A New Model for the Etching Characteristics of Corners Formed by Si {111} Planes on Si {110} Wafer Surface

Abstract

The etching characteristics of concave and convex corners formed in a microstructure by the intersection of {111} planes in wet anisotropic etchant are exactly opposite to each other. The convex corners are severely attacked by anisotropic etchant, while the concave corners remain unaffected. In this paper, we present a new model which explains the root cause of the initiation and advancement of undercutting phenomenon at convex corners and its absence at concave corners on {110} silicon wafers. This contrary etching characteristics of convex and concave corners is explained by utilizing the role of dangling bond in etching process and the etching behavior of the tangent plane at the convex corner. The silicon atoms at the convex edge/ridge belong to a high etch rate tangent plane as compared to {111} sidewalls, which leads to the initiation of undercutting at the convex corner. On the other hand, all the bonds of silicon atoms pertaining to concave edges/ridge are engaged with neighboring atoms and consequently contain no dangling bond, thus resulting in no-undercutting at concave edges/corners.