JP2011203081A - Defect inspection device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To detect a defect in the front surface of a specimen (glass plate) more accurately than that inside or in the rear surface of the specimen.SOLUTION: Diffraction light 19 is generated by inserting a shield member 20 into a part of an inspection light 17 projected from a projector. Inspection light 17 passing through the outside of the shield member 20 illuminates an inspection range 14 on the front surface 11a of the glass plate 11, and the diffraction light 19 illuminates an inspection range 22 of the rear surface 11c of the glass plate 11 and an internal inspection range 23. The light intensity of the diffraction light 19 is weaker than that of the inspection light 17, and becomes weaker as it becomes close to the rear surface 11c. When defects exist in the inspection ranges 14, 22 and 23, a CCD line sensor camera 15 receives the scattered light from each defect. The scattered light from the defect in the inspection range 14 is strong, so that even a fine defect can be detected. The scattered light from the defect in the inspection range 23 is weak, so that only a large defect can be detected. The scattered light from the defect in the inspection range 22 is weaker than the scattered light from the defect in the inspection range 23, so that only a further large defect can be detected.

Description

  The present invention relates to a defect inspection apparatus that detects defects on the surface of a plate-like subject that transmits light.

  Transparent glass substrates used for flat panel displays such as liquid crystal display devices and plasma display devices, and glass plates for photofabrication (photomasks for making printed circuit boards, etc.) have problems in forming thin films and transparent electrodes. Therefore, it is necessary to inspect for defects such as foreign matter and foreign matter traces adhering to the surface in addition to the tear bubbles on the front and back surfaces and the internal bubbles.

  As a defect inspection apparatus for inspecting defects of such glass plates, those described in Patent Documents 1 and 2 are known. In the apparatus described in Patent Document 1, a light beam is projected onto a glass plate that is a subject, and a CCD image sensor (area (two-dimensional) sensor) receives scattered light from defects existing on the front or back surface of the glass plate. To do. Then, an image of the defect is imaged on a plurality of elements of the CCD image sensor, and based on the image output, the signal intensity and area of each defect are obtained. Depending on whether the signal intensity and area are equal to or greater than each threshold, the transparent electrode It is determined whether the defect is a harmless defect (good defect) that does not affect the formation or the like, or a harmful defect that affects the defect (defective defect).

  In the apparatus described in Patent Document 2, when the surface of the glass plate is irradiated with inspection light, and the detection camera detects the scattered light twice, the scattered light is generated by a defect on the surface, and this scattered light is converted into glass. When it is assumed that the surface of the glass plate has a defect because it propagates through the inside of the plate and is reflected by the back surface, and the detection camera detects only one scattered light, it is scattered on the surface of the glass plate. Without considering that the inspection light incident on the inside is scattered by the defects on the back surface, it is determined that there is a defect on the back surface.

Japanese Patent Laid-Open No. 10-267858 JP 2006-71284 A

  In the apparatus described in Patent Document 1, since the signal intensity and area of the defect are obtained using the CCD image sensor, the time required for detecting the defect becomes long, and the CCD image sensor is used, which increases the manufacturing cost. Further, in the apparatus described in Patent Document 2, there is no problem when the defect on the surface of the glass plate is large, but when the defect is small, the scattered light at the surface defect is attenuated while propagating inside the glass plate. The reflected light on the back side becomes very weak. For this reason, although it is a surface defect, the second scattered light may not be detected and may be erroneously determined as a back surface defect.

  Further, in the case of a glass plate used for a liquid crystal display device or the like, since the surface of the glass plate is more important than the back surface, there is a strong demand for reliably detecting defects on the surface. In any of these apparatuses, since defects on the back surface are detected at the same level as defects on the front surface, there is a problem in that the quality becomes excessive and the yield decreases.

  The present invention has been made in view of the above problems, and can detect fine defects on the surface of a light-transmitting plate-like object (such as a glass plate or a resin plate) and An object of the present invention is to provide a low-cost defect inspection apparatus with a relatively simple configuration that detects only large defects on the back surface.

  The defect inspection apparatus according to the present invention projects inspection light from an oblique direction onto the surface of a plate-like subject having optical transparency, and the elongated second set on the surface of the subject by the inspection light. A light projecting means for illuminating one examination range; and diffracted light is generated by inserting into the examination light and blocking a part of the examination light; and by the diffracted light, a subject facing the first examination range is generated. A shielding member that illuminates a second examination range on the back side and a third examination range that is inside the subject between the first examination range and the second examination range, and the examination light is in the first examination range. Scattered light generated by scattering at a certain defect, and scattered light generated by scattering of the diffracted light at a defect in the second and third inspection ranges, respectively, with respect to the surface of the subject than the light projecting means. And a light receiving means for receiving light from a direction close to vertical. That.

  The subject is preferably transported in a direction perpendicular to the longitudinal direction of the first examination range. The light receiving means is preferably a line sensor camera arranged such that the longitudinal direction of the light receiving field is parallel to the longitudinal direction of the first inspection range.

  It is preferable that the shielding member is movably installed along the irradiation direction of the inspection light, and the distance from the subject can be changed.

  The shielding member has a substantially rectangular shape whose longitudinal direction is long in parallel with the longitudinal direction of the first inspection range, and one end portion in the longitudinal direction inserted into the inspection light is pointed in the thickness direction of the distal end. It is preferable that the shape is different.

  It is preferable that the end portion of the shielding member inserted into the inspection light is inserted into the inspection light so as to be close to the center line of the inspection light.

  According to the present invention, the diffracted light is generated by inserting the shielding member into a part of the inspection light projected from the light projecting unit toward the plate-shaped subject having optical transparency, and the outside of the shielding member. The elongated first examination range set on the surface of the subject is illuminated with the examination light that has passed through, the second examination range on the back side of the subject and the third examination range inside are illuminated with the diffracted light, and the first When the defect exists in the third inspection range, since the light receiving means receives scattered light from the defect, the surface of the subject has a minute defect while being relatively simple and low cost. In addition to detection, only large defects can be detected on the inside and back of the subject.

  Since the subject is transported in the direction orthogonal to the longitudinal direction of the first examination range, the examination can be performed over the entire subject as the subject is transported. In addition, since a line sensor camera is used as the light receiving means, it can contribute to cost reduction.

  Since the distance between the shielding member and the subject can be changed, the light intensity of the diffracted light applied to the second and third inspection ranges can be adjusted.

  Since the end of the shielding member has a sharp shape in the thickness direction of the tip, diffracted light can be generated efficiently.

  Since the end of the shielding member is arranged so as to be close to the center line of the inspection light, the center line of the inspection light having the strongest light intensity is not shielded and illuminates the first inspection range, and gradually increases as the distance from the center line increases. It is possible to generate diffracted light having a weak light intensity. Since this diffracted light irradiates light whose light intensity gradually decreases from the second inspection range to the third inspection range, small defects are not detected in the second and third inspection ranges, and only large defects are detected. Can be detected.

It is an external appearance perspective view which shows roughly the main structures of the defect inspection apparatus which concerns on this invention. It is explanatory drawing which shows a mode that diffracted light is produced | generated by a shielding member, and shows each test | inspection range of the surface of a glass plate, a back surface, and an inside. It is explanatory drawing about the diffraction fringe (light intensity distribution) of a diffracted light. It is explanatory drawing about the light intensity distribution of the test | inspection light and diffracted light with which a glass plate is irradiated. It is explanatory drawing which shows a mode that the defect which exists in the test | inspection range of the surface of a glass plate is detected. It is explanatory drawing which shows a mode that the defect which exists in the test | inspection range inside a glass plate is detected. It is explanatory drawing which shows a mode that the defect which exists in the test | inspection range of the back surface of a glass plate is detected.

  In FIG. 1 which shows the external appearance of the defect inspection apparatus 10 of the present invention, the defect inspection apparatus 10 is a plate-like material having a light transmission property while having a relatively simple configuration such as a projector, a shielding member, and a CCD line sensor camera at a low cost. A minute defect is detected on the front surface 11a of the transparent glass plate 11 as an object, and only a large defect is detected on the inside 11b and the back surface 11c of the glass plate 11 without detecting a minute defect. This prevents excessive quality detecting defects in the interior 11b and the back surface 11c at the same level as the defects in the front surface 11a.

  The glass plate 11 has a certain thickness of 1 mm or more, for example. The defect of the glass plate 11 refers to a foreign matter or a foreign matter trace attached to the front or back surface, in addition to a tear bubble or internal bubble on the front or back surface of the glass plate 11.

  The glass plate 11 is conveyed at a constant speed in a certain direction indicated by an arrow 12 with the surface 11a facing upward by a conveying means such as a belt conveyor. A CCD line sensor camera 15 (light receiving means) having a long light receiving field in a direction orthogonal to the conveying direction of the glass plate 11 is provided above the conveying line of the glass plate 11.

  The CCD line sensor camera 15 exists in a line-shaped inspection range 14 (first inspection range) that is long in a direction perpendicular to the conveying direction of the glass plate 11 from a direction perpendicular to the glass surface with respect to the surface 11a. Detect defects. The inspection range 14 represents an inspection range on the surface 11 a by the CCD line sensor camera 15. The CCD line sensor camera 15 is focused on the inspection range 14 on the surface 11a, and receives scattered light from defects present in the inspection range 14 most efficiently. The scattered light from the defect is generated when the inspection light is irregularly reflected by the defect when the inspection light described later is irradiated onto the defect.

  The CCD line sensor camera 15 is connected to a personal computer (not shown). The personal computer determines the presence or absence of a defect based on the strength of the output signal from the CCD line sensor camera 15.

  A light projector 18 (light projecting means) is provided which is elongated in a direction orthogonal to the conveyance direction of the glass plate 11 and projects the inspection light 17 toward the illumination range 16 (hatched portion) including the inspection range 14. Yes. The projector 18 includes, for example, a large number of LEDs (not shown) arranged in a line and a cylindrical lens (not shown) arranged in front of the LEDs, and the width is slightly smaller than the width of the glass plate 11. Widely thin and almost parallel inspection light 17 is emitted toward the illumination range 16. The illumination range 16 includes not only the inspection light 17 but also an illumination range by diffracted light described later.

  An end 20a having a pointed shape is inserted in the middle of the inspection light 17 radiated from the projector 18, and a shielding member 20 that shields a part of the inspection light 17 and generates the diffracted light 19 is provided. Yes. As will be described later in detail, the shielding member 20 is provided so as to be movable along the center line 17a in the width direction of the inspection light 17, and the distance from the glass plate 11 can be changed.

  As shown in FIG. 2, the inspection light 17 forms an angle θ (for example, θ = 45 °) with respect to the surface 11 a of the glass plate 11, and the center line 17 a having the strongest light intensity in the thickness direction of the inspection light 17. Coincides with the center line 14 a of the inspection range 14, and the inspection range 14 is configured to be illuminated by a portion having the highest light intensity of the inspection light 17.

  The end 20a of the shielding member 20 is inserted into the inspection light 17 at a position close to the center line 17a of the inspection light 17, for example, a distance of 2 mm to the center line 17a. The inspection light 17 that has passed through the outside of the end portion 20a of the shielding member 20 reaches the surface 11a of the glass plate 11 with the strongest light intensity, and illuminates an elongated region in the width direction of the glass plate 11 including the inspection range 14. .

  As shown by hatching, the diffracted light 19 generated by the end portion 20a of the shielding member 20 has an inspection range 22 (second inspection range) on the back surface 11c facing the inspection range 14 on the front surface 11a, an inspection range 14, and an inspection range. The inspection range 23 inside the glass plate 11 sandwiched between the range 22 is illuminated.

  The light intensity of the diffracted light 19 gradually decreases with distance from the center line 17a, and the light that illuminates the inspection range 22 on the back surface 11c is weaker than the inspection range 23 on the inside 11b. This point will be described with reference to FIGS.

  As shown in FIG. 3A, when light is handled as a wave, if there is an obstacle (shielding member 25) against the wave propagating in the medium, the background of the obstacle, such as the background of the obstacle, geometrically appears at first glance. Goes around in areas that cannot be reached. According to Huygens' principle, the wavefront of the next moment of the propagating wave is considered to be a spherical secondary wave from each point of the wavefront. The envelope surface of this secondary wave forms a new wavefront at the next moment. Waves wrap around by the shielding member 25. At that time, diffraction fringes 26 as shown in FIG. The diffraction fringes 26 correspond to the light intensity distribution of the diffracted light by the shielding member 25. The width X0 from the peak of the diffraction fringe 26 to the end of the shielding member 25 is expressed by the following formula 1.

[Equation 1]
X0 = √ (λz / π)

For example, if z (distance from the end of the shielding member to the surface of the glass plate) = 50 mm and the average wavelength λ = 600 nm, the value of X0 is as follows.
X0 ≒ 0.1mm

  The width at which the light intensity gradually attenuates from the peak of the diffraction fringe 26 and the light intensity becomes almost zero is about 0.2 mm when the width α is about twice as large as X0. However, this is a theoretical value assuming that the shape of the end portion of the shielding member 25 is an ideal knife edge shape, and the sharpness of the end portion of the shielding member 25 is actually poor, and this end portion Since scattered light is also generated, it is assumed to be about 10 mm of the theoretical value and about 2 mm. Therefore, when the distance z between the end of the shielding member 20 according to the present embodiment and the glass plate 11 is 50 mm, the width is about 2.8 mm on the surface 11a of the glass plate 11 (the incident angle of the inspection light is 45). √2 times because it is °).

  As shown in FIG. 4, the diffracted light enters the inside of the glass plate 11 and crosses the light receiving optical axis 27 of the CCD line sensor camera 15. As indicated by phantom lines in the figure, the light intensity distribution 28 of the diffracted light has a shape in which the light intensity gradually decreases, so that the light intensity is strongest on the surface 11 a of the glass plate 11 on the light receiving optical axis 27. The light intensity decreases as the back surface 11c is approached. As a result, the closer the position where the defect (foreign matter or the like) in the inside 11b exists to the back surface 11c, the weaker the intensity of the scattered light from the defect caused by the diffracted light, and the weaker the defect detection power by the CCD line sensor camera 15 becomes. The detection power of defects existing on the back surface 11c is the weakest. Further, the end of the diffracted light is arranged in the vicinity where the light receiving optical axis 27 intersects the back surface 11c so that the detection power of the defect existing on the back surface 11c becomes the weakest.

  The shielding member 20 is configured to be movable along the center line 17a of the inspection light 17 like the shielding member 24 indicated by a broken line, and the distance z with the surface 11a of the glass plate 11 is changed within a predetermined range. can do. By changing the distance z, the light intensity with which the diffracted light 19 illuminates the inspection ranges 22 and 23 can be adjusted. The smaller the distance z, the light intensity of the diffracted light 19 irradiated on the inspection ranges 22 and 23. Becomes weaker.

  The moving mechanism of the shielding member 20 may have any configuration. For example, the shielding member 20 is held by an elongated screw installed in parallel to the center line 17a, and the shielding member 20 is centered by rotating the screw. You may make it move in parallel with the line 17a. The rotation of the screw may be manual or motor driven.

  The operation of the defect inspection apparatus 10 configured as described above will be described. When there is no defect in any of the inspection ranges 14, 22 and 23, as shown in FIG. 2, the inspection light 17 and the diffracted light 19 are specularly reflected by the front surface 11a and the back surface 11c of the glass plate 11, and the CCD line sensor camera. 15 is not incident. Therefore, no detection signal is output from the CCD line sensor camera 15.

  As shown in FIG. 5, if there is a defect 30 such as a broken bubble, a foreign object, a dirt, a scratch or the like in the inspection range 14 of the surface 11 a of the glass plate 11, the inspection light 17 having a high light intensity hits the defect 30. Since the scattered light is incident on the CCD line sensor camera 15, a high output detection signal is output from the CCD line sensor camera 15. Therefore, when the defect 30 exists in the inspection range 14, even if the defect 30 is fine, it is detected.

  As shown in FIG. 6, when there is a defect 31 such as a bubble or a foreign substance in the inspection range 23 of the inside 11 b, the diffracted light 19 whose light intensity is much weaker than the inspection light 17 strikes the defect 31. The light is quite weak. Therefore, the defect 31 is not detected by the CCD line sensor camera 15 unless it is of a considerably large size, and the defect in the inspection range 23 is not excessively detected.

  As shown in FIG. 7, when the inspection range 22 on the back surface 11c has a defect 32 such as a broken bubble, a foreign object, a dirt, or a scratch, the light intensity is weaker than the diffracted light 19 applied to the inspection range 23 in the inside 11b. Since the diffracted light 19 strikes the defect 32, the scattered light at the defect 32 is much weaker than the scattered light at the defect 31. Therefore, the defect 32 is not detected by the CCD line sensor camera 15 unless it is of a considerably large size, and the defect in the inspection range 22 is not excessively detected.

  The defect detection sensitivity in the inspection ranges 22 and 23 is adjusted within a predetermined range by moving the shielding member 20 along the center line 17a of the inspection light 17 and changing the distance z from the surface 11a of the glass plate 11. Is possible.

  When the shielding member 20 is not provided [Condition 1], when the distance z is 50 mm [Condition 2], and when the distance z is 20 mm [Condition 3], the results of experiments are shown in Tables 1 to 3 below. Shown in The end 20a inserted into the inspection light 17 of the shielding member 20 has a shape in which the angle in the thickness direction of the tip is sharpened to 80 degrees or less. The distance from the projector 18 to the center of the inspection range 14 was set to 100 mm, and the light shielding amount by which the inspection light 17 emitted from the projector 18 was shielded by the shielding member 20 was 30% to 50%. Further, the resolution of the CCD line sensor camera 15 was set to about 20 μm / pixel at the center of the inspection range 14. Moreover, as the glass plate 11, the thing of thickness 5mm and refractive index 1.5 was used.

The detection ability was evaluated for each of the front surface, the inside (approximately the center of the thickness of the glass plate), and the back surface as the presence site of the defect (foreign material). The evaluation result index is as follows.
○: The scattered light reception signal is sufficient and the defect is detected stably. Not detect

Result of [Condition 1] (no shielding member)

Result by [Condition 2] (distance z = 50 mm)

Result according to [Condition 3] (distance z = 20 mm)

  By adjusting the distance z in this way, the detection accuracy of the defects 31 and 27 existing on the inside 11b and the back surface 11c can be changed without affecting the detection accuracy of the defect 30 existing on the front surface 11a. Thereby, it is possible to prevent excessive detection of defects existing in the inside and the back surface or to detect as much as possible according to the use of the subject to be inspected. Of course, the present invention is not limited to the numerical values in this experiment.

  In the embodiment described above, the shielding member formed with a sharp end is used to generate diffracted light. However, the present invention is not limited to this, and for example, a shielding member having a slit is used. You can also

  In the above-described embodiment, a case where a transparent glass plate is inspected as a subject has been described. However, the present invention is not limited to this, and is completely transparent, for example, a resin plate having a certain degree of light transmittance. Non-plate-like subjects can also be examined.

DESCRIPTION OF SYMBOLS 10 Defect inspection apparatus 11 Glass plate 14,22,23 Inspection range 15 CCD line sensor camera 16 Illumination range 17 Inspection light 18 Projector 19 Diffracted light 20,25 Shielding member 28 Light intensity distribution 27 Light-receiving optical axis 30-32 Defect

Claims (6)

The projection light is projected from an oblique direction to the surface of the plate-like subject having light transmittance, and the first elongated examination range set on the surface of the subject is illuminated by the examination light. Means,
A diffracted light is generated by inserting into the inspection light and blocking a part of the inspection light, and by this diffracted light, a second inspection range on the back side of the subject facing the first inspection range, and the first A shielding member that illuminates a third examination range that is inside the subject between the first examination range and the second examination range;
Scattered light generated when the inspection light is scattered by a defect in the first inspection range, and scattered light generated when the diffracted light is scattered by a defect in the second and third inspection ranges, respectively. And a light receiving means for receiving light from a direction closer to the vertical than the light projecting means.   The defect inspection apparatus according to claim 1, wherein the object is transported in a direction orthogonal to a longitudinal direction of the first inspection range.   3. The defect inspection apparatus according to claim 1, wherein the light receiving means is a line sensor camera arranged so that the longitudinal direction of the light receiving field is parallel to the longitudinal direction of the first inspection range.   The defect inspection apparatus according to claim 1, wherein the shielding member is movably installed along an irradiation direction of the inspection light, and a distance from the subject can be changed. .   The shielding member has a substantially rectangular shape whose longitudinal direction is long in parallel with the longitudinal direction of the first inspection range, and one end portion in the longitudinal direction inserted into the inspection light is pointed in the thickness direction of the distal end. The defect inspection apparatus according to claim 1, wherein the defect inspection apparatus has a curved shape.   6. The end of the shielding member inserted into the inspection light is inserted into the inspection light so as to be close to a center line of the inspection light. Defect inspection equipment.

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