Method of making released micromachined structures by directional etching

Abstract

A method of making released structures by using at least two directional etching steps. Cantilevers, bridges and many other structures can be made with the present invention. In a preferred embodiment, two directional etching steps are performed at opposing angles nonnormal to the substrate surface such that the substrate is undercut and a structure is released. Alternatively, more than two directional etching steps may be performed at various angles. For example, the substrate may be rotated continuously during the directional etching process. A cantilever formed by the method of the present invention necessarily has a substantially triangular cross section. Directional etching processes that can be used include focused ion beam etching and ECR plasma etching. Some directional etching processes may require the use of a patterned etch resist layer. Other etching processes such as focused ion beam etching may use scanning techniques to select which regions are etched. A backside etch can be performed to remove remaining substrate material under the released micromachined structure. The method is particularly well suited for making released cantilevers.