Full frame thermal pump probe technique for detecting subsurface defects
First Claim
1. A method of identifying a defect in a substrate, the method comprising:
- imaging an area of the substrate with and without application of heat, to obtain a hot image and a cold image respectively;
comparing at least a portion of the hot image with a corresponding portion of the cold image; and
providing an indication about a suspected defect in response to the comparison.
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Accused Products
Abstract
An area of a substrate is imaged with and without heating, to obtain a hot image and a cold image respectively. The hot and cold images are compared with one another to identify one or more locations as being defective, e.g. if the result of comparison at one location differs significantly relative to other locations. The comparison results in all locations form a differential image, and in several embodiments a number of differential images are obtained by repeatedly heating, imaging and comparing. In such embodiments, multiple differential images are averaged at each location, to improve the signal to noise ratio. Pump and probe lasers may be used for heating and for illumination respectively, or alternatively a single laser may be employed to generate both pump and probe beams.
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Citations
46 Claims
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1. A method of identifying a defect in a substrate, the method comprising:
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imaging an area of the substrate with and without application of heat, to obtain a hot image and a cold image respectively;
comparing at least a portion of the hot image with a corresponding portion of the cold image; and
providing an indication about a suspected defect in response to the comparison. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24)
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25. A method of identifying a defect in a substrate, the method comprising:
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heating an area of said substrate with a heating beam;
imaging said area while heat is dissipating therefrom, thereby to obtain a hot image;
imaging said area either prior to said heating or after a majority of said heat is dissipated, thereby to obtain a cold image; and
comparing the hot image with the cold image to obtain a differential image;
repeating said heating, said imaging and said comparing; and
averaging results of said comparing at each location across all differential images, to obtain an averaged differential image; and
identifying a location as having said defect if a value in the averaged differential image at said location differs significantly relative to corresponding values at other locations. - View Dependent Claims (26)
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27. An apparatus for identifying a defect in a substrate, the apparatus comprising:
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a heating source, for heating an area of the substrate;
an illumination source, for illuminating the area being heated by the heating source;
a plurality of sensors, for obtaining a hot image and a cold image respectively of the area; and
a processor, for comparing at least a portion of the hot image with a corresponding portion of the cold image, and providing an indication about a suspected defect in response to the comparison. - View Dependent Claims (28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38)
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39. An apparatus for identifying a defect in a substrate, the apparatus comprising:
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a first source of electromagnetic radiation;
a second source of electromagnetic radiation, the second source being located relative to the first source to illuminate an area of the substrate to be illuminated by said first source;
a plurality of photodetectors sensitive to electromagnetic radiation from the second source; and
a switching circuit having a first line connected to said first source, and a second line connected to said plurality of sensors;
wherein the switching circuit supplies a first control signal on the first line to automatically turn on and off said first source at a first frequency;
wherein the switching circuit a second control signal on the second line to turn on and off the photodetectors at a second frequency, the second frequency being twice the first frequency;
wherein a first phase difference between turning on of the first source and a first turning on of the photodetectors immediately thereafter, is sufficiently small to ensure that the photodetectors capture a first image of said area while heat is dissipating therefrom; and
wherein a second phase difference between turning on of the first source and a second turning on of the photodetectors immediately after the first turning on is sufficiently large to ensure that said photodetectors capture a second image of said area after a majority of said heat is dissipated therefrom. - View Dependent Claims (40, 41, 42, 43, 44, 45, 46)
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Specification