Device and method for measuring the orientation angle of an X-ray imaging system

Abstract

The present invention relates to a device and a method for measuring the orientation angle of an X-ray imaging system, the X-ray imaging system comprising an X-ray light source, an X-ray detector and a sample holder, the sample holder being arranged to receive a sample to be analyzed. According to the present invention, the method (40) comprises: - emitting (42) a polychromatic X-ray beam that passes through a reference sample mounted on the sample holder to form a diffraction pattern on the sensitive area of the X-ray detector, - generating (43) an observation image with the X-ray detector, the observation image comprising the diffraction pattern, and - determining (44) the orientation of the X-ray light source and the orientation of the X-ray detector by comparing the observation image with at least one target image, the target image comprising the diffraction pattern obtained for the reference sample with a preset orientation of the X-ray light source and a preset orientation of the X-ray detector.

Description

Technical Field

[0001] The present invention belongs to the field of X-ray imaging, and more particularly, to the field of alignment of optical elements of an X-ray imaging system. The present invention relates to an apparatus and method for measuring the orientation angle of an X-ray imaging system, the X-ray imaging system including an X-ray source, an X-ray detector, and a sample holder arranged to receive a sample to be analyzed, the sample holder being arranged between the X-ray source and the X-ray detector.

[0002] The present invention is particularly applicable to X-ray imaging systems for controlling single crystal components by the Laue method. Such systems are based on the study of diffraction patterns generated on a sensor by the diffraction of a polychromatic X-ray beam during its passage through a single crystal component. In particular, the shape and position of the light spots constituting the diffraction pattern can be compared with the shape and position of a reference set of diffraction patterns in order to determine the crystal orientation of the single crystal component. However, the present invention is applicable to any X-ray imaging system including an X-ray light source and an X-ray detector, the X-ray light source and the X-ray detector being desired to determine the alignment with respect to a sample to be imaged. Background Art

[0003] In any X-ray imaging system, the correct alignment of various optical elements is necessary to obtain the desired image resolution. At least, the orientation of the optical elements with respect to the optical axis of the system must be known with sufficient accuracy so that the image can be reconstructed at the desired resolution. Most of the techniques that enable the alignment of an X-ray imaging system require the use of dedicated equipment, which is unnecessary during the operational image acquisition phase. For example, a laser pointer system can be used, such as that described in B. Fay, J. Trotel, and A. Frichet, Optical alignment for submicrons X-ray lithography, Journal of Vacuum Science and Technology.

[0004] The alignment system can also be based on the use of a reticle specifically designed for this task arranged in the path of the X-ray beam, between the radiation source and the detector. As long as the size and absorption characteristics of the reticle are known, the image produced by the detector enables the relative positions of the radiation source, the reticle, and the detector to be determined. The main drawback of this technique is that the alignment of the imaging system is determined with limited accuracy (limited by the spatial resolution of the detector).

[0005] Patent US 6,453,006 B1 describes techniques for the calibration and alignment of an x-ray reflectometry system, which includes an x-ray light source, a reflector, a sample to be tested, and a detector. This patent particularly describes a method for aligning the reflector with the x-ray light source, which includes arranging a filament between these elements to produce a shadow, and orienting the reflector to obtain a shadow with the smallest possible width. Here, the alignment accuracy is also limited by the spatial resolution of the detector.

[0006] Therefore, the above solution for aligning the optical elements of an x-ray imaging system is not entirely satisfactory. The first object of the present invention is to propose a technique that enables the alignment of an x-ray imaging system, which requires only a limited number of optical elements in addition to the optical elements useful during the stage of measuring a sample. The second object of the present invention is to propose a technique that enables better alignment accuracy (in particular, greater than the resolution of the x-ray detector of the imaging system). Summary of the Invention

[0007] To this end, the present invention is based on the use of the Laue method. This method is not used to study the crystal structure of a sample, but to determine the orientation of the optical elements of an x-ray imaging system by referring to a sample, the crystal structure and orientation of which are known. The method according to the present invention includes: mounting a reference sample on a sample holder; emitting an x-ray beam that passes through the reference sample and forms a diffraction pattern on the detector of the x-ray imaging system; generating an image including the diffraction pattern; and determining the orientation of the x-ray beam and the orientation of the detector by comparing the obtained diffraction pattern with at least one target image, the at least one target image including a diffraction pattern corresponding to the known orientation of the x-ray beam and the known orientation of the detector.

[0008] More particularly, the object of the present invention is a method for measuring the orientation angle of an x-ray imaging system, which includes an x-ray light source, an x-ray detector, and a sample holder arranged to receive a sample to be analyzed. The x-ray imaging system is configured such that the x-ray light source can emit a polychromatic x-ray beam along the main propagation axis, the x-ray beam passes through the sample to be analyzed and reaches the sensitive area of the x-ray detector. The optical axis of the x-ray imaging system is defined between the center of the x-ray light source and the x-ray detector. The method includes the following steps:

[0009] - Emitting a polychromatic x-ray beam along the main propagation axis from the x-ray light source such that the x-ray beam passes through a reference sample mounted on the sample holder and forms a diffraction pattern on the sensitive area of the x-ray detector,

[0010] - Generating an observation image with an x-ray detector, the observation image including a diffraction pattern, and

[0011] - Determining the orientation of the main propagation axis and the orientation of the sensitive area of the x-ray detector by comparing the observation image with at least one target image, the target image including a diffraction pattern obtained for a reference sample with a preset orientation of the main propagation axis and a preset orientation of the sensitive area of the x-ray detector.

[0012] Each diffraction pattern is formed by a set of light spots, and the shape, size, and position of these light spots in a given plane depend on the orientation of the main propagation axis of the x-ray source, the orientation of the sensitive area of the x-ray detector, and the diffraction characteristics of the reference sample.

[0013] The optical axis of the x-ray imaging system is denoted as X. The optical axis, together with a second axis (denoted as Y) and a third axis (denoted as Z), defines a direct orthogonal coordinate system XYZ. The plane passing through axis X and axis Y is denoted as "plane XY"; the plane passing through axis X and axis Z is called "plane XZ"; and the plane passing through axis Y and axis Z is called "plane YZ". In addition to passing through the emission center of the x-ray source, the optical axis X may also pass through the center of the x-ray detector or be close to this position.

[0014] The x-ray source generally emits an x-ray beam in a conical shape along the main propagation axis X s The emission center of the x-ray source corresponds to the vertex of the cone, and the main propagation axis X s corresponds to the axis of the cone. The main propagation axis X s In the plane XY, that is, by rotating around axis Z, forms an angle ξ with the optical axis X xy , and in the plane XZ, that is, by rotating around axis Y, forms an angle ξ with the optical axis X xz .

[0015] The x-ray detector may include a set of sensing elements arranged in a plane Y d Z d substantially orthogonal to the optical axis X. The orientation of the x-ray detector is defined in the direct orthogonal coordinate system X d Y d Z d The markers X d Y d Z d With respect to the coordinate system XYZ, form an angle α by rotating around axis Z, form an angle β by rotating around axis Y, and form an angle γ by rotating around axis X. It should be noted that the x-ray detector may also include a set of sensing elements, and this set of sensing elements are respectively along axis Y d or axis Z dArranged linearly and along the orthogonal axis Z d or the orthogonal axis Y d Shifted linearly to reconstitute the plane Y d Z d 。

[0016] According to the first embodiment, the step of determining the orientation of the main propagation axis X s and the orientation of the sensitive area of the x-ray detector includes comparing the observed image with a set of target images, each target image showing a diffraction pattern for a preset orientation of the main propagation axis and a preset orientation of the sensitive area of the x-ray detector, said orientations being different for each target image.

[0017] In particular, the orientation of the main propagation axis X s and the orientation of the sensitive area of the x-ray detector can correspond to the corresponding orientations for the target image whose diffraction pattern is most similar to the diffraction pattern of the observed image. The criterion for the similarity between the diffraction pattern of the target image and the diffraction pattern of the observed image includes, for example, the average distance between each spot in the observed image and the corresponding spot in the target image.

[0018] According to the second embodiment, the step of determining the orientation of the main propagation axis and the orientation of the sensitive area of the x-ray detector includes the following sub-steps:

[0019] - Determine a similarity parameter, which represents the degree of similarity between the diffraction pattern of the observed image and the diffraction pattern of the current target image for a given orientation of the main propagation axis X s and a given orientation of the sensitive area of the x-ray detector,

[0020] - Compare the similarity parameter with a similarity threshold,

[0021] - When the similarity parameter is less than the similarity threshold, identify the given orientation of the main propagation axis X s and the given orientation of the sensitive area of the x-ray detector as the effective orientation of the main propagation axis X s and the effective orientation of the sensitive area of the x-ray detector,

[0022] - When the similarity parameter is greater than or equal to the similarity threshold, generate a new current target image, at least one of the given orientations in the given orientation of the current target image being different from the corresponding given orientation of the previous target image, and repeat the previous sub-steps until the similarity parameter is less than the similarity threshold.

[0023] For a given orientation of the main propagation axis and a given orientation of the sensitive area of the X-ray detector, each target image can be determined by digitally modeling the diffraction produced by a reference sample mounted on the sample holder. For this purpose, Laue diffraction modeling software can be used. The Laue diffraction modeling software is, for example, the PyMicro software developed by Henry Proudhon. This software is based on the VTK and Python libraries.

[0024] Before the step of emitting the X-ray beam, the method for measuring the orientation angle of the X-ray can further include the step of mounting the reference sample on the sample holder.

[0025] The sample holder can include a support surface for alternately receiving the sample to be analyzed or the reference sample. Conventionally, the support surface can define a reference plane. The reference plane can be the plane XZ.

[0026] The reference sample can be formed of a single crystal material, for example, formed of single crystal silicon. Preferably, the reference sample is arranged on the sample holder such that one of the crystal surfaces of the reference sample is parallel to the plane YZ.

[0027] Another object of the present invention is a device for measuring the orientation angle of an X-ray imaging system, the X-ray imaging system including an X-ray light source, an X-ray detector, and a sample holder arranged to receive the sample to be analyzed. The X-ray imaging system is configured such that the X-ray light source can emit a polychromatic X-ray beam along the main propagation axis, the X-ray beam passing through the sample to be analyzed and reaching the sensitive area of the X-ray detector. The optical axis of the X-ray imaging system is defined between the center of the X-ray light source and the X-ray detector. The device includes a processing unit configured to:

[0028] - emit a polychromatic X-ray beam along the main propagation axis by the X-ray light source such that the X-ray beam passes through the reference sample mounted on the sample holder and forms a diffraction pattern on the sensitive area of the X-ray detector,

[0029] - generate an observation image with the X-ray detector, the observation image including the diffraction pattern, and

[0030] - determine the orientation of the main propagation axis and the orientation of the sensitive area of the X-ray detector by comparing the observation image with at least one target image, the target image including the diffraction pattern obtained for the reference sample for a preset orientation of the main propagation axis and a preset orientation of the sensitive area of the X-ray detector.

[0031] In addition, the device may include a first diaphragm, which is arranged upstream of the sample holding part and is arranged to limit the lateral area of the x-ray beam. The lateral area is defined in the YZ plane. Limiting the lateral area enables ensuring that the entire x-ray beam reaching the x-ray detector has truly passed through the reference sample. Therefore, the first diaphragm may include an opening, and the size of the opening in the YZ plane is smaller than the corresponding size of the reference sample.

[0032] The device for measuring the orientation angle of an x-ray imaging system may further include a second diaphragm and / or a collimator, which are arranged between the x-ray source and the first diaphragm and are arranged to obtain a collimated x-ray beam at the sample holding part. The second diaphragm and / or the collimator are particularly beneficial when the distance between the x-ray source and the x-ray detector is greater than or equal to 30 cm.

[0033] According to a specific embodiment, the device further includes a light valve element, which is arranged downstream of the sample holding part and is arranged to prevent the non-diffracted part of the beam that has passed through the reference sample from reaching the sensitive area of the x-ray detector. Therefore, the light valve element enables forming an image on the x-ray detector that includes only the diffraction pattern and does not include the transmitted part of the x-ray beam. Therefore, compared with the case where the transmitted part of the x-ray beam is also received by the detector, the intensity range of the received x-ray beam is reduced. As a result, there is a greater dynamic range of the observed intensity of the light spot (for sampling), thereby limiting the electronic noise and having better resolution for measuring the intensity of the image.

[0034] The light valve element is formed of an x-ray-impermeable material. The light valve element is made of lead, for example.

[0035] In the presence of the first diaphragm, preferably, the size of the light valve element in the YZ plane is larger than the corresponding size of the opening of the first diaphragm.

[0036] The device for measuring the orientation angle of an x-ray imaging system may further include a reference sample. As described above, the reference sample may be formed of a single crystal material, for example, formed of single crystal silicon.

[0037] The optical elements (i.e., the first diaphragm, the second diaphragm, the collimator, and / or the light valve element) of the device for measuring the orientation angle of an x-ray imaging system may be integrated with each other or form independent separate elements.

[0038] Finally, another object of the present invention is a computer program, which includes the following instructions: when the program is executed by a computer, the instructions direct the computer to execute the method for measuring the orientation angle of an x-ray imaging system as described above. Description of the Drawings

[0039] Other features, objects, and advantages of the present invention will become apparent from the following description, given by way of example only and with reference to the accompanying drawings, in which:

[0040] - Figure 1 An example of an x-ray imaging system and an apparatus for measuring the orientation angle of the system is schematically shown;

[0041] - Figure 2 The orientation of the main propagation axis of the x-ray source of the x-ray imaging system with respect to the orthogonal markers is shown with reference to the orthogonal markers;

[0042] - Figure 3 The orientation of the orthogonal markers associated with the x-ray detector of the x-ray imaging system with respect to the reference orthogonal markers is shown with reference to the orthogonal markers;

[0043] - Figure 4 An example of a method for measuring the orientation angle of an x-ray imaging system according to the present invention is shown;

[0044] - Figure 5 Is shown in Figure 4 A specific embodiment of the steps for determining the orientation of the main propagation axis of the x-ray source and the orientation of the orthogonal markers associated with the x-ray detector in the method shown. DETAILED DESCRIPTION

[0045] Figure 1 An example of an x-ray imaging system according to the present invention and an apparatus for measuring the orientation angle of the x-ray imaging system are schematically shown. The x-ray imaging system 10 includes an x-ray source 11, a sample holder 12, and an x-ray detector 13. The x-ray source 11 is arranged to emit a polychromatic x-ray beam 14 along the main propagation axis X s The x-ray beam 14 has a conical shape, and the emission center of the source 11 corresponds to the vertex of the cone, and the main propagation axis X s corresponds to the axis of the cone. The sample holder 12 is positioned between the source 11 and the detector 13. The sample holder is arranged to receive a sample to be analyzed by the x-ray imaging system and hold the sample in place such that the sample can be traversed by the x-ray beam 14. A plurality of support surfaces of the sample holder 12 form a reference plane that defines a direct orthogonal marker XYZ of the axis X, axis Y, and axis Z. The axis X, referred to as the "optical axis," passes through the emission center of the source 11. The x-ray detector 13 is a planar detector. The x-ray detector includes a plurality of x-ray sensing elements, and the sensing elements are arranged in the plane Y d Z d in a plane that is substantially parallel to the plane YZ and forms a sensing area 131.

[0046] Figure 2 shows the orthogonal markers XYZ associated with the sample holding part 12 and the main propagation axis X of the x-ray source 11 s . The main propagation axis X s In the plane XY, i.e., by rotating around the axis Z, forms an angle ξ with the optical axis X xy , and in the plane XZ, i.e., by rotating around the axis Y, forms an angle ξ with the optical axis X xz .

[0047] Figure 3 shows the orthogonal markers XYZ associated with the sample holding part 12 and the orthogonal markers X d Y d Z d . The transition from the markers XYZ to the markers X d Y d Z d is carried out by rotating the axis Z by an angle α, rotating the axis Y by an angle β, and rotating the axis X by an angle γ.

[0048] Consider again Figure 1 . The device 20 for measuring the orientation angles of an x-ray imaging system includes a processing unit 21, a reference sample 22, a first diaphragm 23, a second diaphragm 24, and a light valve (obturateur) element 25. The reference sample 22 is formed of a single crystal material, for example, made of silicon. The reference sample is arranged on the sample holding part 12 such that one of the crystal surfaces in the crystal surface of the reference sample is parallel to the plane YZ. When passing through the reference sample 22, the polychromatic x-ray beam 14 is partially diffracted and is called the "diffracted beam 15". In fact, according to Bragg's law, the wavelengths of the x-ray beam 14 that satisfy the Bragg condition with the crystal planes of the reference sample 22 will produce constructive interference and destructive interference, causing the x-ray beam to be diffracted. The shape and position of the diffracted beam 15 depend on the orientation of the x-ray source 11 and the orientation of the reference sample 22. When the sample holding part 12 and the reference sample 22 are conventionally used to define the reference markers, the shape and position of the diffracted beam 15 actually depend on the angle ξ xy and the angle ξ xz . The projection of the diffracted beam 15 on the sensitive area 131 of the detector 13 forms a diffraction pattern composed of light spots. Therefore, the shape and position of the light spots of the diffraction pattern depend on the orientation of the source 11, but also on the orientation of the detector 13, that is, on the angle α, the angle β, and the angle γ. The detector 13 is configured to generate an image that includes the diffraction pattern thus formed on the sensitive area 131 of the detector. This image is called the "observed image".

[0049] The processing unit 21 is configured to synchronize the light source 11 and the detector 13. In particular, the processing unit is configured to emit an x-ray beam 14 through the light source 11 and generate an observation image through the detector 13. The processing unit 21 is further configured to determine the orientation of the light source 11 and the orientation of the detector 13 by performing image processing on the observation image. The image processing may include a first step in which the position of the centroid of the diffraction spot is determined. A segmentation method combined with centroid calculation can be used, such as a deep learning technique using a neural network to distinguish the diffraction spots in the image. Subsequently, in a second step, the orientation of the light source 11 and the orientation of the detector 13 are determined by comparing the position of the centroid of the diffraction spot in the observation image with the position of the centroid of the diffraction spot in at least one reference image (referred to as the "target image"). The target image includes a diffraction pattern obtained for a reference sample 22 with a preset orientation (known) of the light source 11 and a preset orientation (known) of the detector 13. The target image includes, for example, a diffraction pattern obtained through the light source 11 and the detector 13, with the light source and the detector being perfectly aligned with the reference sample 22, i.e., with the main propagation axis X s and the marker X mixed with the marker XYZ d Y d Z d being perfectly aligned, and the main propagation axis being parallel to the optical axis X. The determination of the orientation of the light source 11 and the determination of the orientation of the detector 13 are described in more detail below with reference to Figure 4 more specifically describes the determination of the orientation of the light source 11 and the determination of the orientation of the detector 13.

[0050] The first diaphragm 23 is arranged upstream of the sample holder 12, for example as close as possible to the sample holder 12. The first diaphragm is arranged to limit the lateral area of the x-ray beam 14 in the plane xy. This limitation of the area enables ensuring that the entire x-ray beam reaching the detector 13 effectively passes through the reference sample 22. The first diaphragm 23 includes, for example, an opening whose size in the plane YZ is smaller than the corresponding size of the reference sample 22.

[0051] The second diaphragm 24 is arranged between the light source 11 and the first diaphragm 23. The second diaphragm is arranged as close as possible to the light source 11, for example. The second diaphragm is arranged to obtain a collimated x-ray beam at the sample holder 12. When the distance between the light source 11 and the detector 13 is greater than or equal to 30 cm, the second diaphragm 24 is mainly beneficial. Advantageously, the diaphragm 24 can be replaced by a collimator arranged such that the focus of the collimator is located at the center of the light source 11.

[0052] The light valve element 25 is arranged downstream of the sample holding part 12. The light valve element is arranged as close as possible to the detector 13, for example. The light valve element 25 is arranged to prevent the part of the x-ray beam 14 that has passed through the reference sample 22 and has not undergone diffraction from reaching the sensitive area 131 of the detector 13. This part of the x-ray beam 14 would form a relatively high-intensity central spot on the detector 13 if not blocked. This central spot would involve relatively high electronic noise, and thus the intensity measurement resolution of the observed image would be low. The light valve element 25 is formed of an x-ray-impermeable material, for example, made of lead. When the x-ray beam 14 is collimated, the size of the light valve element 25 can be equal to or slightly larger than the corresponding size of the opening of the first diaphragm 23.

[0053] The first diaphragm 23, the second diaphragm 24 (or collimator), and the light valve element 25 can form an integral unit. The reference sample 22 can also be integrated with these optical elements.

[0054] Figure 4 An example of a method for measuring the orientation angle of the x-ray imaging system 10 shown in Figure 1 is shown. The method 40 includes a step 41 of mounting the reference sample 22, a step 42 of emitting the x-ray beam 14, a step 43 of generating an observed image, and a step 44 of determining the orientation of the light source and the orientation of the detector. During step 41, the reference sample 22 is mounted on the sample holding part 12 such that one of the crystal planes of the reference sample is parallel to the plane YZ. Then, in step 42, the radiation light source 11 can be controlled by the processing unit 21 to emit a polychromatic x-ray beam 14 according to the main propagation axis X s . At the same time, in step 43, the processing unit 21 can control the x-ray detector 13 such that the x-ray detector generates an observed image that includes the diffraction pattern produced by the reference sample 22. Finally, during step 44, the processing unit 21 determines the orientation of the main propagation axis X xy defined by the angle ξ xz and the angle ξ s , and the orientation of the sensitive area 131 of the x-ray detector 13 defined by the angles α, β, and γ. As described above, these orientations are determined by comparing the observed image with at least one target image that includes the diffraction pattern obtained for the reference sample with a preset orientation of the main propagation axis X s of the light source 11 and a preset orientation of the sensitive area 131 of the x-ray detector 13.

[0055] According to the first embodiment, determining the orientation of the light source 11 and the orientation of the detector 13 includes a first step of determining the centroid position of the spots of the diffraction pattern in the observed image, and a second step of comparing the observed image with a predetermined set of target images. Each target image shows a diffraction pattern obtained by a preset orientation with respect to the main propagation axis X for the reference sample 22 s and a preset orientation with respect to the induction region 131. For each target image, the orientation is different, such that the set of target images provides a representative sample of the diffraction patterns that may be obtained with the x-ray imaging system 10. The comparison of the observed image with the target images includes, for example, determining the average value of the distances between the centroid of each spot in the observed image and the centroid of each corresponding spot in the target image. Then, the angle ξ xy and the angle ξ xz , as well as the angles α, β, and γ are determined as those angles associated with the target image for which the average value of the distances is the smallest. This target image has a diffraction pattern that best corresponds to the diffraction pattern of the observed image.

[0056] For the preset orientation of the main propagation axis X s (angles ξ xy and ξ xz ) and the preset orientation of the induction region 131 of the detector 13 (angles α, β, and γ), various target images can be obtained by digitally modeling the diffraction generated by the reference sample 22 mounted on the sample holder 12. This digital modeling is performed, for example, by Laue diffraction modeling software (such as PyMicro software). Alternatively, the target images can be generated by a calibrated x-ray imaging system, and the orientation of the light source and the orientation of the detector of the calibrated x-ray imaging system are precisely controlled and measured. The position of the centroid of the spots of the diffraction pattern in each target image can be determined as the position of the centroid of the spots of the diffraction pattern in the observed image.

[0057] Figure 5 Shows a second embodiment of step 44 for determining the orientation of the main propagation axis X s and the orientation of the induction region 131 of the x-ray detector 13. In this embodiment, an iterative process is applied starting from an initial target image. More specifically, in the first sub-step 441, the position of the centroid of the diffraction spots in the observed image is determined in a manner similar to the first embodiment. In the second sub-step 442, the distance between the centroid of each spot of the diffraction pattern in the observed image and the centroid of the corresponding spot in the target image under consideration (i.e., the initial target image during the first occurrence of sub-step 442) is calculated. In the third sub-step 443, the average distance is calculated, which is the average value of the distances between the individual spots in the observed image and the corresponding spots in the target image under consideration. In the fourth sub-step 444, the average distance is compared with a threshold distance Dth is compared. The threshold distance D th is determined according to the desired precision of measuring the angles ξ xy 、angles ξ xz 、angle α, angle β, and angle γ. If the average distance is less than the threshold distance D th , then in sub-step 445, the angles ξ xy 、angles ξ xz 、angle α, angle β, and angle γ associated with the target image under consideration are identified as the angles defining the orientation of the light source 11 and the orientation of the detector 13. On the other hand, if during sub-step 444, it is determined that the average distance is greater than or equal to the threshold distance D th , then in sub-step 446, a new target image is generated, and sub-steps 442, 443, and 444 are repeated with this new target image. The new target image is generated by an orientation of the main propagation axis of the light source 11 different from the orientation of the current target image and / or by an orientation of the sensing region 131 of the detector 13 different from the orientation of the current target image. Preferably, the angles ξ xy 、angles ξ xz 、angle α, angle β, and angle γ are selected such that a new target image different from all previous target images is generated. In addition, the angles ξ xy 、angles ξ xz 、angle α, angle β, and angle γ can be selected according to the average distance calculated for the current target image or the various average distances calculated for the previous target images.

[0058] It should be noted that in the above description, it has been considered that the reference sample 22 is aligned with the reference marker XYZ, and in particular, the reference sample is aligned with the optical axis X of the x-ray imaging system 10. However, when this condition is not met, the present invention can also be implemented. Therefore, additional angles defining the orientation of the reference sample need to be determined. For embodiments including comparing with the diffraction patterns of a set of target images, this involves having a larger image library and taking one or more angles defining the orientation of the reference sample 22 as additional degrees of freedom.

[0059] On the other hand, in the two embodiments of step 44 for determining the orientation of the x-ray light source 11 and the x-ray detector 13, it has been considered to compare the observed image with the target image based on the position of the centroid of the spot of the diffraction pattern of the observed image and the target image. However, instead of the centroid, other sites of the diffraction spot can be considered. In addition, the comparison between the observed image and the target image can consider other characteristics of the diffraction pattern, such as the shape of the spot.

Claims

1. A method for measuring the orientation angle of an X-ray imaging system, the X-ray imaging system (10) comprising an X-ray light source (11), an X-ray detector (13) and a sample holding part (12), the sample holding part being arranged to receive a sample to be analyzed, the X-ray imaging system (10) being configured such that the X-ray light source (11) is capable of emitting a polychromatic X-ray beam (14) along the main propagation axis (X s )), the X-ray beam passing through the sample to be analyzed and reaching the sensing area (131) of the X-ray detector (13), the optical axis (X) of the X-ray imaging system being defined between the center of the X-ray light source (11) and the X-ray detector (13). The method includes the following steps: - Step 42: Emit a polychromatic x-ray beam (14) from the x-ray source along the main propagation axis (X s ), such that the x-ray beam passes through the sample holder (12) installed a reference sample (22) thereon, and forming a diffraction pattern on the sensing area (131) of the x-ray detector (13), - Step 43: generating an observation image with the x-ray detector (13), the observation image including the diffraction pattern, and - Step 44: Determine the orientation (ξ s , ξ xy , ξ xz ) of the main propagation axis (X s ) and the orientation (α, β, γ) of the sensitive area (131) of the x-ray detector (13) by comparing the observed image with at least one target image, the target image including a diffraction pattern obtained for the reference sample (22) with a preset orientation of the main propagation axis and a preset orientation of the sensitive area of the x-ray detector.

2. The method according to claim 1, wherein, Determining the orientation (ξ s ) of the main propagation axis (X xy , ξ xz ) and the orientation (α, β, γ) of the sensitive area (131) of the x-ray detector (13) in step 44 comprises comparing the observed image with a set of target images, each target image showing a diffraction pattern for a preset orientation of the main propagation axis (X s ) and a preset orientation of the sensitive area (131) of the x-ray detector (13), these orientations being different for each target image.

3. The method according to claim 1, wherein, Determine the orientation (ξ s ) of the main propagation axis (X xy , ξ xz ), and the step 44 of determining the orientation (α, β, γ) of the sensitive area (131) of the x-ray detector (13) includes the following sub-steps: - Sub-step 443: Determine a similarity parameter that represents the degree of similarity between the diffraction pattern of the observed image and the diffraction pattern of the current target image for a given orientation of the main propagation axis (X s ) and a given orientation of the induction area (131) of the x-ray detector (13). - Sub-step 444: comparing the similarity parameter with a similarity threshold, - Sub-step 445: When the similarity parameter is less than the similarity threshold, identify the given orientation of the main propagation axis (X s ) and the given orientation of the sensing area (131) of the X-ray detector (13) as the effective orientation of the main propagation axis (X s ) and the effective orientation of the sensing area (131) of the X-ray detector (13), and - Sub-step 446: when the similarity parameter is greater than or equal to the similarity threshold, generating a new current target image, at least one of the given orientations in the given orientation of the current target image being different from the corresponding given orientation of the previous target image, and repeating the previous sub-step until the similarity parameter is less than the similarity threshold.

4. The method according to claim 2 or 3, wherein For a given orientation of the main propagation axis (X s ), and a given orientation of the sensitive area (131) of the X-ray detector (13), each target image is determined by digitally modeling the diffraction produced by a reference sample (22) mounted on the sample holder (12).

5. The method according to any one of claims 1 to 3, before the step 42 of emitting the x-ray beam, the method further includes a step 41 of mounting the reference sample (22) on the sample holder (12).

6. The method according to any one of claims 1 to 3, wherein, The reference sample (22) is made of silicon.

7. A device for measuring the orientation angle of an X-ray imaging system, the X-ray imaging system (10) comprising an X-ray light source (11), an X-ray detector (13), and a sample holding part (12), the sample holding part being arranged to receive a sample to be analyzed, the X-ray imaging system (10) being configured such that the X-ray light source (11) is capable of emitting a polychromatic X-ray beam (14) along the main propagation axis (X s )), the X-ray beam passing through the sample to be analyzed and reaching the sensing area (131) of the X-ray detector (13), the optical axis (X) of the X-ray imaging system being defined between the center of the X-ray light source (11) and the X-ray detector (13). The device includes a processing unit (21), the processing unit being configured to: - An x-ray beam (14) that is polychromatic and is emitted by the x-ray source (11) along the main propagation axis (X s ) passes through a reference sample (22) mounted on the sample holder (12) and forms a diffraction pattern on the sensing area (131) of the x-ray detector (13). - generate an observation image with the x-ray detector (13), the observation image including the diffraction pattern, and - Determining the orientation (ξ s , ξ xy , ξ xz ) of the main propagation axis (X) and the orientation (α, β, γ) of the sensitive area (131) of the x-ray detector (13) by comparing the observed image with at least one target image, the target image including a diffraction pattern obtained for the reference sample (22) through a preset orientation of the main propagation axis and a preset orientation of the sensitive area of the x-ray detector.

8. The device according to claim 7, the device further includes a first partition (23), the first partition being arranged upstream of the sample holder (12) and being arranged to limit the lateral area of the x-ray beam (14).

9. The device according to claim 8, wherein The first partition (23) includes an opening, the lateral area of the opening being smaller than the lateral area of the reference sample (22).

10. The device according to claim 8 or 9, the device further includes a second partition (24) and / or a collimator, the second partition and / or the collimator being arranged between the x-ray source (11) and the first partition (23) and being arranged to obtain a collimated x-ray beam at the sample holder (12).

11. The device according to any one of claims 7 to 9, the device further includes a light valve element (25), the light valve element being arranged downstream of the sample holder (12) and being arranged to prevent the non-diffracted part of the x-ray beam that has passed through the reference sample from reaching the sensing area (131) of the x-ray detector (13).

12. The device according to any one of claims 7 to 9, the device further includes the reference sample (22).

13. The device according to any one of claims 7 to 9, wherein The reference sample (22) is made of silicon.

14. A computer program product, the computer program product including instructions that, when the computer program product is executed by a computer, guide the computer to execute the method according to any one of claims 1 to 4.

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