Zirconia grown by ultraviolet ozone oxidation on germanium (100) substrates

Growth of zirconia $({\mathrm{ZrO}}_2)$ -based gate dielectrics on germanium (Ge) substrates by oxidation using activated oxygen species produced by ultraviolet radiation (UV/ozone) is reported here. In this technique, a thin layer of zirconium (Zr) metal (10–30 Å) is deposited by physical vapor deposition on Ge and subsequently oxidized in reactive oxygen. X-ray photoelectron spectroscopy (XPS) analysis indicates complete oxidation of the Zr metal. High resolution transmission electron microscopy (TEM) of UV-ozone oxidized ${\mathrm{ZrO}}_2$ on Ge indicates a sharp interface between the oxide and the substrate. However, conventional TEM is not well suited for identifying a Ge oxide layer in this system due to the closeness in atomic number of Zr and Ge. XPS spectra suggest the presence of a substoichiometric Ge oxide phase at the ${\mathrm{ZrO}}_2/\mathrm{Ge}$ interface. Depth profiling using angle-resolved XPS was performed on ${\mathrm{ZrO}}_2/\mathrm{Ge}$ gate stacks of varying oxide thickness. The results indicate that the amount of Ge oxide is dependent upon the ${\mathrm{ZrO}}_2$ overlayer thickness, suggesting that the interfacial layer can be controlled by the oxidation conditions.