KR100249270B1 - Method and system for inspecting unevenness - Google Patents

Abstract

Quantitatively examine non-uniformity of the contrast pattern that is formed at approximately periodic intervals.

The bokeh image of the shadow mask is picked up, the power spectrum distribution is obtained for each processing region in the bokeh image, and the power spectrum addition values S1 to S6 in the specific frequency region FR are calculated. Then, the maximum value of the power spectrum addition values S1 to S6 is compared with a predetermined threshold value, and the quality of the nonuniformity is determined according to the comparison result.

Description

Non-Uniform Test Method and Device

1 is a conceptual diagram showing a shadow mask inspection apparatus 30 to apply an embodiment of the present invention,

2 is a block diagram showing the electrical configuration of the shadow mask inspection apparatus 30,

3 is a flowchart showing the procedure of the nonuniformity inspection method in the embodiment;

4 is an explanatory diagram showing six processing regions R1 to R6 cut out at step T2,

5 is a graph showing an example of a power spectrum distribution obtained for good and defective products,

6 is an explanatory diagram showing the definition of the spatial frequency fsp in the embodiment,

7 is a conceptual diagram showing a power spectrum distribution obtained for each of the processing regions R1 to R6,

8 is a graph showing the relationship between the power spectral sum of the shadow mask and the positive and negative ranks of the shadow mask by humans,

9 is a conceptual diagram showing the configuration of the lens system 80 of the CCD camera 49. As shown in FIG.

* Explanation of symbols on the main parts of the drawings

30: shadow mask inspection device 40: optical measuring device

41: plate 42: measurement table

43: glass plate 44: light source

46: stand support arm 47: camera maintenance beam

48: Z axis stage 49: CCD camera

50: data processing device 52: display

54: image processing apparatus 56: Z-axis stage controller

58: secondary display 60: external storage device

62: camera control unit 64: bus line

66: CPU 68: RAM

70: keyboard 72: flexible disk device

74: printer 76: Z-axis rotary encoder

80 lens system 82 barrel

84, 85, 86: lens 88: aperture stop

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and apparatus for inspecting nonuniformity in an almost periodic light and dark pattern such as a transparent hole pattern of a shadow mask or a shade pattern formed on an original plate (usually, a glass plate) for producing a shadow mask.

The shadow mask of a CRT is a through hole plate in which minute through holes are formed at a substantially periodic pitch in a metal plate. In the original plate used in the photoetching step of the shadow mask or the color filter for the liquid crystal display panel, a black and white image is formed to expose a fine pattern. In this specification, the pattern of the transmission hole formed in the shadow mask or the pattern of the black and white image formed on the original plate is called a "contrast pattern".

The quality of the shadow mask or its original quality depends on the error of the contrast pattern (pore diameter or pitch error). Since the hole diameter of the penetrating hole is about 100 μm, the penetrating hole itself cannot be seen even if the shadow mask is visually observed. However, there is an error in the light and dark pattern of the shadow mask or the disc, and in particular, when the error is locally biased, the unevenness of the shade is recognized when the shadow mask or the disc is visually observed. For this reason, conventionally, in the quality inspection of a shadow mask or an original disc, the inspector visually inspects the optical light and shade nonuniformity, and judges the quality of a contrast pattern error.

Such a test result of non-uniformity with the naked eye is largely dependent on the skill and condition of the inspector, so that a stable test result may not be obtained. In addition, since the test requires concentration, it is difficult to perform a continuous test for a long time, and there is a problem that there is a limit in the amount of test for a day. Therefore, a method or apparatus for inspecting nonuniformity quantitatively without visual observation has been desired.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems in the prior art, and an object thereof is to provide a method and apparatus for quantitatively inspecting a non-uniformity of a contrast pattern formed almost periodically.

A first invention for solving at least part of the above-described problem is a method for inspecting a non-uniformity of a contrast pattern formed almost periodically, the method comprising: (a) obtaining a bokeh image of the contrast pattern; and (b) in the bokeh image. Obtaining a power spectral distribution for at least a portion of the region, (c) adding a power spectral value in a predetermined spatial frequency region of the power spectral distribution to obtain a power spectral addition, and (d) the power spectral addition and the predetermined Comparing the dress hold value, the process of determining the non-uniformity of the light and dark pattern is provided.

In the bokeh image, unevenness of the light and dark pattern is shown, and thus the power spectrum value is large at the uneven spatial frequency. Therefore, the power spectrum addition value which adds the power spectrum value of the predetermined spatial frequency area | region becomes a large value when there are many nonuniformities, and becomes a small value when there are few nonuniformities. By comparing the power spectral addition value with the threshold value, it is possible to determine whether the variation is uneven. Therefore, it is possible to quantitatively inspect the nonuniformity of the contrast pattern formed almost periodically.

In the first aspect of the invention, the step (a) comprises the steps of (1) obtaining a focusing position between the imaging means for imaging the bokeh image and the contrast pattern, and (2) the focus of the imaging means. It is preferable to include the step of shifting the position by a predetermined amount from the focusing position, and (3) the step of obtaining the bokeh image by imaging the image of the contrast pattern at the focus position shifted from the focusing position.

In this way, a bokeh image suitable for the nonuniform device can be easily generated.

Alternatively, in the first aspect of the invention, the step (a) includes (1) an imaging aperture for imaging the bokeh image and an aperture stop of the imaging means at a confocal position between the light and dark patterns. And (2) the step of tightening the dog stopper, and (3) the step of obtaining the bokeh image by imaging the image of the light and dark pattern at the confocal position with the dog stopper fastened. You may provide it.

In this way, a bokeh image suitable for nonuniformity inspection can be easily produced without changing the imaging magnification.

A second invention is an apparatus for inspecting a non-uniformity of a contrast pattern formed almost periodically, comprising: bokeh image generation means for obtaining a bokeh image of the contrast pattern, and power spectrum calculation for obtaining a power spectral distribution for at least a portion of the bokeh image; Means for adding power spectral values in a predetermined spatial frequency region of the power spectral distribution to obtain a power spectral summation value, and comparing the power spectral summation value with a predetermined threshold value to determine the non-uniformity of the contrast pattern. The determination means is provided.

The second invention also has the same effect and effect as the first invention, and it is possible to quantitatively inspect the nonuniformity of the contrast pattern formed almost periodically.

Further, in the second invention, the bokeh image generating means includes: imaging means for imaging the bokeh image, a confocal position calculating means for obtaining a confocal position between the light and dark patterns, and a focal point of the imaging means. It is preferable to include a focus position adjusting means for shifting the position by a predetermined amount from the focusing position, and an imaging means for obtaining the bokeh image by imaging the image of the contrast pattern at the focus position shifted from the focusing position.

Alternatively, in the second aspect of the present invention, the bokeh image generating means includes: an image focusing means having an aperture stop and a focal point for obtaining a confocal position between the image pickup means and the light and dark pattern with the aperture stop open; Positioning means may be provided, and the imaging means may obtain the bokeh image by capturing an image of the light and dark pattern at the confocal position with the aperture stop fastened.

Next, embodiment of this invention is described based on an Example. 1 is a conceptual diagram illustrating a shadow mask inspection apparatus 30 to which an embodiment of the present invention is applied. The shadow mask inspection device 30 is an optical measuring device 40 for capturing a shadow mask SM and obtaining image data thereof, and a data processing device 50 for processing various data based on the image data. Consists of.

The optical measuring device 40 is provided with a surface plate 41, and on the surface plate 41, a measurement table 42 having a transmission hole for passing illumination light is almost formed in the center. In addition, a glass plate (for example, opaque glass) 43 which diffuses and transmits light is mounted on the upper surface of the measurement table 42, and below the measurement table 42, a light source is provided. 44 is arrange | positioned. Instead of the glass plate 43, a diffusion plate may be employed. As this light source 44, a high frequency lighting type fluorescent lamp is used, for example. In addition, the shadow mask SM is tightly fixed to the upper surface of the glass plate 43 by an adhesive tape or the like.

In the surface plate 41, the stand support arm 46 which extends upwards is provided, and the camera support beam 47 for holding the CCD camera 49 as an imaging means is provided in the stand support arm 46 so-called one side. It is installed as a support. The Z-axis stage 48 is fixed to the front end of the camera holding beam 47. The camera retaining beam 47 is connected to a ball screw unit (not shown) built in the stand supporting arm 46 along the Z axis in the drawing, and is driven by a Z axis driving motor (not shown) to move in the Z direction (up and down). Move). Thus, the CCD camera 49 moves up and down together with the camera retaining beam 47. For this reason, in the shadow mask SM of various sizes, the CCD camera 49 can be moved up and down so that the perforated area of the transmission hole and the imaging area of the CCD camera 49 can be imaged to capture the shadow mask SM.

The CCD camera 49 is a CCD camera having two-dimensionally arranged CCD elements, and outputs the image of the contrast pattern of the shadow mask SM as digital image data of 10 bits / pixel. On the other hand, the CCD camera 49 can acquire an image of 1534 pixels x 1024 pixel areas.

The data processing apparatus 50 includes a display 52 for displaying an image to be described later, an image processing apparatus 54 for performing various image processing, and a Z-axis stage controller 56 for moving the CCD camera 49. And an auxiliary display 58 for displaying the captured image for confirmation of the imaging area of the CCD camera 49, an external storage device 60 for storing image data, a focus of the CCD camera 49, and the like. The camera control device 62 is provided. On the other hand, the camera control device 62 also has a function of receiving image data captured by the CCD camera 49 and sending it to another device.

2 is a block diagram showing the electrical configuration of the shadow mask inspection apparatus 30. The light emitted from the light source 44 passes through the measuring table 42, the glass plate 43, and the transmission holes of the shadow mask SM and enters the CCD camera 49. The CCD camera 49 obtains the image of the shadow mask SM as image data of a shaded image (multi-valued image) arranged in two dimensions. This image data Di enters the camera control device 62 and is output to the auxiliary display 58. Therefore, the auxiliary image 58 displays the live image obtained by the CCD camera 49.

The image processing apparatus 54 is a computer system which performs various processes by executing a software program. This image processing apparatus 54 includes a CPU 66, a RAM 68 as a temporary storage means for data, a keyboard 70 as a data input means, and a flexible disk device 72 for driving a flexible disk FD. And an output print 74 such as an inspection result, which are connected to each other via a bus line 64.

The Z-axis of the display 52 and the CCD camera 49, in addition to the camera controller 62, the Z-axis stage controller 56, and the external storage device 60, is provided on the bus line 64 of the image processing apparatus 54. A Z-axis rotary encoder 76 for detecting the position is connected. The Z-axis rotary encoder 76 is provided on a drive shaft of a Z-axis drive motor (not shown) for moving the CCD camera 49 together with the camera holding beam 47, and Z of the CCD camera 49 is provided. Outputs the signal of the axis position. On the other hand, this signal is input to the image processing apparatus 54, the camera control apparatus 62, and the Z-axis stage controller 56. Based on this signal and the control signal from the image processing apparatus 54, the focus adjustment of the CCD camera 49 by the camera controller 62 and the CCD camera 49 by the Z-axis stage controller 56 are performed. Z-axis position adjustment is performed.

On the other hand, by executing the software program, the CPU 66 shifts the focal point position calculating means for obtaining the focal point position of the CCD camera 49 or the focal position of the CCD camera 49 by a predetermined amount from the focal point position. Focus position adjusting means, power spectrum calculating means for obtaining a power spectrum distribution of a bokeh image obtained from the CCD camera 49, adding means for adding a power spectrum value of a predetermined spatial frequency region to obtain a power spectrum addition value, and the contrast from the power spectrum addition value. Functions of various means such as determination means for determining whether the pattern is uneven or not are realized.

3 is a flowchart showing the procedure of the nonuniformity inspection method in this embodiment. In step T1, the shadow mask SM to be subjected to nonuniform inspection is picked up by the CCD camera 49 and the image is input. At this time, in order to pick up the bokeh image, the distance L (see FIG. 1) between the CCD camera 49 and the shadow mask SM is set to be shorter than the confocal position by a predetermined amount. For example, when the focusing position of the CDD camera 49 is 1 m from the CCD camera 49, the distance between the CCD camera 49 and the shadow mask SM is 20 cm short (80 cm) from the focusing position. Set to). By doing this, a bokeh image can be obtained intentionally. The intentional imaging of the bokeh image is to prevent an interference fringe, called a beat, from occurring in the image due to interference between the pixel array of the CCD camera 49 and the light and dark patterns of the shadow mask SM. will be. That is, in step T1, a bokeh image without bits may be generated. Although individual transmission holes cannot be observed in a Bokeh image without bits, unevenness of shade due to an error in the transmission hole pattern is shown in the image.

On the other hand, in order to obtain a bitless bokeh image, the CCD camera 49 is set at a distance obtained by adding or subtracting a value of about 10% to 30% of the distance between the CCD camera 49 and the shadow mask SM at the confocal position. It is desirable to. Alternatively, it is preferable to set the CCD camera 49 at a distance where a value of about 1.5 times to about 4 times the depth of focus of the CCD camera 49 is added or subtracted in the photographing state.

In step T2 of FIG. 3, the process area is cut out from the bokeh image of the shadow mask SM picked up, and it is made into a process object. 4 is an explanatory diagram showing six processing regions R1 to R6 cut out in step T2. The six processing regions R1 to R6 are square regions, respectively, and are arranged so as to partially overlap each other to cover almost the entire surface of the bokeh image of the shadow mask. As described later, in this embodiment, since the two-dimensional Fourier transform is performed, each processing area needs to be square. On the other hand, since the shadow mask SM is almost rectangular, as shown in FIG. 4, the entire rectangular shadow mask SM is inspected by setting a plurality of square processing regions. On the other hand, the respective processing regions do not necessarily overlap each other. In addition, at least one may be described as the processing region.

In step T3 of FIG. 3, a two-dimensional Fourier transform (2d-FET) is performed for each of the processing regions R1 to R6, and a power spectrum is calculated from the conversion coefficient in step T4. The power spectrum is the quadratic sum of the real part and the imaginary part of the Fourier transform coefficient. The power spectrum thus obtained is mathematically equivalent to that obtained by Fourier transforming the autocorrelation of the image data of each processing region. Therefore, in steps T3 and T4, the mutual relation of the image data of each processing area may be obtained and Fourier transformed. That is, in steps T3 and T4, the power spectrum of each of the processing regions R1 to R6 may be obtained by any method.

5 is a graph showing an example of a power spectrum distribution obtained for good and defective products. The horizontal axis of the graph is the spatial frequency (fsp), and the vertical axis is the power spectrum value. Here, the spatial frequency fsp is defined as the frequency at the length W of one side of each processing area as shown in FIG.

As shown in FIG. 5, the power spectrum distribution is relatively flat in good products, but in the case of defective products (large deviation of hole diameter and pitch error of through holes), the power spectrum value tends to increase at a specific spatial frequency. The reason for this is that there is a bias in error in the defective product, so that the power spectrum value at the frequency of the bias becomes large.

7 is a conceptual diagram showing the power spectrum distribution obtained for each of the processing regions R1 to R6. In step T5 of FIG. 3, the power spectrum addition value is calculated by adding the power spectrum value of the specific frequency region FR with respect to each processing region. As shown in FIG. 7, each of the processing regions R1 to R6 has different power spectrum distributions, and therefore, the power spectrum addition values S1 to S6 also have different values. On the other hand, the power spectrum addition value is a value obtained by integrating the power spectrum distribution with respect to a specific frequency region FR.

As a specific frequency area | region FR for obtaining an addition value, the value of the spatial frequency fsp is 5-19, for example. The power spectrum having a spatial frequency fsp of less than 5 is affected by the grade of the shadow mask SM. [Grade] here means that the design value of the hole diameter and pitch of a permeation | transmission hole is changed in the vicinity of the periphery part of shadow mask SM. For example, the pitch of the transmission hole in the outer periphery of shadow mask SM is designed larger than the pitch in the center part. Such grade pitches appear in a region of relatively low spatial frequency. Therefore, in the nonuniformity inspection apparatus, in order to remove the influence of the grade, a relatively low spatial frequency region of less than about 5 is removed and the power spectral value is added. On the other hand, the power spectrum value in the relatively high spatial frequency region does not have a large difference between good and bad products, as can be seen from FIG. Therefore, in the non-uniformity test, a relatively high spatial frequency region of more than about 20 is removed to add the power spectrum value.

As can be seen from the above description, the specific spatial frequency region FR indicating the addition range in step T5 does not include the relatively low spatial frequency region affected by the grade of the shadow mask SM and at the same time. This region does not include a relatively high spatial frequency region over a predetermined frequency. On the other hand, the range of the spatial frequency region FR to be added is set to an appropriate range that differs depending on the design of the shadow mask, the size of the processing region, and the like.

In step T6 of FIG. 3, the maximum value of the power spectrum addition values S1 to S6 for the six processing regions R1 to R6 is obtained, and the maximum value thereof is compared with a predetermined threshold value to determine the shadow mask SM. Determine the non-uniformity. And in step T7, the determination result is displayed on the display 52. As shown in FIG. The larger the nonuniformity, the larger the power spectrum addition. The maximum value of the power spectrum addition values S1 to S6 is compared with the threshold value in order to determine whether the non-uniformity is in the processing area having the largest nonuniformity among the six processing areas R1 to R6.

8 is a graph showing the relationship between the sum of the power spectrum of the shadow mask and the rank of both parts of the shadow mask by humans. The graph of FIG. 8 is the graph which matched the rank of both parts of the nonuniformity which the inspector performed by the non-uniformity test with the naked eye corresponded with the power spectrum addition value obtained by the nonuniformity tester of an Example. In the inspection of the rank of the inspector, the thing of rank 3.5 or more is defective goods, and the thing of rank 3 or less is good products. As can be seen from FIG. 8, there is an extremely high correlation between the added value of the power spectrum obtained by the nonuniform inspection apparatus of this embodiment and the rank assigned by the inspector. For example, in the graph of FIG. 8, the power spectrum addition value f3 corresponding to the lowest rank 3 of the good in a visual inspection by an inspection person, and the power spectrum addition value corresponding to the highest rank 3.5 of the defective product f3. Using 5) as the threshold value, respectively, it is possible to automatically determine whether the shadow mask is nonuniform. On the other hand, in consideration of the error of non-uniformity inspection, the rank is defined as a gray area between 3 and 3.5, and the shadow mask entering the gray area may be inspected by the inspector visually. In this case, since the inspector only needs to visually inspect the shadow mask entering the gray area, the inspection efficiency is improved. In addition, since most of the shadow masks are automatically determined whether or not unevenness, the stability of the inspection results can be ensured.

As described above, according to this embodiment, since the bokeh image without bit influence of the shadow mask SM is picked up, the influence of the bit of the shadow mask SM on the result of nonuniformity inspection can be reduced. Further, the power spectrum is obtained by calculating the power spectrum of the bokeh image, adding the power spectrum value in a specific spatial frequency region from which the frequency of the shadow mask SM is removed, and determining whether the non-uniformity is determined according to the power spectrum addition value. The influence of the grade of SM) on the result of nonuniformity inspection can be made small. That is, according to this embodiment, it is possible to inspect the nonuniformity quantitatively while minimizing the influence of the bit or the grade of the shadow mask SM.

In addition, this invention is not limited to the said Example, It can implement in various forms in the range which does not deviate from the summary, For example, the following modification is also possible.

(1) In the above embodiment, a plurality of processing regions R1 to R6 are set in the shadow mask, but at least one may be set as the processing region. However, as shown in FIG. 4, when a plurality of processing regions are set to cover almost the entire surface of the shadow mask, a region having a large non-uniformity can be detected among the plurality of processing regions, so that local nonuniformity can be determined more reliably. There is an advantage to that.

(2) In the above embodiment, the bokeh image without the influence of the bit is directly captured by the CCD camera 49. However, the CCD camera 49 captures the sharp original image and processes the original image. A bokeh image without the influence of may be obtained. For example, a bokeh image can be created by performing a smoothing process such as a median filter on the sharp original image picked up by the CCD camera 49. Alternatively, by dividing the image data of the original image by the image data of the bokeh image after the smoothing process, an image from which the influence of the grade is removed is obtained. Such a grade removal image may be subjected to nonuniform inspection as a processing target.

(3) In the above embodiment, in order to obtain a bokeh image without influence of bits, the CCD camera 49 is set at a position out of the focusing position, but the CCD camera 49 is set at the focusing position, and the resolution By lowering (optical MTF), a bokeh image may be obtained. 9 is a conceptual diagram showing the configuration of the lens system 80 of the CCD camera 49. As shown in FIG. This lens system 80 has a barrel 82, lenses 84, 85, 86 and an aperture stop 88 provided in the center of the barrel 82. By using the lens system 80 as described above, the confocal position is obtained in the state where the aperture stop is opened (Fig. 9a), and while the aperture stop is tightened until the bit is no longer affected (Fig. 9b). By imaging, a bokeh image can be obtained. In this case, there is an advantage that a bokeh image can be generated without changing the imaging magnification.

Claims (6)

A method for inspecting a non-uniformity of a light intensity pattern formed on a periodic basis, the method comprising: (a) obtaining a bokeh image of the light intensity pattern; (b) obtaining a power spectral distribution for at least a portion of the area of the bokeh image; c) adding a power spectrum value in a predetermined spatial frequency region of the power spectrum distribution to obtain a power spectrum addition value; and (d) the power spectrum addition value and a predetermined threshold ( And (b) to determine whether the unevenness of the light and shade pattern is uneven. 2. The process according to claim 1, wherein the step (a) comprises the steps of (1) obtaining a confocal position between the imaging means for imaging the bokeh image and the contrast pattern, and (2) the imaging means. And (3) obtaining the bokeh image by capturing an image of the contrast pattern at a focal position shifted from the focal point by a predetermined amount by shifting a focal position from the focal point. Non-uniformity test method. 2. The process according to claim 1, wherein the step (a) comprises the steps of: (1) obtaining a confocal position between the image pickup means for picking up the bokeh image and the light and dark pattern with the aperture stop of the image pickup means open; (2) a step of tightening the aperture stop and (3) a step of obtaining the bokeh image by imaging an image of the light and dark pattern at the confocal position with the aperture stop tight. Non-uniformity test method. An apparatus for inspecting a non-uniformity of a light pattern that is formed periodically, the apparatus comprising: bokeh image generating means for obtaining a bokeh image of the light pattern and power spectrum calculating means for obtaining a power spectrum distribution of at least a part of the area of the bokeh image; Adding means for adding a power spectral value in a predetermined spatial frequency region of the spectral distribution to obtain a power spectral addition value, the power spectral addition value and a predetermined threshold ( And judging means for judging whether the unevenness of the light and shade pattern is uneven. 5. The apparatus according to claim 4, wherein said bokeh image generating means comprises: a focal point position calculating means for obtaining a confocal position between an image capturing means for imaging said bokeh image and said contrast pattern, and a focal position of said image capturing means; And an image capturing means for obtaining the bokeh image by capturing an image of the contrast pattern at a focal position shifted from the confocal position and a focal position adjusting means shifting a predetermined amount from the position. 5. The apparatus according to claim 4, wherein said bokeh image generating means comprises: imaging means having an aperture stop and a focal point position calculation means for obtaining a focal point position between the imaging means and the contrast pattern with the aperture stop open; And the imaging means obtains the bokeh image by capturing an image of the contrast pattern at the confocal position with the aperture stop fastened.