Mueller matrix ellipsometry on advanced nanostructures

Abstract: Ellipsometry is an optical technique used for studies of thin films and surfaces. The technique is based on measurement and analysis of the changes in the state of polarization that occur when polarized light is reflected on a sample surface. The multichannel Mueller matrix ellipsometer is a new system that is about to enter the commercial market. It can measure the full 4x4 Mueller matrix of a sample. The Laboratory of Applied Optics at the Department of Physics, Chemistry and Biology at Linköpings University has purchased one such multichannel Mueller matrix ellipsometer, called RC2, from J.A. Woollam Co., Inc. This project has the objective to investigate potentials and limitations of this new ellipsometer. This is done by comparing measurements carried out on RC2 with similar measurements made on a different, well known ellipsometer system, the VASE ellipsometer. A study of the theoretical background of ellipsometry has been made including a description of the Jones formalism of describing optical properties as well as the Stokes/ Mueller formalism. A short theoretical description of the RC2 principles, in order to better understand the new ellipsometer is also given. Measurements have been made on samples of varying complexity, including isotropic and anisotropic samples with in-plane anisotropy and out-of-plane anisotropy. On samples with no depolarization there should be no difference between the two ellipsometers. As can be seen in the experimental results there is some difference, but very little. Both for the isotropic samples, where Δ and ψ have been measured, and anisotropic, where the full Mueller matrix has been measured, we find a good match between VASE and RC2. When the samples are depolarizing, we expect to see a difference in the Mueller matrix. We do notice a significant difference in the measurements on tilted nanometer rods of TiO2, which has an advanced nano-structure in the upper layer. We can thus conclude that samples with depolarizing properties reveal this when measured with the new RC2 ellipsometer.