Low-NA focused vortex beam lithography for below 100-nm feature size at 405 nm illumination
There are varieties of novel methods, which demonstrate the super-resolution. For instance, an optically trapped sub-micron dielectric sphere serves as a near-field focusing lens to directly write patterns of 100 nm in liquid, and accelerated metallic nanoparticles by optical force form a stamp on the substrate, coined optical force stamping lithography. Two-photon absorption lithography is another good example of super-resolution techniques for 100-nm target. Other breakthrough to achieve sub-100-nm pattern size is using two beams: for initiation and deactivation of polymerization with one color or with two colors and for absorbance modulation. Generally, such two-beam techniques rely on doughnut-shape spots, whose tiny dark center is a key feature to achieve such a small size. Here, we propose a new method to fabricate well-isolated single nano-structures using this doughnut-shape vortex beam but a single beam illumination is applied. Regardless of the NA, focusing of azimuthal polarization always assures the dark center while the radial polarization is often used to create a bright center by a high NA. When such vortex beams at λ=405 nm expose the positive photoresist, nano-cylinder are formed in the center of the circular exposed area. A decomposition of the doughnut beam leads to the two-half-lobes spot and the linear scanning of the decomposed spot produces nano-size line patterns. This is a fast and inexpensive way to fabricate well-isolated nano-solid-immersion-lenses or plasmonic nano-waveguides compared to other nano-fabrication methods, such as, electron beam lithography.