Method for determining aberration of a charged particle beam, and charged particle beam system

Abstract

A method for determining an image aberration of a charged particle beam (11) focused by a focusing lens (120) toward a sample (10) in a charged particle beam system is described. The method comprises: (a) capturing one or more images of the sample at one or more defocus settings to provide one or more captured images (h 1…N ); (b) based on the beam aberration coefficient set ( i (c) and a focused image of the sample, simulating one or more images of the sample captured at one or more defocused settings to provide one or more simulated images; (c) comparing the one or more captured images with the one or more simulated images to determine a magnitude of a difference between the two (R i ); and (d) a set of varying beam aberration coefficients ( i C) to provide an updated set of beam aberration coefficients ( i+1 C), and uses the updated set of beam aberration coefficients ( i+1 C) Repeat (b) and (c) to minimize the size (R i Alternatively, in (b), one or more beam cross sections may be simulated, and in (c), the simulated beam cross sections may be compared with one or more captured beam cross sections retrieved from one or more captured images to determine the magnitude of the difference between the two (R i ). Further, a charged particle beam system for imaging and / or inspecting a sample, configured for use in any such method, is provided.

Description

Technical Field

[0001] Embodiments described herein relate to methods for determining aberrations of a charged particle beam in a charged particle beam system, such as in an electron microscope, particularly in a scanning electron microscope (SEM). Specifically, actual values ​​of beam aberration coefficients may be determined, thereby facilitating correction of beam aberrations and improving resolution. More specifically, embodiments described herein relate to methods for determining beam aberration coefficients of a charged particle beam focused toward a sample by a focusing lens in a charged particle beam system, which facilitates providing an aberration-corrected charged particle beam. Embodiments further relate to a charged particle beam system for inspecting and / or imaging a sample, the system being configured for use in any of the methods described herein. Background Art

[0002] Modern semiconductor technology places high demands on structuring and probing samples at the nanometer or even sub-nanometer scale. Process control, inspection or structuring at the micrometer and nanometer scale is usually accomplished with charged particle beams (e.g., electron beams) that 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 higher spatial resolution than, for example, photon beams.

[0003] Inspection devices using charged particle beams, such as scanning electron microscopes (SEMs), have many functions in multiple industrial fields, including but not limited to inspection of electronic circuits, exposure systems for photolithography, detection systems, defect inspection tools, and test systems for integrated circuits. In such particle beam systems, fine beam probes with high current density can be used. For example, in the case of an SEM, a primary electron beam generates signal particles, such as secondary electrons (SE) and / or backscattered electrons (BSE), that can be used to image and / or inspect a sample.

[0004] However, it is challenging to reliably inspect and / or image samples with good resolution using a charged particle beam system because charged particle beams are often affected by beam aberrations, which limit the achievable resolution. In a typical charged particle beam system, an aberration corrector is provided for at least partially compensating for aberrations of the charged particle beam, such as spherical aberration, astigmatism, and / or chromatic aberration. An aberration-corrected charged particle beam can provide a smaller probe focus, thereby providing better resolution, compared to an uncorrected beam. However, since the beam aberrations present in the system are generally unknown, it is challenging to appropriately adjust the settings of the aberration correctors, which may have a large number of controls, such as to satisfactorily correct the beam aberrations.

[0005] In view of the above, it is beneficial to provide a method for accurately and reliably determining the aberration of a charged particle beam focused by a focusing lens in a charged particle beam system (particularly determining the actual value of the beam aberration coefficient, i.e. the beam aberration coefficient of the absolute value). In addition, it would be beneficial to provide a charged particle beam system for testing and / or imaging a sample, the system being configured to operate according to any of the methods described herein. Summary of the invention

[0006] In view of the above, according to the independent claims, a method of determining a beam aberration of a charged particle beam and a charged particle beam system configured for determining a beam aberration of a charged particle beam are provided.

[0007] According to a first aspect, a method for determining the aberration of a charged particle beam focused by a focusing lens toward a sample in a charged particle beam system is provided. The method comprises: (a) taking 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 beam aberration coefficient set and a focused image of the sample to provide one or more simulated images; (c) comparing the one or more captured images with the one or more simulated images to determine the magnitude of the difference between the two; and (d) changing the beam aberration coefficient set to provide an updated beam aberration coefficient set, and repeating (b) and (c) using the updated beam aberration coefficient set in an iterative process to minimize the magnitude.

[0008] According to a second aspect, a method for determining the aberration of a charged particle beam focused by a focusing lens toward a sample in a charged particle beam system is provided. The method comprises: (a) taking one or more images of the sample with one or more defocus settings to provide one or more captured images, and extracting one or more captured beam cross sections from the one or more captured images; (b) simulating one or more beam cross sections with the 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 captured beam cross sections with the one or more simulated beam cross sections to determine the size of the difference between the two; and (d) changing the set of beam aberration coefficients to provide an updated set of beam aberration coefficients, and repeating (b) and (c) using the updated set of beam aberration coefficients in an iterative process to minimize the size.

[0009] In some embodiments, the one or more defocus settings include one or more defocus distances, and (a) includes: taking the one or more images of the sample when the sample is arranged at the one or more defocus distances from the corresponding beam focus of the charged particle beam. Alternatively or additionally, the one or more defocus settings include one or more beam landing energies of the charged particle beam that vary from a focal beam landing energy, and (a) includes: taking the one or more images of the sample at the one or more beam landing energies.

[0010] The methods described in the first aspect and the second aspect both rely on comparing an image taken out of focus or a beam cross section extracted therefrom with a corresponding simulated out of focus image or a corresponding simulated out of focus beam cross section, wherein the corresponding simulated out of focus image or the corresponding simulated out of focus beam cross section is simulated based on a set of beam aberration coefficients. The initial set of beam aberration coefficients is varied during the iteration process in order to provide a simulated out of focus image or a simulated out of focus beam cross section, which is close to the image actually taken or close to the beam cross section extracted therefrom. The corresponding set of beam aberration coefficients can then be considered to correspond substantially to the beam aberration coefficients actually present in the system. Accordingly, the actual values ​​of the beam aberration coefficients 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 with a charged particle beam, in particular with an electron beam. The charged particle beam system comprises: 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 placed on the sample stage; a charged particle detector for detecting signal particles emitted from the sample; and a processor and a memory storing instructions, which, when executed by the processor, cause the system to perform any method described herein.

[0012] In particular, a charged particle beam system for imaging and / or inspecting a sample with a charged particle beam, in particular with an electron beam, is provided. The charged particle beam system comprises: 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 placed 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 storing instructions, which, when executed by the processor, cause the system to: (x1) simulate one or more images of the sample with 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 simulate one or more beam cross-sections with one or more defocus settings based on the set of beam aberration coefficients to provide one or more simulated beam cross-sections; (x2) compare one or more captured images of the sample captured with the one or more defocus settings with the one or more simulated images to determine the size of the difference between the two; or compare one or more captured beam cross-sections retrieved from one or more captured images of the sample captured with the one or more defocus settings with the one or more simulated beam cross-sections to determine the size of the difference between the two; and (x3) change the set of beam aberration coefficients to provide an updated set of beam aberration coefficients, and use the updated set of beam aberration coefficients in subsequent iterations of (x1) and (x2) to minimize the size.

[0013] Embodiments are also directed to apparatuses for implementing the disclosed methods, and include apparatus parts for performing the various method actions. The methods may be performed by hardware parts, computers programmed by appropriate software, any combination of the two, or in any other manner. In addition, embodiments are also directed to methods of operating the apparatuses.

[0014] Further advantages, features, aspects and details can be seen from the dependent claims, the description and the drawings, which can be combined with the embodiments described herein. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] In order that the above-mentioned features of the present disclosure can be understood in detail, a more detailed description briefly summarized above may be obtained by reference to the embodiments. The accompanying drawings are related to one or more embodiments and are described below.

[0016] Figure 1 a schematic diagram showing a charged particle beam system according to embodiments described herein, the charged particle beam system being adapted to operate according to any of the methods described herein;

[0017] Figure 2shows a diagram illustrating a method of determining an aberration of a charged particle beam according to embodiments described herein;

[0018] Figure 3 It shows how Figure 2 A more detailed illustration of the method shown;

[0019] Figure 4 shows a diagram illustrating a variant method of determining an aberration of a charged particle beam according to embodiments described herein;

[0020] Figure 5 Shown Figure 4 A more detailed illustration of the variant method shown; and

[0021] Figure 6 is a flow chart illustrating a variant method of determining an aberration of a charged particle beam. DETAILED DESCRIPTION

[0022] Reference will now be made in detail to various embodiments, one or more examples of which are illustrated in the accompanying drawings. In the following description of the drawings, like reference numerals refer to like parts. In general, only the differences associated with individual embodiments are described. Each example is provided as an explanation and is not meant to be limiting. In addition, features illustrated or described as part of one embodiment may be used in other embodiments or used in conjunction with other embodiments to generate yet further embodiments. This description is intended to include such modifications and variations.

[0023] Figure 1 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 comprises 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 comprises a sample stage 108 and a focusing lens 120 (in particular an objective lens) for focusing the charged particle beam 11 on the sample 10 placed on the sample stage 108. The charged particle beam system 100 further comprises 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. Further, an image generation unit 160 may be provided, which generates one or more images of the sample 10 based on the charged particle signal received from the charged particle detector 118. The image generation unit 160 may forward the one or more images of the sample to a processing unit 170, which is configured to determine aberration coefficients according to the one or more images according to the method described herein.

[0024] The sample stage 108 may be a movable platform. In particular, the sample stage 108 may be movable in the Z direction (ie, in the direction of the optical axis A), so that the distance between the focusing lens 120 and the sample stage 108 may be varied (see Figure 1 By moving the sample stage 108 in the Z direction, the sample 10 can be moved to a focal plane p away from the focusing lens 120. I The sample stage 108 can be moved in a plane perpendicular 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 the area below the focusing lens 120 so that the designated surface area can be imaged by focusing the charged particle beam 11 thereon.

[0025] The beam-optical components of the charged particle beam system 100 are typically placed in a vacuum chamber 101, which can be evacuated so that the charged particle beam 11 can propagate from the charged particle source 105 along the optical axis A toward the sample stage 108 and is heated at a sub-atmospheric pressure (e.g., less than 10 -3 mbar pressure or less than 10 -5 The sample 10 is hit at a pressure of 100 mbar.

[0026] 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 over the surface of the sample 10 along a predetermined scanning pattern (eg, in the X direction and / or the Y direction).

[0027] In some embodiments, a condenser lens system 106 may be arranged downstream of the charged particle source 105, in particular for collimating the charged particle beam 11 propagating toward a focusing lens 120. In some embodiments, the focusing lens 120 is an objective lens configured to focus the charged particle beam 11 on the sample 10, in particular a magnetic objective lens, an electrostatic magnetic lens, or a combined magnetic-electrostatic lens.

[0028] One or more surface areas of the sample 10 may be inspected and / or imaged using the charged particle beam system 100. As used herein, the term "sample" may be associated with a substrate (e.g., 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 may be inspected for one or more of the following: (1) imaging the surface of the sample; (2) measuring the dimensions of one or more features of the sample (e.g., the dimensions in the lateral direction, i.e., the dimensions in the XY plane); (3) performing critical dimension measurements and / or metrology; (4) detecting defects; and / or (5) investigating the quality of the sample.

[0029] In order to examine the sample 10 with the charged particle beam 11, the charged particle beam 11 is typically focused onto the sample surface using a focusing lens 120. When the charged particle beam 11 irradiates the sample surface, secondary electrons and / or backscattered electrons (referred to as "signal electrons") are emitted from the sample. The signal electrons provide information about the spatial characteristics and size of the features of the sample and can be detected using a charged particle detector 118. By scanning the charged particle beam 11 over the sample surface (e.g., using a scanning deflector 107) and detecting the signal electrons as a function of the location at which the signal electrons are generated, the sample surface or a portion thereof can be imaged, for example, using an image generation unit 160, which can be configured to provide an image of the sample 10 based on the received signal electrons.

[0030] The small spot of the focused charged particle beam 11 on the sample surface increases the achievable image resolution. Therefore, during inspection, the sample surface should be arranged in the focal plane p of the focusing lens 120. I The sample 10 is captured in focus to obtain a clear in-focus image. The clear image of the sample 10 captured in focus is also referred to as a “focus image” herein. I ”, the subscript I indicates “focusing”. Similarly, the charged particle beam 11 is at the focal plane p I The beam cross section within the focal point is referred to herein as the "focal beam cross section g I ", and the subscript I indicates "in focus".

[0031] It is worth noting that images can be mathematically represented in real space (= in the image domain, i.e. as a function of spatial coordinates) or in Fourier space (= in the frequency domain, i.e. as a function of spatial frequencies). Images in Fourier space can be calculated from images in real space via Fourier transform (FT). Both representations contain the corresponding information of the image. As used herein, images in real space are represented by lowercase letters " n ", while the image in Fourier space is represented by the capital letter "H n " means. For example, "h I” represents the focused image of the sample in real space, and “H I " represents the focused image of the sample in Fourier space, which is h I Similarly, beam cross sections in real space are denoted herein by lowercase letters “g n ", while the beam cross section in Fourier space is represented in this paper by the capital letter "G n " means. For example, "g I ” represents the focal beam cross section of the charged particle beam in real space, and “G I " represents the focal beam cross section of the charged particle beam in Fourier space, which is g I In some embodiments described herein, images and beam cross sections in real space may be Fourier transformed into Fourier space, and vice versa, via a fast Fourier transform (FFT) algorithm.

[0032] Simulated images and simulated beam cross sections are indicated herein by a tilde above the corresponding letter, such as a simulated image of The simulated beam cross section is The actual image captured by the charged particle beam system and the beam cross section extracted from the actual captured image are not indicated herein with a tilde above the corresponding letters, such as the captured image (h 1...N ), from which the beam cross section is extracted is (g 1...N ).

[0033] In charged particle beam systems, beam aberrations often result in an expansion or deformation of the beam cross section, which reduces the achievable resolution. For example, spherical aberration, usually introduced by lenses in the system, causes the focal plane p to be I The focal beam cross section g I expansion, and astigmatism may cause rays propagating in different planes to have different focuses, blurring the image.

[0034] Different types of beam aberrations may exist in charged particle beam systems and may need to be corrected, such as, for example: (1) spherical aberration (determined by the beam aberration coefficient C 3,0 or C s Quantitative expression); (2) defocus (by beam aberration coefficient C 1,0 Quantitative expression, also referred to in this article as C 散焦 ); (3) first-order astigmatism (given by the beam aberration coefficient C 1,2 Quantitative expression, also referred to in this article as C 像散，2重 ); (4) second-order astigmatism (given by the beam aberration coefficient C 2,3 Quantitative expression, also referred to in this article as C 像散，3重); (5) third-order astigmatism (given by the beam aberration coefficient C 3,4 Quantitative expression, also referred to in this article as C 像散，4重 ); (6) coma (given by the beam aberration coefficient C 2,1 Quantitative expression, also referred to in this article as C 彗形像差 ); (7) Star aberration (given by the beam aberration coefficient C 3,2 Quantitative expression, also referred to in this article as C 星形 ). Further, depending on the energy spread of the charged particle beam and the dispersion effects of the beam-optical components of the system, multiple chromatic aberrations may exist, which can be quantitatively represented by one or more chromatic aberration coefficients. i C may include the above-mentioned beam aberration coefficients and two, three or more beam aberration coefficients, for example i C=[ i C s , i C 散焦 , i C 像散，2重 ].

[0035] Beam aberrations can be corrected using an aberration corrector (for example, using an electrostatic or magnetic multipole corrector). Figure 1 The aberration corrector 109 is schematically depicted in FIG. 1 , but it should be understood that the charged particle beam system may also include two or more aberration correctors that are not necessarily provided at one position along the optical axis A. For example, an stigmator including a quadrupole may be provided to correct C 像散，2重 and can provide higher order multipoles to correct C 像散，3重 and / or C 像散，4重 More sophisticated correctors can be provided to compensate for C s Various types of aberration correctors are known for correcting various beam aberrations.

[0036] Adjusting the aberration corrector so that one or more types of beam aberrations are properly corrected is a challenge because the amount of beam aberrations present in the system is generally unknown. It is possible to set one or more aberration correctors so that pre-calculated beam aberrations theoretically introduced by the beam-optical components of the system are compensated, but this approach is generally not accurate enough. In particular, not all sources of beam aberrations are known, especially quantitatively. For example, beam aberrations may also be introduced by inaccuracies in the system, such as mechanical, magnetic or electrostatic inaccuracies, charge contamination, material inhomogeneities, manufacturing defects, which are not initially known. The beam-optical components may include one or more of an objective, a collimator, a deflector, a scanning deflector, a beam splitter, a charged particle detector, and an aberration corrector.

[0037] In charged particle beam systems, different methods can be used to estimate beam aberrations so that appropriate corrections can be made to the beam aberrations. Some methods rely on visible inspection of the charged particle beam, such as visible inspection in the far field, which can provide an indication of the aberrations present in the system. Other methods rely on analysis of captured images. Specifically, through corresponding calculations, images captured out of focus can generate information about the beam cross section (i.e., the probe shape), and the probe shape can provide information about specific types of beam aberrations. For example, image scattering beams are generally non-rotationally symmetric. Known methods rely on extracting line profiles from the beam cross section, and beam aberrations can be estimated based on such line profiles.

[0038] However, this concept only allows a relative estimation of the aberrations, but does not allow the absolute values ​​of the aberration coefficients to be retrieved. The "absolute values" of the beam aberration coefficients may be understood as the actual quantitative values ​​of the beam aberration coefficients, such as C in [mm]. s , these values ​​directly allow appropriate settings of the aberration corrector based on the determined absolute values ​​of the beam aberration coefficients. It is worth noting that previously known methods are only able to make relative estimates of the beam aberrations, which may vary from measurement to measurement and may depend on the choice of numerical parameters in the extraction algorithm.

[0039] The method described herein allows accurate and reliable determination of aberrations of a charged particle beam, in particular determination of quantitative values ​​of a set of beam aberration coefficients describing the beam aberrations present in the system. The charged particle beam system 100 described herein comprises a processor and a memory storing instructions (in Figure 1 The instructions are shown as processing unit 170 in the figure, which, 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 forwarded to the aberration corrector 109 so that the aberration corrector can compensate for one or more beam aberrations and can provide an aberration-compensated charged particle beam.

[0040] Figure 2 and Figure 3 A diagram illustrating one method of determining an aberration of a charged particle beam according to embodiments described herein is shown. Figure 3 The picture and Figure 2 Optional further details are shown compared to FIG. Figure 2 and Figure 3 The method uses an image-based aberration coefficient fitting routine, while Figure 4 and Figure 5 The method uses a spot-based aberration coefficient fitting routine.

[0041] exist Figure 2In block 210, one or more images of the sample 10 are captured at one or more defocus settings to provide one or more captured images (h 1…N ), in particular by the image generation unit 160 ( Figure 1 The one or more defocus settings may include one or more defocus distances (z) between the sample 10 and a corresponding beam focus of the charged particle beam. 1...N ). The defocus distance in this article is understood as the distance between the sample and the beam focus when the image is taken (>0). Specifically, when the sample is arranged at a distance of 0.000 Å from the corresponding beam focus of the charged particle beam, the sample is Figure 1 One or more defocus distances (z 1...N ), the one or more images of the sample may be captured so that the one or more captured images (h 1…N ) is the out-of-focus image of the sample. Of course, increasing the defocus distance will result in a more blurred corresponding captured image, because the probe size usually increases and the resolution usually decreases with increasing defocus distance.

[0042] In some embodiments, a plurality of two, three, six or more images may be taken at two, three, six or more different defocus distances between the sample and the respective beam focus. In particular, at least one image of the sample may be taken at an overfocus distance, i.e., at a defocus setting in which the sample is arranged further from the focusing lens 120 than the beam focus of the charged particle beam (see Figure 1 The defocus distance z shown 1 ). Further, at least one image of the sample can be taken at an underfocus distance, i.e. with a defocused setting, wherein the sample is arranged closer to the focusing lens 120 than the corresponding beam focus of the charged particle beam (see Figure 1 The defocus distance z shown 2...N ). At the first defocus distance z 1 The image captured at is denoted as captured image h in this paper. 1 , and at the nth defocus distance z n The image captured at is denoted as captured image h in this paper. n A total of N images can be taken, expressed as (h 1...N ).

[0043] The defocus distance may be varied by varying the focus strength of the focusing lens 120, for example, in predetermined increments (e.g., Figure 1). Specifically, an increase in the focusing strength of the focusing lens moves the corresponding beam focus and focal plane toward the focusing lens relative to the sample, while a decrease in the focusing strength moves the corresponding beam focus and focal plane away from the focusing lens relative to the sample, so that the defocus distance varies. Alternatively or additionally, the defocus distance can be varied by moving the sample stage 108 (e.g., by predetermined increments, particularly in the Z direction (along the optical axis A)), particularly while maintaining the focus strength provided by the focusing lens 120 constant.

[0044] In some embodiments, which may be combined with other embodiments described herein, the one or more defocus settings may include one or more beam landing energies (E 1...N ). Focus beam landing energy E I It can be understood as providing a beam focus on the sample so that the sample is arranged in the focus. The beam landing energy E I Varying the beam landing energy (e.g., by varying the potential of the particle source (emitter) or the potential of the sample (wafer bias)) can move the beam focus away from the sample, so that the varying beam landing energy results in a "defocused image" of the sample.

[0045] The one or more defocus settings may include landing energy E from the focal beam I Varying the landing energy of one or more beams (E 1...N ), in particular two, three, six or more different beam landing energies. Specifically, multiple images of the sample 10 can be taken at multiple different beam landing energies (E 1...N ) is captured, so that the one or more captured images (h 1…N ) includes multiple energy defocused images of the sample.

[0046] In some embodiments, the one or more defocus settings may include one or more different defocus distances (z 1...N ) and one or more different beam landing energies (E 1...N ). If the images are taken not only at one or more different defocus distances, but also at one or more different defocus energies, this can help to reliably and accurately determine "geometric" beam aberration coefficients (such as astigmatism and spherical aberration), as well as one or more "chromatic" aberration coefficients.

[0047] Back to Figure 2 and Figure 3 In block 220, one or more images of the sample 10 are simulated to provide one or more simulated images. The simulation can be performed by Figure 1The processing unit 170 shown is performed. These images are simulated with the one or more defocus settings used to capture the images in block 210. In other words, the defocus settings used to capture the images in block 210 are taken into account for the simulated images in block 220. For example, if the one or more captured images (h 1...N ) is at one or more defocus distances (z 1...N ), then the one or more defocus distances (z 1...N ) may be forwarded to a processing unit, or otherwise known to a processing unit, and the one or more simulated images is a defocused image that looks like an image taken at the defocus distance.

[0048] Based on the focused image of the sample (h I ) and based on the beam aberration coefficient set i C, the image in the simulation frame 220 for each defocus setting. Focused image (h I ) can be generated by the image generation unit 160 with the focus setting of the charged particle beam system and can be forwarded to the processing unit 170, that is, the focused image can be actually taken by the charged particle beam system with the focus setting. Alternatively, the focused image h I may already be known in advance by the processing unit 170, for example, because a sample with a known design is used to determine the beam aberrations. As described above, the focused image may be in real space (h I ) or Fourier space (H I ) is provided in .

[0049] Initial set of beam aberration coefficients 1 C may be used initially for simulation in block 220. The initial set of beam aberration coefficients 1 C may be an initial estimate of the beam aberration coefficients, for example, based on experience, based on an aberration estimation procedure known in the art, and / or based on knowledge of the beam-optical components of the system. Alternatively, some or all of the beam aberration coefficients may be included in the initial set of beam aberration coefficients. 1 C is set to zero.

[0050] If the one or more defocus settings include one or more defocus distances (z 1...N ), then the one or more simulated images include the one or more defocus distances (z 1...N Alternatively or additionally, if the one or more defocus settings include one or more beam landing energies (E 1...N ), then the one or more simulated images include the one or more beam landing energies (E 1...N ) is a simulated image of a sample taken under .

[0051] like Figure 2 and Figure 3 Schematically depicted, the input data for the simulation in block 220 may include the defocus settings previously used to capture the image, the focused image H I , and the initial or updated set of beam aberration coefficients i C / i+1 C.

[0052] In block 230, the one or more captured images (h 1…N ) and the one or more simulated images to compare the one or more captured images (h 1…N ) and the one or more simulated images The size of the difference between i ).like Figure 2 and Figure 3 Schematically depicted, the one or more captured images (h 1…N ) and the one or more simulated images can be compared with each other in Fourier space in block 230, i.e. by comparing (H 1…N )and To this end, the one or more captured images may be Fourier transformed for comparison to provide the one or more captured images in Fourier space (H 1…N ). Comparisons in Fourier space may be advantageous because (when comparing (H 1...N ) and (H 1...N ) in Fourier space, there will be no inaccuracy due to the erroneous superposition of the captured image for comparison and the corresponding simulated image, because the linear displacement in the real space only appears as a phase term in Fourier space. Alternatively, even if not shown in the drawings, the one or more captured images (h 1…N ) and the one or more simulated images in real space Make a comparison.

[0053] The comparison in block 230 may include calculating the one or more captured images (H n ) and the corresponding simulated image in the one or more simulated images and sum up the difference values ​​to obtain the size (R i ), particularly in Fourier space. In particular, in some embodiments, the size (R i ) can be performed according to the one or more captured images (H) in Fourier space as follows 1…N ) and Fourier space based on the beam aberration coefficient seti C to simulate the one or more simulation images To calculate:

[0054]

[0055] If the initial set of beam aberration coefficients is used in the simulation 1 C, then the size R will be calculated 1 In subsequent iterations, the updated beam aberration coefficient sets are used respectively. i+1 C and calculate (R i+1 ), the goal is to determine the size that leads to the minimization (R 最小 ) is a set of beam aberration coefficients.

[0056] It is noteworthy that different types of beam aberrations may be more or less apparent at different defocus settings. For example, some beam aberrations may be better determined at locations close to the focal plane, while other beam aberrations may be better determined at locations far from the focal plane, and some beam aberrations (such as higher-order astigmatism) may be best detected by comparing one or more overfocus images with corresponding one or more underfocus images. Therefore, in order to reliably determine a set of several beam aberration coefficients, it is helpful to compare multiple captured images (e.g., six, eight, ten or more images, some captured when underfocus and some captured when overfocus) with corresponding multiple simulated images at corresponding defocus settings. By minimizing the aggregated differences between the corresponding images, several beam aberration coefficients can be determined that, through the fitting routines described herein, are very close to the corresponding actual beam aberration coefficients present in the system.

[0057] In the calculation (R i ) after changing the beam aberration coefficient set i C, to provide an updated set of beam aberration coefficients i+1 C, and uses the updated set of beam aberration coefficients in the iterative process i+1 C to repeat the simulation in block 220 and the comparison in block 230. Specifically, then in block 220 based on the updated beam aberration coefficient set i+1 C to calculate one or more updated simulated images, and in block 230 the one or more captured images (h 1...N ) is compared with the one or more updated simulation images, with the aim of minimizing the size (R i ).

[0058] In particular, the simulation in block 220, the comparison in block 230 and the variation i C to provide i+1C may be repeated in an iterative process until a minimized size (R 最小 ), and the corresponding updated set of beam aberration coefficients at the corresponding iteration constitutes the actual beam aberration 拟合 C. Specifically, Figure 2 and Figure 3 As schematically illustrated in block 240 of FIG. 1 , after each iteration, it may be checked whether (R i =R 最小 ). If (R i =R 最小 ), the iteration process can be stopped and the i C is considered to be the actual beam aberration 拟合 C. Otherwise, the next iteration can be performed.

[0059] In some embodiments, the beam aberration coefficients in the set of beam aberration coefficients are varied sequentially and / or in parallel until a minimized magnitude (R 最小 In particular, a multidimensional variation routine may be used to vary the beam aberration coefficients in the beam aberration coefficient set to retrieve the beam aberration coefficients (R 最小 ) is a set of beam aberration coefficients.

[0060] In some embodiments, which may be combined with other embodiments described herein, the actual beam aberrations may be partially or fully corrected with one or more aberration correctors, in particular with one or more electrostatic and / or magnetic multipole correctors. 拟合 C, to provide an aberration-corrected charged particle beam.

[0061] In some embodiments, which may be combined with other embodiments described herein, the beam aberration coefficient set ( i C) can include i C s , i C 散焦 , i C 像散，2重 , i C 像散，3重 , i C 像散，4重 , i C 星形 and i C 彗形像差 Two, three or more coefficients in a group, and one, two or more color difference coefficients i C cThe method described herein allows accurate determination of geometric beam aberration coefficients, in particular by varying the defocus distance z when capturing and simulating the one or more defocused images. n Further, the method described herein allows accurate determination of the beam chromatic aberration coefficient, in particular by varying the beam landing energy E when capturing and simulating the one or more defocused images. n Thus, by providing absolute values ​​of the corresponding beam aberration coefficients as a result of the iterative process described herein, all relevant beam aberration coefficients can be accurately determined (in particular quantitatively determined).

[0062] In some embodiments, the simulation in block 220 may include a simulation based on a set of beam aberration coefficients. i C, calculating the beam cross section of the charged particle beam at each of the one or more defocus settings. Calculating the beam cross section at a specific defocus setting can be performed by wave optics simulation, with aberration coefficients as input parameters. The beam cross section in real space can be calculated A Fourier transform can then be performed to provide the beam cross section in Fourier space like Figure 3 As shown in box 220.

[0063] Thereafter, for each defocus setting, the focused image of the sample in Fourier space (H I ) and the simulated beam cross section in Fourier space Compute the corresponding simulation image in Fourier space In particular, it is based on the product of the beam cross section in Fourier space and the focus image in Fourier space If the image of the sample is taken with a defocused setting, the resulting defocused image corresponds to the convolution of the focused image (i.e. the actual sample) with the defocused beam cross section in real space. The convolution in real space corresponds to the product in Fourier space. Therefore, the simulated image in Fourier space is Can be based on the product Of course, the simulated image can also be calculated in real space based on With h I The convolution is calculated by the convolution, which is equivalent to the product in the above Fourier space.

[0064] In some embodiments, a simulated image in Fourier space is calculated It may further include: multiplying the above product Divided by the focal beam cross section in Fourier space like Figure 3 As schematically depicted in box 220 of .

[0065] The above and Figure 2 and Figure 3 The determination method shown 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 with one or more defocus settings. In contrast to other methods, no deconvolution of the one or more taken images is required in order to retrieve information about the corresponding beam cross section from the one or more taken images. A goodness of fit routine in the processing unit can provide the obtained aberration coefficients 拟合 C's accuracy with a level of confidence that was not possible before.

[0066] Accurate knowledge of beam aberrations in charged particle beam systems, particularly for imaging, defect review, metrology, electron beam inspection and / or critical dimension measurement, is key to improving system performance. Beam aberrations obtained by the methods described herein can be used, for example, to (1) reduce beam aberrations by corresponding aberration correctors, (2) serve as an empirical basis for developing beam-optical components for future systems, (3) ensure repeatability and matching, and (4) compare determined values ​​with simulations.

[0067] Figure 4 and Figure 5 A diagram illustrating a variant method of determining an aberration of a charged particle beam according to embodiments described herein is shown. Figure 5 The icon and Figure 4 Compared to the illustration of FIG, optional further details are shown. Figure 2 and Figure 3 The method shown is different in that the variant method uses a spot-based aberration coefficient fitting routine instead of an image-based aberration coefficient fitting routine. In addition to the differences, the variant method may include any of the features of the above methods, which will be readily understood by the skilled person, and the corresponding features and explanations will not be repeated below.

[0068] In block 210, one or more images of the sample 10 are captured at the one or more defocus settings to provide one or more captured images (h 1…N ). As mentioned above Figure 2 and Figure 3 As already explained, the one or more defocus settings may comprise one or more defocus distances (z 1...N Alternatively or additionally, the one or more defocus settings may include landing energy (E I ) varies the landing energy (E) of one or more beams of a charged particle beam 1...N). In particular, a plurality of two, three, six or more images of the sample are taken at two, three, six 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 varied by varying the focus strength of the focusing lens or by moving the sample stage relative to a constant focal plane of the focusing lens.

[0069] and Figure 2 and Figure 3 Unlike the method described in FIG. 4 , in block 410, from the one or more captured images (h 1…N ) to retrieve one or more retrieval beam cross sections (g 1…N ). The out-of-focus beam profile can be extracted from the out-of-focus image via several different profile extraction methods. An exemplary probe profile extraction method will be explained below.

[0070] From the one or more captured images (h 1…N ) to retrieve the one or more retrieved beam cross sections (g 1…N ) can be based on deconvolution in real space, which is equivalent to division in Fourier space. Figure 5 As depicted in block 410, from the one or more captured images (h 1…N ) to retrieve the one or more retrieved beam cross sections (g 1…N ) may specifically include: performing a scan of the one or more captured images (h 1...N ) is Fourier transformed to provide the one or more captured images (H) in Fourier space 1…N ), and the one or more captured images (H 1…N ) divided by the focused image of the sample in Fourier space (H I The above beam profile extraction method is based on the fact that in Fourier space, the captured defocused image (H n ) divided by the focused image of the sample (H I ) removes the structure of the sample, so that the division generates a pure beam profile, i.e. a beam cross section without sample information. The retrieved beam cross section (G) in Fourier space n ) can be inverse Fourier transformed to obtain the extraction beam cross section (g n ).

[0071] like Figure 5 As further described in block 410 of the present invention, from the one or more captured images (h 1…N ) to retrieve the one or more retrieved beam cross sections (g 1…N ) may optionally include: If the retrieval is performed in Fourier space (such as Figure 5 ), then apply the filter, especially with the adaptive filter term Multiplied, or if the extraction is done in real space, convolved with the adaptive filter term. The adaptive filter unit 450 may be provided, and the adaptive filter unit may receive the captured image as input information. The adaptive filter unit 450 may be provided by the adaptive filter unit 450, and the adaptive filter unit may receive the captured image as input information. 1...N ) provides an adaptive filter term. If there is no adaptive filter term Then the focused image H whose denominator is close to zero is I This may cause the noise in the image to be overweighted. Reduce or avoid the calculation of the focal beam cross section G 1...N Focus image H I The adverse effect of noise in the image can be reduced, and the adaptive filter unit 450 can determine the corresponding filter item for each captured image separately. Can also be applied to the corresponding simulated beam cross section This allows for a better comparison between the retrieved beam cross section and the corresponding simulated beam cross section in block 430. is applied in block 410 to retrieve the beam cross section and in block 420 to simulate the beam cross section, Figure 5 Alternatively or additionally to applying an adaptive filter term, from the one or more captured images (h 1…N ) to retrieve the one or more retrieved beam cross sections (g 1…N ) may include: with the focal beam cross section in Fourier space Multiply, such as Figure 5 As shown in box 410.

[0072] In block 420, one or more beam cross sections at the one or more defocus settings are simulated to provide one or more simulated beam cross sections. The simulation can be performed by Figure 1 The beam cross section is simulated with the one or more defocus settings used in block 210. In other words, the defocus settings used for capturing the image in block 210 are taken into account in block 220 for simulating the beam cross section. For example, if the one or more captured images (h 1...N ) is at one or more defocus distances (z 1...N ), then the one or more defocus distances (z 1...N ) can be forwarded to a processing unit, and the one or more simulated beam cross sections is the defocused cross section of the charged particle beam at said defocusing distance.

[0073] Based on the beam aberration coefficient set i C sets the beam cross section in the simulation box 420 for each defocus. Optionally, the focus beam cross section can also be simulated is the beam cross section in the focal plane and can be Fourier transformed to provide It can then be provided to calculate the one or more retrieved beam cross sections (G 1…N ),like Figure 6 Schematically illustrated.

[0074] Initial set of beam aberration coefficients 1 C may be used for the one or more simulated beam cross sections in block 420 Initial simulation of the beam aberration coefficients. 1 C may be an initial estimate, for example, based on experience, based on an aberration estimation procedure known in the art, and / or based on knowledge of the beam-optical components of the system. Alternatively, some or all of the beam aberration coefficients may be included in the initial set of beam aberration coefficients. 1 C is set to zero. The input data for the simulation in block 420 may include the defocus setting previously used to capture the image, and an initial or updated set of beam aberration coefficients i C / i+1 C.

[0075] In block 430, the one or more retrieved beam cross sections (g 1…N ) and the one or more simulated beam cross sections The comparison is performed to determine the one or more acquisition beam cross sections (g 1…N ) and the one or more simulated beam cross sections The size of the difference between i ).like Figure 4 and Figure 5 Schematically depicted, the one or more acquisition beam cross sections (g 1…N ) and the one or more simulated beam cross sections can be compared with each other in real space, that is, by comparing (g 1…N )and To this end, the one or more retrieved beam cross sections in Fourier space are An inverse Fourier transform may be performed to provide the one or more retrieved beam cross sections in real space to be used for comparison Compared to the corresponding images, the picked-up beam cross section and the simulated beam cross section can be more easily superimposed so that the comparison can be made in real space. Alternatively, even if not shown in the drawings, the one or more picked-up beam cross sections (G 1…N ) and the one or more simulated beam cross sections in Fourier space Make a comparison.

[0076] The comparison in block 430 may include calculating each retrieved beam cross section (g n ) and the corresponding simulated beam cross section and sum up the difference values ​​to obtain the size (R i ), in particular in real space. In particular, in some embodiments, the size (R i ) can be obtained according to the one or more retrieved beam cross sections (g 1…N ) and the beam aberration coefficient set i C The one or more simulated beam cross sections simulated To calculate:

[0077]

[0078] If the initial set of beam aberration coefficients is used in the simulation 1 C, then the size R will be calculated 1 In subsequent iterations, the updated beam aberration coefficient sets are used respectively. i+1 C and calculate (R i+1 ), the goal is to determine the size that leads to the minimization (R 最小 ) is a set of beam aberration coefficients.

[0079] In the calculation (R i ) after changing the beam aberration coefficient set i C, to provide an updated set of beam aberration coefficients i+1 C, and uses the updated set of beam aberration coefficients in the iterative process i+1 C to repeat the simulation in block 420 and the comparison in block 430. Specifically, then in block 420 based on the updated beam aberration coefficient set i+1 C to calculate one or more updated simulated beam cross sections, and in block 430 the one or more retrieved beam cross sections (g 1...N ) is compared with the one or more updated simulation images, with the aim of minimizing the size (R i ).

[0080] In particular, the simulation in block 420, the comparison in block 430 and the variation iC to provide i+1 C may be repeated in an iterative process until a minimized size (R 最小 ), and the corresponding updated set of beam aberration coefficients at the corresponding iteration constitutes the actual beam aberration 拟合 C. Specifically, Figure 4 and Figure 5 As schematically illustrated in block 240 in FIG. 2 , after each iteration, it may be checked whether (R i =R 最小 ). If (Ri=R 最小 ), then the iteration process can be ended, and i C is considered to be the actual beam aberration 拟合 C. Otherwise, the next iteration can be performed.

[0081] Optionally, the beam aberrations may then be partially or fully corrected using one or more beam aberration correctors. 拟合 C, to provide a corrected charged particle beam. For further details and other optional features, please refer to the above Figure 2 and Figure 3 The explanation will not be repeated here.

[0082] Figure 4 and Figure 5 The variant determination method shown allows obtaining the absolute values ​​of the beam aberration coefficients of a charged particle beam in a charged particle beam system, which is different from other estimation methods that only allow relative estimation of the beam aberration coefficients. The aberration coefficients that can be obtained by the goodness of fit routine in the processing unit 拟合 C's accuracy with a level of confidence that was not possible before.

[0083] Figure 6 is a flow chart illustrating a variant method for determining the aberration of a charged particle beam as described herein. First, at a plurality of different defocus distances z 1...N Take multiple images at 1...N )( Figure 6 The six images in Figure 6 In the example, three images are over-focused and three images are under-focused). 1...N ) to retrieve multiple beam cross sections (g) at the corresponding defocus distance 1...N ). Further, based on the initial set of beam aberration coefficients, and then based on the corresponding updated set of beam aberration coefficients, multiple beam cross sections are iteratively simulated at the multiple different defocus distances. ( Figure 6 The six simulated beam cross sections in the above formula are as follows: 1...N) and the plurality of simulated beam cross sections The comparison between the two generates a minimum value, which means that the multiple simulated beam cross sections Close to the plurality of retrieved beam cross sections (g 1...N ), i.e., the corresponding beam aberration coefficient set is close to the actual beam aberration coefficient set. Then, the corresponding beam aberration coefficient set at the corresponding iteration can be used as an input parameter of one or more aberration correctors to provide an aberration-corrected charged particle beam.

[0084] Specifically, the following embodiments are described herein:

[0085] Embodiment 1: A method for determining an image aberration of a charged particle beam (11) focused by a focusing lens (120) toward a sample (10) in a charged particle beam system (100), the method comprising: (a) capturing one or more images of the sample at one or more defocus settings to provide one or more captured images (h 1…N ); (b) based on the beam aberration coefficient set ( i C) and the focused image of the sample (h I ), simulating one or more images of the sample captured with the one or more defocus settings to provide one or more simulated images (c) comparing the one or more captured images with the one or more simulated images to determine the magnitude of the difference between the two (R i ); and (d) varying the beam aberration coefficient set ( i C) to provide an updated set of beam aberration coefficients ( i+1 C), and use the updated beam aberration coefficient set ( i+1 C) Repeat (b) and (c) to minimize the size (R i ).

[0086] Embodiment 2: The method of embodiment 1, wherein the one or more defocus settings include one or more defocus distances (z 1...N ), so that in (a), the one or more images are taken when the sample is arranged at the one or more defocus distances (z 1...N ), and in (b), the one or more simulated images include the one or more defocus distances (z 1...N ) is a simulated image of the sample taken at .

[0087] Embodiment 3: A method as described in 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 varying the focusing strength of the focusing lens by predetermined increments or by moving the sample stage by predetermined increments relative to the focusing lens.

[0088] Embodiment 4: The method as described in Embodiment 3, wherein the one or more captured images include at least one or more images captured at an over-focus distance and at least one or more images captured at an under-focus distance.

[0089] Embodiment 5: A method as described in any one of embodiments 1 to 4, wherein the one or more defocus settings include one or more beam landing energies (E 1...N ), such that in (a), the one or more captured images are captured at the one or more beam landing energies, and in (b), the one or more simulated images include simulated images of the sample captured at the one or more beam landing energies. In particular, the one or more defocus settings include a plurality of different beam landing energies of the charged particle beam irradiated on the sample. In some embodiments, the one or more defocus settings include different defocus distances and different beam landing energies.

[0090] Embodiment 6: A method as described in any one of embodiments 1 to 5, wherein (b) and (c) are repeated until a minimized size (R 最小 ), and the updated beam aberration coefficient set at the corresponding iteration ( i+1 C) constitutes the actual beam aberration ( 拟合 C), especially expressed in absolute terms.

[0091] Embodiment 7: The method as described in Embodiment 6 further comprises: correcting the actual beam aberration ( 拟合 C), in particular with one or more electrostatic or magnetic multipole correctors, to provide a corrected charged particle beam.

[0092] 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.

[0093] Embodiment 9: A method as described in any one of embodiments 1 to 8, wherein in (c), the comparison includes: calculating a difference value between each image in the one or more captured images and a corresponding simulated image in the one or more simulated images, and summing up the difference values ​​to obtain the size (R i ), in particular wherein the calculations are performed in Fourier space.

[0094] Embodiment 10: A method as described in any one of embodiments 1 to 9, wherein in (b), the simulation includes: at each defocus setting in the one or more defocus settings, based on the beam aberration coefficient set ( i C), calculating a beam cross section of the charged particle beam; and calculating a corresponding simulation image in Fourier space based on the product of the beam cross section in Fourier space and the focused image in Fourier space.

[0095] Embodiment 11: The method as described in Embodiment 10, wherein calculating the corresponding simulated image in Fourier space further comprises: dividing by the focal beam cross section in Fourier space.

[0096] Embodiment 12: A method for determining an aberration of a charged particle beam (11) focused by a focusing lens (120) toward a sample (10) in a charged particle beam system (100), the method comprising: (a) capturing one or more images of the sample with one or more defocus settings to provide one or more captured images, and extracting one or more captured beam cross sections from the one or more captured images; (b) ... extracting an aberration of a charged particle beam (11) based on a beam aberration coefficient set ( i (c) simulating one or more beam cross sections with the one or more defocus settings to provide one or more simulated beam cross sections; (c) comparing the one or more captured beam cross sections with the one or more simulated beam cross sections to determine a magnitude of a difference between the two (R i ); and (d) varying the beam aberration coefficient set ( i C) to provide an updated set of beam aberration coefficients ( i+1 C), and use the updated beam aberration coefficient set ( i+1 C) Repeat (b) and (c) to minimize the size (R i ).

[0097] Embodiment 13: The method of embodiment 12, wherein the one or more defocus settings include one or more defocus distances (z 1...N ), so that in (a), the one or more images are at the one or more defocus distances (z 1...N) and in (b), the one or more beam cross sections are taken at the one or more defocus distances (z 1...N ) is simulated.

[0098] Embodiment 14: A method as 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 varying the focusing strength of the focusing lens by predetermined increments or by moving the sample stage by predetermined increments relative to the focusing lens.

[0099] Embodiment 15: The method as described in Embodiment 14, wherein the multiple captured images include at least one image captured at an over-focus distance and at least one image captured at an under-focus distance.

[0100] Embodiment 16: A method as described in any one of Embodiments 12 to 15, wherein the one or more defocus settings include one or more beam landing energies (E 1...N ), such that in (a), the one or more images are taken at the one or more beam landing energies, and in (b), the one or more beam cross sections are taken at the one or more beam landing energies (E 1...N In particular, the one or more defocus settings include a plurality of beam landing energies, such as one or more beam energies greater than the focal beam landing energy and one or more beam energies less than the focal beam landing energy.

[0101] Embodiment 17: A method as described in any one of Embodiments 12 to 16, wherein (b) and (c) are repeated until a minimized size (R 最小 ), and the updated beam aberration coefficient set at the corresponding iteration ( i+1 C) constitutes the actual beam aberration of absolute value ( 拟合 C).

[0102] Embodiment 18: The method as described in Embodiment 17 further comprises: correcting the actual beam aberration ( 拟合 C), in particular with one or more electrostatic or magnetic multipole correctors, to provide a corrected charged particle beam.

[0103] Embodiment 19: A method as described in any one 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.

[0104] Embodiment 20: A method as described in any one of embodiments 12 to 19, wherein in (c), the comparison includes: calculating a difference value between each retrieved beam cross section and the corresponding simulated beam cross section, and summing up the difference values ​​to obtain the size (R i ), in particular in real space, or alternatively in Fourier space.

[0105] Embodiment 21: A method as described in any one of embodiments 12 to 20, wherein in (c), extracting the one or more extracted beam cross sections from the one or more captured images includes: dividing the one or more captured images in Fourier space by the focused image of the sample in Fourier space.

[0106] Embodiment 22: The method of embodiment 21, wherein retrieving the one or more retrieved beam cross sections from the one or more captured images further comprises: At least one of multiplying and multiplying with a focal beam cross section in Fourier space.

[0107] Embodiment 23: A method as described in any one of embodiments 1 to 22, wherein in (d), the beam aberration coefficients in the set of beam aberration coefficients are changed sequentially and / or in parallel, in particular based on a multidimensional change routine, until a minimized size (R) as a function of all beam aberration coefficients in the set of beam aberration coefficients is obtained. 最小 ). For example, the beam aberration coefficient set ( i C) can be varied until the magnitude (R) as a function of the first beam aberration coefficient is obtained. i ), then the beam aberration coefficient set ( i C) can be varied until said magnitude (R) is obtained as a function of said next beam aberration coefficient. i ), etc. Alternatively, several beam aberration coefficients may be varied in parallel.

[0108] Embodiment 24: A method as described in any one of Embodiments 1 to 23, wherein capturing the one or more images of the sample includes: capturing the one or more images of the sample at one or more under-focus distances and capturing the one or more images of the sample at one or more over-focus distances.

[0109] Embodiment 25: A method as described in any one of Embodiments 1 to 24, wherein capturing the one or more images of the sample includes: capturing multiple images of the sample at multiple different defocus distances, in particular by varying the focusing strength of the focusing lens by predetermined increments, or alternatively by varying the distance between the focusing lens and the sample by predetermined increments, in particular by equal increments of, for example, 0.1 micrometers or greater and 2 micrometers or less, respectively.

[0110] Embodiment 26: A method as described in any one of Embodiments 1 to 25, wherein the beam aberration coefficient set ( i C) includes i C s , i C 散焦 , i C 像散，2重 , i C 像散，3重 , i C 像散，4重 , i C 星形 , i C 彗形像差 Two, three or more coefficients in the group, and one, two or more chromatic aberration coefficients.

[0111] The methods described in the above embodiments can be performed by any charged particle beam system described herein.

[0112] 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 placed on the sample stage; a charged particle detector 118 for detecting signal particles emitted from the sample; and a processor and a memory storing instructions, which, when executed by the processor, cause the system to perform a method as described in any one of the above embodiments.

[0113] 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 toward a sample placed on the sample stage; a charged particle detector for detecting signal particles emitted from the sample; and a processor and a memory storing instructions, which, when executed by the processor, cause the system to: (x1) when photographing with one or more defocus settings, based on a set of beam aberration coefficients ( i(x2) comparing the one or more captured images of the sample captured with the one or more defocused settings with the one or more simulated images to determine the magnitude of the difference between the two (R i ); and (x3) changing the beam aberration coefficient set ( i C) to provide an updated set of beam aberration coefficients ( i+1 C), and use the updated set of beam aberration coefficients ( i+1 C) to minimize the size (R i ).

[0114] 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 toward a sample placed on the sample stage; a charged particle detector for detecting signal particles emitted from the sample; and a processor and a memory storing instructions, which, when executed by the processor, cause the system to: (x1) based on a set of beam aberration coefficients ( i (c) simulating one or more beam cross sections with one or more defocus settings to provide one or more simulated beam cross sections; (x2) performing one or more captured images (h) of the sample captured with the one or more defocus settings. 1…N ) and the one or more simulated beam cross sections to determine the magnitude of the difference between the two (R i ); and (x3) changing the beam aberration coefficient set ( i C) to provide an updated set of beam aberration coefficients ( i+1 C), and use the updated set of beam aberration coefficients ( i+1 C) to minimize the size (R i ).

[0115] Embodiment 29: A charged particle beam system as described in Embodiment 27 or 28, wherein when the one or more images are captured and simulated, the one or more defocus settings include one or more defocus distances, in particular multiple different defocus distances, between the sample and the corresponding beam focus of the charged particle beam.

[0116] Embodiment 30: A charged particle beam system as described in any one of Embodiments 27 to 29, wherein when the one or more images are captured and simulated, the one or more defocus settings include one or more beam landing energies of the charged particle beam that vary from a focal beam landing energy, in particular a plurality of different beam landing energies.

[0117] Embodiment 31: The charged particle beam system as described in any one of Embodiments 27 to 30 further comprises: an image generation unit for generating the one or more captured images of the sample with the one or more defocus settings, for forwarding information about the one or more defocus settings for simulation in (x1), and for forwarding the one or more captured images for comparison in (x2).

[0118] The charged particle beam systems described herein may be configured to operate according to any of the methods described herein.

[0119] While the foregoing is directed to embodiments, other and further embodiments may be devised without departing from the basic scope thereof, and the scope thereof is determined by the following claims.

Claims

1. A method for determining an aberration of a charged particle beam focused by a focusing lens toward a sample in a charged particle beam system, the method comprising: (a) capturing one or more images of the sample at one or more defocus settings to provide one or more captured images; (b) Based on the beam aberration coefficient set ( i C) and a focused image of the sample, simulating one or more images of the sample taken with the one or more defocus settings to provide one or more simulated images; (c) comparing the one or more captured images with the one or more simulated images to determine a magnitude (R) of a difference therebetween; and (d) changing the beam aberration coefficient set ( i C) to provide an updated set of beam aberration coefficients ( i+1 C), and use the updated beam aberration coefficient set ( i+1 C) Repeat (b) and (c) to minimize the size (R).

2. A method as claimed in claim 1, wherein the one or more defocus settings include one or more defocus distances between the sample and the corresponding beam focus of the charged particle beam, so that in (a), the one or more images are taken when the sample is arranged at the one or more defocus distances, and in (b), the one or more simulated images include simulated images of the sample taken at the one or more defocus distances.

3. The method of claim 2, wherein in (a), the plurality of six or more images are taken at six or more different defocus distances. 4 . The method of claim 3 , wherein the plurality of six or more images are taken by varying the focus strength of the focusing lens or by moving a sample stage relative to the focusing lens.

5. A method as claimed in claim 1, wherein the one or more defocus settings include one or more beam landing energies of the charged particle beam that vary from a focal beam landing energy, such that in (a), the one or more captured images are captured at the one or more beam landing energies, and in (b), the one or more simulated images include simulated images of the sample captured at the one or more beam landing energies.

6. The method of claim 1, wherein (b) and (c) are repeated until the one or more captured images are obtained. 1…N ) and the minimized size (R 最小 ), and the updated beam aberration coefficient set at the corresponding iteration in the iterative process ( i+1 C) constitutes the actual beam aberration ( 拟合 C).

7. The method of claim 6, further comprising: The actual beam aberration is corrected using one or more aberration correctors ( 拟合 C) to provide a corrected charged particle beam.

8. The method of claim 7, wherein the one or more aberration correctors are one or more electrostatic or magnetic multipole correctors.

9. 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.

10. The method of claim 1, wherein in (c), comparing comprises: A difference value between each of the one or more captured images and a corresponding simulated image of the one or more simulated images is calculated, and the difference values ​​are summed to obtain the size (R).

11. The method of claim 10, wherein the calculating of the difference value between each of the one or more captured images and the corresponding simulated image of the one or more simulated images and the aggregating of the difference values ​​to obtain the size (R) are in Fourier space.

12. The method of claim 1, wherein in (b), simulating comprises: At each defocus setting of the one or more defocus settings: -Based on the beam aberration coefficient set ( i C), calculating the beam cross section of the charged particle beam, and - calculating a corresponding simulated image in Fourier space based on the product of said beam cross section in Fourier space and said focused image in Fourier space, or calculating a corresponding simulated image in real space based on convolution.

13. The method of claim 12, wherein calculating the corresponding simulated image in Fourier space further comprises: Divide by the focal beam cross section in Fourier space.

14. The method of claim 1, wherein the beam aberration coefficient set ( i C) includes i C s , i C 散焦 , i C 像散，2重 , i C 像散，3重 , i C 像散，4重 , i C 星形 and i C 彗形像差 Two, three or more coefficients in the group, and one, two or more chromatic aberration coefficients.

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

16. A method of determining an aberration of a charged particle beam focused by a focusing lens toward a sample in a charged particle beam system, the method comprising: (a) capturing one or more images of the sample at one or more defocus settings to provide one or more captured images, and retrieving one or more retrieved beam cross sections from the one or more captured images; (b) Based on the beam aberration coefficient set ( i C), simulating one or more beam cross sections with the one or more defocus settings to provide one or more simulated beam cross sections; (c) comparing the one or more retrieved beam cross sections to the one or more simulated beam cross sections to determine a magnitude (R) of a difference therebetween; and (d) changing the beam aberration coefficient set ( i C) to provide an updated set of beam aberration coefficients ( i+1 C), and use the updated beam aberration coefficient set ( i+1 C) Repeat (b) and (c) to minimize the size (R).

17. A method as claimed in claim 16, wherein the one or more defocus settings include one or more defocus distances of the sample from a beam focus corresponding to the charged particle beam, or wherein the one or more defocus settings include one or more beam landing energies of the charged particle beam that vary from a focal beam landing energy.

18. The method of claim 16, wherein (b) and (c) are repeated until a minimized size (R) of the difference between the one or more retrieved beam cross sections and the one or more simulated beam cross sections is obtained. 最小 ), and the updated beam aberration coefficient set ( i+1 C) constitutes the actual beam aberration of absolute value ( 拟合 C).

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

20. The method of claim 16, wherein in (c), comparing comprises: The difference value between each retrieved beam cross section and the corresponding simulated beam cross section is calculated and summed to obtain the size (R).

21. The method of claim 20, wherein said calculating a difference value between each retrieved beam cross section and a corresponding simulated beam cross section and said aggregating said difference values ​​to obtain said size (R) is in real space.

22. The method of claim 16, wherein in (a), retrieving the one or more retrieved beam cross sections from the one or more captured images comprises: The one or more captured images in Fourier space are divided by a focused image of the sample in Fourier space, or wherein the one or more retrieved beam cross sections are retrieved based on a deconvolution in real space.

23. The method of claim 22, wherein retrieving the one or more retrieved beam cross sections from the one or more captured images further comprises at least one of applying an adaptive filter term and multiplying with a focal beam cross section in Fourier space.

24. The method of claim 16, wherein in (d), the beam aberration coefficients in the set of beam aberration coefficients are varied sequentially and / or in parallel until a minimized magnitude (R ) as a function of all beam aberration coefficients in the set of beam aberration coefficients is obtained. 最小 ).

25. The method of claim 24, wherein beam aberration coefficients in the set of beam aberration coefficients are varied based on a multi-dimensional variation routine.

26. A charged particle beam system comprising: a charged particle source for emitting a charged particle beam propagating along the optical axis; Sample table; a focusing lens for focusing the charged particle beam toward a sample placed on the sample stage; a charged particle detector for detecting signal particles emitted from the sample; as well as a processor and a memory storing instructions that, when executed by the processor, cause the charged particle beam system to: (x1) Based on the beam aberration coefficient set ( i C) and a focused image of the sample, simulating one or more images of the sample with one or more defocus settings to provide one or more simulated images; or Based on the beam aberration coefficient set ( i C), simulating one or more beam cross sections with one or more defocus settings to provide one or more simulated beam cross sections; (x2) comparing one or more captured images of the sample captured with the one or more defocus settings with the one or more simulated images to determine the magnitude of the difference between the two; or comparing one or more retrieved beam cross sections retrieved from one or more captured images of the sample captured at the one or more defocus settings and the one or more simulated beam cross sections to determine a magnitude of a difference therebetween; as well as (x3) Change the beam aberration coefficient set ( i C) to provide an updated set of beam aberration coefficients ( i+1 C), and use the updated set of beam aberration coefficients ( i+1 C) to minimize the size.

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