Simultaneous measurement of the refractive index, thickness, and position of suspended thin film

Abstract

We proposed and developed a low-cost system for profilometry and thin film measurement at nanometer resolution. The system is based on the concept of a dual interferometer. The sample was measured while a simultaneous compensation of the phase deviation due to the instability of piezoelectric transducer served as an optical delay component was performed. In the application of profilometry, the information of the surface profile of a material was obtained from the phase shift of the interference signal. By using the proposed compensation mechanism, an axial resolution of 1.09 nm was achieved. For the measurement of a thin film or membrane, the probe beam was prepared to polarize at 45° and was oblique incident on the sample. The system can perform a simultaneous measurement of the refractive index and the geometrical thickness as well as the position when the thin film is suspended. In order to calculate the refractive index and thickness of the thin film, the phase shifts and intensities of the interferograms of TE and TM waves were measured independently. By comparing the ratio of intensities and the phase shifts of the interferograms, the refractive index and the thickness of the thin film can then be obtained simultaneously.