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-inch glass wafer to a three-inch silicon wafer. Flat, smooth silica surfaces were patterned with gold millimeter-scale borders enclosing micrometer-scale 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 interface. The accuracy of this alignment was better than one micrometer. Gravitational energy was used to systematically study the alignment force as a function of pattern parameters. These data can be modeled by interfacial energy theory. These experiments identify a clear set of conditions necessary for the use of this technique for high-precision alignment.