JPS62120039A - Image processor - Google Patents

Abstract

PURPOSE:To discriminate a small defect of a work by comparing the circular- arc of a wafer with a radius of a true circle reversely calculated from the area of the two-dimensional profile of the wafer, and comparing the chord of the wafer with a linear line calculated from the least square method. CONSTITUTION:A computer first writes a video signal in an image memory 15 to display the profile 13A of a wafer 12 on a display unit 18, counts the picture elements on the wafer 12 to calculate the area S of the profile of the wafer 12 and a histogram, calculates the position (GX, GY) of the centroid of the profile of the wafer 12, measures the distance to the outer edge of the profile, and detects the minimum of the distance. It then obtains dot positions P1-P5 of the suitable number near the minimum portion to obtain a formula y=ax+b for approximating the linear line corresponding to the chord of the profile of the wafer 12 by the least square method. Then, it compares the circle of a radius (r) with the position (SX, SY) calculated from the centroid position, y=ax+b, d as a center with the circular arc of the outer edge of the profile along the circumference to obtain the displacement. It also compares the linear line of the linear approximate equation y=ax+b wit the chord of the outer edge of the profile to obtain the displacement.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Field of Application) The present invention relates to an image processing apparatus for detecting notch damage in an object to be detected (hereinafter referred to as a workpiece) such as a wafer.

(Prior Art) A method for detecting defects (missing) in the external shape of a wafer is carried out by visually determining defects in the external shape of the wafer based only on the area of the wafer.

(Problems to be Solved by the Invention) In the conventional method described above, defects in the external shape of the wafer are visually determined based only on the area of the wafer, and therefore small defects in the wafer cannot be determined. For example, the tolerance of radius r is 〇mm−0,
In the case of a 5-inch wafer with a diameter of 5 mm, the area difference within the tolerance is πr”?Cbi' =?C((127mnzo2)
2 (127mm/2-0.5mm)” = 2cm+
"2 cm" = 14 x 14 mm or less cannot be determined. This also applies when attempting to detect missing outlines of workpieces other than wafers.

(Means for Solving the Problems) As shown in FIG. 1, the present invention includes means 1 for calculating the area and center of gravity of an image of a workpiece, and means for measuring the radial distance from the center of gravity to the outer edge of the image of the workpiece. 2, a means 3 for calculating a linear equation of a portion corresponding to the chord part of the workpiece from an image near the shortest distance of the radial distance, and an appropriate number of dot positions around the outer edge; means 4 for calculating the center of a circle including the arc portion of the workpiece by shifting the center of gravity by an appropriate distance; means 5 for calculating the radius of the circle including the arc portion from the area of the image of the work; and the center of the circle. and a means 6 for comparing the arc portion based on the radius and the chord based on the linear equation and the outer edge of the image of the workpiece.

(Function) The area and center of gravity of the image of the workpiece are calculated by means 1,
The radial distance from the center of gravity to the outer edge of the image of the workpiece is measured by means 2, and the linear equation of the part corresponding to the chord part of the workpiece is calculated from the position of an appropriate number of dots on the outer edge of the image near the shortest radial distance. 3. Means 5 calculates the radius of a circle including the circular arc portion of the workpiece on a perpendicular line drawn from the center of gravity to the straight line, shifted by an appropriate interval from the center of gravity, and means 6 calculates the circular arc portion based on the center and radius of the circle and the straight line. The string according to the formula and the image outer edge of the workpiece are compared.

(Example) FIG. 2 shows an embodiment of the invention.

In this embodiment, the two-dimensional outer shape (planar shape) of the wafer is a partially cut-off circular shape formed by the chord part and the circular arc part obtained by cutting a part of the circle by the chord. Missing wafers are detected by comparing the radius with a perfect circle calculated from the area of the two-dimensional outer shape and by comparing the chord part of the wafer with a straight line calculated by the least squares method.

The video camera 11 images the wafer 12 from above and outputs a video signal to the processing circuit 13, and the processing circuit 13 converts the video signal from the video camera 11 into a binarization circuit 14.
It is binarized by The synchronization separation timing generation circuit 15 separates a synchronization signal from the video signal from the video camera 11, generates a data acquisition timing signal using this synchronization signal, and uses this timing signal to convert the video signal from the binarization circuit 14 into an image. is written to memory 16. The synchronization generation memory readout circuit 17 generates a synchronization signal and reads the cathode ray tube (
CRT) Data is read from the image memory 16 at a timing that can be displayed on the display device 18, and this data is sent to the display device 18 to be displayed. central processing unit (CPU
) 19 and a memory 20 are connected by an internal bus 21 and constitute a microcomputer, and the memory 20 is composed of a processing program memory, a histogram creation memory, and the like.

FIG. 3 shows the processing flow of the computer and an explanatory diagram thereof.The computer first writes the video signal from the binarization circuit 14 into the image memory 16, and
The two-dimensional outline 12A of the wafer 12 is shown in FIG.
), count the pixels of the wafer 12 (pixels within the two-dimensional outline of the wafer 12) from the video signal in the one-image bridge memory 16, and calculate the area S of the outline of the wafer 12.
and calculate the histogram. As shown in Figure 3 (b2), this histogram is X.

■The coordinates are determined on the orthogonal X and Y axes, and from these histograms the position of the center of gravity of the outer shape of the wafer 12 (
GX, GY). Next, the outer edge of the wafer 12 is determined using the video signal in the 1-image memo January 6, and the center of gravity position (GX,
GV) to the outer edge of the wafer 12 as the entire circumference of the center of gravity (GX, GY) (0' to 360')
and find the minimum of this distance.

Then, as shown in FIG. 3 (b5), an appropriate number of dots are located before and after this minimum part, that is, near the position closest to the center of gravity (GX, G'/) on the outer edge of the wafer 12. Fixed number of dots (pixels) position P1~
Determine P5 and use the least squares method to calculate wafer 12.
The formula for approximating the straight line corresponding to the chord part of the outer shape y =ax+
Find b. Here it is. Next, as shown in Fig. 3 (b6), the center of gravity position (GX) is determined.

Calculate the position @ (SX, SY) moved by a certain distance d in the extension direction of the perpendicular line drawn from G"/) to the above straight line from the center of gravity position (GX, GY), y = ax + b, d, As shown in figure (b7), this degree [(SX, SY
) and the circular arc portion of the outer edge of the outer shape are compared along the circumference to determine the amount of deviation. here 12
Let O5 be the difference between the area S of and the area of a circle with radius r, then α
=0 to O5. Next, the straight line based on the linear approximation formula y=ax+b is compared with the chord part of the outer edge of the above-mentioned outer shape to find the amount of deviation. And these deviation amounts (arc part 1 of wafer 12
The chord part and the above circle for it.

The amount of deviation from the straight line) is determined to be within a reference value, and from this, it is determined whether two adjacent dots on the outer edge of the wafer 12 are within twice the regular dot spacing, and the result is Display it on a display device.

Note that the present invention can be applied not only to wafers but also to the case of detecting notch damage in a partially cut circular object that has been cut linearly, in the same manner as in the above embodiment.

(Effects of the Invention) As described above, according to the present invention, the image and the center of gravity of the image of the workpiece are calculated, the radial distance from the center of gravity to the outer edge of the image of the workpiece is measured, and the shortest distance of this radial distance is calculated. Calculate the linear equation of a straight line corresponding to the chord part of the workpiece from the positions of an appropriate number of dots on the outer edge of the nearby image, and include the circular arc part of the workpiece by shifting an appropriate distance from the center of gravity on a perpendicular line drawn from the center of gravity to the straight line. Calculate the center of the circle, calculate the radius of the circle including the circular arc part from the area of the image of the workpiece, and compare the arc based on the center and radius of this circle, the chord according to the linear equation above, and the outer edge of the image of the workpiece. , it becomes possible to identify small defects in the workpiece.

Furthermore, if the external proportions of wafers are almost the same, such as a 4-inch wafer and a 5-inch wafer, they can be inspected with the same equipment without any changes, and no matter what direction the workpiece is placed (workpiece ) can be inspected for notch damage even when set in any direction.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing the configuration of the present invention, FIG. 2 is a block diagram showing an embodiment of the invention, and FIG. 3 is a flowchart 1 and an explanatory diagram showing the processing flow of the embodiment. 1... Area and center of gravity calculation means, 2... Radial distance measurement means, 3... Linear formula calculation means, 4...
Center calculation means, 5... Radius calculation means, 6... Comparison means. 1st Special 2 田）Give ℃σ (αJn ■ 3 cut (α2)

Claims (1)

[Claims] An image processing device for detecting notch damage in a partially cut-off circular-shaped detected object formed by a circular arc portion obtained by cutting out a part of a circle by a chord, and a chord portion, the area and area of the image of the detected object being means for calculating the center of gravity; means for measuring the radial distance from the center of gravity to the outer edge of the image of the detected object; means for calculating a linear equation of a portion corresponding to the detected object; means for calculating the center of a circle including the circular arc portion by shifting an appropriate distance from the center of gravity on a perpendicular line drawn from the center of gravity to the straight line; A means for calculating the radius of a circle including the arc part from the area of the image, and a means for calculating the radius of the circle including the arc part of the image of the object to be detected using the above means. An image processing device comprising means for comparing an arc based on a radius of a circle including an arc portion and a chord based on the linear equation with an outer edge of the image of the detected object.