Molecular dynamics of TTIP and Ti(OCH3)4 reaction with H2O in thermal ALD–TiO2 Processes: A DFT study

The reaction mechanisms between Titanium(IV) isopropoxide (TTIP), Titanium(IV) methoxide [Ti(OCH₃)₄] as titanium precursors and water as oxygen agent respectively, were investigated. Atomic layer deposition (ALD)–TiO₂ thin film deposition process was assumed focusing on their molecular dynamics through interaction with hydroxyl molecule and titanium organic bonds. Based on the computational results obtained by performing the density functional theory (DFT) calculations, the sequence of bonds formation and interaction in these precursor molecules during their reaction with water align with the adsorption mechanism on the Si(100) surface. The differences in the relative energy at each stage of the reaction allow their comparison in terms of the reaction rate and process temperature. When interacted with the H₂O molecule, the ligands of TTIP and Ti(OCH₃)₄ molecules dissociate with average activation barriers of 15.9 and 14.5 kcal/mol, respectively, indicating that Ti(OCH₃)₄ can undergo decomposition at lower temperatures compared to TTIP. This observation aligns with the adsorption behavior of TTIP and Ti(OCH₃)₄ molecules on hydroxylated Si(100) surfaces, which exhibit activation barriers of 13.4 and 11.5 kcal/mol, respectively. These findings support the hypothesis that precursor molecules with lower decomposition barriers tend to adsorb more readily onto substrate surfaces and generally require lower process temperatures. These insights enabled us to predict the adsorption mechanisms of these titanium precursors based on their interactions with water molecules. Based on molecular behavior, it should provide a framework for the reaction mechanisms of various precursors on different substrate surfaces for producing a broad range of ALD metal oxide thin films.