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

TLDR

High‑K dielectrics are increasingly considered as substitutes for SiO₂ in aggressively scaled silicon devices. A far‑UV spectroscopic ellipsometer operating up to 9 eV was developed and used to measure the optical properties of LaAlO₃, Y₂O₃‑stabilized HfO₂, GdScO₃, and SmScO₃, with the data interpreted via a universal electronic‑structure scheme from ab initio calculations. The measurements yielded optical dielectric functions and band‑gap energies for these materials, informing the selection of viable gate‑dielectric candidates and providing optical metrology for silicon‑substrate films.

Abstract

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.