JP2002148210A - Method and apparatus for inspecting irregularity of periodic pattern - Google Patents

Abstract

PROBLEM TO BE SOLVED: To highly accurately inspect periodic patterns without being affected by moire fringes by inputting focused images of an object. SOLUTION: When the object W having patterns P of a narrow breadth repeatedly formed in a breadth direction is to be inspected by imaging the object under a transmission illumination, a CCD camera (imaging means) 12 is set to be in focus with its pixel array direction being agreed with the breadth direction of the patterns. A relative position between the imaging means and the object is shifted on condition that all patterns are once accommodated in a visual field of one pixel over the entire breadth. Positionally shifted object images are imaged, and positionally shifted transmittance images are formed by dividing the images by a light source image at an image processing part 14. A maximum luminance value among pixels of the same coordinate of all transmittance images is made a luminance value of the pixels to obtain a maximum value image. The object is inspected on the basis of a pattern image formed by extracting only pixels corresponding to the entire breadth of the pattern from the maximum value image.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and an apparatus for inspecting a periodic pattern, and more particularly to an area of a pattern in a product in which a pattern is periodically formed on a substrate such as an aperture grill used for a cathode ray tube of a color television. The present invention relates to a method and an apparatus for inspecting a periodic pattern, which are preferably applied when detecting a deviation or unevenness thereof.

[0002]

2. Description of the Related Art An industrial product having a periodic pattern in which a fine pattern as a unit is repeated includes an aperture grill used in a cathode ray tube of a color television. In an industrial product having such a periodic pattern, each pattern has a predetermined shape and area (size) based on a design value, and a pattern existing around the pattern has a shape corresponding to each adjacent pattern. They are arranged repeatedly with a predetermined interval between them.

[0003] The area (size) of such an individual pattern is to be always (1) always the same regardless of the location on the entire surface of the sample (entire product), or (2) depending on the location in the sample. Some are formed according to a predetermined arrangement rule, such as gradually changing (for example, increasing the area from the center to the periphery).

[0004] When such an industrial product is manufactured, it is necessary to perform the following inspection for deviation (area deviation) of the area of each pattern from the design value. (1) If even one pattern has an area deviation exceeding the limit level, it is determined as a defect. (2) In the evaluation of each pattern, even if the area deviation can be regarded as normal within the limit level, it is determined as a defect if the area deviation occurs locally in a plurality of patterns within a certain range. In the latter case, the detection of local occurrence is not limited to the individual patterns within the limit level. Means inspecting the non-uniformity (unevenness) of the area.

[0005] As a method of inspecting the above-mentioned pattern deviation or non-uniformity occurring in a pattern, there is a method in which an inspector directly looks at an object. However, with this visual inspection method, even if the same inspector performs the inspection, it is difficult to maintain the repeatability of the defect detection.
Defects of the same degree may be determined to be good or defective. Furthermore, when the inspectors are different, it is more difficult to make the quality judgment based on the same criteria.

Therefore, an automatic inspection for inputting an image of a target object and performing image processing on the input target image (product image) to determine the presence or absence of a defect is also performed. FIG. 15 schematically shows an inspection apparatus applied to such an automatic inspection, in which an inspection stage 10 having a built-in transmission light source (not shown) is mounted, and the stage 10 is mounted on the stage 10 so that the back light can be illuminated by the light source. CCD (Charge Coupled Device) that captures the target object (product) W and inputs the target image (product image)
The camera 12 processes the input product image to process the object W
Processing device 14 for inspecting patterns formed on
A camera controller 16 that adjusts the CCD camera 12 when capturing an image of the object W, a light source controller 18 that adjusts a transmission light source in the inspection stage 10,
An apparatus control unit 20 for controlling the entire apparatus including the image processing unit 14, the camera controller 16 and the light source controller 18 is provided.

When inspecting with this inspection apparatus, in order to eliminate the influence of shading in which the brightness differs depending on the location of the light source included in the product image, an image of the light source is taken without the product W, and the product image is obtained using the light source image. 2. Description of the Related Art A transmittance image is created by dividing an image, and the transmittance image is processed and inspected.

However, in the automatic inspection using the above-described apparatus, when an object is imaged with the lens of the optical system being in the just focus, the pitch of the periodic pattern and the arrangement of the light receiving elements (pixels) of the CCD camera are taken. Moire fringes due to the interference due to the difference in pitch inevitably cause defects that cannot be detected. Therefore, in order to suppress the occurrence of moiré fringes, the lens is defocused and the image is blurred.

[0009]

However, in the case where an image of an object is blurred as described above, inspection cannot be performed because unevenness having a small area and unevenness having a small difference in shading cannot be captured in an image. There is another problem.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned conventional problems. An image of an object is taken with a lens of an optical system being just focused, and a periodic pattern is obtained without being affected by moire fringes. It is an object of the present invention to provide a method and an apparatus for inspecting unevenness of a periodic pattern, which can inspect a pattern with high accuracy.

[0011]

SUMMARY OF THE INVENTION According to the present invention, an object in which a narrow pattern is repeatedly formed with the width direction formed between the patterns is imaged under reflected illumination by imaging means, In the periodic pattern unevenness inspection method for inspecting the pattern by image processing the obtained image,
The imaging unit is arranged so that its pixel column direction and the direction in which the object is formed are aligned, and the optical lens of the imaging unit is set to just focus, and all the patterns included in the imaging range are at least one. Under the optical condition and the position shift condition that can be included in the field of view of one pixel over the entire width, a plurality of position shift target images are shifted while shifting the relative position of the imaging unit and the object in the forming direction. And the maximum luminance value among the pixels at the same coordinates in all the position shift target images is set to the luminance value of the same pixel to create one maximum value image, and the maximum value image By creating a pattern image consisting of pixels corresponding to the full width luminance value of each pattern formed on the object, and inspecting the pattern using the pattern image as an image to be inspected, It is obtained by solving.

According to the present invention, an object in which a narrow pattern is repeatedly formed in a width direction with a pattern formed between the patterns is imaged under transmitted illumination by an imaging means, and an image obtained is obtained. In the periodic pattern unevenness inspection method for inspecting the pattern by performing image processing, the imaging unit is arranged so that a pixel column direction thereof is aligned with a forming direction of the object, and an optical lens of the imaging unit is disposed. Under the optical condition and the position shift condition that can be set to the just focus and all the patterns included in the imaging range can be included in the visual field of one pixel at least once over the entire width,
While shifting the relative positions of the imaging unit and the object in the forming direction, a plurality of position shift target images are captured, and a light source image is imaged excluding the object, and the plurality of position shift target images are captured. Are divided by the light source images to generate the same number of shifted-position transmittance images, and the maximum luminance value among the pixels at the same coordinates in all the shifted-position transmittance images is set to the luminance value of the same pixel. To create a single maximum value image, and from the maximum value image, create a pattern image consisting of pixels corresponding to the full width luminance value of each pattern formed on the object, and inspect the pattern image. Inspection of the pattern as an image solves the above-mentioned problem.

According to the present invention, an object in which a narrow pattern is repeatedly formed with the width direction formed between the patterns in a width direction is imaged by an image pickup means under reflected illumination, and an image obtained is obtained. A periodic pattern unevenness inspection apparatus that inspects the pattern by performing image processing, a function of arranging the imaging unit so that a pixel column direction is aligned with a forming direction of the object, and an optical lens of the imaging unit Is set to just focus, and all the patterns included in the imaging range are at least once over the entire width.
Moving / imaging having a function of imaging a plurality of position-shifted target images while shifting the relative position of the imaging unit and the object in the forming direction under a position shift condition that can be accommodated in the field of view of the pixel. Means for setting a maximum luminance value among pixels at the same coordinates in all the position shift target images to the luminance value of the same pixel, and creating one maximum value image; Means for creating a pattern image composed of pixels corresponding to the full width luminance value of each pattern formed on the object from the maximum value image, and means for inspecting the pattern using the pattern image as an image to be inspected As a result, the above problem has been solved.

According to the present invention, an object in which a pattern having a small width is repeatedly formed with the width direction formed between the patterns is imaged under transmitted illumination by an imaging means, and an image obtained is obtained. A periodic pattern unevenness inspection apparatus that inspects the pattern by performing image processing, a function of arranging the imaging unit so that a pixel column direction is aligned with a forming direction of the object, and an optical lens of the imaging unit Is set to just focus, and all the patterns included in the imaging range are at least once over the entire width.
A function of imaging a plurality of position shift target images while shifting the relative position of the imaging unit and the target in the forming direction under a position shift condition that can be included in the field of view of the pixel; And a moving / imaging control unit having a function of imaging a light source image, and dividing the plurality of position shift target images by the light source image to generate the same number of position shifted transmittance images. Means for setting the maximum luminance value among the pixels at the same coordinates in all the position-shifted transmittance images to the luminance value of the same pixel to create one maximum value image; and Means for creating a pattern image composed of pixels corresponding to the full width luminance value of each pattern formed on the object, and means for inspecting the pattern using the pattern image as an image to be inspected. By the, it is obtained by solving the above problems as well.

That is, in the present invention, on the assumption that moiré fringes are generated, an image is taken with just focus under reflected illumination or transmitted illumination, and the entire width of the pattern of light non-transmission or transmission is always once. Image is taken while shifting the position so that an image is input in the field of view of one pixel, and one maximum value image is created from each of the obtained plurality of position shift target images or transmittance images, and the full width of the pattern is obtained from the image. A pattern image consisting only of the pixels corresponding to the pattern, which has been input as an image, is created and inspected as an image to be inspected.In each case, the pattern unevenness is not affected by the moire fringes. Can be inspected with high accuracy.

[0016]

Embodiments of the present invention will be described below in detail with reference to the drawings.

FIG. 1 is a schematic perspective view showing a main part of a periodic pattern unevenness inspection apparatus according to an embodiment of the present invention, including a block diagram corresponding to FIG.

In the inspection apparatus of this embodiment, an aperture grill (object) W on which a strip-shaped narrow pattern P is formed is placed, and the width direction of the pattern orthogonal to the long side direction of the pattern P is placed. An object position shifting unit 22 that can be accurately moved in a position shifting direction parallel to the forming direction is installed on the inspection stage 10, and a CCD camera (imaging means) 12 comprising an area sensor in the same direction. A camera position shifting unit 24 that can accurately move the camera is provided. The inspection apparatus of the present embodiment shifts the object W by the object position shifting unit 22 or the camera 12 by the camera position shifting unit 24 in the forming direction, and then details the object W by the camera 12 later. The basic hardware configuration is substantially the same as that of the conventional device shown in FIG. 15 except that the operation of imaging under the conditions described above is controlled by the device control unit 20.

That is, as will be described in detail later, the inspection apparatus of the present embodiment is capable of repetitively forming an object in which a narrow pattern P is repeatedly formed in the width direction with a pattern formed between the patterns. It has a function of taking an image under transmitted illumination by an imaging means (CCD camera 12), performing image processing on the obtained image, and inspecting the pattern.

A function of arranging the imaging means so that its pixel column direction is aligned with a width direction of the pattern of the object; a function of setting an optical system lens of the imaging means to just focus; The relative position of the means and the object in the formation direction, that is, the pixel column direction, is an optical condition and position that allows all the patterns included in the imaging range to be included in the field of view of one pixel at least once over the entire width. A movement / imaging control unit having a function of imaging a plurality of position shift target images while shifting under a shift condition and a function of imaging a light source image excluding the object is provided to the CCD camera 12 by a camera. It comprises a controller 16, a light source controller 18, a device control unit 20, position shift units 22, 24, and the like.

In the inspection apparatus according to the present embodiment, the plurality of images to be shifted are each divided by the light source image to generate the same number of shifted transmittance images.
Means for setting the maximum luminance value among the pixels at the same coordinates in all the displaced transmittance images to the luminance value of the same pixel to create one maximum value image; Means for creating a pattern image composed of pixels corresponding to the full-width luminance value of each pattern formed on the pattern, and means for inspecting the pattern using the pattern image as an image to be inspected, Has been realized.

As shown in FIG. 2, the inspection apparatus according to the present embodiment is roughly divided into a data processing unit 26, a human interface unit 28, and a machine interface unit 30. The entire operation of each of the included functional units is controlled by the device control unit 24. Then, the data processing unit 2
6 includes, as functional units, the image input unit 20 and the image processing unit 22 that processes image data input by the image input unit 20. Similarly, the human interface unit 28 is processed by the image processing unit 22. The information display unit 32 for displaying the results and the like, the personal operation unit 34 for exchanging information with the operator, and the machine interface unit 30 are connected to an external machine such as a belt conveyor (not shown) for transporting the object. And a machine interlocking unit 36 for exchanging information between the two.
For the devices 6 to 30, etc., the entire operation is managed by the device control unit 24.

Each of these functional units will be described in detail. A device control unit 24 for managing the operation of each of the above functional units 26 to 30
For example, a dedicated device, a general-purpose sequencer, a personal computer, or the like can be used. An area sensor camera can be used as the CCD camera 12 of the image input unit 20.
OMS (Complementary Metal Oxide Semicondu
ctor) Area sensor cameras, imaging tubes, etc. can also be used.

As the image processing unit 22, a dedicated image processing device, a personal computer, or the like can be used. or,
The information display unit 32 displays the inspection progress status for the operator,
It has the function of presenting inspection results, counting results, history of past inspection results, etc., and displaying captured images, images in the course of processing, or images after processing, such as CRT monitors, liquid crystal monitors, and LED arrays. Etc. are available.

The interpersonal operation unit 34 (1) accepts an input operation required for an inspection from the operator, (2) sets the characteristics (size, etc.) of the inspection object, and (3) the image processing unit 22 Set adjustment values (filter size, etc.), (4)
It has a function of setting an adjustment value (shutter speed or the like) of the image input unit 20, and can use a mechanical button, a touch panel, a keyboard, a mouse, and the like.

The machine interlocking unit 36 synchronizes with an external device at the time of the automatic inspection, for example, synchronizes the supply of the inspection target to the image input unit 20 with a timing, etc. Instructions for sorting and sorting the inspection target,
(Supply stop to the inspection unit). LAN (Ethernet), RS
-232C, RS-422, GPIB (General Pur
Pose Interface Bus), parallel I / O, relay, etc. can be used.

The aperture grill (object) W to be inspected is described in detail in FIG.
As shown in (A), a pattern P having a width La formed of a narrow rectangular (rectangular) through hole shown by a hatched portion is formed on a thin metal plate shown by a white background so as to show an image of the feature. One that is repeatedly formed in a forming direction (width direction) indicated by an arrow in the drawing via a pattern having a width Lb, which is an adjacent metal portion, can be given.

In the object W, a strip pattern as shown in the figure is repeatedly formed in a certain direction, and the narrow side of the strip is repeated in the above-described forming direction parallel to the repetition direction. When the pattern is viewed in this formation direction, the width La of the pattern and the width Lb between the patterns corresponding to the formation interval are each constant or at least one of them is formed so as to gradually change. When the pattern is viewed in a direction perpendicular to the forming direction, the long sides of the pattern are formed in the forming direction, that is, at right angles to the short sides. However, the target object W to which the present embodiment is applicable includes FIG.
As shown in FIG. 2, the pattern P is formed repeatedly with a certain curvature, and as shown in FIG. 3C, the pattern P is formed with a gradually changing curvature.

In the inspection apparatus of this embodiment, as described above, the camera system (optical condition setting means) 16 sets the optical system lens of the CCD camera 12 to just focus, and sets all the patterns included in the imaging range. Is set to an optical condition, which will be described later, which can be included in the visual field of one pixel over the entire width at least once.

The object position shifting unit 22 or the camera position shifting unit 24 aligns the pixel column direction of the CCD camera 12 with the width direction of the pattern P of the object W in the same direction. Can be shifted under the position shifting condition described later. However, here, the former camera 12
Let's move

Then, while shifting the position in this way,
The CCD camera 12 captures a plurality of target images for position shift, and removes the target object W from the inspection stage 10 under the same conditions as the position shift conditions.
Are moved, and only the light source is imaged, and the same number of shifted position light source images are input.

When an image is input as described above, the following image processing is executed in the image processing device 14. The plurality of position shift target images are divided by the corresponding position shift light source images to create the same number of position shift transmittance images. Next, the maximum luminance value among the corresponding pixels of all the position shifted transmittance images is set to the luminance value of the same pixel, and one maximum value image is created. Further, a pixel corresponding to the pattern formed on the object is extracted from the maximum value image to create a pattern image, and the pattern is inspected based on the image.

Hereinafter, the present embodiment will be described in more detail with reference to specific examples. Here, a description will be given on the assumption that a pattern is formed on the inspection object W according to a repetition rule such that a part is extracted in FIG. However, in this figure, the pattern portion (through hole) is made brighter and the portion between the patterns (metal) is made opposite to the case of FIG. 3 in correspondence with the target image captured by the CCD camera 12 under transmitted illumination. Is shown darkly. It is assumed that the unit of length is μm.

Assuming that the width of the pattern (part) is La [i] and the width of the pattern (part) is Lb [i] for the i-th arbitrary pattern set, the pattern of FIG. Is a constant 16 μm, but the pattern width is formed according to a repetition rule that increases by 1 μm from the first La [0] = 4.

First, with respect to the CCD camera 12, pattern extraction conditions 1 to 3 are defined as optical conditions under which all patterns included in the imaging range can be included in a field of view of one pixel at least once over the entire width. explain.

In this embodiment, as described above, the CCD camera 1 in which the lens of the optical system is set to just focus
2, the target object W is imaged and a target image is input. At this time, H: camera resolution [μm / Pel], La: pattern width in the forming direction [μm], Lb: width between patterns in the forming direction [μm], N: number of patterns in the camera field of view [pieces] , R: When the position shift range [μm] is set, all of the following pattern extractable conditions 1 to 3 are satisfied between the pattern and the resolution H of the camera. Can be visualized.

<Pattern Extractable Condition 1> When the object W is picked up by the CCD camera 12 and the field of view contains N patterns as described above, the resolution H [μm / Pel] is equal to or larger than the width (maximum width) of the largest pattern among the N patterns. This means that the entire width of a pattern having the maximum width can be input as an image with a visual field of one pixel (Pel).

For the sake of convenience, FIG. 5A, which corresponds to an image corresponding to one row of pixels when the pattern of FIG. 4 is captured, has a visual field size of one pixel indicated by a solid-line rectangle, that is, the resolution H of the camera. The image of the correspondence relationship with the pattern P is shown. Condition 1 can be expressed by the following equation (1).

H ≧ max (La [i]) (1) i {0, 1,..., N−1}

<Pattern extractable condition 2> For each of the N patterns, the resolution H of the CCD camera 12 is the sum of the width of the pattern and the width between the patterns adjacent on the upstream side, and the width of the pattern and the downstream side. The smallest pattern width (minimum width) in the sum of the widths between adjacent patterns
Less than. This means that for each combination of any pattern and its upstream and downstream patterns,
In the one-pixel field of view, even the smallest pattern set (pattern + pattern) cannot be imaged in the entire width of the set, and the image was taken in a state where two adjacent patterns were included in the one-pixel field. This means that the luminance values are not equal between the case and the case where the image is captured in a state where only one of the patterns is included. Condition 2 can be expressed by the following equations (2) and (3).

H <min (La [i] + Lb [i]) (2) and H <min (La [i] + Lb [i−1]) (3) i∈ ｛0, 1,.・, N-1｝

<Pattern Extractable Condition 3> For a given pixel of the CCD camera 12, when a plurality of images to be shifted are picked up, two adjacent pixels are interposed between the patterns.
The resolution H is set so that the full width of both patterns cannot be input simultaneously. This condition 3 satisfies the following (4)
It can be expressed by an equation.

H <min (La [i] + Lb [i] + La [i + 1]) − R (4) i {0, 1,..., N−1}

The meaning of the pattern extractable condition 3 becomes clearer if the above equation (4) is transformed into {H + R} <min (La [i] + Lb [i] + La [i + 1]) (4 '). become. In this formula,
The left side represents the maximum width of a moving range in which one pixel inputs an image by shifting the position, and the right side represents the minimum width of the moving range (pattern + pattern + pattern) necessary to input the entire width of each of two adjacent patterns. ). This condition means that if one CCD element can simultaneously input the full width of each of the two patterns, it will not be possible to correctly extract the pattern in subsequent processing, and this will be avoided.

Next, in imaging the object W by setting all three of the above-described three pattern extractable conditions 1 to 3 to be satisfied, the camera 12 is shifted by a predetermined position by a predetermined size in the forming direction of the pattern P. The position shift condition when a plurality of target images are imaged while moving along the direction and shifting their relative positions will be described.

Now, a total of Z position shift target images (WI
[0] to WI [Z-1]) will be considered. When capturing these images, the object W and the camera 1
It can be obtained by repeating the operation of inputting an image one by one each time the position of the camera 12 is shifted in parallel to the forming direction without changing the distance between the two.

The position shift conditions include the position shift range R and the position shift size (pitch) S for one time, which are set by the following equations (5) and (6), respectively. The actual position shift range may be R or more.

R ≧ max (La [i]) (5) i {0, 1,..., N−1} S = R / (Z−1) (6)

The expression (5) also means that the movement is performed within the range equal to or higher than the resolution. That is, when sequentially inputting images while shifting the position, the pattern having the widest width
The positional relationship of the corresponding CCD pixels is represented by max (L
a [i]), so at least max (La
If the position is shifted in the range of [i]), it is guaranteed that the full width of the pattern having the widest pattern width can be input as an image at a certain position in a field of view of one pixel. Further, the smaller the position shift dimension S of the equation (6) is, that is, the number of image pickups Z
The larger the number is, the higher the probability that the entire width of the pattern having the largest pattern width can be input as an image in a field of view of one pixel is higher. However, the actual number of captured images Z is determined within a range in which the detection accuracy does not pose a problem in the operation of the apparatus, in consideration of the time of image input and image conversion processing.

As described above, in the present embodiment, under the above conditions, the Z-position-shifted images of the object W are taken under the same conditions, and the object W is removed from the inspection stage 10 under the same conditions. Z light source images (LI [0] to L
I [Z-1]), each position shift target image is divided by the corresponding light source image, and Z transmittance images (TI
[0] to TI [Z-1]). By converting the position shift target image into the transmittance image in this manner, even if shading (difference in brightness depending on a place) is present in a transmission light source (not shown) installed in the inspection stage 10, the image is not affected. The effect can be ruled out.

When a total of Z position-shifted transmittance images have been created as described above, a pattern is finally extracted from these images, and a pattern image (image to be inspected) consisting of only pixels corresponding to the pattern is extracted. ) To create.

This pattern extraction processing is roughly divided into (A) processing of generating one maximum value image from the Z position shifted transmittance images, and (B) extraction of pixels corresponding to the pattern from the maximum value image. And (C) connecting a pixel corresponding to the pattern from the pattern extraction image to create a pattern image.

In the generation of the maximum value image of (A), the maximum value image of one sheet is applied by applying an inter-image maximum value filter for performing an operation represented by the following equation (7) to the Z position-shifted transmittance images. Make a value image. This filter performs a process of comparing pixels at the same coordinates of all images, and setting a luminance value of a pixel having the highest luminance value to a luminance value (pixel value) of a corresponding pixel of the maximum value image. do.

MI [x, y] = max (TI [z, x, y]) (7) x∈ ｛0, 1,..., X−1｝ y∈ ｛0, 1,. , Y-1} z {0, 1,..., Z-1}

In this equation, X is the number of pixels in the horizontal direction of the image, Y is the number of pixels in the vertical direction of the image, and MI [x, y] is the luminance value of the pixel in the y-th row and the x-th column in the maximum value image. , TI
[Z, x, y] is the luminance value of the pixel in the y-th row and the x-th column in the z-th position shifted transmittance image.

To create the pattern extraction image of (B), the pixel extraction conditions 1 and (9) of the following expression (8) are applied to the maximum value image MI [x, y] generated as described above. When the pixel satisfies the pixel extraction condition 2 of the expression or the pixel extraction condition 3 of the expression (10), the pixel of the pattern extraction image is E
For I [x, y] = MI [x, y], and for other pixels, EI [x, y] = 0, a pattern extraction filter that performs processing to replace the luminance value is applied.

<Pattern extraction condition 1> (MI [x, y]> MI [x-1, y]) and (MI [x, y]> MI [x + 1, y]) (8)

<Pattern extraction condition 2> (MI [x, y]> MI [x-1, y]) and (MI [x, y] = MI [x + 1, y]) (9)

<Pattern extraction condition 3> (MI [x, y] = MI [x-1, y]) and (MI [x, y]> MI [x + 1, y]) (10)

That is, applying this pattern extraction filter means that, for each pixel of the generated maximum value image, a pixel adjacent to the downstream side and an upstream side for each pixel row in the horizontal direction (X direction). (Condition 1), which is equal to the luminance value on the upstream side but exceeds the luminance value on the downstream side (condition 2). Conversely, the luminance value is equal to the luminance value on the downstream side but upstream. The luminance value of the maximum value image is set to the corresponding pixel of the pattern extraction image EI only when one of the conditions (condition 3) that exceeds the luminance value of It means that 0 is set.

In the connection process (C), a pattern connection filter is applied to the created pattern extraction image. This filter functions to leave pixels with a luminance value of ≠ 0 and discard pixels with a luminance value of 0. As described above, since a pixel corresponding to the pattern brightness value and a pixel having a brightness value = 0 that do not correspond to the pattern are mixed in the pattern extraction image, by applying this filter, only the pixels corresponding to the pattern are obtained. A different image, that is, a pattern image can be created.

The pattern image created as described above is used as the image to be inspected, and based on the image to be inspected, the unevenness of each pattern, that is, the unevenness of the luminance value of the pixel is inspected. As the method, even if the created image to be inspected (pattern image) itself is displayed on a monitor screen and the inspector looks at the displayed image and determines whether or not there is unevenness by visual inspection,
Alternatively, for example, the same processing as the inspection processing applied to the transmittance image disclosed in JP-A-6-229736 is applied to the pattern image to determine whether or not there is unevenness by an automatic inspection. You may do so.

The automatic inspection disclosed in this publication will be briefly described.
Assuming the shape of the unevenness that is expected to occur, an enhancement process is performed by applying a spatial filter such as a secondary differential filter different for each shape to create an enhanced image, and the image is binarized by a predetermined threshold value This is an automatic inspection method based on the number of binary pixels (area) on a binary image.

Next, the operation of the present embodiment will be described more specifically with reference to the flowcharts of FIGS.

In this embodiment, as schematically shown in FIG. 6, the processing procedure is roughly divided into initialization (step 10), image input (step 20), and image conversion (step 3).
0), analysis of the image (step 40), identification of the image (step 50), and output of the result (step 60).

First, in the initialization of step 10, various parameters necessary for executing the inspection processing are set. Specifically, various parameters necessary for operating the apparatus are set. As for the image input of the target object W, setting of the feature amount (inspection range) of the target object, adjustment (setting) of the optical condition for satisfying the above-described pattern extractable condition, and position shift for obtaining a position shifted image are performed. Set conditions such as calculation and setting of conditions. Furthermore, in order to apply the automatic inspection for unevenness to the target object, inspection parameters such as a type of a spatial filter for obtaining an emphasized image, a threshold for obtaining a determination image, and a condition for determining the presence or absence of a defect from the determination image are used. Make settings.

Next, in the image input in step 20,
Optically, the object W is imaged under the above-described pattern extractable conditions 1-3. Accordingly, as shown in FIG. 5A, the relationship between the pattern P and the field of view (resolution) H of the pixels for one column is shown in FIG. As shown in correspondence, there are a type in which the entire width can be fully imaged with one pixel (shaded portion) and a type in which the pixel is divided into two pixels (white portion). That is, there is an advantage that, when imaging is performed with just focus, the area of one pattern, that is, the luminance, can be accurately reflected on one pixel. On the other hand, there are some pixels that straddle two pixels, so that correct luminance cannot be obtained in accordance with the area of the pattern. This causes moiré fringes as described above and impairs inspection accuracy. are doing.

Therefore, in the present embodiment, image input is performed according to the detailed procedure shown in FIG. First, an initial setting for setting parameters required for image input is performed (step 20).
2). The initial setting performed here is substantially the same as the content related to the image in the initialization in step 10.

After the completion of the initial setting, the object W is placed (loaded) on the stage 10 as shown in FIG. 1 (step 204). Next, a product image (target image) is captured (step 206). Here, imaging is performed with just focus with the object W placed on the stage 10. Then, while moving the camera 12 in the width direction of the forming direction pattern by the position shift pitch S set by the formula (5), the object W is moved until a total of Z position shift product images WI [i] are captured. Are repeated (steps 208 and 210). FIG.
(I) shows the position-shifted product images [i] to [i] obtained by imaging the object W having the characteristics shown in FIG. 4 under these conditions.
+8], each of which represents an image of one pixel column, and corresponds to an example of a total of nine position-shifted product images, ie, Z = 9.

Next, the object W is removed from the stage 10 (step 212), and the camera position for returning the camera 12 to the position before capturing the product image is initialized (step 21).
4) In the state where there is no object W, the above steps 208 to 2 are performed.
Image capturing is performed under the same conditions as in step 10, and a total of Z position shifted light source images LI [i] are captured (steps 216 to 22).
0).

Thereafter, in the image conversion in step 30 in FIG. 6, a process for generating an image to be analyzed from each image input as described above is performed. As the image conversion, each process shown in FIG. 8 is executed. First,
From the position-shifted product image WI [i] created according to the flowchart of FIG. 7 and the corresponding position-shifted light source image LI [i], the position-shifted transmittance image TI [i that has been subjected to shading correction by the following equation (11). ] Is created (step 302). This process is repeated until a total of Z position shifted transmittance images are created (step 30).
4).

TI [i] = WI [i] / LI [i] (11)

FIG. 11 shows the image of the relationship between the pattern and the pixel shown in FIG. 10 above. The position-shifted transmittance images obtained from the position-shifted product images from [i] to [i + 8] are shown in FIG. As in FIG. 7B for A), each pixel is shown with a corresponding brightness value. In addition,
Each transmittance image is substantially the same as the product image in FIG. 10 except that the shading of the light source is corrected, so that the illustration is omitted.

Next, a total of Z position-shifted transmittance images composed of luminance values as shown in FIGS.
A maximum image MI [i] is generated (created) by applying a maximum filter having the calculation function of the equation (7) (step 306). FIG. 12 shows the distribution of the luminance values of one maximum-value image generated in this manner for the same pixel rows Pel [0] to Pel [11] as in FIG. This maximum value image is shown in FIG.
The maximum luminance value is selected from the corresponding pixels of the position-shifted transmittance image (I), and corresponds to one image. Therefore, some pixels do not capture the full width of one pattern (Pel [2], [4],
[7], [9], [11]) are also included.

Therefore, in order to exclude pixels in which the area of the pattern is not reflected as described above, a pixel extraction condition 1 shown in the above equation (8) and a pixel extraction condition 2 shown in the above equation (9) are used. In order to extract only pixels that satisfy one of the pixel extraction conditions 3 shown in the above equation (10), a pattern extraction image is created by applying a pattern extraction filter to the maximum value image (step 308). FIG. 13 shows an image of the filtering process. However, this figure does not include an example corresponding to the pixel extraction condition 3. In this process, only the pixels marked with a circle are extracted from the maximum value image of FIG. 12 again shown in FIG. 12A, and a pattern extraction image composed of the luminance values shown in FIG. In this extraction processing, the following processing is executed by applying the above filter to each pixel. In addition,
Here, for convenience, the order of processing for pixels Pel [0] to Pel [11] indicated by circled numbers in FIG. 13A is indicated by numbers in parentheses.

(1) Excluded ← Pel [0] <Pel [1] (2) Remaining ← Pel [1]> Pel [0], Pel [1]
> Pel [2] (3) Excluded ← Pel [2] <Pel [1], Pel [2]
<Pel [3] (4) Residual ← Pel [3]> Pel [2], Pel [3]
> Pel [4] (5) Excluded ← Pel [4] <Pel [3], Pel [4]
<Pel [5] (6) Residual ← Pel [5]> Pel [4], Pel [5]
= Pel [6] (7) Excluded ← Pel [6] = Pel [5], Pel [6]
= Pel [7] (8) Excluded ← Pel [7] = Pel [6], Pel [7]
<Pel [8] (9) Remaining ← Pel [8]> Pel [7], Pel [8]
> Pel [9] (10) Excluded ← Pel [9] <Pel [8], Pel [9]
<Pel [10] (11) The remaining ← Pel [10]> Pel [9], Pel [10]
> Pel [11] (12) Excluded ← Pel [11] <Pel [10]

As shown in FIG. 13B, a pixel having a pattern area correctly reflected as described above and a pixel having a luminance value of 0 are used.
After the pattern extraction image shown in FIG. 14 is created, a pattern connection filter is applied to the extraction image to exclude pixels having a luminance value of 0, and a pattern image consisting of only pixels corresponding to the pattern shown in FIG. 14 is created. Is the image to be inspected.

This image to be inspected may be displayed on a monitor screen and visually inspected by an inspector. However, in this case, in order to perform an automatic inspection, step 4 in FIG.
The processing of 0, 50, and 60 is performed. However, illustration of images created in the following processes is omitted.

In the analysis of the image in step 40, the pattern image (image to be inspected) generated by the image conversion in step 30 described in detail above is applied to the method disclosed in JP-A-6-2297.
When a spatial filter such as a secondary differential filter disclosed in Japanese Patent Publication No. 36 is applied, and if there is unevenness in luminance in the image, a process of enhancing the unevenness is performed to create an enhanced image.

In the identification of the image in step 50, as shown in detail in FIG. 9, the determination image is created (step 502), the shape is measured (step 504), and the determination process (step 50)
6) The three processes are performed. In the creation of the judgment image in step 502, a predetermined threshold value is set on the emphasized image created in step 40 to binarize the image, and a judgment image JI including defect candidate pixels is created. In this determination image, a luminance value of 0 is set for a pixel smaller than the threshold value as a background, and a luminance value of, for example, 255 is set for a pixel higher than the threshold value so as to be extracted as a defect candidate.

In the shape measurement in the next step 504, the characteristic amount is measured for the defect candidate included in the judgment image. Specifically, each defect candidate included in the determination image is subjected to a labeling process, and the size, the horizontal and vertical fillet diameters, and the like of each of the labeled defect candidates (image regions) are determined to determine the size. Measure.

In the next determination process in step 506, the feature amount of the defect candidate measured above is compared with a preset feature amount of unevenness to be a defect, and if the feature amount is within a predetermined threshold value, for example, The presence or absence of an unevenness defect is determined by determining that there is unevenness.

In the output of the result of step 60, after the judgment processing is completed as described above, finally, the judgment result as to whether the object W is good or defective is output, and the automatic inspection ends.

According to the present embodiment described above, when a fine strip-like pattern formed on an object such as an aperture grill is imaged under transmitted illumination and inspected, the object is just focused. Only the luminance signal when one pixel (light receiving element of a CCD camera) has just captured one of the periodic patterns is selectively selected from a plurality of position-shifted transmissivity images in which moiré fringes obtained by imaging in step (1) are generated. As a result, unevenness with a small area and unevenness with a small difference in shading occurring in the pattern can be imaged (visualized), and a more accurate inspection can be performed.

As described above, the present invention has been specifically described. However, the present invention is not limited to the above-described embodiment, and can be variously modified without departing from the gist thereof.

For example, in the above embodiment, the CCD camera 1
2 is moved in the forming direction by the camera position shifting unit 24. However, the present invention is not limited to this. By moving the object W in the forming direction by fixing the camera and the light source and moving the object W in the forming direction by the object position shifting unit 22. May be shifted. In this case, since there is no change in the positional relationship between the camera 12 and the light source, one light source image is captured with the workpiece W removed, and this one light source image is used to create each position-shifted transmittance image. Since the light source image may be used, there is an advantage that it is not necessary to acquire a plurality of position shifted light source images while moving the camera.

Further, as shown in the above-mentioned embodiment, the present invention is not limited to the case where an object on which a pattern of light-transmitting through holes is formed is imaged under transmitted illumination, but is not limited to the non-transmissive image captured under reflected illumination. It may be an object on which a sex pattern is formed. As a specific example, even in the case of an aperture grill of the same object, when inspecting a variation in width of a flat portion (front side) of a plate material remaining without being etched, not a through hole formed by etching. Can be mentioned. That is, since the through-hole formed by etching does not penetrate perpendicularly to the material surface, the width of the flat portion varies, but when inspecting the variation, it is more difficult to reflect light than to transmit light. Lighting is suitable. By performing reflection illumination in this way, if the flat portion on the front side of the aperture grill is imaged as a bright pixel, and the rest, that is, the opening and the wall portion of the hole are input as dark pixels, the case of the transmissive illumination is the same as the pattern. Although the relationship between the patterns is reversed, the unevenness can be similarly visualized.

In the above-described embodiment, the case where the width between the patterns is constant and the width of the pattern is gradually increased is described. However, the width may be gradually increased. In addition, the inspection can be performed not only when both widths are constant but also when both widths change. Further, in the above embodiment, the case where the unit of length is μm is shown, but it is needless to say that the present invention is not limited to this.

[0089]

As described above, according to the present invention,
After taking an image of a target object with the optical system lens being in just focus, the periodic pattern can be inspected with high accuracy without being affected by moire fringes.

[Brief description of the drawings]

FIG. 1 is a schematic perspective view including a block diagram showing a main part of an inspection apparatus according to an embodiment of the present invention.

FIG. 2 is a block diagram showing an outline of the entire inspection apparatus.

FIG. 3 is an image diagram showing types and characteristics of patterns to be inspected according to the present invention.

FIG. 4 is an explanatory diagram showing characteristics of a pattern to be inspected in the embodiment.

FIG. 5 is an explanatory diagram showing a relationship between a pixel for imaging a pattern and a luminance value.

FIG. 6 is a flowchart showing an outline of an inspection procedure according to the embodiment;

FIG. 7 is a flowchart showing a procedure of image input according to the embodiment;

FIG. 8 is a flowchart showing a procedure for creating a transmittance image to a pattern image according to the embodiment;

FIG. 9 is a flowchart showing a procedure for determining whether a pattern is good or bad according to the embodiment;

FIG. 10 is an explanatory diagram showing an image of a shifted product image.

FIG. 11 is an explanatory diagram showing characteristics of luminance values of a shifted-position transmittance image.

FIG. 12 is an explanatory diagram showing characteristics of luminance values of a maximum value image created from a position shifted transmittance image;

FIG. 13 is an explanatory diagram showing an image of a process of creating a pattern extraction image from a maximum value image

FIG. 14 is an explanatory diagram showing an image of a pattern image created from a pattern extraction image.

FIG. 15 is a schematic perspective view including a block diagram showing a main part of a conventional inspection apparatus.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 ... Inspection stage 12 ... CCD camera 14 ... Image processing part 16 ... Camera controller 18 ... Light source controller 20 ... Device control part 22 ... Object position shift unit 24 ... Camera position shift unit

Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat II (Reference) G01B 11/24 K (72) Inventor Atsushi Okazawa 1-1-1, Ichigaya-Kagacho, Shinjuku-ku, Tokyo Dai Nippon Printing Co., Ltd. (72) Inventor Takutetsu Jinmori 1-1-1, Ichigaya-Kaga-cho, Shinjuku-ku, Tokyo Dai-Nippon Printing Co., Ltd.F-term (reference) QQ33 SS13 2G051 AA90 AB20 BA00 CA03 CA04 CB02 DA07 EA11 EC02 EC05 ED07 FA10 5C012 AA02 BE03 5C027 HH29

Claims (12)

[Claims] An object in which a narrow pattern is repeatedly formed with the width direction formed between the patterns in a width direction is imaged under reflective illumination by an image pickup means, and the obtained image is subjected to image processing. In the periodic pattern unevenness inspection method for inspecting a pattern, the imaging unit is arranged so that a pixel column direction thereof is aligned with a forming direction of the object, and an optical lens of the imaging unit is set to just focus. The formation direction of the imaging unit and the object under the optical condition and the position shift condition that all the patterns included in the imaging range can be included in the visual field of one pixel at least once over the entire width. While shifting the relative positions of the images, a plurality of images of the position shift target images are taken, and the maximum luminance value among the pixels of the same coordinates in all the position shift target images is set to the same pixel. A single maximum value image is created by setting the brightness value, and a pattern image consisting of pixels corresponding to the full width brightness value of each pattern formed on the object is created from the maximum value image. A method for inspecting unevenness of a periodic pattern, comprising inspecting the pattern using an image as an image to be inspected. 2. An object in which a narrow pattern is repeatedly formed with the width direction formed between the patterns in a width direction is imaged under transmitted illumination by an image pickup means, and the obtained image is subjected to image processing. In the periodic pattern unevenness inspection method for inspecting a pattern, the imaging unit is arranged so that a pixel column direction thereof is aligned with a forming direction of the object, and an optical lens of the imaging unit is set to just focus. The formation direction of the imaging unit and the object under the optical condition and the position shift condition that all the patterns included in the imaging range can be included in the visual field of one pixel at least once over the entire width. While shifting the relative position of, a plurality of position shift target images are captured, and a light source image is imaged excluding the object, and the plurality of position shift target images are captured. Divide by the light source image to create the same number of position-shifted transmittance images, and set the maximum brightness value among the pixels at the same coordinates in all the position-shifted transmittance images to the brightness value of the same pixel. One maximum value image is created, and a pattern image composed of pixels corresponding to the full width luminance value of each pattern formed on the target object is created from the maximum value image, and the pattern image is used as an image to be inspected. A periodic pattern unevenness inspection method, wherein the pattern is inspected. 3. A relative position between the image pickup means and the object,
When the former is moved and shifted, the position shift light source images are imaged while shifting the imaging means under the same conditions as the position shift conditions, and the plurality of position shift target images are divided by the corresponding position shift light source images. 3. The method of claim 2, wherein the same number of the shifted-position transmittance images are generated. 4. As the optical conditions, the pattern width in the forming direction of the object is La, the width between patterns in the same direction is Lb, the number of patterns in the visual field at the time of imaging by the imaging means is N, and the position is shifted. When the range is R and i is any integer from 0 to N-1, the resolution H of the imaging means is H ≧ max (La [i]) H <min (La [i] + Lb [i]) H <Min (La [i] + Lb [i-1]) H <min (La [i] + Lb [i] + La [i +
1])-R is set so that all the relations are satisfied. When the number of images to be shifted is set to Z as the position shift condition, the position shift range R is set to R ≧ max (La [i] The position shift dimension S for one time is set as S = R / (Z-1), respectively.
3. The method for inspecting unevenness of a periodic pattern according to 1. 5. A pattern extraction image is created by setting the luminance value of the full width of the pattern to the same value for each pixel of the maximum value image, and setting the other values to 0 otherwise, and removing pixels having a luminance value of 0 from the image. The unevenness inspection method for a periodic pattern according to claim 1, wherein the pattern image is created by performing a pixel connection process. 6. A condition [MI [x, y]> MI [x, y]> MI [x-1, y] where MI [x, y] is a luminance value of a pixel on the y-th row and the x-th column of the maximum value image. ]) And (MI
[X, y]> MI [x + 1, y]) <Condition 2> (MI [x, y]> MI [x−1, y]) and (MI
[X, y] = MI [x + 1, y]) <Condition 3> (MI [x, y] = MI [x−1, y]) and (MI
[X, y]> MI [x + 1, y]), the luminance value EI [x, y] = MI [x, y] of the pixel of the corresponding pattern extraction image.
The method for inspecting unevenness of a periodic pattern according to claim 5, wherein the pattern extraction image is created by replacing EI [x, y] = 0 with y]. 7. An object in which a narrow pattern is repeatedly formed with the width direction formed between the patterns in a forming direction is imaged under reflected illumination by an image pickup means, and the obtained image is subjected to image processing. In the periodic pattern unevenness inspection apparatus for inspecting the pattern, a function of arranging the imaging unit so that a pixel column direction thereof is aligned with a forming direction of the target object, and an optical system lens of the imaging unit to just focus The setting function and the formation direction of the imaging unit and the object under a position shift condition that all the patterns included in the imaging range can be included in the visual field of one pixel at least once over the entire width. Moving / imaging control means having a function of imaging a plurality of position shift target images while shifting the relative position of Means for setting a maximum luminance value among pixels having the same coordinates to the luminance value of the same pixel to create one maximum value image, and each pattern formed on the object from the maximum value image A periodic pattern unevenness inspection apparatus, comprising: means for creating a pattern image composed of pixels corresponding to the full width of the luminance value; and means for inspecting the pattern using the pattern image as an image to be inspected. . 8. An object in which a narrow pattern is repeatedly formed with the width direction formed between the patterns in a forming direction is imaged under transmitted illumination by an imaging means, and the obtained image is subjected to image processing. In the periodic pattern unevenness inspection apparatus for inspecting the pattern, a function of arranging the imaging unit so that a pixel column direction thereof is aligned with a forming direction of the target object, and an optical system lens of the imaging unit to just focus The setting function and the formation direction of the imaging unit and the object under a position shift condition that all the patterns included in the imaging range can be included in the visual field of one pixel at least once over the entire width. Moving / imaging control means having a function of imaging a plurality of position-shifting target images while shifting the relative position of, and a function of imaging a light source image excluding the object. Means for dividing the plurality of target images for position shift by the light source images to create the same number of position-shifted transmittance images, and among the pixels having the same coordinates in all the position-shifted transmittance images. Means for setting the maximum luminance value to the luminance value of the same pixel to create one maximum value image, and corresponding to the full width luminance value of each pattern formed on the object from the maximum value image A periodic pattern unevenness inspection apparatus, comprising: means for creating a pattern image including pixels to be inspected; and means for inspecting the pattern using the pattern image as an image to be inspected. 9. A relative position between the image pickup means and the object,
In the case of moving and shifting the former, the shift means is imaged while shifting the imaging means under the same condition as the shift condition, and the plurality of shift target images are divided by the corresponding shift light source images, respectively. The unevenness inspection apparatus for a periodic pattern according to claim 8, wherein the same number of the shifted-position transmittance images are created. 10. As the optical conditions, the pattern width in the forming direction of the object is La, the width between patterns in the same direction is Lb, the number of patterns in the field of view at the time of imaging by the imaging means is N, and the position is shifted. Assuming that the range is R and i is any integer from 0 to N-1, the resolution H of the imaging means is H ≧ max (La [i]) H <min (La [i] + Lb [i]) H < min (La [i] + Lb [i-1]) H <min (La [i] + Lb [i] + La [i +
1])-R is set so that all the relations are satisfied. When the number of images to be shifted is set to Z as the position shift condition, the position shift range R is set to R ≧ max (La [i] The position shift dimension S for one time is set as S = R / (Z-1), respectively.
3. The periodic pattern unevenness inspection apparatus according to 1. 11. A pattern extraction image is created by setting the luminance value of the full width of the pattern to the same value for each pixel of the maximum value image, and setting the other values to 0 otherwise, and excluding pixels having a luminance value of 0 from the image. The unevenness inspection apparatus for a periodic pattern according to claim 5, wherein the pattern image is created by performing a pixel connection process. 12. A condition [MI [x, y]> MI [x, y]> MI [x-1, y] where a luminance value of a pixel on the y-th row and the x-th column of the maximum value image is MI [x, y]. ]) And (MI
[X, y]> MI [x + 1, y]) <Condition 2> (MI [x, y]> MI [x−1, y]) and (MI
[X, y] = MI [x + 1, y]) <Condition 3> (MI [x, y] = MI [x−1, y]) and (MI
[X, y]> MI [x + 1, y]), the luminance value EI [x, y] = MI [x, y] of the pixel of the corresponding pattern extraction image.
12. The periodic pattern unevenness inspection apparatus according to claim 11, wherein the pattern extraction image is created by replacing y [] with EI [x, y] = 0 otherwise.