Capillary force lithography : fabrication of functional polymer templates as versatile tools for nanolithography

The implementation of high-resolution polymer templates fabricated by capillary force lithography (CFL) is explored both in nanoimprint lithography (NIL) and in the wet-etching of metals. Several different thermoplastic and UV-curable polymers and types of substrates are incorporated into the general CFL procedure to meet the diverging requirements of these two applications. The mechanical stability of UV-curable templates for imprinting in polymers, as examined by atomic force microscopy (AFM), and their anti-adhesive properties are excellent for application in NIL. The conditions for curing the UV-curable polymer are optimized in order to obtain high-stability polymer templates. Gold patterns on silicon with a lateral resolution of 150 nm are fabricated by subsequent lift-off in acetone. Similar patterns with a lateral resolution of 100 nm are fabricated using templates of thermoplastic polymers on gold layers on silicon as an etch mask. The transfer of stamp residues during CFL with these polymer templates is proven by X-ray photoelectron spectroscopy (XPS) and AFM friction analysis. For poly(methylmethacrylate) (PMMA), the presence of large amounts of silicon-containing residues is found to compromise the processability of the resulting template in subsequent O2 reactive-ion etching (RIE) treatment. The extent of silicon contamination is up to six times less for polystyrene (PS). At this level, the etch performance of the PS etch mask is not affected, as was the case for PMMA. Accurate downscaling of the lateral dimensions of the resulting metal patterns by several factors with respect to the dimensions of the PS etch mask is achieved by over-etching of the gold. Overall, the results in this paper demonstrate the potential of CFL templates as tools for high-resolution soft lithography.

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