Optimization of process parameters for sputtering of ceramic ZnO:Al2O3 targets for a-Si:H/µc-Si:H solar cells

Aluminum doped ZnO layers with a thickness of 800 nm were deposited dynamically by d.c. magnetron sputtering from a ceramic planar ZnO:Al2O3 target (1 wt.%). A wide range of process parameters, namely oxygen partial pressure, total pressure and power, was covered, while temperature was held constant at 300 °C. Visual absorption in the range of 2.3-4.7% and resistivities between 380 and 2150 µ ohm cm were obtained. In addition static imprints were performed to reveal the dependence of layer properties on target erosion. It was shown, that films deposited from targets with a race track deeper than 1.8 mm had very stable etching morphologies as well as optical and electrical properties in the range of the observed process parameters. In contrast, a new target yields very different etching structures and an increased resistivity.