Correlation between the density of TiO2 films and their properties

Stress, density and refractive index of approximate 100 nm thick titania films are determined for layers deposited on fused silica substrates by reactive evaporation (RE), reactive ion plating (IP), plasma impulse chemical vapour deposition (PICVD) and spin coating (SC). Relative densities (ϱfilmϱana) vary between 0.7 and 1.0 with respect to the crystal phase of anatase (ϱana = 3.84 g cm−3). The refractive index depends linearly on density. Film stress is tensile at low densities and compressive for layers with densities of the order of anatase. A strong correlation between stress and density is found to be independent from the deposition conditions and the crystal structure of the as-deposited films. The phase transition from amorphous to anatase caused by annealing induces an increase in stress. The film density is correlated to the crystallization temperature, the size of stress increase during crystallization and the grain size.