Method and device of removing boron in polysilicon by local evaporation

Abstract

The invention provides a method and a device of removing boron in polysilicon by local evaporation, belonging to the technical field of purifying the polysilicon by using the physical metallurgy technology, in particular relating to a method and a device of removing boron impurities in the polysilicon by using the electron beam melting technology. The method comprises the steps of: locally melting the polysilicon in a graphite crucible by using electron beams, evaporating the liquid silicon onto a deposition plate above the graphite crucible, and collecting the polysilicon deposited on the deposition plate. The shell of the device comprises a vacuum cover and a vacuum drum, the inner cavity of the vacuum drum is a vacuum chamber, a melting system is arranged in the vacuum chamber, and the melting system comprises an electron gun, the graphite crucible and a water cooled copper tray. The method has the advantages of simple processes, low energy consumption, little environmental pollution, high purifying precision and stable technology, and is beneficial to large scale production.

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 impurity boron in polysilicon by electron beam smelting technology. Background technique [0002] High-purity polysilicon is the main raw material for solar cells. The preparation of high-purity polysilicon abroad mainly uses the Siemens method, specifically the silane decomposition method and the gas-phase hydrogen reduction method of chlorosilane. The Siemens method is currently the mainstream technology for polysilicon preparation. Its useful deposition ratio is 1×10 3 , 100 times that of silane. The deposition rate of the Siemens method can reach 8-10 μm / min. The conversion efficiency of one pass is 5% to 20%, and the deposition temperature is 1100°C, second only to SiCl 4 (1200°C), the power consumption is about 120kWh / kg, and the power consumption is also relatively high. Domestic Si...

AI Technical Summary

Problems solved by technology

The disadvantage of the Siemens method is that it adopts backward thermal chemical vapor deposition in the core link of the process. There are too many links in the process and the conversion rate is low at one time, which leads to a long process time and increases the cost of materials and energy consumption.

The simple directional solidification method cannot remove the impurity phosphorus with a large segregation coefficient. Among the many impurities in polysilicon, boron is a harmful impurity, which directly affects the resistivity and minority carrier lifetime of silicon materials, and then affects the performance of solar cells. Photoelectric conversion efficiency

The polycrystalline silicon phosphorus content that can be used to prepare solar cells is required to be reduced to below 0.00003%, and there is no application of electron beams to remove boron in the known invention patents and scientific papers

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