Region-Selective Oxygen Vacancy Engineering for Ferroelectric Hf<sub>0.5</sub>Zr<sub>0.5</sub>O<sub>2</sub> Thin Films Processed at 300 °C
Ruifeng Tang, Yifan Zhang, Yang Yang, Chuanli Zhang, Xun Yu, Yuan Wang, Xiao Long, Pengfei Jiang, Tiancheng Gong, Yan Wang, Wei Wei, Qing Luo
Abstract
The discovery of ferroelectricity in hafnium oxide (HfO 2 ) thin films has positioned it as a leading material for next-generation nonvolatile memory. However, the integration of HfO 2 -based ferroelectric thin films into back-end-of-line (BEOL) processes remains challenging due to the high thermal budget required to stabilize the ferroelectric orthorhombic (O) phase. In this work, we achieve robust stabilization of the O-phase at a significantly reduced annealing temperature of 300 °C solely through oxygen vacancy engineering. We introduce a region-selective oxygen vacancy engineering strategy to form oxygen vacancy engineering layers (Vo-ELs) within Hf 0.5 Zr 0.5 O 2 (HZO) thin films during atomic layer deposition (ALD). By delaying the introduction of the oxygen precursor, multiple cycles of metal precursors are deposited before a single oxidation step, creating well-defined Vo-ELs. These Vo-ELs induce a vertical gradient in the oxygen vacancy concentration, as confirmed by electron energy loss spectroscopy (EELS). First-principles calculations further reveal that oxygen vacancies reduce the energy barrier for the tetragonal-to-orthorhombic (T–O) phase transition and enhance the thermodynamic stability of the ferroelectric O-phase. Utilizing this technique, we successfully realize low-temperature (300 °C) fabrication of HZO ferroelectric capacitors, which exhibit a high remanent polarization of 36.4 μC/cm 2 and outstanding endurance exceeding 10 9 cycles. This work demonstrates the effectiveness of Vo-ELs in enabling low-thermal-budget, high-performance ferroelectric devices compatible with advanced BEOL integration.