JP2002005639A - Apparatus for inspecting surface - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent lowering of the resolution of an optical system used in a surface inspection apparatus. SOLUTION: When the surface state of a specimen 4 is detected by having the surface of the specimen 4 irradiated with a light source 10 and lenses 11-13, receiving a plurality of reflected light 25a, 25b and 25c, having a different reflection angle range using lenses 21-23 and a trihedral prism 24, and picking up a plurality of images by means of light-receiving elements 25a, 25b and 25c, resolution is prevented from lowering by setting the aperture angle of illumination light irradiated via the light source 10 and lenses 11-13 larger than that of a focusing system.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a surface inspection apparatus for optically detecting slight irregularities on a planar surface of a metal plate, a film, or the like, and more particularly to an improvement of an optical system thereof.

[0002]

2. Description of the Related Art As an inspection apparatus of this kind, the applicant has previously proposed an inspection apparatus disclosed in Japanese Patent Application Laid-Open No. Hei 11-201913 (hereinafter also referred to as a proposed apparatus). FIG. 4 shows a main part of the embodiment. This method depends on the surface condition of the subject,
Using the fact that the angular distribution of the reflected light intensity from the subject surface changes from the angular distribution of the illumination light intensity applied to the subject surface, the same location on the illuminated subject surface has a different angular range from each other. This is to detect and change the angular distribution of reflected light intensity by receiving and imaging a plurality of reflected light, and by combining and processing the captured images, the unevenness, reflectivity and roughness of the surface of the subject are processed. Can be tested.

That is, the illuminating means for illuminating the surface of the subject includes a light source 10, a lens 11, a lens 12, a lens 13, and a diffusion plate 14, and light emitted from the light source 10 passes through the lens 11 and the diffusion plate 14 to a predetermined position. And the portion transmitted through the splitter 30 through the lenses 12 and 13 illuminates the surface of the subject 4 via the objective lens 31. The angular distribution of the intensity of the illumination light 15 illuminating the surface of the subject 4 is determined from the spatial intensity distribution of the illumination light 15 on the diffusion plate 14 at the light source-side focal position of the lens 12. The reflected light 26 from one portion of the surface of the subject 4 passes through the objective lens 31 and is reflected by the splitter 30 again. The portion is once converged by the lens 23 of the imaging means, and further refracted by the lens 22 into parallel light. Followed by 3
The plane prism 24 splits the light into light beams traveling in different directions depending on the incident position.

Since the entrance / exit surface of the three-sided prism 24 is configured to be perpendicular to the zx plane of the coordinate system in the figure, any light incident on the three-sided prism 24 is parallel to the zx plane of the coordinate system in the figure. In a different direction. These light beams are all transmitted through the lens 2
1, the light is condensed and formed on the light receiving surfaces of the respective light receiving elements 20a, 20b, 20c. The luminous flux affecting these images is 3
Before being split by the surface prism 24, the light fluxes 25a, 25b, and 25c of the reflected light 26 from the surface of the subject that have different reflection angles are included. In other words, a plurality of images obtained by imaging the same location on the surface of the subject with reflected light in different angular ranges from each other are obtained from the respective light receiving elements 20a, 20b, and 20c by the imaging means having the imaging lens system as shown in the figure. In the example shown in FIG. 4, the reflected light from the surface of the subject is divided into three by the three-sided prism 24 and received by the corresponding three light receiving elements. That is, a polygon mirror may be used, or a polygon mirror or a diffraction grating may be used. Further, they are installed at a position to be the aperture stop of the imaging lens system in the same manner as in the case of the above-mentioned proposed device.

[0005]

In the configuration as shown in FIG. 4, the aperture of the optical system relating to the imaging of the image pickup means is provided on each surface of the polygonal prism which splits the light beam. Since the aperture angle of the removed imaging optical system is divided, the aperture angle is smaller than that of the imaging optical system excluding the polygonal prism (without the polygonal prism). In general, since the spatial resolution of the imaging optical system is determined by the size of the aperture angle, in this case, the resolution in the direction in which the aperture is divided is lower than in the case where the imaging system is used without a polygonal prism. This is a limitation in improving the resolution of this device. In the configuration of FIG. 4, the speed can be increased by simultaneously imaging a plurality of linearly arranged portions on the surface of the subject using a line sensor having a plurality of linearly arranged light receiving surfaces as light receiving elements. However, for that purpose, the illumination light applied to the surface of the subject needs an illumination range that covers a portion to be imaged, and the angular distribution of the intensity is desirably uniform within the imaging range. Therefore, a first object of the present invention is to improve the resolution by eliminating the above-mentioned restrictions, and a second object is to obtain uniform illumination light within an imaging range. It is in.

[0006]

According to the first aspect of the present invention, there is provided an illumination unit for illuminating a surface of an object, an imaging unit for imaging an illuminated surface of the object, and An illumination lens and one objective lens shared by the imaging means; and the imaging means is constituted by one or a plurality of lenses and generates an image of the surface of the subject; A polyhedral prism, polygon mirror, or diffraction grating that is disposed in the middle of the image lens system and splits an incident light beam into a plurality of light beams having different traveling directions, and a plurality of light receiving elements arranged at an image forming position for each of the branched light beams The reflected light intensity, which varies according to the surface state, by obtaining images with reflected light included in the same incident surface and different reflection angle ranges for the same spot on the surface of the subject. In a surface inspection device that detects an angular distribution, an angular distribution range of an illumination light intensity applied to the object surface via the objective lens by the illumination unit is such that the angle distribution range is in a direction along the incident surface by the imaging unit. It is characterized in that it has a size equal to or larger than 1/2 of the aperture angle of the objective lens. According to the first aspect of the present invention, the polyhedral prism, the polyhedral mirror, or the diffraction grating can be arranged at a position to be an aperture stop of the imaging lens system (the invention of the second aspect).
In the invention according to the second aspect, the angle distribution of the intensity of the illumination light applied to the surface of the subject includes the objective lens in a direction along the incident surface including mutually different angular ranges in which the imaging unit looks at the surface of the subject. (The invention of claim 3).

[0007] Illumination means for illuminating the surface of the subject, imaging means for imaging the surface of the illuminated subject, and one objective lens shared by the illumination means and the imaging means, further comprising: the imaging means Is an imaging lens system composed of one or a plurality of lenses and generates an image of the surface of the subject, and is arranged in the middle of the imaging lens system and splits an incident light beam into a plurality of light beams having different traveling directions. A polygonal prism or polygonal mirror or diffraction grating, and a plurality of light receiving elements arranged at an image forming position for each of the branched light fluxes. In a surface inspection device that detects an angle distribution of the reflected light intensity that changes according to the surface state by obtaining an image by reflected light in an angle range, the light receiving elements are respectively A plurality of light-receiving surfaces arranged in a line, and a linear visual field imaged on the plurality of light-receiving surfaces is disposed so as to be in a direction orthogonal to the incident surface on the surface of the subject; Is provided with a lens system including a cylindrical surface, and becomes critical illumination on the incident surface by the imaging means, and becomes Koehler illumination on a surface orthogonal to the incident surface and including a linear visual field of the light receiving element. It is characterized by comprising.

[0008]

FIG. 1 is a configuration diagram showing a first embodiment of the present invention. Illumination means for irradiating the surface of the subject includes a light source 10, a lens 11, a lens 12, and a lens 13.
The light emitted from the light source 10 passes through the lens 11 through the lens 13 and passes through the splitter 30 to illuminate the surface of the subject 4 via the objective lens 31 as in FIG. Accordingly, here, the angular distribution range of the intensity of the illumination light 15 (see FIG. 4) irradiating the surface of the subject 4 along the zx plane of the coordinate system shown in FIG.
1 light source 1
The feature is that the arrangement from 0 to the objective lens 31 and the specifications of each lens are determined.

For example, if the focal length f of the objective lens 31 is 2
mm, the numerical aperture NA is 0.73, and the lens barrel length is corrected to infinity, the full aperture angle θ is θ = 2 sin ⁻¹ (NA) = 94.
°, the diameter w of the aperture on the incident side is w = 2 · f · NA = 2.9.
Assuming that the diameter d of the light beam entering the objective lens 31 from the lens 13 is 2.0 mm, the coordinate system shown in FIG. 1 of the intensity of the illumination light 15 (see FIG. 4) applied to the subject 4 is 2 mm. Of the angular distribution along the zx plane is φ = sin ^-1
(D / 2f) = 60 °, which is equal to or more than 開口 of the total opening angle width θ of the objective lens 31.

The reflected light 26 from one location on the surface of the subject 4
4 (see FIG. 4), the portion reflected by the splitter 30 again through the objective lens 31 is once converged by the lens 23 of the imaging means, further refracted by the lens 22 so as to become parallel light, and subsequently by the three-sided prism 24. Are split into light beams that travel in different directions depending on the incident position.
Here, the entrance / exit surface of the three-sided prism 24 is perpendicular to the zx plane of the coordinate system shown in FIG.
Any light incident on the coordinate system is deflected in a direction parallel to the zx plane of the coordinate system. All of these light beams are condensed by the lens 21 on the light receiving surfaces of the respective light receiving elements 20a, 20b, and 20c to form an image. Before being split by the three-sided prism 24, the light flux contributing to these images is reflected light 26 from the subject surface.
Since the light beams 25a, 25b, and 25c in the ranges of the different reflection angles in FIG. 4 are different from each other, a plurality of images obtained by imaging the same portion of the surface of the subject with the reflected lights in the different angle ranges are different from each other. Obtained from the output of the device.

Here, assuming that the image forming optical system including the objective lens 31 to the lens 21 is configured such that the aperture stop of the system without the three-sided prism 24 is determined by the aperture angle of the objective lens, 3 The resolution δ of the imaging optical system without the plane prism 24 is such that the wavelength λ of the illumination light 15 (see FIG. 4) is 650 nm and the numerical aperture NA of the objective lens 31 is 0.7.
If it is 3, δ = 0.61 · λ / NA = 0.53 μm. However, if the three-sided prism 24 is provided, the aperture angle of this system for each light receiving element is divided, so that the three-sided prism 24 has its aperture angle. Is divided into three equal parts, the effective numerical aperture NA ′ of the imaging optical system including the three-plane prism 24 is 0.24, and the resolution δ ′ at that time is δ ′ = 0.61 · λ / NA. '
= 1.6 μm.

On the other hand, the subject 4 is exposed to the illumination light 15 (see FIG. 4).
The spot size s on the surface of the illumination light 1
Assuming that the full width φ of the angular distribution of No. 5 is 60 °, s = 0.61 · λ
/Sin(φ/2)=0.79 μm. Eventually, in the image formation on each light receiving element, x
Although the resolution in the direction is 1.6 μm, what actually affects the image formation is the 0.79 μm width illuminated in the field of view.
Since there is only the reflected light from the portion m, an image having a resolution determined by the illumination light exceeding the resolution of the imaging optical system can be obtained. As described above, since the light flux is split into a plurality of rays in the middle of the imaging optical system, the effective numerical aperture of each is at least half or less of the numerical aperture of the objective lens, whereas the angular distribution range of the illumination light is limited. By setting the size equal to or more than の of the aperture angle of the objective lens, it is possible to obtain an image with a resolution exceeding the resolution of the imaging optical system. When the angular distribution of the illumination light intensity is not limited to being symmetrical with respect to the optical axis of the objective lens, the light source may be shifted from the optical axis of the illumination optical system, but as shown in FIG. If it is configured symmetrically with respect to the optical axis of the objective lens, the angle distribution range of the illumination light intensity can be maximized.

FIG. 2 is a configuration diagram showing a second embodiment of the present invention. The illumination means for irradiating the surface of the subject is a light source 1
0, a lens 11, and cylindrical lenses 16 and 17, and a portion where light emitted from the light source 10 passes from the lens 11 through the cylindrical lens 17 and passes through the splitter 30 illuminates the surface of the subject 4 via the objective lens 31. . The reflected light 26 (see FIG. 4) from the surface of the subject 4 is
The portion reflected by the splitter 30 again through the objective lens 31 is once converged by the lens 23 of the imaging means, further refracted by the lens 22 so as to become parallel light, and subsequently by the three-sided prism 24 in accordance with the incident position. The light is split into light beams traveling in different directions. Here, since the input / output surface of the three-sided prism 24 is configured to be perpendicular to the zx plane of the coordinate system shown in FIG. 2, any light incident on the three-sided prism 24 is directed in a direction parallel to the zx plane of the coordinate system. Is deflected to These light beams are all transmitted to the respective light receiving elements 27 by the lens 21.
The light is condensed on the light receiving surfaces a, 27b and 27c to form an image.

Before being split by the three-sided prism 24, the light beams contributing to the image formation are reflected by the light beams 25a and 25a of the reflected light 26 (see FIG. 4) from the surface of the subject which have different angles of reflection. 25b and 25c, a plurality of images obtained by imaging the same location on the surface of the object with reflected light in different angular ranges are obtained from the outputs of the respective light receiving elements. Each of the light receiving elements 27a, 27b, and 27c has a plurality of light receiving surfaces, which are linearly arranged in a direction perpendicular to the zx plane of the illustrated coordinate system. In this case, an image of a linear portion parallel to the y-axis of the illustrated coordinate system is taken. From this, each light receiving element 27a, 27
b and 27c assume line sensors extending in the y-axis direction, for example.

The illumination means of FIG. 2 will be described with reference to FIG. FIG. 3 (a) is a front view of the illumination means of FIG. 2, and is therefore the same as FIG. FIG. 3B is a side view of the illumination unit of FIG. That is, in FIGS. 2 and 3A, the cylindrical lenses 16 and 17 are arranged so as not to have a refractive power in the zx plane of the illustrated coordinate system, and the image of the light source 10 is formed on the surface of the subject 4. It is an optical system. Such a light distribution method of illumination light is widely known as critical illumination. The angular distribution of the radiation intensity of the light source 10 on the zx plane of the illustrated coordinate system determines the angular distribution of the illumination light intensity applied to the surface of the subject 4 on the zx plane of the illustrated coordinate system.

In FIG. 3B, the cylindrical lens 1
6 and 17 have refractive power in the yz plane of the illustrated coordinate system,
All the light rays emitted from each point of the light source 10 reach the entire illumination range extending along the y-axis of the illustrated coordinate system on the surface of the subject 4. Such a light distribution system of illumination light is widely known as Koehler illumination. As described above, the imaging unit captures an image of the subject surface with a plurality of reflected lights having different reflection angles along the zx plane of the coordinate system in the drawing, and detects the angular distribution of the reflected light intensity in this direction. However, the angular distribution of the original illumination light in this direction is given by the angular distribution of the radiation intensity of the light source 10. The imaging range on the surface of the subject is linear in the y direction of the coordinate system in the figure due to the arrangement of the light receiving surfaces of the respective light receiving elements, but the illumination range is also widened in this direction to cover the entire imaging location. it can. By making the illumination range sufficiently larger than the imaging range,
It is possible to make the angular distribution of the illumination light intensity along the zx plane uniform within the imaging range.

[0017]

According to the first aspect of the present invention, the decrease in resolution due to the division of the aperture angle of the imaging optical system is compensated for by the illumination light, so that a resolution close to the case where there is no division of the aperture can be ensured. The possible advantages are obtained. Further, according to the second aspect, a line sensor having a plurality of light receiving surfaces on a straight line can be used as the light receiving element, and a plurality of locations on the surface of the subject can be simultaneously imaged in parallel to increase the speed. become.

[Brief description of the drawings]

FIG. 1 is a configuration diagram showing a first embodiment of the present invention.

FIG. 2 is a configuration diagram showing a second embodiment of the present invention.

FIG. 3 is an explanatory diagram illustrating the illumination unit of FIG. 2;

FIG. 4 is a configuration diagram showing a proposed device.

[Explanation of symbols]

10 light source, 11, 12, 13, 21, 22, 23 ... lens, 16, 17 ... cylindrical lens, 20a, 2
0b, 20c: light receiving element, 24: three-sided prism, 25
a, 25b, 25c: luminous flux, 27a, 27b, 27c
... Light receiving element (line sensor), 30 ... Splitter, 31
... Objective lens, 4 ... Subject.

Claims (4)

[Claims] An illumination unit configured to illuminate a surface of the object; an imaging unit configured to image an illuminated surface of the object; and an objective lens shared by the illumination unit and the imaging unit. The imaging means includes an imaging lens system including one or a plurality of lenses to generate an image of the surface of the subject, and an incident light beam disposed in the middle of the imaging lens system and a plurality of light beams having different traveling directions from each other. A multifaceted prism or a multifaceted mirror or a diffraction grating that branches, and a plurality of light receiving elements arranged at an image forming position for each of the branched light fluxes. In a surface inspection device that obtains images by reflected light in different reflection angle ranges and detects an angular distribution of the reflected light intensity that changes according to the surface state, The angle distribution range of the intensity of the illumination light applied to the surface of the subject via the object lens is at least 以上 of the aperture angle of the objective lens in a direction along the incident surface by the imaging unit. A surface inspection device characterized by the above-mentioned. 2. The surface inspection apparatus according to claim 1, wherein the polygon prism, the polygon mirror, or the diffraction grating is arranged at a position to be an aperture stop of the imaging lens system. 3. The light of the objective lens in a direction along the incident surface, wherein the angular distribution of the intensity of the illumination light applied to the surface of the object includes different angular ranges in which the imaging means looks at the surface of the object. The surface inspection apparatus according to claim 1, wherein the surface inspection apparatus is symmetric with respect to an axis. 4. An illumination device for illuminating a surface of a subject, an imaging device for imaging an illuminated surface of the subject, and one objective lens shared by the illumination device and the imaging device. The imaging means includes an imaging lens system including one or a plurality of lenses to generate an image of the surface of the subject, and an incident light beam disposed in the middle of the imaging lens system and a plurality of light beams having different traveling directions from each other. A multifaceted prism or a multifaceted mirror or a diffraction grating that branches, and a plurality of light receiving elements arranged at an image forming position for each of the branched light fluxes. In a surface inspection device that obtains images by reflected light in different reflection angle ranges and detects an angular distribution of the reflected light intensity that changes according to the surface state, the light receiving elements each include: A plurality of light receiving surfaces arranged in a straight line, and a linear visual field imaged on the plurality of light receiving surfaces is disposed so as to be in a direction orthogonal to the incident surface on the surface of the subject; Is provided with a lens system including a cylindrical surface, and becomes critical illumination on the incident surface by the imaging means, and becomes Koehler illumination on a surface orthogonal to the incident surface and including a linear visual field of the light receiving element. A surface inspection device characterized by being constituted.