pubs.acs.org/Langmuir © 2010 American Chemical Society
Photo-Pens: A Simple and Versatile Tool for Maskless Photolithography Chuanhong Zhou, Pradeep Ramiah Rajasekaran, Justin Wolff, Xuelian Li, and Punit Kohli* Department of Chemistry & Biochemistry, Southern Illinois University, Carbondale, Illinois 62901 Received July 16, 2010 We demonstrate conical pores etched in tracked glass chips for fabricating patterns at the micrometer scale. Highly fluorescent patterns based on photopolymerization of diacetylene films were formed by irradiating UV light through conical pores called “photo-pens”. The properties of photopens were investigated through experiments, finite-differencetime-domain (FDTD) simulations and numerical calculations based on Fresnel equations. We show that the pattern dimensions are easily controlled by adjusting the exposure time. Thus, patterns with a range of dimensions can be fabricated without any need of changes in the pore diameter. Parallel patterning was also demonstrated by simultaneously exposing the films to photons through multiple pores in the chip. Our method provides an inexpensive, versatile, and efficient way for patterning without the use of sophisticated masks.
Introduction Photolithography is a microfabrication technology widely used to selectively remove parts of a thin film or a bulk substrate.1-4 It uses light to transfer a geometric shape present in a mask onto an optically sensitive resist on the substrate. The pattern on the photoresist is then generated on the substrate with a series of chemical or physical development processes.3 To date, photolithography is the most commonly employed form of lithography.4 Therefore, it has been extensively used in the fabrication of electronic integrated circuits (IC),1,2 optical circuits,5 microelectromechanical systems (MEMS),6 microfluidic devices,7 and biochips.8 Compared with other lithographic methods such as dip-pen lithography,9 nanopipette-based10 and nanofountain lithography,11 and electrified jet printing,12 photolithography is a massively parallel, costeffective, and high output process. Its resolution is, however, limited due to diffraction limit. Unless special and expensive *To whom correspondence should be addressed. E-mail: pkohli@ chem.siu.edu. (1) Madou, M. J. Fundamentals of microfabrication: the science of miniaturization, 2nd ed.; CRC Press: Boca Raton, 2002. (2) Sheats, J. R.; Smith, B. W. Microlithography: science and technology; CRC Press: Boca Raton, 1998. (3) Van Zant, P. Microchip Fabrication, 5th ed.; McGraw-Hill Professional: New York, 2004. (4) Razeghi, M. Fundamentals of solid state engineering; Springer, 2002. (5) Li, Y. P.; Henry, C. H. IEE Proc. Optoelectron. 1996, 143, 263. (6) Miyajima, H.; Mehregany, M. J. Microelectromech. Syst. 1995, 4, 220. (7) Anderson, J. R.; Chiu, D. T.; Jackman, R. J.; Cherniavskaya, O.; McDonald, J. C.; Wu, H.; Whitesides, S. H.; Whitesides, G. M. Anal. Chem. 2000, 72, 3158–3164. (8) Blawas, A. S.; Reichert, W. M. Biomaterials 1998, 19, 595. (9) (a) Piner, R. D.; Zhu, J.; Xu, F.; Hong, S.; Mirkin, C. A. Science 1999, 283, 661–663. (b) Li, Y.; Maynor, B. W.; Liu, J. J. Am. Chem. Soc. 2001, 123, 2105–2106. (c) Lee, K. B.; Park, S. J.; Mirkin, C. A.; Smith, J. C.; Mrksich, M. Science 2002, 295, 1702–1705. (10) (a) Rodolfa, K. T.; Bruckbauer, A.; Zhou, D.; Korchev, Y. E.; Klenerman, D. Angew. Chem., Int. Ed. 2005, 44, 6854–6859. (b) Bruckbauer, A.; Zhou, D.; Ying, L.; Abell, C.; Klenerman, D. Nano Lett. 2004, 4, 1859–1862. (c) Bruckbauer, A.; Zhou, D.; Ying, L.; Korchev, Y. E.; Abell, C.; Klenerman, D. J. Am. Chem. Soc. 2003, 125, 9834–9839. (11) (a) Loh, O. Y.; Ho, A. M.; Rim, J. E.; Kohli, P.; Patankar, N. A.; Espinosa, H. D. Proc. Natl. Acad. Sci. U.S.A. 2008, 105, 16443. (b) Kim, K. H.; Moldovan, N.; Espinosa, H. D. Small 2005, 1(6), 632–635. (c) Wu, B.; Ho, A.; Moldova, N.; Espinosa, H. D. Langmuir 2007, 23, 9120–9123. (12) (a) Park, J.-U.; Hardy, M.; Kang, S. J.; Barton, K.; Adair, K.; Mukhopadhyay, D. K.; Lee, C. Y.; Strano, M. S.; Georgiadis, J. G.; Ferreira, P. M.; Rogers, J. A. Nat. Mater. 2007, 6, 782–789. (b) Park, J.-U.; Lee, S.; Unarunotai, S.; Sun, Y.; Dunham, S.; Song, T.; Ferreira, P. M.; Alleyene, A. G.; Paik, U.; Rogers, J. A. Nano Lett. 2010, 10, 584–591.
17726 DOI: 10.1021/la1028433
methods are employed, photolithography renders a poorer resolution than probe-based lithography techniques. This is because diffraction imposes physical limitations on the photons irradiating the photoresist through the masks where the resolution is limited to ∼λ/2 (λ is the wavelength of the irradiation light).1 An important consideration in photolithography is the cost of the photomask fabrication with features
