Oxidative stability of WS₂ during O₃-based atomic layer deposition and annealing of ferroelectric Hf_1−xZr_xO₂ film

In this study, the thermal stability of WS₂ crystals during O₃-based atomic layer deposition (ALD) and subsequent high-temperature post-deposition annealing (PDA) processes to form ferroelectric Hf_1-xZr_xO₂ (HZO) films was comprehensively investigated. The oxidation of approximately one monolayer and its subsequent incorporation into the HZO film during the O₃-based ALD process at 260 °C were confirmed through various characterization techniques, including Raman spectroscopy, photoluminescence (PL) spectroscopy, and transmission electron microscopy analyses. This phenomenon was attributed to the high oxidizing power of the O₃ oxidant, as demonstrated by comparisons with density functional theory calculations and by conducting the same experiment using H₂O as the oxidant in the ALD process. Unlike MoS₂, which undergoes significant oxidation-induced thermal decomposition, the WS₂ monolayer remained largely intact during the PDA process in the temperature range of 400–600 °C, with only a slight suppression of the PL peak owing to the formation of sulfur vacancies. Thermogravimetric analysis further showed that WS₂ exhibits superior resistance to high-temperature oxidation compared with MoS₂, even at 600 °C. This study provides fundamental insights into the thermal and oxidative stabilities of WS₂, which are crucial for the fabrication of nanoelectronic devices that incorporate the ferroelectric properties of HZO films.