High-aspect-ratio plasmonic lithography via decaying feature amplification

Plasmonic lithography, which utilizes surface plasmon polaritons (SPPs) to amplify evanescent waves, enables sub-diffraction-limited optical imaging. However, as feature size shrinks to the nanoscale, challenges arise from shallow imaging depth and poor patterning fidelity in the photoresist (PR) layer due to the rapid decay of evanescent waves, limiting practical applications. This work introduces a metamaterial photoresist resonance cavity (MPRC) structure engineered to amplify the decay feature. The MPRC incorporates a periodic silver nanosphere array embedded within the PR layer, which excites localized surface plasmon resonance (LSPR). This LSPR field can couple with both mask-coupled surface plasmon polaritons (SPPs) at the mask-PR interface and reflector-enhanced SPPs at the PR-silver reflector interface. This interaction forms double catenary fields, establishing a strongly coupled field throughout the PR layer via a cascaded coupling mechanism. This reduces the loss of high-k information, enhancing its imaging transfer capability. As a result, the MPRC achieves a patterning depth of at least 72 nm with an aspect ratio exceeding 1.0, while maintaining high pattern fidelity, which represents a substantial improvement over a conventional photoresist plasmonic lithography (CPPL) structure. This approach of evanescent-wave decay amplification provides a fundamental and practical pathway toward high-aspect-ratio nanomanufacturing.