Effect of postdeposition annealing on the ferroelectricity of ultrathin Hf0.5Zr0.5O2 films

The severe degradation of ferroelectricity in Hf0.5Zr0.5O2 (HZO) films thinner than 5 nm poses a significant challenge for device applications. In this study, we demonstrate that the crystallization of ultrathin HZO films can be improved simply by optimizing the annealing sequence, without introducing additional dopants or structural modifications. Specifically, postdeposition annealing (PDA) and postmetallization annealing (PMA), conducted before and after the deposition of the top electrode, respectively, were applied to HZO films of varying thicknesses to investigate their ferroelectric properties. PMA led to a significant reduction in remnant polarization (Pr), primarily due to insufficient crystallization in 3 nm-thick HZO films. By contrast, PDA in an O2 atmosphere resulted in enhanced crystallization and a smaller decrease in Pr, achieving a maximum 2Pr value of 12 μC/cm2. Additionally, this annealing condition resulted in reduced leakage current and improved endurance, which could be attributed to the suppression of oxygen-vacancy formation in the HZO films. These findings highlight that a simple modification of the annealing scheme enables ultrathin HZO films to retain sufficient ferroelectricity for practical implementation in low-power, high-density next-generation devices.