Fabrication of photonic crystals consisting of Si nanopillars by plasma etching using self-formed masks

We have fabricated 2D photonic crystals (square and triangular lattice) with a photonic band gap in the visible light range by periodically arranging Si nanopillars. The fabrication process uses iron clusters as nuclei for self-formation of etching masks to obtain high-aspect-ratio Si nanopillars. First, arrays of openings (30-40 nm in diameter) were defined in resist layers (PMMA) by electron beam patterning. Then iron was deposited with vacuum evaporation to a nominal thickness of 1-2 nm, resulting in cluster formation in the bottom of the openings. After removing the resist by dipping in acetone for 2 minutes, the substrates were ECR etched with SF/sub 6/. During the etching, reaction products in the plasma condense around the clusters, leading to the self-formation of uniform size etching masks. Then Si nanopillars with a high aspect ratio were fabricated. The iron clusters enable fabrication of the nanopillars with an aspect ratio higher than 20, probably owing to their catalytic properties.