Effect of post-deposition annealing on the interfacial chemical bonding states and band alignment of atomic layer deposited neodymium oxide on silicon

The influence of post-deposition annealing on the interfacial chemical bonding states and the band offset of Nd2O3/Si is analyzed by x-ray photoelectron spectroscopy (XPS) and variable angle spectroscopic ellipsometry (VASE). By investigating the chemical shifts of the Nd 3d, O 1s and Si 2p core level spectra, it is found that the diffusion of the Si atoms from the substrates to the films occurs, and the interfacial Nd silicate-like configuration is subject to a transformation from Nd2SiO5 to Nd2Si2O7 with the annealing temperature. Moreover, the direct optical band-gap energy obtained from the VASE data shifts to a higher energy with the increasing annealing temperature and varies from 5.86 to 6.24 eV. The valence band spectra of the measured XPS gives the VBO (valance band offset) value of 1.5 eV for the as-grown annealed samples and 3.2 and 3.0 eV for the annealed samples at 700 and 900 °C, respectively. Therefore, the calculated CBO (conduction band offset) are 3.24 eV, 1.85 eV and 2.12 eV for the as-grown and annealed films at 700 °C and 900 °C. The suitable band-gap and band offsets relative to Si make Nd2O3 films one of the promising high-k dielectric candidates.