JP3375007B2 - Soft X-ray microscope - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention provides a soft X-ray wavelength selection for performing elemental analysis of a coating film whose constituent elements are unknown, quantitative and qualitative analysis of constituent elements of the internal structure and observing the internal structure with high contrast. A possible soft X-ray microscope.

[0002]

2. Description of the Related Art In recent years, a soft X-ray microscope using soft X-rays having a wavelength in the soft X-ray region has been developed for the purpose of observing a living body. This soft X-ray microscope irradiates an object with soft X-rays emitted from a light source, and the light transmitted through this object is detected by a soft X-ray detector to determine the soft X-ray transmittance due to the difference in composition inside the object. The difference between the two is used to observe the internal tissue of the object.

Radiation light (synchrotron light) and laser plasma soft X-ray light sources are available as soft X-ray light sources. Among these, synchrotron radiation has a problem that the device is large and cannot be easily used for living body observation and the like, but laser plasma soft X-rays can be easily generated by a simple device, and a pulsed soft X-ray light source with high brightness Therefore, dynamic observation of the living body is expected. As a soft X-ray microscope system using such a laser plasma soft X-ray, an image-forming soft X-ray microscope mainly using a soft X-ray focusing optical system is disclosed (Japanese Patent Laid-Open No. H04-264,
-264300), the soft X-ray detector and the material to be measured are brought into close contact with each other, and the material to be measured is irradiated with soft X-rays to detect the detected soft X-ray.
There is a contact type soft X-ray microscope for enlarging and observing a line image with an optical microscope, an electron microscope, an atomic force microscope, or the like. This contact type soft X-ray microscope has been conventionally used in a laboratory or the like. Image-forming soft X of the two types of soft X-ray microscopes
At present, the line microscope is far from practical use because the resolution of the optical system for image formation is not sufficient. On the other hand, the contact type soft X-ray microscope does not have the above-mentioned problems of the image forming type soft X-ray microscope, and is currently being studied for use in living body observation.

In order to utilize for living body observation, it is necessary to use soft X-rays in the so-called "water window" wavelength range (2.5 to 4.4 nanometers), and to obtain a selection window in that wavelength range. Diffraction gratings, filters, multilayer films, zone plates, etc. have been studied in the above, and soft X-rays in the "water window" wavelength range have been obtained by combining some of these. By using the soft X-rays in this wavelength range, the difference in the soft X-ray transmittance between water and substances other than water can be used to observe bacteria and cells that are active in an aqueous solution, and It enables observation of structures and tissues.

A conventional soft X-ray microscope uses white X-rays which are not spectrally separated or monochromatic X-rays obtained from a white X-ray by a diffraction grating having a wavelength selection window, a filter, a multilayer film or the like. The soft X-ray absorption coefficients of the elements that make up the substance are
It varies greatly depending on the element and the wavelength of the soft X-ray. When the constituent elements of the internal structure are known, high contrast can be obtained by observing the structure using soft X-rays having a wavelength (optimal wavelength) at which the absorption difference between the element forming the internal structure and the element forming the medium becomes large. The image is obtained. As described above, in order to observe the internal structure, it is necessary to select an optimum wavelength for the sample and perform the observation. Therefore, for the structure observation and elemental analysis of coating films whose constituent elements are unknown, various soft X-ray light sources and the position of the selection window of the diffraction grating having the wavelength selection window can be changed variously, and filters of different thickness and materials can be used. Or it is necessary to use a multilayer film having various periodic structures or materials. Each combination produces monochromatic X-rays of various wavelengths,
Observation and analysis of samples whose constituent elements are unknown using each monochromatic X-ray, and when internal tissues cannot be obtained with high contrast, monochromatic X-rays of different wavelengths are generated by different combinations to observe and analyze the sample. There is a problem that it takes labor and time to perform an operation such as the above by trial and error.

[0006]

(Points to be Solved) Conventional soft X
Since line microscope does not use a spectrometer, if there is no filter is soft X-rays transmitted through the sample is irradiated on the sample becomes the white X-rays. This white X-ray is a combination of lights of all wavelengths, and no contrast is obtained. for that reason
Set up filters in the conventional soft X-ray microscope, in Succoth eject the X-ray of a certain wavelength, so that the contrast may appear clearly. The present inventors considered converting white wavelength X-rays into spatial data by using a spectroscope to disperse white X-rays in order to select an optimum wavelength with which high contrast can be obtained. Also, when using a spectroscope,
If a slit that is normally used to block the generated X-rays is used, the line of spectra (line spectrum) is strong.
Strength and ing. In this case , there is a problem that it is difficult to distinguish the contrast due to the uneven light source due to the spectrum and the image due to the internal tissue. The present invention, etc., did not use a slit when conducting diligent research in order to reduce the light source unevenness due to the spectrum as much as possible, or widen the width of the slit.
The light source irregularity found that it is possible to minimize the case was. With such a device, the problem that the contrast due to the unevenness of the light source and the image due to the internal tissue are difficult to distinguish is solved.

The present invention provides a soft X-ray wavelength selectable soft X-ray for elemental analysis of a coating film whose constituent elements are unknown, quantitative and qualitative analysis of constituent elements of the internal structure and observation of the internal structure with high contrast. An object is to provide a line microscope.

[0008]

(Structure of the First Invention) The soft X-ray microscope of the first invention is composed of a laser generating means 1 and a laser generating means as shown in FIG. a target 3 for generating soft X-rays by irradiating a laser that occurred, spectroscopic for the apparently continuous soft X-ray spectra at the sample position broaden each line spectrum disperses the soft X-ray A means 6 and a soft X-ray detection means 5 for detecting the apparently continuous soft X-ray spectrum transmitted through the material to be measured, and a slit is provided.
It is characterized by not being installed.

The laser generating means is 10 ⁹ w / c
There is no particular limitation as long as it is an apparatus that satisfies the condition that an irradiation intensity of m ² or more can be achieved. For example, a YAG laser,
A gas laser, an excimer laser, or a carbon dioxide laser may be used. As the target, atomic number 3
.About.82 as a main component. The reason is that the irradiation intensity is 1
A wavelength of at least 1 at 0 ⁹ to 10 ¹³ w / cm ² or more
This is because it is possible to generate soft X-rays having a sufficient light amount at 5 nm or more.

The spectroscopic means is not limited as long as it can disperse the soft X-ray into a spectrum for each wavelength, and a diffraction grating is usually used. Further, the soft X-ray detecting means is not particularly limited as long as it is a device having a spatial resolution of micron or less and having sensitivity to soft X-rays having a wavelength of 1 to 80 nm, and examples thereof include a resist, a soft X-ray dry plate, and a soft X-ray. A solid film detector for X-ray film or soft X-ray (such as MCP having X-ray photocathode, CCD, zooming tube) may be used.

The material to be measured is a polymer material or a material containing a polymer, for example, a structural plastic such as ABS resin or vinyl chloride, a coating film, or the like. The thickness of the material to be measured is preferably submicron to several tens of microns.
If the thickness is less than submicron, it is difficult to obtain the contrast due to the difference in structure (type and density of elements). is there.

[0012] Soft X-ray microscope (second configuration of the invention) the present second invention, a laser generating means, and the target for generating soft X-rays by irradiating a laser that occurred from the laser over generating means , This soft X-ray is spectrally analyzed
The width of the tor is widened and the soft X-ray sp
And a slit with a wide slit for keeping the wavelength resolution low while blocking X-rays off the optical axis disposed between the target and the spectroscope (as an example). In FIG. 1 shown, 8) and a soft X-ray detection means for detecting the apparently continuous soft X-ray spectrum transmitted through the material to be measured.

The slit is arranged near the optical axis connecting the light source, the collecting mirror and the diffraction grating, and has a function of blocking paraxial rays and blocking X-rays or diffusely reflected X-rays from sources other than the light source. That is good.

[0014]

[Action]

(Operation of First Invention) The laser plasma soft X-ray light source focuses the laser on the target to generate it. Atomic number 3
Since a target mainly containing the element of ~ 82 is used, it is possible to generate a soft X-ray having a sufficient amount of light at a wavelength of 1 nanometer (nm) or more at an irradiation intensity of 10 ⁹ to 10 ¹³ w / cm ² or more. it can. Wavelength 1-40 generated from the target focused and irradiated with laser
Laser plasma soft X-rays containing nm soft X-rays are designed to be focused at the position of the soft X-ray detection means. When the intensity of the laser plasma soft X-ray generated from the target is weak, a toroidal mirror that is a focusing mirror may be installed between the target and the spectroscopic means. In this case,
The intensity of the spectrum of each soft X-ray focused on the position of the soft X-ray detecting means can be increased.

In the first aspect of the present invention, for example, a slit which is usually used for blocking the rays other than the paraxial rays and limiting the visual field of the paraxial rays to improve the wavelength resolution of the spectrum is provided between the condenser mirror and the diffraction grating. By removing it, the spectrum width of each line spectrum was widened, and a soft X-ray spectrum apparently continuous at the sample position was obtained.

The material to be measured is formed on the soft X-ray detecting means,
The dispersed soft X-rays pass through the material to be measured, and the internal tissue is formed in the soft X-ray detecting means. This structure is formed by the contrast due to the difference in the soft X-ray absorption characteristics for each wavelength of the constituent elements of the material to be measured. Therefore, the soft X-ray image obtained by the soft X-ray detection means represents the relationship between the wavelength and the sharpness of the tissue. Further, the elements constituting the tissue can be clarified from the relationship between the lightness and darkness of the tissue and the wavelength. In addition, quantitative analysis of the composition becomes possible by quantitatively evaluating the density of the tissue.

The reason why the soft X-ray microscope image with the best contrast can be easily obtained is as follows. The absorption coefficients of the elements that constitute the substance for soft X-rays vary greatly depending on the wavelength. The K-shell absorption edge and the L-shell absorption edge of carbon, nitrogen, oxygen, fluorine, sodium, magnesium, aluminum, silicon, phosphorus, and titanium are between 1 and 20 nm in wavelength, and the absorption coefficient is large at wavelengths near this absorption edge. Change. Also, since the absorption edge wavelength varies greatly depending on the type of constituent elements, it is comparatively possible to select a wavelength between the internal tissue of the substance to be observed and the absorption edge of the element constituting the medium or a wavelength with a large difference in absorption coefficient. An image of internal tissue with high contrast can be obtained.

The reason why the elemental analysis can be performed is as follows. There are wavelengths at which the contrast of a tissue image changes and is reversed by a spectroscopic soft X-ray microscope. This wavelength is the absorption edge of the elements constituting the tissue. Since the absorption edge wavelength of an element is uniquely determined by the type of the element, the constituent element can be determined from the wavelength. For example, in carbon in water, inversion of contrast and a sharp decrease in contrast are observed at wavelengths of 2.4 nm and 4.4 nm. This agrees with a K-shell absorption edge of 2.4 nm for oxygen and a K-shell absorption edge of 4.4 nm for carbon. In the case of silicon in carbon, the wavelength is 4.4.
There was a contrast inversion and a sharp decrease in contrast at nm and 12.3 nm, which is consistent with the K-shell absorption edge of carbon and the L-shell absorption edge of silicon. .

(Operation of the second invention) The reason for using the slit is that X-rays from sources other than the original light source and X-rays from the original light source are used.
This is because the rays block the X-rays reflected by the substance such as the container. When X-rays largely deviated from the optical axis as described above enter the diffraction grating, they are dispersed regardless of the relationship between the wavelength of the X-rays from the original light source and the spatial position, and overlap with the X-rays from the original light source to be absorbed. May cause confusion in determining edge wavelengths. However, if the inner surface of the container or the like is processed to prevent X-ray reflection, or if the processing is performed to block X-rays from sources other than the original light source or X-rays from the original light source, The effect of X-rays off the optical axis is almost negligible.

[0020]

The soft X-ray microscope of the present invention enables elemental analysis of a coating film whose constituent elements are unknown. In addition, quantitative and qualitative analysis of the constituent elements of the internal structure becomes possible. Further, according to the soft X-ray microscope of the present invention, it becomes possible to select the soft X-ray wavelength for observing the internal structure with high contrast.

[0021]

EXAMPLES The present invention will be described in detail below based on examples. (Embodiment 1) FIG. 1 is a view showing a schematic configuration of a soft X-ray microscope of this embodiment. In FIG. 1, a YAG laser device 1
Laser light having an energy of 0.4 Joule (J) and a pulse width of 8 nanoseconds (ns) was collected by the lens 2 and irradiated on the target 3 made of iron. This target 3
The converging diameter (diameter) was set to 40 to 80 μm or less. Therefore, considering the surface reflection by the lens 2 and the vacuum window 4, the irradiation intensity of the laser beam on the iron target 3 is 10 ¹¹ to 10 ¹³ w / cm ² . Thereby, laser plasma soft X-rays can be generated. The laser plasma soft X-rays generated from the iron target 2 irradiated with the laser light are focused on the position of the soft X-ray detecting means 5 by the toroidal mirror which is the focusing mirror 4. The soft X-rays that have passed through the toroidal mirror are separated by the spectroscope 6. The measured material 7 is formed on a soft X-ray dry plate which is a soft X-ray detecting means. Irradiating the measured soft X-rays onto the material to be measured,
The transmitted soft X-rays were exposed to a soft X-ray dry plate and a soft X-ray image of the internal structure of the material to be measured was taken. As the material to be measured, carbon,
A coating film having a composition of nitrogen, oxygen, hydrogen and silicon was used.

The iron target, the spectroscope, the soft X-ray detecting means and the like are arranged in a vacuum container 9, and the inside of the vacuum container 9 is decompressed by a vacuum pump (not shown). The elements constituting the coating film were determined by utilizing the difference in the soft X-ray transmittance due to the difference in the composition of the coating film with the soft X-ray microscope having such a structure.

FIG. 2 shows the result of measurement of the soft X-ray spectrum from the iron target using a spectroscope composed of an oblique incidence type diffraction grating. Irradiation intensity 10 ¹¹ to 10 ¹³ w /
At cm ² , soft X-rays are mainly generated from ions of pentavalent to octavalent iron, so that the wavelength of the soft X-rays is a high-luminance soft X-ray spectrum of 7 nm or more.

FIG. 3 is an X-ray photograph of a coating film prepared by bleaching a silicon-containing acrylic resin and a silicon-free acrylic resin, taken by a soft X-ray microscope. (1)
Is an X-ray photograph of an image in the wavelength range of 4 nm to 40 nm, and (2) is an X-ray photograph in which (1) is magnified 40 times. A circular tissue with a darkish inside and whitish edges is observed in the tissue near the wavelength of 4 nm, and at the wavelength of 5 to 10 nm,
The contrast of the circular structure is inverted from the contrast of the image near the wavelength of 4 nm. Further, at a wavelength of 13 nm or more, the contrast of the circular structure was sharply weakened. From these, it is expected that the circular structure and the constituent elements of the medium around it have an absorption edge between a wavelength of 4 to 5 nm and a wavelength of 10 to 13 nm.

Table 1 (BL HENKE "ATOMIC DATA" showing the absorption edge wavelengths of K shell and L shell of various elements as elements having an absorption edge of wavelength 4 to 5 nm.
AND NECLEEAR DATA TABLES "2
7-1, P34 (1982), there is only carbon (absorption edge wavelength about 4.4 nm), and as an element having an absorption edge at a wavelength of 10 to 13 nm, silicon (absorption edge wavelength). Since it is only about 12.3 nm), carbon and silicon are determined as constituent elements of the circular structure and the medium around it. Furthermore, it can be seen that the inside of the circular structure is made of silicon depending on the magnitude of the absorption coefficient.

[0026]

[Table 1]

[0027]

[Brief description of drawings]

FIG. 1 is a diagram showing a schematic configuration of a soft X-ray microscope used in Example 1.

FIG. 2 is a diagram showing continuous soft X-rays when an iron target is used.

FIG. 3 is a view showing an X-ray photograph of a coating film obtained by a soft X-ray microscope in Example 1.

[Explanation of symbols]

1 laser generation means 2 lens 3 targets 4 Focusing mirror 5 Soft X-ray detection means 6 Spectral means 7 Material to be measured 8 slits 9 reflection mirror

─────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-4-264300 (JP, A) JP-A-3-71100 (JP, A) JP-A-5-224000 (JP, A) JP-A-6- 255699 (JP, A) JP-A-7-146400 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) G21K 7/00

Claims (2)

(57) [Claims] And 1. A laser generating means, for detecting a target for generating soft X-rays, soft X-rays generated from the target and transmitted through the DUT material by irradiating a laser that occurred from the laser generating means A soft X-ray detecting means for producing a soft X-ray microscope, wherein the soft X-ray microscope is not provided with a slit , and is generated from the target between the target and the material to be measured. Dispersing means for dispersing the soft X-rays is provided, and the spectral width of each line spectrum of the soft X-rays is broadened by the dispersing means, and the soft X-rays apparently continuous at the sample position are provided.
A soft X-ray microscope, wherein the soft X-ray spectrum is detected and the apparently continuous soft X-ray spectrum transmitted through the material to be measured is detected by the soft X-ray detecting means. 2. A laser generator and a laser generator.
Soft X-rays can be emitted by irradiating the laser generated from the step
Generated target and measured from the target
Soft X-ray detection means for detecting soft X-rays transmitted through a material
A soft X-ray microscope including: and a target between the target and the material to be measured.
Is equipped with a spectroscopic means for spectroscopically analyzing the soft X-rays generated from the
Between the target and the spectroscopic means.
To keep the wavelength resolution low while blocking out X-rays
A slit with a wider slit width is provided,
At the sample position, widen the spectrum width of each X-ray spectrum
The apparently continuous soft X-ray spectrum is used for the soft X-ray inspection.
The apparently continuous material that has passed through the material to be measured by the output means.
Soft X-ray characterized by detecting a soft X-ray spectrum
microscope.