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 (In 2 O 3 ) was deposited using alternating exposures to cyclopentadienyl indium (InCp) and ozone, and the tin oxide (SnO 2 ) used alternating exposures to tetrakis(dimethylamino) tin (TDMASn) and hydrogen peroxide. By adjusting the relative number of In 2 O 3 and SnO 2 ALD cycles, we deposited ITO films with well-controlled SnO 2 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% SnO 2 . The ITO films were slightly thinner and contained more SnO 2 than expected on the basis of rule-of-mixtures predictions. In situ measurements revealed that these discrepancies result from an inhibition of the In 2 O 3 growth following the SnO 2 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.