Method for operating 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] The present application relates to a method of operating an electron beam system. [Background technology]

[0002] The electron beam system comprises a beam source which generates an electron beam. The electron beam illuminates a spot on the 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 comprises a detector, which can be used to detect electrons emitted by the object, generated when the electron beam is incident on the object. An electron microscope image is generated by mapping 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 is.

[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. An electric potential is applied to the beam tube to accelerate the electrons in the beam when they enter the beam tube and when they leave the beam tube due to the electrostatic lens field of the electron beam system, and to decelerate them between the beam tube and the object. As a result, the electrons in the beam reach the object faster and therefore experience less electrostatic repulsion due to other electrons in the beam that increase the beam spot on the object. The electric potential applied to the beam tube is therefore chosen to be as high as possible during 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, users may find the conventional operation of the electron beam system to be inadequate. Summary of the Invention [Problem to be solved by the invention]

[0005] It is therefore an object of the invention to propose a method for improving the operation of an electron beam system having a beam tube. [Means for solving the problem]

[0006] According to an embodiment of the invention, a method of operating an electron beam system includes setting a first potential supplied to the electron beam source to a first value, setting a second potential supplied to the beam tube to a second value, and setting 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. Furthermore, the potential supplied to the object is greater than the potential supplied to the electron beam source, such that the electrons in the beam actually enter the object.

[0007] When a potential is supplied to the electron beam system as described above, an electrostatic field prevails between the beam tube and the object, which already deflects the electrons of the electron beam due to the electrostatic interaction between them and acts on the electrons like a focusing lens. The electron beam system therefore has a focusing effect on the electron beam even if no current is supplied to any magnetic lens, for example the objective lens, provided for this purpose. When such a condition is reached, for example during focusing of the electron beam on an object arranged at a large distance from the electron beam system, if the potential supplied to the beam tube is lowered, the focusing can be continued. If the potential supplied to the beam tube is lowered, the current supplied to the objective lens can be increased for an unchanged focusing effect, since the focusing effect of the electrostatic field is smaller. The focusing can therefore be continued. In this case the potential supplied to the beam tube can also correspond to ground potential.

[0008] Thus, according to an embodiment, the method also includes focusing the beam on the object by modifying at least one current supplied to at least one magnetic lens, for example an objective lens, and if during focusing the at least one current meets a predetermined criterion, the following is performed: setting the potential supplied to the beam tube to a fourth value less than the second value by modifying the at least one current, raising the at least one current and then continuing to focus the beam on the object, or keeping the at least one current constant by modifying the second potential and then continuing to focus the beam on the object. This means that if, while the beam is focusing on the object, a predetermined criterion is met, the potential supplied to the beam tube is lowered and, for example, the current supplied to the objective lens is raised. Focusing can then be continued by modifying the current of the objective lens or modifying the potential supplied to the beam tube.

[0009] The method can be performed using an electron beam system comprising an electron beam source generating an electron beam, a beam tube having a first end and a second end and 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 electric potential to an electron emitter of the electron beam source, a second electric potential to the beam tube, a third electric potential to the target, and at least one current to the at least one magnetic lens.

[0010] For example, the at least one magnetic lens can be an objective lens of an electron beam system or an objective lens and a condenser lens of an electron beam system. Focusing is generally a long process involving several steps. It is therefore possible to start with focusing the beam on the object and to adopt further measures during focusing, for example lowering 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 predefined criterion can be performed, for example, during each focusing step. Alternatively, said checks may be performed after every second step, after every third step, etc.

[0011] According to some embodiments, the predetermined criterion is met when the current supplied to the objective lens falls below a predetermined value. In particular, the predetermined value can be approximately zero, whereby the criterion is met when the current supplied to the objective lens is approximately zero.

[0012] According to a further embodiment, the method comprises setting the first potential supplied to the electron beam source to a first value, setting the second potential supplied to the beam tube to a second value, and setting the 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. The method also comprises focusing the beam on the object by modifying at least one current supplied to at least one magnetic lens, and if during focusing the at least one current meets a predetermined criterion, the following is performed: setting the second potential to a fourth value greater than the second value by modifying the at least one current, lowering the at least one current, and then continuing to focus the beam on the object, or keeping the at least one current constant and continuing to focus the beam on the object by modifying the second potential. The method according to this embodiment is the inverse of the above method, and in particular comprises increasing the potential supplied to the beam tube and lowering the current supplied to the objective lens while focusing the beam on the object, if the predetermined criterion is met.

[0013] According to some embodiments, the predetermined criterion is met if a current of at least one of the currents exceeds a predetermined value.

[0014] According to some embodiments, electrons between the second end of the beam tube and the object are affected by an electric field generated by the difference between the second potential and a third potential and a field generated by the magnetic lens. In particular, the beam tube and 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 the 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 created by the current supplied to the objective lens and the potential supplied to the beam tube. As in the above embodiment, the criterion is met when the current supplied to the objective lens falls below the predetermined value, and if the predetermined value is small, the focusing effect of the electron beam system in a setting where the criterion is met will depend almost exclusively 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 the beam on the object includes detecting electrons generated by the electron beam, determining a change in a value of a current supplied to the magnetic lens based on the detected electrons, and setting the value of the current according to the determined change. For example, focusing can be performed as follows: an electron microscope image is recorded by the electron beam system, the electron microscope image is analyzed, and a value of at least one current is changed based on the results 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 determined by subjecting the electron microscope image to a Fourier transform and observing the frequency contribution.

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

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

[0020] As already mentioned above, the potential supplied to the beam tube is conventionally set as high as possible in electron beam systems in order to increase the resulting resolution. However, situations may arise in which the user of the electron beam system finds that the image, once recorded, is not suitable for the purpose, for example because certain structures are not recognizable. It may therefore be advantageous to switch from an operating mode with a high resolution to an operating mode with a high detection signal from the detector. In this case, an operating mode with a high detection signal from the detector means that the number of electrons incident on the detector is as high as possible. This is possible because the electrostatic field between the beam tube and the object and the magnetic objective lens field also act on the electrons, such as potentials emitted by the object, which pass through the beam tube in the opposite direction to the electron beam. The trajectory of such electrons is therefore directly influenced 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. The composition of the magnetic and electrostatic influences on the electrons emitted by the object is therefore always changed.

[0021] Thus, the method according to this further embodiment comprises setting a first potential supplied to the electron emitter of the electron beam source to a first value, setting a second potential supplied to the beam tube to a second value, and setting 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. Furthermore, the potential supplied to the object is greater than the potential supplied to the electron beam source, such that the electrons in the beam actually enter the object.

[0022] The method also includes focusing the beam on the object by changing at least one current to a fourth value, recording a first electron microscope image at the first potential of the first value, the second potential of the second value, the third potential of the third value, and the current of the fourth value, setting the second potential of the second value to a fifth value less than the fourth value, setting the current of the fourth value to a sixth value less than the fourth value, and recording a second electron microscope image 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, which means that a first image is first recorded at the originally set values ​​and then a second image is recorded at new values ​​where the potential supplied to the beam tube and the current supplied to the magnetic lens are lowered.

[0023] According to some embodiments, the method also includes determining the fifth and sixth values ​​based on the first, second, third and fourth values ​​such that at a first value of potential supplied to the electron tube, a fifth value of potential supplied to the beam tube, a third value of potential supplied to the target and a sixth value of current, the beam is substantially focused on the target. For example, this may include causing the electron beam to create a small spot on the target, as already discussed above.

[0024] According to some embodiments, the method also includes using a predefined data record when determining the fifth and sixth values, the data record including multiple tuples of values ​​of potentials supplied to the electron beam source, potentials supplied to the beam tube, potentials supplied to the target, current, and distance of the electron beam system at which focusing of the beam occurs. For example, the predefined data record can be generated by trajectory simulation of electrons in the beam. Alternatively, the predefined data record can be created by operation of the electron beam system, whereby used settings of the electron beam system are recorded. The data record can be stored in a local memory of the electron beam system or can be stored in a cloud, for example, accessible to the electron beam system.

[0025] According to some embodiments, the electron beam system further comprises a detector arranged next to the electron beam in the beam tube, the determination being performed such that the intensity of the electrons incident on the detector or the ratio between the current of the electron beam focused on the object and 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 the electrons entering the scintillator crystal. The scintillator crystal may be held by a mount next to the electron beam in the beam tube. Alternatively, the detector may have a structure that guides the electrons entering it to the scintillator crystal and the detector area, which is then capable of detecting the electrons. The detector may be a semiconductor detector or have a different structure.

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

[0027] According to some embodiments, the determination is performed such that the convergence angle of the electron beam focused on the object is smaller than during 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 to an area of ​​the object that may 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 target using the ion beam or severing material from the target with the ion beam.

[0030] According to some embodiments, an electron beam system comprises an electron beam source generating an electron beam, a beam tube with 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 a target, and at least one current to the at least one magnetic lens, and a controller configured to perform the method according to any one of claims 1 to 17. Additionally, the electron beam system may comprise an ion beam column configured to direct an ion beam towards the target.

[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 may comprise multiple beam tube sections, each having multiple ends. In such a case, it is possible, for example, that the first end is an end of a first beam tube section and the second end is an end of a second beam tube section. Furthermore, it should be observed that the second end of the beam tube in an advantageous embodiment is arranged in the vicinity of the objective lens, in particular at a distance from the objective lens that is less than 0.1 times the distance between the electron beam source and the objective lens. Furthermore, the first end of the beam tube does not necessarily have to be arranged in the vicinity of the focusing lens of the electron beam system. What is important is that the beam tube has an extent along the beam path and thus the beam tube is able to produce the above-mentioned effect on the acceleration of the electrons in the beam.

[0032] Moreover, in the above case where the beam tube comprises several mutually separated beam tube sections, it should be observed that different potentials can be supplied to the beam tube sections, in such a case, for example, the following description of the potentials supplied to the beam tube can apply to a lower beam tube section having a second lower end arranged near 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] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described in detail below with reference to the drawings. [Brief description of the drawings]

[0035] [Figure 1] 1 shows a schematic configuration of an electron beam system according to an embodiment. [Diagram 2] 2 shows a flow chart illustrating a method of operating the electron beam system from FIG. 1 according to one embodiment. [Diagram 3] 4 shows a flow chart illustrating a method of operating the electron beam system from FIG. 1 according to a further embodiment. [Figure 4] 3 shows a diagram illustrating the curve of the voltage applied to the beam tube by the method shown in FIG. 2. [Diagram 5] 2 shows three schematic diagrams of electron trajectories for different setups of the electron beam system shown in FIG. 1 . [Figure 6] 4 shows a flow chart illustrating a method of operating the electron beam system from FIG. 1 according to a further embodiment. [Figure 7] 7 shows several electron microscope images recorded using the method shown in FIG. 6 of operating the electron beam system shown in FIG. [Figure 8] 1 shows a schematic configuration of an electron beam system according to a further embodiment; DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

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

[0037] The electron beam system 1 also comprises a beam tube 11 having an interior 12, an upper end 13 and a lower end 14. The beam tube 11 is connected to the supply system 9 via a connecting 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 13 of the beam tube 11 acts as an anode which accelerates electrons in a beam 17 generated by the electron beam source 3 into the beam tube 11. The beam 17 of electrons passes through the beam tube 11. The interior 12 of the beam tube 11 serves to accommodate further components of the electron beam system 1 within the beam tube 11. To this end, the interior 12 is wider than elsewhere in the beam tube 11, so that further components can be arranged in the interior 12 without obstructing the beam 17 of electrons.

[0038] The beam of electrons 17 passes through a collecting lens 19. The collecting lens 19 is a magnetic lens which deflects the electrons in the beam 17 by generating a magnetic field. For this purpose, the collecting lens 19 comprises a solenoid 21 which is connected to a 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 collecting lens 19. The collecting lens 19 also comprises a pole shoe 22 which influences the magnetic field generated by the current I1 supplied to the solenoid 21 in such a way that such a magnetic field is appropriately in the path of the beam of electrons 17 in order to achieve a focusing effect on the beam of electrons 17.

[0039] After the electrons in the beam 17 have passed through any components arranged in the interior 12 of the beam tube 11, the beam 17 passes through a magnetic field of an objective lens 25 acting both inside and outside the beam tube 11. The objective lens 25 is a magnetic lens with a solenoid 27. The solenoid 27 is connected to a supply system 9 via a connecting line 29. The supply system 9 is also configured to supply a current I2 to the solenoid 27 via the connecting line 29. When the current I2 is supplied to the coil 27, a magnetic field is generated by the coil 27 which deflects the electrons passing through it from their trajectory. The objective lens 25 also comprises a pole shoe 28 which influences the magnetic field so that the magnetic field enters the path of the beam 17 accordingly and acts on the electrons in the beam 17 so as to obtain a focusing effect.

[0040] The lower end 14 of the beam tube 11 is disposed in the vicinity of the objective lens 25. As shown in Figure 1, the end 14 of the beam tube 11 can be disposed at the opening of a pole shoe 28 of the objective lens 25. As a result, the magnetic field of the objective lens 25 acts both inside and outside the beam tube 11. In fact, a non-negligible component of the magnetic field of the objective lens 25 acts in some embodiments up to the object 35. 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] Although the top end 13 of the beam tube 11 is shown near the collecting lens 19 in FIG. 1, the top end 13 may be disposed at any other location along the beam path of the beam 17, so long as the beam tube 11 extends along the beam path of the beam 17 between the top end 13 and the bottom end 14. For example, the top end 13 may be disposed near the objective lens 25, such that the beam tube 11 encloses the beam 17 only where the beam 17 passes through the objective lens 25. Furthermore, the beam tube 11 may comprise multiple portions, each having two ends. For example, an upper portion may enclose the beam 17 where the beam 17 passes through the collecting lens 19, the upper portion constituting the top end 13 and the further end of the beam tube 11, and thus not necessarily contacting the lower end of the beam tube 11. Such a lower portion may enclose the beam 17 where the beam 17 passes through the objective lens 25, in which case the lower portion constitutes the lower end 14 and the further end of the beam tube 11. Likewise, the beam tube 11 may comprise multiple components, for example multiple layered tube elements.

[0042] The electron beam system 1 also comprises an electrode 31 which is connected to the supply system 9 via a connecting line 33. The supply system 9 is able to supply the electrode 31 with a potential U4 via the connecting line 33. If 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 14 of the beam tube 11. More precisely, an electrostatic lens is formed by the electrode 31 together with the lower end 14 of the beam tube 11.

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

[0044] 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 they strike 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 bottom end 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 bottom end 14 of the beam tube 11.

[0045] The electron beam system 1 also comprises a detector 41 for detecting electrons emitted by the object 35. The detector 41 is disposed in the beam tube 11 and comprises an aperture 43 that allows the beam of electrons 17 to pass through the detector 41. The detector 41 is connected via a connection line 45 to a controller 47, which can receive measurement data from the detector 41 via the connection line 45.

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

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

[0048] Figure 2 shows a flow chart illustrating a method of operating the electron beam system 1 shown in Figure 1 according to one embodiment. Figure 2 shows steps S1-S9 performed by the electron beam system 1. In particular, steps S1-S9 can be commanded by a controller 47.

[0049] In step S1, 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 command the supply system 9 to supply a first potential U1 of a first value to the electron emitter 5, a second potential U3 of a second value to the beam tube 11 and a third potential U5 of a 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, firstly, 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 can be subjected to an acceleration force along the path and, in fact, can be incident on the object 35 accordingly. The difference between the potential U3 supplied to the beam tube 11 and the potential U5 supplied to the object 35 is then negative so that the electrons in the beam decelerate as they leave the lower end 14 of the beam tube 11 before they impinge on the object 35. Such deceleration is advantageous because the electrons then impinge on the object 35 with a lower kinetic energy and do not damage said object or cause other unwanted effects, such as a significant change in the shape of the object 35.

[0050] Then, in step S2, the beam 17 is focused on the object 35 by modifying the current I2 of the objective lens 25. Focusing the beam on 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 a current value of the objective lens 25 current I2. Then, in step S3, the recorded electron microscope image is analyzed for the effect of focusing or not focusing the beam of electrons 17 using the current values ​​of the operating parameters. For example, this analysis can be performed by a user of the electron beam system 1 or on a software basis. For example, for this purpose, the sharpness of the electron microscope image is checked. For example, the sharpness can be determined by subjecting the image to a Fourier transformation and evaluating the contribution of high frequency components. Whether or not focusing is completed can be determined by this analysis, as shown in step S4. If focusing is completed, the electron beam system 1 finishes focusing the beam 17 and proceeds to step S9, in which an electron microscope image is recorded using the set operating parameters.

[0052] If focusing is not yet complete, the electron beam system 1 proceeds to step S5, in which it performs a check as to whether the current in the objective lens 25 is below a predetermined value, which may depend on the setting of the potential U3 supplied to the beam tube 11.

[0053] If in step S5 it is determined that the current I2 of the objective lens 25 is less than a predetermined value, then 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, at which the current of the objective lens 25 cannot be further lowered. After increasing the current of the objective lens 25, the electron beam system 1 continues to step S8, in which the current I2 of the objective lens is modified based on the results of the analysis performed in step S3. In this case, the modification performed in step S8 corresponds to a modification of the current I2 supplied to the objective lens 25, which is also performed within the scope of conventional methods of focusing the beam 17 on the object 35.

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

[0055] Observe that FIG. 2 illustrates the case where steps S2-S8 are iterative steps of focusing the beam 17 on the object 35. However, in an alternative, steps S5-S7 may be performed every other iterative step, every third iterative step, etc. of focusing the beam 17 on the object 35. Furthermore, steps S5-S7 may alternatively be performed after step S8. In such a case, when it is determined in step S5 that the current I2 supplied to the objective lens 25 is not less than the 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 the electron beam system 1 returns to step S2 after performing step S7 or after it is determined in step S5 that the current supplied to the objective lens 25 is not less than the predetermined value.

[0056] As a result of the method described above with reference to Fig. 2, it is possible to further reduce the current supplied to the objective lens 25, even if said current becomes approximately zero. For example, if the distance s at which the object 35 is arranged in relation to the electron beam system 1 is large, a situation may arise in which, at a constant potential U3 supplied to the beam tube 11, the beam 17 cannot be focused on the object 35, 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 beam 17 of electrons. Thus, the beam 17 of electrons converges, even if no current is supplied to the objective lens 25. However, if the voltage supplied to the beam tube 11 is reduced, the focusing effect of the electrostatic field also decreases. As a result, the same focusing effect can be obtained with a smaller potential U3 supplied to the beam tube 11 and a higher current supplied to the objective lens 25.

[0057] It should be observed that in the above description, an electric current is supplied to the objective lens 25 in order to obtain the focusing effect. However, alternatively or additionally, an electric current may be supplied to the collecting lens 19.

[0058] A further embodiment will now be described with reference to figure 3. Figure 3 shows a flow chart illustrating a method of operating the electron beam system 1 from figure 1 according to a further embodiment. In this case, the method illustrated in figure 3 is the inverse of the method illustrated in figure 2 and differs in particular with regard to steps S5', S6' and S7', i.e. the distance of the focal point of the beam 17 from the electron beam system 1 is reduced in the method illustrated in figure 3, whereas in the method illustrated in figure 2 this distance is increased.

[0059] A further embodiment will now be described with reference to Fig. 3. Fig. 3 shows a flow chart 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 inverse of the method shown in Fig. 2, i.e. the distance of the focal point of the beam 17 from the electron beam system 1 is reduced in the method shown in Fig. 3, whereas in the method shown in Fig. 2 this distance is increased.

[0060] If the current supplied to the solenoid 27 of the objective lens 25 is determined to be greater than a predetermined value in step S5' shown in Figure 3, the electron beam system 1 continues 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 performed, the electron beam system 1 returns to step S2. Thus, the corresponding description of the alternative embodiment with respect to Figure 2 also applies to the method shown in Figure 3 with steps S5'-S7'.

[0061] In the following, the method shown in figure 2 will be explained in detail with reference to figure 4. Figure 4 shows a diagram illustrating the curve of the voltage applied to the beam tube according to the method shown in figure 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 called the distance between the object 35 and the electron beam system 1. Furthermore, 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 with sections 57 and 59. The constant section 57 is the area in which the conventional method can be applied without the functioning of the electron beam system 1 being impaired. The constant section 57 reaches up to the working distance s0. If the object 35 is arranged at a distance greater than the distance s0, the conventional method of operating the electron beam system cannot focus the beam 17 on the object 35.

[0063] The curve section 59 shows the potential U3 supplied to the beam tube 11 after carrying out the method shown in Fig. 2. In other words, the 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 and supplied to the beam tube 11 after the method has been carried out is no longer constant but is reduced when the working distance s is large. As a result, the electron beam system 1 can be operated without loss of functionality.

[0064] A further embodiment of a method for operating the electron beam system 1 is explained on the basis of the schematic diagram shown in Fig. 5. Fig. 5 shows three schematic diagrams 5A, 5B and 5C of electron trajectories for different settings of the electron beam system 1 shown in Fig. 1. In particular, 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 lowest in the case of schematic diagram 5A and highest in the case of schematic diagram 5C.

[0065] The schematic figures 5A, 5B and 5C show the components of the electron beam system 1 already described in relation to figure 1. In this case, a detector 41 having an aperture 43 through which the beam of electrons 17 passes is arranged in the beam tube 11. The beam tube 11 further comprises a lower end 14 which together with the electrode 31 and the object 35 mounted on the object mount 37 generates an electrostatic field. The beam of electrons 17 is not deflected by the deflection device 51 in the case of the schematic figures 5A, 5B and 5C.

[0066] The case where a high potential U3 is applied to the beam tube 11 will now be described with reference to schematic diagram 5C. An electron in the beam 17 incident on the object 35 causes the object 35 to emit an electron 65. The electron 65 is 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. Because the potential U3 applied to the beam tube 11 is high, the electron 65 undergoes a large acceleration in the direction of the beam tube 11 and is further subjected to 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 electron 65 crosses the beam 17 at a first crossing point 66. It should be observed that this does not mean that the electron 65 actually passes through the beam 17. Even if the electron 65 comes close to the beam 17 and does not move beyond the beam 17 in the dimension perpendicular to the plane of the drawing, the electron 65 does not collide with the electron in the beam 17 due to the electric repulsion between the electron 65 and said beam.

[0067] The electron 65 continues to intersect with the beam 17 at a second intersection point 67. The electron 65 cannot collide with the beam 17 at this intersection point 67 either. Due to the high potential U3 supplied to the beam tube 11, the electron 65 is accelerated significantly along its trajectory through the beam tube 11 and passes through the beam tube 11 at a high speed or with a high energy. Further interactions, such as the focusing effect of an electrostatic lens, therefore act on the electron 65 only for a short time, so that the trajectory of the electron 65 extends close to the beam 17. This is why the electron 65 passes through the aperture 43 of the detector 41 and cannot be detected by the detector 41.

[0068] Schematic diagram 5B shows the case where the beam tube 11 is supplied with a potential U3 lower than the potential U3 supplied to the beam tube 11 in the case of schematic diagram 5C. The 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 in schematic diagram 5C, the electrons 64 are accelerated less strongly into the beam tube 11 than the electrons 65. Thus, the electrons 64 are exposed longer to each interaction, for example the electrostatic field between the lower end 14 of the beam tube 11 and the focusing effect of the magnetic field of the objective lens 25. Furthermore, the magnetic field of the objective lens 25 is stronger in FIG. 5B than in FIG. 5C, because a larger current I2 is supplied to the objective lens 25 to maintain the focusing effect of the electron beam system 1. For these reasons, electron 64 intersects beam 17 at intersection point 66, which is much closer to object 35 than first intersection point 66 of electron 65. Electron 64 continues to intersect beam 17 at second intersection point 67, which is also closer to object 35 than second intersection point 67 of electron 65. In other words, electron 64 passes along a much more curved trajectory than electron 65. Thus, electron 64 is incident on detector 41 and can be detected by detector 41.

[0069] Schematic diagram 5A shows the case where the beam tube 11 is supplied with a potential U3 that is lower than the potential U3 supplied to the beam tube 11 in the case of schematic diagrams 5B and 5C. The electrons in the beam 17 that are incident on the object 35 cause the object 35 to emit an electron 63. In this case, the electron 63 is 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 case of schematic diagrams 5B and 5C, the electron 63 is accelerated into the beam tube 11 with a much lower strength, so that the electron 63 passes through the beam tube 11 at a slower speed. Furthermore, the magnetic field of the objective lens 25 in FIG. 5A is stronger than in FIG. 5B and 5C, because a larger current I2 is supplied to the objective lens 25 in order to maintain the focusing effect of the electron beam system 1. For these reasons, the electron 63 is affected more than the electrons 64 and 65 in the schematic diagrams 5B and 5C. In the case shown in schematic diagrams 5A, 5B, and 5C, the first intersection point 66 where electron 63 crosses beam 17 is closest to object 35. The same is true for the second intersection point 67 where electron 63 crosses beam 17 a second time. In other words, the trajectory of electron 63 is more curved than the trajectories of electrons 64 and 65. As a result, electron 63 hits beam tube 11 instead of detector 41, and thus electron 63 cannot be detected by detector 41.

[0070] For the sake of understanding, it should be observed that the diagrams 5A, 5B and 5C in FIG. 5 show the trajectory of only one electron emitted by the object 35. However, in reality, the object 35 will emit multiple electrons in different directions and with different energies. FIG. 5 is intended to be understood in the sense that the probability of an electron impinging on the detector 41 is higher in the diagram 5B than in the diagrams 5A and 5C. It is therefore self-evident that switching from the case shown in the diagram 5C to the case shown in the diagram 5B will increase the signal detected by the detector 41. This can improve the quality of the electron microscope image. It should also be observed that if the potential U3 supplied to the beam tube 11 is too low, as shown, for example, in the diagram 5A in FIG. 5, the incidence probability decreases.

[0071] 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 reduce the incidence probability of electrons emitted by the object 35 at much higher voltage values. The incidence probability of electrons emitted by the object 35 can be determined for a particular setting and configuration of the electron beam system 1 by simulating the electron trajectories and determining the number of electrons that are incident on the detector 41.

[0072] Fig. 6 shows a flow chart illustrating 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, values ​​of 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 a first potential U1 of a first value to the electron emitter 5, a second potential U3 of a second value to the beam tube 11, and a third potential U5 of a third value to the object 35.

[0073] Then, in step S12, the beam 17 is focused on the object 35 by modifying the current in the objective lens 25. In contrast to the methods described above with respect to Figures 2 and 3, the focusing of the beam 17 on the object 35 is in this embodiment completely finished before moving to the next step. As soon as the electron beam system 1 reaches a focused state, it continues to step S13. Observe that the focusing may now also include iterative steps: as with steps S2, S3, S4 and S7, these may include recording an electron microscope image, analysing the recorded electron microscope image and modifying 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 on which a user of the electron beam system 1 decides that it is necessary to switch to an operating mode that increases the signal detected by the detector 41 more than the resolution of the electron beam system 1. In step S14, the operating parameters are then compared to a predefined tuple of values ​​of the operating parameters. The tuple comprises values ​​resulting from a simulation in which the number of electrons incident on the detector 41 at different operating parameter settings is determined. For example, such a simulation can be realized by simulating trajectories of electrons with different emission energies and directions, corresponding to the example shown in FIG. 5. The values ​​determined by the simulation can then be stored in the memory or cloud of the electron beam system 1 in the form of a tuple that can be accessed by the electron beam system 1. Alternatively, the tuple can comprise values ​​determined by experiment. For example, the experimental determination can be performed by collecting and processing feedback from a user of the electron beam system. Based on the predefined 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 done by inputting a read tuple in which the current values ​​of the operating parameters, except for 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] Then, in step S15, the potential U3 supplied to the beam tube 11 is lowered according to the value determined in step S14, and in step S16, the current supplied to the objective lens 25 is lowered. In this case, the current supplied to the objective lens 25 in step S16 is lowered so as to maintain the focus on the object 35. 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 have been set, the method continues to step S17. In step S17 a second electron microscope image is recorded using the electron beam system 1 at the set values.

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

[0078] According to a further embodiment, the second operating mode can alternatively be chosen such that steps S14 to S16 are performed in order to reduce the convergence angle of the beam of electrons 17 focused on the object 35 in relation to the convergence angle in the first operating mode. The convergence angle influences 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 if the focus of the beam of electrons 17 does not change. The smaller the convergence angle, the lower the theoretically possible resolution but the greater the depth of field. This is advantageous when large areas of the sample are to be recorded, since the sharpness of the electron microscope image at the sides, where there is a large deflection by the deflection device 51, is similar to the sharpness of the electron microscope image in the center, where there is a small deflection by the deflection device 51. In such a case, the theoretically possible resolution is less relevant, since in order to reduce the recording time of a large area of ​​the object 35, a large area of ​​the object 35 is recorded with a lower density of data points. A larger depth of field is also advantageous, for example, if the object 35 is very uneven and therefore the raised areas of the object 35 should be recorded with similar resolution as the depressed areas of the object 35.

[0079] The method may further include switching from the second mode of operation to the first mode of operation, in which 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 a manner opposite to the manner in which the potential U3 supplied to the beam tube 11 and the current I2 supplied to the objective lens 25 are decreased in steps S15 and S16 shown in FIG.

[0080] Figure 7 shows several electron microscope images 68, 69, 71, 73, 75, 77, 79, 81, 83, and 85 recorded using the method shown in Figure 6 for operating the electron beam system 1 shown in Figure 1. In this case, electron microscope images 68, 69, 71, 73, 75, 77, 79, 81, 83, and 85 were recorded using a Zeiss Gemini SEM 560. Images 68, 69, 71, 73, 75, 77, 79, 81, 83, and 85 show electron microscope recordings of an object showing structures 87 arranged in a checkerboard pattern.

[0081] Image 68 was recorded with a potential U3 of 8000 volts applied to the beam tube 11 and a voltage of 90 volts between the electron emitter 5 and the object 35. Image 69 was recorded with a potential U3 of 8000 volts applied to the beam tube 11 and a voltage of 80 volts between the electron emitter 5 and the object 35. Image 71 was recorded with a potential U3 of 8000 volts applied to the beam tube 11 and a voltage of 70 volts between the electron emitter 5 and the object 35. Image 73 was recorded with a potential U3 of 8000 volts applied to the beam tube 11 and a voltage of 60 volts between the electron emitter 5 and the object 35. Image 75 was recorded with a potential U3 of 8000 volts applied 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 with a potential U3 of 8000 volts applied to the beam tube 11 and a voltage of 40 volts between the electron emitter 5 and the object 35. Image 79 was recorded with a potential U3 of 6000 volts applied to the beam tube 11 and a voltage of 40 volts between the electron emitter 5 and the object 35. Image 81 was recorded with a potential U3 of 5000 volts applied to the beam tube 11 and a voltage of 40 volts between the electron emitter 5 and the object 35. Image 83 was recorded with a potential U3 of 4000 volts applied to the beam tube 11 and a voltage of 40 volts between the electron emitter 5 and the object 35. Image 85 was recorded with a potential U3 of 3400 volts applied to the beam tube 11 and a voltage of 40 volts between the electron emitter 5 and the object 35.

[0083] It is clear that the method described above with reference to Fig. 6 is advantageous in particular when the voltage between the electron beam emitter 5 and the object 35 is low. Images 68 to 77 show that an incremental 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, in image 77 it is almost impossible to identify the structural elements 87. However, if, as shown incrementally in images 79 to 85, the potential U3 supplied to the beam tube 11 is lowered while the focusing of the beam of electrons 17 remains unchanged, the quality of the recorded electron microscope image increases, in particular with regard to the contrast of the structural elements 87. In the enlarged image 85, in particular fine details on the object 35 can be identified.

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

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

[0086] The ion beam column 91 also includes a variable aperture 101 in the path of the beam 99. The variable aperture 101 is in a plane optically conjugate with the ion beam source 93, allowing the intensity of the beam 99 incident on the target 35 to be adjusted. The beam 99 can be deflected in two dimensions relative to the target 35 by deflection electrodes 103, 105. As a result, the beam 99 can be directed to a specific processing location on the target 35.

[0087] The ion beam column 91 further comprises an objective lens 107. The objective lens 107 can be, for example, a single lens or an electrostatic lens. The objective lens shown in Fig. 8 comprises three ring electrodes between which an electric field can be generated, said field entering the path of the beam 99. As a result, the ions of the beam 99 are deflected, whereby the objective lens 107 has a focusing effect. As a result of the influence of the incident ions, the beam 99 focused at a 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 with the ion beam column 91, the electron beam system 1 can operate in various modes of operation. For example, the electron beam source 3 can be switched off, i.e., no voltage is applied to the electron emitter 5, and electrons emitted by the object 35 by the incident beam of ions 99 can be detected by the detector 41 of the electron beam column 89. In another exemplary mode of operation, the electron beam column 89 and the ion beam column 91 both operate as described above.

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

[0090] In the method, the second operating mode can alternatively be, for example, a mode in which the voltage supplied to the beam tube 11 is as low as possible, so that the beam 99 of ions 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, while the electrons emitted by the object 35 are nevertheless accelerated into the beam tube 11 to the desired extent. Also in this operating mode, it can be advantageous for the method if the values ​​to be set are predetermined. 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 operating mode and stored in a memory or cloud to which the electron beam system 1 can have access. [Explanation of symbols]

[0091] 1. Electron beam system 3. Electron beam source 4 Connection Lines 5 Electron Emitter 6 Extraction electrode 7 Connection Lines 9. Supply System 11 Beam tube 12 Inside 13 Upper end 14 Lower end 15 Connection Lines 17 Beam 19 Condenser lens 21 Solenoid 22 Pole shoe 23 Connection Line 25 Objective Lens 27 Coil 28 Pole shoe 29 Connection Lines 31 Connection Line 33 Connection Line 35 Object 37 Object Mount 39 Connection Lines 41 Detector 43 Opening 45 Connection Line 47 Controller 49 Connection Lines 51 Deflection Device 53 Connection Line 57 Section 59 Section 63 electronic 64 electronic 65 electron 66 First Intersection 67 Second Intersection 68 statue 69 statue 71 statue 73 statue 75 statue 77 statue 79 statue 81 statue 83 statue 85 statue 87 Structural Elements 89 Electron Beam Column 91 Ion Beam Column 93 Ion Beam Source 97 Condenser Lens 99 Beam 101 Variable Aperture 103 Deflection electrode 105 Deflection electrode 107 Objective Lens 109 Case I1 current I2 current s Distance from 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 comprising:

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 comprising:

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