Manipulating interface dipoles of opposing polarity for work function engineering within a single metal gate stack

We show, for the first time, a reversal in net interface dipole polarity (initially n-type) for a metal gate stack by forming p-type interface dipoles after a 950degC anneal. This was achieved in both TaN/SiO₂ and TaN/high-k gate stacks whereby terbium (Tb) and aluminum (Al)-based interlayers were used to form n-type and p-type dipoles, respectively. We also demonstrate the continuous tunability of TaN gate work function (Phi_m) by controlling the n-type and p-type interface dipole densities within the same metal gate stack. The dominant dipole that results in the metal gate stack hinges critically on the reactions of Al and Tb with SiO₂ (or underlying SiO₂ for high-k stacks) for Al-O-(Si) and Tb-O-Si bond formation, respectively. The manipulation of interface dipoles with opposing polarity could enable multiple Phi_m to be achieved using a single metal gate and a simple integration scheme.