Bulk defect generation during B-diffusion and oxidation of CZ wafers: Mechanism for degrading solar cell performance

We describe results of our experimental study to investigate the effect of B diffusion and drive-in/oxidation on minority carrier lifetime of the wafer. We have observed that B diffusion generates stacking faults that can be attributed to injection of Si interstitials into the wafer by formation of a boron rich layer at the wafer surface. These Si interstitials are also believed to enhance interactions between the native point defects and impurities (such as O, Fe) in the wafers during subsequent processing leading to the development of swirl patterns. Spatial variation of the lifetime degradation follows the point defect interactions and impurity segregation/precipitation. Lifetime can be partially recovered by Phosphorous (P) gettering. The overall effect on the cell performance due to Si interstitial generation, impurity/point defect interactions, and P-gettering is briefly discussed.