Enhanced Phosphorus Gettering of Impurities in Multicrystalline Silicon at Low Temperature

We demonstrate the enhancements of phosphorus (P) gettering efficiency to remove impurities in multicrystalline silicon (mc-Si) using multiple cycles of annealing and cooling technique at low temperature. The gettering effect was evaluated by photoluminescence (PL) imaging and microwave photoconductance decay (micro-PCD) measurement. Optimal low temperature annealing was pursued to suppress the defects formation during annealing. Multiple cycles of annealing and cooling technique was utilized to enhance the P gettering efficiency by collecting the dissolved impurities at P-diffused layer. The results show that the proposed annealing technique gives a significantly greater enhancement of P gettering than continuous annealing, particularly in regions of low defect density. This could possibly be explained by the increased collections of dissolved impurities both of remaining impurity atoms and frozen precipitates. The best gettering parameter was achieved at 400 °C for 35 min of annealing time. These results further confirmed the benefit of P gettering using multiple cycles of annealing and cooling technique in order to improve the electrical properties and yield of mc-Si for solar cells.