Large plasmonic color metasurfaces fabricated by super resolution deep UV lithography

In this paper, we demonstrate plasmonic color metasurfaces as large as ∼60 cm² fabricated by deep UV projection lithography employing an innovative combination of resolution enhancement techniques. Briefly, in addition to the established off-axis dipole illumination, double- and cross-exposure resolution enhancement of lithography, we introduce a novel element, the inclusion of transparent assist features to the mask layout. With this approach, we demonstrate the fabrication of relief arrays having critical dimensions such as 159 nm nanopillars or 210 nm nanoholes with 300 nm pitches, which is near the theoretical resolution limit expressed by the Rayleigh criterion for the 248 nm lithography tool used in this work. The type of surface structure, i.e. nanopillar or nanohole, and their diameters can be tailored simply by changing the width of the assist features included in the mask layout. By coating the obtained nanopatterns with thin layers of either Au or Al, we observe color spectra originating from the phenomenon known as localized surface plasmon resonance (LSPR). We demonstrate the generation of color palettes representing a broad spectral range of colors, and we employ finite element modelling to corroborate the measured LSPR fingerprint spectra. Most importantly, the ∼60 cm² nanostructure arrays can be written in only a few minutes, which is a tremendous improvement compared to the more established techniques employed for fabricating similar structures.