Measurements of the thickness distribution of thin films with a slit-beam-profile reflectometer (original) (raw)
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Thin Solid Films, 1997
We report here a method for determining the thickness of semiconductor and dielectric thin fihns based on the optical transmission turning points. An analytical treatment of the transmittance taking into account the shrinkage of the interference fringes caused by thickness inhomogeneities and the bandwidth of the incoming radiation is used. The computation algorithm is original, simple and straightforward. The accuracy of the method is studied, and the effects of the experimental noise, the uncertainty in the value of the substrate refractive index and of the number of available fringes on the spectra are considered. The precision of the thickness is estimated to be around 0.4% (or less) for films whose optical thicknesses (product of the refractive index and the thickness) are in the range 0.5-10 b~m. The method is applied to obtain large-area thickness profiles by computing the thickness from spectra taken over different positions of the film surface. In this case, a special mechanical mounting is needed for the acquisition of the transmission data. This procedure presents the advantage of local analysis of the films, allowing the non-flatness of the substrate to be ignored. This last is the major inconvenience in the use of a surface profile measurement system. Results are given for films up to 7 cm large (there is no difficulty in increasing this value even further) and with different thickness profiles.
Thin film thickness profile measurement using an interferometric surface profiler
2007
The technique of surface profile measurement using white-light interferometry is widely used in industry. However, its application to transparent thin films has been limited to date because the reflection signals from the front and back surfaces are mixed and must be separated in order to obtain correct measurements. This paper introduces four of our recent developments in this application field: 1) profiling of a thick transparent film, 2) profiling of a thin transparent film, 3) thickness profiling of a freestanding film, and 4) simultaneous measurement of the thickness and refractive index of a freestanding film.
Thin film thickness profile measurement using an interferometric surface profiler
Optomechatronic Sensors and Instrumentation III, 2007
The technique of surface profile measurement using white-light interferometry is widely used in industry. However, its application to transparent thin films has been limited to date because the reflection signals from the front and back surfaces are mixed and must be separated in order to obtain correct measurements. This paper introduces four of our recent developments in this application field: 1) profiling of a thick transparent film, 2) profiling of a thin transparent film, 3) thickness profiling of a freestanding film, and 4) simultaneous measurement of the thickness and refractive index of a freestanding film.
Measurement of the thickness distribution and optical constants of non-uniform thin films
Measurement Science and Technology, 2011
In this paper, an original method for the complete optical characterization of thin films exhibiting area thickness non-uniformity is presented. This method is based on interpreting experimental data obtained using an original imaging spectroscopic photometer operating in the reflection mode at normal incidence of light. A CCD camera is employed as a detector of the photometer. The spectral dependences of the reflectance measured simultaneously by individual pixels of the CCD camera correspond to the local reflectance of small areas of the non-uniform thin films characterized. These areas form a matrix along a relatively large part of the substrate covered with the non-uniform film. The spectral dependences of the local reflectance measured by the individual pixels are treated separately by means of the formulae for the reflectance valid for uniform thin films. The reason is that the local areas corresponding to the pixels are sufficiently small so that the film characterized can be considered to be uniform within these local areas. Using this approach, it is possible to determine the values of the local thickness and local optical constants for every small area of the matrix. Thus, in principle it is possible to determine the distributions (maps) of the local thickness and the local optical constants of the non-uniform films simultaneously. This method is used to characterize carbon-nitride thin films exhibiting only the thickness area non-uniformity.
Thickness Profile Measurement of a Transparent Film using Transmission Interferometry
Proc. of Symposium on Optical Measurement and Imaging Technology (SOMIT), 2007
We proposed a method of inserting the transparent film to be measured into the measurement optical path of the interference system and determining the film thickness from the change in the measurement result of the reference plane. First, we confirmed the basic principle with a wide-field interferometer. Furthermore, in the microscope type interferometer, the effect of the height of the sample was investigated, and the practicality of the two-step measurement method was confirmed. According to this method, the thickness distribution of the transparent film can be measured easily and stably by using a commercially available reflection type surface profiler without being affected by the position of the sample or the waviness. In addition, this method can be applied to ultra-thin films and multilayer films.
Thin Solid Films, 2000
In this work a method for the determination of the thickness and optical properties of low optical thickness films D-600 nm , Ž. Ž. from the experimental transmittance T and back reflectance RЈ measurements, is proposed. An original analytical formulation without any kind of approximation is employed for the computations. The computing algorithm is presented in detail and an error study is given. The method is applied for the characterization of sputtered CdTe and a-Si thin films of optical thickness in the range of 250 nm.
Simultaneous reflectometry and interferometry for measuring thin-film thickness and curvature
Review of Scientific Instruments, 2018
A coupled reflectometer-interferometer apparatus is described for thin-film thickness and curvature characterization in the three-phase contact line region of evaporating fluids. Validation reflectometry studies are provided for Au, Ge, and Si substrates and thin-film coatings of SiO 2 and hydrogel/Ti/SiO 2. For interferometry, liquid/air and solid/air interferences are studied, where the solid/air samples consisted of glass/air/glass wedges, cylindrical lenses, and molded polydimethylsiloxane lenses. The liquid/air studies are based on steady-state evaporation experiments of water and isooctane on Si and SiO 2 /Ti/SiO 2 wafers. The liquid thin-films facilitate characterization of both (i) the nano-scale thickness of the absorbed fluid layer and (ii) the macro-scale liquid meniscus thickness, curvature, and curvature gradient profiles. For our validation studies with commercial lenses, the apparatus is shown to measure thickness profiles within 4.1%-10.8% error.
Application of Fresnel diffraction from a phase step to the measurement of film thickness
Applied Optics, 2009
When a thin film that is prepared in a step form on a substrate and coated uniformly with a reflective material is illuminated by a parallel coherent beam of monochromatic light, the Fresnel diffraction fringes are formed on a screen perpendicular to the reflected beam. The visibility of the fringes depends on film thickness, angle of incidence, and light wavelength. Measuring visibility versus incident angle provides the film thickness with an accuracy of a few nanometers. The technique is easily applicable and it covers a wide range of thicknesses with highly reliable results.
Applied Optics, 2006
The optical parameters of a SiO 2 thin-film coating determined from the spectral reflectance and transmittance measurements at various incidence angles, including the normal incidence and the Brewster's angle, are compared in this paper. The high-accuracy measurements were carried out through visiblenear-infrared spectral regions by using our purpose-built instruments. The optical parameters obtained from the reflectance and the transmittance data are consistent over the angles of incidence and agree within 0.2%. The effect of important systematic factors in the oblique-incidence spectrophotometric measurements is also discussed.