Shrinking of silicon nanopore arrays by direct dry-oxygen oxidation

Solid-state nanopores have emerged as useful single-molecule sensors for DNA and proteins. Dry-oxygen oxidation was proposed to directly shrink pyramidal silicon (Si) pore arrays. With this method, inverted-pyramid Si nanopore arrays with feature sizes of over 60 nm, prepared using a combination of dry and wet etching, were shrunk to be less than 20 nm with nanometer precision. The shrinkage was found to be dominated by the deposition of the SiO₂ layer on the nanopore surface and its surface-tension-driven mass flow. The inner structure of the nanopore after the shrinkage kept its typical inverted-pyramid shape, which theoretically permits high-resolution DNA sequencing. Furthermore, this method can process many nanopore samples at one time and reduce the inbuilt stress in the Si nanopores during the annealing.