Exploring BEOL-Compatible Ferroelectricity in Ultra-Thin Hafnium–Zirconium Oxide: Thermal Budget, FTJ Characteristics, and Device Reliability

Abstract

The use of hafnium-zirconium oxide (HZO) in ferroelectric memory has garnered significant interest due to its excellent scalability and compatibility with complementary metal-oxide-semiconductor and back-end-of-line processes. However, a significant challenge is the reduction of operational voltage. While thickness scaling is straightforward, it faces crystallization issues below 5 nm, necessitating extremely high annealing temperatures. This paper investigates the thermal budget and ferroelectric properties of ultra-thin HZO in metal-ferroelectric-metal structures. The focus is on the feasibility of low-temperature, extended-duration furnace annealing as a process compatible with the back-end-of-line. The results demonstrate that 4 nm HZO devices can achieve significant ferroelectricity without polarization degradation, unlike typical rapid thermal annealing at much higher temperatures. The study also explores ferroelectric tunnel junction properties related to bottom interface oxidation. We also analyze wake-up behavior through various field cycling methods, confirming the dominance of the interfacial layer soft breakdown mechanism in these devices. Additionally, the study includes endurance and retention assessments, providing a comprehensive analysis of ultra-thin HZO devices from annealing to electrical characteristics.