CN101412512A - Process for producing purified silicon - Google Patents
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- CN101412512A CN101412512A CNA2008101703418A CN200810170341A CN101412512A CN 101412512 A CN101412512 A CN 101412512A CN A2008101703418 A CNA2008101703418 A CN A2008101703418A CN 200810170341 A CN200810170341 A CN 200810170341A CN 101412512 A CN101412512 A CN 101412512A
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- 239000010703 silicon Substances 0.000 title claims abstract description 161
- 229910052710 silicon Inorganic materials 0.000 title claims abstract description 159
- 238000000034 method Methods 0.000 title abstract description 37
- XUIMIQQOPSSXEZ-UHFFFAOYSA-N Silicon Chemical compound [Si] XUIMIQQOPSSXEZ-UHFFFAOYSA-N 0.000 claims abstract description 157
- 229910052782 aluminium Inorganic materials 0.000 claims abstract description 117
- XAGFODPZIPBFFR-UHFFFAOYSA-N aluminium Chemical compound [Al] XAGFODPZIPBFFR-UHFFFAOYSA-N 0.000 claims abstract description 117
- 238000007711 solidification Methods 0.000 claims abstract description 86
- 230000008023 solidification Effects 0.000 claims abstract description 86
- 238000005520 cutting process Methods 0.000 claims abstract description 17
- 239000002994 raw material Substances 0.000 claims description 44
- 238000009826 distribution Methods 0.000 claims description 22
- 230000015271 coagulation Effects 0.000 claims description 20
- 238000005345 coagulation Methods 0.000 claims description 20
- 238000004519 manufacturing process Methods 0.000 claims description 17
- 239000004411 aluminium Substances 0.000 abstract 5
- 238000000638 solvent extraction Methods 0.000 abstract 2
- 239000002210 silicon-based material Substances 0.000 abstract 1
- 238000002474 experimental method Methods 0.000 description 29
- 238000001816 cooling Methods 0.000 description 16
- 239000000126 substance Substances 0.000 description 12
- 230000014509 gene expression Effects 0.000 description 7
- 239000007790 solid phase Substances 0.000 description 6
- 239000002253 acid Substances 0.000 description 5
- VYPSYNLAJGMNEJ-UHFFFAOYSA-N Silicium dioxide Chemical compound O=[Si]=O VYPSYNLAJGMNEJ-UHFFFAOYSA-N 0.000 description 4
- 238000010438 heat treatment Methods 0.000 description 4
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 description 3
- VZSRBBMJRBPUNF-UHFFFAOYSA-N 2-(2,3-dihydro-1H-inden-2-ylamino)-N-[3-oxo-3-(2,4,6,7-tetrahydrotriazolo[4,5-c]pyridin-5-yl)propyl]pyrimidine-5-carboxamide Chemical compound C1C(CC2=CC=CC=C12)NC1=NC=C(C=N1)C(=O)NCCC(N1CC2=C(CC1)NN=N2)=O VZSRBBMJRBPUNF-UHFFFAOYSA-N 0.000 description 2
- IJGRMHOSHXDMSA-UHFFFAOYSA-N Atomic nitrogen Chemical compound N#N IJGRMHOSHXDMSA-UHFFFAOYSA-N 0.000 description 2
- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 description 2
- VEXZGXHMUGYJMC-UHFFFAOYSA-N Hydrochloric acid Chemical compound Cl VEXZGXHMUGYJMC-UHFFFAOYSA-N 0.000 description 2
- QAOWNCQODCNURD-UHFFFAOYSA-N Sulfuric acid Chemical compound OS(O)(=O)=O QAOWNCQODCNURD-UHFFFAOYSA-N 0.000 description 2
- 150000007513 acids Chemical class 0.000 description 2
- PNEYBMLMFCGWSK-UHFFFAOYSA-N aluminium oxide Inorganic materials [O-2].[O-2].[O-2].[Al+3].[Al+3] PNEYBMLMFCGWSK-UHFFFAOYSA-N 0.000 description 2
- 230000005484 gravity Effects 0.000 description 2
- 239000012535 impurity Substances 0.000 description 2
- 238000009616 inductively coupled plasma Methods 0.000 description 2
- 229910052500 inorganic mineral Inorganic materials 0.000 description 2
- 239000007791 liquid phase Substances 0.000 description 2
- 239000000463 material Substances 0.000 description 2
- 229910052751 metal Inorganic materials 0.000 description 2
- 239000002184 metal Substances 0.000 description 2
- 239000011707 mineral Substances 0.000 description 2
- 238000005406 washing Methods 0.000 description 2
- ZOXJGFHDIHLPTG-UHFFFAOYSA-N Boron Chemical compound [B] ZOXJGFHDIHLPTG-UHFFFAOYSA-N 0.000 description 1
- GRYLNZFGIOXLOG-UHFFFAOYSA-N Nitric acid Chemical compound O[N+]([O-])=O GRYLNZFGIOXLOG-UHFFFAOYSA-N 0.000 description 1
- OAICVXFJPJFONN-UHFFFAOYSA-N Phosphorus Chemical compound [P] OAICVXFJPJFONN-UHFFFAOYSA-N 0.000 description 1
- 229910000831 Steel Inorganic materials 0.000 description 1
- 238000004458 analytical method Methods 0.000 description 1
- 229910052796 boron Inorganic materials 0.000 description 1
- 238000004364 calculation method Methods 0.000 description 1
- 229910052799 carbon Inorganic materials 0.000 description 1
- 238000011109 contamination Methods 0.000 description 1
- 238000009795 derivation Methods 0.000 description 1
- 229910003460 diamond Inorganic materials 0.000 description 1
- 239000010432 diamond Substances 0.000 description 1
- 229910002804 graphite Inorganic materials 0.000 description 1
- 239000010439 graphite Substances 0.000 description 1
- 238000004020 luminiscence type Methods 0.000 description 1
- 238000004949 mass spectrometry Methods 0.000 description 1
- 238000002844 melting Methods 0.000 description 1
- 230000008018 melting Effects 0.000 description 1
- 229910017604 nitric acid Inorganic materials 0.000 description 1
- 229910052757 nitrogen Inorganic materials 0.000 description 1
- 229910052698 phosphorus Inorganic materials 0.000 description 1
- 239000011574 phosphorus Substances 0.000 description 1
- 238000001556 precipitation Methods 0.000 description 1
- -1 quartz Chemical compound 0.000 description 1
- 239000010453 quartz Substances 0.000 description 1
- 238000005204 segregation Methods 0.000 description 1
- 150000003376 silicon Chemical class 0.000 description 1
- HBMJWWWQQXIZIP-UHFFFAOYSA-N silicon carbide Chemical compound [Si+]#[C-] HBMJWWWQQXIZIP-UHFFFAOYSA-N 0.000 description 1
- 229910010271 silicon carbide Inorganic materials 0.000 description 1
- 239000000377 silicon dioxide Substances 0.000 description 1
- 229910052814 silicon oxide Inorganic materials 0.000 description 1
- 239000010959 steel Substances 0.000 description 1
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- C—CHEMISTRY; METALLURGY
- C01—INORGANIC CHEMISTRY
- C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
- C01B33/00—Silicon; Compounds thereof
- C01B33/02—Silicon
- C01B33/037—Purification
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B22—CASTING; POWDER METALLURGY
- B22D—CASTING OF METALS; CASTING OF OTHER SUBSTANCES BY THE SAME PROCESSES OR DEVICES
- B22D27/00—Treating the metal in the mould while it is molten or ductile ; Pressure or vacuum casting
- B22D27/04—Influencing the temperature of the metal, e.g. by heating or cooling the mould
- B22D27/045—Directionally solidified castings
-
- C—CHEMISTRY; METALLURGY
- C01—INORGANIC CHEMISTRY
- C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
- C01B33/00—Silicon; Compounds thereof
- C01B33/02—Silicon
- C01B33/037—Purification
- C01B33/039—Purification by conversion of the silicon into a compound, optional purification of the compound, and reconversion into silicon
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- Chemical & Material Sciences (AREA)
- Organic Chemistry (AREA)
- Inorganic Chemistry (AREA)
- Engineering & Computer Science (AREA)
- Mechanical Engineering (AREA)
- Silicon Compounds (AREA)
- Manufacture And Refinement Of Metals (AREA)
Abstract
Provided is a process for producing a purified silicon by cutting off a crude silicon region, without determining the aluminium concentration in a directionally-solidified silicon. In the process of the invention, a standard solidification fraction (f0) satisfying the following formula (1) and formula (2) is obtained from the predetermined maximum level of aluminium concentration (C10max), the temperature gradient (T) and the solidification speed (R), and the directionally-solidified silicon is cut at the part having a solidification fraction (f) in the solidification step corresponding to f0. K={K1*ln(R)+K2}*{K3*exp[K4*RRK5*C2+K6]}*{K7*T+K8}-K9, wherein k is a coefficient selected from a range of from 0.9 times to 1.1 times the effective aluminium partitioning coefficient k', as obtained so as to satisfy the following formula (2): C10max=k'xC2x(1-f0)k'-1 (2), k' is an effective aluminium partitioning coefficient, C2 is the aluminium concentration of the starting silicon material melt)].
Description
Technical Field
The present invention relates to a method for producing purified silicon, and more particularly to a method for producing purified silicon by a so-called directional solidification method, in which a solidified substance (hereinafter referred to as "silicon directional solidified substance") is obtained by a method in which a raw silicon melt containing aluminum is cooled and solidified so as to provide a temperature gradient in one direction in a mold.
Background
As a method for producing purified silicon 1 by removing aluminum from aluminum-containing silicon melt 2 as a raw material, a so-called directional solidification method is known, in which silicon melt 2 as a raw material is cooled and solidified so as to provide a temperature gradient (T) in one direction in mold 3, as shown in fig. 1 and 2. According to this method, aluminum precipitation is reduced on the low temperature side 21 of the temperature gradient (T), and aluminum segregation with a higher concentration is caused on the side closer to the high temperature side 22, and in this case, the raw material silicon melt 2 is solidified to form a silicon directional solidified substance 4. This silicon directional solidified product 4 is divided into 2 regions, namely, a purified silicon region 41 having a relatively low aluminum concentration (C) on the low temperature side 21 of the temperature gradient (T) and a coarse silicon region 45 having a relatively high aluminum concentration (C) on the high temperature side 22 of the temperature gradient (T) at the time of solidification (fig. 2). Among them, by cutting the coarse silicon region 45 from the directional solidified silicon 4, the target purified silicon 1 as the purified silicon region 41 having a relatively low aluminum concentration (C) can be obtained (japanese patent application laid-open No. 2004-196577).
According to this method, when the target maximum (predetermined maximum) aluminum concentration (C) of the purified silicon 1 is set10max) If the solidification rate (f) is set to be large as the raw material silicon melt 2 is solidified by the directional solidification method, the target purified silicon 1 corresponds to the purified silicon region 41 even when the value of the solidification rate (f) (see fig. 2) is large. Therefore, the desired purified silicon 1 can be obtained by cutting off the solidification product 4 in the silicon direction at a portion where the solidification rate (f) is large. Conversely, when the allowable limit of aluminum is set to be small, the target purified silicon 1 can be obtained by cutting off the directional solidified silicon 4 at a portion where the solidification rate (f) is low.
However, conventionally, the relationship between the temperature gradient (T) and the solidification rate (R) and the aluminum concentration (C) and the solidification rate (f) in the obtained silicon directional solidified product 4 in the process of solidifying the product has not been clarified, and when the product is solidified under the condition that the concentration gradient (T) and the solidification rate (R) are different in an unclear case, the aluminum concentration (C) in all the obtained silicon directional solidified products (4) is actually measured to find out the aluminum concentration (C) as the target maximum aluminum concentration (C)10max) And (3) cutting the portion.
Disclosure of Invention
Therefore, the present inventors have conducted intensive studies to develop the following method, and finally completed the present invention. The method is a method that can produce the target purified silicon 1 by cutting out the coarse silicon region 45 without actually measuring the aluminum concentration (C) in all the directional solidified silicon 4.
Namely, the present invention
A method for producing purified silicon 1 using a silicon melt 2 as a raw material, comprising:
an aluminum-containing raw material silicon melt 2 is cooled and solidified in a mold 3 so as to provide a temperature gradient (T (DEG C/mm)) in one direction, thereby obtaining a target maximum aluminum concentration (C) containing aluminum (C) (ppm)10max(ppm)) or less of the purified silicon region 41 and the aluminum concentration exceeding the target maximum aluminum concentration (C)10max) The solidification 4 in the silicon direction in the coarse silicon region; and
by cutting off coarse silicon regions 45 from the obtained directional solidification of silicon 4, the aluminum concentration (C) is obtained at the target maximum aluminum concentration (C)10max) The following procedure for purifying silicon 1 was carried out,
wherein,
in the step of cutting off the coarse silicon region 45, the aluminum concentration (C) is controlled from the target maximum10max) And a temperature gradient (T) and a solidification rate (R (mm/min)) when the raw material silicon melt 2 is cooled, and a standard solidification rate (f) satisfying the following expressions (1) and (2)0) By the ratio corresponding to the reference coagulation rate (f)0) The coarse silicon region 45 is cut off by cutting the silicon directional solidification product 4. The above-mentioned standard solidification rate (f)0) Shows that the aluminum concentration (C) (ppm)) in the above all directional solidified silicon 4 is at the target maximum aluminum concentration (C)10max(ppm)) or less, and 0. ltoreq. f0≤1，
k＝{K1×Ln(R)+K2}
×{K3×e x p[K4×R×(K5×C2+K6)]}
×{K7×T+K8}—K9 (1)
In the formula (1), k is a coefficient selected from the range of 0.9 to 1.1 times the aluminum effective distribution coefficient k' obtained so as to satisfy the following formula (2),
C10max＝k′×C2×(1—f0)k′-1 (2)
k1represents from 1.1X 10-3±0.1×10-3Is selected from the range of (a) to (b),
k2expressed from 4.2X 10-3±0.1×10-3Is selected from the range of (a) to (b),
k3represents a constant selected from the range of 1.2 + -0.1,
k4represents a constant selected from the range of 2.2 + -0.1,
k5represents from-1.0X 10-3±0.1×10-3Is selected from the range of (a) to (b),
k6represents a constant selected from the range of 1.0 + -0.1,
k7represents a constant selected from the range of-0.4 + -0.1,
k8represents a constant selected from the range of 1.36 + -0.01,
k9represents from 2.0X 10-4±1.0×10-4Is selected from the range of (a) to (b),
r represents the solidification rate (mm/min),
t represents a temperature gradient (. degree. C./mm),
in the formula (2), C10maxRepresents the target maximum aluminum concentration (ppm), C, of the purified silicon2Represents the aluminum concentration (ppm), f, of the raw material silicon melt0Indicating the baseline coagulation rate.
According to the manufacturing method of the present invention, since it is based on the maximum aluminum concentration (C) from the target10max) And a reference solidification rate (f) obtained from a temperature gradient (T) and a solidification rate (R) in the process of solidifying the raw material silicon melt (2)0) To cut off the silicon directional solidified substance 4, it is possible to produce the aluminum concentration (C) at the target maximum aluminum concentration (C) without actually measuring the aluminum concentration (C) in the silicon directional solidified substance 410max) The following purified silicon 1.
Drawings
FIG. 1 is a sectional view schematically showing a process of obtaining a directional silicon solidified substance from a raw material silicon melt by the directional solidification method.
FIG. 2 is a sectional view schematically showing a step of obtaining purified silicon from a solidification in the silicon direction.
Detailed Description
The production method of the present invention will be described below with reference to fig. 1 and 2. The symbols used in fig. 1 and 2 are as follows. Symbol 1 represents purified silicon, symbol 2 represents a raw material silicon melt, symbol 21 represents a low temperature side of a temperature gradient, symbol 22 represents a high temperature side of a temperature gradient, symbol 24 represents a solid phase, symbol 25 represents a liquid phase, symbol 26 represents an interface, symbol 3 represents a mold, symbol 4 represents a solidification in a silicon direction, symbol 41 represents a purified silicon region, symbol 45 represents a crude silicon region, symbol 5 represents crude silicon, symbol 6 represents a heater, symbol 7 represents a furnace, and symbol 8 represents a water cooling plate. In the following description, symbol T represents a temperature gradient, and symbol f represents a temperature gradient0Indicating the baseline coagulation rate.
The silicon melt 2 as the raw material used in the production process of the present invention is silicon which is brought into a molten state by heating, and the temperature thereof exceeds the melting point of silicon (about 1414 ℃) and is usually 1420 to 1580 ℃.
The raw material silicon melt 2 contains aluminum. Aluminum concentration (C) in raw silicon melt 22) Usually 10ppm to 1000ppm, preferably 15ppm or less. If the aluminum concentration (C) in the raw silicon melt2) Less than 10ppm, further removal of aluminum is difficult; if it exceeds 1000ppm, in order to obtainThe purified silicon 1 requires an excessive temperature gradient (T) and a solidification rate (R), and is not practical.
The raw material silicon melt 2 may contain a small amount, specifically 1ppm or less in total, of other impurity elements other than silicon and aluminum in addition to aluminum, and the content of boron, phosphorus, and the like is preferably as small as possible, specifically 0.3ppm or less, and more preferably 0.1ppm or less, respectively.
In the production method of the present invention, the raw material silicon melt 2 is cooled in the mold 3 in the same manner as in the normal directional solidification method. As the mold 3, a mold inert to the raw material silicon melt 2 and having heat resistance is generally used, and specifically, a mold made of carbon such as graphite, silicon carbide, nitrogen carbide, alumina (alumina), silica (silicon oxide) such as quartz, or the like is used.
The raw material silicon melt 2 is cooled with a unidirectional temperature gradient (T). The temperature gradient (T) may be set so as to be unidirectional, may be set so that the low temperature side 21 and the high temperature side 22 have the same height in the horizontal direction, or may be set so that the low temperature side 21 is above and the high temperature side 22 is below in the direction of gravity. In general, as shown in fig. 1, the low temperature side 21 is at the bottom and the high temperature side 22 is at the top, so that a temperature gradient (T) is generated in the direction of gravity. The temperature gradient (T) does not need to be set excessively large, and is usually 0.2 ℃/mm to 1.5 ℃/mm, preferably 0.4 ℃/mm to 0.9 ℃/mm, and more preferably 0.7 ℃/mm or more, in view of practicality.
The temperature gradient (T) can be generated, for example, by a method of cooling the lower portion of the mold 3 in the lower portion of the furnace 7 while heating the upper portion of the mold 3 by the heater 6 in the furnace 7 having the heater 6 and the lower side opened to the atmosphere. For cooling the lower portion of the mold 3, the lower portion may be left to cool in the atmosphere, or a water cooling plate 8 may be attached to the lower portion of the furnace 7 by a temperature gradient (T), for example, and the lower portion of the mold 3 may be cooled by the water cooling plate 8.
For example, the raw material silicon melt 2 can be cooled from below by moving the mold 3 containing the raw material silicon melt downward and moving the mold from the bottom to the outside of the furnace 7. Thereby, raw silicon melt 2 is cooled from below, and raw silicon melt 2 starts to form solid phase 24 from low temperature side 21 and solidifies to form silicon directional solidified substance 4.
The solidification rate R is represented by a moving speed of an interface 26 between a solid phase 24 formed on the low temperature side 21 and a liquid phase 25 not solidified on the high temperature side 22, and can be adjusted by a moving speed of the mold 3 when the mold 3 is moved to the outside of the furnace 7. The solidification rate (R) is usually 0.05 mm/min to 2 mm/min, preferably 0.1 mm/min to 1 mm/min.
In this way, in the process of cooling and solidifying the raw material silicon melt 2, aluminum contained in the raw material silicon melt 2 is segregated on the high temperature side 22. Therefore, the aluminum content (C) in the solidified silicon directional solidified material 4 after solidification increases in one direction from the low temperature side 21 to the high temperature side 22 of the temperature gradient [ T ]. In the solidified material 4, the region on the low temperature side 21, which is the temperature gradient (T) during cooling, becomes a purified silicon region 41 having a small aluminum content, and the region on the high temperature side 22 becomes a coarse silicon region 45 containing a large amount of segregated aluminum. The desired purified silicon 1 can be obtained by cutting off the coarse silicon region 45 in the directional solidification product 4 of silicon. The method of cutting the coarse silicon region 45 is not particularly limited, and the coarse silicon region 45 may be cut by a usual method such as cutting with a diamond cutter.
In the above-mentioned solidification method in which solidification of raw material silicon melt 2 is carried out unidirectionally, when a solidification rate (f) that increases along the solidification direction is set as an index indicating the degree of progress of solidification, in the production method of the present invention, a reference solidification rate (f) is calculated by a predetermined method described below0) And when the coagulation rate (f) is equivalent to the reference coagulation rate (f)0) The coarse silicon region 45 is cut by cutting the silicon directional solidification product 4. The coagulation rate (f) at the coagulation start site is 0, and the coagulation rate (f) at the coagulation completion site is 1.
Specifically, the solidification rate (f) represents the proportion of a substance that solidifies and becomes a solid phase 24 in the process of cooling and solidifying the raw material silicon melt 2 in the raw material silicon melt 2 used. In the production method of the present invention, since the silicon directional solidified substance 4 is obtained by cooling so as to provide the temperature gradient (T) in one direction, the solidification rate (f) in the obtained silicon directional solidified substance 4 becomes large along the direction of the temperature gradient (T).
Reference coagulation rate (f)0) The calculation is performed so as to satisfy the above equation (1). The coefficient k in the formula (1) is considered to be the same as the aluminum effective distribution coefficient (k') if a deviation of ± 0.1 times is allowed, and hereinafter, the coefficient k is also referred to as the aluminum effective distribution coefficient. The effective aluminum distribution coefficient (k') having a close relationship with the coefficient k is determined so as to satisfy the above expression (2).
The above formula (2) is a relational expression derived from the following formula (2-1), and the formula (2-1) represents a relationship between the solidification rate (f) and the aluminum concentration (C) in a portion to become the solid phase 23 (a portion corresponding to the solidification rate (f)).
C＝k′×C2×(1—f)k′-1 (2—1)
[ wherein C represents the aluminum concentration (ppm) in the solid phase, k' represents the effective aluminum distribution coefficient, C2The aluminum concentration (ppm) of the raw material silicon melt 2 used is shown, and f represents the solidification rate.]
In general, this equation (2-1) is a relational equation called シャイル (metal solidification (published by pill-mart corporation, 12/25 1971), pages 121 to 134).
Generally, the target maximum aluminum concentration (C)10max) Aluminum concentration (C) of the raw silicon melt 22) 1/1000 times to 3/100 times.
The expression (1) is a relational expression showing the relationship among the effective distribution coefficient (k) of aluminum, the solidification rate (R) and the temperature gradient (R), and has been found by the inventors.
The production method of the present invention is a method for producing a steel sheet having a standard solidification rate (f) satisfying the above formula (1)0) A method of cutting the directional solidification product 4 of silicon after solidification.
In the case of obtaining silicon directional solidified product 4 by solidifying raw material silicon melt 2 by the method of the present invention, low temperature side 21 of temperature gradient (T) in the cooling process is refined silicon region 41, and high temperature side 22 is coarse silicon region 45. The coagulation rate (f) in the coagulation process corresponds to the reference coagulation rate (f)0) Or a specific coagulation rate (f) from a reference0) Small fraction, aluminum content (C) and target maximum aluminum concentration (C)10max) Equal to or less than the numerical value; when the solidification rate (f) is greater than the reference solidification rate (f)0) Due to the aluminum concentration (C) being greater than the target maximum aluminum concentration (C)10max) Therefore, the coagulation rate (f) corresponds to the reference coagulation rate (f)0) The coarse silicon region 45 can be removed by cutting off the silicon directional solidification product 4, whereby the aluminum concentration (C) can be obtained at the target maximum aluminum concentration (C)10max) The following target purified silicon 1.
The obtained purified silicon 1 may be further purified by a method such as acid washing. Mineral acids such as hydrochloric acid, nitric acid, and sulfuric acid are generally used as the acid used for the acid washing, and mineral acids containing less metal impurities are generally used from the viewpoint of preventing contamination. The obtained purified silicon 1 is melted by heating and used as the raw material silicon melt 2 in the production method of the present invention, whereby purified silicon having a low aluminum content can be further obtained.
The removed crude silicon 5 and silicon with a small aluminum content are melted by heating and can be reused as the raw material silicon melt 2 of the present invention.
The purified silicon 1 obtained by the production method of the present invention is suitably used as a raw material for solar cells, for example.
[ examples ]
The present invention will be described in more detail with reference to examples, but the present invention is not limited to the contents of the examples.
Reference example 1 derivation of formula 1
In the following example, k is calculated as 1.0 × k'.
Using the apparatus shown in FIG. 1, the aluminum concentration (C) was solidified in the mold 3 at a solidification rate (R) of 0.4 mm/min while providing a temperature gradient (T) (0.9 ℃/mm)2) The raw material silicon melt 2 of 1000ppm was cooled to obtain a silicon directional solidified substance 4. The aluminum concentrations (C) of the portions of the obtained silicon directional solidified product 4 having solidification rates (f) of 0.18 and 0.38 in the cooling process were determined by ICP (inductively coupled plasma) luminescence analysis or IPC mass spectrometry, and as a result, were 4.0ppm (f ═ 0.18) and 4.9ppm (f ═ 0.38). The effective distribution coefficient (k) of aluminum satisfying the formula (2-1) was determined from the solidification rate (f) and the aluminum concentration (C), and was found to be 3.1X 10-3. The results are summarized in Table 1.
Experiment 2 and experiment 3
Instead of raw material silicon melt 2 used in experiment 1, aluminum concentration (C) shown in table 1 was solidified at solidification rate (R) shown in table 1 while providing temperature gradient (T) shown in table 12) The raw material silicon melt 2 of (1) was cooled, and the effective aluminum distribution coefficient (k) was determined in the same manner as in experiment 1 except that the aluminum concentration (C) was determined in the portion where the solidification rate (f) was the value shown in table 1 in the cooling process, in the obtained solidified substance 4 in the silicon direction, and the results are shown in table 1.
[ Table 1]
From the results of experiments 1 to 3, the relationship between the solidification rate (R) and the aluminum effective distribution coefficient (k) was obtained, and as a result, expression (1-1) was obtained.
k＝{K1′×Ln(R)+K2′} (1—1)
[ in the formula, k represents an effective aluminum distribution coefficient, and R represents a solidification rate (mm/min). ]
In the formula (1-)1) In k1' is 1.1X 10-3，k2' is 4.2X 10-3。
The temperature gradient (T), the solidification rate (R), and the aluminum effective distribution coefficient (k) in experiments 1 to 3 satisfy the formula (1-1).
The temperature gradient (T) was the same as in experiments 1 to 3, and the aluminum concentration (C) of the raw material silicon melt 2 was2) Experiments 4 to 6 were performed, respectively. Aluminum concentration (C) of raw silicon melt 22) The temperature gradient (T) and the solidification rate (R) are shown in Table 2. In the obtained silicon directional solidified product 4, the aluminum concentration (C) was determined for the portion where the solidification rate (f) in the cooling process was the value shown in table 2, and the effective aluminum distribution coefficient (k) was determined in the same manner as in experiment 1, and the results are shown in table 2.
[ Table 2]
In experiments 4 to 6, the temperature gradient (T) was consistent with those in experiments 1 to 3, but the aluminum concentration (C) of silicon melt 2 as the raw material was2) Different. The effective aluminum distribution coefficient (k) determined in the above experiments 4 to 6 does not satisfy the above formula (1-1).
The formula (1-2) is obtained as a relational expression that satisfies the aluminum effective distribution coefficient (k) obtained in the above experiments 1 to 3 and the aluminum effective distribution coefficient (k) obtained in the experiments 4 to 6.
k＝{K1′×Ln(R)+K2′}
×{K3′×e x p[K4′×R×(K5′×C2+K6′)]} (1—2)
[ in the formula, k, R, k1' and k2' means the same meaning as described above, respectively. C2Representation sourceAluminum concentration (ppm) in the silicon melt.]
In the formula (1-2), k3' is 1.2, k4' is 2.2, k5' is-1.0X 10-3，k6' is 1.0.
Temperature gradient (T), solidification rate (R) in experiments 1 to 3 and experiments 4 to 6, and aluminum concentration (C) of raw material silicon melt 2 used2) And the effective aluminum distribution coefficient (k) satisfies the formula (1-2).
Experiment 7
Aluminum concentration (C) in raw silicon melt 22) In agreement with experiment 2 above, but with a different temperature gradient (T), experiment 7 was performed. Aluminum concentration (C) in raw silicon melt 22) The temperature gradient (T) and the solidification rate (R) are shown in Table 3. In the obtained silicon directional solidified product 4, the aluminum concentration (C) was obtained for the portion where the solidification rate (f) in the cooling process was the value shown in table 3, and the effective aluminum distribution coefficient (k) was obtained in the same manner as in experiment 1, and the results are shown in table 3.
[ Table 3]
Although in experiment 7, the aluminum concentration (C) of the raw material silicon melt 22) Consistent with experiment 2, but the temperature gradient (T) was different. Therefore, the effective aluminum distribution coefficient (k) obtained in experiment 7 does not satisfy the above equations (1-1) and (1-2).
Equations (1 to 3) are obtained as relational equations that satisfy the aluminum effective distribution coefficient (k) obtained in experiments 1 to 3 and 4 to 6 and also satisfy the aluminum effective distribution coefficient (k) obtained in experiment 7.
k＝{K1′×Ln(R)+K2′}
×{K3′×e x p[K4′×R×(K5′×C2+K6′)]}
×{K7′×T+K8′}—K9′ (1—3)
[ in the formula, k, R, C2、k1′、k2′、k3′、k4′、k5' and k6' means the same meaning as described above, respectively. T represents a temperature gradient (. degree. C./mm).]
In the formula (1-3), k7' is-0.4, k8' is 1.36, k9' is 2.0X 10-4。
Temperature gradient (T), solidification rate (R) in experiments 1 to 3, 4 to 6, and 7, and aluminum concentration (C) of raw material silicon melt 2 used2) And the effective aluminum distribution coefficient (k) satisfies the formula (1-3).
With the above k in the formula (1-3) obtained by the above method1′～k9' if k is a number1～k9The numerical values of (A) are respectively shown in the above formula (1), and the above formula (1) can be obtained.
[ examples 1-1 ]
The aluminum concentration (C) of the raw material silicon melt 2 is set2)1000ppm, target maximum aluminum concentration (C)10max) 4.0ppm, a temperature gradient (T) of 0.9 ℃/mm and a solidification rate (R) of 0.4 mm/min, and the following equation (1) [ wherein k is1～k9Are respectively equal to k1′～k9' same numerical value.]Reference coagulation rate (f)0) The result was 0.18.
Using the apparatus shown in fig. 1, by adjusting the aluminum concentration (C) in the mold 32)1000ppm of raw material silicon melt 2 was cooled with a setting temperature gradient (T) of 0.9 ℃/mm so that the solidification rate (R) was 0.4 mm/fractional solidification, and a silicon directional solidification product 4 was obtained as shown in FIG. 2.
By solidification during cooling, in the manner shown in figure 2The portion where the ratio (f) was 0.18 cuts off the obtained directional solidification product 4 of silicon, and removes the region 45 on the high temperature side 22, which is the temperature gradient (T), to obtain purified silicon 1. The maximum value (C) of the aluminum concentration of the purified silicon 11max) It was 4.0 ppm.
Examples 1-2 and 2-1 to 7-2
The aluminum concentration (C) of the raw material silicon melt 2 was set as shown in Table 42) Target maximum aluminum concentration (C)10max) Temperature gradient (T) and solidification rate (R)0Otherwise, the same procedure as in example 1-1 was repeated to obtain the standard coagulation rate (f)0) A solidification product 4 in the silicon direction was obtained by following the same operations as in example 1-1, except that the temperature gradient (T) and the solidification rate (R) were set to the same values as those shown in Table 4, and the solidification rate (f) in the cooling process and the reference solidification rate (f) were used0) The portions having the same numerical value were cut to obtain purified silicon 1. The maximum value (C) of the aluminum concentration of the purified silicon 11max) As shown in table 4.
[ Table 4]
Claims (2)
1. A method for producing purified silicon using a silicon melt as a raw material, comprising:
an aluminum-containing raw material silicon melt is cooled and solidified in a mold so as to provide a temperature gradient (T (DEG C/mm)) in one direction, and thereby aluminum concentration (C (ppm)) is obtained at a target (maximum aluminum concentration (C)10max(ppm)) or less, a purified silicon region and an aluminum concentration exceeding a target maximum aluminum concentration (C)10max) A solidification in the silicon direction in the coarse silicon region of (3); and
by cutting off coarse silicon regions from the directional solidification of silicon obtainedTo obtain the aluminum concentration (C) at the target maximum aluminum concentration (C)10max) The following steps for purifying silicon are described,
wherein,
in the step of cutting off the coarse silicon region, the aluminum concentration (C) is controlled from the target maximum10max) And a temperature gradient (T) and a solidification rate (R (mm/min)) when the raw material silicon melt is cooled, and a standard solidification rate (f) satisfying the following formulas (1) and (2)0) By the ratio corresponding to the reference coagulation rate (f)0) The region of silicon directional solidification is cut to cut off a coarse silicon region, and the reference solidification rate (f)0) Shows that the aluminum concentration (C) (ppm)) in the above all directional solidified silicon is at the target maximum aluminum concentration (C)10max(ppm)) or less, and 0. ltoreq. f0≤1，
k＝{K1×Ln(R)+K2}
×{K3×exp[K4×R×(K5×C2+K6)]}
×{K7×T+K8}—K9 (1)
In the formula (1), k is a coefficient selected from the range of 0.9 to 1.1 times the aluminum effective distribution coefficient k' obtained so as to satisfy the following formula (2),
C10max＝k＇×C2×(1—f0)k＇-1 (2)
k1represents from 1.1X 10-3±0.1×10-3Is selected from the range of (a) to (b),
k2expressed from 4.2X 10-3±0.1×10-3Is selected from the range of (a) to (b),
k3represents a constant selected from the range of 1.2 + -0.1,
k4represents a constant selected from the range of 2.2 + -0.1,
k5represents from-1.0X 10-3±0.1×10-3Is selected from the range of (a) to (b),
k6represents a constant selected from the range of 1.0 + -0.1,
k7means selected from the range of-0.4. + -. 0.1The constant number is a constant number,
k8represents a constant selected from the range of 1.36 + -0.01,
k9represents from 2.0X 10-4±1.0×10-4Is selected from the range of (a) to (b),
r represents the solidification rate (mm/min),
t represents a temperature gradient (. degree. C./mm),
in the formula (2), C10maxRepresents the target maximum aluminum concentration (ppm), C, of the purified silicon2Represents the aluminum concentration (ppm), f, of the raw material silicon melt0Indicating the baseline coagulation rate.
2. The manufacturing method according to claim 1, wherein the target maximum aluminum concentration (C)10max) Is the aluminum concentration (C) of the raw silicon melt2) 1/1000 times to 3/100 times.
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| NO329987B1 (en) | 2009-02-26 | 2011-01-31 | Harsharn Tathgar | Semi-Continuous Process for Formation, Separation and Melting of Large, Clean Silicon Crystals |
| TWI393805B (en) * | 2009-11-16 | 2013-04-21 | Masahiro Hoshino | Purification method of metallurgical silicon |
| CN102639439B (en) * | 2009-12-01 | 2014-05-07 | 道康宁公司 | Rotational casting process |
| JP2012106886A (en) * | 2010-11-17 | 2012-06-07 | Nippon Steel Materials Co Ltd | Method and apparatus for solidification refining metallic silicon |
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| WO1998016466A1 (en) * | 1996-10-14 | 1998-04-23 | Kawasaki Steel Corporation | Process and apparatus for preparing polycrystalline silicon and process for preparing silicon substrate for solar cell |
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