Method for producing a silicon-on-insulator capacitive surface micromachined absolute pressure sensor

A method for producing a capacitive transducer, comprising the steps of:

• (a) selectively forming a first well within the substrate of an SOI wafer having a top silicon layer and a sacrificial layer of known thickness therebetween,
• (b) depositing an epitaxial layer of silicon on said top silicon layer, said epitaxial silicon layer combining with said top silicon layer to form a single crystal silicon layer supported by said sacrificial layer,
• (c) masking and etching said epitaxial layer and said sacrificial layer down to said substrate so as to define a diaphragm from said epitaxial layer,
• (d) depositing an electrically insulating conformal support layer for coupling to and supporting said diaphragm above said substrate so as to seal said sacrificial layer therebetween,
• (e) selectively etching an access opening through said diaphragm,
• (f) selectively etching, through said access opening, and removing said sacrificial layer from between said diaphragm and said substrate so as to form a diaphragm cavity therebetween, said diaphragm cavity having a thickness substantially equal to said known thickness of said sacrificial layer, and
• (g) diffusing conductive ions through said diaphragm cavity and into opposing sections of said flexible diaphragm and said substrate for defining deformable and fixed conductive electrodes of the capacitive transducer,
• (h) selectively depositing a plug within and for sealing said access opening without significantly reducing the volume of said diaphragm cavity, wherein the deflection of said flexible diaphragm responsive to variations between the ambient pressure and the pressure sealed within said diaphragm cavity causes a corresponding change in the capacitance between said fixed and deformable electrodes.