High throughput 3D x-ray imaging system using a transmission x-ray source

Abstract

A three-dimensional x-ray imaging system includes at least one detector and an x-ray source including an x-ray transparent vacuum window. The x-ray source is configured to generate divergent x-rays that exit the vacuum window and propagate to the at least one detector along an x-ray propagation axis that extends through a region of interest of an object. The divergent x-rays have propagation paths within an angular divergence of greater than 1 degree centered on the x-ray propagation axis. The system further includes at least one sample motion stage configured to rotate the object about an axis of rotation. The system further includes a sample holder configured to hold the object and comprising a first portion that is in a propagation path of at least some of the divergent x-rays and has an x-ray transmissivity greater than 30% for x-rays having an energy greater than 50% of a maximum x-ray energy of an x-ray spectrum of the divergent x-rays.

Description

[0001] Claim of priority

[0002] This application claims priority to U.S. Provisional Application No. 63 / 122,354, filed December 7, 2020, and U.S. Provisional Application No. 63 / 274,367, filed November 1, 2021, the full text of which is incorporated herein by reference. Technical Field

[0003] This application generally relates to tomographic and computed tomographic X-ray imaging systems. Background Technology

[0004] Three-dimensional (3D) X-ray imaging technology can be used to image the internal structure of an object. Typically, a tomographic dataset consists of X-ray transmission images collected over a wide angular range (e.g., approximately 180 degrees; approximately 360 degrees) and subsequently reconstructed to obtain 3D images. The wide angular range is used to avoid (e.g., minimize) 3D image artifacts. A 3D X-ray imaging system includes an X-ray source configured to irradiate an object for imaging, a position-sensitive X-ray detector configured to record transmission X-ray images, and an electromechanical system for manipulating the object relative to the X-ray source and the position-sensitive X-ray detector.

[0005] The X-ray flux incident on a region of interest (ROI) of an object is inversely proportional to the square of the distance between the ROI and the X-ray source; this distance is referred to as the focal object distance (FOD). To achieve high throughput in 3D X-ray imaging, the FOD is chosen to be small (e.g., placing the ROI as close as possible to the X-ray source). For example, given the small voxel volume required to achieve spatial resolution, placing the ROI close to the X-ray source can be used for high spatial resolution 3D X-ray imaging using a laboratory microfocus X-ray source. Furthermore, for 3D X-ray imaging of small ROIs within larger objects (e.g., small ROIs in laterally extending planar objects, examples of which include (but are not limited to) interconnects in semiconductor integrated circuit (IC) packages and fine structural details in large fiber-reinforced composites), the minimum FOD is limited by the object size, which effectively limits the throughput achievable because the object will be rotated 180 degrees.

[0006] However, existing microscopic X-ray computed tomography (μXCT) and microscopic X-ray computed tomography imaging (μXCL) systems have many limitations. For example, Figure 1A and Figure 1B Conventional tomographic and computed tomographic configurations of laterally extending objects (e.g., printed circuit boards; wafers) are schematically illustrated, where the region of interest (ROI) is located at or near the center of the object. An X-ray source emits an X-ray beam (indicated by horizontal dashed lines) and Figure 1A and Figure 1B The thickness of the object in the direction perpendicular to the page can be equal to or less than the object's dimension along the x-ray beam (e.g., to allow sufficient space between the x-ray source and the x-ray detector for rotating the object about the axis of rotation). Figure 1A As observed, in tomography, the axis of rotation is approximately parallel to the surface normal of the object and approximately perpendicular to the X-ray beam. For example... Figure 1B As seen in the figure, for tomographic imaging, the axis of rotation is approximately parallel to the surface normal of the object and tilted by an angle β from a direction approximately perpendicular to the X-ray beam. Figure 1A and Figure 1B These conventional tomography and computed tomography configurations are not well-suited for imaging defects in planes parallel to the surfaces of laterally extended objects (e.g., semiconductor IC packages) because the transmitted X-ray spectrum in the tomography / computed tomography dataset varies with the angle of the X-ray beam axis relative to the object. Consequently, reconstructed images (e.g., computed tomography or CT images) are affected by radiation hardening and photon starvation artifacts, introducing a dependence of the fidelity of the reconstructed features on their orientation relative to the object's axis of rotation. The resolution and image quality of reconstructed images in planes parallel to the surfaces of laterally extended objects are generally worse than those along the surface normal. Furthermore, neither technique is optimized for small FOD due to physical interference from the object and the X-ray source. Improving image resolution by reducing the size of high-throughput X-ray sources (desirable for many applications) is limited by these existing XCT and XCL systems and methods, and higher depth resolution along the surface normal of these extended and / or flat objects is particularly difficult to achieve. Summary of the Invention

[0007] In a particular embodiment, a three-dimensional x-ray imaging system is configured to generate a transmission image of a region of interest in an object. The system includes at least one position-sensitive x-ray detector, which includes at least one active element. The system further includes an x-ray source comprising an x-ray transmission vacuum window having an outer surface. The x-ray source is configured to generate divergent x-rays, at least some of which exit from the vacuum window and propagate along an x-ray propagation axis extending from the x-ray source, passing through the region of interest of the object and reaching the at least one active element of the at least one position-sensitive x-ray detector. The divergent x-rays have a propagation path centered on the x-ray propagation axis within an angular divergence angle greater than 1 degree. The x-ray propagation axis forms a first angle relative to the outer surface of the vacuum window, the first angle being in the range of 3 degrees to 45 degrees. The system further includes at least one sample stage configured to rotate the object about a rotation axis and configured such that the rotation axis has a second angle relative to the x-ray propagation axis, the second angle being in the range of 45 degrees to 90 degrees. The system further includes a sample holder located on the at least one sample stage. The sample holder is configured to hold the object and include a first portion in the propagation path of at least some of the diverging X-rays propagating through the object to the at least one position-sensitive X-ray detector. This first portion has an X-ray transmittance greater than 30% for X-rays with energies greater than 50% of the maximum X-ray energy of the diverging X-ray spectrum.

[0008] In a particular embodiment, a three-dimensional x-ray imaging system includes at least one position-sensitive x-ray detector. The system further includes an x-ray source comprising an x-ray transmission vacuum window having an outer surface. The x-ray source is configured to generate divergent x-rays, at least some of which exit from the vacuum window and propagate along an x-ray propagation axis extending from the x-ray source. The divergent x-rays propagate through the region of interest of the object to the at least one position-sensitive x-ray detector and have an angular divergence angle greater than 1 degree centered on the x-ray propagation axis. The x-ray propagation axis forms a first angle relative to the outer surface of the vacuum window, the first angle being in the range of 3 to 45 degrees. The system further includes at least one sample stage configured to rotate the object about a rotation axis and configured to adjust the rotation axis to have a second angle relative to the x-ray propagation axis, the at least one sample stage having a non-systematic angular oscillation of less than 5 microradians. Attached Figure Description

[0009] Figure 1A and Figure 1B The conventional tomographic and tomographic configurations for laterally extended objects are schematically illustrated, with the region of interest (ROI) located at or near the center of the object.

[0010] Figure 2 An example x-ray 3D imaging system compatible with a particular implementation described herein is schematically illustrated.

[0011] Figure 3A A schematic cross-sectional view of an X-ray spot produced by an electron beam striking at least one X-ray target, according to a specific embodiment described herein.

[0012] Figure 3B and Figure 3C A schematic illustration of a specific implementation scheme described herein. Figure 3A Top view of two example configurations of an electron beam and at least one X-ray target.

[0013] Figure 4 Another example system including at least one hole is schematically illustrated according to a particular embodiment described herein.

[0014] Figure 5A and Figure 5B An example system according to a specific embodiment described herein is schematically illustrated, wherein the sample stage and sample holder are configured to hold and rotate the object.

[0015] Figure 6A and Figure 6B Two examples of systems according to a particular embodiment described herein are schematically illustrated, wherein at least one position-sensitive x-ray detector includes a first position-sensitive x-ray detector and a second position-sensitive x-ray detector.

[0016] Figure 7 An example system configured to perform multi-contrast X-ray imaging using Talbot interferometry or Talbot-Lau interferometry, according to a specific implementation described herein, is illustrated schematically.

[0017] Figure 8 An example system compatible with generating translational tomography images according to a specific implementation described herein is schematically illustrated. Detailed Implementation

[0018] In certain embodiments, the 3D x-ray imaging system is capable of imaging ROIs with very small FODs in large objects to reduce tomographic dataset collection time (e.g., increase imaging data collection speed). In certain embodiments, the system also provides improved image quality (e.g., fidelity) and higher image resolution in a plane parallel to the surface of the laterally extending object, which can be important for many applications such as metrology, inspection, fault analysis, and process development for semiconductor IC packages (e.g., as solder bumps and Cu interconnects). The x-ray source can be configured to achieve small FODs and improve spatial resolution. Certain embodiments are configured to use metrological geometry to “compress” the electron beam focus in one dimension, which allows for greater asymmetry and therefore higher power, with the focus becoming symmetrical or nearly symmetrical after projection, which can be expected to have isotropic spatial resolution. Certain embodiments are configured to have an x-ray source comprising x-ray generating material having a thickness configured to achieve high spatial resolution in a direction substantially perpendicular to the surface of the laterally extending object being analyzed. Additionally, specific implementations include extra components and / or methods for implementing several imaging contrast modes, including Talbot interferometry for obtaining absorption, phase, and dark field (scattering) contrast, dark field (scattering) contrast only, and enhanced absorption contrast.

[0019] Figure 2 An example x-ray 3D imaging system 5, compatible with a particular embodiment described herein, is schematically illustrated. System 5 includes an x-ray source 20 and at least one position-sensitive x-ray detector 50 including at least one active element 52. The x-ray source 20 includes an x-ray transmission vacuum window 29 having an outer surface 27, and is configured to generate divergent x-rays. At least some divergent x-rays 60 exit from the vacuum window 29 and propagate along an x-ray propagation axis 10 extending from the x-ray source 20, passing through the region of interest 31 of the object 30, and reaching at least one active element 52 of the position-sensitive x-ray detector 50. The divergent x-rays 60 impacting at least one active element 52 have a propagation path within an angular divergence angle 12 greater than 1 degree centered on the x-ray propagation axis 10. The x-ray propagation axis 10 forms a first angle 11 with respect to the outer surface 27 of the vacuum window 29. The first angle 11 is within the range of less than or equal to 45 degrees (e.g., less than or equal to 30 degrees; within the range of 3 degrees to 45 degrees; between 5 degrees and 30 degrees; less than 3 degrees).

[0020] In a particular embodiment, system 5 further includes at least one sample stage 80 (e.g., motorized and computer-controlled; including electromechanical systems). The at least one sample stage 80 is configured to rotate the object 30 about a rotation axis 19. The sample stage 80 is configured such that the rotation axis 19 has a second angle 16 relative to the x-ray propagation axis 10, the second angle 16 being greater than or equal to 45 degrees (e.g., in the range of 45 to 90 degrees). In other particular embodiments, the second angle 16 is less than 45 degrees. In a particular embodiment, the second angle 16 may be greater than or equal to 45 degrees and the rotation axis 19 may form a third angle relative to the surface normal of the outer surface 27 of the vacuum window 29, the third angle being less than 45 degrees (e.g., less than 30 degrees). In a particular embodiment, system 5 includes a mechanism configured to change the third angle. For example, the mechanism may include at least one tilting stage (e.g., goniometer; electromechanical motion driver; rotary motor; stepper motor; motor with encoder; linear motion driver with worm gear drive) configured to tilt the x-ray source 20 relative to the axis of rotation 19 and / or relative to the axis of rotation 19 of the x-ray source 20.

[0021] In a particular embodiment, system 5 further includes a sample holder 85 on at least one sample motion stage 80 and configured to hold the object 30. The sample holder 85 includes a first portion 86 in the propagation path of at least some divergent x-rays 60 propagating through the object 30 to at least one position-sensitive x-ray detector 50. The first portion 86 has an x-ray transmittance greater than 30% (e.g., greater than 50%) for x-rays with energies greater than 50% of the maximum x-ray energy of the divergent x-ray spectrum of the x-rays 60.

[0022] Figure 2Example system 5 is configured to image a region of interest (ROI) 31 in a large or laterally extended object 30 (e.g., positioned substantially parallel to the outer surface 27 of the vacuum window 29) to minimize the field of view (FOD) between the ROI 31 and the x-ray source 20. For example, to image the ROI 31 in a large three-dimensional object 30, the object 30 can be placed close to the x-ray source 20 (e.g., at a distance of less than 70 mm between the outer surface 27 of the vacuum window 29 and the surface 32 of the object 30) and centered on the rotation axis 19 of at least one sample stage 80. The three-dimensional (3D) image dataset of the ROI 31 can be collected by a series of x-ray transmission images recording divergent x-rays 60 transmitted through the ROI 31 of the object 30 to at least one active element 52 of at least one position-sensitive x-ray detector 50, wherein the object 30 is rotated about the rotation axis 19 within an angular range (e.g., between 180 and 360 degrees). Known tomographic reconstruction methods can be used to reconstruct the computational tomographic dataset to obtain a 3D image of ROI 31. For another example, for imaging ROI 31 in a planar object 30 (e.g., solder bumps and / or interconnects in a semiconductor IC package), the object 30 can be positioned such that the surface 32 of the object 30 closer to ROI 31 faces the vacuum window 29. For a larger / planar object 30, a small angle 14 between the outer surface 27 of the vacuum window 29 and the surface 32 of the object 30 can be used to position the ROI 31 closer to the x-ray source 20 to increase the x-ray flux on the ROI 31 and thus increase imaging yield. In another example, the surface 32 of the object 30 is positioned away from the outer surface 27 of the vacuum window 29 (e.g., to reduce or minimize the radiation dose to the ROI 31).

[0023] X-ray source

[0024] like Figure 2 Schematably illustrated, in a particular embodiment, the x-ray source 20 includes a vacuum chamber 21 containing a vacuum region 23 and an electron beam source 22 within the vacuum region 23. The x-ray source 20 further includes electron optics 25 (e.g., electrodes) configured to direct at least some electrons from the electron beam source 22 to an electron beam 24 focused at at least one x-ray target 28. For example, the electron beam source 22 and electron optics 25 are configured to generate and bombard at least one x-ray target 28 with the focused electron beam 24, wherein a selectable maximum focused electron energy in the range of 10 kVp to 250 kVp is present at the at least one x-ray target 28. In a particular embodiment, the vacuum chamber 21 includes a vacuum-sealed tube containing the electron beam source 22, electron optics 25, and at least one x-ray target 28. Compared to an open-tube x-ray source, the x-ray source 20 of this particular embodiment is not actively pumped.

[0025] At least one x-ray target 28 is located within a vacuum region 23 and configured to generate divergent x-rays 60 in response to bombardment by a focused electron beam 24. The at least one x-ray target 28 comprises at least one x-ray generating material selected for its x-ray spectral generation properties (e.g., characteristic x-ray energy) and / or other properties affecting the x-ray generating capability of the at least one x-ray generating material (e.g., atomic number Z; electron density). The at least one x-ray generating material may have a sufficiently high thermal conductivity to dissipate the heat generated by bombardment by the high-power electron beam 24. Examples of x-ray generating materials include (but are not limited to): Cr, Fe, Co, Ni, Cu, W, Rh, Mo, Au, Pt, Ag, SrB6, LaB6, and CeB6. Figure 2 The insert diagram schematically illustrates that at least one x-ray target 28 may be fixed to (e.g., integrated with; as a component of; in contact with) a vacuum window 29, which separates the vacuum region 23 from the non-vacuum region outside the x-ray source 20. The thickness of at least one x-ray generating material along a direction substantially perpendicular to the outer surface 27 of the vacuum window 29 may range from 0.1 micrometers to 15 micrometers (e.g., 0.1 micrometers to 10 micrometers), and the thickness of the vacuum window 29 in the direction substantially perpendicular to the outer surface 27 of the vacuum window 29 may range from 0.05 millimeters to 3 millimeters. As described herein, the thickness of at least one x-ray generating material may be configured to optimize high spatial resolution (e.g., by minimizing electron beam scattering within the material) and / or high system yield (e.g., maximizing electron energy deposition within at least one x-ray generating material). For example, the thickness of at least one x-ray generating material may be less than twice the image resolution along the rotation axis 19. In a particular embodiment, at least one X-ray generating material has multiple regions that can be bombarded by an electron beam 24 (e.g., by translating the electron beam focus), each region having a corresponding thickness along a direction generally perpendicular to the outer surface 27 of the vacuum window 29. The electron beam 24 can be guided by electron optics 25 to bombard selected regions with corresponding thicknesses that provide a selected trade-off between yield and resolution.

[0026] In a particular embodiment, the vacuum window 29 is substantially composed of atomic elements having an atomic number (Z) less than 14 and is substantially transmissive to higher-energy x-rays generated by at least one x-ray generating material. For example, the vacuum window 29 may have sufficiently high thermal conductivity to provide a heat conduit to prevent thermal damage (e.g., melting) to at least one x-ray generating material (e.g., a material selected from beryllium, diamond, boron carbide, silicon carbide, aluminum, and beryllium oxide (BeO)). The vacuum window 29 may further provide a sufficiently conductive path to dissipate charge from at least one x-ray generating material and / or the vacuum window 29. In a particular embodiment, the vacuum window 29 is configured to have x-ray transmission such that more than 50% of the x-rays generated by at least one x-ray source 28 having an energy greater than half the selected maximum focusing electron energy are transmitted through the vacuum window 29. In a particular embodiment, divergent x-rays 60 emitted from the outer surface 27 of the vacuum window 29 are not blocked by the x-ray source 20 along the x-ray propagation axis 10. Although X-ray source 20 emits X-rays into a solid angle of 4π, Figure 2 The diagram only schematically illustrates divergent x-rays 60 (e.g., x-rays contributing to image formation) propagating along the x-ray propagation axis 10 within an angular divergence angle 12 to at least one active element 52 of at least one position-sensitive x-ray detector 50, wherein other divergent x-rays generated by at least one x-ray target 28 and emitted in other directions from the outer surface 27 of the vacuum window 29 are not shown. Figure 2 middle.

[0027] In a particular embodiment, system 5 further includes a thermal cooling mechanism configured to reduce the heating of object 30 by heat generated by x-ray source 20. For example, the thermal cooling mechanism may include an infrared (IR) reflective material (e.g., a thin IR-reflective and high x-ray transmission film or layer, an example of which is an aluminized polyester film) between vacuum window 29 and object 30. The IR reflective material is configured to reflect heat generated by x-ray source 20 (e.g., power attributable to the electron beam converted into heat in at least one x-ray target 28) to prevent it from reaching object 30 and sample holder 85 (e.g., directing thermal energy away from object 30 and sample holder 85 to reduce or minimize heat transfer to object 30 and / or sample holder 85). In this way, the IR reflective material protects object 30 and sample holder 85 from sample temperature variations that would otherwise cause thermal expansion that could harmfully affect the accuracy of ROI selection and / or the fidelity of 3D volumetric reconstruction. The IR reflective material is thin enough (e.g., less than 1500 micrometers thick; less than 100 micrometers thick) to not substantially impair the positioning of the object 30 near the electron beam focus of the X-ray source 20.

[0028] In a particular embodiment, the x-ray source 20 includes a grounded anode transmission x-ray source (e.g., a vacuum enclosure electrically grounded), examples of which include (but are not limited to): DAGE available from Nordson Corporation in Westlake, Ohio. X-ray sources; L10711-03 microfocus X-ray source available from Hamamatsu Photonics KK, Hamamatsu, Japan; Excillum Nanotube N1 and N2 X-ray sources available from Excillum Corporation, Kista, Sweden; X-ray Worx GmbH, Gabsen, Germany; X-ray sources available from COMET Technologies, San Jose, California. These example X-ray sources 20 can be configured to have an X-ray source point integrated with the vacuum window 29 and to place the object 30 close to the X-ray source 20 to reduce (e.g., minimize) FOD and thus increase (e.g., maximize) the X-ray flux at the object 30. Due to electrical and mechanical constraints, the X-ray source 20 can have a large plane that is the end of the vacuum housing and coplanar with the vacuum window 29, but cannot be made smaller without affecting the electron beam focusing quality. For existing x-ray tomography and computed tomography techniques utilizing these x-ray sources 20, this large plane limits the ability to place large and / or planar objects 30 close to the x-ray source 20 and to rotate the object 30 (e.g., up to 180 degrees) about a rotation axis 19 that is substantially perpendicular to the large plane. The specific embodiments described herein advantageously avoid this major drawback of existing x-ray imaging systems.

[0029] In a particular embodiment, the x-ray source 20 is configured to have a small x-ray spot size (e.g., a size of less than 7 micrometers in at least one lateral direction generally parallel to the outer surface 27 of the vacuum window 29) while generating sufficient x-ray flux to facilitate a sufficiently short image acquisition time. Generally, the x-ray spot size is approximately equal to the cyclotron of the focused electron beam spot size (e.g., radius) at at least one x-ray target 28 and the size (e.g., radius) of the x-ray generation volume within at least one x-ray target 28, due to electron scattering within at least one x-ray target 28. Therefore, a larger focused electron beam spot size promotes higher electron beam power, accompanied by higher x-ray flux and shorter image acquisition time, at the cost of lower spatial resolution, while a smaller focused electron beam spot size promotes higher spatial resolution, at the cost of lower x-ray flux and longer image acquisition time. Furthermore, since a large portion (e.g., about 99%) of the incident power from the focused electron beam 24 is converted into heat in at least one x-ray target 28, it is desirable to limit the incident electron beam power, which typically decreases linearly with the x-ray spot size.

[0030] In a particular embodiment, higher spatial resolution of the x-ray transmission image in the direction of the surface normal of the outer surface 27 containing the vacuum window 29 and the plane of the rotation axis 19 is provided by reducing the thickness t of at least one x-ray generating material of at least one x-ray target 28, which reduces the effective x-ray source size s. For example, the thickness t of at least one x-ray generating material in a direction generally perpendicular to the outer surface 27 of the vacuum window 29 can be in the range of 0.1 micrometers to 15 micrometers. Figure 3A A schematic cross-sectional view of an X-ray spot produced by an electron beam 24 impacting at least one X-ray target 28, according to a specific embodiment described herein. Figure 3B and Figure 3C A schematic illustration of a specific implementation scheme described herein. Figure 3A Top view of two example configurations of the electron beam 24 and at least one X-ray target 28. Figure 3A Schematic illustration: The size of the x-ray spot observed along the x-ray propagation axis 10 can be smaller than the width W (e.g., diameter) of the electron beam 24 on the x-ray target 28. For an x-ray generating material with a thickness t, the effective width s of the full width at half maximum (FWHM) of the x-ray spot observed along the x-ray propagation axis 10 can be approximately smaller than t / 2 ( Figure 3A (Not drawn to scale). In a particular embodiment, at least one X-ray generating material includes a thin high-Z material layer (e.g., thickness t in the range of 0.1 micrometers to 3 micrometers) on or inside a low-Z material substrate (e.g., vacuum window 29) to... Figure 3A A small X-ray spot size (e.g., less than 5 micrometers) is achieved in the cross-section along the X-ray propagation axis 10 at an angle of less than 30 degrees relative to the outer surface 27 of the vacuum window 29. The effective width s of the X-ray spot size in the cross-section, representing the FWHM, can be approximately equal to s = {(t / 2)}. 2 +[W·sin(θ)] 2} 0.5 Where t is the thickness of the high-Z material, and W is the effective width of the electron beam size in the cross-section. For example, when t = 1 micrometer, θ = 10 degrees, and W = 1 micrometer, the effective width s of the X-ray spot size in the cross-section is 0.53 micrometers, which is smaller than W. Therefore, the effective X-ray source size in the cross-section along the X-ray propagation axis 10 can be compressed compared to the width of the electron beam 24 in the cross-section.

[0031] Since the effective X-ray spot size on the cross-section is approximately smaller than the electron beam width W, a specific embodiment can further be implemented approximately perpendicular to... Figure 3A Achieving a small X-ray spot size along the direction of the cross-section. For example, such as Figure 3BSchematic illustration shows that the electron beam 24 can be focused and compressed in a direction generally perpendicular to the cross-section. The focused electron beam 24, having an elongated (e.g., rectangular) shape or footprint at the X-ray target 28, is... Figure 3A The cross-section may have a long dimension (e.g., width W of FHWM) and be approximately perpendicular to Figure 3A The cross-section has a short dimension (e.g., FWHM width w) in one direction (e.g., in a plane containing the surface normal of the outer surface 27 of the x-ray propagation axis 10 and the vacuum window 29), and the short dimension is smaller than the long dimension.

[0032] For another example, such as Figure 3C Schematic illustration of at least one high-Z material of X-ray generating material at approximately perpendicular to Figure 3A The width d of the cross-section in the direction of the focused electron beam can be smaller than that of the 24-pole beam in a direction approximately perpendicular to the cross-section. Figure 3A The FWHM width w in the direction of the cross section. Since at least one x-ray generating material generates x-rays more efficiently than the vacuum window 29 (e.g., because the x-ray generation efficiency is approximately proportional to the average atomic number of the material), the portion of the electron beam 24 that does not strike at least one x-ray generating material does not generate x-rays efficiently and has approximately no effect on the x-ray spot size, thus in a direction approximately perpendicular to... Figure 3A The size of the X-ray spot is limited to a width d along the direction of the cross-section. In a particular embodiment, the width d of at least one X-ray generating material is in the range of 0.1 micrometers to 5 micrometers.

[0033] When viewed along the x-ray propagation axis 10 (e.g., from the direction of at least one position-sensitive x-ray detector 50), and taking into account the takeoff angle between the outer surface 27 and the x-ray propagation axis 10, Figure 3B and Figure 3C The X-ray spot can be presented as a square or circle at at least one position-sensitive X-ray detector 50. For example, at a takeoff angle of 10 degrees, an electron beam 24 with a rectangular focal point having an aspect ratio of 5:1 can appear approximately symmetrical. Because the electron beam 24 is elongated and impacts a larger area compared to a narrow focus in two directions, higher electron power can be used to increase the X-ray flux (e.g., to achieve higher X-ray brightness) and thus reduce image acquisition time while maintaining spatial resolution. For example, an electron beam 24 with an aspect ratio of 5:1 can provide up to a five-fold increase in apparent power density. Further reducing the takeoff angle in conjunction with a higher aspect ratio focused electron beam can further improve apparent power density. Specific embodiments are described in... Figure 3AThe depth resolution is higher in the cross-section than in the direction orthogonal to the cross-section. For many applications, high depth resolution (e.g., in the direction generally perpendicular to the surface 32 of the laterally extending object 30) is more important than lateral resolution (e.g., imaging of layering of solder bumps parallel to the surface in a semiconductor package or cracks caused by stress in solder bumps).

[0034] hole

[0035] Figure 4 Another example system 5, including at least one aperture 70, is schematically illustrated according to a particular embodiment described herein. In a particular embodiment, at least one aperture 70 includes at least one orifice 72 (e.g., a slit; having a width of less than 100 micrometers) in at least one solid material (e.g., a plate), the at least one orifice 72 being positioned on the x-ray propagation axis 10 and between the vacuum window 29 and the object 30 (e.g., downstream of the vacuum window 29 and upstream of the object 30). At least one aperture 70 is configured not to attenuate divergent x-rays 60 (e.g., x-rays used for imaging) propagating along the x-ray propagation axis 10 within an angular divergence angle 12 to reach the ROI 31 and / or at least one position-sensitive x-ray detector 50, but is configured to attenuate at least some x-rays emitted from the vacuum window 29 in other directions and / or scattered x-rays (e.g., x-rays not used for imaging) to reach the ROI 31 and / or at least one position-sensitive x-ray detector 50. In a particular embodiment, at least one solid material of at least one aperture 70 has a sufficiently high Z (e.g., W; Au), a sufficiently high electron density, and a substantially small thickness, such that at least one aperture 70 is configured to attenuate x-rays without substantially limiting FOD. In a particular embodiment, at least one aperture 70 is configured to attenuate the amount of external x-ray flux emitted by x-ray source 20 beyond the angular divergence angle 12 reaching object 30. By attenuating this external x-ray flux, at least one aperture 70 can reduce harmful background contributions to the image from the external x-ray flux and / or reduce harmful x-ray dose to object 30 from external x-ray flux that does not contribute to the imaging. The edge of at least one aperture 72 of at least one aperture 70 can define the angular divergence angle 12 by allowing only x-rays within at least one aperture 72 to propagate further along the x-ray propagation axis 10. In a particular embodiment, the distance between one aperture 70 and vacuum window 29 is configured (e.g., a distance in the range of 0.3 mm to 5 mm) to achieve a small FOD between the x-ray source point and ROI 31.

[0036] Sample movement stage and sample rack

[0037] In a particular embodiment, at least one sample motion stage 80 is configured to move an object 30 relative to an x-ray source 20 and / or at least one position-sensitive x-ray detector 50. In a particular embodiment, at least one sample motion stage 80 includes at least one linear motion substage 82 configured to controllably adjust the position of the object 30 (e.g., along substantially perpendicular x, y, and z directions) and at least one rotary motion substage 84 configured to controllably adjust the orientation of the object 30 (e.g., rotating the object 30 about a rotation axis 19). For example, at least one linear motion substage 82 may include one, two, or three electromechanical linear motion actuators (e.g., linear motors; stepper motors; motors with encoders; piezoelectric motors; rotary motors with screws) configured to move the object 30 such that the ROI 31 is located at a selected position along the x-ray propagation axis 10, and at least one rotary motion substage 84 may include at least one electromechanical motion actuator (e.g., rotary motors; stepper motors; motors with encoders; linear motion actuators with worm gear drives) configured to rotate the object 30 and the ROI 31 about a rotation axis 19.

[0038] In a specific implementation, such as Figure 2 Schematably illustrated, a laterally extending object 30 may be mounted on at least one sample motion stage 80 such that the surface 32 of the object 30, parallel to its elongated dimension, is tilted relative to the x-ray propagation axis 10 at an angle β (e.g., in the range of 1 to 30 degrees). In a particular embodiment, at least one rotary motion substage 84 is further configured to controllably adjust the angle β, and at least one linear motion substage 82 is further configured to linearly translate the object 30 and / or at least one rotary motion substage 84, such that the ROI 31 is positioned on both the rotation axis 19 and the x-ray propagation axis 10. In a particular embodiment, at least one sample motion stage 80 is configured to controllably adjust the distance between the rotation axis 19 and the x-ray spot (e.g., the electron beam focus).

[0039] In a particular embodiment, the sample holder 85 is configured to hold the object 30 while it is being irradiated by the x-ray 60, such that the x-ray 60 is projected through the ROI 31 to at least one position-sensitive x-ray detector 50. The sample holder 85 is configured such that the x-ray 60 interacts minimally (e.g., is minimally scattered and / or absorbed by) the solid components of at least one sample motion stage 80 (e.g., at least one linear motion substage 82 and at least one rotary motion substage 84). The sample holder 85 is configured to reduce (e.g., minimize) the portion of the diverging x-ray 60 that interacts with the solid portion of at least one sample motion stage 80 as the object 30 rotates about the rotation axis 19.

[0040] In a particular embodiment, at least one sample stage 80 and sample holder 85 are configured to hold and rotate the object 30 without affecting throughput. For example, since throughput in microfocus transmission X-ray computed tomography is inversely proportional to the square of the focal distance to object (FOD), a small FOD (e.g., bringing the object 30 as close as possible to the X-ray source 20) can be used to achieve high throughput.

[0041] Figure 5A and Figure 5B Example system 5 is schematically illustrated, wherein, according to a specific embodiment described herein, at least one sample motion stage 80 and sample holder 85 are configured to hold and rotate the object 30. Figure 5A In Example System 5, object 30 is located between x-ray source 20 and at least one sample stage 80. With at least one linear motion substage 82 and at least one rotary motion substage 84 on opposite sides of object 30 and at least one x-ray source 20, at least one sample stage 80 does not obstruct x-rays 60 from reaching object 30. However, as... Figure 5A As shown, after propagating through ROI 31, x-ray 60 propagates through at least a portion of the sample holder 85 before reaching at least one position-sensitive x-ray detector 50. Figure 5B In Example System 5, the x-ray source 20 and at least one sample stage 80 are located on the same side of the object 30, and the x-ray 60 propagates through at least a portion of the sample holder 85 before reaching the object 30 (e.g., the sample holder 85 may limit the x-ray source 20 to being closest to the object 30). Although Figure 5A An example embodiment is shown in which the X-ray source 20 is above the object 30 and at least one sample stage 80. However, in other embodiments, the X-ray source 20, the object 30, and at least one sample stage 80 may have any orientation while maintaining the same relative positioning to each other. Although Figure 5B An example embodiment is shown in which the x-ray source 20 is below the object 30, but in other embodiments, the x-ray source 20, the object 30 and at least one sample stage 80 may have any orientation while maintaining the same relative positioning to each other.

[0042] In a particular embodiment, the sample holder 85 is configured to offset the object 30 from at least one sample stage 80 such that at least one sample stage 80 (e.g., at least one linear motion substage 82 and at least one rotary motion substage 84) is not within the imaging field of view of at least one position-sensitive X-ray detector 50 (e.g., reducing, avoiding, or minimizing X-ray scattering and / or absorption that would adversely affect image reconstruction fidelity). For example, the sample holder 85 may offset the object 30 from at least one sample stage 80 by a distance greater than 50 mm (e.g., greater than 100 mm; in the range of 100 mm to 500 mm; in the range of 100 mm to 200 mm). The sample holder 85 of a particular embodiment includes a first portion 86 configured to be struck by at least a portion of X-rays 60 as the object 30 and the sample holder 85 rotate about a rotation axis 19, and a second portion 87 mechanically coupling the first portion 86 to at least one motion substage (e.g., at least one linear motion substage 82 and / or at least one rotary motion substage 84). The first part 86 and the second part 87 are configured to deflect the ROI 31 of the object 30 from at least one motion substage such that the diverging X-ray 60 does not strike at least one motion substage or the second part 87 (e.g., when the object 30 and the sample holder 85 are rotating about the rotation axis 19).

[0043] In a particular embodiment, the first portion 86 is substantially composed of low-Z elements (e.g., atomic elements with atomic numbers less than 14) and / or thin materials (e.g., a thickness of less than 10 mm along the rotation axis 19). In a particular embodiment, the first portion 86 has an x-ray transmittance greater than 50% for x-rays with energies greater than 50% of the maximum x-ray energy of the x-ray spectrum of x-ray 60 (e.g., x-rays emitted by x-ray source 20). These particular embodiments simultaneously provide sufficiently high throughput and sufficiently low radiation damage to the object 30 (e.g., because the x-rays do not need to be projected through the absorbing material of at least one sample motion stage 80, the x-ray flux irradiating the object 30 can be kept sufficiently low to avoid radiation damage, while providing a sufficient amount of detected x-rays for high-throughput imaging). For example, the first portion 86 may comprise a carbon fiber or quartz plate (e.g., having a projected thickness of less than or equal to 2 mm along the x-ray propagation axis 10). The second portion 87 is mechanically coupled to the first portion 86 and at least one linear motion substage 82 and / or at least one rotary motion substage 84. In certain embodiments, the second portion 87 is substantially composed of the same low-Z element and / or thin material as the first portion 86 (e.g., a low-Z rod or hollow tube, such as a carbon fiber or quartz tube, having a projected thickness of less than or equal to 2 mm along the x-ray propagation axis 10); however, in other specific embodiments, the second portion 87 includes any solid material (e.g., regardless of the solid material's x-ray absorption and / or scattering). In certain embodiments, the second portion 87 is a part of at least one linear motion substage 82 and / or at least one rotary motion substage 84.

[0044] For example, such as Figure 5A Schematably illustrated, the first portion 86 and the second portion 87 extend along the rotation axis 19 and are configured such that, for all tomographic imaging angles of interest and for all rotation angles of interest, the x-ray 60 does not impinge on at least one linear motion substage 82 and / or at least one rotary motion substage 84. For at least one sample motion stage 80 having a maximum dimension (e.g., radius) R from the rotation axis 19 and in a direction substantially perpendicular to the rotation axis 19, the first portion 86 and the second portion 87 are configured to maintain the object 30 at a distance z from at least one linear motion substage 82 and / or at least one rotary motion substage 84 along the rotation axis 19, such that the envelope of the x-ray 60 does not impinge on the portion of the at least one sample motion stage 80 that would scatter and / or absorb the x-ray 60 (e.g., the portion including at least one element with an atomic number Z greater than 14; at least one linear motion substage 82; at least one rotary motion substage 84).

[0045] For another example, such as Figure 5BSchematic illustration shows a first portion 86 configured to hold (e.g., clamp) the sides and / or edges of an object 30, and a second portion 87 mechanically couples the first portion 86 to at least one sample motion stage 80 (not shown). Figure 5B middle). Figure 5B At least one sample stage 80 further includes a through-hole region 88 (e.g., a region at least partially defined by a second portion 87) configured to have an x-ray source 20 extending at least partially through it. These specific embodiments allow the x-ray source 20 to be placed arbitrarily close to one side of the object 30, thereby providing high throughput when the object 30 is rigidly mounted. An example second portion 87 compatible with the specific embodiments described herein is a large-aperture, ultra-high-precision, air-bearing rotary stage available from PI (Physik Instrumente) in Auburn, Massachusetts.

[0046] Image reconstruction fidelity depends on the precise rotation of object 30 during measurement, and uncontrolled motion of object 30 can cause deviations between the actual recorded projection data and the tomographic reconstruction algorithm's expectations. Therefore, these uncontrolled movements can produce blurring in the back-projected data, reducing the resolution and contrast of the reconstructed volume. In a particular embodiment, at least one sample motion stage 80 reduces (e.g., avoids; minimizes) the deviation from pure rotation that causes translation and / or orientation changes of object 30 within the image's field of view. At least one sample motion stage 80 may have sufficiently low non-system angular oscillation (e.g., uncontrolled angular motion of the axis of rotation 19 varying with rotation about the axis of rotation 19), sufficiently low radial runout (e.g., uncontrolled translation of the axis of rotation 19 varying with rotation about the axis of rotation 19, resulting in lateral movement of the object 30 approximately perpendicular to the axis of rotation 19), and / or sufficiently low axial runout (e.g., uncontrolled axial movement of the object 30 approximately parallel to the axis of rotation 19) during the rotation of the object 30, such that the uncontrolled motion of the object 30 is less than one-fifth of the system resolution (e.g., less than 0.1 micrometers of uncontrolled motion for a system resolution of 0.5 micrometers). For example, for an object 30 positioned at a distance L above at least one rotary stage 84 of at least one sample motion stage 80 and with an image resolution (e.g., detector resolution divided by image magnification) of δ, a non-systematic angular wobble ω (e.g., less than 100 nanoradians; less than 200 nanoradians; less than 1 microradian; less than 5 microradians) can result in radial runout R = ωL < δ / 5 (e.g., less than δ / 3; less than δ / 2; less than 1 micrometer; less than 0.5 micrometer; less than 200 nanometers; less than 100 nanometers) and / or an axial runout A < δ / 5 (e.g., less than δ / 3; less than δ / 2; less than 1 micrometer; less than 0.5 micrometer; less than 200 nanometers; less than 100 nanometers). In a particular embodiment, at least one sample motion stage 80 has a non-systematic angular wobble (e.g., error) of less than 5 microradians (e.g., less than 1 microradian), radial runout repeatability better than 1000 nanometers, and axial runout repeatability better than 1000 nanometers. In a particular embodiment, system 5 further includes a metrology system configured to measure the angular oscillation of at least one sample stage 80 with an accuracy better than less than 5 microradians (e.g., less than 1 microradian), the radial runout of at least one sample stage 80 with an accuracy better than 1000 nanometers, and / or the axial runout of at least one sample stage 80 with an accuracy better than 1000 nanometers.

[0047] In a particular embodiment, at least one rotary motion substage 84 of at least one sample motion stage 80 may include an air-bearing rotary stage (e.g., less than 5 microradians; less than 1 microradian; less than 200 nanoradians) with a swing angle of less than 5 microradians (e.g., less than 1 microradian; less than 200 nanoradians) and radial and axial runout of less than 100 nanometers. The position of the object 30 within an angular range (e.g., 360 degrees) about the rotation axis 19 can be accurate to better than half the system resolution.

[0048] Position-sensitive X-ray detector

[0049] In a particular embodiment, at least one position-sensitive x-ray detector 50 is configured to record an image of the x-rays 60 received after transmission through ROI 31. Examples of at least one position-sensitive x-ray detector 50 include (but are not limited to): photon counting detectors (e.g., including silicon, CdTe, and / or CdZnTe and configured to directly convert x-rays into electrons with or without energy discrimination; Eiger ASIC and Pilatus ASIC available from Dectris, Baden-Dartwell, Switzerland); including scintillator materials (e.g., CdWO4, CsI, Gd2O2S, LSO, GAGG, and / or LYSO; Shad-o-Box HS detector available from Teledyne Dalsa, Waterloo, Canada; 2315N detector available from Varex Imaging, Salt Lake City, Utah; Athena and Onyx detectors available from Nordson, Westlake, Ohio; Spectrum, Boulder, Colorado). The detectors include a flat panel detector (FPD) with a 1412HR detector obtained from Logic; fiber optic plates and CMOS or CCD detectors; scintillator materials (e.g., CdWO4, CsI, Gd2O2S, LSO, GAGG, and / or LYSO); and objectives configured to magnify the image onto the CMOS or CCD detector. In a particular embodiment, at least one position-sensitive X-ray detector 50 includes a plurality of active elements 52 (e.g., pixels) having a lateral dimension (e.g., along the surface of detector 50) of less than 70 micrometers (e.g., less than 50 micrometers).

[0050] In a particular embodiment, at least one position-sensitive x-ray detector 50 is configured to receive and image x-rays 60 transmitted through object 30, including a region of interest (ROI) 31. The x-rays 60 have a predetermined range of energies (e.g., x-ray spectra) that promote (e.g., optimize) sufficient image contrast to distinguish features of interest in the ROI 31 and / or reduce imaging collection time. For example, the predetermined x-ray spectrum can be generated by selecting the focusing electron energy of at least one x-ray target 28 and / or at least one x-ray generating material, such that the generated x-rays 60 in the predetermined x-ray spectrum have a sufficiently large x-ray flux to promote image contrast and / or imaging collection time. For x-ray imaging using absorption contrast, the predetermined x-ray spectrum may contain energies in which object 30 has x-ray transmittance in the range of 5% to 85% (e.g., 8% to 30%). This x-ray transmittance range can provide a favorable trade-off between image contrast (which favors lower energy x-rays) and transmission through object 30 (which favors higher energy x-rays).

[0051] As another example, at least one position-sensitive x-ray detector 50 may be configured to have at least one energy threshold for detecting x-rays (e.g., at least one position-sensitive x-ray detector 50 may be configured to reject and / or suppress the detection of x-rays with energies below a first energy threshold and / or above a second energy threshold). For example, the at least one energy threshold may include a threshold-cutoff x-ray energy, and the at least one position-sensitive x-ray detector 50 is configured to image only x-rays with energies below the threshold-cutoff x-ray energy. The threshold-cutoff x-ray energy of a particular embodiment corresponds to x-rays on object 30 having less than 85% (e.g., less than 50%) x-ray transmittance. For example, at least one position-sensitive x-ray detector 50 may include a photon-counting detector configured to select at least one threshold-cutoff x-ray energy (e.g., to controllably adjust the threshold-cutoff x-ray energy). The photon-counting detector may be further configured to collect energy-dependent x-ray transmission images (e.g., using multiple operator-selectable energy windows to reduce noise, image artifacts, and / or provide material differentiation). In another example, at least one position-sensitive x-ray detector 50 may include a combination of a scintillation screen and a material configured to image only x-rays below a threshold cutoff x-ray energy.

[0052] Figure 6A and Figure 6BTwo examples of system 5 according to a particular embodiment described herein are schematically illustrated, wherein at least one position-sensitive x-ray detector 50 includes a first position-sensitive x-ray detector 54 and a second position-sensitive x-ray detector 56. The second position-sensitive x-ray detector 56 may be configured to provide gain sensitivity to a different portion of the x-ray spectrum obtained from the first position-sensitive x-ray detector 54 to increase overall yield, and / or to provide measurements with a different spatial resolution than the first position-sensitive x-ray detector 54. For example, the first position-sensitive x-ray detector 54 and the second position-sensitive x-ray detector 56 may have different scintillator materials and / or different scintillator thicknesses than each other.

[0053] For example, such as Figure 6A Schematably illustrated, a first detector 54 may be configured to absorb and detect a first spectral portion of x-rays 60 transmitted through ROI 31, and a second detector 56 may be configured to absorb and detect a second spectral portion of x-rays 60 transmitted through ROI 31 that is not absorbed by the first detector 54. The first detector 54 may be configured (e.g., optimized) for at least some of the high-resolution x-ray flux received from ROI 31, and the second detector 56 may be positioned behind the first detector 54 (see, for example). Figure 6A And configured to detect at least some of the X-ray flux transmitted through the first detector 56. For another example, such as... Figure 6B Schematally illustrated, a first spectral portion of the x-ray 60 propagating along the x-ray propagation axis 10 can be absorbed by the scintillator screen 55 of the first detector 54, and a second spectral portion of the x-ray 60 propagating along the x-ray propagation axis 10 can be transmitted through the scintillator screen 55 to strike the second detector 56. The x-rays absorbed by the scintillator screen 55 can generate scintillation photons (e.g., visible light photons), which are reflected by the mirror 57 and imaged onto the position-sensitive photon detector 59 by the objective lens 58. The material and thickness of the mirror 57 can be selected to have high transmittance for transmitting the x-ray 60 through the object 30.

[0054] although Figure 6A and Figure 6BThe diagram schematically illustrates a configuration in which two detectors 54, 56 are positioned to detect x-rays 60 propagating in the same direction as each other. However, in other specific embodiments, the two detectors 54, 56 are positioned to collect x-rays from at least one x-ray source 20 propagating in different directions (e.g., at angles less than 45 degrees relative to the outer surface 27 of the vacuum window 29). In a particular embodiment, the two detectors 54, 56 are used simultaneously with each other, while in other specific embodiments, the two detectors 54, 56 are used separately (e.g., sequentially). In a particular embodiment, the two detectors 54, 56 are configured to have different pixel resolutions at object 30 (e.g., approximately equal to the pixel size of the detector divided by its geometric image magnification). Combining the outputs of the two detectors 54, 56 in a particular embodiment improves the overall detection efficiency of system 5 and allows access to a wider range of object spatial frequencies, thus improving yield and reconstruction quality. In a particular embodiment, the second detector 56 is configured (e.g., optimized) to be sensitive to different portions of the x-ray spectrum of x-rays 60, which allows for corrections for beam hardening and / or material identification.

[0055] Figure 7 An example system 5, configured to perform multi-contrast X-ray imaging using Talbot interferometry or Talbot-Lau interferometry according to a specific embodiment described herein, is schematically illustrated. System 5 can be configured to provide high resolution and sensitivity, as well as unique imaging capabilities (e.g., absorption, phase, and dark-field image contrast in 2D and 3D; dark-field; enhanced absorption contrast imaging) for a wide range of applications. In a specific embodiment, system 5 is configured to collect a 3D imaging dataset using Talbot-Lau interferometry, dark-field contrast, and enhanced absorption contrast, and reconstruct the dataset to obtain a 3D image of object 30 and / or ROI 31 within object 30. In a specific embodiment, such as Figure 7 As schematically illustrated, system 5 further includes at least one sample motion stage 80 and a sample holder 85 (see, for example). Figure 5A The configuration is designed to reduce (e.g., minimize) the interaction between the portion of the diverging x-ray 60 propagating along the x-ray propagation axis 10 and the solid portion having at least one sample motion stage 80.

[0056] like Figure 7Schematably illustrated, system 5 includes a first grating G1 (e.g., a phase grating) configured to generate a Talbot self-image interferometry pattern at a first location along the x-ray propagation axis 10, and a second grating G2 (e.g., an analyzer grating) positioned at a second location along the x-ray propagation axis 10. The first grating G1 and the second grating G2 are configured to be compatible with Talbot interferometry, such that the Talbot pattern is indirectly imaged by at least one position-sensitive x-ray detector 50. In other specific embodiments, the second grating G2 may be omitted, and the at least one position-sensitive x-ray detector 50 may have an active element 52 having spatial resolution (e.g., size in a transverse direction generally perpendicular to the x-ray propagation axis 10) sufficiently small (e.g., less than or equal to half the pitch of the second grating G2) to be compatible with Talbot interferometry, such that the Talbot pattern is directly imaged by at least one position-sensitive x-ray detector 50. In a particular embodiment, system 5 further includes a source grating and is configured to perform Talbot-Lau interferometry. In other specific embodiments, the x-ray source 20 includes a plurality of x-ray targets 28 arranged in a regular array of one-dimensional or two-dimensional shapes. The geometric parameters of the plurality of x-ray targets 28, the first grating G1, and the second grating G2 are configured to satisfy Talbot-Lau interferometer conditions. Various configurations of the x-ray source 20 and the first grating G1 and the second grating G2 are disclosed in U.S. Patent Nos. 9,719,947 and 10,349,908, the entire contents of which are incorporated herein by reference.

[0057] In a particular embodiment, the first grating G1 includes an absorption grating. For example, one or both of the first grating G1 and the second grating G2 may comprise an array of patterned one-dimensional or two-dimensional x-ray generally absorptive (e.g., absorption greater than 50%) structures having a width in the range of 0.5 micrometers to 20 micrometers and spaced apart from each other by generally non-absorbent (e.g., absorption less than 50%) gaps having a width in the range of 0.5 micrometers to 20 micrometers. In addition to using techniques such as phase stepping for three-contrast imaging (e.g., absorption, phase, and scattering), the system 5 of a particular embodiment may be configured to obtain only dark-field (e.g., scattering) contrast imaging by configuring the pitch, the distance from the x-ray source 20, and the alignment of the first and second gratings, such that x-rays transmitted through the opening of the first (e.g., upstream) grating G1 are incident on the absorbing portion of the second (e.g., downstream) grating G2. For example, the first grating G1 and the second grating G2 may be positioned along the x-ray propagation axis 10 between at least one x-ray source 20 and at least one position-sensitive x-ray detector 50 (e.g., the first grating G1 is closer to the at least one x-ray source 20 than to the at least one position-selective x-ray detector 50), such that the generally non-absorbent structure of the second grating G2 is aligned with the generally absorbing structure of the first grating G1 (e.g., in its shadow) and the generally absorbing structure of the second grating G2 is aligned with the generally non-absorbent structure of the first grating G1. In this configuration, in the absence of an object 30, no x-rays are expected to be transmitted through both the first grating G1 and the second grating G2; however, in the presence of scattering features of the object 30, at least some of the scattered x-rays are transmitted through the second grating G2, resulting in imaging of features in the object 30 responsible for the scattered x-rays. In a particular embodiment, an enhanced absorption contrast image can be obtained by shifting the relative alignment of the first and second gratings by half a pitch from the configuration used in dark-field imaging, such that the X-rays scattered by the object 30 are reduced by the absorbing structure of the second grating G2. In a particular embodiment, instead of having the second grating G2, a first set of active elements 52 (e.g., pixels) of at least one position-sensitive X-ray detector 50 is aligned with the generally absorbing structure of the first grating G1 (e.g., in its shadow), and a second set of active elements 52 of at least one position-sensitive X-ray detector 50 is aligned with the generally non-absorbing structure of the first grating G1. In this configuration, when the object 30 is positioned along the X-ray propagation axis 10, the X-ray counts recorded by the second set of active elements 52 can be used to generate an absorption contrast image, while the X-ray counts recorded by the first set of active elements 52 can be used to generate a scattered / dark-field and / or refractive image.

[0058] In a particular embodiment where a semiconductor IC package is to be 3D imaged, system 5 is configured to acquire an X-ray transmission image along an X-ray propagation axis 10 at a small angle (e.g., within a range of less than 45 degrees) relative to the surface normal of the semiconductor chip surface 32. For example, rotational tomography over a large angle range (e.g., 180 degrees to 630 degrees) or limited-angle translational tomography over a limited angle range (e.g., ±30 degrees) can be performed. The 3D image can be combined with a tomographic 3D image acquired at a large angle (e.g., greater than 60 degrees) relative to the surface normal of the semiconductor chip surface 32 along the X-ray propagation axis 10 to produce a 3D image. Figure 8 An example system 5 compatible with generating translational tomography images according to a specific embodiment described herein is schematically illustrated. System 5 includes an additional X-ray detector 90 and at least one detector stage 92 configured to translate detector 90 and object 30 relative to X-ray source 20. In a specific embodiment, at least one detector stage 92 includes at least one sample motion stage 80. For example, detector 90 and object 30 can be moved proportionally in the same direction (e.g., along a line from X-ray source 20 through ROI 31 to the center of detector 90). In a specific embodiment, Figure 8 System 5 is configured to achieve higher spatial resolution and / or better image sharpness for features (e.g., sidewalls of copper interconnects) that extend in a direction generally parallel to the surface normal of the semiconductor chip.

[0059] In a particular embodiment, system 5 further includes at least one motion mechanism configured to change the geometric magnification of an image of the region of interest of an object generated by at least one position-sensitive detector. For example, the at least one motion mechanism may include at least one first motion stage (e.g., a linear motion stage; an electromechanical linear motion driver; a linear motor; a stepper motor; a motor with an encoder; a piezoelectric motor; a rotary motor with a screw) configured to move the x-ray source 20 relative to the object 30, at least one second motion stage (e.g., a linear motion stage; an electromechanical linear motion driver; a linear motor; a stepper motor; a motor with an encoder; a piezoelectric motor; a rotary motor with a screw) configured to move at least one position-sensitive detector 50 relative to the object 30, and / or at least one third motion stage (e.g., a linear motion stage; an electromechanical linear motion driver; a linear motor; a stepper motor; a motor with an encoder; a piezoelectric motor; a rotary motor with a screw; at least one linear motion substage 82) configured to move the object 30 relative to the x-ray source 20 and / or at least one position-sensitive detector 50.

[0060] While common terms are used to describe systems and methods of particular embodiments for ease of understanding, these terms are used herein for their broadest reasonable interpretation. Although various aspects of this disclosure are described with respect to illustrative examples and embodiments, the disclosed examples and embodiments should not be construed as limiting. Unless otherwise specifically stated or otherwise understood in the context in which they are used, conditional language (such as “can,” “could,” “might,” or “may”) is generally intended to convey that a particular embodiment includes, while other embodiments do not include, a particular feature, element, and / or step. Therefore, this conditional language is generally not intended to imply any manner in which features, elements, and / or steps are required in one or more embodiments. Specifically, the terms “comprises” and “comprising” should be interpreted as referring to an element, component, or step in a non-exclusive manner, indicating that the referenced element, component, or step may be present, used, or combined with other elements, components, or steps not expressly referenced.

[0061] Unless otherwise specified, connective language (such as the phrase "at least one of X, Y, and Z") should be understood within the context in which items, terms, etc., can be X, Y, or Z. Therefore, this connective language is not generally intended to imply that a particular implementation requires the presence of at least one of X, at least one of Y, and at least one of Z.

[0062] As used herein, degree language (such as the terms "approximately," "about," "generally," and "approximately") refers to a value, quantity, or characteristic that is close to the stated value, quantity, or characteristic while still performing the desired function or achieving the desired result. For example, the terms "approximately," "about," "generally," and "approximately" may refer to a quantity within ±10%, ±5%, ±2%, ±1%, or ±0.1% of the stated quantity. As another example, the terms "generally parallel" and "approximately parallel" refer to a value, quantity, or characteristic that deviates from perfect parallelism by ±10 degrees, ±5 degrees, ±2 degrees, ±1 degree, or ±0.1 degrees, and the terms "generally perpendicular" and "approximately perpendicular" refer to a value, quantity, or characteristic that deviates from perfect perpendicularity by ±10 degrees, ±5 degrees, ±2 degrees, ±1 degree, or ±0.1 degrees. The scopes disclosed herein also cover any and all overlapping, sub-scopes, and combinations thereof. Language (such as "up to," "at least," "greater than," "less than," "between," and the like) includes the stated numbers. As used herein, the meanings of “a,” “an,” and “the” include multiple references unless the context clearly indicates otherwise. Although this document discusses structures and / or methods based on elements marked by ordinal adjectives (e.g., first, second, etc.), ordinal adjectives are used only as labels to distinguish one element from another, and are not used to indicate the order in which these elements or the like are used.

[0063] Various configurations have been described above. It should be understood that the embodiments disclosed herein are not mutually exclusive and can be combined with each other in various configurations. Although the invention has been described with reference to these specific configurations, these descriptions are intended to illustrate the invention and not to limit it. Various modifications and applications will be apparent to those skilled in the art without departing from the true spirit and scope of the invention. Thus, for example, in any method or procedure disclosed herein, the actions or operations constituting the method / procedure can be performed in any suitable sequence and are not necessarily limited to any particular disclosed sequence. Features or elements from the various embodiments and examples discussed above can be combined with each other to produce alternative configurations compatible with the embodiments disclosed herein. Various aspects and advantages of the embodiments have been described where appropriate. It should be understood that not all of these aspects or advantages can be achieved according to any particular embodiment. Therefore, for example, it should be recognized that various embodiments can be performed in a manner that achieves or optimizes one or a group of advantages as taught herein without necessarily achieving other aspects or advantages as taught or suggested herein.

Claims

1. A three-dimensional X-ray imaging system configured to generate a transmission image of a region of interest in an object, the system comprising: At least one position-sensitive X-ray detector, which includes at least one active element; An X-ray source includes an X-ray transmission vacuum window with an outer surface less than 70 mm from the region of interest of the object. The X-ray source has at least one X-ray target configured to be struck by an electron beam to generate divergent X-rays from an X-ray spot having a practical width in a cross-section, wherein the cross-section includes the electron beam and an X-ray propagation axis, and the X-ray propagation axis extends from the X-ray spot, through the region of interest of the object, to at least one active element of the at least one position-sensitive X-ray detector. At least some of the divergent X-rays exit from the vacuum window and propagate along the X-ray propagation axis. The divergent X-rays received by the at least one active element have a propagation path centered on the X-ray propagation axis within an angular divergence angle greater than 1 degree. The X-ray propagation axis forms a first angle relative to the outer surface of the vacuum window, the first angle being in the range of 3 to 45 degrees. The X-ray spot has an effective width in the cross-section observed along the X-ray propagation axis, the effective width being less than the practical width. At least one sample stage configured to rotate the object about a rotation axis and configured such that the rotation axis has a second angle relative to the x-ray propagation axis, the second angle being in the range of 45 degrees to 90 degrees; and A sample holder, located on the at least one sample motion stage, configured to hold the object, the sample holder including a first portion in at least some of the propagation paths of the diverging X-rays propagating through the object to the at least one position-sensitive X-ray detector, and having an X-ray transmittance greater than 30% for X-rays having an energy greater than 50% of the maximum X-ray energy of the diverging X-ray spectrum.

2. The system of claim 1, wherein the second angle is greater than or equal to 45 degrees and the rotation axis forms a third angle with respect to the surface normal of the outer surface of the vacuum window, the third angle being less than 30 degrees.

3. The system of claim 2, further comprising a mechanism configured to change the third angle.

4. The system of claim 1, wherein the diverging X-rays do not intersect with the at least one sample motion stage.

5. The system of claim 1, wherein the first portion consists of atomic elements with an atomic number less than 14.

6. The system of claim 1, wherein the sample holder further comprises a second portion mechanically coupling the first portion to the at least one sample motion stage, the first portion and the second portion being configured to offset the region of interest of the object from the at least one sample motion stage such that the diverging X-rays do not impinge on the at least one sample motion stage or the second portion.

7. The system of claim 1, wherein the at least one sample motion stage has a non-system angular oscillation of less than 5 microradians, a radial runout of less than 500 nanometers, and an axial runout of less than 500 nanometers.

8. The system of claim 1, wherein the at least one sample stage has a non-system angular oscillation error of less than 5 microradians, radial runout repeatability of better than 1000 nanometers, and axial runout repeatability of better than 1000 nanometers.

9. The system of claim 1, further comprising a metrology system configured to measure the angular oscillation of the at least one sample stage with an accuracy better than less than 1 microradian, the radial oscillation accuracy of the at least one sample stage with an accuracy better than 1000 nanometers, and / or the axial runout of the at least one sample stage with an accuracy better than 1000 nanometers.

10. The system of claim 1, wherein the first angle between the x-ray propagation axis and the outer surface of the vacuum window is less than 30 degrees, less than 5 degrees, or less than 3 degrees.

11. The system of claim 1, wherein the x-ray source further comprises: A vacuum chamber containing a vacuum zone, the vacuum chamber including the vacuum window, the vacuum window separating the vacuum zone from a non-vacuum zone outside the x-ray source and contacting the at least one x-ray target; An electron beam source is located in the vacuum region; and An electron optics device configured to direct at least some electrons from the electron beam source into an electron beam focused at the at least one x-ray target, the electron beam having a maximum focused electron energy in the range of 10 kVp to 250 kVp at the at least one x-ray target, the at least one x-ray target being configured to generate the diverging x-rays in response to bombardment by the electron beam.

12. The system of claim 11, wherein the at least one X-ray target comprises at least one X-ray generating material selected from the group consisting of: Cr, Fe, Co, Ni, Cu, W, Rh, Mo, Au, Pt, Ag, SrB6, LaB6, GdB6, and CeB6.

13. The system of claim 12, wherein the at least one X-ray generating material has a plurality of regions that can be bombarded by a focused electron beam, each of the regions having a corresponding thickness along a direction perpendicular to the outer surface of the vacuum window.

14. The system of claim 12, wherein the at least one X-ray generating material is fixed to the vacuum window and has a thickness in the range of 0.1 micrometer to 15 micrometers along a direction perpendicular to the outer surface of the vacuum window, and the vacuum window has a thickness in the range of 0.05 millimeters to 3 millimeters along the direction perpendicular to the outer surface of the vacuum window.

15. The system of claim 11, wherein the vacuum window is composed of a material selected from the group consisting of beryllium, diamond, boron carbide, silicon carbide, aluminum, and beryllium oxide.

16. The system of claim 11, wherein the focused electron beam comprises a spot size having a dimension of less than 7 micrometers in at least one lateral direction parallel to the outer surface of the vacuum window.

17. The system of claim 11, wherein the focused electron beam at the at least one x-ray target has a spot shape having a first dimension in a plane containing the surface normal of the outer surface of the x-ray propagation axis and the vacuum window, and a second dimension in a second lateral direction along the at least one x-ray target and perpendicular to the first lateral direction, the first dimension being greater than the second dimension.

18. The system of claim 1, wherein the at least one position-sensitive x-ray detector comprises silicon, CdTe and / or CdZnTe and is configured to directly convert x-rays into electrons.

19. The system of claim 1, wherein the at least one position-sensitive x-ray detector has at least one energy threshold for detecting x-rays, the at least one position-sensitive x-ray detector being configured to reject and / or suppress the detection of x-rays having energy below a first energy threshold and / or energy above a second energy threshold.

20. The system of claim 1, wherein the at least one position-sensitive X-ray detector comprises a scintillator material selected from the group consisting of: CdWO4, CsI, Gd2O2S, LSO, GAGG, and LYSO.

21. The system of claim 20, wherein the at least one position-sensitive X-ray detector further comprises an objective lens and a CMOS or CCD detector, the objective lens being configured to magnify an image from the scintillator material onto the CMOS or CCD detector.

22. The system of claim 1, wherein the at least one position-sensitive X-ray detector comprises a first detector and a second detector, the first detector being configured to absorb and detect a first spectral portion of the X-rays transmitted through the region of interest, and the second detector being configured to absorb and detect a second spectral portion of the X-rays transmitted through the region of interest and the first detector.

23. The system of claim 1, further comprising a first grating at a first position along the x-ray propagation axis, the first grating comprising an absorption grating or a phase grating.

24. The system of claim 23, wherein the at least one position-sensitive X-ray detector is configured to record a Talbot pattern formed by the first grating.

25. The system of claim 23, wherein the first grating, the second grating, and the at least one position-sensitive X-ray detector are configured to record dark-field contrast images.

26. The system of claim 1, further comprising a thermal cooling mechanism configured to reduce the heating of the object by heat generated by the x-ray source.

27. The system of claim 26, wherein the thermal cooling mechanism includes an infrared reflective material located between the vacuum window and the object, the infrared reflective material having a thickness of less than 1500 micrometers and configured to reflect heat generated by the X-ray source to prevent it from reaching the object and the sample holder.

28. The system of claim 1, further comprising at least one aperture having at least one opening in at least one solid material, the at least one opening being positioned on the x-ray propagation axis and between the vacuum window and the object, the at least one aperture being configured to not attenuate the diverging x-rays propagating along the x-ray propagation axis within the angular divergence angle to the region of interest and / or the at least one position-sensitive x-ray detector, while attenuating at least some x-rays emitted from the vacuum window and / or by scattered x-rays from other directions to the region of interest and / or the at least one position-sensitive x-ray detector.

29. The system of claim 1, wherein the at least one sample motion stage comprises an air-bearing rotary table.

30. The system of claim 1, further comprising at least one motion mechanism configured to change the geometric magnification of an image of the region of interest of the object generated by the at least one position-sensitive detector.

31. The system of claim 30, wherein the at least one motion mechanism is configured to move the x-ray source and / or the at least one position-sensitive detector relative to the object.

32. The system of claim 1, wherein the actual width has an actual full width at half maximum (FWHM) in the cross-section. W The X-ray target has a thickness along a direction perpendicular to the outer surface of the vacuum window. t And the effective width has an effective full width at half maximum (FWHM) in the cross-section. s It is equal to s ={( t / 2) 2 + [ W sin( θ )] 2 } 0.5 ,in θ That's the first perspective.

33. The system of claim 1, wherein the effective width is less than 5 micrometers.

34. The system of claim 1, wherein the effective width is less than 1 micrometer.

35. The system of claim 1, wherein the effective width is less than 0.5 micrometers.

36. A three-dimensional X-ray imaging system, comprising: At least one position-sensitive X-ray detector; An X-ray source includes an X-ray transmission vacuum window with an outer surface, the X-ray source being configured to generate divergent X-rays, the outer surface of the vacuum window being less than 70 mm from the region of interest of an object, at least some of the divergent X-rays exiting from the vacuum window and propagating along an X-ray propagation axis extending from the X-ray source, the divergent X-rays propagating through the region of interest of the object to the at least one position-sensitive X-ray detector, the divergent X-rays received by the at least one position-sensitive detector having an angular divergence angle greater than 1 degree centered on the X-ray propagation axis, the X-ray propagation axis forming a first angle relative to the outer surface of the vacuum window, the first angle being in the range of 3 degrees to 45 degrees; At least one sample motion stage is configured to rotate the object about a rotation axis and to adjust the rotation axis to have a second angle relative to the x-ray propagation axis, the at least one sample motion stage having a non-systematic angular oscillation of less than 5 microradians, and An infrared reflective material is located between the vacuum window and the object, the infrared reflective material having a thickness of less than 1500 micrometers and configured to reflect heat generated by the X-ray source so as not to reach the object and the sample holder.

37. The system of claim 36, further comprising a sample holder on the at least one sample movement stage and configured to hold the object, the sample holder comprising a first portion configured to be struck by at least some of the divergent X-rays propagating through the object to the at least one position-sensitive X-ray detector, the first portion being composed of atomic elements having an atomic number less than 14 and / or having a thickness of less than 10 millimeters along the axis of rotation.

38. The system of claim 36, wherein the at least one sample motion stage comprises an air-bearing rotary table.

Images