Aider (angle-of-incidence derivative ellipsometry and reflectometry) — Implementation and application

An experimental arrangement is described whereby spectroscopic polarization-modulation ellipsometry can be extended to the measurement of both the usual parameters ψ and Δ and the derivatives with respect to the angle of incidence, $\text{?ψ}\text{?θ}$ and $\text{?Δ}\text{?θ}$. Reflectance measurements can also be made, giving R and $\text{?(ln R)}\text{?θ}$. Expressions are given for the second-derivative quantities $\text{?}{}^2\text{ψ}\text{?n?θ}$, etc. that are used in an iterative solution of the Fresnel relations. The system is used in a reexamination of the color-center layer formed on the surface of KCI during vacuum-ultraviolet irradiation in ultrahigh vacuum. It is found that only F-centers are present in the damage-layer, with no evidence for aggregate centers (i.e., M-centers). The AIDER data indicate a layer thickness of about 75 Å.     

Optical constants of nanofilms of J aggregates of organic dyes, measured by spectral ellipsometry and polarization reflectometry

The dispersion of the complex refractive index of thin films of J aggregates of organic dyes has been measured by spectral ellipsometry and polarization reflectometry. It is found that almost all films of J aggregates exhibit normal dispersion in the long-wavelength region, where the films are transparent. In the spectral range where the films absorb, anomalous dispersion is observed with a maximum in the J peak. The refractive index n in this range becomes as high as ?2.5–3.5. It is revealed that polarization reflectometry provides adequate accuracy in determining the optical constants n and κ of nanofilms of organic dyes.     

Comparative study of the oxidation of thin porous silicon layers studied by reflectometry, spectroscopic ellipsometry and secondary ion mass spectroscopy

We present a systematic study on ultrathin porous silicon (PS) layers (40–120 nm) of different porosities, formed by electrochemical etching and followed by thermal oxidation treatment (300°C and 600°C) and by electrochemical oxidation. The oxidised and non-oxidised PS layers have been analysed by spectroscopic reflectometry (SR), spectroscopic ellipsometry (SE) and secondary ion mass spectroscopy (SIMS). The SR and SE spectra were fitted by a multiparameter fit program and the composition and the thickness of the PS layers were evaluated by different optical models. PS layers, formed electrochemically in the outermost layer of a p/n⁺ monocrystalline silicon junction were successfully evaluated using a gradient porosity optical model. The non-oxidised PS, formed in p-type silicon, can be well described by a simple optical model (one-layer of two-components, silicon and voids). The spectra of the oxidised PS layers can be fitted better using an optical model with three interdependent components (crystalline-silicon, silicon-dioxide, voids). The SIMS results give a strong support for the optical model used for SR and SE.     

Magneto-optical ellipsometry

Through the extension of the Yeh's formalism (Surf. Sci.96 (1980) 41) to magnetic crystalline media the formulas of the magneto-optic ellipsometry and the dispersion relations for wave-guiding in multilayer magnetic crystalline structures are obtained. The theory covers most of the situations considered so far in the magneto-optics in which the optical response of the structures is linear in the amplitude of the incident wave. It is capable of treating the interfaces between two magnetic media and the structures containing such interfaces with no restrictions on the orientation of the magnetizations and crystalline axes at an arbitrary angle of incidence. The polar, longitudinal and transversal magnetizations in the structures are considered as special cases. Possible applications of the theory are in the analysis of the planar multilayer magneto-optic systems in the integrated optics and magneto-optic memory technology, in the study of profiles of magnetic surfaces subjected to mechanical wear, ion implantation, etc.     

Surface raman ellipsometry

A method for achieving the ultrahigh sensitivity required for surface Raman spectroscopy is described. Polarization selective heterodyne detection permits shot-noise limited subnomolayer detection with classically noisy picosecond laser sources. Preliminary experimental results show that the polarization selectivity can be used to reduce the overwhelming thermally induced changes in metal surface reflectivity.     

Regularization in ellipsometry

The continuous variation of the refractive index with the depth in the vicinity of surfaces can be determined by ellipsometry without destroying the object of measurements. The presented method does not impress any given structure to the profile and is applicable to just the range of layer thicknesses interesting to optics (about /4 to /2). The theoretical approach to interpret the measured data leads to an integral equation that is numerically inverted by regularization to filter out the destabilizing effects of measurement errors. The regularizing operator and regularization parameter responsible for this filtering are founded on physical arguments and experiment, respectively. These results can be transferred to other regularization problems based on quantities related to volume (e.g. density, temperature).     

Generalized rotating-compensator ellipsometry

The extension of rotating-compensator ellipsometry (RCE) to measurements of the system Jones matrix J of optical systems is reported. The similarities and differences of generalized RCE as compared to other methods are noted. Measurements of several anisotropic materials, as well as of “standard” optical systems having one, two and three essential (complex) elements of J are described. Finally, a completely automated procedure for the measurement and analysis of a uniaxially anisotropic surface with the optic axis in the plane of the surface is presented.     

Principal angle-of-incidence ellipsometry

In principal angle-of-incidence ellipsometry, or ?_P - K ellipsometry, one makes measurements of the principal angle of incidence, ?_P, and the imaginary part of the ellipsometric function ? for this angle of incidence, K, in place of Δ and tan ψ. The parameter K has often been referred to as the ellipticity at principal angle incidence. Following a discussion of the sensitivity of ?_P-K ellipsometry, the results obtained in recent years by ?_P-K ellipsometry are reviewed. A return-path type ellipsometer for use in ?_P-K ellipsometry is described, which requires no compensator and can be a powerful tool for spectroscopic ellipsometry.     

Density, thickness and composition measurements of TiO2SiO2 thin films by coupling X-ray reflectometry, ellipsometry and electron probe microanalysis-X

Mixed TiO₂SiO₂ thin films were deposited by aerosol atmospheric CVD method by using di-acetoxi di-butoxi silane (DADBS) and Ti tetra-butoxide as precursors. By varying the deposition temperatures between 470 and 600 °C and the ratios between the Si and Ti precursors (Si/Ti) from 2 up to 16, films with different compositions and thicknesses were deposited. The coupled analysis of the results of different characterisation methods was used in order to determine the variation of the composition, the thickness and the density of the films. First EPMA measurements were performed at different acceleration voltages with a Cameca SX50 system. By analysing, with specific software, the evolution of the intensity ratio I_x/I_std versus the voltage, the composition and the mass thickness (product of density by the thickness) were determined. In order to measure independently the density, X-ray reflectometry experiments were performed. By analysing the value of the critical angle and the Kiessig fringes, the density and the thickness of the layers were determined. The refractive index and the thickness of the films were also measured by ellipsometry. By assuming a linear interpolation between the index value of the pure SiO₂ and TiO₂ films, the film composition was deduced from the refractive index value. XPS measurements were also performed in order to obtain an independent value of the composition. A good agreement between the ways to measure the density is obtained.     

Automated Mueller matrix ellipsometry

The application of rotating-compensator ellipsometry (RCE) to measurements of the system Mueller matrix M of linear optical systems is reported. This technique extends a previously reported procedure for automated Jones matrix ellipsometry to include systems that depolarize light.     

Neutron reflectometry with vector polarization analysis: First steps

The most detailed and reliable information about the magnetic state (magnetization depth profiles) of layers can be obtained by neutron reflectometry with vector polarization analysis. Two schemes of realization of this technique are considered. Precession coils designed to manipulate the polarization vector of monochromatic beams are used in scheme I. This scheme was tested at the neutron reflectometer NR-4M (PNPI, Gatchina). The earliest experimental data on the polarization vector rotation are reported, giving direct evidence of the wave function phase shift of a massive particle, the neutron, under total reflection. The basic elements for scheme II are remanent supermirrors. This scheme is designed for use with a white beam and is advantageous for pulse neutron sources. The effect of stray fields produced by remanent supermirrors on the neutron polarization has been theoretically and experimentally evaluated; efficient ways of compensating the stray fields are proposed.     

A perspective on ellipsometry

Two distinct and general definitions of ellipsometry and polarimetry are stated ab initio that account for the existing duality in usage of both terms. Ellipsometers and polarimeters are next defined accordingly. The definitions contrast these commonly used similar terms against one another. Viewed within the framework established by these general definitions, optical ellipsometry of interfaces and films (the main topic of this conference) is recognized as a narrow particularization of a broad scheme. Examples of ellipsometry (polarimetry) in different regions of the electromagnetic spectrum provide important perspective on the considerable extent of the field. Another perspective (in a different dimension) is gained when the application of ellipsometry (polarimetry) to different samples is considered. This relates ellipsometry of interfaces and films to polarimetry of bulk anisotropic samples and light scattering by systems of particles. Three individual procedures (namely, polarization measurement, application of electromagnetic theory, and computation) are identified as essential to the complete utilization of ellipsometry (polarimetry).     

Femtosecond Kerr ellipsometry in polydiacetylene solutions: Two-photon effects

We describe a pump-probe femtosecond Kerr experiment in polydiacetylene solutions (4BCMU, yellow form). The Kerr ellipsometry technique permits a separate determination of the real and of the imaginary part of anisotropic index changes. The wavelength (620 nm) of the pump pulses lies in the transparency region of polydiacetylene while the probe pulses have a broad white spectrum. The largest contribution to the Kerr signal is a quasi-resonant stimulated anti-Stokes Raman absorption. A flat two-photon transition spectrum with 4×10^–3 cm/MW is observed close to 4 eV. The two-photon excited states have a life time close to 12 ps and they present a broad absorption band in the 2 eV range.     

Phase-detected Brillouin optical correlation-domain reflectometry

Optical Review - Optical fiber sensing techniques based on Brillouin scattering have been extensively studied for structural health monitoring owing to their capability of distributed strain and...     

Neutron reflectometry on Co-Cr layers

Polarized neutron reflection experiments were performed on a thin in-plane magnetized Co-Cr layer deposited on a quartz substrate. Data taken at a low magnetic field ( 0.1 T) clearly indicate the existence of an initial layer at the substrate side, whereas data at saturation ( 0.7 T) are consistent with a rather homogeneous magnetization.     

The ultimate in real-time ellipsometry: Multichannel Mueller matrix spectroscopy

A review of the techniques and applications of multichannel ellipsometry in the dual-rotating-compensator configuration is given. This ellipsometric approach has been established as the ultimate in real-time, single-spot optical measurement, as it determines the entire 16-element Mueller matrix of a sample over a wide spectral range (up to 1.7-5.3 eV) from raw data collected over a single optical period of 0.25 s. The sequence of optical elements for this ellipsometer is denoted PC_1rSC_2rA, where P, S, and A represent the polarizer, sample, and analyzer. C_1r and C_2r represent two MgF₂ rotating compensators, either biplates or monoplates that rotate synchronously at frequencies of ω₁ = 5ω and ω₂ = 3ω, where π/ω is the fundamental optical period. Previous high-speed Mueller matrix measurements with this instrument have been performed on uniform, weakly anisotropic samples such as (110) Si, in which case one can extract the bulk isotropic and near-surface anisotropic optical responses simultaneously. In such an application, the instrument is operated at its precision/accuracy limits. Here, ex situ results on a strongly anisotropic, locally biaxial film are presented that demonstrate instrument capabilities for real-time analysis of such films during fabrication or modification. In addition, the use of the instrument as a real-time probe to extract surface roughness evolution on three different in-plane scales for an isotropic film surface is demonstrated for the first time.     

Generalized ellipsometry of anisotropic media

The determination of the parameters of an arbitrary reflection matrix of a medium using PCSA null ellipsometry with a fixed compensator is considered. The ordinary four-zone scheme of measurements is shown to have limited capabilities of determining the matrix components. Additional measurements in the Kerr zones for the compensator axis oriented parallel to the plane of incidence or reflection extends the capabilities of the method and allows the problem to be solved completely in the case of small off-diagonal components.