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

Abstract

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.

Optimization of exposure parameters for direct laser writing in optical lithography

“…To characterize the thickness of the photoresist, it is necessary to know the refractive index. This can be done by spectroscopic ellipsometry measurement, 5 we use the RC2D ellipsometer from J.A.Woollam, which measures the complete Müller matrix in the spectral range from 193 nm to 1700 nm. The measured transmitted intensity data and the reflected ellipsometry data from 50 • to 70 • with step 5 • of the photoresist of different thicknesses on the glass substrate are fitted with Kramers-Kronig relations complying B-SPLINE model 6 to obtain the complex refractive index.…”