Design and application of high-sensitivity two-photon initiators for three-dimensional microfabrication

A new photoacid generator (PAG) is described that can be efficiently activated by two-photon excitation (TPE) and can be used for high-sensitivity three-dimensional micro-patterning of acid-sensitive media. The molecule has a large two-photon absorption cross-section that peaks near 705 nm (delta = 690 x 10(-50) cm(4)s photon(-1)) and a high quantum yield for the photochemical generation of acid (phi(H+) approximate to 0.5). Under near-infrared laser irradiation, the molecule produces acid subsequent to TPE and initiates the polymerization of epoxides at an incident intensity that is one to two orders of magnitude lower than that needed for conventional ultraviolet-sensitive initiators. The new PAG was used in conjunction with the solid epoxide resist Epon SU-8 for negative-tone three-dimensional microfabrication and was incorporated into a chemically amplified resist for positive-tone fabrication of a three-dimensional microchannel structure. (C) 2003 Elsevier Science B.V. All rights reserved.