U.S. patent application number 16/247229 was filed with the patent office on 2019-05-16 for apparatus and method for managing a temperature profile using reflective energy in a thermal decomposition reactor.
This patent application is currently assigned to REC Silicon Inc. The applicant listed for this patent is REC Silicon Inc. Invention is credited to Bryan J. Loushin, Joe Ruschetti, Timothy Troutman.
Application Number | 20190145004 16/247229 |
Document ID | / |
Family ID | 56128759 |
Filed Date | 2019-05-16 |
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United States Patent
Application |
20190145004 |
Kind Code |
A1 |
Troutman; Timothy ; et
al. |
May 16, 2019 |
APPARATUS AND METHOD FOR MANAGING A TEMPERATURE PROFILE USING
REFLECTIVE ENERGY IN A THERMAL DECOMPOSITION REACTOR
Abstract
Embodiments of a reflective surface and a reflector comprising a
reflective surface for use in a thermal decomposition reactor are
disclosed. Methods for using the reflective surface, or reflector
comprising the reflective surface, to manage a temperature profile
in a silicon rod grown in the thermal decomposition reactor are
also disclosed. The reflective surface is configured to receive
radiant heat energy emitted from an energy emitting region of an
elongated polysilicon body grown during chemical vapor deposition
onto a silicon filament and reflect at least a portion of the
received radiant heat energy to a reflected energy receiving region
of the elongated polysilicon body or to a reflected energy
receiving region of a second elongated polysilicon body, to thereby
add radiant heat energy to the reflected energy receiving
region.
Inventors: |
Troutman; Timothy; (Butte,
MT) ; Loushin; Bryan J.; (Butte, MT) ;
Ruschetti; Joe; (Butte, MT) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
REC Silicon Inc |
Moses Lake |
WA |
US |
|
|
Assignee: |
REC Silicon Inc
Moses Lake
WA
|
Family ID: |
56128759 |
Appl. No.: |
16/247229 |
Filed: |
January 14, 2019 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
14979934 |
Dec 28, 2015 |
10208381 |
|
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16247229 |
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PCT/US2015/067423 |
Dec 22, 2015 |
|
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14979934 |
|
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|
62096435 |
Dec 23, 2014 |
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Current U.S.
Class: |
427/585 ;
118/715; 118/725 |
Current CPC
Class: |
C01B 33/035 20130101;
C23C 16/46 20130101; C23C 16/4418 20130101; C23C 16/24 20130101;
C23C 16/481 20130101 |
International
Class: |
C23C 16/48 20060101
C23C016/48; C23C 16/44 20060101 C23C016/44; C23C 16/24 20060101
C23C016/24; C23C 16/46 20060101 C23C016/46; C01B 33/035 20060101
C01B033/035 |
Claims
1. A three-sided, frusto-pyramidal reflector comprising: an upper
surface; a lower surface; and first, second, and third side
surfaces, wherein the first side surface is a first concave
reflective surface.
2. The reflector of claim 1, wherein: the first concave reflective
surface is in the shape of a portion of a paraboloid, a sphere, a
tapered cylinder, or a cylinder, the cylinder having a longitudinal
axis at an angle .theta. relative to vertical.
3. The reflector of claim 1, wherein the first concave reflective
surface has a focal length of 10-50 cm, providing an optical power
from 20 to 100 m.sup.-1.
4. The reflector of claim 1, wherein the first concave reflective
surface is in the shape of a portion of a paraboloid.
5. The reflector of claim 4, wherein the paraboloid has a vertex, a
focus point, and a paraboloid axis of symmetry offset from a
midpoint of the first concave reflective surface.
6. The reflector of claim 5, wherein the vertex is not a point on
the first concave reflective surface.
7. The reflector of claim 1, wherein the first concave reflective
surface is configured to receive radiant heat energy and reflect at
least a portion of the received radiant energy, wherein reflected
radiant heat energy is directed at a three-dimensional surface, a
two-dimensional area, a point, or a line on a receiving energy
region of a body.
8. The reflector of claim 1, wherein the first concave reflective
surface is substantially smooth with any surface irregularities
having an average amplitude of less than 3 mm.
9. The reflector of claim 1, wherein the second side surface is a
second concave reflective surface.
10. The reflector of claim 9, wherein the second concave reflective
surface is in the shape of a portion of a paraboloid, a sphere, a
tapered cylinder, or a cylinder, the cylinder having a longitudinal
axis at an angle .theta. relative to vertical.
11. The reflector of claim 9, wherein the first and second concave
reflective surfaces are mirror images of one another and have the
same optical power.
12. The reflector of claim 9 wherein the first and second concave
reflective surfaces have different configurations and do not have
the same optical power.
13. The reflector of claim 1, wherein: the lower surface of the
reflector defines one or more depressions configured to receive one
or more protrusions of a structure on which the reflector is
positioned; the third side surface is a rear surface, and the
reflector further comprises a cavity defined by portions of the
lower surface and the rear surface; the upper surface of the
reflector comprises one or more features to facilitate positioning,
alignment, or positioning and alignment of the reflector; or any
combination thereof.
14. The reflector of claim 1, wherein the lower surface of the
reflector defines one or more depressions configured to receive one
or more protrusions of a structure on which the reflector is
positioned, and inner walls of the depressions include internal
threads.
15. The reflector of claim 1, wherein the lower surface has a
triangular configuration with concave arc edges.
16. The reflector of claim 1, wherein: the reflector is constructed
of a material that does not evolve chemical species comprising
Group III elements, Group V elements, metals, oxygen, or carbon
during reactor operation. the reflector is constructed of, or
plated with, a material having an emissivity <0.5; or a
combination thereof.
17. The reflector of claim 1, wherein the reflector is constructed
of, or plated with, nickel, a nickel alloy, stainless steel,
molybdenum, a molybdenum alloy, tungsten, a tungsten alloy, cobalt,
a cobalt alloy, titanium, a titanium alloy, gold, a gold alloy,
silver, a silver alloy, tantalum, or a tantalum alloy.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This is a continuation of U.S. application Ser. No.
14/979,934, filed Dec. 28, 2015, which is a continuation of
International Application No. PCT/US2015/067423, filed Dec. 22,
2015, which in turn claims the benefit of U.S. Provisional
Application No. 62/096,435, filed Dec. 23, 2014, all of which are
incorporated herein in their entireties by reference.
FIELD
[0002] This disclosure concerns a reflective surface and a
reflector comprising a reflective surface for use in a thermal
decomposition reactor, as well as a method of using a reflective
surface and/or reflector in a thermal decomposition reactor.
BACKGROUND
[0003] In the semiconductor industry it is common practice to
produce high purity silicon by a process known as chemical vapor
deposition ("CVD"). In brief, certain substances having silicon
content are heated to high temperatures within a reaction chamber
causing them to undergo decomposition, while in the vapor state,
and produce elemental silicon. Depending on the design of the
reaction chamber, and whether or not it additionally contains
deposition surfaces, the elemental silicon may be collected as a
powder or as a rod. Such silicon is frequently referred to as
polysilicon or polycrystalline silicon.
[0004] One of the widely practiced conventional methods of
polysilicon production is via chemical vapor deposition of
polysilicon in a thermal decomposition reactor, and is generally
identified as the Siemens method. In this method polysilicon is
deposited by decomposition of a silicon-containing gas such as for
example trichlorosilane or monosilane (SiH.sub.4), within the
thermal decomposition reactor onto high-purity, joule or resistance
heated, thin silicon filaments. Silicon deposits on the filaments,
thereby growing elongated polysilicon bodies of increasing
diameter, while the polysilicon bodies are maintained at elevated
temperatures, typically from 700.degree. C. to 1200.degree. C.
[0005] Stresses are stored in the elongated polysilicon bodies
following growth in a thermal decomposition reactor due to
temperature differences across the diameter of the elongated bodies
and/or throughout the length of the elongated bodies. Once growth
is complete, and the rod begins to cool, the variance in
temperature during growth manifests as stress due to the
coefficient of thermal expansion. The magnitude of the stored
stress increases with diameter. The filaments, and resulting
elongated bodies formed in a thermal decomposition reactor,
typically have an inverted U-shaped configuration with two vertical
portions and a relatively horizontal bridge portion between the
tops of the two vertical portions. The two vertical portions of the
elongated body are connected to the bridge at bend, or corner,
portions. As an elongated polysilicon body shrinks due to thermal
contractions, the bridge portion tends to separate from the
vertical portions of the elongated body. A fracture can propagate
down the vertical portion of the elongated body, e.g., for a
distance of 200-1000 mm. Intact vertical portions, or rods,
obtained from an elongated polysilicon body are of greatest
commercial value due to their length with uniform diameter.
Fractures reduce the yield of such vertical portions. Fractured
rods may not meet customers' minimum length requirements. In some
cases, product losses reach 50% due to fractures. Accordingly,
there is a need to mitigate or control stresses in the elongated
polysilicon body, thereby mitigating or controlling fractures
produced by the stresses.
SUMMARY
[0006] Embodiments of a reflective surface, a reflector comprising
a reflective surface, and methods for use of the reflective surface
in a thermal deposition reactor, such as a Siemens-type reactor,
are disclosed. A device in a thermal decomposition reactor for
producing one or more elongated polysilicon bodies by chemical
vapor deposition of silicon onto one or more heated silicon
filaments in a chamber of a reactor vessel comprises a reflector
situated in the chamber, the reflector having at least one
reflective surface. The reflective surface is configured to receive
radiant heat energy emitted from an energy emitting region of an
elongated polysilicon body grown during chemical vapor deposition
onto a silicon filament and reflect at least a portion of the
received radiant heat energy to a reflected energy receiving region
of the elongated polysilicon body or to a reflected energy
receiving region of a second elongated polysilicon body, to thereby
supply radiant heat energy to the reflected energy receiving
region. In one embodiment, the reflective surface is a surface of a
reflector. In another embodiment, the reflective surface is
provided as an integral portion of a component within the reactor,
such as a nozzle, a pipe, a heat exchanger, a tube, a chamber wall,
or the like. In some embodiments, the reflective surface is
configured to direct reflected radiant heat energy at a
three-dimensional surface, a two-dimensional area, a point, or a
line on a polysilicon body surface at the reflected energy
receiving region.
[0007] The reflective surface may be concave and in the shape of a
portion of a paraboloid, a sphere, a tapered cylinder, or a
cylinder, the cylinder having a longitudinal axis that is not
parallel to a longitudinal axis of the energy emitting region of
the elongated polysilicon body. In some embodiments, the reflective
surface is substantially smooth with any surface irregularities
having an average amplitude of less than 3 mm.
[0008] In some embodiments, the reflective surface or a reflector
comprising the reflective surface is constructed of a material that
does not evolve chemical species comprising Group III elements,
Group V elements, metals, oxygen, or carbon during reactor
operation; the reflector is constructed of, or plated with, a
material having an emissivity <0.5; or a combination thereof. In
certain embodiments, the reflective surface and/or the reflector is
constructed of, or plated with, nickel, a nickel alloy, stainless
steel, molybdenum, a molybdenum alloy, tungsten, a tungsten alloy,
cobalt, a cobalt alloy, titanium, a titanium alloy, gold, a gold
alloy, silver, a silver alloy, tantalum, or a tantalum alloy.
[0009] In some embodiments, a lower surface of the reflector
defines one or more depressions configured to receive one or more
protrusions of a structure on which the reflector is positioned,
the reflector further comprises a cavity defined by portions of a
lower surface and a rear surface of the reflector, and/or a surface
of the reflector comprises one or more features to facilitate
positioning, alignment, or positioning and alignment of the
reflector within the thermal decomposition reactor.
[0010] When the reactor contains more than one elongated
polysilicon body, the reflector may further have a second
reflective surface to receive radiant heat energy from an energy
emitting region of a second elongated polysilicon body during
chemical vapor deposition and reflect at least a portion of the
received radiant heat energy to a reflected energy receiving region
of the second elongated polysilicon body or to a region of another
elongated polysilicon body within the chamber, wherein the other
elongated polysilicon body is the first elongated polysilicon body
or a third elongated polysilicon body within the thermal
decomposition reactor.
[0011] In some embodiments, the reactor vessel comprises adjacent
first and second tubes that are configured to receive first and
second vertical portions of the elongated polysilicon body grown by
chemical vapor deposition onto an inverted U-shaped silicon
filament comprising two vertical silicon filaments and a horizontal
silicon filament, and the elongated polysilicon body has one or
more bend portions between the first and second vertical portions
of the elongated polysilicon body, which bend portions are situated
outside the first and second tubes. In such embodiments, the
reflector may be situated such that the reflective surface is
positioned to (i) receive at least some radiant heat energy emitted
from the energy emitting region of the elongated polysilicon body
formed during the chemical vapor deposition and (ii) reflect at
least a portion of the received radiant heat energy to the
reflected energy receiving region. In one embodiment, the energy
emitting region is a portion of the surface of the first vertical
portion of the elongated polysilicon body, and the reflected energy
receiving region is a portion of the surface of the elongated
polysilicon body, which portion is at or near a bend portion of the
elongated polysilicon body. In an independent embodiment, the
energy emitting region is a portion of the surface of a bend
portion or a horizontal portion of the elongated polysilicon body,
which horizontal portion is between the first and second vertical
portions, and the reflected energy receiving region is a portion of
the surface of the first or second vertical portion of the
elongated polysilicon body. In another independent embodiment, the
reflective surface is an integral portion of the first tube and is
located at the upper rim with the reflective surface oriented to
receive radiant heat energy emitted from the energy emitting region
of the elongated polysilicon body grown during the chemical vapor
deposition, wherein the energy emitting region is a portion of the
surface of the first vertical portion of the elongated polysilicon
body.
[0012] Embodiments of a thermal decomposition reactor for producing
an elongated polysilicon body comprise (i) a reactor vessel having
a wall that defines a chamber, a gas inlet for admitting gas into
the chamber, and a gas outlet for exhausting gas out of the
chamber; (ii) a silicon filament in the chamber; (iii) an energy
source for heating the silicon filament; (iv) a source of
silicon-bearing gas fluidly connected to the gas inlet of the
reactor vessel, wherein the silicon-bearing gas is a gas that is
capable of decomposition at elevated temperatures to deposit
silicon onto the silicon filament by chemical vapor deposition and
grow an elongated polysilicon body; and (v) at least one reflective
surface situated in the chamber, the reflective surface configured
to receive radiant heat energy emitted from an energy emitting
region of the elongated polysilicon body grown during chemical
vapor deposition and reflect at least a portion of the received
radiant heat energy to a reflected energy receiving region of the
elongated polysilicon body or to a region of a second elongated
polysilicon body within the chamber. The reflective surface may be
formed on a component within the chamber and be an integral portion
of the component, or the reflective surface may be provided by a
reflector comprising the reflective surface as disclosed
herein.
[0013] Embodiments of a method for producing an elongated
polysilicon body include depositing silicon by chemical vapor
deposition onto one or more heated silicon filaments heated in a
chamber of a reaction vessel to grow one or more elongated
polysilicon bodies, and during the depositing, reflecting radiant
heat energy off of a first reflective surface positioned at a
location within the reaction chamber such that the first reflective
surface receives radiant heat energy emitted from an energy
emitting region of a first elongated polysilicon body and reflects
at least a portion of the received radiant heat energy to a
reflected energy receiving region of the first elongated
polysilicon body or to a second elongated polysilicon body. In some
embodiments, providing the reflective surface comprises providing a
reflector comprising the reflective surface as disclosed herein. In
certain embodiments, the reflective surface is formed to be an
integral portion of a component within the chamber, such as a pipe,
a nozzle, a heat exchanger, a tube, a chamber wall, or the like.
The reflective surface may be concave and in the shape of a portion
of a paraboloid, a sphere, a tapered cylinder, or a cylinder, the
cylinder having a longitudinal axis that is not parallel to a
longitudinal axis of the energy emitting region of the first
elongated polysilicon body when the reflective surface is provided
at the location within the chamber.
[0014] In one embodiment, the energy emitting and reflected energy
receiving regions are on the first elongated polysilicon body,
wherein the energy emitting region is a relatively hot region and
the reflected energy receiving region is a relatively cool region,
and the method further includes positioning the reflective surface
at a location within the chamber such that the radiant heat energy
received from the energy emitting region and reflected to the
reflected energy receiving region decreases a temperature gradient
within the elongated polysilicon body. In an independent
embodiment, (i) the energy emitting region is a portion of the
surface of a vertical portion of the first elongated polysilicon
body, (ii) the reflected energy receiving region is a portion of
the surface of the elongated polysilicon body, which portion is at
or near a bend portion of the first elongated polysilicon body, and
(iii) the temperature gradient is within the bend portion, and the
method further includes positioning the reflective surface at a
location within the chamber such that received radiant heat energy
is convergently reflected to the reflected energy receiving region.
In another independent embodiment, the method further includes
positioning the reflective surface at a location within the chamber
such that the reflective surface is located (i) above the heated
silicon filament from which the first elongated polysilicon body is
grown or (ii) on an upper rim of a first tube pair within the
chamber, wherein the first tube pair comprises adjacent first and
second tubes that are configured to receive first and second
vertical portions of a first elongated polysilicon body grown from
a first heated, inverted U-shaped silicon filament comprising two
vertical silicon filaments and a horizontal silicon filament, which
horizontal silicon filament is situated outside the first and
second tubes. When the reflective surface is positioned on the
upper rim, the reflective surface may be an integral portion of the
upper rim.
[0015] The method may further include providing a second reflective
surface at a location within the chamber such that the second
reflective surface receives radiant heat energy emitted from the
energy emitting region of the first elongated polysilicon body
during the chemical vapor deposition and reflects at least a
portion of the received radiant heat energy to the reflected energy
receiving region of the first elongated polysilicon body.
[0016] In some embodiments, the chamber comprises a first tube pair
comprising adjacent first and second tubes that are configured to
receive first and second vertical portions of a first heated,
inverted U-shaped silicon filament comprising two vertical silicon
filaments and a horizontal silicon filament, which horizontal
silicon filament is situated outside the first and second tubes,
and the method further includes positioning the reflective surface
and the second reflective surface such that the reflective surface
and the second reflective surface are located above the horizontal
silicon filament or directly or indirectly on an upper rim of the
first tube pair.
[0017] In some embodiments, a second elongated polysilicon body is
grown in the chamber by chemical vapor deposition, and the method
further includes providing a second reflective surface at a
location within the chamber such that the second reflective surface
receives radiant heat energy emitted from an energy emitting region
of the second elongated polysilicon body and reflects at least a
portion of the received radiant heat energy to a reflected energy
receiving region of the second elongated polysilicon body or to a
region of another elongated polysilicon body within the chamber,
wherein the other elongated polysilicon body is the first elongated
polysilicon body or a third elongated polysilicon body within the
thermal decomposition reactor.
[0018] In any or all of the foregoing methods, the reflective
surface is a surface of a reflector or an integral portion of a
component within the chamber, and the second reflective surface, if
present, independently is a second surface of the reflector, a
surface of a second reflector, or an integral portion of a
component within the chamber.
[0019] In some embodiments, a method of mitigating spall formation
of an elongated polysilicon body prepared in a thermal
decomposition reactor includes depositing silicon by chemical vapor
deposition onto one or more heated silicon filaments heated in a
reaction chamber of a reaction vessel to grow one or more elongated
polysilicon bodies, and during the depositing, reflecting with a
device as disclosed herein at least a portion of radiant heat
energy emitted from an energy emitting region of the one or more
elongated polysilicon bodies to a reflected energy receiving region
of the one or more elongated polysilicon bodies, thereby reducing
spall formation in the elongated polysilicon body compared to an
elongated polysilicon body produced in a thermal decomposition
reactor in the absence of the device.
[0020] The foregoing and other objects, features, and advantages of
the invention will become more apparent from the following detailed
description, which proceeds with reference to the accompanying
figures.
BRIEF DESCRIPTION OF THE DRAWINGS
[0021] FIG. 1 is a schematic vertical sectional view showing a
thermal decomposition reactor for the production of elongated
polysilicon bodies by deposition of silicon from a silicon-bearing
gas.
[0022] FIG. 2 is a sectional view taken along line 2-2 of FIG. 1
showing the cross section of a polysilicon body after it has been
grown to a diameter greater than 150 mm.
[0023] FIG. 3 is an oblique view of an exemplary reflector as
viewed from the front and top.
[0024] FIG. 4 is a bottom plan view of an exemplary reflector.
[0025] FIG. 5 is an oblique view of the reflector of FIG. 4 as
viewed from the rear and bottom.
[0026] FIG. 6 is an oblique view of the reflector of FIG. 4 as
viewed from the rear and top.
[0027] FIG. 7 is a schematic oblique view of a component for use in
a thermal decomposition reactor, the component having an integral
reflective surface.
[0028] FIG. 8 is a partial schematic oblique view of an interior
portion of a thermal decomposition reactor containing an exemplary
reflector having a reflective paraboloidal surface.
[0029] FIG. 9 is a partial schematic oblique view of an interior
portion of a thermal decomposition reactor containing an exemplary
reflector having a reflective cylindrical surface.
[0030] FIG. 10 is a schematic oblique view of a component for use
in a thermal decomposition reactor, the component having a
reflector mounted above an upper surface of the component.
[0031] FIG. 11 is a schematic oblique view of a component for use
in a thermal decomposition reactor, the component comprising
protrusions, or pins, for receiving a reflector.
[0032] FIG. 12 is a schematic oblique view of a tube pair for use
in a thermal decomposition reactor, the tube pair having an upper
rim with a reflector mounted on or above the upper rim.
[0033] FIG. 13 is a partial schematic oblique sectional view of an
exemplary thermal decomposition reactor vessel including reflectors
mounted via extenders to a cover of the reactor vessel.
[0034] FIG. 14 is a schematic elevational view of an elongated
polysilicon body grown in a thermal decomposition reactor.
[0035] FIG. 15 is a partial schematic oblique view of an interior
portion of a thermal decomposition reactor containing an exemplary
reflector positioned to receive radiant heat energy emitted from a
portion of the surface of a vertical region of an elongated
polysilicon body and reflect at least a portion of the received
energy to an outer surface of a bend portion of the elongated
polysilicon body.
[0036] FIG. 16 is a partial schematic oblique view of an interior
portion of a thermal decomposition reactor containing an exemplary
reflector positioned to receive radiant heat energy emitted from a
portion of the surface of a vertical region of an elongated
polysilicon body and reflect at least a portion of the received
energy to an inner surface of a bend portion of the elongated
polysilicon body.
[0037] FIG. 17 is a partial schematic oblique view of an interior
portion of a thermal decomposition reactor containing an exemplary
reflector positioned to receive radiant heat energy emitted from a
portion of the surface of a vertical region of an elongated
polysilicon body and reflect at least a portion of the received
energy to a side surface of a bend portion of the elongated
polysilicon body.
[0038] FIG. 18 is a partial schematic oblique view of an interior
portion of a thermal decomposition reactor containing two exemplary
reflectors positioned to receive radiant heat energy emitted from
an energy emitting region of an elongated polysilicon body and
reflect at least a portion of the received energy to a reflected
energy receiving region of the elongated polysilicon body.
[0039] FIG. 19 is a top plan view of an interior portion of a
thermal decomposition reactor containing the two exemplary
reflectors and elongated polysilicon body of FIG. 18.
[0040] FIG. 20 is a partial schematic oblique view of an interior
portion of a thermal decomposition reactor containing an exemplary
reflector with two reflective surfaces positioned to receive
radiant heat energy emitted from vertical regions of adjacent first
and second elongated polysilicon bodies, and reflect at least a
portion of the received energy to bend portions of the first and
second elongated polysilicon bodies.
DETAILED DESCRIPTION
[0041] A reflector comprising a reflective surface and methods for
use of a reflective surface in a thermal deposition reactor, such
as a Siemens-type reactor, are disclosed. Elongated polysilicon
bodies produced in a reactor including the reflector have a lower
propensity to fracture down the length of the polysilicon body. In
some instances where the elongated polysilicon body is U-shaped
with two vertical portions, a horizontal bridge portion, and bend
portions where the horizontal bridge portion connects with the
vertical portions, the elongated polysilicon body is more likely to
break through the bend portion.
I. Definitions and Abbreviations
[0042] The following explanations of terms and abbreviations are
provided to better describe the present disclosure and to guide
those of ordinary skill in the art in the practice of the present
disclosure. As used herein, "comprising" means "including" and the
singular forms "a" or "an" or "the" include plural references
unless the context clearly dictates otherwise. The term "or" refers
to a single element of stated alternative elements or a combination
of two or more elements, unless the context clearly indicates
otherwise.
[0043] Unless explained otherwise, all technical and scientific
terms used herein have the same meaning as commonly understood to
one of ordinary skill in the art to which this disclosure belongs.
Although methods and materials similar or equivalent to those
described herein can be used in the practice or testing of the
present disclosure, suitable methods and materials are described
below. The materials, methods, and examples are illustrative only
and not intended to be limiting. Other features of the disclosure
are apparent from the following detailed description and the
claims.
[0044] In order to facilitate review of the various embodiments of
the disclosure, the following explanations of specific terms are
provided:
[0045] Elongated polysilicon body: As used herein, the term
"elongated polysilicon body" may refer to a substantially linear
body, such as a polysilicon rod, or to a U-shaped polysilicon body
including two vertical portions and a horizontal bridge portion
connecting the two vertical portions.
[0046] Emissivity: Emissivity is a measure of the efficiency with
which a surface emits thermal radiation. Mathematically, emissivity
is the ratio of thermal radiation from a surface to the radiation
from an ideal black surface at the same temperature. The ratio
varies from 0 to 1. An emissivity of 1 indicates complete
absorption of all incident light. Mirror-like, metallic surfaces
that reflect light well have low emissivities. For example, a
polished silver surface has an emissivity of about 0.02 near room
temperature (20-23.degree. C.).
[0047] Morphology: As used herein with respect to elongated
polysilicon bodies produced by a chemical vapor deposition process,
such as the Siemens process, the term "morphology" refers to
defects in the polysilicon body, for example, cracks, stress lines,
and/or deformities. In some examples, morphology refers to defects
at the bend portions of the polysilicon body. The defects may
produce a textured surface on the polysilicon body. Morphology may
be classified by degree, e.g., minimal, light, heavy, etc.
Alternatively, the degree of morphology may be assigned a numeric
classification, e.g., on a scale from 0 to 10, where 0 indicates no
defects, 1 indicates minimal morphology, 5 indicates moderate
morphology, and 10 indicates heavy morphology.
[0048] Optical power: As used herein, the term "optical power"
refers to the degree to which a reflective surface converges
reflected radiant heat energy. Optical power is reciprocal of the
focal length of the reflective surface--P=1/f, where f is the focal
length in meters.
[0049] Radiant heat energy: The energy of electromagnetic waves,
e.g., thermal radiation.
[0050] Region: As used herein, the term "region" refers to a
portion or volume of a polysilicon body.
[0051] Spall: As used herein, the term "spall" refers to cracks or
fractures that form as a result of stresses (e.g., heat stresses)
in elongated polysilicon bodies produced by a chemical vapor
deposition process, such as the Siemens process. Spall may be
characterized by degree of severity as determined, for example, by
the distance that the cracks propagate down the vertical portions
of an inverted U-shaped polysilicon body. Spall may be
characterized as minimal, moderate, or severe. Alternatively, spall
may be characterized on a numeric scale, e.g., from 0 to 15, where
0 indicates no spall, 1 indicates minimal spall, 5 indicates spall
extending 1/5 the length of the vertical portion, 10 indicates
spall extending 1/3 the length of the vertical portion, and 15
indicates spall extending 1/2 the length of the vertical
portion.
II. Elongated Polysilicon Body Production
[0052] Elongated polysilicon bodies may be produced by chemical
vapor deposition in a thermal deposition reactor, e.g., a
Siemens-type reactor. One exemplary thermal decomposition reactor
is described in U.S. Pat. No. 6,221,155, the pertinent portions of
which are incorporated herein by reference, and shown in FIG. 1. A
reactor vessel includes a cover or bell 1 and a base plate 2 that
are mated together to provide a gas-tight wall that defines a
chamber. A partition member 4, that is a heat exchanger or water
jacket having a cooling water inlet pipe 5 and outlet pipe 6 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.
[0053] The cover 1 is at least partially hollow and serves as a
water cooled heat exchanger or cooling jacket. Provided in the
cover section are a cooling water inlet 1c and a cooling water
outlet 1d. 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. 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
that are water cooled through inlet and outlet cooling pipes 7. The
water flowing through the water cooling jacket may be replaced by
another fluid cooling or a heating medium.
[0054] A reactant gas delivery pipe, or gas inlet, 11 extends
upwardly from below through the base plate 2 and connects a
plurality of gas nozzles 13 that are spaced to distribute a silicon
bearing gas, such as monosilane gas, along the reaction chambers 3.
An exhaust pipe, or gas outlet, 16 is used to remove spent reactant
gas. Viewing windows 12 may be provided through the cover 1 and its
cooling jacket to enable observation of the polysilicon bodies 14
during the deposition process. One or more sensors 23, such as
pyrometers (not shown), may be used to monitor the surface
temperature of polysilicon bodies growing in the reactor.
[0055] One or more energy sources are connected to the electrodes 9
to pass current through the polysilicon bodies 14 for heating the
polysilicon bodies. The exemplary system shown in FIG. 1 includes a
low frequency power supply 20, a high frequency power supply 21,
and a switch 22 suitable to connect one or the other of the power
supplies 20, 21 to the electrodes 9. Alternatively, the power
supplies 20, 21 could be combined in a single, variable current
power supply (not shown) that has integral switching circuitry and
is capable of operating at both low and high frequencies.
[0056] Silicon filaments 17 are positioned in the reaction chambers
3 and held at their lower ends by the chucks 10. In the exemplary
arrangement of FIG. 1, two silicon filaments 17 are connected to
each other at their upper ends through a horizontal silicon
filament, or bridge, 18 to provide a U-shaped filament on which an
elongated polysilicon body 14 is formed. Cooling water is
circulated through the cover 1.
[0057] Because silicon is not sufficiently electrically conductive
at ambient temperature, the silicon filaments 17 may be preheated
to a desired temperature, typically at least 200.degree. C., to
increase their conductivity. The surfaces of the preheated
filaments then can be maintained at an elevated temperature by
supplying electricity to the filaments through the electrodes 9 so
the surfaces can serve as silicon deposition surfaces. Preheating
can be accomplished by supplying a blast of hot inert gas through
inlet 15 in the base plate 2 as described in U.S. Pat. No.
4,150,168 of Yatsurugi. Preheating can also be accomplished by
operation of a radiant heat source (not shown) inside the
reactor.
[0058] The filaments also may be preheated by directly supplying
low frequency A.C. current thereto through the electrodes 9, as
described in U.S. Pat. No. 4,150,168, but at a high voltage. For
example, filaments may be heated by applying a voltage as high as
30,000 volts at a frequency of 60 Hz. After the silicon heats up
beyond a temperature of 200.degree. C., its resistance decreases
with increasing temperature, so it has "broken into conduction." At
that point, the voltage can be decreased to about 3,000 V and the
60 Hz current regulated to provide a desired silicon deposition
surface temperature in the range of 600.degree. C. to 1200.degree.
C. A silane gas, such as monosilane gas, is fed into the reactor
through the gas pipe 11 and the gas nozzles 13. While ascending
inside the reaction chambers 3, that are heated by the silicon
starter filaments 17, the gas reacts to deposit polycrystalline
silicon 19 on the surfaces of the silicon starter filaments 17. The
deposited silicon builds up to grow elongated polysilicon bodies
14. Each starter filament 17 thus provides an initial silicon
deposition surface, and after silicon is deposited on the filament,
the outer surface of the deposited silicon serves as the deposition
surface. With monosilane gas, desirable results are obtained when
the deposition surface of a growing polysilicon body is maintained
at a temperature of about 850.degree. C. during deposition of
silicon on the polysilicon body. Reactant gas that has been blown
upwards beyond the reaction chambers 3 is removed through the
exhaust pipe 16. While the growing polysilicon bodies are small,
the current can be as low as 20 amps. As the polysilicon bodies
increase in diameter, the current necessary to keep the silicon
deposition surface at a constant temperature steadily increases
while the required voltage decreases.
[0059] At some point, determined by the measurement of one or more
parameters such as elapsed time, current consumption, a product
attribute such as diameter, surface temperature or the like, the 60
Hz current may be turned off, for example by automated operation of
the switch 22, and the elongated polysilicon body may be further
maintained at a desired temperature by high frequency current
supplied by the high frequency power source 21.
[0060] Heating current passing through a polysilicon body migrates
to the surface of the polysilicon body because of the "skin
effect." To take best advantage of the skin effect, the power
supply may be configured to deliver current such that at least
about 70% of the current is concentrated in an annular outer region
of the polysilicon body 26 shown in FIG. 2, which outer region is
the outer 15% of the radius of a polysilicon body being grown in a
reactor. A lesser amount of current flows through a core or inner
region 28 of the polysilicon body located inside the outer region
26.
[0061] Other configurations also may be suitable for growing
elongated polysilicon bodies by CVD. For example, the reactor
vessel may not include reaction chambers 3 as shown in FIG. 1. In
some embodiments, silicon filaments 17 are not connected by a
bridge portion 18 as shown in FIG. 1.
[0062] As elongated polysilicon bodies grow, stresses are stored
within the polysilicon bodies. Internal stresses are caused, for
example, by temperature variations across the diameter of the
polysilicon body during CVD. The temperature in the polysilicon
body's core may be 20-100.degree. C. greater than the surface
temperature during CVD. At the bend portions, in particular, hotter
sections will contract more than cooler sections upon cooling,
leading to spall and fractures. When making large-diameter
elongated polysilicon bodies (e.g., .gtoreq.130 mm diameter, such
as .gtoreq.150 mm diameter), slower growth rate conditions may be
utilized to minimize risk of powder fall (i.e., formation of
silicon powder and/or powder clumps instead of polysilicon body
growth). Without wishing to be bound by a particular theory of
operation, the slower growth rate conditions, however, may reduce
bend portion morphology and increase internal stresses within the
polysilicon body. The lack of morphology, or defects, combined with
elevated internal stresses due to the increased diameter, increases
spall and results in elongated polysilicon bodies of lesser value.
Fractures that propagate down the vertical portion of the
polysilicon body are of particular concern. Controlling the
elevated internal stresses is difficult. For example, increasing
the growth rate to increase morphology could result in a less
desirable product and/or increase the probability of powder-fall,
which in turn contributes to product fallout due to warts (i.e.,
protuberances caused by powder clumps adhering to the vertical
portion of the polysilicon body).
III. Reflector
[0063] Disclosed herein are embodiments of a reflector for use in a
thermal decomposition reactor. In some embodiments the reflector is
useful for managing a temperature profile within an elongated
polysilicon body grown by chemical vapor deposition onto a silicon
filament in a thermal decomposition reactor. The reflector 100 has
at least one reflective surface 110 configured to receive radiant
heat energy emitted from an energy emitting region of a growing
polysilicon body and direct at least a portion of the received
radiant heat energy to a reflected energy receiving region of the
elongated polysilicon body or to another elongated polysilicon body
within the reactor, thereby managing a temperature profile with the
elongated polysilicon body (FIG. 3). In some embodiments, the
energy emitting region and the reflected energy receiving region
are not coextensive. The reflective surface may have optical power.
In some embodiments, the reflective surface has a focal length of
10-50 cm, such as a focal length of 15-40 cm, providing an optical
power from 20 to 100 m.sup.-1, or from 25 to 67 m.sup.-1.
[0064] In some embodiments, the reflective surface 110 is concave
and in the shape of a portion of a paraboloid, a sphere, a tapered
cylinder (i.e., a conical shape), or a cylinder. The paraboloid
reflecting surface may be designed by means of superposition of
more than one parabolic surface to tailor the intended origin and
destination of electromagnetic radiation. In some embodiments, the
parabolic reflective surface may incorporate an astigmatism, that
is: a surface with differing optical power on two orthogonal axes.
For example, in FIG. 3, the reflective surface 110 has a first
parabolic curvature along a first axis A1 and a second parabolic
curvature along a second axis A2. The first and second parabolic
curvatures may have optical powers that are the same or different
from one another.
[0065] In some embodiments, the reflector 100 has a second
reflective surface 120 that is configured to receive radiant heat
energy emitted from an energy emitting region of a second
polysilicon rod and direct at least a portion of the received
radiant heat energy to a reflected energy receiving region of the
second polysilicon rod or to a region of another polysilicon rod.
The second reflective surface 120 also may be concave and in the
shape of a portion of a paraboloid, a sphere, a tapered cylinder,
or a cylinder. Reflective surfaces 110, 120 independently are
concave portions of a paraboloid, a sphere, a tapered cylinder, or
a cylinder that may be the same or different from one another. In
one embodiment, reflective surfaces 110, 120 are mirror images of
one another and have the same optical power. In another embodiment,
reflective surfaces 110, 120 have different configurations and do
not have the same optical power. A person of ordinary skill in the
art understands that embodiments of the reflector could include one
or more additional reflective surfaces, such that the reflector has
3, 4, or more reflective surfaces.
[0066] A surface of the reflector 100, such as an upper surface 130
of the reflector, may include one or more features 132, 134, which
facilitate alignment and/or positioning of the reflector 100 prior
to use. Alignment and/or positioning of the reflector also may
include fixation of the reflector 100 in the thermal decomposition
reactor. In some embodiments, edges and corners (e.g., corner 115)
of the reflector may be rounded or squared for operator safety. A
surface of the reflector 100, such as a lower surface 140 of the
reflector, may include one or more depressions, such as depressions
150, 152 shown in FIGS. 4 and 5. Depressions 150, 152 may be used
to position and/or align the reflector 100 on one or more retaining
pins on a surface that receives the reflector. In one embodiment,
the depressions include internal threads on inner walls of the
depressions, and the retaining pins include external threads
cooperatively dimensioned to engage with the internal threads of
the depressions. Alternatively, other fixation means (e.g.,
welding, adhesives, etc.) may be utilized to align and retain the
reflector.
[0067] A notch or cavity may be formed in a surface of the
reflector. In the embodiment of FIGS. 4-6 a rectangular cavity 160
is provided in the lower surface 140 and rear surface 170 of the
reflector 100. The cavity 160 is a holding cavity capable of
receiving a tool or an operator's finger(s) to facilitate
manipulation and positioning of the reflector 100.
[0068] In certain embodiments, the reflector is not a stand-alone
device, and the reflective surface 110 instead is formed as an
integral part of another reactor component with the chamber. For
example, FIG. 7 illustrates a reactor component 300 having an upper
surface 310. A reflective surface 110 is formed as the reactor
component 300 is formed, or it may be subsequently machined into
the reactor component.
[0069] The following discussion of reflective surface
characteristics proceeds with reference to reflective surface 110.
It should be understood, however, that the features described for
reflective surface 110 also are applicable to reflective surface
120. If the reflector has more than two reflective surfaces, the
features described for reflective surface 110 are applicable to
each reflective surface.
[0070] In some embodiments, reflective surface 110 is concave in
the shape of a portion of a paraboloid P. The reflective surface
110 receives radiant heat energy emitted from an energy emitting
region 210 of an elongated polysilicon body 200. In the embodiment
of FIG. 8, the energy emitting region 210 is a portion of the
surface of a first vertical portion 204 of the polysilicon body
200. In some embodiments, the paraboloid P has a vertex V, a focus
point F, and a paraboloid axis of symmetry As offset from a
midpoint 112 of the reflective surface 110 (wherein, with reference
to FIG. 3, the midpoint is equidistant from side edges 111a and
111b of the reflector surface 110) and parallel to a line L1
between the midpoint 112 of the reflective surface 110 and a center
222 of a reflected energy receiving region 220 of the polysilicon
body 200, wherein the center 222 is defined as a point on the
reflected energy receiving region intersected by line L1, which
extends to the midpoint 112 of the reflective surface 110. In
certain embodiments, L1 may extend to a point on the reflective
surface 110 other than the midpoint 112, or may not intersect the
reflective surface 110 at all. In the embodiment of FIG. 8, the
reflected energy receiving region 220 is a portion of the surface
of a bend portion 250 of the polysilicon rod 200.
[0071] The focus point F1 may be beyond the reflected energy
receiving region 220, or between the reflector surface 110 and the
reflected energy receiving region 220. When the focus point F1 is
not on the reflected energy receiving region 220, the reflected
energy is not focused at a point or a line on the reflected energy
receiving region 220. Instead, the reflected energy strikes a
three-dimensional surface as a receiving zone 224 on the reflected
energy receiving region 220, wherein the receiving zone 224 has
dimensions that vary based on the focus point F1 and the increasing
diameter of the elongated polysilicon body 200 as it grows during
the CVD process. In the embodiment of FIG. 8, the focus point F1 is
beyond the reflected energy receiving region 220. In some
embodiments, the focus point F1 may be on reflected energy
receiving region 220 at a time point before or during CVD. Because
the diameter of the elongated polysilicon body increases during
CVD, the focus point F1 will not remain on the surface of the bend
portion 250 throughout CVD. When the focus point F1 is on the
reflected energy receiving region 220, the reflected energy will be
focused at a point or a line on the reflected energy receiving
region. The vertex V may or may not be included as a point on the
reflective surface 110. In the illustrated embodiment of FIG. 8,
the vertex V is not on the reflective surface 110.
[0072] When reflective surface 110 is a concave portion of a
cylinder, the cylinder has a longitudinal axis that is not parallel
to a longitudinal axis of the energy emitting region of the
elongated polysilicon body. For example, in some embodiments, the
elongated polysilicon body 200 comprises a first vertical portion
204 and the energy emitting region 210 is a portion of the surface
of the vertical portion 204. In such embodiments, when reflective
surface 110 is a concave portion of a cylinder, the cylinder has a
longitudinal axis A3 that is not parallel to a longitudinal axis A4
of the first vertical portion 204 of the elongated polysilicon body
200 (FIG. 9). The angle .theta. of axis A3, relative to vertical,
may be selected to provide a desired angle of reflection .alpha.
for the radiant heat energy received from the energy emitting
region 210. Accordingly, the reflective surface 110 reflects at
least a portion of received radiant heat energy to a location other
than the energy emitting region 210.
[0073] In an independent embodiment (not shown), the reflective
surface is configured and/or positioned such that at least a
portion of the received radiant energy is reflected back to the
energy emitting region. In other words, the energy emitting region
and reflected energy receiving region are the same region in this
embodiment.
[0074] Advantageously, reflective surface 110 is substantially
smooth with any surface irregularities having an average amplitude
of less than 3 mm, such as an average amplitude of less than 1 mm,
less than 100 .mu.m, less than 50 .mu.m, less than 30 .mu.m, from
10 .mu.m to 3 mm, from 10 .mu.m to 1 mm, from 10-100 .mu.m, from
10-50 .mu.m, from 10-30 .mu.m, or from 15-20 .mu.m. The surface may
be polished using a CNC (computer numerical control) optical
polishing machine, e.g., to achieve a variance of less than 30
.mu.m. The surface optionally is further electropolished
(electrochemically polished). In another embodiment (not shown),
the reflective surface 110 may be a Fresnel surface.
[0075] The surface area and emissivity of the reflective surfaces
110, 120 can be tuned to increase or decrease the amount of energy
reflected back to the growing elongated polysilicon body. For
example, as the surface area increases, the amount of energy
received by the reflector and reflected back to the rod increases.
Additionally, the reflective surface area may be increased to
increase the size of the region that receives the reflected energy
while maintaining uniform energy density. Emissivity is inversely
correlated to the amount of energy received and reflected by the
reflector. The reflector, and reflective surface, size may be
determined at least in part by the placement of the reflector 100
in the thermal decomposition reactor vessel.
[0076] In some embodiments, the reflector 100 is sized
appropriately for placement on an upper surface 310 of a reactor
component 300 (FIGS. 8, 9). In one embodiment, the reflector 100
simply rests on the upper surface 310 of the reactor component 300.
In an independent embodiment, the reflector 100 is secured directly
to the upper surface 310 by any suitable means, e.g., by brazing or
welding, using bolts or screws, or using a suitable adhesive.
[0077] In an independent embodiment, the reflector is mounted above
the upper surface of the reactor component. In the exemplary
embodiment of FIG. 10, the reflector 100 is mounted above the upper
surface 310 of the reactor component 300 by means of an extender
315. In the exemplary embodiment of FIG. 11, protrusions, or pins,
316, 317 extend from the upper surface 310 of the reactor component
300. A reflector 100 is positioned on the upper surface 310. The
lower surface of the reflector defines depressions that are sized
and located to receive the pins 316, 317. The pins 316, 317 and
reflector depressions (e.g., depressions 150, 152 shown in FIG. 4)
may be sized so that the lower surface 140 of the reflector 100
contacts the upper surface 310 when the pins 316, 317 are received
within the depressions. The pins 316, 317 also may aid in
positioning and/or aligning the reflector 100 within the thermal
decomposition reactor vessel 30.
[0078] In some embodiments, the thermal decomposition reactor
includes a pair of tubes 300a, 300b, dimensioned to receive first
and second vertical portions 204, 206 of an elongated polysilicon
body 200. In the exemplary embodiment of FIG. 12, tubes 300a, 300b
share a common wall portion 311 and have upper rims 310a, 310b. The
reflector 100 is mounted on the shared portion 311 of the upper
rims 310a, 310b, or alternatively above the shared portion 311 of
the upper rims 310a, 310b by means of an extender 315. In an
independent embodiment, protrusions, or pins, 316, 317 extend from
the shared portion 311 and may be used to position and/or align the
reflector on the shared portion 311 when the lower surface of the
reflector defines depressions that are sized and located to receive
the pins 316, 317.
[0079] In another independent embodiment, the reflector is mounted
to a component of, or within, a thermal decomposition reactor
vessel 30 comprising a cover 1 that defines a chamber 32 (FIG. 13).
One or more reflectors 100a, 100b may be mounted, for example, to
the cover 1. The reflectors 100a, 100b may be mounted by any
suitable means. In the exemplary embodiment of FIG. 11, reflectors
100a, 100b are mounted to the cover by means of extenders 315a,
315b. Advantageously, the reflectors 100a, 100b are mounted such
that at least one reflective surface 110a, 110b, 120a, 120b of each
reflector is positioned to receive and reflect radiant heat energy
emitted from elongated polysilicon bodies 200a, 200b being grown in
tubes 300a, 300b, 300c, 300d in the reactor. One or more reflectors
may be mounted, optionally via an extender, to any other component
within the reactor vessel, e.g., a pipe, a nozzle, a heat
exchanger, an outer surface of a tube, or the like. In one
non-limiting embodiment, the reflector 100a is positioned such that
the reflective surface 110a receives radiant heat energy emitted
from a bridge portion 208a of elongated polysilicon body 200a and
directs at least a portion of the received radiant heat energy to a
vertical portion 204a of the elongated polysilicon body 200a as
indicated by the dashed arrow.
[0080] Advantageously, the reflector is constructed of a material
capable of withstanding operating temperatures within the thermal
decomposition reactor vessel without the reflector thermally
decomposing or reacting with gases in the reactor vessel. In some
arrangements, the reflector surface may be maintained at a
temperature less than 450.degree. C., such as less than 400.degree.
C., so that the silicon-bearing gas does not decompose and deposit
silicon onto the reflector surface. The reflector may be kept at a
suitable temperature by placing the reflector at a sufficient
distance from the polysilicon rod surface. In one non-limiting
example, the reflector is placed at a distance that is
approximately 10-25 cm from an outer surface of the polysilicon rod
when the polysilicon rod is fully grown, i.e., at its maximum
diameter. In another non-limiting example, the reflector is placed
at a distance that is approximately 75-100 cm from the center of
the starter filament. In another example, the reflector may be
placed on or connected to a cooled surface. The tubes may be
water-cooled, and the reflector may be placed on an upper rim of a
water-cooled tube.
[0081] In some embodiments, the reflector is made of, or plated
with, a material that does not evolve chemical species comprising
Group III elements (e.g., boron, aluminum), Group V elements (e.g.,
phosphorus), metals, oxygen, or carbon during reactor operations.
The reflector may be constructed from, or plated with, a material
having an emissivity <0.5.
[0082] In some embodiments, the reflector is constructed of, or
plated with, stainless steel, or a metal or metal alloy, wherein
the metal is nickel, molybdenum, tungsten, cobalt, titanium, gold,
silver, or tantalum. Suitable alloys include, but are not limited
to, 304L stainless steel (.ltoreq.0.03% C, .ltoreq.2% Mn,
.ltoreq.0.045% P, .ltoreq.0.03% S, .ltoreq.0.75% Si, 18-20% Cr,
8-12% Ni, .ltoreq.0.1% N, balance Fe), 316 stainless steel
(.ltoreq.0.08% C, .ltoreq.2% Mn, .ltoreq.0.045% P, .ltoreq.0.03% S,
.ltoreq.0.75% Si, 16-18% Cr, 10-14% Ni, 2-3% Mo, .ltoreq.0.1% N,
balance Fe), 321 stainless steel (.ltoreq.0.08% C, .ltoreq.2% Mn,
.ltoreq.0.045% P, .ltoreq.0.03% S, .ltoreq.0.75% Si, 17-19% Cr,
9-12% Ni, .ltoreq.0.7% Ti, .ltoreq.0.1% N, balance Fe), 405
stainless steel (0.1-0.3% Al, .ltoreq.0.08% C, 11.5-14.5% Cr,
.ltoreq.1% Mn, .ltoreq.0.5% Ni, .ltoreq.0.04% P, .ltoreq.1% Si,
.ltoreq.0.03% S, balance Fe), 440 stainless steel (440A=0.6-0.75%
C, .ltoreq.1% Mn, .ltoreq.0.04% P, .ltoreq.0.03% S, .ltoreq.1% Si,
16-18% Cr, .ltoreq.0.75% Mo, balance Fe), 2011 aluminum (0.2-0.6%
Bi, 5-6% Cu, .ltoreq.0.7% Fe, 0.2-0.6% Fe, .ltoreq.0.4% Si,
.ltoreq.0.3% Zn, other .ltoreq.0.005% each/.ltoreq.0.15% total,
balance Al), 6061 aluminum (0.04-0.35% Cr, 0.15-0.4% Cu, 0-0.7% Fe,
0.8-1.2% Mg, .ltoreq.0.15% Mn, other .ltoreq.0.005%
each/.ltoreq.0.15% total, 0.4-0.8% Si, .ltoreq.0.15% Ti,
.ltoreq.0.25% Zn, balance Al), 200 nickel (.ltoreq.0.15% C,
.ltoreq.0.25% Cu, .ltoreq.0.4% Fe, .ltoreq.0.35% Mn, .ltoreq.0.35%
Si, .ltoreq.0.01% S, .gtoreq.99% Ni), 270 nickel (.ltoreq.0.01% Cu,
.ltoreq.0.05% Fe, .ltoreq.0.003% Mn, .ltoreq.0.02% C,
.ltoreq.0.003% S, .ltoreq.0.005% Ti, .ltoreq.0.005% Mg,
.ltoreq.0.005% Si, .gtoreq.99.9% Ni), and titanium 6-4 (6% Al,
.ltoreq.0.25% Fe, .ltoreq.0.2% 0, 90% Ti, 4% V).
IV. Reflector Positioning and Methods of Using the Reflector
[0083] When an electrical current passes through a polysilicon
filament and an elongated polysilicon body grows via silicon
deposition within the thermal decomposition reactor, there is a
radial temperature gradient in the elongated polysilicon body,
which can affect growth rates and/or morphology in regions of the
elongated polysilicon body. In the exemplary embodiment of FIG. 14,
the elongated polysilicon body 200 grown by silicon deposition onto
an inverted U-shaped filament 202 has a first vertical portion 204,
a second vertical portion 206, and a bridge portion 208 between the
first and second vertical portions 204, 206. The portions of the
elongated polysilicon body at the junctions between the bridge
portion 208 and the first and second vertical portions 204, 206 are
referred to as bend portions 250. As indicated by the arrows of the
line T1, the core temperature of the polysilicon body 200 near the
filament 202 is higher than the temperature near the polysilicon
body surface. The temperature gradient results from the current
flowing through the polysilicon body 200, which current flow is
greater near the center of the polysilicon body 200. The
temperature gradient T1 is further increased because silicon
resistance is lower in regions where the temperature is higher and
thus more current flows through the hotter regions. In some
instances, the core temperature near the silicon filament 202 may
be 20-100.degree. C. hotter than the polysilicon body surface.
[0084] As the electrical current passes through a bend portion 250
of the elongated polysilicon body 200, the path 240 of the current
passes closer to an inner surface 251 of the bend portion 250 than
to an outer surface 252 of the bend portion, thereby producing an
additional temperature gradient T2 through the bend portion 250,
wherein the temperature increases in the direction of the arrow. In
some embodiments, the inner surface 251 has a temperature greater
than 900.degree. C., such as a temperature from 900-1200.degree. C.
or from 1000-1200.degree. C. The outer surface 252 has a
temperature less than the outer surface 251, producing a
temperature gradient T2 greater than 200.degree. C. through the
bend portion 250. For example, the outer surface 252 may have a
temperature less than 700.degree. C.
[0085] In some embodiments, a reflective surface is positioned
relative to an elongated polysilicon body being grown during
chemical vapor deposition onto a silicon filament such that the
reflective surface receives radiant heat energy emitted from an
energy emitting region of the elongated polysilicon body and
reflects at least a portion of the received radiant heat energy to
a reflected energy receiving region of the elongated polysilicon
body or to another elongated polysilicon body within the thermal
decomposition reactor; in some embodiments, the energy emitting
region and the reflected energy receiving region are not
coextensive. The reflective surface may be an integral portion of a
component within the reactor, e.g., a pipe, a nozzle, a heat
exchanger, an outer surface of a tube, or the like. Alternatively,
the reflective surface may be a surface of a reflector as disclosed
herein. In embodiments where the reflector has a second reflective
surface, the second reflective surface may receive radiant heat
energy from an energy emitting region of a second elongated
polysilicon body and reflect at least a portion of the received
radiant heat energy to a reflected energy receiving region of the
second elongated polysilicon body or to another elongated
polysilicon body within the thermal decomposition reactor. Many
arrangements of the reflective surfaces, reflectors including the
reflective surfaces, and the elongated polysilicon bodies are
contemplated within the scope of this disclosure.
[0086] In some embodiments, the energy emitting region is a portion
of the surface of a vertical portion of the elongated polysilicon
body and the reflected energy receiving region is a portion of the
surface of a bend portion of the elongated polysilicon body.
Reflecting radiant heat to the bend portion is a method to alter
bend portion morphology (e.g., increase or decrease texture the
bend portion surface and/or within the bend portion). A suitably
shaped and positioned reflective surface will reflect radiant heat
energy from a portion of the surface of a vertical portion of the
elongated polysilicon body to a portion of the surface of the bend
portion, thereby affecting the bend portion morphology and/or rate
of growth. Advantageously, the reflective surface is shaped and
positioned to have little or no effect on the morphology of the
vertical portions of the polysilicon body. The surface area and
emissivity of the reflective surfaces can be tuned to increase or
decrease the amount of energy reflected back to the growing
polysilicon body and to optimize the bend portion morphology and/or
growth rate. Decreasing the bend portion morphology decreases the
likelihood that the elongated polysilicon body will fracture
through the bend portion as it cools and decreases the likelihood
that an uncontrolled fracture will propagate down the vertical
portion of the elongated polysilicon body. The elongated
polysilicon body can be cut as desired after it has cooled. In
contrast, increasing the bend portion morphology increases the
likelihood that the elongated polysilicon body will fracture
through the bend portion, and may reduce undesirable fracture
propagation down the vertical portion of the polysilicon body by
controlling where the fracture occurs and confining the fracture to
the bridge portion.
[0087] In one embodiment, a reflective surface 110 is positioned
lateral to a vertical portion 204 of an elongated polysilicon body
200 (FIG. 7). The reflective surface 110 may be an integral part of
an upper portion 310 of a reactor component 300, such as a pipe, a
nozzle, a heat exchanger, an outer surface of a tube, or the like.
The reflective surface 110 is configured to receive radiant heat
energy emitted from an energy emitting region 210 and reflect at
least a portion of the received radiant heat energy to a reflected
energy receiving region 220 of the elongated polysilicon body 200
as indicated by the dashed arrow.
[0088] In one embodiment, a reflector 100 is positioned lateral to
an energy emitting region 210 of an elongated polysilicon body 200
(FIG. 15). The reflector 100 has a reflective surface 110
configured to receive radiant heat energy emitted from the energy
emitting region 210 and reflect at least a portion of the received
radiant heat energy to a reflected energy receiving region 220 of
the elongated polysilicon body 200 as indicated by the dashed
arrow. In the embodiment of FIG. 15, the reflected energy receiving
region 220 is an outer surface 252 of a bend portion 250. The
reflector 100 is effective to reduce a temperature gradient through
the bend portion 250 by reflecting thermal radiation to the cooler
outer surface 252 of the bend portion 250. The reduced temperature
gradient regionally changes the surface temperature which modifies
the radial growth rate.
[0089] In an independent embodiment, a reflector 100 is positioned
medial to an energy emitting region 210 of an elongated polysilicon
body 200 (FIG. 16). The reflector 100 has a reflective surface 110
configured to receive radiant heat energy emitted from the energy
emitting region 210 and reflect at least a portion of the received
radiant heat energy to a reflected energy receiving region 220 of
the elongated polysilicon body 200 as indicated by the dashed
arrow. In the embodiment of FIG. 16, the reflected energy receiving
region 220 is an inner surface 251 of a bend portion 250.
[0090] In an independent embodiment, a reflector 100 is positioned
lateral to an energy emitting region 210 of an elongated
polysilicon body 200 (FIG. 17). The reflector 100 has a reflective
surface 110 configured to receive radiant heat energy emitted from
the energy emitting region 210 and reflect at least a portion of
the received radiant heat energy to a reflected energy receiving
region 220 of the elongated polysilicon body 200 as indicated by
the dashed arrow. In the embodiment of FIG. 17, the reflected
energy receiving region 220 is a side surface 253 of a bend portion
250.
[0091] Two or more reflectors may be positioned to reflect radiant
heat energy to a single elongated polysilicon body. In one
embodiment, two reflectors 100a, 100b are positioned to reflect
radiant heat energy to an elongated polysilicon body 200 (FIGS. 18,
19). Reflectors 100a, 100b are positioned lateral to an energy
emitting region 210 of the elongated polysilicon body 200.
Reflective surfaces 110a, 110b are configured to receive radiant
heat energy emitted from the energy emitting region 210 and reflect
at least a portion of the received radiant heat energy to a
reflected energy receiving region 220 of the elongated polysilicon
body 200 as indicated by the dashed arrows. Each reflector 110,
110a has a focus point F1, F2, respectively, beyond the reflected
energy receiving region 220.
[0092] A reflector 100 with first and second reflective surfaces
110, 120, may be positioned between two adjacent elongated
polysilicon bodies 200a, 200b (FIG. 20). In some embodiments, the
reflector 100 is placed equidistant from the two polysilicon bodies
200a, 200b. The reflector 100 receives radiant heat energy from,
and reflects at least a portion of the received radiant heat energy
to, the adjacent polysilicon bodies 200a, 200b. The first
reflective surface 110 is configured to receive radiant heat energy
emitted from an energy emitting region 210a of a first elongated
polysilicon body 200a, and reflect at least a portion of the
received radiant heat energy to a reflected energy receiving region
220a of the first elongated polysilicon body 200a. The reflective
surface 110 has a focus point F110 beyond the reflected energy
receiving region 220a. A second reflective surface 120 is
configured to receive radiant heat energy emitted from an energy
emitting region 210b of a second, adjacent elongated polysilicon
body 200b, and reflect at least a portion of the received radiant
heat energy to a reflected energy receiving region 220b of the
second elongated polysilicon body 220b. The reflective surface 120
has a focus point F120 beyond the reflected energy receiving region
220b.
[0093] Optionally, a second reflector 100b with first and second
reflective surfaces 110b, 120b is positioned between the two
adjacent elongated polysilicon bodies 200a, 200b (FIG. 20). The
second reflector 100b also receives radiant heat energy from, and
reflects at least a portion of the received radiant heat energy to,
the adjacent polysilicon bodies 200a, 200b. The regions from which
the reflective surfaces 110b, 120b receive radiant heat energy, and
reflect radiant heat energy to, may be the same or different than
the regions upon which the first reflector 100 acts. In the
exemplary embodiment of FIG. 20, the first reflective surface 110b
is configured to receive radiant heat energy emitted from the
energy emitting region 210a of the first elongated polysilicon body
200a, and reflect at least a portion of the received radiant heat
energy to the reflected energy receiving region 220a of the first
elongated polysilicon body 200a. The second reflective surface 120
is configured to receive radiant heat energy emitted from the
energy emitting region 210b of the second elongated polysilicon
body 200b, and reflect at least a portion of the received radiant
heat energy to the reflected energy receiving region 220b of the
second elongated polysilicon body 220b.
[0094] In some embodiments, a thermal decomposition reactor vessel
has a cover defining a chamber that contains a first tube pair
comprising adjacent first and second tubes that are configured to
receive first and second vertical portions of an elongated
polysilicon body grown by chemical vapor deposition onto a silicon
filament. The elongated polysilicon body has one or more bend
portions between the first and second vertical portions which are
situated outside the tubes. The bridge portion of the polysilicon
body is also situated outside the tubes. A reflector is positioned
on an upper rim of the first tube such that the reflective surface
receives at least some radiant heat energy emitted from the energy
emitting region of the elongated polysilicon body during the
chemical vapor deposition, and reflects at least a portion of the
received radiant heat energy to the second portion of the elongated
polysilicon body. In another embodiment, the energy emitting region
is the first vertical portion of the polysilicon body, and the
reflected energy receiving region is a bend portion adjacent to the
first vertical portion.
[0095] In some embodiments, the chamber further contains a second
tube pair proximate the first tube of the first tube pair. The
second tube pair comprises adjacent third and fourth tubes that are
configured to receive first and second vertical portions of a
second elongated polysilicon body grown on a second silicon
filament during the chemical vapor deposition. The fourth tube has
an upper rim contiguous with the upper rim of the first tube. The
reflector is positioned on a shared portion of the upper rims. A
second reflective surface of the reflector receives radiant heat
energy emitted from an energy emitting region of the second
elongated polysilicon body, and directs at least a portion of the
received radiant heat energy to a reflected energy receiving region
of the second polysilicon body.
[0096] In an independent embodiment, a thermal decomposition
reactor comprises a cover that defines a chamber. The chamber
contains a first tube pair comprising adjacent first and second
tubes that are configured to receive first and second vertical
portions of an elongated polysilicon body. The chamber further
contains a second tube pair comprising adjacent third and fourth
tubes that are configured to receive first and second vertical
portions of a second elongated polysilicon body. A reflector is
positioned such that a first reflective surface receives radiant
heat energy emitted from an energy emitting region of the first
polysilicon body and directs at least a portion of the received
radiant heat energy to a reflected energy receiving region of the
second polysilicon body. The reflector may be mounted via an
extender to the cover of the reactor vessel. Alternatively, the
reflector may be positioned on an upper rim of one of the tubes, or
it may be mounted directly or via an extender to another component
within the chamber.
[0097] In an independent embodiment, a reactor vessel comprises a
cover that defines a chamber. The chamber contains a first tube
pair comprising adjacent first and second tubes that are configured
to receive first and second vertical portions of an elongated
polysilicon body grown by chemical vapor deposition onto a silicon
filament. The elongated polysilicon body has one or more bend
portions between the first and second vertical portions of the
polysilicon body, which bend portions are situated outside the
first and second tubes. The bridge portion of the polysilicon body
is also situated outside the first and second tubes. A reflective
surface is an integral portion of an upper rim of the first tube
with the reflective surface oriented to receive at least some
radiant heat energy emitted from the energy emitting region of the
polysilicon body during the chemical vapor deposition, and reflect
at least a portion of the received radiant heat energy to the
second portion of the polysilicon body. In an exemplary embodiment,
the energy emitting region is a portion of the surface of the first
vertical portion of the elongated polysilicon body, and the
reflected energy receiving region is a portion of the surface of a
bend portion adjacent to the first vertical portion.
[0098] In view of the many possible embodiments to which the
principles of the disclosed invention may be applied, it should be
recognized that the illustrated embodiments are only preferred
examples of the invention and should not be taken as limiting the
scope of the invention. Rather, the scope of the invention is
defined by the following claims.
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