Alignment correction prio to image sampling in inspection systems
a technology of alignment correction and image sampling, applied in image data processing, instruments, material analysis, etc., can solve the problems of limited sensitivity, errors in determining the intensities of resulting pixels,
Inactive Publication Date: 2008-12-11
KLA INSTR CORP
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Benefits of technology
The present invention is a method and apparatus for inspecting a wafer with dies on it. The method involves obtaining the electronic image of two dies and aligning them by adjusting their positions. The aligned images are then compared to detect any defects on one of the dies. The technical effect of this invention is to provide a more accurate and efficient way to inspect wafers with dies for defects.
Problems solved by technology
However, the Specht method had the shortcoming that in re-registering (also known as resampling) the two images with respect to each other, interpolation of the scanned image was used, which in turn introduced errors in determining the intensities of the resulting pixels.
These errors limited sensitivity (the smallest detectable defect).
Method used
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[0016]The key to the present invention is the use of the same sampling points for both images, or the image of the die being viewed and the die equivalent in the data base, to be compared as will be seen from the following discussion.
[0017]FIGS. 3a and 3b illustrate the typical serpentine scanning technique for multiple patterns and for a single pattern, respectively. In FIG. 3a wafer 14 is scanned in a serpentine path 31, sweeping out several dies 33, 35 and 37 in die-to-die inspection, and in FIG. 3b only a single die is scanned in serpentine path 31′ when die-to-database inspection is employed. Each sweep of the path is designated a swath. A typical swath may have a height of 500 to 2,000 pixels and may have a length of 500,000 pixels.
[0018]FIG. 1 illustrates two identical forms 20 and 30 superimposed on a grid that represents the boundaries of pixels 10 as defined by the inspection system of the present invention. The nominal sampling point of each pixel is the center of that pi...
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Abstract
A method and apparatus, and variations of each, for inspecting a wafer defining at least one die thereon is disclosed. The present invention first obtains the electronic image equivalent of two die, and then determines the x and y offset between those electronic images. Prior to inspection for defects, those two electronic images are aligned by adjusting the x and y positions of one electronic image of one die with respect to the electronic image of the other die. Once that is accomplished, the those electronic images are compared to detect any defects that may exist on one of the die.
Description
FIELD OF THE INVENTION [0001]The present invention is related to sub-pixel image alignment in wafer inspection machines, particularly to the alignment of images both prior to and subsequent to scanning. Two alternate methods are taught, one for laser scanning and the other for scanning with a linear array.BACKGROUND OF THE INVENTION [0002]It is well known in the wafer inspection art that when two similar images are to be compared, sub-pixel alignment is often necessary to obtain the degree of accuracy that is desired. Traditionally that alignment was accomplished by digitally interpolating the image after scanning.[0003]The most frequently used method for automatic inspection of photomasks or patterned semiconductor wafers utilizes comparison to detect defects. Typically, two supposedly identical patterns are compared by scanning and digitizing the images. The digitized images are then compared in high speed digital logic, or an image is compared with data stored in the CADS (Comput...
Claims
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IPC IPC(8): G06K9/00G01N21/95G01N21/956G06T7/00H04N7/18
CPCG01N21/9501G01N21/95607G06T7/001G06T2207/30148
Inventor YOUNG, SCOTT A.KROEZE, ROGERCHADWICK, CURT H.SZABO, NICHOLASDOUGLAS, KENT E.BABIAN, FRED E.
Owner KLA INSTR CORP