Interstitial oxygen induced Fermi level pinning in the Al2O3-based high-k MISFET with heavy-doped n-type poly-Si gates

We study the origin of substantial threshold voltage (Vth) shifts observed in Al2O3-based MISFETs with n+poly-Si gate, by focusing on the effect of an interstitial oxygen (Oi) formation in Al2O3. We observed that the Oi level in Al2O3 is 1 eV above the valence band top of Al2O3 by first-principles calculation. Therefore, Oi formation and subsequent electron transfer from Fermi level to the Oi level allows the system to overcome the energy loss by the Oi formation, which depends on the position of Fermi level. In case of n+poly-Si gate, this electron transfer across the interface occurs and results in substantial Vth shifts. The proposed mechanism reproduces experimental result and provides a good understanding of nano-interfacial interactions.