14 June 1999 Comparison of optical, SEM, and AFM overlay measurement
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Abstract
Shrinking device geometry places increasing demands on alignment between successive processing levels. In addition to precise measurement of the overlay, accuracy with respect to the product has to be ascertained. In this study we attempt to address the accuracy of overlay measurement in 175 nm ground rule DRAM products. Optical overlay is a precise technique, however, process induced degradation of mark integrity increases the measurement uncertainty. AFM and SEM techniques are explored as alternative techniques for overlay measurement uncertainty. AFM and SEM techniques are explored as an alternative technique for overlay measurement. Comparison of box-in-box and product measurements by Optical, AFM and SEM is presented. Estimation of lens induced aberrations show that their order of magnitude becomes comparable to the total overlay budget as the resolution limits of optical lithography are reached. Lens induced aberrations manifests in the form of across field overlay variation (AFOV) and the measurement of AFOV via SEM and AFM established that the estimation of overlay on BIB structures by optical methods is insufficient in characterizing the product within the exposure field.
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V.C. Jai Prakash, V.C. Jai Prakash, Christopher J. Gould, Christopher J. Gould, } "Comparison of optical, SEM, and AFM overlay measurement", Proc. SPIE 3677, Metrology, Inspection, and Process Control for Microlithography XIII, (14 June 1999); doi: 10.1117/12.350810; https://doi.org/10.1117/12.350810
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