Wet
Chemical Etching of Silicon {111}: Autocatalysis in Pit Formation
I. A. Shah, B. M. A. van der Wolf, W.
J. P. van Enckevort, and E. Vlieg
J. Electrochem. Soc., Volume 155,
Issue 3, pp. J79-J84 (2008)
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.