High precision electron-beam-lithography for optical high performance applications
Due to its high resolution end flexibility, electron beam lithography (EBL) became an essential fabrication technique for micro-optical elements that are used in high performance applications. Nevertheless, the sequential writing strategy used in EBL enforces a stitching approach in order to fabricate large area micro-optical elements. Inherently, the stitching of special subareas leads to inaccuracies in the optical function of the fabricated micro-optics, which usually appears as stray light. In this paper we report about a method to calibrate the stitching process and to reduce the stray light artefacts, respectively. The optimization method is based on the evaluation of angle resolved stray light measurements of special test gratings. In particular, the optimization concerns about spurious stray light peaks, also known as “Rowland ghosts”. In a first step, the qualitative and quantitative characteristics of the observed Rowland ghosts are investigated in a theoretical model in order to deduce the modality of the stitching inaccuracy and the strength of the alignment error. In a second step, the calibration of the subarea-stitching is demonstrated on the example of a contemporary spectrometer grating. It is shown that the Rowland ghosts can be reduced significantly and the stitching process can be controlled in the nm-range.