Soft x-ray photoelectron spectroscopy of (HfO2)x(SiO2)1−x high-k gate-dielectric structures

Abstract

Soft x-ray photoelectron spectroscopy has been used to study several (HfO2)x(SiO2)1−x film compositions. The relationships between composition and Si 2p and Hf 4f core level binding energies were investigated using nominally thick films. Both the Si 2p [Si4+] and Hf 4f features shift to lower binding energy by approximately 1.3 eV as the composition is varied from SiO2 to HfO2. The shift to lower binding energy is consistent with both an electron transfer model of the chemical environment and final-state core-hole screening resulting from differences in material polarizability. In addition, the Gaussian widths of the core levels narrow with increasing HfO2 content. Calculations of phonon broadening indicate that this trend is due instead to inhomogeneous disorder. The dielectric/Si interface was investigated with ultrathin (∼10–20 Å) films. There was virtually no difference in binding energies or Gaussian width among the various compositions, indicating a preferential composition of approximately x=0.5 at the interface. Interface suboxides were also investigated and indicate a quality entropy-driven oxide/silicon interface.