Modification of Molybdenum Gate Electrode Work Function via (La-, Al-Induced) Dipole Effect at High-k/SiO₂ Interface

This letter demonstrates a way for modifying the effective work function Phi m of a molybdenum (Mo) gate electrode by interface dipole engineering in a metal gate/high- k gate stack. N-type Mo gate Phi m (~4.2 eV) was achieved on a HfLaO gate dielectric even after 950-degC rapid thermal annealing (RTA) due to the presence of a La-induced interface dipole layer. By alloying with ~14%-19% of aluminum (Al), the effective Mo gate Phi m on HfLaO significantly increased by ~0.6 eV after 950-degC RTA. The incorporation of Al into the HfLaO gate dielectric was evident after the high-temperature anneal. The Phi m modulation was attributed to Al-induced interface dipole formation, of which has opposite polarity to the La-induced dipole, at the high- k /SiO 2 interface. This novel concept of employing two opposing interface dipoles in the same metal gate/high- k stack for Phi m tunability would provide insights for future gate stack interface engineering.