Micromachining of {111} plates in 〈001〉 oriented silicon

There are basically two ways to etch silicon: dry and wet chemical etching. In micromachining, the control of the shape of the structure is accomplished by anisotropic etching through mask openings. The anisotropy of wet chemical etching is related to the crystal structure of silicon, while that of dry etching stems from the momentum of ions impinging the substrate. The latter gives us much more freedom of design, however, the control of dry etching is much more cumbersome and the equipment much more expensive. Therefore, any new process trick to increase the number of geometries that can be obtained by wet chemical anisotropic etching is of interest. In this paper, techniques are demonstrated to etch thin {111} plates in 〈100〉 silicon. These plates can be used as building blocks in, for example, microfluidic systems for valves and pumps. All micromaching processes described in this paper are accomplished in 25 wt% KOH at 78 ◦C.