In this letter, the ferroelectric (FE) properties of 5-nm-thick Hf0.5Zr0.5O2 (HZO) films deposited by atomic layer deposition have been investigated. By reducing the HZO film thickness to 5 nm, low-voltage operation (1.0 V) of the HZO-based capacitor was achieved while maintaining a remnant polarization (Pr) of about 10 μC/cm2 (i.e., 2Pr of 20 μC/cm2). Meanwhile, in order to form an orthorhombic phase, which is responsible for FE properties, a rapid thermal annealing process was performed after TiN top electrode deposition. The FE properties were realized after low temperature annealing (450 °C for 1 min), making them compatible with the back-end of the line. In addition, the low operating voltage and the suppression of an additional monoclinic phase formation by stress-induced crystallization induced a robust endurance (>1010 cycles at 1.2 V) of the 5-nm-thick HZO sample.

In this work, a novel chlorodisilane precursor, pentachlorodisilane (PCDS, HSiCl), was investigated for the growth of silicon nitride (SiN ) via hollow cathode plasma-enhanced atomic layer deposition (PEALD). A well-defined self-limiting growth behavior was successfully demonstrated over the growth temperature range of 270-360 °C. At identical process conditions, PCDS not only demonstrated approximately>20% higher growth per cycle than that of a commercially available chlorodisilane precursor, hexachlorodisilane (SiCl), but also delivered a better or at least comparable film quality determined by characterizing the refractive index, wet etch rate, and density of the films. The composition of the SiN films grown at 360 °C using PCDS, as determined by X-ray photoelectron spectroscopy, showed low O content (∼2 at. %) and Cl content (<1 at. %; below the detection limit). Fourier transform infrared spectroscopy spectra suggested that N-H bonds were the dominant hydrogen-containing bonds in the SiN films without a significant amount of Si-H bonds originating from the precursor molecules. The possible surface reaction pathways of the PEALD SiN using PCDS on the surface terminated with amine groups (-NH and -NH-) are proposed. The PEALD SiN films grown using PCDS also exhibited a leakage current density as low as 1-2 nA/cm at 2 MV/cm and a breakdown electric field as high as ∼12 MV/cm.

Since the first report on the unexpected ferroelectricity of fluorite-structure oxides in 2011, this topic has provided a pathway for new research directions and opportunities. Based on theoretical calculations and experimental demonstrations, it is now well known that fluorite-structure ferroelectrics are compatible with complementary metal-oxide-semiconductor technology and exhibit ferroelectric properties at extremely thin (<10 nm) thicknesses. It should be noted that the noncentrosymmetric orthorhombic phase, which is responsible for ferroelectric behavior, is formed even at low temperatures (400 C or less). Herein, the various factors such as doping effects, deposition method, annealing method and conditions, and substrate material are reviewed, focusing on thermal budget, especially the low-temperature annealing process for formation of the ferroelectric phase. These low-thermal-budget processes facilitate not only the integration of ferroelectric circuits in the back-end-of-line to increase the effective memory area and add more functionalities but also applications for flexible and wearable electronics.

The ferroelectric (FE) properties of 10-nm-thick Hf0.5Zr0.5O2 (HZO) films deposited by an atomic layer deposition technique were improved by adopting O3 as an oxygen source instead of H2O. All HZO films were annealed at 400 °C for 1 min in an N2 atmosphere after TiN top electrode deposition. Regardless of the oxygen source, the HZO films exhibited the formation of a noncentrosymmetric orthorhombic phase, which is responsible for FE behavior with the suppression of the monoclinic phase. However, compared to the O3-based HZO film, it was confirmed that the H2O-based HZO film was more incorporated with hydrogen derived from H2O, thereby degrading FE polarization and leakage behavior. The results indicate that the strategy of using O3 as the oxygen source is useful for the fabrication and integration of FE HZO films for next-generation memory applications.

Increasing interest in the development of alternative energy storage technologies has led to efforts being taken to improve the energy density of dielectric capacitors with high power density. However, dielectric polymer materials still have low energy densities because of their low dielectric constant, whereas Pb-based materials are limited by environmental issues and regulations. Here, the energy storage behaviors of atomic layer-deposited Hf 1−X Zr X O 2 (X = 0−1) thin films (10 nm) and the phase transformation mechanism associated with an enhancement of their energy density are reported using unipolar pulse measurements. Based on electrical and material characterization, the energy density and energy efficiency are dependent on the Zr content, and stress-induced crystallization by the encapsulating Hf 1−X Zr X O 2 films with TiN top electrodes prior to annealing can enhance the energy density (up to 47 J/cm 3 at a small voltage value of 3.5 MV/cm) while minimizing energy loss even at low process temperatures (400 °C). This work will facilitate the realization of Hf 1−X Zr X O 2 -based capacitors for lead-free electrostatic energy storage applications.

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.

The discovery of ferroelectricity in HfO2-based materials in 2011 provided new research directions and opportunities. In particular, for atomic layer deposited Hf0.5Zr0.5O2 (HZO) films, it is possible to obtain homogenous thin films with satisfactory ferroelectric properties at a low thermal budget process. Based on experiment demonstrations over the past 10 years, it is well known that HZO films show excellent ferroelectricity when sandwiched between TiN top and bottom electrodes. This work reports a comprehensive study on the effect of TiN top and bottom electrodes on the ferroelectric properties of HZO thin films (10 nm). Investigations showed that during HZO crystallization, the TiN bottom electrode promoted ferroelectric phase formation (by oxygen scavenging) and the TiN top electrode inhibited non-ferroelectric phase formation (by stress-induced crystallization). In addition, it was confirmed that the TiN top and bottom electrodes acted as a barrier layer to hydrogen diffusion into the HZO thin film during annealing in a hydrogen-containing atmosphere. These features make the TiN electrodes a useful strategy for improving and preserving the ferroelectric properties of HZO thin films for next-generation memory applications.

In this Letter, a high-pressure annealing (HPA) process is proposed as a way to reduce the thermal budget of Hf0.5Zr0.5O2 (HZO) thin films with ferroelectric behaviors. The low-thermal-budget process is essential for integrating ferroelectric devices in the back-end-of-line to provide more functionalities and effective memory area. For the HZO film annealed at 300 °C using the HPA process, an orthorhombic phase responsible for ferroelectric behavior was formed with a decrease in film thickness, resulting in a remanent polarization (Pr) of ∼13 μC/cm2 (i.e., 2Pr of ∼26 μC/cm2). Meanwhile, when only the annealing time was increased at 300 °C without applying pressure, the HZO film did not crystallize and exhibited linear dielectric properties. Consequently, the HZO films (&lt;10 nm) can be crystallized by applying pressure (15 atm) even at low temperatures of 300 °C, thereby obtaining ferroelectric properties.