Water Vapor-Plasma-Enhanced Oxidation of Thin Titanium Films

It is shown that the water vapor plasma processing offers modified Ti oxidation thermodynamics and kinetics over conventional, thermal oxidation. The 0.3-0.6 μm thick Ti films were sputter-deposited on silicon substrates and subsequently treated with low-pressure water vapor plasma at room temperature under continuous injection of water cloud vapor into the vacuum chamber from the heated water container. The changes of microstructure, phase composition, elemental composition and surface morphology upon the RF-power dissipated in plasma and treatment duration were investigated. We conclude that oxygen diffusion is enhanced in the presence of water vapor plasma, and deduce that fast $H^+$ transients because of their high mobility may be responsible for oxygen diffusion enhancement. This phenomenon can be explained as the result of two coexisting and competing reactions of oxidation and reduction on the surface. The different plasma reduction/oxidation state on the surface can be maintained by coordinated adjustment of an intensity of plasma radiation. Analysis of the experimental results is used to obtain important insights into the behavior of water molecules adsorbed on the oxidized titanium surfaces exposed to water vapor plasma at room temperature.