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.
Highlights
Considerable research efforts have been channeled on improving the integration density of semiconductors via device scaling, and attention has been focused on developing materials to overcome various problems induced by the miniaturization of metal-oxide-semiconductor field-effect transistors (MOSFETs) [1]
Interpolating thewhich free energy of molecular lone pairwas electrons of than the surface functional group element (O or N), affected the Ti–Cl adsorption at each temperature, we find that the temperatures at which the change in
atomic layer deposition (ALD) processes utilizing TiCl4 with H2O and NH3, respectively [43,44], which are mostly above the we realized that there could be multiple reaction pathways to remove the ligand for each surface model employed, and we classified the reaction pathways according to the adsorption sites and investigated the preferred structures from the thermodynamic and kinetic perspectives
Summary
Considerable research efforts have been channeled on improving the integration density of semiconductors via device scaling, and attention has been focused on developing materials to overcome various problems induced by the miniaturization of metal-oxide-semiconductor field-effect transistors (MOSFETs) [1]. TiCl4 has a higher vapor pressure than other halides, including fluorides, bromides, and iodides and exists in a liquid phase at room temperature [22] It is, a good precursor candidate for the CVD/ALD technique [23]. The initial adsorption reactions of titanium halide precursors, including TiCl4 , TiBr4 , and TiI4 , are analyzed on Si surfaces bearing –OH and –NH2 functional groups. To analyze this initial nucleation mechanism, quantum simulations based on density functional theory (DFT) were performed, and the calculation results obtained were evaluated based on thermodynamic and kinetic perspectives. Current study may contribute to further understanding on the experimental behaviors of these titanium halide molecules on the surfaces
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