TITLE:
A New Model for the Etching Characteristics of Corners Formed by Si{111} Planes on Si{110} Wafer Surface
AUTHORS:
Prem Pal, Sajal Sagar Singh
KEYWORDS:
MEMS; Silicon; Anisotropic Etching; Micromachining; KOH; TMAH; Convex Corner; Concave Corner
JOURNAL NAME:
Engineering,
Vol.5 No.11A,
October
22,
2013
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.