Method for purifying polycrystalline silicon by electron beam gradient smelting

Abstract

The invention discloses a method for purifying polycrystalline silicon by electron beam gradient smelting, belonging to the technical field of polycrystalline silicon purification by using a physical metallurgy technology and relating to a method for removing phosphorus and metal impurities in the polycrystalline silicon by utilizing an electron beam smelting technology. The method realizes the directional solidification effect while removing volatile impurity phosphorus by changing beam current of electron beams to generate different energy distributions. The method comprises the following steps of: weighing silicon materials with high content of phosphorus and metal impurities, cleaning, drying and then putting into an electron beam smelting furnace, and completely smelting the silicon materials by using the electron beams with high current; then gradually reducing the beam current of the electron beams, and preserving the temperature under the low beam current; shutting the beam current off and then cooling, finally taking a silicon ingot out, and cutting the top of the silicon ingot off to obtain the silicon ingot with lower content of phosphorus and metal impurities. The invention has good removal effect on the phosphorus and the metal impurities and the dual effects of removing phosphorus by adopting the electron beams and removing metals by adopting directional solidification, improves the purification efficiency, reduces the process loops, and also has the advantages of stable technology, short cycle, energy source saving and low cost.

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 phosphorus and metal impurities in polysilicon by using electron beam melting technology. Background technique [0002] Solar-grade polysilicon is currently the most important photovoltaic material. Its high manufacturing cost and complicated manufacturing process are the bottlenecks restricting the development of the photovoltaic industry, which seriously hinders the promotion and use of solar cells in my country. my country's self-produced solar-grade polysilicon is less than 5% of the demand, and most of the raw materials need to be imported. The development of solar-grade polysilicon preparation technology suitable for my country's national conditions meets the requirements of the national energy strategy and is the only way for the development of my country's photovoltaic industry. [0003...

AI Technical Summary

Problems solved by technology

Electron beam smelting technology is one of the important methods in the metallurgical preparation of solar grades. It is a process that uses high-energy density electron beams as a melting heat source. The general electron beam smelting method is to remove high-saturated vapor pressure through high-temperature evaporation. Impurities such as phosphorus, aluminum, etc. Among the many impurities in polysilicon, metals are harmful impurities that will affect the resistivity and minority carrier lifetime of silicon materials, thereby affecting the photoelectric conversion efficiency of solar cells.

In Japan, there is a method of using electron beam technology to remove phosphorus in polysilicon, but the disadvantage of this method is that it uses two electron guns to enter the electron beam, which consumes a lot of energy, does not have the effect of directional solidification, and cannot remove metal impurities.

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