Recent advances in materials science have made it possible to perform photolithography at the nanoscale using visible light. One approach to visible-light nanolithography (resolution augmentation through photo-induced deactivation) uses a negative-tone photoresist incorporating a radical photoinitiator that can be excited by two-photon absorption. With subsequent absorption of light, the photoinitiator can also be deactivated before polymerization occurs. This deactivation step can therefore be used for spatial limitation of photopatterning. In previous work, continuous-wave light was used for the deactivation step in such photoresists. Here we identify three broad classes of photoinitiators for which deactivation is efficient enough to be accomplished by the ultrafast excitation pulses themselves. The remarkable properties of these initiators result in the inverse scaling of lithographic feature size with exposure time. By combining different photoinitiators it is further possible to create a photoresist for which the resolution is independent of exposure over a broad range of fabrication speeds.
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The authors acknowledge the support of the Maryland NanoCenter and its NispLab. The NispLab is supported in part by the National Science Foundation (NSF) as a Materials Research Science and Engineering Center (MRSEC) Shared Experimental Facility. This work was supported in part by the UMD-NSF-MRSEC (grant DMR 05-20471). The authors are grateful to A. Mullin and D. Falvey for helpful discussions.
The authors declare no competing financial interests.
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Stocker, M., Li, L., Gattass, R. et al. Multiphoton photoresists giving nanoscale resolution that is inversely dependent on exposure time. Nature Chem 3, 223–227 (2011) doi:10.1038/nchem.965
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