Improved ferroelectric properties of CMOS back-end-of-line compatible Hf_0.5Zr_0.5O₂ thin films by introducing dielectric layers

Hf_0.5Zr_0.5O₂ (HZO) ferroelectric thin films have gained significant attention for the development of next-generation ferroelectric memories by complementary-metal-oxide semiconductor (CMOS) back-end-of-line (BEOL) processing, due to their relatively low crystallization temperature. However, it remains challenging to achieve excellent ferroelectric properties with post deposition annealing (PDA) process at a BEOL compatible temperature. Along these lines, in this work, it is demonstrated that the ferroelectricity of 15 nm thick HZO thin film prepared by PDA process at 400 °C can be improved to varying degrees, via depositing 2 nm thick dielectric layers of Al₂O₃, HfO₂, or ZrO₂ at either the bottom or the top of the film. Notably, the HZO thin film with the top-Al₂O₃ layer exhibits remarkable ferroelectric properties, which are independent of the thickness of HZO. The 6 nm thick HZO thin film shows a total remanent polarization (2P_r) of 31 μC/cm² under an operating voltage of 2.5 V. These results represent a significant advancement in the fabrication of high-performance, BEOL compatible ferroelectric memories, as compared to previously reported state-of-the-art works.