Analysis and prevention of convex corner undercutting in bulk micromachined silicon microstructures

Convex corner undercutting in <100> silicon is an undesired phenomena during bulk micromachining of crystalline silicon substrate using anisotropic wet chemical etching process. The present investigation concentrates on the studies of convex corner undercutting at the free end of silicon cantilever beams released by anisotropic etching process. It also reports a simple, space efficient compensation design for complete prevention of corner deformation. Various compensation patterns such as square, rectangle and superposition of square and rectangular blocks of various dimensions have been employed at the free end corners of cantilever beam to protect corner deformation due to undercutting. The experiment was carried out in 44 wt.% KOH at 70 °C using <100> oriented silicon wafer. Both n-type and p-type silicon wafers were used to study the variations in the nature of corner deformation. A simple empirical relation has been obtained from the experimental data to calculate the lateral dimensions of the compensation layout from the total etch depth required to release the structure.