Theoretical Investigation Of Improvingspot Quality For Near-field Probe Directwriting Lithography

The SPPs direct writing lithography not only possesses the advantage of simplesystem structure, flexible image pattern, but more importantly,it can overcome thediffraction limit compared to conventional lithography, and reach high lithographyresolution. However, due to the inherent localization properties of SPPs which can onlybe excited at the metal/insulator surface and attenuated along the normal direction, theimage pattern got shallow depth and coarse edges, which greatly hinder its furtherapplication.Our investigationis mainly focus on this problem. Firstly, the SPPs’ excitationconditions, dispersion property and resonance enhancement are theoretically deduced.Then spot influence factors are analyzed respectively from aspects of probe structure,coupled substrate and illumination mode. Moreover, the different probe exciting hasbeen numerical simulated, including bowtie antenna probe, SNOM fiber probe and themetal aperture-less probe. Based on the numerical analysis, a tip-insulator-metalstructure with bottom-up light illumination is proposed and theoretically analyzed. Itshows that there is a strong plasmonic coupling between Ag tip and metallic surface.And the spot quality is improved effectively,influences of tip size, insulator and metalliclayer thickness are also studied,different from oblique light illumination, this noveldesign possesses unique advantages of symmetrical hot spot profile and enlarged depthof focus at a sub-10nm spatial resolution.