Study for the micromachining optimization of micro hotplates used in MEMS-CMOS gas sensors

Etching post-processes are usually done with systems based on MEMS structures compatible with CMOS technology like micro hotplates membranes used in MEMS gas sensors. Silicon anisotsropic etch steps follows fabrication of the integrated circuit in a silicon foundry for the release of the membrane but care should be taken to avoid damage to other layers used for integrated circuit fabrication, as aluminum for example. Therefore, a short time micromachining process can relieve these concerns but also should proceed to obtain a well defined suspended structure. This work shows an analysis that takes advantage of the different etching rate depending on the crystalline planes of the silicon substrate, in order to propose a geometry that could help to meet the objectives mentioned. Different geometries and orientation are studied using TMAHW as the anisotropic etching solution. Experimental results confirm previous simulations from AnisE® regarding the etching trend of four geometries analyzed, as the final geometry reduced the etching time substantially, in the order of 20%. The strategy defined in this work can be extended to other designs and applications.