Advances in sub-wavelength characterization of metamaterials with far-field spectroscopic ellipsometry

The ability of SE to provide non-imaging subwavelength scale information has been widely used in the semiconductor industry to determine optical critical dimension (OCD) of purposely made 1D gratings to monitor the status of a fabrication line. In this case, the Rigorous Coupled-Wave Analysis (RCWA) technique is the standard technique for data analysis. However, RCWA has unresolved difficulties for the modeling of 2D and plasmonic structures. Our group provided the first systematic demonstration of an alternative to RCWA namely, Finite-Difference Time-Domain (FDTD) method. [1] We have shown that for isotropic layers FDTD can provide numerical results with precision equivalent to ~ 1/2-monolayer thickness sensitivity even at angels of incidence (AoI) as large as 80 (deg). [2] This strategy can extend the application of SE to provide detailed information on complex samples including photonic and plasmonic subwavelength structures of interest for sensing and energy applications. We will review the fundamental challenges and applications as well as our current work on intrinsic and extrinsic optical anisotropy effects and their modeling by the simple, yet versatile and powerful FDTD method approach.