Robust micromachining of compliant mechanisms by nickel silicide

We are introducing an innovative sacrificial surface micromachining process that enhances the robustness of freestanding microstructures and compliant mechanisms. Fabrication of a compliant mechanism using conventional sacrificial surface micromachining results in a non-planar structure with a step between the structure and its anchor. During mechanism actuation or assembly, stress accumulation at the structure step can easily pass the yield strength of the material and lead to structure failure. Our process overcomes this problem by eliminating the step between the structure and its anchor, and achieves planarization without using Chemical Mechanical Polishing (CMP). The process is based on low temperature and post-CMOS compatible nickel silicide technology. We use a layer of amorphous silicon (a-Si) as the sacrificial layer. High etch selectivity between silicon and nickel silicide in the XeF₂ gas enables us to use the silicide to anchor the structures to the substrate. The sacrificial layer is locally converted to nickel silicide to form the anchors. The formed silicide has the same thickness as the sacrificial layer; therefore, the structure is virtually flat. The maximum measured step between the anchor and the sacrificial layer is about 10 nm on a 300 nm thick sacrificial layer.