26 July 1999 Study of the impact to image quality and overlay by different pupil fills in a DUV scanner via overlay metrology
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Abstract
The impact to image quality and overlay by using different pupil fills in a DUV scanner of 0.6 NA studied by using overlay metrology. primary optical aberrations such as spherical aberration, field curvature, astigmatism were studied using the Phase Shift Focus (PSF) monitor, while coma was studied by using coma monitor structure. Distortion was studied by using telecentricity and overlay-through- focus test. It was found that different illumination mode contributes to different extent of these aberrations, confirming that illumination aberrations couple with projection lens aberrations to affect image quality. We also observed partial coherence variation across field as well the orientational dependency of partial coherence. Coma was found to introduce a second order curvature in the displacement curve and it affects distortion by the effect of field magnification error, as indicated by the telecentricity and overlay-through-focus test. It is concluded that optical aberration is the worst for low sigma illumination however, it provides the least variation in partial coherence across field. Off Axis Illumination also impacts distortion pattern and overlay results, so any application using mixed pupil fills needs to be addressed carefully, accuracy of the PSF measurement has to be improved to apply this method to augment the advantage of speed and convenience in collecting a lot of across field data. It is also found that PSF monitor is not applicable for quadrupole illumination.
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Kafai Lai, Kafai Lai, Pedro Tasaico, Pedro Tasaico, Theodore G. Doros, Theodore G. Doros, Dan W. Holladay, Dan W. Holladay, } "Study of the impact to image quality and overlay by different pupil fills in a DUV scanner via overlay metrology", Proc. SPIE 3679, Optical Microlithography XII, (26 July 1999); doi: 10.1117/12.354394; https://doi.org/10.1117/12.354394
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