Improvement in chemical-vapor-deposited-SiO₂ film properties by annealing with UV-light-excited ozone

Ultraviolet-enhanced, highly concentrated (>90vol%) ozone gas annealing was carried out at 200 °C to fabricate as-deposited tetraethoxysilane chemical vapor deposited SiO2 film (TEOS-CVD films) applicable as a gate dielectric material for thin-film transistors. As a result of this annealing, the leakage current density, fixed charge density, and dielectric constant of the films decreased to those of thermally grown silicon oxide. The relative dielectric constant, for example, was reduced from 5.4 to 4.0. The films' resistance to wet-etching solution was also improved, particularly within the region located 3-5 nm from the films' surface. In the region, the reduction in the amount of the excess positive charges of Si and the increase in the density of an ideal Si-O bonding network were confirmed from X-ray photoelectron spectroscopy measurements. These results suggest that oxygen atoms are incorporated into the film, while impurities contained in the film such as OH are out gassed by the diffusion of oxygen atoms generated from the photo dissociation of ozone in the gas phase. The annealing effects with and without oxygen atom supply were compared and the mechanism of the annealing is discussed.