Three-Dimensional Sacrificial Etching

In MEMS fabrication micro-mechanical components have to be partially released from a substrate. Selectively etching away sacrificial layers, such that a free standing structure remains, is a widely used technique for this purpose. Free standing structures allow MEMS devices to induce or to sense mechanical movements or vibrations.

During sacrificial etching lower etch rates than the blanket ones are observed. This reduction can be explained by additional factors like the transport of the etch medium and its etch reactants via the relatively narrow (in relation to the etch depth) already etched channel under the free standing structure.

Sacrificial etching is mainly controlled by process parameters like the etch agent concentration, chamber temperature, and pressure. Furthermore, local geometrical features and the nature of chemical reactions are responsible for different etch speeds at material boundaries and, therefore, they influence the propagation of the etch front. In order to analyze these effects we have developed a three-dimensional topography simulation tool and the required models for the etch rates.