Transition metals in photovoltaic-grade ingot-cast multicrystalline silicon: Assessing the role of impurities in silicon nitride crucible lining material

We assess the contamination potential of crucibles used during directionally solidified multicrystalline silicon (mc-Si) ingot casting for cost-effective solar cell wafer production. Highly sensitive, synchrotron-based analytical microprobe techniques were used to study the distributions, sizes, elemental natures and chemical states of impurity-rich particles in α-Si3N4 powder representative of what is used to coat the inside of mc-Si ingot-casting crucibles, as well as the as-grown cast mc-Si material. Correlations between the elemental species, chemical states, particle sizes, relative concentrations and locations of impurities (e.g. Fe, Ti, Ca, Zn, Ni, Cu, N, C) concomitant in α-Si3N4 and as-grown mc-Si lead us to conclude that α-Si3N4 could be a significant source of contaminants during the ingot-casting mc-Si growth process.