Origins of silicon solar cell passivation by SiN x:H anneal

Abstract

The origin of silicon solar cell passivation by the post-deposition anneal of hydrogenated silicon nitride (SiN x :H) anti-reflection (AR) coatings is investigated. The diffusion of hydrogen (H) in SiN x :H is dominated by fast diffusion of molecular hydrogen (H 2) and ammonia (NH 3) and not by slow atomic diffusion through covalent bonding sites. An anneal of the SiN x :H layers leads therefore to a rapid H loss into the environment and not into the silicon bulk. Instead of bulk passivation by H atoms, the improvement of the electronic properties is due to an Si/SiN x :H-interface passivation caused by the formation of a few monolayers of silicon dioxide, which removes the bonding topology related stress at the interface. Secondary ion mass spectroscopy (SIMS) scans on various Si/SiN x :H stacks with mono- and polycrystalline substrates and remote and direct plasma enhanced chemical vapor deposited nitrides were carried out and showed strong interface accumulation of oxygen.