Dielectric functions and optical bandgaps of high-$K$ dielectrics for metal-oxide-semiconductor field-effect transistors by far ultraviolet spectroscopic ellipsometry

A far ultraviolet (UV) spectroscopic ellipsometer system working up to 9 eV has been developed, and applied to characterize high-K-dielectric materials. These materials have been gaining greater attention as possible substitutes for $SiO2$ as gate dielectrics in aggressively scaled silicon devices. The optical properties of four representative high-K bulk crystalline dielectrics, $LaAlO3,$ $Y2O3$-stabilized $HfO2$ $(Y2O3)0.15–(HfO2)0.85,$ $GdScO3,$ and $SmScO3,$ were investigated with far UV spectroscopic ellipsometry and visible-near UV optical transmission measurements. Optical dielectric functions and optical band gap energies for these materials are obtained from these studies. The spectroscopic data have been interpreted in terms of a universal electronic structure energy scheme developed form ab initio quantum chemical calculations. The spectroscopic data and results provide information that is needed to select viable alternative dielectric candidate materials with adequate band gaps, and conduction and valence band offset energies for this application, and additionally to provide an optical metrology for gate dielectric films on silicon substrates.