Variable Angle Of Incidence Spectroscopic Ellipsometry Research Articles

Optical characterization of the annealing effect on Ge5Te20Se75 thin films by variable angle of-incidence spectroscopic ellipsometry

Ternary Ge5Te20Se75 thin films deposited by thermal evaporation were annealed at different temperatures below the crystallization temperature for 15min under vacuum. The annealing effect on the optical properties of the Ge5Te20Se75 thin films was studied by means of variable angle spectroscopic ellipsometry (VASE) in the spectral range from 245 to 1700nm. The measured VASE spectra were examined using individual Tauc–Lorentz (TL) and Cody–Lorentz (CL) dispersion models, and linear combinations of the TL or CL model with multiple Gaussian functions (G). It is demonstrated that the individual TL and CL models are not appropriate for the optical characterization of the Ge5Te20Se75 thin films. Moreover, it is shown that both the CL+3G and TL+3G models are satisfactory ones for the optical characterization of these films. It is found that the optical energy gap (Eg) obtained by Tauc method decreases from 1.2 to 0.86eV with increasing the annealing temperature from room temperature to 150°C. This result can be interpreted by the chemical bond arrangement approach. On the other hand, the maximum value of the refractive index (n) is shifted toward the long wavelength by increasing the annealing temperature.

Analysis of inhomogeneous thin films of ZrO2 by the combined optical method and atomic force microscopy

AbstractIn this paper results concerning the complete optical analysis of inhomogeneous ZrO2 films are introduced. The optical analysis of these films is carried out using the combined optical method based on interpreting experimental data corresponding to variable angle of incidence spectroscopic ellipsometry (VASE) and near‐normal incidence spectroscopic reflectometry (NNSR). The model of the ZrO2 films used for interpretation of the experimental data achieved using the combined method exhibits a continuous refractive index profile. It is shown that this model is satisfactory for treating the experimental data. Further, it is shown that all the parameters characterizing the model mentioned can be determined with high accuracy. By means of atomic force microscopy (AFM) it is found that the upper boundaries of the inhomogeneous ZrO2 films are slightly rough. The values of the basic statistical quantities characterizing this boundary roughness are evaluated using the AFM data. The optical inhomogeneity of the ZrO2 films studied is explained by the columnar structure of these films. Copyright © 2001 John Wiley & Sons, Ltd.

Optical characterization of chalcogenide thin films

In this paper, the optical characterization of a film of amorphous As–S chalcogenides evaporated on glass substrates will be performed using variable angle of incidence spectroscopic ellipsometry (VASE) and near-normal incidence spectroscopic reflectometry (NNSR). The spectral dependences of the ellipsometric parameters and reflectance of the chalcogenide thin film mentioned is measured within the near-UV, visible and near-IR spectral regions. For interpreting these optical quantities the new dispersion model of the spectral dependences of the optical constants of amorphous solids is employed. This model is based on the modified Lorentz oscillator. Within this model the concepts of the band gap and Urbach tail are respected.

Optical characterization of diamond-like carbon films

In this contribution, the results achieved by the optical characterization of diamond-like carbon (DLC) films are presented. A multi-sample modification of variable angle of incidence spectroscopic ellipsometry (VASE) is used to determine the values of the thicknesses and spectral dependences of the optical constants of these films. It is shown that this optical method is very suitable for characterizing the films studied because the influences of some defects of these films are suppressed within this method. Further, the spectral dependences of the optical constants determined for the DLC films studied are interpreted using a new model of dispersion based on the existence of two oscillators corresponding to both the π→π∗ and σ→σ∗ interband transitions. Within this model of dispersion of the optical constants, the concept of the band gap is respected as well.

Optical characterization of inhomogeneous thin films of ZrO2 by spectroscopic ellipsometry and spectroscopic reflectometry

In this paper results concerning the optical characterization of inhomogeneous thin films of ZrO2 are presented. The optical characterization of these films is performed using the simultaneous interpretation of experimental data corresponding to variable angle of incidence spectroscopic ellipsometry (VASE) and near-normal incidence spectroscopic reflectometry (NNSR). It is shown that the ZrO2 films exhibit a depth inhomogeneity concerning their refractive indices. Further, it is shown that the ZrO2 films studied can be replaced by the four-layer system from the point of view of satisfactory fits of the experimental data. The values of the thicknesses and spectral dependences of the refractive indices of these four films are determined. Moreover, it is proved that the individual methods, i.e. VASE and especially NNSR, cannot be used separately to characterize the ZrO2 films investigated. The simultaneous treatment of the spectral dependences of the ellipsometric parameters and the reflectance measured for different angles of incidence allows complete optical characterization of these inhomogeneous films to be performed, i.e. only a combination of VASE and NNSR enables us to determine the values of both the refractive indices and the thicknesses of the films replacing the inhomogeneous ZrO2 films investigated from the optical point of view. Copyright © 2000 John Wiley & Sons, Ltd.

Ellipsometric investigation of damage distribution in low energy boron implantation of silicon

As the scaling of silicon devices to 100 nm channel length requires the formation of ultra-shallow (< 60 nm) junctions, high depth resolution analytical techniques become necessary for the characterization of the dopant and damage distributions. In situ single wavelength Ellipsometric Etch Depth Profiling (EEDP) and non-destructive Variable Angle of incidence Spectroscopic Ellipsometry (VASE) have been used to obtain accurate and quantitative information on the depth profiles of radiation damage produced by low energy, room temperature ion implantation of B + into Si. Implantation energy ranged from 250 eV to 10 keV and the dose was in the range 5 × 10 14 B + cm −2 to 5 × 10 15 B + cm −2. EEDP has been applied to damage depth profiling of low energy implanted silicon for the first time. The range and shape of the damage distributions obtained from optical model calculations are in good agreement with TRIM calculations for the energy range investigated. However, for the 10 keV implant, EEDP results unambiguously show the presence of a 6 nm thick amorphous silicon layer at the surface which is not predicted by TRIM. In the case of the 250 eV implant the presence of an amorphous Si surface layer can not be inferred from VASE data analysis although the existence of a 1 nm thick amorphous Si surface layer is indicated by EEDP.

Optical analysis of complex multilayer structures using multiple data types

Variable angle of incidence spectroscopic ellipsometry (VASE) is commonly used for multilayer optical analysis, but in sone cases this experiment (performed in reflection) does not provide sufficient information for the unique determination of the thicknesses and optical constants of the films in the given multilayer. We have found that augmenting the VASE data with data from other optical experiments greatly increases the amount of information which can be obtained for multilayers, particularly when they are deposited onto transparent substrates. In this work, we demonstrate the characterization of complex multilayer structures using combined reflection and transmission ellipsometry, ellipsometry through the substrate, and intensity transmission measurements. We also demonstrate the usefulness of dispersion parameterizations for the optical constants in the analysis of multilayers.

Sensitivity of variable angle of incidence spectroscopic ellipsometry to compositional profiles of graded Al xGa 1-xAs-GaAs structures

A new algorithm for the variable angle of incidence spectroscopic ellipsometry (VASE) data interpretation for an inhomogeneous compound or composite layers whose composition varies in depth is developed. The numerical experiments are performed on the determination of compositional profiles of very thin graded interfaces in Al x Ga 1- x As-GaAs heterostructures from VASE data. It is demonstrated that the new algorithm, utilizing the sensitivity of the ellipsometry to optical characteristics of the compositionally graded surface layers, gives a possibility for accurate determination of the thickness and the compositional profiles of thin graded band-gap layers and interfaces.

Carbon overcoats with controlled properties: non-destructive ellipsometry evaluation

Abstract Hard carbon thin films have been prepared on fused silica substrates by r.f. plasma deposition and magnetron sputtering using mixtures of argon and methane gases. By controlling the deposition power and gas pressure amorphous carbon films with optical energy gaps ranging from zero to above 2.0 eV were prepared and characterized by variable-angle-of-incidence spectroscopic ellipsometry (VASE). A parametric model was developed based on the measured optical constants as function of optical energy gap which allows the measurement of the thickness and optical constants of thin carbon films on opaque substrates with the VASE technique only. Applications of this model to the characterization of carbon overcoats on magnetic disk structures are presented as well.

Variable angle of incidence analysis of magneto-optic multilayers

We have applied the technique of variable angle of incidence spectroscopic ellipsometry (VASE) to the analysis of multilayered magneto-optic structures. With this instrument we measure the complete pseudodielectric tensor (diagonal and off-diagonal elements) for the sample of interest at variable angles of incidence. We have also developed computer software to perform a best-fit analysis of the measured data, providing optical constants, Voigt parameters, and layer thicknesses for the individual layers in the sample. Additionally, given an estimate of the material parameters, this software will provide an estimate of the optimum spectral range and angles of incidence for accurate characterization of the sample. An example of the above is given for a series of thicknesses of Dy/Co compositionally modulated multilayers deposited on a thick silver layer and subsequently overcoated with a thick layer of SiO. Results confirm the predicted optimum range of accuracy for this material system and effectively delineate the useful spectral range of this technique.

Determination of optical constants of silver layers in ZnO/Ag/ZnO coatings using variable angle spectroscopic ellipsometry

ZnO/Ag/ZnO coatings on glass with different silver layer thickness were studied using variable angle of incidence spectroscopic ellipsometry (VASE). Different optimization procedures were used to calculate the thicknesses of all layers and the optical constants of the Ag layers in the 300–800 nm spectral region. The silver layer thickness determined from ellipsometry are consistent, within evaluated regions of uncertainty, with those obtained by cross sectional transmission electron microscopy (XTEM). The calculated Ag dielectric constants and the Drude parameters are close to those of bulk Ag, but depend on the layer thickness. It is proposed that some peaks found in the calculated energy loss spectra are due to the generation of surface plasmons.

Characterization of Multilayer GaAs/AlGaAs Transistor Structures by Variable Angle Spectroscopic Ellipsometry

Variable angle of incidence spectroscopic ellipsometry (VASE) has been implemented as a means of determining layer thickness, alloy composition, and growth quality of GaAs/AlGaAs samples composed of relatively thick layers as well as superlattices. The structures studied in this work contained GaAs/AlGaAs multilayers with a superlattice “barrier” and were grown for later formation of modulation-doped field effect transistors (MODFETs). Sample modeling was performed by treating the superlattice as a bulk AlGaAs layer of unknown composition. Extremely good data fits were realized when five layer thicknesses and two alloy ratios were allowed to vary in a regression analysis. Room temperature excitonic effects associated with the e-hh(1), e-lh(1) and e-hh(2) transitions were observed in the VASE data.