Challenges with soft stamps for guiding of diblock copolymers

The preparation of nanostructures by guiding the phase separation of a block copolymer (BCP) is an attractive technique to overcome the limitations of conventional lithography. Well-established methods for guiding are to provide a topographical pattern (grapho-epitaxy) or a chemical pattern (chemo-epitaxy) on the substrate before BCP application. This paper reports on an alternative technique, the guiding of the BCP without pre-patterning the substrate, by providing the guiding pattern from the top, by nanoimprint. This approach offers the benefit of a multiple use of the same stamp. In the work reported here, we use an elastomeric stamp and examine capillary force lithography (CFL) with respect to guiding. The processing temperature is chosen high in order to provide fast phase separation. For the control of the surface energy of the substrate, a silane deposition from the gas phase is utilized. The ordering behavior of a lamellar polystyrene–polymethylmethacrylate BCP with CFL is studied. In particular, the issues specific with phase separation in an imprint situation are addressed, the locally differing layer thickness and the fact that two surface energies contribute to the ordering process, the one of the substrate and the one of the stamp. Though further optimization is required to make use of CFL for efficient guiding, the first results reported here indicate the potential of this technique for stamp-induced guiding of BCPs. As it allows a multiple use of the stamp, such guiding is interesting and may replace the time- and cost-consuming pre-patterning of each substrate.