Modification of molybdenum gate electrode work function via (La-, Al-Induced) dipole effect at High-κ/SiO2 interface

Abstract

This letter demonstrates a way for modifying the effective work function Φm of a molybdenum (Mo) gate electrode by interface dipole engineering in a metal gate/high-κ gate stack. N-type Mo gate Φm (∼4.2 eV) was achieved on a HfLaO gate dielectric even after 950-°C 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 Φm on HfLaO significantly increased by ∼0.6 eV after 950-°C RTA. The incorporation of Al into the HfLaO gate dielectric was evident after the high-temperature anneal. The Φm modulation was attributed to Al-induced interface dipole formation, of which has opposite polarity to the La-induced dipole, at the high-κ/SiO2 interface. This novel concept of employing two opposing interface dipoles in the same metal gate/high-κ stack for Φm tunability would provide insights for future gate stack interface engineering. © 2008 IEEE.