Wet etching of undercut sidewalls in {001}-silicon

The development of undercut sidewalls along [100] directions of {001}-silic on by a two-step orientation dependent wet etching process is described. Th ereby the first step generates vertical {100}-sidewalls in a pure aqueous p otassium hydroxide etchant (KOH). The following second step in an etchant c onsisting of KOH saturated with isopropanol (KOH:IPA) develops slowly etche d {101}-faces with undercutting inclination. A principal calculation is giv en of the expected sidewall dimensions and a comparison is also done with e xperimental prepared sidewalls. The differences are small. An application i s proposed where sidewalls prepared in this way have a function as bending spring or free standing bridge. (C) 2000 Elsevier Science S.A. All rights r eserved.