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Methods and Material Developed beyond Conventional Nanoimprint
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Nanoimprint lithography (NIL) has been regarded as one of the next-generation lithography techniques due to its ability to fabricate nanoscale structures with low cost and high throughput. Although both thermal and UV nanoimprint have demonstrated sub-10 nm resolution, the adoption of NIL by industry has been very limited. The main reasons are that the density of pattern defects and low throughput cannot satisfy the stringent requirement of commercial lithographic technique. In this study, methods and material have been developed to overcome the limitations beyond conventional nanoimprint by utilizing three main factors: mold, the interface between mold and resist, and resist. In the study, we first developed a new synergistic thermal and UV nanoimprint lithography (STUV-NIL). A transparent mold is integrated with a transparent metal oxide heater, which enables resists to be cured by thermal energy and UV light spontaneously. This new STUV-NIL combines thermal and UV techniques into one module and helps throughput improvement and reducing mold-resist adhesion and hence defect generation. In the second part of this study, the thermal behavior of a polycarbonate resist was investigated by characterization of polycarbonate gratings reflow after thermal annealing. The observation of exceptional thermal stability of entangled polycarbonate polymer opens up new routes of step-and-repeat thermal nanoimprint and high resolution patterning. The adhesion characteristic between polymers and the mold is a critical factor in the demolding process. In the third part of our study, polycarbonate residual layer has been applied as an anti sticking treatment on nanoimprint molds, replacing the self-assembled monolayer currently used. It satisfies the requirements of not only low surface energy but also low reactivity for durability. Polymerizations in UV NIL are generally accompanied by shrinkage in volume, which causes serious problems such as residual stress, demolding problems and defects. Epoxy-based UV resists have a volume shrinkage in the range of 3% to 10%. In the fourth part of our study, spiro-orthocarbonate, which undergoes volume expansion upon cationic ring-opening polymerization, has been mixed with an epoxy monomer to adjust the volume shrinkage of the cured resist and achieve zero volume change after curing.
Luo, Bingqing (2016). Methods and Material Developed beyond Conventional Nanoimprint. Doctoral dissertation, Texas A & M University. Available electronically from