Resolution Limits of Nanoimprinted Patterns by Fluorescence Microscopy

Abstract

The authors investigated optical resolution limits to identify minimum distances between convex lines of fluorescent dye-doped nanoimprinted resist patterns by fluorescence microscopy. Fluorescent ultraviolet (UV)-curable resin and thermoplastic resin films were transformed into line-and-space patterns by UV nanoimprinting and thermal nanoimprinting, respectively. Fluorescence immersion observation needed an immersion medium immiscible to the resist films, and an ionic liquid of triisobutyl methylphosphonium tosylate was appropriate for soluble thermoplastic polystyrene patterns. Observation with various numerical aperture (NA) values and two detection wavelength ranges showed that the resolution limits were smaller than the values estimated by the Sparrow criterion. The space width to identify line patterns became narrower as the line width increased. The space width of 100 nm was demonstrated to be sufficient to resolve 300-nm-wide lines in the detection wavelength range of 575–625 nm using an objective lens of NA= 1.40.

Breakthrough Achievement In Nanoimprint Lithography Using PFP Condensable Gas

“…UV-curable resins before UV-exposure and UV-cured resins after UV-exposure could be visualized by fluorescence microscopy, and modified mold surfaces after UV nanoimprinting and cured resin patterns on substrates could be observed in a non-destructive optical way. We have demonstrated the defect inspection of cured resin patterns on substrates [40], the optical measurement of residual layer thickness [41], the optical resolution limit of nanoimprinted patterns [42], and the distinction of resin adsorption, adhesion, and pull-out occurring on mold surfaces [43], as illustrated in Fig. 9.…”

Selection of Di(meth)acrylate Monomers for Low Pollution of Fluorinated Mold Surfaces in Ultraviolet Nanoimprint Lithography

“…We found that an increase in the amount of resin components adsorbed by the mold surface made demolding difficult. We also showed that fluorescent UV-curable resins are useful for determining the thickness of a residual layer by measuring the fluorescence intensity; resist pattern defects , can be investigated at a resolution limit of a space width of 100 nm for line and space patterns …”

Development of UV-curable liquid for in-liquid fluorescence alignment in ultraviolet nanoimprint lithography

“…22) We demonstrate that the optical resolution limit of fluorescent imprinted resist patterns was beyond the diffraction limits defined by Rayleigh and Sparrow, because fluorescent resist patterns have a height. 23) Taking account of these advantages of fluorescent UVcurable resins and UV-cured resist patterns, we have recently demonstrated a fluorescence alignment method performed under an in-liquid condition where silica mold recesses are filled with a fluorescent liquid in a contact with a patterned substrate surface. 24,25) The fluorescence alignment has a unique advantage of using silica molds without an optically functional layer of light-shielding metals or high-refractiveindex inorganic materials, which will be able to reduce the mold cost.…”