Actinic critical dimension measurement of contaminated extreme ultraviolet mask using coherent scattering microscopy

Abstract

The authors evaluated the feasibility of using coherent scattering microscopy (CSM) as an actinic metrology tool by employing it to determine the critical dimension (CD) and normalized image log-slope (NILS) values of contaminated extreme ultraviolet (EUV) masks. CSM was as effective as CD scanning electron microscopy (CD-SEM) in measuring the CD values of clean EUV masks in the case of vertical patterns (nonshadowing effect); however, only the CSM could detect shadowing effect for horizontal patterns resulting in smaller clear mask CD values. Owing to weak interaction between the low-density contaminant layer and EUV radiation, the CSM-based CD measurements were not as affected by contamination as were those made using CD-SEM. Furthermore, CSM could be used to determine the NILS values under illumination conditions corresponding to a high-volume manufacturing tool.