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AlN films were deposited by reactive magnetron sputtering with a roof-shaped Al target and conventional planar target. The c-axis orientation and the grain growth of AlN films were improved and the defects in the film were decreased, when the ion flux bombarding the film decreased. This trend was confirmed by depositing AlN films under various N2 gas pressures or external magnetic fields. These data indicate that there remains a considerable influence of ion bombardment in conventional planar magnetron sputtering, but the use of a rooftype target is effective for decreasing the exposure of the film to plasma as a result of a decrease in ion bombardment.

AlN films were prepared in N2 and N2/Ar gas by the alternating DC sputtering method wherein two Al targets facing each other were sputtered alternately, and the mechanism of film damage in AlN film preparation was investigated. When the gas pressure was lower than 3 mTorr, the crystalline orientation of the film inclined slightly toward the direction of incidence of depositing atoms. In this system, the influence of plasma exposure on the film properties was decreased. This was due to the decrease of electron flow into the substrate. Degradation of the c-axis orientation was ascribed to both the tilt of the growth direction of the (00·2) plane at low gas pressures and film bombardment by positive ions with energies above 60 eV.

In AlN films prepared by the facing target system, a decrease in degree of c-axis orientation, film coloring and film cracking or peeling from the substrate were observed. This film degradation is thought to be related to insulative films in general. In order to clarify how these phenomena are induced, we prepared samples under various sputtering conditions; i.e., by changing target holders, placing a ground mesh in front of the substrate and using a positively biased electrode. It is confirmed that plasma exposure severely influences c-axis orientation of AlN films. To decrease this influence, it is important that electrons flow adequately into the anode.