CN118266055A

CN118266055A - Charged particle evaluation system and method

Info

Publication number: CN118266055A
Application number: CN202280074777.5A
Authority: CN
Inventors: N·J·M·博世; M·J-J·维兰德; P·P·亨佩尼尤斯; E·斯洛特
Original assignee: ASML Holding NV
Current assignee: ASML Holding NV
Priority date: 2021-11-11
Filing date: 2022-10-11
Publication date: 2024-06-28

Abstract

The present invention provides a charged particle evaluation system for projecting a charged particle beam towards a sample. The system comprises: a sample holder configured to hold a sample; a charged particle optical system configured to project a charged particle beam from a charged particle source downstream toward the sample and comprising a cleaning target; a cleaning device. The cleaning device is configured to supply the cleaning medium in a cleaning flow incident on the cleaning target to the cleaning target such that the cleaning flow approaches the cleaning target from downstream of the cleaning target, and to energize the cleaning medium at or near the cleaning target such that the cleaning medium cleans at least a portion of a surface of the cleaning target.

Description

Charged particle evaluation system and method

Cross Reference to Related Applications

The present application claims priority from EP application 21207845 filed 11/2021 and EP application 22161715 filed 3/2022, which are incorporated herein by reference in their entirety.

Technical Field

Embodiments provided herein relate generally to charged particle evaluation systems and methods of operating charged particle evaluation systems.

Background

When manufacturing semiconductor Integrated Circuit (IC) chips, undesirable pattern defects inevitably occur on a substrate (i.e., wafer) or mask during a manufacturing process as a result of, for example, optical effects and incidental particles, thereby reducing yield. Therefore, monitoring the extent of undesired pattern defects is an important process in the manufacture of IC chips. More generally, inspection and/or measurement of the surface of a substrate or other object/material is an important process during and/or after its manufacture.

Pattern inspection tools with charged particle beams have been used for inspecting objects, for example for detecting pattern defects. These tools typically use electron microscopy techniques, such as electron optical systems in Scanning Electron Microscopes (SEM). In an exemplary electron optical system such as an SEM, a primary electron beam of electrons having a relatively high energy is targeted to a final deceleration step in order to land on the sample with a relatively low landing energy. The electron beam is focused as a probe spot on the sample. The interaction between the material structure at the detection point and the landing electrons from the electron beam causes electrons to be emitted from the surface, such as secondary electrons, backscattered electrons, or auger electrons. The generated secondary electrons may be emitted from the material structure of the sample. By scanning the primary electron beam as a detection point over the sample surface, secondary electrons can be emitted over the sample surface. By collecting these emitted secondary electrons from the sample surface, the pattern inspection tool can obtain an image that is representative of the characteristics of the material structure of the sample surface. The intensity of the electron beam, including the backscattered electrons and the secondary electrons, may vary based on the nature of the internal and external structure of the sample, and may thus indicate whether the sample has defects.

The inspection tool may be contaminated with hydrocarbons. This occurs when molecular carbon contaminants grow on surfaces in a vacuum atmosphere having a high hydrocarbon partial pressure and are exposed to electrons, a process known as Electron Beam Induced Deposition (EBID). One technique to limit contamination on components of a charged particle optical system is differential pumping. However, there is still the problem that in the inspection tool there is a limited space, in particular between the charged particle optical system and the sample that can be coated with resist. Furthermore, the effectiveness of techniques such as differential pumping may be limited in proximity to the sample. There is not enough space available in a typical design structure of a charged particle optical system for solutions such as differential pumping for limiting, if not preventing, contamination on all components of the charged particle optical system that may be contaminated.

Disclosure of Invention

It is an object of the present disclosure to provide embodiments of a charged particle evaluation system and a method of operating a charged particle evaluation system.

According to a first aspect of the present invention, there is provided a charged particle evaluation system for projecting a charged particle beam towards a sample. The system includes being: a sample holder configured for holding a sample; a charged particle optical system configured to project a charged particle beam from a charged particle source downstream toward the sample and comprising a cleaning target; a cleaning device. The cleaning device is configured to supply the cleaning medium in a cleaning flow incident on the cleaning target to the cleaning target such that the cleaning flow approaches the cleaning target from downstream of the cleaning target, and to energize the cleaning medium at or near the cleaning target such that the cleaning medium cleans at least a portion of a surface of the cleaning target.

According to a second aspect of the present invention, there is provided a method of operating a charged particle evaluation system configured to project a charged particle beam towards a sample. A charged particle evaluation system comprising: a sample holder configured to hold a sample, and a charged particle optical system configured to project a charged particle beam from a charged particle source downstream toward the sample. The charged particle optical system includes a cleaning target. The method comprises the following steps: supplying a cleaning medium in a cleaning flow incident on the cleaning target to the cleaning target, the supply of the cleaning flow being such that the cleaning flow approaches the cleaning target from downstream of the cleaning target; and energizing the cleaning medium at or near the cleaning target such that the cleaning medium cleans at least a portion of the surface of the cleaning target.

According to a third aspect of the present invention there is provided a charged particle evaluation system for projecting a charged particle beam towards a sample, the system comprising: a sample holder configured to hold a sample; a charged particle optical system configured to project a charged particle beam from a charged particle source downstream towards the sample, the charged particle optical system comprising a cleaning target; a cleaning arrangement comprising: a cleaning device for supplying cleaning medium in a cleaning flow; a cleaning guide configured to guide and direct a cleaning flow from the cleaning device toward the cleaning target such that the cleaning flow is incident on the cleaning target such that the cleaning flow approaches the cleaning target from downstream of the cleaning target, wherein the cleaning device is positioned in an upstream direction relative to the sample holder, and the cleaning guide comprises a flow deflector configured to deflect the cleaning flow toward the cleaning target.

According to a fourth aspect of the present invention there is provided a charged particle evaluation system for projecting a charged particle beam towards a sample, the system comprising: a sample holder configured to hold a sample; a charged particle optical system configured to project a charged particle beam from a charged particle source downstream toward the sample and comprising a cleaning target; and a cleaning device configured to supply the cleaning medium in a cleaning flow incident on the cleaning target to the cleaning target such that the cleaning flow approaches the cleaning target from downstream of the cleaning target. The charged particle evaluation system is configured to actively direct a cleaning flow toward a cleaning target.

According to a fifth aspect of the present invention, there is provided a method of operating a charged particle evaluation system configured to project a charged particle beam towards a sample. The charged particle evaluation system includes: a sample holder configured to hold a sample; a charged particle optical system configured to project a charged particle beam from a charged particle source downstream towards the sample; the charged particle optical system includes a cleaning target. The method comprises the following steps: 1) Supplying the cleaning medium in the cleaning flow to the cleaning target so as to be incident on the cleaning target, the cleaning flow being supplied so that the cleaning flow approaches the cleaning target from downstream of the cleaning target; and 2) actively directing the cleaning flow toward the cleaning target.

Drawings

The above and other aspects of the present disclosure will become more apparent from the description of exemplary embodiments, which is to be read in connection with the accompanying drawings.

Fig. 1 is a schematic diagram illustrating an exemplary electron beam inspection apparatus.

Fig. 2 is a schematic diagram illustrating an exemplary multi-beam charged particle evaluation system as part of the exemplary electron beam inspection apparatus of fig. 1.

FIG. 3 is a schematic diagram of an exemplary multi-beam charged particle evaluation system according to one embodiment.

FIG. 4 is a schematic diagram of an exemplary charged particle evaluation system including a macro-collimator and a macro-scanning deflector.

FIG. 5 is a schematic diagram of an exemplary multi-beam charged particle evaluation system according to one embodiment.

Fig. 6 is a schematic diagram of a portion of the multi-beam charged particle evaluation system of fig. 5.

Fig. 7 is a schematic cross-sectional view of an objective lens array of a charged particle evaluation system according to one embodiment.

Fig. 8 is a bottom view of a variation of the objective lens array of fig. 7.

Fig. 9 is an enlarged cross-sectional view of a detector incorporated in the objective lens array of fig. 7.

Fig. 10 is a bottom view of a detector element of the detector.

FIG. 11 is a schematic diagram of an exemplary charged particle evaluation system including a cleaning device according to one embodiment.

FIG. 12 is a schematic diagram of an exemplary charged particle evaluation system including a cleaning device disposed on a stage, according to one embodiment.

FIG. 13 is a schematic diagram of an exemplary charged particle evaluation system including a cleaning device and a cleaning guide, according to one embodiment.

FIG. 14 is a schematic diagram of an exemplary charged particle evaluation system in which the charged particle source includes a cleaning device, according to one embodiment.

FIG. 15 is a schematic diagram of an exemplary charged particle evaluation system including a cleaning device configured to supply a cleaning medium and emit excitation light, according to one embodiment.

Fig. 16A and 16B are schematic diagrams of an exemplary charged particle evaluation system including a cleaning device and a light emitter, according to one embodiment.

FIG. 17 is a schematic diagram of an exemplary charged particle evaluation system including a cleaning device configured to actively direct a cleaning flow to a cleaning target, according to one embodiment.

Fig. 18A and 18B are schematic diagrams of an exemplary charged particle evaluation system configured to actively direct a cleaning flow to a cleaning target, wherein a curved deflector is disposed on an actuation stage, according to one embodiment.

FIG. 19 is a schematic diagram of an exemplary charged particle evaluation system in which a deflector is configured to be actuated to actively direct a cleaning flow to a cleaning target, according to one embodiment.

FIG. 20 is a schematic diagram of an exemplary charged particle evaluation system in which a deflector is disposed on an actuation stage to actively direct a cleaning flow to a cleaning target, according to one embodiment.

The schematic and view shows the following components. However, the components illustrated in the figures are not drawn to scale.

Detailed Description

Reference will now be made in detail to exemplary embodiments, examples of which are illustrated in the accompanying drawings. The following description refers to the accompanying drawings, in which the same reference numerals in different drawings denote the same or similar elements, unless otherwise specified. The implementations set forth in the following description of exemplary embodiments do not represent all implementations consistent with the present invention. Rather, they are merely examples of apparatus and methods consistent with aspects related to the invention as set forth in the following claims.

The enhanced computational power of electronic devices (which reduces the physical size of the device) can be achieved by significantly increasing the packing density of circuit components (such as transistors, capacitors, diodes, etc.) on an IC chip. This can be achieved by increasing the resolution, enabling smaller structures to be fabricated. For example, the IC chip of a smartphone may include more than 20 hundred million transistors, each transistor having a size less than 1/1000 of human hair, the size of the IC chip being the size of a thumb nail and available in 2019 or earlier. Thus, semiconductor IC fabrication is a complex and time-consuming process with many individual steps. Errors in one of these steps may significantly affect the functionality of the final product. The goal of the manufacturing process is to increase the overall yield of the process. For example, for a 50 step process (where a step may represent the number of layers formed on a wafer), each individual step must have a yield of greater than 99.4% in order to achieve a 75% yield. If each individual step has a yield of 95%, the overall process yield will be as low as 7%.

Although high process yields are required in IC chip manufacturing equipment, it is also necessary to maintain high substrate (i.e., wafer) yields (defined as the number of substrates processed per hour). The presence of defects can affect high process yields and high substrate yields. This is especially true if operator intervention is required to inspect the defect. Thus, high throughput detection and identification of micro-scale and nano-scale defects by inspection tools such as scanning electron microscopy ("SEM") is necessary to maintain high yields and low cost.

The SEM includes a scanning device and a detector arrangement. The scanning device comprises an illumination means comprising an electron source for generating primary electrons and a projection means for scanning a sample, such as a substrate, with one or more focused beams of primary electrons. At least the illumination device or illumination system and the projection device or projection system may together be referred to as an electron optical system or device. The primary electrons interact with the sample and generate secondary electrons. As the sample is scanned, the detection device captures secondary electrons from the sample so that the SEM can produce an image of the scanned area of the sample. Such an inspection device may utilize a single primary electron beam incident on the sample. For high throughput inspection, some inspection devices use multiple focused beams of primary electrons, i.e., multiple beams. The component beams of the multiple beams may be referred to as beamlets or beamlets. The beamlets may be arranged within the multi-beam with respect to each other in a multi-beam arrangement. Multiple beams may scan different portions of the sample simultaneously. Thus, the multi-beam inspection apparatus is capable of inspecting a sample at a much higher speed than a single-beam inspection apparatus.

One implementation of the known multi-beam inspection device is described below.

The figures are schematic. Accordingly, the relative dimensions of the components in the drawings are exaggerated for clarity. In the following description of the drawings, the same or similar reference numerals refer to the same or similar components or entities, and only differences with respect to the respective embodiments are described. While the description and drawings are directed to electron optical systems, it should be understood that these embodiments are not intended to limit the disclosure to particular charged particles. Thus, references to electrons in this document may be more generally considered to be references to charged particles, which are not necessarily electrons.

Referring now to fig. 1, fig. 1 is a schematic diagram illustrating an exemplary charged particle beam inspection apparatus 100. The charged particle beam inspection apparatus 100 of fig. 1 includes a main chamber 10, a load lock chamber 20, a charged particle evaluation system 40 (which may also be referred to as an electron beam system or tool), an Equipment Front End Module (EFEM) 30, and a controller 50. A charged particle evaluation system 40 is located within the main chamber 10.

The EFEM 30 includes a first load port 30a and a second load port 30b. The EFEM 30 may include additional load port(s). For example, the first load port 30a and the second load port 30b may receive a substrate Front Opening Unified Pod (FOUP) containing a substrate (e.g., a semiconductor substrate or a substrate made of other material (s)) or a sample to be inspected (substrate, wafer, and sample are collectively referred to hereinafter as "sample"). One or more robotic arms (not shown) in the EFEM 30 transfer samples to the load lock chamber 20.

The load lock chamber 20 is used to remove gas around the sample. This creates a vacuum with a partial gas pressure lower than the pressure in the surrounding environment. The load lock chamber 20 may be connected to a load lock vacuum pump system (not shown) that removes gas particles from the load lock chamber 20. The operation of the load lock vacuum pump system enables the load lock chamber to reach a first pressure below atmospheric pressure. After reaching the first pressure, one or more robotic arms (not shown) transfer the sample from the load lock chamber 20 to the main chamber 10. The main chamber 10 is connected to a main chamber vacuum pump system (not shown). The main chamber vacuum pump system removes gas particles in the main chamber 10 so that the pressure around the sample reaches a second pressure lower than the first pressure. After reaching the second pressure, the sample is transferred to a charged particle evaluation system 40, through which the sample can be inspected. The charged particle evaluation system 40 comprises an electron optical system 41. The term "electron optical apparatus" may be synonymous with electron optical system 41. The electron optical system 41 may be a multi-beam electron optical system 41 configured to project multiple beams towards the sample, e.g. beamlets arranged in a multi-beam arrangement with respect to each other. Alternatively, the electron optical system 41 may be a single beam electron optical system 41 configured to project a single beam towards the sample.

The controller 50 is electrically connected to the charged particle evaluation system 40. The controller 50 may be a processor (such as 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. Although 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 the structure. The controller 50 may be located in one of the constituent elements of the charged particle beam inspection device or it may be distributed over at least two constituent elements. Although the present disclosure provides an example of a main chamber 10 housing an electron beam inspection tool, it should be noted that aspects of the present disclosure are not limited in their broadest sense to chambers housing electron beam inspection tools. Instead, it should be understood that the above-described principles may also be applied to other arrangements of other tools and devices operating at the second pressure.

Referring now to fig. 2, fig. 2 is a schematic diagram illustrating an exemplary charged particle evaluation system 40 including a multi-beam electron optical system 41 as part of the exemplary charged particle beam inspection apparatus 100 of fig. 1. The multi-beam electron optical system 41 includes an electron source 201 and a projection device 230. The charged particle evaluation system 40 further comprises an actuation stage 209 and a sample holder 207. The sample holder may have a holding surface (not shown) for supporting and holding the sample. Thus, the sample holder may be configured to support a sample. Such a holding surface may be an electrostatic clamp operable to hold the sample during operation of the electron optical system 41 (e.g., evaluation or inspection of the sample). The holding surface may be recessed into the sample holder, e.g. the surface of the sample holder is oriented to face the electron optical system 41. The electron source 201 and the projection device 230 may together be referred to as an electron optical system 41. The sample holder 207 is supported by an actuation stage 209 for holding a sample 208 (e.g., a substrate or a mask) for inspection. The multi-beam electron optical system 41 further includes a detector 240 (e.g., an electron detection device).

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

The projection device 230 is configured to convert the primary electron beam 202 into a plurality of beamlets 211, 212, 213 and to direct each beamlet onto the sample 208. Although three beamlets are shown for simplicity, there may be tens, hundreds or thousands of beamlets. The beamlets may be referred to as beamlets.

The controller 50 may be connected to various parts of the charged particle beam inspection device 100 of fig. 1, such as the electron source 201, the detector 240, the projection device 230, and the actuation stage 209. The controller 50 may perform various image and signal processing functions. The controller 50 may also generate various control signals to control the operation of a charged particle beam inspection device, including a charged particle multi-beam device.

Projection device 230 may be configured to focus beamlets 211, 212, and 213 onto sample 208 for inspection, and may form three detection points 221, 222, and 223 on the surface of sample 208. Projection device 230 may be configured to deflect primary beamlets 211, 212, and 213 to scan detection points 221, 222, and 223 across respective scanning regions in a portion of a surface of sample 208. Electrons including secondary electrons and backscattered electrons are generated from the sample 208 in response to incidence of the primary beamlets 211, 212 and 213 on detection points 221, 222 and 223 on the sample 208. The secondary electrons typically have electron energies of 50eV or less. The actual secondary electrons may have an energy of less than 5eV, but any electrons below 50eV are typically treated as secondary electrons. The backscattered electrons typically have electron energies between 0eV and the landing energies of the primary beamlets 211, 212 and 213. Because electrons detected with an energy of less than 50eV are typically regarded as secondary electrons, a portion of the actual backscattered electrons will be regarded as secondary electrons.

The detector 240 is configured to detect signal particles, such as secondary electrons and/or backscattered electrons, and generate corresponding signals that are sent to the signal processing system 280, for example, to construct an image of a corresponding scanned region of the sample 208. The detector 240 may be incorporated into the projection device 230.

The signal processing system 280 may include circuitry (not shown) configured to process signals from the detector 240 to form an image. The signal processing system 280 may also be referred to as an image processing system. The signal processing system may be incorporated into a component of the multi-beam charged particle evaluation system 40, such as the detector 240 (shown in fig. 2). However, the signal processing system 280 may be incorporated into any component of the inspection device 100 or the multi-beam charged particle evaluation system 40, such as part of the projection device 230 or the controller 50. The signal processing system 280 may include an image acquirer (not shown) and a storage device (not shown). For example, the signal processing system may include a processor, a computer, a server, a mainframe, a terminal, a personal computer, any type of mobile computing device, etc., or a combination thereof. The image acquirer may include at least a portion of the processing functionality of the controller. Thus, the image acquirer may include at least one or more processors. The image acquirer is communicatively coupled to a detector 240 that allows signal communication, such as an electrical conductor, fiber optic cable, portable storage medium, IR, bluetooth, the internet, wireless network, radio, or the like, or a combination thereof. The image acquirer may receive the signal from the detector 240, may process the data included in the signal, and may construct an image therefrom. Thus, the image acquirer can acquire an image of the sample 208. The image acquirer may also perform various post-processing functions, such as generating contours, superimposing indicators on the acquired image, and the like. The image acquirer may be configured to perform adjustment of brightness, contrast, and the like of the acquired image. The memory may be a storage medium such as a hard disk, flash drive, cloud memory, random Access Memory (RAM), other types of computer readable memory, and the like. The memory may be coupled to the image acquirer and may be used to save scanned raw image data as raw images and post-processed images.

The signal processing system 280 may include measurement circuitry (e.g., analog-to-digital converter) to obtain a distribution of the detected secondary electrons. The electron distribution data collected during the detection time window may be used in combination with the corresponding scan path data of each of the primary beamlets 211, 212 and 213 incident on the sample surface to reconstruct an image of the sample structure under examination. The reconstructed image may be used to reveal various features of internal or external structures of the sample 208. Thus, the reconstructed image may be used to reveal any defects that may be present in the sample.

The controller 50 may control the actuation stage 209 to move the sample 208 during inspection of the sample 208. At least during sample inspection, the controller 50 may cause the actuator stage 209 to move the sample 208 in a direction, preferably continuously, e.g., at a constant speed. The controller 50 may control the movement of the actuator table 209 such that it varies the speed of movement of the sample 208 in accordance with various parameters. For example, the controller 50 may control the stage speed (including its direction) based on characteristics of the inspection step of the scanning process.

Known multibeam systems, such as the charged particle evaluation system 40 and the charged particle beam inspection apparatus 100 described above, are disclosed in US2020118784, US20200203116, US2019/0259570 and US 2019/0259464, which are incorporated herein by reference.

As shown in fig. 2, in one embodiment, charged particle evaluation system 40 includes a projection assembly 60. The projection assembly 60 may be a module and may be referred to as an ACC module. Projection assembly 60 is arranged to direct light beam 62 such that light beam 62 enters between electron optical system 41 and sample 208.

As the electron beam scans the sample 208, charge may accumulate on the sample 208 due to the large beam current, which may affect the quality of the image. To condition the charge accumulated on the sample, the projection assembly 60 may be employed to illuminate the beam 62 on the sample 208 to control the accumulated charge due to effects such as photoconductive, photoelectric, or thermal effects.

The components of a charged particle evaluation system 40 that may be used in the present invention are described below in connection with fig. 3, fig. 3 being a schematic diagram of the charged particle evaluation system 40. The charged particle evaluation system 40 of fig. 3 may correspond to the charged particle evaluation system 40 described above (which may also be referred to as a device or tool).

The electron source 201 directs the electrodes to a converging lens array 231 (alternatively referred to as a converging lens array). Ideally, the electron source 201 is a high brightness thermal field emitter arranged to operate within an optimized electron optical performance range, which is a trade-off between brightness and total emission current (such a trade-off may be considered a "good" trade-off). There may be tens, hundreds or thousands of converging lenses 231. The converging lens 231 may comprise a multi-electrode lens and have a configuration based on EP1602121A1, which is incorporated herein by reference in its entirety for the disclosure of a lens array for dividing an electron beam into a plurality of sub-beams, wherein the array provides a lens for each sub-beam. The array of converging lenses 231 may take the form of at least two plates acting as electrodes, with the apertures in each plate being aligned with each other and corresponding to the position of the beamlets. During operation, at least two plates are maintained at different electrical potentials to achieve the desired lens effect.

In an arrangement, which may be referred to as a single lens (Einzel lens), the array of converging lenses 231 is formed of an array of three plates, where the energy of the charged particles is the same as they enter and leave each lens. Thus, chromatic dispersion occurs only within the single lens itself (between the entrance and exit electrodes of the lens), thereby limiting off-axis chromatic aberration. When the thickness of the converging lens is small, e.g. a few millimeters, such aberrations have little or negligible effect.

Each converging lens 231 in the array directs electrons into a respective sub-beam 211, 212, 213, the sub-beams 211, 212, 213 being focused at a respective intermediate focus downstream of the converging lens array. The beamlets diverge with respect to each other. In one embodiment, a deflector 235 is provided at the intermediate focus. The deflector 235 is positioned in the beamlet path at or at least around the position of the corresponding intermediate focus. The deflector 235 is positioned in or near the beamlet path at the intermediate image plane of the associated beamlet. The deflector 235 is configured to operate on the respective beamlets 211, 212, 213. The deflector 235 is configured to bend the respective beamlets 211, 212, 213 an effective amount to ensure that the primary rays (which may also be referred to as beam axes) are incident on the sample 208 substantially perpendicularly (i.e., substantially 90 ° from the nominal surface of the sample). The deflector 235 may also be referred to as a collimator or collimator deflector. The deflector 235 effectively collimates the paths of the beamlets such that the beamlet paths are divergent with respect to each other prior to the deflector. The beamlet paths downstream of the deflector are substantially parallel to each other, i.e. substantially collimated. A suitable collimator is the deflector disclosed in EP application 20156253.5 filed on 7, 2, 2020, which is incorporated herein by reference for the application of the deflector to multi-beam arrays. Instead of the deflector 235 or in addition to the deflector 235, the collimator may comprise a macro-collimator 270 (e.g., as shown in fig. 4). Thus, the macro collimator 270 described below with respect to fig. 4 may be provided with the features of fig. 3. This is generally less preferred than providing a collimator array as deflector 235.

Below the deflector 235 (i.e., downstream of the source 201 or farther from the source 201) is a control lens array 250. The beamlets 211, 212, 213 that pass through the deflector 235 are substantially parallel when entering the steering lens array 250. The control lens pre-focuses the beamlets (e.g., applies a focusing action to the beamlets before they reach the objective lens array 241). Prefocusing may reduce the divergence of the beamlets or increase the convergence rate of the beamlets. The lens array 250 and the objective lens array 241 are controlled to operate together to provide a combined focal length. The combined operation without intermediate focus may reduce the risk of aberrations.

In more detail, it is desirable to use the control lens array 250 to determine landing energy. However, the objective lens array 241 may be additionally used to control landing energy. In this case, the potential difference across the objective lens is changed when a different landing energy is selected. One example of a situation where it is desirable to change the landing energy partly by changing the potential difference over the objective lens is to prevent the focus of the beamlets from being too close to the objective lens. In this case, there is a risk that the components of the objective array 241 must be too thin to be manufactured. The same may be true of the detector at this location. This may occur, for example, in the event of a reduced landing energy. This is because the focal length of the objective lens is approximately proportional to the landing energy used. By reducing the potential difference over the objective lens, the electric field within the objective lens is reduced, causing the focal length of the objective lens to become larger again, resulting in a focal position further below the objective lens. Note that using only an objective lens will limit the control of the magnification. This arrangement does not allow control of the reduction rate and/or the opening angle. Furthermore, the use of an objective lens to control landing energy may mean that the objective lens will operate away from its optimal field strength. That is, unless the mechanical parameters of the objective (such as the spacing between its electrodes) can be adjusted, for example, by changing the objective.

The control lens array 250 includes a plurality of control lenses. Each control lens includes at least two electrodes (e.g., two or three electrodes) connected to a respective potential source. The control lens array 250 may include two or more (e.g., three) plate electrode arrays connected to respective potential sources. The control lens array 250 is associated with the objective lens array 241 (e.g., the two arrays are positioned close to each other and/or mechanically connected to each other and/or controlled together as a unit). Each control lens may be associated with a respective objective lens. The control lens array 250 is positioned upstream of the objective lens array 241.

The control lens array 250 comprises a control lens for each beamlet 211, 212, 213. The function of the control lens array 250 is to optimize the beam opening angle with respect to the demagnification of the beam and/or to control the beam energy delivered to the objective lens array 241. The objective lens array 241 directs the beamlets 211, 212, 213 onto the sample 208. The objective lens array 241 may be positioned at or near the base of the electron optical system 41. The control lens array 250 is optional but is preferably used to optimize the beamlets upstream of the objective lens array.

For ease of illustration, the lens array is schematically depicted herein with an elliptical array (as shown in fig. 3). Each oval represents a lens in the lens array. Oval shapes are conventionally used to represent lenses, similar to the biconvex shape commonly employed in optical lenses. However, in the context of charged particle devices such as those discussed herein, it should be understood that the lens array will typically operate electrostatically and thus may not require any physical elements in the form of biconvex shapes. The lens array may alternatively comprise a plurality of plates having apertures.

Optionally, an array of scan deflectors 260 is provided between the control lens array 250 and the array of objective lenses 234. The array of scan deflectors 260 comprises a scan deflector for each beamlet 211, 212, 213. Each scan deflector is configured to deflect a respective beamlet 211, 212, 213 in one or both directions in order to scan the beamlet across the sample 208 in one or both directions.

Fig. 4 is a schematic diagram of an exemplary charged particle evaluation system 40 with an alternative electron optical system 41. The electron optical system 41 includes an objective lens array 241. The objective lens array 241 includes a plurality of objective lenses. The objective lens array 241 may be a replaceable module. For brevity, the features of the objective lens array 241 that have been described above are not repeated here.

The electron optical device 41 may be used for electron detection in the system of fig. 4. As shown in fig. 4, the electron optical system 41 includes a source 201. The source 201 provides a charged particle beam (e.g., electrons). The multiple beams focused on the sample 208 are derived from the beams provided by the source 201. The beamlets may be derived from the beam, for example, using a beam limiter defining an array of beam limiting apertures. The beam limiting aperture array may define a mutual arrangement of sub-beams in a multi-beam arrangement of the multi-beams. The beam may be split into sub-beams upon encountering the control lens array 250. The most upstream electrode of the control lens array may be such a beam limiter with an array of beam limiting apertures. The beamlets are substantially parallel when entering the control lens array 250. Source 201 is ideally a high brightness thermal field emitter with a good tradeoff between brightness and total emission current, as noted with respect to the arrangement described with reference to fig. 3.

In the example shown, the collimator is arranged in the upstream of the objective lens array assembly. The collimator may include a macro collimator 270. The macro collimator 270 acts on the beam from the source 201 before the beam is split into multiple beams. The macro-collimator 270 bends the respective portions of the beam by an effective amount to ensure that the beam axis of each sub-beam derived from the beam is incident on the sample 208 substantially perpendicularly (i.e., substantially 90 deg. from the nominal surface of the sample 208). The macrocollimator 270 applies macrocollimation to the beam. Thus, instead of comprising an array of collimator elements, the macro-collimator 270 may act on all beams, each collimator element being configured to act on a different individual portion of the beam. The macro-collimator 270 may include a magnetic lens or a magnetic lens arrangement including a plurality of magnetic lens subunits (e.g., a plurality of electromagnets forming a multipole arrangement). Alternatively or additionally, the macro-collimator may be at least partially electrostatically implemented. The macro-collimator may comprise an electrostatic lens or an electrostatic lens arrangement comprising a plurality of electrostatic lens subunits. The macro collimator 270 may use a combination of magnetic and electrostatic lenses.

In another arrangement (not shown), the macro collimator may be partly or entirely replaced by an array of collimator elements arranged downstream of the upper beam limiter. Each collimator element collimates a respective sub-beam. The array of collimator elements may be formed using MEMS fabrication techniques so as to be spatially compact. The array of collimator elements may be a first deflecting or focusing electron optical array element in the beam path downstream of the source 201. The array of collimator elements may be upstream of the control lens array 250. The array of collimator elements may be in the same module as the control lens array 250.

In the embodiment of fig. 4, a macro-scan deflector 265 is provided to cause beamlets to be scanned across the sample 208. The macro-scan deflector 265 deflects a corresponding portion of the beam so that the beamlets are scanned over the sample 208. In one embodiment, macro-scan deflector 265 comprises a macro-multipole deflector, e.g., having eight or more poles. Deflection causes sub-beams derived from the beam to be scanned across the sample 208 in one direction (e.g., parallel to a single axis, such as the X-axis) or in two directions (e.g., relative to two non-parallel axes, such as the X-and Y-axes). Instead of comprising an array of deflector elements, each deflector element is configured to act on a different individual portion of the beam, the macro-scan deflector 265 acts macroscopically on all of the beam. In the illustrated embodiment, macro-scan deflector 265 is disposed between macro-collimator 270 and control lens array 250.

In another arrangement (not shown), macro scan deflector 265 may be replaced in part or in whole by an array of scan deflectors. The scan deflector array includes a plurality of scan deflectors. The scanning deflector array may be formed using MEMS fabrication techniques. Each scanning deflector scans a respective beamlet over sample 208. Thus, the scan deflector array may comprise a scan deflector for each beamlet. Each scan deflector may deflect the beamlets in one direction (e.g., parallel to a single axis, such as the X-axis) or in two directions (e.g., relative to two non-parallel axes, such as the X-and Y-axes). Deflection causes the beamlets to be scanned across the sample 208 in one or both directions (i.e., one or two dimensions). The scan deflector array may be upstream of the objective lens array 241. The scan deflector array may be downstream of the control lens array 250. Although reference is made to a single beamlet associated with a scan deflector, a beamlet group may be associated with a scan deflector. In one embodiment, the scan deflector described in EP2425444, which is incorporated herein by reference in its entirety, particularly with respect to portions of the scan deflector, may be used to implement a scan deflector array. The scan deflector array (e.g., formed using MEMS fabrication techniques as described above) may be more spatially compact than the macro-scan deflector. The scan deflector array may be in the same module as the objective lens array 241.

In other embodiments, a macro scan deflector 265 and a scan deflector array are provided. In such an arrangement, scanning of the beamlets over the sample surface may be achieved by controlling the macro-and scan deflector arrays together, preferably synchronously.

In some embodiments, the electron optical system 41 further comprises an upper beam limiter 252. The upper beam limiter 252 defines an array of beam limiting apertures. The upper beam limiter 252 may be referred to as an upper beam-making aperture array or an upstream beam-limiting aperture array. The upper beam limiter 252 may comprise a plate (which may be a plate-like body) having a plurality of apertures. The upper beam limiter 252 forms beamlets from the charged particle beam emitted by the source 201. Beam portions other than those contributing to the formation of the beamlets may be blocked (e.g., absorbed) by the upper beam limiter 252 so as not to interfere with the downstream beamlets. The upper beam limiter 252 may be referred to as a beamlet-defined aperture array.

In some embodiments, as shown in fig. 4, the objective lens array assembly (which is a unit comprising an objective lens array 241) further comprises a beam shaping limiter 262. The beam shaping limiter 262 defines an array of beam limiting apertures. The beam shaping limiter 262 may be referred to as a lower beam limiter, a lower beam limiting aperture array or a final beam limiting aperture array. The beam shaping limiter 262 may include a plate (which may be a plate-like body) having a plurality of apertures. The beam shaping limiter 262 may be downstream of at least one electrode (optionally from all electrodes) of the control lens array 250. In some embodiments, the beam shaping limiter 262 is downstream of at least one electrode (and optionally all electrodes) of the objective lens array 241.

In an arrangement, the beam shaping limiter 262 is structurally integrated with the electrodes of the objective lens array 241. Ideally, the beam shaping limiter 262 is positioned in a region of low electrostatic field strength. Each beam limiting aperture is aligned with a corresponding objective lens in the objective lens array 241. The alignment is such that a portion of the beamlets from the corresponding objective lens may pass through the beam limiting aperture and impinge on the sample 208. Each beam limiting aperture has a beam limiting effect that allows only a selected portion of the beamlets incident on the beam shaping limiter 262 to pass through the beam limiting aperture. The selected portions may be such that only a portion of the respective beamlets that pass through a central portion of the respective aperture in the objective lens array reach the sample. The central portion may have a circular cross-section and/or be centered on the beam axis of the sub-beam.

Any of the objective lens array assemblies described herein may also include a detector 240. The detector detects electrons emitted from the sample 208. The detected electrons may include any electrons detected by SEM, including secondary and/or backscattered electrons emitted from sample 208. An exemplary configuration of the detector 240 is shown in fig. 3 and described in more detail below with reference to fig. 7-10.

Fig. 5 schematically illustrates a charged particle evaluation system 40 according to an embodiment. Features identical to those described above are denoted by identical reference numerals. For brevity, these features are not described in detail with reference to fig. 5. For example, the source 201, the converging lens 231, the macro collimator 270, the objective array 241, and the sample 208 may be as described above.

As described above, in one embodiment, the detector 240 is between the objective lens array 241 and the sample 208. The detector 240 may face the sample 208. Alternatively, as shown in FIG. 5, in one embodiment, an objective array 241 comprising a plurality of objectives is located between the detector 240 and the sample 208.

In one embodiment, deflector array 95 is located between detector 240 and objective lens array 241. In one embodiment, the deflector array 95 includes a Wien filter (or even a Wien filter array) such that the deflector array may be referred to as a beam splitter. The deflector array 95 is configured to provide a magnetic field to separate charged particles projected onto the sample 208 from secondary electrons from the sample 208.

In one embodiment, detector 240 is configured to detect signal particles by referencing the energy of the charged particles (i.e., according to the band gap). Such a detector 240 may be referred to as an indirect current detector. The secondary electrons emitted from the sample 208 gain energy from the field between the electrodes. The secondary electrode has sufficient energy once it reaches the detector 240.

Fig. 6 is a close-up view of a portion of the charged particle evaluation system 40 shown in fig. 5. In one embodiment, detector 240 includes an array of electron-to-photon converters 91. The electron-photon converter array 91 includes a plurality of phosphor stripes 92, such as scintillators. Each phosphor stripe 92 is located in the plane of the electron-photon converter array 91. At least one phosphor stripe 92 is arranged between two adjacent charged particle beams projected towards the sample 208. In an arrangement, the or each phosphor strip 92 may in fact pass through the path of the multiple beams, i.e. the arrangement of sub-beams in a multi-beam arrangement.

In one embodiment, the phosphor strips 92 extend in a substantially horizontal direction. Alternatively, the electron-photon converter array 91 may comprise a plate of fluorescent material with an opening 93 for projecting a charged particle beam.

The charged particle beam is projected, indicated by a broken line in fig. 6, through the plane of the electron-photon converter array 91, through the openings 93 between the phosphor stripes 92, towards the deflector array 95.

In one embodiment, the deflector array 95 includes a magnetic deflector 96 and an electrostatic deflector 97. The electrostatic deflector 97 is configured to counteract the deflection of the projected charged particle beam transmitted toward the sample 208 by the magnetic deflector 96. Thus, the projected charged particle beam may be moved to a small extent in the horizontal plane. The beam downstream of the deflector array 95 is substantially parallel to the beam upstream of the deflector array 95.

In one embodiment, the objective lens array 241 includes a plurality of plates for directing secondary electrons generated in the sample 208 toward the deflector array 95. For secondary electrons traveling in the opposite direction to the projected charged particle beam, the electrostatic deflector 97 does not counteract the deflection of the magnetic deflector 96. In contrast, the deflection of the secondary electrons caused by the electrostatic deflector 97 and the magnetic deflector 96 is added. Thus, the secondary electrons are deflected to travel at an angle relative to the optical axis so as to transfer the secondary electrons onto the phosphor stripes 92 of the detector 240.

At the phosphor stripes 92, photons are generated upon incidence of the secondary electrons. In one embodiment, photons are transmitted from phosphor strip 92 to a photodetector (not shown) via a photon transmission unit. In one embodiment, the photon transfer unit includes an optical fiber array 98. Each optical fiber 98 includes an end portion arranged adjacent to or attached to one of the phosphor stripes 92 for coupling photons from the phosphor stripe 92 into the optical fiber 98 and another end portion arranged to project photons from the optical fiber 98 onto a photodetector.

The objective lens array 241 of any embodiment may comprise at least two electrodes, wherein an aperture array is defined. In other words, the objective lens array comprises at least two electrodes with a plurality of holes or apertures. Fig. 7 shows electrodes 242, 243 which are part of an exemplary objective lens array 241 having corresponding aperture arrays 245, 246. The position of each aperture in an electrode corresponds to the position of the corresponding aperture in the other electrode. The corresponding apertures operate in use on the same beam, sub-beam or group of beams in the multi-beam. In other words, the corresponding apertures in the at least two electrodes are aligned with and arranged along the beamlet path (i.e., one of beamlet paths 220). Thus, each electrode is provided with an aperture through which the respective beamlet 211, 212, 213 propagates.

As shown in fig. 7, the objective lens array 241 may include two electrodes, or three electrodes, or may have more electrodes (not shown). The objective lens array 241 having only two electrodes may have lower aberration than the objective lens array 241 having more electrodes. A three-electrode objective lens can have a larger potential difference between the electrodes, enabling a stronger lens. The additional electrodes (i.e. more than two electrodes) provide additional degrees of freedom for controlling the electron trajectories, e.g. to focus the secondary electrons as well as the incident beam. The advantage of a double electrode lens compared to a single lens is that the energy of the incoming beam does not have to be the same as the outgoing beam. Advantageously, such a potential difference across the two-electrode lens array enables it to be used as an accelerating or decelerating lens array.

Adjacent electrodes of the objective lens array 241 are spaced apart from each other along the beamlet path. The distance between adjacent electrodes, in which the insulating structure can be positioned as described below, is larger than the objective lens.

Preferably, each electrode provided in the objective lens array 241 is a plate. The electrodes may be described further as flat plates. Preferably, each electrode is planar. In other words, each electrode will preferably be provided as a thin flat plate in planar form. Of course, the electrodes need not be planar. For example, the electrodes may bend due to the force generated by the high electrostatic field. It is preferred to provide planar electrodes as this makes the manufacture of the electrodes easier as known manufacturing methods can be used. Planar electrodes may also be preferred because they may provide more accurate aperture alignment between the different electrodes.

The objective lens array 241 may be configured to demagnify the charged particle beam by a factor of greater than 10, desirably in the range of 50 to 100 or more.

A detector 240 is provided to detect secondary and/or backscattered charged particles emitted from the sample 208. The detector 240 is positioned between the objective 234 and the sample 208. The detector 240 may be otherwise referred to as a detector array or a sensor array, and the terms "detector" and "sensor" are used interchangeably throughout the application.

An electro-optical device 41 may be provided. The electron optical device is configured to project an electron beam toward the sample 208, for example, in a multi-beam or single beam as described in detail herein. The electron optical device may comprise an objective lens array 241, for example as described herein. The electro-optical device may include a detector 240. The objective lens array (i.e., objective lens array 241) may correspond to a detector array (i.e., detector 240) and/or any beam (i.e., sub-beam). However, the invention may be applied to other arrangements of objective lenses, such as magnetic objective lens arrangements for single or multiple beams. Such a magnetic objective lens arrangement may have a single aperture for all beams towards the sample and optionally signal particles from the sample. The magnetic objective lens arrangement may comprise a plurality of magnetic lenses arranged along the beam path. The magnetic objective arrangement may have an electrode element, which may be positioned further downstream during operation, e.g. closer to the sample, than the magnetic objective arrangement.

An exemplary detector 240 is described below. However, any reference to detector 240 may be, for example, a single detector (i.e., at least one detector) or multiple detectors as appropriate for a single beam electron optical system. The detector 240 may include a detector element 405 (e.g., a sensor element such as a capture electrode). The detector 240 may comprise any suitable type of detector. For example, a trapping electrode, a scintillator, or a PIN element, for example, for directly detecting electron charges may be used. The detector 240 may be a direct current detector or an indirect current detector. The detector 240 may be a detector as described below with respect to fig. 8, 9, 10.

For example, in the embodiment shown in fig. 7 and described with reference to fig. 7, the detector 240 may be positioned between the objective lens array 241 and the sample 208. The detector 240 is configured as the most downstream feature of the electron optical device, e.g., proximate to the sample 208. The detector 240 may be in close proximity to the sample 208, e.g., less than 300 μm, preferably between 200 μm and 10 μm, more preferably between 100 μm and 30 μm, e.g., less than or equal to about 50 μm. Alternatively, there may be a larger gap between the detector 240 and the sample 208, for example at most 5mm, for example at most 3mm, more preferably at most 1.5mm; in an arrangement, such as for a single beam electron optical device, the gap is at least 750 μm.

The detector 240 may be positioned in the device so as to face the sample 208. Alternatively, the detector 240 may be positioned elsewhere in the electron optical system 41 such that the portion of the electron optical device facing the sample 208 is different from and therefore not a detector; such as an electrode of an objective lens arrangement, for example an arrangement for a multibeam electron optical apparatus as shown and described with reference to fig. 5 and 6, wherein the sample facing electrode is part of an objective lens array. In such other arrangements, such as the mentioned single beam electron optical system, the detector components may be located at different positions along the beam path, one or more of which may feature an array of detector elements, for example as the most downstream feature of the electron optical device, for example closest to the sample.

In one embodiment, the gap between the electron optical device and the sample 208 is at most about 1.5mm. For a single beam system, the gap may be at least 0.75mm. For a multi-beam system, the distance L between the electron optical device and the sample 208 is less than or equal to about 50 μm. The distance L is determined as the distance from the surface of the sample 208 facing the electron optical system 41 to the surface of the electron optical device facing the sample 208. Preferably, the distance L is less than or equal to about 40 μm. Preferably, the distance L is less than or equal to about 30 μm. Preferably, the distance L is less than or equal to about 20 μm. Preferably, the distance L is less than or equal to 10 μm.

Fig. 8 is a bottom view of detector 240, detector 240 including a substrate 404, a plurality of detector elements 405 provided on substrate 404, each detector element 405 surrounding a beam aperture 406. The beam aperture 406 may be formed by etching through the substrate 404. In the arrangement shown in fig. 8, the beam apertures 406 are in a hexagonal close-packed array. The beam apertures 406 may also be arranged differently, for example in a rectangular array. The hexagonal arrangement of beams in fig. 8 may be more densely packed than square beam arrangements. The detector elements 405 may be arranged in a rectangular array or a hexagonal array.

Fig. 9 depicts a cross section of a portion of the detector 240 on a larger scale. The detector element 405 forms the bottommost surface of the detector 240, i.e., the surface closest to the sample 208. A logic layer 407 may be provided between the detector element 405 and the body of the substrate 404. At least a portion of the signal processing system may be incorporated into the logic layer 407.

The wiring layer 408 is disposed on the back side or inside of the substrate 404 and is connected to the logic layer 407 through a through-substrate via 409. The number of through-substrate vias 409 need not be the same as the number of beam apertures 406. In particular, if the electrode signals are digitized in the logic layer 407, only a small number of through silicon vias may be required to provide a data bus. The wiring layer 408 may include control lines, data lines, and power lines. It should be noted that despite the beam aperture 406, there is sufficient space for all necessary connections. The detection module 402 may also be fabricated using bipolar or other fabrication techniques. A printed circuit board and/or other semiconductor chips may be provided on the back side of the detector 240.

The above-described integrated detector array is particularly advantageous when used with tools having tunable landing energies, as the secondary electron capture can be optimized for the landing energy range.

The detector 240 may be implemented by integrating a CMOS chip detector into an electrode of the objective lens array 241, such as a bottom electrode of the objective lens array 241. Integration of the detector 240 into the objective lens array 241 or other component of the electron optical system 41 allows detection of electrons emitted with respect to a plurality of corresponding beamlets. The CMOS chip is preferably oriented to face the sample (because the distance between the bottom of the charged particle optical device and/or the electron optical system and the sample is small (e.g., 200 μm or less, 100 μm or less, 50 μm or less, 40 μm or less, 30 μm or less, or 20 μm or less)). In one embodiment, the detector element 405 for capturing secondary charged particles is formed in a surface metal layer of a CMOS device. The detector element 405 may be formed in other layers. The power and control signals of the CMOS may be connected to the CMOS through silicon vias. For robustness, it is preferable that the passive silicon substrate with holes shield the CMOS chip from high electric fields.

In order to maximize detection efficiency, it is desirable to make the surface of the detector element 405 as large as possible so that substantially all of the area of the objective lens array 240 (except the aperture) is occupied by the detector element 405. Additionally or alternatively, each detector element 405 has a diameter substantially equal to the array pitch (i.e., the aperture array pitch described above with respect to the electrodes of the objective lens assembly 241). Thus, the diameter of each detector element may be less than about 600 μm, and preferably between about 50 μm and 500 μm. As described above, the pitch may be selected based on the expected distance between the sample 208 and the detector 240. In one embodiment, the outer shape of the detector element 405 is circular, but this may be made square to maximize the detection area. The diameter of the through-substrate via 409 may also be minimized. Typical dimensions of the electron beam are in the order of 5 to 15 μm.

In one embodiment, a single detector element 405 surrounds each beam aperture 406. In another embodiment, a plurality of detector elements 405 are disposed around each beam aperture 406. Electrons captured by detector elements 405 surrounding one beam aperture 406 may be combined into a single signal or used to generate separate signals. The detector elements 405 may be radially separated. The detector elements 405 may form a plurality of concentric rings or annuli. The detector elements 405 may be angularly separated. The detector element 405 may form a plurality of segments or segments. The segments may have similar angular dimensions and/or similar areas. The electrode elements may be separated radially and angularly or in any other convenient manner.

However, a larger surface of the detector element 405 results in a larger parasitic capacitance and thus a lower bandwidth. For this reason, it may be desirable to limit the outer diameter of the detector element 405. Particularly if the larger detector element 405 gives only a slightly larger detection efficiency, but a significantly larger capacitance. The circular (annular) detector element 405 may provide a good compromise between collection efficiency and parasitic capacitance. Thus, such a tradeoff is an optimal balance between collection efficiency and parasitic capacitance such that the detection signal from the detector is sufficient, even if the degradation of parasitic capacitance is not minimal, acceptable.

A larger outer diameter of the detector element 405 may also result in greater cross-talk (sensitivity to signals of adjacent holes). This may also be the reason for making the outer diameter of the detector element 405 smaller. Particularly if the larger detector element 405 gives only a slightly larger detection efficiency, but gives significantly larger cross-talk.

The charged particle current collected by the detector element 405 is amplified, for example, by an amplifier such as a TIA.

In one embodiment, the objective lens array 241 is a replaceable module alone or in combination with other elements such as a control lens array and/or detector array. The replaceable module may be field replaceable, i.e. the module may be exchanged for a new module by a field engineer. In one embodiment, a plurality of replaceable modules are contained within the tool and can be exchanged between an operable position and an inoperable position without turning on the charged particle evaluation system 40.

In one embodiment, the replaceable module comprises an electron optical component, and in particular may be a charged particle optical arrangement arranged on a stage allowing positioning of the actuation component. In one embodiment, the replaceable module includes a table. In an arrangement, the table and replaceable module may be an integral part of the tool 40. In an arrangement, the replaceable module is limited to the stage and the equipment it supports, such as a charged particle optical arrangement. In an arrangement, the table is detachable.

In an alternative design, the replaceable module including the table is removable. The portion of the charged particle evaluation system 40 for the replaceable module is isolatable, i.e. the portion of the charged particle evaluation system 40 is defined by the upstream and downstream valves of the replaceable module. The valves may be operated to isolate the environment between the valves from the vacuum upstream and downstream of the valves, respectively, thereby enabling the replaceable module to be removed from the charged particle evaluation system 40 while maintaining the vacuum upstream and downstream of the portion of the charged particle evaluation system 40 associated with the replaceable module. In one embodiment, the replaceable module includes a table. The stage is configured to support a device such as a charged particle optical arrangement relative to the beam path. In one embodiment, the module includes one or more actuators. An actuator is associated with the table. The actuator is configured to move the device relative to the beam path. Such actuation may be used to align the device and the beam path relative to each other.

In one embodiment, the replaceable module is a microelectromechanical system (MEMS) module. MEMS are miniaturized mechanical and electromechanical elements fabricated using micro-fabrication techniques. In one embodiment, the replaceable module is configured to be replaceable within the charged particle evaluation system 40. In one embodiment, the replaceable module is configured to be field replaceable. In situ interchangeable means that the module can be removed and replaced with the same or a different module while maintaining the vacuum in which the electro-optic tool 40 is located. Only the portion of the charged particle evaluation system 40 corresponding to the module is ventilated so that the module is removed and returned or replaced.

The control lens array 250 may be in the same module as the objective lens array 241, i.e. forming an objective lens array assembly or an objective lens arrangement, or it may be in a separate module.

In some embodiments, one or more aberration correctors are provided that reduce one or more aberrations in the beamlets. One or more aberration correctors may be provided in any embodiment, for example as part of a charged particle optical apparatus, and/or as part of an optical lens array assembly, and/or as part of an evaluation system, and/or as part of an electro-optical arrangement. In one embodiment, each of at least a subset of the aberration correctors is positioned in or directly adjacent to a respective one of the intermediate foci (e.g., in or adjacent to the intermediate image plane). The beamlets have a smallest cross-sectional area in or near a focal plane, such as the mid-plane. This provides more space for the aberration corrector (or space available in alternative arrangements without intermediate image planes) than is otherwise available (i.e. upstream or downstream of the intermediate plane).

In one embodiment, an aberration corrector positioned in or directly adjacent to the intermediate focus (or intermediate image plane) comprises a deflector to correct the source 201 that appears to the different beams to be in different positions. The corrector may be used to correct macroscopic aberrations generated by the source, preventing good alignment between each beamlet and the corresponding objective lens.

The aberration corrector can correct aberrations that prevent correct column alignment. Such aberrations may also lead to misalignment between the beamlets and the corrector. To this end, it may be desirable to additionally or alternatively locate an aberration corrector at or near the converging lenses 231 (e.g., each such aberration corrector is integrated with one or more converging lenses 231 or directly adjacent to one or more converging lenses 231). This is desirable because at or near the converging lens 231, the aberrations also do not cause a shift of the corresponding beamlets, because the converging lens is vertically close to or coincident with the beam aperture. However, a challenge in positioning the corrector at or near the converging lens is that each beamlet has a relatively large cross-sectional area and a relatively small pitch at that location relative to a further downstream location. The aberration corrector may be a CMOS-based independently programmable deflector as disclosed in EP2702595A1 or a multipole deflector array as disclosed in EP2715768A2, the description of the beamlet manipulator in both of which documents is incorporated herein by reference.

In some embodiments, each of at least a subset of the aberration correctors is integrated with or directly adjacent to the objective array 241. In one embodiment, the aberration correctors reduce one or more of the following: field curvature; a focus error; and astigmatism. Additionally or alternatively, one or more scanning deflectors (not shown) may be integrated with or directly adjacent to the objective lens array 241 for scanning the beamlets 211, 212, 213 across the sample 208. In one embodiment, a scanning deflector as described in US2010/0276606, which is incorporated herein by reference in its entirety, may be used.

The detector may have multiple parts, more specifically, multiple detection parts. A detector comprising a plurality of portions may be associated with one of the beamlets 211, 212, 213. Thus, portions of one detector 240 may be configured to detect signal particles emitted from the sample 208 that are associated with one of the primary beams (which may otherwise be referred to as beamlets 211, 212, 213). In other words, a detector comprising a plurality of parts may be associated with one aperture in at least one electrode of the objective lens assembly. More specifically, as shown in fig. 10, a detector 405 comprising multiple portions may be disposed around a single aperture 406, which provides one example of such a detector. In one embodiment, the single beam system of fig. 11 includes such a detector that includes multiple sections.

As shown in fig. 10, the detector element 405 includes an inner detection portion 405A and an outer detection portion 405B, and an aperture 406 is defined and configured in the detector element 405 for passage of the charged particle beam. The inner detection portion 405A surrounds the aperture 406 of the detector. The outer detection portion 405B is located radially outward of the inner detection portion 405A. The detector may be generally circular in shape. Thus, the inner and outer detection portions may be concentric rings.

The present invention may be applied to a variety of different tool configurations. For example, charged particle evaluation system 40 may be a single beam tool, or may include multiple single beam columns of devices, or may include multiple beam columns of devices. These columns of devices may include the electron optical system 41 described in any of the above embodiments or aspects. As a plurality of columns of devices (or a multi-column tool), the apparatuses may be arranged in an array of two to one hundred columns of devices or more in number. The charged particle evaluation system 40 may take the form of one embodiment as described and depicted with respect to fig. 3 or as described and depicted with respect to fig. 4, although preferably having an electrostatic scanning deflector array and an electrostatic collimator array. The charged particle device column may optionally include a source.

As shown in fig. 2 (as shown and described in fig. 3-5 when read in the context of the electro-optical device 41), in one embodiment, the projection assembly 60 includes an optical system 63. In one embodiment, projection system 60 includes a light source 61. The light source 61 is configured to emit a light beam 62. In one embodiment, the light source 61 is a laser light source. The laser provides a coherent light beam 62. However, other types of light sources may be used. As described above, the projection assembly 60 is used to illuminate the light beam 62 on the sample 208 in order to control the charge accumulated due to effects such as photoconductive, photoelectric or thermal effects; thereby adjusting the accumulated charge on the sample.

In one embodiment, optical system 63 includes a cylindrical lens 64. The cylindrical lens 64 is configured to focus the light beam 62 more in one direction than in the orthogonal direction. The cylindrical lens increases the degree of freedom in design of the light source 61. In one embodiment, the light source 61 is configured to emit a light beam 62 having a circular cross-section. The cylindrical lens 64 is configured to focus the light beam 62 such that the light beam has an elliptical cross-section.

The cylindrical lens 64 does not have to be provided. In an alternative embodiment, another optical component that is capable of focusing more strongly in one direction than in the other direction may be used. In alternative embodiments, the light source is configured to emit a light beam 62, for example, elliptical or rectangular. Although the dimension between the most downstream surface of the electron optical apparatus 41 and the sample is small and the large dimension of the downstream surface of the electron optical apparatus is orthogonal to the orientation of the beam path, it is desirable to ensure that the beam reaches the portion of the sample that needs to be illuminated.

In one embodiment, the optical system 63 includes reflective surfaces 65, 66, such as mirrors. For example, two reflective surfaces 65, 66 may be provided. In an alternative embodiment, optical system 63 does not reflect light beam 62. In an alternative embodiment, the optical system 63 may include one, three, or more than three reflective surfaces. The number and arrangement of reflective surfaces may be selected according to the size of the volume of projection system 60 to be assembled. Such a reflective surface may be desirable to improve the arrival of the beam 62 between the most downstream surface of the electron optical device and the sample.

As described above, in one embodiment, charged particle evaluation system 40 includes detector 240 configured to detect signal particles emitted by sample 208. As shown in fig. 3, in one embodiment, the detector 240 forms the most downstream of the surface of the electron optical device 41 with respect to the electron beams 211, 212, 213. In other arrangements, as mentioned herein, the detector 240 may be associated with, and even include a portion of, an objective lens arrangement. For example, the detector 240 may be associated with the objective array, but with different locations along the primary beam path, such as with electrodes of the objective array, just upstream of the objective array, distributed at different locations along the beam path near and within the objective array. In another arrangement, the detector is located in a secondary column of devices adjacent to or connected to a charged particle column comprising the electron optical apparatus 41. In all of these arrangements, there is the most downstream element of the electron optical system that is closest to the sample, such as detector 240. The downstream-most surface of the downstream-most element may face the sample. The most downstream surface may be referred to as a facing surface.

Referring now to fig. 11, fig. 11 is a schematic diagram illustrating a charged particle evaluation system including a charged particle system according to one embodiment. The charged particle evaluation system comprises an electron optical device 41, the electron optical device 41 comprising a cleaning target 290. The charged particle evaluation system further comprises a sample holder 207 and a cleaning device 70.

The electron optical apparatus 41 of fig. 11 includes an electron source 201 and a projection device 230. The projection device 230 is configured to direct an electron beam from the electron source 201 downstream towards the sample 207, for example during sample inspection.

The cleaning device is configured to supply the cleaning medium in the cleaning flow 75 to the cleaning target. The cleaning flow 75 approaches the cleaning target from downstream of the cleaning target and is incident on the cleaning target. The cleaning device is configured such that the cleaning medium is energized at or near the cleaning target such that the cleaning medium cleans at least a portion of the surface 291 of the cleaning target 290. Desirably, the distance between the location where the cleaning medium is fired and the cleaning target is less than about 100mm, desirably less than about 10mm.

The cleaning target is, for example, a component of the electron optical apparatus 41. As described above, components of the electron optical apparatus 41 may be contaminated with, for example, hydrocarbon deposits. In particular, the electron-optical elements of the projection device 230, such as the objective array 241 and/or the detector 240, may be contaminated. Such contamination may result from resist coating left over from earlier processing of the sample. In the application of the charged particle evaluation apparatus, the resist may be derived from a sample evaluated during post-development inspection. In the post-development inspection, the sample exposed with the pattern was inspected after development but before etching. The resist coating may completely cover such a sample. When most, if not all, of the resist coating is removed from the sample, inspection of such resist covered samples can be a source of greater contamination than post-etch inspection samples.

The sample inspected after etching may still be a source of contamination during inspection due to the proximity, proximity or small gap between the facing surface of the electron optical device 41 and the sample. The cleaning target is preferably an electron optical element of the electron optical apparatus 41, more preferably the cleaning target is the objective lens array 241 and/or the detector 240. A cleaning target, such as a detector, is preferably disposed near the sample location. For example, at least a part of the cleaning target is preferably disposed at a cleaning distance of 10 μm to 1mm, preferably 10 μm to 200 μm, more preferably 20 to 150 μm, still more preferably 30 μm to 80 μm from the sample position on the sample holder.

In the charged particle evaluation system shown in fig. 11, the cleaning device 70 is arranged on the downstream of the cleaning target, and is configured to emit the cleaning medium in the cleaning flow 75 from the downstream of the cleaning target. The charged particle evaluation system is configured such that the cleaning device 70 is disposed downstream of the cleaning target under cleaning conditions. Specifically, the charged particle evaluation system shown in fig. 11 is configured such that, under cleaning conditions, the cleaning device 70 is disposed downstream of the electron optical apparatus 41. That is, under the cleaning condition, the cleaning device 70 is positioned at the cleaning position such that the cleaning device is downstream of the cleaning target. Preferably, the guide member comprises a deflector and/or a guide tube. Preferably, the guiding member is configured to guide the cleaning flow from a downstream position of the optical system to the cleaning target along a portion of the cleaning path.

The charged particle evaluation system is configured such that, under evaluation conditions, the electron optical device 41 is arranged upstream of the sample on the sample holder 207. Under evaluation conditions, the relative position of the sample and the electron optical apparatus 41 can be moved through a range of relative positions so that the electron optical apparatus 41 can operate, whereby the sample can be evaluated. In the embodiment shown in fig. 11, the sample holder 207 is supported on a sample stage 209, which sample stage 209 may be actuatable and thus may be referred to as an actuation stage 209, e.g. a motorized stage. The actuation stage 209 is preferably configured to be movable. The cleaning device 70 is supported by an actuator table 209. More specifically, in the embodiment of fig. 11, the cleaning device 70 is disposed within the actuation stage 209.

The actuator table 209 is movable to change the relative positions of the electron optical apparatus 41 and the sample holder 207 and the cleaning device 70 between the evaluation condition and the cleaning condition. Alternatively, or in addition, the electron optical device 41 is movable to change the relative position of the electron optical device 41 with the sample holder 207 and the cleaning means 70. Thus, actuation of one or both of the actuation stage 209 and the electro-optical device 41 enables adjustment of the relative positions of the actuation stage 209 and the electro-optical device: such that under evaluation conditions, the electron-optical device can be used to evaluate the sample on the actuation stage 209, 207; and, such that the cleaning device is positioned relative to the cleaning target under the cleaning condition such that the cleaning flow of the cleaning medium is available for cleaning the cleaning target. The actuation stage may be displaced in up to six degrees of freedom with respect to the path of the charged particles from the electron optical device 41 to the sample position. The actuation stage 209 may be actuated in a direction in a plane orthogonal to the beam path. The actuation stage is tiltable with respect to a direction in a plane orthogonal to the beam path and rotates about the beam path. The actuating stage may be displaceable in a downstream direction. Movement in the downstream direction may help ensure a gap between the cleaning target and the cleaning device. This movement in any degree of freedom relative to the beam path may be performed during operation of the cleaning device.

The sample stage optionally includes a short stroke stage 215 (or short stage) and a long stroke stage 216 (or long stage). Short stage 215 is configured to support sample holder 207. The short stage 215 is configured to be movable relative to the long stage 216. The range of motion is up to about 5mm, preferably 1mm, more preferably 500 μm, most preferably 350 μm. The long stage 216 is configured to support the short stage 215. The range of long travel 216 is sufficient to position the sample relative to the electron optical apparatus 41; except for the fine resolution achievable with the short stroke 215. As shown in fig. 11, the cleaning device 70 is disposed in the sample stage 209, preferably in the long stroke 216. Preferably, the cleaning device is within a long stroke of the arrangement shown in fig. 11, as the additional mass of the device does not affect the positioning of the sample 207 by a short stroke, which may have an accuracy of nanometers. Within the long stroke 216, the device may be positioned farther from the cleaning target 290 than if the device was positioned in the short stroke 215. In another embodiment, the cleaning device 70 may be disposed in a short stage 215 of the sample stage 209. The cleaning device 70 is preferably disposed in the long stage 215 of the sample stage.

In one embodiment, the cleaning device may be positioned in a surface of the sample stage 209 facing the cleaning target 290, the cleaning target 290 being recessed into the sample stage 209 relative to the sample holder 207. The surface of the sample stage 209 in which the cleaning device 70 may be positioned may be recessed relative to the sample surface, e.g., stepped in the direction of the beam path. The cleaning device located in or on the recess of the sample stage 209 may have a larger gap relative to the cleaning target. Cleaning devices located in or on such recessed surfaces may be supported by long travel 216. The long stroke 216 may be actuated in the direction of the beam path. The long stroke may be actuated to move the sample closer or farther from the electron optical apparatus 41, which direction may be referred to as along the z-axis. Since the device is supported by the long stroke, either directly or indirectly (i.e., via the short stroke 215), the cleaning device can be positioned closer to or farther from the cleaning target in the direction of the beam path. Preferably, the cleaning device is moved by actuating a long stroke to position the cleaning device away from the cleaning sample. This actuation ensures that there is sufficient clearance between the cleaning device 70 and the cleaning target 290 for positioning the cleaning device relative to the cleaning target such that the path of the cleaning flow is directed toward the cleaning target.

To help direct the cleaning flow of cleaning medium toward the cleaning target, the cleaning device 70 may have a cleaning guide 72. The cleaning guide is arranged to guide a path from the cleaning device 70 toward the cleaning target 290. Additional details regarding the cleaning guide are disclosed and described below with reference to fig. 13.

The depicted arrangement features the sample stage 209, and thus the device 70 in a vacuum chamber (not depicted). Associated with the electro-optical device 41 may be a vacuum chamber. Accordingly, the sample stage 70, the electron optical apparatus, the cleaning device 70, and the cleaning target 290 may be in a negative pressure environment having a vacuum chamber (not shown).

In another embodiment, the cleaning device 70 is held by a cleaning device holder 210. In the embodiment shown in fig. 12, the cleaning device is disposed in a cleaning device holder 210. The arrangement shown in fig. 12 has the same components, with the same reference numerals, functions and structure as shown in fig. 11, unless otherwise specified. The cleaning device holder 210 may be separate from the actuation stage 209 arranged to support the sample 207. The cleaning device holder 210 may be supported and actuated by a cleaning station 214. The movement of the cleaning device holder 210 is preferably independent of the movement of the actuation stage 209. The cleaning stage 214 may be independently positioned relative to the cleaning target.

By actuating the cleaning stage 214 and actuating the actuating stage 209, the charged particle evaluation system can be changed between the evaluation conditions and the cleaning conditions. Thus, the positions of the sample 207 and the cleaning device 70 may be exchanged between the evaluation condition and the cleaning condition to occupy a position downstream of the electron optical apparatus 41. In one arrangement, the cleaning stage 214 includes a long stroke (not shown) to actuate the stage. Preferably, the cleaning stage 214 does not include a short stroke for fine positioning of the cleaning device relative to the cleaning target 290, although in embodiments the cleaning stage is characterized by a short stroke.

In an alternative arrangement, the cleaning device is provided upstream of the sample holder. Preferably, in this configuration, the cleaning device is disposed upstream of the downstream-most portion of the charged particle optical system (which may be referred to as an electron optical apparatus, as described above). Such downstream-most portion may have a downstream surface that is at least a portion of the cleaning target. For example, in a preferred arrangement, the cleaning device is disposed upstream of, for example, cleaning of a cleaning target such as a detector. Preferably, the cleaning device is separate from the charged particle optical system, e.g. spaced apart from the charged particle optical system. In plan view, the cleaning device may be located at a side of the charged particle optical system.

In the charged particle evaluation system shown in fig. 13, a cleaning device 70 is disposed upstream of the sample and the cleaning target 290. With this arrangement, the possibility of the cleaning device interfering with or limiting movement of the sample stage can be avoided. The arrangement shown in fig. 13 has the same components as those shown in fig. 11 or 12, and these components have the same reference numerals, functions and structures unless otherwise specified. The cleaning device 70 is configured to supply cleaning medium in the cleaning flow 75 from upstream of the projection device 230. The cleaning medium flows in a cleaning stream along a path away from the cleaning device 70. The charged particle evaluation system shown in fig. 13 includes cleaning guides 72, 71, the cleaning guides 72, 71 being configured to guide a cleaning flow 75 from the cleaning device 70 to a portion of a cleaning target. Preferably, the cleaning guide is configured to guide a cleaning flow from the cleaning device to the cleaning target along the cleaning path.

The cleaning guide of fig. 13 includes a flow deflector 71 disposed downstream of the cleaning target. The flow deflector 71 is shown on a long stroke 216 of the sample stage 209. For example, the flow deflector 71 is shown coplanar with a surrounding surface of a portion of the stage. However, the flow deflector 71 may be recessed into the sample stage or raised relative to the surrounding surface of the sample stage; in an arrangement, the flow deflector 71 may have a surface that is angled with respect to the surrounding surface of the sample stage and/or sample support 207. This embodiment is advantageous because the gap between the flow deflector 71 and the cleaning target is larger than the gap between the facing surfaces of the sample or sample holder and the electron optical device 41. The sample stage may be actuated to adjust the gap between the cleaning target 290 and the flow deflector 71. However, other arrangements may exist, for example, the flow deflector 71 may be located on a short stroke 215 of the sample stage, or the flow deflector 71 may be located on a cleaning stage having a long stroke but no short stroke, for example.

The flow deflector 71 comprises a deflector surface configured to deflect the cleaning flow 75 upstream towards the portion of the cleaning target to be cleaned by the cleaning flow. Conceptually, the flow deflector may be thought of as a flow mirror that "mirrors" the cleaning flow from the direction of the cleaning device 70 to the direction of the cleaning target along a path incident on the flow deflector. In an arrangement, the flow deflector having a surface that is angled relative to the surface of the sample support 207 may be angled so as to deflect the cleaning flow preferably towards the cleaning target. In this way, the cleaning flow 75 is directed downstream from the cleaning target. The cleaning flow 75 has a path toward the cleaning target in an upstream direction toward the cleaning target, although the cleaning device 70 is disposed upstream of the cleaning target.

With this arrangement, the cleaning device 70 can be provided within the charged particle evaluation device. The charged particle evaluation device has a sufficient volume to house the cleaning device; that is, the cleaning device can be easily positioned within the charged particle evaluation device without compromising the function of the charged particle evaluation device or the cleaning device. Further, with this arrangement, the cleaning device 70 can be disposed outside the vacuum environment. For example, as shown in fig. 13, a separation flange 73 is provided to separate the cleaning device 70 from the vacuum environment. The flange may separate (and thus connect) two parts of the vacuum chamber and/or mount the component on the structure of the vacuum chamber. At least a portion of the cleaning device within the vacuum chamber may be secured (such as mounted) to the flange. The location of the cleaning device above the flange and adjacent to the electron optical apparatus 41 is intended to mean that the device, or at least a portion thereof, has a flange disposed between the portion and the environment within the vacuum chamber, is outside the vacuum chamber enclosing the electron optical apparatus and the sample stage 209, and the flange 73 forms a part of the vacuum chamber. It may be desirable to provide at least a part of the cleaning device outside the vacuum chamber, for example components of the cleaning device comprising elements of the cleaning device, which components may interact with functions of the electro-optical apparatus, such as electronic and electromagnetic elements, such as coils. Note that the precise arrangement of flange 73 and other elements of the chamber wall is intended to be a schematic representation of the structural function of the flange, and is not representative of any particular structural configuration.

The deflector surface is positioned relative to at least a portion of the cleaning target to deflect the cleaning flow toward at least a portion of the surface of the cleaning target. The deflection of the cleaning flow toward the surface portion of the cleaning target surface can be improved by the shape that the deflector surface can take. The position or shape or both the shape and the position of the deflector surface may concentrate the cleaning flow on the surface of the cleaning target, preferably at least at a portion of the surface of the cleaning target.

At least in the cleaning condition, preferably in the cleaning condition, the deflector surface is arranged such that the cleaning flow guided from the cleaning device is incident on a portion of the cleaning target. As described above, the sample holder 207 includes a holding surface 217 configured to hold a sample. In one embodiment, the retaining surface may be recessed into the sample holder 207. The deflector surface of the flow deflector 71 is preferably arranged at a position downstream of the holding surface 217, preferably between 5mm and 15 mm. However, the deflector surface may be 100mm downstream of the holding surface. Preferably, the flow deflector 71 is supported by the long stroke 216 of the sample holder 207, or alternatively by the long stroke 216 of the cleaning stage 214, such that adjustment in the direction of the beam path facilitates, if not further increases, the clearance between the cleaning guide 71 (e.g., the flow deflector 71) and the cleaning target 290.

The deflector surface may be planar. The deflector surface is preferably curved. Additionally or alternatively, the deflector surface optionally includes an array of different angle surfaces. With such topography, e.g. a curved arrangement, the detector surface may advantageously focus the cleaning flow towards at least a portion of the cleaning target, e.g. along the cleaning path. Thus, the deflector surface may have a topography, for example, for focusing the cleaning flow along the cleaning path towards the cleaning target. Thus, the cleaning medium is concentrated in a place where cleaning is required, and is not wasted on parts that do not require cleaning. Thus, cleaning may be faster and more efficient, for example, in terms of time and use of cleaning media and energy.

The flow deflector 71 and/or other components and features of the cleaning device may comprise a material that is resilient and durable to exposure to the cleaning medium. The flow deflector 71 preferably comprises a chemically inert material, in other words, has low chemical adsorptivity. In addition, the material preferably has a small number of physical adsorption sites. By ensuring that the surface of the flow deflector is smooth, a desired small number of physisorption sites can be obtained. For example, the flow deflector 71 may comprise glass. Preferably, the flow deflector 71 comprises quartz.

The cleaning device may include, for example, a cleaning source configured to generate a cleaning medium. The cleaning medium may be any medium that reacts with contaminants deposited on the cleaning target to convert the contaminated deposits into a gas that may be drawn from the vacuum chamber, for example, by pumping. The cleaning medium is for example a cleaning agent as described in EP3446325 and US20170304878, which are incorporated herein by reference at least in respect of the cleaning agent and the disclosure of its production. The cleaning medium may be a cleaning fluid. Preferably, the cleaning medium is or comprises a gas or plasma. The cleaning medium is generated as a result of the generation of the plasma. Preferably or alternatively, the cleaning medium comprises free radicals. The cleaning medium may be oxygen ions and/or radicals, or hydrogen ions and/or radicals. Preferably, the cleaning medium comprises oxygen radicals, for example, disposed in the cleaning stream.

In order to increase the cleaning rate of the cleaning flow, it is preferable to provide excitation energy to excite the cleaning medium at or near the cleaning target. The excitation energy should be at least sufficient to react the cleaning medium with the chemical components of the contaminants on the cleaning surface portion. For example, sufficient excitation energy may be provided by heating, for example, a volume (bulk) of a cleaning target, such as the most downstream electron optical element such as detector 240. Additionally or alternatively, the excitation energy is provided by a charged particle beam, e.g. an electron beam during operation of the electron optical device, e.g. during evaluation of the sample. Alternatively or additionally, the excitation energy is provided by excitation light (e.g., ultraviolet (UV) light), such as by illuminating at least a portion of the surface of the cleaning target.

Bulk heating may be used to perform cleaning by supplying a cleaning flow during baking. During baking, when the vacuum chamber is depressurized or repressurized. In baking, the temperature of the electron optical system 41 is generally raised to 100 degrees celsius or more. Therefore, in order to supply heat of excitation energy to the cleaning medium, the cleaning flow is supplied when the temperature of the electron optical system 41 increases. Accordingly, the heat source is configured to energize the cleaning medium at or near the cleaning target such that the cleaning medium cleans at least a portion of the cleaning target. The heat source may be configured to apply a heat load to the cleaning target.

Referring now to fig. 14, fig. 14 is a schematic diagram showing a charged particle evaluation system including an electron optical system 41. The arrangement shown in fig. 14 has the same components as shown in fig. 11, 12 or 13 and described with reference to fig. 11, 12 or 13, including variants having the same reference numerals, functions and structures, unless otherwise specified. The electron optical system 41 is configured to project an electron beam towards the sample 207, for example during an evaluation operation. The cleaning operation is intended to occur during operation of the electron optical device 41 to project an electron beam or beams towards the sample or another surface. In this way, the electron optical system 41 partially includes the cleaning device 70. As shown, the cleaning device directs a cleaning flow toward the sample, which deflects (or reflects) the cleaning flow toward the cleaning target. In operating the electron optical system 41, the electron beam is configured to excite the cleaning medium at or near the cleaning target such that the cleaning medium cleans at least a portion of the surface of the cleaning target.

A benefit of this arrangement is that the cleaning device may be configured to operate to clean portions of the cleaning target during operation of the charged particle evaluation tool. Therefore, it is not necessary to delay evaluation in order to perform the cleaning operation. However, in a different arrangement, the flow deflector on the sample stage 209 or on the cleaning stage 214 may be positioned below the electron optical apparatus 41. Note that the operation of the electron optical device does not require directing the charged particle beam towards a sample, for example for evaluation.

The sample stage 209 (and optional cleaning stage) and electron optical system 41 are configured to be controlled such that the path of the electron beam is reflected upstream onto at least a portion of the cleaning target. When the electron optical apparatus is operated to generate an electron optical beam, the cleaning device is operable to generate a cleaning flow towards the flow deflector or sample and/or sample holder 207, which deflects (or reflects) the cleaning flow towards the cleaning target. Thus, the cleaning flow approaches the cleaning target from downstream of the cleaning target. The electron beam may be deflected from the sample, the sample holder 207, or both. This arrangement may be beneficial because it enables cleaning of the cleaning target in a continuously operating electron optical apparatus 41 without causing instability in the operation of the source 201.

The cleaning apparatus includes a plasma generator configured to generate plasma from which a cleaning medium is supplied. The plasma generator emits photon radiation when generating the plasma. The photon radiation may be light having a wavelength such as UV light, which excites the cleaning medium at the cleaning target when a portion of the cleaning target is irradiated to at least clean the irradiated portion of the cleaning target. Additionally or alternatively, the cleaning device comprises a photon generator separate from the plasma generator. The photon generator is a light emitter. Alternatively, the photon generator may be provided separately from the cleaning device 70.

In the embodiment of fig. 11 and 12, the cleaning device 70 includes a plasma generator; the cleaning device 70 has a light generating function. The cleaning medium may be plasma generated using light emitted by a plasma generator. The light generated by the plasma generator may provide excitation energy for cleaning the target. Thus, the plasma provides excitation light, in particular the generation of the plasma provides excitation light, more in particular UV light. The plasma generator emits UV light. Additionally or alternatively, the plasma generator may have a light emitter which may preferably generate light at the frequency of the UV light. With this arrangement, light is emitted by the plasma generator, the individual light emitters, or both, and excitation light is provided along the optical path from the cleaning device 70 to the cleaning target portion. Thus, light is directed from the cleaning device 70 along the same or a similar path as the cleaning flow. The excitation light is directed toward the cleaning target such that the excitation light can excite the cleaning medium at or near the cleaning target, e.g., to clean a surface of the cleaning target, particularly a surface near the cleaning target.

Referring now to fig. 15, fig. 15 is a schematic diagram illustrating a charged particle evaluation system similar to the charged particle evaluation system of fig. 13 described above. The arrangement depicted in fig. 15 has the same components as those depicted in any of fig. 11, 12, 13 and 14 and described with reference to fig. 11, 12, 13 and 14, including variants having the same reference numerals, functions and structure, unless otherwise mentioned. The cleaning device 70 of the arrangement shown in fig. 15 has a cleaning medium generator, optionally with a light emitter as described above. The charged particle evaluation system of fig. 15 comprises at least one light guide configured to guide excitation light along the light path from the cleaning device 70 to a portion of the cleaning target. Preferably, the portion is cleaned using a cleaning medium supplied by the cleaning device 70. The light guide of fig. 15 comprises a reflector 81. The reflector 81 serves to reflect the excitation light from the cleaning device 70 toward a cleaning target, such as a detector portion to be cleaned. The reflector 81 is configured or simply arranged to reflect the excitation light.

The reflector 81 comprises a reflector surface. The reflector surface is configured to reflect the excitation light. The reflector surface may be positioned relative to at least a portion of the cleaning target to reflect, preferably focus, the excitation light toward at least a portion of the cleaning target surface. The reflector surface of the reflector surface may be shaped such that when positioned relative to the path of the excitation beam and the portion of the cleaning target, at least that portion is reflected towards the cleaning target surface, preferably focusing the excitation light.

The cleaning device 70 of the charged particle evaluation system shown in fig. 15 is arranged in the same position relative to the other components as described above with reference to a similar embodiment shown in fig. 13. In one embodiment, the reflector surface may be substantially coplanar with a table supporting the reflector surface. The reflector may be raised or recessed relative to the table surface. The reflector may be angled with respect to a common plane with the support surface 207. Thus, the cleaning device 70 is arranged upstream in a direction along at least the electron beam path of the sample holder 207. The cleaning device is optionally disposed upstream of the cleaning target. The reflector surface is disposed in a downstream direction along a beam path of the cleaning target. In particular, as shown in fig. 15, the reflector surface is preferably disposed downstream of the electron optical system 41. The reflector surface is preferably located between 5mm and 15mm downstream of the holding surface 217, but may be up to 100mm from the holding surface.

The reflector surface may be planar. The reflector surface may reflect the excitation light toward at least a portion of the cleaning target. The reflector surface may preferably be angled with respect to the plane of the support surface to reflect the excitation light to the cleaning target 290. The reflector surface is preferably curved. The reflectors may be composite surfaces of planar or curved elements that together functionally approximate a curved surface. The reflector surface more preferably comprises a fresnel lens. A reflector such as one having a curved or fresnel surface may advantageously focus the excitation light toward at least a portion of the cleaning target, for example, along the beam path to a point just before or just after that portion, thereby maximizing the cleaning surface of the cleaning target being cleaned. However, the excitation light is directed, e.g. focused, onto a surface to be cleaned, and is not directed, e.g. wasted, on a surface not to be cleaned, e.g. a surface of a cleaning target or a component surrounding the cleaning target. Thus, cleaning may be accomplished faster and more efficiently, for example, when using a cleaning medium or excitation energy per cleaning surface area.

In the arrangement shown in fig. 15, at least a portion of the flow deflector 71 is transparent to the excitation light (i.e., the wavelength of the excitation light). The flow deflector 71 is arranged between the cleaning device 70 and the reflector 81, the cleaning device 70 being configured to emit excitation light. The flow deflector 71 is provided on the outer surface of the reflector 81. The outer surface of the reflector 81 is optionally a reflector surface.

In alternative arrangements, the flow deflector is different and optionally spaced from the reflector. For example, the flow deflector and the reflector may be offset relative to each other in a plane orthogonal to the charged particle beam path or in a plane coplanar with the support surface of the sample support 207.

As an alternative to having a reflector 81, another component of the cleaning device, such as the flow deflector 71, may have the function of a reflector. In one arrangement, a separate flow deflector 71 may not be required. In another arrangement, the reflector 81 may not be required. Thus, the diverter may function to redirect both the cleaning flow of the cleaning medium and the excitation radiation from the cleaning device towards the cleaning target.

The charged particle evaluation system of fig. 16A and 16B includes a light emitter 80. The arrangements depicted in each of fig. 16A and 16B each have the same components as depicted and described in any of fig. 11, 12, 13, 14, and 15, including variants having the same reference numerals, functions, and structures, unless otherwise mentioned. The light emitter 80 is configured to emit excitation light. The light emitter 80 is preferably a UV light emitter configured to emit UV light as excitation light. However, the excitation light may have any wavelength capable of exciting the cleaning medium to perform cleaning when the cleaning medium is irradiated with the excitation radiation. The excitation light follows the light path 85 from the light emitter 80 to the portion of the cleaning target. The light emitter 80 may be an LED or a laser diode.

In one arrangement, the light emitter 80 may be associated with but separate from the cleaning device 70. For example, the light emitter may be arranged in the charged particle evaluation system of fig. 11 or 12 associated with the cleaning device 70. The light emitters 80 may be positioned in the stations 209, 210 such that the emitted excitation light is directed toward the cleaning target 290. In another arrangement, the light emitter may be connected to or at least positioned adjacent to or abutting the cleaning device 70 of the charged particle evaluation system of fig. 15, so as to direct excitation light along the same path as the cleaning flow of the diverter, such that the excitation light irradiates the cleaning target in the presence of the cleaning medium. In these arrangements, cleaning of at least a portion of the cleaning target is thus achieved.

Referring now to fig. 16A, fig. 16A is a schematic diagram illustrating a charged particle evaluation system similar to fig. 13. The light emitter 80 is disposed downstream of the cleaning target and is configured to emit excitation light along the light path 85 from downstream of the cleaning target. The light emitter 80 in the embodiment of fig. 16A is preferably arranged in the same position as the cleaning device arranged in the embodiment of fig. 11. Thus, the light emitter 80 in the embodiment of fig. 16A is preferably disposed in or on the sample stage 209.

The cleaning device 70 is arranged at least at a position upstream of the sample holder 207. The cleaning device 70 in the embodiment of fig. 16A is preferably provided in the same position as the cleaning device 70 provided in the embodiment of fig. 13 and 15. The flow deflector 71 in the embodiment of fig. 16A is preferably provided in the same position as the flow deflector 71 provided in the embodiment of fig. 13 and 15.

Thus, the charged particle evaluation system of fig. 16A is arranged such that excitation light is directed along the light path 85 from the light emitter 80 downstream of the cleaning target to a portion of the cleaning target. The cleaning flow 75 is directed from the cleaning device 70 to the flow deflector 71. The flow deflector 71 deflects the cleaning medium such that the cleaning flow 75 is directed toward the cleaning target. The cleaning flow 75 is incident on the cleaning target such that the cleaning flow 75 approaches the cleaning target from downstream of the cleaning target. The cleaning flow 75 and the light path 85 are thus directed to the cleaning target such that the excitation light excites the cleaning medium at or near the cleaning target. The relative positions of the flow deflector 71, the light emitter 80 and the cleaning target, and optionally the angle of each flow deflector 71, the angle of illumination of the light emitter 80 and thus the light path 85, and topography, help direct excitation light and cleaning medium to the cleaning target for cleaning.

In an alternative embodiment, the light emitters 80 are provided on a separate support, such as an actuation stage, for example a light emitter holder similar to the cleaning device holder 214 of fig. 12. The light emitter holder optionally comprises a movable, preferably actuated stage 210. The table 210 for the cleaning device may include an actuator. The cleaning device may be configured to support a cleaning guide, such as the flow deflector 71 or the reflector 81, and thus the cleaning guide may be referred to as a guide holder. Such a guide holder is configured to be positioned relative to the cleaning device and a portion of the cleaning target such that a portion of the cleaning guide such a reflector 81 is operable to reflect excitation light to that portion of the cleaning target. Additionally or alternatively, the guide holder is configured to be positioned relative to the cleaning device and the portion of the cleaning target such that any portion of the cleaning guide (such as the flow deflector 71) is operable between the cleaning device and the portion of the cleaning target to direct the cleaning flow thereto. Another additional or alternative embodiment is that the guide holder is configured to be positioned relative to the cleaning device such that a portion of the cleaning guide both reflects the excitation light and directs the cleaning flow.

Referring now to fig. 16B, fig. 16B is a schematic diagram illustrating a charged particle evaluation system similar to fig. 11; similar inclusion variant features bear similar reference numerals unless otherwise indicated to the contrary. The light emitter 80 is disposed at least at a location upstream of the sample holder 207 (i.e., along the beam path). The light emitter 80 in the embodiment of fig. 16B is preferably arranged in the same position as the cleaning device 70 arranged in the embodiment described in relation to the arrangement depicted in fig. 13, 15 and 16A. With this arrangement, the light emitter 80 is preferably disposed outside of the vacuum environment. Such an arrangement is beneficial if the light emitters are cumbersome, such as a laser arrangement. For example, as shown in fig. 16B, a separation flange 73 is provided to separate the light emitter 80 from the vacuum environment. The light emitters 80 may be mounted on or in the flange; such a location may be suitable as a light emitter for an LED or laser diode.

Thus, the charged particle evaluation system of fig. 16B is arranged such that the cleaning flow 75 is guided from the cleaning device 70 to the cleaning target portion from downstream of the cleaning target. Excitation light is directed along an optical path 85 from the light emitter 80 to the reflector 81. The reflector 81 reflects the excitation light so that the excitation light is directed to the cleaning target. The excitation light is incident on the cleaning target such that the optical path approaches the cleaning target from downstream of the cleaning target. The cleaning flow 75 and the light path 85 are thus directed to the cleaning target such that the excitation light excites the cleaning medium at or near the cleaning target.

In an alternative embodiment, the cleaning device 70 is provided on a separate support, such as the cleaning device holder 210 shown and described with reference to FIG. 12.

In the embodiment of fig. 16B, the reflector 81 is provided on the actuation stage, in particular on the long stroke 215 of the actuation stage. Additionally or alternatively, the charged particle evaluation system may further comprise an actuation holder, referred to as a guide holder. The guide holder 210 may be configured to support a cleaning guide, such as a reflector 81. The guide holder 210 may be similar to the cleaning device holder 210 depicted and described with reference to fig. 12 or the guide holder or light emitter holder depicted and described with reference to fig. 16A. The guide holder is optionally configured to be movable, e.g. actuated. The guide holder is preferably comprised in or on the table. The guide holder is configured to be positioned relative to the cleaning device and the portion of the cleaning target such that the portion of the reflector 81 therebetween is operable to reflect the excitation light to the portion of the cleaning target. Thereby achieving cleaning of the cleaning target.

Preferably, the cleaning device 70 of the embodiment of fig. 16A and 16B may include a plasma generator, as described above with reference to fig. 15. In addition to supplying the cleaning flow 75, the plasma generator may also contribute excitation energy by providing excitation light. That is, the plasma generator may have a light generating function. The light generated may be UV light. The generated light may be directed toward the cleaning target together with the cleaning flow to contribute to the excitation light for cleaning the cleaning target.

In the arrangement of fig. 16A, the flow deflector 71 and the reflector 81 may be arranged as described above with reference to fig. 15 and as shown in fig. 15. At least a portion of the flow deflector 71 is transparent to the excitation light. At least a portion of the flow deflector 71 is disposed between the cleaning device 70 and the reflector 81. The cleaning medium is deflected toward the cleaning target by the flow deflector 71, and additional excitation light provided by the cleaning flow is reflected toward the cleaning target by the reflector 81. Since the flow deflector 71 is transparent to the excitation light, the reflector 81 does not suppress the incidence of the excitation light on the reflector 81.

The charged particle evaluation system may comprise a guide tube. The guide tube is part of the cleaning device for guiding the cleaning flow of the cleaning medium to the cleaning medium required for cleaning. For example, the cleaning device may take the form of a conduit or guide tube similar to the cleaning agent source for introducing cleaning medium or cleaning agent into the electron optical column as disclosed in US2017/0304878, which is incorporated herein by reference at least with respect to the operation and structure of the cleaning agent source (or cleaning device) and the conduit (or guide tube) and associated functions. The guide tube is optionally a cleaning guide tube configured to guide the cleaning flow along at least a portion of a path of the cleaning flow from the cleaning device to the cleaning target. In the embodiment shown and described with reference to fig. 13, 15 and 16A, for example, the cleaning guide tube 72 extends downstream from the cleaning device 70. The cleaning guide tube 72 is configured to guide the cleaning flow to the flow deflector 71. The flow deflector 71 is positioned to deflect the cleaning flow toward a portion of the cleaning target.

For example, as shown in fig. 11, 12, and 16B, the cleaning guide pipe 72 is provided to guide the cleaning flow upstream from the cleaning device 70 toward the portion of the cleaning target. Thus, the cleaning guide tube is optionally supported by the same support that holds the cleaning device 70, such as a cleaning device holder 210 that may be included in the actuation stage 209.

The cleaning guide tube 72 shown in fig. 11 to 16 is a straight tube. Alternatively, the cleaning guide tube may be curved or bent, for example, such that the cleaning guide tube is configured to change the direction of the cleaning flow. The degree of curvature or deviation from a straight path may be limited to ensure that the cleaning medium reaches the cleaning target. The guide tube may comprise the same material as the flow deflector. The guide tube may include a material having elasticity and durability to exposure to the cleaning medium. The flow deflector preferably comprises a chemically inert material, in other words has low chemisorption, preferably a small number of physisorption sites. For example, the flow deflector may comprise glass. Preferably, the flow deflector comprises quartz.

Alternatively or additionally, the guide tube serves as a waveguide to guide light from the cleaning device. The guide tube may be used as a light guide, for example in the arrangement described and depicted with reference to fig. 12, 13 and 15, when featuring the plasma generator generating excitation radiation, which is directed along the cleaning path towards the cleaning target. Additionally or alternatively, there may be a separate light emitter associated with the plasma generator to emit excitation radiation along the cleaning path. Thus, the guide tube serves to guide the excitation light from the cleaning device 70 to the cleaning target. The light guide tube is configured to guide the excitation light along at least a portion of the optical path of the excitation light from the light emitter (and/or the cleaning device if it includes a plasma generator) toward the cleaning target. In one variation, the light guide is a structure separate from the guide tube, such as one or more optical fibers. Separate guiding structures may be used in parallel to guide the excitation light along the light guide and the guiding tube for guiding the cleaning flow, which may guide the light to the reflector, the cleaning flow to the flow deflector, or the excitation light and the cleaning flow towards the deflector, respectively, for redirecting the cleaning flow and the cleaning light towards the cleaning target.

In another arrangement, the guiding tube may serve only as a light guide for light. For example, the light guiding tube 82 described with reference to fig. 16B and arranged as shown in fig. 16B extends downstream from the light emitter 80. The light guiding tube 82 guides the emitted light to the reflector 8. Thus, the light guide tube 82 guides the excitation light along the optical path to the reflector 81. The reflector 81 is positioned to reflect the excitation light toward the portion of the cleaning target. In one variation, the light guiding tube 82 is a light guide that does not require a structural form with a tube. For example, the light guide may be one or more optical fibers, as in the arrangement shown and described with reference to fig. 16B, the light guide is used to guide light. The light guide is not suitable for guiding a cleaning flow.

The light guide tube 82 is provided to guide the excitation light beam from the light emitter 80 upstream toward the portion of the cleaning target, for example, as shown in fig. 16A. Thus, the light guiding tube may optionally be supported by the same support holding the light emitters 80, such as a light emitter holder or an actuation stage 209.

As shown in fig. 15, for example, the cleaning guide tube 72 may be configured to guide a cleaning flow and excitation light from the cleaning device 70, the cleaning device 70 including a photon generator. Preferably, the interior of the cleaning guide tube comprises an outer layer, optionally comprising the same materials as described above for the flow deflector, configured to deflect the cleaning flow. The outer layer is transparent to the excitation light. The outer layer is disposed on the inner layer configured to reflect excitation light. In this way, the same guide tube can guide the cleaning flow and the excitation light.

The guide tube may be provided as an alternative or in addition to the flow deflector and/or reflector.

The guide tube has the advantage of aiming the cleaning flow and/or the excitation light in a desired direction, so that the cleaning medium and/or the excitation light is not wasted by being directed partly to parts, surfaces or parts of surfaces that do not need cleaning.

The charged particle evaluation system may be configured to actively direct a cleaning flow towards the cleaning target. In this way, the cleaning flow can be more accurately directed to the cleaning target. Thus, cleaning may be more efficient because it would otherwise be difficult to reach areas that may be reached by the cleaning flow. In addition, by directing the cleaning flow to a wider area than the specific area that needs to be cleaned, time and cleaning media are not wasted.

In the arrangements of fig. 11, 12, and 16B, the cleaning device is disposed downstream of the cleaning target. With these arrangements, the cleaning device may be configured to be actuated in at least one degree of freedom to actively direct the cleaning flow towards the cleaning target.

For example, with arrangements such as fig. 11, 12 and 16B, in order to actively direct a cleaning flow from the cleaning device to the cleaning target, the cleaning device may be provided on an actuation support. The actuation support is configured to move in at least one degree of freedom. The at least one degree of freedom preferably comprises a degree of freedom with respect to a pivot point on the actuation support or at least with respect to rotation of the actuation support to desirably adjust the portion of the cleaning target to which the cleaning flow is directed. More preferably, the actuation support is configured to be actuated in at least two rotational degrees of freedom to actively direct the cleaning flow. More preferably, the actuation support is configured to actuate in six degrees of freedom.

The actuation support may be an actuation stage 209, for example in the arrangement of fig. 11, wherein the actuation stage 209 is also configured to support a sample. Alternatively, the actuation support may be a cleaning device holder 210, such as in the arrangement of fig. 12.

Alternatively or additionally, the cleaning device may be configured to be actuated in at least one degree of freedom for being provided on the actuation support. In particular, the cleaning device is desirably configured to be actuated to direct the cleaning flow toward the cleaning target. The cleaning device may be configured to be actuated in at least one degree of freedom in any of the arrangements shown in fig. 11-16. For example, the cleaning device 70 may be actuated such that the path direction of the cleaning flow 75 from the cleaning device 70 to the cleaning target 290 may be changed within the range of the actuation direction 76, as shown in fig. 17. In order to adjust the portion of the cleaning target to which the cleaning flow is directed, it is desirable that the actuation direction be different from the path direction of the cleaning flow 75. The arrangement shown in fig. 17 is otherwise identical to the arrangement of fig. 13, as described above, the details of which are incorporated herein by reference.

The cleaning device may be actuated such that all or part of the cleaning device is actuated. For example, the entire cleaning device 70 may be actuated. Alternatively or additionally, a cleaning guide of the cleaning device 70 (such as guide tube 72) may be actuated to direct the cleaning flow toward the cleaning target. At least one of the degrees of freedom desirably includes a rotational degree of freedom relative to the pivot point of the guide tube 72.

The guide tube 72 may include a distal end configured for flow of the cleaning flow 75 to flow out of the guide tube 72 toward the cleaning target 290. The distal end of the guide tube 72 is located at the opposite end of the guide tube 72 from the proximal end of the guide tube 72 where the cleaning medium enters. The pivot point is desirably remote from the distal end of the guide tube 72. The pivot point is desirably near the proximal end of the guide tube 72.

The charged particle evaluation systems of the arrangements of fig. 13-16A and 17 each include a deflector having a deflector surface configured to deflect a cleaning flow from a cleaning device toward a cleaning target. In particular, the deflector surface is configured to deflect the cleaning flow from the cleaning device towards the cleaning target when the deflector surface is positioned in the path of the cleaning flow. In these arrangements, the guide tube 72 is desirably arranged to extend downstream from the cleaning device to direct the cleaning flow toward the deflector surface.

With the arrangement of fig. 17, similar to the arrangement of fig. 13 to 16A, the cleaning device 70 is provided on the side of the separation flange 73 opposite to the vacuum environment. The separation flange 73 may include a seal around the guide tube 72. The seal may be configured to allow the guide tube to move relative to the separation flange 73.

With the arrangement of fig. 17, similar to the arrangement of fig. 13 to 16A, the cleaning flow is guided to the cleaning target 290 via the deflector 71. In the arrangement of fig. 17, the cleaning device 70 is configured to be actuated to actively direct a cleaning flow from the cleaning device 70 to the deflector 71. In other words, the cleaning device is configured to control the angle and/or position at which the cleaning flow is incident on the deflector surface. The angle and/or position at which the cleaning flow is incident on the deflector surface affects the cleaning flow path from the deflector to the cleaning target.

In this way, the cleaning flow can be directed to the area most in need of cleaning. The at least one degree of freedom desirably includes a rotational degree of freedom relative to a pivot point on the cleaning device. With this arrangement the angle and/or position of incidence of the cleaning path on the deflector can be controlled by actuation of the cleaning device.

Alternatively, or in addition, for the charged particle evaluation systems of fig. 13-16A or 17, to actively direct the cleaning flow towards the cleaning target, a deflector may be provided on an actuation support configured to move in at least one degree of freedom. Preferably, the actuation support is configured to actuate the deflector surface with respect to a cleaning flow from the cleaning device. The actuation support may be configured to move in one degree of freedom. Preferably, the actuation support is configured to move in two or three or more degrees of freedom. The actuation support may be configured to move in six degrees of freedom. The path of the cleaning flow may be adjusted so as to direct the cleaning flow to a desired portion of the cleaning target.

In one arrangement, the deflector surface may be configured such that movement of the actuation support changes the path of the cleaning flow when the deflector surface is positioned in the path of the cleaning flow. For example, in the arrangement of fig. 18A and 18B, the deflector is curved, i.e., the deflector has a curved surface. The charged particle evaluation system of fig. 18A and 18B is otherwise identical to the system of fig. 13. In the arrangement of fig. 18A and 18B, the deflector 71 is provided with an actuation support, for example in the form of a long stroke stage 216. When the cleaning flow is incident on the deflector surface, movement of the long stroke stage 216 changes the position of the point of contact of the cleaning flow on the deflector surface and/or the angle of the deflector surface relative to the cleaning flow. Thus, the stage 216 may be actuated to control the path of the cleaning flow from the deflector to the cleaning surface. For example, as shown in fig. 18A and 18B, movement of the stage 216 in the translational direction 77, e.g., a direction across (e.g., orthogonal to) the charged particle beam path, results in a change in the direction 76 of the cleaning flow 76 deflected from the deflector 71 toward the cleaning target 290, e.g., adjusting the portion of the cleaning target to which the cleaning flow is directed. Thus, the portion of the cleaning target to which the cleaning flow is directed can be selected. Instead of an actuation support as a long stroke stage 216 as in the arrangement of fig. 18A and 18B, the actuation support may be in the form of a short stroke stage, for example.

In the arrangement of fig. 18B, the deflector surface is concave. The deflector surface is desirably configured to increase the divergence of the cleaning flow toward the cleaning target. In the charged particle evaluation system of fig. 18A, the deflector surface is convex. The convex deflector surface may be configured to at least maintain the cleaning flow toward the cleaning target (if not converging), even focusing the cleaning flow. The curved surface may have one axis of curvature, for example, a cylindrical curved surface, or two axes of curvature, for example, a spherical curved surface.

While fig. 18A and 18B depict the entire long stroke stage 216 actuated to move in at least one degree of freedom, the actuation support may alternatively or additionally be configured to actuate the deflector surface relative to the stage. For example, fig. 19 shows an arrangement similar to that of fig. 18A and 18B except that the deflector surface shown in fig. 19 is not curved. Although in another embodiment the deflector surface may be curved and have any of the features described and depicted with reference to fig. 18A and 18B. In the arrangement of fig. 19, the actuation support is configured to actuate the position of the deflector surface relative to the path of the cleaning flow 75 from the cleaning device 70. In particular, the actuation support is desirably configured to actuate the position of the deflector surface in a rotational degree of freedom relative to a pivot point near, on, or in the long-stroke stage 216 (i.e., in the frame of reference of the long-stroke stage 216). Alternatively, the actuation support may be configured to actuate the position of the deflector surface in a rotational degree of freedom relative to a pivot point near, on, or in (i.e., in the frame of reference of) the short stroke stage. When the cleaning flow 75 is incident on the deflector 71, actuation of the deflector surface in the direction of rotation 78 may cause a change in the direction 76 of the cleaning flow 75 from the deflector 71 to the cleaning target 290. In this way, the actuation support is configured to control the path of the cleaning flow 75 from the deflector 71 to the cleaning target 290. The deflector 71 may comprise an actuation support. Alternatively, the table may comprise an actuation support, for example the actuation support may be in the table.

The actuation support may be configured to support a sample. The actuation support may also be configured to support the deflector surface, or the actuation support may comprise a deflector surface. For example, FIG. 20 shows an arrangement similar to that of FIG. 19 except that in the arrangement of FIG. 20, the short stroke stage 215 actuated relative to the long stroke stage 216 includes a deflector 71 (rather than supporting the deflector on the long stroke stage 216 as in the arrangement of FIG. 19; however, in one embodiment, the deflector may be included in a long stroke stage having all of the features described herein with respect to FIG. 19 and depicted in FIG. 19). In an arrangement where the short stroke stage 215 includes a deflector 71, the deflector may be actuated relative to the short stroke stage.

The short stroke stage 215 may be configured to actuate the position of the deflector surface relative to the cleaning flow 75 from the cleaning device 70. Specifically, the short stroke stage 215 is configured to actuate the position of the deflector surface with respect to a pivot point near, in, or on the short stroke stage 215 (i.e., in the frame of reference of the short stroke stage 216) in a rotational degree of freedom. Actuation of the short stroke stage 215 in the direction of rotation 78 (e.g., about a pivot point) may cause a change in the direction 76 of the cleaning flow 75 from the deflector 71 to the cleaning target 290 when the cleaning flow 75 is incident on the deflector 71. In this way, the short stroke stage 215 is configured to control the path of the cleaning flow 75 from the deflector 71 to the cleaning target 290. The portion of the cleaning target to which the cleaning flow 75 is directed may be adjusted or even selected.

The charged particle evaluation system may be configured to actively direct excitation light toward the cleaning target. In particular, the charged particle evaluation system may be configured to actively direct UV light towards the cleaning target. As described above, the excitation light can be guided similarly to the cleaning flow of the arrangement in fig. 17 to 20.

In some arrangements, the excitation light is directed with a different actuation than the path of the cleaning flow. For example, the different actuation of the excitation light may include additional actuation of the cleaning flow. For example, in the arrangement of fig. 16A and 16B, the light emitter 80 and/or reflector 81 (at least in fig. 16B) may be actuated to actively direct excitation light toward the cleaning target. Desirably, the light guiding tube 82 may be actuated to actively guide the excitation light toward the cleaning target. The reflector may be actuated in any of the ways described and depicted with reference to fig. 16A-20. The light guide tube 82 may be actuated in the same manner as the actuation of the guide tube 72. Desirably, different actuation of the excitation light may help ensure that the light reaches the same portion of the cleaning target even if the path of the cleaning flow is actively adjusted.

Furthermore, in the arrangement shown in fig. 15, the reflector 81 as well as the deflector 71 may be provided on an actuation support such as a long stroke stage 216. The reflector 81 and the deflector 71 may be actuated relative to each other. Alternatively, the reflector may be disposed on a short stroke stage, alternatively, the deflector may be disposed on a long stroke stage 216. Alternatively or additionally, the reflective surface of the reflector may be actuated relative to a table on which the reflector is supported. Therefore, the excitation light and the cleaning medium can be actively guided to the cleaning target. Active guiding of the excitation light and the cleaning medium may be controlled independently or jointly such that they are guided to the same portion of the cleaning target.

The following clauses are provided:

Clause 1: a charged particle evaluation system for projecting a charged particle beam towards a sample, the system comprising: a sample holder configured to hold a sample; a charged particle optical system configured to project a charged particle beam from a charged particle source downstream towards the sample and comprising a cleaning target; the cleaning device is configured to: supplying the cleaning target with a cleaning medium in a cleaning flow incident on the cleaning target such that the cleaning flow approaches the cleaning target from downstream of the cleaning target, and exciting the cleaning medium at or near the cleaning target such that the cleaning medium cleans at least a portion of a surface of the cleaning target.

Clause 2: the charged particle evaluation system of clause 1, wherein the charged particle optical system comprises a plurality of electron optical elements and the cleaning target comprises one of the plurality of electron optical elements.

Clause 3: the charged particle evaluation system of clause 2, wherein: the plurality of electron optical elements comprises an objective lens arrangement configured to focus the charged particle beam on the sample; and the cleaning target includes an objective lens.

Clause 4: the charged particle evaluation system of clause 2 or 3, wherein the electron optical element comprises a detector configured to detect signal particles emitted from the sample in response to the charged particle beam.

Clause 5: the charged particle evaluation system of clause 4, wherein the cleaning target comprises the detector.

Clause 6: charged particle evaluation system according to clause 4 or 5, wherein the detector comprises an array of detector elements, preferably each detector element being assigned to a beamlet of the charged particle beam, preferably an aperture is defined in the detector for each beamlet.

Clause 7: a charged particle evaluation system according to any of clauses 4-6, wherein the cleaning device is arranged upstream of the detector, preferably remote from the charged particle optical system.

Clause 8: the charged particle evaluation system of any of clauses 2-7, wherein one or more of the electron optical elements comprises a plurality of plate electrodes in which one or more apertures are defined for the path of the charged particle beam.

Clause 9: the charged particle evaluation system of any preceding clause, wherein at least a portion of the cleaning target is positioned proximate to the sample.

Clause 10: the charged particle evaluation system according to any of the preceding clauses, wherein the cleaning device comprises a cleaning guide configured to guide the cleaning flow to the cleaning target, preferably the cleaning guide is configured to guide the cleaning flow to the cleaning target along a cleaning path.

Clause 11: the charged particle evaluation system of clause 10, further comprising a guide holder configured to support at least a portion of the cleaning guide.

Clause 12: the charged particle evaluation system of clause 10 or 11, wherein the at least a portion of the cleaning guide is disposed in the support, preferably wherein the support is a table.

Clause 13: the charged particle evaluation system of clause 12, wherein the sample holder or guide holder is configured to be positioned relative to the cleaning device and the portion of the cleaning target such that a portion of the cleaning guide between the cleaning device and the portion of the cleaning target is operable to direct the cleaning flow to the portion of the cleaning target.

Clause 14: the charged particle evaluation system of clause 13, wherein the sample holder or guide holder is configured to be displaceable in a downstream direction during operation of the cleaning device.

Clause 15: the charged particle evaluation system of any of clauses 10-14, wherein the cleaning guide comprises a guide member disposed downstream of the optical system.

Clause 16: the charged particle evaluation system of clause 15, wherein the sample holder comprises a holding surface configured to hold the sample, preferably the holding surface is recessed into the sample holder.

Clause 17: the charged particle evaluation system of clause 16, wherein the guide member is provided at a position between 2mm and 50mm, desirably between 5mm and 15mm, downstream of the sample holder, preferably the holding surface.

Clause 18: the charged particle evaluation system of any of clauses 15-17, wherein the guide member comprises a deflector having a deflector surface configured to deflect the cleaning flow upstream toward the portion of the cleaning target.

Clause 19: the charged particle evaluation system of clause 18, wherein the deflector surface is disposed such that the cleaning flow from the cleaning device is directed to be incident on the cleaning target.

Clause 20: the charged particle evaluation system of clauses 18 or 19, wherein the deflector surface is shaped and positioned relative to the at least a portion of the cleaning target to deflect, preferably focus, the cleaning flow toward the at least a portion of the cleaning target.

Clause 21: the charged particle evaluation system of clause 20, wherein the deflector surface is curved.

Clause 22: the charged particle evaluation system of clause 20 or 21, wherein the deflector surface comprises a fresnel lens, preferably the deflector surface has a topography that acts as a fresnel lens, preferably so as to focus the cleaning flow along the cleaning path toward the cleaning target.

Clause 23: the charged particle evaluation system of clause 20, wherein the deflector surface is planar.

Clause 24: the charged particle evaluation system of clauses 15-23, wherein the cleaning guide comprises a guide tube to guide the cleaning flow along at least a portion of a path, such as a cleaning path of the cleaning flow from the cleaning device to the cleaning target.

Clause 25: the charged particle evaluation system of clause 24, wherein the guide tube preferably extends upstream from a support toward the cleaning target, preferably the support is the sample holder or the guide holder.

Clause 26: the charged particle evaluation system of clauses 24 or 25, wherein the guide tube extends downstream from the cleaning device, preferably the guide tube is directed towards the sample holder or guide holder, preferably to direct the cleaning flow towards the deflector, preferably the deflector is positioned to deflect cleaning flow towards the at least a portion of the target location.

Clause 27: a charged particle evaluation system according to any of the preceding clauses, further comprising a charged particle source configured to project the charged particle beam towards the sample, preferably the charged particle source comprises in part the cleaning device such that, upon operation of the charged particle source, the charged particle beam is configured to excite the cleaning medium at or near the cleaning target such that the cleaning medium cleans at least a portion of the cleaning target.

Clause 28: the charged particle evaluation system of clause 27, wherein during operation of the charged particle evaluation tool, the cleaning device operates to clean the portion of the cleaning target.

Clause 29: the charged particle evaluation system of clause 27 or 28, comprising an electron optical arrangement comprising the cleaning target, wherein the sample holder and the charged particle device are controlled during operation of the charged particle source such that the path of the charged particle beam is reflected upstream from the sample, the sample holder, or both at least onto the cleaning target.

Clause 30: the charged particle evaluation system of any of the preceding clauses, further comprising a heat source configured to energize the cleaning medium at or near the cleaning target such that the cleaning medium cleans at least a portion of the cleaning target, preferably the heat source is configured to apply a thermal load to the cleaning target.

Clause 31: the charged particle evaluation system of any of the preceding clauses, further comprising a light emitter configured to emit excitation light having a wavelength that excites the cleaning medium to clean at least a portion of the cleaning target, preferably the light excites the cleaning medium at or near the cleaning target.

Clause 32: the charged particle evaluation system of clause 30, further comprising a light guide configured to guide excitation light along a light path from a light emitter to the portion of the cleaning target.

Clause 33: the charged particle evaluation system of clause 32, wherein the light emitter is disposed upstream of the cleaning target, preferably the cleaning target is a detector within the charged particle optical system.

Clause 34: the charged particle evaluation system of clause 31 or 32, wherein the light guide is disposed downstream of the charged particle optical system.

Clause 35: the charged particle evaluation system of any of clauses 31-34, wherein the light guide comprises a reflector configured to reflect the excitation light.

Clause 36: the charged particle evaluation system of clause 35, wherein the sample holder comprises a holding surface configured to hold the sample, preferably the holding surface is recessed into the sample holder, and preferably the reflector is disposed at a position between 5mm and 15mm downstream of the holding surface.

Clause 37: the charged particle evaluation system of clause 35 or 36, wherein the reflector comprises a reflector surface shaped and positioned relative to the at least a portion of the cleaning target to reflect, preferably focus, the excitation light toward the at least a portion of the cleaning target.

Clause 38: the charged particle evaluation system of clause 37, wherein the reflector surface is curved.

Clause 39: the charged particle evaluation system of clause 37 or 38, wherein the reflector surface comprises a fresnel lens.

Clause 40: the charged particle evaluation system of clause 37, wherein the reflector surface is planar.

Clause 41: the charged particle evaluation system of any of clauses 35-40, wherein the reflector is included in a guiding member configured to guide the cleaning flow along a portion of the cleaning path from the cleaning device towards the cleaning target, the guiding member preferably comprising a deflector for guiding the fluid flow towards the cleaning target.

Clause 42: a charged particle evaluation system according to any of clauses 30-40, wherein at least a part of the light emitter is comprised in the cleaning device, and preferably a plasma generator configured to generate a plasma for providing the cleaning medium and light, e.g. having UV wavelength.

Clause 43: the charged particle evaluation system of any of clauses 31-42, wherein at least a portion of the light emitter is separate from the cleaning device, preferably the light emitter is associated with the cleaning device such that the light path from the light emitter is substantially similar to a cleaning path from the cleaning device to the target, preferably the light emitter is positioned downstream of the cleaning target, e.g., included in or associated with the sample holder.

Clause 44: the charged particle evaluation system of any of clauses 31-43, wherein at least a portion of the cleaning guide is transparent to excitation light and is disposed between the light emitter and the reflector.

Clause 45: the charged particle evaluation system of clause 44, wherein the reflector comprises an outer surface configured to reflect excitation light, and wherein the cleaning guide is disposed on the outer surface of the reflector.

Clause 46: the charged particle evaluation system of any of clauses 31-45, wherein the light emitter is a UV emitter.

Clause 47: the charged particle evaluation system of any of clauses 35-46, further comprising a guide holder configured to support the reflector.

Clause 48: the charged particle evaluation system of clauses 11-14 or 47, wherein the guide holder is configured to be movable.

Clause 49: the charged particle evaluation system of clause 47 or 48, wherein the reflector is disposed in the sample holder, preferably comprising a stage.

Clause 50: the charged particle evaluation system of any of clauses 47-49, wherein the sample holder or guide holder is configured to be positioned relative to the cleaning device and the portion of the cleaning target such that any portion of the cleaning guide therebetween is operable to reflect the excitation light to the portion of the cleaning target.

Clause 51: the charged particle evaluation system according to any of the preceding clauses, wherein the cleaning device comprises a cleaning guide and/or a light emitter, which is arranged downstream of the optical system.

Clause 52: the charged particle evaluation system of any of the preceding clauses, further comprising a cleaning device holder configured to support the cleaning device and/or the light emitter.

Clause 53: the charged particle evaluation system of clause 52, wherein the cleaning device holder is configured to be movable, preferably in the direction of the beam path.

Clause 54: the charged particle evaluation system of clause 52, wherein the cleaning source and/or the light emitter are disposed in the cleaning device holder, which may comprise a table.

Clause 55: a charged particle evaluation system according to any of the preceding clauses wherein at least a part of the charged particle optical system is arranged in a vacuum chamber and the cleaning device (e.g. cleaning source) and/or the light emitter (e.g. UV light source) is separated from the vacuum chamber by a separation flange.

Clause 56: a charged particle evaluation system according to any of the preceding clauses, wherein at least a part of the charged particle optical system is arranged in a vacuum chamber and the cleaning device (e.g. cleaning source and/or the light emitter) is arranged in the vacuum chamber.

Clause 57: the charged particle evaluation system of any of the preceding clauses, wherein the component or feature of the charged particle evaluation system configured to direct and/or direct a cleaning flow from the cleaning device to the cleaning target comprises: such a component can preferably be at least one of the reflector and the cleaning guide, such as a deflector and the guide tube, preferably the charged particle evaluation system comprises a cleaning arrangement comprising the cleaning device and at least one of the reflector, the deflector and the guide tube, for example quartz, which is resilient and durable to the material exposed to the cleaning medium.

Clause 58: the charged particle evaluation system of any of the preceding clauses, wherein the charged particle evaluation system is configured to actively direct the cleaning flow toward the cleaning target.

Clause 59: a method of operating a charged particle evaluation system configured to project a charged particle beam towards a sample, the charged particle evaluation system comprising: a sample holder configured to hold a sample; a charged particle optical system configured to project a charged particle beam from a charged particle source downstream towards the sample; a charged particle optical system comprising a cleaning target, the method comprising: 1) Supplying a cleaning medium in a cleaning flow incident on the cleaning target to the cleaning target, the supply of the cleaning flow causing the cleaning flow to approach the cleaning target from downstream of the cleaning target; and 2) exciting the cleaning medium at or near the cleaning target such that the cleaning medium cleans at least a portion of a surface of the cleaning target.

Clause 60: the method of clause 59, wherein the supplying of the cleaning medium is by a cleaning device.

Clause 61: the method of clause 59 or 60, wherein the energizing is by operating a charged particle source of the charged particle evaluation system that projects a charged particle beam at or near the cleaning target such that the cleaning medium cleans at least a portion of the surface of the cleaning target.

Clause 62: the method of any of clauses 59 to 61, wherein the energizing is by directing energizing light from a light emitter at or near the cleaning target such that the cleaning medium cleans at least a portion of the surface of the cleaning target.

Clause 63: the method of any of clauses 59 to 62, wherein the cleaning flow toward the cleaning target is along a cleaning path from a downstream location of the optical system to the cleaning target, preferably to the portion of the surface of the cleaning target.

Clause 64: a charged particle evaluation system for projecting a charged particle beam towards a sample, the system comprising: a sample holder configured to hold a sample; a charged particle optical system configured to project a charged particle beam from a charged particle source downstream towards the sample; the charged particle optical system comprises a cleaning target and a cleaning arrangement comprising: a cleaning device for supplying a cleaning medium in a cleaning flow; a cleaning guide configured to guide and direct the cleaning flow from the cleaning device toward the cleaning target such that the cleaning flow is incident on the cleaning target such that the cleaning flow approaches the cleaning target from downstream of the cleaning target, wherein the cleaning device is positioned in an upstream direction relative to the sample holder, and the cleaning guide comprises a flow deflector configured to deflect the cleaning flow toward the cleaning target.

Clause 65: the charged particle evaluation system of clause 64, wherein the flow deflector is positioned in a downstream direction of the cleaning target at least during a cleaning operation.

Clause 66: the charged particle evaluation system of clause 64 or 65, wherein the flow deflector is included in a support that is a stage comprising the sample holder or a guide stage separate from the stage comprising the sample holder.

Clause 67: the charged particle evaluation system of clause 64, 65, or 66, wherein the cleaning arrangement is configured to excite the cleaning medium at or near the cleaning target such that the cleaning fluid cleaning medium cleans at least a portion of the surface of the cleaning target.

Clause 68: the charged particle evaluation system of any of clauses 64-67, wherein the cleaning device further comprises a light emitter configured to excite the cleaning medium.

Clause 69: a charged particle evaluation system for projecting a charged particle beam towards a sample, the system comprising: a sample holder configured to hold a sample; a charged particle optical system configured to project a charged particle beam from a charged particle source downstream towards the sample and comprising a cleaning target; and a cleaning device configured to supply cleaning medium in a cleaning flow incident on the cleaning target toward the cleaning target such that the cleaning flow approaches the cleaning target from downstream of the cleaning target, wherein the charged particle evaluation system is configured to actively direct the cleaning flow toward the cleaning target.

Clause 70: the charged particle evaluation system of any of clauses 58 and 69, wherein the cleaning device is configured to be actuated to move in at least one degree of freedom to direct the cleaning flow toward the cleaning target.

Clause 71: the charged particle evaluation system of any of clauses 58, 69, and 70, further comprising a cleaning guide configured to direct the cleaning flow to the cleaning target.

Clause 72: the charged particle evaluation system of clause 71, wherein the cleaning guide comprises a guide tube configured to: directing the cleaning flow from the cleaning device to the cleaning target along at least a portion of a path of the cleaning flow; and to be actuated in at least one degree of freedom to direct the cleaning flow toward the cleaning target, the guide tube may include an end configured for flow of cleaning flow to exit the guide tube toward the cleaning target, desirably the at least one degree of freedom is a degree of rotational freedom relative to a pivot point of the guide tube, desirably the pivot point is remote from the end of the guide tube.

Clause 73: the charged particle evaluation system of any of clauses 58 and 69-72, wherein the cleaning device is disposed downstream of the cleaning target.

Clause 74: the charged particle evaluation system of clause 73, wherein the cleaning device is disposed on an actuated support configured to move in at least one degree of freedom.

Clause 75: the charged particle evaluation system of any of clauses 71 and 72, wherein the cleaning guide comprises a guide member disposed downstream of the charged particle optical system, wherein the guide member is a deflector having a deflector surface configured to desirably deflect the cleaning flow from the cleaning device toward the cleaning target when the deflector surface is positioned in the path of the cleaning flow.

Clause 76: the charged particle evaluation system of clause 75, wherein the guide tube extends downstream from the cleaning device to guide the cleaning flow toward the deflector surface.

Clause 77: the charged particle evaluation system of any of clauses 75 and 76, wherein the deflector is disposed on an actuation support configured to move in at least one degree of freedom.

Clause 78: the charged particle evaluation system of clause 77, wherein when the deflector surface is positioned in the path of the cleaning flow from the cleaning device, the deflector surface is configured such that movement of the actuation support alters the path of the cleaning flow, desirably from the cleaning device toward the target surface, and/or actuation of the deflector surface actuates the position of the deflector surface relative to the cleaning flow from the cleaning device.

Clause 79: the charged particle evaluation system of any of clauses 74, 77, and 78, wherein the actuation support is configured to move in six degrees of freedom.

Clause 80: the charged particle evaluation system of any of clauses 74 and 77-79, wherein the actuation support is a stage, desirably the stage is configured to support a sample, desirably the stage comprises a support configured to support the sample, and the support may comprise the deflector surface, desirably the actuation support is configured to actuate the deflector surface relative to the stage, desirably the actuation support is configured to actuate the deflector relative to the cleaning flow by actuating the stage and/or the support.

Clause 81: the charged particle evaluation system of any of clauses 75-80, wherein the deflector surface is desirably curved to increase the divergence of the cleaning flow toward the cleaning target.

Clause 82: the charged particle evaluation system of clause 81, wherein the deflector surface is concave.

Clause 83: the charged particle evaluation system of any of clauses 69-82, wherein the cleaning device is configured to excite the cleaning medium at or near the cleaning target such that the cleaning medium cleans at least a portion of the surface of the cleaning target.

Clause 84: a method of operating a charged particle evaluation system configured to project a charged particle beam towards a sample, the charged particle evaluation system comprising: a sample holder configured to hold a sample; a charged particle optical system configured to project a charged particle beam from a charged particle source downstream towards the sample; the charged particle optical system comprises a cleaning target, the method comprising: 1) Supplying a cleaning medium in a cleaning flow toward the cleaning target so as to be incident on the cleaning target, the supply of the cleaning flow causing the cleaning flow to approach the cleaning target from downstream of the cleaning target; and 2) actively directing the cleaning flow toward the cleaning target.

References to a system or element that can be controlled to manipulate a charged particle beam in a certain way include configuring a controller or control system or control unit to control the component to manipulate the charged particle beam in the manner described, and optionally using other controllers or devices (e.g., voltage and/or current sources) to control the component to manipulate the charged particle beam in this way. For example, under the control of a controller or control system or control unit, a voltage source may be electrically connected to one or more components to apply an electrical potential to the components, such as control lens array 250, objective lens array 241, converging lens 231, corrector, collimator element array, and scanning deflector array 260, in a non-limiting list. An actuatable component, such as a stage, may be controllable to actuate, and thus move relative to, another component, such as a beam path, using one or more controllers, control systems, or control units to control actuation of the component.

Embodiments described herein may take the form of a series of aperture arrays or electron-optical elements arranged in an array along a beam or multiple beam paths. Such electron optical elements may be electrostatic. In one embodiment, all electron optical elements, e.g. the last electron optical element in the sub-beam path from the beam limiting aperture array to the sample front, may be electrostatic and/or may be in the form of an aperture array or a plate array. In some arrangements, one or more electro-optical elements are fabricated as microelectromechanical systems (MEMS) (i.e., using MEMS fabrication techniques).

References to upper, lower, above, below are understood to refer to directions parallel (typically but not always perpendicular) to the upstream and downstream directions in which the electron beam or beams strike the sample 208. Thus, references to upstream and downstream are intended to mean directions about the beam path independent of any gravitational field present.

An evaluation system according to one embodiment of the present disclosure may be a tool that performs a qualitative evaluation (e.g., pass/fail) of a sample, a tool that performs a quantitative measurement (e.g., size of a feature) of a sample, or a tool that generates an image of a map of a sample. Examples of evaluation systems are inspection tools (e.g., for identifying defects), inspection tools (e.g., for classifying defects), and metrology tools, or tools capable of performing any combination of evaluation functions associated with an inspection tool, or a metrology tool (e.g., a metrology inspection tool). The electron optical column 40 may be a component of an evaluation system; such as an inspection tool or a metrology inspection tool, or a portion of an e-beam lithography tool. Any reference herein to a tool is intended to encompass an apparatus, device, or system that includes various components that may or may not be collocated, and may even be located in a separate room, particularly for example, a data processing element.

The terms "beamlet" and "beamlet" are used interchangeably herein and are understood to include any radiation beam derived from a parent radiation beam by dividing or splitting the parent radiation beam. The term "manipulator" is used to include any element affecting the beamlets or paths of beamlets, such as lenses or deflectors.

References to elements aligned along a beam path or sub-beam path are understood to mean that the respective element is positioned along the beam path or sub-beam path.

While the invention has been described in conjunction with various embodiments, other embodiments of the invention will be 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 a true scope and spirit of the invention being indicated by the following claims and terms disclosed herein.

The above description is intended to be illustrative, and not restrictive. It will therefore be apparent to those skilled in the art that modifications may be made as described without departing from the scope of the claims set out below and the terms set out herein.

Claims

1. A charged particle evaluation system for projecting a charged particle beam towards a sample, the system comprising:

a sample holder configured to hold a sample;

A charged particle optical system configured to project a charged particle beam from a charged particle source downstream towards the sample and comprising a cleaning target;

A cleaning device configured to: supplying the cleaning target with a cleaning medium in a cleaning flow incident on the cleaning target such that the cleaning flow approaches the cleaning target from downstream of the cleaning target, and exciting the cleaning medium at or near the cleaning target such that the cleaning medium cleans at least a portion of a surface of the cleaning target.

2. The charged particle evaluation system of claim 1 wherein at least a portion of the cleaning target is positioned in proximity to the sample.

3. The charged particle evaluation system according to claim 1 or 2, wherein the cleaning device comprises a cleaning guide configured to guide the cleaning flow to the cleaning target.

4. A charged particle evaluation system according to claim 3 wherein the at least part of the cleaning guide is provided in the support, preferably wherein the support is a table.

5. A charged particle evaluation system according to claim 3 or 4 wherein the cleaning guide comprises a guide member arranged downstream of the optical system.

6. The charged particle evaluation system according to claim 5 wherein the guide member comprises a deflector having a deflector surface configured to deflect the cleaning flow upstream toward the portion of the cleaning target.

7. The charged particle evaluation system according to claim 6 wherein the deflector surface is shaped and positioned relative to the at least a portion of the cleaning target to deflect the cleaning flow toward the at least a portion of the cleaning target.

8. The charged particle evaluation system according to claims 5-7 wherein the cleaning guide comprises a guide tube for guiding the cleaning flow from the cleaning device to the cleaning target along at least a portion of the path of the cleaning flow.

9. The charged particle evaluation system according to any of the preceding claims further comprising a light emitter configured to emit excitation light having a wavelength that excites the cleaning medium to clean at least a portion of the cleaning target.

10. The charged particle evaluation system according to claim 9 further comprising a light guide configured to guide excitation light along a light path from the light emitter to the portion of the cleaning target.

11. The charged particle evaluation system according to claim 10 wherein the light guide comprises a reflector configured to reflect the excitation light.

12. A charged particle evaluation system according to any of the preceding claims wherein the charged particle optical system comprises a plurality of electron optical elements and the cleaning target comprises one of the plurality of electron optical elements.

13. The charged particle evaluation system of claim 12 wherein

The plurality of electron optical elements comprises an objective lens arrangement configured to focus the charged particle beam on the sample; and

The cleaning target includes the objective lens.

14. A charged particle evaluation system according to claim 12 or 13 wherein the electron optical element comprises a detector configured to detect signal particles emitted from the sample in response to the charged particle beam.

15. The charged particle evaluation system of claim 14, wherein the cleaning device is disposed upstream of the detector.