Difference in activated atomic steps on (111) silicon surface during KOH and TMAH etching

Anisotropic etching of (111) silicon surface using potassium hydroxide (KOH) and tetra-methyl ammonium hydroxide (TMAH) solutions was experimentally investigated. Etching advanced as a result of lateral movement of steps of 20-50 nm in height. Steps on the (111) surface are classified into two groups, those that are perpendicular to [112] and, those that are perpendicular to [112]. Steps having a three-backbonded edge were more stable than those having a two-backbonded edge in case of KOH etching. On the contrary, in case of TMAH, steps having a three-backbonded edge were more active than steps having a two-backbonded edge. This fact explains the difference in macroscopic anisotropy in KOH and TMAH etching in the vicinity of (111).