Title of Invention

PROCESS FOR PRODUCING A SOLAR POLYCRYSTALLINE SILICON INGOT

Abstract Provided is a process in which a polycrystalline silicon ingot improved in life time characteristics, which are correlated with the conversion efficiency of solar wafers, is inexpensively produced by the ordinary-pressure hydrogen-atmosphere melting method. In the process, the generation of oxygen and impurities in the silicon melt is inhibited and light-element impurities are removed through reaction or crystallization. Fine crystal grains can be grown at a high rate, and a high-purity polycrystalline silicon ingot having a crystal structure reduced in crystal defect can be grown. A silicon raw material is melted in an atmosphere of 100% hydrogen at ordinary pressure or an elevated pressure to prepare a silicon melt and simultaneously dissolve hydrogen in the silicon melt. The silicon melt containing hydrogen dissolved therein is solidified. Thereafter, the solid is held at a high temperature around the solidification temperature to grow silicon crystal grains in the solid phase and thereby obtain a polycrystalline silicon ingot.
Full Text DESCRIPTION
Technical Field
[0001]
The present invention relates to a process for producing a polycrystalline silicon ingot to be
used for a solar cell or the like.
Background Art
[0002]
As a conventional process for producing a polycrystalline silicon ingot for a solar cell, a
method of melting and solidifying a silicon raw material in an argon atmosphere under reduced
pressure similar to a single crystal pulling method is generally known. Fig. 2 describes a melting
furnace to be used in the conventional method. Fig. 2 is a schematic diagram showing an example
of a conventional melting furnace. In Fig. 2, reference symbol 10a represents a melting furnace.
The melting furnace 10a includes: a sagger 12; heating means 14 for heating the sagger 12; support
means 16 for placing and raising or lowering the sagger 12 by rotating; a heat insulation material
18; and a chamber 20. The heat insulation material 18 is provided on inner surfaces of side walls of
the chamber 20. An atmospheric gas such as an argon gas is introduced from a gas introduction
port 22a and discharged from a discharge port 24. An operation of this structure will be described.
The argon gas is introduced into


the melting furnace 10a from the introduction port 22a for operation of the
furnace under reduced pressure. In the chamber 20 in an argon atmosphere
under reduced pressure, the sagger 12 having a silicon raw material charged
therein is heated by the heating means 14 providedon side parts of the sagger 12,
and the silicon raw material is melted under heating into a silicon melt 26.
Then, the support means 16 having the sagger 12 placed thereon is lowered by
rotating to lower the sagger 12 from a heated region. Thus, the silicon melt is
cooled from a lower part of the sagger, solidified, and subjected to crystal growth,
to thereby produce a polycrystalline silicon ingot. There is also known a method
of melting and solidifying a silicon raw material under reduced pressure in an
inert gas atmosphere containing hydrogen or in a hydrogen atmosphere (Patent
Document 1).
[0003]
Polycrystalline silicon for a solar cell has a crystal grain boundary, has
unbonded active bonds (atomic defects), and contains impurities aggregated at
the grain boundary compared with those of single crystal silicon to trap electrons
in silicon during electron transfer and degrade life time characteristics of a
silicon ingot. Further, a crystal grain itself has crystal defects including atomic
defects and causes degradation of life time characteristics.
[0004]
As described above, a method of producing polycrystalline silicon from a
silicon ingot having a composition and a structure accelerating grain growth has
been studied. However, acceleration of grain growth requires a long
solidification time, and causes problems of increasing generation amounts of


oxygen and carbon from a silicon dioxide sintered sagger to be used for a melting
container in an argon atmosphere under reduced pressure and a carbon sagger,
and carbon from a heater, dissolving oxygen and carbon in a silicon ingot, and
increasing a concentration of oxygen, carbon, and other impurities to be melted in
the silicon ingot. The increase of oxygen, carbon, and the impurities causes
degradation of life time characteristics.
[0005]
Meanwhile, grain growth is inhibited in the presence of atomic or lattice
defects in crystal grains or in the presence of impurities at a crystal grain
boundary. Grain growth for obtaining a target crystal grain size involves
disadvantages in that a solidification rate must be low and ingot production
requires a long period of time.
[0006]
In a liquid phase solidification method, anisotropic growth is significant
in grain growth with a low solidification rate for formation of crystals with few
impurity defects or lattice defects, and non-uniform grains are formed. The
formation of non-uniform grains involves formation of fine grains and causes
mechanical damages in thickness reduction of a solar wafer.
[0007]
A semiconductor wafer technique generally involves hydrogen treatment
under low temperature heating for passivation of a dangling bond (active bond) to
a single crystal silicon wafer. However, the hydrogen treatment is effective only
for a surface layer of several tens µm, and a passivation effect cannot be obtained
inside silicon. A solar cell wafer utilizes a total wafer thickness of several


hundreds µm, and thus the hydrogen treatment is not in practical use for a
method of producing a solar cell wafer because of problems including the
passivation effect and increase in production cost such as a heat treatment cost.
For a solar cell amorphous silicon wafer, hydrogen -treatment employing plasma
or the like is in practical use for crystallization acceleration and passivation of a
dangling bond.
Patent Document 1: JP 58-99115 A
Disclosure of the Invention
Problems to be solved by the Invention
[0008]
As described above, a conventional method involves the following
phenomena, (1) For accelerating grain growth of a polycrystalline silicon melt, a
long solidification time is required, and an electric power cost for production
increases. (2) Melting for a long period of time increases concentrations of
oxygen, carbon, and other impurities in an ingot and causes degradation of life
time characteristics. (3) A liquid phase solidification method through
argon/reduced pressure melting is liable to cause atomic and lattice defects
during crystal formation and is more liable to form fine crystals. Such
phenomena cause problems of degrading mechanical strength with thickness
reduction and degrading life time characteristics.
[0009]
An object of the present invention is to provide a method of
polycrystalline silicon ingot having improved life time characteristics compared


with those of a conventional product capable of producing a polycrystalline
silicon ingot having a structure with few crystal defects and few fine crystal
grains at low cost; and forming a high-purity silicon ingot compared with that
produced by a conventional method by suppressing -formation of impurities such
as oxygen from a melting sagger and carbon from a furnace member, preventing
melting and mixing of light-element impurities in a silicon melt, and removing
the impurities in the melt through crystallization.
Means for solving the Problems
[0010]
For solving problems described above, a process for producing a
polycrystalline silicon ingot of the present invention includes: melting a silicon
raw material in a 100% hydrogen atmosphere under ordinary pressure or
elevated pressure to prepare a silicon melt and simultaneously dissolving
hydrogen in the silicon melt; solidifying the silicon melt containing hydrogen
dissolved therein; maintaining the solid at a high temperature of about a
solidification temperature for crystal growth to obtain a polycrystalline silicon
ingot. The method of the present invention allows production of a
polycrystalline silicon ingot having reduced fine crystals and reduced crystal
defects.
[0011]
In the method of the present invention, hydrogen dissolved in the silicon
melt reacts with, gasifies, and removes light-element impurities such as oxygen
and silicon monoxide in the silicon melt. Further, metal impurities including


transition elements such as iron are removed through crystallization, and
purification of the polycrystalline silicon ingot to be obtained is accelerated. A
concentration of hydrogen dissolved in the silicon melt is high, and dissolution of
other impurities in the silicon melt is reduced. Those effects improve life time
characteristics of the polycrystalline silicon ingot to be obtained.
[0012]
According to the method of the present invention, alignment of silicon
atoms is accelerated through hydrogen dissolution in the silicon melt to form
silicon crystals with little atomic defects. Further, hydrogen is bonded to atomic
defects in a lattice to correct the atomic defects and improve life time
characteristics. Generation of silicon monoxide through a reaction of a sagger
formed of a silicon dioxide material to be used in melting of the silicon raw
material and the silicon melt is suppressed through the hydrogen dissolution to
reduce an oxygen concentration in the polycrystalline silicon ingot. Further,
diffusion of impurities to be generated from a melting member, a releasing
material, a heater, and the like to be used in melting of the silicon raw material
into the silicon melt can be prevented.
Effects of the Invention
[0013]
According to the method of the present invention, a silicon raw material
is melted in a 100% hydrogen atmosphere under ordinary pressure or elevated
pressure to dissolve hydrogen in a silicon melt, and formation of atomic and
lattice defects of a polycrystalline silicon ingot can be suppressed during


solidification and solid phase growth. The dissolved hydrogen is subjected to reactive gasification
with oxygen, accelerates crystallization of impurities in the silicon melt, and provides an effect of
highly purifying the polycrystalline silicon ingot.
[0014]
The method of the present invention accelerates lattice alignment at a grain boundary during
grain growth after solidification and provides an effect of accelerating a crystal growth rate, leading
to saving of electric power for melting.
[0015]
The method of the present invention provides a passivation effect of hydrogen atoms to a
dangling bond through solidification and solid phase growth of silicon in a state where hydrogen is
dissolved in the silicon melt, and improves life time characteristics of the polycrystalline silicon
ingot. Note that hydrogen passivation refers to an action of hydrogen atoms bonding to free bonds
of silicon atomic defects, to thereby prevent electron annihilation during electron transfer in silicon.
Brief Description of the Accompanying Drawings
[0016]
Fig. 1 is a schematic diagram showing an example of a melting furnace to be used in the
present invention.
Fig. 2 is a schematic diagram showing an example of a conventional melting furnace.
Fig. 3 is a graph showing fluctuation of upper temperature and lower


temperature of a sagger with time in Example 1.
Fig. 4 is a graph showing fluctuation of upper temperature and lower
temperature of a sagger in Comparative Example 1.
Fig. 5 is a graph showing a temperature program of upper temperature
and lower temperature of a sagger employed in Example 2 and Comparative
Example 2.
Fig. 6 is a photograph showing a crystal formation state of an ingot in
Example 1.
Fig. 7 is a microphotograph showing an etch pit formation state in the
ingot in Example 1.
Fig. 8 is a photograph showing a crystal formation state of an ingot in
Comparative Example 1.
Fig. 9 is a microphotograph showing an etch pit formation state of the
ingot in Comparative Example 1.
Fig. 10 is a photograph showing a crystal formation state (direction
perpendicular to solidification axis) of an ingot in Example 2.
Fig. 11 is a photograph showing a crystal formation state (solidification
axis direction) of the ingot in Example 2.
Fig. 12 is a microphotograph showing an etch pit formation state of the
ingot in Example 2.
Fig. 13 is a photograph showing a crystal formation state (direction
perpendicular to solidification axis) of an ingot in Comparative Example 2.
Fig. 14 is a photograph showing a crystal formation state (solidification
axis direction) of the ingot in Comparative Example 2.


Fig. 15 is a microphotograph showing an etch pit formation state of the
ingot in Comparative Example 2.
Fig. 16 is a graph showing Fe concentration distribution characteristics
(section along solidification axis) of the ingot in Example 2.
Fig. 17 is a graph showing Fe concentration distribution characteristics
(section perpendicular to solidification axis) of the ingot in Example 2.
Fig. 18 is a graph showing Fe concentration distribution characteristics
(section along solidification axis) of the ingot in Comparative Example 2.
Fig. 19 is a graph showing Fe concentration distribution characteristics
(section perpendicular to solidification axis) of the ingot in Comparative Example
2.
Fig. 20 is a graph showing life time characteristics (section along
solidification axis) of the ingot in Example 2.
Fig. 21 is a graph showing life time characteristics (section perpendicular
to solidification axis) of the ingot in Example 2.
Fig. 22 is a graph showing life time characteristics (section along
solidification axis) of the ingot in Comparative Example 2.
Fig. 23 is a graph showing life time characteristics (section perpendicular
to solidification axis) of the ingot in Comparative Example 2.
Description of Reference Numerals
[0017]
10a, 10b" melting furnace, 12: sagger, 14: heating means, 14a: upper side
heating means, 14b: lower side heating means, 14c: upper heating means, 16:


support means, 18: heat insulation material, 20: chamber, 22a, 22b: gas
introduction port, 24: discharge port, 26: silicon melt, 28: inner cylinder tube, 30:
furnace hearth
Best Mode for carrying out the Invention
[0018]
Hereinafter, embodiments of the present invention will be described
based on attached drawings. However, the drawings are mere examples, and it
is obvious that various changes may be made without departing from the scope of
the invention.
[0019]
The present invention refers to a process for producing a polycrystalline
silicon ingot having reduced fine crystals of silicon including: removing through a
reaction light-element impurities such as oxygen and nitrogen in a silicon melt
during melting and solidification of a high-purity silicon raw material in a 100%
hydrogen atmosphere under ordinary pressure or elevated pressure,' reducing
crystal defects through crystallization of other metal impurities; and conducting
crystal growth. Through those effects, life time characteristics of the
polycrystalline silicon ingot can be improved.
[0020]
In the present invention, hydrogen is bonded to atomic defects in a lattice
to be developed in the polycrystalline silicon ingot to correct the atomic defects, to
thereby improve life time characteristics. Further, diffusion of impurities from
silicon nitride used for a melting member or a releasing material to be used in


melting of the silicon raw material in a hydrogen atmosphere into the
polycrystalline silicon ingot can be prevented.
[0021]
Fig. 1 is a schematic diagram showing an example of a melting furnace to
be preferably used in the method of the present invention. In the method of the
present invention, a melting furnace to be used generally employs a tungsten
heater or molybdenum silicide not reacting with hydrogen in high temperatures.
A furnace inner wall, a furnace hearth plate, or the like may employ silicon
nitride, carbon nitride, or the like in addition to tungsten. A melting furnace
shown in Fig. 1 is preferably used.
[0022]
In Fig. 1, reference symbol 10b represents a melting furnace. The
melting furnace 10b includes: a sagger 12; heating means 14 for heating the
sagger 12; support means 16 for placing the sagger 12; a heat insulation material
18; and a chamber 20. The heat insulation material 18 is provided to cover an
entire surface of an inner wall of the chamber 20. A hydrogen gas is introduced
from a gas introduction port 22b and discharged from a discharge port 24. The
heating means 14 as structural members of a furnace such as the heat insulation
material 18 and a heating element or the like of the heating means 14 has a
structure in which upper heating means 14c, upper side heating means 14a, and
lower side heating means 14b are provided separately in an upper part, an upper
side part, and a lower side part of the sagger 12, respectively, by splitting a
heater circuit. The upper heating means 14c, the upper side heating means 14a,
and the lower side heating means 14b separately conduct temperature control,


and this structure has a function of providing a temperature gradient in a
vertical direction of the sagger 12.
[0023]
An operation of this structure will be described. The hydrogen gas is
introduced into the melting furnace 10b from the introduction port 22b for
operation of the furnace in a 100% hydrogen atmosphere under ordinary pressure
or elevated pressure. In the chamber 20 in a hydrogen atmosphere under
ordinary pressure or elevated pressure, the sagger 12 having a silicon raw
material charged therein is heated by the upper heating means 14c provided
above the sagger 12 and the upper side heating means 14a provided in an upper
side part the sagger 12, and the silicon raw material is melted under heating into
a silicon melt 26. Then, a furnace hearth 30 having the sagger 12 placed
thereon is lowered and is positioned halfway between the upper side heating
means 14a and the lower side heating means 14b for providing a vertical
temperature gradient in the sagger 12, and the support means 16 is rotated.
The upper heating means 14c, the upper side heating means 14a, and the lower
side heating means 14b are controlled, to thereby cool and solidify the silicon
melt from a lower part of the sagger 12 to a crystal growth temperature. Then,
the heating means 14c, 14a, and 14b are maintained at a certain temperature for
sufficient crystal growth, and the support means 16 is lowered, to thereby
produce a polycrystalline silicon ingot.
Examples
[0024]


Hereinafter, the present invention will be described more specifically with
reference to examples. However, the examples are mere examples and are not to
be interpreted limitedly.
[0025]
(Example 1)
A releasing material (high-purity silicon nitride powder) was applied and
dried on an inner wall of a silica-sintered sagger (inner dimensions of 175 mm x
350 mm), and a high-purity silicon raw material was charged into the sagger.
The sagger was placed in a melting furnace having the same structure as that
shown in Fig. 1 for melting. In Example 1, a polycrystalline silicon ingot was
produced by'- melting silicon in the melting furnace at 1,460°C and under slightly
elevated pressure (500 Pa) with a hydrogen gas; reducing a temperature of a
lower part of the sagger; sequentially cooling the entire sagger to 1,380°C at
25°C/hr while a vertical temperature gradient was provided in the sagger;
solidifying a silicon melt from a lower part of the sagger; and maintaining the
sagger at 1,380°C for 10 hr. An upper temperature (upper edge part) and a
lower temperature (base part) of the sagger at this time were measured with a
thermocouple, and Fig. 3 shows measured values of the temperatures.
[0026]
(Comparative Example 1)
An ingot was produced by a conventional sagger-lowered solidification
method in an argon atmosphere. A melting furnace having the same structure
as that shown in Fig. 1 was used, and the furnace atmosphere was changed to
argon. Silicon was melted at 1,460°C, and then the sagger was lowered at 7


mm/hr. Upper and lower temperatures of the sagger at this time were measured
in the same manner as in Example 1, and Fig. 4 shows the measured values of
the temperatures. A cooling rate of the ingot was 4°C/hr.
[0027]
(Example 2)
An ingot was produced in a hydrogen gas atmosphere in the same
manner as in Example 1 by using the same temperature program shown in Fig. 5
at 4°C/hr as that of argon atmosphere melting of Comparative Example 1.
[0028]
(Comparative Example 2)
An ingot was produced by using the temperature program shown in Fig. 5
in the same manner as in Example 2 and using an argon gas instead of the
hydrogen gas.
[0029]
Figs. 6 to 15 each show a crystal formation state after cutting the
polycrystalline silicon ingot obtained in each of Examples 1 and 2 and
Comparative Examples 1 and 2 along a section perpendicular to a crystal growth
axis and conducting alkali anisotropic etching treatment (Figs. 6 and 7: Example
1, Figs. 8 and 9: Comparative Example 1, Figs. 10 to 12: Example 2, Figs. 13 to
15: Comparative Example 2). Figs. 6, 8, 10, 11, 13, and 14 are each a
photograph showing a crystal formation state, and Figs. 7, 9, 12, and 15 are each
a microphotograph showing an etch pit formation state. The ingot of
Comparative Example 1 was produced by lowering the sagger in an argon
atmosphere as in the conventional method and cooling and solidifying at 4°C/hr.


As shown in Fig. 8, crystal shapes varied significantly and included distorted
shapes. Fig. 6 shows a crystal formation state of the ingot produced by rapidly
solidifying at a cooling rate of 25°C/hr in a hydrogen atmosphere as Example 1.
Crystal grains each had a relatively fine structure with a round grain boundary,
and each had a structure with little anisotropic growth compared with crystals
formed in an argon atmosphere shown in Fig. 8 (Comparative Example 1).
Further, Fig. 9 (Comparative Example 1) and Fig. 7 (Example 1) each show etch
pits indicating significant crystal defects. The argon-melt ingot of Fig. 9
(Comparative Example 1) had many etch pits observed, but the hydrogen-melt
ingot of Fig. 7 (Example 1) had significantly reduced etch pits. The results
revealed that the hydrogen-melting method allowed formation of an ingot having
reduced crystal defects compared with that obtained by the conventional
argon-melting method. Further, the results revealed that the ingot had a round
crystal shape, and an occupancy ratio of a fine grain along a section
perpendicular to a crystal axis was about 10% or less.
[0030]
Example 2 and Comparative Example 2 each involved production by
using a conventional cooling rate of 4°C/hr and by using a temperature program
including maintaining the temperature for 10 hr after solidification as shown in
Fig. 5. Figs. 10 to 12 (Example 2) and Figs. 13 to 15 (Comparative Example 2)
each show a crystal formation state of the ingot solidified in a hydrogen
atmosphere or an argon atmosphere. The ingots produced in the hydrogen
atmosphere and the argon atmosphere had substantially similar characteristics
of crystal size and crystal anisotropy by maintaining the temperature after

solidification.
[0031]
Table 1 shows evaluation results of characteristics of each of the ingots
produced in Examples 1 and 2 and Comparative Examples 1 and 2. Life time
characteristics of the obtained polycrystalline silicon ingots were 3.13 µs for
Example 1 and 0.48 µs for Comparative Example 1, indicating that the life time
characteristics were improved by the method of the present invention. The
polycrystalline silicon ingots obtained in Example 1 and Comparative Example 1
were each subjected to anisotropic etching treatment and observed. As a result,
the polycrystalline silicon ingot of Example 1 had reduced fine crystals and
improved uniformity with small variation in grain size.


Comparative Example 1 employed the method of lowering the sagger
according to the existing production method, and the ingot had rather degraded
life time characteristics of 0.48 p.s compared with those of an existing product.
The reason for the degraded life time characteristics is an effect of impurities
diffused from a releasing material used for an inner surface of the sagger due to a
small ingot shape. The Fe concentration was 425 x 1010 atoms/cc, which was a
high value. The ingot of Example 1 was an ingot produced in a hydrogen
atmosphere at the same cooling rate as that of Comparative Example 1. The
ingot had reduced impurities such as Fe and improved life time characteristics.
[0034]
The ingots of Example 2 and Comparative Example 2 each were ingots
each produced in a hydrogen or argon atmosphere hy using the temperature
program of Fig. 5 including maintaining the temperature at a solidification
temperature. The hydrogen atmosphere ingot (Example 2) had life time
characteristics of 6.87 µs in a center part with little Fe diffusion. Meanwhile,


the argon atmosphere ingot (Comparative Example 2) had life time
characteristics of 1.2 µs, which was a low value.
[0035]
As reasons for the results, Figs. 16 and 17 (Example 2) and Figs. 18 and
19 (Comparative Example 2) show Fe distribution concentration characteristics,
and Figs. 20 and 21 (Example 2) and Figs. 22 and 23 (Comparative Example 2)
show life time characteristics. The life time characteristics were measured with
a life time measuring device manufactured by SEMILAB (Semiconductor Physics
Laboratory, Inc). Distribution on a section along a solidification axis of the
hydrogen-melt ingot indicated a correlation among the Fe concentration of Fig.
16 (Example 2), the life time characteristics of Fig. 20 (Example 2), and the
crystal formation state of Fig. 12 (Example 2). Meanwhile, the argon-melt ingot
had no correlation among the Fe concentration of Fig. 18 (Comparative Example
2), the life time characteristics of Fig. 22 (Comparative Example 2), and the
crystal formation state of Fig. 15 (Comparative Example 2). As shown in Fig. 17
(Example 2), the hydrogen-melt ingot had a small absolute value of the Fe
concentration and had a concentration difference in Fe diffusion from the sagger
on the section perpendicular to the solidification axis, but the argon-melt ingot
shown in Fig. 19 (Comparative Example 2) had high concentration and had no
significant concentration gradient. This phenomenon provides a purification
action involving- reducing diffusion amounts of impurities into silicon because
hydrogen is dissolved in a silicon melt; and crystallizing the impurities in silicon
crystal formation.
[0036]


The results of a hydrogen gas analysis of the hydrogen-melt ingot
(Examples 1 and 2) of the present invention confirmed hydrogen, but
quantitative determination of radical hydrogen is not possible by the current
analysis method. However, the silicon ingot produced by the current argon-melt
method contains no hydrogen. A semiconductor wafer may be subjected to
hydrogen treatment, but it is not possible costwise that an inexpensive solar
wafer be subjected to hydrogen treatment because the treatment cost is high.
[0037]
The method of the present invention allows melting of silicon in a
hydrogen atmosphere under ordinary pressure, reduction of fine crystals by a
solidification method employing a solid phase growth method, reduction of
impurities through hydrogen dissolution, and purification of silicon through
crystallization of the impurities.
[0038]
In Example 1, rapid solidification was conducted at a cooling rate of
25°C/hr, and in Example 2, gradual solidification as in the conventional method
was conducted at a cooling rate of 4°C/hr. The results revealed that the ingot of
Example 2 had improved life time characteristics and reduced impurities such as
Fe compared with those of the ingot of Example 1. The results revealed that a
favorable ingot can be obtained through gradual solidification than rapid
solidification. However, a gradual cooling rate reduces a crystal formation rate
of the ingot and reduces efficiency. Thus, in an actual operation, an appropriate
cooling rate is set in consideration of quality and economical effects.


WE CLAIM:
1. A process for producing a solar polycrystalline silicon ingot comprising: melting a silicon
raw material in a silica-sintered sagger in a 100% hydrogen atmosphere under ordinary pressure or
elevated pressure with a tungsten heater to prepare a silicon melt and simultaneously dissolving
hydrogen in the silicon melt; solidifying the silicon melt containing hydrogen dissolved therein; and
maintaining the solid at a high temperature of about a solidification temperature for growth of
silicon crystal grains in a solid phase to obtain a polycrystalline silicon ingot.
2. The process for producing a solar polycrystalline silicon ingot as claimed in claim 1,
involving the step of:
bonding hydrogen to atomic defects in a lattice to be developed in the polycrystalline silicon
ingot for correcting the atomic defects and for improving life time characteristics.
3. The process for producing a solar polycrystalline silicon ingot as claimed in claim 1 or 2,
involving the steps of:
dissolving hydrogen in the silicon melt for preventing diffusion and mixing of impurities
into the silicon melt; and
removing the impurities in the silicon melt through reactive gasification or cystallization for
accelerating purification of the polycrystalline silicon ingot.
4. The process for producing a solar polycrystalline silicon ingot as claimed in claims 1 to 3,
involving the steps of:
suppressing generation of silicon monoxide through a reaction of a sagger formed of a
silicon dioxide material to be used in melting of the silicon raw material and the silicon raw
material in the hydrogen atmosphere; and
reducing an oxygen concentration in the polycrystalline silicon ingot.

5. The process for producing a solar polycrystalline silicon ingot as claimed in claims 1 to 4,
involving the step of:
preventing diffusion of impurities to be generated from a melting member to be used in
melting of the silicon raw material into the polycrystalline silicon ingot.


Provided is a process in which a polycrystalline silicon ingot improved in life time
characteristics, which are correlated with the conversion efficiency of solar wafers, is inexpensively
produced by the ordinary-pressure hydrogen-atmosphere melting method. In the process, the
generation of oxygen and impurities in the silicon melt is inhibited and light-element impurities are
removed through reaction or crystallization. Fine crystal grains can be grown at a high rate, and a
high-purity polycrystalline silicon ingot having a crystal structure reduced in crystal defect can be
grown.
A silicon raw material is melted in an atmosphere of 100% hydrogen at ordinary pressure or
an elevated pressure to prepare a silicon melt and simultaneously dissolve hydrogen in the silicon
melt. The silicon melt containing hydrogen dissolved therein is solidified. Thereafter, the solid is
held at a high temperature around the solidification temperature to grow silicon crystal grains in the
solid phase and thereby obtain a polycrystalline silicon ingot.

Documents:

01553-kolnp-2007-abstract.pdf

01553-kolnp-2007-assignment.pdf

01553-kolnp-2007-claims.pdf

01553-kolnp-2007-correspondence others 1.1.pdf

01553-kolnp-2007-correspondence others.pdf

01553-kolnp-2007-description complete.pdf

01553-kolnp-2007-drawings.pdf

01553-kolnp-2007-form 1.pdf

01553-kolnp-2007-form 3.pdf

01553-kolnp-2007-form 5.pdf

01553-kolnp-2007-gpa.pdf

01553-kolnp-2007-international publication.pdf

01553-kolnp-2007-international search report.pdf

01553-kolnp-2007-priority document.pdf

01553-kolnp-2007-translated copy of priority document.pdf

1553-KOLNP-2007-ABSTRACT.pdf

1553-KOLNP-2007-AMANDED CLAIMS.pdf

1553-kolnp-2007-assignment.pdf

1553-KOLNP-2007-CORRESPONDENCE 1.1.pdf

1553-kolnp-2007-correspondence.pdf

1553-KOLNP-2007-DESCRIPTION (COMPLETE).pdf

1553-KOLNP-2007-DRAWINGS.pdf

1553-KOLNP-2007-ENGLISH TRANSLATION.pdf

1553-KOLNP-2007-EXAMINATION REPORT REPLY RECIEVED.pdf

1553-kolnp-2007-examination report.pdf

1553-KOLNP-2007-FORM 1.pdf

1553-kolnp-2007-form 18.1.pdf

1553-kolnp-2007-form 18.pdf

1553-KOLNP-2007-FORM 2.pdf

1553-kolnp-2007-form 3.1.pdf

1553-KOLNP-2007-FORM 3.pdf

1553-kolnp-2007-form 5.pdf

1553-KOLNP-2007-FORM-27.pdf

1553-kolnp-2007-gpa.pdf

1553-kolnp-2007-granted-abstract.pdf

1553-kolnp-2007-granted-claims.pdf

1553-kolnp-2007-granted-description (complete).pdf

1553-kolnp-2007-granted-drawings.pdf

1553-kolnp-2007-granted-form 1.pdf

1553-kolnp-2007-granted-form 2.pdf

1553-kolnp-2007-granted-specification.pdf

1553-KOLNP-2007-MISCLLENIOUS.pdf

1553-KOLNP-2007-OTHERS.pdf

1553-kolnp-2007-others1.1.pdf

1553-KOLNP-2007-PA.pdf

1553-KOLNP-2007-PETITION UNDER RULE 137-1.1.pdf

1553-KOLNP-2007-PETITION UNDER RULE 137.pdf

1553-kolnp-2007-reply to examination report.pdf

1553-kolnp-2007-translated copy of priority document.pdf

abstract-01553-kolnp-2007.jpg


Patent Number 249077
Indian Patent Application Number 1553/KOLNP/2007
PG Journal Number 39/2011
Publication Date 30-Sep-2011
Grant Date 28-Sep-2011
Date of Filing 01-May-2007
Name of Patentee SPACE ENERGY CORPORATION
Applicant Address 20-11, UENO 1-CHOME, TAITO-KU, TOKYO
Inventors:
# Inventor's Name Inventor's Address
1 KIMURA YOSHIMICHI C/O SPACE ENERGY CORPORATION, 20-11, UENO 1-CHOME, TAITO-KU, TOKYO 1100005
2 SAKAI YUICHI C/O NORITAKE TCF CO., LTD. TOGANE PLACE OF BUSINESS, 1573-8, KONUMATA, TOGANE-SHI, CHIBA 2830044
PCT International Classification Number C01B 33/02
PCT International Application Number PCT/JP2005/021969
PCT International Filing date 2005-11-30
PCT Conventions:
# PCT Application Number Date of Convention Priority Country
1 2004-347083 2004-11-30 Japan