Anisotropic etching on Si{110}: experiment and simulation for the formation of microstructures with convex corners

Abstract

We combine experiment, theory and simulation to design and fabricate 3D structures with protected edges and corners on Si{110} using anisotropic wet chemical etching in 25wt% tetramethylammonium hydroxide (TMAH) at 71°C. In order to protect the convex corners formed by <112 > and <110 > directions, two methods are considered, namely, corner compensation and two-step etching. The mask design methodology for corner compensation is explained for various microstructures whose edges are aligned along different directions. The detailed geometry of each compensation pattern is shown to depend on the desired etch depth. The two-step wet etching process is explored in order to realize improved sharp convex corners. Using the same etchant concentration and temperature, the second etching is carried out after mask inversion from silicon nitride (Si3N4) to silicon dioxide (SiO2), obtained by local oxidation of silicon (LOCOS) followed by nitride etching. Based on the use of the continuous cellular automaton (CCA), the simulation results for both corner undercutting and two-step etching show that the CCA is suitable for the analysis and prediction of anisotropic etching on Si{110} wafers.