Transducer having a silicon diaphragm and method for forming same

A method of forming apparatus including a force transducer on a silicon substrate having an upper surface, the silicon substrate including a p-type dopant, the force transducer including a cavity having spaced side walls and a diaphragm supported in the cavity, the diaphragm extending between the side walls of the cavity, said method comprising the steps of:

• a. implant a p-type layer in the p-type substrate;
• b. deposit an epitaxial n-type layer on the upper surface of the substrate;
• c. implant spaced p-type sinkers through the epitaxial n-type layer and into connection with the p-type layer;
• d. form porous silicon of the p-type layer and the p-type sinkers by anodization;
• e. oxidize the porous silicon to form silicon dioxide;
• f. deposit a polysilicon cover layer over the sinkers;
• and then
• g. etch the silicon dioxide to form open etch channels, the cavity and the diaphragm;
• h. sealing the cavity by forming SiO.sub.2 layers within the etch channels to substantially close the etch channels;
• i. depositing a second polysilicon layer on the diaphragm;
• j. implanting a p-type dopant in the second polysilicon layer;
• and
• k. etching the second polysilicon layer to form a piezoresistor.