High-throughput 3D X-ray imaging system using a transmitted X-ray source

Abstract

The three-dimensional x-ray imaging system includes at least one detector and an x-ray source including an x-ray transmissive vacuum window. The x-ray source is configured to generate divergent x-rays that exit the vacuum window and propagate along an x-ray propagation axis extending through a region of interest of the object to the at least one detector. The divergent x-rays have a propagation path within an angular divergence angle greater than 1 degree about the x-ray propagation axis. The system further includes at least one sample motion stage configured to rotate the object about a rotation axis. The system further includes a sample mount configured to hold the object, and includes a first portion within a propagation path of at least a portion of the divergent x-rays having an x-ray transmittance 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

[Technical field]

[0001] Priority claim This application claims the benefit of priority to U.S. Provisional Patent Application No. 63 / 122,354, filed December 7, 2020, and U.S. Provisional Patent Application No. 63 / 274,367, filed November 1, 2021, both of which are incorporated by reference in their entireties.

[0002] background Field This application relates generally to tomographic and laminographic x-ray imaging systems. [Background technology]

[0003] 2. Description of Related Art Three-dimensional (3D) X-ray imaging techniques are useful for imaging the internal structure of an object. Typically, a tomographic data set is collected over a wide angular range (e.g., about 180 degrees, about 360 degrees) and subsequently reconstructed to obtain a 3D image. The large angular range is used to avoid (e.g., minimize) 3D image artifacts. The 3D X-ray imaging system comprises an X-ray source configured to irradiate the object for imaging, a position-sensitive X-ray detector configured to record the transmission X-ray image, and an electromechanical system for manipulating the object relative to the X-ray source and the position-sensitive X-ray detector.

[0004] The X-ray flux incident on a region of interest of an object is inversely proportional to the square of the distance of the region of interest from the X-ray source, and this distance can be called the focal object distance (FOD). To achieve high throughput in 3D X-ray imaging, the FOD is chosen to be small (e.g., the region of interest is placed as close to the X-ray source as possible). For example, considering the small voxel volumes used to achieve spatial resolution, placing the region of interest close to the X-ray source can be used for 3D X-ray imaging with high spatial resolution using laboratory microfocus X-ray sources. Furthermore, for 3D X-ray imaging of small regions of interest within larger objects (e.g., small regions of interest within laterally extending planar objects, examples of which include, but are not limited to, wiring within semiconductor integrated circuit (IC) packages, and fine structural details within large fiber-reinforced composite panels), the minimum FOD is limited by the dimensions of the object, and the achievable throughput is practically limited because the object is rotated 180 degrees.

[0005] However, prior art micro X-ray computed tomography (μXCT) and micro X-ray computed laminography (μXCL) systems have many limitations. For example, Figures 1A and 1B show schematic diagrams of conventional tomography and laminography configurations, respectively, of a laterally extending object (e.g., a printed circuit board, a wafer) with a region of interest (ROI) at or near the center of the object. The X-ray source emits an X-ray beam (shown by a horizontal dashed line), and the thickness of the object in Figures 1A and 1B in a direction perpendicular to the page can be less than or equal to the object's dimension along the X-ray beam (e.g., such that there is sufficient space between the X-ray source and the X-ray detector to rotate the object about the rotation axis). As seen in Figure 1A, for tomography, the rotation axis is substantially parallel to the object's surface normal and substantially perpendicular to the X-ray beam. As seen in Figure 1B, for laminography, the rotation axis is substantially parallel to the object's surface normal and tilted by an angle β from a direction substantially perpendicular to the X-ray beam. 1A and 1B show that such conventional tomography and laminography configurations are not well suited to imaging defects in a plane parallel to the surface of a laterally extending object (e.g., a semiconductor IC package), because the transmitted X-ray spectrum in the tomography / laminography data set varies with the angle of the X-ray beam axis relative to the object. As a result, reconstructed images (e.g., computer tomography or CT images) suffer from radiation hardening and photon starvation artifacts, resulting in a dependence of the fidelity of reconstructed features on their orientation relative to the object rotation axis. The resolution and image quality of reconstructed images in a plane parallel to the surface of a laterally extending object are typically worse than in the direction along the surface normal. In addition, neither technique is optimized to achieve a small FOD due to the physical interference of the object and the X-ray source. Improving image resolution by reducing X-ray source size at high flux, which may be desirable for many applications, is significantly limited in such prior art XCT and XCL systems and methods, and higher depth resolution along the surface normal of such extended and / or planar objects is particularly difficult to achieve. Summary of the Invention [Means for solving the problem]

[0006] overview In certain embodiments, a three-dimensional X-ray imaging system is configured to generate a transmission image of a region of interest in an object. The system comprises at least one position-sensitive X-ray detector comprising at least one active element. The system further comprises an X-ray source comprising an X-ray transparent vacuum window having an outer surface. The X-ray source is configured to generate divergent X-rays, at least a portion of the divergent X-rays exiting the vacuum window and propagating along an X-ray propagation axis extending from the X-ray source through the region of interest of the object to at least one active element of the at least one position-sensitive X-ray detector. The divergent X-rays have a propagation path within an angular divergence angle greater than 1 degree about the X-ray propagation axis. The X-ray propagation axis is at a first angle with respect to the outer surface of the vacuum window, the first angle being in a range of 3 degrees to 45 degrees. The system further comprises at least one sample translation stage configured to rotate the object about a rotation axis, the rotation axis being configured to have a second angle with respect to the X-ray propagation axis being in a range of 45 degrees to 90 degrees. The system further comprises a sample mount on the at least one sample motion stage, the sample mount configured to hold the object and comprising a first portion in a propagation path of at least a portion of the divergent x-rays propagating through the object to the at least one position sensitive x-ray detector, the first portion having an x-ray transmittance of 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.

[0007] In certain embodiments, a three-dimensional x-ray imaging system includes at least one position-sensitive x-ray detector. The system further includes an x-ray source including an x-ray transmissive vacuum window having an outer surface. The x-ray source is configured to generate divergent x-rays, at least a portion of the divergent x-rays exiting the vacuum window and propagating along an x-ray propagation axis extending from the x-ray source. The divergent x-rays propagate through a 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 about the x-ray propagation axis. The x-ray propagation axis is at 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 translation 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 translation stage having a non-systematic angular wobble of less than 5 microradians. [Brief description of the drawings]

[0008] [Figure 1A] 1 is a schematic diagram of a conventional tomography setup for a laterally extending object with a region of interest (ROI) at or near the center of the object. [Figure 1B] FIG. 1 is a schematic diagram of a conventional laminography setup for a laterally extending object with a region of interest (ROI) at or near the center of the object. [Diagram 2] 1 is a schematic diagram of an exemplary X-ray 3D imaging system consistent with certain embodiments described herein. [Figure 3A] 2 is a schematic cross-sectional view of an X-ray spot produced by an electron beam impinging on at least one X-ray target, according to certain embodiments described herein. [Figure 3B] 3B is a schematic top view of an exemplary configuration of the electron beam and at least one X-ray target of FIG. 3A in accordance with certain embodiments described herein. [Figure 3C] 3B is a schematic top view of an exemplary configuration of the electron beam and at least one X-ray target of FIG. 3A in accordance with certain embodiments described herein. [Figure 4]1 is a schematic diagram of another exemplary system comprising at least one opening, according to certain embodiments described herein. [Figure 5A] FIG. 2 is a schematic diagram of an exemplary system in which a sample stage and a sample mount are configured to hold and rotate an object, according to certain implementations described herein. [Figure 5B] FIG. 2 is a schematic diagram of an exemplary system in which a sample stage and a sample mount are configured to hold and rotate an object, according to certain implementations described herein. [Figure 6A] 1 is a schematic diagram of an example system in which at least one position sensitive X-ray detector comprises a first position sensitive X-ray detector and a second position sensitive X-ray detector, according to certain embodiments described herein. [Figure 6B] 1 is a schematic diagram of an example system in which at least one position sensitive X-ray detector comprises a first position sensitive X-ray detector and a second position sensitive X-ray detector, according to certain embodiments described herein. [Figure 7] 1 is a schematic diagram of an exemplary system configured to perform multi-contrast X-ray imaging using Talbot interferometry or Talbot-Lau interferometry, in accordance with certain embodiments described herein. [Figure 8] FIG. 1 is a schematic diagram of an exemplary system adapted for generating translational laminographic images, according to certain embodiments described herein. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0009] Detailed Description In certain embodiments, the 3D X-ray imaging system enables imaging of ROIs with very small FODs within large objects to reduce laminographic dataset collection time (e.g., to 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 may be important for many applications such as metrology, inspection, failure analysis, and process development of 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 implementations are configured to "compress" the electron beam focal spot into one dimension using a measurement geometry, which can enable the use of an asymmetric larger and therefore higher power focal spot, which becomes symmetric or nearly symmetric after projection, which may be desirable to have an isotropic spatial resolution. Certain embodiments are configured to have an X-ray source including an 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, certain embodiments include additional components and / or methods for implementing several modes of imaging contrast, including absorption, phase, and dark field (scattering) contrast, dark field (scattering) contrast only, and Talbot interferometry for enhanced absorption contrast.

[0010] 2 illustrates a schematic diagram of an exemplary X-ray 3D imaging system 5 compatible with certain embodiments described herein. The 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 transmissive vacuum window 29 having an outer surface 27, and the X-ray source 20 is configured to generate divergent X-rays. At least a portion of the divergent X-rays 60 exit the vacuum window 29 and propagate along an X-ray propagation axis 10 that extends from the X-ray source 20 through a region of interest 31 of the object 30 to at least one active element 52 of the at least one position-sensitive X-ray detector 50. The divergent X-rays 60 that impinge on the at least one active element 52 have a propagation path within an angular divergence angle 12 greater than 1 degree about the X-ray propagation axis 10. The X-ray propagation axis 10 is at a first angle 11 relative to the outer surface 27 of the vacuum window 29, the first angle 11 being in a range of 45 degrees or less (e.g., 30 degrees or less, in a range of 3 degrees to 45 degrees, 5 degrees to 30 degrees, less than 3 degrees).

[0011] In certain embodiments, the system 5 further comprises at least one sample translation stage 80 (e.g., motorized and computer controlled, comprising an electromechanical system). The at least one sample translation stage 80 is configured to rotate the object 30 about a rotation axis 19. The sample translation stage 80 is configured such that the rotation axis 19 has a second angle 16 with respect to the x-ray propagation axis 10, the second angle 16 being in a range of 45 degrees or more (e.g., in a range of 45 degrees to 90 degrees). In certain other embodiments, the second angle 16 is less than 45 degrees. The second angle 16 of certain embodiments can be in a range of 45 degrees or more, and the rotation axis 19 can be at a third angle with respect to a surface normal of the outer surface 27 of the vacuum window 29, the third angle being in a range of less than 45 degrees (e.g., less than 30 degrees). In certain embodiments, the system 5 comprises a mechanism configured to vary the third angle. For example, the mechanism can include at least one tilt stage (e.g., a goniometer, an electromechanical motion driver, a rotary motor, a stepper motor, a motor with an encoder, a linear motion driver with a worm drive) configured to tilt the X-ray source 20 relative to the rotation axis 19 and / or the rotation axis 19 relative to the X-ray source 20.

[0012] In certain embodiments, system 5 further comprises a sample mount 85 on at least one sample motion stage 80 and configured to hold object 30. Sample mount 85 comprises a first portion 86 in a propagation path of at least a portion of divergent x-rays 60 propagating through object 30 to at least one position sensitive x-ray detector 50. First portion 86 has an x-ray transmittance of greater than 30% (e.g., greater than 50%) for x-rays having an energy greater than 50% of a maximum x-ray energy of the x-ray spectrum of divergent x-rays 60.

[0013] The exemplary system 5 of FIG. 2 is configured to image a region of interest (ROI) 31 within a large or laterally extending object 30 (e.g., positioned to be substantially parallel to the outer surface 27 of the vacuum window 29) so as to minimize FOD between the ROI 31 and the X-ray source 20. For example, to image the ROI 31 within a large three-dimensional object 30, the object 30 can be positioned close to the X-ray source 20 (e.g., at a distance of less than 70 millimeters between the outer surface 27 of the vacuum window 29 and the surface 32 of the object 30) and centered on a rotation axis 19 of at least one sample motion stage 80. A three-dimensional (3D) image dataset of the ROI 31 can be collected by recording a series of X-ray transmission images of 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 while the object 30 rotates about the rotation axis 19 over an angular range (e.g., between 180 degrees and 360 degrees). The computational laminography data set can be reconstructed using known laminography reconstruction methods to obtain a 3D image of the ROI 31. As another example, to image the ROI 31 in a planar object 30 (e.g., solder bumps and / or traces in a semiconductor IC package), the object 30 can be positioned such that the surface 32 of the object 30 closer to the ROI 31 faces the vacuum window 29. For large / planar objects 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 improve imaging throughput. In another example, the surface 32 of the object 30 faces away from the outer surface 27 of the vacuum window 29 (e.g., to reduce or minimize the radiation dose to the ROI 31).

[0014] x-ray source As shown generally in FIG. 2, in certain embodiments, the X-ray source 20 comprises a vacuum chamber 21 including a vacuum region 23 and an electron beam source 22 within the vacuum region 23. The X-ray source 20 further comprises electron optics 25 (e.g., electrodes) configured to direct at least a portion of electrons from the electron beam source 22 into an electron beam 24 focused on at least one X-ray target 28. For example, the electron beam source 22 and the electron optics 25 are configured to generate the focused electron beam 24 and irradiate the focused electron beam 24 on the at least one X-ray target 28 at a selectable maximum focused electron energy at the at least one X-ray target 28 in the range of 10 kVp to 250 kVp. In certain embodiments, the vacuum chamber 21 comprises a vacuum sealed tube that includes the electron beam source 22, the electron optics 25, and the at least one X-ray target 28. In contrast to open tube X-ray sources, the X-ray source 20 of certain embodiments is not actively pumped.

[0015] At least one X-ray target 28 is within the vacuum region 23 and is configured to generate divergent X-rays 60 in response to irradiation by the focused electron beam 24. The at least one X-ray target 28 includes at least one X-ray generating material selected for its X-ray spectrum generating characteristics (e.g., characteristic X-ray energy) and / or other characteristics (e.g., atomic number Z, electron density) that affect the X-ray generating capability of the at least one X-ray generating material. The at least one X-ray generating material can have a sufficiently high thermal conductivity to dissipate heat generated by irradiation by the electron beam 24 at high power. 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. As shown diagrammatically by the inset of FIG. 2, the at least one X-ray target 28 is attached to (e.g., integral with, is a component of, is in contact with) a vacuum window 29, which separates the vacuum region 23 from a non-vacuum region outside the X-ray source 20. The thickness of the at least one X-ray generating material along a direction substantially perpendicular to the outer surface 27 of the vacuum window 29 can be in the range of 0.1 microns to 15 microns (e.g., 0.1 microns to 10 microns), and the thickness of the vacuum window 29 in a direction substantially perpendicular to the outer surface 27 of the vacuum window 29 can be in the range of 0.05 millimeters to 3 millimeters. As described herein, the thickness of the at least one X-ray generating material can be configured to optimize for high spatial resolution (e.g., by minimizing electron beam scattering inside the material) and / or high system throughput (e.g., maximizing electron energy deposition inside the at least one X-ray generating material). For example, the thickness of the at least one X-ray generating material can be less than two times the image resolution along the axis of rotation 19. In certain embodiments, the at least one x-ray generating material has multiple regions that can be irradiated by the electron beam 24 (e.g., by translating the electron beam focus), each region having a corresponding thickness along a direction substantially perpendicular to the outer surface 27 of the vacuum window 29.The electron beam 24 can be directed by electron optics 25 to illuminate a selected area with a corresponding thickness that provides a selected tradeoff between throughput and resolution.

[0016] In certain embodiments, the vacuum window 29 consists essentially of atomic elements having an atomic number (Z) less than 14 and is substantially transparent to the high energy x-rays generated by the at least one x-ray generating material. For example, the vacuum window 29 can have a thermal conductivity high enough to provide a thermal conduit to prevent thermal damage (e.g., melting) of the at least one x-ray generating material (e.g., one or more materials selected from the group consisting of beryllium, diamond, boron carbide, silicon carbide, aluminum, and beryllium oxide (BeO)). The vacuum window 29 can further provide a conductive path sufficient to dissipate charge from the at least one x-ray generating material and / or the vacuum window 29. In certain embodiments, the vacuum window 29 can be substantially transparent to the at least one x-ray having an energy greater than half of the selected maximum focused electron energy. target 2. The vacuum window 29 is configured to have an X-ray transmittance such that greater than 50% of the X-rays generated by the at least one X-ray target 28 are transmitted through the vacuum window 29. In certain embodiments, 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 the X-ray source 20 emits X-rays in a solid angle of 4π, FIG. 2 only shows diagrammatically the divergent X-rays 60 (e.g., X-rays that contribute to image formation) propagating along the X-ray propagation axis 10 within the angular divergence angle 12 to the at least one active element 52 of the at least one position sensitive X-ray detector 50, while other divergent X-rays are generated by the at least one X-ray target 28 and emitted in other directions from the outer surface 27 of the vacuum window 29, not shown in FIG. 2.

[0017] In certain embodiments, the system 5 further comprises a thermal cooling mechanism configured to reduce heating of the object 30 due to heat generated by the X-ray source 20. For example, the thermal cooling mechanism can comprise an infrared (IR) reflective material (e.g., a thin IR-reflective, highly X-ray transparent film or layer, an example of which is aluminized mylar) between the vacuum window 29 and the object 30. The IR reflective material is configured to reflect heat generated by the X-ray source 20 (e.g., due to the power of the electron beam being converted into heat in the at least one X-ray target 28) from reaching the object 30 and the sample mount 85 (e.g., direct thermal energy away from the object 30 and the sample mount 85 to reduce or minimize heat transport to the object 30 and / or the sample mount 85). In this manner, the IR reflective material can protect the object 30 and the sample mount 85 from temperature changes of the sample that could otherwise cause thermal expansion that could adversely affect the accuracy of the ROI selection and / or the 3D volumetric reconstruction fidelity. The IR reflective material is sufficiently thin (eg, less than 1500 microns thick, less than 100 microns thick) so as not to substantially impair positioning of object 30 near the electron beam focal point of x-ray source 20 .

[0018] In certain embodiments, the X-ray source 20 comprises a grounded anode transmission X-ray source (e.g., the vacuum housing is electrically grounded), examples of which include, but are not limited to, the DAGE BrightHawk® X-ray source available from Nordson Corporation of Westlake, Ohio, the L10711-03 microfocus X-ray source available from Hamamatsu Photonics K.K. of Hamamatsu, Japan, the Excillum nanotube N1 and N2 X-ray sources available from Excillum Corporation of Kista, Sweden, X-ray Worx GmbH of Garbsen, Germany, and COMET Technologies of San Jose, Calif. These exemplary X-ray sources 20 have an X-ray source point integrated with the vacuum window 29, and can be configured to position the object 30 close to the X-ray source 20 to reduce (e.g., minimize) FOD and therefore 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 flat surface that terminates in the vacuum envelope and is coplanar with the vacuum window 29, but cannot be made small without interfering with the quality of the electron beam focus. In existing X-ray tomography and laminography imaging techniques that utilize such X-ray sources 20, this large flat surface limits the ability to place a large and / or planar object 30 near the X-ray source 20 and rotate the object 30 (e.g., up to 180 degrees) about a rotation axis 19 that is substantially perpendicular to the large flat surface. Certain implementations described herein advantageously avoid this major drawback of previously existing X-ray imaging systems.

[0019] In certain implementations, the x-ray source 20 is configured to have a small x-ray spot size (e.g., having a dimension of less than 7 microns in at least one lateral direction substantially parallel to the exterior surface 27 of the vacuum window 29) while producing sufficient x-ray flux to facilitate sufficiently short image acquisition times. In general, the x-ray spot size is approximately equal to a convolution of the focused electron beam spot size (e.g., radius) at the at least one x-ray target 28 and the size (e.g., radius) of the x-ray generating volume within the at least one x-ray target 28 due to scattering of electrons within the at least one x-ray target 28. Thus, a larger focused electron beam spot size can facilitate higher electron beam power, concomitant with higher x-ray flux and shorter image acquisition times, at the expense of lower spatial resolution, and a smaller focused electron beam spot size can facilitate higher spatial resolution, at the expense of lower x-ray flux and longer image acquisition times. In addition, because a large portion (e.g., about 99%) of the incident power from the focused electron beam 24 is converted to heat in at least one X-ray target 28, it may be desirable to limit the incident electron beam power, which typically decreases linearly with the X-ray spot size.

[0020] In certain embodiments, higher spatial resolution of the X-ray transmission image in the direction of the plane including the surface normal of the outer surface 27 of the vacuum window 29 and the rotation axis 19 is provided by decreasing the thickness t of the at least one X-ray generating material of the at least one X-ray target 28, thereby decreasing the effective X-ray source size s. For example, the thickness t of the at least one X-ray generating material along a direction substantially perpendicular to the outer surface 27 of the vacuum window 29 can be in the range of 0.1 microns to 15 microns. FIG. 3A illustrates a schematic cross-sectional view of an X-ray spot generated by the electron beam 24 impinging on the at least one X-ray target 28 according to certain embodiments described herein. FIGS. 3B and 3C illustrate schematic top views of exemplary configurations of the electron beam 24 and at least one X-ray target 28 of FIG. 3A according to certain embodiments described herein. As illustrated diagrammatically in FIG. 3A, the X-ray spot size as viewed 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 having a thickness t, the full width at half maximum (FWHM) effective width s of the x-ray spot as viewed along the x-ray propagation axis 10 can be less than about t / 2 (FIG. 3A is not to scale). In certain embodiments, at least one x-ray generating material includes a thin high-Z material layer (e.g., thickness t in the range of 0.1 microns to 3 microns) on or within a low-Z material substrate (e.g., vacuum window 29) to achieve a small x-ray spot size (e.g., less than 5 microns) in the cross-sectional plane of FIG. 3A 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 FWHM effective width s of the x-ray spot size in the cross-section is given by s={(t / 2) 2 +[W sin(θ)] 2} 0.5 where t is the thickness of the high-Z material and W is the FWHM width of the electron beam size in the cross section. For example, for t=1 micron, θ=10 degrees, and W=1 micron, the FWHM effective width s of the x-ray spot size in the cross section plane is 0.53 microns, which is smaller than W. Thus, the effective x-ray source size in the cross section plane along the x-ray propagation axis 10 can be compressed compared to the width of the electron beam 24 in the cross section plane.

[0021] By having an effective x-ray spot size in the cross section that is substantially smaller than the electron beam width W, certain implementations can further achieve a small x-ray spot size in a direction substantially perpendicular to the cross section of Figure 3A. For example, as shown diagrammatically in Figure 3B, the electron beam 24 can be compressed and focused in a direction generally perpendicular to the cross section plane. A focused electron beam 24 having an elongated (e.g., rectangular) shape or footprint on the x-ray target 28 can have a long dimension (e.g., FWHM width W) in the cross section plane of Figure 3A and a short dimension (e.g., FWHM width w) in a direction substantially perpendicular to the cross section plane of Figure 3A (e.g., in a plane that includes the x-ray propagation axis 10 and a surface normal to the outer surface 27 of the vacuum window 29), where the short dimension is smaller than the long dimension.

[0022] In another example, as shown generally in Figure 3C, a width d of the high-Z material of the at least one x-ray generating material in a direction substantially perpendicular to the cross-section of Figure 3A can be less than a FWHM width w of the focused electron beam 24 in a direction substantially perpendicular to the cross-section of Figure 3A. Because the at least one x-ray generating material generates x-rays more efficiently than the vacuum window 29 (e.g., because the efficiency of x-ray production is approximately proportional to the average atomic number of the material), the portion of the electron beam 24 that does not impinge on the at least one x-ray generating material does not generate x-rays efficiently and does not contribute substantially to the x-ray spot size, thereby limiting the x-ray spot size to width d in a direction substantially perpendicular to the cross-section of Figure 3A. In certain embodiments, the width d of the at least one x-ray generating material is in the range of 0.1 microns to 5 microns.

[0023] When viewed along the x-ray propagation axis 10 (e.g., in a direction from the at least one position sensitive x-ray detector 50), and taking into account the take-off angle between the outer surface 27 and the x-ray propagation axis 10, the x-ray spots of Figures 3B and 3C may appear square or circular at the at least one position sensitive x-ray detector 50. For example, at a take-off angle of 10 degrees, an electron beam 24 having a rectangular focus with an aspect ratio of 5:1 may appear substantially symmetric. Because the electron beam 24 is elongated and impinges on a larger area than if the electron beam 24 were narrowly focused in both directions, higher electron power may be used to increase the x-ray flux (e.g., to achieve higher x-ray brightness) and reduce image acquisition time while maintaining spatial resolution. For example, an electron beam 24 having an aspect ratio of 5:1 may provide up to a five-fold increase in apparent power density. Further reduction in the take-off angle in conjunction with a higher aspect ratio focused electron beam may facilitate further improvements in apparent power density. do. Certain embodiments provide higher spatial resolution in the cross-sectional plane of Figure 3A than in a direction orthogonal to the cross-sectional plane. In many applications, high depth resolution (e.g., in a direction substantially perpendicular to the surface 32 of the laterally extending object 30) is more important than lateral resolution (e.g., imaging solder bump delamination or stress-induced cracking of solder bumps parallel to the surface of a semiconductor package). Opening

[0024] Opening 4 illustrates a schematic diagram of another exemplary system 5 including at least one aperture 70 according to certain embodiments described herein. In certain embodiments, the at least one aperture 70 includes at least one orifice 72 (e.g., a slit, having a width of less than 100 microns) in at least one solid material (e.g., a plate), the at least one orifice 72 being disposed between the vacuum window 29 and the object 30 (e.g., downstream of the vacuum window 29 and upstream of the object 30) on the X-ray propagation axis 10. The at least one aperture 70 is configured to not attenuate divergent X-rays 60 (e.g., X-rays used for imaging) propagating along the X-ray propagation axis 10 within the angular divergence angle 12 from reaching the ROI 31 and / or the at least one position-sensitive X-ray detector 50, but to attenuate at least some X-rays and / or scattered X-rays (e.g., X-rays not used for imaging) emitted from the vacuum window 29 in other directions from reaching the ROI 31 and / or the at least one position-sensitive X-ray detector 50. In certain embodiments, the at least one solid material of the at least one aperture 70 has a sufficiently high Z (e.g., W, Au), a sufficiently high electron density, and a substantially thin thickness such that the at least one aperture 70 is configured to attenuate the X-rays without substantially limiting the FOD. In certain embodiments, the at least one aperture 70 is configured to attenuate an amount of external X-ray flux outside of the angular divergence angle 12 emitted by the X-ray source 20 that reaches the object 30. By attenuating this external X-ray flux, the at least one aperture 70 can reduce harmful background contributions in the image from the external X-ray flux and / or reduce harmful X-ray dose to the object 30 from external X-ray flux that does not contribute to imaging. An edge of the at least one orifice 72 of the at least one aperture 70 can define the angular divergence angle 12 by only allowing X-rays within the at least one orifice 72 to propagate further along the X-ray propagation axis 10. In a particular embodiment, the distance between one opening 70 and the vacuum window 29 is configured to achieve a small FOD between the X-ray source point and the ROI 31 (eg, a distance in the range of 0.3 millimeters to 5 millimeters).

[0025] Sample translation stage and sample mount In certain embodiments, the at least one sample translation stage 80 is configured to translate the object 30 relative to the X-ray source 20 and / or the at least one position sensitive X-ray detector 50. In certain embodiments, the at least one sample translation stage 80 comprises at least one linear translation sub-stage 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 rotational translation sub-stage 84 configured to controllably adjust the orientation of the object 30 (e.g., rotate the object 30 about the axis of rotation 19). For example, the at least one linear motion sub-stage 82 may include one, two, or three electromechanical linear motion drivers (e.g., a linear motor, a stepper motor, a motor with an encoder, a piezoelectric motor, a rotary motor with a screw) configured to move the object 30 so that the ROI 31 is at a selected position along the X-ray propagation axis 10, and the at least one rotational motion sub-stage 84 may include at least one electromechanical motion driver (e.g., a rotary motor, a stepper motor, a motor with an encoder, a linear motion driver with a worm drive) configured to rotate the object 30 and ROI 31 around the rotation axis 19.

[0026] In certain embodiments, as shown generally in FIG. 2, a laterally extending object 30 can be mounted on at least one sample translation stage 80, with a surface 32 of the object 30 parallel to a long dimension of the object 30 tilted at an angle β (e.g., in a range of 1°-30°) with respect to the X-ray propagation axis 10. In certain embodiments, the at least one rotational translation substage 84 is further configured to controllably adjust the angle β, and the at least one linear translation substage 82 is further configured to linearly translate the object 30 and / or the at least one rotational translation substage 84 such that the ROI 31 is located on the rotational axis 19 and on the X-ray propagation axis 10. In certain embodiments, the at least one sample translation stage 80 is configured to controllably adjust the distance between the rotational axis 19 and the X-ray spot (e.g., electron beam focal spot).

[0027] In certain embodiments, the sample mount 85 is configured to hold the object 30 while it is illuminated by the X-rays 60 such that the X-rays 60 transmit through the ROI 31 to the at least one position-sensitive X-ray detector 50. The sample mount 85 is configured to minimize the X-rays 60 to interact with (e.g., be minimally scattered and / or absorbed by) solid components of the at least one sample translation stage 80 (e.g., the at least one linear translation sub-stage 82 and the at least one rotational translation sub-stage 84). The sample mount 85 is configured to reduce (e.g., minimize) the portion of the divergent X-rays 60 that interact with solid portions of the at least one sample translation stage 80 as the object 30 rotates about the rotation axis 19.

[0028] In certain embodiments, at least one sample motion stage 80 and sample mount 85 are configured to hold and rotate object 30 without compromising throughput. For example, because throughput in microfocus transmission X-ray computed laminography is inversely proportional to the square of the focal distance (FOD), high throughput can be achieved using a small FOD (e.g., object 30 as close as possible to X-ray source 20).

[0029] 5A and 5B illustrate schematic diagrams of an exemplary system 5 in which at least one sample translation stage 80 and a sample mount 85 are configured to hold and rotate an object 30, according to certain implementations described herein. In the exemplary system 5 of FIG. 5A, the object 30 is between the X-ray source 20 and the at least one sample translation stage 80. With at least one linear translation sub-stage 82 and at least one rotational translation sub-stage 84 on the opposite side of the object 30 from the at least one X-ray source 20, the at least one sample translation stage 80 ensures that the X-rays 60 are aligned with the object 30. 30 5A, after propagating through the ROI 31, the X-rays 60 propagate through at least a portion of the sample mount 85 before reaching the at least one position-sensitive X-ray detector 50. In the exemplary system 5 of FIG. 5B, the X-ray source 20 and the at least one sample motion stage 80 are on the same side of the object 30, and the X-rays 60 propagate through at least a portion of the sample mount 85 before reaching the object 30 (e.g., the sample mount 85 can limit the closest approach of the X-ray source 20 to the object 30). Although FIG. 5A shows an exemplary embodiment in which the X-ray source 20 is above the object 30 and the at least one sample motion stage 80, in other embodiments, the X-ray source 20, the object 30, and the at least one sample motion stage 80 can have any orientation while retaining the same relative positioning to one another. Although FIG. 5B shows an exemplary embodiment in which the X-ray source 20 is below the object 30, in other embodiments, the X-ray source 20, the object 30, and the at least one sample motion stage 80 can have any orientation while retaining the same relative positioning to one another.

[0030] In certain embodiments, the sample mount 85 is configured to offset the object 30 from the at least one sample stage 80 such that the at least one sample stage 80 (e.g., the at least one linear translation sub-stage 82 and the at least one rotational translation sub-stage 84) is not within the imaging field of view of the at least one position sensitive X-ray detector 50 (e.g., to reduce, avoid, or minimize X-ray scattering and / or absorption that adversely affects the fidelity of image reconstruction). For example, the sample mount 85 can offset the object 30 by a distance of more than 50 millimeters (e.g., greater than 100 millimeters, in the range of 100 millimeters to 500 millimeters, in the range of 100 millimeters to 200 millimeters) from the at least one sample stage 80. The sample mount 85 of certain embodiments includes a first portion 86 configured to be impinged by at least a portion of the X-rays 60 when the object 30 and sample mount 85 rotate about the rotation axis 19, and a second portion 87 that mechanically couples the first portion 86 to at least one translation substage (e.g., at least one linear translation substage 82 and / or at least one rotational translation substage 84). The first portion 86 and the second portion 87 are configured to offset the ROI 31 of the object 30 from the at least one translation substage such that the diverging X-rays 60 do not impinge on the at least one translation substage or the second portion 87 (e.g., when the object 30 and sample mount 85 rotate about the rotation axis 19).

[0031] In certain implementations, the first portion 86 consists essentially of low-Z elements (e.g., atomic elements with atomic numbers less than 14) and / or thin materials (e.g., having a thickness along the axis of rotation 19 of less than 10 millimeters). In certain implementations, the first portion 86 has an x-ray transmittance of greater than 50% for x-rays having an energy greater than 50% of the maximum x-ray energy of the x-ray spectrum of the x-rays 60 (e.g., x-rays emitted by the x-ray source 20). Certain such implementations simultaneously provide a sufficiently high throughput with sufficiently low radiation damage to the object 30 (e.g., because the x-rays do not have to penetrate the absorbing material of the at least one sample motion stage 80, the x-ray flux irradiating the object 30 can be kept low enough to avoid radiation damage while providing a sufficiently large amount of detected x-rays for high throughput imaging). For example, the first portion 86 can comprise a carbon fiber or quartz plate (e.g., having a thickness projected along the axis of x-ray propagation 10 of less than 2 millimeters). The second portion 87 is mechanically coupled to the first portion 86 and to the at least one linear translation sub-stage 82 and / or the at least one rotational translation sub-stage 84. In certain embodiments, the second portion 87 is composed of essentially the same low-Z elements and / or thin materials 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 along the x-ray propagation axis 10 of 2 millimeters or less), while in certain other embodiments, the second portion 87 comprises any solid material (e.g., regardless of the x-ray absorption and / or scattering of the solid material). In certain embodiments, the second portion 87 is part of the at least one linear translation sub-stage 82 and / or the at least one rotational translation sub-stage 84.

[0032] For example, as shown diagrammatically by FIG. 5A, the first portion 86 and the second portion 87 may be configured to extend along the rotation axis 19 and to prevent the X-rays 60 from impinging on the at least one linear translation sub-stage 82 and / or the at least one rotational translation sub-stage 84 for all laminography angles of interest and all rotation angles of interest. For at least one sample translation stage 80 having a maximum dimension (e.g., radius) R along a direction substantially perpendicular to the rotation axis 19 from the rotation axis 19, the first and second portions 86, 87 may be configured to hold the object 30 a distance z along the rotation axis 19 from the at least one linear translation sub-stage 82 and / or the at least one rotational translation sub-stage 84 such that the envelope of the X-rays 60 does not impinge on a portion of the at least one sample translation stage 80 that scatters and / or absorbs the X-rays 60 (e.g., a portion including at least one element having an atomic number Z greater than 14, the at least one linear translation sub-stage 82, the at least one rotational translation sub-stage 84).

[0033] In another example, as shown generally in FIG. 5B, the first portion 86 is configured to hold (e.g., clamp) the sides and / or edges of the object 30, and the second portion 87 mechanically couples the first portion 86 to at least one sample translation stage 80 (not shown in FIG. 5B). The at least one sample translation stage 80 of FIG. 5B further comprises a transparent aperture region 88 (e.g., a region at least partially bounded by the second portion 87) configured to have the X-ray source 20 extending at least partially therethrough. Certain such implementations allow the X-ray source 20 to be positioned anywhere near the surface of the object 30, thereby providing high throughput while rigidly mounting the object 30. An exemplary second portion 87 compatible with certain embodiments described herein is a large aperture ultra-precision air-bearing rotary stage available from PI (Physik Instrumente) of Auburn, Massachusetts.

[0034] The fidelity of the image reconstruction depends on the correct rotation of the object 30 during the measurement, and uncontrolled movements of the object 30 can cause deviations of the actually recorded projection data from those expected by the laminographic reconstruction algorithm. As a result, these uncontrolled movements can cause blurring in the backprojection data that reduces the resolution and contrast of the reconstructed volume. In certain embodiments, at least one sample translation stage 80 reduces (e.g., avoids, minimizes) deviations from pure rotation that cause translation and / or orientation changes of the object 30 within the image field of view. At least one sample movement stage 80 may have a sufficiently low non-systematic angular wobble (e.g., uncontrolled angular movement of the rotation axis 19 as a function of rotation about the rotation axis 19), a sufficiently low radial runout (e.g., uncontrolled translation of the rotation axis 19 as a function of rotation about the rotation axis 19 results in lateral movement of the object 30 substantially perpendicular to the rotation axis 19), and / or a sufficiently low axial runout (e.g., uncontrolled axial movement of the object 30 substantially parallel to the rotation axis 19) during rotation of the object 30 about the rotation axis 19 such that uncontrolled movement of the object 30 is less than 1 / 5 of the system resolution (e.g., uncontrolled movement of less than 0.1 micron for a system resolution of 0.5 microns). For example, for an object 30 positioned at a distance L above at least one rotational translation sub-stage 84 of at least one sample translation stage 80 and an image resolution of δ (e.g., detector resolution divided by image magnification), a non-systematic angular wobble in ω (e.g., less than 100 nanoradians, less than 200 nanoradians, less than 1 microradian, less than 5 microradians) may result in a radial runout of R=ωL<δ / 5 (e.g., less than δ / 3, less than δ / 2, less than 1 micron, less than 0.5 micron, 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 micron, less than 0.5 micron, less than 200 nanometers, less than 100 nanometers).In certain embodiments, the at least one sample movement stage 80 has a non-systematic angular wobble (e.g., error) of less than 5 microradians (e.g., less than 1 microradian), a radial runout repeatability of better than 1000 nanometers, and an axial runout repeatability of better than 1000 nanometers. In certain embodiments, the system 5 further comprises a metrology system configured to measure the angular wobble of the at least one sample movement stage 80 with an accuracy of better than 5 microradians (e.g., less than 1 microradian), measure the radial runout of the at least one sample movement stage 80 with an accuracy of better than 1000 nanometers, and / or measure the axial runout of the at least one sample movement stage 80 with an accuracy of better than 1000 nanometers.

[0035] In certain embodiments, at least one rotational translation sub-stage 84 of at least one sample translation stage 80 may include an air-bearing rotation stage (e.g., A-62X or A-688 rotation stages available from PI (Physik Instrumente, Auburn, Mass.); ABRX00, ABRX150, or ABRX250 rotation stages available from Aerotech, Inc. (Pittsburgh, Pa.)) having a wobble 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 object 30 over an angular range of rotation (e.g., 360 degrees) about rotation axis 19 may be accurate to better than half the system resolution.

[0036] Position-sensitive X-ray detector In certain embodiments, the at least one position sensitive X-ray detector 50 is configured to record an image of the X-rays 60 received after passing through the ROI 31 . Examples of at least one position sensitive x-ray detector 50 include photon counting detectors (e.g., including silicon, CdTe, and / or CdZnTe and configured to directly convert x-rays to electrons with or without energy discrimination; Eiger ASIC and Pilatus ASIC available from Dectris, Baden-Daettwil, Switzerland), flat panel detectors (FPDs) including scintillator materials (e.g., CdWO4, CsI, Gd2O2S, LSO, GAGG, and / or LYSO; Sad-o-Box HS detectors available from Teledyne Dalsa, Waterloo, Canada; 2315N detectors available from Varex Imaging, Salt Lake City, Utah; Athena and Onyx detectors available from Nordson Corporation, Westlake, Ohio; Spectrum Logic, Inc., Boulder, Colorado; Examples of suitable position sensitive x-ray detectors include, but are not limited to, a 1412HR detector available from Sigma Corporation, a fiber optic plate and a CMOS or CCD detector, a scintillator material (e.g., CdWO4, CsI, Gd2O2S, LSO, GAGG, and / or LYSO) and an objective lens configured to magnify an image onto the CMOS or CCD detector. In certain embodiments, the 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 a surface of the detector 50) of less than 70 microns (e.g., less than 50 microns).

[0037] In certain implementations, the at least one position-sensitive X-ray detector 50 is configured to receive and image X-rays 60 transmitted through the object 30 including the ROI 31, the X-rays 60 having a predetermined range of energies (e.g., X-ray spectrum) that facilitate (e.g., optimize) sufficient image contrast to identify features of interest within the ROI 31 and / or reduce imaging acquisition time. For example, the predetermined X-ray spectrum can be generated by selecting the focused electron energy of the at least one X-ray target 28 and / or the at least one X-ray generating material such that the generated X-rays 60 within the predetermined X-ray spectrum have a sufficiently large X-ray flux to facilitate image contrast and / or imaging acquisition time. For X-ray imaging using absorption contrast, the predetermined X-ray spectrum can include energies at which the object 30 has an X-ray transmission within a range of 5%-85% (e.g., within a range of 8%-30%). This range of X-ray transmission can provide a beneficial tradeoff between image contrast (favoring lower energy X-rays) and transmission through the object 30 (favoring higher energy X-rays).

[0038] In other examples, the at least one position sensitive X-ray detector 50 can be configured to have at least one energy threshold for detecting X-rays (e.g., the at least one position sensitive X-ray detector 50 can be configured to reject and / or suppress detection of X-rays having energies below a first energy threshold and / or above a second energy threshold). For example, the at least one energy threshold can 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 having energies below the threshold cutoff X-ray energy. The threshold cutoff X-ray energy of certain embodiments corresponds to X-rays for which the object 30 has an X-ray transmission of less than 85% (e.g., less than 50%). For example, the at least one position sensitive X-ray detector 50 can include a photon-counting detector configured to select the 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 comprise a combination of a scintillation screen and a material configured to image only x-rays below a threshold cutoff x-ray energy.

[0039] 6A and 6B show schematic diagrams of two examples of a system 5 in which at least one position sensitive X-ray detector 50 comprises a first position sensitive X-ray detector 54 and a second position sensitive X-ray detector 56, according to certain implementations described herein. The second position sensitive X-ray detector 56 can be configured to provide gain sensitivity to a different portion of the X-ray spectrum than that obtained from the first position sensitive X-ray detector 54, increase overall throughput, and / or provide measurements at a different spatial resolution than that of the first position sensitive X-ray detector 54. For example, the first and second position sensitive X-ray detectors 54, 56 can have different scintillation materials and / or different scintillator thicknesses.

[0040] For example, as shown generally in FIG. 6A, the first detector 54 may be configured to absorb and detect a first spectral portion of the X-rays 60 transmitted through the ROI 31, and the second detector 56 may be configured to absorb and detect a second spectral portion of the X-rays 60 transmitted through the ROI 31 that is not absorbed by the first detector 54. The first detector 54 may be configured (e.g., optimized) for high resolution and may transmit at least a portion of the X-ray flux received from the ROI 31, and the second detector 56 may be positioned behind the first detector 54 (e.g., see FIG. 6A) and may be configured to detect at least a portion of the X-ray flux transmitted through the first detector 56. In another example, as shown diagrammatically in FIG. 6B, a first spectral portion of the X-rays 60 propagating along the X-ray propagation axis 10 can be absorbed by a scintillator screen 55 of a first detector 54, and a second spectral portion of the X-rays 60 propagating along the X-ray propagation axis 10 can be transmitted by the scintillator screen 55 to impinge on a second detector 56. The X-rays absorbed by the scintillator screen 55 can generate scintillation photons (e.g., visible light photons) that are reflected by a mirror 57 and imaged by an objective lens 58 onto a position sensitive photon detector 59. The material and thickness of the mirror 57 can be selected to have a high transmission of the X-rays 60 through the object 30.

[0041] 6A and 6B show a schematic configuration in which the two detectors 54, 56 are arranged to detect X-rays 60 propagating along the same direction as each other, while in certain other implementations, the two detectors 54, 56 are arranged to collect X-rays propagating along different directions from each other (e.g., different directions at an angle of less than 45 degrees to the outer surface 27 of the vacuum window 29) from at least one X-ray source 20. In certain implementations, the two detectors 54, 56 are used simultaneously with each other, while in certain other implementations, the two detectors 54, 56 are used separately from each other (e.g., sequentially). In certain implementations, the two detectors 54, 56 are configured to have different pixel resolutions at the object 30 (e.g., approximately equal to the pixel size of the detector divided by its geometric image magnification). In certain implementations, combining the outputs of the two detectors 54, 56 can increase the overall detection efficiency of the system 5 and can access a wider range of object spatial frequencies, thus improving throughput and reconstruction quality. In certain embodiments, the second detector 56 may be configured (e.g., optimized) to be sensitive to a different portion of the x-ray spectrum of the x-rays 60, allowing for correction for beam hardening and / or material identification.

[0042] FIG. 7 illustrates an exemplary system 5 configured to perform multi-contrast X-ray imaging using Talbot or Talbot-Lau interferometry according to certain embodiments described herein. System 5 can be configured to provide high resolution and sensitivity and unique imaging capabilities (e.g., absorption, phase, and dark-field image contrast, dark-field, enhanced absorption contrast imaging in 2D and 3D) for a wide range of applications. In certain embodiments, system 5 is configured to collect 3D imaging datasets using Talbot-Lau interferometry, dark-field contrast, and enhanced absorption contrast, and reconstruct the datasets to obtain 3D images of object 30 and / or ROI 31 within object 30. In certain embodiments, as illustrated generally in FIG. 7, system 5 further includes at least one sample motion stage 80 and a sample mount 85 (see, e.g., FIG. 5A) configured to reduce (e.g., minimize) interactions between a portion of divergent X-rays 60 propagating along X-ray propagation axis 10 and solid portions of at least one sample motion stage 80.

[0043] As shown diagrammatically in FIG. 7, the system 5 comprises a first grating G1 (e.g., a phase grating) configured to generate a Talbot self-image interference pattern at a first position along the X-ray propagation axis 10, and a second grating G2 (e.g., an analyzer grating) disposed at a second position 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 certain other embodiments, the second grating G2 can be omitted, and the at least one position-sensitive X-ray detector 50 can have an active element 52 having a spatial resolution (e.g., a lateral size substantially 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, and the Talbot pattern is directly imaged by the at least one position-sensitive X-ray detector 50. In certain embodiments, the system 5 further comprises a source grating and is configured to perform Talbot-Lau interferometry. In certain other embodiments, the X-ray source 20 includes a plurality of X-ray targets 28 in a one- or two-dimensional regular array, and the geometric parameters of the plurality of X-ray targets 28, the first grating G1, and the second grating G2 are configured to satisfy the Talbot-Lau interferometer condition. Various configurations of the X-ray source 20 and the first and second gratings G1, G2 are disclosed in U.S. Patent Nos. 9,719,947 and 10,349,908, each of which is incorporated herein by reference in its entirety.

[0044] In certain embodiments, the first grating G1 comprises an absorbing grating. For example, one or both of the first grating G1 and the second grating G2 can include an array of patterned one-dimensional or two-dimensional X-ray substantially absorbing (e.g., more than 50% absorbing) structures having widths in the range of 0.5 microns to 20 microns and spaced apart from each other by substantially non-absorbing (e.g., less than 50% absorbing) gaps having widths in the range of 0.5 microns to 20 microns. In addition to using techniques such as phase stepping for tri-contrast imaging (e.g., absorption, phase, and scattering), the system 5 of certain embodiments can be configured to obtain only dark-field (e.g., scattering) contrast imaging by configuring the pitch, distance from the X-ray source 20, and alignment of the first and second gratings, such that X-rays transmitted through the openings of the first (e.g., upstream) grating G1 are incident on the absorbing portions of the second (e.g., downstream) grating G2. For example, the first grating G1 and the second grating G2 can be positioned along the X-ray propagation axis 10 between the at least one X-ray source 20 and the 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 the at least one position-selective X-ray detector 50) such that the substantially non-absorbing structures of the second grating G2 are aligned with (e.g., in the shadow of) the substantially absorbing structures of the first grating G1 and the substantially absorbing structures of the second grating G2 are aligned with the substantially non-absorbing structures of the first grating G1. In such a configuration, in the absence of the object 30, the X-rays are not expected to penetrate both the first grating G1 and the second grating G2, but in the presence of a scattering mechanism of the object 30, at least a portion of the scattered X-rays will penetrate the second grating G2 and a mechanism in the object 30 corresponding to the scattered X-rays will be imaged. In certain embodiments, an enhanced absorption contrast image can be obtained by displacing the relative alignment of the first and second gratings by half a pitch from the configuration used for dark field imaging, such that X-rays scattered by the object 30 are reduced by the absorbing structure of the second grating G2.In certain embodiments, instead of having a second grating G2, a first set of active elements 52 (e.g., pixels) of at least one position sensitive X-ray detector 50 are aligned with (e.g., in the shadow of) the substantially absorbing structures of the first grating G1, and a second set of active elements 52 of the at least one position sensitive X-ray detector 50 are aligned with the substantially non-absorbing structures of the first grating G1. In such a configuration, when an object 30 is positioned along the X-ray propagation axis 10, X-ray counts recorded by the second set of active elements 52 can be used to generate an absorption contrast image, while X-ray counts recorded by the first set of active elements 52 can be used to generate a scatter / dark field and / or refraction image.

[0045] In certain implementations where a semiconductor IC package is imaged in 3D, the system 5 is configured to acquire X-ray transmission images with an X-ray propagation axis 10 at a small angle (e.g., in the range of less than 45 degrees) relative to the surface normal of the surface 32 of the semiconductor chip. For example, rotational laminography over a large angle range (e.g., 180 degrees to 630 degrees) or limited angle translational laminography over a finite angle range (e.g., ±30 degrees) can be performed. The 3D images can be combined with laminographic 3D images acquired with an X-ray propagation axis 10 at a large angle (e.g., greater than 60 degrees) relative to the surface normal of the surface 32 of the semiconductor chip to generate a 3D image. FIG. 8 illustrates a schematic of an exemplary system 5 adapted for generating translational laminographic images according to certain embodiments described herein. The system 5 includes an additional X-ray detector 90 and at least one detector stage 92 configured to translate the detector 90 and the object 30 relative to the X-ray source 20. In certain implementations, the at least one detector stage 92 comprises at least one sample motion stage 80. For example, the detector 90 and the object 30 can be moved proportionally in the same direction (e.g., along a line from the X-ray source 20 through the ROI 31 to the center of the detector 90). In certain implementations, the system 5 of FIG. 8 is configured to achieve higher spatial resolution and / or better image clarity for features (e.g., sidewalls of copper interconnects) that extend in a direction substantially parallel to the surface normal of the semiconductor chip.

[0046] In certain embodiments, the system 5 further comprises at least one movement mechanism configured to change the geometric magnification of an image of a region of interest of the object generated by the at least one position-sensitive detector. For example, the at least one motion mechanism may include at least one first motion stage (e.g., linear motion stage, electromechanical linear motion drive, linear motor, stepper motor, motor with encoder, piezoelectric motor, rotary motor with screw) configured to move the X-ray source 20 relative to the object 30, at least one second motion stage (e.g., linear motion stage, electromechanical linear motion drive, linear motor, stepper motor, motor with encoder, piezoelectric motor, rotary motor with screw) configured to move the at least one position sensitive detector 50 relative to the object 30, and / or at least one third motion stage (e.g., linear motion stage, electromechanical linear motion drive, linear motor, stepper motor, motor with encoder, piezoelectric motor, rotary motor with screw, at least one linear motion sub-stage 82) configured to move the object 30 relative to the X-ray source 20 and / or the at least one position sensitive detector 50.

[0047] Although commonly used terms are used to describe systems and methods of particular embodiments for ease of understanding, these terms are used herein to have their broadest reasonable interpretation. Various aspects of the present disclosure are described with respect to illustrative examples and embodiments, but the disclosed examples and embodiments should not be construed as limiting. Conditional terms such as "can," "could," "might," or "may," unless otherwise specified or understood otherwise within the context in which they are used, are generally intended to convey that certain embodiments include certain features, elements, and / or steps, while other embodiments do not. Thus, such conditional terms are generally not intended to imply that the features, elements, and / or steps are somehow required for one or more embodiments. In particular, the terms "comprises" and "comprising" should be construed as referring to elements, components, or steps in a non-exclusive manner, indicating that the referenced element, component, or step may be present or utilized or may be combined with other elements, components, or steps not expressly referenced.

[0048] Conjunction terms such as the phrase "at least one of X, Y, and Z" should be understood within the context in which they are generally used to convey that an item, term, etc., can be either X, Y, or Z, unless otherwise indicated. Thus, such conjunctive terms are generally not intended to imply that a particular embodiment requires the presence of at least one of X, at least one of Y, and at least one of Z.

[0049] Terms of degree as used herein, such as the terms "approximately," "about," "generally," and "substantially," refer to values, amounts, or characteristics that are close to the stated value, amount, or characteristic that still performs a desired function or achieves a desired result. For example, the terms "approximately," "about," "generally," and "substantially" may refer to amounts that are within ±10%, ±5%, ±2%, ±1%, or ±0.1% of the stated amount. As another example, the terms "approximately parallel" and "substantially parallel" refer to values, amounts, or characteristics that deviate from exactly parallel by ±10 degrees, ±5 degrees, ±2 degrees, ±1 degree, or ±0.1 degrees, and the terms "approximately perpendicular" and "substantially perpendicular" refer to values, amounts, or characteristics that deviate from exactly perpendicular by ±10 degrees, ±5 degrees, ±2 degrees, ±1 degree, or ±0.1 degrees. Ranges disclosed herein also encompass any and all overlaps, subranges, and combinations thereof. Words such as "up to," "at least," "greater than," "less than," "between," and the like, include the recited numbers. As used herein, the meaning of "a," "an," and "said" includes plural references unless the context clearly dictates otherwise. Although structures and / or methods are described herein with respect to elements labeled with ordinal adjectives (e.g., first, second, etc.), the ordinal adjectives are used merely as labels to distinguish one element from another, and the ordinal adjectives are not used to indicate the order of these elements or their use.

[0050] 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 present invention has been described with reference to these specific configurations, the description is intended to illustrate the present invention and not to limit it. Various modifications and applications will occur to those skilled in the art without departing from the true spirit and scope of the present invention. Thus, for example, in any method or process disclosed herein, the acts or operations constituting the method / process may be performed in any suitable order and are not necessarily limited to any particular disclosed order. Features or elements from the various embodiments and examples described above can be combined with each other to generate alternative configurations that conform to the embodiments disclosed herein. Various aspects and advantages of the embodiments have been described where appropriate. It should be understood that not all such aspects or advantages are necessarily achieved in accordance with any particular embodiment. Thus, for example, it should be recognized that various embodiments may be implemented to achieve or optimize one advantage or group of advantages as taught herein without necessarily achieving other aspects or advantages as may be taught or suggested herein.

Claims

1. 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 comprising at least one active element; an x-ray source comprising an x-ray transmissive vacuum window having an outer surface less than 70 millimeters from the region of interest in the object, the x-ray source having at least one x-ray target configured to generate divergent x-rays from an x-ray spot having a width in a cross section having the electron beam and an x-ray axis of propagation, the x-ray axis of propagation extending from the x-ray spot through the region of interest in the object to the at least one active element of the at least one position sensitive x-ray detector upon impingement of the electron beam; an X-ray source configured as follows: at least a portion of the diverging X-rays exit the vacuum window and propagate along the X-ray propagation axis, the diverging X-rays received by the at least one active element have propagation paths within an angular divergence angle greater than 1 degree about the X-ray propagation axis, the X-ray propagation axis being at a first angle with respect to the outer surface of the vacuum window, the first angle being in a range of 3 degrees to 45 degrees, the X-ray spot having an effective width in the cross section taken along the X-ray propagation axis, the effective width being less than the width; at least one sample translation stage configured to rotate the object about an axis of rotation, the axis of rotation being configured to have a second angle with respect to the axis of x-ray propagation, the second angle being in the range of 45 degrees to 90 degrees; a sample mount on the at least one sample movement stage, the sample mount configured to hold the object, the sample mount comprising a first portion in the propagation path of 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 having an x-ray transmittance of 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; at least one movement mechanism configured to move the at least one position sensitive X-ray detector relative to the object to change a geometric magnification of an image of a region of interest of the object produced by the at least one position sensitive X-ray detector.

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

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

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

5. The system of claim 1 , wherein the first portion is composed of atomic elements having atomic numbers less than 14.

6. 2. The system of claim 1 , wherein the sample mount further comprises a second part that mechanically couples the first part to the at least one sample movement stage, the first part and the second part being configured to offset the region of interest of the object from the at least one sample movement stage such that the divergent x-rays do not impinge on the at least one sample movement stage or the second part.

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

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

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

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

11. The X-ray source includes: a vacuum chamber including a vacuum region, the vacuum chamber including the vacuum window, the vacuum window separating the vacuum region from a non-vacuum region outside the x-ray source and contacting the at least one x-ray target; an electron beam source within the vacuum region; 2. The system of claim 1, further comprising: electron optics configured to direct at least a portion of electrons from the electron beam source into the focused electron beam at the at least one X-ray target, the focused electron beam having a maximum focused electron energy at the at least one X-ray target in a range of 10 kVp to 250 kVp, the at least one X-ray target configured to produce the diverging x-rays in response to illumination by the focused electron beam.

12. The at least one X-ray target is selected from the group consisting of Cr, Fe, Co, Ni, Cu, W, Rh, Mo, Au, Pt, Ag, and SrB. ６ , LaB ６ , GdB ６ , and CeB ６ 12. The system of claim 11, comprising at least one x-ray generating material selected from the group consisting of:

13. 13. The system of claim 12, wherein the at least one x-ray generating material has multiple regions that can be irradiated by the focused electron beam, each region having a corresponding thickness along a direction perpendicular to the exterior surface of the vacuum window to provide different tradeoffs between throughput and resolution.

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

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

16. 12. The system of claim 11, wherein the focused electron beam has a spot size measuring less than 7 microns in at least one lateral direction parallel to the exterior surface of the vacuum window.

17. 12. 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 X-ray propagation axis and a surface normal to the outer surface of the vacuum window and a second dimension in a direction perpendicular to the plane, 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 to electrons.

19. 2. 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, and the at least one position sensitive X-ray detector is configured to reject and / or suppress detection of X-rays having energies below a first energy threshold and / or above a second energy threshold.

20. The at least one position sensitive X-ray detector is a CdWO ４ , CsI, Gd ２ O ２ 10. The system of claim 1 , comprising a scintillator material selected from the group consisting of S, LSO, GAGG, and LYSO.

21. 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 configured to magnify an image from the scintillator material onto the CMOS or CCD detector.

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

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

24. 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. 24. The system of claim 23, wherein the first grating and the at least one position sensitive x-ray detector are configured to record a dark field contrast image.

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

27. 27. The system of claim 26, wherein the thermal cooling mechanism comprises an infrared (IR) reflective material between the vacuum window and the object, the IR reflective material having a thickness less than 1500 microns and configured to reflect heat generated by the x-ray source away from the object and the sample mount.

28. 2. The system of claim 1, further comprising at least one opening with at least one orifice in at least one solid material, the at least one orifice being disposed on the X-ray propagation axis between the vacuum window and the object, the at least one opening being configured to not attenuate the divergent X-rays propagating along the X-ray propagation axis within the angular divergence angle from reaching the region of interest and / or the at least one position sensitive X-ray detector, while attenuating at least a portion of the X-rays and / or scattered X-rays emitted in other directions from the vacuum window from reaching 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 movement stage comprises an air-bearing rotary stage.

30. The system of claim 1, wherein the at least one moving mechanism includes at least one detector moving stage configured to move the at least one position-sensitive X-ray detector relative to the object.

31. 1. A three-dimensional x-ray imaging system, comprising: at least one position sensitive x-ray detector; an x-ray source configured to generate divergent x-rays comprising an x-ray transmissive vacuum window having an outer surface, the x-ray source configured to generate divergent x-rays, the outer surface of the vacuum window being less than 70 millimeters from a region of interest of an object, at least a portion of the divergent x-rays exiting 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 x-ray detector having an angular divergence angle greater than 1 degree about the x-ray propagation axis, the x-ray propagation axis being at a first angle with respect to the outer surface of the vacuum window, the first angle being in a range of 3 degrees to 45 degrees; at least one sample translation stage configured to rotate the object about an axis of rotation and configured to adjust the axis of rotation to have a second angle with respect to the axis of x-ray propagation, the at least one sample translation stage having a non-systematic angular wobble of less than 5 microradians; an infrared (IR) reflective material between the vacuum window and the object, the IR reflective material having a thickness less than 1500 microns and configured to reflect heat generated by the x-ray source from reaching the object.

32. 32. The system of claim 31 , further comprising a sample mount configured to hold the object on the at least one sample motion stage, the sample mount comprising a first portion configured to be impinged by at least a portion 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 along the axis of rotation less than 10 millimeters.

33. The system of claim 31 , wherein the at least one sample movement stage comprises an air-bearing rotary stage.

34. The system of claim 1 , further comprising at least one movement mechanism for varying a geometric magnification of an image of the region of interest of the object produced by the at least one position sensitive detector.

35. 35. The system of claim 34, wherein the at least one movement mechanism is configured to move the X-ray source and / or the at least one position sensitive detector relative to the object.

36. The width has a full width at half maximum (FWHM) W in the cross section, the X-ray target has a thickness t along a direction perpendicular to the outer surface of the vacuum window, and the effective width has a FWHM effective width s in the cross section, the FWHM effective width s being defined as s={(t / 2) ２ +[W・sin(θ)] ２ } ０．５ 5. The system of claim 1 , wherein θ is the first angle.

37. The system of claim 1 , wherein the effective width is less than 5 microns.

38. The system of claim 1 , wherein the effective width is less than 1 micron.

39. The system of claim 1 , wherein the effective width is less than 0.5 microns.

40. The system described in claim 1, wherein the rotation axis is at a third non-zero angle less than 30 degrees relative to a surface normal of the outer surface of the vacuum window.

41. The system of claim 1, further comprising at least one tilt stage configured to tilt the X-ray source relative to the axis of rotation and / or tilt the axis of rotation relative to the X-ray source.

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