JP2002023061A - Device and method for illuminating dark field of microscope - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a device and a method for illuminating dark field, by which dark field illumination having sufficient lightness and satisfactorily suppressed non-uniformity in lightness can be conducted. SOLUTION: This dark field illuminating device for microscope is configured by arranging a light source for supplying illumination light for illuminating an object to be observed, an optical shaping system for shaping luminous flux from the light source into almost parallel luminous flux having an annular cross section, an optical divergence element for converting the almost parallel luminous flux having the annular cross section to a plurality of divergent luminous flux, and an optical convergence element for converging and overlapping the divergent luminous flux on the surface of the object. It is preferable that an optical diffraction element or microlens array is used as an optical divergence element.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a dark field illumination device and a dark field illumination method, and more particularly to an epi-illumination type dark field illumination for an object to be observed by a microscope.

[0002]

2. Description of the Related Art In a semiconductor manufacturing process, microscopic observation using dark-field illumination is often used to inspect dust, scratches, and the like attached to a semiconductor wafer, a liquid crystal substrate, and the like.
In microscopic observation using dark-field illumination, instead of directly observing reflected light or transmitted light from an object to be observed, it observes scattered light from the object. Dark-field illumination has higher resolution than bright-field illumination and enables observation with good contrast.

[0003]

In the conventional dark-field illuminating device, the optical arrangement is made so that the object is almost critically illuminated. Therefore, the illuminating light is formed so that the illuminating light flux does not form an image on the object surface. Is spreading. In particular,
When guiding an illumination light flux to an object through an annular concave reflecting mirror,
A diffusion plate is arranged on the light source side of the concave reflecting mirror to diffuse the illumination light. In this case, a part of the light diffused by the diffusion plate does not contribute to illumination, and a light amount loss occurs.

On the other hand, when an illumination light beam is guided to an object via an annular condenser lens, there is a method in which a diffusion film is formed on the incident surface of the condenser lens, and the illumination light is diffused by the action of the diffusion film. In this case, a fixed diaphragm for preventing flare is placed between the condenser lens and the object so that the light flux diffused by the diffusion film does not illuminate outside the field of view, especially when using a low-magnification microscope objective lens. In the optical path of As a result, a part of the light passing through the condenser lens is blocked by the fixed diaphragm and is lost without contributing to illumination, and the arrangement of the fixed diaphragm shortens the working distance and impairs operability. As described above, in the conventional dark-field illumination device, there is a disadvantage that sufficient brightness cannot be obtained in an illumination field on an object due to a light amount loss caused by the diffusion plate or a light amount loss caused by the fixed stop. .

Further, in the conventional dark-field illuminating apparatus, the optical arrangement of so-called Koehler illumination is not used. Therefore, when a low-magnification microscope objective lens is used, brightness unevenness occurs in a wide visual field to be observed. There was an inconvenience.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned problems, and has a dark-field illumination device capable of performing dark-field illumination with sufficient brightness and with reduced unevenness in brightness. It is an object to provide a dark field illumination method.

[0007]

In order to solve the above-mentioned problems, a dark-field illuminating device for a microscope according to the present invention comprises a light source for supplying illumination light and a light beam from the light source being substantially parallel having an annular cross section. A shaping optical system for shaping the light beam into a divergent light beam, a diverging optical element for converting a substantially parallel light beam having an annular cross section into a plurality of divergent light beams, and a light source for condensing the divergent light beams and superimposing them on the object plane And a light-collecting optical element.

According to a preferred aspect of the present invention, the diverging optical element is a diffractive optical element or a microlens array, and has an overall annular shape. Further, according to a preferred aspect of the present invention, the dark field illumination device of the present invention illuminates an object with a light beam having a numerical aperture larger than the numerical aperture of the objective lens of the microscope, and the diverging optical element includes It is positioned closer to the object side than the body-attached surface. Further, it is desirable that the diverging optical element is integrally attached to each of a plurality of objective lenses selectively inserted into an imaging optical path of a microscope (claim 4).

Further, according to a preferred embodiment of the present invention,
The light-collecting optical element has an annular lens component, and at least one of the light-source-side surface and the object-side surface of the lens component is formed to be aspherical.
The above-mentioned condensing optical element has an annular concave mirror, and the reflection surface of the concave mirror is formed in an aspherical shape.

Further, according to another aspect of the present invention, the illumination light beam from the light source is shaped into a substantially parallel light beam having an annular cross section, and the substantially parallel light beam having an annular cross section is converted into a plurality of divergent light beams. The present invention also provides a dark-field illumination method characterized in that a plurality of divergent light beams are collected and superimposed on an object plane.

[0011]

DETAILED DESCRIPTION OF THE INVENTION In the present invention, after an illumination light beam from a light source is shaped into a substantially parallel light beam having an annular cross section,
The light enters the diffractive optical element or the microlens array and is converted into a large number of divergent light beams having an arbitrary divergence angle, and these are overlapped on the object plane by the condensing optical element.

As described above, according to the present invention, a substantially parallel light beam or a suitable divergence angle (or
A light beam having a convergent angle) illuminates the object plane in a superimposed manner in Koehler illumination or an illumination state close thereto. As a result, an illuminated field in which the unevenness in brightness is well controlled is formed on the object plane. Further, in the present invention, since the object surface is illuminated in Koehler illumination or an illumination state similar thereto, it is not necessary to diffuse a light beam using a diffusion plate or the like in the related art. Therefore, the light beam incident on the diffractive optical element or the microlens array does not substantially lose the light amount,
The light is guided to the object plane via the condensing optical element. As a result, an illumination field having sufficient brightness is formed on the object plane.

Each of the diffractive optical element and the microlens array used in the dark-field illumination device of the present invention comprises a plurality of lens elements integrally arranged in a ring.
The substantially parallel light beams incident on the annular entrance surface of the diffractive optical element or the microlens array form a plurality of light source images arranged annularly in the vicinity of the exit surface (that is, in the vicinity of the rear focal plane). The luminous flux from these multiple light source images is
After being focused by the focusing optics, they overlap on the object plane.

In the present invention, it is preferable that the diffractive optical element or the microlens array is arranged so as to be the front focal plane of the condensing optical element. In this case, by converting light beams from a plurality of light source images into parallel light beams and illuminating the object surface with Koehler illumination, brightness unevenness in the illumination field can be further suppressed.

When manufacturing a diffractive optical element or a microlens array, a mask pattern is transferred by photolithography or the like, and etching is performed. Once a mask pattern has been produced, it can be used repeatedly. Diffractive optical elements or microlens arrays used in the dark field illumination device of the present invention require lower alignment accuracy and the like than diffractive optical elements or microlens arrays used in imaging optical systems and the like. Is inexpensive.

The diffraction efficiency of the diffractive optical element used in the dark field illumination device of the present invention is desirably 4 or more.
If the diffraction efficiency is at least four levels, a high diffraction efficiency of 80% or more can be obtained, so that the effect of reducing the light amount loss is large. When the diffraction efficiency is set to a high level, more mask patterns must be prepared accordingly, and the number of steps for positioning and patterning each mask pattern increases. Therefore, it is not desirable to set the level too high. This is the same in the case of a microlens array manufactured by a similar manufacturing method.

Each of the diffractive optical element and the micro lens array is an aggregate of minute lenses, and has an irregular pattern that repeats regularly. Therefore, as compared with the diffusion plate, these can be controlled so that a large number of divergence angles are constant, and irregular reflection and scattering on the surface can be reduced.
Further, since the diffractive optical element or the microlens array is manufactured by photolithography or the like, and a fine repetitive uneven pattern is obtained, the uniformity of the brightness of the illumination field is improved.

In a microscope, a plurality of objective lens barrels having different magnifications are mounted on a rotatable revolver, and an objective lens having a desired magnification is selectively inserted into an imaging optical path by rotation of the revolver. In this case, since the numerical aperture and the field of view are substantially different depending on the magnification of each objective lens,
In order to favorably form an illumination field having a size corresponding to the field of view with a light beam having a numerical aperture larger than the numerical aperture of each objective lens, a diverging optical element (diffractive optical element or microlens array) and a collecting lens must be provided for each objective lens. It is necessary to provide an optical optical element. For this purpose, it is preferable that the diverging optical element and the condensing optical element are arranged on the object side with respect to the body-mounted surface of the objective lens barrel (the surface that becomes a reference when the objective lens barrel is mounted on the revolver). .

According to this configuration, one set of a diverging optical element and a condensing optical system can be integrally attached to each of the plurality of objective lenses selectively positioned in the imaging optical path of the microscope, Good operability can be ensured without forcing the speculum operator to perform extra operations when switching the objective lens. If the diverging optical element and the condensing optical element are arranged inside the microscope base, not only good illumination itself tends to be impossible, but also an extra operation for the speculum is required every time the objective lens is switched. And operability deteriorates.

If a certain amount of aberration remains in the light-collecting optical system, it becomes impossible to convert light beams from a plurality of light source images into parallel light beams, and as a result, there is a certain degree of unevenness in brightness on the object plane. Teruno is formed. Therefore, when an annular lens component is used as the condensing optical system, it is preferable that the condensing optical system be configured so as to have as little aberration as possible by introducing an aspherical surface to at least one surface of the lens component. Alternatively, in place of a refraction system such as a lens component, by using an annular parabolic concave reflecting mirror as a focusing optical system having no aberration in principle, it is possible to further suppress unevenness in brightness in an illumination field. Is preferred.

Hereinafter, the dark field illumination device of the present invention will be described.
This will be specifically described with reference to the drawings. FIG. 1 is a diagram schematically illustrating an overall configuration of a dark field illumination device according to an embodiment of the present invention. FIG. 2 is a partially enlarged view for explaining the optical function of the microlens array of FIG. Hereinafter, since the diffractive optical element and the microlens array have substantially the same optical action, the description will be made with the microlens array as a representative.

As shown in FIG. 1, the dark-field illumination device of the present embodiment includes a light source 1 for supplying illumination light. As the light source 1, for example, a halogen lamp is used. The light from the light source 1 becomes a substantially parallel light flux through the collector lens 2, and then passes through the condenser lens 3 to form a light source image 4.
Is formed near the aperture stop 5. The illumination light emitted from the aperture stop 5 is converted into a substantially parallel light beam via the field lens 6 and then enters the ring stop 7. Ring aperture 7
Has an annular opening centered on the optical axis.

A substantially parallel light beam having an annular cross section that has passed through the opening of the ring stop 7 enters the hollow reflecting mirror 8. The hollow reflecting mirror 8 includes a generally circular opening 8b formed at the center and a generally annular reflecting portion 8a formed outside the opening 8b.

The substantially parallel light flux having an annular cross section reflected by the reflecting portion 8 a of the hollow reflecting mirror 8 enters the microlens array 9. The micro lens array 9
As shown in FIG. 2, a large number of lens elements 9a are arranged in an annular shape as a whole. Therefore, the entrance surface and the exit surface of the microlens array 9 have an annular shape corresponding to the cross section of the incident light beam. Each lens element 9a is a positive single lens having an entrance surface having a convex surface facing the light source side and an exit surface having a convex surface facing the object side. Further, each lens element 9a is formed such that its front (light source side) focal plane substantially coincides with the incident plane, and its rear focal plane substantially coincides with the exit plane.

Accordingly, substantially parallel light beams having an annular cross section incident on the microlens array 9 are diffused by a large number of lens elements 9a. In other words, the microlens array 9 forms a large number of light source images arranged in an annular shape in the vicinity of the exit surface based on substantially parallel incident light beams having an annular cross section. Light beams from a large number of light source images formed in a ring shape by the micro lens array 9 are condensed by a ring-shaped condenser lens 10 and then superimposed on a predetermined area on the object plane 11a.

As shown in FIG. 2, the exit surface of the microlens array 9 and the front focal plane of the condenser lens 10 are arranged so as to substantially coincide with each other. Further, as shown in FIG. 1, the condenser lens 10 is disposed such that the rear focal plane thereof substantially coincides with the object plane 11a. Accordingly, light beams from a number of light source images formed by the microlens array 9 are converted into substantially parallel light beams by the condenser lens 10, and then illuminate a predetermined area of the object plane 11a in a superimposed manner.

As described above, in the dark field illumination device of FIG.
The exit surface of the microlens array 9 and the light source 1 (therefore, the light source image 4 and the aperture stop 5) are almost optically conjugate.

The objective lens of the microscope is disposed so as to penetrate the hollow portion of the annular micro lens array 9 and the hollow portion of the annular condenser lens 10.
That is, in the objective lens barrel of the microscope, in addition to the objective lens, a set of a microlens array 9 and a condenser lens 10 corresponding to the numerical aperture and the field of view are integrally mounted. Therefore, the reflected light from the object surface 11a illuminated with the dark field does not enter the objective lens, and only the scattered light from the object surface 11a is imaged by the objective lens to form a dark field image. This dark field image is observed by, for example, an eyepiece (not shown).

Referring again to FIG. 1, the objective lens barrel 1
2, an objective lens (not shown), a hollow reflecting mirror 8,
Micro lens array 9 and condenser lens 10
Is stored. The microlens array 9 and the condenser lens 10 are attached to the body-mounted surface 1 of the objective lens barrel 12.
It is positioned and fixed on the object side of 2a. Therefore,
When switching the objective lens, the examiner does not need to pay attention to what microlens array 9 should be selected.

As described above, in the dark-field illumination device of the present embodiment, the light beams from the multiple light source images formed by the microlens array 9 are converted by the condenser lens 10 into substantially parallel light beams, The same area of the surface 11a is subjected to Koehler illumination in a superimposed manner. As a result, the object plane 11
An illumination field in which unevenness in brightness is well suppressed is formed on a. Also, since the object surface is illuminated with Koehler, it is not necessary to diffuse the light beam using a diffusion plate or the like in the prior art, so that the light beam incident on the microlens array 9 passes through the condenser lens 10 without substantial loss of light amount. To the object plane 11a. As a result, the object plane 11a
An illuminated field having sufficient brightness is formed thereon.

In the above-described embodiment, an annular condenser is used as a condensing optical system for condensing light beams from a large number of light source images formed by the microlens array 9 and superimposing them on the object surface 11a. The lens 10 is used. In this case, if a certain amount of aberration remains in the condenser lens 10, it becomes impossible to convert light beams from a large number of light source images into parallel light beams.
A slightly uneven illuminated field is formed on a.

In order to further suppress the slightly remaining uneven brightness, an aspheric surface is introduced into at least one of the light source side surface and the object side surface of the condenser lens 10. Instead of a refraction system such as the condenser lens 10, an annular parabolic concave reflecting mirror which is a condensing optical system having no aberration is used in principle. In this way, the unevenness in brightness in the illuminated field can be further suppressed.

[0033]

As described above, according to the present invention,
Since the plurality of substantially parallel light beams generated by the diverging optical element superimpose substantially the Koehler illumination on the object plane, an illuminated field in which unevenness of brightness is suppressed well is formed on the object plane. In addition, in the present invention, since the object surface is almost Koehler-illuminated, there is no need to diffuse the light beam using a conventional diffuser, so that the object surface has sufficient brightness without substantial light amount loss. Teruno is formed.

Further, according to the present invention, the ring-shaped diffractive optical element or microlens array is used as the diverging optical element, so that the dark field illumination device can be made compact. Furthermore, many divergence angles can be controlled to be constant, irregular reflection and scattering on the surface can be reduced,
Further, the uniformity of the brightness of the illuminated field is improved.

Further, according to the present invention, since the diverging optical element is arranged on the object side of the body surface of the objective lens, the operation of switching the objective lens can be easily performed. Furthermore, since a diverging optical element can be attached to each objective lens, an appropriate illumination field is automatically obtained in the field of view of the objective lens, and the operability of observation is improved.

[Brief description of the drawings]

FIG. 1 is a diagram schematically illustrating an entire configuration of a dark field illumination device according to an embodiment of the present invention.

FIG. 2 is a partially enlarged view illustrating an optical function of the microlens array of FIG. 1;

[Explanation of symbols]

 Reference Signs List 1 light source 2 collector lens 3 condenser lens 4 light source image 5 aperture stop 6 field lens 7 ring stop 8 hollow reflection mirror 9 micro lens array (diffractive optical element) 10 condenser lens 11 object 11a object plane 12 objective lens barrel 12a with body surface

Claims (7)

[Claims] A light source for supplying illumination light for illuminating an object to be observed; a shaping optical system for shaping a light beam from the light source into a substantially parallel light beam having an annular cross section;
A diverging optical element for converting the substantially parallel light beam having the annular cross section into a plurality of divergent light beams, and a condensing optical element for condensing the divergent light beams and superimposing them on an object plane,
A dark field illumination device for a microscope, comprising: 2. The dark-field illumination device for a microscope according to claim 1, wherein the diverging optical element is a diffractive optical element or a microlens array, and has an annular shape as a whole. 3. The object is illuminated with a light beam having a numerical aperture larger than a numerical aperture of an objective lens of a microscope, wherein the diverging optical element is positioned closer to the object side than a body surface of the objective lens. 3. The dark-field illuminating device for a microscope according to claim 1, wherein: 4. The apparatus according to claim 1, wherein the diverging optical element is integrally attached to each of a plurality of objective lenses selectively inserted into an imaging optical path of the microscope. The dark-field illumination device for a microscope according to any one of claims 1 to 7. 5. The condensing optical element has an annular lens component, and at least one of a light source side surface and an object side surface of the lens component is formed in an aspherical shape. The dark-field illumination device for a microscope according to any one of claims 1 to 4, wherein: 6. The condensing optical element according to claim 1, wherein the converging optical element has an annular concave mirror, and the reflecting surface of the concave mirror is formed in an aspherical shape. Microscope dark field illuminator. 7. An illumination light beam from a light source is shaped into a substantially parallel light beam having an annular cross section, the substantially parallel light beam having the annular cross section is converted into a plurality of divergent light beams, and the plurality of divergent light beams are collected. A dark-field illumination method for a microscope, comprising illuminating and superimposing on an object plane.