JPH0666997A - Lighting optical system - Google Patents

Abstract

PURPOSE:To obtain a lighting optical system effectively applicable to object lens with large numerical aperture corresponding to a light source with strong directivity without bending the light axis of the optical system. CONSTITUTION:In a lighting optical system of a focusing optical system, a secondary light source is formed with a zone plate. The light from this secondary light source is cast on a sample through a slanting incidence mirror 3 having a curved surface of revolution formed by revolving a non-spherical surface. For example, a small-diameter beam 1 from a light source with strong directivity is transmitted in the zone plate 2 and the light beam is converged with the zone plate 2 and then transmitted to a slanting incidence mirror 3 formed with an ellipsoidal or revolution. By placing a light shield plate 6 having a pin hole through which the light beam is penetratable, at the convergence point in this case, the incidence light can be separated into spectrum.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an illumination optical system suitable for use in combination with a directional light source such as a synchrotron radiation (SR) beam line and an X-ray laser.

[0002]

2. Description of the Related Art Generally, in a soft X-ray region, the refractive index of a substance is close to 1, so that a refracting optical system or a normal reflecting optical system used in a visible light region cannot be used. Therefore, an oblique-incidence reflection optical system utilizing total reflection, a zone plate utilizing a diffraction phenomenon, or a multilayer film reflection optical system for increasing reflectance by a multilayer film is used.

FIG. 6 shows an example of the configuration of these optical systems. In the example in which a Walter type reflecting mirror, which is one of the grazing incidence reflecting mirrors, is used as a condenser (FIG. 6A), the condenser 2 is used.
Both 1 and the objective lens 22 are Walter-type reflecting mirrors, and the numerical apertures of both optical systems can be matched. In FIG. 6A, 23 is a light source, 24 is a light shielding plate, 25 is a sample, and 26 is an image. Also, in the example in which the zone plate is a capacitor (FIG. 6B),
Both the condenser 27 and the objective lens 28 are zone plates, and the numerical apertures of both optical systems can be matched. In FIG. 6B, 29 is a light source, 3
0 is a pinhole sample and 31 is an image.

Similarly, even when an objective lens of a Schwarzschild type multilayer film reflection optical system having a numerical aperture larger than that of the above two optical systems (approximately 0.25) is used, a Schwarzschild type condenser is used. If used, the imaging optical system can be constructed by matching the numerical apertures of both. FIG. 6C shows a configuration example of such a multilayer optical system, in which 32 is a Schwarzschild type condenser, 33 is a Schwarzschild type objective lens, 34 is a light source, and 35 is an image.

However, in a multilayer optical system, it is necessary to mold a multilayer film formed of extremely thin layers into a curved surface, and the thickness of the layer is equivalent to that of four sheets required for constructing an imaging optical system. Uniform alignment is difficult. Especially in the case of a so-called water window wavelength in biological applications, for example, 40 Å, the peak of reflection exceeds the half-value width of the multilayer film reflecting mirror even if the manufacturing error is about 1%, and the total transmittance of the optical system is It is significantly reduced (see FIG. 7). Therefore, it is not appropriate to use the Schwarzschild optical system as a condenser for the Schwarzschild type objective lens.

By the way, in the case of a zone plate, the relationship between the outermost shell zone width d, the wavelength λ and the numerical aperture NA is expressed by the following equation.

NA = λ / 2d

The minimum line width of the zone plate that can be formed is about 300Å, and the maximum numerical aperture is limited to about NA = 0.07 for a wavelength of 40Å. Incidentally, even in the case of the Walter type reflecting mirror, the numerical aperture is limited to about NA = 0.1. For this reason, a method using an oblique-incidence type condenser has been proposed for specifications of an objective lens having a large numerical aperture (Japanese Patent Application No. 3-97414). In this case, for example, a paraboloid of revolution is adopted.

[0009]

However, when a light source having a strong directivity is used, the diameter of the light beam is small, so that the cylindrical shape is not appropriate in view of the ease of manufacturing the oblique incidence type capacitor. As shown in FIG. 8, the shape is such that a part of the paraboloid of revolution is used. However, in this case, the optical axis is bent, which makes alignment of the optical system and deviceization extremely difficult. Further, due to the difference in reflectance and the difference in luminous flux density due to the change in incident angle due to the difference in ray height, the light amount distribution in the pupil as shown in FIG. 9 is caused. It should be noted that such a light amount distribution of the pupil can contribute to the improvement of the transfer function as shown in FIG. 10, but in the case of a thick sample due to an oblique illumination, there is a risk that the image looks stereoscopic. Consideration must be given to image analysis. In this way, when using an oblique-incidence type condenser suitable for the specifications of a light source with strong directivity and a large numerical aperture, problems such as bending of the optical axis of the optical system and difficulty of alignment occur. was there.

In view of the above situation, the present invention can be effectively applied to an objective lens having a large numerical aperture, and further, it can be applied to a light source having a strong directivity without bending the optical axis of the optical system. The purpose is to provide a system.

[0011]

The illumination optical system of the present invention comprises:
In the illumination optical system of the imaging optical system, a secondary light source is formed by a zone plate, and light from this secondary light source is formed by an oblique incidence mirror having a rotating curved surface formed by rotating an aspherical surface.
Irradiation is performed on the sample. That is, although FIG. 1 shows the outline of the present invention, a beam 1 having a small diameter from a light source having a strong directivity is made incident on the zone plate 2. Although the light flux is converged (first-order diffracted light) or diverged (−1st-order diffracted light) by the zone plate 2, it is assumed here that it is incident on the oblique incidence reflecting mirror 3 formed of a spheroidal surface.

FIG. 1 shows an example in which a light beam is converged. In this case, a light shielding plate 6 having a pinhole 5 through which a light beam passes is installed at the convergence point 4 to disperse the incident light. be able to. Further, in the case of light having a continuous wavelength such as emitted light, unnecessary light can be blocked, so that the amount of light incident on the sample can be reduced and damage to the sample can be reduced. There are advantages.

[0013]

According to the present invention, since the oblique-incidence reflecting mirror 3 may be installed at a position where the luminous flux is sufficiently spread, a spheroidal mirror can be used as the oblique-incident reflecting mirror 3, whereby the optical axis can be improved. Can be held straight. When such a spheroidal mirror is used, the light quantity distribution of the pupil as shown in FIG. 2 is caused based on the difference in reflectance and the difference in luminous flux density due to the change in incident angle due to the difference in ray height. It causes a change in the transfer function as shown. If the above transfer function cannot be accepted,
By forming a multi-layered film designed on the basis of a portion having a small incident angle with respect to the spheroidal surface on the spheroidal surface, the reflectance of the portion having a small incident angle is improved and the change in the light amount distribution of the pupil is changed. Can be reduced.

[0014]

EXAMPLE An example of the illumination optical system of the present invention will be described below with reference to FIGS. This example is an example of an illumination optical system configured for a Schwarzschild type objective lens. In the figure, 10 is a radiation light source, 11 is a zone plate, 12 is a spheroidal mirror, 13 is a light shielding plate having a pinhole, and 14 is a Schwarzschild type objective lens.

The light from the radiation source 10 is collected by the zone plate 11. In this case, the zone plate 11 is preferably as large as possible, which generally means that the beam of the radiation source has a diameter of 10 mm or more, while the soft X
This is because the zone plate for wire is only a few mm. Even if the width of the outermost shell zone is increased, it is a good idea to give priority to increasing the diameter of the beam and reduce the light quantity loss. As a result, even if the beam convergent angle θ becomes small (this is because the numerical aperture becomes small), the zone plate 11 and the spheroidal mirror 1 are arranged.
By increasing the interval of 2, it can be made sufficiently large so that it can be manufactured.

In the spheroidal mirror 12, as shown in FIG. 5, a multilayer film optimally designed in a portion having a small incident angle (θ ₁ ) is formed on the curved surface of the spheroidal mirror to change the light amount distribution of the pupil. Can be reduced. In this case, since the allowable amount of manufacturing error is larger than that in the case of direct incidence, it is possible to avoid the inconvenience of using the Schwarzschild optical system for the condenser.

[0017]

As described above, according to the present invention, in this type of imaging optical system, it can be effectively applied to an objective lens having a large numerical aperture, and further, the optical axis of the optical system can be prevented from being bent. Moreover, it is possible to effectively realize an illumination optical system that can cope with a light source having a strong directivity.

[Brief description of drawings]

FIG. 1 is a diagram showing a configuration of an illumination optical system according to the present invention.

FIG. 2 is a diagram showing a light amount distribution in a pupil according to the illumination optical system of the present invention.

FIG. 3 is a diagram showing a change in a transfer function according to the illumination optical system of the present invention.

FIG. 4 is a diagram showing a configuration according to an embodiment of an illumination optical system of the present invention.

FIG. 5 is a partial enlarged view of a spheroidal mirror in an embodiment of the illumination optical system of the present invention.

FIG. 6 is a diagram showing a configuration example of a conventional illumination optical system.

FIG. 7 is a diagram showing a relationship between wavelength and reflectance in a conventional multilayer optical system.

FIG. 8 is a diagram showing a configuration example of an optical system using a conventional oblique incidence type condenser having a paraboloid of revolution.

FIG. 9 is a diagram showing a light amount distribution in a pupil relating to an optical system using the conventional grazing incidence type condenser.

FIG. 10 is a diagram showing changes in the transfer function of an optical system using the conventional grazing incidence type condenser.

[Explanation of symbols]

 1 Beam 2,11 Zone Plate 3 Oblique Incident Reflector 4 Convergence Point 5 Pinhole 6,13 Light-Shielding Plate 10 Radiation Light Source 12 Spherical Mirror 13 Light-Shielding Plate 14 Objective Lens

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[Procedure amendment]

[Submission date] January 26, 1993

[Procedure Amendment 1]

[Document name to be amended] Statement

[Name of item to be amended] Claims

[Correction method] Change

[Correction content]

[Claims]

[Procedure Amendment 2]

[Document name to be amended] Statement

[Name of item to be corrected] 0003

[Correction method] Change

[Correction content]

FIG. 6B shows an example in which the zone plate is a condenser, and FIG. 6A shows an example in which one of the grazing incidence reflecting mirrors is a Walter type reflecting mirror. The objective lens of the example in which the zone plate is a condenser is also a zone plate, and the numerical apertures of both optical systems can be matched. In the example in which the Walter type reflecting mirror is used as a condenser, the objective lens is also the same Walter type reflecting mirror, and the numerical apertures of both optical systems can be matched.

[Procedure 3]

[Document name to be amended] Statement

[Correction target item name] 0004

[Correction method] Change

[Correction content]

Considering in this way, when using a Schwarzschild type objective lens of a multilayer reflection optical system having a numerical aperture larger than the former two (about 0.25), the same Schwarzschild type condenser is used to open the aperture. It is easily conceivable that the numbers can be matched and the imaging optical system can be constructed. FIG. 6C shows a configuration example of such a multilayer optical system, in which 32 is a Schwarzschild type condenser, 33 is a Schwarzschild type objective lens, 34 is a light source, and 35 is an image.

[Procedure amendment 4]

[Document name to be amended] Statement

[Correction target item name] 0009

[Correction method] Change

[Correction content]

[0009]

However, when a light source having a strong directivity is used, the diameter of the light beam is small, so that the cylindrical shape is not appropriate in view of the ease of manufacturing the oblique incidence type capacitor. As shown in FIG. 8, the shape is such that a part of the paraboloid of revolution is used. However, in this case, the optical axis is bent, which makes alignment of the optical system and deviceization extremely difficult. Further, due to the difference in reflectance and the difference in luminous flux density due to the change in incident angle due to the difference in ray height, the light quantity distribution of the pupil as shown in FIG. 9 is caused. It should be noted that such a light amount distribution of the pupil can contribute to the improvement of the transfer function as shown in FIG. 10, but in the case of a thick sample due to an oblique illumination, there is a risk that the image looks stereoscopic. Consideration must be given to image analysis. In this way, when using an oblique-incidence type condenser suitable for the specifications of a light source with strong directivity and a large numerical aperture, problems such as bending of the optical axis of the optical system and difficulty of alignment occur. was there.

[Procedure Amendment 5]

[Document name to be amended] Statement

[Correction target item name] 0011

[Correction method] Change

[Correction content]

[0011]

According to the present invention, in an illumination optical system of an image forming optical system, a secondary light source is formed by a zone plate, and the light from this secondary light source is formed by an oblique incidence mirror having a rotating curved surface. , The sample is irradiated. That is, FIG. 1 shows an outline of the present invention, in which a small-diameter beam 1 from a light source having a strong directivity is applied to a zone plate 2
Incident on. Although the light flux is converged (first-order diffracted light) or diverged (−1st-order diffracted light) by the zone plate 2, it is assumed here that it is incident on the oblique incidence reflecting mirror 3 formed of a spheroidal surface.

Claims (3)

[Claims] 1. An illumination optical system of an imaging optical system, wherein a secondary light source is formed by a zone plate, and light from the secondary light source is formed by an oblique incidence mirror having a rotating curved surface formed by rotating an aspherical surface, An illumination optical system characterized in that a sample is irradiated. 2. The multilayer film optimized with reference to a portion having the smallest incident angle on the rotation curved surface, and the reflectance of this portion is increased. Illumination optics. 3. The illumination optical system according to claim 1, wherein the rotating curved surface on which the multilayer film is formed is used as the oblique incidence mirror.