Low pressure and low temperature hermetic wafer bonding using microwave heating

We bonded gold on silicon substrates (Au/Si) for a MEMS application by using microwave radiation in a single-mode cavity. Microwave radiation selectively heats materials; the energy is deposited in the metallic portion of the substrates in this application. This concentration of the energy forms the bonding rather quickly and with minimal heating of the substrate. The short bonding process-time allows for minimal diffusion of the Si into the metallization. Since no pressure is applied to form the bonding, mechanical stresses are minimized. The substrates bonded by our technique formed a hermetically sealed micro-cavity. Preliminary He leak-tests from these bonded samples show leak-rates on the order of 3/spl times/10/sup 9/ atom cc/s.