Abstract
We have developed an actinic full-field inspection system to detect multilayer phase defect with dark field imaging. With this system, programmed phase defects on a mask blank were observed. The system can detect phase defects caused by a 1.5 nm high and 60 nm wide protrusion on a multilayer surface. Background intensity and signal to background ratio (SBR) of the observed defect images are analyzed with simulation. The background intensities were calculated with the model that it is generated by light scattered from mask surface roughness. The result indicates that the larger outer NA (numerical aperture) leads to an increase in the background intensity. In this correlation of NA with the background intensity, the calculation and experimental results correspond well. The defect images were simulated using the point spread function (PSF) of flare generated by mirror surface roughness employing Fourier technique. The SBRs of simulated defect images corresponded well with the SBRs of the observed images. These results support the calculation and simulation models are proper.
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