U.S. patent number RE36,936 [Application Number 09/133,933] was granted by the patent office on 2000-10-31 for production of high-purity polycrystalline silicon rod for semiconductor applications.
This patent grant is currently assigned to Advanced Silicon Materials, Inc.. Invention is credited to Junji Izawa, David W. Keck, Hiroshi Morihara, Kenichi Nagai, Yoshifumi Yatsurugi, Renzin Paljor Yuthok.
United States Patent |
RE36,936 |
Keck , et al. |
October 31, 2000 |
**Please see images for:
( Certificate of Correction ) ** |
Production of high-purity polycrystalline silicon rod for
semiconductor applications
Abstract
Disclosed are .[.a.]. processes and reactors for rapidly
producing large diameter, high-purity polycrystalline silicon rods
for semiconductor applications by the deposition of silicon from a
gas containing a silane compound. The equipment includes a reactor
vessel which encloses a powder catcher having a cooled surface.
Also within the vessel is a cylindrical water jacket which defines
multiple reaction chambers. The silicon powder generated in this
process adheres to the coolest surfaces, which are those of the
powder catcher, and is thereby collected. Little of the powder
adheres to the walls of the reaction chambers. In some embodiments,
a fan can be provided to increase gas circulation.
Inventors: |
Keck; David W. (Butte, MT),
Nagai; Kenichi (Moses Lake, WA), Yatsurugi; Yoshifumi
(Fujisawa, JP), Morihara; Hiroshi (Gresham, OR),
Izawa; Junji (Hadano, JP), Yuthok; Renzin Paljor
(Moses Lake, WA) |
Assignee: |
Advanced Silicon Materials,
Inc. (Moses Lake, WA)
|
Family
ID: |
26969923 |
Appl.
No.: |
09/133,933 |
Filed: |
August 13, 1998 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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296964 |
Aug 26, 1994 |
5478896 |
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953480 |
Sep 28, 1992 |
5382419 |
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Reissue of: |
488103 |
Jun 7, 1995 |
05545387 |
Aug 13, 1996 |
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Current U.S.
Class: |
423/348; 118/719;
118/725; 264/81; 423/349; 427/248.1 |
Current CPC
Class: |
C01B
33/035 (20130101); C23C 16/4401 (20130101); C23C
16/4418 (20130101); C23C 16/45589 (20130101); C23C
16/45593 (20130101) |
Current International
Class: |
C01B
33/00 (20060101); C01B 33/035 (20060101); C23C
16/44 (20060101); C01B 033/02 () |
Field of
Search: |
;423/348,349 ;264/81
;427/248.1 ;118/719,725 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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728584 |
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Feb 1966 |
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CA |
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0181803 |
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Oct 1985 |
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EP |
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0180397 |
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Oct 1985 |
|
EP |
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0324504 |
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Jan 1989 |
|
EP |
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2808462 |
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Sep 1978 |
|
DE |
|
2808461 |
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Sep 1978 |
|
DE |
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44-31717 |
|
Dec 1969 |
|
JP |
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63-123806 |
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May 1988 |
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JP |
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Other References
Blocher et al., "Survey of Options in a Balanced System for
Production of Silicon by Thermal Decomposition of Trichlorosilane",
Columbus Laboratories, Columbus, Ohio, pp. 140-158, published
before Apr. 1, 1992..
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Primary Examiner: Bueker; Richard
Attorney, Agent or Firm: Klarquist Sparkman Campbell &
Leigh & Whinston, LLP
Parent Case Text
This is a continuation of application Ser. No. 296,964, filed Aug.
26, 1994, .Iadd.now U.S. Pat. No. 5,478,396, .Iaddend.which is a
continuation-in-part of application Ser. No. 953,480, filed Sep.
28, 1992, now U.S. Pat. No. 5,382,419.
Claims
We claim:
1. A process for the production of polycrystalline silicon rods
from a silicon-bearing gas, the process comprising:
providing a reactor vessel having an interior surface including a
floor, a wall and a ceiling, the vessel containing .[.a cooled
partition with a wall which defines.]. multiple reaction chambers
and containing a powder catcher which is displaced from the
reaction chambers, has a cooled wall, and is in the form of a heat
exchange tube array;
positioning a starter filament in each reaction chamber where a
polycrystalline silicon rod is to be grown;
heating the starter filaments;
passing a silicon-bearing reactant gas through the reaction
chambers such that polycrystalline silicon deposits on the starter
filaments and forms silicon powder due to the thermal decomposition
of a silicon compound in the reactant gas; and
passing the reactant gas, with entrained silicon powder, from the
reaction chambers into contact with the cooled wall of the powder
catcher.
2. The process as defined by claim 1, further comprising regulating
the flow of the reactant gas by positioning a flow resistant plate
along the
path of reactant gas flowing inside the reactor vessel.
3. The process as defined by claim 1, further comprising inhibiting
deposition of silicon powder on the ceiling of the reactor above
the reaction chambers by positioning a metal or ceramic heat shield
plate above the reaction chambers such that reactant gas exiting
the reaction chambers is diverted from flowing directly to the
ceiling of the vessel.
4. The process as defined by claim 1, further comprising:
providing the powder catcher in the shape of a cylinder; and
injecting the reactant gas alongside and in a circumferential
direction with respect to the powder catcher.
5. The process as defined by claim 1, further comprising
maintaining the relationship of
T2.[..ltoreq..]..Iadd.<.Iaddend.T1.[..ltoreq..]..Iadd.<.Iaddend.T3
where T1 is the wall temperature of the reaction chambers, T2 is
the wall temperature of the powder catcher, and T3 is the reactor
ceiling temperature.
6. The process as defined by claim 5, further comprising
maintaining the temperature to be T1>25.degree. C.,
T2<25.degree. C., and T3>70.degree. C.
7. A process for the production of polycrystalline silicon rods
from a silicon-bearing gas, the process comprising:
providing a reactor vessel having an interior surface including a
floor, a wall and a ceiling, the vessel containing .[.a cooled
partition with a wall which defines.]. multiple reaction chambers
and containing a powder catcher which is displaced from the
reaction chambers, has a cooled wall, and is in the shape of a disk
that defines a central vertical passageway and that is located at
an elevation above the tops of the reaction chambers;
positioning a starter filament in each reaction chamber where a
polycrystalline silicon rod is to be grown;
heating the starter filaments;
passing a silicon-bearing reactant gas through the reaction
chambers such that polycrystalline silicon deposits on the starter
filaments and forms silicon powder due to the thermal decomposition
of a silicon compound in the reactant gas; and
passing the reactant gas, with entrained silicon powder, from the
reaction chambers into contact with the cooled wall of the powder
catcher.
8. A process for the production of polycrystalline silicon rods
from a silicon-bearing gas, the process comprising:
providing a reactor vessel having an interior surface including a
floor, a wall, and a ceiling, the vessel containing (a) .[.a cooled
partition with a wall which defines.]. multiple reaction chambers,
(b) a powder catcher which is displaced from the reaction chambers,
has a cooled wall, and is in the form of a heat exchange tube
array, and (c) a recirculation fan positioned between the powder
catcher and the reaction chambers;
positioning a starter filament in each reaction chamber where a
polycrystalline silicon rod is to be grown;
heating the starter filaments;
passing a silicon-bearing reactant gas through the reaction
chambers such that polycrystalline silicon deposits on the starter
filaments and forms silicon powder due to the thermal decomposition
of a silane gas in the reactant gas, the silane gas being selected
from the group consisting of monosilane, disilane, and mixtures
thereof;
passing the reactant gas, with entrained silicon powder, from the
reaction chambers into contact with the cooled wall of the powder
catcher; and
operating the recirculation fan to move reactant gas from the
vicinity of the powder catcher back into the reaction chambers.
9. The process as defined by claim 8, wherein a metal or ceramic
heat shield plate is installed in the top section of the
reactor.
10. The process as defined by claim 8, further comprising
channeling all reactant gas in the vicinity of the powder catcher
through the recirculation fan.
11. The process as defined by claim 8, further comprising
inhibiting deposition of silicon powder on the ceiling of the
reactor above the reaction chambers by positioning a metal or
ceramic heat shield plate above the reaction chambers such that
reactant gas exiting the reaction chambers is diverted from flowing
directly to the ceiling of the vessel.
12. The process as defined by claim 8, further comprising:
providing the powder catcher in the shape of a cylinder; and
injecting monosilane gas alongside and in a circumferential
direction with respect to the powder catcher.
13. The process as defined by claim 8, further comprising
maintaining the relationship of
T2.[..ltoreq..]..Iadd.<.Iaddend.T1.[..ltoreq..]..Iadd.<.Iaddend.T3
where Ti is the wall temperature of the reaction chambers, T2 is
the wall temperature of the powder catcher, and T3 is the reactor
ceiling temperature.
14. The process as defined by claim 13, further comprising
maintaining the temperature to be T1>25.degree. C.,
T2<25.degree. C., and T3>70.degree. C.
15. A process for the production of polycrystalline silicon rods
from a silicon-bearing gas, the process comprising:
providing a reactor vessel having an interior surface including a
floor, a wall, and a ceiling, the vessel containing (a) .[.a cooled
partition with a wall which defines.]. multiple reaction chambers,
and (b) a powder catcher which comprises a cooled wall provided by
a heat exchange tube array in the shape of disk that defines a
vertical passageway and which is displaced from and located at an
elevation above the reaction chambers;
positioning a starter filament in each reaction chamber where a
polycrystalline silicon rod is to be grown;
heating the starter filaments;
passing a silicon-bearing reactant gas through the reaction
chambers such that polycrystalline silicon deposits on the starter
filaments and forms silicon powder due to the thermal decomposition
of a silane gas in the reactant gas, the silane gas being selected
from the group consisting of monosilane, disilane, and mixtures
thereof;
passing the reactant gas, with entrained silicon powder, from the
reaction chambers into the tube array where the silicon powder
deposits the cooled wall;
passing the reactant gas from the tube array into the passageway;
and
recirculating at least a portion of the reactant gas from the
passageway into the reaction chambers. .Iadd.16. The process as
defined by claim 1, further comprising providing the powder catcher
at a location that is not
over the reaction chambers..Iaddend..Iadd.17. The process as
defined by claim 7, further comprising providing the powder catcher
at a location that is not over the reaction
chambers..Iaddend..Iadd.18. The process as defined by claim 8,
further comprising providing the powder catcher at a location that
is not over the reaction chambers..Iaddend..Iadd.19. The process as
defined by claim 10, further comprising providing the powder
catcher at a location that is not over the reaction
chambers..Iaddend..Iadd.20. The process as defined by claim 12,
further comprising providing the powder catcher at a location that
is not over the reaction chambers..Iaddend..Iadd.21. The process as
defined by claim 15, further comprising providing the powder
catcher at a location that is not over the reaction
chambers..Iaddend.
Description
BACKGROUND OF THE INVENTION
The present invention relates to a process and equipment for the
production of high-purity polycrystalline silicon in rod form for
semiconductor applications. The polycrystalline silicon is used as
the raw material in the fabrication of single crystal silicon for
semiconductors by the CZ (Czochralski) method or the FZ (float
zone) method.
The most common method of producing polycrystalline silicon, which
is a raw material used for the production of single crystal silicon
for semiconductors, has been to deposit silicon on starter
filaments by thermal decomposition of a halosilane compound, such
as trichlorosilane, so as to produce large-diameter silicon rods.
Japanese Patent Laid-Open No. 56-105622 discloses a reactor
structure using a chloride-type silane in which a large number of
electrodes are arranged on a circular plate and a large number of
silicon starter filaments are arranged in a reverse-U-shaped or a
square-reverse-U-shaped form.
This technique, however, is not suitable for industrial scale
production of polycrystalline silicon from a silane compound, such
as monosilane gas or disilane gas, which is not halogenated. At a
temperature of several hundred degrees or more, monosilane gas
decomposes and thereby generates a fine silicon powder. The
presence of such powder causes a number of difficulties and, in
particular, can seriously hinder the growth of silicon rods.
Further, where the high-temperature silicon rods face each other,
surface irregularities are generated, thereby deteriorating product
quality.
A known technique for dealing with the above problems is disclosed
in U.S. Pat. No. 4,150,168, according to which red-hot silicon
starter filaments are thermally insulated from each other so as to
prevent vapor-phase temperature rise and as to eliminate thermal
influences from the adjacent heated silicon rods, thereby obtaining
uniform silicon rods.
However, in the industrial scale production of silicon rods by
thermal decomposition of monosilane, it is impossible, even with
the above-mentioned technique, to reduce the silicon powder
generation to zero. The generated silicon powder is deposited on
the reactor walls. When it has accumulated to a thickness of
several mm, the silicon powder spontaneously separates from the
walls and falls, part of the falling powder contacting and adhering
to the growing silicon rods. The portion of the powder which
adheres to the silicon rods may lead to powder intrusion, abnormal
dendrite growth or the like, resulting in defective products.
Japanese Patent Laid-Open No. 61-101410 discloses a technique which
is somewhat improved over that of U.S. Pat. No. 4,150,168, in that
the reactor has a different heat insulation structure. However, for
reasons given in a reference by Hogness et al. (Hogness, T. R.,
Wilson, T. L., Johnson, W. C.: "The Thermal Decomposition of
Silane" J. Am. Chem. Soc. 58: 108-112, 1936), the new technique is
likely to require a serious decrease in reaction speed in order to
obtain the restraint of the silicon powder growth.
Japanese Patent Publication No. 44-31717 discloses a technique for
collecting silicon powder outside a reactor. With this technique,
the silicon powder generated in the course of production of
polycrystalline silicon rods is taken out of the reactor along with
the partially spent reactant gas. The powder is collected by means
of a filter, and the gas cleared of powder is re-circulated through
the reactor. A similar technique is disclosed in U.S. Pat. No.
4,831,964. A problem with these techniques is that they require
large scale equipment external to the reactor. Thus, they involve
an increase in the number of components, resulting in an increase
in the opportunity of contamination. Further, the silicon powder
adhering to such components accumulates in places where it cannot
be easily removed by cleaning or in places which are hard to clean.
The silicon powder is very active, so that it is easily ignited by
static electricity or the like. And, an ignition of a mixture of
air and silicon powder can cause a detonation. It is another
problem that silicon powder deteriorates the sealing property of
valves used to isolate the reactor from the external equipment when
extracting silicon rods, performing cleaning, etc. Thus, handling
of the silicon powder is best kept to a minimum.
Japanese Patent Publication No. 52-36490 discloses a special method
of causing a reactive gas to circulate in a reactor. The method
employs a means for uniformalizing the concentration of monosilane
gas in the reactor. It prevents monosilane gas at high
concentration or pure monosilane gas from reaching a
high-temperature section of the reactor in the vicinity of the
silicon starter filaments, thereby restraining the generation of
silicon powder. A problem with this method is that no measure is
taken to contain the radiation of heat from the heat generating
elements. Thus, the technique is not suitable for the thermal
decomposition of monosilane gas. Further, because the rods are not
grown in separate reaction chambers, it is difficult to supply the
reactive gas in a uniform fashion. As a result, it is hard for the
grown silicon rods to attain a high level of roundness in cross
section, the rod diameter differing from rod to rod.
A technique for increasing the flow velocity of reactive gas is
disclosed in Japanese Patent Laid-Open No. 63-123806, according to
which an agitator is provided in the top or bottom section of a
reactor. This technique, however, is not suitable where a
nonhalogenated silane compound gas is used since silicon powder
would be generated and dispersed by the agitator.
Apart from the problems discussed above, these prior techniques
have a problem which is common to them: the absence of a means for
preventing the silicon powder which is generated by vapor-phase
homogeneous reaction, from accumulating on the walls around the
silicon rods and on the reactor ceiling. Defective products result
due to the adhesion of silicon powder detached from the reactor
walls. Silicon rods are hard to dissolve where the silicon powder
has adhered, thus making monocrystallization difficult. Therefore,
silicon rods with adhered powder are suitable for neither the CZ or
the FZ method.
Further, it is considered that the precipitation rate of
polycrystalline silicon will be low when a reactor structure
encourages the accumulation of silicon powder on the walls around
growing polycrystalline silicon rods and on walls in the reactor
ceiling section.
Polycrystalline silicon, in the form of rods or chunks obtained by
crushing rods, is being widely used in the production of single
crystal silicon by the CZ or FZ method. A high purity level and
competitive cost are particularly required of polycrystalline
silicon rods for semiconductor applications. These requirements are
becoming severer from year to year. The present invention has been
made in view of the above problems in the prior art.
Accordingly, there is a need to provide a process and equipment
which make it possible to produce large diameter polycrystalline
silicon rods rapidly while making efficient use of a gas feedstock
that contains a nonhalogenated silane compound.
SUMMARY OF THE INVENTION
The present invention provides a process and equipment for the
production of polycrystalline silicon in rod form for semiconductor
applications by thermal decomposition of a highly refined reactant
gas containing a nonhalogenated silane compound such as monosilane
or disilane.
Walls inside a reactor define multiple reaction chambers for
growing polycrystalline silicon in rod form and provide powder
catchers for collecting silicon powder generated during the thermal
decomposition of the silane compound. The powder catcher walls
define at least one powder catcher chamber that is separate from,
but communicates with, the reaction chambers. Both the reaction and
powder catcher chambers define flow paths for the reactant gas.
In a first embodiment, the reactor contains a plurality of powder
catchers consisting of vertically-extending cylindrical water
jackets which are arranged concentrically, and multiple reaction
chambers which are cylindrical channels defined by an outer
cylindrical water jacket surrounding the powder catchers. The
powder catcher chambers and reaction chambers communicate via
spaces defined above and below the outer water jacket.
Preferably, the total cross-sectional area of the powder catcher
chambers is larger than that of the reaction chambers,
.[.and-the.]. .Iadd.and the .Iaddend.total surface area of the
powder catcher walls is larger than that of the walls which define
the reaction chambers. Resistant baffle plates are provided at the
lower ends of the reaction chambers and at the upper or the lower
ends of the powder catcher chambers for the purpose of controlling
reactant gas flow; a metal or ceramic plate is installed as a heat
shield plate in the top section of the reactor; and a plurality of
nozzles for feeding monosilane gas into the reactor are positioned
within the upper regions of the powder catcher chambers and
directed circumferentially with respect to the powder catchers.
Further, in a method of producing polycrystalline silicon using the
above-described equipment for the production of polycrystalline
silicon in rod form for semiconductor applications, the
relationship
T2.[..ltoreq..]..Iadd.<.Iaddend.T1.[..ltoreq..]..Iadd.<.Iaddend.T3
is maintained, where T1 is the wall temperature of the reaction
chambers, T2 is the wall temperature of the powder catchers, and T3
is the wall temperature of the reactor ceiling. For optimum
results, temperature control is effected in such a way that T1 is
.[.b.]. 25.degree. C. or more, T2 is 25.degree. C. or less, and T3
is 70.degree. C. or more.
In other embodiments, the powder catcher is located at an elevation
above the reaction chambers. The powder catcher, which most
advantageously includes an array of heat exchange tubes, is
preferably offset horizontally so that the tubes are not located
directly above the reaction chambers. The tubes are positioned such
that gas flowing from the reaction chambers flows through the array
of tubes where powder deposits on the cooled surface provided by
the tubes. At least a portion of the reactant gas that passes
through the tubes is recirculated into the reaction chambers.
.[.In-either.]. .Iadd.In either .Iaddend.embodiment, a fan can be
installed at a position in the reactant gas flow and, more
specifically, at a position below the powder catcher(s) so as to
control the reactant gas circulation in the reactor on the basis of
the rotating speed of the fan. To direct the reactive gas flow to
pass through the fan, a shroud can be provided to isolate the
powder catcher chamber(s) and the reaction chambers from each
other.
The above-described apparatuses provide one or more of the
following advantages:
(1) The degree of freedom in setting the reaction conditions is
substantially increased, as compared with the prior art, by virtue
of a construction in which a large number of reaction chambers for
growing polycrystalline silicon in rod form and one or more powder
catchers for collecting silicon powder are arranged inside a common
reactor vessel in such a way as to extend along a reactant gas flow
path and as to be separate from each other. Since the reaction
chambers and the powder catcher(s) are separated from each other
and installed inside the same reactor, optimum conditions can be
obtained for their respective functions. That is, by making the
cooling temperature of the powder catcher(s) lower than that of the
reaction chambers, the flow velocity of the descending gas is
increased, with the result that the ascending speed of the gas flow
in the reaction chambers is increased, thereby making it possible
to increase the rate of reactant gas supply, produce large diameter
polycrystalline silicon rods in a short time, and reduce production
costs.
(2) When the wall surfaces of the powder catchers or the gas return
passageways are vertical and the total space cross-sectional area
of vertical powder catcher chambers or gas return passageways is
larger than that of the reaction chambers, the resistance with
respect to the downward flow of the reactant gas is reduced,
thereby increasing the flow velocity of the gas flowing upwards in
the reaction chambers. Accordingly, it is possible to feed a larger
amount of reactant gas, thereby raising the growth speed of the
polycrystalline silicon rods. Further, the adhesion of silicon
powder to the reaction chamber walls can be prevented to a large
degree.
(3) By making the total surface area of the powder catchers larger
than that of the reaction chamber walls, the collection of silicon
powder by the powder catchers is facilitated.
(4) When resistant plates for reactant gas flow control are
provided at the upper ends of the reaction chambers and/or at the
upper or the lower ends of vertical powder catcher chambers, it is
possible to adjust the supply of gas to the reaction chambers and
thereby obtain a predetermined uniform flow rate where there would
otherwise be some irregularity in the gas flow pattern inside the
reactor. As a result, the gas flow in the reactor is uniformalized,
and the growing conditions for the polycrystalline silicon rods can
be optimized.
(5) When a shield plate is provided above the reaction chambers, it
is possible to maintain the ceiling section of the reactor vessel
at a higher temperature, thereby more reliably preventing the
adhesion of silicon powder to the ceiling section of the reactor
vessel.
(6) When a plurality of feed nozzles for feeding part of the
reactant gas into the reactor are arranged at a level corresponding
to the upper regions of vertical powder catcher chambers and in
such a way as to be directed in the circumferential direction with
respect to the powder catchers, new reactant gas can be injected
horizontally at an angle of 90.degree. with respect to the
downstream flow in the powder catcher chamber(s). This agitates the
recirculating reactant gas and makes the overall concentration of
silicon compound gas more uniform. Due to this enhancement in
mixing, it is possible to feed a large amount of reactant gas under
optimum gas distribution conditions. Accordingly, the growing speed
of the polycrystalline silicon rods is increased.
(7) Since the temperature control can be effected in such a way
that the reaction chamber wall temperature T1 is 25.degree. C. or
more, the powder-catcher wall temperature T2 is 25.degree. C. or
less, and the reactor-ceiling wall temperature T3 is 70.degree. C.
or more, the velocity of the monosilane gas, flowing downwards
along the powder catcher walls, is increased, thereby increasing
the velocity of the gas flowing upwards inside the reaction
chambers. Due to this arrangement, reactant gas can be supplied to
the reaction chambers at a high rate, thereby making it possible to
produce large-diameter silicon rods in a short period of time.
Further, as a result of the increase in the gas flow velocity, gas
does not linger in the reaction chambers so that adhesion of
silicon powder to the reaction chamber walls can be avoided. Since
the temperature of the powder catcher walls is set to be lower than
that of the other surfaces inside the reactor, the silicon powder
collecting effect is enhanced remarkably.
(8) When a fan is provided below the powder catcher(s) and a shroud
isolates the powder catcher chambers or gas return passageway(s)
.[.from-the.]. .Iadd.from the .Iaddend.reaction chambers, the flow
velocity of the gas fed into the reaction chambers can be
controlled by adjusting the fan rotating speed and it is possible
to further increase the rate of reactant gas feed through the
reaction chambers. By adjusting the fan velocity, it is possible to
achieve the optimum gas flow rate, thereby increasing the growing
speed of the polycrystalline rods.
Most reactors in use nowadays are made of metal, taking into
consideration equipment cost, management, safety, and the like. In
the production equipment of the present invention, a nonhalogenated
silane gas is used instead of a chloride-type silane gas, which is
highly corrosive. Therefore, a secondary contamination of
polycrystalline silicon due to corrosion of the reactor can be
avoided. Further, the thermal decomposition of nonhalogenated
silane compound gas is accompanied by a vapor-phase uniform
decomposition, which is a reaction involving the generation of
silicon powder, so that it is remarkably different from the thermal
decomposition of a chloride-type silane gas. Therefore, adopting a
reactor configuration which is the same as that of a reactor using
a halogenated silane gas, would result in a rather low reaction
speed and yield at a very low level.
BRIEF DESCRIPTION OF THE DRAWINGS
In the Drawings:
FIG. 1 is a schematic vertical sectional view showing a first
reactor according to the present invention for the production of
high-purity polycrystalline silicon rods for semiconductor
applications;
FIG. 2 is a partial perspective view showing an upper portion of a
cooling jacket and of reaction chambers defined thereby;
FIG. 3 is a partial schematic sectional view taken along line 3--3
of FIG. 1;
FIG. 4 is a schematic vertical sectional view showing a second
reactor according to the present invention;
FIG. 5 is a schematic vertical sectional view showing a third
reactor according to the present invention;
FIG. 6 is a schematic vertical sectional view showing a fourth
reactor according to the present invention.
DETAILED DESCRIPTION
Preferred embodiments of processes and equipment for the production
of high-purity polycrystalline silicon in rod form for
semiconductor applications, according to the present invention,
will now be described with reference to the drawings.
In the equipment shown in FIGS. 1-3, a verger-type cover or bell 1
and a round base plate 2 provide a reactor vessel. A cylindrical
partition member 4, that is a heat exchanger or water jacket and
that is shaped to define multiple reaction chambers 3, is provided
inside a cylindrical space defined by the cover 1 and base plate 2.
Cylindrical powder catchers 5 and 6 are concentrically arranged
within the partition member 4. The water jacket 4 and powder
catchers 5 and 6 are sized and spaced such that there are annular
powder catcher chambers therebetween and a cylindrical powder
catcher chamber at the center of the powder catcher 6. The powder
catcher chambers serve as gas downflow passageways. The reaction
chambers 3 consist of cylindrical spaces arranged at equal
intervals in the vicinity of the outer periphery of the water
jacket 4. Openings 4a leading from the outer periphery of the water
jacket 4 to the reaction chambers 3 are provided for purpose of
enabling the extraction of polycrystalline silicon rods which have
been completely grown.
The cover 1 and the powder catchers 5 and 6 are at least partially
hollow and serve as water cooled heat exchangers or cooling
jackets. The cover 1 is formed by connecting upper and lower cover
sections 1a and 1b with each other. The lower surface of the upper
cover section 1a serves as the reactor vessel ceiling. Provided in
the upper cover section 1a are a cooling water inlet 1c and a
cooling water outlet 1d. Provided in the lower cover section 1b are
a cooling water inlet 1e and a cooling water outlet 1f. As it moves
from the inlet 1c to the outlet 1d, cooling water flows through the
space between the inner and outer walls of the cover. Connected to
the bottoms of the water jacket 4 and the powder catchers 5 and 6
are cooling water supply pipes 7a, 7b, 7c and 7d which extend from
below through the base plate 2. The pipes 7b and 7d are used to
supply cooling water to spaces inside the powder catchers 5 and 6
and to discharge it therefrom. Electrodes 9 extend from below
through the base plate 2, through the intermediation of insulating
members 8, and are arranged at positions corresponding to the
centers of the reaction chambers 3. Chucks 10 are attached to the
tips of the electrodes 9. The water flowing through the water
cooling jackets may be replaced by another fluid cooling or a
heating medium. Further, the powder catcher may be a bundle of
pipes or of a coil type.
In the embodiment of FIG. 1, a fan 20 and a shroud 21 are provided
below the powder catchers 6 to enhance and control the circulation
of gas inside the reactor.
A silane gas pipe 11 extends from below through the base plate 2
and upwards between powder catchers 5 and 6. Connected to an
annular header 12, which is connected to the upper end of the
silane gas pipe 11, are a plurality of gas nozzles 13 which are
open in the same circumferential direction. The nozzles are thus
aimed to cause silane gas to move circumferentially along walls of
the powder catchers 5 and 6. Provided inside each of the gas
nozzles 13 is a capillary or an orifice to enable the silane gas to
be ejected uniformly through the nozzles 13.
Resistant plates 14 are arranged at appropriate intervals inside
the reactor. The plates extend transversely to gas downflow
passageways to regulate gas flow. In the illustrated embodiment,
the plates 14 are firmly attached to the upper ends of the powder
catchers 5 and 6. Such resistant plates may also be firmly attached
to the lower end of the water jacket 4 and/or the powder catchers 5
and 6, and/or connected to the header 12 above the powder catchers
5 and 6. Provided in the space above the water jacket 4 is a heat
shield plate 15. An exhaust pipe 16 extends through the base plate
2 and can be used to remove spent reactant gas. Silane gas pipes
11a allow silane gas to be evenly ejected into each reaction
chamber at an arbitrary position 13a on the water cooling jacket
4.
Next, a process for producing polycrystalline silicon rods using
the above apparatus will be described. Silicon starter filaments 17
are positioned in the reaction chambers 3 and held by the chucks
10. Above each of stepped sections 4b of the water cooling jacket
4, a pair of silicon starter filaments 17 are connected to each
other at their upper ends through a silicon bridge 18. Cooling
water is circulated through the cover 1, the water jacket 4 and the
powder catchers 5 and 6. The silicon starter filaments 17 are
heated by directly supplying electricity thereto through the
electrodes 9.
Reactant gas, which contains a silane gas, is fed into the reactor
through the reactant gas pipes 11, the header 12 and the gas
nozzles 13. Reactors according to the present invention are
particularly suited for use with a reactant gas that contains
silicon in the form of a nonhalogenated silane compound, such as
monosilane or disilane, or a mixture of such compounds. The
reactant gas, which is ejected horizontally in the circumferential
direction, is agitated by a downward gas flow along the wall
surfaces of the powder catchers 5 and 6. Because they are moving in
different directions, the gas streams mix and are agitated to
produce a combined reactant gas having a uniform concentration of
the silicon-containing compound(s). Then, while ascending inside
the reaction chambers 3, which are heated by the silicon starter
filaments 17, the gas reacts to deposit polycrystalline silicon 19
on the silicon starter filaments 17. Reactant gas which has been
blown upwards beyond the reaction chambers 3 next descends along
the wall surfaces of the powder catchers 5 and 6 and then returns
to the reaction chambers 3. It is advantageous to circulate
reactant gas at a high flow rate so that any silicon powder will
remain entrained in the gas until it reaches a cooled surface of
the powder catcher. To operate at an increased gas flow rate, the
reactant gas can comprise a mixture that includes one or more
nonhalogenated silane compounds and a diluent, such as hydrogen gas
or an inert gas such as helium or argon. And, conversely, to
achieve a desired rate of silicon deposition on the rods, the rate
of gas flow should be increased when the
concentration of silicon-containing compounds in the reactant gas
is reduced. The diluent gas is preferably mixed, using mass flow
controllers to maintain a desired ratio, with the silane-containing
gas before the reactant gas is injected into the reactor. However,
it would be possible to have a separate set of injection nozzles
(not shown) for injection of the diluent gas.
To inhibit uneven growth in the diameter of the polycrystalline
silicon rods at different elevations, a supplementary stream of
reactant gas can be provided through the reactant gas pipe 11a and
the gas nozzle 13a. The added gas makes up for the depletion of
silane from the reactant gas that moves upwardly in the reaction
chambers 3.
The powder catchers 5 and 6 perform the two functions of collecting
silicon powder and effecting heat exchange. Accordingly, the
temperature in the reaction chambers 3 can be independently
regulated to achieve the best growth conditions for polycrystalline
silicon rods.
If the regions surrounding the powder catchers 5 and 6 are cooled
to a temperature lower than that of other regions inside the
reactor, the velocity of downward gas flow along the powder
catchers 5 and 6 is increased, with the result that the velocity of
the upwards flow in the reaction chambers 3 is increased. As a
result, it is possible to circulate a large volume of
silane-containing gas through the reactor chambers 3. Further,
since floating silicon powder collects on cool surfaces, such as on
the walls of the powder catchers 5 and 6, accumulation thereof on
the walls of the reaction chambers 3 and the reactor ceiling
section can be avoided to a large degree.
Because of the multi-layer structure in the horizontal direction of
the powder catchers, it is possible to enhance the cooling effect
and the collection of the silicon powder while suppressing
resistance to downward gas flow. However, it is difficult to attach
a plurality of powder catchers while maintaining a high degree of
concentricity thereof. If the gaps between the powder catchers are
not uniform, the reactant gas cannot flow uniformly into the
different sections of the reactor. To compensate for uneven
spacing, the resistant plates or baffles 14 are attached to the
bottom section of the water cooling jacket 4 and to the top or the
bottom sections of the powder catchers 5 and 6 for the purpose of
controlling the gas flow. The width, length and mounting angle of
the resistant plates 14 are selected to achieve optimum results.
The resistant plates 14 can also be used to control any turbulence
in the gas flow caused by supports or like structures attached to
the water jacket 4 or the powder catchers 5 and 6 due to any
requirement in strength.
It is especially important to maintain the relationship:
T2.[..ltoreq..]..Iadd.<.Iaddend.T1.[..ltoreq..]..Iadd.<.Iaddend.T3,
where T1 is the wall temperature of the reaction chambers 3, T2 is
the wall temperature of the powder catchers 5 and 6, and T3 is the
wall temperature of the upper section of the verger-type cover 1.
By making the wall temperature T3 of the reactor ceiling section
high, the adhesion of silicon powder to the ceiling section further
decreases.
It is desirable that the wall temperature T1 of the reaction
chambers 3 be 25.degree. C. or more. Further, the temperature of
the lower cover section 1b opposed to the reaction chambers 3 is
also set to be 25.degree. C. or more. A cooling water at a
temperature of 30.degree. C. to 40.degree. C. can be easily
obtained by utilizing equipment such as a cooling tower. It is
desirable for the wall temperature T2 of the powder catchers 5 and
6 to be 25.degree. C. or less. Also in this regard, a cooling water
at a temperature of 10.degree. C. to 15.degree. C. can be easily
achieved by directly utilizing water drawn from a well. Cooling
water at a temperature of approximately 5.degree. C. can be easily
supplied by utilizing equipment such as a chiller.
It has been experimentally ascertained that circulating silicon
powder is most likely to adhere to and accumulate on surfaces of
the lowest temperature. The lower the temperature, the greater the
amount of adhesion. A cooling water temperature around 5.degree. C.
is desirable for the powder catchers 5 and 6 for powder removal
efficiency. It is desirable that the wall temperature of the
reactor ceiling section, i.e., the temperature T3 of the upper
cover section 1a, be 70.degree. C. or more. When using water, the
phenomenon of boiling may take place at a mean water temperature of
around 85.degree. C., depending upon the conditions, so that it is
more desirable to use a heating medium other than water when a
temperature of 85.degree. C. or more is involved. When the
difference between the temperatures T1 and T3 becomes approximately
30.degree. C. or more, the effect of preventing the silicon powder
adhesion to the reactor ceiling section becomes remarkably
high.
By installing the heat shield plate 15 above the reaction chambers
3 and keeping the walls in the region above the reaction chambers
3, to which silicon powder should not adhere, at high temperature,
little silicon powder adheres in this region. The heat shield plate
15 may consist of a polished metal plate having high reflectance,
for example, a stainless steel plate, which excels in heat
resistance and corrosion resistance. A ceramic plate excelling in
heat resistance, such as a quartz glass plate, may also be used for
the heat shield plate 15. The plate 15 may be annular or a series
of separate plates.
While, in the embodiment described above, the reaction chambers 3
are formed as cylindrical spaces having vertical openings through
the outer peripheral surface of the water jacket 4, from which the
grown polycrystalline silicon rods are extracted, this should not
be construed restrictively. It is also possible to form the
reaction chambers as completely cylindrical spaces having no such
openings, the grown polycrystalline silicon rods being extracted by
pulling them upwards out of the reaction chambers. Further, it is
also possible to provide reaction chambers on both the outer and
the inner peripheral surfaces of the water jacket 4. Or, the water
jacket that is equipped with reaction chambers may be provided in a
central region of the reactor, with the powder catchers arranged
around it.
When the fan 20 is used, its rotating drive shaft extends through
the base plate 2 and connects to a driving motor (not shown). To
prevent the escape of silane gas, which is inclined to ignite
spontaneously upon coming into contact with air, a shaft seal or
insulation is provided. Such sealing can be easily realized
utilizing known devices such as magnetic seals. The speed of
rotation is selected to provide a gas flow rate which minimizes the
deposition of powder at locations from which it can slough off onto
the growing rods. The optimum speed will depend on the size and
shape of the reactor and composition of the circulating gas. Thus,
for any given reactor, the best speed is determined by
experimentation.
In the embodiment of FIG. 4, a verger-type cover or bell 101 and a
round base plate 102 provide a reactor vessel. A cylindrical
partition member 103, that is a heat exchanger or water jacket and
that is shaped to define multiple reaction chambers 103, is
provided inside a cylindrical space defined by the cover 101 and
base plate 102. A powder catcher 105 is positioned at an elevation
above the tops of the reaction chambers 103. The illustrated powder
catcher is a cylindrical array of heat exchange tubes 130 that are
concentrically arranged. The array is in the shape of a disk having
a central vertical passageway 132. Multiple thin fins (not shown)
may be attached to the tubes 130 to increase the area of the cooled
surface that is provided by the powder catcher. The illustrated
powder catcher 105 is positioned so that it is not directly over
the reaction chambers 103. This arrangement reduces the small
likelihood of agglomerated powder falling from the powder catcher
into one of the reaction chambers. The arrangement is also
advantageous in that an unobstructed region 133 is provided over
the reaction chambers so that heated gas is free to rise up and
away from the growing rods 119 at a rapid rate.
The water jacket 104 and powder catcher 105 are positioned and
spaced such that gas which exits from the tops of the reaction
chambers 103 flows through the array of tubes 130 and into the
passageway 132. The passageway 132, along with a central passageway
134 defined by the water jacket 104, serves as gas downflow
passageway. The reaction chambers 103 consist of cylindrical spaces
arranged at equal intervals in the vicinity of the outer periphery
of the water jacket 104. Openings leading from the outer periphery
of the water jacket 104 to the reaction chambers 103 are provided
for purpose of enabling the extraction of polycrystalline silicon
rods which have been completely grown.
The cover 101 and the tubes 130 of the powder catcher 105 are at
least partially hollow and serve as water cooled heat exchangers.
The cover 101 is formed by connecting upper and lower cover
sections 101a and 101b with each other. The lower surface of the
upper cover section 101a serves as the reactor vessel ceiling.
Provided in the upper cover section 101a are a cooling water inlet
101c and a cooling water outlet 101d. Provided in the lower cover
section 101b are a cooling water inlet 101e and a cooling water
outlet 101f. As it moves from the inlet 101c to the outlet 101d,
cooling water flows through the space between the inner and outer
walls of the cover. Connected to the bottom of the water jacket 104
are cooling water supply pipes 107a and 107c which extend from
below through the base plate 102. Extending through the upper cover
section 101a are water supply pipes 107b which provide cooling
water to manifolds 136 for distribution into the tubes 130. Heated
water from the tubes 130 is removed via a discharge pipe 107d which
also extends through the upper cover section 101a. The water
flowing through the water cooling jacket 104 and tubes 130 may be
replaced by another fluid cooling or a heating medium.
Electrodes 109 extend from below through the base plate 102,
through the intermediation of insulating members 108, and are
arranged at positions corresponding to the centers of the reaction
chambers 103. Chucks 110 are attached to the tips of the electrodes
109.
Resistant plates (not shown) can be arranged at appropriate
intervals inside the reactor as explained with regard to the
embodiment of FIGS. 1-3. The plates extend transversely to gas
downflow passageways to regulate gas flow. Provided in the space
above the water jacket 4 .[.is.]. are heat shield/deflector plates
115. The plates 115 are positioned so that gas which rises from the
reaction chambers 103 is channeled into the powder catcher 105.
An exhaust pipe 116 extends through the base plate 102 and can be
used to remove spent reactant gas. Reactant gas pipes 111a allow
reactant gas to be evenly ejected into each reaction chamber
through openings 113a on the surface of the water cooling jacket
104. To provide an even gas distribution, the openings are provided
at multiple positions and at multiple elevations. Gas added at the
higher elevations makes up for the depletion of silicon from the
reactant gas that moves upwardly in the reaction chambers 103.
Polycrystalline silicon rods are produced .Iadd.by .Iaddend.the
apparatus of FIG. 4 by positioning silicon starter filaments 117
are in the reaction chambers 103 where they are held by the chucks
110. Pairs of silicon starter filaments 117 are connected to each
other at their upper ends through silicon bridges 118. Cooling
water is circulated through the cover 101, the water jacket 104 and
the powder catcher 105. The silicon starter filaments 117 are
heated by directly supplying electricity thereto through the
electrodes 109. Then, a silicon-bearing reactant gas is fed into
the reactor through the reactant gas pipes 111a and the gas nozzles
113a. Then, while ascending inside the reaction chambers 103, which
are heated by the silicon starter filaments 117, the gas reacts to
deposit polycrystalline silicon 119 on the silicon starter
filaments 117. Reactant gas which has moved upwards beyond the
reaction chambers 103, in a laminar convection flow, next passes
through the heat exchange tube array and along the wall surfaces of
the powder catcher tubes 130, descends through the passageways 132
and 134, and then returns to the reaction chambers 103. A fan
mechanism (not shown) can be located in or below the passageway
134.
The powder catcher 105 performs the two functions of collecting
silicon powder and effecting heat exchange. Accordingly, the
temperature in the reaction chambers 103 can be independently
regulated to achieve the best growth conditions for polycrystalline
silicon rods. Since floating silicon powder collects on cool
surfaces, such as on the walls of the powder catcher tubes 130,
accumulation thereof on the walls of the reaction chambers 103 and
the reactor ceiling section can be avoided to a large degree.
Another embodiment, as shown in FIG. 5, is closely related to the
embodiment of FIG. 4, with like elements being similarly numbered,
but incremented by 100 in FIG. 5. In the apparatus of FIG. 5,
reactant gas moves upwardly from the reaction chambers 203 into a
tube array of the powder catcher 205 where the gas is cooled and
powder deposits. The cooled gas is not returned to the bottom of
the reactor via a central passageway, but instead moves down from
the powder catcher and descends along the cooled wall 240 of the
water jacket 204. A top plate 242 is provided at the top of the
water jacket 204 to direct gas back outwardly to the region above
the reaction chambers 203. An exhaust pipe 216 extends through the
base plate 202 and top plate 242, for removing spent reactant gas
when necessary.
Yet another embodiment is shown in FIG. 6. This embodiment is
closely related to the embodiment of FIG. 5, with like elements
being similarly numbered, but incremented by 100 in FIG. 6. In the
apparatus of FIG. 5, reactant gas moves upwardly from the reaction
chambers 303 into a powder catcher 305 having two concentric tube
arrays. An inner array 350 is similar to the tube array of FIGS. 4
and 5. An outer tube array 352 concentrically surrounds the inner
array 350. The outer tube array 352 provides an additional surface
for the deposit of powder. Most conveniently the inner and outer
arrays are in fluid communication with one another so that a single
source of cooled water can feed both arrays. In the illustrated
.[.embodiment cooling.]. .Iadd.embodiment, .Iaddend.both a cooling
water supply pipe 307b and a cooling water discharge pipe 307d
enter the reactor through the same opening. And, both
.[.pipe.]..Iadd.pipes .Iaddend.are connected to both arrays by
manifolds 356b and 356d .[.respectively. e.]. .Iadd.respectively,
.Iaddend.where the gas is cooled and powder deposits.
Having illustrated and described the principles of our invention,
it should be apparent to those persons skilled in the art that such
an invention may be modified in arrangement and detail without
departing from such principles. For example the powder catcher used
in the above described reactors could be constructed in a variety
of configurations, including some combination of cooled tubes,
cooled plates, and/or cooled wall surfaces, or the like. We claim
as our invention all such modifications as come within the true
spirit and scope of the following claims.
* * * * *