Design of sealed cavity microstructures formed by silicon wafer bonding

Three fabrication issues related to the design and fabrication of micromechanical devices using sealed cavities within bonded silicon wafers are discussed. The first concerns the resultant residual gas pressure within a sealed cavity between two bonded wafers after bonding and a high-temperature anneal. The second concerns the prediction of plastic deformation in capping layers of single-crystal silicon over sealed cavities. Exposure of sealed cavity structures to a high-temperature environment causes the trapped residual gas to expand, which can result in the plastic deformation of the capping layer. A model for analytically predicting the occurrence of plastic deformatio in these silicon capping layers has been developed. The third fabrication issue concerns the prediction of the resultant height of plastically deformed capping layers of silicon after cooling. A model which gives a lower and an upper bound on the height, based on an analytical spherical shell membrane stress equation, has been developed