Ferroelectric Hf0.5Zr0.5O2 has recently attracted significant attention as a promising material in memory applications due to its low thermal budget requirements making it suitable for BEOL integration, as well as its CMOS compatibility. Researchers at UT Dallas have previously reported 10nm HZO with excellent total polarization, 2Pr, and retention. As the film scales further down to sub-6nm, one key challenge arises: reducing coercive voltage, Vc (voltage required for net polarization to be 0) to below 1V while maintaining similar level of 2Pr.
90/X/90nm TiN/HZO/TiN stack with varying HZO thickness MIM structures were fabricated on 300nm thermally grown SiO2 on n-Si. HZO was deposited employing thermal ALD technique at 275°C using TDMA-Hf, and TDMA-Zr as metal precursors, and anhydrous H2O2 as the co-reactant in a super cycle manner. TiN top and bottom electrodes were deposited using sputter method. P-V measurements on 5nm HZO showed 2Pr of 52µC/cm2 which suggests formation of orthorhombic phase without any post-deposition anneal process. Devices configured to 2Pr of ~40µC/cm2 achieved 2Vc ~0.88V with reasonable batch/device reproducibility, with 70% retention of 2Pr over extrapolated 10-year period. 4nm HZO subjected to 400°C RTA was found to have operation voltage of 0.5V with 2Pr of ~55µC/cm2 with breakdown field of 7.1MV/cm and 109 cycle endurance, demonstrating robust film quality and performance.
