A Comprehensive Study of Ferroelectric Properties of Fluorite-Structured Hf1-XZrxO2 Thin Films Grown on Mo Electrode with Various Thicknesses and Compositions

Since ferroelectricity in Si-doped HfO2 was first reported in 2011,[1] HfO2-based thin films have attracted significant attention as an emerging material for ferroelectric devices due to their advantages such as scalability and compatibility with Complementary Metal-Oxide-Semiconductor (CMOS) processes. Generally, TiN has been used as electrode material in semiconductor processes. However, other electrode materials such as W and Mo have attracted increasing interest for HfO2-based ferroelectric thin films due to their higher remanent polarization (Pr) than the TiN electrode.[2 ,3 ] Recently, it has been reported that Mo electrodes can be easily oxidized even at low temperatures such as atomic layer deposition (ALD) processes, and the formed MoOx layer can sufficiently act as the oxygen supplier, resulting in the larger orthorhombic phase fraction and higher remanent polarization compared with TiN electrodes.[3] Nevertheless, the effect of the film thickness and composition on the ferroelectric properties of HZO thin films grown on Mo electrodes is yet to be elucidated. Therefore, in this study, the electrical, physical, and chemical properties of HZO films with various thicknesses (6 – 11 nm) and Zr/(Hf+Zr) ratios (0.5 – 0.7) are examined. In the case of the HZO films grown on the TiN electrode, when the film thickness decreases or the Zr/(Hf+Zr) ratio increases, the switchable polarization (2Pr) decreases with a distortion of polarization-electric field (P-E) curves owing to the increased fraction of the antiferroelectric tetragonal phase. However, 2Pr as high as 57.5 µC/cm2 on the Mo electrode could be achieved even in the 7.6 nm-thick Hf0.4Zr0. 6O2 thin film with a little distortion of the P-E curve. The highest 2Pr of 68.3 µC/cm2 was observed in the 10.9 nm thick Hf0.4Zr0. 6O2 film, which is 31.3 % higher than the highest 2Pr (52.0 µC/cm2) of the HZO thin film on TiN reported so far.[ 4] Additionally, in the (Grazing Incidence X-ray Diffraction) results of all samples, it can be observed that the m-phase which deteriorates the Pr values is sufficiently suppressed. These results are consistent with the tendency of previously reported results.[3] Therefore, It is believed that the Mo electrode would induce a higher orthorhombic phase fraction in HZO thin films compared to the TiN electrode resulting in higher 2Pr values. This enables ferroelectricity to be achievable within a wider range of film thicknesses and Zr/(Hf+Zr) ratios. References [1] Boescke et al., Appl. Phys. Lett., 99, 102903 (2011) [2] K. Yang et al., Mater. Sci. Semicond. Process., 164, 107565 (2023) [3] Y. Lee et al., Appl. Surf. Sci., 648, 158948 (2024) [4] S. J. Kim et al., Appl. Phys. Lett., 111, 242901 (2017) Figure 1