Effective work function modulation of TaN metal gate on HfO2 after postmetallization annealing

The effective work function (Phi(m,eff)) of TaN on HfO2 after postmetallization annealing (PMA) was investigated using TaN/HfO2/SiO2/Si as a sample structure. We found that Phi(m,eff) on HfO2 is stable at PMA temperatures of less than 600 degrees C and is 4.6 eV, which is approximately 0.2 eV higher than that on SiO2. In contrast, Phi(m,eff) is modulated by PMA at temperatures greater than 750 degrees C. An analysis by x-ray photoelectron spectroscopy suggests that the increased Phi(m,eff) is strongly related to Ta oxide formation near the TaN/HfO2 interface. The modulation of Phi(m,eff) on HfO2 is discussed on the basis of intrinsic and extrinsic Fermi level pinning due to Ta-O bond formation at the TaN/HfO2 interface.