Inspection device and inspection method

Abstract

A half mirror 52 is disposed between an inspection stage 11 (workpiece holding part) for holding a workpiece W and a camera 32 (imaging part), and the camera 32 captures an image of pattern light Lp (laser light) transmitted through the half mirror 52. In particular, the half mirror 52 has an antireflection film 55 for preventing reflection of the pattern light Lp on an emission surface 522 for emitting the pattern light Lp passing through the half mirror 52 from the workpiece W toward the camera 32. Consequently, reduction of the pattern light Lp (light Lpi an image of which is to be captured) transmitted through the half mirror 52 and reaching the camera 32 can be suppressed, and occurrence of stray light Ls on the emission surface 522 of the half mirror 52 can be suppressed.

Description

Technical Field

[0001] This invention relates to a technique for performing an inspection by irradiating a workpiece to be inspected with a laser beam while imaging the workpiece.

Background Art

[0002] For the inspection of a workpiece, an inspection apparatus can be configured to acquire each of a two-dimensional image and a three-dimensional image of the workpiece. In such an inspection apparatus, in order to make compatible the irradiation / imaging of illumination to the workpiece for imaging the two-dimensional image and the irradiation / imaging of a laser beam to the workpiece for imaging the three-dimensional image, for example, a half mirror shown in Patent Document 1 can be used.

Prior Art Documents

[0006] This invention has been made in view of the above problems, and aims to provide a technology that enables suppressing the amount of laser light irradiated onto the workpiece and suppressing the generation of virtual images in the captured image, in a technology for inspecting a workpiece by imaging laser light that has been reflected by the workpiece and passed through a half mirror. [Means for solving the problem]

[0007] The inspection apparatus according to the present invention comprises a workpiece holding unit for holding a workpiece, a laser irradiation unit for irradiating the workpiece with laser light, an imaging unit for imaging the workpiece by receiving the laser light reflected by the workpiece, and a half-mirror disposed between the workpiece holding unit and the imaging unit for transmitting laser light from the workpiece toward the imaging unit. The half-mirror has an anti-reflective coating on its emission surface, which emits the laser light passing through the half-mirror toward the imaging unit, to prevent reflection of the laser light.

[0008] The inspection method according to the present invention comprises the steps of irradiating a workpiece held in a workpiece holding unit with laser light, and imaging the workpiece with an imaging unit by receiving the laser light reflected from the workpiece. A half-mirror is placed between the workpiece holding unit and the imaging unit to transmit laser light from the workpiece toward the imaging unit, and the half-mirror has an anti-reflective coating on the emission surface that emits the laser light passing through the half-mirror toward the imaging unit, which prevents the reflection of the laser light.

[0009] In the present invention (inspection apparatus and inspection method) configured as described above, a half-mirror is placed between a workpiece holding unit that holds the workpiece and an imaging unit, and the imaging unit captures the laser light that has passed through the half-mirror. In particular, the half-mirror has an anti-reflective coating on the emission surface that emits the laser light passing through the half-mirror toward the imaging unit, preventing the reflection of the laser light. This suppresses the reduction of laser light that passes through the half-mirror and reaches the imaging unit, and also suppresses the generation of stray light on the emission surface of the half-mirror. As a result, it is possible to suppress the amount of laser light irradiated onto the workpiece and suppress the generation of virtual images in the captured image.

[0010] Alternatively, the inspection device may be configured such that the half-mirror has an optical filter on the incident surface into which the laser light reflected from the workpiece is incident, the laser light incident on the optical filter passes through the half-mirror and is emitted from the anti-reflective coating, the optical filter reflects light with wavelengths included in a predetermined reflection wavelength band with a predetermined reflectance and transmits it with a predetermined first transmittance, the wavelength of the laser light is outside the reflection wavelength band, and the optical filter transmits the laser light with a second transmittance higher than the first transmittance. In such a configuration, the reflection of the laser light reflected from the workpiece by the half-mirror can be suppressed, and the amount of laser light reaching the imaging unit can be secured. Therefore, the amount of laser light irradiated onto the workpiece can be suppressed.

[0011] Furthermore, the inspection device may be configured such that the half-mirror has a substrate having a first surface and a second surface facing the first surface, with an optical filter provided on the first surface of the substrate and an anti-reflective coating provided on the second surface of the substrate. In such a configuration, the amount of laser light irradiated onto the workpiece can be suppressed, and the generation of virtual images in the captured image can be suppressed.

[0012] Alternatively, the inspection apparatus may be configured such that, of the laser light that passes through the optical filter and reaches the second surface, some of the laser light passes through the anti-reflective coating and heads toward the imaging unit as the target light for imaging, while other parts of the laser light, which are different from some of the laser light, are reflected toward the first surface at the second surface to become primary reflected light. Of the primary reflected light that reaches the first surface, some of the primary reflected light passes through the optical filter with a second transmittance, while other parts of the primary reflected light, which are different from some of the primary reflected light, are reflected toward the second surface at the first surface of the substrate to become secondary reflected light. Of the secondary reflected light that reaches the second surface, some of the secondary reflected light passes through the anti-reflective coating and heads toward the imaging unit as stray light. In this configuration, primary reflected light is generated when the laser light is reflected by the second surface of the substrate, secondary reflected light is generated when the primary reflected light is reflected by the first surface of the substrate, and the secondary reflected light is the cause of stray light. In this case, since an optical filter that transmits a relatively large amount of laser light is provided on the first surface of the substrate, a relatively large amount of primary reflected light passes through the optical filter without being reflected by the first surface. As a result, the generation of secondary reflected light, which is a cause of stray light, is suppressed. Therefore, the generation of virtual images in the captured image can be suppressed.

[0013] Furthermore, the imaging unit may output level data in N steps (where N is an integer of 2 or more) corresponding to the amount of light from the received laser beam, and the inspection device may be configured such that the ratio of the amount of stray light to the amount of light to be imaged is less than 1 / N. With such a configuration, the occurrence of virtual images in the captured image can be reliably suppressed.

[0014] Various specific configurations of optical filters are possible. For example, an optical filter may be a dielectric multilayer film.

[0015] Furthermore, the inspection device may be configured such that the first transmittance is in the range of 40% or more and 60% or less, and the second transmittance is in the range of 90% or more and 100% or less. With such a configuration, it becomes possible to suppress the amount of laser light irradiated onto the workpiece and to suppress the generation of virtual images in the captured image.

[0016] In addition, various specific configurations of the antireflection film are conceivable. For example, the antireflection film may be a single-layer AR coat or a multi-layer AR coat.

Advantages of the Invention

[0017] According to the present invention, in a technique for inspecting a workpiece by imaging laser light reflected by the workpiece and transmitted through a half mirror, it is possible to suppress the amount of laser light irradiated onto the workpiece and to suppress the generation of virtual images in the captured image.

Brief Description of the Drawings

[0018] [Figure 1A] A plan view schematically showing an example of an inspection apparatus according to the present invention. [Figure 1B] A side view schematically showing the configuration of an inspection head included in the inspection apparatus of FIG. 1. [Figure 2] A block diagram showing the electrical configuration of the inspection apparatus of FIG. 1. [Figure 3] A side view schematically showing the configuration of the inspection head. [Figure 4] A diagram schematically showing a line image captured by the inspection head. [Figure 5A] A diagram schematically explaining a first example of a method for acquiring a three-dimensional image. [Figure 5B] A diagram schematically explaining a first example of a method for acquiring a three-dimensional image. [Figure 5C] A diagram schematically explaining a first example of a method for acquiring a three-dimensional image. [Figure 6] A diagram schematically explaining a second example of a method for acquiring a three-dimensional image. [Figure 7] A diagram schematically showing the configuration of a half mirror. [Figure 8] A diagram schematically showing the filter characteristics of a wavelength selection filter.

Embodiments for Carrying Out the Invention

[0019] Figure 1A is a schematic plan view showing an example of an inspection device according to the present invention, Figure 1B is a schematic side view showing the configuration of the inspection head of the inspection device in Figure 1, and Figure 2 is a block diagram showing the electrical configuration of the inspection device in Figure 1. In Figures 1A, 1B, and the following figures, the horizontal direction X, the horizontal direction Y perpendicular to the X direction, and the vertical direction Z are indicated as appropriate. This inspection device 1 measures the two-dimensional and three-dimensional shapes of the workpiece W to be inspected.

[0020] The inspection device 1 includes a horizontally positioned inspection stage 11, the upper surface of which is a workpiece mounting plane 12 for placing the workpiece W. The workpiece mounting plane 12 is a horizontal plane parallel to the X and Y directions.

[0021] The inspection device 1 includes a head drive mechanism 2 positioned above the inspection stage 11. The head drive mechanism 2 has a pair of Y-axis rails 21 spaced apart in the X direction. Each of the pair of Y-axis rails 21 extends parallel to the Y direction, and a workpiece mounting plane 12 is provided between the pair of Y-axis rails 21. The head drive mechanism 2 also has an X-axis rail 22 extending in the X direction, and both ends of the X-axis rail 22 in the X direction are supported by the pair of Y-axis rails 21 so as to be movable in the Y direction. Furthermore, the head drive mechanism 2 has a head holder 23, which is supported by the X-axis rails 22 so as to be movable in the X direction.

[0022] Furthermore, the head drive mechanism 2 has a Y-axis motor 24 that drives the X-axis rail 22 in the Y direction relative to the Y-axis rail 21. That is, one of the pair of Y-axis rails 21 has a built-in ball screw, and the X-axis rail 22 is attached to the nut of this ball screw. The Y-axis motor 24 is coupled to one end of the ball screw built into the Y-axis rail 21, and by rotating this ball screw, it drives the X-axis rail 22 in the Y direction. In addition, the head drive mechanism 2 has an X-axis motor 25 that drives the head holder 23 in the X direction relative to the X-axis rail 22. That is, the X-axis rail 22 has a built-in ball screw, and the head holder 23 is attached to the nut of this ball screw. The X-axis motor 25 is coupled to one end of the ball screw built into the X-axis rail 22, and by rotating this ball screw, it drives the head holder 23 in the X direction.

[0023] The head holder 23 has a Z-axis rail 231 supported by an X-axis rail 22, and a lifting frame 232 supported by the Z-axis rail 231 so as to be movable in the Z direction. Furthermore, the head drive mechanism 2 has a Z-axis motor 26 (Figure 2) that drives the lifting frame 232 in the Z direction relative to the Z-axis rail 231. In other words, the Z-axis rail 231 has a ball screw built in, and the lifting frame 232 is attached to the nut of this ball screw. The Z-axis motor 26 is coupled to one end of the ball screw built into the Z-axis rail 231, and drives the lifting frame 232 in the Z direction by rotating this ball screw.

[0024] Furthermore, the inspection device 1 includes an inspection head 3 held by a head holder 23. The inspection head 3 is held on a lifting frame 232 so as to be rotatable in a rotational direction R about a rotation axis Az parallel to the Z direction. In other words, the lifting frame 232 has a rotation mechanism 233 that rotates the inspection head 3 in the rotational direction R, and an R-axis motor 27 is attached to the lifting frame 232. The rotation mechanism 233 rotates the inspection head 3 in the rotational direction R by the torque output by the R-axis motor 27.

[0025] Note that the specific configuration for driving the inspection head 3 in the X, Y, Z, and rotational R directions is not limited to this example. For example, the Y-axis motor 24, X-axis motor 25, Z-axis motor 26, or R-axis motor 27 may be configured using linear motors.

[0026] As shown in Figure 2, the inspection device 1 includes a controller 9 that controls the head drive mechanism 2 and the inspection head 3. The controller 9 has an arithmetic processing unit 91, a Y position detection signal receiving unit 94, an X position detection signal receiving unit 95, a Z position detection signal receiving unit 96, and an R position detection signal receiving unit 97. The arithmetic processing unit 91 is a processor such as a CPU (Central Processing Unit) and is responsible for the control of the inspection device 1.

[0027] The Y-position detection signal receiving unit 94 acquires a Y-axis position detection signal Sy, which indicates the position of the inspection head 3 in the Y direction, from the encoder of the Y-axis motor 24 and transmits it to the arithmetic processing unit 91. The arithmetic processing unit 91 transmits a Y-axis motion command Cy, which indicates the amount of drive of the inspection head 3 in the Y direction, to the Y-position detection signal receiving unit 94, and the Y-position detection signal receiving unit 94 transmits the Y-axis motion command Cy to the Y-axis motor 24. The Y-axis motor 24 then drives the inspection head 3 in the Y direction by the amount of drive indicated by the Y-axis motion command Cy. At this time, the arithmetic processing unit 91 positions the inspection head 3 at the target position in the Y direction by feedback control of the Y-axis motion command Cy based on the Y-axis position detection signal Sy.

[0028] The X-position detection signal receiving unit 95 acquires an X-axis position detection signal Sx, which indicates the position of the inspection head 3 in the X direction, from the encoder of the X-axis motor 25 and transmits it to the arithmetic processing unit 91. The arithmetic processing unit 91 transmits an X-axis motion command Cx, which indicates the amount of drive of the inspection head 3 in the X direction, to the X-position detection signal receiving unit 95, and the X-position detection signal receiving unit 95 transmits the X-axis motion command Cx to the X-axis motor 25. The X-axis motor 25 then drives the inspection head 3 in the X direction by the amount of drive indicated by the X-axis motion command Cx. At this time, the arithmetic processing unit 91 positions the inspection head 3 at the target position in the X direction by feedback control of the X-axis motion command Cx based on the X-axis position detection signal Sx.

[0029] The Z-position detection signal receiving unit 96 acquires a Z-axis position detection signal Sz, which indicates the position of the inspection head 3 in the Z direction, from the encoder of the Z-axis motor 26 and transmits it to the arithmetic processing unit 91. The arithmetic processing unit 91 transmits a Z-axis motion command Cz, which indicates the amount of drive of the inspection head 3 in the Z direction, to the Z-position detection signal receiving unit 96, and the Z-position detection signal receiving unit 96 transmits the Z-axis motion command Cz to the Z-axis motor 26. The Z-axis motor 26 then drives the inspection head 3 in the Z direction by the amount of drive indicated by the Z-axis motion command Cz. At this time, the arithmetic processing unit 91 positions the inspection head 3 at the target position in the Z direction by feedback control of the Z-axis motion command Cz based on the Z-axis position detection signal Sz.

[0030] The R position detection signal receiving unit 97 acquires an R-axis position detection signal Sr, which indicates the position of the inspection head 3 in the R direction, from the encoder of the R-axis motor 27 and transmits it to the arithmetic processing unit 91. The arithmetic processing unit 91 transmits an R-axis motion command Cr, which indicates the amount of drive of the inspection head 3 in the R direction, to the R position detection signal receiving unit 97, and the R position detection signal receiving unit 97 transmits the R-axis motion command Cr to the R-axis motor 27. The R-axis motor 27 then drives the inspection head 3 in the R direction by the amount of drive indicated by the R-axis motion command Cr. At this time, the arithmetic processing unit 91 positions the inspection head 3 at the target position in the R direction by feedback control of the R-axis motion command Cr based on the R-axis position detection signal Sr.

[0031] Furthermore, the arithmetic processing unit 91 transmits an imaging command Ci to the inspection head 3, indicating the execution of imaging. Upon receiving the imaging command Ci, the inspection head 3 images the workpiece W and transmits the image data Di of the workpiece W to the arithmetic processing unit 91.

[0032] Figure 3 is a schematic side view showing the configuration of the inspection head. In Figure 3, the scan direction N of the inspection head 3 and the N1 and N2 sides of the scan direction N are shown. Here, the scan direction N is horizontal, and the N1 and N2 sides of the scan direction N are opposite to each other. This scan direction N is set relative to the inspection head 3, and when the inspection head 3 rotates in the rotation direction R, the scan direction N also rotates in the rotation direction R along with the inspection head 3.

[0033] The inspection head 3 includes a cylindrical lens barrel 31 extending in the Z direction, a camera 32 attached to the upper end of the lens barrel 31, and an imaging lens 33 attached to the lower end of the lens barrel 31. Furthermore, the inspection head 3 includes an illumination system 34 that emits illumination for measuring two-dimensional shapes, and a pattern illumination system 35 that emits linear pattern light for measuring three-dimensional shapes using the light section method.

[0034] The imaging lens 33 is located above the workpiece mounting plane 12 and faces the workpiece mounting plane 12 from the Z direction, with the optical axis Ao of the imaging lens 33 extending parallel to the Z direction. That is, the optical axis Ao of the imaging lens 33 is perpendicular to the workpiece mounting plane 12, and the imaging lens 33 faces the workpiece mounting plane 12 from the direction in which the normal to the workpiece mounting plane 12 extends (the Z direction). This imaging lens 33 emits light incident from the object side of the imaging lens 33 toward the camera 32 positioned on the image side of the imaging lens 33, and the camera 32 images the light emitted from the imaging lens 33. This imaging lens 33 is a telecentric lens on both the object side and the image side (i.e., both sides), and forms an image of the object surface P1 on the image surface by focusing light from the object surface P1 corresponding to the workpiece mounting plane 12 onto the image surface.

[0035] The camera 32 has a solid-state image sensor 41. The solid-state image sensor 41 has a plurality of pixels arranged in two dimensions, and each of the plurality of pixels detects light and outputs luminance data having a level corresponding to the amount of light. The luminance data is grayscale data that indicates the amount of light corresponding to the luminance data in N steps. In this example, N is 256, and the luminance data indicates the amount of light in 256 steps. The camera 32 outputs image data Di, which consists of luminance data, to the arithmetic processing unit 91. An example of such a solid-state image sensor 41 is a CMOS sensor. This solid-state image sensor 41 is arranged on the image plane of the imaging lens 33 and receives light imaged by the imaging lens 33 to generate image data Di.

[0036] The illumination system 34 has a coaxial illumination unit 51 that generates coaxial illumination light Lc that passes through the imaging lens 33 in the Z direction from the image side to the object side of the imaging lens 33. The coaxial illumination unit 51 has a coaxial illuminator 511 attached to the side of the lens barrel 31 and a half mirror 52 placed inside the lens barrel 31. The coaxial illuminator 511 illuminates the half mirror 52 with R (red), G (green), and B (blue) light (illumination light Le). The coaxial illuminator 511 can illuminate with illumination light Le containing only one of the three colors (R, G, B) selected, or with illumination light Le containing all three colors (R, G, B). The half mirror 52 is positioned between the imaging lens 33 and the camera 32, tilted at 45 degrees with respect to the Z direction (in other words, the optical axis Ao). This half mirror 52 reflects the illumination light Le from the coaxial illuminator 511 toward the imaging lens 33. The imaging lens 33 emits the illumination light Le reflected by the half mirror 52 as coaxial illumination light Lc towards the object side of the imaging lens 33. This coaxial illumination light Lc is emitted from the imaging lens 33 towards the object side parallel to the Z direction. In other words, the coaxial illumination light Lc emitted from the imaging lens 33 towards the object side is collimated light parallel to the Z direction. The coaxial illumination light Lc emitted from the imaging lens 33 travels parallel to the Z direction (i.e., in a straight line) from the imaging lens 33 to the object surface P1 and illuminates the object surface P1.

[0037] As described above, the imaging lens 33 focuses light from the object surface P1 onto the solid-state image sensor 41 positioned on the image plane. In this case, a direct optical path Oo is provided as the optical path to reach the solid-state image sensor 41. That is, of the coaxial illumination light Lc reflected from the object surface P1 (workpiece W), the illumination light Le traveling parallel to the Z direction from the object surface P1 enters the imaging lens 33 and is imaged onto the solid-state image sensor 41 by the imaging lens 33. In other words, a direct optical path Oo is provided, which is the optical path through which the illumination light Le emitted from the object surface P1 in the Z direction reaches the solid-state image sensor 41 via the imaging lens 33. In this case, the illumination light Le emitted from the imaging lens 33 towards the image side passes through the half mirror 52 before reaching the solid-state image sensor 41.

[0038] The pattern irradiation system 35 has a first pattern irradiation unit 81. The first pattern irradiation unit 81 irradiates the object surface P1 with pattern light Lp1 for measuring the three-dimensional shape by the optical section method. The pattern light Lp1 is laser light and has a linear shape extending in an orthogonal direction perpendicular to the scanning direction N and Z. The first pattern irradiation unit 81 is positioned on the N2 side of the optical axis Ao of the imaging lens 33 and emits pattern light Lp1 that is incident on the object surface P1 along a first section direction Q1 that is inclined with respect to the Z direction. In a plan view from the Z direction, the first section direction Q1 is parallel to the scanning direction N, and the pattern light Lp1 is incident on the object surface P1 from the N2 side.

[0039] Of the pattern light Lp1 irradiated onto the object surface P1, the pattern light Lp1 reflected in the Z direction by the object surface P1 (workpiece W) is guided to the solid-state image sensor 41 by the direct optical path Oo. In other words, the pattern light Lp1 travels in the Z direction from the object surface P1 and enters the imaging lens 33. The pattern light Lp1 that enters the imaging lens 33 is imaged onto the solid-state image sensor 41 by the imaging lens 33. At this time, the pattern light Lp1 emitted from the imaging lens 33 toward the image side passes through the half mirror 52 before reaching the solid-state image sensor 41.

[0040] Furthermore, the pattern irradiation system 35 has a second pattern irradiation unit 82. The second pattern irradiation unit 82 irradiates the object surface P1 with pattern light Lp2 for measuring the three-dimensional shape by the optical section method. The pattern light Lp2 is laser light and has a linear shape extending in an orthogonal direction perpendicular to the scanning direction N and Z. The second pattern irradiation unit 82 is positioned on the N1 side of the optical axis Ao of the imaging lens 33 and emits pattern light Lp2 that is incident on the object surface P1 along a second section direction Q2 that is inclined with respect to the Z direction. In a plan view from the Z direction, the second section direction Q2 is parallel to the scanning direction N, and the pattern light Lp2 is incident on the object surface P1 from the N1 side.

[0041] Of the pattern light Lp2 irradiated onto the object surface P1, the pattern light Lp2 reflected in the Z direction by the object surface P1 (workpiece W) is guided to the solid-state image sensor 41 by the direct optical path Oo. In other words, the pattern light Lp2 travels in the Z direction from the object surface P1 and enters the imaging lens 33. The pattern light Lp2 that enters the imaging lens 33 is imaged onto the solid-state image sensor 41 by the imaging lens 33. At this time, the pattern light Lp2 emitted from the imaging lens 33 toward the image side passes through the half mirror 52 before reaching the solid-state image sensor 41.

[0042] Figure 4 schematically shows a line image captured by the inspection head. The processing unit 91 causes the inspection head 3 to capture a linear line image Il that extends parallel to the orthogonal direction M perpendicular to the scan direction N. In other words, light from the object surface P1 or object surface P2 is imaged onto the solid-state image sensor 41 by the imaging lens 33, and the solid-state image sensor 41 captures a line image Il composed of luminance data output from each pixel of the solid-state image sensor 41 corresponding to the line image Il. Here, the line image Il has a width of one or more predetermined pixels in the scan direction N.

[0043] In this configuration, the arithmetic processing unit 91 can acquire a two-dimensional image of the workpiece W placed on the workpiece mounting plane 12 by imaging it from the Z direction. The image acquired by the inspection head 3 in one imaging is a linear line image Il extending in an orthogonal direction M perpendicular to the scan direction N. Therefore, the arithmetic processing unit 91 acquires a two-dimensional image composed of multiple line images Il by having the inspection head 3 capture multiple line images Il while moving the inspection head 3 relative to the workpiece mounting plane 12 (i.e., scanning it).

[0044] When acquiring a two-dimensional image from the Z direction, the arithmetic processing unit 91 adjusts the position (i.e., height) of the inspection head 3 in the Z direction by controlling the Z-axis motor 26 so that the object plane P1 coincides with the workpiece mounting plane 12. Next, the arithmetic processing unit 91 adjusts the scan direction N. For example, when acquiring a two-dimensional image while moving the inspection head 3 in the X direction, the arithmetic processing unit 91 adjusts the position (i.e., rotation angle) of the inspection head 3 in the rotation direction R by controlling the R-axis motor 27 so that the scan direction N coincides with the X direction. Similarly, when acquiring a two-dimensional image while moving the inspection head 3 in the Y direction, the arithmetic processing unit 91 adjusts the position of the inspection head 3 in the rotation direction R by controlling the R-axis motor 27 so that the scan direction N coincides with the Y direction. Note that the direction in which the inspection head 3 is moved for the acquisition of a two-dimensional image does not need to be parallel to the X or Y direction; it may be inclined relative to them.

[0045] Once the rotation angle of the inspection head 3 has been adjusted, the arithmetic processing unit 91 controls the head drive mechanism 2 so that the inspection head 3 moves in the scan direction N, and transmits an imaging command Ci to the inspection head 3 instructing it to capture line images Il to obtain a two-dimensional image viewed from the Z direction. Upon receiving this imaging command Ci, the inspection head 3 turns on the coaxial illumination 511 to irradiate the object surface P1 with coaxial illumination light Lc, and captures line images Il multiple times using the illumination light Le that has passed through the direct optical path Oo and reached the solid-state image sensor 41. In this way, the inspection head 3 acquires multiple line images Il (in other words, image data Di) and transmits them to the arithmetic processing unit 91. The arithmetic processing unit 91 then arranges the multiple line images Il in the scan direction N to obtain a two-dimensional image of the workpiece W viewed from the Z direction.

[0046] Furthermore, the arithmetic processing unit 91 can acquire a three-dimensional image of the workpiece W placed on the workpiece mounting plane 12 by imaging it from the Z direction. The image acquired by the inspection head 3 in a single imaging pass is a linear line image Il extending in an orthogonal direction M perpendicular to the scan direction N. Therefore, the arithmetic processing unit 91 acquires a three-dimensional image composed of multiple line images Il by having the inspection head 3 acquire multiple line images Il while moving the inspection head 3 relative to the workpiece mounting plane 12 (i.e., scanning it).

[0047] Figures 5A, 5B, and 5C schematically illustrate a first example of a method for acquiring a three-dimensional image. The workpiece W shown in Figures 5A, 5B, and 5C has a length Wx in the X direction, a width Wy in the Y direction, and a height Wz in the Z direction. Pattern light Lp1 is irradiated onto the workpiece W from a first cutting direction Q1. In these examples, the scan direction N is set to the X direction.

[0048] Therefore, the position Xh in the X direction of the pattern light Lp1 on the upper surface of the workpiece W and the position Xl in the X direction of the pattern light Lp1 on the workpiece mounting plane 12 differ depending on the height difference between the upper surface of the workpiece W and the workpiece mounting plane 12. In this case, the height Wx of the workpiece W is given by the following equation, using the angle θ between the pattern light Lp1 and the workpiece mounting plane 12. Wx = |Xh - Xl| × tanθ It is given by [formula]. Therefore, the arithmetic processing unit 91 can acquire a three-dimensional image of the workpiece W by capturing multiple line images Il and obtaining information indicating the height of the workpiece W based on the position where the pattern light Lp1 is irradiated in each line image Il.

[0049] Specifically, when acquiring a three-dimensional image, the arithmetic processing unit 91 adjusts the position (i.e., height) of the inspection head 3 in the Z direction by controlling the Z-axis motor 26 so that the object surface P1 coincides with the workpiece mounting plane 12. Next, the arithmetic processing unit 91 adjusts the scan direction N. Once the adjustment of the rotation angle of the inspection head 3 is complete, the arithmetic processing unit 91 controls the head drive mechanism 2 so that the inspection head 3 moves in the scan direction N, and transmits an imaging command Ci to the inspection head 3 instructing it to capture line images Il for acquiring a three-dimensional image. Upon receiving this imaging command Ci, the inspection head 3 lights up the first pattern illumination unit 81 to illuminate the object surface P1 with pattern light Lp1, and captures line images Il multiple times using light that has passed through the direct optical path Oo and reached the solid-state image sensor 41. In this way, the inspection head 3 acquires multiple line images Il (in other words, image data Di) and transmits them to the arithmetic processing unit 91. The arithmetic processing unit 91 then arranges multiple line images Il in the scanning direction N to acquire a three-dimensional image of the workpiece W as viewed from the Z direction.

[0050] Figure 6 schematically illustrates a second example of a method for acquiring a three-dimensional image. Figure 6 shows multiple pixel rows 411 to 415, each composed of multiple pixels arranged in an orthogonal direction M perpendicular to the scan direction N. In particular, Figure 6 shows in time series (times T1 to T5) how, each time the inspection head 3 moves one pixel of the solid-state image sensor 41 in the scan direction N, the pixel rows 411 to 415 sequentially image the point of interest Nt.

[0051] In the examples in Figures 5A, 5B, and 5C, a three-dimensional image of the workpiece W is acquired based on the difference in the irradiation position of the pattern light Lp1 in the scanning direction N (X direction). In contrast, in the example in Figure 6, a three-dimensional image of the workpiece W is acquired based on the difference in the time taken to image the pattern light Lp1.

[0052] At time T1, pixel array 411 captures an image of the target position Nt. At time T1, the pattern light Lp1 is not illuminating the target position Nt, and therefore the image captured by pixel array 411 does not include the pattern light Lp1.

[0053] At time T2, following time T1, pixel array 412 images the position of interest Nt. At time T2, the pattern light Lp1 illuminating the upper surface of the workpiece W is located at position of interest Nt. Therefore, among the multiple pixels belonging to pixel array 412, the pixel corresponding to the upper surface of the workpiece W images the pattern light Lp1, while the pixel corresponding to the workpiece mounting plane 12 does not image the pattern light Lp1.

[0054] At time T3, following time T2, pixel array 413 images the target position Nt. At time T3, the pattern light Lp1 is not illuminating the target position Nt, and therefore the image captured by pixel array 413 does not include the pattern light Lp1.

[0055] At time T4, following time T3, pixel array 414 images the position of interest Nt. At time T4, the pattern light Lp1 irradiated onto the workpiece mounting plane 12 is located at position of interest Nt. Therefore, among the multiple pixels belonging to pixel array 414, the pixel corresponding to the workpiece mounting plane 12 images the pattern light Lp1, while the pixel corresponding to the upper surface of the workpiece W does not image the pattern light Lp1.

[0056] At time T5, following time T4, pixel array 415 images the target position Nt. At time T5, the pattern light Lp1 is not illuminating the target position Nt, and therefore the image captured by pixel array 415 does not include the pattern light Lp1.

[0057] Thus, the times T2 and T4 at which the pattern light Lp1 irradiated onto the same point of interest Nt is captured differ depending on the height at which the pattern light Lp1 is irradiated (the top surface of the workpiece W, the workpiece mounting plane 12). This difference between times T2 and T4 corresponds to the distance in the scan direction N between the pixel 412 that detected the pattern light Lp1 at time T2 and the pixel 414 that detected the pattern light Lp1 at time T4. Therefore, a three-dimensional image of the workpiece W can be obtained in the same manner as the principle explained using Figures 5A to 5C.

[0058] In the example above, the three-dimensional shape is obtained by irradiating the workpiece W with pattern light Lp1. However, the three-dimensional shape can also be obtained in the same way by irradiating the workpiece W with pattern light Lp2.

[0059] Figure 7 is a schematic diagram showing the configuration of a half mirror. As described above, the half mirror 52 is provided to reflect the illumination light Le emitted from the coaxial illumination 511 toward the imaging lens 33. This half mirror 52 is provided in the middle of the direct optical path Oo from which the pattern lights Lp1 and Lp2 emitted from the object surface P1 reach the solid-state image sensor 41. Therefore, the pattern lights Lp1 and Lp2 pass through the half mirror 52 before reaching the solid-state image sensor 41. Note that in Figure 7, the pattern lights Lp1 and Lp2 are not distinguished and are denoted by the symbol Lp.

[0060] As shown in Figure 7, the half mirror 52 has a substrate 53 which is a flat plate made of, for example, glass. The substrate 53 has an incident plane 531 and an exit plane 532, which are arranged parallel to each other and face each other. The substrate 53 has light transmittance that allows both illumination light Le and pattern light Lp to pass through. Furthermore, the half mirror 52 has a wavelength selective filter 54 and an anti-reflective coating 55 which are provided so as to sandwich the substrate 53.

[0061] The wavelength-selective filter 54 is a thin film provided on the incident plane 531 of the substrate 53 so as to cover the incident plane 531, and is, for example, a dielectric multilayer film. Figure 8 is a schematic diagram showing the filter characteristics of the wavelength-selective filter. The wavelength-selective filter 54 transmits light with wavelengths within the reflection wavelength band Λ with a transmittance of Gl1. In other words, the wavelength-selective filter 54 reflects light with wavelengths within the reflection wavelength band Λ with a reflectance of Gl2 (=100%-Gl1). The wavelengths of blue light λb, green light λg, and red light λr that constitute the illumination light Le are all included in the reflection wavelength band Λ. As described above, the half mirror 52 is required to have the function of reflecting the illumination light Le emitted from the coaxial illumination unit 51 to the imaging lens 33, and the function of transmitting the illumination light Le emitted from the imaging lens 33 to the solid-state image sensor 41. Therefore, the wavelength selective filter 54 is configured such that its transmittance Gl1 and reflectance Gl2 are approximately 50%.

[0062] The wavelength λp of the pattern light Lp is outside the reflection wavelength band Λ (less than the reflection wavelength band Λ), and the wavelength selective filter 54 transmits the pattern light Lp with wavelength λp with a transmittance Gh1. With respect to the pattern light Lp, the wavelength selective filter 54 only needs to transmit it toward the solid image sensor 41 and does not need to reflect it. Therefore, the wavelength selective filter 54 is configured such that its transmittance Gh1 is approximately 100%. However, the transmittance Gh1 is not strictly 100%, and the wavelength selective filter 54 reflects the pattern light Lp with a reflectance Gh2 (=100% - Gh1).

[0063] Incidentally, the wavelength λb for blue light is 449-458 nm, the wavelength λg for green light is 519-531 nm, the wavelength λr for red light is 620-632 nm, and the wavelength λp for pattern light Lp is 400-410 nm. However, the range of the wavelength λp for pattern light Lp is not limited to this example.

[0064] The anti-reflective film 55 is a thin film provided on the injection plane 532 of the substrate 53 so as to cover the injection plane 532, and is composed of, for example, an AR coating (Anti Reflection Coating). The anti-reflective film 55 may be composed of a single layer of AR coating or a multilayer AR coating. The pattern light Lp is ejected toward the solid-state image sensor 41 while preventing reflection of the pattern light Lp on the injection plane 532 of the substrate 53. In other words, the anti-reflective film 55 transmits the pattern light Lp that reaches the injection plane 532 with a transmittance of approximately 100% Ga1. However, the transmittance Ga1 is not strictly 100%, and the anti-reflective film 55 reflects the pattern light Lp with a reflectance of Ga2 (=100% - Ga1).

[0065] When such a half-mirror 52 is used, the pattern light Lp emitted from the imaging lens 33 is incident on the wavelength-selective filter 54. In other words, the surface 541 of the wavelength-selective filter 54 corresponds to the incident surface 521 of the half-mirror 52. The pattern light Lp incident on the surface 541 of the wavelength-selective filter 54 passes through the wavelength-selective filter 54 with a transmittance Gh1 and reaches the incident plane 531 of the substrate 53. The pattern light Lp that reaches the incident plane 531 passes through the substrate 53 and reaches the exit plane 532 of the substrate 53. The pattern light Lp that reaches the exit plane 532 passes through the anti-reflective coating 55 and is emitted from the surface 551 of the anti-reflective coating 55 toward the solid-state image sensor 41. In other words, the surface 551 of the anti-reflective coating 55 corresponds to the exit surface 522 of the half-mirror 52.

[0066] Furthermore, of the pattern light Lpt that passes through the wavelength-selective filter 54 and reaches the emission plane 532 of the substrate 53, the pattern light Lpt with transmittance Ga1 passes through the anti-reflective film 55 and is emitted from the anti-reflective film 55 to the solid-state image sensor 41 as the target light Lpi. On the other hand, of the pattern light Lpt that reaches the emission plane 532, the pattern light Lpt with reflectance Ga2 is reflected toward the incident plane 531 at the emission plane 532 and becomes the primary reflected light Lr1. Of the primary reflected light Lr1 that reaches the incident plane 531, the primary reflected light Lr1 with transmittance Gh1 passes through the incident plane 531 and is emitted from the wavelength-selective filter 54 in the opposite direction to the solid-state image sensor 41 as transmitted light Lt. On the other hand, of the primary reflected light Lr1 that reaches the incident plane 531, the primary reflected light Lr1 with reflectance Gh2 is reflected toward the emission plane 532 at the incident plane 531 and becomes the secondary reflected light Lr2. Of the secondary reflected light Lr2 that reaches the emission plane 532, the secondary reflected light Lr2 with transmittance Ga1 passes through the anti-reflective coating 55 and is emitted from the anti-reflective coating 55 to the solid-state image sensor 41 as stray light Ls.

[0067] In this case, the following equation applies between the target light Lpi and the pattern light Lpt: Lpi = Ga1 × Lpt The following equation holds true. Between the primary reflected light Lr1 and the pattern light Lpt, the following equation Lr1 = Ga2 × Lpt The following equation holds true. Between the secondary reflected light Lr2 and the primary reflected light Lr1, the following equation Lr² = Gh² × Lr¹ The following equation holds true. Between stray light Ls and secondary reflected light Lr2, the following equation Ls = Ga1 × Lr2 The following equation holds true. Therefore, the relationship between stray light Ls and pattern light Lpt is given by the following equation. Ls = Ga1 × Gh2 × Ga2 × Lpt The following equation holds true. Therefore, the ratio of stray light Ls to the target light Lpi is given by the following equation Ls / Lpi = Gh² × Ga² This is true.

[0068] For example, if the transmittance Gh1 of the wavelength-selective filter 54 is 95% and the transmittance Ga1 of the anti-reflective coating 55 is 95%, Ls / Lpi = (100% - Gh1) × (100% - Ga1) = 5% × 5% = 1 / 400 This is the result.

[0069] On the other hand, if the transmittance Gh1 of the wavelength-selective filter 54 is 50% and the transmittance Ga1 of the anti-reflective coating 55 is 95%, Ls / Lpi = (100% - Gh1) × (100% - Ga1) = 50% × 5% = 1 / 40 This means that the wavelength-selective filter 54, having the filter characteristics shown in Figure 8, can reduce the effect of stray light Ls on the pattern light Lp1 to one-tenth.

[0070] In the embodiment described above, a half-mirror 52 is positioned between the inspection stage 11 (workpiece holding unit) that holds the workpiece W and the camera 32 (imaging unit), and the camera 32 images the pattern light Lp (laser light) that has passed through the half-mirror 52. In particular, the half-mirror 52 has an anti-reflective coating 55 on the emission surface 522 that emits the pattern light Lp passing through the half-mirror 52 toward the camera 32 from the workpiece W toward the camera 32, which prevents the reflection of the pattern light Lp. This suppresses the reduction of pattern light Lp (image target light Lpi) that passes through the half-mirror 52 and reaches the camera 32, and also suppresses the generation of stray light Ls on the emission surface 522 of the half-mirror 52. As a result, it is possible to suppress the amount of pattern light Lp irradiated onto the workpiece W and suppress the generation of virtual images in the captured image.

[0071] Furthermore, the half mirror 52 has a wavelength-selective filter 54 (optical filter) on its incident surface 521 into which the pattern light Lp reflected from the workpiece W is incident. The pattern light Lp incident on the wavelength-selective filter 54 passes through the half mirror 52 and is emitted from the anti-reflective coating 55. This wavelength-selective filter 54 reflects illumination light Le with wavelengths included in the reflection wavelength band Λ with a reflectance Gl2 and transmits it with a transmittance Gl1. In contrast, the wavelength λp of the pattern light Lp is outside the reflection wavelength band Λ, so the wavelength-selective filter 54 transmits the pattern light Lp with a transmittance Gh1 (second transmittance) that is higher than the transmittance Gl1 (first transmittance). With this configuration, the reflection of the pattern light Lp reflected from the workpiece W by the half mirror 52 is suppressed, and the amount of pattern light Lp reaching the camera 32 can be secured. Therefore, the amount of pattern light Lp irradiating the workpiece W can be suppressed.

[0072] Furthermore, the half-mirror 52 has a substrate 53 having an incident plane 531 (first surface) and an exit plane 532 (second surface) facing the incident plane 531. A wavelength-selective filter 54 is provided on the incident plane 531 of the substrate 53, and an anti-reflective coating 55 is provided on the exit plane 532 of the substrate 53. With this configuration, the amount of pattern light Lp irradiated onto the workpiece W can be suppressed, and the generation of virtual images in the captured image can be suppressed.

[0073] Furthermore, of the pattern light Lpt (laser light) that passes through the wavelength-selective filter 54 and reaches the exit plane 532, some of the pattern light Lpt passes through the anti-reflective coating 55 as imaging target light Lpi and heads toward the camera 32, while other parts of the pattern light Lpt that are different from some of the pattern light Lpt are reflected toward the incident plane 531 at the exit plane 532 and become primary reflected light Lr1. Of the primary reflected light Lr1 that reaches the incident plane 531, some of the primary reflected light Lr1 passes through the wavelength-selective filter 54 with transmittance Gh1, while other parts of the primary reflected light Lr1 that are different from some of the primary reflected light Lr1 are reflected toward the exit plane 532 at the incident plane 531 of the substrate 53 and become secondary reflected light Lr2. Then, of the secondary reflected light Lr2 that reaches the exit plane 532, some of the secondary reflected light Lr2 passes through the anti-reflective coating 55 and heads toward the camera 32 as stray light Ls. In this configuration, pattern light Lp is reflected by the exit plane 532 of the substrate 53 to generate primary reflected light Lr1, and primary reflected light Lr1 is reflected by the incident plane 531 of the substrate 53 to generate secondary reflected light Lr2, which is the cause of stray light Ls. However, since a wavelength-selective filter 54 that transmits a relatively large amount of pattern light Lp is provided on the incident plane 531 of the substrate 53, a relatively large amount of primary reflected light Lr1 passes through the wavelength-selective filter 54 without being reflected by the incident plane 531. As a result, the generation of secondary reflected light Lr2, which is the cause of stray light Ls, is suppressed. Therefore, the generation of virtual images in the captured image can be suppressed.

[0074] Furthermore, the camera 32 outputs level data in N steps (where N is an integer greater than or equal to 2) corresponding to the amount of light in the received pattern light Lp (in the example above, N=256). In contrast, the ratio of the amount of stray light Ls to the amount of light in the target light Lpi is 1 / 400, which is less than 1 / N. With this configuration, the occurrence of virtual images in the captured image can be reliably suppressed.

[0075] In the above embodiment, the inspection device 1 corresponds to an example of the "inspection device" of the present invention, the inspection stage 11 corresponds to an example of the "workpiece holding unit" of the present invention, the camera 32 corresponds to an example of the "imaging unit" of the present invention, the half mirror 52 corresponds to an example of the "half mirror" of the present invention, the incident surface 521 corresponds to an example of the "incident surface" of the present invention, the ejection surface 522 corresponds to an example of the "ejection surface" of the present invention, the substrate 53 corresponds to an example of the "substrate" of the present invention, the incident plane 531 corresponds to an example of the "first surface" of the present invention, the ejection plane 532 corresponds to an example of the "second surface" of the present invention, the wavelength selective filter 54 corresponds to an example of the "optical filter" of the present invention, and the anti-reflective coating 55 corresponds to an example of the "anti-reflective coating" of the present invention. In this invention, the first pattern irradiation unit 81 or the second pattern irradiation unit 82 corresponds to an example of the "laser irradiation unit" of the present invention, the transmittance Gl1 corresponds to an example of the "first transmittance" of the present invention, the reflectance Gl2 corresponds to an example of the "second transmittance" of the present invention, the workpiece W corresponds to an example of the "workpiece" of the present invention, the pattern light Lp1 or the pattern light Lp2 corresponds to an example of the "laser light" of the present invention, the imaging target light Lpi corresponds to an example of the "imaging target light" of the present invention, the primary reflected light Lr1 corresponds to an example of the "primary reflected light" of the present invention, the secondary reflected light Lr2 corresponds to an example of the "secondary reflected light" of the present invention, the stray light Ls corresponds to an example of the "stray light" of the present invention, and the reflection wavelength band Λ corresponds to an example of the "reflection wavelength band" of the present invention.

[0076] It should be noted that the present invention is not limited to the embodiments described above, and various modifications can be made to those described above without departing from the spirit of the invention. For example, the specific value of the transmittance Gl1 can be set as appropriate. For example, the transmittance Gh1 can be set to be in the range of 40% or more and 60% or less. Also, the specific value of the transmittance Gh1 can be set as appropriate. For example, the transmittance Gh1 can be set to be in the range of 90% or more and 100% or less. In such a configuration, it is possible to suppress the amount of pattern light Lp irradiated onto the workpiece W and to suppress the generation of virtual images in the captured image.

[0077] Furthermore, the direction in which the workpiece W is imaged is not limited to the Z direction; the workpiece W may also be imaged from a direction inclined in the Z direction. [Explanation of Symbols]

[0078] 1…Inspection device 11…Inspection stage (workpiece holding section) 32...Camera (imaging unit) 52... Half mirror 521...Incidence plane 522...Injection surface 53…Substrate (base material) 531...Incidence plane (first surface) 532...Injection plane (second surface) 54…Wavelength-selective filter (optical filter) 55...Anti-reflection film 81...First pattern irradiation section (laser irradiation section) 82...Second pattern irradiation area (laser irradiation area) Gl1…Transmittance (1st transmittance) Gl2…Reflectance (second transmittance) W...work Lp1…Patterned light (laser light) Lp2…Patterned light (laser light) Lpi…Light source to be imaged Lr1…Primary reflected light Lr2…Secondary reflected light Ls…Stray light Λ...Reflection wavelength band

Claims

1. A workpiece holding section that holds the workpiece, A laser irradiation unit that irradiates the workpiece with laser light, An imaging unit that captures an image of the workpiece by receiving the laser light reflected from the workpiece, A half-mirror is positioned between the workpiece holding unit and the imaging unit, and transmits the laser light from the workpiece toward the imaging unit. Equipped with, The half-mirror has an optical filter on the incident surface into which the laser light reflected from the workpiece is incident, and has an anti-reflective coating on the exit surface that emits the laser light passing through the half-mirror from the workpiece toward the imaging unit toward the imaging unit, thereby preventing reflection of the laser light. The laser light incident on the optical filter passes through the half mirror and is emitted from the anti-reflective coating. The optical filter reflects light of wavelengths included in a predetermined reflection wavelength band with a predetermined reflectance and transmits it with a predetermined first transmittance. The wavelength of the laser light is outside the reflection wavelength band. The optical filter transmits the laser light with a second transmittance higher than the first transmittance. The half-mirror has a substrate having a first surface and a second surface facing the first surface, The optical filter is provided on the first surface of the substrate. The anti-reflective film is provided on the second surface of the substrate. Of the laser light that has passed through the optical filter and reached the second surface, some of the laser light passes through the anti-reflective coating as imaging target light and heads toward the imaging unit, while the other portion of the laser light, which is different from the aforementioned portion, is reflected toward the first surface at the second surface and becomes primary reflected light. Of the primary reflected light that reaches the first surface, a portion of the primary reflected light passes through the optical filter at the second transmittance, while the remaining primary reflected light, which differs from the portion of primary reflected light, is reflected from the first surface of the substrate toward the second surface and becomes secondary reflected light. An inspection device in which, of the secondary reflected light that reaches the second surface, some of the secondary reflected light passes through the anti-reflective coating and becomes stray light directed toward the imaging unit.

2. The imaging unit outputs level data in N steps (where N is an integer of 2 or more) corresponding to the amount of light from the received laser beam. The inspection apparatus according to claim 1, wherein the ratio of the amount of stray light to the amount of light to be imaged is less than 1 / N.

3. The inspection apparatus according to claim 1 or 2, wherein the optical filter is a dielectric multilayer film.

4. The first transmittance is included in the range of 40% or more and 60% or less. The inspection apparatus according to claim 1 or 2, wherein the second transmittance is in the range of 90% or more and 100% or less.

5. The inspection apparatus according to claim 1 or 2, wherein the anti-reflective coating is a single layer AR coating.

6. The inspection apparatus according to claim 1 or 2, wherein the anti-reflective coating is a multilayer AR coating.

7. A process of irradiating a workpiece held in a workpiece holding section with laser light, The process involves receiving the laser light reflected from the workpiece and imaging the workpiece with the imaging unit. Equipped with, A half-mirror is placed between the workpiece holding unit and the imaging unit to transmit the laser light from the workpiece toward the imaging unit. The half-mirror has an optical filter on the incident surface into which the laser light reflected from the workpiece is incident, and has an anti-reflective coating on the exit surface that emits the laser light passing through the half-mirror from the workpiece toward the imaging unit toward the imaging unit, thereby preventing reflection of the laser light. The laser light incident on the optical filter passes through the half mirror and is emitted from the anti-reflective coating. The optical filter reflects light of wavelengths included in a predetermined reflection wavelength band with a predetermined reflectance and transmits it with a predetermined first transmittance. The wavelength of the laser light is outside the reflection wavelength band. The optical filter transmits the laser light with a second transmittance higher than the first transmittance. The half-mirror has a substrate having a first surface and a second surface facing the first surface, The optical filter is provided on the first surface of the substrate. The anti-reflective film is provided on the second surface of the substrate. Of the laser light that has passed through the optical filter and reached the second surface, some of the laser light passes through the anti-reflective coating as imaging target light and heads toward the imaging unit, while the other portion of the laser light, which is different from the aforementioned portion, is reflected toward the first surface at the second surface and becomes primary reflected light. Of the primary reflected light that reaches the first surface, a portion of the primary reflected light passes through the optical filter at the second transmittance, while the remaining primary reflected light, which differs from the portion of primary reflected light, is reflected from the first surface of the substrate toward the second surface and becomes secondary reflected light. An inspection method in which, of the secondary reflected light that reaches the second surface, a portion of the secondary reflected light passes through the anti-reflective film and becomes stray light directed toward the imaging unit.

Images