Phase defect analysis with actinic full-field EUVL mask blank inspection
2011
We had developed an actinic full-field inspection system to detect multilayer phase-defects with dark field imaging.
Regarding the actinic inspection of native defects, the influence of the defect's surface dimension and multilayer
structure, on the intensity-signal obtained from the inspection was analyzed. Three mask blanks were inspected from
which 55 defects, observed with AFM and SEM, were classified as amplitude-defects or phase-defects. The surface
dimensions and SEVDs (sphere equivalent volume diameters) of the defects were measured with the AFM. In the case
where their SEVDs were same as of the programmed phase-defects, they were found to produce stronger intensitysignals
in comparison to the ones from the programmed phase-defects. Cross-sectional multilayer structures of two
native phase-defects were observed with TEM, and those defects formed non-conformal structures in the multilayer. This
result means that most of the native phase-defects tend to form a non-conformal structure, and can make large impact on
the wafer image in comparison to the ones from a conformal structure. Besides phase-defects, the actinic inspection also
detected amplitude-defects. Although the sensitivities of the amplitude-defects were found to be lower than those of the
phase-defects, an amplitude-defect higher than 30 nm could be detected with high probability.
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