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

Abstract

This letter demonstrates a way for modifying the effective work function Phi <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">m</i> of a molybdenum (Mo) gate electrode by interface dipole engineering in a metal gate/high- <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">k</i> gate stack. N-type Mo gate Phi <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">m</i> (~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 <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">m</i> 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 <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">m</i> modulation was attributed to Al-induced interface dipole formation, of which has opposite polarity to the La-induced dipole, at the high- <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">k</i> /SiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> interface. This novel concept of employing two opposing interface dipoles in the same metal gate/high- <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">k</i> stack for Phi <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">m</i> tunability would provide insights for future gate stack interface engineering.