Method for characterizing defects on semiconductor wafers
First Claim
1. A method comprising:
- representing a three-dimensional surface, using a Cartesian coordinate system having x, y, and z axes, as a plurality of points on the surface, wherein each point is defined by an intensity value, a unique x-y coordinate, and a z coordinate specified by a z value;
collecting a first group of the points having similar z values, the first group representing a first layer of the surface;
collecting a second group of the points, each point of the second group having a z value similar to the z values of other points of the second group and dissimilar to the z values of the points of the first group, the second group representing a second layer of the surface;
determining a first error threshold for the intensity values of the first group of points; and
determining a second error threshold for the intensity values of the second group of points.
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Abstract
10A method is described for detecting and characterizing defects on a test surface of a semiconductor wafer. A three-dimensional image of the test surface is aligned and compared with a three-dimensional image of a defect-free reference surface. Intensity differences between corresponding pixels in the two images that exceed a predefined threshold value are deemed defect pixels. According to the method, the pixels of the reference image are grouped according to their respective z values (elevation) to identify different physical layers of the reference surface. Because different surface layers can have different image properties, such as reflectance and image texture, the groups of pixels are analyzed separately to determine an optimal threshold value for each of the groups, and therefore for each layer of the reference surface.
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Citations
14 Claims
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1. A method comprising:
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representing a three-dimensional surface, using a Cartesian coordinate system having x, y, and z axes, as a plurality of points on the surface, wherein each point is defined by an intensity value, a unique x-y coordinate, and a z coordinate specified by a z value; collecting a first group of the points having similar z values, the first group representing a first layer of the surface; collecting a second group of the points, each point of the second group having a z value similar to the z values of other points of the second group and dissimilar to the z values of the points of the first group, the second group representing a second layer of the surface; determining a first error threshold for the intensity values of the first group of points; and determining a second error threshold for the intensity values of the second group of points. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9)
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10. A method of locating defects on a test surface, wherein the test surface is contained within a test volume represented by a Cartesian coordinate system having x, y, and z axes describing a set of unique x-y-z coordinates, the method comprising the steps of:
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scanning the test surface in the test volume with a focused beam so that the focal point of the focused beam coincides, in turn, with each unique x-y-z coordinate within the test volume; determining, for each column of points specified by a unique x-y coordinate in the test volume, a maximum reflected intensity value of the focused beam; determining, for each column of points specified by a unique x-y coordinate in the test volume, a Z value corresponding to the maximum reflected intensity value of the focused beam; storing all the Z values to form an array of test data representing a three-dimensional image of the test surface; and comparing the array of test data with an array of reference data to identify elevational differences between the array of test data and the array of reference data. - View Dependent Claims (11, 12, 13)
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14. A defect characterization system comprising:
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a microscope configured to obtain a three-dimensional image of a surface, the image including a plurality of pixels each of which is expressed an intensity value and x, y, and z coordinates of a Cartesian coordinate system; means for collecting a first group of the pixels having similar z coordinates, the first group representing a first physical layer of the surface; means for collecting a second group of the pixels, each pixel of the second group having a z coordinate similar to the z coordinates of other pixels of the second group and dissimilar to the z coordinates of the pixels of the first group, the second group representing a second physical layer of the surface; means for determining a first error threshold for the intensity values of the first group of pixels; and means for determining a second error threshold for the intensity values of the second group of pixels.
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Specification