Interferometric profile measurement of optical-thickness by wavelength tuning with suppression of spatially uniform error

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. The characteristics of 9-sample algorithm is discussed using Fourier representation and RMS error analysis. Finally, optical-thickness variation of transparent plate is measured using the proposed algorithm and wavelength-tuning Fizeau interferometer and the error is compared with 7-sample algorithm.