Illumination device for inspection, illumination optical system, and inspection system

Abstract

[Problem] To solve the problem in which: object light returned from an inspection object irradiated with light includes direct light and scattered light at a given ratio; object light returned from a glossy surface or a metal surface is mainly direct light; using direct light cannot quantitatively captures a change in various light physical properties of an inspection object unless a certain solid angle element is uniformly set in a relative relationship between an irradiation solid angle and an observation solid angle; and it is necessary to reduce both the irradiation solid angle and the observation solid angle in order to capture a slight change in the surface shape, but the object light itself cannot be captured when a normal line of the inspection surface is slightly deviated from the observation optical axis. [Solution] In contrast, in the present invention, to achieve a feature in which object light can be captured up to a fixed inclination of the inspection surface while keeping the detection sensitivity to the inclination constant even if the irradiation solid angle and the observation solid angle are set to be small, first, a plurality of annular solid angle regions which are not adjacent to each other are formed concentrically in the irradiation solid angle in an irradiation optical system in which the solid angle element is constant, so that even if the inspection object has a curved surface, the inclination is converted into bright and dark information with the same sensitivity, bright and dark information as a differential image of the surface is obtained, so that minute unevenness can be detected with uniform detection sensitivity up to a fixed inclination of the inspection object isotropically with no direction dependence, and a minute change in light physical properties of the inspection object is quantitatively converted into bright and dark information, and the minute change can be easily detected using one image captured by a normal camera and a lens.

Description

Inspection illumination device, illumination optical system, and inspection system

[0001] The present invention relates to an inspection illumination device, an illumination optical system, and an inspection system that are used to irradiate an inspection object with inspection light and inspect the product for appearance, scratches, defects, etc.

[0002] An example of an inspection illumination device used for visual inspection of products, etc., is a coaxial illumination device in which the imaging direction and the direction of illuminating the inspection object are aligned, as shown in Patent Document 1. This coaxial illumination device includes a light source that emits inspection light in a direction parallel to the inspection object surface of the inspection object, and a half mirror that is tilted and disposed between the inspection object and an imaging device disposed above the inspection object, and that reflects the inspection light toward the inspection object while transmitting the reflected light from the inspection object toward the imaging device.

[0003] Coaxial illumination can roughly align the direction of illumination light and the direction of observation of object light returned from the object to be inspected, and can set roughly uniform illumination and observation conditions for each point on the object to be inspected. This has the effect of making it easier to capture changes in the physical properties of light at each point on the object to be inspected as changes in the object light emitted from each point on the object. However, in order to detect and capture changes in the physical properties of light due to minute defects in the object to be inspected, it is still necessary to set the illumination and observation conditions at each point more uniformly, and so the inventions disclosed in Patent Documents 1, 2, 3 and 4 have been implemented.

[0004] In recent years, there has been a demand for the ability to detect, from captured images, feature points such as defects that are difficult to detect even with the above-mentioned inspection illumination device. More specifically, in cases where the surface of the product to be inspected is a perfectly matte surface that returns scattered light with the same brightness regardless of the direction of observation as object light, but also where the surface is glossy or metallic and returns direct light such as specularly reflected light or specularly transmitted light whose brightness varies greatly depending on the direction of illumination of the inspection light and the direction of observation of the object light, it is difficult to precisely control the illumination optical axis and the shape of the illumination solid angle of the inspection light to obtain the desired shading information at the feature points. Even if the inspection light can be irradiated, the observation direction of the object light changes depending on the position of the feature point on the inspection object, resulting in a large change in brightness difference, making it difficult to identify the feature points.

[0005] More specifically, even if the reflection direction of the irradiated inspection light changes slightly due to a minute defect or the like on the inspection object, if the change is within the observation solid angle of the imaging device, there will be no change in the brightness of the captured image, regardless of whether or not there is a defect. Alternatively, if the irradiation solid angle of the inspection light is large and the tilt of the optical axis is different at each point on the inspection object, not only will a slight change in the reflection direction not be perceived as a change in the amount of light within the observation solid angle of the imaging device, but the change in the amount of light within the observation solid angle of the imaging device will vary at each point on the inspection object, and ultimately, machine vision will not be able to accurately capture such minute defects or the like within the inspection object range.

[0006] Patent No. 5866573 Patent No. 5866586 Patent No. 6451821 Patent No. 7206020

[0007] The present invention has been made in consideration of the above-mentioned problems, and aims to provide an inspection illumination device, illumination optical system, and inspection system that can change the amount of light within the observation solid angle of the imaging device by a fixed amount at each point in the imaging range of the inspection object, regardless of where the feature point is located within the field of view, even if the feature point, such as a defect, is very small or faint and the change in reflection or scattering caused by the feature point is slight, thereby making it possible to detect the details of such minute feature points.

[0008] Even if a feature point such as a defect is very small or faint and the change in reflection or scattering at the feature point is slight, or even if the feature point is located anywhere within the field of view at each point in the imaging range of the inspection object, for example, the illumination solid angle of the illumination light at each point on the inspection object and the observation solid angle formed by the imaging device that observes the object light returned from the inspection object are in the direction of regular reflection, and changes in the physical properties of light, such as the reflection direction at the feature point, cause changes in the radiant energy of the object light itself, such as reflection or scattering, returned from the object and reflecting the illumination solid angle, and changes in the relative relationship between the solid angle of the object light and the observation solid angle.This changes the optical energy of the object light captured within the observation solid angle, and makes it possible to detect the feature point as a difference in luminance of the object light.However, the amount of change in luminance of this object light is greatly influenced by the amount of change in the relative relationship, such as the relative angle, of the solid angle of the object light reflecting the solid angle of the illumination light and the observation solid angle that captures the object light, as well as the respective sizes of the solid angle of the object light reflecting the solid angle of the illumination light and the observation solid angle that captures the object light.

[0009] More specifically, when either the solid angle of the object light or the solid angle of the observation is completely contained within the other, no change in brightness occurs due to a change in the relative relationship between the two solid angles; alternatively, when the solid angle of the object light and the solid angle of the observation do not contain any part of each other, the brightness of the object light cannot be detected within the solid angle of the observation; alternatively, when the solid angle of the object light and the solid angle of the observation are large, the change in brightness of the object light relative to the change in the solid angle of the object light becomes relatively small, making it difficult to detect feature points.

[0010] In particular, when the inspection object is composed of a curved surface, the relative relationship between the solid angle of the object light, which reflects the solid angle of the illumination light, and the observation solid angle, which captures the object light, changes depending on the position of the feature point on the curved surface, and the magnitudes and relative angles of the solid angle of the object light change. This results in a large or small change in the brightness of the object light, even for the same feature point. Furthermore, when the change in the tilt of the solid angle of the object light due to the feature point is small, it is necessary to set both the illumination solid angle and the observation solid angle small so that the change in the tilt of the solid angle of the object light results in a larger change in brightness. In this case, however, if the surface of the inspection object is tilted by an angle equal to or greater than half the sum of the planar half angles of the illumination solid angle and the observation solid angle, the object light due to reflection cannot be captured by the observation solid angle, and it becomes impossible to detect the change in the solid angle of the object light due to feature points within that surface.

[0011] The present invention aims to solve the problem that, as described above, the change in the relative relationship between the solid angle of the object light, which reflects the illumination solid angle, and the observation solid angle of the imaging device results in a reduction in the change in brightness of the object light due to a change in the light energy captured at the observation solid angle, or inability to capture the change in brightness, depending on the inclination of the surface of the object to be inspected, and ultimately to provide an inspection illumination device, illumination optical system, and inspection system that make it possible to detect the details of such minute feature points.

[0012] The present invention is based on a novel idea that the size, shape, inclination, etc. of the illumination solid angle of the inspection light emitted from the inspection illumination device and the illumination optical system are made uniform for each point on the inspection object, and that within that illumination solid angle, variables other than the direction of light propagation, such as different wavelengths, polarization planes, or light quantities, are arbitrarily divided and irradiated, and that this can be adjusted.By doing so, even if the defects on the inspection object are minute and the changes in reflection or scattering due to these defects are very small, they can be captured as changes in the light quantity for each divided different wavelength band, polarization plane, or light quantity region within the observation solid angle formed by the imaging device, and an image can be obtained that uses these changes as brightness information.

[0013] More specifically, the inspection illumination device and illumination optical system of the present invention are applied to an inspection system comprising an inspection illumination device that irradiates an inspection object with inspection light, and an illumination optical system that is an inspection object and an observation optical system that captures light reflected, transmitted or scattered by the inspection object, and the inspection illumination device and illumination optical system comprise a surface light source that emits inspection light, a lens that is provided between the surface light source and the inspection object and that forms an illumination solid angle with respect to the inspection object as inspection light that irradiates the inspection object with light emitted from the surface light source, and a lens that is provided between the surface light source and the lens and in front of and behind the focal position of the lens, and that forms an illumination solid angle with respect to the inspection object. An inspection illumination device and illumination optical system that can simultaneously form the same illumination solid angle for each point on the inspection object, regardless of the distance from the inspection illumination device and illumination optical system to the inspection object or the position of each point on the inspection object, and that includes a first light-shielding mask that shields and forms an illumination solid angle of inspection light that is irradiated to each point on the inspection object, the first light-shielding mask being concentrically arranged within the illumination solid angle and forming multiple annular solid angle regions that do not have adjacent portions.The inspection illumination device and illumination optical system can simultaneously form the same illumination solid angle for each point on the inspection object, regardless of the distance from the inspection illumination device and illumination optical system to the inspection object or the position of each point on the inspection object, and the illumination solid angle can be set to have the same relative angle at the same time with respect to the observation solid angle for each point on the inspection object that is formed when the imaging device images the light from the inspection object through the observation optical system.

[0014] Furthermore, the inspection illumination device and illumination optical system of the present invention may further comprise a first filter means adjacent to the first light-shielding mask, which can divide the inspection light into any solid angle region having partially different optical attributes using light of different wavelength bands, different polarization planes, or light having different light amounts, or can set the optical attributes to change continuously; and the first light-shielding mask and the first filter means may be a third filter means unified as a means for forming a solid angle region and an illumination solid angle, having at least any of the functions thereof.

[0015] Furthermore, between the first light-shielding mask and the surface light source, near where the lens forms an image on the inspection object, there may be further provided at least one of a second light-shielding mask and a fourth filter means that transmits only light with a specific attribute, and the second light-shielding mask or the fourth filter means may be capable of arbitrarily generating the irradiation area and irradiation pattern of the inspection light on the inspection object, and the second light-shielding mask and the fourth filter means that transmits only light with a specific attribute may be a fifth filter means that has at least the functions of at least one of the second light-shielding mask and the fourth filter means.

[0016] Furthermore, the first light-shielding mask, the first filter means, and the third filter means may be disposed between the surface light source and a relay optical system (e.g., lenses arranged in tandem), and a relay image formed by the relay optical system may be used instead of the first light-shielding mask, the first filter means, and the third filter means. The relay image is a reduced image of the first light-shielding mask, the first filter means, and the third filter means. The positions of the first light-shielding mask, the first filter means, and the third filter means may also be changeable along the illumination light path (i.e., a configuration in which the relay images of the first light-shielding mask, the first filter means, and the third filter means can be positioned near the focal position of the lens). Furthermore, the light-shielding mask may be a means that completely blocks light, or may have a certain low transmittance, or may have optical attributes that do not allow light to pass through or have a transmittance that is lower than a certain level due to the sixth filter means on the imaging device side, and although the first light-shielding mask, the first filter means, and the third filter means are transmissive, they may also be reflective.

[0017] The brightness of each point on the inspection target is determined by the light energy captured within the observation solid angle formed at each point, and the amount of this light energy is determined by the light energy contained in the portion of the solid angle formed by the light reflected, transmitted, or scattered from each point, which is generated by the illumination solid angle for each point, and the observation solid angle. If the light returned from each point is direct light such as specularly reflected light or specularly transmitted light, the solid angle of the direct light will be the same as the shape and size of the illumination solid angle, but if it is scattered light, light energy determined by the spectral illuminance near each point will be radiated evenly across the entire observable solid angle.

[0018] When the light returned from each point on the inspection object is scattered light, the illuminance at each point is determined by the angle relative to the solid angle of illumination at each point, which depends on the tilt of the surface near each point on the inspection object. The radiant energy of the scattered light over the entire solid angle changes in proportion to the illuminance, and this is captured by the solid angle of observation, changing the brightness of each point. Therefore, to detect even smaller tilts near each point on the inspection object, it is necessary to set the solid angle of illumination small so that the illuminance changes more significantly depending on the small tilt.

[0019] Furthermore, when the light returned from each point on the inspection object is direct light, the inclination of the solid angle of the direct light, which has the same shape as the illumination solid angle, changes depending on the inclination of the surface near each point on the inspection object. As a result, if the inclusion relationship with the observation solid angle changes, the brightness of each point changes in conjunction with the inclination of the surface near each point. However, if the inclination of the surface near each point is small compared to the illumination solid angle or observation solid angle, the amount of change in brightness will be small. Therefore, in order to detect even smaller inclinations near each point on the inspection object, it is necessary to set the illumination solid angle and observation solid angle small so that the size of the included area of ​​the solid angle of the direct light and the solid angle of the observation light changes depending on the slight inclination.

[0020] Here, even if the illumination solid angle is small, if the light returned from each point on the object of inspection is scattered light, the light emitted from each point on the object of inspection is emitted evenly over the entire solid angle. Therefore, even if the surface near each point is tilted significantly, the change in illuminance can be detected as the brightness of scattered light as long as it is within the range in which the illumination solid angle is formed. However, if the light returned from each point on the object of inspection is direct light, the solid angle of the direct light also becomes small, and the angular range in which the light energy can be captured by the observation solid angle becomes smaller. If the tilt of the surface near each point becomes larger than the range that can be captured by the observation solid angle, the light energy of the direct light cannot be captured, and the magnitude of the tilt of the surface near each point on the object of inspection that can be observed is limited.

[0021] Therefore, with such an inspection illumination device and illumination optical system, even if the inclination of the surface near each point of the inspection target is slight, by appropriately setting the change in the inclusion relationship between the annular solid angle area and the observation solid angle, the slight inclination can be expressed as a change in the observation brightness at each point, and even if the inclination of the surface near each point is large, the slight change in inclination on the surface can be detected with the same detection sensitivity up to the angle determined by the outermost boundary of the illumination solid angle.

[0022] In other words, at each point on the object to be inspected, while maintaining the change in the relative relationship between the annular solid angle region formed within the illumination solid angle and the observation solid angle, it is now possible to detect minute changes in tilt from that tilt, up to the range of tilt determined by the outermost contour of the illumination solid angle, even if the tilt of the surface near each point on the object to be inspected is large.In particular, when the object to be inspected is a curved surface, the detection range has previously been limited when detecting minute changes in tilt, but it is now possible to make the detection range that can be imaged at one time larger.

[0023] Furthermore, even if the intensity or direction of reflected light, transmitted light, or scattered light changes slightly due to a minute defect or the like in the object to be inspected, the amount of light will change for each solid angle region having a different light attribute within the solid angle of observation of the imaging device depending on the changed portion. In this way, the shape and angle of the solid angle of illumination of the inspection light irradiated to each point on the object to be inspected can be appropriately set by the first light-shielding mask or the first filter means in relation to the size, shape, and angle of the solid angle of observation of the imaging device, and can be appropriately set to match the surface properties of the characteristic points on the object surface, making it easier to detect minute defects, or conversely, making them less likely to be detected.

[0024] Furthermore, various types of illumination solid angles can be formed, and by forming solid angle regions with different optical attributes within the illumination solid angle, it is possible to prevent reflected light and transmitted light from the inspection object from entering the observation solid angle of the imaging device and capture only scattered light, or to observe changes in the propagation direction of the reflected light and transmitted light from the inspection object as brightness information for each point on the inspection object, with the reflected light and transmitted light being in an inclusive relationship with the observation solid angle.Furthermore, by providing the imaging device with second filter means that can selectively capture solid angle regions within the illumination solid angle with different optical attributes that are reflected in the solid angle of the reflected light or transmitted light, it is possible to capture changes that occur at feature points on the inspection object for each of the arbitrary solid angle regions, and to irradiate inspection light at an illumination solid angle of an appropriate type according to minute changes in light that occur in various inspection objects and various feature points to be detected.

[0025] The second filter means referred to here may be, for example, the imaging device selectively splitting the reflected light or transmitted light from the object to be inspected into different light attributes and then imaging the respective light quantities with an optical sensor, or it may be provided with a filter that selectively transmits only light with different optical attributes for each pixel of the optical sensor.

[0026] In accordance with the present invention, when an inspection light having a substantially uniform illumination solid angle is irradiated onto an inspection object, even slight changes in the solid angle of the reflected or transmitted light that occur when the reflection or transmission direction of the reflected or transmitted light changes due to a defect or the like can be detected. The relative relationship between the observation solid angle of the imaging device and the concentric annular solid angle regions formed within the illumination solid angle of the inspection light is adjusted in terms of their shape, angle, and size so that the change in light intensity within the observation solid angle is maximized and the change in other solid angles is minimized. This allows selective detection of only the change in the solid angle of the reflected or transmitted light. Furthermore, by setting any solid angle region with different optical attributes within the illumination solid angle, the change in light intensity for each solid angle region can be simultaneously observed, enabling continuous capture of light changes corresponding to light changes at various feature points on the inspection object. Therefore, capturing such slight changes in light due to minute defects or the like was difficult with conventional illumination devices because the shape, angle, and size of the illumination solid angle of the inspection light differed for each point on the inspection object surface, but the illumination device according to the present invention makes it possible.

[0027] To substantially uniformly control the size of the illumination solid angle of the inspection light irradiated at each point on the inspection object and adjust the tilt distribution of the illumination solid angle relative to the optical axis center, the first light-shielding mask and the first filter means, or the third filter means that integrates the functions of both, or the relay images of the first light-shielding mask and the first filter means, or the third filter means that integrates the functions of both, may be positioned in front of or behind the focal position of the lens. Hereinafter, referring to the first light-shielding mask as a representative, that is, by changing the opening of the first light-shielding mask, the illumination solid angle at each point on the inspection object can be set to a desired shape and size. Furthermore, if the first light-shielding mask is positioned at the focal position of the lens, the optical axes of the illumination solid angles of the inspection light are all parallel to the optical axis of the inspection light. If the first light-shielding mask is positioned closer to the lens than the focal position of the lens, the illumination solid angle of the inspection light can be tilted in the direction in which the inspection light widens, and if the first light-shielding mask is positioned outside the focal position of the lens, the illumination solid angle of the inspection light can be tilted in the direction in which the inspection light narrows. In this way, by changing the arrangement of the first light-shielding mask and its openings, it is possible to make various adjustments to the illumination solid angle of the inspection light, which directly affects the solid angle of the reflected light or transmitted light from the inspection object, and the relative relationship between the inspection object and the observation solid angle of the imaging device that observes the reflected light, transmitted light, or scattered light from the inspection object can be made suitable for obtaining desired brightness information. In other words, in this way, even if the observation optical system used is not a telecentric optical system but an optical system in which the tilt of the optical axis of the observation solid angle changes between outside the field of view and at the optical axis center, it is possible to set the illumination solid angle and observation solid angle at each point over the entire field of view so that they are in the specular reflection direction.

[0028] Furthermore, any of the solid angle regions having different optical attributes set within the illumination solid angle can be further set as any other solid angle region within the illumination solid angle that is set uniformly for the inspection object. This not only determines the brightness of each point on the inspection object based on the relative relationship between the illumination solid angle and the observation solid angle, but also makes it possible to simultaneously observe even subtler changes in light for each solid angle region as changes in the relative relationship with the observation solid angle under substantially the same conditions at all points within the field of view of the inspection object, without having to reset the relative relationship between the illumination solid angle and the observation solid angle in terms of the shapes, optical axis, etc.

[0029] In this way, in an inspection system comprising an inspection illumination device according to the present invention and an imaging device that uses the inspection illumination device and images light reflected, transmitted or scattered by the inspection object, desired brightness information for minute feature points can be obtained because the brightness at each point of the inspection object is determined by the amount of reflected light, transmitted light or scattered light from each point of the inspection object directed toward the imaging device, and the amount of light is determined by the inclusion relationship between the solid angle of the reflected light, transmitted light or scattered light from each point of the inspection object and the observation solid angle of the imaging device. The imaging device has a function of adjusting the illumination solid angle to be approximately uniform, and divides the illumination solid angle into arbitrary solid angle regions having different wavelength bands, planes of polarization, or light amounts. Furthermore, it forms a plurality of annular solid angle regions that are concentrically arranged within the illumination solid angle and have no adjacent regions. This enables the imaging device to selectively observe the light amount for each divided region of a surface of the object to be inspected, even if the surface normal does not coincide with the observation optical axis, with the same uniform detection sensitivity as for a surface of the object to be inspected, where the surface normal coincides with the observation optical axis.

[0030] In order to make the brightness information of the inspection object imaged by the imaging device show a substantially uniform change throughout the entire imaging range, the inclusion relationship between the observation solid angle formed at each point on the inspection object by the imaging device and the solid angle of the reflected light, transmitted light, or scattered light from each point on the inspection object must be maintained substantially constant. This can be achieved by moving the first light-shielding mask and the first filter means or the third filter means, or the first light-shielding mask and the first filter means or the relay image of the third filter means, back and forth around the focal position of the lens, so that the illumination solid angle of the inspection light and the solid angle region formed within that illumination solid angle have a substantially uniform shape and size, and adjusting the tilt angle to match the tilt of the observation solid angle at each point on the inspection object.

[0031] In order to arbitrarily generate an illumination area, illumination shape, or illumination pattern while maintaining a substantially constant relationship between the illumination solid angle of the inspection light on the inspection object and any solid angle area formed within that illumination solid angle and the observation solid angle for each point in the illumination range, it is sufficient to provide, in addition to at least one of the first light-shielding mask or the first filter means, or the third filter means, at least one of the second light-shielding mask or the fourth filter means, or a fifth filter means having the function of at least one of the second light-shielding mask or the fourth filter means, and place it near the position where the image is formed on the inspection object by the lens. In this way, while maintaining a substantially uniform illumination solid angle of the inspection light and the shape, size, and inclination of any solid angle area formed within that illumination solid angle, it is possible to independently adjust both the illumination area of ​​the inspection light on the inspection object and the optical attributes of that illumination area, and the illumination solid angle and the solid angle area having a specific optical attribute for each point on the inspection object.

[0032] In order to easily inspect the three-dimensional shape of the inspection object, etc., it is sufficient to use the second light-shielding mask and fourth filter means, on which a predetermined mask pattern is formed, in addition to the first light-shielding mask and first filter means, or the third filter means, or a relay image thereof, and to image this pattern onto the inspection object. In this way, the substantially uniform illumination solid angle and the solid angle region having a specific light attribute adjusted by the first light-shielding mask and the first filter means can obtain light-dark information with uniform light-dark changes with the imaging device, and if there is a problem with the shape of the inspection object, distortion will occur in the pattern obtained as light-dark information with the imaging device, making it possible to easily detect shape defects.

[0033] If the solid angle of the reflected or transmitted light at each point on the inspection object and the solid angle of the observation formed by the imaging device at each point on the inspection object are made to approximately match in shape, size, and inclination, the inclusion relationship between the solid angle of the reflected or transmitted light and the solid angle of the observation will change even if the inspection object has a small feature point, and changes in brightness information for the small feature point can be obtained. The rate of change in brightness information due to this change in inclusion relationship can be controlled by appropriately setting the solid angle of the reflected or transmitted light and the size of the solid angle of the observation. However, if left as is, only constant brightness information can be obtained that depends on the size of the solid angles of both. Therefore, if any solid angle region having a different wavelength band, plane of polarization, or light amount is formed within the solid angle of illumination for each point on the inspection object, this will be reflected as a solid angle region having a different wavelength band, plane of polarization, or light amount within the solid angle of the reflected light or the transmitted light from each point on the inspection object. Therefore, if the change in brightness information for the feature point changes depending on the inclusion relationship between the solid angle region reflected within the solid angle of the reflected light or the transmitted light and the observation solid angle, it will be possible to simultaneously detect minute changes corresponding to each of the solid angle regions.

[0034] As an example of how this can be achieved, the observation solid angle of the imaging device is set in a direction that is linearly symmetrical with respect to a normal line erected on the inspection object, with respect to the illumination light path of the illumination solid angle formed by the inspection light on the inspection object, and the reflection / transmission light path of the solid angle formed by the reflected light or transmitted light from each point on the inspection object and the observation light path of the observation solid angle of the imaging device for each point on the inspection object are made to approximately coincide with each other.

[0035] As another example of how to achieve this, a beam splitter is provided to reflect the inspection light to change the direction of its irradiation light path, and transmit the reflected light from the inspection object without changing the direction of the reflected light path so that it can be imaged by the imaging device as an observation light path that enters the observation optical system, or to transmit the inspection light without changing the direction of its irradiation light path, and reflect the reflected light from the inspection object to change the direction of the reflected light path so that it can be imaged by the imaging device as an observation light path that enters the observation optical system, and to appropriately adjust the irradiation solid angle of the inspection light for each point on the inspection object so that the observation solid angle of the imaging device for each point on the inspection object and the optical axis of the solid angle of the reflected light or transmitted light emitted from each point approximately coincide. Furthermore, this beam splitter may be installed so that the illumination light path and the reflection light path, and the illumination light path and the observation light path are aligned and coaxial with respect to the object to be inspected, and so as to perform the function of separating the illumination light path and the observation light path between the first light-shielding mask and the first filter means, or the third filter means, or the relay optical system for forming a relay image thereof, and the object to be inspected.

[0036] Furthermore, by providing the imaging device with a sixth filter means capable of selectively capturing images of light in the solid angle region, which has a different wavelength band, plane of polarization, or amount of light reflected within the solid angle of the reflected light or the transmitted light, it is possible to simultaneously detect changes in brightness that occur due to the inclusion relationship between each of the solid angle regions and the observation solid angle.

[0037] As described above, according to the inspection illumination device and illumination optical system of the present invention, the size and shape of the solid angle areas formed within the illumination solid angle of the inspection light concentrically arranged within the illumination solid angle of each point on the inspection object can be freely adjusted, while maintaining constant sensitivity for detecting the tilt near each point on the inspection object, by using the bright and dark areas that reflect the tilt near each point on the inspection object and the brightness of the intermediate gradations.Therefore, it is possible to uniformly set the inclusion relationship between the solid angle of the reflected light, transmitted light, or scattered light from each point on the inspection object, and the solid angle areas reflected within that solid angle and having different wavelength bands, polarization planes, or light amounts, and the observation solid angle formed at each point on the inspection object by the imaging device, and it becomes possible to detect even minute defects, etc. that were previously difficult to detect, with the same detection sensitivity.

[0038]

[0023] Fig. 1 is a schematic diagram showing components of an inspection illumination device, an illumination optical system, and an inspection system according to a first embodiment of the present invention, and the relationship between the illumination light path and the observation light path, the illumination solid angle, the solid angle of reflected and transmitted light, and the observation solid angle. Fig. 2 is a schematic diagram showing components of an inspection illumination device, an illumination optical system, and an inspection system including a relay optical system according to a second embodiment of the present invention, and the relationship between the illumination light path and the observation light path, the illumination solid angle, the solid angle of reflected and transmitted light, and the observation solid angle. Fig. 3 is a schematic diagram showing components of an inspection illumination device, an illumination optical system, and an inspection system including a beam splitter, and the relationship between the illumination light path and the observation light path, the illumination solid angle, the solid angle of reflected and transmitted light, and the observation solid angle. Fig. 4 is a schematic diagram showing components of an inspection illumination device, an illumination optical system, and an inspection system including a relay optical system and a beam splitter, and the relationship between the illumination light path and the observation light path, the illumination solid angle, the solid angle of reflected and transmitted light, and the observation solid angle. 1 is a schematic diagram showing the components of an inspection illumination device, illumination optical system, and inspection system including a beam splitter, and the relationship between the illumination light path and the observation light path, the illumination solid angle, the solid angle of reflected and transmitted light, and the observation solid angle according to a fifth embodiment of the present invention. 2 is a schematic diagram showing the components of an inspection illumination device, illumination optical system, and inspection system including a relay optical system and a beam splitter, and the relationship between the illumination light path and the observation light path, the illumination solid angle, the solid angle of reflected and transmitted light, and the observation solid angle according to a sixth embodiment of the present invention. 3 is a schematic diagram showing the components of an inspection illumination device, illumination optical system, and inspection system including a relay optical system and a beam splitter, and the relationship between the illumination light path and the observation light path, the illumination solid angle, the solid angle of reflected and transmitted light, and the observation solid angle according to a sixth embodiment of the present invention. 4 is a schematic diagram comparing the illumination solid angle of illumination light. 5 is a schematic diagram showing the change in the relative relationship between the illumination solid angle, the solid angle of reflected light, and the observation solid angle due to the tilt of the inspection object ((a) illumination solid angle formed by a surface light source (b) illumination solid angle in the present invention). (a) Change in the solid angle of reflected light, (b) Change in the inclusive relationship between the solid angle of reflected light and the solid angle of observation) One embodiment of a first light-shielding mask for forming a plurality of annular solid angle regions arranged concentrically so as not to have adjacent portions, a first filter means having solid angle regions with different optical attributes, and a third filter means integrating both.Schematic diagram showing the relative relationship between the solid angle of reflected light and the solid angle of observation due to the tilt of an inspection object in an illumination solid angle having multiple annular solid angle regions arranged concentrically so as not to adjoin each other. Schematic diagram showing the relative relationship between the solid angle of reflected light and the solid angle of observation due to the tilt of an inspection object when an illumination solid angle having multiple annular solid angle regions arranged concentrically so as not to adjoin each other and the observation solid angle are coaxial, and the relationship with the change in brightness of the inspection object.

[0039] A first embodiment of the present invention will be described with reference to FIG. 1. Note that the present invention is not limited to the contents described in the following embodiment. Furthermore, the components in the embodiment described below include those that can be easily imagined by a person skilled in the art, those that are substantially the same, and those that are within the so-called equivalent range. Furthermore, the components disclosed in the embodiment described below may be appropriately combined or appropriately selected for use.

[0040] In the inspection system 200 of the present invention, the inspection illumination device 100 and the illumination optical system 101 irradiate the inspection object W with illumination light through an illumination light path L1, forming an illumination solid angle IS at each point on the inspection object W, and the reflected and transmitted light L2 returned from the inspection object W is captured by the observation optical system K of the imaging device C to capture an image of the inspection object W, and inspection is performed using the image information. In Fig. 1, the observation optical system that captures the transmitted light L2 of the inspection object W is shown as K1 and the imaging device as C1, and the observation optical system that captures the reflected light L2 of the inspection object W is shown as K2 and the imaging device as C2, but the imaging device that captures the reflected light and transmitted light may be either one of them, or both.

[0041] The inspection illumination device 100 and the illumination optical system 101 comprise: a surface light source 1 that emits inspection light; a lens 2 that is provided between the surface light source 1 and the inspection object W, and that forms an illumination solid angle IS for the inspection object with light emitted from the surface light source 1 as inspection light L1 that is irradiated onto the inspection object; and a first light-shielding mask M1 that is provided between the surface light source 1 and the lens 2, in front of and behind the focal position of the lens 2, and that shields and forms the illumination solid angle IS of the inspection light that is irradiated onto each point on the inspection object, the first light-shielding mask M1 being arranged concentrically within the illumination solid angle IS as shown in FIG. 10 described later, and that forms a plurality of annular solid angle regions that are arranged above the concentric circles so as not to have adjacent portions to each other; and the inspection illumination device 100 and the illumination optical system 101 can form the same illumination solid angle IS for each point on the inspection object W, regardless of the distance from the inspection illumination device 100 and the illumination optical system 101 to the inspection object W or the position of each point on the inspection object W, The illumination solid angle IS can be set to have the same relative angle with respect to the observation solid angle OS for each point on the inspection object W formed when the imaging device C captures the reflected and transmitted light L2 from the inspection object W through the observation optical system K.

[0042] In addition, the inspection illumination device 100 and the illumination optical system 101 may further include a first filter means F1 adjacent to the first shading mask M1, which can divide the inspection light into any solid angle region having partially different optical attributes using light of different wavelength bands, different polarization planes, or light having different light amounts, or set the optical attributes to change continuously; and the first shading mask M1 and the first filter means F1 may be a unified third filter means F3 having at least any of the functions thereof as a means for forming a solid angle region and an illumination solid angle.

[0043] Furthermore, between the first light-shielding mask M1 and the surface light source 1, near where the lens 2 forms an image on the inspection object W, at least one of a second light-shielding mask M2 and a fourth filter means F4 that transmits only light with a specific attribute may be further provided, and the second light-shielding mask M2 or the fourth filter means F4 may be capable of arbitrarily generating the irradiation area and irradiation pattern of the inspection light on the inspection object, and further, the second light-shielding mask M2 and the fourth filter means F4 that transmits only light with a specific attribute may be a fifth filter means F5 that has at least the functions of at least one of the second light-shielding mask M2 and the fourth filter means F4. In the explanation of Figure 2 and Figures 3, 4, 5, 6 and 7, the explanation and description of the second light-shielding mask M2, the fourth filter means F4 and the fifth filter means F5 are omitted for simplicity, but in any of the embodiments, the second light-shielding mask M2, the fourth filter means F4 and the fifth filter means F5 may be installed in the same manner as in Figure 1.

[0044] Next, a second embodiment of the present invention will be described with reference to FIG. 2. The first light-shielding mask M1, first filter unit F1, and third filter unit F3 described in FIG. 1 may be disposed between the surface light source 1 and a relay optical system 106 (e.g., lenses arranged in tandem), and a relay image RI formed by the relay optical system 106 may be used instead of the first light-shielding mask M1, first filter unit F1, and third filter unit F3. The relay image RI is a reduced image of the first light-shielding mask M1, first filter unit F1, and third filter unit F3. The positions of the first light-shielding mask M1, first filter unit F1, and third filter unit F3 may also be changeable along the illumination light path L1 (i.e., the relay image RI of the first light-shielding mask M1, first filter unit F1, and third filter unit F3 may be positioned near the focal position of the lens 2).

[0045] The inspection light irradiated onto each point on the inspection object W by the inspection illumination device 100 and the illumination optical system 101 has a constant shape regardless of the position on the inspection object W or the distance from the inspection illumination device 100 and the illumination optical system 101. By adjusting the first light-shielding mask M1, the first filter means F1, and the third filter means F3, which form the illumination solid angle IS, or the relay image RI formed by the relay optical system 106, along the illumination light path L1 near the focal position of the lens 2, the inclination of each illumination solid angle IS relative to the inspection object W can be made constant, or the inclination can be adjusted around the illumination optical axis. Furthermore, the solid angle of illumination thus formed is formed by shaped transmitted light emitted from the lens 2 at an equal angle by the lens 2, the first light-shielding mask M1 arranged near its focal point, the first filter means F1, and the third filter means F3, or the relay image RI formed by the relay optical system 106, and is not necessarily formed by the imaging light formed by the lens 2 from the surface light source 1 onto the inspection object W.

[0046] If the object light returned from the object W is direct light such as specularly reflected light or specularly transmitted light, the shape and size of the illumination light IS are maintained as the solid angle of that object light, and the solid angle DS of this direct light has the same shape as the illumination solid angle IS. Only the light energy contained within the solid angle DS of the direct light is captured within the observation solid angle OS formed at each point on the object by the imaging device, and is captured as the brightness of each point. Therefore, by maintaining the solid angle elements, which are the relative relationships of these solid angles, uniform, changes in the optical properties of the object can be quantitatively reflected in the captured image. The mechanism behind this will be described later.

[0047] FIG. 3 shows a third embodiment of the present invention, in addition to the first embodiment described in FIG. 1 , which includes a beam splitter 4 that reflects the inspection light emitted from a surface light source 1 to change the direction of the illumination light path L1, transmits the reflected light from the inspection object W1 without changing the direction of the reflected light path L2, so that the light can be captured by the imaging device as the observation light path L3 that enters the observation optical system K, or transmits the inspection light without changing the direction of the illumination light path L1, but reflects the reflected light from the inspection object W2 to change the direction of the reflected light path L2, so that the light can be captured by the imaging device as the observation light path L3 that enters the observation optical system K, and the third embodiment of the present invention, in which the illumination solid angle of the inspection light at each point on the inspection object can be appropriately adjusted so that the observation solid angle of the imaging device at each point on the inspection object and the optical axis of the solid angle of the reflected light or the transmitted light emitted from each point are approximately aligned.

[0048] The beam splitter 4 described in FIG. 3 may be installed so that, with respect to the inspection object W, the illumination light path L1 and the reflected light path L2, and the illumination light path L1 and the observation light path L3, are aligned and coaxial, and the illumination light path L1 and the observation light path L3 are separated from the inspection object W by the first light-shielding mask M1 and the first filter means F1 or the third filter means F3, or a relay optical system 106 for forming a relay image RI thereof. The fourth embodiment of FIG. 4 is obtained by adding the relay optical system 106 to the third embodiment, and the fifth embodiment of the present invention shown in FIG. 5 is obtained by arranging the beam splitter 4 between the lens 2 and the first light-shielding mask M1 and the first filter means F1 or the third filter means F3 in the third embodiment, and the sixth and seventh embodiments of the present invention shown in FIGS. 6 and 7 are obtained by adding the relay optical system 106 to the fifth embodiment, and the sixth embodiment is the case where the relay image RI is located on the opposite side of the inspection object from the beam splitter 4. The seventh embodiment is a case where the relay image RI is positioned on the inspection object side of the beam splitter 4, and both embodiments function effectively as embodiments of the present invention.

[0049] In the fifth, sixth and seventh embodiments, the lens 2 or 3 is also used by the imaging device to capture reflected light from the inspection object W through its observation solid angle, and is therefore used to form both the illumination solid angle and the observation solid angle at the same time. When the lens 3 is included in the imaging device as part of the observation optical system, the illumination optical system is the part that includes from the surface light source 1 to the beam splitter 4. Conversely, when the lens 2 is included in the inspection illumination device, the imaging device including the observation optical system also extends up to the beam splitter.

[0050] Furthermore, in the fifth, sixth, and seventh embodiments, lens 2 or lens 3 is used in common by both the illumination optical system and the observation optical system, and therefore, on the observation optical system side, there is a problem that part of the illumination light emitted from the illumination optical system is reflected back toward the observation optical system by lens 2 or lens 3. In a normal coaxial optical system, uniform illumination light is applied to the entire opening, so the reflection from this lens is relatively dark compared to the light reflected from the object to be inspected, and can be ignored if the reflection from the lens is uniform. However, in the present invention, illumination light including a pattern for forming an illumination solid angle is applied by first light-shielding mask M1 and first filter means F1, or third filter means F3, or relay optical system 106, and this pattern is also visible in the reflected stray light reflected from lens 2 or lens 3, so it is necessary to block only the reflected stray light from this lens.

[0051] Therefore, in the fifth, sixth and seventh embodiments, the reflected stray light generated when the illumination light is reflected by the lens is cut by installing a first polarizing filter PL1 on the illumination light path L1 on the side opposite the inspection object of the beam splitter 4, installing a second polarizing filter PL2 on the observation light path L3 on the side opposite the inspection object of the beam splitter 4, and installing a wave plate WS1 or WS2 on the inspection object side of the lens 2 or lens 3. The first polarizing filter PL1 and the second polarizing filter PL2 have their easy transmission axes orthogonal to each other to form a crossed Nichols configuration, thereby cutting the reflected stray light from the lens. The easy transmission axis of the quarter-wave plate WS1 or WS2 is set to the first polarizing filter PL1. When the optical filter PL1 is installed at a 45-degree angle with respect to the easy axis of the first polarizing filter PL1, the light irradiated onto the object under inspection W becomes circularly polarized. The light reflected from the object under inspection, preserving this polarization, passes through the quarter-wave plate WS1 or WS2 again to become linearly polarized light tilted 90 degrees with respect to the easy axis of the first polarizing filter PL1, and can then pass through the second polarizing filter PL2 installed in the observation optical path. As a result, only the stray light reflected from the lens, which is linearly polarized in the easy axis direction of the first polarizing filter PL1, can be cut out, allowing the reflected light from the object under inspection to be observed. Furthermore, if the object light returned from the object under inspection W is scattered light, even if the irradiated light is polarized, it becomes unpolarized and can also pass through the second polarizing filter PL2 installed in the observation optical path. Furthermore, if the easy transmission axis of the quarter-wave plate WS1 or WS2 is installed in the same direction as the easy transmission axis of the first polarizing filter PL1 or tilted 90 degrees, the irradiated light linearly polarized by the first polarizing filter PL1 will be directly irradiated onto the inspection object W. In this case, the reflected light from the inspection object W will remain linearly polarized and will be blocked by the second polarizing filter installed in the observation light path, but the unpolarized scattered light component will be transmitted, allowing only the scattered light from the inspection object to be observed. Note that if only scattered light is to be observed, the quarter-wave plate need not be installed. The first polarizing filter PL1, the second polarizing filter PL2, and the quarter-wave plate WS1 or WS2 are only shown in FIG. 5 and are omitted in FIGS. 6 and 7 for simplicity, but they may be installed in the same manner as in FIG. 5.

[0052] Here, the object light is composed of a fixed ratio of direct light that preserves polarization and unpolarized scattered light components. Compared to the ratio of direct light and scattered light components when unpolarized light is irradiated, the ratio of direct light that is returned with polarization preserved and scattered light that is returned as unpolarized light when irradiated with polarized light and observed through an analyzer that transmits this polarized light is greater due to the law of conservation of energy. In bright-field observation using direct light, the scattered light component often becomes noise. Reducing this component leads to an improved S / N (signal-to-noise ratio) when converting changes in the optical properties of the object W into light brightness information. Although the observation brightness itself is reduced by a polarizing filter, etc., being able to detect changes in the optical properties of the object W with a higher S / N is advantageous, especially when the changes are subtle.

[0053] The relative relationship between the illumination solid angle IS, the solid angle DS of direct light such as specularly reflected light and specularly transmitted light that reflects this illumination solid angle IS directly and returns from the object, and the observation solid angle OS is called a solid angle element, and in a bright field that captures the brightness and darkness of direct light, the brightness and darkness profile of the image changes depending on this solid angle element. The brightness of the inspection object W in response to its tilt in a bright field is determined by the planar half angle θi of the illumination solid angle IS and the planar half angle θo of the observation solid angle OS, and the maximum detectable tilt angle of the inspection object W is ½ of θi + θo. If an imaging device C that outputs 8-bit gradations of brightness between these two angles is used, the theoretical detection sensitivity for the tilt of the inspection object W is ½ of θi + θo. For example, if θi and θo are each 1 degree, a 1x lens is used, and an optical sensor with 3.45 μm square pixels per pixel is used, using visible light under the imaging conditions of a normal camera, and light is irradiated with the inspection illumination according to the present invention, the theoretical detection resolution for the tilt of the inspection object W is 0.0039 degrees, and the theoretical resolution in the depth direction is 0.24 nm. This is an incredible value that already exceeds the Rayleigh diffraction limit, with a horizontal resolution of at most 3.45 μm, the pixel size. By observing with visible light using a normal camera, and taking normal images without using a microscope or anything else, the resolution is more than 1,000 times that of a regular microscope, which is already at the level of an electron microscope.

[0054] Therefore, when observing the inspection object W using the present invention, a brightness accuracy of approximately 1 / 1000th that of normal observation is required, so it is necessary to minimize stray light within the observation optical system, and a mechanism for cutting stray light by combining the crossed Nichols polarizing filter and a quarter-wave plate is essential.

[0055] Next, using Figures 8 and 9, we will explain the relationship between the illumination solid angle IS and the solid angle RS of reflected light, which is the solid angle DS of object light returned from the inspection object W at the same solid angle as the illumination solid angle.

[0056] In the present invention, the first light-shielding mask and the first filter means or the third filter means form multiple annular solid angle regions arranged concentrically so that no adjacent regions are adjacent to each other, and the optical attributes of these regions can be freely changed. This allows the illumination light to be irradiated under the same conditions at all positions throughout the entire field of view of the inspection object W imaged by the imaging device C, and the illumination optical axis and illumination solid angle can be set to a state suitable for the optical characteristics of the imaging device. Figure 8(a) shows the illumination solid angles IS, IS' at different positions P, P' on the inspection object W when illuminated with a surface light source 1, which is a typical conventional illumination source. It can be seen that the shape of the illumination solid angle and the optical axis are different between the two. Figure 8(b) shows the illumination light according to the present invention, which allows the illumination solid angle to be formed under the same conditions not only at different positions P, P' on the inspection object W but also at all positions throughout the field of view of the inspection object W. This can be expected to have a significant effect, particularly in bright-field illumination, which observes reflected light returned from the inspection object W or direct light transmitted through it. Here, reflected light refers to specularly reflected light returned from a mirror surface or the like, and transmitted light refers to specularly transmitted light that passes through a transparent object. Also, in dark-field illumination, which observes scattered light, much of the scattered light changes depending on the optical attributes of the light being irradiated and the solid angle of illumination, making it possible to detect minute changes in the optical properties of the inspection object W that could not be achieved with conventional illumination.

[0057] FIG. 9A focuses on a point P on the inspection object W, and considers a case where inspection light having an irradiation solid angle IS is irradiated onto the point P. When the surface including the point P of the inspection object is partially tilted by φ, how the brightness of the point P changes is shown. This shows the relative relationship of each solid angle when the solid angle RS1 of the reflected light from the point P changes to a solid angle RS2 with respect to the observation solid angle OS formed at the point P by the imaging device C.

[0058] In Figure 9(a), the shape and size of the solid angles RS1 and RS2 of the reflected light from point P are equal to the illumination solid angle IS of the inspection light relative to point P. The inclination of the solid angle RS1 of the reflected light is the same as the inclination θ of the illumination solid angle IS of the inspection light, in a direction that is symmetrical to the illumination solid angle IS of the inspection light with respect to the normal to point P. In this case, if the observation solid angle OS formed by the imaging device C at point P is aligned with the optical axis of the solid angle RS1 of the reflected light and is very small compared to the solid angle RS1 of the reflected light, the brightness of point P captured by the imaging device C is limited by the size of the observation solid angle OS and does not change even if the solid angle RS1 of the reflected light is tilted to the extent that this inclusion relationship remains unchanged. However, it is assumed that the light energy within the illumination solid angle IS and the solid angles RS1 and RS2 of the reflected light is uniformly distributed within those solid angles.

[0059] 9(a) and 9(b), if we consider a case where the plane including point P of the inspection target W is partially tilted by φ, the solid angle RS1 of the reflected light from point P will be tilted by 2φ as shown by RS2 indicated by the dotted line in the figure. In this case, if the solid angle RS2 of the reflected light from point P does not have any inclusion relationship with the observation solid angle OS formed by the imaging device C with respect to point P, the brightness of point P as seen from the imaging device C will be 0, but if there is a partial inclusion relationship with the observation solid angle OS formed by the imaging device C with respect to point P, the light included in the solid angle portion where the two overlap will be reflected as the brightness of point P. That is, if the planar half angle θi of the solid angle RS2 of the reflected light from point P is greater than the angle obtained by subtracting the planar half angle θo of the observation solid angle OS from the inclination angle 2φ of the reflected light and is smaller than the angle obtained by adding the planar half angle θo of the observation solid angle OS to the inclination angle 2φ of the reflected light, the brightness of point P changes depending on the inclination angle 2φ of the reflected light. However, if the planar half angle θi of the illumination solid angle IS is greater than the angle obtained by adding the inclination angle 2φ of the reflected light caused by a partial tilt of the object W to the planar half angle θo of the observation solid angle OS, the brightness of point P does not change. Also, if the planar half angle θo of the observation solid angle OS is greater than the angle obtained by adding the inclination angle 2φ of the reflected light to the planar half angle θi of the solid angle RS of the reflected light, the brightness of point P also does not change. This means that the brightness of point P is ultimately determined by the inclusion relationship between the solid angle RS of the reflected light from point P and the solid observation angle OS relative to point P, and that changes in the brightness of point P can be controlled by setting the relative relationship in terms of shape, size, and inclination between the solid angle IS of the illumination light irradiated onto point P and the solid observation angle OS relative to point P.

[0060] Here, the larger the sum θi + θo of the planar half angles of the illumination solid angle IS and the observation solid angle OS, or the larger the absolute value |θi - θo| of the difference between the planar half angles of the illumination solid angle IS and the observation solid angle OS, the smaller the sensitivity to changes in tilt of the inspection object W, i.e., the amount of change when the tilt angle is captured as a change in brightness of point P. In other words, in order to detect slight tilts of the inspection object W with high sensitivity, the smaller the sum θi + θo of the planar half angles θi + θo of the illumination solid angle IS and the observation solid angle OS, or the smaller the absolute value |θi - θo| of the difference between the planar half angles of the illumination solid angle IS and the observation solid angle OS, the better. However, if this is done, it will not be possible to capture the object light returned from the inspection object W in areas where the tilt of the inspection object W is greater than 1 / 2 of the sum θi + θo of the planar half angles of the illumination solid angle IS and the observation solid angle OS.As a result, even though the sensitivity to the tilt of the inspection object W is increased, the detection field of view range for the inspection object W will be narrowed.

[0061] Figure 9(b) is a cross-sectional view of the plane containing the illumination optical axis of the inspection light, the normal to point P, and the reflected optical axis from point P in Figure 9(a), allowing for a more quantitative understanding of the tilt of each element and its inclusion relationship. However, Figure 9(b) illustrates a case in which the observation solid angle OS is larger than the illumination solid angle IS, i.e., the solid angle RS1 of the reflected light. If the inspection object W is tilted and the solid angle RS1 of the reflected light from point P becomes RS2, as shown by the dotted line, the inclusion relationship with the observation solid angle OS disappears in this figure, and the light energy within the observation solid angle OS becomes zero. Therefore, even if the light contained within this observation solid angle OS is refocused and imaged at a point, point P appears completely dark. However, even in this case, if the relative relationship between the illumination solid angle IS and the observation solid angle OS is adjusted to create an inclusion relationship between the solid angle RS of the reflected light and the observation solid angle OS, the brightness of point P will change according to the size of the overlapping area.

[0062] 9(b), if the shape and size of the observation solid angle OS are the same as the illumination solid angle IS and match the inclination of the solid angle RS of reflected light from point P, then tilting the object of inspection W even slightly from that state will reduce the overlap between the observation solid angle OS and the solid angle RS of reflected light by at least that much, thereby changing the brightness of point P as seen through the observation solid angle OS. Furthermore, the smaller each solid angle, the greater the change in brightness of point P when the object of inspection W is tilted by the same angle; conversely, the larger each solid angle, the smaller the change in brightness of point P when the object of inspection W is tilted by the same angle. Furthermore, by appropriately setting the shape, size, and inclination of the illumination solid angle IS and the observation solid angle OS in accordance with the change in light occurring at a desired feature point on the object of inspection, it becomes possible to accurately detect feature points that previously could not be detected reliably. In the present invention, attention is paid to this principle, and as will be described later, the shape of the illumination solid angle is made to include a plurality of concentric annular solid angle regions that are arranged so that there are no adjacent portions, and the inclusion relationship between these annular solid angle regions and the observation solid angle OS is kept constant even in parts of the inspection object W where the inclination is greater, thereby making it possible to maintain sensitivity to inclination.

[0063] Next, an embodiment of the first light-shielding mask M1, the first filter means F1, and the third filter means F3 will be described with reference to FIG.

[0064] As shown in FIG. 10A, the first light-shielding mask M1 has light-shielding portions M11, M12, and M13 that almost completely block light, forming non-adjacent annular openings T1, T2, and T3. While FIG. 10A illustrates the light-shielding portion M13 at the periphery and the opening at the center, the center may be the light-shielding portion instead. Alternatively, the light-shielding portion may be a portion that blocks only light with a specific attribute. As shown in FIG. 10B, the first filter means F1 has patterns F11, F12, and F13 that form three solid angle regions with different light attributes. Here, the patterns are radial, centered on the optical axis, but they may also be optimized to any pattern depending on the feature of interest of the inspection object. The first light-shielding mask M1 and the first filter means F1 are integrated into the third filter means F3 shown in Figure 10(c), and the non-adjacent annular solid angle regions T1, T2, and T3 shown in (a) are each divided into three portions F11, F12, and F13 with different optical attributes, making it possible to determine the direction in which the inspection object is tilted. Note that the optical attributes of the three portions F11, F12, and F13 with different optical attributes may change continuously, or the optical attributes may change for each annular transparent portion.

[0065] FIG. 11 shows the relationship between the reflected light RS1 and RS2 and the observation solid angle OS formed at point P by the imaging device C when an illumination solid angle having a plurality of concentric annular solid angle regions arranged so as not to adjoin each other is formed at point P on the inspection object W. FIG. 11(a) shows the case where the illumination solid angle IS and the observation solid angle OS are in the regular reflection direction with respect to the inspection object W, and the observation solid angle OS has an inclusive relationship with the bright part at the center of the illumination solid angle, and point P is observed as bright. However, in FIG. 11(b), when the inspection object W is tilted by φ, the solid angle RS2 of the reflected light that is reflected while maintaining the solid angle IS of the irradiated light is tilted by 2φ with respect to the solid angle RS1 of the reflected light that was reflected in the specular direction in FIG. 11(a). As a result, the observation solid angle OS is also tilted by 2φ with respect to the optical axis. In the example shown in FIG. 11(b), the observation solid angle OS is included in an annular solid angle region that is formed concentrically within the solid angle RS2 of the reflected light, and the brightness of point P becomes darker accordingly.

[0066] 12 shows the relationship between the solid angle RS of the reflected light returned from the inspection object W and the observation solid angle OS when the beam splitter is used to form an illumination solid angle having a plurality of concentric annular solid angle regions arranged so as not to adjoin each other at point P on the inspection object W, and when the illumination optical axis of the illumination solid angle is coaxial with the observation optical axis of the observation solid angle OS formed at point P by the imaging device C. It also shows how the brightness of point P varies with the inclination of the inspection object W. In FIG. 12, the planar half angle θi of the bright portion solid angle region at the center of the illumination solid angle is set equal to the planar half angle θo of the observation solid angle OS, and the width of the bright portion annular solid angle regions arranged concentrically within the illumination solid angle and the dark portion annular solid angle region between adjacent bright portion annular solid angle regions is set to twice the planar half angle θo of the observation solid angle OS, i.e., 2θo.

[0067] 12A shows a state in which the normal to the surface near point P of the inspection object is aligned with the illumination optical axis and the observation optical axis, at which point P is at its maximum brightness. As the inspection object W is tilted, the brightness of point P gradually decreases as shown in (b). When the inspection object W is tilted to an angle θo, the observation solid angle OS overlaps with the dark annular solid angle region within the solid angle of the reflected light RS that reflects the illumination solid angle IS, as shown in (c), and the brightness of point P reaches its minimum. As the inspection object W is further tilted, via (d), and the tilt reaches 2θo, the observation solid angle OS overlaps with the bright annular solid angle region within the solid angle of the reflected light RS that reflects the illumination solid angle IS, as shown in (e), and the brightness of point P returns to its maximum value. During this time, the brightness of point P changes almost linearly with respect to the tilt of inspection object W, and alternates from the maximum value to the minimum value and from the minimum value to the maximum value each time the tilt of inspection object W becomes an integer multiple of θo. After the tilt exceeds half the sum θi + θo of the planar half angle θi of the illumination solid angle and the planar half angle θo of the observation solid angle, the inclusion relationship between illumination solid angle IS and observation solid angle OS is lost, and the brightness of point P remains at its minimum value.

[0068] Each element will be described in detail below.

[0069] The surface light source 1 may be one having one or more chip-type LEDs, an organic electroluminescent (EL), a sidelight, or a light guide plate. The position of the surface light source 1 may be changeable along the illumination optical axis L1. A uniform illumination solid angle IS can be formed by the lens 2 via a first light-shielding mask M1, a first filter means F1, and a third filter means F3, which are arranged near the focal position of the lens 2 and before and after the focal position of the lens 2, regardless of the distance to the inspection object W. The light forming this illumination solid angle IS is composed of light emitted from each point on the surface light source. The point from which the light is emitted is determined by the distance from the lens 2 on the illumination optical axis L1 and the distance and direction perpendicular to the illumination optical axis L1. This also varies depending on the distance between the surface light source 1 and the lens 2. However, for all illumination solid angles IS, the bundle of rays forming one illumination solid angle is not necessarily light emitted from a single point on the surface light source. If a bundle of rays forming a certain illumination solid angle is formed by a bundle of rays emitted from a single point on the surface light source 1, the position at which the illumination solid angle is formed is the position at which the surface light source 1 is imaged by the lens 2. The illumination solid angle used in the present invention is not limited to the bundle of rays at the image-forming position, but if it also includes bundles of rays emitted from multiple points on the surface light source, a more uniform illumination solid angle can be formed without reflecting uneven brightness of the surface light source.

[0070] Furthermore, by configuring the portion of the illumination light path L1 from the surface light source 1 to the first light-shielding mask M1 and the first filter means F1 or the third filter means F3 with a flat panel display such as an LCD monitor device that combines a white light source with a color LCD or the like that can dynamically change the emission wavelength distribution, luminance distribution, and polarization state distribution of the illumination surface, it becomes possible to accommodate even more types of inspection objects, and by doing so, it becomes possible to control the display in real time and form various illumination solid angles, making it possible to construct inspection lighting and illumination optical systems, and ultimately inspection systems, that have a greater degree of freedom in optimization.

[0071] The relay optical system 116 is, for example, a refractive lens system that transmits illumination light that has passed through the first light-shielding mask M1 and the first filter means F1 or the third filter means F3, and may be composed of a single lens or multiple lenses. Note that the lens may be a concave-convex lens or a gradient index lens.

[0072] The first light-shielding mask M1 and the first filter means F1 or the third filter means F3 for forming an illumination solid angle with respect to the lens 2 are optical elements that determine the numerical aperture of the illumination optical system, and since the lens 2 is a nearly telecentric optical system on the side of the inspection object W, they are arranged near the focal position of the lens 2 on the side opposite to the inspection object. In the fifth, sixth, and seventh embodiments, however, in order to function as an objective lens of the observation optical system as well, an aperture stop that forms an observation solid angle is installed near the focal position of the lens 2 on the side opposite to the inspection object, which is the same as the illumination system. Therefore, this focal position is set to the position of the beam that separates the illumination optical axis and the observation optical axis. On the side of the splitter 4 opposite the object to be inspected, an aperture stop can be installed separately from the first light-shielding mask M1 and the first filter means F1 or the third filter means F3 for forming the illumination solid angle, which determine the numerical aperture of the illumination system, i.e., the size, shape, pattern, etc. of the illumination solid angle. However, if the focal position of the lens 2 is on the side of the beam splitter to be inspected, a relay optical system can be used to form a relay image for forming the illumination solid angle on the inner diameter part of the aperture stop at the same position as the aperture stop that determines the size and shape of the observation solid angle, and it is possible to freely form the illumination solid angle within that range.

[0073] If the planar half angle of the solid angle region that forms the central opening of the illumination solid angle IS formed by the first light-shielding mask M1 is the same as the planar half angle θo of the observation solid angle OS, the reflected light RS, which has the same solid angle as the illumination solid angle, will be tilted with respect to the tilt of the inspection object W, and the area included by the observation solid angle OS and the central solid angle region of the reflected light RS will necessarily change, resulting in the condition with the highest tilt detection sensitivity. Furthermore, the smaller the planar half angle θo of the observation solid angle, the higher the detection sensitivity. To maximize the change in brightness of the observation luminance with respect to the tilt of the inspection object W, a concentric, annular, light-shielding solid angle region is provided outside the central opening, and the width of the light-shielding region is twice the planar half angle θo of the observation solid angle OS. If this width is twice the planar half angle θo of the observation solid angle OS, then when the inspection object W is tilted by θo, the observation solid angle OS will be completely within the solid angle region that serves as the light-shielding region, regardless of the direction of tilt. Therefore, the light energy captured by the observation solid angle will be minimized, and the change in brightness will be maximized. Furthermore, if a concentric, annular, opening solid angle region is provided outside the light-shielding region, and the width of the opening is twice the planar half angle θo of the observation solid angle OS, then when the inspection object W is tilted further by θo, the observation solid angle OS will be completely within the solid angle region that serves as the opening. Therefore, the light energy captured by the observation solid angle will be maximized, and the change in brightness will be maximized, resulting in the same brightness as when the observation solid angle OS coincides with the optical axis of the solid angle RS of the reflected light. Thereafter, if the annular solid angle regions of the light-shielding portion and the opening are arranged concentrically with the same width, the change in brightness relative to the tilt of the inspection object W will be repeated with the same sensitivity until the tilt of the inspection object W exceeds 1 / 2 of the sum θi + θo of the planar half angle θi of the illumination solid angle and the planar half angle θo of the observation solid angle. Once the tilt of the inspection object W exceeds 1 / 2 of the sum θi + θo of the planar half angle θi of the illumination solid angle and the planar half angle θo of the observation solid angle, the observation solid angle OS will reach its minimum brightness even if the inspection object is tilted any further, because it will not be able to capture light energy from the solid angle RS of the reflected light from the inspection object W.Therefore, if the width of the dark areas, which are the light-shielding portions of the first light-shielding mask M1, and the light areas, which are the unshielded openings, are twice the planar half angle θo of the observation solid angle OS, and if annular openings and annular light-shielding portions are formed at equal intervals in a concentric pattern, and the central portion is formed as an opening having the same planar half angle as the planar half angle θo of the observation solid angle OS, then the detection sensitivity for the tilt of the inspection object W can be set to the most uniform and highest sensitivity for that observation solid OS.

[0074] In the first light-shielding mask M1, the center portion may be a light-shielding portion having a planar half angle equal to the planar half angle θo of the observation solid angle OS, and the outer portion may be a concentric ring-shaped opening portion having a width of 2θo, and the outer portion may be a concentric ring-shaped light-shielding portion having a width of 2θo, and so on, alternately arranged in the same manner up to the planar half angle θi of the illumination solid angle IS. Furthermore, by keeping the spacing between the light-shielding portion and the opening portion the same and varying its width, it is possible to change the region in which brightness changes with tilt, or to change the minimum brightness to a constant brightness, and further to change the degree of change in brightness with tilt of the inspection object W. Furthermore, the spacing between the light-shielding portion and the opening portion may be varied, and the inclusion relationship with the observation solid angle OS may be set arbitrarily within any angle range.

[0075] 200: Inspection system 100: Inspection illumination device C: Imaging device C1: Imaging device (used under different conditions as shown in the same figure) C2: Imaging device (used under different conditions as shown in the same figure) K: Observation optical system K1: Observation optical system (used under different conditions as shown in the same figure) K2: Observation optical system (used under different conditions as shown in the same figure) 1: Surface light source 11: Light exit surface 2: Lens 3: Lens (used under different conditions as shown in the same figure) 4: Beam splitter L1: Irradiation optical path L2: Reflection / transmission optical path (object optical path) L3: Observation optical path (observation optical axis) M1: First light-shielding mask M11: Light-shielding portion of first light-shielding mask M12: Light-shielding portion of first light-shielding mask M13: Light-shielding portion of first light-shielding mask F1: First filter means F11 : Portion of first filter means that transmits light having a certain optical attribute 1 F12: Portion of first filter means that transmits light having a certain optical attribute 2 F13: Portion of first filter means that transmits light having a certain optical attribute 3 F2: Second filter means (in imaging device) F3: Third filter means M2: Second light-shielding mask F4: Fourth filter means F4: Fifth filter means 106: Relay optical system RI: Relay image R1: Relay image (used under different conditions in the same figure) R2: Relay image (used under different conditions in the same figure) W: Inspection object W1: Inspection object (used under different conditions in the same figure) W2: Inspection object (used under different conditions in the same figure) P: A certain point on inspection object W P': Another point on inspection object W φ: Tilt angle of inspection object IS: Illumination solid angle IS' : Another solid angle of illumination θi : Planar half angle of the solid angle of illumination OS : Observation solid angle θo : Planar half angle of the solid angle of observation RS : Solid angle of reflected light RS1 : Solid angle of reflected light (used under different conditions in the same figure) RS2 : Solid angle of reflected light (used under different conditions in the same figure)

Claims

1. An inspection lighting device that irradiates an inspection object with inspection light, comprising: a surface light source that emits the inspection light; a lens that is provided between the surface light source and the inspection object and that irradiates the inspection object with light emitted from the surface light source, and that forms an illumination solid angle for each point on the inspection object; and a first light-shielding mask that is concentrically arranged within the illumination solid angle and forms a plurality of annular solid angle regions that have no adjacent portions, or a relay image of the first light-shielding mask that is provided between the surface light source and the lens, and that can simultaneously form the same illumination solid angle for each point on the inspection object regardless of the distance from the lens and the position of each point on the inspection object.

2. An inspection lighting device as claimed in claim 1, wherein a first filter means, or a third filter means integrating the functions of the first light-shielding mask and the first filter means, or a relay image of the first light-shielding mask and the first filter means, or a relay image of the third filter means is disposed between the surface light source and the lens, and which can further form a solid angle region having specific optical attributes within the irradiation solid angle.

3. An inspection lighting device as claimed in claim 1 or 2, further comprising at least one of a second light-shielding mask and a fourth filter means, or a fifth filter means combining the functions of the second light-shielding mask and the fourth filter means, between the surface light source and the lens, and capable of arbitrarily setting the irradiation area, irradiation shape, irradiation pattern, or light attributes of the inspection light for the inspection object.

4. An inspection illumination device according to any one of claims 1 to 3, further comprising an imaging device for capturing an object light returned from the inspection object to capture an image, the illumination solid angle being set to have the same relative angle as an observation solid angle formed by the imaging device at each point on the inspection object in order to capture the object light.

5. An inspection illumination device according to any one of claims 1 to 4, comprising, on the inspection object side of the lens, the illumination light path and the reflected light path of the light reflected from the inspection object are coaxial with each other, and the lens is provided with a beam splitter which separates the illumination light path from the reflected light path.

6. An inspection illumination device according to any one of claims 1 to 4, comprising a beam splitter on the opposite side of the lens to the inspection object, the beam splitter making the illumination light path coaxial with the reflection light path of light reflected from the inspection object, and a beam splitter separating the illumination light path from the reflection light path for the first light-shielding mask.

7. An inspection illumination device as claimed in claim 6, in which a first polarizing filter is provided on the side of the illumination light path input to the beam splitter, and a second polarizing filter is provided on the side of the reflected light path output from the beam splitter, and the easy transmission axes of the first polarizing filter and the second polarizing filter are set to be perpendicular to each other.

8. An inspection illumination device according to claim 7, further comprising a quarter-wave plate on the inspection object side of said lens.

9. An inspection illumination device according to any one of claims 1 to 8, comprising an imaging device which images light reflected, transmitted or scattered by the inspection object, or an illumination optical system incorporated in the observation optical system thereof which irradiates the inspection object with inspection light.

10. An inspection system comprising an inspection lighting device according to any one of claims 1 to 8 and an imaging device which images the light reflected, transmitted or scattered by the inspection object, characterized in that, in the inspection light irradiated to the inspection object by the inspection lighting device, the shape, size or inclination of the illumination solid angle at each point of the inspection object can be set based on the shape, size or inclination of the observation solid angle at each point of the inspection object of the imaging device, or the illumination solid angle and the shape, size or inclination of the observation solid angle can be set to be approximately the same relative to each other.

Images