Method and system for element mapping

Abstract

To provide a method and a system for imaging a sample using a charged particle microscope.SOLUTION: A method and a system for imaging a sample using a charged particle microscope scans a region of interest (ROI) of the sample using an electron beam, acquires X-rays emitted from the sample, and then scans the ROI using the ion beam to acquire ion-induced photons emitted from the sample. The spatial distribution of multiple elements within the sample can be determined on the basis of both the acquired X-rays and the acquired ion-induced photons.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] This specification generally relates to methods and systems for determining the composition of a sample, and more specifically to mapping elements within a sample using a charged particle microscope. [Background technology]

[0002] Charged particle microscopy is a well-known and increasingly important technique for imaging microscopic objects. Multiple types of emissions from a sample in response to charged particle irradiation can provide structural and compositional information about the sample. For example, energy-dispersive X-ray spectroscopy (EDS or EDX) can be used for elemental analysis or chemical characterization based on the energy spectrum of X-ray emissions in response to electron beam irradiation. However, the applicant recognizes that some light elements are difficult or impossible to detect using EDS. [Overview of the project]

[0003] In one embodiment, the method includes scanning a region of interest (ROI) of a sample with an electron beam and acquiring X-rays emitted from the sample; scanning the ROI with an ion beam after scanning the ROI with an electron beam and acquiring ion-induced photons emitted from the sample; and determining the spatial distribution of multiple elements in the sample based on both the acquired X-rays and the acquired ion-induced photons. In this way, the spatial distribution of elements that cannot be detected by EDS can be mapped based on ion beam-induced photon emission.

[0004] In another embodiment, a charged particle microscope system for determining the composition of a sample comprises an ion source for generating an ion beam, an electron source for generating an electron beam, a first detector for detecting X-rays emitted from the sample, a second detector for detecting ion-induced photons emitted from the sample, and a controller including non-temporary memory for storing computer-readable instructions. By executing instructions, the controller is configured to scan a region of interest (ROI) of the sample using the electron beam and acquire X-rays emitted from the sample using the first detector; scan the ROI using the ion beam after scanning the ROI with the electron beam and acquire ion-induced photons emitted from the sample using the second detector; and determine the spatial distribution of multiple elements in the sample based on both the acquired X-rays and the acquired ion-induced photons. In one example, the second detector is retractable from the imaging position where ion beam-induced photon emission is detected.

[0005] It should be understood that the above summary is provided in a simplified form to introduce a selection of concepts that will be further explained in the detailed description. It is not intended to identify any significant or essential features of the claimed subject matter, the scope of which will be uniquely defined by the claims that follow the detailed description. Furthermore, the subject matter of the claims is not limited to embodiments that resolve any defects described above or in any part of this disclosure. [Brief explanation of the drawing]

[0006] [Figure 1] Several embodiments of charged particle microscopes for elemental mapping are illustrated.

[0007] [Figure 2A] This shows the distal end of the light collection system for detecting ion-induced light.

[0008] [Figure 2B] Figure 1 shows the light collection system in the vacuum chamber of the microscope, as shown in Figure 2A.

[0009] [Figure 3] It is a flowchart of an exemplary method for element mapping.

[0010] [Figure 4] It shows a method for optimizing parameters for ion beam scanning.

[0011] [Figure 5] It shows an exemplary calibration table generated using the method of FIG. 4.

[0012] [Figure 6] It is an exemplary method for performing ion beam scanning.

[0013] [Figure 7A] It shows an exemplary optical spectrum obtained using heavy ions. [Figure 7B] It shows an exemplary optical spectrum obtained using light ions.

[0014] [Figure 8A] It is an image generated from ion beam induced light after injecting light ions into a sample.

[0015] [Figure 8B] It is the integrated spectrum of FIG. 8A.

[0016] [Figure 9A] It shows the amplitude of ion beam induced light that changes over time when using heavy ions. [Figure 9B] It shows the amplitude of ion beam induced light that changes over time when using light ions.

[0017] [Figure 9C] It is a SEM image showing a sample after scanning the sample with heavy ions and light ions respectively.

[0018] [Figure 10] An example of a sample analyzed using the method shown in Figure 3 is illustrated.

[0019] [Figure 11A] This is an SEM image of a cross-section of the sample.

[0020] [Figure 11B] This is an EDS image of the same sample cross-section as Figure 11A. [Figure 11C] This is an ion beam-induced light image of the same sample cross-section as Figure 11A.

[0021] [Figure 11D] This is an EDS image of the same sample cross-section as Figure 11A. [Figure 11E] This is an ion beam-induced light image of the same sample cross-section as Figure 11A.

[0022] [Figure 12A] This is a FIB-SE image of the cross-section of the sample. [Figure 12B] This is an ion-induced photon image of a cross-section of the sample.

[0023] [Figure 12C] Figure 12B shows the integrated spectra in different regions. [Figure 12D] Figure 12B shows the integrated spectra in different regions.

[0024] [Figure 13] This is a composite image created by cutting and pasting SEM and EDS images of a battery sample.

[0025] [Figure 14A] Figure 13 shows an ion beam-induced photographic image of Ni in a battery sample. [Figure 14B] Figure 13 shows an ion beam-induced photographic image of Fe in a battery sample. [Figure 14C]Figure 13 shows an ion beam-induced photographic image of Al in a battery sample. [Figure 14D] Figure 13 shows an ion beam-induced photographic image of Li in a battery sample.

[0026] Similar reference numbers refer to corresponding parts across several figures in the drawing. [Modes for carrying out the invention]

[0027] The following description concerns systems and methods for determining the composition of a sample. Sample composition can be determined via charged particle-based spectroscopic techniques such as energy-dispersive X-ray spectroscopy (EDS or EDX) and secondary ion mass microscopy (SIMS). These spectroscopic techniques can be combined with scanning electron microscopy (SEM) or transmission electron microscopy (TEM) to provide commonly registered compositional and structural information of a sample. However, some elements, particularly light elements (i.e., elements with atomic numbers not greater than 11), are difficult or impossible to detect by EDS or SIMS. For example, hydrogen cannot be detected by EDS and is difficult to detect by SIMS. EDS is also poorly sensitive to alkali metals such as lithium, and trace metals / elements. Understanding the spatial distribution of elements, including H and Li, can be critical for fabricating and evaluating certain samples, such as battery samples, and therefore a complete elemental map of the sample is necessary. Furthermore, SEM-based techniques have difficulty detecting trace elements due to their large interaction volume, resolution limits, and lack of surface sensitivity.

[0028] The applicant understands that ion beam-induced photon emission is more sensitive to heavy elements, alkali metals, and trace elements compared to EDS and SIMS. By scanning the sample with an electron beam in front of the ion beam, both X-ray and photon emissions from the sample can be obtained. By combining the information obtained from ion beam-induced photon emission using EDS, a complete elemental mapping of the sample can be generated.

[0029] In one example, the region of interest (ROI) of a sample is first scanned with an electron beam, and X-rays emitted from the sample are acquired. Then, the ROI is scanned with an ion beam, and photon emissions from the sample are acquired. Elements within the ROI on the sample surface can be determined by analyzing the acquired X-rays and optical spectra. Because EDS and ion beam-induced photon emission have different sensitivities to different elements, combining EDS with ion beam-induced photon emission allows for the identification and mapping of a greater number of elements. For example, EDS detects elements with atomic numbers greater than 11, while ion beam-induced photon emission detects elements with atomic numbers not greater than 11. Ion beam-induced photon emission detects alkali metals, while EDS detects non-alkali metals. EDS detects elements at higher gravimetric densities, while ion beam-induced photon emission detects elements at lower gravimetric densities. For example, FIB-iLE can detect several elements with gravimetric densities below 100 ppm. The detection limit of FIB-iLE is element-dependent.

[0030] In some cases, the ion beam is a focused ion beam (FIB), and ion beam-induced photoemission is also referred to herein as focused ion beam-induced photoemission (FIB-iLE). Due to the destructive nature of ion beam scanning, the sample surface is first scanned with an electron beam before being scanned with an ion beam, and as a result, the same sample layer is analyzed by both EDS and FIB-iLE. Since the interaction volume between the electron beam and the sample is generally larger than that of the ion beam, at each scan location, the EDS signal may contain information about a larger sample volume than the FIB-iLE signal. Therefore, FIB-iLE imaging can achieve higher resolution than EDS imaging.

[0031] In one example, the elemental composition of the first sample layer is determined based on signals acquired during electron beam and ion beam scans of the first sample surface. While the first sample surface is scanned with an ion beam, it is milled by the ion beam to expose the second sample surface at an increased sample depth. The second sample surface is scanned using both electron and ion beams, and its elemental composition is determined. The above procedure can be repeated multiple times to reproduce the three-dimensional elemental composition of the sample.

[0032] In some examples, one or more elemental maps showing the distribution of multiple elements are generated based on acquired X-ray and photon emissions. The spatial distribution of multiple elements can be shown within a single elemental map by color-coding each element.

[0033] The combined EDS and FIB-iLE sample analysis can be performed within a charged particle microscope (CPM) as shown in Figure 1. The CPM comprises an ion source and an electron source for generating the FIB and focused electron beam, respectively. The CPM includes a first detector (such as an EDS detector) for detecting X-rays emitted from the sample in response to electron beam irradiation, and a second detector (such as a FIB-iLE detector) for detecting ion-induced photons emitted from the sample in response to FIB irradiation.

[0034] In one example, the ion source is a liquid metal ion source (LMIS). In another example, the ion source is a plasma ion source capable of generating a focused ion beam of one or more gas species. The FIB-iLE signal intensity can be enhanced by tuning the gas chemical reactions of the plasma ion beam. In one embodiment, scanning the ROI with the ion beam involves simultaneously directing at least two ion species toward the sample surface. One of the at least two ion species may be lighter and more chemically active than the other. In one example, the difference in atomic number between the at least two ion species may not be less than 8. In another example, the difference in atomic number between the at least two ion species may not be less than 10. Lighter ions (i.e., ions with lower atomic numbers) yield higher FIB-iLE photon yields, while heavier ions (i.e., ions with higher atomic numbers) yield higher sputtering rates. By scanning the ROI with both lighter and heavier ions, the FIB-iLE signal can be enhanced, and at the same time, the sample can be removed with a high sputtering rate. In another embodiment, scanning an ROI with an ion beam involves first scanning a selected region within the ROI with lighter ions to inject the lighter ions into the sample, and then scanning the ROI with heavier ions for FIB-iLE signal acquisition. By injecting lighter, chemically active ions into the selected region within the ROI, the photon yield in these selected regions during subsequent ion beam scans using heavier, inert ions can be enhanced.

[0035] A second FIB-iLE detector may include a light collection system that can be retracted from the vacuum chamber in which the sample is imaged. The light collection system may include an optical fiber having a first distal end sealed within an elongated sheath. A lens is optically coupled to the first distal end of the optical fiber to directly collect photons emitted from the sample. The lens is mechanically coupled to the sheath. Light emitted from the sample is collected by the FIB-iLE detector when the detector is positioned at the imaging position, with the first distal end of the detector positioned between the magnetic pole piece (either an ion column or an electron column) and the sample. The FIB-iLE detector may be inserted into and / or retracted from the imaging position via a flange on the vacuum chamber of the charged particle microscope. Due to the compact contour of the FIB-iLE detector, alternating EDS and FIB-iLE sample scanning can be performed without retracting the FIB-iLE detector from the imaging position. In some cases, the FIB-iLE detector may be retracted from the imaging position during sample preparation and / or for detector maintenance.

[0036] FIB-iLE detectors can be used to detect photon emission in response to irradiation other than ion beams. For example, photon emission in response to electron beam or light irradiation can also be collected using a FIB-iLE detector. The FIB-iLE detector can be introduced into the vacuum chamber of a gas intrusion system (GIS) compatible charged particle microscope via the same flange as the GIS system. Thus, photon detection can be achieved without significant modification of the system. The FIB-iLE detector can also be used to deliver light toward a sample.

[0037] For example, a method for detecting photon emission in response to charged particle or photon irradiation using a FIB-iLE detector includes: inserting the FIB-iLE detector's light collection system into the vacuum chamber through an opening in the vacuum chamber before pumping out the vacuum chamber in which the sample is positioned; pumping out the vacuum chamber; irradiating the sample with a charged particle beam or photons; and receiving the photon emission from the sample via the light collection system positioned at the imaging location. The condition of the lens or lens system of the light collection system can be determined by monitoring the signal decay of the detected photons over time. The lens or lens system may be replaced or cleaned after a certain period of use based on its condition.

[0038] Turning to Figure 1, Figure 1 is a very schematic depiction of an embodiment of a dual-beam charged particle microscope (CPM) in which the present invention is implemented, more specifically, it shows an embodiment of a FIB-SEM. Coordinates 110 are system coordinates. The microscope 100 comprises a particle optical column 1, which generates a beam 3 of charged particles (in this case, an electron beam) propagating along the electron optical axis 101. The electron optical axis 101 may be aligned with the Z axis of the system. The column 1 is mounted in a vacuum chamber 5, which comprises a sample holder 7 and associated actuator 8 for holding / positioning a sample 6. The vacuum chamber 5 is evacuated using a vacuum pump (not shown). Also shown are vacuum ports 9, which may be opened for the introduction / extraction of supplies (parts, samples) into / out of the vacuum chamber 5. The microscope 100 may have multiple such ports 9 as needed.

[0039] The electron column 1 comprises an electron source 10 and an illuminator 2. The illuminator 2 comprises lenses 11 and 13 for focusing the electron beam 3 onto the sample 6, and a deflection unit 15 (for performing beam steering / scanning of the beam 3). The microscope 100 further comprises, among other things, a controller / computer processing unit 26 for controlling the deflection unit 15, lenses 11 and 13, and detectors 19, 21, and 41, and for displaying the information collected from the detectors 19, 21, and 41 on a display unit 27.

[0040] Detectors 19 and 21 can be selected from a variety of potential detector types that can be used to examine different types of "induced" radiation emitted from the sample 6 in response to irradiation by the (incident) electron beam 3. Alternatively, they may be X-ray detectors such as silicon drift detectors (SDDs) or silicon lithium (Si(Li)) detectors. Detector 21 may be an electron detector in the form of a solid-state photomultiplier tube (SSPM) or vacuum photomultiplier tube (PMT), for example. This may be used to detect backscattered and / or secondary electrons emitted from the sample 6. The microscope 100 may also include an ion detector and a mass spectrometer for SIMS imaging. Those skilled in the art will understand that many different types of detectors can be selected in a configuration such as the one shown, including, for example, annular / segmented detectors.

[0041] The detector 41 includes a retractable light collection system 42 for detecting photon emission from the sample 6. Photon emission may result from ion and / or electron beam irradiation of the sample surface. The light collection system 42 can be introduced into the vacuum chamber 5 via a flange 52 on the vacuum chamber 5. Photons collected by the first distal end 51 of the light collection system 42 may be converted and amplified by an imaging sensor before being transferred to the controller 26. In some embodiments, the light collection system may also be used to deliver light toward the sample 6. The detector 41 is referred to herein as a FIB-iLE detector for detecting photon emission in response to FIB irradiation. However, the detector 41 may also be used to detect cathodoluminescence resulting from electron beam irradiation.

[0042] By scanning beam 3 over sample 6, stimulated radiation, including, for example, X-rays, infrared / visible / ultraviolet rays, secondary electrons (SE), and / or backscattered electrons (BSE), is emitted from sample 6. Since such stimulated radiation is position-sensitive (due to the scanning motion), the information acquired from detectors 19, 21, and 41 is also position-dependent.

[0043] Signals from the detectors (19, 21, and 41) pass along the control line (bus) 25, are processed by the controller 26, and are displayed on the display unit 27. Such processing may include operations such as coupling, integration, subtraction, false coloring, edge enhancement, and other processes known to those skilled in the art. Furthermore, automated recognition processes (such as those used in particle analysis) may be included in such processing. The controller includes non-temporary memory for storing computer-readable instructions and a processor for executing computer-readable instructions. The methods disclosed herein may be carried out by executing computer-readable instructions within the processor.

[0044] In addition to the electron column 1 described above, the microscope 100 also includes an ion column 31. This includes an ion source 39 and an illuminator 32, which generate / direct a focused ion beam (FIB) 33 along the ion optical axis 34. To facilitate easy access to the sample 6 on the holder 7, the ion optical axis 34 is inclined with respect to the electron optical axis 101. As described above, such an ion column 31 can be used to perform processing / machining operations on the sample 6, such as cutting, milling, etching, and deposition. Furthermore, the ion column 31 can be used to generate an image of the sample 6. It should be noted that the ion column 31 may generate a variety of different ion species, and therefore, a reference to the ion beam 33 is not necessarily considered to specify a particular species in the beam at any given time—in other words, the ion beam 33 may include ion species A for operation A (e.g., milling) and ion species B for operation B (e.g., implantation), in which case species A and B may be selected from a variety of possible choices.

[0045] The microscope may include a gas injection system (GIS) that can be used to locally inject gases, such as etching gases or precursor gases, for the purpose of performing gas-assisted etching or deposition. Such gases may be stored / buffered in a reservoir and administered through a narrow nozzle, resulting in appearance, for example, near the intersection of axes 101 and 34. The GIS system may be introduced into the vacuum chamber 5 via the same flange 52 used for introducing the detector 41.

[0046] It should be noted that many improvements and alternatives to such settings are known to those skilled in the art, such as the use of a controlled environment inside the microscope 100 (of a relatively large volume), for example, maintaining a background pressure of several millibars (as used in environmental SEMs or low-pressure SEMs).

[0047] Figure 2A is a magnified view of the first distal end 51 of a light collection system 42 of a detector 41 for detecting photons from a sample in response to charged particle irradiation. The light collection system includes an optical fiber 202 having a first distal end 208 sealed within an elongated sheath 201. The outer diameter of the sheath 201 is less than 4 mm. In this example, the first distal end 208 of the fiber enters the lumen of the sheath laterally through a channel 207. The channel 207 is not aligned with the axis 209 and is fluidly connected to the opening of the sheath. Alternatively, the first distal end of the fiber may enter the lumen via a second distal end of the light collection system along the axis 209 so that the fiber aligns with the axis 209. A lens 204 positioned at the first distal end 51 of the light collection system is optically coupled to the optical fiber 202. The lens 204 is mechanically coupled to the sheath 201. Lens 204 focuses light to reach the first distal end 51 of the light collection system and the first distal end 208 of the optical fiber 202. Lens 204 has an NA higher than 0.22 for large light collection angles. Figure 2A shows a single lens 204. In some embodiments, lens 204 may be a lens system comprising multiple lenses. These multiple lenses may have the same outer diameter. In Figure 2A, the first distal end 208 of the optical fiber 202 and lens 204 are separated by a gap 205. The length of the gap 205 along axis 209 depends on the focal length of lens 204. An opening 203 on the sheath provides a fluid connection between the gap 205 and the outside of the photodetector system. Thus, gas in the gap 205 can be removed from the photodetector system while the vacuum chamber is being pumped evacuated. The axial position of the first distal end 208 relative to the axis 209 can be adjusted using one or more set screws through one or more holes 206 to optimize the optical coupling between the fiber and the lens. In other examples, the lens or lens system can be directly fused onto the distal end 208 of the optical fiber.

[0048] In one example, the outer diameter of lens 204 matches the inner diameter of sheath 201, so the lens can be inserted into the lumen of sheath 201. The outer diameter of sheath 201 is larger than the outer diameter of the lens. At least a portion of lens 204 is sealed within the sheath. In another example, the lens may have the same outer diameter as the outer diameter of sheath 201. The lens can be fixed to the tip of the first distal end 208 using an adhesive. The lens or lens system may be replaced or removed after a period of use to remove any contamination on the lens surface, such as deposits resulting from ion milling.

[0049] Figure 2B shows the relative positions of the optical collection system 42 with respect to the sample 6 and the magnetic pole pieces of the ion column 31 and electron column 1. The optical collection system can collect photons emitted from the sample 6 when positioned at the imaging location. At the imaging location, the distal end of the optical collection system is located between the column's magnetic pole piece and the sample, in a direction along the column's optical axis. Photons emitted from the sample are collected directly by the optical collection system 42 without passing through or being reflected from any optical components. In one example, the tip of the optical collection system is within 2 mm of the eucentric height of the microscope system. The low profile of the optical collection system allows the microscope system to be configured so that the collection angle of the optical collection system does not overlap with the collection angles of other detectors (such as the secondary electron detector 212). The optical collection system can be used to acquire light in response to electron beam irradiation and / or ion beam irradiation. The light collection system 42 may remain in the same location (e.g., the imaging location) inside the vacuum chamber for light collection when switching from one type of charged particle beam irradiation to another type of charged particle beam irradiation during an imaging session. Thus, the imaging location is a fixed position in the microscope's coordinate system and does not change between electron beam scans and ion beam scans. Alternatively, the light collection system 42 may be retracted from the imaging location to allow more space for other detectors or sample preparation. In another embodiment, the imaging locations for electron beam scans and ion beam scans may differ. For example, the light collection system of a FIB-iLE detector may be adjusted along axis 209 between electron beam scans and ion beam scans.

[0050] In one example, the sample is tilted to face either the ion column or the electron column for ion beam scanning or electron beam scanning. Figure 2B shows sample 6 facing electron column 1, with an incident electron beam angle of 90 degrees. In another example, the sample may be positioned acutely with respect to both the ion and electron optical axes, and as a result, the sample does not need to be tilted between ion beam scanning and electron beam scanning. The angle between the electron optical axis and the axis 209 of the photodetector system is greater than the angle between the ion optical axis and the axis 209 of the photoacquisition system. This configuration can achieve high photon collection in both FIB-iLE and cathodoluminescence imaging because FIB-iLE has more isotropic photon emission compared to cathodoluminescence.

[0051] Figure 3 shows a method 300 for mapping the elemental composition of a sample using EDS and FIB-iLE. Electron beam scans and ion beam scans are performed alternately within the sample's ROI. X-ray signals acquired during electron beam scans provide information about the distribution of Group 1 elements, and ion-induced photons acquired during ion beam scans provide information about the distribution of Group 2 elements. By performing electron beam scans before ion beam scans, elemental information for the same sample layer can be obtained. During ion beam scans, the sample layer is removed, exposing a new sample surface. By alternating between electron beam scans and ion beam scans, the elemental distribution within the sample volume can be mapped.

[0052] In one example, the sample may be tilted to face the electron beam or ion beam between scans. Each of the charged particle beams may irradiate the sample at an incident angle of 90 degrees for scanning. In another example, the sample may be held stationary relative to the ion and electron columns throughout the entire imaging session. Both the electron and ion beams may scan the sample at incident angles less than 90 degrees.

[0053] In 301, the FIB-iLE detector can be optionally positioned within the vacuum chamber of the charged particle microscope. Positioning the FIB-iLE detector may involve inserting the FIB-iLE detector's light collection system into the vacuum chamber via a flange. Furthermore, the first distal end of the light collection system can be positioned at the imaging position. The vacuum chamber can be pumped evacuated after the light collection system has been introduced into the vacuum chamber.

[0054] In 302, beam parameters and scan parameters are optionally determined by performing a parameter optimization procedure on a sacrificial region of the sample or reference sample. In one example, ion beam scan parameters are determined from a calibration table generated based on ion scans in multiple areas within the sacrificial region. Details of the parameter optimization procedure are shown in Figure 4. In some examples, if a calibration table for the sample type is known, beam parameters and scan parameters can be determined based on the calibration table.

[0055] In 304, system parameters are set for sample imaging. These system parameters may include one or more of the following: beam current, beam size, beam energy, residence time, detector integration time, and scan patterns for both electron and ion beams. The scan patterns for electron and ion beam scans may differ. The optimal beam and scan parameters determined in 302 may be used for the system parameters. Furthermore, the ROI of the sample (i.e., ROI relative to the sample's coordinates) may be determined. The ROI may be determined based on the SEM scan of the sample.

[0056] In 306, the ROI is scanned with an electron beam according to the parameters set in 304, and X-ray emissions from each scan location within the ROI are acquired using an EDS detector. During scanning, images showing structural information of the sample surface (such as SEM images) can also be acquired by detecting backscattered electrons from the sample. In some examples, secondary ion emissions from the sample are acquired for SIMS.

[0057] In 308, the sample can be optionally tilted from the electron column towards the ion column.

[0058] In step 310, method 300 checks whether the imaging session has finished. For example, the progress of the imaging session may be determined based on the SEM image acquired in step 306. If the imaging session is complete, method 300 terminates. Otherwise, the ROI is scanned with an ion beam in step 312.

[0059] In 312, the ROI is scanned with an ion beam, and photon emissions at each scan location are acquired using a FIB-iLE detector. The ion beam scan can be adjusted based on the configuration of the microscope system and the sample type to enhance FIB-iLE detection. In one example, scanning the ROI with an ion beam involves directing a single ion species to each of the scan locations. In another example, scanning the ROI with an ion beam involves simultaneously directing at least two ion species to each of the scan locations. In yet another example, scanning the ROI with an ion beam involves first directing a first ion species towards each of the scan locations, and then directing a second ion species towards each of the scan locations, with photons collected in response to irradiating the sample with the second ion species. Details of the ion beam scan are shown in Figure 6.

[0060] In 314, one or more elemental maps of the sample surface are generated based on the acquired X-ray and photon emissions. The elemental map may show the spatial distribution of multiple detected elements within the ROI. Each element may be color-coded separately within the elemental map. Secondary electron (SE) images in response to ion irradiation may be acquired simultaneously during the ion scan. FIB-induced SE (FIB-SE) images can show the structure of the sample surface. In some examples, the elemental map can be combined with structural images or FIB-SE images acquired in 306 to display both structural and compositional information in a single image.

[0061] In step 316, method 300 checks whether the imaging session is complete. In one example, the progress of the imaging session may be determined based on the structural and / or compositional images generated in step 306 and / or step 314. In another example, the imaging session may be completed after reaching a predetermined sample depth or after milling a predetermined number of sample layers. If the imaging session is complete, method 300 terminates. If the imaging session is not complete, method 300 proceeds to 318 to adjust the electron and ion beams to image the sample surface at a greater sample depth. The sample may also be optionally tilted again in 320 before being scanned with the electron beam.

[0062] In this way, by sequentially scanning the same ROI using electron and ion beams within a charged particle microscope, a complete elemental map of one or more sample surfaces / layers can be obtained. Various elements can be detected by EDS and FIB-iLE.

[0063] In one embodiment, instead of acquiring photons in response to ion irradiation, or in addition to that, secondary ions may be acquired for SIMS. Elemental information acquired from SIMS can be combined with elemental information acquired via FIB-iLE and / or EDS to obtain a complete elemental mapping of the sample. In another embodiment, cathodoluminescence may be collected during electron beam scanning using a FIB-iLE detector.

[0064] Figure 4 shows Method 400 for optimizing parameters related to the charged particle beam used in the method of Figure 3. These parameters may include ion beam parameters and / or electron beam parameters such as beam size, beam shape, residence time, beam energy, beam / stage angle, pitch and overlap between scan locations, and beam resolution. These parameters may also include scan patterns and scan areas for the electron beam and ion beam, respectively. Method 400 optimizes the ion beam and scan parameters by performing a parameter optimization procedure on a sample sacrificial area or reference sample. During the optimization procedure, one or more beam parameters or scan parameters are adjusted to generate one or more calibration tables. The optimal beam and scan parameters can then be selected based on the calibration tables.

[0065] In one example, the optimal parameters for a FIB are determined to enhance the image quality of FIB-iLE and / or SIMS. FIBs are commonly used for milling samples. However, parameters used for FIB milling may not be optimal for FIB-iLE or SIMS. This is because increasing the current density and / or residence time used within the FIB increases ion implantation and sample damage, while reducing the inherent photon or secondary ion yield. During ion beam scanning, the photon or secondary ion yield is affected by the sample's composition and structure, as well as the state of the microscope system. Multiple factors, including matrix effects, preferential sputtering, and ion implantation, influence the photon or secondary ion yield. Therefore, determining the optimal beam and scan parameters for FIB-iLE or SIMS is extremely difficult, or even impossible.

[0066] In step 402, system parameters for the parameter optimization procedure are set. These system parameters may include one or more of the following: beam size, beam current, beam energy, residence time, and scan area. Furthermore, a sacrificial region may be identified. The sacrificial region may be a sample area that does not overlap with the ROI when EDS and FIB-iLE imaging are combined. Alternatively, the sacrificial region may be a region on the reference sample.

[0067] In 404, the ion beam is directed toward an area within the sacrificial region.

[0068] In 406, one or more areas within the sacrificial region are irradiated using different beam or scan parameters of the ion beam, and photon and / or secondary electron yields are recorded. Calibration tables may be generated based on the yields recorded for those corresponding beam / or scan parameters. In one example, generating a calibration table involves generating a photon yield versus beam flux plot in 408. Due to injection, damage, and sputtering rate variations at different energies, multiple calibration tables may be generated for various ion beam acceleration energies. The generated calibration tables may be saved to determine parameters for future imaging sessions.

[0069] One exemplary calibration table is the photon yield versus beam flux plot shown in Figure 5, where the photon yield is recorded for each of several ion beam fluxes. The normalized photon yield is shown in Figure 5. Multiple beam fluxes can be obtained by adjusting one or more of the scan area, beam spot size, and beam current. In one example, the beam flux is adjusted by adjusting the scan area while maintaining the same beam current and spot size. The beam flux value is calculated as the average beam current for the scanned area. Multiple scan areas of different sizes within the sacrificial region are repeatedly scanned using the same beam parameters. The scan parameters remain the same, except for the scan area. The photon yield of one or more elements is monitored while each scan area is repeatedly scanned. If the change in photon yield is within a predetermined range of yield change (e.g., within 10% of the maximum photon yield), the steady-state photon yield corresponding to the scan area is recorded. In another example, the beam flux is adjusted by adjusting the beam spot size while maintaining the beam current. Multiple beam fluxes are obtained by monitoring the photon yield of one or more elements while decreasing the beam spot size. The beam flux value is calculated as the beam current divided by the beam spot size. The beam spot size can be adjusted by adjusting the focusing lens. In yet another example, the beam flux is adjusted by adjusting the beam current while maintaining the scan area and / or beam spot size. The beam current can be adjusted by adjusting the ion beam aperture and / or focusing lens.

[0070] Figure 5 shows 30 keV Xe + An exemplary photon yield vs. ion beam flux plot is shown, generated using a reference sample containing Mg in the beam. The steady-state photon yield of Mg at wavelengths of 517 nm and 518 nm is 0.5 pA / µm² to 100 pA / µm². 2The results were recorded with ion beam fluxes in the specified range. Photon yield decreases with increasing flux. This decrease reverses the rate of oxygen replenishment from the water vapor in the original vacuum chamber in the sacrificial region. As the beam flux increases, the oxygen replenishment rate decreases. This means that at higher beam fluxes, the sample surface does not have enough time to be oxidized, resulting in a reduced photon yield.

[0071] In some examples, plots similar to those in Figure 5 may be generated for SIMS. In some examples, different calibration tables may be generated for different elements or components.

[0072] In 412, the beam and scan parameters that are optimal for FIB-iLE and / or SIMS imaging are selected based on the calibration table. For example, the beam and scan parameters corresponding to the ion beam flux within range 501 in Figure 5 are selected for ion beam scanning. Ion beam scanning with the optimal beam and scan parameters can acquire a strong FIB-iLE signal with a relatively high sputtering rate. Parameters corresponding to the highest photon yield are not selected because those parameters may cause an increase in the total scan time.

[0073] In some cases, a trained neural network (NN) can be used to determine optimal beam and scan parameters from calibration data collected within the sacrificial region. The NN can be trained using training data generated by finding the optimal imaging conditions for a given sample type. For example, the training data may consist of photon yields as a function of ion dose to the sample area, similar to the plot shown in Figure 5. The optimal beam and scan parameters predicted by the NN will maximize the FIB-iLE signal while minimizing acquisition time, taking into account surface conditions that change during milling. In addition to optimizing parameters before analyzing the sample, the NN can also be used to optimize parameters during the imaging session based on the received optical signal. Machine learning techniques such as deep NNs and convolutional NNs can be used to optimize beam and scan parameters.

[0074] Figure 6 shows a method 600 for performing an ion beam scan to enhance photon and / or secondary ion yields. The photon or secondary ion yield in response to FIB bombardment can be enhanced by tuning the chemistry of the ion beam. For example, different gas ion species can be used for the ion beam scan.

[0075] Different ions will interact with the sample differently. For example, Xe + Heavy ions such as He have a smaller interaction volume in the sample, which promotes sputtering. The signals generated from heavy ions mainly consist of elemental emission. + and O + Light ions such as (i.e., ions with an atomic number not greater than 11) have a larger interaction volume in the sample and promote electron-hole recombination. The signal generated from light ions includes band gap and crystal information. Figure 7A shows Xe at 30 KeV. + Figure 7B shows the photon emission in spectral form from a silicon sample in response to irradiation.+ Figure 7A shows photon emission from the same sample in response to irradiation. Compared to Figure 7B, Figure 7A mainly contains elemental emission lines from Si with little broadband ionluminescence emission. Figure 7B mainly contains broadband ionluminescence from electron-hole recombination. The FIB-iLE and / or SIM signals can be enhanced by tuning the ion species used for ion beam scanning.

[0076] In 602, the signal enhancement method for ion beam scanning is selected based on one or more of the sample composition, sample characteristics, and microscope parameters. For example, the signal enhancement method may be selected based on one or more of the sample material, the oxygen supply rate of the sample in the microscope's vacuum chamber, and the requirements for sample analysis. The oxygen supply rate may be determined in 302 of Figure 3. Furthermore, the signal enhancement method may also be selected based on prior experimental knowledge. The signal enhancement method may include A) sequentially scanning the sample surface with light and heavy ions (604 and 606), B) scanning the sample surface with an ion beam containing at least two ion species (608), and C) scanning the sample surface with an ion beam containing a single ion species (610). In one example, method A) may be selected for direct writing of ROI and localized signal enhancement. Method B) may be selected for overall signal enhancement and improved planar layer reduction of ion beam scanning. Methods B) and C) may be selected to reduce the total imaging session duration and / or the maximum possible sputtering / removal. Method C) may be selected to minimize sample damage and chemical changes to the sample.

[0077] At 604, the selected regions within the ROI are first scanned with a lighter, more reactive ion type to precondition the sample surface by implanting lighter ions. The regions within the ROI can be selected based on the SEM images collected during the electron beam scan at 306. Then, at 606, the ion source is switched from a lighter ion type to a heavier, less reactive ion type to scan the entire ROI. Photon emissions are acquired during the scan using the heavier ions. In one example, the difference in atomic number between the lighter and heavier ions is greater than 10. By implanting light ions within one or more sub-areas of the ROI, the FIB-iLE signals within these selected regions can be enhanced. The selected regions can contain elements with lower photon yields. By selectively enhancing the FIB-iLE signals within these regions, the signal-to-noise ratio of the entire ROI in the FIB-iLE image acquired at 606 can be improved. Further, by restricting the area of light ion implantation, sample damage and / or chemical changes to the sample surface can be minimized. In some embodiments, at 606, in addition to or as an alternative to acquiring photon emissions, secondary ions can be acquired during the scan using the heavier ions.

[0078] Figures 8A and 8B illustrate enhanced photon emissions after oxygen implantation. O according to the lattice pattern + After irradiating the Be sample surface with an ion beam, the sample surface was scanned with a 30 keV Xe + beam and photon emissions were acquired. Figure 8A shows the signal intensity at the Be emission lines (wavelengths 333 nm and 457 nm) at each scan location. A lattice pattern with oxygen implantation can be seen, indicating that the implantation of lighter ions enhanced the FIB-iLE signals acquired in subsequent ion beam scans using heavier ions. Figure 8B shows the signal integrated along the Y-axis of Figure 8A.

[0079] In 608, photons are acquired in response to scanning the ROI using an ion beam containing at least two ion species. Unlike 604 and 606, where the sample surface is scanned first with lighter ion species and then with heavier ion species, here multiple ion species are directed simultaneously onto the sample surface. In one example, the ion beam contains both lighter and heavier ion species. The atomic weight difference between the two ion species may be no less than 8, 10, or 20. The acquired photon emission includes both narrowband elemental beam emission from the light-ion bombardment and broadband electron-hole recombination from the heavy-ion bombardment. By simultaneously irradiating the sample surface with both light and heavy ions, the FIB-iLE and / or SIMS signals are enhanced while maintaining a minimal reduction in sputtering rate. Compared to ion beam scanning using heavy ions only, the FIB-iLE and / or SIMS signals are more powerful. Compared to ion beam scanning using only light ions, the layer reduction (or sputtering) rate is higher.

[0080] Figures 9A and 9B show the sample area as Xe + (Figure 9A) only, or O +Figure 9B shows the FIB-iLE signal intensity over time at the Mg emission lines (wavelengths 517 nm and 518 nm) while the sample area is repeatedly irradiated with only an ion beam. To generate each figure, the sample area was scanned using different beam conditions, namely 30 KeV 13 nA (901 and 904), 16 KeV 8.8 nA (902 and 905), and 8 KeV 8.3 nA (903 and 906). The signal amplitudes for the different beam conditions were normalized and offset in each figure. In Figure 9A, for all beam conditions, the FIB-iLE signal amplitude peaks when the ion beam begins to collide with the sample at approximately 1.6 seconds, and then decreases over time. The signal amplitude corresponding to higher beam energies and higher beam currents decreases rapidly over time. In Figure 9B, for all beam conditions, the FIB-iLE signal amplitude remained high after peaking at the start of the ion beam, as the sample was repeatedly scanned by the ion beam. The different signal behavior between Figure 9A and Figure 9B is due to the ion beam being Xe + When only O is present, the native oxide layer on the sample surface is rapidly sputtered, leaving little time to replenish oxygen to the newly exposed sample surface, which results in the rapid decay of photon yield shown in Figure 9A. The higher the beam energy and beam current, the more rapidly the decay of photon yield occurs. However, O + In the case of an ion beam containing only oxygen, the newly exposed sample surface is constantly replenished with oxygen provided by the ion beam. Therefore, the signal amplitude remains high over time.

[0081] Figure 9C(C)(D) shows Xe at 30KeV on a sample having alternating layers of nickel and chromium. + (Figure 9C(C)) and 30KeV O + SEM images of the box mill sidewalls 907 and 908 using only (Figure 9C(D)) are shown. Compared to Figure 9C(C), in Figure 9C(D) the ion beam with light ions results in a more planar delay surface 909, and the chromium island 910 present in Figure 9C(C) is absent.

[0082] In 610, photons are acquired in response to irradiating the sample with a single ion type.

[0083] In this way, the FIB-iLE signal can be enhanced by using ions or multiple gas species. The SIMS signal can be enhanced through the same process.

[0084] Figure 10 illustrates sample 6 analyzed by method 300 in Figure 3. Coordinates 1010 are sample coordinates and are different from the microscope coordinates (110 in Figure 1). Sample 6 may be irradiated with a charged particle beam along direction 1001, where the sample is tilted to face each of the charged particle beams during the imaging session. Alternatively, sample 6 may be irradiated with a charged particle beam along direction 1002, where the sample is not tilted when switching between charged particle beams. The sample is positioned in the XY plane, and the sample depth increases along the Z axis. For ion beam and electron beam scans, the ROI 1006 is defined using the X and Y axes of the sample coordinates. Region 1007 may be a sacrificial region for performing the parameter optimization procedure in Figure 6. After scanning the ROI with electron and ion beams, the first layer 1003 of the sample is sputtered off by the ion beam scan. The elemental distribution of the first layer can be analyzed using acquired X-ray and photon emissions. The ROI can then be scanned again using electron and ion beams. The second layer 1004 of the sample is removed by sputtering, and an elemental mapping of the second layer can be formed using acquired X-ray and photon emissions. The second layer is located at a deeper sample depth compared to the first layer.

[0085] Figures 11A to 11E are cross-sectional images of a Si-C cathode sample acquired using the microscope system in Figure 1. Figure 11A is an SEM image generated from secondary electrons acquired during electron beam scanning. Figures 11B and 11D are EDS images generated from X-ray emission acquired during electron beam scanning. Figure 11B shows the distribution of C, and Figure 11D shows the distribution of Si. Figures 11C and 11E are FIB-iLE images generated from photon emission acquired during ion beam scanning. Figures 11C and 11E show the distribution of Li and Na, respectively. Li and Na cannot be detected by EDS. Because EDS and FIB-iLE have different sensitivities for different elements, complete elemental mapping of the battery sample can be obtained.

[0086] Figures 12A and 12B are FIB-SE and FIB-iLE images of a cross-section of a lithium-ion battery cathode sample. The distribution of H, which cannot be imaged using EDS or SIMS, can be seen in the FIB-iLE image Figure 12B, generated from the FIB-iLE signal at the H emission line (wavelength 656.3 nm). Figures 12C and 12D are integrated spectra corresponding to regions 1202 and 1203 in Figure 12B, respectively. Photon emission from H at wavelength 656.3 nm was evident, as indicated by arrows 1204 and 1205.

[0087] Figure 13 is a composite image of SEM and EDS images of a nickel-manganese-cobalt (NMC) cathode sample collected during electron beam scanning. SEM image 1302 shows the surface structure of the sample. EDS images 1302-1308 show the spatial distribution of Ni, O, Co, Fe, C, Mn, and Al. Image 3019 shows bremsstrahlung. Figures 14A-14D show FIB-iLE images of Ni, Fe, Al, and Li obtained from the same sample shown in Figure 13. The EDS images of Ni, Fe, and Al (1302, 1305, and 1308 in Figure 13) mainly show bremsstrahlung, but the distribution of these elements is clearly shown in the FIB-iLE images (Figures 14A-14C).

[0088] The technical advantage of performing an electron beam scan before an ion beam scan is that it allows for the analysis of elements within the same sample layer. Furthermore, the different sensitivities of FIB-iLE and EDS to different elements can generate a complete elemental map. The technical advantage of optimizing the ion beam before the imaging session is that it allows for the acquisition of a high FIB-iLE signal at the desired sample sputtering rate. The technical advantage of using a retractable optical collection system for FIB-iLE imaging is that it allows the optical collection system to remain in the imaging position when switching charged particle beams. Furthermore, the retractable optical collection system can be used as a conventional dual-beam system. The technical advantage of using multiple ion species together or sequentially during an ion beam scan is that the FIB-iLE signal is enhanced.

[0089] In one presentation, a light collection system for collecting light in response to charged particle irradiation comprises an optical fiber having a first distal end sealed within an elongated sheath, and a lens positioned at the first distal end of the light collection system, wherein the lens is optically coupled to the optical fiber for directly collecting light emitted from a sample in response to charged particle irradiation, and the lens is mechanically coupled to the sheath, the light collection system is retractable from an imaging position located close to the sample, and the sample is positioned on a sample stage in a vacuum chamber. In the first example of the system, the first distal end of the light collection system can be retracted from the imaging position, and the first distal end of the light collection system is positioned between a magnetic pole piece and the sample while at the imaging position. A second example of the system optionally includes the first example and further includes the light collection system being retractable from the vacuum chamber via a flange. A third example of the system optionally includes one or more of the first and second examples and further includes the lens diameter being less than or equal to the sheath diameter. A fourth example of the system optionally includes one or more of the first to third examples, further comprising that at least a portion of the lens is sealed by a sheath. A fifth example of the system optionally includes one or more of the first to fourth examples, further comprising that the lens comprises multiple lenses of the same diameter. A sixth example of the system optionally includes one or more of the first to fifth examples, further comprising that the lens focuses a beam into an optical fiber. A seventh example of the system optionally includes one or more of the first to sixth examples, further comprising that the lens is fused to a first distal end of the fiber. An eighth example of the system optionally includes one or more of the first to seventh examples, further comprising that the lens is spaced apart from the first distal end of the fiber, the sheath has at least one opening that fluidly connects to a vacuum chamber, and a space between the fiber and the lens in the sheath. A ninth example of this system optionally includes one or more of the first to eighth examples, and further includes the fact that the lens is removable from the light collection system.

[0090] In another presentation, the charged particle microscope system includes an electron column, an ion column, and detectors for collecting photons generated in response to electron and / or ion irradiation. In the first example of the system, the detector includes a retractable light-collecting system. The second example of the system optionally includes the first example and further includes a vacuum chamber, the light-collecting system being retractably removed from the vacuum chamber through an opening in the vacuum chamber. The third example of the system optionally includes one or more of the first and second examples and further includes a GIS system, the GIS system being inserted into and removed from an opening in the vacuum chamber. The fourth example of the system optionally includes one or more of the first to third examples and further includes the light-collecting system collecting photons at the imaging position, the collection angle of the light-collecting system at the imaging position not overlapping with the collection angles of other detectors in the microscope system.

[0091] In yet another presentation, a method for collecting light emitted from a sample using a photodetector system includes inserting the photocollection system through an opening in a vacuum chamber before pumping out the vacuum chamber in which the sample is positioned; irradiating the sample with a charged particle beam or photons; and receiving photons emitted from the sample in response to irradiation of the first distal end of the photocollection system at the imaging position. A first example of this method further includes monitoring signal decay over time and replacing or cleaning the lenses in the photocollection system. A second example of this method optionally includes the first example and further includes delivering light to the sample using the photocollection system.

Claims

1. 1. A charged particle microscope system for determining the composition of a sample, comprising: an ion source for generating an ion beam; an electron source for generating an electron beam; a vacuum chamber; a first detector for detecting x-rays emitted from the sample positioned within the vacuum chamber; a second detector for detecting ion-induced photons emitted from the sample; wherein the second detector includes a light collection system retractably inserted into the vacuum chamber via a flange on the vacuum chamber. Charged particle microscope system.

2. a magnetic pole piece through which the ion beam is directed to the sample, and acquiring ion-induced photons emitted from the sample using the second detector includes acquiring ion-induced photons that enter a first distal end of the light collection system positioned between the magnetic pole piece and the sample. The charged particle microscope system of claim 1 .

3. the light collection system includes an optical fiber having a distal end enclosed within an elongated sheath, and a lens optically coupled to the distal end of the optical fiber for directly collecting the ion-induced photons emitted from the sample. The charged particle microscope system of claim 1 .

4. The NA of the lens is higher than 0.

22. The charged particle microscope system according to claim 3 .

5. The lens and the distal end of the optical fiber are spaced apart with a gap, and the sheath includes an opening that provides a fluid connection between the gap and the exterior of the light collection system. The charged particle microscope system according to claim 3 .

6. At least a portion of the lens is sealed by the sheath. The charged particle microscope system according to claim 3 .

7. a gas injection system (GIS) that is introduced into and removed from the vacuum chamber via the flange; The charged particle microscope system of claim 1 .

8. The method of claim 7, further comprising: a controller including a non-transitory memory for storing computer-readable instructions, wherein by executing said instructions, said controller: scanning a region of interest (ROI) of the sample with the electron beam and acquiring, using the first detector, x-rays emitted in response to irradiating the sample with the electron beam; scanning the ROI with the ion beam and using the second detector to acquire ion-induced photons emitted in response to irradiating the sample with the ion beam; The charged particle microscope system according to claim 1 , configured as follows:

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