Polycrystalline aluminum nitride films were deposited by reactive radio frequency magnetron sputtering on silicon and molybdenum substrates without substrate heating. Surface and microstructure properties were investigated by atomic force microscopy and x-ray diffraction. X-ray photoelectron spectroscopy was used to study the composition of the surface. Their optical properties were studied by spectroscopic ellipsometry in the 430-850 nm wavelength range and modeling was carried out. The optical properties so obtained were correlated with the AlN films' structure and crystalline quality.