Back-End-of-Line Compatible HfO₂/ZrO₂ Superlattice Ferroelectric Capacitor With High Endurance and Remnant Polarization

Abstract

The hafnium-zirconium oxide (HZO) has been reported to be a promising candidate for low-power VLSI logic and memory applications. However, the demand for high processing temperatures above 500 °C keeps it away from the Back-End-of-Line (BEOL) process. Many reports have explored various methods to facilitate the formation of orthorhombic phases at lower temperatures, but these methods have typically resulted in low remnant polarization ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${P}\text{r}$ </tex-math></inline-formula> ) and poor reliability due to poor crystallinity and oxygen vacancy (Ov) accumulation. To address these challenges, we have chosen tungsten (W) as the capping electrode due to its superior capability for inducing orthorhombic phases. We have also replaced the conventional HZO layer with a stacked HfO2-ZrO2 superlattice with optimized Ov distribution and improved crystallinity. As a result, our sample processed at 400 °C exhibits a maximum <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$2{P}\text{r}$ </tex-math></inline-formula> of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$32 ~\mu \text{C}$ </tex-math></inline-formula> /cm2 at 2.5 MV/cm. It demonstrates the stable endurance cycles up to <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${2} \times {10} ^{{9}}$ </tex-math></inline-formula> exceeding the performance of the W-HZO control sample and remaining competitive with the most recent results in the literature.