Planar sacrificial surface micromachining by nickel silicide

This paper introduces an innovative sacrificial surface micromachining process that enhances the fabrication of freestanding microstructures and compliant mechanisms. This process eliminates the topography issues related to the fabrication of these microstructures and achieves planarization without using Chemical-Mechanical Polishing (CMP). The process is based on the silicide technology, which is low temperature and post-CMOS compatible. 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. To anchor the structure, the a-Si over the structure´s anchor is converted to the nickel silicide. The silicide layer has the same thickness as the sacrificial layer, producing a virtually flat freestanding structure. The maximum measured step between the anchor and the sacrificial layer was about 4nm on a 100nm thick sacrificial layer.