Approach of enhancing exposure depth for evanescent wave interference lithography

Theoretically evanescent wave lithography can achieve the feature size with dimensions less than one fifth of the wavelength of irradiation source, it can meet the resolution of the nano-grating. However, according to the theoretical calculation and the experimental results, the amplitude of evanescent wave away from the surface of the medium decays exponentially, it will cause short exposure depth, low contrast in photoresist so that the pattern is unable to transfer accurately to the substrate. In this paper, in order to explore the possibility for fabricating large-area nano-grating by interference lithography, we try to enhance the exposure depth of the evanescent interference lithography based on the Surface Plasmon Polarization (SPP) near-field technologies. The theoretical analysis and parameters optimization show that the improving interference lithography technology can be used to fabricate the grating with 60nm feature size.