Thermal Budget Analysis of Ferroelectric ALD-(Hf,Zr)O₂ Thin Films Using the JMAK Model

Recent advances in AI technology have led to a rapid increase in the amount of data generated and stored, and high-performance non-volatile memory (NVM) with low-voltage operation and fast switching speed is urgently needed to manage it. In this regard, atomic layer deposited ferroelectric (Hf,Zr)O₂ (HZO) thin films are in the spotlight due to their advantages of satisfying the requirements while being compatible with CMOS technology [1,2]. Over the past decade, various theoretical and experimental studies have been conducted to elucidate the mechanisms for improving the ferroelectric properties of HZO thin films, which have revealed that the ferroelectricity is caused by the presence of a non-centrosymmetric orthorhombic phase (o-phase) [2,3]. However, the annealing temperature exceeding 400°C required to induce and promote o-phase formation in HZO thin films makes the back-end-of-line (BEOL) integration of HZO thin films difficult [3,4]. Although various attempts have been reported to reduce the annealing temperature to below 400°C [3,4], including doping, electrode replacement, high-pressure annealing, etc., a comprehensive analysis of the crystallization behavior of HZO thin films is still necessary to stabilize the low-temperature process and thereby achieve excellent low-temperature ferroelectric properties. Therefore, this study aims to investigate the crystallization behavior of HZO thin films annealed at below 400°C by considering the thermal budget and using the Johnson-Mehl-Avrami-Kolmogorov (JMAK) model. Specifically, the ferroelectric polarization of 10-nm-thick HZO thin films annealed by a furnace at various temperatures (300-400°C) for different times (1-48 h) were measured, and the crystallization kinetics were evaluated by applying the JMAK model. For all HZO-based devices annealed in the range of 300-400°C, remanent polarization values of ~30 μC/cm² were achieved, which meets the requirements (>24 μC/cm²) by the International Roadmap for Devices and Systems. Analysis of crystallization behavior using the JMAK model confirmed that the Avrami constant decreases as the annealing temperature decreases. It means the lower the annealing temperature for crystallization of HZO thin films, the longer the annealing time is required. Therefore, the analysis of HZO crystallization via the JMAK model can provide new directions for optimizing the annealing process to achieve a low thermal budget for BEOL integration.

This research was supported by the Nano & Material Technology Development Program through the National Research Foundation of Korea (NRF) funded by Ministry of Science and ICT (RS-2024-00450836). This work was also partially supported by Korea Institute for Advancement of Technology (KIAT) grant funded by the Korea government (MOTIE) (P0017011 and P0020966, HRD Program for Industrial Innovation).

[1] M. Lee et al., ACS Appl. Electron. Mater. 6, 5391 (2024).
[2] S. J. Kim et al., JOM 71, 246 (2019).
[3] H. J. Kim et al., Phys. Status Solidi RRL 15, 2100028 (2021).
[4] J.-H. Kim et al., ACS Appl. Electron. Mater. 5, 4726 (2023).