Interface engineering through atomic dopants in HfO₂-based gate stacks

Controlling the effective work function (⁠$ϕeff$⁠) of metal electrodes is critical and challenging in metal-oxide-semiconductor field effect transistors. The introduction of atomic dopants (also referred to as “capping” layers) is an emerging approach to controllably modify $ϕeff$⁠. Here, we investigate the energetic preference of the location of La, Y, Sc, Al, Ce, Ti, and Zr as atomic dopants within a model Pt/HfO₂/Si stack and the resulting variation of $ϕeff$ using density functional theory calculations. Our results indicate that all the considered atomic dopants prefer to be situated at the interfaces. The dopant-induced variation of $ϕeff$ is found to be strongly correlated to the dopant electronegativity and location. Dopants at the metal/HfO₂ interface decrease $ϕeff$ with increasing dopant electronegativity, while a contrary trend is seen for dopants at the Si/HfO₂ interface. These results are consistent with available experimental data for La, Al, and Ti doping. Our findings, especially the identified correlations, have important implications for the further optimization and “scaling down” of transistors.