Technique for high-energy-loss electron energy loss spectroscopy using magnetic immersion objective lenses

Abstract

This invention provides a method for energy loss spectroscopy in relatively large energy loss scenarios. [Solution] The method includes modifying the acceleration voltage of the system's source from a first energy to a second energy. The method may also include modifying one or more optical elements of the system according to the calibration of the second energy. The method may also include generating a set of operating conditions for the projection optical system. The method may also include modifying one or more elements of the projection optical system at least in accordance with the set of operating conditions. The method may also include modifying the condenser lens of the system in accordance with focusing the beam of charged particles to the sample position. The method may also include modifying the acceleration voltage from a second energy to a first energy.

Description

Technical Field

[0001] Embodiments of the present disclosure relate to charged particle beam systems, as well as algorithms and methods for their operation. Specifically, some embodiments are directed to techniques for electron energy loss spectroscopy.

Background Art

[0002] Electron energy loss spectroscopy (EELS) describes a technique that can derive information about the electronic structure of a material sample by passing an electron beam through the sample and scattering a portion of the electrons. An EELS spectrometer operates by collecting electrons that are inelastically scattered downstream of the sample with respect to the position of the electron source, and the energy lost in inelastic scattering spatially disperses these electrons. The spatially dispersed electrons collide with a detector that generates an EELS spectrum. Challenges of EELS include that inelastically scattered electrons become increasingly defocused with increasing energy loss, and the scattering cross section rapidly decreases with increasing energy loss, leading to signal-to-noise limitations for excitations above approximately 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 to a single energy of the electron beam, i.e., the energy of the primary beam of the charged particle microscope. Therefore, EELS spectrometers are constrained to a relatively narrow energy range near the "zero-loss peak" or ZLP corresponding to the primary beam energy. Inelastic collisions involving energy transfers exceeding approximately 1% of the primary beam energy (e.g., exceeding approximately 2 keV for a 200 keV primary beam), such as core-shell ionization and other relatively high-energy interactions between the electron beam and the sample, are generally considered outside the range of quality data for typical EELS spectrometers due to insufficient signal-to-noise and aberration artifacts. Synchrotron systems are typically used to generate such data using beamlines for soft or hard X-rays, typically at significantly lower spatial resolution, higher complexity, and higher cost. Therefore, there is a need for techniques and systems using EELS systems in charged particle microscopes to investigate core-shell transitions and other relatively high-energy transitions in material samples. [Overview of the project]

[0004] Systems, devices, methods, algorithms, and techniques for energy loss spectroscopy at relatively large energy losses are described. In a first aspect, as described with reference to Figures 1 to 6, a method for analyzing a sample using a charged particle beam system includes modifying the accelerating voltage of the source of 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 so that the optical elements are calibrated for the second energy. The method may include generating a set of operating conditions for the projection optical system of the charged particle beam system. The set of operating conditions may be at least partially based on operating the source near the second energy. The method may include modifying one or more elements of the projection optical system at least partially in accordance with the set of operating conditions. The method may include modifying the condenser lens of the charged particle beam system in accordance with focusing the beam of charged particles to the sample position. The beam of charged particles may have an energy close to the second energy. This 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 in accordance with focusing a beam of charged particles onto the detector of the EELS spectrometer. The beam of charged particles may have an energy close to a second energy. The beam of charged particles may be the first beam. The method may further include generating a second beam of charged particles. The second beam of charged particles may have an energy about the first energy. The method may further include directing the first beam of charged particles through a sample position. The method may also 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 in accordance with focusing the beam of charged particles to the sample position. The focusing can accommodate fine focusing with a spatial resolution of about 0.1 nm or less. The second energy can be about 90% to about 98.5% of the first energy. The first energy can be about 300 keV, and the second energy can be about 270 keV to about 295 keV. The first and second energies can be related by the equation A = |(ΔE + E2 - E1) / E2|, where ΔE is the energy loss associated with the edge (keV), E1 is the first energy (keV), E2 is the second energy (keV), and A is about 1% to about 10%.

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

[0008] In a second embodiment, the system may include a charged particle beam source, a charged particle optical column coupled to the source, and a detector section, as will be described in more detail with reference to Figures 1 to 6. The column may be configured to receive a beam of charged particles from the source. The column may include an objective lens section. The objective lens section may include a magnetic immersion objective lens that can define a sample position. The magnetic immersion objective lens may include a probe that forms the objective lens and an imaging objective lens. The sample position may be defined between the probe that forms the objective lens and the imaging objective lens with respect to the beam axis A of the system. The column may further include a projection optical system assembly. The projection optical system assembly may include one or more projection optical systems. The system may further include a detector section coupled to the column. The detector section may include an energy loss spectrometer configured to receive a beam of charged particles through the projection optical system assembly. The spectrometer may include a detector configured to generate detector data in response to the interaction of the charged particles in the beam with the detector.

[0009] The system may also include a control circuit operably coupled to the source, column, and detector sections. The control circuit may, in one or more embodiments, be operably coupled to one or more machine-readable storage media that store instructions causing the system to perform one or more operations of the first aspect when executed by one or more machines.

[0010] In a third embodiment, 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 embodiment. In some embodiments, the media of the third embodiment can be operably coupled with a system of the second embodiment. The media can be operably coupled with a control circuit of the system of the second embodiment.

[0011] Embodiments of this disclosure also include systems, components, and methods in the manner described above. The terms and expressions used are for illustrative purposes only and are not intended to exclude any equivalents of the illustrated and described features or parts thereof, but it should be recognized that various modifications are possible within the scope of the claimed subject matter. Accordingly, although the claimed subject matter is specifically disclosed by embodiments and any features, modifications and variations of the concepts disclosed herein can be made by those skilled in the art, and it should be understood that such modifications and variations are deemed to be within the scope of this disclosure as defined in the appended claims. [Brief explanation of the drawing]

[0012] The aforementioned aspects of this disclosure and the many advantages thereto will be more readily understood by referring to the following detailed description in conjunction with the accompanying drawings. [Figure 1] This is a schematic diagram illustrating an exemplary charged particle light system according to some embodiments of the present disclosure. [Figure 2] Figure 1 is a schematic diagram illustrating the operating principle of an exemplary charged particle beam system according to some embodiments of the present disclosure. [Figure 3] Block diagram shows an exemplary process 300 for analyzing a sample using an exemplary charged particle light system according to some embodiments of the present disclosure. [Figure 4-1] Figures 4A and 4B are schematic diagrams showing the charged particle optical elements of a charged particle beam system according to current technology. [Figure 4-2] Figure 4C is a schematic diagram showing the charged particle optical elements of a charged particle beam system according to the current technology, Figure 4D is a schematic diagram showing the charged particle optical elements of a charged particle beam system according to the current technology, and Figure 4E is a schematic diagram showing the charged particle optical elements of a charged particle beam system according to some embodiments of the present disclosure. [Figure 5A]This graph shows exemplary electron energy loss spectrum (EELS) data of a copper foil sample according to some embodiments of the present disclosure. [Figure 5B] Figure 5A is a graph showing details of exemplary electron energy loss spectrum (EELS) data for a copper sample, compared to EXAFS data, according to some embodiments of the present disclosure. [Figure 6] The present disclosure shows various parameters that can be used to describe the primary particle optical effect of a thick magnetic lens according to some embodiments of this disclosure.

[0013] In drawings, similar reference numbers refer to the same part throughout various drawings unless otherwise specified. Not all instances of an element are necessarily labeled to reduce clutter in the drawings where appropriate. Drawings are not necessarily to scale; instead, the focus is on illustrating the principles being described. [Modes for carrying out the invention]

[0014] While embodiments have been illustrated and described, it will be understood that various modifications can be made without departing from the spirit and scope of this disclosure. The following paragraphs describe embodiments of charged particle beam systems, components, and methods for electron energy loss spectroscopy (EELS). For simplicity of explanation, embodiments of this disclosure focus on the microanalysis of a sample using a transmission electron microscope (TEM) system with EELS. Embodiments are not limited to such systems, but rather are intended for systems where the analysis of inelastic collisions between a beam of charged particles and atoms in a sample may be complicated by the internal configuration of the charged particle optical components. In exemplary examples, a scanning electron microscope (SEM) system can be used for EELS analysis in scanning transmission (STEM in SEM) mode. Similarly, a system can be configured for EELS techniques by specifically omitting typical components of a TEM system adapted for imaging, X-ray trace analysis, etc. Thus, embodiments of this disclosure focus on a TEM platform equipped with a system for generating and processing EELS data, but additional and / or alternative systems and approaches are intended.

[0015] Embodiments of the present 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 section 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, a so-called magnetic immersion objective lens, embodiments of the present disclosure include generating a set of operating conditions for a projection optical system assembly that eliminates one or more beam crossover shifts, allowing the objective optical system assembly to remain calibrated to the energy of the charged particle source while the optical system located downstream of the sample is (re)calibrated for a second energy in response to relatively large inelastic transitions (e.g., 2 keV or greater). Advantageously, embodiments of the present disclosure improve the performance of energy loss spectroscopy systems when measuring relatively large energy losses when operating in an objective field that immerses a sample, thereby reducing reliance on synchrotron systems to produce equivalent data.

[0016] Compared to charged particle microscopes, synchrotron systems are complex, large, and not scalable. The techniques presented herein enable charged particle beam systems to use existing EELS detector systems to generate detector data comparable to extended X-ray absorption fine-structure (EXAFS) spectra. As an additional advantage, EELS in scanning transmission electron microscopes (STEM) generally offers significantly improved spatial resolution (e.g., 10⁻¹⁰). 3It provides a spatial resolution that is [multiple] times larger. Improvements to the spatial resolution at such scales significantly increase the depth of information available from nanostructured samples that can vary chemically and structurally over the length scales typically integrated by synchrotron analysis on the μm - mm scale.

[0017] The following detailed description focuses on embodiments of a transmission electron microscope system, but it is contemplated that additional and / or alternative instrument systems can be improved through the use of the techniques described. The instrument system can include other charged particle systems including, but not limited to, a focused ion beam system, a scanning electron microscope system, an ion - electron dual beam system, etc.

[0018] FIG. 1 is a schematic diagram showing an exemplary charged particle microscope 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 focus is on embodiments of the present disclosure as described in more detail with reference to FIGS. 2 - 5, and techniques for enhancing sample information in a spectrum including relatively strong background information. The exemplary TEM system 100 includes an electron source section 101, a TEM column 105 including a sample section 107, an objective probe - forming lens 108, an objective imaging lens 109, a projection optical system 111, and a detector section 110. The present disclosure focuses on techniques for improving the performance of the detector section 110, with an eye on embodiments of the present disclosure that include one or more electron energy loss spectroscopy (EELS) spectrometers 115.

[0019] In short, the electron source section includes electronic equipment configured to apply a voltage to a source of charged particles 205 (see Figure 2), which may include a high-voltage field emission source or other source of emitted electrons, thereby forming an electron beam that is transmitted through a vacuum to the TEM column 105. The TEM column 105 includes beamforming components, including electromagnetic and / or electrostatic lenses for controlling the characteristics of the electron beam, as well as a plurality of apertures. The components of the TEM column 105 include, among other things, a condenser lens, an objective lens, a projector lens, an aberration corrector, a deflector, a stigmeter, and corresponding apertures. The sample section 107 hosts a sample 225 (see Figure 2) through which the electron beam can be transmitted. In EELS trace analysis, the beam can be focused onto the sample for spot-mode analysis (e.g., through the action of the probe-forming objective lens 108), or the beam can pass through the sample in parallel illumination mode (or at least partially out of focus) to collect data from a relatively large sample area (e.g., through the action of the objective imaging lens 109).

[0020] In some embodiments, the sample section 107 includes a probe-forming objective lens 108 and an imaging objective lens 109 that share the same magnetic field, also referred to as the objective field of the objective lens, for immersing the sample in this magnetic field. Advantageously, disposing the sample within the objective field of the objective lens can provide a good resolution of about 0.05 nm for STEM mode operation. In this context, immersion within the objective field refers to disposing the sample within the magnetic field of the objective lens that extends into the space between the sample and the pole pieces of the objective lens. Such immersion significantly reduces the possible aberrations of the objective lens, which would otherwise reduce the spatial resolution of the microscope. As will be described in more detail with reference to subsequent drawings, configuring the objective lenses 108 and 109 to generate an immersion objective field can limit the operation of the exemplary system 100 to provide a consistent calibration of the objective optics across the sample position. For example, the magnetic lens field shared by the objective lenses 108 and 109 within the immersion objective lens system can constrain the calibration (e.g., operating energy) of the objective lens 109 to depend on the calibration (e.g., operating energy) of the objective lens 108. In conventional methods, such constraints severely limit the proper transmission of unscattered electrons to the EELS detector. For that purpose, embodiments of the present disclosure enable the EELS technique with relatively large energy losses while operating in the objective field at the sample position.

[0021] In some embodiments, the charged particle beam system 100 operates in a field-free STEM mode, and 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 function as a probe-forming lens, and a Lorentz lens downstream of the sample can function as a first imaging lens to provide at least some of the functions of the objective lens. In the field-free STEM mode, detector data can be generated with a spatial resolution of about 0.5 nm. Although several orders of magnitude worse than in the case of immersion, the field-free STEM mode still provides a significantly improved spatial resolution compared to synchrotron-based techniques.

[0022] State-of-the-art TEM columns can have up to four condenser lenses for flexible (e.g., stepwise or gradually changing) reduction and focusing of the electron beam over the sample, up to five projection lenses for flexible expansion of the electron beam downstream of the sample relative to the detector, and up to two aberration correctors. State-of-the-art aberration correctors can include additional lenses and several multipoles (e.g., four lenses and two or more multipoles), so modern TEM columns can contain up to approximately 20 lenses. The coordinated operation of the set of lenses and other optical elements results in a given reduction in the sample and expansion at the detector. In contrast, a lack of coordination leads to aberrations, which are at least partially based on the electron beam traveling off-center through one or more optical elements, the beam having too large a diameter in one or more lenses, or other issues that reduce system performance. In the context of this disclosure, “calibration” and “recalibration” of charged particle optical elements refer to a set of operating parameters for an assembly of elements, which are set and verified so that the excitation parameters give desired beam characteristics in the sample (e.g., probe diameter, current, position) and desired beam characteristics in the detector (e.g., magnification, focus, position). As will be understood by those skilled in the art, (re)calibration of an assembly of optical elements is a complex and cumbersome task that can typically take days or weeks even for an experienced technician. For this reason, TEM columns are typically supplied with calibration settings for a limited number of electron beam energies (e.g., 2–5) (e.g., 300 keV, 200 keV, 60 keV) and make arbitrary changes to the optical system calibration that are substantially unavailable in most conventional TEM systems.

[0023] The optical intensity of lenses and multipoles depends on the energy of electrons in the beam; therefore, calibration is specific to electrons whose calibration setpoint is equal to or close to the energy of the set and verified energy. For example, in a TEM operating at a beam energy of 300 keV, the charged particle optical elements of the TEM column calibrated for the beam at 300 keV introduce minimal aberrations (focus shift, coma, shift, etc.) into the beam. However, in this example, electrons with an energy deviating only 10 eV from 300 keV, i.e., a deviation of about 0.003%, will be focused onto a plane shifted by a distance of about 100 nm from the intended sample plane. In this example, chromatic aberration of the objective lens significantly degrades the spatial resolution of the microscope. For this reason, in a typical calibration scheme, all or almost all elements are calibrated for the same beam energy. For example, the reduction and expansion elements are calibrated for the same beam energy. This approach is further illustrated with reference to Figure 4A.

[0024] The detector section 110 includes one or more types of detectors, sensors, screens, and / or optical components configured to generate images, spectra, and other data for use in sample imaging and / or trace analysis. For example, the imaging section may include, among other things, a scintillator screen, binoculars, a transmission electron microscope (TEM) detector (e.g., a pixelated electron detector, a secondary electron detector, a camera, and an electron energy loss spectroscopy (EELS) spectrometer 115). The EELS spectrometer 115 functions at least partially as an energy filter by focusing the electron beam onto an electrostatic or magnetic dispersion element (also called a “prism”) that deflects the electrons in proportion to their energy. In this way, electrons that have transferred energy to the sample (e.g., by inelastic collisions) can be redirected through the magnetic dispersion element to 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 an EELS spectrum can be derived. In some embodiments, the EELS spectrometer 115 also includes one or more optical elements, such as electromagnetic or electrostatic lenses, and / or multipoles and / or accelerators, to adjust or focus the scattered electrons onto the detector.

[0025] Figure 2 is a schematic diagram illustrating the operating principle of an exemplary charged particle beam system 200 according to several embodiments of the present disclosure. The exemplary system 200 is an example of the charged particle beam system 100 of Figure 1 and includes a microscope 200 corresponding to a source section, TEM column 105, sample section 107, and optionally a portion of a detector section 110 of a charged particle microscope 201. 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 operably coupled to the microscope 201 and the spectrometer 115.

[0026] Microscope 201 may include a charged particle source 205 configured to generate a beam of charged particles 215 (e.g., electrons or ions) with a first energy E1. A small number of particles may be scattered by the sample. Scattering events may include inelastic scattering. In electron energy loss spectroscopy (EELS) techniques, an EELS spectrometer 115 can be used to measure the energy of inelastically scattered electrons, from which the energy loss ΔE associated with the inelastic scattering event can be derived. Electrons that have lost energy during an inelastic scattering event travel through the TEM column and the EELS spectrometer with an energy of E1-ΔE. The magnitude of the deviation of the TEM column and the EELS spectrometer from the calibrated energy E1 affects the effect of the charged particle optical elements on the electrons as they travel between the sample and the detector 245 of the EELS spectrometer 115. The deviation ΔE from the calibration energy causes the force applied by the charged particle optical elements to deviate from their respective calibrated optical intensities, reducing imaging performance.

[0027] For example, if ΔE includes a range of energy loss values, the number of imaging planes can be defined by the energy-dependent performance of the charged particle optical elements. Some scattered electrons can be focused onto the detector in accordance with the system calibration, while others may be focused onto image planes upstream of the detector, downstream of the detector, or at locations away from the spectrometer entrance (e.g., off-axis). In some cases, scattered electrons can be guided to come into contact with the TEM column or the inner surface of the spectrometer, thereby being completely excluded from the EELS signal.

[0028] The calibration scheme described above, as detailed in Figure 4A, typically allows for the detection of electrons with energies deviating by approximately ΔE / E1 ≈ 2% from the calibrated energy, provided that the column lens setting and the spectrometer's multipole setting are carefully selected. However, for ΔE values ​​greater than approximately 1% of the calibration energy E1 (i.e., ΔE / E1 > approximately 1%), the calibration scheme described above cannot direct scattered electrons through the charged particle optics of the TEM column and the EELS spectrometer without introducing artifacts (e.g., magnification / reduction and / or deviation from beam position). Beam magnification and position deviations result in inefficient collection of scattered electrons by the EELS spectrometer. Furthermore, aberrations that exclude some scattered electrons from the detector signal impair the usefulness of the recorded EELS spectrum for appropriately and reliably quantifying the elemental composition of the sample. Such challenges become more significant as the deviation from the beam energy increases.

[0029] In some embodiments of this disclosure, electrons that deviate by about 1% or more from the beam energy (E1) (e.g., ΔE / E1 ≥ about 1%) can be efficiently collected by using a calibration scheme different from that described above, in which case 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 configuring one or more projection optical systems (e.g., projection optical system system 111 in Figure 1) to immerse the sample in the objective field while maintaining one or more constraints on the optical arrangement (e.g., focal plane position, crossover position, etc.), as described in more detail with reference to Figures 4A to 4D.

[0030] Generally, according to this disclosure, one or more charged particle optical elements 220 are calibrated to a first energy E1, and one or more charged particle optical elements 230 are calibrated to a second energy E2. In some embodiments, the optical elements 220 calibrated to the first energy E1 are located upstream of the sample 225, which is placed in a sample section (e.g., sample section 107 in Figure 1), and optical elements 221 and 223 representing magnetic immersion objective lenses (e.g., objective lenses 108 and 109 in Figure 1) are also calibrated to the first energy E1, while the optical elements 230 calibrated to the second energy E2 are located downstream of the sample 225. The first energy E1 and the second energy E2 may be different; for example, E1 may be greater than E2. Electrons that have energy near the first energy E1 upstream of the sample, losing energy (ΔE) due to scattering, will have energy near E1-ΔE downstream of the sample. For this purpose, E2 can be selected such that it is equal to approximately E1 - ΔE. In some embodiments, E2 can be found using the absolute value formula: |(ΔE + E2 - E1) / E2| ≤ approximately A, where A is a value from approximately 1% to approximately 10%, including its subrange, fractions, and interpolations. For example, A may be equal to approximately 1%, approximately 2%, approximately 3%, approximately 4%, approximately 5%, approximately 6%, approximately 7%, approximately 8%, approximately 9%, approximately 10%, etc.

[0031] In the exemplary examples in Figures 3 to 6, the difference between energies E1 and E2 can be approximately 2 keV to approximately 50 keV, including its subrange, fraction, and interpolation. For example, the difference between E1 and E2 can be approximately 2 keV to approximately 35 keV, approximately 2 keV to approximately 10 keV, approximately 10 keV, approximately 20 keV, approximately 30 keV, etc. Energies E1 and E2 can be approximately 50 keV to approximately 500 keV, including its subrange, fraction, and interpolation. In an exemplary example, E1 may be approximately 300 keV, and E2 may be approximately 270 keV to approximately 295 keV, including its subrange, fraction, and interpolation (e.g., approximately 290 keV). In another example, E1 may be approximately 310 keV, and E2 may be approximately 300 keV. In another example, E1 can be approximately 200 keV and E2 can be approximately 190 keV. The cross-section for a given excitation (e.g., core-shell ionization) may depend at least partially on ΔE. For that purpose, for ΔE values ​​outside the above range, high energy loss data may be dominated by noise, at least partially based on the relatively low probability of a charged particle inducing a given excitation.

[0032] The difference between the first and second energies may depend at least partially on the value of the first energy. For example, the second energy can be a fraction of the first energy. In some embodiments, the second energy can be about 60% to about 99% of the first energy, including its subrange, fraction, and interpolation. In exemplary examples, the second energy can be about 90% to about 98.5% of the first energy. The difference between the first and second energies can be selected to be equal to or approximately equal to the energy loss recorded by the EELS spectrometer. The technique described herein enables the charged particle microscope to send a response command signal for an energy range corresponding to a relatively high energy loss, where a larger difference between E1 and E2 will result in detector data (e.g., broadband energy loss fine structure, or EXELFS) corresponding to the excitation energy of a scattering event with an approximate value of that difference. Thus, a difference of about 10 keV can provide detector data for a scattering event with an excitation energy of about 10 keV.

[0033] EXELFS studies the fine structure of the energy dependence of the probability of inter-shell excitations. The total number of electrons N that experience energy loss due to inter-shell excitations is... tot This is the energy loss raised to the power of -1.5, i.e., N tot ∝ΔE 1.5 It is approximately proportional to ΔE. In this way, the number of scattered electrons is within the energy range ΔE. tail It can be distributed over a range of scattering energies (known as the "edge tail") (outside 1) It can be distributed over TIFF2026049697000002.tif1170 (known as the "scattering distribution"). The range of the scattering angle is approximately

number

number

[0034]

number

[0035] This estimation shows that the EXELFS signal in an EELS spectrometer decreases rapidly with increasing energy loss. For example, to reach the same count (and therefore the same statistical data) in the EXELFS region (100 eV width) for the K-shell edge in titanium (5.0 keV), copper (9.0 keV), molybdenum (ΔE=20 keV), and antimony (ΔE=30.5 keV), the associated beam dose scales by a ratio of 1:8:128:560 (for Ti). In this way, the collection solid angle of an EELS spectrometer can determine a large part of the performance of the TEM system when measuring EXELFS spectra. Advantageously, the collection solid angle improves significantly when the TEM column is calibrated better to scatter electrons according to the formula |(ΔE+E2-E1) / E2| < approximately 2%. Thus, the calibration process of this disclosure may include measuring the collection angle and centering the beam relative to the EELS spectrometer. With respect to edge location or edge structure, noise may become more significant as the difference between E1 and E2 increases, and consequently, beyond approximately ΔE = 30 keV, the integration time and total electron dose may be limited, for example, by the sensitivity of the sample.

[0036] The spectrometer 115 may include a dispersion element 235 and charged particle optical elements such as one or more electromagnetic and / or electrostatic elements 240 (e.g., lenses, accelerators, quadrupoles, hexapoles, octapoles, etc.). The dispersion element 235 may comprise one or more magnetic and / or electrostatic dispersion elements (also referred to as "prisms"). The spectrometer 115 may be post-column (located after the TEM column, as shown in Figure 2) or in-column operably coupled to the TEM column. Elements 235 and 240 can be calibrated for a second energy E2. Referring to the dispersion element 235, calibration for a second energy E2 refers to the operation of the dispersion element 235 to disperse charged particles (e.g., electrons) having energies that deviate from E2 by about 2% or less of E2. In this way, charged particles having energies of about E2 can be transferred to element 240 and subsequently directed to the detector 245 of the spectrometer 115. In some embodiments, element 240 also focuses charged particles onto detector 245.

[0037] Other components of system 200 can function to attenuate, redirect, absorb, or otherwise exclude unscattered or weakly scattered charged particles 255 (e.g., electrons passing through sample 225 without scattering) from the detector data. For example, element 230 can apply a force (e.g., magnetic force) proportional to the electron's velocity to the electron, which redirects electrons with energy about E1 away from the beam axis to an absorber material or other surface inside the microscope 201.

[0038] Detector 245 can generate detector data. As will be described in more detail with reference to Figures 3–6, the detector data may include EELS spectra resulting from the interaction of a beam of charged particles 215 with atoms 227 in sample 225. For example, if the microscope 201 operates in STEM mode (e.g., scanning TEM, or STEM within SEM) and sample 225 is thinly fabricated to allow beam transmission, the electron beam can be focused to a point in sample 225, enabling the measurement of a single atom or group of atoms at the nanometer scale. As will be described in more detail with reference to Figures 5A–5B, interactions between adjacent atoms 227 can introduce fine structure into the detector data. In this way, chemical, physical, and / or structural information (e.g., oxidation state, coordination information, etc.) about atoms 227 can be derived using the detector data. Advantageously, embodiments of the present disclosure combine fine structure information with spatial localization, which is unavailable in typical synchrotron systems used to generate comparable detector data. In TEM operating in STEM mode, atomic-scale resolution can be achieved by focusing a beam of charged particles 215, and the system 200 can be used to generate a nanometer-scale map of the material properties of sample 225.

[0039] The control system 210 may include one or more machines (e.g., computing devices) operably coupled to a control circuit located within the microscope 201 and / or spectrometer 115. In an exemplary example, the control circuit may include an arrangement of circuit components connected to a power supply and configured to control the supply of power (e.g., voltage and / or current) to the source 220, elements 220, 230, 235, 240, and / or detector 245. In this way, the process for calibrating and / or recalibrating elements 220, 230, 235, 240, and / or detector 245 may be directed 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, laptops, tablets, servers, application-specific machines (ASMs), and the like. In some embodiments, the control system 210 includes user-interactive elements such as a display and input peripherals (e.g., mouse and keyboard) through which the user can reversibly implement the high energy-loss EELS mode in accordance with the operation described with reference to Figure 3. In an exemplary example, the user can select an interactive graphical element 211 on a user interface (e.g., an application, browser environment, etc.) to initiate the high energy-loss EELS mode. To return the system 200 to its previous state, the user can select an interactive image element 211 to initiate the calibration of elements 220, 230, 235, and / or 240 back to a previous calibration energy (e.g., a first energy E1, a second energy E2, or a third energy E3) from E1 or E2.

[0040] To that end, the process of the present disclosure (e.g., the exemplary process 300 in Figure 3) may include operations for receiving user interaction data (e.g., via an interactive user interface), where the interaction data initiates or reverses the recalibration of one or more elements of a charged particle beam system in response to user actions. Similarly, the process of the present disclosure may include generating user interface data configured to modify a display (e.g., of a control system 210) to present an interactive user interface.

[0041] In some embodiments, the control system 210 is configured to communicate with one or more data stores and / or machine-readable media that store instructions encoding one or more algorithms for generating a set of operating conditions for at least a subset of optical systems in a column (e.g., TEM column 105 in Figure 1). As will be described in more detail with reference to Figures 3 and 6, the control system 210 may be configured to generate and / or implement a set of operating conditions such that at least a subset of optical systems located downstream of the sample 225 can be calibrated to a second energy E2, and optical systems located upstream of the sample 225 can be calibrated to a first energy E1. Advantageously, the technology of the present disclosure enables one or more optical systems downstream of the sample, such as an objective imaging lens 223 (e.g., objective lens 109 in Figure 1), to be calibrated to the first energy E1. In this way, as is typical for STEM-configured TEM instruments, a charged particle beam system with a magnetically immersed objective lens can maintain a common calibration scheme (e.g., calibrated for a first energy E1) for the objective condenser lens 221 and the objective imaging lens 223. In some embodiments, the control system 210 can be configured to generate a set of operating conditions by communicating with a physically remote computing system (e.g., a distributed computing system) and / or to locally execute one or more algorithms based at least in part on the computing and / or network resources available to the control system 210.

[0042] Figure 3 is a block diagram showing an exemplary process 300 for analyzing a sample using an exemplary charged particle light system, according to some embodiments of the present disclosure. One or more operations of the exemplary process 300 can be performed by a computer system communicating with additional systems, including, but not limited to, a characterization system, network infrastructure, a database, and a user interface device. In some embodiments, at least a subset of the operations described with reference to Figure 3 are performed automatically (e.g., without human involvement) or pseudo-automatically (e.g., with human initiation or limited human intervention). In an exemplary example, the operations for generating and shaping an electron beam can be performed automatically, with the TEM system 100 configured to maintain the characteristics of the electron beam at or near a setpoint that can be specified by a human user. In another exemplary example, a human user can initiate the EELS mode using the techniques described herein by activating a subsystem of the charged particle microscope 100 (e.g., via an interactive user environment presented through a user terminal such as a browser or software application, and / or via a push-button control panel), which initiates a recalibration of the charged particle microscope 100 from its imaging mode or conventional EELS mode (i.e., all elements calibrated for the same energy) to a high-loss mode (i.e., some elements calibrated for energy E1, other elements calibrated for energy E2). For that purpose, although the exemplary process 300 is described as a series of operations, it is understood that at least some of the operations can be omitted, repeated, and / or rearranged. In some embodiments, additional operations omitted for clarity of description, such as operations for electron source calibration, electron beam alignment and aberration correction, and probe position initialization, precede and / or follow the operations of the exemplary process 300. Advantageously, embodiments of the present disclosure maintain the spatial resolution of a charged particle beam system operating in a scanning mode in which the sample is immersed in the objective field (e.g., a STEM mode for a TEM instrument).Furthermore, the implementation of algorithmic tuning of the projection optics to compensate for objective field effects allows the method of this disclosure to be at least partially automated, thereby significantly reducing the complexity that enables high-loss EELS modes. Finally, exemplary process 300 provides a significant improvement in the energy resolution of EELS data with energy loss exceeding approximately 1% of the beam energy, resolving most, if not all, artifacts that would be measured in such data under typical STEM modes, thereby enabling microstructural analysis (EXELFS) typically performed using synchrotron instruments.

[0043] In operation 305, the exemplary process 300 includes reducing the high tension applied to the charged particle source (e.g., charged particle source 103 in Figure 1, charged particle source 205 in Figure 2). In this context, “high tension” (or, in short, “tension”) can refer to the accelerating voltage or other operating parameter that describes the energy of the charged particles emitted by the source into the column (e.g., TEM column 105 in Figure 1). For example, the energy E of an electron beam is described by E = eV from the accelerating voltage V, where e is the charge of the electron. Thus, operation 305 may include modifying the operating voltage of the charged particle source from a first energy E1 to a second energy E2, as described with reference to Figure 2. In some embodiments, operation 305 includes reducing the tension from 300kV by a rate of about 1% to about 20%, including its subranges, fractions, and interpolations. The degree to which the tension is changed may correspond to the energy loss being analyzed. For example, in the embodiment described with reference to Figures 5A and 5B, the acceleration voltage of the electron source was reduced by approximately 9 kV, corresponding to the characteristic edge of the core-shell ionization of copper atoms (Cu k edge at 8987.96 EV). Similarly, a target element in a material sample can be analyzed as part of an exemplary process 300 by modifying the tension by a value corresponding to the characteristic energy of a given inelastic transition for that element. Furthermore, operation 305 can be repeated for multiple energy values ​​as part of an iterative approach to improve the energy resolution and signal-to-noise characteristics of the EELS detector data. Advantageously, this approach improves the resolution of the microstructure in the EELS data for relatively large energy loss values ​​(e.g., above approximately 1 keV).

[0044] In operation 310, the exemplary process 300 includes calibrating and / or recalibrating one or more charged particle optical elements. Elements 220, 230, 235, and 240 in Figure 2 are examples of charged particle optical elements in operation 310. Generally, calibrating and recalibrating may include one or more sub-operations that modify the electronic parameters of the element to bring the element to a set of operating conditions, such as the magnification and position of the charged particle beam in an EELS spectrometer, or the magnification and width of the dispersed charged particle beam in a detector. In the context of this disclosure, operation 310 may include the same or similar sub-operations applied to shift the calibration energy of the element from a first energy (e.g., E1 in Figure 2) to a second energy (e.g., E2 in Figure 2). Thus, operation 310 may include recalibrating element 220 to a higher energy, recalibrating elements 230, 235, and 240 to a lower energy, or both. In this context, the term “calibration energy” refers to a set of operating parameters that configure a charged particle optical element to apply an appropriate force to a beam of charged particles (e.g., beam 215 of charged particles in Figure 2) at or near the calibration energy, as part of defining one or more beam crossovers at positions on the beam axis of the column, as described in more detail with reference to Figures 4A–4E. Because electrostatic elements can apply a refractive effect inversely proportional to the beam energy (ignoring relativistic effects), and magnetic elements can apply a refractive effect inversely proportional to the square root of the beam energy (ignoring relativistic effects), miscalibrated elements may exhibit impaired performance for a given beam energy. In an exemplary example where the optical element is a condenser lens, the electron beam may be underfocused or overfocused by about 100 nanometers if the lens is miscalibrated by only 10 eV.

[0045] In 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 the charged partial optical element. For example, a magnetic multipole element can be recalibrated from energy E1 to energy E2 by scaling its known calibration at E1 by a factor of √(E1 / E2) (neglecting relativistic effects). As part of such scaling of calibration, the magnetic element can be operated, configured, or otherwise tuned so that there is virtually no magnetic saturation and hysteresis. Scaling can also be applied to beam deflectors and beam astigmatism correctors, and the mechanical alignment of the optical elements can thus be improved.

[0046] In conventional EELS modes, optical elements 220, 230, 235, and 240 can be calibrated for a first beam energy (e.g., about 300 keV) generated by the charged particle 205 source (as shown in Figure 4A). In contrast, the exemplary process 300 can improve the resolution of EELS data at relatively high energy losses by (re)calibrating additional and / or alternative optical components, and by operating at least one subset of optical elements 220, 230, 235, and 240 with calibration parameters for the first energy E1, and a second subset near the second energy E2. In some embodiments, one or more components of a projection optical system assembly (e.g., the projector optical system 111 in Figure 1) are (re)calibrated as part of operation 310. In one example, the projector optical system may include a diffractive lens, an intermediate lens, and two projector lenses. To that end, an exemplary process may include, in operation 315, modifying one or more elements of the projection optical system assembly to calibrate the assembly for a second energy E2. The results of the modifications (e.g., as a combined effect of multiple changes to the operating parameters of multiple optical systems) can help compensate for the changes in the charged particle beam resulting from calibrating the charged particle optical system for a second energy (e.g., the optical system of a spectrometer). This allows for energy losses different from the zero-loss peak (ZLP) energy of the source. The effect of optical element calibration on the ray path in an exemplary TEM system is described in more detail with reference to Figures 4A–4D.

[0047] Operation 315 may include one or more suboperations for generating a set of operating conditions for the projection optical system. Generating a set of operating conditions may include determining a solution for a first-order approximation of the projection optical system assembly, as will be explained in more detail with reference to Figure 6. As shown in Figure 4D, the solution may configure the projection optical system to define one or more beam crossovers that substantially coincide with the corresponding positions for operation of the charged particle microscope at an accelerating voltage for a first energy, as shown in Figure 4A. Advantageously, the set of operating conditions generated in operation 315 may allow the projection optical system to compensate for the effects of an objective lens assembly maintained at the first energy, including objective lenses located downstream of the sample position (e.g., objective imaging lens 109 in Figure 1, objective imaging lens 223 in Figure 2). Such objective lenses would otherwise shift the position of one or more beam crossovers, as shown in Figure 4C, adversely affecting the resolution of the detector downstream of the sample.

[0048] In some embodiments, operation 315 may be implemented as an algorithm at least partially encoded in software or other programmable logic. For example, a dataset of operating conditions for a projection optical system may be structured as a lookup table or other data store. The dataset may describe multiple sets of operating conditions for projection assemblies associated with one or more accelerating voltages. Thus, determining the solution may involve referencing a dataset of operating conditions for a charged particle beam system using a second energy as an input parameter. In some embodiments, determining the solution may involve solving a mathematical formula describing a first-order approximation of the projection lens assembly. Solving the mathematical formula may involve implementing one or more computational techniques for solving a coupled system of optical equations, as will be described in more detail with reference to Figure 6.

[0049] In some cases, a first-order approximation of a projection optical system assembly can have multiple solutions, one or more of which may be relatively more physically meaningful. For example, a mathematically correct solution may define a beam path that intersects with the physical constraints of a charged particle beam system. Thus, generating a set of operating conditions may include defining a physically meaningful solution.

[0050] In operation 320, the exemplary process 300 includes focusing one or more condenser optics of a charged particle beam system. The charged particle beam system may include one or more optics configured to function as condenser lenses with respect to the refractive effect imparted to the beam of charged particles. In this context, the condenser optics impart an electromagnetic force to the beam of charged particles to make a divergent beam a parallel or convergent beam. Focusing the condenser lenses may involve modifying one or more operating parameters of the condenser optics so that the beam of charged particles at a second energy E2 approaches a probe forming an optical system (e.g., condenser objective lens 108 in Figure 1, objective condenser lens 221 in Figure 2) while substantially parallel or convergent toward the beam axis. In this way, the probe-forming optical system can be configured to focus the beam of charged particles at a sample position at a second energy E2. Focusing the beam of charged particles at a sample position can correspond to fine focusing with a spatial resolution of about 0.5 nm or less, including its fraction (e.g., about 0.1 nm or less, about 0.05 nm or less). Advantageously, exemplary process 300 may be relatively robust to certain operating parameters of the condenser optical system, at least in part, based on the compensatory effect of the modifications made to the projection optical system in operation 315.

[0051] In operation 325, the exemplary process 300 includes focusing one or more charged particle optical elements of an EELS spectrometer (e.g., spectrometer 115 in Figures 1 and 2). In this context, focusing may include modifying one or more operating parameters of the elements (e.g., elements 235 and / or 240 in Figure 2) so that a crossover can be defined at an on-axis position of the spectrometer such that the beam of charged particles collides with a detector (e.g., detector 245 in Figure 2) while being dispersed by energy along the spatial direction, as described with reference to Figure 2.

[0052] In operation 330, exemplary process 300 includes modifying the tension of the charged particle source. As part of the operational configuration described with reference to Figures 2 and 4E, a portion of the elements of the charged particle beam system is configured for a beam of charged particles around E1, and a second portion of the elements constitutes energy E2. The combined effect of these two configurations is that the charged particles at about E2 define one or more crossovers at appropriate positions for corresponding locations such as detectors, apertures, etc., as described with reference to Figures 4A–4E. For that purpose, the charged particle source can be modified from the tension setting defined in operation 305 to the first energy E1. In some embodiments, exemplary process 300 includes modifying the calibration of the condenser optics from the second energy E2 to the first energy E1. Recalibration of the condenser optics can be performed concurrently with operation 330.

[0053] In operation 335, the exemplary process 300 includes generating detector data. The detector data may include EELS data generated by coupling an electron beam (e.g., the charged particle beam 215 in Figure 2) into an EELS spectrometer (e.g., the EELS spectrometer 115 in Figure 1). For that purpose, operation 335 may include generating a beam of charged particles. In the example of a transmission electron microscope (TEM), operation 335 may include operating an electron emitter (e.g., the source of the charged particle 205 in Figure 2) according to a set of parameters such that the beam of charged particles has an energy close to a first energy at which the beam of charged particles is directed through the sample position toward the detector section of the charged particle beam system (e.g., the detector section 110 in Figure 1). In some embodiments, operation 335 includes generating a beam of charged particles having an energy of about 300 keV, or about 200 keV, or about 60 keV.

[0054] The result of operation 305 is that a portion of the electron beam with an energy close to the second energy is directed toward the detector (e.g., detector 245 in Figure 2), and portions of the electron beam scattered by energies different from the second energy in the range greater than about 0.02·E2 may be blocked, otherwise out of focus, or redirected away from detector 245 by a microscope (e.g., TEM column 105 in Figure 1 and electron microscope 201 in Figure 2) or by a spectrometer component (e.g., energy dispersion filter 235).

[0055] In some embodiments, one or more operations of the exemplary process 300 may be repeated in one or more iterations as part of generating a dataset of EELS spectra for a given sample or a set of samples. For example, operations 305–315 may be repeated over a range of second energy values ​​with respect to a given first energy value. In this way, the difference between the first and second energies may be varied over a range, for example, as part of characterizing the sample to detect and identify elements present in the sample (e.g., by measuring the core ionization edge in the 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 chemical and / or physical data to the sample. In this context, “data cube” refers to a hierarchical data structure in which the 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., using elemental information).

[0056] Advantageously, the presence of fine structures in EELS data generated using the techniques described herein makes it possible to derive localized structural information, for example, by fitting one or more models to detector data from which binding information, oxidation state, or other physical and / or chemical properties of the sample can be derived. Using pseudo-models used for broadband X-ray absorption fine structure (EXAFS) analysis, interatomic spacing (e.g., using an EXELFS model), oxidation state, band structure, and / or coordination information (e.g., crystal structure, bonding, etc.) can be determined. Because the spatial resolution of the EELS system in STEM mode can be on the order of a single atom, EELS data generated using the exemplary process 300 can be used to map chemical, physical, and / or structural information over a region of the sample surface.

[0057] Figures 4A to 4E are schematic diagrams showing an exemplary optical system 400 for a charged particle beam system according to current technology. The optical configuration in Figures 4A to 4E includes a projection optical system assembly 440, which includes a condenser system 405 of one or more condenser optical systems 410, a beam limiting aperture 415, a probe-forming objective lens 420, an imaging objective lens 425, and one or more projector optical systems 445. The components of the exemplary optical system 400 can be configured according to their respective operating parameters for shaping, forming, and / or modifying the beam of charged particles together so that the beam defines one or more crossovers along the beam axis B, including an objective crossover, an imaging crossover, and / or a final crossover. The crossover can be substantial, corresponding to a position on beam axis B where the beam converges to a point or line (e.g., the focal point where the particle beam is actually focused), or virtual, corresponding to a position on beam axis B where the beam converges to a point or line, where it can be substantial due to the action of optical elements (e.g., located beyond or in front of a lens that refocuses the beam before the actual crossover occurs). One or more constraints of the charged particle beam system can define a set of planes along beam axis B, including a sample plane 421, a back focal plane (BFP) 430, a first image plane (FIP) 435, a final crossover (FXO) plane 450, and a detector plane 455.

[0058] The configuration of various components of the exemplary system 400 can be at least partially constrained by the operating mode of the charged particle beam system. For example, in STEM mode, the projection optical system assembly 440 and the constituent projection lens 445 can be modified to a set of operating parameters that satisfy the following four boundary conditions: FIP 435 is imaged onto FXO 450, enabling FXO 450 to function as the input image for a spectrometer (e.g., spectrometer 115 in Figure 1). BFP 430 is imaged onto the detector plane 455, and the detector (M PROJThe camera length or magnification in ) satisfies a given value (e.g., 40 mm), and the image orientation in the detector plane 455 satisfies a given value (e.g., 180°). Different sets of conditions described with reference to Figures 4A to 4D each represent different approaches to operating a charged particle beam system in STEM mode. For that purpose, Figure 4A shows a typical STEM configuration, Figure 4B shows an exemplary configuration for energy loss spectroscopy with relatively large energy loss in field-free mode or with inconsistent calibration of the objective optics, Figure 4C shows operating in immersion mode (maintaining consistent calibration of objective lenses 420 and 425 on either side of the sample plane 421), and Figure 4D shows an improvement to the immersion mode by generating set operating conditions for the projection optics according to embodiments of the present disclosure. In Figures 4A to 4D, the various lens ellipse fill patterns represent calibration states in which two lenses with a common fill pattern are calibrated for substantially equal beam energies. In an exemplary example, the capacitor system 405 in Figure 4C is calibrated for a first energy E1 and filled with a first fill pattern, while the projection optical system assembly 440 is calibrated for a second energy E2 and filled with a second fill pattern.

[0059] Figure 4A shows the optical elements consistently calibrated against the source tension (e.g., 300 kV). The filled-in rays represent the probe-forming trajectories that define the first crossover at the sample plane 421, the second crossover at the first image plane (FIP) 435, and the final crossover (FXO) 450 between the projection optical system assembly 440 and the detector plane 455. The dashed lines represent the scanning trajectories in STEM mode, defining the first crossover at the back focus plane (BFP) 430 and the second crossover at the detector plane 455. As explained with reference to Figure 2, in this configuration, EELS data are limited to within approximately 1% of the beam energy, at least in part, based on the fact that the significance of aberrations increases and the signal-to-noise ratio decreases as the energy loss value increases.

[0060] Figure 4B shows an operational configuration for generating large energy loss (XEELS) data with inconsistent calibration across objective lenses. In this configuration, the optics upstream of the sample plane 421 (e.g., condenser system 405, probe-forming objective lens 420) are calibrated for a first energy E1, and the optics downstream of the sample plane 421 (e.g., projection optics assembly 440, imaging objective lens 425, etc.) are calibrated for an energy that reflects the energy loss of the target (e.g., an energy loss of 10kV applied to a first energy E1 of 300kV provides a second energy E2 of 290kV). Advantageously, this configuration provides the transfer of charged particles to the sample plane 421 without having to deal with the individual adjustments of the component lenses 405 of the illumination optics systems 405 and 420. Thus, the approach illustrated in Figure 4B may be successful and advantageous in terms of time and complexity in charged particle beam systems where the objective lens system can be calibrated for different beam energies, such as in a non-immersion mode. However, in the case of magnetic immersion objective lenses, objective lenses 420 and 425 are constrained to a consistent calibration energy for the immersion mode (including, in some cases, a spherical aberration corrector). For that purpose, the probe forming the objective lens 420 must be calibrated to a second energy, even though it is positioned upstream of the sample plane 421. Therefore, the operating configuration in Figure 4B cannot be applied in immersion mode.

[0061] Figure 4C shows an operating configuration for generating large energy loss (XEELS) data in immersion mode. In this configuration, the optical system downstream of the sample plane 421 (e.g., projection optical system assembly 440, sample objective lens 425) is calibrated to an energy that reflects the target energy loss (e.g., a 10kV energy loss, E1, applied to a first energy of 300kV, provides a second energy, E2, at 290kV). Advantageously, the configuration provides the transfer of charged particles to the detector plane 455 without having to deal with the individual adjustments of the component lenses 445 of the projection optical system system 440. However, the probe-forming objective lens 420 is constrained to be calibrated at the same second energy E2. Since the calibration of lens 420 (at energy E2) no longer matches the energy E1 of the beam within lens 420, the condenser assembly 405 and the objective lens assembly (several deflectors and stigmeters (not shown in Figure 4), and objective lens 420) are readjusted to achieve the atomic resolution (e.g., sub-angstroms) of the electron microscope.

[0062] Such recalibration of condenser assemblies and objective lens assemblies can be time-consuming. Furthermore, some charged particle beam systems may include a probe-forming objective lens 420, for which the operating window does not include a set of parameters that allow it to be calibrated for a second energy E2. In such cases, one or more condenser optics 410 can be modified to conform to the constraints imposed by the probe-forming objective lens 420. Such manual recalibration can be technically complex and time-consuming, and may be scaled in particular by producing large energy-loss EELS ("XEELS") data at two or more energy differences.

[0063] Figure 4D shows a configuration that reflects the result of maintaining an objective field calibrated for a first energy, E1 (for example, calibrated for the first energy, E1 even though the sample objective lens 425 is positioned downstream of the sample plane 421). In this configuration, the sample objective lens 425 is too strong for charged particles at a second energy, E2. The overfocus of the sample objective lens 425 shifts the crossover at FIP ​​435 and BFP 430 upstream toward the sample plane 421. The projection optical system assembly 440 calibrated for a second energy, E2, shifts the final crossover (FXO) 450 and detector plane 455 to M Proj It does not return to a position that corresponds to the constraints. Typically, such a shift is relatively large (several millimeters or more in the FXO 450) and causes significant signal loss and a decrease in resolution in EELS. Furthermore, correcting the shift involves recalculating the projector lens settings, which is a technically difficult, time-consuming, and requires significant human intervention.

[0064] Figure 4E is a schematic diagram illustrating the operating principle of an exemplary charged particle beam system according to several embodiments of the present disclosure. Figure 4E shows objective lenses 420 and 425 operating with consistent calibration to immerse the sample plane 421 in the objective field (for example, both the upper and lower objective lenses are calibrated for a first energy E1). The result of this approach is that the image-forming objective lens 425 is improperly calibrated for charged particles at a second energy E2, causing a significant shift in the position of the first image plane (FIP) 435 (the illustration in Figure 4D is for a configuration where the second energy E2 is smaller than the first energy E1, shifting the FIP 435 toward the sample plane 421). Embodiments of the present disclosure address the shift, indicated by the arrows oriented perpendicularly in Figure 4E, at least in part, by recalibrating the projector system 440, as will be described in more detail with reference to Figures 3 and 6. The advantages of this approach are that the STEM resolution is unaffected and artifacts in the XEELS data are reduced. The objective field can be maintained for a first energy (e.g., 300 kV), and the projection optical system assembly 440 can be recalibrated to accommodate the XO shift at the BFP and FIP.

[0065] In an exemplary example, if the number of projector lenses 445 matches the number of boundary conditions, one or more solutions are possible (e.g., the problem is fully defined). However, finding a suitable solution that satisfies the system's boundary conditions is not trivial because the problem is highly nonlinear. Furthermore, the solution should minimize higher-order aberrations and prevent the beam from colliding with the inner surface of the optical system (e.g., TEM column 105 in Figure 1).

[0066] In current technology, generating a single magnification setting that satisfies boundary conditions can take several hours (calculation and testing), and a series of good magnification settings can take several weeks. For these reasons at least, magnification settings are typically pre-calculated, pre-tested, and pre-stored in a magnification table, significantly limiting the flexibility of the STEM system to respond to user input of energy loss data (e.g., energy difference, second energy E2, etc.). A set of pre-calibrated operating conditions is unavailable. For this purpose, the technology of this disclosure can apply a primary transfer optical system, a parameterized thick lens model, and an analytical algorithm to generate a set of operating conditions (e.g., projection lens settings) that satisfy the boundary conditions mentioned above (e.g., attenuating aberrations and collisions on the inner surface). In this way, the time required to generate new magnification settings is significantly reduced from several hours to a fraction of a second.

[0067] Figure 5A is a graph showing exemplary electron energy loss spectrum (EELS) data 500 of a copper foil sample according to several embodiments of the present disclosure. This graph includes data for core-shell ionization, represented as an edge centered at approximately 9 keV, including fine structures. The graph plots the data 500 on a two-dimensional set of axes with energy on the vertical axis and counted in arbitrary units (AU) on the horizontal axis, over a range of approximately 8.0 keV to approximately 10.0 keV. In the exemplary data shown, the EELS data 500 reproduces the location of fine structural features present in the EXAFS data, as detailed in Figure 5B.

[0068] In comparison, current techniques for measuring EELS data with similarly high energy loss typically result in significant signal-to-noise limitations due to miscalibration of the solid angle collected by the EELS spectrometer (leading to inappropriate collection angles) and the introduction of aberrations in the TEM column and EELS spectrometer, which 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 the signal-to-noise characteristics of detector data and a significant improvement in energy resolution, which together greatly facilitate EXELFS analysis.

[0069] Figure 5B is a graph detailing exemplary electron energy loss spectrum (EELS) data 510 for the copper sample in Figure 5A, superimposed with EXAFS data 515 according to some embodiments of the present disclosure. Data 510 presents the EELS spectrum of the copper edge at approximately 9 keV, representing the magnification of the microstructure present within approximately 0.3 keV at the edge location. Data 510 was acquired over 900 seconds using a beam current of 2.3 nA corresponding to a dose of 2.1 μC. Data 510 is presented to further illustrate the energy loss values ​​addressed by embodiments of the present disclosure. The count values ​​presented on the y-axis illustrate the improvement in signal-to-noise characteristics at relatively high energy loss edges, reinforcing the demonstration in Figure 5A, including microstructures from which physical structural information can be derived. Furthermore, the improvement in microstructure resolution further demonstrates the advantages of the present disclosure. In the exemplary data shown, EELS data 410 reproduces the location of microstructure features present in EXAFS data 515.

[0070] Figure 6 shows various parameters that can be used to describe the primary particle optical effect of a thick magnetic lens according to some embodiments of the present disclosure. Figure 6 schematically shows electron beams B1, B2 and the optical axis B. As shown, various parameters that can be used to provide a primary description of a thick magnetic lens are defined. An electron beam B1 entering the lens from the top surface (forward direction) parallel to the optical axis B' is refracted at the principal plane Zpi and crosses the optical axis B' at the focal plane Zfi. The distance between Zpi and Zfi is defined as the focal length fi. An electron beam B2 entering the lens from the bottom surface (rear direction) parallel to the optical axis B' is refracted at the principal plane Zpo and crosses the optical axis B' at the focal plane Zfo. If the potential is constant along the optical axis B', then fo = fi. In Figure 6, Z0 indicates the geometric center of the thick lens.

[0071] The lensing action between the two principal planes Zpi and Zpo can be described by the following determinant:

[0072]

number

[0073] In 3 dimensions, a vector (x, x') is a complex vector (u, u') = (x + iy, x' + iy') (where i is (external 2) This can be replaced by (shown in TIFF2026049697000007.tif35). Furthermore, the magnetic lens also rotates the electron ray vector at an angle θ. This rotation is due to the lens excitation NI (N = coil rotations; I = coil current), and

number

[0074] It may be convenient to explain the lensing action by a matrix acting at the geometric center of the lens using multiple lenses arranged in series to form a composite lens / imaging system. Starting from Z0, the ray first travels to the Zpo plane, then the lensing action described by equation [1] occurs, and subsequently the ray returns from Zpi to the geometric center of the lens, which is,

number

[0075] Furthermore, a drift matrix is ​​used.

[0076]

number

[0077]

number

[0078] In the equation, the Δ term is the drift matrix (see above) and the L term is the lens matrix (see equation [2]). By inverting the entire system matrix, the calculation from the image plane to the object plane can be performed. The magnification M of the imaging / projection system is typically much greater than 1, and therefore the depth of field is much smaller in the object plane than in the image plane, so the calculation for focusing the lens series may be more accurate in the backward direction.

[0079] The optical properties of a given lens system can be calculated by solving equation [3]. In some cases, software employing a root-finding algorithm (such as the Newton-Raphson algorithm) can be used. Similarly, the basis planes Zpi, Zpo, Zfi, and Zfo in the above considerations can be calculated and determined using software.

[0080] The algorithms may be embodied as software or firmware instructions executed by a controller, such as a digital computing device. For example, any of the disclosed calculations relating to a lens system may be executed by a computer or other computing hardware (e.g., an ASIC, FPGA, CPLD, etc.) that is part of a control system (e.g., control system 210 in Figure 2). The control system may be connected to or otherwise communicate with an imaging system (e.g., a lens), receive imaging data from a sensing device or user control input, and be programmed or configured to perform desired calculations relating to the operating parameters of the lens system or lookup table access (e.g., any of the lens parameter variation techniques disclosed herein). The controller may be a computer system comprising one or more processors (processing devices) and tangible non-temporary 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 drives, NVRAM, and solid-state drives (e.g., flash drives)). One or more processors may execute computer-executable instructions stored in one or more of the tangible non-temporary computer-readable media, thereby performing any of the disclosed techniques. For example, software for performing any of the disclosed embodiments may be stored as one or more computer-executable instructions in one or more volatile non-temporary computer-readable media, and when executed by one or more processors, causes one or more processors to perform any of the disclosed techniques for calculating the operating parameters of a lens system. The results of the calculation may be stored in one or more tangible non-temporary computer-readable storage media (e.g., in a suitable data structure or lookup table) and / or may be output to a user, for example, by displaying them on a display device using a graphical user interface.

[0081] The above description has described various embodiments. For explanatory purposes, specific configurations and details have been given to provide a complete understanding of the embodiments. However, it will be apparent to those skilled in the art that embodiments can be practiced without specific details. Furthermore, well-known features may be omitted or simplified in order not to obscure the embodiments described. The exemplary embodiments described herein focus on electron microscope systems, and in particular scanning transmission electron microscope systems, but these are intended as non-limiting exemplary embodiments. Embodiments of the Disclosure are not limited to such embodiments, but rather are intended to cover analytical instrument systems capable of analyzing a wide range of material samples to determine chemical properties, biological properties, physical properties, structural properties, or other properties, including, but not limited to, chemical structure, trace element composition, etc. Accordingly, embodiments of the Disclosure more broadly include charged particle instruments, including focused ion beam systems, scanning electron microscope systems, electron beam trace analysis systems, etc.

[0082] Some embodiments of this disclosure include a system comprising one or more data processors and / or logic circuits. In some embodiments, the system includes a non-temporary computer-readable storage medium containing instructions that, when executed by one or more data processors and / or logic circuits, cause one or more data processors and / or logic circuits to perform some or all of one or more methods disclosed herein and / or some or all of one or more processes and workflows. Some embodiments of this disclosure include a computer program product tangibly embodied in a non-temporary machine-readable storage medium, which contains instructions configured to cause one or more data processors and / or logic circuits to perform some or all of one or more methods disclosed herein and / or some or all of one or more processes.

[0083] The terms and expressions used are for illustrative purposes only and not limiting, and the use of such terms and expressions is not intended to exclude the illustrated and described features or their equivalents, but it should be recognized that various modifications are possible within the scope of the claims. Accordingly, while this disclosure includes specific embodiments and optional features, modifications and changes to the concepts disclosed herein can be made by those skilled in the art, and such modifications and changes should be understood to be within the scope of the appended claims.

[0084] Where terms are used without a clear definition, they should be understood to have their ordinary meaning unless they have a special and / or specific meaning in the field of charged particle microscope systems or other related fields. The terms “approximately” or “substantially” are used to indicate a deviation from a described characteristic, such deviation having little or no effect on the corresponding function, characteristic, or attribute of the described structure. In the illustrated example, 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 not be equal within tolerances such as manufacturing tolerances or confidence intervals inherent to the operation of the system. Similarly, where geometric parameters such as alignment or angular orientation are described as “approximately” perpendicular, “substantially” perpendicular, or “substantially” parallel, the terms “approximately” or “substantially” are intended to reflect that the alignment or angular orientation may differ from the precisely described state within tolerances (e.g., not exactly perpendicular). For numerical values ​​such as diameter, length, and width, the term “approximately” can be understood to describe a deviation of up to ±10% from the stated value. For example, a dimension of "approximately 10mm" can represent a dimension between 9mm and 11mm.

[0085] This specification provides exemplary embodiments and is not intended to limit the scope, applicability, or configuration of the disclosure. Rather, the following description of exemplary embodiments will provide those skilled in the art with a practical guide for implementing various embodiments. It will be understood that various modifications can 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 given in the description to provide a full understanding of the embodiments. However, it will be understood that it is possible to practice without these specific details. For example, specific system components, systems, processes, and other elements of this disclosure may be shown in schematic form or omitted from the drawings so as not to obscure the embodiments with unnecessary details. In other examples, well-known circuits, processes, components, structures, and / or techniques may be shown without unnecessary details.

Claims

1. A method for analyzing a sample using a charged particle beam system, The accelerating voltage of the source of the charged particle beam system is modified from a first energy to a second energy, wherein the first energy and the second energy are separated by an energy difference. Modifying one or more optical elements of the charged particle beam system in accordance with the second energy calibration, To generate a set of operating conditions for the projection optical system of the charged particle beam system, the set of operating conditions being at least partially based on operating the source near the second energy, Modifying one or more elements of the projection optical system in accordance with at least part of the set of operating conditions, The modification involves correcting the condenser lens of the charged particle beam system in accordance with focusing the beam of charged particles to the sample position, such that the beam of charged particles has an energy close to the second energy. A method comprising modifying the acceleration voltage from the second energy to the first energy.

2. The method according to claim 1, further comprising modifying one or more optical elements of the EELS spectrometer of the charged particle beam system in accordance with focusing the beam of charged particles onto a detector of the EELS spectrometer, such that the beam of charged particles has an energy close to the second energy.

3. The beam of charged particles is the first beam, and the method is The method involves generating a second beam of charged particles, wherein the second beam of charged particles has an energy close to that of the first beam. The first beam of the charged particles is directed through the sample position, The method according to claim 2, further comprising generating detector data using the detector of the EELS spectrometer.

4. The method according to claim 1, further comprising modifying one or more optical elements of the charged particle beam system in accordance with focusing the beam of charged particles to the sample position, wherein the focusing corresponds to a fine focus with a spatial resolution of about 0.1 nm or less.

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

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

7. The method according to claim 1, wherein the first energy and the second energy are related by the equation A = |(ΔE + E2 - E1) / E2|, where ΔE is the energy loss associated with the edge (keV), E1 is the first energy (keV), E2 is the second energy (keV), and equation A is about 1% to about 10%.

8. The method according to claim 1, wherein generating the set of operating conditions includes determining a solution for a first-order approximation of a projection optical system assembly, the solution comprising a beam of charged particles defining a final crossover (FXO) between the projection optical system assembly and a detector plane substantially satisfying one or more boundary conditions of the charged particle beam system, the boundary conditions including a magnification in the detector of the charged particle beam system.

9. The method of claim 8, wherein determining the solution involves referring to a dataset of operating conditions for the charged particle beam system using the second energy and input parameters, the dataset describing a plurality of sets of operating conditions for the projection optical system assembly associated with one or more accelerating voltages.

10. The method according to claim 8, wherein determining the solution involves solving a mathematical formula that describes the first-order approximation of the projection optical system assembly.

11. One or more machine-readable storage media, which, when executed by a machine, the machine, Modifying the acceleration voltage of the source of a charged particle beam system from a first energy to a second energy, wherein the first energy and the second energy are separated by an energy difference; Modifying one or more optical elements of the charged particle beam system in accordance with the second energy calibration, To generate a set of operating conditions for the projection optical system of the charged particle beam system, the set of operating conditions being at least partially based on operating the source near the second energy, Modifying one or more elements of the projection optical system in accordance with at least part of the set of operating conditions, The modification involves correcting the condenser lens of the charged particle beam system in accordance with focusing the beam of charged particles to the sample position, such that the beam of charged particles has an energy close to the second energy. A machine-readable storage medium for storing instructions for causing one or more operations to be performed, including modifying the acceleration voltage from the second energy to the first energy.

12. The aforementioned operation is, The medium according to claim 11, further comprising modifying one or more optical elements of the EELS spectrometer of the charged particle beam system in accordance with focusing the beam of charged particles onto the detector of the electron energy loss (EELS) spectrometer, such that the beam of charged particles has an energy close to the second energy.

13. The beam of charged particles is the first beam, and the operation is, The method involves generating a second beam of charged particles, wherein the second beam of charged particles has an energy close to that of the first beam. The second beam of the charged particles is directed through the sample position, The medium according to claim 12, further comprising generating detector data using the detector of the EELS spectrometer.

14. The aforementioned operation, The medium according to claim 11, further comprising modifying one or more optical elements of the charged particle beam system in accordance with focusing the beam of charged particles to the sample position, wherein the focusing corresponds to a fine focus with a spatial resolution of about 0.1 nm or less.

15. The medium according to claim 11, wherein the second energy is about 90% to about 98.5% of the first energy.

16. The medium according to claim 11, wherein generating the set of operating conditions includes determining a solution for a first-order approximation of a projection optical system assembly, the solution comprising the beam of charged particles defining a final crossover (FXO) between the projection optical system assembly and a detector plane substantially satisfying one or more boundary conditions of the charged particle beam system, the boundary conditions including magnification in the detector of the charged particle beam system.

17. Determining the solution involves referencing a dataset of operating conditions for the charged particle beam system using the second energy and input parameters, the dataset describing a plurality of sets of operating conditions for the projection optical system assembly associated with one or more accelerating voltages, according to claim 16.

18. The medium according to claim 16, wherein determining the solution involves solving a mathematical formula describing the first-order approximation of the projection optical system assembly.

19. A charged particle beam system, Charged particle source, A charged particle optical column coupled to the aforementioned source, An objective lens section that defines the sample position, A column and a projection optical system, A detector section coupled to the column, A control circuit operably coupled to the source, the column, and the detector section, One or more machine-readable storage media operably coupled to the control circuit, wherein when executed by a machine, the machine, The accelerating voltage of the source of the charged particle beam system is modified from a first energy to a second energy, wherein the first energy and the second energy are separated by an energy difference. Modifying the optical elements of the charged particle beam system so that the optical elements are calibrated for the second energy, To generate a set of operating conditions for the projection optical system, the set of operating conditions being at least partially based on operating the charged particle source near the second energy, Modifying one or more elements of the projection optical system in accordance with at least part of the set of operating conditions, The modification involves correcting the condenser lens of the charged particle beam system in accordance with focusing the beam of charged particles to the sample position, such that the beam of charged particles has an energy close to the second energy. A system comprising a machine-readable storage medium that stores instructions for performing one or more operations, including modifying the acceleration voltage from the second energy to the first energy.

20. The detector section includes an electron energy loss spectrometer coupled to the column and oriented to receive the beam of charged particles through the projection optical system, and the operation is as follows: The modification involves focusing the beam of charged particles onto the detector of the electron energy loss (EELS) spectrometer, thereby modifying one or more optical elements of the EELS spectrometer in the charged particle beam system, such that the beam of charged particles has an energy close to the second energy. The method involves generating a second beam of charged particles, wherein the second beam of charged particles has an energy close to that of the first beam. The second beam of the charged particles is directed through the sample position, The system according to claim 19, further comprising generating detector data using the detector of the EELS spectrometer.

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