Study on thermal stresses and dislocation in silicon ingot during a unidirectional solidification process
by
Xuejiang Chen
Research Institute for Applied Mechanics, Kyushu University, 6-1 Kasuga-koen, Kasuga, Fukuoka 816-8580, Japan
Coauthors: Satoshi Nakano, Lijun Liu and Koichi Kakimoto

Unidirectional solidification method is an important method for large-scale production of multi-crystalline silicon material for solar cells. The dislocations generated during the growth from the melt of crystals can greatly degrade the ingot quality for high efficient solar cell materials. The generation of dislocations is attributed to excessive thermal stresses inside the grown crystal. It is necessary to simulate the solidification process with a global model, and to investigate the thermal stresses distribution and the dislocation density in the silicon ingot by using thermal stress model and dislocation multiplication model.

In this paper a transient global model was used to obtain the solution of thermal field within the entire furnace of a unidirectional solidification process. The melt-solid interface shape was obtained with a dynamic interface tracking method. And then, based on the global solution of heat transfer, the thermal stresses distribution in the silicon ingot was solved using FVM. Finally, the dislocation density was also simulated by using dislocation multiplication model. Several different melt-solid interface shapes were obtained by using different solidification rates, and then, the thermal stresses and dislocation density for different solidification rates were compared.

Date received: March 12, 2008