Abstract
The authors evaluated the feasibility of using coherent scattering microscopy (CSM) as an actinic metrology tool by employing it to determine the critical dimension (CD) and normalized image log-slope (NILS) values of contaminated extreme ultraviolet (EUV) masks. CSM was as effective as CD scanning electron microscopy (CD-SEM) in measuring the CD values of clean EUV masks in the case of vertical patterns (nonshadowing effect); however, only the CSM could detect shadowing effect for horizontal patterns resulting in smaller clear mask CD values. Owing to weak interaction between the low-density contaminant layer and EUV radiation, the CSM-based CD measurements were not as affected by contamination as were those made using CD-SEM. Furthermore, CSM could be used to determine the NILS values under illumination conditions corresponding to a high-volume manufacturing tool.
Highlights
Critical dimension scanning electron microscopy (CDSEM) is widely used as a metrology tool for optical masks
coherent scattering microscopy (CSM) was as effective as critical dimension (CD) scanning electron microscopy (CD-SEM) in measuring the CD values of clean extreme ultraviolet (EUV) masks in the case of vertical patterns; only the CSM could detect shadowing effect for horizontal patterns resulting in smaller clear mask CD values
In order to investigate the feasibility of using CSM as a metrology tool, we compared the reconstructed CSM images and the CD-SEM images of uncontaminated EUV masks with line and space (L/S) patterns with half pitches of 88, 100, and 128 nm
Summary
Critical dimension scanning electron microscopy (CDSEM) is widely used as a metrology tool for optical masks. There is no appropriate tool to investigate the effects of mask contamination on the imaging properties. Coherent scattering microscopy (CSM) is an actinic inspection and metrology tool that can obtain an aerial image of EUV masks using reverse Fourier transform of the diffraction pattern in conjunction with a phase retrieval algorithm.. The excited electrons of the Ne gas generated high-order harmonic waves that contained a 59th harmonic with a wavelength of 13.5 nm.. The excited electrons of the Ne gas generated high-order harmonic waves that contained a 59th harmonic with a wavelength of 13.5 nm.17–22 This harmonic was filtered by an EUV mirror and Zr spectral-purity filters. The extracted EUV radiation exhibited good spatial and temporal coherence (
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