Apparatus and method for detecting defects and dust on a patterned surface
AssigneeRCA Corporation
InventorsEdgar F. Steigmeier, Heinrich Auderset
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Abstract
Apparatus for detecting defects and dust on patterned surfaces, such as patterned wafers, or grooved video disks, utilizes a scanning laser that provides light scattered by defects and dust. The scattered light is detected substantially free of diffracted beams from the pattern by a mask having apertures arranged to pass to the detector only scattered light and to block diffracted light and specular reflections.
Claims8
In an apparatus of the type for optically detecting microscopic defects in a certain specularly reflecting surface of a given object, said surface having at least on a portion thereof a diffraction grating pattern or at least some elements of a diffraction grating pattern capable of diffracting said beam of light into diffracted beams of various orders, said apparatus comprising first means for scanning said reflecting surface with an incident beam of light that illuminates a relatively small spot area of said entire reflecting surface area, which spot area is large relative to the area of any microscopic defect, the incident beam of light being directed to said surface such that a substantial amount of light scattered from the surface illuminated by the incident beam of light is detected substantially independently of light specularly reflected from the same surface, and a second means for varying the threshold of detection of the scattered light, the improvement characterized by:
- means comprising a disc member positioned in said apparatus between said surface and said detector and having a central aperture with a diameter sufficient to pass a substantial amount of said scattered light, the incident beam of light being directed to said surface at an angle such that diffracted beams of low diffraction orders do not pass through said central aperture.
A method for optically detecting dust and defects on an object surface having surface portions with diffraction grating patterns or at least some elements of a diffraction grating pattern, comprising the steps of:
- scanning said object surface with a beam of incident light having a given spot size, said beam being scanned at an oblique angle to said surface such that diffracted beams from said diffraction grating pattern are spread with lower order diffracted beams being more widely spaced from each other than the higher order diffracted beams and such that scattered light is confined to a cone between a higher order diffracted beam and the incident beam;
- positioning a detector to detect a substantial amount of light scattered from said object surface illuminated by said scanning beam substantially independent of light specularly reflected from the same surface;
- and
- positioning an opaque disc having a central aperture to pass scattered light to said detector and to block diffracted light beams from said detector.
Dependencies are inferred from the claim text.