JP2003294899A - X-ray microscope - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent the degradation of the contrast in the central part of an X-ray image in comparison with that obtained in a peripheral part where a water layer is thin, because an X-ray transmission window warps due to the difference in pressure between a vacuum chamber and a sample holder whose pressure is kept at atmospheric pressure, and a water layer accommodating a sample of a microorganism in the central part of the X-ray window is thicker than the peripheral part of it in conventional technologies. <P>SOLUTION: In order to correct the imbalance in the thickness of the water layer causing ununiform X-ray images inside an X-ray microscope window, the warp of the X-ray window is resolved by filling the inside of the vacuum chamber for generating plasma with an inert gas to lessen the difference in the pressure on the X-ray window. <P>COPYRIGHT: (C)2004,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an X-ray microscope, and more particularly to a field of irradiating X-rays using laser-produced plasma, and a technical field in which an X-ray image is affected by X-ray absorption of a solvent around a sample. .

[0002]

2. Description of the Related Art Plasma is generated by irradiating an X-ray generating target with a pulsed laser, and X generated by this is generated.
An X-ray exposure apparatus that exposes a sample with a line is used to transfer a minute circuit pattern to a photoresist on a circuit board during the manufacture of a semiconductor integrated circuit, or to capture a living sample of a living organism that is impossible with an electron microscope. It has been applied in various fields such as X-ray flash imaging of the state.

FIG. 1 shows a conventional X-ray flash image pickup apparatus, which is an X-ray when applied to a so-called X-ray microscope.
The typical structural example of a line exposure apparatus is shown. This structure is the X-ray exposure apparatus disclosed by the present inventors in Japanese Patent Laid-Open No. 8-338900.

The apparatus has a vacuum chamber 11 which defines a hollow chamber of a predetermined volume, that is, an internal chamber 12, inside.
The internal chamber 12 of the vacuum container 11 can be evacuated through the exhaust pipe 13 by an exhaust device (not shown) so as to have a desired vacuum degree. A glass window 15 for laser light incidence is provided in a part of the wall structure of the vacuum container 11 so as not to break the vacuum of the inner chamber 12, and a pulse from a laser light source (not shown) provided outside is provided. The laser light 14 is appropriately converged through a converging lens or the like, enters the internal chamber 12 through the laser light incident glass window 15, and is fixedly installed in the internal chamber 12 in a predetermined posture. The X-ray generation target (target) 17 is irradiated to generate plasma.

X-rays are generated from such laser-excited plasma, and the sample 20 is irradiated with a unit irradiation time of a time corresponding to the pulse time width of the pulsed laser light 14.
In the case where the sample 20 is the microbiological sample 20, it cannot be stored in the internal chamber 12 of the vacuum container 11 as it is in order to observe it as it is. Microbiological sample 20
The ambient environment of the must generally not be a vacuum and often must be an atmospheric environment.

For this reason, an X-ray transmission window 16 is formed in the inner lid 30 which constitutes a part of the vacuum container 11 for transmitting X-rays but holding a vacuum. This window 16 is formed of a silicon nitride film by forming a silicon nitride film on the silicon substrate and removing the silicon substrate by etching from a surface opposite to the film by a predetermined dimension.

[0007]

As described above, the contact X-ray microscope includes a vacuum chamber for collecting laser pulse light to generate plasma and a PMMA etc. formed on the surface of a silicon substrate or the like. It is composed of a sample holder containing a biological sample placed on a thin film of an X-ray photosensitive material, and a silicon nitride thin film having X-ray transmissivity as well as acting as a pressure partition wall separating the vacuum chamber and the sample installation place. X-ray transmission window.

However, as shown in FIG. 2, in the conventional technique, the X-ray window bends due to the pressure difference between the vacuum chamber and the sample holder kept at atmospheric pressure, and the central portion and the periphery of the X-ray window. In comparison with the portion, the thickness of the water layer containing the microbial sample is thicker in the central portion than in the peripheral portion. Since the soft X-rays used are also absorbed by oxygen,
When the water layer is thick, the X-ray image obtained by performing X-ray irradiation shows the absorption due to oxygen constituting water molecules as a bias in the background, and the X-ray image obtained in the thin peripheral portion of the water layer.
Since the contrast is lower than that of the X-ray image, a uniform X-ray image cannot be obtained in the entire inside of the X-ray window.

[0009]

[Means for Solving the Problem] Inside the X-ray microscope window, X
In order to correct the imbalance in the thickness of the water layer which causes the non-uniformity of the line image, the pressure inside the vacuum chamber for plasma generation is increased to reduce the pressure difference applied to the X-ray window, By eliminating the deflection of the X-ray window, the thickness of the water layer under the X-ray window is made uniform. As a measure for this, a gas having a small absorption for soft X-rays such as helium gas is introduced into the vacuum chamber to eliminate the pressure difference. The gas to be introduced may be of any type as long as it can secure the X-ray dose necessary for obtaining the X-image of the sample with a pressure difference that does not cause the deflection in the X-ray window.

[0010]

Example 1 (a method in which a sample is first placed in an inner lid and then the outer lid is placed in a vacuum container) An X-ray transmission window 16 is attached to an inner lid 30 of the apparatus so that airtightness can be maintained. Target 17 (0.5 mm thick yttrium plate) was attached. Place the X-ray photosensitive film 21 on top of the sample table placed on the table,
Then, an appropriate amount of Sample 20 (Escherichia coli suspended in a liquid medium) was taken and placed on the X-ray photosensitive film. The sample stage, the X-ray photosensitive film 21, and the sample 20 are housed inside the inner lid 30 to which the X-ray transmission window 16 and the target 17 are attached, covered with the outer lid 31, and the inner lid 30.
And the outer lid with screws (not shown) to integrate them. The X-ray transmission window 16 and the sample 20 and the X-ray photosensitive film 21 are brought into close contact with each other using the sample stage fixing screw. While maintaining this state, the inner lid 30 accommodating the sample 20 and integrated with the outer lid 31 is attached to the vacuum container 11, and then the interior of the vacuum container is evacuated by an oil rotary vacuum pump (not shown). did.

At this time, when the shape of the X-ray transmission window 16 attached to the inner lid 30 is observed through the sample observation window for the optical microscope provided on the upper portion of the vacuum container 11, the X-ray transmission window is generated due to the pressure difference inside and outside the vacuum container 11. 16 was convexly bent toward the inside of the vacuum container.

In this state, helium gas was introduced into the vacuum container 11 so that the pressure inside the vacuum container 11 was substantially equal to the atmospheric pressure. At this time, when the shape of the X-ray transmission window 16 was observed, it was held flat without any bending.

After that, pulsed laser light (second harmonic) 14 emitted from a yag laser not shown in the figure is introduced through a glass window 15 for laser light incidence, and the thickness is 0.1 m.
Irradiation was performed on a target 17 made of an yttrium plate of m. Plasma was generated by this laser irradiation, and soft X-rays were generated along with the generation of the plasma. This soft X-ray was applied to a microbial sample (E. coli in the culture solution) 20 through the X-ray transmission window 16.

The transmitted X-rays transmitted through the sample were exposed by the PMMA film 21, which is an X-ray photosensitive film. As a result, in the conventional case, the X and
Comparing the X-ray images, the height of the X-ray image formed in a relief shape was high in the peripheral portion, and the height of the X-ray image was low in the central portion. In the X-ray image obtained by the apparatus of the invention, such a difference in gradation was not observed, and the height of the X-ray image was almost uniform.

[0015]

Second Embodiment (First, an inner lid is attached to the vacuum container,
Inner lid 30 of the apparatus characterized in that the sample can be inserted later and X-ray exposure can be performed immediately after setting the sample.
After attaching the X-ray transmission window 16 so that the airtightness can be maintained, the target 17 (0.1 mm thick yttrium plate) is attached, the inner lid 30 is attached to the vacuum container 11, and the inner lid is vacuumed using screws. It was fixed in the container. The inside of the vacuum vessel was evacuated by an oil rotary vacuum pump not shown in the figure. At this time, the sample observation window 18 for the optical microscope provided on the upper portion of the vacuum container 11
When the shape of the X-ray transmission window 16 attached to the inner lid 30 was observed through, the X-ray transmission window 16 was bent inward toward the inside of the vacuum container due to the pressure difference between the inside and outside of the vacuum container 11.

In this state, helium gas was introduced into the vacuum container 11 so that the pressure inside the vacuum container 11 was substantially equal to the atmospheric pressure. At this time, when the shape of the X-ray transmission window 16 was observed, it was held flat without any bending.

A state in which the sample 20 (neurons cultured on the PMMA film) placed on the X-ray photosensitive film (PMMA film) 21 is placed on the sample stand, and the X-ray transmission window 16 is held flat by the introduction of helium. The inner lid 30 was placed inside. The X-ray transmission window 16 and the sample 20 were brought into close contact with each other by applying a force from the outside to hold the sample table. In this state, laser pulse light 14 emitted from a YAG laser not shown in the figure
(YAG laser second harmonic) was introduced into the vacuum vessel 11 through the laser light incident glass window 15. The laser pulsed light 14 was focused on a target 17 for plasma generation made of an yttrium plate (thickness 0.5 mm) using an optical lens not shown in the figure, and plasma was generated. The X-ray generated from this plasma passes through the X-ray transmission window 16 and then exposes the sample 20, and an X-image that reflects the X-ray absorption rate and the abundance density of each element present inside the X-ray transmission window 16 is obtained. It is recorded on the X-ray photosensitive film 21.

After removing the sample residue from the PMMA film subjected to X-ray exposure, development processing was performed with an organic solvent to obtain PMMA.
An X-ray image formed in a relief pattern on the film was obtained. This X-ray image was observed using an atomic force microscope, and an enlarged image of the X-ray image of the sample was obtained.

As a result of examining the X-ray image obtained by this method, conventionally, when comparing the central portion and the peripheral portion of the X-ray window exposed with X-rays, the X-rays formed in a relief shape in the peripheral portion. The height of the X-ray image was high, and the height of the X-ray image was low at the central portion, and a grayscale difference was observed in the X-ray image. However, such a grayscale difference was observed in the X-ray image by the apparatus of the present invention. The height of the X-ray image was almost uniform.

In the above-mentioned Examples 1 and 2, the biological sample was described as being in water, but a sample in air can be observed in exactly the same manner.

[0021]

According to the present invention, the non-uniformity of the X-ray image inside the X-ray window, which has been a problem in using the contact X-ray microscope, can be eliminated. Conventionally, even if the X window is about 200 μm square, the contrast of the X-ray image is uneven between the central portion and the peripheral portion. However, according to this method, even if the X-ray window is widened to 1 mm square, the X-ray image becomes uneven. The image inside the line window is uniform, which improves the convenience of the X-ray microscope. The same effect is useful not only in the contact X-ray microscope but also in general X-ray microscopes using an X-ray window.

[Brief description of drawings]

FIG. 1 Conceptual diagram of a contact X-ray microscope

FIG. 2 is a conceptual diagram of a state of an X-ray transparent film in a conventional contact X-ray microscope. Since the inside of the vacuum chamber that generates the plasma that serves as the X-ray source is evacuated by the vacuum pump, the X-ray permeable film that also functions as a pressure partition between the sample holder kept at atmospheric pressure causes a pressure difference. Because it is distorted.

FIG. 3 is a conceptual view of the state of an X-ray transparent film in the X-ray microscope of the present invention. Since the helium gas or the like is introduced into the vacuum chamber for generating plasma and the pressure inside and outside the chamber is balanced, the X-ray transparent film is flat.

[Explanation of symbols]

11 ... Vacuum container 12 ... Internal chamber 13 ... Exhaust pipe 14 ... Laser light 15 ... Glass window for laser light incidence 16 ... X-ray transparent window 17 ... Target for plasma generation 18 ... Sample observation glass window for optical microscope 20 …… Sample 21 ... X-ray photosensitive film (PMMA film) 30 ... Inner lid 31 ... Outer lid

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Claims (6)

[Claims] 1. An X-ray having an X-ray source in a closed container, and irradiating an X-ray irradiated sample outside the container with X-rays through an X-ray irradiation window formed in a thin film on a part of the container. In an X-ray microscope, a gas having a low X-ray absorption is filled in the container to balance the pressure inside and outside the container, and the thin film is formed flat. 2. The X-ray microscope according to claim 1, wherein the window is formed of a silicon nitride thin film. 3. The X-ray according to claim 1, wherein the X-ray is an X-ray generated by laser-produced plasma.
Line microscope. 4. The X-ray microscope according to claim 3, wherein the container is provided with a window for laser incidence in a part of the container and a target for generating plasma by laser irradiation. . 5. The X-ray microscope according to claim 1, wherein the biological sample held at atmospheric pressure is held on the X-ray sensitive material and is arranged so as to face the window. 6. The window and the sample are movable relative to each other in a direction perpendicular to the surface of the window.
The X-ray microscope described.