Jul 27, 2010
Nanopatterns deform under pressure, but by how much?
Patterning of surfaces and resist structures in the nanometre range is a key requirement for many applications of nanoscience and nanotechnology. Nanoimprint lithography (NIL) is a simple emerging technology for future nanofabrication that offers low-cost, high-throughput, high-resolution patterning and has been used for microelectronic, optical, medical and biological applications. To pattern a surface by NIL, a structured mould is mechanically pressed into a deformable resist, which is cured by a temperature gradient or UV light. Soft UV-based nanoimprint lithography (soft UV NIL) is a promising variant of NIL that makes use of patterned UV transparent polymer moulds to reduce the corresponding fabrication cost. But how much will a polymer mould deform when the imprint pressure is applied and how does this deformation vary with the size of the pattern?
Scientists from the Forschungszentrum Jülich GmbH and the DWI e.V. in Aachen, Germany, have addressed these questions and evaluated the influence of polymer composition on pattern fidelity during imprinting with an air cushion press system by Nanonex (NX-2000). They found that the corresponding variations in the mechanical properties of the stamps play a minor role in the deformation behaviour of the investigated polymer. Instead, the scientists found that the size of the pattern element is a critical issue and that features of decreased size are more sensitive to pattern distortions than larger patterns.
Sandra Gilles and her co-workers optimized the design by increasing the structure density and using constant size ratios between lines and spaces to improve pattern fidelity. Imprints performed on the basis of these design rules resulted in reduced deformations and repealed size dependence. The observed relation between pattern dimensions and degree of deformation has to be carefully considered during the design of future nanoimprint lithography layouts based on soft moulds to improve the performance of this technique when downscaling feature sizes.
Currently the team employs soft UV NIL to locally address biomolecules to electronic junctions or to apply chemical nanopatterns to functional surfaces. The group is working towards locally controlled adhesion of neurons on device surfaces by biochemical clues to guide the cells into defined neuronal networks.
The researchers presented their work in the journal Nanotechnology.
About the author
The study was performed by a collaboration involving researchers from the Institute of Bio and Nanosystems, IBN-2, of the Forschungszentrum Jülich GmbH and the DWI e.V., Textile Chemistry and Macromolecular Chemistry of RWTH Aachen University. Sandra Gilles accomplished all imprint experiments and analysed the deformations of the generated pattern. Currently she is doing a postdoctoral study at the Institute of Inorganic Chemistry, RWTH Aachen University. Dr Dirk Mayer is senior scientist at the IBN-2 and is working on the assembly and characterization of bioelectronic hybrid systems. Prof. Andreas Offenhäusser is scientific director at IBN-2. Prof. Dr Marga C Lensen was a junior research group leader at the DWI e.V. and now holds a junior professorship at the Technical University Berlin, Institut für Chemie, Nanostrukturierte Biomaterialien. Her research focuses on the manipulation of cell adhesion and migration on nanopatterned biomaterials. Mar Diez, as a graduate student at the DWI e.V., conducted the work on the PFPE polymers, prepared all soft and transparent moulds and determined their mechanical and optical properties.