CN116941009A

CN116941009A - Charged particle optical device

Info

Publication number: CN116941009A
Application number: CN202180093973.2A
Authority: CN
Inventors: M·J-J·维兰德; A·V·G·曼格努斯
Original assignee: ASML Holding NV
Current assignee: ASML Holding NV
Priority date: 2020-12-23
Filing date: 2021-12-15
Publication date: 2023-10-24

Abstract

The present application provides various techniques for detecting backscattered charged particles, including accelerating a charged particle beamlet along a beamlet path to a sample, repelling secondary charged particles from a detector array, and providing a device and detector that can switch between a mode for primarily detecting charged particles and a mode for primarily detecting secondary particles.

Description

Charged particle optical device

Cross Reference to Related Applications

The present application claims priority from european application 20216927.2 filed 12/23 in 2020, EP application 21174518.7 filed 5/18 in 2021, and european application 21191729.9 filed 8/17 in 2021, which are incorporated herein by reference in their entirety.

Technical Field

Embodiments provided herein relate generally to objective lens assemblies, charged particle optical devices, detectors, detector arrays, and methods, and in particular, to objective lens assemblies, charged particle optical devices, detectors, detector arrays, and methods of using multiple beams (e.g., beamlets) of charged particles.

Background

When manufacturing semiconductor Integrated Circuit (IC) chips, undesirable pattern defects are inevitably present on a substrate (i.e., wafer) or mask during manufacturing, for example, due to optical effects and accidental 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 to inspect objects, for example to detect pattern defects. These tools typically use electron microscopy techniques such as Scanning Electron Microscopy (SEM). In SEM, a primary (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. Interactions between the material structure at the probe spot and landing electrons from the electron beam cause 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. Secondary electrons can be emitted on the sample surface by scanning a primary electron beam as a detection spot on the sample surface. By collecting these emitted secondary electrons from the sample surface, the pattern inspection tool may acquire data that may be referred to as an image and that may be rendered as an image. The image represents a property of the material structure of the sample surface.

While images acquired in this manner may be useful, information about the sample acquired from such known electron microscopy techniques has limitations. Often, additional or alternative information needs to be obtained, for example, information related to structures below the sample surface and information related to overlay targets.

Disclosure of Invention

It is an object of the present disclosure to provide embodiments that support the use of charged particles (e.g., using back-scattered charged particles) to obtain information from a sample.

According to a first aspect of the present invention there is provided a charged particle optical apparatus for a charged particle evaluation tool, the apparatus being configured to project a plurality of beams of charged particles along a beamlet path towards a sample, the plurality comprising beamlets, the apparatus comprising: an array of objective lenses configured to project an array of charged particle beamlets onto the sample, wherein the array of objective lenses is arranged to span a beamlet path of the array of charged particle beamlets; an array of control lenses positioned upstream of the beam of the array of objective lenses, wherein each control lens is associated with a respective objective lens; and an array of detectors configured to be positioned near the sample and configured to capture charged particles emitted from the sample, wherein the charged particle optical device is configured to repel secondary charged particles emitted from the sample away from the detectors.

According to a second aspect of the present invention there is provided a method of operating a charged particle evaluation tool for detecting backscattered charged particles, the method comprising: a) Passing a plurality of beams of charged particles through a control lens array and then projecting toward a surface of the sample through the objective lens array in an array of charged particle beamlets that span the objective lens array; b) Rejecting charged particles having an energy less than a threshold value that are emitted from the sample in response to the plurality of beams; and c) detecting charged particles emitted from the sample having an energy of at least a threshold using a detector array positioned near the sample.

Drawings

The above and other aspects of the present disclosure will become more apparent from the description of exemplary embodiments thereof, taken in conjunction with the accompanying drawings.

Fig. 1 is a schematic diagram showing an exemplary charged particle beam inspection apparatus.

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

Fig. 3 is a schematic diagram of an exemplary multibeam apparatus according to an embodiment.

Fig. 4 is a schematic diagram of an exemplary charged particle optical apparatus according to an embodiment.

Fig. 5 is a schematic cross-sectional view of an objective lens of an inspection apparatus according to an embodiment.

Fig. 6 is a schematic cross-sectional view of an objective of an inspection device according to an alternative embodiment.

Fig. 7 is a bottom view of the objective lens of fig. 5 or 6.

Fig. 8 is a bottom view of a modification of the objective lens of fig. 5 or 6.

Fig. 9 is an enlarged schematic cross-sectional view of a detector incorporated in the objective lens of fig. 5 or 6.

Fig. 10, 11, 12 are schematic cross-sectional views of an insulating structure used in the embodiment

Fig. 13A and 13B are bottom views of different modified detectors.

Fig. 14 is a bottom view of the objective lens of fig. 5 or 6 using the modified detector of fig. 13.

Fig. 15 is an enlarged schematic cross-sectional view of a detector incorporated in the objective lens of fig. 5 or 6 using the modified detector of fig. 13.

Fig. 16 is a schematic diagram of an exemplary electron optical system including a macro (macro) collimator and a macro scanning deflector.

The schematic and view diagrams show the components described below. 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.

By significantly increasing the packing density of circuit components such as transistors, capacitors, diodes, etc. on an IC chip, the computing power of the electronic device can be increased, thereby reducing the physical size of the device. This is achieved by the fact that the resolution is increased, enabling smaller structures to be manufactured. For example, a smart phone IC chip of nail size available 2019 or earlier may include over 20 hundred million transistors, each transistor having a size less than 1/1000 of human hair. Thus, it is not surprising that semiconductor IC fabrication is a complex and time consuming process, requiring hundreds of individual steps. Even an error in one step may greatly affect the function of the final product. Only one "fatal defect" may lead to equipment failure. The goal of the manufacturing process is to increase the overall yield of the process. For example, to obtain a 75% yield for a 50 step process (where steps may indicate the number of layers formed on a wafer), each individual step must have a yield of greater than 99.4%. If each individual step had a yield of 95%, the overall process yield would be as low as 7%.

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

The SEM includes a scanning device and a detection apparatus. 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 primary electron beams. At least the illumination device or illumination system, together with the projection device or projection system, may 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 create an image of the scanned area of the sample. For high throughput inspection, some inspection devices use multiple focused beams, i.e., multiple beams, of primary electrons. The multiple component beams may be referred to as sub-beams or sub-beams. The multiple beams may simultaneously scan different portions of the sample. Thus, the multi-beam inspection device can inspect a sample at a much higher speed than a single-beam inspection device.

An implementation of a known multibeam inspection apparatus is described below.

These 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 the embodiments are not intended to limit the disclosure to particular charged particles. Thus, reference to electrons throughout this document may be more generally considered to be a reference to charged particles, where the charged particles are not necessarily electrons.

Referring now to fig. 1, fig. 1 is a schematic diagram of 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, an electron beam tool 40, an Equipment Front End Module (EFEM) 30, and a controller 50. An electron beam tool 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 and second load ports 30a, 30b may receive a substrate Front Opening Unified Pod (FOUP) that houses a substrate (e.g., a semiconductor substrate or a substrate made of other material (s)) or a sample (the substrate, wafer, and sample are collectively referred to hereinafter as a "sample") to be inspected. One or more robotic arms (not shown) in the EFEM 30 transport samples to the load lock chamber 20.

The load lock chamber 20 is used to remove gas around the sample. This creates a vacuum, which is a partial gas pressure that is 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. 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 transported to the electron beam tool 40, through which electron beam tool 40 the sample can be inspected. The electron beam tool 40 may include multiple beam electron optics.

The controller 50 is electronically connected to the electron beam tool 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. While the controller 50 is shown in FIG. 1 as being external to the structure including the main chamber 10, the load lock chamber 20, and the EFEM 30, it should be understood that the controller 50 may be part of the structure. The controller 50 may be located in one component element of the charged particle beam inspection device or may be distributed over at least two component elements. Although the present disclosure provides an example of a main chamber 10 housing an electron beam inspection tool, it should be noted that the broadest aspects of the present disclosure are not limited to chambers housing electron beam inspection tools. Rather, it should be understood that the principles described above 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 electron beam tool 40, the electron beam tool 40 comprising a multibeam inspection tool that is part of the exemplary charged particle beam inspection apparatus 100 of fig. 1. The multi-beam electron beam tool 40 (also referred to herein as the apparatus 40) includes an electron source 201, a projection device 230, a motorized stage 209, and a sample holder 207. The electron source 201 and the projection device 230 may together be referred to as an illumination device. The sample holder 207 is supported by a motorized stage 209 to hold a sample 208 (e.g., a substrate or mask) for inspection. The multi-beam electron beam tool 40 also includes a detector array 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 the 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 direct each beamlet onto the sample 208. Although three sub-beams are shown for simplicity, there may be tens, hundreds, or thousands of sub-beams. The beamlets may be referred to as beamlets.

The controller 50 may be connected to various components of the charged particle beam inspection device 100 of fig. 1, such as the electron source 201, the detector array 240, the projection device 230, and the motorized 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 the charged particle beam inspection device, including the charged particle beam device.

Projection device 230 may be configured to focus beamlets 211, 212, and 213 onto sample 208 for inspection, and may form three probe spots 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 probe spots 221, 222, and 223 over individual scan areas in a portion of the 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 the detection spots 221, 222 and 223 on the sample 208.

The electron energy of the secondary electrons is typically 50eV or less. The actual secondary electron energy may be less than 5eV, but any object below 50eV is generally considered a secondary electron. The backscattered electrons typically have electron energies between 0eV and the landing energies of the primary beamlets 211, 212 and 213. Since electrons with energies detected less than 50eV are generally considered secondary electrons, a part of the actual backscattered electrons will be counted as secondary electrons. Secondary electrons may be more generally referred to as secondary charged particles and may be interchanged therewith. The backscattered electrons may be more generally referred to as and interchangeable with backscattered charged particles. Those skilled in the art will appreciate that the back-scattered charged particles may be more generally described as secondary charged particles. However, for the purposes of this disclosure, the back-scattered charged particles are considered to be different from the secondary charged particles, e.g., having a higher energy. In other words, a secondary charged particle will be understood as a particle with a kinetic energy of 50eV or less, and a back-scattered charged particle will be understood as a particle with a kinetic energy higher than 50eV. The secondary charged particles and the back-scattered charged particles are emitted from the sample. Charged particles (e.g., secondary electrons and backscattered electrons) emitted from the sample may be otherwise referred to as signal particles, e.g., secondary signal particles and backscattered signal particles.

The detector array 240 is configured to detect 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 array 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 array 240 to form an image. The signal processing system 280 may be otherwise referred to as an image processing system. The signal processing system may be incorporated into a component of the multi-beam electron beam tool 40, such as the detector array 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 electron beam tool 40, such as being 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 host, a terminal, a personal computer, any kind 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 may be communicatively coupled to the detector array 240 to allow signal communication, such as electrical conductors, fiber optic cables, portable storage media, IR, bluetooth, the internet, wireless networks, wireless radios, or the like, or combinations thereof. The image acquirer may receive the signal from the detector array 240, may process the data included in the signal, and may construct an image therefrom. The image acquirer can thus 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 storage device may be a storage medium such as a hard disk, flash drive, cloud storage, random Access Memory (RAM), other types of computer readable memory, and the like. A storage device may be coupled to the image acquirer and may be used to save scanned raw image data as raw images and to save post-processed images.

The signal processing system 280 may include measurement circuitry (e.g., analog-to-digital converter) for acquiring the 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 inspection. The reconstructed image may be used to reveal various features of internal or external structures of the sample 208. The reconstructed image may thus be used to reveal any defects that may be present in the sample.

The controller 50 may control the motorized stage 209 to move the sample 208 during inspection of the sample 208. The controller 50 may enable the motorized stage 209 to move the sample 208 in one direction, preferably continuously, e.g., at a constant speed, at least during sample inspection. The controller 50 can control the movement of the motorized stage 209 such that it varies the speed of movement of the sample 208 according to 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 multi-beam systems, such as the electron beam tool 40 and charged particle beam inspection device 100 described above, are disclosed in US2020118784, US20200203116 and US 2019/02595564, which are incorporated herein by reference.

In known single beam systems, it is theoretically possible to detect different signals (e.g. from secondary electrons and/or backscattered electrons). Multi-beam systems are known and advantageous because the throughput may be much higher than when using a single-beam system, e.g. the throughput of a multi-beam inspection system may be 100 times higher than in a single-beam inspection system.

In known multibeam systems, a primary electron beam array of electrons having relatively high energies is targeted at a final deceleration step in order to land on the sample with relatively low landing energies for detecting secondary charged particles as described above. In practice, however, it is not possible to combine multibeam inspection with backscatter detection, or at least to use it by direct backscatter detection, i.e. the multibeam systems known today rely mainly on the detection of secondary electrons.

The backscattered electrons have a wide range of energies, typically between 0eV and landing energy. The backscattered electrons have a large energy range (e.g. up to the landing energy of the primary electron beam) and a wide angle of the emitted backscattered charged particles. Secondary electrons generally have a more limited energy range and tend to be distributed around the energy value. The large energy range and wide angle of the emitted back-scattered charged particles results in cross talk in multi-beam systems. Crosstalk occurs when backscattered charged particles produced by one primary beamlet are detected at the detector assigned to a different beamlet. Crosstalk typically occurs very close to the sample, i.e., to the sample onto which the primary beam impinges. The previously known multibeam evaluation tools are not effective in imaging the backscattered signal due to crosstalk. Therefore, it is not possible to use a multi-beam system to increase the yield of backscatter detection.

As described above, there are limitations in information acquired from secondary electrons. Imaging based on the back scattered beam provides information about the subsurface structure, such as buried defects. Furthermore, the backscatter signal may be used to measure overlapping targets.

By various techniques, it has been found that multiple beam systems can detect backscatter charged particles by controlling certain features. Accordingly, in the present invention, a charged particle optical apparatus capable of detecting back-scattered charged particles is provided. Because the detector array 240 is positioned near the sample 208, multiple beam arrays as in the present invention can be used to detect backscattered electrons. Upon approaching the sample 208, the detector array 240 may be considered to face the sample 208. It has been found that the device can be used to repel secondary charged particles from the detector, which reduces the secondary charged particles detected when attempting to image back-scattered charged particles. Additionally or alternatively, it has been found that the apparatus can be used to accelerate electrons onto a sample to generate an array of beamlets having high landing energies. This is beneficial because the higher landing energy allows the beamlets to reach deeper into the substrate to inspect buried defects and measure overlay targets.

The components of the assessment tool 40 that can be used with the present invention are described below in conjunction with FIG. 3, FIG. 3 being a schematic diagram of the assessment tool 40. The charged particle evaluation tool 40 of fig. 3 may correspond to a multi-beam electron beam tool (also referred to herein as an apparatus 40).

The electron source 201 directs electrodes to an array of converging lenses 231 (also referred to as a converging lens array) that form part of the projection system 230. Desirably, the electron source 201 is a high brightness thermal field emitter with a good tradeoff between brightness and total emission current. There may be tens, hundreds or thousands of converging lenses 231. The converging lens 231 may comprise a multi-electrode lens and have a construction based on EP1602121A1, which is incorporated herein by reference in particular for the disclosure of a lens array splitting an electron beam into a plurality of beamlets, wherein the array provides a lens for each beamlet. The array of converging lenses 231 may take the form of at least two plates acting as electrodes, the apertures in each plate being aligned with each other and corresponding to the positions of the beamlets. At least two plates are maintained at different electrical potentials during operation to achieve the desired lens effect.

In one arrangement, which may be referred to as an Einzel lens, the array of converging lenses 231 is formed of an array of three plates, with charged particles having the same energy as they enter and leave each lens. Therefore, chromatic dispersion occurs only within the Einzel 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 low, e.g. a few millimeters, the effect of such aberrations is small or negligible. More generally, the converging lens array 231 may have two or more plate electrodes, each plate electrode having an aligned array of apertures. Each plate electrode array is mechanically connected to and electrically isolated from adjacent plate electrode arrays by an isolating element, such as a spacer that may comprise ceramic or glass. The converging lens array may be connected by a spacer element (such as the spacers described elsewhere herein) and/or spaced apart from adjacent electron optical elements (preferably electrostatic electron optical elements).

The converging lens is separate from the module housing the objective lens (such as the objective lens array components discussed elsewhere herein). In case the potential applied to the bottom surface of the converging lens is different from the potential applied to the top surface of the module housing the objective lens, the converging lens and the assembly housing the objective lens are spaced apart using a separation spacer. With equal potential, a conductive element may be used to space the converging lens from the module housing the objective lens.

Each converging lens 231 in the array directs electrons into a respective sub-beam 211, 212, 213 focused at a respective intermediate focus downstream of the beams of the converging lens array. The respective beamlets are projected along respective beamlet paths 220. The beamlets diverge from each other. The beamlet path 220 diverges downstream of the beam of the converging lens 231. In one embodiment, the deflector 235 is disposed at an intermediate focus. The deflector 235 is positioned in the beamlet path at or at least around the position of the corresponding intermediate focus 233 or focus (i.e., focal point). The deflector is positioned at or near the intermediate image plane of the associated beamlets in the beamlet path. 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 primary rays (which may also be referred to as beam axes) are incident on the sample 208 substantially orthogonally (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. Downstream of the deflector beam, the beamlet paths are substantially parallel to each other, i.e. substantially collimated. A suitable collimator is the deflector disclosed in european application 20156253.5 filed 2/7/2020, which is incorporated herein by reference for the application of the deflector to multibeam arrays. The collimator may include a macro (macro) collimator 270 in place of or in addition to the deflector 235. Thus, the macrocollimator 270 described below with respect to fig. 16 may have the features of fig. 3 or fig. 4. This is generally less preferred than providing a collimator array as deflector 235.

Below the deflector 235 (i.e., downstream of the beam of the source 201 or remote from the source 201), there is a control lens array 250. The beamlets 211, 212, 213 that have passed through the deflector 235 are substantially parallel when entering the control 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 240 may be additionally used to control landing energy. In this case, the potential difference across the objective lens changes when different landing energies are 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 getting 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 can be said about the detector at this position. 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, and thus the electric field inside the objective lens, the focal length of the objective lens again becomes larger, resulting in a focal position further below the objective lens. Note that the use of only an objective lens limits the control of the magnification. Such an arrangement does not allow control of the reduction rate and/or the opening angle. Furthermore, using an objective lens to control landing energy may indicate 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. Each plate electrode array is mechanically connected to and electrically isolated from adjacent plate electrode arrays by an isolating element, such as a spacer that may comprise ceramic or glass. 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. A control lens array 250 is positioned upstream of the beam of the objective lens array 241.

The control lens array 250 includes a control lens for each sub-beam 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 lenses 234, each of the objective lenses 234 directing a respective sub-beam 211, 212, 213 onto the sample 208. The objective lens may be positioned at or near the base of the electron optical system. More specifically, the objective array may be positioned at or near the base of the projection system 230. The control lens array 250 is optional but is preferably used to optimize the beamlets upstream of the beam of the objective lens array.

The control lens array 250 may be considered to provide electrodes other than the electrodes of the objective lens array 241, for example as part of an objective lens array component (or objective lens arrangement). Controlling the additional electrodes of the lens array 250 enables a further degree of freedom for controlling the electron optical parameters of the beamlets. In one embodiment, the control lens array 250 may be considered as an additional electrode of the objective lens array 241, thereby implementing additional functions of the respective objective lenses in the objective lens array 241. In one arrangement, such electrodes may be considered as part of an objective lens array that provides additional functionality to the objective lenses of the objective lens array 241. In such an arrangement, the control lens is considered to correspond to a portion of the objective lens, even to the extent that the control lens is referred to as only a portion of the objective lens.

For ease of illustration, the lens array is schematically depicted herein by an elliptical array (as shown in fig. 3). Each oval represents a lens in the lens array. Conventionally, an oval shape is used to represent a lens, similar to the biconvex form often employed in optical lenses. However, in the context of charged particle arrangements such as those discussed herein, it will be appreciated 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 with apertures.

Optionally, a scanning deflector array 260 is provided between the control lens array 250 and the array of objective lenses 234. The scan deflector array 260 includes 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 over the sample 208 in one or both directions.

The objective lens array 241 may include at least two electrodes having an aperture array defined therein. In other words, the objective lens array comprises at least two electrodes with a plurality of holes or apertures. Fig. 5 and 6 show electrodes 232, 243, 244 that are part of an exemplary objective lens array 241 having a corresponding aperture array 245, 246, 247. The position of each aperture in an electrode corresponds to the position of the corresponding aperture in the other electrode. The corresponding apertures operate on the same beam, sub-beam or group of beams of the plurality in use. 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). In each electrode are a plurality of apertures. The apertures in the electrodes are aligned with corresponding apertures in all or each of the other electrodes. The beamlet path through an aperture in an electrode passes through all corresponding aperture electrodes in the other electrodes. Such apertures in the electrode are aligned with corresponding apertures in the other electrodes. Thus, all apertures of the aperture array in one electrode are aligned with corresponding apertures of the aperture array in the other electrode. Thus, the aperture arrays in the plurality of electrodes are aligned. Thus, each electrode is provided with an aperture through which the respective sub-beam 211, 212, 213 propagates.

The objective lens array 241 may include two or three electrodes as shown in fig. 5 and 6, respectively, or may have more electrodes (not shown). The objective lens array 241 having only two electrodes may have lower aberrations 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. Additional electrodes (i.e. more than two electrodes) provide additional degrees of freedom for controlling the electron trajectories, e.g. for focusing secondary electrons as well as the incident beam. The advantage of a double electrode lens over an Einzel lens is that the energy of the incoming beam is not necessarily the same as the energy of the outgoing beam. Advantageously, such a potential difference across the two-electrode lens array enables it to act 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 is larger than the objective lens, wherein the insulating structure may be positioned as described below.

Preferably, each electrode provided in the objective lens array 241 is a plate. The electrodes may be described in other ways as flat sheets. 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 a planar electrode, as this makes the manufacture of the electrode easier, as known manufacturing methods may be used. Planar electrodes may also be preferred because they may provide more precise alignment of the apertures between the different electrodes.

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

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

In a first aspect of the invention, a charged particle optical apparatus is provided. The charged particle optical device is configured to detect back-scattered charged particles. The charged particle optical device is suitable for any charged particle system, such as the charged particle evaluation tool shown in fig. 3. The charged particle evaluation tool may be an example of a charged particle system, and any reference to a charged particle evaluation tool may be interchanged with a charged particle system. Thus, a charged particle optical device may be used as part of such a charged particle evaluation tool. The charged particle optical device may include at least one, some or all of the features of the charged particle evaluation tool 40. One embodiment of a charged particle optical apparatus is shown in fig. 4. As shown, the charged particle device may include a controller array 250, an objective lens array 241, and a detector array 240. In fig. 4, a plurality of lenses per array is depicted, e.g., as shown, any one of the beamlets 211, 212, 213 passes through the lenses. Although fig. 4 shows five lenses, any suitable number of lenses may be provided; for example, there may be lenses on the order of 100, 1000 or 10000 in the plane of the lens. Features identical to those described above are given the same reference numerals. For brevity, the description of these features provided above applies to the features shown in FIG. 4. The charged particle optical device may comprise one, some or all of the components shown in fig. 4. Note that this figure is a schematic diagram and may not be drawn to scale. For example, in a non-limiting list: the beamlets may be narrower at the controller array 250 than at the objective lens array 241; the detector array 240 may be closer to the electrodes of the objective lens array 241 than the electrodes of the objective lens array 241 are to each other; and the focal point of each sub-beam between the controller lens array 250 may be closer to the objective lens array 241 than depicted.

Fig. 4 is an enlarged schematic view of a plurality of objective lenses of the objective lens array 241 and a plurality of control lenses of the control lens array 250. As described in further detail below, the lens array may be provided by an electrode having a selected potential applied to the electrode. As shown in fig. 4, the spacing between the electrodes of the control lens array 250 may be greater than the spacing between the electrodes of the objective lens array 241, but this is not required. The voltage sources V3 and V2 (which may be provided by an individual power source or may be provided entirely by the power source 290) are configured to apply potentials to the upper and lower electrodes of the objective lens array 241, respectively. The voltage sources V5, V6, V7 (which may be provided by an individual power source, or may be provided entirely by the power source 290) are configured to apply potentials to the first electrode, the second electrode, and the third electrode, respectively, of the control lens array 250. Another voltage source V4 is connected to the sample to apply a sample potential. Another voltage source V8 is connected to the detector array to apply a detector array potential. Although the control lens array 250 is shown as having three electrodes, the control lens array 25 may be provided with two electrodes (or more than three electrodes). Although the objective lens array 240 is shown as having two electrodes, the objective lens array 240 may be provided with three electrodes (or more than three electrodes). For example, an intermediate electrode with a corresponding voltage source may be provided in the objective lens array 241 between the electrodes shown in fig. 4.

As shown in fig. 4, the beamlets may be parallel when entering the control lens array 250, as shown in fig. 3. However, the same components of fig. 4 may be used in the configuration shown in fig. 16, in which case the beamlets may be separated upon entering the control lens array 250, as shown in fig. 16.

The control lens array electrodes may be spaced apart by a few millimeters (e.g., 3 mm). The spacing between the control lens array 241 and the objective lens array 250 (i.e., the gap between the lower electrode of the control lens array 250 and the upper electrode of the objective lens 241) may be selected from a wide range, for example, from 2mm to 200mm or more. Smaller pitches make alignment easier, while larger pitches allow weaker lenses to be used, thereby reducing aberrations.

Desirably, the potential V5 of the uppermost electrode of the control lens array 250 remains the same as the potential of the next electron-optical element (e.g., deflector 235) upstream of the beam of the control lens. The potential V7 applied to the lower electrode of the control lens array 250 may be varied to determine the beam energy. The potential V6 applied to the intermediate electrode of the control lens array 250 may be varied to determine the lens intensity of the control lens and thus the opening angle and demagnification of the beam. It should be noted that the beam opening angle may be controlled using a control lens even though the landing energy does not need to be changed, or otherwise changed. The focal positions of the beamlets are determined by a combination of actions of the respective control lens array 250 and the respective objective lens 240.

In a first aspect, a charged particle optical apparatus for a charged particle evaluation tool 40 or, more generally, a charged particle optical apparatus for a charged particle system is provided. Charged particle optical devices are hereinafter referred to as devices. The apparatus is configured to project a plurality of beams of charged particles along a beamlet path 220 toward the sample 208. The multiple beams include sub-beams, such as sub-beams 211, 212, 213. The beamlets may alternatively be referred to as beams, e.g. an array of primary beams. In other words, the apparatus is configured to project an array of charged particle beams towards the sample. The device comprises an objective array 241, which objective array 241 comprises a plurality of objectives 234 and may otherwise be referred to as an array of objectives. The objective lens array 241 is configured to project an array of charged particle beamlets 211, 212, 213 onto the sample 208. The array of objectives (i.e., the objective lens array 241) may correspond to an array of detectors (i.e., the detector array 240) and/or any beamlets. Each element in the objective lens array 240 may be a microlens that operates on a different beam or group of beams of the multiple beams. The objective lens array 241 may be configured to accelerate charged particles toward the sample 208. In other words, the objective 234 may be configured to accelerate the charged particle beamlets 211, 212, 213 along the beamlet path 220.

The apparatus includes an array of detectors 240, also referred to as an array of detectors. The detector array 240 is configured to capture charged particles emitted from the sample 208. The detector array is configured to detect the backscattered particles from the sample 208. The detector array 240 may be configured to primarily detect the backscattered charged particles. In other words, the detector array 240 may be configured to detect a majority of the backscattered charged particles. The detector array 240 may be configured to detect more backscattered charged particles than secondary charged particles. As described further below, an advantage of the apparatus is that it provides a multi-beam tool that can be used to directly detect backscattered charged particles emitted from the sample 208. Thus, the backscattered charged particles may be detected directly from the surface of the sample 208. The backscattered charged particles may be detected without having to convert them to another type of signal particles, such as secondary charged particles, which are for example easier to detect. Thus, the backscattered charged particles may be detected by the detector array 241 without encountering (e.g., striking) any other components or surfaces between the sample 208 and the detector array 241.

The detector array 240 includes a plurality of detectors. Each detector is associated with a corresponding sub-beam (which may otherwise be referred to as a beam or primary beam). In other words, the array of detectors (i.e., detector array 240) corresponds to the beamlets. Each detector may be assigned to a sub-beam. The array of detectors may correspond to an array of objectives. In other words, the detector array may be associated with a corresponding objective lens array. The invention makes it possible to reduce, if not avoid, the risk of detection crosstalk of backscattered charged particles originating from a beamlet detected by a detector of a detector array associated with a different beamlet of the beamlet array. The detector array 240 is described below. However, any reference to the detector array 240 may be suitably replaced with a single detector (i.e., at least one detector) or multiple detectors. The detector may additionally be referred to as a detector element 405 (e.g., a sensor element such as a capture electrode). The detector may be any suitable type of detector. For example, a capture electrode (e.g., a capture electrode that directly detects electron charge), a scintillator, or a PIN element may be used. The detector may be a direct current detector or an indirect current detector. The detector may be as described below with respect to fig. 7, 8, 9, 13, 14 and 15.

It should be noted that the scintillator and PIN elements typically detect signal particles above an energy threshold. Since secondary electrons have a low energy of close to 0eV, e.g. 50eV, the skilled person will appreciate that such scintillators and PIN elements cannot detect secondary electrons of such energy. In order for these types of detector elements to be able to detect such electrons, such detector elements should be positioned in the electron beam column where such secondary electrons have sufficient energy for their detection, e.g. above the beam downstream most electrode in the deceleration objective, or at least above the beam downstream most electrode defining the electrode of the deceleration objective arrangement, see e.g. european application No. 20198201.4, which is incorporated herein by reference to the disclosure of at least the in-lens sensor unit and the detector.

The detector array 240 is positioned between the control lens array 250 and the sample 208. The detector array is positioned between the objective lens array 241 and the sample 208. The detector array 240 is configured to be proximate to the sample. The detector array 240 may be in close proximity to the sample to detect the backscattered particles from the sample 208. The detector close to the sample enables to reduce, if not avoid, the risk of crosstalk in detecting the backscattered charged particles generated by the sub-beam corresponding to another detector in the detector array. In other words, the detector array 240 is very close to the sample 208. The detector array 240 may be within a distance of the sample 208, as described below. The detector array 240 may be adjacent to the sample 208. At least one detector may be positioned in the device so as to face the sample. That is, the detector may provide a base for the device. A detector as part of the base may face the surface of the sample. This may be beneficial for positioning the at least one detector at a position where the at least one detector is more likely to detect the backscatter particles than the secondary particles. For example, at least one detector array may be provided on the output side of the objective lens array 241. The output side of the objective lens array 241 is the side from which the beamlets are output from the objective lens array 241, i.e., the bottom or beam downstream side of the objective lens array in the configuration shown in fig. 4, 5 and 6. In other words, the detector array 240 may be disposed downstream of the beam of the objective lens array 241. The detector array may be positioned on or adjacent to the objective array. The detector array 241 may be an integrated component of the objective lens array 241. The detector and the objective lens may be part of the same structure. The detector may be connected to the lens by a spacer element or directly to an electrode of the objective lens. Thus, the at least one detector may be part of an objective lens assembly comprising at least an objective lens array and a detector array. If the detector array is an integrated component of the objective lens array 241, the detector array 240 may be disposed at the base of the objective lens array 241. In one arrangement, the detector array 240 may be integral with an electrode of the objective lens array 241 positioned furthest downstream of the beam.

Ideally, the detector array is as close to the sample as possible. The detector array 240 is preferably very close to the sample 208 such that there is a near focus of the backscattered charged particles at the detector array. As previously mentioned, the energy and angular spread of the backscattered charged particles is typically so large that it is difficult (or impossible in known prior art systems) to maintain separation of the signal from the adjacent beam. However, in the first aspect, near focus means that backscattered charged particles may be detected at an associated one of the detectors without cross-talk (i.e. interference from adjacent beams). Of course, there is a minimum distance between the sample 208 and the detector array 240. However, it is preferable to reduce the distance as much as possible. Some configurations may benefit from shorter distances than others.

Preferably, as shown in FIG. 3, the distance "L" between the detector array 240 and the sample 208 is less than or equal to about 50 μm, i.e., the detector array 240 is positioned within about 50 μm of the sample 208. The distance L is determined as the distance from the surface of the sample 208 facing the detector array 240 to the surface of the detector array 241 facing the sample 208. Preferably, the detector array 240 is positioned within about 40 μm of the sample 208, i.e., the distance L between the detector array 240 and the sample 208 is less than or equal to about 40 μm. Preferably, the detector array 240 is positioned within about 30 μm of the sample 208, i.e., the distance L between the detector array 240 and the sample 208 is less than or equal to about 30 μm. Preferably, the detector array 240 is positioned within about 20 μm of the sample 208, i.e., the distance L between the detector array 240 and the sample 208 is less than or equal to about 20 μm. Preferably, the detector array 240 is positioned within about 10 μm of the sample 208, i.e., the distance L between the detector array 240 and the sample 208 is about less than or equal to 10 μm.

Providing a distance of about 50 μm or less is advantageous because cross-talk between backscattered electrons can be avoided or minimized. Thus, the distance L is preferably kept low, i.e. about 50 μm or less. Theoretically, there is a lower limit on how close the sample 208 and detector array 240 can be while allowing these components to move relative to each other, and this can mean that the distance L can be greater than about 5 μm or 10 μm.

For example, a distance L of about 50 μm or less may be used while still allowing for relatively reliable control of the device, as shown by a portion of the tool in fig. 3. For other configurations, such as the configuration shown and described below with respect to fig. 16, a distance L of about 30 μm or less may be preferred.

The preferred range of distance L between the detector array 240 and the sample 208 may be between about 5 μm and 50 μm, or preferably between about 10 μm and 50 μm, or preferably between about 30 μm and 50 μm. In one arrangement, the detector array 240 may be actuated, i.e., the distance L is varied, relative to the objective lens array 241, e.g., the distance between the sample and the detector array L is substantially maintained.

The detector array 240 may be part of an objective lens assembly. An exemplary embodiment of a detector array 240 integrated into an objective lens array is shown in fig. 5, fig. 5 showing a portion of the objective lens array 240 in a schematic cross-sectional view. In this embodiment, the detector array 240 includes a plurality of detector elements 405 (e.g., sensor elements such as capture electrodes). As described above, the device may be configured to repel secondary charged particles emitted from the sample 208 toward the detector array 240. More specifically, the detector array 240 may be configured to repel secondary charged particles emitted from the sample 208. The detector array 240 may be configured to repel charged particles by controlling the potential of the detector array 240. This is beneficial because it reduces the number of secondary charged particles emitted from the sample 208 back toward the detector array 240.

The detector array 240 may be configured, in use, to have a potential, referred to herein as a detector array potential. The sample 208 may be configured to have an electrical potential, referred to herein as a sample potential, in use. The sample potential may be more positive than the detector array potential. The potential difference between the detector array 240 and the sample 208 repels charged particles emitted from the sample 208 towards the detector array 240. Preferably, the detector array potential may be the same as the second electrode potential (i.e. the potential of the beam downstream electrode of the objective lens array).

The potential difference between the sample potential and the detector array potential is preferably relatively small so that the charged particle beamlets pass through or over the detector array 240 to project to the sample 208 without being significantly affected. The potential difference between the sample potential and the detector array potential is preferably greater than the secondary electron threshold. The secondary electron threshold is a potential difference equivalent to the possible electron energy of the secondary electrons emitted from the sample 208. That is, a relatively small potential difference between the sample potential and the detector array potential is sufficient for secondary electrons to be repelled from the detector array. For example, the potential difference between the sample potential and the detector array potential may be about 20V, 50V, 100V, 150V, or 200V.

Preferably, the potential difference between the detector array potential and the sample potential is small. This means that advantageously the potential difference will have a negligible effect on the path of the backscattered charged particles (which typically have more energy up to the landing energy), which means that backscattered electrons can still be detected while reducing or avoiding detection of secondary charged particles. Thus, a small difference between the detector array potential and the sample potential is effectively an energy barrier that allows detection of backscattered charged particles while also ensuring that detection of secondary charged particles is reduced or avoided.

For example, the detector array potential may be greater than about +10kV to about +100kV, or preferably between about +20kV to +100kV, relative to a charged particle beam source. Preferably, the detector array potential is between about +20kV and +70kV relative to the charged particle beam source.

Although it is described elsewhere that a portion of the device may be configured to repel secondary charged particles, this will typically be done by the detector array 240. The lowermost electrodes of both the detector array and the objective lens array 241 may theoretically have a repulsive effect on the secondary charged particles emitted from the sample back towards the detector array 240. However, since the detector array 240 is closer to the sample 208 than the objective lens array 241, it is typical that the detector array 240 will provide a repulsive force to the secondary charged particles.

The aperture arrays 245, 246, 247 of the objective lens array 241 may be comprised of a plurality of apertures, preferably having a substantially uniform diameter d. However, as described in european application 20207178.3 filed 11/12 2020, which is incorporated herein by reference at least with respect to correction achieved by changing the aperture, there may be some variation for optimizing aberration correction. The diameter d of the aperture in the at least one electrode may be less than about 400 μm. Preferably, the diameter d of the aperture in the at least one electrode is between about 30 μm and 300 μm. For a given aperture pitch, a smaller aperture diameter may provide a larger detector, thereby increasing the chance of capturing back-scattered charged particles. Thus, the signal of the backscattered charged particles may be improved. However, making the aperture too small may cause aberration in the primary sub-beam.

The plurality of holes in the electrode may be spaced apart from each other by a pitch p. Pitch is defined as the distance from the middle of one aperture to the middle of an adjacent aperture. The pitch between adjacent apertures in at least one electrode may be less than about 600 μm. Preferably, the pitch between adjacent apertures in at least one electrode is between about 50 μm and 500 μm. Preferably, the pitch between adjacent apertures on each electrode is substantially uniform.

The backscattered electrons emitted from the sample 208 have a very large energy spread and typically have an angular spread following a cosine distribution. The farther from the sample 208 to the detector array 240, the larger the cone of the emitted beam becomes. Due to the very large energy spread, it may not be possible to image the backscattered charged particles from the different beams onto the detector without introducing significant crosstalk. The solution is to place the detector near the substrate and to select the pitch of the beams such that the backscattered charged particle signals of adjacent beams do not overlap.

Thus, the pitch size may be selected based on the distance between the detector array 240 and the sample 208 (and vice versa). For example only, the beam pitch p may be equal to or greater than about 300 microns for a distance L of about 50 microns between the sample 208 and the detector array 240. For example only, the beam pitch p may be equal to or greater than about 60 microns for a distance L of about 10 microns between the sample 208 and the detector array 240. Providing a closer detector array allows for the use of a smaller beam pitch p. This may be beneficial when using certain configurations in which the beam pitch is advantageously smaller, such as the configuration described with respect to fig. 16 below and shown in fig. 16.

The values of the above-mentioned diameters and/or pitches may be provided in at least one electrode, a plurality of electrodes or all electrodes in the objective lens array. Preferably, the dimensions referred to and described apply to all electrodes arranged in the objective lens array.

The objective lens array 241 may include a first electrode 242 having a first aperture array 245 and a second electrode 243 having a second aperture array 246. The first electrode 242 may be upstream of the beam of the second electrode 243, as shown in fig. 5 and 6. The beam upstream may be defined as closer to the source 201. The beam upstream may be defined further from the sample 208. The first electrode 242 may be referred to as an upper electrode. The second electrode 243 may be referred to as a lower electrode.

Additional electrodes may be included as part of the objective lens array. The additional electrode may be positioned between the first electrode and the second electrode. In other words, the first electrode 242 and the second electrode 243 may be external electrodes. The first electrode 242 may be positioned upstream of the beam of any other electrode included in the objective lens array 241. The second electrode 243 may be positioned downstream of the beam of any other electrode included in the objective lens array 241. As shown in fig. 5, the third electrode 244 may be provided with a third aperture array 247. The third electrode 244 may be an intermediate electrode.

As described above, a voltage source may be provided to the electrodes of the objective lens array such that each electrode has an electrical potential. The first electrode 242 may be configured to have a first electrode potential in use and/or the second electrode 243 may be configured to have a second electrode potential in use. Additionally or alternatively, the sample 208 may be configured to have a sample potential in use.

As described above, accelerating the beamlets 211, 212, 213 that impinge on the sample 208 is beneficial because it can be used to generate an array of beamlets that have high landing energies. The potential of the electrodes of the objective lens array may be selected to provide acceleration through the objective lens array 241.

The potentials and values of the potentials defined herein are defined with respect to the sources; the potential of the charged particles at the surface of the sample may thus be referred to as the landing energy, since the energy of the charged particles is related to the potential of the charged particles and the potential of the charged particles at the sample is defined with respect to the source. However, since the potential is a relative value, the potential may be defined with respect to other components (such as a sample). In this case, the potential differences applied to the different components are preferably as discussed below with respect to the source. During use, i.e. when the device is operated, an electrical potential is applied to the relevant components, such as the electrodes and the sample.

Preferably, the potential of the second electrode 243 (i.e., the second electrode potential) is more positive than the potential of the first electrode 242 (e.g., the first electrode potential). This facilitates acceleration of the charged particles from the first electrode 242 towards the second electrode 243. In other words, the potential difference of the electrodes may be used to accelerate charged particles in the objective lens array 241.

Preferably, the second electrode potential is substantially the same as the detector array potential.

Preferably, the sample potential is more positive than the potential of the first electrode (i.e., the first electrode potential). This facilitates accelerating the charged particles from the first electrode 242 towards the sample 208.

Preferably, the sample potential is more positive than the potential of the second electrode (i.e., the second electrode potential). This facilitates acceleration of the charged particles from the second electrode towards the sample. Furthermore, this is advantageous because charged particles are more easily attracted to the sample 208 than the second electrode 243 of the objective lens array 241. This has the effect of repelling charged particles emitted from the sample 208 away from the path towards the second electrode 243 (i.e. towards the detector array 240 as described above).

The device may be configured to repel secondary charged particles from the beam downstream electrode of the objective lens array 241. The beam downstream electrode of the objective lens array 241 may be the portion of the objective lens array 241 that is positioned furthest along the beam, i.e. downstream of the light source 201/furthest from the light source 201 in use. In this case, the device may be configured to reject secondary electrons from the detector array 241 (using the objective lens array 240) such that the detector array 240 may detect backscattered charged particles more effectively than secondary electrons, i.e. by reducing or preventing secondary charged particles from being detected.

As mentioned above, it is preferred that at least the second electrode potential is more positive than the first electrode potential, as this accelerates the charged particles projected in the objective part 241. When the first electrode potential is low, a larger potential difference can be provided between the first electrode and the second electrode. A larger difference between the first electrode potential and the second electrode potential will result in a larger acceleration. Thus, the first electrode potential is preferably relatively low. However, if the first electrode potential is too small, e.g. less than +2kV or less than +3kV, it has been found that the focal spot of the charged particle beamlets may form inside the objective lens array 241. Thus, the value of the first electrode is selected to be small without causing a focus to be formed within the objective lens array. For example, the potential of the first electrode may be between about +1kV and +10kV relative to a charged particle beam source. For example, the potential of the first electrode may be between about +3kV and +8kV relative to a charged particle beam source. Preferably, the potential of the first electrode is about +5kV with respect to the charged particle beam source.

The potential of the second electrode may be more positive than the potential of the first electrode to accelerate the charged particles. Therefore, it is preferable that the second electrode potential value is relatively large. The second electrode potential value may be greater than about +10kV up to about +100kV, or preferably between about +20kV and +100kV relative to the charged particle beam source. Preferably, the potential of the second electrode is between about +20kV and +70kV relative to the charged particle beam source.

As described above, the sample potential is preferably more positive than the second electrode potential, as this repels the secondary charged particles from the objective lens array 241. However, as the particles accelerate from the first electrode and through the second electrode to the sample, it is beneficial to maintain the value of the sample potential similar to the value of the second electrode potential so that the charged particles accelerate to the surface of the sample 208. That is, the potential difference between the second potential and the sample potential is relatively small, but sufficient to accelerate the charged particles towards the sample. The sample potential may be greater than about +10kV up to about +100kV, or preferably may be between about +20kV and +100kV relative to the charged particle beam source. Preferably, the potential of the sample is about +20kV to +70kV relative to the charged particle beam source. Preferably, the sample potential is about 10V, 20V, 50V, 100V, 150V or 200V positive to the second electrode potential.

The potential difference between the sample potential and the second electrode potential is preferably greater than the secondary electron threshold. The secondary electron threshold is a potential difference corresponding to the possible electron energy of the secondary electrons emitted from the sample. That is, a relatively small potential difference between the sample potential and the second electrode potential is sufficient to repel secondary electrons from the detector array. For example, the potential difference between the sample potential and the bottom electrode potential may be about 10V, 20V, 50V, 100V, 150V, or 200V.

For example, as described above, a device configured to accelerate a charged particle beamlet and repel secondary charged particles may have a potential as shown in the context of fig. 4, the values of which are in table 1 below. As described above, the objective lens array as shown in fig. 4 may include additional electrodes, for example, an intermediate electrode located between an upper electrode (first electrode) and a lower electrode (second electrode) of the objective lens array 241 as shown in fig. 4. The voltage source V1 (not shown) may be configured to apply a potential to the intermediate electrode. This intermediate electrode is optional and may not be included in electrodes having other potentials listed in table 1. The middle electrode of the objective lens array may have the same potential (i.e., V3) as the upper electrode of the objective lens array.

As described above, exemplary ranges are shown in the left column of table 1. The middle and right columns show more specific example values for each of V1 through V8 within the example range. The middle column may be provided for a smaller resolution than the right hand side. If the resolution is larger (as shown in the right column), the current per sub-beam is larger and thus the number of beams can be lower. The advantage of using a larger resolution is that the time required to scan the "continuous area" is shorter (which may be a practical limitation). Thus, the overall throughput may be lower, but the time required to scan the beam region is shorter (because the beam region is smaller).

The apparatus may include a control lens array 250 as described above. The control lens array 250 may be configured to decelerate the charged particle beamlets along a beamlet path. This may be accomplished by controlling the electrical potential of the electrodes within the control lens array 250. The main reason for using a control lens to decelerate the charged particle beamlets is that this improves the performance of the objective lens array 241. The objective lens array comprises a positive base lens and a negative base lens, which partially cancel each other out, but the aberrations add. In general, the larger the beam energy difference between the two electrodes, the lower the aberration coefficient

The charged particle optical device of the present invention may comprise a power supply 290, the power supply 290 being configured to apply, in use, a respective electrical potential to at least one electrode of the control lens array 250 and/or the objective lens of the objective lens array 241. More specifically, the power source may be configured to provide an electrical potential to the first electrode 242 and/or the second electrode 243. The power supply 290 may be configured to apply any potential to any other additional electrode provided as part of the objective lens array, including the third electrode 244 (if present) as described above. The power supply may additionally or alternatively be configured to apply an electrical potential to the sample 208 in use. The power supply may additionally or alternatively be configured to apply an electrical potential to the detector array 240 in use. The power supply may include a plurality of power supplies, each configured to provide an electrical potential to any of the above components.

Fig. 7 is a bottom view of the detector array 240, the detector array 240 including a substrate 404 with a plurality of detector elements 405 provided on the substrate 404, each detector element 405 surrounding a beam aperture (or aperture) 406. The beam aperture 406 may be formed by etching through the substrate 404. In the arrangement shown in fig. 7, the beam apertures 406 are shown in a rectangular array. The beam apertures 406 may also be arranged differently, for example in a hexagonal close-packed array as shown in fig. 8. The hexagonal arrangement of bundles in fig. 8 may be denser than the square bundle arrangement shown in fig. 7. As shown, 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 array 240 on a larger scale. The detector elements 405 form the bottommost, i.e., closest surface to the sample 208, of the detector array 240. 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 signal is 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 still 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 disposed on the back side of the detector array 240.

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

The detector array 240 may be implemented by integrating CMOS chip detectors into the bottom electrode of the objective lens array. Integrating the detector array 240 into the objective lens array 241 or other component of the charged particle optical device allows detection of charged particles emitted with respect to a plurality of respective beamlets. The CMOS chip is preferably oriented to face the sample (because the distance between the sample and the bottom of the charged particle optical device and/or electron optical system is small (e.g., 50 μm or less, 40 μm or less, 30 μm or less, 20 μm or less, or 10 μm)). In one embodiment, the detector element 405 for capturing the secondary charged particles is formed in the surface metal layer of the 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 (except the aperture) of the objective lens array 240 is occupied by the detector element 405. Additionally or alternatively, the diameter of each detector element 405 is substantially equal to the array pitch (i.e., the aperture array pitch described above with respect to the electrodes of the objective lens component 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 desired distance L between the sample and the detector array 240. In one embodiment, the detector element 405 is circular in shape, but may be made square to maximize detection area. In addition, the diameter of the through-substrate via 409 may be minimized. Typical dimensions of the electron beam are on the order of 5 to 15 microns.

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 circular rings or loops. The detector elements 405 may be divided angularly. The detector element 405 may form a plurality of sectors or segments. The segments may have similar angular sizes 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.

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 in the case of larger detector elements 405 giving only slightly greater detection efficiency, but significantly greater crosstalk.

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

The detector used in the detector array of the charged particle optical apparatus may alternatively be the detector described below with respect to fig. 10, 11 and 12.

The charged particle optical device may comprise a control lens array 250 as described above. As described above, a control lens array may be positioned upstream of the beam of the objective lens array 241, and each control lens may be associated with a respective objective lens 234. The charged particle optical device may be configured to form an intermediate focus between the control lens array 250 and the objective lens array 241. More specifically, the control lens array 230 may be configured to provide an intermediate focus between the respective control lens and the corresponding objective lens. As described above, the electron optical apparatus may be configured to control the objective lens component (e.g., by controlling the potential applied to the electrodes of the control lens array 250) to control the focal length of the control lens, thereby forming an intermediate focus between the control lens array 250 and the objective lens array 241.

As previously described, in addition to the objective lens array 241, a control lens array 250 is provided, which provides an additional degree of freedom for controlling the characteristics of the beamlets. Even when the control lens array 250 and the objective lens array 241 are disposed relatively close together, an additional degree of freedom is provided, for example, such that no intermediate focus is formed between the control lens array 250 and the objective lens array 241. The control lens array 250 may be used 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 control lens may include 2 or 3 or more electrodes. If there are two electrodes, the shrinkage and landing energy are controlled together. If there are three or more electrodes, the reduction rate and landing energy can be independently controlled. The control lens may thus be configured to adjust the demagnification and/or beam opening angle of the respective beamlets (e.g. using a power supply to apply appropriate respective potentials to the electrodes controlling the lens and the objective lens). Such optimization can be achieved without unduly negatively affecting the number of objectives and without unduly deteriorating the aberrations of the objectives (e.g., without increasing the intensity of the objectives).

The control lens array 250 may be used to deliver low beam energy to the objective lens array 241. This may be similar to the potential applied to the first electrode of the objective lens array 241 as described above, i.e. between about +3kV to +8kV, or preferably about +5kV. The lower the input beam energy of the objective lens, the shorter the focal length of the objective lens. Thus, as described above, an incident beam energy below 5kV typically results in a focal point inside the objective lens array 241. Typically, in order to provide a charged particle beam having an associated energy into the objective lens array 241, the lens array 250 is controlled for decelerating the charged particle beam, e.g. from about +30kV to +5kV. This will create a crossover due to the large beam energy difference.

Preferably, the intermediate focus 236 (alternatively referred to as the intermediate focus) between the respective control lens and the corresponding objective lens lies in a common plane, as shown in fig. 3. Thus, it is preferred that the intermediate focus 236 is positioned in one plane, in particular the plane between the control lens array and the objective lens array. Preferably, the plane of the intermediate focus is positioned in a plane parallel to the control lens array and/or the objective lens array. Preferably, intermediate focus 236 is in an array of intermediate focuses.

The charged particle optical device may comprise an insulating structure, which may also be referred to as a spacer. The insulating structure may be provided in the objective lens array. An insulating structure may be provided to separate, i.e. space apart, adjacent electrodes. The shape of the insulating structure may be chosen specifically for the objective lens array and how it is used. Insulation structures may be provided to separate any adjacent electrodes provided, such as in objective lens array 240, converging lens array (shown in fig. 3), and/or control lens array 250.

The insulating structure may be arranged between any adjacent electrodes in the objective lens array. For example, if two electrodes are provided (as shown in fig. 5), an insulating structure may be positioned between the first electrode and the second electrode, for example. For example, if three electrodes are provided (as shown in fig. 6), an insulating structure may be positioned between the first electrode and the third electrode and/or between the second electrode and the third electrode.

Exemplary shapes of the insulating structure 500 are shown in cross-section in fig. 10, 11, 12. The insulating structure 500 may include a body 501 and a protrusion radially inward from the body 501. The body 501 and the protrusion may be integral, i.e. may be formed from one single piece. The protrusions may provide a stepped surface. The insulating structure 500, and more particularly the body, may include a first face 502 and a second face 503. The second face 503 may be opposite the first face 502. For example, the first face 502 may be a bottom surface of the insulating structure 500 and the second face 503 may be a top surface of the insulating structure 500. The body may surround the multibeam path. The body may be a ring. The inner surface of the ring may provide a protrusion and a stepped surface.

The insulating structure 500 may be configured to optimize the projection of the charged particle beam through a lens array, such as an objective lens array. In particular, the shape of the insulating structure 500 may be advantageous to help the objective lens withstand high electrostatic fields, such as in the acceleration direction, and to reduce the risk of discharge. As shown in fig. 10 and 11, the insulating structure may be asymmetric when viewed in cross section. That is, in cross section, the surface of the insulating structure facing the beam path may be stepped. The stepped surface may extend a path length over a surface of the insulating structure. The shortest path length on the step surface may exceed the creep length. At or below the creep length for the expected operating potential difference between the electrodes at the first and second faces of the insulating structure, the risk of discharge between the electrodes increases. The shape and/or geometry, in particular the stepped surface and the protrusions, may reduce the risk of discharge between the field radially inwards of the insulating structure and the electrode. In particular, the gap and geometry of the spacer is selected to reduce the field at the more negative three points (vacuum, electrode, spacer) in the electrode on either side of the spacer. The use of an insulating structure as shown in fig. 11 is described in US 2011/0216299, the content of which is incorporated herein by reference at least in respect of the geometry of the insulating structure and its function.

In embodiments where the charged particles are accelerated toward the sample 208 by the objective lens array 241, the insulating structure 500 may be positioned between adjacent electrodes of the objective lens array 241 to optimize the acceleration of the charged particles by the objective lens array.

When in place between adjacent electrodes of the objective lens array, one of the electrodes contacts the body and the protrusion on a first face of the insulating structure and the body contacts the other of the electrodes on a second face of the insulating structure with a gap defined between the protrusion and the other electrode. In other words, the body and the protrusion contact one of the electrodes, but only the body contacts the other electrode. Thus, the insulating structure provides a gap between the protrusion and the at least one electrode

Such an insulating structure 500 is shown in fig. 11, wherein the first electrode 242 contacts the body and the protrusion 506 on a first face 503 of the insulating structure 500. The body 501 contacts the second electrode 243 on the second face of the insulating structure 500. A gap 507 is provided between the protrusion 506 and the second electrode 243 (downstream of the beam of the first electrode 242).

In one embodiment, the objective lens array 241 is a replaceable module that may be used alone or in combination with other elements such as a steering lens array and/or a detector array. The replaceable module may be field replaceable, i.e. a field engineer may replace the module with a new module. In one embodiment, a plurality of replaceable modules are included within the tool and can be exchanged between an operable position and an inoperable position without opening the tool.

In one embodiment, the replaceable module includes an electron optical assembly, in particular, a charged particle optical device, located on a stage that allows actuation to position the assembly. In one embodiment, the replaceable module includes a stage. In one arrangement, the stage and replaceable module may be integral parts of the tool 40. In one arrangement, the replaceable module is limited to the stage and the device it supports, such as a charged particle optical device. In one arrangement, the stage is removable. In an alternative design, the replaceable module, including the stage, is removable. The part of the tool 40 for the replaceable module is isolatable, that is, the part of the tool 40 is defined by a valve upstream of the bundle of replaceable modules and a valve downstream of the bundle thereof. The valves may be operated to isolate the environment between the valves from the vacuum upstream and downstream of the bundles of the valves, respectively, so that the replaceable module can be removed from the tool 40 while maintaining the vacuum upstream and downstream of the bundles of the portion of the tool 40 associated with the replaceable module. In one embodiment, the replaceable module includes a stage. The stage is configured to support a device such as a charged particle optical device with respect to the beam path. In one embodiment, the module includes one or more actuators. An actuator is associated with the stage. The actuator is configured to move the device relative to the beam path. Such actuation may be used to align the device and 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 electro-optical tool 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-optical tool 40 is located. Only the portion of the tool 40 corresponding to the module is vented for removal and return or replacement of the module.

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

In some embodiments, one or more aberration correctors are provided to 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 component and/or as part of an evaluation tool. 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 a mid-plane. This provides more space for the aberration corrector than is available elsewhere, i.e. upstream or downstream of the beam of the intermediate plane (or than is available in alternative arrangements without an intermediate image plane).

In one embodiment, the aberration corrector positioned in or directly adjacent to the intermediate focus (or intermediate image plane) includes a deflector to correct the source 201 that appears to be in a different position for the different beams. The corrector may be used to correct macroscopic aberrations generated by the source that prevent good alignment between each sub-beam and the corresponding objective lens.

The aberration corrector can correct aberrations that prevent proper column alignment. Such aberrations may also lead to misalignment between the beamlets and the corrector. For this reason, it may be desirable to additionally or alternatively locate an aberration corrector at or near the converging lens 231 (e.g., each such aberration corrector is integrated with or directly adjacent to one or more of the converging lenses 231). This is desirable because at or near the converging lens 231, aberrations will not yet result in a shift of the corresponding beamlets, as 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 location further downstream (or downstream of the beam). The converging lens and the corrector may be part of the same structure. For example, they may be connected to each other, for example by an electrically isolating element. The aberration corrector may be a CMOS based individually programmable deflector as disclosed in EP2702595A1 or a multipole deflector array as disclosed in EP2715768A2, the description of which is incorporated herein by reference for the sub-beam manipulator.

In some embodiments, each of at least a subset of the aberration correctors is integrated with or directly adjacent to one or more of the objective lenses 234. In one embodiment, the aberration correctors reduce one or more of the following: field curvature; a focus error; and astigmatism. The objective lens and/or the control lens and the corrector may be part of the same structure. For example, they may be connected to each other, for example by an electrically isolating element. Additionally or alternatively, one or more scanning deflectors (not shown) may be integrated with or directly adjacent to one or more of the objective lenses 234 to scan 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 charged particle optical device described above may comprise at least an objective lens array 241. Thus, in certain embodiments, the charged particle optical device may be an objective lens array component and may have an assembly as described above with respect to the objective lens array component.

For example, in a second aspect, the objective lens component is for projecting a plurality of beams of charged particles towards a sample surface. The objective part comprises an objective array 241 and a detector array 240. The objective lens array 241 may include any or all of the features described above with respect to the objective lens array 241. The detector array 240 may include any or all of the features described above with respect to the detector array 240. The objective lens component is configured to detect the backscattered charged particles.

The objective lens array 241 includes at least two electrodes arranged along the path of the plurality of beams and having a plurality of apertures defined therein. For example, the objective lens array 241 includes at least a first electrode 242 and a second electrode 243. The detector array 240 is configured to detect charged particles emanating from the sample in response to the plurality of beams. The detector array 240 is positioned downstream of the beam of the objective lens array 241.

The detector array 240 is configured to be positionable adjacent to the sample 208 and, as described in the first aspect, may have a distance L between the sample 208 and the detector array.

The detector array potential, the sample potential, the first electrode potential and/or the second electrode potential may be set as described above in relation to the first aspect.

For example, the objective lens component of the second aspect may have any or all of the features of the charged particle optical apparatus described above. In particular, the objective lens array component may include a control lens array 250 and/or a scanning deflector array 260.

In a third aspect of the invention, for example, a charged particle optical apparatus is provided, wherein the charged particle optical apparatus is configured to switch between two operating states. These two operating states change between primary detection of backscattered charged particles and primary detection of secondary charged particles. For example, the charged particle optical apparatus of the third aspect may comprise any or all of the features described in relation to the above aspects and embodiments. Features identical to those described above are given the same reference numerals. For brevity, these features are not described in detail below.

As described above, detection of both the secondary charged particles and the back-scattered charged particles is useful, but different information can be acquired by detection of the secondary charged particles and the back-scattered charged particles. It would therefore be of significant benefit to provide an apparatus that supports the detection of both secondary charged particles and backscattered charged particles. In particular, it would be advantageous to provide a device that can easily support switching between detection of secondary charged particles and backscattered charged particles, and vice versa.

As mentioned above, the charged particle optical apparatus is suitable for any charged particle system, such as a charged particle evaluation tool, i.e. the evaluation tool 40. The apparatus is configured to project an array of charged particle beams towards the sample; that is, the apparatus is configured to project a plurality of beams of charged particles along a beamlet path towards the sample 208. The plurality of bundles includes sub-bundles. The apparatus comprises an objective lens array 241, the objective lens array 241 being configured to project an array of charged particle beamlets onto the sample 208. In other words, the device comprises an objective array 241, which objective array 241 is configured to project a beam onto the sample 208. The apparatus also includes a detector array configured to capture charged particles emitted from the sample 208. In other words, the apparatus comprises a detector array (i.e. detector array 240) configured to detect the backscattered particles from the sample. As described above, the detector array 240 may be positioned to face the sample 208. Preferably, as described above, the objective lens array 241 includes the detector array 240 and/or the detector array 240 is positioned on or near the objective lens array 241.

The device is configured to switch between two operating states. In a first operating state, the detector is configured to detect more secondary charged particles than the back-scattered charged particles. In other words, in the first operating state, the detector is configured to mainly detect the secondary charged particles. In the second operating state, the detector is configured to detect more backscattered charged particles than secondary charged particles. In other words, in the second operating state, the detector is configured to mainly detect the backscattered charged particles.

Various features of the device may be switched between a first operating state and a second operating state. It will be appreciated that in the first operating state the device is configured to optimise the detection of secondary charged particles and in the second operating state the device is arranged to optimise the detection of backscattered charged particles. Thus, in the first operating state, the secondary charged particles can be detected mainly. In the second operating state, the backscattered charged particles may be detected mainly.

In the second operating state, the device is configured to accelerate the charged particle beam onto the sample 208, and preferably the objective lens is configured to accelerate the charged particle beam onto the sample 208. Thus, in the second operating state, the apparatus, and more particularly the objective lens array 241, may operate as described above to accelerate the charged particle beam onto the sample 208. In the second operating state, the objective lens array 241 may be configured to repel secondary charged particles as described above.

In the first operating state, the objective lens is configured to decelerate the charged particle beam onto the sample 208. Multi-beam systems that are operated to decelerate a charged particle beam onto a sample, such as the electron beam tool 40 and the charged particle beam inspection device 100, are known and may be used in a first operating state. As mentioned above, these known systems can be used to detect secondary charged particles. Thus, the device may operate in concert with such a system when information is acquired from the secondary charged particles.

For example, deceleration may be performed by selecting which potential to apply to the electrodes of objective lens array 240. Fig. 4 describes above with respect to the system to show how electrical potentials can be applied to the control lens array 250, the objective lens array 240, and the sample 280. The value of the electrical potential provided for the acceleration lens may be exchanged and adjusted to provide deceleration.

For example only, the electrons may be decelerated from 30kV to 2.5kV in the objective lens. In one example, to obtain landing energy in the range of 1.5kV to 5kV, the potentials shown in fig. 4 may be set as shown in table 2 below, such as V2, V3, V4, V5, V6, and V7. The potentials in this table are given as values of beam energy in keV, which are equal to the electrode potential relative to the cathode of the beam source 201. It will be appreciated that there is a considerable degree of freedom in designing an electron optical system with respect to which point in the system is set to ground potential, and that the operation of the system is determined by the potential difference rather than the absolute potential.

As described above, the objective lens array as shown in fig. 4 may include additional electrodes, for example, an intermediate electrode located between the upper electrode and the lower electrode of the objective lens array, as shown in fig. 4. The voltage source V1 may be configured to apply a potential to the intermediate electrode. This intermediate electrode is optional and may not be included in an electrode having the other potentials listed in table 2.

It can be seen that the beam energy at V1, V3 and V7 is the same. In an embodiment, the beam energy at these points may be between 10keV and 50 keV. If a lower potential is chosen, the electrode spacing can be reduced, especially in the objective lens, to limit the reduction of the electric field.

Although the control lens array 250 and the objective lens array 240 are shown in fig. 4 as having three electrodes, the control lens array 250 and/or the objective lens array 240 may be provided with two lenses.

As described above, the objective lens array includes at least the first electrode 242 configured to have the first electrode potential and the second electrode 243 configured to have the second electrode potential. The first electrode 242 is upstream of the beam of the second electrode 243. As described above, the power supply 290 for supplying electric potential may be provided. Accordingly, the power supply 290 is configured to apply a first electrode potential to the first electrode 242 and a second electrode potential to the second electrode 243. The power supply 290 is configured to apply an associated potential according to an operating state. Thus, the potentials applied to the first and second electrodes may vary depending on the relevant operating state of the device.

In the first operating state, the first electrode potential may be more positive than the second electrode potential. Additionally or alternatively, in the second operating state, the second electrode potential may be more positive than the first electrode potential. Controlling the potential and changing the potential between the first and second operating states will change how the charged particle beam travels through the objective lens array and will thus affect whether the charged particles are accelerating or decelerating. Changing the electrodes in this way will affect the landing energy of the charged particle beamlets. Thus, the apparatus may be configured to project the charged particle beamlets onto the sample at a lower landing energy in the first operating state and at a higher landing energy in the second operating state.

The potentials applied to the first electrode and the second electrode may be as described above and may be exchanged. Furthermore, the sample may be at a sample potential as described above, such that the secondary charged particles are repelled by the objective lens array.

Additional or alternative adjustments may also be made when switching between the first operating state and the second operating state.

For example, the apparatus may be configured to maintain the charged particle beamlets focused on the sample in the first and second operating states. More specifically, the objective lens array 241 may be configured to maintain the charged particle beamlets focused on the sample in the first and second operating states. For example, when switching between the first operating state and the second operating state and vice versa, the first electrode potential of the objective lens array 241 (i.e., the potential of the upper electrode) may be adjusted to maintain the focus of the primary beam on the sample 208 in the first operating state and the second operating state. The distance between the objective lens array 241 and the sample 208 may be maintained if the first electrode potential is adjusted to maintain the focusing of the charged particle beamlets on the sample 208.

For example, the device may be configured to change the distance between the objective lens array 241 and the sample 208 when switching between the first and second operating states, and vice versa. The distance between the objective lens array 241 and the sample 208 may be adjusted to account for the difference in landing energy between the first and second operating states. The distance may vary on the order of a few millimeters or less than a millimeter, or on the order of hundreds of micrometers or less.

For example, the device may be configured to reduce the distance between the objective lens array 241 and the sample 208 in order to switch from the first operating state to the second operating state. Additionally or alternatively, the device may be configured to increase the distance between the objective lens array 241 and the sample 208 in order to switch from the second operating state to the first operating state.

Preferably, in the above example, i.e. when the first electrode potential and/or the distance between the objective lens array 241 and the sample 208 is changed, the distance between the detector array 240 and the sample 208 is advantageously maintained. The detector array 240 may be moved relative to the objective lens array 241 to maintain the distance between the detector array 240 and the sample 208. The movement of the detector array 240 may be performed while the objective lens array 241 is moved relative to the sample 208, or while the position of the sample is changed relative to the objective lens array 241 along the beam path (i.e., the detector array 240 tracks the sample along the beam path).

Alternatively, it may be beneficial to vary the distance between the detector array 240 and the sample 208 to focus charged particles emitted from the sample 208 onto the detector array 240. In particular, the distance between the detector array 240 and the sample 208 may be changed between a first operating state and a second operating state such that secondary charged particles are focused on the detector array 240 when in the first operating state and back-scattered charged particles are focused on the detector array 240 when in the second operating state.

If the detector array 240 is to be moved relative to the sample 208, this may be achieved by controlling the position of the detector array 240 relative to the objective lens array 241 or by controlling the position of the detector array 240 relative to the sample 208. Any suitable actuator may be used to move the detector array 240, i.e., to move the detector array 240 relative to the objective lens array 241 and/or relative to the sample 208.

One way in which the device may be switched between the first and second operating states includes providing a charged particle optical device comprising or in the form of a switchable module. The switchable module may comprise an objective lens array and a detector array, and optionally a control lens array. Thus, the switchable module may be a switchable objective lens array part. A switchable module may be provided for each operating state. Thus, different switchable modules may be provided with different insulating structures, depending on which operating state is to be used. The switchable module may provide the objective array 241 in different positions such that the objective array is disposed in different positions relative to the sample 208. In other words, different switchable modules may have detector arrays located at different distances from the sample along the beamlet path 220. The detector used in the detector array may be different for different switchable modules, depending on which operational state it is to be used for. The detector arrays 240 in different modules may be maintained at the same distance relative to the sample 208, or the distance between the detectors and the sample may vary from module to account for charged particles emitted from the sample 208 to be detected by the detector arrays 241.

In this device, as described above, an insulating structure may be provided between adjacent electrodes. The insulation structure may be different depending on which operating state is preferred. For example, for the second operational state, the insulating structure may be as described with respect to fig. 11. For the first operating state, an insulating structure as shown in fig. 10 may be provided. This is similar to the insulating structure of fig. 11, except that a gap 505 is provided between the beam upstream electrode (i.e., the first electrode 242) and the radially inward protrusion 504. Such an insulating structure may be particularly beneficial for optimizing the passage of the charged particle beam through the objective lens array 241 when the beam is decelerated, for example, for reasons described herein. In the arrangement shown in fig. 11, the first electrode 242 has a potential that is less positive than that of the second electrode 243. In this arrangement, the protrusion is in contact with the first electrode 242. Whereas in the arrangement of fig. 10 the first electrode 242 has a more positive potential than the second electrode 243, so the direction of the potential difference between the electrodes is different from, i.e. opposite to, the arrangement shown in fig. 11. This is why the protrusion is in contact with the second electrode 243 in the present embodiment. By choosing the position of the protrusion, i.e. in contact with the first electrode or the second electrode, the risk of undesired discharge can be reduced.

The switchable module may be controlled and adapted as described above in relation to the first aspect.

Another way in which the device can be switched between the first and second operating states includes providing a charged particle optical device that can be tuned to operate in both operating states, i.e. a hybrid charged particle optical device (referred to as a hybrid device) that can be used in both the first and second operating states. In this case, when the state is switched, the distance between the objective lens array 241 and the sample 208 can be adjusted. In this case, when the state is switched, the potential applied to the electrode can be adjusted. In this case, an insulating structure suitable for both operating states can be provided. In this case, a detector array suitable for both modes of operation may be provided (as described in the fourth aspect below).

In the hybrid device, adjacent electrodes are separated by an insulating structure configured for a first operation and a second operation, preferably wherein the objective lens array comprises an insulating structure. Such an insulating structure may be provided as shown in fig. 12, and may be referred to as a hybrid insulating structure. The hybrid insulation structure is similar to that shown in fig. 10 and 11, except that gaps 509, 510 are provided on either side of the radially inward projection 508. Thus, the electrodes on either side of the hybrid insulating structure are in contact with the body 501. However, the radially inward projection 508 does not contact either of the first electrode 242 or the second electrode 243.

In more detail, the insulating structure 500 is formed by a body 501 and a protrusion 508 radially inward from the body 501. The body 501 has a first face and a second face, the first face 503 being opposite the second face 502. On the first face 503 of the insulating structure, the body 501 contacts one of the electrodes (e.g., the first electrode 242), and a first gap 509 is formed between the protrusion 508 and the one of the electrodes 242. On the second face 502 of the insulating structure, the body 501 contacts the other of the electrodes (e.g., the second electrode 243), and a second gap is formed between the protrusion 508 and the other of the electrodes (e.g., the second electrode 243).

The mixing device may be configured to move the objective lens array and/or the sample relative to each other along the beamlet path 220 in order to switch between the first and second operating states. For example, the apparatus may comprise an actuator 248, the actuator 248 being configured to move the objective array in order to change the distance between the objective array and the sample. The actuator 248 may be part of an objective lens array assembly. A publication of an apparatus with an actuator for displacing the detector along a multi-beam path is european patent application 20198201.4 filed on 9/24/2020, which is incorporated herein by reference, as regards the design and use of an actuator for actuating a detector array with respect to an objective lens array.

Additionally or alternatively, the mixing device is configured to move the sample to change the distance between the objective lens array 241 and the sample 208. For example, the apparatus may include a motorized stage 209 (and optionally a sample holder 207) that may be used to change the position of the sample.

As described above, the device may be switched between different operating states or modes. In any of the above examples, switching between operating states may be used to detect different types of charged particles in different operating states. For example, the device may operate in a first operating state to detect more of one type of signal particles (e.g., secondary charged particles) and then in a second operating state to detect more of a different type of signal particles (e.g., backscatter charged particles). The device may be configured to operate in the first operating state or the second operating state for a given period of time, depending on which particles are of more interest. The device may be configured to switch between any number of additional states or modes.

As previously described, different information related to the sample 208 may be obtained by measuring different types of charged particles. For example, measurement of secondary charged particles may be used to obtain information about the top surface, e.g., for imaging the top surface, and backscattered charged particles may be used to obtain data of features beneath the surface of the relevant sample, e.g., for imaging beneath the surface. Acquiring data from different types of charged particles can be used to compare the surface of the sample to features below the surface of the sample. For example, this may be advantageous to identify information related to features already defined in the sample, which information may be used to determine the positioning of the features in different layers of the sample. For example, such data associated with different layers may be used to identify overlay errors of features in different layers at the overlay location using signal electrons (e.g., different types of signal electrons). Thus, as mentioned above, switching of the device between different operating states can be used to detect different types of signal particles, which is particularly useful for such overlay measurements. Typically, when switching modes, the electrostatic field between the sample and the detector is reversed, so that in one mode, the secondary signal particles are repelled from the detector array 241; in another mode, the secondary charged particles are accelerated toward the detector array 241. In the above-described embodiments, the landing energy is typically varied between different operating states. For example, in a first operating state (when more secondary charged particles than backscattered charged particles are detected), the landing energy may be about 2.5kV, and in a second operating state the landing energy may be greater than or equal to about 30kV. However, when switching between different modes (i.e. operating states), there is a risk of system drift (i.e. movement of sample position or beam position), which may lead to overlay measurement errors.

In one embodiment of the third aspect, for example, the apparatus may be configured to continuously switch between the first and second operating states, i.e. to allow continuous or near continuous detection of the secondary charged particles and the backscattered charged particles, as described below. In other words, detection may be switched back and forth between operating states to allow detection of backscattered charged particles and then detection of secondary charged particles, and vice versa. The operational staggering of the device detects signal particles preferred by the different modes of operation.

Preferably, the switching occurs very fast, as will be described in further detail below. In general, continuous switching between the first and second operating states may provide detection of backscattered charged particles and secondary charged particles substantially or at least almost simultaneously. The switching may be controlled by a controller as described below.

Switching includes the device switching between a first potential and a second potential. In other words, the device may turn the repulsive potential on and off such that when repulsive on, the detector array 240 is configured to repel the secondary charged particles. Typically, the detector array 240 is provided with a repulsive potential for repelling the secondary charged particles, as the detector array 240 tends to be closer to the sample 208 than the objective lens array 240. However, the repulsive potential may also be provided to the objective lens array 240, or alternatively to the detector array 241.

Since secondary charged particles tend to have low energy (e.g., as compared to back-scattered charged particles), they can be effectively repelled by a relatively low repulsive potential. This is advantageous in that the repulsive potential can be switched on and off rapidly.

For example only, in one arrangement, a potential of +5v may be applied to the detector array 240 for acceleration, and a potential of-25V may be applied to the detector array 240 for repulsion. The electrical potential may also be applied to at least a portion of the objective lens array 241, or instead of to the detector array 240. Some secondary charged particles may still be detected during the back-scattered charged particle mode and vice versa. However, in the first operating state (when the detector detects more secondary charged particles than the back-scattered charged particles), the proportion of back-scattered charged particles may be about 20%. Additionally or alternatively, in the second operating state (when the detector detects more back-scattered charged particles than back-scattered charged particles), the proportion of secondary charged particles may be about 35%.

Typically, the voltage difference between the first and second operating states may be several tens of volts, for example 30 volts as described above. A voltage difference with such an amplitude is advantageous because the switching can be done very fast, e.g. on the order of milliseconds, so that multiple switching can be done during the acquisition of data (from which, e.g. an image can be rendered). Furthermore, this is advantageous because the effect of the voltage variations on the primary beamlets is negligible.

The apparatus may include a controller configured to control switching between operating states. For example, the controller may be configured to control the repulsive potential applied to the detector array 240 and/or the objective lens array 241. The controller may be the same as the controller 50 described above.

The landing energy in the first and second operating states may be substantially the same and/or substantially maintained. In other words, with a fast switching between the first and second operating states, the landing energy may be substantially constant. In particular, when the same landing energy is used, a signal may be generated from the secondary charged particle detection and a signal may be generated from the backscatter charged particle detection. Generally, backscatter charged particles require higher landing energies than secondary charged particles to acquire sufficient signals. Accordingly, the landing energy is preferably high enough to provide a backscatter charged particle signal. For example, in one arrangement, the landing energy may be greater than or equal to 10kV, between about 10-15kV, greater than or equal to about 15kV, or greater than or equal to about 30kV. At such landing energies, useful secondary charged particle signals may also be generated. When the landing energy remains substantially constant, the only voltage change may be related to the repulsive potential.

Preferably, the switching rate of the device between the first and second operating states or vice versa is between about 10ms and 1s, or preferably between about 10ms and 100ms, or preferably between about 20ms and 50 ms. As described above, the device may drift between measurements. Thus, if the device switches between the first and second modes of operation and vice versa, this may reduce or avoid the effects of drift. This will depend on the magnitude of the drift and the speed at which the device switches between modes. In general, drift tends to be small, on the order of milliseconds, so every 10ms or so of switching should be fast enough to avoid drift. At this switching rate, the device can operate in two different modes of operation over the same portion of the sample surface within 50ms, 30ms, or about 20 ms. Thus, a continuous switching between the first and second operating states may provide detection of backscattered charged particles and secondary charged particles substantially or at least almost simultaneously. Note that the potential can be switched on this time scale. Preferably, the device switches between the first and second operating states, or vice versa, at least once every few seconds, or at least once every second, or at least once every 100ms, or at least once every 10 ms. The shorter time scale avoids significant repositioning of the beam path and sample relative to each other so that the device can operate on the same portion of the sample in both modes. More generally, the faster the switching rate between operating states, the better the drift can be considered. However, considering the overhead time required to switch between operating states, it may be more difficult to switch between operating states faster, which may reduce yield. Thus, the rate may be preferably selected based on the above ranges and values to optimize the loss of accuracy due to drift and yield due to overhead time.

It should be noted that when the device is operated in a mode in which the backscattered signal particles are detected, for example in order to make a backscattered image, it may take longer to acquire data than when the device is operated in a mode in which the secondary signal particles are detected (for example in order to make an image using the secondary charged particles). Thus, the device may be switched every 10ms to 100ms to cause the device to treat a portion of the surface to detect the backscattered charged particles. Acquisition of detection data of secondary charged particles of the same portion of the sample surface can be about ten (10) times faster. In one arrangement, the device may operate sequentially in different modes of operation on the same surface portion. In another arrangement, the apparatus may be used to generate partial data sets over sequential portions of the sample surface in different modes. For example, the device may be used to scan one portion in a first mode of operation and then scan the next portion in a second mode of operation. Only a portion of the image may be scanned in one mode prior to switching.

This embodiment can have higher backscatter charged particle detection efficiency than other detection modes (e.g., simultaneous detection described below), which is advantageous for yield. The reason for this is as follows.

As described above in relation to the third aspect of the invention, it is for example advantageous to provide a device capable of switching between detection of secondary charged particles and detection of backscattered charged particles. A fourth aspect of the invention provides a detector which may be provided to be operable in two operating states. The detector may be provided as part of a charged particle optical device of any of the preceding aspects and embodiments, and may include any or all of the features described in relation to the detector and/or detector array of the preceding aspects and embodiments. Features identical to those described above are given the same reference numerals. For brevity, these features are not described in detail below.

In a fourth aspect, a detector for a charged particle evaluation tool is provided, wherein the detector is configured to capture charged particles emitted from a sample. In other words, the detector is configured to detect charged particles emitted from the sample.

The detector is configured to switch between two operating states. In the first operating state the at least one detector is configured to detect more secondary charged particles than secondary charged particles, and in the second operating state the at least one detector is arranged to detect more back-scattered charged particles than secondary charged particles.

The detector is configured to switch between two operating states. The detector may include an inner detection portion surrounding the aperture and an outer detection portion radially outward from the inner detection portion (as shown and described with respect to fig. 13A). The detection section will be described in further detail below. These two states may use different configurations of the detector (i.e., different configurations of the detection portion).

The energy difference between the secondary charged particles and the back-scattered charged particles results in the charged particles being affected by different amounts of the above-mentioned potential. The backscattered charged particles may be more likely to be detected over the whole area of the detector. However, secondary charged particles tend to be more prone to be detected in the middle of the detector. As described in further detail below, because the secondary charged particles typically have a smaller average energy (i.e., less than the back-scattered charged particles, and typically near 0V). Thus, the trajectories of the secondary charged particles are changed (i.e. collimated) more significantly by the field, for example compared to back-scattered charged particles having on average a larger energy. The more the secondary charged particles are accelerated, the more their angle becomes parallel to the optical axis (i.e., the beamlet path). Thus, the secondary charged particles do not spread as much, i.e. the trajectories of the secondary charged particles tend to be more collimated with the beamlet paths than the trajectories of the back-scattered charged particles. It would be advantageous to provide a detector that is capable of supporting the detection of secondary charged particles and the detection of backscattered charged particles that are separated from each other. In particular, since charged particles can be used to determine different information, it is beneficial to control the detection to detect secondary charged particles or backscattered charged particles.

The detector of the fourth aspect is therefore particularly useful in that it may allow switching between two different detection states. Thus, the detector is configured to operate to detect predominantly back-scattered charged particles in one state and to detect predominantly secondary charged particles in another state. As described in further detail below, the detectors are radially separated (i.e., forming a plurality of concentric rings).

Although the detector of the fourth aspect is described above in the context of switching between two operating states, a detector as described herein may be provided more generally. The detectors described herein may be used for continuous or substantially continuous detection.

In a fourth aspect, a detector for a charged particle evaluation tool is provided; the detector includes a plurality of sections. Thus, the detector may be provided with a plurality of parts, more specifically, a plurality of detection parts. The different portions may be referred to as different regions. Thus, the detector may be described as having multiple regions or detection regions. Such a detector may be referred to as a partition detector.

The partition detector may be associated with one of the sub-beams 211, 212, 213. Thus, portions of one detector may be configured to detect signal particles emitted from the sample 208 in relation to one of the beamlets 211, 212, 213. The detector comprising a plurality of parts may be associated with one aperture in at least one electrode of the objective lens component. More specifically, a detector 405 comprising multiple portions may be disposed around a single aperture 406, as shown in fig. 13A and 13B, which provide examples of such detectors.

The sections of the segmented detector may be separated in a variety of different ways, such as radial, annular, or any other suitable way. Preferably, the portions are of substantially the same size and/or shape. The separate portions may be provided as a plurality of sections, a plurality of annular portions (e.g., a plurality of concentric rings), a plurality of sector portions (i.e., radial portions or sectors). For example, the at least one detector 405 may be provided as a ring-shaped part comprising 2, 3, 4 or more parts. More specifically, as shown in fig. 13A, the detector 405 may include an inner annular portion 405A surrounding an aperture 406, and an outer annular portion 405B radially outward from the inner annular portion 405A. Alternatively, the detector may be arranged as a sector portion comprising 2, 3, 4 or more portions. If the detector is set to two sectors, each sector portion may be a semicircle. If the detector is set to four sectors, each sector portion may be a quarter circle. This is shown in fig. 13B, where 405 is divided into quarter circles, i.e., fig. 13B shows four sector portions as described below. Alternatively, the detector may be provided with at least one segment portion.

Each section may have a separate signal readout. The detector is divided into a plurality of parts, e.g. a ring-shaped part or a sector-shaped part, which is advantageous in that it allows more information about the detected signal particles to be acquired. Thus, providing the detector 405 with multiple portions may be advantageous for obtaining additional information related to the detected signal particles. This may be used to improve the signal-to-noise ratio of the detected signal particles. However, there is additional cost in terms of the complexity of the detector.

In one example, the detector may be divided into two (or more) concentric rings, for example, as shown in fig. 13A.

As shown in fig. 13A, the detector includes an inner detection portion 405A and an outer detection portion 405B, in which an aperture 406 configured for passage of a charged particle beam is defined. The inner detection portion 405A surrounds the aperture 406 of the detector. The outer detection portion 405B is radially outward from the inner detection portion 405A. The detector may be generally circular in shape. Thus, the inner and outer detection portions may be concentric rings. Such detectors may be used to detect configurations that switch between different operating states or modes (e.g., as described above) and/or to detect configurations simultaneously (e.g., as described below).

It may be beneficial to provide multiple sections concentrically or otherwise, even without switching the operating state of the detector. In particular, different parts of the detector may be used to detect different signal particles, which may be smaller angle signal particles and/or larger angle signal particles, or secondary charged particles and/or back-scattered charged particles. This configuration of different signal particles may be applied to concentric partitioned detectors.

In this case, signal particles with smaller angles (e.g., small angle back-scattered charged particles) may contribute primarily to inner annular portion 405A, while signal particles with larger angles (e.g., large angle back-scattered charged particles) may contribute mostly to outer annular portion 405B. In other words, the inner ring may be used to detect low angle back-scattered charged particles, while the outer ring may be used to detect high angle back-scattered charged particles. Since separate signals may be generated by the parts of the detector, this means that the detection of low-angle and high-angle charged particles may be detected separately. Different angles of the backscattered charged particles may be beneficial in providing different information. For example, for signal electrons emitted from a deep hole, low angle back-scattered charged particles may come more from the bottom of the hole, while high angle back-scattered charged particles may come more from the surface and material surrounding the hole. In alternative examples, the low angle back-scattered charged particles may come more from the buried feature deeper, while the high angle back-scattered charged particles may come more from the sample surface or material above the buried feature.

The width (e.g., diameter) of the first detection portion may be about 2 μm to 100 μm. The width (e.g., diameter) of the first detection portion may be less than or equal to about 100 μm. The width (e.g., diameter) of the first detection portion may be greater than or equal to about 2 μm. The width (e.g., diameter) of the second detection portion may be less than or equal to about 250 μm. The width (e.g., diameter) of the second detection portion may be less than or equal to about 150 μm. The width (e.g., diameter) of the second detection portion may be greater than or equal to about 10 μm. The width (e.g., diameter) of the second detection portion may be about 10 μm to 250 μm. Preferably, the width of the second detecting portion may be about 10 μm to 150 μm. The dimensions of the respective portions (e.g., the width/diameter of the inner annular portion 405A and/or the outer annular portion 405B) may be designed or selected so as to detect particular charged particles of interest at each portion of the detector.

For a switching configuration of the device with concentric zone detectors, where the zones are used alternately, as shown in fig. 13A, in this arrangement the diameter of the first detection portion is preferably about 40-60 μm, preferably about 30-50 μm. In such an arrangement, the diameter of the second detection portion is preferably about 150 μm to 250 μm, and preferably about 200 μm. In such an arrangement, the diameter of the aperture of the detector may be about 5 μm to 30 μm, preferably about 10 μm.

In the first operating state, the detector 406 uses the inner detection portion 405A and does not use the outer detection portion 405B. This is advantageous because it limits the detection of backscattered charged particles during detection of secondary charged particles. Since most of the secondary charged particles will be detected by the internal detection portion, this does not lead to too much information being lost due to non-detected secondary charged particles.

In the second operating state, the detector 406 uses at least the external detection portion 405B. When backscattered charged particles are detected, the device as described above may be arranged to repel secondary charged particles, which will reduce the number of secondary charged particles detected. Thus, since other mechanisms may be employed to reduce or avoid detection of secondary electrons in detecting the backscattered charged particles, the entire detector available may be used to detect the backscattered charged particles, which facilitates capturing information related to more of the backscattered charged particles.

Providing the distance and/or pitch p of the detector relative to the sample 208 may affect which of the outer detection portion and/or the inner detection portion may be used to detect the backscattered charged particles and/or the secondary charged particles. For example, the inner detection section is generally described above as being used to detect secondary charged particles and the outer detection section (and optionally the inner detection section) is used to detect backscattered charged particles. This may be the case, for example, only when the detectors are disposed at a pitch of about 300 microns at about 50 microns from the sample. However, if the distance between the detector and the sample is about 10 microns, the pitch p is about 70 microns, the detector may be used only to detect back-scattered charged particles (since the secondary charged particles will likely eventually enter the aperture), and the internal detection portion may be used to detect back-scattered charged particles. In either case, it should be appreciated that separate inner and outer portions may be used to advantageously switch between primary detection of backscattered charged particles and/or primary detection of secondary charged particles.

Multiple detectors may be provided. A plurality of detectors may be provided as a detector array as shown in fig. 14. The detector array is for a charged particle evaluation tool configured to operate in a backscatter operating state (i.e., a second state) to preferentially detect backscatter charged particles and in a secondary charged particle state (i.e., a first state) to preferentially detect secondary charged particles. The detectors of the detector array may be as described in any variation of the fourth aspect.

The detector may have the features as described in relation to the detector/detector array of the first aspect. For example, although the detector is shown as circular in shape, it may be made square to maximize the detection area. For example, while fig. 14 shows a rectangular array of beam apertures 406, the beam apertures 406 may be arranged differently, such as a hexagonal close-packed array as shown in fig. 8. For example, the cross-section of fig. 15 corresponds to the cross-section of fig. 9, except that the detection portions are provided as an inner portion 405A and an outer portion 405B, and thus the detector may include the same features as described above with respect to fig. 9.

As described above, the detector of the fourth aspect may be used in any of the above aspects and embodiments, for example. In particular, a charged particle optical apparatus for a multi-beam charged particle evaluation tool may be provided. The charged particle optical device comprises an objective lens array and a detector array comprising a detector array as described in relation to the fourth aspect. Apertures in the electrodes of the objective lens array and the detector array are arranged in the beamlet path of the charged particle beam. Furthermore, if the charged particle optical device of the third aspect is used, for example, with the detector of the fourth aspect, the detector may be used with any variation. However, the detector of the fourth aspect will be particularly useful for a mixing device, as the detector may be switched between a first and a second operating state depending on the mixing device. For example, in a third aspect, using the detector of the fourth aspect, the apparatus may be configured to use the detector in a suitable operating state.

It may be advantageous to provide a device that may be used to detect different types of signal particles, e.g. both backscatter particles and secondary charged particles, simultaneously. However, devices for detecting different types of signal particles (such as both backscattered charged particles and secondary charged particles) simultaneously may not be able to effectively distinguish between the different types of signal particles, i.e. in the example provided, the secondary charged particles and the backscattered charged particles. This may be the case, for example, if the detector detects without distinguishing between different types of signal particles, for example by detecting the net charge arriving thereon (i.e. a charge detector), or if the detector acts as a counter, or if the detector is an integrating detector (i.e. a detector summing the energy deposited by particles falling thereon during a particular time). The generated detection signal and any corresponding image will be created by a mixture of different signal particles, e.g. secondary charged particles and back-scattered charged particles. Since the secondary charged particles and the back-scattered charged particles may have different detection contrasts, for example, image contrasts when rendering an image, this means that information about the contrast between the secondary charged particles and the back-scattered charged particles may not be detected.

The embodiments described below provide some additional/alternative configurations for detecting different signal particles simultaneously, e.g. detecting secondary charged particles and back-scattered charged particles. For example, by more easily distinguishing detection signals of different signal particles (e.g., secondary charged particles and back-scattered charged particles) that can be detected simultaneously, these embodiments may be beneficial in improving detection of different signal particles (e.g., secondary charged particles and back-scattered charged particles). It may be advantageous to provide a detector and/or a device that may be used to detect different types of signal particles (e.g. back-scattered charged particles and secondary charged particles) without switching, as the operation of the device may be simpler. The embodiments described below may be combined with any and all of the variations, aspects, and embodiments described above.

In one embodiment, an apparatus as described in any of the variations, aspects, and embodiments above is provided. The apparatus comprises an objective lens array as described above. The apparatus includes a detector array 240 associated with an objective lens array 241. The detector array 240 may be proximate to the sample 208. Each detector element comprises at least two detection portions configured to detect charged particles from the sample. In other words, each detector may include two detection portions (e.g., a first detection portion and a second detection portion). Each detector may be otherwise referred to as a detector element 405. The detection portions are separated from each other. The detection portions may detect the charged particles independently of each other. In other words, each detection section may operate independently of the other.

Different detection elements 405 may be configured to preferentially detect different types of signal electrons. For example, the detector element may have two or more detection portions. In one arrangement, the detector element has two differently configured detection portions: configured to detect more back-scattered charged particles than secondary charged particles; and configured to detect more secondary charged particles than the back-scattered charged particles. The two detection sections may be used simultaneously. This may be beneficial because the landing energy may be kept constant while using a detector with at least two detection portions. The detector element comprising at least two detection portions as described above may be provided in combination with any of the above embodiments, aspects and variations.

One of the detection portions may be an external detection portion and the other detection portion may be an internal detection portion. The detection portion surrounds an aperture (or beam aperture), such as an aperture defined in a detector array, for passage of the charged particle beam. The inner detection portion 405A may be proximate to the aperture; the inner detection portion is closer to the aperture than the outer detection portion. The inner detection portion 405A is radially inward from the outer detection portion 405B. The detector may be configured as described above, for example, as shown in fig. 13A, in which two annular detection portions are provided; the detector array may be arranged as shown in fig. 14 or as shown in fig. 8 with the detector elements shown in fig. 13A. Each detector comprises an inner detection portion 405A and an outer detection portion 405B, the inner detection portion 405A being configured to detect more secondary charged particles than the secondary charged particles, the outer detection portion 405B being configured to detect more back-scattered charged particles than the secondary charged particles. Preferably, the inner detecting portion 405A and the outer detecting portion 405B are formed in a ring shape. In this case, the detector may be otherwise referred to as a multi (e.g., dual) ring detector.

Detector arrays (such as multi-ring detectors) can be used to distinguish between different types of signal particles from a sample based on their trajectories. This application of a multi-ring detector is beneficial for distinguishing between secondary charged particles and back-scattered charged particles. This application of the detector array exploits the fact that the angular trajectories of the secondary charged particles from the sample tend to end up with their corresponding detector elements in the region of the detector surface that is closer to the primary sub-beam than the backscattered charged particles.

In particular, application of a field between the sample and the detector (e.g., to slow down the primary beamlets) may accelerate the secondary charged particles and backscatter charged particles. The effect of the field on the signal particles is different from the primary sub-beam because the signal particles are directed in opposite directions with respect to the field. The field will generally be more able to affect the secondary charged particles than the back-scattered charged particles and will cause the trajectories of the secondary charged particles to be radially inward (i.e. toward the path of the primary beamlets). The larger the electric field between the sample and the detector, the stronger this effect. This is because, as mentioned elsewhere, the average energy of the secondary charged particles is smaller (i.e. typically close to 0V, for example about 50eV, which is essentially 0V with respect to potentials exceeding 10 keV). Thus, the trajectories of the secondary charged particles are changed (i.e. collimated) more significantly by the field, for example compared to back-scattered charged particles having on average a larger energy. The more the secondary charged particles are accelerated, the more their angle is parallel to the optical axis (i.e., the beamlet path). Thus, the secondary charged particles do not spread as much, i.e. the trajectories of the secondary charged particles tend to be more aligned with the beamlet path than the trajectories of the backscattered charged particles. The trajectories of the secondary charged particles are improved in terms of collimation towards the inner detection portion. However, the path of the backscattered charged particles is hardly affected; i.e. the path of the backscattered charged particles remains relatively unaffected by changes in the electric field compared to the path of the secondary charged particles. Accordingly, the secondary charged particles may be detected by the inner detection portion 405A, or at least preferentially detected, and the backscattered charged particles may be detected by the outer detection portion 405B (i.e., radially outward from the inner portion), or at least preferentially detected. In other words, the separation of the secondary charged particles and the backscattered charged particles may be improved over earlier designs of detectors. The performance of the detector is improved towards detection of substantially separate types of signal particles (e.g. secondary charged particles and backscattered charged particles) by different detection portions. Such detection is preferably performed simultaneously. These improvements using different detection positions can be achieved using differences in the trajectories of the secondary charged particles and the backscattered charged particles relative to different detection portions of the detector element.

Each detection section may have a separate signal readout. Insulating portions may be provided between the detection portions to prevent signals from passing between these portions. The insulating portions may be any suitable material that prevents the passage of signals between the detection portions. The insulating portions are preferably as small as possible while preventing signals from passing between these portions. The insulating portion may be about 0.5 μm to 2 μm, for example 1 μm.

Since the inner detection portion 405A is located within the outer detection portion 405B, the outer diameter of the inner detection portion 405A may be similar to the inner diameter of the outer portion 405B. Parameters that can be optimized are the dimensions of the inner detection portion 405A and the outer detection portion 405B.

By way of example only, in one arrangement, the secondary charged particle coefficient is assumed to be 1 and the backscatter charged particle coefficient is 20%. The secondary charged particle coefficient is the average number of secondary charged particles emitted per incident primary charged particle (i.e., of a beamlet) striking the sample. The back-scattered charged particle coefficient is the average number of back-scattered charged particles emitted per incident primary charged particle (i.e., sub-beam) striking the sample. Assuming a distance between the sample and the detector of about 10 microns, the beam pitch (distance between adjacent beamlets) is about 70 microns, the aperture of the detector has a diameter of about 10 microns, and the outer diameter of the detector is about 50 microns. The potential difference between the sample and the detector array is assumed to be approximately +27V (this is the maximum field assumed in HMI tools of 2.7 kV/mm). Note that the detection efficiency of the inner detection portion 405A and the outer detection portion 405B may be optimized by selecting the diameter of the first detection portion 405. In general, it is found that the smaller the inner detection portion 405A (i.e., the larger the outer detection portion 405B), the greater the backscatter signal on the outer detection portion 405B. However, for detection of secondary signal particles on the internal detection portion 405A, it was found that when the internal detection portion 405A reached a certain size, the improvement in detection gradually decreased. It was found that when the diameter of the inner detection portion 405A was between 20 micrometers and 30 micrometers, the secondary signal detection was close to the maximum detection (and there was no significant improvement when the size of the inner detection portion 405A was increased).

In more detail, as mentioned above, the trajectories of the secondary signal particles are very close to the beamlets, which means that some secondary signal particles may pass through the aperture in the detector. There is a minimum aperture in the detector to allow the beamlets to pass through the detector, which means that the aperture must be large enough to allow the beamlets to pass through (towards the sample) so that a proportion of the signal particles will pass through the aperture (away from the sample) without being detected. Since the trajectories of the secondary charged particles tend to be very close to the primary beam, increasing the size of the inner detection portion 405A beyond a certain diameter is unlikely to result in significantly more secondary signal particles being detected (since the secondary charged particles do not tend to have trajectories that cause them to fall further outward on the detector). Thus, the dimensions of the inner detection section may be selected to optimize detection using both sections of the detector, taking into account the detection of secondary signal particles on the inner detection section 405A and the detection of backscattered signal particles on the outer detection section 405B. It should be understood that the values provided in this arrangement are for background information only.

In general, acquiring data related to one type of signal particle may take longer than another type. For example, acquiring data related to the backscattered signal particles typically takes longer than the secondary signal particles. Therefore, when the optimal sizes of the inner and outer detection portions are considered, improving the detection efficiency of the backscattered signal particles (e.g., by making the inner detection portion 405A smaller) may improve the overall detection efficiency even though the secondary signal particle detection efficiency may be reduced.

Using a detector with an inner detection portion 405A and an outer detection portion 405B as described above without switching any operation mode or state is advantageous because no additional control for switching is required, so the system can be simpler. Furthermore, different types of signal particles may be detected simultaneously (and may be distinguished from each other). However, the detection efficiency for detecting each type of signal particle may generally be low, at least in part because the area of the detector for detecting the signal particle is reduced for each different type of signal particle.

The width (e.g., diameter) of the first detection portion 405A may be about 2 μm to 100 μm. Preferably, the width (e.g., diameter) of the first detection portion 405A may be about 10 μm to 50 μm. Preferably, the width (e.g., diameter) of the first detection portion 405A may be about 20 μm to 30 μm. The width (e.g., diameter) of the first detection portion 405A may be less than or equal to about 100 μm. The width (e.g., diameter) of the first detection portion 405A may be less than or equal to about 50 μm. The width (e.g., diameter) of the first detection portion 405A may be less than or equal to about 30 μm. The width (e.g., diameter) of the first detection portion 405A may be greater than or equal to about 2 μm. The width (e.g., diameter) of the first detection portion 405A may be greater than or equal to about 10 μm. The width (e.g., diameter) of the first detection portion 405A may be greater than or equal to about 20 μm.

The width (e.g., diameter) of the second detection portion 405B may be about 10 μm to 250 μm. Preferably, the width of the second detecting portion 405B may be about 10 μm to 150 μm. The width (e.g., diameter) of the second detection portion 405B may be less than or equal to about 250 μm. The width (e.g., diameter) of the second detection portion 405B may be less than or equal to about 150 μm. The width (e.g., diameter) of the second detection portion 405B may be greater than or equal to about 10 μm. The dimensions of the corresponding portions (e.g., the width/diameter of the inner annular portion 405A and/or the outer annular portion 405B) may be designed or selected so as to detect particular charged particles of interest at each portion of the detector.

Although the above embodiments are used to detect secondary charged particles, the same dual ring detector (including any/all of the variants described above) may be used to distinguish between different backscattered charged particles based on their trajectories.

The detector for detecting the back-scattered charged particles may be limited in mainly detecting the back-scattered charged particles within a specific angular range (e.g. a large angular range) with respect to the optical axis of the primary sub-beam. The backscattered charged particles having different trajectory ranges provide different information about the structure within the sample. For example, back-scattered charged particles with small trajectory angles (i.e. with small angles to the optical axis) may have information about features of presentation depth within the sample. The back-scattered charged particles with larger angular trajectories have information such as sample topology. However, the detection signal derived from the detected charged particles may have a component from the larger angle backscattered charged particles providing a large background. Thus, the detection signal component from the low angle backscatter charged particles may be pushed or submerged by the component from the higher angle backscatter charged particles. The components of the detection signal from the low angle backscattered charged particles may be substantially indistinguishable in the net detection signal. Since the information of the detected charged particles can be rendered as an image from which contrast can be perceived, the contrast of the buried features of the presentation depth can be overwhelmed or overwhelmed by the topological contrast derived from the charged larger angle backscatter.

In this example, the detection signal is back-scattered of charged particles. The secondary charged particles are filtered out. For this purpose, the secondary charged particles are repelled as described in any of the above embodiments. Thus, the difference from the above-described embodiment, in which both secondary charged particles and back-scattered charged particles are detected, may be the field applied to the charged particles. In particular, in this case, the field between the sample 208 and the detector array 241 (e.g., for accelerating the primary beamlets) decelerates the secondary charged particles and the backscattered charged particles. The field will typically have a greater effect on the secondary charged particles than on the back-scattered charged particles and will repel the secondary charged particles (i.e., again toward the sample 208). The greater the electric field between the sample 208 and the detector array 241, the stronger this effect. Thus, the detector array 241 may be used to primarily detect back-scattered charged particles, where smaller angle charged particles may be detected by the inner detection portion 405A and back-scattered charged particles may be detected by the outer detection portion 405B (i.e., radially outward from the inner portion). In other words, by using the differences in the trajectories of the back-scattered charged particles, the smaller and larger angles of back-scattered charged particles can be detected substantially individually, preferably simultaneously. The dimensions of the inner and outer detection portions may be optimized or selected based on the detection of the backscattered charged particles (e.g. using the dimensions described above).

A detector comprising multiple portions as described above (e.g., as shown with respect to fig. 13A and/or 13B) may be provided in any of the embodiments or variations described herein. Further, a detector comprising multiple portions as described above (e.g., as shown with respect to fig. 13A and/or 13B) may be provided in combination with any additional detector array. For example, the detector as shown in fig. 13A and/or 13B may be provided in combination with another detector array located above or below any of the electrodes of the objective lens array. Any additional detector array may face the sample as shown in fig. 15, or may face the beam upstream of the primary sub-beam, i.e. away from the sample.

In the above aspects, the charged particle optical apparatus is described as being provided as, or as part of, a charged particle system or an evaluation tool. It is not necessary to include all of the features of such larger systems or tools, although they may alternatively be included as part of a charged particle optical apparatus.

Fig. 16 is a schematic diagram of an exemplary electron optical system having a charged particle device as in any of the options or aspects described above. The charged particle device may be provided as an objective lens array component. The charged particle device comprises an objective lens array 241. The objective lens array 241 includes a plurality of objective lenses. The charged particle optical device having at least an objective lens array 241 as described in any of the aspects or embodiments above (e.g. at least the first and second aspects above and any suitable variations) may be used in an electron optical system as shown in fig. 16. The objective lens array 241 may be a replaceable module as described above. The features of the objective lens array 241 that have been described above may not be repeated here for brevity.

The charged particle optical device as described above may be used to detect back-scattered charged particles in the system of fig. 16 (as described above).

There are some specific considerations for the arrangement of fig. 16. In this embodiment, the pitch is preferably kept small to avoid negative effects on the yield. However, when the pitch is too small, this may cause crosstalk. Thus, pitch size is a balance of effective backscatter charged particle detection and yield. Therefore, when detecting secondary charged particles, the pitch is preferably about 300 μm, which is 4-5 times larger than the pitch of the embodiment of fig. 16. As the distance between the detector and the sample 208 is reduced, the pitch size may also be reduced without adversely affecting crosstalk. It is therefore advantageous to provide a detector as close to the sample as possible (i.e. the distance L is as small as possible, preferably less than or equal to about 50 μm, or less than or equal to about 40 μm, or less than or equal to about 30 μm, or less than or equal to about 20 μm, or equal to about 10 μm) to allow the pitch to be as large as possible (which improves yield).

As shown in fig. 16, the electron optical system includes a source 201. The source 201 provides a beam of charged particles (e.g., electrons). The multiple beams focused on the sample 208 are derived from the beams provided by the source 201. The beamlets 211, 212, 213 may be derived from the beam, for example, using beam limiters defining an array of beam limiting apertures. The beam may be split into sub-beams 211, 212, 213 upon encountering the control lens array 250. The beamlets 211, 212, 213 are substantially parallel when entering the control lens array 250. Desirably, source 201 is a high brightness thermal field emitter with a good tradeoff between brightness and total emission current. In the example shown, the collimator is arranged upstream of the beam of the objective lens array part. The collimator may include a macrocollimator 270. The macrocollimator 270 acts on the beam from the source 201 before the beam is split into multiple beams. The macrocollimator 270 bends a corresponding portion of the beam by an effective amount to ensure that the beam axis of each sub-beam derived from the beam is incident substantially orthogonally on the sample 208 (i.e., substantially 90 deg. from the nominal surface of the sample 208). The macrocollimator 270 applies macrocollimation to the beam. The macrocollimator 270 may thus act on all beams, rather than comprising an array of collimator elements, each collimator element being configured to act on a different individual portion of a beam. The macrocollimator 270 may include a magnetic lens or magnetic lens arrangement that includes a plurality of magnetic lens subunits (e.g., a plurality of electromagnets forming a multipole arrangement). Alternatively or additionally, the macrocollimator may be at least partly realized electrostatically. The macrocollimator may comprise an electrostatic lens or an electrostatic lens arrangement comprising a plurality of electrostatic lens subunits. The macrocollimator 270 may use a combination of magnetic and electrostatic lenses.

In another arrangement (not shown), the macrocollimator may be partly or wholly replaced by an array of collimator elements arranged downstream of the beam 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, and thus be spatially compact. The array of collimator elements may be a first deflecting or focusing electron optical array element downstream of the beam of source 201 in the beam path. The array of collimator elements may be upstream of the beam of 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. 16, a macro-scanning deflector 265 is provided to scan beamlets over the sample 208. The macro scan deflector 265 deflects a corresponding portion of the beam to scan the beamlets over the sample 208. In one embodiment, the macro-scanning deflector 265 comprises a macro-multipole deflector, e.g., having eight or more poles. Deflection causes beamlets derived from the beam to scan over 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-axis and the Y-axis). The macro-scanning deflector 265 acts macroscopically on all of the beams, rather than comprising an array of deflector elements, each deflector element being configured to act on a different individual portion of the beams. In the illustrated embodiment, a macro-scanning deflector 265 is disposed between the macro-collimator 270 and the control lens array 250.

In another arrangement (not shown), the macro scan deflector 265 may be replaced in part or in whole by an array of scan deflectors. The scan deflector array 260 includes a plurality of scan deflectors. The scanning deflector array 260 may be formed using MEMS fabrication techniques. Each scanning deflector scans a respective beamlet over sample 208. The scan deflector array 260 may thus 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 scan over the sample 208 in one or two directions (i.e., one or two dimensions). The scanning deflector array may be upstream of the beam of the objective lens array 241. The scanning deflector array may be downstream of the beam controlling lens array 250. Although reference is made to a single beamlet associated with a scanning deflector, a group of beamlets may be associated with a scanning polarizer. In one embodiment, the scanning deflector described in EP2425444 may be used to implement a scanning deflector array, which is incorporated herein by reference in its entirety, in particular to scanning deflectors. The scanning deflector array (e.g., formed using MEMS fabrication techniques as described above) may be more spatially compact than the macroscopic scanning deflector. The scan deflector array may be in the same module as the objective lens array 241.

In other embodiments, both 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, preferably synchronously, the macro-scanning deflector together with the scanning deflector array 260.

The objective lens array component may also comprise a collimator array and/or a scanning deflector array.

The present invention may be applied to a variety of different tool architectures. For example, the electron beam tool 40 may be a single beam tool, or may include a plurality of single beam columns or may include a plurality of multi beam columns. The column may comprise a charged particle optical device as described in any of the above embodiments or aspects. As a plurality of columns (or multi-column tool), the apparatus may be arranged in an array of a number of two columns to one hundred columns or more. The charged particle device may take the form of the embodiment as described with respect to fig. 3 and shown in fig. 3, or the embodiment as described with respect to fig. 16 and shown in fig. 16, although preferably having an array of electrostatic scanning deflectors and an array of electrostatic collimators. The charged particle optical device may be a charged particle optical column. The charged particle column may optionally include a source.

The assessment tool according to an embodiment of the present invention may be a tool that performs a qualitative assessment (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 a map image of a sample. Examples of evaluation tools 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 subway inspection tool). The electron optical column 40 may be a component of an evaluation tool; such as an inspection tool or a metro inspection tool or a part of an electron beam lithography tool. Any reference herein to a tool is intended to encompass a device, apparatus or system that includes various components, which may or may not be collocated, and which may even be located in a separate room, particularly for example, a data processing element.

References to a component or system of components or elements that are controllable to manipulate a charged particle beam in some 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 above, 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 components in a non-limiting list comprising control lens array 250, objective lens array 241, converging lens 231, corrector, collimating element array 271, and scanning deflector array 260. An actuatable component, such as a stage, may be controllable to control actuation of the component, using one or more controllers, control systems or control units, to actuate and thus move relative to another component, such as a beam path.

The 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 path. Such electron optical elements may be electrostatic. In one embodiment, all electron optical elements (e.g., the last electron optical element in the beamlet 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).

A system or apparatus of such architecture as at least shown in fig. 3 and 16 and described above may include components such as an upper beam limiter 252, an array of collimator elements 271, a control lens array 250, a scanning deflector array 260, an objective lens array 241, a beam shaping limiter 242, and/or a detector array 240; one or more of these elements present may be connected to one or more adjacent elements by an isolating element such as a ceramic or glass spacer.

The present invention may be embodied as a computer program. For example, the computer program may include instructions for instructing the controller 50 to perform the following steps. The controller 50 controls the electron beam device to project an electron beam toward the sample 208. In one embodiment, the controller 50 controls at least one electron optical element (e.g., a plurality of deflectors or an array of scanning deflectors 260, 265) to operate on the electron beam in the electron beam path. Additionally or alternatively, in one embodiment, the controller 50 controls at least one electron optical element (e.g., the detector array 240) to operate on an electron beam emitted from the sample 208 in response to the electron beam.

References to upper and lower, above and below should be understood to refer to directions parallel (typically but not always perpendicular) to the beam upstream and beam downstream directions of the electron beam or beams impinging on the sample 208. Thus, references to beam upstream and beam downstream are intended to refer to the direction of the beam path independent of any current gravitational field. The beam is directed upstream toward the light source and the beam is directed downstream toward the sample.

In one embodiment, a method of projecting a plurality of charged particle beams (e.g., beamlets) onto the sample 208 is provided to generate a greater proportion of backscattered charged particles in the charged particles emitted from the sample 208. As described above, this facilitates acquisition of information that can only be acquired from the backscattered signal.

The method includes projecting a charged particle beam onto a surface of the sample 208, including accelerating the charged particle beam in an objective lens array 241. As described above, the acceleration may be performed by providing electrodes (e.g., the first electrode 242 and the second electrode 243) through which the charged particle beam travels, and the electrodes have a potential for accelerating the charged particle beam. Preferably, the method includes providing a plurality of objectives (e.g., objective lens array 241); projecting a charged particle beam onto a surface of the sample 208 using a plurality of objective lenses; a plurality of objective lenses are used to accelerate the charged particle beam onto the sample 208 and to detect charged particles emitted from the sample.

Additionally or alternatively, the method includes repelling secondary charged particles emitted from the sample. Preferably, the method includes providing a plurality of objectives (such as an objective array 241); projecting a charged particle beam onto a surface of the sample 208 using a plurality of objective lenses; using the device to repel secondary charged particles emitted from the sample 208; and detecting charged particles emitted from the sample.

In one embodiment, a method is provided that includes directing an array of charged particle beams to a sample surface and directly detecting backscattered charged particles from the surface. The method may further comprise repelling the secondary charged particles from the surface of the sample.

In one embodiment, a method of selectively detecting secondary charged particles and backscattered charged particles emitted from a sample 208 is provided. The method includes selecting an operational mode of the detector between: for detecting a backscatter mode of more backscatter charged particles than secondary charged particles; and a secondary mode for detecting more secondary charged particles than the back-scattered charged particles. The detection of back-scattered charged particles may be optimized in the back-scattering mode, while the detection of secondary charged particles may be optimized in the secondary mode. The method further includes projecting a plurality of charged particle beams (e.g., beamlets 211, 212, 213) onto a surface of the sample 208 and detecting charged particles emitted from the sample 208 in a selected mode of operation. Preferably, the method includes providing a plurality of objectives (such as an objective lens array 241) and at least one sensor, and projecting the charged particle beam onto the surface of the sample 208 using the plurality of objectives. In a first operating state the method comprises detecting more secondary charged particles than secondary charged particles and in a second operating state the method comprises detecting more back-scattered charged particles than secondary charged particles. Optionally, the method further comprises accelerating the charged particle beam in the objective lens array in a backscatter mode and/or decelerating the charged particle beam in the objective lens array in a secondary mode.

In one embodiment, a method of simultaneously detecting secondary charged particles and backscattered charged particles emitted from a sample is provided. The method comprises providing a detector array comprising at least two detection portions configured to detect signal particles from the sample simultaneously, wherein one of the detection portions is configured to detect more backscattered charged particles than secondary charged particles and the other detection portion is configured to detect more secondary charged particles than backscattered charged particles. The method includes projecting a charged particle beam toward a sample. The method further includes capturing charged particles emitted from the sample so as to detect primarily secondary charged particles at one detection portion and primarily backscattered charged particles at another detection portion.

In one embodiment, a method of detecting secondary charged particles and backscattered charged particles emitted from the sample 208 is provided. The method includes selecting an operating mode of the detector between a backscatter mode for detecting more backscatter charged particles than secondary charged particles and a secondary mode for detecting more secondary charged particles than secondary charged particles. The method includes capturing charged particles emitted from the sample 208 to detect the charged particles in a selected mode. Preferably, the method comprises: at least one sensor configured to capture charged particles emitted from the sample 208 is provided. The method comprises in a first operating state detecting more secondary charged particles than secondary charged particles and in a second operating state detecting more back-scattered charged particles than secondary charged particles.

Preferably, the previous method further comprises repelling the secondary charged particles emitted from the sample 208. As described above, the repulsion may be performed by controlling the potential of the electrodes in the objective lens array 241 and the potential of the sample.

In one embodiment, a method of operating a charged particle evaluation tool for detecting backscatter charged particles is provided, the method comprising: projecting a plurality of beams of charged particles towards a sample surface; charged particles having energies less than a threshold value emitted (i.e., radiated) from the sample in response to the multiple beams are repelled. The method includes detecting charged particles emitted from the sample and having an energy of at least a threshold using a detector array 240 positioned near the sample 208. Preferably, the threshold exceeds the energy of the secondary charged particles emitted from the sample. Preferably, the projection comprises accelerating the plurality of charged particles towards the sample 208, preferably in the objective lens array 241. Preferably, the repeller uses an electrode of the objective lens.

Preferably, the methods described herein further comprise providing an intermediate focus 236 between the respective control lens and the corresponding objective lens.

In either method, more backscattered charged particles than secondary charged particles may be detected in the detection. Thus, as described above, these methods can be used to primarily detect backscatter charged particles.

The terms "beamlet" and "beamlet" are used interchangeably herein and are understood to encompass any radiation beam derived from a parent radiation beam by dividing or splitting the parent radiation beam. The term "manipulator" is used to encompass any element affecting the beamlets or the paths of the beamlets, such as lenses or deflectors. References to elements aligned along a beam path or a beamlet path are understood to mean that the corresponding element is positioned along the beam path or beamlet path. References to optical devices refer to electro-optical devices.

The charged particle optical device may be a negatively charged particle device. Charged particle optical devices may be otherwise referred to as electron optical devices. It should be understood that electrons are specific charged particles and that all examples of charged particles mentioned throughout the application may be appropriately substituted. For example, the source may provide electrons exclusively. The charged particles mentioned throughout the specification may in particular be negatively charged particles.

The charged particle optical device may be more specifically defined as a charged particle optical column. In other words, the device may be provided as a column. Thus, the column may comprise an objective lens array component as described above. Thus, the column may comprise a charged particle optical system as described above, for example comprising an objective lens array and optionally a detector array and/or optionally a converging lens array.

The charged particle optical device comprises at least an objective lens array 240. The charged particle optical device may comprise a detector array 241. The charged particle optical device may comprise a control lens array 250. Accordingly, a charged particle optical device comprising an objective lens array and a detector array may be interchangeable with and referred to as an objective lens array component, which may optionally comprise a control lens array 250. The charged particle optical device may comprise additional components described in relation to any of fig. 3 and/or 16. Accordingly, the charged particle optical apparatus may be interchanged with the charged particle evaluation tool 40 and/or the electron optical system, and may be referred to as the charged particle evaluation tool 40 and/or the electron optical system (if additional components in these figures are included).

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.

An insulating structure is described with respect to the adjacent electrodes above. In some cases, the insulating structure is described in particular with respect to the first electrode and/or the second electrode. The insulating structure may be applied to any adjacent electrode and references to the first and second electrodes may be replaced with other electrodes. If more than two electrodes are provided, a plurality of insulating structures may be provided. For example, a series of insulating structures may be present.

Any element or collection of elements within the electron beam tool 40 may be replaceable or field replaceable. One or more of the electron optical components in the electron beam tool 40, particularly those that operate on or generate beamlets, such as an aperture array and a manipulator array, may include one or more MEMS.

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.

In one arrangement, there is provided: clause 1: a charged particle optical apparatus for a charged particle evaluation tool, the apparatus being configured to project a plurality of beams of charged particles along a beamlet path towards a sample, the plurality of beams comprising beamlets, the apparatus comprising: an array of objective lenses configured to project an array of charged particle beamlets onto the sample, desirably the array of objective lenses is arranged to span the beamlet paths of the array of charged particle beamlets, desirably the array of objective lenses is arranged to correspond to the beamlet paths of the array of charged particle beamlets, desirably each objective lens corresponds to a beamlet of the array of charged particle beamlets; and a detector array configured to be located in proximity to the sample and configured to capture charged particles emitted from the sample, desirably the detector array is arranged to span the beamlet path of the array of charged particle beamlets, desirably the detector array is arranged to correspond to the beamlet path of the array of charged particle beamlets, desirably each detector of the detector array corresponds to a beamlet of the array of charged particle beamlets, desirably the detector array is configured to be expected to face the sample during operation, desirably the detector array is a beam downstream-most component of the apparatus, wherein the charged particle optical device is configured to repel secondary charged particles emitted from the sample away from the detector.

Clause 2: a charged particle optical apparatus for a charged particle system, the apparatus being configured to project an array of charged particle beams towards a sample, the apparatus comprising: an objective lens array configured to project the beam onto the sample and repel secondary charged particles emitted from the sample; and a detector array positioned adjacent to the sample to detect backscatter particles from the sample.

Clause 3: the charged particle optical apparatus of clause 1 or 2, wherein the objective lens is configured to accelerate the charged particle beamlets along the beamlet path.

Clause 4: a charged particle optical apparatus for a charged particle evaluation tool, the apparatus being configured to project a plurality of beams of charged particles along a beamlet path towards a sample, the plurality of beams comprising beamlets, the apparatus comprising: an objective lens array configured to project an array of charged particle beamlets onto the sample, wherein desirably the objective lens array comprises at least two electrodes having an array of apertures defined therein, desirably corresponding apertures of the array of apertures in the at least two electrodes are each aligned with and arranged along a beamlet path of the array of charged particle beamlets; and a detector array configured to be positioned near a sample and configured to capture charged particles emitted from the sample, wherein the objective lens is configured to accelerate the charged particle beamlets along the beamlet path.

Clause 5: a charged particle optical apparatus for a charged particle system, the apparatus being configured to project an array of charged particle beams towards a sample, the apparatus comprising: an objective lens array configured to project the beam onto the sample and accelerate the charged particles toward the sample; and a detector array positioned adjacent to the sample to detect backscatter particles from the sample.

Clause 6: the charged particle optical apparatus of clause 4 or 5, wherein the charged particle optical apparatus is configured to repel secondary charged particles emitted from the sample away from the detector.

Clause 7: a charged particle optical apparatus according to any preceding clause, wherein the detector array is configured to have an electrical potential in use and the sample is configured to have an electrical potential in use, wherein the electrical potential of the sample is more positive than the electrical potential of the detector array.

Clause 8: the charged particle optical apparatus of clause 7, wherein the potential difference between the potential of the sample and the potential of the detector array is greater than a secondary electron threshold.

Clause 9: a charged particle optical apparatus according to any preceding clause, wherein the objective lens array comprises at least two electrodes in which an array of apertures is defined, corresponding apertures in the at least two electrodes being aligned with and arranged along the beamlet path, desirably the detector array can be provided on or adjacent to or integrated into one of the at least two electrodes.

Clause 10: the charged particle optical apparatus of clause 9, wherein a first electrode of the at least two electrodes is located upstream of the beam of a second electrode of the at least two electrodes, the first electrode being configured to have a first electrode potential in use and the second electrode being configured to have a second electrode potential in use, wherein the second electrode potential is more positive than the first electrode potential, desirably the detector array is positioned on, or in, or integrated into the second electrode, desirably the detector array is positioned on, or in, or integrated into the beam-most downstream electrode of the at least two electrodes.

Clause 11: the charged particle optical apparatus of clause 10, wherein the sample is configured to be at an electrical potential in use, wherein the electrical potential of the sample is more positive than the second electrode potential.

Clause 12: the charged particle optical apparatus of clause 11, wherein the potential of the sample is about +20kV to +100kV relative to the source of the charged particle beam, and preferably the potential of the sample is about +20kV to +70kV.

Clause 13: charged particle optical apparatus according to any of clauses 10-12, wherein the first electrode potential is between about +3kV to +8kV relative to the source of the charged particle beam, and preferably the first electrode potential is about +5kV.

Clause 14: charged particle optical apparatus according to any of clauses 10-13, wherein the second electrode potential is about +20kV to +100kV relative to the source of the charged particle beam, and preferably the second electrode potential is about +20kV to +70kV.

Clause 15: the charged particle optical apparatus of any of clauses 9-14, wherein the diameter of the aperture in at least one electrode is between about 30 μιη and 300 μιη.

Clause 16: charged particle optical apparatus according to any of clauses 9-15, wherein the pitch between adjacent apertures in at least one electrode is between about 50 μm and 500 μm.

Clause 17: the charged particle optical apparatus of any of clauses 9-16, further comprising an insulating structure separating adjacent electrodes, the insulating structure comprising a body having a first face and a second face opposite the first face, and a protrusion radially inward from the body, wherein one of the electrodes contacts the body and the protrusion on the first face of the insulating structure and the body contacts the other of the electrodes on the second face of the insulating structure and a gap is defined between the protrusion and the other of the electrodes.

Clause 18: a charged particle optical apparatus according to any preceding clause, further comprising an array of control lenses positioned upstream of the beams of the array of objective lenses, wherein each control lens is associated with a respective objective lens; desirably, the control lens array is arranged to correspond to the objective lens array, desirably the control lens array is arranged across the beamlet paths of the array of charged particle beamlets, desirably the control lens array corresponds to a beamlet path array of the array of charged particle beamlets, desirably each control lens is associated with a respective beamlet path of the array of charged particle beamlets.

Clause 19: the charged particle optical apparatus of clause 18, wherein the control lens array is configured to provide an intermediate focus between the respective control lens and the corresponding objective lens.

Clause 20: the charged particle optical apparatus of any of clauses 18 or 19, wherein the control lens array is configured to decelerate the charged particle beamlets along the beamlet path.

Clause 21: the charged particle optical apparatus of any preceding clause, wherein the detector array is configured to detect more backscattered charged particles than secondary charged particles.

Clause 22: the charged particle optical apparatus of any preceding clause, wherein the detector array is positioned between about 10 μιη to 50 μιη of the sample.

Clause 23: a charged particle optical apparatus according to any preceding clause, further comprising a power supply configured to apply, in use, an electrical potential to at least one electrode of the objective lens array and/or the sample.

Clause 24: an objective lens component for projecting a plurality of beams of charged particles towards a sample surface, the objective lens component comprising: an objective lens array comprising at least two electrodes arranged along a path of the plurality of bundles and having a plurality of apertures defined therein, desirably, a corresponding aperture of the plurality of apertures in each of the at least two electrodes is aligned with and arranged along a beamlet path of the plurality of bundles; and a detector array configured to detect charged particles emitted from the sample in response to the plurality of beams, wherein: the detector array is configured to be positionable in proximity to the sample and is configured to repel secondary electrons emitted from the sample away from the detector.

Clause 25: the objective lens component of clause 24, wherein the sample is set to a sample potential and the detector array is set to a detector array potential, and a potential difference between the sample potential and the detector array potential is greater than a secondary electron threshold.

Clause 26: the objective lens component of clause 25, wherein the secondary electron threshold is a potential difference equivalent to a possible electron energy of secondary electrons emitted from the sample.

Clause 27: the objective lens component of any one of clauses 24-26, wherein the detector array is configured to detect more backscattered electrons than secondary electrons.

Clause 28: a charged particle optical apparatus for a multi-beam charged particle evaluation tool, the apparatus being configured to project a plurality of beams of charged particles along a beamlet path towards a sample, the plurality comprising beamlets, the apparatus comprising: an objective lens array configured to project an array of charged particle beamlets onto the sample; and a detector array configured to capture charged particles emitted from the sample, wherein the device is configured to switch between two operating states, wherein in a first operating state the detector array is configured to detect more secondary charged particles than secondary charged particles, and in a second operating state the detector array is configured to detect more back-scattered charged particles than secondary charged particles.

Clause 29: a charged particle optical apparatus for a charged particle system, the apparatus being configured to project an array of charged particle beams towards a sample, the apparatus comprising: an objective lens array configured to project the beam onto the sample; and a detector array configured to detect back-scattered particles from the sample, wherein the device is configured to switch between two operating states, wherein in a first operating state the detector array is configured to detect more secondary charged particles than back-scattered charged particles, and in a second operating state the detector array is configured to detect more back-scattered charged particles than secondary charged particles.

Clause 30: the charged particle optical apparatus of clause 28 or 29, wherein in the first operating state the objective lens is configured to decelerate the charged particle beam onto the sample, and in the second operating state the objective lens is configured to accelerate the charged particle beam onto the sample.

Clause 31: the charged particle optical apparatus of any of clauses 24, 29, or 30, wherein the objective lens array is configured to maintain the charged particle beamlets focused on the sample in the first and second operating states.

Clause 32: charged particle optical apparatus according to any of clauses 28-31, wherein the objective lens array comprises a first electrode configured to have a first electrode potential, and a second electrode configured to have a second electrode potential, the first electrode being located upstream of the beam of the second electrode.

Clause 33: the charged particle optical apparatus of clause 32, wherein in the first operating state, the first electrode potential is more positive than the second electrode potential.

Clause 34: a charged particle optical apparatus according to any of clauses 32 or 33, wherein in the second operating state the second electrode potential is more positive than the first electrode potential.

Clause 35: the charged particle optical apparatus of any of clauses 32-34, wherein at least the first electrode potential is adjusted between the first and second operating states to maintain the primary beam focused on the sample in the first and second operating states.

Clause 36: charged particle optical apparatus according to any of clauses 32-35, wherein adjacent electrodes are separated by an insulating structure configured for use in the first and second operating states, preferably wherein the objective lens array comprises the insulating structure

Clause 37: the charged particle optical apparatus of clause 36, wherein the insulating structure is formed from a body having a first face and a second face, the first face being opposite the second face, and a protrusion radially inward from the body, wherein: on the first face of the insulating structure, the main body contacts one of the electrodes with a first gap formed between the protrusion and the one of the electrodes, and on the second face of the insulating structure, the main body contacts the other of the electrodes with a second gap formed between the protrusion and the other of the electrodes.

Clause 38: a charged particle optical apparatus according to any of clauses 32-31, further comprising a power supply configured to apply the first electrode potential to the first electrode and/or the second electrode potential to the second electrode.

Clause 39: the charged particle optical apparatus of any of clauses 28-38, wherein the detector array is configured to be positioned near the sample.

Clause 40: the charged particle optical apparatus of any of clauses 28-39, wherein the apparatus is configured to maintain a distance between the detector array and the sample between the first and second operating states, and vice versa.

Clause 41: the charged particle optical apparatus of any of clauses 28-40, wherein the apparatus is configured to change the distance between the detector array 240 and the sample 208 such that the secondary charged particles are focused on the detector array 240 when in the first operating state and the backscattered charged particles are focused on the detector array 240 when in the second operating state.

Clause 42: charged particle optical apparatus according to any of clauses 28-41, wherein the apparatus is configured to change the distance between the objective lens array and the sample, and vice versa, when switching between the first and second operating states, in use.

Clause 43: the charged particle optical apparatus of clause 42, wherein the apparatus is configured to reduce the distance between the objective lens array and the sample when switching to the second operating state.

Clause 44: the charged particle optical apparatus of clause 42 or clause 43, wherein the apparatus is configured to increase the distance between the objective lens array and the sample when switching to the first operating state.

Clause 45: charged particle optical apparatus according to any of clauses 42-44, wherein the apparatus is configured to move the objective lens array and/or the sample relative to each other along the beamlet path in order to switch between the first and second operating states.

Clause 46: the charged particle optical apparatus of any of clauses 42-45, further comprising an actuator configured to move the objective lens array to change a distance between the objective lens array and the sample.

Clause 47: a charged particle optical apparatus according to any of clauses 42-46, wherein the apparatus is configured to move the sample to change the distance between the objective lens array and the sample.

Clause 48: charged particle optical apparatus according to any of clauses 42-47, wherein the objective lens array is configured as part of a switchable module, different modules having objective lens arrays at different distances from the sample along the beamlet path.

Clause 49: charged particle optical apparatus according to any of clauses 28-48, wherein the apparatus is configured to continuously switch the apparatus between the first and second operating states.

Clause 50: the charged particle optical apparatus of clause 49, wherein the switching comprises turning on and off a repulsive potential, such that when the repulsive is on, is configured to repel secondary charged particles.

Clause 51: the charged particle optical apparatus of clause 49 or 50, wherein the continuous switching between the first and second operating states provides substantially simultaneous detection of backscattered charged particles and secondary charged particles.

Clause 52: charged particle optical apparatus according to any of clauses 49-51, wherein the apparatus switches between the first and second operating states at least once every few seconds, or at least once every second, or at least once every 100ms, or at least once every 10ms, or vice versa.

Clause 53: charged particle optical apparatus according to any of clauses 49-52, wherein landing energies in the first and second operating states are substantially the same and/or substantially maintained.

Clause 54: a detector for a charged particle evaluation tool, wherein the detector is configured to capture charged particles emitted from a sample, and wherein the detector is configured to switch between two operating states, wherein in a first operating state at least one detector is configured to detect more secondary charged particles than secondary charged particles and in a second operating state at least one detector is configured to detect more back-scattered charged particles than secondary charged particles.

Clause 55: a detector for a charged particle evaluation tool, wherein the detector is configured to capture charged particles emitted from a sample and the detector comprises an inner detection portion surrounding an aperture; and an outer detection portion radially outward from the inner detection portion, wherein the detector is configured to switch between two operating states, the two states respectively using different configurations of the detection portion.

Clause 56: the detector of clauses 54 or 55, wherein an aperture is defined and configured for passing a charged particle beam, the detector comprising: an internal detection portion surrounding the aperture; and an outer detection portion radially outward from the inner detection portion.

Clause 57: the detector of clause 56, wherein in the first operating state, the detector uses the inner detection portion instead of the outer detection portion.

Clause 58: the detector of any of clauses 56 or 57, wherein in the second operating state, the detector uses at least the external detection portion.

Item 59: the detector of any one of clauses 54 to 58, wherein the diameter of the first detection portion is about 40-60 μm and/or the diameter of the second detection portion is about 150 μm to 250 μm.

Clause 60: a detector array for a charged particle evaluation tool configured to: operating in a backscatter operating state to preferentially detect backscatter charged particles; and operating in a secondary charged particle state to preferentially detect secondary charged particles, the detector array comprising a detector array according to any of clauses 54-59.

Clause 61: a charged particle optical apparatus for a multi-beam charged particle evaluation tool, comprising: an objective lens array; and a detector array comprising the detector array of any of clauses 54-59, wherein apertures in the electrodes of the detector array and the objective lens array are arranged on a beamlet path of the charged particle beam.

Clause 62: a charged particle optical apparatus for a multi-charged particle beam evaluation tool, the apparatus being configured to project a charged particle beam along a primary beam path towards a sample, the apparatus comprising: an objective lens array configured to project an array of charged particle beamlets onto the sample; and a detector array associated with the objective lens array and comprising at least two detection portions configured to detect charged particles from the sample simultaneously, wherein one of the detection portions is configured to detect more backscattered charged particles than secondary charged particles and the other detection portion is configured to detect more secondary charged particles than backscattered charged particles.

Clause 63: the charged particle optical apparatus of any of clauses 62, wherein the one of the detection portions is an outer detection portion and the other detection portion is an inner detection portion surrounding an aperture for passage of a charged particle beam, the inner detection portion being radially inward from the outer detection portion, preferably wherein the inner and outer portions are annular.

Clause 64: the charged particle optical apparatus of clause 62 or 63, wherein the diameter of the inner portion is between about 10 microns and 50 microns.

Clause 65: charged particle optical apparatus according to any of clauses 62-64, wherein an insulating part is provided between the detection parts to prevent signals from passing between the parts.

Clause 66: a charged particle optical apparatus for a multi-charged particle beam evaluation tool, the apparatus being configured to project a charged particle beam along a primary beam path towards a sample, the apparatus comprising: an objective lens array configured to project an array of charged particle beamlets onto the sample; and a detector array associated with the objective lens array, and at least one detector of the detector array comprising at least two detection portions configured to detect signal particles from the sample simultaneously, wherein different detection portions are configured to detect predominantly signal particles of different types from each other.

Clause 67: the charged particle optical apparatus of any of clauses 1-23 or 28-53, wherein the detector array comprises detectors according to any of clauses 54-59.

Clause 68: the objective lens component of any one of clauses 24 to 27, wherein the detector array comprises a detector according to any one of clauses 54 to 59.

Clause 69: a method of projecting a plurality of charged particle beams onto a sample to detect a greater proportion of backscattered charged particles from charged particles emitted from the sample, the method comprising: a) Projecting the charged particle beam onto a surface of the sample; and b) repelling secondary charged particles emitted from the sample.

Clause 70: a method of projecting a plurality of charged particle beams onto a sample to detect a greater proportion of backscattered charged particles from charged particles emitted from the sample, the method comprising: a) Projecting the charged particle beam onto a surface of the sample includes accelerating the charged particle beam in an objective lens array.

Clause 71: a method, comprising: directing an array of charged particle beams onto a sample surface; and directly detecting the backscattered charged particles from the surface.

Clause 72: the method of clause 71, further comprising repelling the secondary charged particles from the sample surface.

Clause 73: a method of selectively detecting secondary charged particles and backscattered charged particles emitted from a sample, the method comprising: a) The mode of operation of the detector is selected between: for detecting a backscatter mode of more backscatter charged particles than secondary charged particles; and a secondary mode for detecting more secondary charged particles than the back-scattered charged particles; b) Projecting a plurality of charged particle beams onto a surface of the sample; and c) detecting charged particles emitted from the sample in the selected mode of operation.

Clause 74: the method of clause 73, further comprising accelerating the charged particle beam in the objective lens array in the backscatter mode and/or decelerating the charged particle beam in the objective lens array in the secondary mode.

Clause 75: a method of detecting secondary charged particles and backscattered charged particles emitted from a sample, the method comprising: a) The mode of operation of the detector is selected between: for detecting a backscatter mode of more backscatter charged particles than secondary charged particles; and a secondary mode for detecting more secondary charged particles than the back-scattered charged particles; b) Charged particles emitted from the sample are captured to detect charged particles in a selected mode.

Clause 76: a method of simultaneously detecting secondary charged particles and backscattered charged particles emitted from a sample, the method comprising: a) Providing an array of detectors, at least one detector of the array comprising at least two detection sections configured to detect charged particles from the sample simultaneously, wherein one of the detection sections is configured to detect more backscattered charged particles than secondary charged particles and the other detection section is configured to detect more secondary charged particles than backscattered charged particles; b) Projecting a charged particle beam towards the sample; c) Charged particles emitted from the sample are captured so that secondary charged particles are detected predominantly at one detection portion and backscattered charged particles are detected predominantly at the other detection portion.

Clause 77: a method of simultaneously detecting different types of signal particles emitted from a sample using an array of detectors, wherein at least one detector of the array comprises at least two detection portions configured to simultaneously detect signal particles from the sample, different detection portions being configured to preferentially detect different types of signal particles, the method comprising: a) Projecting a charged particle beam towards the sample; b) Capturing signal particles emitted from the sample with the detector array, including preferentially detecting different signal particles with different detection moieties.

Clause 78: the method of clause 77, wherein the different signal particles comprise back-scattered charged particles and secondary charged particles

Clause 79: the method of any one of clauses 70 to 76 and 78, further comprising repelling secondary charged particles emitted from the sample.

Clause 80: a method of operating a charged particle evaluation tool for detecting backscatter charged particles, the method comprising: a) Projecting a plurality of beams of charged particles towards a sample surface; desirably, the at least two electrodes of the aperture array in which the objective array is defined are traversed by an array of charged particle beamlets, or desirably, the objective array is traversed by an array of charged particle beamlets that span the objective array, desirably, by controlling the lens array, and then through the objective array, desirably, the objective array comprises at least two electrodes, desirably, the aperture array is defined in the at least two electrodes; desirably, the corresponding apertures of the aperture array in the at least two electrodes are aligned with beamlets of the array of charged particle beamlets, desirably the beamlets pass through the corresponding apertures of the aperture array in a different one of the at least two electrodes; b) Rejecting charged particles having less than a threshold energy emitted from the sample in response to the plurality of beams; and c) detecting charged particles emitted from the sample having an energy of at least a threshold using a detector array positioned in proximity to the sample.

Clause 81: the method of clause 80, wherein the threshold exceeds the energy of the secondary charged particles emanating from the sample.

Clause 82: the method of clause 80 or 81, wherein the projecting comprises accelerating the multiple beams of charged particles toward the sample, the accelerating preferably being performed in the objective lens array.

Clause 83: the method of any one of clauses 80 to 82, wherein the rejecting uses at least the detector array.

Clause 84: the method of any one of clauses 69 to 83, further comprising providing an intermediate focus between the respective control lens and the corresponding objective lens.

Clause 85: the method of any one of clauses 69 to 84, wherein in the detecting, more backscattered charged particles than secondary charged particles are detected.

Clause 86: a method of detecting backscatter charged particles, the method comprising using a multi-beam charged particle evaluation tool comprising a charged particle optical apparatus according to any one of clauses 1 to 23, 28 to 53 and 61 to 67, or an objective lens component according to any one of clauses 24 to 27 and 68.

Claims

1. A charged particle optical apparatus for a charged particle evaluation tool, the apparatus being configured to project a plurality of beams of charged particles along a beamlet path towards a sample, the plurality of beams comprising beamlets, the apparatus comprising:

An array of objective lenses configured to project an array of charged particle beamlets onto the sample, wherein the array of objective lenses is arranged across the beamlet paths of the array of charged particle beamlets;

an array of control lenses positioned upstream of the array of objectives, wherein each control lens is associated with a respective objective; and

an array of detectors configured to be positioned in proximity to the sample and configured to capture charged particles emitted from the sample,

wherein the charged particle optical device is configured to repel secondary charged particles emitted from the sample away from the detector.

2. The charged particle optical device according to claim 1, wherein the objective lens is configured to accelerate the charged particle beamlets along the beamlet path.

3. A charged particle optical apparatus according to any preceding claim, wherein the array of detectors is configured to have an electrical potential in use and the sample is configured to have an electrical potential in use, wherein the electrical potential of the sample is more positive than the electrical potential of the array of detectors.

4. A charged particle optical apparatus according to claim 3 wherein the potential difference between the potential of the sample and the potential of the array of detectors is greater than a secondary electron threshold.

5. Charged particle optical apparatus according to any preceding claim, wherein the array of objective lenses comprises at least two electrodes in which an array of apertures is defined, corresponding apertures of the at least two electrodes being aligned with and arranged along a beamlet path, desirably the array of detectors can be provided on or adjacent to or integrated into one of the at least two electrodes.

6. Charged particle optical device according to claim 5, wherein a first electrode of the at least two electrodes is located upstream of the beam of a second electrode of the at least two electrodes, the first electrode being configured to have a first electrode potential in use and the second electrode being configured to have a second electrode potential in use, wherein the second electrode potential is more positive than the first electrode potential, desirably the array of detectors is located on, or in, or integrated into the second electrode, desirably the array of detectors is located on, or in, or integrated into the beam-most downstream electrode of the at least two electrodes.

7. A charged particle optical apparatus according to claim 6, wherein the sample is configured to be at an electrical potential in use, wherein the electrical potential of the sample is more positive than the second electrode potential.

8. A charged particle optical device according to any one of claims 5 to 7, further comprising an insulating structure separating adjacent electrodes, the insulating structure comprising a body having a first face and a second face opposite the first face, and a protrusion radially inwards from the body, wherein one of the electrodes contacts the body and the protrusion on the first face of the insulating structure and the body contacts the other of the electrodes on the second face of the insulating structure and a gap is defined between the protrusion and the other of the electrodes.

9. A charged particle optical apparatus according to any preceding claim, wherein the array of control lenses is configured to provide an intermediate focus between the respective control lenses and the corresponding objective lens.

10. A charged particle optical apparatus according to any preceding claim, wherein the array of control lenses is configured to decelerate the charged particle beamlets along the beamlet path.

11. A charged particle optical apparatus according to any preceding claim, wherein the array of detectors is configured to detect more backscattered charged particles than secondary charged particles.

12. A charged particle optical apparatus according to any preceding claim, wherein the array of detectors is positioned between about 10 μm and 50 μm of the sample.

13. A charged particle optical device according to any preceding claim, further comprising a power supply configured to apply, in use, an electrical potential to at least one electrode of the array of objective lenses and/or the sample.

14. A method of operating a charged particle evaluation tool for detecting backscatter charged particles, the method comprising:

a) Passing a plurality of beams of charged particles through a control lens array and then projecting toward a surface of a sample through an objective lens array with an array of charged particle beamlets that span the objective lens array;

b) Rejecting charged particles having an energy less than a threshold value emitted from the sample in response to the plurality of beams; and

c) Charged particles emitted from the sample having an energy of at least the threshold are detected using a detector array positioned near the sample.

15. The method of claim 14, wherein the rejecting uses at least the detector array.