Systems and methods for multi-beam electron microscopy using detector arrays

Abstract

A system and method for an electron multi-beam imaging system are disclosed. The system may include an imaging subsystem. The imaging subsystem may include one or more electron beam sources configured to generate multiple beamlets that simultaneously probe multiple measurement regions on the sample. The imaging subsystem may further include one or more electron optical components configured to condition the multiple beamlets. The imaging subsystem may further include a detector array, the detector array including multiple detectors configured to detect electrons arriving from the measurement regions of the sample. In the system and method, each detector may include a pass-through channel configured to receive one beamlet of the multiple beamlets.

Description

[Technical Field]

[0001] The present disclosure relates generally to electron beam devices, and more particularly to electron beam devices having multiple beams and retractable detector arrays for high throughput sampling. [Background technology]

[0002] Semiconductor devices such as 3D NAND flash, 3D DRAM, and 3D logic contain deep features such as memory holes, channel holes, staircase steps, deep trenches, etc. For example, some 96-layer 3D NAND flash devices contain hundreds of billions of memory holes tens of microns deep from the top surface.

[0003] As reliability constraints become more stringent, it is increasingly desirable to inspect and verify these features for defects at high throughput. However, deeper features are particularly difficult to inspect and verify at high throughput using multi-beam techniques. Generally, electron beamlets, including primary electrons, transmitted to a sample generate secondary electrons (SEs) and backscattered electrons (BSEs). Using SEs for high-throughput imaging of deeper features can be impractical because SEs cannot escape from the bottom of features such as memory holes. Using BSEs also presents challenges. For at least some BSE detection methods, utilizing a high density (e.g., tens or hundreds) of beamlets is impractical because signal crosstalk between BSEs of closely spaced beamlets degrades the image. Generally, crosstalk between adjacent beamlets occurs when detectable electrons corresponding to adjacent beamlets overlap, creating "ghost" features in the image. Crosstalk can degrade the accuracy, resolution, and / or throughput of the imaging system. As the number and density of beamlets increases, solving crosstalk using other methods can become impractical. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] U.S. Patent Application Publication No. 2021 / 0210309 [Patent Document 2] U.S. Patent Application Publication No. 2013 / 0320220 [Patent Document 3] U.S. Patent Application Publication No. 2017 / 0090051 Summary of the Invention [Problem to be solved by the invention]

[0005] It would therefore be advantageous to provide a system that overcomes the aforementioned challenges. [Means for solving the problem]

[0006] An electron multi-beam imaging system is disclosed in accordance with one or more embodiments of the present disclosure. The electron multi-beam imaging system may include an imaging subsystem. In one exemplary embodiment, the imaging subsystem may include one or more electron beam sources configured to generate multiple beamlets that simultaneously probe multiple measurement regions on the sample. In another exemplary embodiment, the imaging subsystem may further include one or more electron optical components configured to condition the multiple beamlets. In another exemplary embodiment, the imaging subsystem may further include a detector array, the detector array including multiple detectors configured to detect electrons arriving from the measurement regions of the sample. In another exemplary embodiment, each detector may include a pass-through channel configured to accept one beamlet of the multiple beamlets.

[0007] In other exemplary embodiments, the detector array may be movable between a first position and a second position.

[0008] A method is disclosed according to one or more embodiments of the present disclosure. In one exemplary embodiment, the method may include generating electrons in a plurality of beamlets using one or more electron beam sources. In another exemplary embodiment, the method may include conditioning the plurality of beamlets using one or more electron optics configured to receive the plurality of beamlets. In another exemplary embodiment, the method may include receiving each beamlet of the plurality of beamlets from a passing channel of a respective detector of a detector array. In another exemplary embodiment, the method may include each beamlet irradiating a measurement region of the sample. In another exemplary embodiment, the method may include collecting electrons arriving from the measurement region for each beamlet using a separate detector. In another exemplary embodiment, the method may include detecting the electrons using a separate detector.

[0009] In another exemplary embodiment, the method may include moving the detector from the second position to the first position.

[0010] It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are not necessarily restrictive of the invention as claimed. The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and, together with the general description, serve to explain the principles of the invention. [Brief explanation of the drawings]

[0011] The many advantages of the present disclosure may be better understood by those skilled in the art by reference to the accompanying drawings, which are described below.

[0012] [Figure 1] FIG. 1 is a simplified schematic diagram showing an electron beam imaging system with backscattered electrons coming from a sample. [Figure 2] FIG. 1 is a simplified block diagram illustrating an electron multi-beam imaging system according to one or more embodiments of the present disclosure. [Figure 3]FIG. 1 is a simplified schematic diagram of an imaging subsystem in accordance with one or more embodiments of the present disclosure. [Figure 4] FIG. 1 is a simplified schematic diagram of a detector array in accordance with one or more embodiments of the present disclosure. [Figure 5] FIG. 1 is a schematic simplified top view of a detector array according to one or more embodiments of the present disclosure. [Figure 6] FIG. 1 is a simplified schematic diagram of an imaging subsystem in accordance with one or more embodiments of the present disclosure. [Figure 7] FIG. 1 is a simplified schematic diagram illustrating secondary electron trajectories and image formation relationships in accordance with one or more embodiments of the present disclosure. [Figure 8] FIG. 1 is a simplified schematic diagram of an imaging subsystem in accordance with one or more embodiments of the present disclosure. [Figure 9] FIG. 1 is a simplified schematic diagram of a detector array with a cap, in accordance with one or more embodiments of the present disclosure. [Figure 10] FIG. 1 is a simplified schematic diagram of a detector without a cap, in accordance with one or more embodiments of the present disclosure. [Figure 11] FIG. 1 is a simplified schematic diagram of a detector having a scintillator layer in accordance with one or more embodiments of the present disclosure. [Figure 12] FIG. 1 is a simplified schematic diagram of a detector array having coplanar detectors, in accordance with one or more embodiments of the present disclosure. [Figure 13] FIG. 1 is a schematic diagram of a field array corresponding to multiple beamlets, in accordance with one or more embodiments of the present disclosure. [Figure 14] FIG. 1 is a simplified schematic diagram illustrating nine fields of view, according to one or more embodiments of the present disclosure. DETAILED DESCRIPTION OF THE INVENTION

[0013] Reference will now be made in detail to the disclosure illustrated in the accompanying drawings. The disclosure has been particularly shown and described with reference to certain embodiments and individual features thereof. The embodiments described herein are intended to be illustrative and not limiting. Moreover, those skilled in the art will readily recognize that various changes or modifications in form and detail may be made therein without departing from the spirit and scope of the disclosure.

[0014] One method for detecting SEs and BSEs using a single beam is described in U.S. Patent Application No. 17 / 224,407, filed April 7, 2021, the entire disclosure of which is incorporated herein by reference. However, a single beam may not provide the throughput required for imaging billions of features.

[0015] Embodiments of the present disclosure are directed to electron multi-beam imaging systems including a detector array capable of achieving high throughput by simultaneously probing multiple measurement regions on a sample. For example, each detector in the detector array may receive a beamlet from a pass channel and may be positioned to detect electrons corresponding to the received beamlet. This may reduce crosstalk between detected electrons of different beamlets compared to other approaches. Additional embodiments of the present disclosure are directed to electron multi-beam imaging systems having two imaging modes enabled by a retractable detector array. For example, the detector array may be positioned near the sample when imaging BSE and in a retracted position when operating in an alternative imaging mode utilizing a secondary detector.

[0016] 1 shows a simplified schematic of an electron beam imaging system with BSEs arriving from a sample 118. Depending on the angle of emission from the sample 118, not all BSEs will be able to reach the detector (not shown) on the left side of FIG. 1. For example, 10° BSE 108b, 30° BSE 108c, 60° BSE 108d, and 80° BSE 108e are all blocked by various components, such as the ground electrode 102, amplifier electrode 104, and charge control plate 106. The remaining portions of BSE 108 that pass through these components, such as 0° BSE 108a, are not sufficient to generate a signal of sufficient quality for imaging purposes.

[0017] 2 shows a simplified block diagram of an electron multi-beam imaging system 200 in accordance with one or more embodiments of the present disclosure. In an embodiment, the electron multi-beam imaging system 200 is configured for inspection (e.g., mask inspection or wafer inspection) or image-based metrology.

[0018] In an embodiment, the electron multi-beam imaging system 200 includes an imaging subsystem 202 and a controller 204. The controller 204 may include one or more processors 206 configured to execute program instructions stored in a memory 208.

[0019] In an embodiment, the imaging subsystem 202 includes one or more electron beam sources 212 configured to generate a set of beamlets 210 that simultaneously probe a set of measurement regions on the sample 118. For example, the imaging subsystem 202 may include a single electron beam source 212 and an aperture / lens array configured to split the single beamlet into a set of beamlets.

[0020] In an embodiment, the imaging subsystem 202 includes electron optics 214 configured to condition the beamlets 210. The electron optics 214 may include relatively small components that condition each beamlet 210 individually and / or a general-purpose component that conditions all of the beamlets 210 simultaneously. For example, the electron optics 214 may include an array of components, each of which is configured to receive and condition one beamlet 210. The components may condition the beamlets 210 in any manner known in the art. Methods include, but are not limited to, adjusting the focus, acceleration, uniformity, aperture size, or other quality of the beamlets 210 with electrostatic fields, magnetic fields, apertures, etc. Thus, for example, an array of stigmators may be utilized to correct astigmatism for each beamlet 210. As another example, a single general-purpose component may be configured to condition all of the beamlets 210 simultaneously, for example, using relatively large electrostatic and / or magnetic fields.

[0021] In an embodiment, the imaging subsystem 202 includes a sample stage 222 configured to move and / or rotate the sample 118 .

[0022] In an embodiment, the imaging subsystem 202 includes a detector array 216. The detector array 216 may provide crosstalk reduction, overcoming problems with other methods. Various embodiments utilizing the detector array 216 are described herein. In an embodiment, the detector array 216 includes a set of pass-through channels 218. The set of pass-through channels 218 allows individual incident beamlets 210 to pass through the detector array 216. The use of individual beamlet pass-through channels 218 allows the detector array 216 to be positioned closer to the sample 118 without blocking the incident beamlets 210. Because the BSEs 108 scatter outward from the sample 118 in all directions, positioning the detector array 216 closer to the sample 118 prevents the BSEs 108 from radially scattering too far. Reducing the radial scattering distance of the BSEs 108 reduces crosstalk (i.e., overlap) of the BSEs 108, improving the signal and enabling a higher density of beamlets 210. The increased density of beamlets 210 allows for a greater number of beamlets 210 to be utilized, enabling high throughput for imaging billions of features. Thus, the pass-through channel 218 provides an improved electron multi-beam imaging system.

[0023] FIG. 3 shows a simplified schematic diagram of an imaging subsystem 202 in accordance with one or more embodiments of the present disclosure.

[0024] In an embodiment, the imaging subsystem 202 includes an illumination path 304 and a collection path 306. The illumination path 304 is defined to include the path of travel of electrons (e.g., beamlets 210, etc.) from their generation in a source (e.g., electron beam source 212) to the sample 118 and corresponding components along the path, such as a modulator. Modulators typically include, but are not limited to, apertures, deflectors, lenses, filters, accelerators, etc. The collection path 306 is defined to include the path of travel of electrons (e.g., SEs, BSEs, etc.) arriving from the sample 118 to the detectors and various components along the path, such as the detector array 216, the secondary detector 220, and modulators (e.g., Wien filters, apertures, attractors, etc.).

[0025] In an embodiment, the imaging subsystem 202 includes a secondary detector 220. For example, the secondary detector 220 may be an alternate detector in some sense. For example, when the detector array 216 is in a first position as shown, electrons 332 may, but are not necessarily, blocked from reaching the secondary detector 220. However, when the detector array 216 is in a second position (not shown), the electrons 332 may reach the secondary detector 220 unblocked. Thus, by moving the detector array 216 toward or away from the first / detection position, switching between an imaging mode using the detector array 216 and an alternate imaging mode using the secondary detector 220 can be achieved. For example, the imaging subsystem 202 may be configured to detect BSEs using the detector array 216 in the first / detection position and to detect SEs with the secondary detector 220 when the detector array 216 is in the second / retracted position. Thus, for example, detector array 216 can be used to detect BSEs of features such as memory holes in a first imaging mode, while imaging subsystem 202 can also detect SEs in an alternate imaging mode. Note, however, that utilizing secondary detector 220 in an alternate imaging mode is merely an example. In some configurations, secondary detector 220 may function in tandem with detector array 220 for detection purposes, which can occur in some scintillator configurations.

[0026] In an embodiment, the detector array 216 is configured to be located between the electron optics 214 and the sample 118. For example, the secondary detector 220 may be positioned further from the sample 118 than the detector array 216. Thus, the detector array 216 can be closer to the sample 118, thereby reducing crosstalk / overlap of BSEs of different beamlets 210.

[0027] In an embodiment, the imaging subsystem 202 includes a Wien filter 330 configured to separate / deflect electrons 332 (e.g., SEs) from the primary electrons of the beamlet 210 so that the electrons 332 can be detected by the secondary detector 220.

[0028] In an embodiment, the imaging subsystem 202 has a depth of focus range (i.e., the distance / depth of material that appears in focus when imaging the sample 118) of at least 10 μm (e.g., at least 20 μm). For example, the depth of focus range may be at least 20 μm when imaging a memory hole with a width-to-depth aspect ratio (AR) of 1:2000.

[0029] In an embodiment, the imaging subsystem 202 includes an objective lens 324 configured to focus and image the beamlets 210 telecentrically onto (or into) the sample 118. For example, the objective lens can be used to set the focal depth of the beamlets 210 deeper or closer to the surface of the sample 118.

[0030] In an embodiment, the imaging subsystem 202 includes an aperture array electrode 308, a microlens array 310, a microdeflector array 312, a microstigmator array 314, a transfer lens 318, an upper scanner deflector 320, and / or a lower scanner deflector 332. Such electronic optical components 214 can be used to condition the beamlets 210.

[0031] Intermediate image plane 316 and sample 118 are respectively the object plane and the image plane of electron optics 216. Common crossover volume 326 is where beamlets 210 intersect.

[0032] FIG. 4 shows a simplified schematic diagram 400 of a detector array 216 in accordance with one or more embodiments of the present disclosure.

[0033] In an embodiment, the detector array 216 includes a set of detectors 420. For example, each detector 420 may be associated with a respective beamlet 210.

[0034] In an embodiment, each detector 420 includes a pass channel 218 configured to accept the beamlet 210. The pass channel 218 may be defined by an inner surface 404 of the detector 420. As such, each detector 420 may be configured to be aligned with a detector 420 on the path to the sample 118 to allow the beamlet 210 to pass through the corresponding detector 420. In an embodiment, each detector 420 may be configured to detect electrons 108 arriving from a measurement region of the sample 118 corresponding to one beamlet 210. For example, a first detector may be configured to detect BSE 108f arriving from the first measurement region 328, and a second detector may be configured to detect BSE 108e arriving from the second measurement region.

[0035] For example, the location, size, structure, and detection / material qualities of the detector 420 may be configured to detect BSEs. For example, by being positioned near the measurement region 328 through which a particular beamlet 210 is transmitted, the particular detector 420 may detect electrons 108 corresponding to the transmitted particular beamlet 210.

[0036] Additionally, being relatively close to the sample 118 may reduce the distance over which the diffuse BSEs 108 will scatter and overlap each other, thereby reducing crosstalk. For example, the detector 420 sample separation 408 may define the distance between the sample 118 and the detector 420. In embodiments, the desired magnitude of the sample separation 408 may depend on a number of factors, such as the desired image quality required, the pitch between the beamlets 210, the emission path angle (ρ), and the energy of the BSEs 108. For example, the sample separation 408 may be less than 500 μm, less than 100 μm, less than 50 μm, less than 20 μm, less than 5 μm, etc. This may reduce crosstalk.

[0037] In an embodiment, the detector array 216 is configured to detect dark-field BSE. Dark-field BSE may include electrons with relatively large polar angles, as indicated by a relatively large emission angle ρ of the electrons 108f. The emission angle ρ may be measured between the path of the electrons 108f and a normal to the upper exterior surface 428 of the sample 118.

[0038] In an embodiment, a design strategy for the detector array 216 is adopted. For example, the geometric parameters of the dimensions of the detector array 216 may be constrained by other geometric parameters. For example, the design strategy may satisfy the following:

[0039]

number

[0040]

number

[0041]

number

[0042] The function sin(2*ρ) can be used to approximate the distribution of BSE108 as a function of emission angle ρ, with the peak intensity of this distribution occurring at an emission angle ρ of 45°.

[0043] As an illustrative example, consider the above-described design method for detecting BSEs between ρ of 34° and ρ of 72°. These values ​​of ρ and ρ can achieve detection of most dark-field BSEs, while bright-field SEs with relatively small emission angles (e.g., less than 20°) can preferably pass through the pass-through channel 218. In an embodiment, the SEs pass through the detector 420, are imaged by the objective lens 324, and are detected by the secondary detector 220. Using the above-described equations with such a design scheme, the pass-through channel size 406 (d) can be 20 μm, the pitch 412 (p) can be 100 μm, the sample separation 408 (h) can be 15 μm, and the gap width (g) can be 10 μm. Note that there are more than one solution that follows the above-described design scheme, and constraining one parameter constrains another, but does not necessarily produce a uniquely accurate solution.

[0044] In an embodiment, the detector array 216 includes a substrate 418. For example, the substrate 418 may be a layer. For example, the substrate 418 of each detector 420 may be coplanar.

[0045] In embodiments, the detector array 216 includes an active layer. For example, the active layer may include at least one of an n-type layer 414 or a p-type layer 416. For example, each detector 420 may have a substrate 418 between and adjacent to the p-type layer 416 and the n-type layer 414. Thus, the detector array 216 may include (or be) a chip by disposing the p-type layer and the n-type layer on a silicon substrate during a chip manufacturing process. In some examples, the p-type layer 416 and / or the n-type layer 414 have a height / thickness on the micron scale (e.g., less than 10 μm).

[0046] In an embodiment, the imaging subsystem 202 is configured to include a working distance passage channel between the electron optics 214 and the sample 118. For example, the working distance passage channel may be defined by a working distance 424 between a component (e.g., a bottom component) of the electron optics 214 and the sample 118. For example, this component may be the charge control plate 106, and the working distance 424 may be sufficient to provide sufficient space to move the detector array 216 to the first position. In an embodiment, the working distance 424 is on the scale of hundreds of microns to several millimeters or more (e.g., 100 μm or more, 500 μm or more, 1 mm or more, 2 mm or more, 5 mm or more, etc.). Such a working distance 424 can be utilized to accommodate z-direction thicknesses of the detector array 216 (e.g., detector array chip) on the order of tens or hundreds of microns (e.g., 10 μm or less, 20 μm or less, 50 μm or less, 100 μm or less, 200 μm or less, 500 μm or less, 1 mm or less, 2 mm or less, etc.).

[0047] In an embodiment, the gap width 410 of the gap material 426 disposed between the detectors 420 is on the scale of microns (e.g., 10 μm or less). The gap material 426 may be configured to shield (e.g., electrically insulate) each detector 420, such as by including an electrically insulating material known in the art.

[0048] In an embodiment, the charge control plate passing channel size 422 is on the scale of hundreds of microns or more (eg, at least 100 microns, at least 1 mm) and is configured to accommodate all beamlets 210 .

[0049] 5 shows a schematic simplified top view 500 of the detector array 216 according to one or more embodiments of the present disclosure. Note that the number and arrangement of the detectors 420 shown are simplified for illustrative purposes and are not limiting.

[0050] In an embodiment, the detector array 216 includes connection elements 504 that are coupled (e.g., electrically connected) to the detectors 420. For example, the connection elements 504 may include wires for transmitting signals, embedded silicon chip conductive lines, through-vias, etc. For example, the connection elements 504 may be wires that are soldered or embedded in a substrate. In an embodiment, the connection elements 504 may be coupled (e.g., electrically connected) to other components, such as a preamp PCB 502.

[0051] In an embodiment, each detector 420 includes a circular and / or cylindrical component, for example, the inward-facing detection surface of the pass-through channel 218 and / or active layer may be circular.

[0052] FIG. 6 illustrates a simplified schematic diagram 600 of the imaging subsystem 202 in accordance with one or more embodiments of the present disclosure.

[0053] As previously described herein, the detector array 216 may be configured to be operable between a first position 602 and a second position 604 .

[0054] In an embodiment, the Wien filter 330 includes an E×B (Eacrosby) energy filter consisting of electrostatic and magnetic deflectors, in which the electrostatic deflection field is perpendicular to the magnetic deflection field.

[0055] In an embodiment, the objective lens 324 includes a magnetic lens section and an electrostatic section. The magnetic lens section may include an upper pole piece 614, a lower pole piece 608, and a coil 606. The electrostatic section may include a ground electrode 102, an amplifier electrode 104, and a charge control plate 106. The amplifier electrode 104 may be configured to boost the primary electrons of the beamlet 210 when a voltage is applied to it, reducing Coulomb interactions and improving resolution. In an embodiment, a preferred location for the common crossover volume 326 is around the amplifier electrode 104, where improved resolution is achieved. The charge control plate 106 can be used to charge the sample 118 according to a specific extraction area, thereby controlling the depth of the imaged field.

[0056] In embodiments, the upper scanner deflector 320 and the lower scanner deflector 322 may be preferable to electrostatic deflectors for high-speed, high-throughput scanning of the field of view. In embodiments, scanning of the field of view may be performed using the upper scanner deflector 320 and the lower scanner deflector 322. For example, the beamlet 210 may continue to pass through the center (not numbered) of the objective lens 324 during the scanning process. For example, the deflectors 320 and 322 may be used cooperatively, such that one deflects the beamlet 210 off-center and the other deflects the beamlet 210 back to the center. The deflections of the deflectors 320 and 322 may be proportional to each other, thereby maintaining the beamlet 210 passing through a constant center point along a central axis parallel to the z-direction. For example, the deflection may be oriented along an angle that is not parallel to the central axis, thereby enabling scanning along the x- and y-directions of the sample 118. By changing the amount of deflection and changing the angle through the center point, a movement of the field of view can be achieved within the scanning field of view (SFOV). For an example of an SFOV, see the SFOV in Figure 13. Having the beamlet 210 pass through the center of the objective lens (OL) main image plane (see, for example, main image plane 702 in Figure 7) can reduce off-axis aberrations and distortions.

[0057] 7 shows a simplified schematic diagram illustrating the trajectories and imaging relationships of SEs according to one or more embodiments of the present disclosure. FIG. 7 can be generated, for example, by ray tracing simulations using computer modeling of components according to one or more embodiments. The main image plane 702 can be the image plane of the objective lens 324. The main image plane 702 is highly dependent on the landing energy of the beamlets 210.

[0058] 8 shows a simplified schematic diagram 800 of the imaging subsystem 202 in accordance with one or more embodiments of the present disclosure. Figure 8 can be used to illustrate the detection of SE 332 as the detector array (not shown) retracts.

[0059] The SEs 332a, 332b, and 332c may be associated with three beamlets 210. In an embodiment, the SEs 332a, 332b, and 332c are simultaneously focused by the objective lens 324 and imaged by the second crossover volume 804 onto an image plane.

[0060] In an embodiment, an alternative imaging mode utilizes a Wien filter 330 to deflect the SEs 332 (e.g., 332a, 332b, 332c) toward the secondary detector 220. In practice, the SEs 332 may be adjusted using secondary electron optics 802. The secondary electron optics 802 may include any optical component, such as a modulator. The secondary electron optics 802 may modulate the SEs 332 to adjust the image plane on the secondary detector 220 in response to large changes caused by user-selected changes in the landing energy of a particular measurement. The secondary electron optics may be used to adjust the SEs 332, for example, but not limited to, rotation, magnification, descanning (e.g., scanning correction), spatial filtering, and / or energy dispersion correction. Energy dispersion correction may be performed to improve SE collection efficiency and reduce crosstalk corresponding to the secondary detector 220. An example of the arrangement of the SEs 332 when imaged on the secondary detector 220 may be shown similar to the arrangement of the beamlets 202 shown in FIG. 13.

[0061] In an example, if the placement of the SEs 332 is enlarged by a factor of 5 to 12 compared to the placement of the beamlets 210 on the sample 118, a larger, more cost-effective, and / or easier to manufacture secondary electron optics 802 can be realized.

[0062] FIG. 9 shows a simplified schematic diagram 900 of a detector array 216 with a cap, in accordance with one or more embodiments of the present disclosure.

[0063] In embodiments, each detector 420 has a recess. For example, this recess may include a surface facing the sample 118 (including a surface perpendicular to the sample 118), and may be configured to transmit electrons 108 emitted from the sample to this surface. In embodiments, each detector 420 may increase the surface area of ​​the detection surface by utilizing a detection surface that extends along the direction of propagation of the beamlets 210. For example, instead of detection surfaces as shown by the coplanar detection surfaces in FIG. 12 that do not generally extend along the direction of propagation (e.g., the z-direction), each detector 420 may include at least some non-coplanar surfaces. For example, the inner surface of the cylinder of a first detector may not be coplanar with the inner surface of the second cylinder of a second detector. In some embodiments, the inner surface of the cylinder and the inner surface of the cap (even if coplanar with the other cap) may define a recess as shown in FIG. 9. This example is for illustrative purposes only, and the detection surface extending along the direction of travel that defines the recess may be of any shape / profile (e.g., the inner surface of a cone and / or a curved surface, e.g., the interior of a hemisphere, the interior of a semi-ellipsoid, any other concave surface, etc.). Compared to a flat surface perpendicular to the direction of travel, the surface extending along the direction of travel has a larger surface area. In embodiments, the larger surface area can provide improved image metrics such as sharpness and resolution.

[0064] In an embodiment, the sample separation distance 408 is changed by movement of the sample stage using an actuator (not shown) and / or movement of the detector array 216. In an optional step, the controller 204 may command that this movement be performed based on a distance sensor (e.g., any sensor, such as a laser optical distance sensor) configured to sense the sample separation distance 408. For example, the detector array 216 may include one or more capacitance sensor heads 910 configured to sense and / or control the position of the detector array 216 relative to the sample 118. For example, the capacitance sensor heads 910 may be configured to sense a change in capacitance that varies as a function of the sample separation distance 408 relative to the sample 118. The controller 204 may be configured to calculate the sample separation distance 408 based on this function and the sensed capacitance. Additionally, based on the sample separation distance 408 and the desired distance, the controller may be configured to change the sample separation distance 408 of the detector array 216 by commanding an actuator to move the detector array 216 along the travel direction (e.g., Z direction) by the difference between the sample separation distance 408 and the desired distance. Thus, the capacitive sensor head 910 may be used to control the sample separation distance 408 to the sample 118. This movement may be performed using actuators (not shown) known in the art, including, but not limited to, piezoelectric actuators, screw drives with electric motors, pneumatic actuators, etc. For example, three or four actuators symmetrically arranged about the detector array 216 may be used to tilt and translate the detector array 216 with two or more degrees of freedom.

[0065] As previously mentioned, each detector array 216 may include an active layer 912 configured to detect electrons 108 .

[0066] In an embodiment, the active layer 912 has a cylindrical shape configured to align with the beamlets at the detection locations. For example, as shown, an inner cylindrical surface of the active layer 912 may be aligned with the beamlets 210. The active layer 912 may also include a cap. For example, the cap may contact the cylindrical shape at an upper end of the cylindrical shape and include an inner cap surface facing the sample 118. For example, the cap may include and / or define the through channel 218.

[0067] In an embodiment, the active layer 912 includes a PN detection structure or a PIN detection structure. For example, the active layer 912 may include p-type silicon and n-type silicon stacked on a silicon substrate. For example, the active layer 912 may include a PIN layer having a p-type layer and an n-type layer on each side of an undoped native semiconductor layer.

[0068] In an embodiment, the inner surface of the active layer 912 is coated with an aluminum coating layer (no reference number). For example, the aluminum coating layer may be about 10 nanometers (e.g., less than 50 nanometers and greater than or equal to 1 nanometer) thick. The aluminum coating layer can block low-energy SEs, but high-energy BSEs can pass through the aluminum coating layer and impinge on the active layer 912, such as the PN layer or PIN layer.

[0069] In an embodiment, a recess design method for a recessed detector may be adopted. For example, the recess design method may satisfy the following equation:

[0070]

number

[0071]

number

[0072]

number

[0073] As an illustrative example, consider the recess design scheme described above for detecting electrons 108 between ρ of 5° and ρ of 66°. For this recess design scheme, using the equations described above, the pass channel size 406 (d) may be 20 μm, the pitch 412 (p) may be 100 μm, the gap width (g) may be 10 μm, the sample separation distance 408 (h) may be 10 μm, the add-on distance to the active layer 906 (h) may be 10 μm, and the recess depth 904 (h) may be 100 μm.

[0074] Figure 10 shows a simplified schematic diagram 1000 of a detector 420 without a cap, in accordance with one or more embodiments of the present disclosure. Compared to the detector 420 of Figure 9, the detector 420 of Figure 10 may be a cylindrical structure and may have, without limitation, a relatively thicker substrate layer and be deeper in the Z direction.

[0075] In an embodiment, a cylindrical design scheme for a cylindrical detector is adopted. For example, the cylindrical design scheme may follow the formula:

[0076]

number

[0077]

number

[0078]

number

[0079] As an illustrative example, consider the cylindrical design scheme described above when detecting electrons 108 between ρ of 4° and ρ of 74°. In this cylindrical design scheme, the pass channel size 406 (d) may be 70 μm, the sample separation distance 408 (h) may be 10 μm, and the active layer depth 1014 (h) may be 500 μm.

[0080] In an embodiment, each detector 420 includes an aluminum coating layer 1012. For example, the aluminum coating layer 1012 may be attached to an inner surface as shown. For example, the aluminum coating layer 1012 may help detect BSE while filtering out SE.

[0081] 11 illustrates a simplified schematic diagram 1100 of a (scintillator) detector 420 having a scintillation layer 1102 in accordance with one or more embodiments of the present disclosure. The (scintillator) detector 420 may be configured for scintillator-to-photoemission detection of electrons 108. Compared to the (cylindrical) detector 420 of Figure 10 at a comparable active layer depth 1014 and sample separation distance 408, the (scintillator) detector 420 may have the following advantages: it can convert a large energy band from BSE to SE with little or no energy loss; it can convert a wide range of BSE emission angles to near-normal SE angles; it can utilize the detection electronics of the secondary detector 220, potentially eliminating the need for the detection electronics of the detector array 216; and it can filter out SE 1106 with a negatively charged surface 1110 (which may, for example, include another scintillator layer).

[0082] In an embodiment, each detector 420 includes a scintillation layer 1102. The scintillation layer 1102 may be coated on an inner surface (e.g., an inner cylindrical surface as shown) and / or a surface facing the sample (e.g., a distal end region as shown). The scintillation layer 1102 may be configured to generate photons based on received electrons 108.

[0083] In an embodiment, each detector 420 includes an aluminum coating layer 1110. For example, the aluminum coating layer 1110 may be attached to an outer surface as shown. For example, the aluminum coating layer 1110 may be biased at a voltage (e.g., −100 V) so that SEs 1106 emitted from the sample 1118 may be repelled / flickered due to their low energy. In this way, the aluminum coating layer 1110 can help filter out SEs while allowing detection of other electrons 108, such as BSEs.

[0084] In an embodiment, each detector 420 includes a photocathode element 1112. For example, the photocathode element 1112 may include a photocathode material and may be disposed on the top surface as shown.

[0085] The photons 1108 may be internally reflected by at least one of the aluminum coating layer 1110 or the scintillation layer 1102, and may be directed to ultimately impinge on a photocathode element 1112. The photocathode element 1112 may be configured to generate new electrons 1114 based on the photons 1108. The new electrons 1114 may have a low initial energy. For example, this low initial energy may be approximately equal to the energy of the SE 1106.

[0086] In an embodiment, the new electrons 1114 are sent to and detected by the secondary detector 220 .

[0087] 12 shows a schematic diagram 1200 of a detector array 216 having coplanar detectors 420, in accordance with one or more embodiments of the present disclosure. In an embodiment, the detectors 420 may be coplanar. Also, for example, the substrate 1204 and the active layer facing the sample 118 may be coplanar.

[0088] FIG. 13 illustrates a schematic diagram 1300 of a field array corresponding to a plurality of beamlets 210, in accordance with one or more embodiments of the present disclosure.

[0089] The field array represents the imageable area of ​​the imaging subsystem 202. For example, the field array may have a width 1306 and height of 220 μm by 220 μm.

[0090] In an embodiment, the field array includes scanning fields of view (SFOVs) of dimensions 1308 (e.g., 20 μm×20 μm), each corresponding to a beamlet 210. In an embodiment, the number of SFOVs may be 121, forming an 11×11 grid. The pitch between the SFOVs may be 20 μm. In an embodiment, each beamlet 210 is simultaneously scanned (e.g., raster scanned) across its respective SFOV. For example, this scanning may be performed by a general-purpose component of the electron optics 214 configured to simultaneously adjust all beamlets. For example, such a general-purpose component may include the bottom scanner deflector 322.

[0091] In embodiments, a step-and-scan method is used to scan a large area of ​​the sample 118. For example, the field array may be scanned as described above at a first position. Additionally, the field array may be scanned at a second position (e.g., a position adjacent to the first position). For example, the field array may be tilted relative to the sample 118 to scan a large area. The movement of the field array may be performed by the sample stage 222 and / or by deflection of the beamlets by the electron optics 214.

[0092] FIG. 14 shows a schematic diagram 1400 of nine fields of view 1402 in accordance with one or more embodiments of the present disclosure.

[0093] In an embodiment, the pitch between the beamlets 210 is dynamically adjusted, in a sense, by selectively controlling the beamlets 210. For example, a subset of beamlets 210 may be selected that has a larger pitch between adjacent beamlets 210. For example, the remaining beamlets 210 in the subset may be spaced further apart by blocking other beamlets 210 (e.g., by deflecting the beamlets 210 in a direction that prevents them from reaching the sample 118). For example, a micro-deflector array 312 may be used to block the beamlets 210. An advantage of increasing the pitch between the beamlets 210 is reduced crosstalk.

[0094] For example, a subset may include multiple beamlets 210, where at most every other beamlet 210 is used. For example, in a 3×3 beamlet arrangement, every fifth beamlet 210 may be used, as shown in FIG. 14, resulting in a pitch of at least 100 μm. Thus, the pitch 412 may be increased by a factor of five.

[0095] A scanning method may be performed for a subset of the beamlets 210. For example, this method may detect BSEs using the detector array 216 at a first position. In a first step, a subset may be scanned within each SFOV. For example, the nine beamlets 210 of FIG. 14 may be scanned. In a second step, the sample 118 may be moved (e.g., by the sample stage 222) so that the beamlets 210 are in different SVOFs. For example, each of the nine beamlets 210 may be moved to an adjacent SVOF, such as the SVOF immediately to the right. In a third step, the remaining SVOFs may be imaged in a similar manner. For example, all 25 SVOFs corresponding to each beamlet 210 may be scanned in a 5x5 pattern. This allows the entire 300 μm x 300 μm field array to be imaged over time. In a fourth step, the field array may be moved to a different position, such as a position adjacent to the previous field array position. For this reason, a gradient process may be performed to image a large area of ​​the sample 118.

[0096] Referring again to Figures 2-14, additional details regarding the embodiments and various components will now be described.

[0097] In embodiments, the sample stage 222 may include any sample stage known in the field of electron beam microscopy. In embodiments, the sample stage 222 is a drivable stage. For example, the sample stage 222 may include, but is not limited to, one or more translatable stages suitable for selectively translating the sample 118 along one or more linear directions (e.g., x-direction, y-direction, and / or z-direction). As another example, the sample stage 222 may include, but is not limited to, one or more rotatable stages suitable for selectively rotating the sample 118 along a rotational direction. As another example, the sample stage 222 may include, but is not limited to, a rotational stage and a translation stage suitable for selectively translating the sample along a linear direction and / or rotating the sample 118 along a rotational direction.

[0098] The specimen 118 may include any specimen suitable for characterization (e.g., inspection or verification) by electron beam microscopy. In embodiments, the specimen 118 includes a wafer, die, chip, etc. For example, the specimen may include, but is not limited to, a semiconductor wafer. As used throughout this disclosure, the term "wafer" refers to a substrate formed of semiconductor and / or non-semiconductor materials. For example, in the case of semiconductor materials, the wafer may be formed of, but is not limited to, single crystal silicon, gallium arsenide, and / or indium phosphide. In other embodiments, the specimen includes a photomask / reticle. In embodiments, the specimen 118 includes a mask, such as a reticle mask, a lithography mask, etc.

[0099] The detector array 216 and / or secondary detector 220 may include any type of electron detector assembly known in the art configured to detect electrons (e.g., secondary electrons and / or backscattered electrons). For example, the detector array 216 may collect and image SEs using an Everhart-Thornley detector (or other type of scintillator-based detector). In other embodiments, the SEs may be collected and imaged using a micro-channel plate (MCP). In other embodiments, the electrons may be collected and imaged using a PIN or pn junction detector, such as a diode or diode array. In other embodiments, the electrons may be collected and imaged using one or more avalanche photodiodes (PDS).

[0100] As previously described herein, one or more processors 206 of the control device 204 may be communicatively coupled to memory 208, and the one or more processors 206 may be configured to execute a set of program instructions retained in memory 208, which may be configured to cause the one or more processors 206 to perform various functions and steps of the present disclosure.

[0101] It should be noted that one or more components of the electronic multi-beam imaging system 200 may be communicatively coupled to various other components of the electronic multi-beam imaging system 200 in any manner known in the art. For example, the one or more processors 206 may be communicatively coupled to each other and to the other components via a wired (e.g., copper wire, fiber optic cable, etc.) or wireless connection (e.g., RF connection, IR connection, WiMax, Bluetooth, 3G, 4G, 4G LTE, 5G, etc.). As another example, the controller 204 may be communicatively coupled to one or more components of the electronic multi-beam imaging system 200 via a wired or wireless connection known in the art.

[0102] In embodiments, the one or more processors 206 include one or more processing elements known in the art. In this sense, the one or more processors 206 may include microprocessor-type devices configured to execute software algorithms and / or instructions. In embodiments, the one or more processors 206 may comprise a desktop computer, mainframe computer system, workstation, image computer, parallel processor, or other computer system (e.g., network computer) configured to execute programs configured to operate the electron multi-beam imaging system 200 as described throughout this disclosure. It should be appreciated that the steps described throughout this disclosure may be performed by a single computer system or, alternatively, by multiple computer systems. It should also be appreciated that the steps described throughout this disclosure may be performed by any one or more of the one or more processors 206. In general, the term “processor” may be broadly defined to encompass any device having one or more processing elements that execute program instructions retrieved from memory 208. Additionally, different subsystems of the electronic multi-beam imaging system 200 (e.g., imaging subsystem 202, controller 204, user interface, etc.) may include processors or logic elements suitable for performing at least some of the steps described throughout this disclosure. Accordingly, the foregoing should not be construed as limitations on the present disclosure, but rather as merely illustrative.

[0103] The memory 208 may include any storage medium known in the art suitable for storing program instructions executed by the associated one or more processors 206 and data received from the electronic multi-beam imaging system 200. For example, the memory 208 may include a non-transitory storage medium. For example, the memory 208 may include, but is not limited to, read-only memory (ROM), random access memory (RAM), magnetic or optical memory (e.g., disk), magnetic tape, solid-state drive, etc. Moreover, the memory 208 may be contained within a common controller housing with the one or more processors 206. In alternative embodiments, the memory 208 may be located remotely relative to the physical locations of the processors 206, controller 204, etc. In other embodiments, the memory 208 holds program instructions that cause the one or more processors 206 to perform the various steps described throughout this disclosure.

[0104] In an embodiment, a user interface is communicatively coupled to the controller 204. The user interface may include, but is not limited to, one or more desktops, tablets, smartphones, smartwatches, etc. In another embodiment, the user interface includes a display used to display data from the electronic multi-beam imaging system 200 to a user. The user interface display may include any display known in the art. For example, the display may include, but is not limited to, a liquid crystal display (LCD), an organic light emitting diode (OLED)-based display, or a CRT display. As will be appreciated by those skilled in the art, various display devices that can be incorporated into a user interface are suitable for implementation in the present disclosure. In another embodiment, a user can input selections and / or commands in response to data displayed to the user via a user input device of the user interface.

[0105] All methods described herein may include storing results of one or more steps of a method embodiment in memory. The results may include various results described herein and may be stored in a manner known in the art. The memory may include any memory described herein, as well as other suitable storage media known in the art. After the results are stored, they are accessible in memory and available to any of the method or system embodiments described herein, formatted for display to a user, available to other software modules, methods, or systems, etc. Additionally, the results may be stored "permanently," "semi-permanently," "temporarily," or for a predetermined period of time. For example, the memory may be random access memory (RAM), and the results need not necessarily remain in memory indefinitely.

[0106] Furthermore, it is contemplated that each of the above-described method embodiments may include any one or more steps of one or more of the other methods described herein, and each of the above-described method embodiments may be performed by any of the systems described herein.

[0107] Those skilled in the art will recognize that the components, operations, devices, objectives, and related discussions described herein are used as examples for conceptual clarity, and that various configuration variations are contemplated. Thus, as used herein, the specific exemplars set forth and the accompanying discussion are intended to be representative of more general classes. Generally, the use of a specific exemplar is intended to be representative of that class, and the absence of a specific component, operation, device, or objective should not be considered limiting.

[0108] In this specification, directional expressions such as "upper," "lower," "above," "below," "upper," "upward," "lower," "downward," "X direction," etc. are intended to indicate relative positions for purposes of explanation and are not intended to specify an absolute reference system. Various modifications of the described embodiments will be apparent to those skilled in the art, and the general principles defined herein may be applied to other embodiments.

[0109] With respect to the use of substantially all plural and / or singular terms herein, those skilled in the art can convert from plural to singular and / or from singular to plural as appropriate to the context and / or application. Various singular / plural permutations are not specifically set forth herein for the sake of brevity.

[0110] The description herein may illustrate different components contained within or connected to other components. It is understood that the architectures described are merely examples, and that in fact many other architectures can be implemented that achieve similar functionality. In conceptual terms, any arrangement of components that achieves similar functionality is effectively "associated" to achieve the desired functionality. Thus, any two components combined herein to achieve a particular functionality can be considered to be "associated" with each other to achieve the desired functionality, regardless of the architecture or intervening components. Similarly, any two components so associated can also be considered to be "connected" or "coupled" with each other to achieve the desired functionality, and any two components capable of such association can be considered to be "couplable" with each other to achieve the desired functionality. Specific examples of "couplable" include, but are not limited to, physically coupleable and / or physically interacting components, wired and / or wirelessly interacting components, and / or logically interacting and / or logically interacting components.

[0111] It should also be understood that the present invention is defined by the appended claims. As those skilled in the art will understand, in general, the terms used in this specification, and particularly in the appended claims (e.g., the body of the appended claims), are generally intended as "open" terms (e.g., the term "including" should be interpreted as "including, but not limited to," the term "having" should be interpreted as "having at least," the term "includes" should be interpreted as "including, but not limited to," etc.). It should also be understood by those skilled in the art that if a specific number of introduced claim recitations is intended, this intention will be explicitly stated in the claim, and in the absence of an explicit recitation, such intention is not present. For example, to aid in understanding, the appended claims set forth below may be written out including the use of the prefaces "at least one" and "one or more." However, the use of this preamble should not be construed as suggesting that introducing a claim recitation with the indefinite article "a" or "an" implies that a particular claim containing the claim recitation so introduced is limited to an invention containing only one recitation, even if the same claim includes the preamble "one or more" or "at least one" and an indefinite article such as "a" or "an" (e.g., "a" and / or "an" should generally be understood to mean "at least one" or "one or more"). This also applies to the use of definite articles when introducing claim recitations. Also, even if a specific number of introduced claim recitations is explicitly recited, those skilled in the art will recognize that this recitation should generally be construed to mean at least the recited number (e.g., the simple recitation "two" without any other modifier should generally be construed to mean at least two or more than two).Furthermore, when a notation such as "at least one of A, B, and C, etc." is used, it is generally intended to be interpreted in a way that a person skilled in the art would understand the notation (e.g., "a system having at least one of A, B, and C" includes, but is not limited to, a system having only A, only B, only C, A and B together, A and C together, B and C together, and / or A, B, and C together). When a notation such as "at least one of A, B, or C, etc." is used, it is generally intended to be interpreted in a way that a person skilled in the art would understand the notation (e.g., "a system having at least one of A, B, or C" includes, but is not limited to, a system having only A, only B, only C, A and B together, A and C together, B and C together, and / or A, B, and C together). Those skilled in the art will further appreciate that almost all disjunctive conjunctions such as and / or presenting two or more alternative terms, whether in the specification, claims, or drawings, should be understood to contemplate the inclusion of one of the terms, either one of the terms, or both of the terms. For example, the phrase "A or B" will be understood to include the possibilities of "A" or "B," or "A and B."

[0112] The present disclosure and many of its attendant advantages will be believed to be understood from the foregoing description, and it will be apparent that various changes can be made in the form, construction, and arrangement of components without departing from the disclosure or sacrificing all of the advantages thereof. The described embodiments are merely illustrative, and the following claims are intended to encompass and include all such modifications. It is to be understood that the invention is defined by the appended claims.

[0113] Finally, references herein to "an embodiment," "one embodiment," "some embodiments," etc., mean that the particular component, feature, structure, or characteristic described for that embodiment is included in at least one embodiment disclosed herein. The occurrence of the phrase "in an embodiment" in various places in the specification does not necessarily refer to the same embodiment, and an embodiment may include one or more features or subcombinations of two or more features explicitly described or implied herein, as well as combinations with other features not necessarily explicitly described or implied in the present disclosure.

Claims

1. 1. An electron multi-beam imaging system including an imaging subsystem, the imaging subsystem: one or more electron beam sources configured to generate multiple beamlets that simultaneously probe multiple measurement areas on the sample; one or more electron-optical components configured to condition the plurality of beamlets; a detector array; and an imaging subsystem including:

1. An electron multi-beam imaging system, wherein the detector array includes a plurality of detectors, each detector of the detector array including a pass channel, each pass channel configured to accept a respective beamlet of the plurality of beamlets directed toward the sample, and each detector configured to detect electrons arriving from a measurement region of the sample.

2. 10. The electron multi-beam imaging system of claim 1, wherein the electrons include backscattered electrons.

3. 2. The electron multi-beam imaging system of claim 1, wherein the detector array is configured to be positioned between the one or more electron optical components and the sample.

4. 10. The electron multi-beam imaging system of claim 1, wherein the detector array is operable between a first position and a second position.

5. 5. The electron multi-beam imaging system of claim 4, wherein the first position comprises a detection position configured to detect backscattered electrons coming from the specimen, and the second position comprises a retracted position.

6. 6. The electron multi-beam imaging system of claim 5, wherein the imaging subsystem is configured to detect secondary electrons using a secondary detector when the detector array is in the retracted position.

7. 10. The electron multi-beam imaging system of claim 1, wherein the plurality of detectors are coplanar.

8. 10. The electron multi-beam imaging system of claim 1, wherein each detector includes a recess facing the sample.

9. 10. The electron multi-beam imaging system of claim 1, wherein each detector comprises an active layer.

10. 10. The electron multi-beam imaging system of claim 9, wherein the active layer comprises at least one of an n-type material or a p-type material.

11. 11. The electron multi-beam imaging system of claim 10, wherein the active layer comprises an aluminum cladding layer.

12. 10. The electron multi-beam imaging system of claim 9, wherein the active layers include a substrate layer, a p-type layer, and an n-type layer.

13. 10. The electron multi-beam imaging system of claim 9, wherein the active layer has a cylindrical shape configured to align with the beamlets at detection locations.

14. 14. The electron multi-beam imaging system of claim 13, wherein the cylindrical shape is adjacent a cap at an end of the cylindrical shape, the cap containing the through channel.

15. 14. The electron multi-beam imaging system of claim 13, wherein the cylindrical shape includes a scintillator layer.

16. 16. The electron multi-beam imaging system of claim 15, wherein the scintillator layer includes a distal end region and an inner cylindrical surface region.

17. 16. The electron multi-beam imaging system of claim 15, wherein the detector comprises a photocathode element.

18. 2. The electron multi-beam imaging system of claim 1, wherein the detector includes a capacitance sensor head configured to at least one of detect and control a position of the detector array relative to the sample.

19. 2. The electron multi-beam imaging system of claim 1, wherein the control device is further configured to select a subset of the plurality of beamlets, the subset having a larger pitch than the plurality of beamlets.

20. generating a plurality of beamlets of electrons using one or more electron beam sources; conditioning the plurality of beamlets using one or more electron-optical components configured to receive the plurality of beamlets; receiving each beamlet of the plurality of beamlets from a passing channel of each detector of a detector array; Each beamlet irradiates a measurement area of ​​the sample, collecting electrons from the measurement region for each beamlet using each detector; detecting the electrons with each of the detectors.

21. 21. The method of claim 20, wherein the electrons comprise backscattered electrons.

22. 21. The method of claim 20, wherein the detector array is positioned between the one or more electron optics and the sample while each detector is used to detect the electrons.

23. 21. The method of claim 20, further comprising moving the detector array from a second position to a first position.

24. 24. The method of claim 23, wherein the first position comprises a detection position configured to detect the electrons coming from the sample, and the second position comprises a retracted position.

25. 25. The method of claim 24, further comprising detecting secondary electrons with a secondary detector when the detector array is in the retracted position.

26. 21. The method of claim 20, further comprising selecting a subset of the plurality of beamlets, the subset having a larger pitch than the plurality of beamlets.

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