Inelastic electron tunneling study of crystallization effects and defect energies in hafnium oxide gate dielectrics

Changes in phonon spectra and point defect populations that accompany crystallization of HfO₂ were investigated by inelastic tunneling across Al/ HfO₂ / SiO₂ /Si. Spectral features from tetragonal- and monoclinic- HfO₂ vibrational modes are observed in annealed films, while they are not detected in as-deposited samples, consistent with selected area electron diffraction analysis. In addition to features indexed as vibrational modes, peaks whose amplitude and energy vary with bias history were detected for p-type Si. We attribute these features to point defect-related states in the HfO₂ band gap and find good agreement between their energies and those predicted theoretically for oxygen vacancy levels in HfO₂.