Analysis of relevant plasma parameters for ZnO:Al film deposition based on data from reactive and non-reactive DC magnetron sputtering

ZnO:Al (ZAO) films were prepared by reactive DC/DC dual magnetron sputtering from metallic Zn:Al targets and by non-reactive DC magnetron sputtering from ceramic ZnO:Al2O3 targets. The origin of the high resistivity shown by the films at the substrate position facing the erosion area of the target was investigated. By comparison of both sputter modes it could be shown that a nonuniformity in oxygen distribution cannot be its reason. Ion energy distributions measured with an energy selective mass spectrometer system revealed that differences in particle bombardement energies are mainly responsible for the spatial distribution of ZAO film properties. Significant variations in plasma composition between both sputter modes were found: reactive DC sputtering from metallic targets requires at least one order of magnitude more oxygen to produce ZAO films with equally high transmittance and low resistivity. This could be the reason for the differences in the spatial distributions of ZAO film properties DC sputter deposited from ceramic and metallic targets.