Response of sputtered titanium films on silicon to thermal oxidation

Rutile-TiO2 films have been fabricated by thermal oxidation of titanium films, which were deposited on silicon (100) wafers using dc magnetron sputtering technique. The thermal oxidation response of titanium films with varying thickness from 450 nm to 1140 nm was investigated in the oxidation temperature range of 600 °C to 900 °C, in terms of phase evolution, interface structure and film-substrate adhesion. It was found that the thickness of the titanium film significantly influenced its response to thermal oxidation treatment. Thinner films had better response to thermal oxidation at all investigated temperatures and times, such that an adherent rutile film could be produced on silicon. The critical thickness for achieving adherent oxidised films was approximately 570 nm. Film spallation was observed after oxidation of thicker films (i.e. 770 and 1140 nm). X-ray diffraction and electron probe microanalysis revealed that titanium silicides formed in the film-substrate interfacial region during the oxidation process. Microscratch tests showed that the adhesion of the film to the silicon substrate was deteriorated after thermal oxidation. The evolution of the rutile phase and the formation of brittle silicides at the interface were responsible for the observed reduction in adhesion strength.