Automatic correction of energy dependent defocus in particle beam system due to configuration change

Abstract

To provide a method for automatically correcting energy dependent focus in electron beam systems due to a configuration change.SOLUTION: A method implemented by an electron microscope system can involve receiving an electron beam from a transmission electron microscope. The transmission electron microscope can include an imaging system arranged after a sample plane. The electron beam can include an electron energy loss spectrum due to an interaction with a sample. The method can further involve focusing, by optical components of an energy spectrometer, the electron energy loss spectrum on a detector. Additionally, the method can involve determining information about a change in magnification of the imaging system. The method can involve adjusting, based on the change to the magnification, an operation of one or more optical components such that at least a portion of the electron energy loss spectrum is refocused onto the detector.SELECTED DRAWING: Figure 10

Description

[Technical Field]

[0001] The present disclosure is directed to electron microscope system components, systems, and methods. More particularly, the present disclosure describes automatic refocusing of an electron beam based on detected configuration changes in an electron microscope system. [Background technology]

[0002] Transmission electron microscopy Charged particle microscopy, such as electron microscopy (TEM), can use a range of detection methods to obtain information about a sample. TEM can be used to image various types of samples, such as the interior of a cell, the structure of protein molecules, and the organization of molecules within viruses and cytoskeletal filaments. TEM can use a variety of techniques 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 can be dispersed into an energy spectrum that is then imaged. Unlike scanning electron microscopes (SEMs), which only examine surface topography, TEM devices utilize an electron beam to pass completely through a sample and examine the sample's internal topography. Due to inherent laws of nature, electrons in an electron beam scatter after interacting with the sample. As a result, many of the electrons experience energy loss, resulting in a focus shift of the image plane, which necessitates adjustments to the lens optics to obtain a focused image. Therefore, the degree of energy loss can depend on the scattered electrons, and solutions to obtain a focused image may be required for TEM devices that change their configuration. Summary of the Invention

[0003] Techniques described herein are directed to systems, detector devices, and methods for automatically correcting energy-dependent defocus in an electron beam due to configuration changes. One embodiment relates to a method implemented by an electron microscope system. The method may include receiving an electron beam from a transmission electron microscope. The transmission electron microscope may include an imaging system positioned after a sample plane. The electron beam may include an energy loss spectrum due to interaction with the sample. The method may further include focusing the electron energy loss spectrum onto a detector by optical components of an energy spectrometer. Additionally, the method may include determining information related to a change in magnification of the imaging system. The method may include adjusting operation of one or more optical components based on the change in magnification such that at least a portion of the electron energy loss spectrum is refocused onto the detector.

[0004] Another embodiment is directed to one or more computer-readable storage media. The one or more computer-readable storage media may store instructions that, when executed by one or more processors of the energy spectrometer, can cause the energy spectrometer to perform operations. The operations may include receiving an electron beam from a transmission electron microscope. The transmission electron microscope may include an imaging system disposed after a sample plane. The electron beam may include an energy loss spectrum resulting from interaction with the sample. The operations may further include focusing the electron energy loss spectrum onto a detector by optical components of the energy spectrometer. Furthermore, the operations may include determining information related to a change to a magnification of the imaging system. The operations may include adjusting the operation of one or more of the optical components based on the change to the magnification such that at least a portion of the electron energy loss spectrum is refocused onto the detector.

[0005] Yet another embodiment is directed to an apparatus. The apparatus may include an energy spectrometer coupled to a transmission electron microscope to acquire one or more energy loss spectra. The transmission electron microscope may include an imaging system disposed after the sample plane. The energy spectrometer may include optical components. The optical components may focus the energy loss spectra onto a detector. The energy spectrometer may further include a detector disposed conjugate to the spectral plane. Additionally, the energy spectrometer may include a controller. The controller may determine a change to the magnification of the imaging system. The controller may also adjust operation of one or more of the optical components based on the change to the magnification such that at least a portion of the electron energy loss spectrum is refocused onto the detector. [Brief explanation of the drawings]

[0006] The foregoing aspects and many of the attendant advantages of the present disclosure will become more readily appreciated as the same become better understood by reference to the following detailed description, when taken in conjunction with the accompanying drawings, in which: [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 an electron microscope system, according to some embodiments. [Figure 3] FIG. 1 is a schematic diagram illustrating an example of energy-dependent defocus in an electron microscope system, according to some embodiments. [Figure 4] 1 is a set of images of various beam spectra at different beam energies, according to some embodiments. [Figure 5] FIG. 1 is a schematic diagram illustrating an electron microscope system with energy-dependent defocus correction, according to some embodiments. [Figure 6] 10 is a set of images of various beam spectra for different primary beam energies after correction for energy dependent defocus, according to some embodiments. [Figure 7]FIG. 1 is a flow diagram of an exemplary process for compensating for offset shifts across an energy loss spectrum, according to some embodiments. [Figure 8] FIG. 1 is an iterative flowchart diagram of an exemplary process for operating an electron microscope system, according to some embodiments. [Figure 9] 1 is an exemplary graph of crossover shift across an energy loss spectrum according to some embodiments. [Figure 10] FIG. 1 is a flow diagram of an exemplary process for operating a transmission electron microscope using an electron microscope system, according to some embodiments. [Figure 11] FIG. 1 is a block diagram of a controller of an electron microscope system in accordance with certain aspects of the present disclosure.

[0007] In the drawings, like reference numbers refer to like parts throughout the various views unless otherwise specified. Not every instance of an element is necessarily labeled, to reduce clutter in the drawings where necessary. The drawings are not necessarily to scale, emphasis instead being placed upon illustrating the principles being described. DETAILED DESCRIPTION OF THE INVENTION

[0008] Embodiments of the present invention are described below in the context of an electron microscope system including an electron microscope for acquiring an energy spectrum of a sample, where the electron microscope system can automatically make adjustments to correct for energy-dependent defocus that may occur due to configuration changes. For example, depending on operating conditions and configuration changes, the excitation (electrical or magnetic) of at least one optical component in the energy spectrometer can be adjusted to address the energy-dependent defocus. The configuration changes may include changing the magnification setting of a portion of the electron microscope imaging system. However, it should be understood that the methods described herein are generally applicable to a wide range of different methods and apparatus, including both scanning probe systems and parallel illumination systems, and are not limited to a particular apparatus type, beam type, object type, length scale, or scanning trajectory.

[0009] 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. Additionally, the term "includes" means "comprises." Furthermore, the term "coupled" does not exclude the presence of intermediate elements between the coupled items.

[0010] 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.

[0011] Although some operations of the disclosed methods are described in a particular sequential order for convenient presentation, it should be understood that this description style 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. Additionally, the description may use terms such as "produce" and "provide" to describe the disclosed methods. These terms are high-level abstractions of actual operations that take place. The actual operations corresponding to these terms will vary depending on the particular implementation and are readily discernible by one of ordinary skill in the art.

[0012] In some examples, values, procedures, or devices are referred to as "lowest," "best," "minimum," 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, smaller, or otherwise preferred than other selections.

[0013] Electron energy loss spectroscopy (EELS) is a detection method typically incorporated into transmission electron microscopes (TEMs) to analyze the composition or other chemical properties of a sample. EELS is traditionally performed using an energy spectrometer attached to the end of the TEM column. Such an energy spectrometer may be referred to as a post-column filter (PCF). In some alternative examples, the spectrometer may be incorporated into the TEM's imaging system. Such an alternative spectrometer may be referred to as an in-column filter (ICF). The methods of the present disclosure can be applied to PCFs as well as ICFs. An energy spectrometer may be used to obtain an energy spectrum of transmission data. For example, a sample (e.g., a substrate) in a TEM is probed with an electron beam of a desired energy. A portion of the electrons exiting the sample may have reduced energy, thus characterizing various properties of the sample (e.g., nanostructure, topography, etc.). The energy spectrometer can then be used to view the energy distribution of the electron beam after passing through the sample and look for peaks 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 down to the millielectronvolt level. However, imperfections in the transmission electron microscope can blur the data, reducing or even eliminating the desired resolution of sample characteristics. The loss of resolution can result from a variety of factors, including mechanical and electrical instabilities (vibrations), the energy spread of the incident beam due to the inherent energy spread of the electron source, the finite resolution of the detector due to the finite pixel size of the detector, and chromatic defocusing of the electron beam as it propagates through parts of the transmission electron microscope and energy spectrometer (e.g., lenses, multipoles, etc.). The level of such defocusing depends on the electron energy. However, because the chromatic aberration of each lens, multipole, etc., changes with its excitation, it also changes depending on microscope settings, such as changing (increasing or decreasing) the magnification settings of the microscope, energy spectrometer, or both components.As higher resolution energy spectra are desired, chromatic defocus may become a greater problem, potentially requiring frequent adjustments of the spectrometer, to the point where such adjustments are needed as frequently as a user changes the magnification of the microscope system or the magnification of the energy spectrometer.

[0014] 1 is an exemplary diagram of a portion of a microscope system 100 currently known in the art. The microscope system 100 includes a portion of a transmission electron microscope 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 at the detector 122 due to operating parameters (such as magnification setting adjustments) of the TEM 102 and the energy spectrometer 104.

[0015] 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 also depend on the operating parameters of the microscope 102. The operating parameters may include operating parameters of the imaging system 108, such as adjusting the magnification setting of the microscope 102 relative to the magnification from the sample 106 toward the crossover point 107 at the end of the microscope 102. This magnification may determine how much the cone of the electron beam 124 exiting the sample 106 is compressed toward the energy spectrometer 104, so this freedom to change magnification is desirable for users of the microscope system 100. More compression may result in a larger portion of the cone of the electron beam 124 being accepted by the entrance aperture of the spectrometer. The operating parameters may determine the excitation settings of optical components, such as lenses, multipole, and quadrupole elements, of the energy spectrometer 104. The operating parameters may 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 the interaction of the electrons with the sample, the electron beam emerging from the sample 106 may contain some energy loss. However, measuring the loss over a range of energies with the energy spectrometer 104 may be useful for phase measurements, so the energy loss may be desirable. However, the energy loss may also affect the crossover position, e.g., the focus, of the electron beam 124 at the microscope 102 and the energy spectrometer 104. This change in the crossover may result in a defocusing of the electron beam spectrum at the detector 122.

[0016] For example, an electron beam propagating through the microscope 102 without any energy loss may have a crossover position as shown. However, an electron beam with some energy loss may propagate through the microscope 102 and the energy spectrometer 104 with a different crossover position, with an offset ΔZ as shown.

[0017] The energy spectrometer 104 may include a lens 110 and a dispersive element 112. The dispersive element 112 may 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 may be energized to disperse, or "fan out," the electron beam 124 into a band of different energies that interact with it. The multiple optical components 120 may focus and expand this band onto the detector 122. Typically, this band of different energies may be smaller than (e.g., may not encompass) the entire range of EELS spectra that an operator may be interested in and wish to record. Therefore, the bias tube 113 may be electrically biased to add various amounts of energy (e.g., up to 2 keV) to the electron beam 124. The added energy can be used to shift the band recorded by detector 122 (such a shift in energy band 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 may have the disadvantage of being subject to relatively long settling times and / or magnetic hysteresis). Due to their electrostatic nature, liner tubes can establish a shift from one energy band to another in less than a millisecond, and thus can record multiple energy bands nearly simultaneously (e.g., as described in U.S. Pat. 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.

[0018] The energy spectrometer 104 includes optical components, such as multipoles, that may be 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) may be controlled to correct for defocus based on the offset ΔZ. Various parameters, such as magnification and chromatic aberration constants, may be determined for the image detected at the detector 122. Using these parameters, the operation of the optical components may be adjusted to correct for defocus based on the offset ΔZ. Additionally, valid configurations of parameters may be tabulated for future use when a particular configuration is commonly used or when a search for a particular configuration may be necessary.

[0019] 2 is a schematic diagram of an electron microscope system (EMS) 200, according to some embodiments. The EMS 200 may include a TEM 202, in some examples, and may include an energy spectrometer 204. The energy spectrometer 204 may be used, for example, to acquire an EEL spectrum. The EMS 200 may include optical components to reduce or eliminate defocusing issues that occur during acquisition of the spectrum. 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.

[0020] 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 an electron beam that propagates along the optical axis of the TEM 202 and interacts with the sample 206. The illumination system 230 may include multiple electron optical components for conditioning the electron beam for delivery to the sample 206. Conditioning the electron beam may include collimation, astigmatism correction, and focusing of the electron beam onto the sample plane. The projection system 208 may include various electrostatic / magnetic lenses, deflectors, correctors (e.g., astigmatism adjusters), etc., that may be used to focus the electron beam emerging from the sample 206 onto one of the various detectors 232. The projection system 208 may be configured to focus an image of the sample 206 onto the detector 232 at a particular (adjustable) magnification, which is commonly referred to as the “imaging mode” of the projection system. Alternatively, the projection system 208 may be configured to focus an image (or “diffraction pattern”) of the angular distribution of emerging electrons onto the detector 232 at a particular (adjustable) magnification. Such a diffraction pattern is formed at the back focal plane of a first magnifying lens (“objective lens,” not shown in FIG. 2 ). This alternative mode of the projection system is commonly referred to as the “diffraction mode,” and the magnification in this alternative mode is commonly referred to as the “camera length.” However, for simplicity, when this disclosure refers to an “image” or “focus,” etc., this refers to both the “imaging mode” and the “diffraction mode” of the imaging system. Similarly, when this disclosure refers to a “magnification setting,” etc., this refers to both the “magnification setting” and the “camera length setting” of the imaging system.

[0021] In some examples, the projection system 208 focuses and conditions the electron beam for delivery to the energy spectrometer 204. The various detectors 232 can be individually moved in and out of the optical path to provide different detection schemes for the TEM 202. The various detectors 232 can include an imaging screen, a TEM camera, and a STEM camera.

[0022] The energy spectrometer 204 may include a dispersive element 212 (with a bias tube 214), an optical component 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 excluded from FIG. 2. As noted, an additional component, namely, the optical component 234, is included in the energy spectrometer 204 to correct for focal gradients in the electron energy loss spectrum across the detector. The optical component 234 may be a single element, such as a magnetic hexapole. Alternatively, the optical component 234 may comprise multiple multipole elements (quadrupoles, hexapoles, octopoles, etc.), which may be electric or magnetic in nature of their operation. Also, apart from spectral refocusing, the optical component 234 may perform multiple alternative functions, simultaneously or non-simultaneously, such as correcting image distortion or correcting spectral distortion. 2, the optical component 234 is shown downstream of the dispersive element 212, but this is not the only location for placing the optical component 234. In general, some elements of the optical component 234 may be placed upstream of the dispersive element 212 (but downstream of the sample 206), and some elements of the optical component 234 may be placed downstream of the dispersive element 212, either within or after the plurality of optical systems 220.

[0023] The controller 226 may include one or more processing cores and a memory that stores executable code. The controller 226 may also provide operating voltages to some components of the EMS 200 or may be coupled to a voltage source (not shown) that can provide 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, or the optical components 234. The controller 226 may also control the operation of and / or receive data from the detector 222. Generally, the controller 226 may set operating parameters of the EMS 200 and adjust the electrical bias of the optical components 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.

[0024] The optical component 234 may be formed from a multipole element including two or more conductive elements. In some examples, the optical component 234 may be 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, magnetic, or a combination thereof, 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.

[0025] During operation, an electron beam generated by the light source 228 at a primary energy may be projected toward the sample 206, where it interacts with the sample 206. The interaction may cause some of the electrons to lose energy by an amount related to various material properties of the sample 206. The electron beam emerging from the sample 206 may then include 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 focal point, e.g., crossover position, along the remaining optical path, including the energy spectrometer 204 and the TEM 202. In some examples, operation of any component capable of steering the electron beam may subsequently result in defocusing within the spectral plane or a focus gradient across the spectral plane. In this example, the optical component 234 may be excited based on current operating parameters to refocus the electron beam. In various examples, exciting the optical component 234 may align the crossover position with the spectral plane and, therefore, the detector 222.

[0026] FIG. 3 is a schematic diagram illustrating an example of energy-dependent defocusing in an electron microscope system 300, according to some embodiments. The electron microscope system 300 can incorporate some or all of the components (e.g., electron microscope system) of the EMS 200 of FIG. 2 . As an example, an electron beam 229 can interrogate a sample 206 along the optical axis of a transmission electron microscope 202 (e.g., a TEM 202). The electron beam 229 interacts with the sample 206, causing electrons in the electron beam 229 to acquire various attributes, such as energy loss resulting in scattering (e.g., inelasticity, etc.) substantially along the optical axis. In some examples, the electron beam 229 scattered by the sample 206 passes through an objective lens 332, which can result in chromatic focusing (e.g., chromatic aberration) for charged particles with various energies.

[0027] In some examples, the electron trajectory shift may depend on the energy of the electrons in the electron beam 229 and may further depend on the microscope's operating parameters, such as magnification. For example, the operating parameters may include adjusting the magnification setting of the magnification element 333 from the sample 206 (e.g., adjusting the amount of magnification of the electron beam). The magnification element 333 may include any number of intermediate lenses that can assist in the magnification operation to obtain an image. In one example, the magnification may determine the degree to which the cone of the electron beam 229 exiting the sample 206 is compressed toward the energy spectrometer 204. More compression may result in a larger portion of the electron beam cone being accepted by the transmission electron microscope aperture 317, thus increasing the signal and thereby increasing accuracy. On the other hand, if only a specific portion of the cone requires extraction by the energy spectrometer, less compression may be required. However, in some examples, the magnification element 333 may propagate, and in some cases magnify, the chromatic defocus 323, resulting in a crossover position difference ΔZ 315.

[0028] In one example, the crossover position difference ΔZ 315 may be defined as the difference between the first crossover position 310 and the second crossover position 312 or the third crossover position 314. While crossover positions 310-314 are shown, it should be understood that any number of crossover positions may exist depending on the charged particle energies (e.g., trajectories). Additionally, the crossover position difference ΔZ 315 may depend, at least in part, on the operating parameters of the transmission electron microscope 202 and the energy loss shifts of various charged particles within the electron beam 229. For example, as described above, the chromatic defocus 323 introduced by the objective lens 332 may be magnified by the magnifying element 333, resulting in a characteristic chromatic aberration across the crossover position difference ΔZ 315. In some examples, increasing the magnification of the magnifying element 333 by controlling the distance between the intermediate lenses may increase the magnitude of the crossover position difference ΔZ 315. In another example, decreasing the magnification of the magnifying element 333 by controlling the distance between the intermediate lenses may decrease the magnitude of the crossover position difference ΔZ 315. The magnitude of the change in the crossover position difference ΔZ 315 may further depend on the specific energy of the charged particles propagating along the optical axis.

[0029] The electron beam 229 emerging from the sample 206 may experience varying degrees of energy loss due to interactions between the sample and charged particles (e.g., scattering, X-ray emission, etc.), which may subsequently shift the image away from or towards the spectral plane 307 (e.g., image plane) of the energy spectrometer 204. For example, the energy E of the primary electron beam 305, e.g., the subsequent energy of the electron beam 229 without interrogating the sample 206 (e.g., the appearance of the electron beam when the sample 206 is removed), will have several crossover positions as the charged particles are lensed through the transmission electron microscope 202. In some examples, the primary electron beam 305 can be used to initially calibrate the projection system 208 of the transmission electron microscope 202 and the optical components (e.g., multipoles such as hexapoles, octopoles, decapoles, etc.) of the energy spectrometer 204 to obtain an image in the spectral plane 307.

[0030] Electron beams of various energies, such as a primary electron beam 305 having energy E, a secondary electron beam 303 having energy E-ΔE, and a tertiary electron beam 301 having energy E-ΔE, each traverse separate trajectories substantially along the optical axis of the transmission electron microscope 202. While three electron beams of three distinct energies are shown in FIG. 3, the electron beam may include any number of beams of different energies due to energy loss interactions with the sample 206. Energy loss may be desirable because measurement of energy loss by the energy spectrometer 204 may be useful in determining characteristics of the sample 206. However, energy loss may affect the focusing position of charged particles in the transmission electron microscope 202 and the energy spectrometer 204, as discussed above. This change in focus may result in a defocused image on a detector located conjugate to the spectral plane 307.

[0031] For example, a primary electron beam 305 having energy E may propagate through the transmission electron microscope 202 and have a first crossover position, e.g., a focal position, as indicated by first crossover position 310. A secondary electron beam 303 having some energy loss ΔE1 compared to E will have a different crossover position indicated by second crossover position 312 with a distance offset ΔZ1. Furthermore, a tertiary electron beam 301 having some energy loss ΔE2 compared to E will also have another crossover position indicated by third crossover position 314 with a distance offset ΔZ2. In one example, for a given E0, ΔE2 > ΔE1, and thus ΔZ2 > ΔZ1. Because both distance offsets ΔZ2 312 and ΔZ1 314 can propagate through the transmission electron microscope 202, the secondary electron beam 303 and the tertiary electron beam 301 can result in a distance offset ΔZ' 2 341 and a distance offset ΔZ' 1 342, respectively, within the detector. ΔZ2 and ΔZ1 can be greater than, equal to, or less than ΔZ'2 and ΔZ'1, respectively, depending on the operational parameters (e.g., magnification, chromatic aberration constant, etc.) as described above. However, any distance offset (e.g., any shift) between the respective electron beams may result in defocusing and blurring of the image in the spectral plane 307 if ΔZ'2 is not approximately equal to ΔZ'1, and similarly, if either ΔZ'2 or ΔZ'1 is not located at a distance that is approximately collinear with the focal plane 308 where the primary electron beam 305 is focused (e.g., all imaging foci are not in the same imaging plane).

[0032] FIG. 4 illustrates an image set 400 of various beam spectra at different beam energies, according to some embodiments. The image set of various beam spectra at different beam energies may represent several images from the perspective of the spectral plane 307 of the transmission electron microscope 202 of FIG. 3 . The electron beam spectrum images include images 401, 403, 405, 407, and 409, with electron beam energy decreasing from top to bottom. In one example, image 401 may represent a first image generated by a properly focused primary electron beam 305 at the spectral plane 307, image 405 may represent a second image generated by a secondary electron beam 303 at the spectral plane 307, and image 409 may represent a third image generated by a tertiary electron beam 301 at the spectral plane 307. As shown, image 401 is in focus with sharp contrast and minimal defocus and blur. Image 405 is defocused relative to image 401, resulting in increased blur. Image 409 shows the greatest amount of defocus and blur.

[0033] In addition to parameters related to magnification and imaging (e.g., chromatic aberration) that can affect the crossover position, environmental factors such as temperature changes (e.g., a drop of 10°C over a few hours) can change the crossover position over time (e.g., focus drift). For example, an image set acquired in cold weather may have a configuration (e.g., user-defined or computer-defined) for acquiring an in-focus image set. In contrast, if the configuration remains unchanged from cold to hot weather, the image set may be out of focus because some or all of the intermediate lens components still have their cold-season configuration (e.g., internal components calibrated at colder temperatures may behave differently than internal components calibrated at warmer temperatures). In one example, calibration of transmission electron microscope 202 may involve adjusting (e.g., translating, rotating, etc.) one or more of magnification elements 333 until at least one image from each image 401, 403, 405, 407, or 409 is in focus. Thus, changes to the magnification settings of the transmission electron microscope 202 and environmental factors can result in defocusing of one or more of the images 401, 403, 405, 407, and 409 depending on the spread of energy in the electron beam 229, as described above.

[0034] The optical components (shown in FIG. 5 ) may include one or more multipole sets that can be controlled to adjust one or more of the primary electron beam 305, secondary electron beam 303, and tertiary electron beam 301, for example, to account for changes in charged particle energy loss, magnification, intermediate lens components, environmental factors, and focus drift over time. For example, the multipole set can help remove blur and defocus in at least one image from each image 401, 403, 405, 407, or 409 by shifting one or more of the primary electron beam 305, secondary electron beam 303, and tertiary electron beam 301 to be substantially co-aligned (e.g., co-planar) with the spectral plane 307 to reduce the crossover distance ΔZ′ 434 to be co-planar with the spectral plane 307. In other examples, the multipole set may include several multipoles positioned in front of and behind (e.g., behind) the spectral plane 307.

[0035] 5 is a schematic diagram illustrating an electron microscope system 500 in which energy-dependent defocus has been corrected, according to some embodiments. Electron microscope system 500 may include some or all of the components described with reference to electron microscope system 300 of FIG. 3 and / or EMS 200 of FIG. 2. An electron beam may emerge from a sample, and the electron beam may follow a trajectory along the optical axis of a transmission electron microscope 202, such as a TEM. The trajectory may depend on the energy of the electrons in the electron beam and may further depend on operating parameters of the transmission electron microscope 202, which may be controlled by controller 226 (e.g., its firmware, hardware, and / or software components).

[0036] In some examples, the controller 226 can store a magnification setting 552 for the imaging system (including the projection system 208 and the objective lens) of the transmission electron microscope 202. For example, the controller 226 can adjust the magnification setting 552 to control some or all of the components of the imaging system (e.g., the objective lens, the condenser, the magnification lens, etc.) to achieve a desired focus of the electron beam. Freedom to change the magnification is desirable for users of the microscope system 500 because the magnification can determine how much the cone of the electron beam exiting the sample is compressed toward the energy spectrometer 204. More compression can result in a larger portion of the electron beam cone being accepted by the entrance aperture of the spectrometer.

[0037] In addition to the magnification setting 552, the controller 226 may also include a defocusing component 553. The defocusing component 553 may detect defocus of the projection system 208 by using different techniques. Defocus may depend on many factors, including, but not limited to, changes to the magnification of the projection system 208 and / or the operating parameters of the electron microscope system 500. The change to magnification may be made automatically by the controller 226 or by a user of the electron microscope system 500. The defocusing component 553 may detect a change in magnification by receiving data indicative of a particular magnification setting among the magnification settings 552 currently being used. More generally, the defocusing component 553 may detect defocus using different techniques, such as one or a combination of receiving an indication of a magnification change, receiving image data from an image detector (e.g., detector 232) and processing the image data using image analysis to detect defocus, receiving data indicative of a change to magnification from an encoder connected to the magnification element, and / or receiving data from a detector (e.g., detector 222) in the energy spectrometer 204 that monitors the spectral plane 307. In some examples, detecting defocus can trigger a multipole control component 554 of the controller 226 to adjust operating parameters of the energy spectrometer 204, such as the optical component 548, to resolve the defocus.

[0038] In some examples, operating parameters may vary depending on the energy E of the primary electron beam 305, e.g., the energy of the electron beam, without examining the sample 206. However, due to interactions between the sample and charged particles, the electron beam emerging from the sample may contain some energy loss. Thus, the electron beam may include multiple electron beams with various energies, such as the secondary electron beam 303 and the tertiary electron beam 301. Multiple electron beams with various energies may be referred to as an energy loss spectrum. While electron beams of three distinct energies are shown in FIG. 5, the electron beam may include any number of multiple beams with different energies due to energy loss interactions with the sample. Energy loss may be desirable because measuring the loss over a range of energies with the energy spectrometer 204 can be useful in determining the structure and composition of a material. However, energy loss may also affect the crossover position of the electron beam in the electron microscope 202 and the energy spectrometer 204.

[0039] For example, a primary electron beam 305 having energy E0 propagating through the transmission electron microscope 202 and through the sample may experience some or no energy loss, which may have a first crossover position, e.g., a focal position, as indicated by crossover position 510. However, a secondary electron beam 303 having some energy loss ΔE1 may have a different crossover position, indicated by offset ΔZ1 312, and may propagate through the transmission electron microscope 202 and the energy spectrometer 204. In addition, a tertiary electron beam 301 having some energy loss ΔE2 may also have a different crossover position, indicated by offset ΔZ2 314, and may propagate through the transmission electron microscope 202 and the energy spectrometer 204, e.g., when ΔE2 > ΔE1, ΔZ2 > ΔZ1. In this example, a crossover focal difference ΔZ 315 between the primary electron beam 305 having energy E0 and the tertiary particle beam 301 having energy ΔE2 may be determined by defocus component 553 and stored in memory.

[0040] In one example, the energy spectrometer 504 may include optical components, such as optical component 548, to shape the electron beam for imaging. In some examples, the optical component 548 may be any optical component that can be used to focus the electron energy loss spectrum 541. In some examples, the loss of focus in the spectral plane 307 may be approximated as having a linear dependence on the energy loss. In such use, the optical component 548 may include one or more hexapole elements. In other examples, the energy loss may be higher, and the linear approximation must be extended with higher order contributions (quadratic, cubic in energy loss) to properly focus in the spectral plane. In other examples, the optical component 548 may include one or more hexapole elements, one or more octopole elements, etc. In FIG. 5, the optical component 548 is shown as a hexapole to shift the crossover positions of the primary electron beam 305, the secondary electron beam 303, and the tertiary electron beam 301 to co-align them in the spectral plane 307 to form their respective images. In this manner, using optical component 548 as a multipole can be useful in compensating for and correcting chromatic and spherical aberrations by adjusting the individual poles of the multipole until a focused image can be formed from electron energy loss spectrum 541.

[0041] As an example, the operation of optical component 548 may be adjusted by multipole control component 554 based on the type of optical component 548. For example, if optical component 548 is a hexapole including six separate excitation poles, the hexapole may be adjusted by multipole control component 554 by exciting (e.g., applying a current and / or voltage) three of the six poles with a first voltage and exciting the other three of the six poles with a second voltage. This adjustment of the hexapole may separately focus each of electron beams 305, 303, and 301 onto the same spectral plane 307 for imaging. In another example, if optical component 548 is an octopole, one or more of the poles may be uniquely adjusted based on an energy loss greater than a threshold to obtain a focused image free of chromatic aberration.

[0042] In some examples, the multipole control component 554 can adjust the operation of the optical component 548 based on one or more parameters of the projection system 208, such as based on a change to the magnification setting 552 (e.g., increasing or decreasing the magnification). For example, if a user increases the magnification of the transmission electron microscope 202, the crossover positions 510, 512, 514 may shift accordingly (as described above). In response to an adjustment to the magnification setting 552 of the transmission electron microscope 202, the operation of the optical component 548 can be adjusted to compensate for defocusing or refocusing of at least a portion of the electron energy loss spectrum 541 onto a detector (not shown) of the energy spectrometer 204. In some examples, the entire electron energy loss spectrum 541 can be refocused onto the detector. Control of the optical component 548 can be achieved based on a set of parameters. The parameters can include the magnification M of the projection system 208, the crossover positions 510, 512, 514 may shift accordingly (as described above). In response to an adjustment to the magnification setting 552 of the transmission electron microscope 202, the operation of the optical component 548 can be adjusted to compensate for defocusing or refocusing of at least a portion of the electron energy loss spectrum 541 onto a detector (not shown) of the energy spectrometer 204. In some examples, the entire electron energy loss spectrum 541 can be refocused onto the detector. The control of the optical component 548 can be achieved based on a set of parameters. The parameters can include the magnification M of the projection system 208, the crossover positions 510, 512, 514 may shift accordingly (as described above). proj , the chromatic aberration constant C of the projection system 208 c (proj) , the energy E of the multiple electron beams 305, the total energy spread ΔE of the electron energy loss spectrum, the crossover position difference ΔZ between the electron beams 301, 303, 305, etc. In some embodiments, controlling the optical component 548 may include altering the electromagnetic field of the optical component 548. As an example, the crossover position difference ΔZ 315 (e.g., shift) may be determined at the end of the transmission electron microscope 202, and based on that determination, adjustments to the electromagnetic fields of the multipoles of the optical component 548 may be made based on the crossover position difference ΔZ.

[0043] Although only one optical component 548 is shown in FIG. 5 , the energy spectrometer 204 may include several optical components. In one example, adjusting to compensate for chromatic defocus caused by a change in magnification setting 552 may include adjusting the operation of multiple optical components. In some examples, the total energy spread ΔE may be compared to a predetermined energy spread threshold. The comparison may assist in determining adjustments to the operation of multiple optical components. For example, if the total energy spread ΔE is less than the predetermined threshold, adjusting the operation may include adjusting the operation of a first multipole set (e.g., at least one hexapole). If the total energy spread ΔE is greater than the predetermined threshold, adjusting the operation may include adjusting the operation of a second multipole set (e.g., at least one hexapole and at least one octapole). The two sets may, but need not, include a common multipole. In another example, adjusting the operation includes controlling the hexapole of the optical component 548 based on an energy loss less than a threshold. In a further example, adjusting the operation includes controlling an octopole of optical component 548 based on the energy loss being greater than a threshold value.

[0044] Thus far, the defocusing component 553 and the multipole control component 554 have been described. Such components 553 and 554 may be implemented as software components of the controller 226. Such components 553 and 554 may be optional. For example, a lookup table may be pre-stored and used, as described herein below. In this case, components 553 and 554 may not be used. This lookup table may relate different parameters to each other to enable refocusing of the electron energy loss spectrum 541. In this case, the software component of the TEM may determine new settings for the imaging system and notify the software component of the energy spectrometer 204 about the new settings. The software component of the energy spectrometer 204 may then use the lookup table to determine, for the new settings, the controls that need to be applied to the energy spectrometer 204 so that the electron energy loss spectrum 541 is properly refocused. Depending on the implementation of the electron microscope system 500, these two software components may be part of the controller 226 or may be separate components, one specific to the TEM controller and one specific to the energy spectrometer 204 controller.

[0045] FIG. 6 illustrates a set of images of various beam spectra 600 at different primary beam energies after correction for energy-dependent defocus, according to some embodiments. The set of images of various beam spectra 600 at different beam energies may represent several images from the perspective of the spectral plane 307 of the transmission electron microscope 202 of FIG. 5. The beam spectrum images include images 601, 603, 605, 607, and 609, with electron beam energy increasing from top to bottom. As described above, adjusting the operation of at least one optical component 548 of the energy spectrometer can correct for defocus (i.e., position the focal point position at a common spectral plane 307) in each of the primary electron beam 305 having energy E in image 601, the secondary electron beam 303 having energy E-ΔE in image 605, and the tertiary electron beam 301 having energy E-ΔE in image 609. Images 603 and 607 may represent intermediate electron beams (not shown).

[0046] 7 is a flow diagram of an exemplary process 700 for operating a transmission electron microscope using an electron microscope system, according to some embodiments. The electron microscope system may be an example of other electron microscope systems described herein, such as electron microscope system 500 of FIG. 5.

[0047] The exemplary process 700 begins at step 705, where a controller (e.g., software of the TEM) may store a lookup table of parameters. The parameters may include and be related to configuration parameters and control parameters. Given a particular value of a configuration parameter, the lookup table may be used to determine the associated value of the control parameter. The configuration parameters may be parameters of optical components of the imaging system of the electron microscope system (e.g., the objective lens and / or the lenses of the projection system 208). The control parameters may be used to control the energy spectrometer 204, as described further herein below. In one example, the configuration parameters include the magnification M of the projection system 208, proj and one or more chromatic aberration constants C of the projection system 208c (proj) The control parameters may include, but may not be limited to, offset shifts (ΔZ) and / or electrical controls (e.g., current, voltage, etc.) for one or more optical components (e.g., multipoles) of the energy spectrometer 204. Values ​​for the control parameters may be derived using a pre-calibration process. For example, during the pre-calibration process, certain values ​​for the setting parameters are used. Given these values, the pre-calibration process derives values ​​for the control parameters such that the electron microscope system is precisely focused (e.g., the offset shift (ΔZ) is zero or near zero, or conversely, variations to focus across the electron energy loss spectrum are corrected and the electron energy loss spectrum is refocused onto the detector). The pre-calibration process may be iterative, such that values ​​for the control parameters are determined over a range of values ​​for the setting parameters. A lookup table is one example of a data structure for storing and associating different parameters. Of course, other data structures are possible, such as lists, arrays, databases, etc.

[0048] In step 710, the controller (e.g., software in the TEM) can identify when new settings for the imaging system have been set. The settings can include changing the values ​​of one or more of the setting parameters described in step 705 (e.g., magnification M proj and / or one or more chromatic aberration constants C c (proj) The controller (e.g., the TEM software) can then adjust the magnification (e.g., the new value of M proj and / or the chromatic aberration constant C c (proj) The energy spectrometer 204 can be primed (by informing the software of the energy spectrometer 204 of new settings, such as new values ​​of .times. ...

[0049] In step 715, the new settings (e.g., new M proj and / or new C c(proj) ), the controller (software of the energy spectrometer 204) can use a lookup table to derive new values ​​for the offset shift ΔZ across the electron energy loss spectrum 541. These new values ​​can be associated with the new settings in the lookup table, as described herein above, to indicate a new defocus across the electron energy loss spectrum 541. Other techniques are also possible for deriving new values ​​for the offset shift ΔZ without relying on a lookup table. For example, a detector in the spectral plane 307 can relay an image (e.g., similar to images 405 and 405 in FIG. 4) to the controller 226 for analysis by the defocusing component 553. The defocusing component 553 can be configured to calculate the offset shift ΔZ across the electron energy loss spectrum 541 by using a lookup table. proj and C c (proj) Based on the value of , it can be determined that the image is out of focus and a new value for the distance offset shift ΔZ needs to be calculated to focus some or all of the electron energy loss spectrum 541 in the spectral plane 307.

[0050] In step 720, the controller (e.g., software of the energy spectrometer 204) can apply pre-calibrated multipole settings (e.g., settings applied to some or all of the optical components 548) to compensate for the new value of the distance offset shift ΔZ across the electron energy loss spectrum 541. In one example, the lookup table can also associate electrical controls (e.g., currents, voltages, etc.) of one or more optical components (e.g., multipoles) of the energy spectrometer 204 with the new value of the offset shift ΔZ. Thus, the lookup table can return the electrical controls that the energy spectrometer 204 then applies to its associated optical components. For example, a particular excitation current and / or voltage is applied to the multipole to compensate for the new value of the distance offset shift ΔZ across the electron energy loss spectrum 541. In this example, adjusting the operation of optical components 548 (e.g., excitation of poles) based on changes to magnification (e.g., changes to magnification settings) to correct for focus variations across at least a portion of electron energy loss spectrum 541 can ensure that at least a portion of electron energy loss spectrum 541 is refocused onto the detector (e.g., using techniques the same as or similar to those described in FIG. 6 ). Again, other techniques for deriving electrical control are possible without relying on lookup tables. For example, while the operation of the multipoles is controllably adjusted, the detectors in spectral plane 307 can relay resulting images (e.g., similar to images 405 and 409 in FIG. 4 ) to controller 226 for analysis by defocusing component 553. Based on the operation adjustments, defocusing component 553 can determine whether the image is in focus. This process can be repeated iteratively until the image is in focus, at which point the operation adjustments to the multipoles can be stopped.

[0051] 8 is an iterative flowchart diagram of an exemplary process 800 for operating an electron microscope system, according to some embodiments. The electron microscope system may be an example of other electron microscope systems described herein, such as the electron microscope system 500 of FIG. 5. The electron microscope system may include a controller 226 configured to perform the operations of the process 800. The process 800 begins at step 810, in which the controller 226 monitors the transmission electron microscope 202 for changes in settings. In some examples, the changes in settings include changing the magnification M of the projection system 208. proj That is, one or more magnification elements 333 have been adjusted by a user of the electron microscope system 500 or automatically by the controller 226 in response to predetermined information (e.g., start-up process, calibration, etc.). Additionally, the setting changes may include changes in the chromatic aberration constant C of the projection system 208. c (proj) , the chromatic aberration constant of the objective lens of the projection system 208, the change in the energy spectrum, or any combination thereof.

[0052] In step 812, the controller 226 determines whether the setting change is new or whether it occurred previously during a previous operation of the electron microscope system 500. The controller 226 determines whether the setting change is new or whether it occurred previously during a previous operation of the electron microscope system 500. The controller 226 determines whether the setting change is new or whether it occurred previously during a previous operation of the electron microscope system 500. The controller 226 determines whether the setting change is new or has ... proj , the position of the objective lens 332, the previously determined chromatic aberration constant C of the projection system 208 c (proj) A lookup table containing information and settings relating to previously determined chromatic aberration constants of the objective lens 332 of the projection system 208, previously determined changes in the energy spectrum, previously determined multipole configuration settings of the optical components 548, previously analyzed images from the defocus component 553, or combinations thereof, can be examined to determine whether an approximate match exists.

[0053] If the controller 226 determines that there is no match in the lookup table, the process 800 proceeds to step 814, where the controller 226 uses the defocus component 553 and the multipole control component 554 to determine the offset ΔZ' 434 shown in FIG. 4. In some examples, the offset ΔZ' 434 may be approximately equal to the distance offset ΔZ 315, depending on the configuration of the projection system 208. In other examples, the offset ΔZ' 434 may be different from the distance offset ΔZ 315, as described above. In some examples, the controller 226 determines the offset ΔZ' 434 by analyzing the image in the spectral plane 307 with the current settings. The controller 226 can analyze the offset ΔZ' 434 to determine whether a similar offset exists in the lookup table to arrive at a "best guess" initial multipole configuration. For example, the controller 226 may calculate a previously determined magnification M for a configuration of the projection system 208 (e.g., the position of the magnifying element 333, the position of the objective lens 332, etc.) that is within a threshold percentage (e.g., a difference of 1 to 10 percent) of the current configuration of the projection system 208. proj In another example, the controller 226 may specify a chromatic aberration constant of the magnification M proj and the chromatic aberration constant C c (proj) approximations M′ of the new setup configuration in preparation for adjusting the optical components 548. proj New settings such as the chromatic aberration constants can be set and recorded (eg, in a temporary table or matrix).

[0054] In step 816, the controller 226 uses the multipole control component 554 to increase or decrease the voltage and / or current to one or more poles (e.g., magnetic poles) of the optical components 548 in the energy spectrometer 204 by a pre-calibrated amount (e.g., an increment or table definition) to generate a new image in the spectral plane 307. In some examples, the multipole control component 554 increases or decreases the voltage and / or current by using a correction matrix of the pole voltages and / or currents of the optical components 548 based on an earlier calibration of the projection system 208 and the energy spectrometer 204. For example, based on observed effects (such as skew, defocus, and blur in the images 405 / 409), a correction matrix of specific currents for specific poles on individual optical components 548 can be generated to compensate for the observed effects. The correction matrix can be used in conjunction with or independently of the lookup table.

[0055] In step 818, controller 226 uses defocus component 553 to determine whether the new image is in focus, free of blur, and / or free of chromatic aberrations. For example, if the new image contains optical aberrations similar to those shown in images 403, 405, 407, and 409, the new image is determined to be out of focus, and the new settings are determined to be incorrect. If the new image is not in focus, the process returns to step 814 to re-measure offset ΔZ′. If the new image is determined to be in focus (e.g., offset ΔZ′ 434 of electron energy loss spectrum 541 is close to zero), process 800 proceeds to step 820.

[0056] In step 820, the controller 226 stores the new settings and new parameters (e.g., M' proj , C' c (proj), multipole excitation settings, etc.) in a lookup table. In some examples, the controller 226 can update the previous settings with newer, more accurate parameters. In other examples, the controller 226 can store the new parameters along with additional variables such as temperature, date, and manufacturing information associated with various components of the electron microscope system 500. For example, M' proj , C' c (proj) The new calculated value of may be stored along with the current temperature (e.g., 21° C.) to avoid duplicate settings that may occur when the electron microscope system 500 has not experienced a physical configuration change, but the environmental temperature has changed relative to when the electron microscope system 500 was previously used (e.g., two months ago). The use of additional variables may increase the functionality of the electron microscope system 500 by using a more robust lookup table and reducing the time required to focus an image. Once the lookup table has been appropriately updated, process 800 returns to step 810.

[0057] Returning now to step 812, if the controller 226 determines that the entered settings have already been used previously, then the process 800 proceeds to step 822. In step 822, the controller 226 determines whether M' proj , C' c (proj) The configuration settings, such as the values ​​of , and excitation parameters of the optical component 548 for imaging, may be looked up from a look-up table.

[0058] In step 824, the controller 226 uses the multipole control component 554 to increase or decrease the voltage and / or current (e.g., using settings from a lookup table) to one or more poles of the optical component 548 in the energy spectrometer 204 to generate a new image in the spectral plane 307.

[0059] In step 826, controller 226 uses defocus component 553 to determine whether the new image is in focus, free of blur, and / or free of chromatic aberrations. For example, if the new image contains optical aberrations similar to those shown in images 403, 405, 407, and 409, the new image may be determined to be out of focus, and the new settings are determined to be incorrect. If the new image is not in focus, the process returns to step 814 to re-measure offset ΔZ′. If the new image is determined to be in focus, process 800 returns to step 810.

[0060] 9 is an example graph 900 of crossover shifts across an energy loss spectrum, according to some embodiments. Graph 900 includes metrics related to parameterized configuration changes 912, effective configurations 910, and estimated parameterized gradients 914 that may be calculated from process 800 of FIG. 8. Estimated parameterized gradients 914 are calculated based on the M proj , C c (proj) The estimated parameterized gradient 914 may represent a "best guess" for the focusing configuration using parameters such as values ​​of M for various configurations of the optical components 548. proj , C c (proj) can be used as a starting point for determining the unknown value of , thereby reducing the time required to find the focus of the electron energy loss spectrum 541.

[0061] In some examples, once the process 800 of FIG. 8 has completed several iterative cycles (e.g., from a few to several thousand configurations) and obtained valid configurations for correcting the focus gradient of the electron energy loss spectrum 541, including values ​​such as the magnification, aberration constants, and polar configuration (e.g., voltage / current) of the optical components 548, the data points of the valid configuration 910 line are populated and stored in a lookup table similar to or identical to the lookup table described in the process of FIG. 7 or the process of FIG. 8. The valid configuration 910 line may represent a parameterization of the configuration in use that produced an in-focus image (e.g., focusing the electron energy loss spectrum 541 over several hundred configurations) without blur or aberration. As more data points are discovered during the iterative process of FIG. 8, more valid configuration 910 lines continue to grow until they nearly or exactly match the parameterized configuration change 912 line.

[0062] 7, the parameterized configuration changes 912 lines represent all configurations of the electron microscope system 500 for each configuration of magnification (or camera length as in FIG. 9), energy loss, chromatic aberration constant, etc. (e.g., lines representing all valid configurations that focus the electron energy loss spectrum 541). The parameterized configuration changes 912 lines represent the magnification of the magnifying element 333, the power and configuration of the objective lens 332, the magnification M of the projection system 208, etc. proj the chromatic aberration constant C of the projection system 208 c (proj) , the energy E of the primary electron beam 505, the total energy spread ΔE of the electron energy loss spectrum, or a combination thereof. When the process 800 of FIG. 8 determines the offset ΔZ′, the controller 226 can determine a corresponding configuration based on the parameterized configuration change 912 line to properly focus the electron energy loss spectrum 541.

[0063] FIG. 10 is a flow diagram of an exemplary process 1000 for operating a transmission electron microscope using an electron microscope system, according to some embodiments. The electron microscope system may be an example of other electron microscope systems described herein, including the microscope system 100 of FIG. 1. The electron microscope system may include a computer system configured to perform the operations of processes 700, 800, and 1000. For example, the computer system may be configured to adjust electron beam parameters (e.g., accelerating potential, beam focus parameters, beam current, beam deflection, etc.), scanning / imaging parameters for SEM and / or STEM modes (e.g., sweep time, dwell time, etc.), detector settings (e.g., bias voltage, collector grid voltage, etc.), and other parameters suitable for operation of such a microscopy system. The computer system may be a single system that controls the operation of both the microscope and the energy spectrometer, or the computer system may include multiple systems that separately control the operation of the microscope and the energy spectrometer.

[0064] In block 1005, the process 1000 includes receiving an electron beam from a transmission electron microscope. The electron beam may be received by an energy spectrometer. The transmission electron microscope may include an imaging system disposed after the sample plane. The electron beam may include an energy loss spectrum due to interaction with the sample. For example, a sample in the sample plane may be interrogated with an electron beam of a desired energy (e.g., primary beam energy), and some of the electrons exiting the sample have reduced energies characteristic of various properties of the sample, contributing to an electron energy loss spectrum in the electron beam. Energy-dependent defocusing may occur when the electron energy loss spectrum passes through an imaging system or other components of the transmission electron microscope or energy spectrometer.

[0065] At block 1010, the process 1000 includes focusing the electron energy loss spectrum onto a detector. Focusing the electron energy loss spectrum may include controlling the operation of optical components in the energy spectrometer. For example, the optical components may include multipoles. Controlling the operation of the optical components may include causing the multipoles to apply electromagnetic fields to affect the charged particles in the electron energy loss spectrum.

[0066] In block 1015, process 1000 includes determining information regarding changes to the magnification of the imaging system. The imaging system may include multiple lenses, such as magnetic lenses and / or magnetic quadrupoles. The information may include contributions to energy-dependent defocus caused by changes in magnification. In some embodiments, information may be pre-stored by the TEM and may associate chromatic defocus or energy-dependent defocus with changes to magnification (e.g., changes in magnification value, changes in camera length associated with the imaging system, etc.). The information may be transmitted from the TEM to a controller of the energy spectrometer. The information may be based on intentional changes in magnification initiated by a user or on magnification changes due to environmentally induced instrument drift. The changes in magnification may defocus the electron energy loss spectrum on the detector.

[0067] At block 1020, process 1000 includes adjusting the operation of one or more optical components so that at least a portion of the electron energy loss spectrum is refocused onto the detector. In some examples, the entire energy loss spectrum can be refocused onto the detector. The adjustment of the one or more optical components may depend on parameters of the microscope or energy spectrometer. In some examples, the controller may adjust the operation of the one or more optical components by determining an amount of defocus. The parameters may include an adjustment amount to magnification, the energy E of the primary electron beam in the electron energy loss spectrum, and the total energy spread ΔE of the electron energy loss spectrum. In some examples, the controller may calculate the amount of defocus based on the parameters. The one or more optical components may include a multipole, such as a hexapole or octapole. Adjusting the operation of the one or more optical components may include changing an electromagnetic field applied by the one or more optical components.

[0068] In some examples, the total energy spread ΔE can be compared to a predetermined threshold value of energy spread. The comparison can assist in determining adjustments to the operation of multiple optical components. For example, if the total energy spread ΔE is less than the predetermined threshold value, adjusting the operation can include adjusting the operation of at least one hexapole. If the total energy spread ΔE is greater than the predetermined threshold value, adjusting the operation can include adjusting the operation of at least one hexapole and at least one octapole.

[0069] FIG. 11 is a block diagram of a controller 1101 of an electron microscope system according to certain embodiments of the present disclosure. An example of an electron microscope system may include the microscope system 100 of FIG. 1. As shown, the controller 1101 includes a processor 1102 communicatively coupled to a memory 1004. The processor 1102 may include one processing device or multiple processing devices. Non-limiting examples of the processor 1102 include a field-programmable gate array (FPGA), an application-specific integrated circuit (ASIC), a microprocessor, or any combination thereof. The processor 1102 may execute instructions 1110 stored in the memory 1004 to perform operations such as those of process 700 of FIG. 7, process 800 of FIG. 8, or process 1000 of FIG. 10. In some examples, the instructions 1110 may include processor-specific instructions generated by a compiler or interpreter from code written in any suitable computer programming language, such as C, C++, C#, Python, or Java.

[0070] The memory 1004 may include one or more memory devices. The memory 1004 may include any type of memory device that may be non-volatile and retains stored information when powered off. Non-limiting examples of the memory 1004 include electrically erasable and programmable read-only memory (EEPROM), flash memory, or any other type of non-volatile memory. At least a portion of the memory 1004 may include a non-transitory computer-readable medium from which the processor 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 1004. The non-transitory computer-readable medium may include electronic, optical, magnetic, or other storage devices capable of providing instructions 1110 or other program code to the processor 1102. Non-limiting examples of non-transitory computer-readable media include magnetic disks, memory chips, RAM, ASICs, or any other medium from which a computer processor can read instructions 1110.

[0071] The memory 1004 may further include information 1112 related to magnification adjustment, parameters 1114, a defocus amount 1116, and a predetermined threshold 1118. The controller 1101 may receive information related to magnification adjustment from a microscope, such as a TEM. At least a portion of the information 1112 related to magnification adjustment may be pre-stored and may be associated with chromatic defocus correction for defocus caused by changes in magnification. The parameters 1114 may include operational parameters related to the electron microscope system, such as a desired energy / primary energy of the electron beam, an energy spread of the energy loss spectrum, etc. The controller may determine or calculate the defocus amount 1116 based on the magnification adjustment 1112 and the parameters 1114. In some examples, a portion of the parameters 1114 may be compared to a predetermined threshold 1118. The comparison may determine how to determine the defocus amount 1116. The defocus amount 1116 may be used to adjust the operation of optical components within the energy spectrometer.

[0072] Various embodiments have been described in the preceding specification. 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, specifically 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 electron beam systems capable of applying a wide range of particles to the imaging, microanalysis, and / or processing of 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.

[0073] Some embodiments of the present disclosure include a system including one or more data processors and / or logic circuits. 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, such as, for example, process 1000 of FIG. 10 .

[0074] 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 or portions thereof shown and described, 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.

[0075] When a term is used without 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” or “substantially” are used to indicate a deviation from a stated characteristic or value, where the deviation has 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” to another dimensional parameter, the term “substantially” is 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, the term “about” or “substantially” is intended to reflect that the alignment or angular orientation may differ from the strictly stated condition (e.g., not be strictly perpendicular) within tolerance limits. For dimensional values ​​such as diameter, length, and width, 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 between 9 mm and 11 mm. In this disclosure, a "subrange" refers to a range of values ​​between two stated limits and / or a range of values ​​that includes one of the two stated limits.

[0076] 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 will 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.

[0077] 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 performed by an electron microscope system, the method comprising: receiving an electron beam from a transmission electron microscope, the transmission electron microscope including an imaging system positioned after a sample plane, the electron beam including an electron energy loss spectrum due to interaction with the sample; focusing the electron energy loss spectrum onto a detector by optical components of the electron microscope system; determining information regarding a change to the magnification of the imaging system; and adjusting operation of one or more of the optical components based on the change to the magnification such that variations to focus across at least a portion of the electron energy loss spectrum are corrected and at least the portion of the electron energy loss spectrum is refocused onto the detector.

2. Determining information regarding the change to the magnification of the imaging system includes: providing the information to a controller connected to one or more of the optical components, the information being provided to the controller by the transmission electron microscope; Adjusting the operation of one or more of the optical components may include: retrieving at least one setting from a lookup table based on the change to the scaling factor; 10. The method of claim 1, further comprising: controlling the operation of one or more of the optical components to adjust at least one magnetic pole of one or more of the optical components based on the at least one setting.

3. The method of claim 2 , wherein adjusting the at least one magnetic pole of one or more of the optical components compensates for defocus across the electron energy loss spectrum.

4. The method of claim 3 , wherein the information is pre-stored by the transmission electron microscope and associates a chromatic defocus correction with the change to the magnification.

5. The method of claim 2 , wherein the information is transmitted from the transmission electron microscope based on the change to the magnification of the imaging system.

6. 2. The method of claim 1, wherein the change to the magnification is associated with a shift to a crossover point at an end of the transmission electron microscope, and the operation of one or more of the optical components is adjusted to compensate for a shift to focus across the electron energy loss spectrum, the shift to focus being caused by the shift to the crossover point.

7. 10. The method of claim 1, further comprising determining a shift to a crossover point at an end of the transmission electron microscope based on the information, and wherein the operation of one or more of the optical components is adjusted based on the shift.

8. 3. The method of claim 2, wherein the information includes a value for chromatic defocus correction, and further comprising determining a shift to a crossover point at an end of the transmission electron microscope based on the value, and wherein the operation of one or more of the optical components is adjusted based on the shift.

9. The method of claim 8 , wherein the association between the value and the shift is pre-stored in the look-up table by the controller.

10. One or more computer-readable storage media storing instructions that, when executed by one or more processors of an energy spectrometer, cause the energy spectrometer to perform operations including: receiving an electron beam from a transmission electron microscope, the transmission electron microscope including an imaging system positioned after a sample plane, the electron beam including an electron energy loss spectrum resulting from interaction with a sample; focusing, by optical components of the energy spectrometer, the electron energy loss spectrum onto a detector; and determining information related to changes to the magnification of the imaging system. and adjusting operation of one or more of the optical components based on the change to the magnification such that variations to focus across at least a portion of the electron energy loss spectrum are corrected and at least the portion of the electron energy loss spectrum is refocused onto the detector.

11. The operation is 11. The one or more computer-readable storage media of claim 10, further comprising: determining an adjustment to one or more multipoles of the optical components based on the information, wherein adjusting the operation of one or more of the optical components comprises applying the adjustment to the multipoles.

12. The operation is 12. The one or more computer-readable storage media of claim 11, further comprising determining a shift to a crossover point at an end of the transmission electron microscope based on the information, the adjustment being determined based on the shift.

13. The one or more computer-readable storage media of claim 12 , wherein the association between the adjustment and the shift is pre-stored by the energy spectrometer.

14. The one or more computer-readable storage media of claim 11 , wherein the adjustment causes a change to an electromagnetic field applied by the multipole.

15. 12. The one or more computer-readable storage media of claim 11, wherein the adjustment is determined based on a correction matrix defined based on a calibration of the imaging system and the energy spectrometer.

16. 12. The one or more computer-readable storage media of claim 11, wherein adjusting the operation of one or more of the optical components comprises adjusting a first operation of a first multipole disposed before a spectral surface of the energy spectrometer and adjusting a second operation of a second multipole disposed after the spectral surface.

17. 1. An apparatus comprising: an energy spectrometer coupled to a transmission electron microscope for acquiring one or more energy loss spectra, the transmission electron microscope including an imaging system positioned after a sample plane, the energy spectrometer comprising optical components configured to focus an electron energy loss spectrum onto a detector, the detector positioned conjugate to a spectral plane, and a controller configured to determine a change to a magnification of the imaging system and, based on the change to the magnification, adjust operation of one or more of the optical components such that at least a portion of the electron energy loss spectrum is corrected and at least the portion of the electron energy loss spectrum is refocused onto the detector.

18. 20. The apparatus of claim 17, wherein adjusting the operation comprises controlling one or more hexapoles of the optical components based on an energy loss being less than a threshold value.

19. 20. The apparatus of claim 17, wherein adjusting the operation comprises controlling an octopole of one or more of the optical components based on an energy loss greater than a threshold.

20. 18. The apparatus of claim 17, wherein the change to the magnification is determined by the controller by at least receiving information regarding the change from the transmission electron microscope, the information indicating a value of chromatic defocus correction, the controller being further configured to determine a shift to a crossover point at an end of the transmission electron microscope based on the value, and wherein adjusting operation includes modifying electromagnetic fields of one or more multipole of the optical components based on the shift.

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