NMOS Compatible Work Function of TaN Metal Gate With Gadolinium Oxide Buffer Layer on Hf-Based Dielectrics

Reduction in effective work function (EWF) of midgap-tantalum nitride (TaN) metal gate with gadolinium-oxide buffer layer on Hafnium-based high-kappa gate stack has been demonstrated. EWF of 4.2 eV is achieved for TaN with a bilayer arrangement of Gd₂O₃/HfSiO_x dielectric. By using Gd-Si cosputtered layer on HfO₂, a reduction in EWF to nMOS compatible value of 4.05 eV is obtained. Electrical and material characterization indicate that the conversion of gadolinium to gadolinium oxide and presence of silicon in the high-kappa layer are responsible for the EWF shift. nMOSFETs with improved output current, transconductance, and channel electron mobility highlight the approach of using gadolinium in the gate stack