All-Polymer, High-Aspect-Ratio, Soft Lithography
Microfluidic ?chips? are commonly produced by molding or embossing from master structures: the masters need to be able to withstand many cycles of molding. We describe a novel method for fabricating extremely robust, micro-master molds in SU-8 photoresist. A wholly cross-linked adhesion layer of SU-8 is formed which bonds chemically to its PMMA (acrylate) substrate: on top comes a patterned layer of SU-8. The resulting micro-master molds have high strength and solvent resistance, permitting vigorous development procedures without undermining. Thus fine features are readily produced without concern for overdevelopment, and these molds may be used for many cycles of soft lithographic casting.