Correlation between ferroelectricity and ferroelectric orthorhombic phase of HfxZr1−xO2 thin films using synchrotron x-ray analysis

Abstract

The change in the interplanar spacing (d-spacing) including the ferroelectric orthorhombic (O) phase in the low-temperature fabricated HfxZr1−xO2 (HZO) films was studied using synchrotron grazing-incidence wide-angle x-ray scattering analysis. The 10-nm-thick HZO films were fabricated by thermal and plasma-enhanced atomic layer deposition (TH- and PE-ALD) methods using H2O gas and O2 plasma as oxidants, respectively, and a post-metallization annealing (PMA) was performed at 300–400 °C. The d-spacing of the mixture of (111)-, (101)-, and (111)-planes of O, tetragonal (T), and cubic (C) phases, respectively, for the TH- and PE-ALD HZO films increased up to 2.99 Å with an increase in PMA temperature, while the d-spacing estimated by conventional x-ray diffraction was 2.92 Å regardless of the PMA temperature. The remanent polarization (2Pr = Pr+ − Pr−) of the HZO films increased as the PMA temperature increased. It is clear that the 2Pr value satisfied a linear relationship as a function of the d-spacing of O(111)/T(101)/C(111) phases. Furthermore, the wake-up effect was found to depend on the ferroelectric O phase formation. The wake-up effect was significantly reduced in both the TH- and PE-ALD HZO films after the PMA at 400 °C due to the increase in the ferroelectric O phase formation. The leakage current density (J)–electric field properties of the PE-ALD HZO film with the lowest d-spacing were divided into three steps, such as low, middle, and large J values, in the wake-up (103 cycles), pristine (100 cycle), and fatigue (107 cycles) states, respectively. Therefore, an analysis of the ferroelectric O phase is very important for understanding the ferroelectricity including endurance.

Toward Low-Thermal-Budget Hafnia-Based Ferroelectrics via Atomic Layer Deposition

“…As reported in the literature, common oxidants used to deposit ferroelectric HZO include water (H 2 O), 49−54,56,58,66−68 ozone (O 3 ), 25,55,64,69 hydrogen peroxide (H 2 O 2 ), 29 and oxygen (O 2 ) plasma. 57,58 Unlike other molecular oxygen sources, O 2 plasma consists of highly reactive oxygen radicals and ions, providing extra energy during reactions. 19,34,79,80 The additional energy supplied during the plasma cycle reduces the process temperature for ALD reaction and enhances the crystallization of plasma-enhanced ALD (PEALD) compared to TALD.…”

“…19,34,79,80 The additional energy supplied during the plasma cycle reduces the process temperature for ALD reaction and enhances the crystallization of plasma-enhanced ALD (PEALD) compared to TALD. 57,58 However, unlike TALD, the anisotropic nature of the plasma source is difficult to implement in complicated 3D structures and can produce a thick interfacial layer due to excessively strong oxidation power. 74,81,82 Consequently, the use of TALD is preferable to deposit a thin film on complex 3D structures conformally and minimize interface formation.…”

“…The highest temperature step in the fabrication process, which includes annealing and deposition, was referred to as the process temperature. (a) Effect of dopants on ferroelectricity of HfO 2 -based film. ,,,,− ,,− ,,, (b) Effect of precursor selection in HZO films ferroelectricity. ,,,− ,− (c) Oxygen source effect on the ferroelectric temperature of HZO films. ,,− ,,− …”

“…As reported in the literature, common oxidants used to deposit ferroelectric HZO include water (H 2 O), − ,,,− ozone (O 3 ), ,,, hydrogen peroxide (H 2 O 2 ), and oxygen (O 2 ) plasma. , Unlike other molecular oxygen sources, O 2 plasma consists of highly reactive oxygen radicals and ions, providing extra energy during reactions. ,,, The additional energy supplied during the plasma cycle reduces the process temperature for ALD reaction and enhances the crystallization of plasma-enhanced ALD (PEALD) compared to TALD. , However, unlike TALD, the anisotropic nature of the plasma source is difficult to implement in complicated 3D structures and can produce a thick interfacial layer due to excessively strong oxidation power. ,, Consequently, the use of TALD is preferable to deposit a thin film on complex 3D structures conformally and minimize interface formation. Therefore, this section focuses on oxygen sources that are mainly used in TALD processes.…”

Nanocrystallite Seeding of Metastable Ferroelectric Phase Formation in Atomic Layer-Deposited Hafnia–Zirconia Alloys

“…Orthorhombic phase formation in HfO 2 -based thin films has been postulated to follow a particular transformation sequence: the as-deposited amorphous films first form the T-phase during annealing and then transform to the O-phase during cooling under appropriate conditions (e.g., for particular film composition and under the confinement of a capping layer, often a metal or metal nitride electrode), such that the T-phase to M-phase transition is suppressed due to mechanical stress. ,,, However, this pathway does not consider seed crystallites that may have already formed in these thin films during the deposition process prior to thermal annealing, and which alter the crystallization pathway described above. Nanocrystalline structures have been observed in the as-grown HZO thin films fabricated using plasma-enhanced (PE) and thermal (TH) atomic layer deposition (ALD) at 300 °C and serve as nuclei in the subsequent post-metallization annealing (PMA) at 300–400 °C to form completely crystallized films. , However, the phase of the nanocrystalline structures was not precisely determined, and therefore, the crystallization pathway was not determined.…”