JP2006258778A - Method and device for inspecting surface defect - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method and device for inspecting a surface defect constituted to surely detect a fatal defect, and capable of selecting optionally a degree of unevenness detected as the defect in response to an inspected object. <P>SOLUTION: A surface of the inspected object is illuminated with a diffusing light illumination means, illumination light from the diffusing light illumination means reflected on the object surface is returned again along a substantially same optical path by a recurrent reflection member provided in the vicinity of the inspection object, so as to image direct light reflected directly from the object surface together with recurrent light reflected on the object surface through the recurrent reflection member, by an imaging means. A shallow flaw is thereby precluded from forming a shadow, because of the illumination from various directions, so as to be prevented from being recognized as the defect. On the other hand, the deep flaw is determined as the defect, because a clear shadow is formed therein. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a surface defect inspection method and a surface defect inspection apparatus for inspecting a fine irregularity defect on a surface of a mirror-like inspection object, particularly a semiconductor silicon wafer and a minute irregularity defect at an edge portion thereof.

  As a method for inspecting fine irregularities on a mirror-like surface, particularly micro-defects existing on a mirror-like surface such as a silicon wafer used for forming a semiconductor, the surface of the mirror-like inspection object is illuminated by illumination means. A method for detecting defects by illuminating and imaging the reflected light with an imaging means is known.

  If there are no scratches or irregularities on the mirror-like surface, the illumination light is reflected in a certain direction, resulting in a uniform image, whereas if there are scratches or irregularities, the illumination light will be scratched or irregular Due to scattering at certain locations, variations in brightness appear. Utilizing this fact, it is determined that a portion having a variation in brightness is a defective portion having unevenness.

  Japanese Patent Laid-Open No. 8-304048 proposes a method capable of detecting even fine irregularities. That is, by using a reflecting member that retroreflects in a certain direction to increase the degree of scattering on the surface of the inspection object, even fine unevenness of about 10 μm can be captured as an image.

  On the other hand, the purpose of inspection in the manufacturing process is to detect defects that may affect the quality, and even the slight irregularities that do not affect the quality of the product are judged as defects. It is not preferable to make it worse.

  In conventional optical detection means, a defect is determined by setting a threshold according to the degree and size of brightness, but if optical means is configured so that even fine irregularities are captured in an image, it is a defect. As a result, even a slight unevenness of a slight degree was determined to be a defect, and there was a problem that the yield was lowered and a re-inspection by an inspector was required in a subsequent process.

JP-A-8-304048

  As described above, the defect inspection method using the conventional imaging means has a problem that even when a fine flaw or unevenness is detected, even an unevenness that does not affect the quality is detected as a defect. On the other hand, if it is configured to ignore fine scratches, a fatal defect such as a crack may be missed.

  The present invention provides a surface defect inspection method and apparatus capable of reliably detecting a fatal defect and capable of arbitrarily selecting the degree of unevenness detected as a defect according to an inspection object. With the goal.

  In order to achieve the above object, the first solving means of the present invention is a surface inspection in which the surface of the inspection object is illuminated by the diffused light illuminating means and a micro defect is detected by taking an image of the surface of the inspection object. A method of retroreflecting direct light reflected directly from an object surface by causing the illumination light from the diffused light illumination means reflected on the object surface by a retroreflective member provided in the vicinity of the inspection object to recur in substantially the same optical path. Both the retroreflected light reflected from the surface of the object via the member are imaged by the imaging means.

  According to the first problem solving means, the object to be inspected is illuminated by the illuminating means, and illuminated from various directions different from the illuminating means by the light returning from the retroreflective member. That is, by illuminating from various directions, shallow scratches do not become shadows and are not recognized as defects. On the other hand, when the flaw is deep, a clear shadow is formed, so that it can be determined as a defect.

  The second problem-solving means is the first problem-solving means, characterized in that the retroreflective surface of the retroreflective member is a dome-shaped concave surface portion, and the retrolight recurs from various directions. As a result, the surface of the inspection object is illuminated uniformly.

  The third problem solving means is the first and second problem solving means, wherein the imaging means is a linear sensor camera, and is suitable for imaging a moving inspection object. .

  The fourth problem solving means is the first to third problem solving means, characterized by using a telecentric optical system, and can confirm the shape and position irrespective of the distance to the inspection object.

  The fifth problem solving means is the first and second problem solving means, characterized in that the retroreflective surface of the retroreflective member is configured to have a variable size, and the depth of the unevenness that can be detected as an image Can be selected.

  The sixth problem solving means is the first and second problem solving means, characterized in that the distance between the surface of the inspection object and the retroreflective member is variably configured, and the unevenness that can be detected as an image The depth can be selected.

  The seventh problem solving means is a surface defect inspection apparatus for detecting a micro defect on the surface of the inspection object, and an imaging means for capturing an image of the surface of the inspection object, and diffusion for illuminating the surface of the inspection object It is characterized by comprising a light illumination means and a retroreflective member provided above the inspection object.

  The eighth problem-solving means is the seventh problem-solving means, characterized in that the retroreflective surface of the retroreflective member is provided in a dome-shaped concave surface portion.

  The ninth problem solving means is the seventh and eighth problem solving means, wherein a window is provided in a part of the dome shape of the retroreflective member, and the illumination means illuminates the object to be inspected through the window. In addition, the reflected light from the inspection object that has passed through the window is imaged by the imaging means. It becomes possible to freely select the directions of the illumination means and the imaging means.

  A tenth problem-solving means is a seventh to ninth problem-solving means, in which a half mirror is provided on the upper portion of the window, and the object to be inspected is refracted by the illuminating means of the illuminating means. The light transmitted through the mirror is imaged by the imaging means. It is possible to make the illumination direction of the illumination means coincide with the optical axis direction of the imaging means.

  The eleventh problem solving means is the seventh and eighth problem solving means, wherein the imaging means is a linear sensor camera.

  A twelfth problem solving means is a seventh and eleventh problem solving means, wherein the imaging means uses a telecentric optical system.

  The thirteenth problem solving means is the seventh to tenth problem solving means, characterized by comprising retroreflective surface variable means for changing the area of the retroreflective surface of the retroreflective member.

  The fourteenth problem solving means is the seventh to tenth problem solving means, characterized by comprising retroreflective member position varying means for changing the distance between the surface of the inspection object and the retroreflective member.

  The fifteenth problem solving means is the seventh to fourteenth problem solving means, characterized in that a plurality of imaging means and a plurality of retroreflective members corresponding to each of the imaging means are provided.

  As described above, in the surface inspection method of the present invention, the retroreflective member is provided in the vicinity of the inspection object, and most of the light reflected from the illumination object by the inspection object passes through the substantially original optical path by the retroreflection member. It is configured to return to the object. As a result, the direct light from the illumination means and the recursive light that recurs from the retroreflective member reach the inspection object. In other words, the object to be inspected is exposed to light from various directions, which is equivalent to being illuminated from various directions.

  In the case of illumination from one direction, if there is a shallow flaw or a gentle swell on the surface of the object to be inspected, a dark part is generated in the captured image, but illumination is performed from a direction opposite to the illumination direction of one illumination means. If an illumination unit is provided and illuminated at the same time, depending on the degree of scratches and unevenness, a dark part that is formed when illuminated from one direction may not be visible.

  By using a retroreflective member, the reflected light from scratches and uneven slopes is canceled because it returns to the same optical path, and images taken with shallow scratches, gentle undulations, film peeling, etc. are not recognized as dark parts, and as a result Since it is not determined to be a defect, only unevenness having a depth or height larger than a predetermined value is determined to be a defect, and only a fatal defect can be detected.

  Furthermore, it was recognized that the depth or height of the scratches and irregularities that can be recognized in the captured image differs by limiting the angle and direction of the light returning from the retroreflective member. As a result, the surface defect inspection capable of selecting the defect level is realized by changing the area of the retroreflective member or the distance between the retroreflective member and the inspection object.

BEST MODE FOR CARRYING OUT THE INVENTION

  The surface defect inspection method and inspection 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 is an explanatory diagram for explaining a surface defect inspection method and inspection apparatus according to a first embodiment of the present invention.
As shown in FIG. 1, an imaging means 1 that images the surface of the inspection object 5 is disposed above the inspection object 5, and a dome-shaped retroreflective member is disposed between the imaging means 1 and the inspection object 5. 4 is arranged. A part of the retroreflective member 4 is provided with a window 41, and the imaging unit 1 is configured to be able to image the surface of the inspection object 5 through the window 41.

  The illuminating means 2 is a diffused light illuminating means for illuminating the surface of the inspection object 5, and is reflected by the half mirror 3 disposed at an inclination of 45 ° between the imaging means 1, the retroreflective member 4 and the inspection object 5. Then, the inspection object 5 is illuminated through the window 41 provided in the retroreflective member 4.

  The imaging means 1 may use an area sensor camera or a linear sensor camera. However, in the case of using a linear sensor camera, it is necessary to make a relative movement in a direction orthogonal to the arrangement direction of the elements of the linear sensor array mounted on the linear sensor camera. Usually, the moving inspection object is imaged. Used when For example, it is suitable for imaging an inspection object moving at a constant speed by a conveying means such as a belt conveyor or a disk-shaped inspection object rotating at a constant speed.

  The retroreflective member 4 shown in FIG. 1 has a dome shape, but is not limited to this, and may be any shape as long as the center is high and decreases toward the periphery. For example, an umbrella shape or a polygonal pyramid shape may be used. Shape may be sufficient.

  The retroreflective member 4 is a reflective material that retroreflects unlike the reflection of an ordinary plane mirror or the like, and has the property of reflecting in the direction of the original light source, regardless of the direction from which the light comes. In the concave surface portion, the umbrella-like shape or the polygonal pyramid shape of the retroreflective member 4, a minute material that realizes recursion is embedded in the inner surface portion.

  As a material for realizing retroreflection, a system using glass beads and a system using prisms are known, and FIG. 2 shows an example of a system using glass beads. As shown in FIG. 2, spherical glass beads 41 are arranged in close contact with the entire base material 42, and by appropriately selecting the refractive index of the optical beads, regardless of the direction in which light enters. , It returns in the same direction as the direction in which the light is incident. Since the diameter of the substrate of the minute glass beads is very small, the deviation between the incident path and the reflection path is small, and the incident light returns in the direction of incidence through substantially the same path.

  Furthermore, the optical system of the imaging means may be a telecentric optical system. By using a telecentric optical system as the optical system of the imaging means, it is possible to perform imaging where observation of the position and size of the imaging target is not related to the focus position.

  Next, the function and detection procedure of the surface defect inspection apparatus of the first embodiment will be described. For convenience of explanation, it is assumed that the inspection object is placed on an inspection table (not shown), and an area sensor camera is used as the imaging means. When a line sensor camera is used for the imaging unit 1, it is necessary that the inspection object is transported at a constant speed by the transport unit or rotated at a constant speed.

  3 and 4 are explanatory diagrams for explaining the path of light emitted from the illumination means. FIG. 3A shows the case where the illumination light hits a flat portion of the inspection object 5, the light L 11 emitted from the illumination means 2 is reflected by the half mirror 3, and the light L 12 whose direction is changed by 90 ° is recursively. The light is reflected on the surface of the inspection object 5 through the window 41 provided in the reflecting member 4. At this time, if the surface of the inspection object is flat, it is regularly reflected to become light L13, which passes through the half mirror 3 and is detected by the imaging means 1.

  FIG. 3B shows a case where the illumination light hits a shallow concave portion of the inspection object 5, and the light L21 emitted from the illumination means 2 is reflected by the half mirror 3 to become the light L22, and the inspection object 5 The light is reflected on the surface of the retroreflective member 4 to become light L23, further reflected on the concave surface of the retroreflective member 4 and returned to the path L24, reflected on the surface of the inspection object 5 to become L25, and passes through the half mirror 3. Then, the imaging means 1 detects.

  FIG. 4A shows a case where the illumination light hits a deep concave portion of the inspection object 5, and the light L31 emitted from the illumination means 2 is reflected by the half mirror 3 to become the light L32, and the inspection object 5 Is reflected on the surface of the light and proceeds in the direction of the light L33. Since the light L33 does not strike the retroreflective member 4, the imaging means 1 cannot detect it.

  FIG. 4B shows a case where illumination light hits a deep crack portion of the inspection object 5, and the light L 42 incident on the crack portion in the inspection object 5 is reflected in the direction of the imaging means 1. There is no.

  In the case shown in FIG. 3, since the imaging means 1 detects reflected light or retroreflected light from the inspection object, the corresponding portion of the image obtained by the imaging means 1 is a bright image. On the other hand, in the case shown in FIG. 4, since the imaging means 1 cannot detect reflected light or retroreflected light from the inspection object, the image becomes dark. Further, a bright image is obtained in the case of a shallow concave portion as shown in FIG. 3B, whereas a dark image is obtained in the case of a deep concave portion shown in FIG.

  That is, the light that has traveled in the direction that hits the retroreflective member 4 is always detected by the imaging unit 1, and the light that does not hit the retroreflective member 4 cannot be detected by the imaging unit 1 except for light that passes through the window 41. Further, the light reflected by the inspection object 5 hits the retroreflective member 4 in the case of a shallow scratch, but the reflection angle increases as the scratch becomes deeper, and is reflected in a direction away from the retroreflective member 4.

  From the above, it can be seen that the depth of the flaws that can be detected changes depending on the position of the lower end of the retroreflective member 4. Therefore, the position of the lower end portion of the retroreflective member 4 is changed by changing the size of the retroreflective member 4, in other words, changing the size of the retroreflective member 4. The degree can be changed.

  Alternatively, by changing the distance between the retroreflective member 4 and the inspection object 5, it is possible to change the degree of the depth of the scratch obtained by the imaging unit 1.

  The telecentric optical system whose explanatory diagram is shown in FIG. 5 can be used for the imaging means 1. As can be seen from FIG. 5, a diaphragm 62 is disposed between the objective lens 61 and the imaging element side lens 63, and the position thereof is the rear focal point of the objective lens 61 and the front side of the imaging element side lens 63. Placed in focus position. In the optical system configured in this way, the principal ray becomes a ray parallel to the optical axis of the objective lens 61 and further becomes parallel to the optical axis of the imaging element side lens 63. That is, light rays that are substantially parallel to the optical axis of the telecentric optical system are mainly incident on the image sensor 64.

  By using the telecentric optical system, the size of the image to be captured does not change even if the distance to the object to be imaged changes. Therefore, it has a feature that the position or size can be accurately observed even when there is a step on the surface of the inspection object.

  A second embodiment of the present invention is shown in FIG. The imaging means 1 is disposed above the inspection object 5 at a predetermined angle with respect to the inspection object 5. The illumination unit 2 is a diffused light source, and is arranged so that the irradiation direction reflected by the half mirror 3 is substantially coincident with the optical axis of the imaging unit 1.

  The retroreflective member 8 is disposed above the inspection object 4 so that the illumination light of the illumination means 2 is reflected by the light reflected from the surface of the inspection object 4. The retroreflective member 8 used in the second embodiment has a substantially planar shape, and has a property of reflecting in the direction of the original light source, regardless of which direction the light comes from. The external shape of the retroreflective member 8 may be an arbitrary shape such as a circle or a polygon. Moreover, although the arrangement | positioning angle may be arbitrary, it is desirable to set it as the direction where the light reflected by the test object 5 with the illumination light of the illumination means 2 hits efficiently.

  In the case of the first embodiment, since it has a dome shape, there is a high probability that the light reflected by the inspection object 5 will return to the retroreflective member in any direction. On the other hand, in the second embodiment, since there is light that is reflected in the direction without the retroreflective member 8 on the surface of the inspection object 5, the probability of recursion is low, but the illumination light is effectively retroreflected. By appropriately selecting the direction of the illumination means 2 and the position and posture of the retroreflective member so as to enter the member 8, the same effect as in the first embodiment is produced.

  Next, an example in which an edge portion of a silicon wafer for manufacturing a semiconductor is inspected using the surface inspection apparatus of the present invention will be described. As shown in FIG. 8, the edge portion of the silicon wafer 7 includes an upper tapered surface 91, a lower tapered surface 93, and a side surface 92 which are two tapered portions. The intersection between each surface and the other surface is smoothly connected by the R surface.

  FIG. 7 shows a case where the surface inspection apparatus of the present invention is used to inspect the upper taper surface of the edge portion of the silicon wafer 9 for manufacturing semiconductors as an inspection object. With respect to 92, the entire edge can be inspected by arranging the inspection devices with the same configuration.

  The silicon wafer 9 is mounted on a rotating mounting means (not shown) and rotates at a constant speed. In addition, it is appropriate to use a line sensor camera as the imaging means used for imaging when the inspection object is moving at a constant speed.

  The upper surface imaging means 11 scans the upper tapered surface 71 of the silicon wafer 7 in the radial direction, and the silicon wafer 7 rotates at a constant speed, so that a two-dimensional image of the upper tapered surface 71 is obtained.

  Similarly, a two-dimensional image of the side surface 72 and the lower tapered surface 73 of the silicon wafer 7 is also obtained. According to the present embodiment, the images of the upper tapered surface 71, the side surface 72, and the lower tapered surface 73 are taken at the same position on the silicon wafer. Using this image data, the silicon taper edge is observed in the form of a development view in the form of a monitor by combining the image of the upper taper surface, the image of the side surface and the image of the lower taper surface in a control unit (not shown). Can do.

  In the defect inspection method of the present invention, by using the retroreflective member, the same effect as that obtained by illuminating from multiple directions can be obtained. For this reason, shallow unevenness and gentle undulations are not determined as defects because appropriate brightness is obtained.

  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.

The invention's effect

  The surface defect inspection method and the surface defect inspection apparatus of the present invention illuminate the surface of an inspection object with diffused light illuminating means, and substantially reflect the light reflected on the object surface by a retroreflective member provided in the vicinity of the inspection object. Thus, both the direct light reflected directly from the object surface and the retrolight reflected from the object surface via the retroreflective member are both imaged by the imaging means.

  Therefore, since the direct light from the illumination means and the retroreflected light from the retroreflective member reach the surface of the object to be inspected, it is equivalent to illuminating from multiple directions, and shallow irregularities that become shadows when illuminated from one direction The gentle swell is not recognized as a defect according to the surface defect inspection method of the present invention.

  In conventional defect inspection methods using optical means, shadows appear even with shallow irregularities and gentle undulations. As a result, even slight irregularities and gentle undulations that do not interfere with actual use are judged as defects. However, according to the present invention, these problems can be solved for the reasons described above.

  Further, by changing the size of the retroreflective member or making the distance between the inspection object and the retroreflective member variable, it is possible to arbitrarily set the brightness of the image of the defective portion. As a result, since the brightness of the image to be captured can be changed according to the depth of the unevenness, the inspection result can be appropriately managed according to the property of the inspection object.

  In addition, the same effect can be obtained by two illuminations without using a retroreflective member. However, when illumination is performed with two illumination means, the appearance of the dark part changes depending on the illumination direction. Although adjustment is necessary, according to the surface inspection method of the present invention using a retroreflective member, such adjustment of the illumination means is unnecessary.

  In the surface defect inspection apparatus using one type of illumination means, there is a high possibility that an erroneous determination will be made depending on the shape of the scratch or the deposit, no matter how well the threshold is selected. By providing a reflective member, the same effect as when using illumination from multiple directions is exhibited, and shallow irregularities and gentle undulations that cannot be said to be defects become images with high brightness, and thresholds for determining defects Is easy to set. From this, in the actual production line, fatal defects can be detected reliably, and minor scratches and irregularities can be judged as acceptable, and high productivity can be secured, contributing to the industry. Is a big thing.

  In addition, the surface inspection method of the present invention changes the size of the retroreflective member or changes the distance between the object to be inspected and the retroreflective member so that the image is picked up according to the depth of the unevenness. It has the feature that the brightness of the can be freely changed. Therefore, by changing the size of the retroreflective member or adjusting the distance between the inspection object and the retroreflective member, the pass / fail judgment level can be easily set, and the reliability of the inspection result is increased. . Since the brightness of the image to be captured can be changed according to the depth of the unevenness, the inspection result can be appropriately managed according to the property of the inspection object.

It is explanatory drawing explaining the surface defect inspection method of a 1st Example. It is explanatory drawing explaining the principle of a retroreflection member. It is explanatory drawing which shows the specific example of the defect inspection of this invention. It is explanatory drawing which shows another specific example of the defect inspection of this invention. It is explanatory drawing explaining a telecentric optical system. It is explanatory drawing which shows the surface defect inspection method of a 2nd Example. It is a front view which shows the Example which test | inspects a silicon wafer edge. It is detailed explanatory drawing of the edge part of a silicon wafer.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Image pickup means 2 Illumination means 3 Half mirror 4 Retroreflective member 5 Inspection object 6 Telecentric optical system 7 Silicon wafer 8 Retroreflective member 41 Glass bead 42 Base material 61 Image side lens 62 Diaphragm 63 Image sensor side lens 64 Image sensor 71 Upper side Tapered surface 72 Side surface 73 Lower tapered surface

Claims (15)

  A surface inspection method for detecting a micro defect by illuminating the surface of an inspection object with a diffused light illuminating means and capturing an image of the surface of the inspection object, and the object by a recursive mirror provided in the vicinity of the inspection object The light reflected on the surface is recursed in substantially the same optical path, and both the direct light directly reflected from the surface of the object and the recursive light reflected on the surface of the object via the recursive mirror are imaged by the imaging means. Surface inspection method.   The surface inspection method according to claim 1, wherein the recursive surface of the recursive mirror is a dome-shaped concave surface portion.   The surface inspection method according to claim 1, wherein the imaging unit is a linear sensor camera.   The surface inspection method according to claim 1, wherein the imaging unit uses a telecentric optical system.   3. The surface inspection method according to claim 1, wherein the size of the recursive surface of the recursive mirror is variably configured.   The surface inspection method according to claim 1 or 2, wherein the distance between the surface of the inspection object and the recursive mirror is configured to be variable.   A surface inspection apparatus for detecting minute defects on the surface of an inspection object, an imaging means for capturing an image of the surface of the inspection object, a diffused light illuminating means for illuminating the surface of the inspection object, and an inspection object A surface inspection apparatus comprising a recursive mirror provided above.   The surface inspection apparatus according to claim 8, wherein a recursive surface of the recursive mirror is provided in a dome-shaped concave surface portion.   A window is provided in a part of the dome shape of the recursive mirror, and the illumination means illuminates the inspection object through the window, and the reflected light from the inspection object passing through the window is imaged by the imaging means. The surface inspection apparatus according to claim 7 or 8.   A half mirror is provided on an upper part of the window, refracted by the illuminating means of the illuminating means to illuminate the inspection object, and the light transmitted through the half mirror is imaged by the imaging means. 9. The surface inspection apparatus according to 9.   9. The surface inspection apparatus according to claim 7, wherein the image pickup means is a linear sensor camera.   The surface inspection apparatus according to claim 7, wherein the imaging unit uses a telecentric optical system.   The surface inspection apparatus according to claim 7, further comprising a recursive surface changing unit that changes an area of a recursive surface of the recursive mirror.   The surface inspection apparatus according to claim 7, further comprising a recursive mirror position varying unit that changes a distance between the surface of the inspection object and the recursive mirror.   15. The surface inspection apparatus according to claim 7, wherein a plurality of imaging means and a plurality of recursive mirrors corresponding to each of the imaging means are provided.

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