Method and device for preparing 6N polycrystalline silicon by vacuum microwave refining of industrial silicon

Abstract

The invention discloses a method and a device for preparing 6N polycrystalline silicon by vacuum microwave refining of industrial silicon, wherein the method comprises the following steps: flowing industrial silicon melt into a primary oxidation refining furnace, introducing mixed gas I, adding SiO2 powder to perform primary oxidation refining, flowing into a secondary oxidation refining furnace, vacuumizing the system, and introducing mixed gas II; then adding SiO2 powder to perform secondary oxidation refining, enabling the mixture to flow into a directional solidification crucible to be subjected to primary vacuum evaporation and directional solidification refining, and heating the materials to be subjected to secondary vacuum evaporation refining; cooling and taking out the silicon ingot, removing the head, tail and edge portions, and crushing and screening the product; then feeding the product into a reactor and vacuumizing the equipment, feeding argon and mixed gas III, and carrying out microwave plasma vacuum evaporation and oxidizing volatilization refining to prepare polycrystalline silicon of which the purity is not less than 6N, the content of metal impurities such as boron, phosphorus, iron and the like is less than 0.1 ppm, the resistivity is about 2.5 ohm.cm. According to the invention, the quality requirement of the polycrystalline silicon solar cell material is met, and the high-quality and high-efficiency monocrystalline silicon solar cell material can be obtained through subsequent casting or single crystal drawing.

Description

technical field [0001] The invention relates to a method and a device for preparing 6N polysilicon by vacuum microwave continuous refining of industrial silicon, and belongs to the field of technology and equipment for preparing polysilicon solar cell materials by purifying industrial silicon by metallurgical methods. Background technique [0002] Industrial silicon mainly contains metal impurities (such as active metal impurities Al, Ca, etc. and transition metal impurities Fe, Co, Ni, Cu, Zn, Mn, Cr, V, Ti, Zr, etc.) and non-metal impurities (such as B, P, C, O, etc.); various grades of industrial silicon products mainly limit the content of Fe, Al, and Ca, but are not limited due to traces of non-metallic impurities, such as 553 ＃ (Fe≤0.5%, Al≤0.5%, Ca≤0.3%); 441 ＃ (Fe≤0.4%, Al≤0.4%, Ca≤0.1%); 3303 # (Fe≤0.3%, Al≤0.3%, Ca≤0.03%); 2202 # (Fe≤0.2%, Al≤0.2%, Ca≤0.02%); 1101 # (Fe≤0.1%, Al≤0.1%, Ca≤0.01%); the purity of industrial silicon is above 98%, the total impurity ...

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Problems solved by technology

[0006] Existing problems in boron and phosphorus removal by metallurgical methods: First, the problem that low-cost boron removal meets the standard but phosphorus does not meet the standard, such as oxidation slagging, segregation, Ca doping combined acid leaching, smelting method combined acid leaching, low temperature alloying directional solidification boron removal and phosphorus, boron removal can be lower than 0.1ppm, but the phosphorus removal effect has not reached 0.1ppm; the second is the problem that the phosphorus removal effect is up to standard but the cost is high, such as electron beam melting and vacuum induction melting. Removing impurities under high temperature and high vacuum takes a long time, high energy consumption, large silicon volatilization loss, expensive equipment, not high enough yield, and the initial concentration of phosphorus has a great influence on the effect of impurity removal, so the cost is high, which is not conducive to the industry change

In recent years, vacuum induction melting has improved in terms of enhancing impurity diffusion, reducing silicon volatilization loss, reducing equipment costs and optimizing process parameters, but it is still under study

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