Effects of a Gd capping layer on electrical characteristics of metal-oxide-semiconductor field effect transistors with a TaC gate electrode and a HfSiON gate dielectric

Effects of Gd capping of HfSiON gate dielectric on the characteristics of n metal-oxide-semiconductor field effect transistor (nMOSFET) with TaC gate electrode were investigated. MOSFETs with an in situ deposited Gd/TaC bilayer demonstrated a reduced equivalent oxide thickness, 0.9 nm, and low $VTH$⁠, 0.25 V, compared with MOSFETs without Gd capping layer. Backside secondary ion mass spectroscopy revealed that Gd atoms were diffused into the high-k gate dielectric and interfacial layer between high-k dielectric and Si substrate. The dipole moment at the high-$k/SiO2$ interface due to Hf–O and RE–O bonds is used to explain the $VTH$ change.