26 June 2017 Sub-diffraction surface topography measurement using a microsphere-assisted Linnik interferometer
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Microscopic surface topography measurement is an important aspect of industrial inspection. Optical and near field scanning techniques are increasingly replacing the use of the traditional mechanical stylus since they provide better lateral resolutions and higher measurement speeds. The main far field optical techniques used are interference microscopy and confocal microscopy, with the advantages of having larger fields of view and higher measurement speeds. Interference microscopy is now widely used, mainly because of its nanometric axial measurement sensitivity and its ease of use but suffers from a limitation in lateral resolution of about /2 due to diffraction. A new technique for high resolution 2D imaging using a microsphere placed on the sample has been recently combined with interferometry by several groups to greatly improve the lateral resolution. In this paper we present some of our own first results using glass microspheres with a white light Linnik interferometer and demonstrate a lateral resolution of /4 and an axial measurement sensitivity of several nm. Results are shown on calibrated square profile gratings with periods down to 400 nm, with a minimum feature size of 200 nm and a height of 148 nm and a field of view of several μm. While these features are not visible directly with the microscope objective, they become observable and measurable through the microsphere. An analysis using rigorous electromagnetic simulations is also given to help better understand the imaging properties of the technique. These first experimental and simulation results clearly indicate that this is an important new technique that opens new possibilities for surface metrology with a lateral resolution well beyond the diffraction limit.
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Paul C. Montgomery, Paul C. Montgomery, Sylvain Lecler, Sylvain Lecler, Audrey Leong-Hoï, Audrey Leong-Hoï, Stéphane Perrin, Stéphane Perrin, Pierre Pfeiffer, Pierre Pfeiffer, } "Sub-diffraction surface topography measurement using a microsphere-assisted Linnik interferometer", Proc. SPIE 10329, Optical Measurement Systems for Industrial Inspection X, 1032918 (26 June 2017); doi: 10.1117/12.2270223; https://doi.org/10.1117/12.2270223

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