Low Temperature Wafer Bonding On SiliconNitride

In the fabrication of micromachined devices, wafer bonding is an increasingly used technique for joining wafers. Most wafer bonding processes used today require firing temperatures above 800°C, which limits the use of this technique. For application in back-end processing, we developed a low temperature wafer bonding technique on LPCVD Si,N4 coated wafers. After firing bonded wafers at 250-350°C, the bonding strength was about 200erg/cnf. However, the presence of gas bubbles at the bonded interface was observed. As a demonstrator application, a micromachined Si wafer containing membranes was bonded to a finished Si/Pyrex micromachined device wafer.