Oxidation behavior of AlN films at high temperature under controlled atmosphere

Oxidation behavior of AlN films deposited on Si substrates by unbalanced magnetron sputtering was investigated over temperatures of 700–1200 °C in different atmospheres by analyzing changes in appearance and crystalline phases, as well as microstructures. The atmospheres contained air, nitrogen, and forming gas (N2/H2 = 9), which exhibited drastically different nitrogen/oxygen partial pressure ratios. Observed color changes in appearance were associated with oxidation of the nitride film, which was analyzed by exploring Gibbs free-energy changes at various temperatures and nitrogen/oxygen partial pressures. Different phases of oxidants including intermediate δ-Al2O3 and thermodynamically stable α-Al2O3 were discerned by X-ray diffraction. Oxidation of AlN and phase transformation in Al2O3 depended on not only the temperature but the nitrogen/oxygen partial pressures. Microstructures of both oxide phases could be resolved by micro-Raman spectroscopy.