Apparatus for inspecting defects in a periodic pattern
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United States of America Patent
Stats
-
May 18, 1982
Grant Date -
N/A
app pub date -
Mar 14, 1980
filing date -
Mar 19, 1979
priority date (Note) -
Expired
status (Latency Note)
Importance
Abstract
An apparatus for inspecting a defect in a periodic pattern on an object is provided with a laser device for projecting a laser beam toward the object. A mechanism further included in the defect inspecting apparatus rotates the object in a plane orthogonal to an optical path of the laser beam while moving in the same plane. A spatial band-pass filter is located at the backward focal plane of a lens for Fourier-transforming the laser beam including the information of the periodic pattern and a defect, the laser beam coming from the object. The band-pass filter has a spot-like area for blocking the zeroth order diffraction light transmitted through the periodic pattern a peripheral light blocking area for blocking the first and higher order diffracted light beams, and a ring-like light transmission area permitting the light beam component including the information of a defect to pass therethrough, the light transmission area being located between the spot-like area and the peripheral area. A photo-electric converter for picking up the light beam component including the defect information transmitted through the filter is located on an image forming plane where an image of the object is formed by a lens.
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