Effects of Ultraviolet Irradiation on the Properties of Evaporated Silicon Oxide Films

The optical and dielectric properties of silicon oxide films formed by reactive evaporation of silicon monoxide are investigated. The films are prepared at a deposition rate of 4 Å/sec in 1×10−4 Torr oxygen. The optical absorption of the films is found to increase with increasing substrate and source temperatures; these variations are consistent with previously reported chemisorbed oxygen and gas-phase oxidation film-growth mechanisms. Post-deposition exposure to uv radiation affects both the optical and dielectric properties of these films. Optical absorption in the 200 to 400-mμ wavelength region is essentially eliminated by 1 h irradiation for films deposited at 145°C or less; a residual absorption is evident for films prepared at a higher substrate temperature. The magnitude of the dielectric loss and relative dielectric constant, the variation of the dielectric loss and dielectric constant with frequency, and instabilities of the dielectric properties are decreased by the uv treatment. For example, at 10 Hz, the loss was decreased by an order of magnitude while the dielectric constant decreased by 12% for a typical experimental series. A model based on oxide defects, e.g., oxygen-ion vacancies and interstitial oxygen, is consistent with the experimental results.