The comparison of multi-stepping algorithms for real-time thickness measurement of transparent thin films using polarization settings

This paper presents the comparison of three-, four- and five-step techniques for measuring
transparent thin-film thickness of Ta2O5 and WO3 deposited on BK-7 substrates. The Sagnac
interferometer was modified with phase shifting approach for the determination of thin-film
thickness. The input light beam was split into reference and testing beams. Before the output
light reaching the balanced photodetectors, the real-time signal detection was performed to
obtain the output intensities of both beams using three-, four-, and five-polarization settings of
an analyzer. The thicknesses could then be efficiently translated from the measured intensities.
Thicknesses from three-, four- and five-stepping algorithms were compared with ones from the
conventional FE-SEM measurement, and it was discovered that the former performed better
with less errors. The findings show that the phase-shifting technique using three-polarization
settings is more suitable for the thickness measurement of the transparent thin film.