Low temperature deposition of ITO thin films by ion beam sputtering

An ion beam sputtering system was used for the deposition of indium-tin-oxide (ITO) films at low temperatures (below 200 °C). The electrical and optical properties and the microstructure were highly dependent on the growth temperature, the oxygen partial pressure and the ion beam energy. A reasonable resistivity (3.5×10^-4 Ωcm) was measured in the films deposited by Ar ion sputtering at as low as 50 °C. In the films by Ar ion sputtering, the lowest resistivity was 1.5×10^-4 Ωcm at 100 °C. Oxygen addition to the sputtering gas increased the resistivity, especially at low substrate temperatures. The addition of oxygen to the sputtering gas changed the microstructure from `domain' (sub-grain) structure at 100 °C to `grain' structure. The oxygen addition induced the change in O/In ratios. The film composition also depended on the ion beam energy. The optical transmittance higher than 80% in the visible range was measured in the films deposited at above 100 °C. The optical band gap calculated from the transmittance spectra was approximately 4.2 eV.