Physico-chemical elucidation of the mechanism involved in optical lithography: Micro-fabrication of 2D and 3D platforms

Direct laser lithography has attracted much attention as a convenient micro-fabrication method to develop rapid, free-form, and low-cost microstructures. In this work, different microdevices were fabricated using a home-made two-photon excitation microscope and a commercial negative UV photoresin. The mechanism involved during the fabrication of the devices as well as the effects of the irradiation intensity and removal time on micro-patterns was investigated by optical microscopy. For the characterization of the microstructures, scanning electron microscopy, atomic force microscopy, Nuclear Magnetic Resonance (1H-NMR), and Fourier transform infrared spectroscopy were used. High-resolution optical characterization shows an enormous uniformity and high reproducibility of fabricated platforms in two and three dimensions. These results prompted us to propose a different mechanism not compatible with a polymerization reaction as the triggering mechanism for the interaction between light and the photoresin. We demonstrate the coexistence of an allylic photo-induced reaction with a photo-induced polymerization effect during the fabrication process. We studied the influence of these mechanisms by fabricating micro-patterns in two conditions, with and without the presence of a polymerization initiator [azobisisobutyronitrile (AIBN)], which boots the polymerization reaction. Even though the two mechanisms are present during the fabrication process, the polymerization is dominant in the presence of a photo-initiator as AIBN. Finally, we discuss the applications of our microdevices as suitable platforms for industry and biomedical applications.