Microlens array fabrication by backside exposure using Fraunhofer diffraction
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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.
KeywordsAperture Diameter Microlens Array Glass Wafer Structure Height Fraunhofer Diffraction
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.