Experimental investigation of dipole formation and modulation at Hf0.5Zr0.5O2/SiO2 interface

Abstract

HfO2-doped ferroelectric field-effect transistors have been extensively studied since the discovery of ferroelectricity in HfO2. A metal/ferroelectric/insulator/semiconductor structure is widely used in FeFETs. The dipole at the doped-HfO2/SiO2 interface is not well understood, though it plays an important role in the flat voltage shift and band alignment which strongly affects charge trapping. This study investigates the band alignment and dipole distribution at the Hf0.5Zr0.5O2 /SiO2 interface using x-ray photoelectron spectroscopy. The band bending of the Hf0.5Zr0.5O2 /SiO2/Si structure is found to vary with Hf0.5Zr0.5O2 layer thickness. The valence band offset (VBO) at the Hf0.5Zr0.5O2 /SiO2 interface decreases with increasing Hf0.5Zr0.5O2 thickness. It is confirmed that the dipole contributes to the dependence of band bending and VBO on Hf0.5Zr0.5O2 thickness. Dipole formation is caused by the charge neutral level mismatch between Hf0.5Zr0.5O2 and the SiO2/Si stack, which induces electron transfer and band bending. O2 post deposition annealing (PDA) can modulate the dipole distribution and generate a larger dipole at the Hf0.5Zr0.5O2 /SiO2 interface than that of the sample not subjected PDA.