EUV scattering from carbon nanotube pellicles: measurement and control

Background: EUV lithography has been introduced for semiconductor fabrication, which makes maximizing yield and throughput increasingly important. One key component is the use of a high-transmission pellicle to keep particles out of the focal plane and thereby minimize their impact on imaging. Imec initiated the development of a promising pellicle approach based on a network of carbon nanotubes (CNT), which has the advantage of many tunable structural parameters to form a pellicle membrane. A balance between membrane robustness and particle nonpermeability on one side and low EUV absorption and membrane scattering on the other must be found. The membrane scatter is important for EUV flare effects during wafer printing. Aim: The experimental measurement of the flare must be determined as a function of the tunable CNT structural parameters. However, this measurement can be very challenging for the low-flare requirements involved. Approach: The EUV scatter measurements on CNT-based pellicle membranes have been performed and optimized in a stand-alone irradiation setup at RWTH Aachen University. The measurement results were compared to flare simulations using a CNT cylinder model, which is used to improve the experimental measurements. Results: With this approach, the flare of pellicles with different CNT structures and network parameters are investigated, as well as CNT pellicles that incorporate protective coatings. Conclusion: The proposed flare measurement procedure can be used to test for acceptable scattering levels for EUV imaging applications.