Thermal Nanoimprint and Resolution Limits of Hybrid H-PDMS/PDMS Mold

Soft nanoimprint lithography replicates nanopatterns from elastomeric mold, most common materials for which made of Polydimethylsilane (PDMS). It is a popular nanofabrication approach due to its robustness, simplicity, flexibility, and low sensitivity to surface defects and contaminations. However, the resolution and minimal feature size of soft nanoimprint are limited to ~100 nm because of the softness of the relief features that define the pattern. The resolution can be improved to 50 nm by using hybrid PDMS/hard-PDMS molds, in which layer made of hard PDMS and soft PDMS substrate are combined. Also, additional hybrid elastic molds have been reported to achieve imprint resolution down to sub- 20 nm. Still, soft nanoimprint mold has been used so far mostly with UV curable resist, whereas thermal imprint with soft molds has been unexplored. In this work, we demonstrate two main novelties. First, we show that soft nanoimprint can produce pattern features downsized to 10 nm – the smallest critical dimensions achieved so far for soft nanoimprint. Second, we show that ultra-high resolution soft nanoimprint is possible in combination with thermoplastic imprint resists. For this purpose, we replicated hybrid PDMS molds from electron-beam patterned master, and used them for thermal imprint of poly(benzyl-methacrylate) – PBMA . To exploit the flexibility of soft mold, we also demonstrate thermal nanoimprint on lens. Furthermore, we demonstrated that soft thermal nanoimprint can produce relief nanopattern with no need for pattern transfer, by direct imprinting of bulk chalcogenide glass. Our nanofabrication approach opens the pathway to the realization of novel nanosized devices and structures on non-planar surfaces, with endless possible applications including but not limited to plasmonics, photovoltaics, nano-photonics, and nano-medicine.