Fabrication of ultrathin p/sup ++/ silicon microstructures using ion implantation and boron etch-stop

This paper discusses the fabrication of submicron p/sup ++/ silicon microstructures for a number of MEMS applications using boron ion implantation, rapid thermal annealing, and boron etch-stop. To form these thin structures, the silicon is implanted with boron at an energy of 40 keV and doses of 5/spl times/10/sup 15/ cm/sup -2/ and 7/spl times/10/sup 15/ cm/sup -2/, which produce a peak concentration of more than 10/sup 20/ cm/sup -3/, sufficient for achieving an effective etch-stop in ethylene diamine pyrocathecol. The thickness of the p/sup ++/ layer varies from 0.2 to 0.3 /spl mu/m depending on the annealing time and temperature. SUPREM simulation has been used to determine optimum implantation and annealing conditions. A number of microstructures, including thin silicon diaphragms as large as 2 mm on a side and 0.2 /spl mu/m thick, hot wire anemometers with a temperature coefficient of resistance of /spl sim/1600 ppm//spl deg/C, and piezoresistive sound detectors, have been fabricated with high reproducibility, uniformity, and yield.