Assessment of residual melt removal as approach to reduce the top redzone of cast silicon ingots

Abstract

We studied the impact of melt removal on the formation of the top redzone in directionally solidified silicon. Solidification experiments in G1-scale were carried out during which the residual melt was removed before full solidification by dumping. The impact of this procedure on the extension of the top redzone was evaluated by lifetime mappings and lifetime profiles extracted therefrom. A lineshape analysis of these profiles enabled to distinguish between cooldown time effects and the impact of the iron contamination at the ingot top. The experiments show that the contamination and thereby the size of the top redzone can be slightly reduced by the melt removal. We found indications that a contamination via the gas phase is partially or fully responsible for the remaining top redzone and corroborated this by analysis of an annealing experiment in the crystallization furnace.