Physical and Electrical Properties of Yttrium Silicate Thin Films

Abstract

This article reports on the physical and electrical properties of yttrium silicate, which is a possible high-k replacement for the SiO₂ gate dielectric in CMOS devices. The yttrium silicate (Y-O-Si) films are formed by sputtering yttrium onto clean silicon, annealing in vacuum to form yttrium silicide and then oxidizing in N₂O to form the silicate. Shifts in the Y 3d, Si 2p and O 1s photoelectron spectra with respect to Y₂O₃ and SiO₂ indicate that the films are fully oxidized yttrium silicate. FTIR results that reveal a Si-O stretching mode at 950 cm⁻¹ and Y-O stretching modes in the far-IR are consistent with XPS. XPS and FTIR results are in accordance with the donation of electron density from the yttrium to the Si-O bond in the silicate. The yttrium silicate films contain a fixed charge density of ∼9×10¹⁰ cm⁻² negative charges as calculated from measured C-V behavior. The properties of ultra-thin yttrium silicate films with an equivalent silicon dioxide thickness (electrical) of ∼1.0 nm will be discussed elsewhere.