Phase extraction formula for glass thickness measurement using Fizeau interferometer

The thickness variation of transparent optical flats has become a crucial parameter owing to the development of display and semiconductor technologies. Systematic offset phase errors can be generated when the absolute thickness of samples is profiled using a Fizeau interferometer. In this study, a novel 11-sample phase extraction formula was developed to suppress offset phase errors during thickness measurements. The newly developed 11-sample formula was visualized on the frequency domain and complex plane by using Fourier description and the algorithmic polynomial theory. The offset error compensation capability of the 11-sample formula was confirmed based on the results of a numerical analysis. Finally, the glass thickness was measured using a wavelength-scanning Fizeau interferometer and the proposed 11-sample formula. The standard deviation was 9.654 nm, which demonstrates the superior capability of this formula.