Numerical Investigation of Bottom Grille for Improving Large-Size Silicon Quality in Directional Solidification Process

Abstract

2D global transient numerical model based on a new large-size ALD-G7 (G7) crystalline silicon ingot furnace is established and experimentally verified. A new pyramid-shaped bottom grille structure is designed. The temperature field, flow field, crystal growth rate, crystal-melt (c-m) interface and thermal stress during the crystal growth process for the furnace with and without pyramid grille are compared and studied. Simulation results indicate that the supercooling of silicon ingot center and excessive crystal growth rate are easily caused when original grille is used, which will lead to the over-convexity of c-m interface and higher thermal stress. The addition of pyramid grille reduces crystal growth rate in the early stage. By reducing heat flux at heat exchange block center, the pyramid grille improves the supercooling of the center area and the shape of c-m interface significantly. Furthermore, the thermal stress at the bottom center and bottom corner of the silicon ingot is reduced by 20.22 and 16.14 % in the modified furnace, respectively.