A quantum chemical study of ZrO2 atomic layer deposition growth reactions on the SiO2 surface

Zirconium oxide (ZrO2) is one of the leading candidates to replace silicon oxide (SiO2) as the gate dielectric for future generation metal-oxide-semiconductor (MOS) based nanoelectronic devices. Experimental studies have shown that a 1–3 monolayer SiO2 film between the high permittivity metal oxide and the substrate silicon is needed to minimize electrical degradation. This study uses density functional theory (DFT) to investigate the initial growth reactions of ZrO2 on hydroxylated SiO2 by atomic layer deposition (ALD). The reactants investigated in this study are zirconium tetrachloride (ZrCl4) and water (H2O). Exchange reaction mechanisms for the two reaction half-cycles were investigated. For the first half-reaction, reaction of gaseous ZrCl4 with the hydroxylated SiO2 surface was studied. Upon adsorption, ZrCl4 forms a stable intermediate complex with the surface SiO2–OH∗ site, followed by formation of SiO2–O–Zr–Cl∗ surface sites and HCl. For the second half-reaction, reaction of H2O on SiO2–O–Zr–Cl∗ surface sites was investigated. The reaction pathway is analogous to that of the first half-reaction; water first forms a stable intermediate complex followed by evolution of HCl through combination of a Cl atom from the surface site and an H atom from H2O. The results reveal that the stable intermediate complexes formed in both half-reactions can lead to a slow film growth rate unless process parameters are adjusted to lower the stability of the complex. The energetics of the two half-reactions are similar to those of ZrO2 ALD on ZrO2 and as well as the energetics of ZrO2 ALD on hydroxylated silicon. The energetics of the growth reactions with two surface hydroxyl sites are also described.