Photocopying – Projection printing and copying cameras – Focus or magnification control
Reexamination Certificate
2008-03-11
2008-03-11
Nguyen, Henry Hung (Department: 2851)
Photocopying
Projection printing and copying cameras
Focus or magnification control
C355S067000
Reexamination Certificate
active
11064169
ABSTRACT:
Improved autofocusing (“AF”) methods and devices for lithography are provided. Some embodiments of the invention provide an AF system that includes one or more interferometers for measuring a distance to a wafer surface or a reticle surface. The invention includes methods and devices for calibrating the interferometer(s) according to known distances to a target. According to some embodiments of the invention, a spatial filter reduces the amount of undesired signal coming from the wafer or reticle surface. In some such embodiments, higher orders of diffracted light from the wafer or reticle multilayer surfaces are eliminated with a pinhole filter oriented to reject light that is not vertically directed. Other embodiments include a spatial filtering system that passes a selected diffraction order, e.g., the first order of diffracted light, from the target.
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Beyer & Weaver, LLP
Nguyen Henry Hung
Nikon Corporation
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