The effective Work-Function of atomic layer deposited TaN thin film using TBTDET precursor and NH3 reactant gas

Abstract

We investigated the effect of capping metals and post annealing on the effective work function (EWF) of atomic layer deposited (ALD) tantalum nitride (TaN) using a metal oxide semiconductor (MOS) device with HfO2 gate dielectric. The tris(diethylam-ido)(tert-butylimido) tantalum (TBTDET) precursor and ammonia (NH3) were used as the tantalum precursor and the reactant gas, respectively. Increasing ALD TaN thickness leads to higher EWF regardless of the capping metals. When aluminum (Al) is used as the capping metal, the EWF range is 4.06 eV to 4.45 eV, which is suitable for the gate electrode of the n-type device, and for the tungsten (W) capping metal, the EWF range is 4.43 eV to 4.80 eV, acceptable for the gate electrode of the p-type device. These results are attributed that Al causes oxygen-scavenging, resulting in more oxygen vacancies within HfO2, whereas W reacts little with oxygen. The EWF versus ALD TaN thickness dependence of the Al and W capping cases is 55.7 meV/nm and 52.8 meV/nm, respectively. Additional heat treatment further increases EWF further for both cases, which is attributed to the reduction of carbon contents within TaN.