X-ray imaging system

Abstract

An x-ray imaging system (A#100) for imaging a sample (A#102), comprising an x-ray source (A#112) for generating x-rays (A#114), and a shield stop (A#132) with an aperture (A#136), the shield stop (A#132) being configured for transmitting an x-ray beam (A#134) of the generated x-rays (A#114) through the aperture (A#136) and along an x-ray propagation axis (A#140) of the system (A#100) towards a region of interest (A#104) of the sample (A#102) and for blocking remaining x-rays (A#114), wherein a geometric shape (A#146) of the aperture (A#136) is adapted to a diverging nature of the transmitted x-ray beam (A#134).

Description

[0001] Carl Zeiss SMT GmbH

[0002] 1

[0003] X-RAY IMAGING SYSTEM

[0004] The present invention relates to an x-ray imaging system for imaging a sample.

[0005] The contents of the priority applications US 19 / 015,774, US 19 / 015,801 and US 19 / 015,842 is incorporated by reference in its entirety (incorporation by reference).

[0006] X-rays are widely used in microscopy because of their short wavelengths and ability to penetrate objects. Three-dimensional (3D) x-ray imaging techniques are useful to image internal structures of objects. Typically, based on a dataset including x-ray transmission images of a sample that are collected over a large angular range, 3D images are reconstructed. An x-ray imaging system usually comprises a rotatable sample mount to support a sample, an x-ray source configured to illuminate a region of interest of the sample, and a positionsensitive x-ray detector configured to record x-rays transmitted through the region of interest of the sample.

[0007] The x-ray source usually emits non-directed diverging x-rays from which only a fraction is used for inspecting the region of interest of the sample. When the sample is exposed to a high x-ray radiation amount, damages of the sample are possible. US 2023 / 046 280 A1 proposes an x-ray imaging system with a shield stop arranged between an x-ray source and a sample to protect uninspected regions of the sample.

[0008] It is one object of the present invention to provide an improved x-ray imaging system.

[0009] Accordingly, an x-ray imaging system for imaging a sample is provided. The x-ray imaging system comprises:

[0010] an x-ray source for generating x-rays, and

[0011] a shield stop with an aperture, the shield stop being configured for transmitting an x-ray beam of the generated x-rays through the aperture and along an x-ray propagation axis of the system towards a region of interest of the sample and for blocking remaining x-rays,

[0012] wherein a geometric shape of the aperture is adapted to a diverging nature of the transmitted x-ray beam.

[0013] Having the shield stop with the geometric shape of its aperture adapted to the diverging nature of the transmitted x-ray beam, x-rays emitted by the x-rayCarl Zeiss SMT GmbH

[0014] 2

[0015] source and not used for inspection of the sample can be better blocked from the sample. Therefore, the uninspected regions of the sample can be better protected from x-ray exposure. Hence, damage of the sample caused by x-rays can be reduced and / or avoided.

[0016] The x-ray imaging system is configured for imaging a region of interest of a sample. The sample is, for example, a flat extended object. The sample is, for example, a wafer. The wafer includes, for example, electronic and / or semiconductor components. Just as an example, the x-ray imaging system may be used to inspect the wafer to investigate the quality of packaging of electronic components of the wafer. For example, the quality of mechanical and electrical bonding (e.g., buried interconnections) of the electronic components may be controlled. However, the sample may also be another type of object than a wafer. The sample may, for example, be a circuit board or a battery.

[0017] The x-ray imaging system is, in particular, a transmission x-ray imaging system, wherein the x-rays impacting on the region of interest of the sample are partly transmitting the region of interest and are partly absorbed by the region of interest. The position-dependent transmitted portion of the x-rays is detected by a position -sensitive x-ray detector assembly as a two-dimensional image.

[0018] The x-ray imaging system is, for example, an imaging system for three- dimensional x-ray imaging. The x-ray imaging system is, for example, configured to obtain two-dimensional transmission images of the region of interest for different rotation angles of the sample. Based on the obtained two-dimensional transmission images, a three-dimensional image of the region of interest is, for example, reconstructed to reveal interior structures of the region of interest. The x-ray imaging system is, for example, an x-ray imaging system for obtaining three-dimensional images by x-ray laminography and / or x-ray tomography.

[0019] The x-ray source generates diverging x-rays, i. e. a cone (conus) of x-rays. A portion (e.g., a sub cone) of the generated diverging x-rays is irradiating the region of interest of the sample. A center line of this portion (e.g., sub cone) of x-rays is referred herein as x-ray propagation axis of the system. In particular, the x-ray propagation axis extends from the x-ray source (e.g., a source region of the x-ray source), through the region of interest of the sample, and to an x-ray detector assembly of the system. This means that the x-ray propagation axis indicates the direction of an x-ray beam which is a portion of the total generated diverging x-rays of the x-ray source.Carl Zeiss SMT GmbH

[0020] 3

[0021] The shield stop is, in particular, arranged between the x-ray source and / or an x-ray target of the x-ray source and the sample. In other words, the shield stop is, in particular, arranged between the x-ray source and / or the x-ray target of the x-ray source and an object plane of the system, the object plane being configured for arranging the sample.

[0022] The shield stop is, for example, arranged spaced apart from the x-ray source. Alternatively, the shield stop is, for example, arranged adjacent the x-ray source (e.g., back-to-back with the x-ray source) and / or integrated with / embedded into the x-ray source.

[0023] The shield stop comprises, in particular, an x-ray blocking material. Hence, the shield stop is configured for transmitting x-rays through its aperture and blocking x-rays in the remaining part of the shield stop. In other words, the shield stop is configured for transmitting a first portion of the generated x-rays ("transmitted x-ray beam") through the aperture and towards the sample and for blocking a second portion of the generated x-rays such that the second portion does not reach the sample.

[0024] The shield stop is, in particular, arranged in a light path of the diverging x-rays emitted from the x-ray source. The shield stop serves to select a usable portion (e.g., sub cone) of the x-ray cone generated by the x-ray source. The x-ray beam transmitted through the aperture of the shield stop propagates in the direction of the region of interest of the sample and (partly) transmits through the region of interest of the sample towards the detector assembly. The x-ray beam transmitted through the aperture of the shield stop propagates, in particular, along the x-ray propagation axis of the system.

[0025] The aperture of the shield stop is, in particular, a through opening. The shield stop has, for example, an entrance face facing the x-ray source and / or the x-ray target of the x-ray source. Further, the shield stop has, for example, an exit face facing the object plane of the system (e.g., the sample arranged in the object plane). The aperture of the shield stop is, in particular, extending from the entrance face to the exit face of the shield stop.

[0026] The shield stop is, for example, an extended object with a main plane of extension. The main plane of extension of the shield stop is, for example, arranged parallel to the object plane of the system. Further, the entrance face and the exit face of the shield stop are, for example, arranged parallel to each other and / or parallel to the main plane of extension of the shield stop.Carl Zeiss SMT GmbH

[0027] 4

[0028] The geometric shape of the aperture is adapted to a diverging nature of the transmitted x-ray beam. In particular, the transmitted x-ray has a diverging beam shape. The diverging beam shape includes an opening angle of the beam larger than zero (e.g., an opening angle between 3° and 45°, between 5° and 30° and / or between 10° and 20°).

[0029] The geometric shape of the aperture is, in particular, a three-dimensional shape of the aperture.

[0030] Furthermore, the geometric shape of the aperture is, for example, - in addition to being adapted to the diverging nature of the transmitted beam - adapted to an orientation of the x-ray propagation axis.

[0031] The aperture of the shield stop is, for example, a closed aperture as seen in cross section, the cross section taken parallel to the main plane of extension of the shield stop and / or perpendicular to the x-ray propagation axis. An inner wall of the shield stop defining the aperture has, for example, a ring shape. Further, the cross section of the aperture (parallel to the main plane of extension of the shield stop and / or perpendicular to the x-ray propagation axis) has, for example, a circular, ellipsoidal, oval, trapezoidal, rectangular, quadratic and / or polygonal shape.

[0032] Alternatively, the aperture of the shield stop may, for example, also be a nonclosed aperture as seen in cross section parallel to the main plane of extension of the shield stop and / or perpendicular to the x-ray propagation axis. In this case, the shield stop shields the x-rays generated by the x-ray source only on one side of the x-ray propagation axis but not on the other side.

[0033] The aperture of the shield stop is, for example, unfilled. Unfilled means herein free of (e.g., solid) material and includes that the aperture is filled with air and / or another gas (including a low-pressure atmosphere and / or vacuum atmosphere). Alternatively, the aperture of the shield stop is, for example, filled with an x-ray transmissive material.

[0034] In this application, "x-ray transmissive" means, for example, that the respective element has an x-ray transmission such that more than 50% of the x-rays generated by an x-ray target of the x-ray source having energies greater than one-half of the selected maximum focused electron energy are transmitted through the respective element.Carl Zeiss SMT GmbH

[0035] 5

[0036] In this application, "x-ray blocking" means, for example, that the respective element has an x-ray blocking effect such that more than 70%, more than 80% and / or more than 90% of the x-rays generated by an x-ray target of the x-ray source having energies greater than one-half of the selected maximum focused electron energy are blocked by the respective element.

[0037] The x-ray imaging system comprises, for example, a rotatable sample mount for supporting and rotating the sample. The sample mount comprises, for example, a support surface for supporting the sample. The support surface defines, for example, an object plane of the system.

[0038] The main plane of extension of the shield stop is, for example, arranged parallel to the object plane.

[0039] The x-ray propagation axis of the x-ray imaging system is, for example, inclined relative to the object plane by an acute angle.

[0040] The x-ray source comprises, for example, a vacuum chamber. Further, the x-ray source comprises, for example, a pump for evacuating the vacuum chamber. The x-ray source further comprises, for example, an electron source accommodated in the vacuum chamber. The electron source is configured for emitting an electron beam towards an x-ray target of the x-ray source. The electron source includes, for example, a cathode and an anode and the like for generating electrons and for accelerating the generated electrons. The x-ray source further comprises, for example, one or more electron optics units for directing, deflecting and / or shaping the electron beam emitted from the electron source. The electron optics include, for example, one or more magnetic lenses for focusing the electron beam and / or one or more deflection units for deflecting the electron beam.

[0041] The x-ray source further comprises, for example, at least one x-ray target. The x-ray target is configured for emitting x-rays when bombarded with the focused electron beam. A material of the at least one x-ray target comprises, for example, one or more of a group including tungsten (W), copper (Cu), chromium (Cr), molybdenum (Mo), rhodium (Rh) and platinum (Pt). The x-rays generated by the at least one x-ray target include characteristic lines determined by the target's composition and broad bremsstrahlung radiation.

[0042] The x-ray source includes, for example, a carrier element carrying the x-ray target (or carrying multiple of the x-ray targets which can be selected byCarl Zeiss SMT GmbH

[0043] 6

[0044] directing the electron beam accordingly). The carrier element is, for example, x-ray transmissive. The carrier element forms, for example, a vacuum window of the vacuum chamber. Alternatively, an additional vacuum window may be provided. A material of the carrier element and / or the vacuum window includes, for example, atomic elements having atomic numbers less than 14. The material of the carrier element and / or the vacuum window includes, for example, one or more of a group including beryllium (Be), diamond, boron carbide (B4C), silicon carbide (SiC), aluminum (Al), and beryllium oxide (BeO). The material of the carrier element and / or the vacuum window is, preferentially, diamond.

[0045] The carrier element has, for example, a sufficiently high thermal conductivity to provide a thermal conduit to prevent thermal damage (e.g., melting) of the at least one x-ray target. Further, the carrier element can, for example, also provide an electrically conductive path to dissipate electric charge from the at least one x-ray target and / or the carrier element itself.

[0046] The x-ray source is, in particular, a transmission target type x-ray source. The electron beam strikes the at least one x-ray target of the x-ray source at its backside and the at least one x-ray target emits x-rays at its front side, the emitted x-rays are used to irradiate the sample.

[0047] The x-ray imaging system comprises, for example, an x-ray detector assembly. The x-ray detector assembly is, for example, configured for position -sensitive x-ray detection of x-rays transmitted through the region of interest of the sample. The x-ray detector assembly includes, for example, a scintillator element for converting incoming x-rays into detectable light (for example light of longer wavelength, e.g., ultraviolet light, visible light or infrared light). The x-ray detector assembly further includes, for example, a detector unit with a two- dimensional detector array (e.g., CMOS sensor, CCD) for detecting the detectable light. In addition, the x-ray detector assembly includes, for example, a unit (e.g., optics unit) for transferring the detectable light (magnified or non-magnified) from the scintillator element to the detector unit.

[0048] According to an embodiment, a cross-section size of the aperture parallel to a main plane of extension of the shield stop increases in a direction of the x-ray propagation axis.

[0049] Hence, a cross section of the aperture broadens from an entrance of the aperture (at the entrance face of the shield stop) to an exit of the aperture (at the exit faceCarl Zeiss SMT GmbH

[0050] 7

[0051] of the shield stop) to adapt the geometric shape of the aperture to the diverging nature of the transmitted x-ray beam.

[0052] The cross-section size is, for example, a size of a cross-section area of the aperture parallel to a main plane of extension of the shield stop.

[0053] Further, also a cross-section size of the aperture perpendicular to the x-ray propagation axis increases in the direction of the x-ray propagation axis.

[0054] According to a further embodiment, the aperture comprises, as seen in a cross section along the x-ray propagation axis, at least one inclined inner wall inclined with respect to the x-ray propagation axis of the transmitted x-ray beam by half of an opening angle of the transmitted x-ray beam.

[0055] Thus, the at least one inner wall of the aperture of the shield stop is inclined by an inclination angle which corresponds to half of the opening angle of the diverging x-ray beam (i.e. the transmitted x-ray beam).

[0056] The inclination angle of the inclined inner wall relative to the x-ray propagation axis has, for example, a value between 3° and 45°, between 5° and 30° and / or between 10° and 20°.

[0057] According to a further embodiment, the x-ray imaging system comprises an object plane for arranging the sample, wherein the x-ray propagation axis of the system is inclined relative to the object plane.

[0058] According to a further embodiment, the x-ray imaging system comprises an x-ray detector assembly with a two-dimensional detector array for detecting the x-ray beam transmitted through the region of interest of the sample and traveled along the x-ray propagation axis. Further, the x-ray propagation axis is inclined relative to a main plane of extension of the shield stop. Furthermore, an actual cross-section shape of the aperture of the shield stop parallel to its main plane of extension has, as seen in perspective from the detector array, an apparent shape matching a geometric shape of the detector array.

[0059] The detector array has a two-dimensional detection field and / or pixel array with the two-dimensional geometric shape. The geometric shape of the detector array is, for example, a quadratic, rectangular, circular, polygonal shape and / or another two-dimensional shape.Carl Zeiss SMT GmbH

[0060] 8

[0061] Further, the (two-dimensional) cross-section shape of the aperture of the shield stop (parallel to its main plane of extension) is configured such that it matches, in a perspective view from the detector array, the (two-dimensional) geometric shape of the detector array. In other words, the apparent (two-dimensional) geometric shape of the cross section of the aperture of the shield stop, as viewed from the detector array, has the same shape as the geometric shape of the detector array. Thus, the geometric shape of the aperture of the shield stop is adapted to the geometric shape of the detector array to improve the shielding effect of the shield stop.

[0062] The actual cross-section shape of the aperture of the shield stop parallel to its main plane of extension includes, for example, the actual cross-section shape of the aperture in the main plane of extension of the shield stop, in a plane of the exit face of the shield stop, in a plane of the entrance face of the shield stop and / or in any plane between the entrance and exit planes.

[0063] The x-ray propagation axis of the system is, in particular, inclined relative to the main plane of extension of the shield stop. Further, the detector array is, for example, arranged perpendicular to the x-ray propagation axis.

[0064] Furthermore, also the actual cross-section size (e.g., cross-section area) of the aperture of the shield stop parallel to its main plane of extension has, as seen in perspective from the detector array, an apparent size (e.g., cross-section area) matching a size (e.g., area) of the detector array.

[0065] According to a further embodiment, the geometric shape of the detector array is a quadratic and / or a rectangular shape. Further, the actual cross-section shape of the aperture of the shield stop parallel to its main plane of extension has a trapezoidal cross-section shape with, as seen in perspective from the detector array, an apparent shape matching the quadratic and / or rectangular shape of the detector array.

[0066] According to a further embodiment, the geometric shape of the detector array is a circular shape. In addition, the actual cross-section shape of the aperture of the shield stop parallel to its main plane of extension has an ellipsoidal cross-section shape with, as seen in perspective from the detector array, an apparent shape matching the circular shape of the detector array.

[0067] According to a further embodiment, the x-ray source comprises a vacuum chamber with an x-ray transmissive vacuum window, and at least one x-rayCarl Zeiss SMT GmbH

[0068] 9

[0069] target arranged in the vacuum chamber for generating x-rays and transmitting the generated x-rays through the vacuum window. Moreover, the shield stop is integrated in the vacuum window.

[0070] By integrating the shield stop in the vacuum window of the x-ray source, a distance between the x-ray source and the sample can be configured small despite the presence of the shield stop.

[0071] A small distance between the x-ray source and the region of interest of the sample is beneficial because the x-ray flux incident on the region of interest of the sample is inversely proportional to the square of the distance of the region of interest from the x-ray source, in particular the x-ray target of the x-ray source. With the proposed configuration, a high x-ray flux density at the region of interest of the sample is achieved. Further, a high x-ray flux density at the region of interest of the sample implies short exposures times and, therefore, a high throughput rate of samples during imaging.

[0072] According to a further embodiment, the shield stop is embedded in the vacuum window such that the shield stop is accommodated in at least one recess of the vacuum window.

[0073] In particular, an x-ray blocking material of the shield stop is accommodated in the at least one recess of the vacuum window. The x-ray blocking material of the shield stop is, for example, accommodated in the at least one recess of the vacuum window without a gap between the x-ray blocking material of the shield stop and the x-ray transmissive material of the vacuum window.

[0074] Having the shield stop embedded in the vacuum window of the x-ray source, a distance between the x-ray source and the sample can be configured even smaller. Thus, an x-ray flux density at the region of interest of the sample can be increased further leading to even shorter exposure times and a higher throughput rate.

[0075] According to a further embodiment, the aperture of the shield stop is filled with an x-ray transmissive material of the vacuum window.

[0076] According to a further embodiment, the shield stop is arranged at an outside surface of the vacuum window.Carl Zeiss SMT GmbH

[0077] 10

[0078] The shield stop is, for example, attached (e.g., glued etc.) to the outside surface of the vacuum window.

[0079] According to a further embodiment, the x-ray source comprises a plurality of x-ray targets, and the x-ray imaging system comprises a plurality of shield stops, each shield stop being arranged corresponding to one of the x-ray targets.

[0080] Having the plurality of x-ray targets, another x-ray target can be easily selected and used in case that an already used x-ray target became unusable. For example, an electron source of the x-ray source is configured to direct an emitted electron beam to a respective one of the plurality of x-ray targets to select it as current x-ray target.

[0081] The plurality of x-ray targets are, for example, arranged (e.g., spaced apart from each other) in a one- dimensional or a two-dimensional array as viewed in a direction perpendicular to an outer surface of the vacuum window. The outer surface of the vacuum window is facing the object plane of the system (e.g., the sample arranged in the object plane). The x-ray source comprises, for example, 50 or more x-ray targets, 100 or more x-ray targets and / or 1000 or more x-ray targets. The number of shield stops equals, for example, the number of x-ray targets.

[0082] According to a further embodiment, a thickness of the shield stop is 1000 μm (1 mm) or smaller, 500 μm or smaller, 200 μm or smaller, 100 μm or smaller and / or 50 μm or smaller.

[0083] Thus, the shield stop is thin enough to allow arranging the sample close to the x-ray source. The thickness of the shield stop should be, on the other hand, large enough to stop, for example, 90% of incoming x-rays. A minimum thickness is, for example, 50 μm or 100 μm.

[0084] The thickness of the shield stop is, in particular, a dimension of the shield stop in a direction perpendicular to its main plane of extension.

[0085] According to a further embodiment, a material of the shield stop includes tungsten, bismuth, lead, platinum, depleted uranium, gold and / or one or more chemical elements with an atomic number above 70.Carl Zeiss SMT GmbH

[0086] 11

[0087] A chemical element with a high atomic number (e.g., above 70), such as tungsten (W), bismuth (Bi), lead (Pb), platinum (Pt) and depleted uranium (U), has a good x-ray blocking property.

[0088] According to a further embodiment, the shield stop is configured for adapting a size of the aperture.

[0089] Thus, the size of the aperture can be adapted for transmitting x-ray beams with different opening angles.

[0090] The shield stop is, for example, configured for adapting a cross-section size (e.g., cross-section area) of the aperture in a plane parallel to the main plane of extension of the shield stop.

[0091] The shield stop includes, for example, several shield elements being configured movable such that by moving the individual shield elements, the aperture can be increased or decreased. The shield stop is, for example, configured similar as an iris stop.

[0092] In embodiments, the x-ray imaging system comprises a sample mount for supporting the sample rotatably around a rotation axis, wherein the x-ray imaging system is configured for obtaining two-dimensional transmission images of the region of interest of the sample for different rotation angles of the sample with respect to the rotation axis, and for reconstructing a three-dimensional image of the region of interest based on the two-dimensional transmission images.

[0093] The x-ray imaging system comprises, for example, a control device for reconstructing the three-dimensional images.

[0094] For example, the x-ray imaging system is configured for obtaining two- dimensional transmission images of the region of interest of the sample for different rotation angles of the sample with respect to the rotation axis, wherein the rotation angles span a large angular range of, for example, 180° or larger, 270° or larger and / or 360°.

[0095] According to a further embodiment, the x-ray imaging system is configured for emitting x-rays towards a first side of the sample and for imaging a region of interest of the sample arranged on a second side of the sample, the second side isCarl Zeiss SMT GmbH

[0096] 12

[0097] arranged opposite the first side, and the second side is configured for facing away from the x-ray source during x-ray imaging.

[0098] Thus, the region of interest (e.g., a component and / or semiconductor component to be inspected by x-ray imaging) is arranged on that side of the sample which is facing away from the x-ray source. Hence, advantageously the x-rays are attenuated by transmitting the sample body (e.g., a substrate of a wafer) before they reach the region of interest. Therefore, an x-ray dose of the region of interest is further reduced and, hence, a risk of damaging the region of interest by x-ray exposure is further reduced. In addition, also neighboring areas (e.g., with sensitive components) of the region of interest on the second side of the sample can be better protected from x-ray exposure.

[0099] According to a further aspect, a method for x-ray imaging of a region of interest of a sample is provided. The method comprises the steps:

[0100] arranging a sample on a sample mount of an x-ray imaging system, wherein the sample has a first side and a second side arranged opposite the first side, the sample comprises a region of interest arranged on the second side, and the sample is arranged on the sample mount such that the first side faces an x-ray source of the x-ray imaging system and the second side faces away from the x-ray source, and

[0101] x-ray imaging of the region of interest.

[0102] According to an embodiment of the x-ray imaging system and / or of the method, the second side of the sample is free of regions of interest and / or the second side of the sample is free of components to be inspected by x-ray imaging.

[0103] Thus, the second side can be used to hold and / or fix the sample without damaging sensitive features of the sample.

[0104] Further possible implementations or alternative solutions of the invention also encompass combinations – that are not explicitly mentioned herein – of features described above or below with regard to the embodiments. The person skilled in the art may also add individual or isolated aspects and features to the most basic form of the invention.

[0105] Further embodiments, features and advantages of the present invention will become apparent from the subsequent description and dependent claims, taken in conjunction with the accompanying drawings, in which:Carl Zeiss SMT GmbH

[0106] 13

[0107] Fig. A#1 shows a schematic view of an x-ray imaging system for imaging a sample according to an embodiment;

[0108] Fig. A#2 shows a partial view of a shield stop together with a transmitted x-ray beam of the x-ray imaging system of Fig. A#1 according to an embodiment;

[0109] Fig. A#3 shows a schematic view of an x-ray imaging system for imaging a sample according to a further embodiment;

[0110] Fig. A#4 shows a partial view of a shield stop of the x-ray imaging system of Fig.

[0111] A#3;

[0112] Fig. A#5 shows a schematic view of an x-ray imaging system for imaging a sample according to a further embodiment;

[0113] Fig. A#6 shows a partial view of a shield stop of the x-ray imaging system of Fig.

[0114] A#5;

[0115] Fig. A#7 shows a schematic view of an x-ray imaging system for imaging a sample according to a further embodiment;

[0116] Fig. A#8 shows a shield stop integrated into a vacuum window of an x-ray source of the x-ray imaging system of Fig. A#7 according to an embodiment;

[0117] Fig. A#9 shows a plurality of shield stops integrated into a vacuum window of an x-ray source of the x-ray imaging system of Fig. A#7 according to a further embodiment;

[0118] Fig. A#10 shows a shield stop integrated into a vacuum window of an x-ray source of the x-ray imaging system of Fig. A#7 according to a further embodiment; and

[0119] Fig. A#11 shows a shield stop integrated into a vacuum window of an x-ray source of the x-ray imaging system of Fig. A#7 according to a further embodiment.

[0120] In the Figures, like reference numerals designate like or functionally equivalent elements, unless otherwise indicated.Carl Zeiss SMT GmbH

[0121] 14

[0122] Fig. A#1 shows a schematic view of an x-ray imaging system A# 100 according to an embodiment. The x-ray imaging system A# 100 is used for imaging a sample A#102, in particular a region of interest A#104 of the sample A#102. The x-ray imaging system A#100 is configured to obtain two-dimensional transmission images A# 106 of the region of interest A# 104 for different rotation angles A#α of the sample A#102. Based on the two-dimensional transmission images A# 106, a three-dimensional (3D) image A#108 of the region of interest A#104 is reconstructed to reveal interior structures of the region of interest A# 104. The x-ray imaging system A# 100 is, hence, an x-ray 3D imaging system obtaining 3D images A# 108 by x-ray laminography and / or x-ray tomography.

[0123] The sample A#102 is, for example, a flat object extended in a main plane (e.g., the A#xA#y-plane in Fig. A#l). The sample A#102 is, for example, a wafer A#110 comprising electronic and / or semiconductor components. Just as an example, the x-ray imaging system A# 100 may be used to inspect the wafer A# 110 to investigate the quality of packaging of electronic components of the wafer A#110. For example, the quality of mechanical and electrical bonding (e.g., buried interconnections) of the electronic components may be controlled.

[0124] The x-ray imaging system A#100 comprises an x-ray source A#112 for emitting x-rays A# 114. The x-rays A# 114 are emitted from a source region A# 116 of the x-ray source A#112. The x-ray source A#112 emits a diverging beam A#118 of x-rays A#114. In other words, the x-ray source A#112 emits a cone A#120 of x-rays A#114. The sample A#102 is arranged within the x-ray emission cone A#120.

[0125] The x-ray imaging system A# 100 further comprises a sample mount A# 122 for supporting the sample A# 102. The sample mount A# 122 is configured rotatable around a rotation axis A#124. The rotation axis A#124 passes, for example, through the region of interest A# 104 of the sample A# 102. In particular, the rotation axis A# 124 can be arranged off-center with respect to a center of the sample A# 102. A rotation drive A# 126 for rotating the sample mount A# 122 and, hence, the sample A#102, is shown schematically in Fig. A#l. Furthermore, the sample mount A# 122 has a support surface A# 128 for supporting the sample A#102, wherein the support surface A#128 defines an object plane A#130 of the x-ray imaging system A#100.

[0126] The x-ray imaging system A#100 comprise in addition a shield stop A#132 arranged between the x-ray source A#112 and the object plane A#130 (or between an x-ray target A#482 of the x-ray source A#412 and the object plane A#130, seeCarl Zeiss SMT GmbH

[0127] 15

[0128] Figs. A#7, A#8). The shield stop A#132 is, in particular, arranged in a light path of the x-rays A#114 emitted from the x-ray source A#112. The shield stop A#132 serves to select a usable portion A#134 of the x-ray cone A#120. Moreover, the shield stop A# 132 protects uninspected regions of the sample A# 102 from x-ray exposure. The shield stop A#132 has an aperture A#136 through which the usable portion A#134 (e.g., a sub cone A#134) of the x-ray light A#114 (A#114') propagates in the direction of the region of interest A#104 of the sample A#102 and (at least partly) transmits the region of interest A#104 of the sample A#102.

[0129] The x-ray imaging system A# 100 further comprises a position-sensitive x-ray detector assembly A#138 for detecting x-rays A#114" transmitted through the region of interest A# 104 of the sample A# 102. The position-sensitive x-ray detector assembly A#138 is, for example, configured to convert the incoming x-rays A#114" into light of longer wavelength, e.g., ultraviolet light, visible light or infrared light. The x-ray detector assembly A#138 includes, for example, a scintillator material at an entrance window of the detector assembly A# 138 for converting the incoming x-rays A#114" into detectable light. The x-ray detector assembly A#138 further includes, for example, and a detector array (e.g., a CMOS sensor or CCD) for detecting the detectable light (see detector array A#262 in Fig. A#3).

[0130] Fig. A#1 displays an x-ray propagation axis A# 140 of the x-ray imaging system A#100. In particular, a central axis of the portion A#134 (e.g., sub light cone A#134) of the x-ray light A#114 passing through the shield stop A#132 defines the x-ray propagation axis A#140. The x-ray propagation axis A#140 extends from the x-ray source A#112 (i.e., the source region A#116 of the x-ray

[0131] source A#112), through the region of interest A#104 of the sample A#102, and to the position -sensitive x-ray detector assembly A#138.

[0132] As can be seen in Fig. A#l, the x-ray propagation axis A#140 of the x-ray imaging system A#100 is, in particular, inclined with respect to a surface normal A#142 of the sample mount A#122 by a first angle A#β. In addition, the x-ray propagation axis A# 140 is, in particular, inclined with respect to the rotation axis A#124 by a second angle A#γ. In the example of Fig. A#l, the surface normal A#142 of the sample mount A# 122 and the rotation axis A# 124 are arranged parallel to each other and, hence, the first angle A#β and the second angle A#γ have the same size.

[0133] Furthermore, the x-ray propagation axis A#140 of the x-ray imaging system A#100 is, in particular, inclined with respect to the object plane A#130 by a thirdCarl Zeiss SMT GmbH

[0134] 16

[0135] angle A#δ. Since the surface normal A#142 of the sample mount A#122 is perpendicular to the object plane A#130 in Fig. A#1, the sum of the first angle A#β and the third angle A#δ is 90° in Fig. A#1 (A#β + A#δ = 90°).

[0136] The x-ray exposures A# 106 obtained at different rotation angles A#α of the sample A#102 are reconstructed to a 3D image A# 108 by a control system A# 144 of the imaging system A#100.

[0137] Fig. A#2 shows a partial view of the shield stop A#132 of Fig. A#l. Visible in Fig. A#2 is, in particular, the aperture A#136 of the shield stop A#132. Furthermore, the x-ray beam A#134 transmitted through the aperture A#136 is shown in Fig. A#l.

[0138] The shield stop A#132 is configured for blocking that portion of the x-rays A#114 emitted by the x-ray source A#112 which is not used for inspection of the region of interest A#104 of the sample A#102. The shield stop A#132 comprises, in particular, an x-ray blocking material such as lead or the like.

[0139] The x-ray propagation axis A# 140 of the system A# 100 is inclined relative to the object plane A#130 by the angle A#δ (Fig. A#1). Further, a main plane A#E1 of extension of the shield stop A#132 is, for example, arranged parallel to the object plane A#130. Hence, the x-ray propagation axis A#140 of the system A#100 is also inclined relative to the main plane A#E1 of extension of the shield stop A#132 by the angle A#δ (Fig. A#2).

[0140] The shield stop A#132 has an entrance face A#152 facing the x-ray source A#112 (Fig. A#l) and / or an x-ray target of the x-ray source A#112 (Figs. A#l, A#7 and A#8). Further, the shield stop A#132 has an exit face A#154 facing the object plane A#130 of the system A#100 (e.g., facing the sample A#102 arranged in the object plane A#130). A thickness A#T of the shield stop A#132 between its entrance face A# 152 and its exit face A# 154 is, for example, 1 mm or smaller, 500 pm or smaller, 200 pm or smaller, 100 pm or smaller and / or 50 pm or smaller. Further, the aperture A#136 of the shield stop A#132 is, in particular, extending from the entrance face A# 152 to the exit face A# 154 of the shield stop A#132. The entrance face A#152 is arranged in an entrance plane A#E2 of the shield stop A#132. Further, the exit face A#154 is arranged in an exit plane A#E3 of the shield stop A#132. The entrance plane A#E2, the exit plane A#E3 and the main plane A#E1 of extension of the shield stop A#132 are, for example, arranged parallel to each other.Carl Zeiss SMT GmbH

[0141] 17

[0142] As can be seen in Fig. A#2, a geometric shape A#146 of the aperture A#136 is adapted to a diverging nature A# 148 of the transmitted x-ray beam A# 134. In particular, the transmitted x-ray beam A#134 is radiated along the x-ray propagation axis A#140 and in the direction A#150 of the x-ray propagation axis A#140. Further, an opening angle A#ε of the x-ray beam A#134 is larger than zero (e.g., 10° or larger, 20° or larger and / or 30° or larger) such that the x-ray beam A#134 diverges during propagation.

[0143] The geometric shape A#146 of the aperture A#136 of the shield stop A#132 is, for example, adapted to the diverging nature A# 148 of the transmitted x-ray beam A#134 such that the cross section of the aperture A#136 broadens in the direction A#150 of the x-ray propagation axis A#140. In particular, a cross¬ section size A#S1 (e.g., cross-section area A#A1) of the aperture A#136 in the entrance plane A#E2 is smaller than a cross-section size A#S2 (e.g., cross-section area A#A2) of the aperture A#136 in the exit plane A#E3 (Fig. A#3). Hence, the cross-section size A#S1, A#S2 (e.g., cross-section area A#A1, A#A2) of the aperture A#136 parallel to the main plane A#E1 of extension of the shield stop A#132 increases in the direction A#150 of the x-ray propagation axis A#140.

[0144] Furthermore, the geometric shape A#146 of the aperture A#136 of the shield stop A#132 is, for example, adapted to the diverging nature A#148 of the transmitted x-ray beam A#134 by at least one inclined wall A#156, A#158. In particular, Fig. A#2 shows a cross-section view taken along the x-ray propagation axis A#140. Further, the aperture A#136 comprises in the view of Fig. A#2 at least one inclined inner wall A#156, A#158 which is inclined with respect to the x-ray propagation axis A#140. In the example of Fig. A#2, two inclined walls A#156, A#158 of the aperture A#136 are visible in the cross-section view. A first inclined wall A#156 of the aperture A#136 is inclined relative to the x-ray propagation axis by an angle of + A#ε / 2, wherein A#ε is the opening angle of the transmitted x-ray beam A#134. Further, a second inclined wall A#158 of the aperture A#136 is inclined relative to the x-ray propagation axis by an angle of - A#ε / 2.

[0145] Optional, the shield stop A# 132 may be configured for adapting a size A#S1, A#S2 of the aperture A#136. For example, if the shield stop A#132 comprises two or more shielding elements (not shown), the two or more shielding elements may be configured movable relative to each other such that the aperture A# 136 can be increased or decreased. Hence, a shield stop A#132 with a variable size may be provided. The shield stop A# 132 may, for example, be configured similar as an iris stop.Carl Zeiss SMT GmbH

[0146] 18

[0147] Figs. A#3 and A#4 show an x-ray imaging system A#200 according to a further embodiment. The x-ray imaging system A#200 of Figs. A#3 and A#4 is configured similar as the x-ray imaging system A#100 of Figs. A#1 and A#2. In the following, mainly only differences to the embodiment of Figs. A#1 and A#2 are described. The x-ray imaging system A#200 (Figs. A#3, A#4) comprises, similar as the x-ray imaging system A#100 (Figs. A#l, A#2), an x-ray source and a sample mount (not shown in Figs. A#3, A#4) and a shield stop A#232. Further, the x-ray imaging system A#200 comprises, similar as the x-ray imaging system A#100, an x-ray detector assembly A#238 with a scintillator element A#260 and a two-dimensional detector array A#262 (e.g., a CMOS sensor or CCD). Although not shown in the figures, between the scintillator element A#260 and the two- dimensional detector array A#262, a transmitting unit (e.g., optics unit) is arranged for transmitting the detectable light generated by the scintillator element A#260 (magnified or non-magnified) to the detector array A#262.

[0148] Further, similar as for the x-ray imaging system A#100, the x-ray propagation axis A# 140 of the x-ray imaging system A#200 is inclined relative to the object plane A#130 and to the main plane A#E1 of extension of the shield stop A#232. Further, the two-dimensional detector array A#262 is arranged perpendicular to the x-ray propagation axis A# 140.

[0149] In the embodiment of Figs. A#3, A#4, the two-dimensional detector array A#262 has a geometric shape A#264 which is exemplarily a circular shape A#266. In Fig. A#3, a detector plane A#E4 of the detector array A#262 is illustrated. In other words, the two-dimensional detector array A#262 is arranged in the detector plane A#E4. Further, the geometric shape A#264 of the detector array A#262 is, as an example, circular in the detector plane A#E4.

[0150] Moreover, the cross-section shape A#268 of the aperture A#236 of the shield stop A#232 (parallel to its main plane of extension A#E1) is configured such that it matches, in a perspective view from the detector array A#262, the geometric shape A#264 of the detector array A#262. In other words, an apparent geometric shape A#270 of the cross-section A#268 of the aperture A#236 of the shield stop A#232, as viewed from the detector assembly A#238, has the same shape as the geometric shape A#264, A#266 of the detector array A#262. Thus, the geometric shape A#268 of the aperture A#236 of the shield stop A#232 is adapted to the geometric shape A#264, A#266 of the detector array A#262 to improve a shielding effect of the shield stop A#232.Carl Zeiss SMT GmbH

[0151] 19

[0152] In the embodiment of Figs. A#3, A#4, the actual cross-section shape A#268 of the aperture A#236 of the shield stop A#232 parallel to its main plane A#E1 of extension is an ellipsoidal shape A#272. In Figs. A#3, A#4, actual cross-section shapes A#272a, A#272b of the aperture A#236 of the shield stop A#232 in both the entrance plane A#E2 and the exit plane A#E3 of the shield stop A#232 are illustrated. In both planes A#E2, A#E3, the actual shape A#272a, A#272b of the aperture's cross section is an ellipsoidal shape. Further, a cross-section size A#S1 (e.g., a cross-section area A#A1) of the aperture A#236 in the entrance plane A#E2 is smaller than a cross-section size A#S2 (e.g., a cross-section area A#A2) of the aperture A#236 in the exit plane A#E3.

[0153] Figs. A#5, A#6 show another example of a shield stop A#332 having an aperture A#336 whose cross-section shape A#368 (parallel to its main plane of extension A#E1) is configured such that it matches, in a perspective view, the geometric shape A#364 of the detector array A#362. In the example of Figs. A#5, A#6 the geometric shape A#364 of the detector array A#362 of the detector assembly A#338 is a quadratic shape A#366. Further, the actual cross-section shape A#368 of the aperture A#336 of the shield stop A#332 parallel to its main plane A#E1 of extension (e.g., in the plane A#E1, A#E2 and / or A#E3) has a trapezoidal cross¬ section shape A#372. As illustrated in Fig. A#5, an apparent shape A#370 of the actual cross-section shape A#368 of the aperture A#336 is a quadratic shape when viewed in perspective from the detector array A#362. Hence, the apparent shape A#370 of the actual cross-section shape A#368 of the aperture A#336 (which is quadratic) matches the quadratic shape A#366 of the detector array A#362.

[0154] Fig. A#7 shows an x-ray imaging system A#400 according to a further embodiment. In the following mainly only differences to the x-ray imaging system A# 100 in Fig. A#1 are described.

[0155] The x-ray imaging system A#400 (Fig. A#7) comprises, similar as the x-ray imaging system A#100 (Figs. A#l, A#2), an x-ray source A#412, a sample mount (not shown in Fig. A#7) defining an object plane A#130 and an x-ray detector assembly A#438. Further, similar as for the x-ray imaging system A#100, the x-ray propagation axis A# 140 of the x-ray imaging system A#400 is inclined relative to the object plane A#130.

[0156] Furthermore, the x-ray imaging system A#400 (Figs. A#7, A#8) comprises, similar as the x-ray imaging system A#100 (Figs. A#l, A#2), a shield stop A#432 for shielding uninspected regions of the sample A#102 from x-rays A#114Carl Zeiss SMT GmbH

[0157] 20

[0158] (Fig. A#l). However, in contrast to the x-ray imaging systems A#100, A#200, A#300 (Figs. A#1 to A#6), the shield stop A#432 of the x-ray imaging system A#400 (Figs. A#7, A#8) is integrated in the x-ray source A#412.

[0159] As shown in Fig. A#7, the x-ray source A#412 comprises a vacuum chamber A#474 with an x-ray transmissive vacuum window A#476. Further, the x-ray source A#412 comprises inside the vacuum chamber A#474, similar as the x-ray source A#112 in Figs. A#1 to A#6, an electron source A#478 for emitting an electron beam, electron optics A#480 for directing and shaping the electron beam and at least one x-ray target A#482 for generating x-rays when irradiated with the electron beam. The generated x-rays are transmitted through the vacuum window A#476. It is noted that although not shown, also the x-ray source A#112 of the x-ray imaging systems A#100, A#200, A#300 (Figs. A#1 to A#6) may comprise a similar vacuum chamber, vacuum window, electron source, electron optics and x-ray target.

[0160] Fig. A#8 shows a detailed view of the vacuum window A#476 of the x-ray source of Fig. A#7. The vacuum window A#476 comprises an outside surface A#484 facing an outside of the vacuum chamber A#474 and an inside surface A#486 facing an inside of the vacuum chamber A#474. As can be seen in Fig. A#8, the vacuum window A#476 functions as a carrier element for carrying the at least one x-ray target A#482. In other examples, also a separate carrier element for carrying the at least one x-ray target A#482 may be provided in addition to the vacuum window A#476.

[0161] In the example of Fig. A#8, the vacuum window A#476 (or alternatively a separate carrier element) has an inclined surface A#488 for carrying the x-ray target A#482 such that a longitudinal direction of the elongated x-ray target A#482 coincides with the x-ray propagation axis A#140. This configuration is beneficial for achieving a small source spot size of the x-ray source A#412 and, hence, a high spatial resolution. Further, a large volume of the x-ray target A#482 can be used for generating x-rays such that a high flux density at the region of interest A# 104 of the sample A# 102 is achieved. However, the at least one x-ray target A#482 of the x-ray source A#412 of any herein described x-ray imaging systems A# 100 to A#400 may also have another configuration and / or orientation than that shown in Fig. A#8.

[0162] In contrast to the embodiments of Figs. A#1 to A#6, the shield stop A#432 in Figs. A#7 to A#11 is integrated in the vacuum window A#476 of the x-ray source A#412. In the example of Fig. A#8, the vacuum window A#476 comprises at leastCarl Zeiss SMT GmbH

[0163] 21

[0164] one recess A#490, wherein an x-ray transmissive material of the vacuum window A#476 is recessed. Further, the shield stop A#432 is accommodated in the at least one recess A#490 of the vacuum window A#476 such that the at least one recess A#490 is filled with x-ray blocking material of the shield stop A#432. Thus, the shield stop A#432 is embedded in the vacuum window A#476.

[0165] In the example of Fig. A#8, two recesses A#490a, A#490b are provided and filled with x-ray blocking material of the shield stop A#432. Hence, an aperture 436 of the shield stop A#432 is a closed aperture as seen in a cross section perpendicular to the x-ray propagation axis A#140, similar as in Figs. A#1 to A#6.

[0166] However, the second recess A#490b is optional and it is possible to provide the x-ray blocking material of the shield stop A#432 only in the first recess A#490a. In this case, the aperture A#432 would be a non-closed aperture as seen in a cross section perpendicular to the x-ray propagation axis A#140.

[0167] A geometric shape 446 of the shield stop A#432 is, similar as for the shield stop A#132, A#232, A#332 in Figs. A#1 to A#6, adapted to the diverging nature A#148 of the transmitted x-ray beam A#134 (Fig. A#1). The configurations described with respect to the geometric shape A#146 of the shield stop A#132, A#232, A#332 in Figs. A#1 to A#6 apply, mutatis mutandis, to the shield stop A#432 to A#732 in Figs. A#7 to A#ll. For example, also a cross-section size of the aperture 436 of the shield stope A#432 increases in a direction A#150 of the x-ray propagation axis A#140. Further, the aperture 436 includes at least one inclined inner wall A#456, A#458 inclined with respect to the x-ray propagation

[0168] axis A# 140 by half of an opening angle A#ε (i.e. A#ε / 2) of the transmitted x-ray beam A#134 (Fig. A#1).

[0169] In the embodiment of Figs. A#7, A#8, the aperture 436 of the shield stop A#432 is filled with an x-ray transmissive material of the vacuum window A#476.

[0170] As shown in Fig. A#9, the x-ray source A#112, A#412 of any herein described x-ray imaging system A#100 to A#400 (Figs. A#1 to A#ll) may also comprise a plurality of x-ray targets A#582, A#582' and a plurality of shield stops A#532, A#532' with apertures A#536, A#536'. Fig. A#9 shows exemplarily two x-ray targets A#582, A#582' and two shield stops A#532, A#532'. However, there may be provided many more than two x-ray targets A#582, A#582' and two shield stops A#532, A#532'. As shown in Fig. A#9, each shield stop A#532, A#532' is arranged corresponding to one of the x-ray targets A#582, A#582'. Further, theCarl Zeiss SMT GmbH

[0171] 22

[0172] shield stops A#532, A#532' are integrated in a vacuum window A#576 of the x-ray source A#412.

[0173] Fig. A# 10 shows a further example of a shield stop A#632 integrated in a vacuum window A#676 of an x-ray source A#412 (Fig. A#7). The shield stop A#632 has an aperture A#636 adapted to the diverging nature of the transmitted x-ray beam A#134 (Fig. A#1). As illustrated in Fig. A#10, the at least one shield stop A#632 may also be arranged at an outside surface A#684 of the vacuum window A#676. The shield stop A#632 is, for example, attached to the outside surface A#684 of the vacuum window A#676. The reference sign A#682 denotes an x-ray target of the x-ray source A#412.

[0174] Fig. A#ll shows a further example of a shield stop A#732 integrated in a vacuum window A#767 of an x-ray source A#412 (Fig. A#7). The shield stop A#732 has an aperture A#736. Similar as in Fig. A#10, the shield stop A#732 is arranged at an outside surface A#784 of the vacuum window A#767. In Fig. A#ll, the x-ray target A#782 has - in comparison to Figs. A#8 to A#10 - a different orientation relative to the vacuum window A#767, in particular to the outside surface A#784 of the vacuum window.

[0175] Although the present invention has been described in accordance with preferred embodiments, it is obvious for the person skilled in the art that modifications are possible in all embodiments.Carl Zeiss SMT GmbH

[0176] 23 REFERENCE NUMERALS

[0177] A# 100 System

[0178] A# 102 Sample

[0179] A#104 Region of interest

[0180] A#106 2D-Image

[0181] A#108 3D-Image

[0182] A# 110 Wafer

[0183] A# 112 Source

[0184] A# 114 X-ray

[0185] A# 114', A# 114" X-ray

[0186] A#116 Source region

[0187] A# 118 Beam

[0188] A# 120 Cone

[0189] A# 122 Mount

[0190] A# 124 Axis

[0191] A# 126 Rotation drive

[0192] A# 128 Surface

[0193] A# 130 Plane

[0194] A#132 Shield stop

[0195] A# 134 Portion

[0196] A# 136 Aperture

[0197] A# 138 Detector assembly

[0198] A# 140 Axis

[0199] A# 142 Surface normal

[0200] A# 144 Control system

[0201] A# 146 Shape

[0202] A#148 Diverging nature

[0203] A# 150 Direction

[0204] A# 152 Entrance face

[0205] A# 154 Exit face

[0206] A# 156 Wall

[0207] A# 158 Wall

[0208] A#200 Imaging system

[0209] A#232 Shield stop

[0210] A#236 Aperture

[0211] A#238 Detector assembly

[0212] A#260 Scintillator element

[0213] A#262 Detector array

[0214] A#264 ShapeCarl Zeiss SMT GmbH

[0215] 24 A#266 Shape

[0216] A#268 Shape

[0217] A#270 Shape

[0218] A#272 Shape

[0219] A#272a, A#272b Shape

[0220] A#300 X-ray imaging system A#332 Shield stop

[0221] A#336 Aperture

[0222] A#338 Detector assembly A#362 Detector array

[0223] A#364 Shape

[0224] A#366 Quadratic shape

[0225] A#368 Cross-section shape A#370 Apparent shape

[0226] A#372 Cross -section shape A#372a, A#372b Cross -section shape A#400 Imaging system

[0227] A#412 X-ray source

[0228] A#432 Shield stop

[0229] A#436 Aperture

[0230] A#438 Detector assembly A#456 Wall

[0231] A#458 Wall

[0232] A#474 Vacuum chamber A#476 Vacuum window

[0233] A#478 Electron source

[0234] A#480 Electron optics

[0235] A#482 X-ray target

[0236] A#484 Surface

[0237] A#486 Surface

[0238] A#488 Surface

[0239] A#490 Recess

[0240] A#490a, A#490b Recess

[0241] A#532, A#532’ Shield stop A#536, A#536’ Aperture

[0242] A#576 Vacuum window A#582, A#582' X-ray target A#632 Shield stop

[0243] A#636 Aperture

[0244] A#676 Vacuum windowCarl Zeiss SMT GmbH

[0245] 25

[0246] A#682 X-ray target A#684 Outside surface A#732 Shield stop A#736 Aperture

[0247] A# 767 Vacuum window A#782 X-ray target A#784 Surface

[0248] A#α Angle

[0249] A#β Angle

[0250] A#γ Angle

[0251] A#δ Angle

[0252] A#ε Angle

[0253] A#A1, A#A2 Area

[0254] A#E1-A#E4 Plane

[0255] A#S1, A#S2 Cross-section size A#T Thickness A#X, A#Y, A#Z DirectionCarl Zeiss SMT GmbH

[0256] 26

[0257] X-RAY SOURCE FOR AN X-RAY IMAGING SYSTEM AND

[0258] X-RAY IMAGING SYSTEM

[0259] The present invention relates to an x-ray source for an x-ray imaging system and an x-ray imaging system with such an x-ray source.

[0260] The contents of the priority applications US 19 / 015,774, US 19 / 015,801 and US 19 / 015,842 is incorporated by reference in its entirety (incorporation by reference).

[0261] X-rays are widely used in microscopy because of their short wavelengths and ability to penetrate objects. In x-ray imaging systems, usually so-called tube or laboratory x-ray sources are used in which an electron beam bombards a target such that the target emits x-rays. The resulting x-rays include characteristic lines determined by the target's composition and broad bremsstrahlung radiation.

[0262] Some x-ray imaging systems employ a projection configuration in which a small x-ray source spot is used in conjunction with geometric magnification to image the object. A spatial resolution of such an x-ray imaging system depends, amongst others, on the size of the x-ray source spot. Ideally, the x-ray source spot would be a point spot. In practice, the x-ray source spot is considerably larger. Generally, the source spot size is determined by the electron optics and the ability of those optics to focus the electron beam down to a point. Source spot sizes are generally around 50 to 200 micrometers (pm) with good electron optics; although in other examples x-ray-source spot size may be 1 to 5 millimeters (mm) when power is a more important figure of merit. In particular, the larger the volume of the x-ray target generating the x-rays, the larger is the power of the generated x-ray flux. Hence, there is a trade-off between a small source spot size (i.e. high spatial resolution) and large x-ray power (i.e. high throughput) of an x-ray imaging system.

[0263] It is one object of the present invention to provide an improved x-ray source for an x-ray imaging system.

[0264] Accordingly, an x-ray source for an x-ray imaging system is provided. The x-ray source comprises:

[0265] a vacuum chamber with a vacuum window including a flat outer surface, at least one elongated x-ray target arranged inside the chamber such that its longitudinal axis is inclined relative to the outer surface, andCarl Zeiss SMT GmbH

[0266] 27

[0267] an electron source, preferably accommodated in the chamber, for emitting a focused electron beam towards the x-ray target causing the x-ray target to emit x-rays through the vacuum window.

[0268] Thus, the x-ray target is inclined with respect to the outer surface of the vacuum window. This allows to orientate the elongated x-ray target in an advantageous way with respect to an x-ray propagation axis of the x-ray imaging system. In particular, the elongated x-ray target can be orientated with respect to an x-ray detector of the x-ray imaging system such that a source spot of the x-ray source is very small. For example, the elongated x-ray target can be orientated with respect to the x-ray detector such that an x-ray propagation axis from the x-ray target to the detector is coinciding with the longitudinal axis of the x-ray target. In this case, the source spot size of the x-ray source is given by a cross-section area of a cross section of the x-ray target, the cross section being arranged perpendicular to the longitudinal axis of the x-ray target.

[0269] By achieving a small source spot size of the x-ray source, a high spatial resolution of the x-ray imaging system can be provided. Thus, small internal structures of the sample can be resolved.

[0270] Furthermore, since the x-ray target is an elongated target with the described advantageous orientation, the x-ray target provides a small source spot and can at the same time emit x-rays from its entire volume. Therefore, the proposed x-ray source has a high power output of x-rays. Due to the high power of the x-rays radiated onto the region of interest of the sample, x-ray exposure times of the sample (e.g., x-ray image acquisition times) can be short. Therefore, a series of samples can be analyzed quickly with the x-ray imaging system resulting in a high throughput rate.

[0271] Thus, with the proposed x-ray source high spatial resolution x-ray imaging with a high throughput rate of samples is possible.

[0272] The x-ray imaging system is configured for imaging a region of interest of a sample. The sample is, for example, a flat extended object. The sample is, for example, a wafer. The wafer includes, for example, electronic and / or semiconductor components. Just as an example, the x-ray imaging system may be used to inspect the wafer to investigate the quality of packaging of electronic components of the wafer. For example, the quality of mechanical and electrical bonding (e.g., buried interconnections) of the electronic components may beCarl Zeiss SMT GmbH

[0273] 28

[0274] controlled. However, the sample may also be another object than a wafer. The sample is, for example, a circuit board or a battery.

[0275] The x-ray imaging system is, in particular, a transmission x-ray imaging system, wherein the x-rays impacting on the region of interest of the sample are partly transmitting the region of interest and are partly absorbed by the region of interest. The position-dependent transmitted portion of the x-rays is detected by the position -sensitive x-ray detector as a two-dimensional x-ray image.

[0276] The x-ray imaging system is, for example, a three-dimensional imaging system. The x-ray imaging system is, for example, configured to obtain two-dimensional transmission images of the region of interest for different rotation angles of the sample. Based on the two-dimensional transmission images, a three-dimensional image of the region of interest is reconstructed to reveal interior structures of the region of interest. The x-ray imaging system is, for example, an x-ray three- dimensional imaging system obtaining three-dimensional images by x-ray laminography and / or x-ray tomography.

[0277] The x-ray source is, in particular, a transmission target type x-ray source. The electron beam strikes the at least one x-ray target of the x-ray source at its backside and the at least one x-ray target emits x-rays at its front side, the emitted x-rays are used to irradiate the sample.

[0278] The x-ray source generates diverging x-rays, i. e. a cone (conus) of x-rays. A portion (i.e. a sub cone) of the generated diverging x-rays is irradiating the region of interest of the sample. A center line of this sub cone of x-rays is referred herein as x-ray propagation axis.

[0279] The x-ray source comprises the vacuum chamber. The electron source and the at least one x-ray target are accommodated inside the vacuum chamber in a vacuum atmosphere.

[0280] The vacuum window of the vacuum chamber is, in particular x-ray transmissive. The flat outer surface of the vacuum window is an outer surface with respect to the vacuum chamber, i.e. the outer surface faces an exterior space of the vacuum chamber.

[0281] A material of the vacuum window (and / or of a carrier element described below) includes, for example, atomic elements having atomic numbers less than 14. The material of the carrier element includes, for example, one or more of a groupCarl Zeiss SMT GmbH

[0282] 29

[0283] including beryllium, diamond, boron carbide, silicon carbide, aluminum, and beryllium oxide. The material of the carrier element is, preferentially, diamond.

[0284] The vacuum window (and / or the carrier element described below) being x-ray transmissive means, for example, that it has an x-ray transmission such that more than 50% of the x-rays generated by the at least one x-ray target having energies greater than one-half of the selected maximum focused electron energy are transmitted through the carrier element.

[0285] The vacuum window (and / or the carrier element described below) has, for example, a sufficiently high thermal conductivity to provide a thermal conduit to prevent thermal damage (e.g., melting) of the at least one x-ray target.

[0286] The vacuum window (and / or the carrier element described below) can, for example, also provide an electrically conductive path to dissipate electric charge from the at least one x-ray target, the carrier element itself and / or the vacuum window itself.

[0287] The at least one x-ray target is configured for emitting x-rays when bombard with the focused electron beam. A material of the at least one x-ray target comprises, for example, one or more of a group including tungsten (W), copper (Cu), chromium (Cr), molybdenum (Mo), rhodium (Rh) and platinum (Pt). The x-rays generated by the at least one x-ray target include characteristic lines determined by the target's composition and broad bremsstrahlung radiation.

[0288] The at least one x-ray target is an elongated x-ray target which is elongated along its longitudinal axis. This means that the at least one x-ray target has a length with respect to its longitudinal axis that is larger than any of its onedimensional cross -section sizes of its cross section perpendicular to the longitudinal axis. The one -dimensional cross -section sizes include a side length of a square (in case of a squared cross section), a diameter (in case of a circular cross section), side lengths of a rectangular (in case of a rectangular cross section) and a semiaxis, e.g., semimajor axis, of an ellipse (in case of an elliptic crosssection).

[0289] A spot size of a source spot of the x-ray source corresponds to (i.e. is equal to) a cross-section size (area) of the at least one x-ray target.

[0290] The at least one x-ray target has, for example, a cylindrical geometric shape with a squared, circular, rectangular, polygonal and / or elliptic footprint.Carl Zeiss SMT GmbH

[0291] 30

[0292] The electron source includes, for example, electron optics, to focus and / or direct the electron beam. The electron optics include, for example, one or more magnetic lenses for focusing the electron beam and / or one or more deflection units for deflecting the electron beam.

[0293] The electron beam may include a line profile which can, for example, hit the x-ray target at least partly.

[0294] A cross section of the focused electron beam at the location of the x-ray target is, for example, as large as or larger than a length of the x-ray target. Hence, the entire x-ray target is bombarded by electrons and exited to generate x-rays. Just as an example, the cross section of the focused electron beam has a size (e.g., full width at half maximum, FWHM) at the location of the x-ray target of, for example, a few micrometer, e.g., 5 pm or larger, 3 pm or larger and / or 2 pm or larger.

[0295] A power of the focused electron beam has, for example, a value of 5 W or larger, 10 W or larger, 20 W or larger, 30 W or larger, 50 W or larger and / or 70 W or larger.

[0296] Because of the inclined x-ray target, the electron beam hits the x-ray target at an angle which is different from 90° (e.g., an angle of 90° minus the inclination angle of the longitudinal axis of the x-ray target). For example, the electron beam hits the x-ray target at an angle of 85° or smaller, 80° or smaller, 70° or smaller, 60° or smaller, 45° or smaller and / or 20° or smaller.

[0297] For example, the longitudinal axis being inclined relative to the outer surface excludes an angle of 90° between the longitudinal axis and the outer surface.

[0298] The energy of the electron beam hitting the x-ray target and the generated x-ray flux of the x-ray source are as usual for x-ray sources. Just as an example, the generated x-ray flux of the x-ray source has a value of 8 • 1013photons / second per Watt for an electron beam with an energy of 75 kV. However, also other numbers can be applied.

[0299] According to an embodiment, the x-ray source comprises an x-ray transmissive carrier element, wherein the carrier element includes at least one carrying surface carrying the at least one x-ray target, and the longitudinal axis of the at least one x-ray target is arranged parallel to the at least one carrying surface.Carl Zeiss SMT GmbH

[0300] 31

[0301] The at least one carrying surface of the carrier element carries the at least one x-ray target. The at least one x-ray target is, for example, at least one thin coating of a target material on the at least one carrying surface of the carrier element. The target material is, for example, grown on the at least one carrying surface of the carrier element.

[0302] The at least one carrying surface of the carrier element is, in particular, a flat surface inclined relative to the outer surface of the carrier element by the inclination angle.

[0303] According to a further embodiment,

[0304] the carrier element forms the vacuum window, the carrier element including the flat outer surface and an inner surface comprising the at least one carrying surface, or

[0305] the carrier element is a separate component from the vacuum window.

[0306] By the carrier element forming the vacuum window, the at least one target carried by the carrier element can be arranged as close as possible to the flat outer surface, i.e. to the exit surface, of the vacuum window.

[0307] The inner surface of the carrier element is an inner surface with respect to the vacuum chamber, i.e. the inner surface faces an interior space of the vacuum chamber.

[0308] In case that the carrier element is a separate component from the vacuum window, the carrier element is arranged inside the vacuum chamber and may be arranged at and / or attached to the vacuum window.

[0309] According to a further embodiment, the x-ray source is configured to be arranged in the x-ray imaging system such that:

[0310] the at least one carrying surface of the carrier element is arranged parallel to an x-ray propagation axis of the x-ray imaging system, and / or

[0311] the longitudinal axis of the at least one x-ray target coincides with the x-ray propagation axis of the x-ray imaging system.

[0312] The x-ray propagation axis extends, in particular, from the x-ray source through a region of interest of the sample to an x-ray detector of the x-ray imaging system.Carl Zeiss SMT GmbH

[0313] 32

[0314] In particular, the x-ray source generates diverging x-rays, i. e. a cone of x-rays. A portion (i.e. a sub cone) of the generated diverging x-rays is irradiating the region of interest of the sample. The x-ray propagation axis is a center beam of the sub cone of x-rays emitted from the x-ray source to the region of interest of the sample. That means the x-ray propagation axis indicates the direction of an x-ray beam which is a portion of the total generated diverging x-rays of the x-ray source.

[0315] Furthermore, the x-ray transmissive vacuum window (e. g., the carrier element forming the vacuum window) of the x-ray source is configured to be arranged such that the x-ray propagation axis of the x-ray imaging system intersects the vacuum window.

[0316] According to a further embodiment, the at least one carrying surface of the carrier element and / or the longitudinal axis of the at least one x-ray target is / are inclined by an inclination angle of 5° or larger, 10° or larger, 20° or larger, 30° or larger and / or 45° or larger relative to the outer surface of the vacuum window.

[0317] In particular, the longitudinal axis of the at least one x-ray target may, for example, be arranged at said inclination angle relative to an object plane of the x-ray imaging system.

[0318] In embodiments, the inclination angle can be even smaller than 5° or can be even larger than 45° (e.g., even up to 80° or 89°).

[0319] According to a further embodiment, the at least one x-ray target has a length with respect to its longitudinal axis that is larger by a factor of 2 or more, 5 or more, 10 or more, 20 or more, 50 or more and / or 100 or more than any of its one¬ dimensional cross -section sizes of its cross -section perpendicular to the longitudinal axis.

[0320] The smaller the one -dimensional cross-section sizes of the at least one x-ray target, the smaller the spot size of the x-ray source is and, hence, the higher the spatial resolution of the x-ray imaging system is.

[0321] Furthermore, a larger length of the at least one x-ray target provides a larger volume for generating x-rays and, thus, a higher power output of the x-ray source.Carl Zeiss SMT GmbH

[0322] 33

[0323] Hence, by choosing the dimensions of the at least one x-ray target a trade-off between source spot size (and, hence, spatial resolution) and target volume (and, hence, x-ray power and throughput) can be made.

[0324] The one-dimensional cross-section sizes include a side length of a square (in case of a squared cross section), a diameter (in case of a circular cross section), side lengths of a rectangular (in case of a rectangular cross section) and a semiaxis, e.g., semimajor axis, of an ellipse (in case of an elliptic cross -section).

[0325] According to a further embodiment,

[0326] a length of the at least one x-ray target is between 2 μm and 10 μm, between 3 μm and 8 μm and / or between 4 μm and 5 μm, and / or

[0327] one-dimensional cross-section sizes of the at least one x-ray target are 2 μm or smaller, 1 μm or smaller, 500 nm or smaller, 300 nm or smaller, 100 nm or smaller and / or 50 nm or smaller.

[0328] The length of the at least one target is its length with respect to its longitudinal axis. Further, the one- dimensional cross-section sizes are one -dimensional sizes of a cross-section of the at least one x-ray target, wherein the cross-section is perpendicular to the longitudinal axis.

[0329] By having a larger length of the at least one x-ray target, x-rays are generated in a larger volume (higher power output of the x-ray source). However, there is a limit with respect to a maximum distance that the x-rays can travel through the at least one x-ray source. Hence, an upper limit for the length of 10 μm, 8 μm and / or 5 μm may be suitable with respect to this maximum travel distance.

[0330] According to a further embodiment, the vacuum window and / or a carrier element carrying the at least one x-ray target comprises lateral surfaces, the x-ray source comprises heat dissipation elements in contact with the lateral surfaces, and the vacuum window and / or the carrier element is configured for dissipating heat transmitted from the at least one x-ray target and for transmitting the heat to the lateral surfaces.

[0331] Thus, heat generated in the at least one x-ray target by the impacting electron beam can be transmitted to the vacuum window and / or the carrier element and dissipated to the dissipation elements. The dissipation elements (e.g., copper elements) are, for example, in contact with a water bath for cooling.Carl Zeiss SMT GmbH

[0332] 34

[0333] For example, in case that the carrier element forms the vacuum window, the carrier element comprises the lateral surfaces connecting its outer surface with its inner surface, the x-ray source comprises the heat dissipation elements in contact with portions of the lateral surfaces that are arranged outside of the vacuum chamber, and the at least one carrying surface of the inner surface of the carrier element is configured for absorbing heat transmitted from the at least one x-ray target and for transmitting the heat to the lateral surfaces.

[0334] A thickness of the vacuum window and / or of the carrier element in a direction perpendicular to the outer surface is, for example, sufficiently large (e.g., 100 μm or larger, 200 μm or larger, 250 μm or larger and / or 300 μm or larger) to provide a good heat dissipation.

[0335] The lateral surfaces of the vacuum window and / or the carrier element are arranged, for example, perpendicular to the outer surface of the vacuum window.

[0336] According to a further embodiment, the carrier element comprises at least one notch, and the at least one notch comprises the at least one carrying surface for carrying the at least one x-ray target such that the at least one x-ray target is arranged in the at least one notch.

[0337] Thus, the at least one target is partly embedded in the carrier element.

[0338] Therefore, a larger surface of the at least one target is in contact with the carrier element which improves heat dissipation from the at least one target to the carrier element.

[0339] According to a further embodiment, the x-ray source comprises a plurality of the x-ray targets, wherein the inner surface of the carrier element comprises a plurality of the carrying surfaces carrying the plurality of x-ray targets, respectively, and the plurality of x-ray targets and its corresponding carrying surfaces are arranged in a one- dimensional or a two-dimensional array as viewed in a direction perpendicular to the outer surface of the vacuum window.

[0340] By having a plurality of x-ray targets on the carrier element, another x-ray target can be easily selected and used in case that an already used x-ray target became unusable.

[0341] The plurality of x-ray targets arranged in said array are, for example, separate x-ray targets which are spaced apart from each other on the carrier element.Carl Zeiss SMT GmbH

[0342] 35

[0343] The x-ray source comprises, for example, 50 or more x-ray targets, 100 or more x-ray targets and / or 1000 or more x-ray targets.

[0344] The plurality of x-ray targets are, for example, arranged in a one -dimensional or a two-dimensional array as viewed from a sample mount of the x-ray imaging system.

[0345] The plurality of x-ray targets may have all the same properties with respect to their geometric shape, length, one-dimensional cross-section sizes, inclination angles or may differ from each other.

[0346] According to a further embodiment, the inner surface of the carrier element has a sawtooth shape, each sawtooth of the sawtooth shape comprises a first surface region inclining with a first inclination towards the outer surface and a second surface region declining from the first surface region with a second inclination away from the outer surface, an absolute value of the second inclination is larger than an absolute value of the first inclination, and each first surface region of the sawtooth shape comprises a respective one of the carrying regions for carrying a respective one of the x-ray targets.

[0347] According to a further embodiment, the electron source is configured to direct the electron beam to a respective one of the plurality of x-ray targets to select it as current x-ray target.

[0348] Thus, a specific one of the plurality of x-ray targets can be easily selected solely by electronic control of the electron source.

[0349] The electron source has, for example, electron optics to direct the electron beam to a specific one of the plurality of x-ray targets.

[0350] According to a further embodiment, two, more or all of the plurality of x-ray targets differ from each other with respect to their length, their one -dimensional cross-section sizes and / or the inclination angle of their longitudinal axes relative to the outer surface of the carrier element.

[0351] Hence, by selecting an x-ray target with a specific length and one- dimensional cross-section sizes, a trade-off can be selected between spatial resolution and throughput. By selecting an x-ray target with a specific inclination angle, a suitable inclination angle, e.g., with respect to a region of interest of the sample, can be selected.Carl Zeiss SMT GmbH

[0352] 36

[0353] That two, more or all of the plurality of x-ray targets differ from each other with respect to the inclination angle of their longitudinal axes relative to the outer surface of the carrier element means also that two, more or all of the plurality of carrying surfaces differ from each other with respect to their inclination angles relative to the outer surface.

[0354] According to a further aspect, an x-ray imaging system for imaging a sample is provided. The x-ray imaging system comprises the above-described x-ray source.

[0355] According to an embodiment of the further aspect, the x-ray imaging system comprises a position -sensitive x-ray detector for detecting x-rays propagated along an x-ray propagation axis from the x-ray source through a region of interest of the sample to the x-ray detector. Furthermore, the x-ray imaging system is configured for arranging the x-ray propagation axis:

[0356] parallel to the at least one carrying surface of the x-ray source and / or coinciding with the longitudinal axis of the at least one x-ray target of the x-ray source.

[0357] The x-ray detector is configured for detecting x-rays transmitted through the region of interest of the sample. The position -sensitive x-ray detector is, for example, configured to convert the incoming x-rays into light of longer wavelength, e.g., UV-light, visible light or infrared light. The x-ray detector includes, for example, a scintillator material at a transfer field of the detector for converting the x-rays into detectable light and a two-dimensional detector array (e.g., a CCD or CMOS array) for detecting the detectable light. The two-dimensional detector array is, for example, arranged perpendicular to the x-ray propagation axis. A pixel size of the x-ray detector is, for example, 0.5 pm or smaller, 0.3 μm or smaller and / or 0.1 μm or smaller.

[0358] According to a further embodiment of the further aspect, the x-ray imaging system comprises a sample mount with a support surface for supporting the sample, the support surface defining an object plane of the x-ray imaging system, In addition, the at least one carrying surface of the carrier element of the x-ray source and / or the longitudinal axis of the at least one x-ray target of the x-ray source is / are inclined by an inclination angle of 5° or larger, 10° or larger, 20° or larger, 30° or larger and / or 45° or larger relative to the object plane, and / or the outer surface of the vacuum window is arranged parallel to the object plane.Carl Zeiss SMT GmbH

[0359] 37

[0360] According to a further embodiment of the further aspect, the x-ray imaging system comprises a sample mount for supporting the sample rotatably around a rotation axis, wherein the x-ray imaging system is configured for obtaining two- dimensional transmission images of the region of interest of the sample for different rotation angles of the sample with respect to the rotation axis, and for reconstructing a three-dimensional image of the region of interest based on the two-dimensional transmission images.

[0361] The x-ray imaging system comprises, for example, a control device for reconstructing the three-dimensional images.

[0362] For example, the x-ray imaging system is configured for obtaining two- dimensional transmission images of the region of interest of the sample for different rotation angles of the sample with respect to the rotation axis, wherein the rotation angles span a large angular range of, for example, 180° or larger, 270° or larger and / or 360°.

[0363] The embodiments and features described with reference to the x-ray source of the present invention apply mutatis mutandis to the x-ray imaging system of the present invention.

[0364] Further possible implementations or alternative solutions of the invention also encompass combinations – that are not explicitly mentioned herein – of features described above or below with regard to the embodiments. The person skilled in the art may also add individual or isolated aspects and features to the most basic form of the invention.

[0365] Further embodiments, features and advantages of the present invention will become apparent from the subsequent description and dependent claims, taken in conjunction with the accompanying drawings, in which:

[0366] Fig. B#1 shows a schematic view of an x-ray imaging system for imaging a sample according to an embodiment;

[0367] Fig. B#2 shows an x-ray source of the x-ray imaging system of Fig. B#1

[0368] according to an embodiment;

[0369] Fig. B#3 shows a carrier element with x-ray targets of the x-ray source of Fig. B#2 according to an embodiment;Carl Zeiss SMT GmbH

[0370] 38

[0371] Fig. B#4 shows an x-ray target of the x-ray source of Fig. B#3 in a perspective view;

[0372] Fig. B#5 shows an enlarged cut-out V of the Fig. B#3 displaying a carrying surface of the carrier element with an x-ray target;

[0373] Fig. B#6 shows a view similar as Fig. B#5, wherein the carrier element comprises a notch in which the x-ray target is embedded; and

[0374] Fig. B#7 shows a carrier element with a plurality x-ray targets of the x-ray source of Fig. B#2 according to a further embodiment.

[0375] In the Figures, like reference numerals designate like or functionally equivalent elements, unless otherwise indicated.

[0376] Fig. B#1 shows a schematic view of an x-ray imaging system B#100 according to an embodiment. The x-ray imaging system B#100 is used for imaging a sample B#102, in particular a region of interest B#104 of the sample B#102. The x-ray imaging system B#100 is configured to obtain two-dimensional transmission images B#106 of the region of interest B#104 for different rotation angles B#a of the sample B#102. Based on the two-dimensional transmission images B#106, a three-dimensional (3D) image B#108 of the region of interest B#104 is reconstructed to reveal interior structures of the region of interest B#104. The x-ray imaging system B#100 is, hence, an x-ray 3D imaging system obtaining 3D images B#108 by x-ray laminography and / or x-ray tomography.

[0377] The sample B#102 is, for example, a flat object extended in a main plane (e.g., the B#xB#y-plane in Fig. B#1). The sample B#102 is, for example, a wafer B#110 comprising electronic and / or semiconductor components. Just as an example, the x-ray imaging system B#100 may be used to inspect the wafer B#110 to investigate the quality of packaging of electronic components of the wafer B#110. For example, the quality of mechanical and electrical bonding (e.g., buried interconnections) of the electronic components may be controlled.

[0378] The x-ray imaging system B#100 comprises an x-ray source B#112 for emitting x-rays B#114. The x-rays B#114 are emitted from a source region B#116 of the x-ray source B#112. The reference sign B#S denotes a spot size of the source region B#116. The x-ray source B#112 emits a diverging beam B#118 of x-rays B#114. In other words, the x-ray source B#112 emits a cone B#120 of x-rays B#114. The sample B#102 is arranged within the x-ray emission cone B#120.Carl Zeiss SMT GmbH

[0379] 39

[0380] The x-ray imaging system B#100 further comprises a sample mount B#122 for supporting the sample B#102 rotatably around a rotation axis B#124. The rotation axis B#124 passes, for example, through the region of interest B#104 of the sample B#102. In particular, the rotation axis B#124 can be arranged off- center with respect to a center of the sample B#102. A rotation drive B#126 for rotating the sample mount B#122 and, hence, the sample B#102, is shown schematically in Fig. B#1. Furthermore, the sample mount B#122 has a support surface B#128 for supporting the sample B#102, wherein the support

[0381] surface B#128 defines an object plane B#130 of the x-ray imaging system B#100.

[0382] The x-ray imaging system B#100 may further comprise, for example, a shield stop B#132 arranged between the x-ray source B#112 and the sample mount B#122. The shield stop B#132 is, in particular, arranged in a light path of the x-rays B#114 emitted from the x-ray source B#112. The shield stop B#132 serves to select a usable portion B#134 of the x-ray cone B#120. Moreover, the shield stop B#132 protects uninspected regions of the sample B#102 from x-ray exposure. The shield stop B#132 has an aperture B#136 through which the usable portion B#134 (sub cone B#134) of the x-ray light B#114 (B#114') propagates in the direction of the region of interest B#104 of the sample B#102 and transmits the region of interest B#104 of the sample B#102.

[0383] The x-ray imaging system B#100 further comprises a position -sensitive x-ray detector B#138 for detecting x-rays B#114" transmitted through the region of interest B#104 of the sample B#102. The position -sensitive x-ray detector B#138 is, for example, configured to convert the incoming x-rays B#114" into light of longer wavelength, e.g., UV-light, visible light or infrared light. The x-ray detector B#138 includes, for example, a scintillator material at a transfer field of the detector B#138 for converting the x-rays B#114" into detectable light and a detector array B#138 (e.g., a CCD or CMOS array) for detecting the detectable light.

[0384] Fig. B#1 displays an x-ray propagation axis B#140 of the x-ray imaging system B#100. In particular, a central axis of the portion B#134 (sub light cone B#134) of the x-ray light B#114 passing through the shield stop B#132 defines the x-ray propagation axis B#140. The x-ray propagation axis B#140 extends from the x-ray source B#112 (i.e., the source region B#116 of the x-ray source B#112), through the region of interest B#104 of the sample B#102, and to the positionsensitive x-ray detector B#138.Carl Zeiss SMT GmbH

[0385] 40

[0386] As can be seen in Fig. B#1, the x-ray propagation axis B#140 of the x-ray imaging system B#100 is, in particular, inclined with respect to a surface normal B#142 of the sample mount B#122 by a first angle B#β. In addition, the x-ray propagation axis B#140 is, in particular, inclined with respect to the rotation axis B#124 by a second angle B#γ. In the example of Fig. B#1, the surface normal B#142 of the sample mount B#122 and the rotation axis B#124 are arranged parallel to each other and, hence, the first angle B#β and the second angle B#γ have the same size.

[0387] The x-ray exposures B#106 obtained at different rotation angles B#a of the sample B#102 are reconstructed to a 3D image B#108 by a control system B#144 of the imaging system B#100.

[0388] The x-ray imaging system B#100 provides microscopic imaging. A magnification and, hence, a spatial resolution, of the x-ray imaging system B#100 depends on the size of the source region B#116 of the x-ray source B#112.

[0389] Moreover, an imaging time necessary to obtain a 3D image B#108 of the region of interest B#104 of the sample B#102 depends on the x-ray flux density at the region of interest B#104. Said imaging time limits, for example, a throughput rate when imaging multiple samples B#102 with the x-ray imaging system B#100.

[0390] Fig. B#2 shows an x-ray source B#200 for the x-ray imaging system B#100 of Fig. B#1. The x-ray source B#200 comprises a vacuum chamber B#202. The x-ray source B#200 further comprises an x-ray transmissive carrier element B#204 forming a vacuum window B#206 of the vacuum chamber B#202. The carrier element B#204 is, for example, made from diamond or another suitable material.

[0391] In the embodiments shown in the figures and described in the figure description, the x-ray transmissive carrier element B#204 forms the vacuum window B#206 of the vacuum chamber B#202. It is noted that in other embodiments (not shown), the x-ray transmissive carrier element B#204 and the vacuum window B#206 may be two separate components. In such an embodiment, the x-ray transmissive carrier element B#204 may be arranged at and / or attached to the vacuum window B#206.

[0392] The carrier element B#204 carries at least one x-ray target B#208. In the example of Fig. B#2 four x-ray targets B#208 are shown. However, the carrier element B#204 may also carry only one x-ray target B#208 or may carry moreCarl Zeiss SMT GmbH

[0393] 41

[0394] (e.g., many more) than four x-ray targets B#208 (e.g., 100 x-ray targets B#208 or another number of x-ray targets B#208). The at least one x-ray target B#208 is, for example, made from tungsten or another suitable material.

[0395] It is noted that the carrier element B#204 and the x-ray targets B#208 are shown at an exaggerated scale in the figures for illustration purposes.

[0396] The x-ray source B#200 further comprises an electron source B#210 accommodated in the vacuum chamber B#202. The electron source B#210 is configured for emitting a focused electron beam B#212 towards the x-ray target B#208 (e.g., to a selected one of a plurality of x-ray targets B#208). The impacting electron beam B#212 causes the (selected) x-ray target B#208 to emit x-rays B#214 through the vacuum window B#206 formed by the carrier element B#204. The electron source B#210 comprises, for example, electron optics B#216 for focusing and directing the electron beam B#212 to the (selected) x-ray target B#208.

[0397] The carrier element B#204 has a flat outer surface B#218. The outer surface B#218 is facing an exterior space B#220 of the vacuum chamber B#202. The outer surface B#218 is, for example, facing the sample mount B#122 of the x-ray imaging system B#100. Moreover, the outer surface B#218 is, for example, arranged parallel to an object plane B#130 of the x-ray imaging system B#100.

[0398] The carrier element B#204 has an inner surface B#222 arranged opposite its outer surface B#218. The inner surface B#222 is facing an interior space B#224 of the vacuum chamber B#202. The at least one x-ray target B#208 is carried by the inner surface B#222 of the carrier element B#204, as can be seen in Fig. B#3. In particular, the inner surface B#222 comprises at least one carrying surface B#226 carrying the at least one x-ray target B#208. In the example of Figs. B#2, B#3, the inner surface B#222 comprises five carrying surfaces B#226 each carrying one x-ray target B#208. However, also more than five carrying surfaces B#226 or less than five carrying surfaces B#226 can be provided.

[0399] The at least one carrying surface B#226 of the carrier element B#204 is inclined relative to the outer surface B#218 of the carrier element B#204 by an inclination angle B#6. The inclination angle B#6 has, for example, a value of 20°. However, the inclination angle B#6 can also have a value different from 20°. Since a longitudinal axis B#A of the at least one elongated x-ray target B#208 is arranged parallel to the at least one carrying surface B#226, also the at least oneCarl Zeiss SMT GmbH

[0400] 42

[0401] x-ray target B#208 is inclined relative to the outer surface B#218 of the carrier element B#204 by said inclination angle B#δ.

[0402] The outer surface B#218 of the carrier element B#204 may be arranged parallel to the object plane B#130 of the x-ray imaging system B#100. In this case, the at least one carrying surface B#226 of the carrier element B#204 and the longitudinal axis B#A of the at least one x-ray target B#208 are inclined by said inclination angle relative to the object plane B#130.

[0403] As shown in Fig. B#3, the carrier element B#204 may have a height B#H1 in a B#z-direction (e. g., a direction perpendicular to the outer surface B#218) which is, for example, 100 μm or larger, 200 μm or larger, 250 μm or larger, 300 μm or larger and / or 400 μm or larger. Further, the indentations of the carrier element B#204 which form the inclined carrying surfaces B#226, may have a height B#H2 in the B#z-direction of, for example, 5 μm or smaller, 3 μm or smaller, 2 μm or smaller and / or 1 μm or smaller.

[0404] Fig. B#4 shows a perspective view of one of the x-ray targets B#208 of Fig. B#3. The x-ray target B#208 has as an example a cylindrical geometric shape B#228 with a squared footprint B#230. The reference sign B#L denotes a length of the at least one elongated x-ray target B#208 with respect to its longitudinal axis B#A. Further, the reference signs B#B, B#C each denotes a side length of the squared footprint (here B#B = B#C, since it is a square) of the at least one elongated x-ray target B#208. However, the x-ray targets B#208 of the x-ray source B#200 can also have a different geometric shape. In any case, a length B#L of the at least one elongated x-ray target B#208 is much larger than any of its one- dimensional cross-section sizes B#B, B#C of its cross-section perpendicular to the longitudinal axis B#A. The length B#L is, for example, 20 times larger than any of its one¬ dimensional cross-section sizes B#B, B#C. However, the at least one elongated x-ray target B#208 may also have another ratio of its length B#L and one¬ dimensional cross-section sizes B#B, B#C than 20.

[0405] Just as an example, is a length of the at least one x-ray target B#208 5 μm and is the one-dimensional cross-section size B#B, B#C of the at least one x-ray target B#208 300 nm. However, also different numbers can be applied for these dimensions B#L, B#B, B#C.

[0406] As displayed in Figs. B#2 and B#3, having the described configuration of the carrier element B#204 with the inclined carrying surfaces B#226 and the inclined elongated x-ray targets B#208 allows an advantageous use of the x-ray sourceCarl Zeiss SMT GmbH

[0407] 43

[0408] B#200 in the imaging system B#100. In particular, the at least one carrying surface B#226 of the carrier element B#204 can be arranged parallel to the x-ray propagation axis B#140 of the x-ray imaging system B#100. Further, the longitudinal axis B#A of the at least one x-ray target B#208 can be arranged such that it coincides with the x-ray propagation axis B#140 of the x-ray imaging system B#100. Thus, with such an arrangement the spot size B#S of the source region B#116 (Fig. B#l) is defined by the cross-section area B#232 (Fig. B#4) of the at least one x-ray target B#208. Since the cross-section area B#232 is small, the spatial resolution of the x-ray imaging system B#100 is high (e.g., sufficient to resolve 300 nm large structures of the sample B#102). Nevertheless, x-rays B#114, B#214 can be generated in the whole volume B#V of the at least one x-ray target B#208 and emitted through the cross-section area B#232 along the x-ray propagation axis B#140. Therefore, the x-ray source B#200 can output a large x-ray flux.

[0409] As shown in Fig. B#3, the carrier element B#204 can be used for dissipating heat from the at least one x-ray target B#208. In particular, the carrier element B#204 comprises lateral surfaces B#234 connecting the outer surface B#218 with the inner surface B#222. The x-ray source B#200 further comprises heat dissipation elements B#236 in contact with portions B#238 of the lateral surfaces B#234 that are arranged outside of the vacuum chamber B#202 (Fig. B#2). Furthermore, the at least one carrying surface B#226 of the inner surface B#222 of the carrier element B#204 is configured for absorbing heat transmitted from the at least one x-ray target B#208 and for transmitting the heat to the lateral surfaces B#234 and to the heat dissipation elements B#236. The heat dissipation elements B#236 may be in contact with a water bath (not shown) or the like for cooling.

[0410] Fig. B#5 shows an enlarged cut-out V from Fig. B#3. In Fig. B#5, a portion of the inner surface B#222 of the carrier element B#204 is shown. In particular, in Fig. B#5 one of the carrying surfaces B#226 of the inner surface B#222 are visible. Further, one of the x-ray targets B#208 arranged on the carrying surfaces B#226 is displayed in Fig. B#5.

[0411] Fig. B#6 shows a view similar as Fig. B#5, but with an inner surface B#222' of a carrier element B#204' configured according to a further embodiment. In particular, the carrier element B#204' comprises at least one notch B#240.

[0412] Further, the at least one notch B#240 comprises the at least one carrying surface B#226' for carrying the at least one x-ray target B#208 such that the at least one x-ray target B#208 is arranged in the at least one notch B#240.Carl Zeiss SMT GmbH

[0413] 44

[0414] By arranging the at least one x-ray target B#208 in the at least one notch B#240, a cooling of the at least one x-ray target B#208 can be improved since a larger surface B#242 of the at least one x-ray target B#208 is in contact with the carrier element B#204' for heat dissipation.

[0415] As shown in Figs. B#2 and B#3, the x-ray source B#200 can comprise a plurality of x-ray targets B#208 carried by a plurality of carrying surfaces B#226, each carrying surfaces B#226 being inclined with respect to the outer surface B#218 and, for example, also inclined with respect to the object plane B#130. Hence, in the inner surface B#222 of the carrier element B#204 can have a sawtooth shape B#244, as can be seen in Fig. B#3. Each sawtooth B#246 (one of them is denoted with a reference sign in Fig. B#3) of the sawtooth shape B#244 comprises a first surface region B#248 inclining with a first inclination B#250 (angle B#δ) towards the outer surface B#218. Further, each sawtooth B#246 comprises a second surface region B#252 declining from the first surface region B#248 with a second inclination B#254 (angle B#ε) away from the outer surface B#218. An absolute value of the second inclination B#254 is larger than an absolute value of the first inclination B#250. In addition, each first surface region B#248 of the sawtooth shape B#244 comprises a respective one of the carrying regions B#226 for carrying a respective one of the x-ray targets B#208.

[0416] Fig. B#7 shows a bottom view (view in positive B#z-direction in Fig. B#3) of a carrier element B#204" according to a further embodiment. The inner surface B#222" of the carrier element B#204" comprises a plurality of carrying surfaces carrying a plurality of x-ray targets B#208 (two of them are denoted with a reference sign in Fig. B#7), respectively. As can be seen in Fig. B#7, the plurality of x-ray targets B#208 and their corresponding carrying surfaces (not visible in Fig. B#7 because they are arranged below the x-ray targets B#208) are arranged in a two-dimensional array B#256 as viewed in a direction B#z perpendicular to the outer surface B#218 (Fig. B#3) of the carrier element B#204".

[0417] The x-ray targets B#208 of the array B#256 can have all the same properties. Alternatively, two, more or all of the plurality of x-ray targets B#208 may differ from each other with respect to their length B#L1, B#L2, B#L3, their one¬ dimensional cross-section sizes B#B1, B#B2, B#B3, B#C1, B#C2, B#C3 and / or the inclination angle B#61, B#62, B#63 of their longitudinal axes B#A (Fig. B#3) relative to the outer surface B#218 of the carrier element B#204, B#204". Such different properties are indicated for some of the of x-ray targets B#208 in Fig. B#7 by reference signs. Hence, by selecting a specific x-ray target B#208 with a specific length B#L1 and specific one- dimensional cross-section sizesCarl Zeiss SMT GmbH

[0418] 45

[0419] B#B1, B#C1, a trade-off can be selected between the spatial resolution and the throughput of the imaging system B#100. In addition, by selecting an x-ray target B#208 with a specific inclination angle B#δ1, a suitable inclination angle, e.g., with respect to a region of interest B#104 of the sample B#102, can be selected.

[0420] Further aspects of the invention are disclosed in the following clauses:

[0421] B#l. An x-ray source (B#200) for an x-ray imaging system (B#100), comprising a vacuum chamber (B#202) with a vacuum window (B#206) including a flat outer surface (B#218),

[0422] at least one elongated x-ray target (B#208) arranged inside the chamber (B#202) such that its longitudinal axis (B#A) is inclined relative to the outer surface (B#218), and

[0423] an electron source (B#210) for emitting a focused electron beam (B#212) towards the x-ray target (B#208) causing the x-ray target (B#208) to emit x-rays (B#214) through the vacuum window (B#206).

[0424] B#2. The x-ray source according to clause B#l, comprising an x-ray transmissive carrier element (B#204), wherein the carrier element (B#204) includes at least one carrying surface (B#226) carrying the at least one x-ray target (B#208), and the longitudinal axis of the at least one x-ray target (B#208) is arranged parallel to the at least one carrying surface (B#226).

[0425] B#3. The x-ray source according to clause B#2, wherein

[0426] the carrier element (B#204) forms the vacuum window (B#206), the carrier element (B#204) including the flat outer surface (B#218) and an inner surface (B#222) comprising the at least one carrying surface (B#226), or

[0427] the carrier element (B#204) is a separate component from the vacuum window (B#206).

[0428] B#4. The x-ray source according to any of clauses B#1 to B#3, wherein the x-ray source (B#200) is configured to be arranged in the x-ray imaging system (B#100) such that

[0429] the at least one carrying surface (B#226) of the carrier element (B#204) is arranged parallel to an x-ray propagation axis (B#140) of the x-ray imaging system (B#100), and / or

[0430] the longitudinal axis (B#A) of the at least one x-ray target (B#208) coincides with the x-ray propagation axis (B#140) of the x-ray imaging system (B#100).Carl Zeiss SMT GmbH

[0431] 46

[0432] B#5. The x-ray source according to any of clauses B#1 to B#4, wherein the at least one carrying surface (B#226) of the carrier element (B#204) and / or the longitudinal axis (B#A) of the at least one x-ray target (B#208) is / are inclined by an inclination angle (B#5) of 5° or larger, 10° or larger, 20° or larger, 30° or larger and / or 45° or larger relative to the outer surface (B#218) of the vacuum window (B#206).

[0433] B#6. The x-ray source according to any of clauses B#1 to B#5, wherein the at least one x-ray target (B#208) has a length (B#L) with respect to its longitudinal axis (B#A) that is larger by a factor of 2 or more, 5 or more, 10 or more, 20 or more, 50 or more and / or 100 or more than any of its one- dimensional cross¬ section sizes (B#B, B#C) of its cross-section perpendicular to the longitudinal axis (B#A).

[0434] B#7. The x-ray source according to any of clauses B#1 to B#6, wherein

[0435] a length (B#L) of the at least one x-ray target (B#208) is between 2 μm and 10 μm, between 3 μm and 8 μm and / or between 4 μm and 5 μm, and / or

[0436] one-dimensional cross-section sizes (B#B, B#C) of the at least one x-ray target (B#208) are 2 μm or smaller, 1 μm or smaller, 500 nm or smaller, 300 nm or smaller, 100 nm or smaller and / or 50 nm or smaller.

[0437] B#8. The x-ray source according to any of clauses B#1 to B#7, wherein the vacuum window (B#206) and / or a carrier element (B#204) carrying the at least one x-ray target (B#208) comprises lateral surfaces (B#234), the x-ray source (B#200) comprises heat dissipation elements (B#236) in contact with the lateral surfaces (B#234), and the vacuum window (B#206) and / or the carrier element (B#204) is configured for dissipating heat transmitted from the at least one x-ray target (B#208) and for transmitting the heat to the lateral surfaces (B#234).

[0438] B#9. The x-ray source according to any of clauses B#2 to B#8, wherein the carrier element (B#204') comprises at least one notch (B#240), and the at least one notch (B#240) comprises the at least one carrying surface (B#226') for carrying the at least one x-ray target (B#208) such that the at least one x-ray target (B#208) is arranged in the at least one notch (B#240).

[0439] B#10. The x-ray source according to any one of clauses B#2 to B#9, comprising a plurality of the x-ray targets (B#208), wherein the inner surface (B#222") of the carrier element (B#204") comprises a plurality of the carrying surfaces (B#226) carrying the plurality of x-ray targets (B#208), respectively, and the plurality of x-ray targets (B#208) and its corresponding carrying surfaces (B#226) areCarl Zeiss SMT GmbH

[0440] 47

[0441] arranged in a one-dimensional or a two-dimensional array (B#256) as viewed in a direction (B#z) perpendicular to the outer surface (B#218) of the vacuum window (B#206).

[0442] B#11. The x-ray source according to clause B#10, wherein the inner surface (B#222, B#222") of the carrier element (B#204, B#204") has a sawtooth shape (B#244), each sawtooth (B#246) of the sawtooth shape (B#244) comprises a first surface region (B#248) inclining with a first inclination (B#250) towards the outer surface (B#218) and a second surface region (B#252) declining from the first surface region (B#248) with a second inclination (B#254) away from the outer surface (B#218), an absolute value of the second inclination (B#254) is larger than an absolute value of the first inclination (B#250), and each first surface region (B#248) of the sawtooth shape (B#244) comprises a respective one of the carrying regions (B#226) for carrying a respective one of the x-ray targets (B#208).

[0443] B#12. The x-ray source according to clause B#10 or B#ll, wherein the electron source (B#210) is configured to direct the electron beam (B#212) to a respective one of the plurality of x-ray targets (B#208) to select it as current x-ray target (B#208).

[0444] B#13. The x-ray source according to any one of clauses B#10 to B#12, wherein two, more or all of the plurality of x-ray targets (B#208) differ from each other with respect to their length (B#L1, B#L2, B#L3), their one- dimensional cross¬ section sizes (B#B1, B#B2, B#B3, B#C1, B#C2, B#C3) and / or the inclination angle (B#61, B#62, B#63) of their longitudinal axes (B#A) relative to the outer surface (B#218) of the carrier element (B#204).

[0445] B#14. An x-ray imaging system (B#100) for imaging a sample (B#102), comprising an x-ray source (B#200) according to any one of clauses B#1 to B#13.

[0446] B#15. The x-ray imaging system according to clause B#14, comprising a positionsensitive x-ray detector (B#138) for detecting x-rays (B#114") propagated along an x-ray propagation axis (B#140) from the x-ray source (B#112, B#200) through a region of interest (B#104) of the sample (B#102) to the x-ray detector (B#138), wherein the x-ray imaging system (B#100) is configured for arranging the x-ray propagation axis (B#140)

[0447] parallel to the at least one carrying surface (B#226) of the x-ray source (B#200) and / orCarl Zeiss SMT GmbH

[0448] 48

[0449] coinciding with the longitudinal axis (B#A) of the at least one x-ray target (B#208) of the x-ray source (B#200).

[0450] B#16. The x-ray imaging system according to clause B#14 or B#15, comprising a sample mount (B#122) with a support surface (B#128) for supporting the sample (B#102), the support surface (B#128) defining an object plane (B#130) of the x-ray imaging system (B#100), wherein

[0451] the at least one carrying surface (B#226) of the carrier element (B#204) of the x-ray source (B#200) and / or the longitudinal axis (B#A) of the at least one x-ray target (B#208) of the x-ray source (B#200) is / are inclined by an inclination angle (B#5) of 5° or larger, 10° or larger, 20° or larger, 30° or larger and / or 45° or larger relative to the object plane (B#130), and / or

[0452] the outer surface (B#218) of the vacuum window (B#206) is arranged parallel to the object plane (B#130).

[0453] B#17. The x-ray imaging system according to any one of clauses B#14 to B#16, comprising a sample mount (B#122) for supporting the sample (B#102) rotatably around a rotation axis (B#124), wherein the x-ray imaging system (B#100) is configured for obtaining two-dimensional transmission images (B#106) of the region of interest (B#104) of the sample (B#102) for different rotation angles (B#α) of the sample (B#102) with respect to the rotation axis (B#124), and for reconstructing a three-dimensional image (B#108) of the region of interest (B#104) based on the two-dimensional transmission images (B#106).

[0454] Although the present invention has been described in accordance with preferred embodiments, it is obvious for the person skilled in the art that modifications are possible in all embodiments.Carl Zeiss SMT GmbH

[0455] 49 REFERENCE NUMERALS

[0456] B#100 System

[0457] B#102 Sample

[0458] B#104 Region of interest

[0459] B#106 2D-Image

[0460] B#108 3D-Image

[0461] B#110 Wafer

[0462] B#112 Source

[0463] B#114 X-ray

[0464] B#114', B#114" X-ray

[0465] B#116 Source region

[0466] B#118 Beam

[0467] B#120 Cone

[0468] B#122 Mount

[0469] B#124 Axis

[0470] B#126 Rotation drive

[0471] B#128 Surface

[0472] B#130 Plane

[0473] B#132 Shield stop

[0474] B#134 Portion

[0475] B#136 Aperture

[0476] B#138 Detector

[0477] B#140 Axis

[0478] B#142 Surface normal

[0479] B#144 Control system

[0480] B#200 Source

[0481] B#202 Vacuum chamber

[0482] B#204 Carrier element

[0483] B#204', B#204" Carrier element

[0484] B#206 Window

[0485] B#208 Target

[0486] B#210 Source

[0487] B#212 Beam

[0488] B#214 X-ray

[0489] B#216 Optics

[0490] B#218 Outer surface

[0491] B#220 Exterior space

[0492] B#222 Inner surfaceCarl Zeiss SMT GmbH

[0493] 50

[0494] B#222', B#222" Inner surface B#224 Interior space B#226, B#226' Carrying surface B#228 Shape

[0495] B#230 Footprint

[0496] B#232 Area

[0497] B#234 Lateral surface B#236 Element

[0498] B#238 Portion

[0499] B#240 Notch

[0500] B#242 Surface

[0501] B#244 Sawtooth shape B#246 Sawtooth

[0502] B#248 Surface region B#250 Inclination

[0503] B#252 Surface region B#254 Inclination

[0504] B#256 Array

[0505] B#α Angle

[0506] B#β Angle

[0507] B#γ Angle

[0508] B#δ Angle

[0509] B#δ1-B#δ3 Inclination angle B#ε Angle

[0510] B#A Axis

[0511] B#B Size

[0512] B#B1-B#B3 Size

[0513] B#C Size

[0514] B#C1-B#C3 Size

[0515] B#H1, B#H2 Height

[0516] B#L Length

[0517] B#L1-B#L3 Length

[0518] B#S Size

[0519] B#V Volume

[0520] B#X Direction

[0521] B#Y DirectionCarl Zeiss SMT GmbH 51

[0522] B#Z DirectionCarl Zeiss SMT GmbH

[0523] 52

[0524] X-RAY SOURCE FOR AN X-RAY IMAGING SYSTEM, X-RAY IMAGING SYSTEM AND METHOD FOR OPERATING AN X-RAY IMAGING SYSTEM

[0525] The present invention relates to an x-ray source for an x-ray imaging system, an x-ray imaging system with such an x-ray source and a method for operating such an x-ray imaging system.

[0526] The contents of the priority applications US 19 / 015,774, US 19 / 015,801 and US 19 / 015,842 is incorporated by reference in its entirety (incorporation by reference).

[0527] X-rays are widely used in microscopy because of their short wavelengths and ability to penetrate objects. Three-dimensional (3D) x-ray imaging techniques are useful to image internal structures of objects. Typically, based on a dataset including x-ray transmission images of a sample that are collected over a large angular range, 3D images are reconstructed. An x-ray imaging system usually comprises a sample mount to support a sample, an x-ray source configured to illuminate a region of interest of the sample, and a position-sensitive x-ray detector configured to record x-rays transmitted through the region of interest of the sample.

[0528] The x-ray flux incident on the region of interest of the sample is inversely proportional to the square of the distance of the region of interest from the x-ray source. To achieve high throughput for x-ray imaging, this distance should be small. In other words, the region of interest of the sample should be placed as close to the x-ray source as possible such that the x-ray flux density at the region of interest is as high as possible. In particular, a high x-ray flux density at the region of interest of the sample implies short exposures times and, hence, a high throughput of a series of samples imaged with the x-ray imaging system.

[0529] It is one object of the present invention to provide an improved x-ray source for an x-ray imaging system, an improved x-ray imaging system and an improved method for operating an x-ray imaging system.

[0530] According to a first aspect, an x-ray source for an x-ray imaging system is provided. The x-ray source comprises:

[0531] a vacuum chamber,

[0532] an electron source accommodated in the chamber for emitting an electron beam, andCarl Zeiss SMT GmbH

[0533] 53

[0534] an x-ray target accommodated in the chamber for generating x-rays when irradiated with the electron beam,

[0535] wherein the x-ray source comprises, with respect to an outer shape thereof, a protruding portion protruding from a remaining portion of the x-ray source, the protruding portion including at its distal end the x-ray target.

[0536] Having the protruding portion with the x-ray target protruding from the remaining portion of the x-ray source allows to arrange the x-ray target of the x-ray source close to a region of interest of a sample which is imaged with the x-ray imaging system. For example, the x-ray target of the x-ray source can be arranged at a distance to the region of interest of the sample of 0.5 mm or smaller, 0.4 mm or smaller, 0.3 mm or smaller, 0.2 mm or smaller, 0.1 mm or smaller and / or 0.05 mm or smaller. Even a physical contact of the x-ray target with the region of interest of the sample (zero distance between the x-ray target and the region of interest) is possible. In particular, with the proposed configuration of the x-ray source, the distance between the x-ray target and the sample is not limited by the outer geometry of the remaining portion (e.g., a magnetic focus lens). Hence, the region of interest of the sample can be arranged very close to the x-ray source. Since the x-ray flux incident on the region of interest is inversely proportional to the square of the distance of the region of interest from the x-ray target, with the proposed configuration a high x-ray flux density at the region of interest of the sample is achieved. A high x-ray flux density at the region of interest implies short exposures times and, therefore, a series of samples can be analyzed quickly with the x-ray imaging system resulting in a high throughput rate.

[0537] Furthermore, the samples analyzed with the proposed x-ray imaging system are, for example, flat extended objects, such as wafers. In cases in which the samples deviate slightly from a flat geometry and are, instead, curved away from the x-ray source (e.g. by a few micrometers), it might be difficult to achieve a small source-sample-distance. Such curved samples may, for example, arise from the energy input when printing different layers (e.g., 50 to 100 layers) of semiconductor circuits onto a wafer as a sample. However, with the proposed x-ray source having the protruding portion holding the x-ray target, a small source- sample-distance is still possible in a case in which the sample is slightly curved away from the x-ray source.

[0538] The x-ray imaging system is configured for imaging a region of interest of a sample. The sample is, for example, a flat extended object. The sample is, for example, a wafer. The wafer includes, for example, electronic and / orCarl Zeiss SMT GmbH

[0539] 54

[0540] semiconductor components. Just as an example, the x-ray imaging system may be used to inspect the wafer to investigate the quality of packaging of electronic components of the wafer. For example, the quality of mechanical and electrical bonding (e.g., buried interconnections) of the electronic components may be controlled. However, the sample may also be another object than a wafer. The sample is, for example, a circuit board or a battery.

[0541] The x-ray imaging system is, in particular, a transmission x-ray imaging system, wherein the x-rays impacting on the region of interest of the sample are partly transmitting through the region of interest and are partly absorbed by the region of interest. The position-dependent transmitted portion of the x-rays is detected by the position-sensitive x-ray detector as a two-dimensional x-ray image.

[0542] The x-ray imaging system is, for example, a three-dimensional imaging system. The x-ray imaging system is, for example, configured to obtain two-dimensional transmission images of the region of interest for different rotation angles of the sample. Based on the two-dimensional transmission images, a three-dimensional image of the region of interest is reconstructed to reveal interior structures of the region of interest. The x-ray imaging system is, for example, an x-ray three- dimensional imaging system obtaining three-dimensional images by x-ray laminography and / or x-ray tomography.

[0543] The x-ray source is, in particular, a transmission target type x-ray source. The electron beam strikes the at least one x-ray target of the x-ray source at its backside and the at least one x-ray target emits x-rays at its front side, the emitted x-rays are used to irradiate the sample.

[0544] The x-ray source generates diverging x-rays, i. e. a cone (conus) of x-rays. A portion (i.e. a sub cone) of the generated diverging x-rays is irradiating the region of interest of the sample. A center line of this sub cone of x-rays is referred herein as x-ray propagation axis. That means the x-ray propagation axis indicates the direction of an x-ray beam which is a portion of the total generated diverging x-rays of the x-ray source.

[0545] The x-ray source comprises the vacuum chamber. The x-ray source comprises, for example, a pump for evacuating the vacuum chamber (or optionally the vacuum chamber and a fluidly connected flight tube).

[0546] The electron source includes, for example, a cathode and an anode and the like for generating electrons and for accelerating the generated electrons.Carl Zeiss SMT GmbH

[0547] 55

[0548] The electron beam may include a line profile which can, for example, hit the x-ray target at least partly.

[0549] The x-ray target is configured for emitting x-rays when bombard with the focused electron beam. A material of the at least one x-ray target comprises, for example, one or more of a group including tungsten (W), copper (Cu), chromium (Cr), molybdenum (Mo), rhodium (Rh) and platinum (Pt). The x-rays generated by the at least one x-ray target include characteristic lines determined by the target's composition and broad bremsstrahlung radiation.

[0550] The x-ray source includes, in particular, a carrier element carrying the x-ray target (or carrying multiple of the x-ray targets which can be selected by directing the electron beam accordingly). The carrier element is, in particular, x-ray transmissive. The carrier element forms, for example, a vacuum window of the flight tube. Alternatively, an additional vacuum window may be provided. A material of the carrier element and / or the vacuum window includes, for example, atomic elements having atomic numbers less than 14. The material of the carrier element and / or the vacuum window includes, for example, one or more of a group including beryllium, diamond, boron carbide, silicon carbide, aluminum, and beryllium oxide. The material of the carrier element and / or the vacuum window is, preferentially, diamond.

[0551] The carrier element and / or the vacuum window being x-ray transmissive means, for example, that it has an x-ray transmission such that more than 50% of the x-rays generated by the at least one x-ray target having energies greater than one-half of the selected maximum focused electron energy are transmitted through the carrier element.

[0552] The carrier element has, for example, a sufficiently high thermal conductivity to provide a thermal conduit to prevent thermal damage (e.g., melting) of the at least one x-ray target.

[0553] The carrier element can, for example, also provide an electrically conductive path to dissipate electric charge from the at least one x-ray target and / or the carrier element itself.

[0554] According to an embodiment, the x-ray source comprises:

[0555] a flight tube fluidly connected at its proximal end to the vacuum chamber for providing a vacuum atmosphere inside the chamber and the tube, andCarl Zeiss SMT GmbH

[0556] 56

[0557] a magnetic focus lens arranged around the flight tube for focusing the electron beam,

[0558] wherein the electron source is configured for emitting the electron beam into the flight tube, the x-ray target is arranged at the distal end of the flight tube, and the distal end of the flight tube is protruding from an outer wall of the magnetic focus lens.

[0559] Having the distal end of the flight tube with the x-ray target protruding from the outer wall of the magnetic focus lens allows an arrangement of the x-ray target close to the region of interest of the sample. In particular, with the proposed configuration of the x-ray source, the distance between the x-ray target and the sample is not limited by the outer geometry of the magnetic focus lens.

[0560] In particular, the flight tube comprises at its distal end the protruding portion protruding from the outer wall of the magnetic focus lens.

[0561] The vacuum chamber and the flight tube being fluidly connected means, in particular, that an interior space of the vacuum chamber and an interior space of the flight tube are continuous with each other and / or that the vacuum of the vacuum chamber extends into the flight tube.

[0562] The flight tube is configured for guiding the electron beam emitted from the electron source to the x-ray target. The flight tube has, for example, a cylindrical outer shape with a circular footprint. However, the flight tube can, for example, also have a cylindrical outer shape with a footprint different from a circular footprint (e.g., having a squared, rectangular or polygonal footprint). The flight tube is, for example, made from a material including copper.

[0563] The magnetic focus lens is configured for focusing the electron beam before the electron beam hits the x-ray target. The magnetic focus lens comprises, for example, a yoke, a coil wound around the yoke and a yoke cap. The outer wall of the magnetic focus lens has, for example, a ring shape with a central opening through which the distal end of the flight tube protrudes. The outer wall of the magnetic focus lens is, for example, a portion of an outer wall of the magnetic focus lens. The outer wall of the magnetic focus lens is, for example, a portion of an outer wall of the yoke cap.

[0564] According to a further embodiment, a length of the protruding portion is 200 μm or smaller, between 100 μm and 200 μm, between 200 μm and 1 mm and / or between 1 mm and 20 mm.Carl Zeiss SMT GmbH

[0565] 57

[0566] According to a further embodiment, the x-ray source comprises a cooling arrangement for cooling the protruding portion and / or the flight tube including its distal end.

[0567] Having the cooling arrangement allows cooling the protruding portion and / or the distal end of the flight tube with the x-ray target even though it is protruding from the remaining portion of the x-ray source and / or the outer wall of the magnetic lens.

[0568] For example, a carrier element carrying the x-ray target is configured to dissipate heat from the x-ray target, the carrier element is mechanically connected to the flight tube, and the cooling arrangement of the flight tube is configured to cool the carrier element. Thus, heat generated in the x-ray target by the impacting electron beam can be transmitted to the carrier element and dissipated to the flight tube.

[0569] According to a further embodiment, the flight tube comprises at least three concentric walls forming at least two concentric ring-shaped conduits between them, the at least two concentric ring-shaped conduits are configured for guiding a coolant through a first one of the at least two conduits from the proximal end to the distal end of the flight tube and for guiding the coolant through a second one of the at least two conduits from the distal end to the proximal end of the flight tube.

[0570] Thus, the flight tube can be cooled at its entire lateral area.

[0571] The coolant includes, for example, water or another suitable cooling liquid.

[0572] According to a further embodiment, the x-ray source comprises one or more electron optics units arranged around the flight tube for deflecting and / or shaping the electron beam emitted from the electron source before the magnetic focus lens is focusing the electron beam.

[0573] The one or more electron optics units are, for example, configured to direct, deflect and / or shape the electron beam. The electron optics include, for example, one or more magnetic lenses for focusing the electron beam and / or one or more deflection units for deflecting the electron beam.Carl Zeiss SMT GmbH

[0574] 58

[0575] The one or more electron optics units are arranged with respect to a direction of the electron beam (i.e. with respect to a direction pointing from the proximal end to the distal end of the flight tube) such that the electron beam is firstly deflected and / or shaped by the one or more electron optics units before it is focused by the magnetic focus lens.

[0576] According to a further embodiment, the outer wall of the magnetic focus lens from which the distal end of the flight tube with the x-ray target protrudes, has a flat surface portion.

[0577] According to a further embodiment, the outer wall of the magnetic focus lens from which the distal end of the flight tube with the x-ray target protrudes, has a convex surface portion curved in a direction pointing from the proximal end to the distal end of the flight tube, the convex surface portion comprising a central opening through which the flight tube protrudes.

[0578] According to a further embodiment, the x-ray source is configured for irradiating a sample with x-rays, and the x-ray source comprises a sensor unit for detecting a distance between the x-ray target and the sample.

[0579] Thus, when arranging the x-ray source very close to the sample, a distance between the x-ray source and the sample can be monitored. For example, the distance between the x-ray source and the sample can be controlled to be at a predetermined desired distance (e.g., at a distance ensuring a desired x-ray flux density at the region of interest of the sample and / or at a distance being not smaller than a predetermined minimum distance).

[0580] The sensor unit comprises, for example, one or more sensors arranged on the outer wall of the magnetic focus lens of the x-ray source. The sensor unit comprises, for example, three or more sensors arranged on a circle on the outer wall of the magnetic focus lens.

[0581] According to a further embodiment, the sensor unit comprises one or more distance sensors, one or more capacitive sensors, one or more inductive sensors, one or more optical sensors, one or more interferometers, and / or one or more cameras.

[0582] According to a second aspect, an x-ray imaging system for imaging a region of interest of a sample is provided. The x-ray imaging system comprises an x-ray source as described above.Carl Zeiss SMT GmbH

[0583] 59

[0584] According to an embodiment of the second aspect, the x-ray imaging system comprises a sample mount for supporting the sample. Further, the sample mount comprises an opening such that an x-ray beam emitted from the x-ray source to the region of interest of the sample passes through the opening of the sample mount.

[0585] Having the sample mount with the opening allows to prevent that the x-ray beam traveling to the x-ray detector transmits through the sample mount.

[0586] Furthermore, having the sample mount with the opening, the x-ray source (i.e. the x-ray target of the x-ray source) can be arranged even closer to the region of interest of the sample.

[0587] For example, in comparison with a sample without said opening, a distance between the x-ray target and the sample is at least the thickness of the sample mount (e.g., 2.5 mm). However, having the opening and the proposed x-ray source with the protruding distal end of the flight tube with the x-ray target, the x-ray target can, for example, be arranged at a distance to the sample of 0.3 mm. Given that the x-ray flux incident on the region of interest of the sample is inversely proportional to the square of the distance of the region of interest from the x-ray source, the difference in x-ray power at the region of interest is a factor of about 70, since (2.5 / 0.3)2is equal to 69. In other words, by moving the x-ray target from a distance of 2.5 mm to a distance of 0.3 mm to the region of interest of the sample, a gain in x-ray power of about 70 is achieved.

[0588] The sample mount has, for example, a support surface for supporting the sample, the support surface defining an object plane of the x-ray imaging system.

[0589] The sample mount and / or a sample mount assembly including the sample mount is, for example, configured for supporting the sample rotatably around a rotation axis. In addition, the x-ray imaging system is, for example, configured for obtaining two-dimensional transmission images of the region of interest of the sample for different rotation angles of the sample with respect to the rotation axis. For example, the x-ray imaging system is configured for obtaining two- dimensional transmission images of the region of interest of the sample for different rotation angles of the sample with respect to the rotation axis, wherein the rotation angles span a large angular range of, for example, 180° or larger, 270° or larger and / or 360°. Furthermore, the x-ray imaging system is, for example, configured for reconstructing a three-dimensional image of the region ofCarl Zeiss SMT GmbH

[0590] 60

[0591] interest based on the two-dimensional transmission images. The x-ray imaging system comprises, for example, a control device for reconstructing the three- dimensional images.

[0592] According to a further embodiment of the second aspect, the x-ray imaging system comprises:

[0593] a drive unit for displacing the sample mount in a direction towards the x-ray source and away from the x-ray source, and / or

[0594] a further drive unit for displacing the x-ray source in a direction towards the sample mount and away from the sample mount.

[0595] Having the drive unit and / or the further drive unit, a distance between the x-ray target and the sample can be adjusted.

[0596] According to a further embodiment of the second aspect, the x-ray imaging system comprises a feedback control device for performing a feedback control of a distance between the x-ray target and the sample.

[0597] Having the feedback control device, a distance between the x-ray target and the sample can be controlled such that it is maintained in a closed control loop at a predetermined set distance. For example, a distance between the x-ray target and the sample can be maintained at a value corresponding to a desired x-ray flux density at the region of interest of the sample, and, hence, to a desired exposure time of the sample and desired throughput of the imaging system.

[0598] Further, by the closed control loop, undesired distance values can be avoided. For example, a physical contact of the x-ray target and the sample can be avoided.

[0599] According to a further embodiment of the second aspect, the feedback control device is configured to:

[0600] receive an actual value of a distance indicative for a distance between the x-ray target and the sample from a sensor unit,

[0601] derive a further actual value of the distance between the x-ray target and the sample based on the received actual value,

[0602] determine a deviation of the derived further actual value from a predetermined set value of the distance between the x-ray target and the sample, determine a control value based on the determined deviation, and generate a control signal for controlling a drive unit of the sample mount and / or of the x-ray source based on the determined control value.Carl Zeiss SMT GmbH

[0603] 61

[0604] The respective unit described above and / or below, e.g., the control device, the feedback control device, the feedback control unit, and the deviation determining unit, can be implemented in hardware or in software. When implemented in hardware, the respective unit can be configured as device and / or as part of a device, e.g., a computer or a microprocessor. When implemented in software, the respective unit can be configured as computer program product, as routine, as algorithm, as part of a program code and / or as executable object.

[0605] According to a third aspect, a method for operating an x-ray imaging system as described above is provided. The method comprises the steps:

[0606] a) generating x-rays with an x-ray source of the x-ray imaging system such that the x-rays transmit through a region of interest of a sample,

[0607] b) detecting an actual distance between the x-ray source and the sample, and

[0608] c) performing a feedback control of the distance between the x-ray source and the sample based on the detected actual distance and a predetermined set distance between the x-ray source and the sample.

[0609] The embodiments and features described with reference to the x-ray source of the present invention apply mutatis mutandis to the x-ray imaging system and the method of the present invention.

[0610] Further possible implementations or alternative solutions of the invention also encompass combinations – that are not explicitly mentioned herein – of features described above or below with regard to the embodiments. The person skilled in the art may also add individual or isolated aspects and features to the most basic form of the invention.

[0611] Further embodiments, features and advantages of the present invention will become apparent from the subsequent description and dependent claims, taken in conjunction with the accompanying drawings, in which:

[0612] Fig. C#1 shows a schematic view of an x-ray imaging system for imaging a sample according to an embodiment;

[0613] Fig. C#2 shows an x-ray source of the x-ray imaging system of Fig. C#1

[0614] according to an embodiment;

[0615] Fig. C#3 shows an x-ray source of the x-ray imaging system of Fig. C#1

[0616] according to a further embodiment;Carl Zeiss SMT GmbH

[0617] 62

[0618] Fig. C#4 shows the x-ray source of Fig. C#2 together with a sample mount, a sample, a detector and a feedback control device according to an embodiment;

[0619] Fig. C#5 shows a control loop for a feedback control of a distance between an x- ray target of the x-ray source and the sample of Fig. C#4 according to an embodiment; and

[0620] Fig. C#6 shows a flow chart illustrating a method for operating an x-ray imaging system according to an embodiment.

[0621] In the Figures, like reference numerals designate like or functionally equivalent elements, unless otherwise indicated.

[0622] Fig. C#1 shows a schematic view of an x-ray imaging system C#100 according to an embodiment. The x-ray imaging system C#100 is used for imaging a sample C#102, in particular a region of interest C#104 of the sample C#102. The x-ray imaging system C#100 is configured to obtain two-dimensional transmission images C#106 of the region of interest C#104 for different rotation angles C#α of the sample C#102. Based on the two-dimensional transmission images C#106, a three-dimensional (3D) image C#108 of the region of interest C#104 is reconstructed to reveal interior structures of the region of interest C#104. The x-ray imaging system C#100 is, hence, an x-ray 3D imaging system obtaining 3D images C#108 by x-ray laminography and / or x-ray tomography.

[0623] The sample C#102 is, for example, a flat object extended in a main plane (e.g., the C#xC#y-plane in Fig. C#l). The sample C#102 is, for example, a wafer C#110 comprising electronic and / or semiconductor components. Just as an example, the x-ray imaging system C#100 may be used to inspect the wafer C#110 to investigate the quality of packaging of electronic components of the wafer C#110. For example, the quality of mechanical and electrical bonding (e.g., buried interconnections) of the electronic components may be controlled.

[0624] The x-ray imaging system C#100 comprises an x-ray source C#112 for emitting x-rays C#114. The x-rays C#114 are emitted from a source region C#116 of the x-ray source C#112. The reference sign C#S denotes a spot size of the source region C#116. The x-ray source C#112 emits a diverging beam C#118 of x-rays C#114. In other words, the x-ray source C#112 emits a cone C#120 of x-rays C#114. The sample C#102 is arranged within the x-ray emission cone C#120.Carl Zeiss SMT GmbH

[0625] 63

[0626] The x-ray imaging system C#100 further comprises a sample mount C#122 for supporting the sample C#102 rotatably around a rotation axis C#124. The rotation axis C#124 passes, for example, through the region of interest C#104 of the sample C#102. In particular, the rotation axis C#124 can be arranged off- center with respect to a center of the sample C#102. A rotation drive C#126 for rotating the sample mount C#122 and, hence, the sample C#102, is shown schematically in Fig. C#l. Furthermore, the sample mount C#122 has a support surface C#128 for supporting the sample C#102, wherein the support

[0627] surface C#128 defines an object plane C#130 of the x-ray imaging system C#100.

[0628] The x-ray imaging system C#100 may further comprise, for example, a shield stop C#132 arranged between the x-ray source C#112 and the sample mount C#122. The shield stop C#132 is, in particular, arranged in a light path of the x-rays C#114 emitted from the x-ray source C#112. The shield stop C#132 serves to select a usable portion C#134 (sub cone C#134) of the x-ray cone C#120.

[0629] Moreover, the shield stop C#132 protects uninspected regions of the sample C#102 from x-ray exposure. The shield stop C#132 has an aperture C#136 through which the usable portion C#134 of the x-ray light C#114 (C#114') propagates in the direction of the region of interest C#104 of the sample C#102 and transmits through the region of interest C#104 of the sample C#102.

[0630] The x-ray imaging system C#100 further comprises a position -sensitive x-ray detector C#138 for detecting x-rays C#114" transmitted through the region of interest C#104 of the sample C#102. The position -sensitive x-ray detector C#138 is, for example, configured to convert the incoming x-rays C#114" into light of longer wavelength, e.g., UV-light, visible light or infrared light. The x-ray detector C#138 includes, for example, a scintillator material at a transfer field of the detector C#138 for converting the x-rays C#114" into detectable light and a detector array C#138 (e.g., a CCD or CMOS array) for detecting the detectable light.

[0631] Fig. C#1 displays an x-ray propagation axis C#140 of the x-ray imaging system C#100. In particular, a central axis of the portion C#134 (sub light cone C#134) of the x-ray light C#114 passing through the shield stop C#132 defines the x-ray propagation axis C#140. The x-ray propagation axis C#140 extends from the x-ray source C#112 (i.e., the source region C#116 of the x-ray source C#112), through the region of interest C#104 of the sample C#102, and to the positionsensitive x-ray detector C#138.Carl Zeiss SMT GmbH

[0632] 64

[0633] As can be seen in Fig. C#l, the x-ray propagation axis C#140 of the x-ray imaging system C#100 is, in particular, inclined with respect to a surface normal C#142 of the sample mount C#122 by a first angle C#β. In addition, the x-ray propagation axis C#140 is, in particular, inclined with respect to the rotation axis C#124 by a second angle C#γ. In the example of Fig. C#l, the surface normal C#142 of the sample mount C#122 and the rotation axis C#124 are arranged parallel to each other and, hence, the first angle C#β and the second angle C#γ have the same size.

[0634] The x-ray exposures C#106 obtained at different rotation angles C#α of the sample C#102 are reconstructed to a 3D image C#108 by a control system C#144 of the imaging system C#100.

[0635] The x-ray imaging system C#100 provides microscopic imaging. A magnification and, hence, a spatial resolution, of the x-ray imaging system C#100 depends on the size of the source region C#116 of the x-ray source C#112.

[0636] Moreover, an imaging time necessary to obtain a 3D image C#108 of the region of interest C#104 of the sample C#102 depends on the x-ray flux density C#FXat the region of interest C#104. Said imaging time (exposure time) limits, for example, a throughput rate when imaging multiple samples C#102 with the x-ray imaging system C#100.

[0637] Fig. C#2 shows an x-ray source C#200 for the x-ray imaging system C#100 of Fig. C#l. The x-ray source C#200 comprises a vacuum chamber C#202. The x-ray source C#200 further comprises, for example, a flight tube C#204 fluidly connected at its proximal end C#206 to the vacuum chamber C#202. A vacuum atmosphere C#208 (vacuum condition) is provided inside the vacuum chamber C#202 and the flight tube C#204.

[0638] The x-ray source C#200 further incudes an electron source C#210 accommodated in the vacuum chamber C#202. The electron source C#210 is configured for emitting an electron beam C#212 towards an x-ray target C#224 (e.g., towards the flight tube C#204 such that the electron beam C#212 flies through the flight tube C#204 to the x-ray target C#224).

[0639] The x-ray source C#200 comprises in addition a carrier element C#214 (e.g., made from diamond) arranged at a distal end C#216 of the flight tube C#204. The carrier element C#214 is x-ray transmissive and forms a vacuum window C#218 of the flight tube C#204. The carrier element C#214 comprises an outer surfaceCarl Zeiss SMT GmbH

[0640] 65

[0641] C#220 with respect to the flight tube C#204 and an inner surface C#222, arranged inside the vacuum atmosphere C#208 of the flight tube C#204. The carrier element C#214 carries at its inner surface C#222 an x-ray target C#224 (e.g., made from tungsten).

[0642] The electron beam C#212 (e.g., traveling through the flight tube C#204) hits the x-ray target C#224 and causes the x-ray target C#224 to generate x-rays C#226. The generated x-rays C#226 are emitted from the x-ray source C#200 through the vacuum window C#218.

[0643] The x-ray source further comprises, for example, a magnetic focus lens C#228 arranged around the flight tube C#204. The magnetic focus lens C#228 is, in particular, arranged such that it surrounds the flight tube C#204 from an outside along an entire circumference of the flight tube C#204. The magnetic focus lens C#228 is configured for focusing the electron beam C#212 traveling through the flight tube C#204. In particular, the magnetic focus lens C#228 generates a magnetic field at the location of the electron beam C#212 that has a focusing effect on the electron beam C#212.

[0644] The magnetic focus lens C#228 comprises, for example, a yoke C#230, a coil C#232 wound around the yoke C#230 and a yoke cap C#234.

[0645] As can be seen in Fig. C#2, the x-ray source C#200 comprises, with respect to an outer (geometric) shape C#237 thereof, a protruding portion C#238 protruding from a remaining portion C#239 of the x-ray source C#200. Further, the protruding portion C#238 includes at its distal end C#216 the x-ray target C#224.

[0646] In the example of Fig. C#2, the distal end C#216 of the flight tube C#204 is protruding from an outer wall C#236 of the magnetic focus lens C#228. In particular, the flight tube C#204 comprises at its distal end C#216 the protruding portion C#238 protruding from the outer wall C#236 of the magnetic focus lens C#228. A length of the protruding portion C#238 is denoted with the reference sign C#L in Fig. C#2.

[0647] The outer wall C#236 of the magnetic focus lens C#228 has, for example, a ring shape with a central opening C#240 through which the distal end C#216 of the flight tube C#204 protrudes.Carl Zeiss SMT GmbH

[0648] 66

[0649] The outer wall C#236 of the magnetic focus lens C#228 from which the distal end C#216 of the flight tube protrudes is, for example, a portion C#242 of an outer wall C#244 of the yoke cap C#234 of the magnetic focus lens C#228.

[0650] The x-ray source C#200 comprises further one or more electron optics units C#246, C#248 arranged around the flight tube C#204. The one or more electron optics units C#246, C#248 are configured for deflecting and / or shaping the electron beam C#212 emitted from the electron source C#210. The electron beam C#212 emitted from the electron source C#210 enters, for example, the flight tube C#204 at the proximal end C#206 of the flight tube C#204. Then, in a lower portion of the flight tube C#204 adjacent the proximal end C#206 of the flight tube C#204, the electron beam C#212 is shaped (e.g., focused) and deflected by means of a magnetic, electric and / or electromagnetic field generated by the one or more electron optics units C#246, C#248. For example, the electron beam C#212 is directed by means of the one or more electron optics units C#246, C#248 towards the x-ray target C#224 or towards a specific one of several x-ray targets C#224 carried by the carrier element C#214. Subsequently, the electron beam C#212 is focused by the magnetic focus lens C#228 before the electron beam C#212 hits the x-ray target C#224.

[0651] As illustrated in Fig. C#2, the x-ray source C#200 may comprise a cooling arrangement C#250 for cooling the flight tube C#204 including its distal end C#216. In the example of Fig. C#2, the cooling arrangement C#250 comprises concentric ring-shaped conduits C#252, C#254 arranged at a wall of the flight tube C#204. The concentric ring-shaped conduits C#252, C#254 are configured for guiding a coolant, e.g., water, through them. In particular, the flight tube C#204 comprises at least three concentric walls C#256 forming at least two concentric ring-shaped conduits C#252, C#254 between them. The cooling

[0652] arrangement C#250 further comprises a supply conduct C#258 for supplying the coolant to a first one C#252 of the concentric ring-shaped conduits C#252, C#254. The cooling arrangement C#250 comprises in addition a discharge conduct C#260 for discharging the coolant from a second one C#254 of the concentric ring-shaped conduits C#252, C#254. The first and second ring-shaped conduits C#252, C#254 are, in particular, fluidly connected with each (e.g., at the distal end C#216 of the flight tube C#204). Hence, the first and second ring-shaped conduits C#252, C#254 are, for example, configured for guiding a coolant through the first ringshaped conduit C#252 from the proximal end C#206 to the distal end C#216 of the flight tube C#204 and for guiding the coolant through the second ring-shaped conduit C#254 from the distal end C#216 to the proximal end 205 of the flight tube C#204.Carl Zeiss SMT GmbH

[0653] 67

[0654] Although not shown in the figures, the cooling arrangement C#250 comprises, for example, further conduits, one or more pumps, a cooling unit, one or more valves and the like.

[0655] Having the cooling arrangement C#250 the distal end C#216 of the flight tube C#204 with the x-ray target C#224 can be cooled even though it is protruding from the outer wall C#236 of the magnetic lens C#228. Cooling of the x-ray target C#224 is particularly important since a significant amount of heat is generated in the x-ray target C#224 by the impacting electron beam C#212.

[0656] In the example of Fig. C#2, the carrier element C#214 carrying the x-ray target C#224 is configured to dissipate heat from the x-ray target C#224. The carrier element C#214 is mechanically connected to the flight tube C#204 such that the concentric ring-shaped conduits C#252, C#254 can cool the carrier element C#214. Thus, heat generated in the x-ray target C#224 can be transmitted to the carrier element C#214 and dissipated to the flight tube C#204.

[0657] In the example of Fig. C#2, the outer wall portion C#236 of the magnetic focus lens C#228 from which the protruding portion C#238 of the flight tube C#204 protrudes, has a flat surface portion C#262.

[0658] However, as shown in Fig. C#3, the outer wall portion C#236' of the magnetic focus lens C#228' from which the protruding portion C#238 of the flight tube C#204 protrudes, can also have a convex surface portion C#264 curved in a direction C#R pointing from the proximal end C#206 to the distal end C#216 of the flight tube C#204. The convex surface portion C#264 comprises a central opening C#240' through which the flight tube C#204 protrudes.

[0659] Fig. C#4 shows the x-ray source C#200 of Fig. C#2 together with a sample mount assembly C#300 for supporting a sample C#102. The sample mount assembly C#300 comprises a sample mount C#302 configured similar as the sample mount C#122 in Fig. C#1 apart from that the sample mount C#302 comprises an opening C#304 such that an x-ray beam C#226 emitted from the x-ray source C#200 to a region of interest C#104 of the sample C#102 passes through the opening C#304 of the sample mount C#302. In other words, the x-ray beam C#226 emitted from the x-ray source C#200 to the region of interest C#104 of the sample C#102 does advantageously not transmit through material of the sample mount C#302.Carl Zeiss SMT GmbH

[0660] 68

[0661] Having the x-ray source C#200 with the protruding portion C#238 with the x-ray target C#224 and having the sample mount C#302 with the opening C#304 allows to arranged the x-ray target C#224 very close to the region of interest C#104 of the sample C#102. With a very small distance C#D1 between the x-ray target C#224 and the sample C#102 (see also reference sign C#146 in Fig. C#l), a high of x-ray flux density C#FXat the region of interest C#104 of the sample C#102 can be provided. Therefore, a series of samples C#102 can be analyzed with the x-ray imaging system C#100 with a high throughput.

[0662] The distance C#D1 between the x-ray target C#224 and the sample C#102 is, for example, a distance between a top surface C#266 of the carrier element C#214 carrying the x-ray target C#224 and a bottom surface C#306 of the sample C#102.

[0663] The x-ray source C#200 may comprise a sensor unit C#268 for monitoring the distance C#D1 between the x-ray target C#224 and the sample C#102, as illustrated in Fig. C#4. The sensor unit C#268 comprises, for example, one or more distance sensors C#270. The one or more distance sensors C#270 are, for example, arranged on the ring-shaped outer wall C#236 of the magnetic focus lens C#228. In this case, the sensor unit C#268 is configured for measuring a distance C#D2 between the outer wall C#236 of the magnetic focus lens C#228 and the sample C#102 (e.g., the bottom surface C#304 of the sample C#102). A control device C#400 of the x-ray imaging system may be configured for deriving the distance C#D1 from the measured distance C#D2.

[0664] The x-ray imaging system C#100, e.g., the sample mount assembly C#300, may comprise a drive unit C#308 for displacing the sample mount C#302 in a direction C#R1 towards the x-ray source C#200 and a direction C#R2 away from the x-ray source C#200. By using the drive unit C#308 of the sample mount assembly C#300, the distance C#D1 between the x-ray target C#224 and the sample C#102 can be set. The directions C#R, C#R1, and C#R2 are arranged parallel to a C#z-direction in the figures.

[0665] In addition or alternative to the drive unit C#308 of the sample mount assembly C#300, the x-ray imaging system C#100, e.g., the x-ray source C#200, may comprise a further drive unit C#272 (Fig. C#2) for displacing the x-ray source C#200 in a direction C#R2 towards the sample mount C#302 and a direction C#R1 away from the sample mount C#302.Carl Zeiss SMT GmbH

[0666] 69

[0667] The x-ray imaging system C#100 may include the control device C#400. The control device C#400 may, for example, be a feedback control device for performing a feedback control of the distance C#D1 between the x-ray target C#224 and the sample C#102. With such a feedback control, the distance C#D1 between the x-ray target C#224 and the sample C#102 can be monitored and maintained at a desired distance C#Ds.

[0668] The feedback control device C#400 is, for example, configured to receive an actual value C#DA of a distance C#D2 indicative for a distance C#D 1 between the x-ray target C#224 and the sample C#102 from the sensor unit C#268. The feedback control device C#400 is further configured to derive a further actual value C#DA' of the distance C#D1 between the x-ray target C#224 and the sample C#102 based on the received actual value C#DA. Moreover, the feedback control device C#400 is configured to determine a deviation C#e(t) of the derived further actual value C#DA' from a predetermined set value C#Ds of the distance C#D 1 between the x-ray target C#224 and the sample C#102. Then, the feedback control device C#400 determines a control value C#u(t) based on the determined deviation C#e(t), and generates a control signal C#A for controlling a drive unit of the sample mount and / or of the x-ray source based on the determined control value.

[0669] Fig. C#5 shows a control loop C#500 for performing a feedback control of the distance C#D1 between the x-ray target C#224 and the sample C#102. The control device C#400 includes, for example, a control unit 402 for determining the control value C#u(t). The control device C#400 includes further, for example, a deviation determining unit 402 for determining the deviation C#e(t).

[0670] The reference sign C#r(t) in Fig. C#5 denotes a reference variable of the control loop C#500. The reference variable C#r(t) corresponds to the set value C#Ds of the distance C#D1 between the target C#224 and the sample C#102. The reference variable C#r(t) may be a time -dependent parameter (time t) or may be a constant parameter. The reference sign C#y(t) denotes a (time-dependent) control variable of the control loop C#500. The control variable C#y(t) corresponds to the further actual value C#DA' of the distance C#D1.

[0671] The deviation determining unit C#504 is configured for determining the deviation C#e(t) of the control variable C#y(t) (i.e. the further actual value C#DA') from the reference variable C#r(t) (i.e. the set value C#Ds). Then, the feedback control unit C#502 determines the control value C#u(t) based on the determined deviation C#e(t). In particular, the feedback control unit C#502 generates, based on the determined control value C#u(t), a control signal C#A (Fig. C#4) forCarl Zeiss SMT GmbH

[0672] 70

[0673] controlling the drive unit C#308 of the sample mount assembly C#300 and / or for controlling the further drive unit C#272 (Fig. C#2) of the x-ray source C#200

[0674] The reference sign C#506 in Fig. C#5 denotes a control section of the control loop C#500. The control section C#506 includes a sensor unit C#508 (sensor unit C#268 in Fig. C#4), for determining the actual value C#y(t) of the distance C#D1. The control section C#506 includes an actuator unit C#510 (e.g., the drive unit C#308 in Fig. C#4 and / or the further drive unit C#272 in Fig. C#2) for setting the distance C#D1. Furthermore, the reference sign C#512 of the control section C#506 of the control loop C#500 indicates the system to be actuated, e.g., the x-ray source C#200 and / or the sample mount assembly C#300.

[0675] In the following, a method for operating an x-ray imaging system C#100 (Fig. C#l) is described with reference to Fig. C#6.

[0676] In a first step C#S1 of the method, x-rays C#226 are generated with an x-ray source C#200 (Fig. C#2) of the x-ray imaging system C#100 such that the x-rays C#226 transmit through a region of interest C#104 of a sample C#102 (Fig. C#l).

[0677] In a second step C#S2 of the method, an actual distance C#D1, C#DA' between the x-ray source C#200 and the sample C#102 is detected.

[0678] In a third step C#S3 of the method, a feedback control of the distance C#D1 between the x-ray source C#200 and the sample C#102 is performed based on the detected actual distance C#DA' and a predetermined set distance C#Ds between the x-ray source C#200 and the sample C#102.

[0679] Further aspects of the invention are disclosed in the following clauses:

[0680] C#l. An x-ray source (C#200) for an x-ray imaging system (C#100), comprising a vacuum chamber (C#202),

[0681] an electron source (C#210) accommodated in the chamber (C#202) for emitting an electron beam (C#212), and

[0682] an x-ray target (C#224) accommodated in the chamber (C#202) for generating x-rays (C#226) when irradiated with the electron beam (C#212), wherein the x-ray source (C#200) comprises, with respect to an outer shape (C#237) thereof, a protruding portion (C#238) protruding from a remaining portion (C#239) of the x-ray source (C#200), the protruding portion (C#238) including at its distal end (C#216) the x-ray target (C#224).Carl Zeiss SMT GmbH

[0683] 71

[0684] C#2. The x-ray source (C#200) according to clause C#l, comprising

[0685] a flight tube (C#204) fluidly connected at its proximal end (C#206) to the vacuum chamber (C#202) for providing a vacuum atmosphere (C#208) inside the chamber (C#202) and the tube (C#204), and

[0686] a magnetic focus lens (C#228) arranged around the flight tube (C#204) for focusing the electron beam (C#212),

[0687] wherein the electron source (C#210) is configured for emitting the electron beam (C#212) into the flight tube (C#204), the x-ray target (C#224) is arranged at the distal end (C#216) of the flight tube (C#204), and the distal end (C#216) of the flight tube (C#204) is protruding from an outer wall (C#236) of the magnetic focus lens (C#228).

[0688] C#3. The x-ray source according to clause C#1 or C#2, wherein a length (C#L) of the protruding portion (C#238) is 200 μm or smaller, between 100 μm and 200 μm, between 200 μm and 1 mm and / or between 1 mm and 20 mm.

[0689] C#4. The x-ray source according to any one of clauses C#1 to C#3, comprising a cooling arrangement (C#250) for cooling the protruding portion (C#238) and / or the flight tube (C#204) including its distal end (C#216).

[0690] C#5. The x-ray source according to any one of clauses C#2 to C#4, wherein the flight tube (C#204) comprises at least three concentric walls (C#256) forming at least two concentric ring-shaped conduits (C#252, C#254) between them, the at least two concentric ring-shaped conduits (C#252, C#254) are configured for guiding a coolant through a first one of the at least two conduits (C#252, C#254) from the proximal end (C#206) to the distal end (C#216) of the flight tube (C#204) and for guiding the coolant through a second one of the at least two conduits (C#252, C#254) from the distal end (C#216) to the proximal end (C#208) of the flight tube (C#204).

[0691] C#6. The x-ray source according to any one of clauses C#2 to C#5, comprising one or more electron optics units (C#246, C#248) arranged around the flight tube (C#204) for deflecting and / or shaping the electron beam (C#212) emitted from the electron source (C#210) before the magnetic focus lens (C#228) is focusing the electron beam.

[0692] C#7. The x-ray source according to any one of clauses C#2 to C#6, wherein the outer wall (C#236) of the magnetic focus lens (C#228) from which the distal end (C#216) of the flight tube (C#204) with the x-ray target (C#224) protrudes, has a flat surface portion (C#262).Carl Zeiss SMT GmbH

[0693] 72

[0694] C#8. The x-ray source according to any one of clauses C#2 to C#6, wherein the outer wall (C#236') of the magnetic focus lens (C#228') from which the distal end (C#216) of the flight tube (C#204) with the x-ray target (C#224) protrudes, has a convex surface portion (C#264) curved in a direction (C#R) pointing from the proximal end (C#208) to the distal end (C#216) of the flight tube (C#204), the convex surface portion (C#264) comprising a central opening (C#240') through which the flight tube (C#204) protrudes.

[0695] C#9. The x-ray source according to any one of clauses C#1 to C#8, wherein the x-ray source (C#200) is configured for irradiating a sample (C#102) with x-rays (C#226), and

[0696] the x-ray source (C#200) comprises a sensor unit (C#268) for detecting a distance (C#D1) between the x-ray target (C#224) and the sample (C#102).

[0697] C#10. The x-ray source according to clause C#9, wherein the sensor unit (C#268) comprises one or more distance sensors (C#270), one or more capacitive sensors, one or more inductive sensors, one or more optical sensors, one or more interferometers, and / or one or more cameras.

[0698] C#11. An x-ray imaging system (C#100) for imaging a region of interest (C#104) of a sample (C#102), comprising an x-ray source (C#200) according to any one of clauses C#1 to C#10.

[0699] C#12. The x-ray imaging system according to clause C#11, comprising a sample mount (C#302) for supporting the sample (C#102), the sample mount (C#302) comprises an opening (C#304) such that an x-ray beam (C#226) emitted from the x-ray source (C#200) to the region of interest (C#104) of the sample (C#102) passes through the opening (C#304) of the sample mount (C#302).

[0700] C#13. The x-ray imaging system according to clause C#11 or C#12, comprising a drive unit (C#308) for displacing the sample mount (C#302) in a direction (C#R1, C#R2) towards the x-ray source (C#200) and away from the x-ray source (C#200), and / or

[0701] a further drive unit (C#272) for displacing the x-ray source (C#200) in a direction (C#R1, C#R2) towards the sample mount (C#302) and away from the sample mount (C#302).Carl Zeiss SMT GmbH

[0702] 73

[0703] C#14. The x-ray imaging system according to any one of clauses C#11 to C#13, comprising a feedback control device (C#400) for performing a feedback control of a distance (C#D1) between the x-ray target (C#224) and the sample (C#102).

[0704] C#15. The x-ray imaging system according to clause C#14, wherein the feedback control device (C#400) is configured to

[0705] receive an actual value (C#DA) of a distance (C#D2) indicative for a distance (C#D1)

[0706] between the x-ray target (C#224) and the sample (C#102) from a sensor unit (C#268),

[0707] derive a further actual value (C#DA') of the distance (C#D 1) between the x-ray target (C#224) and the sample (C#102) based on the received actual value (C#DA),

[0708] determine a deviation (C#e) of the derived further actual value (C#DA') from a predetermined set value (C#Ds) of the distance (C#D 1) between the x-ray target (C#224) and the sample (C#102),

[0709] determine a control value (C#u) based on the determined deviation (C#e), and

[0710] generate a control signal (C#A) for controlling a drive unit (C#308, C#272) of the sample mount (C#302) and / or of the x-ray source (C#200) based on the determined control value (C#u).

[0711] C#16. A method for operating an x-ray imaging system (C#100) according to any one of clauses C#11 to C#15, comprising the steps

[0712] a) generating (C#S1) x-rays (C#226) with an x-ray source (C#200) of the x-ray imaging system (C#100) such that the x-rays (C#226) transmit through a region of interest (C#104) of a sample (C#102),

[0713] b) detecting (C#S2) an actual distance (C#DA') between the x-ray source (C#200) and the sample (C#102), and

[0714] c) performing (C#S3) a feedback control of the distance (C#D1) between the x-ray source (C#200) and the sample (C#102) based on the detected actual distance (C#DA') and a predetermined set distance (C#Ds) between the x-ray source (C#200) and the sample (C#102).

[0715] Although the present invention has been described in accordance with preferred embodiments, it is obvious for the person skilled in the art that modifications are possible in all embodiments.

[0716] The disclosures of the inventions " A#", B#" and " C#" may be combined as required and deemed fit by the skilled person.Carl Zeiss SMT GmbH

[0717] 74 REFERENCE NUMERALS

[0718] C#100 System

[0719] C#102 Sample

[0720] C#104 Region of interest

[0721] C#106 2D image

[0722] C#108 3D image

[0723] C#110 Wafer

[0724] C#112 Source

[0725] C#114 X-ray

[0726] C#114', C#114" X-ray

[0727] C#116 Source region

[0728] C#118 Beam

[0729] C#120 Cone

[0730] C#122 Sample mount

[0731] C#124 Rotation axis

[0732] C#126 Rotation drive

[0733] C#128 Surface

[0734] C#130 Object plane

[0735] C#132 Shield stop

[0736] C#134 Portion

[0737] C#136 Aperture

[0738] C#138 Detector

[0739] C#140 Axis

[0740] C#142 Surface normal

[0741] C#144 Control system

[0742] C#146 Sign

[0743] C#200 Source

[0744] C#202 Vacuum chamber

[0745] C#204 Tube

[0746] C#206 End

[0747] C#208 Vacuum atmosphere

[0748] C#210 Source

[0749] C#212 Beam

[0750] C#214 Carrier element

[0751] C#216 End

[0752] C#218 Vacuum window

[0753] C#220 Outer surface

[0754] C#222 Inner surface

[0755] C#224 TargetCarl Zeiss SMT GmbH

[0756] 75 C#226 X-ray

[0757] C#228, C#228' Lens

[0758] C#230 Yoke

[0759] C#232 Coil

[0760] C#234 Yoke cap

[0761] C#236, C#236' Outer wall C#237 Shape

[0762] C#238 Portion

[0763] C#239 Portion

[0764] C#240, C#240' Opening

[0765] C#242 Portion

[0766] C#244 Outer wall

[0767] C#246 Optic unit

[0768] C#248 Optic unit

[0769] C#250 Cooling arrangement C#252 Conduit

[0770] C#254 Conduit

[0771] C#256 Wall

[0772] C#258 Conduct

[0773] C#260 Conduct

[0774] C#262 Surface portion

[0775] C#264 Surface portion

[0776] C#268 Sensor unit

[0777] C#270 Sensor

[0778] C#272 Unit

[0779] C#300 Sample mount assembly C#302 Sample mount

[0780] C#304 Opening

[0781] C#306 Surface

[0782] C#308 Unit

[0783] C#400 Control device

[0784] C#500 Control loop

[0785] C#502 Control unit

[0786] C#504 Determining unit C#506 Control section

[0787] C#508 Sensor unit

[0788] C#510 Actuator unit

[0789] C#512 System

[0790] C#a AngleCarl Zeiss SMT GmbH

[0791] 76

[0792] C#β Angle

[0793] C#γ Angle

[0794] C#A Signal

[0795] C#DA, C#DA' Value

[0796] C#Ds Set value

[0797] C#D1, C#D2 Distance

[0798] C#e(t) Deviation

[0799] C#Fx Flux Density

[0800] C#L Length

[0801] C#R Direction

[0802] C#R1, C#R2 Direction

[0803] C#r(t) Reference variable C#S1-C#S3 Step

[0804] C#u(t) Control Value C#y(t) Reference sign C#x, C#y, C#z Direction

Claims

Carl Zeiss SMT GmbH77CLAIMS1. An x-ray imaging system (A#100) for imaging a sample (A# 102), comprising an x-ray source (A#112) for generating x-rays (A#114), anda shield stop (A#132) with an aperture (A#136), the shield stop (A#132) being configured for transmitting an x-ray beam (A# 134) of the generated x-rays (A#114) through the aperture (A#136) and along an x-ray propagation axis (A# 140) of the system (A#100) towards a region of interest (A# 104) of the sample (A#102) and for blocking remaining x-rays (A#114),wherein a geometric shape (A#146) of the aperture (A#136) is adapted to a diverging nature of the transmitted x-ray beam (A# 134).

2. The x-ray imaging system according to claim 1, wherein a cross-section size (A#S1, A#S2) of the aperture (A#136) parallel to a main plane (A#E1) of extension of the shield stop (A# 132) increases in a direction (A# 150) of the x-ray propagation axis (A# 140).

3. The x-ray imaging system according to claim 1 or 2, wherein the aperture (A# 136) comprises, as seen in a cross section along the x-ray propagation axis (A# 140), at least one inclined inner wall (A# 156) inclined with respect to the x-ray propagation axis (A#140) of the transmitted x-ray beam (A#134) by half of an opening angle (A#ε) of the transmitted x-ray beam (A#134).

4. The x-ray imaging system according to any one of claims 1 to 3, comprising an object plane (A# 130) for arranging the sample (A# 102), wherein the x-ray propagation axis (A#140) of the system (A#100) is inclined relative to the object plane (A# 130).

5. The x-ray imaging system according to any one of claims 1 to 4, comprising an x-ray detector assembly (A#238) with a two-dimensional detector array (A#262) for detecting the x-ray beam (A#134) transmitted through the region of interest (A#104) of the sample (A#102) and traveled along the x-ray propagation axis (A# 140), whereinthe x-ray propagation axis (A# 140) is inclined relative to a main plane (A#E1) of extension of the shield stop (A#232), andan actual cross-section shape (A#268) of the aperture (A#236) of the shield stop (A#232) parallel to its main plane (A#E1) of extension has, as seen in perspective from the detector array (A#262), an apparent shape (A#270) matching a geometric shape (A#264) of the detector array (A#262).Carl Zeiss SMT GmbH786. The x-ray imaging system according to claim 5, whereinthe geometric shape (A#364) of the detector array (A#362) is a quadratic shape (A#366) and / or a rectangular shape, andthe actual cross-section shape (A#368) of the aperture (A#136) of the shield stop (A#332) parallel to its main plane (A#E1) of extension has a trapezoidal cross-section shape (A#372) with, as seen in perspective from the detector array (A#362), an apparent shape (A#370) matching the quadratic shape (A#366) and / or rectangular shape of the detector array (A#362).

7. The x-ray imaging system according to claim 5, whereinthe geometric shape (A#264) of the detector array (A#262) is a circular shape (A#266), andthe actual cross-section shape (A#268) of the aperture (A#336) of the shield stop (A#332) parallel to its main plane (A#E1) of extension has an ellipsoidal cross-section shape (A#272) with, as seen in perspective from the detector array (A#262), an apparent shape (A#270) matching the circular shape (A#266) of the detector array (A#262).

8. The x-ray imaging system according to any one of claims 1 to 7, wherein the x-ray source (A#412) comprises a vacuum chamber (A#474) with an x-ray transmissive vacuum window (A#476), and at least one x-ray target (A#482) arranged in the vacuum chamber (A#474) for generating x-rays (A#114) and transmitting the generated x-rays (A#114) through the vacuum window (A#476), andthe shield stop (A#432) is integrated in the vacuum window (A#476).

9. The x-ray imaging system according to claim 8, wherein the shield stop (A#432) is embedded in the vacuum window (A#476) such that the shield stop (A#432) is accommodated in at least one recess (A#490) of the vacuum window (A#476).

10. The x-ray imaging system according to claim 8 or 9, wherein the aperture (A#436) of the shield stop (A#432) is filled with an x-ray transmissive material of the vacuum window (A#476).

11. The x-ray imaging system according to any one of claims 8 to 10, wherein the shield stop (A#632) is arranged at an outside surface (A#684) of the vacuum window (A#676).Carl Zeiss SMT GmbH7912. The x-ray imaging system according to any one of claims 8 to 11, wherein the x-ray source (A#412) comprises a plurality of x-ray targets (A#582, A#582'), and the x-ray imaging system (A#400) comprises a plurality of shield stops (A#532, A#532'), each shield stop (A#532, A#532') being arranged corresponding to one of the x-ray targets (A#582, A#582').

13. The x-ray imaging system according to any one of claims 1 to 12, wherein a thickness (A#T) of the shield stop (A# 132) is 1000 pm or smaller, 500 pm or smaller, 200 pm or smaller, 100 pm or smaller and / or 50 pm or smaller.

14. The x-ray imaging system according to any one of claims 1 to 13, wherein a material of the shield stop (A# 132) includes tungsten, bismuth, lead, platinum, depleted uranium, gold and / or one or more chemical elements with an atomic number above 70.

15. The x-ray imaging system according to any one of claims 1 to 14, wherein the shield stop (A#132) is configured for adapting a size (A#S1) of the aperture (A# 136).

16. The x-ray imaging system according to any one of claims 1 to 15, wherein the x-ray imaging system (A#100) is configured for emitting x-rays (A#114) towards a first side of the sample (A# 102) and for imaging a region of interest (A# 104) of the sample (A# 102) arranged on a second side of the sample (A# 102), the second side is arranged opposite the first side, and the second side is configured for facing away from the x-ray source (A#112) during x-ray imaging.

17. A method for x-ray imaging of a region of interest (A# 104) of a sample (A#102), comprising the steps: arranging a sample (A#102) on a sample mount (A#122) of an x-ray imaging system (A#100), wherein the sample (A#102) has a first side and a second side arranged opposite the first side, the sample (A# 102) comprises a region of interest (A# 104) arranged on the second side, and the sample (A# 102) is arranged on the sample mount (A# 122) such that the first side faces an x-ray source (A#112) of the x-ray imaging system and the second side faces away from the x-ray source (A#112), andx-ray imaging of the region of interest (A#104).

18. The x-ray imaging system according to claim 16 or the method according to claim 17, wherein the second side of the sample (A# 102) is free of regions of interest (A#104) and / or the second side of the sample (A#102) is free of components to be inspected by x-ray imaging.

Images