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 (similar to 4.1 eV) or Ta (4.2 eV) gates on SiO2 at 400 degrees C. 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 similar to 5.1 eV after a 1000 degrees C anneal, making them suitable for PMOS gate applications.