Direct CW-Laser Writing Sub-Diffraction-Limit Nanopore Array Based on the Low One-Photon Absorption of Polymer

Abstract

A large area nanopore array with controllable consistency has been fabricated by direct laser writing (DLW) technique with ultralow one-photon absorption (LOPA). In this technique, a doughnut-shape beam generated by 532 nm continuous-wave laser through a vortex phase plate was focused into the thin film of SU8 photoresist by a high numerical aperture objective. The low absorption of the photoresist at the excitation wavelength allowed controllable fabricating structures with sub-diffraction-limit feature size and high aspect ratio. With point-by-point scanning fabrication, nanopore array with the pore's internal diameter, about ten percent of incident laser wavelength, far smaller than Abbe's diffraction limit was achieved. The influences of the exposure intensity and exposure time on the fabricated nanopore size and shape were also investigated by scanning electron microscope (SEM).