JPH09202611A - Removal of boron from metallic silicon - Google Patents

Abstract

PROBLEM TO BE SOLVED: To remove boron from metallic silicon in high accuracy without causing the clogging of a blowing nozzle by using a solid decomposable at a specific high temperature to generate H2 O and/or CO2 and blowing the solid into a molten Si bath together with a carrier gas. SOLUTION: One or more kinds of solids decomposable at <=1400 deg.C to generate H2 O and/or CO2 are blown into a molten Si bath together with a carrier gas. Ar, H2 , CO, etc., can be used as the carrier gas. The solid is e.g. Ca(OH)2 , CaCO3 or their mixture.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for removing boron in metallic silicon, and more particularly to the production of high-purity silicon used for semiconductors or solar cells.

[0002]

2. Description of the Related Art Si used in semiconductors and solar cells is required to have a high degree of purity (generally said to be 6-N or more) so as to exhibit semiconductor characteristics. Conventionally, silane gas obtained by chlorinating metallic silicon is purified to remove impurities. However, a method of removing this again and obtaining high-purity Si is used. This method is high in cost, and particularly Si used for solar cells is cost-reduced, so a metallurgical refining method is being studied. For example, in Japanese Examined Patent Publication No. 5-31488, high-purity silicon is produced by injecting powdery silica stone into molten metal silicon to generate SiO gas and reducing the SiO gas into metal Si in a layer filled with a reducing agent. A method of trying to obtain is proposed.

Further, in Japanese Patent Laid-Open No. 246706/1993, silicon for metallurgy is melted as a starting material, and an arc is blown between the molten silicon and an electrode provided on the upper part.
A method for obtaining high-purity silicon by purifying by adding an inert gas, preferably an oxidizing gas, has been proposed. By the way, metal Si usually contains about 20 ppm of boron (B).
Removal of B in i is difficult, and many studies have been conducted.
As a method of metallurgically removing B in Si, for example,
JP-A-4-193706 or JP-A-5-24
Japanese Patent No. 6706 proposes a method of oxidizing and removing B by blowing H ₂ O, or CO ₂ or O ₂ gas into a Si bath, and at the same time, SiO ₂ , CaO, and C.
The effect is further enhanced by blowing in aCl ₂ , CaF _2, etc. Further, JP-A-58-130114 discloses a method of removing B by mixing and dissolving slag containing an oxide of an alkali metal or an alkaline earth metal and dissolving it.

[0004]

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention
In the method disclosed in Japanese Patent Publication No. 3706 or Japanese Patent Laid-Open No. 246706/1993, H ₂ O that reacts with B in Si or an oxidizing gas such as CO ₂ or O ₂ is blown as a gas, and is blown into Si. Immediately oxidizes Si,
A part of SiO ₂ is generated. Therefore, the tip of the nozzle is likely to be clogged and the amount is limited, which makes it difficult to perform stable operation. Further, Japanese Patent Application Laid-Open No. 58-1
According to the method disclosed in Japanese Patent No. 30114, all the reactions are completed at the time of melting, and in principle, B between slag and Si is
Since the removal equilibrium determines the upper limit of removal, the B content cannot be reduced to such an extent that it can be used in solar cells, and there is a problem in that it cannot go beyond the scope of preliminary treatment.

It is an object of the present invention to solve these problems and to provide a technique capable of removing boron accurately without causing clogging of a blowing nozzle.

[0006]

The present invention has solved the above problems by the following method. That is, the technical means is to blow one or more solids that decompose at 1400 ° C. or lower to generate H ₂ O and / or CO ₂ into a molten Si bath together with a carrier gas. This is a method for removing boron in silicon.

Ar, H ₂ , CO and the like are used as a carrier gas for carrying the solid into the Si bath. Further, Ca (OH) ₂ , CaCO ₃ or a mixture thereof is used as the solid, but any solid can be used as long as it decomposes at 1400 ° C. or lower to generate H ₂ O or CO ₂ .

[0008]

DETAILED DESCRIPTION OF THE INVENTION According to the present invention, a solid blown into a Si bath decomposes in the Si bath depending on the temperature of the Si bath to generate H ₂ O or CO ₂ . This generated CO ₂
Alternatively, H ₂ O reacts with B in Si as an oxidizing gas to form B
B in Si is removed by generating the oxide gas of No. 3 and discharging it out of the Si bath together with the carrier gas.

A solid that decomposes at a temperature of 1400 ° C. or lower to generate H ₂ O or CO ₂ (hereinafter referred to as a solid blown substance)
Is blown into the Si bath, abrupt gas generation occurs due to decomposition, which causes stirring of Si and an increase in reaction interfacial area, which allows the reaction to proceed advantageously and at the same time silicon oxidation at the nozzle tip. It can be suppressed, and the nozzle clogging can be prevented. Further, even when treating a large amount of Si, sufficient stirring and a reaction interfacial area can be secured. Furthermore, in this method, since H ₂ O, CO _{2 and the} like are blown in as a solid, a large amount of H ₂ O or CO ₂ can be easily converted into S.
It can be introduced into the i-bath and the reaction time can be shortened. The carrier gas plays a role of carrier of the solid blown product, and as the gas species, Ar inert to Si or H ₂ or CO which is a reaction product is desirable. In addition, from the experiment, the addition amount of the solid blowing material was determined to be H ₂ O and / or C generated from the solid blowing material blown every minute.
When the amount of O ₂ is m (g / min), the amount of Si to be treated is M (kg), and the treatment time is (t) minutes, the following ranges are suitable.

M ≧ (12 × M) / t (g / min) The particle size of the solid blown product is preferably 100 mesh or less. When it exceeds 100 mesh, the nozzle is clogged and the blowing is not stable, which is not preferable.

[0011]

EXAMPLES Siri shown in Table 1 containing 22 to 7 ppm of B
Dissolve 20 kg of con in a silica crucible under Ar atmosphere
Was. Inner diameter covered with alumina tube at a melt temperature of 1500 ℃
Dip an 8 mm silica tube into the melt from above and
The carrier gas was blown in at 1 / min. At this time, Ca
(OH)_Two (Average particle size 325 mesh), CaCO _Three 
(Average particle size 200 mesh) or MgCO_Three Carry
It was blown into molten silicon together with Agus. Blowing time
For 20 to 120 minutes, and after cooling and solidifying in the silicon
The B content was analyzed by the ICP method. Put these together
Are shown in Table 2.

From these results, H _{2 in} molten silicon
B in the silicon can be lowered by blowing a solid that generates O or CO ₂ into the silicon.
In particular, Example No. As is clear from comparison with 1 to 5, m ^* = 12 M / t (where M; silicon amount k
The effect is great when the amount of generated gas is larger than m ^* defined by g, t; blowing time min).

The maximum amount of Ca that enters the silicon by these treatments is 90 ppm, and this amount can be removed by carrying out directional solidification refining during the production of a silicon ingot, and there is no problem. It was No clogging of the blowing nozzle and no scattering of molten silicon due to bumping when gas was generated were observed.

[0014]

[Table 1]

[0015]

[Table 2]

[0016]

According to the present invention, B, which is the most difficult to remove from Si, can be removed. Therefore, A
By combining conventional methods for removing l, Ca, Fe, etc., it is possible to inexpensively and in large quantities manufacture raw material Si for solar cells from metallic Si. As a result, it is possible to solve the raw material problem, which is the only bottleneck in the solar cell industry, which is expected to develop at present.

Claims (3)

[Claims] 1. In metallic silicon, characterized in that one or more solids which decompose at 1400 ° C. or lower and generate H ₂ O and / or CO ₂ are blown into a molten Si bath together with a carrier gas. How to remove boron. 2. The carrier gas is Ar, H ₂ and CO
The method for removing boron in metallic silicon according to claim 1, which is a mixture of one or more selected from the group consisting of: 3. The solid is Ca (OH) ₂ and / or C
The method for removing boron in metallic silicon according to claim 1 or 2, which is aCO ₃ .