Three-step mechanism of the water recombination reactions on SiO2/Si surface in the first stage of ZrO2 atomic layer deposition

The hydrolysis pathway reaction of the initial stage of Atomic Layer Deposition (ALD) of the high-k zirconium oxide on SiO2/Si(1 0 0)-(2 × 1) reconstructed surface is investigated using a hybrid density functional method. Mechanisms in the hydrolysis reaction of the chemisorbed complexes formed at the surface as a result of the interaction of zirconium tetrachloride (ZrCl4) as precursor with the model of SiO2 surface are proposed. The calculated reaction pathways address a three-step mechanism of the hydrolysis reaction. Each step describes the interaction of a single H2O molecule with the active complex of the surface and ends through the replacement of one chlorine atom in the metallic complex by an OH group. For typical ALD conditions, the results exhibit endothermic recombination reactions (overall enthalpy ΔH is +0.78 eV/particle) of all water-decomposed molecules. The end product, HCl, is carried out after each reaction step, but it remains hydrogen bonded at the surface (∼0.2 eV/product) in the absence of appropriate purge periods.