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Proceedings Paper

Impact of mask blank and mirror surface roughness on actinic EUVL mask blank inspection signal
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Paper Abstract

The impact of mask blank surface roughness and mirror surface roughness on the defect inspection signal is presented. The power spectrum density (PSD) of the roughness is assumed to be inversely proportional to the square of the spatial frequency. The PSD was estimated based on the mask blank surface roughness (rms), and then the background intensity was calculated using the PSD of the spatial frequencies between the inner and outer NA. The results indicate that the larger outer NA leads to an increase in the background intensity, and that a mask blank roughness of 0.15 nm generates a background intensity of 0.15 - 0.23 %. We also analyzed the effect of the mirror surface roughness on the background intensity and on the defect signal contrast. A point spread function (PSF) of scattered light from the mirror surface was calculated using the estimated PSD, and the defect images were simulated for the inspection optics by employing Fourier technique. The degradation of defect images caused by the mirror roughness was calculated by using the convolution of the PSF with the simulated images. Based on the results, it is concluded that the roughness has a large impact on the maximum intensity of the defect signal but has little effect on the background intensity. It was also learned that the degradation rate of the defect signal contrast is approximately proportional to the square of the mirror roughness.

Paper Details

Date Published: 19 May 2008
PDF: 8 pages
Proc. SPIE 7028, Photomask and Next-Generation Lithography Mask Technology XV, 70281S (19 May 2008); doi: 10.1117/12.793070
Show Author Affiliations
Takeshi Yamane, MIRAI-Semiconductor Leading Edge Technologies, Inc. (Japan)
Toshihiko Tanaka, MIRAI-Semiconductor Leading Edge Technologies, Inc. (Japan)
Tsuneo Terasawa, MIRAI-Semiconductor Leading Edge Technologies, Inc. (Japan)
Osamu Suga, MIRAI-Semiconductor Leading Edge Technologies, Inc. (Japan)
Toshihisa Tomie, National Institute of Advanced Industrial Science and Technology (Japan)


Published in SPIE Proceedings Vol. 7028:
Photomask and Next-Generation Lithography Mask Technology XV
Toshiyuki Horiuchi, Editor(s)

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