Method and measuring device for measuring a test object by means of x-ray fluorescence

Abstract

The invention relates to a method for measuring a test object (27) using a measuring device (11) by means of x-ray fluorescence, more particularly for measuring the thickness of thin layers on the test object (27) or for determining an element concentration in the test object (27), wherein: before a measuring task is carried out for the test object (27) positioned in the measuring device (11), a structure of the measuring point (25) on the test object (27) is captured; starting from a distance Ds, which determines a position of the focal plane above the measuring table (21), a focal plane of a controllable focusing optical unit (42) is moved towards the measuring point (45) on the test object (27); an apex of the measuring point on the test object (27) is captured by an image of the image capture apparatus (33) and a distance D1 to the measuring table (21) is assigned; starting from the distance D1, the focusing optical unit (42) is controlled in a plurality of steps and the focal plane of the beam path (41) of the image capture apparatus (33) is moved by the focusing optical unit (42) in the direction of the measuring table (21) and an image of the measuring point (45) on the test object (27) is captured from every step of the shifted focal plane and a distance D2... Dn is assigned; all images captured by the image capture apparatus (33) are transferred by the evaluation apparatus (32) into a summed image and are output in a display (39) that is connected to the measuring device (12).

Description

[0001] Method and measuring device for measuring a measuring object using X-ray fluorescence

[0002] The invention relates to a method for measuring a measurement object with a measuring device by means of X-ray fluorescence, as well as such a measuring device which is intended in particular for measuring the thickness of thin layers on the measurement object or for determining an element concentration of the measurement object.

[0003] In many areas of industrial production, increasingly small structures are being used, such as so-called bond pads on circuit boards. Individual areas of these structures lie in different planes, which must be inspected depending on the measurement task. Measuring devices for performing measurements using X-ray fluorescence are provided with optical devices whose beam path is coupled via a coupling element into the primary radiation of a radiation source directed at the measurement object by an X-ray fluorescence device. This allows an image to be captured of a measuring point on the measurement object. These optical devices have a limited depth of field due to physical reasons. This makes it difficult for the user to adjust the measuring device to the measurement plane of the structure of the measurement object for the X-ray fluorescence measurement, which is the basis for the measurement task.Adjusting the measuring device for X-ray fluorescence measurements to the correct measurement plane within the structure of the measurement object is important in order to achieve an increased intensity of the emitted secondary radiation for improved evaluation. This increased intensity can only be achieved if a focal plane of the primary beam lies in the measurement plane of the small structure of the measurement object to be tested. Furthermore, adjusting the measurement object to the correct measurement plane is important in order to avoid illuminating structures on the measurement object that are not of interest and that would enlarge the measurement spot. Furthermore, measuring devices are known that provide X-ray optics, in particular so-called polycapillaries, between the radiation source of the X-ray fluorescence device and the measurement object, through which the intensity in a small measurement spot can be increased.However, this measurement spot is larger than the measurement location of such small structures on the target, so that neighboring areas of the measurement location are also excited by the primary radiation within the measurement spot. The smaller the measurement spot, the closer the focal plane is to the exit of the polycapillary. This creates the problem that coupling the beam path to capture an image of the measurement location is difficult or even impossible.

[0004] The invention is based on the object of proposing a method for measuring a measurement object with a measuring device by means of X-ray fluorescence as well as a measuring device by means of which a structure with differing measuring planes in the measuring point of the measurement object is detected and thereby the alignment of the primary beam to a specific measuring plane is made possible.

[0005] This problem is solved by a method for measuring a measurement object with a measuring device using X-ray fluorescence. In this method, a primary beam from a radiation source is directed by an X-ray fluorescence device onto the measurement object positioned on a measuring table of the measuring device. In this method, secondary radiation emitted by the measurement object is detected by a detector of the X-ray fluorescence device and forwarded to an evaluation device and evaluated. By means of an optical device comprising an image capture device and focusing optics, a beam path of the image capture device is coupled into the primary beam via a coupling element and directed onto a measuring point on the measurement object. An image of the measuring point is captured. Before a measurement task is carried out for one or more measurement objects, a structure of the measuring point of the measurement object is recorded.A controllable focusing optic creates a focal plane starting from a distance D. s above the measuring table, towards the measuring point of the measuring object until a highest point of the measuring point of the measuring object is captured by an image and a distance Di is determined. Starting from this distance Di, the focusing optics are controlled in several steps so that the focal plane of the beam path of the image capture device is moved towards the surface of the measuring table and from each step of the displaced focal plane of the beam path of the image capture device towards the measuring table, an image and the corresponding distance D2, D3 ... D nis captured, and a composite image of all captured images is determined by the evaluation device and output on a display connected to the measuring device. This method has the advantage that the different measurement planes in the small structures of the measuring point of the measuring object can be clearly shown on the display. This allows the user to precisely navigate to and adjust the corresponding measurement plane on the small structure of the measuring point for the subsequent measurement task.

[0006] Preferably, all captured images of the measuring point of the measurement object are converted into the summed image by an algorithm, in which the measuring point is displayed with a depth of field spanning the entire height of the structure at the measuring point. Such an algorithm can be configured to perform an image transformation for the individual images for subsequent, best possible overlay. Such algorithms are used as a basis for special software, for example, to perform so-called focus stacking or focus variation. This thus makes it possible, with optics with a limited depth of field, to acquire an image at the measuring point of the measurement object with a full depth of field spanning the entire height of the structure and with three-dimensional information about the structure at the measuring point.

[0007] Furthermore, it is preferably provided that the distance Ds above the measuring table or the measuring object, from which the movement of the focal plane of the focusing optics from the beam path of the image acquisition device to the measuring point of the measuring object takes place, is determined in the evaluation device or is specified by calibrating the measuring device. This allows a recurring starting point for the determination of the structures for this detection of the small structures for a subsequent measurement of a measuring point in a predetermined measuring plane of the measuring object.

[0008] Advantageously, the highest point of the measuring point of the measuring object is detected by an autofocus measurement to determine a first distance Di or a minimum distance of the measuring object. This allows the highest point of the measuring point to be determined automatically.

[0009] To change the focal plane of the beam path of the image capture device, an electrically controllable focusing optic is preferably provided. The preferably step-by-step shifting of the focal plane of the beam path or image capture device for capturing the small structures at the measuring point on the measurement object is preferably carried out by changing the voltage values ​​for controlling the focusing optics, whereby each change in the voltage value results in a shift of the focal plane and each voltage value is assigned a distance Di to D nto determine the position of the focal plane. In each focal plane, an image is preferably captured by the image acquisition device, which in turn is used to create the composite image. At the same time, the individual voltage values ​​for the determined distances are stored in the evaluation device, so that the values ​​for a specific focal plane on the small structure can be used to adjust the measurement spot of the primary beam on the structure of the measurement object.

[0010] Advantageously, the evaluation device also detects a maximum distance Dmax, which lies in the surface of the measuring table. This allows the range of movement of the focal plane to be determined between the distance D s and Dmax are stored so that a plausibility check can be performed simultaneously if a distance is detected that lies outside this travel range. Preferably, the distance Ds , Tue ... D n , Dmax is determined starting from a coupling plane of the beam path of the image acquisition device into the primary beam in the direction of the surface of the measuring table.

[0011] An electrically controllable liquid lens, for example, can be used as the electrically controllable focusing optics for implementing the method. Alternatively, the focusing optics can also be controlled by a geometric movement of lenses and / or an image plane of the image capture device.

[0012] Furthermore, it is preferably provided that before the structures of the measurement object are recorded, a calibration of the optical device is carried out by placing a calibration standard with a known structure on the measuring table, which comprises several focal planes. By changing the voltage values ​​for each voltage value, the distance of the focal plane of the calibration standard is recorded. If the distance from the known focal plane of the calibration standard deviates at a certain voltage value from the nearest recorded focal plane of the calibration standard, the voltage value is corrected. Through this calibration step, the measuring device, in particular the optical device, can be optically calibrated before the subsequent measuring task. This can achieve increased measurement quality.

[0013] The object underlying the invention is further achieved by a measuring device for measuring measurement objects with X-ray fluorescence, which comprises a housing with a measuring table, on the surface of which a measurement object can be positioned and with an X-ray fluorescence device which comprises a radiation source for emitting a primary beam and a detector for detecting emitted secondary radiation from the measurement object and with an optical device which comprises an image capture device and a focusing optics, wherein an evaluation device is provided for carrying out the method according to one of the previously described embodiments.

[0014] The invention, as well as further advantageous embodiments and developments thereof, are described and explained in more detail below with reference to the examples shown in the drawings. The features shown in the description and the drawings can be used individually or in any combination according to the invention. They show:

[0015] Figure 1 is a perspective view of a measuring device,

[0016] Figure 2 is a schematic sectional view of the measuring device according to Figure 1, and

[0017] Figure 3 is a schematic side view of the optical device with focusing optics for detecting structures at the measuring point of the measuring object.

[0018] Figure 1 shows a perspective view of a measuring device 11. Figure 2 shows a schematic side view of the measuring device according to Figure 1 in a sectional view. This measuring device 11 is used to perform measurements on measurement objects using X-ray fluorescence. Measurements using X-ray fluorescence can be used to measure the layer thickness of coatings on measurement objects and / or to analyze the material of the measurement object.

[0019] The measuring device 11 comprises a housing 12 with a lower housing part 14 and an upper housing part 15, as well as a housing cover 16. The housing cover 16 is pivotally mounted, for example, about a pivot axis 17, so that a measuring chamber 18 provided in the housing 12 is accessible. Alternatively, the housing cover 16 can also be movable or displaceable relative to the housing 12 by means of another mechanism. Instead of a pivotable housing cover 16, a housing opening can also be provided, which allows access to the measuring chamber 18.

[0020] The housing lower part 14 accommodates a movable measuring table 21 on its upper side. This measuring table 21 is driven in the X and Y directions by a motor 22. Preferably, the measuring table 21 is guided to the housing lower part 14 by a cross table or the like.

[0021] An X-ray fluorescence device 23 is provided in the upper housing section 15. This device comprises a radiation source 24, through which primary radiation 25 is directed onto a measurement point 26. Individual components arranged in the primary beam 25, such as a shutter, a primary filter, and / or a collimator, are not shown in detail. Aligned with the measurement point 26, individual measurement objects 27, which rest, for example, on the measurement table 21, can be positioned to perform a measurement. Adjacent to the radiation source 24 is a detector 28, which detects secondary radiation 29 emitted by the measurement object 27. Both the radiation source 24 and the detector 28 are connected to a control device 31.

[0022] The control device 31 comprises an evaluation device 32 so that measurement tasks can be stored and retrieved and / or so that determined measured values ​​can be recorded, stored and / or evaluated and / or output in a display or the like.

[0023] An optical device 40 is provided in the upper housing part 15, which comprises an image capture device 33, such as a CCD camera, and focusing optics 42, through which an image or an overview image of at least one area of ​​the measuring table 21 or preferably of the entire measuring table 21 can be captured. The optical device 33 can capture images of the measuring point 26 and / or of the measuring table 21 via a deflecting mirror 20. The housing cover 16 can be automatically opened and closed via a motor 34, which in turn is connected to the control device 31. This provides easy access to the measuring chamber 18. A sensing element 36 is preferably provided on the lower housing part 14, by means of which the control device 31 can be started or stopped and / or controlled.

[0024] Advantageously, a display, screen, or the like can be connected to the measuring device 11. A display, screen, or indicator can also be provided on the housing 12.

[0025] To facilitate loading the measuring table 21 with at least one measurement object 27 for the subsequent measuring task, the measuring table 21 can be transferred into a loading and unloading position 35. In this loading and unloading position 35, the measuring table 21 is at least partially extended relative to the housing base 14. The housing cover 16, which can be lifted from the housing base 14, can provide improved accessibility to the measuring table 21, which is arranged in the loading and unloading position 35. This loading and unloading position 35 of the measuring table is shown in Figure 1.

[0026] To perform the upcoming measurement task, the measuring table 21 is moved from the loading and unloading position 35 to a working position 37. This working position 37 is shown in Figure 2. The measuring table 21 is positioned completely within the measuring chamber 18. After the housing cover 16 is closed, the measuring table 21 is positioned completely within the closed measuring chamber 18.

[0027] Alternatively, it can be provided that the loading and unloading position 35 and the working position 37 are the same position. In this case, the housing cover 16 can preferably be lifted off or laterally displaced relative to the housing base 14, so that good accessibility is again provided for loading and unloading the measuring table 21 with the at least one measurement object 27. Alternatively, it can also be provided that the measuring table 21 of the measuring device 11 is stationary. In this case, the measurement objects 27 can be placed individually or in groups on the measuring table 21. The X-ray fluorescence device 23 and / or the optical device 33 can then be moved accordingly to the measuring point 45 of the measurement object 27.

[0028] Figure 3 shows a schematic side view of the X-ray fluorescence device 23 and the optical device 33 with the image capture device 33 and the focusing optics 42. The measurement object 27 is placed on the measuring table 21. This measurement object 27 comprises a measuring point 45, which, for example, comprises a structure having measuring planes at different heights. The structure of the measuring point 45 is shown significantly enlarged. These structures can be smaller than 500 pm, in particular smaller than an optical wavelength of 600 nm. In other words, such structures are preferably smaller than a microfocus of an optics in which a measuring spot of greater than 500 pm can be set. The representation of the structure is only an exemplary embodiment, and this structure can have any desired shape and does not have to include the illustrated staircase or column structure.

[0029] An optical beam path 41 of the image capture device 33 is coupled into the primary beam 25 via a coupling element 20 or a deflecting mirror. Starting from a beam axis of the image capture device 33 or coupling plane 46, a distance to the surface of the measuring table 21 and / or to the structure of the measuring point 45 of the measurement object 27 is detected. A collimator 47 can preferably also be provided between the coupling element 20 and the measuring table 21. This serves in particular to adjust the size of the measuring spot of the primary beam 25 in a measuring plane on the measuring point 45 of the measurement object 27. A measuring task for measuring the measuring point 45 on the measurement object 27 can consist of determining the thickness of a coating on the measurement object 27. The measuring task can also consist of determining a material analysis or an element concentration from individual measuring planes within the structure.This can be done against the background of checking whether there is a sufficient layer thickness of the coating within the individual structures or whether the required element concentrations are present.

[0030] To record the structure of the measuring point 45 on the measuring object 27, proceed as follows:

[0031] The electrically controllable focusing optics 42 are adjusted so that the focal plane of the beam path 41 is in the plane according to the distance D s This distance D s can be a fixed, calibrated or programmed distance in the evaluation device 32. The distance D sis preferably determined starting from the coupling plane 46. It can also be determined starting from the surface of the measuring table 21. Starting from this starting point, the focal plane of the beam path 41 is moved in the direction of the measuring table 42. The highest point of the measuring point 45 of the measuring object 27 is recorded by an autofocus measurement. This simultaneously represents the smallest distance of the structure of the measuring object 27 to the coupling plane 46. This highest point of the structure of the measuring point 45 of the measuring object 27 can be recorded and saved as Dmin or as Di. The electrically controllable focusing optics 42 applies a specific voltage value to the focal plane at the distance Di. This voltage is assigned to the distance Di. In this focal plane at the distance Di, an image is recorded and saved by the optical device 40.Subsequently, a change in the focal plane is preferably controlled stepwise by a correlating change in the voltage value for controlling the focusing optics 42. For example, the focal planes are subsequently adjusted at a distance Di, D2 ... D. n approached. From any distance Di ... D n The respective voltage value is recorded, and an image is created by the image acquisition device 33. This movement ends at the latest when the focal plane is at a distance Dmax. The distance Dmax corresponds to the distance between the coupling plane 46 and the surface of the measuring stage 21.

[0032] The individual captured images are then processed using an image transformation, preferably a Fourier transformation, for subsequent superimposition. Through so-called focus stacking or focus variation, a sharp overview image of the structure of the measuring point 45 can be output and displayed on a display of the measuring device 11.

[0033] This procedure allows the user of the measuring device 11 to clearly see the entire structure of the measuring point 45 of the measuring object 47, even in depth, and thus to select and define the desired measuring point or measuring plane for the primary beam 25 for the measurement to be performed. This has the advantage that a maximum intensity can be introduced into the measuring plane, which is to be captured by the measurement task, in order to achieve sufficient secondary radiation for the subsequent evaluation of the measuring point 45.

[0034] This method for detecting the structure of the measuring point 45 on the measuring object 27 has the further advantage that, for example, a pattern recognition of a measuring object 27 is also possible, since the detection of specific target patterns from a three-dimensional and depth-sharp overall image is easier to determine.

[0035] Before recording the structure of the measuring point 45 on the measurement object 27, a calibration of the measurement object 11 can be carried out in a first step. Preferably, a calibration standard with a known structure comprising several measuring planes is placed on the measuring table 21. This known structure, also called a focus standard, comprises several differing focus planes (measurement planes), wherein the distance of at least one focus plane to a support plane of the calibration standard on the measuring table 21 is known. Subsequently, the electrically controllable focusing optics 42 moves the beam path 41 with respect to the focal plane within the calibration standard 42 and the respective associated voltage values ​​are recorded. If the voltage value deviates from the known focus plane of the calibration standard 42 to the nearest focus plane of the calibration standard 42, the voltage value is corrected.The voltage value correlates with a defined distance of the focal plane of the beam path 41 to the coupling plane 46 or surface of the measuring table 21, so that any tolerances or errors can be corrected.

Claims

Claims Method for measuring a measurement object (27) with a measuring device (11) by means of X-ray fluorescence, in particular for measuring the thickness of thin layers on the measurement object (27) or for determining an element concentration of the measurement object (27), in which a primary beam (25) of a radiation source (24) is directed by an X-ray fluorescence device (23) onto a measurement object (27) which is positioned on a measuring table (21), in which a secondary radiation (24) emitted by the measurement object (27) is detected by a detector (28) of the X-ray fluorescence device (23) and forwarded to an evaluation device (32), in which with an optical device (40) which comprises an image capture device (33) and a focusing optics (42),a beam path (41) of the optical device (30) is coupled into the primary beam (25) via a coupling element (20) and directed onto a measuring point (45) of the measurement object (27), and an image is captured from the measuring point (45), characterized in that, before carrying out a measurement task for the measurement object (27) positioned in the measuring device (11), a structure of the measuring point (25) of the measurement object (27) is captured, that a focal plane of the beam path (41) of the image capture device (33) is approached with a controllable focusing optics (42) at a distance Ds, wherein the distance Ds corresponds to a position of the focal plane above the measuring table (21) and above the measurement object (27), that the focal plane is subsequently moved by the focusing optics (42) towards the measuring point (45) of the measuring object (27), that a highest point of the measuring point (45) of the measuring object (27) is recorded by an image of the image recording device (33) and a distance Di to the measuring table (21) is assigned, that starting from the distance Di the focusing optics (42) are controlled in several steps and the focal plane of the beam path (41) of the image recording device (33) is moved by the focusing optics (42) in the direction of the measuring table (21) and from each step of the displaced focal plane an image of the measuring point (45) of the measuring object (27) is recorded and a distance D2 ... D nis assigned that all images captured by the image capture device (33) are converted into a summed image by the evaluation device (32) and output on a display (39) which is connected to the measuring device (12). Method according to claim 1, characterized in that all captured images of the measuring point (45) of the measuring object (27) are converted into a summed image by an algorithm, in particular focus stacking or focus variation, and the measuring point (45) of the measuring object (27) is output on the display (39) with a depth of field over the entire height of the structure of the measuring point (45). Method according to claim 1 or 2, characterized in that the distance D s above the measuring table (21), in particular above the measuring object (27), from which the movement of the focal plane of the beam path (41) towards the measuring point (45) of the measuring object (27) takes place, in the evaluation device (32) or is determined by calibrating the measuring device (11). Method according to one of the preceding claims, characterized in that the detection of the highest point of the measuring point (45) of the measuring object (27) for determining the distance Di is controlled and detected by an autofocus measurement. Method according to one of the preceding claims, characterized in that an electrically controllable focusing optics (42) is used and each step for shifting the focal plane of the beam path (41) is controlled by a stepwise change in the voltage values ​​of the focusing optics (42), and in that a distance Di ... D is assigned to each voltage value. nfor determining the respective focal plane in connection with the structure of the measurement object (27). Method according to one of the preceding claims, characterized in that a distance Dmax, at which the focal plane of the beam path (41) lies in the surface of the measuring table (21), is detected by a measurement with the optical device (33) and stored in the evaluation device (32). Method according to one of the preceding claims, characterized in that the distance D s , Tue ... D n Starting from a coupling plane (46) of the beam path (41) of the optical device (33) into the primary beam (25) in the direction of the surface of the measuring table (21), the optical path is determined. Method according to claim 1, characterized in that at least one liquid lens or at least one geometrically movable optic is used as the electrically controllable focusing optic (42). Method according to one of the preceding claims, characterized in that before the structure of the measuring point (45) of the measurement object (27) is detected, a calibration of the optical device (40) is carried out by placing a calibration standard with a known structure on the measuring table (21), which calibration standard comprises a plurality of different focal planes, and by changing the voltage values ​​for controlling the focusing optics (42) for each voltage value, a distance of the focal plane of the known structure of the calibration feature to the coupling plane (46) is detected, and in the event of a deviation of the voltage value from the known focal plane of the calibration standard to the determined voltage value of the same focal plane, a correction of the voltage value is carried out.Measuring device for measuring a measurement object (27) by means of X-ray fluorescence, in particular for measuring the thickness of thin layers on the measurement object (27) or for determining an element concentration, comprising a housing (12), a measuring table (21) provided in the housing (12), on the surface of which a measurement object (27) can be positioned, an X-ray fluorescence device (23) which comprises a radiation source (24) for emitting a primary beam (25) and a detector (28) for detecting secondary radiation (29) emitted by the measurement object (27), an optical device (40) which comprises an image capture device (33) and a focusing optics (42), and a coupling element (20) by means of which a beam path (41) of the image capture device (33) can be coupled into the primary beam (25). characterized in that an evaluation device (32) for carrying out the Method according to one of claims 1 to 9.

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