Electron beam microscope and method for operating same

Abstract

The present disclosure provides an electron beam microscope and a method for operating an electron beam microscope. The electron beam microscope comprises an electron beam source (3), a magnetic objective (23) having magnetic pole ends (35, 37), a scintillator (61) having a hole diameter (D), a first electrode (80), a second electrode (97), and a potential supply device (11) for these elements. The hole diameter (D) of the scintillator is smaller than the hole diameter of the second electrode (97). In addition, E (z) / r (z) < = L is established for all points z within the range [z1, z2] in the vicinity of the scintillator on the axis of symmetry (29). In this case, E (z) is the field strength of the electric field at the point z, r (z) is the radius of curvature of the equipotential line 91 of the electric field at the point z, and L is equal to 3.0 kV / mm2.

Description

TECHNICAL FIELD

[0001] The invention relates to an electron beam microscope and to a method for operating an electron beam microscope.

[0002] In particular, the invention relates to an electron beam microscope having an electron beam source, a magnetic objective, an object holder and an electron detector. The electron beam source generates an electron beam, the electrons of which are accelerated and focused by the magnetic objective on an object plane. An object to be examined is mounted in the object plane by the object holder such that the focused electron beam is incident on a surface of the object. The electron beam incident on the object there generates electrons, such as secondary electrons and backscattered electrons, which leave the object. Such electrons are detected by the electron detector. The detected electron intensity allows conclusions to be drawn about the structure of the object at the location where the electron beam is incident on the object. The electron detector comprises a converter arrangement onto which the electrons generated at the object are incident and which generates signals representing the intensity of the electrons generated at the object by the incident electron beam and which can be evaluated by a controller of the electron beam microscope. The converter arrangement can comprise a scintillator body onto which the electrons generated at the object are incident and which generate light by the electrons. Such an electron detector then further comprises a light detector which detects the light generated by the scintillator arrangement and converts the light into electrical signals which can be evaluated by a controller of the electron beam microscope. The converter arrangement can also comprise a semiconductor detector onto which the generated electrons are incident and which generate electrical signals by the electrons which can be evaluated by a controller of the electron beam microscope. BACKGROUND

[0003] In some cases, it is desirable to detect a large proportion of the backscattered electrons generated at the object. These backscattered electrons have a higher kinetic energy upon exit from the object than the likewise generated secondary electrons. It is desirable to position the scintillator body of the scintillator arrangement close to the object plane in order to be able to detect as many of these backscattered electrons as possible.

[0004] US 9 029 766 B2 discloses an electron beam microscope of this type which comprises a scintillator arrangement having a scintillator body arranged close to the object.

[0005] It has been found that this conventionally known electron beam microscope does not meet certain desires. SUMMARY

[0006] It is therefore an object of the present invention to propose an electron beam microscope having an electron beam source, a magnetic objective and a converter arrangement in proximity to the object plane, which exhibits improved properties. Furthermore, it is an object of the present invention to propose a method for operating such an electron beam microscope.

[0007] The present invention proposes an electron beam microscope comprising an electron beam source for generating an electron beam, a magnetic objective for generating a magnetic field focusing the electron beam, an electrode for generating an electric field decelerating electrons of the electron beam, and a converter arrangement of an electron detector.

[0008] The magnetic objective comprises a solenoid and a magnetic yoke having a first pole end and a second pole end extending about a symmetry axis. The electron beam can be focused by the objective on a surface of an object mounted on an object mount of the electron beam microscope. The electric field decelerating the electrons of the electron beam accelerates electrons generated at the object by electrons of the electron beam incident on the object such that these electrons can be incident on the converter arrangement of the electron detector with increased kinetic energy.

[0009] According to an exemplary embodiment, the converter arrangement has a circular aperture centered about the symmetry axis and having its smallest diameter in a converter plane orthogonal to the symmetry axis. The converter arrangement comprises at least one converter generating an optical or electrical signal using the incident electrons.

[0010] The electron beam microscope then further comprises a first electrode having a circular aperture centered about the symmetry axis on a side facing the converter arrangement and being arranged closer to the electron beam source than the converter arrangement, and a second electrode having a circular aperture centered about the symmetry axis on a side facing the converter arrangement and being arranged further away from the electron beam source than the converter arrangement.

[0011] The electron beam microscope then further comprises a potential supply configured to feed mutually different potentials two by two to the first electrode, the second electrode and the converter arrangement in order to generate the electric field decelerating the electrons of the electron beam. Thus, in addition to the first electrode and the second electrode, the converter arrangement provides a further electrode for shaping the electric field decelerating the electrons of the electron beam. The geometry of the first electrode, the second electrode and the converter arrangement and the potentials applied by the potential supply to the first electrode, the second electrode and the converter arrangement determine the properties of the electric field generated by these elements and through which the electrons of the electron beam pass on their way to the object. Furthermore, the part of the electrons generated at the object that is incident on the converter arrangement passes through a part of this field.

[0012] According to an exemplary embodiment, the minimum diameter of the aperture of the converter arrangement is smaller than the diameter of the aperture of the second electrode. The diameter of the aperture of the converter arrangement can be chosen to be small in order to provide the maximum possible area of the converter arrangement on which the electrons generated at the object can be incident in order to be detected. Correspondingly, the diameter of the aperture of the second electrode is larger than the minimum diameter of the aperture of the converter arrangement in order to prevent an excessive number of electrons generated at the object from being incident on the second electrode instead of the converter arrangement.

[0013] According to an exemplary embodiment, the diameters of the apertures of the first electrode, the second electrode and the third electrode, the distances between the first electrode and the converter arrangement and between the converter arrangement and the second electrode, as well as the electric potentials fed to these elements are chosen such that, in the range [z1, z2], for all z, the relationship |E(z) / r(z)| < L holds. In this case, z denotes a point on the axis of symmetry in the range [z1, z2]. z1 is a point on the axis of symmetry which defines one limit of the range [z1, z2] and which, in the direction towards the first electrode, is at a distance of 0.35 times the minimum diameter of the aperture of the converter arrangement from the converter plane. z2 denotes a point on the axis of symmetry which defines the other limit of the range [z1, z2] and which, in the direction towards the second electrode, is at a distance of 0.35 times the minimum diameter of the aperture of the converter arrangement from the converter plane. E(z) denotes the field strength of the electric field at the point z. r(z) denotes the radius of curvature of the equipotential line of the electric field which passes through the point z in a plane containing the axis of symmetry. Finally, L denotes a limit value which is equal to 3.0 kV / mm 2 In the above relationship, the absolute value of E(z) / r(z) is used when compared to the limit value in order to be independent of the signs of E(z) and r(z).

[0014] The range [z1, z2] is the range of points on the axis of symmetry between the limits z1 and z2. By way of example, if a coordinate system has its origin placed at the intersection between the axis of symmetry and the surface of the object such that the z-axis of the coordinate system coincides with the axis of symmetry, the z-coordinate of the point z2 is smaller than the z-coordinate of the point z1. The converter plane, i.e. the plane orthogonal to the z-axis at which the aperture of the converter arrangement has its minimum diameter, is exactly halfway between z2 and z1.

[0015] The equipotential surface of the generated electric field is substantially rotationally symmetric about the axis of symmetry, because the apertures of the elements that substantially determine the electric field (specifically the transducer arrangement and the first and second electrodes) and the rest of the geometry near the axis are also substantially symmetric about the axis of symmetry. Therefore, the curvature of the equipotential surface of the electric field on the axis of symmetry can be described by the curvature of the equipotential line in any plane containing the axis of symmetry. The curvature of the equipotential line at a particular point can then be described by its radius of curvature, which is defined as the radius of the circle that intersects the potential line at that point. It should be noted that the apertures of the first and second electrodes and the transducer arrangement are advantageously circular. However, a deviation from a circular shape is permissible, provided that other requirements regarding the performance of the electron beam microscope are met. Deviations may be due to limitations during production or other reasons. The shape of the aperture can be, for example, polygonal, such as a dodecagon.

[0016] The requirement that the relation |E(z) / r(z)| ≤ L must hold within the range [z1, z2] dictates that the curvature of the equipotential surface along the axis of symmetry must be small in the region around and near the aperture of the transducer arrangement. The electron beam focused onto the object passes through the aperture of the transducer arrangement, which, as described above, advantageously has a relatively small diameter. If the equipotential lines of the electric field are significantly bent in the region around the aperture, the electric field will affect the focusing of the electron beam guided onto the object. Furthermore, if the electron beam is scanned across the object to record an electron microscope image, the electron beam guided onto the object will not pass precisely through the aperture of the transducer arrangement along the axis of symmetry in all operating modes of the electron beam microscope, even when using an oscillating beam method. The electric field with significantly bent equipotential lines will then further adversely affect the focusing of the electron beam guided onto the object. The curvature of the equipotential surface of the electric field that decelerates the electron beam can also be reduced by increasing the minimum diameter of the aperture of the transducer arrangement and applying the same voltage to the first electrode, the transducer arrangement, and the second electrode. However, the converter arrangement can only detect a small proportion of electrons generated at the object whose trajectories cross the converter plane at a small distance from the axis of symmetry. Therefore, conforming to the above relationship allows the diameter of the aperture in the converter arrangement to remain small, and allows for good focusing of the particle beam at the object even when a strong electric field slows down the electrons in the electron beam.

[0017] According to an exemplary embodiment, the electric field strength in the converter plane along the axis of symmetry is greater than or equal to 0.5 kV / mm or greater than or equal to 1.0 kV / mm. A favorable electric field strength in the converter plane along the axis of symmetry is in the range between 0.5 kV / mm and 5 kV / mm, particularly in the range between 1.0 kV / mm and 2.5 kV / mm.

[0018] According to an exemplary embodiment, the limiting value L is equal to 1.0 kV / mm. 2 Specifically, it equals 0.5 kV / mm. 2 This makes the curvature of the equipotential surface of the electric field even smaller in the region where the holes of the converter are arranged.

[0019] According to an exemplary embodiment, as observed in a cross-section containing the axis of symmetry, the converter arrangement has a wedge-shaped design whose extent in the direction parallel to the axis of symmetry increases with increasing distance from the axis of symmetry. In this cross-section, in other words, the converter arrangement has a shape that tapers towards the axis of symmetry. Since the entire surface of the converter arrangement is at the same potential, the equipotential surface of the electric field extends parallel to the surface directly adjacent to it. Therefore, the design of the converter body shape allows the path of the equipotential surface of the field to be influenced even at locations far from the surface of the converter arrangement. In particular, by means of the aforementioned wedge-shaped design of the converter body in the cross-section, the curvature of the equipotential surface in the region surrounding the converter plane can be kept small in order to obtain the aforementioned advantages.

[0020] The wedge-shaped design of the converter body in cross-section can be described by a wedge angle α, which can be measured in an annular region of the converter arrangement. This annular region has an inner diameter on both surfaces of the converter arrangement that is at most 3 mm larger than the minimum diameter of the bore in the converter arrangement. The annular region typically does not begin at the minimum diameter of the bore in the converter arrangement, as there the converter arrangement may have intentional rounding or rounding done simply for manufacturing engineering reasons. The outer diameter of the annular region can be 3 mm larger than the inner diameter. Within this annular region, as observed in cross-section, each of the two surfaces of the converter body extends linearly far enough that the angle between the directions of extension of these surfaces can be determined. The two surfaces of the converter body can extend at an angle relative to each other, in the range of 8° to 75°, or in the range of 10° to 65°, or in the range of 15° to 40°.

[0021] Furthermore, the aforementioned wedge-shaped design of the converter arrangement in the cross-section does not require symmetrical arrangement about the converter plane. According to an exemplary embodiment, a first surface of the converter arrangement (facing the first electrode) extends at a first angle relative to the converter plane, and another surface of the converter arrangement extends at a second angle relative to the converter plane in the annular region, wherein the second angle is at least 10° greater than the first angle. Specifically, the first surface may extend parallel to the converter plane in the annular region.

[0022] According to an exemplary embodiment, H ≤ 0.5 * Ds, and more particularly H ≤ 0.2 * Ds, holds true, where Ds is the maximum extent or outer diameter of the converter arranged in a direction orthogonal to the axis of symmetry, and H is the maximum extent of the converter arranged in a direction parallel to the axis of symmetry. This means that the converter has a relatively small extent arranged in the direction of the axis of symmetry and is thin in this direction.

[0023] According to an exemplary embodiment, the shape of the converter arrangement is thin, particularly in the region near the aperture. This can be described by the requirement that the converter arrangement at the aforementioned inner edge of the annular region has a range h in a direction parallel to the axis of symmetry, for which the following formula holds: h ≤ 0.7 * D, particularly h ≤ 0.5 * D and particularly h ≤ 0.25 * D, where D is the minimum diameter of the aperture of the converter arrangement.

[0024] According to an exemplary embodiment, the converter arrangement includes at least one scintillator body formed of a scintillator material that generates light using incident electrons. The electron beam microscope then further includes a photodetector configured to detect the light generated by the scintillator body and convert the light into an electrical signal.

[0025] According to other exemplary embodiments, the conversion arrangement includes a semiconductor detector comprising a semiconductor material in which incident electrons generate electrical signals, which are output by the semiconductor detector.

[0026] According to an exemplary embodiment, the converter arrangement is mounted on the first magnetic end or the second magnetic end of the objective lens. Attached Figure Description

[0027] The embodiments of the present invention will be described in more detail below with reference to the figures.

[0028] Figure 1 A schematic cross-sectional view of an electron beam microscope according to a first embodiment is shown.

[0029] Figure 2 by Figure 1 The partial view of the electron beam microscope shown depicts details of the objective lens and electron detector.

[0030] Figure 3 A schematic cross-sectional view of a partial view of an electron beam microscope according to a second embodiment is shown. Detailed Implementation

[0031] Figure 1 A schematic cross-sectional view of an electron beam microscope according to a first embodiment is shown. Figure 2This is a cross-sectional view of a portion of an electron beam microscope, showing magnified details of the objective lens and electron detector.

[0032] The electron beam microscope 1 includes an electron beam source 3 having an electron emitter 5 and an extraction electrode 7. A voltage is applied to the extraction electrode to extract electrons from the electron emitter 5, which form an electron beam 9. In this case, a potential U5 supplied by a potential supply system 11 is applied to the electron emitter 5. The potential supply system 11 is part of the controller 12 of the electron beam microscope 1. Before the electron beam 9 is incident on the object 19 to be examined, the electron beam... Figure 1 The electrons enter the bundle tube 15 at its upper first end 13, pass through the bundle tube, and exit at its lower second end 17. The bundle tube 15 includes a conductive inner side surface at a potential U1 provided by the potential supply system 11. For example, the potential difference U1 – U5 is 8 kV or greater, and therefore the electrons in the electron beam 9 pass through the bundle tube 15 rapidly between the first end 13 and the second end 17 with increased kinetic energy.

[0033] Object 19 is mounted on object holder 21, which is fed a potential U4 by potential supply system 11, so that object 19 is also at potential U4. The potential difference U4 – U5 defines the kinetic energy of the electrons of electron beam 9 incident on object 19. In this case, the difference U4 – U5 is less than the potential difference U1 – U5, and therefore the electrons of electron beam 9 are decelerated between the second end 17 of beam tube 15 and the surface of object 19, as will be explained below.

[0034] The electron beam microscope 1 also includes a magnetic objective lens 23 for focusing the electron beam 9 onto the object plane 25. Due to the object mount 21, the object 19 is positioned such that its surface substantially coincides with the object plane 25, and thus the electron beam 9 is focused on the object position 27 on the surface of the object 19.

[0035] The magnetic objective lens 23 has an axis of symmetry 29 and two solenoids 31 and 32 surrounding the axis of symmetry 29. The controller 12 feeds solenoid excitation currents to these solenoids to generate a magnetic field that focuses the electron beam. The solenoids 31 and 32 are surrounded by a magnetic yoke 33, which... Figure 1 The cross-section of the solenoid 31 contains a first magnetic end 35, a second magnetic end 37, and a third magnetic end 36. The yoke 33 and the magnetic ends 35, 37, and 36 are arranged in a ring around an axis of symmetry 29. The magnetic ends 35, 37, and 36 are arranged at a certain distance from each other, such that the current flowing in the solenoid 31 generates a symmetrical magnetic field about the axis of symmetry 29 around the magnetic ends 35 and 37.

[0036] The current flowing in solenoid 32 generates symmetrical magnetic fields about axis 29 around magnetic ends 37 and 36. These two magnetic fields are superimposed in the region near axis 29 to form a magnetic field that has a focusing effect on electron beam 9.

[0037] The electron beam microscope 1 includes beam deflectors 38 and 39, which are controlled by a controller 12 to deflect the electron beam 9 and thus move the object position 27 where the electron beam 9 is incident on the object 19 over a region of the object 19, for example, line by line, and thus scan this region of the object 19 using the electron beam 9.

[0038] Due to the interaction with object 19, electrons in the electron beam 9 incident on object 19 at object position 27 generate electrons that leave the object. A first electron detector 41 and a second electron detector 43 are provided to detect the generated electrons. When scanning object 19 using electron beam 9, the controller records the detection signal S1 generated by electron detector 41 and the detection signal S2 generated by electron detector 43 to ultimately generate an electron beam microscope image of the scanned area of ​​object 19.

[0039] By way of example, trajectory 45 represents an electron leaving object 19 at object position 27, which is detected by a first electron detector 41, and by way of example, trajectory 47 represents an electron leaving object 19 at object position 27, which is detected by a second electron detector 43.

[0040] The second electron detector 43 includes a scintillator body 49 formed of a scintillator material that generates light using incident electrons. The scintillator body 49 is attached to a light guide 51, which guides the light generated by the scintillator body 49, exiting the scintillator body 49 and entering the light guide 51, to the photodetector 53. By way of example, line 55 represents this light. The photodetector 53 generates electrical signals S2 from the detected light, and these electrical signals can be evaluated by the controller 12 of the electron beam microscope 1. These electrical signals represent the intensity of electrons generated by the electron beam 9 at object position 27 and emitted from object 19, which are emitted in a certain direction and with a certain kinetic energy such that they can be incident on the scintillator body 49. The scintillator body 49 and the light guide 51 have apertures 57 to allow the electron beam 9 to pass through.

[0041] The first electron detector 41 includes a transducer arrangement 60 and a photodetector 63. The transducer arrangement 60 includes a scintillator body 61 on which electrons 45 are incident, generating light 65. This light propagates within the scintillator body 61, exits at a light-exiting surface 67 into a vacuum, and then incidents on a light-incident surface 69 of the photodetector 63 for detection. The photodetector 63 generates electrical signals S1, which are guided out of the objective lens 23 via wires 70 laid in the objective lens 23 to the controller 12 of the electron beam microscope 1. The controller evaluates these electrical signals. These electrical signals S1 represent the intensity of electrons generated by the electron beam 9 at the object position 27 and emitted from the object 19, these electrons being emitted with a certain energy and in a certain direction, allowing them to incident on the scintillator body 61.

[0042] The transducer arrangement 60 is mounted on the first magnetic end 35 of the yoke of the magnetic objective lens 23. The photodetector 63 is mounted on the second magnetic end 37 of the yoke 33 of the magnetic objective lens 23. In this configuration, the light incident surface 69 of the photodetector faces away from the object plane 25 and towards the electron beam source 3.

[0043] The first electron detector 41 also includes a specular reflective surface 72 disposed on the second magnetic end 37 of the magnetic objective lens 23. The specular reflective surface 72 surrounds the electron beam 9 in a ring-like manner and symmetrically about the axis of symmetry 29. At the reflective surface 72, some of the light leaving the light exiting the scintillator body 61 from the light exiting surface 67 and not directly incident on the photodetector 63 is reflected in a certain way, such that the light reflected from the reflective surface 72 is incident on the light incident surface 69 of the photodetector 63 so that it can be detected by the photodetector. Figure 2 An exemplary beam 73 of this light is shown. The reflector 71 increases the probability that the photodetector 63 detects electrons 45 incident on the scintillator body 61.

[0044] The bundle tube 15 has a diameter D1 of 4.6 mm at its lower second end 17 near the converter arrangement 60 and is arranged in a manner centered about the axis of symmetry 29. Therefore, the lower end of the bundle tube 15 forms a first annular electrode 80, which is positioned relative to the converter arrangement 60 and has an aperture of diameter D1, and the first annular electrode is at a potential U1.

[0045] The bundle tube 15 is surrounded by an electrical insulator 81, which in turn is surrounded by a conductive sleeve 83. The scintillator body 61 of the converter arrangement 60 is fixed to the lower end 85 of the conductive sleeve. A potential U2 is fed to the sleeve by a potential supply device. A conductive layer is provided on the surface of the scintillator body 61 that is in electrical contact with the sleeve 83, such that the converter arrangement 60 is also at potential U2. The scintillator body 61 has an annular shape, which has a polygonal shape in a cross-section containing the axis of symmetry 29. The minimum diameter D of the hole in the annular shape is 1.2 mm. The plane orthogonal to the axis of symmetry 29 and containing the position of the hole with the minimum diameter D in the cross-section is called the converter plane 87.

[0046] The surface 89 of the scintillator body 61 (facing the first annular electrode 80) extends parallel to the transducer plane 87 and is 0.4 mm away from the first electrode 80 at a distance d1. The surface 92 of the scintillator body 61 (facing away from the surface 89 and near the axis of symmetry 29) extends at an angle α of 25° relative to the surface 89. Figure 2 In the illustration, the extent of the scintillator body in the direction parallel to the axis of symmetry 29 increases continuously with increasing distance from the axis of symmetry 29. The scintillator body has a wedge-shaped design in its region near the axis of symmetry 29. Angle α can be measured in a suitable annular region in which the two surfaces 89 and 92 extend sufficiently linearly in the cross-section to determine the angle. This annular region has an inner diameter Di and an outer diameter Do. The inner diameter Di can be up to 3 mm larger than the minimum diameter D of the aperture of the transducer arrangement 60, and the outer diameter Do can be 3 mm larger than the inner diameter Di. Because of the small extent of the scintillator body 61 in the direction parallel to the axis of symmetry 29 near the aperture of the scintillator arrangement 60, the shape of the scintillator body in its region near the axis of symmetry 29 is not only wedge-shaped but also pointed and thin. By way of example, at the inner edge with diameter Di, the extent of the scintillator body in the direction parallel to the axis of symmetry 29 is 0.1 mm.

[0047] Another surface 93 of the scintillator body 61 extends parallel to surface 89, and the other surface faces away from surface 89 of the scintillator body 61.

[0048] The conductive coating on the light-emitting surface 67 of the scintillator body 61 is transparent, while the other conductive coatings on surfaces 89, 92, and 93 of the scintillator body 61 are designed to reflect light. In this case, surfaces 92 and 93 are electron-receiving surfaces of the converter arrangement 60, i.e., surfaces on the converter arrangement 60 where electrons generated by the electron beam 9 are incident on these surfaces for detection, and the scintillator body 61 uses these electrons to generate light.

[0049] The range H of the scintillator body 61 and the transducer arrangement 60 in the direction of the axis of symmetry 29 is 1 mm, and the range Ds of the scintillator body 61 and the transducer arrangement 60 in the direction of the transducer plane 87 is 9.0 mm.

[0050] A photodetector 63 is embedded in a recess 77 disposed in the second magnetic pole 37. The photodetector 63 is at a potential U3, which is equal to the potential of the first magnetic pole 35 and the yoke 33 and is provided by the potential supply system 11. The inner edge 79 of the second magnetic pole 37 facing the axis of symmetry 29 extends symmetrically about the axis of symmetry 29. The second magnetic pole 37 at potential U3 thus forms a second annular electrode 97, the aperture of which is defined by the inner edge 79. The diameter D2 of the aperture of the second annular electrode 97 is 5 mm. The annular electrode 97 is 1.2 mm away from the transducer arrangement 60 in the direction of the axis of symmetry 29.

[0051] Figure 2 The cross-sectional view shows the equipotential lines 91 of the electric field generated by the first annular electrode 80, the transducer arrangement 60, and the second annular electrode 97 in the central region around the axis of symmetry 29, with U1 equal to 8.0 kV, U2 equal to 7.0 kV, and U3 equal to 0 V. The potential U4 of the object is also 0 V. In this case, the potential lines 91 in the cross-sectional view represent the equipotential surface of the electric field.

[0052] from Figure 2 It is evident that the curvature of the potential line 91 in the region of the aperture of the converter arrangement 60 is relatively small. To quantify this, the following procedure can be used: On the axis of symmetry 29, the range [z1, z2] between two points z1 and z2 on the axis of symmetry 29 is defined. Point z1 is located between the converter plane 87 and the electron beam source 3, and its distance from the converter plane 87 in the direction toward the first annular electrode 80 is 0.35 times the minimum diameter D of the aperture of the converter arrangement 60. Point z2 is located between the converter plane 87 and the object 19, and its distance from the converter plane 87 in the direction toward the second annular electrode 97 is also 0.35 times the minimum diameter D of the aperture of the converter arrangement 60. Within this range [z1, z2], the maximum value of |E(z) / r(z)| is then calculated, where E(z) is the electric field strength at point z, and r(z) is the radius of curvature of the equipotential line at point z in the plane containing the axis of symmetry. Figure 2 The drawing plane in the diagram. If the maximum value determined in this way is less than the limit value L, the curvature of the equipotential line 91 in the area of ​​the holes of the converter arrangement 60 is relatively small.

[0053] A value of 3.0 kV / mm can be selected. 2 or 1.0 kV / mm2 or 0.5 kV / mm 2 As the limit value L.

[0054] exist Figure 2 In this context, the maximum value occurs at an equipotential line with a potential of approximately 6.5 kV, and the radius of curvature of this equipotential line at the axis of symmetry 29 is approximately 3.4 mm. Therefore, the radius r of the circle intersecting the equipotential line at this point is approximately 3.4 mm. The electric field strength E(z) at this point is approximately 1.3 kV / mm. Therefore, in Figure 2 In this case, approximately 0.4 kV / mm was obtained. 2 The value is the maximum value of |E(z) / r(z)| within the range [z1, z2].

[0055] To calculate the characteristics of the electric field on the axis of symmetry 29 and determine the variables E(z) and r(z), a simulation program can be used, in which the geometry of the first ring electrode 80, the converter arrangement 60, and the second ring electrode 97, as well as the potential applied to these elements, are available.

[0056] Furthermore, this simulation program can be used to change the geometry of these components and the potential applied to them until the expression |E(z) / r(z)| obtains a particularly small value over the entire range [z1, z2].

[0057] Simulation programs suitable for these calculations are available from Comsol Multiphysics GmbH, Göttingen, Germany (postcode 37073), under the trade name "COMSOL".

[0058] The following describes another embodiment of an electron beam microscope with reference to the accompanying drawings. In this embodiment, it is similar to the referenced one in terms of structure or function. Figure 1 Components in the explained embodiments are labeled with the same reference numerals but with additional letters to allow for differentiation. For an understanding of the structure and function of these components, refer to the entire foregoing description.

[0059] Figure 3 A partial view of the electron beam microscope according to the second embodiment is shown in cross-section.

[0060] Figure 3 The electron beam microscope 1a shown has the same characteristics as the reference microscope. Figure 1 and Figure 2 The electron beam microscope 1a has a similar structure to the electron beam microscope 1a. Figure 1 and Figure 2The electron beam microscope 1 differs only in the configuration of the transducer arrangement 60a used to detect electrons generated at the object. Therefore, the electron beam microscope 1a has an electron beam source, a beam tube 15a, an objective lens 23a, and an object holder, as explained above. The objective lens 23a again has a magnetic yoke with a first magnetic end and a second magnetic end 37a. A first annular electrode 80a with a diameter D1 of 5 mm is formed at the lower end 17a of the beam tube 15a. The second magnetic end 37a, symmetrically arranged about the axis of symmetry 29a, has an inner edge 79a with a diameter D2 of 6 mm, resulting in the formation of a second annular electrode 97a.

[0061] A converter arrangement 60a is positioned between a first annular electrode 80a and a second annular electrode 97a along an axis of symmetry 29a. The converter arrangement 60a has an aperture centered about the axis of symmetry 29a with a minimum diameter D of 1.2 mm. The converter arrangement 60a includes a semiconductor detector 62 arranged in the converter plane. Electrons 45a generated at the object are incident on this semiconductor detector and generate electrical signals in the semiconductor material of the semiconductor detector 62. These electrical signals are transmitted by the semiconductor detector 62 via… Figure 3 The line output, not shown, is sent to the controller of the electron beam microscope 1a. Figure 3 Similarly, no mounting for the converter arrangement 60a is shown between the first annular electrode 80a and the second annular electrode 97a. However, the semiconductor detector 62 can be mounted on, for example, the second magnetic pole 37a using a suitable element made of an insulating material. In this case, the mounting for the semiconductor detector 62 can have a rounded element at the lower end 85 of the sleeve 83 for mounting the scintillator body 60, such as... Figure 2 The example illustrates how to avoid flashover in strong electric fields.

[0062] The distance d1 between the first annular electrode 80a and the semiconductor detector in the direction of the axis of symmetry 29a is 0.6 mm. The distance d2 between the semiconductor detector 62 and the second annular electrode 97a is 0.8 mm. As in the first embodiment, a potential U1 of 8 kV is fed to the first annular electrode 80a. As in the first embodiment, a potential U3 of 0 kV is also fed to the second annular electrode 97a. The potential fed to the object is also 0 V. A potential U2 of 4.5 kV is fed to the converter arrangement 60a. This potential can be fed to the converter arrangement 60a via the leads of the semiconductor detector 62. The semiconductor detector 62 arranged in the converter plane 87a is particularly thin, and its thickness H in the direction of the axis of symmetry 29a is 0.3 mm. The range Ds of the semiconductor detector 62 in the direction orthogonal to the axis of symmetry 29a is 8 mm.

[0063] In the region near the axis of symmetry 29a Figure 3 Also shown is the equipotential line 91a of the electric field generated by the first annular electrode 80a, the transducer arrangement 60a, the second annular electrode 97a, and the object, as well as the potentials U1, U2, U3, and U4 fed to these elements. Clearly, near the transducer plane 87a, the equipotential line with an electric field strength of 4.5 kV has almost no curvature. Therefore, in Figure 3 The condition |E(z) / r(z)| ≤ 0.5 kV / mm is reliably satisfied under the conditions shown in the figure. 2 .

[0064] In summary, the electron beam microscope disclosed herein includes: an electron beam source 3, a magnetic objective lens 23 with magnetic poles 35 and 37, a scintillator 61 with an aperture diameter D, a first electrode 80, a second electrode 97, and a potential supply device 11 for these elements. The aperture diameter D of the scintillator is smaller than the aperture diameter of the second electrode 97. Furthermore, |E(z) / r(z)| ≤ L holds for all points z within the range [z1, z2] near the scintillator on the axis of symmetry 29. In this case, E(z) is the electric field strength at point z, r(z) is the radius of curvature of the equipotential line 91 at point z, and L is equal to 3.0 kV / mm. 2 .

Claims

1. An electron beam microscope, comprising: an electron beam source (3) configured to generate an electron beam (9); a magnetic objective (23) for generating a magnetic field that focuses the electron beam (9), wherein the magnetic objective (23) has a solenoid (31) and a magnetic yoke (33) having a first magnetic pole end (35) and a second magnetic pole end (37), each extending around a symmetry axis (29); a converter arrangement (60) having a circular aperture that is centered with respect to the symmetry axis (29) and has its smallest diameter (D) in a converter plane (87) orthogonal to the symmetry axis (29), and comprising at least one converter that generates light (65) or an electrical signal using incident electrons (45); a first electrode (80) having a circular aperture centered with respect to the symmetry axis (29) on a side facing the converter arrangement (60) and arranged closer to the electron beam source (3) than the converter arrangement (60); a second electrode (97) having a circular aperture centered with respect to the symmetry axis (29) on a side facing the converter arrangement (60) and arranged further away from the electron beam source (3) than the converter arrangement (60); and a potential supply (11) configured to feed mutually different potentials (Ul, U2, U3) two by two to the first electrode (80), the second electrode (97), and the converter arrangement (60) in order to generate an electric field that decelerates electrons of the electron beam (9); wherein the smallest diameter (D) of the aperture of the converter arrangement (60) is smaller than a diameter (D2) of the aperture of the second electrode (97); wherein |E(z) / r(z)| < L holds for all z within a range [zl, z2], wherein z is a point on the symmetry axis (29); zl is a point on the symmetry axis (29) that is 0.35 times the smallest diameter (D) of the aperture of the converter arrangement (60) away from the converter plane (87) in a direction towards the first electrode (80); z2 is a point on the symmetry axis (29) that is 0.35 times the smallest diameter (D) of the aperture of the converter arrangement (60) away from the converter plane (87) in a direction towards the second electrode (97); E(z) is a field strength of the electric field at point z; r(z) is a radius of curvature of an equipotential line (91) of the electric field at point z; and L is equal to 3.0 kV / mm 2 the limit value of 3.0 kV / mm.

2. The electron beam microscope of claim 1, wherein L is equal to 1.0 kV / mm 2 , in particular equal to 0.5 kV / mm 2 .

3. An electron beam microscope, comprising: an electron beam source (3) configured to generate an electron beam (9); a magnetic objective (23) for generating a magnetic field that focuses the electron beam (9), wherein the magnetic objective (23) has a solenoid (31) and a magnetic yoke (33) having a first magnetic pole end (35) and a second magnetic pole end (37), each extending around a symmetry axis (29); a converter arrangement (60) having a circular aperture which is centered with respect to the symmetry axis (29) and has its smallest diameter (D) in a converter plane (87) orthogonal to the symmetry axis (29), and comprising at least one converter which generates light (65) or electrical signals using incident electrons (45); a first electrode (80) having a circular aperture centered with respect to the symmetry axis (29) on a side facing the converter arrangement (60) and arranged closer to the electron beam source (3) than the converter arrangement (60); a second electrode (97) having a circular aperture centered with respect to the symmetry axis (29) on a side facing the converter arrangement (60) and arranged further away from the electron beam source (3) than the converter arrangement (60); and a potential supply (11) configured to feed mutually different potentials (Ul, U2, U3) two by two to the first electrode (80), the second electrode (97) and the converter arrangement (60) in order to generate an electric field which decelerates the electrons of the electron beam (9); wherein the smallest diameter (D) of the aperture of the converter arrangement (60) is smaller than the diameter (D2) of the aperture of the second electrode (97); wherein the converter arrangement (60) has a wedge-shaped design as observed in a cross-section containing the symmetry axis (29) which increases in extent in a direction parallel to the symmetry axis (29) with increasing distance from the symmetry axis (29).

4. Electron beam microscope according to claim 3, wherein the converter arrangement (60) has a first surface (89) facing the first electrode (80) and a second surface (92) facing the second electrode (97) in the cross-section; wherein the first and second surfaces (89, 92) each have an annular region, wherein the annular region has an inner diameter (Di) which is at most 3 mm larger than the smallest diameter (D) of the aperture of the converter arrangement (60) and an outer diameter (Do) which is 3 mm larger than the inner diameter (Di); wherein the first surface (89) and the second surface (92) extend in the annular region relative to each other at an angle which is larger than 8° and smaller than 75°, in particular larger than 10° and smaller than 65°, and in particular larger than 15° and smaller than 40° as observed in the cross-section.

5. Electron beam microscope according to claim 4, wherein the first surface (89) extends in the annular region relative to a plane orthogonal to the symmetry axis (29) at a first angle as observed in the cross-section; wherein the second surface (92) extends in the annular region relative to a plane orthogonal to the symmetry axis (29) at a second angle as observed in the cross-section; and wherein the second angle is at least 10° larger than the first angle.

6. Electron beam microscope according to claim 5, wherein the first surface (89) extends in the annular region parallel to a plane orthogonal to the symmetry axis (29).

7. The electron beam microscope according to any one of claims 1 to 6, wherein H ≤ 0.5 * Ds, in particular H ≤ 0.2 * Ds, holds, wherein Ds is a maximum extent of the converter arrangement (60) in a direction orthogonal to the symmetry axis (29); and H is a maximum extent of the converter arrangement (60) in a direction parallel to the symmetry axis (29).

8. The electron beam microscope according to any one of claims 1 to 7, wherein at a position (Di) of the converter arrangement (60) at a distance from the symmetry axis (29) that is 0.1 mm or 0.3 mm greater than half of a minimum diameter (D) of an aperture of the converter arrangement (60), h ≤ 0.7 * D, in particular h ≤ 0.5 * D and in particular h ≤ 0.25 * D, holds, wherein D is a minimum diameter of an aperture of the converter arrangement (60); and h is an extent of the converter arrangement (60) in a direction parallel to the symmetry axis (29).

9. The electron beam microscope according to any one of claims 1 to 8, wherein the converter arrangement (60) comprises at least one scintillator body (61) formed of a scintillator material that generates light (65) using incident electrons (45).

10. The electron beam microscope according to any one of claims 1 to 9, wherein, the converter arrangement (60) is mounted on the first or second pole end (35, 37).

11. The electron beam microscope according to any one of claims 1 to 10, further comprising a light detector (63) configured to detect light (65) generated by the converter arrangement (60) and to convert said light into an electrical signal (SI).

12. The electron beam microscope according to claim 11, wherein, the light detector is mounted on the first or second pole end (35, 37).

13. The electron beam microscope according to any one of claims 1 to 8, wherein, the converter arrangement (60a) comprises at least one semiconductor detector (62).

14. The electron beam microscope according to any one of claims 1 to 13, wherein at least one of the following relationships is fulfilled: (U2 - U3) ≤ (Ul - U3); (U2 - U3) ≥ 0.3 * (Ul - U3); (U2 - U3) ≥ 2 kV; and (U2 - U3) ≤ 15 kV; wherein Ul is a potential fed to the first electrode (80), U2 is a potential fed to the second electrode (97), and U3 is a potential fed to the converter arrangement (60).

15. The electron beam microscope according to claim 14, wherein at least one of the following relationships is fulfilled: (U2 - U3) ≤ 0.9 * (Ul - U3); (U2 - U3) ≥ 0.5 * (Ul - U3); (U2 - U3) ≥ 3 kV; (U2 - U3) ≤ 9 kV.

16. The electron beam microscope according to claim 14 or 15, further comprising an object mount (21) for mounting an object (19) to be inspected; wherein, the potential supply device (11) is configured to feed a potential to the object mount (21); wherein the following holds: | U4 - U3 | ≥ 2 kV; wherein U4 is the potential fed to the object mount (21).

17. The electron beam microscope according to any one of claims 1 to 16, wherein, a smallest diameter (D) of the aperture of the converter arrangement (60) in the scintillator plane (87) is less than 2.4 mm and more than 0.6 mm.

18. The electron beam microscope according to any one of claims 1 to 17, wherein, a smallest diameter (D1) of the aperture of the first electrode (80) is more than twice the diameter (D) of the aperture of the converter arrangement (60) in the converter plane (87).

19. The electron beam microscope according to any one of claims 1 to 18, wherein a diameter (D2) of the aperture of the second electrode (97) is more than twice the diameter (D) of the aperture of the converter arrangement (60) in the converter plane (87).

20. The electron beam microscope according to any one of claims 1 to 18, wherein a distance (d1) between the first electrode (80) and the converter arrangement (60) as measured in the direction of the symmetry axis (29) is less than a distance (d2) between the second electrode (97) and the converter arrangement (60).

21. The electron beam microscope according to claim 20, wherein, a distance (d1) between the first electrode (80) and the converter arrangement (60) is more than 0.3 mm less than a distance (d2) between the second electrode (97) and the converter arrangement (60).

22. The electron beam microscope according to any one of claims 1 to 21, wherein at a position arranged on the symmetry axis (29) and within the converter plane (87), one of the following relationships holds: 0.5 kV / mm ≤ E; 0.5 kV / mm ≤ E ≤ 5 kV / mm; and 1.0 kV / mm ≤ E ≤ 2.5 kV / mm.

23. The electron beam microscope according to any one of claims 1 to 22, wherein, at a position arranged on a surface of the converter arrangement (60) facing the second electrode (97) and at a distance from the symmetry axis which is more than 1.0 mm than half the smallest diameter (D) of the aperture of the converter arrangement (60), the following holds: E ≥ 0.5 kV / mm, in particular E ≥ 1.0 kV / mm and in particular E ≥ 2.0 kV / mm.

24. A method for operating an electron beam microscope, in particular in combination with the electron beam microscope according to any one of claims 1 to 23, wherein, The electron beam microscope comprises: an electron beam source; a magnetic objective lens having a solenoid and a magnetic yoke having a first magnetic pole end and a second magnetic pole end, each magnetic pole end extending around a symmetry axis; the magnetic yoke is arranged such that the symmetry axis is parallel to a longitudinal axis of the electron beam source. a converter arrangement having a circular aperture that is centered with respect to the symmetry axis and has its smallest diameter in a converter plane that is orthogonal to the symmetry axis, and comprising at least one converter; a first electrode having a circular aperture on a side facing the converter arrangement that is centered with respect to the symmetry axis and arranged closer to the electron beam source than the converter arrangement; a second electrode having a circular aperture on a side facing the converter arrangement that is centered with respect to the symmetry axis and arranged further away from the electron beam source than the converter arrangement; and a potential supply; wherein the smallest diameter of the aperture of the converter arrangement is smaller than the diameter of the aperture of the second electrode; and wherein the method comprises: generating a magnetic field using the objective; feeding pairwise mutually different potentials to the first electrode, the second electrode, and the converter arrangement so as to generate an electric field; generating an electron beam using the electron beam source; focusing the generated electron beam using the magnetic field; decelerating electrons of the electron beam using the electric field; directing the decelerated electrons of the electron beam onto an object; generating a signal using the converter using electrons generated at the object by electrons of the electron beam that are directed onto the object; capturing the generated signal; wherein |E(z) / r(z)| < L holds for all z in the range [z1, z2]; wherein z is a point on the symmetry axis; z1 is a point on the symmetry axis that is 0.35 times the smallest diameter of the aperture of the converter arrangement further away from the converter plane in the direction towards the first electrode; z2 is a point on the symmetry axis that is 0.35 times the smallest diameter of the aperture of the converter arrangement further away from the converter plane in the direction towards the second electrode; E(z) is the field strength of the electric field at point z; r(z) is the radius of curvature of an equipotential line of the electric field that passes through point z in a plane containing the symmetry axis; and L is equal to 3.0 kV / mm 2 the limit value of 3.0 kV / mm.

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