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

Hafnium dioxide (HfO2) gate dielectrics formed by the atomic layer deposition (ALD) process were fabricated to investigate the flatband voltage shift (ΔVFB) relative to SiO2. It is found that the direction of ΔVFB 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 HfO2 dielectric. A model is proposed to explain the effects of poly-Si gate type on the flatband voltage shift in MOSFETs.