JP2007333491A - Appearance inspection device for plate - Google Patents

Abstract

An apparatus for inspecting the appearance of a plate-like member capable of accurately detecting surface defects is provided.
An illuminating means (first illuminating means 51) for irradiating light on a surface of a plate-like member 2 and an entire surface of the plate-like member 2 are divided into a plurality of imaging regions, and the plate-like member is divided into each imaging region. The imaging means (first camera 41) for imaging the surface of 2 and all the captured images taken by the imaging means are connected so as to constitute the entire surface of the plate-like member 2, and Image processing means 6 for synthesizing the surface images, performing image processing on the synthesized images, and inspecting defects on the surface of the plate-like member is provided.
[Selection] Figure 1

Description

  The present invention relates to a plate member appearance inspection apparatus that inspects a surface defect of a plate member having a large area, such as a semiconductor wafer, by image processing.

  Conventionally, when inspecting a defective portion on the surface of a plate-like member such as a semiconductor wafer, an operator has visually identified the defective portion. However, when the appearance inspection is performed manually, the inspection results vary and it is difficult to perform a stable inspection.

  In addition, in order to find minute defects, skill level is also required, which imposes a burden on the operator and prevents efficient inspection.

  Further, an apparatus for automatically inspecting a surface defect of a plate-like member has been conventionally proposed (see, for example, Patent Document 1 and Patent Document 2).

  The appearance inspection apparatus disclosed in Patent Document 1 binarizes a measurement image of a semiconductor substrate to be measured, which is taken using an optical microscope and a CCD camera, and the area and shape of a defect portion are obtained from the binarized image. A surface defect inspection method for extracting the number of defects and measuring the number of defects is disclosed.

  In Patent Document 1, a background image is removed from a measurement image including a surface defect, and image enhancement processing is performed. Furthermore, a measurement screen is created by removing fine particles as noise. And a flow pattern and a small pit are measured from this measurement screen.

  The appearance inspection apparatus disclosed in Patent Document 2 irradiates illumination light on the entire surface of a semiconductor wafer and receives light reflected on the semiconductor wafer, thereby imaging the received light by an imaging unit. ing. A binarization process is performed on the image captured by the image processing apparatus to detect defects on the surface of the semiconductor wafer.

JP 09-199560 A Japanese Patent Laid-Open No. 10-325805

  Usually, in the visual inspection apparatus disclosed in Patent Document 1 or Patent Document 2, the field of view size of the two-dimensional camera is an imaging region, and image processing is performed using this imaging region as one image frame. Yes.

  By the way, when imaging the whole surface of a plate-shaped member at once, since it images with low magnification, it is difficult to detect a minute defect. On the other hand, in order to detect minute defects, the surface of the plate-like member is divided into several imaging regions, and images are taken at a high magnification, and minute defects are detected for each captured image. ing.

  However, the conventional appearance inspection apparatus performs image processing for each image picked up by the CCD camera and inspects the surface of the plate-like member. Therefore, accurate detection cannot be performed depending on the location and size of the defect.

  That is, as shown in FIG. 7 (a), the defect can be determined to be one defect if the entire defect fits in one captured image on the surface of the plate member. This defect does not always occur at the specified location, but occurs randomly. Therefore, as shown in FIG. 7B, when the entire defect is not contained in one captured image and one large defect is imaged over two screens, the appearance inspection apparatus has two defects. I will judge.

  As described above, if one defect is determined as two defects, accurate defect detection cannot be performed.

  Therefore, the present invention has been made in view of the above problems, and an object of the present invention is to provide a plate-like member appearance inspection apparatus capable of accurately detecting surface defects.

  The plate-like member appearance inspection apparatus of the present invention performs image processing on an imaged image, an illuminating unit that irradiates light on the surface of the plate-like member, an imaging unit that images the surface of the plate-like member. And image processing means for inspecting the surface of the plate member for defects.

  The imaging unit divides the entire surface of the plate-shaped member into a plurality of imaging regions, and images the surface of the plate-shaped member for each imaging region.

  Examples of the imaging means include a two-dimensional camera such as a CCD camera. The imaging means obtains a two-dimensional image using the visual field size as an imaging region. This two-dimensional image is sent to the image processing means.

  Moreover, when obtaining the picked-up image of the surface of a plate-shaped member with an imaging means, it is preferable to image by mounting a plate-shaped member on a sample stand. This sample stage can be moved in a plane direction (X-axis direction and Y-axis direction) by a driving means. Specifically, the imaging unit is fixed above the sample stage, and the sample stage is moved so that an imaging region to be imaged from now on is arranged directly below the imaging unit. That is, among the plurality of imaging areas, with respect to the imaging area to be imaged from now on, the driving means is driven and the sample stage is moved in the horizontal direction so that the imaging area falls within the field of view size of the imaging means, and the sample stage Adjust the position of.

  In the present invention, the picked-up image picked up by the pick-up means may be set so that a part (edge) of the pick-up area overlaps with a part of the pick-up area adjacent to the pick-up area, The imaging areas may be set so that the imaging areas do not overlap. In the present invention, it is preferable to perform imaging so that imaging areas do not overlap.

  As described above, when imaging is performed so that the imaging regions do not overlap, the entire area to be captured is minimized, and the number of imaging can be minimized. When imaging is performed so that the imaging areas do not overlap, the dividing line when the entire surface of the plate-shaped member is divided into a plurality of imaging areas becomes a boundary line between adjacent imaging areas, and the gap is Take an image so that there is no.

  Further, when an image is picked up by the image pickup means, the surface of the plate member is irradiated with light by the illumination means. Therefore, the illumination unit is arranged so as to illuminate the imaging region in the plate member. For example, the illuminating means is arranged coaxially with the imaging means above the sample stage, or obliquely above the plate-like member on the sample stage.

  When the imaging unit and the illumination unit are arranged coaxially, coaxial ring illumination or coaxial epi-illumination can be used as the illumination unit.

  Further, the illumination means may change the wavelength of light depending on the type of defect to be detected. For example, a halogen light lamp or an ultraviolet light lamp can be used.

  When using illumination means with one type of wavelength, a defect may not be detected depending on the wavelength. Therefore, if two or more illumination means with different wavelengths are provided, and each of them is switched as appropriate, or the illumination is applied at the same time, imaging is performed to deal with defects that appear differently depending on the illumination wavelength. can do.

  The image processing means connects all the picked-up images picked up by the image pick-up means so as to constitute the entire surface of the plate-like member, synthesizes the surface image of one plate-like member, and the image is combined with this combined image. Processing is performed to inspect the surface of the plate member for defects.

  The image processing means is constituted by, for example, a computer, and an image composition unit that synthesizes a plurality of captured images, an image processing unit that performs binarization processing on the image, and the size of the abnormal part with respect to the processed image. It can be set as the structure provided with the determination part which measures and determines the presence or absence of a defect.

  The image combining unit combines all the captured images captured by the imaging unit for each imaging region so that the entire surface of the plate-shaped member is configured, and combines the surface image of one plate-shaped member.

  For example, the image processing unit performs binarization processing on the combined image combined by the image combining unit.

  The determination unit measures the size of the abnormal part of the image data that has been binarized (abnormal part) that has a possibility of a defect. It is determined that there is a defect, and when it is equal to or less than the threshold, it is determined that the defect is not present.

  As described above, the present invention divides and captures the surface of the plate-shaped member, and synthesizes all these captured images to produce a surface image (composite image) of one plate-shaped member. Then, this combined image is processed in a batch. As a result, even when there is a defect extending over two screens in the past, it can be accurately inspected as one defect.

  Incidentally, some plate-like members have a stripe structure on the surface. The stripe structure is configured, for example, by forming stripe edges on the surface of a plate-like member. When a surface defect is inspected for a strip-shaped plate member, the defect is usually inspected along this edge. At this time, if an image is taken along the edge of the stripe, the distance between the edges can be measured accurately, and a more accurate surface inspection can be performed.

  When the plate-like member has a quadrangular outline or a straight part at a part of the end, the straight part of the outline may be formed on the plate-like member so as to be parallel to the edge. it can. As a result, the edge direction can be easily adjusted by aligning the straight line portion of the contour line with the linear positioning portion formed on the sample stage.

  However, there are plate-like members having a shape in which the contour line is entirely formed of a curve, such as a complete circle. In the case of such a circular plate member, the alignment in the edge direction cannot be performed by the linear positioning portion. For this reason, when a plate-like member is placed on the sample stage, the edge may not be perpendicular or parallel to the X-axis direction of the sample stage. In this case, the imaging area of the CCD camera (inside the image frame) ), The edge is not perpendicular to the X axis of the imaging region. Therefore, it is necessary to adjust the edge direction, but it is very difficult for a person to visually adjust the edge direction.

  Therefore, the plate-like member surface inspection apparatus of the present invention not only enables the sample stage on which the plate-like member is placed to be moved in the plane direction (X-axis direction and Y-axis direction) using the driving means. Further, it may be rotated in the plane direction.

  Furthermore, the image processing means includes an angle measuring unit that obtains an angle θ formed by the edge line of the stripe structure in the plate-like member and the X-axis or Y-axis of the sample stage in the surface image of the plate-like member picked up by the image pickup means. A configuration is preferable.

  And it is preferable to comprise so that a drive means may perform control which rotates a sample stand so that an edge line becomes perpendicular | vertical with respect to an X-axis or a Y-axis based on angle (theta) measured by the angle measurement part.

  By rotating the sample stage so that the edge line is perpendicular to the X axis or the Y axis, for example, when the surface of the plate member is imaged by the imaging unit, the edge line is X in the image frame of the imaging unit. The plate-like member can be arranged so as to be perpendicular to the axis. In this way, the edge line can be perpendicular to the X axis in the image frame. Therefore, even if the edge line of the stripe in the circular plate member is inclined with respect to the Y axis of the imaging means, By rotating and moving, the edge line and the Y-axis direction of the imaging means can be easily matched. As a result, it is possible not only to accurately measure the edge-to-edge spacing of the stripe structure, but also the width of the portion having a large electric resistance existing between the edges, for example, the FACET plane and the C plane appearing on the surface of the GaN semiconductor substrate, When measuring the width of the C plane, the edge line can be aligned with the Y axis of the image pickup means, so that the width of the C plane can be easily measured.

  The plate-like member surface inspection apparatus of the present invention combines all the surface-captured images of the plate-like members that are divided and imaged, and performs image processing on the combined surface images collectively to inspect defects. The number of defects on the member surface can be accurately inspected.

  Embodiments of a plate-like member appearance inspection apparatus according to the present invention will be described below with reference to the drawings. As shown in the schematic configuration diagram of FIG. 1, the appearance inspection apparatus 1 according to the present embodiment includes a sample stage 3 on which a plate-like member 2 to be inspected is placed, a first camera (imaging means) 41, and a second camera. (Imaging means) 42, first illuminating means 51, second illuminating means 52, image processing means 6, and driving means 7 for driving the sample stage 3 are provided. In the present embodiment, the plate-like member 2 whose appearance is to be inspected is a circular semiconductor substrate.

  The sample stage 3, the first camera 41, the second camera 42, the first illuminating means 51, the second illuminating means 52, and the driving means 7 are disposed in the casing 11.

  The sample table 3 is configured to mount six plate-like members 2 and is arranged in two rows as shown in the plan view of the sample table 3 shown in FIG. The sample base 3 has six base bodies 31 and six L-shaped positioning members 32 that determine the position of the plate-like member 2 fixed on the base body 31. The outer peripheral portion of the circular plate-shaped member is brought into contact with the two L-side surfaces of the positioning member 32.

Below the sample stage 3, there is provided driving means 7 for moving the sample stage 3 in the horizontal direction (in this embodiment, the X-axis direction and the Y-axis direction) and rotating in the horizontal direction. This driving means 7 is provided at the bottom of the casing 11. The driving means 7 is controlled by a control device 12 provided outside the casing 11 for the amount of movement in the X-axis direction, the amount of movement in the Y-axis direction, and the rotation angle. As the driving means 7, a stepping motor is used. A rotation shaft is attached to the rotation center (x ₀ , y ₀ ) shown in FIG. 2 on the bottom surface of the sample table 3, and the sample table 3 rotates around the rotation axis.

  Above the sample stage 3, a first camera 41 and a second camera 42 are provided side by side. Each camera is a CCD camera, and the first camera 41 and the second camera 42 are used for imaging every predetermined imaging area obtained by dividing the entire surface of the plate-like member 2.

  The first illumination means 51 is a halogen lamp that emits halogen light, and the second illumination means 52 is a UV lamp that emits ultraviolet light. The first illumination means 51 uses coaxial epi-illumination arranged coaxially with the first camera 41. The second illumination means 52 is disposed obliquely above the sample stage 3. The first camera 41 is used for imaging the surface of the plate-like member 2 when the first illumination means 51 is used to irradiate the surface of the plate-like member 2 with halogen light. The second camera 42 is used to image the surface of the plate member 2 when the surface of the plate member 2 is irradiated with ultraviolet (UV) light using the second illumination means 52.

  The halogen lamp is used to find a large defect formed on the surface of the plate-like member 2. Examples of the large defect include a collection of defective crystals.

  In the case of a UV light lamp, it is used to detect a portion having a large electric resistance on the surface of the plate-like member 2. For example, when the plate-like member 2 is a GaN semiconductor substrate, a FACET surface and a C surface having a large electric resistance appear on the surface of the substrate. In this case, when UV light is irradiated onto the plate-like member, the FACET surface and the C surface appear in the captured image, and the defect on the C surface, which is a portion having a large electrical resistance, can be detected using the UV light. it can.

  The image processing means 6 is composed of a computer and also includes a monitor 61. The image processing means 6 stores a storage unit that stores image data captured by the first camera 41 and image data captured by the second camera 42, and a number of images captured by the first camera 41 and the second camera 42. And an image composition unit that combines the images into one image. The image composition unit combines a number of images captured by the first camera 41 to combine them into a single image, and a case where the images combined by the second camera 42 combine to combine them into a single image There is.

  The image processing means 6 includes an image processing unit that performs binarization processing on the image combined by the image combining unit, and an abnormal portion (normal portion is detected with respect to the combined image binarized by the image processing unit. A determination unit that measures the size of white and the black part when the abnormal part is binarized so as to be black, and determines the presence or absence of a defect.

  In the present embodiment, the surface of the GaN semiconductor substrate that becomes the plate-like member 2 is inspected for defects. When inspecting a large defect on the surface of the GaN semiconductor substrate, the first camera 41 divides the surface of the GaN semiconductor substrate with the first camera 41 while irradiating the surface of the plate-like member 2 with the halogen light. To do. Thereafter, the plurality of captured images are combined and binarized, and the binarized image is inspected for defects. In this case, assuming that the normal part is white and the abnormal part is black, the size of the abnormal part is measured to determine the presence or absence of a defect.

  Further, a FACET plane and a C plane appear on the surface of the GaN semiconductor substrate, and the portion of the C plane has a large electric resistance. In the present embodiment, the surface of the GaN semiconductor substrate is divided and imaged by the second camera 42 while the second illumination means 52 irradiates the surface of the plate-like member 2 with UV light. Thereafter, the plurality of captured images are combined and binarized, and the binarized image is inspected for defects on the C-plane having a large electrical resistance appearing on the surface of the GaN semiconductor substrate. In this case, the FACET surface is a normal part, the normal part is black, the C surface is an abnormal part, and the abnormal part is white. judge.

  An image captured by the first camera 41 and the second camera 42 is a two-dimensional image with the field of view size of the camera as an imaging region.

  The first illuminating means 51, the second illuminating means 52, and the driving means 7 are driven and controlled by commands from the control device 12, and the first camera 41 and the second camera 42 are supplied from the image processing processing means 6. Controlled by command.

  In the present embodiment, the plate-like member 2 is set on the sample stage 3, and in the image processing means 6, as shown in FIG. 3, a large number of image frames 8 serving as imaging regions of the first camera 41 are adjacently connected. The position of each image frame 8 with respect to the plate-like member 2 is calculated so that the entire surface of the plate-like member 2 fits within the image frame. The position of the image frame 8 is calculated so that no gap is formed when the image frames 8 are continuously arranged so that the entire surface of the plate-like member 2 can be imaged without leakage.

  When the position of the image frame 8 is calculated, the image processing means 6 sends this calculation result to the control device 12. The control device 12 drives and controls the driving means 7 so as to move the sample table 3 in the horizontal direction so that the surface of the plate-like member 2 is imaged according to the position of the image frame 8.

  Then, as shown in FIG. 3, the surface of the plate-like member 2 is imaged by the first camera 41 for each image frame 8 whose position is calculated.

  The data of the image captured by the first camera 41 is stored in the storage unit of the image processing means 6. The image processing means 6 reads the image from the storage unit, and combines the images in the image combining unit to combine the surface images of one plate-like member 2 as shown in FIG.

  Thereafter, the image processing unit performs binarization processing on the composite image. In the binarization process, as shown in FIG. 5, the normal part on the surface of the plate-like member 2 is shown in white where it is below the threshold, the part larger than the threshold is shown in black, and this black part is It becomes an abnormal part.

  Then, the defect inspection process is completed by determining whether the abnormal part is a defect or not from the result of the binarization process. In the determination unit, the size of the abnormal part detected by the binarization process is measured, and when the size of the abnormal part is larger than the threshold value, the determination unit determines that it is a defect (dotted circle in FIG. 5). The part surrounded by) is counted as a defect.

  In the present embodiment, by imaging the plate member 2 with the first camera 41 while illuminating the plate member 2 with halogen light by the first illumination means 51, the defective crystals appearing on the surface of the plate member 2 can be obtained. A defect such as a gathering was detected.

  In the present embodiment, the second illumination unit 52 switches the first illumination unit 51 to the second illumination unit 52, and the second illumination unit 52 irradiates the plate member 2 with UV light. The surface is imaged. At this time, the imaging area captured by the second camera 42 is set to the same position of the image frame 8 as the imaging area captured by the first camera 41 while irradiating light with the first illumination means 51.

  Also in this case, a plurality of images picked up by the second camera 42 are combined, a single surface image is combined, binarization processing is performed on the combined image, and then the presence or absence of a defect is determined.

  The binarization process at this time is not shown, but the normal portion (FACET surface) on the surface of the plate-like member 2 is shown in black, and the abnormal portion (C surface having a large electrical resistance) is shown in white. Yes. Then, a portion in which the size (width) of the white portion is within the threshold range is not determined as a defect, and is determined as a defect when it is outside the threshold range.

  Further, in the present embodiment, even when the surface of the plate-like member 2 has a stripe structure, the above-described measurement of the width of the C surface having a large electric resistance can be easily performed while inspecting a large defect on the surface. To be able to.

  In the stripe structure formed on the surface of the plate-like member 2 used in the present embodiment, the stripe is formed by an edge. When inspecting a surface defect for a plate-shaped member having a stripe structure, if the defect is inspected along the edges, it becomes easier to measure the width of the C surface having a large electric resistance between the edges. Accurate surface inspection can be performed.

  Since the plate-like member 2 used in the present embodiment has a circular outline shape, when the plate-like member 2 is set on the sample stage 3 by an operator, the edge line with respect to the X-axis direction of the sample stage 3 It is difficult to set so that is vertical.

  Therefore, in the present embodiment, the sample stage 3 is not only movable in the plane direction (X-axis direction and Y-axis direction) using the driving means, but is also rotatable in the plane direction.

  Furthermore, in order to obtain the angle of the edge line of the stripe formed on the plate member 2 with respect to the X axis of the sample table 3, first, after setting the plate member 2 on the sample table 3, using the first camera 41, A part of the surface of the plate-like member 2 is imaged. The captured image is recorded in the recording unit of the image processing means 6, and the image processing unit binarizes the image to detect the edge line of the stripe. Next, an angle θ formed by the edge line of the binarized image and the X axis of the sample stage 3 is obtained in the angle measuring unit of the image processing means 6.

  The driving means 7 is controlled to rotate the sample stage 3 so that the edge line is perpendicular to the X axis based on the angle θ measured by the angle measuring unit. This control is performed based on a command from the control device 12.

The rotation of the sample stage 3 by the driving means 7 is performed by providing a rotation axis at the rotation center (x ₀ , y ₀ ) of the sample stage 3 and rotating the rotation axis. Further, as shown in FIGS. 2 and 6, the center of rotation (x ₀ , y ₀ ) of the sample stage 3 and the center (x _n , y _n ) of the plate-like member 2 (where n is the plate-like member of the sample stage) The locations of positions 1-6 are different.

Therefore, when the sample stage 3 is rotated to the rotation center (x ₀ , y ₀ ), the center (x _n , y _n ) of the plate-like member 2 is shifted from the original position. Therefore, not only the sample stage 3 is rotated at the rotation center (x ₀ , y ₀ ), but also the movement correction amount (correction amount X _n in the X axis direction, It is necessary to move the sample stage 3 in the horizontal direction so that the correction amount in the Y-axis direction is calculated as Y _n ) and the center (x _n , y _n ) of the plate-like member 2 is returned to the original position. .

_{X n = x n -r n cos} (θ n + (- θ))
Y _n = y _n −r _n sin (θ _n + (− θ))
θ: angle between the edge line of the plate member (indicated by a line a in FIG. 6) and the X axis of the sample table _rn : the rotation center (x ₀ , y ₀ ) of the sample table 3 and the plate member 2 center (x _n, y _n) distance between theta _n: the angle with respect to the sample stage rotation center of the 3 (x _0, y ₀₎ with the center (x _n, y _n) of the plate-like member 2 and the X axis of the line connecting the

The position of the center (x _n , y _n ) of the plate-like member 2 can be always kept constant by moving the sample stage 3 by the movement correction amount in the X-axis direction and the Y-axis direction. As a result, the entire image of the surface of the plate-like member 2 can be accurately formed regardless of the angle of the edge line of the plate-like member 2 with respect to the X axis of the sample stage 3, and accurate defect counting can be performed. .

  Moreover, since the sample stage 3 can be rotated so that the edge line is perpendicular to the X axis, the edge line is always the first line when the surface of the plate-like member 2 is imaged by the first camera 41. A plate-like member can be arranged on the sample stage 3 so as to be perpendicular to the X axis in the image frame of the camera 41.

  As a result, since the edge line in the captured image is parallel to the Y axis of the image frames of the first camera 41 and the second camera 42, the C plane width between the edges of the stripe structure is measured. It becomes easier to measure the width of the surface.

  The plate-like member appearance inspection apparatus of the present invention is suitable for inspection of the surface of a semiconductor substrate in which minute defects are likely to occur.

It is a schematic block diagram which shows the whole plate-shaped member external appearance inspection apparatus of this invention. It is a top view of the sample stand in the plate-shaped member appearance inspection apparatus of the present invention. It is explanatory drawing which shows the imaging area imaged with the 1st camera in the plate-shaped member external appearance inspection apparatus of this invention. It is explanatory drawing which shows the state which connected and synthesize | combined the image imaged with the 1st camera. It is explanatory drawing which shows the state which binarized the synthesized image. It is explanatory drawing which shows the positional relationship of the center of a sample stand, the center of a predetermined plate-shaped member, and an edge line. It is an explanatory diagram in the case of inspecting defects by performing image processing for each conventional image, (a) shows a state in which defects are detected in one image, (b) is one A state in which a defect is detected across two images is shown.

Explanation of symbols

1 Visual inspection device
2 Plate member
3 Sample stage
31 Base body 32 Positioning member
41 First camera (imaging means) 42 Second camera (imaging means)
51 First illumination means 52 Second illumination means
6 Image processing means 61 Monitor
7 Driving means 8 Image frame
11 Casing 12 Control device

Claims (3)

Illumination means for irradiating light on the surface of the plate-like member;
Imaging means for dividing the entire surface of the plate-like member into a plurality of imaging regions and imaging the surface of the plate-like member for each imaging region;
All the captured images captured by the imaging means are connected so as to constitute the entire surface of the plate-like member, and the surface image of one plate-like member is synthesized, and image processing is performed on this synthesized image, An apparatus for inspecting the appearance of a plate-like member, comprising: an image processing means for inspecting a defect on the surface of the plate-like member. A sample stage on which a plate-like member is placed;
Driving means for moving and rotating the sample stage in the plane direction (X-axis direction and Y-axis direction);
The image processing means further includes an angle measuring unit that obtains an angle θ formed by the edge line of the stripe structure in the plate-like member and the X-axis or Y-axis of the sample stage in the surface image of the plate-like member picked up by the image pickup means. ,
The drive means performs control to rotate and move the sample stage so that the edge line is perpendicular to the X axis or the Y axis based on the angle θ measured by the angle measuring unit. 2. An apparatus for inspecting the appearance of a plate-like member according to 1.   3. The plate-like member visual inspection apparatus according to claim 1, further comprising two or more illumination units having different wavelengths.

Images