Method and measuring device for measuring a test object using X-ray fluorescence

Abstract

The present invention relates to a method for measuring a test object (27) using a measuring device (11) with X-ray fluorescence, and more specifically, to a method for measuring the thickness of a thin layer of the test object (27) or a method for determining the elemental concentration of the test object (27). Before a measurement task is performed on the test object (27) positioned in the measuring device (11), the structure of the measurement point (25) of the test object (27) is captured, and the distance D for determining the position of the focal plane on the measuring table (21). s Starting from this, the focal plane of the controllable focusing optical unit (42) moves towards the measurement point (45) on the test object (27). The apex of the measurement point on the test object (27) is captured by the image of the image capture device (33), and the 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 device (33) is moved by the focusing optical unit (42) in the direction of the measuring table (21). The image of the measurement point (45) on the test object (27) is captured from each step of the shifted focal plane, and the distances D2...D n are assigned. All the images captured by the image capture device (33) are converted by the evaluation device (32) into a composite image and output on a display (39) connected to the measuring device (12).

Description

Technical Field

[0001] The present invention relates to a method for measuring a test object with a measuring device using X-ray fluorescence, and more particularly to a measuring device provided for measuring the thickness of a thin layer of a test object or for determining the elemental concentration of a test object.

Background Art

[0002] In many fields of industrial production, increasingly small structures such as so-called adhesive pads on printed circuit boards are being used. The individual areas of these structures are located in different planes that need to be inspected depending on the measurement task. In a measuring device for performing a measurement using X-ray fluorescence, an optical device is provided, and its beam path is coupled via a coupling element to the primary radiation of a radiation source directed at the object to be measured by the X-ray fluorescence device. This makes it possible to capture an image of the measurement points on the object to be measured. These optical devices result in a physically determined limitation of the depth of field. This makes it difficult for the user to adjust the measuring device to the measurement surface of the structure of the object to be measured for the X-ray fluorescence measurement underlying the measurement task. Setting the measuring device for X-ray fluorescence measurement correctly in the structure of the object to be measured is important in order to achieve an increase in the intensity of the secondary radiation emitted for improving the evaluation. This increase in intensity can only be achieved if the focal plane of the primary beam lies on the measurement surface of the small structures of the test object being tested. On the other hand, the adjustment of the test object to the correct measurement surface is important in order not to illuminate structures on non-target test objects and not to expand the measurement spot.

[0003] Furthermore, an X-ray optical device, specifically a measurement device that can increase the intensity at a small measurement spot by providing so-called polycapillarity, is known between the radiation source of the X-ray fluorescence device and the object to be measured. However, this measurement spot is larger than the measurement points of such small structures of the object to be measured, and as a result, the adjacent areas of the measurement points are also excited by the primary radiation within the measurement spot. As the measurement spot becomes smaller, the focal plane comes closer to the exit of the polycapillary. The problem here is that it is difficult or impossible to combine the beam paths for capturing the image of the measurement point.

Summary of the Invention

Problems to be Solved by the Invention

[0004] The present invention is based on the purpose of proposing a method for measuring a test object with a measurement device using X-ray fluorescence, and a measurement device that enables alignment of the primary beam with a specific measurement surface by detecting a structure with different measurement surfaces at the measurement points of the test object.

Means for Solving the Problems

[0005] This object is solved by a method for measuring a test object with a measurement device using X-ray fluorescence. In this method, the primary beam of the radiation source is directed by the X-ray fluorescence device towards the test object positioned on the measurement table of the measurement device, and the secondary beam emitted by the test object is detected by the detector of the X-ray fluorescence device and transferred to an evaluation device for evaluation. An optical device comprising an image capture device and a condenser optical unit combines the beam path of the image capture device with the primary beam via a coupling element, directs the primary beam towards the measurement points of the object to be measured, and captures an image of the measurement points. Before performing the measurement task for one or more test objects, the structure of the measurement points of the test object is captured. The distance D on the measurement table sStarting from , until the highest point of the measurement point of the test object is detected by the image and the distance D1 to the test object is determined, the focal plane moves towards the measurement point of the test object by a controllable focusing optical unit. Starting from this distance D1, the focusing optical unit is controlled in several steps, and as a result, the focal plane of the beam path of the image capture device moves towards the surface of the measurement table, and images and related distances D2, D3... D n are captured, and the composite image of all the captured images is determined by an evaluation device and output on a display connected to the measurement device. As an advantage of this method, it can be mentioned that different measurement surfaces of small structures of the measurement points of the measurement object can be clearly shown on the display. This enables the user to accurately approach the corresponding measurement surface on the small structure of the measurement point for subsequent measurement tasks and set that measurement surface.

[0006] All captured images of the measurement points of the test object are preferably converted into a composite image by an algorithm, and the measurement points are output with a depth of field on the display over the entire height of the structure of the measurement points. Such an algorithm can be provided so that the image conversion is performed on individual images for the best possible subsequent overlay. Such an algorithm is used, for example, in special software for performing focus stacking or focus variation. In the case of an optical device with a limited depth of field, this makes it possible to obtain an image at the measurement point of the test object and three-dimensional information regarding the structure of the measurement point with the entire depth of field over the height of the structure.

[0007] Furthermore, over the distance Ds above the measurement table or the measurement object, the movement of the focal plane of the focusing optical unit is performed from the beam path of the image capture device towards the measurement point of the measurement object, and the distance Ds is preferably determined by the evaluation device or by calibration of the measurement device. As a result, the repeatedly occurring starting point for determining the structure can be selected for the detection of this small structure for subsequent measurements of the measurement points at a predetermined measurement surface of the test object.

[0008] It is advantageous for the highest point of the measurement point of the object to be measured to be detected by autofocus measurement in order to determine the first distance D1 or the minimum distance of the object to be measured. Thereby, it becomes possible to automatically determine the highest point of the measurement point.

[0009] The electrically controllable condenser optical unit is preferably provided for changing the focal plane of the beam path of the image capture device. The preferred stepwise displacement of the beam path or the focal plane of the image capture device for detecting small structures at the measurement points on the test object is preferably carried out by changing the voltage value in order to control the condenser optical unit. Thereby, each change in the voltage value results in a displacement of the focal plane, and each voltage value is used to determine the position of the focal plane, for distances D1 to D n is assigned. At each focal plane, the image is preferably captured by the image capture device, and further, a synthetic image is formed using the image capture device. At the same time, the individual voltage values for the determined distances are stored in the evaluation device, and as a result, the value of the specific focal plane on the small structure can be taken into account for adjusting the measurement spot of the primary beam on the structure of the test object.

[0010] Advantageously, the maximum distance D present on the surface of the measuring table max is also recorded in the evaluation device. Thereby, it becomes possible to store the movement range of the focal plane between D s and D max and as a result, when a distance outside this movement range is detected, a validity check can be carried out simultaneously.

[0011] In the direction of the surface of the measuring table, starting from the coupling surface of the beam path of the optical device to the primary beam, the distances D s , D1...D n , D max are preferably determined.

[0012] For example, an electrically controllable liquid lens can be used as an optically controllable focusing optical unit for carrying out a process. Alternatively, the focusing optical unit can also be controlled by the lens of an image capture device and / or by the geometric movement of the image plane.

[0013] Furthermore, before being detected by placing a calibration standard with a known structure on a measuring table, the structure of the test object including several focal planes, the optical device is calibrated, the distance of the focal plane of the calibration standard is recorded by varying the voltage value for each voltage value, and if the distance deviates from the known focal plane of the calibration standard, it is preferable to perform a correction of the voltage value for a specific voltage value with respect to the recorded closest focal plane of the calibration standard. This calibration step enables the optical calibration of the measuring device, specifically the optical device, before subsequent measurement tasks. As a result, an improvement in measurement quality can be achieved.

[0014] The underlying object of the present invention is further solved by a measuring device for a test object using X-ray fluorescence, the measuring device comprising an X-ray fluorescence device with a housing with a measuring table on a surface on which the measuring object can be positioned, a radiation source for emitting a primary beam, and a detector for detecting secondary radiation emitted from the measuring object, and an optical device comprising an image capture device and a focusing optical unit, and an evaluation device is provided for carrying out a method according to one of the embodiments described above.

[0015] The present invention, and other and further embodiments of the present invention, will be described and explained in more detail below with reference to the examples shown in the drawings. According to the present invention, the features understood from the description and the drawings can be used individually or in any combination.

Brief Description of the Drawings

[0016]

Figure 1

Figure 2

Figure 3

Embodiments for Carrying Out the Invention

[0017] FIG. 1 shows the measuring device 11 in a perspective view. FIG. 2 shows a schematic side view of the measuring device according to FIG. 1 in a sectional view. Using this measuring device 11, measurements of a test object using X-ray fluorescence are carried out. Using the measurements using X-ray fluorescence, the thickness of a coating on the test object can be measured and / or the material of the test object can be analyzed.

[0018] The measuring device 11 includes a housing 12, and the housing 12 is accompanied by a lower housing section 14 and an upper housing section 15, and a housing cover 16. The housing cover 16 is mounted so as to be rotatable, for example, about a pivot axis 17, and as a result, access to a measurement chamber 18 provided in the housing 12 becomes possible. Alternatively, the housing cover 16 can also be moved or displaced relative to the housing 12 by a further mechanism. Instead of the rotatable housing cover 16, a housing opening can also be provided to enable access to the measurement chamber 18.

[0019] The lower part of the housing 14 houses a measurement table 21 that can move upward. This measurement table 21 is driven in the X and Y directions by a motor 22. Preferably, the measurement table 21 is guided by a cross table or the like so as to be movable relative to the lower housing part 14.

[0020] The X-ray fluorescence device 23 is provided at the upper part of the housing 15. This includes a radiation source 24 towards which the primary beam 25 is directed at the measurement point 26. Individual components arranged in the primary beam 25 such as shutters, primary filters, and / or collimators are not shown in detail. For example, the individual test objects 27 stationary on the measurement table 21 can be positioned in alignment with the measurement point 26 in order to carry out measurements. The detector 28 is provided adjacent to the radiation source 24 and detects the secondary radiation 29 emitted by the test object 27. Both the radiation source 24 and the detector 28 are connected to the control unit 31.

[0021] The control device 31 includes an evaluation device 32, by which measurement tasks can be stored and called, and / or the determined measured values can be recorded, stored, and / or evaluated, and / or output to a display or the like.

[0022] The optical device 40 is provided at the upper part of the housing 15. The optical device 40 includes an image capture device 33 such as a CCD camera and a condenser optical unit 42. Using the optical device 40, an image or an overview image of the measurement table 21 or preferably at least one area of the entire measurement table 21 can be captured. The optical device 33 can capture an image of the measurement point 26 and / or the measurement table 21 using the deflection mirror 20. The housing cover 16 can be automatically opened and closed via the motor 34. Furthermore, the motor 34 is connected to the control device 31. This provides easy access to the measurement chamber 18. The button element 36 is preferably provided at the lower part of the housing 14. Using the button element 36, the control device 31 can be activated or stopped and / or made active.

[0023] Advantageously, a display, a screen, etc. can be connected to the measurement device 11. Also, the display or the screen can be provided on the housing 12 as well.

[0024] To make it easier to place at least one test object 27 on the measuring table 21 for subsequent measurement tasks, the measuring table 21 can be moved to the loading / unloading position 35. In this loading / unloading position 35, the measuring table 21 extends at least partially relative to the lower part of the housing 14. A housing cover 16 that can lift the lower housing part 14 can provide improved access to the measuring table 21 arranged in the loading / unloading position 35. This loading / unloading position 35 of the measuring table is shown in FIG. 1.

[0025] For performing a measurement task in the vicinity, the measuring table 21 moves from the loading / unloading position 35 to the operating position 37. This operating position 37 is shown in FIG. 2. The measuring table 21 is fully positioned within the measurement chamber 18. Before closing the housing cover 16, the measuring table 21 is fully positioned within the closed measurement chamber 18.

[0026] Alternatively, it is possible to bring about the situation where the loading / unloading position 35 and the operating position 37 are in the same position. In this case, the housing cover 16 is preferably liftable relative to the lower housing part 14 or displaceable laterally, so that good access is again provided for loading / unloading at least one measurement object 27 onto the measuring table 21.

[0027] Alternatively, it is also possible to fix the measuring table 21 of the measuring device 11. In this case, the measurement objects 27 can be placed on the measuring table 21 individually or in groups. Next, the X-ray fluorescence device 23 and / or the optical device 33 can be moved to the measurement points 45 of the test object 27 according to the situation.

[0028] Figure 3 shows a schematic side view of the X-ray fluorescence device 23 and the optical device 33, which includes the image capture device 33 and the condenser optical unit 42. The measurement object 27 can be placed on the measurement table 21. This measurement object 27 includes, for example, measurement points 45 having a structure with measurement surfaces at different heights. The structure of the measurement point 45 is shown as being substantially enlarged. These structures can be smaller than 500 μm and specifically can be smaller than the optical wavelength of 600 nm. In other words, such structures are preferably smaller than the microfocus of an optical system that can set a measurement spot larger than 500 μm. The explanatory diagram of the structure is merely an example of an embodiment, and this structure can have any shape and does not necessarily have the stepped or columnar structure shown.

[0029] The optical beam path 41 of the image capture device 33 is coupled to the primary beam 25 via the coupling element 20 or the deflection mirror. The distance from the beam axis of the image capture device 33 or the coupling surface 46 to the surface of the measurement table 21 and / or the structure of the measurement point 45 of the measurement object 27 is detected. The collimator 47 can preferably be provided between the coupling element 20 and the measurement table 21. Specifically, this is used to adjust the size of the measurement spot of the primary beam 25 on the measurement surface at the measurement point 45 of the test object 27.

[0030] One measurement task for measuring the measurement point 45 on the test object 27 can determine the thickness of the coating on the test object 27. The measurement task can also determine the material analysis or element concentration of the individual measurement surfaces within the structure. By doing this, it can be checked whether the coating within the individual structures is thick enough or whether the required element concentration is present.

[0031] To record the structure of the measurement point 45 on the test object 27, proceed as follows.

[0032] The electrically controllable condenser optical unit 42 is set so that the focal plane of the beam path 41 exists in the plane according to the distance D s corresponding thereto. This distance D scan be a distance that is corrected, calibrated, or programmed in the evaluation unit 32. The distance D s is preferably determined starting from the joint surface 46. Also, the distance can be determined starting from the surface of the measuring table 21. Starting from this starting point, the focal plane of the beam path 41 moves in the direction of the measuring table 42. The highest point of the measuring point 45 of the test object 27 is detected by autofocus measurement. Also, this is the minimum distance between the structure of the test object 27 and the joint surface 46. This highest point of the structure of the measuring point 45 of the test object 27 is D min or can be recorded and stored as D1. By the electrically controllable condenser optical unit 42, a specific voltage value exists on the focal plane at the distance D1. This is assigned to the distance D1. At this focal plane at the distance D1, the image is captured and stored by the optical device 40. Subsequently, the change of the focal plane is preferably triggered stepwise by a correlated change of the voltage value in order to control the condenser optical unit 42. For example, next, the focal plane approaches at distances D1, D2... D n and each voltage value is recorded from each distance D1... D n and the image is created by the image capture device 33. This transverse movement ends at the latest when the focal plane is at the distance D max . The distance D max corresponds to the distance between the joint surface 46 and the surface of the measuring table 21.

[0033] Next, the individual captured images are processed using image conversion, preferably Fourier transform, and as a result, the captured images can be superimposed. Using so-called focus stacking or focus variation, a clear overview image of the structure of the measuring point 45 can be output and displayed on the display of the measuring device 11.

[0034] This procedure enables the user of the measuring device 11 to clearly see the complete structure of the measurement point 45 of the test object 47 down to the depth, and thus to select and define the desired measurement point or measurement surface of the primary beam 25 in order to carry out the measurement. This brings the advantage that the maximum intensity can be introduced into the measurement surface detected by the measurement task in order to achieve sufficient secondary radiation for the subsequent evaluation of the measurement point 45.

[0035] The method for detecting the structure of the measurement point 45 on the test object 27 also has the advantage that it enables, for example, pattern recognition of the test object 27 in order to more easily determine the detection of a dedicated target pattern from the entire three-dimensional image with a sharp depth.

[0036] Before recording the structure of the measurement point 45 on the test object 27, the test object 11 can be calibrated in a first step. Preferably, a calibration standard with a known structure having several measurement surfaces is placed on the measuring table 21. This known structure is also called a focus standard having several different focal planes (measurement surfaces), whereby the distance from at least one focal plane to the support surface of the calibration standard on the measuring table 21 is ascertained. Next, the electrically controllable condenser optical unit 42 moves the beam path 41 with respect to the focal plane in the calibration standard 42 and records the respective associated voltage value. If the voltage value differs from the value of the known focal plane of the calibration standard 42 which is the closest focal plane of the calibration standard 42, the voltage value is corrected. The voltage value correlates with the defined distance between the focal plane of the beam path 41 and the coupling surface 46 or surface of the measuring table 21, so that any tolerance or error can be corrected.

Claims

1. A method for measuring a test object (27) with a measuring device (11) using X-ray fluorescence, specifically, a method for measuring the thickness of a thin layer of the test object (27) or a method for determining the elemental concentration of the test object (27), comprising: - The primary beam (25) of the radiation source (24) is directed from the X-ray fluorescence device (23) towards the test object (27) positioned on the measuring table (21). - The secondary radiation (24) emitted by the test object (27) is detected by the detector (28) of the X-ray fluorescence device (23) and transferred to the evaluation device (32). - Using an optical device (40) comprising an image capture device (33) and a condenser optical unit (42), the beam path (41) of the optical device (30) is coupled to the primary beam (25) via a coupling element (20), and the primary beam (25) is directed towards the measurement point (45) of the test object (27) to be measured, and an image is acquired from the measurement point (45). - The structure of the measurement point (25) of the test object (27) is detected before the measurement task is performed on the test object (27) positioned on the measuring device (11). - The focal plane of the beam path (41) of the image capture device (33) is approached by a focusing optical unit (42) controllable at a distance D ｓ and the distance D ｓ is located on the measurement table (21) and coincides with the position of the focal plane on the object (27) to be measured - Next, the focal plane is moved by the condenser optical unit (42) towards the measurement point (45) of the test object (27). - The highest point of the measurement point (45) of the test object (27) is detected by the image of the image capture device (33), and the distance D to the measurement table (21) １ is assigned, - the distance D １ Starting from this, the condenser optical unit (42) is controlled in a plurality of steps, and the focal plane of the beam path (41) of the image capture device (33) is moved by the condenser optical unit (42) in the direction of the measurement table (21). Images of the measurement points (45) of the test object (27) are captured from each step of the displaced focal plane, and the distances D ２ ... D ｎ are assigned, - All of the images captured by the image capture device (33) are converted by the evaluation device (32) into a composite image and output on a display (39) connected to the measuring device (12). A method characterized by this.

2. All of the captured images of the measurement point (45) of the test object (27) are converted into a composite image by an algorithm, specifically, focus stacking or focus variation, and the measurement point (45) of the test object (27) is output by the display (39) with a depth of field over the entire height of the structure of the measurement point (45). The method according to claim 1, characterized by this.

3. The distance D which is on the measurement table (21), specifically, on the test object (27) ｓ across which a transverse movement of the focal plane of the beam path (41) towards the measurement point (45) of the test object (27) is carried out, the distance D ｓ is set by the evaluation device (32) or determined by calibration of the measuring device (11), a method according to claim 1 or 2, characterized in that.

4. the distance D １ The detection of the highest point of the measurement point (45) of the test object (27) for determining the distance D is controlled and is detected by autofocus measurement, characterized in that the method according to any one of claims 1 to 3.

5. An electrically controllable condenser optical unit (42) is used, and each step for displacing the focal plane of the beam path (41) is controlled by a stepwise change in the voltage value of the condenser optical unit (42), and each voltage value is a distance D for determining each focal plane in connection with the structure of the test object (27). １ ... D ｎ A method according to any one of claims 1 to 4, characterized in that... D is assigned. ｎ

6. The distance D at which the focal plane of the beam path (41) is present on the surface of the measurement table (21) ｍａｘ is detected by measurement with the optical device (33) and stored in the evaluation device (32), and the method according to any one of claims 1 to 5, characterized in that

7. In the direction of the surface of the measurement table (21), starting from the coupling surface (46) of the beam path (41) of the optical device (33) to the primary beam (25), the distance D ｓ , D １ ... D ｎ is determined, characterized in that the method according to any one of claims 1 to 6

8. At least one liquid lens or at least one geometrically movable optical component is used as the electrically controllable condenser optical unit (42). The method according to claim 1, characterized by this.

9. Before the structure of the measurement point (45) of the test object (27) is detected, calibration of the optical device (40) is performed. A calibration standard with a known structure is installed on the measurement table (21), has a plurality of different focusing surfaces, and by changing the voltage value for controlling the condenser optical unit (42), the distance of the focusing surface of the known structure of the calibration function from the coupling surface (46) is detected for each voltage value. When the voltage value is different from the value of the known focusing surface of the calibration standard with respect to the determined voltage value of the same focusing surface, correction of the voltage value is performed. The method according to any one of claims 1 to 8, characterized in that.

10. A measuring device for measuring a test object (27) using X-ray fluorescence, specifically, a measuring device for measuring the thickness of a thin layer of the test object (27), or a measuring device for determining the elemental concentration of the test object (27), comprising: - A housing (12); - A measurement table (21) provided on the housing (12) on a surface where the test object (27) can be positioned; - An X-ray fluorescence device (23) comprising a radiation source (24) for emitting a primary beam (25) and a detector (28) for detecting secondary radiation (29) emitted by the test object (27); - An optical device (40) comprising an image capture device (33) and a condenser optical unit (42), and a coupling element (20) capable of coupling the beam path (41) of the image capture device (33) to the primary beam (25); - An evaluation device (32) is provided for carrying out the method according to any one of claims 1 to 9. A measuring device, characterized in that.

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