Low temperature MEMS manufacturing processes: plasma activated wafer bonding

This paper introduces a new technology: low temperature plasma activated wafer bonding. In this process, the wafers are submitted to a plasma treatment prior to bringing them into contact for bonding. The surface activation allows process temperatures ranging from room temperature to maximum 400 degrees C. For Si direct bonding using plasma activation the Si bulk fracture strength is reached after a thermal annealing of 1 hour at 300 degrees C, much lower than the annealing temperature used for the standard process without plasma activation (similar to 1100 degrees C). Experimental results illustrating the main benefits of the process are presented. The process was successfully applied also for bonding other materials than silicon.