Method and arrangement for determining quality information for a target of a reflection x-ray tube

Abstract

The invention relates to a method for determining quality information (20) for a target (3) of a reflection X-ray tube (2), wherein the quality information (20) represents a surface state of the target (3), wherein the determination comprises: - changing a focal spot size and / or a focal spot position on the target (3), - detecting a respective return signal (5-x) of at least one stationary sensor (4-x) for each of a plurality of focal spot sizes and / or a plurality of focal spot positions, - evaluating the return signals (5-x) corresponding to the plurality of focal spot sizes and / or the plurality of focal spot positions, and - determining the quality information (20) on the basis of an evaluation result, - providing the determined quality information (20). Furthermore, the invention relates to an arrangement (1) for determining quality information (20) for a target (3) of a reflection X-ray tube (2).

Description

[0001] Method and arrangement for determining quality information for a target of a reflection X-ray tube

[0002] The invention relates to a method and a system for determining quality information for a target of a reflection X-ray tube. The quality information represents a surface condition of the target.

[0003] In reflection X-ray tubes, electrons are accelerated using an accelerating voltage and directed at a target. Interaction with the target material and deceleration generate X-rays. The area in which electrons are decelerated is the focal spot. Penetration depth is usually small compared to lateral expansion. Heating of the target material caused by deceleration must be well below its melting point. The usable power density in the focal spot therefore depends on the target material and heat dissipation. Even an increased evaporation rate can cause long-term damage to the target surface. Therefore, a service life for which a target is to be used must be specified. This often corresponds to the service life of the electron emitter. If a maximum power density is exceeded, the surface will be damaged.For example, melting of the target material can cause a hole ("burn-in") to form, disrupting an otherwise flat surface. Such damage has a detrimental effect on the generation of homogeneous X-ray radiation. In particular, it can reduce the resolution achievable with the focal spot of the X-rays.

[0004] The invention is based on the object of providing a method and an arrangement for determining quality information for a target of a reflection X-ray tube.

[0005] The object is achieved according to the invention by a method having the features of patent claim 1 and an arrangement having the features of patent claim 14. Advantageous embodiments of the invention emerge from the subclaims. One of the basic ideas of the invention is to use adjustable electron optics of a reflection X-ray tube to determine quality information for a target of the reflection X-ray tube. The adjustable electron optics permit beam shaping, for example by focusing an X-ray beam on the target and / or by changing the position of the electron beam on the target. To determine the quality information, a focal spot size and / or a focal spot position on a surface of the target is changed. Other parameters, in particular a power or energy of the electrons, are kept constant.However, it can be provided that, given a (changed) focal spot position based on a known target angle and a known focal length, the focusing of the focal spot is adjusted in order to compensate for a change in the focal spot size caused by the change in position. Assuming an undamaged, in particular flat, target surface, changing the focal spot size and / or focal spot position leads to a continued constant radiation; above all, an angle-dependent characteristic of the X-ray radiation remains the same, in particular regardless of the focal spot size and / or focal spot position. A return signal from a sensor, which directly represents an interaction of the electron beam with the target surface, in particular as a convolution of an electron beam profile and the surface profile, should therefore show virtually no change.However, if there is damage on the surface of the target (e.g. a "burn-in"), changing the focal spot size and / or the focal spot position also leads to a change in the X-rays generated in the target, for example because at least the part of the X-rays generated at the location of the damage has to pass through more target material and is thus attenuated and / or has a changed X-ray spectrum. With the surface change, the effective size of the focal spot usually becomes larger. Furthermore, an offset of the effective spot position occurs. In this case, the spot refers in particular to the effective size of the focal spot. All effects occur together and over a large scale of focal spot sizes. It is therefore not necessary to determine a focal spot size and / or a focal spot position and to laboriously generate an expected value in order to make a qualitative statement about the target surface.In any case, if the target surface is damaged, the sensor's return signal will also change when the focal spot size and / or focal spot position are changed. The invention utilizes this effect to determine quality information for the target, in particular for its surface condition.

[0006] In particular, a method is provided for determining quality information for a target of a reflection X-ray tube, wherein the quality information represents a surface condition of the target, wherein the determining comprises:

[0007] - Changing a focal spot size and / or a focal spot position on the target,

[0008] - detecting a return signal from at least one stationary sensor for several focal spot sizes and / or for several focal spot positions,

[0009] - evaluating the return signals corresponding to the multiple focal spot sizes and / or the multiple focal spot positions, and

[0010] - Determining the quality information based on an evaluation result,

[0011] - Providing the specific quality information.

[0012] Furthermore, in particular, an arrangement for determining quality information for a target of a reflection X-ray tube is provided, wherein the quality information represents a surface condition of the target, comprising a reflection X-ray tube, at least one sensor which is stationary with respect to the target and is configured to detect a return signal, and a control device, wherein the control device is configured to initiate and / or carry out the following method steps for determining:

[0013] - Changing a focal spot size and / or a focal spot position on the target,

[0014] - Receiving a return signal from the at least one stationary sensor for several focal spot sizes and / or at several focal spot positions,

[0015] - evaluating the return signals corresponding to the multiple focal spot sizes and / or the multiple focal spot positions, and

[0016] - Determining the quality information based on an evaluation result,

[0017] - Providing the specific quality information.

[0018] An advantage of the method and arrangement is that the surface of the target of the reflection X-ray tube can be characterized without complex sensor technology and / or additional measuring arrangements. In particular, the surface of the target can be characterized in the installed state, thus eliminating the need for, for example, the laborious removal of the reflection X-ray tube. This minimizes the effort required to inspect the target surface. This enables, in particular, routine and, in particular, regular monitoring of the target surface.

[0019] Changing the focal spot size and / or the focal spot position is carried out in a conventional manner using electron optics in the reflection X-ray tube. The focal spot size can be changed by changing the focus of the electron beam. In the focusing area, the electron beam changes direction toward a beam center. This convergence angle results in a location of minimum beam width. This location can also be referred to as the beam waist. Ideally, the beam waist coincides with the surface of the target; this is then referred to as the focused state. The minimum electron beam diameter is limited by the number of electrons (current) and the speed (acceleration voltage) of the electrons. The repulsive effect of the electrons leads to an asymmetry of the electron beam around the beam waist.Since the repulsive motion component in the region of the beam waist always increases and remains constant, the electron beam expands further behind the point of smallest diameter. The focal spot size can therefore be changed by changing the focus position. In other words, by overfocusing (the beam waist lies in front of the target surface) or underfocusing (the beam waist lies behind the target surface in the target), the focal spot size on the surface can be changed, while the number of electrons striking the surface and interacting with the target material remains the same. The focal spot position can be changed by simply deflecting the electron beam. It can be provided that a change in the focal spot size caused by changing the focal spot position due to an angle of incidence of the electron beam on the target surface is corrected by refocusing.

[0020] The reflection X-ray tube comprises, in particular, an electron emitter (cathode), an anode, a deflection unit, a focusing unit, a target, and a window that is transparent to X-rays. When the electron beam hits the target, it interacts with the target material and generates the useful radiation in a very small, but above all, very surface-close area. The intensity of the useful radiation in a solid angle depends on the angle to the surface of the target. If the surface is undamaged, a simple model for the intensity in the useful beam is obtained, the so-called radiation characteristic. If the surface of the target is damaged, for example, due to an overload event, or if the surface degrades over time, the surface of the target becomes more irregular and / or even holes form. The X-ray radiation generated close to the surface from an irregular surface orfrom a hole exhibits a more inhomogeneous radiation characteristic than in the undamaged state; the change in intensity across the solid angle is greater. Furthermore, a hardening of the X-ray spectrum can occur depending on the solid angle. As mentioned above, the focus of the electron beam corresponds to a three-dimensional beam waist. If the surface is displaced by damage, the focal spot, the location of the generated X-ray radiation, will no longer be maximally focused. In particular, with a damaged surface, different areas of the electron beam can hit the surface of the target material at different depths, whereby the depth is defined with reference to the undamaged surface. This leads to reduced imaging resolution. Even the slightest surface changes therefore lead to a change in the radiation characteristic.The minimum focal spot size can no longer be achieved on a damaged target surface, even with optimized focusing. The invention exploits this change in the radiation characteristic by using a stationary sensor.

[0021] Damage refers, in particular, to a local surface contour of the target surface where the surface no longer has a defined or known angle to the sensor, but rather (significantly) deviates from this. Damage can, for example, be a hole in the surface.

[0022] The at least one sensor detects, in particular, a physical quantity (in particular an X-ray or a current) caused by an interaction of the electron beam with the target material. In this case, the angular range or solid angle in which the detection takes place is constant. The return signal is, in particular, a sensor signal. The return signal is, in particular, a sensor signal that is representative of the detected physical quantity.

[0023] It can be provided that, based on the quality information, at least one maintenance information item and / or maintenance request and / or request to replace the reflection X-ray tube is generated and output. This output can be made, for example, on a display device of the system. Furthermore, the output can also be made by another signal generator (e.g., an LED) or in the form of an entry in an error log or test log.

[0024] Parts of the arrangement, in particular the control device, can be designed individually or collectively as a combination of hardware and software, for example as program code executed on a computing device, in particular a microcontroller or microprocessor. However, it can also be provided that parts are designed individually or collectively as an application-specific integrated circuit (ASIC) and / or a field-programmable gate array (FPGA) and / or a graphics processor (GPU) and / or a digital signal processor (DSP). The control device can in particular comprise at least one computing device and at least one memory. The control device can also be designed as part of the reflection X-ray tube.

[0025] In one embodiment, it is provided that the at least one sensor is an X-ray detector that is stationary relative to the target and configured to detect X-rays generated by the target. This allows an existing setup, as is common in X-ray machines, to be used to characterize and / or inspect the surface of the target. It can be provided that an intensity is summed and / or averaged across multiple image elements of at least one partial area of ​​the X-ray detector. In particular, it can be provided that an intensity is summed and / or averaged across all image elements of the X-ray detector. This enables, in particular, simple evaluation, since only a single (single-channel) overall signal from the X-ray detector needs to be processed and taken into account during the evaluation.It may be provided that a bright-field correction is performed and taken into account in a conventional manner. This allows inhomogeneities in the reflection X-ray tube and the X-ray detector to be compensated for that are not due to inhomogeneities in the target surface.

[0026] In one embodiment, the at least one sensor is a current sensor arranged in the reflection X-ray tube, which is configured and arranged to detect electrons backscattered by the target. This makes it possible, in particular, to carry out the method with regard to detecting the return signal entirely in the reflection X-ray tube and thereby, in particular, to provide a high degree of integration, so that the method can be carried out, for example, solely by means of a control of the reflection X-ray tube, without, for example, the need for an X-ray detector. This allows costs and effort to be saved, and the method or an associated function can be fully integrated into a reflection X-ray tube. In a simple embodiment, the current sensor comprises a conductive surface that covers a limited angular range of the emission characteristics of backscattered electrons.The backscattered electrons are low-energy and therefore particularly suitable as a return signal for characterizing the target surface. The current sensor's functionality is comparable to that of an electron microscope. If, for example, the electron beam hits a hole in the surface, the radiation characteristics of the backscattered electrons change significantly. This change can be detected by the current sensor. In contrast to an X-ray detector, such a current sensor is a single-channel sensor.

[0027] In one embodiment, at least part of the current sensor is arranged opposite a surface of the target. This is particularly advantageous because the electron beam, which falls onto the target at a shallow angle, and a window through which the X-ray radiation leaves the reflection X-ray tube are not obscured by the current sensor. In particular, at least part of the current sensor can be arranged in a direction perpendicular to the surface of the target. In particular, it is provided that the current sensor is electrically insulated from directions that do not directly face the surface of the target, for example by applying an insulating layer in these directions. Furthermore, it is particularly provided that the current sensor is thermally conductive and / or heat-resistant in order to be able to withstand thermal radiation emanating from the target.

[0028] In principle, it is also possible to provide multiple sensors whose return signals are taken into account during the evaluation. For example, it is possible to use the return signal from an X-ray detector and the return signal from a current sensor. Both return signals are then taken into account during the evaluation. In one embodiment, it is provided that the evaluation comprises determining a change in the return signal when the focal spot size and / or the focal spot position is changed, wherein the quality information is determined based on the determined change. The basis for this evaluation is the assumption that an undamaged (flat) surface of the target would not lead to any significant change. The greater the determined change caused by changing the focal spot size and / or the focal spot position, the greater the damage to the surface must therefore be.It may be intended to express the quality information as a scalar representing the change. The larger the value of the scalar, the greater the damage to the target surface.

[0029] In one embodiment, the evaluation comprises comparing the determined change with a predefined threshold value, wherein the quality information is determined based on a comparison result. This makes it possible, in particular, to make a decision as to whether damage is present or not. Several levels or classes of damage or inhomogeneity of the surface of the target can also be distinguished. A value for the predefined threshold value or for the values ​​of the individual levels or classes can, for example, be determined empirically based on test series and / or by simulation, in which targets with surface damage (in particular of varying severity) are used.

[0030] In one embodiment, it is provided that two focal spot sizes and / or two focal spot positions are taken into account, wherein the evaluation for determining the change comprises at least determining a difference signal of the return signals corresponding to the two focal spot sizes and / or the two focal spot positions. This is an embodiment in which the detection and evaluation can be carried out particularly easily. In particular, it is provided that exactly two or exclusively two focal spot sizes and / or exactly two or exclusively two focal spot positions are used. However, it can be provided that a return signal is also taken into account that was detected at a focal spot size and / or focal spot position that lies between the two focal spot sizes or between the two focal spot positions.For example, a focal spot size midway between the focal spot sizes can be used, such as a focal spot size that is established when a nominally maximum focus of the electron beam is assumed on an undamaged target surface. The two focal spot sizes can then be created, for example, by overfocusing or underfocusing. For the focal spot positions, it can be provided, for example, to perform a shift in positive and negative directions in one dimension starting from the center position.

[0031] In one embodiment, the evaluation comprises determining and taking into account at least one reference variable. In particular, the above-described center size between the values ​​of the two focal spot sizes and / or between the values ​​of the two focal spot positions can be selected as the reference variable.

[0032] In one embodiment, it is provided that a plurality of focal spot positions are taken into account, with the quality information being provided in a spatially resolved manner based on the respective focal spot positions. This allows a spatially resolved statement to be made about the surface condition. For this purpose, it can be provided, for example, that the focal spot position is varied in a predetermined range, in particular in two dimensions (“sweep”) and simultaneously a return signal is recorded at individual focal spot positions by means of the at least one sensor. Based, for example, on an average value across all recorded return values, which is used as a reference value for normalization, a map of the surface can be generated from the spatially resolved return signals and provided as quality information.

[0033] In one embodiment, it is provided that the evaluation comprises averaging over selected sub-regions of the X-ray detector. This makes it possible to utilize a larger area of ​​the X-ray detector. In particular, this allows the return signal, which represents the X-ray radiation when using an X-ray detector, to be detected using multiple channels, each channel corresponding to an image element of the X-ray detector. The return signal then corresponds to the detected intensity of the X-ray radiation averaged over the multiple channels or image elements. In particular, it can also be provided that an entire active area of ​​the X-ray detector is used and averaged over the entire active area or over all image elements of the active area.In one embodiment, the evaluation comprises determining and evaluating a mean value and / or a gradient of a one-dimensional intensity profile on the X-ray detector with respect to a target angle. This allows a change in a radiation characteristic, particularly in a plane defined by the target angle, to be evaluated when the focal spot size and / or the focal spot position changes. It can be provided that, to determine the mean values ​​of the gradient, an average is taken over one or more surface areas of the X-ray detector.

[0034] In one embodiment, it is provided that the method steps are repeated with at least one changed electron energy of the reflection X-ray tube. In this way, quality information can also be determined and provided for one or more other electron energies. By changing the electron energy and repeating the process, the reliability of a diagnosis can be increased. For example, it can be provided that damage to the surface and / or the condition "not OK" is determined as the end result if, within the scope of determining the quality information, damage and / or the condition "not OK" was determined for a predetermined number of electron energies, e.g., at least two electron energies.

[0035] In one embodiment, the results of multiple evaluation variants are combined in a weighted manner and provided as quality information. This allows return signals from multiple sensors to be taken into account. Furthermore, it is additionally or alternatively possible to evaluate the return signals in multiple ways and to consider the respective results in a weighted manner to determine the quality information.

[0036] Weighting factors for the individual evaluation variants can be determined, for example, using empirical test series. Here, too, it may be planned to carry out this process using specially prepared targets with deliberately damaged surfaces to determine the weighting factors.

[0037] Further features for the configuration of the arrangement will become apparent from the description of embodiments of the method. The advantages of the arrangement are the same as in the embodiments of the method. The invention will be described below with reference to preferred embodiments.

[0038] Reference is made to the figures, which show:

[0039] Fig. 1 is a schematic diagram illustrating embodiments of the arrangement for determining quality information for a target of a reflection X-ray tube;

[0040] Fig. 2a is a schematic representation to illustrate an interaction of the electron beam with a surface of the target (without damage);

[0041] Fig. 2b is a schematic diagram illustrating an interaction of the electron beam with a surface of the target (with damage);

[0042] Fig. 3a is a schematic diagram illustrating the process for changing a focal spot size;

[0043] Fig. 3b is a schematic diagram illustrating the process for changing a focal spot position;

[0044] Fig. 4 is a schematic representation to illustrate an embodiment of the method and the arrangement;

[0045] Fig. 5 is a schematic diagram illustrating an embodiment of the method and arrangement;

[0046] Fig. 6 is a schematic flow diagram to illustrate embodiments of the method.

[0047] Fig. 1 shows a schematic representation to illustrate embodiments of the arrangement 1 for determining quality information 20 for a target of a reflection X-ray tube 2. The arrangement 1 is particularly configured to carry out the method described in this disclosure. The method is explained in more detail below with reference to the arrangement 1. The arrangement 1 comprises a reflection X-ray tube 2 with a target 3, at least one sensor 4-x that is stationary with respect to the target 3 and configured to detect a return signal 5-x, and a control device 6.

[0048] The reflection X-ray tube 2 further comprises a deflection unit 7 and a focusing unit 8, which are controlled in particular by the control device 6. Electrodes are emitted from a cathode (not shown), accelerated to the anode (not shown), and guided behind the anode into a beam tube 22 as an electron beam 9 at a constant speed toward the target 3. In the focusing plane, an aperture 23 can optionally limit the beam diameter.

[0049] Where the electrode beam 9 strikes the target 9, an interaction of the electrons with the target material takes place in the area of ​​a focal spot 10, generating X-rays. A portion of the X-rays exit the reflection X-ray tube 2 through a window 12 that is transparent to X-rays and forms the useful beam 11. The used X-rays 11 are then directed, for example, to a planar X-ray detector 4-1 and can be used in one application to irradiate objects and capture X-ray images of them.

[0050] A focus of the electron beam 9 can be adjusted by means of the focusing unit 8. In particular, a location of a beam waist 15 (Fig. 2a) of the electron beam 9 can be shifted by the focusing unit 8. A focal spot position can be changed by means of the deflection unit 7. In particular, this is possible in two dimensions. It can be provided that a focus is readjusted when the focal spot position is changed in order to always achieve a minimum focus on the target 3. This can be done in particular when a position parallel to the target 3 in the paper or screen plane is changed, because this changes the target angle of the electron beam 9. By changing the focus, a focal spot size can also be changed (e.g., by overfocusing or underfocusing).

[0051] The control device 6 is configured to initiate and / or carry out the following method steps to determine the quality information 20: - Changing a focal spot size and / or a focal spot position on the target 3,

[0052] - Receiving a return signal 5-x from at least one stationary sensor 4-x for multiple focal spot sizes and / or at multiple focal spot positions,

[0053] - Evaluating the return signals 5-x corresponding to the multiple focal spot sizes and / or the multiple focal spot positions, and

[0054] - Determining the quality information 20 based on an evaluation result,

[0055] - Providing the specific quality information 20.

[0056] The specific quality information 20 can be provided, for example, as an analog or digital signal, for example as a digital data packet containing the quality information in coded form.

[0057] Figures 2a and 2b show schematic representations to illustrate an interaction of the electron beam 9 with a surface 13 of the target 3 without damage (Fig. 2a) and with damage 14 (Fig. 2b) in the form of a hole, as occurs when the power of the electron beam 9 was selected to be too high ("penetration"). The electron beam 9 strikes the surface 13 of the target 3 at an angle 17. Where the electrons of the electron beam 9 strike the surface 13, they interact with the target material, creating X-ray radiation 11, which in the example falls onto the X-ray detector 4-1 from a limited angle.

[0058] In the example shown in Fig. 2a, surface 13 is undamaged and therefore flat. A focus of focal spot 10 coincides with a beam waist 15, the narrowest region of electron beam 9. From the perspective of the X-ray detector 4-1, this results in an effective focal spot 16 that is narrower than focal spot 10.

[0059] In the example shown in Fig. 2b, the surface 13 has damage 14 in the form of a deep hole in the target material. The damage 14 in the surface 13 causes the focal spot 10 to lie within the target 3, which leads to a beam expansion beyond the focus or beam waist 15. On the other hand, a surface 13 with which the electrons of the electron beam 9 interact is significantly enlarged compared to the example in Fig. 2a. Since the effective focal spot 16 lies in the hole, the generated X-ray radiation 11 must pass through the target material to be detected by the X-ray detector 4-1. This leads overall to a reduction in intensity and a hardening of the spectrum of the X-ray radiation 11, as well as to an angular dependence of the intensity, since the thickness of the target material that must be penetrated varies for different angles. Furthermore, the focal spot 16 is offset.

[0060] Figures 3a and 3b illustrate the principle utilized by the method and arrangement described in this disclosure, using the example of damage 14 in the form of a hole on the surface 13 shown in Fig. 2b.

[0061] Fig. 3a shows an example of an embodiment in which a focal spot size is changed, wherein the focal spot size is smaller in the case of the more strongly focused electron beam 9 shown above and larger in the case of the underfocused electron beam 9 shown below. It is evident from Fig. 3a that an interaction of the electron beam 9 will be different due to the damage 14 of the surface 13 and therefore an X-ray radiation generated with respect to a constant angular range (or solid angle) will also show a change if the focal spot size is changed as shown. The method makes use of this effect. Analogous to the generated X-ray radiation, the number of backscattered electrons also varies when the focal spot size is changed.Detecting backscattered electrons is very sensitive to even slight changes in the target surface, as the electrons can only reach the sensor directly from the surface. When a hole is formed, electrons generally cannot reach the sensor from the hole. Therefore, using a current sensor and an X-ray detector require different evaluation methods.

[0062] Fig. 3b shows an example of an embodiment in which a focal spot position is changed, wherein in the case shown above the focal spot position coincides directly with the damage 14, i.e. with the hole. In the case shown below, however, two focal spot positions are shown which, in addition to the damage 14, coincide with undamaged parts of the surface 13. It is clear from Fig. 3b that an interaction of the electron beam 9 will be different at the focal spot positions shown as an example due to the damage 14 of the surface 13 and therefore an X-ray generated with respect to a constant angular range (or solid angle) will also show a change if the focal spot position is changed as shown. The method makes use of this effect. Analogous to the number of X-rays generated, a change in the focal spot position also affects the number of backscattered electrons.

[0063] It can be provided that the at least one sensor 4-x (Fig. 1) is an X-ray detector 4-1 that is fixedly positioned relative to the target 3 and configured to detect X-ray radiation 11 generated by the target 3. The X-ray detector 4-1 is, in particular, an area detector with a plurality of image elements. Within the scope of the method, an intensity detected by the X-ray detector 4-1 is used as the return signal 5-1.

[0064] It can be provided that the at least one sensor 4-x (Fig. 1) is a current sensor 4-2 arranged in the reflection X-ray tube 2, which is configured and arranged to detect electrons 18 backscattered from the target 3. In the simplest case, the current sensor 4-2 is designed as a conductive element that is electrically insulated from the rest of the reflection X-ray tube 2 by means of insulation 19. The electrons 18 backscattered in the direction of the current sensor 4-2 can be detected and evaluated as a current, with the detected current forming the return signal 5-2.

[0065] It can further be provided that at least a part of the current sensor 4-2 is arranged opposite a surface 13 of the target 3.

[0066] It can be provided that the evaluation includes determining a change in the return signal 5-x upon changing the focal spot size and / or the focal spot position, wherein the quality information 20 is determined based on the determined change. The change can be determined, for example, by simply calculating the difference between two values.

[0067] It can be provided that the evaluation includes comparing the determined change with a predefined threshold value, wherein the quality information 20 is determined based on a comparison result. For example, in one embodiment, it can be provided to distinguish between the states "OK" and "not OK" depending on whether the predefined threshold value is exceeded. If the determined change is below the predefined threshold value, the quality information is assigned "OK"; if, however, the determined change reaches or exceeds the predefined threshold value, the quality information is assigned "not OK". Multiple gradations, each with a threshold value, can also be provided.

[0068] Furthermore, it can be provided that two focal spot sizes and / or two focal spot positions are taken into account, wherein the evaluation for determining the change comprises at least determining a difference signal of the return signals 5-x corresponding to the two focal spot sizes and / or the two focal spot positions.

[0069] It can be provided that the evaluation includes determining and taking into account at least one reference variable. The reference variable can, for example, be a return signal 5-x for a focal spot size and / or focal spot position that lies midway between two extremes.

[0070] An exemplary embodiment of the method with an exemplary evaluation is described below. This assumes an X-ray detector 4-1 as the stationary sensor 4-x. In principle, however, another sensor 4-x can also be used in the same way.

[0071] An electron energy is set, and the deflection unit 7 and the focusing unit 8 are controlled such that a nominal (i.e., valid in the absence of damage) minimum focal spot is set. A detector image for bright-field correction is acquired with the minimum focal spot size settings. The result is a homogeneous image in which only photon noise is captured. Based on this, a reference image is generated under the conditions of this bright-field correction (hereinafter referred to as "Image 0").

[0072] Subsequently, the focal spot is changed under otherwise identical conditions (same power and electron energy). The focal spot size can be changed by enlarging the electron beam 9 on the surface of the target 3, in particular by overfocusing or underfocusing. Alternatively or additionally, the focal spot position can be shifted laterally with respect to the surface 13 by deflecting the electron beam 9 in a positive or negative direction in one dimension using the deflection unit 7.

[0073] Based on this, for example, two images with different focal spot sizes and / or focal spot positions are acquired using the X-ray detector 4-1 ("Image +" and "Image -"). Acquiring two images with a change in two directions increases reliability; in principle, it would also be possible to acquire only one image with a different focal spot size and / or focal spot position compared to "Image 0."

[0074] A)

[0075] For example, initial quality information is obtained from a change in intensity. For this purpose, a relative change is determined according to

[0076] R1 = (Mean(Image+) - Mean(ImageO) + Mean(Image-) - Mean(ImageO)) / Mean(ImageO)

[0077] This result is weighted, the weighting factor k1 of which is derived from an empirical determination of the image quality for the X-ray application.

[0078] R1w = k1 ■ R1.

[0079] The result can be output, for example, as a percentage value, where 100% corresponds to a confirmed disadvantage for the image quality, while a smaller value is suitable for documenting a deterioration towards a “not OK” status.

[0080] The weighting factor makes it possible, in particular, to shift the obtained value relative to a predefined threshold. This can influence the point at which the surface is assessed as damaged ("not OK"). In particular, it can take a measurement context into account. For example, with increasing surface damage, the resolution deteriorates significantly faster than the intensity. Therefore, if measurements are to be taken with limited resolution, a correction can be made by a factor of 5, for example, so that damage ("not OK") is detected earlier. A value Rw1 is therefore calculated, for example as a percentage. Depending on the application, the surface of the target is already too badly damaged ("not OK") at a value of 20%, for example if the resolution criterion is used, or at 100% if the intensity criterion is used, for example.A change in intensity can be compensated for, in particular, by a longer integration time, so that a measurement is less affected in the event of damage than in the case of resolution.

[0081] B)

[0082] A second quality information item is derived, for example, from a change in the intensity gradient of the images Image+ and / or Image-. Due to image correction under the conditions of Image 0, the images Image+ and Image- show inhomogeneities in the presence of target damage.

[0083] B1) For this purpose, in the first step, two image areas are taken from Image+ and / or Image-. One image area is observed at an effectively smaller target angle, while the other image area is observed at an effectively larger target angle. To explain: If the target angle to the detector center is, for example, 20°, and the useful beam has an aperture angle of, for example, 15°, the effective target angle on one side of the detector is 12.5°, while the effective target angle on the opposite side is 27.5°. In the example, the effective target angle changes horizontally, which is why the selected sub-areas are referred to as left and right.

[0084] ROI1 = mean value from left detector area of ​​image+

[0085] ROI2 = mean value from right detector area of ​​image+

[0086] R2 = abs(ROI1 - ROI2) / ROI1

[0087] Here, too, a weighting with an additional weighting factor k2 takes place based on the effect on the relevant image quality.

[0088] R2w = k2 ■ R2 B2)

[0089] Alternatively, instead of using designated image areas, the gradient can be determined over the entire image and the gradient itself, offset against a weighting factor, can be used to determine the quality information.

[0090] Burn-in affects the quality through:

[0091] Change in intensity of X-rays;

[0092] Inhomogeneous radiation, associated with spectral change (hardening) of the X-ray radiation;

[0093] - Enlargement of the effective spot;

[0094] - Changing the position of the effective spot.

[0095] Complex methods are required to determine the latter two points. However, since all negative influences have a cause, the others can be inferred from the first two points determined using the method described in this disclosure. If the weighting factors are appropriately selected, both calculations will result in a similar value and can thus be mutually confirmed and / or verified (for example, by comparing a deviation of the values ​​with a predetermined threshold value for plausibility purposes, and assessing the values ​​as mutually plausible if they fall below the threshold).

[0096] Fig. 4 shows a schematic representation to illustrate the effect of damage on the surface. Shown is an image captured by the X-ray detector 4-1, which is provided as a return signal 5-1. If, for example, the situation shown in Fig. 2b is assumed, it becomes clear that the X-ray radiation 11 that strikes the image elements of the X-ray detector 4-1 at the right end of the X-ray detector 4-1 has a lower intensity than the X-ray radiation 11 that strikes the image elements at the left end of the X-ray detector 4-1, since the X-ray radiation 11 has to penetrate different amounts of target material and is therefore attenuated to different degrees. Such an intensity curve is shown schematically in Fig. 4. The intensity curve and the gradient can be determined in the plane 21 (which corresponds to a straight line in the image) spanned by the target angle 13.The results from A), B1) or B2) with the empirically determined weighting factors each individually or in combination result in a scalar criterion for the surface condition of the target 3. The scalar can then be compared with (at least) one predetermined threshold value in order to categorize or decide whether the surface 13 is damaged or not or to what degree damage is present.

[0097] It can be provided that a plurality of focal spot positions are taken into account, with the quality information 20 being provided spatially resolved based on the respective focal spot positions. For this purpose, it is particularly provided that a change in the return signal 5-x is determined for each change in the focal spot position. With a two-dimensional change in the focal spot position, a two-dimensional map for the quality information 20 can be generated and provided.

[0098] It can be provided that the evaluation includes calculating an average value over selected subregions of the X-ray detector 4-1. As already described above, such averaging can also include calculating an average value over the entire X-ray detector 4-1. The subregion then encompasses the entire active area of ​​the X-ray detector 4-1. Furthermore, as also described above, an average value can also be calculated only over a subregion ("ROI") of the X-ray detector 4-1.

[0099] It can be provided that the evaluation comprises determining and evaluating a gradient of a one-dimensional intensity profile on the X-ray detector 4-1 with respect to a target angle 17 (Fig. 2a). This has already been described above by way of example.

[0100] In both cases, a two-dimensional map can be generated and provided, the scanning size of which is defined by the change in the position of the electron beam, i.e. the focal spot position, on the target surface. In practice, a step size is chosen that corresponds to the size of the beam waist of the electron beam. The intensity map, as well as the gradient map, shows damaged areas through changed values. This can primarily be used to determine the extent of the damage. The target damage can be large compared to the area of ​​the target surface that can be reached by the electron beam. In these cases, it is necessary to reposition the target itself in order to achieve a perfect surface again. However, if the damaged area is small compared to the reachable target surface, the electron beam orWith suitable beam steering, the focal spot can instead be repositioned on an undamaged area of ​​the surface.

[0101] It can be provided that the process steps are repeated with at least one changed electron energy of the reflection X-ray tube 2.

[0102] It may be provided that the results of several evaluation variants are summarized in a weighted manner and provided as quality information 20. This has already been explained above with reference to the evaluation steps A), B1) and B2).

[0103] It can be provided that, based on the quality information 20, at least one maintenance information item and / or maintenance request and / or request to replace the reflection X-ray tube 2 is generated and output. The output can be made, for example, on a display device (not shown) of the arrangement 1. Furthermore, the output can also be signaled by another signal generator (e.g., an LED) or in the form of an entry in an error log or test log.

[0104] Figure 5 shows a schematic diagram illustrating one embodiment. In this embodiment, the at least one sensor 4-x is a current sensor 4-2 arranged in the reflection X-ray tube 2, which is configured and arranged to detect electrons 18 (Figure 1) backscattered from the target 3.

[0105] Figure 5 shows a current 30 normalized to a mean value resulting from the backscattered electrons 18. The x-axis shows the change in the focus setting compared to a target value, represented by a focus current in mA. Negative values ​​indicate underfocusing, while positive values ​​indicate overfocusing. At approximately 5 mA, the electron beam diameter corresponds to the extent of damage to the target surface. Therefore, a minimum appears in the current 30 of the backscattered electrons 18, since a larger number of electrons remain in the target due to the more inhomogeneous surface.

[0106] Figure 6 shows a schematic flow diagram illustrating embodiments of the method for determining quality information for a target of a reflection X-ray tube. The method can be implemented, for example, using the embodiment of the arrangement shown in Figure 1.

[0107] In a method step 100, a focal spot size and / or a focal spot position is set for an electron energy.

[0108] In a method step 101, a return signal from at least one stationary sensor is detected. The stationary sensor is, in particular, an X-ray detector that detects X-rays generated by the reflection X-ray tube. Alternatively or additionally, a current sensor can also be used, which is configured and arranged to detect electrons backscattered by the target.

[0109] In a method step 102, a focal spot size and / or a focal spot position is changed by controlling the reflection X-ray tube accordingly.

[0110] In a method step 103, a return signal from the at least one stationary sensor is detected.

[0111] In a method step 104, the return signals corresponding to the multiple focal spot sizes and / or the multiple focal spot positions are evaluated. In particular, it can be provided that the evaluation comprises determining a change in the return signal when the focal spot size and / or the focal spot position changes, wherein the quality information is determined based on the determined change. For example, it can be provided to form a difference for the return signals recorded for the two focal spot sizes and / or the two focal spot positions. Ideally, a value of the difference should be zero for an undamaged surface. If, however, the surface is damaged, a value of the difference will be different from zero. In a method step 105, the quality information is determined based on an evaluation result.In the simplest case, the quality information corresponds, for example, to the specific change or the specific difference.

[0112] It can be provided in method steps 104 and 105 that the evaluation comprises a comparison of the determined change with a predetermined threshold value, wherein the quality information is determined on the basis of a comparison result.

[0113] In a method step 106, the determined quality information is provided.

[0114] In a method step 107, it can be provided that, based on the determined quality information, at least one maintenance information item and / or maintenance request and / or request to replace the reflection X-ray tube is generated and output. The output can be made, for example, on a display device of the arrangement. Furthermore, the output can also be signaled by another signal generator (e.g., an LED) or in the form of an entry in an error log or test log. This occurs, in particular, if the quality information contains surface damage that exceeds a predetermined further threshold.For this purpose, it can be provided that the at least one item of quality information is compared with the predefined further threshold value, wherein the at least one item of maintenance information and / or the maintenance request and / or the request to replace the reflection X-ray tube is generated and output when the predefined further threshold value is exceeded.

[0115] Further embodiments of the method have already been described above with reference to the arrangement. List of reference symbols

[0116] 1 arrangement

[0117] 2 reflection X-ray tubes

[0118] 3 T arget

[0119] 4-x sensors

[0120] 4-1 X-ray detector

[0121] 4-2 Current sensor

[0122] 5-x return signal

[0123] 6 Control device

[0124] 7 Deflection unit

[0125] 8 Focusing unit

[0126] 9 Electron beam

[0127] 10 Focal spot

[0128] 11 X-rays (useful ray)

[0129] 12 windows

[0130] 13 Surface

[0131] 14 Damage

[0132] 15 frog waist

[0133] 16 effective focal spot

[0134] 17 Target angles

[0135] 18 backscattered electrons

[0136] 19 Insulation

[0137] 20 Quality information

[0138] 21 Level

[0139] 22 jet pipe

[0140] 23 aperture

[0141] 30 Current (backscattered electrons)

[0142] 100-107 Procedural steps

Claims

Patent claims 1. A method for determining quality information (20) for a target (3) of a reflection X-ray tube (2), wherein the quality information (20) represents a surface condition of the target (3), wherein the determining comprises: - Changing a focal spot size and / or a focal spot position on the target (3), - detecting a return signal (5-x) of at least one stationary sensor (4-x) for several focal spot sizes and / or for several focal spot positions, - evaluating the return signals (5-x) corresponding to the multiple focal spot sizes and / or the multiple focal spot positions, and - determining the quality information (20) based on an evaluation result, - Providing the specific quality information (20).

2. Method according to claim 1, characterized in that the at least one sensor (4-x) is an X-ray detector (4-1) which is in a fixed relationship to the target (3) and is designed to detect X-ray radiation (11) generated by the target (3).

3. Method according to claim 1, characterized in that the at least one sensor (4-x) is a current sensor (4-2) arranged in the reflection X-ray tube (2), which is designed and arranged to detect electrons (18) scattered back from the target (3).

4. Method according to claim 3, characterized in that at least a part of the current sensor (4-2) is arranged opposite a surface (13) of the target (3).

5. Method according to one of the preceding claims, characterized in that the evaluation comprises determining a change in the return signal (5-x) when changing the focal spot size and / or the focal spot position, wherein the quality information (20) is determined based on the determined change.

6. The method according to claim 5, characterized in that the evaluation comprises comparing the determined change with a predetermined threshold value, wherein the quality information (20) is determined on the basis of a comparison result.

7. Method according to one of claims 5 or 6, characterized in that two focal spot sizes and / or two focal spot positions are taken into account, wherein the evaluation for determining the change comprises at least determining a difference signal of the return signals (5-x) corresponding respectively to the two focal spot sizes and / or the two focal spot positions.

8. Method according to one of the preceding claims, characterized in that the evaluation comprises determining and taking into account (5-x) at least one reference variable.

9. Method according to one of the preceding claims, characterized in that a plurality of focal spot positions are taken into account, wherein the quality information (20) is provided in a spatially resolved manner based on the respective focal spot positions.

10. Method according to one of claims 2 to 9, characterized in that the evaluation comprises averaging over selected partial areas of the X-ray detector (2).

11. Method according to one of claims 2 to 10, characterized in that the evaluation comprises determining and evaluating a gradient of a one-dimensional intensity profile on the X-ray detector (4-1) with respect to a target angle (17).

12. Method according to one of the preceding claims, characterized in that the method steps are repeated with at least one changed electron energy of the reflection X-ray tube (2).

13. Method according to one of the preceding claims, characterized in that results of several evaluation variants are summarized in a weighted manner and provided as quality information (20).

14. Arrangement (1) for determining quality information (20) for a target (3) of a reflection X-ray tube (2), wherein the quality information (20) represents a surface condition of the target (3), comprising: a reflection X-ray tube (2), at least one sensor (4-x) which is stationary with respect to the target (3) and is configured to detect a return signal (5-x), and a control device (6), wherein the control device (6) is configured to initiate and / or carry out the following method steps for determining: - Changing a focal spot size and / or a focal spot position on the target (3), - receiving a return signal (5-x) from the at least one stationary sensor (4-x) for a plurality of focal spot sizes and / or at a plurality of focal spot positions, - evaluating the return signals (5-x) corresponding to the multiple focal spot sizes and / or the multiple focal spot positions, and - determining the quality information (20) based on an evaluation result, - Providing the specific quality information (20).

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