<title>Dry micromachining of high-aspect-ratio Si for microsensors</title>

Abstract

Dry micromachining technology is developed for fabricating high aspect ratio Si structrues for microsensors. Two microsensor structures, including Si resonators and field emitters, will be presented in this ppaer. Released Si resonators up to 30 micrometers deep with 2 micrometers wide gap were fabricated. This is accomplished by a novel deep etch and shallow diffusion technique. High aspect ratio Si microstructures with vertical profile were first etched using an electron cyclotron resonance source, followed by a shallow B diffusion to fully convert the etched microstructures to p<SUP>++</SUP> layer. In addition, dry etching was used to form Si emitters with sharp tips and high packing density. Profile for Si emitters is controlled by erosion of the SiO<SUB>2</SUB> mask during dry etching. The ion flux and energy, controlled through coupled microwave and rf power, were used to obtain the desired etch rate and basewidth of the emitters. By increasing the pressure during etching, more vertical Si emitters were developed. Sharp emitter tips in Si with 2.2 micrometers basewidth and 11 micrometers height were fabricated and packing densities up to 1 X 10<SUP>7</SUP> tip/cm<SUP>2</SUP> were achieved.