Method for decreasing content of boron impurity in silicon metal through metallurgical process

Abstract

The invention relates to a method for decreasing content of boron impurities in silicon metal through a metallurgical process. The method comprises the steps of mixing calcium carbonate powder with silicon dioxide powder to obtain a slag forming constituent, mixing the slag forming constituent with silicon metal powder, adding 0.1-10% H2O2, evenly agitating, naturally cooling and drying, adding the mixed materials to one third of the total volume of a ceramic crucible, starting up a heating device consisting of a medium-frequency plasma heater and a medium-frequency induction coil to melt the mixed materials, adding silicon metal powder, shutting down the medium-frequency plasma heater when the silicon metal power is molten, increasing the frequency of the medium-frequency induction coil and continuously heating to fully melt the silicon metal powder into silicon metal liquid; and repetitively dipping quartz rods with a cooling system into the silicon metal liquid and turning the quartz rods to remove a slag phase in the silicon metal liquid. The method has the advantages that the operation steps are simple, the requirement on equipment is not high, the impurities are not apt to be introduced, the wastage of silicon is not caused and the production cost is low; and the content of boron in the purified silicon is below 0.2ppm and the requirement of solar grade polycrystalline silicon is satisfied.

Description

technical field [0001] The invention relates to a method for reducing boron impurity content in metallic silicon by using a metallurgical method. Background technique [0002] Crystalline silicon materials include polycrystalline silicon and monocrystalline silicon, which are the most important solar cell materials, with a market share of more than 90%, and will be the mainstream material for solar cells for a long period of time in the future. The higher the purity of the crystalline silicon material, the higher the photoelectric conversion efficiency and the longer the service life. Therefore, the industry stipulates that the boron content in solar-grade polysilicon should be less than 0.3ppm. [0003] At present, there are mainly Siemens method and physical and chemical method for the purification of metal silicon to prepare solar-grade polysilicon. The Siemens method has high production cost, complex process and pollutes the environment; the physical chemical method has...

AI Technical Summary

Problems solved by technology

Its disadvantages are: adopting the method of passing the mixed gas into the metal silicon liquid, the part of the ventilation part close to the metal silicon liquid is easy to corrode and damage, so the requirements for the equipment are relatively high; and at high temperature, the oxidizing gas in the mixed gas reacts with silicon , resulting in loss of silicon

Its disadvantages are: complex operation steps, easy to introduce impurities for the second time when crushing and grinding metal silicon ingots, serious waste of silicon, and high production costs

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