Deposition of polycrystalline AlN thin films by coherent magnetron sputtering at temperatures < 80 degree C

AlN thin films were reactively deposited onto Al layers on negatively biased glass and Si substrates at temperatures < 80 degree C by coherent magnetron sputtering. The low temperature deposition of the films without substrate heating was achieved by increasing the target-to-substrate distance, and therefore the heating effect of the plasma is relieved. The microstructure and morphology of the films deposited at different bias voltage and target-to-substrate distance were investigated. The films are amorphous when the target is far from the substrate for a bias voltage up to -320 V. When the target-to-substrate distance is decreased to 17 cm a preferred (002) orientation of AlN films is observed at a bias voltage of -240 V. Additionally, the deposited films have specular reflectance and no voids can be observed. This low temperature technique can be used for applications in acoustic wave devices due to the improved homogeneity of the films and step coverage.