Fabrication of ultrathin p(++) silicon microstructures using ion implantation and boron etch-stop

This paper discusses the fabrication of submicron p(++) silicon microstruct ures 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 x 10( 15) cm(-1) and 7 x 10(15) cm(-2), which produce a peak concentration of mor e than 10(20) cm(-3), sufficient for achieving an effective etch-stop in et hylene diamine pyrocathecol. The thickness of the p(++) layer varies from 0 .2 to 03 mum depending on the annealing time and temperature. SUPREM simula tion has been used to determine optimum implantation and annealing conditio ns. A number of microstructures, including thin silicon diaphragms as large as 2 min on a side and 0.2 mum thick, hot wire anemometers with a temperat ure coefficient of resistance of similar to 1600 ppm/degreesC, and piezores istive sound detectors, have been fabricated with high reproducibility, uni formity, and yield.