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Fast character projection electron beam lithography for diffractive optical elements

: Harzendorf, Torsten; Fuchs, Frank; Banasch, Michael; Zeitner, Uwe Detlef


Thienpont, H. ; Society of Photo-Optical Instrumentation Engineers -SPIE-, Bellingham/Wash.:
Micro-Optics 2014 : Brussels, Belgium, April 2014
Bellingham, WA: SPIE, 2014 (Proceedings of SPIE 9130)
ISBN: 978-1-6284-1078-5
Paper 91300Y
Conference "Micro-Optics" <2014, Brussels>
Conference Paper
Fraunhofer IOF ()
antireflection; nanostructures; grating; character projection; electron beam lithography; diffractive optics

Electron beam lithography becomes attractive also for the fabrication of large scale diffractive optical elements by the use of the character projection (CP) technique. Even in the comparable fast variable shaped beam (VSB) exposure approach for conventional electron beam writers optical nanostructures may require very long writing times exceeding 24 hours per wafer because of the high density of features, as required by e.g. sub-wavelength nanostructures. Using character projection, the writing time can be reduced by more than one order of magnitude, due to the simultaneous exposure of multiple features. The benefit of character projection increases with increasing complexity of the features and decreasing period. In this contribution we demonstrate the CP technique for a grating of hexagonal symmetry at 350nm period. The pattern is designed to provide antireflective (AR) properties, which can be adapted in their spectral and angular domain for applications from VIS to NIR by changing the feature size and the etching depth of the nanostructure. This AR nanostructure can be used on the backside of optical elements e.g. gratings, when an AR coating stack could not be applied for the reason of climatic conditions or wave front accuracy.