A new theory for the anisotropic etching of silicon and some underdeveloped chemical micromachining concepts

Abstract

A new model for the anisotropic etching of Si predicts a maximum dissolution rate at 22 wt. % KOH:H2 O and a zero etch rate at the solubility limit of KOH in H2 O, which is in good agreement with experiments on {100} and {110} Si. However, the {111} etch rate may decrease continuously with OH− concentration (no peak) and appears to be blocked by OH:3H2 O or some other threefold complexes that attach themselves to every bond on this surface. The strong effects of organics on the etching of convex corners, groove bottoms, and the relative etch rates on the three major orientations are noted, as are the possible effects of Fe and other impurities on the etching velocity and geometry of misorientation steps. The ability to pass current preferentially down the face of these steps needs to be developed before several unique functions can be tested. These include the fabrication of atomic wires, chiral molecule filters, and a sort of flying carpet type of air foil; the functions of which are based on clockwise facing steps on all four walls of holes in single crystal wafers. Vertical thin studs containing controlled pore diameters ranging from 1 to 1000 nm can be formed easily into semipermeable membranes and other complex structures. These interdigitated three dimensional structures can be applied to desalinization, fuel cells, biological membrane and neuron simulation, chemical and nuclear reaction schemes, and much more. The fabrication of micromirrors and lenses is also discussed.