PbZr1−xTixO3 (PZT) has been intensively studied for various ferroelectric applications. Its promising application for micro-electro-mechanical system has reignited the interests due to its outstanding ferroelectric and piezoelectric properties. Most PZT ceramics employed in devices are synthesized with a Zr/Ti ratio close to the tetragonal–rhombohedral morphotropic phase boundary (x=0.48) due to its high electro-mechanical coupling at this composition. Morphotropic phase boundary is particularly interesting to study for the investigation of phase transition. In this work, we report the epitaxial growth and electrical characterization of epitaxial PZT (Zr/Ti=52/48) thin films on Nb-doped SrTiO3. PZT films, with thickness from 30nm to 65nm, were deposited by sol–gel method and eventually crystallized at 700°C by rapid thermal annealing in oxygen. Film ferroelectricity was confirmed by Sawyer–Tower circuit measurement. X-ray diffraction analysis indicates a thickness-dependent structural phase, i.e., a phase transition from tetragonal phase for the thinner film to a biphasic (tetragonal+pseudo-cubic) structure for the thicker film, which is characterized by ellipsometry as a phase separation from the bottom surface of the film to the top one. This phase transition is related to a composition gradient within the film thickness.

Tantalum oxynitride thin films are deposited by radio-frequency magnetron sputtering using a pure tantalum target under argon/oxygen/nitrogen gas mixture. The argon flow is kept constant while the oxygen and nitrogen flows are changed simultaneously in a way to keep constant the total flow of these reactive gases. We succeed to deposit TaOxNyfilms with stoichiometry ranging between those of TaN and Ta2O5. All films are deposited at room temperature and are amorphous. Spectroscopic ellipsometry and UV-visible spectrometry investigations show a direct relation between the optical properties and the stoichiometry of the films. In particular, the results show a variation of the refractive index from pure tantalum nitride-like films (3.76) to tantalum pentoxyde-like films (2.1), which confirms the possibility to deposit graded antireflective coatings with tantalum oxynitride.

Optical properties of silicon oxynitride thin films of variable composition were investigated. Their refractive index was found to decrease linearly from 1.94 to 1.46 when their composition varies between silicon nitride and silicon oxide. Spectroscopic ellipsometry showed that all samples were transparent over the visible range and that the layer structure also influences their optical properties. Using UV-visible spectroscopy, it was found that the film absorption decreases with increasing the oxygen amount in their composition. The optical gap determined from the transmission spectra showed high values increasing with the oxygen concentration. The Urbach energy was also estimated and linked to the film structure and composition.

We synthesized polycrystalline Bi2+xTe3−x (−0.2<x<0.2) thin films by electrodeposition in acidic medium. Since Bi2Te3-like structure may be uniaxially anisotropic due to its rhombohedral crystallographic system, we investigated their optical behavior using ex and in situ Mueller matrix spectroscopic ellipsometry in the wavelength range of 470 to 830 nm (1.5–2.6 eV). We found that room-temperature electroplated polycrystalline appears optically isotropic and that no depolarization effect occurs from the first steps of growth until several micrometers thick films. Additional ex situ measurements permit to obtain their optical constants from far-ultraviolet to near-infrared (190–2100 nm).

We synthesized polycrystalline Bi 2 + x Te 3 − x (− 0.2 x 2 Te 3 -like structure may be uniaxially anisotropic due to its rhombohedral crystallographic system, we investigated their optical behavior using ex and in situ Mueller matrix spectroscopic ellipsometry in the wavelength range of 470 to 830 nm (1.5–2.6 eV). We found that room-temperature electroplated polycrystalline appears optically isotropic and that no depolarization effect occurs from the first steps of growth until several micrometers thick films. Additional ex situ measurements permit to obtain their optical constants from far-ultraviolet to near-infrared (190–2100 nm).

Composition and interfacial properties of LaAlO3/Si thick (50 nm) and thin (7 nm) films were accessed by Far Ultra-Violet Spectroscopic Ellipsometry (FUV-SE), X-Ray Reflectometry (XRR) and X-Ray Photoelectron Spectroscopy (XPS). FUV-SE correlated to XRR analysis shows that LaAlO3/Si thick and thin films should be modelled by three-layer stacks using Tauc-Lorentz dispersion law. Annealing effects of LaAlO3/Si thin films such as increase of interfacial layer thickness and intermixing between high-κ oxide and Si were demonstrated by FUV-SE, and confirmed by XRR and XPS measurements. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

ABSTRACT Thermal stability, electrical and structural properties induced by nitrogen incorporation in lanthanum-based high-k dielectrics were investigated. Thermal growth of a thin silicon oxynitride previously to LaAlO3 deposition induced higher dielectric constant, lower equivalent oxide thickness, and better interfacial stability during post-deposition annealing of MOS structures. But it also degraded others electrical and structural properties such as leakage current and charges densities, and interfacial roughness. Deposition of LaAlON films, either by reactive sputtering in Ar/N2 plasma, or by thermal nitridation in ammonia of LaAlO3, reduced partially several thermal instabilities after post-deposition annealing in 18O2, such as metallic losses, silicon diffusion and substrate oxidation.

LaAlO3 and HfAlxOy thin films have been deposited by magnetron sputtering for replacement of SiO2 in new Complementary Metal Oxide Semiconductor applications. A three-layer model was found both in X-ray reflectivity (XRR) and spectroscopic ellipsometry (SE) analysis to be the best optical model for these two high-kappa materials. It was composed of an interfacial layer, covered by a layer of pure LaAlO3 or HfAlxOy, and a surface-roughness layer. In the case of LaAlO3 and HfAlxOy directly deposited on Si, the interfacial layer is a mixture of high-k material and amorphous-Si inclusions, which thickness is growing after post-deposition annealinu (PDA) in O-2 at 600 degrees C. On the contrary, for films deposited on thermally nitrided Si, the SiON-like interface did not change significantly after a PDA in 0, XRR analysis showed that the dielectric/Si interface of HfAlxOy/SiON/Si structure had a significantly smaller roughness than those of HfAlxOy/Si. When being deposited on SiON/Si substrates, HfAlxOy, and to a lesser extent LaAlO3, demonstrate superior diffusion barrier properties pointed out by X-ray photoelectron spectroscopy. (C) 2008 Elsevier B.V. All rights reserved.

Electrical and structural properties of metal-oxide-semiconductor capacitors having as dielectric nanoscopic LaAlO3 or HfAlOx films deposited on nitrided or nonnitrided Si substrates were investigated. The electrical superiority of RuO2/HfAlOx/SiON/Si stacks was evidenced by a dielectric constant of 19 and a leakage current density of 67 mA/cm(2) at a gate voltage of -1 V, for a capacitance equivalent to silicon oxide thickness of 1.1 nm. Morphology, composition, and structure of the stacks were accessed by X-ray diffraction and reflectometry, spectroscopic ellipsometry, X-ray photoelectron spectroscopy, and narrow resonant nuclear reaction profiling with isotopic substitution. In spite of presenting crystalline phases associated with HfO2, the HfAlOx dielectric layers led to a smoother and thinner interfacial layer, improved by the thermal nitridation of the Si substrate prior to high-kappa deposition. This SiON-like interlayer thickness is self-limited even after postdeposition annealing owing to the formation of an effective diffusion barrier by the strong N-Si-N and N-Si-O-N bonds, which is also effective in preventing substrate oxidation. (C) 2008 The Electrochemical Society.

We present a quantitative and comparative ellipsometric study of two switchable solids, undergoing a first-order transition around ambient temperature: the spin-crossover (SC), [Fe(NH2-trz)(3)]Br-2 and the cooperative Jahn-Teller (JT) switch, RbMn[Fe(CN)(6)]. Ellipsometric spectra have been recorded in the optical range 240-1000nm and temperature interval 260-380 for both solids. We found that absorption spectra of the SC show temperature invariant isobestic point, while that of the JT clearly indicates a thermally induced energy shift, in relation with the structural transition of this material. Integrating the absorption spectra, we derived the thermal dependence of the fractions of the high-temperature phases for both solids, and found them in excellent agreement with that of magnetic data;

In order to investigate the effects of the sputter deposition parameters and the influence of the post-deposition thermal treatment on the LaAlO3/ Si interface, Rutherford Backscattering Spectrometry (RBS), ion channeling, Nuclear Reaction Analysis (NRA), X-ray Photoemission Spectroscopy (XPS), Capacitance-Voltage measurements and Spectroscopic Ellipsometry (SE) were performed on LaAlO3/Si or RuO2/LaAlO3/Si Metal-Oxide-Semiconductor (MOS) structures. RBS-channeling revealed that the Si surface damage due to sputtering deposition at LaAlO3/Si interface is reduced when increasing the deposition pressure, between 0.5 and 5 Pa, and when annealing the films in 1 atm of O-2 at 450 degrees C. XPS spectra were correlated to RBS and NRA measurements. Even if the formation of a low-kappa interfacial layer is demonstrated by SE measurements, high deposition pressure and post-deposition annealing in O-2 at 600 degrees C were found to be the best procedure to improve the electrical characteristics of MOS structures in terms of fixed charge and slow trap densities. For these parameters, the K value was found to be 14, and the equivalent interfacial thickness was estimated to be 1.3 nm, which is lower that most of the previously reported values. (C) 2007 Elsevier B.V. All rights reserved.

The electrical characteristics of RuO2∕HfAlO∕SiON∕Si(001) capacitors prepared by thermal nitridation of the Si substrate previously to HfAlO ultrathin film deposition were determined. A dielectric constant of 19 and a gate current density of 67mA∕cm2 for an equivalent oxide thickness of 1.1nm have been determined, whereas non-nitrided capacitors gave substantially lower dielectric constant and higher gate current density. The structure and integrity of the stacks after thermal annealing were accessed by means of spectroscopic ellipsometry and x-ray reflectometry, indicating that thermal N incorporation into the gate dielectric stacks forms an effective diffusion barrier, leading to a smoother, SiO2-like interface. The HfAlO films grown on nitrided substrates were seen also to have lower porosity, percentage of voids, and density of oxygen vacancies.

We investigated the thermal hysteresis of a pelleted sample of the spin-crossover compound [Fe(NH2-trz)(3)]Br-2 by means of spectroscopic ellipsometry, in the temperature range 264-358 K. The ellipsometric parameters (psi,Delta) have been recorded in the optical range 240-1000 nm. The corresponding absorption and dispersion spectra show temperature-invariant isobestic points located at 240 and 291 nm, respectively. We found that the high-spin-fraction data, derived from the integrated absorption curves, are in excellent agreement with the magnetic data recorded on the same sample. We also investigated the consistency of the optical data by application of the Kramers-Kronig relations, which are well obeyed above similar to 450 nm. All these results demonstrate that the spectroscopic ellipsometry is well adapted to characterize the spin-crossover transition. We also expect that this nondestructive technique will be highly relevant to investigate the physical properties of thin films of switchable molecular solids, involving a change in the electronic properties upon a thermally or photoinduced phase transition.

In this work. we report on the study of dielectric function of nanocrystalline germanium (nc-Ge) implanted in a host matrix SiO2 on a silicon substrate by spectroscopic ellipsometry (SE). The presence of nc-Ge is observed by transmission electron microscopy (TEM). The SE measurements are performed at 70 degrees of angle of incidence in air at room temperature.We observe that the ellipsometric angles psi and Delta change under specific conditions of elaboration. The dielectric function of germanium nanocrystals epsilon(nc-Ge) is extracted using wavelength by wavelength inversion method, without any dispersion law or adjustment parameters. The critical points are determined from the second derivative of the imaginary part of the dielectric function. As expected the significant broadening of the critical points is observed, the E-0, E-1, E-1 + Delta and E'(0) critical points shift to higher energies, affected by quantum confinement. This implies a significant change in the direct and indirect transitions responsible for the band structure. (c) 2006 Elsevier Ltd. All rights reserved.

In the present paper, we investigate the effect of thermal annealing on optical and microstructural properties of HfO2 thin films (from 20 to 190nm) obtained by plasma ion assisted deposition (PIAD). After deposition, the HfO2 films were annealed in N2 ambient for 3h at 300, 350, 450, 500 and 750°C. Several characterisation techniques including X-ray reflectometry (XRR), X-ray diffraction (XRD), spectroscopic ellipsometry (SE), UV Raman and FTIR were used for the physical characterisation of the as-deposited and annealed HfO2 thin films. The results indicate that as-deposited PIAD HfO2 films are mainly amorphous and a transition to a crystalline phase occurs at a temperature higher than 450°C depending on the layer thickness. The crystalline grains consist of cubic and monoclinic phases already classified in literature but this work provides the first evidence of amorphous-cubic phase transition at a temperature as low as 500°C. According to SE, XRR and FTIR results, an increase in the interfacial layer thickness can be observed only for high temperature annealing. The SE results show that the amorphous phase of HfO2 (in 20nm thick samples) has an optical bandgap of 5.51eV. Following its transition to a crystalline phase upon annealing at 750°C, the optical bandgap increases to 5.85eV.