Evidence for a transitory composition pattern in the early stages of the photochemical deposition of silica films on semiconductors

We have studied the early stages of the photodeposition of SiO₂ on semiconductors from silane-oxygen gaseous mixtures under UV irradiation. For film thicknesses below 100 Å, the films exhibit a specific oxygen-deficient composition which become stoichiometric if deposition lasts longer, producing SiO₂ films with a homogeneous composition throughout the whole dielectric layer. It is shown that the transitory early deposition regime is structurally sensitive to the nature of the substrate. Cathodoluminescence is used to show that the surface carrier recombination properties are altered mostly during this singular early stage of photodeposition.