Grain control using spot cooling in multi-crystalline silicon crystal growth

We report a novel idea for grain control by using spot cooling for multi-crystalline silicon (mc-Si) crystal growth. The method employs a graphite crucible with cooling spots to generate radial thermal gradients of the silicon melt for nucleation during directional solidification. The effect of cooling spots on the grown ingot was studied by minority charge carrier lifetime mapping and electron back scattered diffraction (EBSD) of the grown crystals. It was found that charge carrier lifetime for silicon crystals grown with cooling spots was higher than those grown without cooling spots. The EBSD analysis also showed the formation of dendrite structures during cooling controlled growth. Further, the proposed method was found to be feasible for industrial-scale growth of mc-Si by directional solidification, and some preliminary results are presented.