Synthesis and characterization of heteroleptic titanium MOCVD precursors for TiO₂ thin films

Heteroleptic titanium alkoxides with three different ligands, i.e., [Ti(OⁱPr)(X)(Y)] (X = tridentate, Y = bidentate ligands), were synthesized to find efficient metal organic chemical vapor deposition (MOCVD) precursors for TiO₂ thin films. Acetylacetone (acacH) or 2,2,6,6-tetramethyl-3,5-heptanedione (thdH) was employed as a bidentate ligand, while N-methyldiethanolamine (MDEA) was employed as a tridentate ligand. It was expected that the oxygen and moisture susceptibility of titanium alkoxides, as well as their tendency to form oligomers, would be greatly reduced by placing multidentate and bulky ligands around the center Ti atom. The synthesized heteroleptic titanium alkoxides were characterized both physicochemically and crystallographically, and their thermal behaviors were also investigated. [Ti(OⁱPr)(MDEA)(thd)] was found to be monomeric and stable against moisture; it also showed good volatility in the temperature window between volatilization and decomposition. This material was used as a single-source precursor during MOCVD to generate TiO₂ thin films on silicon wafers. The high thermal stability of [Ti(OⁱPr)(MDEA)(thd)] enabled the fabrication of TiO₂ films over a wide temperature range, with steady growth rates between 500 and 800 °C.