Thin Solid Films (v.519, #9)

Preface by Harland G. Tompkins (2569-2570).

Plasmonics and effective-medium theories by D.E. Aspnes (2571-2574).
I discuss the close connection between the description of plasmons, which are charge excitations localized at the boundaries between dissimilar regions in composite materials, and effective-medium theories (EMTs), which describe the macroscopic dielectric response of such materials. The requirements for the validity of an EMT are also considered.
Keywords: Plasmons; Plasmonics; Effective-medium theory; Dielectric function;

This paper provides an overview of the relationship between optical ellipsometric measurements and nanoscale science. This relationship is discussed by analyzing published papers, patents and nanomaterials investigated in laboratories and constituting commercial products. Specific challenges and needs for advancing ellipsometry exploitation in nanotechnology are also discussed in the frame of nanometrology standardization. The ellipsometric characterization of plasmonic gold nanoparticles supported on a silicon substrate is used as an example to discuss various issues related to the optical characterization of nanomaterials, i.e., the detection of buried interfaces, size effects on the dielectric function and the monitoring in real time of nanoparticles growth.
Keywords: Ellipsometry; Nanoscience; Nanotechnology; Plasmonics; Gold nanoparticles;

Ellipsometry and reflection polarimetry are almost synonymous. Therefore it is not surprising that ellipsometry and polarimetry share a common history which is that of optical polarization. The discoveries in the late 1600s by Bartholinus and Huyghens of double refraction by Iceland spar and the unusual properties of the twin beams thus generated presented insurmountable difficulties for the entrenched corpuscular-ray theory of Newton and caused research on polarization to remain stagnant in the 1700s. Major breakthroughs came in the early 1800s when Malus discovered polarization of light by reflection and his cosine-squared law and Fresnel and Arago enunciated their laws of interference of polarized light that helped establish the transverse vector nature of luminous vibrations. Important further research immediately followed on optical rotatory power by Arago, Biot, and Pasteur that ushered fundamental and practical applications of polarimetry in chemistry and biology. Fresnel deserves to be recognized as a founder of ellipsometry by virtue of his laws of reflection of polarized light at interfaces between dissimilar media and his identification and production of circular and elliptical polarization. The later part of the 19th century witnessed significant discoveries of magneto-optic and electro-optic effects by Faraday, Kerr, and Pockels that greatly enriched polarization optics and physics. The 1896 discovery of the Zeeman effect launched the exciting field of solar polarimetry. The 1864 crown achievement of Maxwell's electromagnetic (EM) theory provided a unified framework for the analysis of polarization phenomena across the entire EM spectrum.
Keywords: Ellipsometry; Polarimetry; Polarized light; History of optics;

Ellipsometry is well-suited for bioadsorption studies and numerous reports, mainly using null ellipsometry, are found on this subject whereas investigations addressing structural properties of thin biolayers are few. Here two examples based on the use of spectroscopic ellipsometry (SE) on the latter are briefly discussed. In the first example, time evolution of thickness, spectral refractive index and surface mass density of a fibrinogen matrix forming on a silicon substrate are investigated with SE and a structural model of the protein matrix is discussed. In the second example a model dielectric function concept for protein monolayers is presented. The model allows parameterization of the optical properties which facilitates monitoring of temperature induced degradation of a protein layer. More recently, photonic structures in beetles have been studied with SE. It is shown here that full Mueller-matrix SE can resolve very complex nanostructures in scarab beetles, more specifically chiral structures causing reflected light to become circularly polarized.
Keywords: Bioadsorption; Mueller-matrix ellipsometry; Infrared ellipsometry; Scarab beetles;

Terahertz ellipsometry and terahertz optical-Hall effect by T. Hofmann; C.M. Herzinger; J.L. Tedesco; D.K. Gaskill; J.A. Woollam; M. Schubert (2593-2600).
Ellipsometry has been proven as an excellent tool for the precise and accurate determination of material optical properties in the spectral range from the far infrared to the vacuum ultraviolet. In the terahertz frequency domain, however, ellipsometry is still in its infancy. Here we report on our recent development of rotating optical element frequency domain terahertz ellipsometry using electron-beam based, quasi-optical light sources. We demonstrate that high power backward wave oscillator type sources are readily available for the use in spectroscopic ellipsometry instrumentation for the terahertz spectral range. We review recent results on the application of terahertz ellipsometry. Exemplarily, the contact-free optical determination of free-charge carrier properties for very small doping concentrations and doping profiles in iso- and aniso-type Si homojunctions will be discussed. Furthermore, terahertz optical-Hall effect measurements on high-mobility epitaxial graphene on SiC and very low-doped Si are presented.
Keywords: Terahertz; Ellipsometry; Frequency domain; Optical-Hall effect; Free-charge carrier properties;

A dual rotating compensator ellipsometer based on the optical PC1SC2A configuration described by Collins [1, chap. 7.3] has been developed. The systematic errors for this configuration if the compensators are quarter-wave plates have been already studied [2, 3, 4]. Smith [5] has demonstrated that the optimum retardance of a dual-rotating-retarder (DRR) instrument must be equal to 127° compared to the quarter-wave (90°) retarders generally used. In this condition random errors are optimized. The aim of this work is to used such retarders and verify if the systematic errors due to uncertainties of the optical elements (i.e. analyzer, polarizer, first and second compensators) are improved too. For each optical element in different configurations like single or 4-zone average measurements, the systematic errors are given and compared according to the compensators. It is demonstrated that using a 127° instead of quarter-wave retarders coupled with 4-zone averaging measurement is the best configuration for this instrument. These results were confirmed by a statistical study.
Keywords: Systematic errors; Mueller matrix ellipsometry;

We present an optical, non-destructive, non-contact method of determining the silicon homojunction epilayer free-charge carrier concentration profile and thickness by means of combined terahertz (0.2–1 THz) and mid-infrared (10–50 THz) spectroscopic ellipsometry investigation. A dual homojunction iso- and aniso-type silicon sample is investigated. Application of analytical models for iso-type and aniso-type homojunctions results in an excellent match between calculated and experimental data. Best-match model calculated parameters are found to be consistent with electrical spreading resistance epilayer thickness and resistivity values.
Keywords: Terahertz; Isotype; Homojunction; Silicon; Spectroscopic ellipsometry;

Current Mueller polarimeters, with either spectral or angular resolution, feature high enough precision and speed to be suitable for many demanding applications, with specific advantages over conventional spectroscopic ellipsometry (SE). Due to the simultaneous determination of depolarization, birefringence and diattenuation Mueller polarimetry (MP) can open new fields in surface and thin film characterization techniques with new and very powerful intrinsic analyses of roughness and/or anisotropy. For more conventional applications, such as scatterometry (i.e. the determination of the shape of periodic structures from optical measurements, mostly used in microelectronics), MP may overpass SE in terms of systematic errors and/or measurement spot size, as discussed from two examples. However, numerical simulations remain a key point to take full advantage of MP capabilities for the new challenges emerging in nanometrology.
Keywords: Polarimetry; Mueller matrix; Surface analysis; Scatterometry; Periodic structures; Gratings; Photonics structure; Angle-resolved polarimeter; Ellipsometer; Instrumentation;

Terahertz optical-Hall effect for multiple valley band materials: n-type silicon by P. Kühne; T. Hofmann; C.M. Herzinger; M. Schubert (2613-2616).
The optical-Hall effect comprises generalized ellipsometry at long wavelengths on samples with free-charge carriers placed within external magnetic fields. Measurement of the anisotropic magneto-optic response allows for the determination of the free-charge carrier properties including spatial anisotropy. In this work we employ the optical-Hall effect at terahertz frequencies for analysis of free-charge carrier properties in multiple valley band materials, for which the optical free-charge carrier contributions originate from multiple Brillouin-zone conduction or valence band minima or maxima, respectively. We investigate exemplarily the room temperature optical-Hall effect in low phosphorous-doped n-type silicon where free electrons are located in six equivalent conduction-band minima near the X-point. We simultaneously determine their free-charge carrier concentration, mobility, and longitudinal and transverse effective mass parameters.
Keywords: Optical-Hall effect; Ellipsometry; THz; Frequency domain; Anisotropic effective mass; Silicon;

Transmission Mueller matrix ellipsometry of chirality switching phenomena by Oriol Arteaga; Zoubir El-Hachemi; Adolf Canillas; Josep Maria Ribó (2617-2623).
Mechanisms of molecular chirality induction are fundamental to many questions in chemistry. Interest in these mechanisms is shifting toward media of increasing complexity that simultaneously exhibit linear birefringence and dichroism and where the common assumption that optical activity is the only optical effect that affects light polarization is no longer valid. Light propagation through several of these anisotropic media can be appropriately studied with transmission Mueller matrix ellipsometry. The applications presented herein include the measurement of optical activity in stirred solutions of soft-matter nanophases and the determination of chiral domains in solid-state samples.
Keywords: Polarimetry; Mueller matrix; Ellipsometry; Optical activity; Anisotropy; Chirality;

Infrared ellipsometry of highly oriented pyrolytic graphite by J. Humlíček; A. Nebojsa; F. Munz; M. Miric; R. Gajic (2624-2626).
We study the anisotropic response of highly oriented pyrolytic graphite (HOPG) in mid-infrared range, utilizing the potential of spectroscopic ellipsometry. We aim at the parameters of the infrared-active vibrations of E1u and A2u symmetry, and examine the phenomena related to the strong uniaxial anisotropy of HOPG. We explain the appearance of the weakly polar out-of-plane vibration in the elipsometric spectra taken on cleaved planes. We find a detectable Fano-type behavior of the in-plane phonon.
Keywords: Ellipsometry; Infrared; Graphite;

Selective sensitivity of ellipsometry to magnetic nanostructures by K. Postava; D. Hrabovský; J. Hamrlová; J. Pištora; A. Wawro; L.T. Baczewski; I. Sveklo; A. Maziewski (2627-2632).
Magneto-optic (MO) ellipsometry of ferromagnetic materials is extremely sensitive to ultra-thin films, multilayers, and nanostructures. It gives a possibility to measure all components of the magnetization vector in the frame of the magneto-optic vector magnetometry and enables us to separate magnetic contributions from different depths and materials in nanostructures, which is reviewed in this article. The method is based on ellipsometric separation using the selective MO Kerr effect. The figure of merit used to quantify the ellipsometric selectivity to magnetic nanostructures is defined on the basis of linear matrix algebra. We show that the method can be also used to separate MO contributions from areas of the same ferromagnetic materials deposited on different buffer layers. The method is demonstrated using both: (i) modeling of the MO ellipsometry response and (ii) MO measurement of ultra-thin Co islands epitaxially grown on self-organized gold islands on Mo/Al2O3 buffer layer prepared using the molecular beam epitaxy at elevated temperatures. The system is studied using longitudinal (in-plane) and polar (perpendicular) MO Kerr effects.
Keywords: Generalized ellipsometry; Magneto-optical ellipsometry; Material sensitivity; Magnetic nanostructures;

Generalized ellipsometry of artificially designed line width roughness by Martin Foldyna; Thomas A. Germer; Brent C. Bergner; Ronald G. Dixson (2633-2636).
We use azimuthally resolved spectroscopic Mueller matrix ellipsometry to study a periodic silicon line structure with and without artificially-generated line width roughness (LWR). We model the artificially perturbed grating using one- and two-dimensional rigorous coupled-wave methods in order to evaluate the sensitivity of the experimental spectrally resolved data, measured using a generalized ellipsometer, to the dimensional parameters of LWR. The sensitivity is investigated in the context of multiple conical mounting (azimuth angle) configurations, providing more information about the grating profile.
Keywords: Biperiodic grating; Diffraction grating; Ellipsometry; Line width roughness; Mueller matrix; Multi-azimuth method; RCWA;

Anisotropy-enhanced depolarization on transparent film/substrate system by Daniel Franta; David Nečas; Ivan Ohlídal (2637-2640).
The combination of spectrophotometry and variable-angle spectroscopic ellipsometry is used for the optical characterization of a system consisting of transparent polymer film on a transparent polycarbonate substrate. In the region of sample transparency a relatively large depolarization is observed in ellipsometry. This can be explained by the presence of anisotropy in the film or substrate. The possibility of distinguishing between the depolarization enhanced by film and substrate anisotropy is discussed and tested using several models. It is shown that it is not possible to distinguish between these effects.
Keywords: Anisotropy; Depolarization; Optical properties; Ellipsometry;

Studies of optical anisotropy in opals by normal incidence ellipsometry by A. Reza; Z. Balevicius; R. Vaisnoras; G.J. Babonas; A. Ramanavicius (2641-2644).
Anisotropy of thin opal films was studied by ellipsometric technique in a visible spectral range. At normal light incidence, the ellipsometric data were directly related to anisotropy parameters measured by polarization modulation technique. In the (111)-oriented thin films, the optical anisotropy was mainly caused by internal strain-induced birefringence with anisotropy axes oriented along [110] and [-112] directions. The deviation from 180°-symmetry, which has been observed for ellipsometric parameters in the in-plane sample rotation experiments at normal incidence, was enhanced at oblique incidence and assigned to particular properties of opal. Experimental data were discussed in the model of stacked anisotropic layers.
Keywords: Spectroscopic ellipsometry; Photonic crystals; Opals; Optical anisotropy;

Optical properties of hybrid titanium chevron sculptured thin films coated with a semiconducting polymer by Daniel Schmidt; Christian Müller; Tino Hofmann; Olle Inganäs; Hans Arwin; Eva Schubert; Mathias Schubert (2645-2649).
Optical and structural properties of a hybrid metallic chevron sculptured thin film from titanium coated with the semiconducting polymer poly(3-dodecylthiophene) (P3DDT) are reported. The nanostructured thin film with two subsequent layers of oppositely slanted nanocolumns was fabricated by glancing angle deposition and coated with P3DDT by a spin-cast process. Spectroscopic generalized ellipsometry is employed to determine geometrical structure properties and the anisotropic optical constants of the coated and uncoated film in the spectral range from 400 to 1700 nm. The nanostructured thin films before and after hybridization show highly anisotropic optical properties. The complex refractive indices along major polarizability directions of the hybridized chevrons are increased in the entire investigated spectral range with respect to the as-deposited chevrons. Changes in birefringence and dichroism upon polymer infiltration are observed.
Keywords: Generalized ellipsometry; Hybrid materials; Glancing angle deposition; Sculptured thin films; Anisotropy;

Nanostructured chiral silver thin films: A route to metamaterials at optical frequencies by B. Gallas; N. Guth; J. Rivory; H. Arwin; R. Magnusson; G. Guida; J. Yang; K. Robbie (2650-2654).
We present a study of the optical properties of three-armed square nanospirals made of silver and realized as nanostructured thin films with Glancing Angle Deposition. Optical property variations with polarization were investigated using numerical simulations. For each polarisation case, two principal resonances were determined corresponding to excitation of plasmonic modes of nanospirals which resonance's frequency depended on the dimensions of the nanospirals. Calculation of current flows in the nanospirals showed patterns resembling those observed in U-shaped resonators. In particular, a mode with anti-parallel current flow in opposite arms indicates the existence of a magnetic-like resonance in the square nanospirals. We present also generalized spectroscopic ellipsometry measurements obtained on one sample at an incidence angle of 25°, and evidence conversion between polarization states even for light polarized in the plane containing one of the arms. The measurements showed good agreement with the results of calculations for an ideal structure. The differences in the conversion of polarization between measurements and calculations were mainly attributed to the existence of structural non-idealities in the actual sample.
Keywords: Ellipsometry; Metamaterials; GLancing Angle Deposition; Thin films;

Suitable combinations of the optical response and geometrical form of flat or curved interfaces of the constituents in nanometer-sized metamaterials can lead to a strong enhancement of local fields, seen typically as sharp spectral resonances in optical spectra. We propose a classification of the resonant phenomena in inhomogeneous systems within the effective-medium approximation, and examine their manifestation in infrared ellipsometry. We report mid-infrared ellipsometric spectra of a doped semiconductor metamaterial, exhibiting negative refraction. We provide a simple explanation for the difference in the directions of the phase- and energy propagation. The resonance responsible for a strong anisotropy and the interesting behavior of refracted light is found to lead to characteristic features in the ellipsometric spectra.
Keywords: Ellipsometry; Infrared; Metamaterials;

Ellipsometric detection of gases with the surface plasmon resonance effect on gold top-coated with sensitive layers by A. Nooke; U. Beck; A. Hertwig; A. Krause; H. Krüger; V. Lohse; D. Negendank; J. Steinbach (2659-2663).
An ellipsometric gas sensor based on the surface Plasmon resonance (SPR) effect of ~ 43 nm thick gold layers was investigated. To protect the gold layer from contamination and to improve the detection limits, the gold layers were top-coated with 5–6 nm thick layers of organic a-C:H or with inorganic metal oxides TiO2 or ZrO2. The additional layers increased the long-term stability, whereas the metal oxide layers protect better than a-C:H. Furthermore, the additional layers decreased the detection limits by one order of magnitude in case of a-C:H and two orders of magnitude in case of the oxides. It could be shown that the detection limits also depend on the kind of preparation (sol–gel process or physical vapour deposition) of the additional layers.
Keywords: Gas sensor; SPR; Ellipsometry; Sensitive layer; TiO2; ZrO2; a-C:H;

Plasmon resonance shift during grazing incidence ion sputtering on Ag(001) by Herbert Wormeester; Frank Everts; Bene Poelsema (2664-2667).
Grazing incidence ion sputtering was used to create shallow ripple patterns on a Ag(001) surface. The anisotropic plasmon resonance associated with this ripple pattern can be sensitively measured with Reflection Anisotropy Spectroscopy. A slight red shift of the resonance energy is observed with increasing ion fluence. The observed resonance feature is described well with a skewed Lorentzian line shape. This line shape is the small roughness length scale limit of the Rayleigh Rice perturbation approach. The width of this line shape is directly related to imaginary part of the dielectric function, which shows a roughness induced reduction of the electron mean free path. The observed change in resonance energy and strength with ion fluence is discussed.
Keywords: RAS; Plasmon resonance; Ion beam induced nanopatterning; Roughness analysis;

Mueller matrices for anisotropic metamaterials generated using 4 × 4 matrix formalism by P.D. Rogers; T.D. Kang; T. Zhou; M. Kotelyanskii; A.A. Sirenko (2668-2673).
Forward models for the Mueller Matrix (MM) components of materials with relative magnetic permeability tensor μ  ≠ 1 are studied. 4 × 4 matrix formalism can be used to calculate the complex reflection coefficients and the MMs of dielectric–magnetic materials having arbitrary crystal symmetry. For materials with simultaneously diagonalizable ε and μ tensors (with coincident principal axes), analytic solutions to the Berreman equation are available. For the single layer thin film configuration, analytic formulas for the complex reflection and transmission coefficients are derived for orthorhombic symmetry or higher. The separation of the magnetic and dielectric contributions to the optical properties as well as the ability to distinguish materials exhibiting negative index of refraction are demonstrated using simulations of the MM at varying angles of incidence.
Keywords: Mueller matrix; 4 × 4 matrix formalism; Dielectric–magnetic; Metamaterial; Anisotropic; Negative refractive index;

Real-time diagnostics are an essential tool in the development and improvement of growth processes for new materials. Here we use real-time spectroscopic polarimetric observations of zinc oxide deposition, and a chemical model derived therefrom, to develop a method of growing dense, two-dimensional zinc oxide epitaxially on sapphire by metalorganic chemical vapor deposition. With the transition between deposition and etching being 13% in the diethylzinc flow rate, it is unlikely that we would have discovered this process without the use of real-time spectroscopic ellipsometry. New photoluminescence data support our conclusion that using this cyclical growth process yields improved material.
Keywords: ZnO; MOCVD; Spectroscopic ellipsometry;

Real-time studies during coating and post-deposition annealing in organic semiconductors by M. Campoy-Quiles; M. Schmidt; D. Nassyrov; O. Peña; A.R. Goñi; M.I. Alonso; M. Garriga (2678-2681).
In this contribution we explore the use of real time spectroscopic probes to gain useful insights into the kinetics of semiconductor polymer chains during thin film formation and upon post-deposition annealing treatments. In-situ ellipsometry is employed to monitor the deposition of thin films of the workhorse material system for organic photovoltaics (soluble derivative fullerene blended with poly(3-hexylthiophene)), when processed from solution using an analogous dip coating deposition method. This allows for detailed time investigation of the dynamics of film formation. Moreover, we applied spectroscopic photometry to study the in-situ crystallization and diffusion of polymer chains during post-deposition solvent annealing.
Keywords: Ellipsometry; Photometry; In-situ; Annealing; Organic semiconductors; Polymers; Photovoltaics; Dip coating;

Real time spectroscopic ellipsometry of Ag/ZnO and Al/ZnO interfaces for back-reflectors in thin film Si:H photovoltaics by Lila Raj Dahal; Deepak Sainju; N.J. Podraza; S. Marsillac; R.W. Collins (2682-2687).
Real time spectroscopic ellipsometry (RTSE) has been applied to analyze the optical characteristics of Ag/ZnO and Al/ZnO interfaces used in back-reflector (BR) structures for thin film silicon photovoltaics. The structures explored here are relevant to the substrate/BR/Si:H(n-i-p) solar cell configuration and consist of opaque Ag or Al films having controllable thicknesses of microscopic surface roughness, followed by a ZnO layer up to ~ 3000 Å thick. The thicknesses of the final surface roughness layers on both Ag and Al have been varied by adjusting magnetron sputtering conditions in order to study the effects of metal film roughness on interface formation and interface optical properties. The primary interface loss mechanisms in reflection are found to be dissipation via absorption through localized plasmon modes for Ag/ZnO and through intraband and interband transitions intrinsic to metallic Al for Al/ZnO.
Keywords: Real time spectroscopic ellipsometry; Interfaces; Plasmons; Metal films; Zinc oxide; Thin silicon solar cells; Reflectors;

Two lithographic test masks, Stokes polarimeter mask and Mueller matrix polarimeter mask, are introduced. Both the masks comprise newly developed thin polarizers and wide-view-angle λ/4 plates. Photomasks are only 6.35 mm in thickness, and the illumination involves the oblique incidence of 20° at the most. Calcite plates thinned to less than 0.1 mm can perform as polarizers only at a wavelength of 193 nm. The combination of quartz and sapphire plates can mitigate the retardation change with angle of incidence. Stokes polarimeter and Mueller matrix polarimeter masks are used for the measurement of the illumination and the projecting optics, respectively.
Keywords: Immersion lithography; Polarimetry; Stokes parameters; Mueller matrix;

Combination of synchrotron ellipsometry and table-top optical measurements for determination of band structure of DLC films by Daniel Franta; David Nečas; Lenka Zajíčková; Vilma Buršíková; Christoph Cobet (2694-2697).
Model of the DLC band structure that took into account valence to conduction band transitions, π  →  π⁎ and σ  →  σ⁎, and valence to extended states transitions σ  →  ξ⁎ was confirmed by using the synchrotron ellipsometry at BESSY II in the range 5–30 eV combined with table-top ellipsometry and spectrophotometry in UV-IR range. The range up to 30 eV covered all the transitions from valence to conduction bands because the maximum energy transition of π  →  π⁎ and σ  →  σ⁎ were 9.03 and 28.1 eV, respectively. The band gaps of these transitions were 0.75 and 4.74 eV, respectively.
Keywords: Diamond-like carbon; Amorphous hydrogenated carbon; Optical properties; Band structure;

Rotatable broadband retarders for far-infrared spectroscopic ellipsometry by T.D. Kang; E. Standard; G.L. Carr; T. Zhou; M. Kotelyanskii; A.A. Sirenko (2698-2702).
Rotatable retarders have been developed for applications in spectroscopic, full Mueller Matrix ellipsometry in the far-IR spectral range. Several materials, such as silicon, KRS-5, and a commercial polymer plastic (TOPAS) have been utilized to achieve a fully adjustable retardation between 0° and 90°. Experimental characteristics of the rotatable retarders that utilize three- and four-bounce designs are compared with calculations. We discuss the effect of light focusing on the performance of these rotatable retarders.
Keywords: Far-infrared retarder; Spectroscopic ellipsometry; Rotatable retarder; Total internal reflection; TOPAS; Double-Fresnel rhomb;

Accurate spectroellipsometric (SE) measurements in the rotating analyzer (RAE) or rotating polarizer (RPE) configurations require accurate values of the polarizer/analyzer(/retarder) azimuths. While the readings are usually fairly accurate, true values are influenced by possible offsets between the plane of incidence, physical axes of the elements, and the instrument scales. The offsets are often determined by specialized calibration procedures. We describe SE measurements designed to obtain the calibration parameters together with the target ellipsometric spectra. We use multiple settings of the polarizer (analyzer) azimuths in RAE (RPE), respectively, to optimize precision and accuracy of SE measurements, and to economize measurement time. The optimization concerns the choice of measurement parameters as well as the subsequent data analysis. We present in detail examples of visible-ultraviolet measurements.
Keywords: Ellipsometry; Spectroscopic; Rotating;

Development of spectroscopic transmission-type four detector polarimeter by T. Tsuru; Y. Kubota; T. Tadokoro; S. Kawabata (2707-2710).
We have developed a spectroscopic transmission-type four detector polarimeter (T-FDP). It consists of a detector head and a multichannel spectrometer equipped with a two-dimensional CCD detector. Inside the T-FDP, three cubic beam splitters are aligned in a straight line and they are rotated relative to each other. From the responses of the spectroscopic T-FDP to five inputs with known polarization states it is possible to determine the characteristic matrices of the T-FDP at various wavelengths. The trajectories of the experimentally measured polarization states on the Poincaré sphere agree well with theoretical predictions. These results demonstrate the feasibility of using the T-FDP for spectroscopic ellipsometry.
Keywords: Polarimetry; Ellipsometry; Polarization; Polarized light;

Accuracy of color determination from spectroscopic ellipsometry measurements by Blaine Johs; Hans Arwin; Thomas Wagner; David Appel; Dimitrios Peros (2711-2714).
In many coating and display applications, quantitative determination of the sample color is required. Standard procedures exist for converting an experimentally measured reflectivity spectrum into color coordinates such as CIE L*a*b*. In this paper we evaluate CIE L*a*b* color coordinates using a reflectivity spectrum which is calculated from an optical model determined by a spectroscopic ellipsometry (SE) analysis of the sample. The accuracy of the SE-determined color coordinates are compared with traditional color measurements, and the advantages of using SE for color determination are discussed.
Keywords: Spectroscopic ellipsometry; Color coordinates; CIE L*a*b*;

Ellipsometric characterisation of thin films non-uniform in thickness by David Nečas; Daniel Franta; Vilma Buršíková; Ivan Ohlídal (2715-2717).
Ellipsometric formulae for thin films non-uniform in thickness are presented. A general type of thickness non-uniformity is considered and the influence of the varying angle of incidence is taken into account. The presented formulae are applied to the optical characterisation of polymer SiO2-like thin films exhibiting a relatively strong thickness non-uniformity. It is shown that the complete optical characterisation of these polymer thin films can be performed. Thus, the spectral dependences of the optical constants, mean thickness and parameters related to the shape of thickness non-uniformity can be determined.
Keywords: Optical characterisation; Variable angle spectroscopic ellipsometry; Phase-modulated ellipsometry; Non-uniform thin films;

There have been numerous attempts to correlate light scattering measurements with the characteristics of surface roughness. Another but considerably more difficult approach is to solve the inverse scattering problem. A number of different empirical models of surface roughness have been used to characterize surfaces including the sine grating, triangle grating (echelette), and rectangle grating. In this paper, we use, for the first time, the random phase mask model, which is a two-dimension orthogonal grating with a stochastic distribution of square “defects” with size a. We describe our calculations of the polarizing characteristics of the random phase mask and discuss the influence of each of the parameters of defects on polarizing angles. The analysis was carried out for multiple-angles-of-incidence ellipsometric measurements.
Keywords: Roughness of surface; Optical properties; Ellipsometry;

Random phase mask as a model of a rough surface by S.N. Svitasheva (2722-2724).
Artificial roughness was created on sample surfaces by etching through a two-dimensional orthogonal grating with a stochastic distribution of square "defects" of size. "Defects" depth was varied from 0.02 μm up to 1.005 μm. The experimental dependences of the scattering of polarized light were studied on four types of surface roughness for two materials: quartz and aluminum. The defect sizes of the random phase mask were 25 × 25 μm and 2.5 × 2.5 μm. The impacts of the sizes and density of artificial defects of rough surfaces on the polarization of reflected light were investigated by multiple-angle-of-incidence (MAI) ellipsometry at a wavelength of 0.63 μm.
Keywords: Surface roughness; Optical properties; Ellipsometry;

Dual rotating compensator ellipsometry: Theory and simulations by Jian Li; Balaji Ramanujam; R.W. Collins (2725-2729).
Systematic methods for data reduction have been developed for the dual rotating-compensator ellipsometer in the PC1r1)SC2r2)A configuration, where P, C1r1), S, C2r2), and A represent the polarizer, first rotating compensator, reflecting sample, second rotating compensator, and analyzer, respectively. The approach used here is more general than previous treatments in that it incorporates dichroic compensators that rotate synchronously at a frequency ratio ω12 of p:q, where p and q are integers. For specific frequency ratios, the 24 ac Fourier coefficients of the irradiance waveform at the detector over-determine the 15 real elements of the (1,1)-normalized Mueller matrix and the 3 complex elements of the (2,2)-normalized Jones matrix. Alternative data reduction approaches resulting from this capability of over-determination are shown through numerical simulations to have different performance characteristics under non-ideal experimental conditions. Finally, the importance of using an achromatic retarder design in the dual rotating-compensator ellipsometer is emphasized through these simulations.
Keywords: Multichannel Mueller matrix ellipsometry; dual rotating-compensator ellipsometer;

Expanded beam (macro-imaging) ellipsometry by M. Fried; G. Juhász; C. Major; P. Petrik; O. Polgár; Z. Horváth; A. Nutsch (2730-2736).
Our aim was to make possible to use spectroscopic ellipsometry for mapping purposes during one measuring cycle (minimum one rotation period of polarizer or analyzer) on many sample points. Our new technique uses non-collimated (non-parallel, mostly diffuse) illumination with an angle of incidence sensitive pinhole camera detector system and it works as an unusual kind of imaging ellipsometry. Adding multicolour supplemets, it provides spectral (a few wavelengths on a 2D image or a full spectrum along a line) information from rapid measurements of many points on a large (several dm2) area. This technique can be expanded by upscaling the geometry (upscaling the dimensions of the instrument, and characteristic imaging parameters such as focal lengths, distances, etc.). The lateral resolution is limited by the minimum resolved-angle determined by the detector system, mainly by the diameter of the pinhole. (The diameter of the pinhole is a compromise between the light intensity and the lateral resolution.) Small-aperture (25 mm diameter) polarizers are incorporated into both the polarization state generator (PSG) and polarization state detection (PSD) components of the instrument.The detection is almost without background because the pinhole serves as a filter against the scattered light. One rapid measuring cycle (less than 10 s) is enough to determine the polarization state at all the points inside the illuminated area. The collected data can be processed very fast (seconds) providing nearly real-time thicknesses and/or refractive index maps over many points of the sample surface even in the case of multilayer samples. The speed of the measuring system makes it suitable for using even on production lines. The necessary (in each sample-point different) angle-of-incidence and the mirror-effect calibration are made via well-known and optimized structures such as silicon/silicon-dioxide samples. The precision is suitable for detecting sub-nanometer thickness and a refractive index change of 0.01.The method can be used for mapping and quality control in the case of large area solar cell table production lines even in a vacuum chamber with 5–10 mm lateral resolution.
Keywords: Ellipsometry; Mapping; Thin film;

Near infra-red Mueller matrix imaging system and application to retardance imaging of strain by Lars Martin Sandvik Aas; Pål Gunnar Ellingsen; Morten Kildemo (2737-2741).
We report on the design and performance of a near infra-red Mueller matrix imaging ellipsometer, and apply the instrument to retardance imaging of strain in near infra-red transparent solids. Particularly, we show that the instrument can be used to investigate complex strain domains in multi-crystalline silicon wafers.
Keywords: Mueller matrix; Imaging; Strain imaging; Polarimetry; Ellipsometry; Silicon wafer;

In this work, a rotating compensator sampling for spectroscopic imaging ellipsometry (SIE) is presented and demonstrated by characterization of a SiO2 nanofilm pattern on Si substrate. Experiment results within spectrum of 400–700 nm show that the rotating compensator sampling is valid for SIE to obtain the ellipsometric angle distributions ψ (x, y, λ) and Δ (x, y, λ) over the thin film pattern, the sampling times of ψ (x, y) and Δ (x, y) with 576 × 768 pixels under each wavelength is less than 8 s, the precision of fitting thickness of SiO2 is about 0.2 nm and the lateral resolution is 60.9 μm × 24.6 μm in the parallel and perpendicular direction with respect to the incident plane.
Keywords: Rotating compensator; Spectroscopic imaging ellipsometry; Spectroscopic ellipsometry; Imaging ellipsometry; Ellipsometry; Nanofilm pattern;

Ultra fast self-corrected polarization modulated ellipsometer by Hsiu-Ming Tsai; Leng-Chun Chen; Yu-Faye Chao (2746-2749).
A high speed self-corrected algorithm is proposed for the polarization modulated ellipsometry (PME). In this post-flight analysis, we prove that a set of optimized ellipsometric parameters (EPs) can be obtained by using the intensities at 4 specific temporal phases. The correction ability to its initial phase by this technique has been demonstrated through a twisted nematic liquid crystals (TN-LC) cell under the driving of a square wave. Furthermore, the optimal modulation amplitude in obtaining the accurate and precise set of EPs will be discussed in this work.
Keywords: Ellipsometry; Polarimetry; Photoelastic modulator;

Development of biosensor based on imaging ellipsometry and biomedical applications by G. Jin; Y.H. Meng; L. Liu; Y. Niu; S. Chen; Q. Cai; T.J. Jiang (2750-2757).
So far, combined with a microfluidic reactor array system, an engineering system of biosensor based on imaging ellipsometry is installed for biomedical applications, such as antibody screen, hepatitis B markers detection, cancer markers spectrum and virus recognition, etc. Furthermore, the biosensor in total internal reflection (TIR) mode has be improved by a spectroscopic light, optimization settings of polarization and low noise CCD which brings an obvious improvement of 10 time increase in the sensitivity and SNR, and 50 times lower concentration in the detection limit with a throughput of 48 independent channels and the time resolution of 0.04 S.
Keywords: Imaging ellipsometry; Biosensor; Protein microarray; Total internal reflection;

Improvement for sensitivity of biosensor with total internal reflection imaging ellipsometry (TIRIE) by Li Liu; Yan-yan Chen; Yong-hong Meng; She Chen; Gang Jin (2758-2762).
The biosensor based on the total internal reflection imaging ellipsometry (TIRIE) is realized as an automatic analysis method for protein interaction processes in real-time, with high throughput and label-free. An evanescent wave is used as the optical probe to monitor bio-molecular interactions on a chip surface with a high sensitivity due to its phase sensitive property. In this paper, the technique is optimized with a polarization setting, a spectroscopic light source and a low noise CCD detector to improve the performance of the biosensor in sensitivity and detection limit, as evidenced by a quantitative detection of Hepatitis B virus surface antigen (HbsAg) with concentrations of 8, 16, 32, 64, 125 and 250 ng/ml. The sensitivity is increased by one order of magnitude and the detection limit has been extended more than 50 times for HbsAg detection.
Keywords: Sensitivity improvement; Imaging ellipsometry; Total internal reflection; Biosensor; HbsAg detection;

Detection of alpha-fetoprotein through biological signal amplification by biosensor based on imaging ellipsometry by Chenghong Huang; Yanyan Chen; Chunxia Wang; Wei Zhu; Hongwei Ma; Gang Jin (2763-2767).
High sensitive and quantitative detection of alpha-fetoprotein (AFP) by biosensor based on imaging ellipsometry (BIE) through biological amplification was investigated. AFP firstly reacted with the rat monoclonal antibody (rat-mAb) initially immobilized on glutaraldehyde modified silicon surface, then rabbit anti-human AFP polyclonal antibodies (Rabbit-pAb) and goat anti-rabbit IgG (goat-IgG) were sequentially applied to amplify signal. Results revealed that signal was enhanced approximately six fold. The linear range of AFP detection was 20.0–200.0 ng/ml with a low limit of 5.0 ng/ml (S/N = 3). The cross-reaction rate was less than 5.2% evaluated by biomarker (carcinoembryonic antigen, carbohydrate 19-9 and carbohydrate antigen 242) and two common proteins (human serum albumin, fibrinogen) and their mixture. Coefficient variation (CV) for intra-slide and inter-slide reproducibility were 10.3%, 6.6%, 6.3% and 10.7%, 7.9%, 6.4% for 41.6 ng/ml, 83.2 ng/ml and 128.4 ng/ml AFP. In clinic application, cut-off value at 28.6 ng/ml was also determined with sensitivity 0.72 and specificity 0.94. Results of 47 clinic patient samples detected by BIE were in good agreement with those of electrochemiluminescence immunoassay (ECLIA) (R2 = 0.9949).The area under receiver operating characteristic curve (ROC) curve is 0.89. Statistical analysis showed that BIE is high agreement with ECLIA (Kappa = 0.733, U = 3.21>U0.01). It shows a potential for hepatocellular carcinoma (HCC) diagnosis.
Keywords: Imaging ellipsometry; Biosensor; Signal amplification; Alpha-fetoprotein; Hepatocellular carcinoma;

In order to meet the requirements of antibody comparison and evaluation, the optimization for the surface modification, ligand immobilization, unspecific blocking and ligand–receptor interaction condition is introduced to the biosensor based on imaging ellipsometry (BIE), so that it may serve as an antibody screening platform to evaluate antibody–antigen interactions. Two kinds of anti-ricin antibody named pVHHS1 and 5S1R are immobilized in a patterned array format on the silicon surface modified with succinic anhydride, respectively, to form a sensing surface. Ricin and its similar toxin abrin as the reference in solution are delivered, respectively, on the patterned sensing surface for anti-ricin antibody and ricin interaction. The limit of detection value of ricin detected by pVHHS1 and 5S1R is obtained as 1 μg/ml and 5 ng/ml, respectively. Results show that pVHHS1 and 5S1R specifically bind with ricin but not with abrin, which is in accordance with ELISA's result.
Keywords: Ricin detection; Antigen–antibody interaction; Biosensor; Imaging ellipsometry;

Spectroscopic ellipsometry (SE) and quartz crystal microbalance with dissipation (QCM-D) techniques have been extensively used as independent surface characterization tools to monitor in-situ thin film formation. They provide different information for ultra-thin films because QCM-D is sensitive to the solvent content while SE is not. For using these two techniques in tandem, we present a virtual separation approach to enable the determination of both ultra-thin film thickness and porosity. Assumptions for the intrinsic molecular polarizability (index of refraction n o) and density (ρ o) of the organic adsorbent must be made, and the consequences for these parameters' values are discussed.
Keywords: Spectroscopic ellipsometry; Quartz crystal microbalance; Organic thin films;

Determination of the refractive index of single crystal bulk samples and micro-structures by R. Schmidt-Grund; P. Kühne; C. Czekalla; D. Schumacher; C. Sturm; M. Grundmann (2777-2781).
We present comparative studies for the exact determination of the refractive index of single crystals using spectroscopic ellipsometry and photonic-mode-structure investigations by means of spatially resolved photoluminescence spectroscopy, especially in the near band-gap spectral range. By applying such complementary methods we can overcome the uncertainties in the determination of the bulk refractive index introduced by surface properties. The physical effects used are the electromagnetic field reflection used by spectroscopic ellipsometry at large scale planar single crystals and the whispering-gallery-mode formation by total internal reflection in confined micro-structures. We demonstrate the applicability of such studies using the example of uniaxial ZnO bulk samples and micro-wires. By assuming a surface near region with electronic properties different from the bulk material, the method presented here gives the refractive index dispersion for both types of samples in an energy range from 1 to 3.4 eV.
Keywords: Refractive index; Surface potential; Spectroscopic ellipsometry; Whispering-gallery modes; ZnO; Micro-wire;

The demand for accurate and highly reliable in-fab characterization of thin layers included in advanced CMOS and MEMS stacks has placed stringent requests on in-line optical metrology methodology and protocols. This work investigates the capability of systematic combination of X-ray reflectometry (XRR) and spectroscopic ellipsometry (SE) to decrease the correlation concerns that sometimes affect the reliability of SE analysis.
Keywords: Spectroscopic ellipsometry; X-ray reflectometry; Transparent conductive oxide; Amorphous carbon;

Silicon nanocrystals embedded in a dielectric matrix are of considerable interest for Si-based optoelectronics and the third generation photovoltaics. This work discusses Si nanocrystals embedded in silicon–carbon, Si1 −  x C x , thin films prepared by plasma-enhanced chemical vapor deposition (PECVD) using a non-conventional fluoride-based precursor mixture, i.e., SiF4–CH4–H2–He plasmas. It is shown that the SiF4/H2 ratio and the He dilution are important parameters to control the volume fraction and the size of nc-Si, and the carbon content of the a-Si1 −  x C x matrix. Films nanostructure and optical properties are studied by spectroscopic ellipsometry and Raman spectroscopy. The correlation existing between plasma processes and the film nanostructure and resulting optical properties is discussed.
Keywords: Si–C alloys; Nanostructuring; PECVD; Ellipsometry;

Characterization of damage structure in ion implanted SiC using high photon energy synchrotron ellipsometry by P. Petrik; Z. Zolnai; O. Polgar; M. Fried; Z. Betyak; E. Agocs; T. Lohner; C. Werner; M. Röppischer; C. Cobet (2791-2794).
The optical properties of ion implantation induced disorder in SiC have been investigated in the photon energy range of 5–9 eV using spectroscopic ellipsometry (SE). The most characteristic interband transitions of SiC are located between 5 and 8 eV. This photon energy region is extremely important for the sensitive characterization of lattice order in SiC. The dielectric function of the disordered layer has been calculated taking into account the surface overlayer consisting of oxide and roughness using complementary characterization tools. The dielectric function of the damaged region has been analyzed using different techniques like second derivative analysis and effective medium approximation (EMA) based on reference dielectric functions. The disorder determined by SE has been verified by Rutherford backscattering spectrometry combined with channelling (RBS/C). Using derivative lineshape analysis combined with simulations, the track size can be estimated. The results can give insight into the effect of the decreasing characteristic size of the unchanged crystalline regions on the optical properties. We created near-surface damage using heavy ions, since the penetration depth of light at photon energies around the direct interband transitions is very small (in the range of 10 nm). We used 100-keV Xe at fluences ranging from a slight damage to full amorphization (between 2.0 × 1013  cm− 2 and 1.6 × 1014  cm− 2).
Keywords: Silicon carbide; Ion implantation; Spectroscopic ellipsometry; Crystal disorder; Damage profile;

Optical spectra of Zn1-xBexTe mixed crystals determined by IR–VIS–UV ellipsometry and photoluminescence measurements by A.A. Wronkowska; H. Arwin; F. Firszt; S. Łęgowski; A. Wronkowski; Ł. Skowroński (2795-2800).
Spectroscopic ellipsometry in the photon energy range from 0.04 eV to 6.50 eV is used for investigation of the optical response of Zn1-xBexTe crystals grown by a high-pressure Bridgman method in the composition range x ≤ 0.12. Infrared spectra display absorption bands centred between 411 cm−1 and 420 cm−1 associated with BeTe-type optical phonon modes. The positions of the transverse-optical and longitudinal-optical phonon modes have been found by modelling the line shape of the complex dielectric functions, ε ˜ and Im ( − ε ˜ − 1 ) , using a classical damped Lorentzian oscillator approach. Ellipsometric measurements in the VIS–UV range allow determination of the fundamental energy-gap (E0) and the higher threshold energies (E1, E1  + Δ1, E2) originating from the band edge and spin-orbit splitting critical points. We have found that the Be content x = 0.12 causes an increase of the fundamental energy gap about 0.15 eV at room temperature when compared to the E0  = 2.23 eV of ZnTe crystal at the same temperature. Photoluminescence spectra were measured in the temperature range from 30 K to room temperature. Luminescence at temperature T > 200 K is very weak. The peak positions of the exciton emission lines agree well with the E0 band-gaps derived from ellipsometric data if corrected for their temperature dependence.
Keywords: ZnBeTe; Ellipsometry; Dielectric function; Lattice vibration; Interband transitions; Photoluminescence;

Detection and characterization of single nanoparticles by interferometric phase modulated ellipsometry by F. Barroso; S. Bosch; N. Tort; O. Arteaga; J. Sancho-Parramon; E. Jover; E. Bertran; A. Canillas (2801-2805).
We introduce a new measurement system called Nanopolar interferometer devoted to monitor and characterize single nanoparticles which is based on the interferometric phase modulated ellipsometry technique. The system collects the backscattered light by the particles in the solid angle subtended by a microscope objective and then analyses its frequency components. The results for the detection of 2 μm and 50 nm particles are explained in terms of a cross polarization effect of the polarization vectors when the beam converts from divergent to parallel in the microscope objective. This explanation is supported with the results of the optical modelling using the exact Mie theory for the light scattered by the particles.
Keywords: Polarimetry; Interferometry; Phase-modulated ellipsometry; Nanoparticles detection;

Spectroellipsometric and ion beam analytical investigation of nanocrystalline diamond layers by T. Lohner; P. Csíkvári; N.Q. Khánh; S. Dávid; Z.E. Horváth; P. Petrik; G. Hárs (2806-2810).
Optical properties of nanocrystalline and ultrananocrystalline diamond films were studied by ex situ variable angle spectroscopic ellipsometry. The films were prepared by Microwave Plasma Enhanced Chemical Vapor Deposition method. In the experiments Ar, CH4, and H2 gases were used as source gases. Elastic recoil detection analysis was applied to measure the hydrogen content of the deposited layers. Three-layer optical models were constructed for the evaluation of the measured ellipsometric spectra. Besides the Cauchy relation, the effective medium approximation and the Tauc–Lorentz dispersion relation were also used for the modeling of the optical properties of the diamond films. Atomic force microscopy was applied to investigate the surface roughness in function of the deposition conditions.
Keywords: Ultrananocrystalline diamond; Microwave plasma enhanced CVD; Spectroscopic ellipsometry; Ion beam analysis; Atomic force microscopy; X-ray diffraction;

In this paper, we will provide an overview of the internal photoemission (IPE) and the significance of this technique when combined with spectroscopic ellipsometry (SE) to investigate the interfacial electronic properties of heterostructures. In particular, the main interest is focused on the electron transport mechanism and properties at and near the interface of the technologically important metal-oxide-semiconductor (MOS) devices. Not until recently, IPE and SE have become important metrology tools in band offset characterization for the MOS materials. The most common and straightforward application of IPE and SE is to determine how the Fermi level of the metal, and the conduction and valence bands of the semiconductor align with those of the oxide of the MOS structure. For demonstration, we will present the results recently obtained on a set of MOS devices consisting of metal gate / high-k dielectric stack / Si and III–V high mobility substrate. The examples include [TaN/TaSiN] metal gate / [HfO2/SiO2] dielectric stack / Si substrate and Al metal gate / Al2O3 dielectric / In x Ga1 −  x As substrate.
Keywords: Internal photoemission; Spectroscopic ellipsometry; High-k dielectric; Metal gate; MOS; Band offsets; Band alignment; Interface;

In-situ monitoring of alkanethiol self-assembled monolayer chemisorption with combined spectroscopic ellipsometry and quartz crystal microbalance techniques by K.B. Rodenhausen; B.A. Duensing; T. Kasputis; A.K. Pannier; T. Hofmann; M. Schubert; T.E. Tiwald; M. Solinsky; M. Wagner (2817-2820).
Self-assembled monolayers (SAMs) formed via chemisorption are important for a variety of surface enhancement and biological applications. We demonstrate that combinatorial spectroscopic ellipsometry (SE) and quartz crystal microbalance with dissipation (QCM-D) provides dynamic, in-situ characterization of the chemisorption process. In agreement with other studies, we find there are two steps for 1-decanethiol, an example alkanethiol SAM, chemisorption onto gold, which are a brief, fast phase followed by one that is long but slower. By using both the optical (SE) and mechanical (QCM-D) techniques, we show that the SAM porosity decreases during the second phase as the coupled ethanol solvent in the disorganized layer is replaced by more alkanethiol.
Keywords: Spectroscopic ellipsometry; Quartz crystal microbalance; Self-assembled monolayers; SAMs; Alkanethiols;

Micelle-assisted bilayer formation of cetyltrimethylammonium bromide thin films studied with combinatorial spectroscopic ellipsometry and quartz crystal microbalance techniques by K.B. Rodenhausen; M. Guericke; A. Sarkar; T. Hofmann; N. Ianno; M. Schubert; T.E. Tiwald; M. Solinsky; M. Wagner (2821-2824).
We report on a combinatorial approach to study the formation of ultra-thin organic films using in-situ spectroscopic ellipsometry and quartz crystal microbalance methods. In contrast to the quartz crystal microbalance, which is sensitive to the total mass attached to the surface, including coupled and entrapped solvent, spectroscopic ellipsometry only measures the amount of adsorbent on the surface. By using these two techniques in tandem, we define and determine the solvent fraction of cetyltrimethylammonium bromide thin films adsorbed onto a gold-coated quartz crystal. Cetyltrimethylammonium bromide thin films grown from aqueous solutions above the critical micelle concentration reveal critical phases in thickness and porosity evolution. We relate these effects to the mechanisms of formation and removal and the structure of cetyltrimethylammonium bromide films, which we determine to have systemic defects due to the presence of micelles.
Keywords: Spectroscopic ellipsometry; Quartz crystal microbalance; Surfactants; CTAB; Cetyltrimethylammonium bromide;

Application of scatterometric porosimetry to characterize porous ultra low-k patterned layers by C. Licitra; R. Bouyssou; M. El Kodadi; G. Haberfehlner; T. Chevolleau; J. Hazart; L. Virot; M. Besacier; P. Schiavone; F. Bertin (2825-2829).
Porous materials such as ultra low-k dielectrics are commonly used in micro and nano technologies. Since porosity leads to an increased sensitivity of the material to etching and post-etching plasma processes, porosity, pore size and surface modifications need to be assessed during material integration. In this work, the recently developed Scatterometric Porosimetry technique using a porosimetry acquisition coupled with a scatterometric analysis is applied to measure the properties of porous patterned layers. Measurements are performed on specially fabricated gratings after exposure to different plasma treatments. A side-by-side comparison between Ellipsometric Porosimetry and Scatterometric Porosimetry is carried out on different plasma-treated samples and shows a different impact of the plasma processes on patterned materials compared with blanket films. These results highlight the interest of Scatterometric Porosimetry to characterize sidewall damage after each step of the process. It also appears as a good complementary technique to Ellipsometric Porosimetry which only allows quantitative measurements on continuous layers.
Keywords: Scatterometry; Ellipsometric porosimetry; Ultra low-k dielectrics; Interconnect;

Vacuum-ultraviolet reflectance difference spectroscopy for characterizing dielectrics–semiconductor interfaces by Shoichi Ogata; Shinya Ohno; Masatoshi Tanaka; Takahiro Mori; Tsuyoshi Horikawa; Tetsuji Yasuda (2830-2833).
Reflectance difference spectroscopy (RDS) was applied to the characterization of SiO2/Si, GeO2/Ge, and high-k/III–V interface structures. We extended the spectral range of RDS to 8.4 eV in order to explore the optical transitions at the dielectrics–semiconductor interfaces as well as to have a high sensitivity to the interface anisotropy. Si surfaces with (110), (113), (331) and (120) orientations showed oxidation-induced RD changes in the vacuum-ultraviolet (VUV) range which were dependent on the surface orientation, oxidation method (dry or wet), and oxidation temperature. The Ge(110) surface also showed characteristic oxidation-induced changes in the VUV range, whereas Al2O3 deposition on GaAs(001) and InP(001) surfaces induced only the RD amplitude changes.
Keywords: RDS; MOS interface; Si; GeO2; Ge; GaAs; InP; Al2O3;

Influence of nanosecond laser irradiation on optical properties of surface layers of CdTe crystals by T. Aoki; D.V. Gnatyuk; V.A. Odarych; L.V. Poperenko; I.V. Yurgelevych; S.N. Levytskyi (2834-2837).
The effect of surface laser processing on the optical properties and structure of the surface region of (111) oriented CdTe single crystals have been studied by multiple-angle-of-incidence single-wavelength ellipsometry. The measurements were performed both on Cd and Te surfaces of CdTe(111) crystals and morphology was monitored by AFM. CdTe crystals were subjected to various treatments including chemical and laser etching. The ellipsometric parameters Δ and Ψ were obtained at several light incidence angles and data were interpreted based on the model of an absorbing surface layer located on an absorbing substrate. Surface roughness was taken into account and the surface layer was considered as an equivalent film with flat boundaries and effective optical parameters. The refraction n and absorption k indexes, and thickness d of the modified surface layer were calculated and features of nanosecond laser irradiation on CdTe(111) polar surfaces were discussed.
Keywords: CdTe crystal; Chemical etching; Laser irradiation; Ellipsometry; Optical constants;

Optical properties of GaAs0.9-xNxSb0.1 alloy films studied by spectroscopic ellipsometry by N. Ben Sedrine; C. Bouhafs; M. Schubert; J.C. Harmand; R. Chtourou; V. Darakchieva (2838-2842).
Spectroscopic ellipsometry from 0.73 to 4.75 eV was used to study the optical properties of epitaxial GaAs0.9-xNxSb0.1 layers with x = 0.00, 0.65, 1.06, 1.45 and 1.90%. The ellipsometric experimental spectra were fitted using a multilayer model employing the model dielectric function to describe the GaAs0.9-xNxSb0.1 optical response. We have identified the Γ-point E0, E+, and E# transitions of GaAs0.9-xNxSb0.1 and have determined the effect of nitrogen on the respective transition energies. We have demonstrated that a lower N content can provide an equal E+-E0 energy splitting for GaAs0.9-xNxSb0.1 with respect to GaAs1-xNx.
Keywords: Dielectric function; III–V semiconductors; Optical properties;

The optical properties of ZnTe and ZnS nanocrystals (ZnTe-NC and ZnS-NC) were determined by Spectroscopic Ellipsometry. The nanocrystals were embedded in a SiO2 matrix by ion implantation technique. Their sizes were characterized by transmission electron microscopy. The ZnTe-NC and ZnS-NC were modelled using Critical Points (CPs) dispersion formulas developed by Adachi. Besides the CPs model, the Tauc–Lorentz model was found to be another choice to get a good spectral fitting. Here we demonstrated that these models yield reasonable values of optical constants of II–VI nanocrystals. The best agreement was found with the experimental data over the entire range of 0.6 to 6.5 eV.
Keywords: ZnTe nanocrystals; ZnS nanocrystals; Ellipsometry; Dielectric function; Critical Points; Tauc–Lorentz;

Characterisation of ultra-shallow disorder profiles and dielectric functions in ion implanted Si by I. Mohacsi; P. Petrik; M. Fried; T. Lohner; J.A. van den Berg; M.A. Reading; D. Giubertoni; M. Barozzi; A. Parisini (2847-2851).
Ultra-shallow (below 20 nm) disorder profiles have been characterized by spectroscopic ellipsometry (SE). The implanted depth region has been divided into sublayers with dielectric functions calculated by the effective medium approximation using single-crystalline and disordered components. The damage depth profile has been parameterized using a box model, an independent multilayer model, a graded multilayer model, an error function, and Gaussian profiles. Literature values and Tauc–Lorentz (TL) parametrization as well as multi-sample and single-sample approaches have been compared to describe the dielectric function of the disordered component. The distribution of the implanted ions and/or damage have been cross-checked using medium energy ion scattering (MEIS), transmission electron microscopy and Monte Carlo simulations. We found a good agreement in the damage profiles obtained by the different methods. There is an offset between the SE and MEIS damage profiles due to the fact that SE is very sensitive to the surface roughness, in contrast to MEIS. The correlation between this offset and the surface roughness has been investigated using atomic force microscopy.
Keywords: Ion implantation; Spectroscopic ellipsometry; Ultra low energy ion implantation; Shallow implantation; Defects in semiconductors;

Temperature dependence of dielectric function and optical transitions in TlInSe2 and TlGaTe2 by YongGu Shim; Hitoshi Aoh; Junichi Sakamoto; Kazuki Wakita; Nazim Mamedov (2852-2854).
The principal components of the dielectric function of TlInSe2 and TlGaTe2 crystals with quasi-one-dimensional chain structure have been studied over the photon energies 1.5–5.0eV in the temperature range 140–400 K, with due regard to the reported phase transitions. For TlGaTe2, the absolute values of the dielectric function experience a sudden temperature-induced change at 290 K in nearly all the accessed photon energy range. The energy and other parameters of the critical points for inter-band optical transitions related to the obtained dielectric function have then been retrieved for both TlInSe2 and TlGaTe2. An abrupt change in the energy of the critical point, positioned at 2.93 eV at room temperature and formed by optical transitions induced by the light polarized along the chains, has then been disclosed for TlGaTe2 at 290 K.
Keywords: TlInSe2; TlGaTe2; Dielectric function; Spectroscopic ellipsometry; Phase transition;

Characterization of pulsed laser deposited hydrogenated amorphous silicon films by spectroscopic ellipsometry by István Hanyecz; Judit Budai; Edit Szilágyi; Zsolt Tóth (2855-2858).
The wide absorption band of hydrogenated amorphous silicon (a-Si:H) is being realized as a key component of solar cells on glass. In this study, a-Si:H films were prepared by reactive pulsed laser deposition onto silicon and glass substrates. Ellipsometry showed that the optical properties of the films are effectively independent on the choice of substrate. According to the optical properties, the character of the films changes from amorphous silicon to dielectric as the hydrogen background pressure increases from 0 to 25 Pa. This observation was attributed to oxygen incorporation indicated by Rutherford Backscattering Spectrometry. Furthermore, a refractive index gradient in depth was revealed, which was attributed to the oxygen concentration gradient.
Keywords: Hydrogenated silicon; Spectroscopic ellipsometry; Backscattering spectrometry; Pulsed laser deposition;

Temperature dependent model dielectric function of highly disordered Ga0.52In0.48P by E. Montgomery; C. Krahmer; K. Streubel; T. Hofmann; E. Schubert; M. Schubert (2859-2862).
We report on the temperature dependence of the dielectric function of Ga0.52In0.48P from room temperature to 500°C, and for photon energies from 0.75 eV to 5 eV. The undoped, highly disordered Ga0.52In0.48P thin film was grown by metal-organic vapor phase epitaxy lattice matched onto a (001) GaAs substrate. The dielectric function of Ga0.52In0.48P was measured by in-situ spectroscopic ellipsometry, and analyzed using Adachi's composite critical point model. We provide a second-order temperature expansion parameter set for calculation of the Ga0.52In0.48P dielectric function and its temperature dependence, and which may become useful for in situ growth control or optoelectronic device performance evaluation at elevated temperatures. We discuss the temperature-induced shift of critical point transition energy parameters.
Keywords: GaInP; Dielectric function; Optical constant; Temperature dependence; Refractive index; Extinction coefficient; Spectroscopic ellipsometry;

Spectroscopic ellipsometry studies on hydrogenated amorphous silicon thin films deposited using DC saddle field plasma enhanced chemical vapor deposition system by Jhantu Kumar Saha; Barzin Bahardoust; Keith Leong; Adel B. Gougam; Nazir P. Kherani; Stefan Zukotynski (2863-2866).
Hydrogenated amorphous silicon (a-Si H) films deposited on crystalline silicon substrates using the DC saddle field (DCSF) plasma enhanced chemical vapor deposition (PECVD) system have been investigated. We have determined the complex dielectric function, ε(E) =  ε 1(E) +  2(E) for hydrogenated amorphous silicon (a-Si:H) thin films by spectroscopic ellipsometry (SE) in the 1.5–4.5 eV energy range at room temperature. The results indicate that there is a change in the structure of the a-Si:H films as the thickness is increased above 4 nm. This is attributed to either an increase in the bonded hydrogen content and, or a decrease of voids during the growth of a-Si:H films. The film thickness and deposition temperature are two important parameters that lead to both hydrogen content variation and silicon bonding change as well as significant variations in the optical band gap. The influence of substrate temperature during deposition on film and interface properties is also included.
Keywords: Hydrogenated amorphous silicon; Spectroscopic ellipsometry; DC saddle field;

Phase-modulated ellipsometry was applied to measure changes in the refractive index of pure and ruthenium (Ru)-doped 0.9Pb (Zn1/3Nb2/3)O3 (PZN)–0.1PbTiO3 (PT) during the heating process in real time. Both samples were heated from room temperature to 200 °C in a thermally insulated chamber. In both samples, the phase transitions were observed to change from tetragonal to cubic. The temperature region at which the phase transition (Curie region) of Ru-doped 0.9PZN–0.1PT occurred not only broadened but also shifted to a lower temperature. The refractive indices were extremely stable in this region, meaning that Ru-doped 0.9PZN–0.1PT is a more favorable medium for the fabrication of optical memories.
Keywords: Refractive index; Perovskite; Curie region; Ellipsometry;

Dielectric functions of PECVD-grown silicon nanoscale inclusions within rapid thermal annealed silicon-rich silicon nitride films by A.-S. Keita; A. En Naciri; F. Delachat; M. Carrada; G. Ferblantier; A. Slaoui; M. Stchakovsky (2870-2873).
Spectroscopic ellipsometry (SE) measurements were carried out in order to characterize the optical properties of silicon nanoscale inclusions (Si-ni) contained in silicon-rich silicon nitride (SRSN) films. These films were deposited using the plasma enhanced chemical vapor deposition (PECVD) technique followed by rapid thermal annealing (RTA) during 1 min. We focus our study on the influence of the deposition and annealing conditions – such as the ammonia to silane flow ratio R, the annealing atmosphere and temperature – on the optical responses of the SRSN layers and the behavior of the Si-ni dielectric functions. Our results suggest that the variation of R affects in a more significant way the structure and optical properties of the SRSN films than the change of the annealing gas or temperature.
Keywords: Spectroscopic ellipsometry; Silicon-rich silicon nitride; Silicon; Nanoscale inclusions; Optical properties; Dielectric functions; Rapid thermal annealing;

The combined optical method enabling us to perform the complete optical characterisation of weakly absorbing non-uniform thin films is described. This method is based on the combination of standard variable angle spectroscopic ellipsometry, standard spectroscopic reflectometry at near normal incidence and spectroscopic imaging reflectometry applied at normal incidence. The spectral dependences of the optical constants are determined using the non-imaging methods by using the dispersion model based on parametrisation of the density of electronic states. The local thickness distribution is then determined by imaging reflectometry. The method is illustrated by means of the complete optical characterisation of SiOxCyHz thin films.
Keywords: Optical characterisation; Non-uniform films; Spectroscopic ellipsometry; Spectroscopic reflectometry; Spectroscopic imaging reflectometry;

Gravitational waves detector mirrors: Spectroscopic ellipsometry study of Ta2O5 films on SiO2 substrates by Mirko Prato; Andrea Chincarini; Gianluca Gemme; Maurizio Canepa (2877-2880).
A stack of Ta2O5/SiO2 layers is presently used as coating layer of mirrors in interferometric detectors for gravitational waves. The sensitivity of these detectors is limited in the 50–300 Hz frequency range by the mirror thermal noise, and it was suggested that mechanical losses in the Ta2O5 are the dominant source of noise. We focus here on Spectroscopic Ellipsometry (SE) results (in the 0.75 ÷ 5 eV spectral range) obtained on high quality Ta2O5 films deposited on SiO2 substrates by Double Ion Beam Sputtering at the Laboratoire des Matériaux Avancés (Lyon, France). The films are extremely flat as indicated by the 0.2 nm RMS roughness determined by Atomic Force Microscopy (AFM) on (20 × 20) μm2 areas. The comparison of the optical properties determined by SE with literature data, corroborated by X-ray Photoelectron Spectroscopy (XPS) data, suggests that the films present a non-ideal bulk stoichiometry and/or some degree of nanoporosity. The possible influence of an interface layer is also discussed.
Keywords: Ta2O5; Spectroscopic Ellipsometry; Gravitational Waves detectors;

Evaluation of coated and uncoated CaF2 optics by variable angle spectroscopic ellipsometry by Jue Wang; Steven VanKerkhove; Horst Schreiber (2881-2884).
CaF2 is one of the dominating optical materials used for ArF excimer laser optics. Surface quality of optically finished CaF2 plays an important role in the components' lifetime. A variable angle spectroscopic ellipsometry was employed to evaluate surface quality of optically finished CaF2 in terms of top surface and subsurface damage. The subsurface damage was revealed by removing the top surface. Combining plasma ion assisted deposition and ellipsometric measurement, a dense smooth F-SiO2 film was developed to prevent fluorine loss of CaF2 optics under ArF excimer laser irradiation, leading to an extended lifetime. In addition, an integrated protective coating approach was established on fluoride multilayer coated CaF2 optics, resulting in environmentally stable optical performance.
Keywords: CaF2; Subsurface damage; Color center; F-doped SiO2 film; ArF laser optics;

Vacuum-ultraviolet ellipsometry spectra and structural properties of Pb(Zr,Ti)O3 films by G. Suchaneck; D. Chvostová; J. Kousal; V. Železný; A. Lynnyk; L. Jastrabík; G. Gerlach; A. Dejneka (2885-2888).
Optical properties of PbZr x Ti1 −  x O3 material have been actively studied in the visible and near band-gap region, but data in the vacuum-ultraviolet spectral region is rather scarce. In this work we focus on well known interband transitions for the perovskite materials, 2p  →  , located in VUV spectral region. Dielectric functions of chemical solution deposited and sputtered PZT were obtained in the spectral range 1–8.8 eV. Differences between the absorption maxima for chemical solution deposited and sputtered PbZr x Ti1 −  x O3 samples near Kahn–Leyendecker 2p  →  interband transition were found and are interpreted by change of interatomic distances. This is confirmed by different lattice constants. In the case of PbZr x Ti1 −  x O3 film with microcracks, the void fraction was estimated from the effective medium approximation. Direct band-gap energies appear to be nearly the same for all reactive sputtered samples weakly depending of Zr/Ti concentration.
Keywords: PZT film; Vacuum-ultraviolet ellipsometry; Film structure; Optical properties;

Spectroscopic ellipsometry characterization of high-k gate stacks with Vt shift layers by Ming Di; Eric Bersch; Robert Clark; Steven Consiglio; Gert Leusink; Alain C. Diebold (2889-2893).
We have used spectroscopic ellipsometry (SE) to measure layer thicknesses of HfO2/La2O3 and La2O3/HfO2 stacks on SiO2/p-Si. Two approaches to extract layer thicknesses from a single SE measurement were shown to be inaccurate, possibly due to similarities in the optical dispersions of HfO2 and La2O3. The approach where SE data was collected after deposition of each layer and only the thickness of the top layer was determined by modeling was found to be capable of accurately measuring the thickness of each layer. These conclusions are supported by angle resolved X-ray photoelectron spectroscopy (ARXPS), X-ray reflectivity (XRR) and Rutherford backscattering spectroscopy (RBS) measurements.
Keywords: High-k dielectrics; Film thickness; Spectroscopic ellipsometry; Vt shift layer; Capping layer; HfO2; La2O3; X-ray reflectivity;

Extension of Far UV spectroscopic ellipsometry studies of High-κ dielectric films to 130 nm by Vimal K. Kamineni; James N. Hilfiker; John L. Freeouf; Steve Consiglio; Robert Clark; Gert J. Leusink; Alain C. Diebold (2894-2898).
Next generation CMOS devices use a high-κ dielectric layer (HfO2, HfSiO, HfSiON and La2O3) grown on thin interfacial silicon dioxide as the gate dielectric. The higher dielectric constant of the Hf oxide based film stack allows a decrease in equivalent oxide thickness (EOT). Because the high-κ film stack has a greater physical thickness than an electrically equivalent SiO2 film, the tunneling current decreases. It is a critical metrology requirement to measure the thickness of silicon dioxide and high-κ film stacks. Spectroscopic ellipsometry (SE) in the far UV wavelength region can be used to differentiate the high-κ films from silicon dioxide. This is due to the non-zero nature of the imaginary part of the dielectric function (beyond 6 eV) in the far UV region for high-κ films. There has been some conjecture that optical studies should be extended beyond 150 nm further into the VUV. This study addresses these concerns through determination of the dielectric function down to 130 nm. We show the fitted dielectric function of hafnium silicates and lanthanum oxide down to 130 nm. X-ray reflectivity (XRR) measurements were also performed on the high-κ films to complement the thickness measurements performed with SE.
Keywords: Spectroscopic ellipsometry; High-κ; Hafnium; Lanthanum; X-ray reflectivity; Cody–Lorentz;

Spectroscopic ellipsometry study of CuCdTeO thin films grown by reactive co-sputtering by A. Mendoza-Galván; S. Jiménez-Sandoval; J. Carmona-Rodríguez (2899-2902).
The complex dielectric function of CdTeO x and CuCdTeO thin films was determined by spectroscopic ellipsometry in the photon energy range of 1.5 to 5 eV. The films were grown onto glass slides substrates by reactive rf co-sputtering using CdTe and Cu targets in an Ar + O2 atmosphere. Films with different Cu concentrations were obtained by varying the power on the Cu target. The dielectric function of the films is represented by a generalized Lorentz harmonic oscillator expression. Three-dimensional type line-shapes for the critical points E 1 and E 1  + Δ1 of CdTe were identified in CdTeO x and CuCdTeO films even for Cu and O concentrations above 20 at.%. This latter result can be indicative of CdTe alloying with those elements widening the possibilities for new photovoltaic materials.
Keywords: Optical properties; Ellipsometry; Dielectric function; Cadmium telluride;

Investigation of surface roughness on etched glass surfaces by Z. Pápa; J. Budai; B. Farkas; Z. Toth (2903-2906).
Roughening the surface of solar cells is a common practice within the photovoltaic industry as it reduces reflectance, and thus enhances the performance of devices. In this work the relationship between reflectance characterized by the haze parameter, surface roughness and optical properties was investigated. To achieve this goal, model samples were prepared by hydrofluoric acid etching of glass for various times and measured by optical microscopy, spectroscopic ellipsometry, scanning electron microscopy, and atomic force microscopy. Our investigation showed that the surface reflectance was decreased not only by the roughening of the surface but also by the modification of the depth profile and lowering of the refractive index of the surface domain of the samples.
Keywords: Texturing; Surface morphology; Optical properties; Ellipsometry; Graded refractive index;

Optical properties of soda-lime float glass from spectroscopic ellipsometry by Ron A. Synowicki; Blaine D. Johs; Andrew C. Martin (2907-2913).
Optical properties of soda-lime glass manufactured by the float process were investigated using spectroscopic ellipsometry and intensity transmission measurements. Thickness and optical properties of surface layers on the air and tin sides were determined with ellipsometry. The tin side surface layer shows a graded refractive index with a non-linear profile. Intensity transmission data were used to quantify absorption in the bulk glass. Transmission-mode generalized ellipsometry characterized residual birefringence in the bulk glass. Birefringence effects on ellipsometric delta data were corrected using a simple empirical offset with 1/wavelength dependence. A general optical model for soda-lime glass is presented which can be used for subsequent analysis of coated soda-lime glass and other transparent substrates.
Keywords: Spectroscopic ellipsometry; Float glass; Soda-lime glass; Refractive index; Birefringence; Air side; Tin side; Index gradient;

Optical properties of thin films of mixed Ni–W oxide made by reactive DC magnetron sputtering by I. Valyukh; S.V. Green; C.G. Granqvist; G.A. Niklasson; S. Valyukh; H. Arwin (2914-2918).
Thin films of Ni x W1 −  x oxides with x  = 0.05, 0.19, 0.43 and 0.90 were studied. Films with thicknesses in the range 125–250 nm were deposited on silicon wafers at room temperature by reactive DC magnetron co-sputtering from targets of Ni and W. The films were characterized with X-ray diffraction (XRD), scanning electron microscopy (SEM), and spectroscopic ellipsometry (SE). XRD spectra and SEM micrographs showed that all films were amorphous and possessed a columnar structure. The ellipsometric angles Ψ and Δ of as-deposited films were measured by a rotating analyzer ellipsometer in the UV–visible-near infrared range (0.63–6.18 eV) and by an infrared Fourier transform rotating compensator ellipsometer in the 500–5200 cm−1 wavenumber range. SE measurements were performed at angles of incidence of from 50 ° to 70 °. Parametric models were used to extract thicknesses of the thin films and overlayers of Ni x W1 −  x oxide at different compositions, band gaps and optical constants. Features in the optical spectra of the Ni x W1 −  x oxides were compared with previous data on tungsten oxide, nickel oxide and nickel tungstate.
Keywords: Tungsten oxide; Nickel oxide; Ellipsometry;

Optical and structural properties of solution deposited nickel manganite thin films by N.J. Podraza; D.B. Saint John; S.W. Ko; H.M. Schulze; J. Li; E.C. Dickey; S. Trolier-McKinstry (2919-2923).
Nickel manganite thin films of interest for microbolometer applications have been prepared using chemical solution and spin spray deposition and studied using transmission electron microscopy to quantify the material crystallinity and spectroscopic ellipsometry to extract the complex dielectric function (ε = ε1  + iε2) and film microstructure. A parameterization for ε over a spectral range from 0.04 to 5.15 eV has been developed to model well-crystallized nickel manganite, and the visible-range critical point features, infrared vibrations, and optical absorption onset have been identified. A multiple sample analysis structural model and procedure has been developed for spin spray deposited films exhibiting complicated void evolutions with thickness. Variations in ε and crystallite grain size have been observed as a function of film processing and indicate that the optical properties and microstructural information gained from spectroscopic ellipsometry is useful in process monitoring for this material system.
Keywords: Nickel manganite; Microbolometer; Spectroscopic ellipsometry;

Investigation of optical properties of benzocyclobutene wafer bonding layer used for 3D interconnects via infrared spectroscopic ellipsometry by Vimal K. Kamineni; Pratibha Singh; LayWai Kong; John Hudnall; Jamal Qureshi; Chris Taylor; Andy Rudack; Sitaram Arkalgud; Alain C. Diebold (2924-2928).
Benzocyclobutene (BCB) used for bonding silicon wafers to enable 3D interconnect technology is characterized using spectroscopic ellipsometry (SE). SE is a non-destructive technique that has been used to characterize the thickness and dielectric properties of BCB. The infrared (IR) absorption spectrum was used to calculate the percentage of curing of BCB on 300 mm bare and bonded wafers. The percentage of curing in BCB is a key parameter that impacts the bond strength and bond quality. This study presents the potential application of IRSE for measurements on bonded wafers to characterize the chemical information, curing percentage, bond quality and thickness of the BCB bonding layer. One of the key issues in the process development and characterization of BCB bonding for 3D interconnects of 300 mm wafers is the presence of dendrites and voids between the bonded wafers. The presence of dendrites and voids was identified by using scanning acoustic microscopy (SAM) and imaged by scanning electron microscope (SEM).
Keywords: 3D interconnects; Benzocyclobutene; Infrared spectroscopic ellipsometry; Scanning acoustic microscopy; Wafer bonding; Curing;

Dielectric properties and thickness metrology of strain engineered GaN/AlN/Si (111) thin films grown by MOCVD by M. Tungare; V.K. Kamineni; F. Shahedipour-Sandvik; A.C. Diebold (2929-2932).
Maturity of silicon nanoelectronics and the high quality of 300 mm epi-Si wafers make these substrates an ideal choice for the growth of high quality III-Nitride devices. The results of our substrate engineering technique, which involves implantation of nitrogen into Si through an AlN thin film, have shown to simultaneously and significantly reduce the dislocation density and macro-cracks in epitaxially grown 2 μm GaN films. In this study, high quality strain engineered GaN films were grown by metalorganic chemical vapor deposition (MOCVD) and spectroscopic ellipsometry was used to characterize the dielectric properties, thickness, and stress of the complex structure. The uniaxial, anisotropic dielectric functions of wurtzite GaN and AlN were determined for the processes used in this study, and using this information, the thickness of each layer was determined in the completed film stack. IR spectroscopic ellipsometry (IRSE) was used as the non-destructive characterization technique to identify the IR sensitive phonon modes in AlN. The stress evolution in the films was investigated as a function of the phonon frequency shift and the broadening of the phonon modes. The results obtained by IRSE were further complemented by high resolution X-ray diffraction (HRXRD) and Raman scattering measurements.
Keywords: Spectroscopic ellipsometry; GaN; III-Nitrides; Raman spectroscopy; MOCVD; Thin films; Substrate engineering; Ion-implantation;

Optical properties of BaTiO3/ZnO heterostructures under the effect of an applied bias by T. Böntgen; S. Schöche; R. Schmidt-Grund; C. Sturm; M. Brandt; H. Hochmuth; M. Lorenz; M. Grundmann (2933-2935).
We report electro-optical measurements of BaTiO3/ZnO heterostructures grown by pulsed laser deposition. The optical properties of the heterostructures were examined with and without an applied bias. A change in the heterostructure optical properties is found and attributed to a linear electro-optical effect causing a change in the band gap. Moreover the formation of an electric polarization in the BaTiO3 layer causes a remanent change in the dielectric function if the bias is removed. The change could be estimated to be around 5 meV.
Keywords: BaTiO3; ZnO; Spectroscopic ellipsometry; PLD;

A broadband analysis of the optical properties of silver nanoparticle films over the range from 0.75 to 6.5 eV was performed by applying in situ real-time spectroscopic ellipsometry (RTSE) during the nucleation, coalescence, and bulk thin film growth regimes. The dielectric functions of the particulate films were found to depend strongly on the particle size and film thickness from the nucleation regime throughout coalescence. These dependences were analyzed by separately characterizing the three types of transitions evident in the dielectric function: intraband, particle plasmon polariton, and interband. Throughout the film growth regimes, the thickness evolution of the amplitude, energy, and broadening parameter for each type of transition is discussed in view of the structural characteristics of the films, as corroborated ex situ by atomic force microscopy for films deposited over different time durations.
Keywords: Spectroscopic ellipsometry; Real time spectroscopic ellipsometry (RTSE); Silver; Nanoparticles; Optical properties; Particle plasmon polariton; Interband transition; Intraband transition;

Ellipsometric study of optical switching processes of Mg–Ni based switchable mirrors by Y. Yamada; K. Tajima; M. Okada; M. Tazawa; A. Roos; K. Yoshimura (2941-2945).
Optical switching processes of MgNi based switchable mirrors were studied “in situ” using spectroscopic ellipsometry. Ellipsometric angles Ψ and Δ of the switchable mirrors varied drastically as a result of hydrogenation and dehydrogenation. These variations are due to transformation between metal and semiconductor of Mg–Ni layers. We have clarified the switching processes by analyzing these variations using the following two steps. First, we evaluated dielectric functions of five materials: metal, hydrogen-solid-solution, hydride states of Mg–Ni alloy, and metal and hydride states of Pd. Using these dielectric functions, we then varied thickness and concentration of each layer.
Keywords: Switchable mirrors; Mg–Ni alloy; In situ ellipsometry; Dielectric constants; Switching processes;

Optical properties of gold island films—a spectroscopic ellipsometry study by Martin Lončarić; Jordi Sancho-Parramon; Hrvoje Zorc (2946-2950).
Metal island films of noble metals are obtained by deposition on glass substrates during the first stage of evaporation process when supported metal nanoparticles are formed. These films show unique optical properties, owing to the localized surface plasmon resonance of free electrons in metal nanoparticles. In the present work we study the optical properties of gold metal island films deposited on glass substrates with different mass thicknesses at different substrate temperatures. The optical characterization is performed by spectroscopic ellipsometry at different angles of incidence and transmittance measurements at normal incidence in the same point of the sample. Fitting of the ellipsometric data allows determining the effective optical constants and thickness of the island film. A multiple oscillator approach was used to successfully represent the dispersion of the effective optical constants of the films.
Keywords: Spectroscopic ellipsometry; Metal islands; Surface plasmon; Optical properties;

Optical conductivity of fci-ZnMgRE quasicrystals by S. Tumėnas; V. Karpus; H. Arwin; W. Assmus (2951-2954).
The results of room-temperature spectroscopic ellipsometry study of single-grain face-centred icosahedral (fci) ZnMgY, ZnMgHo, and ZnMgEr quasicrystals in the spectral range of 0.1–6.5 eV are presented. Analysis of the optical conductivity spectra, carried out within a framework of the band structure hypothesis, reveals that an optical response of the fci-ZnMgRE quasicrystals is determined by a superposition of the intraband Drude-type contribution and that of the interband optical transitions across a pseudogap. The deduced parameters of the fci-ZnMgRE electron energy spectrum are close to their values determined previously from an analysis of the fci-ZnMgRE photoemission data.
Keywords: Quasicrystals; Spectroscopic ellipsometry; Optical conductivity;

Electrodynamics of ultrathin gold films at the insulator-to-metal transition by Martin Hövel; Bruno Gompf; Martin Dressel (2955-2958).
Gold films with a thickness (d  = 3 to 10 nm) around the percolation threshold are investigated in a broad spectral range. Their optical conductivity is dominated by two contributions: a Drude-component present above a critical thickness and a plasmon in the near-infrared region, which shifts down in frequency as d decreases. The interplay of both components leads to a maximum in the dielectric constant ε 1(d) observed right below the insulator-to-metal transition. For even lower coverage, we find an additional dielectric anomaly where the reflectivity for Au on Si/SiO2? completely vanishes in the infrared region.
Keywords: Ultrathin metal films; Optical properties; Percolation threshold; Dielectric anomaly;

Total internal reflection ellipsometry of metal–organic compound structures modified with gold nanoparticles by Z. Balevicius; R. Drevinskas; M. Dapkus; G.J. Babonas; A. Ramanaviciene; A. Ramanavicius (2959-2962).
Total internal reflection ellipsometry (TIRE) technique was used to investigate the optical response of different hybrid multilayer systems. It was shown that the optical response was significantly changed by gold nanoparticles, which have been introduced for modification of functional properties of hybrid system. Nevertheless, the dispersion of optical parameters for gold nanoparticles was quite close in various hybrid systems in the case of adequate models used for interpretation of TIRE data.
Keywords: Total internal reflection ellipsometry; Spectroscopic ellipsometry; Surface plasmons; Gold nanoparticles;

The influence of annealing time and of the silver over polymer ratio on the optical properties of the silver nanoparticles embedded in a poly(vinyl alcohol) matrix has been analyzed by spectroscopic ellipsometry in the visible/near-infrared spectral domains. The complex refractive index shows a localized absorption near 420 nm which can be attributed to localized surface plasmons. An atomic force microscopy topographic analysis shows that the particles were nearly spherical with an average size less than 20 nm, as confirmed by optical transmission measurements with polarized light. The size of the particles and their number respectively decreased and increased as the annealing time of the film increased, yielding a plasmon absorption band whose intensity is correlated to the silver nanoparticles density, estimated from their nearest-neighbour distance.
Keywords: Silver nanoparticles; Localized plasmons; Spectroscopic ellipsometry; Polymer; Poly(vinyl alcohol) (PVA);

The conformational stability of surface immobilized protein monolayers is a key issue in applications requiring preservation of the protein bioactivity such as in biosensors and in vivo implants. Ellipsometry was used to detect conformational changes in a single monolayer of immobilized proteins on plasma polymer surfaces. The areal mass density of immobilized proteins was used to validate the data analysis in the protein denaturation analysis. We observed that the rate of conformation change was strongly dependent on the properties of the immobilized protein. Immobilized catalase showed a significantly slower denaturation rate than the immobilized horseradish peroxidase, indicating that the tetramer catalase is more stable than the immobilized monomer horseradish peroxidase at the surface/air interfaces. The ellipsometry results were in a good agreement with the enzyme activity analysis.
Keywords: Protein denaturation; Protein immobilization; Ellipsometry; Plasma polymer; Protein conformation;

Ellipsometric determination of optical properties of carbazole-containing poly(l-glutamate) thin films prepared from different solvents by Toshihiro Hiejima; Yosuke Takamizawa; Takayuki Uchida; Shuichi Kawabata (2972-2977).
In this study, the refractive indices (n) and thicknesses of carbazole-containing hole-transport materials such as poly(γ-carbazolylethyl l-glutamate) (PCELG) and poly(N-vinyl carbazole) (PVCz) films were determined by carrying out ellipsometric measurements. The thicknesses of PCELG and PVCz films determined by ellipsometric analysis were in good agreement with those determined by surface profilometry. The dependence of the refractive indices of the PCELG films on film thickness was classified into two types on the basis of the solvent from which the films were prepared: the refractive indices either increased with increasing film thickness, as in the case of PCELG films prepared from 1,2-dichloroethane (DCE) and monochlorobenzene (ϕ-Cl), or were independent of the film thickness, as in the case of films prepared from 1,1,2,2-tetrachloroethane (TCE). A comparison of these results with the structures of the polymers, as determined by 1H NMR, reveals that the two types of dependences of the refractive indices of the PCELG thin film on the film thickness can be attributed to the two types of aggregation structures and/or orientational characteristics corresponding to the helical conformation of the polymer. In contrast, the refractive indices of PVCz films are governed mainly by the film thickness. Finally, we would like to emphasize that the combination of ellipsometry and other techniques such as NMR and surface profilometry provide information not only on the film thickness and refractive index but also on the aggregation structure in thin films with thicknesses on the order of 50 nm.
Keywords: Poly(l-glutamate); Ellipsometric analysis; Refractive index; Organic EL device; Hole transport material;

Determination of the Dill parameters of thick positive resist for use in modeling applications by G. Roeder; S. Liu; G. Aygun; P. Evanschitzky; A. Erdmann; M. Schellenberger; L. Pfitzner (2978-2984).
The determination of Dill parameters of thick resist is very important to improve simulation models of resist exposure and real world processes. A new extraction technique of Dill parameters based on spectroscopic ellipsometry in combination with an advanced resist exposure model is proposed for thick resist analysis. The complex refractive index of the resist is related to the relative concentration of the photoactive compound in the resist in order to describe the vertical distribution of the refractive index and the extinction coefficient. Moreover, Dill parameters are extracted by directly fitting the bleaching curves to the measured ellipsometry data. The new approach was investigated experimentally by spectroscopic ellipsometry measurements on AZ5214E resist with two moderate layer thickness values in order to verify the accuracy of the new method. Dill parameters were extracted by using this new technique and by applying resist samples subjected to different exposure doses. Possible reasons for the variation of Dill parameters depending on resist thickness are explained. Furthermore, advantages, limitations and potential improvements of the model are discussed. Finally, the impact of Dill parameter variation on image formation in the resist is demonstrated by applying the spectroscopic ellipsometer analysis results as input parameters to the lithography simulator Dr.LiTHO.
Keywords: Spectroscopic ellipsometry; Dill parameters; Thick resist; Simulation;

Ellipsometric study of SixC films: Analysis of Tauc–Lorentz and Gaussian oscillator models by Judit Budai; István Hanyecz; Edit Szilágyi; Zsolt Tóth (2985-2988).
In this study, the suitability of Tauc–Lorentz and Gaussian oscillator models to describe amorphous silicon–carbon alloys of various compositions was tested. The dependence of the model parameters on the composition showed that the amplitude and broadening of both oscillators behave similarly and significant differences can only be observed in the oscillators’ position in case of high broadening parameter values. It was shown that this difference originates from the different mathematical forms of the oscillators and from the high broadening values. Sensitivity analysis of the parameters showed that the models became less sensitive to their parameters with large broadening values. Furthermore the model parameters were correlated to the various types of chemical bonding present within the samples.
Keywords: Spectroscopic ellipsometry; Tauc–Lorentz oscillator; Gaussian oscillator; Parameter sensitivity analysis; Silicon–carbon films;

Ellipsometric study of nanostructured carbon films deposited by pulsed laser deposition by M. Bereznai; J. Budai; I. Hanyecz; J. Kopniczky; M. Veres; M. Koós; Z. Toth (2989-2993).
When depositing carbon films by plasma processes the resulting structure and bonding nature strongly depends on the plasma energy and background gas pressure. To produce different energy plasma, glassy carbon targets were ablated by laser pulses of different excimer lasers: KrF (248 nm) and ArF (193 nm). To modify plume characteristics argon atmosphere was applied. The laser plume was directed onto Si substrates, where the films were grown. To evaluate ellipsometric measurements first a combination of the Tauc-Lorentz oscillator and the Sellmeier formula (TL/S) was applied. Effective Medium Approximation models were also used to investigate film properties. Applying argon pressures above 10 Pa the deposits became nanostructured as indicated by high resolution scanning electron microscopy. Above ~ 100 and ~ 20 Pa films could not be deposited by KrF and ArF laser, respectively. Our ellipsometric investigations showed, that with increasing pressure the maximal refractive index of both series decreased, while the optical band gap starts with a decrease, but shows a non monotonous course. Correlation between the size of the nanostructures, bonding structure, which was followed by Raman spectroscopy and optical properties were also investigated.
Keywords: Spectroscopic ellipsometry; Nanoporous; Carbon; Thin film; Pulsed laser deposition;

Validity of Lorentz–Lorenz equation in porosimetry studies by Daniel Schwarz; Herbert Wormeester; Bene Poelsema (2994-2997).
Ellipsometric porosimetry is a valuable tool to determine gas loading of porous materials. Usually the Lorentz–Lorenz effective medium theory is used, instead of the more accurate Bruggeman theory. In contrast to Lorentz–Lorenz, the Bruggeman model requires detailed knowledge on the constituents of the porous material. A first order perturbation of both effective medium approximations is used to analyze the difference between these models. Similar results are only found for materials with 70% porosity. Below 50% porosity, the gas load is underestimated with the Lorentz–Lorenz model. For porous silica and alumina with 50% porosity, the use of Lorentz–Lorenz leads to a systematic error of 18% of the load capacity.
Keywords: Ellipsometric porosimetry; Effective medium approximation;

Ellipsometric study of the influence of chemical etching on thin porous silicon structures by J. Selj; A. Thøgersen; S.E. Foss; E.S. Marstein (2998-3001).
The effect of chemical etching on Porous Silicon (PS) samples is studied and quantified by using variable angle spectroscopic ellipsometry (VASE). The main aim of this work is to assess the impact of such etching on the physical properties of electrochemically etched, thin PS antireflection coatings (ARC) for solar cell applications. In this study, detailed models of PS layers etched at constant current densities are created using a graded uniaxial Bruggeman Effective Medium Approximation (BEMA). Changes in porosity, thickness, and optical anisotropy of the PS samples due to chemical etching are determined as a function of etching time after PS formation. Three series of PS films, etched at three different current densities, are investigated. It is shown that significant changes in physical properties occur for chemical etching times longer than ~ 60 s. The anodic etching process for fabricating PS ARC structures can be performed in less than 10 s. Therefore, chemical etching does not lead to significant deviations from the intended PS structure and is not seen as a hindrance to accurate control of processes for fabricating thin PS ARCs.
Keywords: Porous silicon; Ellipsometry; Solar cell; Etching;

Optical characterization of nanocrystals in silicon rich oxide superlattices and porous silicon by E. Agocs; P. Petrik; S. Milita; L. Vanzetti; S. Gardelis; A.G. Nassiopoulou; G. Pucker; R. Balboni; M. Fried (3002-3005).
We propose to analyze ellipsometry data by using effective medium approximation (EMA) models. Thanks to EMA, having nanocrystalline reference dielectric functions and generalized critical point (GCP) model the physical parameters of two series of samples containing silicon nanocrystals, i.e. silicon rich oxide (SRO) superlattices and porous silicon layers (PSL), have been determined. The superlattices, consisting of ten SRO/SiO2 layer pairs, have been prepared using plasma enhanced chemical vapor deposition. The porous silicon layers have been prepared using short monopulses of anodization current in the transition regime between porous silicon formation and electropolishing, in a mixture of hydrofluoric acid and ethanol. The optical modeling of both structures is similar. The effective dielectric function of the layer is calculated by EMA using nanocrystalline components (nc-Si and GCP) in a dielectric matrix (SRO) or voids (PSL). We discuss the two major problems occurring when modeling such structures: (1) the modeling of the vertically non-uniform layer structures (including the interface properties like nanoroughness at the layer boundaries) and (2) the parameterization of the dielectric function of nanocrystals. We used several techniques to reduce the large number of fit parameters of the GCP models. The obtained results are in good agreement with those obtained by X-ray diffraction and electron microscopy. We investigated the correlation of the broadening parameter and characteristic EMA components with the nanocrystal size and the sample preparation conditions, such as the annealing temperatures of the SRO superlattices and the anodization current density of the porous silicon samples. We found that the broadening parameter is a sensitive measure of the nanocrystallinity of the samples, even in cases, where the nanocrystals are too small to be visible for X-ray scattering. Major processes like sintering, phase separation, and intermixing have been revealed as a function of annealing of the SRO superlattices.
Keywords: Ellipsometry; Nanocrystal; Effective medium approximation; MDF; Generalized critical point; GCP;