X-RAY INSPECTION SYSTEM FOR INSPECTION OF AN OBJECT

Abstract

An X-ray inspection system serves for inspection of an object. An X-ray source of the system generates X-rays to propagate through a region of interest of the object. An object mount holds the object to be inspected such that the ROI is accessible for the generated X-rays. A detection system detects the X-rays after propagation through the ROI. The X-ray source generates a plurality of separate X-ray light bundles to propagate through the ROI. Chief rays of at least two of the generated separate X-ray light bundles impinge on the ROI of the object with different chief ray illumination angles. The detection system comprises separate detection areas to detect the separate X-ray light bundles, respectively. Such an inspection system can exhibit relatively fast image data acquisition.

Description

TECHNICAL FIELD

The disclosure refers to an X-ray inspection system for inspection of an object.

BACKGROUND

3D imaging of a sample structure by acquiring a set of 2D images of differently oriented sample planes is known with respect to 3D X-ray imaging. In that respect, it is referred to Kasperl S., Hiller J., Krumm M., Computed tomography metrology in industrial research and development, Materials Testing, Jun. 1, 2009; 51(6):405-11 and to Körner, L., Lawes, S., Senin, N., Leach, R., Simulation of continuous high aspect ratio tomography for surface topography measurements, paper shown in DXCT 2019, Huddersfield. Further, respective projection systems and acquisition methods are known from Welkenhuyzen, F., Kiekens, K., Pierlet, M., Dewulf, W., Bleys, P. & Kruth, J.-P. and Voet, A., Industrial computer tomography for dimensional metrology: Overview of influence factors and improvement strategies, OPTIMESS 2009 or from Hsieh J., Computed tomography principles, design, artifacts, and recent advances, SPIE press, 2003. WO 2008/002132 A1 discloses a method and an apparatus for imaging. Further imaging optical arrangements to image an object illuminated by X-rays are known from U.S. Pat. No. 7,057,187 B1, from U.S. Pat. No. 7,130,375 B1 and from U.S. Pat. No. 9,129,715 B2. Further, from DE 2018 209 570 A1 a method and a device to produce a three-dimensional image is known. US 2022/0178851 A1 discloses a high throughput 3D X-ray laminography imaging system using a transmission X-ray source. US 2011/0249795 A1 discloses an X-ray inspection method and an X-ray inspection apparatus. US 2015/110252 A1 discloses X-ray sources using linear accumulation. US 2022/0328277 A1 discloses a method and a device for producing and using multiple origins of X-radiation. US 2004/0240616 A1 discloses devices and methods for producing multiple X-ray beams from multiple locations.

SUMMARY

The present disclosure seeks to allow for object inspection which, compared to certain 3D X-ray imaging devices, results in faster image data acquisition.

In an aspect, the disclosure provides an X-ray inspection system for inspection of an object. The inspection system comprises: an X-ray source for generating X-rays to propagate through a region of interest of the object; an object mount to hold the object to be inspected such that the ROI is accessible for the generated X-rays; and a detection system to detect the X-rays after propagation through the ROI. The X-ray source generates a plurality of separate X-ray light bundles to propagate through the ROI. Chief rays of at least two of the generated separate X-ray light bundles impinge on the ROI of the object with different chief ray illumination angles. The detection system comprises separate detection areas to detect the separate X-ray light bundles, respectively. The X-ray inspection system is configured such that the ROI of the object to be inspected is illuminated simultaneously with X-ray light bundles impinging on the ROI with different chief illumination angles.

According to the disclosure, a region of interest of the object to be inspected is illuminated simultaneously with X-ray light bundles impinging on the ROI with different chief illumination angles. As a result, with one and the same relative orientation and arrangement of the X-ray source to the object, a respective plurality of differently oriented sample planes may be imaged leading in effect to the possibility of a “one shot” 3D X-ray imaging of the object. The simultaneous illumination with X-ray bundles impinging on the ROI with different chief ray illumination angles can lead to a substantial increase in X-ray throughput.

A chief ray of a respective X-ray light bundle is a central ray within the X-ray light bundle. Such a central ray, i.e., the chief ray, may impinge centrally on the respective detection area. The chief ray may impinge perpendicularly on the respective detection area.

The number of differently generated X-ray light bundles may be in a range between 2 and 20, such as between 2 and 10. For example, the X-ray source may generate 2, 3, 4, 5 or more separate X-ray light bundles impinging on the ROI of the object with different chief illumination angles. In general, the number of generated separate X-ray light bundles impinging on the ROI of the object with different chief illumination angles may be smaller than 50.

Objects to be inspected may have several layers of interconnects and may include absorbing structures such as redistribution layers (RDLs) or metal pads.

Objects to be inspected may be multi-chip modules. For example, whole wafers or printed circuit boards, i.e., objects having lateral dimensions of more than 100 mm and for example up to 300 or 500 mm may be inspected.

The X-ray inspection system may be an X-ray laminography inspection system. The object mount of such an X-ray inspection system may be configured corresponding to a sample motion stage disclosed in US 2022/0178851 A1. The object mount may include a rotary stage to rotate the object around an axis which is perpendicular to an object surface.

Alternatively or in addition, the object mount may be configured to pivot or rotate the object around another pivot or rotation axis.

Via the simultaneous illumination with X-ray light bundles impinging on the ROI with different chief ray illumination angles, simultaneously different perspectives of one and the same ROI may be recorded during operation of the X-ray inspection system. In case the X-ray inspection system is an X-ray laminography imaging system, instead of a full 360° rotation of the object to obtain full inspection information, a half rotation (180°) of the object may be sufficient. Merging the information obtained from two opposing chief ray illumination angles may then deliver the full 360° image and may deliver a full 3D image of the object. If more than two X-ray light bundles are used, for example, if n X-ray light bundles are used, the rotation angle can be reduced to 360°/n. The X-ray source can comprise a plurality of separate electron beam sources with an attributed converting element to convert the generated electron beams at separate X-ray source regions into X-rays. Such an X-ray source having separate electron beam sources can lead to a high flexibility of the X-ray source. Each of the separate electron beams may be controlled independently. Each of the electron beam sources may have an own attributed electron beam acceleration unit.

The converting element may be a tungsten element.

The X-ray source can comprise: a single electron beam source to generate a main electron beam; an electron beam splitting unit to split the main electron beam into a plurality of separate partial electron beams; and an attributed converting element to convert the generated partial electron beams at separate X-ray source regions into X-rays. Such an X-ray source only needs a single electron beam source diminishing in that respect a complexity of the X-ray source. Each split partial electron beam may be equipped with its own acceleration unit. Alternatively, a common acceleration unit may be provided for all split partial electron beams.

The X-ray source can comprise: a single electron beam source to generate a main electron beam; an acceleration unit to accelerate and to split the main electron beam into a plurality of separate partial electron beams; and an attributed converting element to convert the generated partial electron beams at separate X-ray source regions into X-rays. With such an X-ray source, the initially generated main electron beam is accelerated by an acceleration unit. In such embodiments, different acceleration units provided for the split partial electron beams may be omitted. Alternatively, each split partial electron beam may have its own acceleration unit.

The X-ray source regions can be arranged in a source plane of the inspection system. Such an arrangement of the X-ray source regions can facilitate a subsequent guiding of the respectively generated X-ray light bundles to propagate through a region of interest.

Several X-ray source regions can be arranged on at least one circle in the source plane. Such an arrangement may be beneficial with respect to desired space properties of the X-ray source components. A center of such arrangement circles may define an illumination angle “0°”. The X-ray source regions may be arranged on several circles having different circle radii.

Several X-ray source regions can be arranged on several circles in the source plane with different radii, and the X-ray source regions on different circles can be arranged at the same polar angles on the respective circle. Such an arrangement has been proven to be of specific usability. Alternatively or in addition, at least some or all of the X-ray source regions may be arranged at different azimuthal angles on the respective circles.

The X-ray inspection system can comprise an electron beam optics in an electron beam path of the electron beams upwards the X-ray source regions to focus and/or to steer a direction of the separate paths of the respective electron beams. Such an electron beam optics can increase the flexibility of a usability of the X-ray source. Different and for example controllable chief illumination angles via which the separate X-ray light bundles impinge on the ROI of the object may be provided.

The X-ray inspection system can comprise an aperture device arranged in a beam path between the X-ray source region and the region of interest. Such an aperture device can avoid undesired crosstalk between the respective beam paths.

The detection system can comprise a plurality of detection devices, and each of the detection devices can be attributed to a separate X-ray light bundle. Such a plurality of detection devices can improve the flexibility of the X-ray detection of the inspection system.

This, for example, holds true when each of the detection devices comprises a sensor array. A sensor array may be a CCD or a CMOS array.

The detection system may include a post-magnification unit. For example, an optical system may be used to image a magnified image via visible photons which are emitted from a scintillator on which the X-rays impinge after propagation through the ROI. Possible embodiments for such a post-magnification detection are known from U.S. Pat. No. 9,129,715 B2.

Chief ray illumination angles of the respective X-ray light bundles on the one hand and distances between the respective X-ray source regions and the detectors respectively attributed to these light bundles on the other may be chosen such that a geometrical magnification at all detectors of the detection system, for example at all separate detection areas to detect the respective X-ray light bundle, is the same. For example, in case all X-ray light bundles are emitted from sources which are arranged in a plane parallel to an object plane, all detection areas or detectors attributed to the respective X-ray light bundles emitted from the X-ray sources also may be arranged in a plane parallel to the object plane. For example, all detection areas, and optionally all detectors, may be arranged in exactly one plane.

In addition to chief rays of at least two of the generated separate X-ray light bundles which impinge on the ROI of the object with different polar chief ray illumination angles, chief rays of at least two of the generated separate X-ray light bundles may impinge on the ROI of the object with different azimuthal chief ray illumination angles.

As long as the separate X-ray light bundles impinge on the ROI of the object with equal polar chief ray illumination angles, the distance between a respective X-ray source region and an attributed detector may also be equal.

The separate detection areas or the separate detectors may be tilted such that the respectively attributed X-ray light bundle impinges on the detection area or detector with normal incidence. Alternatively, an incidence angle between a chief ray of the respective X-ray light bundle and the attributed detection area or detector may deviate from 0°. Such angle of incidence may be in a range between 0° and 60°, for example in a range between 0° and 45° or in a range between 0° and 30°. The incidence angle may be in a range between 0° and 7°.

It is possible to image object structures which are smaller than 20 μm, smaller than 10 μm and for example which are smaller than 1 μm. Examples for such structures are Cu—Cu hybrid bonding structures between microchips and substrate conductor paths. For example, direct bonds between single dies or between a whole wafer onto a substrate wafer can be inspected.

A 3D tomographic reconstruction of an object sample under investigation by combining several 2D images taken from different directions is possible.

X-ray energies of the used X-rays can range between 5 keV and 160 keV, such as between 15 keV and 90 keV.

With the inspection system, for example, complex 3D IC semiconductor packages may be inspected.

BRIEF DESCRIPTION OF DRAWINGS

Exemplified embodiments of the disclosure hereinafter are described with reference to the accompanying drawings, in which:

FIG. 1 illustrates a schematic working principle of an X-ray inspection system for inspection of an object, embodied as a projection system for acquiring 3D tomographic images of semiconductor structure samples via acquiring a set of 2D images of differently oriented sample planes with a respective acquisition method;

FIG. 2 illustrates, in a sectional view according to the xy-plane in FIG. 1, an embodiment of the X-ray inspection system having an X-ray source being including a multi e-beam column, wherein the X-ray source comprises five X-ray source spots to generate five separate X-ray light bundles to impinge on a region of interest (ROI) of the object;

FIG. 3 illustrates, in a yz-view, an example of a distribution of source spots of another embodiment of an X-ray source of the X-ray inspection system according to FIG. 2;

FIG. 4 illustrates, in a view similar to FIG. 3, another possible distribution of source spots of a respective embodiment of the X-ray source;

FIG. 5 illustrates, in a view similar to FIG. 3, another possible distribution of source spots of a respective embodiment of the X-ray source;

FIG. 6 illustrates, in a view similar to FIG. 3, another possible distribution of source spots of a respective embodiment of the X-ray source;

FIG. 7 illustrates an embodiment of the X-ray source of the X-ray inspection system having a single e-beam emitter and having several separate e-beam acceleration units to generate separate X-ray light bundles to propagate through the ROI of the object in a side view;

FIG. 8 illustrates, in a view similar to FIG. 7, another embodiment of an X-ray source having a single emitter multi e-beam source to generate a plurality of separate X-ray light bundles;

FIG. 9 illustrates the embodiment of FIG. 8 with another position of a multi aperture lenslet array to alter a location of e-beam foci of different e-beams generated by the source;

FIG. 10 illustrates, in a view similar to FIGS. 7 to 9, another embodiment of an X-ray source generating a plurality of separate X-ray light bundles, the X-ray source having an array of multiple, separate single e-beam sources; and

FIG. 11 illustrates, in a view similar to FIG. 10, another X-ray source having an array of multiple, separate single beam sources with another beam optics to alter a location of beam foci of the generated electron beams.

DETAILED DESCRIPTION

FIG. 1 shows schematically certain components of an X-ray inspection system configured as a projection system 1 for acquiring tomographic images of a sample or object 2 by acquiring a set of two-dimensional (2D) images of differently oriented sample planes.

The sample 2 in the shown embodiment is a semiconductor structure.

The projection system 1 comprises a projection light source 3. The projection light source 3 is as an X-ray source.

The sample 2 is held by a sample structure holder 4 which can be rotatable around at least one sample rotating axis 5. According to the disclosure described here, differently oriented sample planes, which are used for 3D image acquisition, are produced different to a sample rotation as explained with respect to FIG. 2 et seq below.

To facilitate the description of the structures and their orientation, in the following a Cartesian xyz coordinate system is used. In FIG. 1, the x-axis runs to the right. The y-axis runs perpendicular to the drawing plane of FIG. 1 away from the viewer. The z-axis runs upwards in FIG. 1.

The sample rotating axis 5 runs parallel to the z-axis.

The sample structure holder 4 holds the sample 2 in a light path 6 of the projection light generated by the projection light source 3.

In the light path 6 after the sample 2 a spatially resolving detector 7 is arranged which can be a CCD or a CMOS detector. The detector 7 may include an optical post-magnification. A respective detector with optical post-magnification is known from U.S. Pat. No. 9,129,715 B2.

A detection plane of the detector 7 is parallel to the yz-plane. The rotation axis 5 of the sample holder 4 runs parallel to the detection plane. The sample structure holder 4 also is referred to as an object mount.

Between the sample 2 and the detector 7 and in the vicinity of the detector 7, a scintillator layer 8 is arranged in the light path 6. The scintillator layer 8 serves to convert a wavelength of the projection light into a wavelength detectable by the detector 7, for example into a UV and/or visible wavelength.

The detector 7 together with the scintillator layer and possible further detection components is referred to herein after also as a detection system 7a.

FIG. 2 shows an embodiment of an X-ray source 9 to generate a plurality of separate X-ray light bundles 9₁ to 9₅ to propagate through a region of interest (ROI) 10 of the object 2.

The X-ray source 9 comprises a multi electron-beam (e-beam) column 11 having a plurality of separate electron beam sources 12₁ to 12₅ to generate respectively separate electron beams 13₁ to 13₅. Further, the X-ray light source 9 includes a converting element attributed to the separate electron beam sources 13_i to convert the generated electron beams 13_i to separate X-source spots or regions 14₁ to 14₅. The converting element may be a respective tungsten layer on an X-ray source body located at the respective X-ray source region 14_i. The tungsten layer may include tungsten regions being embedded in a diamond substrate layer. Such a diamond substrate layer can provide an excellent heat conduction to dissipate a thermal load induced by the electron beams 13_i. The converting element may be a continuous plate carrying respective tungsten layers at least at the position of the X-ray source regions 14_i.

The X-ray light bundles 9; separately generated in the X-ray source regions 14_i are defined with respect to their outer beam boundaries to propagate from the respective X-ray source region 14_i through the region of interest 10 of the object 2. Such propagation definition is given by an aperture device 15 arranged in the beam path of the respective X-ray light bundle 9; between the X-ray source regions 14; and the object 2. The aperture device 15 is an aperture blade having aperture through-holes 15₁ to 15₅ for the passage of the respective X-ray light bundle 9₁ to 9₅.

The detection system 7a of the FIG. 2 embodiment of the X-ray inspection system 1 comprises a plurality of spatially resolving detectors 7₁ to 7₅. Each of those detectors 7_i may be described above with respect to FIG. 1. The respective detection device 7_i defines a detection area to detect the respective X-ray light bundle 9_i. The detectors 7_i may be optically coupled detectors. A conversion of the X-ray wavelength to optical wavelengths may take place.

The detectors 7₁ to 7₅ are located in the beam path of the respective X-ray light bundles 9₁ to 9₅ after their passage through the ROI 10 of the object 2.

Chief rays 16₁ to 16₅ of the separate X-ray light bundles 9₁ to 9₅ impinge on the ROI 10 of the object 2 with different chief ray illumination angles CRA_i. For example, these chief rays 16₁ to 16₅ exhibit different polar chief ray illumination angles CRA_i with respect to an object plane. The chief ray illumination angles CRA₁ and CRA₅ each are approximately 15°. An angle difference between chief ray angles CRA_i and CRA_i+1 is, for i=1 to 4, 37.5° each.

As an alternative to such equispaced arrangements of the chief ray angles CRA_i, also a non-equispaced arrangement is possible. Chief ray angles CRA_i on the one hand, and distances between the respective X-ray source region 14; and the attributed detector 7_i on the other may be in an alternative arrangement chosen such that a geometrical magnification at all detectors 7_i is the same. Such a geometrical magnification can be determined by a projected width of the ROI 10 as seen by the X-ray light bundle 9; having a respective polar chief ray illumination angle CRA_i. Such a projected width, for example, is largest for detector 7₃ (CRA₃=) 90° involving allowance of an equalized geometrical magnification a relatively small distance between the detector 7₃ and the X-ray source region 14₃, and is smallest seen from detectors 7₁ and 7₅ (CRA₁=CRA₅=15°) involving a distance between the X-ray source regions 14₁, 14₅, and the detectors 7₁, 7₅ which is, as compared to the detector 7₃ distance, larger. In other words, to cover a comparable surface area on the detectors 7_i being the result of a respective impingement of the ROI 10 via the X-ray light bundles 9_i having different chief ray illumination angles CRA_i, those detectors 7; assigned to X-ray light bundles 9; with small chief ray angles CRA_i have a larger distance to the ROI 10 and also to the respective X-ray source region 14_i as compared to X-ray light bundles 9_i having a larger chief ray illumination angle CRA_i. The more tilted the ROI 10 is seen by the respective X-ray light bundle 9_i, the more distant the assigned detector 7_i should be arranged to achieve the same geometrical magnification of the ROI 10.

The chief ray 16₃ impinges on the region of interest 10 of the object 2 with normal incidence to the object plane 17 which runs parallel to the yz-plane.

The five different columns of the multi e-beam column (i=1 to 5) 11 each have an electron acceleration unit not shown in detail in FIG. 2.

The acceleration unit may be a common electron acceleration unit for all of such columns of the multi e-beam column 11. Alternatively, each column (i=1 to 5) may have its own electron acceleration unit within the multi e-beam column 11.

In the FIG. 2 embodiment, the X-ray source regions 14_i are arranged in an arrangement plane 18 which runs parallel to object plane 17. For example, the X-ray source regions 14_i may be arranged along a line within such arrangement plane 18. The line may be parallel to the y-direction.

The arrangement plane 18 also is referred to as source plane and defines a source plane of the respective X-ray source of the X-ray inspection system embodiment.

The detectors 7_i may be arranged in the vertical plane according to FIG. 2 in a half circle.

In a different configuration from what is shown in FIG. 2, all detectors 7_i may be arranged in exactly one plane. Such an arrangement plane may be parallel to the object plane 17.

FIG. 3 shows another possible arrangement of X-ray source regions 14_i in the arrangement plane 18. Shown are two X-ray source regions 14₁, 14₂ which both are arranged on an inner arrangement circle 19, such inner arrangement circle 19 being defined by a center Z. These two X-ray source regions 14₁, 14₂ define a same polar chief ray angle, but define different azimuthal chief ray angles with respect to the object plane 17. A y-distance between the X-ray source regions 14₁, 14₂ in the FIG. 3 embodiment may be equal to the y-separation between the X-ray source regions 14₂ and 14₄ in the FIG. 2 embodiment. Further, on an outer arrangement circle 20 defining another polar chief ray angle, further X-ray source regions 14₃, . . . may be arranged, for example along a line 21 parallel to the y-direction defined by the two X-ray source regions 14₁, 14₂ or as indicated with dashed circles on such outer arrangement circle 20, at different circle positions (different azimuthal angles) not coinciding with such line 21. Distances between X-ray source regions 14_i exhibiting the same polar chief ray angle may be attributed to detectors 7_i having the same distance to such X-ray source region 14_i.

The arrangement of n source spots on a single circle helps to increase the throughput by a factor of n, since instead of a full rotation (360°) of the sample only the fraction 360°/n is used to reach the same number of projections. If several source spots are arranged on a single circle, those detection areas or detectors being assigned to the respective source spot also can be arranged on a single circle. If source spots are arranged on different circles, this can help to increase image quality, since different polar angles can be used for the reconstruction. During a scan, both the radii of the source spots 14_i as well as the positions of the detector 7_i might be changed in order to cover a broader angular spectrum.

FIG. 4 shows in a view similar to FIG. 3 an arrangement of three X-ray source regions 14₁, 14₂, 14₃ which, in this case, are equidistantly arranged on the inner arrangement circle 19. With respect to a vertical xy-plane 2, these three X-ray source regions 14₁ to 14₃ in FIG. 4 all are arranged out of plane. This contrasts to the FIG. 3 arrangement, where the X-ray source regions 14₁, 14₂ are arranged in plane. An arrangement of the source spots 14; may follow from a desire to evenly distribute n spots on a respective circle. Dependent on the respective embodiment, an absolute orientation within a coordinate system may not be relevant.

Another arrangement embodiment of the X-ray source regions 14_i is shown in FIG. 5, here in the exemplified case of four X-ray source regions 14₁ to 14₄. Here, all of the X-ray source regions 14₁ to 14₄ are arranged equidistantly on the inner arrangement circle 19.

FIG. 6 shows a further embodiment with another variant of an arrangement of X-ray source regions 14_i. In the FIG. 6 embodiment, nine X-ray source regions 14₁ to 14₉ are depicted with solid lines. A first X-ray source region 14₁ is located in a center of the concentric inner and outer arrangement circles 19, 20. Such central X-ray source region 14₁ has the same coordinates in y- and in z-direction as a center of the region of interest 10. This central X-ray source region 14₁ also may be omitted. Four further X-ray source regions 14₂ to 14₅ are arranged similar to the X-ray source region arrangement of FIG. 5 equidistantly on the inner arrangement circle 19.

Four further X-ray source regions 14₆ to 14₉ also are arranged equidistantly, but now on a first outer arrangement circle 20. X-ray source regions 14₆, 14₂, 14₁, 14₄, 14₈ are arranged in line on a line parallel to the z-axis. X-ray source regions 14₉, 14₅, 14₁, 14₃ and 14₇ are arranged in line on a line parallel to the y-axis. Such in-line y-arrangement is similar to that shown in FIG. 2.

In addition, further X-ray source regions 14₁₀, . . . may be arranged on a further outer arrangement circle 23 which also is concentric to the arrangement circles 19 and 20 and has the largest radius. Such further X-ray source regions 14; are shown with broken lines in FIG. 6. These further X-ray source regions may be also positioned in an in-line configuration (same azimuthal angles, different polar angles) as exemplified by X-ray source regions 14₁₀, 14₁₂, and 14₁₃, but also may be arranged off-line (different azimuthal angles, same or different polar angles), as shown with X-ray source region and 14₁₁. For example, such further X-ray source regions 14₁₀, . . . could be all arranged in an in-line configuration.

The X-ray source regions 14₂ to 14₅ on the one hand and 14₆ to 14₉ on the other are arranged at the same polar angles, respectively, on the respective arrangement circles 19 and 20.

X-ray source region 14_i arrangements of various further kinds also are conceivable. With such further configurations, all X-ray source regions 14_i may be located on an own circle, i.e. no pair of X-ray source regions 14_i, 14_j is located on the same arrangement circle.

FIG. 7 shows a further embodiment of an X-ray source 24 which may be used in the X-ray inspection system 1 instead of the X-ray source 9. Components and functions which already were discussed with respect to FIGS. 1 to 6 above show the same reference numerals and are not discussed in detail again. Further, an embodiment of an X-ray source is possible, wherein such X-ray source consists of n electron beam emitters and each beam gets split into m beamlets thus yielding a total of n×m beamlets.

The X-ray source 24 has a single electron beam source 25 to generate a main electron beam 26 and a subsequent electron beam splitting unit 27 to split the main electron beam 26 into a plurality of separate partial electron beams 13₁, 13₂, 13₃. Subsequently to the electron beam splitting unit 27, the separate partial electron beams 13_i are accelerated via respective acceleration units 28₁, 28₂, and 28₃. Subsequently, the accelerated electron beams 13; are further conditioned regarding their direction towards the arrangement plane 18 and regarding their focal position with a focusing and beam steering unit 29. Such unit 29 in FIG. 7 is depicted as a single unit and is schematically shown as a single lens. Alternatively, each of the accelerated partial electron beams 13_i may have its own, separate focusing and beam steering unit 29_i. Further, the beam steering unit 29 may include several separate sub-units arranged along a respective beam path of the electron beams 13_i.

With the focusing and beam steering unit 29, positions of the respective X-ray source regions 14; at the arrangement plane 18 can be adjusted and controlled. Using a respective number of separate electron beams 13_i split via a respective embodiment of the electron beam splitting unit 27, a corresponding number of X-ray source regions 14; can be generated, for example in one of the source region arrangements discussed above with respect to FIGS. 2 to 6.

At the arrangement plane 18, the electrons of the electron beams 13; again are converted to X-rays using a respectively attributed converting element, for example made of tungsten.

FIG. 8 shows a further embodiment of an X-ray source 30 which may be used in the X-ray inspection system 1 instead of the X-ray source 24. Components and functions which already were discussed with respect to FIGS. 1 to 7 above show the same reference numerals and are not discussed in detail again.

In the X-ray source 30, functions of an electron beam splitting unit 27 and of an acceleration unit 28 are combined within a single emitter multi beam source 31. Such single emitter multi beam source 31 comprises the single electron beam source 25 and further comprises a multi aperture lenslet array 32 which serves to accelerate the electrons generated by the electron source 25 and which further has a plurality of aperture openings 33₁ to 33₅ for the passage of in this way generated separate partial electron beams 13_i.

The multi aperture lenslet array 32 serves for example as an acceleration unit to accelerate and to split the main electron beam 26 into the separate partial electron beams 13₁ to 13₅.

The multi aperture lenslet array 32 may be part of an electron beam optics to focus and/or to steer directions of separate paths of the respective electron beams 13_i.

A macro lens 34 and a further multi aperture lenslet array 35 in a subsequent beam path of the separate partial electron beams 13_i serve to condition propagation directions and/or focusing points of the respective separate partial electron beam 13_i comparable to the focusing and beam steering unit 29 of the X-ray source 24 of FIG. 7.

Via a drive unit 36, the multi aperture lenslet array 35 can be moved along a x-direction, i.e. perpendicular to the arrangement plane 18.

FIGS. 8 and 9 show two different x-positions of the multi aperture lenslet array 35. In the x-position of the multi aperture lenslet array 35 shown in FIG. 8, such array 35 has a larger distance to the arrangement plane 18 as compared to FIG. 9.

In the FIG. 8 position of the multi aperture lenslet array 35, this results in an arrangement of the X-ray source region 14₁ to 14₅ which have a closer distance to each other.

In the FIG. 9 x-position, the multi aperture lenslet array 35 is driven to be positioned more closely to the arrangement plane 18 resulting in an arrangement of the X-ray source regions 14; which are, as compared to FIG. 8, more distant to each other.

Again, with the focusing and beam steering unit 29 of the X-ray source 30 comprising the macro lens 34 and the multi aperture lenslet array 35, arrangements of the X-ray source regions 14_i are possible, dependent on the number of generated separate partial electron beams 14_i, which are discussed above with respect, for example, to FIGS. 2 to 7.

FIGS. 10 and 11 show another embodiment of an X-ray source 37 which may be used in the X-ray inspection system 1 instead of the X-ray source 30. Components and functions which already were discussed with respect to FIGS. 1 to 7 above show the same reference numerals and are not discussed in detail again.

The X-ray source 37 has a plurality of electron beam sources 12₁, 12₂ and 12₃ with attributed acceleration units 28; serving to accelerate a respective one of the separate electron beams 13_i generated by the electron beam sources 12_i. Together with the electron beam sources 12_i and a further electron beam focusing unit (schematically depicted lenses 28a), the acceleration unit 28; constitute a multi e-beam column 11 comparable to that of the embodiment of FIG. 2.

Each of the acceleration units 28; comprises a single aperture lenslet.

In the beam path subsequent to the multi e-beam column 11 of the X-ray source 37, again, a focusing and beam steering unit 29 comparable to that of the embodiment of FIGS. 8 and 9 is arranged comprising a macro lens 34 and a driven multi aperture lenslet array 35.

FIGS. 10 and 11 exemplify two focusing and beam steering positions of the focusing and beam steering unit 29 of the X-ray source 37.

In the position of FIG. 10, closely spaced X-ray source regions 14₁, 14₂, and 14₃ result comparable to the spacing shown in the five beam embodiment of FIG. 8.

In the further focusing and beam steering position of the focusing and beam steering unit 29 shown in FIG. 11 with the multi aperture lenslet array 35 translated along the x-direction, the respective separate electron beams 13; cross each other in a beam crossing region 38.

In a further embodiment based on the FIG. 11 x-ray source 37, the multi aperture lenslet array 35 is omitted and the function of such lenslet array is taken over by another lens 28b which schematically is depicted in FIG. 11. In the embodiment of the x-ray source 37 having the multi aperture lenslet array 35, such lens 28b may be omitted.

Regarding focusing and beam steering mechanisms, concepts may be used which are known from WO 2008/002132 A1.

Claims

1. An X-ray inspection system configured to inspect an object, the X-ray inspection system comprising: an X-ray source configured to generate a plurality of separate X-ray light bundles;an object mount configured to hold the object so that separate X-ray light bundles propagate through a region of interest (ROI) of the object; anda detection system comprising separate detection areas configured to detect the separate X-ray light bundles, respectively, after propagating through the ROI,wherein the X-ray inspection system is configured so that:chief rays of at least two of the separate X-ray light bundles impinge on the ROI with different chief ray illumination angles; andX-ray light bundles with different chief ray illumination angles simultaneously impinge on the ROI.

2. The X-ray inspection system of claim 1, wherein the X-ray source comprises a plurality of separate electron beam sources, and each electron beam source comprises a converting element configured to convert the electron beams into X-rays at separate X-ray source regions.

3. The X-ray inspection system of claim 2, wherein the X-ray source regions are in a source plane of the X-ray inspection system.

4. The X-ray inspection system of claim 3, wherein multiple X-ray source regions are on a circle in the source plane.

5. The X-ray inspection system of claim 3, wherein: multiple X-ray source regions are on multiple circles in the source plane;different circles have different radii; andfor a given circle, the X-ray source regions are at the same polar angles.

6. The X-ray inspection system of claim 2, comprising an electron beam optics in an electron beam path of the electron beams upstream of the X-ray source regions, wherein the electron beam optics are configured to: i) focus the separate paths of the electron beams; and/or ii) steer a direction of the separate paths of the electron beams.

7. The X-ray inspection system of claim 2, wherein the X-ray source comprises: a single electron beam source configured to generate a main electron beam;an electron beam splitting unit configured to split the main electron beam into a plurality of separate partial electron beams; anda converting element to convert the partial electron beams at separate X-ray source regions into X-rays.

8. The X-ray inspection system of claim 2, wherein the X-ray source comprises: a single electron beam source configured to generate a main electron beam; an acceleration unit configured to accelerate and to split the main electron beam into a plurality of separate partial electron beams; anda converting element configured to convert the partial electron beams into X-rays at separate X-ray source regions.

9. The X-ray inspection system of claim 2, further comprising an aperture device in a beam path between the X-ray source region and the ROI.

10. The X-ray inspection system of claim 2, wherein the detection system comprises a plurality of detection devices, and each detection devices is attributed to a separate X-ray light bundle.

11. The X-ray inspection system of claim 2, wherein the detection system comprises a post-magnification unit.

12. The X-ray inspection system of claim 1, wherein the X-ray source comprises: a single electron beam source configured to generate a main electron beam;an electron beam splitting unit configured to split the main electron beam into a plurality of separate partial electron beams; anda converting element to convert the partial electron beams at separate X-ray source regions into X-rays.

13. The X-ray inspection system of claim 1, wherein the X-ray source comprises: a single electron beam source configured to generate a main electron beam; an acceleration unit configured to accelerate and to split the main electron beam into a plurality of separate partial electron beams; anda converting element configured to convert the partial electron beams into X-rays at separate X-ray source regions.

14. The X-ray inspection system of claim 1, further comprising an aperture device in a beam path between the X-ray source region and the ROI.

15. The X-ray inspection system of claim 1, wherein the detection system comprises a plurality of detection devices, and each detection devices is attributed to a separate X-ray light bundle.

16. The X-ray inspection system of claim 15, wherein each detection device comprises a sensor array.

17. A method of inspecting an object, the method comprising: impinging separate X-ray light bundles on a region of interest (ROI) of an object so that chief rays of at least two of the separate X-ray light bundles impinge on the ROI with different chief ray illumination angles, and so that X-ray light bundles with different chief ray illumination angles simultaneously impinge on the ROI;after the separate X-ray light bundles impinge on the ROI, detecting the separate X-ray light bundles at respective separate detection areas.

18. The method of claim 17, further comprising using an X-ray source to generate the separate X-ray light bundles, wherein the X-ray source comprises a plurality of separate electron beam sources, and each electron beam source comprises a converting element configured to convert the electron beams into X-rays at separate X-ray source regions.

19. The method of claim 18, wherein the X-ray source regions are in a source plane of the X-ray inspection system.

20. The method of claim 19, wherein multiple X-ray source regions are on a circle in the source plane.