4 August 1993 Focus vernier for optical lithography
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Abstract
As the depth of focus of optical steppers grows smaller, it becomes more important to determine the position of best focus accurately and quickly. This paper describes the use of phase-shifted mask technology to form a focus vernier: a phase pattern on the stepper reticle which, when imaged in resist, can give both the magnitude and the direction of the focus error. In this, the focus vernier structure is analogous to 3overlay verniers. Thus the determination of focus error can be treated as an alignment problem in the z-axis. This technique is an improvement on previous schemes for the determination of best focus from resist images as it can indicate both the magnitude of the error and its direction in a single exposure.
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William H. Arnold, William H. Arnold, Eytan Barouch, Eytan Barouch, Uwe Hollerbach, Uwe Hollerbach, Steven A. Orszag, Steven A. Orszag, } "Focus vernier for optical lithography", Proc. SPIE 1926, Integrated Circuit Metrology, Inspection, and Process Control VII, (4 August 1993); doi: 10.1117/12.148958; https://doi.org/10.1117/12.148958
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