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1 May 2014 Measurement of the surface shape and optical thickness variation of a polishing crystal wafer by wavelength tuning interferometer
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Abstract
Interferometric surface measurement of parallel plates presents considerable technical difficulties owing to multiple beam interference. To apply the phase-shifting technique, it is necessary to use an optical-path-difference-dependent technique such as wavelength tuning that can separate interference signals in the frequency domain. In this research, the surface shape and optical thickness variation of a lithium niobate wafer for a solid Fabry-Perot etalon during the polishing process were measured simultaneously using a wavelength-tuning Fizeau interferometer with a novel phase shifting algorithm. The novel algorithm suppresses the multiple beam interference noise and has sidelobes with amplitudes of only 1% of that of the main peak. The wafer, which was in contact with a supporting glass parallel plate, generated six different interference fringes that overlapped on the detector. Wavelength-tuning interferometry was employed to separate the specific interference signals associated with the target different optical paths in the frequency domain. Experimental results indicated that the optical thickness variation of a circular crystal wafer 74 mm in diameter and 5-mm thick was measured with an uncertainty of 10 nm PV.
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Yangjin Kim, Kenichi Hibino, Ryohei Hanayama, Naohiko Sugita, and Mamoru Mitsuishi "Measurement of the surface shape and optical thickness variation of a polishing crystal wafer by wavelength tuning interferometer", Proc. SPIE 9132, Optical Micro- and Nanometrology V, 91320V (1 May 2014); https://doi.org/10.1117/12.2051193
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