Wet etching of undercut sidewalls in {001}-silicon

The development of undercut sidewalls along [100] directions of {001}-silicon by a two-step orientation dependent wet etching process is described. Thereby the first step generates vertical {100}-sidewalls in a pure aqueous potassium hydroxide etchant (KOH). The following second step in an etchant consisting of KOH saturated with isopropanol (KOH:IPA) develops slowly etched {101}-faces with undercutting inclination. A principal calculation is given of the expected sidewall dimensions and a comparison is also done with experimental prepared sidewalls. The differences are small. An application is 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 reserved.