Method for making an all-silicon capacitive pressure sensor

A method for forming a capacitive pressure sensor, the method comprising the steps of:

• providing a first semiconductor wafer characterized by a first electrical conductivity type;
• forming a cavity in a surface of the first semiconductor wafer;
• forming a doped region of the first electrical conductivity type in the cavity to yield a fixed capacitor plate of the capacitive pressure sensor;
• forming a dielectric layer over the doped region;
• forming a second semiconductor wafer comprising a substrate and an epitaxial layer doped to be of the first electrical conductivity type;
• bonding the second semiconductor wafer to the first semiconductor wafer such that the epitaxial layer contacts the first semiconductor wafer and overlies the doped region;
• etching the second semiconductor wafer to remove the substrate;
• removing a portion of the epitaxial layer to expose a surface portion of the first semiconductor wafer so as to form a diaphragm that is electrically insulated from the fixed capacitor plates and forms a hermetic seal around the fixed capacitor plate, the diaphragm being a flexible capacitor plate of the capacitive pressure sensor;
• wherein the flexible capacitor plate forms a gap with the fixed capacitor plate of about two to about seven micrometers, such that a capacitive output signal of the capacitive pressure sensor is produced by changes in contact area between the diaphragm and the semiconductor wafer in response to pressure applied to the diaphragm.