High aspect-ratio polysilicon micromachining technology

This paper presents a single wafer, all-silicon, high aspect-ratio multi-layer polysilicon micromachining technology that combines deep dry etching of silicon with conventional surface micromachining to realize tens to hundreds of microns thick, high aspect-ratio, electrically isolated polysilicon structures with sub-micron air-gaps. Vertical polysilicon sense electrodes as tall as the main body polysilicon structure can be realized in this technology. A 70-mum-tall, 2.5-mum-wide polysilicon vibrating ring gyroscope with 1.2 mum capacitive air-gaps and electrodes as tall as the ring structure has been fabricated using this technology. Vertical polysilicon beams that are 220 mum tall with a 100:1 aspect-ratio have been also fabricated. The all-silicon feature of such a technology improves long ten stability and temperature sensitivity, while fabrication of large area, vertical pick-off electrodes with sub-micron gap spacing will increase the sensitivity of MEMS devices by orders of magnitude. This technology is also capable of simultaneously producing electrically isolated 2-D (planar) and 3-D (vertical) polysilicon structures on the same silicon substrate. (C) 2000 Elsevier Science B.V. All rights reserved.