Characterization of the end-of-range geometric effects in complex 3D silicon micro-components formed by proton beam writing

As a new alternative micromachining method to deep reactive ion etching (DRIE), the combination of proton beam writing (PBW) and porous silicon (PS) etching has proved to be a feasible technique to form crystalline silicon microstructures characterized by high aspect ratio and vertical sidewalls. However, the proposed use of the combined technology has been successfully applied to realize microfluidic MEMS components, whilst the undesired effects of ion scattering in the end-of-range (EOR) region are still under investigation. The widening geometry in the vicinity of the Bragg peak of the ion path limits the perfect functionality of the designed microstructures. In this work the effects of EOR volume on the realization of micro-components by PBW and subsequent PS etching are analysed by both experimental and simulation (MatLab, Comsol) methods. A MEMS process sequence, including the elimination of the widening at the bottom of the microstructures, is explained in detail. The elaborated technology provides the complete removal of the EOR volume without any necessary changes to the geometric design. As a result, the beneficial properties of the combined technique can be exploited more effectively and less compromise is needed during the development of complex 3D silicon microstructures.