JPH11218677A - Confocal disk - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce stray light by increasing lighting efficiency by providing reflecting surfaces, which are coaxial with pinholes on the confocal disk and gradually expand from the pinhole openings in the direction where illumination light is made incident, by the pinholes. SOLUTION: On the confocal disk 1, fine light guide parts 2 are arranged spirally. Each light guide part 2 is structured by cutting the pointed part of a cone so that the diameter of the cross section becomes equal to pinhole size needed for confocal constitution and in a tapered cylinder shape whose top and bottom surfaces are not covered, and the internal surface is a mirror surface. Parallel luminous flux which is parallel to the center axis of the cone is made incident as illumination light. The incident luminous flux is reflected repeatedly by the reflecting internal surface of the cone or not reflected at all to travel toward the pointed part of the cone, so that it is emitted from the tip hole finally at a large divergence angle. The illumination light never returns from the reflecting surface of the cone when the angle of the slanting surface of the cone is not very large, and the illumination light which entering the cone is all emitted from the hole.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a structure of a disk in a disk scanning confocal microscope.

[0002]

2. Description of the Related Art FIG. 9 shows a typical conventional confocal disk 81. A spiral pinhole is provided on the disk, and portions other than the pinhole are shielded from light and do not transmit light.

In order to clarify the problem to be solved by the present invention, a disk scanning confocal microscope will be described with reference to FIG. The illumination light emitted from the light source 3 is condensed by the collimator lens 4, passes through the branch optical element 5, and enters the confocal disk 81. Illumination light is confocal disk 8
The light passes through one pinhole, spreads by diffraction, enters the objective lens 6, and is projected on the object 7. The illumination light is reflected by the object 7, becomes reflected light, reenters the objective lens 6, and is collected near the pinhole of the confocal disk 81. When the object 7 is at a position conjugate with the pinhole surface of the confocal disk 81, the reflected light is completely converged on the pinhole and passes through the pinhole. The light passing through the pinhole is deflected in the optical path by the branching optical element 5 and reaches the two-dimensional detector 9. At this time, the pinhole on the confocal disk 81 and the detection surface of the two-dimensional detector 9 are conjugate to the imaging lens 8.

When the confocal disk is rotated by the motor 10 in such a configuration, the image of the pinhole projected on the object 7 scans over the object 7 without any gap. The entire field of view can be scanned within the exposure time of the dimension detector 9, and a confocal image can be obtained. The confocal disk 81 of FIG. 9 used in this example is referred to as Conventional Invention A.

[0005] Problems of the disk scanning confocal microscope using the conventional invention A are illumination efficiency and stray light due to reflection of illumination on the upper surface of the disk. An actual confocal disk has not only one spiral pinhole but also a large number of spiral pinholes, provided that the distance between adjacent pinholes is about 10 times the diameter of the pinhole, and that a pinhole is formed on one surface of the confocal disk. Provided. The distance between the pinholes must be about 10 times the diameter of the pinholes as described above so that blurred light hardly mixes between the pinholes. Is provided, the illumination light that can pass through the pinhole from the confocal disk is 1% or less. Most of the illuminating light that has not passed is reflected on the upper surface of the disk, becomes stray light, and reaches the two-dimensional detector. In order to prevent this stray light, countermeasures using polarized light are taken, but this is not enough because the reflection is too large.

In order to solve this problem, Japanese Patent Laid-Open Publication No. Hei 4 (1999) discloses a method of increasing the illumination efficiency and reducing stray light by providing a micro-condensing lens on the confocal disk coaxially with the pinhole and the same number as the pinhole. The confocal disk is referred to as a conventional invention B (Japanese Patent No. 330412). But,
This invention is also a later invention of the inventor of the present invention.
In the specification of -60980, the inventor himself points out a problem.

When a micro condenser lens and a pinhole are formed on a confocal disk, the rate of illumination light passing through the pinhole is increased, and stray light is reduced accordingly.
However, in such a configuration, since the signal light reflected from the object and passed through the pinhole again becomes parallel light by the micro condenser lens, the image of the pinhole is formed on the two-dimensional detector by the imaging lens. Image cannot be formed. Therefore, there is no choice but to directly guide the parallel light from the micro condenser lens to the two-dimensional detector without the imaging lens, or to condense the image of the micro condenser lens on the two-dimensional detector by the imaging lens. Eventually arrives at the two-dimensional detector as parallel light). In such a case, the beam size of the parallel light with respect to the field size (the size of the entire image formed on the two-dimensional detector on the object plane) becomes
The image (spot) size of the pinhole with respect to the field size of the confocal disk of the invention A without the micro condenser lens is clearly larger, that is, the lateral resolution is reduced. The larger the diameter of the micro condenser lens to increase the illumination efficiency, the lower the lateral resolution decreases. Conversely, the smaller the diameter of the micro condenser lens, the smaller the decrease in the lateral resolution but the higher the illumination efficiency. Become.

Therefore, the above-mentioned Japanese Patent Laid-Open No. 5-60980 discloses a more complete improvement. This will be described with reference to FIG. In the present invention, the array surface of the micro condenser lens and the array surface of the pinhole are separated from each other by a separate disk (micro condenser lens array disk 71, pinhole array disk 72).
And the branch optical element 5 is arranged between the disks. With such a structure, the signal light from the object 7 does not pass through the micro condenser lens, so that it does not become a parallel light flux, and the same lateral resolution as in the case without the micro condenser lens can be obtained. Of course, the illumination light is condensed by the micro condenser lens, so that the illumination efficiency is high. Since most of the illumination light condensed by the micro condenser lens passes through the pinhole, there is almost no reflection of illumination on the upper surface of the pinhole array disk 72, and stray light reaching the two-dimensional detector 9 is not reflected. It becomes significantly smaller. The confocal disk comprising the micro condenser lens array disk 71, the pinhole array disk 72 and the fixed branch optical element 5 according to the present invention is referred to as Conventional Invention C. Conventional invention C is an epoch-making solution which almost completely solves the problem of the disk scanning confocal microscope.

[0009]

However, some problems can be pointed out in the conventional invention C as well. First, it is not essential, but difficult to manufacture. Since the micro condenser lens array disk 71 and the pinhole array disk 72 are separated, it is not easy to align hundreds of thousands of micro condenser lenses and pinholes with an accuracy of the order of μm. Compared to forming a micro condenser lens and a pinhole on the front and back of the disk substrate as in the conventional invention B, there are many difficulties such as a method of detecting a positioning mark and inclination of disks. Further, not only positioning of the disks but also inclination of the branch optical element 5 with respect to the disks requires extremely strict accuracy. Since the branching optical element 5 is required to have a size larger than the field of view, it becomes quite large, so that even if it is slightly tilted, the spot is shifted from above the pinhole.

Further, there is a more essential problem. The size of the branch optical element 5 is essentially the distance between inevitably because it requires the size or the size of the two-dimensional detector 9 disk must be adopted quite large. Therefore, the focal length of the micro condenser lens becomes very long, and the numerical aperture (hereinafter abbreviated as NA) of the micro condenser lens becomes very small or it is necessary to prevent it from being so. The lens diameter must be quite large.
N. A. Is small, a small spot cannot be formed due to the influence of diffraction. In addition, when the lens diameter of the micro condenser lens is increased, the number of pinholes that can be arranged coaxially becomes small, and the obtained confocal image resolution deteriorates. To avoid this, the diameter of the disk must be increased.

Let's consider concretely. In a confocal microscope, the pinhole diameter is an important parameter that determines the imaging performance, so the pinhole diameter is not very free. This is especially true when a commercially available standard lens is used as the objective lens 6 of the microscope. Image side N.N. of general microscope objective lens 6 A. Is about 0.03, so the spot diameter condensed on the pinhole is calculated by a rough calculation as 1.
From 22 × λ / (NA), the illumination wavelength λ is 550 nm.
Is about 22.5 μm. In order to obtain a sufficient confocal effect, the diameter of the pinhole should be around the spot size. In this case, the N.V. A. This size is ideally required. Originally, the purpose of the micro condenser lens is to collect light, so it is not always necessary to focus on a spot close to the diameter of the pinhole if there is a certain effect. Object side N.
A. There is nothing better than making it the same. However, for example, if the distance between the micro condenser lens array 71 disk and the pinhole array disk 72 is 10 mm, the N.D. A. In order to obtain this, the lens diameter of the micro condenser lens must be about 0.6 mm. This is 30 times that when the diameter of the pinhole is considered to be 20 μm, which means that the arrangement of the pinholes on the pinhole disk must be considerably coarse. Conversely, the pinhole interval is 0.2 m, which is 10 times the pinhole diameter.
m, the diameter of the micro condenser lens is 0.2 mm. A. Is about 0.01, and the spot diameter at that time is about 67 μm. In this case, the light collection efficiency is low and stray light increases.

There is still a problem. From the above,
Conversely, the distance between the micro condenser lens array disk 71 and the pinhole array disk 72 should be as short as possible. That is, the branch optical element 5 cannot be made large. Even now, the number of pixels of a typical CCD sensor of the two-dimensional detector 9 has been remarkably increased due to the spread of high-definition television and the like.
Some have a pixel number of 096 × 4096. Considering the sensitivity per pixel, there is a limit to reducing the size of the pixel itself, and the size of the entire CCD sensor is inevitably increased by increasing the number of pixels. Also, the microscope objective lens 6 has a field of view of 30 recently.
What can be obtained about mm is not uncommon. That is,
In the future, the size of the branch optical element 5 will be required to be larger in order to secure a wider field of view.
The conventional invention C has a problem also in this point.

Further, consider a case where a confocal microscope is used as an inspection device in a factory production line or the like.
A confocal microscope is capable of three-dimensional measurement and has a lateral resolution higher than that of a general microscope, and is therefore expected to be used as an inspection device in the semiconductor field. In such a case, there is a possibility that the objective lens 6 with a considerably low magnification is used to view a wide field of view at a time. When used at a low magnification, the spot (pinhole image) diameter projected on the object becomes large. At this time, if the surface of the object is rough, unevenness of the object inside the spot tends to be affected. In the conventional invention, not only C but also A and B in the spot (or the inside of the light beam emitted from one pinhole) are coherent light having the same phase. Interference occurs due to scattered light. That is, speckle occurs. Speckle is not preferable because it not only significantly lowers the image quality but also affects the accuracy of three-dimensional measurement.

Therefore, the present invention solves the problem of alignment caused by dividing the micro condenser lens array disk 71 and the pinhole array disk 72 as in the conventional invention C and the effect of the micro condenser lens. Eliminating the problem of not being effective enough and the problem of not being able to obtain a large field of view, and having the problem that the beam reaching the two-dimensional detector 9 becomes thicker as in the conventional invention B, thereby lowering the lateral resolution, increasing the illumination efficiency, It is an object to provide a confocal disk that reduces stray light.

[0015]

According to the present invention, the illumination light is not focused on the pinhole by a lens, but is guided to the pinhole by a technique of an optical trap.

That is, for each pinhole on the confocal disk, the confocal disk is coaxial with the pinhole so as to have a reflecting surface that gradually spreads in the direction in which the illumination light enters from the pinhole opening. Constitute.

In this way, the illuminating light incident on the confocal disk is trapped and reflected by the reflecting surface, guided to the back of the reflecting surface, ie, toward the pinhole, and finally emitted from the pinhole. Thus, the lighting efficiency can be improved. As the amount of light emitted from the pinhole increases, the amount of stray light reflected by the confocal disk surface and reaching the two-dimensional detector decreases.

Further, the signal light reflected from the object and passing through the pinhole is transmitted to the image side N.P. A. If the angle is smaller than the inclination of the trap reflection surface, the light enters the imaging lens without being converted into a parallel light beam or the like and forms an image of the pinhole on the two-dimensional detector. No problem occurs.

Further, according to the present invention, there is no need to separate the condensing portion and the pinhole portion, so that the problems of the prior art C do not occur at all.

In addition, such a light condensing means does not align the wavefront unlike light condensing by a lens, and mixes light that has been reflected several times on the reflecting surface, light that has never been reflected, and light that has been reflected only once. In addition, the coherency of the illumination light emitted from the pinhole is extremely low. for that reason,
The generation of speckle is suppressed.

Another effect is that when condensing with a lens utilizing refraction or diffraction, if the wavelength of the illumination light is changed, an ideal spot may not be obtained due to chromatic aberration. The invention does not matter because it utilizes reflection.

The present invention has a configuration including a plurality of pinholes and a plurality of light collecting means described in claim 1 of Japanese Patent Application Laid-Open No. Hei 4-330412 described as Conventional Invention B. 1) Claim 1 of the same specification has a description of "focal point of the light condensing means" and is considered to be premised on the lens action. Nothing similar to the invention is described, and Fresnel lenses, quadratic curved mirrors, microconvex lenses, refractive index dispersion type flat lenses, and diffraction, reflection, or refraction are different in physical phenomena, even if they are "focus." (3) The problem of the prior art B by the inventor himself in the specification of Japanese Patent Application Laid-Open No. H5-60980, which is the invention by the same inventor described as the conventional invention C. As a point The contents are base incompatible with clearly present invention, given the present invention is JP-4-
It is considered different from the invention disclosed in the publication No. 330412. The present invention is an application of the technology of an optical trap and does not use a lens function.

[0023]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 shows an example of an embodiment of the present invention. In this example, minute light guides 2 are spirally arranged on a confocal disk 1.

The light guide 2 will be described in detail with reference to FIGS. It has a structure in which the pointed part of a cone is cut so that its cross-sectional diameter becomes the pinhole size required for confocal, and the upper and lower surfaces are unblocked and tapered cylindrical. . The inner surface is a mirror surface. As shown in FIG. 3, the illumination light is a parallel light beam parallel to the central axis of the cone. The incident light beam is repeatedly reflected on the reflection surface on the inner surface of the cone, or travels in a pointed direction of the cone without being reflected at all, and finally exits from the hole at the tip with a wide divergence angle. Unless the angle θ of the inclined surface of the cone shown in FIG. 3 is extremely large, the illumination light does not return from the reflection surface of the cone, and all the illumination light incident on the cone is emitted from the hole at the tip. .

The light guide 2 having such a shape and function is as follows.
As shown in FIG. 1, they are arranged spirally on the confocal disk 1. Although only one spiral is shown in FIG. 1, many spirals are actually formed on the same disk.
The hole at the tip of the conical shape corresponds to a pinhole, and the hole on the illumination side is, for example, 10 times the diameter of the hole at the tip. Thus, a pinhole arrangement similar to that of the conventional invention A can be obtained. FIG. 4 shows the lower portion of the confocal disk 1, that is, the portion corresponding to the pinhole surface. The portion other than the pinhole, which is the tip of the cone, is covered with a light-shielding film, and is not different from the confocal disk according to the conventional invention when viewed from below the disk.

FIG. 5 shows a case where the confocal disk 1 of this embodiment is incorporated in a disk scanning confocal microscope. The illumination light emitted from the light source 3 is collimated by the collimator lens 4 and enters the confocal disk 1. All of the illumination light incident on each light guide 2 is emitted from the pinhole by the above-described action. Since there is almost no gap between the light guide sections 2, the light reflected on the upper surface of the confocal disk 1 is much smaller than that of the conventional invention A. Compared to the conventional invention B, it can be said that there is less light reflected on the surface of the micro condenser lens in the conventional invention B, so that it is smaller.

The illumination light emitted from the pinhole is projected on the surface of the object 7 by the objective lens 6. The light reflected by the object 7 enters the objective lens 6 again as signal light, converges at the pinhole position, and passes through the pinhole. Generally, the image side N.P. A. Is very small, about 0.03, so that the signal light passing through the pinhole does not reflect on the side surface of the light guide 2 or the like (of course, although there is a diffracted light component that is reflected, Then, the light is deflected by the branch optical element 5 and is incident on the imaging lens 8. The imaging lens 8 acts to form an image of the pinhole surface (tip surface of the cone) on the two-dimensional detector 9, and an image of the pinhole is formed on the two-dimensional detector 9.

In this configuration, a significant difference from the conventional invention B is that in the conventional invention B, the signal light reflected by the object 7 and passed through the pinhole is converted into a parallel light beam by the micro condenser lens to the branch optical element 5. It is a point that will be incident. If it becomes a parallel light beam, the image of the pinhole cannot be formed on the two-dimensional detector 9 by the imaging lens 8. Therefore, there is no choice but to directly detect the two-dimensional detector 9 without passing through the lens, or to form an image of the micro condenser lens surface on the two-dimensional detector 9 with a lens of the same magnification. (Although the magnification can be changed to make the parallel light beam thinner, the resolution is the same because the magnification itself of the image on the two-dimensional detector 9 is reduced.) The parallel light beam emitted from the micro condenser lens is Since it becomes about 10 times the diameter of the pinhole, the lateral resolution is inevitably reduced.

However, in the present invention, the signal light reflected by the object 7 and passing through the pinhole is incident on the imaging lens 8 with the light leaving the pinhole. By forming an image on the two-dimensional detector 9 by the imaging lens 8 described above, a spot having almost the same size as a pinhole can be detected. That is, detection with high lateral resolution can be performed. If the imaging lens 8 and the two-dimensional detector 9 are collectively referred to as an imaging optical system, the confocal disk 1 of the present invention is not different from the disk of the conventional invention A at all from the viewpoint of the imaging optical system. Moreover, the illumination efficiency is the same as that of the conventional technology B and is better than that of the conventional technology C.

In this example, the light guide portion 2 has a conical shape. However, it is basically sufficient that the parallel light beam repeats reflection and travels to the back, and may be, for example, a polygonal pyramid. If it is a polygonal pyramid, it is possible to arrange the polygonal pyramids without gaps, so that the illumination efficiency and the stray light countermeasure are more complete.

Also, the slope of the reflecting surface of the light guide 2 does not need to be linear (see FIG. 6A) like a polygonal pyramid or a cone, for example, as shown in FIGS. 6B, 6C, and 6D. A non-linear shape as shown in FIG.

What is important in the practical sense of the present invention is that high processing accuracy is not required unlike a micro condenser lens. In this example, the reflecting surface of the light guide portion 2 is a mirror surface, but the illumination light only needs to go to the back. Therefore, for example, the accuracy (flatness, curvature) of the mirror surface may be rough (scattering should not be performed). ), The accuracy of the shape is not required. That is, for example, in the case of a polygonal pyramid, there is almost no problem even if the plane of the slope is slightly concave or convex. The reflectivity is not particularly important either.

[0033]

According to the present invention, since there is no need to separate the disk of the light condensing means and the pinhole array disk unlike the conventional invention C, there is a problem of alignment between the two disks,
N. of the micro condenser lens A. In this case, there is no problem that the illumination efficiency is reduced due to the decrease of the size, and a problem that a large field of view cannot be obtained because the branch optical element cannot be enlarged. Further, unlike the conventional invention B, the beam reaching the two-dimensional detector becomes thick, so that there is no problem that the horizontal resolution is reduced, and it is possible to increase the illumination efficiency and reduce the stray light.

[Brief description of the drawings]

FIG. 1 is a diagram showing an example of an embodiment of the present invention.

FIG. 2 is a diagram for explaining a light guide unit of the present invention.

FIG. 3 is a diagram for explaining a light guide unit of the present invention.

FIG. 4 is a view of the confocal disk of the present invention as viewed from the objective lens side.

FIG. 5 is a diagram in which the confocal disk of the present invention is incorporated in a disk scanning confocal microscope.

FIG. 6 is a diagram illustrating a reflection surface shape of a light guide unit of the present invention.

FIG. 7 is a diagram for explaining a conventional technique C;

FIG. 8 is a diagram for explaining a conventional technique A.

FIG. 9 is a diagram for explaining a confocal disk according to the related art A.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Confocal disk 2 Light guide part 3 Light source 4 Collimator lens 5 Branch optical element 6 Objective lens 7 Object 8 Imaging lens 9 Two-dimensional detector 10 Motor

Claims (1)

[Claims] 1. A disk scanning confocal microscope that obtains a confocal image by rotating a disk having a large number of pinholes, wherein for each pinhole, illumination light is incident from a pinhole opening coaxially with the pinhole. A confocal disk characterized by having a reflecting surface that gradually spreads in a direction in which the laser beam travels.