Ellipsometry Parameters Research Articles

In situ optical characterizations of the annealing effects upon SnO2:F films by spectroscopic ellipsometry

In situ study of the annealing effects, up to 600 °C, upon the optical performance of SnO2:F films have been successfully conducted with spectroscopic ellipsometry. The thickness and optical parameters were obtained by the regression of the measured ellipsometry parameters using a five-layer model. The results show that the re-densification of the SnO2:F layers occurs at above 200 °C, resulting in an irreversible thickness reducing from about 326 nm to about 321 nm. The refractive index of the SnO2:F layer increases with temperature and decreases in the cooling period. The in situ temperature dependence of the average refractive index has a good agreement with the sheet resistance measurement results, not only verifying the annealing process deteriorates the low-emissivity performance, but also demonstrates that spectroscopic ellipsometry method is a suitable optical characterization technique to adjust the on-line coating process of float glass.

Effect of growth interruptions on TiO2 films deposited by plasma enhanced chemical vapour deposition

TiO2 films of ∼300 nm were deposited at low temperature (<140 °C) and pressure (0.4 Pa) using plasma enhanced chemical vapour deposition at the floating potential (Vf) or the substrate self-bias voltage (Vb) of −50 V. The impact of growth interruptions on the morphology, microstructure and optical properties of the films was investigated. The interruptions were carried out by stopping the plasma generation and gas injection once the increase of the layer thickness during each deposition step was about ∼100 nm. In one case of Vf, the films of ∼300 nm exhibit a columnar morphology consisting of a bottom dense layer, an intermediate gradient layer and a top roughness layer. But the growth interruptions result in an increase of the dense layer thickness and a decrease of surface roughness. The film inhomogeneity has been identified by the in-situ real-time evolution of the kinetic ellipsometry (KE) parameters and the modeling process of spectroscopic ellipsometry (SE). The discrepancy of the refractive index measured by SE between bottom and upper layers can be reduced by growth interruptions. In the other case of Vb = −50 V, the films exhibit a more compact arrangement which is homogeneous along the growth direction as confirmed by KE and SE. Both of Fourier transform infrared spectra and X-ray diffraction illustrate a phase transformation from anatase to rutile with the bias of −50 V, and also evidenced on the evolution of the refractive index dispersion curves. And a greatly increase of the refractive indice in the transparent range can be identified. However, the growth interruptions seem to have no influence on the morphology and optical properties in this case.

Optical Character of Barium Titanate Based Thin Films around the Phase Transition

The 0.5BaZr0.2Ti0.8O3-0.5Ba0.7Ca0.3TiO3 (BCZT50) thin films have been prepared on platinized silicon substrates by spin coating and turned out to be ferroelectrics at room temperature. The spectroscopic ellipsometry parameters are accurately simulated by a three-layer model with a Tauc-Lorentz oscillator formula. The calculated temperature-dependent refractive index is intensively investigated. It shows organized variation and a refractive peak explicitly, indicating a significant reference in ferroelectric optics device fabrication.

Surface modifications caused by a swift heavy ion irradiation on crystalline p-type gallium antimonide

Surface modifications caused by a swift heavy ion irradiation on crystalline p-type gallium antimonide crystal have been reported. Single crystal, 100〉 orientations and ∼500μm thick p-type GaSb samples with carrier concentration of 3.30×1017cm−3 were irradiated at 100MeV Fe7+ ions. We have used 15UD Pelletron facilities at IUAC with varying fluences of 5×1010–1×1014 ions cm−2. The effects of irradiation on these samples have been investigated using, spectroscopic ellipsometry, atomic force microscopy and ultraviolet–visible–NIR spectroscopy techniques. Ellipsometry parameters, psi (Ψ) and delta (Δ) for the unirradiated sample and samples irradiated with different fluences were recorded. The data were fit to a three phase model to determine the refractive index and extinction coefficient. The refractive index and extinction coefficient for various fluences in ultraviolet, visible, and infrared, regimes were evaluated. Atomic force microscopy has been used to study these surface modifications. In order to have more statistical information about the surface, we have plotted the height structure histogram for all the samples. For unirradiated sample, we observed the Gaussian fitting. This result indicates the more ordered height structure symmetry. Whereas for the sample irradiated with the fluence of 1×1013, 5×1013 and 1×1014 ions cm−2, we observed the scattered data. The width of the histogram for samples irradiated up to the fluence of 1×1013 ion cm−2 was found to be almost same however it decreased at higher fluence. UV reflectance spectra of the sample irradiated with increasing fluences exhibit three peaks at 292, 500 and 617nm represent the high energy GaSb; E1, E1+Δ and E2 band gaps in all irradiated samples.

Probing initial-stages of ALD growth with dynamic in situ spectroscopic ellipsometry

The initial stages of ALD surface reactions are probed using dynamic in situ spectroscopic ellipsometry (d-iSE) technique during plasma-enhanced ALD of zirconium nitride (ZrN) thin films in spectral range of 0.73–6.4eV. The measured change in the ellipsometry parameter Δ, with every precursor (TDMAZr) and reactant (forming gas plasma) exposure is interpreted as the combined effect of film growth and change in surface chemistry during ALD. We present application of Bruggeman's effective-medium approximation (B-EMA) in the analysis of d-iSE data to determine fractional surface coverage (θ) of ALD grown film at the end of every deposition cycle. During the deposition of first few ZrN monolayers, d-iSE datasets are analyzed on the basis of surface diffusion enhanced ALD growth, where the surface adsorbed precursor molecules can diffuse over substrate surface to occupy energetically favorable surface sites. The determined surface coverage of ZrN films highlights the effects of substrate enhanced ALD growth.

Infrared optical properties of ferroelectric 0.5BaZr0.2Ti0.8O3–0.5Ba0.7Ca0.3TiO3 thin films

0.5BaZr0.2Ti0.8O3–0.5Ba0.7Ca0.3TiO3 (BCZT50) thin films have been prepared on platinized silicon substrates by a modified sol–gel technique and proved to be well-crystallized perovskite ferroelectrics at room temperature. Optical properties of these films in the 2.5–12.5μm wavelength range have been investigated by infrared spectroscopic ellipsometry (IRSE) at room temperature. The measured ellipsometry parameters are well fitted by Brendel oscillator dispersion formula. The optical functions and thickness of films have been uniquely extracted. As the wavelength increases, the refractive index decreases while its extinction coefficient increases. The calculated infrared absorption coefficient increases with increasing wavelength in measured wavelength range. It is greater than 1000cm−1 for the wavelength over 11.3μm. And it is very small and less than 100cm−1 for the wavelength under 7.5μm. The relatively large of the thin films reveals that it is a promising material for infrared pyroelectric detectors and arrays.

Effect of γ-irradiation on Structural and Optical Ellipsometry Parameters of ZnO Nanocrystalline Thin Films

Effect of γ-irradiation on Structural and Optical Ellipsometry Parameters of ZnO Nanocrystalline Thin Films

Spectroscopic ellipsometry study of 0.5BaZr0.2Ti0.8O3–0.5Ba0.7Ca0.3TiO3 ferroelectric thin films

0.5BaZr0.2Ti0.8O3–0.5Ba0.7Ca0.3TiO3 thin films have been deposited on Pt/Ti/SiO2/Si substrates by a modified sol–gel technique. The samples are well-crystallized perovskite ferroelectrics at room temperature, with good surface topography. Optical properties of these films in the 280–850nm wavelength range have been investigated by spectroscopic ellipsometry at room temperature. The measured ellipsometry parameters are well fitted by Tauc–Lorentz oscillator dispersion formula. As the wavelength increases, the refractive index and extinction coefficient rise in the beginning and then descend, with a peak at about 300nm. The calculated absorption coefficient demonstrates that as-grown films have selective absorption, with a broad transparent range, and possess a big energy gap (4.18eV).

Thickness dependence of the optical constants of oxidized copper thin films based on ellipsometry and transmittance

Thin oxidized copper films in various thickness values are deposited onto quartz glass substrates by electron beam evaporation. The ellipsometry parameters and transmittance in a wavelength range of 300 nm-1000 nm are collected by a spectroscopic ellipsometer and a spectrophotometer respectively. The effective thickness and optical constants, i.e., refractive index n and extinction coefficient k, are accurately determined by using newly developed ellipsometry combined with transmittance iteration method. It is found that the effective thickness determined by this method is close to the physical thickness and has obvious difference from the mass thickness for very thin film due to variable density of film. Furthermore, the thickness dependence of optical constants of thin oxidized Cu films is analyzed.

Argon ion beam assisted magnetron sputtering deposition of boron-doped a-Si:H thin films with improved conductivity

Boron-doped a-Si:H thin films were deposited by ion beam assisted magnetron sputtering under different assisted argon ion beam energies, and the changes of structural and electrical properties of the thin films were investigated using Raman spectroscopy, spectroscopic ellipsometry and semiconductor parameter measurement system. It was observed that the short-range order of boron-doped a-Si:H thin films decreased slightly and the defect density of thin films increased with increasing assisted argon ion beam energy. The dark conductivity of boron-doped a-Si:H thin films improved significantly with increasing assisted argon ion beam energy. The conductivity of the boron-doped a-Si:H thin films with 500eV argon ion beam bombardment was 2.1×10−7S·cm−1, which was about three orders of magnitude higher than that of the thin films deposited without assisted ion beam. The significant change in conductivity of the boron-doped a-Si:H thin films deposited with assisted argon ion beam was mainly ascribed to the activation of threefold coordinated boron atoms.

Spectroscopic ellipsometric properties and resistance switching behavior in Six(ZrO2)100x films

We prepare Six(ZrO2)100?x composite films using the co-sputtering method. The chemical structures of the films which are prepared under different conditions are analyzed with X-ray photoemission spectroscopy. Thermal treatment influences on optical property and resistance switching characteristics of these composite films are investigated by spectroscopic ellipsometry and semiconductor parameter analyzer, respectively. With the proper Si-doped Six(ZrO2)100?x interlayer, the Al/ Six(ZrO2)100?x/Al device cell samples present very reliable and reproducible switching behaviors. It provides a feasible solution for easy multilevel storage and better fault tolerance in nonvolatile memory application.

Subsurface quality of polished SiO 2 surface evaluated by quasi-Brewster angle technique

As a surface-sensitive optical method, the quasi-Brewster angle technique is extended to evaluate the subsurface qualities of quartz crystal and fused silica. By measuring the ellipsometry parameters at λ = 900 nm with variable incidence angle, a fitting process is executed using a proper subsurface nanostructure with an exponential porosity distribution. The fitting results predict the surface and subsurface information which are in good agreement with that of the Zygo interference microscope measurements and etching methods. In addition, the shift characteristics of phase change at the Brewster angle of such crystal and non-crystal material are compared and demonstrated.

In situ spectroscopic ellipsometry studies of trivalent chromium coating on aluminum

In situ spectroscopic ellipsometry in the spectral region of 1.3–4.3 eV has been employed to monitor, in real-time, the formation of trivalent Cr process (TCP) conversion coatings on polished Al substrates. The measured ellipsometry parameters (Ψ and Δ), as a function of immersion time, reveal that the initial stages of film formation include the chemical thinning of the native oxide layer, formation of a very thin initiation layer and the subsequent rapid formation of the TCP film. The film optical constant is modeled using Cauchy dispersion relation and its thickness was determined as a function of immersion time during growth.

Lateral shift effect on the spatial interference of light wave propagating in the single-layered dielectric film

Under the oblique incidence condition, the multiple reflection of wave packets in a layered film structure will have a lateral shift increasing with the film thickness. In the analysis of the spatial interference with consideration of the lateral shift effect, a set of new analytic formulae to normalize the intensity of the s-and p-polarized wave packet was obtained to reduce the error of the ellipsometry parameters significantly as the optical path difference delta is close to mpi. The principle and method developed in this work also can be applied to other film structures in more general applications.

Optical metrology of randomly-distributed Au colloids on a multilayer film

Spectroscopic ellipsometry (SE) measurements coupled with efficient theoretical modeling and scanning electron microscopy analysis are used in the metrology of randomly-distributed gold nanoparticles on a multilayer film. Measurements were conducted in the ultraviolet to near infrared region at several angles of incidence. To understand the size, shape, and distribution of nanoparticles, a finite-element Green's function approach considering the scattering from multiple nanoparticles was employed to calculate the ellipsometry parameters. Our calculations are in fair agreement with the ellipsometry measurements when suitable size, shape, and distribution pattern of nanoparticles are found. This demonstrates that SE could be a useful tool to the metrology of arbitrarily-distributed nanoparticles on a multilayer film.

Accurate determination of optical constants and thickness of absorbing thin films by a combined ellipsometry and spectrophotometry approach

A new approach for accurate measurement of the absorbing film thickness and optical constants by combined ellipsometry and spectrophotometry is introduced. The details are studied in terms of the mathematical models and formulats in comparison with the commonly used method which is only dependent on the ellipsometry data specifically. Using variable angle spectroscopic ellipsometry (VASE), the diamond-like carbon film deposited by a glow discharge technique was characterized at the wavelength range of 250—1700 nm. The results indicate that, generally, it is rather difficult to determine the thickness and optical constants of absorbing film accurately and rapidly due to the strong correlation between thickness and n, k. By simultaneously fitting ellipsometry parameters and film transmittance, however, the optical constants could be obtained easily and accurately from a unique solution without any predetermined dispersion model. The fitting results of DLC show that this approach is a promising method to determine the thicknesses and optical constants of films, especially of the thin absorbing films.

Flow-Based Multiadsorbate Ellipsometric Porosimetry for the Characterization of Mesoporous Pt−TiO2 and Au−TiO2 Nanocomposites

Au and Pt nanoparticle distributions within hierarchically ordered mesoporous TiO2 were explored using a combination of techniques including ellipsometric porosimetry (EP) and X-ray photoelectron spectroscopy (XPS). EP studies were used to examine adsorbate-TiO2 interactions and the influence of adsorbate polarity upon adsorption isotherms for mesoporous TiO2 films with and without Pt and Au nanoparticles. In particular, methods are described for modeling EP data to estimate the surface area and porosity of mesoporous TiO2 films and for estimating the pore size distribution (PSD) directly from the ellipsometry parameters Psi and Delta when fitting parameters alone are unable to extract reliable optical constants from the ellipsometry data. This approach reveals that mesoporous TiO2 films of approximately 200 nm thickness and approximately 10 nm pore diameter can be loaded with 1.7 nm diameter Pt and 3.9 nm diameter Au nanoparticles up to 26 and 21 wt %, respectively. The BET surface area of a representative mesoporous TiO2 sample using toluene as the adsorbate was found to be 44 m2/g with a mean pore diameter of 8.8 nm. EP and XPS depth profiling experiments indicate that 1.7 nm diameter Pt nanoparticles are well dispersed through the mesoporous TiO2 film, while 3.9 nm diameter Au nanoparticles are concentrated at the top of the film, blocking a significant portion of the available TiO2 pore volume. UV irradiation of the TiO2 films indicates that adsorbate-TiO2 interactions and surface wetting effects can play a critical role in the resulting isotherm and in evaluation of PSD.

Ellipsometry on optically thin palladium films on silicon-based substrate: effects of low concentration of hydrogen

Optically thin palladium films evaporated on silicon substrates are investigated following exposure to low concentrations of hydrogen gas in nitrogen using spectroscopic ellipsometry. Changes in the parameters tan Ψ and cos Δ are observed for concentrations as low as 0.01% hydrogen in nitrogen. A nonlinear behavior of the change in the ellipsometry parameters as a function of hydrogen concentration is demonstrated, with saturation occurring at a flow of 0.05% hydrogen in nitrogen.

In situ measurements of chemical sensor film dynamics by spectroscopic ellipsometry. Three case studies

A summary of in situ dynamic studies of three distinctly different chemically selective films is presented. A chemically selective film is a crucial component of a chemical sensor. Spectroscopic ellipsometry was used to determine film thickness and refractive index changes in time as these films were exposed to aqueous electrolyte solution. These three films are presented as case studies illustrating the usefulness of dynamic spectroscopic ellipsometry in deciphering a range of film behaviors—from film robustness to film failure. The three films studied were Nafion–SiO 2, PDMDAAC–SiO 2 and PVTAC–PVA. The first two of these represent rigid silica (SiO 2) networks in which an ion exchange polymer is immobilized. The third film consists of an all polymer based composite with an ion exchange polymer entrapped by cross-linking the host polymer PVA. Each of these three films exhibited different dynamic behavior on soaking in aqueous electrolyte solution. The Nafion–SiO 2 film remained essentially unchanged over time and represents a robust useful sensor film. The PDMDAAC–SiO 2 film underwent large changes and ultimately catastrophically failed when exposed to solution for a long period of time. The PVA–PVTAC film swelled by approximately a factor of 1.5 when exposed to solution but remained intact, fully functional and bound to the substrate surface over time. Knowledge of sensor film properties is important in understanding how a chemical sensor works or fails and in the modeling of chemical sensor response. In the case of film failure, determination of the underlying reasons can often be deduced from dynamic measurements of ellipsometry parameters.

Generalized ellipsometry for materials characterization

Ellipsometry experiments normally measure two to four parameters, which are converted to the ellipsometric parameters ψ and Δ. This is usually sufficient for many samples, but more complicated situations (such as anisotropic or depolarizing samples) require more sophisticated measurements. Over the last 7 years, we have developed the two-modulator generalized ellipsometer (2-MGE), which measures eight elements of the sample Mueller matrix simultaneously either in reflection or transmission. In reflection, the 2-MGE totally characterizes light reflection from anisotropic samples, measuring the normal ellipsometry parameters, as well as the cross-polarization and depolarization effects. Applications include the determination of the spectroscopic optical functions of uniaxial materials (such as TiO 2 and ZnO), and the measurement of cross-polarization from diffractive structures. In transmission, the 2-MGE completely characterizes a general linear diattenuator and retarder. Applications include the measurement of the retardation and diattenuation of film polarizers and internal electric fields in LiNbO 3 and CdZnTe under bias.