NH4Oh-based etchants for silicon micromachining

Wet chemical etchants based on ammonium hydroxide-water (AHW) solutions for micromachining monocrystalline silicon are described. The etchants can be applied under clean-room conditions within standard IC fabrication lines. The nature of AHW solutions is discussed with respect to anisotropy and selectivity. At 75 °C and 9 wt.% AHW, a maximum etch rate for (100) silicon of approximately 30μm/h has been determined. (111):(100) etch rate ratios show values around 4%. AHW etchants exhibit an excellent selectivity to SiO2, Si3N4 and highly boron-doped silicon. Aluminium will not be attacked by silicon-doped AHW etchants. Therefore, standard IC metallization techniques can be used for device fabrication. The application of AHW solutions to the fabrication of basic micromechanical structures is demonstrated.