Long-term critical dimension measurement performance for a new mask CD-SEM, S-9380M

To realize good repeatability in CD measurements, many issues have to be addressed including system stability, sample charging and contamination, measurement conditions, and image processing. The S-9380M is a mask CD-SEM (Critical Dimension Scanning Electron Microscope) system developed for measurement and inspection of 45 nm node photomask. The S-9380M has several innovations like a newly designed optical system to minimize sample charge-up and drift effects, ultra-high resolution (3nm) imaging to enable measurements at high magnification, and an integrated ultra-violet (UV) unit for pre-treatment of the mask to rid the surface of organic contaminants. This paper presents measurements carried out using the S-9380M system, and showed that superior performance is achieved with short-term dynamic repeatability of 3σ less than 0.6 nm (for line patterns), and long-term dynamic repeatability of 3σ less than 1.0 nm without trend modification.