Silica hermetic packages based on laser patterning and localized fusion bonding

We develop a hermetic package process based on laser machining that simultaneously achieves dicing and localized fusion bonding of stacked, patterned bulk silica wafers; this process enables rapid hermetic encapsulation of foundry CMOS/MEMS. Because of the extremely low thermal diffusivity of fused silica, as well as the localized and controllable nature of the laser spot illumination, the interwafer molten bond line penetrates less than 200 microns laterally into the device, sparing the CMOS chip the extreme heat of fusion bonding. Metallic feedthroughs can be incorporated without compromising the hermeticity of the package. Furthermore, excimer laser patterning of fused silica prior to bonding had 100x shorter processing time than patterned wet etching. Such fused silica hermetic packages have many favorable attributes; for example, the excellent chemical inertness enables biocompatibility, and the transparency at radio and optical frequencies enables wireless transmission through the package.