Metal carbide-induced negative flatband voltage shift in TaCx and HfCx/HfO2 gate stacks

Abstract We systematically investigated the role of the top interface for TaC x and HfC x /HfO 2 gate stacks on the effective work function ( Φ m,eff ) shift by inserting a SiN layer at the gate/HfO 2 top interface or HfO 2 /SiO 2 bottom interface. We found that Φ m,eff of the TaN gate electrode on HfO 2 was larger than that on SiO 2 because of the HfO 2 /SiO 2 -bottom-interface dipole. On the other hand, we found that Φ m,eff values of the TaC x and HfC x gate electrodes on HfO 2 agree with Φ m,eff on SiO 2 . This is because the potential offset of the opposite direction with respect to the bottom interface dipole appears at the metal carbide/HfO 2 interface. It is thus concluded that the top interface in the metal carbide/HfO 2 gate stacks causes the negative Φ m,eff shift.