Interdiffusion at TiO2/Ti, TiO2/Ti3Al and TiO2/TiAl interfaces studied in bilayer structures

Early-stage interfacial reactions were studied in three different heat-treated oxide/metal bilayers (the oxide is amorphous (a) TiO2 and the metal is crystalline (c) Ti, c-Ti3Al or amorphous a-TiAl) by means of Auger electron spectroscopy (AES) depth profiling. The oxide/metal bilayers were sputter deposited onto smooth silicon substrates, covered with a TiN or Al2O3 thin-film diffusion barrier. In order to prevent the supply of oxygen from the external atmosphere, selected samples were covered with an additional protective Si3N4 thin film. Reactions at the oxide/metal interfaces were induced by heating the samples in an argon atmosphere at a linear heating rate of 40degreesC min(-1) between room temperature and different final temperatures (350-700degreesC). The composition and microstructure of selected samples were investigated by XPS, x-ray diffraction (XRD) and transmission electron microscopy (TEM). Heating of the a-TiO2/c-Ti, a-TiO2/c-Ti3Al and a-TiO2/a-TiAl bilayers induced a decomposition of the a-TiO2 layers, in association with diffusion and solid solution formation of oxygen in the corresponding metallic layers. In the early stage of the reactions, the presence of Al in the metallic layers resulted in a lower solubility of oxygen compared with a pure Ti layer. The beginning of interdiffusion at the a-TiO2/c-Ti interface was observed at similar to400degreesC and at the other two interfaces at similar to550degreesC. The temperature-dependent effective diffusion coefficients were determined from the rate of increase of the interface width, as obtained in the oxygen depth profiles. The activation energies for oxygen diffusion from a-TiO2 into the c-Ti, c-Ti3Al and a-TiAl layers was found to be 1.5 eV (between 400 and 500degreesC) and 1.7 eV and 1.8 eV (between 550 and 650degreesC), respectively. Copyright (C) 2002 John Wiley Sons, Ltd.