Optical system for plurality of primary beamlets, charged particle multibeam device and method of focusing plurality of primary beamlets

Abstract

A porous lens plate for a multi-beam generator of a charged particle multi-beam apparatus is described. The present invention relates to a porous lens plate comprising a porous lens plate body comprising: an array of N beamlet openings, the array of N beamlet openings having beamlet openings, the array of N beamlet openings configured to produce N primary charged particle beamlets, where N is a number > = 2; and a plurality of correction openings passing through the aperture lens plate body, the correction openings configured to locally affect a lens field of the beamlet openings, where the correction openings are different from the beamlet openings.

Description

Technical Field

[0001] Embodiments relate to charged particle beam apparatus, for example, for inspection system applications, test system applications, defect review, or critical dimension setting applications. Embodiments also relate to methods of operating charged particle beam apparatus, and in particular to a method of generating a plurality of N primary charged particle beamlets to be focused on a sample. More particularly, embodiments relate to charged particle beam apparatus as a multi-beam high-throughput electron beam inspection (EBI). Specifically, embodiments relate to a multi-beam generator with a porous lens plate, a multi-beam generator, a charged particle multi-beam device configured to focus N primary charged particle beamlets on a sample, and a method of generating a plurality of N primary charged particle beamlets to be focused on a sample. Background Art

[0002] Modern semiconductor technology relies heavily on accurate control of the various processes used during the production of integrated circuits. Consequently, wafers are repeatedly inspected to identify problems as early as possible. Furthermore, masks or reticles are inspected prior to actual use during wafer processing to ensure that they accurately define the corresponding pattern. Inspecting wafers or masks for defects can include inspecting the entire wafer or mask area, for example, for 300mm wafer production. In particular, wafer inspection during wafer manufacturing advantageously includes inspecting the entire wafer area in a short period of time, so that production throughput is not limited by the inspection process. Inspecting only portions of a wafer or mask also advantageously increases throughput.

[0003] Scanning electron microscopes (SEMs) have been used to inspect wafers. A single, finely focused electron beam is used to scan the surface of the wafer, for example. When the electron beam strikes the wafer, secondary electrons and / or backscattered electrons, i.e., signal electrons, are generated and measured. Pattern defects at a location on the wafer are detected, for example, by comparing the intensity signal of the secondary electrons with a reference signal corresponding to the same location on the pattern. However, due to the increasing demand for higher resolution, scanning the entire surface of the wafer takes a long time. Consequently, wafer inspection using conventional (single-beam) SEMs is difficult because this approach does not provide a corresponding throughput.

[0004] Wafer and mask defect inspection in semiconductor technology requires high-resolution, fast inspection tools that cover high throughput, full-wafer or mask applications, or hotspot detection. Because optical tools have limited resolution and cannot cope with shrinking defect sizes, electron-beam inspection is becoming increasingly important. In particular, from the 20nm node and beyond, the high-resolution potential of electron-beam-based imaging tools is essential for detecting all defects of interest.

[0005] For example, document US2017 / 287674 describes a particle optics arrangement having: a charged particle source for generating a beam of charged particles; a porous plate arranged in a beam path of the beam of charged particles, wherein the porous plate has a plurality of holes formed in a predetermined first array pattern. Document EP 3703 100 describes a charged particle beam device having: a sample holder for holding a sample; a source for generating a beam of charged particles; and an irradiator for converting the beam of charged particles into a plurality of charged particle beamlets and directing the plurality of charged particle beamlets onto the sample.

[0006] In multi-beam instruments, multiple electron beams may be used to inspect or image an area of ​​a sample (e.g., a wafer). For multi-beam applications, the generation of beamlets may introduce various aberrations that may be introduced by a combination of off-axis beamlets, individual beamlet forming elements, and collective beamlet forming elements, and / or other effects caused by interactions between the beamlets and the elements that form them.

[0007] In view of the above, there are provided a multi-beam generator aperture lens plate, a multi-beam generator, a charged particle multi-beam apparatus, and a method of generating a plurality N of primary charged particle beamlets to be focused on a sample that are improved over previous attempts. Summary of the Invention

[0008] In view of the above, a multi-beam generator, a multi-beam generator, a charged particle multi-beam device and a method of generating a plurality of N primary charged particle beamlets are provided. Further aspects, advantages and features are apparent from the dependent claims, the description and the drawings.

[0009] According to an embodiment, a porous lens plate for a multi-beam generator of a charged particle multi-beam device is provided. The porous lens plate comprises: a porous lens plate body having one or more layers, the porous lens plate body comprising: an array of N beamlet openings, the array of N beamlet openings passing through all of the one or more layers, the array of N beamlet openings having beamlet openings, the array of N beamlet openings being configured to generate N primary charged particle beamlets, wherein N is a number greater than or equal to 2; and a plurality of correction openings passing through all of the one or more layers of the porous lens plate body and configured to locally affect the lens field of the beamlet openings, wherein the correction openings are different from the beamlet openings.

[0010] According to an embodiment, a multi-beam generator for a charged particle multi-beam device is provided. The multi-beam generator includes: a charged particle emitter configured to emit a primary charged particle beam; a porous lens plate arranged to be irradiated with the primary charged particle beam, the porous lens plate including: a porous lens plate body including: an array of N beamlet openings, the array of N beamlet openings having beamlet openings, the array of N beamlet openings configured to generate N primary charged particle beamlets, wherein N is a number greater than or equal to 2; and a plurality of correction openings passing through the porous lens plate body, the plurality of correction openings configured to locally affect the lens field of the beamlet openings, wherein the correction openings are different from the beamlet openings; and an aperture plate located in a field-free region, away from the porous lens plate and downstream of the porous lens plate, wherein the aperture plate body has a plurality of N openings for passing the N primary charged particle beamlets, and the aperture plate body is configured to block electrons passing through the correction openings. In particular, according to some embodiments, which can be combined with other embodiments described herein, the porous lens plate is arranged to be irradiated with the primary charged particle beam directly, i.e. without a focusing lens or another lens between the charged particle emitter and the porous lens plate.

[0011] According to an embodiment, a multi-beam generator for a charged particle multi-beam device is provided. The multi-beam generator comprises: a charged particle emitter, the charged particle emitter being configured to emit a primary charged particle beam; a porous lens plate as described in any one of the embodiments described herein, the porous lens plate being arranged to be irradiated with the primary charged particle beam; and one or more electrodes, the one or more electrodes having a common opening, the common opening being configured to allow the primary charged particle beam or at least one of the N primary charged particle beamlets to pass through, the one or more electrodes being configured to generate an electric field on the porous lens plate to focus the N primary charged particle beamlets in a plane downstream of the porous lens plate.

[0012] According to an embodiment, a charged particle multi-beam apparatus configured to focus N primary charged particle beamlets on a sample is provided, wherein the charged particle multi-beam apparatus comprises a multi-beam generator according to any one of the embodiments described herein.

[0013] According to an embodiment, a method for generating a plurality of N primary charged particle beamlets to be focused on a sample is provided. The method comprises: generating a primary charged particle beam with a charged particle emitter; irradiating a porous lens plate with the primary charged particle beam; generating beamlets, comprising: generating N primary charged particle beamlets generated with an array of N beamlet openings; and generating a first dummy beamlet generated with a plurality of correction openings; focusing the N primary charged particle beamlets by generating an electric field at the porous lens plate with one or more electrodes, the N primary charged particle beamlets being focused in a plane downstream of the porous lens plate; and blocking at least the first dummy beamlet, in particular blocking at least the first dummy beamlet in a field-free region downstream of the porous lens plate.

[0014] The embodiments also relate to apparatus for performing the disclosed methods and include apparatus components for performing each of the described method features. The method features may be performed by hardware components, a computer programmed with appropriate software, any combination of the two, or in any other manner. Furthermore, the embodiments also relate to methods by which the described apparatuses operate. The embodiments include method features for performing each of the functions of the described apparatuses. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] In order that the features recited above of the present disclosure may be understood in detail, a more particular description of the disclosure, briefly summarized above, may be had by reference to embodiments, some of which are illustrated in the accompanying drawings. It is to be noted, however, that the drawings illustrate only typical embodiments of the disclosure and are therefore not to be considered limiting of its scope, as the disclosure may admit to other equally effective embodiments.

[0016] Figure 1 shows a schematic diagram of a portion of a charged particle multi-beam device including a multi-beam generator having a multi-aperture lens plate according to embodiments described herein;

[0017] Figure 2 A schematic diagram of a porous lens plate having beamlet openings and correction openings according to various embodiments of the present disclosure is shown;

[0018] Figure 3 A schematic diagram illustrating a porous lens plate having beamlet openings that compensate for distortion according to various embodiments of the present disclosure is shown;

[0019] Figure 4 A schematic diagram of a porous lens plate having beamlet openings and further openings according to various embodiments of the present disclosure is shown;

[0020] Figure 5 shows a schematic diagram of a porous lens plate according to various embodiments of the present disclosure;

[0021] Figure 6 shows a schematic diagram of an aperture plate having openings for focusing a plurality of primary beamlets on a sample, said aperture plate being included, for example, in a collimator, thereby collimating the primary beamlets;

[0022] Figure 7A and Figure 7B shows a schematic diagram of a portion of a charged particle multi-beam device including a multi-beam generator having a multi-aperture lens plate according to embodiments described herein;

[0023] Figure 8A and Figure 8B shows a schematic diagram of a portion of a charged particle multi-beam device including a multi-beam generator having a multi-aperture lens plate according to embodiments described herein;

[0024] Figure 9 shows a schematic diagram of a charged particle multi-beam apparatus according to embodiments described herein; and

[0025] Figure 10 Shown is a flow chart illustrating a method of generating a plurality of N primary charged particle beamlets to be focused on a sample according to various embodiments of the present disclosure. DETAILED DESCRIPTION

[0026] Reference will now be made in detail to various embodiments, one or more examples of which are illustrated in the accompanying drawings. In the following description of the drawings, like reference numerals refer to like parts. Differences with respect to individual embodiments are described. Each example is provided by way of explanation and is not intended to be limiting. Furthermore, features illustrated or described as part of one embodiment may be used on or in conjunction with other embodiments to produce still further embodiments. The description is intended to encompass modifications and variations.

[0027] Without limiting the scope of protection of the present application, in the following, a charged particle multi-beam device or a component thereof will be referred to exemplarily as a charged particle multi-beam device, including a primary electron beam or primary electron beamlets and detection of secondary or backscattered particles (such as electrons). As described herein, the discussion and description related to detection are described exemplarily with respect to electrons in a scanning electron microscope. In a variety of different instruments, other types of charged particles, such as positive ions, may be emitted and / or detected by the device. Embodiments relate to primary beams, primary beamlets and one or more signal beams, such as electrons. The primary beam, primary beamlets and / or one or more signal beams may be provided by other charged particles that are electrons. The signal beamlets may additionally or alternatively include photons.

[0028] Figure 1A portion of a charged particle multi-beam device is shown. The charged particle multi-beam device includes a multi-beam generator 100. The multi-beam generator includes a charged particle beam source, two or more electrodes 120, and a porous lens plate 200. The charged particle beam source includes an emitter 110, which emits a primary charged particle beam, such as an electron beam. According to the embodiments described herein, the multi-beam generator is configured to generate an array of primary charged particle beamlets. The charged particle beam source emits a primary beam. The porous lens plate 200 generates primary particle beamlets from the primary beam. One or more electrodes 120 and the porous lens plate can operate as microlens electrodes for the primary charged particle beamlets. Therefore, one or more electrodes 120 can be lens electrodes. In particular, one or more electrodes can include an opening for the primary beam. The porous lens plate includes an opening for generating the primary charged particle beamlet. The electrode or electrodes (ie electrodes common to the primary charged particle beam or primary charged particle beamlets and the porous lens plate) act together, in particular as if the beamlets would be affected by respective lenses corresponding to openings or holes in the porous lens plate.

[0029] One or more electrodes and a porous lens plate focus the primary charged particle beamlets in a plane 135 downstream of the porous lens plate. The primary charged particle beamlets generated by the porous lens plate or the porous lens array are collimated with a collimator 130. For example, the collimator may include one or more of the following: Figure 1 13. The deflector array and lens are shown. The divergent pattern or array of the primary charged particle beamlets is redirected by a collimator 130. The collimated beamlets can travel substantially parallel and / or along the optical axis of the objective lens unit onto the sample or specimen. According to some embodiments, which can be combined with other embodiments described herein, the collimator 130 can be located in or near a plane 135 in which the primary charged particle beamlets are focused.

[0030] Figure 1 The porous lens plate 200 shown can be a porous lens plate according to various embodiments of the present disclosure. Various embodiments of the present disclosure allow for a regular pattern of primary charged particle beamlets, for example, a rectangular or square pattern. In particular, a regular pattern of primary charged particle beamlets can be provided in plane 135 (i.e., in the plane of the focused primary charged particle beamlets). Further aberrations of the aperture lens array (ALA) or the porous lens plate can be reduced. For example, the aberrations of the microlenses in the porous lens plate can be smaller than the geometric image of the charged particle emitter.

[0031] Various embodiments of the present disclosure allow for reducing optical effects created by adjacent holes in a porous lens plate (or ALA) to compensate for distortions created by microelectrodes (i.e., one or more electrodes 120 of the multi-beam generator 100) and / or to reduce penetration effects of electric fields through openings in a porous lens plate (or ALA).

[0032] Figure 2 A porous lens plate 200 is shown. The porous lens plate comprises a porous lens plate body 210. A plurality of various openings are provided in the porous lens plate body. In particular, the openings are provided through the porous lens plate body, for example, to allow electrons (or generally charged particles) to pass through the various openings and through the porous lens plate. Figure 2 As shown, the various openings include an array of beamlet openings 220. Furthermore, a plurality of correction openings are provided.

[0033] According to an embodiment, a multi-aperture lens plate for a multi-beam generator of a charged particle multi-beam device is provided. The multi-aperture lens plate (or ALA) includes an aperture lens plate body having one or more layers. The aperture lens plate body includes: an array of N beamlet openings, the array of N beamlet openings extending through all of the one or more layers, the array of N beamlet openings configured to generate N primary charged particle beamlets, where N is a number greater than or equal to 2; and a plurality of correction openings extending through all of the one or more layers of the aperture lens plate body. The correction openings are configured to locally influence the lens field of the beamlet openings, wherein the correction openings are distinct from the beamlet openings. For example, the array of N beamlet openings can be rectangular or square. The phrase "openings provided through all of the one or more layers" should be understood to mean that, when the aperture lens body includes or consists of a layer stack, the openings are formed through the entire stack. Electrons passing through the beamlet openings pass through the aperture lens plate body, for example, until reaching a sample, and electrons passing through the correction openings pass through the aperture lens plate body, for example, until reaching a blocking element located away from the aperture lens plate body (e.g., in a field-free region of the multi-aperture lens). Furthermore, it is understood that a porous lens plate body having one or more layers may be a porous lens plate body composed of one or more layers, in particular one or more layers in direct contact with each other. A porous lens plate body composed of one or more layers may be included in a porous lens plate, which includes a porous lens plate body, a support for a porous lens plate, or further elements of a porous lens plate.

[0034] Figure 2 An array of 25 (5×5) beamlet openings is exemplarily shown. According to embodiments of the present disclosure, there may be 50 or more primary beamlets, such as 200 or more primary beamlets, or even 1000 or more primary beamlets. Figure 2 The array shown is a square array. Rectangular arrays are also available.

[0035] The openings in the rectangular or square beamlet openings cause an octopole effect due to the adjacent beamlet openings. The adjacent beamlet openings "pull" the equipotential surfaces into the holes of the beamlet openings. The correction opening 230 is provided so that the correction opening "pull" the equipotential planes, so that the multipole effect is not four times but eight times, which reduces the aberration effect.

[0036] According to some embodiments, which can be combined with other embodiments described herein, the beamlet openings can be circular. Furthermore, the correction openings can be circular. Thus, the octupole effect produced by the array is not compensated by non-circular openings. Furthermore, the octupole effect produced by the array is not produced by recesses or indentations. According to various embodiments of the present disclosure, a plurality of correction openings extend through the aperture lens body, in particular simultaneously allowing electrons of the primary charged particle beam to pass through the aperture lens plate body.

[0037] like Figure 2 As shown, the correction opening is closer to the beamlet opening than to the adjacent beamlet opening. The diameter of the correction opening may be different from the diameter of the beamlet opening. The correction opening may be smaller than the beamlet opening to produce a symmetrical 16-pole effect. Further, the smaller correction opening allows for the provision of through holes within the array of beamlet openings. According to some embodiments, which may be combined with other embodiments described herein, beamlets other than the N primary charged particle beamlets to be focused on the sample may be blocked downstream of the porous lens plate. Advantageously, the plurality of correction openings may be manufactured on the same manufacturing operation as the array of beamlet openings.

[0038] According to some embodiments, which can be combined with other embodiments described herein, the correction opening can have a diameter that is 60% or less of the diameter of the beamlet opening. In particular, the correction opening can have a diameter that is 45% to 55% of the diameter of the beamlet opening. For example, the beamlet opening can have a diameter of 30 μm to 70 μm, and the correction opening can have a diameter of 10 μm to 30 μm.

[0039] like Figure 2 As shown, the immediately adjacent beamlet opening 220 of the first beamlet opening is arranged in the x-direction and the y-direction, while the immediately adjacent correction opening of the first beamlet opening is arranged in a diagonal direction (xy direction), i.e., a direction at an angle of 45° compared to the x-direction or the y-direction. According to some embodiments, the first adjacent beamlet opening of the first beamlet opening in the array of N beamlet openings is in a first direction having a first vector selected from the group consisting of: [1,0], [0,1], [-1,0], and [0,1], and the first adjacent correction opening of the first beamlet opening is in a second direction selected from the group consisting of: [1,1], [1,-1], [-1,1], and [-1,1]. For example, the adjacent beamlet openings of the first beamlet opening in the array of N beamlet openings are in directions with vectors [1,0], [0,1], [-1,0] and [0,-1], and the adjacent correction openings of the first beamlet opening are in directions with vectors [1 / 2,1 / 2], [1 / 2,-1 / 2], [-1 / 2,1 / 2] and [-1 / 2,-1 / 2].

[0040] Furthermore, additionally or alternatively, the additional correction opening (i.e., the correction opening being a through-opening) is located at an equal distance or substantially an equal distance from the surrounding beamlet openings in the array of N beamlet openings. According to some embodiments of the present disclosure, the term "substantially equal distance" should be understood as "equal distance" that takes into account deviations due to manufacturing inaccuracies and / or deviations due to distortion compensation.

[0041] Figure 3 A porous lens plate 200 for compensating for distortion is shown according to some embodiments of the present disclosure.

[0042] As described herein, one or more electrodes 120 (see Figure 1 ) and the porous lens plate 200 generate microlenses for the primary charged particle beamlets. Additionally, one or more electrodes may generate macrolenses in the multi-beam generator 100. Higher-order effects of the microlenses, such as third-order effects, may introduce distortions to the array of primary charged particle beamlets. Thus, the primary charged particle beamlets are aligned in the plane of the collimator 130 (see Figure 1 ) may be distorted. Even though correction may be provided by the individual alignment deflectors of the collimator 130, misalignment of the array of primary charged particle beamlets leads to other problems for the optical system. For example, one or more aperture plates having a plurality of openings may be provided between the ALA or the porous lens plate and the collimator, wherein the primary charged particle beamlets beneficially pass through the plurality of openings of the one or more aperture plates. Further, the displacement in the plane of the collimator 130 may exceed the diameter of the opening in the collimator, which makes compensation in the collimator difficult or impossible. According to some embodiments, the beam opening in the collimator may have a size that may be 20% to 60% of the local pitch in the plane of the collimator.

[0043] According to some embodiments, which can optionally be combined with other embodiments described herein, the positions of the beamlet openings in the porous lens plate are shifted compared to a pattern of beamlet openings with a constant pitch.

[0044] Figure 2 The illustrated porous lens plate 200 includes a porous lens plate body 210. A plurality of beamlet openings 220 are shown. Dashed lines 320 illustrate squares corresponding to the array of beamlet openings, with distortion added to the pattern of beamlet openings to compensate for the distortions described above. For example, the outer beamlet openings are shifted inward.

[0045] According to some embodiments, which can be combined with other embodiments described herein, the position of the beamlet opening may change with the distance from the center point according to both a linear function and a third-order function of the distance of the beamlet opening. In particular, the position of the beamlet opening may additionally change with the distance according to a fifth-order function of the distance of the beamlet opening from the center point.

[0046] According to some embodiments, which can be combined with other embodiments described herein, the distance between the beamlet openings is varied by providing a function of the pin-pack shape (i.e., the distortion added to the pattern of openings has a pin-pack shape). For example, the distance between adjacent holes increases continuously with increasing distance from the center.

[0047] According to some embodiments, which can be combined with other embodiments described herein, the function used for distortion correction may be any polynomial function of order up to 5 or even up to 7.

[0048] According to an embodiment, a porous lens plate for a multi-beam generator of a charged particle multi-beam device is provided. The porous lens plate includes a porous lens plate body. The porous lens plate body includes an array of N beamlet openings, and the array of N beamlet openings is configured to generate N primary charged particle beamlets, where N is a number greater than or equal to 2. The positions of the beamlet openings in the array of N beamlet openings vary with the distance from the center point according to both a linear function and a third-order function of the distance of the beamlet opening from the center point. Further aspects, advantages and features described in other independent and dependent claims, the description and the drawings can be combined with the porous lens plate having a distorted pattern.

[0049] Figure 4 A porous lens plate 200 for compensating for field penetration is shown according to some embodiments of the present disclosure.

[0050] For example, one or more electrodes 120 (see Figure 1 The electric field generated on the porous lens plate produces a lensing effect. Equipotential planes of the electric field "bulge" out from the beamlet openings in the porous lens plate. For example, the electric field may bulge out from the beamlet openings on the side of the porous lens plate opposite the electrodes in the one or more electrodes. In an example where electrodes 120 are present on both sides, the net field generated by all lens generating components exists on one side, and the net field will bulge out as described herein. Therefore, multiple electric fields or equipotential planes are provided, namely, one for each beamlet opening. These multiple electric fields or equipotential planes may connect at a certain distance from the porous lens plate, forming a weak field, which is referred to as field penetration. The field lines of the weak field extend to the next electrode or free portion of the porous lens plate. For rectangular or square arrays of beamlet openings, the field will not be circularly symmetric, and thus may result in aberrations. For example, undesirable deflections of the outer primary charged particle beamlets may occur. Therefore, various embodiments of the present disclosure may provide a circular pattern of openings. For example, the diameter of the pattern of openings may be larger than the dimensions of the array of beamlet openings, such as a diagonal line.

[0051] Figure 4 A porous lens plate 200 having a porous lens plate body 210 is shown. Figure 4 An array of 25 (5×5) beamlet openings 220 is shown in FIG. Figure 4shows an array of beamlet openings in a first pattern, i.e., a square array with equal pitch in the x- and y-directions. The first pattern is provided in a first region. Further openings 420 are provided in, and in particular through, the aperture lens plate body to extend the first pattern beyond the first region. A second pattern is provided having a second region that is larger than the first region. For example, the second region can be circular, as indicated by dashed line 422.

[0052] According to some embodiments, which can be combined with other embodiments described herein, if the first array is a square pattern of, for example, 15×15 beamlet openings, the second pattern can have an additional 10 to 20 further openings along the diameter of the circle. If the first array is a square pattern of, for example, 25×25 beamlet openings, the second pattern can have an additional 16 to 30 further openings along the diameter of the circle. According to some embodiments, which can be combined with other embodiments described herein, the total number of openings (i.e., beamlet openings and further openings) along the diameter of the circular second area in the porous lens plate can be 150% to 250% of the number of beamlet openings along one side of the twisted angle or square array of beamlet openings.

[0053] Figure 5 A porous lens plate 200 is shown. Figure 6 An aperture plate 600 is shown. The aperture plate 600 can be used in combination with the porous lens plate 200. For example, the aperture plate 600 can be disposed between the collimator and the multi-beam generator, that is, between the collimator and the porous lens plate. The aperture plate can be included in the collimator.

[0054] The porous lens plate 200 includes a porous lens plate body 210. Figure 5 As shown, the aperture lens plate body may be circular. According to some embodiments, which may be combined with other embodiments described herein, the aperture lens plate body may have a polygonal shape, such as a hexagon or an octagon, or may have some non-circular shape to allow for a predetermined orientation during assembly, i.e., to orient the pattern of the array of beamlet openings correctly with respect to rotation.

[0055] According to some embodiments, which can be combined with other embodiments described herein, the aperture lens plate body may comprise a foil having a thickness of 20 μm or less, in particular 5 μm or less, and wherein the array of N beamlet openings and the plurality of correction openings are provided through the foil. According to some embodiments, the aperture lens plate body may consist of a foil.

[0056] Figure 5The illustrated porous lens plate 200 provides a combination of a first aspect of corrective openings 230 according to various embodiments of the present disclosure, a second aspect of distortion of the pattern of beamlet openings as illustrated by dashed lines 320 and according to various embodiments of the present disclosure, and a third aspect of further openings 420 for extending the pattern generated by the beamlet openings and the corrective openings according to various embodiments of the present disclosure. According to some embodiments, which may be combined with other embodiments described herein, the porous lens plate according to various embodiments of the present disclosure includes at least one of the first, second, and third aspects.

[0057] exist Figure 5 , the array of N beamlet openings is a square array, where N = 900, i.e., 30×30 beamlet openings. On the right-hand side of the array (represented by the black beamlet openings 220), the beamlet openings are positioned to compensate for distortion, as indicated by the dashed lines 320. On the left-hand side of the array, the beamlet openings are shown without distortion. The left-hand side illustration is for illustrative purposes only, to better illustrate the corrected positions of the beamlet openings and correction openings. As can be seen from the pattern 670 showing the openings in the aperture lens plate body, the beamlet openings and correction openings on the left-hand side also include positioning or position correction to compensate for distortion.

[0058] According to some embodiments, which can be combined with other embodiments described herein, the pattern formed in the area of ​​the beamlet opening can be extended to a larger area, in particular, wherein the larger area is circular. Figure 5 As shown, a pattern of 30×30 beamlet openings includes beamlet openings and correction openings as described herein. Furthermore, the pattern of beamlet openings and correction openings includes distortion correction, i.e., the pitch varies with distance from the center. Distortion correction applies to the beamlet openings and similarly to the correction openings. Thus, when the first pattern is extended to a larger second pattern, the further openings include openings corresponding to the correction openings. Additionally or alternatively, the distortion correction is extended across a second area for the second pattern.

[0059] According to some embodiments that may be combined with other embodiments described herein, the extended second pattern may have two or more regions. The first region is a region of the first pattern. The second region may be outside the first pattern, continuing the distortion correction of the first pattern. The third region may be outside the second region, wherein the distortion correction is reduced compared to the second region. In some examples, the distortion correction may be reduced to zero. For example, the further opening may have a constant distance in the third region. According to some implementations, the second region described above may be omitted, such that the third region described above is outside the first region of the first pattern, wherein the distortion correction is reduced compared to the first region. In some examples, the distortion correction may be reduced to zero. For example, the further opening may have a constant distance in the third region.

[0060] like Figure 4 As shown, a first pattern in a first region may extend to a second pattern in a second region, wherein the first pattern has a constant pitch. Therefore, the second pattern also has a constant pitch. Figure 3 As shown, the first pattern may include distortion correction in the first area. Therefore, the extended second pattern in the second area also continues the distortion correction. Figure 2 As shown, the first pattern includes small beam openings. Therefore, the extended second pattern in the second area also continues to include small beam openings. It should be understood that Figure 5 As shown, if combinations of aspects are provided, then aspects provided in a first pattern also extend into a larger second pattern.

[0061] Figure 6 An aperture plate 600 is shown in which the array of openings 620 corresponds to Figure 5 The porous lens plate 200. A plurality of openings 620 are provided in the aperture plate body 610. The plurality of openings are configured to allow the primary charged particle beamlets to pass through. Figure 6 The array of openings shown includes N openings, where N=900, i.e., an array of 30×30 openings. N primary charged particle beamlets to be focused on the sample can pass through the aperture plate 600. Other electrons (e.g., electrons that pass through the correction opening and / or the further opening) are blocked by the aperture plate 600. Charged particle beamlets other than the N primary charged particle beamlets are blocked.

[0062] Figure 7A and Figure 7B This is also illustrated in the figure, where Figure 7A and Figure 7B A multi-beam generator 100 comprising an aperture lens plate 200 and a further aperture plate 600 is shown in each case. Figure 7A is based on Figure 6 A cross-sectional view of section AA in FIG. 1 , and Figure 7B is based on Figure 6 . A cross-sectional view of section BB in . The number of openings is reduced for easier illustration. Along section AA, beamlets outside the array of openings 620 are blocked. In other words, beamlets corresponding to further openings 420 in the porous lens plate are blocked. Along section BB, beamlets corresponding to correction openings 230 are blocked. According to some embodiments that may be combined with other embodiments described herein, the charged particle multi-beam device comprises an aperture plate, wherein the aperture plate body has a plurality of N openings for passing N primary charged particle beamlets, the aperture plate body blocking electrons passing through the openings (e.g., correction openings or further openings). According to some embodiments that may be combined with other embodiments described herein, the aperture plate may be in a field-free region relative to the field of one or more electrodes 120 and the porous lens plate.

[0063] According to further embodiments, which can be combined with other embodiments described herein, the array of openings 620 in the aperture plate 600 has a constant pitch. The pattern of openings is distortion-free because the distortion compensation in the porous lens plate produces an undistorted array of primary charged particle beamlets in the plane of the aperture plate. According to some embodiments, which can be combined with other embodiments described herein, the aperture plate can be included in the collimator or can be part of the collimator.

[0064] According to some embodiments, Figure 1 As shown, the porous lens plate 200 may be disposed downstream of the one or more electrodes 120. In other words, the one or more electrodes 120 are disposed between the porous lens plate 200 and the charged particle beam source and / or emitter 110, respectively. According to further embodiments, which may be combined with other embodiments described herein, the one or more electrodes 120 may be located downstream of the porous lens plate 200. In other words, the porous lens plate 200 may be located between the one or more electrodes 120 and the charged particle beam source and / or emitter 110, respectively. For example, Figure 8A According to a further embodiment, as shown in Figure 8B As shown in the exemplary embodiment, two or more electrodes 120 may be provided. The porous lens plate 200 may be provided between two of the two or more electrodes 120. According to various embodiments of the present disclosure, one or more electrodes 120 may have an aperture opening through which the primary charged particle beam may pass. For example, each of the one or more electrodes may have an aperture through which the primary charged particle beam may pass, or, with respect to an electrode downstream of the porous lens plate, each of the one or more electrodes may have an aperture through which the primary charged particle beam may pass.

[0065] According to various embodiments of the present disclosure, a multi-beam generator for a charged particle multi-beam device is provided. The multi-beam generator includes a charged particle emitter configured to emit a primary charged particle beam and a porous lens plate according to any of the embodiments described herein, wherein the porous lens plate is arranged to be irradiated with the primary charged particle beam. The multi-beam generator further includes one or more electrodes having a common opening configured to pass the primary charged particle beam or at least one of the N primary charged particle beamlets, the one or more electrodes being configured to generate an electric field on the porous lens plate to focus the N primary charged particle beamlets in a plane downstream of the porous lens plate.

[0066] Figure 9A charged particle multi-beam device 900 is shown. The charged particle multi-beam device includes a multi-beam generator 100. The multi-beam generator may include a charged particle beam source, one or more electrodes 120, and an aperture lens plate 200 (or aperture lens array ALA). The charged particle beam source includes an emitter 110 that emits a primary charged particle beam, such as an electron beam.

[0067] In particular, a single emitter, such as a high brightness emitter, may be provided. The charged particle beam emitter described herein may be a cold field emitter (CFE), a Schottky emitter, a thermal field emitter (TFE), or another high current, high brightness charged particle beam source (such as an electron beam source). High current is considered to be 0.5 mA / sr or higher, such as 0.5 mA / sr to 1 mA / sr.

[0068] According to embodiments described herein, a multi-beam generator is configured to generate an array of primary charged particle beamlets. An aperture lens array or a porous lens plate 200 generates primary charged particle beamlets from the primary charged particle beam. One or more electrodes and the porous lens plate can operate as electrodes of an electrostatic lens.

[0069] The primary charged particle beamlets generated by the porous lens plate are collimated with a collimator 130. For example, the collimator may include at least one of a deflector array 832 and a lens 834. Figure 9 Both the deflector array and the lens are shown.The collimated beamlets may travel onto the sample or specimen 10 substantially parallel and / or along the optical axis of the objective lens 920.

[0070] According to some embodiments, which can be combined with other embodiments described herein, the collimator can be arranged in or near the focal plane of the primary charged particle beamlets. For example, the distance between the porous lens plate 200 and the collimator 130 can be at least 10 times greater than the distance between the emitter 110 and the porous lens plate 200. Thus, a pitch of about 30 μm to 80 μm of the beamlet openings in the porous lens plate can result in a pitch of 0.5 mm or more of the openings in the collimator. According to some embodiments, which can be combined with other embodiments described herein, the pitch of the openings in the collimator can be responsive to the pitch of the primary charged particle beamlets on the sample 10. For example, the pitch on the sample can be 0.7 mm to 2 mm.

[0071] According to some embodiments, which can be combined with other embodiments described herein, the focus plane of the primary charged particle beamlets is a flat plane, in particular when the primary charged particles travel essentially parallel from the collimator towards the objective and onto the sample.

[0072] Figure 9Schematically illustrated in FIG . The objective lens 920 provides a lenslet for each of the primary charged particle beamlets. For example, the objective lens 920 may include a plurality of electrodes having an array of holes or openings. The plurality of electrodes may act as an electrostatic lens on the primary charged particle beamlets passing through the corresponding holes and openings of the plurality of electrodes. The objective lens unit may be configured as a deceleration lens. The plurality of electrodes may be configured to have a potential that decelerates the primary beamlets before striking the sample. The objective lens 920 focuses the primary charged particle beamlets, in particular individually, on the sample 10. The sample 10 may be arranged on a stage 930 (e.g., a wafer rack having a drive). For example, the drive may move the sample or specimen in the x, y, and z directions.

[0073] According to some embodiments, which can be combined with other embodiments described herein, signal beamlets are generated when the primary charged particle beamlets impinge on the sample 10. The signal beamlets can be detected by a detection unit 940. According to some embodiments, which can be combined with other embodiments described herein, the detection unit can be disposed within the objective lens 920 or between the objective lens 920 and the collimator 130. According to embodiments described herein, each signal beamlet can provide a detection surface. The detection unit can be a detector array.

[0074] According to embodiments of the present invention that can be combined with other embodiments, the signal (charged particle) beamlet refers to a secondary and / or backscattered electron beam. The signal beamlet is generated by the impact of a primary charged particle beamlet on a sample or the backscattering of a primary charged particle beamlet from a sample. The primary charged particle beam or the primary charged particle beamlet is generated by a particle beam source or a multi-beam generator, respectively, and is guided and deflected on a sample to be inspected or imaged. According to some embodiments that can be combined with other embodiments described herein, a scanning deflector may be provided to scan a plurality of primary charged particle beamlets on a sample to generate an image of the sample. The charged particle multi-beam device according to various embodiments of the present disclosure may be a scanning charged particle multi-beam device.

[0075] As referred to herein, "samples" or "specimens" include, but are not limited to, wafers, semiconductor wafers, semiconductor workpieces, photolithography masks, and other workpieces (such as memory disks, etc.). Embodiments may be applied to any workpiece on which material is deposited or any workpiece that is structured. According to some embodiments, which may be combined with other embodiments described herein, the apparatus and method are configured for or applied to electron beam inspection, critical dimension setting applications, and defect review applications.

[0076] According to an embodiment, a charged particle multi-beam device configured to focus N primary charged particle beamlets on a sample is provided. The charged particle multi-beam device comprises a multi-beam generator according to any of the embodiments described herein, and in particular a multi-beam generator comprising a multi-aperture lens plate according to the embodiments described herein.

[0077] The charged particle multi-beam apparatus may further include an aperture plate having an aperture plate body with a plurality of N openings for passing the N primary charged particle beamlets, the aperture plate body blocking electrons that pass through other openings (e.g., correction openings) in the ALA. For example, the aperture plate may be provided by the collimator 130 or may be included in the collimator 130. Furthermore, an additional aperture plate for blocking undesired electrons may be provided between the collimator 130 and the multi-aperture lens plate 200.

[0078] According to some embodiments, which may be combined with other embodiments described herein, and as described with respect to Figure 4 、 Figure 5 、 Figure 6 、 Figure 7A and Figure 7B Specifically, a charged particle multi-beam apparatus configured to focus N primary charged particle beamlets on a sample can be provided, wherein an array of N beamlet openings and a plurality of correction openings form a first pattern within a first area, wherein further openings are provided in the aperture lens plate body such that the first pattern extends beyond the first area to form a second pattern having a second area larger than the first area. For example, the second pattern has a substantially circular shape.

[0079] Figure 10 A flow chart of a method for generating a plurality of N primary charged particle beamlets to be focused on a sample is shown. At block 1010, a primary charged particle beam is generated using a charged particle emitter. At block 1012, a porous lens plate is irradiated with the primary charged particle beam. Thus, beamlets are generated. At block 1014, N primary charged particle beamlets are generated using an array of N beamlet openings, and a first dummy beamlet is generated using a plurality of correction openings. For example, a multi-beam generator focuses the N primary charged particle beamlets by generating an electric field at the porous lens plate using one or more electrodes, as depicted in block 1016. The N primary charged particle beamlets can be focused in a plane downstream of the porous lens plate. At block 1018, at least the first dummy beamlet is blocked. In particular, the first dummy beamlet can be blocked in a field-free region downstream of the porous lens plate.

[0080] According to some embodiments, which can be combined with other embodiments described herein, a method may include generating a second dummy beamlet with a further opening extending beyond the array of N beamlet openings and the first region of the plurality of correction openings.The second dummy beamlet may be blocked.

[0081] The present disclosure discloses a plurality of embodiments, some of which are described below. Embodiment 1. A porous lens plate for a multi-beam generator of a charged particle multi-beam device, the porous lens plate comprising: a porous lens plate body having one or more layers, the porous lens plate body comprising: an array of N beamlet openings, the array of N beamlet openings passing through all of the one or more layers, the array of N beamlet openings having beamlet openings, the array of N beamlet openings being configured to generate N primary charged particle beamlets, wherein N is a number greater than or equal to 2; and a plurality of correction openings passing through all of the one or more layers of the aperture lens plate body and configured to locally affect the lens field of the beamlet openings, wherein the correction openings are different from the beamlet openings.

[0082] Embodiment 2. The porous lens plate of embodiment 1, wherein the beamlet openings are circular.

[0083] Embodiment 3. The porous lens plate of any one of embodiments 1 to 2, wherein the correction openings are circular.

[0084] Embodiment 4. The porous lens plate of embodiment 1, wherein the beamlet openings are circular, wherein the correction openings are circular and have a different diameter than the beamlet openings.

[0085] Embodiment 5. The porous lens plate of any one of embodiments 1 to 4, wherein the correction opening has a diameter that is 60% or less of the diameter of the beamlet opening, in particular 45% to 55% of the diameter of the beamlet opening.

[0086] Embodiment 6. The porous lens plate of any of embodiments 1 to 5, wherein the beamlet openings have a diameter of 30 μm to 70 μm, and the correction openings have a diameter of 10 μm to 30 μm.

[0087] Embodiment 7. The porous lens plate of any one of Embodiments 1 to 6, wherein the array of N beamlet openings is rectangular or square.

[0088] Embodiment 8. A porous lens plate as described in any of Embodiments 1 to 7, wherein a first adjacent beamlet opening of a first beamlet opening in the array of N beamlet openings is in a first direction having a first vector selected from the group consisting of: [1,0], [0,1], [-1,0] and [0,-1], and a first adjacent correction opening of the first beamlet opening is in a second direction selected from the group consisting of: [1 / 2,1 / 2], [1 / 2,-1 / 2], [-1 / 2,1 / 2] and [-1 / 2,-1 / 2].

[0089] Embodiment 9. The porous lens plate of any one of Embodiments 1 to 8, wherein the plurality of correction openings are located at equal distances from surrounding beamlet openings in the array of N beamlet openings.

[0090] Embodiment 10. The porous lens plate of any one of embodiments 1 to 9, wherein the position of the beamlet openings varies with the distance from the center point according to a linear function, a third-order function, and a fifth-order function of the distance of the beamlet openings.

[0091] Embodiment 11. The porous lens plate of any one of embodiments 1 to 10, wherein the porous lens plate body comprises a foil having a thickness of 20 μm or less, and wherein the array of N beamlet openings and the plurality of correction openings are disposed through the foil.

[0092] Embodiment 12. A multi-beam generator for a charged particle multi-beam device, the multi-beam generator comprising: a charged particle emitter, the charged particle emitter being configured to emit a primary charged particle beam; a porous lens plate, the porous lens plate being arranged to be irradiated with the primary charged particle beam, the porous lens plate comprising: a porous lens plate body, the porous lens plate body comprising: an array of N small beam openings, the array of N small beam openings having small beam openings, the array of N small beam openings being configured to generate N primary charged particle small beams , wherein N is a number >= 2; and a plurality of correction openings passing through the aperture lens plate body, the plurality of correction openings being configured to locally influence the lens field of the beamlet openings, wherein the correction openings are different from the beamlet openings; and an aperture plate in a field-free region, distal to the porous lens plate and downstream of the porous lens plate, wherein the aperture plate body has a plurality of N openings for passing the N primary charged particle beamlets, the aperture plate body being configured to block electrons passing through the correction openings. In particular, according to some embodiments, which can be combined with other embodiments described herein, the porous lens plate is arranged to be directly irradiated with the primary charged particle beam, i.e., without requiring a focusing lens or another lens between the charged particle emitter and the porous lens plate.

[0093] Example 13. The multi-beam generator as described in Example 12 further includes: one or more electrodes, the one or more electrodes having a common opening, the common opening being configured to allow the primary charged particle beam or at least one of the N primary charged particle beamlets to pass through, the one or more electrodes being configured to generate an electric field on the porous lens plate to focus the N primary charged particle beamlets in a plane downstream of the porous lens plate.

[0094] Embodiment 14. The multi-beam generator of any one of embodiments 12 to 13, wherein the plane is flat.

[0095] Embodiment 15. A charged particle multi-beam device configured to focus N primary charged particle beamlets on a sample, the charged particle multi-beam device comprising: the multi-beam generator according to any one of Embodiments 12 to 14.

[0096] Example 16. A charged particle multi-beam device as described in Example 15, wherein the array of N small beam openings and the multiple correction openings form a first pattern within a first area, wherein further openings are arranged in the hole lens plate body so that the first pattern extends beyond the first area to form a second pattern having a second area larger than the first area, wherein the second pattern has a substantially circular shape.

[0097] Embodiment 17. A method for generating a plurality of N primary charged particle beamlets to be focused on a sample, the method comprising: generating a primary charged particle beam using a charged particle emitter; irradiating a porous lens plate with the primary charged particle beam; generating beamlets, comprising: generating N primary charged particle beamlets generated using an array of N beamlet openings; and generating a first dummy beamlet generated using a plurality of correction openings; focusing the N primary charged particle beamlets by generating an electric field at the porous lens plate using one or more electrodes, the N primary charged particle beamlets being focused in a plane downstream of the porous lens plate; and blocking at least the first dummy beamlet, in particular, blocking at least the first dummy beamlet in a field-free region downstream of the porous lens plate.

[0098] Embodiment 18. The method of embodiment 17, wherein generating a beamlet further comprises: generating a second dummy beamlet with further openings extending beyond the array of N beamlet openings and the first region of the plurality of correction openings; and blocking the second dummy beamlet.

[0099] Various embodiments of the present disclosure provide a number of advantages, some of which are described below: A multi-aperture lens plate can be provided in which octopole aberrations from adjacent beamlet openings can be reduced to smaller aberrations by a 16-pole effect. Distortions of a multi-beam generator can be compensated. Field penetration through the beamlet openings can be compensated. Thus, an improved primary charged particle beamlet array can be provided with improved pitch uniformity and / or with reduced aberrations in the primary charged particle beamlets.

[0100] While the foregoing is directed to embodiments, other and further embodiments may be devised without departing from the basic scope of the embodiments, and the scope of the embodiments is to be determined by the claims that follow.

Claims

1. A porous lens plate for a multi-beam generator of a charged particle multi-beam device, the porous lens plate comprising: A hole lens plate body, the hole lens plate body having one or more layers, the hole lens plate body comprising: an array of N beamlet openings, the array of N beamlet openings passing through all of the one or more layers, the array of N beamlet openings having beamlet openings, the array of N beamlet openings being configured to produce N primary charged particle beamlets, where N is a number >= 2; and A plurality of correction openings passing through all of the one or more layers of the aperture lens plate body and configured to locally affect the lens field of the beamlet openings, wherein the correction openings are distinct from the beamlet openings.

2. The porous lens plate of claim 1, wherein the beamlet openings are circular.

3. The porous lens plate of claim 1, wherein the correction opening is circular.

4. The porous lens plate of claim 1, wherein the beamlet openings are circular, wherein the correction openings are circular and have a different diameter than the beamlet openings.

5. The porous lens plate of claim 1, wherein the correction opening has a diameter that is 60% or less of a diameter of the beamlet opening.

6. The porous lens plate of claim 5, wherein the correction opening has a diameter that is 45% to 55% of a diameter of the beamlet opening. 7 . The porous lens plate of claim 1 , wherein the beamlet openings have a diameter of 30 μm to 70 μm, and the correction openings have a diameter of 10 μm to 30 μm.

8. The porous lens plate of any one of claims 1 to 7, wherein the array of N beamlet openings is rectangular or square.

9. The porous lens plate of claim 1 , wherein a first adjacent beamlet opening of a first beamlet opening in the array of N beamlet openings is in a first direction having a first vector selected from the group consisting of: [1,0], [0,1], [-1,0], and [0,-1], and a first adjacent correction opening of the first beamlet opening is in a second direction selected from the group consisting of: [1 / 2,1 / 2], [1 / 2,-1 / 2], [-1 / 2,1 / 2], and [-1 / 2,-1 / 2].

10. The porous lens plate of any one of claims 1 to 7, wherein the plurality of correction openings are located at equal distances from surrounding beamlet openings in the array of N beamlet openings.

11. The porous lens plate of any one of claims 1 to 7, wherein the positions of the beamlet openings vary with the distance from the center point according to at least one of a linear function, a third-order function, or a fifth-order function of the distance of the beamlet openings from the center point.

12. The porous lens plate of any one of claims 1 to 7, wherein the porous lens plate body comprises a foil having a thickness of 20 μm or less, and wherein the array of N beamlet openings and the plurality of correction openings are provided through the foil.

13. A multi-beam generator for a charged particle multi-beam device, the multi-beam generator comprising: a charged particle emitter configured to emit a primary charged particle beam; a porous lens plate arranged to be irradiated with the primary charged particle beam, the porous lens plate comprising: The hole lens plate body comprises: an array of N beamlet openings, said array of N beamlet openings having beamlet openings, said array of N beamlet openings being configured to generate N primary charged particle beamlets, wherein N is a number >= 2; and a plurality of correction openings passing through the aperture lens plate body, the plurality of correction openings being configured to locally affect the lens field of the beamlet openings, wherein the correction openings are distinct from the beamlet openings; and An aperture plate is provided in a field-free region, away from the porous lens plate and downstream of the porous lens plate, wherein the aperture plate body has a plurality of N openings for passing the N primary charged particle beamlets, and the aperture plate body is configured to block electrons passing through the correction openings.

14. The multi-beam generator of claim 13, further comprising: One or more electrodes, the one or more electrodes having a common opening, the common opening being configured to allow the primary charged particle beam or at least one of the N primary charged particle beamlets to pass through, the one or more electrodes being configured to generate an electric field on the porous lens plate to focus the N primary charged particle beamlets in a plane downstream of the porous lens plate.

15. The multi-beam generator according to any one of claims 13 to 14, wherein the plane is flat.

16. A charged particle multi-beam apparatus configured to focus N primary charged particle beamlets on a sample, the charged particle multi-beam apparatus comprising: The multi-beam generator according to any one of claims 12 to 14.

17. A charged particle multi-beam device as claimed in claim 16, wherein the array of N small beam openings and the plurality of correction openings form a first pattern within a first area, wherein further openings are provided in the aperture lens plate body so that the first pattern extends beyond the first area to form a second pattern having a second area larger than the first area, wherein the second pattern has a substantially circular shape.

18. A method of generating a plurality N of primary charged particle beamlets to be focused on a sample, the method comprising: generating a primary charged particle beam using a charged particle emitter; irradiating a porous lens plate with the primary charged particle beam; Generates small beams, including: generating N primary charged particle beamlets using an array of N beamlet openings; as well as generating a first dummy beamlet generated using a plurality of correction openings; focusing the N primary charged particle beamlets by generating an electric field at the porous lens plate with one or more electrodes, the N primary charged particle beamlets being focused in a plane downstream of the porous lens plate; and At least the first dummy beamlet is blocked.

19. The method of claim 18, wherein the at least first dummy beamlet is blocked in a field-free region downstream of the porous lens plate.

20. The method of any one of claims 1 to 19, wherein generating the beamlets further comprises: generating a second dummy beamlet with a further opening extending beyond the array of N beamlet openings and the first region of the plurality of correction openings; as well as The second dummy beamlet is blocked.

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