Fabrication of multiple-level electrically isolated high-aspect-ratio single crystal silicon microstructures

A novel self-aligned process is described for the fabrication of multiple levels of electrically isolated, suspended high-aspect-ratio single crystal silicon microstructures. The process requires only two lithography steps (independent of the number of levels) and no critical alignment. The surface roughness of the high-aspect-ratio, self-aligned microstructures is very low (on the order of 5 nm). Contacts to all levels are fabricated in a single metallization step. The process has been used to fabricate a number of two-level high-aspect-ratio silicon structures including electrostatic microlenses. Each structure level is typically 10 μm tall and the gap between levels ranges from 2 μm to 5 μm. We discuss the process including some modifications and extensions and its application to the fabrication of micromachined electron gun arrays