Effect of Marangoni Convection on Ingot Quality During Vacuum Directional Solidification of Polycrystalline Silicon

Marangoni convection caused by the gradient of melt free surface tension has a significant effect on the growth quality of polycrystalline silicon during vertical Bridgman vacuum directional solidification. In this paper,a multi-field coupled mathematical and physical model of thermal field,flow field,and stress field in the vacuum directional solidification process of polycrystalline silicon was established. Numerical simulations and experiments are used to study the influence of factors such as melt heat transfer characteristics,melt flow behavior,and ingot thermal stress on the growth quality of silicon crystals under Marangoni convection. The results show that Marangoni convection can enhance the flow intensity of silicon melt flow field,make the average velocity of silicon melt increase about three times,and then affect the convective heat transfer capacity of silicon melt,make the temperature distribution of silicon melt and silicon solid more uniform,the temperature gradient of the silicon melt is reduced by 4.8%-9.9%,and the temperature gradient of the silicon solid is reduced by 2.1%-2.6%,which makes the polysilicon ingot process produce smaller thermal stress and fewer defects.