Damp-heat degradation and repair of oxide-passivated silicon

SiO ₂-passivated Si degrades when exposed to a 'damp-heat' atmosphere of 85% relative humidity and 85 °C. We find the effective surface recombination velocity at the SiO ₂/Si interface of phosphorus-diffused (111) Si to increase from 2200 to 11 000 cm/s after 7 days of damp-heat exposure. This degradation is of concern to many high-efficiency solar cells, which are manufactured from SiO ₂-passivated Si with phosphorus-diffused (111) facets at the front surface, and which must withstand 1000 h of damp-heat exposure during reliability testing. Our experiments indicate that the damp-heat exposure causes (i) absorption of H ₂O into the SiO ₂, (ii) an increase in the concentration of H at the SiO ₂/Si interface, (iii) a latent source of degradation that continues after samples are returned to room conditions, and (iv) SiO ₂/Si interface damage that can be repaired by a short anneal at 300 °C in N ₂. The results of these experiments are discussed in relation to the various mechanisms that might underlie damp-heat degradation of SiO ₂/Si interfaces.