TiOx film formation process by reactive sputtering

TiOx thin films were prepared by the sputtering of Ti atoms from a Ti target in a discharge gas including Ar and O2. O2 partial pressure during the sputtering was measured as a function of O2 gas flow rate introduced into the sputtering chamber. The pressure was found to increase linearly with the flow rate except for a region related with the sputtering mode change. In order to interpret the pressure change, a simple model for metal thin film formation was modified and applied. Fundamental relations expressing time change of the number density of Ti atoms and O2 molecules on a substrate surface were derived. Two-dimensional (2D) motion of Ti atoms on the substrate was taken into account and 2D mean free path of those atoms was calculated. The collision frequency of Ti atoms with O2 molecules was then estimated and the rate of consumption (gettering) of O2 molecules was evaluated. It was found that the number density of Ti atoms on the substrate is one of the main factors determining the gettering effect. The observed change of the O2 partial pressure with its flow rate can well be interpreted by our model. Deposition rate of TiOx thin films was also measured as a function of O2 flow rate and the results were consistent with our gettering model.