A new model for Si{100} convex corner undercutting in anisotropic KOH etching

In this paper the mechanism of silicon convex corner (CC) undercutting at etch masks in pure aqueous KOH solutions is explained in a new way by the proposed 'step flow model of 3D structuring'. The basic idea is to apply the general atomic explanation of the Si-{111} anisotropic etching as a 'peeling' process of {111} planes at [110] oriented steps with kink site atoms in order to understand the arising shape in Si-{100} etching. By means of this proposed model, we are able to explain and to calculate the microscopic 3D shape of the characteristic CC undercutting in the case without compensation etch mask structures. The stepped morphology of the arising surfaces at a CC were shown by SEM and the quantitative predictions of the model were experimentally confirmed.