A gradual annealing of amorphous sputtered indium tin oxide: Crystalline structure and electrical characteristics

Thin films of amorphous indium tin oxide were deposited by soft sputtering. The film was gradually annealed in air at temperatures from 110 °C to 150 °C. Its structural and electrical properties were monitored in order to get a better understanding of the annealing process. Firstly, carrier density decreases by oxygen intake. Crystallization speeds up at 150 °C, with a 2.5 D growth of crystallites. The preferred orientations come from sputtering induced seeds. Then, the carrier density increases again due to tin activation. Meanwhile, the carrier mobility is more damaged by the low temperature annealing in air than by a standard annealing in a reducing atmosphere. Thus, tin oxide segregation is suspected at grain boundaries.

► By annealing at 150 °C, film carrier density increases with the crystallinity level. ► By low temperature annealing in air, carrier density decreases due to oxygen uptake. ► Preferred orientations of annealed films come from sputtering induced seeds. ► Carrier mobility decreases heavily by air annealing. SnO2 segregation is suspected.