Released Si microstructures fabricated by deep etching and shallowdiffusion |
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Authors: | Wen-Han Juan Pang S.W. |
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Affiliation: | Dept. of Electr. Eng. & Comput. Sci., Michigan Univ., Ann Arbor, MI; |
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Abstract: | 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 μm deep with 2-μm-wide gaps were etched with a Cl2 plasma generated using the ECR source. Vertical profile and smooth morphology were obtained at low pressure. A shallow B diffusion at 1175°C for 5.5 h. was then carried out to convert the 40-μm-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 μm have been demonstrated. At atmospheric pressure, only 5 Vdc driving voltage is needed for 2.5 μm vibration amplitude, which is less than the 10 Vdc required to drive 12-μm-thick resonators fabricated by conventional dissolved wafer process |
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