Parameter study of traveling magnetic field for control of melt convection in directional solidification of crystalline silicon ingots

摘要

Melt convection plays a critical role in the quality of crystalline silicon ingots produced by directional solidification (DS), through influencing the solidification front shape and impurities distribution. The utilization of a traveling magnetic field (TMF) is a promising way to control melt convection pattern. Lorentz forces induced by a TMF will present various characteristics under different imposed electric current parameters, such as current amplitude, frequency and phase shift. Understanding the effects of current parameters on melt convection pattern is crucial for the selection of suitable parameters to achieve the enhancement of melt mixing and a preferable solidification front. Based on a coupled model of global heat transfer, this paper explores the effects of these current parameters on the melt convection pattern in a DS furnace of crystalline silicon ingots under the action of a downward TMF. The melt mixing effect and solidification front shape are further elucidated based on different melt convection patterns. The results indicate that the effects of current parameters on the melt mixing effect and solidification front shape is quite complicated, which is not monotonous. By precisely tailoring the combination of current parameters, a flat or slightly convex solidification front and decent melt mixing are simultaneously obtained. This study can facilitate the successful and optimum utilization of a TMF in the DS process of crystalline silicon ingots.