Magnetron sputtering of InGaZnO and ZnSnO amorphous oxide semiconductors

Amorphous oxide semiconductors (AOS) are exciting materials which combine optical transparency with high electron mobility. AOS are thus suitable for transparent electronics, or, on flexible substrates such as plastic foils, for wearable electronic devices. Although In-Ga-Zn-O is the best performing AOS so far, there is an interest in In-free alternatives. This is due to the concerns about limited In availability and its price. The alternative materials, however, normally require higher deposition temperatures.Here we report on magnetron sputtering of In-Ga-Zn-O (IGZO) and Zn-Sn-O (ZTO) with focus on the effect of deposition conditions on the film properties. IGZO films were deposited by RF sputtering from an oxide target while for ZTO, reactive sputtering from an alloy target was used. All films were deposited without substrate heating and characterized with respect to optical transparency, microstructure, electron mobility and resistivity. The best as-deposited IGZO films had resistivity of about 2∙10-2 ohm∙cm and electron mobility up to 10 cm2∙V-1∙s-1. The properties were very sensitive to the lateral position during deposition. Combination of simulations and experimental characterization was used to understand these effects. There is a strong influence of the composition and energy of the material flux towards the substrate. Reactive deposition process provides more freedom in selecting optimum growth conditions as demonstrated for ZTO films.