WO2015033552A1

WO2015033552A1 - Absorption grating and talbot interferometer

Info

Publication number: WO2015033552A1
Application number: PCT/JP2014/004496
Authority: WO
Inventors: Takashi Nakamura; Genta Sato
Original assignee: Canon Kabushiki Kaisha
Priority date: 2013-09-04
Filing date: 2014-09-02
Publication date: 2015-03-12
Also published as: JP2015072261A; JP6362103B2; WO2015033552A4

Abstract

An absorption grating (3) includes a plurality of small absorption gratings in which transmitting portions configured to transmit X-rays and shielding portions configured to block the X-rays are arranged. Each of the plurality of small absorption gratings includes a two-dimensional grating area in which the transmitting portions and the shielding portions are arranged in two intersecting directions, and a one-dimensional grating area in which the transmitting portions and the shielding portions are arranged in one direction. The one-dimensional grating area is provided in at least a part of an outer periphery of the two-dimensional grating area. At least parts of the one-dimensional grating areas included in the adjacent small absorption gratings are superposed to form an overlapping area. The arrangement directions in the small absorption gratings intersect in the overlapping area.

Description

ABSORPTION GRATING AND TALBOT INTERFEROMETER

The present invention relates to an absorption grating and a Talbot interferometer.

X-ray phase imaging methods acquire information about a subject by producing contrast on the basis of the phase shift of X-rays. One of the X-ray phase imaging methods is Talbot interferometry.

To observe Talbot interference using X-rays, at least an X-ray source for emitting spatially coherent X-rays, a diffraction grating for periodically modulating the phase of the X-rays, and a detector are needed. When the spatially coherent X-rays are transmitted through the diffraction grating, the phase of the X-rays periodically changes while reflecting the shape of the diffraction grating. Then, a first interference pattern called a self-image is formed at a position at a certain distance, called a Talbot distance, from the diffraction grating.

When the subject is disposed between the X-ray source and the diffraction grating or between the diffraction grating and the detector, the self-image is deformed by the shape of the subject and the complex refraction index. From this deformation of the self-image, information about the phase of the subject (hereinafter sometimes referred to as phase information) can be obtained. For example, the information about the phase of the subject includes a differential phase image, a phase image, and a scattering image.

In general, the pitch of a self-image formed in Talbot interferometry using X-rays is less than the pixel pitch of the detector. Hence, it is difficult to directly detect the self-image. Accordingly, a second interference pattern is formed using an absorption grating having a periodic structure in which shielding portions for blocking X-rays and transmitting portions for transmitting the X-rays are periodically arranged.

The period of the shielding portions and the transmitting portions formed in the absorption grating are equal to or substantially equal to the period of the self-image. This allows a moire pattern having a period more than that of the self-image to be formed as a second interference pattern, and allows fringe scanning to be performed by moving the position relative to the self-image.

The shielding portions are formed by metal structures having a high aspect ratio to sufficiently block the X-rays. Hence, it is difficult to produce a large-area absorption grating.
For this reason, PTL 1 describes a large-area absorption grating produced by overlapping a plurality of small absorption gratings including shielding portions of a one-dimensional periodic structure.

Japanese Patent Laid-Open No. 2012-045099 (counterpart: WO 2012/026223 A1)

The present invention provides an absorption grating including
a plurality of small absorption gratings in which transmitting portions configured to transmit X-rays and shielding portions configured to block the X-rays are arranged. Each of the plurality of small absorption gratings includes a two-dimensional grating area in which the transmitting portions and the shielding portions are arranged in two intersecting directions, and a one-dimensional grating area in which the transmitting portions and the shielding portions are arranged in one direction. The one-dimensional grating area is provided in at least a part of an outer periphery of the two-dimensional grating area. At least parts of the one-dimensional grating areas included in the adjacent small absorption gratings, of the plurality of small absorption gratings, are superposed to form an overlapping area. The arrangement directions in the small absorption gratings intersect in the overlapping area.

Further features of the present invention will become apparent from the following description of exemplary embodiments with reference to the attached drawings.

Fig. 1A schematically illustrates a small absorption grating in an absorption grating including a plurality of small absorption gratings according to an embodiment and Example 1 of the present invention. Fig. 1B schematically illustrates the absorption grating according to the embodiment and Example. Fig. 2A schematically illustrates a small absorption grating in an absorption grating including a plurality of small absorption gratings according to an embodiment and a second example of the present invention. Fig. 2B schematically illustrates a small absorption grating in the absorption grating according to the embodiment and the second example. Fig. 2C schematically illustrates the absorption grating according to the embodiment and the second example. Fig. 3A schematically illustrates a small absorption grating in an absorption grating including a plurality of small absorption grating according to an embodiment of the present invention. Fig. 3B schematically illustrates a small absorption grating in the absorption grating of the embodiment. Fig. 3C schematically illustrates the absorption grating according to the embodiment. Fig. 4A schematically illustrates a two-dimensional periodic structure in an embodiment of the present invention. Fig. 4B schematically illustrates a one-dimensional periodic structure in the embodiment of the present invention. Fig. 5A schematically illustrates a small absorption grating in an absorption grating including a plurality of small absorption gratins according to an embodiment of the present invention. Fig. 5B schematically illustrates the absorption grating of the embodiment. Fig. 5C schematically illustrates small absorption gratings in an absorption grating according to an embodiment of the present invention. Fig. 5D schematically illustrates the absorption grating of the embodiment. Fig. 6A schematically illustrates an absorption grating according to an embodiment of the present invention, in which a plurality of small absorption gratings are arranged such that the normals thereto intersect. Fig. 6B schematically illustrates an absorption grating according to an embodiment of the present invention, in which a plurality of small absorption gratings are arranged such that the normals thereto intersect. Fig. 6C schematically illustrates an absorption grating according to an embodiment of the present invention, in which a plurality of small absorption gratings are arranged such that the normals thereto intersect. Fig. 6D schematically illustrates an absorption grating according to an embodiment of the present invention, in which a plurality of small absorption gratings are arranged such that the normals thereto intersect. Fig. 7 schematically illustrates an absorption grating of the related art including a plurality of small absorption gratings. Fig. 8 schematically illustrates a Talbot interferometer including the absorption grating according to the embodiment of the present invention.

When a plurality of small absorption gratings are overlapped, as described in PTL 1, it is difficult to acquire phase information in an area where the small absorption gratings are overlapped, depending on the overlapping accuracy of the small absorption gratings. This is because shielding portions are not located at the positions, where the shielding portions should be located in design, or transmitting portions are not located at the positions, where the transmitting portions should be located in design, owing to misalignment of the small absorption gratings. It is particularly difficult to accurately overlap two-dimensional small absorption gratings in each of which shielding portions and transmitting portions are arranged in two directions.

For this reason, the X-ray transmittance in the area where the small absorption gratings are overlapped (hereinafter sometimes referred to as an overlapping area) is lower than in an area where the small absorption gratings are not overlapped, the number of photons that reach the detector decreases in the overlapping area, and the ratio of the acquired signal to noise of the detector (SN ratio) decreases. Therefore, it may be difficult to acquire phase information in the overlapping area.

Accordingly, an embodiment of the present invention provides an absorption grating that allows phase information in an overlapping area to be more easily acquired than before when two-dimensional small absorption gratings are overlapped. For that purpose, in the absorption grating of the embodiment, the difference between the X-ray transmittance in the area where small absorption gratings are overlapped and the X-ray transmittance in the area where the small absorption gratings are not overlapped is decreased. Specifically, the absorption grating of the embodiment has the following structure. That is, the absorption grating includes a plurality of small absorption gratings in each of which transmitting portions for transmitting X-rays and shielding portions for blocking the X-rays are arranged.

Each of the small absorption gratings includes a two-dimensional grating area where the transmitting portions and the shielding portions are arranged in two intersecting directions and a one-dimensional grating area where the transmitting portions and the shielding portions are arranged in one direction. The one-dimensional grating area is provided in at least a part of the outer periphery of the two-dimensional grating area. The absorption grating includes an overlapping area that is formed by overlapping at least parts of the one-dimensional grating areas included in the adjacent small absorption gratings. In the overlapping area, arrangement directions of the one-dimensional grating areas included in the adjacent small absorption gratings intersect each other. Thus, the transmitting portions and the shielding portions are arranged in two intersecting directions in the overlapping area.

Preferably, in each of the small absorption gratings, any one of the arrangement directions of the transmitting portions and the shielding portions in the two-dimensional grating area is parallel to the arrangement direction of the transmitting portions and the shielding portions in the one-dimensional grating area.

Further preferably, the arrangement directions of the transmitting portions and the shielding portions in the two-dimensional grating area are parallel to the arrangement directions of the transmitting portions and the shielding portions in the one-dimensional grating areas overlapping in the overlapping area.

Further preferably, in the arrangement directions of the transmitting portions and the shielding portions in the two-dimensional grating area, the pitch of the transmitting portions and the shielding portions in the two-dimensional grating area is equal to the pitch of the transmitting portions and the shielding portions in the overlapping area. In the present invention and the description thereof, the phrase that the pitch is equal means that the pitch has a margin of plus or minus 10%. That is, when a certain pitch is within the range of 0.9 to 1.1 A, it is equal to the pitch A. The phrase that the arrangement directions are parallel means that the absolute value of the angle formed by the arrangement directions is 0.1 degrees or less. The phrase that the arrangement directions intersect each other means that the absolute value of the angle formed by the arrangement directions is within the range of 89.9 to 90.1 degrees.

As a specific example, an absorption grating composed of a plurality of small absorption gratings and used for X-ray phase imaging will be described below with reference to the drawings.

Fig. 4A illustrates an example of a structure 1 of a two-dimensional grating area in which transmitting portions and shielding portions are periodically arranged in two intersecting directions (hereinafter sometimes referred to as a two-dimensional periodic structure). Fig. 4B illustrates an example of a structure 2 of a one-dimensional grating area in which transmitting portions and shielding portions are periodically arranged in one direction (hereinafter sometimes referred to as a one-dimensional periodic structure). An absorption grating 4 according to an embodiment is composed of a plurality of small absorption gratings 3 including shielding portions having the two-dimensional periodic structure 1 and shielding portions provided in at least a part of the outer periphery of the two-dimensional periodic structure 1 and having the one-dimensional periodic structure 2.

Preferably, the one-dimensional periodic structure 2 has the same arrangement direction as one of the arrangement directions of the two-dimensional periodic structure 1, and the shielding portions are arranged in that arrangement direction at the same pitch as that in the two-dimensional periodic structure 1.

The small absorption gratings 3 are overlapped such that the one-dimensional periodic structures 2 formed on the outer peripheries of the small absorption gratings 3 are superposed, when viewed from a direction perpendicular to a substrate. At this time, the small absorption gratings 3 are overlapped such that the arrangement directions of the one-dimensional periodic structures 2 intersect each other. Thus, in the overlapping area, the transmitting portions and the shielding portions are periodically arranged in two intersecting directions. In addition, the X-ray transmittance in the overlapping area can be similar to the X-ray transmittance in the two-dimensional periodic structure.

Preferably, the two-dimensional periodic structure 1 is a mesh structure. More preferably, the arrangement directions in the mesh structure intersect at right angles. Further preferably, the two arrangement directions in the two-dimensional periodic structure coincide with the two arrangement directions in the overlapping area. For that purpose, it is only necessary that the two-dimensional periodic structures of the overlapped small absorption gratings should have the same arrangement directions (first and second directions) and that the arrangement direction of one of the first-dimensional periodic structures superposed in the overlapping area should be the first direction and the other arrangement direction should be the second direction.

When the small absorption gratings are mesh gratings, the X-ray transmittance of a single mesh small absorption grating is ideally 1/4 (when the arrangement directions intersect at right angles). However, when two-dimensional periodic structures of two mesh small absorption gratings are superposed, they may completely block light.

As illustrated in Fig. 7, even when moire fringes are formed by overlapping small absorption gratings 31 each having only a two-dimensional periodic structure, the average transmittance in the overlapping area becomes 1/16.

When a plurality of small absorption gratings are accurately positioned and fixed, the X-ray transmittance in the overlapping area is not different from the X-ray transmittance in the areas where the small absorption gratings do not overlap (hereinafter sometimes referred to as center areas). However, since the small absorption gratings include shielding portions of the order of micrometers, a positioning accuracy of the order of at least micrometers is required. Hence, overlapping is difficult.

In contrast, in the embodiment, two small absorption gratings 3 each having a two-dimensional periodic structure 1 in a mesh form are overlapped such that the arrangement directions of one-dimensional periodic structures included in the small absorption gratings 3 intersect each other.

The transmittance of one one-dimensional grating is 1/2 (50%). When the small absorption gratings are overlapped such that the arrangement directions of the one-dimensional periodic structures intersect at right angles, the transmittance becomes 1/4 (25%). At this time, even if there are rotation error of several degrees and positioning error of the order of micrometers, the transmittance rarely changes.

For this reason, a plurality of small absorption gratings 3, in each of which a one-dimensional periodic structure 2 is provided on the outer periphery of a two-dimensional periodic structure 1, are produced, and are overlapped such that the one-dimensional periodic structures 2 are superposed to form an absorption grating 4. This allows a large-area absorption grating 4 to be produced by easier positioning than a absorption grating in which two-dimensional periodic structures of small absorption gratings having only the two-dimensional periodic structures are superposed.

Preferably, when the arrangement directions of the two-dimensional periodic structure intersect at right angles, the arrangement directions of the one-dimensional periodic structures 2 in the overlapping area also intersect at right angles, as viewed from the direction perpendicular to the substrate. Further, when the small absorption gratings are overlapped, each of the one-dimensional periodic structure of each of the small absorption gratings may have an area that is not superposed on the one-dimensional periodic structure of the adjacent small absorption grating, or the one-dimensional periodic structure 2 and a part of the two-dimensional periodic structure 1 may be superposed.

When the one-dimensional periodic structures are partly not superposed, the transmittance in that area is 50%, which is different from the transmittance (25%) of the two-dimensional periodic structure. However, this transmittance is closer to the transmittance of the two-dimensional periodic structure than the transmittance (100%) when the two-dimensional periodic structures of the small absorption gratings, each having only the two-dimensional periodic structure, are not superposed. Thus, it is easy to acquire phase information in the arrangement direction of the one-dimensional periodic structure. Further, when the one-dimensional periodic structure 2 and a part of the two-dimensional periodic structure 1 are superposed, the influence on the transmittance in the superposed area is less than when the two-dimensional periodic structures are superposed. Hence, it is easy to acquire phase information.

However, preferably, the number of areas of the one-dimensional periodic structure 2 that are not superposed on the one-dimensional periodic structure of the adjacent small absorption grating and the number of areas where the one-dimensional periodic structure 2 and the two-dimensional periodic structure 1 are superposed are as small as possible. Preferably, 1/2 or more of the area of one of the one-dimensional periodic structures in adjacent small absorption gratings that form an overlapping area is superposed on the other one-dimensional periodic structure of the adjacent small absorption grating. More preferably, the area is 3/4 or more. Further preferably, only the one-dimensional periodic structures 2 are superposed, but there are no one-dimensional periodic structures that are not superposed.

For this reason, the boundary between the one-dimensional periodic structure 2 and the two-dimensional periodic structure 1 is preferably linear for easy stacking.

When the arrangement directions in the two-dimensional periodic structure 1 intersect at right angles, the region that forms the two-dimensional periodic structure 1 is preferably shaped like a rectangle (including a square).

The absorption grating may be composed of small absorption gratings of one type, or may be composed of a combination of small absorption gratings of a plurality of types. When the small absorption gratings are equal in the shape of the shielding portions, they are regarded as small absorption gratings of the same type. When the small absorption gratings are different in the shape of the shielding portions, they are regarded as small absorption gratings of different types.

Two patterns of the shape of small absorption gratings of one type used to form a large-area absorption grating will be given as examples. Fig. 1A illustrates a first example of the shape of a small absorption grating (first shape) in which the arrangement directions in one-dimensional periodic structures located at positions opposed to each other across a two-dimensional periodic structure (the upper and lower sides of the two-dimensional periodic structure are located at opposed positions and the right and left sides are also located at opposed positions) intersect. However, when the arrangement directions in the two-dimensional periodic structure intersect at right angles, the arrangement directions in the one-dimensional periodic structures located at the opposed positions also preferably intersect at right angles.

Figs. 2A and 2B illustrate a second example of the shape of a small absorption grating (second shape) in which the arrangement directions of four one-dimensional periodic structures 2 located on upper, lower, right, and left sides of a two-dimensional periodic structure 1 are parallel. When small absorption gratings of the second shape are used, they are overlapped while being turned relative to each other such that the arrangement directions of the one-dimensional periodic structures of the adjacent small absorption gratings intersect.

Next, a third shape and a fourth shape of small absorption gratings will be described as exemplary shapes of small absorption gratings of two types used to form a large-area absorption grating.

In both of the small absorption gratings of the third and fourth shapes, arrangement directions in one-dimensional periodic structures located at positions opposed to each other across a two-dimensional periodic structure are parallel, and arrangement directions in one-dimensional periodic structures located at adjacent positions (that is, positions that are not opposed to each other) intersect. However, when arrangement directions in the two-dimensional periodic structure intersect at right angles, the arrangement directions in the one-dimensional periodic structures located at the adjacent positions preferably intersect at right angles.

Fig. 3B illustrates a small absorption grating 3 of the third shape. In the small absorption grating 3 of the third shape, one-dimensional periodic structures 2 are formed by extensions of shielding portions in a two-dimensional periodic structure 1. That is, the one-dimensional periodic structures located on the upper and lower sides of the two-dimensional periodic structure are structured such that shielding portions extending in the up-down direction are arranged in the horizontal direction. The one-dimensional periodic structures located on the right and left sides are structured such that shielding portions extending in the right-left direction are arranged in the vertical direction.

In contrast, Fig. 3A illustrates a small absorption grating 3 of the fourth shape. In the small absorption grating 3 of the fourth shape, one-dimensional periodic structures 2 are formed to surround the outer periphery of a two-dimensional periodic structure 1. That is, the one-dimensional periodic structures located on the right and left sides of the two-dimensional periodic structure are structured such that shielding portions extending in the up-down direction are arranged in the horizontal direction. The one-dimensional periodic structures located on the upper and lower sides are structured such that shielding portions extending in the right-left direction are arranged in the vertical direction.

When a plurality of small absorption gratings 3 are bonded in a planar shape, three or more periodic structures may be superposed. When the number of stacked structures is three or more and three or more one-dimensional periodic structures are superposed, the transmittance in that area sometimes becomes lower than in the center area. Accordingly, when the absorption grating includes three or more small absorption gratings, one-dimensional periodic structures are preferably formed such the overlapping area is formed by superposing one-dimensional periodic structures of two small absorption gratings and the one-dimensional periodic structures of three or more small absorption gratings are not superposed.

For example, in each of the small absorption gratings, as illustrated in Fig. 1A, a one-dimensional periodic structure 2 is preferably not formed in two of the four areas in contact with the vertexes of a two-dimensional periodic structure 1. When the one-dimensional periodic structure is not formed in these two areas, a region of the small absorption grating where the periodic structures (including one-dimensional and two-dimensional periodic structures) are formed is shaped like a rectangle that is cut off at two corners by small rectangles. Preferably, the cut small rectangles have a size of the width of the one-dimensional periodic structure x the height of the one-dimensional periodic structure.

While the one-dimensional periodic structures 2 are provided in contact with four outer peripheral sides of the two-dimensional periodic structure 1 in the small absorption gratings 3 illustrated in Figs. 1 to 3, one-dimensional periodic structures 2 may be provided at opposed positions. For example, small absorption gratings in which the arrangement directions in one-dimensional periodic structures located at opposed positions intersect, as illustrated in Fig. 5A, can be overlapped such that the arrangement directions in the one-dimensional periodic structures intersect, as illustrated in Fig. 5B. Alternatively, small absorption gratings in which the arrangement directions in one-dimensional periodic structures located at opposed positions are parallel, as illustrated in Fig. 5C, may be overlapped such that the arrangement directions of the one-dimensional periodic structures intersect, as illustrated in Fig. 5D.

Each of the small absorption gratings may be flat, or may be curved as illustrated in a cross-sectional view of Fig. 6A. When curved small absorption gratings are used, even if divergent X-rays are used, vignetting (shading) of X-rays occurring in a region remote from the center of the grating can be suppressed. Divergent X-rays refer to X-rays emitted from an X-ray source formed by a point light source, for example, a cone beam and a fan beam. Here, the center of the absorption grating refers to the center of an area of the absorption grating to be irradiated with the X-rays. To suppress vignetting, each of the small absorption gratings preferably has a curved shape using the distance to the X-ray source as the radius of curvature. At this time, each of the small absorption gratings is preferably curved to have a cylindrical surface when the X-rays diverge in one direction like a fan beam, and curved to be provided along a part of the surface of the sphere when the X-rays diverge in two directions like a corn beam. In addition, the small absorption gratings are preferably overlapped such that normals 5 thereto intersect at one point. The distance between the intersection point and the small absorption gratings is preferably equal to the radius of curvature. When the X-ray source is disposed at the intersection point, vignetting can be removed in theory. In actuality, when the normals to the small absorption gratings intersect, the effect of suppressing vignetting can be obtained.

Even if each of the small absorption gratings is flat, similar advantages can be obtained by overlapping the small absorption gratings such that the normals thereto (lines perpendicular to the flat faces) intersect at one point, as illustrated in a cross-sectional view of Fig. 6B. In this case, the small absorption gratings can be arranged such that the normals thereto intersect, by being disposed on an angled support substrate 6. When a support substrate 7 having projections is used instead of the angled support substrate 6, as illustrated in Fig. 6C, similar advantages can also be obtained by disposing the small absorption gratings on the support substrate 7 such that the small absorption gratings are partly disposed on the projections. Alternatively, as illustrated in Fig. 6D, the small absorption gratings may be arranged such that the normals thereto intersect, by utilizing the thickness of the small absorption gratings. In this case, the distance between the intersection point of the normals and the small absorption gratings can be appropriately controlled by adjusting the thickness of the small absorption gratings. In such a case where the small absorption gratings are arranged such that the normals thereto intersect (regardless of whether the small absorption gratings are curved or not curved), the shape of the small absorption gratings is not particularly limited, and may have any of the shapes illustrated in Figs. 1 to 3 and 5, similarly to the case in which the normals are parallel.

While the method for producing the small absorption gratings 3 is not particularly limited, a method for producing small absorption gratings using plating will be described as an example. Structure having a high aspect ratio and made of photosensitive resist or Si are formed on a smooth substrate surface, and the spaces therebetween are filled with a plating material. For example, the structures having the high aspect ratio can be formed by etching a silicon substrate. The structures having the high aspect ratio form transmitting portions, and the structures filled with the plating material form shielding portions. While it is only necessary that the plating material should be a material having low X-ray transmittance, gold, platinum, or an alloy containing these metals is preferably used because it allows comparatively easy plating.

The absorption grating 4 produced as above can constitute an X-ray Talbot interferometer 15 by being used together with a diffraction grating 18 and a detector 19. The Talbot interferometer 15 can constitute an X-ray Talbot interferometer system 150 by being used together with an X-ray source 20 and a calculator 16. The absorption grating 4 can be used in other applications as a grating that periodically blocks the X-rays. For example, the absorption grating 4 can be used as a source grating 12 for enhancing spatial coherence of X-rays while being combined with an X-ray generator 22.

Examples of the present invention will be described below.

With reference to Figs. 1A and 1B, a description will be given of an absorption grating 4 of Example 1 formed by bonding small absorption gratings (small absorption gratings of the first shape) in which the arrangement directions in one-dimensional periodic structures located at opposed positions across a two-dimensional periodic structure intersect at right angles. In Example 1, small absorption gratings of one type can be used. These small absorption gratings 3 are illustrated in Fig. 1A.

A two-dimensional periodic structure 1 is formed in a rectangular area, and one-dimensional periodic structures 2 are formed on the outer periphery of the two-dimensional periodic structure 1. The arrangement directions (x-direction, y-direction) in the two-dimensional periodic structure intersect at right angles, and the arrangement directions in the one-dimensional periodic structures in opposed areas intersect at right angles. The arrangement direction in one of the opposed one-dimensional periodic structures is parallel to one of the arrangement directions in the two-dimensional periodic structure. Similarly, the arrangement direction in the other one-dimensional periodic structure is parallel to one of the arrangement directions in the two-dimensional periodic structure. That is, in Fig. 1A, the arrangement direction in the one-dimensional periodic structure located on the upper side of the two-dimensional periodic structure is the y-direction, and the arrangement direction in the one-dimensional periodic structure located on the lower side of the two-dimensional periodic structure is the x-direction. The arrangement direction in the one-dimensional periodic structure located on the left side of the two-dimensional periodic structure is the y-direction, and the arrangement direction in the one-dimensional periodic structure located on the right side of the two-dimensional periodic structure is the x-direction.

At this time, the pitch in the x-direction in the one-dimensional periodic structures is equal to the pitch in the x-direction in the two-dimensional periodic structure. Similarly, the pitch in the y-direction in the one-dimensional periodic structures is equal to the pitch in the y-direction in the two-dimensional periodic structure. While the pitch in the x-direction and the pitch in the y-direction are equal to each other in Fig. 1A, they may be different from each other. A plurality of small absorption gratings 3 are oriented in the same direction, and one-dimensional periodic structures 2 are superposed to form an absorption grating 4, as illustrated in Fig. 1B. Thus, a grating pattern formed by superposing the one-dimensional periodic structures coincides with a grating pattern of the two-dimensional periodic structure.

That is, in the formed absorption grating 4, the plural small absorption gratings have the same grating pattern formed by the arrangement of the transmitting portions and the shielding portions. In other words, a one-dimensional periodic structure of a first small absorption grating and a one-dimensional periodic structure of a second small absorption grating adjacent to the first small absorption grating constitute a two-dimensional periodic structure having the same shape as that of two-dimensional periodic structures included in the first and second small absorption gratings. Thus, the area of a continuous two-dimensional periodic structure forming region becomes larger than that of a single small absorption grating.

The small absorption gratings can be produced using the LIGA process. A mesh structure having a pitch of 5 micrometers, a line width of 2.5 micrometers, and a thickness of 50 micrometers is formed by gold plating in a 90 x 90-mm area in the center of a Si wafer of 6 inches. On the outer periphery of the mesh structure, one-dimensional periodic structures similar to the one-dimensional periodic structures of Fig. 1A are formed to have a width of 1 mm, a pitch of 5 micrometers, and a line width of 2.5 micrometers. Thus, a small absorption grating 3 is formed to have a grating pattern shaped such that two areas in contact with the same side, of the areas in contact with four vertexes (corners) of the four rectangles, are cut off.

Four small absorption gratings 3 are similarly produced, and are bonded while the one-dimensional periodic structures having a width of 1 mm are superposed, so that an absorption grating 4 of 181 x 181 mm can be obtained.

With reference to Figs. 2A to 2C, a description will be given of an absorption grating 4 of Example 2 in which the arrangement directions of one-dimensional periodic structures are parallel and which is formed by overlapping adjacent small absorption gratings (small absorption gratings of the second shape) 3 while turning the small absorption gratings 90 degrees relative to each other. In Example 2, small absorption gratings 3 of one type can also be used.

The structure of the small absorption gratings 3 is illustrated in Fig. 2A. A two-dimensional periodic structure is formed in a rectangular area, and one-dimensional periodic structures are formed on the outer periphery of the two-dimensional periodic structure. In the small absorption grating 3, the arrangement directions of the one-dimensional periodic structures are parallel to each other. Further, the pitch in the one-dimensional periodic structures and the pitch in the two-dimensional periodic structure are equal to each other.

A small absorption grating obtained by turning the small absorption grating of Fig. 2A 90 degrees, as illustrated in Fig. 2B, is overlapped with the small absorption grating of Fig. 2A. Thus, two arrangement directions in an overlapping area intersect at right angles.

An absorption grating 4 is formed by superposing the one-dimensional periodic structures, as illustrated in Fig. 2C. Thus, the area of a continuous two-dimensional periodic structure forming region becomes larger than that of a single small absorption grating 3.

While the present invention has been described with reference to exemplary embodiments, it is to be understood that the invention is not limited to the disclosed exemplary embodiments. The scope of the following claims is to be accorded the broadest interpretation so as to encompass all such modifications and equivalent structures and functions.

This application claims the benefit of Japanese Patent Application No. 2013-182791 filed September 4, 2013 and No. 2014-160674 filed August 6, 2014, which are hereby incorporated by reference herein in their entirety.

Claims

An absorption grating comprising:
a plurality of small absorption gratings in which transmitting portions configured to transmit X-rays and shielding portions configured to block the X-rays are arranged,
wherein each of the plurality of small absorption gratings includes a two-dimensional grating area in which the transmitting portions and the shielding portions are arranged in two intersecting directions, and a one-dimensional grating area in which the transmitting portions and the shielding portions are arranged in one direction,
wherein the one-dimensional grating area is provided in at least a part of an outer periphery of the two-dimensional grating area,
wherein at least parts of the one-dimensional grating areas included in the adjacent small absorption gratings, of the plurality of small absorption gratings, are superposed to form an overlapping area, and
wherein the arrangement directions in the small absorption gratings intersect in the overlapping area.
The absorption grating according to Claim 1, wherein, in each of the small absorption gratings, one of the arrangement directions of the transmitting portions and the shielding portions in the two-dimensional grating area is parallel to the arrangement direction of the transmitting portions and the shielding portions in the one-dimensional grating area.
The absorption grating according to Claim 1 or 2, wherein the arrangement directions of the transmitting portions and the shielding portions in the two-dimensional grating area are parallel to the arrangement directions of the transmitting portions and the shielding portions in the overlapping area formed by the one-dimensional grating areas.
The absorption grating according to any one of Claims 1 to 3,
wherein the two arrangement directions of the transmitting portions and the shielding portions in the two-dimensional grating area intersect at right angles, and
wherein the arrangement directions of the transmitting portions and the shielding portions in the overlapping area formed by the one-dimensional grating areas intersect at right angles.
The absorption grating according to any one of Claims 1 to 4, wherein, in the arrangement directions of the transmitting portions and the shielding portions in the two-dimensional grating area, a pitch of the transmitting portions and the shielding portions in the two-dimensional grating area is equal to a pitch of the transmitting portions and the shielding portions in the overlapping area.
The absorption grating according to any one of Claims 1 to 5, wherein the two-dimensional grating area is shaped like a rectangle in each of the small absorption gratings.
The absorption grating according to any one of Claims 1 to 6, wherein the plurality of small absorption gratings have the same grating pattern formed by the transmitting portions and the shielding portions arranged in the entire small absorption gratings.
The absorption grating according to any one of Claims 1 to 7,
wherein the plurality of small absorption gratings have the same grating pattern formed by the transmitting portions and the shielding portions arranged in the two-dimensional grating area, and have different grating patterns in the one-dimensional grating area.
The absorption grating according to Claim 8, wherein, in at least one of the plurality of small absorption gratings, the shielding portions in the one-dimensional grating area and the shielding portions in the two-dimensional grating area continuously formed.
The absorption grating according to any one of Claims 1 to 9, wherein a grating pattern formed by the transmitting portions and the shielding portions arranged in the plurality of small absorption gratings is shaped such that two corners located on the same side of four corners of a rectangle are cut off.
A Talbot interferometer comprising:
a diffraction grating configured to diffract X-rays from an X-ray source;
the absorption grating according to any one of Claims 1 to 10; and
a detector configured to detect the X-rays from the absorption grating.