Exploring the Ultimate Limits of Nanoscale Shape Control in Imprint Lithography
Researchers at the NSF-funded Nanosystems Engineering Research Center (NERC) for Nanomanufacturing Systems for Mobile Computing and Mobile Energy Technologies (NASCENT), headquartered at the University of Texas at Austin, have developed a new methodology for creating precise two-dimensional shapes with sharp corners (radii <3 nm) to study the nanoshape replication capability of imprint lithography. The methodology includes a template fabrication process based on atomic layer deposition and chemical staining that enables in-situ shape nanometrology of the template and replicated polymeric structures in order to study shape retention through the replication process.
A diamond-like shape was chosen to explore the ultimate limits of shape control with this patterning process. The corners in the template with 2 nm radii of curvature appear to be substantially retained; however, a consistent increase in the imprinted radius of the corner is observed, indicating relaxation of the resist (Figure 1). Relevant prior literature has not reported such resist relaxation, as sharp nanoshapes were not investigated. A continuum model of the shape change of the polymer resist predicts a sharpening of the corners, contrary to observations. Continuum mechanics appears no longer applicable at the length scale of ~3 nm, indicating that this length is the limit of resolution of a sharp corner set by relaxation of the resist.
This is a novel methodology for creating, imaging and imprinting sharp, complex shapes using imprint lithography. Etched results show that the sharp corners on the template lose about 2.6 nm due to the etch process (Methods) as seen in Figure 2. The nanoshape capability presented here to replicate, hold, and transfer non-standard extreme shapes makes it a potential vehicle for volume fabrication of novel magnetic devices, shaped nano-particles, and optical nanostructures that could enable a wide variety of technological advances in the near future.
Imprint lithography inherently possesses remarkable resolution, having demonstrated sub-3 nm patterning in research with the capability to pattern typical lithographic structures such as lines, gratings, dot arrays, etc. Over the past few years, imprint- based stepper technology has commercially matured based on a specific form of imprint lithography known as Jet and Flash Imprint Lithography (J-FIL®). J-FIL® has made significant progress towards addressing defect control and overlay, making it a viable route for manufacturing cost-sensitive semiconductor devices. Today, pilot manufacturing steppers have been developed and deployed for patterning standard lithographic features. What was unknown prior to this study was the ultimate resolution of nanoimprint lithography for 2D shapes.