Optical Characterization of Nonabsorbing and Weakly Absorbing Thin Films with the Wavelengths Related to Extrema in Spectral Reflectances (original) (raw)
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Applied Optics, 2006
A method for determining the optical constants and the thickness of weakly absorbing thin films on substrates is proposed. In this method only the reflectance and transmittance spectra obtained at a single arbitrary angle of incidence are used, provided that the former reveals several interference extrema. The calculation procedure is based on relatively simple relations suitable for the programmed realization and does not call for the prescription of the initial values of the parameters to be determined. The method proposed is fairly accurate and allows one to uniquely solve the inverse problem of spectrophotometry. The optical constants and the thickness of an As x Se y film formed on a glass substrate have been determined by the proposed method in the visible region of the spectrum.
Surface and Interface Analysis, 2002
An original method enabling us to characterize the non-uniformity of thin-film thickness is described. This method employs the interpretation of data obtained by multiple-wavelength reflectometry (MWR). Within this MWR method the values of the reflectance are measured for several wavelengths in many points lying along the area of the film. The spectral dependence of the refractive index of the material forming the film is determined using variable-angle spectroscopic ellipsometry (VASE). The MWR method is then used to evaluate the values of the thickness along the area of the non-uniform film under investigation. Within the experimental setup employed for applying the MWR method, a multi-wavelength laser is used as a light source. A CCD camera equipped with a zoom objective is utilized as a detector. A suitable beamsplitter allows to measure the values of the relative reflectance of the film against a reference sample with known reflectance. By using the setup employed it is possible to characterize the thin-film spreading over large areas of substrates.
Cumhuriyet Üniversitesi Fen Fakültesi The optical constants determination of thin-films
A method for calculating the optical constants of weakly absorbing homogeneous thin films of refractive index, n lower than substrate index, s (s < n) and extinction coefficient, k from the spectral Transmission information alone with no prior knowledge of their characteristics was studied. Initially the procedure uses transmission turning point data to estimate the refractive index, n and extinction coefficient, k by an analytical approach. The calculations are done from the knowledge of transmission turning point data, which was obtained from Shimadzu UV3100 spectrophotometer. The data are then fitted to a high order polynomial function that undergoes an iterative refinement routine by means of a goal seek routine to determine with good accuracy the film parameters as a function of wavelength.
The optical constants of the metal thin films of Rhodium have been determined, the phase angles was determined using the measured spectral reflectance R(λ) by Kramers-Kronig relations. Then, the real part of the refractive index is calculated by the approach of Heavens when the film is highly absorbing, in that range the real refractive was found to be in order of the extinction coefficient k. The interference reflectance spectra at normal incidence for different thicknesses of amorphous metal films deposited by thermal evaporation have been obtained in the spectral range 400-800 nm. We propose a method for determination of the refractive index and extinction coefficients of highly absorbing films. This method is based on measurements of reflectance of the film at normal incidence alone, simulations of the theoretical accuracy and the effect of the error of the spectral reflectance measurements in the determination of the optical constants of the film are analyzed.
Determination of the thickness and optical constants of thin films from transmission spectra
Thin Solid Films, 1996
A method has been developed to determine the thickness and the wavelength-dependent refractive indices and absorption coefficients of thin optical films by fitting a five parameter function to measured transmission spectra. Initial values for the fitting parameters are obtained from the transmission values at the spectral maxima and minima of the interference patterns created by the films. This is followed by a systematic variation of those parameters which can cause a failure of the calculation by reaching local minima of the residual sum of squares. The final fitting is performed with a Mauluardt algorithm. A Monte Carlo simulation has indicated that the accuracy of this method is at least one order of magnitude better than that of the methods utilising only the interference extrema. Eeywovdf: Amorphous reatedals; Optical properties; Optical spectroscopy; Silicon 004040901961515,00 © 1996 Elsevier Science S.A. All dllhts reserved Pii$0040.6090(96)08737.8
Applied Optics, 2006
Nonuniformity in the thickness of thin films can severely distort their transmission spectra as compared with those of flat, smooth films. Methods that extract properties such as refractive index, thickness, and extinction coefficient of such films can suffer inaccuracies when they are applied to wedged or nonuniformly thick films. To accurately extract optical properties of nonuniform films, we have developed a novel numerical method and efficient constitutive relations that can determine film properties from just the transmission spectrum for films that are locally smooth with negligible scattering loss. This optimum parameter extraction (OPE) method can accommodate films with two-dimensional thickness variation that would result in significant errors in the values of refractive index and film thickness if not considered. We show that for carefully chosen test cases and for actual pulsed-laser-deposition AlN thin films, properties such as refractive index, extinction coefficient, and film thickness were very accurately determined by using our OPE method. These results are compared with previous techniques to determine the properties of thin films, and the accuracy of and applicable conditions for all these methods are discussed.
Applied Optics, 1984
We describe a three-stage process for the determination of the optical constants n and k of thin absorbing films on the basis of reflectance, transmittance, and thickness measurements. The first stage uses a bivariate optimization based on the functions (1 i R)/T, R denoting a reflectance and T the transmittance. The second stage uses a phase-variate approach based on an algorithm for locating the complex zeros of analytic functions. The third stage uses an evolution curve, giving the single-wavelength reflectance as a function of film thickness. We illustrate the process using practical examples drawn from recent studies of films of amorphous silicon, hydrogenated carbon, and hydrogenated silicon.
Optical peculiarities of thin absorbing films
OPTIKA '98: 5th Congress on Modern Optics, 1998
Optical parameters of thin semiconductor films in visible region are investigated with two different methods: use the new analogues of Fresnel's formulas for absorbing media for calculation of reflection and transmission [1] and, use the calculation of an index of refraction on a base of a phase change on reflection. Results of these methods agree well. Thickness dependencies of n(d) and k(d) of Ge,Si,Se, Te were obtained for the experimental data [2]. Curves n(d) have resonance maxima at thicknesses, which are less than light wavelength in a medium in it times. Curves
Determination of (n,k) for absorbing thin films using reflectance measurements
Applied Optics, 1988
We propose a method for determination of the complex refractive index of absorbing materials either in bulk or film geometry by measuring its reflectivity when coated with a well-characterized transparent dielectric at two specific optical thicknesses: ndj = XO/4 and njdj = X 0 /2. The complex refractive index of the sample n =