Papers by Keyword: Ellipsometry

Abstract: Silicon carbide (SiC) MOSFETs are widely utilized in power device applications for their numerous advantages, and the device’s properties can be further optimized through the implementation of trench structures. The formation of the trench structure is a multi-step process, in which it is important to monitor the result of each step and ensure that the structure meets the desired requirements. OCD (optical critical dimension) metrology can provide a fast, non-destructive solution for this purpose. In this article, an OCD analysis of structures at two different process steps is presented and compared with the results from the electron microscopy images. OCD results show high sensitivity to the geometrical dimensions of the structure and produce a good correlation with the electron microscopy images. This metrology can provide a means to detect subtle structural differences without causing any damage to the sample.

Abstract: The work is devoted to preparation and optical study of thin solid films of pseudo-binary AsS₃ - GeS₄ glasses, which are remarkable as topologically belonging to isostatic materials from intermediate phase (IP) region. The glasses from IP are stress free due to their structural self-organization, consequently have to be more stable and viable. To maintain the composition of the bulk source material, the films were grown via a very fast thermal vacuum evaporation of powder of relevant glasses onto optical quartz substrates. The optical properties of (GeS₄)_x(AsS₃)_1-x films (x = 0 ÷ 1) were studied by spectroscopic ellipsometry in the spectral range 0.35 ÷ 1.77 µm. It was pointed out that the films under investigation are entirely transparent in the visible and IR spectral region λ = 0.45 ÷ 1.77 µm. The refractive index follows the usual curves of a normal dispersion, reaching the maximal value around n = 3.0 at λ = 0.35 µm for AsS₃ and the minimal one around n = 1.97 at λ = 1,77 µm for Ge_17.2As_3.5S_79.3. The glass composition strongly influences the refractive index in the visible spectral range but this influence becomes must more moderate in the IR one. It was pointed out that independent on wavelength, both the extinction coefficient and refractive index nearly linearly falls with germanium concentration increase, with an exception related to ternary Ge_17.2As_3.5S_79.3, in which the extinction coefficient shifts toward higher values but the refractive index toward lower values than those expected from aforementioned linearities. The Raman spectra analysis of the studied thin films allowed explanation of this feature in terms of inhomogeneity of the Ge_17.2As_3.5S_79.3 films, caused by a great quantity of the nanoscale - separated stoichiometric As₂S₃ forming in Ge_17.2As_3.5S_79.3 films during their growing.

Abstract: The study of spectroscopic ellipsometry on gold thin film with different thicknesses (30, 50, and 70 nm) for biosensor application has been done. In this work, a rotating analyzer ellipsometer (RAE) has been used to characterize gold thin film and detect microalgae. The measurement was performed at different incidence angles (60°, 65°, 70°, and 75°) assuming the gold film as an isotropic material. The light absorptions of electron represented by the ellipsometer parameter (Δ) and the extinction coefficient (k) are due to the intraband transition of free electrons in the lower photon energy and interband transition of bounded electrons from 5d to 6sp in the higher photon energy. The light absorption increases with the decrease in the thickness of Au thin film. However, for the detection of microalgae, the light absorption of the electron increases with the increase in the thickness of Au thin film due to the dominant absorption by microalgae and PVA. We report that the use of Au thin film with the thickness of 70 nm provides the most sensitive detection of microalgae which is confirmed by the change in Δ (63.1°), at the photon energy of 2.11 eV and the incidence angle of 75°.

Abstract: Cuprous oxide (Cu₂O) has a high optical absorption coefficient and favourable electrical properties, which make Cu₂O thin films attractive for photovoltaic applications. Using reactive radio-frequency magnetron sputtering, high quality Cu₂O thin films with good carrier transport properties were prepared. This paper presents the characteristics of Cu₂O thin films that were sputter deposited on quartz substrates and subjected to post-deposition rapid thermal annealing. The thickness of the thin films and the optical constants were determined by ellipsometry spectroscopy (SE). The optical transmittance increased in lower wavelength region after annealing at 900 ̊C in rapid thermal annealing (RTA). The structural and morphological properties of the Cu₂O thin films were investigated by electronic scanning microscopy (SEM) and atomic force microscopy (AFM), whereas elemental analysis was performed by X-ray fluorescence spectroscopy (XRF). The carrier mobility, carrier density and film resistivity were changed after post-deposition rapid thermal annealing from respectively ~14 cm2/Vs, ~2.3 x 10¹⁵ cm^-3 and ~193 Ωcm for the as-deposited Cu₂O film to ~49 cm2/Vs, ~5.0 x 10¹⁴ cm^-3 and ~218 Ωcm for the annealed Cu₂O film. The investigation suggests that the sputter-deposited Cu₂O thin films have good potential for application as absorber layers in solar cells.

Abstract: The work is devoted to studying the polished surface state of K8 optical glass by ellipsometry, IR spectroscopy and surface roughness measurement methods. It is shown that for chemically stable K8 glass the change of the surface state is insignificant, that is caused by its composition.

Abstract: Nowadays, the magneto-ellipsometry technique is considered as a promising tool for studying nanostructures. It leads to a great demand of both designing set-ups for conducting experiments and developing approaches to data processing. The later one is a problem in framework of in situ analysis as it would be useful to have an approach to data analysis which is reliable, quick and reasonably easy. This work continues our previous study of layered nanostructures by means of magneto-ellipsometry technique and logically generalizes the approach to magneto-ellipsometry data analysis for the multi-layered model use. As a result, the algorithm with detailed description of necessary formulae is presented.

Abstract: Ellipsometry is a non-destructive and indirect technique able to characterize both optical and dielectric properties of thin films and bulks, besides determining the thickness of thin films. This characterization is performed by evaluating the change in the polarization state of the incident light when it interacts with the material of interest. In this work, the ellipsometry technique was used to characterize optical properties of AZ31 magnesium alloy samples. This alloy has several interesting properties such as low density, high thermal conductivity, good machinability, among others, which makes it suitable for use in automotive and aerospace components. However, when this alloy is exposed to ambient atmosphere, it undergoes natural oxidation, developing a surface film of oxides and/or hydroxides. This study aimed to establish an efficient methodology for accessing the optical and dielectric characteristics of the substrate (AZ31 alloy) as well as those for the surface film of oxide/hydroxides, and to obtain the thickness of this film. Four samples mechanically grinded and polished were investigated: One sample, namely P sample, was subjected to the ellipsometric measurements immediately after grinding and polishing and three samples, namely A10, A50 and A60, were exposed to the air at 150°C during 10, 50 e 60 minutes, respectively. From the results of the ellipsometric measurements for P sample, it was possible to determine the refractive index (n) and extinction coefficient (k) curves as a function of the wavelength (λ) for the substrate (AZ31 alloy). Besides, through appropriate modeling, it was possible to determine the thicknesses of the oxides/hydroxides films presented in A10, A50 and A60 samples. The thicknesses values obtained seem to be quite coherent when we analyze the surface roughness of these samples using the confocal microscope, validating the optical model constructed to represent the A10, A50 and A60 samples. The results achieved in this study can contribute to the study of both of oxides/hydroxides layers growth and protective coating films growth for AZ31 magnesium alloy.

Abstract: In this study, cationic membranes based on poly (vinyl alcohol) (PVA) were synthesized, crosslinked with citric acid (carboxylic group) and 4-sulpho-phthalic acid (sulphonic group) for application as proton-conducting membranes of H₃O⁺. The membranes were prepared from the mixture of PVA with the crosslinking agents (CA), previously dissolved and separated with the mixture of these. The CAs proportions used were 10%, 30% and 50%, based on the weight of PVA, and they were crosslinked at the temperatures of 120oC and 140oC. The films were characterized by thermal stability using TGA, spectroscopy ellipsometry (relative refractive index and real part of dielectric constant), swelling degree (water absorption) and conductivity, using electrochemical impedance spectroscopy (EIS). A variation in the refractive index as a function of CA concentration was observed. This fact was corroborated with the results of dielectric constant, because the higher concentration of hydrophilic group added to the film, higher the values of dielectric constant. The membranes which showed lowest swelling degree values were crosslinked with 4-sulpho-phthalic acid (sulphonic group), for example, the PVA membrane crosslinked with 50% of 4-sulpho-phtalic acid, at 140oC, showed 6.4% of water absorption, while the membrane PVA crosslinked with the same content of CA, but of citric acid, and temperature, presented 15.8%. The conductivity of some membranes, under the assay condition evaluated, was the same order of magnitude as the commercial membranes, Nafion^®. The synthesized membranes have been showing potential application as cationic polymer membranes for the transport of H₃O⁺.

Abstract: Titania nanotube arrays were formed by electrochemical anodic etching of titanium from glycerol solutions with addition of 0.5% HF and analyzed by scanning probe microscopy and ellipsometric analyzes. Potentiostatic curves allow identifying several different stages of growth of nanotubes of titanium dioxide, however, this method does not establish specific parameters of the surface. We demonstrated that analysis of the spectrum ellipsometric parameters Psi and Delta can used as a criterion of quality, frequency, depth and other characteristics of the obtained arrays of titania nanotube. The use of these methods of analysis allowed to fully characterize the different stages of growth of titania nanotube from glycerol solutions and can be used for quality control the resulting structures for various applications.

Abstract: On an example of poly(vinylidene fluoride - trifluorethylene) ferroelectric polymer we have shown how different optical methods can be applied for basic optical constants such as refractive index and absorption coefficient obtaining, scattering surface quality control, spectral transmission range control, examining polarization degree etc. Wide range of these methods can be applied not only to thin ferroelectric films but for other different samples.