Formation and oxidation properties of (Ti_1-xAl_x)N thin films prepared by dc reactive sputtering

We prepared (Ti_1-xAl_x)N thin films by dc reactive sputtering using alloy targets and investigated their oxidation properties. The oxidation rate of the (Ti_1-xAl_x)N film decreases with increasing aluminum content because Al₂O₃, with a low oxygen diffusion coefficient, is segregated at the film surface. In particular, the phase separation into a double layer of Al₂O₃ and TiO₂ is more noticeable at high temperature. On the other hand, at an initial stage of oxidation, a mixed oxide of titanium and aluminum (≫5 nm thick) is formed after oxidation at 550 °C for 1 min. This mixed-oxide formation is a result of insufficient growth of the Al₂O₃ layer, which causes fast oxygen diffusion and hence high oxidation rate. We thus conclude that (Ti_1-xAl_x)N is difficult to use as a barrier metal for metal-insulator-metal capacitors as long as the oxidation resistance is based on the growth of a protective Al₂O₃ layer on the film surface. © 2002 American Vacuum Society.