Pressure and angle of incidence effects in reactive planar magnetron sputtered ZnO layers

ZnO films have been prepared by rf sputtering a Zn target in a planar magnetron system with controlled Ar/O2 gas mixtures. The films were deposited on unheated glass substrates which were either stationary in front of the target or in constant motion. Both the system pressure and plasma impedance changed when an oxide layer formed on the target surface. This occurred at an oxygen flow rate which increased almost linearly with rf power; at 500 W, the required flow rate was 9 ml/min and the pressure increased from 0.1 to 1.2 Pa due to the reduced oxygen gettering. High resistance ZnO films were deposited at oxygen flow rates above this threshold value. The target self‐bias voltage increased by 30 V at this value; it is affected by both the system pressure and the power. The deposition rate increased linearly with power at approximately 0.03 (μm/min)/(W/cm2) which appears to be typical of sputtering from a ZnO layer or target. For continuous substrate motion, the average rate was approximately 7% of this val...