Versatile low temperature wafer bonding and bond strength measurement by a blister test method

We present a low temperature plasma assisted bonding process that enables the bonding of silicon, silicon oxide and silicon nitride wafers among each other at annealing temperatures as low as room temperature. The process can be applied using standard clean room equipment. Surface energies of differently treated bonded samples are determined by a blister test method for square shaped cavities. For this reason, we extend the well-known blister test method for round shaped cavities to the square shaped case by a combined analytical and numerical approach. Accordingly, the energetic favored crack front propagation in the bond interface is determined by numerical simulations. The surface energies of the tested samples are calculated and compared to anodic silicon-to-Pyrex(R) bonds. Surface energies of up to 2.6 J/m(2) can be achieved between silicon and silicon oxide wafer pairs at low annealing temperatures. Room temperature bonded samples show a surface energy of 1.9 J/m(2). The surface energy of silicon-to-Pyrex glass bonds yields 1.3 J/m(2). Small structures, e.g., bridges down to 5 mu m can be bonded using the discussed bonding process. Selective bonding of silicon-to-silicon oxide wafer pairs is performed by structuring the oxide layer. The successful integration of the bonding process into the fabrication of micropumps is highlighted.