Bridging Electrical and Structural Interface Properties: a Combined DFT-GW Approach

Abstract

The selection of a proper metal for replacement of polycrystalline silicon as the metal gate in future generation transistors has been hampered by pinning of the metal Fermi level at the metal/dielectric interface. Using monoclinic hafnia and zirconia as the gate dielectric we compare three different metal gate/gate dielectric interface structures where the oxygen affinity of the metal gate varies from low to high under normal processing conditions. For each of the metal gate/gate dielectric combination we considered a number of interface stoichiometries and tried to identify the most likely interface composition by comparing the calculated and measured valence band offsets (VBO). Because density functional theory (DFT) underestimates the dielectric band gap, it also underestimates the VBO thus requiring a correction to the band edges, which we accomplished using GW for cubic and monoclinic hafnia. Our GW shift value for monoclinic hafnia (0.3 eV) indicates mostly reduced interfaces in all metal/dielectric combinations considered.