A charged particle microscope for examining a specimen and a method for determining an aberration of the charged particle microscope

Abstract

The present invention relates to a method for determining the aberration of a charged particle microscope. The method comprises the steps of providing a charged particle microscope, which is at least partly operable by a user. Then, an image data set is obtained with the charged particle microscope. The image data is processed to determine the aberration of the charged particle microscope. According to the invention, the image data set is actively obtained by the user. Specifically, the image data can be obtained during normal operation of the microscope by the user, and the normal operation can include microscope navigation and / or focusing. Thus, the image data set is acquired by the user and not by the controller of the microscope. This allows for background processing of the aberration and aberration correction during use of the charged particle microscope. The present invention also relates to a charged particle microscope incorporating the method.

Description

Technical Field

[0001] The present invention relates to a charged particle microscope for examining a specimen, and a method for determining an aberration of the charged particle microscope. Background Art

[0002] Charged particle microscopes are a well-known and increasingly important technique for imaging microscopic objects, particularly in the form of electron microscopes. Historically, the basic classes of electron microscopes have evolved into many well-known types of equipment, such as transmission electron microscopes (TEMs), scanning electron microscopes (SEMs), and scanning transmission electron microscopes (STEMs); as well as various sub-types, such as so-called "dual-beam" devices (e.g., FIB-SEMs), which additionally employ a "processing" focused ion beam (FIB), thereby allowing support for activities such as, for example, ion beam milling or ion beam induced deposition (IBID).

[0003] In a (S)TEM, irradiation of a specimen by a (scanning) electron beam causes an interaction between the primary electrons and the sample. The interaction may cause elastically scattered electrons to leave the sample, which can be detected to form a microscopic image. Additionally, irradiation of the specimen accelerates the emission of "secondary" radiation from the specimen 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 to generate a microscopic image.

[0004] It is desirable for the charged particle beam to be well-aligned, well-focused, and well-corrected for astigmatism. In a TEM or STEM, this may result in higher-quality imaging. In an FIB, this ensures that the ion beam is brought to an acceptable point of arrival at the specimen surface for more precise sample processing.

[0005] It should be noted that alignment, focusing, and astigmatism correction can be somewhat troublesome for users of charged particle microscopes.

[0006] To set the focus, the user first needs to discern that the beam is defocused. In this regard, it should be noted that the so-called Fresnel fringes create enhanced contrast in TEM imaging, which attracts the (novice) eye but actually indicates that the image is defocused. Secondly, the user needs to determine which way to perform appropriate focusing: the user needs to determine whether the beam is over-focused or under-focused. This requires time and experience to set the correct focus.

[0007] An astigmatic system is a system in which light rays propagating in two perpendicular planes have different foci. This means that different parts of the beam have different foci at different distances from each other. For example, in STEM, if a charged particle microscope is well corrected for astigmatism, then the charged particle beam is circular when it reaches the specimen. Due to astigmatism, the cross-section of the probe is deformed to form an elliptical or cross-shaped shape. An astigmatism corrector can be used to correct astigmatism. Adjusting the astigmatism correction usually requires adjusting two controls (which act in orthogonal directions), both of which can be above or below their optimum strength. It is difficult to set the astigmatism correction well, especially for novice users, because there is no analogy with other (light) optical devices. Manually setting the astigmatism correction well is not intuitive and is slow, and requires training of the user. The user can usually compare the quality of two subsequent images, but it is difficult for him to remember more images and quantitatively evaluate and set the optimum astigmatism and focus corrections in one iteration.

[0008] Some prior art electron microscopes incorporate an autofocus and / or an auto-astigmatism corrector function. Here, the procedure for these functions is generally as follows. First, the operator or user activates the autofocus or astigmatism corrector function. Then, the charged particle device will control the imaging and optics and repeatedly change the focus and astigmatism corrector excitation. At each setting, an image is acquired and then processed to obtain information about the directional sharpness. Once a certain optimization criterion is reached (or based on a timeout), the best focus and / or astigmatism correction settings obtained are applied to the device. These autofocus and / or auto-astigmatism corrector functions are relatively slow.

[0009] In addition to astigmatism, other user controls need to be set correctly to achieve optimum microscope performance. Most commonly, lens centering and astigmatism corrector centering. Appropriate settings for lens centering and astigmatism corrector centering are achieved when the image does not move during focusing and astigmatism correction. Summary of the Invention

[0010] In view of the above, it is an object of the present invention to provide an improved method for determining the aberrations of a charged particle microscope.

[0011] To this end, a method for determining the aberrations of a charged particle microscope is provided.

[0012] The method comprises the steps of: providing a charged particle microscope that is at least partially operable by a user, and obtaining a set of image data using the charged particle microscope; and processing the set of image data to determine the aberrations of the charged particle microscope.

[0013] According to the method disclosed herein, obtaining the set of image data includes the step of the user collecting the set of image data. This means that during the active use of the charged particle microscope by the user, for example, during the user focusing and / or navigating the sample with the device, the set of image data is collected. This means that the user does not have to start an autofocus and / or auto-astigmatism corrector program to collect relevant image data, but the data has been collected (in the background) during the normal use (i.e., dedicated use) of the charged particle microscope. Therefore, data (images, image attributes, and control ranges) from one or more previous operations controlled by the user can be used. This makes the method disclosed herein more efficient. Once the user has collected sufficient image data, the image data can be processed to determine the aberrations of the charged particle microscope. Thereby, the object of the present invention is achieved.

[0014] Note that the term "user" includes the operator of the charged particle microscope, especially an operator who intends to collect specimen data (e.g., one or more images of the specimen). Although a computer operator, i.e., an operator programmed to automatically navigate and collect specimen data, can also be envisaged, the operator can be a human operator. In other words, according to the method disclosed herein, obtaining the set of image data includes the following steps: collecting the set of image data during the preparation and / or navigation of the charged particle microscope by the user, and / or during the collection of specimen data by the user.

[0015] Advantageous embodiments will be discussed below.

[0016] In one embodiment, the processing step is performed during the step of the user collecting the set of image data. This allows for relatively rapid determination of aberrations. In another embodiment,

[0017] In one embodiment, the step of the user collecting the set of image data includes one or more of the following: navigating the charged particle microscope, and / or adjusting the focus settings of the charged particle microscope. This makes the method very effective because the image data is collected during the expected use by the user (for the purpose of determining aberrations).

[0018] In one embodiment, the image data includes images and corresponding image settings. Thereby, the aberrations of the charged particle microscope can be effectively determined.

[0019] Specifically, the image data includes at least a plurality of individual images under different image settings of the charged particle microscope.

[0020] The processing of the set of image data may include the step of analyzing the images. Specifically, this may include the step of using an algorithm for the images, where the algorithm is especially a fast Fourier transform.

[0021] In one embodiment, the analysis includes calculating a relative image displacement. Additionally or alternatively, the analysis may include calculating a relative image sharpness in at least one direction.

[0022] It is contemplated that the method includes the step of instructing the user of the result of the step of processing the set of image data. For example, it may be indicated whether there is an aberration. Additionally, the magnitude of the aberration may be indicated. This may include presenting the information to the user and allowing the user to decide whether (and when) the aberration should be corrected.

[0023] Furthermore, it is contemplated that the instructing step includes the step of indicating that an aberration has been determined.

[0024] Once the aberration has been determined, the method may include the step of adjusting at least one setting of the charged particle microscope based on the determined aberration. The adjustment may be performed by the user or by a controller of the charged particle apparatus. Thus, in one embodiment, the adjustment of at least one setting may be done automatically. The method may include the step of automatically performing the correction without asking the user for any permission. This may be done at the least obtrusive moment, e.g., not while the user is busy with an experiment / acquisition. For example, between two consecutive images, or in case there may be a short delay after the user has stopped changing the focus, etc.

[0025] According to one aspect, there is provided a charged particle microscope for inspecting a specimen, the charged particle microscope comprising:

[0026] - an optical column comprising a charged particle source and an illuminator for guiding a beam of charged particles emitted from the charged particle source onto the specimen;

[0027] - a specimen stage located downstream of the illuminator and arranged for holding the specimen;

[0028] - a detector device for detecting emissions from the specimen in response to the incidence of charged particles emitted from the charged particle source; and

[0029] - a control unit for performing the operation of the charged particle microscope.

[0030] According to the invention, the control unit is arranged to determine at least one aberration of the charged particle microscope by processing a set of image data acquired by the user using the charged particle microscope.

[0031] The advantages of such a charged particle microscope have been elucidated above with respect to the method according to the invention. Specifically, a set of image data for determining aberrations is acquired by the user, i.e., during the active use of the charged particle microscope by the user, for example, during focusing and / or navigating the charged particle microscope. The autofocus and / or auto-astigmatism corrector programs do not have to be initiated by the user, since data has been acquired (in the background) during the normal use (i.e., dedicated use) of the charged particle microscope. Thereby, the charged particle microscope according to the invention provides improved aberration determination and correction. Thereby, the object of the invention is achieved.

[0032] In one embodiment, the control unit is arranged to process the set of image data during acquisition of the set of image data by the user. In other words, aberration determination occurs during the normal use of the charged particle microscope, which allows for automatic aberration detection and correction in the background.

[0033] In one embodiment, the control unit is arranged to process the set of image data during use of the charged particle microscope by the user, in particular during navigation and / or focusing of the charged particle microscope by the user.

[0034] In one embodiment, the charged particle microscope includes a storage unit for storing the set of image data.

[0035] In one embodiment, the control unit may be arranged to perform the method according to one or more of the embodiments disclosed herein.

[0036] In one embodiment, the control unit is arranged to adjust at least one setting of the charged particle microscope based on the determined aberration.

[0037] In an advantageous embodiment, the charged particle microscope does not include one or more of the following: a user lens centering control, a user astigmatism corrector centering control, and a user astigmatism correction control. By including a control unit arranged to determine the aberration of the charged particle microscope during use of the charged particle microscope, the above controls are no longer required. Thus, the embodiment provides an improved charged particle microscope that is easier for the user to use due to the absence of these relatively complex controls. It should be noted that the term "control" refers to physical controls, such as buttons, sliders, dials, etc.; and their digital equivalents (such as buttons, sliders, dials in a graphical user interface). BRIEF DESCRIPTION OF THE DRAWINGS

[0038] The invention will now be explained with reference to the drawings, in which:

[0039] Figure 1 - shows a longitudinal cross-section of a charged particle microscope according to a first embodiment;

[0040] Figure 2 - shows a schematic overview of a charged particle microscope according to a second embodiment;

[0041] Figure 3 - shows a schematic overview of a charged particle microscope according to a third embodiment;

[0042] Figure 4 - a schematic flow chart of an embodiment of a method as disclosed herein;

[0043] Figure 5 - shows a more detailed view of an embodiment of a method as disclosed herein. Detailed Description

[0044] Figure 1 (not to scale) is a highly schematic depiction of an embodiment of a charged particle microscope M according to an embodiment of the present invention. More specifically, it shows an embodiment of a transmission microscope M, which in this case is a TEM / STEM (although, in the context of the present invention, it could effectively be just an SEM, or for example an ion-based microscope). In Figure 1 , within a vacuum enclosure 2, an electron beam B generated by an electron source 4 propagates along an electro-optic axis B' and passes through an electro-optic illuminator 6, directing / focusing the electrons onto a selected portion of a specimen S (e.g., which may be (locally) thinned / flattened). A deflector 8 is also depicted, which can be used (inter alia) to effect a scanning movement of the electron beam B.

[0045] The specimen S is fixed to a specimen holder H, which can be positioned by a positioning device / stage A with multiple degrees of freedom, which moves a cradle A' into a (removably) attached holder H; for example, the specimen holder H may include fingers (inter alia) that can move in the XY plane (see the depicted Cartesian coordinate system; generally, movement parallel to Z and tilting about X / Y are also possible). This movement allows different portions of the specimen S to be illuminated / imaged / examined by the electron beam B traveling along the axis B' (in the Z direction), (and / or allows a scanning movement to be performed, as an alternative to beam scanning). If desired, an optional cooling device (not depicted) can be in close thermal contact with the specimen holder H, in order to maintain it (and the specimen S thereon) at low temperature, for example.

[0046] The electron beam B will interact with the specimen S such that various types of “excited” radiation are emitted from the specimen S, including (for example) secondary electrons, backscattered electrons, X-rays, and optical radiation (cathodoluminescence). If desired, one or more of these radiation types can be detected by means of an analysis device 22, which may be, for example, a combined scintillator / photomultiplier or an energy-dispersive X-ray spectroscopy (EDX) module; in this case, an image can be constructed using essentially the same principles as in an SEM. However, alternatively or additionally, electrons that pass through (traverse) the specimen S, exit / emanate from it, and continue to propagate along axis B' (essentially, although usually with some deflection / scattering) can be studied. This transmitted electron flux enters an imaging system (projection lens) 24, which typically includes various electrostatic / magnetic lenses, deflectors, correctors (especially an astigmatism corrector), etc. In the normal (non-scanning) TEM mode, the imaging system 24 can focus the transmitted electron flux onto a fluorescent screen 26, which can be retracted / withdrawn (as schematically indicated by arrow 26') if desired, to move it away from axis B'. An image (or diffraction pattern) of (a part of) the specimen S will be formed by the imaging system 24 on the screen 26, and this can be viewed through an observation port 28 located in an appropriate part of the wall of the housing 2. For example, the retraction mechanism of the screen 26 is essentially mechanical and / or electrical and is not depicted here.

[0047] As an alternative method of viewing the image on the screen 26, instead, one can use the fact that the depth of focus of the electron flux leaving the imaging system 24 is typically quite large (e.g., about 1 meter). Thus, various other types of analysis devices can be used downstream of the screen 26, such as:

[0048] - A TEM camera 30. At the camera 30, the electron flux can form a static image (or diffraction pattern), which can be processed by a controller / processor 20 and displayed on a display device 14, such as a flat-panel display. When not needed, the camera 30 can be retracted / withdrawn (as schematically indicated by arrow 30') to move it away from axis B'.

[0049] - A STEM detector 32. The output from the detector 32 can be recorded as a function of the (X,Y) scan positions of the beam B on the specimen S, and an image can be constructed that is a “map” of the output from the detector 32 as a function of X,Y. The detector 32 can include a single pixel with a diameter of, for example, 20 mm, as opposed to the pixel matrix characteristically present in the camera 30. Additionally, the detector 32 will typically have a much higher acquisition rate (e.g., 10 2 images per second) than the camera 30 (e.g., 10 6The detector 32 can be retracted / withdrawn (as schematically indicated by arrow 32') when not needed, again, to move it away from axis B' (although in the case of an annular dark field detector 32, for example, such retraction is not necessary; in such a camera, the central aperture will allow the flux to pass through when the camera is not in use).

[0050] - As an alternative to imaging using the camera 30 / detector 32, a spectroscopic device 34 can also be invoked, which can be, for example, an EELS module.

[0051] It should be noted that the order / position of items 30, 32, and 34 is not strict, and many possible variations can be envisioned. For example, the spectroscopic device 34 can also be integrated into the imaging system 24.

[0052] In the illustrated embodiment, the microscope M further includes a retractable computed tomography (CT) module, generally indicated by reference numeral 40. In computed tomography (also known as tomographic imaging), a source and (radially opposed) detectors are used to view the specimen along different lines of sight in order to acquire penetrating views of the specimen from various angles. CT can be performed by acquiring a tilt series (detecting (S)TEM images and / or X-ray maps at each tilt). X-rays can be detected using detector 22 and / or 40, with the difference being that detector 40 collects a larger solid angle and is thus faster.

[0053] Note that the controller (computer processor) 20 is connected to the various illustrated components via control lines (bus) 20'. The controller 20 can provide various functions, such as synchronizing actions, providing setpoints, processing signals, performing calculations, and displaying messages / information on the display device (14). Needless to say, the controller 20 (schematically depicted) can be (partially) inside or outside the housing 2 and can have an integral or composite structure as needed.

[0054] For many of the above analysis devices 26, 30, 32, 34, 40, correct focusing and astigmatism correction are required or at least desirable. As previously mentioned, the user needs to invoke the autofocus and / or auto-astigmatism corrector functions of the prior art. Upon startup, the microscope will control the imaging and optics to acquire images at different focusing and astigmatism corrector settings and then determine the optimal settings. The process is relatively slow and prevents the user from using the charged particle device.

[0055] Generally speaking, Figure 1 An embodiment of a charged particle microscope M for examining a specimen S is shown, including:

[0056] - An optical column O that includes a charged particle source 4 and an illuminator 6 for guiding a charged particle beam B emitted from the charged particle source onto the specimen S;

[0057] - A specimen stage H, which is located downstream of the illuminator 6 and is arranged to hold the specimen S;

[0058] - Detector devices 22, 30, 32, 34, 40, which are arranged to detect emissions from the specimen S in response to the incidence of charged particles B emitted from the charged particle source 4; and

[0059] - A control unit 20, which is arranged to perform the operation of the charged particle microscope.

[0060] According to the method disclosed herein, the aberration of a charged particle microscope is determined using the steps of acquiring and processing a set of image data by the charged particle microscope. Here, obtaining the set of image data includes the following steps: the user acquires the set of image data, especially during the normal operation of the charged particle device, i.e., during specimen image acquisition. The specimen image acquisition may include navigating the specimen with the charged particle microscope and / or adjusting the focusing settings of the charged particle microscope.

[0061] For this purpose, the control unit 20 as Figure 1 shown is arranged to determine at least one aberration of the charged particle microscope by processing a set of image data acquired by the user using the charged particle microscope M.

[0062] The method as described above allows tracking, storing, and processing image data of a shorter or longer history of the control actions of a human or automatic operator during the use of the charged particle device. The image data may include, for example, images, image attributes such as sharpness, histogram, relative image displacement, and analysis results. The image data may be related to image sharpness. The image data may include, for example, images, image attributes such as sharpness, histogram, relative image displacement, and analysis results that may be related to a reference image, stage position, optics, and detector settings, etc. Thus, the aberration can be determined in the background, i.e., while a human or automatic operator is using the charged particle microscope.

[0063] Figure 2 A schematic overview of a transmission electron microscope (TEM) M is shown, and the above method can be performed using the microscope to correct focusing and astigmatism, as an example. The structure is very similar to the device described with respect to Figure 1 and thus similar parts are indicated by the same reference numerals. For the sake of brevity, the focus will be mainly on the differences from Figure 1 the device.

[0064] Now referring to Figure 2 , an embodiment of a transmission microscope M (in this case a TEM) is shown. As in Figure 1In this case, inside the vacuum housing 2, an electron beam B generated by an electron source 4 travels along an electro-optical axis B' and passes through an electro-optical illuminator 6 (including a focus corrector 61 and an astigmatism corrector 62), so as to guide / focus the electrons onto a specimen S.

[0065] Charged particles pass through (traverse) the specimen S, emit / are emitted from the specimen S, and continue to travel along the axis B' (substantially, but usually with some deflection / scattering). This transmitted electron flux enters an imaging system (projection lens) 24, which typically will include various electrostatic / magnetic lenses, deflectors, correctors (especially an astigmatism corrector), etc. In the normal (non-scanning) TEM mode, the imaging system 24 can focus the transmitted electron flux onto a TEM camera 30 located downstream of the column.

[0066] Figure 2 A schematic overview of a controller 20 is also shown, which is specifically connected to the TEM camera 30, as well as the focus corrector 61 and the astigmatism corrector 62. It should be noted that connections to other parts of the microscope M can also be envisaged, in a manner similar to Figure 1 the connections mentioned in

[0067] The controller 20 is connected to a computer screen 14 and is also connected to a user input device 15 having one or more user controls 16 (e.g., buttons and / or dials 16). The input device 15 can be physical, but can also be incorporated into a graphical user interface (GUI).

[0068] The controller 20 includes a focus control element 101, an astigmatism control element 102, an imaging element 110, and a processing element 111. Here, the camera 30 is connected to the imaging element 110 and can be arranged to collect and / or store image data, such as images and corresponding image settings. The imaging element 110 is connected to the processing element 111, through which the image can be directed towards the screen 14. The processing element 111 is arranged to process the images in the imaging element 110 (which can be arranged to serve as a storage unit 110) and determine the aberrations of the charged microscope M based on the images. Using the determined aberrations, the processing element 111 can actuate the focus element 101 and / or the aberration element 102 to change the focus settings and / or aberration settings of the microscope M. The processing of the image data set includes the step of analyzing the image, which, in one embodiment, includes the steps of: using an algorithm on the image, such as a fast Fourier transform. Additionally or alternatively, a relative image displacement can be calculated. In one embodiment, the step includes calculating a relative image sharpness in at least one direction.

[0069] The processing element 111 may be arranged to indicate the result of the steps of processing the set of image data to the user U, for example, via the screen 14 and / or the input device 16. For example, it is conceivable to provide feedback to the user as to whether there is an aberration. The feedback may be displayed on the screen or using an LED on the input device.

[0070] Here, it is specifically envisaged that the controller 20 acts while the user U operates the microscope M using the screen 14 and / or the user control 16 provided on the input device 15. Thus, the controller 20 (control unit 20) is arranged to determine (using the aberration element 111) at least one aberration of the charged particle microscope M by processing a set of image data (obtained by the camera 30 and stored in the image element 110), the set of image data being acquired by the user U using the charged particle microscope M. The processing step (for example, processing the image data to determine the aberration of the charged particle microscope) may in particular be carried out during the step of acquiring the set of image data by the user U. This means that during the step of the user navigating the sample S with the charged particle microscope M and / or the user adjusting the focus settings of the charged particle microscope M, the aberration may be determined by the aberration element 111. When the user navigates the specimen and / or adjusts the focus settings, this will result in a plurality of images with corresponding different settings, such that the image data stored in the image element 110 includes at least a plurality of individual images at different image settings of the charged particle microscope M.

[0071] As described above, the controller 20 is used to determine the aberration of the microscope M during the use of the microscope M by the user U, and the controller 20 is arranged to adjust at least one setting of the charged particle microscope based on the determined aberration. The determination and adjustment may be carried out while the user U is using the microscope. Specifically, the controller may be arranged to determine and adjust the astigmatism based on the images obtained during the use by the user. Thereby, the astigmatism may be corrected during the use of the microscope M by the user U. Thus, in one embodiment, this enables the charged particle microscope to be free of any user-operable astigmatism controls, which is advantageous since astigmatism controls are in particular always difficult to use for a human operator. Similarly, it is conceivable that the microscope is also free of user lens centering controls and / or user astigmatism corrector centering controls.

[0072] Figure 3 An embodiment of the microscope M is shown, in which the control unit 20 is similar to as referred to Figure 2The described control unit. However, a scanning electron microscope (SEM) is shown here. Instead of the TEM camera 30, there is an SEM detector 22 connected to the imaging element 110. The output from the detector 22 can be recorded as a function of the (X,Y) scan position of the beam B on the specimen S, and an image can be constructed, which is a "map" of the output from the camera 22 as a function of X,Y. The image can be stored in the image element 110. A processing unit 111 connected to the image element 110 can determine the aberration, which can be used in the focusing element 101 and / or the astigmatism element 102. This allows the user U to correct it during the use of the charged particle microscope M.

[0073] Figure 4 A diagram showing an embodiment of the method as disclosed herein. Schematically, the method includes the following steps:

[0074] - Provide a charged particle microscope, wherein the charged particle microscope is at least partially operable by a user (201);

[0075] - Obtain a set of image data with the charged particle microscope (202);

[0076] - Process the set of image data to determine the aberration of the charged particle microscope (203).

[0077] According to the illustrated embodiment, the step of obtaining the set of image data (202) is performed by the user. In other words, the user U of the charged particle microscope actively acquires the set of image data. The processing of the image data is performed by the charged particle microscope, in particular by its control unit 20. The processing step can be carried out during the step of the user acquiring the set of image data.

[0078] As shown by line 231, the determined aberration can be fed back to the charged particle microscope 201, indicating that the settings of the charged particle microscope are changed. Additionally, information about the aberration can be indicated to the user U.

[0079] Finally, Figure 5Shows a more detailed view of an embodiment of the method as disclosed herein. Here, the separation between the user U and the controller 20 becomes clearer. Specifically, the user U inspects the monitor 14 and operates the charged particle microscope M, for example, by using the focusing control. The user settings are input by the user U and forwarded to the controller 20, which actuates the focusing lens 61 of the charged particle microscope. With the image 110 obtained by the charged particle microscope, the controller can perform various operations. For example, the DFT and the directional image sharpness can be determined. Additionally, the relative image displacement can be determined, for example, based on a previously acquired reference image. The information obtained can be used to determine the image properties and, in particular, as a function of the working distance WD. Specifically, the FFT asymmetry property as a function of WD can be determined. One or more operations can be performed on these functions, such as determining (local) minima, the distance between peaks, and / or the steepness of the curve. Based on these curves, the focusing settings, the astigmatism magnitude, and the astigmatism orientation can be determined. It is known to those skilled in the art that the magnitude of astigmatism can be determined as the difference in the working distances of the line foci, the best focus appears in the middle of the line foci, the astigmatism orientation is related to the orientation of the line foci, such that the misalignment of the focusing lens can be determined based on the image displacement generated by focusing (expressed as a change in the working distance), and similarly, the misalignment of the astigmatism corrector centering can be determined based on the image displacement generated by exciting the astigmatism corrector. Thus, astigmatism, lens alignment, and the best WD can be corrected, which in turn can be corrected by using the focusing lens 61, the astigmatism corrector 62, and the lens alignment 63. Those skilled in the art will understand that, Figure 5 Substantially shows a highly detailed embodiment of obtaining an image data set and processing the image data set to determine the aberrations of a charged particle microscope. In the embodiment, obtaining the image data set includes the following steps: acquiring the image data set by the user.

[0080] Furthermore, it should be understood that the desired protection is defined by the appended claims.

Claims

1. A method for determining the aberration of a charged particle microscope, the method comprising the following steps: Providing a charged particle microscope, wherein the charged particle microscope is at least partially operated by a user; Obtaining a set of image data with the charged particle microscope; Processing the set of image data to determine the aberration of the charged particle microscope; Characterized in that: The set of image data is obtained by the user during dedicated use of the charged particle microscope; and The processing step is performed during the dedicated use.

2. The method according to claim 1, wherein the processing step is performed during the step of the user acquiring the set of image data.

3. The method according to claim 1 or 2, wherein the step of the user acquiring the set of image data includes one or more of the following cases: navigating the charged particle microscope, and / or adjusting the focusing settings of the charged particle microscope.

4. The method according to claim 1 or 2, wherein the image data includes an image and corresponding image settings.

5. The method according to claim 4, wherein the image data includes at least a plurality of individual images under different image settings of the charged particle microscope.

6. The method according to claim 4, wherein the processing of the set of image data includes the step of analyzing the image.

7. The method according to claim 6, wherein the analysis includes the step of using an algorithm on the image, wherein the algorithm is a fast Fourier transform.

8. The method according to claim 6 or 7, wherein the analysis includes calculating a relative image displacement.

9. The method according to claim 6 or 7, wherein the analysis includes calculating a relative image sharpness in at least one direction.

10. The method according to claim 1 or 2, which includes the step of indicating to the user the result of the step of processing the set of image data.

11. The method according to claim 10, wherein the indicating step includes the step of indicating that an aberration has been determined.

12. The method according to claim 1 or 2, which includes the step of adjusting at least one setting of the charged particle microscope based on the determined aberration.

13. A charged particle microscope for examining a specimen, comprising: An optical column, which includes a charged particle source and an illuminator for guiding a charged particle beam emitted from the charged particle source onto the specimen; A specimen stage, which is located downstream of the illuminator and is arranged for holding the specimen; A detector device, which is used for detecting emissions from the specimen in response to the incidence of charged particles emitted from the charged particle source; And A control unit, which is used for performing the operation of the charged particle microscope; Characterized in that the control unit is arranged to determine at least one aberration of the charged particle microscope by processing a set of image data acquired by a user with the charged particle microscope.

14. The charged particle microscope according to claim 13, wherein the control unit is arranged to process the set of image data during the user's acquisition of the set of image data.

15. The charged particle microscope according to claim 13 or 14, wherein the control unit is arranged to process the set of image data during use of the charged particle microscope by a user.

16. The charged particle microscope according to claim 13 or 14, comprising a storage unit for storing the set of image data.

17. The charged particle microscope according to claim 13 or 14, wherein the control unit is arranged to perform the method according to one or more of method claims 1 - 12.

18. The charged particle microscope according to claim 13 or 14, wherein the control unit is arranged to adjust at least one setting of the charged particle microscope based on the determined aberration.

19. The charged particle microscope according to claim 13 or 14, wherein the charged particle microscope does not include one or more of the following: a user lens centering control, a user astigmatism corrector centering control, and a user astigmatism correction control.

20. The charged particle microscope according to claim 13 or 14, wherein the control unit is arranged to process the set of image data during navigation and / or focusing of the charged particle microscope by a user.

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