Electrical and structural properties of indium tin oxide films deposited by reactive DC sputtering

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Abstract
High-quality indium tin oxide (ITO) films were deposited by reactive DC sputtering on glass and quartz substrates. Both pure H2O vapour and O2 were used as reactive sputtering atmospheres. The electrical parameters, free carrier concentration and carrier mobility as well as the resistivity of the ITO films were optically and contactlessly determined from IR reflection spectra by applying the Drude theory. Electrical properties of ITO films were examined as a function of deposition parameters, layer thickness and annealing procedures. The DC-H2O-sputtered ITO films show improved electrical properties because of a high free carrier concentration of N=6.2*1020 cm-3 immediately after deposition compared with a maximum of N=4*1020 cm-3 for DC-O2-sputtered ITO films occurring only after thermal annealing. Moreover, another annealing characteristic of DC-H2O-sputtered ITO films was detected because of their increasing resistivity during N2 annealing in contrast to DC-O2-sputtered ITO films. The low resistivity of ITO films, deposited by application of H2O as a reactive sputtering atmosphere, is due to an improvement in crystallinity and an increase in the donor level of Sn and O vacancies.