JPH0627299A - Dichroic mirror for soft x-ray and microscope using the same - Google Patents

Abstract

PURPOSE:To make fluorescence excitation light of soft X-rays, provide a dichroic mirror for transmitting the soft X-rays and reflecting the fluorescence light excited with said soft X-rays and a soft X-rays fluorescence microscope equipping it and make possible the observation of a thick specimen which cannot be observed with a conventional soft X-rays microscope. CONSTITUTION:Soft X-rays are made fluorescence excitation light and a thin film of a dichroic mirror is constituted in order that the soft X-rays may transmit it and fluorescence excited with said X-rays may be reflected thereon. A soft X-ray fluorescence microscope equipping the dichroic mirror has a fluorescence excitation light source 1, the dichroic mirror 2 formed of a thin film, an objective lens 3 and a specimen 4 on the same light axis 9. The others include a light (image) detector 5 and a barrier filter 6.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a dichroic mirror for soft X-rays and a soft X-ray fluorescence microscope equipped with the same.

[0002]

2. Description of the Related Art If soft X-rays are used in a microscope, the wavelength range of the soft X-rays is as short as several Å to several hundred Å, and therefore high resolution observation can be expected. As for this resolution, as is well known, the resolution δ of a microscope is generally obtained by the equation (1).

Δ = 0.61λ / NA (1)

In equation (1), λ is the wavelength of light and NA is the numerical aperture of the objective lens. Normal optical microscope, numerical aperture NA
= 1.4, the wavelength λ is 55
When calculated as 00Å, the resolution δ = 2400Å (0.2
4 μm). Further, in the ultraviolet microscope, the wavelength λ becomes shorter than in the case of the normal optical microscope, but since the numerical aperture NA of the ultraviolet objective lens is small, the resolution δ is somewhat lowered as a result. That is, wavelength λ = 3500Å,
When calculated with numerical aperture NA = 0.85, resolution δ = 250
It becomes 0Å (0.25 μm).

Next, the resolution δ of the soft X-ray microscope will be described. As for soft X-rays, for example, when a wavelength λ = 500Å is targeted, even with a Schwarzschild type objective lens having the largest numerical aperture in this wavelength range, the numerical aperture NA = 0.25 is taken into consideration in consideration of the diffraction limit. Is. Therefore,
The resolution δ = 1200Å (0.12 μm). Wavelength λ
= 40Å, resolution δ = 100Å (0.01μ
reach m).

[0006]

However, in the soft X-ray wavelength region, the refractive index of the substance is close to 1, and there is almost no reflection, so it is difficult to see the reflection image of the sample. Even soft X-rays can be expected to reflect to some extent in the wavelength region around 500Å. However, since the absorption of soft X-rays by the substance is large, it is not possible to obtain a beam splitter for soft X-rays with excellent performance that is excellent in the transmittance and reflectance necessary for epi-illumination, and a reflected image can be obtained even in the wavelength range around 500Å. It is difficult to put a soft X-ray microscope for observation into practical use. Therefore,
Up to now, the soft X-ray microscope has been limited in its use form to observing a comparatively thin sample with a transmission microscope, and it has not been possible to observe, for example, a thick semiconductor sample.

As a solution to the above problems, soft X
Since the light energy is large in the wavelength region of the line and almost all substances emit fluorescence, we focused on fluorescence observation. That is, the inventors have invented a dichroic mirror for observing a sample by epi-illumination and making it possible to observe a thick sample, and an epi-illumination fluorescence microscope in the soft X-ray region using this dichroic mirror.

In connection with the above-mentioned dichroic mirror for enabling observation of a thick sample, a conventional epi-illumination type in which light in a wavelength range longer than soft X-rays (ultraviolet light or visible light of a short wavelength) is used as fluorescence excitation light The fluorescence microscope will be described below. FIG. 5 is a basic configuration diagram of a conventional epi-illumination fluorescence microscope. In the figure, 11 is a light source for excitation, 12 is a dichroic mirror, 13 is an objective lens, 14 is a sample, 15 is a barrier filter, 16 is a television camera, 17 is a downward prism, and 18 is an eyepiece.

The excitation light source 11 emits ultraviolet light or visible light of a short wavelength. Dichroic mirror 12
Is a type of beam splitter or interference filter that utilizes the interference of light from a thin film and has the property of reflecting only light in a specific wavelength range and transmitting light in the remaining wavelength range. . In the manufacturing method, a thin glass layer designed to reflect excitation light having a short wavelength and transmit fluorescence having a long wavelength is coated on the upper surface of a thin glass plate. The barrier filter 15 provided in front of the eyepiece lens 18 removes light having a disturbing wavelength, and may be omitted if not necessary. In addition, the downward prism 1
7 is reflected twice by the semi-transmissive reflection surface 17a and the total reflection surface 17b to change the direction of the optical axis.

In the epi-illumination type fluorescence microscope of FIG. 5, the fluorescence excitation light from the excitation light source 11 is reflected by the dichroic mirror 12 and transmitted through the objective lens 13 to hit the sample 14,
Excited fluorescence is generated in the sample 14. The fluorescence generated in the sample 14 passes through the objective lens 13, then passes through the dichroic mirror 12, and enters the eyepiece lens 18 through the prism 17. In this way, the fluorescent image is observed through the eyepiece lens 18 or photographed by the television camera 16. In the case of the wavelength range of the above-mentioned conventional epi-illumination fluorescence microscope, the transmittance of the glass is bad for the ultraviolet ray that is the excitation light and good for the visible light that is the fluorescent light. Therefore, the fluorescence is transmitted by the dichroic mirror 12. is there.

On the other hand, when an epi-illumination fluorescence microscope is applied in the wavelength range of soft X-rays, generally speaking, the transmittance of glass is good for soft X-rays having a short wavelength of excitation light,
Since soft X-rays having a long wavelength, which is fluorescence, is bad, an epi-illumination fluorescence microscope cannot be constructed with a conventional dichroic mirror.
In addition, for many substances, generally, X-rays having a short wavelength are easily transmitted and X-rays having a long wavelength are difficult to be transmitted. Therefore, it is not appropriate that the glass substrate of the dichroic mirror is in the optical path of fluorescence. is there.

The present invention has been made in view of the above circumstances. Focusing on fluorescence observation with a soft X-ray microscope,
This soft X-ray dichroic mirror is used together with a soft X-ray dichroic mirror in which a thin film is formed so that soft X-rays are used as fluorescence excitation light, soft X-rays are transmitted, and fluorescence excited by the soft X-rays is reflected. The purpose of the present invention is to provide a fluorescent microscope in the soft X-ray region.

[0013]

The dichroic mirror for soft X-rays according to the present invention is constructed by forming a single layer film having a thickness d satisfying the following conditions on a transparent substrate.

Λ _f 1- (sin θ ₁ / n _f ) ^{2 1/2} ≦ d ≦ 0.575 λ _e 1- (sin θ ₁ / n _e ) ^{2 1/2} / (πK _e )

Where λ _e is the wavelength of light transmitted through the thin film, λ _f is the wavelength of light reflected by the thin film, n _e is the refractive index of the thin film with respect to the wavelength of the transmitted light, and n _f is the thin film. The refractive index for the reflected light, K _e is the absorption coefficient of the thin film for the transmitted light, and θ ₁ is the incident angle of the transmitted light and the reflected light with respect to the thin film.

Further, the dichroic mirror for soft X-rays of the present invention is formed by forming a multilayer film having a period D satisfying the following conditions on a transparent substrate.

0.8 A ≤ D ≤ 1.2 A, where A = 1- (sin θ ₁ / n _f ) ^{2 1/2} mλ _f / 2 n _f − (sin ² θ ₁ / n _f )

Where λ _f is the wavelength of light reflected by the multilayer film, n _f is the average value of the refractive index with respect to the wavelength of the reflected light for each layer of the multilayer film, and θ ₁ is the transmitted light to the multilayer film. The incident angle of the reflected light, m is a positive integer.

Further, the soft X-ray fluorescence microscope of the present invention is a soft X-ray microscope.
By providing a line light source, a dichroic mirror, an objective lens, and a photodetector, irradiating the sample with soft X-rays emitted from the soft X-ray light source, and detecting fluorescence emitted from the sample with the photodetector. In a soft X-ray microscope adapted to obtain an image of a sample, the soft X-ray light source, the dichroic mirror and the objective lens are provided on the same optical axis, and the soft X-ray is irradiated onto the sample through the dichroic mirror. The fluorescence emitted from the sample is reflected by the dichroic mirror and guided to the photodetector.

[0020]

FIG. 1 is a diagram showing the configuration of a soft X-ray fluorescence microscope using the dichroic mirror for soft X-rays of the present invention. In the figure, 1 is a soft X-ray light source which is also a fluorescence excitation light source, 2 is a dichroic mirror formed of a thin film, 3 is an objective lens, 4
Is a sample, 5 is an image detector as a photodetector, and 6 is a barrier filter. Among the above, the soft X-ray light source 1, which is also a fluorescence excitation light source, the dichroic mirror 2, and the objective lens 3 are provided on the same optical axis 9. The thin film of the dichroic mirror 2 is formed so as to transmit the soft X-rays and reflect the fluorescence excited by the soft X-rays.

Since the soft X-ray fluorescence microscope of the present invention is constructed as described above, the short-wavelength soft X-rays generated by the soft X-ray light source 1 pass through the dichroic mirror 2 and enter the objective lens 3. Then, the light is focused toward the sample 4. When the soft X-ray having a short wavelength is focused and hits the sample 4, excited fluorescence is generated in the sample 4. The fluorescence generated in the sample 4 passes through the objective lens 3, is further reflected by the dichroic mirror 2, and enters the image detector 5 via the barrier filter 6.

As the image detector 5 used for detecting the fluorescence image, it is desirable to use a solid-state image pickup device having a laminated diode structure having excellent sensitivity, but general CCD image sensor, MCP (multi-channel plate), etc. Can also be used. The dichroic mirror for soft X-rays of the present invention can be used not only as a soft X-ray fluorescence microscope but also as a spectroscopic means in the wavelength range of soft X-rays. For example, in the usual fluorescent X-ray analysis, when quantitatively measuring fluorescent X-rays of two lights having different wavelengths, light having a short wavelength is detected by utilizing the optical characteristics of the dichroic mirror for soft X-rays of the present invention. Light having a long wavelength can be detected by transmission, and light having a long wavelength can be detected by reflection.

Next, the function of the thin film in the dichroic mirror 2 will be described. Since the soft X-rays are largely absorbed by the substance, the transmittance is determined by the absorption coefficient of the thin film rather than the interference condition. As illustrated in FIG. 2, the incident angle of the soft X-ray (fluorescence excitation light) to the thin film 2t of the dichroic mirror 2 is θ ₁ , the refraction angle is θ ₂ , the soft X-ray wavelength (excitation light wavelength) of the thin film 2t. Assuming that the complex refractive index with respect to λ _e is n _e , the absorption coefficient is K _e , and the thickness of the thin film 2t is d, the transmittance T _e of the soft X-ray (fluorescent excitation light) with respect to the thin film 2t of the dichroic mirror 2 is given by the formula ( It can be represented by 2).

T _e = exp {−4 πK _e d / [λ _e cos θ ₂ ]} = exp {−4 πK _e d / [λ _e 1− (sin θ ₁ / n _e ) ^{2 1/2} ]} ( 2)

On the other hand, the wavelength λ of the fluorescence which is excited in the sample 4 and is incident on the thin film 2t of the dichroic mirror 2.
_{Since f} is longer than the soft X-ray wavelength (excitation light wavelength) λ _e , and the absorption of fluorescence by the substance is larger than that of soft X-ray, the system in which fluorescence passes through the dichroic mirror 2 is not a good idea.
Therefore, in the present invention, the fluorescence is reflected by the dichroic mirror 2 and detected by the image detector 5.

When the wavelength λ _{f of} fluorescence becomes longer than 500 Å, metal reflection occurs, so the thin film 2t of the dichroic mirror 2 may be a single layer film satisfying the condition of the following expression (3). However, when the fluorescence wavelength λ _f is shorter than 500 Å, a multilayer film is desirable. In order for the reflection in the single-layer thin film 2t of the dichroic mirror 2 to be metallic reflection, it is necessary at a minimum that the thickness d of the thin film 2t be at least the wavelength of the incident wave, that is, the wavelength λ _{f of the} fluorescence. . Assuming that the refraction angle of fluorescence in the thin film 2t is θ ₂ ′, this minimum required condition is expressed by the equation (3).

D ≧ λ _f cos θ ₂ ′ = λ _f 1− (sin θ ₁ / n _f ) ^{2 1/2} (3)

If T _e ≧ 0.1 in formula (2) in order to sufficiently transmit the excitation light, formula (4) is obtained.

D ≦ 0.575 λ _e 1− (sin θ ₁ / n _e ) ^{2 1/2} / (πK _e ) (4)

Next, when the wavelength λ _{f of} fluorescence is shorter than 500 Å and the thin film is composed of a multi-layer film, if the period of the multi-layer film is D, excluding the absorption coefficient for simplification of discussion, If the interference condition expressed by the following equations (5) and (6) is satisfied, a sufficient reflectance for fluorescence can be obtained.

2 D (n _f / cos θ ₂ ) − tan θ ₂ sin θ ₁ = mλ _f (5)

That is,

D = 1− (sin θ ₁ / n _f ) ^{2 1/2} mλ _f / 2 n _f − (sin ² θ ₁ / n _f ) (6)

In the equation (5), n _f is the average value of the refractive index with respect to the wavelength of fluorescence for each layer of the multilayer film. In practice, some deviation from the interference condition is allowed, and when 0.8 A ≦ D ≦ 1.2 A is satisfied when the right side of the equation (6) is set to A, a good reflectance can be obtained.

[0035]

FIG. 3 is a diagram showing the configuration of a first embodiment of a soft X-ray fluorescence microscope using the dichroic mirror for soft X-rays of the present invention. In the figure, 1 is a soft X-ray light source that is a high-intensity light source such as a laser plasma light source or synchrotron radiation, 2 is a dichroic mirror formed of a thin film, 3 is a Schwarzschild type objective lens, 4 is a sample, and 5 is a photodetector. Image detector as
6 is a barrier filter. A soft X-ray light source 1, which is a high-intensity light source such as a laser plasma light source or radiant light, a dichroic mirror 2, and an objective lens 3 are arranged on the same optical axis 9. The Schwarzschild type objective lens uses a multilayer film reflecting mirror and has wavelength selectivity. Therefore, there is a feature that fluorescence can be excited by excitation light of a specific wavelength.

Since the first embodiment is constructed as described above, the soft X-ray (excitation light) generated by the light source 1 passes through the dichroic mirror 2 and enters the Schwarzschild type objective lens 3. The objective lens 3 becomes excitation light of a specific wavelength, and the light is condensed toward the sample 4. When the soft X-ray (excitation light) strikes the sample 4, excited fluorescence is generated in the sample 4. The fluorescence generated in the sample 4 passes through the objective lens 3, is further reflected by the dichroic mirror 2, and enters the image detector 5 via the barrier filter 6.

The thin film forming the dichroic mirror 2 used in the first embodiment is an aluminum thin film, and the thickness d is 1000Å. It assumed excitation wavelength λ refractive index of 39.8Å a _e n _e = 0.9949, the absorption coefficient K _e
= 0.002 and the right side of equation (4) is calculated to be 25
62Å, and the thickness d of the aluminum thin film is 1000
It is larger than Å and satisfies the condition of formula (4).

The assumed fluorescence wavelength λ _f is set to 516.6 Å which is 500 Å or more where metal reflection occurs. At this time, the refractive index n _f = 0.789 and the absorption coefficient K _f = 1.90.
Is. When equation (3) is calculated using these, it is 230
Å, which is smaller than 1000 Å, which is the thickness d of the aluminum thin film, and satisfies the condition of Expression (3). The soft X-ray fluorescence microscope of the first embodiment has a fluorescence wavelength λ _f 516.6Å
The resolution when observed at (0.05 μm) is an excellent value of 0.12 μm from the formula (1) when the NA of the Schwarzschild type objective lens 3 is 0.25.

FIG. 4 is a diagram showing the construction of a second embodiment of a soft X-ray fluorescence microscope using the dichroic mirror for soft X-rays of the present invention. The second embodiment is different from the first embodiment shown in FIG. 2 in that the structure of the thin film of the dichroic mirror 2 and the type of the objective lens 3 are different, and that the barrier filter is not provided. The arrangement and the optical path are the same. That is, the objective lens 3 is a Walter type objective lens. The Wolter type objective lens uses a grazing incidence total reflection mirror and has no wavelength selectivity, and therefore can excite fluorescence at any wavelength in the wavelength region of excitation light.

The thin film forming the dichroic mirror 2 used in the second embodiment is a multilayer film having a thickness of 49.
11 of 98Å molybdenum and 52.021Å silicon
It is a layer film. The refractive index of 39.8Å, which is the assumed excitation wavelength λ _e , is n _em = 0.952 and n _es = 0.995, respectively.
5, the absorption coefficient is K _em = 0.00663, K _es =
0.00209, transmittance is 32% (transmittance 10%
Meets the above). The subscripts m and s indicate molybdenum and silicon, respectively.

The assumed fluorescence wavelength λ _f is 135.5.
Å, and the refractive indices at this time are n _fm = 0.917 and n _fs , respectively.
= 1.008, and the reflectance is 24.6%. n _fm
= 0.917 and n _fs = 1.008, the average value n _f = 0.
When the equation (6) is calculated using 963 and the incident angle of 45 °, D = 95.7Å when m = 1, and the period 102Å (= 49.98Å + 52.01Å) of the second embodiment.
Meets the conditions. The soft X-ray fluorescence microscope of the second embodiment has a fluorescence wavelength λ _f 135.5Å (0.0136 μm).
The resolution when observed with the Walter type objective lens 3
Even if NA of 0.1 is set to 0.1, the excellent value of 0.08 μm is obtained from the formula (1). The optical constants used in both of the above examples were quoted from Handbook of Optical Constants of Solid and the like.

[0042]

As described above, according to the present invention, it becomes possible to observe a thick sample which cannot be observed by the conventional soft X-ray microscope.

[Brief description of drawings]

FIG. 1 is a diagram showing a configuration of a soft X-ray fluorescence microscope using a dichroic mirror for soft X-rays of the present invention.

FIG. 2 is an explanatory diagram of an optical action in a thin film of a dichroic mirror.

FIG. 3 is a diagram showing a configuration of a first embodiment of a soft X-ray fluorescence microscope using the dichroic mirror for soft X-rays of the present invention.

FIG. 4 is a diagram showing a configuration of a second embodiment of a soft X-ray fluorescence microscope using a soft X-ray dichroic mirror of the present invention.

FIG. 5 is a basic configuration diagram of a conventional epi-illumination fluorescence microscope.

[Explanation of symbols]

 1 Fluorescence excitation light source 2 Dichroic mirror 3 Objective lens 4 Sample 5 Photodetector 6 Barrier filter 9 Optical axis

[Procedure amendment]

[Submission date] September 22, 1992

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Λ _f [1 − (sin θ ₁ / n _f ) ² ] ^1/2 ≦ d ≦ 0.575 λ _e [1 − (sin θ ₁ / n _e ) ² ] ^1/2 / (πK _e )

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0.8 A ≤ D ≤ 1.2 A where A = [1− (sin θ ₁ / n _f ) ² ] ^1/2 mλ _f ÷ 2 [n _f − (sin ² θ ₁ / n _f )],

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T _e = exp {−4 πK _e d / [λ _e cos θ ₂ ]} = exp {−4 πK _e d / [λ _e [1- (sin θ ₁ / n _e ) ² ] ^1/2 ] } (2)

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D ≧ λ _f cos θ ₂ ′ = λ _f [1− (sin θ ₁ / n _f ) ² ] ^1/2 (3)

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D ≦ 0.575 λ _e [1− (sin θ ₁ / n _e ) ² ] ^1/2 / (πK _e ) (4)

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2 D [(n _f / cos θ ₂ ) −tan θ ₂ sin θ ₁ ] = mλ _f (5)

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D = [1− (sin θ ₁ / n _f ) ² ] ^1/2 mλ _f ÷ 2 [n _f − (sin ² θ ₁ / n _f )] (6)

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[Submission date] December 17, 1992

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[Submission date] December 17, 1992

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Title: Soft X-ray dichroic mirror and microscope using the same

[Claims]

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a dichroic mirror for soft X-rays and a soft X-ray fluorescence microscope equipped with the same.

[0002]

2. Description of the Related Art Soft X-rays have a wavelength range of several Å to several hundred Å and a shorter wavelength than visible light. Therefore, if this is used as light for image formation in a microscope, high resolution observation is possible. Can be expected. Generally, the resolution δ of a microscope is obtained by the equation (1).

Δ = 0.61λ / NA (1)

In equation (1), λ is the wavelength of light and NA is the numerical aperture of the objective lens. With an ordinary optical microscope using visible light and an oil immersion objective lens with a numerical aperture NA = 1.4, the resolution δ = 2 when the wavelength λ is calculated as 5500Å.
It becomes 400 Å (0.24 μm). Further, in the ultraviolet microscope, the wavelength λ becomes shorter than in the case of the normal optical microscope, but since the numerical aperture NA of the ultraviolet objective lens is small, the resolution δ is somewhat lowered as a result. That is, wavelength λ =
Calculation with 3500Å and numerical aperture NA = 0.85 yields resolution δ = 2500Å (0.25 μm).

Next, the resolution δ of the soft X-ray microscope will be described. As the soft X-rays, for example, for a wavelength λ = 500 Å, even a Schwarzschild type objective lens that can maximize the numerical aperture in this wavelength range has a numerical aperture NA of about 0.25 in consideration of the diffraction limit. However, the resolution δ = 1200Å (0.12 μm) is still obtained.
If wavelength λ = 40Å, resolution δ = 100Å (0.0
1 μm).

[0006]

However, in the soft X-ray wavelength region, the refractive index of the substance is close to 1, and there is almost no reflection, so it is difficult to see the reflection image of the sample. Even soft X-rays can be expected to reflect to some extent in the wavelength region around 500Å. However, since the absorption of soft X-rays by the substance is large, it is not possible to obtain a beam splitter for soft X-rays with excellent performance that is excellent in the transmittance and reflectance necessary for epi-illumination, and a reflected image can be obtained even in the wavelength range around 500Å. It is difficult to put a soft X-ray microscope for observation into practical use. Therefore,
Up to now, the soft X-ray microscope has been limited in its use form to observing a comparatively thin sample with a transmission microscope, and it has not been possible to observe, for example, a thick semiconductor sample.

However, since light energy is large in the soft X-ray wavelength region and almost all substances generate fluorescence, the reflection image of a thick sample can be observed by utilizing the wavelength difference between fluorescence and soft X-rays. Can be expected to be possible.

Therefore, a conventional epi-illumination type fluorescence microscope will be described below. FIG. 5 is a basic configuration diagram of a conventional epi-illumination fluorescence microscope. In the figure, 11 is a light source for excitation,
12 is a dichroic mirror, 13 is an objective lens, 14
Is a sample, 15 is a barrier filter, 16 is a television camera, 17 is a downward prism, and 18 is an eyepiece.

The excitation light source 11 emits ultraviolet light or visible light of a short wavelength. Dichroic mirror 12
Is a type of beam splitter or interference filter that utilizes the interference of light from a thin film and has the property of reflecting only light in a specific wavelength range and transmitting light in the remaining wavelength range. . In the manufacturing method, a thin glass layer designed to reflect excitation light having a short wavelength and transmit fluorescence having a long wavelength is coated on the upper surface of a thin glass plate. The barrier filter 15 provided in front of the eyepiece lens 18 removes light having a disturbing wavelength, and may be omitted if not necessary. In addition, the downward prism 1
7 is reflected twice by the semi-transmissive reflection surface 17a and the total reflection surface 17b to change the direction of the optical axis.

In the epi-illumination type fluorescence microscope of FIG. 5, the fluorescence excitation light from the excitation light source 11 is reflected by the dichroic mirror 12 and transmitted through the objective lens 13 to hit the sample 14,
Excited fluorescence is generated in the sample 14. The fluorescence generated in the sample 14 passes through the objective lens 13, then passes through the dichroic mirror 12, and enters the eyepiece lens 18 through the prism 17. In this way, the fluorescent image is observed through the eyepiece lens 18 or photographed by the television camera 16. In the case of the conventional epi-illumination fluorescence microscope described above, the transmittance of the glass is such that the ultraviolet ray as the excitation light is bad and the visible light as the fluorescence is good, so that the fluorescence passes through the dichroic mirror 12.

On the other hand, when an epi-illumination fluorescence microscope is applied in the wavelength range of soft X-rays, it is generally said that the transmittance of a substance is good for soft X-rays having a short wavelength of excitation light and for fluorescence. Since soft X-rays having a certain wavelength are bad, there is a problem in the conventional configuration that the fluorescence is weakened by the dichroic mirror. Further, particularly when a glass plate is used as the dichroic mirror, there is a problem that even excitation light having a short wavelength is lost due to absorption.

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a fluorescence microscope capable of obtaining a good reflection image in a soft X-ray region and a dichroic mirror for soft X-rays used therein. There is.

[0013]

The dichroic mirror for soft X-rays of the present invention comprises a single layer film having a thickness d satisfying the following conditions.

Λ _f [1− (sin θ ₁ / n _f ) ² ] ^1/2 ≦ d ≦ 0.575 λ _e [1− (sin θ ₁ / n _e ) ² ] ^1/2 / (πK _e )

Where λ _e is the wavelength of light transmitted through the thin film, λ _f is the wavelength of light reflected by the thin film, n _e is the refractive index of the thin film with respect to the wavelength of the transmitted light, and n _f is the thin film. The refractive index for the reflected light, K _e is the absorption coefficient of the thin film for the transmitted light, and θ ₁ is the incident angle of the transmitted light and the reflected light with respect to the thin film.

The dichroic mirror for soft X-rays of the present invention is composed of a multilayer film having a period D satisfying the following conditions.

0.8 A ≤ D ≤ 1.2 A, where A = [1- (sin θ ₁ / n _f ) ² ] ^1/2 mλ _f / 2 [n _f − (sin ² θ ₁ / n _f )]

Where λ _f is the wavelength of light reflected by the multilayer film, n _f is the average value of the refractive index with respect to the wavelength of the reflected light for each layer of the multilayer film, and θ ₁ is the transmitted light to the multilayer film. The incident angle of the reflected light, m is a positive integer.

Further, the soft X-ray fluorescence microscope of the present invention is a soft X-ray microscope.
By providing a line light source, a dichroic mirror, an objective lens, and a photodetector, irradiating the sample with soft X-rays emitted from the soft X-ray light source, and detecting fluorescence emitted from the sample with the photodetector. In a soft X-ray microscope adapted to obtain an image of a sample, the soft X-ray light source, the dichroic mirror and the objective lens are provided on the same optical axis, and the soft X-ray is irradiated onto the sample through the dichroic mirror. The fluorescence emitted from the sample is reflected by the dichroic mirror and guided to the photodetector.

[0020]

FIG. 1 is a diagram showing the configuration of a soft X-ray fluorescence microscope using the dichroic mirror for soft X-rays of the present invention. In the figure, 1 is a soft X-ray light source that emits excitation light, 2 is a dichroic mirror formed of a thin film, 3 is an objective lens, 4 is a sample,
Reference numeral 5 is an image detector as a photodetector, and 6 is a barrier filter. Among the above, the soft X-ray light source 1, the dichroic mirror 2, and the objective lens 3 are provided on the same optical axis 9. The thin film of the dichroic mirror 2 is a soft X
The X-rays are formed so as to pass through and the fluorescence excited by the soft X-rays is reflected.

Since the soft X-ray fluorescence microscope of the present invention is constructed as described above, the short-wavelength soft X-rays generated by the soft X-ray light source 1 pass through the dichroic mirror 2 and enter the objective lens 3. Then, the light is focused toward the sample 4. When the soft X-ray having a short wavelength is focused and hits the sample 4, excited fluorescence is generated in the sample 4. The fluorescence generated in the sample 4 passes through the objective lens 3, is further reflected by the dichroic mirror 2, and enters the image detector 5 via the barrier filter 6. The image detector 5 used for detecting the fluorescence image is preferably a solid-state image sensor having a laminated diode structure with excellent sensitivity, but a general CCD image sensor, MCP (multi-channel plate) or the like can also be used. .

The dichroic mirror for soft X-rays of the present invention can be used not only as a soft X-ray fluorescence microscope but also as a spectroscopic means in the wavelength range of soft X-rays. For example, in the usual fluorescent X-ray analysis, when quantitatively measuring fluorescent X-rays of two lights having different wavelengths, light having a short wavelength is detected by utilizing the optical characteristics of the dichroic mirror for soft X-rays of the present invention. Light having a long wavelength can be detected by transmission, and light having a long wavelength can be detected by reflection.

Next, the dichroic mirror 2 made of a thin film will be described. Since the soft X-rays are largely absorbed by the substance, the transmittance is determined by the absorption coefficient of the thin film rather than the interference condition. FIG. 2 is a schematic drawing of the incident / reflected state of light on the thin film in order to explain the conditions that the dichroic mirror should satisfy. In the figure, the incident angle of the soft X-ray (excitation light) to the dichroic mirror 2 is θ ₁ , the refraction angle is θ ₂ , the complex refractive index of the thin film 2 with respect to the soft X-ray wavelength (excitation light wavelength) λ _e is n _e , and the absorption is When the coefficient is K _e and the thickness of the thin film 2 is d, the soft X for the dichroic mirror 2 is
The transmittance T _e of the line (excitation light) can be expressed by Equation (2).

T _e = exp {−4 πK _e d / [λ _e cos θ ₂ ]} = exp {−4 πK _e d / [λ _e [1- (sin θ ₁ / n _e ) ² ] ^1/2 ] } (2)

On the other hand, the wavelength λ _f of the fluorescence excited in the sample 4 and incident on the dichroic mirror 2 is longer than the soft X-ray wavelength (excitation light wavelength) λ _e , and the absorption by the substance is greater in the fluorescence than in the soft X-ray. Since it is large, the method in which fluorescence passes through the dichroic mirror 2 is not a good idea. Therefore, in the present invention, the fluorescence is reflected by the dichroic mirror 2,
The image is detected by the image detector 5.

Here, when the wavelength λ _f of the fluorescence is longer than 500 Å, the dichroic mirror 2 can be made to have a thickness of about the wavelength or more to cause metal reflection to reflect the fluorescence. Therefore, the dichroic mirror 2
Can be composed of a single-layer film satisfying the condition of the following formula (3).

D ≧ λ _f cos θ ₂ ′ = λ _f [1− (sin θ ₁ / n _f ) ² ] ^1/2 (3) where d is the thickness of the monolayer film.

On the other hand, in order to sufficiently transmit the excitation light, T
_It is necessary to satisfy _e ≧ 0.1, and equation (4) is obtained from equation (2).

D ≦ 0.575 λ _e [1- (sin θ ₁ / n _e ) ² ] ^1/2 / (πK _e ) (4)

Next, when the fluorescence wavelength λ _f is shorter than 500 Å, it is desirable that the dichroic mirror is composed of a multilayer film. In this case, if the cycle of the multilayer film is D,
In order to simplify the discussion, excluding the absorption coefficient, if the interference conditions expressed by the following equations (5) and (6) are satisfied,
Sufficient reflectance for fluorescence is obtained.

2 D [(n _f / cos θ ₂ ) − tan θ ₂ sin θ ₁ ] = mλ _f (5)

That is, D = [1- (sin θ ₁ / n _f ) ² ] ^1/2 mλ _f / 2 [n _f − (sin ² θ ₁ / n _f )] (6)

In the equation (5), n _f is the average value of the refractive index with respect to the wavelength of fluorescence for each layer of the multilayer film. In practice, some deviation from the interference condition is allowed, and when 0.8 A ≦ D ≦ 1.2 A is satisfied when the right side of the equation (6) is set to A, a good reflectance can be obtained.

[0034]

FIG. 3 is a diagram showing the configuration of a first embodiment of a soft X-ray fluorescence microscope using the dichroic mirror for soft X-rays of the present invention. In the figure, 1 is a soft X-ray light source that is a high-intensity light source such as a laser plasma light source or synchrotron radiation, 2 is a dichroic mirror formed of a thin film, 3 is a Schwarzschild type objective lens, 4 is a sample, and 5 is a photodetector. Image detector as
6 is a barrier filter. The soft X-ray light source 1, the dichroic mirror 2, and the objective lens 3 are arranged on the same optical axis 9. The Schwarzschild type objective lens uses a multilayer film reflecting mirror and has wavelength selectivity. For this reason,
It has a feature that fluorescence can be excited by excitation light of a specific wavelength.

Since the first embodiment is constructed as described above, the soft X-ray (excitation light) generated by the light source 1 passes through the dichroic mirror 2 and enters the Schwarzschild type objective lens 3. The objective lens 3 becomes excitation light of a specific wavelength, and the light is condensed toward the sample 4. When the soft X-ray (excitation light) strikes the sample 4, excited fluorescence is generated in the sample 4. The fluorescence generated in the sample 4 passes through the objective lens 3, is further reflected by the dichroic mirror 2, and enters the image detector 5 via the barrier filter 6.

The thin film forming the dichroic mirror 2 used in the first embodiment is an aluminum thin film, and the thickness d is 1000Å. It assumed excitation wavelength λ refractive index of 39.8Å a _e n _e = 0.9949, the absorption coefficient K _e
= 0.002 and the right side of equation (4) is calculated to be 25
62Å, and the thickness d of the aluminum thin film is 1000
It is larger than Å and satisfies the condition of formula (4).

Further, the assumed fluorescence wavelength λ _f is set to 516.6 Å which is 500 Å or more where metal reflection occurs. At this time, the refractive index n _f = 0.789 and the absorption coefficient K _f = 1.90.
Is. When equation (3) is calculated using these, it is 230
Å, which is smaller than 1000 Å, which is the thickness d of the aluminum thin film, and satisfies the condition of Expression (3). The soft X-ray fluorescence microscope of the first embodiment has a fluorescence wavelength λ _f 516.6Å
The resolution when observed at (0.05 μm) is an excellent value of 0.12 μm from the formula (1) when the NA of the Schwarzschild type objective lens 3 is 0.25.

FIG. 4 is a diagram showing the configuration of a second embodiment of a soft X-ray fluorescence microscope using the soft X-ray dichroic mirror of the present invention. The second embodiment is a dichroic mirror 2.
The difference from the first embodiment is that the structure of the thin film is different from the type of the objective lens 3 and that no barrier filter is provided.
That is, the objective lens 3 is a Walter type objective lens.
The Wolter type objective lens uses a grazing incidence total reflection mirror and has no wavelength selectivity, and therefore can excite fluorescence at any wavelength in the wavelength region of excitation light.

The thin film forming the dichroic mirror 2 used in the second embodiment is a multilayer film having a thickness of 49.
11 of 98Å molybdenum and 52.021Å silicon
It is a layer film. The refractive index of 39.8Å, which is the assumed excitation wavelength λ _e , is n _em = 0.952 and n _es = 0.995, respectively.
5, the absorption coefficient is K _em = 0.00663, K _es =
0.00209, transmittance is 32% (transmittance 10%
Meets the above). The subscripts m and s indicate molybdenum and silicon, respectively.

The assumed fluorescence wavelength λ _f is 135.5.
Å, and the refractive indices at this time are n _fm = 0.917 and n _fs , respectively.
= 1.008, and the reflectance is 24.6%. n _fm
= 0.917 and n _fs = 1.008, the average value n _f = 0.
When the right side of the equation (6) is calculated using 963 and the incident angle of 45 °, A = 95.7Å when m = 1,
Cycle 102Å (= 49.98Å + 52.021 in the embodiment)
Å) meets the conditions. The soft X-ray fluorescence microscope of the second embodiment has a fluorescence wavelength λ _f 135.5Å (0.0136μ).
m), the resolution is 0.08 μ according to the formula (1) even if the NA of the Wolter type objective lens 3 is 0.1.
It is an excellent value of m. The optical constants used in both of the above examples are the Handbook of Optical Constants of Solid
Etc.

[0041]

As described above, according to the present invention, it becomes possible to observe a thick sample which cannot be observed by the conventional soft X-ray microscope.

[Brief description of drawings]

FIG. 1 is a diagram showing a configuration of a soft X-ray fluorescence microscope using a dichroic mirror for soft X-rays of the present invention.

FIG. 2 is an explanatory diagram of an optical action in a thin film of a dichroic mirror.

FIG. 3 is a diagram showing a configuration of a first embodiment of a soft X-ray fluorescence microscope using the dichroic mirror for soft X-rays of the present invention.

FIG. 4 is a diagram showing a configuration of a second embodiment of a soft X-ray fluorescence microscope using a soft X-ray dichroic mirror of the present invention.

FIG. 5 is a basic configuration diagram of a conventional epi-illumination fluorescence microscope.

[Explanation of reference numerals] 1 fluorescence excitation light source 2 dichroic mirror 3 objective lens 4 sample 5 photodetector 6 barrier filter 9 optical axis

Claims (3)

[Claims] 1. A dichroic mirror for soft X-rays, which is formed by forming a single-layer film having a thickness d satisfying the following conditions on a transparent substrate. λ _f 1- (sin θ ₁ / n _f ) ^{2 1/2} ≦ d ≦ 0.575 λ _e 1- (sin θ ₁ / n _e ) ^{2 1/2} / (πK _e ), where λ _e is the light transmitted through the thin film. , Λ _f is the wavelength of light reflected by the thin film, n _e is the refractive index of the thin film with respect to the wavelength of the transmitted light, n _f is the refractive index of the thin film with respect to the reflected light, and K _e is the thin film. An absorption coefficient for transmitted light, θ ₁ is an incident angle of the transmitted light and the reflected light with respect to the thin film. 2. A dichroic mirror for soft X-rays, which is formed by forming a multilayer film having a period D satisfying the following conditions on a transparent substrate. 0.8 A ≤ D ≤ 1.2 A where A = 1- (sin θ ₁ / n _f ) ^{2 1/2} mλ _f / 2 n _f
− (Sin ² θ ₁ / n _f ), λ _f is the wavelength of the light reflected by the multilayer film, n _f is the average value of the refractive index with respect to the wavelength of the reflected light for each layer of the multilayer film, and θ ₁ is the above The incident angles of transmitted light and reflected light with respect to the multilayer film, m is a positive integer. 3. A soft X-ray light source, a dichroic mirror, an objective lens, and a photodetector, which irradiate a sample with soft X-rays emitted from the soft X-ray light source to emit fluorescence emitted from the sample into the light. In a soft X-ray microscope configured to obtain an image of a sample by detecting with a detector, the soft X-ray light source, the dichroic mirror, and the objective lens are provided on the same optical axis, and the soft X-ray is passed through the dichroic mirror. A line is irradiated to the sample, and the fluorescence emitted from the sample is reflected by the dichroic mirror and guided to the photodetector.
Line fluorescence microscope.