Single-step directional solidification technology for solar grade polysilicon preparation

Abstract

We propose a modified process for the massive production of polysilicon by directional solidification (DS) technology designed to change the currently used “two-step DS process” into a “single-step DS process”, to enable the efficient production of polysilicon with lower energy and material consumption. The temperature distribution, solid-liquid (s/l) interface shapes, and thermal stresses during the DS process using the conventional process and the modified processes were studied by three-dimensional transient simulations. The simulation results about temperature, s/l interface, and thermal stresses were validated indirectly by corresponding experiments through the test for impurity segregation effect, minority carrier lifetime, and resistivity. It was found that the ingots produced by the modified process showed ideal solidification with uniform temperature distribution, slightly convex interface shapes, and lower thermal stresses, resulting in relatively higher carrier lifetimes and uniform distribution resistivity, which indicates that the single-step DS process is feasible to produce solar grade polysilicon.