Solidification conditions at the early stages for grain control of polycrystalline silicon ingot

The influence of the shape of the crucible base and the solidification condition at an initial stage of unidirectional solidification on the microstructure of the polycrystalline silicon has been investigated. At the slow solidification velocity less than 10 ×10^-6m/s, the thin columnar grains grew. However, in above the velocity around 40 ×10 ^-6m/s, the large grains grew at the base of the crucible. The crystal orientation of 〈211〉 or 〈101〉 was detected at the parallel to the surface of the crucible. Undercooling, anisotropy of growth direction and the twin reentrant corner might cause the priority solidification direction. However, the equiaxed structure was appeared and grains became to be fine at the middle of the crucible. Therefore, the double solidification velocity technique was used. There might be a maximum speed around 10 ×10^-6 m/s at the early stage to maintain the large grain size.