The fundamental properties of SiN/sub x/:H that determine its passivating qualities

Structural properties of SiN/sub x/:H layers deposited with N/sub 2/+SiH/sub 4/ and NH/sub 3/+SiH/sub 4/ are related to the passivation properties. It is shown that the Si-N bond density in the layers is an important parameter for the passivation of mc-Si solar cells. The best bulk and thermally most stable surface passivation is observed for Si-N bond densities around 1.1/spl middot/10/sup 23/ cm/sup -3/. Lower bond densities result in a more open structure and will probably lead to H/sub 2/ formation during annealing. These H/sub 2/ molecules do not contribute to the passivation but will effuse from the layers into the ambient. Higher Si-N bond densities will result in too dense layers with a lower diffusivity of H and less bulk passivation during short anneals like contact firing. This explains why the bulk passivating properties of SiN/sup x/:H layers does not depend on the initial H concentration in those layers.