20 August 1986 Fractured Alignment Mark Technology For Wafer Steppers
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Abstract
The current generation of wafer steppers are routinely called upon to perform automatic site by site alignment to accuracies of ±0.25 microns, 3 sigma. Virtually all wafer steppers currently available use the same general strategy for site by site automatic alignment: a previously printed alignment mark present on the wafer is aligned to a corresponding geometry on the reticle by means of a detection system employing light in the UV or visible range. A large contribution to misalignment on steppers employing optical contrast for alignment mark detection often arises when alignment marks adequate for one process are used for another. Process dependent variables such as step height, substrate reflectivity, and photoresist thickness introduce inconsistencies in target polarity and target appearance to the detection system, especially for systems incorporating narrow bandwidth alignment illumination. Frequently radial related offsets are attributed to resist flow patterns over the alignment marks which are usually orthogonally or diagonally oriented.
© (1986) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.
G. A. Hungerford, D. Rector, D. Sandford, D. W. Tomes, "Fractured Alignment Mark Technology For Wafer Steppers", Proc. SPIE 0633, Optical Microlithography V, (20 August 1986); doi: 10.1117/12.963706; https://doi.org/10.1117/12.963706
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