⟨1 0 0⟩ bar corner compensation for CMOS compatible anisotropic TMAH etching

Abstract

For a long time wet bulk-micromachining has been an easy and cost-effective method for fabricating silicon micro-sensors. Anisotropic wet etching is the key processing step for the fabrication of microstructures. Among different silicon etchants, TMAH based etchants are becoming popular because of their low toxicity and CMOS compatibility. The etch rate of wet anisotropic etching of silicon depends on the crystal plane orientation, type of etchant and their concentrations. In anisotropic etching, convex corners are attacked; therefore, a proper compensating structure design is often required when fabricating microstructures with sharp corners (convex corners). In the present work, two ⟨1 0 0⟩ bar compensation structures have been used for convex corner compensation with 25% wt TMAH–water solution at 90 ± 1 °C temperature. Generalized empirical formulae are also presented for these compensation structures for TMAH–water solution. Both the ⟨1 0 0⟩ bar structures provide perfect convex corners but the ⟨1 0 0⟩ wide bar (structure 2) is more space efficient than the ⟨1 0 0⟩ thin bar (structure 1) and it requires nearly 30% less groove width.