Near field optical lithography using ultra-small gap bowtie apertures

Near filed optical lithography has been a promising alternative to photolithography for its high resolution, low cost and high throughput. Bowtie aperture, one type of nanoscale ridge aperture, is widely used in near filed optical lithography. However, the bowtie structure milled by focused ion beam (FIB) usually suffers from non-vertical sidewall with taper and rounded corner due to Gaussian ion beam profile and redeposition effects. Here, we report a novel method to fabricate bowtie aperture with sub-15 nm gap, producing highly confined electric near-field by localized surface plasmon (LSP) excitation and nanofocusing of the closely tapered gap. Utilizing a passive flexure stage for contact control, we present our recent lithography results with a record 20 nm resolution (FWHM).