Impact and origin of the oxide-interface traps in Al/Yb2O3/n-Si/Al on the electrical characteristics

Abstract

This study presents comprehensive results on the changes of the crystal properties, surface morphology, chemical composition and bonding structures based on X-ray photoelectron spectroscopy (XPS) at different depths of the Yb2O3/Si as depending on post-deposition annealing (PDA) temperature. It also includes a detailed examination of the structural properties and the electrical characteristics of the Yb2O3 MOS capacitors. 125 nm-thick Yb2O3 thin films were deposited on n-Si by RF magnetron sputtering system and the Yb2O3/Si structures were annealed at 200 degrees C, 400 degrees C, 600 degrees C, 800 degrees C under nitrogen ambient. The largest grain size was obtained to be 17.3 nm from the sample annealed at 400 degrees C. The lowest roughness root-mean-square (R-q) value was measured as 0.464 nm in the Yb2O3 film annealed at 200 degrees C. Yb 4 d and O 1s spectra shifted to higher binding energies at Yb2O3/Si interface due to the approaching Si with high electronegativity. The peaks assigned to 2+ oxidation states were observed intensely at 400 degrees C and above due to the conversion of Yb3+-> Yb2+. The intensity of the bonded oxygen species in O 1s spectra measured at surface decreased with increasing annealing temperature, which may cause decreasing in the dielectric constant value. The Yb-O bond was mostly observed within the film, while Si-rich (positively charged interface traps) or Yb-rich (negatively charged interface traps) silicate layers (Yb-Si-O) were formed at the interface depending on the PDA temperature. It has been determined that the thickness of the silicate-like layer increases with PDA temperature, resulting in decreasing dielectric constant. The interface state density (N-ir) decreased with decreasing concentrations of Yb-Yb, Yb-Si and Si-Si at the interface. It was found that the presence of the Yb3+/Yb2+ ions within the film cause of negative oxide charge trapping and they were more active in the electric characteristics that the interface states. Whether the donor-like and acceptor-line interface states are active depending on the frequency makes it difficult to establish a link between the structural analyses and the electrical characteristics in some cases. The barrier height (phi(b)), dopant concentration (N-d), Fermi energy level (E-F) were determined depending on frequency. (C) 2020 Elsevier B.V. All rights reserved.