US 4,314,763 AGranted

Defect detection system

AssigneeRCA Corporation

InventorsEdgar F. Steigmeier, Karl Knop

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Abstract

A laser beam projected through a prism in a direction normal to the surface of a circular wafer is focused into a spot area and scanned along a spiral path on this surface. The focusing means comprises a relatively large aperture lens and the prism is on the lens axis. The retroreflected specular light passes through the lens and is prevented from reaching a light detector in the image plane of the lens by the prism. When the beam illuminates a microscopic surface defect on the wafer, the light is diffracted and reflected therefrom, and the lens captures that portion of the reflected light within the solid angle subtended by the lens, and passes that portion thereof not blocked by the prism, to the light detector. The output of the detector may be employed to intensity modulate the beam of a cathode-ray tube display, the beam of which is spirally scanned in synchronism with the scanning of the light beam.

Claims13

Dependent claims

In a system for optically detecting microscopic defects in a certain specularly reflecting surface of a given object, said system comprising first means for scanning said surface with an incident beam of light that illuminates a relatively small spot area of said entire surface area, which spot area is large relative to the area of any microscopic defect, and second means for detecting substantially only non-specularly reflected light from said surface;

the improvement:
wherein said first means includes third means for directing said incident beam substantially normal to said surface, whereby substantially all said specularly reflected light is reflected in a direction substantially normal to said surface, and
wherein said second means includes a focusing device having a large aperture area relative to said spot area, said device being situated in spaced relationship with said spot area to subtend a certain solid angle disposed about a normal to said spot area, whereby substantially all reflected light within said certain solid angle may be captured by said device, and
wherein said second means further includes a photo detector located in an image plane of said device for receiving light reflected by said surface, and a spatial filter having a small aperture area relative to that of said device situated between said device and said detector in the path of said received reflected light for removing that portion thereof which is specularly reflected.

1 more element

Dependencies are inferred from the claim text.