Counter pole with permanent magnet

Abstract

To provide an improved immersion lens.SOLUTION: A charged particle beam system may include a vacuum chamber, a sample holder for holding a sample in the vacuum chamber, and a charged particle column. The charged particle column may include a charged particle source for generating a beam of charged particles along an optical axis, and a magnetic immersion lens for focusing the beam of charged particles, and the magnetic immersion lens may include a first lens pole placed adjacent to the first surface of the sample, an excitation coil surrounding the first lens pole, and a counter pole placed adjacent to the second surface of the sample. The counter pole includes one or more magnets placed on the counter pole.SELECTED DRAWING: Figure 2

Description

Technical Field

[0001] The present disclosure relates to an apparatus and method for an improved magnetic immersion lens.

Background Art

[0002] Charged particle beam systems are used in a variety of applications such as the manufacture, repair, and inspection of small devices such as integrated circuits, magnetic recording heads, and photolithography masks. Dual beam systems typically include a scanning electron microscope (SEM) that can provide a high-resolution image with minimal damage to the target, and an ion beam system such as a focused beam system or a shaped beam system that can be used for substrate processing (such as milling) and imaging.

[0003] Generally, the final lens of an SEM is a charged particle beam (CBP) lens (e.g., a magnetic immersion lens) that generates a magnetic field. The intensity of such an immersion lens is limited by magnetic circuit saturation and the magnetic flux source (such as a coil). Magnetic saturation is a state that is reached when the magnetization of a material cannot be increased any further by continuously increasing the applied external magnetic field, so the total magnetic flux density levels off. Therefore, improvements to immersion lenses are still being sought.

Summary of the Invention

[0004] In a representative embodiment, a charged particle beam system can include a vacuum chamber, a sample holder for holding a sample within the vacuum chamber, a charged particle column including a charged particle source for generating a beam of charged particles along an optical axis, and a magnetic immersion lens for focusing the beam of charged particles. The magnetic immersion lens can include a first lens pole disposed adjacent to a first surface of the sample, an excitation coil surrounding the first lens pole, and a counter pole configured to be disposed adjacent to a second surface of the sample, the counter pole including one or more magnets disposed on a surface of the counter pole.

[0005] In some embodiments, the surface of the counter pole is the first surface, and one or more additional magnets are disposed on the second surface of the counter pole.

[0006] In some embodiments, the counter pole includes one or more recesses, and each magnet is disposed within a respective recess. In some embodiments, the recesses include tracks, and one or more magnets are slidable within the tracks, such that the magnets can be positioned relative to the optical axis. The tracks can extend radially inward from the outer edge of the counter pole towards the optical axis and / or circumferentially about the optical axis. In other embodiments, one or more magnets can be coupled to the counter pole via an adhesive.

[0007] The counter pole can be attached to a positioning system configured to enable movement of the counter pole between a first position and a second position within a vacuum chamber, and the counter pole is inactive at the first position or the second position. The counter pole can further include an aperture and a detector, and the detector is disposed within or below the aperture.

[0008] In some embodiments, the magnets can be arranged such that they compensate for the asymmetry of the system. In other embodiments, the magnets can be arranged such that they introduce asymmetry into the system.

[0009] In another representative embodiment, the system can be a dual-beam system including a sample holder for holding a sample, an ion beam column configured to direct an ion beam towards the sample, a charged particle source for generating a beam of charged particles along an optical axis, and a charged particle column including a magnetic immersion lens for focusing the beam of charged particles. The magnetic immersion lens can include a first lens pole disposed adjacent to a first surface of the sample and a second lens pole disposed adjacent to a second surface of the sample, and the second lens pole can include one or more magnets. In some embodiments, the magnetic immersion lens can be coupled to a control unit.

[0010] A method of using the dual-beam system can include arranging magnets around the optical axis to create an asymmetry within the system.

[0011] The foregoing and other objects, features, and advantages of the present disclosure will become more apparent from the following detailed description when taken in conjunction with the accompanying drawings.

Brief Description of the Drawings

[0012]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Modes for Carrying Out the Invention

[0013] Introduction Charged particle microscopy is a well-known and increasingly important technique for imaging microscopic objects, particularly in the form of electron microscopy. So far, the basic types of electron microscopes have evolved into many well-known devices such as transmission electron microscopes (TEMs), scanning electron microscopes (SEMs), and scanning transmission electron microscopes (STEMs), and further, for example, "machining" focused ion beams (FIBs) that enable assisting actions such as ion beam milling or ion beam induced deposition (IBID) have been further used to evolve into various auxiliary devices such as so-called "dual-beam" devices (e.g., FIB-SEM).

[0014] In an SEM, by irradiating a scanning electron beam onto a substrate, "auxiliary" radiation from the substrate is generated in the form of secondary electrons, backscattered electrons, transmitted electrons, X-rays, and cathodoluminescence (infrared, visible, and / or ultraviolet photons). For example, one or more components of this auxiliary radiation can be detected and used for imaging. Instead of using electrons as the irradiation beam, charged particle microscopy can also be performed using other species of charged particles. In this regard, the term "charged particle" should be broadly interpreted to include, for example, electrons, positive ions (e.g., Ga or Xe ions), negative ions, protons, and positrons. Note that in addition to imaging and local surface modification (e.g., milling, etching, deposition, etc.), charged particle microscopes can also have other functionalities such as performing spectroscopy and examining diffraction patterns.

[0015] In some examples, the ion beam component is used to mill relevant spots in a test substrate such as a silicon substrate. As used herein, "image" refers to a visual image, as well as a digital or other stored representation of a visual image.

[0016] Generally, the final lens of an SEM is a charged particle beam (CBP) lens such as an electrostatic lens, a magnetic lens, or a composite lens. In the case of a magnetic immersion lens, the strength of such an immersion lens and, often, the image quality are limited by the saturation of the magnetic circuit and the magnetic flux source (e.g., a coil). Using a permanent magnet in combination with the coil of a CBP lens can add magnetic flux to the magnetic circuit or introduce or correct system asymmetries to improve the resolution of the lens.

[0017] As used herein, the singular forms “a,” “an,” and “the” include plural referents unless the context clearly dictates otherwise. Further, the term “includes” is used in the sense of “comprises.” Further, the term “coupled” does not necessarily exclude the presence of intermediate elements between the coupled items.

[0018] The systems, devices, and methods described herein should not be construed as being in any way limiting. Instead, the present disclosure is directed to all novel and non-obvious features and aspects of the various disclosed embodiments, alone and in various combinations and sub-combinations with each other. The disclosed systems, methods, and devices are not limited to any particular aspect or feature or combination thereof, and the disclosed systems, methods, and devices are not required to have any one or more particular advantages or to solve any particular problems. Any theory of operation is for the purpose of facilitating explanation, but the disclosed systems, methods, and devices are not limited to such theory of operation.

[0019] Although some operations of the disclosed method are described in a particular order for convenience, it is to be understood that this description method includes permutations unless a particular order is required by the specific words described below. For example, the operations described sequentially can, in some cases, be permuted or executed simultaneously. Further, for simplicity, the accompanying figures may not show the various ways in which the disclosed system, method, and apparatus can be used with other systems, methods, and apparatuses. Additionally, this description sometimes uses terms such as "generate" and "provide" to describe the disclosed method. These terms are a high-level abstraction of the actual operations performed. The actual operations corresponding to these terms vary depending on the particular implementation and are readily recognizable to those skilled in the art. In some examples, a value, procedure, or apparatus is referred to as "lowest", "best", "minimum", etc. Such expressions are intended to indicate that a selection is possible from among many available functional options, and such a selection need not be better, smaller, or otherwise preferable to other selections. Examples are described with reference to directions indicated as "above", "below", "upper", "lower", etc. These terms are used for convenience of description and do not imply a particular spatial orientation.

[0020] Example 1 FIG. 1 shows a representative embodiment of a dual beam system 100 that includes a scanning electron microscope (SEM) 102 and an ion beam column 104. The SEM 102 may include one or more charged particle beam (CPB) lenses such as a condenser lens 116 and an objective lens 106. In some embodiments, one or more CPB lenses may be magnetic lenses, and in particular, the objective lens 106 may be a magnetic objective lens (e.g., a magnetic immersion objective lens). The ion beam column is arranged to provide a focused ion beam (FIB) to the sample S, and the SEM 102 is positioned to generate an image of the sample S. The SEM 102 and the ion beam column 104 can be attached to a vacuum chamber 108 that houses a movable substrate holder 110 for holding the sample S, and the vacuum chamber 108 can be evacuated using a vacuum pump (not shown). The substrate holder 110 is movable in the X-Y plane as shown with respect to a coordinate system 150 in which the Y-axis is perpendicular to the plane of the drawing. Also, the substrate holder can be further moved in the vertical direction (along the Z-axis) to correct for variations in the height of the sample S.

[0021] In some embodiments, the SEM 102 can be disposed vertically above the sample S and used to image the sample S, and the ion beam column 104 can be disposed at an angle and used to machine and / or process the sample S. FIG. 1 shows an exemplary orientation of the SEM 102 and the ion beam column 104.

[0022] The SEM 102 can include an electron source 112 and is configured to manipulate the "raw" emission beam from the electron source 112 and, based thereon, perform operations such as focusing, aberration reduction, trimming (using apertures), filtering, etc. The SEM 102 can generate a beam 114 of input charged particles (e.g., an electron beam) propagating along a particle optical axis 115. One or more CPB lenses of the SEM column 102, such as the condenser lens 116 and the objective lens 106, focus the beam 114 onto the sample S. In some embodiments, the SEM 102 can be provided with a deflection unit 118 configured to steer the beam 114. For example, the beam 114 can be steered in a scanning operation (e.g., a raster scan or a vector scan) across the sample to be investigated.

[0023] In some embodiments, as shown in FIG. 1, the dual-beam system 100 can further include a magnetic field generating coil 107 arranged to provide an additional magnetic field to create an additional immersion magnetic lens, thereby improving the resolution of the SEM optical system.

[0024] The dual-beam system 100 can further include a computer processing device and / or a controller 128 for controlling, among other things, the deflection unit 118, the CPB lenses 106, 116, and a detector (not shown), and for displaying information collected from the detector on a display unit. In some cases, a control computer 130 is provided to establish various excitations, record image data, and generally control the operation of both the SEM and the FIB.

[0025] The ion beam column 104 can include an ion source (e.g., plasma source 120) and an ion beam optical system 122. In the illustrated embodiment, the ion beam column 104 is a plasma focused ion beam (PFIB), but in other embodiments, the ion beam column 104 can be a standard focused ion beam (FIB) having a liquid metal ion source (LMIS), or other ion sources compatible with a focused ion beam column. The ion beam column 104 can generate and / or direct (steer) an ion beam 124 along an ion optical axis 125. As described above, the ion column 104 can be used to perform imaging, processing, and / or machining operations on a substrate, such as incising, milling, etching, deposition, etc.

[0026] In embodiments where the ion beam is a PFIB, the ion source 120 can be fluidly coupled to a plurality of gases via a gas manifold 126 that includes gas sources 142A - 142D coupled to the ion source 120 by respective valves 141A - 141D. A valve 140 is installed to selectively couple the gas from the gas manifold 126 to the ion source 120. Exemplary gases include, but are not limited to, xenon, argon, oxygen, and nitrogen as shown in FIG. 1. During operation of the ion source 120, gas can be introduced where it is charged or ionized, thereby forming a plasma. Next, the ions extracted from the plasma can be accelerated through the ion beam column 104 to form an ion beam.

[0027] Example 2 In another representative embodiment, the system 200 can include a scanning electron microscope (SEM) 202 attached to a vacuum chamber 204. The vacuum chamber 204 can accommodate a first movable stage 206 for holding a sample S. The sample S can be introduced through a load lock 208. The vacuum chamber 202 can be evacuated using a vacuum pump (not shown).

[0028] The SEM202 can include one or more CPB lenses such as a condenser lens 210 and an objective lens 212. In some embodiments, the one or more CPB lenses can be magnetic lenses, and in particular, the objective lens 212 can be a magnetic objective lens (e.g., a magnetic immersion objective lens). In some embodiments, the SEM202 can be disposed vertically above the sample S and can be used to image the sample S. The SEM202 can include an electron source 214 and can be configured to manipulate the "raw" radiation beam from the electron source 214 and perform operations such as focusing, aberration reduction, trimming (using an aperture), filtering, etc. based thereon. The SEM202 can generate a beam 216 of input charged particles (e.g., an electron beam) propagating along the particle optical axis 218. The SEM202 generally includes one or more CPB lenses such as a condenser lens 210 and an objective lens 212 to focus the beam 216 onto the sample S. In some embodiments, the SEM202 can be provided with a deflection unit 220 configured to manipulate the beam 216. For example, the beam 216 can be manipulated in a scanning operation (e.g., a raster scan or a vector scan) across the sample S to be investigated. The objective lens 212 can include an excitation coil 222 surrounding the first pole 224 of the lens 212 to generate a focusing magnetic field in the gap between the first lens pole 224 and the sample S.

[0029] The system 200 can further include, among other things, a computer processing device and / or a controller 250 for controlling the deflection unit 220, the charged particle beam (CPB) lenses 210, 212, and the detector, and for displaying the information collected from the detector on a display unit 252 (e.g., a computer, a mobile device, etc.).

[0030] As described above, the objective lens 212 is a magnetic immersion objective lens that includes an excitation coil 222. However, the intensity of the magnetic immersion lens 212 is limited by the maximum magnetomotive force generated by the coil 222. The disclosed embodiments provide a solution to this problem by applying a magnetomotive force to the lens 212 via a second lens pole and one or more permanent magnets that generate an additional magnetic field. Such embodiments can be used in STEM operation (e.g., high-resolution, high-voltage STEM) and / or in conventional SEM mode when using secondary electrons or backscattered electrons.

[0031] The system 200 can include a second movable stage 226 that includes a second lens pole 228 (also referred to as a counter pole 228) disposed adjacent to the substrate S (e.g., under the substrate in the orientation shown in FIG. 2). The first stage 206 can be a stage such as used in transmission electron microscopy (TEM), and the second stage 226 can be a conventional SEM or dual-beam stage (see, e.g., FIG. 5). The counter pole 228 can include a central aperture 230 and a detector 232 disposed below the aperture 230. When the sample S is sufficiently thin (e.g., preferably less than 50 nm for semiconductor materials and less than 100 nm for biological materials), electrons can travel through the sample S and be detected by the detector 232. The angular distribution of the scattering angles of the detected electrons can provide information about the sample S. In some embodiments, the detector 232 is, for example, a high-angle annular dark-field detector (HAADF detector), an annular dark-field detector (ADF detector), and / or a bright-field detector.

[0032] One or more magnets 234 can be coupled to the counterpole to improve the performance of the magnetic immersion objective lens 212 (e.g., improve the resolution). The magnet 234 can be a permanent magnet (e.g., a permanent neodymium magnet or a permanent samarium cobalt magnet). The permanent magnet 234 creates its own permanent magnetic field with a given excitation. In some particular embodiments, the addition of the permanent magnet 234 to the counterpole 228 is equivalent to adding an excitation of about 1500 AT (ampere-turns) to the coil 222.

[0033] In other particular embodiments, the addition of the permanent magnet can achieve a higher beam energy by increasing the strength of the magnetic field. The magnet adds magnetic flux to the magnetic circuit and increases the strength of the magnetic field. As the magnetic field increases, the use of a higher energy electron beam becomes possible.

[0034] Further details of the advantages of permanent magnets in electron microscopes can be found, for example, in Principles of Electron Optics Volume Two: Applied Geometrical Optics, by Hawkes et al., Academic Press (2 nd Ed) (2017), which is hereby incorporated by reference in its entirety.

[0035] In other embodiments, each magnet 234 can be a magnet that includes its own energized coil.

[0036] In some particular embodiments, the sample S can be placed on the surface of the counterpole 228. The magnet 234 can be arranged laterally adjacent to the sample, enabling magnetic immersion in a system without an immersion lens coil.

[0037] The magnet 234 can be arranged centered on the optical axis 218. In some embodiments, the magnet 234 can be arranged symmetrically about the axis 218. In other embodiments, for example, to introduce a desired asymmetry or correct an undesired asymmetry of other components of the optical system, the magnet 234 can be placed asymmetrically about the axis 218. The magnet 234 can be arranged on one or more surfaces of the counter pole 228. For example, in the illustrated embodiment, the magnet 234 is arranged on the first surface 236 of the counter pole adjacent to the sample S (e.g., the upper surface in the orientation shown in FIG. 2). In other embodiments, instead of or in addition to arranging the magnet 234 on the first surface 236, one or more magnets 234 can be arranged on the second surface 237 of the counter pole (e.g., the lower surface in the orientation shown in FIG. 2). In the illustrated embodiment, the magnet 234 is arranged under the sample S (in the direction shown in FIG. 2), but in other embodiments, the magnet 234 can be arranged laterally adjacent to the sample S. In still other embodiments, the magnet 234 can be placed on top of the sample in the orientation shown in FIG. 2.

[0038] In the illustrated embodiment, only a single magnet 234 arranged at each circumferential position around the optical axis is shown, but in other embodiments, the magnets 234 can be stacked on top of each other such that one or more magnets can be arranged at selected circumferential positions. In some such embodiments, the magnets can be coupled to each other using, for example, an adhesive. In other embodiments, the magnets can have mating shapes.

[0039] Referring to FIG. 3, which shows a top view of the counter pole 228, the surface 236 of the counter pole 228 (e.g., the top surface in the orientation shown in FIG. 2) disposed adjacent to the sample S can include one or more grooves or recesses 238 in which the magnet 234 can be disposed. In some embodiments, each recess 238 can be configured (e.g., sized and shaped) to prevent the magnet 234 from inadvertently moving relative to the counter pole 228 (e.g., during movement of the counter pole 228), such that the magnet 234 remains in a desired position relative to the optical axis 218 and / or maintains a selected configuration. In some embodiments, each recess can have a shape corresponding to the shape of the respective magnet. For example, in the illustrated embodiment, each recess 238 has a circular cross-sectional shape corresponding to the circular shape of the magnet 234.

[0040] In other embodiments, as shown in FIG. 5, the magnet 234 can be disposed directly on the first surface 236 of the counter pole 228 and can be coupled to the surface, for example, using an adhesive.

[0041] Referring again to FIG. 3, as illustrated in some embodiments, the recesses 238 can be spaced equidistantly around the optical axis 218 such that they form a symmetric pattern. In other embodiments, the recesses 238 can be arranged asymmetrically about the optical axis 218. The magnets 234 can be arranged symmetrically or asymmetrically within the recesses 238. For example, an asymmetric arrangement of the magnets 234 within the recesses 238 around the optical axis 218 can be used to correct for the asymmetry of other components of the optical system. For example, in the embodiment shown in FIG. 3, the counter pole 228 includes twelve recesses 238, three of which have magnets 234 disposed therein to form an asymmetric pattern.

[0042] In some embodiments, as shown in FIG. 4, the recess can be configured as a track 240 that extends radially from a position adjacent to the optical axis 218 to the edge 242 of the counter pole 228. Each track 240 can be configured such that the respective magnets 234 can slide radially inward or outward with respect to the optical axis 218 within the track 240. Such a configuration advantageously allows the magnets to be easily repositioned and / or adjusted with respect to the axis 218 to correct existing asymmetries within the system 200. In some embodiments, two or more magnets can be disposed in each track 240. The illustrated embodiment shows a plurality of radially extending tracks 240, but in other embodiments, the tracks can extend circumferentially about the optical axis 218.

[0043] In some embodiments, as described above, the counter pole 228 can be movable relative to the sample S. For example, the counter pole 228 can be movable such that it can be completely removed from the sample chamber and / or stored in a "parking bay" connected to the sample chamber. In some embodiments, the counter pole 228 can be moved from a first location within the vacuum chamber where the counter pole 228 is positioned close to the magnetic immersion lens 212 (e.g., an "active" location) such that the counter pole 228 applies an additional magnetomotive force to the immersion lens, to a second location within the vacuum chamber where the counter pole 228 does not affect the lens 212 (e.g., a "non-active" location). The counter pole 228 can be energized by the immersion lens 212 (e.g., the counter pole 228 can be made part of the magnetic circuit of the immersion lens and does not need to be energized by a separate magnetic field such as an auxiliary magnetic coil).

[0044] In other embodiments, the permanent magnets 234 can be disposed on a retractable optical element. Details of such a configuration are described in U.S. Patent Publication No. 2014 / 0110597, which is hereby incorporated by reference in its entirety.

[0045] Although system 200 is shown as including only an SEM column, in some embodiments, system 200 can further include an ion column, similar to ion column 104 of the dual beam system 100 described above. In such embodiments, the magnetic immersion lens described herein (including counter pole 228 with permanent magnet 234) can be used to focus the ion beam from the ion column.

[0046] Example 3 FIG. 6 shows a representative graph of magnetic flux lines of an exemplary system 300. Region 302 corresponds to coil 222, the magnetic flux lines shown in region 304 correspond to the magnetic flux lines of the first lens pole 224, the magnetic flux lines shown in region 308 correspond to the magnetic flux lines of the second lens pole 228, and the magnetic flux lines shown in region 310 correspond to the magnetic flux lines of the vacuum chamber 204. As shown, region 302 shows the limited power of the existing immersion lens coil. The strength of the magnetic field within the first pole of the lens is shown in region 304. Region 306 shows the saturation of the magnetic circuit of the immersion lens. Such saturation and the resulting possible asymmetry of the magnetic circuit can negatively affect the performance of the lens. The embodiments described herein are configured to address these problems and advantageously allow the use of magnets inside the column itself with the magnetic circuit partially open.

[0047] For example, FIG. 7 shows a representative graph of magnetic flux lines of an exemplary system 400 including a permanent magnet. The magnetic flux lines in region 402 correspond to the magnetic flux lines of the permanent magnet 234, region 404 corresponds to coil 222, the magnetic flux lines shown in region 406 correspond to the magnetic flux lines of the first lens pole 224, the magnetic flux lines shown in region 408 correspond to the magnetic flux lines within the second lens pole 228, and the magnetic flux lines shown in region 410 correspond to the magnetic flux lines within the vacuum chamber 204. Region 402 shows the magnetic field strength added by the permanent magnet 234, which can add, for example, the equivalent of a coil of about 1500 AT.

[0048] From the perspective of many possible embodiments to which the principles of the present disclosure are applicable, it should be recognized that the illustrated embodiments are only preferred examples and should not be construed as limiting the scope of the present disclosure. Rather, the scope is defined by the following claims. Accordingly, the inventors claim all that falls within the scope and spirit of the appended claims. The alternatives specifically addressed in these sections are merely illustrative and do not constitute all possible alternatives to the embodiments described herein.

Claims

1. A charged particle beam system, comprising: a vacuum chamber; a sample holder for holding a sample within the vacuum chamber; a charged particle column including a charged particle source for generating a beam of charged particles along an optical axis and a magnetic immersion lens for focusing the beam of charged particles, wherein the magnetic immersion lens includes: a first lens pole disposed adjacent to a first surface of the sample; an excitation coil surrounding the first lens pole; and a counter pole configured to be disposed adjacent to a second surface of the sample, the counter pole including one or more magnets asymmetric with respect to the optical axis disposed on a surface of the counter pole, wherein the magnets are arranged such that they introduce an asymmetry into the charged particle beam system.

2. The charged particle beam system according to claim 1, wherein the surface of the counter pole is a first surface, and one or more additional magnets are disposed on a second surface of the counter pole with respect to the first surface.

3. The charged particle beam system according to claim 1, wherein the counter pole includes one or more recesses, and each magnet is disposed within a respective recess on the surface of the counter pole.

4. The charged particle beam system according to claim 1, wherein the one or more magnets are coupled to the counter pole via an adhesive.

5. The charged particle beam system according to claim 1, wherein the counter pole is attached to a positioning system configured to enable movement of the counter pole between a first position and a second position within the vacuum chamber, and the counter pole is inactive at the first position or the second position.

6. The charged particle beam system according to claim 1, wherein the counter pole further includes an opening and a detector, and the detector is disposed within or below the opening.

7. The charged particle beam system according to claim 1, wherein the one or more magnets include a plurality of magnets disposed on a first surface of the counter pole.

8. A charged particle beam system, comprising: a vacuum chamber; a sample holder for holding a sample within the vacuum chamber; A charged particle column including a charged particle source for generating a beam of charged particles along an optical axis and a magnetic immersion lens for focusing the beam of charged particles, wherein the magnetic immersion lens a first lens pole disposed adjacent to a first surface of the sample; an excitation coil surrounding the first lens pole; a counter pole configured to be disposed adjacent to a second surface of the sample, the counter pole including one or more magnets disposed within respective recesses on the surface of the counter pole, wherein the recesses include tracks, the one or more magnets are slidable within the tracks, and the magnets are positionable relative to the optical axis, a charged particle beam system. **Claim 9** The charged particle beam system according to claim 8, wherein each track extends radially inward from an outer edge of the counter pole toward the optical axis. **Claim 10** The charged particle beam system according to claim 8, wherein each track extends circumferentially about the optical axis. **Claim 11** A dual beam system, a sample holder for holding a sample, an ion beam column configured to direct an ion beam toward the sample, a charged particle column including a charged particle source for generating a beam of charged particles along an optical axis and a magnetic immersion lens for focusing the beam of charged particles, wherein the magnetic immersion lens a first lens pole disposed adjacent to a first surface of the sample; a second lens pole disposed adjacent to a second surface of the sample, the second lens pole including one or more magnets disposed asymmetrically with respect to the optical axis, wherein the magnets are disposed about the optical axis to create an asymmetry within the dual beam system, a dual beam system. **Claim 12** The dual beam system according to claim 11, wherein the one or more magnets comprise a plurality of magnets disposed on a first surface of the second lens pole, and one or more additional magnets are disposed on a second surface of the second lens pole. **Claim 13** The dual beam system according to claim 11, wherein the second lens pole includes one or more recesses, and each magnet is disposed within a respective recess. **Claim 14** The dual beam system further includes a vacuum chamber, and the second lens pole is attached to a positioning system configured to enable movement of the second lens pole between a first position and a second position within the vacuum chamber, the second lens pole being inactive at the first position or the second position. The dual beam system according to claim 11.

15. The second lens pole further includes an opening and a detector, the detector being disposed within or below the opening. The dual beam system according to claim 11.

16. The magnetic immersion lens is coupled to a control unit. The dual beam system according to claim 11.

17. A method of using the dual beam system according to claim 11, the method including disposing the magnet about the optical axis to create an asymmetry within the dual beam system.

Images