Interdiffusion at TiO ₂ /Ti, TiO ₂ /Ti ₃ Al and TiO ₂ /TiAl interfaces studied in bilayer structures

Abstract

Abstract Early‐stage interfacial reactions were studied in three different heat‐treated oxide/metal bilayers (the oxide is amorphous (a) TiO 2 and the metal is crystalline (c) Ti, c‐Ti 3 Al 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 Al 2 O 3 thin‐film diffusion barrier. In order to prevent the supply of oxygen from the external atmosphere, selected samples were covered with an additional protective Si 3 N 4 thin film. Reactions at the oxide/metal interfaces were induced by heating the samples in an argon atmosphere at a linear heating rate of 40°C min −1 between room temperature and different final temperatures (350–700°C). The composition and microstructure of selected samples were investigated by XPS, x‐ray diffraction (XRD) and transmission electron microscopy (TEM). Heating of the a‐TiO 2 /c‐Ti, a‐TiO 2 /c‐Ti 3 Al and a‐TiO 2 /a‐TiAl bilayers induced a decomposition of the a‐TiO 2 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‐TiO 2 /c‐Ti interface was observed at ∼400°C and at the other two interfaces at ∼550°C. 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‐TiO 2 into the c‐Ti, c‐Ti 3 Al and a‐TiAl layers was found to be 1.5 eV (between 400 and 500°C) and 1.7 eV and 1.8 eV (between 550 and 650°C), respectively. Copyright © 2002 John Wiley & Sons, Ltd.