Influence of Thermoelectric Magnetic Convection on Metal Impurity Behavior in Directionally Solidified Polysilicon

The impurities in silicon ingots during directional solidification (DS) were effectively controlled by Thermoelectric Magnetic Convection (TEMC). In details, the application of a 1 T static magnetic field (SMF) significantly improved the removal efficiency of metallic impurities (Fe, Cu, Mg, and Al), with the proportion of high-purity regions in silicon ingots increased from 70.1% to 80.7%. The SMF generated intense TEMC at the solid-liquid interface, driving upward displacement of metal impurities within the silicon melt. This convection led to a reduction in the diffusion layer thickness and effective segregation coefficient. The changes in the microstructure under the SMF were characterized using Electron Backscatter Diffraction (EBSD). The results revealed that under a 1 T SMF, the average grain size increased by 10.4%, and the proportion of Σ3 grain boundaries rose from 54.55% to 74.3%. The simulation of TEMC further elucidated both the magnitude and direction of induced convective flow at the solid-liquid interface. The results demonstrated a pronounced counterclockwise vortex formation, which critically influenced impurity redistribution. These findings provide valuable insights for optimizing parameters to improve silicon purification techniques, thereby facilitating the production of high-quality polysilicon for photovoltaic applications.