Structural, Optical and Electrical Properties of HfO2 Thin Films Deposited at Low-Temperature Using Plasma-Enhanced Atomic Layer Deposition

Surface Morphology and Optical Properties of Hafnium Oxide Thin Films Produced by Magnetron Sputtering

Hafnium oxide films were deposited on sapphire and silicon (100) substrates using the DC reactive magnetron sputtering technique from a pure hafnium target at different discharge power levels. The influence of the cathode power on the chemical composition, morphology, crystallographic structure and optical properties of the films was investigated. X-ray diffraction (XRD), energy dispersive X-ray analysis (EDX) and Fourier-transform infrared spectroscopy (FTIR) were employed to determine the chemical composition and bonding structure. In all cases, the films were found to be amorphous or nanocrystalline with increased crystalline content as the sputtering power was increased, according to XRD and FTIR. In addition, EDX showed that the films were oxygen-rich. The effect of power deposition on the surface topography and morphology of the films was studied using atomic force microscopy (AFM) and scanning electron microscopy (SEM). The AFM and SEM images revealed the emergence of mound morphologies as the cathode power was increased. These features are related to blistering effects probably due to the presence of stress and its promotion within the film thickness. Finally, the optical properties showed an average transmission of 80% in the visible range, and the refractive index determined by spectral ellipsometry (SE) was found to be in the range of 1.85-1.92, close to the reported bulk value. SE was also used to study the film porosity observed by SEM, which can be related to the oxygen-rich character of the films.

Characteristics of Hf0.5Zr0.5O2 Thin Films Prepared by Direct and Remote Plasma Atomic Layer Deposition for Application to Ferroelectric Memory

Hf_0.5Zr_0.5O₂ (HZO) thin film exhibits ferroelectric properties and is presumed to be suitable for use in next-generation memory devices because of its compatibility with the complementary metal-oxide-semiconductor (CMOS) process. This study examined the physical and electrical properties of HZO thin films deposited by two plasma-enhanced atomic layer deposition (PEALD) methods- direct plasma atomic layer deposition (DPALD) and remote plasma atomic layer deposition (RPALD)-and the effects of plasma application on the properties of HZO thin films. The initial conditions for HZO thin film deposition, depending on the RPALD deposition temperature, were established based on previous research on HZO thin films deposited by the DPALD method. The results show that as the measurement temperature increases, the electric properties of DPALD HZO quickly deteriorate; however, the RPALD HZO thin film exhibited excellent fatigue endurance at a measurement temperature of 60 °C or less. HZO thin films deposited by the DPALD and RPALD methods exhibited relatively good remanent polarization and fatigue endurance, respectively. These results confirm the applicability of the HZO thin films deposited by the RPALD method as ferroelectric memory devices.

Crystallinity Effect on Electrical Properties of PEALD-HfO2 Thin Films Prepared by Different Substrate Temperatures

Hafnium oxide (HfO₂) thin film has remarkable physical and chemical properties, which makes it useful for a variety of applications. In this work, HfO₂ films were prepared on silicon through plasma enhanced atomic layer deposition (PEALD) at various substrate temperatures. The growth per cycle, structural, morphology and crystalline properties of HfO₂ films were measured by spectroscopic ellipsometer, grazing-incidence X-ray diffraction (GIXRD), X-ray reflectivity (XRR), field-emission scanning electron microscopy, atomic force microscopy and x-ray photoelectron spectroscopy. The substrate temperature dependent electrical properties of PEALD-HfO₂ films were obtained by capacitance-voltage and current-voltage measurements. GIXRD patterns and XRR investigations show that increasing the substrate temperature improved the crystallinity and density of HfO₂ films. The crystallinity of HfO₂ films has a major effect on electrical properties of the films. HfO₂ thin film deposited at 300 °C possesses the highest dielectric constant and breakdown electric field.

Role of Oxygen Source on Buried Interfaces in Atomic-Layer-Deposited Ferroelectric Hafnia-Zirconia Thin Films

Hafnia-zirconia (HfO₂-ZrO₂) solid solution thin films have emerged as viable candidates for electronic applications due to their compatibility with Si technology and demonstrated ferroelectricity at the nanoscale. The oxygen source in atomic layer deposition (ALD) plays a crucial role in determining the impurity concentration and phase composition of HfO₂-ZrO₂ within metal-ferroelectric-metal devices, notably at the Hf_0.5Zr_0.5O₂ /TiN interface. The interface characteristics of HZO/TiN are fabricated via sequential no-atmosphere processing (SNAP) with either H₂O or O₂-plasma to study the influence of oxygen source on buried interfaces. Time-of-flight secondary ion mass spectrometry reveals that HZO films grown via O₂-plasma promote the development of an interfacial TiO_x layer at the bottom HZO/TiN interface. The presence of the TiO_x layer leads to the development of 111-fiber texture in HZO as confirmed by two-dimensional X-ray diffraction (2D-XRD). Structural and chemical differences between HZO films grown via H₂O or O₂-plasma were found to strongly affect electrical characteristics such as permittivity, leakage current density, endurance, and switching kinetics. While HZO films grown via H₂O yielded a higher remanent polarization value of 25 μC/cm², HZO films grown via O₂-plasma exhibited a comparable P_r of 21 μC/cm² polarization and enhanced field cycling endurance limit by almost 2 orders of magnitude. Our study illustrates how oxygen sources (O₂-plasma or H₂O) in ALD can be a viable way to engineer the interface and properties in HZO thin films.

Low-Temperature Atomic Layer Deposition of Hafnium Oxide for Gating Applications

We present a novel low-temperature (30 °C) atomic layer deposition process for hafnium oxide and apply the layers as gate dielectric to fabricate devices out of the thermally sensitive topological insulator HgTe. The key to achieving self-limiting growth at these low temperatures is the incorporation of sufficiently long purge times ( ≥150 s) in the deposition cycles. We investigate the structural and compositional properties of these thin films using X-ray reflectometry and photoelectron spectroscopy, finding a growth rate of 1.6 Å per cycle and an atomic ratio of Hf/O of 1:1.85. In addition, we report on the transport properties of the microstructured devices, which are much enhanced compared to previous device generations. We determine a relative permittivity of ∼15 for our HfO2 layers. Our process considerably reduces the thermal load of the samples during microfabrication and can be adapted to a broad range of materials, enabling the fabrication of high-quality gate insulators on various temperature-sensitive materials.

Study on total reflection performance of films grown by atomic layer deposition relevant to X-ray reflective optics

For X-ray reflective optics that work based on the concept of total external reflection, coating the reflector surface with high-density film is a common idea to enhance performance. Atomic layer deposition (ALD) has been proven to be a promising way to coat the reflector surface with a large curvature, even the inner surface of an X-ray capillary. In this paper, HfO₂ and iridium films were prepared on flat silicon and glass substrates via ALD, and X-ray reflectivity (XRR) was used as a main tool to investigate the effect of film properties on the total reflection performance.

Plasma-Enhanced Atomic Layer Deposition of HfO2 with Substrate Biasing: Thin Films for High-Reflective Mirrors

Tuning ion energies in plasma-enhanced atomic layer deposition (PEALD) processes enables fine control over the material properties of functional coatings. The growth, structural, mechanical, and optical properties of HfO₂ thin films are presented in detail toward photonic applications. The influence of the film thickness and bias value on the properties of HfO₂ thin films deposited at 100 °C using tetrakis(dimethylamino)hafnium (TDMAH) and oxygen plasma using substrate biasing is systematically analyzed. The HfO₂ films deposited without a substrate bias show an amorphous microstructure with a low density, low refractive index, high incorporation of residual hydroxyl (OH) content, and high residual tensile stress. The material properties of HfO₂ films significantly improved at a low bias voltage due to the interaction with oxygen ions accelerated to the film. Such HfO₂ films have a higher density, higher refractive index, and lower residual OH incorporation than films without bias. The mechanical stress becomes compressive depending on the bias values. Further increasing the ion energies by applying a larger substrate bias results in a decrease of the film density, refractive index, and a higher residual OH incorporation as well as crystalline inclusions. The comparable material properties of the HfO₂ films have been reported using tris(dimethylamino)cyclopentadienyl hafnium (TDMACpH) in a different apparatus, indicating that this approach can be transferred to various systems and is highly versatile. Finally, the substrate biasing technique has been introduced to deposit stress-compensated, crack- and delamination-free high-reflective (HR) mirrors at 355 and 532 nm wavelengths using HfO₂ and SiO₂ as high and low refractive index materials, respectively. Such mirrors could not be obtained without the substrate biasing during the deposition because of the high tensile stress of HfO₂, leading to cracks in thick multilayer systems. An HR mirror for 532 nm wavelength shows a high reflectance of 99.93%, a residual transmittance of ∼530 ppm, and a low absorption of ∼11 ppm, as well as low scattering losses of ∼4 ppm, high laser-induced damage threshold, low mechanical stress, and high environmental stability.

Effect of Process Temperature on Density and Electrical Characteristics of Hf0.5Zr0.5O2 Thin Films Prepared by Plasma-Enhanced Atomic Layer Deposition

HfxZr1−xO2 (HZO) thin films have excellent potential for application in various devices, including ferroelectric transistors and semiconductor memories. However, such applications are hindered by the low remanent polarization (Pr) and fatigue endurance of these films. To overcome these limitations, in this study, HZO thin films were fabricated via plasma-enhanced atomic layer deposition (PEALD), and the effects of the deposition and post-annealing temperatures on the density, crystallinity, and electrical properties of the thin films were analyzed. The thin films obtained via PEALD were characterized using cross-sectional transmission electron microscopy images and energy-dispersive spectroscopy analysis. An HZO thin film deposited at 180 °C exhibited the highest o-phase proportion as well as the highest density. By contrast, mixed secondary phases were observed in a thin film deposited at 280 °C. Furthermore, a post-annealing temperature of 600 °C yielded the highest thin film density, and the highest 2Pr value and fatigue endurance were obtained for the film deposited at 180 °C and post-annealed at 600 °C. In addition, we developed three different methods to further enhance the density of the films. Consequently, an enhanced maximum density and exceptional fatigue endurance of 2.5 × 107 cycles were obtained.

Characterization of Electrical Traps Formed in Al2O3 under Various ALD Conditions

Frequency dispersion in the accumulation region seen in multifrequency capacitance-voltage characterization, which is believed to be caused mainly by border traps, is a concerning issue in present-day devices. Because these traps are a fundamental property of oxides, their formation is expected to be affected to some extent by the parameters of oxide growth caused by atomic layer deposition (ALD). In this study, the effects of variation in two ALD conditions, deposition temperature and purge time, on the formation of near-interfacial oxide traps in the Al₂O₃ dielectric are examined. In addition to the evaluation of these border traps, the most commonly examined electrical traps-i.e., interface traps-are also investigated along with the hysteresis, permittivity, reliability, and leakage current. The results reveal that a higher deposition temperature helps to minimize the formation of border traps and suppress leakage current but adversely affects the oxide/semiconductor interface and the permittivity of the deposited film. In contrast, a longer purge time provides a high-quality atomic-layer-deposited film which has fewer electrical traps and reasonable values of permittivity and breakdown voltage. These findings indicate that a moderate ALD temperature along with a sufficiently long purge time will provide an oxide film with fewer electrical traps, a reasonable permittivity, and a low leakage current.