Adsorption of titanium halides on nitride and oxide surfaces during atomic layer deposition: A DFT study

Abstract

Various processes based on atomic layer deposition (ALD) have been reported for growing Ti-based thin films such as TiN and TiO2. To improve the uniformity and conformity of thin films grown via ALD, fundamental understanding of the precursor-substrate surface reactions is required. Herein, we present a density functional theory (DFT) study of the initial nucleation process of some titanium halide precursors (TiCl4, TiBr4, and TiI4) on Si surfaces having -OH or -NH2 functional groups. We consider the most favorable adsorption site in the reaction between the precursor and functional group of the surface, based on the thermodynamics and kinetics of the reaction. Sequential dissociation reaction mechanisms of halide ligands were systematically investigated. The exothermicity of the dissociative adsorption was found to be in the order of: TiI4 > TiBr4 > TiCl4. In addition, the precursors were observed to be more exothermic and show higher reaction rate constant when adsorbed on the -OH-terminated surface than on the -NH2-terminated surface. These observations reveal the selectivity of deposition by surface functional groups.