Effect of polycrystalline-silicon gate types on the opposite flatband voltage shift in n-type and p-type metal–oxide–semiconductor field-effect transistors for high-k-HfO2 dielectric

Abstract

Hafnium dioxide $({\mathrm{HfO}}_2)$ gate dielectrics formed by the atomic layer deposition (ALD) process were fabricated to investigate the flatband voltage shift ${\mathrm{(\Delta V}}_{\mathrm{FB}})$ relative to ${\mathrm{SiO}}_2.$ It is found that the direction of ${\mathrm{\Delta V}}_{\mathrm{FB}}$ depends on the Fermi level position in the gate material, which shows respective positive and negative shifts in $n$ -type and $p$ -type metal–oxide–semiconductor field-effect transistors (MOSFETs), regardless of the substrate type. The opposite direction in the flatband voltage shift is attributed to both acceptor- and donor-like interface states existing at the interface between the polycrystalline-silicon (poly-Si) gate and ${\mathrm{HfO}}_2$ dielectric. A model is proposed to explain the effects of poly-Si gate type on the flatband voltage shift in MOSFETs.