Wet Chemical Etching of Silicon {111}: Autocatalysis in Pit Formation

Abstract

Accuracy and reproducibility of etching is essential to obtaining the smallest-scale devices in silicon. The present study focuses on the etching of silicon {111}, the slowest etching face, using different aqueous solutions of KOH. In all cases, shallow, point-bottomed etch pits are formed. It was found that etchant concentration, temperature, transport limitation, and addition of isopropyl alcohol (IPA) change the number, density, and morphology of the pits to a large extent. Sirtl delineation etching proved that the pits are not related to dislocations or stacking faults in the crystals. We propose that etch pit formation is autocatalytic in nature and is triggered by accumulation of reaction products at the bottom of the pits, locally enhancing the downward etch rate. This autocatalytic process also explains the formation of the concave-shaped pits, obtained after etching in KOH solution with IPA additive.