Difficulties of the microscopic theory of leakage current through ultra-thin oxide barriers: point defects

We use a combination of first-principles density functional theory and non-perturbative scattering theory to investigate the effect of point defects on the hole leakage current through ultra thin oxide films. In particular, we consider O vacancies and B interstitial in monoclinic HfO2; five different defects are considered: (1) O vacancy at a three- and (2) a four-coordinated 0 site located in the HfO2 region, (3) O vacancy along a Hf-O-Si bond and (4) along a Si-O-Si bond at the Si/HfO2 interface, and (5) an interstitial B atom in the HfO2 region. We find that the neutral bulk vacancies and an interface vacancy along the Si-O-Si bond have little impact on the leakage current. On the contrary, an interface vacancy along the Hf-O-Si bridge and an interstitial B atom in the HfO2 region introduce states in the Si band gap and in the region just below the Si valence band edge thus strongly enhancing the leakage current at a low bias. (C) 2003 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.