JP7537893B2 - Edge chipping detector - Google Patents

Description

The present invention relates to measuring the shape of the edge of a semiconductor wafer, and in particular to an edge chipping detection device that detects chipping of the edge of a wafer or a truing grindstone based on a captured image of the edge.

During the manufacturing of semiconductor wafers, the edge (rim) of the wafer may become scratched or chipped due to contact with other parts or wafer holding members. Furthermore, such scratches or chips may cause the wafer to crack. For this reason, the wafer manufacturing process requires accurate detection of scratches that occur on the edge.

For example, Patent Document 1 describes that in order to measure the shape of a chamfered edge (chamfer shape: angle and face width), a light beam with an irradiation width greater than the thickness width of the wafer is projected onto the edge of the object to be measured from a direction parallel to both the front and back faces, and images are taken with two cameras from a direction perpendicular to the surface on both the front and back faces. The document describes how the width of the image of the bright part in the captured image is detected as the width of the chamfered edge face.

Patent Document 2 also describes that, in order to visually confirm the grinding marks in the notch portion of the wafer, light rays incident from the illumination means onto any point on the straight portion of the notch portion, whose angle of incidence with respect to the normal to the straight portion is equal to or greater than a reference angle of incidence, are blocked.

JP 2010-181249 A JP 2014-85295 A

In the above-mentioned conventional technology, Patent Document 1 simply measures the width of the chamfered edge, regardless of whether the surfaces other than the chamfered edge are mirror-finished or non-mirror-finished, and performs measurements on both the front and back surfaces simultaneously, so it is not possible to detect the state of chipping at the wafer edge.

Similarly, in Patent Document 2, although it is possible to visually confirm the grinding marks formed on the chamfered surface of the notch of the wafer, it is not possible to evaluate the quality of the wafer based on the state of chipping at the wafer edge. In addition, the detection accuracy is low due to an insufficient amount of light being irradiated onto the chipping, light not being irradiated in the depth direction relative to the chipping, and the chipping being formed by being missing from the face width.

The object of the present invention is to solve the problems of the conventional technology and provide an edge chipping detection device that detects chipping on the wafer edge with high accuracy.

To achieve the above object, the present invention provides a chipping detection device for detecting chipping on a chamfered surface formed on the outer peripheral edge of a wafer and inclined relative to the main surface of the wafer, the device comprising: an LED illumination device that irradiates light onto the chamfered surface from a direction parallel to the main surface of the wafer; imaging means that images the chamfered surface and the main surface illuminated by the light irradiated from the LED illumination device from a direction perpendicular to the main surface; and a reflector that is provided to cover the LED illumination device from the center of the wafer, and the chipping is detected from the image captured by the imaging means.

In addition, in the above chipping detection device, it is preferable that the reflector is installed at a position where the LED illumination device side extends beyond the chamfered surface toward the center of the wafer.

Furthermore, in the above chipping detection device, it is desirable that the reflector has a U-shape or an arc shape when viewed from above, and that a slit is provided in the center in the height direction.

Furthermore, in the above chipping detection device, it is desirable that the reflector facing the LED lighting device is painted white with Munsell value N9.5, RGB (245, 246, 242).

Furthermore, in the above chipping detection device, it is desirable that the reflector has a slope that is inclined at an angle of 30 to 60 degrees with respect to a plane parallel to the LED lighting device.

Furthermore, in the above chipping detection device, it is desirable that the wavelength of the light irradiated from the LED lighting device is 570 nm or less.

Furthermore, in the above chipping detection device, it is desirable to provide a diffusion plate between the LED lighting device and the reflector, closer to the LED lighting device than the chamfered surface.

Furthermore, in the above chipping detection device, it is preferable that the imaging means includes an upper camera arranged on one side of the wafer, and a lower camera arranged on the other side of the wafer.

Furthermore, in the above chipping detection device, it is preferable that the LED lighting device is a panel-type surface light source in which multiple blue-emitting LEDs are arranged.

According to the present invention, a reflector is provided to cover the LED lighting device from the center of the wafer, and the LED lighting device is used to irradiate the wafer from a direction parallel to the wafer. Chipping is detected from an image captured from a direction perpendicular to the wafer's main surface. Light diffused by the reflector is also irradiated in the depth direction of the chipping, allowing the state of the chipping to be detected with high accuracy.

FIG. 1 is a side view showing a main part of a chipping detection device according to an embodiment of the present invention. Plan view of FIG. FIG. 1 is an enlarged cross-sectional view showing the illumination of a chamfered edge according to one embodiment. FIG. 1 is a perspective view of a reflector 1 according to an embodiment; An enlarged cross-sectional view showing the irradiation of light at a conventional chamfered portion (chamfered edge portion). FIG. 13 is a comparison of an image captured by an imaging means according to an embodiment in which chipping 8 is detected with that of the prior art.

Figure 1 is a side view showing the main parts of the chipping detection device, Figure 2 is a plan view, and Figure 3 is an enlarged cross-sectional view showing the irradiation of light at the chamfered portion (chamfered edge portion). Shape measurement of the semiconductor wafer edge portion uses a camera and lighting device to measure the chamfer angle, face width, etc. In this device, the camera is installed perpendicular to the measurement location on the wafer 2, and the lighting device is installed perpendicular to it. Chipping detection is an example of shape measurement, and is considered to be a particularly important shape measurement, and is performed in the same way as face width measurement.

The shape measuring device, or chipping detection device, is equipped with a rotating table 3 that can suction-hold and rotate the main surface P of the wafer 2 in a horizontal position, an LED lighting device 4 as an illumination means, and an upper surface camera 6 arranged on one side of the wafer 2 as an imaging means, and a lower surface camera 5 arranged on the other side of the wafer. Although not shown, the chipping detection device also includes an image processing device, a monitor, etc. The wafer 2 that has been cleaned after the chamfering process is placed on the rotating table 3. The chamfered surface C is formed on the outer periphery of the wafer 2 and is inclined with respect to the main surface P of the wafer 2.

The LED lighting device 4 is disposed to the side of the turntable 3, and irradiates the edge of the wafer 2 with light from a direction parallel to the wafer 2, as indicated by arrow A. The light is also reflected by the reflector 1, as indicated by arrow B. The LED lighting device 4 is rectangular, with a height H and width L of the illumination light so that the illumination light acts as a surface light source. In other words, the LED lighting device 4 has a diffusion plate 7 that diffuses the light.

The top camera 6 is positioned opposite the outer periphery of the top surface of the wafer 2 and captures the shape of the top edge of the wafer 2. The bottom camera 5 is positioned opposite the outer periphery of the bottom surface of the wafer 2 and captures the shape of the bottom edge of the wafer 2. The top camera 6 and bottom camera 5 capture images of the chamfered surface C and main surface P of the wafer 2 illuminated by light emitted from the LED lighting device 4 from a direction perpendicular to the main surface P of the wafer 2.

Of the light irradiated from the LED lighting device 4 onto the wafer 2, only the light reflected by the chamfered surface C is captured by the top camera 6 and the bottom camera 5. As a result, the image showing the chamfered surface C of the wafer 2 is displayed in white, and the image showing the main surface P is displayed in black on the monitor.

The image processing device measures the surface width of the chamfered surface C and detects chipping 8 from the captured image. The image processing device also has a function of extracting an image of the chamfered surface C from the images captured by the top camera 6 and the bottom camera 5, and performing image processing such as edge detection.

Figure 4 is a perspective view of the reflector 1, which is installed so as to cover the LED lighting device 4 from the center of the wafer 2. However, it does not obstruct the field of view of the top camera 6 and the bottom camera 5. The shape of the reflector 1, as seen from above as shown in Figures 2 and 4, is a U-shape or an arc shape with inclined surfaces 1-2 and 1-3, and a slit 1-1 is provided in the center in the height direction.

The slit 1-1 is larger than the thickness of the wafer 2, and the chamfered surface C of the wafer 2 is inserted into the slit 1-1. The reflector 1 is installed at a position where the LED lighting device 4 side of the reflector 1 exceeds the chamfered surface C, i.e. the surface width, towards the center of the wafer 2. The diffusion plate 7 may be provided between the LED lighting device 4 and the reflector 1, on the LED lighting device 4 side of the chamfered surface C.

The inclined surfaces 1-2 and 1-3 are preferably inclined at an angle of 30 to 60 degrees, and preferably about 45 degrees, with respect to the surface 1-4 that is parallel to the LED lighting device 4 and the diffusion plate 7. A similar inclined surface may be formed in the height direction of the reflector 1. The reflector 1 is made of a metal plate and is formed by bending.

The inner side of the reflector 1, the side facing the LED lighting device 4, is roughly finished to Ra 10 to 40 μm, preferably about 25 μm, and is melamine baked in white with Munsell value N9.5 and RGB (245, 246, 242). Improvements can also be made by using white arc-shaped paper for the reflector 1, with the concave surface facing the LED lighting device 4. The paint color can also be ivory.

Figure 5 is an enlarged cross-sectional view of a chamfered portion (chamfered edge portion) measured by a conventional edge shape measuring device without a reflector 1. Figure 5 shows the relationship between the light irradiated from the LED lighting device 4 to the wafer 2 and the representative light reflected by the chamfered surface C and the chipping 8.

As shown in Figure 5, light from the LED lighting device 4 is irradiated onto the chamfered surface C as indicated by arrow A, and is reflected as indicated by arrow F before reaching the upper surface camera 6 and the lower surface camera 5 where it is captured. However, chipping 8 is in a state where the chamfered surface C is chipped, so the inclination of the chipping 8 is different from that of the chamfered surface C. Also, the amount of light reaching chipping 8 is such that some parts are shaded by the LED lighting device 4.

Therefore, the amount of light reaching the upper surface camera 6 and the lower surface camera 5 from the chipping 8 is greatly insufficient. As a result, in the conventional technology, the light from the LED lighting device 4 is somewhat diffused by the diffusion plate 7, which provides some improvement, but the detection accuracy of the chipping 8 is still insufficient.

In contrast to the conventional technology, in this embodiment, a reflector 1 is provided as shown in FIG. 3. The light from the LED lighting device 4 is not only irradiated from the arrow A onto the chamfered surface C, but is also reflected by the reflector 1 as shown by the arrows G and F and reaches the chamfered surface C. The light from the LED lighting device 4 also reaches the chipping 8, which has a different inclination from the chamfered surface C, increasing the amount of light irradiated onto the chipping 8. In other words, the light diffused by the reflector 1 is also irradiated in the depth direction of the chipping 8, allowing the state of the chipping 8 to be detected with high accuracy.

In addition, the reflector 1 has inclined surfaces 1-2 and 1-3, and the inside of the reflector 1, the side facing the LED lighting device 4, is roughly finished and painted in an achromatic color, so the light from the LED lighting device 4 is scattered, further enhancing the effect. Since light scattering is more pronounced the shorter the wavelength of light, it is preferable that the wavelength of the light irradiated from the LED lighting device 4 be a short wavelength of 570 nm or less.

Note that light with a wavelength of 570 nm or less may be a wavelength within the visible light range, or may be a wavelength including the ultraviolet light range. For example, in terms of improving measurement accuracy, it is preferable to use a blue-emitting LED that can stably emit light of a single wavelength and to utilize light with a wavelength of 450 nm to 495 nm. It is also preferable that the LED lighting device 4 be a panel-type surface light source in which multiple blue-emitting LEDs are arranged.

Figure 6 shows images of one embodiment in which chipping 8 is detected by an upper camera 6 (imaging means) compared with the prior art. Images captured by a lower camera 5 are similar. (a) shows the case where there is no reflector 1, (b) shows the case where the LED lighting device 4 is surrounded by white arc-shaped paper instead of the metal reflector 1 shown in Figure 4, and (c) shows the case where the metal reflector 1 shown in Figure 4 is used.

In (a), there is no reflector 1, so the surface width indicating the chamfered surface C of the wafer 2 is displayed in white, and the main surface P is displayed in black, with shading. However, the chipping 8 area (center of the figure) has no shading from the main surface P (right side of the figure), making it difficult to distinguish.

In (b), the reflector 1 is made of white arc-shaped paper with the concave surface facing the LED lighting device 4, so the surface width showing the chamfered surface C of the wafer 2 is displayed in white. However, the difference in shading between the main surface P and the surface width is small. Also, the difference in shading between the main surface P and the chipping 8 is greater than in (a), which is a slight improvement. However, it is difficult to see the positional relationship between the chipping 8 and the surface width.

In (c), the surface width indicating the chamfered surface C of the wafer 2 is displayed in white, and the difference in shading between the main surface P and the surface width can be clearly identified. In addition, there is also a difference in shading between the main surface P and the surface width, improving the detection accuracy of chipping 8.

In addition, as a result of the experiment, when wafer 2 was a silicon wafer and the detection results of chipping 8 were expressed as an evaluation index, (a) there was no reflector 1 and the index was 67, (b) the reflector 1 was paper and the index was 815, and (c) the reflector 1 was the metal plate shown in Figure 4 and the index was 940.

However, the evaluation index is a cumulative value obtained by converting the difference in contrast within the range being measured into a score. For example, when there is no chipping 8, the evaluation index will be 0, the face width will be white, and the surface of the wafer 2 will be black. If chipping 8 is present on the face width, black will appear in a white area, creating a contrast difference that will be converted into a score. Also, if chipping 8 is present on the surface of the wafer 2, a white border will appear in an area that is solid black, creating contrast that will also be converted into a score.

The above explanation was for the wafer 2, but the same applies to the case of a truing grindstone (GC grindstone), and it is possible to detect chipping 8 on the edge. Note that truing requires transferring the shape to the grindstone, so greater shape accuracy is required, and so there is a strong demand to reduce damage such as chipping 8, just as with the wafer 2.

1...reflector 1-1...slit 1-2...inclined surface 1-4...surface 2...wafer 3...rotary table 4...LED lighting device 5...bottom surface camera 6...top surface camera 7...diffuser 8...chipping A...arrow C...beveled surface G...arrow H...height P...main surface

Claims (8)

1. A chipping detection device for detecting chipping on a chamfered surface formed on an outer peripheral edge of a wafer and inclined with respect to a main surface of the wafer, comprising:
an LED illumination device that irradiates the chamfered surface with light in a direction parallel to the main surface of the wafer;
an imaging means for imaging the chamfered surface and the main surface illuminated by light emitted from the LED illumination device in a direction perpendicular to the main surface;
a reflector provided to cover the LED illumination device from a center direction of the wafer, and detecting the chipping from an image captured by the imaging means;
The reflector has a U-shape or an arc-shape when viewed from above, and has a slit in the center in the height direction . The chipping detection device according to claim 1, characterized in that the reflector is installed at a position where the LED lighting device side extends beyond the chamfered surface toward the center of the wafer. 3. The chipping detection device according to claim 1, wherein the reflector facing the LED lighting device is painted white with a Munsell value of N9.5, RGB (245, 246, 242). 4. The chipping detection device according to claim 1 , wherein the reflector has a slope that is inclined at an angle of 30 to 60 degrees with respect to a plane parallel to the LED illumination device. 5. The chipping detection device according to claim 1 , wherein the wavelength of light irradiated from the LED illumination device is 570 nm or less. 6. The chipping detection device according to claim 1, further comprising a diffusion plate disposed between said LED illumination device and said reflector plate on the side of said LED illumination device relative to said chamfered surface. The chipping detection device according to any one of claims 1 to 6, characterized in that the imaging means comprises an upper surface camera arranged on one side of the wafer, and a lower surface camera arranged on the other side of the wafer. 8. The chipping detection device according to claim 1, wherein the LED illumination device is a panel-type surface light source having a plurality of blue-emitting LEDs arranged thereon.