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 °C, 400 °C, 600 °C, 800 °C under nitrogen ambient. The largest grain size was obtained to be 17.3 nm from the sample annealed at 400 °C. The lowest roughness root-mean-square (Rq) value was measured as 0.464 nm in the Yb2O3 film annealed at 200 °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 °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 (Nit) 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 (φb), dopant concentration (Nd), Fermi energy level (EF) were determined depending on frequency.