EUV scattering from CNT pellicles: measurement and control

Abstract

EUV lithography is introduced in semiconductor fabrication processes, 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 non-permeability 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. Therefore, it is important to verify its magnitude experimentally as a function of the tunable CNT structural parameters. However, this measurement can be very challenging for low-flare requirements. In this work, the EUV scatter measurements on CNT-based pellicle membranes have been performed and optimized in a stand-alone irradiation setup at RWTH Aachen University. Membranes with different CNT structures and network parameters are investigated, as well as membranes with protective coatings. These measurements, in combination with scattering calculations and printing performance, can serve as a guideline on acceptable scattering levels for industrial applications.