A Universal Parameter for Silicon Anisotropic Etching Inalkaline Solutions

We propose a new explanation for the difference between the etching properties of potassium-hydroxide (KOH) and tetramethyl-ammonium-hydroxide (TMAH) by focusing on the volume fraction occupied by the corresponding cations, K+for KOH and TMA+(with molecular structure N(CH3)4+) for TMAH. We have found experimentally that the differences in the surface morphology of Si(111) after etching can be explained by considering the cation volume fraction and that this parameter can also be used to explain the changes in the etch rates between different etchants, or between different concentrations of the same etchant, suggesting a universal behavior for any etching system. This finding simplifies the understanding of the mechanism of silicon anisotropic etching.