Absolute flatness measurements by Fizeau interferometer and 3D scanning deflectometric profiler

Yohan Kondo; Youichi Bitou

doi:10.1117/12.2570412

21 August 2020 Absolute flatness measurements by Fizeau interferometer and 3D scanning deflectometric profiler

Yohan Kondo, Youichi Bitou

Proceedings Volume 11492, Advances in Metrology for X-Ray and EUV Optics IX; 1149203 (2020) https://doi.org/10.1117/12.2570412
Event: SPIE Optical Engineering + Applications, 2020, Online Only

Abstract

The National Metrology Institute of Technology provides a flatness calibration service for large flat substrates using a Fizeau interferometer with 10 nm (k = 2) uncertainty over a measurement range of 300 mm. In the Fizeau interferometer, the surface profile of the reference flat is a measurement error factor because the measurand is the gap distance between the reference flat and the specimen. We have reduced uncertainty by constructing a surface profile map of the reference flat based on the three-flat test; however, it is difficult to manufacture a highly accurate reference flat and create a correction surface profile map in order to measure even larger flat substrates. Thus, we developed a three-dimensional scanning deflectometric profiler (3-D SDP) that does not require a reference flat and can directly measure a surface profile. Measuring devices based on deflectometry have been developed by many laboratories for highly accurate straightness profile measurement, but measurement by such systems is limited to a line (two-dimensional) profile. To solve this problem, we developed a novel method of measuring the surface topography by calculating the topography from radial lines obtained by rotating the specimen. In this study, we compared measurements between the Fizeau interferometer and 3-D SDP. We also report the results of measuring an optical flat with a diameter of 300 mm.

Conference Presentation

Citation Download Citation

Yohan Kondo and Youichi Bitou "Absolute flatness measurements by Fizeau interferometer and 3D scanning deflectometric profiler", Proc. SPIE 11492, Advances in Metrology for X-Ray and EUV Optics IX, 1149203 (21 August 2020); https://doi.org/10.1117/12.2570412

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