Angle Of Incidence Spectroscopic Ellipsometry Research Articles

Use of multiple analytical techniques to confirm improved optical modeling of SnO2:F films by atomic force microscopy and spectroscopic ellipsometry

Variable angle of incidence spectroscopic ellipsometry, reflectance, and transmittance techniques were used to determine the optical constants of a fluorine doped tin oxide film deposited by chemical vapor deposition onto a hot soda-lime-silica glass ribbon. To improve the optical characterization, an additional analytical technique, atomic force microscopy (AFM), was used to incorporate information about surface roughness into the optical model. Our earlier work demonstrated the necessity of including a surface roughness layer as six sublayers in the optical model. The present work further confirms the method and demonstrates its accuracy with additional analytical techniques. These include: (1) cross sectional in-lens field emission scanning electron microscopy to measure total film thickness, determine presence of interface roughness and extent of surface roughness; (2) secondary ion mass spectrometry to give a first approximation of the film layer structure for optical modeling by depth profiling the film composition; (3) Hall measurements to identify the semiconductor carrier density and mobility; (4) x-ray diffraction to identify the crystalline phase and preferential growth orientation. The use of AFM surface images and surface roughness plus the other compositional and structural information to improve ellipsometric modeling of thin films has been confirmed.

Microstructural, optical, and mechanical properties of reactive electron-beam-coevaporated TiO_2–MgF_2 composite films

The composition-dependent structural, microstructural, optical, and mechanical properties of TiO(2)-MgF(2) composite films prepared by reactive electron-beam coevaporation at a substrate temperature of 280 °C are systematically investigated with an x-ray diffractometer, transmission electron microscope, spectrophotometer and varied angle of incidence spectroscopic ellipsometry, and microhardness tester, respectively. A comparison of the films prepared by reactive ion-assisted coevaporation shows that the films prepared by reactive electron-beam coevaporation have lower refractive indices and hardnesses. However, TiO(2)-MgF(2) composite films prepared by both techniques exhibit similar softening and hardening phenomena and similar microstructures.

Optical properties of boron carbide (B5C) thin films fabricated by plasma-enhanced chemical-vapor deposition

Variable angle of incidence spectroscopic ellipsometry was used to determine the optical constants near the band edge of boron carbide (B5C) thin films deposited on glass and n-type Si(111) via plasma-enhanced chemical-vapor deposition. The index of refraction n, the extinction coefficient k, and the absorption coefficient are reported in the photon energy spectrum between 1.24 and 4 eV. Ellipsometry analysis of B5C films on silicon indicates a graded material, while the optical constants of B5C on glass are homogeneous. Line shape analyses of absorption data for the films on glass indicate an indirect transition at approximately 0.75 eV and a direct transition at about 1.5 eV.

A novel setup for spectroscopic ellipsometry using an acousto-optic tuneable filter

A rotating-analyzer ellipsometer for fast measurements at multiple wavelengths as well as for spectroscopic measurements has been developed. The most important novelty of the setup is the use of an acousto-optic tuneable filter (AOTF) as dispersing element. This offers advantages with respect to the speed of measurement, the adjustment of the intensity of the light, the use of lock-in techniques, and the stability and size of the setup. Advantages and limitations of the use of AOTF’s in ellipsometry as well as possible changes in the ellipsometric setup are discussed. The ellipsometer has been mounted on an electron cyclotron resonance plasma deposition chamber. As an example, the deposition of amorphous hydrogenated carbon layers has been studied in situ and are compared to ex situ measurements by variable angle of incidence spectroscopic ellipsometry of the same samples.

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.

Spectroscopic ellipsometry studies of indium tin oxide and other flat panel display multilayer materials

Variable angle of incidence spectroscopic ellipsometry (VASE®) ∗ ∗ VASE ® is a Registered Trademark (USA) of the J.A. Woollam Co., Inc. is a rapid and powerful non-destructive optical technique often used to characterize thin films and multilayered structures. A monochromatic, linearly polarized beam of light is reflected from a sample surface at a known angle of incidence, and the resulting polarization state of the reflected beam is measured as a function of wavelength and angle of incidence. Acquired data are then used to determine the optical constants, film thicknesses, and other parameters in the assumed model for the sample. The VASE ® experiment is particularly useful for the characterization of materials for flat panel displays. In the present work, we demonstrate the use of VASE ® on several specific materials for display applications: conducting indium tin oxide (ITO), hydrogenated amorphous silicon, and silicon dioxide, all deposited onto glass substrates.

Study of In 0.53Ga 0.47As/In 0.52Al 0.48As quantum wells on InP by spectroscopic ellipsometry and photoluminescence

inGaAs/InAIAs quantum wells of different well widths were measured by multiple angle of incidence spectroscopic ellipsometry in the wavelength range from 280 to 865 nm. Comparing the experimental data to the calculated results of a theoretical seven-layer model using our refractive index ( n - i k) curves of the materials involved in our structures, we determined all the layer thicknesses, especially the InGaAs well widths. For our samples, in addition, low temperature photoluminescence studies were performed and compared to the results of potential well calculations. A good agreement is obtained between the well widths determined by ellipsometry and photoluminescence, respectively. Thin interface layers, embedding the InGaAs quantum wells are not observed in the wavelength range from 280 to 700 nm.

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.

Ellipsometry and reflectance of inhomogeneous and anisotropic media: a new computationally efficient approach

Dielectric multilayer stacks can display anisotropy as well as inhomogeneity along the normal to the substrate. We present two alternative 2 × 2 matrix methods which allow the electromagnetic field to be calculated in such structures in the particular case where p and s polarization are decoupled. Simple iterative formulae are established for the calculation of reflection and transmission coefficients in the homogeneous case. In the inhomogeneous case the iterative formulae are transformed into Ricatti differential equations. Simulations performed with these equations show that single angle of incidence spectroscopic ellipsometry is insentive to the details of weak index profiles in thin films.

Optical and magneto-optical characterization of TbFeCo thin films in trilayer structures

A series of TbFeCo films ranging in thickness from 100 to 800 Å have been deposited in trilayer structures on silicon wafer substrates, with Si3N4 being employed as the dielectric material. These films have been characterized both optically and magneto-optically by variable angle of incidence spectroscopic ellipsometry, normal angle of incidence reflectometry, and normal angle of incidence Kerr spectroscopy. From these measurements, the optical constants n and k have been determined for the TbFeCo films, as well as the magneto-optical constants Q1 and Q2. Results are presented that demonstrate the lack of dependence of these constants on the thickness of the TbFeCo film, and which can be used for calculating the expected optical and magneto-optical response of any multilayer structure containing similar TbFeCo films.

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.

Enhanced magneto-optic Kerr effects in thin magnetic/metallic layered structures

Enhanced Kerr rotation spectra are measured in thin magnetic layers on silver. Also, variable angle of incidence spectroscopic ellipsometry is employed to measure the optical dielectric function of both the thin magnetic layer and the underlying thick silver layer. These results are explained quantitatively using the electromagnetic theory for reflection of light from multiple layers of isotropic and gyrotropic materials.

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.

Variable angle spectroscopic ellipsometry: A non-destructive characterization technique for ultrathin and multilayer materials

In the most commonly used form of ellipsometry, a monochromatic collimated linearly polarized light beam is directed at an angle ϕ to the normal of a sample under study. The specularly reflected beam is, in general, elloptically polarized, and the state of polarization is analyzed using a second polarizer and photodetector. A rotating analyzer automated spectroscopic ellipsometer has been constructed in our laboratory. The angle of incidence can be set over a wide range of angles, with a precision and repeatibility of ±0.01°. A computer controls the monochromator, the azimuth of a stepper-motor-driven polarizer, a shutter, and the digitization of the detector signal. There are several other schemes used for acquiring ellipsometric data, and these are discussed in several sources. The purpose of this short review is to show how variable angle of incidence spectroscopic ellipsometry can be used as a powerful non-destructive tool for analysis of surfaces and multilayer films.

Variable angle of incidence spectroscopic ellipsometric characterization of TiO2/Ag/TiO2 optical coatings

Optical constants (3000–8000 Å) and layer thicknesses of TiO2/Ag/TiO2 optical coatings are determined using variable angle of incidence spectroscopic ellipsometry. Ellipsometrically determined silver layer thicknesses agree well with those obtained by cross-sectional transmission electron microscopy. Also, spectral characteristics, absent in bulk silver data, are observed in n and k spectra for the thin silver layers. It is suggested that these structures may be caused by plasmon effects from the silver layers.

Measurement of superlattice optical properties by variable angle spectroscopic ellipsometry

Variable angle of incidence spectroscopic ellipsometry is a sensitive, nondestructive technique for determining optical constants, layer thicknesses, microstructure, and other parameters. We have applied this technique to the study of AlAs-GaAs and Al (x)Ga(1−x)AsGaAs superlattices. For a sample with Al (0.5)Ga(0.5)As barrier layers and 20 periods, sharp spectroscopic features were observed at the first electron to heavy hole, e-hh(1), first electron to light hole, e-lh(1), and second electron to heavy hole, e-hh(2) transition energies. Cross sectional transmission electron microscopy (XTEM) showed this superlattice to be of good quality. Ellipsometric data for two other samples, with AlAs barriers, did not contain any sharp features due to quantized level transitions, and XTEM of these samples revealed poor quality superlattice structure. An advantage of ellipsometry is that the complex refractive index can be obtained without Kramers-Kronig analysis. The effective refractive index for a 20 period superlattice was solved using ellipsometric data at three angles of incidence, near 74°. The real part is increased by about 2% at the e-hh(1) peak, and the imaginary part (extinction coefficient) is increased by 0.05.

Ellipsometric measurements of molecular-beam-epitaxy-grown semiconductor multilayer thicknesses: A comparative study

Variable angle of incidence spectroscopic ellipsometry, cross-sectional transmission electron microscopy, and Rutherford backscattering are used to measure heterojunction layer thicknesses in the same AlGaAs/GaAs sample. All three techniques yield the same thickness values within error limits. Two additional samples were implanted with 750-keV Ga ions to fluences of 5×1015 and 1016 cm−2, respectively, and results of diagnostics measurements by the three techniques compared. The three techniques are found to complement each other in providing useful information.

Ellipsometric analysis of built-in electric fields in semiconductor heterostructures

Measurements of Franz–Keldysh (FK) effects in GaAs-AlxGa1−xAs heterostructures by variable angle of incidence spectroscopic ellipsometry are reported. The measured FK effects are due to the built-in band bending at the surface and heterointerfaces, with no externally applied bias or modulating voltage. The polarity of the FK line shape indicates whether the field is uniform or nonuniform (inhomogeneous) in the direction along the growth axis, while the linewidth is determined by the peak field strength. This information can be used to characterize the doping concentration in the AlxGa1−xAs layer.

Superlattice Optical Properties Measured by Variable Angle Spectroscopic Ellipsometry

ABSTRACTVariable Angle of incidence Spectroscopic Ellipsometry (VASE) is a sensitive, nondestructive method of determining optical constants, layer thicknesses, alloy compositions and other parameters. We model the VASE data for a sample containing a 20 period Al0 5Ga0 5As-GaAs superlattice, to obtain the effective index of refraction (n) and e tinction coefficient (k) of the superlattice layer. The room temperature VASE spectra contain strong, sharp features at the e-hh(1), e-lh(1) and e-hh(2) excitonic tran-sition energies. In addition, VASE was used to characterize more compli-cated layered structures, which also contained superlattices.