Numerical analysis and optimization of gas flow and impurity control in directional solidification multi-crystalline Si

Abstract

In order to study the mechanisms of gas flow and impurity transport in an industrial directional solidification furnace for producing multi-crystalline silicon (mc-Si), a 3D global modeling, including argon flow, thermal conduction, thermal radiation, chemical reaction, and mass transfer was established. Simulation results show that the backflow at crucible outlet near the midcourt plane is mainly attributed to buoyancy, which will induce SiO and CO impurities accumulation and affect the chemical reaction intensity on the graphite components. With the increasing of argon flow rate, the backflow is restrained, and the CO concentration at the melt free surface decreases exponentially. When the flow rate is exceed 30 L/min, the benefit is limited. An argon gas guidance system was designed and numerically analyzed, it is found that when the ratio a/b = 0.5, the backflow at crucible outlet almost disappears and the impurity concentration further decreases. According to the newly discovered mechanisms of the flow, chemical reaction and impurity transport, the new designed argon gas guidance system will beneficial for improving the quality of mc-Si.