Actual defect observation results of an extreme-ultraviolet blank mask by coherent diffraction imaging

Extreme-ultraviolet (EUV) lithography poses a number of challenges, one of which is the production of a defect-free mask. To observe the defects on an EUV mask in a quantitative phase image, we have developed a microcoherent EUV scatterometry microscope. The intensity and phase images of the defects are reconstructed using ptychography. We observe four actual defects on an EUV blank mask using the microscope. The reconstructed shapes of the actual defects correspond well to those measured by atomic force microscopy (AFM). Our microscope should therefore function as an essential review tool in characterizing defects.