Investigation of the resolution limit of Talbot lithography with compact EUV exposure tools

This paper focuses on the design and fabrication of phase-shifting transmission masks tailored for high-resolution nanopatterning using a compact EUV exposure tool. The authors analyze various factors that influence the achievable resolution, aiming to push the boundaries towards the sub-10 nm range, approaching the theoretical resolution limit. The demand for high-resolution nanoscale patterns spans across diverse applications, driving the need for compact exposure tools and lithographic concepts. The developed EUV exposure tool can be operated at either 10.9 nm or 13.5 nm exposure wavelengths depending on the specific use case. This capability allows for large area nanopatterning with enhanced throughput as well as industrial resist qualification with focus on highest resolution. The utilized discharge-produced plasma (DPP) EUV source offers partially coherent radiation. For this radiation type, the (achromatic) Talbot lithography has proven to be the most effective with resolution in the sub-30 nm range and a theoretical resolution limit of less than 10 nm. To optimize the intensity distribution in the wafer plane, the authors use rigorous coupled-wave analysis (RCWA) simulations to fine-tune the material composition and geometry of the masks. Various factors influencing the achievable resolution are identified and presented. In addition to simulative optimization, the fabrication of dense periodic nanopatterns poses increasing challenges for smaller periods. In this work, the mask fabrication process is optimized to produce stable and high-resolution periodic mask patterns, leading to record resolutions for both line and contact hole periodic nanopatterns with the presented setup.