Anodization of titanium in radio frequency oxygen discharge — Microstructure, kinetics & transport mechanism

Plasma anodization in oxygen discharges is a prominent technique in semiconductor processing, allowing nearly defect-free oxidation at low temperatures. Here we apply inductively coupled radio frequency oxygen plasma anodization to titanium and study the effect of temperature and dc bias potential on the oxide film morphology. To achieve a detailed understanding of the growth process, the oxide crystal phase is characterized by Raman spectroscopy and the orientation between the oxide film and the substrate is determined by TEM. The constant voltage oxidation kinetics is modelled and growth experiments with inert markers allow to identify the ionic species controlling the growth rate. Plasma anodization experiments in combination with SIMS depth profiling of the interface region add to these experiments and prove that oxygen is the mobile species in the titania layer. The applied kinetic model allowed the determination of the activation energy for ionic transport with values of 1.31eV at 200°C and 1.58eV at 400°C and 550°C. As oxygen ion transport is likely responsible for film growth, the observed surface morphologies were most likely formed by oxygen ion sputtering or result from initial nucleation processes.