Thickness Of HfO2 Film Research Articles

Effect of film growth thickness on the refractive index and crystallization of HfO2 film

A series of Hafnium dioxide (HfO2) thin films with nominal thickness of 5–350 nm were reactively deposited on silicon（100）substrates at 200 °C using electron-beam evaporation. Based on the measurement and characterization techniques of spectroscopic ellipsometry, X ray diffraction, scanning electron microscopy and atomic force microscopy, the effect of growth thickness on the refractive index and crystallization of HfO2 film grown under the same conditions was studied. The results indicate that the change of refractive index of HfO2 film is closely related to the change of microstructure i.e., grain size and crystallization which change obviously with the increasing growth thickness. The average refractive index at 633 nm decreases about from 1.97 to 1.84 with the increase of the average size about from 0.5 nm to 7~8 nm and the crystallinity from zero to 74% when the thickness of HfO2 film increases from 5 nm to 350 nm. Meanwhile, a critical growth thickness of HfO2 film, somewhere on order of 130 nm, is confirmed at which the film transforms from an amorphous to a polycrystalline monoclinic structure. The sharp change of microstructure near the critical thickness value of HfO2 film leads to the abrupt change of optical properties of HfO2 film, such as the turning behaviors of the refractive index curve. The correlation between phase transformation, size and orientation of crystallite, packing density and hence the refractive index is established. The possible interpretations are proposed to well understand the underlying mechanism of the evolution of optical properties in HfO2 film-forming process.

Optimization and integration of ultrathin e-beam grown HfO2 gate dielectrics in MoS2 transistors

Integration of high-k dielectrics with two-dimensional (2D) layered semiconductors is one of the bottleneck in realization of the devices in a viable technology. In this work we report on the optimization and integration of electron beam (e-beam) evaporated, ultrathin (5 nm) HfO2 thin films on a few layer (5–7 nm) MoS2 substrate, without the need for any functionalization and buffer layers. The effect of HfO2 film thickness on optical, compositional and electrical properties of the material has been evaluated using ellipsometry, Rutherford backscattering, x-ray photoelectron spectroscopy and electrical measurements. The estimated dielectric constant and leakage current density values have been correlated with the refractive index and density of the films. It has been observed that the dielectric constant decreased drastically in ultrathin (5 nm) HfO2 film in case of Al as a gate electrode due to the formation of interfacial layer. The effect of gate electrode material and its processing on dielectric properties of ultra-thin films has been studied in detail and it is found that e-beam evaporated Ni seems to be a promising gate electrode. Equivalent oxide thickness of 1.2 nm and leakage current density (J) of 1.1 × 10−4 A cm−2 have been achieved for 5 nm films with Ni as gate electrode. Top gated MoS2 transistors with, 5 nm HfO2 gate dielectric show very good performance with I ON to I OFF ratio of 106. We thus demonstrate e-beam evaporation as a promising technique to directly integrate high-k dielectrics (HfO2) with 2D materials.

Fabrication and performances of double-sided HfO2 anti-reflection films with ultra-high infrared transmittance

Si is one of the most important infrared optical materials. However, the high refraction index of Si in the infrared regions leads to large reflection losses, so increasing the infrared transmittance is of great significance to practical application. HfO2 film is widely investigated due to the high-k gate dielectric properties. And it also has excellent optical properties to be used as anti-reflection film for Si. In this study, doubled-sided HfO2 films (HfO2/Si/HfO2) were fabricated as anti-reflection coating on Si substrate to further enhance the infrared transmittance (99%). And the transmittance peak can be regulated by adjusting the thickness of HfO2 film. Besides, the deposition temperature had been optimized by using XRD, XPS, SEM, AFM, and optical measurements. The results indicate good crystallinity and flat surface for the samples. Furthermore, HfO2 films show surface hydrophobic properties, which can prevent water in the infrared application. These encouraging results show the HfO2 films have excellent application prospective for the infrared optical systems.

Influence of film thickness on the dielectric characteristics of hafnium oxide layers

The present work focuses on the study of properties of hafnium oxide (HfO2) films, deposited by reactive magnetron sputtering of the Hf target in Ar/O2 gas mixture. The X-ray diffraction analysis of the deposited films proved the amorphous structure of the films, which was also confirmed by the Raman spectroscopy.It was determined that as the HfO2 film thickness had been decreased from 98.6 nm to 13.5 nm, film density had dropped from 9.52 to 9.26 g/cm2. At the same time, the dielectric constant dropped from 21.3 to 8.0 units, and the dielectric loss tangent rose, especially at high frequencies. At the same time, the decrease in film thickness resulted in increased leakage currents at low electric field density E, and decreased leakage currents at high E. Improvement of dielectric characteristics and increase in leakage current with film thickness growth is a consequence of film densification and the formation of a crystalline phase. Thickness dependence of the dielectric constant is associated with the violation of the ionic polarization mechanism at the film electrode interface.

Stable ceria-based electrolytes for intermediate temperature-solid oxide fuel cells via hafnium oxide blocking layer

The electronic loss of ceria-based electrolytes is caused by the reduction of ceria at low oxygen partial pressure for intermediate temperature-solid oxide fuel cells. To address this issue, a thin hafnium oxide layer is deposited at the interface between the anode and electrolyte using a magnetron sputtering system, based on the hypothesis that the stability of ceria electrolytes in the anode side can be controlled as a function of the reducibility of the ceria surface. The performance of ceria-based cells (Nd0.1Ce0.9O2-δ; NDC, Sm0.2Ce0.8O2-δ; SDC) is investigated by varying the HfO2 film thickness on the same ceria-based substrate. The range of thickness of the HfO2 film is 121–686 Å for 6–30 min with the deposition rate of 0.38 Å‧S−1. The open-circuit voltages and power densities of NDC- and SDC-based cells are measured at 600–700 °C as a function of HfO2 film thickness. It is clearly observed that open-circuit voltages and the maximum power densities of both cells increase with the increasing of thickness of HfO2 film until a film thickness of 600 Å is reached. This indicates that the HfO2 layer effectively prevents the electron transfer through the electrolytes by the reduction of ceria. Furthermore, the NDC-cell with the HfO2 film shows a stable performance under a constant current density operation of 130 h at 650 °C.

Possibility of measuring range extension of growing thin films thickness control, based on surface plasmon resonance effect

Dependence of excitation angle of surface electromagnetic waves on HfO2 film thickness was investigated. Modeling for different wavelengths showed the method’s applicability for real-time and high-resolution film thickness control. Proposed method can be used for development of fundamentally new nanoscale films thickness control systems.

Damage evaluation in graphene underlying atomic layer deposition dielectrics.

Based on micro-Raman spectroscopy (μRS) and X-ray photoelectron spectroscopy (XPS), we study the structural damage incurred in monolayer (1L) and few-layer (FL) graphene subjected to atomic-layer deposition of HfO2 and Al2O3 upon different oxygen plasma power levels. We evaluate the damage level and the influence of the HfO2 thickness on graphene. The results indicate that in the case of Al2O3/graphene, whether 1L or FL graphene is strongly damaged under our process conditions. For the case of HfO2/graphene, μRS analysis clearly shows that FL graphene is less disordered than 1L graphene. In addition, the damage levels in FL graphene decrease with the number of layers. Moreover, the FL graphene damage is inversely proportional to the thickness of HfO2 film. Particularly, the bottom layer of twisted bilayer (t-2L) has the salient features of 1L graphene. Therefore, FL graphene allows for controlling/limiting the degree of defect during the PE-ALD HfO2 of dielectrics and could be a good starting material for building field effect transistors, sensors, touch screens and solar cells. Besides, the formation of Hf-C bonds may favor growing high-quality and uniform-coverage dielectric. HfO2 could be a suitable high-K gate dielectric with a scaling capability down to sub-5-nm for graphene-based transistors.

Electronic properties at the oxide interface with silicon and germanium through x-ray induced oxide charging

A dependence of the binding energy of the Hf 4f and O 1s photoemission lines on the thickness of the HfO2 film is identified in HfO2/Si heterojunctions and associated with differential charging phenomena. No shifts of Hf 4f and O 1s binding energies are observed in HfO2/Ge heterojunctions, irrespective of the HfO2 film thickness. The time evolution of Hf 4f and Ge 3d signals correlates with a large number of electrically active traps, which are close to the Ge valence bands and determine a negative charge builds-up at the interface, causing the commonly observed p-type surface inversion in n-Ge.

Deposition cycle of atomic layer deposition HfO2 film: Effects on electrical performance and reliability

Varying thicknesses of the HfO2 films prepared by atomic layer deposition (ALD) were compared in terms of electrical properties and reliability. Scaling the physical thickness of the HfO2 dielectric did not increase the capacitance as expected due to the thicker interfacial SiOX layer obtained by the oxidation process used for thermal annealing. After thermal annealing, HfO2 crystallization increased with the thickness of HfO2 film, which then increases the dielectric constant for the bulk HfO2 film. The breakdown behaviors of the HfO2 gate dielectric film were not scaled to thickness, improved with HfO2 thickness until saturation. The reliability characteristics of the HfO2 dielectric under unipolar AC stressing were also evaluated. Dielectric breakdown failure time of unipolar AC stressing becomes longer in comparison to that stressed in constant voltage stress. As the thickness of the HfO2 dielectric increases, a larger lifetime enhancement is detected due to the effective charge de-trapping for thicker dielectrics under AC stressing.

Impact of substrate temperature and film thickness on the interfacial evolution during atomic layer deposition of HfO2 on InP

AbstractThe effects of both the deposition temperature and the HfO2 film thickness on the interfacial layer (IL) evolution were studied when tetrakis(ethylmethylamino)hafnium and H2O based atomic layer deposition (ALD) was performed on InP substrates. While the self‐cleaning effect resulted in an IL‐free structure after formation of ∼2 nm thick HfO2 at 200 °C and 250 °C, substantial IL growth occurred at 300 °C, probably due to simultaneous InP oxidation. Following further growth to ∼8 nm at 300 °C, the IL was almost removed and, in particular, a significant In incorporation into the HfO2 film was observed, which was attributed to IL decomposition and subsequent out‐diffusion of the constituent elements. (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Dielectric thickness dependence of carrier mobility in graphene with HfO2 top dielectric

We investigate the carrier mobility in monolayer and bilayer graphene with a top HfO2 dielectric, as a function of the HfO2 film thickness and temperature. The results show that the carrier mobility decreases during the deposition of the first 2–4 nm of top dielectric and remains constant for thicker layers. The carrier mobility shows a relatively weak dependence on temperature indicating that phonon scattering does not play a dominant role in controlling the carrier mobility. The data strongly suggest that fixed charged impurities located in close proximity to the graphene are responsible for the mobility degradation.

Role of oxygen vacancy in HfO2∕SiO2∕Si(100) interfaces

We have investigated the interface states in HfO2∕SiO2∕Si(100) systems that were prepared by using the in situ pulsed laser deposition technique. X-ray photoelectron spectroscopy data revealed that when the HfO2 film thickness exceeds 11Å, the film composition undergoes a systematic change from Hf silicate to oxygen-deficient HfOx<2. Furthermore, we determined that the evolution of the interface states clearly depends on the oxygen condition applied during the film growth and that the oxygen vacancy is an important parameter for Hf silicate formation.

Control of silicidation in HfO2∕Si(100) interfaces

The interfacial states of the HfO2 thin film grown on the Si(100) substrate by the pulsed laser deposition method is investigated in situ using x-ray photoelectron spectroscopy. They are found to depend on the HfO2 film thickness, oxygen pressure during the pulsed laser deposition growth, and the deposition process. The hafnium silicide is formed in an oxygen-deficient condition, and it can be most effectively controlled by the ambient oxygen pressure during film growth. The close relation between the silicide formation and abundance of the silicon suboxides at the interface is presented.