Reverse-tone ultraviolet nanoimprint lithography with fluorescent UV-curable resins

The usefulness of fluorescent ultraviolet (UV)-curable resins for reverse-tone UV nanoimprint lithography was demonstrated. Nanoimprinted concave patterns were fabricated as an underlayer on a Au-deposited substrate using a fluorescent UV-curable resin with a low etching durability after curing. The underlayer was coated with another fluorescent UV-curable resin with a high etching durability after curing. Fluorescence microscopic observation allowed the inspection of the morphological uniformity and thickness of both under and top layers in a nondestructive manner. UV-curing of the top layer in combination with pressing with a flat substrate was necessary for obtaining a flattened top layer surface, which was responsible for allowing the reverse-tone UV nanoimprint lithography. We demonstrated the fabrication of 10-nm-thick Au split-ring resonator structures with a line width of 55 ± 4 nm corresponding to the underlayer concave resist patterns by dry etching during Ar ion milling under the condition that the etching rate ratio of the underlayer to the top layer was 6.