Impact of structural defect density on gettering of transition metal impurities during phosphorus emitter diffusion in multi-crystalline silicon solar cell processing

The impact of structural defect density on gettering of transition metal impurities during phosphorous emitter diffusion has been investigated using a pair of multi-crystalline silicon (mc-Si) wafers. Chromium (Cr) impurities incorporated during growth were identified by deep level transient spectroscopy (DLTS) and used to evaluate the gettering efficiency. The Cr impurity concentration in the low defect density region of mc-Si wafers was reduced from ~3.5 × 10¹³ cm⁻³ to ~1.7 × 10¹² cm⁻³ after phosphorous diffusion gettering (PDG), while for the high defect density region, there is no appreciable variation in the Cr concentration which only changed from ~3.0 to ~2.2 × 10¹² cm⁻³ following PDG. It was concluded that the gettering process is not effective for highly defective regions of mc-Si wafers due to the ineffective impurity release from structural defects during the PDG process.[Figure not available: see fulltext.]