Industrial fabrication method for arbitrarily shaped silicon N-well micromechanical structures

A new fabrication technology for CMOS-MEMS devices has been developed. It is based on a commercial CMOS process and a single anisotropic etching step with electrochemical etch stop. A process sequence providing contacts for the etching potentials to the wafers and a preparation sequence for the wafer back were implemented into the CMOS process. A new electrical connection concept for the p-type silicon to be removed by the anisotropic etchant is presented. P-well based substrate contacts allow the production of arbitrarily shaped silicon n-well structures. Especially structures with narrow gaps between n-wells or n-well structures enclosing p-type substrate regions can be completely released. Furthermore n-well silicon membranes of different thicknesses for, e.g., pressure sensor applications are producible by the technology. To demonstrate the potential of this technique, complex shaped, decoupled torsional oscillators were fabricated. The devices were characterized by investigating their vibrational modes. Mechanical quality factors of more then 27000 were observed.