Influence of baking conditions on 3D microstructures by direct laser writing in negative photoresist SU-8 via two-photon polymerization

Abstract

Three-dimensional (3D) microstructures are fabricated in negative photoresist SU-8 through two-photon polymerization by direct laser writing using a femtosecond pulse laser. The influence of beam power and baking conditions on the obtained structures is investigated. X-ray photoelectron spectroscopy is used to characterize the crosslinking of SU-8 photoresist after two-photon polymerization. The baking time for prebaking at 65 °C and that for soft baking at 95 °C before laser irradiation are investigated. These conditions are significantly related to the migration of photoacid produced upon laser irradiation. 3D woodpiles, helixes, cylinders, jungle gyms, and double cubic structures are fabricated by controlling the micron scale movement in the X, Y, and Z-axis direction. With a small elevation angle, the overlap of helical lines induces the cylindrical wall structure. Double cubic structures are fabricated: small cubic structure inside the outer large cubic structure.