Study On The Separation Of Impurities In The Purification Process Of Polysilicon By Induction Melting

With the rapid development of the global economy,reserves of coal,oil and other non-renewable resources cannot meet the human demand for energy.Solar energy is the most inexhaustible renewable energy,its research and development is rapid.In recent years,with the rapid development of photovoltaic industry,directional solidification technology can not only be used for the preparation of solar grade polysilicon ingots,but also can be used to remove metal impurities of small separation coefficient in silicon,and it has become the focus of research on polysilicon technology.The segregation behavior of the impurities in the solidification process of polysilicon under industrial conditions was systematically studied that is based on the induction smelting technology and raw materials which is low concentration of boron in industrial silicon.The removal of metal impurities in industrial silicon was realized by adjusting the temperature gradient and coupling.The main conclusions of this paper are as follows:(1)The diameter of the silicon grains is in the range of 2 to 7 mm,the maximum is 14 mm,and the longest is 179.4 mm.The bottom of the grain was vertical distribution,the central part of the columnar grain height is 130 mm,edge columnar grain is 185 mm,the top of the ingot solidification is concave surface from the inference of the top of the crystal surface,and the side wall thickness is about 2cm.The purification effect of ingot is obvious.The metal impurity content is lower than 5.5ppmw when the height is lower than 170 mm,and metal impurity content is about 904-3406 ppmw when from 210 mm to the top of the ingot,so the effect of metal impurity enrichment is obvious.(2)The impurity content of the impurity in the ingot is 3.43 ppmw,while the temperature gradient is 437.62 K/m.The thickness of the diffusion layer of Fe,Cu,Ni and Ti impurity in the silicon melt is 8.44 mm,5.98 mm,8.79 mm and 6.95 mm,respectively.The impurity content of the impurity in the ingot is 0.54 ppmw,while the temperature gradient is 940.51K/m.The thickness of the diffusion layer of Fe,Cu,Ni and Ti impurity in the silicon melt is 7.47 mm,3.20 mm,7.94 mm and 2.06 mm.When the temperature gradient is 437.62 K/m,the effective fractionation coefficient of Fe,Cu,Ni and Ti impurities are 1.52×10-4,1.81×10-3,9.92×10-4? 1.86×10-3.With the increase of the temperature gradient,the effective fractionation coefficient of Fe,Cu,Ni and Ti impurity under the temperature gradient of 940.51K/m is reduced to 1.27×10-3,5.46×10-4,9.05×10-4 and 6.56×10-4.As a result,the removal rate of impurities is improved.