Improving the stoichiometry of RF-sputtered amorphous alumina thin films by thermal annealing

High quality alumina thin films were deposited on glass substrate by reactive radio-frequency sputtering. The deposition process and rate were controlled by radio-frequency power and reactive gas (oxygen) flow rate. The relationships between O/Al ratio contents and the structural, electrical resistivity and optical parameters of the films were investigated. The O/Al of the films varied with change in oxygen flow ratio, power density and post deposition annealing. The structure and phase of the films were unaltered as the deposition parameters and post deposition annealing up to 573 K were varied. O/Al of 1.5 was obtained at oxygen flow ratio of 11 %, radio-frequency power of 250 W and post deposition annealing of 573 K. The sheet resistance of the films were all very high but the same within experimental uncertainties. The optical parameters (transmittance, refractive index and extinction coefficient) of the films varied considerably and depended on the films' stoichiometry.