U.S. patent application number 13/369432 was filed with the patent office on 2012-06-07 for device and process for producing a block of crystalline material.
This patent application is currently assigned to APOLLON SOLAR. Invention is credited to Roland EINHAUS, Francois LISSALDE, Pascal RIVAT.
Application Number | 20120141336 13/369432 |
Document ID | / |
Family ID | 36764649 |
Filed Date | 2012-06-07 |
United States Patent
Application |
20120141336 |
Kind Code |
A1 |
EINHAUS; Roland ; et
al. |
June 7, 2012 |
DEVICE AND PROCESS FOR PRODUCING A BLOCK OF CRYSTALLINE
MATERIAL
Abstract
A temperature gradient is established in a crystallization
crucible by means of a heat source and a cooling system. The
cooling system comprises a heat exchanger and an adjustable
additional heat source. The cooling system is preferably formed by
an induction coil cooled by a coolant liquid circulating in the
induction coil and by an electrically conductive induction
susceptor positioned between the crucible and induction coil. The
fabrication process comprises heating the crucible via the top and
controlling heat extraction from the crucible downwards by means of
the heat exchanger and by means of regulation of the adjustable
additional heat source.
Inventors: |
EINHAUS; Roland; (Bourgoin
Jallieu, FR) ; LISSALDE; Francois; (Seyssins, FR)
; RIVAT; Pascal; (Saint Etienne de Saint Geoirs,
FR) |
Assignee: |
APOLLON SOLAR
Paris
FR
EFD INDUCTION SA
Seyssinet Pariset
FR
CYBERSTAR
Echirolles
FR
|
Family ID: |
36764649 |
Appl. No.: |
13/369432 |
Filed: |
February 9, 2012 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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12087308 |
Jul 1, 2008 |
|
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|
PCT/FR2006/002661 |
Dec 6, 2006 |
|
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13369432 |
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Current U.S.
Class: |
422/245.1 |
Current CPC
Class: |
Y10T 117/1068 20150115;
Y10T 117/102 20150115; C30B 11/002 20130101; C30B 11/003 20130101;
Y10T 117/10 20150115; Y10T 117/1024 20150115; Y10T 117/1088
20150115 |
Class at
Publication: |
422/245.1 |
International
Class: |
B01D 9/00 20060101
B01D009/00 |
Foreign Application Data
Date |
Code |
Application Number |
Jan 4, 2006 |
FR |
06 00049 |
Claims
1. A device for the fabrication of a block of crystalline material
by directional crystallization, the device comprising: heating
means and cooling means arranged such as to establish a temperature
gradient in a crystallization crucible, wherein the cooling means
are arranged under the bottom of the crystallization crucible so as
to cover the bottom of the crystallization crucible and comprise: a
heat exchanger and an adjustable additional heat source, an
induction coil cooled by a coolant liquid circulating in the
induction coil and an electrically conducting induction susceptor
positioned between the crystallization crucible and conduction
coil.
2. The device according to claim 1, wherein the susceptor is made
from a thermally conducting material that absorbs infrared
radiation.
3. The device according to claim 2, wherein the susceptor is made
from one of graphite and silicon carbide.
4. The device according to claim 1, wherein the susceptor forms a
support for the crystallization crucible.
5. The device according to claim 1, further comprising silica
plates arranged around the induction coil.
6. The device according to claim 1, wherein the crystallization
crucible comprises a transparent bottom made from impurity-free
amorphous silica.
7. The device according to claim 1, further comprising a removable
felt positioned above the heat exchanger.
Description
[0001] This is a Continuation of application Ser. No. 12/087,308
filed Jul. 1, 2008, which in turn is a U.S. National Phase of
PCT/FR2006/002661 filed Dec. 6, 2006, which claims the benefit of
French Patent Application No. 06 00049 filed Jan. 4, 2006. The
disclosures of the prior applications are hereby incorporated by
reference herein in their entirety.
BACKGROUND OF THE INVENTION
[0002] The invention relates to an equipment for the fabrication of
a block of crystalline material by directional crystallization
comprising heating means and cooling means arranged such as to
establish a temperature gradient in a crystallization crucible, the
cooling means comprising a heat exchanger and an adjustable
additional heat source.
STATE OF THE ART
[0003] The document WO2004/094704 describes an equipment for
fabrication of a block of crystalline material by directional
crystallization. This material is typically silicon. As represented
in FIG. 1, the device comprises a crystallization crucible 1 the
bottom 7 of which enables heat to be extracted. The bottom 7 of the
crucible 1 has greater thermal transfer properties than those of
the side walls 8. To generate a temperature gradient, a heating
element 3 and a heat exchanger 4 are respectively arranged above
and below the crucible 1.
[0004] The temperature gradient for the solidification of silicon
requires an efficient heat extraction. The anisotropic properties
of the crucible 1 enable substantially flat and parallel isothermal
planes to be obtained. The solidification front is consequently
substantially flat in a direction parallel to the bottom 7 of the
crucible 1.
[0005] When crystallization of the silicon takes place, the
thickness of the solid phase 5 increases so that the solidification
front progresses upwards moving away from the bottom 7 of the
crucible 1, as represented by the arrow 20 in FIG. 1. The melting
temperature of silicon being 1410.degree. C., the 1410.degree. C.
isothermal plane then moves away from the bottom 7 of the crucible
1, resulting from the temperature decrease at the bottom 7 of the
crucible 1 during the crystallization process.
[0006] The increase of the quantity of solidified material at the
bottom 7 of the crucible 1 is accompanied by an increase of the
thermal resistance. To keep the temperature gradient at the
solid/liquid interface constant, the thermal power removed by the
heat exchanger 4 needs however have to remain substantially
constant throughout the solidification sequence. Therefore an
adjustment then has to be provided.
[0007] The heat exchanger 4 thus comprises for example a coolant
fluid circuit and, depending on the applications, the fluid can be
synthetic oil or a fluid operating at high temperature, for example
a gas under pressure such as helium, which can be very costly when
a helium liquefier is required. It is possible to make the
temperature of the coolant fluid vary in a controlled manner to
ensure that the power removed remains constant throughout the
solidification sequence.
[0008] Document WO2004/094704 for example describes a graphite felt
9 arranged between the bottom 7 of the crucible 1 and the cooling
means 4, as illustrated in FIG. 2. The graphite felt 9 is
compressed during solidification of the silicon. The thickness of
the graphite felt 9 thereby decreases and its thermal conductivity
increases. Heat transfer by conductivity of the graphite felt 9 can
then be controlled during the solidification process. The graphite
felt 9 can also be progressively removed to control the cooling.
The temperature gradient in the crucible 1 is typically controlled
and kept at a value comprised between 8.degree. C./cm and
30.degree. C./cm.
[0009] Water cooling systems also exist. However it is difficult to
control the temperature over a wide temperature range unless the
latent heat from water vaporization is used, which is complicated
to implement.
[0010] Document U.S. Pat. No. 6,299,682 describes an apparatus for
producing a silicon ingot for photovoltaic applications. The
apparatus comprises a heating system arranged above a crucible and
cooling means arranged below the crucible. A heat source is also
arranged under the crucible to control the heat removed at the
bottom of crucible.
OBJECT OF THE INVENTION
[0011] The object of the invention is to remedy these drawbacks and
in particular to achieve an efficient temperature adjustment while
at the same time reducing the implementation costs of the
device.
[0012] According to the invention, this object is achieved by the
appended claims and more particularly by the fact that the cooling
means are provided by an induction coil cooled by a cooling liquid
flowing in the induction coil and by an electrically conductive
induction susceptor positioned between the crucible and the
induction coil.
[0013] It is a further object of the invention to provide a process
for fabricating a block of crystalline material by directional
crystallization using an equipment according to the invention, the
process comprising: [0014] heating the crucible via the top and
cooling the crucible via the bottom to establish the temperature
gradient in the crystallization crucible, and [0015] controlling
the heat extraction from the crucible via the bottom by means of
the heat exchanger and by means of regulating of the adjustable
additional heat source, the cooling means being provided by an
induction coil cooled by a cooling liquid circulating in the
induction coil and by an electrically conducting induction
susceptor arranged between the crucible and the induction coil,
[0016] the process simultaneously comprising heating by means of
the induction coil and cooling by means of the cooling liquid
flowing in the induction coil, and [0017] the process comprising
progressive reduction of the heating by means of reduction of the
electric power supply of the induction coil, while a solidification
front progresses in the crucible moving away from the
susceptor.
BRIEF DESCRIPTION OF THE DRAWINGS
[0018] Other advantages and features will become more clearly
apparent from the following description of particular embodiments
of the invention given as non-restrictive examples only and
represented in the accompanying drawings, in which:
[0019] FIG. 1 shows an equipment for the fabrication of a block of
crystalline material by directional crystallization according to
the prior art.
[0020] FIGS. 2 and 3 show two particular embodiments of the
equipment according to the invention, in cross-section.
[0021] FIG. 4 illustrates a particular embodiment of a susceptor of
a device according to the invention, in top view.
DESCRIPTION OF PARTICULAR EMBODIMENTS
[0022] The fabrication equipment represented in FIG. 2 comprises a
heat source 3 and a cooling system 22 arranged such as to establish
a temperature gradient in the crystallization crucible 1. The
cooling system 22 comprises a heat exchanger 17 and an adjustable
additional heat source 18, for example resistive heating elements,
infrared heating or any other suitable adjustable heating. The heat
exchanger 17 preferably comprises a water cooling circuit
represented schematically by arrow 21. The heat exchanger 17 can in
particular be extended over the whole width of crucible 1.
[0023] The heat extraction from the crucible can thus be
controlled, while at the same time benefiting from the advantages
of a constant power heat exchanger, in particular its simple
implementation.
[0024] The equipment can also comprise a removable felt 19
positioned above the heat exchanger 17 and under the adjustable
additional heat source 18, thereby forming a screen preventing
thermal radiation between the heat source 18 and the heat exchanger
17, thus enabling the heat extraction from the crucible 1 to be
further controlled. By placing the removable felt 19 between the
heat source 18 and the heat exchanger 17, the heat extraction is
reduced, whereas removing the felt 19 allows for direct evacuation
of the radiation emitted by the source 18 in the direction of the
heat exchanger 17.
[0025] In the preferred embodiment represented in FIG. 3, the
cooling system 22 comprises an induction coil 10 cooled by a
coolant liquid circulating in the induction coil 10 and an
electrically and thermally conducting induction susceptor 11
positioned between the crucible 1 and the induction coil 10.
[0026] The combination of the induction coil 10 and induction
susceptor 11 thus provides an adjustable additional heat source 18.
Adjustment is performed by means of the electric power supply 24
(see FIG. 3) for the induction coil 10. At the same time, the heat
exchanger 17 is formed by the unit comprising the induction coil 10
and its cooling circuit consisting of a cooling liquid flowing in
the induction coil 10, illustrated by arrow 21 in FIG. 3.
[0027] A heat source 3, for example formed by resistive heating
elements, by an additional induction coil and its additional
susceptor or by any other suitable heating means such as infrared
heating for example, is positioned above the crucible 1. The
induction coil 10 is arranged under the crucible. The induction
susceptor 11 is situated between the crucible 1 and the induction
coil 10. The crucible 1 preferably comprises a transparent bottom 7
made from impurity-free amorphous silica enabling infrared
radiation to be transmitted. When a removable felt 19 is used as
described above, the removable felt 19 can be positioned between
the induction coil 10 and susceptor 11.
[0028] Induction coils according to the prior art are typically
cooled by a cooling liquid circulating in the induction coil.
Heating induction coils are however conventionally not in thermal
contact with the object to be heated, and may even be thermally
insulated from this object. Cooling therefore only acts on the coil
itself and cannot act on the object to be heated.
[0029] The susceptor 11 is preferably made from thermally
conducting material which absorbs infrared radiation, for example
graphite or silicon carbide which are conductors and good black
bodies. The heat emitted by the bottom 7 of the crucible 1 is thus
absorbed by the face 12 of the susceptor arranged facing the
crucible 1, transported through the susceptor 11 and re-emitted via
the face 13 of the susceptor 11 arranged facing the induction coil
10. The induction coil 10 enables the heat to be evacuated. The
susceptor 11 can form a support for the crucible 1 and enables a
good thermal exchange to be obtained between the susceptor 11 and
crucible 1. The induction coil 10 is preferably placed in an
electrically insulated zone, using for example silica plates 23 to
prevent short-circuits and formation of sparks to the neighboring
graphite 14. As represented in FIG. 3, silica plates 23 are
arranged around the induction coil 10.
[0030] The susceptor 11 can simply be formed by a flat plate. In a
particular embodiment, the susceptor 11 comprises zones 15 of lower
electric surface conductivity enabling induction heating to be
locally reduced and also locally provoking heat extraction from the
crucible 1 to the induction coil 10. The zones of crucible 1
situated opposite to zones 15 of lower electric surface
conductivity are consequently less heated and thereby form
nucleation centres for crystallization. In addition, the zones of
crucible 1 opposite to zones 15 of lower electric surface
conductivity are better cooled, since these zones 15 of lower
electric surface conductivity also locally provoke heat removal
from the crucible 1 towards the induction coil 10.
[0031] Zones 15 of lower electric surface conductivity are for
example formed by holes arranged in the susceptor 11, as
represented in FIG. 4. Zones 15 of lower electric surface
conductivity can also be formed by a material having a lower
electric conductivity than the material of susceptor 11 or by a
zone having a smaller thickness than the susceptor. The lateral
dimension of zones 15 of lower electric surface conductivity is
preferably equal to or greater than the thickness of the susceptor.
The distance between zones 15 of lower electric surface
conductivity is for example 10 cm for a susceptor of a few tens of
decimeters in size.
[0032] A process for the fabrication of a block of crystalline
material by directional crystallization using an equipment
according to the invention comprises heating of the crucible 1 via
the top and cooling of the crucible 1 via the bottom to establish
the temperature gradient in the crystallization crucible 1. The
process further comprises heat extraction from the crucible 1
downwards by means of the heat exchanger 17 and by means of a
regulated additional and adjustable heat source 18. The heat
exchanger 17 can in particular operate in constant regime, which
simplifies the implementation of the heat exchanger 17.
[0033] The process for the fabrication of a block of crystalline
material by directional crystallization using the equipment
according to the invention can in particular comprise heating by
means of the induction coil 10 and its susceptor on the one hand,
and at the same time cooling by means of the cooling liquid flowing
inside the induction coil 10 on the other hand. While a
solidification front 16 progresses in the crucible 1 moving away
from the susceptor 11 in the upward direction as represented in
FIG. 3 by arrow 20, heating is progressively reduced by reducing
the electric power supply to the induction coil 10, whereas the
cooling liquid can circulate flow in constant manner inside
induction coil 10.
[0034] Before crystallization, the process can also comprise a
melting step of the material to be crystallized using heat source 3
and adjustable additional heat source 18 comprising for example
induction coil 10 and its susceptor 11. This in particular enables
the material to be crystallized to be completely melted.
[0035] The invention is not limited to the embodiments represented.
In particular, the gradient is not necessarily established from top
to bottom and may be oriented along any axis, for example
horizontal or inclined. In the latter case, the heating and cooling
means are respectively arranged on each side of the gradient
zone.
* * * * *