Method for operating an electron beam system

Abstract

To provide a method for operating an electron beam system.SOLUTION: A method for operating an electron beam system includes setting a first potential supplied to an electron emitter to a first value, setting a second potential supplied to a beam tube to a second value, and setting a third potential supplied to a target to a third value, such that the third potential is greater than the first potential and the second potential is greater than the third potential. The method also includes focusing a beam of the electron beam system on the target by modifying at least one current supplied to at least one focusing magnetic lens. When, during focusing, the at least one current satisfies a predetermined criterion, the method performs one of the following measures of: setting the second potential to a fourth value less than the second value; increasing the at least one current by modifying the at least one current and then continuing to focus the beam on the target; and continuing to focus the beam on the target by modifying the second potential.SELECTED DRAWING: Figure 2

Description

Technical Field

[0001] This application relates to a method of operating an electron beam system.

Background Art

[0002] An electron beam system includes a beam source that generates an electron beam. The electron beam illuminates a spot on an object, and when focused through an objective lens, the size of the spot is reduced as much as possible. The spot illuminated by the electron beam can be scanned over an area on the object by the electron beam system by deflecting the electron beam from its trajectory. The electron beam system also includes a detector that can be used to detect electrons emitted by the object that are generated when the electron beam impinges on the object. An electron microscope image is generated by assigning the deflection of the electron beam to measurements from the detector. The achievable resolution of the electron microscope image is higher the smaller the illumination spot.

[0003] In certain electron beam systems, the electron beam passes through a beam tube for most of the path between the beam source and the object. A potential is supplied to the beam tube to accelerate electrons in the beam as they enter the beam tube and to decelerate them as they exit the beam tube by the field of the electrostatic lenses of the electron beam system. As a result, the electrons in the beam reach the object at high speed, and thus, the electrostatic repulsive force that increases the beam spot on the object due to other electrons in the beam is smaller. Thus, the potential supplied to the beam tube is selected to be as high as possible during the conventional operation of these electron beam systems so that the spot is as small as possible and, thus, the achievable resolution of the recorded electron microscope image is as high as possible.

[0004] However, the user may consider the conventional operation of the electron beam system to be inappropriate.

Summary of the Invention

Problems to be Solved by the Invention

[0005] Accordingly, an object of the present invention is to propose a method for improving the operation of an electron beam system having a beam tube.

Means for Solving the Problems

[0006] According to an embodiment of the present invention, a method of operating an electron beam system includes setting a first potential supplied to an electron beam source to a first value, a second potential supplied to a beam tube to a second value, and a third potential supplied to an object to a third value such that the third potential is greater than the first potential and the second potential is greater than the third potential. This means that the potential supplied to the beam tube is greater than the potential supplied to the object. This is necessary to decelerate the electrons. Further, the potential supplied to the object is greater than the potential supplied to the electron beam source so that the electrons in the beam actually impinge on the object.

[0007] When potentials are supplied to the electron beam system as described above, the electrostatic interaction between them already deflects the electrons of the electron beam, and an electrostatic field acting on the electrons, like a focusing lens, spreads between the beam tube and the object. Thus, the electron beam system has a focusing effect on the electron beam even when no current is supplied to any magnetic lens provided for this purpose, for example, an objective lens. For example, such a state is achieved while focusing an electron beam on an object disposed at a large distance from the electron beam system. When the potential supplied to the beam tube is lowered, focusing can be continued. When the potential supplied to the beam tube is lowered, the focusing effect of the electrostatic field is smaller, so the current supplied to the objective lens can be increased for a constant focusing effect. Thus, focusing can be continued. In this case, the potential supplied to the beam tube can also correspond to the ground potential.

[0008] Thus, according to an embodiment, the method also includes focusing the beam onto the object by changing at least one current supplied to at least one magnetic lens, such as an objective lens, etc., and when during focusing at least one current meets a predetermined criterion In addition to at least Setting the potential supplied to the beam tube to a fourth value less than a second value by changing at least one current in addition to doing raising at least one current, and then by changing at least one current continuing to focus the beam onto the object 、 or 、 keeping at least one current constant, and then by changing a second potential continuing to focus the beam onto the object to perform This means that while the beam is focused onto the object, if a predetermined criterion is met, the potential supplied to the beam tube is lowered, for example, the current supplied to the objective lens is increased. Focusing can then continue by changing the current of the objective lens or by changing the potential supplied to the beam tube.

[0009] The method can be carried out using an electron beam system, which includes an electron beam source for generating an electron beam, a beam tube having a first end and a second end, configured such that the electron beam enters the beam tube at the first end and exits the beam tube at the second end, at least one magnetic focusing lens through which the electron beam passes, and a supply system configured to supply a first potential to the electron emitter of the electron beam source, a second potential to the beam tube, a third potential to the object, and at least one current to at least one magnetic lens.

[0010] For example, at least one magnetic lens can be the objective lens of the electron beam system or the objective lens and the condenser lens of the electron beam system. Focusing is generally a long process involving multiple steps. Thus, it is possible to start by focusing the beam onto the object and, during focusing, adopt further measures, such as reducing the potential supplied to the beam tube. A check as to whether these measures are necessary by comparing the current supplied to the objective lens with a predetermined reference can be performed, for example, during each focusing step. Alternatively, the above check may be performed after every second step, after every third step, etc.

[0011] According to some embodiments, if the current supplied to the objective lens drops below a predetermined value, the predetermined reference is met. In particular, the predetermined value can be substantially zero, whereby the reference is met when the current supplied to the objective lens is substantially zero.

[0012] According to a further embodiment, the method includes setting a first potential supplied to an electron beam source to a first value, a second potential supplied to a beam tube to a second value, and a third potential supplied to an object to a third value such that the third potential is greater than the first potential and the second potential is greater than the third potential. The method also includes focusing the beam onto the object by changing at least one current supplied to at least one magnetic lens, and if during focusing the at least one current meets a predetermined reference In addition to at least setting the second potential to a fourth value greater than the second value by changing at least one current in addition to doing lowering the at least one current and then by changing at least one current continuing to focus the beam onto the object 、 or 、 keeping the at least one current constant then by changing a second potential and continuing to focus the beam onto the object to perform The method according to this embodiment is a method that reverses the above method. In particular, when a predetermined criterion is satisfied, while focusing the beam on the object, it includes increasing the potential supplied to the beam tube and decreasing the current supplied to the objective lens.

[0013] According to some embodiments, the predetermined criterion is satisfied when the current among at least one current exceeds a predetermined value.

[0014] According to some embodiments, electrons between the second end of the beam tube and the object are affected by the electric field generated by the difference between the second potential and the third potential and the field generated by the magnetic lens. In particular, the beam tube and the objective lens of the electron beam system are arranged such that the electric field generated by the potential supplied to the beam tube and the potential supplied to the object spatially overlap with the field generated by the magnetic lens.

[0015] According to some embodiments, the predetermined criterion depends on a second value of the potential supplied to the beam tube. Strictly speaking, the predetermined criterion may depend on the focusing effect of the electron beam system generated by the current supplied to the objective lens and the potential supplied to the beam tube. As in the above embodiment, when the current supplied to the objective lens drops below a predetermined value, the criterion is satisfied, and when the predetermined value is small, the focusing effect of the electron beam system in the setting where the criterion is satisfied will depend substantially only on the second value of the potential supplied to the beam tube.

[0016] According to some embodiments, focusing the beam on the object includes finding a value of the current such that the spot on the object illuminated by the beam is as small as possible.

[0017] According to some embodiments, focusing a beam onto an object includes detecting electrons generated by an electron beam, identifying a change in the value of a current supplied to a magnetic lens based on the detected electrons, and setting the value of the current according to the identified change. For example, focusing can be performed as follows: an electron microscope image is recorded by an electron beam system, the electron microscope image is analyzed, and the value of at least one current is changed based on the result of the analysis. For example, during the process, the sharpness of the electron microscope image can be analyzed. For example, the sharpness of the electron microscope image can be identified by subjecting the electron microscope image to a Fourier transform and observing the frequency contributions.

[0018] According to some embodiments, the method also includes recording at least one electron microscope image at a set value of potential supplied to a beam source, a set value of potential supplied to a beam tube, a set value of potential supplied to an object, and a set value of current supplied to a magnetic lens.

[0019] According to some embodiments, focusing a beam onto an object includes finding a value of current such that the recorded electron microscope image is as sharp as possible. As already mentioned above, the sharpness of the electron microscope image can be defined by the Fourier transform of the image having as many high-frequency contributions as possible.

[0020] As already described above, the potential supplied to the beam tube has conventionally been set as high as possible in an electron beam system in order to increase the resulting resolution. However, when an image is recorded, for example, a user of the electron beam system may find that the image is not suitable for the purpose because a particular structure is unrecognizable. Therefore, it may be advantageous to switch from an operating mode with high resolution to an operating mode with a high detection signal from the detector. In this case, the operating mode with a high detection signal from the detector means that the number of electrons incident on the detector is as large as possible. This is possible because the electrostatic and magnetic objective lens fields between the beam tube and the object also act on the electrons, such as the potential emitted by the object, which passes through the beam tube in the direction opposite to the electron beam. Therefore, the trajectories of such electrons are directly affected by the potential supplied to the beam tube. If the potential supplied to the beam tube is changed for this purpose, it is necessary to adjust the current supplied to the magnetic lens so that the overall focusing effect acting on the electron beam remains the same. Therefore, the composition of the magnetic and electrostatic effects on the electrons emitted by the object is always changed.

[0021] Therefore, the method according to this further embodiment includes setting a first potential supplied to the electron emitter of the electron beam source to a first value, a second potential supplied to the beam tube to a second value, and a third potential supplied to the object to a third value such that the third potential is greater than the first potential and the second potential is greater than the third potential. This means that the potential supplied to the beam tube is greater than the potential supplied to the object. This is necessary to decelerate the electrons. Further, the potential supplied to the object is greater than the potential supplied to the electron beam source so that the electrons in the beam actually impinge on the object.

[0022] This method also includes focusing the beam onto the object by changing at least one current to a fourth value, recording a first electron microscope image at a first potential of a first value, a second potential of a second value, a third potential of a third value, and a current of a fourth value, setting the second potential to a fifth value less than the fourth value, setting the current to a sixth value less than the fourth value, and recording a second electron microscope image at a first potential of a first value, a second potential of a fifth value, a third potential of a third value, and a current of a sixth value. This means that the first image is first recorded at the initially set values, and then the second image is recorded at new values with the potential supplied to the beam tube and the current supplied to the magnetic lens reduced.

[0023] According to some embodiments, the method also includes determining the fifth value and the sixth value based on the first value, the second value, the third value, and the fourth value such that the beam is substantially focused on the object at a potential of a first value supplied to the electron source, a potential of a fifth value supplied to the beam tube, a potential of a third value supplied to the object, and a current of a sixth value. For example, this includes, as already described above, the electron beam creating a small spot on the object.

[0024] According to some embodiments, the method also includes using a predetermined data record when determining the fifth value and the sixth value, the data record including a number of tuples of values of the potential supplied to the electron beam source, the potential supplied to the beam tube, the potential supplied to the object, the current, and the distance of the electron beam system at which beam focusing occurs. For example, the predetermined data record can be generated by simulating the trajectories of electrons in the beam. Alternatively, the predetermined data record can also be created by the operation of the electron beam system by recording the settings used by the electron beam system. The data record may be stored in the local memory of the electron beam system or, for example, in the cloud accessible by the electron beam system.

[0025] According to some embodiments, the electron beam system further comprises a detector disposed adjacent to the electron beam within the beam tube, specifically implemented such that the ratio of the intensity of the electrons incident on the detector or the current of the electron beam focused on the object to the intensity of the electrons incident on the detector is greater than during the recording of the first electron microscope image. For example, the detector may comprise a scintillator crystal and a detector area capable of detecting electrons entering the scintillator crystal. The scintillator crystal can be held by a mount adjacent to the electron beam within the beam tube. Alternatively, the detector may have a structure that guides the electrons entering therein to the scintillator crystal and the detector area, and the detector area can then detect the electrons. The detector may be a semiconductor detector or may have a different structure.

[0026] According to some embodiments, the second value is selected such that the resolution of the first image is maximized.

[0027] According to some embodiments, specifically implemented such that the convergence angle of the electron beam focused on the object is smaller than during the recording of the first electron microscope image.

[0028] According to some embodiments, the electron beam system further comprises an ion beam column configured to direct an ion beam at a region of the object that can also be scanned by the electron beam. The method further includes operating the ion beam column while the second electron microscope image is being recorded. For example, the ions of the ion beam can be gallium ions.

[0029] According to some embodiments, the operation of the ion beam column includes removing material from the object using the ion beam or severing material from the object by the ion beam.

[0030] According to some embodiments, an electron beam system includes an electron beam source that generates an electron beam, a beam tube having a first end and a second end, configured such that the electron beam enters the beam tube at the first end and exits the beam tube at the second end, at least one magnetic focusing lens through which the electron beam passes, a supply system configured to supply a first potential to an electron emitter of the electron beam source, a second potential to the beam tube, a third potential to an object, and at least one current to at least one magnetic lens, and a controller configured to execute the method according to any one of claims 1 to 17. Further, the electron beam system can include an ion beam column configured to direct an ion beam at the object.

[0031] It should be observed that the beam tube of the electron beam system is not limited to a single beam tube. For example, the beam tube can include a plurality of beam tube portions each having a plurality of ends. In such a case, for example, it is possible that the first end is an end of the first beam tube portion and the second end is an end of the second beam tube portion. Further, it should be observed that in an advantageous embodiment, the second end of the beam tube is disposed at a distance from the objective lens in the vicinity of the objective lens, particularly less than 0.1 times the distance between the electron beam source and the objective lens. Further, the first end of the beam tube does not necessarily have to be disposed in the vicinity of the condenser lens of the electron beam system. What is important is that the beam tube has an expansion along the beam path, and thus the beam tube can produce the above effect with respect to the acceleration of electrons in the beam.

[0032] Further, in the above case where the beam tube includes a plurality of mutually separated beam tube portions, it should be observed that different potentials can be supplied to the beam tube portions. In such a case, for example, the following description of the potential supplied to the beam tube can apply to a lower beam tube portion having a second lower end disposed in the vicinity of the objective lens.

[0033] According to some embodiments, a computer program product includes instructions that, when executed by a controller of an electron beam system, cause the electron beam system to perform the method.

[0034] Embodiments of the present invention will be described in detail below with reference to the drawings.

Brief Description of the Drawings

[0035]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Modes for Carrying Out the Invention

[0036] FIG. 1 shows a schematic configuration of an electron beam system 1 according to an embodiment. The electron beam system 1 includes an electron beam source 3 having an electron emitter 5 and an extraction electrode 6. The electron emitter 5 is connected to a supply system 9 via a connection line 7, and the supply system 9 is configured to supply a negative potential U1 to the electron emitter 5 via the connection line 7. Further, the extraction electrode 6 is connected to the supply system 9 via a connection line 4, and the supply system 9 is also configured to supply a positive potential U2 to the extraction electrode 6 via the connection line 4. As a result of the extraction electrode 6 being supplied with a potential U2 that is opposite to the potential U1 supplied to the electron emitter, electrons are extracted from the electron emitter 5, and thus these extracted electrons move away from the electron beam source 3 along the directed beam 17.

[0037] The electron beam system 1 also includes a beam tube 11 having an interior 12, an upper end portion 13, and a lower end portion 14. The beam tube 11 is connected to the supply system 9 via a connection line 15. The supply system 9 is also configured to supply a potential U3 to the beam tube 11. When the potential U3 is supplied to the beam tube 11, the upper end portion 13 of the beam tube 11 acts as an anode that accelerates the electrons in the beam 17 generated by the electron beam source 3 into the beam tube 11. The electron beam 17 passes through the beam tube 11. The interior 12 of the beam tube 11 functions to accommodate further components of the electron beam system 1 within the beam tube 11. For this purpose, the interior 12 is wider than other locations of the beam tube 11, whereby further components can be disposed in the interior 12 without obstructing the electron beam 17.

[0038] The electron beam 17 passes through the focusing lens 19. The focusing lens 19 is a magnetic lens that deflects the electrons in the beam 17 by generating a magnetic field. For this purpose, the focusing lens 19 comprises a solenoid 21 connected to the supply system 9 via a connection line 23. The supply system 9 is also configured to supply a current I1 to the solenoid 21 of the focusing lens 19. The focusing lens 19 also comprises a pole shoe 22 that affects the magnetic field generated by the current I1 supplied to the solenoid 21 such that such a magnetic field appropriately enters the path of the electron beam 17 to achieve a focusing effect on the electron beam 17.

[0039] After the electrons in the beam 17 pass through any component disposed inside 12 of the beam tube 11, the beam 17 passes through the magnetic field of the objective lens 25 acting inside and outside the beam tube 11. The objective lens 25 is a magnetic lens comprising a solenoid 27. The solenoid 27 is connected to the supply system 9 via a connection line 29. The supply system 9 is also configured to supply a current I2 to the solenoid 27 via the connection line 29. When a current I2 is supplied to the coil 27, a magnetic field is generated by the coil 27 that deflects the passing electrons from their orbits. The objective lens 25 also comprises a pole shoe 28 that affects the magnetic field such that the magnetic field appropriately enters the path of the beam 17 and acts on the electrons in the beam 17 so as to obtain a focusing effect.

[0040] The lower end portion 14 of the beam tube 11 is disposed in the vicinity of the objective lens 25. As shown in FIG. 1, the end portion 14 of the beam tube 11 can be disposed in the opening of the pole shoe 28 of the objective lens 25. As a result, the magnetic field of the objective lens 25 acts inside and outside the beam tube 11. In fact, a non-negligible component of the magnetic field of the objective lens 25 acts up to the object 35 in some embodiments. In particular, this means that the electrostatic field between the beam tube 11 and the object 35 overlaps with the magnetic field of the objective lens 25.

[0041] The upper end portion 13 of the beam tube 11 is shown in the vicinity of the condenser lens 19 in FIG. 1. However, the upper end portion 13 may be disposed at any other position along the beam path of the beam 17 as long as the beam tube 11 extends along the beam path of the beam 17 between the upper end portion 13 and the lower end portion 14. For example, the upper end portion 13 may be disposed in the vicinity of the objective lens 25. As a result, the beam tube 11 surrounds the beam 17 only at the location where the beam 17 passes through the objective lens 25. Further, the beam tube 11 may comprise a plurality of parts each having two end portions. For example, the upper part may surround the beam 17 at the location where the beam 17 passes through the condenser lens 19. The upper part constitutes the upper end portion 13 of the beam tube 11 and a further end portion and thus does not necessarily contact the lower end of the beam tube 11. Such a lower part may surround the beam 17 at the location where the beam 17 passes through the objective lens 25. In that case, this lower part constitutes the lower end portion 14 of the beam tube 11 and a further end portion. Similarly, the beam tube 11 may comprise a plurality of components, for example a plurality of layered tube elements.

[0042] The electron beam system 1 also comprises an electrode 31 which is connected to the supply system 9 via a connection line 33. The supply system 9 can supply a potential U4 to the electrode 31 via the connection line 33. When the potential U4 supplied to the electrode 31 is different from the potential U3 supplied to the beam tube 11, an electrostatic field is formed between the electrode 31 and the lower end portion 14 of the beam tube 11. More precisely, an electrostatic lens is formed by the electrode 31 together with the lower end portion 14 of the beam tube 11.

[0043] The electron beam 17 is incident on the object 35. The object 35 is located on the object mount 37 at a distance s from the electrode 31. The object mount 37 is connected to the supply system 9 via a connection line 39. Thus, the supply system 9 can supply a potential U5 to the object 35 via the connection line 39 and the object mount 37. As a result of supplying the potential U5, an electrostatic field is generated between the object 35 and the lower end portion 14 of the beam tube 11 or between the object 35 and the electrode 31.

[0044] The electrons incident on the object 35 cause the object 35 to emit electrons. The electrons emitted by the object 35 include those known as secondary electrons and backscattered electrons. The kinetic energy of the electrons in the beam 17 when it is incident on the object 35 is determined by the difference between the potential U1 of the electron emitter 5 and the potential U5 supplied to the object 35. The electrons emitted by the object 35 are accelerated into the beam tube 11 by the electrostatic field between the object 35 and the lower end portion 14 of the beam tube 11, the electrostatic field between the object 35 and the electrode 31, and / or the electrostatic field between the electrode 31 and the lower end portion 14 of the beam tube 11.

[0045] The electron beam system 1 also includes a detector 41 that detects the electrons emitted by the object 35. The detector 41 is disposed within the beam tube 11 and has an opening 43 that allows the electron beam 17 to pass through the detector 41. The detector 41 is connected to a controller 47 via a connection line 45, and the controller 47 can receive measurement data from the detector 41 via the connection line 45.

[0046] The electron beam system 1 further includes a deflection device 51 that is connected to a supply system 9 via a connection line 53. The supply system 9 can supply a voltage U6 to the deflection device 51 via the connection line 53. An electric field that deflects the electrons passing through the deflection device 51 from their trajectory is generated by the deflection device 51 as a result of the supply of the voltage U6. A given voltage value produces a specific deflection angle with respect to the electron beam 17. The deflection angle also corresponds to the position at which the electron beam 17 is incident on the object 35. As a result, the electron beam 17 can be scanned across the object by having measurement data from the detector 41 assigned to each incident position of the electron beam 17 on the object 35. This means that an electron microscope image can be generated by the electron beam system 1 because the region on the object 35 can be scanned. This means that the measurement data from the detector 41 is recorded at a series of locations where the beam 17 is directed by the deflection device 51. In this case, for example, the locations are a predetermined set of locations in the region of the object 35 being scanned.

[0047] The controller 47 is also connected to the supply system 9 via the connection line 49. As a result of the connection line 49, the controller 47 can provide commands regarding the value of the potential U1 supplied to the electron emitter 5 via the connection line 7, the value of the potential U2 supplied to the extraction electrode 6 via the connection line 4, the value of the potential U3 supplied to the beam tube 11 via the connection line 15, the value of the current I1 supplied to the solenoid 21 of the condenser lens 19 via the connection line 23, the value of the current I2 supplied to the solenoid 27 of the objective lens 25 via the connection line 29, the value of the voltage U6 supplied to the deflection device 51 via the connection line 53, the value of the potential U4 supplied to the electrode 31 via the connection line 33, and the value of the potential U5 supplied to the object 35 via the connection line 39 and the object mount 37.

[0048] Figure 2 shows a flowchart showing a method of operating the electron beam system 1 shown in FIG. 1 according to an embodiment. Figure 2 shows steps S1 to S9 executed by the electron beam system 1. In particular, steps S1 to S9 can be commanded by the controller 47.

[0049] In step S1, the values of the operating parameters of the electron beam system 1 are set. In particular, the controller 47 of the electron beam system 1 can instruct the supply system 9 to supply the first potential U1 of the first value to the electron emitter 5, supply the second potential U3 of the second value to the beam tube 11, and supply the third potential U5 of the third value to the object 35. In this case, the potential U5 supplied to the object 35 is greater than the potential U1 supplied to the electron emitter 5, and the potential U3 supplied to the beam tube 11 is greater than the potential U5 supplied to the object 35. In other words, first, the difference between the potential U1 supplied to the electron emitter 5 and the potential U5 supplied to the object 35 is positive. This is necessary so that the electrons in the beam 17 receive an accelerating force along the path and can actually enter the object 35 accordingly. Next, the difference between the potential U3 supplied to the beam tube 11 and the potential U5 supplied to the object 35 is negative so that the electrons in the beam decelerate until they exit the lower end 14 of the beam tube 11 and enter the object 35. Such deceleration is advantageous in that case because the electrons enter the object 35 with a lower kinetic energy and do not damage the object or cause other unwanted effects, such as significant differences in the object 35.

[0050] Next, in step S2, the beam 17 is focused onto the object 35 by changing the current I2 of the objective lens 25. Focusing the beam onto the object includes steps S2 to S8.

[0051] First, in step S2, an electron microscope image is recorded by the electron beam system 1 at the current value of the current I2 of the objective lens 25. Next, in step S3, the recorded electron microscope image is analyzed for the effect of whether or not the electron beam 17 is focused using the current operating parameters. For example, this analysis can be performed by the user of the electron beam system 1 or in a software-based manner. For example, for this purpose, the sharpness of the electron microscope image is examined. For example, the sharpness can be specified by subjecting the image to a Fourier transform and evaluating the contribution of the high-frequency components. Whether or not the focusing is complete can be determined by this analysis, as shown in step S4. If the focusing is complete, the electron beam system 1 finishes focusing the beam 17 and proceeds to step S9, where an electron microscope image is recorded using the set operating parameters.

[0052] If the focusing is not yet complete, the electron beam system 1 proceeds to step S5, where the electron beam system 1 performs a check on whether the current of the objective lens 25 is less than a predetermined value. In this case, the predetermined value may depend on the set value of the potential U3 supplied to the beam tube 11.

[0053] If it is determined in step S5 that the current I2 of the objective lens 25 is less than the predetermined value, in step S6, the potential U3 supplied to the beam tube 11 is lowered, and in step S7, the current I2 supplied to the objective lens 25 is increased. As a result, the current I2 supplied to the objective lens 25 can be further lowered without dropping below the predetermined value. For example, the predetermined value is a small value close to zero, and at the predetermined value, the current of the objective lens 25 cannot be lowered any further. After increasing the current of the objective lens 25, the electron beam system 1 continues to step S8, where the current I2 of the objective lens is changed based on the result of the analysis performed in step S3. In this case, the change performed in step S8 corresponds to the change in the current I2 supplied to the objective lens 25, and this is also performed within the scope of the conventional method of focusing the beam 17 on the object 35.

[0054] In step S5, if it is determined that the current I2 of the objective lens 25 is not less than a predetermined value, the electron beam system 1 skips steps S6 and S7 and proceeds directly to step S8. As a result, when the current I2 supplied to the objective lens 25 is sufficiently large, the potential U3 supplied to the electron beam tube 11 is not changed.

[0055] It should be observed that FIG. 2 shows the case where steps S2 to S8 are iterative steps for focusing the beam 17 onto the object 35. However, in an alternative, steps S5 to S7 may be executed every other iterative step, every two iterative steps, etc. for focusing the beam 17 onto the object 35. Further, steps S5 to S7 may alternatively be executed after step S8. In such a case, in step S5, when it is determined that the current I2 supplied to the objective lens 25 is not less than a predetermined value, the electron beam system 1 returns directly to step S2. In other words, step S8 in such an embodiment is placed between steps S4 and S5 shown in FIG. 2, and after the execution of step S7 or after it is determined in step S5 that the current supplied to the objective lens 25 is not less than a predetermined value, the electron beam system 1 returns to step S2.

[0056] As a result of the method described above with reference to FIG. 2, even when the current becomes substantially zero, it is possible to further reduce the current supplied to the objective lens 25. For example, when the distance s at which the object 35 is arranged in relation to the electron beam system 1 is large and the potential U3 supplied to the beam tube 11 is constant, since the electrostatic field between the electrode 31 and the lower end 14 of the beam tube 11 and / or between the object 35 and the lower end 14 of the beam tube 11 has a focusing effect on the electron beam 17, a situation may occur where the beam 17 cannot be focused on the object 35. Therefore, even when no current is supplied to the objective lens 25, the electron beam 17 converges. However, when the voltage supplied to the beam tube 11 is decreased, the focusing effect of the electrostatic field also decreases. As a result, the same focusing effect can be obtained in a state where the potential U3 supplied to the beam tube 11 is smaller and the current supplied to the objective lens 25 is higher.

[0057] In the above description, it should be observed that a current is supplied to the objective lens 25 in order to obtain a focusing effect. However, alternatively or in addition to this, a current may be supplied to the condenser lens 19.

[0058] A further embodiment will be described below with reference to FIG. 3. FIG. 3 shows a flowchart showing a method of operating the electron beam system 1 from FIG. 1 according to a further embodiment. In this case, the method shown in FIG. 3 is the reverse of the method shown in FIG. 2 and is different particularly with respect to steps S5’, S6’, and S7’. That is, the focal length of the beam 17 from the electron beam system 1 is decreased in the method shown in FIG. 3, whereas this distance is increased in the method shown in FIG. 2.

[0059] A further embodiment will be described below with reference to FIG. 3. FIG. 3 shows a flowchart illustrating a method of operating the electron beam system 1 from FIG. 1 according to a further embodiment. FIG. 3 shows steps S6 to S10 to be performed by the electron beam system 1. The method shown in FIG. 3 is the reverse of the method shown in FIG. 2. That is, the focal distance of the beam 17 from the electron beam system 1 is reduced in the usage shown in FIG. 3, while this distance is increased in the method shown in FIG. 2.

[0060] If it is determined that the current supplied to the solenoid 27 of the objective lens 25 is greater than a predetermined value in step S5' shown in FIG. 3, the electron beam system 1 proceeds to steps S6' and S7'. In step S6', the potential U3 supplied to the beam tube 11 is increased, and in step S7', the current I2 supplied to the objective lens 25 is decreased. After step S7' is executed, the electron beam system 1 returns to step S2. Therefore, the corresponding description regarding the alternative embodiment related to FIG. 2 also applies to the method shown in FIG. 3 having steps S5' to S7'.

[0061] Hereinafter, the method shown in FIG. 2 will be described in detail in relation to FIG. 4. FIG. 4 shows a diagram showing a curve of the voltage applied to the beam tube according to the method shown in FIG. 2.

[0062] On the horizontal axis, the diagram of FIG. 4 shows the working distance s shown in FIG. 1 between the object 35 and the electrode 31. The working distance s can also be referred to as the distance between the object 35 and the electron beam system 1. Further, on the vertical axis, the diagram of FIG. 4 shows the potential U3 supplied to the beam tube 11. FIG. 4 also shows a graph having sections 57 and 59. The constant section 57 is a region where the conventional method can be applied without impairing the function of the electron beam system 1. The constant section 57 reaches up to the working distance s0. When the object 35 is disposed at a distance greater than the distance s0, the conventional method of operating the electron beam system cannot focus the beam 17 onto the object 35.

[0063] Curve section 59 shows the potential U3 supplied to the beam tube 11 after the method shown in FIG. 2 is executed. In other words, curve section 59 shows the potential U3 supplied to the beam tube 11 and used for the operation of the electron beam system 1 for future use. It is clear here that the potential U3 set after the method is executed and supplied to the beam tube 11 is no longer constant and is reduced when the working distance s is large. As a result, the electron beam system 1 can operate without losing its function.

[0064] A further embodiment of the method for operating the electron beam system 1 will be described based on the schematic diagram shown in FIG. 5. FIG. 5 shows three schematic diagrams 5A, 5B, and 5C of the electron trajectories in different settings of the electron beam system 1 shown in FIG. 1. Specifically, the potential U3 supplied to the beam tube 11 is different in the three schematic diagrams 5A, 5B, and 5C. In this case, the potential U3 supplied to the beam tube 11 is the lowest in the case of schematic diagram 5A and the highest in the case of schematic diagram 5C.

[0065] Schematic diagrams 5A, 5B, and 5C show the components of the electron beam system 1 already described in connection with FIG. 1. In this case, a detector 41 having an opening 43 through which the electron beam 17 passes is disposed in the beam tube 11. Further, the beam tube 11 includes a lower end 14 that generates an electrostatic field together with the electrode 31 and the object 35 mounted on the object mount 37. The electron beam 17 is not deflected by the deflection device 51 in the cases of schematic diagrams 5A, 5B, and 5C.

[0066] The case where the high potential U3 is applied to the beam tube 11 will be described below with reference to the schematic diagram 5C. The electrons in the beam 17 incident on the object 35 cause the object 35 to emit electrons 65. The electrons 65 are emitted in a direction that does not enter the beam tube without being affected by the electrostatic field generated between the beam tube 11 and the object 35. Since the potential U3 applied to the beam tube 11 is high, the electrons 65 are greatly accelerated in the direction of the beam tube 11 and further receive the focusing effect of the electrostatic field generated between the beam tube 11 and the object 35 and the magnetic field generated by the objective lens 25. As a result, the electrons 65 cross the beam 17 at the first intersection 66. It should be observed that this does not mean that the electrons 65 actually pass through the beam 17. Even when the electrons 65 come close to the beam 17 and do not move beyond the beam 17 in the dimension perpendicular to the plane of the drawing, the electrons 65 do not collide with the electrons in the beam 17 due to the electrical repulsive force between the electrons 65 and the above beam.

[0067] Subsequently, the electrons 65 cross the beam 17 at the second intersection 67. The electrons 65 cannot collide with the beam 17 even at this intersection 67. Due to the high potential U3 supplied to the beam tube 11, the electrons 65 are greatly accelerated along the orbit through the beam tube 11 and pass through the beam tube 11 at high speed or with high energy. Therefore, further interactions such as the focusing effect of the electrostatic lens act on the electrons 65 only for a short time, whereby the orbit of the electrons 65 extends near the beam 17. This is why the electrons 65 cannot pass through the opening 43 of the detector 41 and be detected by the detector 41.

[0068] Schematic diagram 5B shows a case where a potential U3 lower than the potential U3 supplied to the beam tube 11 in the case of schematic diagram 5C is supplied to the beam tube 11. Electrons in the beam 17 incident on the object 35 cause the object 35 to emit electrons 64. The electrons 64 are emitted in the same direction and with the same energy as the electrons 65. Since the potential U3 supplied to the beam tube 11 in schematic diagram 5B is lower than that in schematic diagram 5C, the acceleration strength of the electrons 64 into the beam tube 11 is lower than that of the electrons 65. Therefore, the electrons 64 are exposed longer due to the focusing effects of each interaction, for example, the electrostatic field between the lower end portions 14 of the beam tube 11 and the magnetic field of the objective lens 25. Furthermore, since a larger current I2 is supplied to the objective lens 25 to maintain the focusing effect of the electron beam system 1, the magnetic field of the objective lens 25 is stronger in FIG. 5B than in FIG. 5C. For these reasons, the electrons 64 cross the beam 17 at an intersection 66 much closer to the object 35 than the first intersection 66 of the electrons 65. The electrons 64 then continue to cross the beam 17 at a second intersection 67. The second intersection 67 of the electrons 64 is also closer to the object 35 than the second intersection 67 of the electrons 65. In other words, the electrons 64 pass along a much more curved trajectory than the electrons 65. Therefore, the electrons 64 are incident on the detector 41 and can be detected by the detector 41.

[0069] Schematic diagram 5A shows the case where a potential U3 lower than the potential U3 supplied to the beam tube 11 in the cases of schematic diagrams 5B and 5C is supplied to the beam tube 11. Electrons in the beam 17 incident on the object 35 cause the object 35 to emit electrons 63. In this case, the electrons 63 are emitted from the object 35 in the same direction and with the same energy as the electrons 64 and 65. Since the potential U3 supplied to the beam tube 11 is lower than the potential U3 supplied to the beam tube 11 in the cases of schematic diagrams 5B and 5C, the strength of the acceleration of the electrons 63 into the beam tube 11 is considerably low, whereby the electrons 63 pass through the beam tube 11 at a lower speed. Further, since a large current I2 is supplied by the objective lens 25 to maintain the focusing effect of the electron beam system 1, the magnetic field of the objective lens 25 in FIG. 5A is stronger than that in FIGS. 5B and 5C. For these reasons, the electrons 63 are more greatly affected than the electrons 64 and 65 in schematic diagrams 5B and 5C. In the cases shown in schematic diagrams 5A, 5B, and 5C, the first intersection 66 where the electrons 63 cross the beam 17 is closest to the object 35. The same applies to the second intersection 67 where the electrons 63 cross the beam 17 a second time. In other words, the trajectory of the electrons 63 is more curved than the trajectories of the electrons 64 and 65. As a result, the electrons 63 collide with the beam tube 11 instead of the detector 41, whereby the electrons 63 cannot be detected by the detector 41.

[0070] For the sake of facilitation of understanding, it should be observed that schematic diagrams 5A, 5B, and 5C in FIG. 5 show the trajectories of only one electron each emitted by the object 35. However, in reality, the object 35 will emit a plurality of electrons in different directions and with different energies. FIG. 5 is intended to be understood in the sense that the probability of the electrons colliding with the detector 41 is higher in schematic diagram 5B than in the cases of schematic diagrams 5A and 5C. Therefore, it is obvious that switching from the case shown in schematic diagram 5C to the case shown in schematic diagram 5B increases the signal detected by the detector 41. This can improve the quality of the electron microscope image. For example, as shown in schematic diagram 5A in FIG. 5, it should also be observed that when the potential U3 supplied to the beam tube 11 is too low, the incidence probability decreases.

[0071] Since the orbits and interactions of electrons 63, 64, and 65 depend on the multiple settings and configurations of the electron beam system 1, the probability of electron incidence described in FIG. 5 also depends on the settings and configurations of the electron beam system 1. For example, the configuration of the objective lens 25 can already be lowered at a much higher voltage value for the incidence probability of the electrons emitted by the object 35. The incidence probability of the electrons emitted by the object 35 can be specified for a specific setting and configuration of the electron beam system 1 by simulating the orbits of the electrons and specifying the number of electrons incident on the detector 41.

[0072] FIG. 6 shows a flowchart showing a method of operating the electron beam system 1 shown in FIG. 1 according to this embodiment. In this case, FIG. 6 shows steps S11 to S16. First, the values of the operating parameters of the electron beam system 1 are set in step S11. In particular, the controller 47 commands the supply system 9 to supply the first potential U1 of the first value to the electron emitter 5, the second potential U3 of the second value to the beam tube 11, and the third potential U5 of the third value to the object 35.

[0073] Next, in step S12, the beam 17 is focused on the object 35 by changing the current of the objective lens 25. In contrast to the method described above with respect to FIGS. 2 and 3, focusing the beam 17 on the object 35 is completely finished in this embodiment before moving on to the next step. As soon as the electron beam system 1 reaches the focused state, the electron beam system 1 continues to step S13. It should be observed that focusing here can also include iterative steps: similar to steps S2, S3, S4, and S7, these can include recording the electron microscope image, analyzing the recorded electron microscope image, and changing the current supplied to the objective lens 25 based on the analysis of the image.

[0074] Subsequently, in step S13, a first electron microscope image is recorded. For example, this image corresponds to an image that serves as a basis for the user of the electron beam system 1 to determine that it is necessary to switch to an operation mode that increases the signal detected by the detector 41 compared to the resolution of the electron beam system 1. In step S14, the operation parameters are then compared with a predetermined tuple of values of the operation parameters. The tuple includes values resulting from a simulation in which the number of electrons incident on the detector 41 is specified for different operation parameter settings. For example, such a simulation can be realized by simulating the trajectories of electrons having different emission energies and directions, corresponding to the example shown in FIG. 5. Then, the values specified by the simulation can be stored in the memory of the electron beam system 1 or in the cloud in the form of a tuple that can be accessed by the electron beam system 1. Alternatively, the tuple can include values specified experimentally. For example, experimental specification can be performed by collecting and processing feedback from the user of the electron beam system. Based on the predetermined tuple, it is possible to determine the value of the potential U3 supplied to the beam tube 11 and the value of the current supplied to the objective lens 25 that must be set. For example, this can be implemented by inputting the read tuple such that the current values of the operation parameters excluding the potential U3 supplied to the beam tube 11 and the current supplied to the objective lens 25 correspond to the values of the tuple.

[0075] Subsequently, according to the values determined in step S14, in step S15, the potential U3 supplied to the beam tube 11 is decreased, and in step S16, the current supplied to the objective lens 25 is decreased. In this case, the current supplied to the objective lens 25 in step S16 is decreased such that focusing on the object 35 is maintained. That is, the electron beam 17 is focused on the object 35 even after steps S15 and S16.

[0076] After the new values of the potential U3 of the beam tube 11 and the current of the objective lens 25 are set, the method continues with step S17. In step S17, a second electron microscope image is recorded using the electron beam system 1 with the set values.

[0077] For example, the method can be implemented as a switch between two operating modes that can be performed by the user of the electron beam system 1. In such a case, the electron beam system 1 includes a first operating mode in which an electron microscope image is first recorded with the value of the potential U3 supplied to the beam tube 11 remaining unchanged, and a second operating mode in which the electron microscope image is recorded at a second value of the potential U3 supplied to the beam tube 11, and the second value is optimized in relation to the electrons incident on the detector 41. Thus, the method can switch from the first operating mode to the second operating mode as a result of steps S11 - S17.

[0078] According to a further embodiment, the second operating mode can alternatively be chosen such that steps S14 - S16 are performed to reduce the convergence angle of the electron beam 17 that converges on the object 35 in relation to the convergence angle in the first operating mode. The convergence angle affects the theoretically possible resolution of the electron microscope image and the depth of field of the electron microscope image. In this case, the depth of field is a measure of the sharpness of the electron microscope image at different levels of the object 35 when the focus of the electron beam 17 remains unchanged. The smaller the convergence angle, the lower the theoretically possible resolution, but the greater the depth of field. This is advantageous when a large area of the sample should be recorded because the sharpness of the electron microscope image on the side with a large deflection by the deflection device 51 is similar to the sharpness of the electron microscope image in the center where the deflection by the deflection device 51 is small. In such a case, since a large area of the object 35 is recorded with a lower density of data points to shorten the recording time of the large area of the object 35, the theoretically possible resolution is not very relevant. For example, when the object 35 is very uneven, and thus the raised areas of the object 35 should be recorded with the same resolution as the sunken areas of the object 35, a greater depth of field is also advantageous.

[0079] The method may further include switching from the second operating mode to the first operating mode. In such a case, the electron beam system 1 increases the potential U3 supplied to the beam tube 11 and the current I2 supplied to the objective lens 25 in the opposite sense to reducing the potential U3 supplied to the beam tube 11 and the current I2 supplied to the objective lens 25 in steps S15 and S16 shown in FIG. 6.

[0080] FIG. 7 shows some electron microscope images 68, 69, 71, 73, 75, 77, 79, 81, 83, and 85 recorded using the method shown in FIG. 6 for operating the electron beam system 1 shown in FIG. 1. In this case, the electron microscope images 68, 69, 71, 73, 75, 77, 79, 81, 83, and 85 were recorded using a Zeiss GeminiSEM560. The images 68, 69, 71, 73, 75, 77, 79, 81, 83, and 85 show electron microscope recordings of an object showing a structure 87 arranged in a checkerboard pattern.

[0081] Image 68 was recorded at a potential U3 of 8000 volts supplied to the beam tube 11 and a voltage of 90 volts between the electron emitter 5 and the object 35. Image 69 was recorded at a potential U3 of 8000 volts supplied to the beam tube 11 and a voltage of 80 volts between the electron emitter 5 and the object 35. Image 71 was recorded at a potential U3 of 8000 volts supplied to the beam tube 11 and a voltage of 70 volts between the electron emitter 5 and the object 35. Image 73 was recorded at a potential U3 of 8000 volts supplied to the beam tube 11 and a voltage of 60 volts between the electron emitter 5 and the object 35. Image 75 was recorded at a potential U3 of 8000 volts supplied to the beam tube 11 and a voltage of 50 volts between the electron emitter 5 and the object 35.

[0082] Image 77 was recorded at a potential U3 of 8000 volts supplied to the beam tube 11 and a voltage of 40 volts between the electron emitter 5 and the object 35. Image 79 was recorded at a potential U3 of 6000 volts supplied to the beam tube 11 and a voltage of 40 volts between the electron emitter 5 and the object 35. Image 81 was recorded at a potential U3 of 5000 volts supplied to the beam tube 11 and a voltage of 40 volts between the electron emitter 5 and the object 35. Image 83 was recorded at a potential U3 of 4000 volts supplied to the beam tube 11 and a voltage of 40 volts between the electron emitter 5 and the object 35. Image 85 was recorded at a potential U3 of 3400 volts supplied to the beam tube 11 and a voltage of 40 volts between the electron emitter 5 and the object 35.

[0083] Referring to FIG. 6, it is clear that the method described above is particularly advantageous when the voltage between the electron beam emitter 5 and the object 35 is low. Images 68 - 77 show that a gradual decrease in the voltage between the electron beam emitter 5 and the object 35 is accompanied by a decrease in the signal generated by the detector 41, in particular a decrease in the contrast between the structural elements 87. For example, it is almost impossible to identify the structural element 87 in image 77. However, as incrementally shown from image 79 to 85, when the potential U3 supplied to the beam tube 11 is lowered while the focusing of the electron beam 17 remains unchanged, the quality of the recorded electron microscope image increases, particularly with respect to the contrast of the structural element 87. In the magnified image 85, in particular, fine details on the object 35 can be identified.

[0084] Figure 8 shows a schematic configuration of the electron beam system 1 according to a further embodiment. In this case, the electron beam system 1 includes an electron beam column 89 having the components already described above, and an ion beam column 91. The ion beam column 91 includes an ion beam source 93 having a metal reservoir and a tip portion where a small amount of molten metal flows downward from the metal reservoir. For example, the metal can be gallium having a low melting point. The extraction electrode 95 releases ions from the molten material. For this purpose, the extraction electrode 95 is set to a potential lower than the potential of the ion beam source 93. The released ions pass through the extraction electrode 95 to form an ion beam 99.

[0085] The ion beam 99 then passes through a focusing lens 97. The focusing lens 97 can be, for example, an electrostatic lens that can be a single lens as shown in Figure 8. The focusing lens 97 shown in Figure 8 consists of three electrodes between which an electrostatic field is generated in each case, and the above field enters the path of the beam 99. The ions of the beam 99 pass through the electrostatic field of the focusing lens 97 and as a result are collimated.

[0086] The ion beam column 91 also includes a variable aperture 101 in the path of the beam 99. Since the variable aperture 101 is in a plane optically conjugated with the ion beam source 93, it enables adjustment of the intensity of the beam 99 incident on the object 35. The beam 99 can be deflected in two dimensions with respect to the object 35 by the deflection electrodes 103, 105. As a result, the beam 99 can be directed to a specific processing position on the object 35.

[0087] The ion beam column 91 further includes an objective lens 107. The objective lens 107 can be, for example, a single lens and an electrostatic lens. The objective lens shown in Figure 8 includes three ring electrodes capable of generating an electric field therebetween, and the above field enters the path of the beam 99. As a result, the ions of the beam 99 are deflected, and thereby the objective lens 107 has a focusing effect. As a result of the influence of the incident ions, the beam 99 focused on the processing position on the object 35 can be used for cutting, material deposition, etc.

[0088] The ion beam column 91 also includes a housing 109 that houses the components of the ion beam column 91 therein. As a result of coupling the electron beam column 89 to the ion beam column 91, the electron beam system 1 can operate in various operation modes. For example, the electron beam source 3 can be switched off, that is, a voltage is not applied to the electron emitter 5, and electrons emitted by the object 35, which are emitted from the object 35 by the incident ion beam 99, can be detected by the detector 41 of the electron beam column 89. In another exemplary operation mode, both the electron beam column 89 and the ion beam column 91 operate as described above.

[0089] After the ion beam 99 exits the housing 109, the ions are exposed to an electrostatic field that spreads between the electron beam column 89 and the object 35. Therefore, the ions in the beam 99 are undesirably affected. To avoid these situations, the conventional method does not supply a voltage to the beam tube 11 when combined with the ion beam column 91. However, since electrons are not accelerated into the beam tube 11, this reduces the number of electrons captured.

[0090] In the above method, the second operation mode can alternatively be, for example, a mode in which the voltage supplied to the beam tube 11 is as low as possible, whereby the ion beam 99 from the ion beam column 91 is affected as little as possible by the electrostatic field between the object 35 and the electron beam column 89, but the electrons emitted by the object 35 are still accelerated into the beam tube 11 to a desired extent. Even in this operation mode, if the values to be set are predetermined, it can be advantageous for the method. For example, the value of the current supplied to the objective lens 25 and the value of the potential U3 supplied to the beam tube 11 can be determined by simulation for such an operation mode and stored in a memory or cloud accessible by the electron beam system 1.

Description of the reference numerals

[0091] 1 Electron beam system 3 Electron beam source 4 Connection line 5 Electron emitter 6 Extraction electrode 7 Connection line 9 Supply system 11 Beam tube 12 Inside 13 Upper end 14 Lower end 15 Connection line 17 Beam 19 Condensing lens 21 Solenoid 22 Pole shoe 23 Connection line 25 Objective lens 27 Coil 28 Pole shoe 29 Connection line 31 Connection line 33 Connection line 35 Object 37 Object mount 39 Connection line 41 Detector 43 Aperture 45 Connection line 47 Controller 49 Connection line 51 Deflection device 53 Connection line 57 Section 59 Section 63 Electron 64 Electron 65 Electron 66 First intersection 67 Second intersection 68 Image 69 Image 71 Image 73 Image 75 Image 77 Image 79 Image 81 Image 83 Image 85 Image 87 Structural element 89 Electron beam column 91 Ion beam column 93 Ion beam source 97 Condensing lens 99 Beam 101 Variable aperture 103 Deflection electrode 105 Deflection electrode 107 Objective lens 109 Housing I1 Current I2 Current s Distance from the electrode U1 Potential U2 Potential U3 Potential U4 Potential U5 Potential U6 Voltage

Claims

1. 1. A method of operating an electron beam system, the electron beam system comprising: an electron beam source for generating an electron beam; a beam tube having a first end and a second end, the electron beam configured to enter the beam tube at the first end and exit the beam tube at the second end; at least one magnetic focusing lens through which the electron beam passes; a supply system configured to supply a first potential to an electron emitter of the electron beam source, a second potential to the beam tube, a third potential to a target, and at least one current to the at least one magnetic lens; The method comprises: setting the first potential to a first value, the second potential to a second value, and the third potential to a third value, such that the third potential is greater than the first potential and the second potential is greater than the third potential; and focusing the beam on the object by modifying the at least one current; During said focusing, if said at least one current satisfies a predetermined criterion, In addition to setting the second potential to a fourth value that is less than the second value, increasing the at least one current and then varying the at least one current to keep the beam focused on the object; or maintaining the beam focused on the object by varying the second potential; and The method further comprises:

2. 2. The method of claim 1 , wherein the predetermined criterion is met if one of the at least one currents falls below a predetermined value and / or the predetermined criterion is not met if the current of the at least one current does not fall below the predetermined value.

3. 1. A method of operating an electron beam system, the electron beam system comprising: an electron beam source for generating an electron beam; a beam tube having a first end and a second end, the electron beam configured to enter the beam tube at the first end and exit the beam tube at the second end; at least one magnetic focusing lens through which the electron beam passes; a supply system configured to supply a first potential to an electron emitter of the electron beam source, a second potential to the beam tube, a third potential to a target, and at least one current to the at least one magnetic lens; The method comprises: setting the first potential to a first value, the second potential to a second value, and the third potential to a third value, such that the third potential is greater than the first potential and the second potential is greater than the third potential; and focusing the beam on the object by modifying the at least one current; During said focusing, if said at least one current satisfies a predetermined criterion, In addition to setting the second potential to a fourth value greater than the second value, decreasing the at least one current and then varying the at least one current to keep the beam focused on the object; or maintaining the beam focused on the object by varying the second potential; and The method further comprises:

4. 4. The method of claim 3, wherein the predetermined criterion is met if one of the at least one currents exceeds a predetermined value and / or the predetermined criterion is not met if the current of the at least one current does not exceed the predetermined value.

5. 5. The method of claim 1, wherein electrons between the second end of the beam tube and the object are affected by an electric field generated by a difference between the second potential and the third potential and a field generated by the magnetic lens.

6. The method according to any one of claims 1 to 4, wherein the predetermined criterion depends on the second value.

7. A method according to any one of claims 1 to 4, wherein focusing the beam on the object comprises finding the value of the current such that the spot illuminated by the beam on the object is as small as possible.

8. 5. The method of claim 1, wherein focusing the beam on the target comprises detecting electrons generated by the electron beam, determining a change in a value of the at least one current based on the detected electrons, and setting a value of the current in accordance with the determined change.

9. 5. The method of claim 1, further comprising recording at least one electron microscope image at said values ​​set for said first, second and third potentials and said at least one current.

10. 10. The method of claim 9, wherein focusing the beam on the object comprises finding the value of the current such that the recorded electron microscope image is as sharp as possible.

11. 1. A method of operating an electron beam system, the electron beam system comprising: an electron beam source for generating an electron beam; a beam tube having a first end and a second end, the electron beam configured to enter the beam tube at the first end and exit the beam tube at the second end; at least one magnetic focusing lens through which the electron beam passes; a supply system configured to supply a first potential to an electron emitter of the electron beam source, a second potential to the beam tube, a third potential to a target, and at least one current to the at least one magnetic lens; The method comprises: setting the first potential to a first value, the second potential to a second value, and the third potential to a third value, such that the third potential is greater than the first potential and the second potential is greater than the third potential; focusing the beam on the object by changing the at least one current to a fourth value and recording a first electron microscope image at the first potential at the first value, the second potential at the second value, the third potential at the third value, and the current at a fourth value; setting the second potential to a fifth value less than the second value and setting the current to a sixth value less than the fourth value; recording a second electron microscope image at the first potential at the first value, the second potential at the fifth value, the third potential at the third value, and the current at the sixth value; Methods including

12. 12. The method of claim 11, further comprising determining the fifth and sixth values ​​based on the first, second, third, and fourth values ​​such that the beam is substantially focused on the target at the first potential of the first value, the second potential of the fifth value, the third potential of the third value, and the current of the sixth value.

13. using a predetermined data record when determining the fifth value and the sixth value; 13. The method of claim 12, wherein the data record includes multiple tuples of values ​​of the first potential, the second potential, the third potential, the current, and the distance of the electron beam system over which the focusing of the beam occurs.

14. the electron beam system further comprising a detector disposed within the beam tube adjacent the electron beam; A method according to any one of claims 11 to 13, wherein the determination is performed such that the intensity of electrons incident on the detector or the ratio between the current of the electron beam focused on the object and the intensity of the electron beam incident on the detector is greater than during the recording of the first electron microscope image.

15. The method of claim 14 , wherein the second value is chosen such that the resolution of the first image is maximized.

16. The method according to any one of claims 11 to 13, wherein the determining is performed such that the convergence angle of the electron beam focused on the object is smaller than during the recording of the first electron microscope image.

17. the electron beam system further comprising an ion beam column configured to direct an ion beam at the target; The method comprises: The method of any one of claims 11 to 13, further comprising operating the ion beam column while the second electron microscope image is being recorded.

18. 20. The method of claim 17, wherein the operation of the ion beam column includes using the ion beam to remove material from the object or severing material from the object with the ion beam.

19. 1. An electron beam system comprising: an electron beam source for generating an electron beam; a beam tube having a first end and a second end, the electron beam configured to enter the beam tube at the first end and exit the beam tube at the second end; at least one magnetic focusing lens through which the electron beam passes; a supply system configured to supply a first potential to an electron emitter of the electron beam source, a second potential to the beam tube, a third potential to a target, and at least one current to the at least one magnetic lens; A controller configured to carry out the method according to any one of claims 1 to 4, 11 to 13; An electron beam system equipped with

20. A computer program product comprising instructions which, when executed by a controller of an electron beam system according to claim 19, cause the electron beam system to perform a method according to any one of claims 1 to 4, 11 to 13.

Images