Robust micromachining of compliant mechanisms using silicides

• Published in: Journal of micromechanics and microengineering Vol. 23; no. 1; pp. 15015 - 7
• Main Authors: Khosraviani, Kourosh, Leung, Albert M
• Format: Journal Article
• Language: English
• Published: Bristol IOP Publishing 01.01.2013; Institute of Physics
• Subjects: Anchors; Assembly; Etching; Exact sciences and technology; Failure; Instruments, apparatus, components and techniques common to several branches of physics and astronomy; Mechanical instruments, equipment and techniques; Micromachining; Micromechanical devices and systems; Nickel silicide; Physics; Silicides; Silicon substrates; Compliant mechanism; Stress concentration; Micromachining; Nickel silicide; Microactuators; Etching; Amorphous state; Fabrication; Planarization; Complementary MOS technology; Yield strength; Robustness; Silicon; Microstructure; Microsensors; Microelectromechanical device
• ISSN: 0960-1317; 1361-6439
• DOI: 10.1088/0960-1317/23/1/015015

We introduce an innovative sacrificial surface micromachining process that enhances the mechanical robustness of freestanding microstructures and compliant mechanisms. This process facilitates the fabrication, and improves the assembly yield of the out-of-plane micro sensors and actuators. 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 exceed the yield strength of the material and lead to the structure failure. Our process overcomes this topographic issue by virtually eliminating the step between the structure and its anchor, and achieves planarization without using chemical mechanical polishing. The process is based on low temperature and post-CMOS compatible nickel silicide technology. We use a layer of amorphous silicon (a-Si) as a sacrificial layer, which is locally converted to nickel silicide to form the anchors. High etch selectivity between silicon and nickel silicide in the xenon difluoride gas (sacrificial layer etchant) enables us to use the silicide to anchor the structures to the substrate. 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.