Plasmon Printing - a New Approach to Near-Field Lithography
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Plasmon printing – a new approach to near-field lithography Pieter G. Kik, Stefan A. Maier, and Harry A. Atwater Thomas J. Watson Laboratory of Applied Physics, California Institute of Technology, Pasadena, CA 91125, USA ABSTRACT We propose a method for replicating patterns with a resolution well below the diffraction limit, using broad beam illumination and standard photoresist. In particular it is shown that visible exposure (λ=410 nm) of silver nanoparticles in close proximity to a thin film of g-line resist (AZ 1813) can produce selectively exposed areas with a diameter smaller than λ/20. The technique relies on the local field enhancement around metal nanostructures when illuminated at the surface plasmon resonance frequency. The method can be extended to various metals, photosensitive layers, and particle shapes.
INTRODUCTION The continuing size reduction of integrated circuits to nanometer scale dimensions requires the development of new lithographic techniques. It is becoming increasingly difficult and complex to use the established method of optical projection lithography at the short optical wavelengths required to reach the desired feature sizes. For example, the use of wavelengths in the deep ultraviolet,1 the extreme ultraviolet (EUV),2 or the X-ray regime3 requires increasingly difficult adjustments of the lithographic process, including the development of new light sources, photoresists and optics. That this is seen as a major problem in the industry is clear from the large scale efforts to develop alternative approaches to nanolithography. A relatively established method for the production of high-resolution patterns is the use of focused particle beams, e.g. a focused electron beams 4 or ion beams,5 that expose a resist layer as it is scanned across the substrate. Although this produces high-resolution patterns, the sequential nature of the technique results in long writing times. Other sequential techniques involve the use of a local probe such as the tip of an Atomic Force Microscope (AFM)6 or the tip of a Near-field Scanning Optical Microscope (NSOM).7 Two parallel approaches to nanolithography that do not require short-wavelength light are micro-contact printing,8 evanescent near field lithography (ENFOL)9,10 and evanescent interferometric lithography (EIL).11 The latter two methods employ the evanescent optical field set up directly below a contact mask for exposure, and promise a resolution as high as λ/20.12 In this article we propose a new approach to nanolithography that can potentially produce sub-wavelength structures using broad beam illumination of standard photoresist with visible light. The technique is related to ENFOL, but in addition it uses resonant local field enhancement to obtain sub-wavelength resolution. The method is based on the plasmon resonance occurring in nanoscale metallic structures. When a metal nanoparticle is placed in an optical field, it exhibits a collective electron motion known as the surface plasmon oscillation. When the diameter of the particle is much smal
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