High rate deposition of transparent conducting films by modified reactive planar magnetron sputtering of Cd2Sn alloy

Abstract

A Cd2Sn alloy planar magnetron target has been dc sputtered in Ar/O2 mixtures. The variation of both sputtering pressure and discharge impedance indicated the formation of an oxide layer on the target surface at a critical oxygen flow, f2C, and its removal when the flow rate was reduced to f2D. For an average power of 375 W, the pressure increase at f2C was 0.4 Pa and the decrease at f2D was 0.16 Pa; for f2D<f2<f2C, the value of p in the presence of the oxide layer was 0.2 Pa lower than the value with the discharge off. For f2?f2C the film resistivity, ρ, and transparency, T, both increased with the ratio of oxygen flow to deposition rate of metal but the changes were too rapid for good reproducibility; T increased from zero to 80% with a 10% change in f2. The magnetron system was modified to increase the oxidation rate at the substrate relative to the target both by a geometric arrangement of slits and by application of an auxiliary rf discharge. The film properties were controlled by varying both the dc power to the target and the rf power. For a fixed dc voltage, T increased from 25% to 85% as the rf power to the substrate increased from 0 to 100 W. Transparent films with ρ as low as 4.4×10−4 Ωcm were obtained under optimum conditions without any heat treatment.