JPH11343111A - Production of high purity metallic silicon - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method capable of producing a 5-7N high purity metallic silicon suitable for the silicon for a solar battery without using the silicon or MG-Si for a semiconductor. SOLUTION: In the production method of the metallic silicon from a starting material consisting essentially of SiO2 , a stage in which a gaseous SiO is generated by heating the starting material to >=1500 deg.C by using a carbon based material as a reducing agent and a stage in which the gaseous SiO is heated at <=800 deg.C to reduce it to silicon are included. On reducing the gaseous SiO to silicon, a gaseous carbon monoxide (gaseous CO) and/or a gaseous hydrogen are used preferably as the reducing agent, and the gaseous SiO generated at the stage in which the gaseous SiO is generated is cooled and solidified and recovered preferably.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing high-purity metallic Si, and more particularly to a method for producing high-purity metallic Si having a purity of 5N (five nine: 99.999%) or more, which can be used as Si for solar cells. It relates to a manufacturing method.

[0002]

2. Description of the Related Art Metallic Si is used not only for semiconductor substrates but also for solar cells and the like, and its demand is increasing.

As a method for producing metal Si, there is, for example, a method described in JP-A-63-147813. The above method is a method of reducing with carbon or the like using silica (SiO ₂ ) or SiC (SiO ₂ + 2C → Si + 2CO), because the by-produced SiO gas has a high vapor pressure and is easily scattered to the outside. This is a method of increasing the yield of Si by replacing the SiO gas with SiC and refluxing it.

In addition, metal grade Si (hereinafter referred to as MG-S
i) is used as a raw material, and the MG-Si is unidirectionally solidified and melted (high-frequency crucible melting or EB melting)
There is known a method of obtaining metal Si by performing the above.

However, the metal Si obtained by these methods is used.
Have a purity of less than 5N and have a Si
Is required to have a high purity of 5N to 7N, and cannot be used as Si for solar cells. Moreover, in the latter method, the raw material MG-Si itself is expensive, and the unidirectional solidification process for purifying the MG-Si itself is also a very expensive technique.

Therefore, at present, defective silicon Si for semiconductors having a very high purity, such as 9N or 10N, is considered to be inferior to S for solar cells.
i. However, the amount is limited and cannot meet the ever-increasing demand for Si for solar cells.

[0007]

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and is directed to Si for semiconductors and MG-S.
5-7 suitable as Si for solar cells without using i
An object of the present invention is to provide a method capable of producing high-purity metal Si such as N.

[0008]

According to the present invention, there is provided a method for producing metal Si from a raw material containing SiO ₂ as a main component, wherein the raw material is prepared by using a carbon-based material as a reducing agent, and The gist of the present invention is to include a step of generating SiO gas by heating at a temperature of not less than 100 ° C. and a step of heating the SiO gas at 800 ° C. or less to reduce it to Si. In reducing SiO gas to Si, it is desirable to use carbon monoxide gas (CO gas) and / or hydrogen gas as a reducing agent. The SiO gas generated in the step of generating SiO gas is cooled, solidified, and recovered. It is desirable to do.

The heating temperature in the SiO gas generation step is desirably 1800 ° C. or less.
It is recommended that the amount of carbon in the reducing agent in the O gas generation step be 0.15 to 0.35 by weight ratio to the amount of SiO _{2 in} the raw material.

Further, in order to obtain high-purity metallic Si, prior to the SiO gas generating step, a raw material mainly composed of SiO ₂ is heated at a temperature lower than 1600 ° C. to evaporate impurity components to thereby purify the purity of the raw material. Is desirably increased, or prior to the step of reducing to Si,
Oxidizing the SiO gas obtained in the O gas generation step
It is desirable that the purity of the raw material containing SiO ₂ as a main component be increased by making O ₂ and repeating the above-mentioned SiO gas generation step again or a plurality of times.

The present invention also provides a method for producing metal Si from a raw material mainly composed of SiO ₂ , wherein a SiO ₂ gas and SiC are generated by heating the raw material to 1500 ° C. or higher using a carbon-based material as a reducing agent. The step of causing
React SiO gas and SiC in a reducing atmosphere to produce Si
May be employed. At this time, in the step of generating SiO gas and SiC,
It is desirable to generate an intermediate product that generates more SiC (weight ratio) than SiO gas and an intermediate product that generates more SiO gas than SiC, and reacts both intermediate products to generate Si. .

As the raw material, ash obtained by burning pulverized coal of coal may be used, and it is desirable to use ash having an average particle size of 60 μm or more.

Incidentally, the carbon-based substance in the SiO gas generating step of the present invention means a powdery or granular carbon material such as carbon black or activated carbon.

[0014]

BEST MODE FOR CARRYING OUT THE INVENTION The inventors of the present invention have conducted intensive studies on a technique for producing high-purity metallic Si on the premise of a method for producing metallic Si by reducing SiO ₂ using SiO ₂ as a raw material. Was. As a result, they found that SiO gas, which was conventionally considered as a by-product, was rather actively generated as an intermediate product, and that high-purity metal Si could be produced by further reducing this SiO gas. The present invention has been made. That is, while conventionally, it was intended to directly produce Si by reducing SiO ₂ , in the present invention, this was carried out by an SiO gas generation step (hereinafter sometimes referred to as a first step) and a reduction to Si. By dividing the process into steps (hereinafter, sometimes referred to as a second step) and performing respective reduction reactions under optimal conditions, high-purity metal Si was successfully produced.

FIG. 1 is a graph showing the relationship between the heating temperature of silica as a raw material (purity of 99.8%) mainly composed of SiO ₂ and the amount of gas generated due to each component. Until the temperature is saturated at 1800 ° C., the amount of generated SiO gas increases as the temperature increases, and is increased to 1500 ° C. or more (particularly 1600 ° C. or more)
, It can be seen that the amount of generated SiO gas is large. The amount of gas caused by impurity elements such as Fe, Al and Ca is as follows.
It increases rapidly above 1800 ° C. Therefore, from the viewpoint of generating a large amount of SiO gas and minimizing the generation amount of impurity elements, the heating temperature in the first step is set to 1
It is recommended to set the temperature between 500 ° C and 1800 ° C. That is, 1500 to 1800 ° C. (preferably 1600
(1800 ° C.), the difference between the amount of generated SiO gas and the amount of generated other impurity gases is remarkable.
The iO gas can be recovered with very high purification efficiency. When recovering the SiO gas in the first step, it is recommended that it be rapidly cooled and solidified, because handling is easy.

In the following second step, the S obtained in the first step is
By heating iO (for example, SiO gas) together with CO gas, SiO is reduced to obtain metal Si. FIG.
The reaction of this second step [SiO (g) + CO (g) → Si (sl)
+ CO ₂ (g)] is a graph showing the relationship between the reaction temperature and the free energy. That is, the reduction reaction in the second step proceeds at 800 ° C. or lower. From the viewpoint of reaction efficiency, the higher the temperature, the better, and preferably 600 ° C. or higher. In the first step, CO gas is obtained as a by-product, but in the second step, the CO gas obtained in the first step can be used, or another CO gas may be used. Further, hydrogen gas may be used in combination, or hydrogen gas may be used alone.

In addition, Mg, Al, etc. contained in
The pure element is SiO 2 before the first step. _Two Hara whose main component is
Material is removed by preheating at a temperature below 1600 ° C
It is also possible. Set lower preheating temperature
It takes a long time to evaporate impurity elements, while
When the heating temperature is set higher, a large amount of SiO gas is generated.
And adversely affect the Si yield.
It is recommended to set to 0 ° C.

Further, prior to the second step, the first
The SiO gas obtained in the process is oxidized into SiO ₂ ,
It is desirable to increase the purity of the raw material mainly composed of SiO ₂ by repeating the first step again or a plurality of times.

Further, by lowering the temperature in the upper part of the reaction tank in which the first step is carried out, the metal elements (Al, M
(g, Ca, etc.) can be an oxide, so that impurities may be removed by providing a coolable recovery plate above the reaction tank.

Further, in the method of the present invention, it is very important to adjust the amount of a carbon-based substance used as a reducing agent in the first step (hereinafter simply referred to as C amount). FIG. 3 is a graph showing the relationship between the amount of generated SiO gas and impurity gas and the amount of C in the reducing agent when a reduction reaction of a raw material mainly composed of SiO ₂ is performed at 1800 ° C. If the content is too small, the reduction reaction does not proceed sufficiently, so that the weight ratio to SiO ₂ is preferably 0.15 or more, and more preferably 0.18 or more. On the other hand, if the amount of C in the reducing agent is too large, SiC is generated and new impurities are generated.
0.35 or less is desirable, and 0.25 or less is more desirable.

The atmosphere during the reduction is desirably a vacuum atmosphere in order to increase the recovery rate of generated SiO. For example, the reduction reaction may be performed at a degree of vacuum of 10 ^-3 to 10 ^-4 Torr.

In producing metal Si from a raw material mainly composed of SiO ₂ , first, a carbon-based material is used as a reducing agent, and the raw material is heated to 1500 ° C. or higher to generate SiO gas and SiC. Next, a method of producing Si by reacting SiO gas and SiC in a reducing atmosphere may be adopted.

As described above, the amount of generated SiO gas varies greatly depending on the amount of C used as a reducing agent in the first step. FIG. 4 shows SiO gas and SiC when a reduction reaction of a raw material mainly composed of SiO ₂ was performed at 1800 ° C.
Is a graph showing the relationship between the generation amount of C and the C amount of the reducing agent. S
If the ratio of the amount of C to iO ₂ is less than 0.4, SiO
It can be seen that the amount of generated gas increases, and when it exceeds 0.4, the amount of generated SiC increases.

Therefore, in the step of generating SiO gas and SiC, an intermediate product in which the amount of SiC generated (weight ratio) is larger than that of SiO gas and an intermediate product in which the amount of SiO gas generated is larger than SiC are generated, You may produce Si by making both intermediate products react.

Also in this method, high purity metal Si
Prior to the step of generating SiOC and SiC, it is preferable to heat the raw material containing SiO ₂ as a main component at a temperature of less than 1600 ° C. to evaporate the impurity components to increase the purity of the raw material. Alternatively, prior to the step of reducing to Si, the SiO gas and the SiO gas obtained in the SiC generating step are oxidized to form SiO ₂ ,
It is desirable to increase the purity of the raw material mainly composed of SiO ₂ by repeating the iO gas and SiC generation steps again or a plurality of times.

Further, in performing the above-described manufacturing method,
Obtained by burning coal pulverized coal as raw material
Ash may be used. Each particle size obtained by classifying the above ash
As shown in Table 1, the particle size of the ash was 60 μm.
If it exceeds, SiO _Two With a high component ratio of
Since the C content is large, the average particle size is 60
It is recommended to use ash above μm.

[0027]

[Table 1]

The above-mentioned reduction reaction according to the present invention may be carried out by using a fluidized bed type apparatus which blows a reducing gas from below the raw material.

In dissolving the obtained metal Si into an ingot, if a split-type water-cooled copper crucible (cold crucible) is employed, it can be dissolved in the skull of the molten material itself and can be free of contamination. Melting is possible, and it is possible to obtain an ingot having a uniform structure without segregation. The obtained ingot may be made into a high-purity Si material for a solar cell according to a usual method.

Hereinafter, the present invention will be described in more detail with reference to Examples. However, the following Examples are not intended to limit the present invention. Are included within the technical scope of

[0031]

EXAMPLE 1 A first reaction tank for reducing and producing SiO from SiO ₂ ,
A second reaction tank for reducing and generating Si from O was provided in parallel, and the two reaction tanks were connected so that SiO gas generated in the first reaction tank could be transferred to the second reaction tank. Each of the two reactors has a diameter of 160
An induction heating device using a graphite crucible was provided, and the internal atmosphere was adjusted to about 10 ^-4 Torr by a vacuum pump.

First, a raw material (purity of 99.8% or more) mainly composed of SiO ₂ and C powder of 20% by weight based on the above raw material are charged into the first reaction tank, and reduced at a heating temperature of 1850 ° C. for 120 minutes. The reaction was performed to generate SiO gas. CO gas was supplied to the second reaction tank at a flow rate of 10 liters / minute, the internal temperature was set to 800 ° C., and the SiO gas transferred from the first reaction tank was reduced to obtain metal Si.

When the purity of the obtained metal Si was analyzed by an ICP emission spectrometer, the purity was found to be 99.999.
% (5N).

Incidentally, a trace amount of metal element (Al, Mg, etc.) as an impurity in the raw material was adhered above the inner wall of the first reaction tank.

Example 2 In the same manner as in Example 1, except that the raw material mainly composed of SiO ₂ was preheated at 1000 ° C. for 120 minutes before the reduction reaction was performed in the first reaction tank. I got When the purity of the obtained metal Si was analyzed by an ICP emission spectrometer, the purity was 99.9999% (6N).

Example 3 Instead of transferring the SiO gas obtained in the first reaction tank to the second reaction tank, the SiO gas was transferred to a third reaction tank, and the SiO gas was oxidized to SiO _2, and the first reaction was performed again. Metal Si was obtained in the same manner as in Example 1 except that the metal Si was returned to the tank and used as a raw material. When the purity of the obtained metal Si was analyzed by an ICP emission spectrometer, the purity was 99.9.
9999% (7N).

Example 4 A hydrogen gas (containing 40% in Ar) was supplied at a flow rate of 10 l / min as a reducing agent used in the second reaction tank at a flow rate of 10 liter / min, and reduction was performed at 700 ° C. In the same manner as in Example 1, metal Si was obtained. When the purity of the obtained metal Si was analyzed by an ICP emission spectrometer, the purity was 99.999% (5N).

Example 5 The weight ratio of the C powder charged into the first reaction tank was 2
Except that it was set to 5%, the metal S
i was obtained. When the purity of the obtained metal Si was analyzed by an ICP emission spectrometer, the purity was found to be 99.999.
% (5N).

Example 6 A first reactor for reducing and generating SiO and SiC from SiO ₂ and a second reactor for reducing and generating Si from SiO and SiC were provided side by side. Each of the reaction vessels was provided with an induction heating device using a φ160 graphite crucible, and the internal atmosphere was adjusted to a degree of vacuum of about 10 ⁻⁴ Torr by a vacuum pump.

First, a raw material mainly composed of SiO ₂ (purity of 99.8% or more) and a C powder of 20% by weight based on the above raw material are charged into the first reaction tank, and reduced at a heating temperature of 1800 ° C. for 120 minutes. Perform the reaction to produce SiO gas and SiC,
It was quenched and solidified to obtain an intermediate product A.

Next, a raw material (purity of 99.8% or more) mainly composed of SiO ₂ and 50% by weight of C powder based on the raw material are charged into the first reaction tank, and heated at 1800 ° C. for 120 minutes. Perform a reduction reaction to generate SiO gas and SiC,
It was quenched and solidified to obtain an intermediate product B.

The above-mentioned intermediate product A and intermediate product B were mixed and simultaneously heated to 1900 ° C. to obtain metal Si.

When the purity of the obtained metal Si was analyzed by an ICP emission spectrometer, the purity was found to be 99.999.
% (5N).

Example 7 The heating temperature was 1900 ° C., and 25% by weight based on the raw material.
Of the metal Si in the same manner as in Example 6 except that an intermediate product A was produced by introducing the C powder of I got When the purity of the obtained metal Si was analyzed by an ICP emission spectrometer, the purity was found to be 99.999% (5
N).

Example 8 Metal Si was produced in the same manner as in Example 4 except that pulverized coal combustion ash having an average particle size of 60 μm or more was used as a raw material, and a water-cooled copper-type induction heating furnace (φ200) was used as a heating furnace. I got When the purity of the obtained metal Si was analyzed by an ICP emission spectrometer, the purity was found to be 99.999% (5
N).

Example 9 Pulverized coal combustion ash having an average particle size of 50 μm or more was used as a raw material, the heating temperature in the first reaction tank was 1900 ° C., and the heating temperature in the second reaction tank was 720 ° C. Except for the above, a metal Si was obtained in the same manner as in Example 8. When the purity of the obtained metal Si was analyzed by an ICP emission spectrometer, the purity was 99.999% (5N).

Example 10 Metal Si was obtained in the same manner as in Example 6, except that pulverized coal combustion ash having an average particle size of 60 μm or more was used as a raw material. When the purity of the obtained metal Si was analyzed by an ICP emission spectrometer, the purity was found to be 99.999% (5
N).

[0048]

Since the present invention is configured as described above, high purity metal Si such as 5 to 7N suitable for Si for solar cells can be used without using Si for semiconductors or MG-Si.
Can be provided.

[Brief description of the drawings]

FIG. 1 is a graph showing a relationship between a heating temperature of a raw material mainly composed of SiO ₂ and a gas generation amount.

FIG. 2 is a graph showing a relationship between a reaction temperature and a free energy of a reduction reaction of SiO in a second step.

FIG. 3 is a graph showing the relationship between the amount of generated SiO gas and impurity gas in the reduction reaction of SiO ₂ and the amount of C in the reducing agent.

FIG. 4 shows SiO gas and S in the reduction reaction of SiO ₂ .
It is a graph which shows the relationship between the amount of generation of iC, and the amount of C of a reducing agent.

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Hitoshi Ishida 1-5-5 Takatsukadai, Nishi-ku, Kobe City Kobe Steel Works Kobe Research Institute

Claims (11)

[Claims] 1. A method according to claim 1, wherein a raw material containing SiO ₂ as a main component is a metal S.
a process for producing a SiO gas by heating the raw material to 1500 ° C. or higher using a carbon-based material as a reducing agent, and heating the SiO gas to 800 ° C. or lower to reduce to Si A method for producing high-purity metallic Si, comprising the step of: 2. The method according to claim 1, wherein the SiO gas is reduced to Si by using a carbon monoxide gas and / or a hydrogen gas as a reducing agent. 3. The method according to claim 1, wherein the SiO gas generated in the step of generating the SiO gas is cooled, solidified and collected.
The production method according to claim 1 or 2, wherein the reduction is carried out. 4. The method according to claim 1, wherein a heating temperature in the SiO gas generation step is 1800 ° C. or less. 5. The method according to claim 1, wherein the amount of carbon in the reducing agent in the step of generating SiO gas is 0.15 to 0.35 by weight relative to the amount of SiO _{2 in} the raw material. Manufacturing method. 6. Prior to the step of generating SiO gas, S
The process according to claim 1, the impurity components evaporated keep increasing the purity of the raw material by heating the material to the iO ₂ as a main component at less than 1600 ° C.. 7. Prior to the step of reducing to Si, the SiO gas obtained in the step of generating SiO gas is oxidized to form SiO _2, and the step of generating SiO gas is repeated or repeated a plurality of times to convert SiO ₂ into SiO ₂ . The production method according to any one of claims 1 to 6, wherein the purity of a raw material as a main component is increased. 8. A method for producing a metal S from a raw material mainly composed of SiO _2.
a process for producing SiO gas and SiC by heating the raw material to 1500 ° C. or more using a carbon-based material as a reducing agent, and reacting the SiO gas and SiC in a reducing atmosphere. Si
High-purity metal Si, comprising the step of producing
Manufacturing method. 9. In the step of generating SiO gas and SiC, an intermediate product that generates more SiC (weight ratio) than SiO gas and an intermediate product that generates more SiO gas than SiC are generated. The production method according to claim 8, wherein the intermediate product is reacted to produce Si. 10. The production method according to claim 1, wherein ash obtained by burning coal pulverized coal is used as the raw material. 11. The method according to claim 10, wherein the ash has an average particle size of 60 μm or more.