ASSEMBLING 3-DIMENSIONAL MICROSTRUCTURES USING GOLD SILICON EUTECTIC BONDING

An assembly method for three-dimensional microelements is presented. T he assembly is done in situ with a micromanipulator in an SEM using Au -Si eutectic bonding. Microblocks bonded to larger silicon substrates are used for evaluation of the mechanical strength and a microarch is presented to demonstrate the possibilities of the technique. The micro elements are fabricated by bulk micromachining, and sputter deposited with chromium and gold. Etched (111) faces have been successfully bond ed. TEM investigation of samples from vacuum furnace experiments show large gold grains with smaller chromium silicide grains in the bonded region. The silicon in the eutectic liquid precipitates epitaxially on both silicon faces. Mechanical bending tests on the microblocks give sufficiently high fracture stresses for the intended applications in m icrorobotic systems. Average fracture stresses of 65 MPa are measured for one set of parameters. Problems encountered are misalignments of t he microelements during processing and void formation in the bonds. It is believed this is connected to the experimental equipment and setup . The microarch, which consists of three assembled microblocks, reache s a tensile stress of 16 MPa, encouraging further development. In conc lusion, strong microbonds are achieved using a solidified gold-silicon eutectic melt as an adhesive, and it is demonstrated for the first ti me that three-dimensional microassembly by means of eutectic bonding o f micromachined elements can be performed by manipulation and processi ng on a locally heated specimen table.