Effect of processing conditions on the microstructure and electrical resistance of nanocrystalline ITO thin films made by laser ablation

Nanocrystalline indium tin oxide (ITO) thin films were deposited on Si/SiO2 substrates by laser ablation from a ceramic target with a composition of 0.9 In2O3. 0.1 SnO2. Samples were prepared in the pressure range from 10(-1) to 5mbar, either in-situ at 500 degrees C or at room temperature and heat-treated in air at 500 degrees C. X-ray diffraction results show that the films are not oriented, except the ones made at high temperature which exhibit strong (400) orientation. AFM pictures show that the grains are round shaped and the sizes are in the range between 50 and 200nm, except for films made in-situ at 10(-1)mbar which are elongated and faceted. For higher pressures the grains tend to be small and to form agglomerates. The porosity of the films increases with the deposition pressure and the thicknesses reach a maximum of 2.8 mu m at 1mbar for the films made at room temperature and of 1.2 mu m at 2mbar for the ones made in-situ; for higher pressures the growth rate drop drastically, as revealed from SEM observations of cross-sections. The electrical resistance increases with the deposition pressure due to the increase in porosity, changing from 3.3k Omega to 38.9M Omega for films deposited at room temperature and from 20 Omega to 265k Omega for the ones made in-situ.