Aberration corrector and method for aligning the same

Abstract

There is provided an aberration corrector (101) having a plurality of magnetic poles (210, 211) including a first magnetic pole (210) and a further magnetic pole (211), a ring (240) magnetically connecting the plurality of magnetic poles to each other and having a constant distance from at least the first magnetic pole, a plurality of magnetic field modulators (220, 221) including a first magnetic field modulator (220) and a further magnetic field modulator (221), and a plurality of guides (450) including a first guide and a further guide. , the first magnetic field modulator comprises a soft magnetic material, the first magnetic field modulator is positioned at a first location, the first location being one of adjacent a first gap (230) separating the first magnetic pole and the ring, or at the inner ring surface (241), or radially outward of the inner ring surface along the axis of the first magnetic pole, and the first guide constrains the first magnetic field modulator to a position along a first axis substantially parallel to or aligned with the axis of the first magnetic pole.

Description

[Technical Field]

[0001] FIELD OF THE INVENTION The present invention relates to an aberration corrector, and more particularly to an aberration corrector having a plurality of magnetic poles and a ring. More particularly, the present invention relates to an aberration corrector having a plurality of magnetic poles and a ring that magnetically connects the plurality of magnetic poles to one another. The present invention also relates to a charged particle beam device having an aberration corrector and a method for aligning the magnetic field of an aberration corrector. [Background technology]

[0002] In charged particle beam devices such as microscopes, microfabrication devices, and semiconductor manufacturing equipment, single-stage or multi-stage multipoles (dipole, quadrupole, hexapole, octopole, etc.) are used as deflectors and aberration correctors. Using the above-mentioned devices, processing with an accuracy of about 10 micrometers and observation with an accuracy in the sub-micrometer range can be performed.

[0003] In such applications, it is advantageous for the device to have a resolution in the sub-nanometer range. In aberration correctors, imperfections in the field-shaping multipole elements can introduce aberrations that limit the achievable resolution.

[0004] In particular, in aberration correctors such as spherical and chromatic aberration correctors, the multipole fields involved can be very strong, and inaccuracies in such correctors can lead to imperfections in the electric and magnetic field profiles, resulting in the generation of residual aberrations that limit the achievable performance of the device.

[0005] Therefore, high precision is required in manufacturing and assembly, for example, in the positioning of the magnetic poles and other components that make up the magnetic circuit of a magnetic aberration corrector, because inaccuracies in such positioning cause parasitic multipole fields and result in beam blurring. Additionally, solutions to improve precision often involve increased complexity, which adversely affects reproducibility and cost, especially in mass production.

[0006] For example, U.S. Patent No. 9,287,084 B2 describes an adjustment member disposed between a magnetic pole and a magnetic ring to adjust the spacing between the pole and the ring. However, such a solution addresses only a portion of the magnetic circuit. Furthermore, adding components typically increases manufacturing and assembly complexity and introduces additional sources of inaccuracy. Furthermore, even if the system is assembled in sufficiently good condition, such a solution does not address maintenance issues, such as vibrations during the operating life that can lead to degradation of the mechanical positioning of the system's components.

[0007] It would therefore be beneficial to provide an aberration corrector and method for aligning the magnetic field of an aberration corrector that can reliably achieve the required accuracy or better, while at the same time being mass-producible. In particular, it would be beneficial to provide an aberration corrector and method for aligning the magnetic field of an aberration corrector that reliably addresses various sources of inaccuracy (e.g., during manufacturing, assembly, operation, etc.) that lead to performance degradation. Summary of the Invention

[0008] In view of the above, there is provided an invention as defined by the independent claims. According to the aspects described herein, there is provided an aberration corrector and a method for aligning the magnetic field of an aberration corrector. Further aspects, advantages, and features of the embodiments are apparent from the dependent claims, the description, and the accompanying drawings.

[0009] According to one aspect described herein, an aberration corrector is described having a plurality of magnetic poles including a first magnetic pole and an additional magnetic pole, a ring magnetically connecting the plurality of magnetic poles to each other, the ring having a fixed spacing relative to at least the first magnetic pole, a plurality of magnetic field modulators including a first magnetic field modulator and an additional magnetic field modulator, and a plurality of guides including a first guide and an additional guide, wherein the first magnetic field modulator comprises a soft magnetic material, and the first magnetic field modulator is disposed at a first position, the first position being at least one of adjacent to a first gap separating the first magnetic pole and the ring, on an inner ring surface, and radially outward of the inner ring surface along an axis of the first magnetic pole, and the first guide restrains the first magnetic field modulator in a position along a first axis substantially parallel to or coincident with the axis of the first magnetic pole.

[0010] According to a further aspect, an aberration corrector is described having a plurality of magnetic poles including a first magnetic pole and an additional magnetic pole, a ring magnetically connecting the plurality of magnetic poles to each other, the ring having a fixed spacing relative to at least the first magnetic pole, a plurality of magnetic field modulators including a first magnetic field modulator and an additional magnetic field modulator, and a plurality of guides including a first guide and an additional guide, wherein the first magnetic field modulator comprises a soft magnetic material, the first magnetic field modulator is positioned at a first position, and the first guide constrains the first magnetic field modulator to a position along a first axis substantially parallel to or coincident with the axis of the first magnetic pole.

[0011] According to further aspects described herein, a method for aligning a magnetic field of an aberration corrector with an optical axis is described, the aberration corrector having a plurality of magnetic poles including a first magnetic pole and an additional magnetic pole, a ring magnetically connecting the plurality of magnetic poles to each other, the ring having a fixed spacing relative to at least the first magnetic pole, a plurality of magnetic field modulators including a first magnetic field modulator and an additional magnetic field modulator, and a plurality of guides including a first guide and an additional guide, wherein the first magnetic field modulator comprises a soft magnetic material, and the first magnetic field modulator is disposed at a first position, the first position being one of adjacent to a first gap separating the first magnetic pole and the ring, or on an inner ring surface along an axis of the first magnetic pole, or radially outward from the inner ring surface, the method including positioning the first magnetic field modulator at the first position, the first position being one of a plurality of positions along a first axis substantially parallel to or coincident with the axis of the first magnetic pole.

[0012] The embodiments are also directed to apparatus for carrying out the disclosed methods, including apparatus parts for performing individual method operations. These methods may be performed by hardware components, a computer programmed by appropriate software, by any combination of both, or in any other manner. Additionally, the embodiments are also directed to methods of operating the described apparatus.

[0013] Further advantages, features, aspects and details that can be combined with the embodiments described herein are evident from the dependent claims, the description and the drawings.

[0014] So that the recited features of the present invention can be understood in detail, a more particular description of the embodiments briefly summarized above may be had by reference to the accompanying drawings, which relate to one or more embodiments and are described below. [Brief explanation of the drawings]

[0015] [Figure 1] 1 is a cross-sectional view of an aberration corrector according to an embodiment described herein. [Figure 2] 1 is a cross-sectional view of an aberration corrector according to an embodiment described herein. [Figure 3] 1 is a cross-sectional view of an aberration corrector according to an embodiment described herein. [Figure 4] FIG. 2 is a close-up view of a magnetic field modulator according to embodiments described herein. [Figure 5] FIG. 2 is a close-up view of a magnetic field modulator according to embodiments described herein. [Figure 6] FIG. 2 is a schematic diagram of a balancing resistor according to embodiments described herein. [Figure 7] 1 is a schematic diagram of a charged particle beam device according to embodiments described herein; [Figure 8] 1 is a flow chart illustrating a method for aligning a magnetic field of an aberration corrector according to embodiments described herein. [Figure 9] 10 is a plot illustrating the modeled effects of different magnetic field modulators according to embodiments described herein. DETAILED DESCRIPTION OF THE INVENTION

[0016] Reference will now be made in detail to various embodiments, one or more examples of which are illustrated in the figures. Within the following description of the drawings, like reference numerals refer to like components. Generally, only differences with respect to individual embodiments will be described. Each example is provided by way of explanation and is not meant to be limiting. Furthermore, features illustrated or described as part of one embodiment can be used on or in conjunction with other embodiments to yield still further embodiments. The description is intended to include such modifications and variations.

[0017] To improve the resolution of charged particle beam devices such as SEM columns beyond the limits of simple circular lens systems, aberration correctors can be used to correct aberrations. In one example, the aberration corrector is a multipole corrector. The aberration corrector can include at least one of a spherical aberration corrector, a chromatic aberration corrector, a coma aberration corrector, and an additional multipole corrector. The aberration corrector can include multiple multipole stages. Each multipole stage can be a magnetic multipole, an electrostatic multipole, or a combined magnetic / electrostatic multipole. Each multipole stage typically includes multiple poles.

[0018] A magnetic pole can be understood to include a pole head 120 (close to the optical axis 109) and a rod 122 carrying an excitation coil. The pole head 120 may be mounted in a pole head support 140, which may be of a non-magnetic material. The rod 122 may be mounted in a rod support 142, which may be made of a non-magnetic material. The magnetic circuit can be understood to be closed by a ring 240, which may be understood as a magnetic yoke. The ring 240 can be understood to surround multiple poles, with an air gap between each pole and the ring 240. The air gap may be on the order of millimeters.

[0019] According to one embodiment, the aberration corrector 101 includes two or more stages of multipoles, for example, four stages. According to one embodiment, the aberration corrector 101 is used to generate a magnetic quadrupole field, as well as an electric quadrupole field and an octupole field. Aberrations are corrected accordingly. Advantageously, the resolution of the charged particle beam device is improved.

[0020] As described, it is beneficial to have an aberration corrector aligned with the optical axis. In particular, it is beneficial to have an aberration corrector aligned with the optical axis so that tolerances are compensated for. For example, it is beneficial to compensate for tolerances that arise during assembly, manufacturing, and / or operation that cause the aberration corrector to be misaligned with the optical axis.

[0021] Alignment of an aberration corrector can be understood as the alignment of the multipole field with the optical axis. Ideally, each magnetic pole transmits a precise amount of magnetic flux toward the optical axis. In reality, the magnetic flux depends on several factors, including material properties, mechanical tolerances of the air gaps in the magnetic circuit, and mechanical tolerances of the pole head geometry. These tolerances can cause distortions in the magnetic flux distribution at the optical axis, resulting in less-than-optimal alignment with the optical axis.

[0022] One approach to compensating for such tolerances is to provide an auxiliary coil for each pole. However, this requires additional low-noise current sources (specifically, one additional auxiliary coil per pole) and infrastructure to align the magnetic field of each pole. Another approach to compensating for these tolerances is to superimpose electric fields. However, the addition of a compensating field also requires a higher voltage budget for the power supply. Furthermore, the resulting optical path is insufficient when the tolerances are large. This disclosure describes a mechanical design and method for compensating for such tolerances by mechanical means.

[0023] According to one embodiment, an aberration corrector 101 is provided having a plurality of magnetic poles including a first magnetic pole 210 and a further magnetic pole 211, a ring 240 magnetically connecting the plurality of magnetic poles to each other, the ring 240 having a fixed spacing at least relative to the first magnetic pole 210, a plurality of magnetic field modulators including a first magnetic field modulator 220 and a further magnetic field modulator 221, and a plurality of guides including a first guide 450 and a further guide (not shown).

[0024] In one example, the first guide 450 includes a surface that form-fits the outer surface of the first magnetic field modulator 220. The term "form-fitting" can be understood to have a mating configuration, e.g., shape, size, cross-sectional dimensions. In one example, the first guide 450 is the interface between the first magnetic field modulator 220 and the ring 240.

[0025] In one example, the first guide 450 can be understood as a hole in the ring 240 that fits over the outer surface of the first magnetic field modulator 220. In a further example, the hole in the ring 240 can be provided with an internal thread that fits over an external thread on the outer surface of the first magnetic field modulator 220. Further guides (not shown) may be configured according to embodiments of the first guide 450 for further magnetic field modulators 221.

[0026] Further, according to one embodiment, the first magnetic field modulator 220 comprises a magnetic material such as a soft magnetic material, the first magnetic field modulator 220 is positioned at a first position, the first position being at least one of at the inner ring surface 241 along the axis 219 of the first magnetic pole 210 adjacent to the first gap 230 separating the first magnetic pole 210 and the ring 240 or radially outward from the inner ring surface 241, and the first guide 450 restrains the first magnetic field modulator 220 in a position along a first axis substantially parallel to or aligned with the axis 219 of the first magnetic pole 210.

[0027] In an embodiment, which may be combined with other embodiments described herein, the ring 240 has a fixed spacing or distance relative to the first pole 210 and the further pole 211 .

[0028] Thus, by adjusting the first position of the first magnetic field modulator 220 along the first axis 429, the magnetic resistance of the magnetic circuit of the first magnetic pole 210 is adjusted. The magnetic flux of the magnetic pole, and therefore the magnetic field, is modulated accordingly. In this manner, the magnetic field of the aberration corrector 101 can be adjusted. Advantageously, various tolerances that cause imperfections in the magnetic field are corrected or minimized.

[0029] According to one embodiment, a current source 670 is provided adapted to drive the first magnetic pole 210 and the further magnetic pole 211. In one example, the current source 670 is adapted to drive the first excitation coil 350 of the first magnetic pole 210 and the further excitation coil 351 of the further magnetic pole 211. In one example, the first magnetic pole 210 and the further magnetic pole 211 are driven by the current source 670. In one example, multiple magnetic poles of the first multipole stage 103 of the aberration corrector 101 are driven by the current source 670.

[0030] The current source 670 may be understood as a single current source or the same current source. In one example, the aberration corrector 101 includes a first current source that drives multiple magnetic poles of a first multipole stage 103 of the aberration corrector 101 and a second current source that drives a second multiple magnetic poles of a second multipole stage of the aberration corrector 101. In one example, the first excitation coil 350 of the first magnetic pole 210 and the further excitation coil 351 of the further magnetic pole 211 are connected in series.

[0031] In one example, the number of windings on each pole can be configured relative to one another to provide a corrective magnetic field. In one example, the multiple magnetic poles of the aberration corrector 101 include a first subset of magnetic poles and a second subset of magnetic poles. In one example, the first subset of poles and the second subset of poles lie in a plane perpendicular to the axis of the aberration corrector 101.

[0032] In one example, each pole of the first subset of poles lies on an x-axis and a y-axis that are perpendicular to the axis of the aberration corrector 101, and the x-axis and y-axis are perpendicular to each other. In one example, each pole of the second subset of poles lies between the x-axis and the y-axis. In one example, each of the first subset of poles has an excitation coil with N windings. In one example, each of the second subset of poles has an excitation coil with N / 2 windings.

[0033] Thus, a quadrupole field for aberration correction can be provided using a single current source 670. Thus, when the current source 670 drives the first magnetic pole 210 and the further magnetic pole 211, the electrical noises of the first magnetic pole 210 and the further magnetic pole 211 are correlated with each other and cancel each other out. Thus, uncorrelated noise of the poles that leads to dipole deflection fields is avoided. Advantageously, undesired dipole fields are avoided and only the desired multipole field, e.g., a quadrupole field or an octupole field or higher order field, is provided.

[0034] According to one embodiment, the first guide includes a first actuator (not shown). In one example, the additional guide includes an additional actuator. In one example, each of the additional guides includes a respective actuator. In one example, the first guide includes an actuator coupled to a screw mechanism and / or a linear guide. The screw mechanism may be a lead screw, a ball screw, a roller screw, or a jackscrew. The linear guide may include at least one of a rod, a rail, a slide, a linear bearing, a linear housing, a linear groove, and a linear recess.

[0035] In one example, the first guide includes a screw mechanism and / or a linear guide (not shown). In one example, the first magnetic field modulator 220 is positioned by an actuator. The actuator may be at least one of a piezoelectric actuator, an electric motor, a cam mechanism, or a comb drive. In another example, the first magnetic field modulator 220 is positioned manually (without an actuator).

[0036] Therefore, the first position of the first magnetic field modulator 220 can be repeatedly determined in an efficient and reproducible manner. Advantageously, misalignment of the aberration corrector is easily compensated for, and imperfections in the magnetic field are easily corrected or minimized.

[0037] According to one embodiment, the first position of the first magnetic field modulator 220 is based on (determined from) measuring a magnetic field substantially at the position of the optical axis 109. The magnetic field at the optical axis 109 may be understood as the magnetic field of the first magnetic pole 210 and the further magnetic pole 211 of the aberration corrector 101. In one example, the magnetic field is a quadrupole field. In one example, the magnetic field is the magnetic field of the first multipole stage 103 of the aberration corrector 101.

[0038] In one example, the first position is where the parasitic multipole field is minimal or substantially zero. In one example, the parasitic multipole field is determined based on a measurement of a magnetic field substantially at the position of the optical axis 109. In one example, the first position of the first magnetic field modulator 220 and the position of the further magnetic field modulator may be where the parasitic multipole field measured substantially at the position of the optical axis 109 is minimal or substantially zero.

[0039] In one example, measurements of the magnetic field at substantially the position of the optical axis 109 are performed by placing a rotating magnetic field sensor at substantially the position of the optical axis 109. In one example, the magnetic field measurements may be a function of angle. In one example, the magnetic field measurements may be a function of the rotation angle of the magnetic field sensor. Thus, the magnetic field measurements are correlated with respect to multiple magnetic poles. For example, based on a continuous Fourier analysis of the magnetic field versus angle, parasitic multipole fields, such as dipoles, hexapoles, and octopoles, are identified and compensated for by adjusting the position of the first magnetic field modulator 220 and / or the position of the further magnetic field modulator 221.

[0040] Therefore, the first position of the first magnetic field modulator 220 and / or the position of the further magnetic field modulator 221 can be determined without having to excite each magnetic pole individually. Therefore, no special excitation device is required, and the same excitation device can be used for both aligning and operating the aberration corrector 101. Advantageously, misalignments of the aberration corrector are easily compensated for, and imperfections in the magnetic field are easily corrected or minimized.

[0041] According to one embodiment, the first magnetic pole 210, the first magnetic field modulator 220, and the ring 240 are supported such that a first position of the first magnetic field modulator 220 is independent of a first distance between the first magnetic pole 210 and the ring 240.

[0042] In one example, first magnetic pole 210, first magnetic field modulator 220, and ring 240 are supported by the housing (and / or by separate elements) of aberration corrector 101. In another example, first magnetic pole 210 and ring 240 are supported by the housing (and / or by separate elements) of aberration corrector 101, and first magnetic field modulator 220 is supported by ring 240. Thus, the first position of first magnetic field modulator 220 may be independent of the first distance between first magnetic pole 210 and ring 240.

[0043] Therefore, the first position of the first magnetic field modulator 220 can be adjusted independently of the first distance between the first magnetic pole 210 and the ring 240. Accordingly, the magnetic resistance can be easily adjusted, and imperfections in the magnetic field can be easily corrected or minimized.

[0044] According to one embodiment, a second magnetic field modulator of the plurality of magnetic field modulators, a second magnetic pole of the plurality of magnetic poles, and ring 240 may be supported such that a second position of the second magnetic field modulator is independent of a second distance between the second magnetic pole and ring 240.

[0045] According to one embodiment, each of the plurality of magnetic field modulators, each of the plurality of magnetic poles, and ring 240 may be supported such that the position of each of the magnetic field modulators is independent of the respective distance between each of the plurality of magnetic poles and ring 240.

[0046] Therefore, it is possible to achieve precise (well-controlled pole-specific) alignment of the magnetic field of the aberration corrector 101. Therefore, it is easy to align the magnetic poles of the aberration corrector 101. Advantageously, misalignment of the aberration corrector is easily compensated for, and imperfections in the magnetic field are easily corrected or minimized.

[0047] According to one embodiment, the first magnetic field modulator 220 is positioned in a plane substantially parallel to the plane of the magnetic poles. In one example, the axis 429 of the first magnetic field modulator 220 is parallel to the axis 219 of the first magnetic pole 210. In one example, the first magnetic field modulator 220 is positioned above or below the first air gap 230 and / or the first magnetic pole 210.

[0048] In one example, the first magnetic field modulator 220 is separated, for example by a finite distance, from the first air gap 230 and / or the first magnetic pole 210 in a direction parallel to the axis of the aberration corrector 101. In one example, the first magnetic field modulator 220 is positioned adjacent to the first air gap 230 and / or the first magnetic pole 210 in a direction parallel to the axis of the aberration corrector 101.

[0049] Therefore, the sensitivity of the magnetoresistance, and therefore the magnetic flux, to changes in the position of the magnetic field modulator is reduced. The system is therefore easier to align and less susceptible to thermal drift or vibration. Advantageously, misalignment of the aberration corrector is easily and reliably compensated for, and the alignment of the magnetic field of the aberration corrector with the optical axis is better controlled.

[0050] According to one embodiment, a first retainer 321 is provided that is positioned to maintain the first magnetic field modulator in the first position. In one example, the first retainer 321 may be a removable retainer, a temporary retainer, a reusable retainer, and / or a multi-use retainer. In one example, the first retainer 321 may be a spring, a Belleville washer, a spring lock washer, a pin, a clip, a clamp, or a wedge. In one example, the first retainer 321 may be positioned against a surface of the first magnetic field modulator.

[0051] Thus, misalignment due to accidental translation and / or rotation of the magnetic field modulator, which may be caused by vibration and / or thermal effects, is minimized or avoided. Advantageously, alignment with the optical axis of the aberration corrector is ensured.

[0052] According to one embodiment, the first guide has a first extent (not shown), and when the first magnetic field modulator 220 is positioned at a first end of the first extent of the first guide, there is a non-zero overlap (as viewed) between the first magnetic field modulator 220 and the first magnetic pole 210 in a direction perpendicular to the axis 219 of the first magnetic pole 210. In one example, the first end of the first guide is adjacent to the first magnetic pole 210.

[0053] According to one embodiment, the first guide has a first extent (not shown), and when the first magnetic field modulator 220 is positioned at the second end of the first extent of the first guide, the overlap (as viewed) of the first magnetic field modulator 220 with the first air gap 230 in a direction perpendicular to the axis 219 of the first magnetic pole 210 is zero. In one example, the second end of the first guide is adjacent to the ring 240.

[0054] The first extent of the first guide may be understood as the dimension or length of the first guide in a direction parallel to the axis 219 of the first magnetic pole 210. In one example, the axis 429 of the first guide is substantially parallel to or coincides with the axis 219 of the first magnetic pole 210.

[0055] In one embodiment, the dimension of the first guide in a direction parallel to the axis 219 of the first magnetic pole 210 is at least as long as the dimension of the first air gap 230 in a direction parallel to the axis 219 of the first magnetic pole 210.

[0056] According to one embodiment, the first guide is positioned and / or configured to support the first magnetic field modulator 220 at a first end position, a second end position, and a position between the first end position and the second end position.

[0057] The first end position can be understood as the radially inner end position, where there is a non-zero overlap between the first magnetic field modulator 220 and the first magnetic pole 210 (when viewed in a direction perpendicular to the axis 219 of the first magnetic pole 210).

[0058] The first end position may be understood as the position at which the intersection of the first magnetic field modulator 220 with the first magnetic pole 210 in the radial direction relative to the axis 219 of the first magnetic pole 210 is non-zero.

[0059] The first end position can be understood as a position of the first magnetic field modulator 220 where the first magnetic pole 210 at least partially intersects or crosses the first magnetic field modulator 220 when the first magnetic pole 210 is projected radially relative to the axis 219 of the first magnetic pole 210 or when the first magnetic pole 210 is projected perpendicularly relative to the axis 219 of the first magnetic pole 210.

[0060] Advantageously, the upper end of the range of magnetic coupling between the first magnetic pole 210 and the ring 240 is extended. Thus, the modulation range is increased, including the range of the linear portion. Therefore, larger tolerances can be better compensated. Advantageously, misalignment of the aberration corrector is easily compensated.

[0061] The second end position may be understood to be the radially outer end position where the overlap between the first magnetic field modulator 220 and the first magnetic pole 210 in a direction perpendicular to the axis 219 of the first magnetic pole 210 (as viewed) is smaller than the overlap between the first magnetic field modulator 220 and the first magnetic pole 210 when the first magnetic field modulator 220 is in the first end position.

[0062] Advantageously, the lower end of the range of magnetic coupling between the first magnetic pole 210 and the ring 240 is extended. Thus, the modulation range is increased, including the range of the linear portion. Therefore, larger tolerances can be better compensated. Advantageously, misalignment of the aberration corrector is easily compensated.

[0063] The radial direction in the expressions "radially inward" and "radially outward" may be understood as a direction extending perpendicularly or radially from the optical axis 109, or a direction extending parallel to the axis 219 of the first magnetic pole 210 ("radially inward" may be understood as a direction toward the pole head of the first magnetic pole 210, and "radially outward" may be understood as a direction away from the pole head of the first magnetic pole 210).

[0064] In one example, the second end position may be understood as the position where there is zero overlap between the first magnetic field modulator 220 and the first magnetic pole 210 (when viewed in a direction perpendicular to the axis 219 of the first magnetic pole 210).

[0065] Therefore, the modulation range is increased, including the range of the linear portion. Larger tolerances can therefore be better compensated. Advantageously, misalignment of the aberration corrector is easily compensated for.

[0066] According to one embodiment, the first guide and first magnetic field modulator 220 are configured such that the first position of the first magnetic field modulator 220 has a first position limit and a second position limit (not shown), and the first position limit is separated from the second position limit by a length that is at least twice the length of the first gap 230 in a direction parallel to the axis 219 of the first magnetic pole 210.

[0067] In one example, the first guide may be a linear bearing (not shown) disposed adjacent to the ring 240. In one example, the first magnetic field modulator 220 is a rod comprising a soft magnetic material and having a length at least twice the length of the first air gap 230. In another example, the first guide may be a threaded support (not shown) disposed within or adjacent to the housing of the aberration corrector 101. In one example, the first magnetic field modulator 220 is a screw of a soft magnetic material having a length at least twice the length of the first air gap 230.

[0068] In one example, the first position limit is separated from the second position limit by at least three, at least five, or at least ten times the length of the first gap 230 in a direction parallel to the axis 219 of the first magnetic pole 210.

[0069] This allows for an increased correction range, in particular an extended linear behavior range and allows for further modulation of the magnetic field, which advantageously allows for better compensation of tolerances and a better alignment of the aberration corrector with the optical axis.

[0070] According to one embodiment, which can be combined with other embodiments and examples described herein, the first magnetic field modulator 220 is positioned in a plane substantially parallel to the plane of the magnetic poles of the first multipole stage 103. In one example, the first magnetic field modulator 220 can only be positioned in a plane substantially parallel to the plane of the magnetic poles of the first multipole stage 103.

[0071] In one example, the first magnetic field modulator 220 is positioned at a non-zero distance from the first magnetic pole 210 in a direction perpendicular to the plane of the ring 240. In one example, the first magnetic field modulator 220 is positioned above or below the plane of the ring 240.

[0072] The term "parallel" may be understood as "having a continuously non-zero distance between them." The term "parallel" may be understood as "parallel and not coincident."

[0073] Therefore, the magnetic field modulation effect of the magnetic field modulator is less sensitive. Correspondingly, the relative sensitivity of the correction may be less. In particular, tolerances can be compensated for more accurately. Advantageously, imperfections in the magnetic field are corrected or minimized. Advantageously, the multipole field of the aberration corrector is better aligned with the optical axis.

[0074] According to one embodiment, a charged particle beam device 707 is provided having a sample stage 786, a charged particle source 780 adapted to generate a charged particle beam 782, and a charged particle beam manipulation system 784 having an aberration corrector 101.

[0075] According to one embodiment, the first position of the first magnetic field modulator 220 is based on (determined by) a measured effect of the magnetic field of the first magnetic pole 210 at a position substantially aligned with the optical axis 109. In one example, the effect of the magnetic field is an image shift. In one example, the measured effect is a measured deflection sensitivity of the first deflection pole. In one example, the first magnetic pole 210 is driven, but the further magnetic pole 211 is not driven. In one example, when the first magnetic field modulator 220 is in the first position, imperfections in the magnetic field are corrected or minimized.

[0076] In one example, the first position is between the first end position and the second end position. In one example, the first position is a center position between the first end position and the second end position.

[0077] In a specific example, the first magnetic field modulator 220 is provided at an initial position. Additional magnetic field modulators 221 may be provided at respective additional initial positions. The first magnetic field modulator 220 may be repositioned, for example, based on the measured deflection magnetic field strength or the measured deflection sensitivity of the first magnetic pole 210. After adjustment, the first magnetic field modulator 220 may be in the first position. When the first magnetic field modulator 220 is in the first position, magnetic field imperfections in the magnetic field of the first multipole stage 103 are corrected or minimized.

[0078] In one example, the first position of the first magnetic field modulator 220 and the position of the further magnetic field modulator are such that the respective effects of the respective magnetic fields of the respective magnetic poles are equal. In one example, the first position of the first magnetic pole 210 and the position of the further magnetic pole 211 are such that the deflection sensitivity of the first magnetic pole 210 is equal to the deflection sensitivity of each of the further magnetic poles 211.

[0079] Therefore, after assembling a new column, tolerances are easily compensated for by the magnetic field modulators. Advantageously, misalignment of the aberration correctors is easily compensated for, correcting or minimizing imperfections in the magnetic field.

[0080] According to one aspect, a method for aligning a magnetic field of an aberration corrector with an optical axis is provided, the method comprising positioning a first magnetic field modulator at a first position 890, the first position being one of a plurality of positions along a first axis that is substantially parallel to or coincident with an axis of a first magnetic pole.

[0081] Therefore, by adjusting the position of the magnetic field modulator, the magnetic resistance of the magnetic circuit of the magnetic pole is adjusted. The magnetic flux, and therefore the magnetic field of the magnetic pole, is modulated accordingly. This allows the deflection sensitivity of the magnetic poles to be substantially equalized, and the magnetic field of the multipole stage to be aligned with the optical axis. Thus, imperfections in the magnetic field are corrected or minimized.

[0082] In this way, the magnetic multipole fields of the aberration corrector can be adjusted, advantageously compensating for various tolerances that cause misalignment of the aberration corrector and aligning the aberration corrector with the optical axis.

[0083] According to one embodiment, a first deflection sensitivity of the first magnetic pole is measured and a second deflection sensitivity of at least one of the further magnetic poles is measured (893), and the first magnetic field modulator is positioned (890) at a first position such that the first sensitivity and the second sensitivity are substantially equal.

[0084] According to one embodiment, the first position of the first magnetic field modulator 220 is based on (determined from) the measured magnetic field of the first magnetic pole 210. The magnetic field may be measured substantially at the position of the optical axis 109. In one example, the magnetic field is measured with a rotating magnetic sensor. In one example, the first magnetic pole 210 is driven, but the further magnetic pole 211 is not driven. In one example, when the first magnetic field modulator 220 is in the first position, imperfections in the magnetic field are corrected or minimized.

[0085] In one example, the first magnetic pole is magnetized or driven, and in one example, a further magnetic pole 211 of the plurality of magnetic poles of the first multipole stage 103 is not magnetized or driven while the first magnetic pole 210 is magnetized or driven. In response, the first magnetic pole generates a magnetic field.

[0086] In one example, the magnetic field of the first magnetic pole 210 is measured with a rotating magnetic field sensor. In one example, the rotating magnetic field sensor is positioned substantially at the position of the optical axis. In one example, the first position of the first magnetic field modulator 220 is based on (determined from) the measured magnetic field of the first magnetic pole 210.

[0087] In one example, it is disclosed to adjust or determine a first position of the first magnetic field modulator 220 based on the measured magnetic field of the first magnetic pole 210. In one example, when the first magnetic field modulator 220 is in the first position, the measured magnetic field of the first magnetic pole 210 is equal to at least one of the additional magnetic poles 211 or all of the additional magnetic poles 211.

[0088] In one example, a rotating magnetic field sensor is used to measure the magnetic field generated by each individually energized magnetic pole. In one example, a magnetic field sensor is used to measure the magnetic field generated by the individually energized first magnetic pole and the individually energized further magnetic pole.

[0089] In one example, the first magnetic field modulator and the further magnetic field modulator are arranged such that the magnetic field strengths of the first magnetic pole and the further magnetic pole are substantially equal.

[0090] According to one embodiment, a magnetic field is measured (895) using a rotating magnetic field sensor located substantially at the optical axis, a parasitic multipole field is identified based on the measured magnetic field, and a first magnetic field modulator is positioned (890) at a first position such that the parasitic multipole field is minimized.

[0091] According to one embodiment, the excitation of the aberration corrector is wobbled (897) and the first magnetic field modulator is placed at a first position (890) such that image shift during wobbling is minimized. The term "wobble" may be understood as "varying periodically around a mean value."

[0092] According to one embodiment, the aberration corrector is commissioned in a charged particle beam device, and during commissioning, a first magnetic field modulator is positioned (890) at a first position.

[0093] Some further illustrative examples are as follows:

[0094] In an exemplary embodiment, first magnetic field modulator 220 may be a screw or rod of soft magnetic material. In one example, first magnetic field modulator 220 is positioned within the portion of ring 240 where first magnetic pole 210 is closest to ring 240. In one example, first magnetic field modulator 220 is a screw held in place by a spring. In one example, a clamp secures first magnetic field modulator 220 in place.

[0095] In an exemplary embodiment, the first magnetic field modulator 220 includes an external thread and a ratchet surface. In one example, a spring-loaded pawl is provided that acts on the ratchet surface of the first magnetic field modulator 220. Thus, a predetermined position of the first magnetic field modulator 220 is provided.

[0096] In an exemplary embodiment, the first pole 210 includes a rod portion and a pole head portion, each having a thread so that the rod portion can be threaded into and unthreaded from the pole head portion. The size of the first air gap 230 can be varied accordingly. In one example, at least one shim of a predetermined thickness is provided in the first air gap 230 to determine the size of the first air gap 230.

[0097] In an exemplary embodiment, the first magnetic field modulator 220 is actuated. In one example, a piezoelectric driver is coupled to the first magnetic field modulator 220. In one example, the actuator is disposed in the ring 240, for example, in a hole in the ring 240, such as radially outward of the first magnetic pole 210.

[0098] In an exemplary embodiment, the linear motion range of the first magnetic field modulator is between 0.1 mm and 10 mm. In one example, the positioning accuracy of the first magnetic field modulator is at least 0.1 mm or at least 0.01 mm.

[0099] In an exemplary embodiment, the first magnetic field modulator 220 is positioned off-axis relative to the rod portion of the first magnetic pole 210. In one example, the first magnetic field modulator 220 is positioned below the rod portion of the first magnetic pole 210 and / or below the first excitation coil 350. The rod portion of a pole may be understood to be the pole piece portion of a pole. Thus, changing the position, e.g., axial position, of the first magnetic field modulator 220 transfers more or less magnetic flux between the first magnetic pole 210 and the ring 240, thereby affecting the magnetic field on the optical axis 109.

[0100] In an exemplary embodiment, the deflection sensitivity of each magnetic pole can be measured, for example, in a scanning electron microscope, by observing the image shift when a small current is passed through only one of the magnetic poles at a time. For this purpose, the series connection of the excitation coils can be interrupted, and each excitation coil can be individually excited. In one example, the position of each magnetic field modulator can be adjusted so that equal deflection sensitivity is observed for each magnetic pole. In one example, this is an iterative adjustment.

[0101] The embodiments described herein may be performed after assembling a new column. Once tolerances are compensated for by the magnetic field modulators, the magnetic flux can be seen to remain constant, except for transient effects such as thermal or magnetic drift, and to act equally on all poles.

[0102] In an exemplary embodiment, a magnetic pole alignment mode and an operational mode are possible. In one example, in the alignment mode, the excitation coils of multiple magnetic poles are individually excited. In one example, in the operational mode, a current source simultaneously drives the excitation coils of multiple magnetic poles.

[0103] In an exemplary embodiment, before assembling the entire column, the magnetic field of each multipole stage is detected using a rotating magnetic field sensor proximate the optical axis 109 and correlated with the rotation angle of the detector relative to the multipole. In one example, from a continuous Fourier analysis of the magnetic field versus angle function, parasitic multipole fields, e.g., dipoles, hexapoles, and octopoles, can be identified and compensated for with magnetic field modulators. In this embodiment, individual excitation is not required.

[0104] In an exemplary embodiment, the multiple excitation coils of the multiple magnetic poles are connected in series in an operating mode. In one example, the magnetic and electric multipole excitations are wobbled, and the magnetic field modulators are adjusted so that the multipole effect and image shift are minimized for both the magnetic and electric excitations. Thus, the centers of the electric and magnetic multipoles are aligned.

[0105] It will be appreciated that the magnetic circuit may include different elements of soft magnetic material, possibly of the same type, but not necessarily of the same type. It will be appreciated that the magnetic flux of the magnetic poles at the optical axis 109, i.e., the on-axis magnetic flux, is strongly determined by the magnetic reluctance between the magnetic poles and the ring 240. It will therefore be appreciated that magnetic field adjustment can be achieved by introducing a magnetic field modulator, for example, a screw of soft magnetic material, in the vicinity of the ring 240, e.g., at a position where the magnetic poles approach the ring 240.

[0106] Therefore, by varying the magnetic resistance between the magnetic poles and ring 240, the magnetic flux of the magnetic poles can also be varied. The greater the magnetic resistance, the smaller the magnetic flux. Conversely, the smaller the magnetic resistance, the greater the magnetic flux. Therefore, by controlling the magnetic resistance, the magnetic field at optical axis 109 due to each magnetic pole can be independently adjusted.

[0107] That is, fine tuning of the reluctance between the poles and ring 240 can be achieved by mechanical or electromechanical means. For example, a magnetic field modulator can provide fine tuning of the reluctance. The magnetic field modulator can be a variable or adjustable magnetic field clamp.

[0108] Advantageously, the aberration correction can be adjusted to provide a precise magnetic flux distribution on the optical axis, i.e., the aberration corrector provides optimal correction, and more particularly, an aberration corrector with improved performance is provided.

[0109] Further exemplary examples are as follows: These examples relate to balancing resistors for magnetic multipoles.

[0110] In the case of a multipole corrector (Cc-Cs) in which electric and magnetic quadrupole fields are superimposed, a single current source can be used to drive all excitation coils connected in series. The excitation coils can have a predetermined number of turns to generate the quadrupole field. This minimizes the effects of current noise, such as dipole noise, which is caused by uncorrelated current fluctuations in the individual excitation coils. By connecting the excitation coils in series, the noise of each excitation coil is correlated, resulting in only "quadrupole noise."

[0111] It will be appreciated that if all excitation coils are connected in series, mechanical inaccuracies in the multipoles, material inhomogeneities leading to variations in magnetic flux, and winding tolerances can result in undesirable parasitic multipole fields.

[0112] Balance resistors may be used in the deflection coils and magnetic octopoles, which can be used to generate quadrupole fields for astigmatism correction. In particular, balance resistors can be used in conjunction with the multipole aberration corrector 101. Currently, aberration correctors are manufactured with the utmost precision to prevent unwanted residual aberrations. The radial gap around the poles can be adjusted to control magnetic flux non-uniformity.

[0113] In an exemplary embodiment, one or more parallel adjustable resistors (potentiometers) can be added to each excitation coil, and the resistors can be used to adjust the current through the excitation coil within a certain range. p may introduce voltage noise that leads to current fluctuations in the excitation coil. For example, the current fluctuations can be written as: Current Fluctuation,

number

[0114] It will be appreciated that even if mechanical tolerances are very tight and everything in the corrector is manufactured with the utmost precision, there may still be residual aberrations associated with non-uniformities and inaccuracies. These residual aberrations can be corrected by applying correction voltages to the poles or by providing auxiliary windings for correction fields.

[0115] However, it is not easy to obtain a large compensation voltage that meets the noise requirements of the compensator. Moreover, the auxiliary coil requires an additional power supply, which increases the noise of the system, and requires many parts to be manufactured.

[0116] Therefore, especially in the design of aberration correction columns, balancing resistors can be used in the deflection coils and / or magnetic multipoles.

[0117] According to an exemplary embodiment, there is provided a first excitation coil 350 of the first magnetic pole 210 and a first adjustable resistor 660 connected in parallel with the first excitation coil 350. According to an exemplary embodiment, the first adjustable resistor 660 is a balance resistor.

[0118] According to an exemplary embodiment, the first adjustable resistor 660 is adjusted to adjust the current through the first excitation coil 350. Thus, as the first adjustable resistor 660 is adjusted, the excitation changes such that more or less magnetic flux is transferred between the first magnetic pole 210 and the ring 240, thereby affecting the magnetic field on the optical axis 109.

[0119] Thus, the deflection sensitivities of the poles can be substantially equalized and the magnetic fields of the multipole stages can be aligned with the optical axis, thus correcting or minimizing imperfections in the magnetic field.

[0120] According to an exemplary embodiment, each of the further excitation coils 351 of the further magnetic pole 211 is provided with a further adjustable resistor 661. Each of the further adjustable resistors 661 is connected in parallel with each of the further excitation coils 351.

[0121] Referring now to FIG. 1 , a cross-sectional view of an aberration corrector is shown. The aberration corrector 101 is shown relative to an optical axis 109. The aberration corrector 101 is shown to include a first multipole stage 103. The aberration corrector 101 is shown to include an additional multipole stage 105. In one example, the first multipole stage 103 is a multipole stage having multiple magnetic poles. In one example, the additional multipole stage 105 includes a multipole stage having electrostatic and / or magnetic poles.

[0122] Referring now to Figure 2, a cross-sectional view of an aberration corrector is shown. As shown, the aberration corrector 101 has a first magnetic pole 210, a further magnetic pole 211, and a ring 240. Also shown are a first magnetic field modulator 220 and a further magnetic field modulator 221. As can be seen, a first air gap 230 separates the first magnetic pole 210 and the ring 240, and a further air gap 231 separates the further magnetic pole 211 and the ring 240. Also visible are the axis 219 of the first magnetic pole 210 and the inner ring surface 241.

[0123] Referring now to Figure 3, a cross-sectional view of the aberration corrector is shown. As in Figure 2, there are shown a first magnetic pole 210, a further magnetic pole 211, a first magnetic field modulator 220, a further magnetic field modulator 221, and a ring 240. Additionally, there are shown a first excitation coil 350 and a further excitation coil 351.

[0124] 4, an enlarged view of a magnetic field modulator is shown. Shown are a first magnetic pole 210, a first magnetic field modulator 220, a first air gap 230, and a ring 240. As can be seen, the first magnetic field modulator 220 may be positioned adjacent to the first air gap 230, on an inner ring surface 241 of the ring 240, or radially outward of the inner ring surface 241. As can be seen, the first magnetic field modulator 220 may be positioned along an axis extending from the axis of the first magnetic pole 210.

[0125] In the example shown, the first magnetic field modulator 220 may be a screw or may have a screw mechanism. The first magnetic field modulator 220 is shown with a first retainer 321, which is shown as a spring.

[0126] The first magnetic field modulator 220 is supported by a first guide 450, which in the illustration (see FIG. 4 or FIG. 5) is part of or within the ring 240. As shown, the first guide 450 constrains the first magnetic field modulator 220 to a position along a first axis 429 that coincides with the axis 219 of the first magnetic pole 210. As can be seen, the first magnetic field modulator 220 can be adjusted along the first axis 429.

[0127] The first axis 429 may be understood as a direction or a length. Alternatively or additionally, the first axis 429 may be understood as an axis of the first guide 450.

[0128] The first magnetic field modulator 220 may be disposed radially outward of the inner ring surface 241 along the axis 219 of the first magnetic pole 210 .

[0129] Referring now to Figure 5, an expanded view of the magnetic field modulator is shown. Similar to Figure 4, there is shown a first magnetic pole 210, a first magnetic field modulator 220, a first air gap 230, and a ring 240. The first magnetic field modulator 220 is shown positioned adjacent to the first air gap 230 and below the first magnetic pole 210, i.e., in a plane parallel to the plane of the magnetic poles.

[0130] 6, a schematic diagram of a balancing resistor is shown. As shown, a first adjustable resistor 660 is connected in parallel with the first excitation coil 350. Also shown is an additional adjustable resistor 661 connected in parallel with each additional excitation coil 351. Further shown is a current source 670 that drives the first excitation coil 350 of the first magnetic pole 210 and the additional excitation coil 351 of each additional magnetic pole 211. The current source 670 is shown connected in series with the first excitation coil 350 and the additional excitation coil 351.

[0131] 7, a schematic diagram of a charged particle beam device is shown. As shown, the charged particle beam device 707 includes a charged particle source 780, a sample stage 786, and a charged particle beam manipulation system 784 including an aberration corrector 101. As shown, the charged particle source 780 is adapted to generate a charged particle beam 782. As shown, the sample stage 786 is adapted to support a sample 788. An optical axis 109 is shown.

[0132] 8, a flow diagram illustrating a method for aligning a magnetic field of an aberration corrector is shown. The method is shown to include at least one of measuring a first deflection sensitivity and measuring a second deflection sensitivity (893), measuring a magnetic field (895), wobbling an excitation of the aberration corrector (897), and positioning a first magnetic field modulator at a first position (890).

[0133] Referring now to FIG. 9, a plot is shown that schematically illustrates the modeled effects of different magnetic field modulators. The plot shows the relative change in dipole magnitude (vertical axis) versus the relative change in magnetic field modulator position (horizontal axis). The solid line labeled "Magnetic Field Modulator A" shows the relative change in dipole magnitude achieved by a magnetic field modulator whose axis coincides with the axis of the magnetic poles (the magnetic field modulator is in the plane of the magnetic poles). The dashed line labeled "Magnetic Field Modulator B" shows the relative change in dipole magnitude achieved by a magnetic field modulator positioned above or below the plane of the magnetic poles (as shown in FIG. 5). Magnetic Field Modulator B is shown to achieve a greater dipole correction value and exhibit a more linear behavior than Magnetic Field Modulator A.

[0134] The optical axis 109 may be understood to be the optical axis 109 of the charged particle beam device 707 .

[0135] The term "substantially perpendicular" may be understood as an angle within 20 degrees, within 10 degrees, or within 5 degrees of perpendicular. The term "substantially parallel" may be understood as an angle less than 20 degrees, less than 10 degrees, or less than 5 degrees.

[0136] It will also be understood that embodiments of the first magnetic field modulator 220 are disclosed in conjunction with one or more or all of the additional magnetic field modulators 221. It will further be understood that embodiments of the first magnetic pole 210 are disclosed in conjunction with one or more or all of the additional magnetic poles 211. It will further be understood that embodiments of the first multipole stage 103 are disclosed in conjunction with one or more or all of the additional multipole stages 105.

[0137] Further examples are listed below. According to Example 1, the aberration corrector includes a plurality of magnetic poles including a first magnetic pole and an additional magnetic pole, a ring magnetically connecting the plurality of magnetic poles to each other and having a fixed distance from at least the first magnetic pole, a plurality of magnetic field modulators including a first magnetic field modulator and an additional magnetic field modulator, and a plurality of guides including a first guide and an additional guide, wherein the first magnetic field modulator includes a soft magnetic material, and the first magnetic field modulator is arranged at a first position, the first position being at least one of adjacent to a first gap separating the first magnetic pole and the ring, on an inner ring surface, and radially outward of the inner ring surface along the axis of the first magnetic pole, and the first guide restrains the first magnetic field modulator in a position along a first axis substantially parallel to or coincident with the axis of the first magnetic pole. According to Example 2, the aberration corrector is according to Example 1 and further comprises a current source adapted to drive the first magnetic pole and the further magnetic pole. According to Example 3, the aberration corrector is as described in Example 1 or 2 and further includes a holder arranged to maintain the first magnetic field modulator in the first position, or the first guide includes a first actuator. According to Example 4, the aberration corrector is as described in any one of Examples 1 to 3, and the first position of the first magnetic field modulator is based on a measured magnetic field substantially at the position of the optical axis. According to Example 5, the aberration corrector is as described in any one of Examples 1 to 4, and the first magnetic pole, the first magnetic field modulator, and the ring are supported such that the first position of the first magnetic field modulator is independent of the first distance between the first magnetic pole and the ring. According to a sixth embodiment, the aberration corrector is according to any one of the first to fifth embodiments, and the first magnetic field modulator is arranged in a plane substantially parallel to the plane of the plurality of magnetic poles. According to Example 7, the aberration corrector is as described in any one of Examples 1 to 6, and the first guide is configured to support the first magnetic field modulator at a first end position and a second end position, and at the first end position, the overlap between the first magnetic field modulator and the first magnetic pole is not zero when viewed from a direction perpendicular to the axis of the first magnetic pole. According to Example 8, the aberration corrector is as described in any one of Examples 1 to 7, wherein the first guide is adapted to support the first magnetic field modulator at a position along a length at least as long as the first air gap, the length being in a direction parallel to or coincident with the axis of the first magnetic pole. According to Example 9, a charged particle beam device includes a sample stage, a charged particle source adapted to generate a charged particle beam, and a charged particle beam manipulation system including an aberration corrector described in any one of Examples 1 to 8. According to Example 10, the charged particle beam device is as described in Example 9, and the first position of the first magnetic field modulator is based on a measured effect or a measured magnetic field of the magnetic field of the first magnetic pole on the optical axis. According to Example 11, the aberration corrector includes a plurality of magnetic poles including a first magnetic pole and an additional magnetic pole, a ring magnetically connecting the plurality of magnetic poles to each other and having a fixed interval with respect to at least the first magnetic pole, a plurality of magnetic field modulators including a first magnetic field modulator and an additional magnetic field modulator, and a plurality of guides including a first guide and an additional guide, wherein the first magnetic field modulator includes a soft magnetic material, the first magnetic field modulator is disposed at a first position, and the first guide restrains the first magnetic field modulator to a position along a first axis substantially parallel to or coincident with the axis of the first magnetic pole. According to Example 12, the aberration corrector is as described in Example 11, wherein the first magnetic field modulator is disposed in a plane substantially parallel to the plane of the plurality of magnetic poles. According to Example 13, the aberration corrector is as described in Example 11 or 12, and the first guide is configured to support the first magnetic field modulator at a first end position and a second end position, and at the first end position, the intersection of the first magnetic field modulator with the first magnetic pole in a radial direction relative to the axis of the first magnetic pole is not zero. According to Example 14, the aberration corrector is as described in any one of Examples 11 to 13, and the first guide is configured to support the first magnetic field modulator at a first end position and a second end position, and at the first end position, the overlap with the first magnetic pole of the first magnetic field modulator is not zero when viewed from a direction perpendicular to the axis of the first magnetic pole. According to Example 15, there is provided a method for aligning the magnetic field of an aberration corrector with an optical axis, the aberration corrector including a plurality of magnetic poles including a first magnetic pole and an additional magnetic pole, a ring that magnetically connects the plurality of magnetic poles to each other, the ring having a certain distance from at least the first magnetic pole, a plurality of magnetic field modulators including a first magnetic field modulator and an additional magnetic field modulator, and a plurality of guides including a first guide and an additional guide, wherein the first magnetic field modulator includes a soft magnetic material, and the first magnetic field modulator is arranged at a first position, the first position being one of adjacent to a first gap separating the first magnetic pole and the ring, or on an inner ring surface along the axis of the first magnetic pole, or radially outside the inner ring surface, and the method includes a step of positioning the first magnetic field modulator at the first position, the first position being one of a plurality of positions along a first axis that is substantially parallel to or coincident with the axis of the first magnetic pole. According to Example 16, the method is as described in Example 15, and further includes the steps of measuring a first deflection sensitivity of the first magnetic pole, measuring a second deflection sensitivity of at least one of the further magnetic poles, and positioning the first magnetic field modulator at a first position such that the first sensitivity and the second sensitivity are substantially equal. According to Example 17, the method is as described in Example 15 or 16, and further includes the steps of measuring a magnetic field using a rotating magnetic field sensor at a position substantially aligned with the optical axis, identifying a parasitic multipole field based on the measured magnetic field, and positioning a first magnetic field modulator at a first position such that the parasitic multipole field is minimized. According to Example 18, the method is as described in any one of Examples 15 to 17, and further includes the steps of driving the first magnetic pole and measuring the magnetic field of the first magnetic pole using a magnetic field sensor, wherein when the first magnetic field modulator is in the first position, the measured magnetic field of the first magnetic pole is equal to at least one of the additional magnetic poles or all of the additional magnetic poles. According to Example 19, the method is as described in any one of Examples 15 to 18, and further includes a step of wobbling the excitation of the aberration corrector, and a step of positioning the first magnetic field modulator at a first position so that image shift during wobbling is minimized. According to Example 20, the method is as described in any one of Examples 15 to 19, and further includes a step of operating an aberration corrector within the charged particle column, and a step of positioning the first magnetic field modulator at a first position is performed during operation.

[0138] While the forgoing is directed to particular embodiments, other and further embodiments may be devised without departing from the basic scope thereof, which scope is determined by the claims that follow.

Claims

1. a plurality of magnetic poles including a first magnetic pole and a further magnetic pole having an axis; a ring that magnetically connects the plurality of magnetic poles to one another, the ring having a fixed spacing relative to at least the first magnetic pole; a plurality of magnetic field modulators including a first magnetic field modulator and a further magnetic field modulator; a plurality of guides including a first guide and a further guide; Equipped with the first magnetic field modulator comprises a soft magnetic material; the first magnetic field modulator is disposed at a first position; The first position is (1) adjacent to a first gap separating the first magnetic pole and the ring, the first guide constrains the first magnetic field modulator to a position along a first axis substantially parallel to the axis of the first magnetic pole; and When viewed from a direction perpendicular to the axis of the first magnetic pole, the first magnetic field modulator is constrained to a position between a first end position on the inside in the radial direction where the first magnetic field modulator and the first magnetic pole overlap, and a second end position on the outside in the radial direction where the first magnetic field modulator and the first magnetic pole do not overlap. a location adjacent to the first void; (2) A radially inner end surface of the first magnetic field modulator is located on an inner ring surface along the axis of the first magnetic pole, or is located radially outward of the inner ring surface along the axis of the first magnetic pole and adjacent to a first gap separating the first magnetic pole and the ring; the first guide constrains the first magnetic field modulator to a position along a first axis that is coincident with the axis of the first magnetic pole; a location adjacent to the first void; At least one of Aberration corrector.

2. The aberration corrector of claim 1 , further comprising a current source adapted to drive the first magnetic pole and the further magnetic pole.

3. The aberration corrector of claim 1 , further comprising a holder arranged to maintain the first magnetic field modulator in the first position, or wherein the first guide includes a first actuator.

4. 2. The aberration corrector of claim 1, wherein the first position of the first magnetic field modulator is based on a magnetic field measured at a position substantially along the optical axis.

5. 2. The aberration corrector of claim 1, wherein the first magnetic pole, the first magnetic field modulator, and the ring are supported such that the first position of the first magnetic field modulator is independent of a first distance between the first magnetic pole and the ring.

6. 2. The aberration corrector of claim 1, wherein the first magnetic field modulator is disposed in a plane substantially parallel to the plane of the plurality of magnetic poles.

7. 2. The aberration corrector of claim 1, wherein the first guide is configured to support the first magnetic field modulator at the first end position and the second end position, and wherein the first magnetic field modulator and the first magnetic pole overlap at the first end position when viewed in a direction perpendicular to the axis of the first magnetic pole.

8. 2. The aberration corrector of claim 1, wherein the first guide is adapted to support the first magnetic field modulator at a position along at least the same length as the first air gap, the length being in a direction parallel to or coincident with the axis of the first magnetic pole.

9. a sample stage; a charged particle source adapted to generate a charged particle beam; a charged particle beam manipulation system including an aberration corrector according to any one of claims 1 to 8; A charged particle beam device comprising:

10. 10. The charged particle beam device of claim 9, wherein the first position of the first magnetic field modulator is based on a measured magnetic field or a measured effect of the magnetic field of the first magnetic pole at an optical axis.

11. a plurality of magnetic poles including a first magnetic pole and an additional magnetic pole; a ring that magnetically connects the plurality of magnetic poles to one another, the ring having a fixed spacing relative to at least the first magnetic pole; a plurality of magnetic field modulators including a first magnetic field modulator and a further magnetic field modulator; a plurality of guides including a first guide and a further guide; Equipped with the first magnetic field modulator comprises a soft magnetic material; the first magnetic field modulator is positionable within or adjacent to the ring in a radial direction relative to the axis of the first magnetic pole at a position substantially parallel to or coincident with the axis of the first magnetic pole; the first guide constrains the first magnetic field modulator to a position along a first axis substantially parallel to or coincident with the axis of the first magnetic pole; Aberration corrector.

12. 12. The aberration corrector of claim 11, wherein the first magnetic field modulator is disposed in a plane substantially parallel to the plane of the plurality of magnetic poles.

13. 13. The aberration corrector of claim 11 or 12, wherein the first guide is configured to support the first magnetic field modulator at a first end position and a second end position, and the first magnetic field modulator and the first magnetic pole intersect at the first end position in the radial direction relative to the axis of the first magnetic pole.

14. 13. The aberration corrector of claim 11 or 12, wherein the first guide is configured to support the first magnetic field modulator at a first end position and a second end position, and wherein the first magnetic field modulator and the first magnetic pole overlap at the first end position when viewed in a direction perpendicular to the axis of the first magnetic pole.

15. 1. A method for aligning a magnetic field of an aberration corrector with an optical axis, the method comprising: a plurality of magnetic poles including a first magnetic pole and an additional magnetic pole; a ring that magnetically connects the plurality of magnetic poles to one another, the ring having a constant spacing relative to at least the first magnetic pole; a plurality of magnetic field modulators including a first magnetic field modulator and a further magnetic field modulator; a plurality of guides including a first guide and a further guide; Including, the first magnetic field modulator comprises a soft magnetic material; the first magnetic field modulator is disposed at a first position; The first position is (1) adjacent to a first gap separating the first magnetic pole and the ring, the first guide constrains the first magnetic field modulator to a position along a first axis substantially parallel to the axis of the first magnetic pole; and When viewed from a direction perpendicular to the axis of the first magnetic pole, the first magnetic field modulator is constrained to a position between a first end position on the inside in the radial direction where the first magnetic field modulator and the first magnetic pole overlap, and a second end position on the outside in the radial direction where the first magnetic field modulator and the first magnetic pole do not overlap. a location adjacent to the first void; (2) A radially inner end surface of the first magnetic field modulator is located on an inner ring surface along the axis of the first magnetic pole, or is located radially outward of the inner ring surface along the axis of the first magnetic pole and adjacent to a first gap separating the first magnetic pole and the ring; the first guide constrains the first magnetic field modulator to a position along a first axis that is coincident with the axis of the first magnetic pole; a location adjacent to the first void; It is one of the The method comprises: positioning the first magnetic field modulator at the first position, the first position being one of a plurality of positions along a first axis substantially parallel to or aligned with the axis of the first magnetic pole; method.

16. 16. The method of claim 15, further comprising measuring a first deflection sensitivity of the first magnetic pole, measuring a second deflection sensitivity of at least one of the additional magnetic poles, and positioning the first magnetic field modulator at the first position such that the first deflection sensitivity and the second deflection sensitivity are substantially equal.

17. 16. The method of claim 15, further comprising measuring a magnetic field with a rotating magnetic field sensor at a position substantially aligned with the optical axis, identifying a parasitic multipole field based on the measured magnetic field, and positioning the first magnetic field modulator at the first position such that the parasitic multipole field is minimized.

18. 16. The method of claim 15, further comprising the steps of: driving the first magnetic pole; and measuring a magnetic field of the first magnetic pole with a magnetic field sensor, wherein when the first magnetic field modulator is in the first position, the measured magnetic field of the first magnetic pole is equal to at least one of the additional magnetic poles or all of the additional magnetic poles.

19. 19. The method of claim 15, further comprising the steps of: wobbling an excitation of the aberration corrector; and positioning the first magnetic field modulator at the first position so that image shift during the wobbling is minimized.

20. 19. The method of claim 15, further comprising operating the aberration corrector in a charged particle column, wherein the step of positioning the first magnetic field modulator at the first position is performed during the operation.

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