We report an innovative lithography system appropriate for fabricating sharp-edged nanodot patterns with nanoscale accuracy using plasmon-assisted photolithography. The key technology is two-photon photochemical reactions of a photoresist induced by plasmonic near-field light and the scattering component of the light in a photoresist film. The scattering component of the light is a radiation mode from higher order localized surface plasmon resonances scattered by metallic nanostructures. Near-field lithography holds promise for the fabrication of nano-patterns on a photoresist. 1-6 Recently, we reported on the nano-patterning of pits (5 nm in diameter) onto a positive photoresist locally exposed by nanogap-assisted surface plasmon nanolithography. 6 For near-field lithography, however, nano-patterns on a photoresist film are completely defined by the near-field intensity profile. As a result, photoresist patterns do not reflect the photomask design exactly. The near-field intensity profile can be predicted using computational electrodynamics modeling, such as finite-difference time-domain (FDTD) methods. 7 However, the fabricated nano-patterns are shallow and highly dependent on exposure dose.In this letter, we demonstrate a plasmon-assisted photolithography system that is used to fabricate nano-patterns with nanoscale accuracy. The most attractive feature of this system is its ability to form deep nano-patterns on positive photoresist. These formed nano-patterns accurately reflect the photomask's design. Our strategy for making deep nanopatterns involves the use of the radiation mode of localized surface plasmon resonance (LSPR) scattered on nanostructures onto photomasks as the exposure step. To make nanopatterns that accurately preserved our photomask design, we utilized a higher order LSPR mode with multi-wave functions. 8 This mode was used to produce homogeneous scattering light in an x-y plane that propagated the photoresist film along the z-axis. The key to making fine nano-patterns is to utilize scattered light based on a higher order of LSPR and two-photon photochemical reactions in the photoresist. This procedure promotes spatially selective exposure. Most important, we designed the photomasks using FDTD simulations. In addition, the lift-off process after the deposition of the metals onto the fabricated nano-patterns makes it possible to duplicate metallic nanostructures on a substrate. This procedure can be applied to plasmonic materials.Gold-film-coated nanostructured photomasks were prepared by electron-beam (EB) lithography via sputtering onto glass substrates and by being brought into direct contact with a positive photoresist film spin-coated onto a glass substrate (70 nm in thickness). 9 For the photomask fabrication process, nanostructures were directly formed using a negative EB resist on the substrate. 9 Then, a 10-nm-thick gold film was deposited onto a nanostructured substrate. A scanning electron microscope (SEM) image of the photomask is shown in Figure 1(a). Rectangular cuboids were al...

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