On oxidation mechanism of Ti films in water vapour plasma

Abstract

Titanium oxide is widely used in industry for its good mechanical, electrical and optical properties. Physical vapour deposition is a method that enables us to obtain the layers with desirable properties. The aim of this research is to oxidize titanium using water vapour plasma immersion ion implantation (PIII) technology and to develop the understanding about the mechanism of oxygen transport in Ti film. Samples were characterized after treatment at different dissipated power in plasma levels and durations. All of them have been analyzed by nanoprofilometer, SEM (scanning electron microscopy), EDS (energy dispersive X – ray spectroscopy), AES (Auger electron spectroscopy), GDOES (glow discharge optical emission spectroscopy), XRD (X – ray diffraction). A deep penetration of oxygen was observed in plasma treated titanium films after theirs exposition during 5–60 min using AES analysis. XRD analysis reveals the formation of new phases: TiO2 and non – stoichiometric TiOx peaks were identified. Different O/Ti ratio values in the film areas affected by different intensities of plasma radiation have been registered by EDS. EDS results are in agreement with results of film resistivity analysis performed using four – point probe resistivity method. It is shown that the titanium oxidation rate strongly depends on the surface coverage by adsorbed water layers and RF power dissipated in plasma. Plasma radiation activates surface of titania, promotes its superwettability properties and drastically increases the rate of oxidation whereas hydroxyl (OH) radicals are the main oxidant. Furthermore, there are other processes which determine oxygen permeation and transportation mechanism during PIII of water vapour. Such processes are oxygen adsorption, trapping, type and structure of Ti film, presence of Tin+/oxygen vacancies, and etc.