It is possible to encounter thin films exhibiting various defects in practice. One of these defects is area non-uniformity in optical parameters (e.g. in thickness). Therefore it is necessary to have methods for an optical characterization of nonuniform thin films. Imaging spectroscopic reflectometry provides methods enabling us to perform an efficient optical characterization of such films. It gives a possibility to determine spectral dependencies of a local reflectance at normal incidence of light belonging to small areas (37 μm × 37 μm in our case) on these non-uniform films. The local reflectance is measured by individual pixels of a CCD camera serving as a detector of an imaging spectroscopic reflectometer. It is mostly possible to express the local reflectance using formulas corresponding to a uniform thin film. It allows a relatively simple treatment of the experimental data obtained by imaging spectroscopic reflectometry. There are three methods for treating these experimental data in the special case of thickness non-uniformity, i.e. in the case of the same optical constants within a certain area of the film - single pixel imaging spectroscopic reflectometry method, combination of single-pixel imaging spectroscopic reflectometry method and conventional methods (conventional single spot spectroscopic ellipsometry and spectrophotometry), and multi-pixel imaging spectroscopic reflectometry method. These methods are discussed and examples of the optical characterization of thin films non-uniform in thickness corresponding to these methods are presented in this contribution.
Scattermeter II is the second generation device designed and built at The Institute of Physical Engineering, Faculty of Mechanical Engineering, Brno University of Technology. This device has been designed for measuring the angular distribution of the intensity of electromagnetic radiation scattered from a surface of a solid. In this paper, the basic scheme of Scattermeter II and measuring principles with it are described. The results achieved in electromagnetic radiation scattering from surfaces of selected samples of single crystalline silicon wafers used in solar cells are also presented.
A new optical characterization method based on imaging spectroscopic reflectometry (ISR) is presented and illustrated on the characterization of rough non-uniform epitaxial ZnSe films prepared on GaAs substrates. The method allows the determination of all parameters describing the thin films exhibiting boundary roughness and non-uniformity in thickness, i.e. determination of the spectral dependencies of the optical constants, map of local thickness and map of local rms values of heights of the irregularities for the rough boundaries. The local normal reflectance spectra in ISR correspond to small areas (37×37 μm2) on the thin films measured within the spectral range 270{900 nm by pixels of a CCD camera serving as the detector of imaging spectrophotometer constructed in our laboratory. To our experience the small areas corresponding to the pixels are sufficiently small so that the majority of the films can be considered uniform in all parameters within these areas. Boundary roughness is included into the reflectance formulas by means of the scalar diffraction theory (SDT) and the optical constant spectra of the ZnSe films were expressed by the dispersion model based on the parametrization of the joint density of electronic states (PJDOS). In general, there is a correlation between the searched parameters if the individual local reflectance spectra are fitted separately and, therefore, the local reflectance spectra measured for all the pixels are treated simultaneously using so called multi-pixel method in order to remove or reduce this correlation and determine the values of all the parameters with a sufficient accuracy. The results of the optical characterization of the same selected sample of the epitaxial ZnSe thin film obtained using the method presented here and combined method of variable-angle spectroscopic ellipsometry, spectroscopic reflectometry and single-pixel immersion spectroscopic reflectometry are introduced in the contribution as well.
Imaging spectroscopic reflectometry is a technique suitable for measurements of local optical parameters (thickness, refraction index and index of extinction) of non-uniform thin films along their surface. It is usually assumed that gradients of these non-uniformities are reasonably small. A new design of an imaging spectroscopic reflectometer provides the possibility to successfully measure high gradient non-uniformities along relatively large area of a thin film surface. A specialized low cost apparatus was developed to accomplish a higher resolution of surface imaging at the cost of reduction of the spectral range usable. The whole concept of the imaging spectroscopic reflectometer was designed to achieve high light throughput using only prefabricated optical components. Shorter measurement times and lower demands on an imaging camera used were achieved. The imaging spectroscopic reflectometer mentioned above was realized as a compact device with easy calibration and handling. Any monochromator with its output into an optical fiber can be used as a source of light. The potential of the device is demonstrated using samples with high gradients of thickness along their surfaces. A significant improvement in the resolution of thin film interference pattern images was observed in comparison with the same images obtained by means of an older UV-VIS-NIR device.
A new approach to surface roughness measurement based on the digital two-wavelength holographic interference
microscopy with the synthetic wavelength is presented. Two holograms of a randomly rough surface are recorded step by
step at two wavelengths by means of a CCD camera. Both holograms are numerically reconstructed. Two reconstructed
waves obtained numerically interfere. The surface roughness parameters may be determined from the interferogram.
Principle, parameters and selected applications of the optical profilometer MicroProf FRT (Fries Research & Technology
GmbH) in determining surface quality are presented in this contribution.
In this paper the method of imaging spectrophotometry enabling us to characterize non-absorbing thin films non-uniform in the optical parameters is described. This method is based on interpreting the spectral dependences of the local absolute reflectances measured at the normal incidence of light. It is shown how to determine the area distribution of thickness and refractive index of the non-absorbing non-uniform thin films by treating these reflectances. Moreover, the generalization of the method for the optical characterization of slightly absorbing non-uniform thin films is also indicated. Furthermore, the two-channel imaging spectrophotometer enabling us to apply the method of imaging reflectometry is described. The procedure for determining the spectral dependences of the local absolute reflectance in the points aligned in a matrix situated on the illuminated area of the non-uniform thin film by means of the spectrophotometer is also presented. The practical advantages of the method are specified. The method is illustrated by means of the optical characterization of a selected epitaxial ZnSe thin film prepared using molecular beam epitaxy onto gallium arsenide single-crystal substrate.
In this paper the mechanical stresses taking place in diamond like thin films prepared by the plasma enhanced chemical vapor deposition onto silicon single crystal substrates are studied. For determination of the stress values the Stoney's formula is used. The values of the film thicknesses are determined using the combined
method of variable angle spectroscopic ellipsometry and near-normal spectroscopic reflectometry. The values of the curvature radii of the deformed silicon substrates in consequence of the film stresses are evaluated using interferometric method based on two-beam interferometry and chromatic aberration method. The dependence of
the mechanical stress inside these films on their thickness values is determined. It is found that this dependence can be approximate by the straight-line. The results achieved for the mechanical stresses obtained by both the optical methods, i.e. by the interferometric and chromatic aberration method, are compared. It is shown that within the experimental accuracy the stress values determined using both these method are identical. Thus, it is shown that the chromatic aberration method is suitable for measuring the mechanical stresses inside the thin solid films and it is the competitive method for the other optical methods utilized for this purpose so far.
In this paper the quantitative dependence of the mechanical stress inside diamond-like carbon films containing Si and O atoms on a flow rate ratio of methane CH4 and hexamethyldisiloxane C6H18Si2O in the deposition mixture is determined. For this purpose the modified Stoney's formula is employed. The important quantities taking place in this formula, i.e. the radius of curvature of the spherical surface of a deformed silicon substrate because of the film stress and the film thickness, are determined using the combined optical method based on two-beam interferometry, variable angle spectroscopic ellipsometry and near-normal spectroscopic reflectometry. It is shown that the influence of the flow rate ratio on the values of the mechanical stresses taking place inside these films is negligible within the experimental accuracy achieved for determining these stresses if the total flow rate of gases used to be constant in the deposition mixture. A discussion of this fact is also performed. The film studied were prepared using the plasma enhanced chemical vapor deposition.
In this paper, a new optical method for characterizing nonuniform thin films is employed. For applying this method the special experimental arrangement containing CCD camera as a detector is used. Using this experimental arrangement the spectral dependencies of the local reflectances are obtained. After treating these experimental data of the distributions of the values of the local thicknesses and local refractive index along a large areas of the substrates of the nonuniform films are found. Moreover, it is shown that this method can be used to determine strong nonuniformities in both the optical parameters. The method is illustrated through the optical characterization of a nonuniform ZnSe epitaxial thin film deposited onto gallium arsenide single-crystal substrate and nonuniform film formed by the mixture of CNx and SiOy deposited onto silicon single-crystal substrate.
Laser speckle field can be generated as the result of interaction of a laser wave with randomly rough surface. Information on statistical properties of the surface is encoded in statistical properties of the light intensity distribution of the scattered wave. We can get this information from the degree of correlation of two laser speckle fields obtained step by step with two laser waves of different wavelengths scattered from the same area of the surface. The angle of incidence is the same for those two waves. As a quantitative parameter for evaluation of the rate of correlation of those two laser speckle fields we use the autocorrelation function of their sum. We calculate this function in the framework of the scalar Kirrchoff theory of wave scattering from random surfaces. We compare results obtained in the Fresnel approximation and in the Fraunhofer approximation of the scattered wave. We discuss the disparity of solutions from the point of view of surface roughness measurement.
Correlation of laser speckle fields generated by light of two different wavelengths, which illuminates a randomly rough surface, is solved within the framework of the scalar Kirchhoff theory of wave scattering from random rough surfaces. The Fresnel approximation is used in description of the scattered wave. The solution obtained is applied to surface roughness determination.
The topic of this paper is theoretical consideration on utilization of light scattering for measurement of surface roughness. We use correlation of laser speckle fields generated by light of two different wavelengths, which illuminates investigated randomly rough surface. We present the solution of the problem within the framework of the scalar Kirchhoff theory of wave scattering from random rough surfaces. We use the Fresnel approximation in description of the scattered wave. Our solution is a contribution to the Kirchhoff theory of electromagnetic wave scattering from random roughly rough surfaces.
In this contribution examples of the optical characterization of multilayer systems with randomly rough boundaries are presented. The method based on measuring and interpreting the spectral dependences of the coherent reflectance is used to determine the values of the optical and statistical parameters of samples of three-layer and thirteen-layer systems exhibiting the rough boundaries. The systems mentioned are formed by thin films of SiO2 and TiO2.
The values of the basic characteristics of surface roughness measured by means of optical and non-optical methods often differ mutually. So far a systematic comparison of the results obtained by those methods has not been done. The results we have achieved comparing optical and non-optical methods of the surface roughness measurement for selected samples of rough surfaces and for selected methods are presented.
In this paper a method of shearing interferometry enabling us to perform a characterization of the basic statistical properties of non-gaussian randomly rough surfaces of solids will be described. This method is based on a statistical analysis of the form of dark fringe centers taking place in interferograms obtained by using a suitable interference microscope. By means of the method the root-mean-square values of heights and slopes, the values of autocorrelation lengths, autocorrelation coefficients of the heights and autocorrelation coefficient of the slopes of surface irregularities of glass diffusers will be determined.
Optical analysis of rough single and double layers is performed by interpreting the spectral dependences of the measured coherent reflectance. Formulas for the coherent reflectance of these systems derived within the scalar theory of diffraction of light are used for this interpretation. Possibilities and limitations of the method utilized are illustrated using several concrete samples of both the rough single and double layers represented by models corresponding to fully correlated (identical), partially correlated, and fully uncorrelated boundaries. It is shown that the values of the optical parameters, the root-mean-square (rms) values of the heights of the boundary irregularities and the values of the cross-correlation coefficients of the boundaries characterizing the layered systems mentioned can be determined within the method described.
An angle speckle correlation was proposed for a measuring
of surface roughness parameters first in [1) . In this paper we
present some new results of the method which we reached for a
case of randomly rough surfaces in 2D Fresnel approximation. W
made a comparison with 2D Fraunhofer approximation results.
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