Single wafer fabrication of a symmetric double-sided beam-mass structure using DRIE and wet etching by a novel vertical sidewall protection technique

A symmetric double-sided beam-mass structure is of interest for the design of novel MEMS sensors and actuators. Conventional methods to achieve symmetric beam-mass structures have been heavily dependent on bonding or heavy boron doping, which is costly or can notoriously lead to undesirable residual stress as well. In this paper, we report on a novel vertical sidewall protection technique to fabricate symmetric double-sided beam-mass structures (also beams) at a single-wafer level without the need for bonding or doping-based etching, by cleverly taking advantage of the fact that self-stop etching will occur at {111} planes. Moreover, the thickness of the beams is only determined by the depth of dry etching (deep reactive ion etching, DRIE), which excludes the strict dependence on wafer thickness and precise etching time control. We believe that this simple yet powerful technique would open an avenue to fabricate symmetric double-sided structures for various applications.