Effect of thermal annealing on the optical properties and residual stress of TiO2 films produced by ion-assisted deposition

The effects of thermal annealing of titanium oxide films deposited by ion-beam assistance at annealing temperatures from 100 (degree)C to 300 (degree)C on the residual stress and optical properties of the films was investigated. The refractive indices and extinction coefficients increased gradually as the temperature was increased from 100 (degree)C to 200 (degree)C and then declined gradually as the temperature was increased further from 200 (degree)C to 300 (degree)C. The film lost oxygen and slowly generated lower suboxides as the annealing temperature was reduced below 200 (degree)C, as determined by x-ray photoelectron spectroscopy (XPS). As the annealing temperature increased above 200 (degree)C, the lower suboxides began to capture oxygen and form stable oxides. XPS measurements were made to verify both the binding energy associated with the Ti 2p line and the variation of the O 1s line. A Twyman-Green interferometer was employed for phase-shift interferometry to study the residual stress. The residual stress declined as the temperature was reduced from 100 (degree)C to 200 (degree)C because the lower suboxides reduced the stress in the film. Above 200 (degree)C, the film began to capture oxygen, so the residual stress rose. At 300 (degree)C, the film was no longer amorphous as the anatase was observed by x-ray diffraction.