Shedding light on EUV mask inspection

EUV defect detectability is evaluated both through simulation and by conventional mask inspection tools at various wavelengths (13.5, 193, 257, 365, 488 and 532 nm). The simulations reveal that longer wavelength light penetrates deeper into the multilayer than shorter wavelength light, however this additional penetration does not necessarily provide an advantage over shorter wavelengths for detecting defects. Interestingly, for both blank and patterned mask inspections, each wavelength detected unique defects not seen at other wavelengths. In addition, it was confirmed that some of the defects that are detected only by longer wavelengths are printable. This study suggests that a combination of wavelengths may be the most comprehensive approach to finding printable defects as long as actinic inspection is not available.