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Traceable X,Y self-calibration at single nm level of an optical microscope used for coherence scanning interferometry
KTH, School of Industrial Engineering and Management (ITM), Production Engineering.
KTH, School of Industrial Engineering and Management (ITM), Production Engineering.
2018 (English)In: Measurement science and technology, ISSN 0957-0233, E-ISSN 1361-6501, Vol. 29, no 3, article id 035005Article in journal (Refereed) Published
Abstract [en]

Coherence scanning interferometry used in optical profilers are typically good for Z-calibration at nm-levels, but the X,Y accuracy is often left without further notice than typical resolution limits of the optics, i.e. of the order of similar to 1 mu m. For the calibration of metrology tools we rely on traceable artefacts, e.g. gauge blocks for traditional coordinate measurement machines, and lithographically mask made artefacts for microscope calibrations. In situations where the repeatability and accuracy of the measurement tool is much better than the uncertainty of the traceable artefact, we are bound to specify the uncertainty based on the calibration artefact rather than on the measurement tool. This is a big drawback as the specified uncertainty of a calibrated measurement may shrink the available manufacturing tolerance. To improve the uncertainty in X, Y we can use self-calibration. Then, we do not need to know anything more than that the artefact contains a pattern with some nominal grid. This also gives the opportunity to manufacture the artefact in-house, rather than buying a calibrated and expensive artefact. The self-calibration approach we present here is based on an iteration algorithm, rather than the traditional mathematical inversion, and it leads to much more relaxed constrains on the input measurements. In this paper we show how the X, Y errors, primarily optical distortions, within the field of view (FOV) of an optical coherence scanning interferometry microscope, can be reduced with a large factor. By self-calibration we achieve an X, Y consistency in the 175 x 175 mu m(2) FOV of similar to 2.3 nm (1 sigma) using the 50x objective. Besides the calibrated coordinate X, Y system of the microscope we also receive, as a bonus, the absolute positions of the pattern in the artefact with a combined uncertainty of 6 nm (1s) by relying on a traceable 1D linear measurement of a twin artefact at NIST.

Place, publisher, year, edition, pages
IOP PUBLISHING LTD , 2018. Vol. 29, no 3, article id 035005
Keywords [en]
optical microscope, 2D accuracy, self-calibration, traceable, high precision
National Category
Engineering and Technology
Identifiers
URN: urn:nbn:se:kth:diva-223779DOI: 10.1088/1361-6501/aaa39dISI: 000425138000003Scopus ID: 2-s2.0-85042553462OAI: oai:DiVA.org:kth-223779DiVA, id: diva2:1188313
Funder
EU, FP7, Seventh Framework Programme, 309672
Note

QC 20180307

Available from: 2018-03-07 Created: 2018-03-07 Last updated: 2018-03-07Bibliographically approved

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Ekberg, PeterMattsson, Lars

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