Thin Film Thickness Measurement by Surface Plasmon Resonance Using a Modified Otto’s Configuration Combined with Ellipsometry

We have developed a method of measuring thin film thickness by using two optical properties that are highsensitivity for a film thickness, such as surface plasmon resonance (SPR) and elliptical properties with SPR response. The SPR signal is high sensitivity, suitable for measuring the thickness of a sample with a thin layer. This phenomenon can be detected by measuring the absorbance on the sample surface. We focused on the Otto configuration, a famous method for the generation of a SPR signal, which consists of 4 layers such as a SiO 2 substrate, air, dielectric material and a metal layer. It is useful for the measurement of thin film thickness because there is an air layer in the configuration. However, the configuration has the disadvantage: it is necessary to adjust the distance from sample surface to the SiO 2 substrate on a nanometer order. To overcome the problem, we focused on the modified Otto’s configuration proposed by Bliokh et. al [Appl. Phys. Lett. 89, 021908 (2006)]. In the configuration, there is a plano-convex lens of SiO 2 as the substrate. By using its curvature, there is no adjustment process and the SPR signal can be detected easily. The SPR signal has a polarization property that depends on the thin film thickness. By analyzing of polarization properties of the SPR signal by means of ellipsometry, thin film thickness can be measured with sub-nanometer accuracy which is higher than the SPR signals. In this paper, further results involving the measurement are presented and discussed.