Microsystem Technologies

, Volume 14, Issue 9–11, pp 1285–1290 | Cite as

Microlens array fabrication by backside exposure using Fraunhofer diffraction

  • In-Hyouk SongEmail author
  • Kyung-Nam Kang
  • Yoonyoung Jin
  • Daniel S.-W. Park
  • Pratul K. Ajmera
Technical Paper


In UV-lithography, a gap between photoresist and UV-mask results in diffraction. Fresnel or near-field diffraction in thick positive and negative resists for microstructures resulting from a small gap in contact or proximity printing has been previously investigated. In this work, Fraunhofer or far-field diffraction is utilized to form microlens arrays. Backside-exposure of SU-8 resist through Pyrex 7740 transparent glass substrate is conducted. The exposure intensity profile on the interface between Pyrex 7740 glass wafer and negative SU-8 resist is modeled taking into account Fraunhofer diffraction for a circular aperture opening. The effects of varying applied UV-doses and aperture diameters on the formation of microlens arrays are described. The simulated surface profile shows a good agreement with the experimentally observed surface profiles of the microstructures. The paper demonstrates the ease with which a microlens array can be fabricated by backside exposure technique using Fraunhofer diffraction.


Aperture Diameter Microlens Array Glass Wafer Structure Height Fraunhofer Diffraction 
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The authors would like to thank the Center for Advanced Microstructures and Devices (CAMD) for the use of the microfabrication facilities. Any opinions, findings, and conclusions or recommendations expressed here are solely those of the authors.


  1. Cheng Y, Lin CY, Wei DH, Loechel B, Gruetzner G (1999) Wall profile of thick photoresist generated via contact printing. IEEE J Microelectromech Syst 8:18–26CrossRefGoogle Scholar
  2. Chuang YJ, Tseng FG, Lin WK (2002) Reduction of diffraction effect of UV exposure on SU-8 negative thick photoresist by air gap elimination. Microsyst Technol 8:308–313CrossRefGoogle Scholar
  3. Hacht E (2002a) Optics, chap 10, 4th edn. Addison-Wesley, San FranciscoGoogle Scholar
  4. Hacht E (2002b) Optics, chap 4, 4th edn. Addison-Wesley, San FranciscoGoogle Scholar
  5. Kim K, Park DS, Lu HM, Che W, Kim K, Lee JB, Ahn CH (2004) A tapered hollow metallic microneedle array using backside exposure of SU-8. J Micromech Microeng 14:597–603CrossRefGoogle Scholar
  6. Peterman MC, Huie P, Bloom DM, Fishman HA (2003) Building thick photoresist structures from the bottom up. J Micromech Microeng 13:380–382CrossRefGoogle Scholar
  7. Song IH, Jin Y, Ajmera PK (2007) Fabrication of a polymeric tapered HARMs array utilizing a low-cost nickel electroplated mold insert. Microsyst Technol 13:297–291CrossRefGoogle Scholar
  8. Zhang J, Chan-Park MB, Conner SR (2004) Effect of exposure dose on the replication fidelity and profile of very high aspect ratio microchannels in SU-8. Lab Chip 4:646–653CrossRefGoogle Scholar

Copyright information

© Springer-Verlag 2007

Authors and Affiliations

  • In-Hyouk Song
    • 1
    Email author
  • Kyung-Nam Kang
    • 2
  • Yoonyoung Jin
    • 3
  • Daniel S.-W. Park
    • 4
  • Pratul K. Ajmera
    • 2
  1. 1.Department of Physics EngineeringÉcole Polytechnique de MontréalMontréalCanada
  2. 2.Department of Electrical and Computer EngineeringLouisiana State UniversityBaton RougeUSA
  3. 3.Center for Advanced Microstructures and DevicesLouisiana State UniversityBaton RougeUSA
  4. 4.Center for BioModular Multi-scale SystemsLouisiana State UniversityBaton RougeUSA

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