EUV masks under exposure: practical considerations

This paper focuses on the practical side of EUV mask metrology and use. Mask metrics such as film thickness, material properties, feature profile, critical feature size, line edge/width roughness (LER/LWR) and defect levels are measured and monitored on the mask. Any variability in mask properties will be transferred to wafer print results. EUV masks have no pellicle and will be cleaned between exposures to extend use. This additional processing creates new opportunity for modifications to the mask after qualification. This paper quantifies mask variability and the induced change to printed wafer critical dimension (CD). The results are compared to the 56nm wafer pitch targets for CD and LER. This EUV-specific effort is required to determine how close EUV masks are to meeting manufacturing requirements and whether there are areas of development that require additional focus from the industry.