Characterization of indium tin oxide (ITO) thin films prepared by a sol-gel spin coating process

Indium tin oxide (ITO) thin films were prepared by a sol gel spin coating method, fired, and then annealed in the temperature range of 450-600 degrees. The XRD patterns of the thin films indicated the main peak of the (2 2 2) plane and showed a higher degree of crystallinity with an increase in the annealing temperature. Upon annealing the films at 500 and 600 degrees, two binding energy levels of Sn4+ ion of 486.9 eV and 486.6 eV, respectively, were measured in the XPS spectra. The ITO film that was annealed at 600 degrees contained two oxidation states of Sn, Sn2+ and Sn4+, and it had a higher sheet resistance based on a rather low doping concentration of Sn4+. The film that was annealed at 500 degrees and subsequently treated with 0.1 N HCl solution for 40 s showed a sheet resistance of 225 Omega/square. The surface treatment by the acidic solution diminished the RMS (root mean square) roughness value and the residual carbon content (XPS peak intensity of carbon) of the ITO films. It seems that the acid-cleaning of the ITO thin films led to a decrease of the surface roughness and sheet resistance. (C) 2010 Elsevier Ltd and Techna Group S.r.l. All rights reserved.