Composition Dependence Of Electronic Structure And Optical Properties Of Hf1-Xsixoy Gate Dielectrics

Composition-dependent electronic structure and optical properties of Hf1-xSixOy (0.1 <= x <= 0.6) gate dielectrics on Si at 450 degrees C grown by UV-photo-induced chemical vapor deposition (UV-CVD) have been investigated via x-ray photoemission spectroscopy and spectroscopy ellipsometry (SE). By means of the chemical shifts in the Hf 4f, Si 2p, and O 1s spectra, the Hf-O-Si bondings in the as-deposited films have been confirmed. Analyses of composition-dependent band alignment of Hf1-xSixOy/Si gate stacks have shown that the valence band (VB) offset (Delta E-v) demonstrates little change; however, the values of conduction band offset (Delta E-c) increase with the increase in the silicon atomic composition, resulting from the increase in the separation between oxygen 2p orbital VB state and antibonding d states intermixed of Hf and Si. Analysis by SE, based on the Tauc-Lorentz model, has indicated that decreases in the optical dielectric constant and increase in band gap have been observed as a function of silicon contents. Changes in the complex dielectric functions and band gap E-g related to the silicon concentration in the films are discussed systematically. From the band offset and band gap viewpoint, these results suggest that Hf1-xSixOy films provide sufficient tunneling barriers for electrons and holes, making them promising candidates as alternative gate dielectrics.