Robustness optimization of superlens imaging structures in surface plasmon lithography.

Surface plasmon lithography (SPL) overcomes the diffraction limit of conventional projection lithography by utilizing evanescent waves for imaging, offering significant potential for integrated circuit (IC) manufacturing at advanced technology nodes. Previous research on the imaging quality in SPL has primarily focused on enhancing the resolution of imaging structures, neglecting the compatibility with diverse mask patterns. Given the diversity and complexity of patterns in IC layouts, exploring imaging structures compatible with varied mask patterns is essential. This paper focuses on the robustness of superlens imaging structures, introducing the concept of a robust imaging structure. It also establishes a flow for robustness optimization and analyzes imaging quality and compatibility using the coherent transfer function (CTF). This study examines the influences of polymethylmethacrylate (PMMA) and photoresist (Pr) thicknesses on imaging quality, as well as the impact of the top Ag thickness turning point on imaging quality. Simulation experiments and analytical demonstrations reveal that robust imaging structures exhibit higher amplitude and broader high-amplitude bandwidth in the spatial frequencies of evanescent waves, resulting in improved compatibility. This study aims to guide the optimization of imaging structures in practical applications of surface plasmon lithography. The proposed method is suitable for robustness optimization of imaging structures for diverse mask patterns at advanced technology nodes.