JP2007218889A - Surface defect detection method and surface defect detecting device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a surface defect inspection method and a surface defect inspecting device that prevent defects, such as cracks on a three-dimensional surface in a rotating inspection target, from being affected by the brightness of background, prevent confusion with surface state, such as contamination, and detect only the flaws that present seriousness to the quality, without detecting minute flaws that do not affect the quality. <P>SOLUTION: The surface defect inspection apparatus comprises a diffusion light lighting means for lighting a specular surface in the rotating inspection target by diffusion light; a plurality of imaging means, having a linear sensor array for imaging images on the specular surface of the inspection target; and an image processing means for detecting the minute irregular defects on the specular surface, in the inspection target from the intensity of a signal outputted from the linear sensor array. The diffusion light-lighting means lights the specular surface of the inspection target with strip-like and uniform diffusion light and is arranged so that it becomes dark visual field lighting for the imaging means. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a surface defect inspection method for detecting defects existing in a part of a three-dimensional shape inspection target object having a mirror-like surface and including a taper and an R portion, such as a peripheral edge portion of a silicon wafer. And a surface defect inspection apparatus.

  Needless to say, the inspection of the surface flat portion of a silicon wafer used for semiconductor manufacturing is inspected with great care to improve the defect rate. On the other hand, the peripheral edge portion of the silicon wafer and the flat portion that follows the silicon wafer are portions that are not used in the final product, and are discarded portions. Therefore, the inspection of the portions has not been considered very important. In recent years, it has gradually become clear that the minute defects in this part have a great influence on the yield to the post-process. In other words, if there are fine cracks at the end edge (edge part), the distortion of the part spreads to the entire silicon wafer and develops to breakage or peripheral contamination, or fine uneven defects or deposits on the edge part. As a result, it has been regarded as a problem that particles or deposits are scattered and defective products are generated.

  The edge portion of the silicon wafer is tapered in consideration of strength, and includes an upper tapered portion, a side surface portion, and a lower tapered portion, and a rounded portion is provided between the upper and lower tapered portions and the side surface portion. Therefore, the target surface to be observed is a three-dimensional surface. For this reason, when directional illumination is used, a defect can be detected at the inspection site using a flat part such as a taper part or a side part, but the radius between the upper and lower taper parts and the side part is not limited. In the part, there is a problem that even if there is no defect, it becomes a shadow, and even a defect cannot be detected by the imaging means.

  In order to solve the above problems, the present applicant has proposed a surface defect inspection method disclosed in Japanese Patent Laid-Open No. 2003-139523. In the inspection method disclosed in the above publication, the edge portion of the silicon wafer illuminated by the diffused light illuminating means formed in an arc shape or a gate shape has a plurality of imaging means constituted by a telecentric optical system and a linear sensor. Thus, the defects on the surface of the edge portion of the silicon wafer are detected. At this time, the imaging device is arranged so as to capture the regular reflection light reflected on the surface of the edge portion of the silicon wafer out of the illumination light emitted from the light source.

  When the diffused light illumination means formed in an arc shape or a gate shape is used, illumination light is incident from various directions in the main scanning direction of the image pickup device (linear sensor array) of the image pickup means at all locations on the edge portion of the wafer. Therefore, the regular reflection light captured by the imaging device is also applied to the rounded portion connecting the upper and lower taper portions and the side surface portions in the same manner as the flat portions such as the taper portions and the side surface portions because the illumination light strikes from various directions. As a result, the presence or absence of defects can be determined.

  On the other hand, since the illumination is directional in the direction orthogonal to the main scanning direction of the image sensor, that is, the rotational movement direction of the inspection object, the diffused light illuminating means in the inspection method can be viewed from all directions. Unlike the case where the object is illuminated, the moving direction of the inspection object has directivity, and depending on the shape of the defect, it has a feature that even a minute scratch or attached matter is detected.

  JP 2003-139523 A

  In the surface defect inspection method proposed in Japanese Patent Application Laid-Open No. 2003-139523, the determination as to whether or not the defect is made is performed by setting a threshold value. As a result, it is difficult to determine the defect properties. That is, there is a drawback in that it is difficult to determine the difference between a surface state with shallow irregularities such as dirt or slight resist film peeling and a case where irregularities such as chippings and cracks, which are the original defects, are steep and deep. Therefore, due to the characteristics of the diffusive light source formed in the arc shape or the gate shape as described above, a problem that a shallow and slight anomaly that does not affect the product quality is detected as a defect depending on the shape of the defect. There is.

  In view of the above problems, the present invention provides a surface defect inspection method and apparatus that is not affected by the brightness of the background, and that does not detect minor abnormalities such as dirt and shallow unevenness that do not affect quality as defects. The purpose is to provide.

  In order to achieve the above object, the surface defect inspection method for inspecting a three-dimensional mirror surface according to the present invention illuminates the mirror-like surface of a rotating inspection object with diffused light illuminating means, and uses a plurality of imaging means including a linear sensor array. A surface defect detection method for capturing an image of a mirror-like surface of an inspection object and detecting irregularities on the mirror-like surface of the inspection object by an image processing means from a signal output from the linear sensor array, wherein the diffusion The light illuminating means illuminates the specular surface of the object to be inspected with a band-like and uniform diffused light, and is arranged to provide dark field illumination for the imaging means.

  According to the first problem-solving means, when inspecting the three-dimensional mirror surface of the inspection object, the mirror-like surface of the inspection object is shaped like a belt with uniform and diffused light. Illuminated and illuminated by diffused light illumination means arranged to be dark field illumination for the imaging means, so that the surface is not affected by the brightness of the background and is not confused with surface conditions such as dirt. Defect inspection is possible.

  The second problem-solving means is the first problem-solving means, wherein the diffused light illuminating means is characterized in that a light source portion is formed in an arc shape, an elliptic arc shape, or a gate shape, and the edge of the silicon wafer Even a three-dimensional inspection site such as a section can be illuminated with uniform illumination light.

  The third problem solving means is the first problem solving means, wherein the diffused light illuminating means is composed of a plurality of illumination devices, and illuminates the inspection object from different directions, By illuminating the object from the left and right, it becomes possible to detect the defect regardless of the directionality of the defect.

  A fourth problem solving means includes a plurality of imaging means including a diffused light illuminating means for illuminating a mirror-like surface of a rotating inspection object with diffused light, and a linear sensor array for imaging an image of the mirror-like surface of the inspection object. And an image processing means for detecting irregularities on the specular surface of the object to be inspected from the brightness of the signal output from the linear sensor array, wherein the diffused light illuminating means has a belt shape In addition, the mirror surface of the object to be inspected is illuminated with uniform diffused light, and is arranged so as to provide dark field illumination for the imaging means.

  A fifth problem solving means is the fourth problem solving means, characterized in that the diffused light illuminating means has a light source portion formed in an arc shape, an elliptic arc shape, or a gate shape.

  The sixth problem solving means is the fourth problem solving means, wherein the diffused light illuminating means is composed of a plurality of illumination devices, and illuminates the inspection object from different directions.

  The seventh problem-solving means is the sixth problem-solving means, characterized in that the positions of the plurality of illumination devices are adjustable, and an optimum dark field according to the shape of the defect. Illumination means can be arranged at the illumination angle.

  In the conventional surface defect inspection method using bright field illumination, whether or not it is a defect is determined by setting a threshold value, but it is difficult to determine the defect as a result of being affected by the brightness of the background, that is, the normal part. There is a problem that occurs. In addition, there is a drawback that it is difficult to judge the difference between the surface state where the unevenness is shallow such as dirt or a slight scratch, and the case where the unevenness is deep such as chippings and cracks which are the original defects. is there.

  The surface defect inspection method and the surface defect inspection apparatus according to the present invention illuminate a mirror-like surface of an inspection object with a strip-shaped and uniform diffused light illuminating means, and diffuse light illumination so as to provide dark field illumination for the imaging means. Since the means is arranged, a uniform imaging condition is realized for the line sensor array, and an image with high contrast is obtained at the defective portion, so that the determination of the defect is reliable and easy.

  Moreover, even in the case of a shallow surface state where dirt or the like is attached, the bright field illumination may be imaged darkly and erroneously determined as a defect, but the surface defect inspection method of the present invention According to the above, the reflection luminance of the shallow unevenness due to the dark field illumination is at a low level, and there is no possibility of erroneously determining a defect. On the contrary, in the case of a defect shape having a depth such as a crack, an image with high brightness by dark field illumination is captured, so that it can be known as a defect.

  The method and apparatus of the present invention will be described in detail with reference to the drawings. In addition, this invention is not limited by a present Example.

  FIG. 1 shows a surface defect inspection apparatus 1 according to the present invention in a side view, and FIG. 2 is a plan view of the surface defect inspection apparatus 1. A surface defect inspection apparatus 1 shown in FIG. 1 and FIG. 2 shows an embodiment in which an edge portion of a silicon wafer 6 for manufacturing a semiconductor is used as an inspection object. Imaging means 3 for lower surface and imaging means 4 for lower surface. Further, as shown in FIG. 2, C-type light sources 51 and 52 are provided on both sides of the imaging unit as the diffused light illumination unit 5.

  As shown in FIG. 3, the edge portion of the silicon wafer 6 includes two tapered portions, an upper tapered surface 61, a lower tapered surface 63 and a side surface 62. The intersection between each surface and the other surface is smoothly connected by the R surface. Moreover, the part of the flat part following the upper side taper part 61 and the lower side taper part 62 is called a roll-off, and is a part which is not used for a product with a taper part.

  The upper surface imaging unit 2, the side surface imaging unit 3, and the lower surface imaging unit 4 include a linear sensor array as an imaging element. The linear sensor array is a light receiving element that can obtain a high resolution in which CCD charge elements are arranged in a row, and is an imaging element that obtains a two-dimensional image by scanning in a direction orthogonal to the moving direction of the inspection object. is there.

  The silicon wafer 6 has a circular shape, is placed on a rotary table (not shown), and rotates at a constant speed during a defect detection operation. The line sensor arrays of the upper surface imaging means 2, the side surface imaging means 3, and the lower surface imaging means 4 are arranged so that the arrangement direction of the CCD charge elements is orthogonal to the rotation direction of the silicon wafer 6. The image of the edge portion is continuously scanned, and the output is sent to the image processing device 7 to detect the defect. As shown in FIG. 2, the optical axis of the side image pickup means 3 is arranged so as to coincide with the radial direction of the silicon wafer. Further, the upper surface imaging unit 2 and the side surface imaging unit 3 are arranged so as to face the upper tapered surface 61 and the lower tapered surface 63.

  In this embodiment, the diffused light illuminating means 5 is composed of two illuminating devices C-type light sources 51 and 52. As shown in FIG. 1, the C-type light sources 51 and 52 are diffused light sources in which light emitting portions are densely arranged in a C-shaped arc shape or elliptical arc shape, and illumination light is placed inside the C-shaped arc shape. Are arranged. The arc-shaped or elliptical arc-shaped portion having a C shape is supported by a guide guide 54 provided in the holding portion 53. Further, depending on the shape of the inspection object, it may be formed in a gate shape instead of an arc shape.

  As shown in FIG. 5, a guide guide 54 is fixed to the holding portion 53 of the C-type light source 51, and the C-type light source 52 is incorporated so that the guide guide 54 can be moved to guide, and the adjustment screw 55 is rotated. Thus, the position of the illumination device can be adjusted by changing the distance between the C-type light source 51 and the C-type light source 52.

  The C-type light sources 51 and 52 are guided from a halogen lamp (not shown) to the exit of the arc portion of the C-type light sources 51 and 52 via a plurality of optical fibers through the flexible tube 56 and the holding unit 53. Illuminate the surface of the edge with uniform diffused light. Further, as shown in FIG. 2, the C-type light sources 51 and 52 are arranged on both sides of the image pickup means, and are arranged so as to irradiate obliquely with respect to the optical axis of the image pickup means, and on the surface of the edge portion of the silicon wafer 6. The dark field illumination is such that the regular reflection light does not enter the imaging means.

  Next, the function and inspection procedure of the surface defect inspection apparatus of this embodiment will be described. The silicon wafer 6 placed on a turntable (not shown) is rotated at a constant speed with its central axis as the center of rotation. The upper surface imaging means 2, the side surface imaging means 3, and the lower surface imaging means 4 are disposed substantially opposite to the upper tapered surface 61, the side surface 62, and the lower tapered surface 63 of the silicon wafer 6, respectively. The line sensor arrays provided in the means 2, the side image pickup means 3 and the lower surface image pickup means 4 continuously take images of the upper taper surface 61, the side surface 62 and the lower taper surface 63, respectively.

  The rounded portion of the connecting portion between the upper tapered surface 61 and the side surface 62 can be imaged by either the upper surface imaging means 2 or the side surface imaging means 3. Similarly, the rounded portion of the connecting portion between the side surface 62 and the lower tapered surface 63 can be imaged by either the side surface imaging means 3 or the lower surface imaging means 4. Further, the upper surface roll-off portion and the lower surface roll-off portion are imaged by the upper surface imaging means 2 and the lower surface imaging means 4, respectively.

  FIG. 6 is a schematic diagram illustrating the illumination of the illumination light from the diffused light source 5 with the C-type light source 51 as an example. The exit of the optical fiber provided in the C-type light sources 51 and 52 of the diffused light illuminating means 5 is emitted at a wide angle of about 70 ° as shown in FIG. Since the C-type light sources 51 and 52 have an arcuate curvature, the illumination light is incident at a wide angle with respect to the imaging location on the silicon wafer 6 of the imaging means.

  Since the illumination lights of the C-type light sources 51 and 52 provided on both sides of the image pickup means are arranged to irradiate obliquely with respect to the optical axis of the image pickup means, regular reflection light is not incident on the image pickup means. Only the light that has been irregularly reflected is imaged, and so-called dark field illumination is obtained. For this reason, if the surface of the silicon wafer 6 is normal, the reflected light does not enter the image pickup device of the image pickup means, whereas the surface of the silicon wafer 6 has deep irregularities such as chips and cracks. In some cases, the reflected light at the location is incident on the imaging means depending on the abnormal state of the location, and at this time, the image by the imaging device is captured as a bright image.

  FIG. 7 shows the difference in reflected light due to defects formed on the surface of the inspection object. FIG. 7A shows a case where there is no defect such as unevenness on the surface of the inspection object, and the light reflected on the surface of the inspection object does not enter the imaging means and is captured as a dark image. Further, even in the case of the gently undulating surface of FIG. 7B, the reflected light does not enter the image pickup means, and a dark image is formed.

  On the other hand, in the case of the crack-like defect shown in FIGS. 7 (c) and 7 (d), there is a gently inclined surface with a fractured surface in the vicinity, followed by a steep tear. Is common. The figure shown here is only a schematic explanatory diagram, and the actual crack-like defect is not necessarily a symmetrical shape as shown in FIG. 7C and FIG. May exist only on one side of the entrance.

  As shown in FIGS. 7 (c) and 7 (d), the illumination light from the illumination means is irregularly reflected on an inclined surface near the entrance of the crack, and a part of the reflected light is captured by the imaging means, and a bright image is taken. . In the direction of the illumination light shown in FIG. 7 (c), the left inclined surface in the figure is not imaged, but both left and right inclined surfaces are imaged by using illumination means from the opposite direction as shown in FIG. 7 (d). It becomes possible to do. In the present embodiment, illumination light from two directions is realized by disposing the C-type light sources 51 and 52 on both sides of the imaging means. In addition, the light incident on the crack having a sharp angle is not a mirror surface on the facing wall, and the reflected light amount is attenuated one after another to form a dark image.

  FIG. 10A shows an image obtained by dark-field illumination of a crack-like defect imaged with the configuration of this example. On the other hand, FIG.10 (b) is the image which imaged the same crack-like defect with bright field illumination. In the image by dark field illumination in FIG. 10A, a portion without a defect becomes a dark screen, and only a defective portion becomes a bright image. On the other hand, in the image by bright-field illumination in FIG. 10B, only the center portion of the crack is a dark image, and the other portions having no defect are gray regions.

  Although the C-type light sources 51 and 52 provided in this embodiment are incident obliquely on the surface of the silicon wafer 6, the incident angle varies depending on the positions of the C-type light sources 51 and 52. Depending on the relationship between the shape of the defect and the position of the C-type light sources 51 and 52, the imaging means may not be able to capture the light that is irregularly reflected by the defective portion. In such a case, the adjustment screw 55 shown in FIG. By rotating, the distance between the C-type light sources 51 and 52 is adjusted so that irregularly reflected light due to the defect is incident on the image pickup means, whereby appropriate illumination light can be obtained.

  The edge portion of the silicon wafer 6 that is rotated at a constant speed by a rotating device (not shown) is scanned continuously by the upper surface imaging means 2, the side surface imaging means 3, and the lower surface imaging means 4, thereby forming the edge portion of the silicon wafer 6. An image of the entire circumference can be obtained. When there is a defect such as a crack on the surface of the edge portion of the silicon wafer 6, the corresponding portion of the image is a video with high brightness as shown in FIG.

  The determination of the defect is performed according to the procedure shown in the flowchart shown in FIG. Two levels of low luminance value and high luminance value are provided as threshold values for defect determination. First, binarization is performed with a low luminance threshold value. Where there is no defect such as a crack, dent or deposit, the image is dark, and if there is a defect such as a chip or a crack, a bright image is obtained. A portion brighter than the low luminance threshold is extracted, and the portion is managed by labeling. Here, paying attention to the shape of the labeled part, an elongated shape is determined as a crack. Next, the remaining labeling location is determined using a high brightness threshold. If the luminance is higher than the threshold value, it is determined as a chip or a crack. Otherwise, it is determined that the shallow resist film is a slight change such as a peeling or a deposit.

  According to the surface defect detection method using dark field illumination of the present invention, it is possible to easily discriminate between a critical defect such as a chipped defect or a crack and a defect having a shallow unevenness that can be repaired. . Further, since only the light reflected from the defective portion is imaged, there is an advantage that the defect can be easily detected as a result of obtaining an image of the defective portion with high contrast. Depending on the shape of the defect, the diffused light source placed at a fixed position may not be detected, but detection according to the shape of the flaw can be performed by adjusting the position of the diffused light source.

  The C-type light sources 51 and 52 used in the present embodiment are illumination devices that guarantee illumination light that is uniform and incident at a wide angle at any position in the imaging range of a three-dimensional inspection object. Even in a three-dimensional portion such as a round portion at the edge portion of the silicon wafer 6 described in the present embodiment, illumination that is incident at a uniform and wide angle can be ensured.

  Furthermore, by using near-infrared light as a light source or using a filter that allows only near-infrared light to pass through the imaging means, an inspection apparatus that is not easily affected by dirt can be configured.

  Moreover, in the surface defect inspection method and the surface defect inspection apparatus of the present invention, since a linear sensor array is used for the image sensor, it is possible to obtain a higher resolution than a two-dimensional area sensor, and the uneven defect Can be detected. Further, since the scanning speed of the linear sensor array is much faster than that of the area sensor, high throughput is ensured and inspection processing capability is high.

  In this embodiment, the C-type light source, which is a diffused light source, is arranged on both sides of the imaging device. However, if the nature of the flaw can be predicted, only one may be arranged.

  In the defect inspection method of the present invention, the diffused light illuminating means illuminates the specular surface of the inspection object with a strip-shaped and uniform diffused light, and the diffused light illuminating means is dark field illumination for the imaging means. Since the diffused light illuminating means is configured so as to be arranged, uniform imaging conditions are realized for the linear sensor array, and an image of a defective portion with high contrast is obtained.

  Further, even in a surface state having no irregularities such as dirt, a high contrast image such as a chipped defect or a crack is not generated, and there is no risk of erroneous determination. As a result, the determination of defects is easy and reliable, and the time required for inspection is reduced, so that a high production yield rate can be ensured and the contribution to the industry is great.

  It is a side view which shows the external appearance of the surface defect apparatus of a present Example.   It is a top view of the surface defect apparatus of a present Example.   It is detailed explanatory drawing of the edge part of a silicon wafer.   It is explanatory drawing which shows the relationship between an illumination means and an imaging device.   It is explanatory drawing which shows the space | interval adjustment mechanism of an illumination means.   It is explanatory drawing explaining the mode of illumination of a diffused light source.   It is explanatory drawing which shows the state of the reflected light by the shape of a defect.   It is a flowchart which shows the procedure of a crack determination.   It is the image which imaged the actual crack.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Surface defect inspection apparatus 2 Imaging means for upper surfaces 3 Imaging means for side surfaces 4 Imaging means for lower surfaces 5 Diffused light illumination means 6 Silicon wafer 7 Image processing device 51, 52 C-type light source 53 Holding part 54 Guide guide 55 Adjustment screw 61 Upper taper Surface 62 Side surface 63 Lower tapered surface

Claims (7)

  Signals output from the linear sensor array by illuminating the mirror-like surface of the rotating inspection object with diffused light illuminating means, taking images of the mirror-like surface of the inspection object with a plurality of imaging means including a linear sensor array A surface defect detection method for detecting irregularities on a specular surface of an inspection object by an image processing means, wherein the diffused light illuminating means is a band-like and uniform diffusion of an imaging portion of a linear sensor array on the inspection object A surface defect detection method characterized by being illuminated with light and arranged to be dark field illumination for an imaging means.   The surface defect detection method according to claim 1, wherein the diffused light illuminating means has a light source portion formed in an arc shape, an elliptical arc shape, or a gate shape.   The surface defect detection method according to claim 1, wherein the diffused light illuminating unit includes a plurality of illuminating devices, and illuminates the inspection object from different directions.   Diffused light illuminating means for illuminating the mirror-like surface of the rotating inspection object with diffused light, a plurality of imaging means including a linear sensor array for taking an image of the mirror-like surface of the inspection object, and output from the linear sensor array An image processing means for detecting irregularities on the specular surface of the object to be inspected from the intensity of the signal to be inspected, wherein the diffused light illuminating means is inspected with a band-like and uniform diffused light A surface defect detection apparatus characterized by being arranged to illuminate a mirror-like surface of an object and to provide dark field illumination for an imaging means.   The surface defect detection apparatus according to claim 4, wherein the diffused light illuminating means has a light source portion formed in an arc shape, an elliptical arc shape, or a gate shape.   The surface defect detection device according to claim 4, wherein the diffused light illuminating unit includes a plurality of illumination devices, and illuminates the inspection object from different directions.   The surface defect detection device according to claim 6, wherein the plurality of illumination devices are configured to be capable of adjusting an angle at which the inspection object is illuminated.

Images