Evaluation of 25-nm pitch SiO 2 /Si multilayer grating reference using CD-SEM

Abstract

We have developed a 25-nm pitch multilayer grating pattern for CD-SEM magnification calibration instead of the conventional 100-nm pitch grating reference. The 25-nm pitch grating reference was fabricated by multilayer deposition of alternative alternating SiO₂ and Si layers and then the reference chip was fabricated by substrate bonding and polishing process. Finally the 25-nm pitch grating pattern was achieved using the material-selective chemical etching of the polished cross-sectional surface. We evaluated the 25-nm pitch grating reference chip using CD-SEM. A high-contrast secondary electron image of the grating pattern was obtained under 1-kV acceleration voltage. The uniformity of the 25-nm pitch size of the grating was less than 1 nm in 3σ. The line edge roughness of the grating pattern was also less than 1 nm. Such a fine and uniform grating pattern will fulfill the requirements of a magnification calibration reference for next-generation CD-SEM.