Patent Grant
11817231
The invention refers to a detection system for X-ray inspection of an object. Further, the invention refers to an X-ray inspection method using such a detection system.
A detection system for X-ray inspection of an object is known from U.S. Pat. No. 9,129,715 B2. Other such detection systems are known from U.S. Pat. No. 7,057,187 B1 and from DE 10 2018 209 570 A1.
Further, for object imaging, X-ray inspection microscopes (μCTs) and optical assisted X-ray microscopes (XRM) are known in the art. For μCTs several tomosynthesis geometries are known, wherein detectors are placed at different positions with respect to a central inspection axis. A detector and/or the sample may be moved. In that respect, it is referred to U.S. Pat. No. 7,130,375 B1 and to U.S. Pat. No. 7,057,187 B1.
In a general aspect, the invention optimizes an X-Ray illumination of the object giving in particular the possibility to achieve a high-resolution object imaging.
The aspect described above is achieved by a detection system that includes an X-ray source for generating X-rays, and an imaging optical arrangement to image the object in an object plane illuminated by the X-rays, the imaging optical arrangement including an imaging optics to image a transfer field in a field plane into a detection field in a detection plane. The detection system includes a detection array, arranged at the detection field of the imaging optics, and an object mount to hold the object to be imaged via the imaging optics, in which the object mount is movable relative to the light source via an object displacement drive along at least one lateral object displacement direction in the object plane. The detection system includes a shield stop having a shield stop aperture transmissive for the X-rays used to image the object, the shield stop being arranged in an arrangement plane in a light path of the X-rays between the X-ray source and the object mount, the shield stop being movable via a shield stop displacement drive along at least one stop displacement direction in the arrangement plane. The detection system includes a control device having a drive control unit being in signal connection with the shield stop displacement drive and with the object displacement drive for synchronizing a movement of the shield stop displacement drive and the object displacement drive.
A movable shield stop gives the possibility to safeguard that only those regions of the object are illuminated with the X-rays which are imaged by the imaging optical arrangement. Uninspected optic regions, i.e. those regions of the object which actually are not imaged by the imaging optical arrangement, then are protected from unnecessary X-ray exposure. In some implementations, a synchronized movement of the shield stop displacement drive and of the object displacement drive ensures that a used light path of the X-rays to illuminate the object always (or during substantially most of the operating period of the detection system) impinges on the object at a desired object region to be imaged.
In particular, it is possible to image object structures, which are smaller than 20 μm, smaller than 10 μm and in particular which are smaller than 1 μm. Examples for such structures are Cu—Cu hybrid bonding structures between microchips and substrate conductor paths. In particular, direct bonds between single dies or between a whole wafer onto a substrate wafer can be inspected.
In particular, a 3D tomographic reconstruction of an object sample under investigation by combining several 2D images taken from different directions is possible.
X-ray energies of the used X-rays can range between 5 keV and 160 keV, preferably between 15 and 90 keV
In some implementations, the object mount can be movable along at least one linear displacement direction. The shield stop is movable along at least one linear displacement direction. The object mount/shield stop movability described above have proven to be particularly advantageous to acquire a high-resolution object image. The object mount can be movable along two lateral displacement directions. Such two displacement directions can span up the object plane. The shield stop can be movable along two lateral displacement directions. Such two displacement directions can span up the shield stop arrangement plane.
In some implementations, the object mount and/or the shield stop is movable along at least one circular direction. The above-mentioned advantages also hold for movable variants in at least one circular direction as described above.
In some implementations, a shield stop having a shield stop aperture being variable in size enables an adaption of the field stop size to the requirements, which are to be met by the used X-ray path to impinge on the object region to be imaged. Such variability in size can be realized by an iris stop. The shield stop having a shield stop aperture with variable size can be equipped with an aperture variation drive. Such aperture variation drive also can be in signal connection with the drive control unit of the control device. The aperture size controlled via the aperture variation drive can depend on the positions of the shield stop displacement drive and/or of the object displacement drive.
The shield stop can include several shield blades. An embodiment of the shield stop described above can have a relatively simple structure. The shield blades can be movable relative to each other to enable a variable shield stop aperture size. The several shield blades can be arranged as at least one pair or as several pairs of shield blades. In case two pairs of shield blades are used, these can be oriented 90 deg to each other to give, e.g., the possibility to result in a square or in a rectangular shield stop aperture.
In some implementations, the shield stop aperture can be equipped with a filter. A filter described above gives the possibility to filter out undesired wavelengths and/or debris.
In some implementations, the detection system can include a shield stop exchange mount to exchange between different shield stops. The shield stop exchange mount described above can facilitate an exchange between different shield stops. This can be used to replace a worn-out shield stop or to adapt a shield stop aperture size.
In some implementations, the detection system can include a layer of scintillator material arranged at the transfer field. The layer of scintillator material described above enables a good imaging from the transfer field to the detection field.
In some implementations, the detection system can include a pupil stop being arranged in a pupil plane of the imaging optics. The pupil stop described above enables an adaption, in particular of a numerical aperture of the imaging optics, to imaging requirements of the detection system.
This in particular holds for a pupil stop that is movable via a pupil stop decentering drive to translate the pupil stop in the pupil plane. In particular, it has been realized by the inventors, that a stop arranged at a decentering distance with respect to the optical axis of the imaging optics of the imaging optical arrangement makes it possible to adapt such decentering distance to an angle of an oblique or tilted entry of X-rays to the transfer field of the imaging optics. With a respective decentering of the stop opening, a mean spot size of the imaging spots of points of origin from different positions of the layer of scintillator material can be kept advantageously small. This gives a good imaging from the transfer field to the detection field even in case of obliquely entering rays on the layer of scintillator material.
In some implementations, the drive control unit can be in signal connection with the pupil stop decentering drive. The drive control unit described above enables a synchronization of a movement of the shield stop displacement drive, the lateral displacement drive and the pupil stop displacement drive. This enables an automatic measuring process to produce a 3-dimensional image of the object. Data with respect to the dependency between the actions of the shield stop displacement drive, the lateral displacement drive and the pupil stop displacement drive can be gathered from a look-up table. Such look-up table can be produced in a preparational calibration step of the detection system.
In some implementations, the X-ray source can be an open transmissive source or a liquid metal jet source. The X-ray sources described above have proven to be suited for the detection system.
The object mount can be from the type of a ring mount. Such an object mount can have no additional mount material between a used light path and the object. This avoids undesired X-ray absorption.
In some implementations, the object mount can include at least one organic tray or can include an aluminum and/or glass tray, the tray in particular including a dopant to filter a low energy part of a spectrum of the generated X-rays. The object mount described above can minimize an X-ray absorption and/or filter a low, unwanted energy part of the X-ray spectrum.
In another general aspect, an X-ray inspection method is performed using a detection system for X-ray inspection of an object, in which the detection system includes an X-ray source for generating X-rays, and an imaging optical arrangement to image the object in an object plane illuminated by the X-rays, the imaging optical arrangement including an imaging optics to image a transfer field in a field plane into a detection field in a detection plane. The detection system includes a detection array, arranged at the detection field of the imaging optics, and an object mount to hold the object to be imaged via the imaging optics, in which the object mount is movable relative to the light source via an object displacement drive along at least one lateral object displacement direction in the object plane. The detection system includes a shield stop having a shield stop aperture transmissive for the X-rays used to image the object, the shield stop being arranged in an arrangement plane in a light path of the X-rays between the X-ray source and the object mount, the shield stop being movable via a shield stop displacement drive along at least one stop displacement direction in the arrangement plane. The detection system includes a control device having a drive control unit being in signal connection with the shield stop displacement drive and with the object displacement drive for synchronizing a movement of the shield stop displacement drive and the object displacement drive. The shield stop and the detection array are moved synchronously relative to the object to be inspected to realize different object imaging projections. Advantages of the X-ray inspection method described above correspond to those discussed above with respect to the detection system. Synchronous movement of the shield stop, the detection array and the object ensures that a used light path of the X-rays to illuminate the object always (or during substantially most of the operating period of the detection system) impinges on the object at a desired object region to be imaged to result in the desired object imaging projection.
Exemplified embodiments of the invention hereinafter are described with reference to the accompanying figures. In these show:
A detection system 1 serves to investigate or inspect an object 2 which is illuminated by X-rays 3. The detection system 1 in particular serves to investigate the quality of packaging, i.e. the quality of mechanical and electrical bonding of electronic components in particular on a chip with micro- and/or nanostructures. Such electronic components often are arranged in a layered, three-dimensional (3D) structure. In
To facilitate the further description, a Cartesian x-y-z-coordinate system is used hereinafter. In
The layers 4i are stacked in the z-direction.
The X-rays 3 are emitted from a source region 5 of an X-ray source 6. The X-rays 3 are emitted within an emission cone in which the object 2 is arranged. A typical cone angle of such emission cone is in the range between 90 deg and 175 deg and can be 170 deg. A spot size of the source region 5 can be in the range between 1 μm and 100 μm, depending on the type of the X-ray source 6. A continuous power of the X-ray source 6 can be in the range between 1 W and 200 W and can be, again depending on the type of the light source, 20 W or 50 W.
The X-ray source 6 can be from the type of an open transmissive source or of a liquid metal jet source. An example for an open transmissive X-ray source is a source from the product line “TCHE+” offered from X-RAY WorX GmbH, Germany. An example for a liquid metal jet source is the source “metal jet D2+70 kV” offered by Excillum AB.
The object 2 is held by an object mount 7 defining an object plane 8. The object 2 is arranged with respect to the x-y-dimensions within an object field 8a. The object mount 7 is capable to mount objects 2 having a diameter of up to 300 mm or larger.
The object mount 7 can be embodied as a ring mount to have no additional mount material between the used light path 8e and the object 2. Alternatively, the object mount 7 can include a thin organic tray or a multitude of such trays. Such organic tray functions to minimize an absorption of the used X-rays 3. Alternatively, an aluminum and/or glass tray with an appropriate dopant can be used as part of the object mount 7 to filter a low, unwanted energy part of the spectrum of the X-rays 3.
X-ray energies below 10 keV or 15 keV are filtered via a respective object mount side filter. A typical thickness of the organic tray/the aluminum and/or glass tray in a respective embodiment of the object mount 7 can be in the range between 1 mm and 5 mm.
The glass tray can contain appropriate amounts of dopants materials such as Pb, B, As, Bi, Cd, Co, U in particular to optimize the filtering of low energy X-rays.
Between the source region 5 and the object mount 7, a shield stop 8b is arranged in an arrangement plane 8c. The shield stop 8b is arranged in a general light path 8d of the X-rays 3 and serves to select a usable light path 8e within the total light path 8d defined by the emission cone of the light source 6. In particular, the shield stop 8b protects uninspected regions of the object 2 from X-ray exposure. The shield stop 8b has a stop opening 8f, which also is referred to as a shield stop aperture. Through the shield stop aperture 8f, the usable light path 8e propagates which in the further, downward beam path impinges on the object 2.
The shield stop aperture 8f is transmissive for the X-rays 3, which is used to image the object 2. Such shield stop aperture 8f can be circular, can be a square aperture or can be rectangular. Other boundaries contours of the shield stop aperture 8f are possible, e.g. a hexagonal contour.
The shield stop 8b is movable via a shield stop displacement drive 8g along at least one stop displacement direction x/y in the arrangement plane 8c.
Such movement of the shield stop 8b executed via the shield stop displacement drive 8g can be a linear displacement along at least one linear displacement direction, e.g. along x/y. Alternatively and depending on the embodiment of the shield stop displacement drive 8g, the movability of the shield stop 8b can be along two displacement directions, e.g. x and y, spanning up the arrangement plane 8c. In an alternative or additional embodiment of the shield stop displacement drive 8g, the shield stop 8b can be movable along at least one curved direction and in particular can be movable along at least one circular direction.
The shield stop 8b can be configured such that the shield stop aperture 8f is variable in size. In particular, the shield stop 8b can be configured as an iris stop with variable size of the stop opening 8f Such stop opening size/shape variation can be effected by a respective shield stop aperture drive (not shown).
As shown in the insert
In the embodiment shown in
As indicated by a dashed line in
The detection system 1 can include a shield stop exchange mount 8i, which is indicated schematically in
The material of the shield stop 8b can be from highly absorptive material, e.g. lead, tungsten alloys. A z thickness of the shield step 8b is in the range between 100 μm and 1 mm.
The object 2 is imaged via an imaging optical arrangement 9 including an imaging optics 10 being embodied as a microscope objective. The imaging optical arrangement 9 is part of a detection assembly 11, which also includes the object mount 7 and a detection array 12 held within a detection housing 13. The detection array 12 can be a CCD or a CMOS array. The detection array 12 can be configured as a flat panel detector. The detection array 12 can have a minimum image read out time according to 10 frames per second (fps). Such image read out time can be smaller to achieve a higher fps value, in particular more than 10 fps, more than 25 fps and more than 50 fps. As a rule, the image read out time is larger than 5 ms.
The detection assembly 11 has a large field of view (FOV). The FOV depends strongly on the magnification of the used microobjective and can span a range from 70 mm for a 0.4× objective down to 0.7 mm for a 40× objective. Of course, the FOV depends on the size of the detection array 12.
The imaging optical arrangement 9 can be arranged such that the imaging optics 10 is exchangeable, in particular to switch between different magnification scales.
During a respective imaging measurement, the detection array 12, the imaging optics 10 and the object mount 7 are arranged in a fixed spatial relationship to each other. This component group 7, 10 and 12 is moved relative to the X-ray source 6 as is described further down below. For imaging/adjustment purposes, the detection array 12, the imaging optics 10 and the object mount 7 can be adjustable to each other in particular in the z-direction.
A typical distance d between the imaging optics 10 and the object 2 is in the range of 1 mm.
A typical minimum distance between the object plane 8, i.e. the arrangement plane of the object mount 7, and the arrangement plane 8c of the shield stop 8b is 1 mm. A typical minimum distance between the source region 5 of the X-ray source 6 and the shield stop 8b is in the range of 1 mm.
The resulting low distance between the source region 5 and the object 2 results in a maximum throughput of the used light path 8e. Further, such minimum distance between the object 2 and the imaging optics 10 results in a maximum resolution of the object imaging.
Further details of the imaging optical arrangement 9 hereinafter also are discussed referring to
The imaging optics 10 of the imaging optical arrangement 9 serves to image a transfer field 14 in a field plane 15 into a detection field 16 in a detection or image plane 16a. Such imaging can be done according to the respective embodiment of the imaging optics 10 with a magnification of 1 or with a magnification which is larger than 1, e.g. 2, 3, 4, 5, 8, 10, 15, 20, 25, 50, 100 or even larger.
A typical magnification value can be in the range of 4 to 40.
The detector array 12 of the detection assembly 11 is arranged at the detection field 16 of the imaging optics 10. The detection array 12 can be movable with respect to the position of the image plane 16a of the imaging optics 10 along the z-direction.
As a rule, the X-rays 3 from the X-ray source 6 produce a projection image on the scintillator material layer 17 via radiographically shading casting. No X-ray optics in such embodiment is present to influence a direction of the X-rays 3 within the usable light path 8e.
At the transfer field 14 a layer 17 of scintillator material is arranged. The thickness of such scintillator layer 17 corresponds to the z-extension of the transfer field 14 volume to be imaged by the imaging optics 10. A typical z-extension of the scintillator layer 17, i.e. a typical thickness of such layer 17, is 1 μm to 500 μm and in particular is in the range between 5 μm and 50 μm. The scintillator material layer 17 produces imaging light which can be in the near UV range, in the visible range or in the near infrared region from the X-rays 3 entering the layer 17.
Dependent on the respective embodiment, further X-ray optics can be present to image the object field 8a in the object plane 8 into the transfer field 14.
The imaging optics 10 has an optical axis 18 which also is referred to as a reference axis. The optical components of the imaging optics 10 which can be lenses and/or mirrors exhibit with respect to such reference axis 18 at least a certain degree of symmetry and in particular can exhibit rotational symmetry with respect to such reference axis. In the schematical depiction of the imaging optics 10, two of these optical components 18a, 18b are very schematically indicated.
In
Point of origin 22 is located at an entrance of an exemplified X-ray 25 from the entering X-rays 3 into the scintillator layer 17. Point of origin 23 is located at the crossing point of the X-ray 25 with the field plane 15, in particular in the middle of the z-extension of the scintillator layer 17. Point of origin 24 is located at the exit of the X-ray 25 from the scintillator layer 17.
In the beam path depicted in
The imaging optics 10 further includes a pupil stop 26 which is arranged in a pupil plane 27 of the imaging optics 10. The pupil stop 26 defines the direction of the marginal rays of the respective ray bundles emerging from the different points of origin from the scintillator layer 17. The chief rays 19c, 20c, 21c run collinearly.
The center C of the stop opening 28 of the pupil stop 26 is arranged at a decentering distance DD with respect to the optical axis 18.
The stop opening 28 defines a pupil of the imaging optics 10. A usable object side numerical aperture (NA) of the imaging optics 10, which is defined by the stop opening 28 of the pupil stop 26, i.e. a usable object side NA, is larger than 0.4. In the embodiment shown, the usable object side NA of the imaging optics 10 can amount to 0.6. The usable object side numerical aperture can be 0.5.
The decentering distance DD is at least 10% of a typical width W, in particular of a diameter of the stop opening 28. Such ratio DD/W can be in the range between 10% and 50%, in particular in the range between 25% and 35%.
The pupil stop 26 is mounted on a decentering drive 29. Such decentering drive 29 serves to translate the pupil stop 26 in the pupil plane 27. Such translation can be done along the x-axis and the y-axis or in any direction in the x-y plane. The decentering drive 29 is in signal connection (not shown) to a control unit 30a of a control device 30 of the detection system 1 (compare
The detection assembly 11 includes a lateral displacement drive 31. Such lateral displacement drive 31 serves for relative lateral displacement in the x- and/or y-direction of the object mount 7 with respect to the X-ray source 6. In the embodiment shown in
The control unit 30a of the control device 30 further is in signal connection (not shown) with the lateral displacement drive 31. Further, the control unit 30a of the control device 30 is in signal connection (not shown) with the shield stop displacement drive 8g.
As shown schematically in
The lateral displacement L (compare
The control unit 30 serves to control the decentering drive 29 of the pupil stop 26 and the shield stop displacement drive 8g depending on the lateral displacement of the X-ray source 6 effected by the lateral displacement drive 31. Such corresponding drive amount triples of (1) the decentering drive 29, of (2) the shield stop displacement drive 8g and of (3) the lateral displacement drive 31, which result (1) in a balancing of the X-ray 25 direction through the center of the shield stop aperture 8f and (2) in a balancing of the X-ray 25 direction parallel to the chief rays 19c to 21c direction, can be stored in a look-up table of the control device 30.
The detection system 1 is operated as follows:
In the initial configuration according to
By using a method described in DE 10 2018 209 570 A1, different object imaging projections are utilized via the lateral displacement of the X-ray source 6 as explained above. By doing so, a very small distance between the entrance of the imaging optics 10, i.e. the scintillator layer 17 and the nearest layer 41 of the object 2 is ensured in order to minimize transfer errors from the object 2 to the transfer field 14. The minimum distance d (compare
For example, using an object side numerical aperture of 0.4 defined by the stop opening 28 of the stop 26 and further using a wavelength of the imaging rays 19 to 21 of 400 nm, an effective spot size in the x- and in the y-direction can result, which is in the range of 1 μm (FWHM or full width at half maximum). Here, an angle A of the X-rays 25 to the optical axis 18 of 45° was used.
Further, the use of the shield stop 8b ensures that only that X-rays 3 passes the arrangement plane 8c, which is needed to illuminate the object 2 via the used light path 8e. This avoids unnecessary X-ray load on the object 2 and also on the components of the detection assembly 11.
A nominal object side numerical aperture (NA) of the imaging optics 10, which might be usable without constriction of the decentered pupil stop 26, is larger than the object side numerical aperture as defined by the stop opening 28. For example, in case of a width W of the stop opening 28 resulting in a usable object side numerical aperture of 0.6 and further in case of the angle A amounting to 20 deg, such nominal object side numerical aperture of the imaging optics 10 is (sin 20 deg=0.34) 0.6+0.34, i.e. is 0.94.
Larger nominal object side numerical apertures are possible by using immersion imaging optics 10. Examples and references for such further imaging optics are given in U.S. Pat. No. 7,057,187, the entire content of which is incorporated by reference. For example, the nominal object side numerical aperture of the imaging optics 10 can be up to 1.9.
U.S. Pat. No. 7,057,187 further gives examples for scintillating materials which can be used for the scintillating layer 17. A preferred material is CsI, having a refractive index of 1.95. Other scintillating material having refractive indices between 1.50 and 2.20 also can be used.
Possible scintillator materials for the scintillating layer 17 are NaI:Tl, CsI:Tl, CsI:Na, CsI, BaF2, CeF3, BGO, PWO:Y, LSO/LYSO or perovskites such as CsPbBr3 and CsPbI3.
While this specification contains many implementation details, these should not be construed as limitations on the scope of the invention or of what can be claimed, but rather as descriptions of features specific to particular embodiments of the invention. Certain features that are described in this specification in the context of separate embodiments can also be implemented in combination in a single embodiment. Conversely, various features that are described in the context of a single embodiment can also be implemented in multiple embodiments separately or in any suitable subcombination. The separation of various system components in the embodiments described above should not be understood as requiring such separation in all embodiments. Moreover, although features can be described above as acting in certain combinations and even initially claimed as such, one or more features from a claimed combination can in some cases be excised from the combination, and the claimed combination can be directed to a subcombination or variation of a subcombination.
Thus, particular embodiments of the invention have been described. Other embodiments are within the scope of the following claims. In addition, the actions recited in the claims can be performed in a different order and still achieve desirable results.
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