TiCp*(OMe)₃ versus Ti(OMe)₄ in Atomic Layer Deposition of TiO₂ with Water—Ab Initio Modelling of Atomic Layer Deposition Surface Reactions

It is a common finding that titanocene-derived precursors do not yield TiO₂ films in ALD with water. For instance, ALD with Ti(OMe)₄ and water gives 0.5 Å/cycle, while TiCp*(OMe)₃ does not show any growth (Me = CH₃, Cp* = C₅(CH₃)₅). This is apparently in contradiction with the computed reactivity of the ligands: the energetics of hydrolysis of the gas-phase precursor indicate that TiCp*(OMe)₃ is more reactive to ligand elimination than Ti(OMe)₄. However such a model of precursor reactivity neglects surface reactions such as adsorption, diffusion and desorption, all of which can have an important effect on ALD growth rate. A more accurate model of the surface reaction is needed to find the reason for the different behaviours of Ti(OMe)₄ and TiCp*(OMe)₃ in the ALD process. The more realistic surface model is a TiO₂ slab that is periodic in three dimensions. These calculations reveal that TiCp*(OMe)₃ does not chemisorb in the usual way because of extreme crowding of the Ti centre by Cp* and that this prevents ALD growth.