In this paper, we discuss the impact of various tool design perspectives on defect detection sensitivity for dark-field based EUV actinic blank inspection. We consider the impact from optical resolution (pixel size), EUV source type, and photon collection efficiency on critical defect SNR performance. The results show that as the pixel size approaches the target defect image size, defect SNR increases, and that pixel size also determines the dominant noise source in the inspection system. Moreover, the choice of the EUV source affects the optimal NA and illumination settings. For plasma-discharged sources, more photons provided by larger partial coherent illumination can improve the defect SNR, while coherent illumination is needed to get a higher defect SNR for synchrotron-based source. In the end, we show that simply increasing the photon collection efficiency by using high NA optics or increasing the source power cannot always improve the defect SNR. In a speckle noise dominated situation, larger outer NA includes more noise than defect signal, thus results in a lower SNR. The impact of source power also saturates at certain level as the system becomes speckle noise limited compared to photon noise limited.
Yow-Gwo Wang, Andy Neureuther, and Patrick Naulleau, "Impact of tool design on defect detection sensitivity for EUV actinic blank inspection," Proc. SPIE 10143, Extreme Ultraviolet (EUV) Lithography VIII, 101430M (Presented at SPIE Advanced Lithography: February 28, 2017; Published: 24 March 2017); https://doi.org/10.1117/12.2260193.
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