Influence of hydrogen addition and gas pressure on nitride layer formation on microcrystalline silicon thin films by a hot-wire chemical vapor method using nitrogen gas

Silicon nitride is employed for insulating layers, surface passivation layers and antireflection coatings. In this paper, we report on the influence of the addition of H2 gas to N2 gas and the total gas pressure on the nitride layer formation on a hydrogenated microcrystalline silicon (μc-Si:H) film surface region. Following deposition of the μc-Si:H thin films, a post-deposition treatment was carried out using a hot-wire chemical vapor technique, in a mixture of N2/H2 or in a N2 atmosphere, at varying H2 gas flow rates and total gas pressures, to form a nitride layer in the film surface region. As the H2 gas flow rate, F(H2), was increased from 2 to 10 sccm, at a N2 gas flow rate, F(N2), of 20 sccm, the surface nitridation was dramatically enhanced. Conversely, the degree of surface nitridation remained virtually unchanged with a F(H2) of 10 - 15 sccm and the surface nitridation scarcely took place at F(H2) of 20 sccm. The surface nitridation occurred to some extent at 0.1 Torr (with F(N2) = 20 and F(H2) = 10 sccm) but was dramatically enhanced as the gas pressure was increased from 0.1 to 1.0 Torr. There was a reduction in the densities of both the N and Si atoms as the gas pressure was increased from 1.0 to 6.0 Torr, however, the density of the N atoms on the subsurface region of the films (at a depth of 20 nm from the surface) increased with increasing gas pressure. These findings show the breakdown of the Si network structure by high density H radicals and the diffusion of more N atoms into the deeper region of the films.