Application of double patterning technology to fabricate optical elements: Process simulation, fabrication, and measurement

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Double patterning is an important technique for the improvement of spatial resolution in fabricated micro and nanostructures. In this paper, we investigated and applied the double patterning technique to fabricate diffractive optical elements. Simulations of multiple dry etch and film deposition steps were performed to study and optimize the vertical profiles of the fabricated patterns. Etch and deposition characteristics were varied to study their impact on the resulting vertical profile of the metal layers. The influence of the linewidth of the initial resist pattern and the process-induced tapering of the grating tops on the optical performance were investigated in particular. A variably shaped electron-beam lithography system was used for the fabrication of the initial resist pattern. The spatial frequency was then doubled by means of double patterning. Broadband aluminum and iridium wire grid polarizers were fabricated for applications down to the UV range with a feature size of 30 nm, a period of 100 nm, and a vertical aspect ratio of about 5:1. Optical measurements have confirmed the designed optical properties.