Method for determining aberrations of a charged particle beam and charged particle beam system - Patents.com

Abstract

A method for determining aberrations of a charged particle beam (11) focused by a focusing lens (120) towards a sample (10) in a charged particle beam system is described, the method comprising: (a) taking one or more images of the sample at one or more defocus settings to obtain one or more taken images (h 1...N ), and (b) providing a set of beam aberration coefficients ( i C) and simulating one or more images of the sample taken at one or more defocus settings based on the focused image of the sample to provide one or more simulated images; and (c) comparing the one or more taken images and the one or more simulated images to determine a magnitude of difference (R i ), and (d) determining a set of beam aberration coefficients ( i C) to obtain an updated set of beam aberration coefficients ( i+1 C) and provide an updated set of beam aberration coefficients ( i+1 C) is used in an iterative process to repeat (b) and (c), and the magnitude (R i Alternatively, in (b), one or more beam cross sections can be simulated, and in (c), the simulated beam cross sections are compared to one or more recovered beam cross sections recovered from one or more captured images to determine a magnitude of difference between these cross sections (R i ) can be determined. Additionally, a charged particle beam system for imaging and / or inspecting a sample configured for any of such methods is provided.

Description

[Technical field]

[0001] The embodiments described herein relate to a method for determining aberrations of a charged particle beam in a charged particle beam system, for example in an electron microscope, in particular in a scanning electron microscope (SEM). In particular, the actual value of the beam aberration coefficient can be determined, which can facilitate correction of the beam aberration and improve resolution. More particularly, the embodiments described herein relate to a method for determining beam aberration coefficients of a charged particle beam focused by a focusing lens towards a sample in a charged particle beam system, thereby facilitating the provision of an aberration-corrected charged particle beam. The embodiments further relate to a charged particle beam system for inspecting and / or imaging a sample configured for any of the methods described herein. [Background technology]

[0002] Modern semiconductor technology has created a strong demand for constructing and investigating specimens at the nanometer or even sub-nanometer scale. Micrometer and nanometer scale process control, inspection, or construction is often performed by charged particle beams, e.g., electron beams, which are generated, shaped, deflected, and focused in charged particle beam systems, such as electron microscopes or electron beam pattern generators. For inspection purposes, charged particle beams offer superior spatial resolution compared to, e.g., photon beams.

[0003] Inspection devices using charged particle beams, such as scanning electron microscopes (SEMs), have many functions in multiple industries, including but not limited to inspection of electronic circuits, exposure systems for lithography, detection systems, defect inspection tools, and test systems for integrated circuits. Such particle beam systems can use fine beam probes with high current densities. For example, in an SEM, a primary electron beam generates signal particles, such as secondary electrons (SEs) and / or backscattered electrons (BSEs), which can be used to image and / or inspect a sample.

[0004] However, it is difficult to reliably inspect and / or image a sample with good resolution by a charged particle beam system, since charged particle beams typically suffer from beam aberrations that limit the obtainable resolution. In a typical charged particle beam system, an aberration corrector is provided to at least partially compensate for the aberrations of the charged particle beam, such as spherical aberration, astigmatism, and / or chromatic aberration. The aberration-corrected charged particle beam can provide a smaller probe focus and therefore a better resolution compared to an uncorrected beam. However, it is difficult to properly adjust the settings of the aberration corrector, which may have multiple controls, such as to satisfactorily correct the beam aberrations, because the beam aberrations present in the system are generally unknown.

[0005] In view of the above, it would be beneficial to provide a method for accurately and reliably determining the aberrations of a charged particle beam focused by a focusing lens in a charged particle beam system, in particular a method for determining the actual values ​​of the beam aberration coefficients, i.e., the absolute values ​​of the beam aberration coefficients. It would also be beneficial to provide a charged particle beam system for inspecting and / or imaging a sample configured to operate according to any of the methods described herein. Summary of the Invention

[0006] In light of the above, a method for determining beam aberrations of a charged particle beam and a charged particle beam system configured to determine beam aberrations of a charged particle beam are provided by the independent claims.

[0007] According to a first aspect, there is provided a method for determining aberrations of a charged particle beam focused towards a sample by a focusing lens in a charged particle beam system, the method including: (a) capturing one or more images of the sample at one or more defocus settings to provide one or more captured images, (b) simulating one or more images of the sample captured at one or more defocus settings based on a set of beam aberration coefficients and a focused image of the sample to provide one or more simulated images, (c) comparing the one or more captured images and the one or more simulated images to determine a magnitude of a difference between the images, and (d) modifying the set of beam aberration coefficients to provide an updated set of beam aberration coefficients, and using the updated set of beam aberration coefficients in an iterative process to repeat (b) and (c) to minimize said magnitude.

[0008] According to a second aspect, there is provided a method for determining aberrations of a charged particle beam focused towards a sample by a focusing lens in a charged particle beam system, the method including: (a) taking one or more images of the sample at one or more defocus settings to provide one or more taken images and recovering one or more recovered beam cross sections from the one or more taken images, (b) simulating one or more beam cross sections at one or more defocus settings based on a set of beam aberration coefficients to provide one or more simulated beam cross sections, (c) comparing the one or more recovered beam cross sections and the one or more simulated beam cross sections to determine a magnitude of a difference between the cross sections, and (d) modifying the set of beam aberration coefficients to provide an updated set of beam aberration coefficients and using the updated set of beam aberration coefficients in an iterative process to repeat (b) and (c) to minimize said magnitude.

[0009] In some embodiments, the one or more defocus settings include one or more defocus distances and (a) taking one or more images of the sample when the sample is positioned at the one or more defocus distances from a respective beam focal point of the charged particle beam. Alternatively or additionally, the one or more defocus settings include one or more beam entrance energies of the charged particle beam that are changed from a focal beam entrance energy and (a) taking one or more images of the sample at the one or more beam entrance energies.

[0010] Both the methods according to the first and second aspects rely on comparing the image taken out of focus or the beam cross section recovered therefrom with the respective simulated out-of-focus image or the respective simulated out-of-focus beam cross section simulated based on a set of beam aberration coefficients. The initial set of beam aberration coefficients is modified in an iterative process with the aim of providing a simulated out-of-focus image or a simulated out-of-focus beam cross section close to the image actually taken or the beam cross section recovered therefrom. Then, each set of beam aberration coefficients can be considered to essentially correspond to the beam aberration coefficients actually present in the system. Accordingly, the actual value of the beam aberration coefficient can be quantitatively determined and the charged particle beam can be corrected accordingly.

[0011] According to a third aspect, there is provided a charged particle beam system for imaging and / or inspecting a sample by a charged particle beam, in particular by an electron beam, comprising a charged particle source for emitting a charged particle beam propagating along an optical axis, a sample stage, a focusing lens for focusing the charged particle beam towards a sample arranged on the sample stage, a charged particle detector for detecting signal particles emitted from the sample, a processor and a memory storing instructions that, when executed by the processor, cause the system to perform any of the methods described herein.

[0012] In particular, a charged particle beam system for imaging and / or inspecting a sample by a charged particle beam, in particular by an electron beam, is provided. The charged particle beam system includes a charged particle source for emitting a charged particle beam propagating along an optical axis, a sample stage, a focusing lens for focusing the charged particle beam towards a sample disposed on the sample stage, and a charged particle detector for detecting signal particles emitted from the sample. The system further includes a processor and a memory, the memory, when executed by the processor, causes the system to: (x1) simulate one or more images of the sample at one or more defocus settings based on a set of beam aberration coefficients and a focused image of the sample to provide one or more simulated images, or to simulate one or more beam cross sections at one or more defocus settings based on the set of beam aberration coefficients to provide one or more simulated beam cross sections; and (x2) capture one or more images of the sample imaged at the one or more defocus settings. (x3) stores instructions to compare the multiple captured images and the one or more simulated images to determine a magnitude of a difference between the images, or compare one or more recovered beam cross sections recovered from one or more captured images of the sample captured at one or more defocus settings and one or more simulated beam cross sections to determine a magnitude of a difference between the cross sections, and (x4) in an iteration after (x1) and (x2), modify the set of beam aberration coefficients to provide an updated set of beam aberration coefficients, and use the updated set of beam aberration coefficients to minimize said magnitude.

[0013] The embodiments are also directed to apparatus for carrying out the disclosed methods, including apparatus parts for performing the individual method operations. The methods can be performed by hardware parts, by a computer programmed by appropriate software, by any combination of the two, or in any other manner. Furthermore, the embodiments are also directed to methods of operating the described apparatus.

[0014] Further advantages, features, aspects and details which can be combined with the embodiments described herein are evident from the dependent claims, the description and the drawings.

[0015] So that the above-recited features of the present disclosure can be understood in detail, further details of the briefly summarized description above can be had by reference to the following embodiments, the accompanying drawings of which relate to one or more embodiments and are described below. [Brief description of the drawings]

[0016] [Figure 1] 1 is a schematic diagram of a charged particle beam system according to embodiments described herein adapted to operate according to any of the methods described herein. [Diagram 2] 1 illustrates a method for determining aberrations of a charged particle beam according to embodiments described herein. [Diagram 3] FIG. 3 is a more detailed diagram illustrating the method shown in FIG. 2. [Figure 4] FIG. 2 illustrates another method for determining aberrations of a charged particle beam according to embodiments described herein. [Diagram 5] FIG. 5 is a more detailed view of the alternative method shown in FIG. 4. [Figure 6] 5 is a flow diagram illustrating another method for determining aberrations of a charged particle beam. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0017] Reference will now be made in detail to various embodiments, one or more examples of which are illustrated in the figures. In the following description of the drawings, like reference numerals refer to like components. Generally, only the differences with respect to individual embodiments are described. Each example is provided by way of explanation and not meant as a limitation. Furthermore, features illustrated or described as part of one embodiment can also be used on or in conjunction with other embodiments to yield still further embodiments. It is intended that the description include such modifications and variations.

[0018] 1 is a schematic diagram of a charged particle beam system 100 for inspecting and / or imaging a sample 10 according to an embodiment described herein. The charged particle beam system 100 includes a charged particle source 105, in particular an electron source, for emitting a charged particle beam 11, in particular an electron beam, propagating along an optical axis A. The charged particle beam system 100 further includes a sample stage 108 and a focusing lens 120, in particular an objective lens, for focusing the charged particle beam 11 onto a sample 10 arranged on the sample stage 108. The charged particle beam system 100 further includes a charged particle detector 118, in particular an electron detector, for detecting signal particles (e.g., secondary electrons and / or backscattered electrons) emitted from the sample 10. Furthermore, an image generating unit 160 may be provided for generating one or more images of the sample 10 based on the charged particle signal received from the charged particle detector 118. Image generation unit 160 transfers one or more images of the sample to processing unit 170, which is configured to determine the aberration coefficients therefrom by the methods described herein.

[0019] The sample stage 108 can be a movable stage. In particular, the sample stage 108 can be movable in the Z direction, i.e. along the optical axis A, so that the distance between the focusing lens 120 and the sample stage 108 can be varied (see arrow 112 in FIG. 1 ). By moving the sample stage 108 in the Z direction, the sample 10 is moved toward the focal plane p of the focusing lens 120. Ito different defocus distances, such that with each stage movement, out-of-focus images of the sample 10 can be taken at predetermined increments, e.g., 0.1 μm or more and / or 2 μm or more. In some embodiments, the sample stage 108 can also be movable in a plane orthogonal to the optical axis A (also referred to herein as the XY plane). By moving the sample stage 108 in the XY plane, a designated surface area of ​​the sample 10 can be moved into an area below the focusing lens 120, such that the charged particle beam 11 can be focused thereon to image the designated surface area.

[0020] The beam optical components of the charged particle beam system 100 are typically disposed in a vacuum chamber 101, which can be evacuated, such that the charged particle beam 11 propagates along an optical axis A from a charged particle source 105 towards a sample stage 108 and is subjected to a reduced pressure, e.g. -3 Pressure below 10 mbar or -5 The sample 10 can be impinged under a pressure below mbar.

[0021] In some embodiments, the charged particle beam system 100 may be an electron microscope, in particular a scanning electron microscope. A scanning deflector 107 may be provided for scanning the charged particle beam 11 across the surface of the sample 10 along a predetermined scan pattern, for example in the X and / or Y directions.

[0022] In some embodiments, a condenser lens system 106 can be arranged downstream of the charged particle source 105, in particular for collimating the charged particle beam 11 propagating towards a focusing lens 120. In some embodiments, the focusing lens 120 is an objective lens configured to focus the charged particle beam 11 onto the sample 10, in particular a magnetic objective lens, an electrostatic magnetic lens, or a combined magnetic-electrostatic lens.

[0023] One or more surface regions of the sample 10 can be inspected and / or imaged by the charged particle beam system 100. As used herein, the term "sample" can refer to, for example, a substrate having one or more layers or features formed thereon, a semiconductor wafer, a glass substrate, a web substrate, or another sample to be inspected. The sample can be inspected to one or more of: (1) image the surface of the sample, (2) measure dimensions of one or more features of the sample, for example laterally, i.e., in the XY plane, (3) perform critical dimension measurements and / or metrology, (4) detect defects, and / or (5) investigate the quality of the sample.

[0024] To inspect the sample 10 with the charged particle beam 11, the charged particle beam 11 is typically focused on the sample surface by a focusing lens 120. When the charged particle beam 11 hits the sample surface, secondary electrons and / or backscattered electrons (called "signal electrons") are emitted from the sample. The signal electrons provide information about spatial properties and dimensions of features of the sample and can be detected by a charged particle detector 118. By scanning the charged particle beam 11 across the sample surface, for example by a scanning deflector 107, and detecting the signal electrons depending on the generation position of the signal electrons, the sample surface or a part thereof can be imaged, for example by an image generating unit 160, which can be configured to provide an image of the sample 10 based on the received signal electrons.

[0025] The small spot of the charged particle beam 11 focused on the sample surface increases the obtainable image resolution. Accordingly, to obtain a sharp in-focus image of the sample 10, the sample surface is located within the focal plane p of the focusing lens 120 during inspection. I In this specification, a clear image of the sample 10 taken in focus is referred to as an “in-focus image h I ", where the subscript I denotes "in focus." Similarly, in this specification, the focal plane p IThe beam cross section of the charged particle beam 11 in the focal point is called the "focus beam cross section g I " and the subscript I stands for "in focus."

[0026] In particular, an image can be mathematically represented in real space (= in the image domain, i.e. according to spatial coordinates) or in Fourier space (= in the frequency domain, i.e. according to spatial frequencies). An image in Fourier space can be calculated from an image in real space via the Fourier transform (FT). Both of the above representations contain the corresponding information of the image. In this specification, images in real space are represented by the lowercase "h" n " and the image in Fourier space is represented by a capital "H n For example, "h I ” denotes the focused image of the sample in real space, and “H I ” denotes the focused image of the sample in Fourier space, which is h I Similarly, in this specification, the beam cross section in real space is represented by a lowercase "g n " and in this specification, the beam cross section in Fourier space is denoted by a capital "G n For example, "g I ” denotes the focal beam cross section of a charged particle beam in real space, and “G I ” denotes the focal beam cross section of the charged particle beam in Fourier space, which is g I In some of the embodiments described herein, the image and beam cross section in real space can be Fourier transformed into Fourier space, and vice versa, via a Fast Fourier Transform (FFT) algorithm.

[0027] In this specification, the simulated image and the simulated beam cross section are

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[0028] In charged particle beam systems, beam aberrations typically result in a magnified or distorted beam cross-section, thereby reducing the achievable resolution. For example, spherical aberration in the system, typically introduced by lenses, can cause the focal plane p I The expanded focal beam cross section g I , and astigmatism can result in different focal points for light rays propagating in different planes, resulting in a blurred image.

[0029] Charged particle beam systems have, for example, (1) spherical aberration (beam aberration coefficient C 3,0 or C s ), (2) defocus (quantitatively expressed by the beam aberration coefficient C 1,0 It is quantitatively expressed by, and in this specification, C defocus (3) First-order astigmatism (beam aberration coefficient C 1,2 It is quantitatively expressed by, and in this specification, C ast,2-fold (4) Second-order astigmatism (beam aberration coefficient C 2,3 It is quantitatively expressed by, and in this specification, C ast,3-fold (5) Third-order astigmatism (beam aberration coefficient C 3,4 It is quantitatively expressed by, and in this specification, C ast,4-fold (6) coma aberration (beam aberration coefficient C 2,1 It is quantitatively expressed by, and in this specification, C coma (7) Star aberration (beam aberration coefficient C 3,2 It is quantitatively expressed by, and in this specification, C starDifferent types of beam aberrations may exist and require correction, such as chromatic aberrations (also called chromatic aberrations), depending on the energy spread of the charged particle beam and the dispersion of the beam optical components of the system. In addition, there may be multiple chromatic aberrations, which can be quantitatively represented by one or more chromatic aberration coefficients. A set of beam aberration coefficients i C can include two, three, or more of the beam aberration coefficients listed above, e.g. i C=[ i C s , i C defocus , i C ast,2-fold ].

[0030] The beam aberrations can be corrected by an aberration corrector, for example an electrostatic or magnetic multipole corrector. Although an aberration corrector 109 is shown diagrammatically in FIG. 1, it should be understood that a charged particle beam system can also include more than one aberration corrector, and that these aberration correctors are not necessarily located at one position along the optical axis A. For example, C ast,2-fold In order to correct for , a stigmator including a quadrupole may be provided, and C ast,3-fold and / or C. ast,4-fold To correct for this, higher order multipoles can be provided. s More complex correctors may also be provided to compensate for .Various types of aberration correctors are known for correcting various beam aberrations.

[0031] Adjusting the aberration correctors to properly correct one or more types of beam aberrations is difficult because the amount of beam aberration present in the system is generally unknown. Although it is theoretically possible to set one or more aberration correctors to compensate for pre-calculated beam aberrations introduced by the beam optical components of the system, such an approach is typically not accurate enough. In particular, not all sources of beam aberrations are known, especially quantitatively. For example, beam aberrations may be introduced by initially unknown system inaccuracies such as mechanical, magnetic, or electrostatic inaccuracies, charge contamination, material inhomogeneities, manufacturing imperfections, etc. The beam optical components may include one or more of an objective lens, a collimator, a deflector, a scanning deflector, a beam separator, a charged particle detector, and an aberration corrector.

[0032] Different methods can be used to estimate the beam aberrations in a charged particle beam system so that they can be appropriately corrected. Some methods rely on visual inspection of the charged particle beam, for example in the far field, which can indicate the aberrations present in the system. Other methods rely on the analysis of captured images. In particular, images captured out of focus can provide information about the beam cross section (i.e., the probe shape) through respective calculations, which can give information about the specific type of beam aberrations. For example, astigmatic beams are typically non-rotationally symmetric. Known methods rely on the extraction of line profiles from the beam cross section, from which the beam aberrations can be estimated.

[0033] However, such a concept only allows a relative estimation of the aberrations and does not allow the recovery of the absolute values ​​of the aberration coefficients. The "absolute value" of the beam aberration coefficients is C, expressed in [mm]. sThese values ​​can be understood to be actual quantitative values ​​of the beam aberration coefficients, such as , which directly allow for an appropriate setting of the aberration corrector, based on the determined absolute values ​​of the beam aberration coefficients. In particular, previously known methods only allow for a relative estimation of the beam aberrations, which may vary from measurement to measurement and may depend on the choice of numerical parameters in the retrieval algorithm.

[0034] The methods described herein allow for accurate and reliable determination of the aberrations of a charged particle beam, in particular the determination of a quantitative value of a set of beam aberration coefficients indicative of the beam aberrations present in the system. The charged particle beam system 100 described herein includes a processor and a memory (shown in FIG. 1 as processing unit 170), which stores instructions that, when executed by the processor, cause the system to perform any of the methods described herein. In some embodiments, the set of beam aberration coefficients determined by the processing unit 170 can then be directly transferred to the aberration corrector 109, which can then compensate for one or more of the beam aberrations and provide an aberration-compensated charged particle beam.

[0035] Figures 2 and 3 show diagrams illustrating one method of determining the aberrations of a charged particle beam according to an embodiment described herein. The diagram in Figure 3 shows optional additional details compared to the diagram in Figure 2. The methods in Figures 2 and 3 use an image-based aberration coefficient fitting routine, while the methods in Figures 4 and 5 use a spot-based aberration coefficient fitting routine.

[0036] In block 210 of FIG. 2, one or more images of the sample 10 are captured at one or more defocus settings, in particular by the image generation unit 160 (shown in FIG. 1), to generate one or more captured images (h 1...N ) between the sample 10 and the respective beam focal points of the charged particle beam. 1...N) can be included in the image. As used herein, a defocus distance is understood to be the distance (>0) between the sample and the beam focus when an image is taken. Specifically, it is possible that the sample is one or more defocus distances (z 1...N ), one or more images of the sample can be taken, thus forming one or more captured images (h 1...N ) is an out-of-focus image of the sample. Naturally, increasing the defocus distance results in increased blurring of each captured image, since the probe size generally increases with the defocus distance and the resolution generally decreases.

[0037] In some embodiments, two, three, six, or more multiple images may be taken at two, three, six, or more different defocus distances between the sample and the respective beam focal point. Specifically, at least one image of the sample may be taken at an overfocus distance, i.e., a defocus setting where the sample is positioned further away from the focusing lens 120 than the beam focal point of the charged particle beam (defocus distance z shown in FIG. 1). 1 1. Furthermore, at least one image of the sample can be taken at an underfocus distance, i.e., at a defocus setting where the sample is located closer to the focusing lens 120 than the respective beam focal point of the charged particle beam (see FIG. 1 for the defocus distance z 2...N In this specification, the first defocus distance z 1 The image taken with h 1 In this specification, the nth defocus distance z n The image taken with h n A total of N images can be taken, (h 1...N ) is indicated.

[0038] The defocus distance can be changed by changing the focusing strength of the focusing lens 120, e.g., by a predetermined increment (schematically shown in FIG. 1). In particular, increasing the focusing strength of the focusing lens shifts the respective beam foci and focal planes toward the focusing lens relative to the sample, and decreasing the focusing strength shifts the respective beam foci and focal planes away from the focusing lens relative to the sample, thus changing the defocus distance. Alternatively or additionally, the defocus distance can be changed by moving the sample stage 108, e.g., by a predetermined increment, particularly in the Z direction (along the optical axis A), while maintaining a constant focus strength, particularly provided by the focusing lens 120.

[0039] In some embodiments, which may be combined with other embodiments described herein, the one or more defocus settings may include one or more beam entrance energies (E 1...N ) can be included. I can be understood to be the beam entrance energy that provides a beam focus on the sample such that the sample is located within the focus. Focused beam entrance energy E I Changing the beam incidence energy from (e.g., by changing the potential of the particle source (emitter) or sample (wafer bias)) can shift the beam focus away from the sample, and the changed beam incidence energy thus results in a "defocused image" of the sample.

[0040] One or more defocus settings can be adjusted to achieve a focal beam entrance energy E I , in particular one or more beam entrance energies (E 1...N Specifically, a plurality of different beam incidence energies (E 1...N ), multiple images of the sample 10 can be taken, so that one or more captured images (h 1...N) contains multiple energy defocused images of the sample.

[0041] In some embodiments, the one or more defocus settings may be set to one or more different defocus distances (z 1...N ), and one or more different beam entrance energies (E 1...N ), where images are taken not only at one or more modified defocus distances but also at one or more modified defocus energies, this can facilitate reliable and accurate determination of not only "geometric" beam aberration coefficients such as astigmatism and spherical aberration, but also one or more "chromatic" aberration coefficients.

[0042] 2 and 3, at box 220, one or more images of the sample 10 are simulated to generate one or more simulated images.

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[0044] The image in box 220 is a focused image (h I ) and a set of beam aberration coefficients i Based on C, the in-focus image (h I ) can be generated by the image generating unit 160 at a focused setting of the charged particle beam system and transferred to the processing unit 170, i.e. the focused image can actually be taken by the charged particle beam system at a focused setting. Alternatively, the focused image h I may already be known to the processing unit 170 in advance, for example because a sample with a known design is used to determine the beam aberrations. As explained above, the focused image is calculated in real space (h I ) or Fourier space (H I ) can be provided.

[0045] An initial set of beam aberration coefficients 1 C can be initially used for simulation in box 220. An initial set of beam aberration coefficients 1 C may be an initial estimate of the beam aberration coefficients, e.g., based on experience, aberration estimation processes known in the art, and / or knowledge of the beam optical components of the system. Alternatively, an initial set of beam aberration coefficients 1 At C, some or all of the beam aberration coefficients can be set to zero.

[0046] One or more defocus settings can be adjusted to one or more defocus distances (z 1...N ), the one or more simulated images are at one or more defocus distances (z 1...N Alternatively or additionally, one or more defocus settings may be used to simulate images of the sample taken at one or more beam entrance energies (E 1...N ), the one or more simulated images include one or more beam entrance energies (E 1...N ) includes simulated images of samples taken at

[0047] As shown diagrammatically in FIGS. 2 and 3, the input data for the simulation of frame 220 is the defocus setting previously used for the captured image, the focused image H I , and an initial or updated set of beam aberration coefficients i C / i+1 It may contain C.

[0048] In box 230, one or more captured images (h 1...N ) and one or more simulated images

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[0050]

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[0051] The comparison in frame 230 is performed using one or more captured images (H n ) and a corresponding simulated image of the one or more simulated images.

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[0053] In particular, different types of beam aberrations are exhibited to different degrees at different defocus settings. For example, some beam aberrations may be better determined near the focal plane, while other beam aberrations may be better determined away from the focal plane, and some beam aberrations, such as higher order astigmatism, can be well detected by comparing one or more overfocused images with one or more underfocused images of each. Therefore, to reliably determine some beam aberration coefficients of a set, it is useful to compare multiple captured images (e.g., six, eight, ten or more images, some captured underfocus and some captured overfocus) with multiple simulated images of each defocus setting. By minimizing the summed difference between the respective images, the fitting routine described herein can determine some beam aberration coefficients that are very close to the respective actual beam aberration coefficients present in the system.

[0054] (R i ), a set of beam aberration coefficients is calculated. i By changing C, we obtain an updated set of beam aberration coefficients. i+1 C, providing an updated set of beam aberration coefficients i+1 C is used in an iterative process to repeat the simulation of box 220 and the comparison of box 230. Specifically, the magnitude (R i ), then in box 220, the updated set of beam aberration coefficients is i+1 Based on C, one or more updated simulated images are calculated, and in box 230, one or more captured images (h 1...N ) is compared to one or more updated simulated images.

[0055] In particular, the minimum magnitude of the difference between one or more captured images and one or more simulated images (Rmin ), the simulation in box 220, the comparison in box 230, and i+1 To provide C i The modification of C can be repeated in an iterative process, with each updated set of beam aberration coefficients at each iteration being calculated as the actual beam aberration coefficients, fit Specifically, as shown diagrammatically in box 240 of FIG. 2 and FIG. 3, after each iteration, (R i =R min ) can be checked. (R i =R min ), the iterative process can be stopped, i C is the actual beam aberration fit C. If not, the next iteration can continue.

[0056] In some implementations, a minimum magnitude (R min ) is obtained. In particular, the beam aberration coefficients of the set of beam aberration coefficients are changed to obtain a difference (R min A multi-dimensional transformation routine can be used to recover a set of beam aberration coefficients that result in

[0057] In some embodiments, which can be combined with other embodiments described herein, the actual beam aberrations are corrected by one or more aberration correctors, in particular by one or more electrostatic and / or magnetic multipole correctors. fit C can be partially or fully corrected to provide an aberration-corrected charged particle beam.

[0058] In some embodiments, which can be combined with other embodiments described herein, a set of beam aberration coefficients ( i C) is i C s , i C defocus , iC astigmatism,2-fold , i C astigmatism,3-fold , i C astigmatism,4-fold , i C star , and i C coma , as well as one, two, or more chromatic aberration coefficients i C c The method described herein may include two, three, or more coefficients from the group consisting of: n Moreover, the method described herein allows for accurate determination of the geometric beam aberration coefficients by varying the beam entrance energy E, particularly when taking and simulating one or more defocused images. n By varying the chromatic beam aberration coefficients, it is possible to accurately determine the chromatic beam aberration coefficients. Accordingly, by providing the absolute value of each beam aberration coefficient as a result of the iterative process described herein, all relevant beam aberration coefficients can be accurately, and in particular quantitatively, determined.

[0059] In some embodiments, the simulation of frame 220 is performed using a set of beam aberration coefficients i 3. Calculating the beam cross section of the charged particle beam at each defocus setting of the one or more defocus settings based on C. The calculation of the beam cross section at a specific defocus setting can be performed by a wave optics simulation using the aberration coefficients as input parameters. As shown in box 220 of FIG. 3, the beam cross section can be calculated by a spatial

[0060]

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[0061] Then, for each defocus setting, the respective simulated images in Fourier space

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[0065] In some embodiments, the simulated image in Fourier space

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[0067] The above-described determination method shown in Figures 2 and 3 allows obtaining absolute values ​​of beam aberration coefficients of a charged particle beam in a charged particle beam system, in particular in a scanning electron microscope, directly from one or more SEM images taken at one or more defocus settings. In this method, unlike other methods, a deconvolution of one or more taken images is not required to recover information about the respective beam cross-section from the one or more taken images. A goodness-of-fit routine in the processing unit determines the absolute values ​​of the beam aberration coefficients of a charged particle beam. fit It can provide a level of confidence in C accuracy that has not been possible until now.

[0068] Accurate knowledge of the beam aberrations in a charged particle beam system, especially for imaging, defect review, metrology, electron beam inspection, and / or critical dimensions, is key to improving the performance of the system. The beam aberrations obtained by the methods described herein can be used, for example, (1) to reduce the beam aberrations by respective aberration correctors, (2) as an empirical basis for the development of beam optical components of future systems, (3) to ensure repeatability and consistency, and (4) to compare the determined values ​​with simulations.

[0069] Figures 4 and 5 show diagrams illustrating a modified method of determining the aberration of a charged particle beam according to an embodiment described herein. The diagram in Figure 5 shows optional further details compared to the diagram in Figure 4. Different from the method shown in Figures 2 and 3, this modified method uses a spot-based aberration coefficients fitting routine instead of an image-based aberration coefficients fitting routine. In addition to the difference, the modified method can include any of the features of the above-mentioned methods, as those skilled in the art will easily understand, and the respective features and descriptions will not be repeated below.

[0070] In box 210, one or more images of the sample 10 are captured at one or more defocus settings to obtain one or more captured images (h 1...N ) As already explained above with respect to FIG. 2 and FIG. 3, the one or more defocus settings provide one or more defocus distances (z 1...N Alternatively or additionally, the one or more defocus settings can include a focused beam entrance energy (E I ) to the one or more beam entrance energies (E 1...N ). In particular, a plurality of 2, 3, 6 or more images of the sample are taken at 2, 3, 6 or more different defocus settings, in particular at least one or more images are taken at an underfocus setting and at least one or more images are taken at an overfocus setting. The defocus distance can be changed by changing the focusing strength of the focusing lens or by moving the sample stage relative to a constant focal plane of the focusing lens.

[0071] Unlike the method shown in FIGS. 2 and 3, in box 410, one or more captured images (h 1...N ) to one or more recovery beam cross sections (g 1...N) is retrieved. The out-of-focus beam profile can be extracted from the out-of-focus image via several different profile extraction methods. One exemplary probe profile extraction method is described below.

[0072] One or more captured images (h 1...N ) from one or more recovery beam cross sections (g 1...N The recovery of the image (h) can be based on deconvolution in real space, which is equivalent to division in Fourier space. As shown in box 410 of FIG. 5, one or more captured images (h 1...N ) to one or more recovery beam cross sections (g 1...N ) is specifically obtained by collecting one or more captured images (h 1...N ) to obtain one or more captured images in Fourier space (H 1...N ) and providing one or more captured images in Fourier space (H 1...N ) into the focused image of the sample in Fourier space (H I ) in Fourier space. n ) to the focused image of the sample (H I ) which results in a pure beam profile, i.e. a beam cross section without sample information. The recovered beam cross section in Fourier space (G n ) is inverse Fourier transformed to obtain the cross section of the collected beam in real space (g n ) can be obtained.

[0073] As further shown in box 410 of FIG. 5, one or more captured images (h 1...N ) to one or more recovery beam cross sections (g 1...N ) can optionally include the application of a filter, particularly if the retrieval is performed in Fourier space (as shown in FIG. 5), the adaptive filter term

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[0079] In box 420, one or more beam cross sections are simulated at one or more defocus settings to generate one or more simulated beam cross sections.

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[0081] The beam cross section of frame 420 is a set of beam aberration coefficients iOptionally, a focal beam cross section can be simulated for each defocus setting based on C.

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[0083] An initial set of beam aberration coefficients 1 C is box 420, one or more simulated beam cross sections

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[0084] In box 430, one or more recovery beam cross sections (g 1...N ) and one or more simulated beam cross sections

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[0089] The comparison of frame 430 shows the cross section of each recovery beam (g n ) and the corresponding simulated beam cross section

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[0091] (R i ), a set of beam aberration coefficients is calculated. i By changing C, we obtain an updated set of beam aberration coefficients. i+1 C, providing an updated set of beam aberration coefficients i+1 C is used in an iterative process to repeat the simulation in box 420 and the comparison in box 430. Specifically, the magnitude (R i ), then in box 420, the updated set of beam aberration coefficients is i+1Based on C, one or more updated simulated beam cross sections are calculated, and in box 430, one or more recovered beam cross sections (g 1...N ) is compared to one or more updated simulated images.

[0092] In particular, the minimum magnitude of the difference between one or more recovered beam cross sections and one or more simulated beam cross sections (R min ), the simulation in box 420, the comparison in box 430, and i+1 To provide C i The modification of C can be repeated in an iterative process, and each updated set of beam aberration coefficients in each iteration is calculated as the actual beam aberration coefficient fit Specifically, as shown diagrammatically by box 240 in Figs. 4 and 5, after each iteration, (R i =R min ) can be checked. (R i =R min ), the iterative process can terminate, i C is the actual beam aberration fit C. If not, the next iteration can continue.

[0093] Optionally, one or more beam aberration correctors then correct the beam aberrations. fit C can be partially or fully corrected to provide a corrected charged particle beam. For further details and other optional features, see the above description of Figures 2 and 3, which will not be repeated here.

[0094] The deformation determination method shown in Figures 4 and 5 allows obtaining absolute values ​​of beam aberration coefficients of a charged particle beam in a charged particle beam system, unlike other estimation methods that only allow relative estimation of beam aberration coefficients. A goodness of fit routine in the processing unit calculates the obtained aberration coefficients fit It can provide a level of confidence in C accuracy that has not been possible until now.

[0095] FIG. 6 is a flow diagram illustrating a modified method for determining aberrations of a charged particle beam described herein. First, a number of images (h 1...N ) (six images in Fig. 6) at different defocus distances z 1...N (In Figure 6, three images are overfocused and three are underfocused.) 1...N ) for each defocus distance, 1...N ) are collected. In addition, multiple beam cross sections are

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[0098] Specifically, the following embodiments are described herein:

[0099] Embodiment 1: A method for determining aberrations of a charged particle beam (11) focused by a focusing lens (120) towards a sample (10) in a charged particle beam system (100), comprising: (a) taking one or more images of the sample at one or more defocus settings, and determining one or more taken images (h 1...N ), and (b) providing a set of beam aberration coefficients ( i C) and a focused image of the sample (h I ) to simulate one or more images of the sample taken at one or more defocus settings to obtain one or more simulated images

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[0101] Embodiment 2: One or more defocus settings are configured to adjust one or more defocus distances (z 1...N ), so that in (a), the sample is at one or more defocus distances (z 1...N ), one or more images are taken, and in (b), one or more simulated images are taken at one or more defocus distances (z 1...N 2. The method of claim 1, further comprising a simulated image of the sample taken at 300 nm.

[0102] Embodiment 3: The method of embodiment 1 or 2, wherein in (a), a plurality of six or more images are taken at six or more different defocus distances, in particular by changing the focusing strength of the focusing lens in predetermined increments or by moving the sample stage relative to the focusing lens in predetermined increments.

[0103] Embodiment 4: The method of embodiment 3, wherein the one or more captured images include at least one or more images captured at an over-focus distance, as well as at least one or more images captured at an under-focus distance.

[0104] Embodiment 5: One or more defocus settings are configured to change one or more beam injection energies (E 1...N 5. The method of any of the preceding claims, wherein in (a), the one or more captured images are taken at one or more beam entrance energies, and in (b), the one or more simulated images include simulated images of the sample taken at one or more beam entrance energies. In particular, the one or more defocus settings include a plurality of different beam entrance energies of the charged particle beam impinging on the sample. In some embodiments, the one or more defocus settings include different defocus distances and different beam entrance energies.

[0105] Embodiment 6: A minimum magnitude of difference (R min ), (b) and (c) are repeated until an updated set of beam aberration coefficients ( i+1 C) is the actual beam aberration ( fit The method according to any one of the preceding claims, wherein C) is specifically constituted by an absolute value.

[0106] Embodiment 7: The actual beam aberrations ( fit7. The method of embodiment 6, further comprising correcting C) to provide a corrected charged particle beam.

[0107] Embodiment 8: A method as described in any one of embodiments 1 to 7, wherein in (c), the one or more captured images and the one or more simulated images are compared in Fourier space or, alternatively, in real space.

[0108] In embodiment 9:(c), the comparing includes calculating a difference value between each image of the one or more captured images and a corresponding simulated image of the one or more simulated images, and summing the difference values ​​to obtain a magnitude (R i 9. The method according to any of the preceding claims, comprising obtaining a vector of vectors, each vector being a vector of vectors, each vector being a vector of vectors, and

[0109] In embodiment 10:(b), the simulating includes simulating a set of beam aberration coefficients ( i and calculating a beam cross section of the charged particle beam based on C) and calculating each simulated image in Fourier space based on a product of the beam cross section in Fourier space and the focused image in Fourier space.

[0110] Embodiment 11: The method of embodiment 10, wherein calculating each simulated image in Fourier space further comprises division by a focal beam cross-section in Fourier space.

[0111] Embodiment 12: A method for determining aberrations of a charged particle beam (11) focused by a focusing lens (120) towards a sample (10) in a charged particle beam system (100), comprising: (a) taking one or more images of the sample at one or more defocus settings to provide one or more captured images, and recovering one or more recovered beam cross sections from the one or more captured images; (b) calculating a set of beam aberration coefficients ( iC), simulating one or more beam cross sections at one or more defocus settings to provide one or more simulated beam cross sections; and (c) comparing the one or more recovered beam cross sections and the one or more simulated beam cross sections to determine a magnitude of difference between the cross sections (R i ), and (d) determining a set of beam aberration coefficients ( i C) to obtain an updated set of beam aberration coefficients ( i+1 C) and provide an updated set of beam aberration coefficients ( i+1 C) is used in an iterative process to repeat (b) and (c), and the magnitude (R i and minimizing

[0112] Embodiment 13: One or more defocus settings are configured to adjust one or more defocus distances (z 1...N ), so that in (a), one or more images are captured at one or more defocus distances (z 1...N ), and in (b), one or more beam cross sections are captured at one or more defocus distances (z 1...N 13. The method of claim 12, wherein the method is simulated by

[0113] Embodiment 14: The method described in embodiment 12 or 13, wherein in (a), a plurality of six or more images are taken at six or more different defocus distances, in particular by changing the focusing strength of the focusing lens in predetermined increments or by moving the sample stage relative to the focusing lens in predetermined increments.

[0114] Embodiment 15: The method of embodiment 14, wherein the plurality of captured images includes at least one image captured at an over-focus distance and at least one image captured at an under-focus distance.

[0115] Embodiment 16: One or more defocus settings are configured to change one or more beam entrance energies (E 1...N ), whereby in (a) one or more images are taken at one or more beam entrance energies, and in (b) one or more beam cross sections are taken at one or more beam entrance energies (E 1...N 16. The method according to any one of embodiments 12 to 15, wherein the one or more defocus settings include a plurality of beam entrance energies, such as one or more beam energies above the focal beam entrance energy and one or more beam energies below the focal beam entrance energy.

[0116] Embodiment 17: A minimum magnitude of difference (R) between one or more recovered beam cross sections and one or more simulated beam cross sections. min ), (b) and (c) are repeated until an updated set of beam aberration coefficients ( i+1 C) is the actual beam aberration ( fit 17. The method according to any one of embodiments 12 to 16, wherein C) is an absolute value.

[0117] Embodiment 18: The actual beam aberrations ( fit 18. The method of embodiment 17, further comprising correcting C) to provide a corrected charged particle beam.

[0118] Embodiment 19: A method as described in any of embodiments 12 to 18, wherein in (c), the one or more captured images and the one or more simulated images are compared in real space or, alternatively, in Fourier space.

[0119] In embodiment 20:(c), the comparing includes calculating a difference value between each recovered beam cross-section and a corresponding simulated beam cross-section and summing said difference values ​​to obtain a magnitude (R i and obtaining a signal from the signal generator.

[0120] Embodiment 21: In (c), a method described in any of embodiments 12 to 20, wherein recovering one or more recovery beam cross sections from one or more captured images includes dividing one or more captured images in Fourier space by a focused image of the sample in Fourier space.

[0121]

[0046] Embodiment 22: Recovering one or more recovered beam cross sections from one or more captured images is performed using adaptive filter terms

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[0122] In the embodiment 23:(d), a minimum magnitude (R min 23. The method according to any one of the preceding claims, wherein the beam aberration coefficients of the set of beam aberration coefficients are successively and / or in parallel modified, in particular based on a multi-dimensional modification routine, until a first beam aberration coefficient is obtained. For example, a magnitude (R i ) until we obtain the minimum of a set of beam aberration coefficients ( i C), and then the magnitude (R i ) until a minimum value of the beam aberration coefficients ( i C) can be modified, and so on. Alternatively, several beam aberration coefficients can be modified in parallel.

[0123] Embodiment 24: A method as described in any of embodiments 1 to 23, wherein taking one or more images of the sample includes taking one or more images of the sample at one or more under-focus distances and taking one or more images of the sample at one or more over-focus distances.

[0124] Embodiment 25: A method according to any of embodiments 1 to 24, wherein taking one or more images of the sample comprises taking a plurality of images of the sample at a plurality of different defocus distances, in particular by changing the focusing strength of the focusing lens in predetermined increments, or alternatively by changing the distance between the focusing lens and the sample in predetermined increments, in particular by changing the distance in equal increments, for example of 0.1 μm or more and 2 μm or less, respectively.

[0125] Embodiment 26: A set of beam aberration coefficients ( i C) i C s , i C defocus , i C astigmatism,2-fold , i C astigmatism,3-fold , i C astigmatism,4-fold , i C star , i C coma 26. The method according to any one of the preceding claims, comprising two, three or more coefficients from the group consisting of:

[0126] The methods described in the above embodiments may be performed by any of the charged particle beam systems described herein.

[0127] Embodiment 26: A charged particle beam system for inspecting and / or imaging a sample, comprising a charged particle source 105 for emitting a charged particle beam 11 propagating along an optical axis, a sample stage 108, a focusing lens 120 for focusing the charged particle beam toward a sample 10 positioned on the sample stage, a charged particle detector 118 for detecting signal particles emitted from the sample, a processor and a memory, the memory storing instructions that, when executed by the processor, cause the system to perform a method described in any of the above embodiments.

[0128] Embodiment 27: A charged particle beam system for inspecting and / or imaging a sample, comprising: a charged particle source for emitting a charged particle beam propagating along an optical axis; a sample stage; a focusing lens for focusing the charged particle beam towards a sample disposed on the sample stage; a charged particle detector for detecting signal particles emitted from the sample; a processor; and a memory, wherein the memory, when executed by the processor, provides the system with a (x1) set of beam aberration coefficients ( i C) and simulating one or more images of the sample when taken at one or more defocus settings based on the focused image of the sample to provide one or more simulated images; and (x2) comparing the one or more taken images of the sample taken at the one or more defocus settings and the one or more simulated images to determine a magnitude of difference between the images (R i ), and (x3) in the iterations after (x1) and (x2), a set of beam aberration coefficients ( i C) to obtain an updated set of beam aberration coefficients ( i+1 C) and provide an updated set of beam aberration coefficients ( i+1 C) is used to calculate the magnitude (R i ) to minimize the charge in the charged particle beam.

[0129] Embodiment 28: A charged particle beam system for inspecting and / or imaging a sample, comprising: a charged particle source for emitting a charged particle beam propagating along an optical axis; a sample stage; a focusing lens for focusing the charged particle beam towards a sample disposed on the sample stage; a charged particle detector for detecting signal particles emitted from the sample; a processor; and a memory, wherein the memory, when executed by the processor, provides the system with a (x1) set of beam aberration coefficients ( i C), simulating one or more beam cross sections at one or more defocus settings to provide one or more simulated beam cross sections; and (x2) one or more captured images (h 1...N ) to one or more simulated beam cross sections, and measure the magnitude of the difference between these cross sections (R i ), and (x3) in the iterations after (x1) and (x2), a set of beam aberration coefficients ( i C) to obtain an updated set of beam aberration coefficients ( i+1 C) and provide an updated set of beam aberration coefficients ( i+1 C) is used to calculate the magnitude (R i ) to minimize the charge in the charged particle beam.

[0130] Embodiment 29: A charged particle beam system as described in embodiment 27 or 28, wherein the one or more defocus settings include one or more defocus distances, in particular multiple different defocus distances, of the sample from the respective beam foci of the charged particle beam when the one or more images are taken and simulated.

[0131] Embodiment 30: A charged particle beam system described in any of embodiments 27 to 29, wherein the one or more defocus settings include one or more beam injection energies of the charged particle beam that are changed from the focal beam injection energy when the one or more images are taken and simulated, in particular a plurality of different beam injection energies.

[0132] Embodiment 31: A charged particle beam system described in any of embodiments 27 to 30, further comprising an image generation unit for generating one or more captured images of a sample at one or more defocus settings, transferring information about the one or more defocus settings for simulation at (x1), and transferring the one or more captured images for comparison at (x2).

[0133] The charged particle beam systems described herein can be configured to operate according to any of the methods described herein.

[0134] While the above is directed to embodiments, other and further embodiments may be devised without departing from the scope of the invention, which is determined by the claims that follow.

Claims

1. 1. A method for determining aberrations of a charged particle beam focused by a focusing lens towards a sample in a charged particle beam system, comprising: (a) capturing one or more images of the sample at one or more defocus settings to provide one or more captured images; (b) A set of beam aberration coefficients ( i C) and simulating one or more images of the sample taken at the one or more defocus settings based on the focused image of the sample to provide one or more simulated images. (c) comparing the one or more captured images and the one or more simulated images to determine a magnitude of difference (R) between the images; (d) the set of beam aberration coefficients ( i C) to obtain the updated set of beam aberration coefficients ( i+1 C), and providing the updated set of beam aberration coefficients ( i+1 C) repeating (b) and (c) using in an iterative process to minimize said magnitude (R); the one or more defocus settings include two or more defocus distances of the sample from a respective beam focus of the charged particle beam, such that in (a), two or more images are taken when the sample is positioned at the two or more defocus distances, and in (b), the one or more simulated images include simulated images of the sample taken at the two or more defocus distances. method.

2. The method of claim 1 , wherein in (a), the plurality of six or more images is taken at six or more different defocus distances.

3. The method of claim 1, wherein the two or more images are captured by changing the focusing strength of the focusing lens or by moving a sample stage relative to the focusing lens.

4. 2. The method of claim 1 , wherein the one or more defocus settings include one or more beam entrance energies of the charged particle beam that are changed from a focused beam entrance energy, such that in (a), the one or more captured images are taken at the one or more beam entrance energies, and in (b), the one or more simulated images include simulated images of the sample taken at the one or more beam entrance energies.

5. The one or more captured images (h 1...N ) and the one or more simulated images, min (b) and (c) are repeated until the updated set of beam aberration coefficients ( i+1 C) is the actual beam aberration ( fit The method of claim 1 , further comprising:

6. The actual beam aberrations (e.g., fit 6. The method of claim 5, further comprising correcting C) to provide a corrected charged particle beam.

7. The method of claim 1 , wherein in (c), the one or more captured images and the one or more simulated images are compared in Fourier space.

8. 2. The method of claim 1, wherein in (c), comparing comprises calculating a difference value between each image of the one or more captured images and a corresponding simulated image of the one or more simulated images, and summing the difference values ​​to obtain the magnitude (R), particularly in Fourier space.

9. A method for determining aberrations of a charged particle beam focused by a focusing lens towards a sample in a charged particle beam system, comprising: (a) capturing one or more images of the sample at one or more defocus settings to provide one or more captured images; (b) simulating one or more images of the sample taken at the one or more defocus settings based on a set of beam aberration coefficients (iC) and a focused image of the sample to provide one or more simulated images; (c) comparing the one or more captured images and the one or more simulated images to determine a magnitude of difference (R) between the images; (d) modifying the set of beam aberration coefficients (i+1C) to provide an updated set of beam aberration coefficients (i+1C), and repeating (b) and (c) using the updated set of beam aberration coefficients (i+1C) in an iterative process to minimize the magnitude (R); In (b), simulating includes, at each defocus setting of the one or more defocus settings: said set of beam aberration coefficients ( i C) calculating a beam cross section of the charged particle beam based on the Calculating each simulated image in Fourier space based on a product of the beam cross-section in Fourier space and the focused image in Fourier space, or calculating each simulated image in real space based on a convolution.

10. The method of claim 9 , wherein calculating the respective simulated images in Fourier space further comprises dividing by a focal beam cross section in Fourier space.

11. The set of beam aberration coefficients ( i C) i C s , i C defocus , i C astigmatism,2-fold , i C astigmatism,3-fold , i C astigmatism,4-fold , i C star , and i C coma 13. The method of claim 1, wherein the chromatic aberration coefficients include two, three, or more coefficients of the group consisting of:

12. 1. A charged particle beam system comprising: a charged particle source for emitting a charged particle beam propagating along an optical axis; A sample stage; a focusing lens for focusing the charged particle beam toward a sample disposed on the sample stage; a charged particle detector for detecting signal particles emitted from the sample; A charged particle beam system comprising: a processor; and a memory, the memory storing instructions that, when executed by the processor, cause the charged particle beam system to perform the method of claim 1.

13. 1. A method for determining aberrations of a charged particle beam focused by a focusing lens towards a sample in a charged particle beam system, comprising: (a) capturing one or more images of the sample at one or more defocus settings to provide one or more captured images and recovering one or more collected beam cross sections from the one or more captured images; (b) A set of beam aberration coefficients ( i C), simulating one or more beam cross sections at the one or more defocus settings to provide one or more simulated beam cross sections; (c) comparing the one or more recovered beam cross sections and the one or more simulated beam cross sections to determine a magnitude of difference (R) between the cross sections; (d) the set of beam aberration coefficients ( i C) to obtain the updated set of beam aberration coefficients ( i+1 C), and providing the updated set of beam aberration coefficients ( i+1 and C) repeating (b) and (c) using in an iterative process to minimize said magnitude (R).

14. 14. The method of claim 13, wherein the one or more defocus settings comprise one or more defocus distances of the sample from a respective beam focus of the charged particle beam, or the one or more defocus settings comprise one or more beam entrance energies of the charged particle beam that are changed from a focal beam entrance energy.

15. The minimum magnitude of the difference between the one or more recovered beam cross sections and the one or more simulated beam cross sections (R min (b) and (c) are repeated until the updated set of beam aberration coefficients ( i+1 C) is the actual beam aberration ( fit The method of claim 13, wherein C) comprises an absolute value.

16. The method of claim 13 , wherein in (c), the one or more recovered beam cross sections and the one or more simulated beam cross sections are compared in real space.

17. 14. The method of claim 13, wherein in (c), the comparing comprises calculating a difference value between each recovered beam cross-section and a corresponding simulated beam cross-section, and summing the difference values ​​to obtain the magnitude (R), particularly in real space.

18. 14. The method of claim 13, wherein in (a), recovering the one or more recovery beam cross sections from the one or more captured images comprises dividing the one or more captured images in Fourier space by a focused image of the sample in Fourier space, or the one or more recovery beam cross sections are recovered based on a deconvolution in real space.

19. 20. The method of claim 18, wherein recovering the one or more recovered beam cross sections from the one or more captured images further comprises at least one of applying an adaptive filter term and multiplying by a focal beam cross section in Fourier space.

20. In (d), a minimum magnitude (R min 14. The method according to claim 13, wherein the beam aberration coefficients of the set of beam aberration coefficients are modified in succession and / or in parallel, in particular based on a multi-dimensional modification routine, until a desired beam aberration coefficient is obtained.

21. 1. A charged particle beam system comprising: a charged particle source for emitting a charged particle beam propagating along an optical axis; A sample stage; a focusing lens for focusing the charged particle beam toward a sample disposed on the sample stage; a charged particle detector for detecting signal particles emitted from the sample; a processor and a memory, the memory being configured to, when executed by the processor, cause the charged particle beam system to: (x1) A set of beam aberration coefficients ( i C) and simulating one or more images of the sample at one or more defocus settings based on the focused image of the sample to provide one or more simulated images. (x2) comparing one or more captured images of the sample captured at the one or more defocus settings and the one or more simulated images to determine a magnitude of a difference between the images; (x3) In the iterations after (x1) and (x2), the set of beam aberration coefficients ( i C) to obtain the updated set of beam aberration coefficients ( i+1 C), and providing the updated set of beam aberration coefficients ( i+1 C) minimizing said magnitude using the one or more defocus settings include two or more defocus distances of the sample from a respective beam focus of the charged particle beam, whereby in (x1) two or more images of the sample are simulated at the two or more defocus distances, and in (x2) the two or more images of the sample taken at the two or more defocus distances are compared with the two or more simulated images; a charged particle beam system storing instructions to 22. A charged particle beam system comprising: a charged particle source for emitting a charged particle beam propagating along an optical axis; A sample stage; a focusing lens for focusing the charged particle beam toward a sample disposed on the sample stage; a charged particle detector for detecting signal particles emitted from the sample; a processor and a memory, the memory being configured to, when executed by the processor, cause the charged particle beam system to: (x1) simulating one or more beam cross sections at one or more defocus settings based on a set of beam aberration coefficients (iC) to provide one or more simulated beam cross sections; (x2) comparing one or more recovered beam cross sections recovered from one or more captured images of the sample taken at the one or more defocus settings and the one or more simulated beam cross sections to determine a magnitude of difference between the cross sections; (x3) a charged particle beam system storing instructions to modify the set of beam aberration coefficients (i C) in an iteration after (x1) and (x2) to provide an updated set of beam aberration coefficients (i+1 C) and to minimize the magnitude using the updated set of beam aberration coefficients (i+1 C).

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