The fabrication of nanostructures and nanopatterns is of crucial importance in microelectronics, nanofluidics, and the manufacture of biomedical devices and biosensors. However, the creation of nanopatterns by means of conventional nanofabrication techniques such as electron beam lithography is expensive and time-consuming. Here, we develop a multistep miniaturization approach using prestressed polymer films to generate nanopatterns from microscale patterns without the need of complex nanolithography methods. Prestressed polymer films have been used as a miniaturization technique to fabricate features with a smaller size than the initial imprinted features. However, the height of the imprinted features is significantly reduced after the thermal shrinking of the prestressed films due to the shape memory effect of the polymer, and as a result, the topographical features tend to disappear after shrinking. We have developed a miniaturization approach that controls the material flow and maintains the shrunken patterns by applying mechanical constraints during the shrinking process. The combination of hot embossing and constrained shrinking makes it possible to reduce the size of the initial imprinted features even to the nanoscale. The developed multistep miniaturization approach allows using the shrunken pattern as a master for a subsequent miniaturization cycle. Well-defined patterns as small as 100 nm are fabricated, showing a 10-fold reduction in size from the original master. The developed approach also allows the transfer of the shrunken polymeric patterns to a silicon substrate, which can be used as a functional substrate for many applications or directly as a master for nanoimprint lithography.
The ability to define patterns and fabricate structures at the nanoscale in a scalable manner is crucial not only in integrated circuit fabrication but also in fabrication of nanofluidic devices...
Nanoimprint lithography is an emerging technology to form patterns and features in the nanoscale. Production of nanoscale patterns is challenging particularly in the sub-50 nm range. Pre-stressed polymer films with embedded microscale pattern can be miniaturized by shrinking induced due to thermal stress release. However, when pre-stressed films are thermally nanoimprinted with sub-micron features and shruken, they lose all the topographical features due to material recovery. Here we report a new approach that prevents recovery and allows retention of shrunken patterns even at the scale of <50 nm. We have discovered that when the shrinking process is mechanically constrained in one direction, the thermal treatment only relieves the stress in the orthogonal direction leading to a uniaxial shrinkage in that direction while preserving the topographical features. A second step, with the constraint in the orthogonal direction leads to biaxial shrinkage and preservation of all of the topographical features. This new technique can produce well defined and high resolution nanostructures at dimensions below 50 nm. The process is programmable and the thermal treatment can be tuned to shrink features to various dimension below the original imprint which we use to produce tunable and gradient plasmonic structures.
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