Photomask inspection by real time diffraction pattern analysis

Details Photomask inspection by real time diffraction pattern analysis Photomask inspection by real time diffraction pattern analysis

G - Physics

01

B

88/0.11, 340/124

G01B 11/00 (2006.01) G01B 9/02 (2006.01) G01N 21/956 (2006.01)

Patent

CA 1038948

ABSTRACT A focused beam of laser light producing a spot smaller than the minimum size of any valid feature of the photomask pattern is swept in a raster over the pattern being inspected. The light transmitted and diffracted by the locally illuminated pattern is collected and presented as a stationary but time-varying diffraction pattern to a detector array. The electrical output signals from the detectors are processed to distinguish diffraction patterns which are produced by edges of valid features from patterns produced by edges of defects. This photodetector analysis may involve several types of photodetector arrangements and may further involve analog, digital or hybrid computers.

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