Improvement of Transfer Durability of a Pillar-Shaped Release-Agent-Free Replica Mold in Ultraviolet Nanoimprint Lithography

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Abstract
Ultraviolet nanoimprint lithography (UV-NIL) can be used to fabricate nanoscale patterns with high throughput. It is expected to serve as a low-cost technique for the production of items in large numbers. However, master molds for UV-NIL are expensive and laborious to produce, and there are problems associated with the deterioration of the master mold and damage to its nanopattern due to adhesion of the UV-curable resin. Consequently, the UV-curable resin has to combine low-viscosity characteristics for coatability with an antisticking property. Coating a master mold with a release layer is important in preventing damage to the master mold or adhesion between the mold and the UV-curable resin. However, the released layer deteriorates as the master mold is repeatedly used to fabricate nanopatterns. By contrast, the use of a replica mold is a valuable technique for preventing the deterioration of the master mold, and there have been several studies on the fabrication of replicas of master molds with the use of UV-curable resins. In many cases, the fabrication of nanopatterns with replica molds requires the use of a release agent. In a previous study, we developed a material for replica molds that does not require a release agent. This material consisted of a UV-curable resin with an antifouling effect that was prepared from cationically polymerizable UV-curable and epoxy-modified fluorinated resins. With the use of this material, replica molds with patterns of pillars or holes were fabricated with UV-NIL. The lifetime of the mold with the nanopattern of pillars was shorter than that with holes. In addition, the replica mold with the pillar-shaped nanopattern had numerous defects and allowed adhesion of the transfer resin after repeated efforts. Herein, we describe an improved release-agent-free hard replica mold. We transferred large numbers of nanopatterns of pillars from the replica mold, and evaluated the error rate and contact angle of our improved release-agent-free hard replica mold. The resulting release-agent-free replica mold with a nanopattern of pillars was capable of transferring up to 1000 sequential imprints. In addition, to improve the release properties of the transfer resin, we included an additive to the transfer resin that contained a reactive fluorinated material. This material improved the release properties of the transfer resin and mitigated the deterioration of the contact angle and increase in the error rate.

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