6 December 2004 Actinic detection and signal characterization of multilayer defects on EUV mask blanks
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Actinic (at-wavelength) inspection of EUV mask blanks using a dark-field imaging proved a high sensitivity for detecting multilayer defects through detecting programmed phase defects accurate to 70nm in width and 2nm in height without any detection of false defects. Characterization of the experimental actinic inspection tool is ongoing to find the ultimate sensitivity of this tool to define the detailed specification of a proto-type tool. In this paper, we present a detailed analysis of the defect signal intensity compared with AFM measurements taken from more than 20 programmed phase defects. This analysis proved that the signal intensity is mainly correlated with the volume of bumps whose sizes range from 2.8nm to 6.0nm in height and from 59nm to 86nm in width. The correlation suggests that the intensity variation within the group of the same design size reflects the actual variation of the defect size. Some natural defects other than programmed defects are also detected. The comparison of the defect signal and AFM analysis suggests that one of the detected defects is not a pure phase defect but more like an amplitude defect. The smallest natural defect had a surface height as low as 1.5nm, which can only be detected by lowering the detection threshold to the level with some statistically expected false defect counts. Current efforts to improve its detection capability while minimizing false defect detection are also discussed.
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Yoshihiro Tezuka, Masaaki Ito, Tsuneo Terasawa, Toshihisa Tomie, "Actinic detection and signal characterization of multilayer defects on EUV mask blanks", Proc. SPIE 5567, 24th Annual BACUS Symposium on Photomask Technology, (6 December 2004); doi: 10.1117/12.568379; https://doi.org/10.1117/12.568379

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