Image analysis – Histogram processing – For setting a threshold
Patent
1980-06-23
1983-07-05
Boudreau, Leo H.
Image analysis
Histogram processing
For setting a threshold
250563, 250572, 356237, 356384, 356387, 382 41, G06K 900, G01B 1102
Patent
active
043921205
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The present invention relates to a pattern inspection system for inspecting a pattern formed on a base. The present invention is used for inspecting patterns of photo-masks which are used in the production of printed circuits.
In the prior art there is a method for inspecting patterns of photo-masks which compares a pattern to be inspected with a reference pattern by means of a microscope. This method has two limitations; (1) it is not possible for a person to measure the width of the pattern, and (2) the method requires that the two patterns can be aligned. This prior art method is disclosed in, for example, the thesis "Automated Equipment for 100% Inspection of Photomasks", by K. Levy, Solid State Technology, p. 60 to 71, May 1978.
There is another prior art method for inspecting patterns of photo-masks, in which pattern data consisting of electrical signals transduced from light scanning a pattern to be inspected are compared with reference pattern data converted from the design data of a photo-mask. This method has three limitations in that it requires a process to align the reference and scan data in, the original design data for the reference pattern must be generated and a high speed computer for converting the original design data is necessary. This prior art method is disclosed in, for example, the thesis "Automatic Mask Inspection for Registration Errors and Critical Dimensions", by F. G. O'Callaghan et al, Symposium of Society of Photographic Scientists and Engineers, February 1975.
The present invention has been proposed in order to solve the problem involved in the prior art pattern inspection methods, as set forth above, and to provide a more precise and practical pattern inspection system without using reference pattern data.
A preceding invention regarding a pattern inspection system invented by some of the inventors of the present invention was disclosed in the Japanese Patent Application Laid-open No. 53-24233. This pattern inspection system includes light scanning means for scanning a photo-mask pattern being tested by a light beam, means for providing information indicating the width of the pattern in the direction of scanning by detecting the light transmitted through or reflected by the photo-mask having the pattern, and means for providing information indicating the angle of the pattern with respect to the direction of scanning by detecting the light diffracted at the edge of the pattern. In this system, the width of the pattern is measured by combining the information indicating the width of the pattern and the information indicating the angle of pattern. The present invention utilizes the technique of this preceding invention.
SUMMARY OF THE INVENTION
The present invention includes means for separately examining photo-mask patterns for defects in a plurality of directions and means for separately storing the information obtained from the examination of the patterns in a regions of the memory device corresponding to the plurality of directions, respectively.
A principal object of the present invention is to provide a correct, rapid and practical system for inspecting patterns, eliminating the process of aligning two patterns, eliminating the need for reference data and eliminating the need for a high speed computer.
Another object of the present invention is to provide a pattern inspection system to deal with various types of defects in a pattern.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a schematic diagram of a pattern inspection system in accordance with an embodiment of the present invention;
FIG. 2 illustrates the details of the light signal detecting device in the system of FIG. 1;
FIG. 3 illustrates the details of the pattern width measuring device in the system of FIG. 1;
FIG. 4 illustrates an example of a photo-mask having a pattern for which the inspection is effected in accordance with the present invention;
FIG. 5 illustrates the status of the memory of the memory device in the system of FIG. 1;
FIG. 6 is a schematic diagram of an int
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O'Callaghan et al., "Automatic Mask Inspection . . . ", Symposium of the Society of Photographic Scientists & Engineers, Feb., 1975.
Levy, "Automated Equipment for 100% Inspection of Photomasks", Solid State Technology, May, 1978, pp. 60-71. _
Nakashima et al., "Automatic Mask Pattern Inspection for Printed Circuits . . . ", Proceedings of S.P.I.E., Apr. 1979, vol. 182, pp. 38-48.
Fujihara Katsumi
Mita Kikuo
Nakakuki Tadao
Nakashima Masato
Oyama Masayuki
A. Aoki & Associates
Boudreau Leo H.
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