A comparison of SiO₂ thin-film UVCVD rates and mechanisms from SiH₄/O₂ and SiH₄/N₂O precursor gases by surface-sensitive infrared spectroscopy

With the help of a surface-sensitive multiple internal reflection technique, we have been able to measure photodeposition rates of silica with a low-pressure mercury lamp down to room temperature. At such a temperature, the deposition rates with O₂ or N₂O as the oxidizing precursor are equal. While the oxygen-induced photodeposition rate increases rapidly with temperature in the O₂ system, it saturates at a low value, for a temperature higher than 100°C in the N₂O system. In the first case the surface is covered with hydroxyl groups, adsorbed water, mono- and dihydride species. In the second case we reveal an almost water- and hydroxyl-free bulk and surface material, and the presence of few nitrogen-containing species. These features make the silica films prepared in this latter way an interesting material for various technological processes.