Streamlined fabrication process of Si nanopillars for metasurface applications

Polymethyl methacrylate (PMMA) is the most commonly used electron-beam resist. While it is cost effective and easily available and offers the highest resolution among any polymeric resist, PMMA suffers from poor dry-etch resistance. For that reason, other resists like hydrogen silsesquioxane and ZEP520A are typically preferred. In this work, we present the fabrication of uniform silicon nanopillar arrays using PMMA as a direct etch mask, emphasizing the process optimizations, particularly in reactive-ion etching (RIE) chemistry, required to overcome key roadblocks. Electron-beam lithography was used to write patterns in PMMA positive-tone resist. To transfer the patterns to the substrate and achieve nanopillars of sidewalls with smooth sides, RIE was employed with SF6/O2 chemistry. The fabricated structures were characterized by atomic force microscopy and scanning electron microscopy.