Role of trace moisture in low temperature thermal ALD of titanium dioxide using tetrakis(dimethylamido) titanium (IV) and molecular oxygen

This study addresses the need for low temperature ALD of titania on organic substrates, which are thermally sensitive materials that are incompatible with ozone or plasma and too porous for practical use of water. To address these needs, tetrakis(dimethylamido) titanium (IV) was identified as the precursor for low temperature TiO2 ALD with biomaterial substrates of interest using molecular oxygen as the co-reactant. The ALD of TiO2 was performed between 90 °C and 150 °C using tetrakis(dimethylamido) titanium (IV) and oxygen. The resulting thin films were characterized in terms of thickness, optical properties, composition, and crystallinity using spectroscopic ellipsometry, x-ray reflectance, x-ray photoelectron spectroscopy, and x-ray diffraction, respectively. These studies show promising results for TiO2 deposition at low temperatures with growth rates comparable to ALD with other counterparts such as water and ozone. The results demonstrate the impact of trace ppm level moisture on the ALD process for TiO2 using TDMAT and molecular oxygen without excess moisture or strong co-reactants such as ozone or plasma, but giving growth rates similar to those of conventional co-reactants, opening the ALD process to more sensitive organic materials such as biomedical elastomers. From these experimental findings in comparison with prior ALD studies with similar reaction conditions, conclusions are drawn regarding the effect of trace moisture impurities on the TiO2 ALD process.