The Swelling Effects during the Development Processes of Deep UV Lithography of SU-8 Photoresists: Theoretical Study, Simulation and Verification

A physical model is presented to theoretically study the swelling effects during the development processes of SU-8 photoresists, based on the solvent molecule transportation mechanisms in cross-linked SU-8 photoresist polymer. The swelling model, combining with the image simulation, exposure simulation, post-exposure bake simulation and development models, has been extended to a deep UV lithography simulation system for SU-8 photoresists. The swelling effects are characterized numerically and experimentally by comparisons of pattern width deviations of SU-8 photoresists for various conditions. The results are useful to efficiently optimize the deep UV lithography processes of SU-8 photoresists and to accurately control the dimensions of some MEMS microstructures.