We studied the possibility and implications of using a magnetron-sputtered aluminum-silicon (Al-1%Si) film in developing the fixed electrode for a micro-electro-mechanical radio-frequency switch structure. We describe the electrode qualitative specifications which originate from the performance of an application and from processing, including process-flow integration. Most of our set of limitations and needs to fulfill is general, such that, the solutions and considerations we present for meeting them are of general applicability. The outline of the task was to produce an electrode that retains a smooth surface over subsequent process flow. High conductivity at dc as well as low losses up to GHz-range frequencies was required. The process integration suggested also considering step-coverage issues of later film-deposition steps and electrical contacting to other conductor layers. We studied Mo and Mo/AlSi cap layers for controlling the surface morphology, pattern-edge slope and, the electrical contacts. Implications of the Freckle etching associated with AlSi wet etching are reflected to film characteristics and process-integration choices. We report quantitative data of the etch rates, pattern-edge slopes, pattern edge-line quality and, the surface topography in terms of hillock growth and pit formation. Electrical contacting to below and above layers is also quantified. Furthermore, we present etching behavior not commonly found in the literature.
Tuohiniemi, M. (2012). Micro-electro-mechanical radio-frequency switch fixed electrode by wet etching of AlSi-based multilayer. Thin Solid Films, 520(7), 3084-3090. https://doi.org/10.1016/j.tsf.2011.11.047