Reactive magnetron deposition of transparent conductive films

Transparent conductive films of In 2O 3:SnO 2 were reactively sputter deposited using a d.c. planar magnetron cathode in the moving deposition mode. Deposition times of 1.25–6 min were used to coat soda-lime glass 1 ft 2 with films of optical thickness one-half of a wavelength ( λ = 5500 A ̊ ). The films had a higher transmittance and a lower sheet resistivity R s than those generally used for the small liquid crystal displays in watches or calculators. The as-deposited films were either a hard transparent oxide with a high R s or a soft opaque metal-rich material with a low R s. After sputtering, the films were annealed in air or in a reducing atmosphere at temperatures from 300 to 500°C; thus optical transmissions in excess of 90% (including glass substrates) and sheet resistivities below Ω/□ were obtained. An investigation of films deposited onto sapphire demonstrated that impurity diffusion from soda-lime glass substrates may lead to an anomalous dependence of R s on the annealing conditions. It was found that the type of film deposited, namely oxidized or metal rich, depended on the history of the target. The significance of this observation is discussed with reference to process reproducibility.