Effect of target-substrate distance on the growth and properties of rf-sputtered indium tin oxide films

Indium tin oxide films have been deposited by rf sputtering an oxide target (90% In2O3+10% SnO2). Transparent conducting films have been obtained on room-temperature substrates without any post-deposition annealing. The effects of target-substrate separation on the growth characteristics and film properties have been studied. The virtual-source formation of the sputtered neutrals in the gap between the target and substrate has been observed. The effect of sputtering parameters on the position of the virtual source has been studied. It has been observed that the films deposited onto substrates kept below and above the virtual source have different properties. The films on substrates kept above the virtual source have (222) preferred orientations, with a direct optical band gap of 3.7 eV, an electron effective mass of 0.51 m, and a figure of merit ∼14×10−3 Ω−1. The films on substrates below the virtual source have preferred orientations along (440) and (400), with a band gap of 3.5 eV, an effective mass of 0.2 m, and a higher figure of merit ∼40×10−3 Ω−1.