Phase control of Al2O3 thin films grown at low temperatures

Low-temperature growth (500°C) of alpha-Al2O3 thin films by reactive magnetron sputtering was achieved for the first time. The films were grown onto Cr2O3 nucleation layers and the effects of the total and O2 partial pressures were investigated. At 0.33 Pa total pressure and >16 mPa O2 partial pressure alpha-Al2O3 films formed, while at lower O2 pressure or higher total pressure (0.67 Pa), only gamma phase was detected in the films (which were all stoichiometric). Based on these results we suggest that alpha phase formation was promoted by a high energetic bombardment of the growth surface. This implies that the phase content of Al2O3 films can be controlled by controlling the energy of the depositing species. The effect of residual H2O (approx. 10(-4) Pa) on the films was also studied, showing no change in phase content and no incorporated H (< 0.1%). Overall, these results are of fundamental importance in the further development of low-temperature Al2O3 growth processes.