Optical system for shape measurement device
By diffusing LED light with an optical fiber or integrating sphere and using a telecentric lens to ensure parallel light reaches the image sensor, the optical system addresses luminance unevenness, enabling precise shape measurement of objects with reduced contour distortion.
Patent Information
- Application Number
- JP2021157114
- Authority / Receiving Office
- JP · JP
- Patent Type
- Patents
- Current Assignee / Owner
- Filing Date
- 2021-09-27
- Publication Date
- 2025-07-22
- Estimated Expiration
- 2041-09-27
AI Technical Summary
Existing optical systems for shape measurement devices using high-luminance white LEDs suffer from luminance unevenness, leading to potential distortion in the contour shape of measured objects due to directivity issues.
Incorporating a diffusion member, such as an optical fiber or integrating sphere, to diffuse light from the LED before it enters a pinhole, combined with a telecentric lens to ensure only parallel light reaches the image sensor, thereby reducing luminance unevenness.
The solution effectively reduces luminance unevenness, allowing for accurate measurement of the outer peripheral edge of objects with minimal contour blurring, even for objects with significant depth along the optical axis.
Smart Images
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Abstract
Description
Technical Field
[0001] The present invention relates to an optical system for a shape measurement device used in a shape measurement device that irradiates parallel light through a measurement object toward an image sensor and measures the two-dimensional shape of the measurement object based on the image of the measurement object projected on the image sensor.
Background Art
[0002] An optical system for a shape measurement device used in a shape measurement device that irradiates parallel light through a measurement object toward an image sensor and measures the two-dimensional shape of the measurement object based on the image of the measurement object projected on the image sensor is disclosed, for example, in Patent Document 1.
[0003] The optical system for a shape measurement device disclosed in this Patent Document 1 includes a parallel light irradiation system that irradiates parallel light along the circular surface of the measurement object and such that the measurement part, which is the outer peripheral edge part of the disk-shaped measurement object, is arranged in the light beam, and an imaging optical system that images the image of the measurement part. The parallel light irradiation system includes a point light source having a white LED, a collimator lens for making parallel light by making the light from the point light source incident thereon, and a telecentric lens having a bilateral or object-side telecentric structure through which the light from the collimator lens is irradiated through the measurement object. The imaging optical system includes an image sensor on which the image of the measurement part by the light that has passed through the telecentric lens is projected.
Prior Art Documents
Patent Documents
[0004]
Patent Document 1
Summary of the Invention
Problems to be Solved by the Invention
[0005] By the way, in the optical system for a shape measurement device disclosed in Patent Document 1, when a white LED with high luminance is used, due to its directivity, luminance unevenness occurs in the light after passing through the pinhole. As a result, there is a risk that distortion will occur in the contour shape of the outer peripheral edge portion of the object to be measured.
[0006] The present invention has been made in view of the above circumstances, and an object thereof is to provide an optical system for a shape measurement device that can reduce luminance unevenness.
Means for Solving the Problems
[0007] As a result of various studies, the present inventor has found that the above object is achieved by the following present invention. That is, the optical system for a shape measurement device according to one aspect of the present invention irradiates parallel light to a measurement part, which is an outer peripheral edge part of a disk-shaped object to be measured, along the circular surface of the object to be measured and such that the measurement part of the object to be measured is arranged in the light beam, and includes an imaging optical system that images an image of the measurement part. The parallel light irradiation system includes a point light source, a collimator lens that emits the light from the point light source as parallel light, and a telecentric lens having a bilateral or object-side telecentric structure through which the light from the collimator lens is irradiated through the object to be measured. The imaging optical system includes an image sensor on which an image of the measurement part formed by the light that has passed through the telecentric lens is projected. The point light source includes an LED, a diffusion member that diffuses and emits the light from the LED, and a pinhole member that forms a pinhole into which the light from the diffusion member is incident. Preferably, in the optical system for a shape measurement device described above, the parallel light irradiation system irradiates the parallel light so that the luminance distribution of the light irradiated to the image sensor when the object to be measured is not arranged is 25% or less (more preferably 20% or less).
[0008] Such an optical system for a shape measurement device can reduce luminance unevenness because the light from the white LED is diffused by the diffusion member and then made incident on the pinhole.
[0009] UpperIn the optical system for the shape measurement device described above, the diffusion member is an optical fiber.
[0010] According to this, an optical system for a shape measurement device in which the diffusion member is an optical fiber can be provided.
[0011] Upper In the optical system for the shape measurement device described above, the optical fiber has a bent shape. Preferably, in the optical system for the shape measurement device described above, the optical fiber has a wound shape.
[0012] In such an optical system for a shape measurement device, since the optical fiber has a bent shape, more light is reflected and propagates in the core compared to the case where the optical fiber has a straight shape, so that light can be diffused more suitably and luminance unevenness can be reduced more.
Effect of the Invention
[0015] The optical system for a shape measurement device according to the present invention can reduce luminance unevenness.
Brief Description of the Drawings
[0016]
Figure 1
Figure 2
Figure 3
Mode for Carrying Out the Invention
[0017] Hereinafter, one or more embodiments of the present invention will be described with reference to the drawings. However, the scope of the invention is not limited to the disclosed embodiments. In each figure, components denoted by the same reference numerals are the same components, and the description thereof will be omitted as appropriate. In this specification, when referring to components in general, reference numerals without subscripts are used, and when referring to individual components, reference numerals with subscripts are used.
[0018] FIG. 1 is a schematic diagram for explaining the configuration of an optical system for a shape measurement device according to an embodiment. The optical system A for a shape measurement device according to the embodiment is an optical system used in a shape measurement device that irradiates parallel light through a measurement object toward an image sensor and measures the two-dimensional shape of the measurement object Ob from the image of the measurement object Ob projected onto the image sensor. For example, as shown in FIG. 1, for a measurement part that is the outer peripheral edge part of a disk-shaped measurement object Ob, parallel light is irradiated along the circular surface of the measurement object Ob and in such a manner that the measurement part of the measurement object Ob is arranged in the light beam. The optical system includes a parallel light irradiation system 1 and an imaging optical system 2 that captures an image of the measurement part.
[0019] The measurement object Ob may be any member as long as it is a disk-shaped member. For example, it may be a semiconductor wafer, a substrate of a hard disk (such as an aluminum substrate or a glass substrate), or the like.
[0020] The parallel light irradiation system 1 includes a point light source 11a, a collimator lens 12, and a telecentric lens 13.
[0021] The point light source 11a includes an LED 111 (light-emitting diode) 111, a diffusing member 112 (for example, an optical fiber 112a), and a pinhole member 113.
[0022] The LED 111 is a light source that emits light.
[0023] The diffusion member 112 is a member that diffuses and emits the light from the LED 111. In the example shown in FIG. 1, it is an optical fiber 112a as an example thereof. The optical fiber 112a propagates the light from the LED 111 by repeating reflections within its core and emits it. By repeating this reflection, the light from the LED 111 is diffused. Since more reflections can occur compared to the case where the optical fiber is in a straight shape, the optical fiber 112a preferably has a bent shape. In the example shown in FIG. 1, the optical fiber 112a has a wound shape (coil shape). The diameter and the number of turns of the coil shape in the wound optical fiber 112a are preferably set appropriately according to the required light diffusion. In one example, it has a radius of about 50 mm and the number of turns is 3 or more. The optical fiber 112a may be made of, for example, glass, or may be made of, for example, resin, and its material is not particularly limited.
[0024] The pinhole member 113 is a plate-like member that shields the white light emitted from the LED 111. In the plate-like member, a pinhole of a through-opening is formed through which the light from the diffusion member 112 (the optical fiber 112a in this example) is incident. The smaller the diameter of the pinhole, the more preferable it is. However, if it is too small, sufficient light quantity for shape measurement cannot be obtained. Therefore, it is preferably in the range of 1 μm to 1 mm, and more preferably in the range of 10 μm to 800 μm.
[0025] The diameter of the optical fiber 112a is preferably the same as the diameter of the pinhole. Therefore, it is preferably in the range of 1 μm to 1 mm, and more preferably in the range of 10 μm to 800 μm.
[0026] In the point light source 11a having such a configuration, the white light from the LED 111 is incident on the optical fiber 112a, propagates by repeating reflections within the core of the optical fiber 112a, is emitted from the optical fiber 112a, and is incident on the pinhole of the pinhole member 113.
[0027] The collimator lens 12 is an optical system (including a single lens and a lens group) that emits the light from the point light source 11a as parallel light (parallel light beam). The collimator lens 12 and the pinhole member 113 are arranged such that the pinhole of the pinhole member 113 is located at the focal position of the collimator lens 12.
[0028] The telecentric lens 13 is an optical system with a bilateral or object-side telecentric structure in which the light from the collimator lens 12 is irradiated through the object to be measured Ob. In the example shown in FIG. 1, the telecentric lens 13 is an optical system with a bilateral telecentric structure, and the rear focal point of the first lens (including a lens group) 131 and the front focal point of the second lens (including a lens group) 133 are made to coincide, and the two lenses 131 and 133 are arranged, and a variable aperture (aperture stop) 132 is provided at this focal position. In this telecentric lens 13, the chief ray is parallel to the optical axis AX both on the object side (the object to be measured Ob side) and on the image side (the imaging optical system 2 side), and only parallel light (including light that is extremely close to being parallel) among the light after passing through the object to be measured Ob is allowed to pass through. The distance between the collimator lens 12 and the first lens 131 is set to about 200 mm, for example, and the object to be measured Ob is arranged in the parallel light beam from the collimator lens 12 to the first lens 131. The object to be measured Ob is preferably arranged such that each of its front and back surfaces is parallel to the optical axis AX so that the shape of the measured part, which is the outer peripheral edge part of the object to be measured, can be suitably measured.
[0029] Note that in order to allow only parallel light (including light that is extremely close to being parallel) among the light after passing through the object to be measured Ob to pass through, the telecentric lens 13 may be an optical system with an object-side telecentric structure in which the chief ray is parallel to the optical axis only on the object side (the object to be measured Ob side) instead of the above-described optical system with a bilateral telecentric structure. In the case of this object-side telecentric structure, a general imaging lens is used as the second lens on the rear side of the aperture stop.
[0030] The imaging optical system 2 includes an image sensor on which an image of a measurement target portion, which is an outer peripheral edge portion of the object to be measured Ob, is projected by the light that has passed through the telecentric lens 13. The image sensor is, for example, a two-dimensional CCD image sensor, a two-dimensional CMOS image sensor, or the like.
[0031] In order to more favorably form an image of the outer peripheral edge portion of the object to be measured Ob on the image sensor of the imaging optical system 2, the parallel light irradiation system 1 with the above configuration preferably irradiates the parallel light so that the luminance distribution of the light irradiated on the image sensor when the object to be measured Ob is not arranged is 25% or less, and more preferably irradiates the parallel light so that the luminance distribution is 20% or less. Since the shape measurement device is optimized assuming no luminance distribution, the smaller the luminance distribution, the better. However, in order to further improve it, it is effective to reduce the pinhole diameter and the fiber diameter to approach a more ideal point light source. However, if the diameter is reduced, the amount of incident light decreases, making it unsuitable for measurement. If the voltage is increased to obtain the necessary amount of light, there is a risk of demerits such as shortening the lifespan of the LED 111.
[0032] The shape measurement device equipped with the optical system A for a shape measurement device with such a configuration captures an image (image data) of the outer peripheral edge portion of the object to be measured Ob output from the image sensor of the imaging optical system 2, and by performing predetermined image processing such as edge extraction processing for extracting edges, etc., the outer contour of the outer peripheral edge portion of the object to be measured Ob is extracted, thereby enabling measurement of the shape of the outer peripheral edge portion of the object to be measured Ob.
[0033] The optical system A for a shape measurement device in this embodiment is equipped with a point light source 11a, and thus, through the collimator lens 12, it can irradiate the object to be measured with light that is as parallel as possible. Moreover, with the telecentric lens 13, only the parallel light (including light that is extremely close to being parallel) among the light passing through the object to be measured can be made to pass through. Therefore, even for an object to be measured Ob with a long depth along the optical axis direction, an image of the outer peripheral edge portion of the good object to be measured Ob with a small degree of blurring of the contour can be obtained at the image sensor of the imaging optical system 2. Thus, even if the object to be measured Ob is, for example, a semiconductor wafer with a long depth along the optical axis direction, the degree of blurring of the contour is small at the image sensor of the imaging optical system 2, and an image of the outer peripheral edge portion of the good semiconductor wafer can be captured.
[0034] In the optical system A for a shape measurement device in this embodiment, the light from the LED 111 is diffused by the diffusion member 112, which is the optical fiber 112a in the above example, and then made to enter the pinhole, so that the luminance unevenness can be reduced.
[0035] According to this embodiment, an optical system A for a shape measurement device in which the diffusion member is an optical fiber can be provided.
[0036] In the optical system A for a shape measurement device in this embodiment, since the optical fiber 112a is in a bent shape, more light is reflected and propagates in the core compared to the case where the optical fiber is in a straight shape. Therefore, light can be diffused more preferably, and the luminance unevenness can be reduced more.
[0037] Next, examples and comparative examples will be described. FIG. 2 is a diagram for explaining the calculation method of the luminance distribution.
[0038] In the example, an LED 111 was used as the point light source 11a of the optical system for the shape measurement device. For the diffusion member 112, an optical fiber wound three times in a coil shape with a radius of 50 mm was used. For the pinhole member 113, a plate-like member with a pinhole of φ400 μm formed thereon was used. The surface-emitting LED is composed of an InGaN-based blue LED and a yellow phosphor of YAG:Ce coated on its surface. For the collimator lens 12, a collimator lens with a focal length f: 50 mm was used. For the telecentric lens 13, an object-side telecentric lens with an optical magnification of 2 times was used. A two-dimensional CMOS image sensor was used for the image sensor of the imaging optical system 2. The object-side telecentric lens has a working distance (the distance from the lens tip to the object to be measured): about 110 mm.
[0039] On the other hand, the optical system for the shape measurement device in the comparative example has a configuration obtained by removing the diffusion member 112 (the coiled optical fiber 112a in the above example) from the optical system for the shape measurement device in the above-described example.
[0040] The luminance distribution in the optical system for the shape measurement device of the example was 11%, and the luminance distribution in the optical system for the shape measurement device of the comparative example was 26%. Therefore, the optical system for the shape measurement device of the example has improved luminance unevenness compared to the optical system for the shape measurement device of the comparative example.
[0041] The luminance distribution BD was obtained from the following formula 1 using the maximum luminance Bmax and the minimum luminance Bmin on the diagonal line LN in the image P by the light irradiated on the image sensor of the imaging optical system 2 when the object to be measured Ob is not arranged in the optical system for the shape measurement device, as shown in FIG. 2 for example. Formula 1; BD = (1 - Bmin / Bmax) × 100 [%]
[0042] In the above-described embodiment, the diffusion member 112 was the optical fiber 112a, but the diffusion member 112 may be an integrating sphere. According to this, an optical system for a shape measurement device in which the diffusion member is an integrating sphere can be provided.
[0043] FIG. 3 is a schematic diagram for explaining the configuration of a point light source in a deformed form used in the optical system for the shape measurement device.
[0044] In the optical system A for the shape measurement device of such a deformed form, in the above-described configuration, instead of the point light source 11a, a point light source 11b shown in FIG. 3 is provided. The point light source 11b shown in FIG. 3 includes a white LED 111, an integrating sphere 112b, and a pinhole member 113. Since these white LED 111 and pinhole member 113 are the same as the above-described white LED 111 and pinhole member 113 described with reference to FIG. 1, the description thereof is omitted.
[0045] The integrating sphere 12b is a hollow spherical member and includes an incident opening through which light from the white LED 111 is incident, and an emission opening that emits the light diffusely reflected inside the spherical member to the pinhole of the pinhole member 113. On the inner surface (inner wall surface) of the spherical member, for example, magnesium oxide, barium oxide, zinc oxide, etc. are coated in order to diffusely reflect efficiently.
[0046] In the point light source 11b having such a configuration, the white light from the white LED 111 is incident on the integrating sphere 12b through the incident opening, diffusely reflected inside the integrating sphere, and incident on the pinhole of the pinhole member 113 from the integrating sphere 112b through the emission opening.
[0047] Note that the LED 111 may be disposed inside the integrating sphere and the incident opening may be omitted. In this case, a light shielding plate is provided between the LED 111 and the emission opening so that the light from the LED 111 does not reach the emission opening directly.
[0048] To represent the present invention, the present invention has been appropriately and fully described through embodiments with reference to the drawings above. However, those skilled in the art should recognize that it is easy to make changes and / or improvements to the above-described embodiments. Therefore, as long as the changes or improvements made by those skilled in the art do not depart from the scope of the claims described in the claims, such changes or improvements are construed to be included within the scope of the claims of the claims.
Explanation of Signs
[0049] Optical System for Shape Measuring Device 1 Parallel Light Irradiation System 2 Imaging Optical System 11 Point Light Source 12 Collimator Lens 13 Telecentric Lens 111 LED 112a Optical Fiber 112b Integrating Sphere 113 Pinhole Member
Claims
1. A parallel light irradiation system that irradiates parallel light along the circular surface of the object to be measured and arranges the portion to be measured of the object to be measured in the light beam with respect to the portion to be measured that is the outer peripheral edge portion of the disk-shaped object to be measured, An imaging optical system that images the image of the portion to be measured, The parallel light irradiation system includes a point light source, a collimator lens that emits the light from the point light source as parallel light, and a telecentric lens having a bilateral or object-side telecentric structure in which the light from the collimator lens is irradiated through the object to be measured, The imaging optical system includes an image sensor on which the image of the portion to be measured by the light that has passed through the telecentric lens is projected, The point light source includes an LED, a diffusing member that diffuses and emits the light from the LED, and a pinhole member that forms a pinhole into which the light from the diffusing member is incident, The diffusing member is an optical fiber having a shape bent like a coil, Optical system for shape measurement device.
2. The optical fiber is single-core, The optical system for a shape measurement device according to claim 1.
3. The optical fiber has a coiled shape, The optical system for a shape measurement device according to claim 1 or claim 2.
Citation Information
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