JP5716278B2 - Foreign object detection device and foreign object detection method - Google Patents

Description

  The present invention relates to a foreign object detection device and a foreign object detection method for detecting foreign objects on a workpiece.

Conventionally, as a method for detecting a defect of a workpiece such as a wafer, illumination is applied to the surface of the workpiece, reflected light from the workpiece is captured by a CCD camera, and binarization processing is performed on the luminance in the captured image. Thus, there is a method for detecting a defective portion (foreign matter) (for example, see Patent Document 1).
Since the light source brightness varies due to the deterioration of the light source element and the influence of the usage environment, there is a case where stable inspection cannot be performed. In Patent Document 1, a binarization threshold value is dynamically set to cope with fluctuations in light source luminance of illumination, and more stable inspection is performed.

Japanese Patent Laid-Open No. 2003-215048

  However, when the brightness difference between the foreign object contained in the captured image and its background is small, it is difficult to set a threshold value for distinguishing between the brightness of the foreign object and the background brightness, and erroneous detection may occur. is there. In addition, since the wafer is three-dimensionally formed according to its use, a shadow is generated on the wafer by illumination. Since the difference in luminance between the shadow portion in the captured image and the foreign matter in the shadow is small, it is difficult to detect the foreign matter in the shadow. As described above, the luminance obtained from the image captured by the three-dimensional structure of the inspection object varies, and foreign objects cannot be detected stably.

  An object of the present invention is to provide a foreign object detection device and a foreign object detection method capable of reducing foreign detection due to a change in luminance of an illumination and a change in luminance due to the structure of an inspection object and stably detecting a foreign object.

The foreign object detection device of the present invention detects the luminance of each pixel with respect to a captured image obtained by imaging an inspection target, extracts target pixels from all pixels based on the luminance, the target pixels, and the target pixels A luminance difference detecting means for detecting a luminance difference with a plurality of peripheral pixels located around the target pixel; and a foreign substance determining means for determining the presence or absence of a foreign substance based on the luminance difference, wherein the target pixel extracting means is The selected pixel is selected, and the target pixel is extracted based on the difference between the luminance of the selected pixel and the luminance of the comparison pixel.
Further, the foreign object detection device according to the present invention described above, the target pixel extraction means for detecting the luminance of each pixel with respect to the captured image obtained by imaging the inspection target, and extracting the target pixel from all the pixels based on the luminance, A luminance difference detection unit that detects a luminance difference between the target pixel and a plurality of peripheral pixels located around the target pixel; and a foreign matter determination unit that determines the presence or absence of a foreign matter based on the luminance difference. It is characterized by.

  Depending on the structure of the inspection object, a captured image obtained by imaging the inspection object includes a bright area and a dark area that becomes a shadow. A foreign object in a bright area has a large luminance difference between the foreign object and the bright area that is the background of the foreign object, so that the threshold value can be easily set and the foreign object can be easily detected. On the other hand, it is difficult to set a threshold value for a foreign object in a dark area because the brightness difference between the foreign object and the dark area that is the background is small.

  In the present invention, a pixel to be processed (for example, a dark region) is extracted as a target pixel from all the pixels in the captured image by the target pixel extracting unit, and the peripheral pixel is compared with the target pixel extracted by the luminance difference detecting unit. A two-stage process of detecting a difference in brightness is performed, and a foreign object is detected based on the brightness difference. That is, the process by the luminance difference detection means is executed only for the extracted target pixel.

According to this, by performing the above-described two-stage processing based on the brightness of the captured image, it is possible to reduce false detection due to variations in illumination brightness and brightness variations due to shadows (dark areas) that occur in the inspection target. , Can stably detect foreign matter. In particular, when a dark region is extracted as a processing target by the target pixel extraction unit, the luminance difference detection unit only processes a dark region, so that the luminance difference between the dark region and a foreign object existing there is small. However, the threshold value can be easily set, and foreign matter can be easily determined. That is, foreign matter can be determined with higher accuracy.
In addition, since the above-described processing by the luminance difference detection unit is performed only on a dark region in the captured image, the processing speed can be increased.

  In the foreign matter detection device of the present invention, the luminance difference detection means sets, as the peripheral pixels, pixels that are arranged at four locations on the left and right and top and bottom that are separated from the target pixel by a predetermined distance. The brightness difference between the four surrounding pixels is calculated, and the absolute value of the brightness differences is calculated as a filter output value. The foreign matter determination means determines the presence or absence of foreign matter based on the filter output value. It is preferable to do.

In this invention, the so-called filter processing is performed on the target pixel extracted from the captured image, for example, a pixel in a dark region, by the luminance difference detection means. That is, the filter output value is calculated based on the luminance difference between the target pixel and the peripheral pixels arranged at the left and right and upper and lower four positions that are separated from the target pixel by a predetermined distance, and the presence or absence of foreign matter is determined based on the filter output value. judge. Here, the distance between the target pixel and the surrounding pixels may be adjusted as appropriate so that the foreign object can be detected more accurately.
According to this, the foreign object can be detected with high accuracy even when the luminance difference is small as in the case of the foreign object existing in the dark region, by comparing the target pixel with the peripheral pixels located in the four directions.

  In the foreign matter detection apparatus of the present invention, the luminance difference detection means may detect the luminance difference only in the peripheral pixels to be processed according to a mask pattern in which presence / absence of the processing target is preset for all the pixels of the captured image. Is preferably calculated.

In the present invention, the luminance difference detection means includes a mask pattern in which presence / absence of a processing target is set, and the luminance difference between the peripheral pixel set as a processing target in the mask pattern in four peripheral pixels and the target pixel. calculate.
Here, there is a case where the inspection target does not need to be inspected for foreign object detection. For example, since an edge to be inspected is picked up as a dark region in the captured image, it can be a processing target of the above-described luminance difference detection means, but such an edge or the like does not need to be inspected for foreign matter.
Therefore, a mask corresponding to the captured image is used. The mask has the same number of pixels as the above-described filter, and a mask pattern in which a mask value (for example, 0 is set for a processing target and 1 is set for a non-processing target) is set for each pixel. Have. The brightness difference detecting means collates the mask and the filter and performs processing based on the mask value corresponding to the peripheral pixels. According to this, the amount of calculation can be reduced, and the processing speed can be increased.

  The foreign matter detection apparatus of the present invention further includes image processing means for binarizing the filter output value and performing blob processing on the binarized data, and the foreign matter determination means has a size equal to or larger than a predetermined size. When the blob is detected, it is preferable to determine that there is a foreign object.

In the present invention, the binarization process is performed on the filter output value calculated by the above-described filter process using a preset threshold value, and the blob process is further performed on the binarized data. Blob processing is to detect a block of pixels (blob) having a specific value in an image. A foreign object can be detected as an image by the blob detected by the blob process. According to this, since the determination by the image is possible, the foreign object can be easily detected.
Also, the presence or absence of foreign matter is determined according to the size of the blob formed by the blob process. Some blobs formed by blob processing are very small, and not all are foreign matters. Therefore, a blob having a predetermined size or more is detected as a foreign object. According to this, it is possible to reduce erroneous detection of foreign matters.

  In the foreign matter detection device of the present invention, the target pixel extraction means includes two comparison pixels that are separated from each other by a predetermined distance at a point symmetric with respect to the luminance of each pixel and the center of each pixel with respect to all the pixels of the captured image. The difference value between the small luminance of the two comparison pixels and the luminance of each pixel is used as an extraction filter output value, and a pixel whose extraction filter output value is equal to or greater than a predetermined threshold is determined as a target pixel. It is preferable to extract as

In the present invention, the target pixel extraction means performs so-called filter processing on all the pixels in the captured image. That is, the filter output value is calculated based on the luminance difference between two comparison pixels that are separated from each other by a predetermined distance to a position that is point-symmetric with respect to the pixel (selected pixel) selected as the processing target here. Then, based on this filter output value, the above-described luminance difference detecting means extracts the target pixel to be processed. Here, the distance between the selected pixel and the comparison pixel is appropriately determined according to the width dimension and the extension direction of the region so that a region to be extracted (for example, a dark region such as a shadow) in the inspection target is extracted as the target pixel. adjust. For example, the size is set to about 10 times the distance between the target pixel and the peripheral pixels in the filter processing of the luminance difference detecting means described above.
According to this, it is possible to easily extract a region to be processed (for example, a dark region) in the captured image. Also, since there are only two comparison pixels for the selected pixel, the amount of calculation is small, and the processing speed can be increased.

  In the foreign matter detection apparatus of the present invention, it is preferable that the target pixel extraction unit extracts a target pixel by performing binarization processing on the luminance of each pixel.

In this invention, the target pixel extraction means detects the luminance of all the pixels in the captured image, performs binarization processing based on a predetermined threshold value, and extracts target pixels to be processed. For example, since a threshold value for distinguishing between a bright area and a dark area in a captured image can be easily set, only a dark area can be easily extracted.
According to this, since it is only necessary to detect the luminance of all pixels and compare it with the threshold value, the amount of calculation is small, and the processing speed can be increased.

  The foreign object detection method of the present invention detects a luminance of each pixel with respect to a captured image obtained by imaging an inspection target, extracts a target pixel from all pixels based on the luminance, the target pixel, and the target pixel A luminance difference detecting step for detecting a luminance difference with a plurality of peripheral pixels located around the target pixel, and a foreign substance determining step for determining the presence or absence of a foreign substance based on the luminance difference are provided.

According to this invention, the target pixel extraction step can be performed by the target pixel extraction unit, the luminance difference detection step by the luminance difference detection unit, and the foreign matter determination step by the foreign matter determination unit. Therefore, similarly to the above-described invention, complicated processing by the luminance difference detection means is executed only on the target pixel extracted from the inspection target.
According to this, by performing the above-described two-stage processing based on the luminance of the captured image, it is possible to reduce false detection due to variations in illumination luminance and luminance variations due to shadows (dark areas) generated on the inspection object. In addition, foreign objects can be detected stably. In particular, when a dark region is extracted as a processing target in the target pixel extraction step, it is possible to accurately detect a luminance difference between the dark region and a foreign object existing there.
Further, since the complex process of the luminance difference detection process is executed only for the dark region in the captured image, the process can be speeded up.

The perspective view which shows schematic structure of the foreign material detection apparatus concerning embodiment of this invention. The block diagram which shows the structure of the foreign material detection means in the said embodiment. The figure explaining the filter process of the object pixel extraction means in the said embodiment. The figure explaining the filter process of the brightness | luminance difference detection means in the said embodiment. It is a figure which shows the mask pattern used by the brightness | luminance difference detection means in the said embodiment, (A) shows the case where all the pixels are processing objects, (B) shows the case where some are not processing objects. The perspective view which shows the structure of the semiconductor wafer in the said embodiment. The figure which shows the picked-up image which imaged the principal part of FIG. 6 from the upper surface. The flowchart which shows the detection method of the foreign material detection apparatus in the said embodiment. The flowchart which shows the foreign material detection process in the said embodiment. It is a schematic explanatory drawing which shows each process result with respect to a captured image in the said embodiment, (A) shows before a process, (B) after an object pixel extraction process, (C) shows after an image process process.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
[1. Configuration of foreign object detection device]
The foreign matter detection apparatus 1 detects whether or not foreign matter has adhered to the ink jet printer head formed on the semiconductor wafer 2.
As shown in FIG. 1, the foreign object detection apparatus 1 includes an XY stage 3 that supports a semiconductor wafer 2, a CCD camera 4 that images the semiconductor wafer 2, a Z stage 5 that installs the CCD camera 4, an XY stage 3, It comprises a CCD camera 4 and a control device 6 connected to the Z stage 5.

  The XY stage 3 can be moved in the XY direction, and the Z stage 5 can be moved in the Z direction so that the focus of the CCD camera 4 can be adjusted. Therefore, the positions of the semiconductor wafer 2 and the CCD camera 4 can be relatively moved in the XYZ directions.

  The CCD camera 4 is provided with an objective lens 7 and a lens barrel 8 that holds the objective lens 7. Therefore, the CCD camera 4 is configured to be able to photograph the semiconductor wafer 2 through the objective lens 7.

The control device 6 operates the XY stage 3, the CCD camera 4, and the Z stage 5 to capture the inspection area of the semiconductor wafer 2 and create a captured image, and the captured image creation unit 61 creates the captured image. And foreign matter detection means 62 for detecting foreign matter based on the captured image.
As shown in FIG. 2, the foreign object detection unit 62 includes a target pixel extraction unit 621, a filter processing unit 622 as a luminance difference detection unit, an image processing unit 623, and a foreign object determination unit 624.

The target pixel extraction unit 621 extracts, as a target pixel, a pixel to be processed by the filter processing unit 622 among all the pixels in the captured image by the first filter processing. Here, a processing target is a relatively dark region (low luminance) in the captured image.
Specifically, the target pixel extraction unit 621 sequentially selects all the pixels in the captured image and applies the first filter process to each pixel. In the first filter processing, the filter 25 shown in FIG. 3 is applied to the captured image. One pixel is selected from all the pixels (hereinafter also referred to as a selected pixel), and this selected pixel is aligned with the position of the pixel A set in the filter 25, and the brightness of two corresponding comparison pixels is detected. The difference between the minimum value of these luminances and the luminance of the selected pixel is taken as the filter output value. Then, a pixel whose filter output value is equal to or greater than a predetermined threshold is extracted as a target pixel. In this way, a relatively dark area can be extracted.

The filter processing unit 622 includes a pixel selection unit 6221, a luminance detection unit 6222, and a filter output value calculation unit 6223.
The pixel selection unit 6221 selects one pixel from the target pixels extracted by the target pixel extraction unit 621. The selected target pixel is processed by the following luminance detection means 6222 and filter output value calculation means 6223. When the processing for one pixel is completed, the pixel selection means 6221 selects the next target pixel. The pixel selection unit 6221 sequentially selects until all the target pixels have been processed.

The luminance detection unit 6222 detects the luminance of the selected pixel.
The filter output value calculation unit 6223 performs a second filter process on the selected pixel (hereinafter also referred to as a selected pixel) to calculate a filter output value. In the second filter processing, the filter 26 shown in FIG. 4 is applied to the captured image. The pixel A set in the filter 26 and the selected pixel are combined, the luminance of the corresponding four neighboring pixels is detected, the luminance difference between these neighboring pixels and the selected pixel is calculated, and the absolute value of these luminance differences is calculated. Is the filter output value.
Further, the filter output value calculation means 6223 detects the luminance of the peripheral pixels according to the mask pattern shown in FIG. In the mask pattern, mask values indicating the processing target area and the outside of the processing target area are set in advance, and it is determined based on these mask values whether or not surrounding pixels are the processing target. In FIG. 5, the mask value “0” is set in the processing target area, and the mask value “1” is set outside the processing target area. Then, the process of calculating the luminance difference is performed only for the peripheral pixels that are the processing target area.

The image processing unit 623 performs binarization processing on the filter output values calculated for all target pixels using a predetermined threshold, and performs blob processing on the binarized data. Blob processing is to detect a block of pixels (blob) having a specific value in an image. By the blob process, pixels having a specific value are displayed as a block (blob) on the image. In other words, this blob can be recognized as a foreign object in the image.
The foreign matter determination unit 624 determines the presence or absence of foreign matter based on the image generated by the image processing unit 623. A foreign object expressed as a blob in the image can be easily determined. Further, when the size of the blob is equal to or larger than a predetermined value, it is determined that there is a foreign matter, and when the size of the blob is less than a predetermined value (fine), it is determined that there is no foreign matter.

[2. Semiconductor wafer configuration]
The semiconductor wafer 2 to be inspected in this embodiment constitutes a printer head of an ink jet printer, and is formed with various flow paths for distributing ink, air, etc. by anisotropic etching or the like. As shown in FIG. 6, the semiconductor wafer 2 includes a flow path forming substrate 21 and a nozzle plate 22 fixed to one opening surface of the flow path forming substrate 21 with an adhesive, a heat-welded film, or the like. ing.
A plurality of pressure generation chambers (cavities) 212 partitioned by partition walls 211 are arranged in parallel on the flow path forming substrate 21. Further, a communication part 213 constituting a part of a reservoir serving as a common ink chamber of each pressure generation chamber 212 is formed on the outer side in the longitudinal direction of the pressure generation chamber 212, and this communication part 213 is connected to each pressure generation chamber 212. It communicates with one end in the longitudinal direction via an ink supply path 214. That is, a part of the partition wall 211 is provided with a supply port forming part 215 that is formed thicker than other parts. Each ink supply path 214 communicating with one end of each pressure generating chamber 212 is formed between the supply port forming portion 215 and the other partition wall 211. Therefore, it is formed smaller than the cross-sectional area of the ink supply path 214, and the flow path resistance of the ink flowing through the pressure generation chamber 212 is kept constant.

  When the flow path portion is imaged from above with the semiconductor wafer 2 illuminated, the irradiated light is irradiated from the upper surface portion of the partition wall 211 and the bottom surface portion of the pressure generation chamber 212 as shown in the captured image in FIG. The specularly reflected portion is photographed brightly, and a shadow is generated in the portion where the flow path is narrowed by the supply port forming portion 215 of the pressure generating chamber 212, and the portion is photographed darkly. That is, in the captured image, a bright part having a high luminance value and a shadow part 23 having a low luminance value compared to the bright part are formed.

Here, when a foreign substance adheres to the upper surface (bright part) of the partition wall 211, since the shape of the foreign substance is not constant, the light hitting the foreign substance is irregularly reflected. Accordingly, in the captured image, the foreign matter is darker than the upper surface of the partition wall 211, and a dark portion of the foreign material exists while the upper surface portion of the surrounding partition wall 211 is bright. In such a case, since the brightness difference between the foreign matter portion and the surrounding area is large in the captured image, the foreign matter can be detected relatively easily by image processing. On the other hand, as shown in FIG. 7, when the foreign matter 24 is attached to the shadow portion 23, the brightness difference between the foreign matter 24 and the surrounding area (particularly the dark portion 231) is small, so that it is difficult to discriminate these. It may be difficult to detect.
The foreign object detection device 1 of the present embodiment is configured to detect the foreign object 24 attached to the shadow part 23 when the brightness difference between the foreign object part and the surrounding area is small as described above.

[3. Inspection process]
Next, the foreign substance inspection process executed by the control device 6 will be described.
As shown in FIG. 8, the foreign matter inspection step includes a captured image creation step S1 and a foreign matter detection step S2.

(1. Captured image creation step S1)
When the inspection process is started, the control device 6 operates the captured image creation means 61. The captured image creating means 61 creates a captured image by operating the XY stage 3 and the Z stage 5 and moving the CCD camera 4 relative to the inspection region of the semiconductor wafer 2 to capture an image (S1).

(2. Foreign matter detection step S2)
When the captured image is created, the control device 6 operates the foreign matter detection means 62 and executes a foreign matter detection step (S2).
Below, the detail of foreign material detection process S2 is demonstrated based on the flowchart of FIG.
The foreign matter detection step S2 includes a first pixel selection step S21, a first filter output value calculation step S22, a first end determination step S23, a second pixel selection step S24, a second filter output value calculation step S25, A second end determination step S26, an image processing step S27, and a foreign matter determination step S28 are provided.
Here, the first pixel selection step S21, the first filter output value calculation step S22, and the first end determination step S23 are the first filter processing and function as the target pixel extraction step of the present invention. The second pixel selection step S24, the second filter output value calculation step S25, and the second end determination step S26 are second filter processes, and function as a luminance difference detection step of the present invention.

(2-1. Target pixel extraction process)
In the control device 6, the target pixel extraction unit 621 extracts a pixel to be processed from all the pixels in the captured image as a target pixel.
Here, FIG. 7 shows a captured image of the semiconductor wafer 2. The shadow part 23 includes a dark part 231 having a relatively dark shadow (low brightness) and a weak dark part 232 having a lighter shadow (high brightness) than the dark part 231. In the target pixel extraction step, a region with relatively low luminance is extracted as a processing target region. In this embodiment, the dark portion 231 and the foreign object 24 are to be processed.

In the present embodiment, the pixels existing in the dark part 231 and the foreign matter 24 are extracted as target pixels by the first filter processing. The first filter process will be described in detail below.
First, the target pixel extraction unit 621 selects one pixel to be processed among all the pixels in the captured image (S21). The order of selection is not particularly limited. For example, selection is performed for each pixel (pixel) from the upper left to the lower right of the captured image among all the pixels in the captured image.

  Next, the target pixel extraction unit 621 calculates the first filter output value by applying the filter 25 shown in FIG. 3 (S22). The filter 25 is set with the number of vertical and horizontal pixels (number of pixels). In this embodiment, 81 × 81 pixels are set. The filter 25 includes a pixel A that aligns the position of the selected pixel, and comparison pixels X1 and X2 that are separated by a predetermined distance (40 pixels in the filter 25) to the left and right of the pixel A.

  The target pixel extracting unit 621 measures the luminance of the comparison pixels X1 and X2 corresponding to the selected pixel, and outputs the difference in luminance between the comparison pixel having a smaller luminance and the selected pixel among the comparison pixels X1 and X2 as the first filter output. Calculate as a value.

The target pixel extraction unit 621 further compares the first filter output value with a predetermined threshold value, and if the first filter output value is equal to or greater than the threshold value, the target pixel is set as the target pixel.
For example, when the luminance of the selected pixel (pixel A) is 50, the luminance of the comparison pixel X1 is 180, and the luminance of the comparison pixel X2 is 175, the filter output value is min (180, 175) −50 = 125. . When the predetermined threshold is 100, the selected pixel is a target pixel.

  Next, the target pixel extraction unit 621 determines whether the processes of S21 to S22 have been performed on all the pixels in the captured image (S23). And when determination with respect to all the pixels is not performed, it returns to 1st pixel selection process S21, the next pixel is selected, and the process of S21-S22 is performed repeatedly. On the other hand, if the determination for all the pixels has been completed, the process proceeds to the next process. In this manner, target pixels to be processed in the next process are extracted from all the pixels.

  For example, when the first filter output value is calculated by the above-described processing on the captured image shown in FIG. 10A and image processing is performed on the first filter output value, the image shown in FIG. Is obtained. That is, as shown in FIG. 10B, pixels in the area of the dark portion 231 and the foreign matter 24 having relatively low luminance are extracted as target pixels by the first filter processing described above.

(2-2. Luminance difference detection step)
When the target pixel is extracted, the control device 6 operates the filter processing unit 622 to perform the second filter processing described below on all the extracted target pixels.
The pixel selection unit 6221 selects one pixel to be processed from the target pixels (S24). The order of selection is not particularly limited. For example, among the target pixels in the captured image, selection is performed for each pixel (pixel) from the upper left to the lower right of the captured image.

Next, the filter output value calculation means 6223 calculates the second filter output value by applying the filter 26 shown in FIG. 4 (S25). The number of pixels in the vertical and horizontal directions is set for the filter 26. In this embodiment, 5 × 5 pixels are set. The filter 26 includes a pixel A that aligns the position of the selected pixel, peripheral pixels X1 and X2 that are separated by a predetermined distance (two pixels in the filter 26) to the left and right of the pixel A, and predetermined pixels above and below the target pixel (pixel A). Peripheral pixels Y1 and Y2 that are separated by a distance (two pixels in the filter 26).
Then, the filter output value calculation unit 6223 calculates the luminance difference between the peripheral pixels X1, X2, Y1, and Y2 and the selected pixel using the luminance of the selected pixel and the four peripheral pixels detected by the luminance detection unit 6222, respectively. The minimum value of the absolute value of these luminance differences is set as the second filter output value.

  At this time, the filter output value calculation unit 6223 does not perform the above calculation for peripheral pixels that are outside the processing target region. In the captured image, there is a region (for example, an edge of the semiconductor wafer 2) where it is not necessary to detect foreign matter due to the structure of the semiconductor wafer 2. Therefore, a mask is set so that the second filter processing is not performed on the pixels in such a region. Specifically, as shown in FIG. 5, a mask value is set for each pixel of the mask in which the number of pixels having the same size (5 × 5 pixels) as the filter 26 is set. For example, “0” is set when the area is the processing target area, and “1” is set when the area is not the processing target area. In FIG. 5A, all pixels are within the processing target area, and FIG. 5B is outside the processing target area in which one column in the bottom row is masked. Therefore, the filter output value calculation unit 6223 refers to the mask value corresponding to each peripheral pixel, performs an operation only on the pixels in the processing target region, and calculates the second filter output value.

Here, a specific calculation method will be described. It is assumed that the luminance of the selected pixel (pixel A) is 30, the pixel of the peripheral pixel X1 is 60, the pixel of the peripheral pixel X2 is 75, the pixel of the peripheral pixel Y1 is 65, and the pixel of the peripheral pixel Y2 is 55.
According to the mask pattern shown in FIG. 5A, since all the pixels are within the processing target area, the luminance difference is calculated for all the peripheral pixels. Therefore, the filter output value is min (| 30-60 |, | 30-75 |, | 30-65 |, | 30-55 |) = 25.
On the other hand, according to the mask pattern shown in FIG. 5B, since only the peripheral pixel Y2 is outside the processing target region, the peripheral pixel Y2 is not processed. Therefore, the filter output value is min (| 30-60 |, | 30-75 |, | 30-65 |) = 30.

Next, the filter output value calculation unit 6223 determines whether or not the processing of S24 to S25 has been performed on all the target pixels extracted in the target pixel extraction step (S26). If all the target pixels have not been determined, the process returns to the second pixel selection step S24, the next target pixel is selected, and the processes of S24 to S25 are repeated. On the other hand, if all the target pixels have been determined, the process proceeds to the next step.
(2-3. Image processing step)
Next, the control device 6 operates the image processing means 623 and performs the image processing step S27. In the image processing step S27, the filter output value calculated for each target pixel is binarized using a predetermined threshold, and the blob processing is performed on the binarized data. In the blob-processed image, as shown in FIG. 10C, the outline of the foreign matter 24 is displayed as a ring-shaped blob, and the foreign matter 24 can be recognized.

(2-4. Foreign object determination step)
Next, the control device 6 operates the foreign matter determination means 624 to perform the foreign matter determination step S28. In the foreign matter determination step S28, the blob in the image processed in the image processing step S27 is recognized. If the blob is larger than a predetermined size, it is determined that there is a foreign matter, and if it is less than the predetermined size, it is determined that there is no foreign matter. .
Specifically, as shown in FIG. 10C, a ring-shaped blob is displayed along the contour of the foreign matter 24, so that the foreign matter 24 can be easily recognized.

  And the control apparatus 6 determines whether the test | inspection of the whole surface of the semiconductor wafer 2 was complete | finished in determination process S3 of FIG. In the determination step S3, when it is determined that the inspection is not completed, the control device 6 repeats the captured image creation step S1 and the foreign matter detection step S2. On the other hand, if it is determined in the determination step S3 that the inspection of the entire surface of the semiconductor wafer 2 has been completed, the control device 6 ends the inspection step.

  In the present embodiment, the captured image creation means 61 operates the XY stage 3 while the foreign object detection means 62 is performing processing, and the CCD camera 4 is relative to the next inspection area of the semiconductor wafer 2. To capture an image and create a captured image (S1). Thereby, the captured image creation step S1 and the foreign matter detection step S2 can be executed substantially in parallel, and the inspection time of the entire surface of the semiconductor wafer 2 can be shortened.

[4. Effects of this embodiment]
According to the foreign substance detection device 1 according to the above embodiment, the following operational effects can be achieved.
(1) The target pixel extraction unit 621 extracts pixels in the dark portion 231 and the foreign matter 24 region to be processed as target pixels, and the filter processing unit 622 is based on the luminance difference between the target pixel and the surrounding pixels. The presence or absence of foreign matter is determined based on the filter output value. That is, the filter processing unit 622 that performs complicated processing does not need to perform processing on all the pixels of the captured image. For this reason, the total calculation amount can be reduced, and the processing speed can be increased.

(2) Since two-stage filter processing is performed by the target pixel extraction unit 621 and the filter processing unit 622, it is caused by variations in illumination luminance and variations in luminance due to a dark region (shadow portion 23) generated in the semiconductor wafer 2 to be inspected. False detection can be reduced.
In particular, the foreign matter 24 present in the dark portion 231 of the semiconductor wafer 2 is difficult to discriminate because the luminance difference between the dark portion 231 and the foreign matter 24 is small, but the dark portion 231 and the foreign matter 24 are relatively dark in the second filter processing. The region is set as a processing target, and the presence / absence of the foreign matter 24 is determined based on the luminance difference between the target pixel and the four surrounding pixels. As described above, since the comparison is performed in the dark region of the dark portion 231 and the foreign object 24, the threshold value can be set more easily and erroneous detection can be reduced.

(3) The filter processing unit 622 calculates the luminance difference between the target pixel and the surrounding pixels according to the mask pattern having the same number of pixels as the filter 26 used in the second filter processing. That is, when the mask value is “1”, the surrounding pixels are outside the processing target area, so the brightness difference is not calculated, and the filter output value is calculated using the brightness difference of the surrounding pixels in the other processing target areas. ing.
Since there is an area in the semiconductor wafer 2 where it is not necessary to detect foreign matter, the amount of calculation can be reduced by setting such an area as a mask pattern outside the processing target area. Can be speeded up.

(4) The image processing unit 623 performs binarization processing and blob processing on the filter output value calculated for each target pixel. For this reason, the foreign substance 24 distinguished from the dark part 231 can be recognized as an image, and the presence or absence of the foreign substance can be easily determined.

[5. Modified example]
In addition, this invention is not limited to the above-mentioned embodiment, The deformation | transformation in the range which can achieve the objective of this invention, improvement, etc. are included in this invention.
For example, in the above-described embodiment, the target pixel is extracted using the first filter process in the target pixel extraction step (S21 to S23), but the method of extracting the target pixel is not limited to this. Since it is sufficient that the shadow portion in the entire captured image can be extracted in a wide area, for example, the luminance of all pixels in the captured image may be detected, and binarization processing may be performed on this luminance. In this case, a pixel having a luminance equal to or lower than a predetermined threshold is extracted as a target pixel. According to this, since processing can be performed with simple calculation, the processing speed can be increased.

In the above-described embodiment, in the first filter process of the target pixel extraction step (S21 to S23), the pixel 40 pixels away from the pixel A of the filter 25 is set as the comparison pixel X1 or X2. The distance to the pixel X1 or X2 is not limited to this. It can change suitably according to the size etc. of a captured image.
Similarly, in the second filtering process of the filtering process, a pixel that is two pixels away from the pixel A of the filter 26 is a peripheral pixel, but the distance between the pixel A and the peripheral pixel is not limited to this. It can be changed as appropriate according to the size of the foreign matter.

  In the above-described embodiment, in the second filter process, it is determined whether or not the peripheral pixel is a processing target using a mask, but this process may be omitted.

  In the above-described embodiment, the comparison pixels X1 and X2 are positioned in the left-right direction of the pixel A. Adjust it. In the above-described embodiment, in the captured image shown in FIG. 7, the dark portion 231 is formed extending in the vertical direction in the figure. Therefore, in order to detect the dark portion 231, since the comparison pixel is present in the left-right direction with respect to the central pixel A like the filter 25, the luminance difference is increased, and the dark portion 231 can be detected. On the other hand, when a filter in which comparison pixels are arranged in the vertical direction with respect to the pixel A is used, the dark portion 231 may not be detected because there is almost no difference in luminance. Therefore, it is preferable to set the direction and distance of the filter in accordance with the width dimension and extension direction of the region to be detected.

  DESCRIPTION OF SYMBOLS 1 ... Foreign object detection apparatus, 2 ... Semiconductor wafer, 21 ... Flow path formation board | substrate, 22 ... Nozzle plate, 23 ... Shadow part, 231 ... Dark part, 232 ... Lightly dark part, 24 ... Foreign object, 25 ... 1st filter, 26 ... Second filter, 3... XY stage, 5... Z stage, 6.

Claims (10)

Target pixel extraction means for detecting the luminance of each pixel with respect to a captured image obtained by imaging the inspection target, and extracting the target pixel from all the pixels based on the luminance;
A luminance difference detecting means for detecting a luminance difference between the target pixel and a plurality of peripheral pixels located around the target pixel;
Foreign matter determination means for determining the presence or absence of foreign matter based on the luminance difference;
Equipped with a,
The foreign object detection apparatus, wherein the target pixel extracting unit selects a selected pixel and extracts the target pixel based on a difference between a luminance of the selected pixel and a luminance of a comparison pixel . The foreign object detection device according to claim 1,
The foreign object detection apparatus, wherein the target pixel extraction unit extracts a pixel having a lower luminance than the predetermined threshold value or a predetermined comparison pixel as the target pixel. The foreign object detection device according to claim 1 or 2,
The foreign object detection device, wherein the target pixel extraction unit and the luminance difference detection unit perform different arithmetic processing. In the foreign material detection apparatus in any one of Claims 1-3,
The foreign object detection apparatus, wherein the luminance difference detection unit detects a luminance difference from the target pixel, and the peripheral pixel is a pixel included in the range of the target pixel. In the foreign matter detection device according to any one of claims 1 to 4,
The brightness difference detecting means includes
Pixels arranged at four locations on the left and right and top and bottom that are separated by a predetermined distance from the target pixel are set as the peripheral pixels, and a luminance difference between the target pixel and the four peripheral pixels is calculated, respectively. Calculate the absolute value of the luminance difference as the filter output value,
The foreign matter determining means includes
A foreign object detection device that determines the presence or absence of a foreign object based on the filter output value. The foreign object detection device according to claim 5,
The brightness difference detecting means includes
A foreign object detection device that calculates the luminance difference of only peripheral pixels to be processed according to a mask pattern in which presence / absence of a processing target is set in advance for all pixels of the captured image. The foreign object detection device according to any one of claims 1 to 6,
Image processing means for binarizing the filter output value and performing blob processing on the binarized data;
The foreign matter determining means includes
A foreign object detection device that determines that there is a foreign object when a blob having a size larger than a predetermined size is detected. In the foreign substance detection device according to any one of claims 1 to 7,
The target pixel extracting means includes
For all the pixels of the captured image, the brightness of each pixel and the brightness of two comparison pixels that are separated by a predetermined distance at a point symmetric with respect to each pixel are detected, and the smaller of the two comparison pixels A foreign object detection device, wherein a difference value between luminance and luminance of each pixel is used as an extraction filter output value, and a pixel having the extraction filter output value equal to or greater than a predetermined threshold is extracted as a target pixel. In the foreign substance detection device according to any one of claims 1 to 7,
The foreign object detection apparatus, wherein the target pixel extraction unit extracts a target pixel by performing a binarization process on the luminance of each pixel. A target pixel extraction step of detecting the luminance of each pixel with respect to a captured image obtained by imaging the inspection target, and extracting the target pixel from all the pixels based on the luminance;
A luminance difference detection step of detecting a luminance difference between the target pixel and a plurality of peripheral pixels located around the target pixel;
Foreign matter determination step means for determining the presence or absence of foreign matter based on the luminance difference ,
The foreign object detection method, wherein the target pixel extraction step selects a selected pixel and extracts the target pixel based on a difference between a luminance of the selected pixel and a luminance of a comparison pixel .

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