Electrooptical element and method of evaluating electrooptical

Abstract

The invention relates to an electro-optical element and a method for evaluating an electro-optical element. In one arrangement, an electro-optical element includes a substrate defining at least one aperture extending through the substrate between two planar surfaces. At least one of the planar surfaces includes a plurality of indicia formed on or in the planar surface. The distance between the centers of at least one pair of adjacent marks is equal to or less than half of the maximum size of one of the at least one hole; and / or in the case where at least one hole includes a plurality of holes, equal to or less than half the distance between the centers of at least one pair of adjacent holes.

Description

[0001] Cross - Reference to Related Applications

[0002] This application claims the priority of EP application 22209458.3 filed on November 24, 2022, and this patent application is incorporated herein by reference in its entirety. Technical Field

[0003] The present disclosure relates to electro-optical elements and methods for evaluating electro-optical elements. Background Art

[0004] When manufacturing semiconductor integrated circuit (IC) chips, due to, for example, optical effects and incidental particles, undesirable pattern defects inevitably occur on the substrate (i.e., wafer) or mask during the manufacturing process, thereby reducing the yield. Therefore, monitoring the degree of undesirable pattern defects is an important process in IC chip manufacturing. More generally, evaluating, for example, inspecting and / or measuring the surface of a substrate or other object / material is an important process during and / or after its manufacturing.

[0005] Known evaluation tools (which are referred to herein as evaluation systems) use charged particle beams to evaluate an object (which may be referred to as a sample), for example, to detect pattern defects. These systems typically use electron microscopy techniques, such as scanning electron microscopy (SEM). In SEM, a primary electron beam of electrons at a relatively high energy is targeted at a final deceleration step, so as to land on the sample at a relatively low landing energy. The electron beam is focused on the sample as a probe spot. The interaction between the material structure at the probe spot and the landing electrons from the electron beam causes signal electrons to be emitted from the surface, such as secondary electrons, backscattered electrons, or Auger electrons. The signal electrons can be emitted from the material structure of the sample. By scanning the primary electron beam as a probe spot over the sample surface, the signal electrons can be emitted across the sample surface. By collecting these emitted signal electrons from the sample surface, a pattern inspection system can obtain an image representing the characteristics of the material structure of the sample surface.

[0006] Evaluation systems can use electro-optical elements to control the electron beam. These electro-optical elements can define features such as holes for influencing the electron trajectory, for example, by providing a lens effect. Various aspects of the features can affect the performance of the electro-optical elements, such as the shape, size, and / or position of the features. However, it has proven difficult to measure these characteristics efficiently and with high precision. Summary of the Invention

[0007] An object of the present disclosure is to provide methods and devices that support improved evaluation of electro-optical elements.

[0008] According to one aspect of the present invention, there is provided an electro-optical element for an electro-optical device, the electro-optical element comprising: a substrate having two planar surfaces and defining at least one hole extending through the substrate between the two planar surfaces, wherein: at least one of the planar surfaces includes a plurality of marks formed on or in the planar surface, and the distance between the centers of at least one pair of adjacent marks is: equal to or less than half of the maximum dimension of one of the at least one hole; and / or in the case where the at least one hole includes a plurality of holes, equal to or less than half of the distance between the centers of at least one pair of adjacent holes.

[0009] According to one aspect of the present invention, there is provided a method for evaluating an electro-optical element for an electro-optical device, wherein the electro-optical element comprises: a substrate having two planar surfaces and defining at least one hole extending through the substrate between the two planar surfaces, wherein: at least one of the planar surfaces includes a plurality of marks formed on or in the planar surface, and the distance between the centers of at least one pair of adjacent marks is: equal to or less than half of the maximum dimension of one of the at least one hole; and / or in the case where the at least one hole includes a plurality of holes, equal to or less than half of the distance between the centers of at least one pair of adjacent holes, and wherein the method comprises: capturing one or more images of a corresponding portion of the substrate; detecting the mark positions of at least a subset of the plurality of marks in the image or each image; and determining geometric information about the at least one hole based on the one or more images and the detected mark positions. BRIEF DESCRIPTION OF THE DRAWINGS

[0010] The above and other aspects of the present disclosure will become more apparent from the description of the exemplary embodiments in conjunction with the accompanying drawings.

[0011] Figure 1 Schematic diagram for illustrating an exemplary charged particle beam inspection device.

[0012] Figure 2 For illustrating as Figure 1 Schematic diagram of an exemplary multi-beam device that is part of an exemplary charged particle beam inspection device.

[0013] Figure 3 Schematic diagram of an exemplary electro-optical device including a condenser lens array, an objective lens array, and a detector array.

[0014] Figure 4 Schematic cross-sectional view of a part of an exemplary arrangement of an objective lens array and a detector array.

[0015] Figure 5 For Figure 4 Bottom view of a part of the detector array.

[0016] Figure 6 ForFigure 4 An elevation view of a modified version of a portion of an objective lens array.

[0017] Figure 7 A schematic diagram of an exemplary electro - optical device including an objective lens array and a beam splitter.

[0018] Figure 8 A diagram of another exemplary electro - optical device.

[0019] Figure 9 For example, it can be Figure 3 , 7 and 8, a schematic diagram of an exemplary electro - optical component that can be part of an electro - optical device.

[0020] Figure 10 Depicting a portion of an electro - optical element showing a hole array and a marker array.

[0021] Figure 11 For Figure 10 a close - up view of a portion of the arrangement.

[0022] Figure 12 Depicting Figure 10 a variation of the arrangement where the markers are symmetrically arranged around the holes.

[0023] Figure 13 Depicting Figure 10 another variation of the arrangement where the holes are arranged in a rectangular grid and the markers are provided in a different type of array.

[0024] Figure 14 A schematic side cross - sectional view of a portion of a substrate of an electro - optical element showing exemplary holes.

[0025] Figure 15 For the case where the substrate has a base material (e.g., a substrate layer) and a covering (e.g., a metal) layer and the markers are formed by grooves in the base material Figure 14 an enlarged schematic side cross - sectional view of a portion of the substrate.

[0026] Figure 16 Depicting Figure 15 a variation of the arrangement where the markers are formed by providing changes in surface properties such as composition and / or surface finish.

[0027] Figure 17 Depicting Figure 15 a variation of the arrangement where the markers are formed by local portions of deposited material. Detailed Description

[0028] Reference will now be made in detail to exemplary embodiments, which are illustrated in the accompanying drawings. The following description refers to the accompanying drawings, where the same numbers in different drawings represent the same or similar elements unless otherwise indicated. The implementations set forth in the following description of exemplary embodiments do not represent all implementations consistent with the present invention. Rather, they are merely examples of apparatuses and methods consistent with aspects related to the present invention as recited in the appended claims.

[0029] The enhancement of the computing power of an electronic device can be achieved by significantly increasing the packing density of circuit components such as transistors, capacitors, diodes, etc. on an IC chip, which reduces the physical size of the device. This is achieved by increasing the resolution, enabling smaller structures to be made. For example, an IC chip of a smart phone that is the size of a thumbnail and was available in 2019 or earlier could include more than 2 billion transistors, each transistor being less than 1 / 1000 the size of a human hair. Thus, it is not surprising that semiconductor IC manufacturing is a complex and time-consuming process with hundreds of individual steps. Even an error in a single step has the potential to greatly affect the functionality of the final product. In some cases, even a single defect can cause device failure. The goal of the manufacturing process is to improve the overall yield of the process. For example, for a 50-step process (where a step may indicate the number of layers formed on a wafer), in order to achieve a 75% yield, each individual step must have a yield greater than 99.4%. If each individual step has a yield of 95%, then the overall process yield will be as low as 7%.

[0030] Although a high process yield is desired in an IC chip manufacturing facility, it is also essential to maintain a high substrate (i.e., wafer) throughput, which is defined as the number of substrates processed per hour. The presence of defects can affect both high process yield and high substrate throughput. This is especially true in cases where operator intervention is required to review the defects. Therefore, high-throughput detection and identification of micron- and nano-scale defects by an inspection system such as a scanning electron microscope (‘SEM’) is essential for maintaining high yield and low cost.

[0031] The SEM includes a scanning device and a detector device. The scanning device includes an irradiation device including an electron source for generating primary electrons, and a projection device for scanning a sample such as a substrate with one or more focused beams of the primary electrons. Together, at least the irradiation device or irradiation system and the projection device or projection system can be collectively referred to as an electron optical device or column. The primary electrons interact with the sample and generate secondary electrons. The detection device captures secondary electrons from the sample while the sample is being scanned, so that the SEM can produce an image of the scanned area of the sample. For high-throughput inspection, some of the inspection devices in the inspection device use multiple focused beams of primary electrons, i.e., multi-beams. The component beams of the multi-beams can be referred to as sub-beams or beamlets. The multi-beams can scan different parts of the sample simultaneously. Therefore, the multi-beam inspection device can inspect the sample at a much higher speed than a single-beam inspection device.

[0032] The implementation of known multi-beam inspection devices is described below.

[0033] The drawings are schematic. Therefore, for clarity, the relative sizes of the components in the drawings are exaggerated. In the following description of the drawings, the same or similar reference numerals refer to the same or similar components or entities, and only the differences regarding each embodiment are described. Although the description and the drawings are directed to electron optical devices, it should be understood that the embodiments are not used to limit the present disclosure to specific charged particles. Therefore, references to electrons throughout this document can be more generally considered as references to charged particles, where the charged particles are not necessarily electrons.

[0034] Now refer to Figure 1 , which is a schematic diagram illustrating an exemplary charged particle beam inspection device 100, which can also be referred to as a charged particle beam evaluation system or simply an evaluation system. Figure 1 The charged particle beam inspection device 100 of includes a main chamber 10, a load lock chamber 20, an electron beam device 40, an equipment front-end module (EFEM) 30, and a controller 50. The controller can be distributed among different components of the evaluation system, including, for example, in the electron beam device 40. The electron beam device 40 is located inside the main chamber 10.

[0035] The EFEM 30 includes a first load port 30a and a second load port 30b. The EFEM 30 can include additional load ports. The first load port 30a and the second load port 30b can, for example, receive a front-opening unified pod (FOUP) including a substrate to be inspected (e.g., a semiconductor substrate or a substrate made of other materials) or a sample (substrates, wafers, and samples are collectively referred to as "samples" hereinafter). One or more robotic arms (not shown) in the EFEM 30 transfer the sample to the load lock chamber 20.

[0036] The load lock chamber 20 is used to remove the gas around the sample. This creates a vacuum where the local gas pressure is lower than the pressure in the surrounding environment. The load lock chamber 20 can be connected to a load lock vacuum pump system (not shown), which removes the gas particles in the load lock chamber 20. The operation of the load lock vacuum pump system enables the load lock chamber to reach a first pressure below atmospheric pressure. After reaching the first pressure, one or more robotic arms (not shown) transfer the sample from the load lock chamber 20 to the main chamber 10. The main chamber 10 is connected to a main chamber vacuum pump system (not shown). The main chamber vacuum pump system removes the gas particles in the main chamber 10, such that the pressure around the sample reaches a second pressure lower than the first pressure. After reaching the second pressure, the sample is transferred to an electron beam device through which the sample can be inspected. The electron beam device 40 can include a multi-beam electron optical device.

[0037] The controller 50 is signal-connected (e.g., electronically) to the electron beam device 40, such as being a distributed component of the controller 50. The controller 50 can be a processor (such as a computer) configured to control the charged particle beam inspection device 100. The controller 50 can also include processing circuitry configured to perform various signal and image processing functions. Although the controller 50 is shown in Figure 1 the exterior of the structure including the main chamber 10, the load lock chamber 20, and the EFEM 30, it should be understood that the controller 50 can be part of the structure. The controller 50 can be located in one of the constituent elements of the charged particle beam inspection device, or it can be distributed over at least two of the constituent elements. Although the present disclosure provides an example of the main chamber 10 that houses the electron beam inspection device, it should be noted that the aspects of the present disclosure are not limited, in their broadest sense, to the chamber that houses the electron beam inspection device. Instead, it should be understood that the foregoing principles can also be applied to the arrangement of other systems and other devices operating at the second pressure.

[0038] Now refer to Figure 2 , which is a schematic diagram illustrating an exemplary electron beam device 40. The electron beam device 40 can be provided as Figure 1Part of an exemplary charged particle beam inspection system 100. The electron beam device 40 includes an electron source 201 and a charged particle column (or apparatus) 230. The charged particle apparatus 230 may refer to or include a projection device for directing a primary charged particle beam 202 towards a sample 208. The electron source 201 and associated charged particle optical elements may be referred to as an irradiation device for generating the primary charged particle beam 202. The apparatus includes a sample support for supporting the sample 208. The sample support in this example includes a sample holder 207. The sample holder 207 holds the sample 208 (e.g., a substrate or a mask) for evaluation. The sample holder 207 is supported by a motorized or actuated stage 209. The electron beam device 40 further includes a detector 240. The detector 240 detects signal charged particles (e.g., electrons) from the sample 208. The detector 240 generates a detection signal when signal charged particles are detected.

[0039] The electron source 201 may include a cathode (not shown) and an extractor or anode (not shown). During operation, the electron source 201 is configured to emit electrons from the cathode as primary electrons. The primary electrons are extracted or accelerated by the extractor and / or anode to form the primary electron beam 202.

[0040] The charged particle apparatus 230 is configured to convert the primary electron beam 202 into a plurality of charged particle beams 211, 212, 213, and direct each beam onto the sample 208. Although three beams are illustrated for simplicity, there may be dozens, hundreds, thousands, tens of thousands, or even hundreds of thousands (or more) of beams. The beams may be referred to as beam waves or sub-beams. The plurality of charged particle beams may be collectively referred to as a multi-beam or beam grid. A beam grid having so many beams (e.g., more than a thousand beams) may have a field of view of, for example, more than 0.5 mm, e.g., in the range of 0.5 to 30 mm or 1 to 30 mm, e.g., in the range of 0.5 to 15 mm.

[0041] The controller 50 (e.g., a control system including a distributed controller) may be connected to Figure 1 the various parts of the charged particle beam inspection device 100, such as the electron source 201, the electron detection device 240, the charged particle apparatus 230, and the actuated stage 209. The controller 50 may perform various image and signal processing functions. The controller 50 may also generate various control signals to manage the operation of the charged particle beam inspection device 100, including the operation of the electron beam device 40.

[0042] The charged particle device 230 may be configured to focus beams 211, 212, and 213, for example, onto the sample 208 for inspection, and may form three probe spots 221, 222, and 223 on the surface of the sample 208. The charged particle device 230 may be configured to deflect the primary beams 211, 212, and 213 to scan the probe spots 221, 222, and 223 across separate scan regions in a section of the surface of the sample 208. In response to the incidence of the primary beams 211, 212, and 213 on the probe spots 221, 222, and 223 on the sample 208, electrons are generated from the sample 208, which include secondary electrons and backscattered electrons, and they may be referred to as signal charged particles. Secondary electrons typically have an electron energy of up to fifty electron volts (≤50 eV), and backscattered electrons typically have an electron energy between fifty electron volts (50 eV) and the landing energy of the primary beams 211, 212, and 213.

[0043] The detector 240 may send a detection signal (e.g., as an imaging or detection signal) generated in the detector 240 to the controller 50 or a signal processing system (not shown, which may be part of the controller 50), for example, to construct an image of the corresponding scan region of the sample 208. The detector 240 may be at least partially incorporated into the charged particle device 230, or may be separated from the charged particle device, for example, in the case where a secondary optical column guides secondary electrons to the detector 240.

[0044] The controller 50 may include an image processing system, which includes an image acquirer (not shown) and a storage device (not shown). For example, the controller may include a processor, a computer, a server, a mainframe, a terminal, a personal computer, any kind of mobile computing device, etc., or a combination thereof. The image acquirer may include at least a part of the processing function of the controller. Thus, the image acquirer may include at least one or more processors. The image acquirer may be communicatively coupled to the detector 240 that allows signal communication, such as an electrical conductor, an optical fiber cable, a portable storage medium, IR, Bluetooth, the Internet, a wireless network, radio, etc., or a combination thereof. The image acquirer may receive a detection signal from the detector 240, may process the data included in the signal, and may thereby construct an image. Thus, the image acquirer may acquire an image of the sample 208. The image acquirer may also perform various post-processing functions, such as generating a contour, superimposing an indicator on the acquired image, etc. The image acquirer may be configured to adjust the brightness and contrast, etc., of the acquired image. The storage device may be a storage medium, such as a hard disk, a flash drive, a cloud storage device, a random access memory (RAM), other types of computer-readable memories, etc. The storage device may be coupled to the image acquirer and may be used to save the original image data of the scan as the original image and the post-processed image.

[0045] The image acquirer can acquire one or more images of the sample 208 based on the imaging signal received from the detector 240. The imaging signal can correspond to a scanning operation for performing charged particle imaging. The acquired image can be a single image including a plurality of imaging regions. The single image can be stored in a storage device. The single image can be an original image that can be divided into a plurality of zones. Each of the zones can include one imaging region containing features of the sample 208. The acquired image can include a plurality of images of a single imaging region of the sample 208 sampled multiple times over a period of time. The plurality of images can be stored in the storage device. The controller 50 can be configured to perform an image processing step using the plurality of images of the same location of the sample 208.

[0046] The controller 50 can include measurement circuitry (e.g., an analog-to-digital converter) to obtain the distribution of the detected secondary electrons. A part of the controller for such a function can be included in or near the detector. The electron distribution data collected during the detection time window can be used in combination with the corresponding scan path data of each of the primary beams 211, 212, and 213 incident on the sample surface to reconstruct an image of the sample structure being examined. The reconstructed image can be used to reveal various features of the internal or external structure of the sample 208. Thus, the reconstructed image can be used to reveal any defects that may be present in and / or on the sample.

[0047] The controller 50 can control the actuator stage 209 to move the sample 208 during the examination of the sample 208, for example to provide a scanning motion of the stage relative to the path of the primary beam. The controller 50 can cause the actuator stage 209 to be able to move the sample 208 at least during the sample examination, preferably continuously, for example at a constant speed in a direction such as part of the scanning motion of the stage. The controller 50 can control the movement of the actuator stage 209 such that it changes the movement speed of the sample 208 according to various parameters. For example, the controller can control the stage speed (including its direction) according to the inspection steps of the scanning process and / or the characteristics of the scan, such as disclosed in EPA 21171877.0 filed on May 3, 2021, the combined step and scan strategy of at least the stage of which is incorporated herein by reference. When controlling the actuator stage, the actuation of the stage and thus the sample can enable the sample to be dynamically positioned relative to the path of the primary beam, for example.

[0048] Figure 3Schematic diagram of an exemplary electro - optical device 41 (which may also be referred to as a charged - particle device) for use in an evaluation apparatus. For ease of illustration, the lens array is schematically depicted herein by an elliptical array. Each ellipse represents one of the lenses in the lens array. By convention, ellipses are used to represent lenses, similar to the biconvex form often employed in optical lenses. In the context of electro - optical devices such as those discussed herein, it should be understood that the lens array will typically operate electrostatically and thus may not require any physical elements in the biconvex shape. As described below, the lens array may alternatively comprise a plurality of plates with holes. Each plate with a hole may be referred to as an electrode. The electrodes may be provided in series along the path of a beam grid of a plurality of charged - particle beams (which may also be referred to as sub - beams). Thus, the electrodes are also in series along the path of the charged - particle beams of the beam grid.

[0049] The electron source 201 directs electrons towards the condenser lens array 231 which forms part of the electro - optical device 41. The electron source 201 is desirably a high - brightness thermal field emitter having a good compromise between brightness and total emission current. There may be dozens, hundreds, thousands or even tens of thousands of condenser lenses 231. The array of condenser lenses 231 may comprise multi - electrode lenses and have a construction based on EP1602121A1, which is hereby incorporated by reference in particular to disclose a lens array for splitting an electron beam into a plurality of sub - beams, where the array provides a lens for each sub - beam. The condenser lens array may take the form of at least two, preferably three plates which act as electrodes, where the holes in each plate are aligned with the holes in the other plates to define the path for the charged - particle beam through the plates. During operation, at least two of the plates are maintained at different electric potentials to achieve the desired lens effect. Between the plates of the condenser lens array are electrically insulating plates, which are made of an insulating material such as ceramic or glass, for example, and have one or more holes for the charged - particle beam. Additionally or alternatively, one or more of the plates may be characterized by holes, each hole having its own electrode, for example an electrode array around its perimeter or a group of holes arranged to have a common electrode. In a variant, one or more of the plates may comprise a plurality of sections or strips with a plurality of holes. In another alternative arrangement, a macroscopic collimator is provided instead of the condenser lens array. The macroscopic collimator may act on the beam from the source 201 before the beam is split into multiple beams. The macroscopic collimator may be implemented magnetically, electrostatically or magneto - electrostatically.

[0050] In some embodiments, the condenser lens array is formed by an array of three plates, where the charged particles have the same energy when they enter and leave each lens. This arrangement may be referred to as a single lens. Thus, dispersion occurs only within the single lens itself (between the entrance and exit electrodes of the lens), thereby limiting off - axis chromatic aberration. When the thickness of the condenser lens is low, for example a few mm, the effect of such aberrations is small or negligible.

[0051] Each condenser lens in the array directs electrons into respective beams 211, 212, 213 that are focused at respective intermediate foci 233. A collimator or collimator array may be positioned to operate on the respective intermediate foci 233. The collimator may take the form of a deflector 235 disposed at the intermediate focus 233. The deflector 235 is configured to bend the respective beams 211, 212, 213 by an effective amount to ensure that the principal ray (which may also be referred to as the beam axis) impinges on the sample 208 substantially orthogonally (i.e., at substantially 90° to the nominal surface of the sample). It should be noted that in an arrangement with macroscopic condenser lenses, the condenser lenses may collimate or contribute to the collimation of the source beam, or in one embodiment, the collimation of multiple beams.

[0052] The objective lens array 401 is disposed downstream of the deflector 235. The objective lens array 401 includes objective lenses for each of the beams 211, 212, 213. The objective lens array 401 projects the beams 211, 212, 213 onto the sample 208. The objective lens array 401 may include two or more, preferably at least three, plate electrode arrays connected to respective voltage sources.

[0053] Optionally, a control lens array 250 is disposed between the deflector 235 and the objective lens array 401. The control lens array 250 includes control lenses for each of the beams 211, 212, 213. The control lens array 250 provides additional degrees of freedom for controlling the characteristics of the beams 211, 212, 213. The control lens array 250 may include two or more, preferably at least three, plate electrode arrays connected to respective voltage sources. The function of the control lens array 250 is to optimize the beam opening angle with respect to beam demagnification and / or control the beam energy delivered to the objective lens, each of which directs the respective beams 211, 212, 213 onto the sample 208. In one embodiment, the control lens array may be considered part of the objective lens, such as an additional plate associated with the objective lens array.

[0054] Optionally, a scanning deflector array 260 is disposed between the control lens array 250 and the objective lens array 401. The scanning deflector array 260 includes scanning deflectors for each of the beams 211, 212, 213. Each scanning deflector is configured to deflect the respective beam 211, 212, 213 in one or two directions to scan the beam across the sample 208 in one or two directions. Alternatively, a macroscopic scanning deflector may be provided to scan the charged particle beam over the sample 208. The macroscopic scanning deflector may be disposed upstream of the control lens array 250. In one embodiment, such a macroscopic scanning deflector may operate on the source beam and may be present together with the macroscopic condenser lens.

[0055] The detector module 402 of the detector is disposed within the objective lens or between the objective lens and the sample 208 to detect signal electrons / particles from the sample 208. An exemplary construction of such a detector module 402 is described below. It should be noted that the detector may additionally or alternatively have detector elements upstream along the primary beam path of the objective lens array 401 or even the control lens array 250. The detector module may be an array of detector elements (e.g., a detector array). Each element may be associated with a separate beam, e.g., positioned to detect signal particles generated by the separate beam. The detector module may include at least one of a scintillator element, a semiconductor element, or a charge capture electrode, e.g., for capturing signal electrons as a current.

[0056] Figure 3 The electron optical device 41 may be configured to control the landing energy of electrons on the sample 208 by changing the electric potential applied to the electrodes of the control lens and the objective lens. The control lens and the objective lens work together and may be referred to as an objective lens assembly. The landing energy may be selected according to the nature of the sample to be evaluated to increase the emission and detection of secondary electrons. The detector module may be included in the objective lens assembly.

[0057] The objective lens may be configured to reduce the electron beam by more than 10 times, desirably in the range of 50 to 100 times or more. The objective lens may include three electrodes: an intermediate electrode, a lower electrode, and an upper electrode. The upper electrode may be omitted. An objective lens having only two electrodes may have lower aberration than an objective lens having more electrodes. A three - electrode objective lens may have a larger potential difference between the electrodes and thus achieve a stronger lens. Additional electrodes (i.e., more than two electrodes) provide additional degrees of freedom for controlling the electron trajectory (e.g., for focusing secondary electrons as well as the incident beam).

[0058] In some embodiments, the objective lens array assembly includes a detector having a detector module 402 downstream of at least one electrode of the objective lens array 401. The detector module 402 may comprise or even take the form of a detector array. In one embodiment, at least a portion of the detector is adjacent to and / or integrated with the objective lens array 401. For example, the detector module 402 may be implemented by integrating a CMOS chip detector into the bottom electrode of the objective lens array 401. Integrating the detector module 402 into the objective lens array may replace the secondary column. The CMOS chip is preferably oriented to face the sample (since the distance between the sample and the bottom of the electron optical system is small, which may, for example, be in the range of 10 to 400 microns, desirably in the range of 50 to 200 microns, optionally about 100 microns). It should be noted that even when the detector is upstream of the most downstream electron optical element of the charged particle device, there may be a close, e.g., similar distance, gap (e.g., about 100 microns) between the most downstream electron optical element and the sample. In one embodiment, the electrodes for capturing signal charged particles are formed in the top metal layer of the CMOS device; thus, the electrodes capture charge and can detect individual charged particles as current relative to time. The electrodes may be formed in other layers of the substrate, such as other layers of the CMOS chip. The power signal and control signal of the CMOS may be connected to the CMOS through vias in the silicon. For robustness, preferably, the bottom electrode consists of two elements: a CMOS chip and a passive Si plate with holes. The plate protects the CMOS from high electric fields.

[0059] In one embodiment, a single electrode surrounds at least some of the holes. In one arrangement, for example, a single electrode is allocated around each hole. In another embodiment, a plurality of electrode elements are provided around each hole, for example as detector elements. The signal charged particles captured by the electrode elements surrounding one hole may be combined into a single detection signal or used to generate independent detection signals. The electrode elements may be separated radially (i.e., to form a plurality of concentric rings), angularly (i.e., to form a plurality of fan-shaped sheets), both radially and angularly (providing a dartboard-like arrangement), or in a grid (e.g., as a checkerboard) or in any other convenient manner.

[0060] An exemplary embodiment of the detector integrated into the objective lens array 401 is shown in Figure 4 which schematically illustrates a cross-section of a portion of the objective lens array 401. In this embodiment, the detector includes a detector module 402 which includes as Figure 5A plurality of detector elements (e.g., an array of detector elements) 405 (e.g., sensor elements such as capture electrodes), preferably as an array of detector elements (i.e., preferably a plurality of detector elements in a pattern or arrangement on a two-dimensional surface). In this embodiment, the detector module 402 is disposed on the output side of the objective lens array. The output side is the output side of the objective lens array 401. Figure 5 Is a bottom view of the detector module 402, which includes a substrate 404 on which a plurality of detector elements (or capture electrodes 405) are disposed, and each detector element surrounds a beam aperture 406. The beam aperture 406 can be formed by etching through the substrate 404. In Figure 5 The illustrated arrangement, the beam apertures 406 are shown in a rectangular array. The beam apertures 406 can also be arranged in different ways, such as in a hexagonal close-packed array arrangement as Figure 6 Depicted.

[0061] The above-described integrated detector module 402 is particularly advantageous when used in conjunction with an evaluation device (e.g., including electron optical equipment) having an adjustable landing energy, since secondary electron capture can be optimized for a range of landing energies. A detector module having an array or in the form of an array can also be integrated into other electrode arrays, not just the lowest electrode array. Further details and alternative arrangements of the detector module integrated into the objective lens can be found in EP application No. 20184160.8, which is hereby incorporated by reference.

[0062] A power supply can be provided to apply a corresponding electric potential to, for example, the control lenses of the control lens array 250, the objective lenses of the objective lens array 401, and the condenser lenses of the condenser lens array or any electron optical element or component (e.g., detector module) of the electron optical equipment 41 (such as when integrated into the objective lens array, or when the objective lens and the detector module are separate components). The controller 50 can control the electric potential applied to the electrodes of the electron optical components such as the condenser lens array, the objective lens array, and / or the control lens array.

[0063] The electron optical equipment 41 can include other electron optical components, such as a charged particle corrector, for example as a corrector array, for aligning the source with the sample and between the beams of a multi-beam and for adjusting the focus of different groups of beam grids or individual beams of a beam grid. Such correctors can be controlled to operate dynamically and / or statically, for example during the boost, maintenance, or calibration of the electron optical equipment 41.

[0064] In one embodiment, an array of electro-optical devices (or device array) is provided. The array may include any of the plurality of electro-optical devices described herein (e.g., electro-optical columns or charged particle devices). Each electro-optical device in the array of electro-optical devices focuses a corresponding plurality of charged particle beams onto different regions of the same sample 208. Each electro-optical device in the array may derive a corresponding plurality of charged particle beams from a different respective source 201. Each respective source 201 may be one of the plurality of sources 201. At least one subset of the plurality of sources 201 may be provided as a source array. The source array may include a plurality of emitters on a common substrate. Focusing a plurality of charged particle beams from different electro-optical devices simultaneously onto different regions of the same sample allows an increase in the area of the sample 208 that is simultaneously exposed to the charged particle beams. Thus, an increased sample area can be processed (e.g., evaluated) simultaneously. The electro-optical devices in the device array may be arranged adjacent to each other so as to project the corresponding plurality of beams onto adjacent regions of the sample 208. Any number of electro-optical devices may be used in the array. Preferably, the number of electro-optical devices is in the range of 9 to 200. When referring to a single electro-optical device, charged particle device, or system or column, each electro-optical device in the device array may be configured in any of the ways described herein. Alternatively or additionally, one or more of the electro-optical devices in the array may be configured to project a single beam.

[0065] Figure 7 Another example of an electro-optical device 41 is schematically depicted. Features identical to those described above are given the same reference numerals. For the sake of brevity, such features are not referred to Figure 7 in detail. For example, the source 201, condenser lens 231, objective lens array 401, and sample 208 (e.g., on sample support 207) may be as described above. In this example, a macro collimator 270 is provided in place of the deflector array of the type described above with reference Figure 3 to. Such a macro collimator may be a macro lens, which may be magnetic, electrostatic, or both. In other embodiments, a deflector array may be used to at least assist in the collimation of the beam, and thus the deflector array is used for a more refined collimation-directed deflection than the role of the macro collimator 270. Such an arrangement may also include an array of a plurality of deflectors (e.g., where each aperture has a plurality of electrodes) for more refined collimation. In one arrangement, the condenser lens 231 may include a single plate defining an array of beam-limiting apertures in which a plurality of apertures are defined, and one or more associated macro electrodes have a single aperture. Such an array of beam-limiting apertures and associated macro electrodes may also form a condenser lens array to focus the generated beam at an intermediate focus desirably corresponding to the position of the collimator 270.

[0066] As described above, in some embodiments, the detector may be disposed between the objective lens array 401 and the sample 208. The detector may face the sample 208. Alternatively, as Figure 7 shown, the detector 240 may be implemented such that the objective lens array 401 is between the detector 240 and the sample 208.

[0067] In one embodiment, the deflector array 95 is disposed between the detector 240 and the objective lens array 401. In one embodiment, the deflector array 95 includes a Wien filter array such that the deflector array 95 may be referred to as a beam splitter. The deflector array 95 is configured to provide a magnetic field and an electrostatic field. The electrostatic field and the magnetic field operate together to separate charged particles projected onto the sample 208 from signal particles (e.g., electrons from the sample 208). The operation of the fields guides the signal particles toward the detector 240.

[0068] In one embodiment, the detector 240 is configured to detect signal particles by reference to the energy of the charged particles (i.e., depending on the bandgap), such a semiconductor-based type of detector. Such a detector 240 may be referred to as an indirect current detector. Secondary electrons emitted from the sample 208 obtain energy from the field between the electrodes. The secondary electrons have sufficient energy once they reach the detector 240. In different arrangements, the detector 240 may be an electron-photon converter, such as a scintillator array, e.g., a fluorescent strip between beams located upstream along the primary beam path relative to the Wien filter. The primary beam passing through the Wien filter array (magnetic and electrostatic strips orthogonal to the primary beam path) has upstream and downstream paths that are substantially parallel to the Wien filter array, while signal electrons from the sample are guided by the Wien filter array toward the scintillator array. The electron-photon converter may be photon-coupled to a photon-electron converter to convert any photons generated and emitted by the electron-photon converter. The photon-electron converter may be electrically connected to an electronic circuit device to process the detection signal. In different embodiments, the photon-electron converter may be inside or outside the charged particle device. In one embodiment, the photon coupling may be via a photon transmission unit (e.g., an optical fiber array) to a remote optical detector that generates a detection signal when photons are detected.

[0069] Figure 8 Schematic diagram of another exemplary electron optical device 41 for use in an evaluation device. The electron optical device 41 may be used in combination with any of the embodiments described herein, e.g., instead of the above such as with reference to Figure 3 and / or Figure 7Any one of the described electro - optical devices 41 in the electro - optical device. In this example, the electro - optical device 41 includes an electron source 201, a beam - forming aperture array 502, a condenser lens 504, a source conversion unit 506, an objective lens 508, and a sample 208. The source 201 and the sample 208 can take any one of the forms described above with reference to, for example Figure 2 , Figure 3 and Figure 7 Any one of the forms. The source 201, the beam - forming aperture array 502, the condenser lens 504, the source conversion unit 506, and the objective lens 508 can be aligned with the primary electron optical axis 510 of the charged - particle device 41. The source 201 generates a primary electron beam 512 having a source crossover 514. The beam - forming aperture array 502 forms beams 521, 522, 523 from the primary beam 512. Lines depicting three beams are shown, but the beam - forming aperture array 502 can be configured to form two - beam lines or more than three - beam lines, such as four - beam lines or five - beam lines. The beam - forming aperture array 502 can also be configured to form multiple beam lines, thus forming a beam array. For example, the beam - forming aperture array 502 can be configured to form an n×m beam array, where n and m are integers that can be the same or different, such as a 3×3 beam array, a 4×4 beam array, or a 5×5 beam array.

[0070] The condenser lens 504 can be configured to redirect the paths of the beams 521, 522, 523 to be substantially parallel to each other and / or to be incident on the source conversion unit 506 substantially perpendicularly. The condenser lens 504 can be a macroscopic magnetic lens arrangement, such as a plurality (e.g., two) of lenses arranged in a non - rotating setting (by which the rotational effects of different lenses of the lens arrangement cancel each other out or their net rotational effect on the beam path is substantially zero).

[0071] The source conversion unit 506 can include a beam - limiting aperture array 531 that defines apertures configured to laterally limit each of the beams 521, 522, 523. The beam - limiting aperture array 531 can shape one or more of the beams 521, 522, 523, for example to split a beam into two or more beams downstream of the beam - limiting aperture array 531, such as towards the sample.

[0072] The source conversion unit 506 can include an array of electro - optical components for operating on each beam or a group of beams among the multiple beams. The source conversion unit 506 can include an image - forming element array 532 that includes an array of micro - deflectors configured to deflect the beams 521, 522, 523 towards the axis 510. The deflected beams 521, 522, 523 can form a virtual image of the source crossover 514 on the sample 208.

[0073] The source conversion unit 506 may include an aberration compensator array 534 configured to compensate for aberrations in the beams 521, 522, 523. For example, the aberration compensator array 534 may be configured to compensate for field curvature and / or astigmatism.

[0074] The source conversion unit 506 may include a pre-bending microdeflector array 533 configured to bend the paths of the beams 521, 522, 523 upstream of the beam limiting aperture array 531, e.g., to make the paths of the beams 521, 522, 523 impinge substantially perpendicularly on the beam limiting aperture array 531.

[0075] The image forming element array 532, the aberration compensator array 534, and / or the pre-bending microdeflector array 533 may include multi-layer sub-beam manipulation devices, some of which may be in the form of arrays, e.g.: microdeflectors, microlenses, and / or microastigmators.

[0076] In the illustrated example, the objective lens 508 includes a magnetic lens that macroscopically acts on the beam to focus the beam onto the sample 208. In other embodiments, the objective lens 508 may include an electrostatically implemented objective lens array, or a combination of magnetic and electrostatic lenses may be used; e.g., a macroscopically magnetic objective lens with electrostatic elements.

[0077] Figure 9 An electron optical assembly 700 is depicted. The electron optical assembly may form part of any of the electron optical devices 41 disclosed herein. The electron optical assembly may be an electron optical lens assembly. For example, the electron optical lens assembly may include an objective lens array or assembly, or a condenser lens array or assembly, or may be an objective lens array or assembly, or a condenser lens array or assembly. However, the electron optical assembly 700 need not be or include an electron optical lens assembly. Additionally or alternatively, the electron optical assembly 700 may include one or more elements such as collimators, correctors (such as individual beam correctors), detector arrays, deflectors, and / or Wien filter arrays as corresponding arrays.

[0078] The electron optical assembly 700 may be a macroscopic component that manipulates a single beam passing through a large aperture in the electron optical assembly 700 (which may be separated into multiple beams downstream). Alternatively, the electron optical assembly 700 may include an aperture array and may be configured to manipulate multiple electron beams passing through the apertures.

[0079] As Figure 9Illustrated, in one embodiment, the electro - optical assembly 700 includes a plurality of electro - optical elements. The electro - optical elements may be planar. Each electro - optical element may include plates 710, 720, 730, 740, 240. The plates may each be set to an electric potential and may thus be referred to as electrodes or electrode plates. The depicted arrangement includes five electro - optical elements, where the fifth element is the detector 240. In the depiction, four electrode plates 710, 720, 730, 740 are shown; thus the depicted arrangement may have at least four electro - optical elements. In one arrangement, such an electro - optical assembly may have one or more electro - optical elements, desirably two or more electro - optical elements. Each electro - optical element (or plate) 240, 710, 720, 730, 740 has one or more holes around the beam path of one or more electron beams. Figure 9 The illustrated arrangement shows four electrode plates 710, 720, 730, 740 and the detector plate of the detector 240. The plates may be electrically isolated from each other. In the illustrated arrangement, the isolation spacer 765 electrically isolates the upstream plate 710 from the downstream plate 720. The upstream and downstream plates are located between the most upstream electro - optical element (including the most upstream plate 730) and the most downstream electro - optical element (including the most downstream electrode plate 740) among at least four electro - optical elements.

[0080] As Figure 9 As shown, in one embodiment, one or more plates may be positioned downstream of the most downstream electro - optical element among at least four electro - optical elements. For example, the detector plate forming the detector 240 may be positioned downstream of the most downstream electrode plate 740 of the lens element. In one embodiment, the detector 240 is set to a different electric potential from the adjacent electro - optical element 740 along the path of the charged particle beam. In such an arrangement, the spacer 79 between the most downstream electrode plate 740 and the detector is electrically isolated. In a different arrangement, the detector 240 is set to the same electric potential as the adjacent electro - optical element 740; the spacer 79 (or connecting element) between the detector 240 and the adjacent electro - optical element is conductive.

[0081] In one embodiment, the potential applied to the lowermost electrode plate 740 of the lens element is controlled to have a fixed potential relative to the sample 208. In the operating mode of the electron optical device 41 including the electron optical assembly 700, the potential (or voltage) applied to the lowermost electrode plate 740 can be maintained substantially constant. In one embodiment, the voltage (or potential) applied to the uppermost plate 730 can be controlled to be fixed relative to the source 201. When the voltage (or potential) is controlled to control the landing energy, the electric field in the electron optical assembly 700 can change. When the electric field changes, the focus of the electron beam on the sample can undesirably change. In one embodiment, the controller 50 is configured to control the voltage (potential) applied to the upstream plate 710 and / or the downstream plate 720 to compensate for the focus change caused by the changing electric field. The detector 240 can be considered an additional electron optical element because it can be set to a different potential from the adjacent electron optical element 740 along the path of the charged particle beam; alternatively, the detector is set to the same potential as the adjacent electron optical element.

[0082] As Figure 9 illustrated, the other plates of the electron optical assembly 700 can be separated by different types of spacer elements 750, 760, 765, 770, 79. Some of these spacer elements 750, 760, 770 can be stepped structures. Other spacer elements can have a uniform cross-section. In one embodiment, as Figure 9 illustrated, the detector 240 is attached to one of the spacer elements 770 (or an adjacent spacer element) by a connecting element 79. The connecting element 79 can be an electrical isolator or a spacer element with a hole (i.e., a spacer element that is different in design from the other spacer elements). The size of the hole is designed to receive the lowermost electrode plate 740 and the intermediate thermal isolation gap, which can also be electrically isolated. Thermal separation of the detector 240 and the adjacent plate 720 can be desirable because the thermal requirements of the detector 240 and the adjacent electrode plate 720 are different. In addition to or as an alternative to the adjacent spacer element 770, the connecting element can be connected to a regulating conduit. The connecting element 79 can directly thermally connect the detector 240 to the cooling regulating conduit. The regulating conduit can be positioned outside the adjacent spacer element relative to the adjacent electrode plate 720.

[0083] In contrast to the situation where a conventional isolation spacer (such as the designs of other spacers depicted by 750, 760, 765, and 770) is positioned between the bottommost electrode plate 740 and the detector array 240, thereby setting a focal length defined by the dimensions of the spacer, the detector array 240, and the bottommost electrode plate 740 along the beam path, using a connection element 79 between the adjacent spacer 770 and the detector 240 can enable the positioning of the detector 240 and the adjacent electrode plate 740 to be closer. The connection element 79 can desirably achieve an electron optical design with a short focal length along the beam path; for example, the dimensions along the beam path of the connection element and the detector 240 (i.e., removing the dimensions along the beam path of the bottommost electrode plate 740 and reducing the effective dimensions of the spacer path length). In one variation, the connection element can be included in the adjacent spacer 770 (e.g., a part thereof), for example having the same surface dimensions as the adjacent spacer 770 and the connection element 79. As depicted, the isolator has a uniform diameter along the path of the charged particle beam. The detector can have a separate electrical connection to an adjacent electro - optical element 740 along the path of the charged particle beam (e.g., a multi - beam). The separate connection can be used to connect the detector signal to, for example, a controller such as controller 50 for transmitting control signals to and / or from the detector and for transmitting detection signals from the detector.

[0084] In one embodiment, the electro - optical assembly 700 includes one or more electro - optical elements, which include micro - electromechanical components (e.g., elements fabricated using MEMS technology). The electro - optical assembly 700 can be a module, such as an electro - optical module that can be referred to as a MEMS module (e.g., considering the nature of one or more of the electro - optical components included in the module). In one embodiment, the electro - optical assembly 700 can be replaced within the electro - optical device 41.

[0085] As described above, an electro - optical element can be provided as an electrode, for example as part of an objective lens array. An array of holes in the electrode allows a charged particle beam to pass through the electrode. The electric field near the holes can exert a lens effect on the charged particles. In some arrangements, the holes can be adapted to compensate for aberrations, such as off - axis aberrations in a multi - beam, such as distortion, curvature of field, astigmatism, and coma. For example, the holes in one or more of the electrodes can be shaped, sized, and / or positioned to compensate for off - axis aberrations. For example, the holes can have a series of different areas (or a series of diameters) to compensate for curvature of field, a series of different ellipticities to compensate for astigmatism, and / or a series of displacements different from the nominal grid positions to compensate for distortion caused by telecentric errors. See, for example, EPA 21166214.3 filed on March 31, 2021, which is incorporated herein by reference regarding off - axis aberration correction.

[0086] The performance of electron optical components can be highly sensitive to variations in the characteristics of holes, such as their shape, size, and / or position, especially when these features are deliberately configured to correct aberrations. As described in the introduction section of the specification, it is challenging to measure these characteristics efficiently and with high precision. The characteristics can be measured by capturing an image of the hole. Extracting useful information from such an image requires precise calibration of the length scale in the image. The length scale can vary as a function of the orientation and / or position within each image and / or between images. Inaccuracies in the length scale can accumulate across images and result in relatively large measurement errors for features that are relatively large and / or spaced relatively far apart in the image.

[0087] A scanning electron microscope (SEM) can be used to capture images. The scale accuracy in an SEM can depend on various characteristics of the SEM device, including electronics and internal calibration factors. In some typical implementations, the accuracy error of the scale in an SEM can be a few nm per pixel. Similar limitations exist in other imaging techniques that can be used to capture images of holes. To extract the most accurate information about the shape, size, and / or position of the holes in the image, it is desirable to calibrate the image. Calibration can include calibration of the length scale within the image.

[0088] In some arrangements, calibration of the image is performed using reference features defined in the image that have a known scale. For example, the reference features can include two elements that have a known spatial relationship with respect to each other, such as a known spacing between them. The known spatial relationship can be used to calibrate the scale of the image in at least the region between the two elements. For example, a neighboring hole can be used as a reference feature. The spacing between the centers of neighboring holes can be known with high precision, which can be referred to as the beam pitch. The beam pitch can be defined by a highly accurate reticle (e.g., 10 nm - 20 nm), which can have nanoscale accuracy on a length scale of hundreds of microns after being reduced onto the wafer during manufacturing. For example, in the case where the holes are arranged in an X - Y rectangular grid, the beam pitch along the X direction can be used to calibrate the X - axis scale in the image of the holes and the beam pitch along the Y direction can be used to calibrate the Y - axis scale.

[0089] Using the beam pitch as a reference feature requires that the field of view of the image be larger than the beam pitch, typically at least about 1.5 times the beam pitch, so that multiple holes can be seen and used to obtain the beam pitch. Such a large field of view can limit resolution and / or throughput. Embodiments of the present disclosure are directed to solving this problem.

[0090] In one embodiment, an electron optical component for an electron optical device is provided. The electron optical device can take, for example, the above reference Figure 3 , Figure 7 and Figure 8Any of the described forms. In one arrangement, the electron optical device may include a detector (e.g., including detector module 402) configured to detect signal charged particles from the sample 208. The detector may take any of the forms including the reference above Figures 4 to 6 Any of the described forms. The electron optical element may take any of the forms referenced above Figure 9 Any of the described forms, including, for example, plates 710, 720, 730, 740 that define holes.

[0091] In one arrangement, as Figures 14 - 17 illustrated, the electron optical element includes a substrate 302. As Figure 14 depicted, the substrate 302 has two planar surfaces 304, 306. The substrate 302 defines at least one hole 308 that extends through the substrate 302 between the two planar surfaces 304, 306. The electron optical device may include a stack of electron optical elements to allow manipulation of at least one charged particle beam propagating along a beam path through the stack by applying different electric potentials to the electron optical elements. The holes in the electron optical elements may be aligned along the beam path to allow the charged particle beam to pass through the electron optical elements by passing through the aligned holes. The substrate 302 may be planar, such as a plate. The substrate 302 may be an electrode, such as a planar electrode or an electrode plate (such as a planar component including a series of electrodes with holes defined therein), which may be part of an electron optical lens arranged along the beam path. The substrate 302 may be configured to function as, or as part of, a beam limiting hole array, a corrector array, and / or a detector array.

[0092] At least one of the planar surfaces 304, 306 includes a plurality of marks 310 formed on or in the planar surfaces 304, 306. The distance between the centers of at least one pair of adjacent marks is arranged to be equal to or less than half of the maximum dimension of at least one of the holes. In some arrangements, the distance between the mark centers is significantly smaller, optionally less than 25% of the maximum hole size, optionally less than 10% of the maximum hole size, optionally less than 1% of the maximum hole size, optionally less than 0.1% of the maximum hole size. Alternatively or additionally, in the case where at least one hole includes a plurality of holes, the distance between the centers of at least one pair of adjacent marks is equal to or less than half of the distance between the centers of at least one pair of adjacent holes. In some arrangements, the distance between the mark centers is significantly smaller, optionally less than 25% of the distance between the hole centers, optionally less than 10% of the distance between the hole centers, optionally less than 1% of the distance between the hole centers, optionally less than 0.1% of the distance between the hole centers.

[0093] Accordingly, markers 310 are provided with relatively close spacing compared to the size of the holes 308 and / or the spacing between the holes 308, which may define the beam pitch. The spacing between the markers 310 can be defined with high precision and is known prior to forming any image of the electro-optical element to evaluate the holes 308 in the electro-optical element (e.g., to measure the shape, size, and / or position of the holes as described above). Compared to alternative techniques that may rely on larger reference features such as the beam pitch, an image with a much smaller field of view can be used to obtain calibration information. For example, calibration information can be obtained from an image captured using a field of view small enough to capture the complete profile of only a single hole. Thus, calibration can be performed with higher precision (higher resolution) and / or higher throughput.

[0094] The plurality of markers 310 are arranged in a pattern. Subject to the constraints described above regarding the distance between the centers of adjacent markers, the pattern can take various forms. Examples of the pattern are discussed below with reference to Figures 10 - 13 discussed below.

[0095] In one arrangement, the pattern includes an array of markers 310 having a common pitch. The array of markers 310 can include a plurality of markers 310 arranged along a line with a common pitch, desirably three or more markers, such as four markers, five markers, six markers, ten markers, 50 markers, 100 markers, 500 markers, etc. Providing three or more markers 310 along a line with a common pitch allows for multiple independent measurements of the common pitch. Making multiple measurements allows for improved precision due to averaging. The line can be a straight line. Examples of a plurality of markers 310 arranged along a straight line with a common pitch are shown in Figure 10 , Figure 11 and Figure 13 . For example, the dashed box 311 in Figure 11 shows five markers 310 arranged along a straight line aligned with the X-axis with a common pitch. Figure 11 The dashed box 313 in Figure 12 and Figure 13 shows five markers 310 arranged along a straight line aligned with the Y-axis with a common pitch. In other arrangements, as will be described in more detail below with reference to Figure 12 and Figure 13 , the line can be curved, such as substantially circular. The line can surround one of the holes 308. The line can be coaxial with the hole 308.

[0096] Different pluralities of markers 310 can be arranged along different respective lines (e.g., straight lines) that are angled with respect to each other, such as perpendicularly angled. Markers can be provided, for example, along a line aligned with the X-axis and along a line aligned with the Y-axis perpendicular to the X-axis. Alternatively or additionally, markers can be provided along lines angled with respect to each other at other angles, such as parallel to the axes of a hexagonal grid defining the markers (e.g., at 60 degrees). In such arrangements, the markers can be aligned along the lines of each of the three axes of the hexagonal grid.

[0097] In one arrangement, the array is a two-dimensional array. The markers 310 may have the same common pitch parallel to different axes of the two-dimensional array. Alternatively, the markers 310 may have different pitches parallel to different axes of the two-dimensional array. For example, the markers 310 may have a first common pitch parallel to the X-axis and a second common pitch parallel to the Y-axis perpendicular to (e.g.,) the X-axis, where the first common pitch and the second common pitch are different.

[0098] The two-dimensional array may include a grid. The centers of the markers 310 may be located at grid points defined by corresponding intersections between grid lines defining the grid. The grid may have any geometry, including for example rectangular (including square), hexagonal, and rhombic. The markers 310 may not be present on some of the grid points, such as where there are holes 308 or other features that make it inappropriate or not possible to provide the markers 310 at that location. This is illustrated in Figure 10 for example, in the case where the markers 310 are located at the grid points of a square grid except at the locations where there are holes 308 and in the regions 312 around each hole 308 (the region indicated as the dashed circle in the figure and the area between the outer periphery of each hole 308). It is desirable to ensure that the markers 310 are far enough from the holes 308 such that the markers 310 do not interfere with the edges of the holes 308. For example, the regions 312 may be arranged wide enough to avoid any possibility of interference due to etching effects such as etching tilt and to allow for registration errors between the array of markers 310 and the holes 308. That is, the regions 312 may have an outer boundary that defines the width between the outer boundary in the surface of the substrate 302 and the holes 308.

[0099] In one arrangement, the pattern of the markers 310 includes multiple arrays. The multiple arrays may include two or more arrays having different common pitches. Additionally or alternatively, the multiple arrays may include two or more arrays having the same common pitch. The multiple arrays may include multiple one-dimensional arrays forming a two-dimensional array. As described above, two or more of the arrays in the array may include multiple markers 310 arranged along respective lines that are angled relative to each other. Figure 13 Depicts an example arrangement in which the pattern includes multiple one-dimensional arrays 314, 316 that are angled relative to each other, for example orthogonal (although this need not be the case). The one-dimensional arrays 314, 316 may be angled relative to each other at an acute or obtuse angle. In this example, the pattern includes a set of one-dimensional arrays 314 aligned parallel to the X-axis (horizontal in the plane of the page) and a set of one-dimensional arrays 316 aligned parallel to the Y-axis (vertical in the plane of the page). In the illustrated arrangement, the one-dimensional arrays 314, 316 are positioned relative to the nearest neighboring holes 308 along a plane of mirror symmetry.

[0100] In some arrangements, as Figure 12 andFigure 13 Illustratively, two or more arrays in the array include a plurality of markers arranged along respective lines that are substantially circular and coaxial with different respective holes 308. In Figure 12 and Figure 13 the example of, one such circular array is disposed around each hole 308. In other arrangements, multiple circular concentric arrays may be disposed around each of one or more of the holes 308.

[0101] The circular array of markers 310 around the hole 308 is an example of one class of arrangements, where the plurality of markers includes at least one set (or set of markers) positioned around at least one of the holes 308 in a rotationally symmetric pattern (i.e., a pattern having second-order or higher-order rotational symmetry). The rotational symmetry will typically be about an axis passing through or near the geometric center of the respective hole 308. In the case of a perfectly circular hole, the geometric center will be the center of the circle. The markers 310 in a set of markers may have a common pitch. For example, the markers 310 may be regularly spaced along at least a portion of a circular path around and coaxial with the hole 308. The minimum spacing between markers in the set may be equal to or less than half of the maximum dimension (e.g., the diameter of a circle or the major axis of an ellipse) of the hole 308 around which the markers are positioned.

[0102] Arranging the markers 310 in a circularly symmetric pattern in this way, particularly the markers 310 closest to the hole 308, can reduce or avoid any unnecessary net effect of the markers 310 on the electric field, which can affect electrons passing through the hole 308. Any effect produced by a first marker 310 can be, for example, partially or fully compensated by the effect from a second marker that is symmetrically opposite the first marker. A set of markers including many markers may have less electron optical interference (or aberration effect) on the beam passing through the hole compared to a set of markers with fewer markers. For a given hole size, a set of markers with a smaller pitch between adjacent markers is desired.

[0103] In one arrangement, as Figure 13 illustrated, the pitch by which the markers in a first array in the array (e.g., Figure 13 in the circular array around the upper left hole 308 in Figure 13 ) and the markers in at least one second array adjacent to the first array (e.g., Figure 13 in the linear array 316 between the two upper most holes 308 in Figure 13The pitch of two of a circular array around the uppermost hole 308. Position different arrays such that they are spaced apart from each other by the same pitch as the pitch within the different arrays, creating additional arrays with the same pitch, thereby advantageously providing more pairs of markers separated from each other by a common pitch. Providing more such pairs of markers can allow for improved accuracy by averaging, and / or provide greater flexibility in how markers can be selected for calibration.

[0104] At least one hole 308 can include a plurality of holes 308. The plurality of holes 308 can include a set of holes defining a one-dimensional array. The holes in the one-dimensional array can be regularly spaced apart to define a hole pitch or a bunch pitch. As Figure 10 , Figure 12 and Figure 13 illustrated, a set of holes can be part of an array of holes arranged in a two-dimensional pattern. Figure 14 A cross-section showing such an array of holes depicts a planar element such as a plate (e.g., substrate 302). The planar element has two planar surfaces 304, 306. The one-dimensional arrays of holes 308 each extend through the planar element between the planar surfaces 304, 306. The one-dimensional arrays of holes can be aligned with a plurality of markers 310 arranged along a common pitch. The common pitch can be equal to or less than half of the hole pitch. The common pitch (or when there are multiple different common pitches, e.g., each common pitch corresponding to a different respective array of markers 310) can be equal to or less than half of the maximum dimension of one (or all) of the holes 308. Alternatively or additionally, the common pitch (or each common pitch) can be equal to or less than half of the distance between the centers of at least one pair of adjacent holes 308.

[0105] At least one hole 308 can include a macrohole in a multi-bunch system. The macrohole can be positioned upstream of the bunch-limiting hole array, optionally directly upstream of the bunch-limiting hole array. The macrohole can operate on the beam before the charged particle beam from the source is split into a plurality of bunches by a bunch grid. (For example, when the bunch-limiting hole array is set to a different electric potential from the macrohole array, the macrohole can operate with the bunch-limiting hole array to focus each bunch in the beam. In one arrangement, the macrohole and the bunch-simulating hole array (or hole lens) can be controlled to operate on the beam to focus the beam on a common intermediate focal plane).

[0106] A marker 310 is formed to provide sufficient contrast in the image to allow the detection of the position of the marker 310. In some arrangements, the marker 310 is formed with a relatively low contrast to minimize or avoid any interference with the electric field near the marker 310. For example, the marker 310 can be formed with minimal interference to the structure, composition, and / or surface finish of the electro-optical element. The resulting low contrast may not have a significant negative impact on the calibration measurements performed using the marker 310, since the calibration measurements are based on detecting the spacing between different markers 310 rather than on the details of the marker itself. If the size of the marker 310 is small relative to the spacing between the markers, then the calibration measurements will not be significantly affected by the low contrast.

[0107] Figures 15 - 17 Schematically depicts an example method for providing the marker 310. The marker 310 can in principle take any form that allows the detection of the position of the marker in the image. The marker 310 can be defined by any one of any combination of: local variations in surface topography; local variations in surface finish (such as roughness); local variations in composition.

[0108] As Figure 15 and Figure 16 depicted, in some arrangements, the substrate 302 includes a base material such as the base material 302A and a cover layer 302B on the base material 302A. In one embodiment, the cover layer 302B includes or consists of a metal layer. In one embodiment of this type, as Figure 15 illustrated, the marker 310 is defined by a groove in the base material 302A. For example, the groove can be formed by a shallow etch. The groove in the base material 302A can result in a corresponding groove in the cover layer 302B. When the electro-optical element is used in an electro-optical device, the marker 310 defined by a shallow etched groove in a base material covered by a cover layer such as a metal layer is expected to cause minimal or no significant interference to the local electric field. In another embodiment, as Figure 16 illustrated, the marker can include a local variation in the composition of the cover layer 302B. The local variation in composition can result in a corresponding local variation in density. The region 323 corresponding to the marker 310 can have a different composition from the region 325. When the electro-optical element is used in an electro-optical device, changing the composition while maintaining the metallicity allows the marker 310 to be defined with minimal or no significant interference to the local electric field, while still providing contrast for imaging processes such as SEM.

[0109] Figure 17An example embodiment in which the marker 310 includes a partial portion of the deposited material 327 is illustrated. The partial portion of the deposited material may be referred to as a partial coating or a partial layer or a part of a layer. The partial portion of the deposited material 327 may have one or more different properties relative to the adjacent material. The different properties may include any difference that can provide contrast in an image. The different properties may include different compositions and / or surface finishes relative to the adjacent material in terms of composition and / or surface finish. The difference in composition may result in a difference in density. The partial portion of the deposited material 327 may also provide a local change in topography by protruding above the level of the adjacent material (as Figure 17 schematically depicted).

[0110] As Figure 14 represented, the size of the markers is such that they are not distinguishable in a cross-section of the substrate passing through the plurality of holes 308; or at least the marker 310 has a small enough size relative to the thickness of the substrate 302 such that they are difficult to distinguish at the resolution of a cross-section passing through the plurality of holes 308 in the substrate 302. The layer present on the surface of the substrate 302 may be an applied layer or a covering layer such as the metal layer 302B. The applied layer may be applied to another layer or the material of the substrate itself.

[0111] Any of the arrangements discussed herein can be used in a method for evaluating an electro-optical element for an electro-optical device. The electro-optical element and the electro-optical device of the method may take any of the forms described above. The method may include capturing one or more images of a corresponding portion of the substrate 302 of the electro-optical element. Such image capture may be obtained during the manufacture and assembly of the stack of electro-optical elements, such as during or prior to the manufacture or assembly of a charged particle device, for example for calibration purposes. Such image capture of the electro-optical element may be obtained before fixing the spacer to the electro-optical element. In principle, various techniques can be used, including optical techniques and charged particle-based techniques. A high resolution is desired. In some embodiments, one or more images are captured using a scanning electron microscope (SEM). In some embodiments, for example as Figure 11 schematically depicted, one or more images are captured using a field of view small enough to capture only the complete profile of a single hole. The method may include detecting the marker positions of at least one subset of the plurality of markers 310 in the image or each image. The method may include determining geometric information about one or more holes 308 of the electro-optical element based on the one or more images and the detected marker positions. The detected marker positions can be used to calibrate the length scale along one or more directions in the image or each image.

[0112] Geometric information may include information about the size of one or more of the holes 308 (e.g., cross-sectional area, or diameter information, such as the diameter in the case of a perfect circle, or the average, minimum, or maximum diameter in the case of a deviation from circularity). Geometric information may include information about how the size varies across multiple holes (e.g., to measure the hole size distribution); for example, geometric information can be the relative variation in the size of holes in an entire hole array defined in an electro-optical element such as the substrate 302.

[0113] Geometric information may include information about the relative positions of two or more of the holes 308 (e.g., deviation from the nominal grid positions of a regular grid). Geometric information may include information about how the deviation from the nominal grid positions varies across multiple holes (e.g., to measure the position deviation distribution); for example, the information can be the relative difference in the positions of the holes in a hole array defined in an electro-optical element such as the substrate 302 with respect to the nominal grid positions of the holes in the hole array.

[0114] Geometric information may include information about the shape of one or more of the holes 308 (e.g., ellipticity (second order) or higher-order variations from circularity, such as triangularity (third order), squareness (fourth order), hexagonality, etc.). Geometric information may include information about how the shape varies across multiple holes (e.g., to measure the hole shape distribution), for example, the information can include the relative variation in the shape of holes in an entire hole array defined in an electro-optical element such as the substrate 302.

[0115] Measuring the geometric information of the holes of a hole array with reference to measurements marked on a substrate surface can enable accurate determination of perturbations (such as position, size, and shape) applied to different holes of the hole array. Such measurements of the geometric information of the holes of a hole grid enable verification of the geometric properties of different holes of the grid with respect to the expected geometric properties of the different holes, and with an expected improvement in accuracy compared to known techniques.

[0116] A reference to a component or system of components or elements that can be controlled to manipulate a charged particle beam in a certain way includes configuring a controller or control system or control unit to control the component to manipulate the charged particle beam in said way, and optionally using other controllers or devices (e.g., voltage source and / or current source) to control the component to manipulate the charged particle beam in this way. For example, a voltage source may be electrically connected to one or more components to apply an electric potential to the components in a non-limiting list including a control lens array 250, an objective lens array 241, and a detector array 240.

[0117] References to upper and lower, up and down, above and below, etc. should be understood as referring to directions parallel to the upstream and downstream directions of the charged particle beam impinging on the sample 208 (typically but not always vertical). Thus, references to upstream and downstream are intended to refer to directions with respect to the beam path independent of any existing gravitational field. References to the beam path refer to the expected position of the corresponding beam during the operation of the charged particle aperture. When referring to electron optical elements such as electrode plates, such references are generally understood to be for a collimated beam path, related to the optical axis of the beam, and thus orthogonal to the plane of the electron optical element. With respect to non-collimated beams such as divergent beams, the beam path can be considered as the axis with respect to the midpoint of the beam, or when the beam is a beam of a beam grid, with respect to the midpoint of the beam grid.

[0118] The electron optical devices described herein can take the form of an array of apertures or electron optical elements arranged in an array along a beam or multiple beam paths. Such electron optical elements can be electrostatic. In one embodiment, all electron optical elements, such as from the aperture array that limits the beam to the last electron optical element in the beam path before the sample, can be electrostatic and / or can take the form of an aperture array or a plate array. In some arrangements, one or more of the electron optical elements are fabricated as microelectromechanical systems (MEMS) (i.e., using MEMS fabrication techniques). The electron optical elements can have magnetic elements and electrostatic elements. For example, a composite array lens can feature a macroscopic magnetic lens surrounding a multiple beam path, having an upper plate and a lower plate within the magnetic lens and arranged along the multiple beam path. An array of apertures for the beam paths of multiple beams can be present in the plates. Electrodes can be present above, below, or between the plates to control and optimize the electromagnetic field of the composite lens array.

[0119] An evaluation device, tool, or system according to the present disclosure can include means for qualitatively evaluating a sample (e.g., pass / fail), means for quantitatively measuring a sample (e.g., feature size), or means for generating a sample map image. Examples of evaluation devices, tools, or systems are inspection tools (e.g., for identifying defects), review tools (e.g., for classifying defects), and metrology tools, or any combination of tools capable of performing evaluation functions associated with inspection tools, review tools, or metrology tools (e.g., subway inspection tools).

[0120] The functions provided by a controller or a control system or a control unit can be implemented by a computer. Any suitable combination of components can be used to provide the required functions, including, for example, a CPU, RAM, SSD, motherboard, network connection, firmware, software, and / or other components known in the art that allow performing the required computing operations. The required computing operations can be defined by one or more computer programs. The one or more computer programs can be provided in the form of a medium storing computer-readable instructions, optionally a non-transitory medium. When the computer-readable instructions are read by a computer, the computer performs the required method steps. The computer can consist of a self-contained unit or a distributed computing system having a plurality of different computers connected to each other via a network.

[0121] Although the present invention has been described in conjunction with various embodiments, other embodiments of the present invention will be apparent to those skilled in the art in view of the specification and practice of the invention disclosed herein. It is intended that the specification and examples be considered only as exemplary, with the true scope and spirit of the invention being indicated by the following claims and terms.

[0122] The following terms are provided:

[0123] Clause 1. An electro-optical element for an electro-optical device, the electro-optical element comprising: a substrate having two planar surfaces and defining at least one hole extending through the substrate between the two planar surfaces, wherein: at least one of the planar surfaces includes a plurality of marks formed on or in the planar surface, the distance between the centers of at least one pair of adjacent marks being: equal to or less than half of the maximum dimension of one of the at least one hole; and / or in the case where the at least one hole includes a plurality of holes, equal to or less than half of the distance between the centers of at least one pair of adjacent holes.

[0124] Clause 2. The element according to Clause 1, wherein the plurality of marks are arranged in a pattern.

[0125] Clause 3. The element according to Clause 2, wherein the pattern includes an array of the marks having a common pitch.

[0126] Clause 4. The element according to Clause 3, wherein the array of the marks includes a plurality of marks arranged along a line at the common pitch, desirably three or more marks.

[0127] Clause 5. The element according to Clause 4, wherein the line is straight.

[0128] Clause 6. The element according to Clause 4, wherein the line is curved.

[0129] Clause 7. The element according to Clause 6, wherein the line surrounds one of the holes.

[0130] Clause 8. The element according to Clause 7, wherein the line is substantially circular and coaxial with the hole.

[0131] Clause 9. The element according to any one of Clauses 3 to 8, wherein the array is a two-dimensional array, optionally having different common pitches parallel to different respective axes of the two-dimensional array.

[0132] Clause 10. The element according to Clause 9, wherein the two-dimensional array includes a grid, optionally including a rectangular grid, a hexagonal grid or a rhombic grid.

[0133] Clause 11. The element according to any one of Clauses 3 to 10, wherein the pattern includes a plurality of the arrays.

[0134] Clause 12. The element according to Clause 11, wherein two or more of the arrays include a plurality of marks arranged along respective lines that are angled relative to each other.

[0135] Clause 13. The element according to Clause 12, wherein two or more of the arrays include a plurality of marks arranged along respective lines that are substantially circular and coaxial with different respective holes.

[0136] Clause 14. The element according to any one of Clauses 11 to 13, wherein the plurality of arrays includes: two or more arrays having different common pitches; and / or two or more arrays having the same common pitch.

[0137] Clause 15. The element according to any one of Clauses 11 to 14, wherein the pitch by which the marks in a first array among the arrays are separated from the marks in at least one second array adjacent to the first array is substantially equal to the pitch of the first array and / or the pitch of the at least one second array.

[0138] Clause 16. The element according to any one of Clauses 3 to 15, wherein: the at least one hole includes a plurality of holes; and the plurality of holes includes a set of holes defining a one-dimensional array, desirably the set of holes having a hole pitch, desirably the set of holes being part of an array of holes arranged in a two-dimensional pattern.

[0139] Clause 17. The element according to Clause 16, wherein the one-dimensional array of holes is aligned with a plurality of the marks arranged along the line at the common pitch.

[0140] Clause 18. The element according to Clause 17, wherein the common pitch is equal to or less than half of the hole pitch.

[0141] Clause 19. The element according to any one of Clauses 3 to 18, wherein the common pitch or each common pitch is: equal to or less than half of the maximum dimension of one of the at least one hole; and / or in the case where the at least one hole includes a plurality of holes, equal to or less than half of the distance between the centers of at least a pair of adjacent holes.

[0142] Clause 20. The element according to any one of the preceding clauses, wherein the plurality of marks includes a set of marks positioned around at least one of the holes in a rotationally symmetric pattern, the rotationally symmetric pattern having second-order or higher-order rotational symmetry.

[0143] Clause 21. The element according to Clause 20, wherein the set of marks includes an array of marks having a common pitch.

[0144] Clause 22. The element according to Clause 20 or 21, wherein the minimum spacing between the marks in the set is equal to or less than half of the maximum dimension of the hole around which the marks are positioned.

[0145] Clause 23. The element according to any one of the preceding clauses, wherein the substrate includes a base material and a covering layer on the base material, and the covering layer desirably includes a metal layer.

[0146] Clause 24. The element according to any one of the preceding clauses, wherein the marks are defined by local variations in topography, optionally by local grooves in the substrate or in the base material of the substrate.

[0147] Clause 25. The element according to Clause 23 or 24, wherein the marks are defined by local variations in the composition and / or surface finish of the substrate.

[0148] Clause 26. The element according to any one of the preceding clauses, wherein the marks include local portions of deposited material, the local portions desirably having one or more different properties relative to the adjacent material, such as different composition and / or surface finish relative to the composition and / or surface finish of the adjacent material.

[0149] Clause 27. An electron-optical device including a stack of electron-optical elements, configured to allow manipulation of at least one charged particle beam propagating along a beam path through the stack by applying different electric potentials to the electron-optical elements, wherein the stack includes at least one electron-optical element according to any one of the preceding clauses.

[0150] Clause 28. The device according to Clause 27, further including a detector configured to detect signal charged particles from the sample.

[0151] Clause 29. An evaluation device for evaluating a sample using charged particles, the device comprising: a sample support configured to support the sample; and a device according to Clause 27 or 28, configured to project at least one charged particle beam towards the sample.

[0152] Clause 30. A method for evaluating an electro - optical element for an electro - optical device, wherein the electro - optical element comprises: a substrate having two planar surfaces and defining at least one hole extending through the substrate between the two planar surfaces, wherein: at least one of the planar surfaces comprises a plurality of marks formed on or in the planar surface, the distance between the centers of at least one pair of adjacent marks being: equal to or less than half of the maximum dimension of one of the at least one hole; and / or in the case where the at least one hole comprises a plurality of holes, equal to or less than half of the distance between the centers of at least one pair of adjacent holes, and wherein the method comprises: capturing one or more images of a corresponding portion of the substrate; detecting the mark positions of at least a subset of the plurality of marks in the image or each image; and determining geometric information about the at least one hole based on the one or more images and the detected mark positions.

[0153] Clause 31. The method according to Clause 30, wherein the geometric information comprises one or more of the following: information about the size of one or more of the at least one hole; information about the relative positions of two or more of the holes; and information about the shape of one or more of the at least one hole.

[0154] Clause 32. The method according to Clause 30 or 31, wherein determining the geometric information comprises using the detected mark positions to calibrate a length scale along one or more directions in the image or each image.

[0155] Clause 33. The method according to any one of Clauses 30 to 32, wherein the one or more images are captured using a scanning electron microscope.

Claims

1. An electro - optical element for an electro - optical device, the electro - optical element comprising: a substrate having two planar surfaces and defining at least one hole extending through the substrate between the two planar surfaces, wherein: at least one of the planar surfaces includes a plurality of marks formed on or in the planar surface, the distance between the centers of at least one pair of adjacent marks being: equal to or less than half of the maximum dimension of one of the at least one hole; and / or in the case where the at least one hole includes a plurality of holes, equal to or less than half of the distance between the centers of at least one pair of adjacent holes.

2. The element according to claim 1, wherein the plurality of marks are arranged in a pattern.

3. The element according to claim 2, wherein the pattern includes an array of the marks having a common pitch.

4. The element according to claim 3, wherein the array of marks includes a plurality of marks arranged along a line at the common pitch, desirably three or more marks.

5. The element according to claim 4, wherein the line is straight.

6. The element according to claim 4, wherein the line is curved.

7. The element according to claim 6, wherein the line surrounds one of the holes.

8. The element according to claim 7, wherein the line is substantially circular and coaxial with the hole.

9. The element according to any one of claims 3 to 8, wherein the array is a two - dimensional array, optionally having different common pitches parallel to different respective axes of the two - dimensional array.

10. The element according to any one of claims 3 to 9, wherein the pattern includes a plurality of the arrays, desirably wherein two or more of the arrays include a plurality of marks arranged along respective lines that are angled relative to each other.

11. The element according to claim 10, wherein the plurality of arrays includes: two or more arrays having different common pitches; and / or two or more arrays having the same common pitch.

12. The element according to claim 10 or 11, wherein the pitch by which the marks in a first array among the arrays are separated from the marks in at least one second array adjacent to the first array is substantially equal to the pitch of the first array and / or the pitch of the at least one second array.

13. The element according to any one of claims 3 to 12, wherein: the at least one hole includes a plurality of holes; and the plurality of holes includes a set of holes defining a one - dimensional array, desirably the set of holes having a hole pitch, desirably the set of holes being part of an array of holes arranged in a two - dimensional pattern.

14. The element according to claim 13, wherein the one - dimensional array of holes is aligned with a plurality of the marks arranged along a line at the common pitch.

15. The element according to any one of claims 3 to 14, wherein the common pitch or each common pitch is: equal to or less than half of the maximum dimension of one of the at least one hole; and / or In the case where the at least one hole includes a plurality of holes, it is equal to or less than half of the distance between the centers of at least one pair of adjacent holes.

Images