About the formation and avoidance of C and N related precipitates during directional solidification of multi-crystalline silicon from contaminated feedstock

Multi-crystalline silicon ingots with a diameter of 6 cm and a height of 4–5 cm were directionally solidified in a laboratory scale crystal growth facility within a Si3N4-coated fused silica crucible with a growth rate of 1 cm/h for two different conditions of convective transport in the melt. The feedstock quality was varied from “pure” (electronic grade) to highly carbon-contaminated and highly nitrogen-contaminated. It will be demonstrated that under certain convective process conditions even for a highly contaminated feedstock (C and N) a mc silicon ingot can be grown which has an axially and radially homogenous carbon and nitrogen concentration in the range 3–4×1017 C-atoms/cm3 and 2–4×1015 N-atoms/cm3, respectively, and is free of SiC- and Si3N4-precipitates in the bulk.