Prem Prabhakaran, Christelle Kowandy, Xavier Coqueret, Safi Jradi,
A Prievable Cationic Photoresist for Two-Photon Lithography
2nd International Workshop on Nano- and Bio-Photonics (IWNBP 2013), 3-8 November, Biarritz, France
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Two-photon direct writing is a very promising technique for fabrication of arbitrary three-dimensional structures spanning in application from photonics to healthcare.[1-2] The most common photoresists employed in the above techniques relies on radical polymerization. In the majority of cases structures fabricated from radical polymerization are incompatible for biological applications. Photoacid initiated chemical amplification reactions are an alternative for initiating controlled polymerization in microlithography. The best commercial cationic photoresists require strenuous processing cycles to achieve well fabricated structures.[3-4] Presented here is the systematic optimization of cationic photoresists. The results from fabrication were used as a norm to establish a feedback loop for improving the formulations. The work demonstrates the difference in the macroscopic behavior of photoresists characterized in the linear one-photon regime and the microscopic behavior of the structures fabricated in the two-photon regime. A highly viscous photoresist is crucial to two-photon lithography since it’s a layer by layer process. The viscosity was controlled by selecting the right combination of monomers. The efficacy of initiation-photoacid generation processes was investigated for photoresists containing different photoacid generation. The fabrication of high resolution three-dimensional structures is demonstrated from the optimized cationic photoresists.