Computer modelling of a silicon ingot casting process and growth of high quality test ingots

An industrial silicon ingot casting process for the production of multicrystalline wafers was modelled on a computer. The time dependent temperature distribution in the ingot, in the crucible and in the isolation devices was calculated for the whole solidification period and compared with measured temperatures at different positions of a real system. In addition, the shape of the solidification front was calculated and compared with the grain structure of the ingot. Excellent conformity was found. Besides the standard system leading to ingots with inhomogeneous grain structure, an improved system with columnar grain structure and homogeneous ingot quality was modelled and also realized. The quality of the silicon material obtained with the improved system was demonstrated by test solar cells which showed very good homogeneity across the ingot and efficiency values up to 15,2 % employing only standard cell technology