Abstract
Hf0.5Zr0.5O2 films are one of the most attractive HfO2-based ferroelectric films because of good ferroelectricity, extreme thinness, and excellent compatibility with silicon devices. The origin of the ferroelectricity of Hf0.5Zr0.5O2 films is the noncentrosymmetric orthorhombic phase (space group Pca21). The effects of process temperature, annealing temperature, thickness, and doping to increase the portion of the orthorhombic phase, which contributes to ferroelectricity, have been studied extensively. However, although most studies have used atomic layer deposition, no study has been reported on the effect of the deposition rate on the ferroelectricity of Hf0.5Zr0.5O2 films. In this work, the influences of the deposition rate on the ferroelectricity and crystal structure of Hf0.5Zr0.5O2 films were examined. In order to conduct systematic and quantitative analysis, measurements of switching transient current, ferroelectric P-E curve, dielectric constant, deconvolution of grazing angle incidence X-ray diffraction, and piezoresponse force microscopy were performed. Hf0.5Zr0.5O2 films with a deposition rate of 1.1 Å/cycle have a more ideal hysteresis curve shape, higher remanent polarization (initial state: 16 μC/cm2, wake up state: 22 μC/cm2), and a higher orthorhombic phase portion than other deposition rates.
Highlights
IntroductionSeveral doped distorted fluorite structured HfO2 ferroelectric materials have been extensively investigated. In particular, the admixture of 50 mol. % HfO2-50 mol. % ZrO2 solid-solution (Hf0.5Zr0.5O2) has drawn a lot of interest for semiconductor memory applications, thanks to their high remanent polarization (Pr), wide tunability, and reliability. In general, it is accepted that the origin of the ferroelectricity of HfO2-based thin films is the formation of the noncentrosymmetric orthorhombic phase (o-phase, space group Pca21). Even though the noncentrosymmetric o-phase is desirable for the ferroelectricity of Hf0.5Zr0.5O2 films, the o-phase is a thermodynamically unstable phase. Several recent theoretical and experimental studies demonstrated the origin of the ferroelectric o-phase and the influences of the various conditions such as film thickness, annealing temperature, process temperature, and doping cations on the formation and portion of the ferroelectric o-phase.5,15,20–22Despite recent active studies, the focus of most studies on the emergence origin of the o-phase is tailored to subsequent processes. The films could have in situ crystallized nuclei of about 1 nm during atomic layer deposition (ALD), and the initial nuclei act as seeds to affect the final grain of more than 5 nm in size, which crystallizes during postmetallization annealing (PMA)
When the Hf0.5Zr0.5O2 films are in the initial state, the hysteresis curve shapes were tilted with small humps, especially in the deposition rates of 0.9 and 1.4 Å/cycle
The influence of the deposition rate on Hf0.5Zr0.5O2 films was systematically examined from the viewpoint of the crystallographic structures and interface properties
Summary
Several doped distorted fluorite structured HfO2 ferroelectric materials have been extensively investigated. In particular, the admixture of 50 mol. % HfO2-50 mol. % ZrO2 solid-solution (Hf0.5Zr0.5O2) has drawn a lot of interest for semiconductor memory applications, thanks to their high remanent polarization (Pr), wide tunability, and reliability. In general, it is accepted that the origin of the ferroelectricity of HfO2-based thin films is the formation of the noncentrosymmetric orthorhombic phase (o-phase, space group Pca21). Even though the noncentrosymmetric o-phase is desirable for the ferroelectricity of Hf0.5Zr0.5O2 films, the o-phase is a thermodynamically unstable phase. Several recent theoretical and experimental studies demonstrated the origin of the ferroelectric o-phase and the influences of the various conditions such as film thickness, annealing temperature, process temperature, and doping cations on the formation and portion of the ferroelectric o-phase.5,15,20–22Despite recent active studies, the focus of most studies on the emergence origin of the o-phase is tailored to subsequent processes. The films could have in situ crystallized nuclei of about 1 nm during atomic layer deposition (ALD), and the initial nuclei act as seeds to affect the final grain of more than 5 nm in size, which crystallizes during postmetallization annealing (PMA). Several doped distorted fluorite structured HfO2 ferroelectric materials have been extensively investigated.. It is accepted that the origin of the ferroelectricity of HfO2-based thin films is the formation of the noncentrosymmetric orthorhombic phase (o-phase, space group Pca21).. Even though the noncentrosymmetric o-phase is desirable for the ferroelectricity of Hf0.5Zr0.5O2 films, the o-phase is a thermodynamically unstable phase.. Several recent theoretical and experimental studies demonstrated the origin of the ferroelectric o-phase and the influences of the various conditions such as film thickness, annealing temperature, process temperature, and doping cations on the formation and portion of the ferroelectric o-phase.. Previous studies have suggested that the o-phase is thermodynamically stabilized at a particular grain size, the effect of the initial nuclei on the as-deposited state of the grain size accompanying the ferroelectricity-induced crystal structure has been overlooked
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