A 7-nm nanocolumn structure fabricated by using a ferritin iron-core mask and low-energy Cl neutral beams

A 7-nm silicon column structure was fabricated by using a Cl neutral beam we developed. The neutral beam achieved a high etching selectivity to a ferritin iron-core mask by using charge-free and damage-free etching processes. The silicon etching selectivity ratio to the iron core was measured to be about 59. The iron core in the ferritin was 7 nm in diameter, which was identical to that of the etched nanocolumn. This indicates that neutral-beam etching transferred the structure and size of the iron core to the silicon substrate.