Precise structuring by 2-photon absorption in positive photoresist materials

Two-photon polymerization, based on two-photon absorption, is a convenient direct laser writing process to fabricate maskless structures in microand nanometer range with submicrometer resolution. Negative photoresists are used in combination with this technique, however, utilization of positive resists with two-photon absorption is very innovative. Due to less shrinkage and economic manufacturing, positive photoresists have many advantages. Possible applications of this technique are the production of micro-electromechanical systems (MEMS) or micro-opto-electro-mechanical systems (MOEMS). In this paper, two-photon absorption of positive photoresist is discussed to be a potential basis for LIGA-process (lithography, electroplating, and molding) by two-photon absorption of positive photoresist is discussed. The maskless ultra short pulse illumination by femtosecond laser pulses with 780nm wavelength for generation of microstructures in positive photoresist is demonstrated. To assure high quality structure surfaces, the influence of processing parameters on the pattern width are studied. Therefore, the influence of average power of femtosecond laser pulses, as well as the influence of the scan velocity on the resolution for 3D-grid structure is experimental tested. These studies enable fabrication of arbitrary 3D-structures with high resolution and high aspect ratio. By utilizing a commercial positive photoresist, a minimum linewidth in submicron order with essential rise of the aspect ratio has been accomplished. Furthermore, the test of a precise structuring of complex geometry fabrication is presented with an elastomeric molding. Based on these results, the application possibility for LIGA-process is demonstrated.