High-precision thickness control of silicon membranes using etching techniques

A visual method is demonstrated for fabrication of silicon membranes by deep reactive ion etching (DRIE) and wet etching techniques. A DRIE cavity is created on silicon substrate closed to the membrane recess, and the backside of the wafer is etched by a wet etching process until it reaches the bottom of the DRIE cavity. Both isotropic and anisotropic wet etching with a loose control of temperature and concentration could be used. Because of the high accuracy etch rate of the silicon by DRIE, the depth of the cavity could be defined accurately and the fabricated membrane thickness would be precise.