Origins of silicon solar cell passivation by SiN :H anneal

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.