Low-NA focused vortex beam lithography for below 100-nm feature size at 405 nm illumination

We present a novel method for the optical fabrication of particular structures with sub-100-nm features by using direct-write laser lithography at 405-nm wavelength. A doughnut-shaped spot, generated by focusing an azimuthally polarized beam using an NA=0.2 lens, exhibits a central dark region, i.e., optical vortex. This is the key to write well-isolated nano-structures like nano-cylinders. A decomposition of such doughnut spots leads to two-half-lobes spots that can create line patterns when linearly scanned. This method is fast and inexpensive to fabricate well-isolated nano-cylinders or nano-holes and nanometer-size line patterns or trenches compared to other nano-fabrication methods. They can find applications for the fabrication of a nano solid immersion lens, an isolated quantum dot, plasmonic waveguides, and for micro- and nano-fluidics.