Femtosecond optical curing of SU-8 photoresist

SU-8 photoresist has been applied to three-dimensional (3D) patterning of photonics, micro/nanoelectromechanical systems and microfluidics. SU-8 photoresist can be patterned by absorption of ultraviolet radiation using a photomask; however, diffraction effects in the bulk resist and the use of a 2D mask limits complex 3D structure design. Direct laser writing (DLW) using multiphoton absorption can produce complex, sub-diffraction limited structures in the resist, but controlling DLW in SU-8 is complicated by many competing processes. Using 100 fs pulses at 1.7 μm, we reliably develop SU-8 photoresist via femtosecond optical curing on glass substrate and avoid competition from two, three, and four photon absorption processes. We verify optical curing of the resist by developing the resist without a post-bake.