Work Function Tuning Via Interface Dipole by Ultrathin Reaction Layers Using AlTa and AlTaN Alloys

This letter presents a route for tuning the metal gate effective work function via interface dipoles formed using AlTa and AlTaN alloys. It was found that the AlTa alloy has a higher effective work function (4.45 eV) compared to either Al (~ 4.1 eV) or Ta (4.2 eV) gates on SiO ₂ at 400 degC. This increase in effective work function was attributed to interface dipoles formed at the gate electrode and dielectric interface. The origin of this dipole is attributed to a reaction between the AlTa alloy and the dielectric layer. Similar AlTa effective work function tuning was also observed on high-k dielectrics. However, since the AlTa alloy is not thermally stable on SiO₂, nitrogen was added to stabilize the electrode. The addition of N stabilizes the equivalent oxide thickness while still allowing for work function tuning under high temperatures. AlTaN alloys were deposited by reactive sputtering and resulted in an effective work function of ~ 5.1 eV after a 1000 degC anneal, making them suitable for PMOS gate applications