Optics: measuring and testing – Inspection of flaws or impurities – Having predetermined light transmission regions
Patent
1985-03-18
1987-07-21
Willis, Davis L.
Optics: measuring and testing
Inspection of flaws or impurities
Having predetermined light transmission regions
250 63, 250572, 356239, G01N 288
Patent
active
046814426
ABSTRACT:
This teaches a method and device for testing of the surface of a transparent object such as a photolithographic mask in which respective recordings with darkfield reflection illumination and darkfield transmission illumination is made, and the intensities measured are compared to form a different image, in which defects are characterized by high local levels of light intensity. Both recordings can be generated in a point-by-point mode if the surface is scanned by a focussed laser beam. In another embodiment, two recordings of the entire surface are digitized, and examined arithmetically for local image differences. Surfaces of opaque bodies can also be examined with the difference image of two darkfield reflection recordings made at different angles of illumination.
REFERENCES:
patent: 4468120 (1984-08-01), Tanimoto et al.
patent: 4541715 (1985-09-01), Akiyama et al.
Ross, "Optical Scanning System for Defect Detection", IBM Tech. Discl. Bull. vol. 20, No. 9, p. 3431, 2/78.
Rapa, "Inspection System for Particulate Contamination" IBM Tech. Discl. Bull. vol. 20, No. 11A, p. 4359, 4/78.
International Business Machines - Corporation
Koren Matthew W.
Thornton Francis J.
Willis Davis L.
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