Influence of Additives on Alkaline Etching of Silicon(111)

Apart from temperature and alkaline concentration, the surface morphology of silicon surfaces after wet chemical etching is also profoundly influenced by the presence of additives in the etchant solution. In this study, the influence of several organic (aprotic, protic, and ionic) additives on the density and shape of etch pits on etched Si-(111) surfaces is investigated using optical microscopy and the Lichtfigur technique. For all the additives used, the number density of the pits increases by 1-3 orders of magnitude. The triangularity of the pit shape, expressed by a dimensionless number, R-ab, increases substantially as well. These alterations are attributed to local desolvation of reaction products by the organic additives in a thin surfactant layer in the vicinity of the silicon surface. Chemisorption of additive molecules does not play a role in this process.