JPH05270814A - Production of silicon for solar battery - Google Patents

Abstract

PURPOSE:To obtain the silicon for solar batteries by removing the impurities in the silicon waste generated in semiconductor industry by melting, filtering, oxidizing, pressure reducing, unidirectional solidifying, etc. CONSTITUTION:The waste contg. the impurities, such as contaminants, doping components, abrasive grains, etc., is first fused and passed through a particle packed layer of silica, quartz, etc., by which the SiC occurring in the abrasive grains, etc., contained in the silicon is filtered away. The filtrate is then subjected to an oxidation treatment. An oxidative gas may be blown from the bottom of a filtering container into the filtrate during the treatment or the molten silicon after the filtration may be subjected to the oxidation treatment in the container lined with silica while the oxidative gas, such as steam, is blown thereto. The carbon and boron, etc., are removed by the treatment. The pressure is then reduced to <=10Torr and the impurities, such as phosphorus and arsenic, are removed. The silicon is cast into a casting mold for unidirectional solidification and is unidirectionally solidified, by which the impurities, such as Fe, Al and Ca, are removed. The head of the final solidified part of the resulted silicon ingot is cut away by about 20%, by which the silicon is obtd.

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 silicon used for solar cells.

[0002]

2. Description of the Related Art Silicon used as a raw material for solar cells requires high-purity silicon with an impurity content of 1 ppm or less.
For this reason, extraordinary products of single-crystal silicon used in the electronics industry have been used. For example, crucible residue when pulling a single crystal and saws used when cutting a single crystal into a substrate. The ground slurry has a large amount of impurities and is practically discarded.

On the other hand, Japanese Unexamined Patent Publication No. 62-252393 discloses a method of removing impurities of such a waste by a combination of high frequency plasma and zone melting. There is a limit to its use, such as the inability to remove SiC, and there is a problem with poor energy efficiency and productivity due to the use of high-frequency plasma.

[0004]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a method for producing high-purity silicon for solar cells, which can easily remove impurities that are easily mixed in silicon waste discharged from the semiconductor industry. It is to be.

[0005]

The present invention relates to a method for producing silicon for solar cells, in which silicon waste generated in the semiconductor industry is used as a starting material, which is first melted and then has a through hole at the bottom, Filtration treatment is performed by a filtering device in which a substance having a silicon compound as a main component is filled as a filter material in a filtration container made of a substance having a silicon compound as a main component,
Next, the method is a method for producing silicon for a solar cell, which comprises subjecting the material to a filtration treatment, an oxidation treatment, a depressurization treatment, and a unidirectional solidification.

[0006]

The single crystal silicon substrate itself used in the semiconductor industry has a sufficient purity as a raw material for solar cells, but the waste in the manufacturing process is a component that is polluted from the environment and doped. Alternatively, impurities are mixed due to mixing of abrasive grains at the time of cutting, and it is difficult to separate them, so that they were not actually used and discarded.

On the other hand, in the present invention, first, waste silicon is melted and passed through a particle packing layer of silica, quartz or the like to remove SiC caused by abrasive grains mixed in silicon. It can be filtered off. A more specific method of this filtration is disclosed in Japanese Patent Application No. 2-4085 filed by the present applicant.
It is described in detail in Japanese Patent Publication No. 17. Next, the filtrate is subjected to an oxidation treatment, but an oxidizing gas may be blown from the bottom of the filtration container during the filtration treatment, or alternatively, an oxidizing gas such as water vapor may be added in a container obtained by lining the fused silicon with silica after filtration. The oxidation treatment may be performed while blowing gas. By this treatment, it is possible to remove carbon that is inevitably entered from the atmosphere when pulling the single crystal, boron added as a doping element, and the like.

Subsequently, the atmosphere of the processing container is preferably kept under a reduced pressure of 10 torr or less to remove easily evaporated impurities such as phosphorus and arsenic. Then, it is cast into a mold for unidirectional solidification and unidirectionally solidified. Unidirectional solidification removes impurities such as Fe, Al, and Ca that are harmful to solar cells (this is an element that easily mixes from the work environment during the production of silicon single crystals for semiconductors) and other metal impurities. Since these impurities have a very small equilibrium partition coefficient between solid and liquid, they can all be concentrated in the final solidification part (20% or less of the whole). About the head of the final solidification part of the unidirectionally solidified silicon ingot obtained by such treatment.
By cutting and removing 20%, the remaining 80% can be recycled as silicon for solar cells.

[0009]

【Example】

Example 1 A mixture of residual silicon in a crucible at the time of pulling a single crystal for semiconductors and a sawing slurry generated at the time of melting was melted at 1480 ° C., passed through a silica particle packed bed, and then at 1570 ° C. in a silica crucible Ar + 5% H ₂ O Blow in the mixed gas for 3 hours, and then put it under a reduced pressure of 10 torr for 1 hour, then 1 mm /
Unidirectionally solidified at min. Table 1 shows typical changes in the content of impurities in each step at this time, and a solar cell using this obtained a photoelectric conversion efficiency of 10.2%.

[0010]

[Table 1]

[0011]

The refining of metallic Si has been researched in the past, but the development of such a technique for effectively treating industrial wastes has the potential to greatly solve the problem of insufficient raw materials for solar cells. Opened.

Claims (1)

[Claims] 1. A method for producing silicon for solar cells, wherein a silicon waste generated in the semiconductor industry is used as a starting material, which is first melted and then has a through hole at the bottom,
A filtration container composed of a substance containing a silicon compound as a main component is subjected to a filtration treatment with a filtration device in which a substance containing a silicon compound as a main component is filled as a filter material, then the filtration treatment is followed by an oxidation treatment, and then a pressure reduction treatment. And then unidirectionally solidifying, a method for producing silicon for solar cells.