Micromachining of silicon using ion beams and electrochemical etching

Abstract

Numerous silicon micromachining methods are available, none of them leading to multi-level structures in one single process. A micromachining process enabling multi-level structures and high aspect ratio needles is studied here.Ion beam irradiation of a silicon sample is combined with Porous Silicon formation. The irradiation of protons or helium ions induces damage in the sample crystal proportionaly to the irradiation dose. These defects will alter the process of electro-chemical etching, leaving a shallower layer of Porous Silicon where the sample underwent irradiation. This part will then stand up once porous silicon is removed.The dose dependency allows local variations of height in the structures. In one single irradiation, multi-level structures are created. Undercut and free standing structures are accessible once the etching reaches the beam end of range. High aspect-ratio structures like silicon pillars arrays have been achieved, opening the way to photonic crystal applications.