Soft nanoimprint mold with rigid relief features for improved pattern transfer

Rigid nanoimprint molds offer the best possible pattern-transfer fidelity and resolution, but are also sensitive to surface contamination and defects. Alternatively, soft nanoimprint molds are insensitive to defects and can imprint nonplanar surfaces, but have limited resolution. Here, the author combined the advantages of the rigid and soft molds by producing a novel mold, in which rigid relief features are chemically attached to a soft substrate. The features were produced by electron-beam patterning of hydrogen silsesquioxane (HSQ) on a sacrificial substrate, and mechanically transferred to polydimethylsiloxane (PDMS). The attachment of the HSQ to PDMS is most likely due to Si-O-Si bonds formed on their interface. Using this molds, the authors obtained nanoimprinted pattern transfer with the fidelity typical for the hard molds. They found that a mold-release agent is essential to prevent the detachment of the rigid features from PDMS. To this end, the authors applied fluorinated silane onto the mold surface and showed that functionalized silane monolayers can effectively modify the surface properties of spin-on-glass materials like HSQ.