Low energy ion assisted reactive electron beam evaporation of TiO2 and SiO2 films. Influence of deposition conditions on optical properties

Titanium dioxide and silicon dioxide films are extensively used in the fabrication of various optical and optoelectronic thin film devices. The refractive index and absorption coefficient of these films are strongly influenced by the deposition conditions and post deposition heat treatment. In the present investigation, TiO2 and SiO2 films have been depositied onto polished quartz substrates by reactive electron beam evaporation assisted by an oxygen discharge produced by a Heitmann ion source. The refractive index and absorption coefficient of the films as measured by transmission envelope technique and ellipsometry have been studied as a function of substrate temperature (30-250°C) partial oxygen pressure (6.6 × 10-5-2.6 × 10-4 mbar) deposition rates (60-200 A min-1) and oxygen discharge current (0-250 mA). Post deposition heat treatment of these films up to 250°C showed further decrease in the absorption coefficient of the films. The influence of the above mentioned parameters on the refractive index and absorption coefficient of the films has been discussed in detail. The laser induced damage in these films has been measured with a Nd-YAG (1060 nm) laser and correlated with the absorption of the films. The advantage of using ion beams in reducing absorption in films even at high substrate temperatures is highlighted.