Study on forbidden pitch in plasmonic lithography: taking 365 nm wavelength thin silver film-based superlens imaging lithography as an example.

Plasmonic lithography can make the evanescent wave at the mask be resonantly amplified by exciting surface plasmon polariton (SPP) and participate in imaging, which can break through the diffraction limit in conventional lithography. It provides a reliable technical way for the study of low-cost, large-area and efficient nanolithography technology. However, there is also a phenomenon in plasmonic lithography similar to the forbidden pitch in conventional projection lithography. In this paper, combined with the imaging model and the optical transfer function (OTF), the theoretical analysis points out the reasons for the existence of the phenomenon of forbidden pitch in plasmonic lithography. Taking the 365 nm wavelength Ag thin film-based superlens imaging lithography as an example, the positions of the forbidden pitches of the 1:1 mask, the bright-field mask and the dark-field mask are calculated separately, and the key factors affecting their positions are pointed out. Simulation is carried out through commercial software, and the correctness of theoretical analysis is verified. Finally, we summarize and give some possible suggestions for solving this problem, including exploring better illumination methods, avoiding the patterns with forbidden pitch in the design, or by adding assistant feature to the design.