Abstract
The inspection sensitivity of a patterned extreme ultraviolet mask with B4C-capped multilayer (ML) was investigated using a simulated projection electron microscope (PEM) image. Extrusion and intrusion defects with 16-nm size were detected with their intensity of >10 times the standard deviation of the background level on a half-pitch 64-nm line-and-space pattern. The defect detection sensitivity in this case was higher than that of a Ru-capped ML sample and has a potential to meet the requirement for beyond 16-nm node generation from the standpoint of patterned mask inspection using the PEM technique. These results indicate that the B4C capping layer, besides its good durability, has an advantage for high sensitivity of patterned mask inspection. The optimal condition of the incident beam energy was found to be 500 and 1,000 eV for the samples of B4C-capped ML and B4C-buffered Ru-capped ML, respectively. The sensitivity of defect detection was strongly affected by the difference of secondary electron emission coefficients (SEECs) between the absorber layer and capping layer. However, the small incident beam energy was found to be preferable when the SEEC difference was relatively high.
Highlights
Extreme ultraviolet lithography (EUVL) is a promising technique for post-2X nm generation lithography
The secondary electron emission coefficients (SEECs) of B4C-capped ML remain almost constant as the incident electron beam current increases, and this effect is similar to the Ru-capped ML
It was found that the sensitivity of defect detection using B4C-capped ML has a potential to meet the requirements for beyond 16-nm node generation from the standpoint of patterned mask inspection using projection electron microscope (PEM) technique
Summary
Extreme ultraviolet lithography (EUVL) is a promising technique for post-2X nm generation lithography. We have been developing a projection electron microscope (PEM)[2,3] for pattern inspection and have evaluated its feasibility.[4,5,6,7] In order to accelerate this development program, the optimal inspection condition was investigated by using a computer simulation.[8,9,10,11] We already reported that 16-nm-sized defect on hp 64-nm mask pattern was detectable with a 10-times higher signal intensity than that of the standard deviation of the background intensity level by using the PEM technique when the Ru capped multilayer (ML) was used in EUV mask,[9] and the simulated detectability was found to be in good agreement with experimental results.[7] It was found that the sensitivity of defect detection was predictable by measuring the secondary electron yield curves of a Ta-based absorber layer and Ru-capped ML.
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