Observation Results of Actual Phase Defects Using Micro Coherent EUV Scatterometry Microscope

摘要

One of the critical issue of EUV lithography is fabrication of defect-free mask. The origin of the defect is a particle inside the multilayer and bump or pit on glass substrate. This type of defect is called a phase defect. If there is a phase defect, the reflection phase is disordered. As a result, the phase structure is printed as a defect on a wafer. Thus, we have developed micro coherent EUV scatterometry microscope (we called micro-CSM) for phase defect characterization. Micro-CSM records scattering signal from a defect directly exposed by focused coherent EUV having a spot size of Φl40-nm in diameter. An off-axis-type Fresnel zone plate was employed as a focusing optics. Phase distribution of the defect is reconstructed with the scattering image by the coherent-diffraction-imaging method. We observed actual phase defects in this work. Actual phase defects were on a mask blanks which was the same grade of the pre-production mask of the semiconductor devices. The positions of actual phase defects have been already inspected by the actinic blank inspection tool. And, the actual phase defects have been already observed using an atomic force microscope. A purpose of this work is observation of these actual defects using micro-CSM and comparison of the results.