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6 May 2005 Maskless origination of microstructures with optical functions on large areas
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Interference lithography is a manufacturing technique which allows the origination of various types of microstructures on large areas. Micro-structured surfaces with optical functions are useful for radiation power management applications as well as light management applications in displays and in solar energy systems. This paper presents the interference lithography process, different types of possible structures, replication technologies, some applications and new approaches with high aspect ratio photoresists. Both conventional positive-tone diazonaphthoquinone (DNQ)-photoresists like AZ9260 and chemically amplified negative-tone photoresists like NANOTM SU-8 have been investigated. For the structure origination a large scale interferometer setup with an argon ion laser is used. To this end the laser beam is divided into two beams in a first step. Then the two beams are directed by mirrors, expanded and finally superposed. The exposure intensity profile resulting of two superposed coherent light waves is sinusoidal. Therefore in general continuous microstructure profiles will result after development. In this paper thick film photoresists and their usability for interference lithography are demonstrated. Therefore one-dimensional microstructures as well as prismatic microstructures for daylighting applications have been fabricated in AZ9260. Two-dimensional photoresist structures in NANOTM SU-8 for display applications are also introduced. With these new approaches, microstructures with high aspect ratios and structure depths up to 100μm and more have been realised due to the low UV-absorptance of such photoresists. Additional replication processes such as electroforming and soft-embossing as well as replicas in polymers are presented. Thus a complete process chain for a cost-effective fabrication of micro-structured optical components is given.
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Jorg Mick, Andreas Gombert, Benedikt Blasi, and Claas Muller "Maskless origination of microstructures with optical functions on large areas", Proc. SPIE 5751, Emerging Lithographic Technologies IX, (6 May 2005);

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