A white-light interferometer as a gauge to measure the thickness of thin film: a practical extension of the phase method and correlogram summation

In this paper we discuss the method to evaluate the thickness of transparent films employing nonlinear phase spectrum of white-light interferogram. To be practically reliable in the 60–1000 nm range of film thicknesses, the method considers a simple compensation of the disturbing spectrum nonlinearities induced by outer inputs (optical instrumentation, substrate) that allows one to deal with fringe data distortion. The method has been validated by fundamental theory considerations and tested on several types of the films under different interferometer objective magnifications. The application of high objective magnifications has been found to require an additional correction. We also introduce rather simple method of spatial wave packet fitting which has demonstrated the promising statistics in primary tests to gauge the film thickness with advanced lateral resolution. (paper)