Charged-particle microscope with multiple imaging modes

Abstract

A scanning charged particle microscope (400-5) includes an acceleration electrode (408) arranged between a sample plane and a beam splitter (406, 409). The acceleration electrode (408) is configured to accelerate the secondary charged particles towards the beam splitter. that separates a primary charged-particle beam path (451) from a secondary charged-particle beam path (452). Also provided is an energy-selective element (490, 491) to selectively deflect the secondary charged particles depending on their kinetic energies. Various imaging modes such as momentum-resolved and energy-resolved imaging are supported.

Description

[0001] D E S C R I P T I O N

[0002] CHARGED-PARTICLE MICROSCOPE WITH MULTIPLE IMAGING MODES

[0003] PRIORITY

[0004] The subject application claims priority of German patent application 10 2024 136 270.7, filed December 5, 2024, the disclosure of which is incorporated herein by reference.

[0005] TECHNICAL FIELD

[0006] The present disclosure relates to the field of charged-particle microscopy, particularly scanning electron microscopy (SEM). More specifically, it pertains to charged-particle microscopes and metrology systems with energy-resolved and / or momentum- resolved imaging of electrons from secondary emission (SE) and / or backscattered electrons (BSE).

[0007] BACKGROUND

[0008] SEMs scan primary electrons across a sample plane and secondary electrons including SEs and BSEs are detected. The BSEs and SEs are detected for each position of the primary electrons in the sample plane.

[0009] In a basic imaging mode, a flux of the BSEs and SEs is detected. This intensity is translated into a greyscale pixel value of the raster image for that scanning position.

[0010] In some cases, it may be desirable to measure energy or even momentum of the SEs and / or BSEs.

[0011] Measuring the momentum includes detecting the angles and energies of electrons reaching the detector from the sample plane. For instance, to probe a nanoscale surface potential, a signal can be analyzed in different directions extending away from the sample plane, as the effect of surface potentials is most pronounced for the slowest electrons. By employing both angular and energy-resolved (momentum resolved) detection techniques, it is possible to probe surface potentials by detecting local changes in the trajectories of these slow electrons. By analyzing the momentum of electrons, insights may be obtained about the material under examination. For instance, information about the band structure, which includes the density of states and doping levels, or surface potentials can be discerned. This analysis typically requires an energy resolution on the order of a few electron volts (eV) or, preferably, less than 1 eV. Further, a distribution of kinetic energy of electrons may be measured using spectroscopic techniques, e.g., as disclosed in US 2020 / 0273665 A1 and US 11 ,710,615 B2.

[0012] It is recognized that SEs and BSEs provide valuable additional information regarding their momenta and points of origin. Unfortunately, such detailed information is not captured with sufficient resolution by current methods employing energy-threshold detectors, chicanes, or 4-quadrant detectors. For example, the energy resolution of current detectors is often in the range of hundreds of eV, which can limit the detail and accuracy of energy and momentum imaging. Also, angular information of the SEs and BSEs may sometimes be lost, preventing momentum-resolved imaging.

[0013] SUMMARY

[0014] Accordingly, a need exists for advanced techniques of momentum-resolved imaging and / or energy-resolved imaging in charged-particle microscopes. Specifically, a need exists for momentum-resolved imaging and / or energy-resolved imaging of SEs and / or BSEs.

[0015] This need is met by the subject matter of the independent claims. Further advantageous features are subject matter of the dependent claims.

[0016] In the following, the solution according to the present disclosure will be described with respect to charged-particle microscopes as well as with respect to cross-beam systems employing a combination of a primary electron beam and a primary ion beam at a crossed configuration. Features, advantages, or alternative embodiments explained in connection with a charged-particle microscope such as a SEM are applicable to cross-beam systems, and vice versa.

[0017] A scanning charged particle microscope is disclosed. The scanning charged particle microscope includes an illumination column. The illumination column is configured to emit primary charged particles along a primary charged-particle beam path towards a sample plane. The scanning charged particle microscope also includes a detection column configured to guide secondary charged particles -e.g., SEs and / or BSEs for a SEM - from the sample plane along a secondary charged-particle beam path. The primary charged-particle beam path and the secondary charged-particle beam path overlap in an overlap region, the overlap region extending between a beam splitter and the sample plane. The scanning charged particle microscope also includes an acceleration electrode arranged between the sample plane and the beam splitter and configured to accelerate the secondary charged particles along the secondary charged-particle beam path towards the beam splitter. The scanning charged particle microscope also includes the beam splitter configured to separate the primary charged-particle beam path from the secondary charged-particle beam path. The scanning charged particle microscope also includes an energy-selective element configured to be arranged in the secondary charged-particle beam path downstream of the beam splitter and to selectively deflect trajectories of the secondary charged particles along the secondary charged-particle beam path depending on their kinetic energies. The scanning charged particle microscope also includes a multi-pixel detector arranged downstream of the energy-selective element and to detect the manipulated trajectories of the secondary charged particles. Different pixels of the multi-pixel detector can provide separate signals, e.g., indicative of the local charged- particle flux.

[0018] The charged particles may be electrons or other particles. The scanning charged particle microscope may be a SEM.

[0019] An illumination column may correspond to the primary beam path and may refer to a component of the scanning charged-particle microscope that generates and directs the primary charged-particle beam towards the sample. It may comprise a charged- particle source, such as an electron gun, and a series of electromagnetic lenses and apertures that shape and focus the beam onto the sample surface.

[0020] A detection column may correspond to the secondary beam path and may refer to the part of the microscope that collects and analyzes the secondary charged particles originating from the sample. It may comprise a series of electromagnetic lenses, deflectors, analyzers, and detectors that guide and characterize the secondary particles.

[0021] By implementing the overlap region, it is possible to detect the secondary charged particles in a broad spectrum of the momentum, i.e., for various angles of departure from the sample plane. In particular, it is not required to limit detection of the secondary charged particles to certain angular spectra as defined by circular detectors in the prior art. Thereby, momentum-resolved imaging is facilitated.

[0022] In particular, low-energy charged particles may be detected, e.g., secondary electrons, by employing the acceleration electrode. The acceleration electrode increases the kinetic energy of such charged particles so that interference becomes relatively less pronounced.

[0023] In various examples, the scanning charged-particle microscope may further include a detector optics arranged in the secondary charged-particle beam path between the energy-selective element and the multi-pixel detector. The detector optics may be configured to selectively switch between projecting a backfocal plane along the secondary charged-particle beam path onto a detector plane of the multi-pixel detector, and projecting a crossover plane onto the detector plane of the multi-pixel detector. This selective switching capability of the detector optics between different projection modes may enable the microscope to adapt to various imaging requirements, such as momentum-resolved or position-resolved imaging, thereby enhancing the versatility and functionality of the instrument.

[0024] The detector optics manipulates and projects the trajectories of the secondary charged particles onto the detector plane in a controlled manner. The backfocal plane may refer to a plane conjugate to the focal plane of an objective lens, where the angular distribution of the secondary particles is mapped to spatial coordinates. A crossover plane, on the other hand, may correspond to an image plane that is conjugate to the sample surface, preserving the spatial distribution of the secondary particles. By selectively switching between these two projection modes, the detector optics enables the microscope to capture either momentum-resolved or position- resolved information (associated with the angle) of the secondary particles, depending on the specific imaging requirements. Thus, it is possible to selectively activate momentum-resolved or position-resolved imaging, respectively.

[0025] In various examples, the scanning charged-particle microscope may further include electronic circuitry configured to analyze a detector image of the multi-pixel detector to determine at least one of an energy distribution, a one-dimensional or two- dimensional momentum distribution of the secondary charged particles. The energy distribution may represent the histogram or spectrum of the kinetic energies of the detected secondary particles, which can provide insights into the electronic states and chemical composition of the sample. The one-dimensional or two-dimensional momentum distribution may correspond to the angular or directional distribution of the secondary particles' momenta, which can reflect the local band structure, scattering processes, or surface dynamics of the sample materials under investigation.

[0026] This analysis capability may provide quantitative information about the sample's electronic structure, surface potential, or material properties from the spatially resolved measurements of the secondary particle energies and / or momenta, thereby enabling various imaging modes. Spatial information in the detector plane of the multi-pixel detector can be translated into energy or momentum information.

[0027] In various examples, the beam splitter of the scanning charged-particle microscope may be configured to image (in other words provide a one-to-one correspondence I bijective mapping from an input to an output) a momentum (or momentum distribution), particularly an in-plane momentum (distribution), of the secondary charged particles as emitted from the sample. The in-plane momentum may refer to the component of the secondary particle's momentum that is parallel to the sample surface plane (e.g., pxand py). This momentum-imaging property of the beam splitter allows measurements of the angular distribution and directional properties of the secondary particles.

[0028] Imaging the momentum may involve using specific beam splitter designs, such as magnetic prisms or electrostatic deflectors, that can separate the primary and secondary beam paths while minimizing distortions or aberrations in the secondary particle trajectories. Furthermore, by using a correction element such as a mirror in the primary particle trajectory, resolution can be further increased.

[0029] In various examples, the beam splitter of the scanning charged-particle microscope may include a magnetic prism.

[0030] A magnetic prism may include a magnetic yoke or pole piece that generates a magnetic field perpendicular to the beam paths. As the charged particles traverse this magnetic field region, they experience a Lorentz force that deflects their beam paths depending on their momenta and the field strength. By appropriately designing the shape and intensity of the magnetic field, the magnetic prism may achieve efficient spatial separation of the primary and secondary beams while unambiguously mapping the angular and momentum distribution of the secondary particles from an input to the magnetic prism to an output of the magnetic prism.

[0031] In various examples, the energy-selective element of the scanning charged-particle microscope may include at least one of a hemispherical analyzer, a spectrometer, a filter, a magnetic-field separator, or an electric-field separator. These different types of energy-selective elements may provide versatile and adaptable methods for discriminating the kinetic energies of the secondary charged particles, enabling energy-resolved imaging.

[0032] A hemispherical analyzer may refer to an electrostatic energy analyzer that includes two concentric hemispherical electrodes with a potential difference applied between them. This creates a radial electric field that disperses the incoming charged particles based on their kinetic energies. This is an energy-dispersive element.

[0033] A spectrometer may be a general term for an energy-dispersive device that can measure the energy distribution of the charged-particles, such as a time-of-flight spectrometer, a retarding field analyzer, or a sector field energy analyzer. A filter may refer to an energy-selective element that transmits particles within a specific energy range while rejecting others, such as a bandpass, high-pass, or low-pass energy filter. These filters can be implemented using electrostatic or magnetic fields, or a combination of both.

[0034] A magnetic-field separator may use a magnetic field to deflect and separate the charged-particles based on their momenta, similar to how a magnetic prism functions as a beam splitter. An electric-field separator, on the other hand, may employ an electrostatic field to disperse the particles according to their kinetic energies, analogous to an electrostatic analyzer.

[0035] In various examples, the energy-selective element of the scanning charged-particle microscope may include a first element, and a second element arranged downstream along the secondary charged-particle beam path. The first element may be configured to apply a first deflection to the trajectories of the secondary charged particles depending on their kinetic energies, while the second element may be configured to apply a second deflection to the trajectories of the secondary charged particles depending on their kinetic energies. The second deflection may counteract or cancel the first deflection. This combination of two deflection elements with opposite dispersion characteristics may allow for a more precise control and selection of the energy range of interest while minimizing aberrations and improving the overall energy resolution of the microscope.

[0036] The first and second elements of the energy-selective element may refer to two separate stages or components of an energy-dispersive device that act together to define the energy selective process. The first deflection applied by the first element may spatially separate the secondary charged particles based on their kinetic energies, creating an energy-dispersed profile along the beam path. The second deflection applied by the second element may then counteract or cancel this energy dispersion, effectively reversing the separation caused by the first element.

[0037] An energy selection thereby becomes possible, by selecting a certain trajectory I kinetic energy in-between the first and second elements. In various examples, the scanning charged-particle microscope may further include a slit aperture configured to be arranged between the first element and the second element of the energy- selective element. The slit aperture may serve as a spatial filter that selects a specific portion of the energy-dispersed secondary charged-particle beam, allowing only particles within a narrow energy range to pass through to the second element. By adjusting the position and width of the slit aperture, the energy passband of the microscope may be controlled, in order to enable energy-filtered imaging and spectroscopy. Alternatively or additionally, the slit aperture may be fixed while the trajectories are adjusted; e.g., by adjusting the dispersion applied by the first and second elements or using a dedicated electrooptical element such as deflector coils I a deflector plate ahead of the slit aperture. Then the slit aperture may remain fixed which may be preferrable for increased stability.

[0038] A slit aperture, in the context of an energy-selective element with two deflection stages, may refer to a narrow, for example rectangular opening positioned in the space between the first and second deflection elements. This slit aperture may function as a physical barrier that blocks particles outside a specific energy range while allowing those within the selected range to pass through to the second deflection element. The width of the slit aperture may determine the energy passband, or the range of kinetic energies that are transmitted by the energy- selective element. According to various examples, an energy-dispersive element may achieve a separation of trajectories of the charged particles such that a 10 pm wide slit aperture achieves a 1 eV energy resolution. A narrower slit may result in a smaller energy passband and higher energy resolution, while a wider slit may increase the signal intensity at the cost of reduced energy resolution. The position of the slit aperture along the energy-dispersed beam profile may define the central energy of the passband, enabling the selection of specific energy regions of interest for imaging or spectroscopy.

[0039] In various examples, the slit aperture of the scanning charged-particle microscope may be motorized and configured to be positioned at different positions associated with different kinetic energies of the secondary charged particles. This motorized positioning capability of the slit aperture may enable the microscope to switch between different energy passbands without the need for manual adjustments. By electronically controlling the position of the slit aperture, the microscope may acquire energy-filtered images or spectra over a range of kinetic energies. Alternatively or additionally, the slit aperture may be fixed while the trajectories are adjusted; e.g., by adjusting the dispersion applied by the first and second elements or using a dedicated electrooptical element such as deflector coils I a deflector plate ahead of the slit aperture. Then the slit aperture may remain fixed which may be preferrable for increased stability.

[0040] A motorized aperture may refer to an aperture that is equipped with a mechanical actuator, such as a stepper motor or a piezoelectric transducer, which allows for its position to be electronically controlled and adjusted along the energy-dispersed secondary charged-particle beam path. By changing the position of the aperture, the central energy of the transmitted passband may be selected, enabling the microscope to probe different regions of the kinetic energy spectrum.

[0041] In various examples, the scanning charged-particle microscope may further include an aperture arranged in a backfocal plane or an image of the backfocal plane of the secondary charged-particle beam path upstream of the energy-selective element. This aperture may function as a spatial filter that selects a specific angular range of the secondary charged particles, effectively controlling the angular acceptance of the multi-pixel detector.

[0042] Such aperture may be a slit aperture or a pinhole aperture. A pinhole may include a circular opening.

[0043] A backfocal plane may refer to a plane conjugate to the focal plane of an objective lens, where the angular distribution of the secondary charged particles is mapped to spatial coordinates. In other words, particles emitted from the sample at the same angle but from different positions converge to a single point in the backfocal plane. Similarly, particles emitted from the sample at different angles but from the same positions do not converge at a single point in the backfocal plane.

[0044] Placing an aperture - e.g., a slit aperture or a pinhole aperture - in the backfocal plane or an image of the backfocal plane upstream of the energy-selective element may allow for the selection of a specific range of emission angles for the secondary charged particles. This angular filtering enables momentum-resolved imaging. By adjusting the position of the aperture along the angular axis, specific regions of interest in the momentum space may be selected, while the width of the aperture determines the angular resolution and collection efficiency. Similarly, an electrooptical deflector may be used to select specific regions of interest.

[0045] In various examples, the scanning charged-particle microscope may further include electronic circuitry configured to operate one or more components of the microscope in accordance with an active one of multiple imaging modes. The multiple imaging modes may be selected from the group comprising one-dimensional momentum- resolved imaging, two-dimensional momentum-resolved imaging, energy-resolved imaging, energy-selective imaging, and combined energy-momentum-resolved imaging. This multi-modal operation capability of the microscope may enable versatile and comprehensive characterization of the sample's surface and electronic properties by allowing for the acquisition of complementary and correlated information through different imaging techniques.

[0046] The electronic circuitry, in this context, may refer to the control and data acquisition systems that coordinate the operation of the various components of the scanning charged-particle microscope, such as the beam splitter, the energy-selective element, the detector optics, and the multi-pixel detector, to achieve the desired imaging mode. These systems may include hardware components, such as microcontrollers, field-programmable gate arrays (FPGAs), and digital signal processors (DSPs), as well as software modules for instrument control, data acquisition, and image processing.

[0047] One-dimensional momentum-resolved imaging may involve measuring the angular distribution of the secondary charged particles along a single axis, typically perpendicular to the energy-dispersive direction of the energy-selective element.

[0048] Two-dimensional momentum-resolved imaging extends this concept to measure the angular distribution along two orthogonal axes.

[0049] Energy-resolved imaging focuses on measuring the kinetic energy distribution of the secondary particles, typically by scanning the pass energy of the energy-selective element and acquiring images at different energy values to map the spatial distribution of electronic states or chemical phases.

[0050] Energy-selective imaging is similar to energy-resolved imaging but involves acquiring images using a fixed energy passband to highlight specific electronic or chemical features of interest.

[0051] Combined energy-momentum-resolved imaging simultaneously measures, i.e. takes into account, the energy and momentum distribution of the secondary particles, often by using a two-dimensional multi-pixel detector to capture the energy-dispersed and momentum-resolved pattern in a single acquisition, enabling the study of electronic structures and dynamics in the sample.

[0052] In various examples, the energy-selective element of the scanning charged-particle microscope may be electronically switchable between an active mode for the energy- resolved imaging and an inactive mode for the two-dimensional momentum-resolved imaging. This switchable operation of the energy-selective element may allow for transition between the two imaging modes without the need for mechanical reconfiguration of the microscope. In the active mode, the energy-selective element may, e.g., a field that disperses the secondary charged particles based on their kinetic energies, allowing for energy-resolved imaging or spectroscopy. In this mode, the energy distribution of the particles is measured, while the momentum information may be partially or completely lost due to the dispersive action of the fields. In the inactive mode, the energy-selective element is turned off by removing the applied fields, allowing the secondary particles to pass through without being dispersed. This mode provides a different mapping of the momentum distribution of the particles, enabling two-dimensional momentum-resolved imaging, where the angular distribution along two orthogonal axes can be measured using a position-sensitive detector.

[0053] In various examples, the scanning charged-particle microscope may include at least one switchable component configured to be arranged in the secondary charged- particle beam path upstream of the energy-selective element.

[0054] The secondary charge-particle beam path may selectively bypass the energy- selective element depending on a setting of the switchable component. For instance, the switchable component may be a motorized component. The secondary charged- particle beam path may selectively bypass the energy-selective element depending on at least one of a position or orientation of the motorized component. Alternatively or additionally, it would be possible that the switchable component can be electronically switch between different settings, e.g., by applying or adjusting an electric or magnetic field. Such switchable component may enable the microscope to physically redirect the secondary charged-particle beam around the energy-selective element when it is in the inactive mode, while imaging the momentum distribution of the particles for two-dimensional momentum-resolved imaging.

[0055] The switchable component may refer to a movable element such as a retractable electrode or an electronically-controllable element such as a deflector, a beam shift coil. This component may be positioned upstream of the energy-selective element, allowing it to redirect the beam path before it enters the dispersive fields of the energy-selective element.

[0056] When the energy-selective element is in the active mode for energy-resolved imaging, the switchable component may be operated such that the secondary charged-particle beam passes through the energy-selective element, allowing for the dispersion and analysis of the particles based on their kinetic energies.

[0057] In the inactive mode for two-dimensional momentum-resolved imaging, the switchable component may be set to redirect the secondary charged-particle beam around the dispersive field of the energy-selective element, effectively bypassing it. This bypass may be achieved by deflecting the beam through a different path in the microscope column or by retracting the energy-selective element itself to allow the beam to pass through unobstructed.

[0058] If a motorized component is used, this motorized component may be controlled, for example, by mechanical actuators, such as stepper motors or piezoelectric transducers, which can be electronically driven by the microscope's control system.

[0059] In various examples, when the secondary charged-particle beam path bypasses the energy-selective element in the scanning charged-particle microscope, it may pass through a bore (i.e. , an opening) provided at the energy-selective element. This bore may serve as a clear aperture that allows the secondary charged-particle beam to traverse the energy-selective element without being affected by its dispersive fields. By redirecting the beam through this bore when the energy-selective element is in the inactive mode, the microscope may ensure that the momentum distribution of the secondary particles is imaged for two-dimensional momentum-resolved imaging.

[0060] When the energy-selective element is in the active mode for energy-resolved imaging, the secondary charged-particle beam may enter the dispersive fields of the device, where the particles are separated based on their kinetic energies. In this mode, the bore may not play a significant role, as the beam is intentionally subjected to the dispersive action of the energy-selective element. However, when the energy- selective element is switched to the inactive mode for two-dimensional momentum- resolved imaging, the switchable component upstream of the energy-selective element may redirect the secondary charged-particle beam through the bore.

[0061] In various examples, the switchable component configured to redirect the secondary charged-particle beam path in the scanning charged-particle microscope may be the beam splitter itself. By adjusting the electronic setting and / or the position and / or orientation of the beam splitter, the microscope may control whether the secondary charged-particle beam is directed through the energy-selective element for energy- resolved imaging or bypasses it for two-dimensional momentum-resolved imaging. This dual-purpose functionality of the beam splitter may simplify the design and operation of the microscope, as it eliminates the need for additional components in the beam path.

[0062] In the active mode for energy-resolved imaging, the beam splitter may be operated to direct the secondary charged-particle beam towards the energy-selective element. The particles then enter the dispersive fields of the energy-selective element, where they are separated based on their kinetic energies before reaching the detector. When the microscope is switched to the inactive mode for two-dimensional momentum-resolved imaging, the beam splitter may be operated to redirect the secondary charged-particle beam path away from the energy-selective element. This redirection may involve deflecting the beam through a different trajectory in the microscope column or guiding it through the bore in the energy-selective element, effectively bypassing the dispersive fields.

[0063] The beam splitter may be equipped with mechanical actuators, such as stepper motors or piezoelectric transducers, which can be electronically controlled by the microscope's system. Such mechanical actuators are not required in case electronic switching of the beam splitter is used.

[0064] In various examples, the scanning charged-particle microscope may further include electronic circuitry configured to operate one or more components of the microscope in a combined energy-momentum-resolved imaging mode. In this mode, the momentum of the secondary charged particles along a first direction may be resolved along a first detector direction along a detector plane of the multi-pixel detector. Additionally, a superposition of the momentum of the secondary charged particles and kinetic energy along a second direction that is perpendicular to the first direction may be resolved along a second detector direction of the detector plane, with the second detector direction being perpendicular to the first detector direction. This combined energy-momentum-resolved imaging mode may enable the microscope to simultaneously capture both the energy and momentum distribution of the secondary particles, providing a comprehensive and detailed characterization of the sample's electronic structure and surface properties in a single measurement. The combined energy-momentum-resolved imaging mode may involve the use of a two-dimensional position-sensitive multi-pixel detector, such as a multi-pixel detector, to simultaneously measure both the energy and momentum distribution of the secondary charged particles.

[0065] In this mode, the energy-selective element may be oriented such that its dispersive direction is aligned with one of the detector axes, typically referred to as the energy axis. Along this direction, the secondary charged particles are dispersed based on their kinetic energies, forming an energy spectrum on the detector plane.

[0066] Perpendicular to the energy axis, the detector may resolve the momentum distribution of the secondary particles along the other axis, referred to as the momentum axis. This momentum information may be imaged by the beam splitter and the detector optics, which may be configured to map the angular distribution of the particles onto the detector plane.

[0067] As a result, the detector captures a two-dimensional pattern where one axis represents the energy distribution, and the other axis represents the momentum distribution. Each pixel on the detector corresponds to a specific combination of energy and momentum values, allowing for a detailed analysis of the electronic structure and dynamics of the sample.

[0068] The electronic circuitry of the microscope, which includes the control and data acquisition systems, may be designed to process and interpret the energymomentum pattern or distribution acquired by the detector. This may involve algorithms for data reduction, calibration, and visualization.

[0069] In various examples, the electronic circuitry of the scanning charged-particle microscope may be configured to determine a surface potential, surface potential gradient, and / or a surface potential difference between two sample regions of a sample arranged in the sample plane. This determination may depend on a detector image acquired by the multi-pixel detector in the combined energy-momentum- resolved imaging mode. By analyzing the energy-momentum pattern captured by the detector, the microscope may extract quantitative information about the local electrostatic properties of the sample surface. The surface potential and its spatial variations may provide insights into the electronic structure, work function, and charge distribution of the sample.

[0070] In various examples, the scanning charged-particle microscope may include a field separation electrode arranged along the secondary charged-particle beam path between the sample plane and the beam splitter. The field separation electrode may be configured to control an electrostatic field at the sample surface independently from a landing energy of the primary charged-particles. By decoupling the surface field control from the primary beam energy, the field separation electrode may enable the microscope to optimize the collection and analysis of the secondary charged particles without affecting the primary beam's interaction with the sample. This independent control of the surface field may be particularly useful for studying the electronic properties and dynamics of materials under different electrostatic conditions, such as varying surface potentials, charge distributions, or band bending, without compromising the spatial resolution or imaging performance of the microscope.

[0071] The field separation electrode may refer to an additional electrode or a set of electrodes positioned in the space between the sample plane and the beam splitter in the scanning charged-particle microscope. This electrode may be designed to generate a controllable electrostatic field near the sample surface, which can influence the trajectories and energies of the secondary charged particles emitted from the sample.

[0072] The landing energy of the primary charged-particles, which determines their interaction with the sample and the spatial resolution of the microscope, is typically controlled by the accelerating voltage and the objective lens settings. In conventional scanning charged-particle microscopes, the surface field is often coupled to the landing energy, as both are affected by the same set of electrodes and potentials.

[0073] In various examples, a cross-beam system may comprise the scanning charged- particle microscope, as described in the preceding claims, and an ion-source column configured to emit charged ions along an ion charged-particle beam path towards the sample plane. This combination of electron and ion beams in a single system may enable a wide range of complementary analysis and processing capabilities, such as high-resolution imaging, surface modification, material deposition, and nanofabrication. The ion beam may be used for tasks such as milling, sputtering, or ion-induced deposition, while the scanning charged-particle microscope provides advanced energy-momentum-resolved imaging and spectroscopy modes for detailed characterization of the sample's surface and electronic properties. The integration of these two beam technologies in a cross-beam system may offer a powerful and versatile tool for multidisciplinary research and industrial applications in fields such as materials science, nanotechnology, and semiconductor devices. The cross-beam system may optionally also include a photon source, e.g., for coherent photons. A laser may be used. The photons are directed to a sample position coincident with the incident primary charged particles. Using photo-excitation of the material under investigation, different electronic states can be excited and observed and be monitored using, in particular, momentum-resolved imaging using the secondary charged particles. This may, e.g., enable in-situ testing of semiconductor devices. Signals can be observed for boundaries between different types of materials or local doping. Integration of a light source into conventional charged particle microscopes has been, in principle, disclosed in US 8,759,760 B2 and US 11 ,087,955 B2 and techniques disclosed in these documents are incorporated herein by reference.

[0074] A further aspect of the present disclosure relates to a cross-beam system. The crossbeam system comprises a scanning charged-particle microscope as described in the present disclosure.

[0075] The cross-beam system further comprises an ion-source column. The ion-source column is configured to emit charged ions along an ion charged-particle beam path towards the sample plane.

[0076] Therefore, a cross-beam system may refer to a combined microscopy system that integrates two or more charged-particle beams, typically an electron beam and an ion beam, to perform complementary analysis and manipulation tasks on the same sample. The electron beam is usually used for high-resolution imaging and spectroscopy, while the ion beam enables sample modification, such as milling, deposition, or implantation.

[0077] A cross-beam system may refer to a hybrid instrumentation platform that combines the capabilities of a scanning charged-particle microscope, typically a SEM, with an ion-source column, such as a focused ion beam (FIB) column. An ion-source column may be understood as a component of the cross-beam system that generates and directs a focused beam of charged ions towards the sample. It may comprise, for example, an ion source, such as a liquid metal ion source (LMIS) or a gas field ionization source (GFIS), and a series of electromagnetic lenses and apertures that shape and focus the ion beam onto the sample surface.

[0078] The ion-source column in a cross-beam system may generate a focused beam of charged ions, such as gallium (Ga+), helium (He+), or neon (Ne+), which can be accelerated and directed towards the sample plane. The ion beam can be used for a range of applications, including milling or sputtering, ion-induced deposition, surface modification.

[0079] The ion beam is tilted relative to the primary charged particle beam of the microscopy system and they intersect I cross each other in the sample plane.

[0080] Although specific features described in the above summary and the following detailed description are described in connection with specific examples, it is to be understood that the features may not only be used in the respective combinations, but may also be used isolated, and features from different examples may be combined with each other, and correlate to each other, unless specifically noted otherwise.

[0081] Therefore, the above summary is merely intended to give a short overview of some features of some embodiments and implementations and is not to be construed as limiting. Other embodiments may comprise other features than the ones explained above.

[0082] BRIEF DESCRIPTION OF THE DRAWINGS

[0083] In the following, concepts in accordance with exemplary embodiments of the invention will be explained in more detail with reference to the following drawings.

[0084] FIG. 1 schematically illustrates general principles of a SEM, in which the techniques according to the present disclosure can be applied.

[0085] FIG. 2 schematically illustrates a distribution of detected electrons with respect to their kinetic energies, according to various examples. FIG. 3 schematically illustrates a momentum distribution of SEs for a material configuration with regions of differing charges, according to various examples.

[0086] FIG. 4 schematically illustrates FIG. 4 schematically illustrates a SEM, according to various examples.

[0087] FIG. 5 schematically illustrates a further SEM, according to various examples.

[0088] FIG. 6 schematically illustrates a SEM with energy-selective element, according to various examples.

[0089] FIG. 7 schematically illustrates a SEM with an energy analyzer as in FIG. 6 and a first shortcut configuration of the SE beam path, according to various examples.

[0090] FIG. 8 schematically illustrates a SEM with an energy analyzer as in FIG. 6 and a second shortcut configuration of the SE beam path, according to various examples.

[0091] FIG. 9 schematically illustrates a SEM with an energy analyzer comprising two hemispherical energy-selective elements, according to various examples.

[0092] FIG. 10 schematically illustrates a SEM with a mono-chromated source and with an energy analyzer as in FIG. 9, according to various examples.

[0093] FIG. 11 schematically illustrates a SEM with an energy filter, configured for operation modes (b), (c), and (d), according to various examples.

[0094] FIG. 12 schematically illustrates an objective lens setup for a SEM, which can be combined with any charged-particle microscope as described herein.

[0095] FIG. 13 schematically illustrates aspects with regard to operation modes (a), (c), and (d) of TAB. 1 of a SEM, according to various examples.

[0096] FIG. 14 schematically illustrates aspects with regard to operation mode (f) according to TAB. 1 of a SEM, according to various examples.

[0097] FIGs. 15A-C schematically illustrate for energy- and momentum-resolved imaging, according to various examples.

[0098] FIGs. 16A-C schematically illustrate an operation mode of a SEM, according to various examples. FIGs. 17A-C schematically illustrate an operation mode of a SEM, according to various examples.

[0099] FIGs. 18A-C schematically illustrate an operation mode of a SEM, according to various examples.

[0100] FIG. 19 schematically illustrates an electronic circuitry according to various examples.

[0101] DETAILED DESCRIPTION

[0102] The above and other elements, features, and concepts of the present disclosure will be more apparent from the following detailed description in accordance with exemplary embodiments of the invention, which will be explained with reference to the accompanying drawings.

[0103] Some examples of the present disclosure generally provide for a plurality of circuits, data storage, connections, or electrical devices such as e.g., processors, which may be contained in a charged-particle microscope and / or cross-beam system. All references to these entities, other electrical devices, and the functionality provided by each are not intended to be limited to encompassing only what is illustrated and described herein. While particular labels may be assigned to the various circuits or other electrical devices disclosed, such labels are not intended to limit the scope of operation for the circuits and the other electrical devices. Such circuits and other electrical devices may be combined with each other and / or separated in any manner based on the particular type of electrical implementation that is desired. It is recognized that any circuit or other electrical device disclosed herein may include any number of microcontrollers, a graphics processor unit (GPU), integrated circuits, memory devices (e.g., FLASH, random access memory (RAM), read only memory (ROM), electrically programmable read only memory (EPROM), electrically erasable programmable read only memory (EEPROM), or other suitable variants thereof), and software which co-act with one another to perform operation(s) disclosed herein. In addition, any one or more of the electrical devices may be configured to execute a program code that is embodied in a non-transitory computer readable medium programmed to perform any number of the functions as disclosed. In the following, embodiments of the invention will be described in detail with reference to the accompanying drawings. It is to be understood that the following description of embodiments is not to be taken in a limiting sense. The scope of the invention is not intended to be limited by the embodiments described hereinafter or by the drawings, which are taken to be illustrative only.

[0104] The drawings are to be regarded as being schematic representations and elements illustrated in the drawings are not necessarily shown to scale. Rather, the various elements are represented such that their function and general purpose become apparent to a person skilled in the art. Any connection or coupling between functional blocks, devices, components, or other physical or functional units shown in the drawings or described herein may also be implemented by an indirect connection or coupling. A coupling between components may also be established over a wireless connection. Functional blocks may be implemented in hardware, firmware, software, or a combination thereof.

[0105] Various examples of the disclosure generally pertain to charged-particle microscopes and imaging techniques employing charged-particles. Such charged-particle microscopes generate images by scanning a primary beam of the charged-particles across a sample plane in which a sample may be arranged. The primary charged particles travel along a primary beam path. An illumination column includes respective scanning and focusing optics. Then, further charged particles returning from the sample plane along a secondary beam path can be detected, in a detection column.

[0106] According to various examples, the charged particles are electrons. A SEM is disclosed. Hereinafter, techniques are specifically explained in the context of an SEM; while other types of charged particles may also be used, e.g., charged-particle microscopes using Helium ions.

[0107] Hereinafter, various examples are disclosed for imaging SEs, i.e. , those electrons returning from the sample along a secondary electron beam path that have been generated by secondary emission at the sample. However, while various examples are explained and illustrated hereinafter in the context of SEs, techniques are equally applicable for imaging BSEs. SEs are ejected from the surface of the sample as a result of interactions between the sample atoms and the incoming beam of primary electrons. The SEs typically have lower energies and are used to generate high-resolution images of the sample's surface topology. BSEs, on the other hand, are the primary electrons that are reflected I scattered back from the sample after striking the atomic orbitals. Depending on the energy of the primary electrons, BSEs are generated after striking inner orbitals (e.g., for energies of the primary electrons above 500 eV; so called z- contrast that depends on the atomic number, i.e. , charge number of the nucleus) or outer orbitals of valence electrons. They generally retain a significant portion of their original energy, which makes them useful for examining compositional contrasts across different regions of the sample.

[0108] Imaging based on SEs - if compared to imaging based on BSEs - requires advanced suppression of electromagnetic interference, e.g., if compared to imaging of BSEs: SEs have kinetic energies of a few eV up to 50 eV. Because of their low energy, they are more susceptible to any kind of electromagnetic interference or perturbations in the electromagnetic fields within the SEM vacuum chamber. Further, specific detectors are required to detect the low-energy SEs. For instance, an Everhart-Thornley Detector (ETD) may be used. This is a scintillator-photomultiplier system. A multi-pixel ETD can be realized by segmenting the scintillator into multiple areas, each coupled with its own photodetector, such as a photomultiplier tube (PMT) or avalanche photodiode. This segmentation allows for spatial resolution by detecting where on the scintillator SEs impact. Alternatively, silicon photomultipliers (SiPMs) can replace PMTs, as SiPMs consist of an array of photodetection cells, each acting as an independent pixel to detect photons from the scintillator. Another method involves using charge-coupled devices (CCD) or complementary metal-oxide- semiconductor (CMOS) sensors to detect emitted photons, with each sensor pixel capturing individual photon events. Implementing CCD or CMOS sensors requires efficient coupling between the scintillator and the sensor to minimize light loss and distortion. Digital photon counting systems can enhance resolution by counting photons at each pixel of the multi-pixel detector, providing quantitative data on SE distribution. A fiber optic plate can be used to channel light from the scintillator to a photodetector array, with each fiber corresponding to a detector pixel, preserving spatial information. Integration of these technologies into SEM requires addressing challenges in light collection efficiency, signal processing capacity, and physical configuration within the SEM column. As will be appreciated from the above, various options for multi-pixel detectors that are configured to detect SEs or BSEs are available in the present disclosure.

[0109] Various examples are based on the finding that for a momentum-resolved imaging it may be required to implement an overlap region in which the primary electron beam path and the SE beam path overlap. This is because for momentum-resolved imaging it may be required to detect SEs having secondary electron beam path oriented approximately perpendicular to the sample plane, i.e., anti-parallel to the primary electron beam path. Thus, a beam splitter may be required to separate the SE beam path from the primary beam path, at the end of the overlap region.

[0110] Various examples are further based on the finding that, to detect the SEs, it is helpful to use an acceleration electrode that is arranged adjacent to the sample plane and configured to accelerate the SEs along the SE beam path and specifically along the overlap region towards the beam splitter. Thereby, the low-energy SEs can be accelerated to higher energies, making them less susceptible to interference. A higher conversion yield at the detector can be achieved.

[0111] The beam splitter may be configured to map the momentum of the SEs. For instance, a magnetic prism may be used.

[0112] Then, the SEs are available at a boosted kinetic energy level in the detector column. This allows to map their original lateral or longitudinal momentum distribution onto a detection system. For instance, even when boosting kinetic energy, the ratio of inplane momenta (i.e., px / py) is preserved. This enables various imaging modes.

[0113] According to various examples, multiple imaging modes can be used. The SEM can be operated in multiple imaging modes. Some imaging modes are listed below, in TAB. 1 .

[0114] TAB. 1 : Various possible imaging modes. The various imaging modes can be combined with a reflection imaging mode (f) or a meV imaging mode (g), e.g., with an energy filter (e) in the primary beam path. Furthermore, an energy filter may be used to filter certain kinetic energies. For instance, a bandpass energy filter may be used. Furthermore, the imaging modes listed in the table above can be combined with (h) photon illumination of the sample. For instance, while operating in accordance with momentum-resolved imaging or energy-resolved imaging, the sample can be illuminated with the laser light source for photo-excitation of electronic states. Then, it is possible to probe this photo-excitation. More generally, the illumination of the sample using photons can bring the electronic system of the sample into a disequilibrium detected by a signal using the SEs and / or BSEs.

[0115] According to various examples, an electronic circuitry associated with the SEM may be configured to selectively activate different ones of the imaging modes described in TAB. 1 . For instance, this can include motorized actuation of one or more components of the SEM and / or electronic control of one or more components of the SEM. However, in some scenarios, certain imaging modes may be fixedly activated, e.g., depending on the hardware configuration of the SEM.

[0116] Depending on the particular imaging mode, different components of the SEM may be activated or deactivated and / or one or more components of the SEM may be configured differently and / or present or absent. Details will be described hereinafter, wherein different options for a hardware implementation of such configurable components (FIG. 1 through FIG. 10) on the one hand as well as a different functional implementation of the various imaging modes will be disclosed (FIG. 15A and following). The different functional implementations of the various imaging modes can be flexibly combined with different hardware implementations for such configurable components of the SEM (and vice versa).

[0117] FIG. 1 schematically illustrates the general principles of a scanning charged-particle microscope. FIG. 1 , in particular, shows a schematic illustration of an SEM 100 according to prior-art implementations. The SEM 100 serves as a reference against which the SEM according to the disclosed techniques can be discriminated.

[0118] The SEM 100 has a first beam generator in the form of an electron source 101 which is embodied as a cathode. Furthermore, the SEM 100 is provided with an extraction electrode 102 and with an anode 103 which is placed onto one end of a beam guiding tube 104 of the SEM 100. By way of example, the electron source 101 is embodied as thermal field emitter. However, the invention is not restricted to such an electron source 101. Rather, any electron source is utilizable.

[0119] Electrons emerging from the electron source 101 form a primary electron beam. The electrons are accelerated to the anode potential due to a potential difference between the electron source 101 and the anode 103. In the exemplary embodiment depicted here, the anode potential is 1 kV to 30 kV, e.g., 5 kV to 15 kV, in particular 8 kV, in relation to a ground potential of a housing of a sample chamber 120. However, alternatively it could be at ground potential.

[0120] Two condenser lenses, namely a first condenser lens 105 and a second condenser lens 106, are arranged at the beam guiding tube 104 (illumination column). Here, proceeding from the electron source 101 as viewed in the direction of a first objective lens 107, the first condenser lens 105 is arranged first along the primary electron beam path, followed by the second condenser lens 106. Reference is explicitly made to the fact that further embodiments of the SEM 100 may have only a single condenser lens. A first aperture unit 108 is arranged between the anode 103 and the first condenser lens 105. Together with the anode 103 and the beam guiding tube 104, the first aperture unit 108 is at a high voltage potential, namely the potential of the anode 103, or it is connected to ground. The first aperture unit 108 may have numerous first apertures 108A, of which one is depicted in FIG. 1 . Two first apertures 108A are present, for example. Each one of the numerous first apertures 108A has a different aperture diameter. By means of an adjustment mechanism (not depicted here), it is possible to set a desired first aperture 108A onto an optical axis OA of the SEM 100. Reference is explicitly made to the fact that, in further embodiments, the first aperture unit 108 can be provided with only a single aperture 108A. In this embodiment, the adjustment mechanism may be absent. The first aperture unit 108 is then designed in a stationary fashion. A stationary second aperture unit 109 is arranged between the first condenser lens 105 and the second condenser lens 106. The second aperture unit 109 may be designed in a movable fashion as an alternative thereto.

[0121] The first objective lens 107 has pole pieces 110 in which a bore is formed. The beam guiding tube 104 is guided through this bore. Furthermore, coils 111 are arranged in the pole pieces 110. An electrostatic retardation device is arranged in a lower region of the beam guiding tube 104. It has a single electrode 112 and a tube electrode 113. The tube electrode 113 is arranged at one end of the beam guiding tube 104, which faces a sample 114. Together with the beam guiding tube 104, the tube electrode 113 is at the potential of the anode 103, while the single electrode 112 and the sample 114 are at a lower potential in relation to the potential of the anode 103. In the present case, this is the ground potential of the housing of the sample chamber 120. In this manner, the electrons of the primary electron beam can be decelerated to a desired energy which is required for examining the sample 114.

[0122] The SEM 100 furthermore has a scanning device 115, by means of which the primary electron beam can be deflected and scanned over the sample 114 arranged in a sample plane. Here, the electrons of the primary electron beam interact with the sample 114. As a result of the interaction, interaction particles are produced, which are detected. In particular, electrons are emitted from the surface of the sample 114 — the so-called SEs - or electrons of the primary electron beam are scattered back - the so-called BSEs - as interaction particles.

[0123] The sample 114 and the single electrode 112 may also be at different potentials and potentials different than ground. It is thereby possible to set the location of the retardation of the primary electron beam in relation to the sample 114. By way of example, if the retardation is applied near to the sample 114, imaging aberrations become smaller.

[0124] A detector arrangement comprising a first detector 116 and a second detector 117 (both in a circular arrangement around the center axis of the primary electron beam path) is arranged in the beam guiding tube 104 for detecting the SEs and / or the BSEs. Note that the SEM 100 does not include a separate detection column. Here, the first detector 116 is arranged on the source-side along the optical axis OA, while the second detector 117 is arranged on the object-side along the optical axis OA in the beam guiding tube 104. The first detector 116 and the second detector 117 are arranged offset from one another in the direction of the optical axis OA of the SEM 100. Both the first detector 116 and the second detector 117 each have a passage opening, through which the primary electron beam can pass. The first detector 116 and the second detector 117 are approximately at the potential of the anode 103 and of the beam guiding tube 104. The optical axis OA of the SEM 100 extends through the respective passage openings.

[0125] The second detector 117 serves principally for detecting SEs. Upon emerging from the sample 114, the SEs initially have a low kinetic energy and a distribution of directions of motion (momentum distribution). By means of the extraction field emanating from the tube electrode 113, the SEs are accelerated in the direction of the first objective lens 107. The SEs enter the first objective lens 107 approximately parallel. The beam diameter of the beam of SEs remains small in the first objective lens 107 as well. The objective lens 107 then has a strong effect on the SEs and generates a comparatively short focus of the SEs with sufficiently steep angles with respect to the optical axis OA, such that the SEs diverge far apart from one another downstream of the focus and impinge on the second detector 117 on the active area thereof. By contrast, only a small proportion of electrons that are backscattered at the sample 114 — that is to say BSEs — which have a relatively high kinetic energy in comparison with the SEs upon emerging from the sample 114, are detected by the second detector 117. The high kinetic energy and the angles of the BSEs with respect to the optical axis OA upon emerging from the sample 114 have the effect that a beam waist, that is to say a beam region having a minimum diameter, of the BSEs lies in the vicinity of the second detector 117. A large portion of the BSEs passes through the passage opening of the second detector 117. Therefore, the first detector 116 substantially serves to detect the BSEs. The first detector 116 may be embodied with an opposing field grid 116A. The opposing field grid 116A is arranged at the side of the first detector 116 directed toward the sample 114. With respect to the potential of the beam guiding tube 104, the opposing field grid 116A has such a negative potential that only BSEs with a high energy pass through the opposing field grid 116Ato the first detector 116. Additionally or alternatively, the second detector 117 has a further opposing field grid, which has an analogous embodiment to the aforementioned opposing field grid 116A of the first detector 116 and which has an analogous function. The detection signals generated by the first detector 116 and the second detector 117 are used to generate an image or images of the surface of the sample 114.

[0126] In the prior art implementation of FIG. 1 , a beam splitter is not required, because there is no separate detection column required, since annular detectors are positioned around the primary beam path. Further, momentum-resolved imaging (of. TAB. 1 ) is not possible in the scenario of FIG. 1. This is explained next. In general, the fraction of SEs that are not detected depends on the landing energy of primary electrons or respectively the booster voltage. The smaller the ratio of landing energy to booster voltage, the smaller the magnetic excitation of the objective lens 107. This causes a shift of the focus of the SEs away from the sample in this results in a larger fraction of the SEs being undetectable. Due to Larmor rotation of the electrons in the magnetic field of the objective lens 107, the point of incidence on the detector is dependent on the initial energy, polar angle and azimuthal angle of the SEs. This effect depends on the booster field strength (controlled via the booster voltage) and magnetic immersion, i.e. , depends on the optical design. The stronger the booster field, the smaller this phenomenon, and the fewer electrons are detectable. I.e., measurement of the angle as part of the momentum-resolved imaging either is not possible due to Larmor rotation or inefficient at the detector.

[0127] Furthermore, due to the circular arrangement of the detector 117 in the scenario of FIG. 1 , a sufficient energy resolution, e.g., 1 eV, for energy-resolved imaging cannot be easily achieved. Typical energy resolutions achievable using a set up as illustrated in FIG. 1 are on the order of 100 eV.

[0128] According to various examples, implementations of SEMs are discussed that enable momentum-resolved and energy-resolved imaging of SEs. Before such hardware implementations are discussed, various aspects relating to SEs and the momentum distribution are discussed in connection with FIG. 2 and FIG. 3, respectively.

[0129] FIG. 2 schematically illustrates a distribution of detected electrons with respect to their kinetic energies, according to various examples. As can be seen in FIG. 2, the vertical axis represents the density of states I frequency of occurrence N(E), while the horizontal axis denotes the kinetic energy Ekin in electron volts (eV).

[0130] Electrons leave the SEM column with a kinetic energy Eo= eUgun.Wfil. Here, Ugun-is the negative potential set to the electron gun, e the (negative) elemental charge and Wfilthe positive work function of the electron gun filament. The effective impact or landing energy LE of the electrons reaching the sample surface is defined with respect to the column level as: LE = e(Ugun-Us)-(Wfil+Ws), where Usis the sample surface potential and Wsthe sample work function. Both Usand Wsare not necessarily homogeneous across the sample, but local values depending on material composition and surface charge.

[0131] Elastically reflected electrons (BSE) are first reaccelerated to Eo, and then within the column to the positive column potential Ucolto the kinetic energy at the detector of e(Ugun-Ucoi). Secondary electrons leave the sample with a minimal kinetic energy of ~0eV. They arrive at the detector with kinetic energy e(Ugun-Ucol).

[0132] The kinetic energy of BSE electrons at the detector is independent of (local) sample surface potential Us, while the kinetic energy of SE electrons depends on Us.

[0133] The maximum difference in kinetic energy between BSE and SE electrons is equal to LE - which represents the energy range accessible for analysis. The distribution shown in FIG. 2 exhibits several characteristics. At the low energy end, Emin marks the beginning of electron emission. Emin depends on sample surface potential Usand work function Ws. The curve then rises and forms a peak, centered typically between 5-1 OeV. The lower half of this peak typically features arising from density of states.

[0134] Following the SE maximum, the distribution decreases to a low-density region where Auger electrons are observed. Further along the energy scale, an elevation in the curve represents low-loss BSEs. Near the high energy end of the spectrum, an elastic peak is visible, which corresponds to electrons that have minimal energy loss during elastic scattering events.

[0135] FIG. 3 schematically illustrates trajectories of SEs for a material configuration with regions of different charges, according to various examples. As can be seen in FIG.

[0136] 3, two adjacent materials A and B of the sample have an interface or transition region, wherein material A has a positive charge U, and material B has no charge. A similar effect can be observed for different work functions of material A and material B. Arrows representing SE / BSE electron trajectories originate from the surface of these materials at exemplary locations, to which primary electrons are directed. The diagram shows distinct electron trajectories for the locations as caused by the different surface potential conditions (U=0V, U>0V, U»0V). For a location on material A, the trajectories curve inwards towards the center of material A, with the degree of curvature increasing as the surface potential (U) increases. This curvature is indicative of the effect of the positive charge on the emitted electrons.

[0137] The trajectories from the location at the interface towards material A show a similar behavior, whereas the trajectories emitted in the direction of material B show a different behavior, where the trajectories are closes to each other and deflected towards material A. This illustrates the influence of the charged region on electrons from nearby uncharged areas, and can be used to identify, for example, such material interfaces - even if there is not significant difference in the SE or BSE signal yield between material A and material B, i.e., if the SE or BSE flux at the detector is comparable for material A and material B. The varying trajectories demonstrate the sensitivity of SEs to local electric fields, which enables the detection and analysis of surface potential variations across different materials or regions. Such information can be retrieved using momentum-resolved imaging (cf. TAB. 1 ), in particular, by analyzing the pxdistribution (since the change of the material occurs along the x- axis).

[0138] FIG. 4 schematically illustrates a SEM 400 according to various examples. FIG. 4, in particular, illustrates a primary electron beam path 451 and a SE beam path 452. The SEM 400 can operate in one or more of the imaging modes (a) and (d) according to TAB. 1 . For instance, it would be possible to selectively switch between momentum- resolved imaging and position-resolved imaging.

[0139] As can be seen in FIG. 4, the primary electron beam path 451 starts at the primary electron source 401 .The primary electron beam is emitted from the primary electron source 401 , which generates a focused stream of high-energy electrons. The primary electrons emitted from the source are directed through a series of condenser and projector lenses 402, 403, 404 in the illumination column. Stigmator lenses may be provided. The primary electrons may be accelerated by a beam guiding tube. Between lenses 402,403, the electron beam passes through a beam defining aperture. This restricts the diameter of the electron beam. After passing through magnetic prism 405, the electron beam is reflected by an electron mirror 1415. The mirror can function as correction element to correct chromatic aberrations, i.e., energy-dependent aberrations. Chromatic aberration is the effect in which electrons of different energy are focused to different planes. Chromatic aberration puts a diffuse ring of scattered electrons around the probe, degrading image contrast and broadening the probe size. From the mirror 1415 through magnetic prisms 405, 406, the primary electrons are directed through acceleration electrode (liner tube) 408 towards the sample 407.

[0140] The SE path in the scanning charged-particle microscope starts at the sample 407, where the primary beam interaction leads to the emission SEs; also BSE are attained. There is an overlap region 455 in which the primary electron beam path and the SE / BSE beam path overlap; this overlap region 455 is between the sample plane at which the sample 407 is arranged and the magnetic prims 406 implementing a beamsplitter.

[0141] These SE / BSE electrons are accelerated by the acceleration electrode 408 to increase their kinetic energy by an amount defined by the column potential Ucol. Thus, in particular the SEs are less susceptible to interference; or, in other words, external interferences have a smaller relative impact on their energies. This enables reliable imaging, because signal-to-noise is increased. Furthermore, by using the acceleration electrode 408 to accelerate the SEs, a smaller impact of Larmor rotation is observed. In particular, differences in the Larmor rotation between SEs of different kinetic energies become relatively less important.

[0142] The SE / BSEs are then directed by magnetic prism 406 towards the detection column 460, where they are further redirected by magnetic prism 409. The magnetic prisms 406, 409, thus, implement a beam splitter. The are configured to image an in-plane momentum of the SEs, i.e., pxand py, from their input plane to their output plane, thereby enabling imaging the in-plane momentum. The SE beam follows a controlled path towards the spatially resolved detector, without losing momentum information.

[0143] The SE beam is focused through one or more projector lenses 461 , 462, 463 of a detection column 460 which converge and refine the SE beam path for detection. For this, a multi-pixel detector 465 is provided. The magnetic prisms 405, 406, 409 may each be implemented using one or more magnetic coils. Each magnetic prism 405, 406, 409 may define a deflection symmetric to respective symmetry planes (dotted lines in FIG. 4). A mirror plane of the mirror 1415 may be imaged to or next to the adjacent symmetry planes. By arranging the mirror 1415 to image the deflector’s symmetry planes, the deflector’s second-order errors and dispersion cancel after the second pass, so there remain only the negative chromatic and spherical aberrations of the mirror 1415. These can be so adjusted that the chromatic and spherical aberrations of other elements are compensated.

[0144] The detector optics in FIG. 4 - e.g., one or more of the projector lenses 461 , 462, 463 - may also be configured to selectively switch between projecting a backfocal plane along the secondary charged-particle beam path onto a detector plane of the multi-pixel detector and projecting a crossover plane onto the detector plane of the multi-pixel detector (The position of the backfocal plane and the crossover plane vary depending on the particular implementation of the electron optics; and, as such, can be at various positions along the secondary electron beam path 452). For instance, switching between projection of the backfocal plane or the crossover plane can be achieved by selectively inserting a specific lens into the SE beam path or removing that lens. A motorized actuator may be provided that moves the lens into the SE beam path or removes the lens from the SE beam path. Instead of such mechanical switching, it would be possible to use electronic switching, i.e., electronically switch / on switch off such lens.

[0145] Generally, the backfocal plane is defined by the plane in which the trajectories of the secondary charged-particles start with the same angle intersect independent of the starting position on the sample. In contrast, the crossover plane is defined by the plane in which the trajectories start from the same point intersect. On the detector, the crossover plane can be translated to a sample starting position of each electron.

[0146] By projecting the backfocal plane onto the detector plane, angles of incidence (corresponding to different angles of departure of the SEs from the sample plane) in the backfocal plane can be translated into different positions on the detector plane.

[0147] As a general rule, various modifications to the SEM 400 are conceivable. For instance, one variation is illustrated in FIG. 5. FIG. 5 schematically illustrates a further SEM 400-1 , according to various examples.

[0148] The SEM according to FIG. 5 may operate in imaging modes (a) and (d) according to TAB. 1 .

[0149] Further variations include, e.g., the number of optical elements arranged in the detection column, the implementation of the beam splitter, e.g., the number of magnetic prisms employed, to give just a few examples.

[0150] Sometimes, it may be preferable to not only be able to switch between the momentum-resolved imaging and the position-resolved imaging (cf. TAB. 1 ), but alternatively or additionally also obtain energy resolution, i.e. , operate in an energy- resolved imaging mode (cf. TAB. 1 ). To this end, an energy-selective element may be used in the SE beam path.

[0151] To achieve this, irrespective of the particular implementation of the SEM 400, 400-1 , an energy-selective element can be selectively arranged in the SE beam path 452, in between the beam splitter and the multi-pixel detector, i.e., downstream of the magnetic prism 409 (this energy-selective element is not present I shown in FIG. 4 and FIG. 5). The energy-selective element, upon being arranged in the SE beam path, is configured to selectively deflect trajectories of the secondary electrons along the secondary electron beam path 452 depending on their kinetic energies. For instance, the energy-selective element may be implemented as an energy-dispersive element, i.e., an element that separates the trajectories along a spatial direction depending on the kinetic energy. An example hardware implementation of a respective energy-selective element will be described with regard to FIG. 6.

[0152] FIG. 6 schematically illustrates a further SEM 400-2 with energy-selective element, according to various examples. The SEM 400-2 is variation of the SEM 400 of FIG. 4. The SEM 400-2 in FIG. 6 includes, in the SE beam path 452, an energy-dispersive element separating trajectories of the secondary electrons. In the scenario of FIG. 6, the energy-selective element is implemented as a hemispherical analyzer 490. The SEM is configured for operation in imaging modes (b), (c), (d), and (e) according to TAB. 1 . The hemispherical analyzer 490 optionally includes an aperture 495 (typically a slit aperture), which selects an energy band. The aperture 495 may be switchable, i.e., activated or deactivated depending on the desired imaging modes. The hemispherical analyzer 490 is configured to project an entrance plane 490A onto an exit plane 490B with added energy dispersion.

[0153] The SEM may also one or more apertures 480, 481 , 495 to select a pxand / or pymomentum range. As a general rule, such apertures 480, 481 - e.g., slit apertures or circular apertures - are optional.

[0154] Next, various options for operating the SEM 400-2 are disclosed. In particular, various imaging modes are discussed that can be activated or deactivated depending on activation or deactivation or configuration of certain elements, apertures, etc.

[0155] In one operation mode, all apertures 480, 481 and 495 are deactivated. For example, a backfocal plane is projected into the entrance plane of the hemispherical analyzer 490 via lens(es) 461 . On the detector 465, it is possible to detect an energy dispersive image of the backfocal plane (details will be explained later on in connection with FIG. 15A, FIG. 15B, and FIG. 15C; also cf. TAB. 1 , imaging mode b)

[0156] By activating the aperture 480 or 481 using pinhole openings (e.g., circular openings), the px / py momentum is restricted before entering the energy analyzer (details will be explained later on in connection with FIG. 16A, FIG. 16B, and FIG. 16C; also cf. TAB. 1 , imaging mode c).

[0157] By activating apertures 480, 481 using slit openings, it is possible to select a fixed px value range before entering the energy analyzer. By projecting the detector exit plane onto detector 465 via lenses 462, 463, an image of the energy spectrum as a function of py moment is obtained (details will be explained later on in connection with FIG. 17A, FIG. 17B, and FIG. 17C).

[0158] Now, assume that the crossover plane is focused onto the entrance plane 490A using lens(es) 461 . The aperture 481 has a circular opening or is deactivated altogether. Further, the aperture 495 has a slit opening oriented perpendicular to the dispersive direction. The backfocal plane is projected on detector 465. Thereby, an image of the px / py distribution at constant energy is obtained, where the energy is determined by position of the slit of the slit aperture 495.

[0159] It would be possible that further switchable electro-optical elements are provided before or after the slit aperture 481 and / or before or after the slit aperture 495. By setting such electro-optical elements (e.g., a deflection plate or a lens), it is possible to to select certain kinetic energies and / or as certain momentum allowed to pass through the respective slit aperture. Note that in FIG. 6 such further switchable electro-optical element is not illustrated for sake of simplicity.

[0160] The hemispherical analyzer 490 is an example for an energy-selective element and specifically an energy-dispersive element configured to be arranged in the secondary charged-particle beam path downstream of the beam splitter and to selectively deflect trajectories of the secondary charged particles along the secondary charged- particle beam path depending on their kinetic energies. Other possibilities for the energy-selective element include at least one of a spectrometer, a grid filter, a magnetic-field separator, or an electric-field separator.

[0161] Further, as will be appreciated, the hemispherical analyzer 490 or generally an energy-dispersive element images an entrance plane to an exit plane using energy dispersion; various imaging modes - such as those described in TAB. 1 - depend on which particular apertures are used in which lanes and which planes are imaged onto the detector.

[0162] The SEM 400-2 further includes electronic circuitry (not depicted) configured to analyze a detector image of the multi-pixel detector to determine an energy distribution based on the detector image.

[0163] For example, the SEM 400-2 may include electronic circuitry configured to operate one or more components of the scanning charged particle microscope in a combined energy-momentum-resolved imaging mode, wherein a momentum of the secondary charged particles along a first direction is resolved along a first detector direction along a detector plane of the multi-pixel detector 465, wherein a superposition of the momentum of the secondary charged particles and kinetic energy is resolved along a second direction that is perpendicular to the first direction is resolved along a second detector direction of the detector plane, the second detector direction being perpendicular to the first detector direction. The electronic circuitry may be configured to determine a surface potential, and / or surface potential gradient, and / or a surface potential difference between two sample regions, of a sample arranged in the sample plane depending on a detector image acquired by the multi-pixel detector in the combined energy-momentum-resolved imaging mode. As a general rule, as previously discussed in connection with FIG. 3, a surface potential difference can be obtained either intrinsically through differences in the work function of the involved materials and / or extrinsically by local charging. Local charging can have different reasons, e.g., may be due to local charging from incident electrons of the primary electron beam. Furthermore, different electronic states may be observed in different regions of the sample, resulting from local illumination using photons. Also such differences in the electronic states due to photo-excitation can be visualized by the electronic circuitry.

[0164] In FIG. 6, the hemispherical analyzer 490 is fixedly arranged in the SE beam path to separate the trajectories of the SEs. Sometimes, it may be helpful to selectively activate the energy dispersion provided by the energy-selective or specifically the energy-dispersive element. One hardware implementation option for such selective activation is shown in FIG. 7.

[0165] FIG. 7 schematically illustrates a SEM 400-3 with an energy analyzer as in FIG. 6 and a first shortcut configuration of the SE beam path. The SEM is configured for operation in imaging modes (b), (c), (d), and (e) according to TAB. 1 . The setup as depicted in FIG. 7 builds upon the configuration shown in FIG. 6, with several modifications.

[0166] In particular, in this configuration two spatially resolving detectors are included. Spatially resolving detector 465 is positioned downstream the hemispherical analyzer 490 as in FIG. 6, while spatially resolving detector 475 is located at the end of the secondary electron path when bypassing the hemispherical analyzer 490. The respective bypass SE beam path 452-1 is shown in FIG. 7 using a dashed line. A selection between the SE beam path 452 through the hemispherical analyzer 490 or the bypass SE beam path 452-1 is possible by setting the magnetic field of the magnetic prism 409. This adjustable magnetic excitation of the magnetic prism 409 is schematically illustrated in FIG. 7 using a rotation of the prism element 409, for illustrative purposes only. Projector lenses 462 and 463 are positioned downstream energy dispersive element along the SE beam path 452, while projector lenses 472 and 473 are located in the bypass SE beam path 452-1 upstream the detector 475.

[0167] While in FIG. 7 the switchable component is the magnetic prism 409, i.e. , a part of the beam splitter, other components may be switchable, e.g., a lens, a beam deflection element, etc.. Electronic and / or mechanical switching is generally possible; but electronic switching would be generally preferrable.

[0168] Using one or motorized components - as in FIG. 7 the magnetic prism 409 - for switching the energy-selective element between an active mode and an inactive mode is only one example. Sometimes, it can be preferable to use electronic switching between an inactive mode and an active mode. Such a scenario is explained next.

[0169] FIG. 8 schematically illustrates a SEM with an energy analyzer as in FIG. 6 and a second shortcut configuration of the SE beam path, according to various examples.

[0170] As can be seen in FIG. 8, a SEM 400-4 includes an energy analyzer as in FIG. 7, e.g., configured for operation modes (b), (c), (d), and (e), according to TAB. 1. In FIG.

[0171] 8 - rather than using a switchable magnetic prism as in FIG. 7 - the energy-selective element 490 is electronically switchable between an active mode for the energy- resolved imaging and an inactive mode for the two-dimensional momentum-resolved imaging. The voltage between the electrodes of the hemispherical analyzer can be switched off to active the inactive mode.

[0172] Also, in FIG. 8, the projector lens configuration has been slightly modified if compared to FIG. 7, with projector lenses 472 and 473 after part of the energy dispersive element 490.

[0173] Unlike the complete bypass as in FIG. 7, in FIG. 8, the shortcut is represented by a dashed line that passes straight through a portion of the energy dispersive element 490 or through a bore 490A in the energy dispersive element 490. When deactivating the hemispherical analyzer 490, the SEs can pass through the bore 490A.

[0174] Since the bore 490A may disturb the symmetry of the hemispherical analyzer - e.g., in the energy-resolved imaging mode - there may be a compensation element (not shown in FIG. 8) that reduces the impact of the bore 490A on the energy dispersion when the hemispherical analyzer 490 is activated. This can be, for example, a diaphragm that closes the bore or an electrode that generates a corresponding field that compensates for the disturbing effect of the bore 490A.

[0175] FIG. 9 schematically illustrates a SEM 400-5 with an energy analyzer comprising two hemispherical energy-selective elements 490 and 491 , e.g., configured for operation modes (b), (c), (d), and (e) according to TAB. 1 . As can be seen in FIG. 9, the energy dispersive element includes two hemispherical analyzers 490, 491 . The analyzer 491 reverses the separation of trajectories by energy applied by the analyzer 490.

[0176] An optional energy selector slit / aperture 495 is positioned within between the two analyzers 490, 491 ; thereby, a certain kinetic energy can be selected. This allows to image the px / py distribution on the 2D detector for a narrow energy pass range (Fig. 18). Further, the chromatic aberrations introduced by the hemispherical analyzer 490 are compensated by the hemispherical analyzer 491 , achieving a better imaging quality.

[0177] The slit may be motorized to adjust the selected kinetic energy. A variable energy bandpass filter is thereby enabled. This may be combined, e.g., with momentum- resolved imaging or position-resolved imaging.

[0178] Using a (fully) motorized slit 495 is only one option. In another scenario, the slit 495 may be fixed. It would be possible that the slit 495 is motorized but can only be positioned to be either within the SE beam path 452 or outside of the SE beam path 452. in other words, a fine adjustment of the slit position within the footprint of the SE beam path 452 may not be possible, while it is still possible to altogether remove or insert the slit 495. In one example, it would be possible that the particular pass kinetic energy is not selected by translating the slit 495, but rather using a slit 495 at a fixed position and adjusting the voltage is at the hemispherical analyzers 490, 491 . This electronic switching of the hemispherical analyzers 490, 491 results in a different mapping of kinetic energies to lateral positions in the plane of the slit 495, thereby enabling electronic selection of the appropriate pass kinetic energy.

[0179] FIG. 10 schematically illustrates a SEM 400-6 with a mono-chromated source and with an energy-selective element including two sequential hemispherical analyzers 490, 491 as in FIG. 9. The SEM 400-6 in FIG. 10 is configured for operation modes (b), (c), (d), and (g), according to various examples.

[0180] As can be seen in FIG. 10, the primary electron source 401 is followed by a series of lenses and apertures 702, 703, 703 that shape and focus the primary electron beam.

[0181] The configuration includes two pairs of hemispherical analyzers 792, 793. The first pair is positioned in the primary electron path to select a specific energy band for the primary electrons. This arrangement functions as a monochromator, narrowing the energy spread of the primary beam before it interacts with the sample.

[0182] FIG. 11 illustrates the SEM 400-6 that is based on the SEM 400-1 of FIG. 5 but including a filter electrode system 510 as another example of an energy-selective element. The filter electrode system 510 includes a sequence of filter electrodes or grids. These electrodes are set at specific potentials to create an energy-dispersive field, e.g., selectively along a spatial direction associated with x-direction or y- direction. The first and last electrodes may be held at the column potential, while the central electrode(s) are set to a different potential (dV) relative to the column potential. This arrangement creates an energy barrier that only electrons with specific kinetic energies can overcome, effectively filtering the SEs based on their energies. After passing through the energy filter, the SE / BSE electrons continue towards the detector for momentum-resolved characterization.

[0183] FIG. 12 schematically illustrates an objective lens setup for a SEM, which can be combined with any SEM as described herein.

[0184] As can be seen in FIG. 12, a multi-element lens arrangement is provided to focus and control the charged particle beam near the sample surface. The topmost element of the objective lens assembly is magnetic pole piece 1203. A non-magnetic liner tube extension 1204 is included as acceleration electrode for the SE / BSE electrons, embodied as a tubular structure extending downward from magnetic pole piece 1203. The middle element of the lens assembly is magnetic pole piece 1202. The lowest of the three pole pieces, positioned closest to the sample, is magnetic pole piece 1201 . A thin, non-magnetic element located just above the sample plane is included as field separator 1205.

[0185] The field separation electrode 1205 may be arranged along the secondary charged- particle beam path between the sample plane and the beam splitter and configured to control an electrostatic field at the sample surface independently from a landing energy of the primary charged particles.

[0186] The combinative action of the three pole pieces 1201 , 1202, 1203 allows to adjust the magnetic field at the sample surface, independently from a focusing condition. I.e., the magnetic field can be adjusted without changing the focal plane. This enables to freely set magnetic or electric immersion. For instance, this arrangement allows to control the pole pieces 1201 , 1202, 1203 to thereby switch between the following modes: (i) magnetic field immersion, (ii) electrostatic field immersion, (iii) combined magnetic and electrostatic field immersion; and (iv) no immersion.

[0187] The magnetic and electrostatic field immersion modes are preferable to achieve the smallest spot size of the primary charged particles. However, large magnetic or electrostatic immersion fields may negatively interact with the sample or with ions when operating in a cross-beam configuration. The option to adjust the immersion field strength freely allows for example to quickly switch between a high resolution mode and a cross-beam mode.

[0188] FIG. 13 schematically illustrates aspects with respect to modes (a), (c), and (d) according to TAB. 1 . As can be seen in FIG. 13, a sample 407 is mounted on a substrate or stage, with a primary electron beam represented by a downward arrow incident on the sample surface. SEs, shown as upward arrows, are emitted from the sample surface with different trajectories. Curved field lines around the sample indicate the presence of local electric fields.

[0189] In this mode, the momentum distribution analysis can be used to detect surface fields. By examining the center of gravity and shape of the SE momentum distribution, the microscope can estimate the local field distribution at the sample surface. This method is particularly sensitive to lateral (horizontal) components of the electric field at the surface.

[0190] FIG. 14 schematically illustrates aspects with respect to imaging mode (f) according to TAB. 1. Operation mode (f) of TAB. 1 employs a mirror / reflection mode for the detection of surface fields. This configuration allows for estimating the local field distribution, particularly the lateral components, by analyzing the momentum distribution of reflected electrons.

[0191] FIG. 14 depicts a sample 407 mounted on a substrate, with curved field lines surrounding it, indicating the presence of local electric fields. Two upward-curving arrows represent the trajectories of reflected electrons.

[0192] In this mirror mode operation, electrons are directed towards the sample surface at a low landing energy, causing them to be reflected before actually impacting the surface. The trajectories of these reflected electrons are sensitive to the local electric fields present at and near the sample surface.

[0193] By examining the center of gravity and shape of the momentum distribution of these reflected electrons, the microscope can estimate the local field distribution at the sample surface. This method is particularly effective for detecting lateral (horizontal) components of the electric field, as these components have a strong influence on the reflection angles and trajectories of the electrons.

[0194] FIGs. 15A-15C schematically illustrate operation modes for energy- and momentum- resolved imaging, cf. TAB. 1. In particular, combined energy-momentum-resolved imaging is discussed, i.e., mode (c) in TAB. 1. In detail, FIG. 15A schematically illustrates the kinetic energy as a function of momentum (dispersion) of the SEs along x direction and y direction, e.g., downstream of the beam splitter. Then, the energy-dispersive element (e.g., a hemispherical analyzer as previously discussed in connection with FIG. 6) separates trajectories along x direction. This results in an energy-dependent shift of the dispersion as shown in FIG. 15B. FIG. 15C illustrates the associated footprints of the SEs in the detector plane xd,ydof the multi-pixel detector. The position of the SEs along ydis proportional to the momentum in y direction, i.e., ydoc py, the position of the SEs along xdis a function of their kinetic energy and their momentum in x direction, i.e., xd= f(Ek,Px). I.e., a superposition of the distribution of the x-momentum and the kinetic energy is resolved along the x direction of the detector plane (xd). As will be appreciated, a 2-D projection of the 3-D dispersion of the SEs can be measured on the multi-pixel detector. Even in this 2-D projection of the 3-D dispersion, the left edge of the 2-D projection marks Ek, min, and thus represents the electrons with the minimum kinetic energy. Ek min(indicative of the work function or surface potential of the material or electron affinity of a semiconductor) can be resolved if the energy-dispersive element separates the trajectories sufficiently strongly.

[0195] FIGs. 16A-C generally correspond to FIG. 15A-C; however, in FIG. 16A-C, an aperture for limiting the in-plane momentum of the SEs is used. The respective cut- off-momenta are the filled circles in FIGs. 16A-C. For instance, such low-pass momentum filtering could be achieved by apertures 480, 481 having circular or round openings in FIG. 6. Due to the low-pass filter used for suppressing large in-plane momenta, the energy dispersion is better resolved along xd(as is apparent from a comparison of FIG. 15C with FIG. 16C). The combination of energy dispersion in one direction and momentum information in the orthogonal direction allows for analysis of the sample's electronic structure and surface properties. Despite the aperture's effect in emphasizing slower electrons and reducing large in-plane momenta, the superposition between energy and momentum information still prevents full spectroscopic analysis. The distribution shows how electrons with different energies and momenta are spread across the detector, with the aperture providing some selective filtering. Another option is shown in the following FIGs.

[0196] FIGs. 17A-C schematically illustrate aspects with respect to operation mode (c) according to TAB. 1. FIGs. 17A-C generally correspond to FIGs. 16A-C. Figure 17A illustrates the effect of a slit aperture on the SE distribution in momentum px, pyand kinetic energy space when the aperture 480 or 481 having a slit opening is arranged at a backfocal plane (in which position corresponds to px / py momentum) before the energy-dispersive element. As previously discussed in connection with FIG. 16A, a certain filtering of the in-plane momentum is used. In FIG. 16A, the pxcomponent of momentum is limited to a specific value or value range, px,o, while allowing a range of pyvalues to pass through. This configuration allows for selective analysis of electrons within a narrow range of x-direction momenta. The superposition of the x-momentum distribution and the kinetic energy along xdis reduced. It preserves the full distribution in the y-direction and across all energies. Such a setup can be useful for isolating electrons emitted at specific angles in one dimension, potentially enhancing sensitivity to certain surface features or electronic states.

[0197] FIGs. 18A-C schematically illustrate operation modes (a) in combination with (e) according to TAB. 1 . In this scenario, a narrow energy band Ek,Pis selected (e.g., using the configuration of FIG. 9). This configuration allows for energy-selective imaging of the px- pydistribution, i.e. , 2-D distribution of in-plane momentum, where only electrons with a specific kinetic energy are analyzed. It provides a means to examine the momentum distribution of electrons at a particular energy, which can be useful for studying specific electronic states or topographic features in the sample.

[0198] FIG. 19 illustrates an electronic circuitry 910 according to various examples. The electronic circuitry can be associated with any of the SEMs disclosed herein. The electronic circuitry 910 includes a processor 912 and the memory 913. The processor 912 can load program code from the memory 913 and execute the program code. Executing the program code causes the processor 912 to perform techniques as disclosed herein, e.g., operating one or more components of the SEM in accordance with an active imaging mode, e.g., one or more of the imaging modes as discussed in connection with TAB. 1. For instance, one or more components can be operated in a combined energy-momentum-resolved imaging mode, e.g., as discussed in connection with FIGs. 15A through 18C. For instance, a surface potential and / or surface potential gradient can be determined. A surface potential difference between different sample regions may be determined.

[0199] The processor 912 can selectively activate different imaging modes. For this, the processor 912 may control one or more components of the SEM by providing respective control instructions via a communication interface 911. For instance, with reference to FIG. 7, the processor 912 may provide control instructions to a motor of the magnetic prism 409 to rotate the magnetic prism 409 to either select the SE beam path 452 of the bypass SE beam path 452-1 . For instance, when selecting the bypass SE beam path 452, this equates to energy-resolved imaging; while selecting the SE beam path 452-1 may correspond to either momentum-resolved imaging or position-resolved imaging. A further scenario would be to control a position of a slit aperture, e.g., in the energy-dispersed plane (cf. FIG. 9: slit aperture 495) by providing respective control data to an associated motor. Thereby, a respective energy band can be filtered (cf. FIG. 18A through FIG. 18C). Also, the electric potential or magnetic field of electrically-controllable components may be controlled. An example would be setting a certain electric potential to the filter electrode system 510, thereby selecting a certain cutoff kinetic energy. Yet another example would be to switch on / switch off the magnetic field in the hemispherical analyzer 419 the scenario FIG. 8.

[0200] In summary, the scanning charged-particle microscope and / or the cross-beam system described in the claims offer several technical advantages for advanced surface and material analysis. The combination of the beam splitter, acceleration electrode, energy-selective element, and multi-pixel detector enables high-resolution energy-momentum-resolved imaging and / or energy-resolved imaging modes. Although the invention has been shown and described with respect to certain preferred embodiments, equivalents and modifications will occur to those skilled in the art upon the reading and understanding of the specification. The present invention includes all such equivalents and modifications and is limited only by the scope of the appended claims.

[0201] Furthermore, techniques have been disclosed in which the trajectories of secondary charged particles, in particular the trajectories of SEs or BSEs, are selectively affected by motorized components. Instead of using motorized components that can be translated and / or rotated, it is generally possible to use electronically switchable components that can be controlled by adjusting the current - e.g., excitation of deflection coils - and / or the voltage - e.g., for deflection plates. Generally, electronic control may be faster and more reliable and wearout may be reduced, if compared to motorized control.

[0202] For illustration, above, various scenarios have been disclosed in the context of imaging and the detecting SEs. Similar techniques may be used for imaging and detecting higher-energy electrons returning from the sample along a secondary electron beam path, such as BSEs.

[0203] While various examples have been disclosed in connection with a SEM, similar techniques can be used for other types of charged-particle microscopes.

[0204] Furthermore, the SEM or other types of charged-particle microscopes may be integrated into a cross-beam system that also includes an ion-source column and / or a photon source with a common coincidence point.

[0205] For further illustration, above, various aspects with switchable apertures have been disclosed. Such switchable apertures may be switched to be activated or to be deactivated. Alternatively or additionally, such switchable apertures may be switched to provide different aperture openings, e.g., a slit opening or a circular opening. Furthermore, the position of a given opening - e.g., of a slit opening or of a circular opening - may be movable by switching such aperture.

[0206] For still further illustration, above, various aspects with respect to an energy- dispersive element being implemented by a hemispherical analyzer have been disclosed. Other implementations of an energy-dispersive element, in particular, of an energy-selective element are conceivable. For instance, such energy-dispersive element can operate using a magnetic field or an electrostatic field or a combination of a magnetic and electrostatic field. The hemispherical analyzer, using an electric field with two concentric electrodes, is only one option. The various concepts and architectures of an SEM or another type of scanning charged-particle microscope can be applied to different implementations of energy-selective elements, e.g., using a magnetic-field separator, another type of spectrometer, etc.

Claims

C L A I M S1 . A scanning charged particle microscope (400, 400-1 , 400-2, 400-3, 400-4, 400-5, 400-6), comprising:- an illumination column (104) configured to emit primary charged particles along a primary charged-particle beam path (451 ) towards a sample plane (407),- a detection column (460) configured to guide secondary charged particles from the sample plane along a secondary charged-particle beam path, the primary charged-particle beam path and the secondary charged-particle beam path (452) overlapping in an overlap region (455), the overlap region (455) extending between a beam splitter (406, 409) and the sample plane,- an acceleration electrode (408) arranged between the sample plane and the beam splitter (406, 409) and configured to accelerate the secondary charged particles along the secondary charged-particle beam path towards the beam splitter,- the beam splitter (406, 409) configured to separate the primary charged- particle beam path from the secondary charged-particle beam path,- an energy-selective element (490, 491 ) configured to be arranged in the secondary charged-particle beam path downstream of the beam splitter (406, 409) and to selectively deflect trajectories of the secondary charged particles along the secondary charged-particle beam path depending on their kinetic energies, and- a multi-pixel detector (465) arranged downstream of the energy-selective element and configured to detect the manipulated trajectories of the secondary charged particles with a spatial resolution.

2. The scanning charged particle microscope of claim 1 , further comprising:- a detector optics (461 ) arranged in the secondary charged-particle beam path between the energy-selective element and the multi-pixel detector, the detector optics configured to selectively switch between projecting a backfocal plane along the secondary charged-particle beam path onto a detector plane of the multi-pixel detector, and project a crossover plane onto the detector plane of the multi-pixel detector.

3. The scanning charged particle microscope of claim 1 or 2, further comprising:- electronic circuitry (910, 912, 913) configured to analyze a detector image of the multi-pixel detector to determine at least one of an energy distribution, a onedimensional or two-dimensional momentum distribution of the secondary charged particles.

4. The scanning charged particle microscope of any one of the preceding claims, wherein the beam splitter (406, 409) is configured to image an in-plane momentum of the secondary charged particles.

5. The scanning charged particle microscope of any one of the preceding claims, wherein the beam splitter (406, 409) comprises a magnetic prism (406, 409).

6. The scanning charged particle microscope of any one of the preceding claims wherein the energy-selective element comprises at least one of a hemispherical analyzer, a spectrometer, a grid filter, a magnetic-field separator, or an electric-field separator.

7. The scanning charged particle microscope of any one of the preceding claims, wherein the energy-selective element (490, 491 ) comprises a first element(490) and a second element (491 ) arranged downstream along the secondary charged-particle beam path, the first element being configured to apply a first deflection to the trajectories of the secondary charged particles depending on their kinetic energies and the second element being configured to apply a second deflection to the trajectories of the secondary charged particles depending on their kinetic energies, the second deflection counteracting or canceling the first deflection.

8. The scanning charged particle microscope of claim 7, further comprising a slit aperture (495) configured to be arranged between the first element and the second element.

9. The scanning charged particle microscope of claim 8, wherein the slit aperture (495) is motorized and configured to position a slit opening at different positions associated with different kinetic energies of the secondary charged particles.

10. The scanning charged particle microscope of any one of the preceding claims, further comprising:- an aperture arranged (481 ) in a backfocal plane or an image of the backfocal plane of the secondary charged-particle beam path upstream of the energy-selective element.11 . The scanning charged particle microscope of any one of the preceding claims, further comprising:- an electronic circuitry (910, 912, 913) configured to operate one or more components of the scanning charged particle microscope in accordance with an active one of multiple imaging modes, the multiple imaging modes being selected from the group comprising: one-dimensional momentum-resolved imaging, two- dimensional momentum-resolved imaging, energy-resolved imaging, energy- selective imaging, and combined energy-momentum-resolved imaging.

12. The scanning charged particle microscope of any one of the preceding claims, wherein the energy-selective element is electronically switchable between an active mode for the energy-resolved imaging and an inactive mode for the two- dimensional momentum-resolved imaging.

13. The scanning charged particle microscope of any one of the preceding claims, wherein the scanning charged particle microscope comprises at least one switchable component, wherein the secondary charged-particle beam path selectively bypasses the energy-selective element depending on a setting of the switchable component.

14. The scanning charged particle microscope of claim 13, wherein the secondary charged-particle beam path passes through a bore provided at the energy-selective element when bypassing the energy-selective element.

15. The scanning charged particle microscope of claim 13 or 14, wherein the switchable component is the beam splitter.

16. The scanning charged particle microscope of any one of the preceding claims, further comprising:- an electronic circuitry (910, 912, 913) configured to operate one or more components of the scanning charged particle microscope in a combined energy- momentum-resolved imaging mode, wherein a momentum of the secondary charged particles along a first direction is resolved along a first detector direction along a detector plane of the multi-pixel detector, wherein a superposition of the momentum of the secondary charged particles and kinetic energy is resolved along a second direction that is mostly perpendicular to the first direction is resolved along a second detector direction of the detector plane, the second detector direction being perpendicular to the first detector direction.

17. The scanning charged particle microscope of claim 16, wherein the electronic circuitry (910, 912, 913) is configured to determine a surface potential, and / or surface potential gradient, and / or a surface potential difference between two sample regions, of a sample arranged in the sample plane depending on a detector image acquired by the multi-pixel detector in the combined energy-momentum-resolved imaging mode.

18. The scanning charged particle microscope of any one of the preceding claims, further comprising:- a field separation electrode (1205) arranged along the secondary charged- particle beam path between the sample plane and the beam splitter and configured to control an electrostatic field at the sample surface independently from a landing energy of the primary charged particles.

19. The scanning charged particle microscope of any one of the preceding claims, further comprising:- three or more pole pieces (1201 , 1202, 1203) configured for setting a magnetic field at the sample plane.

20. The scanning charged particle microscope of claim 19, further comprising:- an electronic circuitry (910, 912, 913) configured to operate the three or more pole pieces in accordance with an active one of multiple immersion modes, the multiple immersion modes being selected from a group comprising: magnetic field immersion; electrostatic field immersion; combined magnetic and electrostatic field immersion; no immersion.

21. A cross-beam system, comprising:- the scanning charged particle microscope of any one of the preceding claims; and - an ion-source column configured to emit charged ions along an ion charged- particle beam path towards the sample plane.

22. The cross-beam system of claim 21 , further comprising:- a photon source configured to emit photons towards the sample plane.

Images