Back diffusion of iron impurity during silicon purification by vacuum directional solidification

• Back diffusion during Si purification by directional solidification is investigated.
• Affecting factors of iron impurity back diffusion are discussed.
• Back diffusion degree of iron in solidification process is calculated.
• Distribution of iron can be more accurately calculated or predicted.

A theoretical model for investigating the back diffusion of iron impurity during silicon purification by vacuum directional solidification is proposed in this paper. The back diffusion of iron impurity in directional solidification process can markedly reduce the purifying effect; thus, clarifying the back-diffusion behavior of iron impurity has great significance in silicon purification by directional solidification. Results show that the influence of back diffusion becomes more obvious with increased solidification proportion. At the end of solidification, the degree of back diffusion relative to Scheil equation calculation reaches nearly 200%. Experimental verification reveals that the calculation that considers back diffusion is more consistent with experimental results than when back diffusion is ignored. Thus, the distribution of iron impurity during silicon purification by directional solidification can be more accurately calculated or predicted when back-diffusion is considered in solidification.