Wide-field parallel mapping of local spectral and topographic information with white light interference microscopy

Abstract

Fourier analysis of interferograms captured in white light interference microscopy is proposed for performing simultaneous local spectral and topographic measurements at high spatial resolution over a large field of view. The technique provides a wealth of key information on local sample properties. We describe the necessary processing and calibration involved to produce reflectivity maps of spatially extended samples. This enables precise and fast identification between different materials at a local scale of 1 µm. We also show that the recovered spectral information can be further used for improving topography measurements, particularly in the case of samples combining dielectric and conducting materials in which the complex refractive index can result in nanometric height errors.

Characterization of Functional Materials Using Coherence Scanning Interferometry and Environmental Chambers

“…This algorithm is generally used for measuring small surface roughness. For surface structures higher than λ/2, white light interferometry is used, in which polychromatic light produces an envelope of fringes (Figure 1(c)), the sum of the interference at the different wavelengths being: (5) where [λ 1 , λ 2 ] is the spectral bandwidth of the light source and the term I 0 takes into account the intensity and the spectral distribution of the light source, as well as the spectral response of the different optical components. The phase term ϕ, as well as being the difference in phase between the two paths of the interferometer, also takes into account the phase on reflection difference at the surfaces of the sample and reference mirror, which is also wavelength dependent.…”

“…For example, areas of different materials can be automatically identified, for example using Otsu’s algorithm to binarize the reflectivity map. 5 The results can also be used in colorimetry to determine the colors of different materials. By windowing the fringe signal, this technique has also been adapted to performing local spectroscopy on interfaces and structures buried under transparent layers, 17 for carrying out local measurements of refractive index and thickness of transparent layers, 18 and for studying the properties of particles buried in transparent and diffusing layers.…”

“…2 Since interference microscopy uses an optical probe, at ICube (IPP photonics team), we have recognized for a long time that it is possible to extend the different possibilities in characterization with this technique, and the results of this work are summarized in this paper. Results are presented of measuring, for example, the 3D structure of changing surfaces in real time, 3 visualizing and characterizing defects inside transparent layers, 4 measuring the local optical properties of inhomogeneous materials using local spectroscopy, 5 and observing and measuring details with higher lateral resolution using microspheres placed between the sample and the microscope objective. 6,7 Some more recent applications have involved some challenging characterization conditions for measuring specific material parameters, notably requiring the development of environmental chambers placed under the interference microscope.…”

Measurement of Film Structure Using Time-Frequency-Domain Fitting and White-Light Scanning Interferometry

“…Machines 2021, 9, x FOR PEER REVIEW 2 of 12 measurements, thereby setting higher requirements for the experimental equipment and operation [21][22][23][24]. Herein, we propose a method for measuring films in the full field of view based on single VSI scanning.…”

“…de Groot and de Lega proposed a VSI signal model [17], and several researchers have used it to obtain the film reflectivity and thickness from Fourier-transform information [18][19][20]. In those methods, the tested sample is compared with a reference sample to solve the film-thickness issue, but such approaches usually require the tested and reference samples to be scanned separately and the light-source intensity and experimental parameters to remain consistent in the two measurements, thereby setting higher requirements for the experimental equipment and operation [21][22][23][24].…”