Released Si microstructures fabricated by deep etching and shallow diffusion

A novel etch-diffusion process is developed for fabricating high-aspect-ratio Si structures for microsensors, This is accomplished by first dry etching narrow gap Si microstructures using an electron cyclotron resonance (ECR) source, followed by a shallow B diffusion to fully convert the etched microstructures to p(++) layer, Microstructures up to 40 mu m deep with 2-mu m-wide gaps were etched with a Cia plasma generated using the ECR source, Vertical profile and smooth morphology were obtained at low pressure, A shallow B diffusion at 1175 degrees C for 5.5 h. was then carried out to convert the 40-mu m-thick resonant elements to p(++) layer, A second dry etching step was used to remove the thin p(++) layer around the bottom of the resonant elements, followed by bonding to glass and selective wet etch, Released high-aspect-ratio Si microsensors with thicknesses of 35 mu m have been demonstrated, At atmospheric pressure, only 5 V-dc driving voltage is needed for 2.5 mu m vibration amplitude, which is less than the 10 V-dc required to drive 12-mu m-thick resonators fabricated by conventional dissolved wafer process. [157]