MEMS-Compatible Hard Coating Technique of Moveable 3D Silicon Microstructures

Abstract

Mechanical degradation of mobile silicon components of complex MEMS reduces device reliability and operation time. Although the considerable wear of the surface micromachined poly-crystalline elements can be decreased by substitution of crystalline-silicon-based equivalent, there is still room for further improvement in device durability. The demonstration device is the recently presented 3D crystalline silicon micro-turbine formed by the combination of proton beam writing (PBW) and subsequent selective porous silicon (PorSi) etching. Similarly to the DRIE (deep reactive ion etching) process the novel technique is capable to provide elements of vertical walls of high aspect ratio. The 3D silicon components were uniformly covered with LPCVD Si3N4 protective layer. The Si3N4 coating improves the chemical and mechanical properties; strength, hardness and chemical resistance. The elaborated processing technology can easily be adapted for deposition of protective materials of superior properties, e.g. TiN and DLC (diamond like carbon). Present work describes alternative hard coating technique integrated in the MEMS processing sequence. The feasibility of the proposed technique is demonstrated by preliminary qualitative wear tests.