The etch rates and plane selectivity for single-crystal silicon anisot
ropic etching in aqueous rubidium hydroxide are reported. Silicon wafe
rs of (100) and (110) orientation were etched in 25, 30, 40, and 50 we
ight percent (w/o) aqueous RbOH at 50, 60, 70, and 80-degrees-C. The a
ctivation 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} pla
nes in the vicinity of the [100] direction.