HfO2-ZrO2 Doped Silica Thin Films by XPS

Silica thin films embedding ZrO2 and HfO2 were prepared by spin-coating on silica glass via a modified sol-gel processing. The novel synthetic route is based on the co-polymerization of two organically modified oxozirconium and oxohafnium clusters ~M4O2~OMc!12 with M 5 Zr, Hf and OMc 5 OC~O!-C~CH3!5CH2!! with ~methacryloxypropyl!trimethoxysilane ~MAPTMS!. The crystalline clusters, which are the precursors for the corresponding metal oxides ~MO2! were prepared via the sol-gel route by reacting zirconium or hafnium butoxide with methacrylic acid. The copolymerization of the cluster with previously prehydrolyzed methacrylate-functionalized siloxane, allows the anchoring of the oxoclusters to the forming silica network. Thin films were prepared starting from a THF ~tetrahydrofurane! solution with molar ratios Hf4O2~OMc!12 : Zr4O2~OMc!12:MAPTMS of 1:1:88. After deposition, the films were annealed 3 h at 800 °C in air to promote the decomposition of the hafnium and zirconium oxoclusters to give the corresponding HfO2 and ZrO2 oxides. The obtained HfO2-ZrO2-SiO2 films resulted transparent, homogeneous and displayed a very good adhesion to the substrate. The composition of the films was investigated by secondary ionization mass spectrometry ~SIMS! and x-ray photoelectron spectroscopy ~XPS!. The depth profiles evidenced a very homogenous distribution of both zirconium or hafnium species within the whole silica films and sharp film-substrate interfaces. As far as XPS analyses are concerned, the main XPS core-levels were analyzed for the annealed sample and the formation of hafnium and zirconium oxides was evidenced.