Tilt-column multi-beam electron microscopy system and method

Abstract

A system and method for a tilted-column electron beam imaging system are disclosed. The system may include an imaging subsystem. The imaging subsystem includes a plurality of electron beam sources configured to generate a plurality of beamlets. The imaging subsystem may further include a plurality of tilted illumination columns, each configured to receive a respective beamlet from a respective electron beam source. In the system and method, a first tilt axis of a first tilted illumination column may be oriented along a first angle, and at least one additional tilt axis of at least one additional tilted illumination column may be oriented along at least one additional angle different from the first angle, and each of the plurality of beamlets passes through a first common crossover volume.

Description

[Technical Field]

[0001] The present disclosure relates generally to electron beam devices, and more particularly to electron beam devices with multiple illumination columns for high throughput sampling. [Background technology]

[0002] The fabrication of semiconductor devices, such as logic devices and memory devices, typically involves fabricating the semiconductor device using a number of semiconductor manufacturing processes to create various features and multiple levels of the semiconductor device. Some manufacturing processes utilize photomasks / reticles to print features onto semiconductor devices, such as wafers. As semiconductor devices become smaller, it becomes important to develop advanced inspections to interrogate the devices and processing steps and improve the resolution, speed, and throughput of wafer and photomask / reticle inspection processes.

[0003] One inspection technique is electron beam-based inspection, such as scanning electron microscopy (SEM). In some instances, scanning electron microscopy is performed by splitting a single electron beam into multiple beams / beamlets and individually aligning and scanning the multiple beamlets using a single electron optical column. This inspection method can introduce potential problems across multiple beamlets, such as beamlet non-uniformity due to non-uniform electron sources. Additional issues include field curvature, astigmatism, distortion, and other undesirable effects that can be difficult to correct. As the number of beamlets increases, the aforementioned problems can become more difficult to correct for all beamlets. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] U.S. Patent Application Publication No. 2019 / 0227010 [Patent Document 2] U.S. Patent Application Publication No. 2017 / 0084424 Summary of the Invention [Problem to be solved by the invention]

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

[0006] A tilted-column electron beam imaging system is disclosed in accordance with one or more embodiments of the present disclosure. The system may include an imaging subsystem. In one exemplary embodiment, the imaging subsystem may include multiple 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 multiple tilted illumination columns, each configured to receive a separate beamlet from each electron beam source. In another exemplary embodiment, each tilted illumination column includes one or more sets of electron optical components configured to condition the separate beamlets. In another exemplary embodiment, a first tilt axis of the first tilted illumination column may be oriented along a first angle, and at least one additional tilt axis of the at least one additional tilted illumination column may be oriented along at least one additional angle different from the first angle, and each of the multiple beamlets passes through a first common crossover volume.

[0007] A method is disclosed in accordance with one or more embodiments of the present disclosure. In an exemplary embodiment, the method may include, but is not limited to, generating electrons in multiple beamlets using multiple electron beam sources. In another exemplary embodiment, the method may include conditioning the individual beamlets using respective electron optics of respective tilted illumination columns configured to receive respective individual beamlets from the respective electron beam sources. In another exemplary embodiment, the method may include simultaneously irradiating multiple regions of the sample with the multiple beamlets. In another exemplary embodiment, the method may include collecting secondary electrons from multiple measurement regions of the sample using a detector. In another exemplary embodiment, the method may include detecting the secondary electrons using a detector. In another exemplary embodiment, a first tilt axis of the first tilted illumination column may be oriented along a first angle, and at least one additional tilt axis of the at least one additional tilted illumination column may be oriented along at least one additional angle different from the first angle, and the multiple beamlets each pass through a first common crossover volume.

[0008] It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are not 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]

[0009] 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.

[0010] [Figure 1] FIG. 1 is a simplified schematic diagram of a system with a single electron beam source. [Figure 2] FIG. 1 is a simplified block diagram illustrating a tilt column electron beam imaging system in accordance with one or more embodiments of the present disclosure. [Figure 3A]FIG. 1 is a simplified schematic diagram of a tilted column electron beam imaging system with multiple electron beam sources, in accordance with one or more embodiments of the present disclosure. [Figure 3B] FIG. 1 is a simplified schematic diagram illustrating the upper column region of a tilted column electron beam imaging system according to one or more embodiments of the present disclosure. [Figure 3C] FIG. 1 is a simplified schematic diagram illustrating the upper central column region of a tilted column electron beam imaging system in accordance with one or more embodiments of the present disclosure. [Figure 4] FIG. 1 is a simplified schematic diagram illustrating the upper column region of a tilted column electron beam imaging system according to one or more embodiments of the present disclosure. [Figure 5] 1 is a schematic diagram of a two-dimensional projection of a spherical electrode layer of a concentrating lens array in accordance with one or more embodiments of the present disclosure. [Figure 6] FIG. 1 is a schematic diagram illustrating a set of seamlessly butted hexagonal field arrays in accordance with one or more embodiments of the present disclosure. [Figure 7] FIG. 1B is a schematic diagram of a two-dimensional projection of a spherical gun focus lens layer of a gun lens array in accordance with one or more embodiments of the present disclosure. [Figure 8] FIG. 1 is a simplified schematic diagram illustrating projection optics of a tilt column electron beam imaging system in accordance with one or more embodiments of the present disclosure. [Figure 9A] FIG. 9 is a simplified schematic diagram illustrating a vertically expanded view of the primary electron trajectory and image formation relationship of FIG. 8, in accordance with one or more embodiments of the present disclosure. [Figure 9B] FIG. 9B is a simplified schematic diagram showing an enlarged portion of FIG. 9A including an imaging relationship near the sample, in accordance with one or more embodiments of the present disclosure. [Figure 10] FIG. 1 is a conceptual diagram illustrating image formation in a field of view before correction for astigmatism and field curvature, in accordance with one or more embodiments of the present disclosure. [Figure 11] FIG. 11 is a conceptual diagram illustrating image formation in the field of view of FIG. 10 after astigmatism correction, in accordance with one or more embodiments of the present disclosure. [Figure 12]FIG. 12 is a conceptual diagram illustrating image formation in the field of view of FIG. 11 after field curvature correction, in accordance with one or more embodiments of the present disclosure. [Figure 13] FIG. 1 is a simplified schematic diagram of a dual tilt column electron beam imaging system in accordance with one or more embodiments of the present disclosure. [Figure 14] FIG. 1 is a simplified schematic diagram of a tilted column electron beam imaging system including a general purpose focusing lens, in accordance with one or more embodiments of the present disclosure. [Figure 15] FIG. 1 is a simplified schematic diagram of a dual tilt column electron beam imaging system including a general purpose focusing lens, in accordance with one or more embodiments of the present disclosure. [Figure 16] 1 is a flow diagram illustrating steps performed in a method according to one or more embodiments of the present disclosure. DETAILED DESCRIPTION OF THE INVENTION

[0011] 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.

[0012] Embodiments of the present disclosure relate to electron beam systems including a set of tilted illumination columns that generate a set of beamlets that simultaneously probe a set of regions on a sample. Additional embodiments of the present disclosure relate to electron beam systems including a set of dual tilt columns, in which the beamlets travel along a second tilt axis. Additional embodiments of the present disclosure relate to electron beam systems having a general purpose focusing lens. Additional embodiments of the present disclosure relate to electron beam systems and methods including a set of tilted illumination columns arranged in an array (e.g., a hexagonal array).

[0013] One method for generating a set of beamlets involves using a single source to generate a single beam that is transmitted along a central axis and then splitting the single beam into multiple beamlets. For example, generating an electron beam and splitting it into multiple beamlets is disclosed in U.S. Patent No. 8,362,425, issued January 29, 2013, the entire disclosure of which is incorporated herein by reference. FIG. 1 illustrates how a single-source electron beam is split into multiple beamlets, as further described below. It should be noted that generating a uniform single beam is difficult. Variations in the beamlets due to the original non-uniform beam can result in undesirable variations in the sampled data obtained from each beamlet.

[0014] It is recognized that as the number of beamlets split from a single source increases, it may become unfeasible to overcome problems related to source emission uniformity, as well as beamlet field curvature, astigmatism, and distortion.

[0015] It would be advantageous to provide a system that overcomes the problems observed in single-source electron beam imaging systems. While the use of multiple electron beam sources may solve some of the problems, some configurations (e.g., non-tilted configurations) may present challenges. For example, the use of an individual electron beam source for each beamlet may improve beamlet uniformity. However, the use of multiple beam sources poses a risk of excessive heat buildup. For example, for an array of beamlets, closely spaced beam sources parallel to the central axis may result in damaging levels of heat buildup, require complex cooling mechanisms, and / or introduce distortions due to thermal expansion that affect optical alignment. For example, a parallel array of thermal field emission (TFE) sources may cause such excessive heat buildup. Additionally, each illumination column, one for each beamlet, may have its own illumination components (e.g., illumination optics) to individually adjust each beamlet, such as those used to adjust for astigmatism, field curvature, distortion, etc.

[0016] Typically, the emission angle distribution of a TFE source is Gaussian. If the emission angle is too large, the angular intensity distribution can become quite inhomogeneous. Producing a larger number of beamlets may require a wider emission angle. For example, using an emission angle of ~90 mrad with a single beam-limiting aperture of 800 μm diameter can result in inhomogeneity between the beamlets.

[0017] For a set of beamlets generated using a microlens array (MLA), field curvature, astigmatism, and distortion can be directly proportional to the square or cube of the field of view (FOV) size at the sample. Increasing the FOV size for higher throughput or increasing the number of beamlets can lead to a rapid increase in field curvature, astigmatism, and distortion, potentially making correction impractical. MLAs are chip devices with fine dimensions, requiring relatively complex microfabrication techniques and advanced manipulation capabilities.

[0018] These problems may be overcome by utilizing a configuration of multiple electron beam sources and a tilted illumination column. In this regard, tilting each column allows for greater separation between the individual electron beam sources and between the illumination components of each column. The separation between components in such a system offers advantages, such as reduced heat buildup, increased space for individual beamlet illumination optics, no need for complex MLAs, and reduced crosstalk between beamlets. This is because the focusing and deflection fields of each beamlet in a tilted illumination column can be relatively far apart and independent of one another, and the tilted orientation of the column allows for the use of general-purpose focusing optics. The separate illumination optics allow for tuning the numerical aperture (NA) of each beamlet to improve uniformity of resolution across the FOV, tuning the brightness of each beamlet to make resolution more uniform across the FOV, modular replacement of each electron beam source in the field, accurate measurement of beam current for each beamlet by blocking all other beamlets to precisely calibrate each detector channel, and modular replacement of the gun lens module, which includes the beam limiting aperture, gun lens, modulator, and secondary beam limiting aperture.

[0019] FIG. 1 shows a simplified schematic diagram of a single source system 100.

[0020] As previously described herein, using a single electron beam source to generate beamlets can lead to problems related to source uniformity, as well as problems related to beamlet astigmatism, distortion, and field curvature.

[0021] The single source system 100 may include a single electron beam source 106. The single source system 100 may further include a beam-limiting aperture 104, a gun lens 102, a collimation lens 116, a microlens array (MLA) chip 120, an imaging lens 124, a field lens 128, a transfer lens 130, and / or an objective lens 134. The microlens array (MLA) chip may include a defocusing lens array that splits a global telecentric beam into multiple beamlets 132. The imaging lens 124 may form the multiple beamlets 132 at an intermediate image plane 126 at the field lens 128. The plane 112 may be considered a virtual object plane (VOP) for the multiple electron beamlets 132.

[0022] 2 illustrates a simplified block diagram of a tilt-column electron beam imaging system 200 in accordance with one or more embodiments of the present disclosure. In an embodiment, the tilt-column electron beam imaging system 200 is configured to generate a set of beamlets that simultaneously probe a set of measurement areas on the specimen 118. In an embodiment, the tilt-column electron beam imaging system 200 is configured for inspection (e.g., mask inspection or wafer inspection) or image-based metrology.

[0023] In an embodiment, tilting column electron beam imaging system 200 includes an imaging subsystem 202 and a controller 204. Controller 204 may include one or more processors 206 configured to execute program instructions stored in memory 208.

[0024] In an embodiment, the imaging subsystem 202 includes a set of electron beam sources 214 configured to generate a set of beamlets that simultaneously probe a set of measurement areas on the specimen 118. For example, the imaging subsystem 202 may include, but is not limited to, electron beam sources 214a, 214b, and 214c.

[0025] By utilizing multiple electron beam sources 214, the beam current can be independently selected to correct for distortion, field curvature blur, and astigmatism for each beamlet. Compared to the beamlets of an MLA, the electron beam sources 214 can be spaced apart at relatively large distances (e.g., tens of millimeters, 10 mm or more, 20 mm or more, 30 mm or more, 40 mm or more, etc.). Also, because the beamlets 394 can be spaced apart at distances greater than the average separation of electrons in a single-source beam, the impact of Coulomb interactions between the beamlets 394 on resolution can be negligible.

[0026] In an embodiment, the imaging subsystem 202 includes a set of tilted illumination columns 212. For example, the tilted illumination columns 212 may include tilted illumination columns 212a, 212b, and 212c. In an embodiment, each tilted illumination column 212 is configured to receive a beamlet from an electron beam source 214.

[0027] In an embodiment, each tilted illumination column 212 includes a set of one or more electron optical components 220 configured to condition a beamlet. For example, the electron optical components 220 may include, but are not limited to, electron optical components 220 a, 220 b, and 220 c. Thus, for example, each tilted illumination column 212 may be associated with a beamlet generated by the electron beam source 214 and configured to condition the corresponding beamlet.

[0028] In an embodiment, the imaging subsystem 202 includes one or more detectors 216 .

[0029] FIG. 3A shows a simplified schematic diagram 300 of a tilt column electron beam imaging system 200 in accordance with one or more embodiments of the present disclosure.

[0030] In an embodiment, the tilted column electron beam imaging system 200 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 394, etc.) from their generation in a source (e.g., electron beam source 214) to the sample 118 and corresponding components along the path, such as a modulator. Modulators include, but are not limited to, apertures, deflectors, lenses, filters, etc. The collection path 306 is defined to include the path of travel of electrons (e.g., secondary electrons, backscattered electrons, etc.) arriving from the sample 118 to the detector 216 and corresponding components along the path, such as the detector 216 or a particle modulator (e.g., a Wien filter, aperture, attractor, etc.).

[0031] In an embodiment, the tilt axis 340 can be used to define a tilted direction that is the general direction in which at least a portion of the beamlet 394 propagates. In an embodiment, at least a portion of the path of the beamlet 394 is formed to pass through the first common crossover volume 322 along the first tilt axis 340. For example, the tilt axis 340 corresponding to a particular beamlet 394 is defined along the propagation direction of the portion of the beamlet 394 that is located in front of the corresponding electron beam source 214 and / or just before the first common crossover volume 322.

[0032] In an embodiment, the first tilt axis 340 of the first tilted illumination column 212 is oriented along (e.g., parallel to) a first angle 336, and the at least one additional tilt axis 340 of the at least one additional tilted illumination column 212 is oriented along at least one additional angle 336 that is different from the first angle. Referring to FIG. 3A , the first tilt axis 340 may be the axis labeled 340 near the top, and the at least one other tilt axis 340 may be the axis labeled 340 near the bottom.

[0033] In an embodiment, each of the multiple beamlets 394 passes through a first common crossover volume 322 .

[0034] In an embodiment, angle 336 is a non-zero angle between a first tilt axis 340 of tilted illumination column 212 and a central axis 338. Thus, tilted illumination column 212 is non-parallel to central axis 338. Although angle 336 is illustrated with respect to central illumination column 342, angle 336 may be measured between tilt axes 340 of different tilted illumination columns 212.

[0035] In an embodiment, the first tilt axis 340 of each tilted illumination column 212 is positioned at a particular (non-zero) angle 336 relative to the other first tilt axes 340 of the other tilted illumination columns 212. For example, the first tilt axes 340 of the multiple tilted illumination columns 212 may be arranged radially, normal (i.e., perpendicular) to a three-dimensional curved surface, etc. For example, the beamlets 394 allow for spacing of multiple electron beam sources 214. Thus, the three-dimensional curved surface may be a portion of a sphere. However, this example is not limiting, and the first tilt axes 340 may be normal to portions of other curved shapes, such as, but not limited to, an ellipsoid, a cone, a donut-shaped cylinder, etc. For example, such a curved surface may be convex when viewed in the propagation direction of the beamlets 394.

[0036] In embodiments, the beamlets 394 are (at least partially) rotationally symmetric about the central axis 338. For example, the angular spacing between the beamlets 394 may be equal. In some embodiments, the beamlets 394 may be in a particular distribution (e.g., a hexagonal distribution as shown in FIG. 5).

[0037] In an embodiment, each tilted illumination column 212 includes one or more sets of electron-optical components 220. For example, the one or more sets of electron-optical components 220 may be used to individually modulate (e.g., steer, deflect, focus, selectively filter, condition, and / or similarly manipulate) the beamlets 394 in the illumination path 304. Thus, each tilted illumination column 212 may individually adjust its own beamlets 394, for example, adjustments for astigmatism, field curvature, focusing, etc.

[0038] In an embodiment, the imaging subsystem 202 includes a set of electron source emitter tips 308 in the illumination path 304. In an embodiment, the imaging subsystem 202 includes a set of gun lenses 312 in the illumination path 304. For example, each electron beam source 214 is coupled to (or includes) a gun lens 312 corresponding to a source emitter tip 308 and / or beamlet 394.

[0039] In an embodiment, a gun lens 312 is utilized to focus the beamlets 394 into a beamlet crossover 316 .

[0040] In an embodiment, the imaging subsystem 202 (e.g., a set of one or more electron-optical components 220) includes a beam-limiting aperture 310 for each beamlet 394. For example, the beam-limiting aperture 310 may be positioned before the gun lens 312 relative to the propagation direction of the beamlet 394. The beam-limiting aperture 310 may be used to select the original beam current of the beamlet 394.

[0041] In an embodiment, the set of one or more electron optical components 220 includes a collection lens 320 for each beamlet 394. For example, each beamlet 394 may be associated with one collection lens 320.

[0042] In an embodiment, the set of one or more electron-optical components 220 includes a modulator 314 for each beamlet 394. For example, the modulator 314 may be configured to deflect the beamlet 394 and / or perform other adjustments (e.g., focusing, etc.) on the beamlet 394. In an embodiment, the modulator 314 is used to correct astigmatism and / or deflect the beamlet 394 to correct distortion. For example, the modulator 314 may be a stigmator that corrects astigmatism. As another example, the modulator 314 may be used as a deflector that aligns the beamlet 394 to account for mechanical tolerances and to correct distortion. As another example, the modulator 314 may be used as a scanner. For example, the modulator 314 may be used to scan the beamlet along a scan direction of the sample 118 to expand the measurement region 346 in the scanned direction. In an embodiment, the modulator 314 is comprised of eight cylindrical plates. This configuration can generally be utilized as an octuple configuration in electron optics, where different voltages are applied to the modulator 314 depending on its use as a stigmator or deflector.

[0043] For example, the modulator 314 may include an electron beam stigmeter 314. For example, the one or more electron beam stigmeters may include, but are not limited to, one or more multipole beam deflectors. In this regard, the one or more multipole beam deflectors may include, but are not limited to, one or more quadrupole beam deflectors and / or one or more octapole beam deflectors. As another example, the one or more electron beam stigmeters may include, but are not limited to, one or more sets of slit beam stigmeters. For example, the one or more sets of slit beam stigmeters may include apertures. In an embodiment, the one or more modulators 314 adjust one or more characteristics of the beamlets 394 (e.g., field position on the sample 118, magnitude of lens field astigmatism, etc.).

[0044] In an embodiment, the set of one or more electron-optical components 220 includes a secondary beam-limiting aperture 318 for each beamlet 318. For example, the secondary beam-limiting aperture 318 may be located after the gun lens 312. The secondary beam-limiting aperture 318 can be used to adjust the original beam current. For example, by adjusting the voltage applied to the gun lens 312, the position of the beamlet crossover 316 can be changed, and therefore the extent to which the beamlet 394 is affected by the secondary beam-limiting aperture 318.

[0045] In some embodiments, beamlets 394 are illustrated with beamlet crossovers 316, but beamlet crossovers 316 are not required. For example, in some embodiments, beamlet crossovers 316 are not necessarily present between gun lens 312 and secondary beam-limiting aperture 318.

[0046] In an embodiment, the illumination path 304 further includes a global transfer lens 326. For example, the global transfer lens 326 can be configured to direct each beamlet 394 from a diverging path to a converging path toward the second common crossover volume 322. For example, the global transfer lens 326 can be positioned after the first common crossover volume 322.

[0047] In an embodiment, the illumination path 304 further includes a general-purpose objective lens 332. For example, the general-purpose objective lens 332 may be configured to send each beamlet 394 to reach the sample telecentrically (i.e., to focus on the sample). For example, the general-purpose objective lens 332 may be positioned after the second common crossover volume 334.

[0048] In an embodiment, each beamlet 394 is directed to a different measurement region 346 as shown, where each beamlet 394 can be considered to be configured to measure a field of view (FOV). Multiple FOVs (e.g., several, tens, hundreds, etc.) can be arranged in an ordered array on the sample, allowing multiple beamlets 394 to simultaneously probe (e.g., measure) multiple measurement regions 346 on the sample 118.

[0049] In an embodiment, the collection path 306 includes a Wien filter 330 configured to separate primary electrons from secondary electrons. Primary electrons are generally electrons in the beamlet 394 directed toward the sample 118, and secondary electrons are electrons that return from the sample 118. The Wien filter 330 can be used to direct (e.g., separate) the secondary electrons toward a detector 216 configured to detect the secondary electrons.

[0050] In an embodiment, the imaging subsystem 202 includes a central illumination column 342. The central illumination column 342 may include, for example, a central electron beam source 392 configured to generate a central beamlet 394 along a central axis 338.

[0051] 3B shows a simplified schematic diagram 348 of the upper column region of the tilted-column electron beam imaging system 200 in accordance with one or more embodiments of the present disclosure. While FIG. 3A shows two tilted-illumination columns 212, one on each side of the central illumination column 342, FIG. 3B shows ten tilted-illumination columns 212, five on each side of the central illumination column 342.

[0052] In embodiments, the components are arranged in a layer array. For example, the illumination path 304 can include multiple layers, each of which includes an array of components. Layers can be adjacent to other layers to form adjacent layer groups (i.e., sets of adjacent layer arrays, such as the gun lens array 352). In embodiments, the components within a layer can be electrically coupled or independent. For example, a single, non-separated, conductive spherical plate with gaps for the beamlets 394 can be grounded or energized as a single component. As another example, each component of a layer can be individually electrically isolated, e.g., such that different voltages can be applied to each component within a layer individually and simultaneously. Components can include, but are not limited to, gaps configured to accept beamlets, apertures sized to selectively block portions of beamlets, or other types of modulators. Layers and / or components can be grounded (i.e., have a zero ground potential) or energized (e.g., excited by an applied voltage). For example, the energizable elements may be configured to accelerate, decelerate, focus, and / or deflect the beamlets 394. Each element of the array may be associated with an electrostatic field. Each element may be the same size as other gaps in the same layer, although this is not required.

[0053] In an embodiment, each layer includes multiple “dummy” elements 366 (e.g., dummy ground elements, dummy excitation elements) that are not associated with beamlets 394 but are incorporated to provide constant / uniform properties (e.g., constant electrostatic field for each element, constant acceleration / focusing of beamlets, constant thermal expansion, etc.). For example, the dummy elements 366 can be used to create a homogeneous electrostatic field in the active gap. For example, the dummy elements 366 can be dummy gaps that can be used to provide more uniform electrical properties for the grounded elements 360 near the outer edges of the array of grounded elements 360. For example, one or more rows of additional gaps can be incorporated outside and adjacent to the gaps configured to accept the beamlets 394. For example, the additional gaps and the gaps configured to accept the beamlets 394 can be equidistant from each other.

[0054] 3B shows the layers of components as two-dimensional, arc-shaped layers arranged radially in cross section, any number (e.g., any number) of components (e.g., modulators 314) can be arranged in a three-dimensional array according to embodiments of the present disclosure. For example, each layer can be spherical, with beamlets 394 corresponding to each layer being transmitted through that layer.

[0055] In an embodiment, each of the plurality of tilted illumination columns 212 is associated with an electron beam source 214. For example, the tilted column electron beam imaging system 200 may include an array of electron beam sources 214 in an electron beam source array 350.

[0056] In an embodiment, each of the plurality of tilted illumination columns 212 includes a modulator 314. For example, the tilted column electron beam imaging system 200 may include an array of modulators 314 in a modulator layer of the modulator array 354. For example, each modulator 314 may be configured to modulate a beamlet 394.

[0057] In an embodiment, each of the plurality of tilted illumination columns 212 includes a secondary beam-limiting aperture 318. For example, the tilted column electron beam imaging system 200 may include an array of secondary beam-limiting apertures 318 in a secondary beam-limiting aperture layer of the secondary beam-limiting aperture array 356.

[0058] In an embodiment, each of the plurality of tilted illumination columns 212 includes a condenser lens 320. For example, the tilted column electron beam imaging system 200 may include an array of condenser lenses 320 in a condenser lens layer of the condenser lens array 358.

[0059] In an embodiment, tilt column electron beam imaging system 200 includes an array of various components in various layers in a gun lens array 352. An example of a gun lens array 354 is further described below with reference to FIG.

[0060] Figure 3C shows a simplified schematic diagram 364 of the central upper column region of the tilted column electron beam imaging system 200, in accordance with one or more embodiments of the present disclosure. Figure 3C is an enlarged view of a portion of Figure 3B.

[0061] In an embodiment, the secondary beam-limiting aperture array 356 includes an array of secondary beam-limiting apertures 318 .

[0062] In an embodiment, the focusing lens array 358 includes multiple (e.g., three) adjacent focusing layers. For example, each focusing layer may be an electrode having a gap (e.g., a hole). For example, the size (e.g., diameter) of each gap may be several hundred microns. As another example, each hole axis may intersect at the first common crossover volume 322. The gaps may be aligned so that the beamlets 394 pass through the gaps. For example, the gaps may be spaced at intervals of several hundred microns. This dimension may also apply to components in other layers of other arrays (e.g., arrays 350, 352, 354, and 356). However, it should be noted that components of aperture arrays, such as the aperture array 356, may be smaller, such as on the order of tens of microns. The focusing lens 320 of FIG. 3A may include the focusing lens element 320 of FIG. 3C.

[0063] In an embodiment, the adjacent collection layers include a collection pump layer and two ground collection layers. For example, the collection pump layer includes a collection lens 320 configured for pumping. For example, a selected voltage can be applied to the collection pump layer to focus beamlets 394 at the intermediate image plane 324 in FIG. 3A . Thus, changing the selected voltage can change the location of the intermediate image plane 324 at which each beamlet 394 focuses. In a similar or alternative example, the collection lens array 358 may include two ground collection layers, collection ground elements 360 and 362. The ground collection layers may be positioned adjacent to each other, one on each side of the collection pump layer. Each collection ground element 360, 362 may include a gap (e.g., a hole) defined by a surface (e.g., the inner surface of the hole). For example, the ground collection layer may be a spherical plate with a spherical array of holes formed by processing (e.g., machining, molding, etching).

[0064] The intermediate image plane is the object plane of the projection optical system. The plane (not shown) that is focused onto the sample 118 is the image plane of the projection optical system. This plane may be located, for example, on the outer surface of the sample 118 or at some depth within the sample 118.

[0065] Figure 4 shows a simplified schematic diagram 400 of the upper column region above the tilted column electron beam imaging system 200, in accordance with one or more embodiments of the present disclosure. Figure 4 is an enlarged view of a portion of Figure 3B.

[0066] As previously described herein, in an embodiment, tilt column electron beam imaging system 200 includes an electron beam source array 350, a gun lens array 352, and a modulator array 354.

[0067] In an embodiment, the electron beam source array 350 includes an array of electron beam sources 214. For example, the electron beam source array 350 may include adjacent layers of source emitter tips 308, source holder elements 370, and source excitation elements 372. In an embodiment, the gap dimensions (e.g., hole diameter) of the source holder elements 370 are several millimeters (e.g., on the order of more than 1 mm), and the gap dimensions of the source excitation elements 372 are on the order of hundreds of microns (e.g., greater than 200 microns but less than 1 mm).

[0068] In an embodiment, gun lens array 352 includes an array of gun lens subsystems 380. For example, gun lens array 352 may include adjacent layers of beam-limiting aperture 310, gun lens excitation element 384, gun lens element 386, and gun lens ground element 388.

[0069] In an embodiment, the voltage applied to source excitation element 372 is equal to the voltage applied to gun lens excitation element 384. For example, the potential at source excitation element 372 and gun lens excitation element 384 may be several kilovolts, higher than the potential at source emitter tip 308. Also, the potential at gun lens element 386 may be between the potential at gun lens ground element 388 (e.g., zero) and the potential at gun lens excitation element 384. For example, for a 30 kV energy beamlet, if the potential at source emitter tip 308 is approximately −30 kV (minus 30 kV), the potential at source excitation element 372 and gun lens excitation element 384 is approximately −25 kV, and the potential at gun lens element 386 is between −10 kV and −20 kV, beamlet 394 can be focused and the beam current selected to move beamlet crossover 316.

[0070] FIG. 5 illustrates a schematic diagram 500 of a two-dimensional projection of a spherical electrode layer of a condenser lens array 358, according to one or more embodiments of the present disclosure. In an embodiment, the condenser lens array 358 is an array of condenser lenses 320. In an embodiment, FIG. 5 may illustrate an XY-planar view of the condenser lens array 358 of FIG. 3B projected onto the XY plane. Note that the projection of the condenser lens array 358 may be equal to or similar to a stereographic projection (rather than a planar projection), but that equidistant elements on the sphere are also equidistant in the projection. Thus, the projection may be a simplified representation of equidistant elements shown in two dimensions. This projection depiction should not be considered limiting, but rather provides a conceptual understanding that the elements of the illumination path 304 may be arranged to correspond to various arrangements of measurement areas 346 on the sample 118. For example, the elements of the angled illumination column 212 may be arranged in a hexagonal array, as shown in FIG. 5, to provide an arrangement of measurement areas 346 that are also hexagonal. For example, 331 measurement areas 346 may be arranged in a hexagonal shape as shown.

[0071] FIG. 6 illustrates a schematic diagram 600 of a set of seamlessly joined hexagonal field-of-view arrays 602, according to one or more embodiments of the present disclosure. The hexagonal field-of-view array 602 may be advantageous over other field-of-view arrays (e.g., circular arrays) because it can provide seamless joining between arrays of measurement regions 346. In an embodiment, the field-of-view arrays 602 are measured during a measurement process of the sample 118. In a first step, a first field-of-view array (not labeled) is measured. In a second step, a second field-of-view array (not labeled) is measured. For example, the field-of-view arrays 602 may be positioned relative to one another during this process so that there are no gaps between the field-of-view arrays 602. These steps may be performed by the controller 204. Thus, a sample 118 (e.g., a wafer) having a diameter of several hundred millimeters can be seamlessly covered by multiple hexagonally arranged FOVs 604. For example, each FOV 604 may be several hundred microns in size.

[0072] 7 illustrates a schematic diagram 700 of a spherical gun focusing lens array projection of gun lens array 352 in two dimensions, in accordance with one or more embodiments of the present disclosure. In an embodiment, the arrangement of gun lens elements 386 of gun lens array 352 may be hexagonal as shown.

[0073] In embodiments, each gun lens element 386 is spaced apart from the other gun lens elements 386, allowing a focusing voltage to be applied to each gun lens element 386 individually. This spacing of the gun lens elements 386 is also illustrated in FIG. 4. For example, the voltage distribution subsystem (not shown) may include a voltage regulator electrically coupled (e.g., coupled by individual wires) to each gun lens element 386 and a controller configured to adjust the focusing voltage applied to each gun lens element 386. As other examples, each gun lens element 386 may be rectangular (not shown), square, or cylindrical. In some examples, the gap between each gun lens element 386 may be on the order of tens of millimeters in size.

[0074] Here, the gap between each gun lens element 386 may be relatively small because the potential difference between each gun lens element 386 is generally low. In this regard, a low potential difference means that a gun lens element 386 has a negligible effect on the beamlets 394 of adjacent gun lens elements 386. In an embodiment, the gun lens elements 386 may be embedded in (e.g., connected to) an insulating (e.g., non-conductive) substrate (not shown). Power lines (not shown) that apply the focusing voltage may be provided below the gap to avoid electrostatic field redistribution in the focusing lens.

[0075] FIG. 8 shows a simplified schematic diagram 800 of the projection optics of the tilt column electron beam imaging system 200 in accordance with one or more embodiments of the present disclosure.

[0076] In an embodiment, the tilted column electron beam imaging system 200 includes a general purpose transfer lens 326 , a ground electrode 802 , an acceleration-focusing electrode 810 , and / or a charge control plate 804 .

[0077] 3A , the objective lens 332 may include a magnetic and / or electrostatic objective lens. For example, the objective lens 332 may include a magnetic section (not labeled) and an electrostatic section (not labeled). For example, the electric field of the electrostatic section may be used to accelerate and / or decelerate the beamlet electron energy before the primary electrons land on the sample 118, and the magnetic field of the magnetic section may be used to focus the primary electron beam on the sample 118. As another example, the objective lens 332 may include an electrostatic lens without a magnetic lens. For example, the objective lens 332 may include a ground electrode 802, an acceleration-focusing electrode 810, and / or a charge control plate 804.

[0078] In an embodiment, the charge control plate 804 is configured to selectively charge the specimen 118 according to a particular (selected) extraction area to inspect and / or identify a particular (selected) layer of the specimen 118 at a particular depth. For example, to measure a lower layer at a certain depth of the specimen 118, the voltage on the charge control plate 804 can be varied to selectively adjust the charge imparted to the specimen 118, and the beamlets 394 can be directed into the specimen 118 at a selected distance (or range of distances) to measure the lower layer.

[0079] In embodiments, the acceleration-focusing electrodes 810 are used to accelerate the primary electrons of the beamlets 394 to reduce Coulomb interactions. For example, the acceleration-focusing electrodes 810 may be positioned near the second common crossover volume 334. Such a positioning may be desirable, for example, to counteract particularly strong Coulomb interactions near the second common crossover volume 334. In some examples, the acceleration-focusing electrodes 810 may be used as an alternative or additional configuration to focus the beamlets 394. For example, the acceleration-focusing electrodes 810 can adjust the focusing plane of the beamlets 394 to a specific (selected) position / depth of the sample 118.

[0080] The general-purpose transfer lens 326 may be any lens. For example, the general-purpose transfer lens 326 may be an electrostatic lens or a magnetic lens. It is noted that a magnetic lens may exhibit superior optical properties in at least some embodiments. In an embodiment, a magnetic-type general-purpose transfer lens 326 may be provided as shown in FIG. 8. For example, the general-purpose transfer lens 326 may include a magnetic coil 806 configured to carry an excitation current. The magnetic coil 806 may also be shielded with a magnetic pole 808.

[0081] Figure 9A shows a simplified schematic diagram 900 with a vertical expansion of the primary electron trajectories and image-forming relationships shown in Figure 8, in accordance with one or more embodiments of the present disclosure. For example, Figure 9A can be generated by a ray-tracing simulation using computer modeling of the components of Figure 8.

[0082] 9B shows a simplified schematic diagram 902 that is an expanded view of a portion of FIG. 9A including imaging relationships near the sample 118, in accordance with one or more embodiments of the present disclosure. As shown, the intersection of the paths of beam lines 904, 906, 908, and 910 with a central beam line 912 that is parallel to the Z axis is illustrated. Also shown is the telecentricity of beam lines 904, 906, 908, and 910 near the sample 118.

[0083] 10-12 show the image formation across the field of view (i.e., measurement area 346) before and after correction. As previously described herein, the tilted illumination column 212 can be used to adjust and correct the astigmatism and / or field curvature of each beamlet 394. The optical performance of the tilted-column electron beam imaging system 200 of FIG. 3A can be characterized by metrics such as the resolution (or spot size) of the beamlets 394, the size of the field of view, and the uniformity of the beamlet images within the field of view. FIGS. 10-12 may show examples of computer simulations to evaluate these metrics.

[0084] FIG. 10 is a conceptual diagram 1000 illustrating the imaging state across a field of view before astigmatism and field curvature correction, according to one or more embodiments of the present disclosure. The beamlet spot sizes are shown as ten closed lines corresponding to the distribution of beamlet electrons on the sample 118. While a 240×240 μm square FOV at the wafer is considered, this consideration is for illustrative purposes only and does not necessarily limit the size or shape of the FOV. In this example, which should not be considered limiting, the distance between the corners of the image formation section in FIG. 10 is considered to be equal to the distance between the farthest corners of the hexagonal field array 602 in FIG. 6. FIG. 10 illustrates that the projection optics of FIG. 8 can produce relatively large off-axis astigmatism and field curvature blur (e.g., without correction).

[0085] FIG. 11 is a conceptual diagram 1100 illustrating the imaging state across the field of view of FIG. 10 after astigmatism correction, in accordance with one or more embodiments of the present disclosure. In an embodiment, astigmatism can be corrected using, for example, the modulator array 354 of FIG. 4. Correction of astigmatism in multi-beam scanning electron microscope systems is disclosed in U.S. Pat. No. 10,497,536, issued December 3, 2019, the entire disclosure of which is incorporated herein by reference. After astigmatism correction, the blurring of field curvature is shown to dominate the spot size.

[0086] FIG. 12 is a conceptual diagram 1200 illustrating the imaging state across the field of view of FIG. 11 after field curvature correction (and astigmatism correction) in accordance with one or more embodiments of the present disclosure. In an embodiment, field curvature blur is corrected by the gun lens array 352 of FIG. 4. For example, each gun lens element 386 may be configured to have an individually adjustable focus voltage. Thus, fine-tuning each gun lens focus voltage can individually correct the field curvature blur for each beamlet 394. For example, fine-tuning the focus voltage can reposition the beamlet crossover 316 shown in FIG. 3A. This field curvature blur correction eliminates (or reduces) crosstalk with other beamlets 394, making each beamlet 394 independent.

[0087] Referring to FIG. 12 , the beamlet image across the FOV is uniform, but in some embodiments, some coma may still remain. In embodiments, this coma is negligible when viewed at a certain magnification (e.g., the size of the FOV). The electron spot of the beamlet 394 may have any distribution at the sample 118. In embodiments, the electron spot is generally Gaussian. Also, in embodiments, the spot size is typically measured at the center of the electrons. For example, the full width of the distribution for the FW50 spot size is where 50% of the electrons are contained. For example, the measured size of the FW50 distribution is shown by the fifth circle of the central spot in the concentric circles shown in FIG. 12 .

[0088] FIG. 13 shows a simplified schematic diagram of a dual-tilt column electron beam imaging system 300 according to one or more embodiments of the present disclosure. In an embodiment, the imaging subsystem 202 includes a set of dual-tilt illumination columns 1306. For example, the tilt illumination column 212 may be (or may include) the dual-tilt illumination column 1306. The dual tilt can provide greater separation between illumination columns than a single tilt. Advantages include reduced heat buildup and increased spacing / gap between components. For example, a dual-tilt configuration can provide a wider pitch between each gun lens 312. The increased pitch between the gun lenses 312 reduces overlap in the electrostatic focusing fields of each gun lens 312, thereby reducing crosstalk between beamlets 394 and providing a larger gap for locating and integrating the focusing voltages of the gun lenses 312.

[0089] In an embodiment, each dual tilt illumination column 1306 includes a modulator 314. For example, the modulators 314 can be used to modulate (e.g., deflect) the beamlets 394 along different axes. For example, although not shown in FIG. 13 , the modulator array can include multiple modulators 314 in a single layer.

[0090] In an embodiment, each beamlet 394 of each dual-tilt illumination column 1306 is directed by a modulator 314 from a direction along a first dual-tilt axis 1304 to a direction along a second dual-tilt axis 1308. The angle between the second dual-tilt axis 1308 and the first dual-tilt axis 1304 may be referred to as the inter-axis angle 1302. Thus, the two axes can provide two angles of tilt for the tilted illumination column 212. Any number of axes and modulators 314 can be used to provide any number of angles of tilt for the tilted illumination column 212.

[0091] FIG. 14 illustrates a simplified schematic diagram of a tilted column electron beam imaging system 1400 including a generalized condenser lens 1402 in accordance with one or more embodiments of the present disclosure. For example, rather than an array of individual condenser lens elements, a single generalized condenser lens 1402 may be used to condition all of the beamlets 394. Advantages of the generalized condenser lens 1402 include the fact that its larger components are easier to manufacture than its smaller individual condenser lens components, and that the generalized condenser lens 1402 introduces relatively less geometric aberration blur. For example, the generalized condenser lens 1402 may be more easily fabricated using less sophisticated, but lower-cost, machining tools. For example, referring to FIG. 3C , the condenser lens array 358 may introduce spherical aberration blur at the intermediate image plane 324 due to the hole size and pitch between each condenser element 320, which may be on the order of hundreds of microns. In embodiments, this spherical aberration blur may be reduced or eliminated by using the generalized condenser lens 1402. This is because the bore diameter of the gap in the general-purpose focusing lens 1402 may be, but is not limited to, on the order of several tens of millimeters (for example, 10 mm or more, 20 mm or more, 30 mm or more, 50 mm or more, 100 mm or more).

[0092] In an embodiment, the general purpose focusing lens 1402 is configured to adjust the intermediate image plane 324 of the beamlets 394. In an embodiment, the general purpose focusing lens 1402 overlaps with the first common crossover volume 322.

[0093] 15 illustrates a simplified schematic diagram of a dual-tilt column electron beam imaging system 1500 with a general purpose condenser lens 1302 in accordance with one or more embodiments of the present disclosure. In embodiments, the dual-tilt configuration of FIG. 13 can be combined with the general purpose condenser lens 1302 of FIG. 14 to provide both a dual-tilt and general purpose condenser lens 1302. In embodiments, the dual-tilt and general purpose condenser lens configuration provides a combination of the advantages described with reference to FIGS. 13 and 14.

[0094] 16 illustrates a flow diagram of steps performed in a method 1600, in accordance with one or more embodiments of the present disclosure. However, it is recognized that the method 1600 is not limited to the tilted column electron beam imaging system 200, and that additional or alternative system-level embodiments may perform all or some of the steps of the method 1600.

[0095] In step 1602, electrons of a plurality of beamlets 394 are generated using a plurality of electron beam sources 214. For example, a first tilt axis 340 of a first tilted illumination column 212 may be disposed along a first angle (e.g., an angle relative to any z-axis), and at least one additional tilt axis 340 of at least one additional tilted illumination column 212 may be disposed along at least one other angle different from the first angle. Also, for example, each of the plurality of beamlets 394 may pass through a first common crossover volume 322.

[0096] In step 1604, each beamlet 394 is adjusted using a respective electron optics 220 of a respective tilted illumination column 212 configured to receive the beamlet 394 from a respective electron beam source. For example, astigmatism and field curvature blur may be corrected.

[0097] In step 1606, multiple measurement areas 346 of the sample 118 are simultaneously irradiated with multiple beamlets 394. For example, to increase the throughput of the inspection process, multiple beamlets 394 can be utilized simultaneously (or nearly simultaneously) to image multiple measurement areas 346 of the sample 118.

[0098] In step 1608, secondary electrons coming from multiple measurement areas 346 of the sample 118 are collected using the detector 216. Note that this description is not limiting and backscattered electrons may also be collected.

[0099] In step 1610, the secondary electrons are detected using detector 216. Based on the detected secondary electrons, for example, an image (e.g., an SEM image) of each measurement area 346 can be generated.

[0100] In an optional step, one or more properties of the specimen 118 are determined based on the detection of secondary electrons in step 1610 .

[0101] Referring again to Figures 2-16, additional details regarding the embodiments and various components will now be described.

[0102] In an embodiment, the tilting column electron beam imaging system 200 includes a sample stage 396 configured to secure the sample 118. The sample stage 396 may include any sample stage known in the field of electron beam microscopy. In an embodiment, the sample stage 396 is a drivable stage. For example, the sample stage 396 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 396 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 396 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.

[0103] 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.

[0104] Detector 216 may include any type of electron detector known in the art configured to detect electrons (e.g., secondary electrons and / or backscattered electrons). For example, secondary electrons may be collected and imaged using an Everhart-Thornley detector (or other type of scintillator-based detector). In other embodiments, secondary electrons may be collected and imaged using a micro-channel plate (MCP). In other embodiments, electrons may be collected and imaged using a PIN or pn junction detector, such as a diode or diode array. In other embodiments, electrons may be collected and imaged using one or more avalanche photodiodes (PDS).

[0105] 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.

[0106] It should be noted that one or more components of the tilting-column electron beam imaging system 200 may be communicatively coupled to various other components of the tilting-column electron 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 tilting-column electron beam imaging system 200 via a wired or wireless connection known in the art.

[0107] In embodiments, the one or more processors 206 may 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 a program configured to operate the tilting column electron 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 tilt-column electron 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.

[0108] 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 tilting column electron 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.

[0109] 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 that displays data from the tilting column electron 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.

[0110] 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.

[0111] 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.

[0112] 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.

[0113] 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.

[0114] 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.

[0115] 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.

[0116] 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."

[0117] 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.

[0118] 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. A tilted column electron beam imaging system, comprising: an imaging subsystem, the imaging subsystem comprising: a plurality of electron beam sources configured to generate a plurality of beamlets that simultaneously probe a plurality of measurement regions on the sample; a collection path including one or more detectors; an illumination path; the illumination path includes a plurality of tilted illumination columns configured to receive a respective beamlet from a respective electron beam source, each tilted illumination column including a set of one or more electron optical components configured to condition the respective beamlet; a first tilt axis of a first tilted illumination column disposed along a first angle; and at least one additional tilt axis of at least one additional tilted illumination column disposed along at least one additional angle different from the first angle; and wherein each of the plurality of beamlets passes through a first common crossover volume.

2. 10. The tilted column electron beam imaging system of claim 1, wherein each electron beam source comprises one or more electron source emitter tips.

3. 2. The tilted-column electron beam imaging system of claim 1, wherein the plurality of tilted illumination columns each include a gun lens.

4. 2. The tilted-column electron beam imaging system of claim 1, wherein each of the plurality of tilted illumination columns includes a focusing lens.

5. 2. The tilted column electron beam imaging system of claim 1, each of the plurality of tilted illumination columns includes a modulator; The tilt column electron beam imaging system, wherein the modulator is configured to at least one of deflect the individual beamlets or adjust the individual beamlets.

6. 2. The tilted column electron beam imaging system of claim 1, wherein each of the plurality of tilted illumination columns includes a beam-limiting aperture.

7. 7. The tilted column electron beam imaging system of claim 6, wherein the beam-limiting aperture is positioned before a gun lens in a direction of travel of the individual beamlets.

8. 2. The tilted-column electron beam imaging system of claim 1, wherein the plurality of tilted illumination columns each include a secondary beam-limiting aperture.

9. 9. The tilted column electron beam imaging system of claim 8, wherein the secondary beam limiting aperture is located after a gun lens.

10. 2. The tilted-column electron beam imaging system of claim 1, wherein the illumination path further includes a general-purpose transfer lens configured to direct each of the plurality of beamlets from a diverging path to a converging path toward a second common crossover volume, and the general-purpose transfer lens is positioned after the first common crossover volume.

11. 2. The tilting column electron beam imaging system of claim 1, wherein the illumination path includes a general purpose focusing lens configured to adjust an intermediate image plane of the plurality of beamlets.

12. 12. The tilted-column electron beam imaging system of claim 11, wherein the general purpose focusing lens overlaps with the first common crossover volume.

13. 2. The tilted-column electron beam imaging system of claim 1, wherein the illumination path further includes a general-purpose objective lens configured to transmit each of the plurality of beamlets so that they are formed telecentrically on the sample.

14. 10. The tilted column electron beam imaging system of claim 1, wherein the collection path further comprises a Wien filter configured to separate primary electrons from secondary electrons.

15. 2. The tilted-column electron beam imaging system of claim 1, wherein the plurality of tilted illumination columns comprises a plurality of dual-tilt illumination columns, each dual-tilt column comprising a modulator, and wherein the beamlets of each dual-tilt illumination column are directed by the modulator from an orientation along a first dual-tilt axis to a second dual-tilt axis.

16. 2. The tilted column electron beam imaging system of claim 1, wherein the illumination path includes a central illumination column having a central electron beam source configured to generate a central beamlet along a central axis of the imaging subsystem.

17. 10. The tilted column electron beam imaging system of claim 1, wherein the plurality of tilted illumination columns are arranged in an array.

18. 20. The tilted column electron beam imaging system of claim 17, wherein the array is a spherical array.

19. 20. The tilted column electron beam imaging system of claim 17, wherein the array is a hexagonal array.

20. 2. The tilted column electron beam imaging system of claim 1, wherein at least a portion of the set of one or more electron optical components is arranged in a set of stacked arrays, the set of stacked arrays comprising: a beam-limiting aperture array layer; and a gun lens array layer; a ground layer.

21. 10. The tilted-column electron beam imaging system of claim 1, wherein the modulators are arranged in a modulator array.

22. 10. The tilted-column electron beam imaging system of claim 1, wherein the electron beam sources are arranged in an electron beam source array.

23. 2. The tilted column electron beam imaging system of claim 1, wherein the plurality of beamlets are arranged radially.

24. 2. The tilted-column electron beam imaging system according to claim 1, wherein the plurality of beamlets are radially arranged perpendicular to a three-dimensional curved surface.

25. 25. The tilting column electron beam imaging system of claim 24, wherein the three-dimensional curved surface is a portion of a sphere.

26. generating a plurality of beamlets of electrons using a plurality of electron beam sources; conditioning each beamlet with a respective electron optics of a respective tilted illumination column configured to receive said beamlet from a respective electron beam source; simultaneously irradiating a plurality of measurement regions of a sample with the plurality of beamlets; collecting secondary electrons from the plurality of measurement regions of the sample using a detector; detecting the secondary electrons with the detector, a first tilt axis of a first tilted illumination column oriented along a first angle, and at least one additional tilt axis of at least one additional tilted illumination column oriented along at least one additional angle different from the first angle, and wherein each of the plurality of beamlets passes through a first common crossover volume.

27. 27. The method of claim 26, further comprising identifying one or more characteristics of the specimen based on the detection of the secondary electrons.

28. 27. The method of claim 26, further comprising conditioning the beamlets with a general purpose focusing lens configured to adjust an intermediate image plane of the plurality of beamlets.

29. 27. The method of claim 26, wherein each tilted illumination column includes a modulator, and each beamlet is directed by the modulator from an orientation along a respective first dual tilt axis to a respective second dual tilt axis.

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