ANISOTROPIC ETCHING OF SILICON-CRYSTALS IN KOH SOLUTION - PART III - EXPERIMENTAL AND THEORETICAL SHAPES FOR 3D STRUCTURES MICRO-MACHINED IN (HK0) PLATES

The micro-machining of various (hk0) silicon plates in an aqueous KOH solution was studied. Orientation effects, the formation of limiting f acets and concave or convex undercuttings have been analysed for (hk0) membranes and mesa obtained starting with circular masks. Procedures have been derived to predict 3D etching shapes using a tensorial model for the chemical etching. Predicted shapes for membranes have been fo und to closely agree with experimental shapes because of the important role played by limiting {111} facets. Theoretical general shapes for etched mesa were also in crude accord with experiments. Consequently s ome attempts have been made to identify limiting (hhl) planes which ca n participate to convex undercutting and to discuss the role of the di ssolution slowness surface.