Aluminum nitride (A1N) thin films were reactively deposited onto Al layers on negatively biased glass substrates by radio frequency magnetron sputtering at a target-to-substrate distance of 17 cm. The microstructures and morphology of the films grown at different bias voltages on the substrates were investigated. Typical thickness of the deposited film is 600 nm. The films were amorphous when no bias was applied to the substrates. Diffraction peak of AlN (0 0 2) direction was observed at bias voltages of - 180 and - 210 V. At a bias voltage of - 210 V, the (0 0 2) granular crystal with the maximum diameter of 80 mn was obtained. In addition to the AlN (0 0 2) direction, AIN (10 0) direction was observed when the bias voltage was increased to 240 and - 270 V The peak of (0 0 2) plane vanished at a bias voltage of - 320 V Moreover, the deposited AIN films have specular reflectance owning to the large target-to-substrate distance. The maximum roughness of the films was 47.2 +/- 5.0 nm at a bias voltage of - 2 10 V.