A new approach to silicon bulk micromachining

This paper presents a novel approach to wet chemical etching of (100) silicon with dual level bulk micromachining technique, using advantage of selective etching of silicon nitride to silicon oxide masking layers. Normally, anisotropically wet etched structures are bounded by {111} slow etching planes and have undercut convex corners by fast etching {114} planes. In this work it is shown that new beveling planes appear if we selectively remove the etching mask after first standard anisotropic etch and then proceed with etching. The new planes, replacing progressively {111} sidewalls are recognized as {311}, forming an angle of 25 degrees toward (100) plane. This new technique is demonstrated by boss diaphragm structure, where truncated pyramid height in the center can be chosen optionally. Interestingly, by this method the undercutting of convex corners is mitigated to a certain degree.