Feeding of liquid silicon for high performance multicrystalline silicon with increased ingot height and homogenized resistivity

Feeding of liquid silicon during the directional solidification process is a promising opportunity for cost reduction by increased throughput and improved material homogeneity due to constant resistivity over ingot height. In this work, a liquid feeding apparatus was developed for an industrial type directional solidification furnace. One n-type G2 sized High Performance multicrystalline ingot with liquid feeding of additional 14 kg of undoped silicon feedstock was crystallized. The resistivity was kept within a range of ±0.1 Ω cm of the target resistivity during the feeding sequence. A smaller mean grain area growth was observed during feeding, whereas the area fraction of recombination active dislocation structures was as low as in a reference ingot. Increased interstitial oxygen and substitutional carbon concentrations were measured for the ingot with liquid feeding. The measured mean bulk lifetime of 190 µs for passivated wafers in the feeding sequence can probably be increased by further pre-melting crucible improvements. For this laboratory experiment, energy reductions of 2% per wafer and time savings of 16% per wafer were realized.