Surface plasmons for nanofabrication

The diffraction limit is the major stumbling block in pushing optical lithography to feature sizes smaller than ∼50 nm. One approach to circumvent the diffraction limit in optical lithography has been to use optical near-field probes to perform local writing of resist layers. This approach suffers from low writing speeds due to the sequential nature of the process. We discuss two near-field optical illumination schemes that are compatible with broad-beam exposure and high throughput nanofabrication. The first approach concerns a method that can be used to print patterns with feature sizes below 50 nm using standard photoresist. The method relies on the plasmon resonance occurring in nanoscale metallic particles. Nanoparticle surface plasmons can be excited resonantly, producing a strongly enhanced dipole field around the particle. This enhanced near field can be used to locally expose a thin resist layer. Experiments and simulations show that feature sizes < 50nm can be produced using an exposure wavelength of 400 nm. The second approach involves projecting near-field patterns using planar metal films. It has been predicted that thin metal films may be used to generate images with a spatial resolution better than the diffraction limit. We present simulations that reveal the role of surface plasmons in such near-field imaging with planar metal films.