Shape measurement of a thin glass plate through analyzing dispersion effects in a white-light scanning interferometer

Abstract

• Phase position Z p of π nearest to a maximum amplitude position Z a in a complex-valued interference signal (CVIS) is analyzed for measuring thickness T of thin glass plates by simulations. • Coefficients that relate the Z a and Z p values to the physical thickness T are obtained. • Periodical position jumps occurred in Z p are made clear, and the number of occurrences of the jump is calculated from the Z a and Z p values. • In experiments, a shape of 20 μm-thickness glass plate is measured exactly with an accuracy of 6 nm from the Z a and Z p values. Utilization of a complex-valued interference signal (CVIS) in a white-light scanning interferometer is a powerful method to measure exactly surface positions of a glass plate. In this method a zero phase position nearest to a maximum amplitude position in the CVIS is a measured surface position. Proportional coefficients that relate the maximum amplitude position and the zero phase position of a rear surface to the thickness of a glass plate are required for measuring exactly the thickness. These coefficients and periodical position jump occurring on the zero phase position are investigated by simulations. The number of occurrences of the position jump is calculated from the maximum amplitude and zero phase positions. Shape measurement of a glass plate with about 20 μm-thickness is achieved by using the coefficients and the number of occurrences of the position jump.