Electro-optical stacks, modules, evaluation equipment, and methods for manufacturing electro-optical stacks.

Abstract

This disclosure relates to an electron-optical stack and related apparatus and methods for manipulating one or more charged particle beams. In one configuration, a plurality of electron-optical plates have principal surfaces on both sides of the plate. The plates define a set of channels that are aligned along the beam path of a charged particle beam and configured to allow the charged particle beam to pass through the plates through the channels. Each channel defines an aperture on two principal surfaces of the plate that define the channel. The apertures have different shapes from each other. The plates are arranged in an orientation such that the apertures include one or more pairs of matched apertures along the beam path. Each pair of matched apertures, or each pair of matched apertures, consists of apertures of the same shape defined on adjacent principal surfaces of adjacent plates.

Description

Technical Field

[0001] Cross - reference to related applications

[0001] This application claims priority to European Patent Application Publication No. 22211495.1, filed on December 5, 2022, the entire content of which is incorporated herein by reference.

[0002]

[0002] The present disclosure relates to an electron - optical stack for manipulating one or more charged - particle beams, a module including the stack, an evaluation apparatus including the stack, and a method of manufacturing the stack.

Background Art

[0003]

[0003] When manufacturing a semiconductor integrated circuit (IC) chip, unwanted pattern defects inevitably occur on a substrate (i.e., a wafer) or a mask during the manufacturing process, for example, as a result of optical effects and incidental particles, thereby reducing the yield. Therefore, monitoring the degree of unwanted pattern defects is an important process in the manufacture of IC chips. More generally, the evaluation of the surface of a substrate or other object / material, such as inspection and / or measurement, is an important process during and / or after its manufacture.

[0004]

[0004] For example, there are known evaluation tools, which may be called evaluation devices or evaluation systems, that use a charged particle beam to evaluate an object, which may be called a sample, in order to detect pattern defects. These systems generally use electron microscopy techniques, such as scanning electron microscopes (SEMs). In an SEM, a primary electron beam of relatively high-energy electrons is targeted in a final deceleration step to land on the sample with a relatively low landing energy. The electron beam is focused onto the sample as a probing spot. Interaction between the material structure at the probing spot and the landed electrons from the electron beam causes signal electrons, such as secondary electrons, backscattered electrons, or Auger electrons, to be emitted from the surface. Signal electrons can be emitted from the material structure of the sample. By scanning the primary electron beam as a probing spot across the sample surface, signal electrons can be emitted across the sample surface. By collecting these emitted signal electrons from the sample surface, it is possible to obtain an image that represents the features of the material structure on the sample surface.

[0005]

[0005] Electro-optical stacks for electro-optical devices may be used to control electron beams. These electro-optical stacks may include plates that define features such as apertures, which are used to influence the electron trajectory by providing lensing effects, deflection and / or corrective effects (e.g., astigmatism correction and / or higher-order corrections). Various aspects of the features may affect the performance of the electro-optical stack, such as the shape, size and / or position of the features. Imperfections in the manufacturing process used to produce the features (e.g., unexpected structural features created during processing steps) may degrade the performance of the electro-optical stack. [Overview of the project]

[0006]

[0006] The object of this disclosure is to provide an apparatus and method that contribute to improving the electro-optical performance of an electro-optical device including an electro-optical stack and a stack of such plates.

[0007]

[0007] According to one aspect of the present invention, an electron-optical stack is provided, comprising a plurality of electron-optical plates having main surfaces on both sides of a plate, wherein the plates define a set of channels aligned along a beam path of a charged particle beam and configured to allow the charged particle beam to pass through the plates through the channels, each channel defining apertures on two main surfaces of the plate defining the channel, the apertures having different shapes from each other, and the plates are arranged in such a manner that the apertures include one or more pairs of matched apertures along the beam path, each pair of matched apertures or each pair of matched apertures consisting of apertures of the same shape defined on adjacent main surfaces of adjacent plates.

[0008]

[0008] According to one aspect of the present invention, a method for manufacturing an electron-optical stack is provided, the method comprising etching channels into each plate of a plurality of electron-optical plates having main surfaces on both sides of the plate, wherein the etching process is a process such that apertures defined at both ends of each channel have different shapes, and positioning the plates to align a set of channels so that a charged particle beam passes through the channels, wherein the plates are arranged in such a way that one or more pairs of matched apertures are defined along the beam path, and each pair of matched apertures or each pair of matched apertures consists of apertures of the same shape defined on adjacent main surfaces of adjacent plates.

[0009]

[0009] The above and other aspects of the present disclosure will become more apparent from the description of exemplary embodiments in conjunction with the accompanying drawings. [Brief explanation of the drawing]

[0010] [Figure 1]

[0010] This is a schematic diagram showing an exemplary charged particle beam inspection apparatus. [Figure 2]

[0011] Figure 1 is a schematic diagram showing an exemplary multi-beam system, which is part of an exemplary charged particle beam inspection system. [Figure 3]

[0012] This is a schematic diagram of an exemplary electro-optical device including a focusing lens array, an objective lens array, and a detector array. [Figure 4]

[0013] This is a schematic cross-sectional view of a portion of the objective lens array and detector array in an exemplary configuration. [Figure 5]

[0014] Figure 4 is a bottom view of a portion of the detector array. [Figure 6]

[0015] Figure 4 is a bottom view of a modified version of a portion of the objective lens array. [Figure 7]

[0016] This is a schematic diagram of an exemplary electro-optical device including an objective lens array and a beam separator. [Figure 8]

[0017] This is a schematic diagram of a further exemplary electro-optical device. [Figure 9]

[0018] For example, Figures 3, 7, and 8 show schematic diagrams of exemplary electro-optical stacks that may be part of the electro-optical devices. [Figure 10]

[0019] This is a schematic perspective view of three plates in an exemplary electro-optical stack. [Figure 11]

[0020] This is a schematic side view showing exemplary lines of equal electric field intensity in regions adjacent to apertures on adjacent main surfaces of adjacent plates. [Modes for carrying out the invention]

[0011]

[0021] Herein, exemplary embodiments are given in detail, examples of which are shown in the accompanying drawings. The following description refers to the accompanying drawings, and unless otherwise indicated, the same numbers in different drawings represent the same or similar elements. The implementations described below in the description of exemplary embodiments do not represent all implementations consistent with the present invention. Instead, those implementations are merely examples of apparatus and methods consistent with embodiments related to the present invention as described in the accompanying claims.

[0012]

[0022] Improving the computing power of electronic devices, which reduces the physical size of the device, can be achieved by significantly increasing the mounting density of circuit components such as transistors, capacitors, and diodes on an IC chip. This has been made possible by improvements in resolution, which allows for the fabrication of even smaller structures. For example, an IC chip in a smartphone available before 2019, the size of a thumbnail, could contain more than 2 billion transistors, with each transistor being less than 1 / 1000th the size of a human hair. Therefore, 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 can dramatically affect the functionality of the final product. In certain situations, 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, to achieve a 75% yield for a process with 50 steps (where a step may indicate the number of layers formed on a wafer), each individual step must have a yield of more than 99.4%. If each individual step has a yield of 95%, the overall process yield is a low 7%.

[0013]

[0023] In IC chip manufacturing equipment, while a high process yield is desirable, it is also essential to maintain a high substrate (i.e., wafer) throughput defined as the number of substrates processed per hour. High process yield and high substrate throughput can be affected by the presence of defects. This is especially true when operator intervention is required to investigate the defects. Therefore, high-throughput detection and identification of microscale and nanoscale defects by an inspection system (such as a scanning electron microscope ("SEM")) are essential to maintain high yield and low cost.

[0014]

[0024] An SEM includes a scanning device and a detector device. The scanning device includes an illumination 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 primary electrons. Together, at least the illumination device or illumination 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 when the sample is scanned so that the SEM can generate an image of the scanned area of the sample. For high-throughput inspection, a part of the inspection device uses a plurality of focused beams of primary electrons, i.e., a multi-beam. The component beams of the multi-beam can be referred to as sub-beams or beamlets. The multi-beam can scan different parts of the sample simultaneously. Therefore, a multi-beam inspection device can inspect a sample much faster than a single-beam inspection device.

[0015]

[0025] Embodiments of known multi-beam inspection devices will be described below.

[0016]

[0026] The figures are schematic. Accordingly, the relative dimensions of the components in the drawings are exaggerated for clarity. 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 between individual embodiments are described. The description and the drawings are directed to an electron optical device, but it is understood that the embodiments are not used to limit the present disclosure to specific charged particles. Accordingly, throughout this specification, references to electrons can be considered more generally as references to charged particles, which are not necessarily electrons.

[0017]

[0027] Refer to FIG. 1, which is a schematic diagram showing an exemplary charged particle beam inspection apparatus 100, which may also be referred to herein as a charged particle beam evaluation system or simply an evaluation system. The charged particle beam inspection apparatus 100 of FIG. 1 includes a main chamber 10, a load lock chamber 20, an electron beam apparatus 40, an equipment front end module (EFEM) 30, and a controller 50. The controller may be distributed among different components of the evaluation system, including, for example, within the electron beam apparatus 40. The electron beam apparatus 40 is located within the main chamber 10.

[0018]

[0028] The EFEM 30 includes a first loading port 30a and a second loading port 30b. The EFEM 30 may include one or more additional loading ports. The first loading port 30a and the second loading port 30b can receive, for example, a front-opening unified pod (FOUP) that houses a substrate (e.g., a semiconductor substrate or a substrate made of other materials) or a sample to be inspected (hereinafter, the substrate, wafer, and sample are collectively referred to as "sample"). One or more robot arms (not shown) within the EFEM 30 carry the sample to the load lock chamber 20.

[0019]

[0029] The loading lock chamber 20 is used to remove gas from the sample. This creates a vacuum, which is a local gas pressure lower than the ambient pressure. The loading lock chamber 20 may be connected to a loading lock vacuum pump system (not shown), which removes gas particles from within the loading lock chamber 20. The operation of the loading lock vacuum pump system allows the loading lock chamber to reach a first pressure below atmospheric pressure. After reaching the first pressure, one or more robotic arms (not shown) carry the sample from the loading 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 gas particles from within the main chamber 10 so that the pressure around the sample reaches a second pressure below the first pressure. After reaching the second pressure, the sample is carried to an electron beam apparatus, which can then examine the sample. The electron beam apparatus 40 may include a multibeam electron optics apparatus.

[0020]

[0030] The controller 50 is, for example, electronically signal-connected to the electron beam apparatus 40 as a distributed component of the controller 50. The controller 50 may be a processor (such as a computer) configured to control the charged particle beam inspection apparatus 100. The controller 50 may also include processing circuits configured to perform various signal and image processing functions. In Figure 1, the controller 50 is shown as an external component of the structure including the main chamber 10, the loading lock chamber 20, and the EFEM 30, but it is understood that the controller 50 may be part of the structure. The controller 50 may be located inside one of the component elements of the charged particle beam inspection apparatus, or the controller 50 may be distributed across at least two of the component elements. While this disclosure provides an example of a main chamber 10 housing an electron beam inspection apparatus, it should be noted that aspects of this disclosure are not, in a broad sense, limited to chambers housing electron beam inspection apparatus. Rather, it is understood that the principles described above may also apply to other apparatuses and other arrangements of apparatus operating under a second pressure.

[0021]

[0031] Referring now to Figure 2, this is a schematic diagram representing an exemplary electron beam apparatus 40. The electron beam apparatus 40 may be provided as part of the exemplary charged particle beam inspection system 100 shown in Figure 1. The electron beam apparatus 40 includes an electron source 201 and a charged particle column (or device) 230. The charged particle device 230 may be called a projection device for guiding the primary charged particle beam 202 toward the sample 208, or may include it. The electron source 201 and its associated components, the charged particle optical components, may be called an illumination device for generating the primary charged particle beam 202. The apparatus includes a sample support for supporting the sample 208. In this example, the sample support 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 an electric stage or actuation stage 209. The electron beam apparatus 40 further includes a detector 240. Detector 240 detects signal-charged particles (e.g., electrons) from sample 208. When detector 240 detects signal-charged particles, it generates a detection signal.

[0022]

[0032] 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 a primary electron beam 202.

[0023]

[0033] The charged particle device 230 is configured to convert the primary electron beam 202 into multiple charged particle beams 211, 212, and 213, and guide each beam onto the sample 208. Although three beams are shown for simplicity, tens, hundreds, thousands, tens of thousands, or even hundreds of thousands (or more) beams may exist. Beams may be called beamlets or subbeams. Multiple charged particle beams may be collectively called multibeams or beam gratings. A beam grating with so many beams (e.g., more than a thousand beams) may have a field of view greater than 0.5 mm, for example, in the range of 0.5 to 30 mm or 1 to 30 mm, for example, in the range of 0.5 to 15 mm.

[0024]

[0034] The controller 50 (for example, a control system including distributed controllers) may be connected to various parts of the charged particle beam inspection apparatus 100 in Figure 1, such as the electron source 201, the electron detection device 240, the charged particle device 230, and the operating 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 apparatus 100, including the operation of the electron beam apparatus 40.

[0025]

[0035] The charged particle device 230 may be configured to focus, for example, beams 211, 212, and 213 onto the sample 208 for inspection, thereby forming 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 individual scanning areas within sections of the surface of the sample 208. In response to the incidence of the primary beams 211, 212, and 213 onto the probe spots 221, 222, and 223 on the sample 208, electrons, including secondary and backscattered electrons which may be called signal charged particles, are generated from the sample 208. Secondary electrons typically have an electron energy of 50 electron volts (≤50 eV), while backscattered electrons typically have an electron energy between 50 electron volts (50 eV) and the landing energies of the primary beams 211, 212, and 213.

[0026]

[0036] The detector 240 sends the detection signal it generates, for example, as an image signal or detection signal to the controller 50 or a signal processing system (not shown, which may be part of the controller 50) to construct, for example, an image of the corresponding scanned region of the sample 208. The detector 240 may be at least partially incorporated into or separated from the charged particle device 230, for example, a second optical column may guide secondary electrons to the detector 240.

[0027]

[0037] The controller 50 may include an image processing system including an image acquirer (not shown) and a storage device (not shown). For example, the controller may include a processor, computer, server, mainframe host, terminal, personal computer, any type of mobile computing device, or a combination thereof. The image acquirer may include at least some of the processing functions of the controller. Therefore, the image acquirer may include at least one or more processors. The image acquirer may be communicatively coupled to a detector 240 that enables signal communication, such as a conductor, optical fiber cable, portable storage medium, IR, Bluetooth, the internet, wireless network, wireless radio, or a combination thereof. The image acquirer can receive a detection signal from the detector 240, process the data contained in the signal, and construct an image from it. Therefore, the image acquirer can acquire an image of sample 208. The image acquirer can also perform various post-processing functions, such as contour generation and superimposition of indicators onto the acquired image. The image acquirer may be configured to adjust the brightness and contrast of the acquired image. Storage can be a storage medium such as a hard disk, flash drive, cloud storage, random access memory (RAM), or other types of computer-readable memory. Storage may be combined with an image acquisition device and used to store scanned raw image data as the original image, or to store post-processed images.

[0028]

[0038] The image acquirer may acquire one or more images of sample 208 based on the imaging signal received from detector 240. The imaging signal may correspond to a scanning operation for imaging charged particles. The acquired image may be a single image containing multiple imaging areas. The single image may be stored in a storage device. The single image may be a source image that can be divided into multiple regions. Each of these regions may contain one imaging area containing features of sample 208. The acquired image may contain multiple images of a single imaging area of ​​sample 208 sampled multiple times over a period of time. These multiple images may be stored in a storage device. The controller 50 may be configured to perform image processing steps using multiple images of the same location of sample 208.

[0029]

[0039] The controller 50 may include a measurement circuit (e.g., an analog-to-digital converter) to obtain the distribution of detected secondary electrons. Part of the controller for such functions may be contained within or adjacent to the detector. The electron distribution data collected during the detection time window may be used in combination with the corresponding scanning path data of the primary beams 211, 212, and 213 incident on the sample surface to reconstruct an image of the sample structure under inspection. The reconstructed image may be used to reveal various features of the internal or external structure of the sample 208. Thus, the reconstructed image may be used to reveal any defects that may be present in the sample.

[0030]

[0040] The controller 50 may, for example, control the working stage 209 to move the sample 208 during inspection of the sample 208 in order to provide scanning motion of the stage relative to the path of the primary beam. The controller 50 may enable the working stage 209 to move the sample 208 in a certain direction, such as a part of the scanning motion of the stage, preferably at a constant speed, at least during the inspection of the sample. The controller 50 may control the movement of the working stage 209 so that the working stage 209 changes the moving speed of the sample 208 according to various parameters. For example, the controller may control the stage speed (including its direction) according to the characteristics of the inspection step and / or the scanning of the scanning process, as disclosed, for example, in European Patent Application Publication A21171877.0 filed on 3 May 2021, which is incorporated herein by reference, at least with respect to strategies combining the stepping and scanning of the stage. In controlling the working stage, the movement of the stage, and therefore the movement of the sample, may enable, for example, dynamic positioning of the sample relative to the path of the primary beam.

[0031]

[0041] Figure 3 is a schematic diagram of an exemplary electro-optical device 41 (which may also be called a charged particle device) used in the evaluation apparatus. For simplicity of illustration, the lens array is schematically depicted herein by an elliptical array. Each ellipse represents one of the lenses in the lens array. The elliptical shape is conventionally used to represent lenses by analogy to the biconvex shape often employed in optical lenses. It should be understood that, in relation to electro-optical devices such as those discussed herein, the lens array does not necessarily require any physical elements employing a biconvex shape, as it typically operates electrostatically. As will be described below, the lens array may instead include multiple plates having apertures. Each plate having an aperture may be called an electrode. The electrodes may be provided in series along the paths of multiple charged particle beams (which may also be called subbeams) in the beam grating. Thus, the electrodes are also in series along the paths of the charged particle beams in the beam grating.

[0032]

[0042] The electron source 201 directs electrons toward an array of focusing lenses 231 that form part of the electron-optical device 41. The electron source 201 is preferably a high-brightness heat field emitter having a good compromise between brightness and total emission current. Dozens, hundreds, thousands, or even tens of thousands of focusing lenses 231 may be present. The array of focusing lenses 231 may include multi-electrode lenses and may have a structure based on European Patent Application Publication 1602121A1, which incorporates herein by reference a disclosure of a lens array for splitting an electron beam into multiple sub-beams (providing one lens for each sub-beam). The focusing lens array may take the form of at least two (preferably three) plates that act as electrodes, and apertures in each plate are aligned with apertures in other plates to define the path of a charged particle beam through the plate. At least two of the plates are maintained at different potentials during operation to achieve a desired lensing effect. Between the plates of the focusing lens array are electrically insulating plates, for example, made of an insulating material such as ceramic or glass, which have one or more apertures for the charged particle beam. In addition or alternatively, one or more plates may feature apertures, each having its own electrodes, arranged, for example, with an array of electrodes around it or as a group of apertures having a common electrode. In a variant, one or more plates may include multiple parts or strips having multiple apertures. In a further alternative configuration, a macrocollimator is provided instead of the focusing lens array. The macrocollimator acts on the beam from the electron source 201 before the beam is split into multiple beams. The macrocollimator may be implemented magnetically, electrostatically, or magnetically and electrostatically.

[0033]

[0043] In some embodiments, the focusing lens array is formed from three plate arrays, in which charged particles have the same energy when entering and exiting each lens, and this configuration may be called an Einzel lens. Thus, dispersion occurs only within the Einzel lens itself (between the inlet and outlet electrodes of the lens), thereby limiting off-axis chromatic aberration. When the thickness of the focusing lens is thin, for example a few millimeters, the effect of such aberration is small or negligible.

[0034]

[0044] Each focusing lens in the array directs electrons into their respective beams 211, 212, and 213, which are focused at their respective intermediate focal points 233. A collimator or array of collimators may be positioned to operate on each intermediate focal point 233. The collimator may take the form of a deflector 235 located at the intermediate focal point 233. The deflector 235 is configured to bend each beam 211, 212, and 213 by an effective amount to ensure that the principal ray (also called the beam axis) is incident on the sample 208 nearly perpendicularly (i.e., at approximately 90° with respect to the nominal surface of the sample). Note that in configurations with macro-focusing lenses, the focusing lenses may perform or contribute to the collimation of the source beam or, in one embodiment, multiple beams.

[0035]

[0045] The objective lens array 401 is located on the downbeam side of the deflector 235. The objective lens array 401 includes objective lenses for each beam 211, 212, and 213. The objective lens array 401 projects beams 211, 212, and 213 onto the sample 208. The objective lens array 401 may include two or more, preferably at least three, plate electrode arrays connected to their respective potential sources.

[0036]

[0046] Optionally, a control lens array 250 is provided between the deflector 235 and the objective lens array 401. The control lens array 250 includes control lenses for each beam 211, 212, and 213. The control lens array 250 provides additional degrees of freedom for controlling the characteristics of beams 211, 212, and 213. The control lens array 250 may include two or more, preferably at least three, plate electrode arrays connected to their respective potential sources. The function of the control lens array 250 is to optimize the beam opening angle with respect to the beam reduction ratio and / or control the beam energy delivered to the objective lenses, each of which guides its respective beam 211, 212, and 213 onto the sample 208. In one embodiment, the control lens array may be considered part of the objective lens, for example, as an additional plate associated with the objective lens array.

[0037]

[0047] Optionally, an array of scanning deflectors 260 is provided between the control lens array 250 and the objective lens array 401. The array of scanning deflectors 260 includes scanning deflectors for each beam 211, 212, and 213. Each scanning deflector is configured to deflect each beam 211, 212, and 213 in one or two directions to scan the beam in one or two directions across the entire sample 208. Alternatively, a macro scanning deflector may be provided for scanning a charged particle beam over the sample 208. The macro scanning deflector may be located on the up-beam side of the control lens array 250. In one embodiment, such a macro scanning deflector may act on the source beam and may be present with a macro focusing lens.

[0038]

[0048] The detector module 402 of the detector is located within the objective lens or between the objective lens and the sample 208 to detect signal electrons / particles from the sample 208. An exemplary structure of such a detector module 402 is described below. Note that the detector may also have detector elements on the up-beam side along the primary beam path of the objective lens array 401 or further of 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 an individual beam and positioned to detect, for example, signal particles generated by an individual beam. The detector module may include at least one of a scintillator element, a semiconductor element, or a charge trapping electrode to capture signal electrons as an electric current, for example.

[0039]

[0049] The electron-optical device 41 in Figure 3 may be configured to control the landing energy of electrons on the sample 208 by changing the potential applied to the electrodes of the control lens and objective lens. The electrodes include a plate and may be called a plate or electron-optical plate. The control lens and objective lens work together and may be called an objective lens assembly. The landing energy can be selected to increase the emission and detection of secondary electrons depending on the properties of the sample being evaluated. The detector module may be included in the objective lens assembly.

[0040]

[0050] The objective lens may be configured to reduce the electron beam by a coefficient greater than 10, preferably in the range of 50 to 100 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 with only two electrodes may have lower aberrations than an objective lens with more electrodes. A three-electrode objective lens may allow for a more powerful lens because it has a larger potential difference between the electrodes. Additional electrodes (i.e., three or more electrodes) provide additional degrees of freedom for controlling the electron trajectory, for example, to focus not only secondary electrons but also the incident beam.

[0041]

[0051] In some embodiments, the objective lens array assembly includes a detector having a detector module 402 on the down-beam side of at least one electrode of the objective lens array 401. The detector module 402 may include or further 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 with the lowest electrode of the objective lens array 401. Integration of the detector module 402 with the objective lens array may replace a secondary column. The CMOS chip is preferably oriented to face the sample (e.g., 10 to 400 micrometers, preferably 50 to 200 micrometers, optionally about 100 micrometers, due to the small distance between the sample and the bottom of the electron-optical system). It should be noted that even when the detector is located on the up-beam side of the most down-beam side electron-optic element of the charged particle device, the separation distance between the most down-beam side electron-optic element and the sample (e.g., about 100 micrometers) can be close, for example, a similar distance. In one embodiment, electrodes for capturing signal-charged particles are formed in the top metal layer of the CMOS device. The electrodes may be formed in other layers of the substrate (e.g., of the CMOS chip). Power and control signals of the CMOS may be connected to the CMOS by through-silicon vias. For robustness, preferably, the bottom electrode consists of two elements: a CMOS chip and a passive silicon plate with holes. The plate shields the CMOS from high electric fields.

[0042]

[0052] In one embodiment, a single electrode surrounds at least some of the apertures. In one configuration, the single electrode is assigned, for example, around each aperture. In another embodiment, multiple electrode elements are provided around each aperture, for example, as detector elements. Signal-charged particles captured by electrode elements surrounding one aperture can be combined into a single detection signal or used to generate independent detection signals. The electrode elements can be divided radially (i.e., to form multiple concentric rings), angularly (i.e., to form multiple fan-shaped sections), both radially and angularly (to provide a configuration like a dirt board), or in a grid (e.g., like a chessboard), or in any other convenient way.

[0043]

[0053] An exemplary embodiment of a detector integrated with an objective lens array 401 is shown in Figure 4, which shows a schematic cross-sectional view of a portion of the objective lens array 401. In this embodiment, the detector preferably includes a detector module 402 that includes a plurality (e.g., arrays) of detector elements 405 (e.g., sensor elements such as capture electrodes) as an array of detector elements (i.e., a plurality of detector elements in a pattern or arrangement over the entire two-dimensional plane), as shown in Figure 5. In this embodiment, the detector module 402 is located 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 (capture electrodes 405) are provided, each surrounding a beam aperture 406. The beam aperture 406 may be formed by etching the substrate 404. In the configuration shown in Figure 5, the beam aperture 406 is shown as a rectangular array. The beam aperture 406 can also be arranged in a different way (for example, a close-packed hexagonal array as depicted in Figure 6).

[0044]

[0054] The integrated detector module 402 described above is particularly advantageous when used with an evaluation device (e.g., including an electro-optical device) having adjustable landing energy, because secondary electron capture can be optimized for a certain range of landing energy. Detector modules having or in the form of arrays can be integrated not only with the lowest electrode array but also with other electrode arrays. Further details and alternative configurations of detector modules integrated with objective lenses can be found in European Patent Application Publication No. 20184160.8, which is incorporated herein by reference.

[0045]

[0055] The power supply may be provided to apply the respective potentials to, for example, the electrodes of the control lenses of the control lens array 250, the electrodes of the objective lenses of the objective lens array 401, and the electrodes of the focusing lenses of the focusing lens array, or to any of the electro-optic elements or components of the electro-optic device 41, such as a detector module (for example, if it is integrated with the objective lens array or if the objective lenses and the detector module are separate components). The controller 50 can control the potentials applied to the electro-optic components such as the electrodes of the focusing lens array, the objective lens array, and / or the control lens array.

[0046]

[0056] The electro-optical device 41 may include other electro-optical components, such as charged particle correctors, as a corrector array for, for example, aligning electron sources with respect to a sample or aligning multiple beams and adjusting the focus of different groups of beam gratings or individual beams of a beam grating. Such correctors may be controlled to operate dynamically and / or statically, for example, during setup, maintenance, or calibration of the electro-optical device 41.

[0047]

[0057] In one embodiment, an array of electron-optical devices (or device array) is provided. The array may include any multiple of the electron-optical devices described herein (e.g., electron-optical columns or charged particle devices). Each electron-optical device in the array focuses each of the multiple charged particle beams onto different regions of the same sample 208. Each electron-optical device in the array may derive each of the multiple charged particle beams from different electron sources 201. Each electron source 201 may be one of multiple electron sources 201. At least a subset of multiple electron sources 201 may be provided as an electron source array. The electron source array may include multiple emitters on a common substrate. By simultaneously focusing multiple charged particle beams from different electron-optical devices onto different regions of the same sample, a wider area of ​​the sample 208 can be simultaneously exposed to the charged particle beams. Thus, a wider area of ​​the sample can be processed (e.g., evaluated) at once. To project each of the multiple beams onto adjacent areas of sample 208, the electron-optical devices in the device array may be arranged adjacent to one another. Any number of electron-optical devices may be used in the array. Preferably, the number of electron-optical devices is in the range of 9 to 200. When referring to a single electron-optical device, charged particle device, system, or column, each electron-optical device in the device array may be configured in any of the methods described herein. Alternatively or in addition, one or more electron-optical devices in the array may be configured to project a single beam.

[0048]

[0058] Figure 7 schematically shows a further example of the electro-optical device 41. The same features as described above are given the same reference numbers. For simplicity, such features are not described in detail with respect to Figure 7. For example, the electron source 201, focusing lens 231, objective lens array 401 and sample 208 (e.g., on sample support 207) may be as described above. In this example, a macrocollimator 270 is provided instead of the type of deflector array described above with reference to Figure 3. Such a macrocollimator may be a macrolens that is magnetic, electrostatic, or both. In other embodiments, a deflector array may be used to contribute at least to beam collimation, and thus the deflector array is for finer deflection in the collimation direction than the operation of the macrocollimator 270. Such a configuration may also include an array of multiple deflectors for even finer collimation (e.g., each aperture has multiple electrodes). In one configuration, the focusing lens 231 may include a single plate that defines a beam-limiting aperture array, with multiple apertures defined within the single plate and one or more macroelectrodes associated with each aperture. Such a beam-limiting aperture array and associated macroelectrodes can also form a focusing lens array to focus the generated beam to an intermediate focal point, preferably corresponding to the position of the collimator 270.

[0049]

[0059] As described above, in some embodiments, a detector may be provided between the objective lens array 401 and the sample 208. The detector may face the sample 208. Alternatively, as shown in Figure 7, the detector 240 may be implemented such that the objective lens array 401 is located between the detector 240 and the sample 208.

[0050]

[0060] In one embodiment, the deflector array 95 is located between the detector 240 and the objective lens array 401. In one embodiment, the deflector array 95 includes a Wien filter array, and therefore the deflector array 95 may be called a beam separator. The deflector array 95 is configured to provide a magnetic field and an electrostatic field. The electrostatic and magnetic fields act together to separate charged particles projected onto the sample 208 from signal particles, such as electrons from the sample 208. Due to the action of the fields, the signal particles are guided toward the detector 240.

[0051]

[0061] In one embodiment, the detector 240 is configured to detect signal particles by reference to the energy of charged particles, i.e., according to the band gap in such semiconductor-based detectors. Such a detector 240 may be called an indirect current detector. Secondary electrons emitted from the sample 208 gain energy from the field between the electrodes. The secondary electrons have sufficient energy to reach the detector 240. In a different configuration, the detector 240 may be, for example, an electron-photon converter of an inter-beam fluorescence strip located on the up-beam side along the main beam path with respect to a Wien filter, such as a scintillator array. The main beam passing through the Wien filter array (of magnetic and electrostatic strips orthogonal to the main beam path) has a path substantially parallel to the up-beam and down-beam sides of 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 is optically coupled to a photon-electron converter so that it can convert any photons produced in the electron-photon converter and emitted by the electron-photon converter. The photon-electron converter may be electrically connected to an electronic circuit for processing the detection signal. In different embodiments, the photon-electron converter may be located inside or outside the charged particle device. In one embodiment, photon coupling may occur to a remote photodetector via a photon transport unit (e.g., an array of optical fibers), which generates a detection signal when it detects a photon.

[0052]

[0062] Figure 8 is a schematic diagram of a further exemplary electron-optical device 41 used in the evaluation apparatus. The electron-optical device 41 may be used in place of any of the electron-optical devices 41 described above, or in combination with any of the embodiments described herein, for example, with reference to Figure 3 and / or Figure 7. In this example, the electron-optical device 41 includes an electron source 201, a beamforming aperture array 502, a focusing lens 504, an electron source conversion unit 506, an objective lens 508, and a sample 208. The electron source 201 and sample 208 may take any of the forms described above, for example, with reference to Figures 2, 3 and 7. The electron source 201, beamforming aperture array 502, focusing lens 504, electron source conversion unit 506, and objective lens 508 may be aligned to the primary electron-optical axis 510 of the charged particle device 41. The electron source 201 generates a primary electron beam 512 using an electron source crossover 514. The beamforming aperture array 502 forms beams 521, 522, and 523 from the primary beam 512. Although a line of three beams is shown, the beamforming aperture array 502 may be configured to form a line of two beams or more than three beams, for example, a line of four beams or a line of five beams. The beamforming aperture array 502 may also be configured to form multiple lines of beams, thereby forming an array of beams. For example, the beamforming aperture array 502 may be configured to form an n × m array of beams, where n and m are integers that may be the same or different, for example, a 3 × 3 array of beams, a 4 × 4 array of beams, or a 5 × 5 array of beams.

[0053]

[0063] The focusing lens 504 may be configured to redirect the paths of beams 521, 522, and 523 so that they are substantially parallel to each other and / or incident substantially perpendicular to the electron source conversion unit 506. The focusing lens 504 may be a macromagnetic lens configuration, such as two lenses, with multiple lenses set to a non-rotating configuration (where the rotational effects of lenses with different lens configurations cancel each other out, or their net rotational effect on the beam path is substantially zero).

[0054]

[0064] The electron source conversion unit 506 may include a beam limiting aperture array 531 that defines apertures configured to limit beams 521, 522, and 523 laterally. The beam limiting aperture array 531 can shape, for example, one or more of beams 521, 522, and 523 to split the beam into two or more beams toward, for example, the sample on the downbeam side of the beam limiting aperture array 531.

[0055]

[0065] The electron source conversion unit 506 may include an array of electron-optical components for acting on each beam or beam group of multiple beams. The electron source conversion unit 506 may include an image forming element array 532 which includes an array of micro-deflectors configured to deflect beams 521, 522, and 523 toward axis 510. The deflected beams 521, 522, and 523 may form a virtual image of the electron source crossover 514 on the sample 208.

[0056]

[0066] The electron source conversion unit 506 may include an aberration compensator array 534 configured to compensate for aberrations in beams 521, 522, and 523. The aberration compensator array 534 may be configured, for example, to compensate for field curvature and / or astigmatism.

[0057]

[0067] The electron source conversion unit 506 may include a pre-bending micro-deflector array 533 configured to bend the paths of the up-beam beams 521, 522, and 523 on the beam-limiting aperture array 531 so that the paths of the beams 521, 522, and 523 are incident substantially perpendicularly onto the beam-limiting aperture array 531.

[0058]

[0068] The image forming element array 532, the aberration compensator array 534, and / or the pre-bending micro-deflector array 533 may include multiple layers of sub-beam manipulating devices, some of which may be in the form of arrays, such as micro-deflectors, microlenses, and / or micro-astigmatism correctors.

[0059]

[0069] In the illustrated example, the objective lens 508 includes a magnetic lens that acts macroscopically on the beam to focus it onto the sample 208. In other embodiments, the objective lens 508 may include an electrostatically realized objective lens array, or a combination of magnetic and electrostatic lenses, such as a macro magnetic objective lens with an electrostatic element, may be used.

[0060]

[0070] Figure 9 shows an electro-optic module 55. The electro-optic module 55 may include an electro-optic stack. The electro-optic stack includes a plurality of electro-optic plates 60. The electro-optic stack may form part of any of the electro-optic devices 41 disclosed herein, as described with reference to, for example, Figures 3, 7, and 8. The electro-optic stack may be provided as part of an evaluation device for evaluating a sample. The electro-optic stack may be an electro-optic lens assembly or may form part of an electro-optic lens assembly. The electro-optic lens assembly may include an objective lens array or assembly, or a focusing lens array or assembly, or may be an objective lens array or assembly, or a focusing lens array or assembly. In addition or alternatively, the electro-optic stack may be, or form part of, one or more elements of, for example, collimators, correctors such as individual beam correctors, detector arrays, deflectors, and / or Wien filter arrays, each as an array. For example, in the embodiment shown in and described with reference to Figure 3, the stack 55 may include a detector module 402, an objective lens array 401, and a control lens array 250. In the embodiment shown in and described with reference to Figure 8, the stack may include at least a portion of an electron source conversion module 506. That is, the electron-optical module 55 may include the electron source conversion module 506, or may even be the electron source conversion module 506.

[0061]

[0071] The electron-optical module 55 is configured to guide charged particles toward the sample position along at least one beampath. In the orientation shown in Figure 9, at least one beampath extends vertically from top to bottom through the center of the electron-optical stack. There may be one beampath corresponding to one charged particle beam. Alternatively, there may be multiple beampaths corresponding to multiple charged particle beams in a multi-beam system.

[0062]

[0072] As shown in Figure 9, in one embodiment, the electron-optic module 55 includes a plurality of planar elements arranged across the beampath. In one embodiment, one or more of the planar elements are electron-optic plates 60 (which may also be called electron-optic elements). The electron-optic plates 60 are configured to act on one or more electron beams. As shown in Figure 9, in one embodiment, all the planar elements are electron-optic plates 60. Alternatively, one or more of the planar elements may be planar elements other than electron-optic plates. For example, one or more of the planar elements may be elements that do not require a voltage to be applied to the planar element in order to perform their function, or the planar elements may require a voltage to be applied to the planar element such that the potential difference between the element and adjacent elements along the beampath is substantially zero. One example is a planar element that is a beam-limiting aperture array containing apertures sized to shape a charged particle beam. For example, the apertures may allow a charged particle beam of a particular shape to pass through, while preventing other charged particles from propagating through the beam-limiting aperture array. As a further alternative, planar elements configured to shape a charged particle beam may also have a potential difference with respect to the up-beam and / or down-beam planar elements so that the electromagnetic field influences the charged particle beam in addition to its beam-shaping function. In one embodiment, one or more planar elements may be detectors, such as a detector array.

[0063]

[0073] As shown in Figure 9, in one embodiment, the electro-optic module 55 includes one or more spacers 70. The spacers 70 are configured to mechanically support planar elements. As shown in Figure 9, in one embodiment, the spacers 70 are configured to mechanically separate planar elements such as electro-optic plates 60 from each other. In one embodiment, the spacers 70 are configured to electrically insulate planar elements such as electro-optic plates 60 from each other. However, it is not essential that the spacers 70 provide electrical insulation. For example, two adjacent electro-optic plates 60 may be arranged to operate at the same voltage (i.e., there is no potential difference between them), in which case electrical insulation may not be necessary. In one embodiment, one or more pairs of adjacent planar elements are joined directly to each other, i.e., without intermediate spacers 70. The spacers 70 are an optional feature.

[0064]

[0074] In one embodiment, the electro-optical module 55 is configured such that a charged particle beam passes through the beam area 62 of the electro-optical module 55. As shown in Figure 9, the beam area 62 may be located in the central portion of the electro-optical module 55. The beam area 62 is located approximately in the center when viewed in a direction parallel to at least one beam path. The beam area 62 is located in the center when viewed from a direction perpendicular to the plane of the planar element. Note that in one embodiment, one or more of the plates 60 may be a single macro-aperture. Such a macro-aperture may be positioned to correspond to the beam area of ​​another plate of plate 60. Such a stack with a macro-aperture may be or include a focusing lens array 231, as shown in and described with reference to Figures 3 and 7. In one configuration, one or more of the plates 60 may include multiple apertures (or a central aperture) corresponding to groups of beam paths within the beam area. A stack containing one or more plates with a central aperture may include a Wien filter array 95.

[0065]

[0075] In one embodiment, the electro-optical module 55 is included in the electro-optical device 41, for example, as shown in Figures 3, 7, or 8. In one embodiment, the electro-optical module 55 is field-replaceable. The electro-optical module 55 can be removed from and / or inserted into the electro-optical device 41 without requiring substantial disassembly of the other parts of the electro-optical device 41. That is, the electro-optical module 55 can be removed from and / or inserted into the electro-optical device 41.

[0066]

[0076] As described above, electro-optical elements such as plate 60 can be configured to act as electrodes, for example, as part of an objective lens array. Geometric features of plate 60 allow a charged particle beam to pass through plate 60. Such features are channels penetrating plate 60 and apertures defined on the surface of the plate. Apertures can be defined by the openings of each channel on the surface. Channels (which may be called through-holes) can connect different apertures on opposite surfaces of the plate. An electric field adjacent to an aperture associated with a channel can give a lensing effect to the charged particle. In some configurations, apertures can be adapted to compensate for off-axis aberrations in multi-beams, such as distortion, focal curvature, astigmatism, and coma aberration. For example, the apertures of one or more electrodes can be shaped, sized, and / or positioned to compensate for off-axis aberrations. The aperture may have, for example, a range of different areas (or diameters) for compensating for field curvature, a range of different ellipticities for compensating for astigmatism, and / or a range of different displacements from the nominal grid position for compensating for distortion caused by telecentricity errors. For example, with respect to off-axis aberration correction, see, European Patent Application Publication A21166214.3, filed on 31 March 2021, which is incorporated herein by reference.

[0067]

[0077] The performance of electro-optical elements can be highly sensitive to variations in aperture characteristics, such as aperture shape, size, and / or position, especially when these features are intentionally configured to compensate for aberrations.

[0068]

[0078] As mentioned in the introduction to this description, manufacturing errors in the electro-optical plate 60 can affect the electro-optical performance of the plate. Such errors may be unexpected structural features that occur during the manufacturing process steps. Small perturbations to the nominal shape of the aperture can result in large aberrations in the charged particle beam passing through the aperture. The effect of the perturbation is amplified by the strongly curved field near the aperture. Such perturbations can be up to two orders of magnitude larger than compensation intentionally applied to the aperture, for example, to compensate for off-axis aberrations. However, such perturbations are often expected to be smaller than the magnitude of compensation applied to the aperture.

[0069]

[0079] Features in the electro-optical plate 60 can be manufactured using techniques from micro-electromechanical systems (MEMS) (i.e., using MEMS manufacturing techniques). While these manufacturing techniques produce small structures with high precision, they are prone to imperfections, for example, with respect to the intended design. Some of such imperfections can be induced by the processing steps used. The inventors have noticed that techniques for forming channels through the plate can result in slight differences in the shape of apertures defined at the ends of the channels (or apertures on the plate surface through which the channels extend, or apertures defined on opposite surfaces of the plate by the intersection of the channels and the opposite surfaces of the plate). This is particularly true when the channels have a relatively high aspect ratio (i.e., channels that are relatively long compared to the diameter of the channels, or the cross-sectional dimensions of the apertures, i.e., the distance between apertures on opposite surfaces relative to the cross-sectional dimensions of the channels at any point between the apertures). For example, such channels can be formed in the plate 60 by an etching process carried out from one side of the plate 60. In other words, the aperture is formed by etching a channel that penetrates the plate, for example, from one surface of the plate to the opposite surface. In such embodiments, the shape of the channel can be controlled with greater precision at the beginning of the channel (i.e., where the etching of the channel begins, for example, at the beginning aperture) than at the end of the channel (i.e., where the etching of the channel is completed, for example, at the end aperture). That is, the cross-sectional shape of the channel may change with increasing distance from the beginning aperture (e.g., the shape and / or size and / or orientation of the surface on which the beginning aperture is formed relative to a reference frame). As a result, the channel has apertures formed differently (e.g., different shapes, sizes and / or orientations) at each end. That is, two apertures (such as a beginning aperture and a end aperture) may have different shapes (e.g., different shapes, sizes and / or orientations).The inventors have observed that, if no countermeasures are taken or only insufficient countermeasures are taken, different shapes can cause undesirable aberrations in the charged particle beam. The embodiments described below aim to address this problem.

[0070]

[0080] Figure 10 shows an exemplary electron-optical stack 64 configured to manipulate multiple charged particle beams. Figure 11 shows a portion of the electron-optical stack 64 in the region of a single charged particle beam. The stack 64 includes multiple electron-optical plates 60. As described above with reference to Figure 9, the stack 64 may be part of an electron-optical module 55. The stack 64 and / or module 55 may take any of the forms described above with reference to Figure 9. Thus, the multiple plates 60 may be configured to allow at least adjacent plates 60 to be maintained at different potentials, for example, to produce a lensing effect. Therefore, adjacent plates may be electrically isolated from each other. In some embodiments, spacers 70 are provided between adjacent plates. The spacers 70 may electrically isolate and / or support adjacent plates 60.

[0071]

[0081] As shown in Figures 10 and 11, the multiple plates 60 have main surfaces 72A and 72B on both sides of the plate 60. Thus, each plate 60 has two main surfaces 72A and 72B. The main surfaces 72A and 72B are the widest surfaces of the plate 60. The main surfaces 72A and 72B are typically planar and / or have a much larger surface area than the other surfaces of the plate 60 (e.g., the sides of the plate). In the orientation of the stack 64 shown in Figures 10 and 11, each plate 60 has a main surface at the top of the plate 60 and a main surface at the bottom of the plate 60.

[0072]

[0082] The plate 60 defines, for example, one or more sets of channels 74 between the main surfaces of the plate. Thus, apertures on the main surfaces of the plate can define each channel that penetrates the plate. As shown in the figure, each set of channels 74 is configured to be aligned along the beam path of each charged particle beam. In the illustrated configuration, the channels and each beam path of a set of channels are substantially orthogonal to the planes of different plates 60 (however this is not necessarily true when beams are aligned to different channels). The alignment of the channels 74 in each set allows the charged particle beam to pass through the plate 60 through the channels 74 of that set. In embodiments configured to operate with a single charged particle beam, a corresponding single set of channels 74 may be provided. In embodiments configured to operate with multiple charged particle beams (which may be called beam gratings), multiple plates 60 can define multiple sets of channels 74 (or arrays of channels or channel gratings) for multiple corresponding paths (e.g., beam gratings) of different charged particle beams. Each set of channels 74 corresponds to each charged particle beam. As shown in the figure, the beam paths of the beam grating are collimated, and substantially all beam paths are perpendicular to the plane of the plate, such as one of the main surfaces of the plate, and the beam paths are parallel to the axis of the corresponding channel.

[0073]

[0083] For example, each channel 74 defines apertures 76A and 76B on two main surfaces 72A and 72B of the plate 60 that define the channel 74. Thus, in the example in Figures 10 and 11, six apertures are defined along each of the beam paths penetrating the plate 60. Two apertures 72A and 72B are associated with each channel 74. The apertures 72A and 72B defined by each channel 74 have different shapes from each other. The different shapes can consist of nominal shapes and perturbed shapes. A perturbed shape can be a perturbed version of a nominal shape. In the example in Figures 10 and 11, aperture 76B with a perturbed shape is schematically shown in bold.

[0074]

[0084] The difference between the nominal shape and the perturbed shape may be relatively small. For example, with respect to an axis perpendicular to the plane of plate 60 and passing through the geometric center of the aperture, the average azimuth angle variation of the radius of an aperture with a perturbed shape may represent less than 10%, optionally less than 5%, or optionally less than 1% of the average or absolute radius of the corresponding nominal shape. For example, if the nominal shape is a perfect circle, the perturbed shape may have an average azimuth angle variation of radius of less than 10%, optionally less than 5%, or optionally less than 1%. In one embodiment, within each set of channels 74, apertures 76A (or simply apertures with nominal shape) with nominal shape are more similar in shape to each other than any of the apertures 76B (or apertures with perturbed shape) with perturbed shape. In addition, or instead, in one embodiment, within each set of channels 74, the apertures 76B having a perturbed shape (or perturbed apertures) are more similar in shape to each other than any of the apertures 76A having a nominal shape (or nominal apertures). For example, the nominal apertures may have substantially the same shape, the perturbed apertures may have substantially the same shape, and the nominal apertures and perturbed apertures may have substantially different shapes.

[0075]

[0085] In some embodiments, as described above, channels 74 defined in the plate 60 are obtained on each plate by an etching process. The etching process may result in apertures 76A and 76B of different shapes on the main surfaces 72A and 72B of the plate 60. The channels are etched such that the aperture shapes differ on the main surfaces on both sides of the plate. The channels 74 may be referred to as etched channels. Imperfections in the etching process may result in apertures of different shapes. It may be possible to reduce or eliminate the differences in shape by improving the etching process recipe, but this would be time-consuming and / or costly. Also, the impact of imperfections in the etching process can be significant as far as the formation of nominal shapes compared to the formation of perturbative shapes. The aperture at one end of the channel where etching begins may have a nominal shape, while the aperture at the other end of the channel (where etching is finished) may have a perturbative shape. For example, when etching a channel that penetrates a thick substrate (which may be called a "deep channel" or deep etching), it may be relatively difficult to etch the terminal aperture more accurately than the starting aperture. In other words, when etching the terminal aperture by such deep etching, it may be difficult to maintain the cross-sectional shape of the starting aperture, particularly as the cross-sectional shape of the channel with respect to the entire etching and / or channel depth (e.g., as the nominal shape), and as a result, the terminal aperture may have a perturbed shape.

[0076]

[0086] In one embodiment, the nominal shape is the same for two or more channels 74 of at least one set of channels, all of which are arbitrarily selected. The nominal shape may be, for example, a circle or an ellipse. The nominal shape is not particularly limited and is selected according to the electro-optical requirements of the stack 64. As described above, these requirements may include aberration correction. Aberration correction may be performed using apertures of different shapes for different charged particle beams. In one embodiment, such correction may be in the range of 0.1% to 1% of the aperture dimensions. Thus, the nominal shape may differ for two or more of the set of channels 74. Alternatively, or in addition, the nominal shape may be identical for two or more of the set of channels 74.

[0077]

[0087] In one embodiment, as illustrated in Figure 10, the plate 60 is oriented such that apertures 76A, 76B include one or more pairs of matched apertures along the beam path. Each pair of matched apertures consists of apertures 76A, 76B having the same shape defined on adjacent main surfaces 72A, 72B of adjacent plates 60. For example, if apertures 76A, 76B have either a nominal shape or a perturbed shape, each pair of matched apertures may include either a pair of apertures having a nominal shape or a pair of apertures having a perturbed shape. Those skilled in the art will understand that the term "matched aperture pair" implies substantially similar or even substantially identical shapes, rather than atomically identical shapes (which such a person will understand is impossible to achieve). The apertures in each matching aperture pair are consistent in the sense that they are of the same type (i.e., both are nominal shapes, or both are perturbed shapes with perturbations, preferably similar in size and / or orientation).

[0078]

[0088] Adjacent principal surfaces can be called opposing surfaces because they may face each other. Adjacent principal surfaces may be adjacent surfaces that are closer to each other than any other principal surface of plate 60. In the examples of Figures 10 and 11, the aperture labeled 76A on the principal surface labeled 72A has a nominal shape. Thus, these opposing surfaces have apertures with nominal shapes, and the nominal apertures on the opposing surfaces face each other. The aperture labeled 76B on the principal surface labeled 72B has a perturbed shape. A matched aperture pair consisting of a pair of perturbed apertures 76B is provided by the opposing principal surfaces 72B of the top plate 60 and the middle plate 60 in the illustrated stack 64. Thus, these opposing surfaces have apertures with similar perturbed shapes, and the perturbed apertures on the opposing surfaces face each other. A pair of aligned apertures, consisting of a pair of apertures 76A having a nominal shape, is provided by opposing main surfaces 72A of the central plate 60 and the bottom plate 60. The aligned apertures are located on the opposing surfaces. In one embodiment, at least one of the pair of aligned apertures consists of an aperture 76A having a nominal shape. In one embodiment, at least one of the pair of aligned apertures consists of an aperture 76B having a perturbed shape.

[0079]

[0089] As schematically shown by the exemplary lines of equal electric field strength (shown by dashed lines) in Figure 11, the effect of apertures on the opposing main surfaces of adjacent plates 60 on the electric field is opposite in sign. Therefore, the effect of perturbations in aperture shape on the electric field cancels out partially or completely if the perturbations are the same in both apertures. Thus, by oriented the plates 60 in a way that provides one or more matching pairs, adverse effects on the electron-optical performance that would otherwise occur due to differences in aperture shape at both ends of the channel 74 are suppressed or eliminated.

[0080]

[0090] The inventors have found that the perturbation shape includes a perturbation component that depends on the crystal symmetry of plate 60. The perturbation component may be the dominant component of the perturbation. In some embodiments, the perturbation shape includes a perturbation component having 2 or more rotational symmetries. In some embodiments, the perturbation shape includes a perturbation component having fewer than 10 rotational symmetries. In one embodiment, the perturbation component has 4 or multiples of 4 rotational symmetries. This has been found to be the case when plate 60 is made of silicon, essentially made of silicon, or contains silicon. In one embodiment, the perturbation component has 6 or multiples of 6 rotational symmetries. This can occur for different crystal orientations in plate 60. For example, if the silicon in plate 60 is oriented such that the main surface of plate 60 is perpendicular to the crystal direction, the crystal structure of plate 60 parallel to the plane has hexagonal symmetry and contributes to a perturbation component with 6 rotational symmetries. More generally, in one embodiment, the perturbation component has rotational symmetry determined by the crystal structure of the plate material, for example, the crystal orientation of the plate material. Therefore, such a perturbation component may depend, for example, on the number of symmetries of the main surface of the plate 60 and the crystal structure of the material, on the crystal orientation within the plate.

[0081]

[0091] In some embodiments, the apertures 76B of a matched aperture pair having a perturbed shape have substantially the same rotational orientation, for example, with respect to the beam path as the axis of rotation or to the direction perpendicular to the plane of the plate 60 as the axis of rotation (for example, when the beam path is angled obliquely to the plane). Thus, in any reference system of adjacent plates 60, the apertures are aligned in the rotational direction when viewed along the beam path. The apertures match not only in shape but also in orientation. By arranging the apertures to have the same rotational orientation, the cancellation of the effect of perturbation on the electric field is improved, and performance is improved.

[0082]

[0092] In some embodiments, as illustrated in Figures 10 and 11, the plurality of plates 60 define at least two matched aperture pairs along the same beam path. The plurality of plates 60 may include three adjacent plates 60 defining two matched aperture pairs along the same beam path. In such a configuration, the apertures of the two matched aperture pairs may have different shapes. That is, the aperture of one matched aperture pair of matched aperture pairs has a different shape (e.g., nominal shape) compared to the aperture of the other matched aperture pair of matched aperture pairs (e.g., having a perturbed shape). In one embodiment, the plurality of plates 60 are configured to operate as an Einzel lens.

[0083]

[0093] In one embodiment, a method for manufacturing an electron-optical stack 64 is provided. The stack 64 may take any of the forms described above with reference to Figures 9 to 11. The method involves etching channels 74 into each plate 60 of a plurality of plates 60. The etching process is such that apertures 76A, 76B defined at both ends of each channel 74 have different shapes. The method involves aligning a set of channels 74 along the beam path of a charged particle beam and positioning the plates 60 to allow the charged particle beam to pass through the channels. The plates 60 are arranged in such an orientation that one or more pairs of matched apertures are defined along the beam path. Each pair of matched apertures consists of apertures 76A, 76B having the same shape defined on adjacent main surfaces of adjacent plates.

[0084]

[0094] In preferred embodiments, a configuration in which the beam paths are collimated has been described, but this is not necessarily required; for example, the beam paths may diverge or converge (to be aligned with corresponding channels penetrating the plate). In a convergent or diverging beam grating, at least one of the beam paths is perpendicular to the plane of the plate. In one configuration, the beam paths may be controlled by electron-optic electrodes in one or more plates, such as a multipole array, and at least one of the surfaces and / or associated apertures of each channel in the plate includes a plurality of apertures that can be controlled to deflect the beam paths relative to each other.

[0085]

[0095] This description refers to channels that extend through the entire thickness of the plate, but such channels or grids of channels may be located in thinned areas of the plate. For example, one or both of the apertures of each channel in such channels or grids may be defined within recesses in the surface of the plate, and thus one or both of the main surfaces of the plate may be recessed.

[0086]

[0096] References that a component or system of components or elements can be controlled to manipulate a charged particle beam in a particular manner include configuring a controller or control system or control unit to control the component to manipulate the charged particle beam in the manner described, and optionally, using other controllers or devices (e.g., voltage and / or current) to control the component to manipulate the charged particle beam in this manner. For example, a voltage supply may be electrically connected to one or more components, including, for example, a control lens array 250, an objective lens array 241, and a detector array 240, to apply a potential to the component.

[0087]

[0097] References to the upper and lower sides, up and down, upward and downward should be understood as referring to directions parallel to the (with some exceptions, typically perpendicular) up-beam and down-beam directions of the charged particle beam impacting Sample 208. Thus, references to the up-beam and down-beam are intended to refer to directions related to the beam path, independently of the current gravitational field. References to the beam path refer to the intended position of the corresponding beam during the operation of the charged particle aperture. When such references are made in relation to electro-optical elements such as electrode plates, they can generally be understood as relating to the optical axis of the beam and therefore to a direction perpendicular to the plane of the electro-optical element, for collimated beam paths. For non-collimated beams such as divergent beams, the beam path can be considered relative to the axis of the beam's center point, or, if the beam is a beam of a beam grating, the axis of the beam grating's center point. Therefore, the direction of the beam path can be considered as an axis perpendicular to the plane of the planar electro-optic element, but this is not necessarily required, and in some embodiments, the beam path is angled (for example, obliquely) with respect to such planar electro-optic element.

[0088]

[0098] The electro-optical devices described herein may take the form of a series of aperture arrays or electro-optical elements arranged in an array along a beam path or multi-beam path. Such electro-optical elements may be electrostatic. In one embodiment, for example, all electro-optical elements from the beam-limiting aperture array to the final electro-optical element in the beam path before the sample may be electrostatic and / or in the form of an aperture array or plate array. In some configurations, one or more of the electro-optical elements are manufactured as a micro-electromechanical system (MEMS) (i.e., by using MEMS manufacturing techniques). Electro-optical elements may have magnetic and electrostatic elements. For example, a composite array lens may feature macro-magnetic lenses arranged along the multi-beam path, with upper and lower pole plates enclosing the multi-beam path within a magnetic lens. Within the pole plates, there may be an array of apertures for the multi-beam beam path. Electrodes may be located above, below, or between the pole plates to control and optimize the electromagnetic field of the composite lens array.

[0089]

[0099] The evaluation apparatus, tools, or systems described herein may include apparatus for performing qualitative evaluation of a sample (e.g., pass / fail), apparatus for performing quantitative measurement of a sample (e.g., feature size), or apparatus for generating an image of a map of a sample. Examples of evaluation apparatus, tools, or systems include inspection tools (e.g., for identifying defects), review tools (e.g., for classifying defects), and metronome tools, or tools capable of performing any combination of evaluation functions related to inspection tools, review tools, or metronome tools (e.g., metronome inspection tools). It is understood that the present invention may also be applicable to other types of apparatus, such as charged particle lithography apparatus used in generating patterns on a sample.

[0090]

[0100] The functions provided by a controller, or control system, or control unit, may be computer-implemented. Any preferred combination of elements may be used to provide the necessary functions, including, for example, a CPU, RAM, SSD, motherboard, network connectivity, firmware, software, and / or other elements known in the art that enable the required computing operations to be performed. The required computing operations may be defined by one or more computer programs. One or more computer programs may be provided in the form of a medium for storing computer-readable instructions, optionally a non-temporary medium. Once the computer-readable instructions are read by the computer, the computer performs the required method steps. The computer may consist of a distributed computing system having multiple different computers connected to each other in internal units or via a network.

[0091]

[0101] Although the present invention has been described in relation to various embodiments, other embodiments of the invention will become apparent to those skilled in the art by considering the specifications and practices of the invention disclosed herein. This specification and examples are to be considered merely illustrative, and the true scope and spirit of the invention are intended to be shown by the following claims and clauses.

[0092]

[0102] The following terms and conditions are provided.

[0093]

[0103] Clause 1. An electron-optical stack comprising a plurality of electron-optical plates having principal surfaces on both sides of a plate, wherein the plates define a set of channels aligned along the beampath of a charged particle beam and configured to allow the charged particle beam to pass through the plates through the channels, each channel defining apertures on two principal surfaces of the plate defining the channel, the apertures having different shapes from each other, and the plates being oriented such that the apertures include one or more pairs of matched apertures along the beampath, each pair of matched apertures or each pair of matched apertures consisting of apertures of the same shape defined on adjacent principal surfaces of adjacent plates.

[0094]

[0104] Clause 2. The stack according to claim 1, wherein the different shapes consist of a nominal shape and a perturbed shape, the perturbed shape being preferably a perturbed version of the nominal shape.

[0095]

[0105] Clause 3. The stack according to claim 2, wherein the nominal shape is the same for two or more channels in the set, and the nominal shape is preferably a circle or an ellipse.

[0096]

[0106] Clause 4. The stack according to claim 2 or 3, wherein the perturbation shape includes a perturbation component having less than 10 rotational symmetries.

[0097]

[0107] Clause 5. The stack according to claim 4, wherein the perturbation component has rotational symmetry of 4 or multiples of 4, or 6 or multiples of 6.

[0098]

[0108] Clause 6. The stack according to any one of claims 2 to 5, wherein at least one of the harmonized aperture pairs comprises an aperture having a perturbed shape.

[0099]

[0109] Clause 7. The stack according to claim 6, wherein the apertures of a pair of aligned apertures having a perturbed shape preferably have substantially the same rotational orientation with respect to the beam path as the axis of rotation.

[0100]

[0110] Clause 8. The stack according to any one of claims 2 to 7, wherein at least one of the harmonized aperture pairs comprises an aperture having a nominal shape.

[0101]

[0111] Clause 9. The stack according to any one of claims 1 to 8, wherein the multiple plates define at least two matched aperture pairs along the same beam path.

[0102]

[0112] Clause 10. The stack according to claim 9, wherein the plurality of plates include three adjacent plates that define two matched aperture pairs along the same beam path.

[0103]

[0113] Clause 11. The stack according to claim 10, wherein the apertures of two aligned aperture pairs are of different shapes.

[0104]

[0114] Clause 12. The stack according to any one of claims 1 to 11, wherein the plate comprises silicon.

[0105]

[0115] Clause 13. The stack according to any one of claims 1 to 12, wherein the channels defined in the plates are obtained in each plate by an etching process that brings apart apertures of different shapes on the main surface of the plates.

[0106]

[0116] Clause 14. The stack according to any one of claims 1 to 13, wherein the channels are etched channels, preferably etched such that the aperture shapes on the main surfaces on both sides of the plate are different.

[0107]

[0117] Clause 15. The stack according to any one of claims 1 to 14, wherein the multiple plates are configured to allow at least adjacent plates to be maintained at different potentials.

[0108]

[0118] Clause 16. The stack according to any one of claims 1 to 15, wherein a spacer is present between adjacent plates and the spacer is configured to electrically insulate and / or support adjacent plates.

[0109]

[0119] Clause 17. The stack according to any one of claims 1 to 16, wherein the multiple plates define multiple sets of channels configured to be aligned to multiple corresponding beampaths of different charged particle beams of a beam grating.

[0110]

[0120] Clause 18. The stack according to any one of claims 1 to 17, wherein the multiple plates are configured to operate as an Einzel lens, and preferably the multiple plates are included in a stack of plates comprising three plates.

[0111]

[0121] Clause 19. A module comprising the stack described in any one of claims 1 to 18.

[0112]

[0122] Clause 20. An electro-optical device comprising a stack as described in any one of claims 1 to 18 or a module as described in claim 19.

[0113]

[0123] Clause 21. An evaluation apparatus for evaluating a sample by projecting a plurality of charged particle beams toward the sample, comprising a stage configured to support a sample for evaluation, a stack according to any one of claims 1 to 18, and a module according to claim 19, or a device according to claim 20.

[0114]

[0124] Clause 22. A method for manufacturing an electro-optical stack, the method is: Etching channels into each plate of a plurality of electro-optical plates having main surfaces on both sides of the plate, wherein the etching process is such that the apertures defined at both ends of each channel have different shapes, and Positioning a plate to align a set of channels so that a charged particle beam passes through the channel, wherein the plate is oriented such that one or more pairs of matched apertures define along the beam path, and each pair of matched apertures or each pair of matched apertures consists of apertures of the same shape defined on adjacent main surfaces of adjacent plates. Methods that include...

[0115]

[0125] Clause 23. The method according to claim 22, wherein the different shapes consist of a nominal shape and a perturbed shape.

[0116]

[0126] Clause 24. The method according to claim 23, wherein the plate is arranged in such an orientation that the apertures of a pair of aligned apertures having a perturbed shape have substantially the same rotational orientation with respect to the beam path as the axis of rotation.

[0117]

[0127] Clause 25. The method according to any one of claims 22 to 24, wherein the plate comprises silicone.

[0118]

[0128] Clause 26. The method according to any one of claims 22 to 25, wherein the positioning of the plates such that the channels of the set are aligned is relative to the apertures of the channels on the opposing surfaces of adjacent plates in the stack.

Claims

1. An electron-optical stack comprising a plurality of electron-optical plates having main surfaces on both sides of the plate, The plate defines a set of channels, which are aligned along the beam path of a charged particle beam and configured to allow the charged particle beam to pass through the plate through the channels. Each channel defines apertures on the two main surfaces of the plate that define the channel, and the apertures have different shapes from each other. An electron-optical stack, wherein the plates are arranged in such a manner that the apertures include one or more pairs of matched apertures along the beam path, and each pair of matched apertures or each pair of matched apertures consists of apertures of the same shape defined on adjacent main surfaces of adjacent plates.

2. The stack according to claim 1, wherein the different shapes consist of a nominal shape and a perturbed shape, the perturbed shape preferably being a perturbed version of the nominal shape.

3. The stack according to claim 2, wherein the nominal shape is the same for two or more of the channels in the set, and the nominal shape is preferably an ellipse such as a circle.

4. The stack according to claim 2 or 3, wherein the perturbation shape includes a perturbation component having less than 10 rotational symmetries.

5. The stack according to any one of claims 2 to 4, wherein at least one of the matching aperture pairs comprises an aperture having the perturbed shape.

6. The stack according to claim 5, wherein the apertures of the matching aperture pair having the perturbation shape preferably have substantially the same rotational orientation with respect to the beam path as the axis of rotation.

7. The stack according to any one of claims 2 to 6, wherein at least one of the matching aperture pairs consists of an aperture having the nominal shape.

8. The stack according to any one of claims 1 to 7, wherein the plurality of plates define at least two matched aperture pairs along the same beam path.

9. The stack according to claim 8, wherein the plurality of plates include three adjacent plates that define two matched aperture pairs along the same beam path.

10. The stack according to claim 9, wherein the apertures of the two matching aperture pairs have different shapes.

11. The stack according to any one of claims 1 to 10, wherein the channels defined in the plate are obtained in each plate by an etching process that brings the apertures of different shapes to the main surface of the plate.

12. The stack according to any one of claims 1 to 11, wherein the plurality of plates are configured to allow at least adjacent plates to be maintained at different potentials.

13. The stack according to any one of claims 1 to 12, wherein a spacer is located between adjacent plates, and the spacer is configured to electrically insulate and / or support the adjacent plates.

14. The stack according to any one of claims 1 to 13, wherein the plurality of plates define channels of a plurality of sets configured to be aligned to a plurality of corresponding beampaths of charged particle beams of different types in a beam grating.

15. A method for manufacturing an electro-optical stack, wherein the method is Etching channels into each of the plurality of electro-optical plates having main surfaces on both sides of the plate, wherein the etching process is such that the apertures defined at both ends of each channel have different shapes, Positioning a plate such that a charged particle beam passes through a set of channels, wherein the plate is oriented such that one or more pairs of matched apertures are defined along the beam path, and each pair of matched apertures or each pair of matched apertures consists of apertures of the same shape defined on adjacent main surfaces of adjacent plates. Methods that include...

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