Realization of suspended silicon-based structures using a smart three-dimensional etching method

The authors report a smart three-dimensional etching method to realize complex floating structures on silicon substrates with a single masking layer. This method is established on two vertical etching processes, a sequential vertical etching process based on SF6, H2, and O2 gases and a novel nonsequential hydrogen-pulsed deep reactive ion etching in a low-density capacitive-coupled RF-reactor. By controlling the flows of gases and plasma parameters, it is possible to achieve desired deep vertical etching with controlled underetching. In addition, the use of tilted chromium deposition as a self-aligned deposition technique and reticular contact configuration to eliminate the parasitic resistance and capacitance between substrate and floating structures, have been exploited. Moreover, in order to investigate the efficacy of this etching method to produce complex features, the authors have designed an interdigital structure suitable for accelerometers and fabricated it by our 3D-etching process.