Deep reactive ion etching for photonic crystals

Photonic crystals are powerful tools to control light by a photonic band gap, analogous to the band gap in semiconductors. A functional class of photonic crystals can be fabricated by etching nanopores in silicon with controlled shape, size and reproducibility. These nanopores are created by deep reactive ion etching. Due to the decreased effective concentration of reactive ions with increasing aspect ratio, it is challenging to produce nanopores with the same diameter for the whole pore length. A 3-step (deposition, remove, etch) Bosch process has been developed to control the etching process and create straight walled nanopores. Nanopores with a diameter of 320 nm and high aspect ratios, > 20, have been achieved. The process was optimised to achieve as close to cylindrical pore profile as possible, minimising scallops, tapering and other deviations.