Dipole model explaining high-k/metal gate field effect transistor threshold voltage tuning

Abstract

An interface dipole model explaining threshold voltage $\left(V_t\right)$ tuning in HfSiON gated $n$ -channel field effect transistors $\left(n\mathrm{FETs}\right)$ is proposed. $V_t$ tuning depends on rare earth (RE) type and diffusion in $\mathrm{Si}∕\mathrm{Si}{\mathrm{O}}_x∕\mathrm{Hf}\mathrm{Si}\mathrm{O}\mathrm{N}∕{\mathrm{REO}}_x$ /metal gated $n\mathrm{FETs}$ as follows: $\mathrm{Sr}<\mathrm{Er}<\mathrm{Sc}+\mathrm{Er}<\mathrm{La}<\mathrm{Sc}<\text{none}$ . This $V_t$ ordering is very similar to the trends in dopant electronegativity (EN) (dipole charge transfer) and ionic radius $\left(r\right)$ (dipole separation) expected for a interfacial dipole mechanism. The resulting $V_t$ dependence on RE dopant allows distinction between a dipole model (dependent on EN and $r$ ) and an oxygen vacancy model (dependent on valence).