Nov 6, 2008
Self-perfection by liquefaction for high-quality nanoimprint moulds
Nanoimprint lithography (NIL) has been repeatedly demonstrated as a low-cost and high-throughput solution to nanostructure manufacturing – a critical bottleneck in nanotechnology, significantly impacting a broad range of fields such as electronics, optics, magnetic data storage, biotechnology and materials. However, a key issue in NIL is the mould fabrication – without a mould nothing would happen. Conventional mould fabrication methods have many limitations, such as significant shape deformation (due to imperfection of a lithography system) and edge roughness (due to the intrinsic noises).
To address this challenge, in a recent paper published in Nanotechnology, researchers at Princeton University applied a novel technology that they developed earlier – self-perfection by liquefaction (SPEL) (Nature Nanotechnology 3 295–300), to fabricate the moulds with near-perfect structures that are unachievable with conventional methods. SPEL can “remove” the defects that are generated initially by a conventional lithography.
Schematic of our process to make cylindrical pillar moulds with smooth sidewalls.
In Princeton’s work, they fabricated pillar moulds with a pillar diameter of 25 nm or smaller. At such small dimensions, a designed-to-be-circular disk made by a conventional lithography such as electron or ion beam has a non-circular shape and significant edge roughness. Indeed, the initial Cr patterns were more square-shaped with rough edges. But after SPEL, which selectively melts the Cr structures for a very short period of time (hundreds of nanoseconds by an ultrafast laser pulse), the Cr squares were turned into perfect semi-spheres with a reduced edge roughness.
Another advantage of SPEL was a further reduction of the pillar diameter by 43%. With the perfected Cr mask, pillar moulds were made by reactive ion etching. The high-quality moulds will have wide applications in plamoniscs, nanobiotechnology and patterned magnetic media.
About the author
Dr Qiangfei Xia received his PhD in electrical engineering from Princeton University and is currently a research associate at Hewlett-Packard Labs. His research interests include nanoimprint lithography, nanofabrication and their applications in nanoscale devices. Dr Stephen Y Chou is the Joseph C Elgin Pprofessor of engineering and head of the NanoStructure Laboratory at Princeton University. Dr Chou is a world leader, pioneer and inventor in a broad range of nanotechnologies, among which are nanoimprint lithography, quantized magnetic disks (bit-patterned media), ultra-small transistors and sub-wavelength optical elements.