HfO 2 – SiO 2 interface in PVD coatings

Hafnium oxide presents a strong interest either for optical coatings or for microelectronic applications. An important parameter to control is its chemical interaction with silicon oxide, since those two materials are usually in direct contact in both applications: For optical coatings, silica is the low refractive index used to make interference filters [see M. R. Kozlowski, Thin Films for Optical Systems (Marcel Dekker, New York)], in microelectronics HfO 2 could be used as a gate insulator in metal-oxide semiconductor technology [B. H. Lee, Tech. Dig. Int. Electron Devices Meet. 99, 133]. One interesting characterization method of the created interface is infrared spectroscopy in the so-called multiple internal reflection (MIR) technique. Mono- and bilayers of HfO 2 and SiO 2 have been deposited on germanium substrates by e-beam evaporation and ion beam sputtering. MIR measurements made on those samples show that when HfO 2 is deposited on SiO 2 , parts of the Si–O–Si bonds are broken and Hf–O–Si bonds, representative of hafnium silicate ( HfSiO 4 ), are formed at the interface. Hafnium and silicon oxide have also been coevaporated in a reactive atmosphere to deposit the silicate and confirm the position of the Hf–O–Si bond. The results obtained by MIR are confirmed with x-ray photoelectron spectroscopy and transmission electron microscopy analysis.