Thermal stability of alumina thin films containing γ-Al2O3 phase prepared by reactive magnetron sputtering

The paper reports on thermal stability of alumina thin films containing γ-Al2O3 phase and its conversion to a thermodynamically stable α-Al2O3 phase during a post-deposition equilibrium thermal annealing. The films were prepared by reactive magnetron sputtering and subsequently post-deposition annealing was carried out in air at temperatures ranging from 700 deg. C to 1150 deg. C and annealing times up to 5 h using a thermogravimetric system. The evolution of the structure was investigated by means of X-ray diffraction after cooling down of the films. It was found that (1) the nanocrystalline γ-Al2O3 phase in the films is thermally stable up to 1000 deg. C even after 5 h of annealing, (2) the nanocrystalline θ-Al2O3 phase was observed in a narrow time and temperature region at ≥1050 deg. C, and (3) annealing at 1100 deg. C for 2 h resulted in a dominance of the α-Al2O3 phase only in the films with a sufficient thickness.