14 June 1999 Distinguishing dose from defocus for in-line lithography control
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Manufacturing control of a lithographic process must guarantee that the pattern features on a masking level stay within a common process window, the focus-exposure space over which all pattern tolerances are met. To do so at focus latitudes below 1 micrometers , simultaneous determination and correction of dose and defocus error is required. In-line metrology practice has been to measure a single pattern attribute, usually the dimension of the smallest feature, at each of several locations on a wafer. Since the measurement of one pattern attribute, regardless of its accuracy or precision, cannot distinguish two variables - this approach is inherently inadequate for lithography control. We demonstrate how dose and defocus can be derived from the attributes of dual-tone, optically measurable targets on product wafers. Our method is applied to the in-line control of sub-0.25 micrometers step-and-scan lithography.
© (1999) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.
Christopher P. Ausschnitt, Christopher P. Ausschnitt, "Distinguishing dose from defocus for in-line lithography control", Proc. SPIE 3677, Metrology, Inspection, and Process Control for Microlithography XIII, (14 June 1999); doi: 10.1117/12.350800; https://doi.org/10.1117/12.350800

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