Subwavelength interference nanolithography based on metallic–insulator–metallic waveguide with a trapezoid metallic nanoslit coupler

A subwavelength interference nanolithography scheme is numerically demonstrated based on a metallic–insulator–metallic waveguide combined with unidirectional couplers. The coupler is a single right-angled (or left-angled) trapezoid metallic nanoslit that can carry out efficient unidirectional generation of surface plasmon polaritons under normal incidence. Simulation results show that a feature size to 50 nm half-pitch uniformity pattern can be obtained at the working wavelength of 365 nm with the proposed scheme. This proposed scheme can enhance the intensity of the interference pattern with higher contrast and field depth and is advantageous for the fabrication process in practical applications.