Microstructure and Electrical Properties of Multi-Crystalline Silicon Ingots Made in Silicon Nitride Crucibles

Silicon nitride is a more sustainable crucible material than silica, due to the larger potential for re-use. In this work, two directionally solidified high-performance multi-crystalline silicon (HPMC-Si) ingots have been made in silicon nitride crucibles. The oxygen distribution in the ingots is comparable to ingots grown in silica crucibles, while lower carbon levels are obtained in this study with a higher argon flow during the directional solidification process. The main source of oxygen contamination is the deoxidation of the coating during melting. The carbon levels in the ingots are affected by the dissolution of CO in the melt. Preliminary minority carrier lifetime measurements show a significant improvement upon gettering and hydrogenation of samples at different relative heights. Electron backscattered diffraction (EBSD) mappings of horizontal slabs reveal a decrease in the random grain boundaries over height. The grain structure and the lifetime improvements during processing are comparable to the high-performance ingots solidified in conventional crucibles. However, there is a potential for improvement due to the reduced contamination of light elements from the nitride crucible. The results also suggest that improvements can be achieved by adjusting the solidification parameters, i.e. the argon gas flow.