Dark correction for long-term acquisition

Abstract

A charged particle beam (CPB) imaging device intermittently acquires dark frames when the CPB is intercepted, and updates a dark reference using these intermittently acquired dark frames. The dark reference is used for compensating additive noise components in a collected sample frame, and is particularly used for compensating additive noise which is gradually increased in a long-time and multi-time image collection process.

Description

Technical Field

[0001] This disclosure relates to charged particle beam (CPB) imaging. Background Technology

[0002] Some applications of charged particle beam (CPB) imaging devices require long acquisition times, based on acquiring a large number of sample images over extended periods, such as in computed tomography (CT) electron microscopy. These sample images can be compensated for using a dark reference to correct for the presence of additive noise components (e.g., 1 / f and / or random telegraph signal (RTS) noise). In some instances, the dark reference comprises a combination of dark frames acquired before or after the sample image acquisition. A challenge with this traditional approach is that additive noise levels can change during image acquisition, and the dark reference acquired before or after acquisition may not reflect the actual noise during the acquisition process. This is generally not a problem for relatively short exposures, but such dark references are unsuitable for longer exposures (e.g., 30-second tomographic runs). Furthermore, in some cases, sample images are used for feature tracking, a process that uses artificial features (such as gold markers or identifiable intrinsic sample features) as a basis for image alignment. When sample images are used for feature tracking, fixed-pattern noise associated with additive noise components can be mishandled, causing the position of target features in the sample image to be misjudged as unchanged. For these and other reasons, alternative methods are needed. Summary of the Invention

[0003] This paper describes a charged particle beam (CPB) imaging apparatus and method for acquiring sample images and compensating for the images based on a dark reference frame.

[0004] A CPB imaging apparatus may include: a CPB source operable to illuminate a sample with CPB; a beam cutoff operable to selectively direct the CPB toward the sample; and a detection system operable to acquire a series of frames, the series of frames including a first set of sample frames, a second set of sample frames, a first set of dark frames, and a second set of dark frames, wherein the first and second sets of sample frames are associated with the operational beam cutoff to illuminate the sample with CPB, and the first and second sets of dark frames are associated with the operational beam cutoff to deflect at least a portion of the CPB away from the sample. The dark frames may be used to define a dark reference or as a dark reference to reduce detector noise.

[0005] A method of using the CPB imaging apparatus may include: acquiring a first set of one or more sample frames associated with a sample; compensating the first set of one or more sample frames based on a first dark reference to generate a first set of one or more compensated sample frames; acquiring a second set of one or more sample frames; acquiring one or more dark frames after acquiring the first set of one or more frames, wherein the one or more dark frames are acquired before, after, or both before and after the acquisition of the second set of one or more sample frames; updating the first dark reference based on the acquired one or more dark frames to create a second dark reference; and compensating the second set of one or more frames based on the second dark reference to generate a second set of one or more compensated sample frames.

[0006] The above and other objects, features and advantages of this disclosure will become more apparent from the following detailed description taken in conjunction with the accompanying drawings. Attached Figure Description

[0007] Figure 1 An exemplary charged particle beam (CPB) imaging system for updating a dark reference is shown.

[0008] Figure 2A-2C This demonstrates the impact of noise, such as 1 / f noise, on image quality during long-term image acquisition.

[0009] Figure 2D The example sequence shows the acquisition of sample frames, dark frames, and the updating of the dark reference.

[0010] Figure 3 An example method for dark correction of updating a dark reference is shown.

[0011] Figures 4A-4B An example method for dark correction is shown, which involves acquiring dark frames during pulse intervals.

[0012] Figures 5A-5B The diagram shows the acquisition of dark frames and image frames using a subset of the detector array pixels.

[0013] Figure 6 An example method is shown that uses a subset of the detector array pixels to acquire sample frames and dark frames.

[0014] Figure 7 A block diagram illustrating an example computing system or operating environment that can implement various disclosed embodiments. Detailed Implementation

[0015] This document discloses apparatus and methods for charged particle beam (CPB) imaging, such as CPB tomography. In CPB tomography, the sample is typically located on a rotatable sample stage and repeatedly exposed to the light at multiple angles. CPB. The disclosed examples are typically described with reference to transmission electron microscopy used for tomographic reconstruction, but other CPBs and other types of imaging may also be used. Alternatively, the sample may also be irradiated with X-rays and X-ray-based images acquired.

[0016] According to some aspects of this disclosure, during CPB imaging (e.g., transmission electron microscopy (TEM)), an image correction is performed to convert the raw detector data into frames that can be used for further processing (such as "dark correction"). Dark correction can compensate for additive noise components (e.g., 1 / f and / or RTS noise) present in the detector data. To achieve this correction, a small number of dark frames are typically collected before (and sometimes after) the sample is exposed to the CPB. These dark frames can be combined to create a dark reference, which is then used to compensate for the sample frames. While a dark reference can be created using a single dark frame, in some instances, multiple dark frames can be combined to create a dark reference. In some instances, an improved dark reference is required by averaging multiple dark frames. In some instances, as disclosed below, each dark frame can be assigned a weighting factor (e.g., relative to time and / or relative to the additive noise level), and the dark reference comprises a weighted average of the dark frames. General considerations

[0017] Here, "column" or "optical column" typically refers to one or more CPB optical elements or combinations thereof, such as a CPB source, CPB lens, CPB deflector, CPB stop, astigmatism corrector, or other CPB optical elements. One or more such optical elements can be used to generate pulsed CPB, which can be directed towards the sample to provide pulsed illumination. This pulsed illumination is often referred to as "stroboscopic" illumination, indicating that the effective exposure time is short enough relative to sample rotation to produce a suitable image, i.e., without excessive motion blur. A suitable exposure time can correspond to rotation amounts less than 0.0001 degrees, 0.001 degrees, 0.01 degrees, or other angles. The maximum permissible exposure duration can be set depending on the image magnification and the desired resolution. In stroboscopic illumination, the CPB can also have a continuous component in addition to the stroboscopic component. In many practical applications, pulsed illumination is preferred to reduce sample degradation caused by continuous CPB component illumination. Continuous components can lead to undesirable changes in the sample and do not improve tomographic imaging quality.

[0018] As used herein, the term "image" refers to an image displayed on a computer monitor, or a digital or analog representation that can be used to generate a displayed image. Digital representations can be stored in various formats, such as JPEG, TIFF, or others. Image signals can be generated by using an array detector or a unit detector in conjunction with appropriate scanning of the sample. In most practical examples, the image generated by the detector is two-dimensional, such as a two-dimensional array of pixels. In some examples, the image can be three-dimensional. In some examples, the image can be a composite image composed of multiple images. In one example, a composite image may include a tomographic reconstruction of the sample.

[0019] As used herein, the term "frame" refers to data associated with a detector and can be used as an image, to form an image, or to compensate for an image. "Sample frame" as used herein refers to an image frame obtained by exposing a sample to a CPB (charged particle beam); while "dark frame" refers to an image frame obtained without exposure to (or with reduced exposure to) the CPB, typically achieved by blocking or attenuating the CPB that would otherwise be directed at the sample. In most practical examples, a frame is a two-dimensional pixel array and can be obtained in many cases by an array detector, particularly in a TEM. In most cases, an image frame contains two-dimensional image data arranged in rows and columns. The term "subframe" can be used to describe a portion of a frame, for example, a one-dimensional row of pixels in a two-dimensional frame or other parts of the frame.

[0020] In some cases, the detector used to generate sample frames comprises a pixel array, where each pixel stores charge due to the sample S being exposed to the CPB. Because of this charge storage, the sample frame can still be obtained from the detector even after the CPB is blocked, at least for a period of time related to the charge storage time constant. Furthermore, with this charge storage, the timing of dark frame acquisition is preferably set to ensure that all charge associated with the previous CPB exposure has dissipated. Specific implementations include: reading it out as a sample frame, discarding it after reading it out, or allowing it to decay naturally based on the device charge storage time constant. In some applications, a large number of sample frames are acquired, and the process of switching the CPB current supplied to the sample from a higher value to a lower value (or zero value) requires a rapid response. In this document, switching the supplied CPB current from a higher value to a lower value is generally referred to as "blocking," which typically reduces the CPB current at the sample to zero. More generally, blocking can refer to reducing the CPB current supplied to the sample from a value I associated with acquiring the sample frame to less than or equal to I / 4, I / 5, I / 10, I / 20, I / 50, or I / 100. In these examples, blocking is illustrated using an electrostatic beam deflector, but blocking can also be achieved using a magnetic beam deflector, a combination of electrostatic and magnetic beam deflectors, direct modulation of CPB emission, focusing and defocusing using one or more CPB lenses, or other methods.

[0021] As used in this application and claims, the singular forms “a,” “an,” and “the” include the plural forms unless the context clearly indicates otherwise. Additionally, the term “comprising” means “including.” Furthermore, the term “coupled” does not exclude the presence of intermediate elements between the coupled elements.

[0022] The systems, apparatuses, and methods described herein should not be construed as limiting in any way. Rather, this disclosure is directed primarily at all novel and non-obvious features and aspects of the various embodiments disclosed, whether alone or in various combinations and sub-combinations with each other. The disclosed systems, methods, and apparatuses are not limited to any particular aspect or feature or combination thereof, nor are they required to possess any one or more particular advantages or problems solved. Any operational theories are provided for ease of explanation only, and the systems, methods, and apparatuses of this disclosure are not limited by such operational theories.

[0023] While some disclosed methods are described in a specific order for ease of presentation, it should be understood that this descriptive approach encompasses rearrangement unless the specific language below requires a particular order. For example, operations described in sequence may be rearranged or performed concurrently in certain situations. Furthermore, for the sake of brevity, the accompanying drawings may not show the various ways in which the disclosed systems, methods, and apparatus may be used in conjunction with other systems, methods, and apparatuses. Additionally, the description sometimes uses terms such as “produce” and “provide” to describe the disclosed methods. These terms are high-level abstract expressions of the actual operations performed. The actual operations corresponding to these terms will vary depending on the specific implementation and will be readily apparent to those skilled in the art.

[0024] In some examples, relevant parameter values, operating procedures, or devices may be described as "lowest," "best," "smallest," etc. It should be understood that these descriptions are intended to indicate that a selection can be made from many functional alternatives, and that such selection is not necessarily superior to, smaller than, or preferred over other options.

[0025] The examples are described using directions such as "up," "down," "above," and "below." These terms are used for ease of description and do not imply any specific spatial direction. Example 1

[0026] See Figure 1The CPB microscope or other CPB imaging system 100 includes a CPB source and an optical column 113 operable to illuminate a sample S with a CPB 114. A beam interruption system 103 (also referred to as a “beam interruptor”) is arranged to interrupt, deflect, or otherwise modulate the CPB 114 at predetermined times. In some examples, the CPB source may include an electron beam source. In some examples, the beam interruption system 103 is operable to intermittently interrupt the CPB, thereby allowing the acquisition of dark frames or sample frames. As used herein, “intermittent interruption” includes interruption at periodic time intervals, random time intervals, after the acquisition of a predetermined number of sample frames, and / or at time intervals determined based on the magnitude of noise amplitude in the dark frame, or interruption at other times.

[0027] In some examples, the beam blocking system 103 includes an aperture defined in an aperture plate 118, which can be used to interrupt or attenuate the CPB 114 when the deflection driver 130 applies a deflection voltage to the beam deflector 132 (e.g., a resonant beam deflector). The deflection driver 130 can be driven to produce deflection of the CPB 114. When the beam deflector 132 is activated, the CPB 114 is deflected to form a deflected beam 116, which is blocked by the aperture plate 118. In some examples, the CPB 114 is completely blocked by the aperture plate 118. In some examples, the deflected beam 116 is deflected such that only a portion of the CPB 114 is blocked by the aperture plate 118, thereby ensuring that the sample S receives attenuated CPB beam irradiation. In some cases, the area of ​​the sample S irradiated by the blocked CPB 114 is smaller than the area irradiated by the unblocked CPB; or although the same area is irradiated, it has a lower beam density.

[0028] During the period when the CPB 114 is not deflected by the beam blocking system 103, the detection system (including detector 119) can operate to acquire a series of sample frames associated with the sample S's exposure to the CPB 114. When the CPB 114 is deflected to form the deflected beam 116, detector 119 can operate to acquire one or more dark frames associated with additive noise components (e.g., background noise). As described above, in some cases, the charge associated with non-blank sample irradiation and stored by detector 119 needs to be read out or otherwise removed before acquiring the dark frames. Figure 1In some examples, the deflected CPB 116 is completely blocked by the aperture 118, and the dark frame includes only additive noise components or other signal portions not based on CPB illumination. In some examples, only a portion of the deflected beam is attenuated, and the dark frame includes both sample-based components and additive noise components. In other examples, the deflected CPB is incident on the sample S to acquire a sample frame, while the undeflected CPB is associated with acquiring the dark frame. In still other examples, the beam blocking system can be operated to provide the appropriate deflection to generate both the dark frame and the sample frame.

[0029] A deflection driver 130 is typically coupled to a controller 110, which can initiate or regulate beam deflection. In some examples, the controller 110 can be programmed to block the CPB 114 as described above. The controller 110 is coupled to the CPB source and optical column 113 and can generate the CPB 114 as a pulsed CPB to provide stroboscopic sample illumination. A detector 119 is arranged to receive charged particles or electromagnetic radiation induced by the CPB 114, such as scattered electrons, secondary electrons, X-rays, other charged or neutral particles, or other electromagnetic radiation. The detector 119 is coupled to the controller 110 so that computer-executable instructions stored in portion 120 of memory 121 can be used to acquire sample frames associated with CPB illumination and dark frames associated with attenuated (or no) illumination. Memory 121 may also store one or more sample frames, dark frames, dark references, and computer-executable instructions for determining the dark reference in portion 122. These sample frames, dark frames, and dark references can be stored together with a series of exposure times, sample tilt angles, or relative phases or time differences between acquisitions. In a typical example, dark frames acquired sequentially are averaged to generate a dark reference, but a single dark frame can also be selected as a dark reference to compensate for sample frames by removing or reducing components irrelevant to the sample to generate image frames (in some cases referred to as "compensated image frames"). In some examples, compensation means reducing the dark noise amplitude in the image frame by more than 80%, in some examples more than 90%, in some examples more than 95%, and in some examples even more than 99%. Compensation is typically based on subtracting the appropriate dark reference from the sample frame pixel-by-pixel to generate image frames, which the controller 110 can then combine into a composite image of the sample S. In some examples, the sample stage 102 is configured to rotate the sample S about axis 101. Exposure times can be determined based on a predetermined rotation rate of the sample S or based on a fixed or variable rotation speed of the sample stage 102. Alternatively, the controller 110 can transmit the sample frames and dark frames to arbitrary locations via wired or wireless networks for noise component correction, tomography, reconstruction, and display. Example 2

[0030] Figure 2A-2BThis shows the first ( ) during a 30-second acquisition process using a fixed dark reference to compensate for noise. Figure 2A ) and the last one ( Figure 2B Example of a sample image, where the fixed dark reference is obtained before the first sample frame is acquired. Figure 2C It shows the relationship with Figure 2A-2B Related noise. Figure 2B The visible striped pattern is due to changes in noise (e.g., 1 / f noise) during acquisition, causing compensation to neither reduce nor reduce image artifacts. Fixed dark references, during acquisition, become less effective at correcting sample frames due to variations in additive noise or other noise components (such as 1 / f noise and random telegraph signal (RTS) noise). Fixed dark references introduce fixed patterns into the compensated sample image sequence. In some examples, sample image sequences are used for feature tracking, allowing the use of artificial features (e.g., gold markers) or identifiable intrinsic sample features as a basis for image registration and / or determining sample drift. When tracking sample images using inappropriate or outdated dark references, fixed pattern noise associated with noise components can lead to inaccurate tracking, failing to detect sample shifts, or tracking noise features instead of sample features.

[0031] For short exposures (in some cases, about 1-10 seconds), a dark reference based on the dark frame prior to acquisition may be sufficient (see example). Figure 2A The image shown does not exhibit the aforementioned "striped pattern." For longer exposures, such as a 30-second tomographic scan run, the use of a fixed dark reference based on the pre-acquisition dark frame can be very effective, and the dark reference will introduce a fixed pattern into the compensated image sequence, such as... Figure 2B The vertical stripes are shown in the image.

[0032] Figure 2C Curves 204 and 206 are shown, illustrating the standard deviation of dark frames obtained using an exemplary charged particle detector as a function of time t. Curve 204 represents data based on a fixed dark reference obtained before acquiring sample frames, without sample components. As time progresses (from the first frame to which the fixed dark reference was applied), the initial dark image becomes irrelevant. The effect of the mismatch between the dark reference and the noise level is expected to increase approximately proportionally to the square root of time. Curve 206 represents data based on updating the dark reference every 32 sample frames acquired. It can be seen that when the dark reference is updated intermittently, the impact of dark noise on the sample image decreases.

[0033] Figure 2DRepresentative sequences 210, 220, and 230 of the acquired frames are shown. These sequences include sample frames (SF) and dark frames (DF) used to construct the associated dark reference (DR) and sample image (SI). Representative sequence 210 of the frames is associated with the initial dark reference DR0 constructed before acquiring any sample frames. Samples are placed in the CPB to obtain the sample frame set SF. 1 SF 2 SF 3 ..., which contains sample frames Where j is a positive integer. After acquiring each set of sample frames, the beam is blocked to obtain the corresponding dark frame set DF. 1 ,DF 2 ,DF 3 In Where k is a positive integer used to construct additional dark reference frames DR1, DR2, DR3. ... In sequence 210, each group of sample frames contains j sample frames, and each group of dark frames contains k dark frames; these frames are acquired alternately. In some examples, the number of frames contained in one or more sample frame groups may differ from the number of frames contained in one or more dark frame groups. As shown in representative frame sequence 220, the sample frame set SF... 1 ,SF 2 ,SF 3 ...containing frames j1, j2, j3,..., where j1, j2, j3,... are positive integers and can be the same or different; meanwhile, the dark frame set DF... 1 ,DF 2 ,DF 3 ... each contains k1, k2, k3 dark frames, where k1, k2, k3 are positive integers and can be the same or different. In some examples, the number of frames in any particular dark frame group or sample frame group can be determined based on factors such as: the time elapsed since the dark reference DR was determined, random time, the angular orientation of the sample, the magnitude of change of one or more recently determined dark references, technician preference, total exposure time, signal or signal-to-noise ratio in the sample frame, or other criteria. In one example, the dark frame group includes a single dark frame, while the sample frame group contains the same number of frames.

[0034] Dark frames can be used to generate a dark reference (DR), for example, by averaging frames within a group of dark frames or by selecting a representative dark frame from the group. An updated dark reference can be constructed using a weighted average of dark frames or previous dark references, where dark frames or dark references that are temporally distant from the sample frames are given lower weights. In some examples, spatial context can be utilized to construct the updated dark reference. In some examples, known spatial correlations exist between different pixels, which can be used to obtain a low-noise dark reference more quickly. In some examples, based on the precise camera chip layout, dark noise is correlated with the digital-to-analog converter module, as well as rows and columns, and known spatial correlations exist between different pixels, which can be used to quickly obtain a low-noise dark reference. In some examples, a model of the rate of change of dark noise patterns can be built for better estimation. In some examples, this modeling is primarily based on the 1 / f characteristic.

[0035] In some examples, the dark reference DR is calculated by updating the previously stored dark reference using a subsequently acquired set of dark frames. Dark references can also be obtained by combining multiple dark references, typically a combination of dark references associated with sequentially acquired groups of dark frames. Within any given set of sample frames, sample frames are typically calibrated using the same dark reference, but this is not mandatory. For example, a subset of sample frames acquired at the beginning of a set of sample frames can use a previously established dark reference, while a subset of sample frames acquired at the end of the set can use a subsequently determined dark reference that incorporates contributions from the relevant subsequent groups of dark frames.

[0036] Sample frames and dark references (based on dark frames) can be used to generate sample images (SIs) by compensating a given set of one or more sample frames based on the corresponding dark references. For example, sample frames (Taken from sample frame set SF) 2 Compensation can be performed based on DR1 to generate sample images. Right now Similarly, for other sample frames, compensation can be achieved using other dark references. In other examples, a set of SFs can be used. N Compensation is performed on sampled frames (e.g., time-weighted averaging or other average values) (based on dark reference DR). N-M ,...,DR N, ...DR N+L, (the average value of M and L), where M and L are non-negative integers.

[0037] In some examples, dark frames are acquired with the CPB attenuated but not completely blocked. For example, the CPB current I associated with sample illumination at the time of sample frame acquisition can be attenuated to (1–α)I during dark frame acquisition, where 0 ≤ α < 1. For sample frames and dark frames associated with common additive noise, subtracting the dark reference frame from the sample frame removes the common noise, but the resulting difference reduces the brightness of the sample image (SI), which can be reduced by... recover,, Where SFa represents the sample frame, DR is the associated dark reference frame, and α is defined as described above. For a fully occluded CPB, α = 0, and the sample image SI = SF. a –DR.

[0038] Typically, multiple sample images can be obtained by compensating multiple sets of sample frames based on their respective dark references. Compensation can be performed in real-time and / or near real-time during sample frame acquisition to track sample image features during acquisition. In other examples, sample frames and dark frames are stored, and sample images are generated at other times (e.g., after sample and dark frame acquisition). Example 3

[0039] See Figure 3 A representative method 300 includes acquiring one or more dark frames and constructing a dark reference (DR) in step 302. In some examples, constructing the dark reference includes averaging the one or more dark frames. In some examples, these dark frames are correlated with the level of additive noise present before acquiring any sample frames, or the initial dark reference DR0 may be defined as a zero array. In step 304, the CPB is deblanched, and the sample is exposed to the CPB.

[0040] In step 306, when the sample is exposed to the CPB, one or more frames associated with the sample (sample frames) are acquired until a preset criterion is met. This preset criterion can be a predetermined number of sample frames, a fixed time interval, or any other desired criterion. Once the preset criterion is met, the beam is blocked again in step 308, and in step 310, a second set of one or more dark frames is acquired. This second set of dark frames can be a set number of dark frames. The dark reference is then updated based on these acquired dark frames.

[0041] In step 312, it is determined whether the acquisition should be terminated. If acquisition continues, the process returns to step 304. In this way, the dark reference can be updated intermittently between sample frames, effectively utilizing the dark reference to compensate for noise in the sample frames to generate image frames. Sample images can be... Figure 3 The frames shown are generated during the acquisition process, or they can be generated after all or part of the acquisition is completed. Example 4

[0042] When using pulsed illumination, dark frames and sample frames can be acquired without the need for additional beam blocking. See also Figure 4A Method 400 includes selecting the CPB pulse duration and repetition frequency, or other CPB pulse time intervals, in step 402. An initial dark reference is established in step 404, and one or more CPB pulses are applied and corresponding sample frames are acquired in step 406. In step 408, one or more dark frames are acquired during the pulse interval. Dark frame acquisition may require reading the charge stored in the detector based on previous pulse illumination, or providing a delay to allow the stored charge to dissipate. In some cases, dark frames are acquired during each pulse interval after each CPB pulse and sample frame acquisition. Alternatively, dark frames can be acquired within a selected pulse period, and the pulse repetition frequency can be reduced if necessary to accommodate longer dark frame acquisition times. In step 410, it is determined whether more sample frames and dark frames need to be acquired; if so, the process returns to step 406. If acquisition is complete, the sample frames and dark frames are transmitted in step 412. In this method, beam interruption is associated with pulsed CPB illumination and compensated for after all sample frames and dark frames have been acquired.

[0043] In some examples, the CPB pulse is achieved by pulsed deflection of a constant beam. In some examples, the CPB pulse is generated directly from a pulsed beam. In some examples, the CPB is generated by photoelectron emission, while the beam pulse is obtained by blocking the beam.

[0044] See Figure 4B Method 450 includes selecting the CPB pulse duration and repetition frequency, or other CPB pulse time intervals, in step 452. An initial dark reference is established in step 454. One or more CPB pulses are applied and corresponding sample frames are acquired in step 456. One or more dark frames are acquired during the pulse interval in step 458. In step 460, the sample frames and dark frames are combined to generate a compensated image. In some examples, one or more dark frames may be acquired before applying one or more CPB pulses and acquiring the corresponding sample frames. In some examples, one or more dark frames may be acquired after applying one or more CPB pulses and acquiring the corresponding sample frames. In some examples, one or more dark frames may be acquired both before and after applying one or more CPB pulses and acquiring the corresponding sample frames. In step 462, it is determined whether more sample frames and dark frames need to be acquired; if so, the process returns to step 456. Example 5

[0045] In typical applications, the common pixel set of the array detector (usually almost all pixels) is used to acquire sample frames and dark frames, which can be acquired and read out separately in different readout operations; therefore, the sample frames and dark frames can be collectively referred to as the "full frame". If the exposed portion of the sample is imaged onto a subset of the detector array pixels, the readout of the complete detector array includes the sample subframe corresponding to that exposed sample portion, as well as the dark subframes corresponding to the other detector pixels (referred to herein as the "complementary" set or region).

[0046] In some examples, sample images are obtained by sequentially exposing sample regions smaller than the entire ROI and mapping them to a subset of detector pixels. This allows for the simultaneous acquisition of sample and dark subframes in a single acquisition, and the acquisition of the full frame through multiple acquisitions of different sample regions. See also Figures 5A-5B A subset 504 of pixels on the effective surface 500 of the detector receives radiation from the corresponding sample region. A subset 502 of pixels remains unexposed and can be used to acquire dark frames. Figure 5B In this method, a subset 514 of pixels on detector surface 500 receives radiation from the corresponding sample region. A subset 512 of pixels is unexposed and can be used to acquire dark frames. By combining multiple sample subframes, a sample frame associated with the entire effective surface of the detector can be generated; by combining multiple dark frames, a dark frame associated with the entire effective surface of the detector can be generated. Pixel subsets can have various shapes and sizes. In this method, the CPB is limited to illuminating only the sample portion imaged onto the pixel subset of the detector. In this example, the CPB is blocked (or shaped) to illuminate only selected areas. As mentioned above, the CPB in the dark frame region does not need to be completely blocked. Example 6

[0047] See Figure 6 Representative method 600 includes illuminating a selected portion of the target region of interest (ROI) in step 602, and imaging the selected portion onto a subset of the detector array pixels in step 604. In step 606, a sample subframe corresponding to the illuminated sample portion and a dark subframe corresponding to the complementary (unilluminated) sample portion are acquired. In step 608, other portions of the sample region can be selected for imaging, and the acquisition process can be repeated. After completion, the sample subframe and dark subframe are stitched together in steps 612 and 614 respectively to form a sample frame and a dark frame, and in step 616, the sample frame is compensated based on the dark frame to form a sample image. A specific arrangement of sample values ​​and dark frame values ​​according to the corresponding array can be used, but other suitable mapping methods can also be used. Example 7

[0048] Figure 7The following discussion is intended to provide a brief general description of an exemplary computing environment in which the disclosed techniques can be implemented. For example, one or more aspects of the CPB instrument controller and frame processing can be performed in this computing environment, which can also be used to control a beam blocking system, control a charged particle microscope system, and / or perform any part of the methods described above.

[0049] While not mandatory, the disclosed techniques are described in a general environment where computer-executable instructions (such as program modules) are executed by a personal computer (PC). Typically, program modules include routines, programs, objects, components, data structures, etc., that perform specific tasks or implement specific abstract data types. Furthermore, the disclosed techniques can be implemented using other computer system configurations, including handheld devices, tablets, multiprocessor systems, microprocessor-based or programmable consumer electronics devices, network PCs, minicomputers, mainframes, virtual machines, containerized applications, etc. The disclosed techniques can also be implemented in distributed computing environments where tasks are executed by remote processing devices connected via a communication network. In distributed computing environments, program modules can reside in both local and remote memory storage devices. The disclosed system can be used to control image acquisition and provide a user interface, or it can be used as an image processor.

[0050] Combination Figure 7 An example system implementing the disclosed technology includes a general-purpose computing device in the form of an exemplary conventional PC 700, including one or more processing units 702, system memory 704, and a system bus 706 coupling various system components, including the system memory 704, to the one or more processing units 702. The system bus 706 can be any of several types of bus structures, including a memory bus or memory controller, a peripheral bus, and a local bus using various bus architectures. The exemplary system memory 704 may include read-only memory (ROM) and random access memory (RAM), wherein the ROM stores a basic input / output system (BIOS) containing basic routines for facilitating information transfer between components within the PC 700.

[0051] The exemplary PC 700 also includes one or more storage devices 730, such as hard disk drives (HDDs) for reading from and writing to hard disk drives or solid-state drives (SSDs), which can be connected to the system bus 706 via a hard disk drive interface. These devices and their associated computer-readable media provide the PC 700 with non-volatile storage of computer-readable instructions, data structures, program modules, and other data. Multiple program modules can be stored in the storage device 730, including operating systems, multiple operating systems, virtual operating systems, one or more applications, other program modules, and / or program data.

[0052] The exemplary PC 700 may include various devices configured as user interfaces. For example, a user may input commands and information to the PC 700 via one or more input devices 740, such as a keyboard and pointing devices, such as a mouse. For example, a user may input commands to initiate image acquisition and / or initiate one or more methods disclosed herein. Input devices are typically connected to one or more processing units 702 via a serial port interface and coupled to the system bus 706, but may also be connected via other interfaces, such as a parallel port, a universal serial bus (USB), or a wired or wireless network connection. A display 746 or other type of display device may also be connected to the system bus 706 via an interface such as a video adapter and may display, for example, images of one or more samples or specimens before, after, and / or during the execution of one or more methods disclosed herein.

[0053] like Figure 7 As shown, memory 704 includes portions 771 and 772 for storing sample frames and dark frames, portion 773 for storing computer-executable instructions for sample frame compensation and image frame storage, and portion 774 for providing CPB control, occlusion, frame acquisition, and other operation instructions related to the disclosed method.

[0054] PC 700 can operate in a network environment through a logical connection to one or more remote computers (such as remote computer 760). In some examples, one or more network or communication connections 750 are included for wired or wireless communication and data acquisition and control, such as digital-to-analog converters and analog-to-digital converters. Remote computer 760 can be another PC, server, router, network PC, peer device, or other common network node, and typically includes many or all of the components associated with PC 700, although... Figure 7 Only memory storage device 762 is shown. PC 700 and / or remote computer 760 can be connected to a local area network (LAN) and a wide area network (WAN). Such network environments are common in offices, enterprise-wide computer networks, intranets, and the Internet. The network connections shown are exemplary, and communication links can be established between computers in other ways. Example 8: CPB imaging for fault reconstruction

[0055] The disclosed method is particularly useful in CPB tomography because the acquisition process for obtaining a large number of images that need to be combined is relatively lengthy. In some CPB tomography examples, a series of frames for tomographic reconstruction is acquired using stroboscopic illumination of a rotating sample at random or other angular sequences. The sample can rotate at a constant angular velocity, and random angular exposures can be established based on one or more sequences of angle values, which can be generated on demand or retrieved from computer-readable storage (such as memory). Angles can be based on the phase associated with the sample rotation, a set of exposure times based on the sample rotation speed, randomly generated during image acquisition, or otherwise determined. The sample can rotate at a fixed or variable speed and be stroboscopically illuminated during rotation. The stroboscopic illumination can be at a fixed or variable rate, including rotations of random duration. Illumination angles can be determined before, during, or after illumination and can be a fixed or variable angular distribution, including random angles. Dark frames can be acquired between stroboscopic pulses or at times associated with sample rotation where sample frames are not required. As mentioned earlier, during dark frame acquisition, the pulsed CPB radiation does not need to be completely attenuated because noise will still be attenuated by compensating the sample frame by subtracting the dark reference. However, the signal frame amplitude will be reduced due to the sample being irradiated with non-zero CPB. For unidirectionally rotating samples, dark frames can be acquired at a fixed angle for each rotation, such as the angle at which no sample frame is acquired or any other convenient angle.

[0056] In some examples, for convenience, sample exposure uses a constant rotational speed to produce uniformly spaced exposures, but non-uniform speeds can also be used, such as monotonically increasing or decreasing speeds, or arbitrarily increasing and decreasing rotational speeds. With constant rotation, samples can be acquired at random exposure angles at appropriate pulse rates or pulse intervals. As previously mentioned, this random exposure can be based on random exposure times or rotational phases that can be stored or generated on demand. Alternatively, sample rotation can use a variable speed (such as a random speed), and exposure times can be separated by constant delays. Example 9 Other Examples

[0057] Besides its use in tomographic reconstruction imaging, the disclosed method is useful for a variety of other applications. For example, applications requiring long acquisition times relative to the rate of change of dark noise. In some examples, these applications include sample navigation or search. In some examples, these applications include dynamic image processing of samples. In some examples, applications require very high total doses relative to the dose per unit time, which may be limited by the CPB source intensity or camera characteristics, thus requiring long accumulation periods.

[0058] In some examples, a subsequent set of one or more sample frames is acquired after acquiring one or more sets of predetermined sample frames. In some examples, any parameter can be varied based on user input, presets, or other inputs. In some examples, the number of samples in the first and / or second sets is dynamically changed, for example, the size and / or duration of the frame sets are adjusted in real-time during acquisition based on data quality. Disclosure of Examples

[0059] In view of the above specific implementations of the disclosed subject matter, this application discloses additional embodiments listed below. It should be noted that both a single feature of an embodiment, or a combination of multiple features of that embodiment (or selectively combined with features of one or more other embodiments), are additional embodiments covered by the scope of this application.

[0060] Example 1 is a method comprising: acquiring one or more sample frames in a first group related to a sample; compensating the one or more sample frames in the first group based on a first dark reference to generate one or more compensated sample frames in the first group; acquiring one or more sample frames in a second group; acquiring one or more dark frames after acquiring the one or more frames in the first group, wherein the one or more dark frames are acquired before, after, or both before and after acquiring the one or more sample frames in the second group; updating the first dark reference based on the acquired one or more dark frames to create a second dark reference; and compensating the one or more frames in the second group based on the second dark reference to generate one or more compensated sample frames in the second group.

[0061] Example 2 includes the subject matter of Example 1, and further specifies that each frame in the first group of one or more sample frames and the second group of one or more sample frames is acquired by detecting charged particles or electromagnetic radiation generated by irradiation of the sample by a charged particle beam (CPB).

[0062] Example 3 includes the subject matter of any of Examples 1-2, and further specifies that the CPB includes an electron beam.

[0063] Example 4 includes the subject matter of any of Examples 1-3, and further specifies that one or more sample frames of the first and second groups are acquired at one or more tilt angles relative to the charged particle beam (CPB).

[0064] Example 5 includes the subject matter of any of Examples 1-4, and further includes combining one or more compensated first group of sample frames with one or more compensated second group of sample frames to create a composite image of the sample.

[0065] Example 6 includes the subject matter of any of Examples 1-5, and further specifies that the composite image includes tomographic reconstruction of the sample.

[0066] Example 7 includes the subject matter of any of Examples 1-6, and further includes continuously rotating the sample while acquiring one or more sample frames in the first group and one or more sample frames in the second group.

[0067] Example 8 includes the subject matter of any of Examples 1-9, and further specifies that each frame in the first group of one or more sample frames, the second group of one or more sample frames, and one or more acquired dark frames includes a two-dimensional pixel array.

[0068] Example 9 includes the subject matter of any of Examples 1-8, and further specifies that the acquisition of the second group of one or more sample frames is performed after a predetermined number of sample frames in the first group of one or more sample frames have been acquired.

[0069] Example 10 includes the subject matter of any of Examples 1-9, and further specifies that the acquisition of the second group of one or more sample frames is performed at a fixed time interval after the acquisition of one or more sample frames in the first group of one or more sample frames.

[0070] Example 11 includes the subject matter of any of Examples 1-10, and further includes tracking sample features using a compensated first set of one or more sample frames and a compensated second set of one or more sample frames.

[0071] Example 12 includes the subject matter of any of Examples 1-11, and further includes: acquiring a second group of one or more dark frames after acquiring a second group of one or more sample frames; acquiring a third group of one or more sample frames; and compensating the third group of one or more sample frames based on at least the first and second groups of one or more dark frames.

[0072] Example 13 A charged particle beam (CPB) device includes: a charged particle beam (CPB) imaging apparatus comprising: a CPB source operable to irradiate a sample with CPB; a beam cutoff operable to selectively direct the CPB toward the sample; and a detection system operable to acquire a frame sequence including a first set of sample frames, a second set of sample frames, a first set of dark frames, and a second set of dark frames, wherein the first set of sample frames and the second set of sample frames are associated with the operational beam cutoff to irradiate the sample with CPB, and the first set of dark frames and the second set of dark frames are associated with the operational beam cutoff to deflect at least a portion of the CPB from the sample.

[0073] Example 14 includes the subject matter of Example 13 and further specifies that the beam blocker includes a beam deflector and an aperture plate, wherein the beam deflector selectively deflects the CPB away from the aperture plate in the aperture plate.

[0074] Example 15 includes the subject matter of any of Examples 13-14 and further includes a controller configured to control a beam blocker to generate a first set of frames, a second set of frames, a first set of dark frames, and a second set of dark frames.

[0075] Example 16 includes the subject matter of any of Examples 13-15, and further specifies that the controller is configured to: establish a first dark reference based on a first set of dark frames; update the first dark reference based on a second set of dark frames to create a second dark reference; compensate the first set of sample frames using the first dark reference to create a compensated first set of sample frames; and compensate the second set of frames using the second dark reference to create a compensated second set of sample frames.

[0076] Example 17 includes the subject matter of any of Examples 13-16, and further specifies that the controller is operable to combine the compensated first set of sample frames with the compensated second set of sample frames to generate a composite image.

[0077] Example 18 includes the subject matter of any of Examples 13-17, and further specifies that the controller is also operable to combine the compensated first set of sample frames with the compensated second set of sample frames to calculate the tomographic reconstruction of the sample.

[0078] Example 19 includes the subject matter of any of Examples 13-18, and further specifies that the CPB source includes an electron beam source, and that the CPB includes an electron beam.

[0079] Example 20 is a charged particle beam (CPB) imaging method, comprising: intermittently interrupting the acquisition of sample frames based on radiation received from the sample in response to CPB, so as to acquire one or more dark frames during each intermittent interruption; and constructing a sample image based on the sample frames and the one or more dark frames acquired during each intermittent interruption.

[0080] Example 21 includes the subject matter of Example 20 and further specifies that establishing a sample image includes compensating multiple sets of sample frames based on each set of dark frames acquired during relevant intermittent interruptions, wherein the sample image is established by combining the compensated multiple sets of sample frames.

[0081] Example 22 includes the subject matter of any of Examples 20-21, and further specifies that the sample frame is acquired at one or more tilt angles of the sample relative to the CPB.

[0082] In light of the various possible examples of the disclosed technology, it should be recognized that the illustrated embodiments are merely preferred embodiments and should not be considered as limiting.

Claims

1. A method comprising: Acquire one or more sample frames in the first set related to the sample; The first group of one or more sample frames are compensated based on the first dark reference to generate the first group of one or more compensated sample frames. Acquire one or more sample frames from the second group; After acquiring one or more frames in the first group, one or more dark frames are acquired, wherein the one or more dark frames are acquired before, after, or both before and after acquiring one or more sample frames in the second group. The first dark reference is updated based on one or more dark frames acquired to create a second dark reference; as well as The second group of one or more frames is compensated based on the second dark reference to generate the second group of one or more compensated sample frames.

2. The method of claim 1, wherein each of the first group of one or more sample frames and the second group of one or more sample frames is obtained by detecting charged particles or electromagnetic radiation generated in response to the sample being irradiated by a charged particle beam (CPB).

3. The method of claim 2, wherein the CPB comprises an electron beam.

4. The method of claim 2, wherein the first group of one or more sample frames and the second group of one or more sample frames are acquired at one or more tilt angles of the sample relative to the CPB.

5. The method of claim 4, further comprising combining the compensated first group of one or more sample frames with the compensated second group of one or more sample frames to create a composite image of the samples.

6. The method of claim 5, wherein the composite image comprises tomographic reconstruction of the sample.

7. The method of claim 4, further comprising continuously rotating the sample while acquiring the first group of one or more sample frames and the second group of one or more sample frames.

8. The method of claim 1, wherein each of the first group of one or more sample frames, the second group of one or more sample frames, and the one or more acquired dark frames comprises a two-dimensional pixel array.

9. The method of claim 1, wherein the acquisition of the second group of one or more sample frames is performed after acquiring a predetermined number of sample frames from the first group of one or more sample frames.

10. The method of claim 1, wherein the acquisition of the second group of one or more sample frames is performed at a fixed time interval after the acquisition of one or more sample frames in the first group of one or more sample frames.

11. The method of claim 4, further comprising tracking sample features using a compensated first set of one or more sample frames and a compensated second set of one or more sample frames.

12. The method of claim 4, further comprising: After acquiring one or more sample frames from the second group, acquire one or more dark frames from the second group. Acquire one or more sample frames from the third group; as well as Based on at least one or more dark frames from the first and second groups, compensation is applied to one or more sample frames from the third group.

13. A charged particle beam (CPB) imaging device, comprising: A CPB source operable to irradiate a sample with CPB; Operable beam cutoff to selectively direct CPB toward the sample; as well as A detection system operable to acquire a frame sequence including a first set of sample frames, a second set of sample frames, a first set of dark frames, and a second set of dark frames, wherein the first set of sample frames and the second set of sample frames are associated with an operational beam cutoff to illuminate the sample with CPB, and the first set of dark frames and the second set of dark frames are associated with an operational beam cutoff to deflect at least a portion of the CPB from the sample.

14. The CPB imaging apparatus of claim 13, wherein the beam blocker comprises a beam deflector and an aperture plate, and the beam deflector selectively deflects the CPB away from the aperture plate in the aperture plate.

15. The CPB imaging apparatus of claim 13, further comprising a controller configured to control a beam cutoff to generate a first set of frames, a second set of frames, a first set of dark frames, and a second set of dark frames.

16. The CPB imaging apparatus of claim 15, wherein the controller is configured to: A first dark reference is established based on the first set of dark frames; The first dark reference is updated based on the second set of dark frames to create the second dark reference; The first set of sample frames is compensated using the first dark reference to generate the compensated first set of sample frames. as well as The second set of frames is compensated using a second dark reference to generate a compensated second set of sample frames.

17. The CPB imaging apparatus according to claim 16, wherein the controller is operable to combine the compensated first set of sample frames with the compensated second set of sample frames to generate a composite image.

18. The CPB imaging apparatus according to claim 16, wherein the controller is further operable to combine the compensated first set of sample frames with the compensated second set of sample frames to calculate the tomographic reconstruction of the sample.

19. The CPB imaging apparatus of claim 13, wherein the CPB source comprises an electron beam source, and the CPB comprises an electron beam.

20. A charged particle beam (CPB) imaging method, comprising: Based on the radiation received from the sample in response to CPB, the acquisition of sample frames is intermittently interrupted to acquire one or more dark frames during each intermittent interruption. as well as A sample image is constructed based on the sample frame and one or more dark frames acquired during each intermittent interruption.

21. The CPB imaging method according to claim 20, wherein establishing the sample image comprises: Based on the dark frames acquired during the corresponding intermittent interruptions, multiple sample frame sets are compensated separately, and sample images are constructed by combining these compensated sample frame sets.

22. The CPB imaging method of claim 20, wherein the sample frame is acquired at one or more tilt angles of the sample relative to the CPB.

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