Self-alignment of patterned wafers using capillary forces at a water-air interface

Capillary interactions at a water-air interface were used to align a two-in ch glass wafer to a three-inch silicon wafer. Flat, smooth silica surfaces were patterned with gold millimeter-scale borders enclosing micrometer-scal e features. The gold features were rendered hydrophobic through the use of self-assembled monolayers, the silica was wetted with water, and the wafers were pressed together. The assembly snapped into alignment based upon the minimization of the curvature of the meniscus formed at the water-air inter face. The accuracy of this alignment was better than one micrometer. Gravit ational energy was used to systematically study the alignment force as a fu nction of pattern parameters. These data can be modelled by interfacial ene rgy theory. These experiments identify a clear set of conditions necessary for the use of this technique for high-precision alignment.