Novel heteroleptic precursors for atomic layer deposition of TiO2

Two novel heteroleptic titanium precursors for the atomic layer deposition (ALD) of TiO2 were investigated, namely, titanium (N,N'-diisopropylacetamidinate)tris(isopropoxide) (Ti(OiPr)3(NiPr-Me-amd)) and titanium bis(dimethylamide)bis(isopropoxide) (Ti(NMe2)2(OiPr)2). Water was used as the oxygen source. These two precursors are liquid at room temperature and present good volatility, thermal stability and reactivity. The self-limiting ALD-growth mode was confirmed at 325 °C for both precursors. The titanium (N,N'-diisopropylacetamidinate)tri(isopropoxide)/water process showed an ALD window at 300–350 °C, and titanium bis(dimethylamide)bis(isopropoxide) exhibited an interestingly high growth rate of 0.75 Å/cycle at 325 °C. The films were crystallized to the anatase phase in the as-deposited state. X-ray photoelectron spectroscopy analysis demonstrated that the films were pure and close to the stoichiometric composition. The refractive indexes and absorption coefficient of the films were measured by spectroscopic ellipsometry.