Process parameters influence on the growth rate during silicon purification by vacuum directional solidification

A numerical model is proposed to investigate influences of process parameters, including crucible pulling down rates and heater temperature, on crystal growth rates for silicon purification by vacuum directional solidification. The crystal growth rates of a silicon ingot are analyzed based on the interface energy balance equation combining with the temperature field calculated by software of ProCAST, and the segregation behavior of impurities is investigated with the Scheil's equation. The results show that the crystal growth rates decrease linearly with the increase of heater temperature at a fixed value of the crucible pulling down rate, and increase exponentially with the increase of the crucible pulling down rates at a fixed value of the heater temperature. The numerical model is verified by removal of iron impurity from 300 ppmw to 1 ppmw and by the temperature of melt silicon which is recorded by a thermocouple. The results show that numerical results agree well with experimental results. This research is used for adjusting process parameters to control crystal growth during silicon purification by directional solidification.