Dispersive imaging enables sample relaxation.

Abstract

Disclosed are a method and apparatus for providing repeated exposure of a sample area to a charged particle beam (CPB) such that effective exposure is controlled to avoid or reduce sample damage caused by the CPB. [Solution] CPB images are acquired using pulsed exposures to a defined field of view (FOV) within the region of interest of the sample. Multiple exposures are performed at time intervals longer than the phonon lifetime to reduce sample damage induced by CPB exposure. The FOV can be defined to be spaced apart in order to control the effective radiation dose based on a combination of direct and evanescent exposures.

Description

[Technical Field]

[0001] This application relates to charged particle beam imaging with reduced sample damage. [Background technology]

[0002] Many samples of interest in electron microscopy imaging are beam-sensitive and are destroyed or otherwise altered in response to electron beam exposure. Such alterations can significantly change the properties of the sample and limit the usefulness of subsequent imaging. Damage can be associated with, for example, atomic emission or displacement, secondary electron emission, or bond breakage in response to the electron beam. While damage can be mitigated to some extent by using very low beam doses, such low doses typically cannot provide satisfactory image quality. Therefore, an approach is needed that can reduce or eliminate the effects of such damage on sample images while still providing a suitable image signal-to-noise ratio. [Overview of the Initiative]

[0003] A method and apparatus for providing repeated exposure of a sample region to a charged particle beam (CPB) is disclosed, such that effective exposure is controlled to avoid or reduce sample damage by the CPB. CPB exposures can be temporally separated so that subsequent exposure of the sample region occurs after the reversible CPB-induced sample changes from previous CPB exposures have dissipated or mitigated. This mitigation ensures that the sample region is effectively exposed only by the currently applied CPB, avoiding the combined effects of previous exposures. In addition, CPB exposures can be temporally or spatially separated to avoid the combined effects of current CPB exposure of a selected sample region with evanescent exposure from previously exposed sample regions. According to the disclosed approach, the total charge, such as the number of electrons applied to the sample region, can be controlled to as little as 1. Such limited exposures may be particularly useful for samples such as frozen samples of biological materials.

[0004] The aforementioned and other features and advantages will become clearer from the following detailed description, which will proceed with reference to the attached drawings. [Brief explanation of the drawing]

[0005] [Figure 1] This illustrates a typical CPB imaging system that provides pulsed CPB exposure across multiple fields of view (FOV) defined within a region of interest (ROI) of a sample. [Figure 2] The diagram illustrates a set of FOVs arranged in a rectangular array of spaced-out FOVs and the corresponding FOV images in response to pulsed CPB exposure. Figure 2 illustrates a specific sequence of FOV image acquisition. [Figure 3A] The example illustrates first and second rectangular arrays of separated FOVs, where the first and second sets are offset along the axis. [Figure 3B] The example illustrates first and second rectangular arrays of separated FOVs, where the first and second sets are offset along the axis. [Figure 4] This example illustrates a typical CPB imaging system that provides pulsed CPB exposure across multiple FOVs by deflecting the CPB to each FOV and deflecting the associated FOV image beam along the axis of the CPB detector. [Figure 5A] Typical FOV and surrounding evanescence regions are illustrated with examples. [Figure 5B] Figure 5A illustrates an example of an FOV, which has a peripheral evanescence region that partially overlaps when exposed with a CPB pulse. [Figure 5C] This illustrates the changes within the peripheral evanescence region after exposure to a CPB. [Figure 6] This document illustrates a typical method of CPB imaging using independently exposed FOVs. [Figure 7A] The examples illustrate separated fields of view (FOVs) that include the features of interest to each individual. [Figure 7B]This illustrates an example of an FOV as shown in Figure 7A, where pixels of an array detector positioned to image the FOV are superimposed. [Figure 8] This illustrates independently exposable FOVs with evanescent boundaries, exposed using different doses. [Figure 9A] This example illustrates adjacent square FOVs that are not separated by the evanescent peripheral region. [Figure 9B] This illustrates overlapping exposures of FOVs with controlled doses. [Figure 10] This document illustrates a typical computing environment adapted to control FOV exposure and image processing. [Modes for carrying out the invention]

[0006] Introduction and Terminology The CPB imaging apparatus and method disclosed herein enable sample imaging with reduced or no contribution associated with reversible sample changes in response to CPB exposure. In an example, a sample region is exposed with a CPB pulse at a pulse timing selected to allow for the recovery of a reversible change in response to a previous CPB exposure. In addition, the CPB exposure may be configured to expose multiple sample regions, which are separated by a peripheral distance associated with evanescent coupling from the exposed region. The sample is maintained at a low temperature, and the CPB exposure may be configured to avoid or suggest irreversible changes to the sample.

[0007] Many types of samples are beam-sensitive, with a maximum of 40 electrons / Å. 2 Some samples, which are destroyed, damaged, or altered in response to electron beam doses exceeding Å (angstroms), but maintained at lower temperatures (typically cryogenic temperatures below 100 K, such as or near the boiling point of liquid nitrogen at 77 K), can tolerate doses more than twice as large. Dose-dependent sample changes include physical, chemical, and other changes that can render post-exposure sample imaging uninformative.

[0008] As used herein, the field of view (FOV) is the area of the sample of interest that is exposed by a single pulse of a charged particle beam (CPB). An image of the sample of interest is obtained by exposing one or more FOVs with multiple CPB pulses. As described below, the FOV can be exposed repeatedly or multiply with the CPB to improve the signal-to-noise ratio in the FOV image. The FOV region can be selected taking into account the available pulsed CPB beam current, for example, by selecting the FOV region such that the CPB dose associated with the CPB pulse does not produce unacceptable changes in the features of interest of the sample. In some cases, it is desirable to use a relatively large CPB beam current and a relatively short exposure time to generate a suitable FOV image.

[0009] Some types of exposure-related effects on the FOV may not be recoverable and may depend on the total dose or total exposure energy, while other exposure-related effects disappear or decrease as a function of the time after exposure. Irrecoverable changes can be associated with so-called knock-on displacements in which atoms in the sample are ejected or displaced by the exposure. Recoverable changes can be associated with the emission of secondary electrons, charging of the sample, and possibly bond breakage. However, the approaches disclosed herein do not depend on any particular mechanism of reversible or irreversible changes.

[0010] As used herein, "FOV relaxation time" or "relaxation time" t relax is the time interval from the time of exposure of the FOV to the CPB pulse to the time associated with sample recovery from the recoverable changes generated by the CPB exposure. The FOV relaxation time is also associated with the time interval after the CPB exposure in which subsequent CPB exposures produce sample changes that do not depend on previous CPB exposures, disregarding the irrecoverable changes generated by the first exposure. The sample can be considered to have returned to the state of the previous exposure, and the effects of subsequent CPB exposures do not depend on the previous exposure, except for the extent to which the previous exposure produced irrecoverable changes. The relaxation time trelax can be associated with the lifetime of phonons generated by CPB exposure, which is typically between 1 μs and 10 μs.

[0011] Exposure of the FOV to CPB also generates a peripheral region of the FOV called the "effective exposure region" herein, based on the evanescent CPB effect from the associated exposed FOV. Evanescent exposure is contrasted with exposure resulting from charged particles incident on a region that can be called "direct" exposure. Effective exposure typically decays with an evanescent time constant that is much shorter than the FOV relaxation time. To reduce sample changes in response to CPB exposure, these peripheral regions are considered to be effectively exposed when the associated FOV is exposed. Thus, the FOVs to be exposed may be separated in consideration of the extent of such effectively exposed regions so as to avoid applying an excessive CPB dose to the peripheral regions. Alternatively, subsequent exposures can be separated in time based on the evanescent relaxation time. As used herein, the distance associated with evanescent exposure is L ev which is called and adjacent, sequentially exposed FOVs can be separated by this distance to avoid or reduce sample changes due to CPB. Evanescent exposure tends to decay much more rapidly than the relaxation time t relax and persists for a time of less than 1 ns, so evanescent exposure is generally only considered for FOVs sequentially exposed within less than 5 - 10 ns. The evanescent distance L ev is a function of the time after exposure and decays rapidly to zero. <(

[0012] "Dose" refers to charge / area or energy / area associated with CPB exposure. The sample response to any CPB dose is a function of both the total charge (the product of the CPB pulse duration and the CPB beam current), the CPB beam energy, the CPB current, and the CPB pulse duration. For the sake of explanation, sample changes in response to CPB exposure are called dose-dependent.

[0013] In some examples, FOV exposures and associated images are paired with a "timestamp" or other indicators that allow the FOV images to be assembled into a larger image of the sample ROI. For FOVs obtained by raster scanning of a CPB, the sequence of FOV images can be assembled based on the number of FOVs in a row and the number of scanned rows, and no other position indicators are required. In some cases, the FOV is arbitrarily selected, and an indication of the CPB (and FOV) at a specific time is required.

[0014] A beam or radiation beam refers to a propagating charged particle or propagating electromagnetic radiation, whether collimated or not. In some examples, the field of view (FOV) is arranged within a rectangular array of rows and columns. Arrangements described in terms of columns or rows can similarly be provided using columns and rows, respectively.

[0015] As used herein, an FOV image beam refers to radiation in response to CPB exposure of an FOV that can be focused in a detector to form an image of the FOV. Such an FOV image beam may or may not be focused at various points within the CPB optical system, and whether focused or not, it may be said to propagate along the axis.

[0016] Various FOV shapes and sizes can be used, and the CPB pulse duration can be varied. The FOV shapes and sizes of different FOVs may vary, and the dose applied to each FOV may also vary. CPB pulse durations of 1 ns, 10 ns, 100 ns, 1 μs, 10 μs, 100 μs, 1 ms, or shorter can be used. The number of CPB pulses applied to each FOV is typically 2 to 10, depending on the beam current and the desired number of charges applied to each pixel region. 9 It can be varied within the above range. The FOV dimension can be a few tenths of a nanometer, a few micrometers, or other larger or smaller sizes. The FOV can be a square, rectangle, polygon, ellipse, circle, or any other shape having any combination of curved and straight sides.

[0017] The CPB pulses are selected to provide a small number of charged particles, approximately 1, 2, 5, 10, or 20, in each pulse, and an acceptable image signal-to-noise ratio is achieved by combining or averaging FOV images from multiple exposures. In a typical example, the CPB is an electron beam, and the imaging system is an electron microscope.

[0018] In some cases, ultrashort electron pulses containing 10,000, 1,000, 100, 50, 25, 10, 5, or 2 or fewer electrons are applied to avoid sample damage. The electron pulses have an FOV of 5, 2, 1, 0.5, or 0.25 times L. ev The image is shifted to a different field of view using a scanning deflection system so that it is separated by a greater distance.

[0019] As used in this application and claims, the singular forms "a," "an," and "the" include the plural form unless otherwise explicitly indicated. Additionally, the term "includes" means "comprises." Furthermore, the term "coupled" does not exclude the presence of intermediate elements between coupled items.

[0020] The systems, apparatus, and methods described herein should not be construed as limiting. Rather, this disclosure covers all novel and non-obvious features and aspects of the various disclosed embodiments, individually and in various combinations and partial combinations thereof. The disclosed systems, methods, and apparatus are not limited to any specific aspects or features or combinations thereof, and the disclosed systems, methods, and apparatus do not require the existence of any one or more specific advantages or the resolution of any problem. Any theory of operation is provided for the sake of explanation, but the disclosed systems, methods, and apparatus are not limited to such theories of operation.

[0021] While some of the operations of the disclosed methods are described in a specific sequential order for convenience, it should be understood that the format of the specification is inclusive of reordering unless a specific ordering is required by the specific wording set forth below. For example, operations described sequentially may, in some cases, be reordered or performed simultaneously. Furthermore, for simplification, the accompanying drawings may not show the various ways in which the disclosed systems, methods, and apparatus may be used with other systems, methods, and apparatus. In addition, this specification may use terms such as “produce” and “provide” to describe the disclosed methods. These terms are high-level abstractions of the actual operations performed. The actual operations corresponding to these terms will vary depending on the specific implementation and will be readily recognizable to those skilled in the art.

[0022] In some examples, values, procedures, or devices are referred to as “lowest,” “best,” “minimum,” etc. Such descriptions are intended to indicate that a choice can be made from among many usable functional alternatives, but it should be understood that such a choice does not need to be better than other choices, not smaller, or otherwise preferable.

[0023] As used herein, “image” means a displayed view of a sample or portion of a sample, such as one presented on a display device, as well as stored data that may be used to generate a displayed image, such as digital data stored on a non-temporary computer-readable medium as, for example, a JPG, TIFF, BMP file or other format. [Examples]

[0024] Example 1 Referring to Figure 1, a typical CPB imaging apparatus 100 includes a pulsed CPB source 102 that can operate to generate CPB pulses in response to a CPB pulse controller 104. The CPB source 102 directs the pulsed CPB 103 to a field of view (FOV) deflector 106 that can operate to deflect the pulsed CPB 103 to several or all of the FOVs on the sample S. For the sake of illustration, the CPB 103 is illustrated as being deflected along axes 111-113 to FOV(x1,y1), FOV(x2,y2), and FOV(x3,y3), respectively, where the x and y coordinates are defined with respect to coordinate system 191. The CPB optical column 108 may include a CPB lens, deflector, stigmatall, aperture, or other charged particle beam optical elements that shape, focus, and direct the deflected CPB to various FOVs. The specific arrangement shown in Figure 1 is merely an example, and the elements of the charged particle beam optical column 108 and the field deflector 106 may be arranged in a different order along the charged particle beam optical axis 126.

[0025] The CPB imaging lens 120 receives radiation beams 151-153 associated with CPB exposure for FOV1-FOV3, respectively, and is positioned to direct the radiation beams 151-153 towards the FOV image deflector 122, which is configured to direct the radiation beams 151-153 along the CPB optical axis 126 towards the radiation detector 124. The radiation beams 151-153 may include some or all of the transmitted or scattered portions of the CPB, secondary emissions such as secondary electrons, or photons, and the radiation detector 124 can be selected accordingly. In some examples, the FOV image deflector is not used, and the imaging lens 120 is sufficient to direct the radiation beams 151-153 towards the radiation detector 124.

[0026] Controller 130 is coupled with the CPB pulse controller 104, the FOV selection deflector 106, and the FOV image deflector 122 to control the irradiation of a selected set or sequence of FOVs and direct the radiation to the radiation detector 124 in response to FOV irradiation. Controller 130 can randomly select FOVs as a set of rasterized FOVs, or it can make other selections using FOV separation that takes into account FOV relaxation time and the effectively exposed peripheral area. Generally, a particular FOV is re-irradiated only after a time longer than the FOV relaxation time has elapsed. If adjacent or nearby FOVs are irradiated sequentially, the controller selects CPB deflection so that the FOVs are separated based on the dimensions of the peripheral area in which they are effectively exposed. Controller 130 typically assembles FOV images to generate one or more images of an ROI for display on a display device 132, but instead, or in addition to that, it can communicate ROI images and / or FOV images for remote display and processing over a network or other connection.

[0027] Example 2 Referring to Figure 2, the surface of sample 200 is the region of interest. Define the region of interest (ROI) 202, which is divided into a plurality of FOVs illustrated as an array of FOVs FOV(i,j) of m×n, where i = 1,..., m and j = 1,..., n, and where m and n are integers greater than 0. Region 206 is selected as a reference region and can be used to establish the selection of FOVs, measurement of the CPB beam current, CPB pulse width, or CPB deflection for other applications. The FOVs can be irradiated row by row, for example, by sequentially irradiating the FOVs in the first row: FOV(1,1), FOV(1,2),..., FOV(1,n), and then starting from FOV(2,1) or FOV(2,n) and irradiating the FOVs in the second row: FOV(2,1), FOV(2,2),..., FOV(2,n). Thus, the FOVs can be scanned for irradiation in a single direction 250 or by alternating scans in direction 250 and direction 252. In the example of FIG. 2, the FOVs within a row are separated by a distance 2L eff only, and L eff is the effective exposure length associated with the exposure of the FOV. The rows of the FOV array can be similarly separated. Since the effective exposure length generally decays rapidly, in image acquisition using single-direction scanning, the scanning of FOVs such as FOV(1,1) can be sufficiently separated in time from the scanning of adjacent FOVs such as FOV(2,1), and as a result, there is no need to separate the rows based on L eff .

[0028] An image is acquired for each FOV. FIG. 2 shows an image I of a representative FOV. For example, the set 2701 of images I(1,1), I(1,2),..., I(1,n) is associated with the first row of FOVs, the set 2702 of images I(2,1), I(2,2),..., I(2,n) is associated with the second row of FOVs, and the set 270 of images I(m,1), I(m,2),..., I(m,n) mThis is associated with the mth row of the FOV. Each of the set of 270 images can be repeatedly acquired to improve image quality using each exposure of the temporally separated FOV based on the FOV relaxation time. In one example, images I(1,1), I(1,2), ..., I(m,n) are associated with the respective time t1, t2, ..., t (m-1)n+1 ,...,t m*n The images are obtained sequentially in this manner. This imaging sequence can be repeated until satisfactory images are obtained for some or all of the FOVs. Other image acquisition sequences can be used, such as random selection of FOVs, or sequentially along the column direction, or in directions that are not parallel to either rows or columns.

[0029] Example 3 In some cases, separating the FOVs may result in insufficient or complete imaging of portions of the ROI. Spacing between FOVs can be imaging as shown in the examples in Figures 3A and 3B. Referring to Figure 3A, similar to Figure 2, the ROI 302 of sample 300 is divided into a first set 314 of FOVs arranged as an m × n array of FOVs, with each FOV separated from the FOVs in adjacent rows and / or columns. As shown in Figure 3A, the first column (and first set 314) of FOVs is at a distance L from the reference location. off1 It is offset by only that distance L. In order to avoid gaps in the image generated by capturing the first set 314 FOV, as shown in Figure 3B, off2A second set of FOVs 316 is defined, offset by a certain distance, and the second set of FOVs 316 has FOVs located between the corresponding FOVs of the first set of FOVs. In this example, the center of the FOV in the second column of the second set of FOVs 316 is aligned on axis 320, which is parallel to the X-axis of coordinate system 310 and equidistant from the FOVs in the first and second columns of the first set of FOVs 314. Other offsets between the first and second sets, e.g., distances corresponding to the separation of FOVs in each row, can be used. In general, any offset that provides CPB exposure to all parts of the ROI can be used. Multiple sets of FOVs, two, three, or more, can be used, and the sets of FOVs do not need to be the same spacing in the X or Y direction, or do not need to use a common FOV size. Both row and column offsets can be provided, and the column offset is shown for illustrative purposes.

[0030] It will be understood that the FOVs to be acquired may be arranged in arrays other than rectangular arrays, or may be randomly or arbitrarily arranged around the ROI. Due to sufficiently long time intervals between consecutive irradiations of FOVs, the FOVs do not need to be separated. The FOVs defined by the array do not need to be acquired sequentially. Examples in Figures 2 and 3A and 3B are provided for illustrative purposes. In some cases, it is more convenient to scan rows of FOVs in a rectangular array in alternating directions to avoid the delay associated with scanning the CPB in the reverse direction toward the first side of the ROI.

[0031] Example 4 Referring to Figure 4, a typical CPB imaging apparatus 400 includes a CPB source 402 positioned to direct the CPB beam along axis 401. A charged particle beam deflector 405 is positioned to selectively deflect the charged particle beam to generate CPB pulses by either transmitting or not transmitting it through the aperture plate 406. In some examples, a pulsed CPB source uses such a photoemission surface in combination with a pulsed laser, and a CPB beam deflector is not required. The FOV selective deflector 410 includes a first deflector 410A that receives the pulsed CPB and generates a CPB 408 that propagates away from axis 410, and a second deflector 410B that redirects the deflected CPB from the first deflector 410A to propagate parallel to axis 401 as a redirected beam 409. The redirected beam 409 is coupled to the FOV on the sample 414 via a first pole piece 411A of a magnetic objective lens. The sample 414 is held within a housing 413, which includes CPB apertures 412 and 415, and is thermally coupled to a cold finger 416 to establish a sample temperature such as cryogenic, and to a sample stage 418 for positioning relative to the axis 401. A radiation beam 417, such as transmitted charged particles or secondary electrons, which responds to the dose applied to the FOV, is coupled by a lower pole piece 411B to an FOV image beam deflector 420, which includes a first deflector 420A and a second deflector 420B that propagate parallel to the axis 401 and direct the radiation beam 417 to be centered on the CPB detector 422 with perpendicular incidence. While such an FOV image beam deflector is not required, it can enable the use of a smaller CPB detector and provide more uniform detection of the radiation beam when the FOV location fluctuates. The selection of CPB deflection, scanning speed, current, FOV size, FOV location, FOV shape, exposure delay, repetition rate, and FOV image averaging and combination may be provided by a controller 424, such as a CPU or other processing device, based on processor-executable instructions and associated input and output data that can be stored in one or more non-temporary processor-readable storage media or device 426.

[0032] Example 5 Figure 5A illustrates FOVs 502, 506 having corresponding peripheral regions 504, 508 associated with evanescent distances based on CPB exposure. In the example of Figure 5A, peripheral regions 504, 508 share a boundary 509 at some time after CPB exposure. The extent of peripheral regions 504, 508 decreases as a function of time after CPB exposure. Peripheral regions 504, 508 are effectively exposed by their respective CPB exposures, and in this example, additional CPB exposure of either FOV does not interact with the exposure of the other FOV to produce damage within the FOV or their respective peripheral regions. Because the extent of the peripheral regions is a function of time, peripheral regions 504, 508 can have different extents and still share a boundary 509. Figure 5B illustrates FOVs 516, 518 having peripheral regions that partially overlap, considering weak evanescent coupling, but where multiple effective exposures of the FOV are not associated with sample change. Figure 5C shows the reduction of the peripheral region 524A–524C around FOV 522 as a function of increasing time t1, t2, and t3 after CPB exposure. As shown in the figure, the evanescence region 524A–524C is a function of distance L from CPB exposure. ev It extends over a certain distance.

[0033] Example 6 Referring to Figure 6, a typical method 600 includes determining the number of FOVs within the ROI in 602. Typically, FOVs are selected by examining images of the ROI to identify features of interest and selecting an FOV for each of the features of interest. In 604, the ROI is divided into one or more sets of FOVs, and the exposure sequence is determined to establish the scanning speed, effective dose, and FOV separation. In 606, counter I is initialized, in 608 the first FOV is irradiated, and in 610 an image of the first FOV is acquired. If more FOV images are acquired, as determined in 612, counter I is incremented in 616, and subsequent FOVs are irradiated and imaged. Each FOV may be exposed once or multiple times to provide a satisfactory FOV image. If all FOVs of one set have been imaged, in 617 it is determined whether an additional set of FOV images should be acquired to provide an acceptable image signal-to-noise ratio. If an additional set of FOV images should be acquired, counter I is reinitialized at 606 to begin acquiring the subsequent set of FOV images. At 622, it may be determined whether the FOV images should be combined, and if desired, at 626, the FOV images are combined to form an ROI image (or an image of a portion of an ROI) larger than the FOV. Alternatively, in many examples, the FOVs are not adjacent, and individual FOV images are provided at 624. As described above, in most cases, a number of images of each FOV are obtained to provide an averaged FOV image with a sufficient image signal-to-noise ratio.

[0034] In the example in Figure 6, multiple FOVs are captured sequentially and then repeatedly re-captured to achieve satisfactory image quality. During exposure of one FOV, the CPB effect in previously exposed FOVs decreases as described above. However, each FOV may be repeatedly exposed before switching to another FOV.

[0035] Example 7. Selective imaging of ROIs In a typical embodiment, only a selected FOV of a much larger ROI is of interest. Referring to Figure 7A, ROI 700 includes FOVs 702, 704, 706, and 708, which are imaged to investigate features of interest 703, 705, 707, and 709, respectively. The FOV is shown as a rectangular region that can be selected to be imaged onto pixels of a rectangular detector array based on the magnification of the imaging system. In the example in Figure 7A, FOVs 704 and 706 define an overlapping region 720, but in most cases such an overlapping region does not contain features of interest, or is unlikely to do so for most samples, and can therefore receive radiation without concern for damage. However, if desired, CPB exposure can be positioned to allow sufficient relaxation in such regions to avoid sample damage by the beam.

[0036] FOV 704 is shown enlarged in Figure 7B and superimposed to illustrate the mapping of a typical detector array, such as pixel 714, to pixel 713. Some pixel sizes of interest are 1 Å × 1 Å, 2 Å × 2 Å, 5 Å × 5 Å, 10 Å × 10 Å, 20 Å × 20 Å, 50 Å × 50 Å, or other sizes. A 4 × 5 pixel array is illustrated, but generally M × N arrays are used, where M and N are integers, typically ranging from 100 to 5000. In some examples, a 2000 × 2000 array (4M pixels) is used. A CPB, such as an electron beam, can irradiate the region 722, which is shown as a circle for convenience. The electron beam intensity is selected so that, during any electron beam pulse, the region of the FOV corresponding to the pixel does not receive more than a single electron to avoid damage or degradation of the feature of interest. A pulse containing a single electron can be used and repeated until the FOV region associated with all pixels receives enough electrons to provide a suitable FOV image signal-to-noise ratio. To provide single-electron exposure for each pixel in a pixel array, the maximum number of electrons is equal to the number of pixels; a pulse charge greater than this will result in more than one electron per FOV area associated with each pixel. Therefore, the number of electrons per pulse ranges from 1 electron / pulse to MN electrons / pulse. However, as the number of electrons / pulse approaches the upper limit MN, it becomes more likely that some FOV regions associated with pixels will receive more than one electron, while others will not. The electrons / pulse can be selected based on the likelihood of multiple electrons in the pixel region, and to maintain spacing between exposed pixels to avoid coupling via evanescent exposure.

[0037] Charge / pulse is a crucial factor in determining the imaging time. Other factors include the preferred number of electrons associated with each pixel and the relaxation time. Each pixel has a relaxation time t with repeating pulses so that each pixel is associated with (on average) Q charges. relax When using single-electron pulses repeatedly and sequentially applied to each pixel of an M×N array pixel in response to irradiation by one pulse during the imaging time Timage When M, N, and Q are non-negative integers, T image =QMNt relax This is the case. A 4M pixel detector array and Q=40 electrons / pixel are used. relax If T = 10 μs, image = 1600 s. For the charge per pulse (i.e., MN electrons / pulse) at the upper limit of single charge / pixel, each FOV region associated with a pixel receives electrons in each pulse, and as a result, the total imaging time T image =Qt relax And, or Q=40 and t relax Using 10μs results in 400μs. However, with such a large number of electrons / pulses, many FOV regions associated with a pixel are likely to receive multiple electrons in a single pulse, and fewer electrons / pulses are generally preferable.

[0038] Referring again to Figure 7A, imaging of FOVs 702, 704, 706, and 708 can be performed by sequentially directing the CPB to each of the FOVs, or by imaging the selected FOVs first and then the remaining FOVs. Continuous imaging allows the time between imaging of each FOV to provide some or all of the relaxation time for subsequent irradiation without damaging the sample.

[0039] Example 8 Figure 8 illustrates a first set 800 of N FOVs and a second set 820 of N FOVs, respectively, exposed with CPB doses D1 and D2, where N is a positive integer. Representative FOVs 804–806 of the first set 800 have surrounding evanescence regions 814–816, and each FOV 824–826 of the second set 820 has surrounding evanescence regions 834–836. Some or all FOVs may receive different CPB doses, and rows or columns of FOVs in a rectangular array do not need to receive a common dose. For some samples, selected FOVs may be more or less sensitive to CPB exposure or exposure parameters such as pulse duration, CPB current, CPB energy, or others, and the CPB pulse may be configured appropriately (and individually) for each FOV. In some examples, selected FOVs are of lower importance, and fewer CPB pulses are applied to speed up FOV image acquisition.

[0040] Example 9 Figures 9A and 9B illustrate additional placement of FOVs and methods for illuminating and imaging them. Figure 9A illustrates an array of FOVs defined within the ROI of sample 902, where the FOVs are in contact with adjacent FOVs without separation based on evanescent exposure. In this example, the FOVs are labeled 1 through 12 to indicate the order of exposure, so that adjacent FOVs are not exposed immediately before or after the exposure of any given FOV. For example, FOV 910, labeled exposure number 11, is adjacent to FOVs 911 and 912, which are exposure numbers 5 and 6, respectively, and as a result, no FOV separation is provided, depending on the time constant associated with evanescent exposure. Similarly, FOV 912 is exposed sixth, well before the exposures of FOVs 911 and 913. While the FOVs in Figure 9A are illustrated to be exposed in a specific order, other orderings, such as random selection of FOVs, can be used, subject to the constraint that the time between multiple exposures is based on the FOV relaxation time as described above.

[0041] Figure 9B illustrates a set of FOVs 960 defined on substrate 950. In this example, FOVs are defined in columns 952, 956 and 954, 958, with the FOVs in columns 952, 956 overlapping with the FOVs in columns 954, 958. In this example, FOV overlap is permitted, but any double exposure, additional exposure of any overlapping FOV region is delayed based on FOV-related time. Multiple FOV overlaps may be used based on a suitable CPB exposure delay to allow FOV relaxation. In some examples, exposure of only selected FOVs is delayed based on FOV relaxation, but not FOV exposure.

[0042] Example 10. Typical Computing Environment Figure 10 and the following discussion are intended to provide a concise and general description of exemplary computing environments in which the disclosed technology may be implemented. In particular, some or all parts of this computing environment can be used together with the above-described methods and apparatus to define, for example, a controller or control system for controlling beam deflection, FOV selection, pulse rate, FOV dose, and processing FOV and ROI images. Although not required, the disclosed technology is described in the general context of computer executable instructions, such as program modules executed by a personal computer (PC). Generally, a program module includes routines, programs, objects, components, data structures, etc., that perform a specific task or implement a specific abstract data type. Furthermore, the disclosed technology may be implemented in other computer system configurations, including handheld devices, tablets, multiprocessor systems, microprocessor-based or programmable consumer electronics, network PCs, minicomputers, and mainframe computers. The disclosed technology may also be practiced in a distributed computing environment in which tasks are performed by remote processing devices linked via a communication network. In a distributed computing environment, program modules may reside in both local and remote memory storage devices. In some cases, such processing is provided remotely, while in other cases, more typically, it is provided in a dedicated microscope system. The system of this disclosure can control image acquisition and provide a user interface, and can also function as an image processor.

[0043] Referring to Figure 10, an exemplary system for implementing the disclosed technology includes a general-purpose computing device in the form of an exemplary conventional PC 1000, comprising one or more processing units 1002, a system memory 1004, and a system bus 1006 that connects various system components, including the system memory 1004, to the one or more processing units 1002. The system bus 1006 may be one of several types of bus structures, including a memory bus or memory controller, peripheral bus, and local bus, using any of various bus architectures. The exemplary system memory 1004 includes read-only memory (ROM) 1008 and random access memory (random This includes access memory (RAM) 1010. The basic input / output system (BIOS) 1012, which contains basic routines that help transfer information between elements within the PC 1000, is stored in ROM 1008.

[0044] The exemplary PC1000 further includes one or more non-storage devices 1030, such as a hard disk drive for reading and writing from a hard disk, a magnetic disk drive for reading and writing from a removable magnetic disk, and an optical disk drive for reading and writing from a removable optical disk. Such storage devices can be connected to the system bus 1006 by hard disk drive interfaces, magnetic disk drive interfaces, and optical drive interfaces, respectively. The drives and associated computer-readable media provide non-volatile storage for computer-readable instructions, data structures, program modules, and other data for the PC1000. Other types of computer-readable media capable of storing data accessible by the PC may also be used in the exemplary operating environment.

[0045] Several program modules may be stored in a storage device 1030 containing the operating system, one or more application programs, other program modules, and program data. The user may input commands and information to the PC 1000 via one or more input devices 1040, such as a keyboard and a pointing device like a mouse. For example, the user may input a command to start image acquisition or select time constants associated with FOV, ROI, dose, evanescence, and FOB relaxation. These and other input devices are often connected to one or more processing units 1002 via a serial port interface coupled to the system bus 1006, but may also be connected via other interfaces such as a parallel port, universal serial bus (USB), or wired or wireless network connection. A monitor 1046 or other type of display device is also connected to the system bus 1006 via an interface such as a video adapter and can display, for example, one or more FOV images, or ROI images, or other raw or processed images used for FOV and ROI alignment and selection. Other peripheral output devices, such as speakers and printers (not shown), may be included.

[0046] PC1000 may operate in a network environment using logical connections to one or more remote computers, such as remote computer 1060. In some examples, one or more network or communication connections 1050 are included. Remote computer 1060 may be another PC, server, router, network PC, or peer device, or other common network node, and typically includes many or all of the elements described above in relation to PC1000, except that only the memory storage device 1062 is illustrated in Figure 10. Personal computer 1000 and / or remote computer 1060 are logical local area networks (LANs) and wide area networks (wide It can be connected to an area network (WAN). Such networking environments are common in offices, enterprise-wide computer networks, intranets, and the internet. In some examples, a stack of aligned images is sent to a remote system for 3D image reconstruction or other processing.

[0047] As shown in Figure 10, memory 1090 (or this memory, or any portion of other memory) controls FOV parameters such as CPB deflector, CPB pulse repetition rate, CPB pulse duration, size, shape, separation, and FOV dose; stores processor-executable instructions for acquiring FOV images and assembling FOV images to form ROI images; and stores associated exposure data, image data, relaxation time, and evanescence length. FOV images may be stored with a timestamp (or other indication of FOV image sequence) indicating when the FOV images were acquired, so that the FOVs can be assembled into FOV images.

[0048] Disclosure paragraph Example 1 is a method comprising applying multiple CPB pulses to at least one field of view (FOV) defined within a region of interest (ROI) of a sample, wherein the multiple CPB pulses are applied to at least one FOV with temporal separation based on FOV relaxation time, and obtaining multiple FOV images of at least one FOV, where each FOV image corresponds to each of the multiple CPB pulses.

[0049] Example 2 includes the subject matter of Example 1, and further specifies that at least one FOV is defined based on a portion of the image of the ROI of the sample encompassing the features of interest.

[0050] Example 3 includes the subject of any of Examples 1-2 and further specifies that at least one FOV is one of two or more FOVs defined based on the portion of the ROI image of the sample containing the respective features of interest.

[0051] Example 4 includes the subject matter of any of Examples 1 to 3 and further comprises combining FOV images associated with multiple CPB pulses to generate a combined FOV image.

[0052] Example 5 includes the subject of any of Examples 1 to 4, and the FOV images are combined by averaging or summing to generate an FOV image.

[0053] Example 6 incorporates themes from any of Examples 1 to 5, wherein multiple CPB pulses are applied to at least one FOV and are temporally separated by at least the FOV relaxation time.

[0054] Example 7 includes the subject matter of any of Examples 1 to 6, and further specifies that the FOV relaxation time is the phonon relaxation time.

[0055] Example 8 includes the subject matter of any of Examples 1 to 7 and further includes applying CPB deflection to generate a CPB pulse.

[0056] Example 9 comprises the subject matter of any of Examples 1 to 8 and further comprises applying image deflection to the FOV image beam associated with the FOV image, wherein the image deflection is selected to orient each of the FOV image beams along the detector axis.

[0057] Example 10 comprises a subject from any of Examples 1 to 9, further specifying that at least one FOV is one of two or more FOVs defined based on the image portion of the ROI of the sample containing the respective features of interest, and further comprising that the image deflection is selected to direct each of the FOV image beams associated with each of the two or more FOVs along the detector axis.

[0058] Example 11 includes a subject from any of Examples 1 to 10, further specifying that at least one FOV is one of two or more FOVs defined based on the image portion of the ROI of the sample containing the respective features of interest, and that the image deflection is selected to direct each of the FOV image beams associated with each of the two or more FOVs towards a common detector region.

[0059] Example 12 comprises the subject matter of any of Examples 1 to 11, further specifying that each of the FOV images is generated by an array detector defining multiple pixels, the CPB is an electron beam, and each CPB pulse is selected to provide fewer than two electrons to the FOV region associated with each pixel defined by the array detector.

[0060] Example 13 is a method comprising: repeatedly exposing a field of view (FOV) on a sample with CPB pulses, the CPB pulses being temporally separated by FOV relaxation times associated with recoverable sample damage; and imaging the FOV using an array detector defining a plurality of pixels, wherein the CPB pulses are configured such that the number of charged particles from the CPB pulses in the FOV region corresponding to the pixels in the array detector FOV image associated with each CPB pulse is less than 10.

[0061] Example 14 is a CPB apparatus comprising a CPB source operable to generate multiple CPB pulses directed to each of a plurality of FOVs defined on a sample, and a CPB beam deflector positioned to receive CPB pulses from the CPB source and direct the multiple CPB pulses to each of the plurality of FOVs, wherein the plurality of CPB pulses applied to each FOV are temporally separated by at least the phonon lifetime associated with the sample.

[0062] Example 15 includes the subject matter of Example 14 and further includes a CPB image deflector that can operate to direct the FOV image beam associated with each of the multiple FOVs defined on the sample along a common axis.

[0063] Example 16 includes the subject matter of any of Examples 14-15 and further includes a CPB image deflector, which is operable to direct the FOV image beam towards a common area of ​​the CPB image detector.

[0064] Example 17 comprises the subject matter of any of Examples 14-16, further specifying that the CPB is an electron beam, and further includes a controller operable to direct the CPB source to generate CPB pulses such that each pixel of a CPB array detector is associated with a corresponding portion of the FOV that receives fewer than five electrons in any CPB pulse.

[0065] Example 18 includes the subject matter of any of Examples 14-17 and further includes a controller that can operate to combine FOV images based on each of the FOV image beams to generate an FOV image.

[0066] Example 19 includes the subject matter of any of Examples 14-18 and further specifies that the CPB is sequentially deflected to multiple FOVs of the region of interest of the sample.

[0067] Example 20 is a method comprising repeatedly directing an electron beam to at least one field of view of a sample and imaging at least one field of view using an array detector that defines a plurality of pixels, wherein the electron beam is configured such that the FOV region associated with the pixels is effectively exposed with a number of electrons less than or equal to a selected number.

[0068] Example 21 includes the subject matter of Example 20 and further specifies that the electron beam is configured to effectively expose the field of view (FOV) based on direct electron beam exposure and evanescent exposure.

[0069] In view of the numerous possible embodiments to which the principles of the art of this disclosure may be applied, it should be recognized that the illustrated embodiments are only preferred examples and should not be construed as limiting the scope of this disclosure.

Claims

1. It is a method, Applying multiple charged particle beam (CPB) pulses to at least one field of view (FOV) defined within a region of interest (ROI) of a sample, wherein the multiple CPB pulses are applied to the at least one FOV with temporal separation based on the FOV relaxation time, A method comprising obtaining a plurality of FOV images of at least one FOV, wherein each FOV image corresponds to each of the plurality of CPB pulses.

2. The method according to claim 1, wherein the at least one FOV is defined based on a portion of the image of the ROI of the sample encompassing a feature of interest.

3. The method according to claim 1, wherein the at least one FOV is two or more FOVs defined based on portions of the image of the ROI of the sample, each containing features of interest.

4. The method according to claim 1, further comprising combining the FOV images associated with each of the plurality of CPB pulses in order to generate a combined FOV image.

5. The method according to claim 4, wherein the FOV images are combined by averaging or summing in order to generate the FOV image.

6. The method according to claim 1, wherein the plurality of CPB pulses applied to the at least one FOV are temporally separated by at least the FOV relaxation time.

7. The method according to claim 1, wherein the FOV relaxation time is the phonon relaxation time.

8. The method according to claim 1, further comprising applying CPB deflection to generate the plurality of CPB pulses.

9. The method according to claim 8, further comprising applying image deflection to the FOV image beam associated with the FOV image, wherein the image deflection is selected to orient each of the FOV image beams along the detector axis.

10. The method according to claim 9, wherein the at least one FOV is two or more FOVs defined based on the image portion of the ROI of the sample containing each of features of interest, and further, the image deflection is selected to direct each of the FOV image beams associated with each of the two or more FOVs along the detector axis.

11. The method according to claim 9, wherein the at least one FOV is two or more FOVs defined based on the image portion of the ROI of the sample containing each of features of interest, and further, the image deflection is selected to direct each of the FOV image beams associated with each of the two or more FOVs towards a common detector region.

12. The method according to claim 1, wherein each of the FOV images is generated by an array detector defining a plurality of pixels, the CPB is an electron beam, and each of the CPB pulses is selected to provide fewer than two electrons to the FOV region associated with each pixel defined by the array detector.

13. It is a method, The FOV on the sample is repeatedly exposed with CPB pulses, wherein the CPB pulses are temporally separated by the FOV relaxation time associated with recoverable sample damage. A method comprising imaging the FOV using an array detector that defines multiple pixels, wherein the CPB pulses are configured such that the number of charged particles in the FOV region corresponding to a pixel is less than 10 in response to each of the CPB pulses.

14. CPB device, A CPB source capable of generating multiple CPB pulses directed towards each of the multiple FOVs defined on the sample, A CPB apparatus comprising: a CPB beam deflector that receives the CPB pulses from the CPB source and directs the plurality of CPB pulses to each of a plurality of FOVs, wherein the plurality of CPB pulses applied to each FOV are temporally separated by at least the phonon lifetime associated with the sample.

15. The CPB apparatus according to claim 14, further comprising a CPB image deflector that is operable to direct the FOV image beams associated with each of the plurality of FOVs defined on the sample along a common axis.

16. The CPB apparatus according to claim 15, further comprising a CPB image deflector, wherein the CPB image deflector is operable to direct the FOV image beam towards a common region of the CPB image detector.

17. The CPB apparatus according to claim 14, wherein the CPB is an electron beam, and further comprises a controller, the controller operable to direct the CPB source to generate CPB pulses such that each pixel of a CPB array detector is associated with an average number of electrons in the CPB pulses less than 1 or with each corresponding portion of the FOV that receives electrons.

18. The CPB apparatus according to claim 15, further comprising a controller capable of combining FOV images based on each of the FOV image beams in order to generate an FOV image.

19. The CPB apparatus according to claim 14, wherein the CPB is sequentially deflected to the plurality of FOVs of the region of interest of the sample.

20. It is a method, Repeatedly directing the electron beam to at least one field of view of the sample, A method comprising imaging the at least one field of view using an array detector that defines a plurality of pixels, wherein the electron beam is configured such that the FOV region associated with the pixels is effectively exposed with a number of electrons less than or equal to a selected number.

21. The method according to claim 20, wherein the electron beam is configured to effectively expose the FOV region based on direct electron beam exposure and evanescent exposure.

Images