13 March 2015 Mitigation of image contrast loss due to mask-side non-telecentricity in an EUV scanner
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Abstract
Due to the use of reflective optics in extreme-ultraviolet lithography (EUVL), the chief ray angle of incidence at the object (mask) side (CRAO) cannot be zero. If the conventional resolution enhancement technique (RET) of off-axis illumination (OAI) is used, such mask-side non-telecentricity degrades aerial image contrast partly because of asymmetry (w.r.t. the mask) of the two beams in an incident beam pair and partly because of asymmetry (w.r.t. the mask) of the two diffraction orders of either incident beam. The former leads to intensity imbalance of the two incident beams (after leaving the mask) and the latter leads to amplitude and phase imbalance of the two diffraction orders of either incident beam. Solutions proposed previously only alleviate the former and have little help for the latter. In this paper, we introduce n=1 absorber to eliminate the phase imbalance so that the transverse shift between the two aerial images formed by the two incident beams can be minimized and the contrast of the final aerial image (by superposition of the two) can be restored.
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Chih-Tsung Shih, Chih-Tsung Shih, Shinn-Sheng Yu, Shinn-Sheng Yu, Yen-Cheng Lu, Yen-Cheng Lu, Chia-Chun Chung, Chia-Chun Chung, Jack J. H. Chen, Jack J. H. Chen, Anthony Yen, Anthony Yen, } "Mitigation of image contrast loss due to mask-side non-telecentricity in an EUV scanner ", Proc. SPIE 9422, Extreme Ultraviolet (EUV) Lithography VI, 94220Y (13 March 2015); doi: 10.1117/12.2085092; https://doi.org/10.1117/12.2085092
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