JPH10167716A - Purification of silicon - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve efficiency of a silicon purifying process of the latter method and to better the yield of a product, by equipping a melting part with a filter and filtering a molten silicon to effectively remove intervening impurities in electron beam melting in purifying silicon by the electron beam melting. SOLUTION: A raw material silicon 3 is supplied to a hearth 1 and melted by electron beam. A filter 4 is installed in the hearth 1 and intervening impurities 5 are caught. The intervening impurities are caught by the filter 4 and a molten silicon 2 is passed through the filter. A sintered filter of high purity SiC is used as the filter 4 and a material which is stable at a high temperature in high vacuum and has a small amount melted into silicon is proper. For example, carbon and silicon carbide are suitable due to stability at high temperature in high vacuum, a small amount melted into molten silicon of about 100ppm and ready oxidation and removal.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to P, Al, Ca in silicon for solar cells using an electron beam under vacuum.
And a method of purifying silicon for removing impurities such as impurities.

[0002]

2. Description of the Related Art In recent years, photovoltaic power generation has been in the spotlight due to the demand for diversification of energy sources, and research and development have been actively conducted for practical use of low-cost power generation devices. Under such circumstances, silicon is the most commonly used material as a material for solar cells, and is regarded as the most important material used for power supply for power.

[0003] Silicon used as a raw material for solar cells
Is a high purity silicon of 99.9999% (6N) or more
is necessary. Conventionally, commercially available metallic silicon (purity 9
9.5%) to produce the high-purity silicon.
P, C in commercially available metallic silicon by electron beam melting
Technology for simultaneously removing a and Al has been developed. WO
WO 93/12272 states that the water level in a water-cooled copper bath
Install a water cooling pipe nearby to remove suspended inclusions
A method is disclosed. The technology is as follows: (1) Accidents such as water leakage due to erosion due to incorrect operation of the electron beam
Likely to cause. (2) The main inclusions are Al_Two O_Three , SiO_Two ,
SiC is mentioned, and in any case, the density is 4.0.
g / cm^Three 2.2g / cm^Three 3.2g / cm ^Three In
Therefore, the density of molten silicon is 2.5 g / cm^Three Close to
Not only floating but also sedimentation.
There were problems such as insufficient removal of inclusions.

[0004]

In the case of electron beam melting, a graphite container or a water-cooled copper container is used. At this time, inclusions contained in the raw silicon or generated after melting, for example, SiC, SiO ₂ , Al ₂ O _3, etc., flow out of the hearth, and the inclusions are included in the next step or further later steps. There is a problem in that it remains without being removed, and in some cases, C and the like are removed only up to the saturation dissolution amount. When such inclusions enter the unidirectional solidification cell in the next step, which is continuous with the electron beam melting, the amount of cut and removed of the unidirectionally solidified ingot increases, and the yield decreases.

It is an object of the present invention to effectively remove such impurity inclusions in the electron beam melting to improve the efficiency of the subsequent silicon refining process and to improve the product yield.

[0006]

DISCLOSURE OF THE INVENTION The present invention has been made to achieve the above-mentioned object. In purifying silicon by electron beam melting, a filter is provided in a melting part to filter molten silicon. This is a method for purifying silicon. In the present invention, the filter is installed not only near the surface of the molten silicon but also over the entire cross section of the molten silicon.

As the filter, a material which is stable at high temperature and high vacuum and has a small amount of dissolved in silicon is suitable. For example, carbon and silicon carbide are suitable because they are stable at high temperatures and high vacuums, dissolve in molten silicon at about 100 ppm, and are easily oxidized and removed. In addition, carbon and silicon carbide are not melted even if the electron beam is directly irradiated, and there is no problem of silicon contamination.

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS According to the present invention, a filter is provided in a hearth for dissolving an electron beam to prevent outflow of impurity inclusions. As the filter, a granular body, a spherical body, a tubular body, an irregular Raschig ring, or the like containing carbon or silicon carbide as a main component can be used.

It is desired that the filter material has a high purity to prevent contamination of silicon. FIG. 2 shows a conventional example, and FIG. 1 shows a sectional view of the embodiment. The raw material silicon 3 is supplied to the hearth 1 and is melted by an electron beam not shown. Conventionally, the inclusions 5 are transferred together with the molten silicon flowing out of the hearth 1 to the mold or crucible 11 in the next step.

Conventionally, the inclusions 5 also flow out together with the molten silicon 6 flowing out of the hearth 1, and the mold or crucible 11
Get in. And these inclusions are solid silicon 1
3 or move to the next step together with the molten silicon 12. Also, the skull 14 generated on the inner wall of the mold or crucible 11 may shift to the downstream process. FIG.
In the embodiment shown in (1), a filter 4 is provided in the hearth 1, and inclusions are captured here. High purity S for filter 4
An iC sintered filter was used. Inclusions are trapped in the filter and the molten silicon passes through it.

[0011]

According to the present invention, a filter is provided in a melting portion in electron beam melting to effectively remove impurity inclusions, thereby improving the efficiency of the downstream silicon purification step, and
It has become possible to improve the yield of products.

[Brief description of the drawings]

FIG. 1 is a sectional view of an electron beam melting hearth of silicon according to an embodiment.

FIG. 2 is a sectional view of a conventional silicon electron beam melting hearth.

[Explanation of symbols]

 Reference Signs List 1 hearth 2 molten silicon 3 raw material silicon 4 filter 5 inclusion 6 molten silicon flowing out 11 mold or crucible 12 molten silicon 13 solid silicon 14 skull

Claims (1)

[Claims] 1. A method for purifying silicon, comprising the steps of: providing a filter in a melting section and filtering molten silicon when purifying silicon by electron beam melting.