Directional Solidification Behaviors of Polycrystalline Silicon by Electron-Beam Melting

Abstract

The advanced electron beam melting (EBM) system with the combination of vacuum refining and directional solidification (DS) performed the purification of large amounts of metallurgical grade silicon (MG-Si). In order to increase grain size or to align columnar grains being parallel to DS pulling direction in Si ingots, non-irradiated inner diameters in an EB pattern in the DS process were varied at a range of 5–35 mm. Average grain size increased with increasing non-irradiated inner diameter due to a smaller temperature gradient during the solidification of Si melts. However, the slope of the grain boundary inclined towards the ingot axis, which led to the formation of a triple junction in the ingot center in the case of large non-irradiated inner diameter. This happened despite there being a large temperature gradient due to the turbulent flow in the pool. This work reported that a purity of 99.8% for MG-Si was improved to above 99.999% with an ingot yield of 90% for 1 h.