Method for focusing and operating a particle beam microscope

Abstract

The invention relates to a method for operating a particle beam microscope, the method comprising setting a distance of an object (92) from an objective (35), setting an excitation of the objective, setting an excitation of a double deflector (75) to a first setting such that a particle beam (103) impinges the object in a first orientation, and recording a first particle microscope image at these settings. The method further comprises setting the excitation of the double deflector to a second setting such that the particle beam impinges the object in a second orientation different from the first orientation, and capturing a second particle microscope image while the double deflector is in the second setting. Then, a new distance of the object from the objective is determined based on an analysis of the first and second particle microscope images, and the distance of the object from the objective is set to the new distance.

Description

Technical Field

[0001] This invention relates to methods for operating a particle beam microscope. In particular, it relates to methods for operating particle beam microscopes that focus one or more particle beams onto an object to be examined. The invention also relates to a particle beam microscope for implementing this method, and a computer program product for controlling such a particle beam microscope. Background Technology

[0002] An example of such particle beam microscopy is scanning electron microscopy, in which a focused electron beam scans the object to be examined and detects secondary electrons or backscattered electrons generated on the object by the incident electron beam in a manner that depends on the deflection of the focused particle beam, in order to generate an electron microscope image of the object.

[0003] The particle beam is generated and accelerated by a particle beam source; this beam may pass through a condenser lens and an astigmatism corrector, and is focused onto the object by the objective lens. To achieve the high spatial resolution of a particle beam microscope, the particle beam must be focused onto the object to the greatest extent possible; that is, the area illuminated by the focused particle beam on the object's surface (the "beam spot") should be as small as possible. This is achieved in practice by the user manually setting the focus of the particle beam by operating the actuators of the particle beam microscope, and by the particle beam microscope's controller changing the excitation of the objective lens or the astigmatism corrector based on the operation of the actuators. During this adjustment process, the particle beam continuously scans the object to record an image. The user can evaluate the quality of the current image and actuate the actuators in a manner dependent on the quality of the current image until they are satisfied with the image quality or can no longer improve it. However, this process is time-consuming and demands a high level of skill, even from experienced users.

[0004] Automated methods also exist, where appropriate settings for particle beam microscopy parameters are automatically found. In these methods, a computer is used to analyze multiple recorded images to calculate parameter settings that allow for recording images with optimal image sharpness or other image quality standards (e.g., low astigmatism values). An example of this method is described in US 6,838,667 B2. However, conventional automated methods, which require a small number of recorded images and therefore can be performed over a relatively short period, do not always provide the desired results.

[0005] Further information on particle beam focusing can be found in the following publications mentioned as examples: US2007 / 0 120 065 A1, US 2013 / 0 320 210 A1 and JP 2007-194 060 A. Summary of the Invention

[0006] The object of this invention is to provide a method for operating a particle beam microscope that simplifies the focusing of the particle beam on the object to be examined, and in particular, enables it to be performed in a fast and reliable manner.

[0007] According to an embodiment of the present invention, a method for operating a particle beam microscope is provided, the particle beam microscope comprising: a particle beam source for generating a particle beam; an objective lens for focusing the particle beam onto an object; and a dual deflector disposed in the beam path of the particle beam between the particle beam source and the objective lens, wherein the method comprises: setting a distance between the object and the objective lens to a given distance; and setting an excitation of the objective lens to a given excitation. Here, the given distance between the object and the objective lens can be selected according to the desired application (e.g., the magnification of the image to be generated and the landing energy of the particles of the particle beam on the object). The given excitation of the objective lens can then be selected in such a way that, at the given distance and when the particles pass through the objective lens with a given kinetic energy, the particle beam microscope can be used to generate a substantially clear particle microscope image of the object. However, in practice this is usually only roughly feasible, and it is necessary to find the setting for changing the excitation of the objective and / or the setting for changing the distance of the object from the objective by repeatedly recording and analyzing the test images. Under the setting of changing the excitation, a particle microscope image of the object that meets more stringent requirements in terms of image sharpness and other image quality can be obtained.

[0008] According to an embodiment, the method includes: setting the excitation of the dual deflector to a first setting such that the particle beam is incident on the object in a first orientation, and acquiring first particle microscopy data, such as recording a first particle microscopy image or a first scan along a line, when the dual deflector is in the first setting. Subsequently, the method includes: setting the excitation of the dual deflector to a second setting such that the particle beam is incident on the object in a second orientation different from the first orientation, and acquiring second particle microscopy data, such as recording a second particle microscopy image or a second scan along a line, when the dual deflector is in the second setting.

[0009] Particle microscopy data can be, for example, measured secondary particle intensities assigned to locations on an object's surface. For instance, particle microscopy data includes: multiple tuples, each representing a location on the object where a particle beam is guided for a predetermined time period; and the intensity of secondary particles detected when the particle beam is guided to that location. If the particle microscopy data is a particle microscopy image, it represents, for example, measured secondary particle intensities assigned to a two-dimensional extended region on the object's surface. The intensity of secondary particles can be detected, for example, when the particle microscopy data is a scan along a line, such as a line-by-line scan of a two-dimensional extended region (also called an image field) on the object's surface. For example, when the particle microscopy data is a scan along a line, these data represent measured secondary particle intensities assigned to points located along the line on the object's surface. The intensity of secondary particles can be detected when the particle beam scans along a specific straight line with a start and end point on the object's surface.

[0010] According to an exemplary embodiment, the line on the object is a straight line having a start point and an end point.

[0011] According to an exemplary embodiment, first and second particle microscopy data are obtained in such a way that they are each assigned to a plurality of locations on an object, and the locations assigned to the first particle microscopy data and the locations assigned to the second particle microscopy data intersect, i.e., the plurality of locations on the object are assigned to both the first and second particle microscopy data. If the first and second particle microscopy data are particle microscopy images, this means that the image fields of the first and second particle microscopy images at least partially overlap. If the first and second particle microscopy data are scans along lines, this means that the lines scanned by the particle beam to obtain the data at least partially overlap on the surface of the object, or extend only at a small angle relative to each other with a tiny gap, i.e., almost parallel to each other.

[0012] According to an embodiment, the method further includes: determining a new distance of the object from the objective lens based on analysis of the first particle microscopy data (e.g., a first particle microscopy image or a first scan along a line) and the second particle microscopy data (e.g., a second particle microscopy image or a second scan along a line); setting the object distance from the objective lens to the new distance; and acquiring third particle microscopy data, such as recording a third particle microscopy image, when the objective lens is given an excitation and the object is at the new distance from the objective lens. Based on the analysis of the first and second particle microscopy data, the new distance of the object from the objective lens can be determined in a way that the third particle microscopy data is obtained by better focusing the particle beam at the object surface. If the third particle microscopy data is a third particle microscopy image, the image is a relatively clear image of the object surface, wherein the image may also optionally meet other potentially higher quality standards. Here, after acquiring the first and second particle microscopy data, the excitation of the objective lens is maintained, i.e., the first, second, and third particle microscopy data are recorded under the same excitation of the objective lens, while the object distance from the objective lens is changed to better focus the particle beam at the object surface.

[0013] According to another embodiment, the method may then alternatively include: determining a new excitation for the objective based on analysis of the first particle microscopy data (e.g., a first particle microscopy image or a first scan along a line) and the second particle microscopy data (e.g., a second particle microscopy image or a second scan along a line); setting the excitation of the objective to the new excitation; and acquiring third particle microscopy data, such as recording a third particle microscopy image, when the objective is under the new excitation and the object is at a given distance from the objective. Based on the analysis of the first and second particle microscopy data, the new excitation for the objective can be determined in a way that the third particle microscopy data is acquired by a particle beam that is particularly well focused at the object surface. Here, after acquiring the first and second particle microscopy data, the object distance from the objective is maintained, i.e., the first, second, and third particle microscopy data are recorded under the same excitation of the objective, while the object distance from the objective is changed to better focus the particle beam at the object surface.

[0014] According to another embodiment, the method may then alternatively include: determining a new distance from the object to the objective and a new excitation of the objective based on analysis of the first particle microscopy data (e.g., a first particle microscopy image or a first scan along a line) and the second particle microscopy data (e.g., a second particle microscopy image or a second scan along a line); setting the distance from the object to the objective to the new distance and setting the excitation of the objective to the new excitation; and acquiring third particle microscopy data, such as recording a third particle microscopy image, when the objective is at the new excitation and the object is at the new distance from the objective. Based on the analysis of the first and second particle microscopy data, the new distance from the object to the objective and the new excitation of the objective can be determined in a way that the third particle microscopy data is acquired by a particle beam that is particularly well focused on the surface of the object. In this case, after the first and second particle microscopy data have been acquired, both the excitation of the objective and the distance from the object to the objective are changed to obtain a clearer image. That is, the first and second particle microscopy data are recorded when the excitation of the objective lens is the same and the distance between the object and the objective lens is the same, while the third particle microscopy data, such as the third image, is obtained when the excitation of the objective lens changes and the distance between the object and the objective lens changes.

[0015] This analysis may include the correlation between the first and second particle microscopy data.

[0016] According to an exemplary embodiment, the method includes: setting the excitation of an astigmatism corrector disposed in the beam path of the particle beam, between the particle beam source and the objective lens, to a given setting; setting the excitation of the dual deflector in a manner such that the particle beam is incident on an object in a third orientation different from the first and second orientations; and acquiring fourth particle microscopy data (e.g., a fourth particle microscopy image or a fourth scan along a line) when the astigmatism corrector is set to the given setting. The method may then further include: determining a new setting for the astigmatism corrector excitation based on analysis of first particle microscopy data, second particle microscopy data, and fourth particle microscopy data (e.g., a first particle microscopy image, a second particle microscopy image, and a fourth particle microscopy image, or a first scan along a line, a second scan along a line, and a fourth scan along a line); and setting the astigmatism corrector excitation to the new excitation. Here, first and second particle microscopy data are acquired when the astigmatism corrector is set to the given setting, and third particle microscopy data, such as a third particle microscopy image, is recorded when the astigmatism corrector excitation is set to the new setting. Here, a new setting for the excitation of the astigmatism corrector can be determined in a way that the particle beam is focused at the object surface with low astigmatism, so that the third particle microscope image that may have been recorded not only has high image sharpness but also low astigmatism.

[0017] According to an exemplary embodiment, here, fourth particle microscopy data is recorded when the objective lens is given an excitation and the object is at a given distance from the objective lens.

[0018] According to an exemplary embodiment, obtaining second particle microscopy data includes scanning a particle beam along a first line on the surface of an object. Obtaining third particle microscopy data may then include scanning a particle beam along a second line on the surface of the object. In this case, the minimum angle between the first and second lines may be greater than 20°, particularly greater than 40°, and particularly greater than 80°.

[0019] According to another exemplary embodiment, first and second particle microscopy data are recorded when the objective lens is under a given excitation and the object is at a given distance from the objective lens.

[0020] According to an exemplary embodiment, the purpose of determining the first setting and the second setting of the dual deflectors is to ensure that, when the distance between the object and the objective lens is a given setting and the objective lens is under a given excitation, there is substantially no image shift or only minimal possible image shift between the first particle microscopy data and the fourth particle microscopy data. If the particle beam is optimally focused on the object surface, the effective particle emitter is optically imaged onto the object surface through the objective lens, any condenser lens present, and other effective particle optics elements in the beam path of the particle beam. Then, particle beams emitted from the source at different angles will land at the same location on the object surface at different angles.

[0021] Now, if no image shift occurs when the particle beam is incident on the object at different orientations during the acquisition of the first and second particle microscopy data, this means that the excitation of the dual deflector is selected such that the particle beam appears to originate directly from the particle emitter after being deflected by the dual deflector. Furthermore, if this dual deflector setting is selected and an image shift occurs between the first and second particle microscopy data, it can be inferred that a change in the given distance and / or the excitation of the objective is needed to obtain third particle optical data, or a particularly clear third particle microscopy image, by focusing the particle beam particularly well on the object surface. In this process, specifically, the necessary change from the given excitation of the objective to the new excitation of the objective, or the necessary change from the given distance of the object from the objective to the new distance of the object from the objective, can be calculated based on the image shift determined between the first and second particle microscopy data (e.g., between the first and second particle microscopy images).

[0022] The first, second, and possibly third settings of the dual deflectors can be determined based on a computational model of the particle beam microscope. In particular, various settings for other parameters of the particle beam microscope, such as high pressure (used to accelerate the particle beam after it exits the particle beam source in order to obtain a focused image), are included in the computational model, which includes a model of the relationship between the excitation of the objective and the distance of the object from the objective.

[0023] The orientation of the particle beam incident on the object can be characterized by its azimuth and elevation angles relative to the principal axis of the objective lens. According to an exemplary embodiment, the first and second orientations differ in their elevation angles relative to the principal axis of the objective lens. They may be the same in their azimuth angles. According to an exemplary embodiment, the second and third orientations differ in their azimuth angles relative to the principal axis of the objective lens and, in this case, may in particular have the same elevation angle.

[0024] The computational model can further include a model of the relationship between the excitation of the deflection device used to scan the particle beam across the object surface and the direction of the line along which the particle beam scans to obtain particle optical data of the object surface. In particular, the model takes into account the magnetic field of the objective lens and the resulting Larmor rotation of the particle beam.

[0025] The present invention further includes a computer program product comprising instructions that, when executed by a controller of a particle beam microscope, cause the particle beam microscope to perform the methods described above. Attached Figure Description

[0026] Embodiments of the present invention will now be explained in more detail with reference to the accompanying drawings, in which:

[0027] Figure 1 A schematic demonstration of a particle beam microscope is shown;

[0028] Figure 2 It shows Figure 1 A schematic representation of the details of the beam path in a particle beam microscope;

[0029] Figure 3 Explanation of the operation is shown. Figure 1 A flowchart of a particle beam microscopy method;

[0030] Figure 4 Explanation of the operation is shown. Figure 1 A flowchart of another method for particle beam microscopy;

[0031] Figure 5 A schematic illustration is shown to explain the image shift when the first and second particle microscopy data are particle microscopy images; and

[0032] Figure 6A schematic illustration is shown to explain the image offset when the first and second particle microscope data are scanned along a line. Detailed Implementation

[0033] Figure 1 This is a schematic diagram of a particle beam microscope 1, which can be operated using methods according to embodiments of the present invention. The particle beam microscope 1 includes a particle beam source 3, which includes a particle emitter 5 and a driver 7. For example, the particle emitter 5 may be a cathode heated by the driver 7 via a wire 9, which emits electrons that are accelerated away from the particle emitter 5 by an anode 11 and shaped to form a particle beam 13. For this purpose, the driver 7 is controlled by a controller 15 of the particle beam microscope 1 via a control line 17, and the potential of the particle emitter 5 is set by a settable voltage source 19, which is controlled by the controller 15 via a control line 21. The potential of the anode 11 is set by a settable voltage source 23, which is also controlled by the controller 15 via a control line 25. The difference between the potential of the particle emitter 5 and the potential of the anode 11 defines the kinetic energy of the particles in the particle beam 13 after passing through the anode 11. The anode 11 forms the upper end of a beam tube 12, into which the particles of the particle beam 13 enter after passing through the anode 11.

[0034] The particle beam 13 passes through a condenser lens 27, which collimates the particle beam 13. In the example shown, the condenser lens 27 is a magnetic lens with a coil 29, which is excited by a current generated by a settable current source 31, which is controlled by a controller 15 via a control line 33.

[0035] The particle beam 13 then passes through objective lens 35, which is designed to focus the particle beam 13 onto the surface of the object 37 to be examined. In the example shown, objective lens 35 includes a magnetic lens whose magnetic field is generated by coil 39, which is excited by a current source 41 controlled by controller 15 via control line 43. Objective lens 35 further includes an electrostatic lens whose electrostatic field is generated between the lower end 45 of beam tube 12 and electrode 49. Beam tube 12 is electrically connected to anode 11, and electrode 49 can be electrically connected to ground potential or via another voltage source controlled by controller 15. Figure 1 (Not shown in the text) is set to a different potential than that of the ground.

[0036] Object 37 is held on stage 51, the potential of which is set by voltage source 53, controlled by controller 15 via control line 55. Object 37 is electrically connected to stage 51 such that it also possesses the potential of stage 51. The difference between the potential of particle emitter 5 and the potential of object 37 defines the kinetic energy of the particles of beam 13 when incident on object 37. In contrast, if the particles are decelerated by the electrostatic field between the end 45 of beam tube 12 and electrode 49 and / or by the electric field between electrode 49 and object 37, the particles can have greater kinetic energy within beam tube 12 and as they pass through condenser lens 27 and objective lens 35. However, the particle beam microscope 1 can also be implemented without beam tube 12 and electrode 49, and thus the particles are decelerated or accelerated by the electric field between anode 11 and object 37 before incident on object 37. Regardless of whether the particle beam microscope 1 has or does not have a beam tube 12, and regardless of the embodiment and arrangement of the electrode 49, the kinetic energy of the particle when incident on the object 37 depends only on the difference between the potential of the particle beam source 3 and the potential of the object 37.

[0037] The particle beam microscope 1 also includes a deflection device 57, which is controlled by a controller 15 via a control line 59, and deflects the particle beam 13 so that the particle beam 13 can scan region 61 on the object 37 under the control of the controller 15. The particle beam microscope 1 further includes a detector 63, which is positioned such that signals generated by the particle beam 13 guided on the object 37 and exiting the object can be incident on the detector 63 for detection. These signals can include particles such as backscattered electrons and secondary electrons, or radiation such as cathodoluminescence radiation.

[0038] exist Figure 1 In the particle beam microscope 1 shown, detector 63 is arranged close to objective lens 35 and near the object. However, the detector can also be arranged in the beam tube 12 or any other suitable location. In particular, if the electric field on the object surface has a decelerating effect on the incident electrons of the particle beam 13, secondary electrons leaving the object at low speed will be accelerated by this electric field into the beam tube and can be detected by the detector arranged in the beam tube 12. Figure 1 (Not shown in the text).

[0039] The particles emitted from object 37 are caused by the particle beam 13 incident on object 37. Specifically, these detected particles can be particles of the particle beam 13 itself, which are scattered or reflected at object 37, such as backscattered electrons, or they can be particles separated from object 37 by the incident particle beam 13, such as secondary electrons. However, detector 63 can also be implemented in a manner that the detector detects radiation, such as X-ray radiation, generated by the particle beam 13 incident on object 37. The detection signal from detector 63 is received by controller 15 via signal line 65. Controller 15 stores data derived from the detection signal during scanning, depending on the current settings of deflection device 57, and thus this data represents a particle beam microscope image of region 61 of object 37. This image can be presented by display device 67 connected to controller 15 and observed by the user of particle beam microscope 1.

[0040] The particle beam microscope 1 further includes dual deflectors 75, which are arranged in the beam path of the particle beam 13, between the particle beam source 3 and the objective lens 35. Figure 1 In the example shown, the dual deflectors 75 are arranged in the region of the anode 11; however, the first deflection device may also be arranged between the particle beam source 3 and the anode 11, between the anode 11 and the condenser lens 27 or objective lens 35, or between the condenser lens 27 and objective lens 35. The dual deflectors 75 include two separate deflectors 77 and 79, which are arranged sequentially in the beam path of the particle beam 13 and each has a plurality of deflecting elements 81 distributed in a circumferential direction around the particle beam 13. The deflecting elements 81 may be formed of electrodes and / or coils, the excitation of which is provided by voltage or current sources 83, controlled by a controller 15 via line 82. Each individual deflector 77, 79 of the dual deflectors 75 is configured to deflect the particle beam 13 passing through the respective individual deflector along an adjustable direction and at an adjustable angle. For example, if the deflection element 81 of the individual deflectors 77, 79 is an electrode, then for example, four electrodes can be provided, arranged in a distributed manner around the particle beam 13. For example, if the deflection element 81 is a coil, then for example, eight coils can be provided, arranged in a circumferential direction around the particle beam 13.

[0041] The dual deflector 75 can be used to adjust the particle beam 13; that is, before the beam passes through the objective lens 35, the beam is aligned in a way that allows it to be focused onto the object 37 to the greatest possible extent possible through the objective lens 35. For example, the excitation of the dual deflector 75 can be set in a way that the particle beam 13 passes through the principal plane of the objective lens 35 along the optical axis. Further, the dual deflector 75 can be used in methods for focusing the particle beam 13 onto the object 37, as described below.

[0042] The particle beam microscope 1 further includes an astigmatism corrector 85 comprising a plurality of astigmatism correction elements 86 arranged in a distributed manner around the particle beam 13. The excitation of the astigmatism correction elements is provided by a driver circuit 87, which is controlled by a controller 15 via a control line 88. The astigmatism corrector 85 is configured to provide an electric or magnetic quadrupole field, the size and orientation of which are settable.

[0043] See below Figure 2 The method used for focusing particle beam microscope 1 is explained below. The figure shows a simplified schematic representation of the beam path of particle beam microscope 1. In this simplified representation, the particle beam 13 generated by particle beam source 3 is focused into focal plane 91 by objective lens 35. Besides objective lens 35, only dual deflectors 75 act on the particle beam. Figure 2 The effect of other particle optics elements (such as condenser lens 27) on the particle beam 13 is not shown in the diagram. However, the principles described below also apply when the effects of other particle optics elements are taken into account. Figure 2 In the demonstration, the action of the optical elements occurs within their principal planes, where the trajectory of the particle beam is "kinked." Thus, objective 35 has a principal plane 93, and the individual deflectors 77 and 79 of the dual deflectors 75 have principal planes 94 and 95, respectively. In practice, the action of each particle optical element extends over a large area along the beam path of the particle beam 13.

[0044] Assuming that the objective lens 35 is given excitation, the voltage applied to the anode 11 is given a setting, and the potential of the particle beam source 3 is set, the particle beam 13 is focused in the focal plane 91. Based on these settings and the calculation model of the particle beam microscope 1, the distance from the focal plane 91 to the objective lens 35 can be calculated with a certain degree of accuracy. Then, an attempt is made to arrange the surface of the object 37 to be examined within the calculated focal plane 91. However, this is usually only achievable with limited accuracy. Figure 2 In the demonstration, it is assumed that the surface of the object 37 to be inspected is arranged in plane 92, which is a distance ΔF from the focal plane 91. For example, the surface of the object can be located in the focal plane 91 with an accuracy of + / -500 μm.

[0045] If the surface of object 37 is not precisely aligned within the focal plane 91, the resulting particle microscope image will exhibit unnecessarily blurred edges. The method for using the focusing particle beam microscope 1 is then initiated. For this purpose, for example, the distance between object 37 and objective lens 35 is changed so that the plane 92 on which the surface of object 37 is arranged is closer to the focal plane 91, or the excitation of objective lens 35 is changed so that the focal plane 91 is closer to the plane 92 on which the surface of object 37 is arranged. To determine the new distance between object 37 and objective lens 35 and / or the new excitation of objective lens 35, it is necessary to record two or more particle optical images under two or more different excitations of the dual deflectors 75 during the executed method.

[0046] Figure 2 Two possible excitations for this purpose are illustrated by example. In the first excitation, the individual deflectors 77 and 79 of the dual deflector 75 do not deflect the particle beam 13 at all, and therefore the particle beam extends along the optical axis 6 of the objective lens 75, along the solid line 3. In the second excitation, the particle beam extends along... Figure 2 The solid line 103 extends in the middle, where Figure 2 The individual first deflector 77 deflects the particle beam 13 (which extends along the optical axis 6 between the particle emitter 5 and the principal plane 94 of the individual deflector 77) to the right by an angle α1, and the individual second deflector 79 then deflects the particle beam to the left by an angle α2. Angles α1 and α2 are determined in such a way that the particle beam 13 appears to originate directly from the particle emitter 5 after passing through the individual second deflector 79, as... Figure 2 The dotted line 105 in the image shows this.

[0047] Since the focal plane 92 of the particle beam microscope 1 is the plane that images the particle emitter 5, line 103 intersects the optical axis 6 in the focal plane 91. However, line 103 intersects the plane 92 of the surface on which the object 37 is actually arranged at a distance w1 from the optical axis 6.

[0048] Particle microscopy images of the object are recorded under two excitation settings of the dual deflector 75, in which the particle beam 13 extends along lines 101 and 103, respectively. Both images show substantially the same structure of the surface of the object 37. However, an image offset corresponding to a distance w1 exists between the two recorded images. Therefore, the distance w1 can be determined by analyzing and comparing the two recorded particle optical images. Based on the distance w1, the magnitude of the defocus, i.e., the distance ΔF between the focal plane 91 and the plane 92 on which the object surface is arranged, can then be determined as a measure of the defocus of the particle beam at the object surface. Figure 2It is evident, for example, that if w1 is known and if the angle β between line 103 and optical axis 6 is known, ΔF can be calculated. For a given excitation of the dual deflector 75, this angle can be calculated based on a computational model of the particle beam microscope 1, which deflects the particle beam by angles α1 and α2. The data for this computational model can be predetermined through simulation or experiment.

[0049] Now see Figure 5 This explains how the distance w1 is determined based on the analysis of the two images. Figure 5 The image shown is a first image recorded when the dual deflector 75 is set to a first excitation setting, superimposed on a second image recorded when the dual deflector 75 is set to a second excitation setting. Figure 5 Reference numeral 131 in the accompanying drawings denotes the outline of a structure present on the object and becoming visible in the first particle microscope image. The outline of structure 131 in the first image is... Figure 5 It is indicated by reference numeral 132 in the accompanying figure because it becomes visible in the second particle microscope image. By analyzing the two images, for example, by correlating them using a Fourier transform, the offset between the two images can be determined, which corresponds to... Figure 5 The middle arrow w1 represents the distance w1.

[0050] exist Figure 2 In this process, particle beam 103 is incident on the surface of the object with the following orientation: this orientation can be characterized by the azimuth and elevation angles relative to the principal axis of objective lens 35. The elevation angle is 90° - β, and the azimuth angle is... Figure 2 The angle between the drawing plane and the principal axis of the objective lens 35.

[0051] Then, based on the calculated ΔF value, a new distance between the object 37 and the objective lens 35 can be determined. At this new distance, a clear particle microscope image of the object can be recorded while the excitation of the objective lens 35 remains unchanged. Alternatively, a new excitation of the objective lens 35 can be determined, and at this new excitation, a clear particle microscope image of the object 37 can be recorded while the distance between the object 37 and the objective lens 35 remains unchanged. Or, a new distance between the object and the objective lens and a new excitation of the objective lens can be determined, and at both the new distance and the new excitation, a clear particle microscope image of the object can be recorded.

[0052] See below Figure 3 The flowchart further explains the method used for focusing particle beam microscopy 1. In this method, a given excitation of the objective lens and a given working distance (the distance between the object and the objective lens) are first determined in step 111. The aim is to generate a particle microscope image of the object that is as sharp as possible under these settings, and the aim is that the offset between two subsequently recorded particle microscope images is equal to zero. Based on these settings, the objective lens is excited and the object is positioned relative to the particle beam microscope.

[0053] Then, in step 113, two different excitations for the dual deflectors are determined. For example, determining each excitation for the dual deflectors includes determining two deflection angles by which the particle beam is deflected by the two separate deflectors, the dimensions of which are determined in such a way that the particle beam appears to originate from particle emitter 5 after passing through the dual deflectors. Then, in step 115, the first excitation for the dual deflectors is set, and subsequently, in step 117, a first particle microscopy image of the object is recorded. Subsequently, in step 119, the second excitation for the dual deflectors is set, and in step 121, a second particle microscopy image is recorded. In step 123, the two recorded particle microscopy images are analyzed, and the image offset between the two images is determined. Then, in step 123, the defocus ΔF is further determined based on the determined image offset and additionally using a particle beam microscopy computational model. Then, in step 125, a new excitation for the objective and / or a new distance of the object from the objective is set based on the defocus ΔF. Subsequently, in step 127, one or more clear particle microscopy images of the object can be recorded.

[0054] See Figure 2 In the illustrated example, the first excitation of the dual deflectors 75 is selected in such a way that the two individual deflectors 77 and 79 do not deflect the particle beam 13, and the particle beam extends along line 101 on the optical axis 6 of the objective lens 35. The second setting of the dual deflectors 75 is selected in such a way that the two individual deflectors 77 and 79 deflect the particle beam 13. Figure 2 The deflection angles α1 and α2 in the plane of the drawing cause the particle beam to follow... Figure 2 Line 103 extends in the drawing plane and is incident on the surface of object 37 at an elevation angle of 90°-β and an azimuth angle corresponding to the drawing plane. The two particle microscope images recorded under both settings of the dual deflector 75 have an image shift w1, which is also located... Figure 2 In the plane of the drawing, and for example in Figure 2 The middle is guided to the right, and the x-direction can be defined, for example.

[0055] Then a third excitation setting can be implemented with the dual deflectors 75, in which the particle beam 13 is again deflected by individual deflectors 77 and 79 by angles α1 and α2, but these deflections are oriented in a way that they are positioned relative to... Figure 2 The drawing plane is orthogonally oriented and contains the optical axis 6 of the objective lens 35. This corresponds to an azimuth angle 90° different from the second setting. Another image of the object 37 can be recorded when the dual deflectors 75 are used for this third excitation setting. By comparing this other image with the first image, the image offset w2 can be further determined, which is along the plane with the optical axis 6 of the objective lens 35. Figure 2 The plane in which the drawing is drawn is orthogonally oriented, and for example, the y-direction can be defined.

[0056] If there is no astigmatism in the imaging of the particle emitter 5 onto the focal plane 91, then the two image offsets w1 and w2 measured in the x and y directions, respectively, will have the same absolute value. Conversely, if the image offset w1 in the x direction and the image offset w2 in the y direction have different absolute values, a corresponding x-direction defocus ΔFx can be assigned to the image offset in the x direction, and a corresponding y-direction defocus ΔFy can be assigned to the image offset in the y direction. The astigmatism in the imaging of the particle emitter 5 onto the focal plane 91 can be determined based on the difference between the x-direction defocus ΔFx and the y-direction defocus ΔFy. The excitation of the astigmatism corrector 85 can then be changed based on this determined astigmatism value to compensate for the astigmatism. Therefore, in addition to determining the defocus ΔF and subsequently improving the focusing of the particle beam microscope, astigmatism can also be determined and subsequently compensated for.

[0057] See below Figure 4 The flowchart further explains the method. In step 211, the given excitation of the objective lens, the given excitation of the astigmatism corrector, and the given working distance are set. The purpose of these settings is to obtain a particle microscope image of the object as sharp as possible. In step 213, three different excitations of the dual deflectors are determined. In step 215, the first excitation of the dual deflectors is set, and then in step 217, the first particle microscope image of the object is recorded. Subsequently, in step 219, the second excitation of the dual deflectors is set, and in step 221, the second particle microscope image of the object is recorded. Then, in step 231, the third excitation of the dual deflectors is set, and in step 233, the fourth particle microscope image is recorded.

[0058] In step 223, the offset between the first and second images is determined, and the defocus ΔF is determined accordingly. In step 235, the offset between the first and third images is determined, and this offset is compared with the offset between the first and second images to determine astigmatism. Then, in step 225, a new excitation for the astigmatism corrector and a new excitation for the objective lens, and / or a new working distance, are determined and set so that one or more clear particle microscope images of the object can be recorded in step 227.

[0059] These images can be displayed on the screen 76 of the particle beam microscope 1. The user of the particle beam microscope 1 can control the particle beam microscope, and in particular, the starting of the focusing method, through operating elements such as the keyboard 69 and mouse 71, as well as the user interface displayed on the screen.

[0060] See Figure 3 , Figure 4 and Figure 5In the example explained, the particle microscopy data obtained with dual deflectors at different excitation settings is a particle microscopy image. An embodiment where the particle microscopy data obtained with dual deflectors at different excitation settings is a scan along a line will now be explained.

[0061] For this purpose, when the dual deflector 75 is set for the first excitation, the particle beam 13 moves along line 135 on the surface of object 37 by actuating the deflection device 57. Line 135 extends along a straight line and has a starting point 135s and an ending point 135e. As the particle beam scans from the starting point 135s along line 135 to the ending point 135e, the intensity of secondary particles, for example, detected by detector 63, is recorded. Figure 6 The results are shown in the graph, which plots the detected intensity I against the distance s on the surface of object 37. Curve 137 shows the intensity recorded while scanning along line 135 when the dual deflectors 75 are set for the first excitation.

[0062] When the dual deflector 75 is set for the second excitation, the particle beam 13 scans the surface of the object 37 along a line 136 having a start point 136s and an end point 136e. Line 136 is chosen to coincide with or be close to line 135 on the object. Specifically, these two lines 135 and 136 are spaced a small distance apart and extend at a small angle to each other, such that they extend almost parallel to each other. For example, the maximum distance between these two lines 135 and 136 on the object 37 is less than tens of nanometers. Curve 138 shows the intensity recorded when scanning along line 136 when the dual deflector 75 is set for the second excitation.

[0063] The offset w1 can be determined by comparing these two curves, 137 and 138. Compared to determining the offset based on two images, for records obtained by scanning a two-dimensional extended region with the particle beam, the offset can be determined more quickly by scanning along the line.

[0064] Therefore, the orientations of lines 135 and 136 need to be appropriately selected on the surface of object 37. The orientations are advantageously selected such that the difference between the first and second orientations of the particle beam 13 incident on the object surface when the dual deflectors 75 are in the first and second settings results in a maximum offset w1 between curves 137 and 138. For this purpose, the orientations of these two lines 135 and 136 are determined using a computational model of the particle beam microscope 1. The computational model here specifically considers the azimuth angles of the first and second orientations of the particle beam 13 incident on the surface of object 37 when the dual deflectors 75 are in the first and second settings. The Larmor rotation of the particle beam 13 in the magnetic field of the objective lens 35 is specifically considered in order to excite the deflection device 57 in a scanning manner along lines 135 and 136. However, the two orientations of the particle beam 13 incident on the surface of object 37 when the dual deflectors 75 are in the first and second settings can also be determined in a corresponding manner based on the previously specified orientations of lines 135 and 136 on the object.

[0065] according to Figure 3 The method (which determines the offset w1 in step 123 by comparing the first image with the second image) can be changed to step 117 where, instead of recording the first image when the dual deflector 75 is set for the first excitation, the image is moved along... Figure 5 The first scan is performed along line 135. Then, in step 121, when the dual deflector 75 is set for the second excitation, the second image is not recorded, but rather along... Figure 5 A second scan is performed along line 136. Then, in step 123, an offset w1 is determined based on data related to the scan along line 135 and data related to the scan along line 136, thereby determining the defocus ΔF. Then, in step 125, a new excitation and / or a new distance for the objective lens are set.

[0066] according to Figure 4 The method (which determines the corresponding offset by comparing the first image with the second image and comparing the first image with the fourth image in steps 223 and 235, respectively) can be similarly modified to use scanning along the line instead of using images and still be able to determine defocus and astigmatism.

[0067] For this purpose, in step 217, instead of recording the first image, a scan along line 135 (oriented in the x-direction) and a scan along line 141 (oriented at an angle to line 135) are performed while the dual deflector 75 is in the first setting. Figure 5In the example, line 141 is oriented approximately 90° to line 135, i.e., in the y-direction. Then, in step 221, a scan along line 136 is performed when the dual deflector 75 is in the second setting. Based on a comparison of the data from the scan along line 135 with the data from the scan along line 136, an offset corresponding to defocus ΔFx can be determined in step 223, since lines 135 and 136 are oriented in the x-direction. Then, in step 233, when the dual deflector 75 is in the third setting, a scan is performed along line 142, which overlaps with or is only slightly spaced from line 141. Based on a comparison of the data from the scan along line 141 with the data from the scan along line 142, an offset corresponding to defocus ΔFy can be determined in step 235, since lines 141 and 142 are oriented in the y-direction. Then in step 225, the defocus ΔF can be determined based on ΔFx and ΔFy (e.g., by averaging ΔFx and ΔFy), and the astigmatism can be determined so as to determine and set a new excitation for objective 35, a new excitation for astigmatism corrector 85, and / or a new working distance, thereby recording an image with improved image sharpness and less astigmatism in step 227.

[0068] In the above embodiments, the particle beam device is an electron microscope. However, the invention can also be applied to other particle beam devices. Examples include ion beam devices and combinations of ion beam devices and electron beam devices, in which an ion beam generated by the ion beam device and an electron beam generated by the electron beam device can both irradiate a position on an object. Further, the particle beam device can also be a multi-beam particle beam device, wherein multiple particle beams are guided onto the object in parallel with each other.

Claims

1. A method for operating a particle beam microscope (1), wherein The particle beam microscope (1) includes: Particle beam source (3) used to generate particle beam (13); Objective lens (35) used to focus the particle beam onto object (37); A dual deflector (75) and an astigmatism corrector (85) are arranged in the beam path of the particle beam (13) between the particle beam source (3) and the objective lens (35); and A deflection device (57) is used to make the particle beam (13) scan the surface of the object (37); The method includes: Set the distance between the object (37) and the objective lens (35) to a given distance; Set the excitation of the objective lens (35) to the given excitation; The excitation of the astigmatism corrector (85) is set to a given setting; The excitation of the dual deflector (75) is set to a first setting such that the particle beam (13) is incident on the object (37) in a first orientation (β), and first particle microscope data is obtained when the dual deflector (75) is set to the first setting by scanning the particle beam (13) along a first line on the surface of the object (37). The excitation of the dual deflector (75) is set to a second setting, such that the particle beam (13) is incident on the object (37) in a second orientation (β) different from the first orientation, and second particle microscope data are obtained when the dual deflector (75) is set to the second setting by making the particle beam (13) scan along a second line on the surface of the object. The excitation of the dual deflector (75) is set to a third setting, such that the particle beam (13) is incident on the object (37) with a third orientation (β) different from the first orientation (β) and the second orientation (β), and third particle microscopy data is obtained when the astigmatism corrector (85) is set to the third setting by scanning the particle beam (13) along the third line on the surface of the object. The minimum angle between the second line and the third line is greater than 10°. -Based on the analysis of the first particle microscope data, the second particle microscope data, and the third particle microscope data, a new distance between the object (37) and the objective lens (35) is determined, and the distance between the object (37) and the objective lens (35) is set as the new distance; or -Based on the analysis of the first particle microscope data, the second particle microscope data, and the third particle microscope data, a new excitation for the objective (35) is determined, and the excitation for the objective (35) is set as the new excitation; or -Based on the analysis of the first particle microscope data, the second particle microscope data, and the third particle microscope data, determine the new distance between the object (37) and the objective lens (35) and the new excitation of the objective lens (35), set the distance between the object (37) and the objective lens (35) as the new distance, and set the excitation of the objective lens (35) as the new excitation; or -Based on the analysis of the first particle microscope data, the second particle microscope data and the third particle microscope data, a new setting for the excitation of the astigmatism corrector (85) is determined, and the excitation of the astigmatism corrector (85) is set to the new excitation.

2. The method of claim 1, further comprising: The orientation of the first line, the second line, and the third line on the surface of the object is determined based on the orientation azimuth angle of the particle beam incident on the object. and / or The orientation azimuth of the particle beam incident on the object is determined based on the orientation of the first line, the second line, and the third line on the surface of the object.

3. The method as described in claim 1 or 2, wherein, A first setting and a second setting of the dual deflector (75) are determined such that when the distance between the object (37) and the objective lens (35) is the given setting and the objective lens (35) is the given excitation, there is substantially no image offset between the first particle microscopy data and the second particle microscopy data.

4. The method of claim 3, wherein, The first and second settings of the dual deflector (75) are determined based on the computational model of the particle beam microscope (1).

5. The method as described in claim 1 or 2, wherein, The first orientation differs from the second orientation by at least 0.01°.

6. The method as described in claim 1 or 2, wherein, The first orientation and the second orientation differ in their elevation angles relative to the principal axis of the objective lens, but are the same in their azimuth angles.

7. The method of claim 1 or 2, further comprising: Fourth particle microscopy data are obtained when the objective (35) is the given excitation and the object (37) is at the new distance from the objective (35); Fourth particle microscopy data are obtained when the objective (35) is the new excitation and the object (37) is at the given distance from the objective (35); Fourth particle microscopy data are obtained when the objective (35) provides the new excitation and the object (37) is at the new distance from the objective (35); or Fourth particle microscopy data are obtained when the excitation of the astigmatism corrector (85) is set to the new setting.

8. The method of claim 7, wherein, The fourth particle microscopy data includes particle microscopy images.

9. The method as claimed in claim 1 or 2, wherein, The purpose of determining the first, second, and third settings of the dual deflector (75) is to ensure that there is no image offset between the first particle microscopy data and the third particle microscopy data when the distance between the object (37) and the objective lens (35) is at the given setting and the objective lens (35) is at the given excitation.

10. The method as claimed in claim 1 or 2, wherein, The second orientation and the third orientation differ in their azimuth angles relative to the principal axis of the objective lens.

11. The method as claimed in claim 1 or 2, wherein, The second orientation and the third orientation are the same in terms of their elevation angles relative to the principal axis of the objective lens.

12. The method as claimed in claim 1 or 2, wherein, The first, second, and third settings of the dual deflector (75) are determined based on the computational model of the particle beam microscope (1).

13. The method as claimed in claim 1 or 2, wherein, The first particle microscopy data and the second particle microscopy data are recorded when the objective (35) is given the excitation and the object (37) is at the given distance from the objective (35).

14. The method as claimed in claim 1 or 2, wherein, The dual deflector (75) includes two separate deflectors (77, 79) arranged at a distance from each other in the beam path of the particle beam (13).

15. The method of claim 14, wherein, The individual deflector (77, 79) includes four or eight deflection elements (81) arranged in a distributed manner in the circumferential direction surrounding the particle beam (13).

16. The method of claim 15, wherein, The deflection element (81) includes electrodes and / or coils.

17. A particle beam microscope configured to perform the method as claimed in any one of claims 1 to 16.

18. A computer program product comprising instructions that, when executed by a controller of a particle beam microscope, cause the particle beam microscope to perform the method as described in any one of claims 1 to 16.

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