Atomistic mechanisms of opposite threshold voltage shift induced by La and Al doping in HfO2-based gate stacks: First-principles insights

Abstract

For multi-threshold voltage device integration, threshold voltage modulation is achieved by depositing La- and Al-based oxide capping layers on high-k dielectric surfaces to induce interfacial dipoles. However, the detailed mechanism of dipole induction by these capping layers remains controversial. In this work, we have employed first-principles calculations to investigate the doping configurations of La and Al in the Si/SiO2/HfO2 stack. It is found that when La is incorporated into HfO2, LaHf− dominates with a high concentration, which reduces the effective metal gate work function and results in a negative threshold voltage shift. For Al doped in HfO2, both AlHf− and 2AlHf2+ concentrations increase at high Al content; however, the dipoles induced by the two configurations have opposite directions and compete with each other. The 2AlHf2+ eventually becomes dominant, which increases the effective metal gate work function and leads to a positive threshold voltage shift. Our results reveal the atomic mechanisms by which La and Al doping induce interfacial dipoles, with their opposite threshold voltage shifts resulting from different doping configurations. The findings provide a theoretical foundation for interface engineering optimization in multi-threshold voltage devices.