Influence of modified bottom insulation on the seeded directional solidification process for high-performance multi-crystalline silicon

Abstract

This study proposes two kinds of bottom insulation with a moveable insulation block, with either a narrower or large horizontal width, for use in an industrial-size seeded directional solidification (DS) furnace to produce high-performance multi-crystalline silicon ingot. A transient global model was established to study the effects of the modified configurations on the thermal field in the solidified silicon ingot during the DS process. The numerical results indicate that the shapes of the s-m and m-c interfaces remained relatively flat or slightly convex throughout the entire DS process when the narrower bottom insulation block design was used, and the highest thermal stress in the bottom corner areas of the ingots was obviously lower. To further verify the simulation results, ingot casting experiments and testing were carried out with the use of photoluminescence and minority lifetime mappings. The results show that the dislocation clusters exhibited a lower density in the modified designs. This phenomenon could be attributed to the uniform impurity and lower thermal stress distributions induced by the flat or slightly convex interface. Additionally, the corresponding average conversion efficiency is discussed.