Deep dry etching techniques as a new IC compatible tool for silicon micromachining

Deep dry etching of single-crystal silicon with IC-compatible masking materials for microstructure fabrication is reported. Reactive ion etching using chlorine/fluorine gases and positive photoresist mask produces up to 30 mu m deep silicon steps with vertical sidewalls. Plasma etching with fluorine/oxygen gas mixtures shows rather isotropic etch behavior; however, high selectivities of 20, 85, and greater than 300 for photoresist, silicon dioxide, and aluminum masks, respectively, permit etch depths of up to several hundreds of microns. Since these dry etching techniques are reproducible and controllable they indicate favorable features for application in silicon micromachining. Several examples are described: bipolar-compatible accelerometers where dry etching and KOH etching are combined, free-standing thin film microstructures (out of aluminum or silicon dioxide) realized by isotropic etching of the substrate, and thin silicon membranes fabricated by plasma etching.<>