Capacitive surface micromachine absolute pressure sensor and method for processing

Claim 1

A method for producing a surface micromachined capacitive absolute pressure sensor, comprising the steps of: a. masking the surface of a semiconductor substrate so as to expose a selected area thereof; b. selectively doping the selected area of the substrate so as to define a first conductive electrode section of the capacitive sensor; c. conformally depositing a first sacrificial layer covering at least the first electrode section of the substrate and circumferential sections of the mask that define the selected area; d. conformally depositing a polysilicon diaphragm layer over the first sacrificial layer; e. selectively doping the diaphragm layer at least in the area generally coextensive with the first electrode section in the substrate so as to make the diaphragm conductive, thereby forming a second electrode section of the capacitive sensor; f. selectively etching an access opening through said diaphragm layer and into the sacrificial layer; g. selectively wet etching through the access opening, and removing the first sacrificial layer in an area juxtaposed with the first and second electrode sections so as to define a diaphragm cavity generally coextensive with the removed portion of the first sacrificial layer; h. freeze-drying the wet etchant within the diaphragm cavity; i. removing the wet etchant from the diaphragm cavity through the access opening by sublimation, thereby preventing the capillary deflection of the polysilicon diaphragm as the wet etchant is removed; and j. selectively depositing a plug within and for sealing the access opening without coating or substantially reducing the volume of the diaphragm cavity adjacent the first electrode section; whereby the deflection of the diaphragm layer responsive to variations between the ambient pressure and the pressure sealed within the sealed diaphragm cavity causes a corresponding change in the capacitance between the first and second electrode sections.

Claim 2

A method for producing a surface micromachined capacitive absolute pressure sensor, comprising the steps of: a. masking the surface of a semiconductor substrate so as to expose a selected area thereof; b. selectively doping the selected area of the substrate so as to define a first conductive electrode section of the capacitive sensor; c. conformally depositing a first sacrificial layer covering at least the first electrode section of the substrate and circumferential sections of the mask that define the selected area; d. conformally depositing a polysilicon diaphragm layer over the first sacrificial layer; e. selectively doping the diaphragm layer at least in the area generally coextensive with the first electrode section in the substrate so as to make the diaphragm conductive, thereby forming a second electrode section of the capacitive sensor; f. selectively etching an access opening through said diaphragm layer and into the sacrificial layer; g. selectively wet etching through the access opening, and removing the first sacrificial layer in an area juxtaposed with the first and second electrode sections so as to define a diaphragm cavity generally coextensive with the removed portion of the first sacrificial layer; h. freeze-drying the wet etchant within the diaphragm cavity; i. removing the wet etchant from the diaphragm cavity through the access opening by sublimation, thereby preventing the capillary deflection of the polysilicon diaphragm as the wet etchant is removed; and j. selectively depositing a plug within and for sealing the access opening without coating or substantially reducing the volume of the diaphragm cavity adjacent the first electrode section; whereby the deflection of the diaphragm layer responsive to variations between the ambient pressure and the pressure sealed within the sealed diaphragm cavity causes a corresponding change in the capacitance between the first and second electrode sections.