Wavelength-tuning interferometry has been widely used for measuring the thickness variation of optical devices used in the semiconductor industry. However, in wavelength-tuning interferometry, the nonlinearity of phase shift causes a spatially uniform error in the calculated phase distribution. In this study, the spatially uniform error is formulated using Taylor series. A new 9-sample phase-shifting algorithm is proposed, with which the uniform spatial phase error can be eliminated. Finally, optical-thickness variation of transparent plate is measured using the proposed algorithm and wavelength-tuning Fizeau interferometer.
The optical thickness is an important property of transparent plates when fabricating critical components. Spatially nonuniform errors, which are major factors in the measurement of the absolute optical thickness, can be brought about by phase errors related to the nonlinear error term. In this study, equations and a new sampling window for suppressing spatially uniform errors were constructed. Using these equations and new sampling amplitudes, we designed a new phase-shifting algorithm with 17 samples. Herein, the characteristics and advantages to the measurement of highly reflective surfaces when applying this new 17-sample algorithm are presented based on a Fourier representation. In addition, the superiority of the new algorithm in terms of its error control is demonstrated by comparing the errors occurring from a varying object phase, as well as root mean square errors, with those from different conventional algorithms.
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