Formation and distribution of silicon carbide (SiC) precipitates in industrial directional solidification of mc-Si ingots

Silicon carbide inclusions in multicrystalline (polycrystalline) silicon ingots affect the cutting process and quality of silicon wafers. The higher density of SiC inclusions relative to the silicon melt suggests that they should sink, but inclusions were observed at the top, middle and bottom of industrial ingots. More inclusions were observed at the top relative to the middle and bottom of the ingot. Small SiC inclusions were found at the bottom and reticular SiC inclusions at the top of the ingot, suggesting that inclusion growth may occur during growth of the ingot. A mechanism to explain the formation and distribution of SiC in industrial silicon directionally solidified ingots, based on the thermodynamics of SiC, is proposed together with strategies to reduce carbon contamination and improve ingot quality.