Velocity sources as an explanation for experimentally observed variations in Si{111} etch rates

In anisotropic wet-chemical etching of silicon the etch rate ratio of [Left Angle Bracket] 100 [Right Angle Bracket] to [Left Angle Bracket] 111 [Right Angle Bracket] orientations is an important parameter that determines the reproducibility and accuracy of microstructures. Up to now, it is not understood why the values found in the literature of this parameter are inconsistent. We think that this can be explained by boundary features, that we have called velocity sources, locations where the etch rate is increased as a consequence of mechanical or kinetic boundary conditions.