Anisotropic Etching of Silicon in Rubidium Hydroxide

The etch rates and plane selectivity for single‐crystal silicon anisotropic etching in aqueous rubidium hydroxide are reported. Silicon wafers of (100) and (110) orientation were etched in 25, 30, 40, and 50 weight percent (w/o) aqueous at 50, 60, 70, and 80°C. The activation energy, based on an Arrhenius equation, was 0.48 eV for the (100) and (110) planes. The etch rate ratio for the (110)/(100) planes was equal to 1.5 at 50 w/o, and 0.6 at 25 w/o. The plane selectivity is not a function of temperature. Silicon spheres, approximately 0.25 in. diam were etched to reveal fast etching high index {522}/{311} planes in the vicinity of the '100' direction.