Plasma influence on the properties and structure of indium tin oxide films produced by reactive middle frequency pulsed magnetron sputtering

Reactive pulsed magnetron sputtering was used to produce conductive and transparent tin-doped indium oxide (ITO) films with low thickness inhomogeneity. Due to the parallel operation of two magnetrons, the deposition system allows in situ investigations of the plasma influence on the film properties. The distribution of the film resistivity, refractive index, structure and stoichiometry along the substrate are presented and related to the spatial distribution of the plasma flow escaping the magnetrons, and the substrate temperature. A higher plasma flow likely causes a localized relaxation of the distorted In-O bonds in amorphous phase which prevails in ITO films prepared at unheated substrates. This leads to a decrease of the film resistivity due to free electrons density and mobility enhancement. The free electron density increase is caused likely by generation of oxygen vacancies. Deposition on a heated substrate (T_s / T_m = 0.3) leads to a change of the film growth mode due to enhanced surface diffusion of the adatoms which results in a textured low resistivity film. This also causes significant improvements of the homogeneity of the film properties that is important for ITO applications.