Role of Nitrogen in Ferroelectricity of Hf_xZr_1-xO₂-Based Capacitors With Metal-Ferroelectric-Insulator-Metal Structure

In this study, HfxZr1-xO2 (HZO)-based capacitors with a metal-ferroelectric-insulator-metal (MFIM) structure were fabricated without and with ammonia (NH3) plasma nitridation at both metal/oxide interfaces to experimentally investigate and discuss the role of nitrogen (N) in the ferroelectric. For the first time, we found that the ferroelectricity in the HZO thin film weakened after NH3 plasma nitridation. Material analysis results indicated that the reduced ferroelectricity was attributable to N diffusion from both metal/oxide interfaces into the HZO thin film to further produce a N-doped HZO thin film with numerous N bonds, leading to the decreased oxygen vacancy mobility during post metal annealing (PMA). However, the ferroelectricity can be effectively improved by increasing the PMA temperature from 300 °C to 650 °C. Furthermore, the NH3 plasma nitridation at both metal/oxide interfaces that can greatly suppress the oxygen vacancy generation results in a significantly improved voltage stress immunity in the HZO-based capacitors under a stress voltage of 3 V.