With the persistent progress in nanotechnology the importance to accurately characterize nanoscale structures steadily increases. Optical measurement techniques have proven to be well suited for this purpose. We investigate different approaches to gain more information about nanoscale features by combining polarimetric setups with specially designed nanostructures. Our experimental setup combines a dual-rotating compensator Mueller matrix ellipsometer with an optical microscope. One arm of the ellipsometer is rigid and consists of a light source, polarization state generator, and optics to focus the light onto a sample. Samples under investigation are mounted on top of a combination of rotation and translation stages to precisely adjust them into the microscope’s focus. The other arm forms the microscope part with a long working distance objective, a polarization state analyser and a CCD camera. A large aperture rotation stage allows to rotate this arm around the sample stage. Thus, measurements in reflection and transmission under different angles of incidence can be performed. The setup measures Mueller matrices for each pixel in the obtained image. Therefore, it allows to examine the polarizing properties of the sample spatially and helps to gain further topological information. This information can be additionally enhanced by supporting nanostructures placed close to the sample to extract information from the near field. Therefore, we designed plasmonic lenses for different measurement configurations. The investigations are complemented by numerical finite element simulations. These are performed to validate the design of the nanostructures and to compare them with measured values. Up to now, we characterized the experimental setup and designed and validated the supporting nanostructures and reference structures. Future steps include extending the setup with a monochromator to ensure flexible illumination, measurement of the reference structures, and the combination of setup and plasmonic lenses to further enhance the sensitivity to subwavelength sized features.
Accurate metrology of nanostructures gains more and more importance and for efficiency reasons optical methods play a significant role here. Unfortunately, conventional optical microscopy is subject to the well-known resolution limit. The necessity to resolve objects smaller than this limit led to the development of superresolution methods which however are barely used in metrology for practical reasons. Non-imaging indirect optical methods like scatterometry and ellipsometry however are not limited by diffraction and are able to determine the critical dimensions of nanostructures. We investigate the application of different approaches for specifically manipulated near-fields in Mueller matrix ellipsometry to achieve an enhanced sensitivity for polarization based sub-wavelength topological information. To this end, we present first numerical simulations of these approaches. To examine the relationship between structural properties and Mueller matrix elements we designed individual structures based on geometrical shapes of varying parameters as well as small arrays. They are realized by lithography as holes in PMMA resist. First, we characterize SEM images of the structures to validate the fabrication process. Numerical simulations of the Mueller matrices of the structures by finite element method are discussed. Results indicate that conventional Mueller matrix ellipsometry alone is unsuitable but the extension to imaging Mueller matrix microscopy is promising for the characterization of sub-wavelength features.