Mechanisms for enhanced ferroelectric properties in ultra-thin Hf0.5Zr0.5O2 film under low-temperature, long-term annealing

Abstract

To gain insight into the ferroelectric mechanisms under reduced thermal budget and thickness scaling, a 4.6 nm ultra-thin ferroelectric Hf0.5Zr0.5O2 capacitor compatible with back-end-of-line (BEOL) processes (all conducted at temperatures ≤350 °C) is investigated in this work. Through O3 pretreatment at the bottom electrode (BE) interface and controlled temperature modulation of the crystalline phase, the capacitor exhibits exceptional ferroelectric (FE) properties following low-temperature (350 °C) and long-term (300 s) rapid thermal annealing (RTA). These properties include high remanent polarization (2Pr ∼ 28.53 μC/cm2), low coercive voltage (Vc ∼ 0.43 V), effective leakage suppression, robust endurance (∼1010 cycles without hard breakdown), and a desirable high dielectric constant. The main mechanisms identified include tetragonal phase nucleation under enhanced tensile stress via the oxidized BE layer (TiO2), crystalline growth controlled through RTA temperature modulation, and phase transition to the ferroelectric orthorhombic phase under electric field cycling. This research provides valuable insights for the development of BEOL-compatible nonvolatile FE memories.