Surface/bulk micromachining (SBM) process and deep trench oxide isolation method for MEMS

This paper presents a new method for micromachining released structures with single crystal silicon, as well as a new method for electrically isolating the released structures with a deep trench oxide. The developed surface/bulk micromachining (SBM) process utilizes (111) silicon wafers. The structural patterns are defined using a reactive ion etcher. Then, the patterns as well as sidewalls are passivated with an oxide film, and bare silicon is exposed at desired areas. The exposed bare silicon is further reactive ion etched, which defines sacrificial gap dimensions. By undercutting the exposed bulk silicon sidewalls in an aqueous alkaline etchant, cleanly released microstructures can be fabricated. For sensing or electrostatic actuation of released microstructures, a deep trench oxide isolation method is developed and applied successfully to actuate a comb-drive actuator. The developed SBM process with deep trench oxide isolation allows fabricating single crystal silicon MEMS with a low parasitic capacitance.