Aberration correction in charged particle spectroscopy

Abstract

To provide a method for correcting aberration in a charged particle spectrometer.SOLUTION: The method includes receiving, by a charged particle spectrometer, a charged particle beam along an axis and applying, by a first optical correction element of the charged particle spectrometer, a first decapole field to the charged particle beam. At least a portion of the first optical correction element is positioned in front of a line focus of the charged particle beam at an on-axis dispersion plane and an on-axis crossover location such that the first decapole field partially attenuates fourth order aberrations associated with the charged particle beam. The method includes increasing the dispersion and applying a second decapole field to the charged particle beam by a second optical correction element of the spectrometer, wherein the second optical correction element is positioned after the crossover such that the second decapole field further attenuates fourth order aberrations.SELECTED DRAWING: Figure 10

Description

[Technical Field]

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS This application claims priority to U.S. Patent Application No. 18 / 748,912, filed June 20, 2024, the disclosure of which is incorporated herein by reference in its entirety.

[0002] The present disclosure is directed to charged particle microscope system components and methods. More particularly, the present disclosure describes aberration correction in high-resolution charged particle spectroscopy. [Background technology]

[0003] Charged particle microscopy, such as transmission electron microscopy (TEM) and scanning electron microscopy (SEM), can use a variety of detection techniques to obtain information about a sample. SEM and TEM techniques can be used to image a variety of sample types, including the surface / interior of a cell, the structure of protein molecules, and the organization of molecules in viruses and cytoskeleton glomeruli. In particular, for TEM, various techniques can be used depending on the type of sample being imaged. One such technique is called electron energy loss spectroscopy (EELS), in which an electron beam emerging from a sample is dispersed into an energy spectrum and subsequently imaged. Unlike SEM techniques, which may also observe surface topography, TEM instruments utilize an electron beam to pass completely through a sample and study the sample's internal topography. Due to inherent laws of nature, electrons in the electron beam scatter after interacting with the sample. As a result, many of the electrons experience electron energy loss and consequently a focus shift at the imaging plane associated with chromatic aberration, necessitating adjustment of the lens optics to obtain high-resolution images and varying degrees of geometric aberrations that can affect image quality by introducing astigmatism and haze. Thus, image resolution can be adversely affected by various aberrations, and solutions may be needed to achieve high-resolution imaging with various TEM and SEM devices. Summary of the Invention

[0004] In some embodiments, a method for correcting aberrations in a charged particle spectrometer includes receiving a charged particle beam along an axis with the charged particle spectrometer and applying a first decapole field to the charged particle beam using a first optical correction element of the charged particle spectrometer. The first optical correction element is positioned before an on-axis crossover, and the first decapole field partially attenuates fourth-order aberrations associated with the charged particle beam. The method further includes applying a second decapole field to the charged particle beam with a second optical correction element of the spectrometer, the second optical correction element having a position after the crossover of the charged particle beam such that dispersion of the charged particle beam after the crossover exists in a dispersion plane at the position of the second optical correction element, and the second decapole field further attenuates fourth-order aberrations.

[0005] In some embodiments, the method includes receiving the charged particle beam through an entrance aperture located in front of a first optical corrective element, the aperture diameter being in a first range of 0.1 mm to 10 mm. The method includes a line focus including one or more of: (i) an x-z ​​line focus along an x-z ​​distribution plane at a focus position before crossover, or (ii) a y-z line focus in a y-z line dispersion plane along the axis at a second focus position after crossover.

[0006] In some embodiments, the method includes measuring the charged particle beam with a detector positioned after the second optical correction element and creating an image using an image resolution ranging from 0.01 mV / pixel to 1000 mV / pixel.

[0007] In some embodiments, the method includes attenuating at least two fourth-order aberration coefficients, and further attenuating the fourth-order aberrations with the second optical corrective element includes attenuating at least one additional fourth-order aberration coefficient and at least two fourth-order aberration coefficients, and further, the at least one additional fourth-order aberration coefficient can be a different fourth-order aberration coefficient.

[0008] In some embodiments, the method includes the first optical correction element and the second optical correction element each including one or more corresponding dodecapole elements.

[0009] In some embodiments, the method includes applying a second decapole field, wherein the first range of ampere rotations comprises 1 to 20 ampere rotations.

[0010] In some embodiments, the method includes at least two fourth order aberration coefficients A 22 , A 40 And one or more of the additional fourth-order aberration coefficients is A 04 , which may include.

[0011] In some embodiments, the method includes partially attenuating geometric aberrations associated with the charged particle beam, and further attenuating fourth order aberrations with the second optical correction element includes attenuating geometric aberrations associated with the charged particle beam with the second optical correction element. 0n <x|δ n > includes attenuating the geometric aberrations, and in this formula, A 0n is the aberration coefficient, x is the imaging axis, n is the specific order of the aberration, and δ is the dispersion angle associated with the charged particle beam in the dispersion plane.

[0012] In some embodiments, the method can include a first multipole element and a second multipole element, and applying the first decapole field to the charged particle beam can include exciting the first multipole element and the second multipole element. The method can include at least partially attenuating up to four orders of geometric aberrations and attenuating chromatic aberrations by one or more orders in response to exciting the first multipole element and the second multipole element.

[0013] In some embodiments, the method may include a second optical correction element including a third multipole element, and applying the second decapole field to the charged particle beam also includes exciting the third multipole element, and attenuating geometric aberrations up to fourth order in response to exciting the third multipole element.

[0014] In some embodiments, a non-transitory computer-readable storage medium may include instructions executable by one or more processing units of a charged particle spectrometer to cause operations such as applying a first decapole field to the charged particle beam by a first optical correction element, receiving the charged particle beam along an axis from an element of the charged particle spectrometer such that at least a portion of the first optical correction element is positioned before a focal point of the charged particle beam in a dispersive plane where an on-axis crossover occurs, the first decapole field partially attenuating fourth-order aberrations associated with the charged particle beam, and applying a second decapole field to the charged particle beam by a second optical correction element of the charged particle spectrometer, the second optical correction element being positioned after the crossover, the dispersive plane of the charged particle beam being after the crossover, dispersion of the charged particle beam being present at the position of the second optical correction element, and the second decapole field further attenuating fourth-order aberrations.

[0015] In some embodiments, the manipulation includes applying one or both of a hexapole field and an octopole field to the charged particle beam.

[0016] In some embodiments, the manipulation includes increasing a first dispersion along a yz dispersion plane of the charged particle beam after crossover relative to the axis, while maintaining a second dispersion along an xz dispersion plane of the charged particle beam at a constant size relative to the axis.

[0017] In some embodiments, the charged particle spectrometer can be configured to use translational motion or electron energy loss mode, and the attenuation of fourth-order aberrations reduces the image distortion along the axis by an order of magnitude.

[0018] In some embodiments, a charged particle spectrometer may include a first optical correction element, a second optical correction element, an entrance aperture configured to receive the charged particle beam, and a controller configuring the first optical correction element to apply a first decapole field to the first optical correction element. The spectrometer may further include positioning the first optical correction element before the crossover such that the first decapole field partially attenuates fourth-order aberrations associated with the charged particle beam. The controller may further include applying a second decapole field to the charged particle beam by a second optical correction element of the spectrometer, the second optical correction element having a post-crossover position of the charged particle beam such that, after the crossover, dispersion of the charged particle beam resides in a dispersion plane at the position of the second optical correction element, and the second decapole field further attenuates fourth-order aberrations.

[0019] In some embodiments, the charged particle analyzer comprises: An entrance aperture may be included with an aperture diameter ranging from 5 mm to 5 mm to produce equal energy resolution.

[0020] In some embodiments, the charged particle analyzer comprises: An entrance aperture may be included with an aperture diameter ranging from 0.5 mm to 5 mm to produce an equal signal-to-noise ratio.

[0021] In some embodiments, the charged particle spectrometer may include a slit and / or a knife edge, and the first optical correction element may be located before the slit and the second optical correction element may be located after the slit.

[0022] In some embodiments, the charged particle spectrometer may cause the first optical correction element to apply a third decapole field to the charged particle beam, and in such cases, applying the third decapole field to the charged particle beam may at least partially modify a y-field dimension of the charged particle beam, and the charged particle beam may have at least two foci before crossover.

[0023] In some embodiments, the charged particle spectrometer can attenuate two fourth-order coefficients before the on-axis crossover and one fourth-order coefficient after the on-axis crossover. [Brief explanation of the drawings]

[0024] The foregoing aspects and many of the associated advantages of the present disclosure will be more readily appreciated as the same becomes better understood by reference to the following detailed description, when taken in conjunction with the accompanying drawings.

[0025] In the drawings, like reference numbers refer to like parts throughout the various views unless otherwise specified. To reduce clutter in the drawings where necessary, not every instance of an element is necessarily labeled. The drawings are not necessarily to scale, emphasis instead being placed upon illustrating the principles being described.

[0026] [Figure 1] 1 is an exemplary diagram of a portion of a microscope system currently known in the art. [Figure 2] FIG. 1 is a schematic diagram of a charged particle microscope system according to some embodiments. [Figure 3] 1 is a schematic diagram illustrating an example of geometric and chromatic aberration correction in a spectrometer, according to some embodiments. [Figure 4] 1 is a spectral image of a monochromatic line showing partial fourth-order correction in a spectrometer according to some embodiments. [Figure 5] FIG. 1 is a schematic diagram illustrating an example of geometric aberration correction by multipole elements after crossover of a spectrometer, according to some embodiments. [Figure 6] 10 is a set of various line spectral images for different adjustments of multipole elements after crossover according to some embodiments. [Figure 7] FIG. 1 is a schematic diagram illustrating an example of a spectrometer with post-crossover aberration correction, according to some embodiments. [Figure 8] 10 is a set of images of various multipole fields produced by multipole elements after crossover, according to some embodiments. [Figure 9] 10 is a set of imaging fields produced by multipole elements after beam crossover, according to some embodiments. [Figure 10] FIG. 1 is a flow diagram of an example process for correcting aberrations in a spectrometer, according to some embodiments. [Figure 11] FIG. 1 is a block diagram of a controller for a charged particle microscope system in accordance with certain aspects of the present disclosure. DETAILED DESCRIPTION OF THE INVENTION

[0027] Embodiments of the present invention are described below in terms of a charged particle microscope system. In one example, the charged particle microscope system is configured to acquire an energy spectrum of a sample. The charged particle microscope can include a charged particle spectrometer configured to correct for spectroscopic aberrations. The charged particle spectrometer (or simply abbreviated as "spectrometer") can include multipole optical correction elements. The excitation (e.g., electrical and / or magnetic) of at least some or all of the optical correction elements can be controlled to attenuate fourth-order aberrations. These and other features of the present disclosure are described below. However, it should be understood that the methods described herein are generally applicable to a wide range of different methods and apparatus, including EELS, EFTEM, TEM, SEM, both scanning probe systems and parallel illumination systems, and are not limited to a particular apparatus type, beam type, object type, length scale, or scan trajectory.

[0028] As used in this application and the claims, the singular forms "a," "an," and "the" include the plural forms unless the content clearly dictates otherwise. Furthermore, the term "includes" means "comprises." Furthermore, the term "coupled" does not exclude the presence of intermediate elements between coupled items.

[0029] The systems, devices, and methods described herein should not be construed as limiting in any way. Instead, the present disclosure is directed to all novel and non-obvious features and aspects of the various disclosed embodiments, alone and in various combinations and subcombinations with one another. The disclosed systems, methods, and devices are not limited to any particular aspect or feature or combination thereof, nor do the disclosed systems, methods, and devices require that any one or more particular advantages be present or problems be solved. While any theory of operation is for ease of explanation, the disclosed systems, methods, and devices are not limited to such theory of operation.

[0030] Although some operations of the disclosed methods are described in a particular sequential order for convenient presentation, it should be understood that this style of description encompasses reordering unless a particular ordering is required by specific language set forth below. For example, operations described in sequence may, in some cases, be reordered or performed simultaneously. Moreover, for simplicity, the accompanying figures may not show the various ways in which the disclosed systems, methods, and apparatuses can be used with other systems, methods, and apparatuses. Furthermore, the description may use terms such as "produce" and "provide" to describe the disclosed methods. These terms are high-level abstractions of the actual operations that take place. The actual operations corresponding to these terms will vary depending on the particular implementation and are readily discernible by those skilled in the art.

[0031] In some instances, values, procedures, or devices are referred to as "lowest," "best," "smallest," etc. Such descriptions are intended to indicate that a selection may be made from among many possible functional alternatives, but it will be understood that such a selection need not be better than, smaller than, or otherwise preferred to other selections.

[0032] Several techniques, including electron energy loss spectroscopy (EELS) and energy-filtered transmission electron microscopy (EFTEM), are detection techniques typically incorporated into transmission electron microscopes (TEMs) to analyze the composition and other chemical properties of samples. The embodiments herein may be applicable to EELS or EFTEM spectroscopy. EELS is traditionally performed using an energy spectrometer mounted at the end of the TEM column. Such energy spectrometers are sometimes referred to as post-column filters (PCFs). In some cases, the spectrometer may be integrated into the TEM's imaging system. Such alternative spectrometers are sometimes referred to as in-column filters (iCFs). The methods disclosed herein may be applicable to PCFs and ICFs. Energy spectrometers can be used to obtain energy spectra of transmission data. For example, a beam of electrons of a desired energy is injected into a TEM sample (e.g., a substrate). Some of the electrons ejected from the sample may have reduced energy, allowing them to characterize various properties of the sample (e.g., nanostructure, topography, etc.). An energy spectrometer can then be used to observe the energy distribution of the electron beam after passing through the sample and determine peak values ​​at various energy levels that provide data (e.g., various properties) of the sample material. Given current TEM and detector technology, for example, peaks can be highly resolved to the millielectronvolt level. However, incomplete data from a transmission electron microscope can obscure data such that the required resolution of sample properties is reduced or lost. This loss of resolution can be due to a variety of factors, including mechanical (parasites) and electrical instabilities (vibrations), energy spread of the incident beam due to the inherent energy spread of the electron source, limited resolution of the detection power due to the finite size of the pixel, and chromatic defocusing of the electron beam as it passes through parts of the transmission electron microscope and energy spectrometer (e.g., lenses, multipoles, or equivalent). The level of such defocusing depends on the electron energy.However, the chromatic aberrations, multipoles (or similar) of each lens vary depending on its excitation and therefore also on the microscope settings, such as changing (increasing / decreasing) the ratio settings of the microscope, the energy spectrometer, or both components. As higher resolution energy spectra are desired for wider aperture diameters, geometric and chromatic aberrations become more of an issue, potentially requiring various adjustments to the spectrometer's optical correction elements.

[0033] The entrance aperture of a spectrometer has traditionally depended, at least in part, on its transmittance for a particular specified energy resolution. For example, low transmittance necessitates the use of a very small aperture size, which can limit the desired number of electrons to be captured. The resolution of an imaging test can be improved by increasing the amount of charged particles reaching the spectrometer through the entrance aperture, but this adds cost and complexity to the creation of undesirable beam characteristics (e.g., astigmatism). Traditionally, spectrometer entrance apertures need to be relatively small (e.g., 2.5 mm or less) to achieve resolutions on the order of 5 mV / pixel. However, reducing the aperture can reduce the amount of charged particles entering the spectrometer, limiting the useful resolution of the resulting image. In the EFTEM example, the crossover may function as a slit plane (e.g., a knife-tip slit or similar plane used in calibration procedures for various types of aberrations that affect imaging quality). Conventional spectroscopy involves correcting at least some geometric and chromatic aberrations before the charged particle beam reaches the crossover (e.g., a focus in at least one of the y / x dimensions relative to z). This is because having a focus beyond the crossover focus can result in a relatively small post-crossover beam waist. Because the post-slit beam waist is relatively small and depends on the size of the entrance aperture, increasingly intense and sometimes impractical electromagnetic fields may need to be applied by several electromagnetic pole elements (e.g., 12 pole elements) at the post-crossover location to affect the charged particle beam to achieve the desired aberration-free resolution. Increasing the number of high-power electromagnetic pole elements is costly, space-consuming, and may be ineffective at correcting high-order aberrations that are difficult to correct with a relatively small post-slit beam waist.

[0034] In the present invention, in some examples, high energy resolution (e.g., 10 mV) can be achieved with a large entrance aperture (e.g., 5 mm) by creating at least one line focus in at least one dimension, which may exist before the crossover (sometimes referred to as the slit plane), and correcting geometric aberrations both before and after the crossover. In some examples, two lines can be created before the crossover, allowing for expansion of the y-dimension of the charged particle beam after the crossover. The large entrance diameter can ensure a proportionally larger number of charged particles (e.g., electrons) enter the spectrometer. At least two multipole elements can be placed before the crossover to attenuate geometric aberrations by three orders of magnitude (e.g., aberration coefficients are reduced to essentially zero), correct chromatic aberrations, attenuate at least two coefficients of fourth-order aberrations, and correct at least one coefficient of fourth-order aberrations after the crossover. By shaping the beam profile in at least one dimension (e.g., the y-dimension) so that the beam profile exhibits at least two line focus locations before crossover, a large dispersion in the y-dimension can be created in that dimension, making it easier to shape and correct higher-order aberrations. For example, with this pre-slit plane (pre-crossover) line configuration, the beam can be expanded in the dispersion plane while also achieving shape A. 0n <x|δ n > aberrations can be efficiently corrected, where n is the order of the specific aberration and δ is the magnitude of the aberration along a particular plane (e.g., along x, n = 4, A 04 <x|δ 4 >) at a dispersion angle (e.g., 0 to 90 degrees relative to the transmission axis). Furthermore, this allows for at least one additional line focus to be relatively large for a selected dimension in the dispersion plane after the crossover, and a reasonably small electromagnetic field (at least By splitting the attenuation of geometric aberrations into pre-crossover and post-crossover corrections, the entrance aperture can be enlarged without compromising the energy resolution or signal-to-noise ratio, while at the same time minimizing the size of a given spot on the sample. The maximum capture scattering angle of the size can be increased by at least a factor of 2.5 compared to conventional techniques. Furthermore, when applied to plasmon and phonon spectroscopy using parallel momentum-resolved EELS (and q-EELS), the fourth-order correction reduces distortions (smearing, coma, etc.) in the dispersion cross section in one dimension of a magnitude that facilitates the use of larger entrance diameters (momentum range, e.g., q-range).

[0035] 1 illustrates a portion of a microscope system 100 currently known in the industry, showing chromatic aberration in dual-EELS mode. The microscope system 100 includes a portion of a TEM 102 and an energy spectrometer 104. The microscope system 100 can be used to acquire an energy spectrum of a sample 106, but can suffer from defocusing of the electron beam 124 on the detector 122 due to the operating parameters of the TEM 102 and the energy spectrometer 104.

[0036] To illustrate, as the electron beam 124 emerges from the sample 106, it follows a trajectory along the optical axis of the microscope 102. This trajectory may depend on the energy of the electrons in the electron beam 124 and may further depend on operational parameters of the microscope 102. The operational parameters may include operational parameters of the imaging system 108, such as adjusting the magnification setting of the microscope 102 for magnification from the sample 106 toward a crossover point 107 at the end of the microscope 102. This magnification can determine how much the cone of the electron beam 124 emerging from the sample 106 is compressed toward the energy spectrometer 104, and it is therefore desirable for a user of the microscope system 100 to be able to freely change this magnification. Stronger compression can result in a larger portion of the cone of the electron beam 124 being accepted into the entrance aperture of the spectrometer. The operational parameters may determine the excitation settings of optical components, such as lenses, multipoles, and quadruples, of the energy spectrometer 104. The operating parameters can vary depending on the energy of the primary electron beam, e.g., the energy of the electron beam used to interrogate the sample 106. However, due to electron interaction with the sample, the electron beam emerging from the sample 106 may contain some energy loss. Measuring the loss over a range of energies using the energy spectrometer 104 can be beneficial for topology measurements, so energy loss may be desirable. However, energy loss can also affect the crossover position (e.g., focal spot) of the electron beam 124 within the microscope 102 and the energy spectrometer 104. This change in intersection can result in defocusing of the electron beam spectrum on the detector 122.

[0037] For example, an electron beam propagating through the microscope 102 without any energy loss may have a crossover location as shown. However, an electron beam with some energy loss may propagate through the microscope 102 and energy spectrometer 104 with a different crossover location with an offset ΔZ as shown.

[0038] The energy spectrometer 104 can include a lens 110 and a dispersive element 112. The dispersive element 112 can include a bias tube 114, lenses (e.g., lenses 116 and 118), multiple optical components (e.g., additional lenses, quadrupoles, multipoles, etc.) 120, and a detector 122. The dispersive element 112 can be activated to disperse or "fan out" the electron beam 124 into various energy bands with which it interacts. The multiple optical components 120 can focus or expand this band onto the detector 122. Generally, these different energy bands may be smaller than (e.g., may not cover) the full range of EELS spectra that an operator may be interested in and wish to record. Therefore, the bias tube 113 can be electrically biased to add various amounts of energy (e.g., up to 2 keV) to the electron beam 124. The applied energy can be used to shift the energy band recorded by detector 122 (such energy band shifting can also be achieved by adjusting the excitation of dispersive element 112 or by adjusting the operating potential of the electron microscope, although such methods have the disadvantage of being subject to relatively long settling times and / or magnetic hysteresis). Electrostatically, liner test tubes can be set to change from one energy band to another in milliseconds, allowing multiple energy bands to be recorded nearly simultaneously (e.g., as described in U.S. Patent No. 10,832,901 B2, incorporated herein by reference). Detector 122 can be positioned at the conjugate of the spectral plane of energy spectrometer 104 so that electron beam 124 is focused onto detector 122.

[0039] The energy analyzer 104 includes optical components, such as multipoles, configured to control (e.g., shape) the electron beam 124. The operation of these optical components (e.g., currents that magnetically excite one or more of the multipoles) can be controlled to correct for defocus based on an offset ΔZ. Various parameters, such as magnification and chromatic aberration constants, can be measured for the image detected by the detector 122. These parameters can be used to adjust the operation of the optical components to correct for defocus based on the offset ΔZ. Effective configurations of parameters can also be compiled for future use, such as when a particular setting is commonly used or when a particular setting needs to be obtained.

[0040] 2 is a schematic diagram of an electron microscope system (EMS) according to some embodiments. The EMS 200 may include a TEM 202 and an energy spectrometer 204, in some examples. The energy spectrometer 204 may be used, for example, to acquire EEL spectra. The EMS 200 may include optical components to reduce or counteract defocusing problems that occur during acquisition of the spectra. In some examples, the optical components may be biased to a level based on operating parameters of the EMS 200 and / or the energy spectrometer 204, such that refocusing is dynamic.

[0041] The TEM 202 may include a light source 228, an illumination system 230, a projection system 208, and various detectors 232, all of which may be controlled by a controller 226. The light source 228 may be an electron source, such as a Schottky source or a (cold) field emission gun (CFEG), and may provide a beam of electrons that propagate along the optical axis of the TEM 202 and interact with the sample 206. The illumination system 230 includes multiple electron optical components for conditioning the electron beam for delivery to the sample 206. Conditioning the electron beam may include collimation, astigmatism adjustment, and focusing of the electron beam at the sample plane. The projection system 208 may include various electrostatic / magnetic lenses, deflectors, correctors (such as astigmatism adjusters), etc., used to focus the electron beam emerging from the sample 206 onto one of the various detectors 232. The projection system 208 can be configured to focus an image of the sample 206 onto the detector 232 at a particular (adjustable) magnification, which is typically referred to as the "imaging" of the projection system. Alternatively, the projection system 208 may be configured to focus an image of the angular distribution of the emerging electrons (or "return pattern") at a particular (adjustable) magnification on the detector 232. Such a return pattern is formed at the back focal plane of the first magnification lens (the "objective lens," not shown in FIG. 2). This alternative mode of the projection system is commonly referred to as the "return mode," and the magnification of this alternative mode is commonly referred to as the "camera length." However, for clarity, this disclosure will refer to "image," "focus," etc., which refer to both the "imaging mode" and the "return mode" of the imaging system. Similarly, this disclosure will refer to "magnification setting," etc., which refer to both the "magnification setting" and the "camera length setting" of the imaging system.

[0042] In some examples, the projection system 208 focuses and conditions the electron beam for delivery to the energy spectrometer 204. Various detectors 232 can be individually moved in and out of the optical path to provide different detection schemes for the TEM 202. The detectors 232 can include an imaging screen, a TEM camera, and a STEM camera.

[0043] The energy spectrometer 204 includes a dispersive element 212 (with bias tube 214), an optical element 234, multiple optical systems 220, and a detector 222. Many of the components of the energy spectrometer 204 have been described with respect to FIG. 1 and will not be revisited for brevity. Other components of the energy spectrometer 104 described in FIG. 1 that are not specifically shown in the energy spectrometer 204 may be included but are omitted from FIG. 2. An additional component, namely, the optical element 234, is included in the energy spectrometer 204 to correct for focal tilt of the electron energy loss spectrum across the detector as described. The optical element 234 may be a single element, such as a magnetic hexapole. Alternatively, the optical element 234 may be composed of multiple multipole elements (quadrupoles, hexapoles, octopoles, etc.), which may be electrical or magnetic in nature of their operation. Additionally, besides spectral refocusing, optical component 234 may perform multiple alternative functions, either simultaneously or non-simultaneously, such as correcting for image distortion and correcting for spectral distortion. While optical component 234 is shown downstream of dispersive element 212 in FIG. 2, this is not the only location for placing optical component 234. In general, optical component 234 may be located upstream of dispersive element 212 (but downstream of sample 206), or may be located within or after optical components 220, downstream of dispersive element 212.

[0044] The controller 226 may include one or more processing cores and memory that stores executable code. The controller 226 may also provide operating voltages to certain components of the EMS 200 or may be coupled to a voltage supply (not shown) that provides operating voltages in response to control signals provided by the controller 226. For example, the controller 226 may provide control and / or voltages to the illumination system 230, the projection system 208, and the optics 234. Additionally, the controller 226 may control the operation of the detector 222 and / or receive data from the detector 222. Generally, the controller 226 sets operating parameters of the EMS 200 and adjusts the electrical bias of the optics 234 to dynamically focus the electron beam onto the detector 222 in response to changes in operating conditions of the EMS 200, such as magnification.

[0045] The optical component 234 may be formed from a multipole element including two or more conductive elements. In some examples, the optical component 234 is formed from two opposing conductive elements, similar to a deflector or shutter-type arrangement housed in an electrical conductor. In other examples, the optical component 234 is formed from a quadrupole or higher-order multipole element. The excitation of the optical component 234 may be electric or magnetic in nature, or a combination of these, or more generally electromagnetic in nature. Regardless of the physical example, the optical component 234 may be excited to a level based on the operating parameters of the TEM 202 and / or energy spectrometer 204.

[0046] During operation, the electron beam generated by the source 228 at a primary energy is projected toward the sample 206, where it interacts with the sample 206. The interaction may result in some electrons losing energy by an amount related to various material properties of the sample 206. The electron beam emerging from the sample 206 may then contain electrons of different energies across a range of energies. The emerging electron beam may then propagate on a different trajectory than the primary energy electrons, which may affect the focus, e.g., crossover location, of the electron beam along the remaining optical path, including the energy spectrometer 204 and the TEM 202. In some examples, operation of equipment that can steer (manipulate) the electron beam may subsequently result in a defocused focus or a gradient of focus across the spectral plane. In this example, the optics 234 may be activated based on current operating parameters to refocus the electron beam. In various examples, activating the optics 234 may align the crossover location with the spectral plane, thereby aligning the detector 222.

[0047] FIG. 3 is a schematic diagram illustrating an example of geometric and chromatic aberration correction in a spectrometer 300, according to some embodiments. Spectrometer 300 may incorporate some or all of the components of spectrometer 204 in FIG. 2 . As an example, a charged particle beam (e.g., electrons) enters an optical system (e.g., first optical correction element 370) at an entrance aperture 320 along optical axis 310 (which corresponds to the optical axis of propagation of the charged particle beam, traveling generally from left to right along the “Z” axis in FIG. 3 ). For example, prism 390 precedes MP2 352, whereas MP2 352 follows prism 390 as shown in FIG. 3 . In some examples, entrance aperture 320 may have an aperture diameter 322 (e.g., 0.1 mm to 10 mm) that controls the beam profile (e.g., two-dimensional particle flux across any plane perpendicular to optical axis 310) entering first optical correction element 370. For example, a 5 mm aperture diameter 322 may provide a larger beam profile (more fluence) at the first optical correction element 370 than a 1.75 mm aperture diameter 322. In some examples, the aperture diameter 322 may be automatically or dynamically adjusted by a user of the spectrometer 300 depending on the desired beam profile. It should be understood that, in general, the terms "front" and "back" describe positions relative to the optical axis 310 and the various subsequent components. Furthermore, XYZ Cartesian coordinates are used to identify positions, orientations, and configurations, and generally in this disclosure, the Y coordinate is vertical (up and down along FIG. 3 ), the Z coordinate is horizontal (left to right along FIG. 3 ), and the X coordinate is from off-page and points toward the page as shown in FIG. 3 . For example, xF 304 is shown in FIG. 3 as moving along the z-axis using a vertical scale. However, the vertical measurements represent distance from off-page relative to the z-axis (if above the z-axis) and on-page spacing relative to the z-axis (if below the z-axis). Also, each field ray may represent only a portion of the overall field in a particular dimension. Cartesian coordinates have been chosen for clarity, but it should be understood that coordinate conventions can be arbitrarily substituted and are not to be considered limiting.

[0048] In some examples, the charged particle beam may enter a series of charged particle beam systems, such as the first optical corrective element 370, which may cause various modifications to the charged particle beam profile (e.g., lowering aberration coefficients). The charged particle beam profile of the charged particle beam includes an x-axis component (e.g., a point on the x-field line 304) and a y-axis component (e.g., a point on the y-field line 306), both of which are perpendicular to the optical axis 310 (e.g., the z-axis) and perpendicular to each other, similar to the propagation direction of electromagnetic waves. Upon entering the first multipole element (MP1) 350 of the first optical corrective element 370, the charged particle beam profile may be adjusted in one or more dimensions (e.g., the x-dimension, the y-dimension, etc.) to reduce aberrations, such as geometric aberrations and chromatic aberrations. MP1 350 may be an electromagnetic beam shaping device that includes one or more physical electromagnetic poles. In a non-limiting example, MP1 350 may be a dodecapole element or other suitable multipole element (e.g., a dodecapole, a 16-pole, etc.), which includes 12 different magnetic, electromagnetic, and / or electrostatic electrodes, each of which can be positively or negatively polarized depending on the desired field to be applied to the charged particle beam. The dodecapole element may be capable of applying a linear superposition of various multipole fields to create a dodecapole field, a dipole field, a quadrupole field, a hexapole field, etc., or any suitable number of shaped fields of any orientation. In some examples, MP1 350 may function to at least partially correct geometric aberrations associated with the charged particle beam. While MP1 350 is shown as a single multipole element, this is not considered limiting, and any suitable number of multipole elements may be sequentially arranged between the entrance aperture 320 and the prism 390 for desired beam shaping.

[0049] In some examples, the prism 390 (e.g., a 90-degree beam-transfer prism) functions to provide beam dispersion, such as broadening of the X-dimension field lines (x-field lines 304) relative to the Y-field lines 306, enabling various degrees of aberration correction (degrees of freedom) with various multipole elements. For example, the prism 390 can broaden the x-field lines 304 more than the y-field lines 306 along the optical axis 310, facilitating aberration correction in each dimension. In various examples, the prism 390 can apply an appropriate field strength to the charged particle beam to pass and disperse charged particles within a predetermined energy range while attenuating charged particles outside the predetermined energy range. While the prism 390 is shown as a single prism element, this is not considered limiting, and an appropriate number of prisms can be arranged in series between the MP1 350 and the second multipole element (MP2) 352 to provide a desired beam dispersion, shape, geometry, charged particle attenuation, or combinations thereof. Also, although the first optical correction element 370 is shown as MP1-Prism-MP2, a suitable configuration of the first optical correction element 370 including additional multipole elements and prisms can be used to arrive at a desired beam profile (e.g., MP1-MP2-MP3-PRISM-MP4, etc.).

[0050] In some instances, MP2 352 may function similarly to MP1 350. For example, MP1 MP1 350 may function to partially correct one or both geometric aberrations of the x / y field light 304 / 306. After the charged particle beam passes through prism 390 and undergoes beam dispersion (essentially "fanning" the beam), MP2 352 may function to further correct the geometric aberrations that MP1 350 partially corrected. For example, MP1 350 and MP2 352 can function simultaneously to correct multiple types of aberrations. In this example, when MP1 350 receives a charged particle beam, MP1 350 may perform partial geometric aberration correction (e.g., correct one or more fourth-order coefficients). MP2 352 receives the partially corrected charged particle beam from prism 390 and can perform additional geometric aberration correction (e.g., correct two or more fourth-order coefficients) and chromatic aberration correction (e.g., adjust the focal plane of the charged particle spectrum). In a non-limiting example, MP1 352 may be a dodecapole element including 12 different magnetic, electromagnetic, and / or electrostatic poles, each capable of polarizing to a positive or negative charge depending on the desired field to be applied to the charged particle beam. The dodecapole element may be capable of applying a linear superposition of various multipolar fields to create a dodecapole field, a dipole field, a quadrupole field, a hexapole field, etc., or any suitable number of shaping fields of any orientation. In some examples, MP1 352 may function to at least partially correct geometric aberrations associated with the charged particle beam. While MP1 352 is shown as a single multipole element, this is not considered limiting, and any suitable number of multipole elements may be sequentially arranged between the prism 390 and the crossover 330 for the desired beam shaping.

[0051] In various examples, the XO plane 330 may represent a plane where the x-field rays 304 and the y-field rays 306 are approximately "focused" along the optical axis 310 (e.g., if the two field rays are fairly close to each other along the same Z coordinate). In this example, the x-field rays 304 may have a crossover point 305 at the XO plane 330, where the x-field rays 304 are approximately 0 millimeters "mm" apart from the z-axis. At the crossover point 305, the y-field rays 306 may have a non-zero spacing to the z-axis, thereby forming a y-z line focus (e.g., no field exists in the x-direction, only along the y-dimensional plane). Furthermore, the y-field rays 306 may have an XO plane crossover point 307 after the XO plane 330. At this post-XO plane crossover point 307, the y-field rays 306 are approximately 0 mm apart from the z-axis, and the x-field rays may be substantially 0 mm apart, forming a focus along the z-axis. The XO plane 330 may dynamically shift left or right along the optical axis 310 depending, at least in part, on the aperture diameter 322, the energy of the charged particle beam, the dispersion of the prism 390, and the contributions of MP1 350 and MP2 352. As a non-limiting example, when using the spectrometer 300 in an EFTEM technique, the XO plane 330 may include a slit and / or knife tip that can be dynamically positioned in or out of the path of the charged particle beam. The spectrometer 300 is calibrated by passing some charged particles while restricting others based on a predefined threshold (e.g., passing charged particle energies below 200 eV and blocking electron energies above 200 eV). In some examples, the XO plane 330 may be shifted to be substantially adjacent to the final beam of the first optical correction element 370, or the XO plane 330 may be shifted to be substantially adjacent to the dispersion magnification optical system 380 (magnification optical system 380) due to the configuration described above. While this non-limiting example presents an EFTEM procedure utilizing a slit lamp or knife edge, it should be understood that embodiments herein include slitless XO planes 330 that do not insert a slit into the spectrometer 300 (e.g., as used in EELS).

[0052] In some examples, magnification optics 380 may receive the charged particle beam from the first optical correction element 370. The magnification optics 380 may function to adjust the energy resolution of the charged particle beam based on the energy dispersion of the spectrum. The magnification optics 380 may condition (e.g., correct dispersion and magnify) the charged particle beam for detection by a detector (not shown) at the imaging plane. The detector may convert the charged particle beam pattern into an image 342 (e.g., an image representing at least a portion of the sample interrogated by the charged particle beam with data prior to the entrance aperture).

[0053] FIG. 4 illustrates a spectral image 400 of a monochromatic beam after the XO plane 330, showing partial fourth-order geometric aberration correction according to some embodiments, using the spectrometer 300 of FIG. 3 . For example, the spectral image 400 shows the xy plane 414 at the imaging plane 340 after MP1 350 and MP2 352 perform at least one partial geometric aberration correction 410 (e.g., attenuating one or more orders of fourth-order coefficients). The bottom axis may indicate dispersion pressure (e.g., -0.4 to 0.4 volts), and the vertical axis indicates various charged particle beam dispersions (e.g., around 1,000 microns “μm”) of the y-field rays 306. In some examples, the partial geometric aberration correction results in an image dispersion 412, which may increase or decrease depending on the operation of the first optical correction element 370. In the example shown in FIG. 4, a dispersion (resolution) of 90 mV is shown in image 342, with MP1 350 and MP2 352 applying their respective decapole fields to the charged particle beam with no geometric aberration correction beyond XO plane 330.

[0054] 5 is a schematic diagram illustrating an example of geometric and chromatic aberration correction in a spectrometer 500, according to some embodiments. The elements shown in FIG. Some or all of the functions of the elements shown in FIG. 3 may be included. FIG. 5 shows a charged particle beam entering a first optical correction element 370 with an aperture diameter 322 of approximately 2.0 mm. The aperture diameter 322 and prism 390 can affect the dispersion of the x-field ray 304 and the y-field ray 306. As an example, the x-field ray 304 and the y-field ray 306 are shown as being approximately aligned with each other relative to the z-axis, indicating a small dispersion spread of the charged particle beam shown in the x and y dimensions (generally circular / annular line waists). Additionally, the aperture diameter 322 functions to increase or decrease the overall energy spread (e.g., charged particle flux) entering the spectrometer 500, which directly translates to the ability to acquire high-resolution images. In some instances, the aperture diameter 322 provides more charged particles to the spectrometer 500, subject to various aberration corrections. Similarly, a small aperture diameter 322 can limit the amount of charged particles entering the spectrometer 500, and therefore limit the information input into the spectrometer about the imaged sample. In some instances, a large aperture diameter 322 is preferred because more information about the sample is received by allowing more charged particles into the spectrometer. In other instances, a small aperture diameter 322 may be desirable due to the material properties (contrast resolution) of the sample.

[0055] In some examples, the spectrometer 500 includes a first optical correction element(s) 370, which may include MP1 350, which may be a decapole element that applies a decapole field (e.g., a polar-induced electromagnetic field with each pole having 1 to 20 ampere-turns) to the charged particle beam to correct various aberrations, including at least one second-order aberration and at least one third-order aberration. The charged particle beam may then enter a prism 390 (e.g., a 90-degree prism), which may introduce further aberrations that need to be corrected due to cylindrical field effects. Similar to MP1 351, MP2 352 may also be a dodecapole field for applying a decapole field to the charged particle beam. In this example, MP2 352 receives the charged particle beam from prism 390 and can correct at least one second-order aberration, at least one three-dimensional aberration, at least one four-dimensional aberration, and chromatic aberration to properly focus the charged particle beam. Also, while the MP1-PRISM-MP2 configuration is shown in FIG. 5, it should be understood that any number of multipoles can be used in combination with prism 390 to achieve the desired correction of aberrations in the charged particle beam. For example, MP1 350 can include two dodecapole elements, and in other examples, MP1 350 can include a dodecapole element and two hexapole elements consecutively along optical axis 310.

[0056] In some examples, the second optical correction element(s) 590 may receive the charged particle beam from the final element of the first optical correction element 370 to provide further aberration correction. As an example, MP3 592 may be a dodecapole element, which may further modify the charged particle beam and attenuate additional orders of aberration. Also, while a single multipole configuration of MP3 592 is shown in FIG. 5, it should be understood that any number of multipole elements may be used in combination after the XO plane 330 to achieve the desired correction of aberrations in the charged particle beam. For example, MP3 592 may include two or more dodecapole elements, while in other examples, MP3 592 may include a dodecapole element and two additional multipole elements in series along the optical axis 310, and various dispersion-enhancing light for appropriate applications. In various examples related to EFTEM techniques, aberrations before the XO plane 330 are measured and one or more of the first optical correction elements 370 are adjusted (e.g., for charged particle beam calibration) to nullify the aberrations before the XO plane 330 by adjusting a slit (e.g., a knife edge) can be positioned approximately in line with the XO plane 330 (eg, the slit plane).

[0057] 6 is a set of images 600 of various beam spectra for different adjustments of the post-XO plane 330 multipole element, according to some embodiments. Images 642A and 642B may be spectra (e.g., images 342) imaged using a monochromator (e.g., no chromatic aberrations) without the excitation MP3 592 (e.g., image 642A) and with the excitation MP3 592 (e.g., image 642B) of FIG. 5. For example, image 642A may show a charged particle beam without the excitation MP3 592 and undergoing partial geometric aberration correction (e.g., attenuating one or more fourth-order aberration coefficients) by the first optical correction element 370 pre-XO plane 330. This may result in flaring of one or more persistent geometric aberrations, as shown in image 642A. Image 642B shows a charged particle beam undergoing fourth-order aberration correction (e.g., partial or total attenuation of three fourth-order aberration coefficients), where MP1 350 and MP2 352 may function to remove some second-, third-, and fourth-order geometric aberrations pre-XO surface 330, and MP3 592 (post-XO surface 330) may function to remove remaining fourth-order geometric aberrations that were not fully corrected by MP1 350 and MP2 352. As a result, image 642B shows a substantially symmetric transparent image 642B.

[0058] FIG. 7 is a schematic diagram illustrating an example spectrometer 700 with post-XO surface 330 fourth-order aberration correction, according to some embodiments. The spectrometer of FIG. 7 may use some or all of the components of spectrometer 300 of FIG. 3 or spectrometer 500 of FIG. 5. In some examples, spectrometer 700 may receive a charged particle beam (e.g., electrons) along optical axis 310 (z-axis) from one or more objective / projection optics 703 (e.g., beam guide and shaping optics), which receive the charged particle beam from sample 702. Spectrometer 700 may accept the charged particle beam through an entrance aperture 720 with an aperture diameter 722 similar to MP1 352. In one example, the entrance aperture diameter may range from 0.1 mm to 10 mm. The aperture diameter 722 can, at least in part, affect the dispersion of the x-field rays 704, y-field rays 706, etc. (e.g., the spread of the rays in the x-axis direction versus the spread of the rays in the y-axis direction along the z-axis) as the charged particle beam propagates through the spectrometer 700. The charged particle beam may be elongated (substantially elliptical) depending on the aperture diameter 722. Note that the x, y, and z coordinates represent vertical displacement along the page with the y-coordinate, in-and-out of the page with the x-coordinate, and left-to-right direction with the z-coordinate. For example, while the x-field ray 704 is depicted as traveling along the z-axis in vertical measurements, the vertical measurements represent distances off-page relative to the z-axis (if above the z-axis) and distances on-page relative to the z-axis (if below the z-axis). Additionally, each field ray may represent only a portion of the overall field in a particular dimension. Additionally, the spectrometer 700 may function in one or more modes, such as a parallel motion-resolved electron energy loss mode.

[0059] In some examples, a 5 mm aperture diameter 722 may increase beam divergence to the amount of charged particles reaching the spectrometer 700. For example, a larger aperture diameter 722 may allow more charged particles to enter the spectrometer 700, allowing more information about the sample to be transmitted to a detector (not shown). The charged particle beam is transmitted from the entrance aperture 720 to the first optical corrective element 370 (e.g., MP1 350, prism 390, MP2 352, etc.), where the charged particle beam undergoes one or more operations to attenuate one or more fourth-order aberration coefficients according to the equation x = A40γ4 + A22γ2δ2 + A04δ4; in this equation, A 40 , A 22 , A 04 is a fourth-order aberration coefficient, the angle γ represents the divergence angle of the beam parallel to the xz plane, and δ represents the divergence angle of the ray perpendicular to the xz plane (e.g., divergence in the yz plane). Furthermore, one or more mechanical aberrations can be corrected by the first optical correction element 370 and / or the second optical correction element 590 (e.g., A 31 and A 13For example, the first optical corrective element 370 may include a first multipole element MP1 350 (e.g., a dodecapole, a hexapole, etc.), which may vary one or more dimensions (e.g., x / y) of the charged particle beam. A dodecapole element (12-pole) provides 12 degrees of freedom for varying the charged particle beam in an axial plane (orthogonal to the z-axis) along the optical axis 310. Similar to FIG. 5 , the first optical corrective element 370 may include at least two multipole elements MP1 350 and MP2 352. The first multipole element MP1 350 may generate a decapole field to partially correct one or more of the second-, third-, and fourth-order aberrations by reducing the aberration coefficients toward zero. The second multipole element MP2 352 may generate a dodecapole field to further correct one or more of the second-, third-, and fourth-order aberrations introduced into the charged particle beam by the prism 390. Additionally, at least one of the pre-XO plane 330 multipole elements may correct chromatic aberrations of the charged particle beam. While only two multipole elements are described herein, it should be understood that any number of multipole elements (e.g., 1-20) may be contemplated in a desired configuration (e.g., 16-pole, 12-pole, 8-pole, etc.) to achieve the desired beam shape. For example, starting from the entrance aperture 720, the optimal configuration of elements, from left to right along the Z axis, may be as follows: MP1 350, prism 390, MP2 352, MPA through MPN (where N is the total number of multipole elements before the XO plane 330).

[0060] In some examples, the x-z ray focus 708 may be formed in the x-z dispersion plane along the optical axis 310. A line focus may exist when one coordinate element (e.g., the y-axis component) is focused along the z-axis (e.g., the y-component of the field is approximately equal to 0 mm relative to the point on the z-axis) at a time when another coordinate element is not focused relative to the z-axis (e.g., the x-component of the field is not equal to 0 mm relative to the point on the z-axis), thus forming a line focus of the charged particle beam. The size of the x-z ray focus 708 is due, at least in part, to the size of the aperture diameter 722 (e.g., 5 mm). The x-z ray focus 708 exists because, at that location, the y-field ray 706 is approximately 0 mm relative to the z-axis. This results in a y-z focus (not a line focus) in the y-z dispersion plane (any plane parallel to the y- and z-axes and perpendicular to the x-axis), and the x-z ray focus and y-z foci are approximately co-located along the optical axis 310. The difference between the xz and yz foci can result in an elliptical field of the charged particle beam (either elongated in the x-axis or elongated in the y-axis, depending on which x / y component is larger compared to the other).

[0061] In various examples, the first optical corrective element 370 optical system transmits the conditioned charged particle beam across the XO plane 330. Within the XO plane 330, the X-field rays 704 are approximately single-focus with respect to the Z-axis at a crossover point (e.g., the axial X-field rays intersect the Z-axis at the same Z coordinate). The charged particle beam may be further conditioned by the second optical corrective element by increasing the beam dispersion along the y-z dispersion plane by intentionally not fully attenuating all fourth-order aberration coefficients before the XO plane 330 and / or by creating two foci before the XO plane 330. For example, MP1 350 and MP2 352 may magnify portions of the charged particle beam in the dispersion plane to reduce the final coefficient A of the fourth-order aberration. 04 Without attenuating A 40 and A 22The y-field ray 706 may function to correct two fourth-order aberration coefficients, such as . In this example, y-field ray 706 may have two crossover locations before XO plane 330, as shown. The first location may be a first y-crossover point at first x-z ray focus 708, and the second location may be a second y-crossover point at second x-z ray focus 710. By influencing y-field ray 706 so that second y-crossover point 710 is located to the left of XO plane 330 (while y-crossover point 307 was located to the right of XO plane 330 as shown in FIG. 3), y-field ray 706 may be positioned to provide a sufficiently large (e.g., expanded) y-field dispersion at MP 792. For example, y-field ray 706 may undergo dispersion expansion to widen y-field ray 706 (e.g., lengthen the ray profile in the xy plane so that the beam waist of the overall beam is not circular). A reasonably low current (e.g., 1-20 ampere-turns, more preferably 1-5 amperes) provided by a multipole element (e.g., MP792) reduces high-order aberrations (e.g., shape A 04 <x|δ 4Broadening the y-field rays 706 can be beneficial for tuning because the y-field rays 706 are used to more easily correct for aberrations (e.g., aberrations > 100°) after the XO plane 330. A smaller broadening of the y-field rays 706 (caused by shifting the y-crossover point, e.g., by moving the x-z ray focus 710 closer to the XO plane 330) may require a larger current through the multipole elements to achieve the same result. The y-z ray focus 712 in the y-z dispersion plane (the x-field rays 704 are approximately point foci along the z-axis and remain nearly constant up to the image plane 340) results in more than one point along the optical axis 310, which results in a broadened y-dimension 714 of the y-field rays 706 (e.g., an increased dispersion angle). At the location of yz-line focus 712, there is an xz-focus (approximately a point focus) along the xz-dispersion plane (any plane parallel to both the x-axis and z-axis), so that the dispersion distance in the x-plane is approximately 0 mm relative to the z-axis (e.g., optical axis 310). Ray profile 715 is an exaggerated three-dimensional representation of the x-field ray 704 crossover dispersion plane (yz-plane) of yz-line focus 712. For clarity, ray profile 715 is exaggerated as a "y-height" line on the z-axis at yz-line focus 712, essentially at 0 mm in the x-dimension. Due to the large aperture diameter 722 (e.g., 5 mm), yz-line focus 712 spreads the spectral energy across multiple points (along the y-axis) on the detector, reducing potential damage to the detector.

[0062] In some cases, one or more multipole elements (e.g., MP792) can correct fourth-order aberrations (e.g., shape A 04 <x|δ 4This may allow partial to complete correction (e.g., between 5% and 100% attenuation) of fourth-order aberrations (e.g., aberrations > 100%). For example, one or more multipole elements may generate a linear superposition of decapole, octapole, and hexapole fields (similar to those in FIG. 8) to further condition the charged particle beam. An extended y-dimension 714, such as the yz-ray focus 712, applies a relatively mild electromagnetic field (or ampere-turns, in the case of magnetic multipoles) to partially or completely correct fourth-order aberrations that the XO plane 330 multipole elements intentionally do not fully correct. The charged particle beam then propagates to the imaging plane 340, where a detector may record an image at a specific resolution (e.g., depending on the spectrometer user).

[0063] In some examples, using two focal points in front of the XO plane 330 results in the same energy resolution (e.g., image resolution at the detector) for different aperture diameters 722. For example, a 2.5 mm aperture diameter 722 may provide the same energy resolution as a 5 mm aperture diameter 722. The first and second energy resolutions are both 0.01 mV / pixel for both the 2.5 mm and 5 mm aperture diameters 722. In other words, the transparency of the spectrometer 700 is improved, decoupling the energy resolution at the detector, at least in part, from the size of the aperture diameter 720 for aperture diameters between 2.0 mm and 10 mm. Furthermore, the signal-to-noise ratio may be substantially improved, as the signal-to-noise ratio may be approximately the same for aperture diameters between 5 mm and 2.5 mm.

[0064] FIG. 8 illustrates a set of images 800 of various multipole fields generated by multipole elements after the XO plane 330, according to some embodiments. The set of images 800 illustrated in FIG. 8 may be generated by one or more pre- or post-XO plane 330 multipole elements of the analyzer of FIG. 7 . In some examples, depending on the shape of the beam profile after the XO plane 330, various multipole fields may be required to attenuate fourth-order aberrations. The post-XO plane 330 multipole elements can apply multipole fields 810 (hexapole), 820 (octapole), or 830 (decapole) as a linear superposition or alone to attenuate fourth-order aberrations. Furthermore, it is contemplated that any suitable multipole field can be applied to achieve a desired beam profile. Note that while the multipole fields are illustrated relative to the x-axis dispersion, these axes can be interchanged depending on the desired direction of dispersion of the beam after the XO plane 330.

[0065] FIG. 9 illustrates a set of imaging fields 900 generated by multipole elements in the xo-plane 330 according to some embodiments. The set of imaging fields 900 in FIG. 9 may be detected by one or more of the xo-plane 330 detectors in the spectrometer of FIG. 7 . For example, the imaging fields 900 depict the xy plane in the imaging plane 340 after MP1 350 and MP2 352 perform at least one partial geometric aberration correction 910 (e.g., attenuating one or more orders of fourth-order coefficients) and chromatic aberration correction. The bottom axis may indicate dispersion voltage (e.g., -0.4 to 0.4 volts), and the vertical axis indicates various charged particle beam dispersions of the y-field rays (e.g., around 1,000 μm). In some examples, the partial geometric aberration correction 910 may result in an energy dispersion (90 mV), which may increase or decrease depending on the placement of the correction optics. In the example shown in Figure 9, a dispersion (resolution) of 90 mV is shown with the decapole fields of MP1 350 and MP2 352 applied to the charged particle beam. Shown on the right is fourth-order geometric aberration correction 920, which is performed in the XO plane 330 by applying one or more of the multipole fields (810, 820, 830) to the charged particle beam as in Figure 8. As a result, an entire order of magnitude in energy resolution (e.g., 9 mV right and 9 mV left) can be achieved by applying multipole fields to the charged particle beam 330 in the XO plane.

[0066] 10 is a flow diagram of an exemplary process for correcting fourth-order aberrations in a spectrometer, according to some embodiments. In block 1005, a spectrometer (such as spectrometer 700) receives a charged particle beam along an axis (optical axis) from a TEM. The process may be implemented with high-resolution electron energy loss spectroscopy (HR-EELS), electron energy loss spectroscopy (EELS), momentum-resolved electron energy loss spectroscopy (q-EELS), plasmon spectroscopy, phonon spectroscopy, energy-filtered electron transmission electron microscope (EFTEM), or the like. The charged particle beam may contain information (e.g., energy loss, etc.) related to the sample imaged in the TEM.

[0067] In block 1010, a first optical correction element may apply a first decapole field to the charged particle beam. For example, the first optical correction element may include a first multipole element (such as a dodecapole element), a 90° prism positioned subsequent to the first multipole element for changing the axis of the charged particle beam, and a second multipole element (e.g., a dodecapole element). In this example, the first multipole element can apply a decapole field to the charged particle beam before it enters the prism. The first decapole field can function to partially attenuate one or more orders of geometric aberrations associated with the charged particle beam. The second multipole element can function to further attenuate one or more orders of geometric aberrations (e.g., partially attenuate one or more orders of geometric aberrations) and chromatic aberrations associated with the charged particle beam before on-axis crossover.

[0068] In block 1015, a line focus (x-z line focus) may be formed after the second multipole element and before the crossover. Additionally, a y-z focus may occur coplanar with the x-z line focus in the dispersion plane along the axis (optical axis). The enhanced dispersion may be due, at least in part, to an increased aperture diameter (e.g., 5 mm). The y-z focus may be, at least in part, unqualified for attenuating fourth-order aberrations after the crossover.

[0069] In block 1015, a multipole field (decapole field) may be applied to the charged particle beam after crossing over the second optical corrective element. For example, the second optical corrective element may include a third multipole element (e.g., a dodecapole element) that applies a decapole field to further attenuate fourth-order aberrations (e.g., attenuate at least three fourth-order aberration coefficients). The combination of the first, second, and third multipole elements that apply decapole fields both before and after crossover allows the spectrometer to attenuate fourth-order aberrations without compromising the energy resolution of the image.

[0070] FIG. 11 is a block diagram of a controller for an electron microscope system according to certain aspects of the present disclosure. An example of an electron microscope system may include the microscope system 100 of FIG. 1. As shown, a controller 1101 includes a processor 1102 communicatively coupled to a memory 1104. The processor 1102 may include one processing unit or multiple processing units. Non-limiting examples of the processor 1102 include a field programmable gate array (FPGA), an application-specific integrated circuit (ASIC), a microprocessor, or a combination thereof. The processor 1102 can execute instructions 1110 stored in the memory 1104 to perform operations such as those of the process 1000 of FIG. 10. In some examples, the instructions 1110 may include processor-specific instructions generated by an editor or interpreter from code written in a suitable computer programming language (e.g., C, C++, C#, Python, or Java).

[0071] The memory 1104 may include one or more memory devices. The memory 1104 is non-volatile and may include any type of memory device that retains stored information even when power is removed. Non-limiting examples of the memory 1104 include electrically erasable programmable read-only memory (EEPROM), flash memory, or other types of non-volatile memory. At least a portion of the memory 1104 may include a non-transitory computer-readable medium from which the computer 1102 can read instructions 1110 via a bus 1106. The bus 1106 may be a communication and / or power bus that allows the processor 1102 to communicate with the memory 1104. Non-transitory computer-readable media include electronic, optical, magnetic, or other storage devices that can provide instructions 1110 or other program code to the processor 1102. Examples of non-transitory computer-readable media include magnetic disks, memory chips, RAM, ASICs, or other media from which a computer processor can read instructions 1110.

[0072] The memory 1104 may further include information related to parameters 1112 (e.g., calibration, slit positioning, tuning, etc.), polar element controls 1114 (e.g., specific voltages applied to multipole elements), imaging 1116 (e.g., detector control, image analysis, etc.), and aberration managers 1118 (e.g., controlling the integrated function of the multipole element combination). The controller 1101 may receive information related to operational parameters from a microscope, such as a TEM. At least some of the information related to parameters 1112 may be pre-stored and may be associated with color defocus correction for defocus caused by changes in magnification. The parameters 1112 may include operational parameters related to the electron microscope system, such as the desired energy / primary energy of the electron beam, the energy spread of the energy loss spectrum, calibration using a knife-edge slit, etc. The controller may calculate the amount of defocus based on the parameters 1112 and the polar element controls 1114. In some examples, some of the parameters 1112 may be compared to predetermined thresholds (e.g., known multipole element placement, known field strength, etc.). The comparison can determine the magnitude of the field intensity that each multipole element applies based on instructions from the aberration manager 1118. The aberration manager 1118 can be used to adjust the operation of one or more optical components within the energy spectrometer.

[0073] Various embodiments have been described in the preceding description. For purposes of explanation, specific configurations and details have been set forth to provide a thorough understanding of the embodiments. However, it will be apparent to those skilled in the art that embodiments may be practiced without the specific details. Furthermore, well-known features may be omitted or simplified so as not to obscure the described embodiments. While the exemplary embodiments described herein focus on electron microscope systems, and in particular TEM / EELS systems, these are intended as non-limiting illustrative embodiments. Embodiments of the present disclosure are not limited to such materials, but rather are intended to address charged particle beam systems capable of applying a wide range of particles to imaging, microanalyzing, and / or processing materials at the atomic scale. Such particles may include, but are not limited to, electrons, ions, or photons in TEM systems, SEM systems, STEM systems, ion beam systems, and / or particle accelerator systems.

[0074] Some embodiments of the present disclosure include a system including one or more data processors and / or logic circuitry. In some embodiments, the system includes a non-transitory computer-readable storage medium including instructions that, when executed on one or more data processors, cause the one or more data processors to perform some or all of one or more methods and / or some or all of one or more processes or workflows disclosed herein. Some embodiments of the present disclosure include a computer program product tangibly embodied in a non-transitory machine-readable storage medium, including instructions configured to cause one or more data processors to perform some or all of one or more methods and / or some or all of one or more processes disclosed herein, including, for example, process 1000 of FIG. 10 .

[0075] The terms and expressions which have been employed are used as terms of description and not as terms of limitation, and in using such terms and expressions there is no intention to exclude any equivalents of the features shown and described or portions thereof, but it is understood that various modifications are possible within the scope of the claims. Thus, while the present disclosure includes specific embodiments and optional features, it should be understood that modifications and variations of the concepts disclosed herein can be made by those skilled in the art, and that such modifications and variations are considered to be within the scope of the appended claims.

[0076] When a term is used without an explicit definition, it should be understood that the ordinary meaning of the word is intended unless the term has a special and / or specific meaning in the field of charged particle microscope systems or other related fields. The terms “about,” “same,” “roughly,” “similar,” or “substantially” are used to indicate deviations from a stated characteristic or value, within which deviations have little or no effect on the corresponding function, characteristic, or attribute of the described structure. In illustrated examples where a dimensional parameter is described as “substantially equal” or “approximating” another dimensional parameter, the terms “substantially” or “approximate” are intended to reflect that the two dimensions being compared may not be equal within tolerance limits, such as manufacturing tolerances. Similarly, when a geometric parameter such as alignment or angular orientation is described as “about” perpendicular, “substantially” perpendicular, or “substantially” parallel, “roughly” equal, or “roughly” the same, the terms “about” or “substantially” as well as “roughly” are intended to reflect that the alignment or angular orientation may differ from the strictly stated condition (e.g., not exactly perpendicular) within tolerance limits. With respect to dimensional values ​​such as diameter, length, width, etc., the term "about" can be understood to describe a deviation of up to ±10% from the stated value. For example, a dimension of "about 10 mm" can describe a dimension of 9 mm to 11 mm. In this disclosure, a "subrange" refers to a range of values ​​between two stated ranges and / or a range of values ​​that includes either of the two stated degrees.

[0077] This specification provides exemplary embodiments and is not intended to limit the scope, applicability, or configuration of the present disclosure. Rather, the description that follows of the exemplary embodiments will provide those skilled in the art with an enabling description for implementing various embodiments. It should be understood that various changes can be made in the function and arrangement of elements without departing from the spirit and scope as set forth in the appended claims.

[0078] Specific details are given herein to provide a thorough understanding of the embodiments. However, it will be understood that the embodiments may be practiced without these specific details. For example, specific system components, systems, processes, and other elements of the disclosure may be shown in schematic form or omitted from illustrations so as not to obscure the embodiments in unnecessary detail. In other instances, well-known circuits, processes, components, structures, and / or techniques may be shown without unnecessary detail.

Claims

1. 1. A method for simultaneously widening a dispersive surface and correcting aberrations in a charged particle spectrometer, said method comprising: the charged particle spectrometer receiving a charged particle beam along an axis; applying a first decapole field to the charged particle beam with a first optical correction element of the charged particle spectrometer, the first optical correction element being located before the on-axis crossover, the first decapole field partially attenuating fourth-order aberrations associated with the charged particle beam; applying a second decapole field to the charged particle beam by a second optical correction element of the charged particle spectrometer, the second optical correction element having a position after the crossover, a dispersion plane of the charged particle beam being present after the crossover, dispersion of the charged particle beam being present at the position of the second optical correction element, and the second decapole field further attenuating the fourth-order aberration.

2. receiving the charged particle beam along the axis; 2. The method of claim 1, further comprising receiving the charged particle beam through an entrance aperture located in front of the first optical correction element, wherein an opening diameter of the entrance aperture is in a first range of 0.1 mm to 10 mm, and wherein a line focus of the charged particle beam comprises at least one of: (i) an x-z ​​line focus along an x-z ​​dispersion plane at a focus position before the crossover, or (ii) a y-z line focus in a y-z dispersion plane along the axis at a second focus position after the crossover.

3. 3. The method of claim 2, further comprising measuring the charged particle beam with a detector located after the second optical correction element to generate an image, wherein a resolution of the image is in the range of 0.01 mV / pixel to 1000 mV / pixel.

4. 2. The method of claim 1, wherein partially attenuating the fourth-order aberrations with the first optical correction element comprises attenuating at least two fourth-order aberration coefficients, and further attenuating the fourth-order aberrations with the second optical correction element comprises attenuating at least one additional fourth-order aberration coefficient, wherein the at least two fourth-order aberration coefficients and the at least one additional fourth-order aberration coefficient are each different coefficients of the fourth-order aberrations.

5. The method of claim 1 , wherein each one of the first optical correction element and the second optical correction element includes one or more corresponding dodecapole elements.

6. 10. The method of claim 1, wherein the second decapole field is applied by using a first range of ampere rotations, the first range of ampere rotations being 1 to 20 ampere rotations.

7. The at least two fourth-order aberration coefficients are A 22 , A 40 and the at least one additional fourth-order aberration coefficient is A 04 The method according to claim 4, wherein

8. Further partially attenuating the fourth-order aberrations with the first optical correction element includes partially attenuating geometric aberrations associated with the charged particle beam, and further attenuating the fourth-order aberrations with the second optical correction element includes attenuating geometric aberrations associated with the charged particle beam. 0n <x|δ n Attenuating geometric aberrations of 0n 2. The method of claim 1, wherein x is an aberration coefficient, x is the imaging axis, n is the characteristic order of the aberration, and δ is the dispersion angle associated with the charged particle beam relative to a dispersion plane.

9. 2. The method of claim 1, wherein the first optical correction element includes a first multipole element and a second multipole element, applying the first decapole field to the charged particle beam includes exciting the first multipole element and the second multipole element, and attenuating geometric aberrations up to fourth order and chromatic aberrations of first order or higher are partially attenuated in response to exciting the first multipole element and the second multipole element.

10. 2. The method of claim 1, wherein the second optical correction element includes a third multipole element, and applying the second decapole field to the charged particle beam includes exciting the third multipole element, and in response to exciting the third multipole element, geometric aberrations up to fourth order are attenuated.

11. 1. A non-transitory computer-readable storage medium containing instructions executable by one or more processors of a charged particle spectrometer, the instructions comprising: applying a first decapole field to the charged particle beam by a first optical correction element of the charged particle spectrometer, the charged particle beam being received by the charged particle spectrometer along an axis, the first optical correction element being located before a crossover on the axis, the first decapole field partially attenuating fourth-order aberrations associated with the charged particle beam; applying a second decapole field to the charged particle beam by a second optical correction element of the charged particle spectrometer, the second optical correction element being located after the crossover, a dispersion plane of the charged particle beam being after the crossover, dispersion of the charged particle beam being in a dispersion plane at the location of the second optical correction element, and the second decapole field further attenuating the fourth-order aberrations.

12. The operation is 12. The non-transitory computer-readable storage medium of claim 11, further comprising applying one or both of a hexapole field and an octopole field to the charged particle beam.

13. performing the operations 12. The non-transitory computer-readable storage medium of claim 11, further comprising: increasing a first dispersion along a yz dispersion plane of the charged particle beam after a crossover relative to the axis, while maintaining a second dispersion along an xz dispersion plane of the charged particle beam at a constant size relative to the axis.

14. 12. The non-transitory computer-readable storage medium of claim 11, wherein the charged particle spectrometer includes a parallel momentum resolved electron energy loss mode, and wherein the attenuation of fourth order aberrations reduces image distortion along the axis by an order of magnitude.

15. 1. A charged particle spectrometer, comprising: a first optical correction element; and a second optical correction element; and an entrance opening configured to receive the charged particle beam; a controller, causing the first optical corrective element to apply a first decapole field to the charged particle beam, the first optical corrective element being positioned before an on-axis crossover, the first decapole field partially attenuating fourth-order aberrations associated with the charged particle beam; and a controller configured to cause the second optical correction element to apply a second decapole field to the charged particle beam, the second optical correction element having a position after the crossover such that dispersion of the charged particle beam is in a dispersion plane at the position of the second optical correction element, and the second decapole field further attenuates the fourth-order aberrations.

16. 16. The charged particle spectrometer of claim 15, wherein the entrance aperture has an aperture diameter, and aperture diameters in the range of 2 mm to 5 mm produce equivalent energy resolution.

17. 16. The charged particle spectrometer of claim 15, wherein the entrance aperture has an aperture diameter, and aperture diameters in the range of 2 mm to 5 mm produce equal signal-to-noise ratios.

18. 16. The charged particle spectrometer of claim 15, wherein the charged particle spectrometer includes a slit or knife edge, the first optical correction element is located in front of the slit or knife edge, and the second optical correction element is located behind the slit or knife edge.

19. The controller:

16. The charged particle spectrometer of claim 15, wherein the first optical correction element applies a third decapole field to the charged particle beam, wherein applying the third decapole field to the charged particle beam at least partially modifies a y-field dimension of the charged particle beam to have at least two foci before the crossover, thereby widening the dispersion of the charged particle beam.

20. 16. The charged particle spectrometer of claim 15, wherein two fourth-order coefficients are attenuated on the axis before the crossover and one fourth-order coefficient is attenuated on the axis after the crossover.

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