Deep dry etching process development for photonic crystals in InP-based planar waveguides

Chlorine-based inductively coupled plasma etching processes are investigated for the purpose of etching two-dimensional photonic crystals in InP-based materials. Etch rates up to 3.7 mm/min and selectivity’s to the SiN mask up to 19 are reported. For the removal of indiumchloride etch products both the application of elevated temperatures and high ion energy’s are investigated. The reactor pressure is an important parameter, as it determines the supply of reactive chlorine. It is shown, that N2 passivates feature sidewalls during etching, improving the anisotropy. Ions that impact onto the sidewalls, either directly or after scattering with the SiN-mask or hole interior, cause sidewall etching. Highly directional ion bombardment and vertical sidewalls in the SiN-mask are therefore crucial for successful etching of fine high aspect ratio structures.