Effect of metal mode and oxide mode on unusual c-axis parallel oriented ZnO film growth on Al/glass substrate in a reactive magnetron sputtering of Zn target

(112̄0) oriented ZnO films where the c-axis is parallel to a substrate are good candidates for acoustic shear wave devices and sensors. Although ZnO film has tendency to develop c-axis normal (0001) orientation, unusual (112̄0) orientation appears in the situation that energetic oxygen ions generated from a target surface bombard the substrate during film growth in a reactive sputtering. The flux and the energy of these ions depend on the transition between the metal mode and the oxide mode on the Zn metal target surface. Here, the effect of the target surface condition on the development of unusual (112̄0) orientation is investigated. The higher crystalline (112̄0) orientation appeared in the oxide mode, probably because a large amount of energetic oxygen ions generated by the oxidized part of the Zn target.