Micromolding of Polymers in Capillaries: Applications in Microfabrication

This paper describes the use of micromolding in capillaries (MIMIC) to produce complex polymeric microstructures supported on different substrates and the applications of these microstructures in microfabrication. Patterned microstructures of several organic polymerspolyurethane, polyacrylate, and epoxywere formed by molding in enclosed, continuous channels formed by conformal contact between a solid support and an elastomeric mold whose surface had been patterned with a relief structure having micrometer-scale dimensions. A liquid prepolymer filled these channels by capillary action and was allowed to cure photochemically or thermally. The mold was then removed. Polymeric microstructures formed on films of Saran Wrap could be folded into different shapes, while these microstructures retained their forms; they could also be stretched uniaxially to generate microstructures having distorted forms. The patterned polymeric microstructures formed on SiO2, glass, and metals (Au, Ag, and Cr) could be used directly as resists in the selective etching of underlying substrates. Free-standing polymeric microstructures fabricated by lift-off were used as disposable masks to generate patterned microfeatures of metals on the surfaces of both planar and nonplanar substrates in two different procedures: (a) evaporation of gold through the polymeric mask supported on a substrate; (b) formation of patterned self-assembled monolayers (SAMs) by exposure of a silver film covered by a polymeric mask to hexadecanethiol (HDT) in vapor, followed by selective etching of the regions that were not exposed to HDT (that is, the parts of the surface protected by the mask) in an aqueous solution containing K2S2O3 and K3Fe(CN)6/K4Fe(CN)6.