MEMS/Microfluidics Packaging Without Heating

The sequentially plasma activated bonding (SPAB) of silicon/silicon interface has been characterized after annealing up to 900 degrees C for packaging of micro-electro mechanical systems (MEMS) and microfluidic devices at low temperature. The bonding strength of the interface in the SPAB was as high as that of the conventional hydrophilic bonding method, which requires annealing as high as 1000 degrees C to achieve covalent bonding. The interfacial voids evolution with annealing temperatures has been correlated with the bonding strength. Although the rearrangement of water such as absorption and desorption across the bonded interface was found below 225 degrees C, the voids were not significant up to 400 degrees C. Annealing above 600 degrees C resulted in a considerable amount of thermal voids due to viscous flow of oxides. The thermal voids were grown preferentially at the plasma induced defect sites. The contact angle and roughness of the sequentially plasma (reactive ion etching plasma followed by microwave radicals) treated surfaces have been observed to explain the void formation and reduction of the bonding strength of the interface. The plasma induced defect sites such as nanopores and craters have been indentified using an atomic force microscope. The electron energy loss spectroscopy showed oxygen deficiency in the nanometer thick interfacial amorphous silicon oxide.