Charged particle optical device, evaluation apparatus, and sample evaluation method

Abstract

The present disclosure relates to a charged particle device for projecting charged particles toward a sample and a method for evaluating a sample using charged particles. The charged particle optical element directs a beam of charged particles toward the sample. The charged particle optical element includes a plate having a beam aperture and a plurality of vent apertures defined therein. The beam tube defines an intratube volume including a path of the charged particles of the beam upstream of the plate and an extratube region outside the beam tube. The beam aperture allows the charged particles of the beam to pass from the intratube volume to a downstream beam volume on the opposite side of the plate from the intratube volume toward the sample. The vent aperture fluidly connects the downstream beam volume to the extratube region.

Description

[Technical Field]

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims priority to European Patent Application No. 22209068.0 filed November 23, 2022, European Patent Application No. 23153993.3 filed January 30, 2023, and European Patent Application No. 23202483.6 filed October 9, 2023, all of which are incorporated by reference in their entireties.

[0002] FIELD OF THE DISCLOSURE

[0002] The present disclosure relates to methods and apparatus for evaluating samples using charged particles. [Background technology]

[0003]

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

[0004]

[0004] Evaluation tools, also referred to herein as evaluation systems, for evaluating an object, which may also be called a sample, using a charged particle beam to detect, for example, pattern defects are known. These systems typically use electron microscopy, such as a scanning electron microscope (SEM). In an SEM, a primary electron beam of relatively high-energy electrons is directed toward a target with a final deceleration stage so that it is incident on the sample with a relatively low incident energy. The electron beam is focused as a probe spot on the sample. Interaction between the material structure of the probe spot and the incident electrons from the electron beam causes signal electrons, such as secondary electrons, backscattered electrons, and Auger electrons, to be emitted from the surface. The signal electrons can be emitted from the material structure of the sample. By scanning the sample surface as the probe spot with the primary electron beam, signal electrons can be emitted across the entire sample surface. By collecting these emitted signal electrons from the sample surface, a pattern inspection system can obtain an image that represents the characteristics of the material structure of the sample surface.

[0005] In an evaluation system using charged particles such as an SEM, an ultra-high vacuum (very low pressure, for example, 10 -9 It is desirable to maintain a pressure of 1000 mbar or less. At the same time, charged particle optical elements (e.g., electron optical elements) must be provided between the charged particle source and the sample in order to project the charged particles onto the sample. At least some of the charged particle optical elements may need to be located relatively close to the sample, where fast outgassing and / or charged particle stimulated desorption processes limit the vacuum level that can be practically achieved, thereby resulting in higher pressures (e.g., not ultra-high vacuum, but e.g., 10 -6 ~10 -8The charged particle optical element is placed in a high vacuum (which can be a pressure in the mbar range). Some samples may have a coating, such as a resist, for sample processing. While samples, particularly resist-coated samples, can be a source of outgassing, outgassing can also occur from samples without such a coating. It is desirable to minimize the flow of gas through the charged particle optical element from a region near the sample (e.g., a high vacuum region) to the charged particle source (e.g., an ultra-high vacuum region). One approach to suppressing gas flow is to reduce the flow conductance (i.e., increase the flow resistance) through the charged particle optical element from the sample to the charged particle source. Flow conductance can be reduced, for example, by providing a tube with a high aspect ratio, such as an elongated tube (i.e., a long tube relative to its cross-sectional size), between the charged particle optical element and the charged particle source. Elongated tubes can allow charged particles to pass through them, but have a relatively low flow conductance due to their relatively long length. However, the relatively long length undesirably increases the length of the charged particle optical path from the charged particle source to the sample, which may result in a loss of brightness and reduced resolution and / or throughput. An alternative (or additional) approach is to use a beam crossover to direct the charged particle beam or multiple beams through a small aperture. Such a small aperture may restrict the flow of gas toward the charged particle source. However, the use of a beam crossover also results in a loss of brightness and may undesirably reduce resolution and / or throughput, and / or its use may be incompatible with some electron-optical designs. Summary of the Invention

[0006]

[0006] An object of the present disclosure is to provide methods and apparatus that at least partially address the above-mentioned problems, for example, that avoid or reduce loss of beam brightness at the sample while limiting undesirable flow of gas from the sample region to the charged particle source.

[0007]

[0007] According to one aspect of the present invention, there is provided a charged particle device for projecting one or more beams of charged particles towards a sample, comprising: a charged particle optical element configured to direct one or more beams of charged particles towards a sample, the charged particle optical element including a plate having one or more beam apertures and a plurality of vent apertures defined therein; a beam tube defining an intratube volume including a path of the charged particles of the one or more beams upstream of the plate; and an extratube region outside the beam tube, wherein the one or more beam apertures are configured to pass the charged particles of the one or more beams from the intratube volume towards the sample to a beam downstream volume opposite the intratube volume of the plate, and the vent apertures are configured to fluidly connect the beam downstream volume to the extratube region.

[0008]

[0008] According to one aspect of the present invention, there is provided a method for evaluating a sample using charged particles, the method comprising projecting one or more beams of charged particles towards the sample using a charged particle device, the device comprising a charged particle optical element that directs the one or more beams towards the sample, the charged particle optical element comprising a plate having one or more beam apertures and a plurality of vent apertures defined therein, the device comprising a beam tube defining an intratube volume including a path of the charged particles of the one or more beams upstream of the plate, and an extratube region outside the beam tube, the one or more beam apertures allowing the charged particles of the one or more beams to pass from the intratube volume to a beam downstream volume on the opposite side of the intratube volume of the plate towards the sample, the vent apertures being configured to fluidly connect the beam downstream volume to the extratube region, and the method comprising delivering fluid from the beam downstream volume to the extratube region through the vent apertures.

[0009]

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

[0010] [Figure 1]FIG. 1 is a schematic diagram illustrating an exemplary charged particle beam inspection apparatus. [Figure 2]

[0011] 2 is a schematic diagram illustrating an exemplary multi-beam charged particle device that is part of the exemplary charged particle beam inspection device of FIG. 1. [Figure 3]

[0012] 1 is a schematic diagram of an exemplary charged particle device including a condenser lens array, an objective lens array, and a detector array. [Figure 4]

[0013] 1 is a schematic diagram of an exemplary charged particle device including a macro-collimator and a macro-scan deflector. [Figure 5]

[0014] 1 is a schematic cross-sectional view of a portion of an objective lens array and detector array in an exemplary configuration. [Figure 6]

[0015] FIG. 6 is a bottom view of a portion of the detector array of FIG. 5. [Figure 7]

[0016] FIG. 6 is a bottom view of a modified version of the detector array portion of FIG. 5. [Figure 8]

[0017] 1 is a schematic diagram of an exemplary charged particle device including an objective lens array and a beam separator. [Figure 9]

[0018] 1 is a schematic diagram of an exemplary charged particle device including a beam tube. [Figure 10]

[0019] 1 is a schematic diagram illustrating a portion of a charged particle device including a charged particle optical element and an adjacent beam tube. [Figure 11]

[0020] FIG. 11 is a schematic diagram illustrating a variation of the configuration of FIG. 10 in which the flow passage is defined higher along the beam tube. [Figure 12]

[0021] 2 is a schematic top view of a portion of an exemplary plate of a charged particle optical element. [Figure 13]

[0022] 10 is a schematic top view of a portion of yet another exemplary plate of a charged particle optical element. [Figure 14]

[0023] FIG. 1 is a schematic diagram illustrating an exemplary configuration for mechanically supporting a beam tube via a plate support. DETAILED DESCRIPTION OF THE INVENTION

[0011]

[0024] Reference will now be made in detail to the exemplary embodiments, examples of which are illustrated in the accompanying drawings. The following description refers to the accompanying drawings, in which like numerals in different drawings represent the same or similar elements unless otherwise indicated. The implementations described in the following description of exemplary embodiments do not represent all implementations that are consistent with the present invention. Instead, they are merely examples of apparatus and methods that are consistent with aspects related to the present invention as recited in the appended claims.

[0012]

[0025] Increases in the computing power of electronic devices can be achieved by significantly increasing the packing density of circuit components such as transistors, capacitors, and diodes on IC chips, which reduces the physical size of the devices. This is made possible by higher resolution, which allows for the fabrication of ever smaller structures. For example, an IC chip in a smartphone, the size of a thumbnail and available before 2019, can contain over 2 billion transistors, each 1000 times the size of a human hair. 分の The yield is less than 1. It is not surprising, therefore, that the manufacturing of semiconductor ICs is a complex and time-consuming process involving hundreds of individual steps. An error in even one step can dramatically affect the functionality of the final product. Even a single defect can cause device failure under certain circumstances. The goal of a manufacturing process is to improve the yield of the overall process. For example, to achieve a 75% yield in a 50-step process (where a step can represent the number of layers formed on a wafer), the yield at each individual step must be greater than 99.4%. Even if each individual step has a 95% yield, the overall process yield would be as low as 7%.

[0013]

[0026] While high process yields are desirable in IC chip manufacturing facilities, it is also important to maintain high substrate (i.e., wafer) throughput, defined as the number of substrates processed per hour. High process yields and high substrate throughput can be affected by the presence of defects. This is especially true when inspection for defects requires operator intervention. Therefore, high-throughput detection and identification of microscale to nanoscale defects by inspection systems (e.g., scanning electron microscopes ("SEMs")) is essential to maintaining high yields and low costs.

[0014]

[0027] An SEM includes a scanning device and a detector device. The scanning device includes an illumination device, which includes an electron beam source for generating primary electrons, and a projection device for scanning one or more focused beams of primary electrons across a sample, such as a substrate. At least the illumination device or illumination system and the projection device or projection system together may be referred to as an electron-optical device or column. The primary electrons interact with the sample and generate secondary electrons. The detector captures the secondary electrons from the sample as it is scanned, allowing the SEM to create an image of the scanned area of ​​the sample. For high-throughput inspection, some inspection systems use multiple focused beams of primary electrons, or multibeams. The component beams of a multibeam may be referred to as subbeams or beamlets. A multibeam can simultaneously scan different portions of a sample. Therefore, multibeam inspection systems can inspect samples much faster than single-beam inspection systems.

[0015]

[0028] Known implementations of multi-beam inspection devices are described below.

[0016]

[0029] The figures are schematic. Accordingly, relative dimensions of components in the figures are exaggerated for clarity. Within the following description of the figures, identical or similar reference numbers refer to identical or similar components or entities, and only differences relative to individual embodiments are described. While the description and figures relate to electron-optical systems, it should be understood that the embodiments are not used to limit the present disclosure to specific charged particles. Thus, references to electrons throughout this specification may be considered to be references to charged particles more broadly, although charged particles are not necessarily electrons. All references to charged particles may be considered to include at least electrons.

[0017]

[0030] Reference is now made to FIG. 1, which is a schematic diagram illustrating an exemplary charged particle beam inspection apparatus 100, which may also be referred to 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 device 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 device 40. The charged particle device 40 is located within the main chamber 10.

[0018]

[0031] The EFEM 30 includes a first load port 30a and a second load port 30b. The EFEM 30 may include additional load ports. The first load port 30a and the second load port 30b may, for example, accept a substrate Front Opening Unified Pod (FOUP), which contains a substrate (semiconductor substrate or substrate made of other material) or a sample to be inspected (hereinafter, substrate, wafer, and sample are collectively referred to as "sample"). One or more robotic arms (not shown) within the EFEM 30 transport the sample to the load lock chamber 20.

[0019]

[0032] The load lock chamber 20 is used to remove gas from around the sample. This creates a vacuum, which is a local gas pressure lower than the pressure of the surrounding environment. The load lock chamber 20 may be connected to a load lock vacuum pumping system (not shown) that removes gas particles from within the load lock chamber 20. Operation of the load lock vacuum pumping system allows the load lock chamber to reach a first pressure below atmospheric pressure. After the first pressure is reached, one or more robotic arms (not shown) transfer the sample from the load lock chamber 20 to the main chamber 10. The main chamber 10 is connected to the main chamber vacuum pumping system (not shown). The main chamber vacuum pumping system removes gas particles from the main chamber 10, causing the pressure around the sample to reach a second pressure lower than the first pressure. After the second pressure is reached, the sample is transferred to an electron beam device where it can be inspected. The charged particle device 40 may include a multi-beam electron optical device.

[0020]

[0033] The controller 50 is signally, e.g., electronically, connected to the electron beam device 40, e.g., as a distributed component of the controller 50. The controller 50 may be a processor (e.g., a computer) configured to control the charged particle beam inspection device 100. The controller 50 may also include processing circuitry configured to perform various signal and image processing functions. While the controller 50 is shown in FIG. 1 as being external to the structure including the main chamber 10, the load lock chamber 20, and the EFEM 30, it should be understood that the controller 50 may be part of that structure. The controller 50 may be located in one of the component elements of the charged particle beam inspection device or distributed among at least two of the component elements. While this disclosure provides an example of a main chamber 10 housing an electron beam inspection device, it should be noted that aspects of this disclosure in its broadest sense are not limited to chambers housing electron beam inspection devices. Rather, it should be understood that the principles described above may also be applied to other systems and other arrangements of devices operating under a second pressure.

[0021]

[0034] Reference is now made to FIG. 2, which is a schematic diagram illustrating an exemplary charged particle device 40. The charged particle device 40 may be provided as part of the exemplary charged particle beam inspection system 100 of FIG. 1. The charged particle device 40 includes an electron beam source 201 and a charged particle column (or device) 230. The charged particle device 230 may be referred to as or include a projection system for directing a primary charged particle beam 202 onto a sample 208. The electron beam source 201 and associated component charged particle optics may be referred to as an illumination system for generating the primary charged particle beam 202. The evaluation system includes a sample support for supporting the sample 208. The sample support in this example includes a sample holder 207. The sample holder 207 holds the sample 208 (e.g., a substrate or a mask) for evaluation. The sample holder 207 is supported by a motorized or actuated stage 209. The charged particle device 40 further includes a detector 240. The detector 240 detects signal charged particles (e.g., electrons) from the sample 208. The detector 240 generates a detection signal when it detects the signal charged particles.

[0022]

[0035] The electron beam source 201 may include a cathode (not shown) and an extraction electrode or anode (not shown). During operation, the electron beam source 201 is configured to emit electrons from the cathode as primary electrons. The primary electrons are extracted or accelerated by the extraction electrode and / or anode to form a primary electron beam 202.

[0023]

[0036] The charged particle device 230 is configured to convert the primary electron beam 202 into multiple charged particle beams 211, 212, 213 and direct each beam onto the sample 208. While three beams are shown for simplicity, there may be tens, hundreds, thousands, tens of thousands, or even hundreds of thousands (or more) of beams. A beam may be referred to as a beamlet or sub-beam. Multiple charged particle beams may be collectively referred to as a multibeam or beam grid. A beam grid with a large number of beams (e.g., more than 1000 beams) may have a field of view of, for example, greater than 0.5 mm, e.g., in the range of 0.5-30 mm or 1-30 mm.

[0024]

[0037] The controller 50 (e.g., a control system including distributed controllers) may be connected to various portions of the charged particle beam inspection apparatus 100 of FIG. 1 , such as the electron beam source 201, the electron detection device 240, the charged particle device 230, and the actuated stage 209. The controller 50 may perform various image and signal processing functions. The controller 50 may also generate various control signals for controlling the operation of the charged particle beam inspection apparatus 100, including the operation of the charged particle device 40.

[0025]

[0038] The charged particle device 230 may be configured, for example, to focus the beams 211, 212, and 213 onto the sample 208 for inspection, to form three probe spots 221, 222, and 223 on the surface of the sample 208. The charged particle device 230 may be configured to deflect the primary beams 211, 212, and 213 to scan individual scanning regions within a section of the surface of the sample 208 with the probe spots 221, 222, and 223. In response to the incidence of the primary beams 211, 212, and 213 on the probe spots 221, 222, and 223 on the sample 208, electrons are generated from the sample 208, including secondary electrons and backscattered electrons, which may be referred to as signal charged particles. Secondary electrons typically have electron energies as high as 50 electron volts (≦50 eV), and backscattered electrons typically have electron energies between 50 electron volts (50 eV) and the incident energy of the primary beams 211, 212, and 213.

[0026]

[0039] Detector 240 may transmit a detection signal generated at detector 240, e.g., as an imaging or detection signal, to controller 50 or a signal processing system (not shown, which may be part of controller 50) to construct, e.g., an image of a corresponding scanned area of ​​sample 208. Detector 240 may be at least partially integrated into charged particle device 230 or may be separate therefrom, e.g., where a secondary optical column directs secondary electrons towards detector 240.

[0027]

[0040] The controller 50 may include an image processing system including an image capture unit (not shown) and a storage device (not shown). For example, the controller may include a processor, a computer, a server, a mainframe host, a terminal, a personal computer, any type of mobile computing device, etc., or a combination thereof. The image capture unit may include at least a portion of the processing functionality of the controller. Thus, the image capture unit may include at least one or more processors. The image capture unit may be communicatively coupled to the detector 240 to enable signal communication, such as via conductors, fiber optic cables, portable storage media, IR, Bluetooth, the Internet, a wireless network, wireless radio, etc., or a combination thereof. The image capture unit may receive detection signals from the detector 240, process data contained in the signals, and construct an image therefrom. Thus, the image capture unit may capture an image of the sample 208. The image capture unit may also perform various post-processing functions, such as generating contours and overlaying indicators on the captured image. The image capture unit may be configured to adjust the brightness and contrast of the captured image, etc. The storage may be a storage medium such as a hard disk, a flash drive, cloud storage, random access memory (RAM), other types of computer-readable memory, etc. The storage may be coupled with the image acquisition unit and used to save scanned raw image data as original images and post-processed images.

[0028]

[0041] The image acquisition unit may acquire one or more images of the sample 208 based on the imaging signal received from the detector 240. The imaging signal may correspond to a scanning operation to perform charged particle imaging. The acquired image may be a single image including multiple imaging regions. The single image may be stored in storage. The single image may be an original image that may be divided into multiple regions. Each region may include one imaging region that includes a feature of the sample 208. The acquired image may include multiple images of a single imaging region of the sample 208 sampled multiple times over a period of time. The multiple images may be stored in storage. The controller 50 may be configured to perform image processing steps using multiple images of the same location on the sample 208.

[0029]

[0042] The controller 50 may include measurement circuitry (e.g., an analog-to-digital converter) for acquiring the distribution of detected secondary electrons. The portion of the controller for such functionality may be included in or proximate to the detector. The electron distribution data collected during the detection time window can be used in combination with the corresponding scan path data for each 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 can be used to reveal various features of the internal or external structure of the sample 208. The reconstructed image can thereby be used to reveal any defects that may be present in and / or on the sample, and therefore the sample.

[0030]

[0043] The controller 50 may control the actuated stage 209 to move the sample 208 during inspection of the sample 208, e.g., to provide scanning motion of the stage relative to the path of the primary beam. The controller 50 may enable the actuated stage 209 to move the sample 208 in a direction, preferably continuously, e.g., at a constant velocity, e.g., as part of a scanning movement of the stage, at least during sample inspection. The controller 50 may control the movement of the actuated stage 209 such that it varies the speed of movement of the sample 208 in response to various parameters. For example, the controller may control the stage velocity (including its direction) in response to the scanning characteristics of the inspection step and / or scanning process, as disclosed, for example, in European Patent Application Publication No. 21171877.0, filed May 3, 2021, which is incorporated herein by reference, at least with respect to the combined stepping and scanning scheme of the stage. When controlling the actuated stage, actuation of the stage, and thus the sample, may enable, for example, dynamic positioning of the sample relative to the path of the primary beam.

[0031]

[0044] FIG. 3 is a schematic diagram of an exemplary charged particle apparatus 40 for use in the evaluation apparatus. The charged particle apparatus 40 includes a charged particle device 41 configured to project charged particles toward a sample 208. Such a charged particle device includes all electron-optical elements intended to operate on charged particles between an electron beam source and a sample. In the illustrated arrangement, all electron-optical elements are electrostatic; in a different arrangement, one or more of the electron-optical elements may be magnetic. For ease of explanation, the lens array is depicted herein schematically as an array of elliptical shapes. Each elliptical shape represents one of the lenses in the lens array. By convention, the elliptical shape is used to represent a lens, similar to the biconvex shape often adopted for optical lenses. It should be understood that in the context of charged particle devices such as those described herein, the lens array will typically operate electrostatically and may not require any physical elements to adopt a biconvex shape. As described below, the lens array may instead include multiple plates having apertures. Each plate having an aperture may be referred to as an electrode. The electrodes may be arranged in series along the paths of a beam grid of multiple charged particle beams (also called sub-beams), and therefore the electrodes are also in series along the paths of the charged particle beams of the beam grid.

[0032]

[0045] The electron beam source 201 directs electrons toward an array of condenser lenses 231, which form part of the charged particle device 230. The electron beam source 201 is preferably a high-brightness thermal field emitter with a good compromise between brightness and total emission current. There may be dozens, hundreds, thousands, or even tens of thousands of condenser lenses 231. The condenser lenses 231 of the array may include multipole lenses and have a configuration based on EP 1 602 121 A1, which is incorporated herein by reference, particularly for its disclosure of a lens array for splitting an electron beam into multiple sub-beams, one lens for each sub-beam. The condenser lens array may take the form of at least two, preferably three, plates that function as electrodes, with the apertures of each plate aligned with the apertures of the other plates to define the path of the charged particle beam through the plate. At least two of the plates are held at different potentials during operation to achieve the desired lens effect. Between the plates of the condenser lens array are electrically insulating plates made of an insulating material, such as ceramic or glass, with one or more apertures for the charged particle beam. Additionally or alternatively, one or more of the plates may feature apertures, each with its own electrode, e.g., an array of electrodes arranged around their periphery as a group of apertures with a common electrode. In a variant, one or more of the plates may include multiple sections or strips with multiple apertures. In yet another alternative configuration, a macro-collimator is provided instead of the condenser lens array. The macro-collimator may act on the beam from the electron beam source 201 before it is split into multiple beams. The macro-collimator may be implemented magnetically, electrostatically, or magnetically and electrostatically.

[0033]

[0046] In some embodiments, the condenser lens array is formed by a three-plate array in which charged particles have the same energy when entering and exiting each lens; this arrangement can be called an Einzel lens. Therefore, dispersion occurs only within the Einzel lens itself (between the entrance and exit electrodes of the lens), thereby limiting off-axis chromatic aberration. If the thickness of the condenser lens is thin, for example, a few mm, the effect of such aberrations is small or negligible.

[0034]

[0047] Each condenser lens in the array directs electrons into a respective beam 211, 212, 213, which is focused to a respective intermediate focus 233. A collimator or an array of collimators may be positioned to operate relative to each intermediate focus 233. The collimator may take the form of a deflector 235 disposed at the intermediate focus 233. The deflector 235 is configured to bend each beam 211, 212, 213 an amount effective to ensure that the chief ray (which may also be referred to as the beam axis) is incident on the sample 208 substantially normally (i.e., at substantially 90° relative to the nominal surface of the sample). It should be noted that in configurations with macro condenser lenses, the condenser lens may collimate or contribute to the collimation of the source beam or, in some embodiments, multiple beams.

[0035]

[0048] An objective lens array 401 is provided in the beam downstream from deflector 235. Objective lens array 501 includes an objective lens for each beam 211, 212, 213. Objective lens array 401 projects beams 211, 212, 213 onto sample 208. Objective lens array 401 may include two or more, preferably at least three, arrays of flat plate electrodes connected to respective voltage sources.

[0036]

[0049] Optionally, a control lens array 250 is provided between the deflector 235 and the objective lens array 401. The control lens array 250 includes a control lens for each of the beams 211, 212, and 213. The control lens array 250 provides additional degrees of freedom for controlling the characteristics of the beams 211, 212, and 213. The control lens array 250 may include two or more, preferably at least three, flat-plate electrode arrays connected to respective potential sources. The function of the control lens array 250 is to optimize the beam divergence angle for beam reduction and / or control the beam energy delivered to the objective lenses, each of which directs a respective beam 211, 212, and 213 toward the sample 208. In some embodiments, the control lens array may be considered part of the objective lens, for example, in that it is an additional plate associated with the objective lens array.

[0037]

[0050] Optionally, an array of scan deflectors 260 is provided between the control lens array 250 and the objective lens array 401. The array of scan deflectors 260 includes a scan deflector for each beam 211, 212, 213. Each scan deflector is configured to deflect the respective beam 211, 212, 213 in one or two directions to scan the beam across the sample 208 in one or two directions. Alternatively, a macro scan deflector may be provided to scan the sample 208 with the charged particle beam. The macro scan deflector may be provided beam upstream of the control lens array 250. In an embodiment, such a macro scan deflector may operate on the source beam and may be present with a macro condenser lens.

[0038]

[0051] The detector module 402 of the detector is provided within the objective lens or between the objective lens and the sample 208 to detect signal electrons / particles from the sample 208. Exemplary configurations of such detector modules 402 are described below. Note that the detector may additionally or alternatively have detector elements beam upstream along the primary beam path of the objective lens array 401 or even the control lens array 250. The detector module may be an array of detector elements (e.g., a detector array). Each element may be associated with an individual beam and may be positioned, for example, to detect signal particles generated by the individual beam.

[0039]

[0052] The charged particle device 41 of Figure 3 can be configured to control the incident energy of electrons onto the sample 208 by varying the potentials applied to electrodes of the control lens and the objective lens. The control lens and the objective lens function together and can be referred to as an objective lens assembly. The incident energy can be selected to increase the emission and detection of secondary electrons depending on the nature of the sample being evaluated. A detector module can be included in the objective lens assembly.

[0040]

[0053] The objective lens can be configured to demagnify the electron beam by more than 10 times, preferably in the range of 50-100 times or more. The objective lens can include three electrodes: a center electrode, a bottom electrode, and a top electrode. The top electrode can 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 allows for a larger potential difference between the electrodes, thus resulting in a stronger lens. Additional electrodes (i.e., two or more electrodes) provide additional degrees of freedom to control the electron trajectory, for example, to focus secondary electrons and the incident beam.

[0041]

[0054] FIG. 4 illustrates a variation on the configuration of FIG. 3 , in which the charged particle device 40 includes a macro-collimator 270 and a macro-scan deflector 265 instead of the condenser lens 231 and deflector 235 of FIG. 3 . Features that are the same as those previously described are labeled with the same reference numerals. For brevity, such features will not be described in detail with respect to FIG. 4 . For example, the electron beam source 201, control lens array 250, objective lens array 401, and sample 208 may be as previously described. The macro-collimator 270 and / or macro-scan deflector 265 may be macro-lenses that may be magnetic, electrostatic, or both. The macro-collimator 270 and macro-scan deflector 265 act on the beam before it is split to form multiple beams. Thus, the macro-collimator 270 and macro-scan deflector 265 may act on the entire beam rather than including an array of elements configured to interact with different individual portions of the beam.

[0042]

[0055] In the configuration of FIG. 4 , the beam from the electron beam source 201 is split into multiple beams by a sub-beam forming array 252, which defines an array of beam-limiting apertures. The objective lens array assembly in this embodiment further includes a beam-shaping aperture array 262 downstream from the sub-beam forming array 252. The beam-shaping aperture array 262 defines an array of beam-limiting apertures. The beam-shaping aperture array 262 can shape the beam defined by the sub-beam forming array 252. The use of two shaping aperture arrays is beneficial in situations where using only the sub-beam forming array 252 risks introducing aberrations into the beam. In variations of the configuration shown in and described with respect to FIG. 4 , the macro scan deflector may be replaced with a scan deflector array associated with the objective lens array, and / or the macro condenser lens may be replaced with a control lens array and / or a collimator deflector array associated with the sub-beam forming array 252.

[0043]

[0056] In some embodiments, the objective lens array assembly includes a detector having a detector module 402 beam-downstream of at least one electrode of the objective lens array 401. The detector module 402 may include or even take the form of a detector array. In certain embodiments, at least a portion of the detector is adjacent to and / or integrated into the objective lens array 401. For example, the detector module 402 may be implemented by incorporating a CMOS chip detector into the bottom electrode of the objective lens array 401. Integrating the detector module 402 into the objective lens array may replace a secondary column. The CMOS chip is preferably oriented to face the sample (since the distance between the sample and the bottom of the electron-optical system is short, which may be, for example, in the range of 10-400 micrometers, desirably in the range of 50-200 micrometers, and optionally about 100 micrometers). It should be noted that even in situations where the detector is located upstream of the most downstream electron-optical element of the charged particle device, there may be a short, e.g., comparable, distance (e.g., about 100 micrometers) between the most downstream electron-optical element and the sample. In one embodiment, an electrode for capturing signal charged particles is formed in the top metal layer of the CMOS device. The electrode can be formed in another layer of the substrate, e.g., the CMOS chip. CMOS power and control signals can be connected to the CMOS by through-silicon vias. For robustness, the bottom electrode preferably consists of two elements: the CMOS chip and a passive Si plate with holes. The plate shields the CMOS from high electric fields.

[0044]

[0057] In some embodiments, a single electrode surrounds at least some of the apertures. In some configurations, a single electrode is assigned to the periphery of each aperture, for example. In other embodiments, multiple electrode elements are provided around each aperture, for example as detector elements. Signal charged particles captured by the electrode elements surrounding an aperture can be combined into a single detection signal or can be 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 sectors), both radially and angularly (providing a dartboard-like arrangement), or in a grid (e.g., as a chessboard), or in any other convenient manner.

[0045]

[0058] An exemplary embodiment of a detector integrated into the objective lens array 401 is shown in FIG. 5, which shows a schematic cross-sectional view of a portion of the objective lens array 401. In this embodiment, the detector includes a detector module 402, which includes a plurality (e.g., an array) of detector elements 405 (shown in FIG. 6), e.g., sensor elements such as capture electrodes, preferably as an array of detector elements (i.e., a plurality of detector elements in a pattern or arrangement, preferably on a two-dimensional surface). In this embodiment, the detector module 402 is provided at the output side of the objective lens array. The output side is the output side of the objective lens array 401. FIG. 6 is a bottom view of the detector module 402, which includes a substrate 404 on which a plurality of detector elements (or capture electrodes 405) are provided, each surrounding a beam aperture 406. The beam aperture 406 may be formed by etching the substrate 404. In the configuration shown in FIG. 6, the beam aperture 406 is shown as a rectangular array. The beam apertures 406 can also be arranged in different configurations, for example, in a hexagonal close-packed array as shown in FIG.

[0046]

[0059] The integrated detector module 402 described above is particularly advantageous when used with an evaluation apparatus (e.g., including a device) having adjustable incident energy, since secondary electron capture can be optimized for a wide range of incident energies. Detector modules having an array or in the form of an array can be integrated into other electrode arrays as well as the bottom electrode array. Further details and alternative configurations of detector modules integrated into objective lenses can be found in European Patent Application No. 20184160.8, which is incorporated herein by reference.

[0047]

[0060] Power supplies may be provided to apply respective electrical potentials to electrodes of the control lenses of the control lens array 250 and the objective lenses of the objective lens array 401 and the condenser lenses of the condenser lens array or any of the electron-optical components, such as the detector module (if integrated into the objective lens array or if the objective lens and detector module are separate components), of the charged particle device 41. The controller 50 may control the electrical potentials applied to the electron-optical components, such as the electrodes of the condenser lens array, the objective lens array, and / or the control lens array.

[0048]

[0061] The charged particle device 41 may include other charged particle optical (e.g., electron-optical) components such as charged particle correctors, for example, for alignment between the electron beam source and the sample and the beams of the multi-beam, and corrector arrays for adjusting the focus of different groups of the beam grid or individual beams of the beam grid. Such correctors may be controlled to operate dynamically and / or statically, for example, during step-up, maintenance, or calibration of the charged particle device 41.

[0049]

[0062] In some embodiments, an array of charged particle devices (or device array) is provided. The array may include a plurality of any of the charged particle devices (e.g., electron optical columns) described herein. Each of the charged particle devices in the array focuses a respective plurality of charged particle beams onto a different region of the same sample 208. Each of the charged particle devices in the array may derive a respective plurality of charged particle beams from a different respective electron beam source 201. Each of the respective electron beam sources 201 may be an electron source of one of the plurality of electron beam sources 201. At least a subset of the plurality of electron beam sources 201 may be provided as an electron beam source array. The electron beam source array may include multiple emitters on a common substrate. Simultaneously focusing multiple charged particle beams from different charged particle devices onto different regions of the same sample allows a larger area of ​​the sample 208 to be simultaneously exposed to the charged particle beam. Thus, a larger area of ​​the sample may be processed (e.g., evaluated) at one time. The charged particle devices in the device array can be positioned adjacent to one another so that each of the multiple beams projects onto adjacent regions of the sample 208. Any number of charged particle devices can be used in the array. Preferably, the number of charged particle devices ranges from 9 to 200. Each charged particle device in the array can be configured as a single charged particle device, an electron-optical device, or any of the methods described herein with respect to a system or column. Alternatively or additionally, one or more of the charged particle devices in the array can be configured to project a single beam.

[0050]

[0063] FIG. 8 schematically illustrates another example of a charged particle apparatus 40 having a charged particle device 41. Features that are the same as those previously described are labeled with the same reference numerals. For brevity, such features will not be described in detail with respect to FIG. 8. For example, the electron beam source 201, condenser lens 231, objective lens array 401, and sample 208 (e.g., on sample support 207) may be as described above. In other configurations, the condenser lens 231 may be an "aperture lens." The aperture lens may comprise a macrolens element and a beam-limiting aperture array that generates sub-beams. The macrolens element may be positioned beam-upstream of the beam-limiting aperture array. The aperture lens may operate to focus the sub-beams to an intermediate focal plane. In this example, a macrocollimator 270 is provided instead of a deflector array of the type previously described with respect to FIG. 3. Such a macrocollimator may be a macrolens, which may be magnetic, electrostatic, or both. In other embodiments, the deflector array may be used to at least contribute to collimation of the beam, such that the deflector array provides finer deflection toward collimation than the operation of the macro-collimator 270. Such configurations may also include an array of multiple deflectors (e.g., each aperture with multiple electrodes) for even finer collimation. In configurations, the condenser lens 231 may comprise a single plate defining a beam-limiting aperture array in which multiple apertures are defined, with one or more associated macro-electrodes having a single aperture. Such a beam-limiting aperture array and associated macro-electrodes may also form a condenser lens array for focusing the generated beam to an intermediate focus, preferably corresponding to the position of the collimator 270.

[0051]

[0064] As mentioned 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 FIG. 8, the detector 240 may be implemented such that the objective lens array 401 is between the detector 240 and the sample 208.

[0052]

[0065] In one embodiment, a deflector array 95 is provided between the detector 240 and the objective lens array 401. In one embodiment, the deflector array 95 includes a Wien filter array, whereby the deflector array 95 may be referred to as a beam separator. The deflector array 95 is configured to provide magnetic and electrostatic fields. The electrostatic and magnetic fields cooperate to separate charged particles projected onto the sample 208 with respect to signal particles, e.g., electrons from the sample 208. The operation of the fields directs the signal particles towards the detector 240.

[0053]

[0066] In some embodiments, the detector 240 is configured to detect signal particles based on the energy of the charged particles, i.e., the bandgap of the detector's semiconductor base type. Such detectors 240 are sometimes referred to as indirect current detectors. Secondary electrons emitted from the sample 208 gain energy from the electric field between the electrodes. The secondary electrons have sufficient energy when they reach the detector 240. In a different configuration, the detector 240 can be an electron-to-photon converter, such as a scintillator array of fluorescent strips between beams positioned upstream along the primary beam path relative to a Wien filter. The primary beam passing through the Wien filter array (of magnetic and electrostatic strips orthogonal to the primary beam path) has substantially parallel paths upstream and downstream of the Wien filter array, while signal electrons from the sample are directed toward the scintillator array by the Wien filter array. The electron-to-photon converter can be optically coupled to the photon-to-electron converter to convert any photons generated in and emitted from the electron-to-photon converter. The photon-to-electron converter can be electrically connected to electronic circuitry for processing the detection signal. In different embodiments, the photon-to-electron converter can be internal or external to the charged particle device. In some embodiments, the photons can be coupled via a photon transport unit (e.g., an array of optical fibers) to a remote optical detector, which generates a detection signal upon detecting the photons.

[0054]

[0067] As shown in FIG. 9 , in some embodiments, the charged particle device 40 includes a beam tube 300 (which may also be referred to as a tube, a liner tube, or a booster tube). In some embodiments, the beam tube 300 is positioned to surround a multi-beam path. The beam tube 300 surrounds a path of charged particles. The charged particles may be a source beam emitted from the electron beam source 121 toward a sample. The charged particles may be from multiple beams of a multi-beam. The beam tube 300 may surround the source beam path or the multi-beam path, for example, when viewed along the primary axis of the charged particle device 40, i.e., in the direction of the charged particle beam. In some embodiments, the beam tube 300 is configured to surround only a portion of the charged particle path, i.e., a portion of the charged particle path along its length, for example, a length along a portion of the charged particle path. For example, as shown in FIG. 9 , in some embodiments, the beam tube 300 surrounds a portion of the multi-beam path from the electron beam source 201 to just above the sub-beamforming array 252. In other embodiments, the beam tube 300 encompasses different portions, eg, lengths, of the multi-beam path.

[0055]

[0068] In one embodiment, the beam tube 300 is configured to operate at a first potential difference with respect to earth. The support may be configured to support the sample 208 at a second potential difference with respect to earth or at earth potential. The first potential difference may be greater than the second potential difference, for example, to accelerate the charged particles of the multi-beam toward the sample 208. By arranging for a relatively low potential difference between the sample and its immediate environment, the likelihood of electrical breakdown in the vicinity of the sample 208 may be reduced. This may reduce the likelihood of damage to the sample 208. The risk of damage to components of the charged particle device 41, such as the detector 240 (which may feature delicate electronic elements), may be reduced.

[0056]

[0069] As described above and illustrated in FIG. 9 , the electron beam source 201 may include a cathode 121 and an anode 122 (which may also be referred to as an extractor electrode). The cathode 121 and the anode 122 are configured to operate with a potential difference between them. The cathode 121 is configured to emit a charged particle beam. The anode 122 is configured to accelerate the charged particle beam toward the sample 208. Note that this electron beam source configuration is a simplified arrangement. The electron beam source 201 may have different arrangements and other electrodes, as long as the electron beam source 201 has a source electrode furthest downstream of the beam, which is referred to herein as the anode 122.

[0057]

[0070] 9, in one embodiment, the beam tube 300 is electrically connected to the anode 122. By electrically connecting the beam tube 300 to the anode 122, no electric field is formed between the electron beam source 201 and the beam tube 300. Any undesirable effects on the beam upstream of the beam tube 300 are avoided. The beam tube 300 may be formed together with the anode 122. The beam tube 300 and the anode 122 may be integral. Alternatively, the beam tube 300 may be separate from the electron beam source 201. The beam tube 300 may be axially spaced apart from the anode 122.

[0058]

[0071] 9 , in an embodiment, at least a portion of the charged particle device 41 is located downstream of the most downstream end of the beam tube 300. For example, the sub-beam forming array 252, the control lens array 250, the objective lens array 241, and the beam shaping aperture array 262 may be provided downstream of the beam tube 300. In an embodiment, the portion of the charged particle device 41 downstream of the beam tube 300 may be configured to decelerate the charged particle beam. The portion of the charged particle device 41 downstream of the beam tube 300 may be referred to as a charged particle optical element.

[0059]

[0072] In an embodiment, the charged particle device 40 is configured so that the charged particle beam passes through the charged particle device 40 without any undesirable lensing effects being applied to the beam. The downstream end of the beam tube 300 may be configured to be in a region with a small or no electric field. This may help reduce or avoid any lensing effects on the charged particle beam that may be caused by the electric field between the beam tube 300 and any portion of the charged particle device 41 downstream of the beam tube 300.

[0060]

[0073] As shown in FIG. 9 , in some embodiments, the beam tube 300 is spaced apart from the portion of the charged particle device 41 that is downstream of the beam tube 300. This spacing may make it easier to manufacture the charged particle apparatus (by relaxing tolerances) and / or replace some or all of the charged particle device 41. In some embodiments, the spacing is at most 1 mm. Any electric field between the beam tube 300 and any portion of the charged particle device 41 that is downstream of the beam tube 300 may be limited to a short distance. This configuration may help reduce or prevent the effects of any electric fields between the beam tube 300 and the portion of the charged particle device 41 that is downstream of the beam tube 300.

[0061]

[0074] In an alternative embodiment, the beam tube 300 is electrically connected to a portion of the charged particle device 41 downstream of the beam tube 300. For example, the beam tube 300 may be structurally connected to and / or integral with an associated plate, such as the sub-beamforming array 252.

[0062]

[0075] 9, a macro-collimator 270 including a magnetic component is provided, for example as part of the charged particle device 41. The magnetic component can affect the trajectories of charged particles within the beam tube 300 while being located outside the beam tube 300.

[0063]

[0076] In alternative embodiments, macro-collimator 270 includes electrostatic components. Such electrostatic components may be affected by beam tube 300, e.g., its shielding of electrostatic fields external to beam tube 300. In certain embodiments, the electrostatic components of macro-collimator 270 are located within beam tube 300 (not shown) or between lengths or sections of the beam tube (see European Patent Application No. 21199203.7, filed September 27, 2021, which is incorporated herein by reference insofar as it relates to designs including at least electron-optical elements and beam tubes and their sections).

[0064]

[0077] In one embodiment, the charged particle device 41 includes a macro scan deflector 265. The macro scan deflector 265 is configured to deflect respective portions of the charged particle beam, each portion corresponding to a different sub-beam further downstream in the beam. Thus, deflection of each sub-beam of charged particles in the multi-beam is scanned with respect to, e.g., over, the sample 208 by deflecting the portion by the macro scan deflector 265. As shown in FIG. 9 , in one embodiment, the macro scan deflector 265 is located upstream of the beam downstream end of the beam tube 300.

[0065]

[0078] 9, in one embodiment, the macro scan deflector 265 includes a magnetic deflector. The macro scan deflector 265 can be positioned outside the beam tube 300.

[0066]

[0079] In an alternative embodiment, instead of a macro scan deflector, a scan deflector including an array of deflectors may be provided, such as provided in the charged particle device 41 as an array of scan deflectors 260, as shown in Figure 3. Such an array of scan deflectors may be associated with an objective lens array, e.g., a deflector of the array is associated with each beam of a multi-beam array.

[0067]

[0080] 9, the beam tube 300 extends continuously from a position close to the sub-beamforming array 252 to the electron beam source 122. If the beam tube 300 is metallic (or coated with a metallic material), it shields the interior of the beam tube 300 from electrostatic fields generated outside the beam tube 300. As explained above, elements can be provided to manipulate the charged particle trajectories within the beam tube 300 via magnetic fields generated outside the beam tube 300 or via magnetic or electrostatic fields generated inside the beam tube 300. Yet another possibility (not shown) is to provide gaps within the beam tube 300 to allow electric fields generated outside the beam tube to influence the charged particle trajectories within the beam tube 300.

[0068]

[0081] As mentioned in the introduction, it is desirable to minimize the flow of gas through the charged particle optical elements toward the charged particle source. This can be achieved by introducing elements with low flow conductance (e.g., long, thin tubes) or by using beam crossovers to direct the charged particles through small apertures, but both approaches can result in a loss of brightness and an undesirably low throughput. The embodiments described below aim to address these issues.

[0069]

[0082] In one embodiment, as illustrated in Figures 10-13, a charged particle device 41 is provided for projecting charged particles toward the sample 208. The charged particle device 41 can take any of the forms already described with respect to Figures 3, 4, 8, and 9. The charged particle device 41 includes a charged particle optical element 310 (e.g., an electron optical element). The charged particle optical element 310 is configured to direct one or more beams of charged particles toward the sample 208. In the illustrated example, the charged particle optical element 310 is configured to direct multiple beams of charged particles toward the sample 208. Multiple beams of charged particles may be referred to as a multibeam or beam grid. In other embodiments, the charged particle optical element 310 may be configured to direct a single beam toward the sample 208.

[0070]

[0083] The charged particle optical element 310 includes a plate 320 having one or more beam apertures 311 and a plurality of vent apertures 312 defined therein. Representative examples of the beam apertures 311 and vent apertures 312 are labeled in Figure 10 (although not all of the respective apertures are labeled). A beam of charged particles passes through the beam aperture 311 as indicated schematically by the dashed arrow in Figure 10. In an embodiment, the plate may be a sub-beamforming array 252, as previously described, for example, with reference to Figures 4 and 9.

[0071]

[0084] The charged particle device 41 includes a beam tube 300. The beam tube 300 may take any of the forms already described with respect to FIG. 9 or other forms. The beam tube 300 may be metallic (or may have a metallic coating) to provide electrostatic shielding. Alternatively or additionally, the beam tube 300 may be configured to shield magnetic fields by including, consisting essentially of, or consisting of a magnetic shielding material, such as a material with a very high relative permeability (e.g., greater than 50,000) such as mu-metal. The beam tube 300 defines an intra-tube volume 340. The intra-tube volume 340 includes (e.g., surrounds and / or contains) the path of one or more beams upstream of the charged particle plate 320 (before or after beam formation), such as a source beam before generation of multiple beams or a primary beam of a multi-beam. In embodiments in which the charged particle optical element 310 is configured to direct multiple beams, which may be referred to as a multibeam or beam grid, toward the sample, the beams may be formed before or after the charged particles of the beams reach the end of the beam tube 300. Accordingly, the paths of the charged particles within the beam tube 300 may or may not be arranged, e.g., grouped, into separate beams at this stage. The beam tube 300 further defines an extratube region 342 that is outside the beam tube 300. Accordingly, the beam tube 300 separates the volume inside the beam tube (referred to as the intratube volume) from the region outside the beam tube (referred to as the extratube region). The extratube region 342, which may also be referred to as the extratube volume, may actually be within a vacuum chamber and may be defined in part by the walls of the vacuum chamber.

[0072]

[0085] The beam aperture 311 is configured to allow passage of charged particles of one or more beams from the intra-tube volume 340 to the beam downstream volume 344 toward the sample 208. The beam aperture 311 thus fluidly connects the intra-tube volume 340 to the beam downstream volume 344. The beam aperture 311 therefore provides a path for gas to flow from the beam downstream volume 344 to the intra-tube volume 340. The beam downstream volume 344 is downstream of the beam from the plate 320, on the opposite side of the plate 320 from the intra-tube volume 340. The beam downstream volume 344 may include a portion adjacent to the sample 208. It may not be desirable for gas to flow from the beam downstream volume 344 to the intra-tube volume 340, but the beam aperture is necessary to allow the beam to propagate to the sample 208.

[0073]

[0086] The vent aperture 312 is configured to fluidly connect the beam downstream volume 344 to the extra-tube volume 342. Thus, the vent aperture 312 provides a path for gas to flow from the beam downstream volume 344 to the extra-tube volume 342. As explained above, due to outgassing and / or charged particle stimulated desorption (e.g., electron stimulated desorption, ESD, and / or electron beam induced deposition), a relatively large amount of gas may be present near the sample 208 and in the portion of the charged particle device 41 near the sample 208. Providing an additional path for gas to exit the beam downstream volume 344 helps to reduce the proportion of this gas that flows through the beam aperture 311 and into the intra-tube volume 340. Reducing the flow of gas into the intra-tube volume 340 reduces the amount of gas that reaches the region near the electron beam source 201, thereby facilitating maintaining an appropriately low pressure (e.g., ultra-high vacuum) in the region of the electron beam source 201. Thus, the vent aperture can be used to inhibit contamination of elements and components of the charged particle device 41, some of which may be more susceptible to contamination such as electron stimulated desorption and / or electron beam induced deposition (EBID) deposits. Exposing a surface to an electron beam in the presence of molecules that may contain carbon, such as hydrocarbons, can result in EBID and contaminate the surface. The electron beam can break down the molecules, which can result in contamination of the surface, for example, as carbon contamination of the surface.

[0074]

[0087] In certain embodiments, the total flow conductance through plate 320 provided by vent apertures 312 is greater than the total flow conductance through plate 320 provided by one or more beam apertures 311. This serves to ensure that more gas flows through plate 320 into extra-luminal region 342 (schematically indicated by two large solid arrows in extra-luminal region 342) than through plate 320 into intra-luminal volume 340 (schematically indicated by the small solid arrow in intra-luminal volume 340). In certain embodiments, the total open area of ​​vent apertures 312 (e.g., the sum of the cross-sectional areas of vent apertures 312) is greater than the total open area of ​​one or more beam apertures 311 (e.g., the sum of the cross-sectional areas of beam apertures 311). Thus, if vent apertures 312 and beam apertures 311 are the same size, there may be more vent apertures 312 than beam apertures 311. Typically, the thickness of plate 320 may be constant, in which case the flow conductance of beam aperture 311 relative to vent aperture 312 is determined by their respective total areas. This is also generally true when the thickness of plate 320 is very small compared to the size of the aperture. If the thickness of plate 320 is relatively large compared to the size of the aperture and varies with position, the effect on flow conductance of differences in the length of the flow path through the aperture may also need to be considered. For example, if the portion of plate 320 defining the vent aperture is thicker than the portion of plate 320 defining the beam aperture, it may be necessary to provide more vent apertures to ensure that the total flow conductance through plate 320 provided by vent aperture 312 remains higher than the total flow conductance through plate 320 provided by beam aperture 311. Conversely, if the thickness of the plate 320 is made thinner at the locations where the vent apertures are defined, fewer vent apertures 312 may be required to provide the required higher flow conductance.

[0075]

[0088] In some embodiments, the one or more beam apertures 311 and the plurality of vent apertures 312 comprise apertures having a common dimension (e.g., a common diameter or a common width when the apertures are formed between strip electrodes), a common shape (e.g., circular or rectangular), and / or a common cross-sectional area. Thus, the apertures may all have the same configuration. Arranging the beam and vent apertures to have the same configuration may facilitate the manufacturing process, especially when the apertures are formed using microelectromechanical systems (MEMS) manufacturing techniques and processing.

[0076]

[0089] In an embodiment, a plurality of beam apertures 311 are provided, with the average spacing between the beam apertures 311 equal to the average spacing between the vent apertures 312. The beam apertures 311 may, for example, be arranged in an aperture pattern having an aperture pitch. The vent apertures 312 may be arranged in a vent pattern having a vent pitch. The aperture pattern and the vent pattern may comprise respective two-dimensional arrays, optionally regular arrays. Optionally, the aperture pattern and the vent pattern are arranged in the same type of array, for example, the same pitch, the same array symmetry (e.g., hexagonal, rectangular, etc.), and / or the same array orientation. The aperture pitch and the vent pitch may be equal. Arranging the beam and vent apertures in similar or identical patterns may facilitate the manufacturing process, especially when the apertures are formed using MEMS manufacturing techniques.

[0077]

[0090] In one embodiment, the beam tube 300 includes a facing surface 301. The facing surface 301 is spaced from a plate 320 of a charged particle optical element to define a flow passage 303. The facing surface 301 faces the plate 320. The facing surface 301 may be the portion of the beam tube 300 furthest downstream of the beam (e.g., closest to the sample 208). The flow passage 303 is configured (e.g., dimensioned) to restrict flow between the intratube volume 340 and the extratube region 342. The gap between the facing surface 301 and the plate 320 to define the flow passage 303 may be considered an aperture. Thus, the flow passage 303 may be configured to provide a relatively high flow resistance (low flow conductance). Thus, the flow passage 303 may be relatively narrow (e.g., the facing surface 301 may be spaced from the plate 320 by a relatively short distance). The flow passage 303 may be relatively long laterally (e.g., along the direction of the flow path through the flow passage 303 between the intraluminal volume 340 and the extraluminal region 342). In some embodiments, the facing surface 301 has an annular shape (e.g., when the beam tube 300 is cylindrical).

[0078]

[0091] Providing a gap between the beam tube 300 and the plate 320, rather than connecting the beam tube 300 to the plate 320, facilitates manufacturing by reducing the need for fine tolerances and also makes component replacement easier. By providing a gap that defines a flow passage 303 with low flow conductance, undesired flow of gas from the extra-tube region 342 into the intra-tube volume 340 is minimized. Thus, the restriction defined by the surfaces of the flow path effectively separates the volumes within the intra-tube volume 340 and the extra-tube region 342.

[0079]

[0092] In one embodiment, as illustrated in FIG. 10 , the beam tube 300 includes a flange portion 304, and the opposing surface 301 is defined by the flange portion 304. The flange portion locally increases the thickness of the beam tube 300, thereby increasing the length of the flow path through the flow passage 303 (thereby increasing flow resistance). In one embodiment, the flange portion 304 extends farther from the path of the charged particles (e.g., farther from the major axis of the beam or multi-beams propagating within the beam tube 300) than adjacent portions of the beam tube 300. The beam tube 300 may include a wall 302. The flange portion 304 may extend farther from the path than the outermost portion of the wall 302 adjacent to the flange portion 304. The flange portion 304 may extend farther from the path than the outermost portion of the wall 302 adjacent to the flange portion 304.

[0080]

[0093] In one embodiment, the passage surface of plate 320 that defines flow passage 303 (e.g., in FIG. 10 , the portion of the top surface of plate 320 facing the opposing surface 301 of beam tube 300) is flush with the surface of plate 320 that defines the opening to beam aperture 311 (e.g., the portion of the top surface of plate 320 facing intra-tube volume 340). Thus, the passage surface is on the plate side of flow passage 303.

[0081]

[0094] In some embodiments, plate 320 includes protrusions, and the flow passage-defining surfaces on the plate side of the flow passages are provided by the protrusions, in which case the flow passage-defining surfaces of plate 320 may not be flush with the surface of plate 320 that defines the opening to beam aperture 311.

[0082]

[0095] In one embodiment, as illustrated in FIG. 11 , beam tube 300 includes proximal portion 300A and distal portion 300B. Proximal portion 300A is connected to plate 320. Distal portion 300B is positioned distal to proximal portion 300A with respect to plate 320. Proximal portion 300A and distal portion 300B include respective opposing surfaces 305, 307. Opposing surfaces 305, 307 are spaced apart from one another to define flow passage 303. Flow passage 303 is configured (e.g., dimensioned) to restrict flow between intraluminal volume 340 and extraluminal region 342. The gap between opposing surface 301 and plate 320 defining flow passage 303 may be considered a restriction. The flow restriction may be achieved using any of the techniques already described for flow passage 303 with respect to FIG. 10 . The proximal and distal portions 300A, 300B can include respective flange portions 308, 309 that include opposing surfaces 305 and 307. The flange portions can be configured using any of the techniques already described for flange portion 304 with respect to Figure 10. Thus, the restriction defined by opposing surfaces 305, 307 in the flow passage between flange portions 308, 309 effectively separates the intraluminal volume 340 and the volume within extraluminal region 342.

[0083]

[0096] In one embodiment, as shown in FIGS. 12 and 13 , the surface of plate 320 on the beam upstream side of plate 320 (e.g., the top side of plate 320 as shown in FIGS. 10 and 11 , which is the uppermost side of electron-optical element 310) has a central region 351, a peripheral region 353 surrounding central region 351, and a buffer region 352 between central region 351 and peripheral region 353. Buffer region 352 separates central region 351 from peripheral region 353. One or more beam apertures 311 are defined in central region 351. A plurality of vent apertures 312 are defined in peripheral region 353. Buffer region 352 surrounds central region 351 and has a finite radial thickness at all azimuthal angles (e.g., with respect to the major axes of one or more beams propagating through beam tube 300). Thus, central region 351 is separated from peripheral region 353 in all radial directions. In some embodiments, at least a portion of the opposing surface 301 of the beam tube 300 faces the buffer region 352. The opposing surface 301 and the buffer region 352 may define the surfaces of the flow passage 303. The opposing surface 301 and the buffer region 352 may define a flow restriction to prevent or otherwise limit gas flow between the intraluminal volume 340 and the extraluminal region 342, separating the intraluminal volume 340 and the extraluminal region 342. In some embodiments, the entire opposing surface 301 faces the buffer region. In some embodiments, the buffer region 352 is an unapertured region of the surface. Reducing the number of apertures (or having no apertures) opening into the flow passage 303 may facilitate the desired restriction of gas flow through the flow passage 303 and into the intraluminal volume 340. That is, a smooth surface, unlike a surface featuring recesses, supports the smooth flow of gas. The aperture opening into the flow passage 303 may otherwise provide a shortcut for gas to enter the intratube volume 340 from the beam downstream volume 344 .

[0084]

[0097] The central region 351, buffer region 352, and peripheral region 353 can take a variety of forms. Their shapes can be determined, for example, by the multi-beam geometry. Figures 12 and 13 show two examples. In Figure 12, the central region 351, buffer region 352, and peripheral region 353 are circular and concentric with one another. This configuration advantageously facilitates alignment with the beam tube 300, which may typically be cylindrical and may have a circular cross-section. For example, this configuration facilitates alignment of most or all of the buffer region 352 with the opposing surface 301 of the beam tube 300. In Figure 13, the central region 351, buffer region 352, and peripheral region 353 are hexagonal. A hexagonal geometry may be desirable for some multi-beam configurations. In this case, in some embodiments, the opposing surface 301 of the cylindrical beam tube faces only a portion of the buffer region 352, as indicated by the concentric dashed circles in Figure 13.

[0085]

[0098] In one embodiment, plate 320 defines a plurality of blind holes 313 that open into beam downstream volume 344, as shown in FIG. 10 . Blind holes 313 are recesses defined in a surface of plate 320, e.g., the sample-facing surface of the plate, which may desirably avoid affecting gas flow over the surface of plate 320 and over charged particle optical element 310. Alternatively, the holes may be through-holes through plate 310 instead of blind holes 313, but this may be less preferred due to the risk of gas passing through the through-holes, i.e., the additional conductance provided by the through-holes. Blind holes 313 (or other holes) may be configured to act as electric field distortion suppression apertures. Electric field distortion suppression apertures (e.g., blind holes) are configured to suppress distortions in the electric fields of peripheral beam apertures of multiple beam apertures 311 relative to more centrally located beam apertures. The electric field distortion suppression apertures allow the environment of the peripheral beam apertures (those without radially outer beam apertures 311) to be more similar to the environment of the more centrally located beam apertures (those with radially outer beam apertures). Therefore, the spacing between the electric field distortion suppression apertures and the peripheral beam apertures can be made substantially the same as the spacing between the peripheral beam apertures and the more centrally located beam apertures.

[0086]

[0099] 10 , at least a subset of the blind holes 313 are positioned on the opposite side of the buffer region 352 (e.g., in X and Y coordinates within the buffer region 352 with respect to a plane parallel to but on the opposite side of the plate 320). Also as illustrated in FIG. 10 , at least a subset of the blind holes 313 may be positioned on the opposite side of the plate 320 from the beam tube 300, opposite the facing surface 301 of the beam tube 300. The plurality of blind holes 313 may have the same dimensions (e.g., diameter), shape (e.g., circular), and / or cross-sectional area as either or both of the one or more beam apertures 311 and the plurality of vent apertures 312.

[0087]

[0100] In one embodiment, as illustrated in FIG. 10 , the charged particle device 41 further includes at least one other plate beam-downstream of and coplanar with the plate 320. In the illustrated example, two other plates 330 and 331 are provided. One of the other plates (the other plate 331 in the illustrated example) provides an opposing surface facing the sample 208. One or more of the other plates have one or more beam apertures and multiple vent apertures defined therein. In one embodiment, one or more of the vent apertures of the plate 320 are aligned with one or more of the vent apertures of the one or more other plates. In other embodiments, the vent apertures may not be aligned. Providing vent apertures in the multiple plates facilitates gas flow from an area adjacent to the sample 208 to the vent aperture 312 of the plate 320. Plate 320 and one or more of the additional plates may be configured to operate at different potentials to manipulate the trajectories of the charged particles as desired, for example, by providing a lens effect and / or decelerating the charged particles. Plate 320 and one or more of the additional plates may include a control lens array and / or an objective lens array and / or a detector according to any of the configurations described above. One or more of the plates may include a deflector array, for example, a scan deflector or a collimator deflector array. One or more of the plates may include a corrector array, for example, an array of strip electrodes or an array of multipole correctors with individually controllable electrodes. Thus, the stack of plates may have any suitable design, such as those described with respect to and shown in FIGS. 3, 4, and 8. Electric field distortion suppression apertures (blind or open holes) may be provided in any or all of the additional plates, particularly when additional plates 330 and 331 are configured to provide a lens effect that would otherwise destroy the peripheral beam aperture of each additional plate. The electric field distortion suppressing apertures in the other plates 330 and 331 may be aligned with the electric field distortion suppressing apertures provided in plate 320 (eg, along the longitudinal axis of the apertures).In the example of FIG. 10, open (not blind) electric field distortion suppressing apertures 315 (or through holes) are provided in further plates 330 and 331 .

[0088]

[0101] In certain embodiments, the charged particle device 41 further includes a detector. The detector can take any of the forms described above, including those described with respect to FIGS. 5-7 . The detector is configured to detect signal charged particles from the sample 208. The detector can be positioned between the plate 320 and the sample 208. The detector can provide a facing surface of the charged particle device 41 facing the sample. This can be at a downstream-most position facing the sample, or at an upstream-most position adjacent a tube 300 included in or associated with the plate 320, or at any other position of a plate within the electron-optical element 310, such as within a stack of plates of the electron-optical element 310. Alternatively or additionally, the charged particle device 41 can include a secondary column including the detector or a portion of the detector.

[0089]

[0102] In certain embodiments, the plates 310 of the charged particle optical device are separated from one another by spacers 325. The spacers 325 may be electrically insulating to electrically insulate the plates from one another. In some embodiments, one or more of the spacers 325 may include channels to allow gas to be pumped laterally from the region between the plates. This may further help reduce gas flow from the beam downstream volume 344 into the intra-tube volume 340. One or more of the spacers may be in thermal contact with a cooling conduit to thermally condition the connected spacer and / or the portion of the stack surrounding the spacer.

[0090]

[0103] FIG. 14 illustrates an exemplary configuration for mechanically supporting the beam tube 300. This configuration may be applied to any of the embodiments previously described with respect to FIGS. 9-13, for example. The beam tube 300 may have some or all of the features of the beam tubes described with respect to FIGS. 9-13. If the beam tube 300 has a flange (i.e., and is not connected to a plate 320 as shown in and described with respect to FIG. 11), one or more vent apertures 392 may be defined in the flange of the beam tube 300. The location of the vent apertures 392 may correspond to the location of the vent apertures 312 of an adjacent plate, such as plate 320. The fluid flow path for ventilation may pass through the vent apertures 392 in the flange of the beam tube 300 in addition to flowing through the vent apertures 312 in the plate. In one embodiment, the charged particle device 41 includes a plate support 360. The plate support 360 is configured to mechanically support at least the plate 320. Plate support 360 may therefore support the weight of plate 320. Plate support 360 may additionally support one or more further plates 330, 331. In the example shown in Figure 14, plate support 360 supports one further plate 330. Plate support 360 may be rigidly connected to outer frame 371, for example, via support members 372, 373.

[0091]

[0104] Plate support 360 is additionally configured to mechanically support beam tube 300. Thus, plate support 360 may support the weight of beam tube 300 in addition to the weight of plate 320. Plate support 360 may be rigidly connected to beam tube 300 and plate 320. Plate support 360 defines the position of beam tube 300, including, for example, the position of the beam tube in a direction parallel to the longitudinal axis of beam tube 300 and / or the beam path or, if applicable, the multi-beam path through beam tube 300.

[0092]

[0105] Supporting both the plate 320 and the beam tube 300 with the plate support 360 avoids or reduces the need to provide a closer mounting arrangement for the beam tube 300 to the electron beam source 201, 121. Such closer mounting arrangements for the electron beam source 201, 121 may need to be relatively large because they must electrically isolate the beam tube 300 by tens of thousands of volts (e.g., on the order of 30 kV) from the support structure at earth potential. Therefore, avoiding or reducing the need for such mounting arrangements may facilitate reducing the distance between the electron beam source 201, 121 and the sample 208. Reducing the distance between the atomic beam source 201, 121 and the sample 208 is desirable because it reduces errors associated with Coulomb interactions between charged particles as they propagate between the electron beam source and the sample 208. Reducing such errors can improve system performance, including improved spatial resolution performance.

[0093]

[0106] Supporting both the plate 320 and the beam tube 300 with the plate support 360 facilitates precise positioning of the beam tube 300 relative to the plate 320. This can be particularly advantageous where the beam tube 300 is spaced apart from the plate 320 and includes a facing surface 301 that defines a flow passage 303, as in the example of Figure 14. Precise positioning of the beam tube 300 relative to the plate 320 ensures that the size and shape of the flow passage 303, and therefore the flow resistance provided by the flow passage 303, are precisely defined.

[0094]

[0107] In certain embodiments, the plate support 360 is configured to hold the plate 320 and the beam tube 300 in electrical contact with each other. The plate support 360 may, for example, cause a portion of the plate 320 to press directly against a portion of the beam tube 300. This portion may protrude relative to the facing surface 301. Alternatively or additionally, the beam tube 300, e.g., a portion thereof, may indirectly contact the plate 320 via an electrically conductive (e.g., metallic) intervening element. For example, a spacer that contacts and supports the plate 320 and portions of the beam tube 300 may be electrically conductive. Providing an electrical connection between the plate 320 and the beam tube 300 as part of the plate support 360 ensures that the beam tube 300 is held at the same potential as the plate 320 without requiring an additional electrical connection. Holding the beam tube 300 and the plate 320 at the same potential may desirably reduce or avoid unwanted disruptions of the electric field at the interface region between the beam tube 300 and the plate 320, which may result in unwanted lensing effects or other errors.

[0095]

[0108] 14, plate support 360 includes clamping members 361 and 362. Plate support 360 includes a peripheral portion of plate 320 and a peripheral portion of beam tube 300 between clamping members 361, 362 (as indicated diagrammatically by arrow 365 in FIG. 14). Supporting plate 320 and beam tube 300 around the periphery in this manner not only avoids loading more mechanically weaker portions of plate 320, but also avoids interference with areas of plate 320 that include flow passage 303 and / or beam aperture (not shown in FIG. 14) and / or vent aperture 312.

[0096]

[0109] In certain embodiments, as illustrated in FIG. 14 , spacer portion 364 engages a peripheral portion of plate 320 and / or a peripheral portion of beam tube 300. Spacer portion 364 defines a flow passage 303 between a portion of plate 320 radially inward of the peripheral portion of plate 320 and a portion of beam tube 300 radially inward of the peripheral portion of beam tube 300. Spacer portion 364 may be integral with (e.g., form part of) beam tube 300 or integral with (e.g., form part of) plate 320, or spacer portion 364 may be a separate element that contacts but is not integral with both beam tube 300 and plate 320 (as shown in FIG. 14 ). In embodiments in which beam tube 300 is not electrically connected to plate 320 by plate support 360, spacer portion 364 may be formed of an electrically insulating material. Alternatively, spacer portion 364 may be formed of an electrically conductive material, such as a metal.

[0097]

[0110] 14, the beam tube 300 includes a radial extension 368 at the longitudinal end of the beam tube 300 closest to the electron beam source 201, 121 (the top end of the beam tube 300 in the orientation of FIG. 14). The radial extension 368 may be at a bifurcation of the beam tube 300. Such a bifurcation may allow the assembly including the plate support 360, plates and other features supported by the plate support 360, and the beam tube 300 to be mechanically removed from the charged particle device 40. The beam tube 300 may include multiple sections, for example, a proximal section (as shown in FIG. 14) and a distal section (not shown) adjacent to the proximal section along the multi-beam path. This configuration may correspond to or at least be similar to the proximal and distal portions 300A, 300B of the beam tube 300 shown in and described with respect to FIG. 11 , for example, with the proximal and distal portions 300A, 300B having opposing flanges 308, 309. The surfaces of the flanges 308, 309 define the flow passage 303. The distal portion may have a similar radial extension facing the radial extension 368 of the proximal portion. The radial extension 368 may have an annular cross-section perpendicular to the longitudinal axis of the beam tube 300 (e.g., a disk with a central hole). The radial extension 368 may help reduce or prevent the electric field outside the beam tube 300 from affecting charged particles propagating between the electron beam source 201, 121 and the sample 208. The optimum outer radius of the radial extension may scale (e.g., increase) with the distance between the beam tube 300 and the electron beam source 201, 121. The outer radius is desirably greater than the spacing between the beam tube 300 and the electron beam source 201, 121, preferably two times greater, preferably three times greater, preferably four times greater, preferably five times greater.The outer radius is dependent on the inner radius, and the width of the radial extension 368, defined as the difference between the outer and inner radii, desirably also scales (e.g., increases) with the distance between the beam tube 300 and the electron beam source 201, 121 or other adjacent module, e.g., is selected to be greater than the spacing between the beam tube 300 and the electron beam source 201, 121 or other adjacent module, preferably two times greater, preferably three times greater, preferably four times greater, or preferably five times greater.

[0098]

[0111] The embodiments of the charged particle device 41 having the beam tube 300 have been illustrated so far with respect to the beam tube 300 and plate 320 being close to the sample, e.g., the plate 320 being part of, connected to, or adjacent to a control lens array or an objective lens array. For example, in a configuration of the type shown in FIG. 3 , the plate 320 can be associated with a control lens 250 or deflector 235 downstream of the condenser lens 231 for beam collimation. Applying this approach to the plate 320 close to the sample 208 is particularly desirable because the amount of gas liberated (e.g., from outgassing and / or ESD) is particularly high in this region. However, this approach can also be applied to other plates in the charged particle instrument 40. For example, in a configuration of the type shown in FIG. 3 , this approach can be applied to a plate forming part of or adjacent to the condenser lens 231.

[0099]

[0112] In a configuration of the charged particle device 41 for a multi-beam system, the plate 320 includes an aperture, which may be set to a potential and function as a lens electrode. The plate 320 may be referred to as a macrolens electrode. The charged particle device 41 further includes at least one other plate beam-downstream and coplanar with the plate 320, such as the other plates 330 and 331 shown in and described with reference to FIG. 10 . One or more of the other plates adjacent to the plate 320 may also be a macrolens electrode. However, at least one of the other plates may define multiple beam apertures 311. For example, the most beam-upstream of the other plates 330 and 331 including multiple beam apertures may generate multiple beams from a source beam and may be a sub-beamforming array 252, as already described with reference to FIGS. 4 and 9 . Such an arrangement, in which plate 320 includes a macro-aperture and is positioned upstream of another plate 330, 331 that functions as a beam-limiting aperture array, may be called an aperture lens. The macro-aperture of plate 320 may operate on the charged particles of the source beam. The macro-aperture may operate together with the beam-limiting aperture array of another plate to focus each of the beams, for example, when the beam-limiting aperture array is set to a different potential than the macro-lens electrodes. In some arrangements, the macro-aperture and beam-limiting aperture array (or aperture lens) may be controlled to operate on the beams to focus them to a common intermediate focal plane. Any of the other plates may also have a macro-aperture or an array of apertures and may be included in a lens arrangement, for example, as part of an aperture lens (or aperture lens arrangement). Such aperture lens arrays (or aperture lenses) of different configurations described herein may be used to replace the condenser lens array 231 shown in and described with respect to Figure 3, or the condenser lens 270 shown in and described with respect to Figures 4, 8 and 9.4 and 9 may therefore have the condenser lens located adjacent to, rather than spaced apart from, the sub-beamforming array 252. The inventions disclosed herein may be applied to such configurations with aperture lenses. Any or all of the features of the invention may be applied to such configurations featuring such aperture lenses. Incorporation of one or more features of the invention may provide one or more of the benefits of the inventions disclosed herein, for example, in reducing the conductance of outgassing into the intratube volume 340, which may increase the risk of contamination and interference with the functioning of the electron beam source 201.

[0100]

[0113] In such configurations with aperture lenses featuring macro apertures in the adjacent plate 320, beam upstream of the sub-beamforming array in the further plates 330, 331, the plate and the further plates 320, 330, 331 may include vent apertures 312. Such vent apertures may have the same features as those described elsewhere herein, e.g., with respect to Figures 10-14, and characterized therein as vent apertures 312. Optionally, at least the further plates 330, 331 may feature blind holes 313 and / or electric field distortion suppression apertures 315, as described with respect to other embodiments herein. Unless otherwise specified, such configurations featuring aperture lenses may have the same features as those described with respect to Figures 10-13, unless stated to the contrary in these respects.

[0101]

[0114] In some configurations, the tube 300 may be set to a different potential than the plate 320. Thus, the flange 304 may include part of an aperture lens. In some embodiments, such an aperture lens may, for example, collimate the source beam. In some configurations, the plate 320 may have a macro aperture, or alternatively, there may be multiple apertures within the plate 320. Such a configuration may be desirable to provide dimensional control of the electron-optical device, which may reduce the required volume by incorporating the electron-optical function between the flange 304 and the plate 320 instead of requiring additional plates 330, 331. However, the gap between the flange 304 and the plate 320 must accommodate different requirements for different functions, such as the electron-optical gap size and the conductance between the flange 304 and the plate 320. Because such requirements are not consistent and conflict, compromises may be necessary.

[0102]

[0115] In some variations, the lens function of the electrostatic aperture lens may additionally or alternatively be realized by a macro-magnetic lens positioned near the end of the liner tube adjacent plate 320, e.g., around the liner tube. In such a configuration in plate 320, multiple apertures may be defined, and plate 320 may be sub-beamforming array 252. In such a configuration, features of the previously described embodiments, e.g., flange portions 304, 308, 309 and flow passage 303, may be present. However, in a different configuration, e.g., where a macro-magnetic lens is present without an electrostatic aperture lens, tube 300 (e.g., wall 302) may be secured to plate 320, e.g., sealed to plate 320. Sealing plate 320 to tube 300 may help keep the ambient atmosphere within intra-tube volume 340 and extra-tube region 342 separate, e.g., by preventing direct communication between the intra-tube volume 340 and extra-tube region 342. While the seal may improve the vacuum in the intra-tube volume 340 by preventing gas intrusion between the end of the liner tube 300 and the plate 320, there may still be a risk of outgassing and / or contamination within the intra-tube volume 340, for example, in the electron beam source 201. That is, outgassing caused by electron-stimulated desorption may occur due to the interaction of the beam (or beams of multiple beams) with the plate 320 and / or any of the other plates 330, 331. In such a configuration, outgassing may enter the intra-tube volume 340 through the beam aperture 311, which may lead to interference of such outgassing with the function of the electron beam source 201. Such an arrangement may include any or all of the disclosed inventive features (e.g., vent holes 312, blind holes 313, electric field distortion suppression apertures 315, etc. in the buffer region 352 and peripheral region 353).

[0103]

[0116] As previously mentioned, such features of the invention disclosed herein can help prevent the ingress of contamination into the intratube volume, for example, through beam aperture 311. For example, even in configurations in which tube 300 and plate 320 are sealed together, operation of at least one aspect of the invention to draw outgassing radially outward of the beam path and beam aperture 311, for example, through a vent aperture, can reduce gas pressure below plate 320 (or at least another plate 330, 331), which functions as a beam-limiting aperture array. Such a pressure reduction in the beam downstream of such a plate, for example, plate 320, can help reduce gas flow into intratube volume 340, for example, through beam aperture 311.

[0104]

[0117] The charged particle device 41 may be provided as part of an evaluation apparatus for evaluating a sample using charged particles. The evaluation apparatus may include a sample support configured to support the sample 208 and a detector configured to detect the charged particles from the sample 208.

[0105]

[0118] The charged particle device 41 according to the above-described embodiments may be used in a method of evaluating a sample 208 using charged particles. The method includes projecting one or more beams of charged particles toward the sample 208 using the charged particle device 41. The charged particle device 41 includes a charged particle optical element 310. The charged particle optical element 310 directs the one or more beams toward the sample 208. The charged particle optical element 310 includes a plate 320 having a plurality of beam apertures 311 and a plurality of vent apertures 312 defined therein. The charged particle device includes a beam tube 300 defining an intratube volume 340 and an extratube region 342. The one or more beam apertures 311 allow the charged particles of one or more beams to pass toward the sample (through the beam apertures) from the intratube volume 340 to a beam downstream volume 344 on the opposite side of the plate from the intratube volume 340. The vent aperture 312 fluidly connects the beam downstream volume 344 to the extravascular region 342. The method includes delivering fluid from the beam downstream volume 344 through the vent aperture 312 to the extravascular region 342.

[0106]

[0119] In some embodiments, the method uses a pumping arrangement to pump down the intraluminal volume 340 separately from the extraluminal region 342. In some embodiments, the extraluminal region 342 is pumped down using a pumping system separate from that used to pump down the intraluminal volume. This allows for independent control of the vacuum in the two volumes. Embodiments of the present disclosure attempt to keep the volumes (and therefore vacuum) in the extraluminal region 342 and the intraluminal volume 340 separate from one another. One pump may be assigned to the intraluminal volume 340 and a different pump may be assigned to the extraluminal region 342.

[0107]

[0120] References to a component or system of components or elements being controllable to manipulate a charged particle beam in a certain manner include configuring a controller or control system or control unit to control that component to manipulate the charged particle beam in the described manner, as well as, optionally, using other controllers or devices (e.g., voltage supplies and / or current supplies) to control that component to manipulate the charged particle beam in this manner. For example, voltage supplies may be electrically connected to one or more components for applying an electrical potential to the components, such as, a non-limiting list including, the control lens array 250 and the objective lens array 241.

[0108]

[0121] References to upper and lower, top and bottom, up and down, etc. should be understood to refer to upstream and downstream beams (typically, but not always, longitudinal) of the charged particle beam impinging on the sample 208. Thus, references to upstream and downstream beams are intended to refer to directions relative to the beam path, independent of any prevailing gravitational fields.

[0109]

[0122] The electron-optical system described herein may take the form of a series of aperture arrays or electron-optical elements arranged in an array along the beam or multi-beam path. Such electron-optical elements may be electrostatic. In some embodiments, for example, all electron-optical elements from the beam-limiting aperture array to the last electron-optical element in the beam path before the sample may be electrostatic and / or in the form of aperture arrays or plate arrays. In some configurations, one or more of the electron-optical elements are fabricated as microelectromechanical systems (MEMS) (i.e., using MEMS fabrication techniques). The electron-optical elements may include magnetic and electrostatic elements. For example, a compound array lens may contain a multi-beam path with upper and lower pole plates within the magnetic lens and feature a macro-magnetic lens positioned along the multi-beam path. The pole plates may have an array of apertures for the beam paths of the multi-beam. Electrodes may be present above, below, or between the pole plates to control and optimize the electromagnetic field of the compound lens array.

[0110]

[0123] An evaluation device, tool, or system according to the present disclosure may include a device that performs a qualitative evaluation (e.g., pass / fail) of a sample, a device that performs a quantitative measurement (e.g., feature size) of a sample, or a device that generates an image of a map of a sample. Examples of evaluation devices, tools, or systems are inspection tools (e.g., to identify defects), review tools (e.g., to classify defects), and metrology tools, or tools that can perform any combination of evaluation functions associated with an inspection tool, review tool, or metrology tool (e.g., metrology tool).

[0111]

[0124] The functions provided by a controller or control system or control unit may be computer-implemented. Any suitable combination of elements may be used to provide the required functionality, including, for example, a CPU, RAM, SSD, motherboard, network connection, firmware, software, and / or other elements known in the art that enable the necessary computing operations to be performed. The necessary computing operations may be defined by one or more computer programs. The one or more computer programs may be provided in the form of a medium, optionally a non-transitory medium, that stores computer-readable instructions. When the computer-readable instructions are read by a computer, the computer performs the necessary method steps. The computer may consist of a self-contained unit or a distributed computing system having several different computers interconnected via a network.

[0112]

[0125] While the invention has been described in connection with various embodiments, other embodiments of the invention will become apparent to those skilled in the art from consideration of the specification and practice of the invention disclosed herein. It is intended that the specification and examples be considered as exemplary only, with the true scope and spirit of the invention being indicated by the following claims and clauses.

[0113]

[0126] Clause 1. A charged particle device for projecting one or more beams of charged particles toward a sample, the device including: a charged particle optical element configured to direct the one or more beams of charged particles toward the sample, the charged particle optical element including: a plate having one or more beam apertures and a plurality of vent apertures defined therein; and a beam tube including an intra-tube volume including a path of charged particles of the one or more beams upstream of the plate and an extra-tube region outside the beam tube, wherein the one or more beam apertures are configured to pass the charged particles of the one or more beams from the intra-tube volume toward the sample to a downstream beam volume on an opposite side of the intra-tube volume of the plate, and the vent apertures are configured to fluidly connect the downstream beam volume to the extra-tube region.

[0114]

[0127] Clause 2. The device of Clause 1, wherein the total open area of ​​the vent apertures is greater than the total open area of ​​the one or more beam apertures.

[0115]

[0128] Clause 3. The device of clause 1 or 2, wherein the vent aperture and the one or more beam apertures are configured such that a total flow conductance through the plate provided by the vent aperture is greater than a total flow conductance through the plate provided by the one or more beam apertures.

[0116]

[0129] Clause 4. A device according to any one of clauses 1 to 3, wherein the number of vent apertures is greater than the number of beam apertures.

[0117]

[0130] Clause 5. The device of any one of clauses 1 to 4, wherein the one or more beam apertures and the plurality of vent apertures comprise apertures having a common size, a common shape, and / or a common cross-sectional area.

[0118]

[0131] Clause 6. The device of any one of clauses 1 to 5, wherein the one or more beam apertures comprise a plurality of beam apertures, wherein an average spacing between the beam apertures is equal to an average spacing between the vent apertures, and preferably the beam apertures are arranged in an aperture pattern having an aperture pitch and the vent apertures are arranged in a vent pattern having a vent pitch, wherein the aperture pitch and the vent pitch are equal, and preferably the beam apertures and vent apertures are arranged in respective two-dimensional arrays having a common pattern.

[0119]

[0132] Clause 7. The device of any one of clauses 1-6, wherein the beam tube includes an opposing surface spaced from the plate to define a flow passage, the flow passage configured to restrict flow between an intratube volume and an extratube region.

[0120]

[0133] Clause 8. The device of clause 7, wherein the beam tube includes a flange portion, the opposing surface being defined by the flange portion, and / or the beam tube includes a flange portion and a vent aperture defined in the flange portion, preferably the vent aperture in the flange portion corresponding in position to the position of at least one of the vent apertures in the plate.

[0121]

[0134] Clause 9. The device of clause 8, wherein the flange portion extends further from the path of the charged particles than an adjacent portion of the beam tube, preferably the beam tube includes a wall, and the flange portion extends further from the path of the charged particles than an outermost portion of the wall, preferably than an outermost portion of the wall adjacent the flange portion.

[0122]

[0135] Clause 10. The device of any one of clauses 7 to 9, wherein the passage surface of the plate defining the flow passage is coplanar with the surface of the plate defining the opening to the beam aperture, and preferably the passage surface is on the plate side of the flow passage.

[0123]

[0136] Clause 11. The device of any one of clauses 7 to 9, wherein the plate includes a protrusion, and the surface defining the flow passage on the plate side of the flow passage is provided by the protrusion.

[0124]

[0137] Clause 12. The device of any one of clauses 1-6, wherein the beam tube includes a proximal portion and a distal portion, the proximal portion connected to the plate, the distal portion positioned distally relative to the plate, the proximal portion and the distal portion including respective opposing surfaces spaced apart from one another to define a flow passage, preferably the flow passage configured to restrict flow between an intraluminal volume and an extraluminal region, preferably the proximal portion and the distal portion including respective flange portions including the opposing surfaces.

[0125]

[0138] Clause 13. The device of any one of clauses 7 to 12, wherein the surface of the plate upstream of the beam has a central region, a peripheral region surrounding the central region, and a buffer region between the central region and the peripheral region and separating the central region from the peripheral region, wherein one or more beam apertures are defined in the central region and a plurality of vent apertures are defined in the peripheral region.

[0126]

[0139] Clause 14. The device of clause 13, wherein at least a portion of the opposing surface of the beam tube faces the buffer region.

[0127]

[0140] Clause 15. The device of clause 13 or 14, wherein the one or more beam apertures include a plurality of beam apertures, and the plate defines a plurality of electric field distortion suppression apertures configured to suppress electric field distortion of beam apertures peripheral to the plurality of beam apertures.

[0128]

[0141] Clause 16. The device of any one of clauses 13-15, wherein the plate defines a plurality of blind holes opening into the downstream beam volume, and preferably the electric field distortion suppression apertures are blind holes.

[0129]

[0142] Clause 17. The device of clause 16, wherein at least a subset of the blind holes are positioned on opposite sides of the buffer area.

[0130]

[0143] Clause 18. The device of clause 16 or 17, wherein at least a subset of the blind holes are positioned on the side of the plate opposite the beam tube and opposite the facing surface of the beam tube.

[0131]

[0144] Clause 19. The device of any one of clauses 16 to 18, wherein the plurality of blind holes have the same size, shape, and / or cross-sectional area as either or both of the one or more beam apertures and the plurality of vent apertures.

[0132]

[0145] Clause 20. A device of any one of clauses 1 to 19, wherein the beam tube is metallic or contains a metallic coating.

[0133]

[0146] Clause 21. The device of any one of clauses 1 to 20, further comprising a detector configured to detect signal charged particles from the sample, preferably the detector being positioned between the plate and the sample, e.g., providing a facing surface of the device for facing the sample, or preferably the device having a secondary column including the detector.

[0134]

[0147] Clause 22. The device of any one of clauses 1 to 21, including at least one further plate beam downstream of and coplanar with the plate, one of the further plates providing an opposing surface of the device facing the sample, and one or more of the further plates defining one or more beam apertures and a plurality of vent apertures, preferably one or more of the vent apertures of the plate and one or more of the further plates being aligned.

[0135]

[0148] Clause 23. The device of clause 22, wherein at least one of the plate and the at least one further plate has a different number of beam apertures defined therein, e.g., defined in at least one of the plates and at least one further plate has a single beam aperture, desirably defined in the plate and having a single beam aperture.

[0136]

[0149] Clause 24. The device of any one of clauses 1 to 23, wherein different potentials are applied to the beam tube and plate, for example to move (e.g., focus) one or more beams.

[0137]

[0150] Clause 25. The device of any one of clauses 1 to 23, wherein the tube and plate are fixed together, e.g., sealed together.

[0138]

[0151] Clause 26. The device of any one of clauses 1 to 25, including a plate support configured to mechanically support at least the plate.

[0139]

[0152] Clause 27. The device of clause 26, wherein the plate support is additionally configured to mechanically support the beam tube.

[0140]

[0153] Clause 28. The device of clause 26 or 27, wherein the plate support is configured to hold the plate and the beam tube in electrical contact with each other.

[0141]

[0154] Clause 29. The device of any one of clauses 26 to 28, wherein the plate support includes clamping members configured to clamp a peripheral portion of the plate and a peripheral portion of the beam tube therebetween.

[0142]

[0155] Clause 30. The device of clause 29, including a spacer portion configured to engage a peripheral portion of the plate and / or a peripheral portion of the beam tube to define a flow passage between the plate and the beam tube, preferably between a portion radially inward of the peripheral portion of the plate and a portion of the beam tube radially inward of the peripheral portion of the beam tube.

[0143]

[0156] Clause 31. The device of any one of clauses 26 to 30, wherein the beam tube includes radial extensions at longitudinal ends of the beam tube configured to be closest to a charged particle source of the charged particle device.

[0144]

[0157] Clause 32. The device of clause 31, wherein the radial extension has an annular cross section perpendicular to the longitudinal axis of the beam tube.

[0145]

[0158] Clause 33. The device of clause 32, wherein the outer radius of the radial extension is greater than the spacing between the beam tube and the charged particle source.

[0146]

[0159] Clause 34. An evaluation apparatus for evaluating a sample using charged particles, the apparatus comprising: a sample support configured to support a sample; a charged particle device of any one of clauses 1 to 33 configured to project one or more beams of charged particles towards the sample; and a detector configured to detect signal charged particles from the sample.

[0147]

[0160] Clause 35. The apparatus of clause 34, including a pumping mechanism configured to pump the intraluminal volume separately from the extraluminal region, preferably the pumping mechanism having separate pumps configured to pump the intraluminal volume and the extraluminal region.

[0148]

[0161] Clause 36. A method for evaluating a sample using charged particles, comprising projecting one or more beams of charged particles toward the sample using a charged particle device, the device comprising a charged particle optical element that directs the one or more beams toward the sample, the charged particle optical element comprising a plate having one or more beam apertures and a plurality of vent apertures defined therein, the device comprising a beam tube defining an intra-tube volume including a path of charged particles of the one or more beams upstream of the plate and an extra-tube region outside the beam tube, the one or more beam apertures allowing the charged particles of the one or more beams to pass from the intra-tube volume to a downstream beam volume opposite the intra-tube volume of the plate toward the sample, the vent aperture configured to fluidly connect the downstream beam volume to the extra-tube region, and the method comprising delivering fluid from the downstream beam volume to the extra-tube region through the vent aperture.

[0149]

[0162] Clause 37. The method of clause 36, further comprising pumping down the intraluminal volume separately from the extraluminal region, preferably pumping down the extraluminal region with one pump and the intraluminal volume with a different pump.

Claims

1. 1. A charged particle device for projecting one or more beams of charged particles towards a sample, comprising: a charged particle optical element configured to direct one or more beams of charged particles at a sample, the charged particle optical element including a plate having one or more beam apertures and a plurality of vent apertures defined therein; a beam tube defining an intra-tube volume including a path of a charged particle plate of the one or more beams upstream of the plate, and an extra-tube volume outside the beam tube; the one or more beam apertures are configured to allow charged particles of the one or more beams to pass from the intra-tube volume to a downstream beam volume on an opposite side of the plate from the intra-tube volume toward the sample; The charged particle device, wherein the vent aperture is configured to fluidly connect the downstream beam volume to the extratubular region.

2. The device of claim 1 , wherein a total opening area of ​​the vent apertures is greater than a total opening area of ​​the one or more beam apertures.

3. 3. The device of claim 1 or 2, wherein the vent aperture and the one or more beam apertures are configured such that a total flow conductance through the plate provided by the vent aperture is greater than a total flow conductance through the plate provided by the one or more beam apertures.

4. The device according to any one of claims 1 to 3, wherein the number of vent apertures is greater than the number of beam apertures.

5. The device of any one of claims 1 to 4, wherein the one or more beam apertures and the plurality of vent apertures comprise apertures having a common size, a common shape, and / or a common cross-sectional area.

6. 6. The device of claim 1, wherein the one or more beam apertures comprise a plurality of beam apertures, an average spacing between the beam apertures being equal to an average spacing between the vent apertures, and wherein the beam apertures are arranged in an aperture pattern having an aperture pitch and the vent apertures are arranged in a vent pattern having a vent pitch, the aperture pitch and the vent pitch being equal, and wherein the beam apertures and the vent apertures are arranged in respective two-dimensional arrays having a common pattern.

7. 7. The device of claim 1, wherein the beam tube includes opposing surfaces spaced apart from the plate to define a flow passage, the flow passage configured to restrict flow between the intratubular volume and the extratubular region.

8. The device of claim 7 , wherein the beam tube includes a flange portion, and the opposing surface is defined by the flange portion.

9. 9. The device of claim 8, wherein the flange portion extends further from the path of the charged particles than an adjacent portion of the beam tube, preferably the beam tube includes a wall and the flange portion extends further from the path of the charged particles than an outermost portion of the wall, preferably than an outermost portion of the wall adjacent the flange portion.

10. 10. A device according to any one of claims 7 to 9, wherein a passage surface of the plate defining the flow passage is flush with a surface of the plate defining an opening to the beam aperture, and preferably the passage surface is on the plate side of the flow passage.

11. a surface of the plate upstream of the beam having a central region, a peripheral region surrounding the central region, and a buffer region between the central region and the peripheral region, separating the central region from the peripheral region; the one or more beam apertures are defined in the central region; the plurality of vent apertures are defined in the peripheral region; A device according to any one of claims 7 to 10.

12. The device of claim 11 , wherein at least a portion of the opposing surface of the beam tube faces the buffer region.

13. 13. The device of claim 11 or 12, wherein the one or more beam apertures comprise a plurality of beam apertures, and the plate defines a plurality of electric field distortion suppressing apertures configured to suppress distortions in electric fields of beam apertures peripheral to the plurality of beam apertures.

14. A device according to any one of claims 11 to 13, wherein the plate defines a plurality of blind holes opening into the downstream beam volume, and preferably the electric field distortion suppression apertures are the blind holes.

15. A device according to any preceding claim, wherein the beam tube is metallic or comprises a metallic coating.

Images