Modification of Molybdenum Gate Electrode Work Function via (La-, Al-Induced) Dipole Effect at High-$k/\hbox{SiO}_{2}$ 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.