Atomic Layer Deposition of Indium Tin Oxide Thin Films Using Nonhalogenated Precursors

This article describes a new atomic layer deposition (ALD) method for preparing indium tin oxide (ITO) thin films using nonhalogenated precursors. The indium oxide (In2O3) was deposited using alternating exposures to cyclopentadienyl indium (InCp) and ozone, and the tin oxide (SnO2) used alternating exposures to tetrakis(dimethylamino) tin (TDMASn) and hydrogen peroxide. By adjusting the relative number of In2O3 and SnO2 ALD cycles, we deposited ITO films with well-controlled SnO2 content. The ITO films were examined using four-point probe and Hall probe measurements, spectrophotometry, ellipsometry, scanning electron microscopy, atomic force microscopy, X-ray fluorescence, and X-ray diffraction. The lowest resistivity (3 × 10-4 Ωcm) and highest optical transparency (92%) were obtained for films containing 5% SnO2. The ITO films were slightly thinner and contained more SnO2 than expected on the basis of rule-of-mixtures predictions. In situ measurements revealed that these discrepancies result from an inhibition of the In2O3 growth following the SnO2 doping layers. This new ALD method is suitable for applying ITO layers on very high aspect ratio nanoporous membranes to be used in photovoltaic or spectroelectrochemical applications.