Metallic colour filtering arrays manufactured by NanoImprint lithography

Abstract

Colour filters using two-dimensional sub-wavelength double-breasted rectangular hole, with a 250nm period, were proposed and manufactured. Using the cost-efficient wafer scale thermal NanoImprint lithography, a thin metallic aluminium silicon alloy layer was patterned into two dimensional structures onto 200mm wafer size. A fine tuning of the manufactured design was proposed with arm widths ranging from 30nm up to 60nm, and arm lengths ranging from 100nm up to 240nm, keeping the period constant at 250nm. Sub 20nm resolution 200mm silicon stamp, with aspect ratio larger than 5 were manufactured using electron beam lithography with proximity correction exposure strategy based on shape modification of the initial design. At the end, 864 different 100×100μm2 patterns were manufactured and etched in thin 40nm thick aluminium layer transferred to transparent glass to perform optical characterisations in transmission. Optical measurements of transmission spectra revealed that the optical transmission ranged up to 55%, slightly lower than the computed one. The short infra-red transmission levels were however larger than expected increasing the bandwidth response of the filtering function. A fine morphological characterisation revealed that the optical properties were very sensitive to the fine shape of the patterns etched in the metallic layer.