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 Fetchant, 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.
Highlights
Silicon micromachining is extensively performed using wet anisotropic etching for the fabrication of simple cavities to complex structures [1,2,3,4,5]
It describes the initiation of undercutting at convex corners, which are formed by the intersection of {111} planes in {110}Si wafer, during wet anisotropic etching process
A new model is developed to explain the undercutting at the convex corners and the no-undercutting at the concave corners, which are formed by the intersection of two {111} planes on {110} wafer surface
Summary
Silicon micromachining is extensively performed using wet anisotropic etching for the fabrication of simple cavities to complex structures [1,2,3,4,5]. The appearance of vertical planes along direction makes {110} silicon wafer an appropriate choice for the formation of deep trenches/ grooves with vertical sidewalls [4,5,6,7,8,9,10] In both these types of wafers, prolonged etched patterns are generally bounded by {111} planes due to their slowest etch rate nature in all kinds of anisotropic etchants. In view of the importance of {110}-oriented silicon wafer for the fabrication of microstructures with vertical sidewalls, a simple model needs to be developed to understand the initiation of undercutting at convex corners, while no-undercutting at the concave corners. This paper presents a new model to explain the etching characteristics of concave and convex corners on {110}Si wafer It describes the initiation of undercutting at con-. It explains the inhibition of undercutting (or no-undercutting) at concave corners which are formed by the intersection of {111} planes
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