Low-temperature deposition of optical films by oxygen radical beam-assisted evaporation

Titanium and silicon oxides were deposited as optical films on glass substrates at low temperature (below 100°C) by oxygen radical beam-assisted evaporation (RBAE). Ti and Si were used as the starting material. Conventional reactive evaporation using neutral oxygen gas was compared with RBAE. The optical properties (refractive index n, and extinction coefficient k) and chemical structures of the deposited films were investigated. The radical beam source used in this study generated oxygen radicals with negligible ionic species. The films deposited by RBAE reached high oxidation states, compared with those deposited by conventional reactive evaporation. The n and k values of the films deposited by RBAE were almost constant over a wide range of Ti and Si evaporation rates. On the other hand, n and k values of the films deposited by conventional evaporation increased immediately with an increase in Ti and Si evaporation rates. An anti-reflective coating based on a multi-layer of TiO 2 and SiO 2 deposited by RBAE, which showed good performance in low reflectance and high transmittance, was demonstrated. It indicates that RBAE is an effective process for film deposition at low temperature.