Wafer bonding with metal layers for MEMS applications

Metal films can be used as bonding layers at wafer-level in MEMS manufacturing processes for device assembly as well as just for electrical integration of different components. One has to distinguish between two categories of processes: metal thermo-compression bonding on one side, and bonding with formation of an eutectic alloy layer or an intermetallic compound. The different process principles determine also the applications area for each. From electrical interconnections to wafer-level packaging (with special emphasis on vacuum packaging) metal wafer bonding is a very important technology in MEMS manufacturing processes.