Thermal activation of hydrogen for defect passivation in poly-Si based passivating contacts

Hydrogenation of poly-Si based passivating contacts (TOPCon) is an essential process to achieve a very high level of surface passivation, especially on textured surface. This contribution is dedicated to improve the understanding of the hydrogenation mechanism. We compare different hydrogen sources with regard to their ability to chemically passivate defects at the Si/SiOx interface and presumably in the doped poly-Si layer as well as their thermal stability in a low and high temperature range. To this end, hotplate annealing series were performed on textured n-type TOPCon structures and Al2O3/SiNx multi-layer stacks were exposed to fast-firing processes. Very distinct activation characteristics were detected. It was also observed that the Al2O3 capping layers enable a higher level of surface passivation and higher thermal stability compared to SiNx. When implemented in multi-layer stacks, Al2O3 acts as a hydrogen diffusion barrier und prevents effusion from the TOPCon structure that deteriorates the passivation quality irreversibly.