Low-Temperature Growth of Ferroelectric Hf_0.5Zr_0.5O₂ Thin Films Assisted by Deep Ultraviolet Light Irradiation

Low-temperature deposition of inorganic ferroelectric (FE) thin films is highly demanded for lowering the environmental impact through lesser energy consumption. Doped HfO2-based FE thin films commonly require high crystalline temperature (>450 °C) to exhibit ferroelectricity. Here, we report that the crystallization temperature of the metastable orthorhombic (O) phase in Hf0.5Zr0.5O2 thin films can be lowered to 350 °C via a deep ultraviolet (DUV) irradiation process carried out before rapid thermal annealing (RTA). The DUV irradiation initializes a nucleation process of the crystal growth through photochemical cleavage of organic residues, followed by the densification of metal oxide films, and the subsequent RTA at 350 °C crystallizes the Hf0.5Zr0.5O2 thin film with a higher O-phase fraction. The DUV-irradiated films annealed at 350 °C exhibited FE characteristics, whereas the non-irradiated films annealed above 450 °C become FE. Our study suggests that DUV irradiation can be successfully utilized to lower the crystallization temperature of HZO thin films and can lead to the realization of flexible FE random access memories.