Phase defect observation using an EUV microscope

Extreme ultraviolet lithography (EUVL) is being introduced as next generation lithography of 32 nm node. Defect-free mask fabrication is one of the critical issues to lead EUVL. There are two types of defects in EUVL mask: amplitude defect and phase defect. However, phase defect due to the multilayer fabrication cannot be resolved with an existing inspection tool. So, we constructed the EUV microscope for at-wavelength mask inspection which consists of Schwarzschild optics and X-ray zooming tube. Magnification of Schwarzschild optics is 30×, and X-ray zooming tube can change the magnification in the range from 10 × to 200 ×. So, the total magnification of the microscope is 300 × to 6000 ×. And the numerical aperture of Schwarzschild optics is 0.3, so, it can inspect the defect of 20 nm in size.