The packaging of microelectronic devices such as Integrated Circuits (ICs) and silicon-based sensors has been a major challenge since the invention of the microchip. While packaging is generally the last step in the overall fabrication process, the handling and packaging of individual circuits can be the most critical steps of all from considerations of cost and reliability.
As those skilled in the art will recognize, the individual IC chips/silicon-based sensors must be connected properly to outside leads and packaged in a way that is convenient for use in a larger circuit or system. The packaging must also be within a suitable medium which can protect the chip from the environment of its intended application. In most cases, this means that the surface of the device must be isolated from moisture and contaminants. The associated bonds and other elements must further be protected from corrosion and mechanical shock.
A microelectronic device is hermetically sealed at the wafer level. A substrate is provided having associated electronics and at least one metal bonding pad. A dielectric layer, such as pyrex glass film, is sputter deposited atop the substrate to form a glass/metal seal. A glass film is thereafter planarized, preferably by chemical-mechanical polishing, to remove surface variations. A cover wafer is thereafter anodically bonded to the dielectric layer/glass film so as to define a sealed cavity for housing and protecting the substrate electronics. The resultant microelectronic device is packaged in its own hermetically sealed container at the wafer level.