Techniques for electron energy loss spectroscopy with magnetic immersion objective at high energy loss

Abstract

Systems, devices, methods, algorithms, and techniques are described for energy loss spectra at relatively large energy losses. A method includes modifying an acceleration voltage of a system source from a first energy to a second energy. The method may include modifying one or more optical elements of the system according to the calibration of the second energy. The method may include generating a set of operating conditions for the projection optics system. The method may include modifying one or more elements of the projection optics system to at least partially comply with the set of operating conditions. The method may include modifying a condenser lens of the system in accordance with focusing a charged particle beam onto a sample location. The method may also include modifying the acceleration voltage from the second energy to the first energy.

Description

TECHNICAL FIELD

[0001] Embodiments of the present disclosure relate to charged particle beam systems, and algorithms and methods for operation thereof. In particular, some embodiments relate to techniques for electron energy loss spectroscopy. BACKGROUND

[0002] Electron energy loss spectroscopy (EELS) describes a technique in which information about the electronic structure of a material sample can be obtained by passing an electron beam through the sample, causing a portion of the electrons to scatter. An EELS spectrometer operates by collecting non- elastically scattered electrons downstream of the sample relative to the electron source location and spatially dispersing these electrons by the energy lost in the non-elastic scattering. The spatially dispersed electrons impinge on a detector that produces EELS spectral data. Challenges faced by EELS include the increasing defocus of non-elastically scattered electrons with increasing energy loss, and the rapid decrease in scattering cross section with increasing energy loss, resulting in a signal-to-noise limit for excitations above about 2 keV.

[0003] In contrast to other techniques that provide similar spectral data, such as synchrotrons, EELS spectrometers configured to operate as part of a charged particle beam system are typically calibrated for a single energy of the electron beam, i.e., the energy of the primary beam of the charged particle microscope. Thus, EELS spectrometers are limited to a relatively narrow energy range around the“zero loss peak” or ZLP corresponding to the primary beam energy. Non-elastic collisions including energy transfers greater than about 1% of the primary beam energy, e.g., greater than about 2 keV for a 200 keV primary beam, such as inner-shell ionization and other relatively high energy interactions between the electron beam and the sample, suffer from poor signal-to-noise and aberration artifacts, and are generally considered outside the range of quality data for a typical EELS spectrometer. Synchrotron systems are typically used to generate such data with significantly lower spatial resolution, higher complexity, and expense using beamlines for soft or hard X-rays. Thus, there is a need for techniques and systems for probing inner-shell and other relatively high energy transitions of a material sample using an EELS system in a charged particle microscope. SUMMARY

[0004] Systems, devices, methods, algorithms, and techniques for energy loss spectroscopy at relatively large energy losses are described. In a first aspect, as referenced to Figures 1-6The described method for interrogating a sample using a charged particle beam system includes modifying the accelerating voltage of a source in the charged particle beam system from a first energy to a second energy. The first and second energies can be separated by an energy difference. The method may include modifying one or more optical elements of the charged particle beam system such that the optical elements are calibrated for the second energy. The method may include generating a set of operating conditions for a projection optics system of the charged particle beam system. This set of operating conditions may be at least partially based on operating the source at approximately the second energy. The method may include modifying one or more elements of the projection optics system to at least partially conform to this set of operating conditions. The method may include modifying a condenser lens of the charged particle beam system according to focusing the charged particle beam onto a sample location. The charged particle beam may have an energy of approximately the second energy. The method may also include modifying the accelerating voltage from the second energy to the first energy.

[0005] In some embodiments, the method further includes modifying one or more optical elements of an electron energy loss (EELS) spectrometer of a charged particle beam system for focusing a charged particle beam onto a detector of an EELS spectrometer. The charged particle beam may have an energy of approximately a second energy. The charged particle beam may be a first beam, and the method may further include generating a second charged particle beam. The second charged particle beam may have an energy of approximately the first energy. The method may further include guiding the first charged particle beam through a sample location. The method may further include generating detector data using the detector of the EELS spectrometer.

[0006] In some embodiments, the method further includes modifying one or more optical elements of the charged particle beam system according to focusing the charged particle beam onto the sample location. The focusing may correspond to fine focusing at a spatial resolution of about 0.1 nm or less. The second energy may be about 90% to about 98.5% of the first energy. The first energy may be about 300 keV, and the second energy may be about 270 keV to about 295 keV. The first and second energies may be related by the expression A = |(ΔE + E2 - E1) / E2|, where ΔE is the energy loss associated with the edge (keV), E1 is the first energy (keV), and E2 is the second energy (keV); and expression A is about 1% to about 10%.

[0007] In some embodiments, generating the set of operating conditions includes determining a solution for a first-order approximation of the projection optics assembly. This solution can configure the charged particle beam to define a final crossover (FXO) between the projection optics assembly and the detector plane, the FXO substantially satisfying one or more boundary conditions of the charged particle beam system. Boundary conditions can include the magnification at the detector of the charged particle beam system. Determining the solution can include a dataset of operating conditions for the charged particle beam system using a second energy and input parameters. This dataset can describe multiple sets of operating conditions for the projection optics assembly associated with one or more accelerating voltages. Determining the solution can include solving a mathematical expression describing a first-order approximation of the projection optics assembly.

[0008] Secondly, the system may include a charged particle beam source, a charged particle optical column coupled to the source, and a detector section, as shown in reference [reference needed]. Figures 1-6 The column can be configured to receive a beam of charged particles from a source. The column may include an objective lens segment. This objective lens segment may include a magnetic immersion objective and may define a sample position. The magnetic immersion objective may include a probe-forming objective and an imaging objective. The sample position may be defined relative to the beam axis A of the system between the probe-forming objective and the imaging objective. The column may further include a projection optics assembly. This projection optics assembly may include one or more projection optics. The system may further include a detector segment coupled to the column. This detector segment may include an energy loss spectrometer configured to receive the beam of charged particles via the projection optics assembly. The spectrometer may include a detector configured to generate detector data in response to the interaction of charged particles in the beam with the detector.

[0009] The system may also include control circuitry operatively coupled to the source, column, and detector sections. This control circuitry may be operatively coupled to one or more machine-readable storage media storing instructions that, when executed by a machine, cause the system to perform one or more operations of the method of the first aspect of one or more embodiments.

[0010] Thirdly, one or more machine-readable storage media store instructions that, when executed by a machine, cause the machine to perform one or more operations of the method of the first aspect in one or more embodiments. In some embodiments, the medium of the third aspect may be operatively coupled to the system of the second aspect. The medium may be operatively coupled to the control circuitry of the system of the second aspect.

[0011] Embodiments of this disclosure also include systems, components, and methods according to the foregoing aspects. The terminology and expressions used herein are descriptive and not restrictive only, and their use is not intended to exclude any equivalents of the shown and described features or portions thereof, but rather to facilitate the understanding that various modifications may be possible within the scope of the claimed subject matter. Therefore, it should be understood that although the claimed subject matter has been clearly disclosed through specific embodiments and optional features, modifications and variations of the concepts disclosed herein can be made by those skilled in the art, and such modifications and variations should be considered to fall within the scope of this disclosure as defined by the appended claims. Attached Figure Description

[0012] The foregoing aspects and many accompanying advantages of this disclosure will become more readily understood when taken in conjunction with the accompanying drawings and the following detailed description.

[0013] Figure 1 This is a schematic diagram illustrating an exemplary charged particle beam system according to some embodiments of the present disclosure.

[0014] Figure 2 These are examples of some embodiments based on this disclosure. Figure 1 A schematic diagram illustrating the operating principle of an exemplary charged particle beam system.

[0015] Figure 3 This is a block diagram illustrating an exemplary process 300 for interrogating a sample using a charged particle beam system, according to some embodiments of the present disclosure.

[0016] Figures 4A-4D This is a schematic diagram illustrating the charged particle optical elements of a charged particle beam system, based on existing technology.

[0017] Figure 4E This is a schematic diagram illustrating charged particle optical elements of a charged particle beam system according to some embodiments of the present disclosure.

[0018] Figure 5A This is a graph illustrating exemplary electron energy loss spectrum (EELS) data for a copper foil sample, according to some embodiments of this disclosure.

[0019] Figure 5B These are examples of some embodiments based on this disclosure. Figure 5A A graph showing details of exemplary electron energy loss spectroscopy (EELS) data comparing a copper sample with EXAFS data.

[0020] Figure 6 Various parameters that can be used to describe the first-order particle optical effects of thick magnetic lenses according to some embodiments of this disclosure are shown.

[0021] In the accompanying drawings, unless otherwise specified, the same reference numerals denote the same parts in each view. Where appropriate, it is not necessary to label all instances of elements to reduce confusion in the drawings. The drawings are not necessarily drawn to scale, but rather focus on illustrating the principles described. Detailed Implementation

[0022] Although embodiments have been shown and described, it should be understood that various changes can be made thereto without departing from the spirit and scope of this disclosure. In the following paragraphs, embodiments of charged particle beam systems, components, and methods for electron energy loss spectroscopy (EELS) are described. For simplicity, embodiments of this disclosure focus on microanalysis of samples using transmission electron microscopy (TEM) systems equipped with EELS. The embodiments are not limited to such systems, but rather envision systems for analysis in which inelastic collisions between charged particle beams and atoms of the sample can be complicated by the internal configuration of the charged particle optics. In an exemplary example, a scanning electron microscope (SEM) system can be used for EELS analysis in scanning-transmission (STEM in SEM) mode. Similarly, systems can be specifically configured for EELS techniques, thus omitting typical components of TEM systems suitable for imaging, X-ray microanalysis, etc. Therefore, while embodiments of this disclosure focus on TEM platforms equipped with systems for generating and processing EELS data, additional and / or alternative systems and methods are contemplated.

[0023] Embodiments of this disclosure include systems, methods, algorithms, and non-transient media for storing computer-readable instructions for electron energy loss spectroscopy (EELS) at relatively high energy losses. In an exemplary example, a charged particle beam system may include a beam column segment comprising one or more charged particle optics calibrated for a first energy and one or more charged particle optics calibrated for a second energy. In a system configured to immerse a sample in an objective field, i.e., a so-called magnetic immersion objective, embodiments of this disclosure include generating a set of operating conditions for resolving offsets in one or more beam crossings of a projection optics assembly, thereby allowing the objective optics assembly to remain calibrated to the energy of the charged particle source while optics positioned downstream of the sample are (re)calibrated for a second energy corresponding to a relatively large inelastic transition (e.g., 2 keV or greater). Advantageously, embodiments of this disclosure improve the performance of energy loss spectroscopy systems when measuring relatively large energy losses while operating with an objective field immersed in the sample, thereby reducing reliance on synchrotron systems for generating comparable data.

[0024] Compared to charged particle microscopy, synchrotron systems are complex, bulky, and non-scalable. The technique presented in this paper allows charged particle beam systems to generate detector data comparable to extended x-ray absorption fine structure (EXAFS) spectra using existing EELS detector systems. As an added advantage, EELS in scanning transmission electron microscopy (STEM) typically provides significantly improved spatial resolution (e.g., approximately 10⁻⁶ Å). 3 (Spatial resolution increased several times over). The improvement in spatial resolution at this scale significantly increases the depth of information that can be obtained from nanostructured samples that can undergo chemical and structural changes on the length scale, which are typically integrated by synchrotron analysis at the μm to mm scale.

[0025] The following detailed description focuses on embodiments of a transmission electron microscope system; however, it is contemplated that additional and / or alternative instrument systems can be improved using the described techniques. Instrument systems may include other charged particle systems, including but not limited to focused ion beam systems, scanning electron microscope systems, ion-electron dual-beam systems, etc.

[0026] Figure 1 This is a schematic diagram illustrating an exemplary charged particle microscopy system 100 according to some embodiments of the present disclosure. In the following description, for simplicity, details of the internal components and functions of the exemplary TEM system 100 are omitted, and the description focuses on embodiments of the present disclosure, as referenced... Figure 2 The following is described in more detail to Figure 5, and focuses on techniques for increasing sample information in the spectrum, including relatively strong background information. An exemplary TEM system 100 includes an electron source segment 101, a TEM column 105 (including a sample segment 107), a probe-forming objective 108, an imaging objective 109, a projection optics system 111, and a detector segment 110. This disclosure focuses on techniques for improving the performance of the detector segment 110, primarily concerning embodiments of this disclosure including one or more electron energy loss spectroscopy (EELS) spectrometers 115.

[0027] In short, the electron source section includes the section configured to excite charged particle source 205 (reference). Figure 2 The electronic device, wherein the charged particle source may include a high-voltage field emission source or other electron emission source, forms an electron beam and conducts it through a vacuum into the TEM column 105. The TEM column 105 includes components for beam formation, including electromagnetic lenses and / or electrostatic lenses, and multiple apertures to control the characteristics of the electron beam. The components of the TEM column 105 include a condenser lens, objective lens, projection lens, aberration corrector, deflector, astigmatism reducer, etc., and corresponding apertures. The sample section 107 accommodates sample 225 (reference). Figure 2An electron beam can be transmitted through the sample. In the case of EELS microanalysis, the beam can be focused onto the sample for point mode analysis (e.g., by the action of probe forming objective 108), or the beam can pass through the sample in parallel illumination mode (or at least partially defocused) to acquire data from a relatively large sample area (e.g., by the action of imaging objective 109).

[0028] In some embodiments, sample segment 107 includes a probe-forming objective 108 and an imaging objective 109 that share the same lens magnetic field, also referred to as the objective field of the objective, to immerse the sample in the magnetic field. Advantageously, setting the sample in the objective field of the objective can provide a resolution of approximately 0.05 nm for STEM mode operation. Herein, immersion in the objective field means setting the sample in the magnetic field of the objective that extends into the space between the sample and the pole pieces of the objective. Such immersion significantly reduces possible aberrations of the objective that would otherwise reduce the spatial resolution of the microscope. As described in more detail with reference to the following figures, configuring objectives 108 and 109 to generate an immersion objective field can constrain the operation of the exemplary system 100 to provide consistent calibration of the objective optics across sample locations. For example, the magnetic mirror field shared by objectives 108 and 109 in an immersion objective system can constrain the calibration (e.g., operating energy) of objective 109 to be dependent on the calibration (e.g., operating energy) of objective 108. In conventional methods, such constraints severely limit the proper transfer of inelastic scattered electrons to the EELS detector. Therefore, embodiments of this disclosure enable EELS technology with relatively large energy losses while operating using an objective field at the sample location.

[0029] In some embodiments, the charged particle beam system 100 operates in a fieldless STEM mode, wherein the objective lens is not used to focus charged particles onto the sample. In some systems, a small condenser lens upstream of the sample can act as a probe-forming lens, and a Lorentz lens downstream of the sample can act as a first imaging lens to provide at least some of the functions of the objective lens. In fieldless STEM mode, detector data can be generated with a spatial resolution of approximately 0.5 nm. While this is an order of magnitude lower than immersion, it still provides significantly improved spatial resolution compared to synchrotron-based techniques.

[0030] State-of-the-art TEM columns can have up to four condenser lenses for flexible (e.g., stepwise or graded) reduction and focusing of the electron beam on the sample, up to five projection lenses for flexible amplification of the electron beam downstream of the sample to the detector, and up to two aberration correctors. Since state-of-the-art aberration correctors can include additional lenses and several multipoles (e.g., four lenses and two to three or more multipoles), modern TEM columns can include up to about twenty lenses. The coordinated operation of the lenses as a whole and other optical elements results in a given reduction at the sample and a given amplification at the detector. Conversely, a lack of coordination leads to aberrations, at least in part, based on an electron beam traveling off-center through one or more optical elements, a beam with an excessively large beam diameter in one or more lenses, or other problems that degrade system performance. In the context of this disclosure, “calibration” and “recalibration” of charged particle optical elements refer to a set of operating parameters for the entire element, setting and verifying excitation parameters to give desired beam properties at the sample (e.g., probe diameter, current, position) and desired beam properties at the detector (e.g., amplification, focal length, position). As those skilled in the art will understand, recalibrating an entire optical system is typically a complex and laborious task, potentially taking experienced engineers days or weeks. Therefore, TEM columns generally offer a limited number (e.g., 2 to 5) of electron beam energies (e.g., 300 keV, 200 keV, 60 keV) for calibration settings, allowing for arbitrary changes to the optical calibration—something virtually impossible in most conventional TEM systems.

[0031] The optical intensity of lenses and multipoles depends on the energy of electrons in the beam, and therefore calibration is specific to electrons with energies equal to or close to those for which the calibration settings have been set and verified. For example, in a TEM operating at a 300 keV beam energy, charged particle optics of a TEM column calibrated for a 300 keV beam introduce minimal in-beam aberrations (e.g., defocus, coma, shift, etc.). However, in this example, electrons with energies deviating by as little as 10 eV (approximately 0.003%) from 300 keV will be focused onto a plane shifted approximately 100 nm from the intended sample plane. In this example, chromatic aberration of the objective lens significantly impairs the spatial resolution of the microscope. Therefore, in typical calibration schemes, each element, or nearly every element, is calibrated for the same energy as the beam energy. For example, reducing and magnifying elements are calibrated for the same beam energy. This method references... Figure 4A Further description was provided.

[0032] The detector section 110 includes one or more types of detectors, sensors, screens, and / or optics configured to generate images, spectra, and other data for use in sample imaging and / or microanalysis. For example, the imaging section may include a scintillator screen, binoculars, a transmission electron microscopy (TEM) detector (e.g., a pixelated electron detector, a secondary electron detector), a camera, and an electron energy loss spectroscopy (EELS) spectrometer 115, etc. The EELS spectrometer 115 acts at least in part as an energy filter by focusing an electron beam onto an electrostatic or magnetic dispersive element (also called a “prism”) that deflects electrons proportionally to their energy. In this way, electrons that have already transferred energy to the sample (e.g., through inelastic collisions) can be redirected through the magnetic dispersive element and toward the detector. The detector may include a pixelated detector (e.g., a CCD device configured to detect electrons) that generates one-dimensional or two-dimensional EELS data from which EELS spectra can be derived. In some embodiments, the EELS spectrometer 115 further includes one or more optical elements, such as electromagnetic or electrostatic lenses and / or multipole and / or accelerators, to modulate the scattered electrons and / or focus the scattered electrons onto the detector.

[0033] Figure 2 This is a schematic diagram illustrating the operating principle of an exemplary charged particle beam system 200 according to some embodiments of the present disclosure. The exemplary system 200 is... Figure 1 An example of a charged particle beam system 100 is provided, and includes a microscope 201 corresponding to a source section, a TEM column 105, a sample section 107, and (in some cases) a portion of a detector section 110 of the charged particle microscope 100. The exemplary system 200 also includes a spectrometer 115, which in the illustrated embodiment is represented by components of an EELS spectrometer. The exemplary system 200 also includes elements of a control system 210 operatively coupled to the microscope 201 and the spectrometer 115.

[0034] Microscope 201 may include a charged particle source 205 configured to generate a beam 215 of charged particles (e.g., electrons or ions) at a first energy E1. A portion of the particles may be scattered by the sample. Scattering events may include inelastic scattering. In electron energy loss spectroscopy (EELS) techniques, an EELS spectrometer 115 may be used to measure the energy of inelastically scattered electrons, thereby deriving the energy loss ΔE associated with the inelastic scattering event. Electrons that have lost energy during the inelastic scattering event travel through the TEM column and through the EELS spectrometer at an energy of E1-ΔE. The magnitude of the deviation from the calibrated energy E1 of the TEM column and the EELS spectrometer affects the effect of the charged particle optics on the electrons, which travel between the sample and the detector 245 of the EELS spectrometer 115. The deviation ΔE from the calibrated energy causes the forces exerted by the charged particle optics to deviate from their corresponding calibrated optical intensities, resulting in impaired imaging performance.

[0035] For example, when ΔE includes a range of energy loss values, multiple imaging planes can be defined by the energy-dependent performance of charged particle optics. While some of the scattered electrons can be focused onto the detector, depending on the system calibration, some electrons may be focused onto the image plane upstream of the detector, downstream of the detector, or far from the spectrometer inlet (e.g., off-axis). In some cases, scattered electrons can be guided to contact the TEM column or the inner surface of the spectrometer, thereby being completely eliminated from the EELS signal.

[0036] For the above calibration scheme, such as Figure 4A As illustrated in more detail, electrons with energies deviating from the calibration energy by up to ΔE / E1 ≈ 2% can typically be detected, provided that the lens setup of the column and the multipole setup in the spectrometer are carefully selected. That is, for values ​​of ΔE greater than approximately 1% of the calibration energy E1 (i.e., ΔE / E1 > ~1%), the aforementioned calibration scheme fails to guide scattered electrons through the charged-particle optics of the TEM column and through the charged-particle optics of the EELS spectrometer without introducing artifacts (e.g., over / under amplification and / or deviation from beam position). Beam amplification and positional deviations result in ineffective collection of scattered electrons by the EELS spectrometer. Furthermore, aberrations that exclude a portion of the scattered electrons from the detector signal impair the usefulness of the recorded EELS spectra for accurately and reliably quantifying the elemental composition of the sample. The greater the beam energy deviation, the more significant these challenges become.

[0037] In some embodiments of this disclosure, electrons with a deviation from the beam energy (E1) equal to or greater than about 1% (e.g., ΔE / E1 ≥ ~1%) can be effectively collected by employing a calibration scheme different from the one described above. In the calibration scheme described above, a second calibration energy E2 is used for one or more charged particle optical elements downstream of the sample. Furthermore, the calibration scheme may include using one or more projection optics (e.g., Figure 1 The projection optics system 111 is configured to maintain one or more constraints on the optical arrangement (e.g., focal plane position, cross position, etc.) while immersing the sample in the objective field, such as a reference. Figures 4A-4D It is described in more detail in the text.

[0038] Typically, according to this disclosure, one or more charged particle optical elements 220 are calibrated for a first energy E1 and one or more charged particle optical elements 230 are calibrated for a second energy E2. In some embodiments, the optical elements 220 calibrated for the first energy E1 are located in a sample section (e.g., Figure 1 Upstream of sample 225 in sample segment 107), indicating the magnetic immersion objective (e.g., Figure 1 Optical elements 221 and 223 of the objectives 108 and 109 are also calibrated for a first energy E1, and optical element 230, calibrated for a second energy E2, is located downstream of the sample 225. The first energy E1 and the second energy E2 can be different; for example, E1 can be greater than E2. Electrons upstream of the sample that lose energy (ΔE) through scattering and have an energy of approximately the first energy E1 will have an energy of approximately E1-ΔE downstream of the sample. For this purpose, E2 can be selected such that E2 is equal to approximately E1-ΔE. In some embodiments, E2 can be determined using an absolute value expression: |(ΔE+E2-E1) / E2|≤approximately A, where A is a value of approximately 1% to approximately 10%, including its subrange, fraction, and interpolation. For example, A can be equal to approximately 1%, approximately 2%, approximately 3%, approximately 4%, approximately 5%, approximately 6%, approximately 7%, approximately 8%, approximately 9%, or approximately 10%, etc.

[0039] exist Figures 3-6In exemplary examples, the difference between E1 and E2 can be from about 2 keV to about 50 keV, including its subranges, fractions, and interpolations. For example, the difference between E1 and E2 can be from about 2 keV to about 35 keV, from about 2 keV to about 10 keV, about 10 keV, about 20 keV, about 30 keV, etc. The energies E1 and E2 can be from about 50 keV to about 500 keV, including their subranges, fractions, and interpolations. In exemplary examples, E1 can be about 300 keV, and E2 can be from about 270 keV to about 295 keV, including its subranges, fractions, and interpolations (e.g., about 290 keV). In another example, E1 can be about 310 keV and E2 can be about 300 keV. In yet another example, E1 can be about 200 keV and E2 can be about 190 keV. The cross-section for a given excitation (e.g., inner-shell ionization) can depend at least in part on ΔE. Therefore, for ΔE values ​​outside the said range, high energy loss data can be dominated by noise, at least in part based on the relatively low probability of charged particles inducing a given excitation.

[0040] The difference between a first energy and a second energy can depend at least in part on the value of the first energy. For example, the second energy can be a portion of the first energy. In some embodiments, the second energy can be about 60% to about 99% of the first energy, including its subranges, fractions, and interpolations. In an exemplary example, the second energy can be about 90% to about 98.5% of the first energy. The difference between the first energy and the second energy can be chosen to be equal to or approximately equal to the energy loss to be recorded by an EELS spectrometer. The technique described herein allows charged particle microscopy to interrogate energy ranges corresponding to relatively high energy losses, where a large difference between E1 and E2 will produce detector data (e.g., extended energy loss fine structure or EXELFS) corresponding to the excitation energy of a scattering event approximately equal to that difference. In this way, a difference of about 10 keV can provide detector data for scattering events with excitation energies of about 10 keV.

[0041] In EXELFS, the fine structure of the energy dependence of the probability of core-shell excitations is investigated. The total number of electrons N- that undergo energy loss due to core-shell excitations is... 总 It is approximately proportional to a power of -1.5 of the energy loss, i.e., N- 总 ∝ΔE -1.5 In this way, the number of scattered electrons can be distributed across the energy range ΔE. 尾部 The upper (referred to as the "tail of the edge") and the range of scattered energy Above (referred to as "scattering distribution"). The range of scattering angles is approximately equal to... When these expressions are combined, it is possible to estimate dE in a specific energy range and at a specific solid angle. The number of electrons lost in the electron pool is proportional to the energy loss, as described in the following expression:

[0042]

[0043] This estimate shows that the EXELFS signal in an EELS spectrometer decreases rapidly with increasing energy loss. For example, to achieve the same number of counts (and therefore the same statistics) in the EXELFS region (100 eV wide) at the edge of the K-shell in titanium (5.0 keV), copper (9.0 keV), molybdenum (ΔE = 20 keV), and antimony (ΔE = 30.5 keV), the beam doses involved are scaled at a ratio of 1:8:128:560. In this way, the collection solid angle of the EELS spectrometer can largely determine the performance of the TEM system when measuring EXELFS spectra. Advantageously, the collection solid angle is significantly improved when the TEM column is calibrated according to the expression |(ΔE + E2 - E1) / E2| < ~2% to better collect scattered electrons. In this way, the calibration process of this disclosure may include measuring the collection angle and centering the beam relative to the EELS spectrometer. Noise can become more significant at larger values ​​of the difference between E1 and E2 relative to edge locations or edge structures, exceeding approximately ΔE = 30 = keV, and the integration time and total electron dose can be limited by, for example, sample sensitivity.

[0044] Spectrometer 115 may include charged particle optical elements, such as dispersive element 235 and one or more electromagnetic and / or electrostatic elements 240 (e.g., lenses, accelerators, quadrupoles, hexapoles, octapoles, etc.). Dispersive element 235 may include one or more magnetic and / or electrostatic dispersive elements (also referred to as "prisms"). Spectrometer 115 may be post-column (e.g., Figure 2 (Located after the TEM column) or it can be inside the column, operatively coupled to the TEM column. Elements 235 and 240 can be calibrated for a second energy E2. Regarding dispersive element 235, calibration for the second energy E2 refers to the operation of dispersive element 235 to disperse charged particles (e.g., electrons) having energies deviating from E2 by no more than about 2% of E2. In this way, charged particles with energies of about E2 can be transmitted to element 240 and subsequently directed to detector 245 of spectrometer 115. In some embodiments, element 240 also focuses the charged particles onto detector 245.

[0045] Other components of system 200 can be used to attenuate, redirect, absorb, or otherwise exclude unscattered charged particles 250 or weakly scattered charged particles 255 (e.g., electrons that pass through sample 225 without scattering) from detector data. For example, element 230 can apply a force (e.g., magnetic force) proportional to the electron's velocity, which will redirect electrons with an energy of about E1 away from the beam axis and into the absorbing material or other surfaces inside microscope 201.

[0046] Detector 245 can generate detector data. (See reference...) Figures 3-6 In a more detailed description, detector data may include EELS spectra generated by the interaction between the charged particle beam 215 and the atoms 227 of the sample 225. For example, with the microscope 201 operating in STEM mode (e.g., STEM in scanning TEM or SEM) and the sample 225 thinned to allow beam transmission, the electron beam can be focused onto a point in the sample 225 that allows for the measurement of individual atoms or groups of atoms at the nanoscale. (See reference...) Figures 5A-5B In more detail, the interactions between adjacent atoms 227 can introduce fine structure into the detector data. In this way, the detector data can be used to derive chemical, physical, and / or structural information (e.g., oxidation state, coordination information, etc.) about atoms 227. Advantageously, embodiments of this disclosure combine fine structure information with spatial localization, which is unavailable in typical synchrotron systems used to generate comparable detector data. In a TEM operating in STEM mode, atomic-scale resolution can be obtained by focusing the charged particle beam 215, thereby allowing the system 200 to generate nanoscale mappings of the material properties of sample 225.

[0047] The control system 210 may include one or more machines (e.g., computing devices) operatively coupled to control circuitry disposed in the microscope 201 and / or spectrometer 115. In an exemplary example, the control circuitry may include an arrangement of circuit components connected to a power source and configured to control the application of power (e.g., voltage and / or current) to sources, elements 220, 230, 235, 240, and / or detector 245. In this way, the process of calibrating and / or recalibrating elements 220, 230, 235, 240, and / or detector 245 can be coordinated by the control system 210 according to one or more operations encoded in machine-executable instructions stored on one or more machine-readable storage media (e.g., local storage media, distributed “cloud” storage media, etc.). The one or more machines may include, but are not limited to, personal computers, laptop computers, tablet computers, servers, dedicated machines (ASMs), etc. In some embodiments, the control system 210 includes user-interactive elements such as a display and input peripherals (e.g., a mouse and keyboard), which a user can refer to... Figure 3 The described operations reversibly implement a high-energy-loss EELS mode through these user-interactive elements. In an exemplary example, a user can select an interactive graphical element 211 on a user interface (e.g., in an application, browser environment, etc.) that initiates a high-energy-loss EELS mode. To return system 200 to its previous state, the user can select interactive graphical element 211, which initiates the calibration of elements 220, 230, 235, and / or 240 from E1 or E2 back to a previously calibrated energy (e.g., a first energy E1, a second energy E2, or a third energy E3).

[0048] Therefore, the process of this disclosure (e.g., Figure 3 The exemplary process 300 may include operations for receiving user interaction data (e.g., via an interactive user interface), wherein the interaction data corresponds to a user-initiated or reversed recalibration action of one or more elements of the charged particle beam system. Similarly, the processes of this disclosure may include generating user interface data configured to modify (e.g., control system 210) a display to present an interactive user interface.

[0049] In some embodiments, the control system 210 is configured to communicate with one or more data repositories and / or machine-readable media storing instructions that encode one or more algorithms for at least a subset of optical devices in a column (e.g., Figure 1 The TEM column 105 generates a set of operating conditions. See reference... Figure 3 and Figure 6In more detail, the control system 210 can be configured to generate and / or implement a set of operating conditions such that at least a subset of optics disposed downstream of sample 225 can be calibrated for a second energy E2, and optics disposed downstream of sample 225 can be calibrated for a first energy E1. Advantageously, the techniques of this disclosure allow for the calibration of one or more optics downstream of the sample for a first energy E1, such as imaging objectives 223 (e.g., Figure 1 (Objective 109). In this way, a charged particle beam system equipped with a magnetic immersion objective (as is typical for TEM instruments in a STEM configuration) can maintain a common calibration scheme for the condenser lens 221 and imaging objective 223 (e.g., calibration for a first energy E1). In some embodiments, the control system 210 may be configured to generate the set of operating conditions by communicating with a physically remote computing system (e.g., a distributed computing system) and / or to execute one or more algorithms locally, at least in part, based on the computing and / or network resources available to the control system 210.

[0050] Figure 3 This is a block diagram illustrating an exemplary process 300 for interrogating a sample using a charged particle beam system, according to some embodiments of the present disclosure. One or more operations of the exemplary process 300 may be performed by a computer system communicating with additional systems, including but not limited to characterization systems, network infrastructure, databases, and user interface devices. In some embodiments, reference is made to... Figure 3At least a subset of the described operations are either automatically performed (e.g., without human intervention) or pseudo-automatically performed (e.g., initiated by a human or with limited human intervention). In an illustrative example, the operations for generating and shaping the electron beam can be automatically performed, where the TEM system 100 is configured to maintain the properties of the electron beam at or near a setpoint that can be specified by a human user. In another illustrative example, a human user can use the techniques described herein to initiate an EELS mode by activating a subsystem of the charged particle microscope 100 (e.g., an interactive user environment presented via a user terminal, such as a browser or software application, and / or a button-type control panel), which can initiate a recalibration of the charged particle microscope 100 from an imaging mode or a conventional EELS mode (i.e., all elements are calibrated for the same energy) to a high-loss mode (i.e., some elements are calibrated for energy E1, and others for energy E2). Therefore, while the exemplary process 300 is described as a sequence of operations, it should be understood that at least some of these operations can be omitted, repeated, and / or reordered. In some embodiments, additional operations precede and / or follow the operations of exemplary process 300, and these operations are omitted for clarity of explanation. Examples include operations such as calibration of the electron source, electron beam coherence and aberration correction, sample loading into the sample position, balancing the vacuum system, etc. Advantageously, embodiments of this disclosure maintain the spatial resolution of charged particle beam systems operating in scanning mode (e.g., STEM mode of a TEM instrument), where the sample is immersed in the objective field. Furthermore, implementing algorithmic tuning of the projection optics to compensate for objective field effects allows the methods of this disclosure to be at least partially automated, thereby significantly reducing the complexity of implementing high-loss EELS modes. Finally, exemplary process 300 significantly improves the energy resolution of EELS data with energy losses greater than about 1% of the beam energy and resolves most (if not all) of the artifacts found in measuring such data in typical STEM modes, enabling fine structure analysis (EXELFS), which is typically performed using synchrotron instruments.

[0051] At operation 305, exemplary process 300 includes reducing the pressure applied to the charged particle source (e.g., Figure 1 Charged particle source 103 Figure 2 The high tension of the charged particle source 205. In this paper, "high tension" (or simply "tension") may refer to the accelerating voltage or describe the voltage emitted from the source to the column (e.g., Figure 1 Other operating parameters for the energy of charged particles in the TEM column 105. For example, the energy E of the electron beam is described by the accelerating voltage V to E = e·V, where e is the electron charge. In this way, as in reference Figure 2As described, operation 305 may include modifying the operating voltage of the charged particle source from a first energy E1 to a second energy E2. In some embodiments, operation 305 includes reducing the tension from 300 kV by a ratio of about 1% to about 20%, including its subrange, fraction, and interpolation. The degree of tension modification may correspond to the energy loss to be inquired. For example, in reference... Figures 5A-5B In the described embodiment, the accelerating voltage of the electron source is reduced by approximately 9 kV, corresponding to the characteristic edge of the inner-shell ionization of copper atoms (the Cu k-edge at 8987.96 eV). Similarly, as part of exemplary process 300, the element of interest in a material sample can be analyzed by modifying the value of the characteristic energy corresponding to a given inelastic transition of that element by adjusting the tension. Furthermore, operation 305 can be repeated for multiple energy values ​​as part of an iterative method to improve the energy resolution and signal-to-noise ratio characteristics of EELS detector data. Advantageously, this method improves the resolution of fine structures in EELS data for relatively large energy loss values ​​(e.g., greater than approximately 1 keV).

[0052] At operation 310, exemplary process 300 includes calibrating and / or recalibrating one or more charged particle optical elements. Figure 2 Elements 220, 230, 235, and 240 are examples of charged particle optical elements of operation 310. Typically, calibration and recalibration may include one or more sub-operations, including modifying the electrical parameters of the element to bring the element to a set of operating conditions, such as the amplification and position of the charged particle beam at an EELS spectrometer, or the amplification and width of the dispersed charged particle beam at a detector. In the context of this disclosure, operation 310 may include changing the calibration energy of the element from a first energy (e.g., ...). Figure 2 The E1) is shifted to the second energy (e.g., Figure 2 The same or similar sub-operations are applied to the charged particle optics at E2. In this way, operation 310 may include recalibrating element 220 for higher energies, recalibrating elements 230, 235, and 240 for lower energies, or both. In this document, the term "calibration energy" refers to a set of operating parameters that, as part of defining one or more beam crossings at a position on the beam axis of the column, configure the charged particle optics to operate at an energy equal to or approximately equal to the calibration energy in a charged particle beam (e.g., E2). Figure 2 Apply an appropriate force to the charged particle beam 215, as referenced Figures 4A-4ETo describe in more detail. Because electrostatic elements can exert a refractive effect inversely proportional to the energy of the beam (ignoring relativistic effects) and magnetic elements can exert a refractive effect inversely proportional to the square root of the energy (ignoring relativistic effects), miscalibrated elements can exhibit impaired performance for a given beam energy. In an exemplary example where the optical element is a condenser lens, when the lens is miscalibrated by as little as 10 eV, the electron beam can be under-focused or over-focused by about 100 nanometers.

[0053] At operation 310, the calibration shift from a first energy (e.g., E1) to a second energy (e.g., E2) can be performed using the energy scaling behavior of charged particle optical elements. For example, a magnetic multipole element can be recalibrated from energy E1 to energy E2 by applying its known calibration scaling factor √(E1 / E2) (ignoring relativistic effects) at E1. As part of such scaling of the calibration, the magnetic element can be operated, configured, or otherwise adjusted to be substantially free of magnetic saturation and hysteresis. Scaling can also be applied to beam deflectors and beam astigmatism cancellers, where the mechanical alignment of the optical elements can be improved in this way.

[0054] In standard EELS mode, optical elements 220, 230, 235, and 240 (e.g., approximately 300 keV) can be calibrated for the first beam energy (e.g., approximately 300 keV) generated by the charged particle source 205. Figure 4A (As shown). Conversely, exemplary process 300 can improve the resolution of EELS data with relatively high energy loss by (re)calibrating additional and / or alternative optical components and by operating at least one subset of optical elements 220, 230, 235, and 240 under calibration parameters for a first energy E1 and under a second subset of approximately a second energy E2. In some embodiments, as part of operation 310, one or more components of the projection optics assembly (e.g., Figure 1 (Projector optics 111). In one example, the projector optics may include a diffraction lens, an intermediate lens, and two projector lenses. For this purpose, an exemplary process may include modifying one or more elements of the projector optics assembly at operation 315 to calibrate the assembly for a second energy E2. The result of the modification (e.g., as a combined effect of multiple changes to the operating parameters of multiple optics) can be used to compensate for changes in the charged particle beam caused by calibrating the charged particle optics (e.g., optics of a spectrometer) for the second energy. This results in different energy losses relative to the zero-loss peak (ZLP) energy of the source. The impact of optical element calibration on the optical beam path in an exemplary TEM system is referenced. Figures 4A-4D A more detailed description was provided.

[0055] Operation 315 may include one or more sub-operations for generating a set of operating conditions for the projection optics system. Generating the set of operating conditions may include determining a first-order approximation solution for the projection optics assembly, as referenced... Figure 6 A more detailed description. For example... Figure 4D As shown, this solution allows the projection optics to be configured to define one or more beam crossings that substantially coincide with corresponding positions for operating a charged particle microscope at an accelerating voltage of approximately a first energy, such as... Figure 4A As shown. Advantageously, the set of operating conditions generated in operation 315 allows the projection optics to compensate for the effect of maintaining the objective lens assembly at the first energy, including the objective lens positioned downstream of the sample location (e.g., Figure 1 Imaging objective 109, Figure 2 Imaging objective 223), otherwise it will cause the position of one or more beam crossings to shift, such as Figure 4C As shown, this adversely affects the resolution of the downstream detector of the sample.

[0056] In some embodiments, operation 315 may be implemented as an algorithm at least partially encoded in software or other programming logic. For example, the dataset of operating conditions for a projection optics system may be structured as a lookup table or other data repository. This dataset may describe multiple sets of operating conditions for a projection component associated with one or more accelerating voltages. In this way, determining the solution may include referencing the dataset of operating conditions for a charged particle beam system using a second energy as an input parameter. In some embodiments, determining the solution includes solving a mathematical expression describing a first-order approximation of the projection lens assembly system. (See reference...) Figure 6 In more detail, solving mathematical expressions may include implementing one or more computational techniques to solve the coupled system of optical equations.

[0057] In some cases, a first-order approximation of a projection optics component can have multiple solutions, one or more of which may be relatively more physically meaningful. As an example, an arithmetically correct solution can define a beam path that intersects with the physical constraints of a charged particle beam system. Therefore, generating this set of operating conditions may include defining physically meaningful solutions.

[0058] At operation 320, exemplary process 300 includes one or more condenser optics for focusing a charged particle beam system. The charged particle beam system may include one or more optics configured to act as a condenser lens with respect to imparting a refractive effect to the charged particle beam. Herein, the condenser optics apply an electromagnetic force to the charged particle beam, causing the diverging beam to become parallel or converged. The focusing condenser lens may include modifying one or more operating parameters of the condenser optics such that the charged particle beam of second energy E2 approaches the probe forming optics (e.g.,Figure 1 Condenser objective lens 108, Figure 2 The condenser lens 221 is positioned substantially parallel to or converges to the beam axis. In this way, the probe forming optics can be configured to focus a beam of charged particles with a second energy E2 onto the sample location. Focusing the charged particle beam onto the sample location can correspond to a fine focal point with a spatial resolution of about 0.5 nm or less, including its fraction (e.g., about 0.1 nm or less, of which about 0.05 nm, etc.). Advantageously, based at least in part on the compensating effect of the modifications made to the projection optics in operation 315, the exemplary process 300 can be relatively robust to the specific operating parameters of the condenser optics.

[0059] At operation 325, exemplary process 300 includes a focused EELS spectrometer (e.g., Figure 1 and Figure 2 The spectrometer 115 contains one or more charged particle optical elements. In this document, focusing may include modifying elements (e.g., Figure 2 One or more operating parameters of elements 235 and / or 240) such that the charged particle beam can be defined to cross at a position on the spectrometer axis, such that the charged particle beam will strike the detector (e.g., Figure 2 The detector 245 is simultaneously dispersed by energy along the spatial direction, as in the reference. Figure 2 As described.

[0060] At operation 330, exemplary process 300 includes modifying the tension of the charged particle source. For reference... Figure 2 and Figure 4E As part of the described operational arrangement, a subset of elements of the charged particle beam system are configured for a charged particle beam at approximately E1, and a second subset of these elements are configured with energy E2. The combined effect of these two configurations is that the charged particles at approximately E2 define one or more intersections at appropriate locations for detectors, apertures, etc., as... Figures 4A-4E As described. For this purpose, the charged particle source can be modified from the tension setting defined in operation 305 to a first energy E1. In some embodiments, exemplary process 300 includes modifying the calibration of the condenser optics from a second energy E2 to the first energy E1. Recalibration of the condenser optics can be performed simultaneously with operation 330.

[0061] At operation 335, exemplary process 300 includes generating detector data. The detector data may include EELS data, which is generated by passing an electron beam (e.g., Figure 2 The charged particle beam 215) is coupled to the EELS spectrometer (e.g., Figure 1The electron beam is generated in the EELS spectrometer 115. For this purpose, operation 335 may include generating a beam of charged particles. In the example of transmission electron microscopy (TEM), operation 335 may include activating an electron emitter (e.g., according to a set of parameters) based on a set of parameters. Figure 2 The charged particle source 205 in the system, this set of parameters will cause a charged particle beam with an energy of approximately a first energy to be guided through the sample location and toward the detector section of the charged particle beam system (e.g., Figure 1 (Detector section 110). In some embodiments, operation 335 includes generating a beam of charged particles with an energy of about 300 keV, or about 200 keV, or about 60 keV.

[0062] The result of operation 305 could be that a portion of an electron beam with an energy of approximately a second energy is directed toward the detector (e.g., Figure 2 The electron beam, guided by detector 245 and scattered by an energy different from the second energy (greater than about 0.02·E2), passes through a microscope (e.g., Figure 1 TEM column 105 and Figure 2 The microscope 201) or a component of the spectrometer (e.g., energy dispersive filter 235) may block or otherwise defocus or otherwise redirect away from the detector 245.

[0063] In some embodiments, one or more operations of exemplary process 300 may be repeated in one or more iterations as part of generating an EELS spectral dataset for a given sample or multiple samples. For example, for a given first energy value, operations 305 to 315 may be repeated within a range of second energy values. In this way, the difference between the first and second energies may vary within a range, for example, as part of characterizing the sample to detect and identify elements present in the sample (e.g., by measuring the inner shell ionization edge in EELS data at multiple energies). In another example, operation 315 may be repeated at multiple points on the sample surface as part of generating an EELS data cube that maps the chemical and / or physical data of the sample. In this document, "data cube" refers to a hierarchical data structure in which EELS data is referenced to one or more pixels of an image of the sample surface as part of "mapping" the sample surface (e.g., having elemental information).

[0064] Advantageously, the presence of fine structures in EELS data generated using the techniques described herein allows for the derivation of local structural information, for example, by fitting one or more models to detector data from which bonding information, oxidation states, or other physical and / or chemical properties of the sample can be inferred. Simulation models used for extended X-ray absorption fine structure (EXAFS) analysis can be used to determine interatomic spacing (e.g., using an EXELFS model), oxidation states, band structure, and / or coordination information (e.g., crystal structure, bonding, etc.). Since the spatial resolution of an EELS system in STEM mode can be on the order of a single atom, EELS data generated using exemplary procedure 300 can be used to map chemical, physical, and / or structural information over regions of the sample surface.

[0065] Figures 4A-4E This is a schematic diagram of an exemplary optical system 400 of a charged particle beam system according to the prior art. Figures 4A-4E The optical arrangement includes a condenser system 405 consisting of one or more condenser optics 410, a beam-limiting stop 415, a probe-forming objective 420, an imaging objective 425, and a projection optics assembly 440 including one or more projection optics 445. The components of the exemplary optical system 400 can be configured according to corresponding operating parameters that collectively shape, form, and / or modify a charged particle beam such that the beam defines one or more crosses along the beam axis B, including objective crosses, imaging crosses, and / or final crosses. A cross can be a real cross, corresponding to a position on the beam axis B where the beam converges to a point or line (e.g., where the focal point is located where the particle beam is actually focused), or a virtual cross, corresponding to a position on the beam axis B where the beam converges to a point or line, and where the optics now act (e.g., behind or in front of a lens that refocuses the beam before a true cross occurs). One or more constraints of the charged particle beam system may define a set of planes along the beam axis B, including the specimen plane 421, the back focal plane (BFP) 430, the first image plane (FIP) 435, the final crossover (FXO) plane 450, and the detector plane 455.

[0066] The configuration of the various components of the exemplary system 400 may be at least partially limited by the operating mode of the charged particle beam system. For example, in STEM mode, the projection optics assembly 440 and the projection lens 445 may be modified to satisfy a set of operating parameters that meet the following four boundary conditions: FIP 435 images to FXO 450, thereby allowing FXO 450 to function as a spectrometer (e.g., Figure 1 The input image of the spectrometer 115; the BFP 430 image onto the detector plane 455; the camera length or magnification (M) at the detector. 投影The image orientation at detector plane 455 satisfies a given value (e.g., 40 mm); and the image orientation at detector plane 455 satisfies a given value (e.g., 180°). Reference Figures 4A-4D The different sets of conditions described illustrate different methods for operating charged particle beam systems in STEM mode. Therefore, according to embodiments of this disclosure, Figure 4A A typical STEM configuration is illustrated. Figure 4B An exemplary configuration of energy loss spectrum with relatively large energy loss is illustrated in fieldless mode or under inconsistent calibration of objective optics. Figure 4C The operation in immersion mode is illustrated (keeping the objectives 420 and 425 aligned on both sides of the specimen plane 421), and Figure 4D An improvement to the immersion mode is illustrated for generating a set of operating conditions for projection optics. Figures 4A-4D In the diagram, the filling patterns within the lens ellipses represent the calibration states, where two lenses with a common filling pattern are calibrated for substantially equal beam energies. In the illustrative example, Figure 4C The condenser system 405 is calibrated for the first energy E1 and filled with the first fill pattern, while the projection optics assembly 440 is calibrated for the second energy E2 and filled with the second fill pattern.

[0067] Figure 4A The conditions for consistent calibration of optical elements under source tension (e.g., 300 kV) are illustrated. Solid rays represent the trajectory forming the probe, defining the first intersection at specimen plane 421, the second intersection at first imaging plane (FIP) 435, and the final intersection (FXO) 450 between projection optics assembly 440 and detector plane 455. Dashed lines represent the scan trajectory in STEM mode, defining the first intersection at back focal plane (BFP) 430 and the second intersection at detector plane 455. (See reference...) Figure 2 The EELS data is limited to about 1% of the beam energy in this configuration, at least in part based on the fact that aberrations increase significantly with increasing energy loss and that the signal-to-noise ratio decreases with increasing energy loss.

[0068] Figure 4BAn operational configuration for generating large energy loss (XEELS) data is shown, where the calibrations between objectives are inconsistent. In this configuration, the optics upstream of the specimen plane 421 (e.g., condenser system 405, probe-forming objective 420) are calibrated for a first energy E1, and the optics downstream of the specimen plane 421 (e.g., projection optics assembly 440, imaging objective 425, etc.) are calibrated for the energy reflecting the energy loss of interest (e.g., applying a 10 kV energy loss to the first energy E1 of 300 kV provides a second energy E2 of 290 kV). Advantageously, this configuration provides the transfer of charged particles to the sample plane 421 without addressing the individualized adjustments of the constituent lenses 405 of the illumination optics systems 405 and 420. In this way, in a charged particle beam system, in terms of time and complexity, Figure 4B The method shown may be successful and advantageous, where the objective system can be calibrated for different beam energies, such as in non-immersion mode. However, for magnetic immersion objectives, objectives 420 and 425 are limited to consistent calibration energy conditions in immersion mode (and in some cases, including spherical aberration correctors). Therefore, although probe-forming objective 420 is positioned upstream of specimen plane 421, probe-forming objective 420 must be calibrated for a second energy. Thus, the operating configuration in 4B cannot be applied to immersion mode.

[0069] Figure 4C An operational configuration for generating large energy loss (XEELS) data in immersion mode is illustrated. In this configuration, the optics downstream of the specimen plane 421 (e.g., projection optics assembly 440, specimen objective 425) are calibrated for the energy reflecting the energy loss of interest (e.g., applying a 10 kV energy loss to a first energy E1 of 300 kV provides a second energy E2 of 290 kV). Advantageously, this configuration provides the transfer of charged particles to the detector plane 455 without addressing the individualized adjustments of the constituent lenses 445 of the projection optics system 440. However, the probe-forming objective 420 is restricted to calibration at the same second energy E2. Since the calibration of lens 420 (at energy E2) is no longer matched to the beam energy E1 of lens 420, the condenser assembly 405 and the objective assembly (including several deflectors and astigmatism correctors (not shown in Figure 4) and objective 420) are returned to achieve atomic resolution (e.g., subangloft) for electron microscopy.

[0070] Such recalibration of the condenser and objective assemblies can be very time-consuming. Furthermore, some charged particle beam systems may include a probe-forming objective 420 whose operating window does not include a set of parameters that allow it to be calibrated for a second energy E2. In this case, one or more condenser optics 410 may be modified to accommodate the limitations imposed by the probe-forming objective 420. Such manual recalibration can involve complex techniques and be time-consuming, especially when generating and scaling large amounts of energy loss EELS (“XEELS”) data across multiple energy differences.

[0071] Figure 4D An example of a configuration reflecting the consequences of maintaining an objective lens calibrated for the first energy E1 is illustrated (e.g., a specimen objective 425 calibrated for the first energy E1, although it is positioned downstream of the specimen plane 421). In this configuration, the specimen objective 425 is too strong for charged particles at the second energy E2. Overfocusing of the specimen objective 425 causes the cross at FIP ​​435 and BFP 430 to shift upstream toward the specimen plane 421. The projection optics assembly 440 calibrated for the second energy E2 does not return the final cross (FXO) 450 and detector plane 455 to the position relative to M. 投影 The offset corresponds to the position of the limit. Typically, such offsets are relatively large (several millimeters or more for the FXO 450) and cause significant signal loss and resolution degradation in the EELS. Furthermore, correcting the offset involves recalculating the projector lens settings, a technically difficult, time-consuming, and highly human-intensive operation.

[0072] Figure 4E This is a schematic diagram illustrating charged particle optical elements of a charged particle beam system according to some embodiments of the present disclosure. Figure 4E Objectives 420 and 425 are shown with consistent calibration operations to immerse the sample plane 421 in the objective field (e.g., calibrating both the upper and lower objectives for a first energy E1). The result of this method is that imaging objective 425 is improperly calibrated for charged particles at a second energy E2, significantly offsetting the position of the first image plane (FIP) 435. Figure 4D The configuration shown is such that the second energy E2 is less than the first energy E1, causing FIP 435 to shift towards specimen plane 421. Figure 4E As indicated by the vertical arrows in the diagram, embodiments of this disclosure address these transformations at least in part by recalibrating the projector system 440, as shown in reference [reference]. Figure 3 and Figure 6 This is described in more detail below. One advantage of this method is that it does not affect STEM resolution and reduces artifacts in XEELS data. The objective field can be maintained for a first energy (e.g., 300 kV), and the projection optics assembly 440 can be recalibrated to accommodate XO shifts at BFP and FIP.

[0073] In the illustrative example where the number of projector lenses 445 matches the number of boundary conditions, one or more results are possible (e.g., the problem is fully defined). However, finding a suitable result that satisfies the system boundary conditions is by no means easy, as the problem is highly nonlinear. Furthermore, the result should minimize higher-order aberrations and prevent the beam from striking the inner surfaces of the optical system (e.g., Figure 1 TEM column 105).

[0074] In existing technologies, generating a single magnification setting that satisfies the boundary conditions can take several hours (calculation and testing), and a series of satisfactory magnification settings can take weeks. At least for these reasons, magnification settings are typically pre-calculated, pre-tested, and pre-stored in magnification tables. This severely limits the flexibility of STEM systems in responding to user-inputted energy loss data (e.g., energy difference, second energy E2, etc.), making it impossible to obtain a pre-calibrated set of operating conditions. To address this, the technique disclosed herein applies first-order transfer optics, a parameterized thick lens model, and a solution algorithm to generate a set of operating conditions (e.g., projection lens settings) that satisfy the aforementioned boundary conditions (e.g., attenuation of aberrations and impacts on the inner surface). In this way, the time to generate a new magnification setting is reduced from hours to fractions of a second.

[0075] Figure 5A This is a graph of exemplary electron energy loss spectrum (EELS) data 500 for an illustrative copper foil sample according to some embodiments of this disclosure. The graph includes data on the ionization of the inner shell, represented as an edge centered at approximately 9 keV, comprising a fine structure. The graph plots the data 500 on a set of two-dimensional axes, with energies ranging from approximately 8.0 keV to approximately 10.0 keV on the ordinate and counts on the abscissa in arbitrary units (AU). Figure 5B As described in detail, in the exemplary data shown, EELS data 500 reproduces the location of features of fine structures present in EXAFS data.

[0076] In contrast, current techniques for measuring EELS data under similar high energy loss typically result in significant signal-to-noise ratio limitations due to miscalibration of the solid angle collected by the EELS spectrometer (leading to insufficient collection angle) and aberrations introduced in the TEM column and EELS spectrometer that negatively impact data quality such as energy resolution. According to the techniques described herein, such miscalibration and aberrations are significantly reduced or eliminated, providing a significant improvement in both the signal-to-noise ratio of the detector data and the energy resolution, which together greatly facilitate EXELFS analysis.

[0077] Figure 5B These are examples of some embodiments based on this disclosure. Figure 5A A graph showing the details of exemplary electron energy loss spectroscopy (EELS) data 510 superimposed on EXAFS data 515 for a copper sample. Data 510 presents the EELS spectrum of the copper edge at approximately 9 keV and shows magnified details of the fine structures present within approximately 0.3 keV at the edge location. Data 510 was obtained over 900 seconds with a beam current of 2.3 nA, corresponding to a dose of approximately 2.1 μC. Data 510 illustrates the energy loss values ​​used to further illustrate the solutions addressed by embodiments of this disclosure. The count values ​​presented on the horizontal axis illustrate the improvement in signal-to-noise ratio at relatively high energy loss edges, thereby enhancing… Figure 5A The demonstration includes a fine structure from which physical structure information can be derived. Furthermore, the improved resolution of the fine structure further demonstrates the advantages of this disclosure. In the exemplary data shown, EELS data 410 reproduces the locations of the fine structure features present in EXAFS data 515.

[0078] Figure 6 Various parameters that can be used to describe the first-order particle optical effects of thick magnetic lenses according to some embodiments of this disclosure are shown. Figure 6 This is a schematic diagram of electron rays B1, B2, and the optical axis B. As shown, various parameters are defined to provide a first-order description of the thick magnetic lens. Electron ray B1 enters the lens from the top (forward direction) and is parallel to the optical axis B'. This ray is refracted at the principal plane Zpi and intersects the optical axis B' at the focal plane Zfi. The distance between Zpi and Zfi is defined as the focal length fi. Electron ray B2 enters the lens from the bottom (backward direction) and is parallel to the optical axis B'. This ray is refracted at the principal plane Zpo and intersects the optical axis B' at the focal plane Zfo. If the potential along the optical axis B' is constant, then fo = fi. Figure 6 In the diagram, Z0 represents the geometric center of the thick lens.

[0079] The lensing effect between the two principal planes Zpi and Zpo can be described by the following matrix equation:

[0080] Where x and x' represent the distance from the ray to the optical axis B' and the angle between the ray and the optical axis B', respectively. Note that this equation describes the lensing effect from the objective principal plane of the lens to the imaging principal plane, i.e., the distance from the ray to the optical axis B'. Figure 6 The light emitted from the top of the lens first moves to the Zpo plane, which is actually the entry point into the lens, and then leaves the lens at the Zpi plane. The unit magnification and refraction angle are -x / fi.

[0081] In three dimensions, the vector (x, x′) can be replaced by the complex vector (u, u′) = (x + iy, x′ + iy′) (where i represents...). Furthermore, the magnetic lens also rotates the electron beam vector by an angle θ. This rotation depends on the lens excitation NI (N = number of coil turns; I = coil current) and the relative correction energy U*, through: However, this can be achieved by multiplying the lens matrix by a complex factor exp. iθ The electron is contained in matrix form [1]. e and m represent the electron charge and mass, respectively, and μ0 is the vacuum permeability.

[0082] By placing multiple lenses in series, a compound lens / imaging system is formed. The lens action can be conveniently described by a matrix running at the geometric center of the lens. Starting from Z0, the ray first moves to the Zpo plane, then the lens action described by equation [1] occurs, and then the ray returns from Zpi to the geometric center of the lens, which can be described as follows:

[0083]

[0084] In addition, a drift matrix was used:

[0085] It does not change the angle u′ of the ray vector, but replaces u with u+d·u′ (drift distance d). For a system consisting of n lenses, it can now be written as:

[0086]

[0087] The Δ term is the drift matrix (see above), and the L term is the lens matrix (see equation [2]). By inverting the total system matrix, the calculation from the imaging plane to the objective plane can be performed. Since the magnification M of the imaging / projection system is usually much greater than 1, the focusing calculation of the lens series may be more accurate in the opposite direction. Therefore, the depth of focus at the objective plane is less than that at the imaging plane.

[0088] The optical properties of a given lens system can be calculated by solving equation [3]. In some examples, software employing a root-finding algorithm (such as the Newton-Raphson algorithm) can be used. Similarly, the principal planes Zpi, Zpo, Zfi, and Zfo discussed above can be calculated and determined using software.

[0089] Algorithms can be embodied, for example, as software or firmware instructions executed by a controller (e.g., a digital computing device). For instance, any publicly disclosed calculations of a lens system can be performed by a computer or other computing hardware (e.g., ASIC, FPGA, CPLD, etc.), which is the control system (e.g., Figure 2It is part of the control system 210. The control system may be connected to or otherwise communicate with the imaging system, and is programmed or configured to receive imaging data from sensing devices or user control inputs, and to perform necessary calculations or lookup table accesses on the operating parameters of the lens system (e.g., any lens parameter variation techniques disclosed herein). The controller may be a computer system comprising one or more processors (processing devices) and tangible, non-transitory computer-readable media (e.g., one or more optical media disks, volatile memory devices (such as DRAM or SRAM) or non-volatile memory or storage devices (such as hard disk drives, NVRAM, and solid-state drives (e.g., flash drives)). The one or more processors may execute computer-executable instructions stored on one or more tangible, non-transitory computer-readable media, thereby performing any of the techniques disclosed. For example, software for performing any of the disclosed embodiments may be stored as computer-executable instructions on one or more volatile, non-transitory computer-readable media, which, when executed by the one or more processors, cause the one or more processors to perform any of the disclosed techniques for calculating operating parameters of the lens system. The results of the calculations may be stored (e.g., in a suitable data structure or lookup table) in one or more tangible, non-transitory computer-readable storage media and / or may also be output to a user, for example, by displaying a graphical user interface on a display device.

[0090] Various embodiments have been described above. Specific configurations and details have been set forth for illustrative purposes to provide a thorough understanding of the embodiments. However, it will also be apparent to those skilled in the art that these embodiments can be practiced without specific details. Furthermore, well-known features may have been omitted or simplified to avoid obscuring the described embodiments. While the exemplary embodiments described herein focus on electron microscopy systems, and more specifically on scanning transmission electron microscopy systems, these are provided as non-limiting illustrative embodiments. The embodiments of this disclosure are not limited to such embodiments, but are intended to address analytical instrument systems in which a wide array of material samples can be analyzed to determine chemical, biological, physical, structural, or other properties, as well as other aspects, including but not limited to chemical structure, trace elemental composition, etc. Therefore, embodiments of this disclosure more broadly include charged particle instruments, including focused ion beam systems, scanning electron microscope systems, electron beam microanalysis systems, etc.

[0091] Some embodiments of this disclosure include systems having one or more data processors and / or logic circuits. In some embodiments, the system includes a non-transitory computer-readable storage medium containing instructions that, when executed on the one or more data processors and / or logic circuits, cause the one or more data processors and / or logic circuits to perform part or all of the one or more methods disclosed herein and / or part or all of one or more processes and workflows. Some embodiments of this disclosure include a computer program product tangibly embodied in a non-transitory machine-readable storage medium, the computer program product including instructions configured to cause one or more data processors and / or logic circuits to perform part or all of the one or more methods disclosed herein and / or part or all of one or more processes.

[0092] The terminology and expressions used herein are descriptive and not restrictive only. Their use is not intended to exclude any equivalents of the shown and described features or portions thereof, but rather to facilitate the understanding that various modifications may be made within the scope of the claims. Therefore, it should be understood that while this disclosure includes specific embodiments and optional features, modifications and alterations to the concepts disclosed herein can be made by those skilled in the art, and such modifications and alterations are considered to be within the scope of the appended claims.

[0093] When a term is used without a clear definition, it should be understood that unless the term has a special and / or specific meaning in the field of charged particle microscopy systems or other related fields, the term refers to its general meaning. The terms “about” or “substantially” are used to indicate a deviation from the stated property, where the deviation has little or no effect on the corresponding function, property, or attribute of the described structure. In the example shown where a dimensional parameter is described as “substantially equal” to another dimensional parameter, the term “substantially” is intended to reflect that the two parameters being compared may be unequal within permissible limits (such as confidence intervals inherent in manufacturing tolerances or system operation). Similarly, where geometric parameters (such as alignment or angular orientation) are described as “about” perpendicular, “substantially” perpendicular, or “substantially” parallel, the terms “about” or “substantially” are intended to reflect that the alignment or angular orientation may differ from the exact stated condition (e.g., not precisely perpendicular) within permissible limits. For numerical 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, the size "about 10mm" can describe sizes ranging from 9mm to 11mm.

[0094] This specification provides exemplary embodiments and is not intended to limit the scope, applicability, or configuration of this disclosure. Rather, the following description of exemplary embodiments will provide guidance to those skilled in the art for implementing various embodiments. It should be understood that various changes may be made to the function and arrangement of elements without departing from the spirit and scope set forth in the appended claims. Specific details are set forth in the description to provide a thorough understanding of the embodiments. However, it should be understood that embodiments may be practiced without these specific details. For example, particular system components, systems, processes, and other elements of this disclosure may be shown schematically or omitted from the illustrations to avoid obscuring the embodiments with unnecessary detail. In other instances, well-known circuits, processes, components, structures, and / or techniques may be shown without unnecessary detail.

Claims

1. A method for interrogating a sample using a charged particle beam system, the method comprising: modifying an acceleration voltage of a source of the charged particle beam system from a first energy to a second energy, the first energy and the second energy separated by an energy difference; modifying one or more optical elements of the charged particle beam system according to a calibration to the second energy; generating a set of operating conditions for a projection optics system of the charged particle beam system, the set of operating conditions based at least in part on operating the source at approximately the second energy; modifying one or more elements of the projection optics system at least in part according to the set of operating conditions; modifying a condenser lens of the charged particle beam system according to focusing a charged particle beam onto a sample location, the charged particle beam having an energy approximately the second energy; and modifying the acceleration voltage from the second energy to the first energy.

2. The method of claim 1, further comprising: modifying one or more optical elements of an electron energy loss (EELS) spectrometer of the charged particle beam system according to focusing the charged particle beam onto a detector of the EELS spectrometer, the charged particle beam having an energy approximately the second energy.

3. The method of claim 2, wherein the charged particle beam is a first beam, the method further comprising: generating a second charged particle beam, the second charged particle beam having an energy approximately the first energy; directing the first charged particle beam through the sample location; and generating detector data using the detector of the EELS spectrometer.

4. The method of claim 1, further comprising: modifying one or more optical elements of the charged particle beam system according to focusing the charged particle beam onto the sample location, the focusing corresponding to a fine focus at a spatial resolution of approximately 0.1 nm or less.

5. The method of claim 1, wherein the second energy is approximately 90% to approximately 98.5% of the first energy.

6. The method of claim 5, wherein the first energy is approximately 300 keV and the second energy is approximately 270 keV to approximately 295 keV.

7. The method of claim 1, wherein the first energy and the second energy can be related by the expression A = |(AE + E2 - El) / E2|, where AE is an energy loss associated with an edge (keV), El is the first energy (keV), and E2 is the second energy (keV); and expression A is approximately 1% to approximately 10%.

8. The method of claim 1, wherein generating the set of operating conditions comprises determining a solution to a first order approximation for the projection optics assembly, the solution configuring the charged particle beam to define a final cross-over (FXO) between the projection optics assembly and a detector plane, the detector plane substantially satisfying one or more boundary conditions of the charged particle beam system, wherein the boundary conditions include a magnification at a detector of the charged particle beam system. ​ ​ 9. The method of claim 8, wherein determining the solution comprises using the second energy and input parameter reference to a data set of operating conditions for the charged particle beam system, the data set describing a plurality of sets of operating conditions for the projection optics assembly associated with one or more acceleration voltages.

10. The method of claim 8, wherein determining the solution comprises solving a mathematical representation of the first order approximation describing the projection optics assembly.

11. One or more machine-readable storage media storing instructions that, when executed by a machine, cause the machine to perform operations comprising: modifying an acceleration voltage of a source of a charged particle beam system from a first energy to a second energy, the first energy and the second energy separated by an energy difference; modifying one or more optical elements of the charged particle beam system according to a calibration of the second energy; generating a set of operating conditions for a projection optics system of the charged particle beam system, the set of operating conditions based at least in part on operating the source at approximately the second energy; modifying one or more elements of the projection optics system at least in part according to the set of operating conditions; modifying a condenser lens of the charged particle beam system according to focusing a charged particle beam onto a sample location, the charged particle beam having an energy approximately the second energy; and modifying the acceleration voltage from the second energy to the first energy.

12. The media of claim 11, the operations further comprising: modifying one or more optical elements of an electron energy loss (EELS) spectrometer of the charged particle beam system according to focusing the charged particle beam onto a detector of the EELS spectrometer, the charged particle beam having an energy approximately the second energy.

13. The media of claim 12, wherein the charged particle beam is a first beam, the method further comprising: generating a second charged particle beam, the second charged particle beam having an energy approximately the first energy; directing the second charged particle beam through the sample location; and generating detector data using the detector of the EELS spectrometer.

14. The media of claim 1, the operations further comprising: modifying one or more optical elements of the charged particle beam system according to focusing the charged particle beam onto the sample location, the focusing corresponding to a fine focus at a spatial resolution of approximately 0.1 nm or less.

15. The media of claim 11, wherein the second energy is approximately 90% to approximately 98.5% of the first energy. ​ ​ 16. The medium of claim 11, wherein generating the set of operating conditions comprises determining a solution for a first order approximation of the projection optics assembly that configures the charged particle beam to define a final cross-over (FXO) between the projection optics assembly and a detector plane that substantially satisfies one or more boundary conditions of the charged particle beam system, wherein the boundary conditions comprise a magnification at a detector of the charged particle beam system.

17. The method of claim 16, wherein determining the solution comprises using the second energy and input parameters to reference a data set of operating conditions for the charged particle beam system, the data set describing a plurality of sets of operating conditions for the projection optics assembly associated with one or more accelerating voltages.

18. The method of claim 16, wherein determining the solution comprises solving a mathematical representation describing the first order approximation of the projection optics assembly.

19. A charged particle beam system comprising: a charged particle source; a charged particle optical column coupled with the source, the charged particle optical column comprising: an objective section defining a sample location; and a projection optics system; a detector section coupled with the column; a control circuit operably coupled with the source, the column, and the detector section; and one or more machine-readable storage media operably coupled with the control circuit and storing instructions that, when executed by a machine, cause the machine to perform one or more operations comprising: modifying an accelerating voltage of a source of the charged particle beam system from a first energy to a second energy, the first energy and the second energy separated by an energy difference; modifying optical elements of the charged particle beam system such that the optical elements are calibrated for the second energy; generating a set of operating conditions for the projection optics system, the set of operating conditions based at least in part on operating the charged particle source at approximately the second energy; modifying one or more elements of the projection optics system at least in part according to the set of operating conditions; modifying a condenser lens of the charged particle beam system according to focusing a charged particle beam having an energy approximately the second energy onto the sample location; and modifying the accelerating voltage from the second energy to the first energy.

20. The system of claim 19, the detector section comprising an electron energy loss spectrometer coupled with the column and oriented to receive the charged particle beam via the projection optics system, the operations further comprising: modifying one or more optical elements of an electron energy loss (EELS) spectrometer of the charged particle beam system according to focusing the charged particle beam having an energy approximately the second energy onto a detector of the EELS spectrometer; generating a second charged particle beam having an energy of about the first energy; directing the second charged particle beam through the sample location; and generating detector data using the detector of the EELS spectrometer.

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