High Photosensitivity Two-Photon Photoresists for Large Area Surface Microstructuring

Two-Photon initiated polymerization (TPIP) has shown great promise for fabrication of complex micro- and nano-structures. The method has been used to fabricate such structures over small areas ( 2 ) because of slow fabrication speeds and resulting long fabrication times. In order for TPIP to reach practical application in a commercial setting fabrication times need to be reduced by orders of magnitude. We report results on a highly photosensitive initiation system for photoresists based on free radical and cationic polymerization, where photosensitivity is increased 10 2 - to 10 3 -fold compared to previously reported photoinitiation systems. Threshold writing speeds are determined for critical exposure conditions, including laser power, type and concentration of photoinitiation system, and photoresist type. Surface roughness, a critical parameter in applications such as optics and microfluidics, for example, is also used to determine threshold writing speed. The utility of the approach is demonstrated by making a cell phone keypad light guide from a microreplication tool fabricated using the highly photosensitive photoresist.