AlN thin films have been grown on R((1-12) surface-cut)-Al₂O₃, SiO₂-glass and C((001) surface-cut)-Al₂O₃ substrates, by using a reactive-RF-sputter-deposition method. X-ray diffraction (XRD) shows that AlN film has (110) orientation of wurtzite crystal structure for R-Al₂O₃ and (001) orientation for SiO₂-glass and C-Al₂O₃ substrates. The film thickness was analyzed by Rutherford backscattering spectroscopy (RBS) and it appears that XRD intensity does not show a linear increase with the film thickness but a correlation with the stress, i.e., deviation of the lattice parameter of the film from that of bulk. The film composition and impurities have been analyzed by ion beam techniques. Effects of high-energy ion beams are briefly presented on atomic structure (whether stress relaxation occurs or not), surface morphology and optical properties.