CN114529500A

CN114529500A - Defect inspection method for display substrate

Info

Publication number: CN114529500A
Application number: CN202111208310.9A
Authority: CN
Inventors: 李东勳; 金孝眞; 崔慧媛; 金明铁; 徐智勳; 粱炅镐
Original assignee: Samsung Display Co Ltd
Current assignee: Samsung Display Co Ltd
Priority date: 2020-11-03
Filing date: 2021-10-18
Publication date: 2022-05-24
Also published as: KR20220060080A

Abstract

A defect inspection method of a display substrate is disclosed. The defect inspection method of the display substrate comprises the following steps: shooting an image of a display substrate; extracting an X-axis distribution of the image; extracting a Y-axis distribution of the image; generating line tracking information based on the X-axis distribution and the Y-axis distribution; acquiring boundary positions of constituent elements of the display substrate based on the line tracing information; matching a preset region of interest with an actual region of interest of the image on the basis of the boundary position; and inspecting the matched actual region of interest for defects.

Description

Defect inspection method for display substrate

Technical Field

The present invention relates to a defect inspection method for a display substrate, and more particularly, to a defect inspection method for a display substrate using an optical inspection apparatus.

Background

Display devices such as organic light emitting display devices and liquid crystal display devices have been continuously developed in the direction of high resolution according to market demands. In this process, in order to achieve high resolution in the same space, development is made in a direction in which a Critical Dimension (CD) of a process and a size of a sub-pixel are gradually reduced, which results in an increase in complexity of a circuit.

However, the increase in resolution is a direct factor of increasing the degree of integration of the wiring in the same area and causing poor miniaturization. Therefore, an increase in the absolute number of defects is caused, and thus the number of defects requiring a repair process increases.

However, since the tact time (tact time) of the process and the capacity of the equipment are limited in terms of the production efficiency of the production line, there is a case where the repair process cannot be performed for all the defects. As a result, in order to maximize production efficiency and yield gain, a method capable of preferentially repairing a defect having a high possibility of exhibiting a fatal (culling) defect is required.

Heretofore, optical inspection has been used to detect defects and prioritize repair based on the size or type of the defect to handle the repair, but this approach has limitations and therefore may require a scheme that selectively enhances inspection and handles repair with a target location within the circuit at which the rate of damage (kill-ratio) is high.

Disclosure of Invention

In view of the above, it is an object of the present invention to provide a defect inspection method for a display substrate capable of acquiring a boundary position of a component of the display substrate based on line trace information.

A defect inspection method of a display substrate according to an embodiment for achieving the above object of the present invention includes the steps of: shooting an image of a display substrate; extracting an X-axis distribution of the image; extracting a Y-axis distribution of the image; generating line tracking information based on the X-axis distribution and the Y-axis distribution; acquiring boundary positions of constituent elements of the display substrate based on the line tracing information; matching a preset region of interest with an actual region of interest of the image on the basis of the boundary position; and inspecting the matched actual region of interest for defects.

In an embodiment of the invention, the X-axis distribution may be generated by accumulating luminance for N sets of camera pixels in the Y-axis direction.

In an embodiment of the invention, the N camera pixel groups may correspond to lengths of first sides of sub-pixels of the display substrate.

In an embodiment of the invention, the Y-axis distribution may be generated by accumulating luminance for M camera pixel groups in the X-axis direction.

In an embodiment of the invention, the M camera pixel groups may correspond to lengths of second sides of the sub-pixels of the display substrate.

In an embodiment of the present invention, the method for inspecting defects of a display substrate may further include, before the step of extracting the X-axis distribution, the steps of: determining a tilt (tilting) of the image at a reference position of the image.

In an embodiment of the present invention, the step of inspecting the actual region of interest for defects may comprise the steps of: generating a difference image of the actual region of interest and an adjacent region of interest adjacent to the actual region of interest.

In an embodiment of the present invention, the step of generating the difference image may include the steps of: generating difference images of the actual region of interest and 4 adjacent regions of interest adjacent to the actual region of interest in upper, lower, right, and left directions.

In an embodiment of the present invention, the method for inspecting defects of a display substrate may further include, after the step of inspecting the defects of the actual region of interest, the steps of: verifying the exact location of the defect.

In an embodiment of the present invention, the step of verifying the exact location of the defect may comprise the steps of: storing a defect position of the defect; and filtering the accuracy of the defect location.

In an embodiment of the present invention, the step of filtering the accuracy of the defect location may include the steps of: the defect location is compared to an adjacent region of interest adjacent to the defect location.

In an embodiment of the present invention, the step of verifying the accurate position of the defect may further include the steps of: moving the defect location based on the comparison of the defect location and the adjacent region of interest; and judging whether the defect exists again at the moved defect position.

A defect inspection method of a display substrate according to an embodiment for achieving the above object of the present invention includes the steps of: shooting a color image of a display substrate at high resolution; obtaining information of a region of interest from the color image; converting the color image into a first black-and-white image; generating a second black-and-white image by compensating for a luminance deviation of the color image and the first black-and-white image; generating a third black-and-white image by blurring a boundary of the second black-and-white image once; generating a fourth black-and-white image by blurring a boundary of the third black-and-white image twice; and generating a fifth black-and-white image by resizing the fourth black-and-white image.

In an embodiment of the invention, the color image includes a red value, a green value and a blue value, the first black-and-white image has a first black-and-white luminance value, and when the red value is R, the green value is G, the blue value is B, the first black-and-white luminance value is GR, a first conversion constant is a, a second conversion constant is B, and a third conversion constant is c, GR ═ R + a + G × B + B ×.

In an embodiment of the present invention, the step of generating the second black-and-white image may reduce the brightness of the first black-and-white image by using a brightness reduction filter.

In an embodiment of the present invention, the step of generating the third black-and-white image may blur the boundary of the second black-and-white image using a boundary blurring filter.

In an embodiment of the present invention, the boundary blurring filter may be any one of a gaussian filter, an average filter, and a median filter.

In an embodiment of the invention, the step of generating the fourth black and white image may change an image characteristic of an area (area) camera to an image characteristic of a Time Delay Integration (TDI) camera.

In an embodiment of the present invention, the method for inspecting defects of a display substrate may further include: capturing an image of the display substrate at a low resolution; and marking a new region of interest in the image taken at the low resolution using the fifth black-and-white image and the region of interest corresponding to the fifth black-and-white image.

According to the defect inspection method of the display substrate as described above, it is possible to selectively inspect defects occurring due to various physical errors and limitations in the optical inspection apparatus by using the compensation techniques such as the position search technique, the defect inspection technique of the composite verification, and the consistency maximization technique using the multi-layer image processing.

For example, poor detection caused by a bright spot defect displayed relatively brighter than the surrounding area may be increased, poor detection caused by a dark spot defect displayed relatively darker than the surrounding area may be increased, a false defect that is considered to be poor although not actually poor may be found, and detailed monitoring and management may be performed by defect type.

Also, the effect of shortening the tact time can be obtained by selective review through selective defect inspection.

Drawings

Fig. 1 is a schematic view illustrating a defect inspection system of a display substrate according to an embodiment of the present invention.

Fig. 2 is a schematic view illustrating a defect inspection method of a display substrate using the defect inspection system of the display substrate of fig. 1.

Fig. 3 is a flowchart illustrating a defect inspection method of the display substrate of fig. 2.

Fig. 4 is a diagram illustrating a defect inspection method of a display substrate according to a comparative example.

Fig. 5 to 8 are diagrams illustrating a defect inspection method of the display substrate of fig. 2.

Fig. 9 is a flowchart illustrating a defect inspection method of a display substrate according to an embodiment of the present invention.

Fig. 10 to 15 are diagrams illustrating a defect inspection method of the display substrate of fig. 9.

Description of reference numerals:

ST: display substrates CM1, CM2, CM3, CM 4: image capturing apparatus

Detailed Description

The present invention will be described in more detail below with reference to the accompanying drawings.

Referring to fig. 1, the defect inspection system of the display substrate includes a display substrate ST and photographing devices CM1, CM2, CM3, and CM4 photographing the display substrate ST.

The display substrate ST may be moved in a specific direction under the photographing devices CM1, CM2, CM3, CM4, and the photographing devices CM1, CM2, CM3, CM4 may photograph a region of the display substrate ST.

The defect inspection system of the display substrate may include software for determining whether a defect exists in the display substrate based on the photographed image of the display substrate. In contrast, the photographed image of the display substrate may be visually inspected to determine whether the display substrate has a defect.

Fig. 2 is a schematic view illustrating a defect inspection method of a display substrate using the defect inspection system of the display substrate of fig. 1. Fig. 3 is a flowchart illustrating a defect inspection method of the display substrate of fig. 2.

Referring to fig. 1 to 3, the defect inspection method of the display substrate ST may include a line tracing step and a double inspection step.

The line tracing step may include the steps of: searching for an image position based on the image of the display substrate ST; and selectively performing defect inspection on a specific region of interest based on the searched image position.

The double inspection step may store the defective positions detected in the line tracing step, perform accurate position verification (e.g., CROP template matching (CROP TEMPLATE MATCHING)) on the defective positions, and perform defect inspection again at the accurate positions.

In the defect inspection method of the display substrate ST, first, an image of the display substrate ST is photographed (step S10). The image of the display substrate ST may be photographed by photographing devices CM1, CM2, CM3, CM4 of fig. 1.

When the image is captured, an X-axis distribution may be extracted from the image (step S20). Also, a Y-axis distribution may be extracted from the image (step S30).

Line tracking information may be generated based on the X-axis distribution and the Y-axis distribution (step S40). For example, the line tracing information may represent luminance distribution information within the image.

The boundary positions of the components of the display substrate ST may be acquired based on the line trace information (step S50). For example, all coordinate information of the sub-pixels within the display substrate ST may be confirmed by the line trace information. For example, all boundaries of gate lines, all boundaries of data lines, and the like within the display substrate ST may be confirmed by the line trace information. For example, all positions of transistors within sub-pixels within the display substrate ST may be confirmed by the line trace information.

A predetermined region of interest may be matched with an actual region of interest of the image based on the boundary position (step S60). The predetermined region of interest indicates a region in which a fatal (culling) defect is highly likely to occur, and may be set in advance by an inspector.

Accordingly, defect inspection can be selectively performed on the actual region of interest that matches (step S70).

Referring to fig. 4, in the conventional method, reference position information is previously set as a light green frame, and the defect inspection can be performed by comparing the photographed image and a previously set reference position with each other.

For example, in fig. 4, a light green box of the reference position may represent one sub-pixel. In fig. 4, the first subpixel at the uppermost left, the fifth subpixel shifted by 4 cells to the right, the ninth subpixel shifted by 4 cells to the right, the thirteenth subpixel shifted by 4 cells to the right, the seventeenth subpixel shifted by 4 cells to the right, the twenty-first subpixel shifted by 4 cells to the right, the twenty-fifth subpixel shifted by 4 cells to the right, the twenty-ninth subpixel shifted by 4 cells to the right, and the like are represented as reference positions. In the case of comparing the reference image and the captured image for the entire area, since the load increase is large and the beat time (tact time) increase is large, the reference position may be set in order to compare only a specific reference position.

In the conventional method, when a reference position set in advance is compared with a reference position of a photographed image, it is confirmed that an error due to a physical error of the device, such as an error of +3 camera pixels (+3px) may occur on the right side and the lower side, respectively, or an error of-2 camera pixels (-2px) may occur on the right side and the lower side, respectively, as shown in fig. 4, occurs.

In contrast, in the aspect of the present embodiment, the reference position does not need to be set separately, and the line trace information for the entire area of the display substrate ST may be generated on the basis of the X-axis distribution and the Y-axis distribution.

Fig. 5 to 8 are diagrams illustrating a defect inspection method of the display substrate ST of fig. 2.

Hereinafter, a defect inspection method of the display substrate ST will be specifically described with reference to fig. 1 to 8.

Referring to fig. 5, an X-axis distribution of the image may be extracted. In fig. 5, the horizontal axis may represent an X-axis position within the display substrate, and the vertical axis may represent luminance at the X-axis position. The periodicity represented by the graph of fig. 5 may be due to the sub-pixels and the constituent elements of the display substrate ST. The X-axis distribution may be generated by accumulating luminance for N sets of camera pixels in the Y-axis direction. The N camera pixel groups may correspond to lengths of first sides of the sub-pixels of the display substrate ST.

Referring to fig. 6, a Y-axis distribution of the image may be extracted. In fig. 6, the horizontal axis may represent a Y-axis position within the display substrate, and the vertical axis may represent luminance at the Y-axis position. The periodicity represented by the graph of fig. 6 may be due to the sub-pixels and the constituent elements of the display substrate ST. The Y-axis distribution may be generated by accumulating the luminance for M camera pixel groups in the X-axis direction. The M camera pixel groups may correspond to lengths of second sides of the sub-pixels of the display substrate ST.

For example, if the sub-pixels are shorter in the X-axis and longer in the Y-axis, N may be greater than M. Conversely, if the sub-pixels are longer in the X-axis and shorter in the Y-axis, M may be greater than N.

Before the step of extracting the X-axis distribution, the following steps may be further included: determining a tilt (tilting) of the image at a reference position of the image. The direction of the X-axis and the direction of the Y-axis may be set to be inclined from the edge of the image according to the inclination (tilting) of the image, and when the direction of the X-axis and the direction of the Y-axis are inclined in advance, the axis direction may be accurately set in the graph of the X-axis distribution and the Y-axis distribution.

In contrast, the step of determining the tilt (tilting) of the image at the reference position of the image may be omitted before the step of extracting the X-axis distribution. The line tracing information may be acquired by a graph of the X-axis distribution and the Y-axis distribution even without considering the tilt (tilting) of the image.

The step of inspecting the actual region of interest for defects may comprise the steps of: generating a difference image between the actual region of interest and an adjacent region of interest adjacent to the actual region of interest. For example, if the difference between the actual region of interest and the adjacent region of interest is 0, the actual region of interest and the adjacent region of interest may be considered to be consistent, and if the difference between the actual region of interest and the adjacent region of interest is not 0, the actual region of interest and the adjacent region of interest may be considered to be inconsistent. And if the difference between the actual region of interest and the adjacent region of interest is large, the actual region of interest and the adjacent region of interest may be considered to be inconsistent to a large extent.

For example, the step of inspecting the actual region of interest for defects may comprise the steps of: generating difference images of the actual region of interest and 4 adjacent regions of interest adjacent to the actual region of interest in upper, lower, right and left directions.

And, in the step of inspecting the defect of the actual region of interest, in a case where P difference images among difference partial images of the actual region of interest and 4 adjacent regions of interest adjacent to the actual region of interest in upper, lower, right, and left directions are not 0, it may be determined that the defect exists. P may be 1 to 4.

In the present embodiment, the region where the defect is detected may be acquired after the step of inspecting the actual region of interest for the defect (step S80). After the defect position is determined, the method may further include: the exact location of the defect is verified (step S90).

The step of verifying the exact location of the defect (step S90) may include the steps of: storing defect locations of the defects and filtering accuracy of the defect locations. For example, if Q defect positions are determined in the selective defect inspection performing step (step S70), R defect positions smaller than Q may be finally determined as defect positions after the step of verifying the accurate positions of the defects.

As a result of the line tracking, the alignment within one camera pixel may be distorted, and therefore, in the step of verifying the accurate position of the defect (step S90), the accuracy of the defect position may be improved, and precise defect judgment may be performed again after improving the accuracy of the defect position, thereby improving the accuracy of the defect judgment.

In the step of filtering the accuracy of the defect location, the step of comparing the defect location with an adjacent region of interest adjacent to the defect location may be performed again. The step of verifying the exact location of the defect (step S90) may include the steps of: moving the defect position based on the comparison result of the defect position and the adjacent region of interest and judging again whether a defect exists at the moved defect position.

Fig. 7 shows the confirmation of the positions of all the sub-pixels by means of line tracking. It is shown that even in this case, it is possible that the alignment within one camera pixel (for example, +1px) is distorted.

Fig. 8 shows a step of acquiring an area where a defect is detected and a step of verifying an accurate position of the defect (step S90).

Fig. 9 is a flowchart illustrating a defect inspection method of a display substrate ST according to an embodiment of the present invention. Fig. 10 to 15 are diagrams illustrating a defect inspection method of the display substrate ST of fig. 9.

Referring to fig. 9 to 15, in the defect inspection method of the display substrate ST of the present embodiment, the display substrate ST is color-photographed at a high resolution, and after a region of interest is marked on a high resolution color image, the color image where the region of interest is marked is converted into a black-and-white image, thereby securing a black-and-white low resolution reference image.

If the defect inspection is performed with a high-resolution color image, the accuracy is high, but since a long time is required, the high-resolution color image cannot be substantially used for the defect inspection.

However, when the defective inspection is performed using the low-resolution black-and-white image, there is a problem in that it is difficult to accurately mark the region of interest. Therefore, after the information of the region of interest is accurately acquired from the high-resolution color image, the high-resolution color image is converted into a low resolution to acquire a low-resolution black-and-white image including the information of the accurate region of interest.

The defect inspection method of the display substrate ST of the present embodiment includes the steps of: capturing a color image of the display substrate ST at high resolution (step S110); obtaining information of a region of interest from the color image (e.g., RGB image); converting the color image into a first black-and-white image (e.g., a grayscale image) (step S120); generating a second black-and-white image by compensating for a luminance deviation of the color image and the first black-and-white image (step S130); generating a third black-and-white image by blurring a boundary of the second black-and-white image once (step S140); generating a fourth black-and-white image by secondarily blurring a boundary of the third black-and-white image (step S150); and generating a fifth black-and-white image by resizing the fourth black-and-white image (step S160).

Fig. 10 illustrates a color image of the display substrate ST. Fig. 11 illustrates the first black and white image of the display substrate ST. Fig. 12 shows the second black-and-white image of the display substrate ST. Fig. 13 illustrates the third black and white image of the display substrate ST. Fig. 14 illustrates the fourth black and white image of the display substrate ST. Fig. 15 illustrates the fifth black and white image of the display substrate ST.

In step S120, the following mathematical expression may be used in converting the color image into the first black-and-white image. The color image comprises a red value, a green value and a blue value, the first black-white image has a first black-white brightness value, and when the red value is R, the green value is G, the blue value is B, the first black-white brightness value is GR, a first conversion constant is a, a second conversion constant is B, and a third conversion constant is c, GR is R a + G B + B c.

The step of generating the second black-and-white image (S130) may reduce the brightness of the first black-and-white image using a brightness reduction filter. For example, the brightness reduction filter may be an averaging filter. For example, in the luminance reduction filter, an average filter may be multiplied by a luminance reduction gain for reducing luminance.

The step of generating the third black-and-white image (S140) may blur the boundary of the second black-and-white image using a boundary blurring filter. The step of generating the third black-and-white image may perform gaussian blurring.

For example, the boundary blurring filter may be a gaussian filter. For example, the boundary blurring filter may be any one of an average filter and a median filter. In the present embodiment, a gaussian filter, an average filter, and a median filter are exemplified as the boundary blurring filter, but the boundary blurring filter is not limited thereto.

For example, in the step of generating the fourth black-and-white image (S150), the image characteristics of the area (area) camera may be changed to those of a Time Delay Integration (TDI) camera. In step S110, a high resolution area (area) camera may be utilized, and an image for inspection may be captured using a low resolution TDI camera. Accordingly, the color image photographed with the high resolution area (area) camera may be converted to conform to the characteristics of the low resolution TDI camera in step S150.

The defect inspection method of the display substrate ST of the present embodiment may further include the steps of: capturing an image of the display substrate ST at a low resolution; and marking a new region of interest in the image taken at a low resolution using the fifth black-and-white image and the region of interest corresponding to the fifth black-and-white image.

The low resolution captured image marked with the new region of interest may be utilized in step S60 of the embodiment of fig. 3.

As shown in fig. 3, in the present embodiment, a preset region of interest may be matched with an actual region of interest of the image based on the boundary position (step S60). Accordingly, defect inspection can be selectively performed on the actual region of interest that matches (step S70). And, after the step of inspecting the actual region of interest for defects, a region in which defects are detected may be acquired (step S80). Also, after the defect position is judged, a step of verifying an accurate position of the defect may be performed (step S90).

According to the present embodiment, it is possible to selectively inspect defects occurring in an optical inspection apparatus due to various physical errors and limitations by using a compensation technique such as a position search technique, a defect inspection technique of composite verification, and a consistency maximization technique using multi-layer image processing.

According to the inspection method and the inspection system for a display substrate of the present invention described above, selective defect inspection can be performed.

Although the present invention has been described with reference to the embodiments, it will be understood by those skilled in the art that various modifications and changes may be made to the present invention without departing from the spirit and scope of the invention as set forth in the appended claims.

Claims

1. A defect inspection method of a display substrate includes the steps of:

shooting an image of a display substrate;

extracting an X-axis distribution of the image;

extracting a Y-axis distribution of the image;

generating line tracking information based on the X-axis distribution and the Y-axis distribution;

acquiring boundary positions of constituent elements of the display substrate based on the line tracing information;

matching a preset region of interest with an actual region of interest of the image on the basis of the boundary position; and

and checking the matched actual region of interest for defects.

2. The method of inspecting defects of a display substrate according to claim 1,

the X-axis distribution is generated by accumulating luminance for N sets of camera pixels in the Y-axis direction.

3. The method of inspecting defects of a display substrate according to claim 2,

the N sets of camera pixels correspond to lengths of first sides of the sub-pixels of the display substrate.

4. The method of inspecting defects of a display substrate according to claim 1,

the Y-axis distribution is generated by accumulating luminance for M camera pixel groups in the X-axis direction.

5. The method of inspecting defects of a display substrate according to claim 4,

the group of M camera pixels corresponds to a length of a second side of a sub-pixel of the display substrate.

6. The method of inspecting defects of a display substrate according to claim 1,

before the step of extracting the X-axis distribution, the method further comprises the following steps: and judging the inclination of the image at the reference position of the image.

7. The method of inspecting defects of a display substrate according to claim 1,

the step of inspecting said actual region of interest for defects comprises the steps of:

generating a difference image of the actual region of interest and an adjacent region of interest adjacent to the actual region of interest.

8. The method of inspecting defects of a display substrate according to claim 7,

the step of generating the difference image comprises the steps of:

generating difference images of the actual region of interest and 4 adjacent regions of interest adjacent to the actual region of interest in upper, lower, right, and left directions.

9. The method of inspecting defects of a display substrate according to claim 1,

after the step of inspecting the actual region of interest for defects, the method further comprises the steps of: verifying the exact location of the defect.

10. The method of inspecting defects of a display substrate according to claim 9,

the step of verifying the exact location of the defect comprises the steps of:

storing a defect position of the defect; and

filtering the accuracy of the defect location.

11. The method of inspecting defects of a display substrate according to claim 10,

the step of filtering the accuracy of the defect location comprises the steps of:

the defect location is compared to an adjacent region of interest adjacent to the defect location.

12. The method of inspecting defects of a display substrate according to claim 11,

the step of verifying the exact location of the defect further comprises the steps of:

moving the defect location based on the comparison of the defect location and the adjacent region of interest; and

and judging whether the defect exists at the moved defect position again.

13. A defect inspection method of a display substrate includes the steps of:

shooting a color image of a display substrate at high resolution;

obtaining information of a region of interest from the color image;

converting the color image into a first black-and-white image;

generating a second black-and-white image by compensating for a luminance deviation of the color image and the first black-and-white image;

generating a third black-and-white image by blurring a boundary of the second black-and-white image once;

generating a fourth black-and-white image by blurring a boundary of the third black-and-white image twice; and

generating a fifth black-and-white image by resizing the fourth black-and-white image.

14. The method of inspecting defects of a display substrate according to claim 13,

the color image comprises a red value, a green value and a blue value, the first black-white image has a first black-white brightness value, and when the red value is R, the green value is G, the blue value is B, the first black-white brightness value is GR, a first conversion constant is a, a second conversion constant is B, and a third conversion constant is c, GR is R a + G B + B c.

15. The method of inspecting defects of a display substrate according to claim 13,

in the step of generating the second black-and-white image,

reducing the brightness of the first black-and-white image using a brightness reduction filter.

16. The method of inspecting defects of a display substrate according to claim 13,

in the step of generating the third black-and-white image,

blurring a boundary of the second black-and-white image with a boundary blurring filter.

17. The method of inspecting defects of a display substrate according to claim 16,

the boundary blurring filter is any one of a gaussian filter, an average filter, and a median filter.

18. The method of inspecting defects of a display substrate according to claim 13,

in the step of generating the fourth black-and-white image,

the image characteristics of the area camera are changed to those of the time delay integration camera.

19. The method of inspecting defects of a display substrate according to claim 13, further comprising the steps of:

capturing an image of the display substrate at a low resolution; and

marking a new region of interest in the image taken at the low resolution using the fifth black-and-white image and the region of interest corresponding to the fifth black-and-white image.