Until now, acrylates have been the monomers of choice for use for step and flash imprint lithography ͑SFIL͒ etch barrier formulations, in part because of the commercial availability of silicon-containing acrylates ͑necessary for etch resistance͒, together with their low viscosities and capability for rapid photopolymerization. However, despite many desirable properties, the polymerization of acrylates via radical chain propagation causes some potential issues in the SFIL process as a result of the inhibition of these processes by oxygen. Vinyl ethers are prime candidates to replace acrylates. Their curing proceeds by a cationic mechanism, which is insensitive to oxygen and very rapid, while the vinyl ether group contribution to viscosity is significantly lower than that of an acrylate, silicon-containing vinyl ethers are not widely commercially available, and so were synthesized for this study. As expected, formulations based on these vinyl ethers were lower viscosity and faster curing than the acrylate etch barrier formulations presently employed, while the tensile strength of cured vinyl ether formulations were found to be higher than their acrylate counterparts. In spite of about twice higher template separation force compared with acrylates, the tensile strength of vinyl ether etch barrier formulations is about five times higher than that of acrylate formulations. Therefore, these vinyl ether-based formulations were used to pattern down to 50 nm features using the SFIL process.
Previous work with the mechanical properties of step and flash imprint lithography etch barrier materials has shown bulk volumetric shrinkage trends that could impact imprinted feature dimensions and profile. This article uses mesoscopic and finite element modeling techniques to model the behavior of the etch barrier during polymerization. Model results are then compared to cross section images of template and etch barrier. Volumetric shrinkage is seen to impact imprinted feature profiles largely as a change in feature height.
Step and Flash Imprint Lithography (SFIL) is an attractive method for printing sub-100 nm geometries. Relative to other imprinting processes SFIL has the advantage that the template is transparent, thereby facilitating conventional overlay techniques. In addition, the imprint process is performed at low pressures and room temperature, minimizing magnification and distortion errors. The purpose of this work was to investigate alternative methods for defining high resolution SFIL templates and study the limits of the SFIL process. Two methods for fabricating templates were considered. The first method used a very thin (< 20 nm) layer of Cr as a hard mask. The second fabrication scheme attempts to address some of the weaknesses associated with a solid glass substrate. Because there is no conductive layer on the final template, SEM and defect inspection are compromised. By incorporating a conductive and transparent layer of indium tin oxide (ITO) on the glass substrate, charging is suppressed during SEM inspection, and the transparent nature of the final template is not affected. Using ZEP-520 as the electron beam imaging resist, features as small as 20 nm were resolved on the templates. Features were also successfully imprinted using both types of templates.
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