Numerical Simulation of Solidification Behavior and Grain Structure for Multi-Crystalline Silicon Casting and its Experimental Verification

Abstract

The quality of multi-crystalline silicon ingot from casting process by heat exchange method (HEM) is significantly affected by the cooling condition and the design of the hot-zone. The shape of the liquid-solid interface has great impact on the direction and orientation of grain growth and the occurrence of defects such as dislocations, impurities segregation, and residual thermal stresses. In this study, the temperature variation/distribution of crystallization process of silicon ingot is investigated through numerical simulation and compared with experimental measurements. In HEM system, the temperature variation/distribution is affected by the adiabatic condition of the furnace and temperature curves of the heaters in the furnace. Incorporated with the Cellular Automaton (CA) method and residual thermal stress computation, the grain structures are also simulated. The different slices of the practical silicon ingot are then compared with the results of grain growth simulation to verify the accuracy of the numerical system. With the numerical system validated, various designs and operating conditions can then be numerically evaluated to obtain the optimal design and operation.