HIGH INDEX PLANE SELECTIVITY OF SILICON ANISOTROPIC ETCHING IN AQUEOUS POTASSIUM HYDROXIDE AND CESIUM HYDROXIDE

Mechanically fabricated single-crystal silicon spheres with diameters of 0.25 in were etched in 40 wt.% aqueous potassium hydroxide at 75-degrees-C and 50 wt.% aqueous cesium hydroxide at 50-degrees-C. The post-etching shapes of both etched spheres show that the [111] and [100] directions were the slowest etching directions in both cases. The characteristic structures formed on the surface of these etched spheres were examined under the scanning electron microscope to study the high index plane selectivity. The [311] directions were found to be the most significant among the higher order crystal planes in both cases. Directions close to [023] were concluded to be the fastest etching in aqueous KOH; however, the [110] directions were the fastest in aqueous CsOH.