Concept for an online material quality control by numerical simulation of a silicon ingot solidification process

The casting of large silicon ingots in stationary moulds is an economic alternative to crystal pulling techniques or to the Bridgman process. The process control of the solidification and the cooling down to room temperature determines the quality of the solar silicon wafers and the efficiency of the solar cells. Numerical modeling is applied to the SOPLIN process (solidification by planar interface) at Bayer AG, Germany. The VCF computer model (virtual casting furnace) has been used to optimise the casting conditions. A variety of material quality criteria are determined by computer simulation. Based on these simulations, a concept for an online process control is presented. The goal of this concept is to develop strategies that minimize deviations from the optimal process control by the use of computer simulation during the casting process.