Method for adjusting a particle beam microscope and particle beam microscope

Abstract

A method for operating a particle beam microscope, comprising recording a first particle microscope image at a given excitation of a deflection device and a first focus setting, recording a second particle microscope image at the given excitation of the deflection device and a second focus setting, and determining a new excitation of the deflection device on the basis of the first particle microscope image, the second particle microscope image and a function relationship known in advance. The function relationship represents a displacement of particle microscope images recorded when the focus setting is changed in dependence on the excitation of the deflection device. By the new excitation, the particle beam microscope is then adjusted so that a sharp image can be recorded therewith.

Description

Technical Field

[0001] This invention relates to methods for adjusting particle beam microscopes. Specifically, this invention relates to methods for adjusting one or more particle beams to be focused onto an object to be examined in particle beam microscopes. Background Technology

[0002] An example of such particle beam microscopy is scanning electron microscopy, in which a focused electron beam scans the area of ​​the object to be examined and detects secondary or backscattered electrons generated at 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 scanned area of ​​the object.

[0003] A particle beam, generated by a particle beam source, may pass through a condenser lens, astigmatism corrector, or other beam-shaping element and be focused onto an object by an objective lens. To achieve the high 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 on the object's surface by the focused particle beam ("beam spot") should be as small as possible. To this end, the particle beam microscope and its particle optics are adjusted to obtain an image plane that coincides with the object's surface, in which the particle source is imaged by the optical system. Given an object positioned at a given distance from the objective lens, this can be achieved by varying the focus setting of the particle beam microscope until the beam spot or image of the particle source on the object's surface is as small as possible. For example, the focus setting of the particle beam microscope can be changed by altering the excitation of the objective lens and / or by changing the kinetic energy of the particles in the particle beam as they pass through the objective lens.

[0004] After setting the focus of a particle beam microscope in this way, further steps can usually be taken to improve the quality of the beam focus on the object surface. This includes adjusting the particle beam so that it passes through the objective lens substantially centrally. This is based on the idea that the lens aberrations of an optical lens become increasingly pronounced as the beam passes through the lens further away from the lens's optical axis. Since the objective lens typically provides most of the refractive power required to image the particle source on the object surface, it is advantageous from the perspective of reducing imaging aberrations involved in this imaging process to adjust the beam relative to the objective lens so that the beam passes through the objective lens as centrally as possible. For example, for this adjustment, a particle beam microscope includes a deflection device for shifting the particle beam within the objective lens and arranging it in the beam path between the particle beam source and the objective lens. By changing the excitation of this deflection device, the position within the principal plane of the objective lens where the center of the particle beam passes through the principal plane can be shifted.

[0005] Finding the right adjustment for the beam is not easy. For this reason, some conventional methods use particle beam microscopy to record images with at least two different focal settings, so that the optimal excitation of the deflection device can be set based on analysis of these recorded images. This is based on the following thinking: if the particle beam passes centered through the objective and focuses on the surface of the object, the recorded particle beam image is essentially sharp. If the focal setting is slightly changed from this setting, and a particle beam image is recorded for this changed setting, the image is only slightly less sharp than the previously recorded particle beam image, and otherwise essentially the same. However, if two images recorded with different focal settings are recorded using a particle beam that does not pass centered through the objective, the two images differ not only in image sharpness but also in their relative positions. The change in focal setting causes the second image to shift or deflect relative to the first image. Therefore, the so-called "wobbling method" is typically performed for the purpose of adjusting the particle beam, within which the focal setting is periodically changed while continuously recording images. The user observes the images shifting back and forth due to improper beam adjustment and changes the excitation of the deflection device until the resulting images are essentially stationary. In addition to this manual method, automated methods are also known, and these methods record multiple images with paired different focus settings and deflection device excitation settings. The optimal settings for the deflection device excitation are calculated and set based on the analysis of the multiple recorded images. These settings are then used to record high-quality particle microscope images of the desired object. Such methods are known, for example, from US6 864 493 B2, US 2012 / 0 138 793 A1, US 8 766 183 B2, and US 7 705 300 B2.

[0006] However, such a method requires recording a minimum number of images for different focus settings and deflection device excitations, which is at least four images. The time required to record this minimum number of images is considered too long, especially in applications designed for high throughput. Summary of the Invention

[0007] Accordingly, the object of the present invention is to provide a method for adjusting a particle beam microscope, by which beam adjustment can be performed with a minimal number of images. According to the present invention, a method for adjusting a particle beam microscope is provided, wherein the particle beam microscope includes a particle beam source for generating a particle beam, an objective lens for focusing the particle beam onto an object, a first deflection device disposed between the particle beam source and the objective lens for deflecting the particle beam, and a second deflection device disposed between the first deflection device and the object. The second deflection device is used to deflect the particle beam during image recording, the deflection allowing the particle beam to scan an area of ​​the object to be imaged, and a detector of the particle beam microscope detects signals generated by the particle beam scanning the image area of ​​the object, from which a particle beam microscope image of the object can be generated. The first deflection device is such that its excitation is set within the range of this adjustment method such that the particle beam passes substantially centrally through the objective lens.

[0008] According to an exemplary embodiment, a method for adjusting a particle beam microscope includes recording a first particle microscope image under a given excitation of a first deflection device and a first focal setting; recording a second particle microscope image under a given excitation of the first deflection device and a second focal setting different from the first focal setting; and determining a new excitation of the first deflection device based on the first particle microscope image, the second particle microscope image, and a previously known functional relationship representing the displacement of the recorded particle microscope image when the focal setting is changed according to the excitation of the first deflection device. According to an exemplary embodiment herein, the deflection device can then be excited with the new excitation, and one or more third particle microscope images can be recorded using the new excitation. In the case of the excitation of the first deflection device determined in this method, a third particle microscope image is then recorded using a particle beam that passes substantially centrally through the objective lens, resulting in improved image quality for the third particle microscope image.

[0009] Two images, recorded to determine the new excitation of the first deflection device, are recorded under the condition of a small excitation of the second deflection device. These images are close to the optical axis of the objective lens. For example, this can be represented as follows: recording the first image includes the particle beam scanning a first region of the object to be imaged, and recording the second image includes the particle beam scanning a second region of the object to be imaged. Here, scanning includes changing the excitation of the second deflection device and maintaining the excitation of the first deflection device, respectively. Both the first and second scanned regions of the object to be imaged have centroids on the object, and in the absence of excitation from the second deflection device, the particle beam is guided to a position on the object that is less than 10 μm away from the centroids of both the first and second scanned regions to be imaged.

[0010] Similar to the first deflection device, the second deflection device can also deflect the particle beam using adjustable electric and / or magnetic deflection fields. To generate the electric deflection field, the deflection device includes opposite electrodes, and different adjustable potentials can be applied to these opposite electrodes via a potential supply device. To generate the magnetic deflection field, the deflection device includes coils, and an adjustable current can be fed to the coils via a current supply device. When the generated electric and magnetic deflection fields are zero—that is, when the same potential is fed to the opposite electrodes and no current is fed to any coil—that is, when the supplied current intensity is zero—the second deflection device, like the first deflection device, is not excited.

[0011] For example, multiple third-particle microscope images can be recorded using different magnifications. However, if it is necessary to record an image of another object that has a different morphology compared to the object used to adjust the particle beam, or that is arranged at a certain distance from the objective lens and requires a significantly different focal setting, then it is advantageous to readjust the particle beam using the method described above.

[0012] According to an exemplary embodiment, the method further includes determining a prior-known functional relationship by recording multiple particle microscope images with different focal settings and excitation from the first deflection device. Specifically, determining the prior-known functional relationship may include setting a first excitation for the first deflection device and recording a fourth particle microscope image and a fifth particle microscope image with different focal settings; setting a second excitation for the first deflection device different from the first excitation and recording a sixth particle microscope image and a seventh particle microscope image with different focal settings; and determining the functional relationship based on the fourth particle microscope image, the fifth particle microscope image, the sixth particle microscope image, and the seventh particle microscope image.

[0013] According to an exemplary embodiment, the method further includes: setting a third focal setting that differs from a first focal setting and a second focal setting by less than a predetermined amount; recording at least four particle microscope images of an object under paired different excitations of the first deflection device; setting a fourth focal setting that differs from the third focal setting by less than a predetermined amount; recording at least four particle microscope images of an object under paired different excitations of the first deflection device; determining at least four displacements between pairs of recorded images recorded for the same excitation of the first deflection device; and determining a functional relationship based on the at least four determined displacements.

[0014] The inventors have recognized that the displacement of particle microscope images that occur when the focus setting changes follows a pattern that depends first on the excitation characteristics of the first deflection device and second on the characteristics of the objective lens. The excitation characteristics dependent on the deflection device correspond to the currently possible suboptimal and unknown adjustment of the particle beam, while the objective lens characteristics do not change over time or change only very slowly over time and are given by the geometry of the objective lens and other characteristics of the particle beam microscope for a given focus setting. In this method, these latter characteristics are captured essentially entirely through pre-known functional relationships, so it is then necessary to record only two particle microscope images for different focus settings to find the new excitation required by the first deflection device to obtain substantially optimal adjustment of the particle beam.

[0015] According to an exemplary embodiment, setting the focus includes setting a high voltage for accelerating the particle beam and / or setting the excitation of the objective lens.

[0016] Therefore, setting a second focus setting starting from a first focus setting may include changing the high voltage used to accelerate the particle beam, wherein the excitation setting of the objective lens remains constant, or it may include changing the excitation of the objective lens, wherein the high voltage used to accelerate the particle beam remains constant.

[0017] According to an exemplary embodiment, the process of recording a first particle microscope image, recording a second particle microscope image, determining a new excitation of the deflection device, and recording at least one third particle microscope image under the new excitation of the first deflection device is repeated.

[0018] As mentioned above, if the functional relationship is known, beam tuning can be obtained by recording a very small number of particle microscope images. Beam tuning requires fewer than four images, that is, three or two, of which two images are needed to determine displacement as the focus changes. However, three images can also be used to determine displacement more accurately as the focus changes.

[0019] Furthermore, according to the present invention, a particle beam microscope is provided, which is configured to perform the above-described method.

[0020] According to the present invention, a computer program product is further provided, the computer program product including instructions that, when executed by a controller of a particle beam microscope, cause the particle beam microscope to perform the above-described method. Attached Figure Description

[0021] Embodiments of the present invention will now be described in more detail with reference to the accompanying drawings, in which:

[0022] Figure 1 A schematic diagram of a particle beam microscope is shown.

[0023] Figure 2The illustration is shown Figure 1 A graph showing the functional relationship between the focal point change and excitation of the deflection device in a particle beam microscope and the image displacement.

[0024] Figure 3 Instructions for operation are shown. Figure 1 A flowchart of a particle beam microscopy method;

[0025] Figure 4A and Figure 4B A diagram is shown for further explanation. Figure 2 The graph showing the functional relationship; and

[0026] Figure 5 A schematic diagram is shown to illustrate the region of the object to be imaged in this method. Detailed Implementation

[0027] 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 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, the cathode emitting electrons that are accelerated away from the emitter 5 via 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 emitter is set via an adjustable voltage source 19, which is controlled by the controller 15 via a control line 21. The potential of the anode 11 is set via an adjustable voltage source 23, which is also controlled by the controller 15 via a control line 25. The difference between the potential of the 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.

[0028] 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 an adjustable current source 31, which is controlled by a controller 15 via a control line 33.

[0029] The particle beam 13 then passes through objective lens 35, which is intended 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.

[0030] Object 37 is held on object holder 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 object holder 51, and therefore object 37 also has the potential of object holder 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 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 the embodiment of the particle beam microscope 1 with or without the 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 source 3 and the potential of the object 37.

[0031] The particle beam microscope 1 further includes two deflection devices that have different functions during operation. A first deflection device 75 is arranged in the beam path of the particle beam 13 between the particle beam source 3 and the objective lens 35, and a second deflection device 57 is arranged in the beam path of the particle beam 13 between the first deflection device 75 and the object 37. The position of the second deflection device relative to the objective lens 35 can be arranged as needed in the beam path upstream of the objective lens 35 or within the objective lens 35, that is, in the region where the electric or magnetic field focused by the particle beam 13 acts on the particle beam. The second deflection device 57 is used to scan the particle beam 13 on the object during image recording. In the method described herein, the excitation of the first deflection device should be configured such that the particle beam passes centrally through the objective lens when the second deflection device is not excited.

[0032] The second deflection device 57 is controlled by the controller 15 via 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 leaving 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.

[0033] 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).

[0034] 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 such a way 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 in a manner dependent 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 displayed by display device 67 connected to controller 15 and observed by the user of particle beam microscope 1.

[0035] exist Figure 1In the example shown, the first deflection device 75 is 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 the objective lens 35. In the example shown, the first deflection device 75 includes 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 deflection elements 81, which are distributed in a circumferential direction around the particle beam 13. The deflection elements 81 may be formed of electrodes and / or coils, the excitation of which is provided by voltage or current sources 83, which are controlled by a controller 15 via line 82. Each individual deflector 77, 79 of the first deflection device 75 is configured to deflect the particle beam 13 passing through the respective individual deflector in 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.

[0036] The first deflection device 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 such that it can be focused onto the object 37 to the greatest extent possible through the objective lens 35. For this purpose, for example, the excitation of the first deflection device 75 can be set such that the particle beam 13 passes through the principal plane of the objective lens 35 in a centered manner. Further, the excitation of the first deflection device 75 can be set such that the particle beam 13 deflected by the first deflection device appears to originate from a particle source. Although the example described herein includes two separate deflectors 77 and 79, a first deflection device 75 comprising only a single deflector (77 or 79) for adjusting the particle beam 13 so that the particle beam passes through the principal plane of the objective lens 35 substantially in a centered manner is also sufficient for the purposes described herein, wherein the deflection makes the particle beam 13 deflected by the first deflection device 75 appear to originate from a particle source, but this cannot be satisfied in that case.

[0037] 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. 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 adjustable.

[0038] It is known that when the particle beam passes through the objective lens out of center, changes in the focal setting in a particle beam microscope will not only cause changes in image sharpness, but also cause displacement of the recorded particle microscope image (see, for example, US2012 / 0 138 793 A1, US 6 864 493 B2). Figure 2 This is a graphical representation of this displacement. The horizontal and vertical axes plot the deflection of the particle beam in the x and y directions as it passes through the first deflection device, respectively, expressed as a percentage of the maximum deflection in the x and y directions. The arrows indicate the absolute value and direction of the image offset between the two recorded particle microscope images, which differ in terms of the particle beam microscope's focus setting. Apart from the focus setting, all other settings of the particle beam microscope are the same in both images. In this case, it is assumed that the focus setting is set in the first particle microscope image, where the image sharpness is essentially maximized, thus focusing the particle beam onto the surface of the object. Then, for the purpose of recording the second particle microscope image, the focus setting is changed by a predetermined amount.

[0039] exist Figure 2 In the example shown, the image offset is zero when the deflection in the x-direction is approximately 17% and the deflection in the y-direction is approximately 4%. When the first deflection device is excited such that these deflections occur in the x and y directions, the particle beam passes through the objective lens in a centered manner, and imaging aberrations caused by the particle beam not passing through the objective lens in a centered manner are eliminated in this setup. Therefore, the goal is to find the excitation of the first deflection device that results in zero image offset when the focus setting is changed. However, in particle beam microscopy, this necessary deflection is not always constant. When the particle beam microscope is restarted, the required excitation may be different from the excitation that served as the optimal excitation for the first deflection device when the particle beam microscope was stopped. Therefore, the particle beam typically needs to be readjusted during particle beam microscopy operation. Furthermore, a significant change in the current fed to coil 39 (i.e., a change in the excitation of the magnetic objective lens) may cause the particle beam 13 to need readjustment. Furthermore, a change in the geometry of the object 37 being examined may cause the particle beam 13 to need readjustment. The geometry of object 37 (that is, the distance and shape between the object and objective lens 35) determines the configuration of the electrostatic field between object 37 and objective lens 35. Therefore, changes in the geometry of object 37 also affect focusing.

[0040] from Figure 2It is evident that the absolute value and direction of the arrows representing image offset follow a functional relationship. The inventors have recognized that this functional relationship remains unchanged after changes in the geometry of object 37, after changes in the current fed to coil 39, and even during reoperation of the particle beam microscope 1. The inventors further recognize that the functional relationship is unique, making it possible to maintain this relationship even with changes in focus, i.e., under conditions such as... Figure 2 Given the absolute value and direction of the measurements of the arrows in the diagram, the position of the base of the corresponding arrow relative to the optimal image offset of 0 is derived from the measured image offset in the diagram. The excitation of the first deflection device can then be changed to set the optimal excitation of the first deflection device, which results in an image offset of 0 under focal length changes. Therefore, if the functional relationship is known, the excitation of the first deflection device can be found solely based on two particle microscope images recorded at different focal length settings, which produces the adjustment of the particle beam so that the particle beam passes centrally through the objective lens.

[0041] Figure 3 Instructions for operation are shown. Figure 1 The flowchart illustrates a particle beam microscopy method. This method primarily involves adjusting the particle beam to ensure it passes centrally through the objective lens, thereby focusing the beam onto the object as optimally as possible.

[0042] exist Figure 3Before the method is described, object 37 is positioned at a given distance in front of objective lens 35, and necessary measures are taken to record a particle microscope image of object 37. However, before a high-quality particle microscope image can be recorded, the optimal focal setting and the optimal excitation of the first deflection device 75 for this purpose must be found. In this case, a given excitation 101 for the first deflection device 75 is used first. For example, this given excitation can be 0 excitation, a previously used excitation, or any other excitation. In step 103, the first deflection device 75 is excited with the given excitation 101. Subsequently, in step 105, a first focal setting 107 is found, which allows for recording a slightly clearer particle microscope image. In step 108, a first particle microscope image 109 is recorded with this first focal setting 107. Then, the first focal setting 107 is changed to a second focal setting 111. In step 113, the second focal setting is set on the particle beam microscope 1, and in step 115, a second particle microscope image 117 is recorded with the second focal setting 111 and the given excitation 101 of the first deflection device 75. The following calculations are then performed: the change in focus setting 119 is determined based on the difference between the second focus setting 111 and the first focus setting 107. For example, by correlation calculation, the displacement 121 between the two images 109 and 117 is determined based on a comparison between the second image 117 and the first image 109. The displacement 121 is given by two variables representing the absolute value and direction of the displacement. The change in focus setting 119 and the displacement 121 are input as parameters into a pre-determined functional relationship 123 to obtain a new excitation 125 for the first deflection device 75. This excitation 125 is set on the first deflection device 75 in step 127. Subsequently, a third particle microscope image 131 with high image quality can be recorded in step 129 because the first deflection device 75 is excited such that the particle beam passes through the objective lens substantially centered. Using this setup of a particle beam microscope, an additional third image 131 can subsequently be recorded, for example, with a changed magnification, a changed resolution, or a changed scanning program. If it is finally determined in step 133 that a sufficient number of object images have been recorded in this setup, the object can be moved relative to the objective or replaced with another object in step 135. This change in object geometry usually requires retuning the particle beam microscope, which is why the method then restarts in step 103 to obtain particle microscope images of the object with the changed geometry.

[0043] The functional relationship 123 can be experimentally obtained by determining, in terms of absolute value and direction, the image displacement between images recorded before and after a focus change for multiple excitations to the first deflection device 75, which cause multiple deflections of the particle beam in the x and y directions (see [link to documentation]). Figure 2 This corresponds to Figure 2The experiment shown in the figure confirms this. The functional relationship 123 can then be stored as a tuple of data records, which includes the absolute value of the displacement, the direction of the displacement, the deflection in the x-direction, and the deflection in the y-direction. The number of tuples can total tens or hundreds. If then... Figure 3 In the method shown, to determine displacement 121, the tuple closest to displacement 121 in terms of absolute value and direction can be searched in the data record representing the functional relationship 123. The excitations corresponding to the displacements in the x and y directions of the tuples can then be used as excitation 125 in this method. In this scenario, interpolation can naturally be used for deflections in the x and y directions, which are generated by interpolation between multiple tuples closest to displacement 121 in terms of absolute value and direction.

[0044] It was found that functional relation 123 can be applied to objects positioned at the same distance from the objective lens. However, it was also found that the functional relation changes when the excitation of the objective lens changes, and this excitation is given by the current intensity fed to the objective lens. Therefore, it is reasonable to parameterize functional relation 123 related to the objective lens excitation. For this purpose, the corresponding functional relation can be determined based on the methods described above for various excitation values ​​of the objective lens. Figure 3 In the method described, the functional relationship corresponding to the excitation of the objective lens used is determined, for example, by interpolation and used as functional relationship 123.

[0045] The change in focus setting 119 can be achieved by altering the excitation of the objective lens, that is, by changing the current fed to the objective lens or by changing the high voltage 19 used to accelerate the particle beam. This change can be very small if it results in a measurable displacement between the image 109 recorded before the change and the image 117 recorded after the change. If the change in focus setting 119 has already blurred the image due to an incorrect focus setting, the focus setting can be returned to the first focus setting 107 before recording the third image in step 129.

[0046] The above is for reference only. Figure 2 This paper explains how to experimentally determine the functional relationship between the displacement of a recorded particle microscope image and the excitation of a first deflection device when the focus setting is changed, using a data record of a stored tuple. This tuple data record includes, for example, the absolute value of the displacement, the direction of the displacement, and the deflection in the x and y directions. The desired excitation of the first deflection device can then be determined based on the tuple data record.

[0047] Figure 5 A schematic diagram of a plan view of object 37 is shown to illustrate the area of ​​object 37 to be imaged in this method. Figure 5 The rectangular region 151 in the figure represents the area of ​​the object 37 that was scanned by the particle beam 13 when the first image was recorded in step 109. Figure 5 The rectangular region 153 in the image represents the area of ​​the object 37 that was scanned by the particle beam 13 during the recording of the second image in step 117. Figure 5 Rectangle 155 in the diagram represents the area of ​​object 37 that was scanned by particle beam 13 during the recording of the third image in step 131.

[0048] Scanning regions 151, 153, and 155 is achieved by changing the excitation of the second deflection device 57 while keeping the excitation of the first deflection device 75 constant. Regions 151 and 153 can have the same size. However, their sizes can also differ. Region 155 can be larger than regions 151 and 153, but this is not necessary.

[0049] In step 125, a new excitation is determined for the first deflection device 75, and in step 131, the third image region 155 to be imaged is recorded with this new excitation. Through this new excitation of the first deflection device 75 and the unexcited second deflection device 57, the particle beam 13 is incident at position 157 of the object 37.

[0050] Figure 5 The geometric centroid of the imaged region 151 is represented by cross 159, while the geometric centroid of the imaged region 153 is represented by cross 161. Centroids 159 and 161 lie within a circle 163 on the object 37 surrounding position 157, with a radius R of 10 μm. This means that the distances of both centroids 159 and 161 from position 157 are less than 10 μm. Position 157 can be the centroid of the imaged region 155 in the third image. However, this is not mandatory, and the centroid of the imaged region 155 can be different from position 157. In this case, position 157 can be located within the imaged region 155; however, it can also be located outside the imaged region 155.

[0051] The following is for reference. Figure 4A and Figure 4B The method describes a method by which parameters representing functional relationships can be determined and can be used to determine the desired excitation of the first deflection device. Figure 4A Four different configurations of the first deflection device are shown, denoted by I to IV. The four different deflections are plotted on the graph, with the horizontal axis showing the deflection of the first deflection device in the x-direction (“alignment-x”) and the vertical axis showing the deflection of the first deflection device in the y-direction (“alignment-y”). The values ​​specified on the graph are given as a percentage of the maximum value of the corresponding deflection. In practice, for example, the current range producing the maximum deflection is, for example, between 100 mA and 400 mA. The four sets of deflections have pairs of distinct deflections in the x-direction and pairs of distinct deflections in the y-direction.

[0052] Figure 4BThis shows the situation where the focus changes. Figure 4A The image displacements caused by the four deflections shown are corresponding to... Figure 4A The image displacements from deflection I to IV are also in Figure 4B The values ​​I through IV represent the focal point settings. Given a specific deflection setting, image shift is generated by changing the focal point setting by a predetermined amount. This predetermined amount is the same for all settings I through IV of the first deflection device. For example, the focal point setting can be changed by altering the accelerating voltage or the excitation of the objective lens. With an accelerating voltage of 1 kV, the accelerating voltage can be changed by 0.5%, i.e., a change of 5 V, for example. When the current fed to the objective lens is set to 1 A, this current can be changed, for example, by 5 mA, i.e., a change of 0.5%. Particle microscope images are recorded for both focal point settings. The image shift can then be calculated from the two recorded images. Figure 4B In the middle, the horizontal axis is 10 -7 The image offset in the x-direction is shown in meters ("shift-x"). Similarly, the vertical axis is also expressed in 10... -7 The image displacement in the y-direction is shown in m ("shift-y").

[0053] from Figure 4A and Figure 4B In the comparison, it is obvious that... Figure 4A Points I to IV in the equation can be mapped to... through three mathematical operations. Figure 4B From point I to IV, these three mathematical operations include rotation, scaling, and shifting. Therefore, using complex numbers, the image offset can be written as:

[0054]

[0055] in This indicates the excitation of the first deflection device. Indicates setting incentives The image offset obtained under the condition, and The excitation of the first deflection device is indicated by the image offset becoming 0. Further, S represents the scaling factor, φ represents the rotation angle, and i represents the imaginary unit.

[0056] according to Figure 4A The four stimulus settings shown, for example, for two settings and It can be determined experimentally. Figure 4B The associated image offset shown in the image and

[0057] Inserting equation (1), we get the following:

[0058]

[0059] as well as

[0060]

[0061] By subtracting equation (3) from equation (2), we obtain the following:

[0062]

[0063] Therefore, the two unknowns S and φ can be determined as follows:

[0064]

[0065] as well as

[0066]

[0067] The values ​​of S and φ thus determined will continue to apply to a particle beam microscope used with a given setting. Using the determined values ​​of S and φ, the above equation (1) is parameterized and can then be used to determine the excitation variation of the first deflection device based on the measured image shift that occurs when the focus changes by a predetermined amount, which produces the optimal setting for the particle beam microscope.

[0068] The method described above in the embodiments uses an electron microscope. However, the method is not limited to this, as other particle beam microscopes, such as ion microscopes or electron microscopes that operate according to other principles and, for example, use multiple electron beams, can be used.

Claims

1. A method for adjusting a particle beam microscope, wherein, This particle beam microscope includes: Particle beam source, used to generate particle beams; An objective lens is used to focus the particle beam onto an object. A first deflection device is used to deflect the particle beam, wherein the first deflection device is arranged in the beam path of the particle beam between the particle beam source and the objective lens; and A second deflection device is used to deflect the particle beam, wherein the second deflection device is arranged on the beam path of the particle beam between the first deflection device and the object. This method includes the following measures: A first particle microscope image is recorded under the given excitation and first focal setting of the first deflection device; A second particle microscope image is recorded under a given excitation from the first deflection device and a second focal setting different from the first focal setting. Based on the first particle microscope image, the second particle microscope image, and a previously known functional relationship, a new excitation for the first deflection device is determined, whereby the functional relationship represents the displacement of the recorded particle microscope image when the first focal point setting is changed according to the excitation of the first deflection device; and Record at least one third-particle microscope image using the new excitation from the first deflection device; Recording the first particle microscope image includes scanning the first region of the object to be imaged using the particle beam. Recording the second particle microscope image includes scanning the second region of the object to be imaged using the particle beam. The scanning process includes changing the excitation of the second deflection device while maintaining the excitation of the first deflection device. In this context, both the first scanning region to be imaged and the second scanning region to be imaged on the object have geometric centroids on the object. In the absence of an excited second deflection device, the particle beam is guided to a position on the object that is less than 10µm away from the centroid of both the first and second scan areas to be imaged.

2. The method according to claim 1, wherein, Setting the focus of this particle beam microscope includes setting a high voltage to accelerate the particle beam and / or setting the excitation of the objective lens.

3. The method according to claim 1 or 2, wherein, Setting the second focal point from the first focal point setting includes changing the high voltage used to accelerate the particle beam, wherein the excitation setting of the objective lens remains constant, or Setting the second focal point from the first focal point setting includes changing the excitation of the objective lens, wherein the high voltage used to accelerate the particle beam remains constant.

4. The method according to claim 1 or 2, wherein, Repeatedly record the first particle microscope image, record the second particle microscope image, determine the new excitation of the deflection device, and record the at least one third particle microscope image under the new excitation of the deflection device.

5. The method according to claim 4, wherein, The determination of the corresponding new excitation of the deflection device during each repetition is based on either an additional particle microscope image or not based on an additional particle microscope image, in addition to the corresponding first and second particle microscope images.

6. The method according to claim 4, wherein, Multiple third-particle microscopy images were recorded in at least some of these replicates.

7. The method according to claim 1 or 2, further comprising determining the prior-known functional relationship, wherein, Determining the known functional relationship in advance includes: The first excitation of the deflection device is set, and the fourth and fifth particle microscope images are recorded with different focal settings respectively. The deflection device is configured with a second excitation different from the first excitation, and the sixth and seventh particle microscope images are recorded with different focal points respectively. The functional relationship was determined based on the fourth, fifth, sixth, and seventh particle microscope images.

8. The method according to claim 1 or 2, wherein, The particle beam microscope further includes a particle detector, and wherein recording these particle microscope images includes using the particle detector to detect particles emitted from the object.

9. A particle beam microscope configured to perform the method according to any one of claims 1 to 8.

10. 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 according to any one of claims 1 to 8.

Images