Purifying multicrystalline silicon by directional solidification method with induced electromagnetic field

Abstract

As an improved directional solidification (DS) method, the complex directional solidification (CDS) method is used for purifying and preparing multicrystalline silicon ingot in this experiment. The induced electromagnetic field is imposed to control refining and solidification process. An integral silicon ingot with the diameter of 130 mm, the length of 130 mm and the weight of 4 kg is successfully fabricated in a self-designed CDS furnace. Metallographic analyses reveal that the direction of the most grains is parallel to the axial of silicon ingot. Analyses proved that the distribution of impurities in the cross-section is more homogeneously, the distribution in axial is improved and the effective length of silicon ingot is increased. Theoretical calculations indicate that the effect of solidified rate on the removal of impurities is limited and the impurities can be removed effectively after more than two times directional solidification process.

Effect of solidification rate on representative impurities distribution in Si–Cu alloy

“…Development of a metallurgical process to produce low cost solar grade silicon (SOG-Si) using metallurgical grade silicon (MG-Si) as feedstock is definitely necessary. For the last few decades, numerous researchers have investigated some metallurgical technologies for production of high purity MG-Si, such as acid leaching, 1,2 slag refining, [3][4][5] directional solidification, 6,7 electron beam melting, [8][9][10] vacuum volatilisation 11 and thermal plasma technology. 12 Since the segregation coefficient of metal impurities is much smaller than non-metallic impurities, 7 most of metal impurities can be effectively removed by directional solidification method.…”