Towards FDTD modeling of spectroscopic ellipsometry data at large angles of incidence

Precise modeling of the spectroscopic ellipsometry (SE) response of arbitrary near-planar structures by finite-difference time-domain method (FDTD) is desirable for developing a general method for advanced quantitative optical characterization of complex samples. Such a synergetic SE–FDTD approach would be of great interest for fundamental applications such as, the understanding and characterization of nanostructure and plasmonic materials, and industrial applications providing additional tools for optical metrology. For both cases it is of great interest to achieve sub-monolayer modeling precision at large angles of incidence (AoI) where SE measurements are usually more sensitive. To advance this goal, we report the correlation between mean square error (MSE) and AoI studied for prototypical thin film structures. We show that an observed increase in FDTD simulation errors at large AoI can be correlated to the development of spurious resonances, resulting from the use of periodic boundary conditions. A solution to this problem is proposed resulting in ∼10× improved MSE values. It is believed that the combined FDTD–SE approach presented in this contribution could enable the SE description of increasingly complex structures thus paving the way for a powerful synergetic and complimentary SE–FDTD approach to study the optical properties at the sub-wavelength scale of complex nanostructures.