A method and system for investigating a sample using a scanning transmission charged particle microscope with reduced beam damage.

Abstract

To provide a method for examining a sample in a scanning transmission charged particle microscope.SOLUTION: The method comprises the steps of providing a scanning transmission charged particle microscope, having an illuminator and a scanning unit. The method comprises the steps of providing a desired dose for at least a first sample location of multiple sample locations; and determining, using a controller of the microscope, a first set of parameter settings for the illuminator and the scanning unit for substantially achieving the desired dose at the first sample location.SELECTED DRAWING: Figure 4

Description

Summary of the Invention

[0001] The present disclosure relates to a method for inspecting a sample in a scanning transmission charged particle microscope. The present disclosure also relates to a scanning transmission charged particle microscope capable of performing the method.

[0002] Charged particle microscopy is a well-known and increasingly important technique for imaging microscopic objects, particularly in the form of electron microscopy. So far, the basic types of electron microscopes have evolved into several well-known apparatuses such as transmission electron microscopes (TEMs), scanning electron microscopes (SEMs), and scanning transmission electron microscopes (STEMs), and further, so-called "dual beam" apparatuses that further employ "machining" focused ion beams (FIBs) that enable assistive actions, such as ion beam milling or ion beam induced deposition (IBID), (e.g., FIB-SEM), have evolved into various auxiliary apparatuses.

[0003] In STEM, irradiation of the sample with a scanning electron beam causes an interaction between the primary electrons and the sample. Due to this interaction, elastically scattered electrons may emerge from the sample, and detecting these can form a microscope image. Further, the irradiation of the sample promotes the emission of "auxiliary" radiation from the sample in the form of secondary electrons, backscattered electrons, X-rays, and cathodoluminescence (infrared, visible, and / or ultraviolet photons). One or more components of this emitted radiation can be detected and used for creating the microscope image.

[0004] Materials scientists have used electron microscopes with high accelerating voltages (e.g., 200kV or 300kV) to achieve sub-1 Å resolution in relatively thick samples. These high-energy electrons limit the range of materials that can be investigated at high resolution without damage. Sub-angstrom low-voltage electron microscopy (60kV or lower accelerating voltages) can expand the range of materials that can be investigated at sub-1 Å resolution by reducing the accelerating voltage, thereby minimizing beam-induced damage due to knock-on damage. Examples include 2D materials such as graphene and MoS2, or MOFs (metal-organic frameworks). However, such low accelerating voltages can increase damage mechanisms, such as ionization damage and beam-induced etching. Therefore, imaging conditions need to be optimized for each sample, but controlling these conditions is not easy and often lacks reproducibility, requiring the user to be an expert. For example, changing the accelerating voltage reduces knock-on damage but potentially introduces several hours of drift, requiring extensive retuning.

[0005] Considering the above, the present invention aims to provide a method and system for minimizing beam-induced damage on beam-sensitive samples when investigating them using scanning charged particle microscopy, such as HRSTEM. In particular, the aim is to provide a method and system that enables non-expert users to successfully achieve these results with beam-sensitive samples.

[0006] Therefore, the present disclosure provides a method for inspecting a sample with a scanning transmission charged particle microscope, the method as defined by claim 1. As described herein, the method includes the step of providing a scanning transmission charged particle microscope, the scanning transmission charged particle microscope comprising a charged particle beam source for emitting a charged particle beam, a sample holder for holding a sample, an illuminator for guiding the charged particle beam emitted from the charged particle source onto the sample, a scanning unit for scanning the beam onto a plurality of sample positions on the sample, and a control unit for controlling the operation of the scanning transmission charged particle microscope.

[0007] As defined herein, the method includes the step of providing a desired dose parameter for at least a first sample location among a plurality of sample locations. The desired dose parameter may be provided, for example, by the user or by the controller. By providing the desired dose parameter, boundary conditions are directly applied to the system, making the system easier to control. The desired dose parameter may include one or more of dose, dose rate, and total dose. Hereinafter, the terms desired dose parameter and desired dose are used interchangeably. Therefore, wherever the general terms “desired dose parameter” or “desired dose” are used, it will be understood that this may refer to the desired dose, desired dose rate, and / or desired total dose, unless explicitly stated otherwise.

[0008] The method defined herein further includes the step of using the controller to determine a first set of parameter settings for the illuminator and the scanning unit to substantially achieve the desired dose parameter at the first sample location. The controller is configured to determine the first set of parameter settings as an output, with the desired dose as an input parameter to the controller. Note that the desired dose may be, for example, a beam current, dose rate, or total dose at the sample.

[0009] The method defined herein provides dose-controlled workflows for scanning transmission electron microscopy, such as STEM. In particular, the method enables low-dose workflows for STEM and materials science applications. It has been noted that in current microscopes, the beam current, i.e., dose rate and dose used in HRSTEM experiments, is not well known or cannot be determined with sufficient reliability. To obtain statistically meaningful data within the limited time on the microscope, customers in the industry need to reproduce results, whether with the same or different tools. This means identifying the initial successful settings for use on the same microscope and across multiple microscopes. Unfortunately, optical settings (e.g., gun lens settings, spot count, extraction voltage, aperture) do not allow for the reproduction of dose or dose rate in STEM.

[0010] The present invention, as defined herein, provides solutions that enable novel handling through different approaches, allowing even non-optics experts to perform experiments reproducibly and increase experimental productivity, for example, by enabling materials scientists to quantitatively model and simulate results.

[0011] The method defined herein does this by providing the desired dose and using a controller for determining the settings of a scanning transmission charged particle microscope, particularly the settings of at least the illuminator and scanning unit, to effectively apply that desired dose to the sample.

[0012] In principle, the controller may determine the settings for the scanning transmission charged particle microscope based on one or more of the following three basic methods. 1) Use a numerical model to calculate the microscope settings based on the desired dose as an input parameter. 2) Use active measurement of the beam current and adjust the microscope settings based on the desired dose as an input parameter. 3) Using the microscope calibration data, determine the microscope settings based on the desired dose as the input parameter.

[0013] These three basic methods and their advantageous embodiments will be further explained below.

[0014] According to the first basic method, a numerical model is used.

[0015] In one embodiment, the controller may be able to determine a first set of parameter settings by using a numerical model of the scanning transmission charged particle microscope and its components. The numerical model of the scanning transmission charged particle microscope can be based, at least in part, on a thick lens model, although other methods of modeling the microscope are also possible.

[0016] Using numerical models, users can change the dose / dose rate without pre-exposing the sample or measuring current with the device. With this method and associated microscope, the dose / dose rate can be predicted by setting the illuminator parameters. This is powerful because it avoids using electrons that could damage the sample before the final experiment is performed.

[0017] The numerical model defined in this embodiment may use one or more boundary conditions. These boundary conditions may be adjusted by at least one of the beam current, dose rate, and / or total dose. In one embodiment, the boundary conditions may be set by the microscope user. The boundary conditions may be set automatically, either additionally or alternatively.

[0018] Therefore, numerical models can determine settings for illuminators or their components, such as arbitrary condenser lenses, to control, for example, the beam current, dose, or dose rate in a sample. Those skilled in the art will be familiar with the development of numerical models for charged particle devices.

[0019] Numerical models may include aberrations and focus as part of their set of parameters. Therefore, numerical models may include focus, astigmatism, and / or coma, and these parameters can be kept constant when changing dose and / or dose rate.

[0020] Active measurement of the beam current is performed according to the second basic method.

[0021] A scanning transmission charged particle microscope may be equipped with a beam current measuring device. This beam current measuring device can be placed near the sample, for example, to measure the beam current received by the sample. Based on the desired beam current, dose rate, or total dose, the controller can determine a first set of microscope parameter settings, where the measured beam current is used. If the desired beam current is equal to the measured beam current, no further action is required. In other cases, the microscope settings can be fine-tuned to approach the desired beam current.

[0022] In one embodiment, the beam current measuring device is configured to measure the beam current upstream of the illuminator. The measured beam current upstream of the illuminator may be, for example, the beam current at the location of the extractor aperture and can be used as an input parameter for a numerical model. In this way, a combination of a first basic method (numerical model) and a second basic method (beam current measurement) is created.

[0023] According to the third basic method, for example, pre-recorded calibration data stored in a calibration data storage unit, which may be part of the controller, is used.

[0024] In this embodiment, if pre-recorded calibration data is used, the desired dose can be compared to the pre-recorded calibration data and the corresponding resulting dose. Based on the desired dose, the controller can select a first set of parameters that yield that desired dose. Other boundary conditions, such as the accelerating voltage of the microscope, can also be provided. It should be noted that these differences in accelerating voltages may also be part of the pre-recorded calibration data.

[0025] In summary, we have described three basic methods. It should be noted that, as already explained, there are combinations of methods that use active measurements within the numerical model, and therefore, it is also possible to combine different basic methods. Furthermore, combinations of any one of the basic methods are also possible. In any case, further embodiments will be described below, but in principle, all further embodiments can utilize one or more of the basic methods described.

[0026] In one embodiment, the method includes the step of illuminating the sample at a first location using the first set of parameter settings. The method may include the step of evaluating the resulting dose based on the first set of parameters. For example, the resulting dose can be measured (directly or indirectly). Modifications to the first set of parameters can be made as needed to achieve a desired dose.

[0027] In one embodiment, the method includes providing a second desired dose and using the controller to determine a second set of parameter settings for the illuminator and the scanning unit to substantially achieve the second desired dose. The second desired dose may be different from the first desired dose. The second desired dose may target the same location on the sample or a different location on the sample. Thus, the sample may be illuminated at the first position using the second set of parameter settings and / or the sample may be illuminated at a second position of the plurality of sample positions. The second desired dose may be higher or lower compared to the first desired dose.

[0028] In one embodiment, the first set of parameter settings is used to illuminate the sample at the second position. <�

[0029] In one embodiment, the controller is configured to track the cumulative dose effect at the corresponding position. This can in principle be any location on the sample being illuminated, such as the first and / or second location. The cumulative dose can be determined for areas already visited. If an area is exposed multiple times, in this embodiment, it is possible to track and display the total cumulative dose. As an example, an image (or map) of the sample can be created and displayed to the user. The image or map may include cumulative dose statistics. When moving to another area, the previous area can be graphically marked and the cumulative dose can be displayed. When searching the entire sample, the user may be provided with a patchwork of areas that have been marked as visited (exposed at a specific dose). Also, by storing the total dose in the metadata of the captured image, it may be possible to document not only the dose and dose rate of the last image but also the cumulative dose. This can enhance the reproducibility of the experiment by documenting and understanding not only the last exposure dose but also the total dose.

[0030] In one embodiment, the scanning transmission electron microscope comprises a temperature control system configured to control the temperature of at least a part of the microscope. The temperature control system may be particularly configured to control the temperature of the microscope when the acceleration voltage is changed. In one embodiment, the temperature control system can be part of the illuminator. The temperature control system ensures that aberrations due to thermal expansion are minimized and even prevented. Thereby, the drift and readjustment required when changing the acceleration voltage can be minimized and even prevented.

[0031] In one embodiment, the temperature control system comprises a so-called constant total power lens, as described, for example, in EP1498929B1 in the name of the applicant. By implementing the constant total power lens, the total power of the microscope can be fixed and maintained when changing the acceleration voltage, and as a result, the temperature is controlled. The advantage is that when investigating a specimen highly sensitive to knock-on damage, the optimal acceleration voltage can be found during the experiment. In other words, it is possible to find the compromise between the highest resolution and minimized knock-on damage "on the fly".

[0032] In one embodiment, the method includes the step of fixing and maintaining the power of all the lenses in the illuminator at a first power setting. By fixing the power of all the lenses when switching the acceleration voltage, it has been found that stage drift, beam drift, focus, and coma drift can be minimized and work can be continued almost immediately after the switching.

[0033] Additionally or alternatively, the temperature control system may comprise a heat exchanger. The heat exchanger may be configured to increase heat dissipation when the microscope consumes more power, and vice versa.

[0034] In one embodiment, a scanning transmission charged particle microscope includes a user interface configured for setting a desired dose. As previously noted, the desired dose may be one or more of the beam current, dose rate, and / or total dose. The user interface may be a graphical user interface. The user interface allows the user to provide input settings for the first and / or second set of parameter settings, which in one embodiment include dose-related settings, including at least one of the dose rate, dose, and total dose.

[0035] In one embodiment, the method includes the step of changing the accelerating voltage of a scanning transmission charged particle microscope. The change in accelerating voltage may be, for example, made by the user or may be part of a set of parameter settings. Thus, the first set of parameter settings may additionally include settings for the beam source or any other part of the microscope. The method may include the step of using the controller to determine the resulting dose and / or dose rate as a result of the provided change in accelerating voltage. This embodiment is particularly powerful in combination with a temperature control system because it allows for rapid (high tension) changes in accelerating voltage, thereby minimizing the effects of knock-on damage quickly and with the lowest dose.

[0036] In one embodiment, the method includes the step of providing a further scanning transmission charged particle microscope. The further scanning transmission charged particle microscope comprises a charged particle beam source for emitting a charged particle beam, a sample holder for holding a sample, an illuminator for guiding the charged particle beam emitted from the charged particle source onto the sample, a scanning unit for scanning the beam over a plurality of sample positions on the sample, and a control unit for controlling the operation of the further scanning transmission charged particle microscope. In this embodiment, the method includes the step of using the respective controllers of the further scanning transmission charged particle microscope to determine a first set of parameter settings for the further scanning transmission charged particle microscope to substantially achieve the desired dose at the sample position. This embodiment enables in-tool reproducibility of the experiment. When the method defined herein is performed with at least two microscopes, not only can the experiment be reproduced with a single tool to predict dose and dose rate, but the same dose / dose rate experiment can also be reproduced with a second tool. This increases the reproducibility of data generation at different locations around the world.

[0037] According to one embodiment, a scanning transmission charged particle microscope is provided as defined in claim 13. The microscope comprises a charged particle beam source for emitting a charged particle beam, a sample holder for holding a sample, an illuminator for guiding the charged particle beam emitted from the charged particle beam source to the sample, and a control unit for controlling the operation of the scanning transmission charged particle microscope. The scanning transmission charged particle microscope as defined herein is - To receive the desired dose at at least the first sample location among the plurality of sample locations, -The controller is configured to determine a first set of parameter settings for the illuminator and the scanning unit to substantially achieve the desired dose at the first sample position.

[0038] The advantages of such microscopes have already been elucidated based on the methods defined herein.

[0039] Further embodiments and their advantages are subject to the dependent claims.

[0040] Scanning transmission charged particle microscopes may include a blanker. The blanker may be used as part of the illuminator to set the dose and / or dose rate. [Brief explanation of the drawing]

[0041] The apparatus and methods disclosed herein will now be described in more detail based on exemplary embodiments and accompanying schematic drawings.

[0042] [Figure 1] A longitudinal cross-sectional view of a charged particle microscope is shown. [Figure 2] A schematic diagram of the method defined herein is shown. [Figure 3] A schematic diagram of the microscope as defined herein is shown. [Figure 4] This specification shows a schematic embodiment of a (graphical) user interface that can be used with the microscope defined herein.

[0043] In drawings, corresponding parts are indicated using corresponding reference numerals where appropriate. It should be noted that, in general, drawings are not to scale.

[0044] Figure 1 is a very schematic diagram of an embodiment of a transmission charged particle microscope M, which in this case is a TEM / STEM (however, in the context of this disclosure, a transmission charged particle microscope may also be, for example, an ion-based microscope or a proton microscope). In Figure 1, within a vacuum housing E, an electron source 4 (such as a Schottky emitter) generates a beam of electrons (B) that passes through an electron-optical illuminator 6, which functions to direct / focus the electron beam onto a selected portion of a sample S (the sample S may, for example, be thinned / planarized (locally)). The illuminator 6 has an electron-optical axis B' and broadly includes a wide variety of electrostatic / magnetic lenses, (scanning) deflectors D, correctors (such as astigmatism correctors), etc. Typically, the illuminator 6 may also include a focusing lens system (the entire component 6 may be referred to as the "focusing lens system").

[0045] The sample S is held on a sample holder H. As shown here, a portion of this holder H (within the housing E) is attached to a cradle A' which can be positioned / moved in multiple degrees of freedom by a positioning device (stage) A. For example, the cradle A' may be displaced in the X, Y, and Z directions (see the Cartesian coordinate system shown), and may be rotated around a longitudinal axis parallel to X. Such movement allows various parts of the sample S to be irradiated / imaged / inspected by an electron beam moving along axis B' (and / or a scanning operation is performed instead of beam scanning [using a deflector D], and / or selected parts of the sample S are machined, for example, by a focused ion beam (not shown)).

[0046] The electron beam B, moving (focusing) along axis B', interacts with the sample S to cause the sample S to emit various types of "induced" radiation, including (e.g.) secondary electrons, backscattered electrons, X-rays, and photoirradiation rays (cathode ray emission). If necessary, one or more of these radiation types can be detected using a detector 22, which may be, for example, a composite scintillator / photomultiplier tube or an EDX (energy-dispersive X-ray spectroscopy) module, in which case the image can be constructed using essentially the same principles as in a SEM. However, alternatively or supplementarily, electrons that traverse (pass through) the sample S, are emitted from the sample, and continue to propagate along axis B' (although substantially, generally, undergo some degree of deflection / scattering) can be investigated. Such transmitted electron beams are incident on an imaging system (composite objective / projection lens) 24, which broadly includes a wide variety of electrostatic / magnetic lenses, deflectors, correctors (such as astigmatism correctors), etc.

[0047] In normal (non-scanning) TEM mode, the imaging system 24 can focus the transmitted electron beam onto the fluorescence screen 26, which can be retracted / retracted as needed so as not to obstruct axis B' (circumstantially indicated by arrow 26'). A (partial) image (or diffractogram) of the sample S is formed on the screen 26 by the imaging system 24, and this image can be viewed through a viewing port 28 located in a suitable portion of the wall of the housing E.

[0048] As an alternative to viewing the image on screen 26, the fact that the electron beam emitted from imaging system 24 typically has a very large focusing depth (e.g., about 1 meter) can be utilized. As a result, various types of detection / analysis devices can be used downstream of screen 26, such as: -TEM camera 30. At the position of camera 30, the electron beam can form a still image (or diffractogram), which can be processed by controller C and displayed on a display device (not shown), such as a flat panel display. When not needed, camera 30 can be retracted / retrieved (as schematically shown by arrow 30') to move the camera off axis B'.

[0049] - STEM recorder 32. The output from recorder 32 can be recorded as a function of the (X,Y) scanning position of beam B on sample S, and an image can be constructed which is a "map" of the output from recorder 32 as a function of X,Y. Unlike the pixel matrix characteristic of camera 30, recorder 32 can include, for example, a single pixel having a diameter of 20 mm. Furthermore, recorder 32 is generally different from camera 30 (e.g., 10 2 A much higher acquisition rate (for example, 10 images / second) 6 It has (locations / second). Here again, if not needed, the recorder 32 can be retracted / retracted (as schematically shown by arrow 32') to move it away from line B' (however, such retraction is not necessary in the case of, for example, a donut-shaped annular dark-field recorder 32, in which case the central hole allows the beam to pass through when the recorder is not in use).

[0050] As an alternative to performing imaging using the camera 30 or recorder 32, a spectrometer 34, which can be an EELS module, can also be driven.

[0051] It should be noted that the order / position of parts 30, 32, and 34 is not strict, and many possible variations are conceivable. For example, the spectrometer 34 can be integrated with the imaging system 24.

[0052] It should be noted that the controller (which may be a composite controller and processor) C is connected to the various components shown in the figure via control lines (buses) C'. The controller may be connected to a computer screen 51 on which a user interface (UI) may be provided. The controller C can provide various functions, such as synchronizing operations, providing setpoints, processing signals, performing calculations, and displaying messages / information on a display device (not shown). It will be understood that the controller C (circumstantial) may be located (partially) inside or outside the enclosure E, and may have a standalone or composite structure as needed. Those skilled in the art will understand that the inside of the enclosure E does not need to be kept in a strict vacuum. For example, in so-called "environmental TEM / STEM," a background atmosphere of a given gas is deliberately introduced / maintained inside the enclosure E. Those skilled in the art will also understand that it may actually be advantageous to limit the volume of the enclosure E. This means that, where possible, the volume of the housing E essentially takes the form of a small tube (for example, about 1 cm in diameter) that extends along axis B' and through which the electron beam used passes, but widens to accommodate structures such as the electron source 4, sample holder H, screen 26, camera 30, recorder 32, and spectrometer 34.

[0053] This disclosure relates to a method for using a charged particle microscope M, illustrated as an example in Figure 1, in scanning transmission mode to examine a sample S. Therefore, the method defined herein can be performed on a STEM. Alternatively, the method can also be performed on a SEM.

[0054] The STEM M, as described with reference to Figure 1, comprises at least a charged particle beam source 4 for emitting a charged particle beam B, a sample holder H for holding a sample S, an illuminator 6 for guiding the charged particle beam B emitted from the charged particle source 4 onto the sample S, a scanning unit D for scanning the beam B over a plurality of sample positions on the sample S, and a control unit C for controlling the operation of the scanning transmission charged particle microscope. The STEM shown herein is configured to perform the methods defined herein, which are described below.

[0055] Now, looking at Figure 2, a schematic block diagram of the method as defined herein is shown. The method as defined herein includes the steps of: providing a scanning transmission charged particle microscope M; providing a desired dose to at least a first sample position of a plurality of sample positions; and using a controller C of the scanning transmission charged particle microscope, determining a first set of parameter settings for the illuminator 6 and the scanning unit D to substantially achieve the desired dose at the first sample position.

[0056] By providing dose-controlled sample testing using a controller that provides the desired dose and allows for settings to achieve that desired dose, more reproducible testing becomes possible. This applies not only to experiments performed with the same microscope M, but also to experiments between different microscopes.

[0057] The desired dose in step 102 may be provided directly by the user. For example, a user interface could be used that allows the user to directly input the desired dose. Alternatively, the user could indicate the type of sample to be investigated, and the controller C could use this information to determine the desired dose based on the sample information provided by the user. Other direct or indirect methods for providing the desired dose are also conceivable.

[0058] Figure 3 shows a schematic configuration of the microscope M as defined herein. Here, the microscope M defines a system 200 including a workstation W having a user interface provided on a computer screen 51, the workstation W constituting at least a portion of a controller C embedded therein. Other parts of the controller (not shown) may be part of the microscope M itself or located outside of it. As shown in Figure 1, the controller C is connected to various parts of the microscope by controller lines C'. Here, for clarity, the microscope M is schematically shown together with a light source 4, an illuminator 6, a sample S on a sample holder H, and a STEM recorder 32. It should be noted that the detector 32 can, in principle, be any desired detector suitable for use in scanning transmission charged particle microscopy. In some embodiments, the detector 32 may be any desired detector suitable for charged particle microscopy in non-transmission applications.

[0059] In the system 200 shown in Figure 3, user U can input a desired dose on the workstation W, for example, using a graphical user interface provided on the computer screen 51. The controller C will use the provided desired dose to determine a first set of parameter settings for the illuminator 6 and the scanning unit D in order to substantially achieve the desired dose at the location of the first sample S.

[0060] As previously shown, there are three main basic methods that the controller can use alone or in any combination to determine the settings for a scanning transmission charged particle microscope. 1) Use a numerical model to calculate the microscope settings based on the desired dose as an input parameter. 2) Use active measurement of the beam current and adjust the microscope settings based on the desired dose as an input parameter. 3) Using the microscope calibration data, determine the microscope settings based on the desired dose as the input parameter.

[0061] For the sake of brevity, these basic methods will not be repeated here.

[0062] Referring to Figure 3 and the basic scheme described above, it will be added that the numerical model can be part of or connected to controller C, for example, in the form of a software module. For example, the numerical model may be part of a separate processor that is part of workstation W. Other embodiments can be considered similarly.

[0063] Furthermore, the microscope M may be equipped with at least one beam current measuring device 211, 212. The beam current measuring device 211 can be configured downstream of the light source 4 and upstream of the illuminator 6, and may be configured to measure the beam current at the extraction aperture of the light source 4. The beam current measuring device 212 can be placed downstream of the illuminator 6, and may be configured to measure the beam current at the position of the sample S. These beam current measuring devices 211, 212 can be used for active measurement of the beam current and are available to the controller C to modify the settings of the microscope M based on these measurements and desired dose settings.

[0064] System 200 may further include calibration data for the microscope M, which may be stored as software data in the workstation W or in the microscope M itself.

[0065] Next, looking at Figure 4, a portion of the user interface (UI) 300 for providing a desired dose is shown. Using the above-described method for controlling the illuminator and / or deflector to obtain the desired dose, the dose can be provided by this UI. The shown UI includes an optimization probe button 301, a calibration button 302, a dose rate display 303, a dose display 304, a total dose display 305, plus buttons 331 and minus buttons 330 for correcting the dose rate, plus buttons 341 and minus buttons 340 for correcting the dose, and a reset button 311 for resetting the displayed total dose 305.

[0066] The calibration button 302 can be used to calibrate the beam current currently supplied to the illuminator 6, as described above. The dose rate 303 can be calculated, for example, from an optical model (i.e., a numerical model) and will be displayed on the UI 300. If the sample S shows beam-induced damage, the user U can press the minus button 330 to lower the dose rate. If there is no damage, the end user can press the plus button 331 to increase the dose rate and improve the signal-to-noise ratio. This allows the customer to find the optimal total dose and dose rate settings for their experiment in STEM.

[0067] In one embodiment, the method includes the step of providing acquisition parameters, which include, for example, pixel residence time, pixel size, and scanning field of view. Using these acquisition parameters, it is possible to calculate the dose per square angstrom for a single acquired image. The end user can adjust the dose 304 by pressing the plus button 341 or the minus button 340. In this case, not only the illuminator settings but also the optimization of the pixel residence time can be considered.

[0068] The displayed total dose 305 is the accumulated dose, which is the sum of all acquired doses in the same area. Here, the user can be notified of how many images can be taken at a specific dose and dose rate before the sample S shows cumulative damage. The reset button 311 can be used to return the total dose 305 to zero.

[0069] In one embodiment, the parameters used in the experiment are stored in the metadata of the experimental dataset, and this documentation allows for the reproduction of previous results. Furthermore, all scanned regions should also be stored in the metadata, so that multiple exposures of the same region can be documented and avoided by the operator.

[0070] In one embodiment, UI calibration can be performed via a STEM detector. BF detectors, such as those used in NGSTEM, are ideal for beam current measurement. The advantage is that the microscope can be kept in the HRSTEM setup. There is no need to move outside the diffraction area and set a small probe in a Faraday cup outside the camera's field of view, thus avoiding the need to shift the beam which could affect aberrations. In the workflow, the stage can be moved to a holed area on the specimen to accurately determine the beam current, which can then be used as input for dose rate calibration, as shown in Figure 4.

[0071] To minimize the cumulative dose in the region of interest, a beam shift deflector D can be used to move the beam away from this region. In principle, beam shifting in a probe-corrected microscope is performed using a coma-free plane "pivot point" of the objective lens. In this way, scanning coma aberration can be minimized. However, large beam shifts also cause parasitic astigmatism. Our proposed low-dose HRSTEM workflow adds beam shift-dependent stigmeter correction to ensure that astigmatism remains fully corrected when creating the beam shift. In principle, similar beam shift-dependent correction can be performed for coma. This is done by adding an "Optimize Probe" button 301 to the UI in Figure 4 to optimize beam shift and optical performance (e.g., by running algorithms such as OptiSTEM to focus on and correct probe astigmatism and coma), and since all optimization steps are performed in a separate region, only one scan in the target region is required for extremely beam-sensitive materials.

[0072] For example, the methods and microscopes defined herein can be used in the following way: 1) Optimize the optical performance in sample region A (including correction of astigmatism and coma aberration). 2) Use a beam shift (or stage) to move to sample area B and maintain optical performance. 3) Optimize the dose (i.e., dose rate) in sample region B through calibrated and reproducible dose (i.e., dose rate) control. 4) If necessary, adjust the intensity on the spot and repeat the previous step. 5) Move to sample region C and perform the final HRSTEM acquisition with the optimized dose (i.e., dose rate). 6) Determine the total cumulative dose. 7) If the total cumulative dose exceeds a specific boundary, move to sample area D, or acquire HRSTEM data using, for example, N×N beam shift patterns. 8) Store all settings in the image set metadata so that the experiment can be repeated later with the exact same dose rate or dose settings.

[0073] In other examples, the methods and microscopes defined herein may be used to acquire images, and the dose and / or dose rate may be determined by a numerical model (optical model) and instructed to the user during the experiment (i.e., "live"). In this case, one or more of the following options may apply: a) If damage is present, the accelerating voltage (HT) may be changed to maintain the same dose and / or dose rate, and a numerical model is used. Further images may be taken to confirm whether the damage has disappeared. If so, the knock-on damage is repaired. b) If damage has occurred, the dose and / or dose rate may be changed, and further images may be taken to confirm whether the damage has disappeared. In this case, the radiolysis / temperature effect is fixed. c) If no damage has occurred, the accelerating voltage (HT) can be increased while keeping the dose and / or dose rate the same to improve optical performance. Further images can be acquired to confirm that the sample is still stable. d) If no damage occurs, the dose and / or dose rate can be increased to improve the signal-to-noise ratio of the image. Further images can be acquired to confirm that the sample is still stable. e) Proceed to diffraction of the oriented sample using stages a and b, measure the total dose during orientation, and indicate what dose and dose rate resulted in good acquisition conditions. Switch to S / TEM mode and record the data. Then, record the total dose of the workflow, the total dose of the final result, and the dose rate for documentation and reproducibility of experiments in other areas or other samples. f) Move the stage to explore features of interest and read camera or STEM images to sequentially identify features. Mark the exposed areas (and images) and illuminated areas with a map that shows the dose / dose rate used in those areas. This provides an overview of where the sample has already been exposed, avoiding revisiting the same previously burned area. g) Change the magnification to inspect finer features and automatically adjust the illuminator to maintain a constant dose and dose rate. h) By changing the sampling method in STEM (changing the resolution, e.g., from 512x512 to 1024x1024) and automatically adapting the illuminator, the dose and dose rate can be made the same. i) Change the probe size to increase resolution and use a numerical model of the illuminator to keep the dose and dose rate the same. j) In each of the workflows a to i above, after exposing the sample, the beam is blanked to minimize the total dose, and scanning is stopped so that the sample is not punctured when the beam remains in one area.

[0074] It should be noted that, in principle, the present invention can also be implemented with non-transmission charged particle microscopes. In that case, the step of providing a scanning transmission charged particle microscope as defined herein will be replaced with the step of providing a non-transmission scanning charged particle microscope in particular. This modification of replacing a transmission charged particle microscope with a non-transmission charged particle microscope may be applied to all embodiments disclosed herein.

[0075] Furthermore, it should be noted that the present invention can, in principle, also be implemented in non-scanning transmission charged particle microscopes such as TEMs. In this case, the numerical model (optical model) can be used similarly. In TEMs, as in STEM mode, the dose and dose rate can be set using the illuminator model. Since no scanning unit is used in TEMs, the first set of parameters defined herein includes only settings for the illuminator. In TEMs, the dose rate can be controlled using the camera exposure time, and additionally, the total illuminated area of ​​the blurred beam can be predicted. Predicting dose / dose rate using numerical models in TEMs can be very useful, particularly in life science applications.

Claims

1. A method for examining a sample using a scanning transmission charged particle microscope, - A step of providing a scanning transmission charged particle microscope, wherein the scanning transmission charged particle microscope is - A charged particle beam source for emitting a charged particle beam, - A sample holder for holding the sample, - An illuminator for guiding the charged particle beam emitted from the charged particle beam source onto the sample, - A scanning unit for scanning the beam at multiple sample positions on the sample, - A temperature control system that controls the temperature of the scanning transmission charged particle microscope when the acceleration voltage is changed, - A step of providing a scanning transmission charged particle microscope comprising a control unit for controlling the operation of the scanning transmission charged particle microscope, - A step of providing a desired dose parameter for at least a first sample position among the plurality of sample positions, - Using the control unit, determine a first set of parameter settings for the illuminator and the scanning unit to substantially achieve the desired dose parameter at the first sample position; Includes, This method further, The steps include changing the acceleration voltage of the scanning transmission charged particle microscope, and using the control unit to determine the dose and / or dose rate resulting from the change in the acceleration voltage, Methods that include...

2. The method according to claim 1, comprising the step of illuminating the sample at a first position using the first set of parameter settings.

3. The method according to claim 1 or 2, comprising the steps of providing a second desired dose parameter and using the control unit to determine a second set of parameter settings for the illuminator and the scanning unit to substantially achieve the second desired dose parameter.

4. The method according to claim 3, wherein the sample is illuminated at the first position using the second set of parameter settings.

5. The method according to claim 1, wherein the sample is illuminated at a second position among the plurality of sample positions.

6. The method according to claim 5, wherein the sample is illuminated at the second position using the first set of parameter settings.

7. The method according to claim 3, wherein the sample is illuminated at the second position using the second set of parameter settings.

8. The method according to claim 1, comprising the step of tracking the cumulative dose effect for the corresponding location.

9. The method according to claim 1, wherein the charged particle microscope includes a user interface such as a graphical user interface, and the user interface enables the provision of input settings for the first and / or second set of parameter settings.

10. The method according to claim 9, wherein the input setting includes a dose parameter comprising at least one of dose rate, dose, and total dose.

11. The method according to claim 1, comprising the steps of providing a further scanning transmission charged particle microscope and determining a first set of parameter settings for each of the further scanning transmission charged particle microscopes to substantially achieve the desired dose parameters using each of the control units of the further scanning transmission charged particle microscopes.

12. A scanning transmission charged particle microscope, - A charged particle beam source for emitting a charged particle beam, - A sample holder for holding the sample, - An illuminator for guiding the charged particle beam emitted from the charged particle beam source onto the sample, - A control unit for controlling the operation of the scanning transmission charged particle microscope, A scanning transmission charged particle microscope comprising: - A temperature control system that controls the temperature of the scanning transmission charged particle microscope when the acceleration voltage is changed, The scanning transmission charged particle microscope, - To receive the desired dose parameter at at least the first sample position among the plurality of sample positions, - Using the control unit, determine a first set of parameter settings for the illuminator and the scanning unit to substantially achieve the desired dose parameter at the first sample position, and A scanning transmission electron microscope, characterized in that it is configured to determine the dose and / or dose rate resulting from a change in the acceleration voltage.

13. The scanning transmission charged particle microscope according to claim 12, comprising a user interface such as a graphical user interface, wherein the user interface enables the user to provide input settings for the desired dose parameters, and the desired dose parameters comprise one or more from a list consisting of dose rate, dose, and total dose.

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