High aspect ratio silicon and polyimide nanopillars by combination of nanosphere lithography and intermediate mask pattern transfer

Silicon and polymer nanopillar structures with sub-100 nm diameter and high aspect ratios were fabricated using a modified nanosphere lithography process. A thin silicon film was sputtered onto spin-coated polyimide films. A self-assembled layer of nanospheres was then formed on the silicon. Reactive ion etching with SF6/C4F8 was used to transfer the nanosphere pattern to the silicon. Oxygen plasma etching then transferred the silicon pattern into the polymer to create nanopillars. The nanopillar diameter could be finely tuned by oxygen plasma thinning of the nanospheres and the conditions for silicon mask etching. In the last step the polyimide pillars served as etch masks to transfer the structures back into the silicon substrate to give well-ordered pillars of 1.3 μm height and 75 nm diameter.