Improved navigation for electron microscopy

Abstract

A method of analyzing a sample in a microscope is described, the method including acquiring a series of composite image frames using a first detector and a second detector different from the first detector, and displaying the series of composite image frames in real time on a visual display that is updated to show each composite image frame in sequence, the acquiring of the composite image frames includes causing a charged particle beam to traverse a sample area corresponding to a field of view of the microscope, the traversal of the beam along a first traversal path over the area and according to a first set of traversal conditions when a mode parameter has a first value, and the traversal of the beam along a second traversal path over the area and according to a second set of traversal conditions when the mode parameter has a second value, wherein a first total time required for the beam to traverse the entire first traversal path according to the first set of traversal conditions is less than a second total time required for the beam to traverse the entire second traversal path according to the second set of traversal conditions, and monitoring a resulting first set of particles generated in the sample at a first plurality of locations within the area with the first detector to acquire first image frames. the step of monitoring, wherein a first image frame includes a plurality of pixels having values ​​corresponding to and derived from monitored particles generated at a first plurality of locations; monitoring with a second detector a second resultant set of particles generated in the sample at a second plurality of locations within the region to obtain a second image frame, wherein the second image frame includes a plurality of pixels having a respective set of values ​​corresponding to and derived from monitored particles generated at the second plurality of locations; and combining the first image frame and the second image frame to generate a composite image frame providing data derived from particles generated at the first and second plurality of locations within the region and monitored by each of the first and second detectors.

Description

[Technical Field]

[0001] The present invention relates to a method and system for analyzing a sample in a microscope, which can provide a user with improved navigation around a sample and can assist the user by combining information from multiple signals, even those with poor signal-to-noise, and by providing a display that allows the user to interact with the information sources to efficiently and virtually explore over large areas. [Background technology]

[0002] Figure 2 shows a typical system used in a scanning electron microscope (SEM) to probe the surface of a sample. An electron beam is generated inside a vacuum chamber and is usually focused using a combination of magnetic or electrostatic lenses. When the beam strikes the sample, some electrons are either backscattered from the sample (backscattered electrons or BSE) or interact with the sample to generate secondary electrons (SE) and some other radiation, such as X-rays.

[0003] An electron detector, typically designed to respond to the intensity of either SE or BSE from the sample, is connected to signal processing electronics and generates a signal corresponding to the portion of the sample that is being struck by the focused beam. X-ray photons emitted from that portion of the sample will also strike the X-ray detector, and associated signal processing can be used to measure the individual photon energies and generate signals corresponding to characteristic emission lines for chemical elements present under the beam. The focused electron beam is scanned across the surface of the sample using beam deflectors to traverse a region that defines the field of view (FOV) of the sample surface that will be shown as a visual image. This traverse is typically performed in a "raster" fashion, where the beam position is driven along a line in the X direction of a Cartesian coordinate system, and at the end of this line, the position is rapidly driven ("flyback") further down the region to the start of the next line, which is a small increment in the Y direction. That is, the region is scanned line by line until the beam has traversed the entire region and covered the FOV. As the beam scans along a line within the FOV, the signal from the electron detector can be electronically filtered and sampled at regular periods Te, or integrated over the periods Te, to provide results representing the sample surface covered in each period. If the FOV is covered by a raster with Ny lines, and each line within the FOV takes time L, then the total number of results recorded will be Ny × L / Te. Each result constitutes a value for a pixel in a digital image, and the total number of pixels for each complete frame of data, Npe = Ny × L / Te, covers the FOV. When this digital image frame is sent to a visual display unit, these pixel values ​​control the brightness, and the pixel location on the display corresponds to the location on the sample surface for each result. That is, if the visual display unit is much larger than the FOV on the sample, the displayed image will show a greatly magnified area of ​​the sample surface, and "magnification" or "MAG" is formally the ratio of the width of the visual display screen to the width of the area scanned on the sample surface. A microscope or SEM visualizes a field of view of an area on the sample surface that is governed by the electron beam energy, the electron lens settings, the field applied to deflect the focused electron beam, and the distance from the sample surface to the final lens.The visual display monitor will typically show the largest possible image, along with other controls and information for the graphical user interface. This largest image of the field of view on the specimen corresponds to a microscope configuration in which the electron beam scans over the entire field of view. When the electron beam is scanned slowly, the signal-to-noise for the electron image is better, but the display update rate is slow. Fast image updates with good S / N are necessary when the user wishes to adjust the focus or astigmatism to obtain a better image. Therefore, many SEMs offer a "reduced raster" function that retains a slow scan rate but scans over a reduced area on the specimen, with the results shown over a correspondingly reduced area on the visual display. That is, magnification and S / N are maintained, but the display update rate is much faster. In this way, the "reduced raster" generates a modified, smaller field of view that is essentially a subsection at the center of the image of the constructed field of view that updates fast enough to allow interactive adjustment of focus and astigmatism.

[0004] Besides traditional "raster" scanning, there are many other ways to enable a focused beam to traverse an FOV with the spatial resolution required for the image. A common method is to use "interlaced raster" scanning, in which two passes through an area are required to collect data for Ny lines. In the first pass, the beam is directed first along a line, then skipping the lines below it, and this is repeated until Ny / 2 "even-numbered" lines have been covered. Then, in the second pass, the beam is directed along all the skipped lines to cover the remaining Ny / 2 lines required for a full traverse of the FOV. In another example, the beam could be driven along a "serpentine" path, as shown in FIG. 1. With this type of traversal, if electronic signal measurements are taken over a period Te, the beam path during this period can be positioned to traverse a small rectangular area that will correspond to a pixel in the acquired digital image frame. If the pixel values ​​acquired during this period are used to control the brightness of an equivalent rectangular area on a visual display unit, the brightness will be more representative of the area than for a traditional raster, in which there is a gap between successive scan lines in the Y direction.

[0005] While the electron beam traverses the FOV and the electron signal measurement values are being recorded, a histogram of X-ray photon energy measurement values equivalent to the X-ray energy spectrum can be obtained over a period Tx in order to obtain a set of values representing the area on the sample surface traversed during the period Tx. By repeating this acquisition at regular intervals Tx while the beam traverses the FOV, a set of pixel values for a single frame of the "spectrum image" that each pixel has, which represents the X-ray spectrum emitted from the area traversed during the period Tx, can be obtained. When Tx = Te, the number of pixels in the X-ray spectrum image is Npx = Npe. However, when Tx > Te, Npx < Npe, and each pixel in the X-ray spectrum image represents a larger area on the sample surface than that corresponding to the pixels in the digital electron image.

[0006] In an alternative scanning strategy, the focused electron beam is held at one position within a rectangular grid of Npe points covering the FOV, and the electron signal is measured over a period Te, with the results stored in the corresponding pixel of the digital image. When this process is repeated for all points within the rectangular grid, one complete "frame" of electronic image data containing Npe pixels is obtained. If the pixel values ​​are used to control the brightness of a rectangular area on a visual display unit corresponding to an equivalent rectangular area centered on the beam position on the sample plane, the displayed image will be a magnified image of the FOV on the sample plane. If the incident electron beam is slightly defocused so that the beam spot covers the area between the grid points, the value for each pixel in the digital electronic image will represent the average signal value over the area near each beam position, thereby obtaining signal from the entire area of ​​the FOV on the sample plane rather than from a grid of discrete positions. An X-ray spectrum can also be acquired while the beam is positioned at the point for a time Tx, which may be longer or shorter than Te. As the beam is positioned at all N lattice locations, a single frame of an X-ray spectrum image can be acquired having N pixels, each having a set of values ​​corresponding to a histogram of photon energies acquired at or near a corresponding location on the surface of the sample. Alternatively, if the beam is positioned sequentially at lattice points along a serpentine path, it is possible to continue acquiring X-ray spectra over a period T while the beam is positioned at a series of lattice locations along this path. If electronic signal measurements are taken at every point while X-ray spectra are acquired for a series of points, a single pixel in the X-ray spectrum image can correspond to a rectangular area on the sample covering many lattice locations, whereas every pixel in the digital electronic image corresponds to a lattice point on the surface of the sample.

[0007] In another strategy for acquiring signals, the beam is positioned at a series of points on a grid covering the FOV, and both electronic signal measurements and X-ray spectra are recorded at every point on the grid. X-ray spectra from points covering small rectangular areas on the sample are then summed to give a single spectrum for each small rectangular area. That is, the acquired X-ray spectrum image will contain fewer pixels than the digital electronic image, and in this case, each pixel in the X-ray spectrum image corresponds to a larger area on the sample surface than a pixel in the digital electronic image.

[0008] In another variation of hopping, the beam is also positioned at a series of Npe points on a rectangular grid that covers the FOV range of the sample. However, the order of the points to which the beam is positioned is such that the beam is first positioned on Npe / 4 grid points that cover the entire FOV range, then positioned on a different set of Npe / 4 grid points that cover the entire FOV range, and this process is repeated four times until the beam has been positioned on all Npe grid points to complete the full area traversal. This can be thought of as the beam making four passes over the entire FOV, each time visiting a position on a four-times coarser sub-grid with twice the point spacing, but the total time to complete a full-resolution traversal of the FOV is still the same as if the beam had been positioned on all grid points in a single traversal of this region. This variation is sometimes referred to as 2x2 hopping.

[0009] The above examples are not comprehensive and are intended to show that a single frame of a digital electronic image containing Ne pixels can be acquired as the electron beam traverses a sample surface area corresponding to the field of view, and an X-ray spectral image containing Nx pixels from the same field of view, where Nx is typically less than or equal to Ne.

[0010] Typically, the "field of view" on an SEM is up to 1 cm in size, but this size can be larger or much smaller; when a digital image is displayed on a fixed-size monitor, the size of the field of view effectively determines the magnification, i.e., a small field of view represents a high magnification. The samples being investigated are typically much larger in size than the maximum field of view that can be achieved by deflecting the electron beam, and to probe the entire sample surface, the holder or stage supporting the sample must usually be moved using a controller, which can typically move the scanned field of view by many centimeters. Similar systems are used in electron microscopes where the sample is thin enough to allow the beam to penetrate it (scanning transmission electron microscopes or STEMs). In this case, the range of beam deflection and stage movement is typically smaller than for SEMs.

[0011] The number of electrons emitted from a sample when an electron beam strikes it is typically several orders of magnitude greater than the number of X-ray photons generated. As a result, any X-ray image derived from acquired X-ray data typically has a much worse signal-to-noise ratio than the electron image, making it desirable to use the best available method to improve the X-ray image. The number of X-rays collected by a detector is governed by the solid angle subtended by the X-ray detector at the point where the electron beam strikes the sample. In the arrangement shown in Figure 2, where the X-ray detector is on one side of the electron beam, the collection solid angle can be maximized by using a large-area detector or by positioning the detector in close proximity to the sample. In a different arrangement, the X-ray detector uses several sensors positioned around the incident electron beam to maximize the total collection solid angle. In this "coaxial" arrangement, the X-ray detector is positioned between the final lens aperture and the sample, and the electron beam travels through the gap between the sensors.

[0012] Even when the collection solid angle is maximized, the signal-to-noise ratio for X-ray images derived for a single frame is typically much worse than that for electronic images, making it difficult for users to see details when the dwell time per pixel is short. If the dwell time is extended to improve the signal-to-noise ratio, it takes longer to complete an image frame, and users must wait longer to see an image that covers the entire field of view. A significant innovation in X-ray imaging has been the technique of recording both the scan position and scan energy of individual photons so that the stored data can be processed to generate X-ray images from any desired characteristic chemical element emission (Mott and Friel, 1999, Journal of Microscopy, Vol. 193, Part 1, January 1999, pp. 2-14). Instead of using long dwell times per pixel for a single scan, Mott and Friel repeatedly scanned the same field of view using short dwell times, frequently accumulating data. Their systems are programmed to repeatedly present X-ray images for display using the spectral data accumulated at each pixel so that a derived X-ray elemental map of progressively lower granularity emerges as the signal-to-noise ratio improves as new data frames are added. This method of acquiring X-ray data, displaying the derived X-ray elemental map, and observing the resulting image improve over time has remained in common use for nearly 20 years.

[0013] When users need to explore a sample to find a region of interest, they typically use an SEM display optimized for rapid interaction with the electron image. Typically, an SEM displays a high-signal-to-noise (S / N) electron image that is refreshed every frame. When the focus or magnification is changed or the field of view is displaced (e.g., by moving the holder or stage supporting the sample or adding an offset to the scan deflection), the user sees a new image at a rate fast enough for efficient interaction. Update rates high enough to track moving features are typically referred to as "TV speed," by analogy with home televisions, although the frame rate may be slower than 50 Hz. After setting the magnification of the electron image so that the field of view covered by the electron beam scan is adequate to display the relevant type of feature on the sample surface, the user moves the stage while observing the electron image to find an area likely to contain the relevant chemical element or chemical compound. When a likely area appears in the field of view, the user stops stage movement, adjusts the scan speed, and begins X-ray acquisition, observing the elemental map as the S / N improves frame by frame, as described by Mott and Friel. If it soon becomes apparent that the distribution of elements or compounds in the field of view is not appropriate, the user will return to interactive exploration using the fast frame rate electronic image and move the stage to find a more appropriate area for acquiring X-ray data. This cycle of repeatedly stopping and exploring to acquire enough X-ray data to return to the electronic image and determine whether the field of view has the appropriate distribution of the required elements, and then returning to the electronic image and exploring again if it does not, is inefficient and may cause the user to miss areas on the sample that contain the material of interest while attempting to navigate over a large area on the sample.

[0014] When a user's task is to find an area containing a particular chemical element, chemical compound, or chemical substance with a certain characteristic, the problem is that electron images do not provide sufficient information. While SE signals clearly show surface topography and BSE signals can indicate the average atomic number of a material, neither signal provides specific information about chemical element content or material properties; the user must infer whether an area is likely to merit acquiring additional data from this area to provide such information. Derived X-ray images can provide information about chemical element content, but they have only poor signal-to-noise ratios and do not provide any detail or sufficiently high resolution of the topography to help the user determine where they are on the sample. What is needed, then, is an effective way to visualize material properties, such as chemical element content, while the user navigates across a large area on the sample to find the material of interest.

[0015] WO 2019 / 016559 A1 involves displaying a combined microscope sample image representing different information about the sample, acquired using two different types of detectors, i.e., with different image acquisition characteristics, in real time as the images are acquired. This technique has improved speed and efficiency, allowing a user of a microscope instrument to navigate through different regions of the sample and locate features of interest on the sample. This benefit arises in no small part because displaying two types of images simultaneously showing the same region of the sample within the same field of view allows a user to quickly identify potential features of interest, for example, while navigating around the sample, based on a first type of image that can show the physical shape or topography of the sample surface, and, upon locating such potential features, maintain the microscope's field of view so that it continues to include those features in order to acquire or accumulate a second type of image data to obtain information about the sample region of a different type than the information provided by the first image type. [Prior art documents] [Patent documents]

[0016] [Patent Document 1] WO 2019 / 016559 A1 [Patent Document 2] WO 2012 / 110754 A1 [Patent Document 3] PCT / GB2011 / 051060 [Patent Document 4] US5357110 [Patent Document 5] PCT / GB2014 / 051555 [Non-patent literature]

[0017] [Non-Patent Document 1] Mott and Friel, 1999, Journal of Microscopy, Vol. 193, No. 1, January 1999, pp. 2-14 [Non-patent document 2] https: / / en.wikipedia.org / wiki / Digital_image_correlation_and_tracking [Non-patent document 3] P.J. Statham, "Deconvolution and background subtraction by least-squares fitting with prefiltering of spectra," Analytical Chemistry 1977, 49(14), pp. 2149-2154, DOI:10.1021 / ac50022a014 Summary of the Invention [Problem to be solved by the invention]

[0018] However, there remains a need for improved methods for analysis that further enhance the speed and efficiency that allows for visualization of material properties while navigating across large sample areas, as well as the quality of visual data that can be obtained for regions of interest. [Means for solving the problem]

[0019] According to a first aspect of the present invention there is provided a method of analysing a sample in a microscope, the method comprising the steps of acquiring a series of composite image frames using a first detector and a second detector different to the first detector, the acquiring of the composite image frames comprising: a) causing a charged particle beam to traverse a sample area corresponding to a field of view of the microscope, the traversing of the beam along a first traversal path over the area and according to a first set of traversal conditions when a mode parameter has a first value, and along a second traversal path over the area and according to a second set of traversal conditions when the mode parameter has a second value, wherein a first total time required for the beam to traverse the entire first traversal path according to the first set of traversal conditions is shorter than a second total time required for the beam to traverse the entire second traversal path according to the second set of traversal conditions; b) monitoring with a first detector a resulting first set of particles generated within the sample at a first plurality of locations within the region to obtain a first image frame including a plurality of pixels corresponding to the first plurality of locations and having values ​​derived from the monitored particles generated thereat; c) monitoring with a second detector a second resulting set of particles generated within the sample at a second plurality of locations within the region to obtain a second image frame including a plurality of pixels corresponding to the second plurality of locations and having a respective set of values ​​derived from the monitored particles generated thereat; and d) combining the first image frame and the second image frame to generate a composite image frame that provides data derived from particles generated at first and second pluralities of locations within the region and monitored by each of the first and second detectors; The obtaining step includes: displaying the series of composite image frames in real time on a visual display that is updated to show each composite image frame in sequence; Includes.

[0020] The present method offers yet another advantage over existing electron microscopy analysis techniques when navigating and collecting data from a sample. The inventors have devised a technique that provides additional benefits in terms of signal-to-noise and efficient, high-speed sample navigation. This is achieved by changing the mode in which the beam scans the sample when acquiring data for an image frame based on whether the microscope's field of view is changing or stationary. In particular, the present method allows for advantageous switching between a high-speed image frame acquisition mode when the field of view is changing and a slower mode when the field of view is unchanged. Varying the time required to acquire data for a composite image frame, the estimated time required for a given mode to acquire data for an entire frame or from an entire traversal path, or the acquisition rate can be achieved in several ways. These techniques include changing the resolution of the acquired image, changing the average time required to acquire data from a location on the sample surface, and changing the extent to which the traversal path covers an area on the sample. Enabling this switching scheme provides significant advantages during sample analysis, where an operator typically navigates a sample within the microscope by moving the field of view relative to the sample until a potential feature or region of interest is identified, and then can stop this movement while collecting further data from such region or feature. By adjusting the manner in which the beam traverses the sample surface and monitors the resulting particles in response to how the microscope is used to navigate the sample, the speed and efficiency with which material features can be visualized while navigating over large sample areas, as well as the quality of the visual data that is available for the region of interest, improves over existing techniques.

[0021] The method facilitates real-time tracking of a sample under a microscope by displaying the combined image in real time. The sequential, rapid presentation of a series of acquired composite image frames provides the operator with a "live" view of the sample being analyzed by the two detectors. In the context of the present disclosure, a series of composite image frames can be understood as a plurality of composite image frames occurring in succession. A series of composite image frames can be considered to have an order. Typically, this order is or corresponds to the order in which the composite image frames were acquired and / or the order in which each of the constituent frames of the composite image frame, i.e., the first image frame and the second image frame, was acquired. Typically, the order of a series of composite image frames is the same order in which these composite image frames are displayed.

[0022] This sequence does not exclude the composite image frame set being a subset of a larger frame set or sequence. This sequence does not necessarily exclude either the possibility of temporal overlap with further sets or sequences of acquired frames and / or overlap with respect to composite image frames within each set or sequence. As discussed later in this disclosure, a series of composite image frames may be interrupted, for example, by further frames that are not considered part of it. For example, it is contemplated that participating composite image frames may be acquired in the same or different manner, and such interactive composite image frames would not be considered part of the series of composite image frames. Preferably, however, the series of composite image frames is an uninterrupted series of composite image frames. In this disclosure, the characteristic that the composite image frame acquisition step includes the above-mentioned steps can be understood to mean that, in typical embodiments, the step of acquiring each composite image frame in the series of composite image frames includes these steps.

[0023] The modal parameters may be referred to as scan mode parameters. This nomenclature is appropriate because the modal parameter values ​​affect the manner in which the traversal of an area by a beam, sometimes referred to as scanning by the beam, is performed.

[0024] Typically, in the present disclosure, a parameter having a value can be understood as a parameter having a value equal to such particular value, which is typically a predetermined value.

[0025] It will be understood that the first and second values ​​will typically be different. Typically, the first value of the mode parameter corresponds to a first scanning mode, which is typically a "fast" scanning mode.

[0026] Typically, the second value that the mode characteristic can have corresponds to a second scanning mode that is different from the first scanning mode and is typically a "slow" scanning mode.

[0027] One way in which a particular mode parameter value can affect the scanning mode is by changing the beam traverse path for the acquisition of a composite image frame. Preferably, either or both of the first and second traverse paths are predetermined at least at the beginning or before the start of the traverse of a given frame. However, if the first and second traverse paths are different, it may be considered that either or both of these first and second traverse paths can themselves be changed by switching the mode parameter value one or more times, i.e., changing to and / or from the first and second values, during the course of traversing the field for a given frame.

[0028] For example, it will be appreciated that switching between two pre-configured or predetermined preliminary paths may require time-consuming or otherwise inefficient beam path changes, and in such cases, deviations from, omissions of, and / or variations of either or both of the pre-configured or predetermined portions may be permitted or made to define the actual first and / or second paths traversed.

[0029] The first and second plurality of locations within the region typically coincide with or lie along the first and second traversal paths, respectively, and one or more, or in some cases all, of the locations included in either or both of the first and second plurality of locations for a given composite image frame may coincide with both the first and second traversal paths.

[0030] In some embodiments, the value of the mode parameter is configured according to whether the constituent field of view is changing or not changing. Preferably, the mode parameter is configured to have a first value or a second value according to whether the constituent field of view is changing or not changing, respectively.

[0031] It can be particularly advantageous to initiate or otherwise trigger the fast scan mode by the configuration field being changed. In some preferred embodiments, therefore, a mode parameter is configured to have a first value in response to the configuration microscope field being changed. Configuring a parameter to have a first value can be understood as the parameter being set to the first value, regardless of the value of the parameter and regardless of whether the parameter actually had a value prior to this setting. In such embodiments, changing the configuration field can automatically engage the fast scan mode.

[0032] Typically, the mode parameter has a first value while the constituent microscope field is changing, i.e., has a changing state.

[0033] The response described above is preferably an immediate response. However, in practice, some delay in the responsive setting of the parameter value may be necessary or desirable; i.e., the response may be, for example, a response after the component field is placed into a changing state, sometimes after a predetermined time or number of frames has passed. Preferably, the mode parameter is maintained at the first value as long as the component field continues to change, or at least as long as the component field continues to change, or until it no longer changes. For example, in embodiments in which the parameter is automatically set to the second value due to the component field becoming or remaining stationary, the switching of the parameter to both the first and second values ​​may be automatic, depending on the component field.

[0034] The mode parameter may have a first value in response to the constituent fields of view being in a changing state, for example, over a predetermined time period or over a predetermined number of frames in a series of composite image frames.

[0035] Preferably, the parameter can be configured to have a first value when the change made to the constituent microscope field is greater than a predetermined threshold, for example according to a measure of the similarity of the constituent field with the field of the previous frame, these measures including the degree of overlap between these constituent fields on the area, the relative or absolute constituent location on the sample, and / or the zoom level.

[0036] That the field of view used to configure the microscope is "changing" can be understood to mean that the field of view can be in a changing state, or in other words, configured in some way to be changing. For example, this configuration change can include panning across the sample and / or zooming in or out, corresponding to a smaller or larger area on the sample, respectively. It will also be understood that the step of setting the parameter to the first value can be in response to either or both of the configuration field of view being in or being put into a changing state. For example, the first value can be set according to or in response to a single configuration field movement.

[0037] As mentioned above, in some embodiments, the mode parameter is configured to have a second value in response to the configured microscope field not changing. This response also need not be immediate and can be delayed, as with the setting to the first value described above. It can be appreciated that the field of view used when configuring the microscope may be static at a given time or configured to change. As discussed in more detail later in this disclosure, in practice, some changes made to the actual microscope field of view can occur regardless of whether the configured field of view is changing. That is, for example, the actual field of view and the configured field of view may differ due to field drift.

[0038] This response may be in response to the completion of any changes made to the constituent fields, as described above. The second value may be set, for example, in response to the constituent fields remaining unchanged for a predetermined period of time or for a predetermined number of frames in a series of composite image frames.

[0039] Setting the mode parameter value in response to a changing or unchanged state of the component fields can allow for changing between scanning modes during the acquisition of a given composite image frame, i.e., the mode parameter can have the same value during the acquisition of a given composite image frame in a series of composite image frames, or can change between different values ​​depending on changes made to the state of the component fields, i.e., whether the component fields are stationary or non-stationary.

[0040] However, in some embodiments, the microscope may be configured with either a changing or unchanged field of view state corresponding to two consecutive composite image frames or their constituent image frames in a series of composite image frames having different or equivalent constituent fields of view. Typically, the composite image frame currently being acquired at a given time is the second, i.e., later, of these two consecutive frames. Making a changing / unchanging determination in this manner may be advantageous to implement when a change in intermediate frame acquisition mode is not expected or desired.

[0041] That is, in some embodiments, particularly during acquisition of a composite image frame, the mode parameter has a first value when the constituent microscope fields differ from those for the immediately preceding composite image frame in the series of composite image frames, and it will be appreciated that the parameter value can be adjusted to that value based, for example, on the conditions for the constituent fields being satisfied, or can remain at an appropriate value while the respective conditions continue to be satisfied.

[0042] In the context of this disclosure, the term "preceding" may be understood to refer to occurring before in time, i.e., a composite frame acquired before the current composite frame. The term "directly" in this context may be understood to mean that there are no intervening frames between the current composite image being acquired and the immediately preceding composite image frame in the series of composite image frames. It will be understood that this does not exclude the acquisition of one or more composite image frames or any other frames, images, signals, or other data between the current composite image frame and the immediately preceding one in the series of composite image frames. Any such other composite image frame may be captured, particularly if it is not part of a second series of composite image frames. That is, although the series of composite image frames is preferably an uninterrupted sequence as described above in this disclosure, which may indicate that no further frames are acquired simultaneously with or between the acquisition of a composite image frame in the series of composite image frames, in some embodiments it may be necessary to interrupt a specified function performed in acquiring successive image frames. For example, a series of composite image frames may be an interrupted sequence in this manner if there is a delay of one or more frames before making a change in scanning mode.

[0043] The above-described functionality may relate to the first scanning mode being used when a difference occurs between consecutive fields of view. Conversely, in some embodiments, the mode parameter has a second value when the constituent microscope fields are the same as those for the immediately preceding composite image frame in the series of composite image frames. As above, this may involve adjusting the parameter value to that value based, for example, on the satisfaction of a condition for the constituent fields of view, or allowing it to remain at an appropriate value while the respective condition continues to be satisfied. In the context of such an embodiment, the immediately preceding composite image frame is substantially the same as the immediately preceding composite image frame mentioned with respect to the mode parameter having a first value. In some implementations, automatic switching to slow mode may be performed based on a determination that consecutive composite image frames have the same constituent fields of view.

[0044] In addition to automatic scanning mode switching, it is also possible for the scanning mode to be user-controllable. That is, in some embodiments, the mode parameter value is user-configurable. In other words, the mode parameter can have a value that the user can configure. In some cases, it is particularly advantageous for a microscope user to be able to set the scanning mode to slow mode. That is, the ability for a user to manually initiate a slow scan can be particularly advantageous when using live monitoring techniques to analyze and describe a sample. That is, in some preferred environments, the mode parameter is set to a second value when a first user input is provided. The first user input can be provided by some type of input, for example, a computer user interface. The input can include a command, key, or toggle to set the mode parameter to a third value, thereby generating a slow scan. In some embodiments, the user input can be used to set the parameter to either or both of the first and second values. The ability to switch the parameter to at least the second value is preferably configurable. This can facilitate greater control over live monitoring and navigation of the sample.

[0045] Providing the user with the ability to initiate a slow scan in this manner is particularly advantageous when the constituent microscope field of view is different from that for the immediately preceding composite image frame in a series of composite image frames, or when the constituent field of view is otherwise in a changing state, when implemented in combination with a configuration in which the mode parameter has a first value. In this manner, the user can set the scan to a slow mode as needed to improve the image data while navigating.

[0046] Typically, the user will interrupt the movement of the construction field when setting the slow mode, i.e., it is advantageous to resume field movement before switching the scan to fast mode.

[0047] In addition to implementing changeable scan modes to facilitate switching between high-speed and high-quality scans as needed during sample navigation, the manner in which required frame data is processed can be adjusted according to similar principles. That is, in some embodiments, acquiring a composite image frame further includes combining the set of derived values ​​of the pixels with a set of derived values ​​of corresponding pixels in each of one or more preceding second image frames in the series of composite image frames to obtain a set of combined pixel values ​​having an increased signal-to-noise ratio when the second mode parameter has a second value for each of at least a subset, preferably all, of the plurality of pixels comprised by the second image frame, and replacing the derived set of pixel values ​​for the second image frame with the set of combined pixel values, or retaining the derived set of values ​​of the pixels in the second image frame for use in the composite image frame when the second mode parameter has a first value.

[0048] Preferably, the plurality of pixels is the same as the set of pixels that make up the frame. However, the plurality of pixels may be a subset of this set of pixels. The second mode parameters may be referred to as frame processing mode parameters. The "corresponding pixels" referred to above typically refer to pixels in different frames that correspond to the same location on the sample and have values ​​derived from particles emitted therefrom.

[0049] The second mode parameter can therefore control whether the second image frame data is processed in "refresh" mode or "accumulate" mode, as discussed in more detail below. In some embodiments, the second mode parameter has a first value when the constituent microscope fields are different from those for the immediately preceding composite image frame in the series of composite image frames. This "accumulate" mode and "refresh" mode functionality is preferably applied to the second image frame, but in various embodiments can also or alternatively be applied to the first image frame as well.

[0050] As with the first mode parameters described above in this disclosure that may be used to control the traversal or scanning of the beam, the second mode parameters that may control the mode of processing the acquired second image frame may be configured to be adjusted according to several factors, and both manual control and automatic switching are specifically contemplated.

[0051] Thus, in some circumstances, automatic switching to the second mode of frame processing, i.e., accumulation mode, may be affected according to the similarity or correspondence between successive constituent microscope fields within a series of composite image frames. In particular, the second mode parameter may have a second value when the constituent microscope fields are the same as for the immediately preceding composite image frame in the series of composite image frames.

[0052] In addition to or instead of the above-described automatic parameter setting for controlling frame processing, the second mode parameter can be user-configurable. In particular, in some embodiments, user input can be used to set the parameter to either or both of a first value and a second value, preferably providing the ability to switch to at least the second value. This can facilitate live monitoring and rapid acquisition of high-quality data when an area of ​​interest enters the field of view during navigation by providing the user with the ability to combine acquired second image frames to improve the signal-to-noise ratio of the data in the second image frames. Similarly, setting a mode parameter to a value can be understood as configuring the mode parameter to have that value. That is, in some embodiments, the second mode parameter is set to the second value in response to user input. This is particularly advantageous in embodiments where switching to a "refresh" frame processing mode occurs automatically based on the state of the field of view used when configuring the microscope, as in the case of a user-selectable scanning mode. In this way, the user can configure the frame processing function to accumulate data for improved data when sample navigation is interrupted. Accordingly, it is advantageous for frame processing to switch to a "refresh" mode to provide rapidly updated data when field of view movement resumes.

[0053] The nature of the user input is typically the same as that described above for the scan mode.

[0054] Some embodiments involve compensating for possible inadvertent drift of the microscope's field of view. Such deviations between the field of view and the intended or constructed field of view can, without such correction, make it very difficult or impossible to combine pixel values ​​from various image frames within a series of composite image frames. This is because, as a result of this inadvertent movement or displacement of the field of view, pixel data representing signals from the same location on the sample will typically be attributed to pixels having different positions in each of the two image frames.

[0055] The present disclosure noted that in some cases, the microscope's actual field of view may not necessarily be the same as the component field of view. This may be due, for example, to thermal effects on the sample stage mechanism or beam deflection electronics. The composite image frame acquisition step further includes acquiring field of view deviation data representing the difference between the microscope's actual field of view and the reference field of view, and determining, for each of at least a subset of the pixels contained by the second image frame, a corresponding pixel in each of one or more preceding second image frames in the series of composite image frames, which pixel is combined with the derived value set for that pixel according to the field of view deviation data to obtain a combined pixel value set. Applying this function when frames are acquired using the "accumulation" mode of processing is particularly advantageous. That is, the composite image frame acquisition step preferably further includes these steps when, i.e., under such conditions, the second mode parameter has a second value. Preferably, the correction is performed only under this condition. However, applying drift correction when this condition is not satisfied is not excluded.

[0056] The "difference" mentioned above can be a difference in linear coverage and / or area coverage and / or position on the sample between fields of view. This difference can typically include the difference between the constructed field of view and the actual field of view of the microscope at a given time, preferably at a time when a composite image frame, particularly a second image frame, is being acquired. The field deviation data can be a measure of this difference, or a calculated, estimated, or predicted index, value, or estimate of this difference. For example, the field deviation data can be expressed using a vector representation or drift vector. This data can indicate the difference between the actual field of view and the constructed field of view, or can indicate drift, for example, relative to other frames in a series of composite image frames. The field deviation data is available according to a plurality of acquired first image frames. The field deviation data can indicate field drift, or can be a measure or representation thereof. In some embodiments, the field deviation data can be determined by cross-correlation of consecutive first image frames, which in some embodiments are electronic images.

[0057] The correction used to combine pixels in some embodiments is typically applied to at least a subset, but preferably all, of the pixels in the second image frame, and may be applied to the pixels of the first image frame if the first image frame data is to be combined in an “accumulation” mode of processing. For example, the subset for a given frame may be able to find corresponding pixels. As noted earlier in this disclosure, two pixels in different image frames can be considered corresponding if they correspond to the same location on the sample. However, for some pixels, a corresponding pixel may not be found or may not be identifiable, such as when surrounding pixels correspond to portions of the sample that have unintentionally drifted into the field of view. It will be appreciated that in embodiments involving substantially simultaneous acquisition of the first and second image frames, inadvertent movement of the sample relative to the beam will typically affect both the first and second image frames. Preferably, alignment between the first and second image frames is maintained during the acquisition of the composite image frame. This alignment may be achieved, for example, by drift correcting both the first image frame data and the second image frame data, or by drift correcting only the second image frame data, for example, using the first image frame data as a reference and / or measure of deviation, where drift correcting only the second image frame data may include using the first image reference data to generate the composite image. That is, the steps described above for drift correcting image frame data when acquiring a composite image frame may be applied to either or both of the first and second image frames.

[0058] Generally, drift correction may be involved to identify drift or deviation in the field of view between frames, thereby enabling pixels in different second or composite image frames that correspond to the same location on the sample to be identified and these value sets to be combined, i.e., preferably the step of obtaining a combined pixel value set is performed such that the corresponding pixels correspond to or represent monitored particles emitted from the same sample location as the current pixel.

[0059] While the construction field and the real field are preferably the same, any inadvertent drift in the position of the real field may reduce the quality of the combined data in the second image frame by disrupting the correspondence between pixels in different frames. Therefore, this inadvertent drift is preferably corrected between consecutive image frames to ensure that pixel values ​​are combined only if the data originates from the same location on the sample. Thus, in some embodiments, the reference field includes either the construction field for the composite image frame being acquired or the real field for the preceding composite image frame in the sequence. This real field is preferably that of the microscope from which the composite image frame is being acquired. Typically, in embodiments involving drift correction, when the second mode parameter has a second value, once the system begins integrating frames, preferably regardless of any delay before starting integration, the first composite image frame in a cycle operating in "integration" mode, typically data from that first image frame, can be used as a drift correction reference so that data from all subsequent frames are combined with positions corrected for drift. Thus, the reference field of view may comprise a real or constructed field of view of a previous composite image frame, typically one obtained subsequent to the second mode parameter being set to the second value.

[0060] In addition to or instead of using the deviation data to establish correspondence between acquired frames in which the field of view has drifted, this data can be used to mitigate the drift itself. Thus, in some embodiments, the composite image frame acquisition step further includes adjusting the field of view according to the field of view deviation data to reduce the difference between the microscope's real field of view and the reference field of view, particularly when the second mode parameter has a second value. In other words, adjustments such as beam deflection or sometimes stage positioning and / or movement can be made to the acquisition conditions for subsequent frames so that the real field of view matches, or at least more closely matches, the reference field of view.

[0061] In some embodiments, particularly those in which data indicative of chemical elements present at the monitored sample location can be derived using particles monitored by the second detector, processing is preferably performed to obtain characteristic line emissions. Preferably, this processing is performed even in the case of overlapping characteristic line distributions, and preferably excludes any bremsstrahlung contributions. In some embodiments, obtaining a composite image frame includes processing spectral data, preferably X-ray spectral data, obtained according to the second particle set to obtain data indicative of the number of particles, each corresponding to one or more characteristic line emissions within the second particle set, e.g., quantities that can be understood as count values, to derive a set of values ​​for each of the pixels included by the second image frame.

[0062] In the context of X-ray data, it will be understood that the second set of particles includes photons and thus X-ray photons. Processing the spectral data may include processing one or more signals output by the second detector. Characteristic line emissions may refer to a set of X-ray transition emission lines corresponding to various transitions between states for a given chemical element, as is well understood in the art.

[0063] Each set of values ​​derived from the monitored second set of particles can be derived by processing the X-ray spectrum data to extract the number of photons corresponding to a particular characteristic line emission, even when the line emissions from two different elements are distributed over an energy range and overlap in energy. Thus, the processing step preferably includes extracting data indicative of the particle abundance when one or more characteristic line emissions are distributed over an energy range and / or correspond to overlapping energy ranges.

[0064] Preferably, in such an embodiment, one or more of the sets of values ​​each include X-ray energy spectrum data that can be represented as a histogram, where the area of ​​each rectangle represents the number of second particles having energies in an energy range corresponding to the width of the rectangle. It will be understood that a "rectangle" in this context does not need to be represented as such, but typically includes data such as a pair of values ​​that can be visualized as the height and width of a rectangle suitable for plotting as a rectangle on a histogram. One or more of the sets of values ​​can each include a set of results from processing a histogram. The area of ​​each rectangle, and therefore the product of the two values ​​in the pair, can represent the number of second particles having energies in an energy range corresponding to the width of the rectangle to extract a set of values ​​representing the number of second particles collected from the characteristic radiation of the set of chemical elements.

[0065] A traversal path can be thought of as the path across or along which the beam is scanned to obtain a frame that covers the area.

[0066] The shorter total time for the beam to traverse the region in the first "fast" traversal mode can be generated using several methods, individually or in combination. For example, the total length of the traversal path of the region in the first mode can be shorter than that for the second mode to allow the beam to traverse the region more quickly. Thus, in some embodiments, the first traversal path has a shorter length than that of the second traversal path, such that the first total time is shorter than the second total time.

[0067] In other embodiments, the first and second traversal paths can be of equal length, in which case the difference in traversal time can be attributed to the different traversal conditions between the first and second traversal conditions. Thus, in some embodiments, the first and second sets of traversal conditions are configured to cause the beam to traverse the first traversal path, particularly according to the first set of traversal conditions, at a faster average speed than the average speed at which the beam traverses the second traversal path, particularly under the second set of traversal conditions, such that the first total time is shorter than the second total time. The average speed is typically an intermediate speed. Thus, the speed can be interpreted as relating to the average speed across the entire traversal path. In this manner, a given traversal path can be traversed faster under the first set of conditions than under the second set of conditions.

[0068] In other words, the first and second paths may be the same while the first and second conditions are different, or the first and second sets of conditions may be the same while the first and second paths are different, or both the first and second paths and the first and second sets of conditions may be different. Advantageously, the first and second paths and conditions may, in any combination with each other, result in a shorter total traversal time for the first path and conditions than for the second path and conditions.

[0069] Typically, in such embodiments, the first and second sets of traversal conditions are configured such that a first linear density along a first traversal path at locations within the region configured to be monitored for a first generated particle set is less than a second linear density along a second traversal path at locations within the region configured to be monitored for the first generated particle set. Typically, this configuration is applied such that an average velocity for traversing the first traversal path under the first set of conditions is greater than an average velocity for the second path and the second set of conditions.

[0070] The linear densities referred to above may be understood to refer to the respective average linear densities for the entire length of a given traversal path or at least a portion thereof.

[0071] Typically, the linear density of a location relates to a (potentially intermittent) portion of a traversed path that corresponds to one or more scan lines, which may, for example, exclude path portions between scan lines in a raster pattern.

[0072] In general, linear density can be interpreted to refer to the distribution density, scale, or number of locations to be monitored per unit length of the traversed path. In some embodiments, the linear density difference mentioned above can mean that the total number of locations to be monitored is less when following a first set of conditions than for a second set of conditions. This can be true, for example, when the first and second path lengths are the same or similar.

[0073] Preferably, in such embodiments, the first and second sets of traversal conditions are configured such that a first linear density along a first traversal path at a location within the region where the second generated particle set is configured to be monitored is lower than a second linear density along a second traversal path at a location within the region where the second generated particle set begins to be monitored, and in particular such that an average velocity for traversing the first traversal path under the first set of conditions is higher than an average velocity for the second path and the second set of conditions. Thus, the velocity difference may be achieved by having different linear densities at either or both of the first and second locations.

[0074] The difference in scan speed between these two modes can be achieved by changing the time required to monitor signals from the monitor locations during a scan. Both the first set of traversal conditions and the second set of traversal conditions can be configured such that a first configuration monitoring duration, during which a first set of particles generated at each of the first plurality of locations along the first traversal path is monitored, is shorter than a second configuration monitoring duration, during which the first set of particles generated at each of the first plurality of locations along the second traversal path is monitored. In some implementations, the monitoring duration for each and every location for which a particle set is monitored when the mode parameter has a first value is shorter than the monitoring duration for any of the locations for which a particle set is monitored when the mode parameter has a second value.

[0075] For example, the monitoring duration for each or at least some of the locations monitored under a given set of conditions may be the same or substantially the same.

[0076] Preferably, the average or median monitoring duration for the locations monitored when the mode parameter has a first value is less than the average or median monitoring duration when the mode parameter has a second value.

[0077] Similarly, the velocity difference can be affected by either or both of the first set of particles and the second set of particles. Accordingly, in some embodiments, the first and second sets of traversal conditions are configured such that a first configuration monitoring duration during which the second set of particles generated at each of the second plurality of locations along the first traversal path is monitored is shorter than a second configuration monitoring duration during which the second set of particles generated at each of the second plurality of locations along the second traversal path is monitored.

[0078] In various embodiments, the first and second traversal paths for a given composite image frame can be the same or different. For example, the paths can be the same, and thus changing the speed at which the paths are traversed can be considered as changing the speed at which the region itself is traversed. Thus, in some embodiments, the beam traverses the first traversal path over the region at a higher average speed than the average speed at which the beam traverses the second traversal path over the region at the same time as the constituent microscope fields of view for the immediately preceding composite image frame in the series of composite image frames.

[0079] However, in some embodiments, the traversal path used for the second mode can be different for a given composite image frame. For example, if interlaced scanning is used to scan at the second average speed, i.e., in the "slow" or "static" mode, and non-interlaced scanning is used for the first "fast" or "dynamic" mode, the time required for one complete scan of the area by the beam can be the same for the first and second modes. In such cases, the time required for the beam to traverse the entire second traversal path, which will preferably include multiple scans that combine to cover the area, remains longer than the time required for the beam to traverse the first traversal path, which may include only a single "pass" over the area and may include a portion of a traversal path that covers, or at least substantially covers, the area.

[0080] In other words, the second traversal path can be longer than the first traversal path, for example, by including more passes over the region. In these cases, an increase in the average traversal speed for the first mode compared to the second mode can be at least partially attributed to the longer path in the second mode. In some embodiments, for example, the time required for one pass over the region can be the same for both the first and second traversal modes or paths. However, in these cases, the requirement that more passes be required to fully traverse the second path than the first path means that the total time required for the second path is longer, and therefore the traversal speed may be considered slower.

[0081] Throughout this disclosure, for any described embodiment that defines a change in traverse velocity in terms of the time required to traverse an area, it is also contemplated that the embodiment can typically be implemented by instead defining the change in traverse velocity in terms of the time required to traverse a traverse path. Similarly, a change in traverse velocity for a first and second acquisition mode can equivalently be defined as a change in the total time required to scan the respective first and second traverse paths, or in some embodiments, the total time required to scan an area. The traverse time is referred to as the "total" time because it includes, for example, the overall time it would take to traverse an entire traverse path in a given mode. As will be understood from the above discussion and throughout this disclosure, the acquisition of a frame in a series of frames may include any interruption due to switching from traversing in one mode to traversing in another mode, and therefore the total time need not necessarily be the same as the actual time it takes the beam to traverse a portion of the sample to generate particles for acquiring the frame.

[0082] Similarly, for any embodiment describing a change in traverse speed, this change can be understood as a change in the total required configuration time or the total time it would take for the beam to traverse the entire traverse path. Thus, this speed need not necessarily be defined as the average speed at which the beam traverses a given distance on the sample surface during monitoring, although in some embodiments the change in speed may additionally correspond to a change in such average speed. In other words, the average traverse speed can be understood as a measure of the speed at which the traverse of the entire path occurs that corresponds to or can be derived from a measure of the time required to scan the entire traverse path.

[0083] Therefore, alternatively, in some embodiments, during acquisition of a composite image frame, step (a) can be understood to include causing the charged particle beam to traverse a sample area corresponding to a constituent microscope field of view, and when the constituent microscope field of view is different from that for the immediately preceding composite image frame in the series of composite image frames, the beam is caused to traverse a first transverse path over the area at an average speed that is faster than the average speed at which the beam traverses a second transverse path over the area when the constituent microscope field of view is the same as that for the immediately preceding composite image frame in the series of composite image frames.

[0084] The traversal of an area by charged particles can be understood as the scanning of a beam, typically an electron beam, across this area. Thus, in the context of the present disclosure, the term "scanning" can be understood as the traversal of a beam across a surface, object, or part of a sample.

[0085] During the traversal of the field by the beam, and during the processing of the pixels of the second image frame, and more typically during the monitoring of the first and second generated particle sets, its function depends on whether the constituent microscope fields of view are different from or the same as the fields of view for the immediately preceding composite image frame in the series of composite image frames. It will be understood that any or all of the above-described portions of the composite image frame acquisition procedure when the constituent microscope fields of view for the currently acquired composite image frame are different from the fields of view of the immediately preceding composite image frame in the series of composite image frames also apply when no such immediately preceding composite image frame exists. Thus, for the first frame in the series of composite image frames, the method typically performs some or all of the composite image frame acquisition procedure as if the constituent microscope fields of view for the current frame were different from the microscope fields of view for the immediately preceding composite image frame in the series of composite image frames.

[0086] Typically, a particular frame acquisition strategy is based on whether the field of view for the current frame differs from the field of view for the immediately preceding frame. This determination can be made, for example, based on the microscope field of view at the time the procedure for acquiring a given composite image frame begins. In some embodiments, this determination can be based on the field of view at the time particles are generated or monitored from the first location and / or multiple locations for each current frame and the immediately preceding frame in the series of frames, or at the time the beam first impinges on the first location. In some embodiments, the determination can be made or evaluated once, multiple times, or continuously throughout some or all of the acquisition of the composite image frame. This can advantageously allow for changing modes before the current frame is fully acquired, as described in more detail below.

[0087] Having the beam traverse the region in a shorter total time can be understood as changing the scan speed, specifically increasing it in this case, depending on whether the field of view is the same. It will be understood that a shorter total time refers to a total traversal time for the first traversal path that is shorter than the total traversal time for the beam to traverse the second traversal path. In some embodiments, the reduced total time is achieved at least in part by having the beam traverse the first traversal path at a faster average speed than the average speed for the beam to traverse the second traversal path. However, additionally and alternatively, the difference in traversal time can be achieved at least in part by using a different traversal path, such as a first traversal path having a shorter overall length than the overall length of the second traversal path.

[0088] It will be appreciated that a changing or different field of view can include either or both of the field of view being moved across or relative to the sample plane and the field of view being enlarged or reduced in size, which can be understood as, for example, a change in magnification level.

[0089] The beam's traversal of an area can typically include any one or more of a "raster" scan pattern, a "skewed raster," and a "serpentine" pattern as shown in FIG. 1 , as well as many other types of scan paths along which a focused beam can traverse a field of view. The conditional application of different average traversal speeds based on a change in the constituent field of view described above can be understood conversely as the beam being caused to traverse an area at a slower average speed when the constituent microscope field of view is the same as the microscope field of view for the immediately preceding image composite frame in the series of composite image frames than the average speed at which the beam traverses the area when the constituent microscope field of view is different from that for the immediately preceding composite image frame in the series of composite image frames. In the context of the present disclosure, the average speed at which the beam is caused to traverse an area can be understood or defined in terms of the total construction time or intended total time required or expected to traverse the area at a given speed if that mode is applied to acquire the entire frame. In some embodiments, the speed at which the intersection between the beam and the sample surface moves across the surface is not constant. For example, the scanning process can include moving between discrete locations on the surface and dwelling there to monitor particles from those locations. "Fast" and "slow" traversal or scanning modes can correspond to relatively short and long pixel dwell times, respectively. These dwell time differences can occur for one, more, or each of the locations monitored and the corresponding pixel values ​​obtained while operating under a given mode. Scanning modes that spend more time collecting signals from traversal locations on the sample and correspondingly collect more data for these locations advantageously provide a higher signal-to-noise ratio.

[0090] More generally, the traverse speed can be configured to vary throughout the scanning process when operating in a given mode or at a given speed, for example, in a raster scanning process, the beam preferably moves faster between the end of one line and the start of the next line as it traverses the lines in the pattern.

[0091] Typically, the "fast" and "slow" average traverse speeds are configured such that, taking into account speed changes during a scan as described above, the total time that would be required to traverse the entire area at the faster speed corresponding to the first mode in some embodiments is less than the total time that would be required to traverse the entire area at the slower speed when operating in the second mode in some embodiments. Furthermore, the traverse patterns for the first mode and the second mode may be the same or different, and if different, this scan pattern difference can contribute to differences in the average traverse speeds.

[0092] Faster and slower traversal speeds, which are conditionally applied depending on whether the field of view is changing or unchanged, respectively, can be defined using first and second traversal durations T1 and T2, where T1 is less than T2 accordingly. Typically, however, these constituent total times need not necessarily be the same for any two composite image frames in a series of composite image frames. In other words, these times are preferably defined individually for a given frame such that the above-mentioned inequality relationship applies for that frame, while for any two given frames in a series, T1 and T2 can each be the same or different.

[0093] Typically, the traversal speed is set at the beginning of acquiring a composite image frame. The speed may not be explicitly set as each frame is acquired, but may have a value, parameter, or configured speed that is retained or signaled, preset, stored, or maintained since the previous composite image frame was acquired. Furthermore, as discussed in more detail below, the speed may be adjusted during the acquisition of a given composite image frame.

[0094] The number of locations from which the first and second sets of particles are monitored can remain constant or can be different for any two given composite image frames within a series of composite image frames, and thus each of the first and second plurality of locations can be different in number for each composite image frame acquisition sequence.

[0095] The sets of values ​​derived from the monitored particles generated at the second plurality of locations can be one or more sets of values. Preferably, however, the sets include one or more values ​​derived from the monitored particles. In a preferred embodiment, a pixel in the second image frame can include each of a plurality of sets of values ​​representing the particle spectrum emitted from the second plurality of locations.

[0096] Typically, the second detector is an X-ray detector. Thus, the second set of particles are X-ray photons, and the set of values ​​for pixels in the second image frame represent an X-ray spectrum. In some embodiments, the derived set of values ​​conditionally maintained in step (d) can be understood as a set of values ​​derived from the particles monitored in step (c).

[0097] To increase the collection solid angle for X-rays, an arrangement can be used in which an X-ray detector is positioned at a position between the beam source and the sample. The X-ray detector can have one or more sensor portions facing the sample and at least partially surrounding the incident charged particle beam. In particular, in a preferred embodiment, the X-ray detector is mounted below the pole piece of the microscope's particle beam lens, e.g., electron lens. In this context, the term "below" can be understood to mean closer to the sample than the pole piece with respect to a position along an axis parallel to the beam or a position along an axis parallel to the beam. Preferably, the X-ray detector is mounted directly below the pole piece. In this way, the solid angle over which the second detector is sensitive to X-rays can be increased to improve the signal-to-noise ratio of the X-ray signal. A secondary pole piece detector close to the sample and / or at least partially surrounding the beam facilitates this increase in the collection solid angle. Therefore, preferably, the X-ray detector has one or more sensor portions facing the sample and at least partially surrounding the beam. Typically, the sensor portions include corresponding sensor surface portions, which preferably face the sample in the sense that they are positioned and / or directed toward the sample. The portions at least partially surrounding the beam can be understood as the portions being distributed around the beam. Thus, one or more sensor portions can be present on all sides of the beam and can be continuous, such as an annulus, or discontinuous. For example, the detector can be positioned in the form of a plurality of individual sensor surfaces spaced apart around the beam. The sensor surface can be understood as an active surface adapted to receive incident particles and generate a signal output accordingly.

[0098] However, it will be appreciated that the sensor portions do not necessarily need to surround the beam to achieve an improved solid angle for signal collection. Other arrangements are envisioned in which the size of the sensor surfaces achieves a large solid angle in combination with the intended working distance of those surfaces, and hence the separation between the plane in which one or more sensor portions are located and the sample surface, particularly at the point of incidence of the beam.

[0099] The size and / or shape of the entire X-ray detector surface, regardless of whether this surface includes one or more sensor portions, is preferably configured so that the total solid angle subtended by one or more sensor portions at the location where the beam strikes the sample is greater than 0.3 steradians when the working distance, and hence the separation between the sensor plane and the beam spot, or the minimum or median separation between any portion of the X-ray sensor surface and the beam spot, is less than or equal to 6 mm. More preferably, the solid angle is greater than 0.4 steradians over this working distance range. Additionally or alternatively, to provide an improved X-ray signal, the X-ray sensor surface may be configured to be less than 10 mm. 2 greater than 20 mm, preferably 2 greater than 30 mm, and even more preferably 2 , 40mm 2 , or 50mm 2 The total area may be greater than

[0100] In some embodiments, the conditionally applied "combining" function in step (d) can include, as described above, the values ​​of corresponding pixels of one or more second image frames that precede the current composite image frame and have the same microscope field of view as the current composite image frame. The set of values ​​of corresponding pixels of one or more preceding second image frames that are used typically depends on which or how many composite image frames have the same field of view as the current composite image frame. Preferably, the above-described combining process uses all derived value sets previously acquired that have the same field of view as the current composite image frame. In some embodiments, the combining can be applied cumulatively, for example, as each composite image frame is acquired. The second image frame that precedes the current composite image frame and has the same microscope field of view as the constituent microscope field of view referred to in step (d) of the frame acquisition process can be understood as one or more second image frames acquired as part of the step of acquiring one or more respective composite image frames preceding the current composite image frame. The constituent microscope field of view referred to in step (d) can also be understood as the current microscope field of view. In various embodiments, the current configuration microscope field of view can be defined as the field of view configured at the start of acquisition of the current composite image frame or at any predetermined time during acquisition. In some embodiments, the current configuration microscope field of view can be defined as the instantaneous configuration field of view at a given time during, for example, acquisition of a composite image frame. Thus, in such embodiments, this instantaneous field of view can be changed throughout acquisition of the composite image frame, and thus, in some embodiments, the acquisition mode or configuration traversal speed can be changed in response to changes in field of view that occur during acquisition of a given composite image frame.

[0101] During a given composite image frame acquisition cycle, the function of step (d) is preferably performed for each pixel of the second image frame. In this way, all pixels of the frame obtained in step (c) are subjected to the conditional "combining" or "refreshing" process, thereby maximizing the improvement of S / N and sample navigation. However, in some embodiments, one or more pixels of a given second image frame can be excluded from this processing step. Thus, the function of step (d) is typically performed for each of the plurality of pixels contained by the second image frame, rather than necessarily for all pixels contained by the second image frame. In other words, in some embodiments, or for one or more frames in a series of frames, the second image frame includes additional pixels in addition to the plurality of pixels. This applies analogously to embodiments in which conditional pixel value combinations are additionally applied to the first image frame, and to embodiments involving pre-setting of acquisition mode parameters, as described later in this disclosure.

[0102] Typically, combining the first and second image frames to generate a composite image frame includes combining the first image frame with a second image frame having pixels with value sets that are either the retained value sets or the combined value sets that replace them, derived during acquisition of the current composite image frame, when the field of view is different from or the same as the field of view of the immediately preceding composite image frame, respectively.

[0103] During acquisition of a composite image frame, steps (b) and (c) are typically performed substantially simultaneously. This can be understood as the entire process of monitoring the first set of particles and the entire process of monitoring the second set of particles occurring simultaneously or substantially simultaneously with respect to the entire region. This substantial simultaneity is such that the first and second image frames provide first and second spatial representations of the region captured substantially simultaneously. However, the monitoring duration and timing for individual locations of the first and second plurality of locations may vary between the first and second detectors, between particle sets, and between locations from which the first and / or second particles are detected. For example, various and / or variable sampling rates and pixel resolutions may be used. Thus, the steps of monitoring particle sets generated at individual ones of the first and second plurality of locations may or may not be simultaneous with the entire collection of signals by the first and second detectors.

[0104] The method can be used to analyze samples in any charged particle beam instrument that uses a focused particle beam. Accordingly, the term microscope is used herein to refer to any such instrument. Typically, the microscope is an electron microscope, where the charged particle beam is an electron beam. In other embodiments, the charged particle beam is an ion beam.

[0105] Furthermore, real-time display of the combination of the first image type and the second image type in the composite image frames as the series of composite frames are acquired can be performed seamlessly "on the fly" without pausing or interrupting the user's navigation of the sample.

[0106] It will be understood that the term "particle" as used in disclosing the present invention includes particles of matter, including subatomic particles such as ions and electrons, as well as particles that represent quanta of electromagnetic radiation and thus photons, e.g., X-ray photons. In some embodiments, for example, the charged particle beam is an ion beam, which will emit from the sample and typically generates resultant particles including electrons and ions that can be monitored by a detector.

[0107] This method is particularly advantageous in embodiments where the second detector is of a type that monitors a signal that typically has a lower signal-to-noise ratio under given microscope conditions than the signal that the first detector is designed to monitor. In such embodiments, the combination of the first and second detectors can be selected so that the first detector provides a high-signal-to-noise image signal at high speed, allowing a user to quickly inspect various regions of the sample. Typically, upon moving the field of view across various regions of the sample or navigating around the sample by adjusting the field of view elsewhere, for example, by magnification, the second, lower-signal-to-noise detector can provide a first image frame of inferior quality compared to the first image frame acquired by the higher-signal-to-noise first detector. However, when the user stops changing the field of view, for example by ceasing to adjust the stage position or microscope conditions to maintain a fixed field of view, a repeat measurement of the same pixel or the same location on the sample can be acquired by the detector, and thus by combining pixel data from the second image frame with corresponding pixel data of a previously acquired second image frame corresponding to the same location within the sample, the lower signal-to-noise ratio of the image acquired using the second detector can be mitigated and a higher quality image derived from the data acquired by the second detector can be obtained.

[0108] As discussed above in this disclosure, faster scan rates applied when the field of view is changing provide the advantage of allowing the microscope operator to more effectively track features of interest while navigating the sample due to the faster frame rate at which the resulting composite image frames can be displayed. The signal-to-noise ratio (SNR), particularly for the second detector, is typically low at faster scan rates. For this reason, the use of such higher speeds is considered unfeasible in the prior art. However, the inventors have surprisingly discovered that when the field of view is rapidly changing, a significant advantage is realized by degrading the SNR in favor of easier navigation. The present method can provide this advantage while allowing a higher SNR to be achieved for a static field of view by switching between faster and slower scan rates.

[0109] In some embodiments, each image frame includes a plurality of pixels corresponding to a plurality of locations within the region and having values ​​representing monitored particles generated thereat. For example, the pixel values ​​may represent the intensity of particles generated at the corresponding locations as monitored by the detectors. As a result, in some embodiments, the composite image frame may provide data for each of the plurality of pixels representing particles generated at the corresponding locations within the region and monitored by each of the first and second detectors. In other embodiments, such as when the image frame is an electron backscatter diffraction image, the pixel values ​​may not directly represent particles generated at these locations, but may instead be computationally derived therefrom.

[0110] According to a second aspect of the present invention there is provided a method of analysing a sample in a microscope, the method comprising: acquiring a series of composite image frames using a first detector and a second detector different from the first detector, the acquiring of the composite image frames comprising: a) causing the charged particle beam to traverse a sample area corresponding to a constituent microscope field of view, wherein when the constituent microscope field of view is different from that for an immediately preceding composite image frame in the series of composite image frames, the beam traverses a first traversal path over the area in a total time that is shorter than the total time that the beam traverses a second traversal path over the area when the constituent microscope field of view is the same as that for an immediately preceding composite image frame in the series of composite image frames; b) monitoring with a first detector a resulting first set of particles generated within the sample at a first plurality of locations within the region to obtain a first image frame including a plurality of pixels corresponding to the first plurality of locations and having values ​​derived from the monitored particles generated thereat; c) monitoring with a second detector a second resulting set of particles generated within the sample at a second plurality of locations within the region to obtain a second image frame including a plurality of pixels corresponding to the second plurality of locations and having respective sets of values ​​derived from the monitored particles generated thereat; d) maintaining a derived set of values ​​for the pixel in the second image frame for use in the composite image frame when the constituent microscope fields for each of a plurality of pixels comprised by the second image frame are different from those for the immediately preceding composite image frame in the series of composite image frames, and when the constituent microscope fields are the same as those for the immediately preceding composite image frame in the series of composite image frames, combining the derived set of values ​​for the pixel with a derived set of values ​​for a corresponding pixel in each of one or more preceding second image frames in the series of composite image frames whose microscope fields are the same as the constituent microscope fields to obtain a combined pixel value set having an increased signal-to-noise ratio; and e) combining the first image frame and the second image frame to generate a composite image frame that provides data derived from particles generated at first and second pluralities of locations within the region and monitored by each of the first and second detectors; The obtaining step includes: displaying the series of composite image frames in real time on a visual display that is updated to show each composite image frame in sequence; Includes.

[0111] The implementations and advantageous features described herein may be used in a method according to the first, second or third aspect described in this disclosure, or any of their specific embodiments.

[0112] In the context of the second aspect, it will be understood that having the beam traverse a first traversal path over an area in a total time that is shorter than the total time for traversing a second traversal path over the area typically represents a first total time required for the beam to traverse the entire first traversal path in accordance with a first set of traversal conditions that is shorter than a second total time required for the beam to traverse the entire second traversal path in accordance with a second set of traversal conditions. In other words, the traversal can be along either of two paths and in accordance with either of two respective sets of traversal conditions.

[0113] Traversing a path generally refers to the beam or beam spot moving along at least a portion of a given traversal path. Typically, the entire first path or the entire second path is traversed if the mode remains unchanged for the duration of acquiring a composite image frame, or more specifically, for the duration of causing the beam to traverse an area to acquire a composite image frame. However, not all of the first or second path is traversed if, for example, the mode is switched during traversal of an area.

[0114] One approach to increasing the overall speed of traversal of the region is to sample data from one or both detectors at fewer locations or less frequently during the traverse. This can be thought of as reducing the spatial resolution at which the monitored particle data is captured. Typically, faster updates of the display can occur by accelerating the acquisition of each composite image frame by acquiring fewer data samples collected for one or both of the first and second image frames, corresponding to generating fewer pixels in a given image frame. In this manner, a series of composite image frames can be displayed at a higher frame rate. Thus, in some embodiments, causing the beam to traverse the first traversal path, or in some embodiments, the region, in a shorter total time or at a faster average speed, includes reducing the total number of locations within the region where the first generated particle set is configured to be monitored to less than the total number of locations within the region where the first generated particle set is configured to be monitored when the constituent microscope field of view is the same as that for the immediately preceding composite image frame in the series of composite image frames. Thus, the scan speed can be varied depending on whether the field of view is the same as that for the immediately preceding frame. The total number of locations within a region is typically an instantaneous configuration number that can be thought of as the intended total number for the region in a given mode, and thus can typically be understood as being similar to the overall rate of traversal in terms of traversing and monitoring the entire region.

[0115] However, the actual number of locations need not necessarily be the same as the number of configurations, for example, when the frame acquisition mode is changed from "fast" mode to "slow" mode such that the total number of configurations of locations monitored during frame acquisition increases from a smaller total to a larger total. It will be appreciated that in the event of such a mode or speed change during frame acquisition, the actual average speed obtained by traversing and monitoring will typically be different from both the "fast" and "slow" configuration speeds, and the actual total number of locations from which signals are collected in steps (b) and (c) will typically be different from both the larger and smaller configuration numbers. Typically, the actual speed and number of locations obtained will be intermediate between these two configuration values.

[0116] It will be appreciated that the configuration of a reduced number of locations that may be implemented in these embodiments may be thought of as switching to a mode in which the number of sampling locations or the temporal and / or spatial sampling frequency is reduced. It will also be appreciated that the first generated particle set is configured to be monitored during step (b).

[0117] In some embodiments, each of the first and / or second plurality of locations can be defined by a finite area within the region. For example, each of the respective plurality of areas from which the first and second particle sets to be monitored originate can define these locations. Typically, each of the fewer plurality of locations when the "fast" acquisition mode is applied is therefore defined by a larger area than the larger plurality of locations or corresponding area for such detector or particle set when the "slow" mode is applied. As a result of traversing fewer locations than when the field of view is unchanged, this fast traversal mode reduces the number of pixel configurations, as described above.

[0118] Those embodiments that include changing the number of locations and / or corresponding pixels can be understood to conversely include causing the beam to traverse the region at a slower average speed when the constituent microscope fields of view are the same as for the immediately preceding composite image frame in the series of composite image frames, increasing the total number of locations within the region configured to monitor the first generated particle set to more than the total number of locations within the region configured to monitor the first generated particle set when the constituent microscope fields of view are different from those for the immediately preceding composite image frame in the series of composite image frames.

[0119] Furthermore, instead of making such a change to the number of locations monitored in step (b), a similar function can be applied to step (c) during frame acquisition. Thus, in some embodiments, causing the beam to traverse the region or first traversal path in a shorter total time or at a faster average speed includes reducing the total number of locations within the region at which the second generated particle set is configured to be monitored to less than the total number of locations within the region at which the second generated particle set is configured to be monitored when the composite microscope field of view is the same as that for the immediately preceding composite image frame in the series of composite image frames.

[0120] Applying a different acquisition speed or acquisition mode can include shortening the time required to acquire data for each pixel instead of or in addition to reducing the resolution or number of pixels. Acquiring derived values ​​more quickly in a "fast mode" when the field of view is changing allows for a faster refresh rate at the expense of signal-to-noise. Conversely, in a "slow mode," because refresh rate is less important when movement or other changes to the field of view are interrupted during sample navigation, taking a longer time to acquire these pixel values ​​when the field of view is unchanged improves the signal-to-noise ratio for the acquired data. Thus, in some embodiments, forcing the beam to traverse the region in a shorter total time or at a faster average speed includes shortening a configuration monitor duration, which can be understood as a configuration average over the entire region and can typically be applied instantaneously at a given time, during which the first set of particles generated at each of the first plurality of locations is monitored. Similarly, as described above, causing the beam to traverse the region at a slower average velocity can include increasing the configuration monitor duration during which the first set of particles generated at each of the first plurality of locations is monitored.

[0121] The monitoring duration can also be changed for particles monitored by the second detector. Thus, in some embodiments, causing the beam to traverse the region or first traversal path in a shorter total time or at a faster average speed includes shortening the constituent monitoring duration during which the second set of particles generated at each of the second plurality of locations are monitored.

[0122] As mentioned above, yet another way in which changes in total traversal time can be implemented is by changing the length of the traversal path, which in some embodiments includes adjusting the size, extent, or coverage area of ​​the traversal path.

[0123] The construction field of a microscope can be thought of as a "default" field of view that the microscope is configured to cover at some point during the acquisition of a composite image frame, typically at the beginning. However, it will be understood that the field of view actually used for some or all of the frames during the acquisition of a frame in a series of frames need not necessarily be the same as the construction field of view. Thus, the construction field of view can continue to be used to determine whether the field of view is conceptually moving or stationary and / or whether a "fast" or "slow" acquisition mode should be used, while still causing the microscope to capture images using a modified field of view. Thus, the area covered by or defined by the extent of a given traversal path may correspond to only a portion of the field of view constructed for a given composite image frame. In that regard, the construction field of view can be understood as being constructed with respect to the composite image frame, rather than necessarily defining the extent of the composite image frame.

[0124] The configuration field is typically configured by the user, although some automation of the sample and / or beam deflection offsets is possible to at least partially automate navigation of the configuration field around the sample.

[0125] Exemplary embodiments may include having either or both of the first and second traversal paths cover or substantially cover the entire constituent field of view of the microscope. However, it is also contemplated that the field of view may be modified to change the time required to scan the field of view as part of acquiring a composite image frame, or, in other words, the time required to traverse a traversal path that covers the field of view. The term "cover" as used in this context may be understood as "extending across." Preferably, a traversal path "covering" a field of view indicates that the path has a spread and pattern configured to monitor particles from all or substantially all portions of a sample within the field of view during its traversal by the beam. However, this "coverage" may alternatively be understood as the path being congruent with the field of view and, therefore, defining an area and / or boundary that coincides with the field of view.

[0126] A "fast" or "dynamic" acquisition mode can include, for example, enabling a first traverse time and a corresponding first traverse pass that are shorter than a second traverse time and a corresponding second traverse pass, respectively. Thus, the first traverse pass can have a smaller coverage area than the second traverse pass. This can be understood, for example, as corresponding to the "smaller raster" configuration mentioned above, or any scanning pattern that covers only a sub-area on the sample plane that is smaller than the area corresponding to the component field, and thus has a reduced area. In this manner, in some embodiments, the first traverse pass covers a modified field of view, which is a field of view modified with respect to the component field of the microscope for a given frame. Typically, in such embodiments, the modified field of view corresponding to the first traverse pass is smaller than the component field, and is preferably partially or entirely covered within it. Thus, the modified field of view can be understood as corresponding to only a portion or sub-area of ​​the area of ​​the sample that would be covered by the component field. Thus, typically, image frames captured when operating in such a "fast" mode represent a reduced area than image frames captured in the alternative "slow" mode. For this reason, the resulting smaller composite image frames within a series of composite image frames are preferably displayed on the visual display at a correspondingly smaller size, for the purpose of maintaining continuity of display size and magnification between frames in the series of composite image frames.

[0127] Such an embodiment can advantageously provide faster image acquisition and display speeds when the component field of view is changing than when it is not, by excluding a portion of the component field of view for frames obtained when the component field of view is changing, and preferably capturing data from anywhere in the entire component field of view when the component field of view is not changing.

[0128] In some embodiments, the field of view applied when capturing frames can alternatively or additionally be enlarged to operate in a "slow" or "static" mode. Thus, in some embodiments, the second traversal path encompasses a modified field of view having an extent that is larger than, and preferably partially or entirely encompasses, the constituent field of view. Thus, the modified field of view can correspond to a longer traversal path than the constituent field of view, requiring a longer traversal time than the constituent field of view.

[0129] The adaptation of the traversal time or traversal speed depending on whether the field of view is changing or unchanged can be performed using an acquisition mode parameter. Thus, in some embodiments, acquiring the series of composite image frames is performed according to an acquisition mode parameter such that, when the acquisition mode parameter is equal to a first value, the beam traverses a first traversal path or region at a faster average speed than the average speed at which the beam traverses a second traversal path or region when the acquisition mode parameter is equal to a second value, the acquisition mode parameter being set to the first value when the constituent microscope fields of view are different from those for the immediately preceding composite image frame in the series of composite image frames, and being set to the second value when the constituent microscope fields of view are the same as those for the immediately preceding composite image frame in the series of composite image frames. Conversely, in such embodiments, typically, when the acquisition mode parameter is equal to a second value, the beam traverses the region at a slower average speed than the average speed at which the beam traverses the region when the acquisition mode parameter is equal to the first value. The mode parameter can thus be used to indicate whether a "fast" or "slow" acquisition mode configuration is to be applied, corresponding to higher and lower average traverse velocities, respectively. Thus, according to some embodiments, the acquisition mode parameter can be equal to either the first mode parameter described with respect to the first aspect in particular and / or the second mode parameter described with respect to certain advantageous embodiments of the first aspect. However, the acquisition mode parameter described with respect to embodiments of the second aspect can be separate and / or independent from the first and second mode parameters described above. Similarly, the first and second values ​​of each of the mode parameters described above and those described below can be the same or different, respectively.

[0130] Typically, the value of the mode parameter is set or at least maintained at the beginning of the acquisition process for each composite image frame. In this way, the traversal speed can be advantageously changed at least on a frame-by-frame basis. However, in some embodiments, this mode-switching functionality is further advantageously applied during acquisition of a composite image frame by adjusting the acquisition mode and instantaneous composite average traversal speed in response to changes in the composite microscope field of view that occur while the frame is being acquired. Thus, in some embodiments, step (d) is performed during said traversal of the field by the beam and said monitoring of the first and second particle sets, and further includes, for each of a plurality of pixels encompassed by the second image frame, setting the acquisition mode parameter to a first value if the microscope field of view is different from that for the immediately preceding pixel of the second image frame and the acquisition mode parameter is equal to a second value, or setting the acquisition mode parameter to a second value if the constituent microscope field of view is the same as that for the immediately preceding pixel of the second image frame and the acquisition mode parameter is equal to the first value.

[0131] It will be appreciated that where the constituent fields of view are changed in intermediate frames, typically the region corresponding to the field of view can be considered to correspond to the field of view at the start of the frame being acquired or at a given or predetermined time point being acquired. The field of view can be considered to correspond to more than one field of view or a combination of fields of view that encompass portions of the sample surface covered within any field of view passed through when the microscope is moved, configured to move, or otherwise changed during frame acquisition.

[0132] Applying an intermediate frame acquisition mode parameter switch can advantageously affect the traversal of the beam across subsequent locations in the plurality of locations. This switch can therefore affect the speed at which subsequent pixels in the second image frame are acquired. The condition of whether the constituent microscope field of view is different from that for the immediately preceding pixel can be evaluated with respect to the time at which the value set for a given pixel is derived or processed, and a value set for the immediately preceding pixel in the frame is derived if the field of view is different from the field of view at this time. A different constituent microscope field of view in this context may include, for example, the absence of an immediately preceding pixel when the current pixel being processed or for which a value set is being acquired is the first pixel in the second image frame. This field of view difference between pixels can be understood as the field of view being changed between the processing and / or acquisition of the immediately preceding pixel and the processing and / or acquisition of the current pixel. An acquisition mode parameter equal to a second value can be understood as an additional condition that the mode parameter is set to "slow" mode.

[0133] A pixel defined as preceding or immediately preceding in the second frame typically refers to a pixel that appears before the current pixel in the order in which pixel values ​​are derived and / or processed. Typically, pixels are processed in an order corresponding to the order in which signals were acquired from locations within the region. Based on these conditions, setting an acquisition mode parameter equal to a first value is typically performed to generate an increase to the average traversal velocity. It will therefore be understood that changing the mode parameter in such an embodiment depends on both a comparison of the constructed fields of view for the two pixels and the current mode parameter value.

[0134] With respect to the above-mentioned condition that the constituent microscope field of view for the current pixel is the same as for the immediately preceding pixel in the second image frame, this condition can be understood as a condition that the movement or change of the field of view has stopped, and therefore there is no change between the immediately preceding pixel and the current pixel being processed or acquired. Furthermore, setting the acquisition mode parameter equal to the second value also depends on the parameter being further set, typically to "high speed" mode. This parameter setting equal to the second value is typically implemented to generate a lower average traversal speed.

[0135] The ability to change acquisition modes midway through acquiring an individual composite image frame in such an embodiment can provide the advantage of slowing beam traversal when movement or changes in the field of view are stopped, resulting in higher signal-to-noise data being acquired sooner than if the speed change were only made at the beginning of the next frame. This advantage is particularly evident in situations where changes to the field of view are discontinued shortly after a composite image frame begins to be acquired in "fast" or "dynamic" mode. In such situations, switching deflection data at higher resolution may need to be delayed until substantially the entire frame acquisition duration data is acquired. Furthermore, in the absence of this mid-frame switching at such times, there may be no signal-to-noise improvement until the next frame can be initiated after this delay, applying the "slow" or "static" acquisition mode.

[0136] Similarly, a significant advantage gained by accelerating traversal in intermediate frames when the field of view begins to change is that the increased refresh rate occurs sooner, resulting in more efficient sample navigation for the user or observer. It will be appreciated that in some embodiments, particularly when a change in mode parameters changes the number of constituent pixels or constituent image frame resolution before monitored data for the composite image frame is obtained, it may be beneficial to process the affected image frames, for example, to approve the appearance and clarity of the frames for when the frames are viewed by the user.

[0137] To perform such image processing, several options are available for constructing a composite image frame for display, such as various techniques for processing data acquired midway through the traverse before a mode change. For example, data acquired at low resolution in "dynamic" mode for a small number of pixels can be interpolated at intermediate locations to provide equivalent values ​​on a grid of pixels with higher resolution corresponding to those in an image frame obtained in "static" mode. In some embodiments, similar interpolation can be applied only to pixels in the composite image frame.

[0138] In light of the above-described advantages, it will be appreciated that it is advantageous to effect a traverse speed change immediately in response to a transition between the acquisition of intermediate frames between a changing field of view and an unchanged field of view. In this way, advantageous effects can occur more quickly. Typically, in certain embodiments, the above-described setting of the acquisition mode parameter equal to the first or second value is performed before monitoring particles generated within the sample at a location within the region corresponding to or represented by the immediately next pixel or immediately next processed pixel in the second image frame. The directness of these mode changes is reflected in the responsiveness of refresh rates, score image resolution improvements, and / or signal-to-noise ratio improvements. It will be appreciated that in some embodiments, acquiring the first image frame may include some field-dependent pixel processing. In particular, this may include processing similar to that applied to the second image frame to enhance signal-to-noise ratio by combining data for corresponding pixels in multiple image frames having the same field of view. Thus, in some embodiments, acquiring the composite image frame further includes, for each of a plurality of pixels included by the first image frame, retaining the derived value of the pixel in the first image frame for use in the composite image frame when the constituent microscope fields are different from those for the immediately preceding composite image frame in the series of composite image frames, or, when the constituent microscope fields are the same as those for the immediately preceding composite image frame in the series of composite image frames, combining the derived value of the pixel with the derived value of the corresponding pixel in each of one or more second image frames preceding in the series of composite image frames and having the same microscope fields, to obtain a combined pixel value having an increased signal-to-noise ratio. Conditions under which the constituent microscope fields are different from those for the immediately preceding composite image frame in the series of composite image frames can include, for example, the absence of an immediately preceding image frame when the current frame is the first frame in the series of composite image frames, as discussed above.

[0139] In addition to changing the acquisition mode to a "static" mode to improve the signal-to-noise ratio of the acquired data, in some embodiments, the process includes aggregating or sorting groups of pixels, typically x-ray pixels, in the second image frame to form an image having fewer pixels for processing and display. It will be appreciated that such sorted pixels will have improved signal-to-noise. Accordingly, in some embodiments, acquiring the composite image frame may further include grouping together sets of pixel values ​​of one or more subsets of pixels in the second image frame to obtain "superpixel" sets having one or more respective sets of aggregate pixel values ​​or values. For example, each aggregate value set may preferably correspond one-to-one to a pixel subset. In such embodiments, acquiring the composite image frame may include replacing each of one or more subsets of pixels in the second image frame with an aggregate pixel or "superpixel" having a value set equal to or corresponding to the pixel subset of the respective set of aggregate pixel values.

[0140] Typically, each of the first and second detectors observes a region of the sample under or according to a set of configured microscope conditions. In each of the first and second acquired image frames, each pixel can have a value that represents or corresponds to a count of particles generated at the location on the sample corresponding to that pixel and monitored by the detector, or can have a set of values ​​that indicate or are indicative of, for example, the energy distribution of these monitored particles. In some embodiments, one or more pixels in either or both of the first and second image frames can have a set of values ​​that typically correspond to a histogram of photon energies acquired at the corresponding location, which can correspond to a small area on the sample surface. It will be understood that the number of values ​​in each set can vary depending on the monitored photon energy.

[0141] In some embodiments, during acquisition of a composite image frame, the step of combining pixel values ​​for each second image frame with corresponding pixel data of a previously acquired second image frame corresponding to the same location within the sample can be performed automatically, relying on the field of view being the same as the field of view for the previously acquired second image frame. Although it is intended that the field of view, and therefore the constituent fields of view, be stationary, if there is some small position drift due, for example, to thermal effects on the stage mechanism or beam deflection electronics, the position difference between successive image frames can be tested by cross-correlation of successive electronic images (e.g., as described in https: / / en.wikipedia.org / wiki / Digital_image_correlation_and_tracking), and this measurement drift can be used to ensure that pixel values ​​are combined only for successive frames whose data comes from the same location on the sample.

[0142] During the combination process for pixel values ​​for a second image frame, the constituent microscope conditions are the same as those for the immediately preceding second image frame, which may have been stored, for example, in memory or any type of machine-readable medium, and this can be considered to mean that the resulting signal content for the pixel is the same. Similarly, in an "accumulation" mode, where data corresponding to a second (or first) image frame is stored, for example, for use in the next frame in a series of frames, it will be understood that pixel data may not necessarily be stored for all positions in the frame. For example, if no changes are made to the focus, astigmatism, magnification, or acceleration voltage of the electron beam or other type of charged particle beam between the acquisition of the second image frame and the immediately preceding image frame, the measurement for a pixel will typically include a repeat measurement of the immediately preceding pixel value for that location on the sample, unless the sample or scanning position has moved, and thus can be used to improve the signal-to-noise ratio for that pixel. In other words, the constituent microscope conditions being the same can be considered to mean that the microscope conditions under which the second image frame was acquired were the same as those under which the previous second image frame was acquired.

[0143] Typically, the real-time display of composite image frames involves processing and displaying image data as it becomes available, so that image frames are available substantially instantaneously. In this manner, a user can use the real-time composite image frames as feedback to guide navigation around a specimen. Examples of suitable approaches for user interaction and methods for synthesizing, formatting, and displaying composite image frames in such live navigation are described on pages 8-10 of WO 2019 / 016559 A1. Techniques such as those described in WO 2012 / 110754 A1 can be used to combine image frames into a colored composite image. "Real-time" display can be understood as having substantially no discernible delay between a user initiating a navigation action and that action being represented on a visual display in the form of a moving or video sequence that constitutes a series of displayed composite image frames.

[0144] For example, a change in field of view can occur by the user changing magnification so that the focused electron beam is deflected over a smaller or larger area on the sample. Alternatively, the user can move the stage or holder supporting the sample so that the sample is moved relative to the focused electron beam, and therefore the field of view reached by the deflected electron beam, moves to a new area on the sample surface. The field of view can be changed by changing the beam deflection so that the focused electron beam is directed across a different area on the sample. Microscope conditions such as beam voltage can be changed, which will change the contrast of the electron image as well as the information content of the additional signal. In either of these cases, the immediate replacement of existing image data with newly acquired data allows the user to verify the new field of view within a single frame time. If the frame time is short enough, the user will be able to use the visual display unit to track features on the surface of the sample while changing the field of view.

[0145] After the acquisition of any frame of data, if the field of view or microscope conditions are the same as for the immediately preceding frame, the acquisition mode typically changes to one that improves the signal-to-noise ratio of the displayed image. This improvement in signal-to-noise ratio may be due to an increase in the time spent accumulating data for the frame and / or signal averaging or accumulation of data from successive frames. Thus, in some embodiments, as a user moves the field of view across the sample surface to find a region of interest, they will be able to see a combination of the shape and morphology of the sample, as shown in the electronic image, and complementary information about the material composition or material properties, as shown in the additional signal. Once the region of interest is within the visual image, the user can stop moving, and the signal-to-noise ratio will rapidly improve without any user interaction or interruption of the analysis session.

[0146] The inventors have found that even if the additional signal provides only a single frame of data with poor S / N, in many cases the image is sufficient to provide a rough location of the region of interest.

[0147] Furthermore, when successive frames are displayed while the field of view is changed, the noise in each frame is different, and the eye / brain combination produces a temporal averaging effect, allowing the user to recognize moving features that may not be readily visible within a single data frame. Once the user has identified a feature of interest, signal averaging can begin automatically when movement is stopped, which will rapidly improve the visibility of the feature after several frames have been recorded.

[0148] The inventors have recognized that the ability to identify moving features in successive frames of high noise data can be further enhanced by increasing the average speed at which the beam is caused to traverse the area in order to increase the frame rate at which new composite images can be generated for display. While increasing the frame rate reduces the effective acquisition time per pixel for monitoring second particles and degrades the signal to noise ratio, the speed can be optimized to allow fast moving features to be imaged without blurring, allowing the user to essentially track the features.

[0149] The inventors have also found that it is much more difficult for the eye / brain to distinguish fine details in a moving image when the field of view is changing. Therefore, the displayed image can have a lower resolution (fewer pixels) without affecting the user's ability to track moving features when the field of view is changing. To generate a second image frame with a lower resolution, sets of pixel values ​​for adjacent pixels can be aggregated or summed to provide a set of pixel values ​​corresponding to a single "superpixel" representing a larger area on the sample. A second image frame can then be generated that covers the same region on the sample and uses "data sorting" to provide a fewer number of "superpixels." The same effect can be achieved by monitoring second particle data while the electron beam traverses an area corresponding to the area covered by the "superpixel." Alternatively, the electron beam can be positioned on a series of more loosely spaced grid points to obtain data for the second particles monitored at fewer pixel locations. Because each set of pixel values ​​can require significant computational cost to derive values ​​that will be used to generate a composite image for display, reducing the number of pixels per frame can substantially reduce overall computer time. Furthermore, when the total acquisition time is substantially allocated among a smaller number of pixels for the same frame time, each set of pixel values ​​will produce a derived value for a composite image with an improved signal-to-noise ratio compared to an image with more pixels. Although the number of pixels per frame can be reduced, the visual display image can be kept the same size by known techniques such as pixel duplication, interpolation, or "upscaling," which maps image data having a given pixel resolution onto a visual display having a different pixel resolution. Furthermore, if the number of pixels in the second image frame is smaller than the number of pixels in the first image frame, the set of pixel values ​​for the second image frame can also be increased, as needed, by duplication, interpolation, or upscaling to facilitate preparation of the composite image frame.

[0150] A key advantage to generating improved navigation efficiency for the above-described stage functions when the user can make decisions "on the fly" is that the user can view both images, or in embodiments with three or more detectors, three or more images simultaneously, so that all images are within at least the user's peripheral vision. Preferably, the additional image information regarding the composition or material properties of the substance is shown as a colored overlay on the electronic image, thereby providing the equivalent of a "heads-up" view that provides additional data without requiring the user to take their eyes off the electronic image.

[0151] As mentioned above, the first detector is typically an electronic detector, although it is contemplated that other types of monitoring equipment may be used.

[0152] In typical embodiments, the first detector monitors the resulting particles to provide data including either or both topographical information about the region of the sample and atomic number information about the sample material. Typically, such data can be provided by a secondary electron detector or a backscattered electron detector. Such detectors can therefore be suitable for rapidly providing image frames containing information suitable for use by a user to rapidly navigate a field of view around the sample surface.

[0153] In some embodiments, the second detector monitors resulting particles generated within the sample at a rate that is less than one-tenth the rate at which resulting particles monitored by the first detector are generated within the sample for a given microscope condition. For example, when the method is used in conjunction with an electron microscope, resulting x-rays generated in response to an electron beam being incident on the sample for a given microscope condition are typically generated at a rate that is an order of magnitude or more slower than the rate at which emitted electrons are generated. Rate in this context refers to the number of particles generated per second, whether the particles are composed of matter or electromagnetic radiation. In some embodiments, the rate at which particles monitored by the second detector are generated is one-hundredth the rate at which particles monitored by the first detector are generated.

[0154] For example, in some embodiments involving electron backscatter diffraction analysis, there may be no such difference between the rate of generation or monitoring of a first particle and the rate of generation or monitoring of a second particle, but the S / N of the signal derived from the data for the second particle may still be significantly lower than the S / N of the signal from the first particle data.

[0155] In various embodiments, the second detector is adapted to monitor various types of particles, for example, x-rays, secondary electrons, and backscattered electrons.

[0156] In some embodiments, the second detector is either an X-ray spectrometer, an electron diffraction pattern camera, an electron energy loss spectrometer, or a cathodoluminescence detector.

[0157] In some embodiments, monitoring the second set of particles to obtain a second image frame comprises acquiring two or more signals of different types from the second detector to obtain respective sub-image frames, and combining the first and second image frames comprises combining the first image frame with one or more of the sub-image frames.

[0158] Thus, in some embodiments, sub-image frames can be used by processing the data from the second detector to derive various types of information. For example, an X-ray spectrum can be processed to provide a measure of the number of photons recorded for each of a set of energy ranges to determine the number of photons corresponding to a particular characteristic radiation, even when the radiation is spread across a range of energies such that the recorded data from two different radiations overlap in terms of energy.

[0159] In some embodiments, the electron diffraction pattern recorded by a second detector, such as an imaging camera, may be processed to determine the crystalline phase and orientation of this phase of the material under the electron beam, thereby generating partial images corresponding to different phases and different crystalline orientations.

[0160] In some embodiments, multiple signals can be derived from the same detector. Typically, in such embodiments, the second detector can output two or more signals of different types, which can correspond to different types of monitored particles and can be used to acquire various sub-image frames. For example, various types of signals that can be output can include spectra acquired by an X-ray spectrometer, electron diffraction patterns acquired by an electron-sensitive camera, and spectra acquired by an electron energy loss spectrometer or cathodoluminescence detector. Any of these signal types can be used to derive either the first or second image frame, or to derive a sub-image frame. Thus, in some embodiments, monitoring the second particle set to acquire the second image frame includes monitoring two or more subsets of the second particle set, each corresponding to a different type of signal acquired from the second detector, to acquire a corresponding sub-image frame.

[0161] Some embodiments include a third detector that is a different type than the first and second detectors, for example, each of the first, second, and third detectors can be one of a secondary electron detector, a backscattered electron detector, and an X-ray detector.

[0162] As described above, pixels of an image frame can have values ​​that represent or are indicative of the energy distribution of monitored particles. This can be achieved by acquiring two or more sub-image frames, each sub-image frame being a subset or component of the image frame, each corresponding to a different particle energy range. Thus, in some embodiments, monitoring the second particle set to acquire a second image frame includes monitoring two or more subsets of the second particle set, each subset corresponding to a different particle energy range, to acquire a respective sub-image frame, each sub-image frame including a plurality of pixels corresponding to a plurality of locations within a region, the plurality of pixels derived from monitored particles contained by the corresponding subset and generated at those locations; and combining the sub-image frames to result in a second image frame that provides, for each of the plurality of pixels, data derived from particles generated at the corresponding location within the region and contained by each of the subsets.

[0163] In this way, more than one related image (sub-image frame) is available to the second detector for separately monitoring the resulting particles of different energies or different energy bands for each composite image frame. These separate sub-images can be combined with each other in a manner that allows for distinguishing pixel values ​​or pixel intensities for a plurality of constituent pixels corresponding to particle count values ​​for a corresponding sample location for each sub-image frame. This distinction can be achieved, for example, by assigning or rendering each sub-image frame with a different color. This rendering can be performed such that the visible contribution to the color obtained at a given location or pixel in the second image frame, and thus the composite image frame, provides a visual indication of the intensity of the monitored particles in the corresponding energy band or corresponding subset generated at that location.

[0164] That is, in some embodiments, a composite color second image frame based on the sub-image frame may be formed and then combined with the first image frame to form a composite image.

[0165] For example, in an embodiment where the second detector is an X-ray detector, for each composite frame in the series of composite frames, the second detector monitors the intensities of characteristic emissions of multiple chemical elements by monitoring multiple particle subsets having energy ranges corresponding to characteristic energies or characteristic energy bands of the multiple chemical elements, thus obtaining multiple sub-images from the single X-ray detector, each corresponding to a different chemical element.

[0166] In some embodiments, two or more sub-image frames are combined to form a second image frame, but are alternatively processed separately in accordance with step (d) of the method before being combined with the first image frame to form the composite image frame. Thus, in various embodiments, for any of the sub-image frames or any of the image frames, the composite image frame may be acquired in both a "store" mode and a "refresh" mode.

[0167] Suitable methods for combining data from a first image frame with data from a second image frame to generate and display a composite image frame are described in WO 2019 / 016559 A1, pages 15-17. For each composite image frame, the first image frame and the second image frame may be combined to form a single image frame that includes data acquired by both the first and second detectors. Preferably, the composition of these two image frames is visually indicated to a user in a manner that allows the first and second particle set information for each location within the image to be individually distinguishable.

[0168] In some other embodiments, instead of overlaying the two image frames, combining the first and second image frames is performed by displaying the first and second image frames side-by-side. Thus, combining the first and second image frames to result in a composite image frame can include juxtaposing the first and second image frames. Preferably, in such embodiments, the two image frames are positioned next to each other such that when the composite image frame is displayed on a visual display, both image frames are simultaneously visible within a user's field of view. Thus, in these embodiments, the composite image frame is typically at least twice as large and therefore includes at least twice as many pixels as each of the individual first and second image frames.

[0169] The microscope conditions for acquiring the first and second image frames can include several different configurable conditions. These conditions, which can be configured for the electron column of the electron microscope, can include magnification, focus, astigmatism, acceleration voltage, beam current, and scan deflection. Thus, the above-mentioned list of microscope conditions can be configured for the charged particle beam. The position and orientation can be configured for the sample or for a sample stage specifically adapted to hold the sample. In other words, the spatial coordinates can include the X-, Y-, and Z-axis positions in a Cartesian coordinate system, as well as the degrees of tilt and rotation of the sample. Brightness and contrast can be configured for each of the first and second detectors.

[0170] Thus, the field of view for an electron microscope can typically be configured by setting microscope conditions such as the position and orientation of the sample stage, the magnification, and the scan deflection, which is the degree of deflection applied to the scanning charged particle beam.

[0171] In some embodiments, combining pixels from image frames may not necessarily be limited to only the second image frame. In some embodiments, the "accumulation" mode of acquiring image frames can be applied to the first image frame as well as the second image frame. Thus, acquiring a composite image frame can further include, for each pixel of the first image frame, combining a value of a stored pixel with a value of the pixel if the configuration microscope conditions are the same as the configuration microscope conditions for the stored first image frame of the immediately preceding acquired composite frame in the series of composite frames, and the pixel corresponds to a corresponding location within the region of the stored pixel contained by the first stored image frame, to increase the signal-to-noise ratio for the pixel. Applying the signal averaging or accumulation mode of acquiring image frames to the image from the first detector can be advantageous in embodiments where the signal-to-noise ratio of the signal from the first detector is low or below a desired threshold.

[0172] The frame rate of the visual display, and therefore the rate at which successive composite images in a composite image sequence are displayed on the visual display, can vary among various embodiments and can be configurable. In some embodiments, the frame rate at which composite image frames are displayed is at least 1 frame per second, preferably at least 3 frames per second, and more preferably 20 frames per second. In some embodiments, a single composite image frame is processed at any given time. In such embodiments, the exemplary frame rates listed above correspond to composite image acquisition or processing times of 1 second or less, 0.3 seconds or less, and 0.05 seconds or less, respectively.

[0173] In some embodiments, the rate at which the sequence of composite image frames is obtained and displayed is at least 10 frames per second, preferably at least 18 frames per second, more preferably at least 25 frames per second, and even more preferably at least 50 frames per second. Preferably, the sequence of composite image frames is therefore displayed in the form of a moving image, and preferably the display frame rate corresponds to the video frame rate.

[0174] In a preferred embodiment, combining stored pixels with a pixel of interest to increase the signal-to-noise ratio for that pixel is performed by signal averaging or signal accumulation. The output from the detector can be considered a signal, and therefore the noise reduction techniques of signal averaging and signal accumulation, and therefore the average or sum over replicate measurement sets, which are sets of measurements under the same conditions for a given pixel or pixel corresponding to a particular location within a region, can be used.

[0175] According to a third aspect of the present invention there is provided a method of analysing a sample in a microscope, the method comprising the steps of using two acquisition modes to acquire a series of composite image frames using a first detector and a second detector different to the first detector, the step of acquiring data for the composite image frames in the first mode comprising: a1) causing the charged particle beam to pass through a region of the sample area corresponding to the field of view of the microscope within a time T1; a2) monitoring a resulting first set of particles generated within the sample with a first detector to obtain a first image frame including N1 pixels whose pixel values ​​correspond to a monitored first particle from a vicinity of a location within the region; a3) monitoring a second resulting set of particles generated within the sample with a second detector to obtain a second image frame including N2 pixels having a set of values ​​derived from a second monitored particle from a vicinity of the location within the region; a4) if the constituent microscope fields are different from those for the immediately preceding composite image frame in the series of composite image frames, then for each pixel in the second image frame, using the pixel value as the value to be used to generate the next composite image frame in the series of composite image frames; a5) changing to a second acquisition mode if the constituent microscope field of view is the same as for the immediately preceding composite image frame in the series of composite image frames; and acquiring a composite image frame in the second mode includes: b1) passing the charged particle beam through a region of the sample area corresponding to the field of view of the microscope within a time T2; b2) monitoring a resulting first set of particles generated within the sample with a first detector to obtain a first image frame including M pixels whose pixel values ​​correspond to the monitored first particles from a vicinity of the location within the region; b3) monitoring a second resulting set of particles generated within the sample with a second detector to obtain a second image frame including M pixels having a set of values ​​derived from a second monitored particle from a vicinity of the location within the region; b4) combining the set of values ​​for the pixel with one or more sets of values ​​for the corresponding pixel in a second image frame previously obtained from the same field of view, so as to increase the signal-to-noise ratio for the value for the corresponding pixel to be used to generate the next composite image frame in the series of composite image frames when the constituent microscope field of view for each pixel of the second image frame is the same as for the immediately preceding composite image frame in the series of composite image frames; b5) changing to the first acquisition mode when the constituent microscope field of view changes from the microscope field of view for the immediately preceding composite image frame in the series of composite image frames; and c) generating a composite image frame using the set of pixel values ​​for the second particle and the pixel values ​​for the first particle to generate a new composite image frame such that the composite image frame is a spatial representation of the region where values ​​for pixels at locations in the composite image frame are generated at corresponding locations within the region and are derived from data derived from particles monitored by each of the first detector and the second detector; the using step comprising: displaying the series of composite image frames in real time on a visual display; Including, The visual display is updated to sequentially show each composite image frame to enable the observer to identify potential features of interest when the field of view is stationary or changing, and the time T1 to traverse the area in the first mode is shorter than the time T2 to traverse the area in the second mode. This method can also be understood to be achieved as an embodiment according to the second aspect. The first and second times T1 and T2 can be understood to correspond, for example, to the total traversal times discussed above with respect to the second aspect of this disclosure. Thus, a mode switching function can be defined in terms of these separate acquisition modes, typically including switching between the two separate acquisition modes based on a movement or other change in the field of view.

[0176] According to a fourth aspect of the present invention there is provided an apparatus for analysing a sample in a microscope, the apparatus comprising an X-ray detector, preferably a second detector according to any of the first, second and third aspects, a processor and a computer program which, when executed by the processor, causes the processor to carry out a method according to any of the first, second and third aspects.

[0177] Such an apparatus may be suitable for carrying out a method according to any of the first, second and third aspects.

[0178] In some embodiments, the apparatus is suitable for displaying signals generated while a focused electron beam in an electron microscope is scanned over a two-dimensional region on the surface of a specimen, a first signal originating from an electron detector and at least one auxiliary signal derived from a different detector providing information about material properties other than the content or atomic number of individual chemical elements, each signal being measured at a two-dimensional array of electron beam positions covering the region, a corresponding pixel array of the measurements comprising a digital image for a field of view covering the region, and a visual display being used to show the digital images for all signals such that multiple images fit within a user's peripheral vision or are combined into a single composite color image, all a complete pixel measurement set for the signal covers the field of view, preparation of the visual display is performed and completed within a short period of time, the complete pixel measurement set covering the field of view and updating of the visual display are continuously repeated for all signals, successive measurements of at least one auxiliary signal at the same pixel location are used to improve the signal-to-noise of the measurement at that pixel under the condition that the field of view or microscope conditions do not change, the next measurement of the signal at the same pixel location is used to replace the previous measurement if there is no change in either the field of view or microscope conditions, and the short period of time is small enough so that the image display is updated quickly enough for an observer to identify moving features when the field of view is changed.

[0179] In such embodiments, the signal-to-noise of the display results of more than one signal measurement is typically improved using Kalman averaging or summing of the measurements and adjusting brightness scaling according to the number of measurements.

[0180] In this manner, when repeated measurements are taken multiple times for a pixel or location on the sample, successive second image frames in a series of composite image frames can be captured by the device, and the multiple pixel measurements can be used to increase the signal-to-noise ratio using a Kalman recursive filter. In some embodiments, improving the image signal is achieved by adding together successive pixel measurements and adjusting the brightness according to the number of measurements and therefore the number of frames in which the pixel is added together by the device.

[0181] Typically, the short period is less than 1 second, preferably less than 0.3 seconds, and ideally less than 0.05 seconds, so that the device can be configured to perform and complete preparation of the visual display fast enough that there is no noticeable delay or only a minimal delay experienced by the user of the device.

[0182] The device can be configured to automatically identify when the field of view is changing, such that it switches from an "averaging" or "accumulation" mode, in which successive frames in a sequence are added together, to a "refresh" mode. In some embodiments, the field of view is considered to be changing if the sample is being moved or the scan area is being intentionally altered under user control.

[0183] In some embodiments, changes in the field of view or microscope conditions are detected by mathematically comparing a new digital image with a previously acquired one. The device can be configured to compare successive frames acquired in sequence to identify changes made to the field of view. The device can be configured to operate in a "refresh" mode for portions of the sample as they are introduced into the field of view as the user navigates the field of view around the sample, and in an "accumulate" mode for portions that remain within the field of view while moving within it.

[0184] Typically, the auxiliary signal is derived from a spectrum acquired by an X-ray spectrometer, an electron diffraction pattern acquired by an electron-sensitive camera, a spectrum acquired by an electron energy loss spectrometer, or a spectrum acquired by a cathodoluminescence detector.

[0185] In some embodiments, there is provided a scanning electron microscope comprising an apparatus according to the fourth aspect, i.e. an electron beam instrument, in particular an electron microscope, suitable and / or configured to perform the advantageous analytical method may be provided.

[0186] According to a fifth aspect of the present invention there is provided a computer readable storage medium having stored thereon program code arranged to carry out a method according to any of the first, second and third aspects.

[0187] According to a sixth aspect of the present invention there is provided a computer program comprising instructions which, when executed, cause an apparatus to perform a method according to any of the first, second and third aspects.

[0188] Examples of the invention will now be described with reference to the accompanying drawings, in which: [Brief explanation of the drawings]

[0189] [Figure 1] FIG. 1 illustrates an exemplary scanning pattern for an electron beam across an area on a sample. [Figure 2]1 is a schematic diagram showing the configuration of a scanning electron microscope system for recording electron and X-ray images from a sample according to the prior art; [Figure 3] FIG. 1 is a schematic diagram showing a scanning electron microscope arrangement in which a detector is positioned between the sample and the final lens pole piece of the microscope. [Figure 4] 1 is a flow chart illustrating an exemplary method according to the present invention. [Figure 5] FIG. 1 shows an exemplary composite image frame showing a sample area from which an electron image and a color-coded X-ray image were obtained in accordance with an example of the present invention. [Figure 6] 1 is a screen capture illustrating functional elements of a visual display screen for user navigation according to an example of the present invention. [Figure 7] 10 is a schematic diagram illustrating a comparison between a constructed field of view and corresponding traversal path covered by a beam in a static frame acquisition mode and a modified field of view and corresponding traversal path covered by a beam in a dynamic acquisition mode according to an example of the present invention. FIG. [Figure 8] 1 is a flow chart illustrating steps of an exemplary method according to the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0190] A method and apparatus for analysing a sample in an electron microscope according to the present invention will now be described with reference to Figures 1 to 6 and 8.

[0191] A schematic diagram of the key steps of an exemplary method according to the present invention is shown in FIG. 8. This flow chart shows the steps, in order, for capturing and displaying a single composite image frame. When the mode parameter has a first or second value, the charged particle beam is traversed according to a first (fast) scan mode (left-hand path) or a second (slow) scan mode (right-hand path), respectively. Although not explicitly shown in this schematic diagram, the mode parameter value can be changed one or more times before the traversal for a given frame is completed. In such cases, the actual path of the beam is switched accordingly between the two paths and corresponding conditions in this example.

[0192] Regardless of the mode parameter value, two sets of particles—electrons and X-ray photons in this example—are monitored by the respective first and second detectors. The frames obtained by these monitors are combined to produce a composite image frame. This frame is then displayed on a visual display as part of a real-time updated stream, video, or frame sequence, thereby facilitating analysis of the sample. The adaptable scanning mode advantageously allows for changing scanning modes between one that provides fast visual response and a high display refresh rate and one that can provide higher quality, less noisy image data. The mode parameters can be automatically changed to provide a high frame rate when the user reconfigures the microscope (e.g., by moving the sample stage) to change the field of view, or to switch to a slow scan when the user stops issuing commands to change the field of view.

[0193] A secondary polepiece detector with a large solid angle can improve live imaging during analysis. Such an arrangement is depicted in Figure 3. The user's ability to interact with the visual display to quickly determine the location of an area of ​​interest on the sample is significantly improved if a second particle detector, providing chemical or material information to complement the primary detector image, provides a signal with a high signal-to-noise ratio. Conventional X-ray detectors mounted on the side port of an SEM have only a small collection solid angle for X-rays. However, an X-ray detector mounted below the polepiece of the electron lens, with sensors surrounding the incident electron beam and a sensitive area facing the sample, can achieve a significantly larger total collection solid angle for all sensors. When a large collection solid angle is used, the signal-to-noise ratio for the derived X-ray signal is significantly higher, and with a significantly faster electron beam traversal of the field of view on the sample, an acceptable image is available for tracking moving features. This allows for a faster frame update rate for the composite image frame, allowing for more rapid changes to be observed when the field of view is changing.

[0194] Using an electron microscope such as the arrangement shown in FIG. 2 or FIG. 3, yet another exemplary method can be performed that advantageously further includes adaptable frame processing dependent on movement of the constituent fields of view, as shown in the flow chart of FIG. 4. The method includes acquiring a series of composite image frames, the acquisition of which is illustrated by the steps of FIG. 4. In this example, the composite image frames are acquired at a predetermined frequency for each of a first "fast" or "dynamic" mode and a second "slow" or "static" mode. The frequency in the first mode is higher than that in the second mode, and therefore updates of the resulting display occur more rapidly when operating in the first mode than in the second mode. In other examples, multiple predetermined or variable frequencies can be applied to either or both of these modes.

[0195] As shown in the flowchart, the applied mode is applied depending on whether the configured microscope field of view is changing or stationary. In this example, the first mode or "Mode 1" includes the steps of monitoring a first set of particles generated at N1 locations to obtain an image frame including N1 pixels, and monitoring a second set of particles generated at N2 locations to obtain an image frame including N2 pixels, where N1 and N2 are integers in this case. Similarly, the second mode or "Mode 2" includes the steps of monitoring a first set of particles generated at M1 locations to obtain an image frame including M1 pixels, and monitoring a second set of particles generated at M2 locations to obtain an image frame including M2 pixels, where M1 and M2 are integers in this case. In this example, N1 < M1 and N2 < M2 so that the first mode generates a faster overall scanning speed than the second mode. However, in other examples, none of these inequalities may apply, and the number of locations for either the first and monitored second sets of particles cannot be changed between the first mode and the second mode. In this example and other examples, the configured average time taken to monitor particles from one given location within the first and second plurality of locations can be shorter for the first mode than for the second mode. This shortening can be achieved by fast continuous scanning or short dwell times for the locations monitored when in the "dynamic" mode.

[0196] Values suitable for the number of pixels and locations in the above example are as follows. For example, Mode 1 is considered to have N1 equal to 49,152 and N2 equal to 12,288. When switching to Mode 2, it is considered that the number of locations can be quadrupled, giving M1 equal to 196,608 and M2 equal to 49,152. In this example, the X-ray data is sorted so that a plurality of groups composed of four pixels are combined into one aggregated "super pixel" to improve the S / N, so N2 < N1 and M2 < M1. When an image frame with a typical aspect ratio of 4:3 is obtained, in the first mode, it results in a first image frame of 256 x 192 pixels and a second image frame of 128 x 96 pixels, and in the second mode, it is considered to result in a first image frame of 512 x 384 pixels and a second image frame of 256 x 192 pixels. Since the number of locations will depend on the use case, acquisition conditions, and the sample being analyzed, it is not necessary for N1 and M1 and N2 and M2 to change by the same multiple. In that sense, N1, M1, N2, and M2 can be changed up to 4,194,304 (2,048 x 2,048) or sometimes more, and can be made as small as 3,072 (64x48), but are not limited to this.

[0197] In this example, during frame acquisition, the acquisition mode is switched from a first mode to a second mode when it is determined that the constituent field of view is different from the immediately preceding frame in the sequence, and from the second mode to the first mode if the field of view is also different from the immediately preceding frame. The flow diagram illustrates this switching as occurring immediately such that the frame acquisition procedure begins anew in the switched-to mode. However, in various examples, the switching can occur at various points during the acquisition cycle. For example, the switching can occur after the acquisition of the current frame is complete. However, in a preferred example, the mode is switched as soon as the conditions for switching are identified. In such a case, the remainder of the traversal and monitoring procedures for the current frame are preferably performed using the switched-to mode, at least until another subsequent switching occurs.

[0198] During frame acquisition, a user of the electron microscope system can move the sample stage to have the microscope's field of view cover various regions of the sample, and when a particular region of interest is found, the user can repeatedly slow or stop the stage movement to accumulate a second image frame of data from that region.

[0199] The electron beam of the electron microscope is made to be incident on multiple locations within the sample area by deflecting the beam to perform a raster scan of the area.

[0200] A first set of particles generated at the locations within the sample as a result of the electron beam impinging on the multiple locations are monitored using a first detector to obtain a first image frame. A second set of particles generated at the locations within the sample as a result of the electron beam impinging on the multiple locations are monitored using a second detector to obtain a second image frame. As the electron beam strikes each location, the first and second detectors monitor signals derived from the first and second particle sets for that location, respectively. Thus, for a given frame, these electron and x-ray monitoring steps for that region are performed substantially simultaneously. The signals from each detector are used to generate an image formed of pixels positioned such that the relative locations of the pixels correspond to the relative locations of the monitored particles that generated the respective pixel values ​​within the region of the multiple locations.

[0201] In this example, if the constituent microscope field of view for each pixel in the second image frame is the same as that for the stored second image frame of the acquired composite frame immediately preceding it in the sequence of frames, then that pixel is combined with the stored pixel to increase the signal-to-noise ratio for that pixel. Thus, portions of the second image frame that correspond to the same present sample portion and that were monitored under the same microscope conditions in the preceding frame in the sequence of second image frames are captured and amplified into the composite image frame in "accumulation" mode. Conversely, if the fields of view are not the same, then that pixel of the second image frame is captured in "refresh" mode and is not combined with the stored pixel.

[0202] The first image frame and the second image frame are combined to provide a composite image frame by overlaying the two images on one another so that the visual data from both image frames can be individually distinguished and associated with the relevant portion of the sample area.

[0203] The composite image frames are displayed in real time on the visual display as they are generated. In this example, the composite image frame for a region is displayed 0.05 seconds after the raster scan for that region is completed.

[0204] The above steps are repeated for each composite image frame in the sequence as it is obtained.

[0205] In an electron microscope, such as the configuration shown in Figure 2, there are many signal sources that provide information about material composition or properties. The BSE detector in an SEM (or the annular dark-field detector in an STEM) is affected by the atomic number of atoms, but does not reveal any information about the content of individual chemical elements and cannot uniquely identify specific materials present under the incident electron beam. However, electron-sensitive imaging cameras can record electron diffraction patterns that show electron intensity variations associated with angular orientation. Analysis of such patterns can reveal crystalline material properties, such as the orientation or presence of specific crystalline phases. For example, if a thin sample is being analyzed, the energy spectrum of electrons transmitted through this film can be acquired using an electron energy-loss spectrometer (EELS), and the presence of core-loss edges in this spectrum can reveal the presence of individual chemical elements. Electron energy spectrometers can also be used to acquire spectra that reveal Auger emission from bulk samples that is unique to the content of individual chemical elements. Light-sensitive detectors can reveal areas where the sample is cathodoluminescent (CL), and their signal is affected by the material's electronic structure. By using crystals, diffraction gratings, or zone plates in geometries that result in selective Bragg reflection of characteristic X-ray emission lines toward an X-ray sensitive sensor, X-ray signals from these emission lines from individual chemical elements are available. All of these are examples where signals provide additional information about the content or material properties of individual chemical elements and could be beneficial adjuncts to electron images from SE or BSE, and could also be used in conjunction with the present invention. However, the following discussion applies to the specific case where an X-ray spectrometer is used to provide additional information about chemical element content.

[0206] Electron microscopes typically have one or more X-ray detectors and associated signal processors that allow recording of the X-ray energy spectrum emitted by the sample. While a focused electron beam is deflected onto a particular pixel location, a histogram of photon energy measurements is recorded over a short period of time. This histogram corresponds to a digital X-ray energy spectrum, and the number of acquired photons corresponding to the characteristic X-ray emissions for a particular chemical element can be derived from the spectrum, given a set of signal values ​​corresponding to a set of chemical elements. (A suitable technique for processing digitized X-ray energy spectra to minimize the effects of background bremsstrahlung and overlap and to extract characteristic emission line intensities is described in P. J. Statham, "Deconvolution and background subtraction by least-squares fitting with prefiltering of spectra," Analytical Chemistry, vol. 1, pp. 111-114, 2003.) 1977, 49(14), pp. 2149-2154, DOI:10.1021 / ac50022a014. Furthermore, signals from an electron detector (such as a secondary electron detector or a backscattered electron detector) can be recorded at the location. Thus, when the electron beam is deflected to a set of pixel locations that constitute a complete image frame, a set of pixel measurements corresponding to a digital electron image and one or more images corresponding to various chemical elements is available. These electron image and X-ray image data are appropriately scaled and typically passed to a visual display unit under computer control. Figure 6 illustrates an example of a suitable display in which an electron image is displayed in the upper left corner and one or more X-ray images corresponding to various chemical elements are displayed immediately to the right of the electron image, so that the electron image and one or more X-ray images can be viewed simultaneously while the user is focused on the electron image.To facilitate simultaneous viewing of this information, X-ray data from one or more chemical elements can be combined and displayed as a colored overlay on the electronic image, using, for example, techniques such as those described in PCT / GB2011 / 051060 or US5357110 and illustrated in Figure 6; the option to overlay the X-ray information on the electronic image can be selected by the user using a computer mouse to position the cursor inside the box labeled "Layer Map" on this display and "click."

[0207] When a user wishes to explore the sample to find an area of ​​interest, the field of view must be moved and the way the image is processed and displayed must be changed to give the user real-time feedback that helps the user to explore the sample efficiently while the field of view is changing.

[0208] The field of view can be changed in several ways: the microscope magnification can be increased by reducing the current provided to the beam deflector coils (or the voltage provided to the beam deflector plates) so that the size of the area scanned on the sample is reduced; an auxiliary deflector set can be used to add an offset to the deflection or shift the area scanned on the sample; or the sample can be physically moved by moving the holder or stage supporting the sample to a new position relative to the electron beam axis. In all these examples, the signal data acquired will correspond to different fields of view on the sample. Furthermore, all signal content will change if the user changes the operating voltage to the microscope.

[0209] When the field of view is changed, the user needs to see the results as quickly as possible. This is achieved by replacing pixel values ​​with new signal measurements at the corresponding beam position as the image is refreshed with each new data frame. A high frame rate ensures that the image refreshes quickly enough for the user to decide whether to continue changing the field of view. To track a feature, it must be visible within at least two consecutive frames; therefore, the frame time limits the speed at which an object can be tracked when the field of view is moving. A frame refresh time of even slightly longer than one second can cause the user to feel distracted and lose their train of thought. A frame refresh time of 0.3 seconds allows the user to adequately track a moving feature, provided that the feature moves only a small fraction of the screen width, but the screen update is noticeable. When frame refresh times are shorter than 0.05 seconds, the screen update is barely noticeable due to user image retention. However, higher frame rates compromise signal-to-noise ratios because image noise for individual frames worsens when the dwell time per pixel is short. If the dwell time per pixel is increased to improve the signal-to-noise ratio, the frame time will also increase unless the number of pixels is reduced. However, reducing the number of pixels in a frame will only provide imaging with lower spatial resolution. Therefore, the dwell time per pixel and the number of pixels per frame must be optimized to match the image signal source and the required movement speed of the field of view.

[0210] When the field of view is moving, a short frame refresh time is highly desirable because it makes it easier for the user to track moving features and make decisions to navigate to different areas. However, if a short frame time is used, the refresh image may become noisy when the user stops moving the field of view. Thus, there is a conflicting requirement between best performance for a moving field of view and best performance for a static field of view. To resolve this conflict, the method of using the data is changed, switching from a "refresh" mode while the field of view is moving to an "averaging" mode when the field of view is stationary.

[0211] When the field of view is not being moved, new results acquired when the focused electron beam returns to a particular position are combined with the existing value set in the corresponding pixel at this stage to improve the overall signal-to-noise ratio. The value sets can constitute an X-ray energy spectrum, which is a histogram, where each bin represents the number of recorded photons in a small energy range, or the result of processing such a histogram to extract a value set representing the number of photons collected from the characteristic emissions of a set of chemical elements. The X-ray signal is typically the number of photons recorded within the pixel dwell time, and for each value in the value set for a particular pixel, the new count value can simply be added to the existing count value; thus, the pixel value represents the total count value accumulated for all new data frames. For display, the total count value is simply divided by the number of frames for which the "averaging" mode was used; thus, the intensity remains constant, but the signal-to-noise ratio is improved due to the reduction of Poisson counting noise. Alternative implementations can be used to provide an S / N improvement for any signal value when the system is in "averaging" mode. For example, a "Kalman" recursive filter for a particular pixel value can be described as follows: Y(N)=A * S(N)+(1-A) * Y(N-1) where S(N) is the signal value for the Nth arriving image data frame, Y(N-1) is the previous value at that pixel, Y(N) is the new value for that pixel, and A is less than or equal to 1. When A=1, the above equation is effectively equivalent to a "refresh" mode, but smaller values ​​of A give an averaging effect that heavily weights the most recent results and weights earlier frames with exponentially decaying weights so that the overall effect is that of a long-term, non-transient picture. However, optimal noise reduction is provided by varying A for each successive data frame so that, starting at a particular point, A=1 / N, which results in the same S / N reduction as averaging with equal weighting over all frames.

[0212] The Kalman recursive filter is a simple method for performing signal averaging using only a single stored image, but alternative signal averaging methods can be used if there is enough computer memory to store data from N new image frames in multiple separate image stores so that data from a sequence of the most recent N image frames is always available for the signal averaging calculation.

[0213] The main requirement for a seamless transition between "refresh" and "averaging" modes is for the system to know that the user is shifting the field of view. The computer controlling signal acquisition can instantly determine which acquisition mode to use if it also recognizes the user's request to adjust the field of view or microscope conditions. Otherwise, the control computer must infer whether the field of view is changing. In this case, the first frame of electronic image data is saved, and each subsequent frame or subframe of electronic image data is compared to the first frame to see if it differs. As soon as a significant shift is detected (e.g., by observing a change in the magnitude or offset of the maximum cross-correlation value between the two image regions), the system switches to "refresh" mode and remains in this mode until two consecutive images no longer show a significant shift, at which point the system reverts to "averaging" mode. This type of test is ideal when the user is moving the sample stage under the beam to ensure a field of view shift occurs. This test is also useful for detecting a change in magnification between the two images, since this change will usually still result in a change in the maximum cross-correlation value. Other tests can be used to detect changes in microscope conditions. For example, if brightness or contrast is changed, the centroid and standard deviation of the histogram of the digital image will change, as will the case when electron beam energy is changed by changing the microscope accelerating voltage. Similarly, changes in focus can be detected by observing changes in the frequency distribution of the power spectrum of the digital image. Similar methods can be used to detect differences between X-ray images for a particular chemical element. Alternatively, an X-ray image using the signal from the full X-ray spectrum recorded at each pixel can be generated so that it has a better signal-to-noise ratio than the image for the particular chemical element. In this case, differences in the full X-ray spectrum image can be used to detect changes in field of view or conditions.The sensitivity of these tests depends on the signal-to-noise ratio of the image, and the criteria for detecting changes must be adjusted to give the best compromise between slow response to changes and false positives in the absence of changes. Therefore, whenever possible, it is preferable to configure the computer to know when the user has intentionally changed the scan area so that the correct acquisition mode can be selected without having to test for image differences.

[0214] It is usually easier to detect whether the field of view has been intentionally changed by the user by sending a command to the SEM or by examining the differences in multiple images obtained in successive scans. However, even if the user did not intend to change the field of view, the field of view may change due to, for example, mechanical or thermal relaxation effects on the sample stage. Therefore, one option is for the user to press a button to switch the acquisition mode to a mode in which successive data frames are signal-averaged or accumulated. In this mode, any inadvertent drift can be corrected before the data frames are combined. Another option, in the absence of the ability to determine whether the field of view has been intentionally changed by the user, is to have the user operate in high-speed acquisition mode by default and have a "pause" / "resume" button that can be pressed to switch to acquisition or accumulation mode to inspect an image with a better signal-to-noise ratio, and then press to resume stage movement.

[0215] An exemplary drift correction mode can be applied to the method as follows.

[0216] As the sample drifts, the beam position can be adjusted to follow the sample and continue to acquire data as long as the acquisition area remains within the field of view. When part of the acquisition area reaches the edge of the field of view, the beam can no longer reach all of the pixels within the acquisition area, reducing data integrity.

[0217] When the size of the acquisition area is close to the size of the field of view, or when the acquisition area is positioned near one or more of the edges of the field of view, the amount that the sample can drift in a given direction before reaching one or more of the limits of the field of view is quite limited. To increase the amount that the sample can drift before this occurs, the scan area used to acquire data must be reduced to a safety area near the center of the field of view. This safety area can be defined using the extended field of view mode.

[0218] When the extended field of view mode is selected, the maximum allowable drift amount is defined as a percentage of the image field width. Available options, in one example, include 50%, 150%, and 350% of the image width. This percentage is the percentage of the image width (and thus the area scanned by the electron beam) that the sample can drift in one direction before touching the edge of the field on the microscope. To allow the sample to drift a predetermined amount, the image must be correspondingly reduced. Thus, the higher the percentage selected, the smaller the image must be to allow the sample to drift the predetermined percentage. Therefore, images obtained after setting drift correction using the extended field of view mode will appear to be for a much smaller area at a higher magnification than before.

[0219] For example, if the maximum drift is set to 150% of the field of view width, the central 25% of the original field of view will be used.

[0220] In some situations where the field of view and acquisition area are set before setting drift correction using the extended field of view mode, it is not ideal to have a reduced field of view. To avoid this reduction, the "Maintain object size" option can be enabled.

[0221] When the Maintain Object Size option is selected, the images obtained after setting drift correction will appear the same as those before it was set (i.e., they have the same magnification and cover the same area of ​​the sample). However, the field of view on the microscope can be enlarged to allow the sample to drift by the amount set in "Maximum Drift" and the image to move until it reaches the edge of the field of view (the area that can be scanned by the electron beam) on the microscope. This enlargement is achieved by changing the magnification in the background on the SEM.

[0222] For example, if the magnification on the SEM is initially set to 1000x and the maximum drift is set to 50% of the field width, then in the background the SEM magnification will be set to approximately 500x.

[0223] X-ray spectral data is acquired for every pixel whenever the field of view and microscope conditions are static, and these data accumulate as successive image data frames are combined to improve signal-to-noise while in "averaging" mode. When a change to the field of view is introduced or detected, acquisition is switched to "refresh" mode, at which point the accumulated X-ray spectral data forms an X-ray "spectral image" in which every pixel has an X-ray energy spectrum associated with that pixel location. The sum of all pixel spectra in the field of view forms a single "sum spectrum" that can be processed to automatically identify chemical elements from characteristic emission peaks appearing in the spectrum ("Auto-ID"). Auto-ID accuracy can be improved by correcting the sum spectrum for pulse pile-up effects using techniques described in patent application PCT / GB2014 / 051555. Clustering techniques, as in PCT / GB2014 / 051555, can be used to identify sets of pixels with similar spectra, and analysis of the sum of all spectra from one set of similar pixels can be used to find matching entries in a spectral library, or the sum spectrum can be analyzed to quantify the elemental composition, which can be used to match against a library of known compound compositions so that the compound can be identified. Thus, just before the field of view is changed, an X-ray spectral image is available from the current field of view, and chemical elements or even compounds can be detected within this field of view. When the field of view is controlled by moving the holder or stage supporting the sample, the stage coordinates (e.g., X, Y, Z) will define the position of the field of view, while the X and Y field extents are defined by the beam deflection. When beam deflection is used to offset the field of view from a central position, there will be additional coordinates that define the beam deflection. The combination of stage and beam coordinates and the size of the scanned area on the sample surface are stored in a database along with a list of detected elements or compounds, and the entire X-ray spectral image for the field of view is stored if storage space allows.

[0224] X-ray data typically have a poor signal-to-noise ratio compared to electronic signal data, and it can be advantageous to sacrifice some of the spatial resolution of the X-ray data to achieve a better signal-to-noise ratio. For example, an X-ray image can be "seeded," in which data from each adjacent pixel group is combined to provide a single output pixel. Thus, the X-ray data can be internally converted into an array of pixels with improved signal-to-noise ratio, but each pixel corresponds to a larger area on the sample than for the pixels on the resolution grid used for acquisition. Reducing the number of pixels for the internal array through seeding also helps shorten the time required to process the data, for example, to identify chemical elements, thus improving response time. When the seeded X-ray data is converted into an X-ray image for display, the X-ray image will have lower spatial resolution than the electronic image, but will have lower statistical noise, which improves feature recognition. By reducing the resolution of the X-ray image, the difference between the signal-to-noise ratio of the electronic image and the signal-to-noise ratio of the X-ray image is visually minimized. When the field of view is stationary and data is accumulating, the selection of resolution for the x-ray image can be adaptive, increasing the resolution of the x-ray image as the number of accumulated frames increases and improving the signal-to-noise ratio. Even if seeding is not used, the signal-to-noise ratio of the displayed x-ray image can be improved by low-pass spatial filtering or "smoothing," at the expense of blurring some image detail. Again, when the field of view is stationary, the degree of smoothing can be reduced as the number of accumulated frames increases.

[0225] Sorting of x-ray data can be accomplished by a combination of electronic and software computer methods. For example, when a beam is scanned across a conventional line-by-line grid raster pattern, instead of saving a set of values ​​for every pixel along a line in a stored image, x-ray data can be accumulated continuously as the beam moves to four successive positions to collect electronic image data, and then a single set of values ​​corresponding to an aggregate of the spectra from four distinct positions on the line is stored for every fourth pixel along the line. When pixel data for the same position along a line for a series of four successive lines is summed, the result is a single set of values ​​representing the sum of the x-ray data across the 4x4 beam position array.

[0226] When using an X-ray detection system, there is a limit due to Poisson arrival times on the speed at which individual X-ray photons can be measured. Thus, the ratio of the output count rate OCR to the input rate ICR drops. When the user is moving over a large area on the sample, the ICR can vary on different materials. When the beam current is too high, the ICR on some materials can saturate the detection system, producing a lower OCR than on materials with a lower ICR. Thus, the beam current must be set to avoid saturation. To properly set the beam current so that no anomalies in chemical element content are shown when exploring an area, a visual tool indicating when the pulse processor is overloaded is advantageous. FIG. 5 shows an example of a display generated by monitoring the ICR and OCR at all positions within the field of view of an area on the sample. The electronic image is displayed in monochrome but is color-coded when the OCR / ICR falls within a certain range. For example, when the OCR / ICR < 0.3, the color can be considered red, and when 0.5 < OCR / ICR < 0.3, the color can be considered amber. Using this display, the user can adjust the beam current to ensure that there are no "red" areas within a typical field of view, i.e., that there is no overload of the electronics within a certain area, even if the average OCR / ICR for the entire field of view appears safe.

[0227] In a typical example, the composite image frame display shows one or more images covering the entire configured field of view in both "static" and "dynamic" modes. These images are the same size, but the total time taken to traverse the field of view to collect new data frames in the "dynamic" mode is shorter than that for the "static" mode.

[0228] In yet another example, as described above, an alternative method is used to speed up data acquisition in dynamic mode, particularly by using a "reduced raster." When using this modified scan pattern, the electron beam traverses a subsection of the constructed field of view on the sample, and only this subsection of the constructed field of view is shown in the composite image frame. That is, the composite image frame has a modified field of view that is smaller than the field of view initially constructed for it. This concept is illustrated in FIG. 7, where a smaller area is scanned in dynamic mode, and only features closer to the center of the field of view are visible in the composite image frame display, but the smaller area on the sample is traversed in a shorter time, allowing for a faster frame rate.

[0229] In this example, the magnification is the same in both static and dynamic modes, so features visible in the central region of the display do not change size when switching from static to dynamic mode, but in dynamic mode only a subsection of the area on the sample is shown in the composite image frame.

Claims

1. 1. A method for analyzing a sample in a microscope, comprising: acquiring a series of composite image frames using a first detector and a second detector different from the first detector, the acquiring of the composite image frames comprising: a) directing a charged particle beam across a sample area corresponding to a field of view of the microscope, when a modal parameter has a first value, the traversal of the beam is along a first traversal path over the region and in accordance with a first set of traversal conditions; when the modal parameter has a second value, the traversal of the beam is along a second traversal path over the region and according to a second set of traversal conditions; a first total time required for the beam to traverse the entire first traversal path according to the first set of traversal conditions is less than a second total time required for the beam to traverse the entire second traversal path according to the second set of traversal conditions; the value of the mode parameter is configured according to whether the configuration field of view is changing or not. the traversing step; b) monitoring with the first detector a resulting first set of particles generated in the sample at a first plurality of locations within the region to obtain a first image frame, the first image frame including a plurality of pixels corresponding to the first plurality of locations and having values ​​derived from the monitored particles generated thereat; c) monitoring with the second detector a resulting second set of particles generated in the sample at a second plurality of locations within the region to obtain a second image frame, the second image frame including a plurality of pixels corresponding to the second plurality of locations and having respective sets of values ​​derived from the monitored particles generated thereat; and d) combining the first image frame and the second image frame to generate the composite image frame such that the composite image frame provides data derived from particles generated at the first and second plurality of locations within the region and monitored by each of the first detector and the second detector; said obtaining step including: displaying said series of composite image frames in real time on a visual display that is updated to show each composite image frame in sequence; A method comprising:

2. The method of claim 1 , wherein the modal parameter is configured to have the first value in response to the configured field of view being changed.

3. 3. The method of claim 1 or claim 2, wherein the mode parameter is configured to have the second value in response to the constructed field of view not being changed.

4. 2. The method of claim 1, wherein said mode parameter has said first value when said constituent fields of view are different from those for an immediately preceding composite image frame in said series of composite image frames.

5. 2. The method of claim 1, wherein said mode parameter has said second value when said constituent fields of view are the same as for an immediately preceding composite image frame in said series of composite image frames.

6. The method of claim 1 , wherein the mode parameter value is user-configurable.

7. The method of claim 6 , wherein the mode parameter is set to the second value when a first user input is provided.

8. acquiring a composite image frame, For each of at least a subset of the plurality of pixels contained by the second image frame, When the second modal parameter has a first value, retaining the derived set of values ​​for the pixels in the second image frame for use in the composite image frame; or when the second modal parameter has a second value, combining the derived set of values ​​for the pixel with a derived set of values ​​for a corresponding pixel in each of one or more preceding second image frames in the series of composite image frames to obtain a set of combined pixel values ​​having an increased signal to noise ratio, and replacing the derived set of pixel values ​​with the combined set of pixel values ​​in the second image frames for use in the composite image frame; Further comprising: The method of claim 1.

9. 9. The method of claim 8, wherein the second mode parameter has the first value when the constituent fields of view are different from those for the immediately preceding composite image frame in the series of composite image frames.

10. 10. A method according to claim 8 or claim 9, wherein the second mode parameter has the second value when the constituent field of view is the same as for the immediately preceding composite image frame in the series of composite image frames.

11. 10. The method of claim 8 or claim 9, wherein the second mode parameter value is user configurable.

12. The method of claim 11 , wherein the second mode parameter is set to the second value in response to a user input.

13. 10. The method of claim 8 or claim 9, wherein the step of acquiring a composite image frame further comprises acquiring field of view deviation data representing a difference between a real field of view and a reference field of view of the microscope when the second mode parameter has the second value.

14. The method of claim 13 , wherein the reference field of view comprises one of a constructed field of view for the composite image frame being acquired and a real field of view for a previous composite image frame in the series of composite image frames.

15. 14. The method of claim 13, wherein the step of obtaining a composite image frame further comprises, when the second mode parameter has the second value, determining, for each of at least a subset of the plurality of pixels comprised by the second image frame, the corresponding pixel in each of one or more preceding second image frames in the series of composite image frames, wherein the derived set of values ​​for the corresponding pixel are combined to obtain a combined pixel value set according to the field of view deviation data.

16. 14. The method of claim 13, wherein the step of acquiring a composite image frame further comprises adjusting the field of view of the microscope in accordance with the field of view deviation data to reduce the difference between the field of view of the microscope and the reference field of view when the second mode parameter has the second value.

17. 2. The method of claim 1, wherein acquiring a composite image frame further comprises processing spectral data acquired in accordance with the second particle set to acquire data indicative of the amount of particles in the second particle set that each correspond to one or more characteristic line emissions to derive the set of values ​​for each of the pixels comprised by the second image frame.

18. 18. The method of claim 17, wherein the processing step includes extracting the data indicative of particle abundance when the one or more characteristic line emissions are distributed over a range of energies and / or correspond to overlapping energy ranges.

19. each of one or more of the sets of values ​​comprises a set of results of processing a histogram, each rectangular area representing a number of second particles having energies within an energy range corresponding to a width of the rectangle to extract a set of values ​​representing the number of second particles collected from the characteristic radiation of the set of chemical elements; 19. The method of claim 17 or claim 18.

20. The method of claim 1 , wherein the first detector is an electron detector.

21. The method of claim 1 , wherein the second detector is an X-ray detector.

22. 22. The method of claim 21, wherein the X-ray detector is disposed between a beam source and the sample, the X-ray detector having one or more sensor portions facing the sample and at least partially surrounding the incident charged particle beam.

23. 2. The method of claim 1, wherein the first traversal path has a length that is shorter than that of the second traversal path, such that the first total time is shorter than the second total time.

24. 2. The method of claim 1, wherein the first and second sets of traversal conditions are configured to cause the beam to traverse the first traversal path at a faster average speed than the beam to traverse the second traversal path, such that the first total time is less than the second total time.

25. 25. The method of claim 24, wherein the first and second sets of traversal conditions are configured such that a first linear density along the first traversal path at locations within the region configured to be monitored for the first generated set of particles is less than a second linear density along the second traversal path at locations within the region configured to be monitored for the first generated set of particles.

26. 26. The method of claim 24 or claim 25, wherein the first and second sets of traversal conditions are configured such that a first linear density along the first traversal path at locations within the region configured to be monitored for the generated second set of particles is lower than a second linear density along the second traversal path at locations within the region configured to be monitored for the generated second set of particles.

27. 26. The method of claim 24 or claim 25, wherein the first and second sets of traversal conditions are configured such that a first configuration monitoring duration during which the first set of particles generated at each of the first plurality of locations along the first traversal path is monitored is shorter than a second configuration monitoring duration during which the first set of particles generated at each of the first plurality of locations along the second traversal path is monitored.

28. 26. The method of claim 24 or claim 25, wherein the first and second sets of traversal conditions are configured such that a first configuration monitoring duration during which the second set of particles generated at each of the second plurality of locations along the first traversal path is monitored is shorter than a second configuration monitoring duration during which the second set of particles generated at each of the second plurality of locations along the second traversal path is monitored.

29. 1. A method for analyzing a sample in a microscope, comprising: acquiring a series of composite image frames using a first detector and a second detector different from the first detector, the acquiring of the composite image frames comprising: a) causing a charged particle beam to traverse a sample area corresponding to a constituent field of view of the microscope, wherein when the constituent field of view is different from that for an immediately preceding composite image frame in the series of composite image frames, causing the beam to traverse a first traverse path over the area in a total time that is shorter than a total time that causes the beam to traverse a second traverse path over the area when the constituent field of view is the same as that for the immediately preceding composite image frame in the series of composite image frames; b) monitoring with the first detector a resulting first set of particles generated in the sample at a first plurality of locations within the region to obtain a first image frame, the first image frame including a plurality of pixels corresponding to the first plurality of locations and having values ​​derived from the monitored particles generated thereat; c) monitoring with the second detector a resulting second set of particles generated in the sample at a second plurality of locations within the region to obtain a second image frame, the second image frame including a plurality of pixels corresponding to the second plurality of locations and having respective sets of values ​​derived from the monitored particles generated thereat; d) for each of the plurality of pixels comprised by the second image frame: if the constructed field of view is different from that for the immediately preceding composite image frame in the series of composite image frames, retaining the derived set of values ​​for the pixels in the second image frame for use in the composite image frame; or if the constructed field of view is the same as for the immediately preceding composite image frame in the series of composite image frames, combining the derived set of values ​​for the pixel with a derived set of values ​​for a corresponding pixel in each of one or more preceding second image frames in the series of composite image frames having the same microscope field of view as the constituent fields of view to obtain a combined pixel value set having an increased signal-to-noise ratio; and replacing the derived set of pixel values ​​with the combined pixel value set in the second image frame for use in the composite image frame; e) combining the first image frame and the second image frame to generate the composite image frame such that the composite image frame provides data derived from particles generated at the first and second plurality of locations within the region and monitored by each of the first and second detectors; said obtaining step including: displaying said series of composite image frames in real time on a visual display that is updated to show each composite image frame in sequence; A method comprising:

30. The method of claim 1 , wherein the first traversal path spans substantially the entire field of view of the microscope.

31. The method of claim 1 , wherein the first traversal path is contained within the constructed field of view and spans a different field of view than the constructed field of view.

32. The method of claim 1 , wherein the second traversal path includes the constructed field of view and spans a different field of view than the constructed field of view.

33. 2. The method of claim 1, wherein the mode parameter is set to the first value when the constituent field of view is different from that for the immediately preceding composite image frame in the series of composite image frames, and is set to the second value when the constituent field of view is the same as that for the immediately preceding composite image frame in the series of composite image frames.

34. said step of acquiring a composite image frame comprising: For each of the plurality of pixels comprised by the second image frame: setting the acquired mode parameter equal to the first value if the constructed field of view is different from that for the immediately preceding pixel of the second image frame and if the acquired mode parameter equals the second value; or setting the acquired mode parameter equal to the second value if the constructed field of view is the same as for the immediately preceding pixel of the second image frame and if the acquired mode parameter equals the first value; Further comprising: The method of claim 1.

35. 35. The method of claim 34, wherein the step of setting the acquired mode parameter equal to the first or second value occurs before monitoring a particle generated in the sample at a location within the region corresponding to an immediately subsequent pixel in the second image frame.

36. acquiring a composite image frame, For each of the plurality of pixels comprised by the first image frame: if the constructed field of view is different from that for the immediately preceding composite image frame in the series of composite image frames, retaining the derived values ​​of the pixels in the first image frame for use in the composite image frame; or if the constituent fields of view are the same as for the immediately preceding composite image frame in the series of composite image frames, combining the derived value of the pixel with a derived value of a corresponding pixel in each of one or more preceding second image frames in the series of composite image frames having the same microscope field of view as the constituent fields of view to obtain a combined pixel value having an increased signal-to-noise ratio; and replacing the derived pixel value with the combined pixel value in the first image frame for use in the composite image frame. Further comprising: The method of claim 1.

37. acquiring a composite image frame, grouping the sets of pixel values ​​of one or more subsets of pixels in the second image frame together to obtain one or more respective aggregate sets of pixel values; replacing each of the one or more subsets of pixels in the second image frame with an aggregate pixel having a set of values ​​equal to the respective set of aggregate pixel values; Further comprising: The method of claim 1.

38. monitoring the second set of particles to acquire the second image frames includes deriving two or more signals of different types from the second detector and acquiring sub-image frames corresponding to each of the signals; combining the first image frame and the second image frame includes combining the first image frame with one or more of the sub-image frames. The method of claim 1.

39. 2. The method of claim 1, wherein combining the first image frame and the second image frame to generate the composite image frame includes overlaying the first and second image frames, whereby the composite image frame includes a plurality of pixels each corresponding to one of the plurality of locations within the region and provides data derived from the particles contained by both the first particle set and the second particle set and generated at each of the locations.

40. 40. The method of claim 39, wherein combining the first image frame and the second image frame includes calculating a color for the composite image pixel based on the intensities of corresponding pixels in the first and second image frames.

41. The method of claim 1 , wherein combining the first image frame and the second image frame to generate the composite image frame comprises juxtaposing the first and second image frames.

42. 2. The method of claim 1, wherein the first and second sets of transverse conditions include any of a sample stage position and orientation, magnification, focus, astigmatism, acceleration voltage, beam current, and scan deflection configured with respect to the charged particle beam, and a position and orientation configured with respect to the sample.

43. 2. The method of claim 1, wherein the sequence of composite image frames is acquired and displayed at a rate of at least 1 frame per second, preferably at least 3 frames per second, and more preferably at least 20 frames per second.

44. 30. The method of claim 29, wherein the step of combining the pixel with the stored pixels to increase the signal-to-noise ratio for the pixel is performed by a method of signal averaging or signal accumulation or Kalman recursive filtering or summation of measurements, and by changing brightness scaling according to the number of measurements.

45. 1. A method for analyzing a sample in a microscope, comprising: using two acquisition modes to acquire a series of composite image frames using a first detector and a second detector different from the first detector, acquiring data for the composite image frames in a first mode, a1) causing a charged particle beam to traverse a sample area corresponding to a field of view of the microscope in a time T1; a2) monitoring a resulting first set of particles generated within the sample with the first detector to obtain a first image frame from a vicinity of a location within the region, the first image frame including N1 pixels whose pixel values ​​correspond to a first particle monitored; a3) monitoring a resulting second set of particles generated within the sample with the second detector to obtain a second image frame from a vicinity of a location within the region, the second image frame including N2 pixels, the pixels having a set of values ​​derived from a second particle monitored; a4) for each pixel in said second image frame if said constituent fields of view are different from those for the immediately preceding composite image frame, using the value for the pixel as the value to be used in generating the next composite image frame in said series of composite image frames; a5) changing to a second mode if the constructed field of view is the same as for the immediately preceding composite image frame in the series of composite image frames, wherein acquiring composite image frames in the second mode comprises: b1) causing a charged particle beam to traverse a sample area corresponding to a field of view of the microscope at a time T2; b2) monitoring a resulting first set of particles generated within the sample with the first detector to obtain a first image frame from a vicinity of a location within the region, the first image frame including M1 pixels whose pixel values ​​correspond to a monitored first particle; b3) monitoring a resulting second set of particles generated within the sample with the second detector to obtain a second image frame from a vicinity of a location within the region, the second image frame including M2 pixels whose pixel values ​​have a set of values ​​derived from a second particle monitored; b4) for each pixel of said second image frame, combining said set of values ​​for said pixel with one or more sets of values ​​of corresponding pixels in a second image frame previously obtained from the same field of view, in order to increase the signal to noise ratio for said value for said corresponding pixel to be used to generate a next composite image frame in said series of composite image frames when said constituent fields of view are the same as for said immediately preceding composite image frame in said series of composite image frames; b5) changing to the first mode if the constructed field of view changes from that for an immediately preceding composite image frame in the series of composite image frames; c) using the set of pixel values ​​for the second particle and the pixel values ​​for the first particle intended to generate a new composite image frame to generate the composite image frame, such that the composite image frame is a spatial representation of the region and values ​​for pixels at locations in the composite image frame are derived from data derived from the particles generated at corresponding locations in the region and monitored by each of the first and second detectors; using the two acquisition modes including: displaying said series of composite image frames in real time on a visual display; Including, the visual display is updated to show each composite image frame in sequence to enable a viewer to identify potential features of interest when the field of view is stationary or changing; the time T1 to traverse the region in the first mode is shorter than the time T2 to traverse the region in the second mode; method.

46. 10. The method of claim 1, wherein the second detector is one of an X-ray spectrometer, an electron diffraction pattern camera, an electron energy loss spectrometer, or a cathodoluminescence detector.

47. 1. An apparatus for analyzing a sample in a microscope, comprising: an X-ray detector; a processor; a computer program which, when executed by said processor, causes said processor to perform the method of claim 1; An apparatus comprising:

48. 48. The apparatus of claim 47, wherein a change in the field of view or the first and second sets of transverse conditions is detected by mathematical comparison of a new digital image with one previously obtained.

49. 49. The apparatus of claim 47 or claim 48, wherein the second image frame comprises data derived from a spectrum acquired by an X-ray spectrometer, an electron diffraction pattern acquired by an electron sensitive camera, an electron energy loss spectrometer, or a spectrum acquired by a cathodoluminescence detector.

50. 1. A scanning electron microscope, comprising:

49. The apparatus of claim 47 or claim 48. Scanning electron microscope including.

51. 10. A computer readable storage medium having stored thereon program code configured to perform the method of claim 1.

52. A computer program comprising: instructions that, when executed, cause a device to perform the method of claim 1; A computer program comprising:

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