Spectroscopic ellipsometry of SU-8 photoresist from 190 to 1680 nm (0.740-6.50 eV)

SU-8 is an important, epoxy-based, negative photoresist that can create high aspect ratio features. Spectroscopic ellipsometry (SE) is a nondestructive analytical technique that can be performed in the open air. In this study, reflection and transmission SE measurement data were combined to model the optical function of SU-8 photoresist. The data were fit using three different models: (i) a B-spline model, (ii) a four-Gaussian oscillator model with an ultraviolet (UV) and an infrared (IR) pole, and (iii) a Cody-Lorentz model with three additional Gaussian oscillators. All three models successfully fit the data, where the B-spline model showed the lowest mean squared error. In situ SE data were also collected and fitted to follow possible changes in the optical properties of the SU-8 during its development. Time-dependent density functional theory (TD-DFT) modeling of a complete SU-8 monomer is qualitatively and quantitatively consistent with the measured optical function.