Nanoparticles of noble metals show localized surface plasmon resonance. Plasmon resonances which are collective oscillations of conduction electrons give rise to the enhancement of electromagnetic field to the local surface of metallic nanoparticles. Therefore, various plasmonic near-field lithography systems were proposed so far. Here, we report on a plasmon-assisted nanolithography used for the fabrication of nano-patterns with nanometric accuracy. The lithography system can form deep nano-patterns on positive photoresist film using scattering component of multipole plasmon resonances as an exposure light. Two-photon-induced reaction of a photoresist enabled the formation of fine patterns even using plasmonic scattering light.
Advanced lithography systems, such as ArF immersion lithography, have achieved a 32 nm node<sup>1, 2</sup> and are already used
in electronic device development. However, the advanced lithography systems are not suitable for fabricating
nanostructures, such as rectangular cuboids, triangular prisms, chains, and nanogaps. These nanostructures are being
used for various applications that include plasmonic solar cells<sup>3-5</sup> and photonic crystal lasers.<sup>6, 7</sup> In this proceeding, we
report an innovative lithography system appropriate for fabricating such nano-patterns with nanometric accuracy based
on plasmon-assisted photolithography. The key technology is the two-photon photochemical reaction of a photoresist
induced by plasmonic near-field light and propagating light in a photoresist film. This propagating light is a radiation
mode from a higher order of localized surface plasmon resonances scattered by metallic nanostructures. The system does
not induce nano-pattern deformation at the time of mask release. This system presents a simple alternative for producing
nano-patterns instead of using nanoimprinting.
Highly homogeneous arrays of Ag, Au and Cu nanorods were fabricated on glass substrates using electron-beam lithography and lift-off techniques. Optical properties of the fabricated structures related to localized surface plasmons (LSP), and their dependencies on the nanorod size were studied experimentally by optical extinction spectroscopy. Spectral tuning of LSP resonant scattering bands in a wide spectral range, from visible to near-infrared wavelengths, can be accomplished by tailoring of the nanorod dimensions, aspect ratios, and heights. The observed results qualitatively agree with Gans theory and numerical modeling by finite-difference time-domain technique.