High-resolution dual-layer two-photon lithography for nanoscale patterning.

Multi-photon lithography (MPL), which predominantly utilises femtosecond lasers, is a significant maskless, high-resolution and ambient (non-vacuum) lithography technique. To achieve a comparable resolution to primary competing solutions, such as electron-beam lithography, and to improve processing efficiency or throughput, the implementation of costly, complex methodologies is usually necessary. These include specialised material customisation, precise control over light-matter interactions, and sophisticated optical instrumentation. In this work, we introduce dual-layer two-photon lithography (DL-TPL), a new patterning approach that combines dual-layer lithography with TPL. By controlling the exposure and development of positive and negative double-layer photoresists, we achieve sub-100 nm graphics with high repeatability without the need for lithographic masks. This advancement is significant for the broader field as it can be applied to the study of two-dimensional materials and the fabrication of optical devices and semiconductor nanodevices.