Method for purifying polycrystalline silicon by directional solidification and slag refining

Abstract

The invention belongs to the technical field of purifying polycrystalline silicon by physical metallurgy technology. A method for purifying polycrystalline silicon by directional solidification and slag refining comprises the following steps: firstly, mixing polycrystalline silicon material and acid slag former uniformly so as to form mixture, then arranging the mixture into a melting crucible ofa directional solidification furnace, slagging and melting the mixture in the melting crucible, simultaneously, conducting directional solidification so as to concentrate metal impurity and waste slag on the top of a silicon ingot, removing boron and metal impurity, and finally cutting the top of the silicon ingot, thus obtaining polycrystalline silicon ingot with low boron and metal content. Themethod has the following obvious effects: the acid slag former for slagging and melting and the directional solidification are adopted simultaneously, the impurity boron in the polycrystalline silicon is removed by the slagging of the acid slag former and the refining, simultaneously, the metal impurity with a smaller segregation coefficient in the polycrystalline silicon is removed by the directional solidification technology, the purity of the polycrystalline silicon material is improved, so that polycrystalline silicon material achieves the using requirement of solar-level polycrystalline silicon material.

Description

technical field [0001] The invention belongs to the technical field of purifying polysilicon by using physical metallurgy technology, and particularly relates to a method for removing boron and metal impurities in polysilicon by using directional solidification technology for slagging and smelting. Background technique [0002] In a society where energy is scarce and low-carbon environmental protection is advocated, solar energy, as an environmentally friendly new energy, has great application value. In recent years, the global solar photovoltaic industry has grown rapidly, and the output of solar cells has increased rapidly, directly driving the rapid expansion of solar polysilicon demand. [0003] At present, the methods of purifying solar polysilicon mainly include chemical purification and physical purification. The chemical purification is mainly the Siemens method. Its advantages lie in high product purity and good quality. Harmful gas will be produced. Metallurgy is...

AI Technical Summary

Problems solved by technology

Japan's Morita et al. did a systematic study on slagging smelting, and concluded that the main factors affecting the distribution coefficient are the basicity of the slag agent, the partial pressure of oxygen and the distribution of B in the melt, but the results are not very good. Ideal, difficult to meet the requirements of industrialization

[0005] A method for preparing solar-grade silicon with a patent number of 200810068908.0 and a metallurgical method for preparing solar-grade polysilicon and the polysilicon prepared by this method with a patent number of 201010215098.4 are disclosed in the prior art. The heating method of the directional solidification furnace is induction smelting heating. This heating method produces a large disturbance to the silicon slag melt, which is not conducive to the stable separation of the waste slag after the reaction from the melt, and the boron removal effect is not good.

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