JP6528264B2 - Imaging apparatus and method - Google Patents

Description

  The present invention relates to an imaging apparatus and method.

  As an imaging technique using coherent light, X-ray ptychography has been proposed (see, for example, Non-Patent Document 1).

  FIG. 19 shows the principle of X-ray ptychography. In X-ray ptychography, while moving the sample to be observed stepwise, coherent (excellent) X-rays are irradiated to each position of the sample, and X-rays are transmitted to each position of the sample. The X-ray intensity and the diffracted X-ray intensity pattern are detected by a two-dimensional X-ray detector. As a result, a plurality of transmission and diffraction intensity patterns are obtained, and an observation image of the sample is generated by applying an operation by an iterative phase recovery algorithm to the plurality of transmission and diffraction intensity patterns. An iterative phase recovery algorithm is disclosed, for example, in Non-Patent Document 2 below.

  In a general X-ray microscope, the formation accuracy of an imaging optical element such as a lens is a factor that limits the resolution, and it is difficult to achieve a resolution better than 10 nm (nanometers). The X-ray ptychography has a feature that the resolution is not limited by the imaging optical element because the computer performs phase recovery calculation instead of image formation by a lens. This feature is attracting attention, and research on x-ray ptychography is being carried out in large-sized radiation facilities scattered around the world, and high resolution of about 10 nm has already been realized for material samples such as metal nanoparticles.

  In addition, the use of in-line holograms and the like is also studied separately (see Non-Patent Document 3; the corresponding URL of Non-Patent Document 3 is “https://www.jstage.jst.go.jp/article/jcrsj1959/18/3 / 18_3_236 / _article ").

Osaka University, "Development of Innovative X-ray Microscopy with High Spatial Resolution and High Sensitivity", [online], March 2013, Osaka University, [December 24, 2014 search], Internet <Http://www.osaka-u.ac.jp/en/news/ResearchRelease/2013/03/20130304_2> Andrew M. Maiden et al., "An improved ptychographical phase retrieval algorithm for differential imaging", Ultramicroscopy, (The Netherlands), 2009, No. 109, p. 1252-1262 Akio Aoki et al., "Microscopic X-ray Holography", Journal of the Crystallographic Society of Japan, 1976, No. 18, No. 3, p. 236-240

  In order to obtain a sample image by X-ray ptychography, not only diffracted X-rays but also transmitted X-rays must be acquired, but the intensity of transmitted X-rays is very large relative to the intensity of diffracted X-rays. For this reason, the dynamic range of the two-dimensional detector has to be correspondingly large. In particular, when a biological sample such as a biological cell is to be observed, since the biological sample is composed of light elements such as oxygen, carbon and nitrogen, the ability to scatter X-rays is small, and usually the intensity of transmitted X-rays is On the other hand, the intensity of the diffracted X-rays is less than one hundred thousandth. Therefore, particularly when a biological sample is to be observed, a large dynamic range is required for the two-dimensional detector.

However, development of a two-dimensional detector with a large dynamic range requires a great deal of cost and time. Even if a two-dimensional detector having the necessary dynamic range still exists, the expansion of the dynamic range leads to an increase in the acquisition cost of the two-dimensional detector. For example, although a pixel array detector having a detection performance of 10 ⁶ photons / pixel / second has been put to practical use, such a two-dimensional detector has a considerably high acquisition cost (for example, tens of millions of yen) and is used Hateful.

It should be noted that for the detector, the numerical value shown in the unit "photon / pixel / second" represents the maximum number of photons detectable per second at each pixel. If it is 10 ^m photons / pixel / sec, 1 photon and 10 ^m photons can be distinguished and detected per second at each pixel (m is a natural number). Can be detected to distinguish photons 1 photon and 10 ^m also means that it is possible to detect and differentiate between photons of 0 photons and one photon and 10 ^m. Hereinafter, the numerical value represented by the unit "photon / pixel / second", which indicates the detection performance of the two-dimensional detector, will be referred to as the detection dynamic range or the dynamic range of the two-dimensional detector. The detection dynamic range or the dynamic range of the two-dimensional detector means the ratio of the minimum value to the maximum value of the number of distinguishable photons per unit time, which is also called the photon detection dynamic range per unit time. As the detection time (i.e., the time used for detection) increases, the ratio of the number of photons distinguishable by the two-dimensional detector increases. That is, for example, if 10 ⁶ photons / pixel / second, one photon and 10 ⁹ photons can be distinguished and detected in each pixel by taking 1000 seconds.

  SUMMARY OF THE INVENTION It is an object of the present invention to provide an imaging device and method that contribute to the reduction of the required detection dynamic range.

  An imaging apparatus according to the present invention is a scattering structure which is disposed upstream of a sample to be irradiated with incident light and scatters a part of the incident light to emit scattered light toward the sample; And a two-dimensional detector for detecting the intensity of light coming from the sample in a predetermined two-dimensional plane based on the incident light, and light from the sample toward the two-dimensional detector A shield for shielding the light having at least the maximum intensity from reaching the two-dimensional detector, and computing means for generating an image of the sample based on the detection result of the two-dimensional detector It features.

  By providing the shield, it is possible to reduce the detection dynamic range required for the two-dimensional detector. The sample structure information missing due to shielding can be complemented by the detection result of the two-dimensional detector based on the scattered light from the scattering structure. That is, it is possible to reduce the detection dynamic range required for the two-dimensional detector while securing the generation of a good image.

  In the imaging method according to the present invention, a scattering structure for scattering a part of the incident light and emitting the scattered light toward the sample is disposed on the upstream side of the sample to which the incident light is irradiated, and On the downstream side of the sample, a two-dimensional detector for detecting the intensity of light coming from the sample based on the incident light in a predetermined two-dimensional plane is disposed, and the light from the sample toward the two-dimensional detector In the state where the light having at least the maximum intensity is blocked from reaching the two-dimensional detector, an image of the sample is generated based on the detection result of the two-dimensional detector.

  The shielding makes it possible to reduce the detection dynamic range required for the two-dimensional detector. The sample structure information missing due to shielding can be complemented by the detection result of the two-dimensional detector based on the scattered light from the scattering structure. That is, it is possible to reduce the detection dynamic range required for the two-dimensional detector while securing the generation of a good image.

  According to the present invention, it is possible to provide an imaging apparatus and method that contributes to the reduction of the required detection dynamic range.

It is a perspective view showing composition of an imaging device concerning a reference embodiment of the present invention. It is a side view showing composition of an imaging device concerning a reference embodiment of the present invention. It is a figure for demonstrating the step movement of a sample, and the position change of the irradiation area | region of incident light. It is an operation | movement operation | movement operation | movement of a sample image by X-ray ptychography concerning the reference embodiment of this invention. It is a figure which shows the basic algorithm of Fourier iterative phase recovery method. It is a figure which shows a test image and light intensity detection pattern in simulation of the reference embodiment of this invention. It is a side view showing composition of an imaging device concerning a 1st embodiment of the present invention. FIG. 7 is a perspective view and a side view of an example of a reference light source structure according to the first embodiment of the present invention. 6 is an operation flowchart of construction of a sample image by X-ray ptychography according to the first embodiment of the present invention. It is a figure which concerns on simulation of 1st Embodiment of this invention, and is a figure which shows the light intensity detection pattern and reconstruction image by the 1st virtual imaging device (structure for reference light source: none, and shield: none). It is a figure which concerns on simulation of 1st Embodiment of this invention, and is a figure which shows the light intensity detection pattern and reconstruction image by the 2nd virtual imaging device (structure for reference light sources: None, and shield: existence). It is a figure which concerns on simulation of 1st Embodiment of this invention, and is a figure which shows the light intensity detection pattern and reconstruction image by the 3rd virtual imaging device (structure for reference light sources: and shield: existence). FIG. 6 is a perspective view of another example of the reference light source structure according to the first embodiment of the present invention. It is a figure which concerns on 1st Embodiment of this invention and shows the SEM image of the structure for reference light sources used by experiment. It is a figure which concerns on 1st Embodiment of this invention and shows the SEM image of the sample (Siemens star test chart) used by experiment. It is a figure which concerns on 1st Embodiment of this invention and shows the light intensity detection pattern obtained by experiment. It is a figure which concerns on 1st Embodiment of this invention and shows the reconstruction image of the sample obtained by experiment. It is a schematic block diagram of the imaging device concerning a 3rd embodiment of the present invention. It is a principle view of X-ray tichography according to prior art.

  Hereinafter, embodiments of the present invention will be specifically described with reference to the drawings. In the respective drawings to be referred to, the same parts are denoted by the same reference numerals, and redundant description of the same parts will be omitted in principle. In the present specification, in order to simplify the description, the names of information, signals, physical quantities, members, etc. corresponding to the symbols or marks are described by marking the symbols or marks referring to information, signals, physical quantities, members, etc. It may be abbreviated or abbreviated.

<< Reference embodiment >>
First, a reference embodiment to be provided for comparison with the later-described first embodiment and the like will be described. 1 and 2 are a perspective view and a side view showing a configuration of an imaging apparatus according to a reference embodiment.

  In FIG. 1 and FIG. 2, the hatched area referred to by the symbol L 0 represents the incident light to the sample 10. However, in FIG. 1 and FIG. 2, the region of the light transmitted through the sample 10 is also hatched (the same applies to FIG. 7 described later). The incident light L0 is light having coherence, that is, coherent light. However, since there is no completely coherent light in reality, coherent light here should be understood to be light with high coherence, both spatially and temporally.

The incident light L0 may be light of any wavelength, but in particular it is assumed to be X-rays. Here, it is assumed that the incident light L0 is an X-ray (coherent X-ray) having an energy of 6.5 keV (electron volts). The incident light L0 may be focused X-rays formed by focusing radiation in the X-ray region generated at the radiation facility. In FIG. 1, an alternate long and _short dash line AX _OPT represents the optical axis of the incident light L0. It is assumed that all the lights described in the reference embodiment are lights based on the incident light L0.

The X axis, the Y axis and the Z axis are orthogonal to one another. The optical axis AX _OPT is parallel to the Z axis, and the incident light L0 travels from the negative side to the positive side of the Z axis. Note that a two-dimensional plane parallel to the X and Y axes, a two-dimensional plane parallel to the Y and Z axes, and a two-dimensional plane parallel to the Z and X axes are the XY, YZ, and ZX planes, respectively. Call.

  The incident light L0 is irradiated to the sample 10. The sample 10 is a sample having a spread in the X-axis and Y-axis directions, and further has a thickness in the Z-axis direction. The sample 10 may be any sample. For example, the sample 10 may be a metal sample or a biological sample. However, among the incident light L0 irradiated to the sample 10, a part is scattered and diffracted, and the remainder is transmitted through the sample 10. Of the incident light L0 (6.5 keV X-ray) irradiated to the sample 10, a sample 10 with a small thickness is assumed, most of which passes through the sample 10.

  The incident light L 0 is condensed at the position of the sample 10 by an optical system (not shown) provided upstream of the sample 10. In FIG. 1, a point O represents the center position of the condensing point of the incident light L0. The upstream refers to the upstream with respect to the traveling direction of the incident light L0, and naturally, the incident light L0 travels from the upstream to the downstream. The incident light L0 spreads like spots along a cross orthogonal to the Z axis. That is, in the XY plane, the incident light L0 is formed from light of a plurality of spots, and the plurality of spots are aligned in the cross direction (that is, aligned along the X-axis and Y-axis directions, for example). In the following, the spot with the highest light intensity located at the center of the plurality of spots is regarded as the incident light L0 and focused, and the size of the focused spot (specifically, the outer edge of the spread of the focused spot is shown The diameter of the circle is called the spot diameter. In particular, the spot diameter of the incident light L0 at the position of the sample 10 is represented by the symbol SR. Here, it is considered that the incident light L0 is collected in a perfect circular shape at the position of the sample 10, and the spot diameter SR is 1 μm (micrometer).

  On the XY plane, the size (spreading area) of the sample 10 is larger than the size (spreading area) of the incident light L 0 at the position of the sample 10. The sample 10 has a plate shape having a thickness in the Z-axis direction. Here, for example, the sample 10 has a rectangular or square shape having a side larger than 1 μm in the XY plane. The thickness of the sample 10 in the Z-axis direction may be nonuniform in the X-axis and Y-axis directions. For example, the thickness of the sample 10 in the Z-axis direction is distributed in the range of several tens of nm to several tens of μm in the X-axis and Y-axis directions.

  The two-dimensional detector 20 is a two-dimensional X-ray detector provided on the downstream side of the sample 10. The two-dimensional detector 20 receives the light from the sample 10 based on the incident light L0, and detects the intensity of the received light in a predetermined two-dimensional plane. The two-dimensional plane here is parallel to the XY plane. The two-dimensional detector 20 has a detection plane parallel to the XY plane, and detects the intensity (received light intensity) of light at each position in the detection plane.

  The area in the detection plane of the two-dimensional detector 20 can be classified into the light receiving area 21 of the transmitted X-ray and the light receiving area 22 of the diffracted X-ray for convenience. Of the incident light L0 irradiated to the sample 10, the light transmitted without being scattered by the sample 10 is called a transmitted X-ray. The light receiving area 21 is an area for receiving the transmitted X-ray. The center of the light receiving area 21 usually coincides with the center of the detection surface. In the following, it is assumed that the center of the light receiving area 21 (the center of the light receiving area that receives the transmitted X-ray) and the center of the detection surface (that is, the center of the two-dimensional detector 20) coincide with each other. The transmitted X-rays do not enter the light receiving area 22. The light receiving region 22 receives the light scattered by the sample 10 among the incident light L0 irradiated to the sample 10. The light scattered by the sample 10 forms diffraction fringes in the light receiving region 22 according to the structure of the sample 10. The scattered light from the sample 10 forming the diffraction fringes is referred to as a diffraction X-ray, and the light reception intensity pattern in the light receiving region 22 representing the diffraction fringe is referred to as a diffraction X-ray intensity pattern or a diffraction intensity pattern. The light reception intensity pattern in the light reception area 21 is referred to as a transmission X-ray intensity pattern or transmission intensity pattern.

  If only transmitted X-rays are used, the system of FIG. 1 can be regarded as an X-ray microscope with a lens with a resolution of 1 μm. What can be observed through a lens with a resolution of 1 μm is limited to information of a size of 1 μm or more. However, information smaller than 1 μm can be obtained by observing diffracted X-rays.

As shown in FIG. 3, the imaging apparatus includes a driving device 30 for stepping the sample 10 in the X-axis direction or the Y-axis direction. The step positions P _{1 to} P _n are different from each other, which are planes parallel to the XY plane and arranged on a common plane located in the sample 10. Although nine step positions P _{1 to} P ₉ are shown in FIG. 3, n is arbitrary as long as it is an integer of 2 or more. The driving device 30 can step-move the sample 10 so that the position of the condensing point O coincides with any of the step positions P _{1 to} P _n . The sample 10 may be moved in a direction different from the X-axis direction and the Y-axis direction by the driving device 30 (in this case, the step positions P _{1 to} P _n are on a plane inclined from the XY plane). It will be placed in different positions). However, it is assumed that the direction of the step movement of the sample 10 has a direction component orthogonal to the optical axis AX _OPT of the incident light L0.

Considering in the XY plane, when the position of the light condensing point O is made to coincide with the step position P _i , an area within a sample 10 and an inner area of a circle with a diameter of 1 μm centered on the step position P _i The incident light L0 is collected and emitted to the light source (i is an integer).

In each of the X-axis and Y-axis directions, the distance between two step positions adjacent to each other is smaller than the spot diameter SR (here, 1 μm). Therefore, the irradiation area of the incident light L0 on the sample 10 when the position of the light condensing point O coincides with the first step position corresponds to when the position of the light condensing point O coincides with the second step position. It overlaps with the irradiation area of the incident light L0 onto the sample 10 in part. The first step position herein refers to any _one of the step positions P1 to _Pn , and the second step position refers to one or more step positions different from the first step position. For example, (internal region of the center of the circle in the nine circles in FIG. 3) the irradiation area of the incident light L0 into the sample 10 when the position of the focal point O is coincident with the step position P ₅ are converging point It partially overlaps with each of the irradiation regions of the incident light L0 incident on the sample 10 when the position of O coincides with the step positions P ₂ , P ₄ , P ₆ and P ₈ .

FIG. 4 is a flowchart of the operation of constructing a sample image by X-ray ptychography of the imaging apparatus of the reference embodiment. First, 1 is substituted for the variable i in step S1. In the subsequent step S2, the driving device 30 drives the sample 10 so that the position of the condensing point O coincides with the step position P _i . In the subsequent step S3, all detection results (all detection results of the light reception intensity) in the detection plane of the two-dimensional detector 20 are acquired as the ith light intensity detection pattern. In the reference embodiment, the transmission intensity pattern and the diffraction intensity pattern obtained simultaneously by the two-dimensional detector 20 (that is, the detection pattern consisting of the transmission intensity pattern and the diffraction intensity pattern detected simultaneously) is the i-th light intensity detection pattern It becomes.

Thereafter, in step S4, it is confirmed by the control unit (not shown) of the imaging apparatus whether or not the variable i matches the predetermined value n (for example, 100). If "i = n", the process proceeds to step S6. On the other hand, in the case of “i <n”, 1 is added to the variable i in step S5, and then the process returns to step S2 to repeat the processing from step S2. As a result, at the time when step S6 is reached, the first to n-th light intensity detection patterns are already acquired. The ith light intensity detection pattern is a pattern in which the transmission intensity pattern and the diffraction intensity pattern from the sample 10 are simultaneously detected in a state in which the position of the condensing point O coincides with the step position P _i .

  In step S6, the operation unit (not shown) of the imaging apparatus performs a predetermined operation according to the repetitive phase recovery algorithm on the first to n-th light intensity detection patterns obtained in step S3 to obtain the sample 10 Generate an image of As the iterative phase recovery algorithm, known iterative phase recovery algorithms applicable to X-ray ptychography can be used. For example, an iterative phase recovery algorithm based on the method described in Non-Patent Document 2 may be used.

  Here, although known, the iterative phase recovery algorithm will be briefly described. A method of obtaining a phase by repeatedly performing Fourier transform in a situation where only the amplitude is known and the phase can not be obtained is known as a Fourier iterative phase recovery method. The iterative phase recovery algorithm of step S6 (in other words, the iterative phase recovery method) belongs to the Fourier iterative phase recovery method.

  FIG. 5 is a diagram showing a basic algorithm of the Fourier iterative phase recovery method. In FIG. 5, an object (strictly speaking, an object wave incident on an object and an object that interacts with each other and emitted from the object) is represented by f, and a Fourier transform FT is applied to the object f (strictly, , And the diffracted wave on the detection surface is represented by F. The object here is the sample 10.

f and F are represented as complex functions. The amplitude and phase of the complex function f are represented by | f | and φ, respectively, and the amplitude and phase of the complex function F are represented by | F | and Φ, respectively. Generally, the physical quantity obtained by the diffraction experiment is only the diffraction intensity, that is, the amplitude | F |, and the phase Φ can not be obtained. If the phase Φ is determined by any method, an object f can be obtained by performing inverse Fourier transform FT ⁻¹ on F. In the Fourier iterative phase recovery method, as shown in FIG. 5, the Fourier transform and the inverse Fourier transform are alternately alternated while imposing the real space constraint condition in the real space and the inverse space constraint condition in the inverse space (frequency space). The phase is obtained by repeated calculations repeated in.

  In the iterative phase recovery algorithm in X-ray ptychography, the fact that the irradiation areas of the incident light L0 on the sample 10 overlap each other when acquiring a plurality of light intensity detection patterns and the overlapping area are taken as a real space constraint condition The above iterative calculation is performed using the first to nth light intensity detection patterns as the inverse space constraint conditions. Thereby, the distortion of the wavefront of the incident light L0 accompanying the passage of the sample 10 is derived as the phase change amount of the incident light L0 at each position on the XY plane, and the image of the sample 10 is generated from the derivation result (reconstruction) can do.

  The results of computer simulation for the imaging apparatus of the reference embodiment will be described with reference to FIGS. 6 (a) and 6 (b). FIG. 6A shows a test image 300 assumed as the sample 10 in the simulation. The test image 300 is a two-dimensional image (two-dimensional projected image) obtained by projecting the amount of phase change due to the sample 10 on the XY plane. The phase change amount refers to the phase change amount of the incident light L0 when the incident light L0 passes through the sample 10.

  In FIG. 6A, the phase change amount is larger as the area is closer to black, and the phase change amount is smaller as the area is closer to white. That is, for example, when the incident light L0 is irradiated to the hair region of the female hair expressed in the test image 300, the phase change amount is about 0.01 radian, and the incident light L0 is irradiated to the cheek region of the female When the phase change amount is about 0.005 radian. The maximum value of the phase change amount in the test image 300 is set to 0.01 radian. A phase shift of 0.01 radians corresponds to a 50 nm (nanometer) thick protein for an X-ray of energy of 6.5 keV. That is, the maximum value of the amount of phase change observed when incident light L0 is irradiated to a 50 nm thick protein is 0.01 radian.

  The light intensity detection pattern 320 of FIG. 6B has transmission and diffraction intensities to be acquired by the two-dimensional detector 20 of FIG. 1 when the region 310 of FIG. 6A is irradiated with the incident light L0. The simulation result of the pattern is shown.

  In principle, in the diffraction intensity pattern, in the spatial frequency components indicating the structure of the sample 10 (here, the test image 300), information of lower frequency components is detected at a position near the center of the detection surface, and higher frequency components Is detected at a position away from the center of the detection surface. Among spatial frequency components indicating the structure of the sample 10 (here, the test image 300), information on relatively low spatial frequency components and information on relatively high spatial frequency components are respectively low resolution information and high resolution information. Call. The light intensity detection pattern 320 contains low resolution information and high resolution information. In the light intensity detection pattern 320, low resolution information is included at a position relatively close to the center of the detection surface, and high resolution information is included at a position relatively far from the center of the detection surface.

  As can be seen from the light intensity detection pattern (transmission and diffraction intensity patterns) 320, the intensity of the diffracted X-rays is considerably smaller than the intensity of the transmitted X-rays, and the intensity of the diffracted X-rays increases with the angle of diffraction. Decrease. In order to obtain higher resolution information from the detection result of the two-dimensional detector 20, it is necessary to detect diffracted X-rays having a larger diffraction angle and hence smaller intensity. Hence, the higher the resolution of interest, the more it is necessary to obtain transmission and diffraction intensity patterns with a wider photon dynamic range.

In the imaging apparatus of FIG. 1, in order to achieve a resolution of 15 nm or less, it is necessary to acquire transmission and diffraction intensity patterns having a photon dynamic range of 10 ⁹ photons / pixel. In the simulation, the transmission and diffraction intensity pattern having a photon dynamic range of 10 ⁹ photons / pixel is obtained as a light intensity detection pattern 320 of FIG. 6 (b). The transmission and diffraction intensity patterns having a photon dynamic range of 10 ⁹ photons / pixel are the transmission and diffraction intensity patterns detected by discriminating the number of photons of 1 and the number of photons of 10 ⁹ (ie, in the two-dimensional detector 20). It means the transmission and diffraction intensity pattern) in which the ratio of the minimum value to the maximum value of the photon number of the received X-ray is 10 ⁹ . If using two-dimensional detector having a relatively low cost into the hands 10 ³ photons / pixel / sec detection performance as a two-dimensional detector 20 of FIG. 1, finally using detection time of ¹⁰⁶ seconds, 10 Transmitted and diffracted intensity patterns can be obtained with a photon dynamic range of ⁹ photons / pixel. However, the increase of the detection time is not allowed infinitely, and the shorter the detection time, the better. If a two-dimensional detector having a detection capability of 10 ⁶ photons / pixel / second is used as the two-dimensional detector 20 of FIG. 1, a photon dynamic range of 10 ⁹ photons / pixel with a detection time of 10 ³ seconds The transmission and diffraction intensity patterns can be obtained. When the detection time is determined to be 10 ³ seconds, with a detection performance of 10 ³ photons / pixel / second, only a photon dynamic range of 10 ⁶ photons / pixel can be achieved, and a desired resolution can not be obtained.

  As understood from this, with a two-dimensional detector having a large detection dynamic range (that is, a two-dimensional detector having high detection performance indicated by a unit “photon / pixel / second”), at a fixed detection time, Higher resolution can be realized. However, development of a two-dimensional detector with a large detection dynamic range requires a great deal of expense and time. Even if a two-dimensional detector having the necessary detection dynamic range still exists, the expansion of the detection dynamic range leads to an increase in the acquisition cost of the two-dimensional detector.

<< First Embodiment >>
The first embodiment of the present invention will be described as an embodiment capable of constructing a sample image with a lower detection dynamic range. The first embodiment and the second and third embodiments to be described later are embodiments based on the reference embodiment, and the matters not particularly described in the first to third embodiments are the reference embodiments unless contradictory. May be applied to the first to third embodiments. About the contradiction between the description of the reference embodiment and the description of the first to third embodiments, the latter description is prioritized in the first to third embodiments.

  FIG. 7 is a side view showing the configuration of the imaging apparatus 1 according to the first embodiment. The imaging apparatus 1 includes a reference light source structure (scattering structure) 40, a shield 50, and an arithmetic unit 60 in addition to the two-dimensional detector 20 and the driving device 30 described above. The nature, configuration and function of the incident light L0, the sample 10, the two-dimensional detector 20 and the drive device 30, and their relationship are as described above.

  The incident light L0 is condensed at the position of the sample 10 by an optical system (not shown) provided on the upstream side of the sample 10 and the reference light source structure 40.

The reference light source structure 40 (hereinafter sometimes referred to as a structure 40) is a structure provided on the upstream side of the sample 10, and the incident light L0 is first incident on the structure 40, and then the sample It is irradiated to ten. Therefore, a part of the incident light L0 is scattered by the structure 40, and the scattered light L1 from the structure 40 is emitted toward the sample 10 and the two-dimensional detector 20. 7, a broken line OE _L1 straight from the center two extending to the two-dimensional detector 20 of the structure 40 is one in which the outer edge of the scattered light L1 emitted from the structure 40 shown schematically.

On the other hand, in FIG. 7, a linear dashed line OE _L2 two extending from two points on the sample 10 to the two-dimensional detector 20, which the outer edge of the scattered light L2 emitted from the sample 10 shown schematically It is. The scattered light L2 is a result of scattering of the incident light L0 irradiated to the sample 10 through the structural body 40 by the sample 10. The distance between the sample 10 and the structure 40 is such that the irradiation area of the scattered light L1 on the sample 10 is larger than the irradiation area of the incident light L0 (that is, the irradiation area of the incident light L0 on the sample 10). To be adjusted.

  The shield 50 is disposed between the sample 10 and the two-dimensional detector 20, and shields light from the sample 10 to a predetermined shielding target area in the detection plane of the two-dimensional detector 20. If the shield 50 is made of tantalum or lead having a thickness of several hundred μm or more, light (X-rays) from the sample 10 can be completely blocked.

  For example, assuming that the minimum value of the light reception intensity to be detected by the two-dimensional detector 20 is constant, if the maximum intensity of light received at the detection surface decreases, the two-dimensional detector 20 is required. The detection dynamic range is smaller. Therefore, of the light traveling from the sample 10 to the two-dimensional detector 20, a shield having at least the light with maximum intensity does not reach the two-dimensional detector 20 (more specifically, the detection surface of the two-dimensional detector 20) 50 are disposed between the sample 10 and the two-dimensional detector 20. Of the light traveling from the sample 10 to the two-dimensional detector 20, the light having the maximum intensity is included in the transmitted X-rays, and thus the shielding target area described above is a light receiving area 21 of the transmitted X-rays (the shield 50 is not present It is an area including an area which is to receive transmitted X-rays.

  Among the diffracted X-rays, the intensity of low angle diffracted X-rays, which is a diffracted X-ray having a relatively small diffraction angle, is considerably larger than the intensity of high angle diffracted X-rays, which is a diffracted X-ray having a relatively large diffraction angle. Therefore, among the light receiving areas of the detection surface, a light receiving area which receives low-angle X-rays having a diffraction angle equal to or less than a predetermined angle may be included in the shielding target area. In the present embodiment, among the light receiving areas of the detection surface, the light receiving area that receives low angle X-rays having a diffraction angle equal to or less than a predetermined angle is also included in the shielding target area. That is, the shield 50 blocks the transmission X-rays and low-angle X-rays from being incident on the two-dimensional detector 20 (more specifically, the detection surface of the two-dimensional detector 20). By providing the shield 50, it is possible to reduce the detection dynamic range of the two-dimensional detector 20, which is required to obtain a desired resolution in a fixed detection time.

Although the transmission intensity pattern (transmission X-ray intensity pattern) is not formed on the detection surface due to the arrangement of the shield 50, the scattered light L1 is emitted from the structure 40 on one side, so an inline hologram using the scattered light L1 as a reference light Is formed on the detection surface. That is, in the two-dimensional detector 20, a diffraction intensity pattern (diffraction X-ray intensity pattern) and an inline hologram are simultaneously acquired. The sample structure information of the transmitted X-ray (information possessed by the transmitted X-ray regarding the structure of the sample 10) is sample information larger than the size of the incident light L0 at the position of the sample 10. That is, the sample structure information of the transmitted X-ray is the size of the incident light L0 at the position of the sample 10 among the spatial frequency components indicating the structure of the sample 10 (the spot diameter in the one-dimensional direction) SR: information of spatial frequency components (for example, information of 1 μm ⁻¹ or 2 μm ⁻¹ ) of a structure of 1 μm or more here. Therefore, if a structure smaller than the size of the incident light L0 at the position of the sample 10 is used for the structure 40, it is possible to complement the sample structure information of the transmitted X-ray with the in-line hologram.

  The in-line hologram is an interference fringe formed on the hologram surface when the object light and the reference light are simultaneously irradiated to the hologram surface, as is well known. The hologram plane here is the detection plane of the two-dimensional detector 20. The reference light is the scattered light L1 of the reference light source structure 40. That is, the reference light source structure 40 functions as a reference light source for forming an in-line hologram. When the reference light is irradiated to the sample 10, the reference light is scattered by the sample 10. However, the light emitted from the sample 10 by the scattering (that is, the scattered light from the sample 10 based on the reference light) is the object light. is there.

  FIGS. 8A and 8B show a perspective view and a side view of a cylindrical structure 40A which is an example of the reference light source structure 40. FIG. The cylindrical structure 40A can be formed of any type of metal. However, in order to enhance the ability to scatter X-rays, it is preferable to form the cylindrical structure 40A of heavy metal, for example, gold or tantalum to form the cylindrical structure 40A (other examples of the structure for reference light source 40 described later) Also in

The cylindrical structure 40A is a structure in which a column 42A is provided on a plate-like body 41A. The plate-like body 41A is a plate-like substance (metal or nonmetal) having an upper surface and a lower surface parallel to the XY plane and having a thickness in the Z-axis direction. Here, of the upper and lower surfaces of the plate-like body 41A, the upper surface is closer to the sample 10. The thickness of the plate-like body 41A is about several 10 nm to 100 nm, and the absorption by the X-ray is small in the plate-like body 41A. In the X-axis and Y-axis directions, the size of the plate-like body 41A is larger than the size of the incident light L0 at the position of the cylindrical structure 40A. The column 42A is a metal column extending vertically from the upper surface of the plate-like body 41A toward the sample 10. The axis of the column 42A is parallel to the Z axis. The cylindrical structure 40A is formed and arranged such that the center of the plate-like body 41A and the axis of the column 42A are positioned on the optical axis AX _OPT of the incident light L0. Here, it is assumed that the cylindrical body 42A is a cylinder having a base of a true circle, and the diameter of the true circle is represented by R.

  The structure 40 exemplified by the cylindrical structure 40A is formed to meet the first and second requirements. In the cylindrical structure 40A, the first necessary condition is a condition that the diameter R is smaller than the spot diameter SR (here, 1 μm) of the incident light L0 at the position of the sample 10. For example, the diameter R is selected from the range of 100 nm to 200 nm. The height of the column 42A is selected, for example, from the range of 500 nm to 1 μm.

  The second requirement is that, at the position of the sample 10, the size of the spread of the scattered light L1 in the X and Y axis directions is larger than the size of the spread of the incident light L0 in the X and Y axes. By satisfying the second necessary condition, the entire irradiation area of the incident light L0 on the sample 10 is included in the irradiation area of the scattered light L1 on the sample 10 at the position of the sample 10. The size of the spread of the scattered light L1 in the X and Y axis directions may be considered to be, for example, the size of the spread of the scattered light L1 in the X and Y axis directions, or X and Y of the scattered light L1. It may be considered as a spread area in the axial direction. The same applies to the incident light L0. The diameter R and height of the column 42A, the material of the column structure 40A, and the distance between the column structure 40A and the sample 10 are determined so that the second requirement is satisfied for the column structure 40A.

In principle, in-line holograms formed on the detection surface include spatial frequency component information on structures having the same size as the diameter R and structures larger than the diameter R in the structural information of the sample 10 . For example, when the diameter R is 100 nm, information of spatial frequency components such as 100 nm ⁻¹ , 500 nm ⁻¹ , 1 μm ⁻¹ and 2 μm ⁻¹ is included in the in-line hologram.

On the other hand, the sample structure information of the transmitted X-ray (information possessed by the transmitted X-ray with respect to the structure of the sample 10) is the space of the structure having the spot diameter SR or more among It is information of frequency components (for example, information of 1 μm ⁻¹ or 2 μm ⁻¹ ). Therefore, by satisfying the first requirement, it is possible to complement the sample structure information possessed by the transmitted X-ray with the in-line hologram. However, even if the first requirement is satisfied, if the size of the reference light L1 at the position of the sample 10 is smaller than the size (1 μm) of the incident light L0, the spatial frequency component of the structure of 1 μm ⁻¹ or more Information will not be included in the in-line hologram (for example, assuming that the diameter of the reference light L1 at the position of the sample 10 is 0.5 μm, the light with a diameter of 0.5 μm is 1 μm in diameter, conceptually) I can not see the structure). Therefore, satisfaction of the second requirement is required.

In addition, if even the light receiving region that receives low-angle diffracted X-rays having a diffraction angle equal to or less than a predetermined angle is included in the shielding target region, information (eg, 1 μm ⁻¹⁾ indicated by the transmitted X-ray In addition to the fact that structural information (for example, information of 500 nm ^-1 ) indicated by low angle diffraction X-rays is also missing from the detection result of the detection surface, in addition to information) It will be included. In other words, the structure of the reference light source structure 40, the size of the shielding plate 50, and the like are determined as such.

  In the cylindrical structure 40A shown in FIGS. 8A and 8B, for example, if the diameter R of the column 42A is made too small, the reference light for inline hologram becomes too weak, and the inline hologram becomes a diffracted X-ray Will be buried in Also, for example, if the height of the column 42A is too large, the reference light becomes too strong, and it becomes difficult to observe diffracted X-rays other than in-line holograms. The specific structure of the cylindrical structure 40A may be determined in consideration of the intensity balance between the in-line hologram and the diffracted X-rays on the detection surface.

  Also, of the spatial frequency components indicating the structure of the sample 10, the information of the lower spatial frequency component is detected at a position near the center of the detection surface and the position of the higher spatial frequency component away from the center of the detection surface As described above, it is an event that applies to the diffraction intensity pattern, and the same thing does not apply to in-line holograms in principle. Therefore, just because the vicinity of the center of the detection surface is shielded by the shield 50, there is no case that the information possessed by the transmitted X-ray and the information possessed by the low angle X-ray are not included in the inline hologram.

FIG. 9 is a flow chart of an operation of constructing a sample image by X-ray ptychography of the imaging apparatus 1. First, 1 is substituted for the variable i in step S11. In the subsequent step S12, the driving device 30 drives the sample 10 so that the position of the light condensing point O coincides with the step position P _i . In the subsequent step S13, all detection results (all detection results of the light reception intensity) in the detection plane of the two-dimensional detector 20 are acquired as the ith light intensity detection pattern. In the first embodiment, the inline hologram and the diffraction intensity pattern obtained simultaneously by the two-dimensional detector 20 (ie, the detection pattern consisting of the inline hologram and the diffraction intensity pattern detected simultaneously) are the i-th light intensity detection pattern Become.

Thereafter, in step S14, the control unit (not shown) of the imaging apparatus 1 confirms whether or not the variable i matches the predetermined value n (for example, 100). If "i = n", the process proceeds to step S16. On the other hand, if “i <n”, 1 is added to the variable i in step S15, and then the process returns to step S12, and the processing after step S12 is repeated. As a result, at the time when step S16 is reached, the first to nth light intensity detection patterns are already acquired. The ith light intensity detection pattern is obtained by simultaneously detecting the in-line hologram and the diffraction intensity pattern from the sample 10 in a state where the position of the condensing point O matches the step position P _i .

  In step S16, the computing device 60 generates an image of the sample 10 by performing a predetermined computation using the repetitive phase recovery algorithm on the first to n-th light intensity detection patterns acquired in step S13. The arithmetic device 60 may be a computer formed of a central processing unit (CPU), a read only memory (ROM), a random access memory (RAM), and the like. The iterative phase recovery algorithm in step S16 is the same as the iterative phase recovery algorithm in the reference embodiment.

[simulation]
In order to verify the compression effect of the detection dynamic range required for the two-dimensional detector 20, the following first to third simulations were performed by a computer. The test image 300 (see FIG. 6A) is used as the sample 10 in the first to third simulations.

  In the first simulation, it is assumed that the first virtual imaging apparatus (that is, the imaging apparatus of the reference embodiment) in which the structure 40 and the shield 50 are removed from the imaging apparatus 1 is used. The light intensity detection pattern acquired by the first virtual imaging device is a transmission and diffraction intensity pattern.

FIG. 10A shows simulation results of light intensity detection patterns (transmission and diffraction intensity patterns) when incident light L0 is irradiated to a certain point of the sample 10 in the first virtual imaging apparatus. For example, the light intensity detection pattern acquired under the detection condition in which the two-dimensional detector 20 having a detection performance of 10 ⁶ photons / pixel / second is used and the detection time is set to 1 second is the light of FIG. It may be considered to correspond to the intensity detection pattern. Alternatively, for example, a light intensity detection pattern obtained using a two-dimensional detector 20 having a detection performance of 10 ³ photons / pixel / sec and detection time set to 10 ³ seconds is shown in FIG. It can be considered to correspond to the light intensity detection pattern of The same applies to the simulation for the second and third virtual imaging apparatuses described later. FIG. 10B is a simulation result of part of the reconstructed image of the test image 300 generated by the iterative phase recovery algorithm from the first to n-th light intensity detection patterns in the first virtual imaging apparatus. In the case where the structure 40 and the shield 50 are not used, under the above-described detection conditions, the light intensity detection pattern (transmission and diffraction intensity patterns) can be detected only up to the photon dynamic range of 10 ⁶ photons / pixel. It can be seen that the diffraction intensity pattern is buried in noise. The resolution of the reconstructed image is poor, and the influence of noise on the diffraction intensity pattern appears notably in the reconstructed image.

  In the second simulation, it is assumed to use a second virtual imaging apparatus in which only the structural body 40 is deleted from the imaging apparatus 1. The light intensity detection pattern acquired by the second virtual imaging apparatus includes only the diffraction intensity pattern.

FIG. 11A shows the simulation result of the light intensity detection pattern (diffraction intensity pattern) when the incident light L0 is irradiated to a certain point of the sample 10 in the second virtual imaging apparatus. In FIG. 11A, the black square area near the center corresponds to the area where the X-ray incidence is blocked by the shield 50. FIG. 11B is a simulation result of part of the reconstructed image of the test image 300 generated by the iterative phase recovery algorithm from the first to n-th light intensity detection patterns in the second virtual imaging apparatus. By shielding transmission X-rays with high intensity and low angle diffraction X-rays by the shield 50, even if the photon dynamic range of the acquired light intensity detection pattern is 10 ⁶ photons / pixel, A high resolution diffraction intensity pattern (that is, information of relatively high spatial frequency components among spatial frequency components indicating the sample structure) is included therein. However, since the low resolution information is missing, an image lacking the low resolution information as shown in FIG. 11B is reconstructed.

  In the third simulation, it is assumed that the imaging apparatus 1 itself is used as a third virtual imaging apparatus. The light intensity detection pattern acquired by the third virtual imaging apparatus includes an inline hologram and a diffraction intensity pattern.

FIG. 12A shows a simulation result of a light intensity detection pattern (in-line hologram and diffraction intensity pattern) when the incident light L0 is irradiated to a certain point of the sample 10 in the third virtual imaging apparatus. In FIG. 12A, the black square area near the center corresponds to the area where the X-ray incidence is blocked by the shield 50. FIG. 12B is a simulation result of part of the reconstructed image of the test image 300 generated by the iterative phase recovery algorithm from the first to n-th light intensity detection patterns in the third virtual imaging apparatus. When the structure 40 and the shield 50 are used, even if the photon dynamic range of the acquired light intensity detection pattern is 10 ⁶ photons / pixel, the scattered light from the structure 40 is included in the light intensity detection pattern. And a high resolution diffraction intensity pattern (that is, information of a relatively high spatial frequency component among spatial frequency components indicating a sample structure). Since the in-line hologram includes low resolution information of the sample 10 (here, the test image 300), even if the transmitted X-rays and low angle diffracted X-rays are blocked by the shield 50, the same re-appearance as the original image (300) A compositional image can be generated.

  In FIG. 7, the idea that the inline hologram is formed only in a region centered on the center of the detector 20 and only in a partial region of the detector 20 is adopted for the sake of convenience, so as to conform to that idea. FIG. 12A shows a broken line circle as an outline of the inline hologram formation region. However, in practice, X-rays indicating the information of the inline hologram are incident on the entire detection surface of the two-dimensional detector 20. That is, it can be considered that the information of the in-line hologram is included throughout the entire light intensity detection pattern shown in FIG.

  In the calculation of step S16 using the iterative phase recovery algorithm, the amplitude and phase of the X-ray that strikes the sample 10 are also derived along with the reconstruction of the image of the sample 10 during the iteration of the iterative calculation. Therefore, there is no problem even if the sample 10 is irradiated with the reference light based on the structure 40, and there is no problem even if the information of the inline hologram and the information of the diffracted X-ray are mixed in one light intensity detection pattern . The amplitude and the phase of the X-ray that strikes the sample 10 become clear in the repetition of the repetitive calculation regardless of the presence or absence of the irradiation of the sample 10 with the reference light based on the structure 40 Is analyzed, and in conjunction with this, the image of the sample 10 is reconstructed.

  The transmission intensity pattern (transmission X-ray intensity pattern) formed on the detection surface in the reference embodiment may also be considered as a type of in-line hologram. In the in-line hologram as the transmission intensity pattern, light from a spherical emission point with a diameter of 1 μm in the sample 10 may be considered as reference light. A part of the light from the light emission point is scattered by the sample 10, and the remainder passes the sample 10 toward the two-dimensional detector 20, but the light from the light emission point is scattered by the sample 10 by the object 10 Think of it as light.

  In the first embodiment, instead of the inline hologram based on the transmission intensity pattern, an inline hologram using the structure 40 is included in the light intensity detection pattern, and the iterative phase recovery algorithm used is the reference embodiment and It may be the same between the first embodiment.

[Modification of structure for reference light source]
A modification of the reference light source structure 40 will be described. The above-mentioned cylindrical structure 40A is a convex cylindrical structure in which metal is disposed in a cylindrical portion. As the structure 40, a concave cylindrical structure in which metal is removed in a cylindrical shape may be employed.

FIG. 13 shows a perspective view of a concave cylindrical structure 40B which is an example of the reference light source structure 40. As shown in FIG. The cylindrical structure 40B can be formed of any type of metal (e.g. tantalum or gold). The cylindrical structure 40B is a member in which a columnar opening 42B is provided in the plate-like body 41B. The plate-like body 41B is a plate-like metal having an upper surface and a lower surface parallel to the XY plane and having a thickness in the Z-axis direction. The thickness of the plate-like body 41B is about several tens of nm to 100 nm. In the X-axis and Y-axis directions, the size of the plate-like body 41B is larger than the size of the incident light L0 at the position of the cylindrical structure 40B. The columnar opening 42B is a columnar hole provided in the plate-like body 41B. The axis of the columnar opening 42B is parallel to the Z axis. The cylindrical structure 40B is formed and arranged such that the center of the plate-like member 41B and the axis of the columnar opening 42B are positioned on the optical axis AX _OPT of the incident light L0. Here, it is assumed that the columnar opening 42B is a cylindrical hole having a bottom of a true circle, and the diameter of the true circle is represented by R.

  In the convex cylindrical structure 40A, the wavefront of the incident light L0 is disturbed (phase is delayed) in the portion of the protruding column 42A compared to the portion other than that (the phase is delayed). On the other hand, in the concave cylindrical structure 40B, the wavefront of the incident light L0 is disturbed (phase is delayed) in the portion where the hole is not formed, compared to the columnar opening 42B (the phase is delayed).

  The cylindrical structure 40B is also formed to satisfy the first and second requirements described above. That is, the first requirement that the diameter R is smaller than the spot diameter SR (here, 1 μm) of the incident light L0 at the position of the sample 10 is satisfied. Further, at the position of the sample 10, the second requirement is satisfied that the size of the spread of the scattered light L1 in the X and Y axis directions is larger than the size of the spread of the incident light L0 in the X and Y axes. By satisfying the second necessary condition, the entire irradiation area of the incident light L0 on the sample 10 is included in the irradiation area of the scattered light L1 on the sample 10 at the position of the sample 10.

  In the convex structure 40A (see FIG. 8A), the bottom surface of the metal column 42A (convex columnar structure) may be elliptical. Similarly, in the concave structure 40B (see FIG. 13), the bottom of the column as a hole by the columnar opening 42B (concave columnar structure) may be elliptical. However, as the shape is closer to a perfect circle, the isotropy of X-ray scattering becomes higher, so the compression effect of the detection dynamic range (the detection dynamic range required to obtain a desired resolution in a predetermined detection time) The reduction effect is further enhanced.

  Further, in the convex structure 40A (see FIG. 8A), the bottom surface of the metal column 42A may be other than a circle (for example, a polygon). Similarly, in the concave structure 40B (see FIG. 13), the bottom of the column as a hole by the columnar opening 42B may be other than a circle (for example, a polygon). However, since the isotropy of X-ray scattering is higher when the shape is closer to a true circle, the compression effect of the detection dynamic range is further enhanced. For example, when the bottom of the column 42A in the convex structure 40A is made into a quadrangle, high intensity spots appear discretely in the in-line hologram, and as a result, detection dynamic is more than when it is made a true circle. The range compression effect is reduced.

  In the case of a cylindrical structure 40A or 40B having a cylindrical body 42A or a columnar opening 42B whose cross section is a true circle, the first requirement can be defined in relation to the diameter R, but a cylindrical body 42A whose cross section is other than a perfect circle Alternatively, in consideration of the structure 40 having the columnar opening 42B, the expression of the first requirement is changed. That is, in the convex structure 40A (see FIG. 8A), the cross-sectional area of the metal column 42A (that is, the area of the bottom surface) is the spread area of the incident light 10 at the position of the sample 10 (X axis and Y It should be smaller than the axial spread area). It may be considered that this is the first requirement to be satisfied by the structure 40A. Similarly, in the concave structure 40B (see FIG. 13), the cross-sectional area of the hole by the columnar opening 42B (the area of the bottom of the column as a hole by the columnar opening 42B) corresponds to the incident light 10 at the position of the sample 10. Should be smaller than the spread area (spread area in the X-axis and Y-axis directions) of It may be considered that this is the first requirement to be satisfied by the structure 40B.

[Experimental result]
Next, the contents and results of experiments using the imaging apparatus 1 will be described. The experiment was performed at beamline BL29 XUL of the radiation facility Spring-8. The electrons traveling around the storage ring of the radiation facility are made to meander by the periodic magnetic field formed by the undulator arrangement located near the base of the beamline and emit radiation. This radiation enters the beamline. The radiation light of the X-ray region which has entered the beam line enters the imaging device 1 as incident light L0 through the condensing optical system.

  Also in the experiment, the spot diameter of the incident light L0 at the position of the sample 10 is 1 μm, and the energy of the X-ray as the incident light L0 is 6.5 keV. As the reference light source structure 40, a concave structure 40B shown in FIG. 13 was used. In the experiment, the material of the structure 40B is gold, the thickness of the plate-like body 41B is 250 nm, and the diameter R of the columnar opening 42B is 200 nm. Such a structure 40B can be manufactured by processing to open a hole in gold foil. FIG. 14 shows an image (SEM image) of the structure 40B in the experiment observed by the scanning electron microscope from the Z-axis direction. Note that the above-mentioned thickness: 250 nm and diameter R: 200 nm are their design values (target values), and those in the actually created structure 40B include an error.

  In the experiment, the distance between the sample 10 and the reference light source structure 40 (here, the structure 40B) is about 1 mm. This interval was determined so as to satisfy the above-mentioned second requirement while considering the thickness of the plate-like member 41B, the diameter R of the columnar opening 42B, and the like. The two-dimensional detector 20 used in the experiment is a direct imaging CCD detector made by Princeton Instruments: PI-LCX1300. As sample 10, a Siemens star test chart made of tantalum and having a thickness of 200 nm was used. FIG. 15 shows an image (SEM image) of a part of the Siemens star test chart observed by a scanning electron microscope from the Z-axis direction.

  In the experiment, while the sample 10 (Siemens Star test chart) was moved stepwise by 500 nm in each of the X-axis direction and the Y-axis direction, a light intensity detection pattern consisting of inline holograms and diffraction intensity patterns was acquired sequentially. The number of acquired light intensity detection patterns is (7 × 7). That is, “n = 7 × 7”.

  In order to compare and verify the influence of the arrangement of the reference light source structure 40, the structure 40 is removed from the imaging device 1 in addition to the imaging device 1 having the structure 40 (hereinafter also referred to as a structure presence imaging device) The experiment was also performed on the device (hereinafter also referred to as a structure-less imaging device).

  In FIG. 16, experimental result patterns 410 and 420 show light intensity detection patterns (in-line hologram and diffraction intensity pattern) obtained by experiment when incident light L0 is irradiated to a certain point of the sample 10. However, the pattern 410 is acquired in the imaging apparatus with structure, and the pattern 420 is acquired in the imaging apparatus without structure. In each of the patterns 410 and 420, the black square area near the center corresponds to the area where the X-ray incidence is blocked by the shield 50. In the pattern 410, it can be seen that inline holograms (concentric interference fringes) resulting from the arrangement of the structures 40 are generated. The information contained in the transmitted X-rays and the low-angle diffracted X-rays is included in the inline hologram.

  An image 430 in FIG. 17 is a re-image of the sample 10 (Siemens Star test chart) generated by the iterative phase recovery algorithm from the first to n-th light intensity detection patterns acquired in the experiment in the imaging apparatus with structure. It is a part of the composition image. An image 440 in FIG. 17 is a re-design of the sample 10 (Siemens Star test chart) generated by the iterative phase recovery algorithm from the first to n-th light intensity detection patterns acquired in the experiment in the structure-free imaging apparatus. It is a part of the composition image.

  Each of the reconstructed images 430 and 440 is a two-dimensional image (two-dimensional projected image) obtained by projecting the amount of phase change due to the sample 10 on the XY plane. The amount of phase change here is the amount of phase change of the incident light L0 when the incident light L0 passes through the sample 10, and repetitive phase recovery based on the first to n-th light intensity detection patterns acquired by experiment. It is the amount recovered (computed) by the algorithm.

  In the reconstructed images 430 and 440, it is shown that the closer the region is black, the larger the amount of phase change. In the reconstructed image 430 by the imaging apparatus with structure, it can be seen that the phase indicating the thickness of the tantalum is well recovered. On the other hand, in the reconstructed image 440 by the structure-less imaging apparatus, since the information of the transmitted X-ray and the low-angle diffracted X-ray is lost in the acquired light intensity detection pattern, the phase can not be recovered accurately. Only the identification degree of the boundary between the existence area and the non-existence area of.

  According to the imaging apparatus 1 of the present embodiment, it is possible to reduce the detection dynamic range required of the two-dimensional detector 20 in order to achieve the target resolution and sensitivity in a predetermined detection time (for example, consider It can be compressed to about 1 in 1000 in comparison with the form). Under the condition that the detection time is constant, according to the imaging device 1 of the present embodiment, even if a direct imaging type CCD detector (for example, available for about several million yen) is used, the pixel in the reference embodiment The same resolution and sensitivity as in the case of using an array detector (for example, costing several tens of millions of yen) can be realized. For this reason, the spread and promotion of high-resolution, high-sensitivity X-ray ptychography utilizing existing radiation beam lines is expected.

  Non-Patent Document 1 and the like show a configuration in which a beam stop is disposed near the center of the front surface of a two-dimensional detector. In the said structure, in order to make the pattern of high angle diffraction X-rays observe with a two-dimensional detector (CCD), the beam stop is arrange | positioned. If the beam stop is not arranged, the high angle diffraction X-ray pattern is buried in the noise due to the very high intensity of the transmitted X-rays, and the high angle diffraction X-ray pattern is completely or precisely two-dimensional. It can not be observed by a detector (CCD). In the conventional method, in order to construct a sample image containing both low resolution and high resolution information from the detection results of the two-dimensional detector, it is necessary to remove the beam stop.

<< Second Embodiment >>
A second embodiment of the present invention will be described. The technique described in the first embodiment may be applied to single shot imaging. Also in this case, the imaging apparatus 1 of the first embodiment can be used. However, the size of the sample 10 is limited to the size of the incident light L 0 at the position of the sample 10 or less in the X-axis and Y-axis directions.

  In the imaging apparatus 1 to which single-shot imaging is applied, one light intensity detection pattern is acquired from the two-dimensional detector 20 without performing step movement of the sample 10 (so that n = 1). An image of the sample 10 is generated by calculation based on a known phase recovery method from the light intensity detection pattern. For example, an image of the sample 10 is generated by performing a predetermined operation according to an iterative phase recovery algorithm on one acquired light intensity detection pattern. The iterative phase recovery algorithm in this case may be similar to that described above. At this time, for example, using the fact that the electron density is zero and that the electron density is not negative outside the region where the sample 10 is presumed to be present is used as the real space constraint condition, and the repetition is performed. It suffices to carry out the operation.

<< Third Embodiment >>
A third embodiment of the present invention will be described. The techniques described in the first embodiment can also be applied to ptychography using EUV light. EUV light is light having a wavelength of extreme ultraviolet light. FIG. 18 shows a schematic configuration diagram of an imaging apparatus 200 that generates an image of a sample by ptychography using EUV light.

  The EUV light 201, the EUV mask 203, the two-dimensional detector 204, the arithmetic device 205, the reference light source structure 210, and the shield 220 respectively correspond to the incident light L0, the sample 10, and the two-dimensional detector 20 in the first embodiment. It corresponds to the arithmetic unit 60, the reference light source structure 40, and the shield 50. As long as there is no contradiction in the matters described in the first embodiment regarding the incident light L0, the sample 10, the two-dimensional detector 20, the arithmetic device 60, the reference light source structure 40 and the shield 50, the EUV light 201, the EUV mask 203, The present invention may be applied to the two-dimensional detector 204, the arithmetic unit 205, the reference light source structure 210, and the shield 220.

  The EUV light 201 is irradiated to the EUV mask 203 at a predetermined incident angle through an optical system including a mirror 202. The EUV mask 203 is a mask in which a pattern is inscribed, and is used for extreme ultraviolet lithography. Light based on the EUV light 201 reflected and diffracted by the EUV mask 203 (hereinafter referred to as EUV reflected / diffracted light) is received by the two-dimensional detector 204 disposed opposite to the EUV mask 203, and the EUV is reflected. An image by diffracted light is detected by the two-dimensional detector 204. That is, the two-dimensional detector 204 is a two-dimensional EUV light detector provided downstream of the EUV mask 203 as a sample, receives light from the sample based on the incident light (201), and receives the intensity of the received light. Detect in a predetermined two-dimensional plane. In the third embodiment, the upstream refers to the upstream of the direction of travel of the EUV light 201 as incident light, and naturally, the incident light (201) travels from the upstream side to the downstream side.

  The reference light source structure 210 (hereinafter sometimes referred to as a structure 210) is a structure provided on the upstream side of the EUV mask 203. The EUV light 201 as incident light is incident on the structure 210 and then irradiated to the EUV mask 203. Therefore, a part of the incident light (201) is scattered by the structure 210, and the scattered light from the structure 210 is emitted toward the EUV mask 203.

  The shield 220 is disposed between the EUV mask 203 and the two-dimensional detector 204, and shields light from the EUV mask 203 for a predetermined shielding target area in the detection plane of the two-dimensional detector 204. At this time, as described in the first embodiment, of the light traveling from the EUV mask 203 to the two-dimensional detector 204, the light having at least the maximum intensity is the two-dimensional detector 204 (more specifically, the two-dimensional detector A shield 220 is disposed between the EUV mask 203 and the two-dimensional detector 204 so as not to reach the detection surface 204). This makes it possible to reduce the detection dynamic range required for the two-dimensional detector 204.

  Of the light traveling from the EUV mask 203 to the two-dimensional detector 204, the light having the maximum intensity is included in the EUV light specularly reflected by the EUV mask 203, and thus the shielding target area in the two-dimensional detector 204 Is a region including a light receiving region of specularly reflected EUV light (a region that is to receive specularly reflected EUV light if there is no shield 220). That is, the reaching of the EUV light specularly reflected by the EUV mask 203 to the two-dimensional detector 204 (more specifically, the detection surface of the two-dimensional detector 204) is blocked by the shield 220.

  As a result of the scattered light from the structure 210 based on the incident EUV light 201 being incident on the EUV mask 203, an inline hologram using the scattered light from the structure 210 as a reference light is formed on the detection surface of the two-dimensional detector 204 And detected. Object light in this in-line hologram is scattered light from the EUV mask 203 based on the reference light. On the other hand, besides the inline hologram, a diffracted EUV light pattern (a pattern by interference fringes formed by diffracted EUV light) according to the surface structure of the EUV mask 203 is also formed and detected on the detection surface of the two-dimensional detector 204. Ru.

  In-line hologram and diffraction are sequentially performed while stepping the EUV mask 203 in a direction parallel to the mask surface of the EUV mask 203 (that is, a direction having a direction component orthogonal to the optical axis of the EUV light 201 incident on the EUV mask 203). A light intensity detection pattern composed of an EUV light pattern is acquired from the two-dimensional detector 204, and the first to nth light intensity detection patterns obtained thereby are supplied to the arithmetic unit 205. As in the first embodiment, the irradiation region of incident light (here, the EUV light 201) on the sample (here, the EUV mask 203) when acquiring the ith light intensity detection pattern is the jth light intensity detection pattern Overlap with the irradiated area of the incident light on the sample when acquiring (where i is any integer not greater than n and j is any integer other than i and not greater than n; 1 There may be multiple values of j for one value of i). Arithmetic unit 205 generates an image of EUV mask 203 by performing a predetermined operation according to a known repetitive phase recovery algorithm based on pylography on the given first to n-th light intensity detection patterns.

<< Modification etc. >>
The embodiment of the present invention can be variously modified as appropriate within the scope of the technical idea shown in the claims. The above embodiment is merely an example of the embodiment of the present invention, and the meaning of the terms of the present invention or each constituent feature is not limited to that described in the above embodiment. The specific numerical values shown in the above description are merely examples, and as a matter of course they can be changed to various numerical values.

Reference Signs List 1 imaging apparatus 10 sample 20 two-dimensional detector 30 driving device 40, 40A, 40B reference light source structure (scattering structure)
41A, 41B Plate-like body 42A Column body (convex columnar structure)
42B Columnar opening (concave columnar structure)
50 shield 60 arithmetic unit L0 incident light 200 imaging unit 201 EUV light 203 EUV mask (sample)
204 Two-dimensional detector 205 Arithmetic unit 210 Reference light source structure (scattering structure)
220 Shield

Claims (7)

A scattering structure disposed upstream of a sample to be irradiated with incident light, for scattering a part of the incident light and emitting the scattered light toward the sample;
A two-dimensional detector disposed downstream of the sample and detecting an intensity of light coming from the sample based on the incident light in a predetermined two-dimensional plane;
A shield for shielding the light having at least the maximum intensity of the light from the sample toward the two-dimensional detector from reaching the two-dimensional detector;
And d) calculating means for generating an image of the sample based on the detection result of the two-dimensional detector. The scattering structure has a convex or concave columnar structure having an axis parallel to the optical axis of the incident light,
The cross-sectional area of the columnar structure portion is smaller than the spread area of the incident light at the position of the sample,
The imaging apparatus according to claim 1, wherein the size of the spread of the scattered light from the scattering structure at the position of the sample is larger than the size of the spread of the incident light at the position of the sample. The imaging apparatus according to claim 1, wherein the shield blocks at least the transmitted light of the sample based on the incident light from reaching the two-dimensional detector. First to n-th light intensity detection patterns are acquired from the two-dimensional detector by repeatedly performing detection by the two-dimensional detector while stepwise moving the sample in a direction having a direction component orthogonal to the optical axis (N is an integer of 2 or more),
The irradiation area of the incident light on the sample when acquiring the i-th light intensity detection pattern is the irradiation area and part of the incident light on the sample when acquiring the j-th light intensity detection pattern Overlap (i is an integer less than or equal to n, j is any integer other than i and less than or equal to n),
The imaging apparatus according to claim 2 , wherein the calculation unit generates an image of the sample based on the first to n-th light intensity detection patterns. The imaging apparatus according to any one of claims 1 to 4, wherein the incident light includes coherent X-rays. A scattering structure that scatters part of the incident light and emits scattered light toward the sample is disposed upstream of the sample to be irradiated with the incident light, and the light is incident on the downstream side of the sample. Arranging a two-dimensional detector for detecting the intensity of light coming from the sample based on the emitted light in a predetermined two-dimensional plane,
An image of the sample based on the detection result of the two-dimensional detector in a state in which the light having at least the maximum intensity of the light from the sample toward the two-dimensional detector is blocked from reaching the two-dimensional detector. An imaging method characterized in that: The scattering structure has a convex or concave columnar structure having an axis parallel to the optical axis of the incident light,
The cross-sectional area of the columnar structure portion is smaller than the spread area of the incident light at the position of the sample,
The imaging method according to claim 6, wherein the size of the spread of the scattered light from the scattering structure at the position of the sample is larger than the size of the spread of the incident light at the position of the sample.