Through-pellicle imaging of extreme ultraviolet mask with extreme ultraviolet ptychography microscope

Background: An extreme ultraviolet (EUV) pellicle is necessary to increase the process yield even though the declining throughput is a big concern. However, an EUV metrology/inspection tool for this pellicle has not been commercialized yet. Aim: The goal of this study is to verify the pellicle/mask inspection feasibility of EUV scanning lensless imaging (ESLI) and verify the impact of contaminants on pellicles depending on their size. Approach: Through-pellicle imaging was implemented by using ESLI, which uses a high-order harmonic generation EUV source and ptychography. Optical characteristics of various sizes of Fe-contaminated EUV pellicles were evaluated to verify their impact on wafer images. Results: Large size (∼10  μm) contaminants on the pellicle were found to contribute to the final wafer pattern loss. However, small size (2 to 3  μm) contaminants on the pellicle do not have substantial impact on the wafer image. Conclusions: The defect detection capability of ESLI for pellicle and mask was confirmed. Therefore, ESLI is useful in applications like pellicle qualification and EUV mask inspection metrology.