystals, the vitreous silica crucible needs to
have durability to endure long use or repetitive use.
[0006] An arc fusing method is used as a method of manufacturing a
vitreous silica crucible. In this method, a deposit layer of silica
powder is formed in a predetermined thickness on an inner surface
of a mold having a bottom and a cylindrical shape, and powder
molded body approximately corresponding to a shape of a target
crucible is formed. Then, the deposit layer of the silica powder is
vitrified by heating and fusing the deposit layer via a discharge
through an arc electrode installed on the mold, while rotating the
mold. According to the arc fusing method, since the silica powder
can be fused without being contacted while limiting a heated
region, contamination due to impurities in an inner surface of a
vitreous silica crucible may be suppressed, thereby providing a
high quality vitreous silica crucible.
[0007] However, even by using the arc fusing method, generation of
silica fume generated as part of silica powder is evaporated during
fusing of the silica powder is unavoidable. Specifically, a
phenomenon called dropping, wherein the silica fume that adheres to
and coheres to a surface of an electrode, drops onto a molten glass
surface, and adheres to a crucible inner surface, has become a
problem.
[0008] Also, a carbon rod is generally used as the arc electrode,
but carbon particles detached when an electrode surface combusts by
arc discharge tend to drop onto the molten glass surface. When the
carbon particles that are dropped onto the glass surface are
combusted in that spot, the carbon particles cause unevenness, and
when the carbon particles remain in that spot as carbon particles,
the carbon particles become impurities, thereby deteriorating
quality of the vitreous silica crucible.
[0009] As countermeasures, a technology for controlling
characteristics of a material of the carbon rod constituting the
arc electrode so as to suppress cohesion of the silica fume or
dropping of the carbon particles is being studied.
[0010] For example, JP-A-2007-273206 discloses a technology for
controlling density of a carbon electrode to be within a
predetermined range (1.60 g/cm.sup.3 to 1.80 g/cm.sup.3) and
controlling a particle size of carbon to be less than or equal to
0.05 mm to suppress adhesion of silica fume to an electrode
surface, thereby preventing dropping of the carbon particles onto
the molten glass surface.
[0011] A technology of preventing leakage generally by setting a
generation source to negative pressure under an environment where
fume is generated is well known (for example, JP-A-2002-241077).
However, in a process of manufacturing a vitreous silica crucible,
external dust intruding into a mold also causes contamination, and
thus such a technology is not preferable. To avoid this intrusion
of dust, for example, JP-A-2003-313035 discloses a technology for
sealing a section where a mold is installed, and circulating clean
air in the section by supplying and exhausting air.
SUMMARY OF THE INVENTION
[0012] However, silica fume cannot be suppressed from floating
inside an apparatus for manufacturing a vitreous silica crucible,
in the technology of controlling the characteristics of a material
of the carbon electrode, as described in JP-A-2007-273206. The
apparatus for manufacturing a vitreous silica crucible includes an
apparatus for driving a mold (mold driving apparatus), and an
apparatus for controlling a location of an arc electrode, wherein a
plurality of metal members are used in these apparatuses. Intrusion
of fume, which is generated during an operation according to
manufacturing of the vitreous silica crucible, into a gap of
control members in these apparatuses is a reason for damage due to
wear. Accordingly, an operation of removing the fume, exchanging
worn out parts, or the like is required during maintenance, and
thus efficiency of the operation of manufacturing a vitreous silica
crucible is diminished.
[0013] Also, when a control device of an electrode disposed on an
upper part of the mold is driven, metal particles or metal
fragments may be detached from a member. When these metal particles
or the like are dropped into the vitreous silica crucible, the
quality of the crucible may be remarkably decreased. A phenomenon
in which the silica fume coheres to worn out metal powder and the
worn out metal powder drops also exists. When minute metal
particles are adhered to an inner surface of the crucible,
impurities may be eluted to a silicon melt when the silicon melt is
formed inside the crucible, and thus it is not preferable in terms
of quality. Also, a foreign body, such as a metal, an aggregation
of the silica fume, or the like adhered to the inner surface of the
crucible, makes stress distribution of a glass surface
heterogeneity, and accelerates deterioration of the crucible as the
foreign body becomes a nucleation field of local crystallization.
Thus, use of the crucible for a long period of time in the
operation of growing a single crystal is hindered. In the method of
setting the generation source of fume in a negative pressure as
disclosed in JP-A-2002-241077, foreign bodies may be attracted near
to the mold.
[0014] Also, recently, a large vitreous silica crucible is required
according to an increasing diameter of silicon single crystal.
Consequently, driving and controlling of the mold or arc electrode
tend to be complex in the apparatus for manufacturing a vitreous
silica crucible. Accordingly, even if the clean air is circulated
by isolating the section where the mold is installed as described
in JP-A-2003-313035, a communication path through which an
electrode penetrates cannot be completely closed, and thus a
phenomenon in which the external dust drops into the mold cannot be
eliminated.
[0015] To solve the above and/or other problems, the present
invention provides an apparatus and method for manufacturing a
vitreous silica crucible, which suppresses wear of an arc electrode
driving member or the like that results from silica fume while
preventing contamination of a vitreous silica crucible due to a
foreign body, while manufacturing a vitreous silica crucible by
using an arc fusing method.
[0016] 1) According to a first embodiment of the present invention,
there is provided an apparatus for manufacturing a vitreous silica
crucible, which includes a mold having an inner surface having a
bottom and a cylindrical shape, a mold driving unit for rotating
the mold, at least two arc electrodes for generating an arc
discharge, and an electrode driving unit for driving the arc
electrodes, and fusing and vitrifying a powder molded body formed
of silica powder deposited on the inner surface of the mold via a
discharge through the arc electrodes, the apparatus including: a
lower section for accommodating the mold and the mold driving unit,
an upper section for accommodating the electrode driving unit, and
a sectioning member for isolating the upper section and the lower
section, the sectioning member having at least one communication
path for allowing penetration of the electrodes; and an air flow
controlling unit for controlling air flow in the communication path
such that an exchange between gas inside the upper section and gas
inside the lower section is suppressed.
[0017] 2) According to a second embodiment of the present
invention, there is provided the apparatus for manufacturing a
vitreous silica crucible according to the first embodiment, wherein
the air flow controlling unit includes an exhaust device capable of
exhausting gas inside the communication path.
[0018] A dust collecting device may be installed in the exhaust
device, as a collecting means that collects silica fume.
[0019] 3) According to a third embodiment of the present invention,
there is provided the apparatus for manufacturing a vitreous silica
crucible according to the first embodiment, wherein the air flow
controlling unit includes an air supply device capable of supplying
gas into the communication path.
[0020] A filter for removing dust of a supplied gas may be
installed in the air supply device.
[0021] 4) According to a fourth embodiment of the present
invention, there is provided the apparatus for manufacturing a
vitreous silica crucible according to any one of the first through
third embodiments, wherein the sectioning member includes first and
second barrier walls having space therebetween, the space being
disposed to separate the upper section and the lower section, the
communication path is provided in the first and second barrier
walls, and, and the air flow controlling unit comprises an exhaust
device for exhausting gas in the space between the first barrier
wall and the second barrier wall.
[0022] 5) According to a fifth embodiment of the present invention,
there is provided the apparatus for manufacturing a vitreous silica
crucible according to any one of the first through third
embodiments, wherein the sectioning member includes first and
second barrier walls having space therebetween, the space being
disposed to separate the upper section and the lower section, the
communication path is provided in the first and second barrier
walls, and the air flow controlling unit comprises an air supply
device for supplying gas to the space between the first barrier
wall and the second barrier wall.
[0023] 6) According to a sixth embodiment of the present invention,
there is provided the apparatus for manufacturing a vitreous silica
crucible according to any one of the first through fifth
embodiments, wherein the air flow controlling unit includes an
exhaust device for exhausting gas from the lower section.
[0024] A dust collecting device for collecting silica fume may be
installed in the exhaust device.
[0025] 7) According to a seventh embodiment of the present
invention, there is provided the apparatus for manufacturing a
vitreous silica crucible according to any one of the first through
sixth embodiments, wherein the air flow controlling unit includes
an air supply device for supplying gas to the lower section.
[0026] A filter for removing dust of a supplied gas may be
installed in the air supply device.
[0027] 8) According to an eighth embodiment of the present
invention, there is provided a method of manufacturing a vitreous
silica crucible, including the steps of: forming a powder molded
body by depositing silica powder on an inner surface of a mold, and
fusing and vitrifying the powder molded body by fusing the powder
molded body through an arc discharge generated from at least two
arc electrodes while rotating the mold, wherein the vitrification
is performed in a state that a lower section for accommodating the
mold and a mold driving unit for driving the mold, and an upper
section for accommodating an electrode driving unit for driving the
arc electrodes are isolated by using a sectioning member having at
least one communication path for allowing penetration of the arc
electrodes; and the air flow inside the communication path is
controlled such that exchange between gas inside the upper section
and gas inside the lower section is suppressed.
[0028] 9) According to a ninth embodiment of the present invention,
there is provided the method of manufacturing a vitreous silica
crucible according to the eighth embodiment, wherein gas inside the
communication path is exhausted.
[0029] 10) According to a tenth embodiment of the present
invention, there is provided the method of manufacturing a vitreous
silica crucible according to the eighth or ninth embodiment,
wherein gas is supplied into the communication path.
[0030] In the method of manufacturing a vitreous silica crucible,
the gas supplied into the communication path may have an air
cleanliness class, which is specified by JIS B 9920 or ISO 14644-1,
of less than or equal to 100000, less than or equal to 10000, more
than or equal to 1 and less than or equal to 7, or preferably less
than or equal to 5. Alternatively, the gas supplied into the
communication path may have an air cleanliness class less than or
equal to 10000, preferably less than or equal to 700 in
FED-STD-209D.
[0031] 11) According to an eleventh embodiment of the present
invention, there is provided the method of manufacturing a vitreous
silica crucible according to any one of the eighth through tenth
embodiments, wherein gas inside the lower section is exhausted.
[0032] 12) According to a twelfth embodiment of the present
invention, there is provided the method of manufacturing a vitreous
silica crucible according to any one of the eighth through eleventh
embodiments, wherein gas is supplied to the lower section.
[0033] In the method of manufacturing a vitreous silica crucible,
the gas supplied into the lower section may have an air cleanliness
class specified by JIS, which is more than or equal to 1,
preferably more than or equal to 8.
[0034] According to an apparatus for manufacturing a vitreous
silica crucible of the present invention, a portion (lower
section), which may have a high temperature due to disposition of a
mold and is likely to generate fume, and is required to be
prevented from being contaminated due to dropping of impurities
while manufacturing the crucible, and a portion (upper section),
which is likely to generate a contamination source, such as minute
particles or the like, due to the manipulation of mechanical
operation or the like, under a temperature condition of about room
temperature and where an electrode controlling unit is disposed,
are isolated by a sectioning member, and thus fusion and
vitrification of silica powder can be performed while suppressing
an exchange of gases between the upper section and the lower
section. According to such a structure of the apparatus for
manufacturing a vitreous silica crucible of the present invention,
the gas is suppressed from moving from the lower section to the
upper section, thereby suppressing an electrode driving unit in the
upper section from being contaminated by silica fume generated in
the lower section while fusing silica powder. Accordingly, the
electrode driving unit is prevented from being damaged and worn out
due to minute silica particles intruding into a sliding portion,
and thus a frequency of replacing an apparatus part can be reduced.
Accordingly, operations according to maintenance of the apparatus,
such as cleaning after use or part replacement, may be simplified.
Consequently, by using the manufacturing apparatus of the present
invention, production efficiency of a vitreous silica crucible can
be improved and production costs can be reduced.
[0035] Also, according to the apparatus for manufacturing a
vitreous silica crucible of the present invention, the gas is
suppressed from moving from the upper section to the lower section
by suppressing the exchange of gases between the upper section and
the lower section, thereby preventing metal fragments or wear
particles generated in the upper section from intruding into the
lower section. Thus, contamination of an inner surface of the
crucible due to foreign bodies other than silica can be prevented.
Also, when a vitreous silica crucible, which is not contaminated by
impurities or to which a foreign body is not adhered, is actually
used to fuse a semiconductor material, or the like, maldistribution
of crystallization portions due to the foreign body or
contamination does not occur. As such, when the manufacturing
apparatus of the present invention is used to pull up a
semiconductor crystal, such as silicon or the like, it is possible
to precisely control composition, and a high quality vitreous
silica crucible that is durable in long period of time can be
provided.
[0036] According to the present invention, suppression of a gas
exchange between the upper section and the lower section is
realized by controlling gases in the communication path of the
sectioning member communicating between the upper section and the
lower section. In detail, in order to suppress the gas from moving
from the upper section to the lower section or from the lower
section to the upper section, and to suppress the gas in the
communication path from being exhausted to the outside or the gas
from being ejected from the communication path, a means (air flow
controlling unit) of ejecting a blocking gas, such as an air
curtain, may be employed near an outlet of the communication
path.
[0037] According to a method of manufacturing a vitreous silica
crucible of the present invention, fusion and vitrification can be
performed on silica powder while suppressing a gas exchange between
the lower section in which the mold is disposed, and the upper
section in which the electrode controlling unit is disposed. When a
vitreous silica crucible is manufactured by using the method, the
electrode driving unit inside the upper section can be suppressed
from being contaminated by the silica fume generated while fusing
the silica powder, and thus the wear particles can be prevented
from being generated according to wear due to minute silica
particles intruding into the sliding portion. Also, the metal
fragments or wear particles generated in the upper section can be
prevented from intruding into the lower section. Accordingly,
according to the method of manufacturing a vitreous silica crucible
of the present invention, a vitreous silica crucible can be
manufactured while preventing contamination of the inner surface of
the crucible due to a foreign body other than silica. Also, when a
vitreous silica crucible, which is not contaminated by impurities
or to which a foreign body is not adhered, is actually used to fuse
a semiconductor material, or the like, maldistribution of
crystallization portions due to the foreign body or contamination
is not generated. Accordingly, when the method of manufacturing a
vitreous silica crucible of the present invention is used to pull
up a semiconductor crystal, such as silicon or the like, it is
possible to precisely control composition, and a high quality
vitreous silica crucible that is durable in long period of time can
be provided.
BRIEF DESCRIPTION OF THE DRAWINGS
[0038] FIG. 1 is a schematic front cross-sectional view for
explaining an embodiment of the present invention, taken along a
line I-I of FIG. 2.
[0039] FIG. 2 is a horizontal cross-sectional view of an apparatus
shown in FIG. 1.
[0040] FIG. 3 is a schematic longitudinal-sectional view for
explaining another embodiment of the present invention.
[0041] FIG. 4 is a schematic longitudinal-sectional view showing
another type of a sectioning member in an apparatus for
manufacturing a vitreous silica crucible of the present invention,
wherein an area of a second barrier wall is small.
[0042] FIG. 5 is a schematic longitudinal-sectional view showing
another type of the sectioning member in the apparatus for
manufacturing a vitreous silica crucible of the present invention,
wherein a double barrier wall is replaced by a sheath body.
[0043] FIGS. 6a and b are schematic views showing an electrode
arrangement state of an apparatus for manufacturing a vitreous
silica crucible, according to the present invention, wherein FIG.
6a is a top perspective view of disposed electrodes, and FIG. 6b is
a side view of the disposed electrodes viewed on the side
thereof.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0044] Hereinafter, embodiments of the present invention will be
described with reference to the attached drawings.
First Embodiment
[0045] FIG. 1 is a schematic front cross-sectional view for
explaining an apparatus for manufacturing a vitreous silica
crucible, according to a first embodiment of the present invention,
taken along a line I-I of FIG. 2, and FIG. 2 is a horizontal
cross-sectional view of the same apparatus for manufacturing a
vitreous silica crucible.
[0046] The apparatus includes an apparatus chamber surrounded by a
side wall 1 capable of blocking the inside of the apparatus where
arc flames are generated from the outside of the apparatus. The
side wall 1 may be formed of a metal or a structural material such
as concrete or the like, as long as blocking (or reduction and
alleviation outside of the apparatus) of an atmosphere gas,
temperature, noise, vibration, etc. required in manufacturing a
vitreous silica crucible is possible in the inside and outside of
the apparatus. Alternatively, a heat resistant material, such as
heat resistant ceramics, or the like, may be used for at least a
part of the side wall 1. A shape of the side wall 1 in a plan view
is not specifically limited, and may be an angled pipe shape or a
cylindrical shape as long as a space for accommodating a mold 2 or
the like, which is to be described later, can be formed
therein.
[0047] A lower portion of the side wall 1 is installed at a bottom
portion and connected to an apparatus bottom (not shown). The side
wall 1, a first barrier wall (to be described later) disposed at an
upper side, and the bottom portion disposed at a lower side form a
processing chamber (apparatus chamber or arc fusion furnace). This
chamber can be isolated or sealed from the outside in terms of air
flow. A door (not shown) that can be opened and closed may be
provided on at least a part of the side wall 1 so as to carry in
and out the mold 2 that will be described later, or to allow an
operator to enter.
[0048] The mold 2 and a mold driving unit 4 for driving the mold 2
are installed in the apparatus chamber. The mold 2 has an inner
surface having a bottom and a cylindrical shape. The mold driving
unit 4 may be provided outside the apparatus chamber, such as at a
side lower than the bottom portion or the like, as long as being
capable of driving the mold 2.
[0049] The mold (rotating mold) 2 may have a cylindrical shape with
a bottom. The inner side (inner surface) of the mold 2 has a
concave portion having a bowl shape and an upward opening. The
inner side defines an outer shape of a vitreous silica crucible.
The material of the mold 2 may be, for example, graphite. A
plurality of vents 2a are provided in the mold 2. The vents are
connected to a depressurizing unit (not shown) and penetrates
through the inner surface of the mold 2. Thus the inside of silica
powder molded body 3 formed on the inner surface of the mold 2 can
be depressurized. The mold driving unit 4 rotates the mold 2 around
a center axis (center axis of a cylinder inner surface).
Furthermore, the mold driving unit 4 may perform, in combination, a
driving of horizontal movement and vertical movement that do not
change an angle of a rotation axis (central axial), inclination
that changes the angle of the rotation axis, or the like.
[0050] A horizontal first barrier wall 6 is provided above the mold
2 in the apparatus chamber over an approximately entire surface
(entire area surrounded by the side wall 1), in a plan view, of the
apparatus chamber, and thus an upper space of the mold 2 in the
apparatus chamber is isolated in terms of air flow from the outside
of the apparatus chamber by the first barrier wall 6.
[0051] A second barrier wall 8 is installed over the approximately
entire surface (the entire area surrounded by the side wall 1), in
a plan view, of the apparatus chamber, parallel to the first
barrier wall 6 at a location above and spaced apart from the first
barrier wall 6.
[0052] A sectioning member 10 consisting of the first barrier wall
6 and the second barrier wall 8 forms an intermediate section
inside in the vertical direction. The sectioning member (ceiling)
10 isolates and blocks an apparatus lower section in which arc
heating is performed in the apparatus chamber from an apparatus
upper section in which heating is not performed. In the present
embodiment, perimeter shapes of the first barrier wall 6 and the
second barrier wall 8 are defined by an inner surface shape of the
side wall 1.
[0053] A plurality of exhaust holes 12 are provided on the second
barrier wall 8 near the side wall 1 separated, in a plan view, from
a center portion of the apparatus chamber where an arc is generated
(to be described later). The exhaust holes 12 are disposed with
equal intervals therebetween in an outline direction of the
apparatus chamber in a plan view. The exhaust holes 12 communicate
with the intermediate section inside the sectioning member 10. In
this example, two exhaust holes 12 are disposed at the opposite
locations, in a plan view, with respect to the central location of
the apparatus chamber where the arc is generated.
[0054] The intermediate section inside the sectioning member 10 is
communicated to an exhaust device 16 through an exhaust path 14
having a pipe shape extending upward from each of the exhaust holes
12. A dust collecting device (not shown) that collects fume is
installed in the exhaust device 16.
[0055] The first barrier wall 6 includes a plurality of lower
communication holes 18 at a center position of the apparatus
chamber where the arc is generated. The lower communication holes
18 are disposed at uniform intervals on a circumference surrounding
a center point set directly above the mold 2 constituting the
center of the apparatus chamber. In this example, three lower
communication holes 18 are disposed at equal intervals on the
circumference, according to the number of arc electrodes 22 which
will be described later. The center of the circumference on which
the lower communication holes 18 are formed is a reference location
in a non-driving state, and is also set to match, in a plan view, a
rotation driving axis of the rotating mold 2, which is a vertical
direction.
[0056] The second barrier wall 8 includes upper communication holes
20. The number of the upper communication holes 20 is identical to
the number of lower communication holes 18. The upper communication
holes 20 are disposed at uniform intervals on the circumference of
the lower communication holes 18. The upper communication holes 20
are provided on a circumference set in the second barrier wall 8.
The center thereof is on a vertical line drawn from the center of
the circumference set in the first barrier wall 6. The
circumference on the second barrier wall 8 has a larger radius than
that of the first barrier wall. Also, the lower communication holes
18 constitutes a figure similar to that constituted by the upper
communication holes 20. Thus the arc electrodes 22 can penetrate
through the holes. In this example, three lower communication holes
18 and three upper communication holes 20 are disposed on three
vertical surfaces each including the vertical line and a line
passing through the lower communication hole 18 and the upper
communication holes 20.
[0057] A communication path 21 is formed by the lower communication
holes 18 and the upper communication holes 20. The communication
path 21 communicates the apparatus lower portion and the apparatus
upper portion via the sectioning member 10. The arc electrodes 22
each having a rod shape are disposed penetrating through the
communication paths 21. The number of the arc electrodes 22 may be
identical to the number of communication paths 21, i.e., the number
of the upper communication holes 20. In this example, three 3-phase
arc electrodes 22 are used. The arc electrode may have a tilt angle
of 5.degree. to 40.degree. with respect to the vertical line. The
arc electrodes 22 may be carbon rods. When the arc electrodes 22
are carbon electrodes, volume density may be adjusted to be within
a predetermined range, for example, from 1.5 g/cm.sup.3 to 2.0
g/cm.sup.3.
[0058] The arc electrodes 22 are, for example, electrode rods each
having the same shape so as to perform an alternating 3-phase
(R-phase, S-phase, and T-phase) arc discharge, and are each
provided such that respective axes 22L form an angle .theta.1 so
that the arc electrodes 22 form an inverted triangular pyramid
shape having the apex at the bottom, as shown in FIGS. 6a and 6b.
Also, the application of electric current to each arc electrode 22
is controllable by a control unit that is not shown. In FIGS. 6a
and 6b, the arc electrodes 22 are provided such that an arc flame
direction matches an electrode central axis LL. The number of
electrodes, an arrangement state, and a power supplying method are
not limited to the above configuration, and other configurations
may be employed.
[0059] An electrode driving unit 24 that drives the arc electrodes
22 is disposed above the second barrier wall 8. Although not shown
herein, the electrode driving unit 24 may be fixed to the side wall
1 and the second barrier wall 8, or may be extended from the upper
portion of the apparatus. The electrode driving unit 24 adjusts a
location of a tip portion of each of the arc electrodes 22 via
stretch and/or vertical movement. Also, the electrode driving unit
24 can set an opening angle formed by the plurality of arc
electrodes 22, by adjusting the inclination of the electrodes 22
with respect to the vertical line.
[0060] As shown in FIGS. 1, 6a, and 6b, the electrode driving unit
(electrode location setting unit) 24 includes a supporter that
supports the arc electrodes 22 such that a distance D between the
electrode tips of the arc electrodes 22 is settable, a horizontal
moving unit that is capable of moving the supporter in a horizontal
direction, a vertical moving unit that is capable of moving the
plurality of supporters and the horizontal moving unit in a
vertical direction as one body, and a rotating angle setting unit
that is capable of changing a supporting angle of the arc
electrode. Here, the supporter includes a rotating unit that
controls a rotating angle of an angle setting axis as the arc
electrodes 22 are supported to be rotatable around the angle
setting axis.
[0061] In order to adjust the distance D between the electrode tips
of the arc electrodes 22 and the electrode location state, the
angle of each of the arc electrodes 22 is controlled by the
rotating angle setting unit, while the horizontal location of the
supporter is controlled by the horizontal moving unit. Also, a
horizontal direction location between the electrode central axis LL
and the mold rotation axis may be controlled by the horizontal
moving unit. Also, a height location of each electrode tip 22a with
respect to the bottom location of the silica powder molded body 3
may be controlled by controlling a height location of the supporter
by using the vertical moving unit. At the same time, it is possible
to displace a direction (the electrode central axis LL) in which
the arc flames are generated by an angle .psi.1 from the vertical
direction by individually setting the angles of the arc electrodes
22 by using the rotating angle setting unit.
[0062] Also, it is possible to control the height location of the
electrode tip 22a by setting the sectioning member (ceiling) 10 to
be moveable up and down with respect to the side wall 1 by using
the vertical moving unit that is not shown.
[0063] A method of manufacturing a vitreous silica crucible
according to the present embodiment will now be described.
[0064] First, silica powder is deposited on the inner surface of
the rotating mold 2, so as to form the silica powder molded body 3
that approximately corresponds to a shape of a target vitreous
silica crucible. Here, the silica powder indicates silicon dioxide
powder whose composition is indicated substantially by SiO.sub.2,
and is selected from among natural and/or artificial crystalline
silica powder, amorphous silica powder, etc. according to its
purpose. Also, another material may be added as occasion
demands.
[0065] Then, the electrode tips are disposed at a predetermined
location facing the silica powder molded body 3 by using the
electrode driving unit 24 and/or the mold driving unit 4.
[0066] Next, the exhaust device 16 is activated before supplying
arc power, and gas in the intermediate section interposed between
the first barrier wall 6 and the second barrier wall 8 is exhausted
via the exhaust path 14, thereby depressurizing the inside of the
intermediate section. An exhaust flow rate of the gas sucked from
the lower communication holes 18 may be from 0 to 0.01 to 2400 to
20000 Nm.sup.3/h as a normal flow rate, and preferably from 1000 to
1200 Nm.sup.3/h. Also, a flow rate of the gas sucked from the upper
communication holes 20 may be from 0 to 0.01 to 2400 to 20000
Nm.sup.3/h, and preferably from 1000 to 1200 Nm.sup.3/h.
Alternatively, a differential pressure may be set to be more than
or equal to 1 to 5 to 10 to 20 Pa and less than or equal to 100 Pa,
between the intermediate section inserted between the first barrier
wall 6 and the second barrier wall 8, and upper side of the
sectioning member 10. Since such conditions can be adjusted based
on an actual opening area obtained by subtracting an electrode
sectional area from the area of each of the upper communication
holes 20 or lower communication holes 18, an exhaust speed of the
exhaust device 16, a gas temperature near the communication path
21, or the like, the conditions may be set with respect to the top
and bottom of the sectioning member 10 in such a way that the fume
generated at the lower side of the sectioning member 10 is blocked,
and a thermal affect of the arc flames to the upper side of the
sectioning member 10 or the like can be reduced. In the present
invention, it is possible to block or seal the air flow via such
blocking of the fume and reduction of thermal effect.
[0067] After starting the exhaust, the powder mold is fused and
vitrified through an arc discharge to manufacture a vitreous silica
crucible by applying a predetermined voltage to the arc electrodes
22 while continuously rotating the mold by using the mold driving
unit 4.
[0068] Arrows of FIG. 1 conceptually show a flow of gas when the
exhaust device 16 is activated. When the powder molded body is
fused during the vitrification process, the silica fume is
generated as a part of the silica powder is evaporated. Since
atmospheric pressure of the intermediate section becomes negative
with respect to atmospheric pressure in the lower section and the
upper section according to exhaustion, the gas including fume is
sucked into the intermediate section via the lower communication
holes 18 and moves to a side portion (radial direction), and is
exhausted to the outside of the apparatus by the exhaust device 16
through the exhaust path 14. Thus, the gas including fume may be
prevented or suppressed from intruding into the upper section
through the upper communication holes 20.
[0069] Also, the gas of the upper section is sucked into the center
section through the upper communication hole 20, moves to the side
portion, and is exhausted to the outside of the apparatus by the
exhaust device 16 through the exhaust path 14. Accordingly, even
when dust or metal fragments are generated in the electrode driving
unit or the like in the upper section, the dust or metal fragments
are prevented from intruding into the lower section, thereby
preventing contamination.
Second Embodiment
[0070] FIG. 3 is a view for explaining another embodiment of the
present invention. The same reference numerals of FIG. 1 are used
for elements having the same structure as the first embodiment, and
descriptions thereof will not be repeated.
[0071] In the present embodiment, a plurality of air supply holes
13 are formed on the second barrier wall, and the intermediate
section communicates with an air supply device 17 through an air
supply path 15 having a pipe shape and extending upward from the
air supply hole. Clean air is supplied from the air supply device
17 through a HEPA filter (high efficiency particulate air
filter).
[0072] A method of manufacturing a vitreous silica crucible,
according to the present embodiment will be described.
[0073] First, silica powder is deposited on the inner surface of
the mold 2, and the silica powder molded body 3 is formed
approximately corresponds to a shape of a target vitreous silica
crucible.
[0074] Next, the electrode tip is disposed at a predetermined
location facing the silica powder molded body 3 by using the
electrode driving unit 24 and/or the mold driving unit 4.
[0075] Then, the air supply device 17 is activated, and air is
supplied into the intermediate section inserted between the first
barrier wall 6 and the second barrier wall 8, through the air
supply path 15. The air flow into the intermediate section is
supplied from an opening of the lower communication hole 18 to the
lower section, and supplied from an opening of the upper
communication hole 20 to the upper section. A flow rate of gas
supplied from the lower communication hole 18 to the lower section
may be from 0 to 0.1 to 20000 Nm.sup.3/h, and preferably from 300
to 8000 Nm.sup.3/h, and a flow rate of gas emitted from the upper
communication hole to the upper section may be from 0 to 0.01 to
20000 Nm.sup.3/h, and preferably from 300 to 8000 Nm.sup.3/h. Such
conditions may be adjusted based on an area of the opening of the
upper communication hole 20 or lower communication hole 18, an air
supply amount of the air supply device, or the like.
[0076] After starting the air supply, a rotation operation of the
mold is started by the mold driving unit 4. Then, a predetermined
voltage is applied to the arc electrodes 22 to fuse and vitrify a
powder molding through an arc discharge, thereby manufacturing a
vitreous silica crucible.
[0077] Arrows of FIG. 3 conceptually show a flow of gas when the
air supply device 17 is activated. The air supplied from the air
supply device 17 flows to the intermediate section through the air
supply path 15. Accordingly, pressure of the intermediate section
becomes positive pressure with respect to those of the lower
section and the upper section, and thus gas is emitted from the
lower communication hole 18 to the lower section while gas is
emitted from the upper communication hole to the upper section.
Accordingly, intrusion of air including fume generated during a
silica vitrification process, into the upper section, is suppressed
or prevented. Also, the air of the upper section is prevented from
intruding into the lower section, and thus the vitreous silica
crucible is prevented from being contaminated by dust, metal
fragments, or the like generated in the upper section.
[0078] Also, the present invention is not limited to the
above-described embodiments.
[0079] For example, FIGS. 4 and 5 are schematic
longitudinal-sectional views of an apparatus for manufacturing a
vitreous silica crucible of the present invention, and show
different configurations of the sectioning member. Also,
descriptions about the elements that are described in the above
embodiments and given the same reference numerals are not
repeated.
[0080] In the apparatuses of the first and second embodiments, the
perimeter of the side wall is disposed on an entire surface of the
range in a plan view defined by the inner surface of the side wall,
together with the first barrier wall and the second barrier wall,
but an area of any one barrier wall may be smaller than that of the
other barrier wall.
[0081] For example, as shown in FIG. 4, the first barrier wall 6
may cover the entire surface of the inner side range of the side
wall in a plan view while a surrounding wall 5 surrounding the
plurality of communication paths 21 is built on the first barrier
wall 6, and a second barrier wall 80 having a perimeter shape
defined by the surrounding wall 5 may be installed thereon while a
plurality of conduit lines 19 are connected to the surrounding wall
5, so that the conduit lines 19 may communicate with the air supply
device or exhaust device (not shown) outside the side wall 1.
[0082] In this case, air supply or exhaustion may be performed on
the intermediate section (only the portions around the
communication path 21) surrounded by the first barrier wall 6, the
surrounding wall 5, and the second barrier wall 80. For example,
the surrounding wall 5 may include the upper communication hole 20
in a plan view, while having a cylindrical shape constituting a
circle in a plan view with respect to the central location of the
apparatus chamber where an arc is generated. Here, the second
barrier wall 80 may have a disk shape, wherein the plurality of
upper communication holes 20 are opened. In the example in the
drawing, two conduit lines 19 are connected to the intermediate
section surrounded by the surrounding wall 5 and the second barrier
wall 80, but the plurality of conduit lines 19 may be connected at
equal intervals in a circumference direction in a plan view of the
second barrier wall 80. Here, a barrier wall having a smaller area
may be the first barrier wall.
[0083] Alternatively, only the first barrier wall 6 may be used as
a barrier wall, and a sheath body 7 having an opening
(communication path) may be installed at a lower location or upper
location near each communication hole 18 formed on the first
barrier wall 6. Then, air supply or exhaustion may be performed on
each sheath body 7 to suck surrounding gas only near the portion of
the communication hole 18, or the sheath body 7 may be used as an
air curtain by ejecting gas only near the portion of the
communication hole 18, thereby suppressing or preventing gas
exchange between top and bottom of the first barrier wall 6 through
the communication hole 18.
[0084] For example, FIG. 5 shows an example where the sheath bodies
7 having a communication hole 210 are respectively installed on the
communication holes 18 of the first barrier wall, at locations
identical to the number of the arc electrodes 22, and a conduit
line 190 is connected to each sheath body 7. The conduit line 190
is led outside the side wall 1, and is connected to the exhaust
device or air supply device (not shown).
[0085] Also, in the first and second embodiments, the exhaust path
or air supply path has a pipe shape extending upward from the
second barrier wall, but the exhaust hole or air supply hole may be
formed on the side wall to communicate with the exhaust device or
air supply device. For example, a pipe body surrounding the side
wall may be installed on an outer side of the side wall, and a
space surrounded by the pipe body and the side wall may be used as
a path for air supply or exhaustion.
[0086] In the second embodiment, gas supplied into the apparatus is
air, but gas having an adjusted composition, such as a mixture gas
of nitrogen and oxygen or the like, an inert gas such as argon or
the like, or the like may be supplied into the apparatus.
[0087] In the first embodiment, exhaustion is performed from the
intermediate section where the communication path is formed, but
air supply may be performed on the lower section at the same time
so as to prevent atmospheric pressure of the lower section from
decreasing. Here, the air supply hole into the apparatus chamber
may be provided at a location lower than the electrode tip 22a in a
vertical direction, and an upper location from the lower end of the
mold 2, so as to promote reduction of contamination due to
fume.
[0088] In the second embodiment, air supply is performed on the
intermediate section where the communication path is formed, but
the air supply may be performed from the lower section at the same
time, so as to reduce density of fume in the lower section.
[0089] Also, in the above embodiment, the lower section has a
bottom surface, but a ceiling may be additionally formed on an
upper side of the upper section. Here, gas may be supplied to the
communication path while exhausting gas from the upper section, or
gas may be exhausted from the communication path while supplying
gas to the upper section.
[0090] Also, in the above embodiments, only exhaustion or air
supply is performed on the communication path, but both exhaustion
and air supply may be performed on the communication path at the
same time.
[0091] For example, a third barrier wall may be formed on the
second barrier wall, and a lower layer inserted between the first
barrier wall and the second barrier wall, and an upper layer
surrounded by the second barrier wall and the third barrier wall
may be set in the intermediate section, so as to connect the air
supply device to the upper layer and connect the exhaust device to
the lower layer. Accordingly, gas is more effectively prevented
from being mixed in the upper section and the lower section.
[0092] The present invention is not limited to the structure of
each embodiment described above, as long as blocking or sealing of
air flow is possible. Another configuration is possible. One
example is a configuration where the through holes 18, 20, 210, or
the like are provided so as to allow adjustment of the opening
angle of the arc electrodes 22 penetrating through the barrier wall
6 constituting a ceiling portion that blocks the upper side of the
apparatus chamber. The through holes 18 etc. are not covered and
air flow is provided to the through holes 18 etc. so as to isolate
the upper and lower portions of the barrier wall 6. Here, for
example, the sheath body 7 in FIG. 5 is removed, and an ejection
angle of the conduit line 190 is adjusted so that the blocking or
sealing by the air flow is possible.
EXAMPLES
Example 1
[0093] One hundred vitreous silica crucibles having an outer
diameter of 802 mm were manufactured by using the apparatus having
the structure of the first embodiment. After the manufacturing, a
yield was determined by visually inspecting products to determine
whether impurities were adhered to the bottom surface and whether
the bottom surface was uneven.
Comparative Example 1
[0094] One hundred vitreous silica crucibles having an outer
diameter of 802 mm were manufactured by using an apparatus having a
structure according to a conventional technology, which performs
air supply and exhaustion to a lower section. After manufacturing,
a yield was determined by visually inspecting products to determine
whether impurities were adhered to the bottom surface and whether
the bottom surface was uneven.
TABLE-US-00001 TABLE 1 Example 1 Comparative Example 1 Yield 95%
82%
[0095] Table 1 shows inspection results of Example 1 and
Comparative Example 1. Based on such results, it can be determined
that productivity of the vitreous silica crucible in Example 1
according to the present embodiment is far better compared to
Comparative Example 1 that does not control air flow inside the
apparatus.
INDUSTRIAL APPLICABILITY
[0096] According to the present invention, in a process of
manufacturing a vitreous silica crucible, circulation of gas may be
separated in an upper section and a lower section of an apparatus
used in the manufacturing process. Accordingly, damage and wear of
an apparatus due to fume generated while vitrifying silica powder
can be prevented while preventing contamination of a vitreous
silica crucible due to dust or the like generated from the
apparatus. Accordingly, according to the present invention, a high
quality vitreous silica crucible that can be used to pull up a high
purity semiconductor crystal can be supplied with stable
productivity.
EXPLANATION OF REFERENCE NUMERALS
[0097] 1: Side wall
[0098] 2: Mold
[0099] 3: Silica powder molded body
[0100] 4: Mold driving unit
[0101] 6: First barrier wall
[0102] 8, 80: Second barrier wall
[0103] 10: Sectioning member
[0104] 7: Sheath body
[0105] 12: Exhaust hole
[0106] 13: Air supply hole
[0107] 14: Exhaust path
[0108] 15: Air supply path
[0109] 16: Exhaust device
[0110] 17: Air supply device
[0111] 18: Lower communication hole
[0112] 20: Upper communication hole
[0113] 21, 210: Communication path
[0114] 19, 190: Conduit line
[0115] 22: Arc electrode
[0116] 24: Electrode driving unit
* * * * *