JP2000215803A - Device and method for detecting defect of shadow mask - Google Patents

Abstract

PROBLEM TO BE SOLVED: To highly distinguishably detect holes-defect of a shadow mask necessary for judging a three dimension shape, uniformly and mechanically regardless of the kindness of the defects, and without necessitating an accuracy of positioning. SOLUTION: An inspecting image signal 10 for expressing an inspection region of a shadow mask is subjected to Fourier transformation, a reference image signal 11 is subjected to Fourier transformation, a composite image signal 16 is obtained by multiplying the complex conjugate of the phase component of the Fourier transform 15 of the reference image signal 11 to the phase component of the Fourier transform 14 of the inspecting image signal 10, the composite image signal 16 is subjected to inverse Fourier transform so as to obtain the correlation intensity signal 18, and the defect of the shadow mask is detected from the peal intensity of the correlation intensity signal 18.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an apparatus and a method for detecting a defect in a hole of a shadow mask. Even when a fine hole cannot be imaged with sufficient resolution, it can be suitably used for detecting a shape defect.

[0002]

2. Description of the Related Art As a method for detecting a hole defect in a shadow mask, an inspection image signal of a shadow mask to be inspected and a reference image signal of a reference shadow mask are used.
There is a method of detecting defects by comparing the sizes and areas of holes. Methods of determining a hole shape defect other than the hole size and hole area include a method of detecting a defect from a cross-correlation value between an inspection image signal and a reference image signal, and a method of detecting a difference between images. is there.

When determining the size and area of a hole, the observation image of the shadow mask is binarized into an opening and a non-opening of the hole, and the determination is performed. However, there is a problem that only a large hole or a small hole can be determined due to a different design, and the three-dimensional shape of the cross section of the hole cannot be determined.

When a defect is detected from a cross-correlation value between an inspection image signal and a reference image signal, the cross-correlation value is reduced when noise or distortion occurs due to the nature of the cross-correlation method, and the discrimination ability is sufficient. There is no problem.

[0005] When detecting and detecting the difference between the inspection image signal and the reference image signal, there is a problem that positioning accuracy is difficult, and in the case of a shadow mask in particular, the pattern of the arrangement of holes is different over the entire surface. In a high-definition shadow mask, the permissible tolerance of the hole diameter is about ± 5 μm, and there is a problem that an image processing method having high discrimination ability is required for detecting a hole defect.

Meanwhile, as a method of detecting a defect in a hole of a shadow mask, there is also a sensory inspection performed visually. In this sensory inspection, since the hole to be a defect is determined by comparison with the surrounding holes, among the holes included in the inspection image signal, not only holes having different sizes and areas from the surroundings,
It is considered that a hole whose cross-sectional shape of the hole is different from the surroundings is also detected. However, the sensory test has a problem that a large number of people are required.

[0007]

SUMMARY OF THE INVENTION The present invention has been made in order to solve the above-mentioned problem, and it is possible to unify hole defects of a shadow mask which need to be determined for a three-dimensional shape, regardless of the type of the defect. It is an object to perform detection with high discrimination ability without mechanically requiring positioning accuracy.

[0008]

In order to achieve the above object, according to the present invention, first, an inspection image signal representing an inspection area of a shadow mask is compared with a reference image signal. A means for performing a Fourier transform on the inspection image signal, a means for performing a Fourier transform on the reference image signal, and a Fourier transform of the reference image signal as a phase component of the Fourier transform of the inspection image signal. Means for obtaining a composite image signal by multiplying the complex conjugate of the phase component of the transformation, means for obtaining a correlation intensity signal by performing an inverse Fourier transform on the composite image signal, and means for detecting a defect in the shadow mask from the peak intensity of the correlation intensity signal And a shadow mask defect detection device characterized by having the following.

According to a second aspect of the present invention, there is provided an apparatus for detecting a defect in a shadow mask by comparing an inspection image signal representing an inspection area of a shadow mask with a reference image signal. Means for obtaining a reference image signal by masking all but one hole of the shadow mask, means for performing a Fourier transform on the inspection image signal, means for performing a Fourier transform on the reference image signal, and Fourier transformation of the inspection image signal Means for obtaining a composite image signal by multiplying the phase component of the reference image signal by the complex conjugate of the phase component of the Fourier transform, means for obtaining a correlation intensity signal by inverse Fourier transforming the composite image signal, and a peak of the correlation intensity signal. Means for detecting a defect in the shadow mask from the intensity.

According to a third aspect of the present invention, there is provided an apparatus for detecting a defect of a shadow mask by comparing an inspection image signal representing an inspection area of the shadow mask with a reference image signal. Means for obtaining an inspection image signal by cutting out an inspection area of a shadow mask from an observation image signal obtained by photographing, and obtaining a reference image signal by masking all but one hole of the shadow mask from the inspection image signal Means, Fourier transform means for the inspection image signal, means for Fourier transform the reference image signal, and a phase component of the Fourier transform of the inspection image signal multiplied by a complex conjugate of a Fourier transform phase component of the reference image signal. A means for obtaining an image signal; a means for obtaining a correlation intensity signal by performing an inverse Fourier transform on the combined image signal; Is obtained by the defect detection apparatus of the shadow mask, characterized by comprising means for detecting and the.

According to a fourth aspect of the present invention, there is provided a method for detecting a defect in a shadow mask by comparing an inspection image signal representing an inspection area of a shadow mask with a reference image signal. And Fourier transforming the reference image signal, and multiplying the Fourier transform phase component of the inspection image signal by the complex conjugate of the Fourier transform phase component of the reference image signal to obtain a combined image signal. A method of detecting a defect of a shadow mask from a peak intensity of the correlation intensity signal, and a step of obtaining a correlation intensity signal by performing an inverse Fourier transform of the synthesized image signal. Things.

According to a fifth aspect of the present invention, there is provided a method for detecting a defect in a shadow mask by comparing an inspection image signal representing an inspection area of a shadow mask with a reference image signal. Obtaining a reference image signal by masking all but one hole of the shadow mask, performing a Fourier transform on the inspection image signal, performing a Fourier transform on the reference image signal, and performing a Fourier transform on the inspection image signal. Multiplying the phase component of the reference image signal by the complex conjugate of the phase component of the Fourier transform to obtain a composite image signal; inverse Fourier transforming the composite image signal to obtain a correlation intensity signal; Detecting a defect of the shadow mask from the intensity.

According to a sixth aspect of the present invention, there is provided a method for detecting a defect of a shadow mask by comparing an inspection image signal representing an inspection area of the shadow mask with a reference image signal. A step of cutting out an inspection area of a shadow mask from an observation image signal obtained by photographing to obtain an inspection image signal, and obtaining a reference image signal by masking all but one hole of the shadow mask from the inspection image signal Combining the Fourier transform of the inspection image signal, the Fourier transform of the reference image signal, and the phase component of the Fourier transform of the inspection image signal by the complex conjugate of the Fourier transform phase component of the reference image signal. Obtaining an image signal, performing an inverse Fourier transform on the combined image signal to obtain a correlation intensity signal, and determining whether a shadow mask is missing from the peak intensity of the correlation intensity signal. A step of detecting, in which a defect detection method of the shadow mask, which comprises a.

[0014]

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

The method of the present invention is an image processing method for imaging a shadow mask as an object to be inspected and detecting a hole defect. FIG. 1 is a block diagram of the apparatus of the present invention for executing the method of the present invention. As shown in FIG. 1, the light emitted from the transmission light source 1 passes through the diffusion plate 2 and becomes uniform in the plane direction. The light transmitted through the shadow mask 3 is imaged by the objective lens 4 and imaged by the solid-state imaging device 5. Imaging is a dark curtain 6
And in a dark room environment to cancel stray light. The image processing unit 7 includes the respective units described in claims 1 to 3, and the respective units execute the respective steps described in claims 4 to 6, thereby performing a correlation process of the phase component of the Fourier transform. To detect a hole defect in the shadow mask. This will be described in detail using the following three embodiments.

[0016]

In the first embodiment of the present invention, each means described in claim 1 executes each step described in claim 4 to perform a correlation process of a phase component of Fourier transform. This is to detect a defect in the hole of the shadow mask. This first
Will be described in detail with reference to FIG.

An inspection image signal 8 obtained by imaging the hole of the shadow mask from the side of the large hole is represented as an inspection image signal 10 as a two-dimensional image signal. The size and shape of the stoma,
If the size and shape of the large hole and the characteristics of the tapered portion are different from those of the reference image signal 9, the defect is determined.

A Fourier transform 12 is performed on the inspection image signal 10 to obtain a Fourier transform 14 of the inspection image signal.
Similarly, a Fourier transform 13 is performed on the two-dimensional reference image signal 11 of the reference image signal 9 to obtain a Fourier transform 15 of the reference image signal. Fourier transform 12, Fourier transform 1
3 is a discrete Fourier transform.

When the amplitude component of the Fourier transform 14 of the inspection image signal is set to 1, the Fourier transform 14 of the inspection image signal is obtained.
Is the phase component of Similarly, when the amplitude component of the Fourier transform 15 of the reference image signal is set to 1, the phase component of the Fourier transform 15 of the reference image signal is obtained. The phase component of the Fourier transform 14 of the inspection image signal is multiplied by the complex conjugate of the phase component of the Fourier transform 15 of the reference image signal to obtain a composite image signal 1
Get 6. A correlation strength signal 18 is obtained by performing an inverse Fourier transform 17 on the composite image signal 16.

Since the phase component of the Fourier transform has information on the shape of the correlation intensity signal 18 and the autocorrelation function is a delta function, the correlation strength signal 18 has a high discriminating ability with respect to a hole defect of the shadow mask. Like the correlation strength signal 19, even if the positions of the holes in the inspection image signal 8 and the reference image signal 9 are different from each other, the inspection image signal 8
A sharp peak appears at the position where the hole exists, and the defect of the hole can be detected based on the peak intensity. That is, if the degree of matching of the hole of the inspection image signal 8 with the reference image signal 9 in its shape increases, the peak intensity increases, and if the degree of matching decreases, the peak intensity decreases.

According to a second embodiment of the present invention, each means described in claim 2 executes each step described in claim 5 to perform a correlation process of a phase component of a Fourier transform to perform shadow processing. This is to detect a defect in the hole of the mask. This second embodiment will be described with reference to FIG.

The inspection image signal 20 obtained by imaging the shadow mask is subjected to a masking process 21 to obtain a reference image signal 22 in which a portion other than one hole is masked. The Fourier transform 25 is performed on the two-dimensional test image signal 23 of the test image signal 20 to obtain the Fourier transform 27 of the test image signal. Similarly, a Fourier transform 26 is performed on the two-dimensional reference image signal 24 of the reference image signal 22 to obtain a Fourier transform 28 of the reference image signal. The Fourier transform 25 and the Fourier transform 26 are both discrete Fourier transforms.

The one in which the amplitude component of the Fourier transform 27 of the inspection image signal is set to 1 is the Fourier transform 27 of the inspection image signal.
Is the phase component of Similarly, one in which the amplitude component of the Fourier transform 28 of the reference image signal is set to 1 is the phase component of the Fourier transform 28 of the reference image signal. The phase component of the Fourier transform 27 of the inspection image signal is multiplied by the complex conjugate of the phase component of the Fourier transform 28 of the reference image signal to obtain a composite image signal 2
Get 9. A correlation strength signal 31 is obtained by performing an inverse Fourier transform 30 on the composite image signal 29.

When the correlation strength signal 31 is two-dimensionally displayed, a peak of the correlation strength with the hole of the reference image signal 22 appears at the position where the hole of the inspection image signal 20 exists, like the correlation strength signal 32. A hole having a low correlation (a hole having a small peak value) among the holes existing in the inspection image signal 20 is obtained based on the peak value of the correlation intensity, and a defect of the hole can be detected.

According to a third embodiment of the present invention, each means described in claim 3 executes each step described in claim 6 to perform a correlation process of a phase component of Fourier transform to perform shadow processing. This is to detect a defect in the hole of the mask. This third embodiment will be described with reference to FIGS.

As shown in FIG. 4, in the observation image signal 33 obtained by imaging the shadow mask, the shape of the hole of the shadow mask differs depending on the region. From the observation image signal 33, a region in which the shape of the hole can be regarded as constant, such as the inspection image signal 34 and the inspection image signal 35, is cut out and used as an inspection image signal. A correlation intensity signal between the inspection image signal and a reference image signal obtained by masking a portion other than the portion corresponding to one reference hole from the inspection image signal is obtained, and a hole defect can be detected from the peak value of the correlation intensity.

FIGS. 5 and 6 show examples applied to an actual shadow mask observation image. From the inspection image signal 36 cut out from the observation image signal of the shadow mask, a reference image signal 38 in which a portion other than a portion corresponding to one hole is masked is obtained.
Correlation strength signal 3 between inspection image signal 36 and reference image signal 38
In FIG. 9, a peak of the correlation strength appears at the position where the hole exists in the inspection image signal 36. In the correlation intensity signal 40 of the inspection image signal 37 and the reference image signal 38 in which the hole having the defect exists, the correlation intensity peak of the hole having the defect is reduced.

[0028]

According to the apparatus and method of the present invention, when the hole shape differs depending on the shadow mask region due to the offset cone processing and the grating processing, the reference image signal is individually applied to the region where the hole shape can be regarded as constant. With such a configuration, there is an effect that a hole having a shape different from that of a peripheral hole can be detected as a defect.

Due to the nature of the Fourier transform, even if a plurality of holes exist in the area of the inspection image signal, if the correlation intensity signal is obtained by masking a part other than one hole in the reference image signal, the inspection is performed. At the position where the hole of the image signal exists, a correlation intensity peak between each hole of the inspection image signal and the hole of the reference image signal appears. There is an effect that the defect of the hole can be detected by the correlation intensity peak.

Since the pitch of the holes differs depending on the shadow mask region due to the variable pitch processing, accurate positioning is required in the conventional method for detecting a defect from the difference between an inspection image signal and a reference image signal. The apparatus and method of the present invention have an effect that the positional deviation between the inspection image signal and the reference image signal is not affected by the nature of the Fourier transform, and the correlation strength between the holes of the inspection image signal and the reference image signal can be obtained.

In this method, since only the phase component is used with the amplitude component of the Fourier transform being a fixed value, the correlation intensity signal is not affected by the illuminance difference as in the conventional method. There is an effect that it is not necessary to perform correction in the processing.

The defect inspection of the holes of the shadow mask, which is performed by the sensory inspection, is made by visually observing the front, oblique or changing the distance from the shadow mask. At this time, when the three-dimensional cross-sectional shape of the hole of the shadow mask is different from the surrounding holes, it is considered that the hole is determined as a defect. In the conventional methods other than the sensory test, the determination is made based on the area of the large hole diameter and the small hole diameter, and the three-dimensional sectional shape of the hole is not considered. In the apparatus and method of the present invention,
Since the correlation between the phase components of the Fourier transform having the shape characteristic information is used, there is an effect that the correlation between the three-dimensional shapes can be compared and determined.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of an apparatus of the present invention for executing a method of the present invention.

FIG. 2 is a view for explaining the flow of each step according to claim 3 executed by each means according to claim 1;

FIG. 3 is a view for explaining the flow of each step according to claim 4 executed by each means according to claim 2;

FIG. 4 is a view for explaining that an inspection image signal is obtained by cutting out a region in which the shape of a hole of a shadow mask can be considered to be constant.

FIG. 5 is a diagram illustrating an example of an actually extracted inspection image signal and an example of a reference image signal obtained from the inspection image signal.

FIG. 6 is a view for explaining detection of a hole defect in a shadow mask based on the intensity of a peak value of a correlation intensity signal.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Transmission light source 2 ... Diffusion plate 3 ... Shadow mask 4 ... Objective lens 5 ... Solid-state image sensor 6 ... Dark curtain 7 ... Image processing unit 8 ... Inspection image signal 9 ... Reference image signal 10 ... Inspection image signal 11... Reference image signal 12... Fourier transformation 13... Fourier transformation 14... Fourier transformation of inspection image signal 15. Conversion 18 Correlation strength signal 19 Correlation strength signal 20 Inspection image signal 21 Mask processing 22 Reference image signal 23 Inspection image signal 24 Reference image signal 25 Fourier transform 26 Fourier transform 27 Fourier transform of inspection image signal 28 Fourier transform of reference image signal 29 Composite image signal 30 Inverse Fourier transform 31 Correlation strength signal 32 ... Correlation strength signal 33... Observation image signal 34... Inspection image signal 35... Inspection image signal 36... Inspection image signal 37... Inspection image signal 38. Correlation strength signal

Claims (6)

[Claims] 1. A comparison between an inspection image signal representing an inspection area of a shadow mask and a reference image signal,
An apparatus for detecting a defect of a shadow mask, comprising: means for performing a Fourier transform on an inspection image signal; means for performing a Fourier transform on a reference image signal; and a Fourier transform of the reference image signal into a phase component of the Fourier transform of the inspection image signal. Means for obtaining a composite image signal by multiplying the complex conjugate of the phase component, means for obtaining a correlation intensity signal by performing an inverse Fourier transform on the composite image signal, means for detecting a defect in the shadow mask from the peak intensity of the correlation intensity signal, A defect detection apparatus for a shadow mask, comprising: 2. By comparing an inspection image signal representing an inspection area of a shadow mask with a reference image signal,
An apparatus for detecting a defect of a shadow mask, a means for masking all but one hole of the shadow mask from an inspection image signal to obtain a reference image signal, a means for performing a Fourier transform on the inspection image signal, Means for Fourier transforming the image signal; means for multiplying the phase component of the Fourier transform of the inspection image signal by the complex conjugate of the phase component of the Fourier transform of the reference image signal to obtain a combined image signal; and inverse Fourier transform of the combined image signal And a means for detecting a defect in the shadow mask from a peak intensity of the correlation intensity signal. 3. A comparison between an inspection image signal representing an inspection area of a shadow mask and a reference image signal,
An apparatus for detecting a defect of a shadow mask, comprising: means for extracting an inspection area of the shadow mask from an observation image signal obtained by photographing the shadow mask to obtain an inspection image signal; and a hole of the shadow mask from the inspection image signal. Means for obtaining a reference image signal by masking all but one of the following, means for performing a Fourier transform on the test image signal, means for performing a Fourier transform on the reference image signal, and a reference component for the phase component of the Fourier transform of the test image signal. Means for obtaining a composite image signal by multiplying the complex conjugate of the phase component of the Fourier transform of the image signal; means for obtaining a correlation intensity signal by inverse Fourier transforming the composite image signal; and a defect of the shadow mask from the peak intensity of the correlation intensity signal A defect detection device for a shadow mask, comprising: 4. A comparison between a reference image signal and an inspection image signal representing an inspection area of a shadow mask,
A method for detecting a defect of a shadow mask, comprising the steps of: Fourier transforming an inspection image signal; Fourier transforming a reference image signal; and applying a Fourier transform of the reference image signal to a phase component of the Fourier transform of the inspection image signal. Obtaining a composite image signal by multiplying the complex conjugate of the phase component, obtaining a correlation intensity signal by performing an inverse Fourier transform on the composite image signal, and detecting a shadow mask defect from the peak intensity of the correlation intensity signal; A defect detection method for a shadow mask. 5. A comparison between an inspection image signal representing an inspection area of a shadow mask and a reference image signal,
A method of detecting a defect of a shadow mask, wherein a mask image is obtained by masking all but one hole of a shadow mask from an inspection image signal to obtain a reference image signal; a step of performing a Fourier transform of the inspection image signal; A step of performing a Fourier transform on the image signal; a step of multiplying a phase component of the Fourier transform of the inspection image signal by a complex conjugate of a phase component of the Fourier transform of the reference image signal to obtain a combined image signal; and an inverse Fourier transform of the combined image signal Obtaining a correlation intensity signal, and detecting a defect of the shadow mask from a peak intensity of the correlation intensity signal. 6. A comparison between an inspection image signal representing an inspection area of a shadow mask and a reference image signal,
A method of detecting a defect of a shadow mask, comprising: a step of cutting out an inspection area of the shadow mask from an observation image signal obtained by photographing the shadow mask to obtain an inspection image signal; Obtaining a reference image signal by masking all but one of the following: a step of performing a Fourier transform of the inspection image signal; a step of performing a Fourier transform of the reference image signal; A step of obtaining a composite image signal by multiplying the complex conjugate of a phase component of a Fourier transform of the image signal; a step of obtaining a correlation intensity signal by performing an inverse Fourier transform of the composite image signal; a defect of the shadow mask from the peak intensity of the correlation intensity signal Detecting a defect of the shadow mask.