A systematic study of DRIE process for high aspect ratio microstructuring

Various MEMS devices like Accelerometers, Resonators, RF- Filters, Micropumps, Microvalves, Microdispensers and Microthrusters are produced by removing the bulk of the substrate materials. Fabrications of such Microsystems requires the ability to engineer precise three-dimensional structures in the silicon substrate. Fabrication of MEMS faces multiple technological challenges before it can become a commercially viable technology. One key fabrication process required is the deep silicon etching for forming high aspect ratio structures. There is an increasing interest in the use of dry plasma etching for this application because of its anisotropic etching behavior, high etch speed, good uniformity and profile control, high aspect ratio capabilities without having any undesired secondary effects i.e. RIE lags, Loading, microloading, loosing of anisotropic nature of etching as aspect ratio increases, micro-grass and even etch stalling. Developing a DRIE micro-machining process requires a thorough understanding of all plasma parameters, which can affect a silicon etching process and their use to suppress the secondary effects. In this paper our intention is to investigate the influence of etching gas flow, etching gas pressure, passivation gas pressure, ICP coil power, Platen power and etch and passivation time sequence on etch rate and side wall profile. Parameter ramping is a powerful technique used to achieve the requirements of high aspect ratio microstructures (HARMS) for MEMS applications by having high etch rate with good profile/CD control. The results presented here can be used to rationally vary processing parameters in order to meet the microstructural requirements for a particular application.