FABRICATION OF MESAS AND OCTAGONAL CONES IN SILICON BY WET CHEMICAL ETCHING

A single-mask fabrication technique using anisotropic silicon etchants of EPW and KOH has been developed to obtain relatively high (approxim ate to 250 mu m) mesas and octagonal cones with controlled dimensions (e.g. height difference between mesas and cones, base widths of mesas and cones, etc) for micropackaging applications. Also obtained by this technique are octagonal: cones with elongated tips which can be usefu l in bulk micromachined silicon microstructures. The lateral dimension s of the mesa and the octagonal core are controlled by varying the siz e of simple square mask patterns. The vertical dimensions of the cone are controlled by a 'street corner compensation' which is designed to reduce and delay the undercutting at convex corners. A combination of EPW and KOH is used to exploit a subtle difference in etching characte ristics: KOH (unlike EPW) can sustain sharp-pointed cone tips, while E PW (unlike KOH) exhibits better side wall features. Provided that the etch rates and undercutting behaviors of EPW and KOH are accurately kn own for a given etching set up, this technique produces reliable resul ts with a relatively easy mask design.