3 September 1999 Asymmetric alignment mark compensation
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Metal deposition equipment typically sputter more from the center of the target than the edge. Features on the wafer can cause a shadowing effect where the metal accumulates on the surfaces that are more incident. This will result in an apparent image shift if viewed from the top. The misplacement will be minimized near the center of the wafer and will be worse toward the edge. Since the actual position of the alignment mark is not visible, only the misplaced image as viewed from the metal covering the mark, direct inline alignment measurement is not possible with optical or SEM methods. Cross sections show that the misplacement is linear and symmetric about the wafer center and takes the form of a scaling misalignment. When overlay is measured on a wafer using traditional means, the scaling correction is added mathematically to the data to compensate for the inability of the tool to measure the actual alignment. Using this technique, standard overlay tools can be used to measure alignment on opaque films.
© (1999) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.
John D. Rose, John D. Rose, Alejandro Velez, Alejandro Velez, Shephen Berger, Shephen Berger, "Asymmetric alignment mark compensation", Proc. SPIE 3882, Process, Equipment, and Materials Control in Integrated Circuit Manufacturing V, (3 September 1999); doi: 10.1117/12.361295; https://doi.org/10.1117/12.361295

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