Region-Selective Oxygen Vacancy Engineering for Ferroelectric Hf_0.5Zr_0.5O₂ Thin Films Processed at 300 °C

The discovery of ferroelectricity in hafnium oxide (HfO₂) thin films has positioned it as a leading material for next-generation nonvolatile memory. However, the integration of HfO₂-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_0.5Zr_0.5O₂ (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/cm² and outstanding endurance exceeding 10⁹ cycles. This work demonstrates the effectiveness of Vo-ELs in enabling low-thermal-budget, high-performance ferroelectric devices compatible with advanced BEOL integration.