A Study of Thin Films of Indium Tin Oxide Using Spectroscopic Ellipsometry

ABSTRACTTransparent, electrically conducting, indium tin oxide films were prepared by r.f. reactive sputtering and electron beam evaporation. The refractive indices, n, and extinction coefficients, k, of the films together with their thicknesses were determined from spectroscopic (250nm–750nm) ellipsometry measurements. Elucidation of these parameters allowed an evaluation of the influence of the deposition conditions on the morphology, stoichionietry and microstructure of the films.Using effective medium theory the effect of the oxygen concentration on the void content of the sputtered films could be modelled. At concentrations greater than 15–20%, a saturation in the optical properties was observed as the films approached ideal stoichionietry. The refractive indices of both annealed and untreated evaporated films exhibited a decrease with increasing substrate temperature (up to 300°C) which is consistent with an increase in the microcrystallite size. Measurements on the annealed samples revealed a blue-shift in both n and k spectra as the oxygen pressure during evaporation was reduced to the background value of about 106 mbar. This, we attribute to the Burstein-Moss shift associated with the increased number of oxygen vacancies.Supplementary investigations using profilometry, atomic force microscopy and optical transmission spectroscopy confirm the reliability of the results obtained by this technique.