Blanker-enhanced moire imaging

Abstract

To provide a scientific instrument with an electron-beam column.SOLUTION: In some embodiments, a scientific instrument includes an electron-beam column configured to scan an electron beam across a sample. The electron-beam column includes a beam blanker configured to gate the electron beam in response to a drive signal. The scientific instrument also includes an electron detector configured to measure a flux of transmitted or scattered electrons having interacted with the sample, and an electronic controller configured to acquire an image of the sample using values of the flux measured with the electron detector for a plurality of electron-beam scan locations. The electronic controller is further configured to cause the drive signal to have a gating frequency at which the image has a moire pattern therein.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] Various examples relate generally to, but are not limited to, electron microscope components, instruments, systems, and methods. Summary of the Invention

[0002] Moiré is a common phenomenon in which two closely related patterns produce a more slowly varying pattern. In scanning transmission electron microscopy (STEM), moiré patterns can be produced when the microscope's sampling interval is relatively close to the periodicity of the crystal lattice of the specimen, or an integer multiple of it. The spacing and orientation of STEM moiré fringes are sensitive to the local lattice periodicity, and can therefore be used, for example, to reveal strain fields within the specimen.

[0003] The microelectronics industry needs effective tools to quantitatively measure strain in semiconductor devices. For example, strain in polycompound semiconductor-based devices can be either undesirable or advantageous, since strain can affect the incorporation of substitutional atoms or provide a way to design electronic devices by strain engineering of band gap and / or carrier mobility. In general, knowledge of the actual strain state of an inspected object is very important for quality control purposes. Therefore, strain mapping methods and instruments that provide suitable spatial resolution and accuracy coupled with sufficiently fast data acquisition and processing are of great interest to semiconductor companies.

[0004] Disclosed herein are various examples, aspects, features, and embodiments of a scientific instrument having, among other things, an electron beam column with a fast pre-sampled beam blanker configured to gate the electron beam during a STEM imaging scan. In some examples, the beam blanker is beneficially used to enable acquisition of high contrast moiré patterns using high scan speeds, e.g., with pixel dwell times of less than about 5 μs / pixel. In some other examples, the beam blanker is beneficially used to implement focusing of the electron probe based on moiré imaging. The latter feature can be used, for example, to achieve fast and accurate optical alignment of the electron beam optics to a dose-sensitive sample, where alternative focusing methods may expose the dose-sensitive sample to degradingly high radiation doses.

[0005] One example provides a scientific instrument that includes an electron beam column configured to scan an electron beam across a sample, the electron beam column including a beam blanker configured to gate the electron beam in response to a drive signal; an electron detector configured to measure a flux of transmitted or scattered electrons that have interacted with the sample; and an electronic controller configured to acquire an image of the sample using values ​​of the flux measured by the electron detector for a plurality of electron beam scan positions, the electronic controller further configured to cause the drive signal to have a gating frequency when the image has a moiré pattern therein.

[0006] Another example provides a moire imaging method that includes scanning an electron beam across a specimen using an electron beam column including a beam blanker configured to gate the electron beam in response to a drive signal, measuring a flux of transmitted or scattered electrons that have interacted with the specimen using an electron detector, acquiring an image of the specimen using values ​​of the measured flux for a plurality of electron beam scan positions using an electronic controller, and causing the drive signal to have a gating frequency when the image has a moire pattern therein using the electronic controller. [Brief description of the drawings]

[0007] The foregoing aspects and many of the attendant advantages of the present disclosure will become more readily appreciated as the same become better understood by reference to the following detailed description, when taken in conjunction with the accompanying drawings, in which: [Figure 1] 1 is a block diagram illustrating an exemplary scientific instrument, according to some embodiments. [Diagram 2] 2 is a block diagram illustrating acquisition of Moiré patterns in the scientific instrument of FIG. 1 in accordance with some embodiments. [Figure 3A] 3 graphically illustrates certain operating characteristics of the scientific instrument of FIG. 1 in the configuration shown in FIG. 2, according to some examples. [Figure 3B] 3 graphically illustrates certain operating characteristics of the scientific instrument of FIG. 1 in the configuration shown in FIG. 2, according to some examples. [Figure 4] 2 is a block diagram illustrating electrical circuitry used in the scientific instrument of FIG. 1 in accordance with some embodiments. [Diagram 5] 2 is a flowchart illustrating a method of Moire imaging based distortion mapping implemented in the scientific instrument of FIG. 1 in accordance with some embodiments. [Figure 6] 2 is a flow chart illustrating a method for low-dose adjustment of electron beam optics in the scientific instrument of FIG. 1 based on Moire imaging, according to some embodiments. [Figure 7] FIG. 1 is a block diagram of an example computing device configured to perform at least some scientific instrument-assisted operations, in accordance with various embodiments. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0008] FIG. 1 is a block diagram illustrating a scientific instrument 100, according to some embodiments. The scientific instrument 100 includes a scanning transmission electron microscope (STEM) column 102 coupled to a vacuum chamber 108. The vacuum chamber 108 houses a movable sample holder 110 therein and can be evacuated using one or more vacuum pumps (not explicitly shown in FIG. 1). In an exemplary embodiment, the sample holder 110 is independently movable parallel to an XY coordinate plane and parallel to a Z coordinate axis, with the corresponding coordinate system depicted by the XYZ coordinate triad shown in FIG. 1. A sample S to be investigated using the scientific instrument 100 is mounted on the sample holder 110 as shown in FIG. 1.

[0009] In the illustrated example, the STEM column 102 comprises an electron source 112 and two or more electron beam lenses, of which only two are shown diagrammatically in FIG. 1 for illustrative purposes: objective lens 106 and condenser lens 116. In some examples, a different number of such lenses may be used in the STEM column 102. In some embodiments, the objective lens 106 may be an ultra-high-resolution (UHR) lens. In at least some embodiments, the STEM column 102 also includes a beam blanker, which is described in more detail below with reference to FIG. 4.

[0010] In operation, the electron source 112 generates an electron beam 114 that propagates generally along a longitudinal axis 115 of the STEM column 102. The electron beam lenses 106 and 116 operate to generate electric and magnetic fields that affect the electron trajectories in the electron beam 114. Control signals 152, 156 generated by the electronic controller 150 are used to modify the strength and / or spatial configuration of these fields to impart desired characteristics to the electron beam 114. In general, the electron beam lenses 106 and 116, the control signals 152 and 156, and other associated components of the STEM column 102 and electronic controller 150 can be used to perform various operations and assist in various functions such as beam focusing, beam gating, aberration mitigation, aperture cropping, filtering, etc. The STEM column 102 further comprises a deflection unit 118 that can steer the electron beam 114 in response to control signals 154 applied by the electronic controller 150. Such beam steering can be used to move a focused portion of the electron beam 114 along a desired path across the sample S, for example to perform a raster or vector scan of the sample S.

[0011] The scientific instrument 100 also includes detectors 160, 170, 180 located within the vacuum chamber 108 in relative proximity to the sample S. During operation, the detectors 160, 170, and 180 generate streams of measurements as respective output signals 162, 172, and 182, which are received by the electronic controller 150. The specific types of the detectors 160, 170, 180 depend on the embodiment of the scientific instrument 100 and can typically be selected from a variety of detector types suitable for detecting different types of emissions and / or radiation from the sample S generated in response to the electron beam 114. Exemplary types of emissions / radiation that may be generated in this manner include, but are not limited to, x-rays, infrared, visible light, ultraviolet light, backscattered electrons, secondary electrons, Auger electrons, elastically scattered electrons, non-scattered (e.g., zero energy loss) electrons, and non-elastically scattered electrons. In various embodiments, a different number (other than three) of such detectors can be used within the scientific instrument 100. In some embodiments, detectors 160, 170, 180 are selected from the group consisting of high angle annular dark field (HAADF) detectors, medium angle annular dark field detectors, annular bright field detectors, segmented annular detectors, differential phase contrast detectors, electron energy loss spectroscopy (EELS) detectors, energy dispersive x-ray spectroscopy (EDS) detectors, and two-dimensional (e.g., pixelated or segmented) electron detectors. Other detectors capable of detecting various of the above-mentioned types of emission / radiation may also be used in various additional embodiments.

[0012] Figure 2 is a block diagram illustrating a configuration 200 of the scientific instrument 100 used to acquire a moiré pattern, according to one example. In the example shown, the moiré pattern is captured using a HAADF detector 180 positioned as shown in Figure 2. In other examples, other suitable detectors available in corresponding embodiments of the scientific instrument 100 can also be used (see also Figure 1).

[0013] In operation, as the focused portion F of the electron beam 114 is scanned by the deflection unit 118 across the sample S in a raster pattern 206, the HAADF detector 180 captures the flux 214 of scattered electrons at each pixel of the raster pattern 206 and communicates the flux measurements to the electronic controller 150 via its output signal 182. The electronic controller 150 then operates to generate a pixelated image representing the Moiré pattern by appropriately sorting and processing the stream of electron flux measurements received via signal 182. As used herein, the term "focused portion of the electron beam" refers to the portion of the electron beam 114 that has approximately (within, for example, ±10%) the smallest cross-sectional area. Those skilled in the art will readily appreciate that for many modalities of the scientific instrument 100, the focused portion F of the electron beam 114 needs to be relatively precisely positioned on the surface of the sample S or appropriately positioned within the sample S.

[0014] The raster pattern 206 has a spacing d between them. s In this specification, the distance between the scan lines 204 is d s is called the "scanning gate interval". Moiré fringes typically occur when the scanning gate interval d s is the crystal lattice spacing (d l ) or an integer multiple thereof. s is the crystal lattice spacing d l In some other configurations of the scientific instrument 100, the scan gate spacing d s is the crystal lattice spacing d l Greater than.

[0015] When the scan line 204 is directly over the lattice atoms of the sample S, relatively strong scattering of the electron beam 114 occurs, resulting in bright bands in the captured STEM image. The scattering of the electron beam 114 is significantly reduced when the scan line 204 is between the lattice planes, resulting in dark bands in the captured STEM image. Such bright and dark bands repeat (quasi-)periodically to form Moiré fringes. The contrast pattern observed with a bright-field detector is substantially the inverse of that observed with a dark-field detector. The corresponding Moiré fringe spacing (d mf ) can be expressed as follows:

[0016]

number

[0017] 3A-3B graphically illustrate certain operating characteristics of scientific instrument 100 in configuration 200, according to some examples. First, the contrast of the moiré pattern in a STEM image acquired using configuration 200 varies with pixel dwell time (t d ) is dependent on the electron beam 114 being sufficiently stationary during the pixel dwell time t d remains in a fixed (stationary) position for a distance d s Then, it jumps rapidly to the next fixed position and at that position, it takes another pixel dwell time t d The electron beam 114 again remains stationary during the pixel dwell time t d This means that the jumps are substantially completed within a time interval that is much shorter (e.g., less than one tenth) than the time required for the raster pattern 206 to be examined (typically in two dimensions, each with a possibly different distance d s In an exemplary implementation of the scanning electronics used in the scientific instrument 100, the time dependence of the position of the electron beam 114 represented by an idealized step function can only be obtained in theory and cannot be obtained in practice, for example due to a slower than ideal frequency response of the scanning electronics to step-like voltage transitions. Thus, exemplary embodiments disclosed herein are directed to providing an alternative solution that is effective for obtaining Moiré patterns, as described in more detail below.

[0018] When the STEM image size is 512 × 512 pixels, the pixel dwell time t d= 40 μs / pixel results in an image acquisition time of about 11 seconds. For a STEM image size of 1024×1024 pixels, the same pixel dwell time would result in an image acquisition time of about 42 seconds. Unfortunately, this long acquisition time may not be acceptable for at least some moiré imaging applications. For example, semiconductor companies appear to be targeting moiré pattern acquisition times of less than about 1 second. For a moiré pattern image size of 1024×1024 pixels, a target acquisition time of 1 second is calculated using a pixel dwell time t of 1 μs / pixel. d become.

[0019] Pixel dwell time t d is close to 1 μs / pixel, the finite frequency response of the deflection unit 118 and associated electronics will typically result in distortion of the step function 310. An example of such a distortion is shown in FIG. 3A by waveform 320. Note that instead of the rapid jumps of the step function 310, waveform 320 has “rounded” steps that cause inter-pixel transitions in which the electron beam 114 gradually drifts between two intended fixed positions, thereby effectively interrogating a continuous range of positions within the crystal lattice of the sample S. A typical adverse effect of such drift is that the corresponding acquired moiré pattern image will be smeared, e.g., have a relatively low moiré fringe contrast, or show no usable moiré fringes at all.

[0020] 3B graphically illustrates signal generation patterns 312, 322 corresponding to step function 310 and waveform 320, respectively. Signal generation pattern 312 is characterized by a high degree of localization causing the corresponding electron flux 214 to originate primarily from a number of equidistant discrete locations (spots) within sample S. In contrast, signal generation pattern 322 has a relatively low degree of localization causing the corresponding detected electron flux 214 to originate from a continuous range of locations within sample S, with only a small portion of flux 214 originating from discrete locations belonging to signal generation pattern 312. The latter attribute of signal generation pattern 322 disadvantageously results in a corresponding moiré fringe contrast that is not optimal at high scanning speeds.

[0021] According to one embodiment, the STEM column 102 of the scientific instrument 100 comprises a beam blanker that is controllably switchable between an on state and an off state in response to a gating signal. The gating signal serves as a control mechanism that determines when the electron beam 114 can pass through the beam blanker towards the sample S and when the electron beam 114 is blocked or diverted from propagating downstream to reach the sample S. In one example, the gating signal is a binary signal that alternates between a first (e.g., high) level and a second (e.g., low) level. When the gating signal is at a first level, the beam blanker operates to pass the electron beam 114 towards the sample S. When the gating signal is at a second level, the beam blanker operates to stop (block) the electron beam 114 from propagating downstream along the longitudinal axis 115 towards the sample S. In one example, the transition between the first and second levels in the gating signal is timed such that the beam blanker converts the signal generation pattern from signal generation pattern 322 (produced without the beam blanker or with the beam blanker turned off) to signal generation pattern 324 shown in Figure 3B. Beneficially, signal generation pattern 324 mimics (e.g., closely approximates) signal generation pattern 312, which corresponds to step function 310, and thus causes a corresponding acquired moiré pattern image to have a relatively high fringe contrast.

[0022] 3A graphically illustrates an exemplary gating signal 330 that can be used to drive a beam blanker. The gating signal 330 includes a series of gating pulses 332 that are synchronized with the acquisition scan such that the electron beam 114 is unblanked for a short period of time for each scanned pixel, e.g., with an unblanking duty cycle of about 10%. The gating signal 330 causes the STEM column 102 to generate an illumination pattern on the sample S that is substantially composed of a series of discrete illumination spots, even when the deflection unit 118 and the scanning electronics connected thereto generate a progressive beam sweep exemplified by the waveform 320. Thus, the signal generation pattern 322 is replaced by a signal generation pattern 324 (see FIG. 3B), and the resulting moiré fringe contrast, at least in some cases, beneficially approaches the optimal contrast typically associated with the step function 310.

[0023] Pixel dwell time t d In an embodiment of the scientific instrument 100 in which a decrease in causes the deflection unit 118 and its connected scanning electronics to produce a “blurred” response (as opposed to the relatively smooth response illustrated by waveform 320 in FIG. 3A ), the gating signal applied to the beam blanker can be phase shifted such that the electron beam 114 is unblanked when the position of the electron beam 114 is most stationary within the “blurred” response.

[0024] 3A, the frequency of the gating signal 330 is phase-locked to the sampling frequency of the STEM acquisition scan, and a selected fixed phase shift between the gating signal and the scan signal aligns the gating pulse 332 with the step transitions of the step function 310. In other examples, other values ​​of the fixed phase shift between the gating signal and the scan signal can also be selected. Typically, better results are obtained when a value of the fixed phase shift between the gating signal and the scan signal is selected such that the gating pulse 332 is aligned with the slower portion of the waveform 320 or its functional equivalent, where the position of the electron beam 114 is more stationary.

[0025] In some examples, the frequency of the gating signal applied to the beam blanker is decoupled from the sampling frequency of the STEM acquisition scan. This configuration can be used, for example, to sweep the frequency of the gating signal around an initial guess value in the fast scan direction until sufficient moiré fringe contrast appears in the STEM image. In FIG. 2, the fast scan direction is represented by scan line 204, and the slow scan direction is orthogonal to scan line 204. To ensure a substantially uniform illumination intensity for each scan pixel, the frequency of the gating signal typically needs to remain equal to or higher than the sampling frequency, and the detector output signal needs to be band-pass filtered to at least below the gating frequency. In such examples, other suitable methods of uniforming the illumination of different scan pixels can also be used.

[0026] In an exemplary workflow based on this method, an experiment may start with a sweep of the gating frequency until a near-maximum moiré fringe contrast is achieved for a region of interest (ROI) or reference region of the sample S. In some examples, the reference region is a region of the sample S where zero distortion is expected. A full scan of the ROI may then be performed at the determined gating frequency to ensure high moiré fringe contrast in the fast scan direction. Optionally, another frequency sweep and another full scan may be performed with the fast and slow scan directions swapped to achieve independently optimized moiré fringe contrast for the orthogonal scan direction. In some examples, the full scan may be performed with two or more slightly different gating frequencies corresponding to near-optimal contrast. This feature may be used, for example, to resolve sign ambiguities (if any) in the distortion map and improve the accuracy and / or spatial resolution of the distortion map.

[0027] 4 is a block diagram illustrating an electrical circuit 400 used in the scientific instrument 100, according to some embodiments. The electrical circuit 400 includes the electronic controller 150, circuit blocks 410, 420, 440, 450, 460, and 470, a pre-sample beam blanker 430 and other related components of the STEM column 102, and the detector 180. The STEM column 102 includes the beam blanker 430. In the illustrated example, the beam blanker 430 is positioned between the electron source 112 (see FIG. 1 ) and the electron beam lens 116. In other examples, the beam blanker 430 can be located at another suitable pre-sample position within the STEM column 102.

[0028] In the illustrated example, the pre-sampled beam blanker 430 includes an electrostatic beam deflector including first and second electrodes 424, 426. When a sufficiently strong electric field exists between the electrodes 424 and 426 (due to their appropriate electrical biasing), the electric field interacts with the electron beam 114, thereby deflecting the beam away from the longitudinal axis 115. A beam catcher (not explicitly shown in FIG. 4 ) then intercepts the deflected electron beam 114 and directs a corresponding current to a charge sink, e.g., to a ground terminal of the electrical circuit 400. When no electric field exists between the electrodes 424 and 426, the electron beam 114 passes through the beam blanker 430 undeflected and continues to propagate along the longitudinal axis 115 toward the sample S. In other examples, other suitable physical mechanisms for gating the electron beam 114 in the beam blanker 430 can also be implemented.

[0029] In response to a drive signal 422 received from the driver circuit 420, the beam blanker 430 operates to stop and pass the electron beam 114 at different times. The driver circuit 420 operates to generate the drive signal 422 in response to a gating signal 412 received from a configurable waveform generator 410. The gating signal 330 shown in FIG. 3A is an example of the gating signal 412. The electronic controller 150 operates to set various parameters of the gating signal 412 via a control signal 408 applied to the configurable waveform generator 410. The common control over the control signals 408 and 154 exercised by the electronic controller 150 allows any desired synchronization of the gating signal 412 with a scan signal 452 applied to a scan coil 454 of the deflection unit 118 via a scan pattern generator 440 and a scan coil driver 450. As already mentioned above, in some configurations, the phase and frequency of the gating signal 412 may be decoupled from the phase and frequency of the scan signal 452.

[0030] In some examples, the scan signal 442 generated by the scan pattern generator 440 in response to the control signal 154 includes the step function 310 shown in FIG. d ), the corresponding scan signal 452 generated by the scan coil driver 450 in response to the scan signal 442 closely follows the step function 310. However, at relatively high scan speeds (relatively short pixel dwell times t d ), the finite frequency response of the scan coil driver 450 can lead to distortion of the step function 310 such that the corresponding scan signal 452 is qualitatively similar to the waveform 320 shown in FIG. 3A.

[0031] The blanking and unblanking of the electron beam 114 imposed by the beam blanker 430 modulates the electron flux 214 accordingly. In some examples, the signal generation pattern of the electron flux 214 resulting from such modulation may be similar to the signal generation pattern 324 shown in FIG. 3B. In response to the modulated electron flux 214, the detector 180 generates a corresponding output signal 458, which is then amplified in an amplifier circuit 460. The resulting amplified signal 462 is converted to digital form in an analog-to-digital converter (ADC) 470, and the resulting digital stream 182 is directed to the electronic controller 150 for processing. Based on the received digital stream 182, the electronic controller 150 constructs a STEM image, which may include a Moiré pattern in at least some cases.

[0032] 5 is a flow chart illustrating a method 500 of strain mapping based on moire imaging implemented in a scientific instrument 100, according to some embodiments. The method 500 is described below with continued reference to FIGS. 1-5. In some examples, a corresponding embodiment of the scientific instrument 100 includes a beam blanker 430 and an electrical circuit 400 (FIG. 4). Exemplary use cases for the method 500 include, but are not limited to, strain mapping in Si-based semiconductor devices, interface strain mapping in polycrystalline materials (e.g., steel) or multilayer strictures, and strain mapping around precipitates or crystal defects (stacking faults, dislocations, etc.).

[0033] The method 500 includes properly orienting the sample S with respect to the longitudinal axis 115 of the STEM column 102 and with respect to a selected scan direction of the raster pattern 206 (block 502) (see also FIG. 1, FIG. 2). In some examples, the orienting operation of block 502 may alternatively include orienting the scan direction to the orientation of the sample S (e.g., about the longitudinal axis of the column). The operation of block 502 also includes the electronic controller 150 operating the movable sample holder 110 via the control signal 158 (FIG. 1) such that the selected zone axis of the sample S is properly aligned for Moiré imaging. In response to the control signal 158, the movable sample holder 110 may perform a suitable translation and / or rotation of the sample S with respect to the XYZ coordinate frame (see also FIG. 1).

[0034] As used herein, the term "zone axis" refers to a selected one of the high symmetry orientations within a crystal that is referenced to the direct lattice (as opposed to the reciprocal lattice) of the crystal in three dimensions. Thus, zone axes are conventionally indexed with the direct lattice indices rather than the Miller indices. Typically, zone axes are aligned with the corresponding directions of the "tunnels" that exist between the planes of atoms in the crystal.

[0035] The method 500 also includes the electronic controller 150 appropriately adjusting the electron beam optics of the STEM column 102 for STEM imaging (block 504). In some examples, the adjustment operation of block 504 includes Ronchigram alignment, which involves adjusting the electron beam optics based on an observed Ronchigram pattern. Ronchigram alignment can be used to correct both low and high order aberrations. In some implementations, after Ronchigram alignment, a condenser lens aperture is inserted and then at least some residual aberrations are finely corrected to obtain a high quality STEM image.

[0036] Method 500 also includes selecting (i) an ROI within sample S, and (ii) a set of parameter values ​​for the Moire imaging scan (block 506). In some examples, electronic controller 150 makes these selections in block 506 based on input from an operator of scientific instrument 100. In some other examples, electronic controller 150 makes these selections in block 506 automatically, for example, by executing a suitable program script. Exemplary parameters selected in block 506 include, but are not limited to, magnification (scan amplitude) and number of scan pixels (e.g., 1024×1024).

[0037] Method 500 also includes electronic controller 150 selecting parameter values ​​for gating signal 412 (block 508). In some examples, electronic controller 150 performs the parameter selection in block 508 based on input from an operator of scientific instrument 100. In some other examples, electronic controller 150 performs the parameter selection in block 506 automatically, for example, by executing a suitable program script. Exemplary parameters selected in block 508 include, but are not limited to, the frequency and duty cycle of gating signal 412.

[0038] As described in more detail below, the operation of block 508 is part of a processing loop that includes blocks 508, 510, and 512. In some examples, the first instance of block 508 includes an initial selection of a parameter value for the gating signal 412. Each subsequent instance of block 508 includes one or more respective adjustments to the previously selected parameter value, e.g., based on the results of blocks 510, 512. For example, in some implementations of processing loop 508 / 510 / 512, block 508 is configured to perform a sweep of the gating frequency while the sampling frequency of the scanning signal 452 remains fixed. In some examples, the frequency increment for the frequency sweep has a fixed value. In some other examples, the frequency increment depends on the difference between the observed Moiré fringe contrast and the threshold contrast value used in decision block 512. More specifically, a more aggressive change in the gating frequency may be performed for a relatively large contrast difference than for a relatively small contrast difference.

[0039] The method 500 also includes the electronic controller 150 acquiring a STEM image (block 510). An exemplary operation of block 510 includes the electronic controller 150 operating various components of the STEM column 102 and various circuit blocks of the electrical circuitry 400, for example, as described above with reference to FIG. 4, and receiving a corresponding digital stream 182 from the detector 180. For example, the STEM column 102 is operated using the selection made in block 506. The beam blanker 430 is driven using a gate signal 412 configured according to the selection made in block 508. In various examples, the detector used for the STEM image acquisition in block 510 is selected from the group consisting of a HAADF detector, a medium angle annular dark field detector, annular bright field detector, a segmented annular detector, a differential phase contrast detector, an EELS detector, an EDS detector, and a two-dimensional (e.g., pixelated or segmented) electronic detector. The operations of block 510 further include the electronic controller 150 synthesizing a STEM image from the data carried by the received digital stream 182 and applying a suitable image processing algorithm to the synthesized STEM image to determine the contrast of the Moiré fringe pattern contained therein.

[0040] The operation of decision block 512 of method 500 includes electronic controller 150 determining whether the contrast of the Moiré fringe pattern is acceptable. In some examples, this determination is made by comparing the Moiré fringe pattern contrast determined in block 510 to a threshold contrast value as described above. If the Moiré fringe contrast is greater than the threshold contrast value ("YES" at decision block 512), processing of method 500 proceeds to block 514. If the Moiré fringe contrast is less than the threshold contrast value ("NO" at decision block 512), processing of method 500 proceeds to block 508.

[0041] The operation of block 514 includes the electronic controller 150 generating a distortion map of the ROI of the sample S based on the Moiré fringe pattern included in the STEM image acquired in the last instance of block 510. In some examples, the electronic controller 150 first determines the crystal lattice spacing d l The electronic controller 150 then operates to determine the spatial variation of the crystal lattice spacing d l 5. Using the known relationship between the spatial variation of the distortion field, the method 500 operates to generate a distortion map of the ROI of the sample S. After the distortion map is generated, processing of the method 500 ends.

[0042] In some embodiments, prior to the above-mentioned operation of block 514, the above-mentioned processes corresponding to blocks 502-512 of method 500 are repeated for one or more rotated scan patterns to acquire at least a second STEM image including at least a second moiré fringe pattern corresponding to the same ROI of sample S. The operation of block 514 then includes electronic controller 150 jointly analyzing the at least two moiré fringe patterns to generate a distortion map of the ROI. Such joint analysis beneficially tends to produce a more accurate and / or detailed distortion map than any of the distortion maps derived from the individual moiré fringe patterns used in the joint analysis.

[0043] FIG. 6 is a flow chart illustrating a method 600 of low dose adjustment of electron beam optics in a scientific instrument 100 based on moiré imaging, according to some embodiments. Exemplary use cases of the method 600 include, but are not limited to, STEM imaging of dose-sensitive materials, such as metal-organic frameworks (MOFs), organic polymers, battery materials, etc. For example, some conventional electron beam optics focusing methods for high-resolution STEM use 5× oversampling, which can disadvantageously expose dose-sensitive materials of the sample S to degradingly high exposure doses. In contrast, exemplary embodiments of the method 600 can advantageously achieve comparable quality optical alignment with lower oversampling or no oversampling at all (e.g., with sampling at about 1×), thereby reducing exposure dose by a factor of 10 or more.

[0044] The method 600 includes properly orienting the sample S with respect to the longitudinal axis 115 of the STEM column 102 and with respect to a selected scan direction of the raster pattern 206 (block 602). In some examples, the orienting operation of block 602 may alternatively include orienting the scan direction to an orientation of the sample S (e.g., about the longitudinal axis of the column). In some examples, the operations of block 602 are similar to the operations of block 502 of method 500 described above.

[0045] The method 600 also includes the electronic controller 150 placing the scientific instrument 100 in a high magnification live STEM image acquisition mode (block 604). When in the live STEM image acquisition mode, the electronic controller 150 operates the STEM column 102, associated circuitry, and detector 180 such that a series of STEM images of the sample S are continuously acquired by the electronic controller 150 via the detector output signal 182. In some examples, the sampling step of the scan for STEM imaging (the distance between adjacent scan pixels) is determined based on the crystal lattice spacing d of the sample S. l is selected to be greater than

[0046] The method 600 also includes the electronic controller 150 selecting a frequency of the gating signal 412 and activating the beam blanker 430 (block 606). In some examples, the electronic controller 150 operates to select the gating frequency at block 606 based on input from an operator of the scientific instrument 100. In some other examples, the electronic controller 150 operates to automatically select the gating frequency at block 606, for example, by executing a program script configured to calculate an estimated preferred value of the gating frequency based on the scanning speed and sampling (nm / pixel) used in the live STEM acquisition mode configured at block 604.

[0047] In some examples, the sampling of the crystal lattice is set based on the field of view (FOV) and the number of pixels scanned. In atomic imaging, a 3- to 10-fold oversampling of the lattice may be used. In some conventional approaches, when the number of pixels is reduced, the scientific instrument still scans the sparse regions between adjacent pixels when moving the probe from one pixel to the next if the probe size is smaller than the pixel spacing. Such scanning can disadvantageously reduce contrast and / or cause smearing effects. The use of blanking substantially avoids these adverse effects, while at the same time beneficially reducing the radiation dose to which the sample S is exposed, since the regions between the pixels are no longer exposed to radiation due to the actuated beam blanker 430. Under conventional approaches with faster scanning, a similar beneficial effect may not be achievable, for example, because the faster the scan, the smaller the ratio of pixel signal to signal originating from the regions between the pixels. Thus, a simple reduction in the sampling rate at a fixed FOV does not provide the same benefit as the use of blanking. In contrast, the use of blanking can advantageously provide the benefits discussed above when used to create Moire conditions and for focus detection applications.

[0048] The method 600 also includes the electronic controller 150 adjusting the electron beam optics of the STEM column 102 (block 608). The adjustment operation of block 608 is configured to move the focused portion F of the electron beam 114 vertically along the longitudinal axis 115 to attempt to find a position where the focused portion F is substantially at a suitable location for imaging (e.g., on the surface of the sample S), as shown in FIG. 2. Because only when the focused portion F of the electron beam 114 is sufficiently close to that location will a Moiré fringe pattern become visible in the continuously acquired STEM images, the electronic controller 150 also operates in block 608 to continuously evaluate the STEM images of the live sequence of STEM images for the presence of a Moiré fringe pattern.

[0049] In some examples of block 608, the increment used when the vertical position of the focused portion F of the electron beam 114 is adjusted depends on whether the moiré fringe pattern is visible in the live STEM image. More specifically, the electronic controller 150 may be configured to use a larger vertical increment when the moiré fringe pattern is not yet visible in the live STEM image. Once the moiré fringe pattern becomes visible in the live STEM image, the electronic controller 150 may reduce the vertical increment and use smaller increments to fine-tune the vertical position of the focused portion F of the electron beam 114 to achieve better contrast of the observed moiré fringe pattern.

[0050] The operation of decision block 610 of method 600 includes the electronic controller 150 determining whether the contrast of the moiré fringe pattern observed in block 608 is acceptable. In some examples, this determination is made by comparing the moiré fringe pattern contrast observed in block 608 to a threshold contrast value. If the moiré fringe contrast is lower than the threshold contrast value ("no" at decision block 610), processing of method 600 proceeds to block 612. As used herein, the term "of a lower value" should be interpreted to encompass the situation where the moiré fringe pattern is not yet present in the live STEM image during the adjustment operation of block 608. If the moiré fringe contrast is higher than the threshold contrast value ("yes" at decision block 610), processing of method 600 proceeds to block 614. It should be noted that a high moiré fringe contrast indicates that the electron beam 114 is in focus, e.g., its focused portion F is near the proper vertical position as shown in FIG. 2.

[0051] The operation of block 612 includes the electronic controller 150 changing the frequency of the gating signal 412. In some examples, the electronic controller 150 operates to change the gating frequency in block 612 based on input from an operator of the scientific instrument 100. In some other examples, the electronic controller 150 operates to automatically increment the gating frequency in block 612, for example, by executing a program script configured to calculate an increment value for the gating frequency based on auxiliary information available to the electronic controller 150. Such auxiliary information may be extracted, for example, from available information regarding the sample S, the current configuration of the STEM scan, and / or the live STEM image. After the gating frequency is changed in block 612, processing of the method 600 returns to block 608.

[0052] The operation of block 614 includes electronic controller 150 stopping beam blanker 430, canceling the live STEM acquisition mode, and optionally entering another mode of operation, such as an operating mode in which focusing of electron beam 114 has been performed by executing method 600. Method 600 then ends.

[0053] 7 is a block diagram of an example computing device 700 configured to perform at least some scientific instrument support operations, according to various embodiments. For example, in some embodiments, the computing device 700 performs at least some operations of the electronic controller 150 (see also FIGS. 1 and 4-6). In various embodiments, the support modules of the scientific instrument 100 may be implemented by a single computing device 700 or by multiple computing devices 700.

[0054] Although the computing device 700 of FIG. 7 is illustrated as having several components, any one or more of these components may be omitted or duplicated as appropriate for the application and setting. In some embodiments, some or all of the components included in the computing device 700 may be mounted on one or more motherboards and enclosed in a housing. In some embodiments, some of these components may be fabricated on a single system-on-a-chip (SoC) (e.g., an SoC may include one or more processing devices 702 and one or more storage devices 704). Additionally, in various embodiments, the computing device 700 may not include one or more components illustrated in FIG. 7, but may include interface circuitry for coupling to one or more components using any suitable interface (e.g., a Universal Serial Bus (USB) interface, a High-Definition Multimedia Interface (HDMI®) interface, a Controller Area Network (CAN®) interface, a Serial Peripheral Interface (SPI) interface, an Ethernet interface, a wireless interface, or any other suitable interface). For example, computing device 700 may not include a display device 710, but may include display device interface circuitry (eg, connector and driver circuitry) to which an external display device 710 may be coupled.

[0055] Computing device 700 includes a processing device 702 (e.g., one or more processing devices). As used herein, the term "processing device" refers to any device or portion of a device that processes electronic data from registers and / or memory and converts the electronic data into other electronic data that may be stored in registers and / or memory. In various embodiments, processing device 702 may include one or more digital signal processors (DSPs), application-specific integrated circuits (ASICs), central processing units (CPUs), graphics processing units (GPUs), server processors, or any other suitable processing devices.

[0056] The computing device 700 also includes a storage device 704 (e.g., one or more storage devices). In various embodiments, the storage device 704 may include one or more memory devices, such as random-access memory (RAM) devices (e.g., static RAM (SRAM) devices, magnetic RAM (MRAM) devices, dynamic RAM (DRAM) devices, resistive RAM (RRAM) devices, or conductive-bridging RAM (CBRAM) devices), hard-drive-based memory devices, solid-state memory devices, network drives, cloud drives, or any combination of memory devices. In some embodiments, the storage device 704 may include memory that shares a die with the processing device 702. In such embodiments, the memory may be used as a cache memory and may include, for example, embedded dynamic random-access memory (eDRAM) or spin transfer torque magnetic random-access memory (STT-MRAM). In some embodiments, the storage device 704 may include a non-transitory computer-readable medium having instructions that, when executed by one or more processing devices (e.g., the processing device 702), cause the computing device 700 to perform any suitable one of the methods, or portions of such methods, disclosed herein below.

[0057] Computing device 700 further includes an interface device 706 (e.g., one or more interface devices 706). In various embodiments, interface device 706 may include one or more communication chips, connectors, and / or other hardware and software to manage communications between computing device 700 and other computing devices. For example, interface device 706 may include circuitry to manage wireless communications to transfer data to and from computing device 700. The term "wireless" and its derivatives may be used to describe circuits, devices, systems, methods, techniques, communication channels, etc. that may communicate data via modulated electromagnetic radiation over a non-solid medium. This term does not imply that the associated device does not include any wiring, although in some embodiments it may not. The circuitry included in the interface device 706 for managing wireless communications may implement any of a number of wireless standards or protocols, including, but not limited to, Wi-Fi (IEEE 802.11 family), Institute for Electrical and Electronic Engineers (IEEE) standards including the IEEE 802.16 standard, the Long-Term Evolution (LTE) project (e.g., advanced LTE project, ultramobile broadband (UMB) project (also referred to as "3GPP2"), etc.) with any amendments, updates, and / or revisions. In some embodiments, the circuitry included in the interface device 706 for managing wireless communications may operate in accordance with a Global System for Mobile Communications (GSM), General Packet Radio Service (GPRS), Universal Mobile Telecommunications System (UMTS), High Speed ​​Packet Access (HSPA), Evolved HSPA (E-HSPA), or LTE network.In some embodiments, the circuitry included in the interface device 706 for managing wireless communications may operate in accordance with GSM Evolved High Speed ​​Data (EDGE), GSM EDGE Radio Access Network (GERAN), Universal Terrestrial Radio Access Network (UTRAN), or Evolved UTRAN (E-UTRAN). In some embodiments, the circuitry included in the interface device 706 for managing wireless communications may operate in accordance with Code Division Multiple Access (CDMA), Time Division Multiple Access (TDMA), Digital Enhanced Cordless Telecommunications (DECT), Evolution-Data Optimized (EV-DO), and derivatives thereof, as well as any other wireless protocols designated as 3G, 4G, 5G, and beyond. In some embodiments, the interface device 706 may include one or more antennas (e.g., one or more antenna arrays) configured to receive and / or transmit wireless signals.

[0058] In some embodiments, the interface device 706 may include circuitry for managing wired communications, such as electrical, optical, or any other suitable communications protocol. For example, the interface device 706 may include circuitry supporting communications according to Ethernet technology. In some embodiments, the interface device 706 may support both wireless and wired communications, and / or support multiple wired and / or multiple wireless communications protocols. For example, a first set of circuits of the interface device 706 may be dedicated to short-range wireless communications, such as Wi-Fi® or Bluetooth®, and a second set of circuits of the interface device 706 may be dedicated to long-range wireless communications, such as Global Positioning System (GPS), EDGE, GPRS, CDMA, WiMAX, LTE, EV-DO, and the like. In some other embodiments, the first set of circuits of the interface device 706 may be dedicated to wireless communications, and the second set of circuits of the interface device 706 may be dedicated to wired communications.

[0059] Computing device 700 also includes battery / power circuitry 708. In various embodiments, battery / power circuitry 708 may include one or more energy storage devices (e.g., batteries or capacitors) and / or circuitry for coupling components of computing device 700 to an energy source separate from computing device 700 (e.g., to an AC line power source).

[0060] Computing device 700 also includes a display device 710 (e.g., one or more individual display devices). In various embodiments, display device 710 may include any visual indicator, such as a head-up display, a computer monitor, a projector, a touch screen display, a liquid crystal display (LCD), a light emitting diode display, or a flat panel display.

[0061] Computing device 700 also includes additional input / output (I / O) devices 712. In various embodiments, I / O devices 712 may include one or more data / signal transfer interfaces, audio I / O devices (e.g., a microphone or microphone array, a speaker, a headset, an earphone, an alarm, etc.), an audio codec, a video codec, a printer, sensors (e.g., a thermocouple or other temperature sensor, a humidity sensor, a pressure sensor, a vibration sensor, etc.), image capture devices (e.g., one or more cameras), human interface devices (e.g., a cursor control device such as a keyboard, a mouse, a stylus, a trackball, or a touchpad), etc.

[0062] Depending on the particular embodiment of the scientific instrument 100 and / or instrument portion 200, various components of the interface device 706 and / or I / O device 712 can be configured to output suitable control signals (e.g., 152, 154, 156, 408) for the various components of the scientific instrument 100, receive suitable control signals / telemetry signals from the various components of the scientific instrument 100, and receive streams of measurements (e.g., 162, 172, 182) from the various detectors of the scientific instrument 100. In some examples, the interface device 706 and / or the I / O device 712 include one or more analog-to-digital converters (ADCs) for converting received analog signals into a digital format suitable for operations performed by the processing device 702 and / or the storage device 704. In some additional examples, the interface device 706 and / or the I / O device 712 include one or more digital-to-analog converters (DACs) for converting digital signals provided by the processing device 702 and / or the storage device 704 into an analog format suitable for communication to corresponding components of the scientific instrument 100.

[0063] According to one example disclosed above, e.g., in the Summary of the Invention and / or with reference to any one or any combination of some or all of Figures 1-7, there is provided a scientific instrument including: an electron beam column configured to scan an electron beam across a sample, the electron beam column including a beam blanker configured to gate the electron beam in response to a binary drive signal having first and second levels, the first and second levels being selected to cause the beam blanker to pass the electron beam towards the sample when the binary drive signal is at the first level and to block the electron beam when the binary drive signal is at the second level; an electron detector configured to measure a flux of transmitted scattered electrons generated by interaction of the electron beam with the sample; and an electronic controller configured to acquire an image of the sample using values ​​of the flux measured for a plurality of electron beam scan positions, the electronic controller configured to cause the binary drive signal to have a gating frequency when the image has a moiré pattern therein.

[0064] In some examples of the above scientific instruments, the scientific instrument further includes a driver circuit configured to generate a binary drive signal in response to the gating signal, the driver circuit further configured to apply the binary drive signal to a beam blanker, and a waveform generator configured to generate the gating signal in response to a control signal received from the electronic controller, the control signal specifying a set of parameter values ​​for the gating signal including a gating frequency.

[0065] In some examples of any of the above scientific instruments, the set of parameter values ​​further includes a value for a duty cycle of the gating signal.

[0066] In some examples of any of the above scientific instruments, the set of parameter values ​​includes an increment value for changing the gating frequency.

[0067] In some examples of any of the above scientific instruments, the set of parameter values ​​includes signal synchronization information for a gating signal relative to a scan signal used to operate a scan coil of the electron beam column during a scan.

[0068] In some examples of any of the above scientific instruments, the scanning signal includes a staircase waveform.

[0069] In some examples of any of the above scientific instruments, the scanning signal is configured to achieve a pixel dwell time of less than 2 μs / pixel (or less than 1 μs / pixel, or less than 5 μs / pixel, or less than 10 μs / pixel).

[0070] In some examples of any of the above scientific instruments, the beam blanker includes an electrostatic beam deflector.

[0071] In some examples of any of the above scientific instruments, the electron detector is selected from the group consisting of a high angle annular dark field detector, a medium angle annular dark field detector, annular bright field detector, a segmented annular detector, a secondary electron detector, a backscattered electron detector, a differential phase contrast detector, an electron energy loss spectroscopy detector, an energy dispersive x-ray spectroscopy detector, and a two-dimensional pixelated or segmented electron detector.

[0072] In some examples of any of the above scientific instruments, the electronic controller is configured to generate a distortion map of the specimen based on the Moiré pattern.

[0073] In some examples of any of the above scientific instruments, the electronic controller is configured to adjust the electron beam column based on the Moiré pattern to position a focused portion of the electron beam at the sample.

[0074] In some examples of any of the above scientific instruments, the electronic controller is configured to perform a sweep of the gating frequency while the sampling frequency of the scan remains fixed.

[0075] According to another example disclosed above, e.g., in the Summary of the Invention, and / or with reference to any one or any combination of some or all of Figures 1-7, there is provided a method of moire imaging comprising: scanning an electron beam across a specimen using an electron beam column, the electron beam column including a beam blanker configured to gate the electron beam in response to a binary drive signal having first and second levels, the first and second levels being selected to cause the beam blanker to pass the electron beam towards the specimen when the binary drive signal is at the first level and to block the electron beam when the binary drive signal is at the second level; measuring with an electron detector a flux of transmitted scattered electrons generated by interaction of the electron beam with the specimen; acquiring with an electronic controller an image of the specimen using values ​​of the flux measured for a plurality of electron beam scan positions; and, with the electronic controller, causing the binary drive signal to have a gating frequency at which the image has a moire pattern therein.

[0076] In some examples of the above Moire imaging methods, the Moire imaging methods further include generating a binary drive signal in response to the gating signal, and generating the gating signal in response to a control signal received from the electronic controller, the control signal specifying a set of parameter values ​​for the gating signal including a gating frequency.

[0077] In some examples of any of the above moire imaging methods, the set of parameter values ​​further includes one or more of a duty cycle value of the gating signal, an increment value for changing the gating frequency, and signal synchronization information of the gating signal relative to a scanning signal used to operate a scanning coil of the electron beam column during scanning.

[0078] In some examples of any of the above Moire imaging methods, the scanning signal includes a staircase waveform.

[0079] In some examples of any of the above moire imaging methods, the scanning signal is configured to achieve a pixel dwell time of less than 2 μs / pixel (or less than 1 μs / pixel, or less than 5 μs / pixel, or less than 10 μs / pixel).

[0080] In some examples of any of the above Moire imaging methods, the Moire imaging method further includes generating a distortion map of the specimen based on the Moire pattern.

[0081] In some examples of any of the above Moire imaging methods, the Moire imaging method further includes adjusting the electron beam column based on the Moire pattern to position a focused portion of the electron beam at the specimen.

[0082] In some examples of any of the above Moire imaging methods, the Moire imaging method further includes sweeping the gating frequency while the sampling frequency of the scan remains fixed.

[0083] In some examples of any of the above Moire imaging methods, the method further includes one or more of: (i) sweeping the gating frequency until a near maximum Moire fringe contrast is achieved for a region of interest (ROI) or reference region of the sample; (ii) performing a full scan of the ROI at the determined gating frequency to ensure high Moire fringe contrast in the complementary scan direction; and (iii) swapping the fast and slow scan directions to perform another frequency sweep and / or another full scan.

[0084] In some examples of any of the above Moire imaging methods, the reference region is a region of the specimen where substantially zero distortion is expected.

[0085] In some examples of any of the above Moire imaging methods, the method further includes repeating one or more full scans with different respective gating frequencies.

[0086] In some examples of any of the above Moire imaging methods, the method further includes resolving sign ambiguity in the distortion map based on the one or more repeated full scans.

[0087] It should be understood that the above description is intended to be illustrative and not restrictive. Many implementations and applications other than the examples provided will become apparent upon reading the above description. The scope should not be determined with reference to the above description, but instead with reference to the appended claims, along with the full scope of equivalents to which such claims are entitled. It is anticipated and intended that future developments will occur in the art discussed herein, and that the disclosed systems and methods will be incorporated into such future examples. In short, it should be understood that this application is capable of modification and variation.

[0088] All terms used in the claims are intended to be given their broadest reasonable interpretation and their ordinary meaning as understood by a person skilled in the art described herein, unless expressly indicated to the contrary herein. In particular, the use of singular articles such as "a," "the," "said," etc., should be read to recite one or more of the indicated elements, unless the claims set forth an express limitation to the contrary.

[0089] The Abstract is provided to enable the reader to quickly ascertain the nature of the technical disclosure. The Abstract is submitted with the understanding that it will not be used to interpret or limit the scope or meaning of the claims. In addition, in the above Detailed Description, it may be seen that various features have been grouped together in various examples for the purpose of streamlining the disclosure. This method of disclosure should not be interpreted as reflecting an intention that the claimed subject matter incorporates more features than are expressly recited in each claim. Rather, as the following claims reflect, inventive subject matter lies in less than all features of a single disclosed example. Accordingly, the following claims are incorporated into the Detailed Description with each claim standing on its own as independently claimed subject matter.

[0090] Unless expressly stated otherwise, each numerical value and range should be construed as being approximate, as if the word "about" or "approximately" were preceding that value or range.

[0091] In the method claims that follow, elements, if any, are recited in a particular order with corresponding labeling, but unless the claim description otherwise suggests a particular order for implementing some or all of the elements, the elements are not necessarily intended to be limited to being implemented in that particular order.

[0092] Unless otherwise specified herein, the use of ordinal adjectives such as "first," "second," "third," etc. to refer to one object of a plurality of similar objects is intended only to indicate that different instances of such similar objects are being referred to, and is not intended to imply that the similar objects so referred to must be in a corresponding order or sequence, either in time, space, ranking, or in any other manner.

[0093] Unless otherwise specified herein, the conjunction "if" may additionally or alternatively be interpreted to mean "when" or "upon" or "in response to determining" or "in response to detecting," in addition to its plain meaning, which interpretation may depend on the corresponding specific context. For example, the phrase "when determined" or "if [a stated condition] is detected" may be interpreted to mean "upon determining" or "in response to determining" or "upon detecting [a stated condition or event]" or "in response to detecting [a stated condition or event]."

[0094] Also, for purposes of this description, the terms "couple," "coupling," "coupled," "connected," "connecting," or "connected" refer to any manner known in the art or later developed that allows energy to be transferred between two or more elements, where the intervening presence of one or more additional elements is contemplated, but not required. Conversely, the terms "directly coupled," "directly connected," and the like, imply the absence of such additional elements.

[0095] The functionality of the various elements shown in the figures, including any functional blocks labeled "processor" and / or "controller," may be provided through the use of dedicated hardware as well as hardware capable of executing software in association with appropriate software. When provided by a processor, the functionality may be provided by a single dedicated processor, by a single shared processor, or by multiple individual processors, some of which may be shared. Furthermore, explicit use of the terms "processor" or "controller" should not be construed as referring exclusively to hardware capable of executing software, and may implicitly include, without limitation, digital signal processor (DSP) hardware, network processors, application specific integrated circuits (ASICs), field programmable gate arrays (FPGAs), read only memory (ROM) for storing software, random access memory (RAM), and non-volatile storage. Other hardware, conventional and / or custom, may also be included. Similarly, any switches shown in the figures are conceptual only. Those functions may be performed through the operation of programmatic logic, through dedicated logic, through the interaction of programmatic control and dedicated logic, or even manually, with the particular technique being selectable by the implementer, as more particularly understood from the context.

[0096] As used in this application, the term "circuit" or "circuitry" may refer to one or more or all of the following: (a) hardware-only circuit implementations (such as implementations with only analog and / or digital circuitry); (b) (where applicable), (i) combinations of analog and / or digital hardware circuitry with software / firmware; and (ii) combinations of hardware circuitry and software, such as any portion of a hardware processor with software (including digital signal processors), software, and memory that work together to cause a device such as a mobile phone or server to perform various functions; and (c) hardware circuits and / or processors, such as a microprocessor or portions of a microprocessor, that require software (e.g., firmware) to operate, but the software may be absent when not required for operation. This definition of circuitry applies to all uses of the term in this application, including any claims. As a further example, as used in this application, the term circuitry also covers merely a hardware circuit or processor (or processors), or portions of a hardware circuit or processor, and its (or their) associated software and / or firmware implementations. The term circuitry also covers, for example, baseband or processor integrated circuits for mobile devices, or similar integrated circuits in servers, cellular network devices, or other computing or network devices, where applicable to particular claim elements.

[0097] Those skilled in the art will appreciate that any block diagrams herein represent conceptual views of illustrative circuitry embodying the principles of the present disclosure. Similarly, any flow charts, flow diagrams, state transition diagrams, pseudocode, or the like, may be substantially represented in a computer-readable medium and may represent various processes that may be performed by such a computer or processor, whether or not a computer or processor is explicitly depicted.

Claims

1. an electron beam column configured to scan an electron beam across a specimen, the electron beam column including a beam blanker configured to gate the electron beam in response to a drive signal; an electron detector configured to measure the flux of transmitted or scattered electrons that have interacted with the sample; 1. An electronic controller comprising: acquiring an image of the sample using values ​​of the flux measured by the electron detector for a plurality of electron beam scan positions; and an electronic controller configured to cause the drive signal to have a gating frequency when the image has a Moire pattern therein.

2. a driver circuit configured to generate the drive signal in response to a gate signal, the driver circuit further configured to apply the drive signal to the beam blanker; 10. The scientific instrument of claim 1, further comprising: a waveform generator configured to generate the gating signal in response to a control signal received from the electronic controller, the control signal specifying a set of parameter values ​​for the gating signal including the gating frequency.

3. The scientific instrument of claim 2 , wherein the set of parameter values ​​further comprises a value for a duty cycle of the gating signal.

4. The scientific instrument of claim 2 , wherein the set of parameter values ​​includes an increment value for changing the gating frequency.

5. 3. The scientific instrument of claim 2, wherein said set of parameter values ​​includes signal synchronization information for said gating signal relative to a scan signal used to operate a scan coil of said electron beam column during said scan.

6. The scientific instrument of claim 5 , wherein the scanning signal comprises a staircase waveform.

7. 6. The scientific instrument of claim 5, wherein the scanning signal is configured to provide a pixel dwell time of less than 2 [mu]s / pixel.

8. The scientific instrument of claim 1 , wherein the beam blanker comprises an electrostatic beam deflector.

9. The electron detector comprises: a high angle annular dark field detector; a medium angle annular dark field detector; an annular brightfield detector; a segmented annular detector; a differential phase contrast detector; A secondary electron detector; A backscattered electron detector; an electron energy loss spectroscopy detector; an energy dispersive X-ray spectrometer; 10. The scientific instrument of claim 1, wherein the detector is selected from the group consisting of: a two-dimensional pixelated or segmented electronic detector.

10. The scientific instrument of claim 1 , wherein the electronic controller is configured to generate a distortion map of the sample based on the Moiré pattern.

11. The scientific instrument of claim 1 , wherein the electronic controller is configured to adjust the electron beam column based on the Moiré pattern to position a focused portion of the electron beam at the sample.

12. The scientific instrument of claim 1 , wherein the electronic controller is configured to perform a sweep of the gating frequency while a sampling frequency of the scan remains fixed.

13. scanning the electron beam across a specimen using an electron beam column including a beam blanker configured to gate the electron beam in response to a drive signal; measuring the flux of transmitted or scattered electrons that have interacted with the sample using an electron detector; acquiring, with an electronic controller, an image of the sample using the measured flux values ​​for a plurality of electron beam scan positions; and using the electronic controller, causing the drive signal to have a gating frequency when the image has a moire pattern therein.

14. generating the drive signal in response to a gating signal; 14. The method of moire imaging of claim 13, further comprising: generating the gating signal in response to a control signal received from the electronic controller, the control signal specifying a set of parameter values ​​for the gating signal including the gating frequency.

15. The set of parameter values: a value of the duty cycle of the gating signal; and an increment value for changing the gating frequency; and signal synchronization information of the gating signal with respect to a scan signal used to operate a scan coil of the electron beam column during the scan.

16. The moire imaging method of claim 15 , wherein the scanning signal includes a staircase waveform.

17. 16. The method of moire imaging of claim 15, wherein the scanning signal is configured to achieve a pixel dwell time of less than 5 μs / pixel.

18. 14. The method of moire imaging of claim 13, further comprising generating a distortion map of the specimen based on the moire pattern.

19. 14. The method of moire imaging of claim 13, further comprising adjusting the electron beam column based on the moire pattern to position a focused portion of the electron beam at the specimen.

20. The method of moire imaging of claim 13 further comprising sweeping the gating frequency while a sampling frequency of the scan remains fixed.

Images