Development of grain structures of multi-crystalline silicon from randomly orientated seeds in directional solidification

Development of grain structures of multi-crystalline silicon from small spherical seeds with random orientations in directional solidification was investigated. The electron backscattered diffraction (EBSD) analyses of the grains at different pulling rates, i.e., 1, 5, and 20 cm/h, were carried out. It was found that {112}/{111} orientations were dominant at the low crucible pulling speed, while {111} at the high pulling speeds. The percentage of {100} grains was found very low near the top of the ingots. The percentage of non-Σ grain boundaries was around 70% at the beginning and decreased with the solidification distance, while Σ3 grain boundaries or twins increased indicating the importance of twin formation during the development of grain structures. The mechanisms for grain competition and selection were further discussed.