Challenges of nanostructure-integration in Fabry-Pérot interferometers as alternative to Bragg reflectors: An example for Match 1:1-, eBeam-, and nanoimprint lithography

We present nanostructured reflectors as alternative for well-known alternating layer stack reflectors for Fabry-Pérot Interferometers (FPI) for the use in miniaturized spectrometry systems. The addressed FPI is part of an online monitoring system for specific molecules by Surface Enhanced Raman Spectroscopy (SERS). Key part is the tunable FPI with nanostructured reflectors, which is fabricated with MEMS and NEMS technologies. Nanostructured Photonic Crystal (PhC) and Sub-Wavelength Grating (SWG) reflectors are developed. The PhC reflectors consisting of 400 nm thin moveable LP-CVD Si3N4 membranes with nanostructured holes realize an aperture of 1 mm with high reflectivity in the VIS range. The SWG reflectors are realized as nanostructured aluminum polygons on 150 nm thin LP-CVD Si3N4 membranes. The challenge in manufacturing of the PhC and SWG structures on 50 μm thin predefined silicon membrane areas is the thin wafer handling, because they are very fragile and tend to warp under their own weight. Further challenges such as delamination of the NIL-stamp from the wafer and eBeam resist homogeneity on the deflected thin silicon membranes for nanostructure replication as well as residual free resist layers for the followed RIE process and the match of the used Nanoimprint, 1:1 and eBeam lithography processes for the different layers have to be considered. The manufacturing and characterization of both alternative reflectors for prospective integration in VIS-FPIs on 6" wafers is described.