Impact of B₄C capping layer for EUV mask on the sensitivity of patterned mask inspection using projection electron microscope

Abstract

The inspection sensitivity of a patterned extreme ultraviolet (EUV) mask with B 4 C capped multilayer (ML) was investigated using a simulated projection electron microscope (PEM) image. Extrusion and intrusion defects with 16 nm in size were detected with their intensity of > 10 times the standard deviation of the background level on a half-pitch (hp) 64 nm line and space pattern. The defect detection sensitivity in this case was higher than that of 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 B 4 C 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 1000 eV for the samples of B 4 C capped ML and B 4 C 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, severely scattered electrons near the pattern edge become a source of noise and then they block the effect of large SEEC difference. Thus, the small incident beam energy was found to be preferable when the SEEC difference was relatively high.