Charged particle evaluation tool and inspection method

Abstract

To support improvement of throughput or other characteristics of a charged particle evaluation tool.SOLUTION: A charged particle evaluation tool including an objective lens configured to project a plurality of charged particle beams onto a sample, the objective lens having a sample-facing surface defining a plurality of beam apertures through which respective ones of the charged particle beams are emitted toward the sample, and a plurality of trapping electrodes adjacent respective ones of the beam apertures and configured to trap charged particles emitted from the sample.SELECTED DRAWING: Figure 4

Description

[Technical Field]

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims priority to European Patent Application No. 20150394.3, filed January 6, 2020, European Patent Application No. 20184160.8, filed July 6, 2020, and European Patent Application No. 20198201.4, filed September 24, 2020. Each of these patent applications is incorporated herein by reference in its entirety.

[0002] FIELD OF THE INVENTION

[0002] Embodiments provided herein relate generally to charged particle evaluation tools and inspection methods, and more particularly to charged particle evaluation tools and inspection methods that use multiple charged particle sub-beams. [Background technology]

[0003]

[0003] When manufacturing semiconductor integrated circuit (IC) chips, undesired pattern defects inevitably occur on substrates (i.e., wafers) or masks during the fabrication process, for example, as a result of 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.

[0004]

[0004] Pattern inspection tools using 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 microscopes (SEMs). In an SEM, a primary electron beam of relatively high-energy electrons is targeted with a final deceleration step to land on a sample with a relatively low landing energy. The electron beam is focused as a probing spot on the sample. Interaction of the landing electrons from the electron beam with material structures at the probing spot causes electrons, such as secondary electrons, backscattered electrons, or Auger electrons, to be emitted from the surface. The generated secondary electrons can be emitted from the material structures of the sample. By scanning the primary electron beam as a probing spot across the sample surface, secondary electrons can be emitted across the surface of the sample. By collecting these emitted secondary electrons from the sample surface, the pattern inspection tool can obtain an image representative of the material structure characteristics of the surface of the sample.

[0005]

[0005] There is a general need to improve the throughput and other characteristics of charged particle inspection tools. Summary of the Invention

[0006]

[0006] It is an object of the present disclosure to provide embodiments that assist in improving the throughput or other characteristics of charged particle characterization tools.

[0007] According to a first aspect of the present invention, an objective lens configured to project the plurality of charged particle beams onto the sample, the objective lens defining a plurality of beam apertures through which each of the charged particle beams can propagate towards the sample; a plurality of sensor units adjacent to respective ones of the beam apertures and configured to capture charged particles emitted from the sample; A charged particle characterization tool is provided, including:

[0008] According to a second aspect of the present invention, there is provided a method of manufacturing an assessment tool, comprising the steps of: forming a plurality of sensor units on a substrate and a plurality of apertures in the substrate; mounting the substrate on an objective lens configured to project a plurality of charged particle beams onto a sample such that the plurality of charged particle beams can be emitted through an aperture; A method is provided that includes:

[0009] According to a third aspect of the present invention, directing a plurality of charged particle beams toward a sample through a plurality of beam apertures; capturing charged particles emitted by the sample in response to the charged particle beam using a plurality of sensor units disposed adjacent to each of the beam apertures; An inspection method is provided, comprising:

[0010] According to a fourth aspect of the present invention, there is provided a multi-beam electron optical system including a last electron optical element in a multi-beam path of the multi-beam electron optical system, the last electron optical element comprising: a multi-manipulator array, each array element configured to manipulate at least one electron beam in multiple beam paths; a detector configured and oriented to detect electrons emitted from a sample positioned in the multi-beam beam path, the detector including a plurality of sensor units integrated into a multi-manipulator array, with at least one sensor unit associated with each array element; A multi-beam electron optical system is provided, including:

[0011] According to a fourth aspect of the present invention, there is provided a final electron optical element of a multi-charged beam projection system configured to project a plurality of charged particle beams onto a sample, comprising: an objective lens having a sample-facing surface defining a plurality of beam apertures through which each of the charged particle beams can propagate toward the sample; a plurality of sensor units adjacent to respective ones of the beam apertures and configured to capture charged particles emitted from the sample; A final electronic optical element is provided, including:

[0012]

[0012] Other advantages of the present invention will become apparent from the following description, taken in conjunction with the accompanying drawings, in which are set forth, by way of illustration and example, certain embodiments of the invention.

[0013]

[0013] The above and other aspects of the present disclosure will become more apparent from the description of exemplary embodiments taken in conjunction with the accompanying drawings. [Brief explanation of the drawings]

[0014] [Figure 1] FIG. 1 is a schematic diagram illustrating an exemplary charged particle beam inspection apparatus. [Figure 2]

[0015] 2 is a schematic diagram illustrating an example multi-beam device that is part of the example charged particle beam inspection system of FIG. 1. [Figure 3]

[0016] 2 is a schematic diagram of an exemplary multi-beam apparatus illustrating an exemplary configuration of a source conversion unit of the exemplary charged particle beam inspection apparatus of FIG. 1. [Figure 4]

[0017] 1 is a schematic cross-sectional view of an objective lens of an inspection apparatus, according to an embodiment. [Figure 5]

[0018] FIG. 5 is a bottom view of the objective lens of FIG. [Figure 6]

[0019] FIG. 5 is a bottom view of a modification of the objective lens of FIG. 4. [Figure 7]

[0020] FIG. 5 is an enlarged schematic cross-sectional view of a detector incorporated in the objective lens of FIG. 4. [Figure 8]

[0021] FIG. 1 is a schematic diagram of a theoretical transimpedance amplifier. [Figure 9]

[0022] FIG. 1 is a schematic diagram of a transimpedance amplifier illustrating the effects of thermal noise. [Figure 10]

[0023] 2 is a schematic diagram illustrating another exemplary multi-beam device that may be part of the exemplary charged particle beam inspection apparatus of FIG. 1. [Figure 11]

[0024] FIG. 1 is a schematic diagram illustrating another exemplary multi-beam device, according to an embodiment. [Figure 12]

[0025] FIG. 2 is a schematic diagram of another exemplary multi-beam device, according to an embodiment. [Figure 13]

[0026] 1 is a schematic cross-sectional view of an objective lens of an inspection apparatus, according to an embodiment. [Figure 14]

[0027] FIG. 14 is a bottom view of a detector unit incorporated into the objective lens of FIG. 13. [Figure 15]

[0028] FIG. 1 is a schematic diagram illustrating another exemplary multi-beam device, according to an embodiment. [Figure 16]

[0029] 16A-16C are enlarged schematic cross-sectional views of a detector incorporated into the objective lens of the apparatus of FIG. 15, with the detector in different positions. [Figure 17]

[0030] FIG. 16 is an enlarged schematic cross-sectional view of an alternative detector that can be used in the objective of the apparatus of FIG. 15. DETAILED DESCRIPTION OF THE INVENTION

[0015]

[0031] 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 like numbers in different drawings represent the same or similar elements unless otherwise indicated. The implementations described in the following description of exemplary embodiments do not represent all implementations consistent with the present invention. Instead, the implementations are merely examples of apparatus and methods consistent with aspects related to the present invention, as set forth in the appended claims.

[0016]

[0032] Increased computing power in electronic devices, which reduces the physical size of devices, can be achieved by significantly increasing the packing density of circuit components such as transistors, capacitors, and diodes on IC chips. This has been made possible by improvements in resolution, which allow for the creation of even smaller structures. For example, an IC chip in a smartphone the size of a thumbnail and available before 2019 can contain over 2 billion transistors, each less than 1 / 1000 the size of a human hair. Therefore, it is not surprising that semiconductor IC manufacturing is a complex and time-consuming process with hundreds of individual steps. An error in even a single step can dramatically affect the functionality of the final product. Just one "killer defect" can cause device failure. The goal of a manufacturing process is to improve the overall yield of the process. For example, to achieve a 75% yield for a 50-step process (where steps can refer to the number of layers formed on a wafer), each individual step must have a yield of greater than 99.4%. If each individual step has a 95% yield, the overall process yield is as low as 7%.

[0017]

[0033] While high process yields are desirable in IC chip manufacturing facilities, maintaining high substrate (i.e., wafer) throughput, defined as the number of substrates processed per hour, is also essential. High process yields and high substrate throughput can be affected by the presence of defects. This is especially true when operator intervention is required to investigate the defects. Therefore, high-throughput detection and identification of microscale and nanoscale defects by inspection tools, such as scanning electron microscopes ("SEMs"), is essential to maintaining high yields and low costs.

[0018]

[0034] An SEM includes a scanning device and a detector system. The scanning device includes an illumination system, which includes an electron source for generating primary electrons, and a projection system for scanning a sample, such as a substrate, with one or more focused beams of primary electrons. Together, at least the illumination system or illumination system and the projection system or projection system are sometimes referred to as an electron-optical system or apparatus. The primary electrons interact with the sample and generate secondary electrons. The detector system captures the secondary electrons from the sample as it is scanned, allowing the SEM to generate an image of the scanned area of ​​the sample. For high-throughput inspection, some inspection systems use multiple focused beams of primary electrons, or multibeams. The component beams of a multibeam are sometimes called subbeams or beamlets. A multibeam can simultaneously scan different portions of the sample. Therefore, a multibeam inspection system can inspect a sample much faster than a single-beam inspection system.

[0019]

[0035] In a multi-beam inspection apparatus, some paths of the primary electron beam deviate from the central axis of the scanning device, i.e., the midpoint of the primary electron optical axis. To ensure that all electron beams reach the sample surface at substantially the same angle of incidence, sub-beam paths with a greater radial distance from the central axis must be manipulated to move through a larger angle than sub-beam paths closer to the central axis. This stronger manipulation can cause aberrations, which result in blurred, out-of-focus images of the sample substrate. Specifically, for sub-beam paths that are not on the central axis, the aberrations of the sub-beams can increase with radial displacement from the central axis. Such aberrations can remain associated with secondary electrons when they are detected. Therefore, such aberrations degrade the quality of the images generated during inspection.

[0020]

[0036] Known implementations of multi-beam inspection devices are described below.

[0021]

[0037] The figures are schematic. Accordingly, in the drawings, the relative dimensions of components are exaggerated for clarity. In the following description of the drawings, the same or similar reference numbers refer to the same or similar components or entities, and only differences relative to individual embodiments are described. While the description and drawings are directed to electron-optical devices, it is understood that the embodiments are not used to limit the present disclosure to specific charged particles. Thus, throughout this document, references to electrons can be considered to be references to charged particles more generally, and charged particles are not necessarily electrons.

[0022]

[0038] Referring now to Figure 1, Figure 1 is a schematic diagram illustrating an exemplary charged particle beam inspection system 100. The charged particle beam inspection system 100 of Figure 1 includes a main chamber 10, a load lock chamber 20, an electron beam tool 40, a front end equipment module (EFEM) 30, and a controller 50. The electron beam tool 40 is located within the main chamber 10.

[0023]

[0039] The EFEM 30 includes a first load port 30a and a second load port 30b. The EFEM 30 may include one or more additional load ports. The first load port 30a and the second load port 30b can, for example, receive substrate front opening unified pods (FOUPs) containing substrates (e.g., semiconductor substrates or substrates made of other materials) or samples to be inspected (hereinafter, substrates, wafers, and samples are collectively referred to as "samples"). One or more robotic arms (not shown) of the EFEM 30 transport the samples to the load lock chamber 20.

[0024]

[0040] The load lock chamber 20 is used to remove gas from around the sample. This creates a vacuum, which is a local gas pressure lower than the pressure of the surrounding environment. The load lock chamber 20 may be connected to a load lock vacuum pumping system (not shown), which removes gas particles from the load lock chamber 20. Operation of the load lock vacuum pumping system allows the load lock chamber to reach a first pressure below atmospheric pressure. After the first pressure is reached, one or more robotic arms (not shown) transport the sample from the load lock chamber 20 to the main chamber 10. The main chamber 10 is connected to the main chamber vacuum pumping system (not shown). The main chamber vacuum pumping system removes gas particles from the main chamber 10 so that the pressure around the sample reaches a second pressure below the first pressure. After the second pressure is reached, the sample is transported to an electron beam tool, where it can be inspected. The electron beam tool 40 may include a multi-beam electron optical device.

[0025]

[0041] The controller 50 is electronically connected to the electron beam tool 40. The controller 50 may be a processor (e.g., a computer) configured to control the charged particle beam inspection apparatus 100. The controller 50 may also include processing circuitry configured to perform various signal and image processing functions. While FIG. 1 illustrates the controller 50 as external to the structure including the main chamber 10, the load lock chamber 20, and the EFEM 30, it is understood that the controller 50 may be part of the structure. The controller 50 may be located within one of the component elements of the charged particle beam inspection apparatus, or the controller 50 may be distributed among at least two of the component elements. While the present disclosure provides an example of a main chamber 10 housing an electron beam inspection tool, it should be noted that aspects of the present disclosure, in a broad sense, are not limited to chambers housing electron beam inspection tools. Rather, it is understood that the principles described above may also be applied to other tools and other arrangements of apparatus operating under a second pressure.

[0026]

[0042] Referring now to FIG. 2, FIG. 2 is a schematic diagram illustrating an exemplary electron beam tool 40, including a multi-beam 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 apparatus 40) includes an electron source 201, a gun aperture plate 271, a condenser lens 210, a source transformation unit 220, a primary projection apparatus 230, a motorized stage 209, and a sample holder 207. The electron source 201, the gun aperture plate 271, the condenser lens 210, and the source transformation unit 220 are components of an illumination apparatus encompassed by the multi-beam electron beam tool 40. The sample holder 207 is supported by the motorized stage 209 for holding a sample 208 (e.g., a substrate or mask) for inspection. The multi-beam electron beam tool 40 may further include a secondary projection apparatus 250 and an associated electron detection device 240. The primary projection device 230 may include an objective lens 231 (e.g., a single lens acting on the entire beam). The objective lens may be the last electron-optical element in the path of the multi-beam or in the electron-optical system, and therefore the objective lens may be referred to as a type of last electron-optical element. The electron detection device 240 may include multiple detection elements 241, 242, and 243. The beam separator 233 and the deflection scanning unit 232 may be located within the primary projection device 230.

[0027]

[0043] The components used to generate the primary beam may be aligned with the primary electron optical axis of apparatus 40. These components may include electron source 201, gun aperture plate 271, condenser lens 210, source conversion unit 220, beam separator 233, deflection scanning unit 232, and primary projection apparatus 230. Secondary projection apparatus 250 and its associated electron detection device 240 may be aligned with the secondary electron optical axis 251 of apparatus 40.

[0028]

[0044] The primary electron optical axis 204 is constituted by the electron optical axis of the portion of the electron beam tool 40 that is the illumination device. The secondary electron optical axis 251 is the electron optical axis of the portion of the electron beam tool 40 that is the detection device. The primary electron optical axis 204 is sometimes referred to herein (for ease of reference) as the main optical axis or the primary charged particle optical axis. The secondary electron optical axis 251 is sometimes referred to herein as the secondary optical axis or the secondary charged particle optical axis.

[0029]

[0045] 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 that forms a primary beam crossover (virtual or real image) 203. The primary electron beam 202 can be visualized as it emerges from the primary beam crossover 203.

[0030]

[0046] In this arrangement, the primary electron beam is multi-beam by the time it reaches the sample, preferably before it reaches the projection device. Such multi-beams can be generated from the primary electron beam in many different ways. For example, the multi-beams can be generated by a multi-beam array located before the crossover, a multi-beam array located in the source conversion unit 220, or a multi-beam array located anywhere in between. The multi-beam array can include multiple electron beam steering elements arranged in an array across the beam path. Each steering element can affect the primary electron beam to generate sub-beams. Thus, the multi-beam array generates multiple beam paths at the down beam of the multi-beam array by interacting with the incoming primary beam path.

[0031]

[0047] In operation, the gun aperture plate 271 is configured to block peripheral electrons of the primary electron beam 202 to reduce the Coulomb effect, which can increase the size of the probe spots 221, 222, and 223 of the primary sub-beams 211, 212, 213, respectively, and thus reduce the inspection resolution. The gun aperture plate 271 is sometimes also referred to as a Coulomb aperture array.

[0032]

[0048] The condenser lens 210 is configured to focus the primary electron beam 202. The condenser lens 210 may be designed to focus the primary electron beam 202 so that it becomes a parallel beam and is perpendicularly incident on the source conversion unit 220. The condenser lens 210 may be a movable condenser lens that may be configured so that the position of its first principal plane is movable. The movable condenser lens may be configured to be magnetic. The condenser lens 210 may be an anti-rotation condenser lens and / or it may be movable.

[0033]

[0049] The source conversion unit 220 may include an image forming element array, an aberration compensator array, a beam-limiting aperture array, and a pre-bending micro-deflector array. The pre-bending micro-deflector array may deflect multiple primary sub-beams 211, 212, 213 of the primary electron beam 202 so that they perpendicularly enter the beam-limiting aperture array, the image forming element array, and the aberration compensator array. In this arrangement, the image forming element array may function as a multi-beam array for generating multiple sub-beams, i.e., primary sub-beams 211, 212, 213, in multiple beam paths. The image forming array may include multiple electron beam manipulators, such as micro-deflectors or micro-lenses (or a combination of both), one for each of the primary sub-beams 211, 212, 213, to influence the multiple primary sub-beams 211, 212, 213 of the primary electron beam 202 and to form multiple parallel images (virtual or real) of the primary beam crossover 203. The aberration compensator array may include a field curvature compensator array (not shown) and an astigmatism compensator array (not shown). The field curvature compensator array may include a plurality of microlenses for compensating for field curvature aberration of the primary sub-beams 211, 212, and 213. The astigmatism compensator array may include a plurality of microastigmatism correctors for compensating for astigmatism of the primary sub-beams 211, 212, and 213. The beam-limiting aperture array may be configured to limit the diameters of the individual primary sub-beams 211, 212, and 213. While FIG. 2 shows three primary sub-beams 211, 212, and 213 as an example, it should be understood that the source conversion unit 220 may be configured to form any number of primary sub-beams. 1, such as the source conversion unit 220, the electron detection device 240, the primary projection device 230, or the motorized stage 209. As will be described in more detail below, the controller 50 may perform various image and signal processing functions. The controller 50 may also generate various control signals for controlling the operation of the charged particle beam inspection apparatus, including the charged particle multi-beam apparatus.

[0034]

[0050] The condenser lens 210 may further be configured to adjust the current of the primary sub-beams 211, 212, 213 at the down-beam of the source conversion unit 220 by varying the focusing power of the condenser lens 210. Alternatively or additionally, the current of the primary sub-beams 211, 212, 213 may be changed by changing the radial size of the beam-limiting aperture in the beam-limiting aperture array corresponding to each primary sub-beam. The current may be changed by changing both the radial size of the beam-limiting aperture and the focusing power of the condenser lens 210. If the condenser lens is movable and magnetic, off-axis sub-beams 212 and 213 illuminating the source conversion unit 220 may have a rotation angle. The rotation angle changes with the focusing power or the position of the first principal plane of the movable condenser lens. A condenser lens 210 that is an anti-rotation condenser lens may be configured such that the rotation angle remains unchanged while the focusing power of the condenser lens 210 is changed. Such a focusing lens 210 that is also movable may not change its rotation angle when the focusing power of the focusing lens 210 and the position of its first principal plane change.

[0035]

[0051] The objective lens 231 can be configured to focus the sub-beams 211, 212, and 213 onto the sample 208 for inspection, and can form three probe spots 221, 222, and 223 on the surface of the sample 208.

[0036]

[0052] The beam separator 233 may be, for example, a Wien filter including electrostatic deflectors that generate electrostatic and magnetic dipole fields (not shown in FIG. 2 ). In operation, the beam separator 233 may be configured to exert an electrostatic force on individual electrons of the primary sub-beams 211, 212, and 213 by the electrostatic dipole field. This electrostatic force is equal in magnitude but opposite in direction to the magnetic force exerted on individual electrons by the magnetic dipole field of the beam separator 233. Thus, the primary sub-beams 211, 212, and 213 may pass at least substantially straight through the beam separator 233 with at least substantially zero deflection angle.

[0037]

[0053] The deflection scanning unit 232 is configured, in operation, to deflect the primary sub-beams 211, 212, and 213 to scan the probe spots 221, 222, and 223 over respective scan areas of a section of the surface of the sample 208. In response to the incidence of the primary sub-beams 211, 212, and 213 or the probe spots 221, 222, and 223 on the sample 208, electrons, including secondary electrons and backscattered electrons, are generated from the sample 208. The secondary electrons propagate in three secondary electron beams 261, 262, and 263. The secondary electron beams 261, 262, and 263 typically comprise secondary electrons (having electron energies of 50 eV or less) and may also comprise at least a portion of backscattered electrons (having electron energies between 50 eV and the landing energies of the primary sub-beams 211, 212, and 213). The beam separator 233 is positioned to deflect the paths of the secondary electron beams 261, 262, and 263 towards the secondary projection arrangement 250. The secondary projection arrangement 250 then focuses the paths of the secondary electron beams 261, 262, and 263 onto a plurality of detection areas 241, 242, and 243 of the electron detection device 240. The detection areas may be separate detection elements 241, 242, and 243 positioned to detect corresponding secondary electron beams 261, 262, and 263. The detection areas generate corresponding signals that are sent to the controller 50 or a signal processing system (not shown), for example, to construct an image of the corresponding scanned area of ​​the sample 208.

[0038]

[0054] Detector elements 241, 242, and 243 can detect corresponding secondary electron beams 261, 262, and 263. Upon incidence of the secondary electron beams on detector elements 241, 242, and 243, the elements can generate corresponding intensity signal outputs (not shown). The outputs can be directed to an image processing system (e.g., controller 50). Each detector element 241, 242, and 243 can include one or more pixels. The intensity signal output of a detector element can be the sum of the signals generated by all pixels within the detector element.

[0039]

[0055] The controller 50 may include an image processing system including an image acquirer (not shown) and a storage device (not shown). For example, the controller may include a processor, a computer, a server, a mainframe host, a terminal, a personal computer, any type of mobile computing device, etc., or a combination thereof. The image 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 electronic detection device 240 of the apparatus 40, enabling signal communication via electrical conductors, fiber optic cables, portable storage media, IR, Bluetooth, the Internet, a wireless network, a wireless radio, or combinations thereof, among others. The image acquirer may receive signals from the electronic detection device 240, process data contained in the signals, and construct an image therefrom. Thus, the image acquirer may acquire an image of the sample 208. The image acquirer may also perform various post-processing functions, such as generating contours and superimposing indicators on the acquired image. The image acquirer may be configured to adjust the brightness and contrast of the acquired image, etc. The storage may be a storage medium such as a hard disk, a flash drive, cloud storage, random access memory (RAM), or other types of computer-readable memory. The storage may be coupled to the image acquirer and may be used to store raw scanned image data as original images or post-processed images.

[0040]

[0056] The image acquirer can acquire one or more images of the sample based on the imaging signal received from the electronic detection device 240. The imaging signal can correspond to a scanning operation to perform charged particle imaging. The acquired image can be a single image including multiple imaging areas. The single image can be saved to storage. The single image can be an original image that can be divided into multiple regions. Each region can include one imaging area that includes a feature of the sample 208. The acquired image can include multiple images of a single imaging area of ​​the sample 208 sampled multiple times over a period of time. The multiple images can be saved to storage. The controller 50 can be configured to perform image processing steps using multiple images of the same location on the sample 208.

[0041]

[0057] The controller 50 may include measurement circuitry (e.g., an analog-to-digital converter) to obtain a distribution of detected secondary electrons. The electron distribution data collected during the detection time window, in combination with the corresponding scan path data of each of the primary sub-beams 211, 212, and 213 incident on the sample surface, can be used to reconstruct an image of the sample structure under inspection. The reconstructed image can be used to reveal various features of the internal or external structure of the sample 208. Thus, the reconstructed image can be used to reveal any defects that may be present in the sample.

[0042]

[0058] 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 a direction, e.g., at a constant velocity, preferably continuously, at least during inspection of the sample. The controller 50 may control the movement of the motorized stage 209 such that the motorized stage 209 varies the speed of movement of the sample 208 depending on various parameters. For example, the controller may control the stage velocity (including its direction) depending on the characteristics of the inspection step of the scanning process.

[0043]

[0059] 2 shows apparatus 40 using three primary electron sub-beams, it is understood that apparatus 40 may use two or more primary electron sub-beams, and the present disclosure does not limit the number of primary electron beams used in apparatus 40.

[0044]

[0060]

[0033] Referring now to Figure 3, Figure 3 is a schematic diagram of an exemplary multi-beam apparatus illustrating an exemplary configuration of a source conversion unit of the exemplary charged particle beam inspection apparatus of Figure 1. Apparatus 300 may include an electron source 301, a pre-sub-beam forming aperture array 372, a condenser lens 310 (similar to condenser lens 210 of Figure 2), a source conversion unit 320, an objective lens 331 (similar to objective lens 231 of Figure 2), and a sample 308 (similar to sample 208 of Figure 2). Electron source 301, pre-sub-beam forming aperture array 372, and condenser lens 310 may be components of an illumination apparatus contained by apparatus 300. Source conversion unit 320 and objective lens 331 may be components of a projection apparatus contained by apparatus 300. 2, where the image forming element array of FIG. 2 is image forming element array 322, the aberration compensator array of FIG. 2 is aberration compensator array 324, the beam limiting aperture array of FIG. 2 is beam limiting aperture array 321, and the pre-bent micro-deflector array of FIG. 2 is pre-bent micro-deflector array 323. Electron source 301, pre-sub-beam forming aperture array 372, condenser lens 310, source conversion unit 320, and objective lens 331 are aligned with a primary electron optical axis 304 of the apparatus. Electron source 301 generates a primary electron beam 302 generally along primary electron optical axis 304 and having a source crossover (virtual or real image) 301S. The pre-sub-beam forming aperture array 372 cuts peripheral electrons from the primary electron beam 302 to reduce the resulting Coulomb effect, which is a cause of aberrations to the sub-beams due to interactions between electrons in different sub-beam paths. The primary electron beam 302 can be reduced to a specified number of sub-beams (e.g., three sub-beams 311, 312, and 313) by the pre-sub-beam forming aperture array 372 of the pre-sub-beam forming mechanism. While three sub-beams and their paths are referenced above and below, it should be understood that the description is intended to apply to an apparatus, tool, or system using any number of sub-beams.

[0045]

[0061] The source conversion unit 320 may include a sub-beam limiting aperture array 321 with beam-limiting apertures configured to limit the sub-beams 311, 312, and 313 of the primary electron beam 302. The source conversion unit 320 may also include an imaging element array 322 with image forming micro-deflectors 322_1, 322_2, and 322_3. There is a respective micro-deflector associated with the path of each sub-beam. The micro-deflectors 322_1, 322_2, and 322_3 are configured to deflect the paths of the sub-beams 311, 312, and 313 toward the electron optical axis 304. The deflected sub-beams 311, 312, and 313 form a virtual image of the source crossover 301S. The virtual image is projected onto the sample 308 by the objective lens 331 and forms probe spots on the sample; these probe spots are three probe spots 391, 392, and 393. Each probe spot corresponds to a location of incidence of a sub-beam path on the sample surface. The source transformation unit 320 may further include an aberration compensator array 324 configured to compensate for aberrations of each sub-beam. The aberrations of each sub-beam are generally present at the probe spots 391, 392, and 393 formed on the sample surface. The aberration compensator array 324 may include a field curvature compensator array (not shown) with microlenses. The field curvature compensators and microlenses are configured to compensate the sub-beams for field curvature aberrations that are significant at the probe spots 391, 392, and 393. The aberration compensator array 324 may include an astigmatism compensator array (not shown) with microastigmatism correctors. The microastigmatism correctors are controlled to act on the sub-beams to compensate for astigmatism that would otherwise be present at the probe spots 391, 392, and 393.

[0046]

[0062] The source conversion unit 320 may further include a pre-bend micro-deflector array 323 having pre-bend micro-deflectors 323_1, 323_2, and 323_3 that bend the sub-beams 311, 312, and 313, respectively. The pre-bend micro-deflectors 323_1, 323_2, and 323_3 may bend the paths of the sub-beams onto the beamlet-limiting aperture array 321. The sub-beam paths of incidence on the beamlet-limiting aperture array 321 may be perpendicular to the orientation plane of the beamlet-limiting aperture array 321. The condenser lens 310 may direct the paths of the sub-beams onto the beamlet-limiting aperture array 321. The focusing lens 310 can focus the three sub-beams 311, 312, and 313 into a parallel beam along the primary electron optical axis 304, so that the sub-beams are perpendicularly incident on the source conversion unit 320, which can correspond to the beamlet limiting aperture array 321.

[0047]

[0063] The image forming element array 322, the aberration compensator array 324, and the pre-bending micro-deflector array 323 may include multiple layers of sub-beam steering devices, some of which may be forms or arrays (e.g., micro-deflectors, micro-lenses, or micro-astigmatists).

[0048]

[0064] In the source conversion unit 320, sub-beams 311, 312, and 313 of the primary electron beam 302 are deflected by micro-deflectors 322_1, 322_2, and 322_3, respectively, of the imaging element array 322 toward the primary electron optical axis 304. It is to be understood that the path of sub-beam 311 does not have to be deflected by micro-deflector 322_1, as the path of sub-beam 311 may already correspond to the electron optical axis 304 before reaching micro-deflector 322_1.

[0049]

[0065] The objective lens 331 focuses the sub-beams onto the surface of the sample 308, i.e., the objective lens 331 projects three virtual images onto the sample surface. The three images formed on the sample surface by the three sub-beams 311-313 form three probe spots 391, 392, and 393 on the sample surface. The deflection angles of the sub-beams 311-313 are adjusted by the objective lens 311 to reduce off-axis aberrations of the three probe spots 391-393. The three deflected sub-beams consequently pass through or approach the front focus of the objective lens 331. As depicted, the objective lens 331 is a magnetic lens that focuses all the sub-beams. In some embodiments of the present invention, the objective lens is preferably an array of electrostatic lenses, which may require multiple beam paths to be directed towards the array of electrostatic lenses of the objective lens 331 by the source conversion unit 320, specifically the image forming element array 322, e.g., with micro-deflectors (e.g., each beam may be directed towards a unique corresponding micro-lens in the array).

[0050]

[0066] At least some of the above components of Figures 2 and 3 may be referred to as manipulator arrays, multi-manipulator arrays, multi-manipulators, or manipulators, either individually or in combination with each other, because they manipulate one or more charged particle beams or sub-beams.

[0051]

[0067] Existing multi-electron beam defect inspection systems have a defect rate of 10 to 6000 mm per hour. 2Such systems have a resolution of approximately 2-10 nm with a throughput of 100 sq m. Such systems have a detector in the secondary column, as mentioned above. Existing multi-electron beam inspection tool architectures have detectors located away from the source of electrons emitted from the sample, such as backscattered and secondary electrons, which are not measurable in multi-beam systems. Incorporating a secondary column into a tool with an array objective lens, such as an electrostatic lens, is also difficult (which requires dealing with Coulomb interactions).

[0052]

[0068] In one embodiment, the objective lens referred to in the previous embodiment is an array objective lens. Typically, such lens arrangements are electrostatic. Each element in the array is a microlens that manipulates a different beam or a group of different beams in the multibeam. An electrostatic array objective lens has at least two plates, each plate having a plurality of holes or apertures. The position of each hole in one plate corresponds to the position of a corresponding hole in the other plate. In use, the corresponding holes act on the same beam or a group of the same beams in the multibeam. A suitable example of the type of lens for each element in the array is an Einzel lens. The bottom electrode of the objective lens is a CMOS chip detector integrated into the multibeam manipulator array. Integrating the detector array into the objective lens eliminates the need for a secondary projection device 250. The CMOS chip is preferably oriented facing the sample (due to the small distance (e.g., 100 μm) between the wafer and the bottom of the electron optical system). In one embodiment, a capture electrode is provided for capturing secondary electron signals. The capture electrode can be formed, for example, in a metal layer of a CMOS device. The capture electrode can form the bottom layer of an objective lens. The capture electrode can form the bottom surface of a CMOS chip. The CMOS chip can be a CMOS chip detector. The CMOS chip can be integrated into the sample-facing surface of an objective lens assembly. The capture electrode is an example of a sensor unit for detecting secondary electrons. The capture electrode can also be formed in other layers. Power and control signals for the CMOS can be connected to the CMOS by through-silicon vias. For robustness, the bottom electrode preferably consists of two elements: the CMOS chip and a passive Si plate with holes. This plate shields the CMOS from high electric fields.

[0053]

[0069] A sensor unit associated with the bottom or sample-facing surface of the objective lens is advantageous because it allows secondary and / or backscattered electrons to be detected before they encounter and are manipulated by electron-optical elements of the electron-optical system. Advantageously, the time taken to detect such electron-emitting samples can be reduced, and preferably minimized.

[0054]

[0070] To maximize detection efficiency, it is desirable to make the electrode surface as large as possible so that substantially all of the area of ​​the array objective (excluding the aperture) is occupied by the electrodes. Each electrode may have a diameter substantially equal to the array pitch. The electrode surface may substantially fill the sample-facing surface of the array objective. In some embodiments, the electrode outline is circular, but this may be squared to maximize the detection area. Also, the diameter of the substrate through-holes can be minimized. The typical size of the electron beam is approximately 5 to 15 microns.

[0055]

[0071] In some embodiments, a single capture electrode surrounds each aperture. The single capture electrode may have a circular perimeter and / or outer diameter. The capture electrode may have an area extending between the aperture and the perimeter of the capture electrode. As shown in FIGS. 5 and 6, the capture electrodes 405 may be arranged in a rectangular or hexagonal array. In another embodiment, multiple electrode elements are provided around each aperture. The multiple electrode elements may, together, have a circular perimeter and / or diameter. The multiple electrode elements may, together, have an area extending between the aperture and the perimeter of the multiple electrode elements. The multiple electrode elements 405 may be arranged in a rectangular or hexagonal array. An electrode element is an example of a sensor element. Electrons captured by multiple electrode elements surrounding an aperture may be combined into a single signal or used to generate independent signals. The electrode elements may be divided radially. The electrode elements may form multiple concentric annuli or rings. The electrode elements may be divided angularly. The electrode elements may form a plurality of sector-like pieces or segments, which may be of similar angular size and / or similar area. The electrode elements may be divided radially and angularly, or in any other convenient manner.

[0056]

[0072] However, increasing the electrode surface results in an increase in parasitic capacitance and therefore a decrease in bandwidth. For this reason, it may be desirable to limit the outer diameter of the electrode, especially if increasing the electrode only provides a slight improvement in detection efficiency but a large increase in capacitance. Circular (annular) electrodes may offer a good compromise between collection efficiency and parasitic capacitance.

[0057]

[0073] Increasing the outer diameter of the electrode can also result in increased crosstalk (sensitivity to signals from neighboring holes). This can also be a reason to make the outer diameter of the electrode smaller, especially if enlarging the electrode only provides a slight improvement in detection efficiency but a large increase in crosstalk.

[0058]

[0074] The backscattered and / or secondary electron current collected by the electrode is amplified. The purpose of the amplifier is to allow a sufficiently sensitive measurement of the current received or collected by the sensor unit, and thus the number of backscattered and / or secondary electrons, to be measured. This can be measured by current measurement or potential difference across a resistor. Several types of amplifier designs can be used to amplify the backscattered and / or secondary electron current collected by the electrode (e.g., transimpedance amplifiers). In such transimpedance amplifiers, the voltage output of the TIA is amplified by the TIA resistor (R TIA ) multiplied by the measured current.

[0059]

[0075] R TIA The larger the , the greater the amplification. However, the bandwidth is determined by the RC time, which is TIA is equal to the sum of the capacitances at the inlet side of the TIA.

[0060]

[0076] Since a finite RC time has a similar effect as a larger electron optics spot size, it effectively signals the blur contribution in the deflection direction. Given the detector blur contribution budget and deflection speed, the allowable RC time is determined. This RC time and the entrance capacitance R TIA is determined.

[0061]

[0077] backscattered and / or secondary electron current, and R TIA Based on this, the signal voltage is determined.

[0062]

[0078] The detector noise contribution should be compared to the shot noise of the backscattered and / or secondary electron current. By considering only the shot noise of the primary electron beam, the current noise per sqrt(Hz) due to shot noise is significantly larger than the voltage noise of state-of-the-art CMOS amplifiers, which is typically about 1 nV / sqrt(Hz), as demonstrated below. The calculations presented below demonstrate that the proposed electrodes are feasible from a noise perspective. N PE_def =5000 (1) I beam =1nA (2) d def =4nm (3) N pix_defect =4 (4) blur rc =0.5nm (5)

number

[0063]

[0079] The above calculations can be explained as follows: Assume the number of primary electrons required to detect a defect is 5000 (Equation 1), the beam current is 1 nA (Equation 2), the defect diameter is 4 nm (Equation 3), and the number of pixels per defect is 4 (Equation 4). Assume that blurring due to the finite RC time of the amplifier of 0.5 nm is acceptable (Equation 5). The detector capacitance can be calculated from the geometry of the arrangement, for example, as shown in Equation 6, where 3 is the dielectric constant of the insulator below the capture electrode, 100 μm is the diameter of the capture electrode, and 1 μm is the thickness of the insulator below the capture electrode. The intrinsic shot noise is calculated as Equation 7. The time to image one defect is calculated as Equation 8, where Q eis the electron charge. The scan length to detect the defect is calculated by Equation 9, and the scan speed is calculated by Equation 10. The RC time to be achieved is calculated by Equation 11, and therefore the detector resistance is calculated by Equation 12, and the resulting voltage noise is calculated by Equation 13. Equation 14 combines the previous equations into a single equation to show the dependencies. A typical voltage noise level achievable in a CMOS amplifier is approximately 1 nV / sqrt(Hz)—a CMOS amplifier of this typical noise level. Therefore, it seems plausible that the noise is dominated by the fundamental shot noise, not by the voltage noise added by the CMOS amplifier. For this reason, it seems plausible that the proposed electrode is feasible from a noise perspective. That is, it is sufficient that typical CMOS amplifier noise has a noise level small compared to the shot noise (if it were large compared to the shot noise, the arrangement would still work, but its effectiveness in terms of bandwidth or throughput (i.e., speed) would be reduced).

[0064]

[0080] Figure 8 shows a schematic diagram of a theoretical transimpedance amplifier (TIA) with a voltage output V out is simply the measured current I in and feedback resistor R f However, in actual TIAs, as shown in Figure 9, noise, specifically, the input i sn and the feedback resistor i n In most cases, the thermal noise dominates. n The voltage noise at

number

number

number

[0065]

[0081] The present invention can be shown to remain practical even when taking into account the effects of shot noise by assuming that the number of electrons required to detect each defect is increased to 10,000, a blur budget of 2 nm is set, and the electrode diameter is reduced to 50 μm. In this case, the electrode capacitance becomes approximately 0.011 pF, which is approximately 3.6×10 7 This requires a resistance of 100 Ω, resulting in a thermal noise level approximately 20% greater than the shot noise. Therefore, a variety of different configurations of the proposed detector are feasible. The capacitance of the electrodes can also be controlled by varying the thickness of the adjacent dielectric layer, which may be in the range of about 1 to about 5 μm.

[0066]

[0082] An exemplary embodiment is shown in FIG. 4, which shows a multi-beam objective lens 401 in a schematic cross section. A detector module 402 is provided on the output side of the objective lens 401 (the side facing the sample 208). FIG. 5 is a bottom view of the detector module 402, which includes a substrate 404 on which a plurality of capture electrodes 405 are provided, each of which surrounds a beam aperture 406. The beam apertures 406 are large enough not to block any of the primary electron beam. The capture electrodes 405 can be considered an example of a sensor unit that receives backscattered or secondary electrons and generates a detection signal (in this case, a current). The beam apertures 406 can be formed by etching through the substrate 404. In the arrangement shown in FIG. 5, the beam apertures 406 are shown in a rectangular array. The beam apertures 406 can also be arranged differently (e.g., in a hexagonal close-packed array, as shown in FIG. 6).

[0067]

[0083] 7 shows, on an increased scale, a portion of the detector module 402 in cross section. The capture electrode 405 forms the bottom surface of the detector module 402, i.e., the surface closest to the sample. Between the capture electrode 405 and the main body of the silicon substrate 404 is a logic layer 407. The logic layer 407 may include an amplifier, e.g., a transimpedance amplifier, an analog-to-digital converter, and readout logic. In one embodiment, there is one amplifier and one analog-to-digital converter per capture electrode 405. The logic layer 407 and the capture electrode 405 may be fabricated using a CMOS process, with the capture electrode 405 forming the final metallization layer.

[0068]

[0084] The wiring layer 408 is provided on the back side of the substrate 404 and is connected to the logic layer 407 by through silicon vias 409. The number of through silicon vias 409 does not need to be the same as the number of beam apertures 406. Specifically, if the electrode signals are digitized in the logic layer 407, only a small number of through silicon vias may be needed to provide a data bus. The wiring layer 408 may include control lines, data lines, and power lines. It will be noted that despite the beam apertures 406, there is sufficient space for all necessary connections. The detection module 402 can also be fabricated using bipolar or other manufacturing techniques. A printed circuit board and / or other semiconductor chips may be provided on the back side of the detector module 402.

[0069]

[0085] Although FIG. 4 shows a three electrode objective, it will be appreciated that any other objective configuration may also be used, for example a two electrode objective.

[0070]

[0086] 10, which is a schematic diagram illustrating another exemplary electron beam tool 40a that may be part of the exemplary charged particle beam inspection apparatus 100 of FIG. 1 in place of tool 40 of FIG. 2. Portions of apparatus 40a that have similar functionality to corresponding portions of apparatus 40 of FIG. 2 are identified with the same reference numerals. In some cases, reduced or simplified descriptions of such portions are included below.

[0071]

[0087] The multi-beam electron beam tool 40a (also referred to herein as apparatus 40a) includes an electron source 201, a projection apparatus 230, a motorized stage 209, and a sample holder 207. The electron source 201 and projection apparatus 230 may collectively be referred to as an illumination apparatus. The sample holder 207 is supported by the motorized stage 209 to hold a sample 208 (e.g., a substrate or a mask) for inspection. The multi-beam electron beam tool 40a further includes an electron detection device 1240 (note that the electron detection device 1240 has the same function (i.e., detecting electrons from the sample) but may be structurally different from the electron detection device 240 in the secondary electron optical column of the embodiment referenced in connection with FIGS. 2 and 3).

[0072]

[0088] 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.

[0073]

[0089] The projection device 230 is configured to convert the primary electron beam 202 into a plurality of sub-beams 211, 212, 213 and direct each sub-beam onto the sample 208. Although three sub-beams are shown for simplicity, there may be tens, hundreds, or thousands of sub-beams. The sub-beams are sometimes referred to as beamlets.

[0074]

[0090] 1 may be connected to various portions of the electron beam tool 40a, such as the electron source 201, the electron detection device 1240, the projection system 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 for controlling the operation of charged particle beam inspection devices, including charged particle multi-beam devices.

[0075]

[0091] The projection device 230 may be configured to focus the sub-beams 211, 212, and 213 onto the sample 208 for inspection, forming three probe spots 221, 222, and 223 on the surface of the sample 208. The projection device 230 may be configured to deflect the primary sub-beams 211, 212, and 213 to scan the probe spots 221, 222, and 223 over respective scan areas of a section of the surface of the sample 208. In response to the incidence of the primary sub-beams 211, 212, and 213 on the probe spots 221, 222, and 223 on the sample 208, electrons, including secondary electrons and backscattered electrons, are generated from the sample 208. The secondary electrons typically have electron energies of 50 eV or less, and the backscattered electrons typically have electron energies between 50 eV and the landing energies of the primary sub-beams 211, 212, and 213.

[0076]

[0092] The electron detection device 1240 is configured to detect the secondary electrons and / or backscattered electrons and generate corresponding signals that are sent to, for example, a controller or signal processing system (not shown) to construct an image of a corresponding scanned area of ​​the sample 208. The electron detection device 1240 may include a detector module 402 integrated with the objective lens 401, as described above with reference to Figures 4-7.

[0077]

[0093] Figure 11 is a schematic diagram illustrating another exemplary electron beam tool 40b that may be part of the exemplary charged particle beam inspection apparatus 100 of Figure 1 in place of tool 40 of Figure 2. Portions of apparatus 40a that have similar functionality to corresponding portions of apparatus 40 of Figure 2 are identified with the same reference numerals. In some cases, reduced or simplified descriptions of such portions are included below.

[0078]

[0094] The electron source 201 directs electrons toward an array of condenser lenses 1231, which form part of the projection system 230. The electron sources are preferably high-brightness thermal field emitters, offering a good compromise between brightness and total emission current. There may be tens, hundreds, or even thousands of condenser lenses 1231. The condenser lenses 1231 may include multi-electrode lenses and may have a structure based on EP 1 602 121 A1, which is incorporated herein by reference, particularly for its disclosure of a lens array for splitting an electron beam into multiple sub-beams (the array providing one lens per sub-beam). The array of condenser lenses may take the form of at least two plates that function as electrodes, with apertures in each plate aligned with each other and corresponding to the locations of the sub-beams. At least two of the plates are maintained at different potentials during operation to achieve the desired lens effect.

[0079]

[0095] In one arrangement, the array of focusing lenses is formed from a three-plate array in which charged particles have the same energy when they enter and leave each lens; this arrangement is sometimes called an Einzel lens. The beam energy when it enters the Einzel lens is the same as when it leaves the Einzel lens. Therefore, dispersion occurs only within the Einzel lens itself (between the entrance and exit electrodes of the lens), thereby limiting off-axis chromatic aberration. When the thickness of the focusing lens is thin, e.g., a few mm, such aberrations have a small or negligible effect.

[0080]

[0096] The array of focusing lenses may include a plurality of beam apertures 110. The beam apertures 110 may be formed, for example, by openings in a substantially planar beam aperture body 111. The beam apertures 110 split the charged particle beam from the source 201 into a corresponding plurality of sub-beams. Each focusing lens in the array directs electrons into a respective sub-beam 1211, 1212, 1213, which are focused at a respective intermediate focus 1233. A deflector 235 is located at the intermediate focus 1233. The deflector 235 is configured to bend each sub-beam 1211, 1212, 1213 by an amount effective to ensure that the chief ray (sometimes referred to as the beam axis) is incident on the sample 208 substantially perpendicularly (i.e., at substantially 90° relative to the nominal plane of the sample). The deflector 235 may also be referred to as a collimator. Down the beam at the intermediate focus 1233 (i.e., closer to the sample) are multiple objective lenses 1234, each of which directs a respective sub-beam 1211, 1212, 1213 onto the sample 208. The objective lenses 1234 can be configured to demagnify the electron beam by a factor of more than 10, preferably in the range of 50-100 or more.

[0081]

[0097] The electron detection device 1240 is provided between the objective lens 1234 and the sample 208 to detect secondary electrons and / or backscattered electrons emitted from the sample 208. The electron detection device 1240 may include a detector module 402 integrated with the objective lens 401, as described above with reference to Figures 4-7. The electron detection device 1240 may include a sensor unit, for example, a capture electrode 402.

[0082]

[0098] The system of FIG. 11 can be configured to control the landing energy of electrons on the sample. The landing energy can be selected to enhance secondary electron emission and detection depending on the properties of the sample being evaluated. A controller provided for controlling the objective lens 1234 can be configured to control the landing energy to any desired value within a predetermined range or to a desired one of multiple predetermined values. In one embodiment, the landing energy can be controlled to a desired value within the range of 1000 eV to 5000 eV. Details of electrode structures and potentials that can be used to control the landing energy are disclosed in European Patent Application No. 20158804.3, which is incorporated herein by reference.

[0083]

[0099] In some embodiments, the charged particle evaluation tool further includes one or more aberration correctors that reduce one or more aberrations in the sub-beams. In certain embodiments, at least one subset of the aberration correctors is positioned at or immediately adjacent to each of the multiple intermediate foci (e.g., in or adjacent to the intermediate image plane). The sub-beams have a minimum cross-sectional area in or near a focal plane, such as the intermediate plane. This provides more space for the aberration correctors than would be available elsewhere, i.e., up beam (closer to the source) or down beam (closer to the sample) at the intermediate plane (or than would be available in an alternative arrangement without an intermediate image plane).

[0084]

[0100] In one embodiment, an aberration corrector positioned at or immediately adjacent to the intermediate focus (or intermediate image plane) includes a deflector to correct for the source 201 appearing to be in different positions for different beams. The corrector can be used to correct for macroscopic aberrations due to the source that prevent good alignment between each sub-beam and the corresponding objective lens.

[0085]

[0101] The aberration correctors can correct aberrations that prevent proper column alignment. Such aberrations can also result in misalignment between the sub-beams and the correctors. For this reason, it may be desirable to additionally or alternatively position the aberration correctors at or near the condenser lenses 1231 (e.g., each such aberration corrector is integrated with or directly adjacent to one or more of the condenser lenses 1231). This is desirable because the condenser lenses 1231 are close to perpendicular to or coincident with the beam aperture, so that aberrations at or near the condenser lenses 1231 have not yet caused shifts in the corresponding sub-beams. However, a challenge with positioning the correctors at or near the condenser lenses 231 is that each sub-beam has a relatively large cross-sectional area and a relatively small pitch at this location compared to the location of the down-beam. The aberration corrector may be a CMOS-based individually programmable deflector as disclosed in EP 2702595A1 or an array of multipole deflectors as disclosed in EP 2715768A2, the descriptions of beamlet manipulators in both documents being incorporated herein by reference.

[0086]

[0102] In some embodiments, at least one subset of aberration correctors each are integrated with or directly adjacent to one or more of the objective lenses 1234. In certain embodiments, these aberration correctors reduce one or more of the following: field curvature, focus error, and astigmatism. 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 1234 for scanning the sub-beams 1211, 1212, 1213 over the sample 208. In certain embodiments, scanning deflectors such as those described in U.S. Patent Application Publication No. 2010 / 0276606 may be used, which is incorporated herein by reference in its entirety.

[0087]

[0103] In one embodiment, the objective lens referred to in the previous embodiment is an array objective lens. Each element in the array is a microlens that manipulates a different beam or a group of different beams in the multi-beam. An electrostatic array objective lens has at least two plates, each plate having a plurality of holes or apertures. The position of each hole in one plate corresponds to the position of a corresponding hole in the other plate. In use, the corresponding holes act on the same beam or a group of the same beams in the multi-beam. A suitable example of the type of lens for each element in the array is a two-electrode deceleration lens.

[0088]

[0104] An electron detection device 1240 is provided between the objective lens 1234 and the sample 208 to detect secondary electrons and / or backscattered electrons emitted from the sample 208. The electron detection device may include a detector module 402 integrated with the objective lens 401, as described above with reference to Figures 4-7. The electron detection device 240 may include a sensor unit, for example, a capture electrode 405.

[0089]

[0105] In one embodiment of the present invention, the corrector 235 at the intermediate focus 1233 is embodied by a slit deflector 300. The slit deflector 300 is an example of a manipulator and may also be referred to as a slit corrector.

[0090]

[0106] As an alternative to tool 40 of Figure 2, another exemplary electron beam tool 40c that may be part of the exemplary charged particle beam inspection apparatus 100 of Figure 1 is shown schematically in Figure 12. Portions of apparatus 40a that have similar functionality to corresponding portions of apparatus 40 of Figure 2 are identified with the same reference numerals. In some cases, reduced or simplified descriptions of such portions are included below.

[0091]

[0107] The tool 40c further includes one or more aberration correctors 124, 125, 126 that reduce one or more aberrations in the sub-beams 114. In an embodiment, each of at least a subset of the aberration correctors 124 is positioned at or directly adjacent to a respective intermediate focus of the plurality of intermediate foci 115 (e.g., in or adjacent to the intermediate image plane 120). The sub-beams 114 have a minimum cross-sectional area at or near a focal plane, such as the intermediate plane 120. This provides more space for the aberration correctors 124 than is available elsewhere, i.e., at the up-beam or down-beam of the intermediate plane 120 (or than would be available in an alternative arrangement without the intermediate image plane 120).

[0092]

[0108] In one embodiment, an aberration corrector 124 positioned at or immediately adjacent to the intermediate focus 115 (or intermediate image plane 120) includes a deflector to correct for the source 201 appearing to be in different positions to different sub-beams 114 arising from the beam 112 emitted from the source 201. The corrector 124 can be used to correct for macroscopic aberrations due to the source 201 that prevent good alignment between each sub-beam 114 and the corresponding objective lens 118.

[0093]

[0109] The aberration correctors 124 can correct aberrations that prevent proper column alignment. Such aberrations can also result in misalignment between the sub-beams 114 and the correctors 124. Therefore, it may be desirable to additionally or alternatively position the aberration correctors 125 at or near the condenser lenses 116 (e.g., each such aberration corrector 125 is integrated with or directly adjacent to one or more of the condenser lenses 116). This is desirable because the condenser lenses 116 are close to perpendicular to or coincident with the beam aperture 110, so that aberrations at or near the condenser lenses 116 have not yet caused shifts in the corresponding sub-beams 114. However, a challenge with positioning the correctors 125 at or near the condenser lenses 116 is that each sub-beam 114 has a relatively large cross-sectional area and a relatively small pitch at this location compared to locations further downstream.

[0094]

[0110] In some embodiments, as illustrated in Figure 12, each of at least a subset of aberration correctors 126 is integrated with or directly adjacent to one or more of the objective lenses 118. In certain embodiments, these aberration correctors 126 reduce one or more of the following: field curvature, focus error, and astigmatism. In the apparatus of Figure 12, any or all of the correctors 124, 125, 126 may be slit deflectors.

[0095]

[0111] Figures 13 and 14 show another example of an electron detection device 240 that may be used in an embodiment of the present invention, for example, that may be incorporated into the electron beam tools 40, 40a, 40b, 40c described above with reference to Figures 2, 10, 11, and 12. Figure 13 is a schematic side view of the electron detection device 240 incorporated within or associated with an objective lens array 501, and Figure 14 is a view from below of the electron detection device 240.

[0096]

[0112] As shown in FIG. 13 , the electronic detection device 240 of this example includes a substrate 502 with multiple sensor units 503 surrounding respective beam apertures 504. The substrate 502 is attached to the upper electrode (farther from the sample 208) of the deceleration array objective lens 501. The sensor units 503 face the sample 208. The sensor units may be positioned such that their sensing surfaces are located between the up-beam-facing and down-beam-facing surfaces of the upper electrode. The sensor units 503 may be integrated into or associated with the electrode of the objective lens 501 that is farthest from the sample 208. This is in contrast to the electronic detection device 240 of FIG. 7 , which is integrated into or associated with the lower electrode of the array objective lens. That is, in both embodiments, the sensor units may be integrated into the objective lens 501. (The sensor unit 503 in Figure 7 may be attached to the electrode of the array objective furthest from the source or closest to the sample, but is not necessarily integrated with it.) While Figure 13 depicts a two-electrode objective, it will be understood that other forms of objective, such as a three-electrode lens, may also be used.

[0097]

[0113] In this example, the electron detection device 240 is positioned away from the electrode of the objective lens 501 farthest from the source, i.e., away from the up-beam electrode of the objective lens 501. In this position, the electrode of the objective lens 501 is closer to the sample, or in the down-beam of the electron detection device 240. Thus, secondary electrons emitted by the sample 208 are accelerated, for example, to many kV (perhaps about 28.5 kV), by the electrode array in the down-beam position of the objective lens 501. The substrate supporting the sensor unit 503 during operation can be held at the same potential difference as the upper electrode. As a result, the sensor unit 503 can include, for example, a PIN detector and / or a scintillator. This has the advantage that there are no significant additional noise sources, since the PIN detector and scintillator have a large initial amplification of the signal. Another advantage of this arrangement is the ease of access to the electron detection device 240, for example, for power and signal connections or for in-use repair. Alternatively, a sensor unit with a capture electrode could be used in this location, but this may result in reduced performance.

[0098]

[0114] A PIN detector contains a reverse-biased PIN diode, with an intrinsic (very lightly doped) semiconductor region sandwiched between a p-doped region and an n-doped region. Secondary electrons incident on the intrinsic semiconductor region generate electron-hole pairs, allowing a current to flow and producing a detection signal.

[0099]

[0115] The scintillator comprises a material that emits light when electrons are incident on it, and a detection signal is generated by imaging the scintillator with a camera or other imaging device.

[0100]

[0116] To properly image the secondary electrodes onto the sensor unit 503, it is desirable to have a relatively large potential difference between the last electrode and the sample 208. For example, the upper electrode of the objective lens may be at about 30 kV, the lower electrode at about 3.5 kV, and the sample 208 at about 2.5 kV. A large potential difference between the lower electrode and the sample 208 may increase the aberrations of the objective lens relative to the primary beam, but an appropriate trade-off can be selected.

[0101]

[0117] The exact dimensions of an embodiment can be determined on a case-by-case basis. The diameter of the beam aperture 504 may be in the range of approximately 5-20 μm (e.g., approximately 10 μm). The width of the electrode slit may be in the range of 50-200 μm (e.g., approximately 100 μm). The pitch of the beam aperture and electrode slit may be in the range of 100-200 μm (e.g., approximately 150 μm). The gap between the upper and lower electrodes may be in the range of approximately 1-1.5 mm (e.g., approximately 1.2 mm). The depth of the lower electrode may be in the range of approximately 0.3-0.6 mm (e.g., approximately 0.48 mm). The working distance between the lower electrode and the sample 208 may be in the range of approximately 0.2-0.5 mm (e.g., approximately 0.37 mm). Desirably, the electric field strength between the lower electrode and the sample 208 is approximately 2.7 kV / mm or less to avoid or reduce damage to the sample 208. The electric field in the gap between the upper and lower electrodes may be larger (eg, greater than 20 kV / mm).

[0102]

[0118] The beam aperture 504 associated with the sensor unit has a smaller diameter than the electrode array to increase the surface of the sensor unit available for capturing electrodes originating from the sample. However, the dimensions of the beam aperture diameter are selected so that they allow the passage of sub-beams; that is, the beam aperture does not restrict the beam. The beam aperture is designed to allow the passage of sub-beams without shaping their cross-sections. The same comments apply to the beam aperture 406 associated with the sensor unit 402 in the embodiment shown in Figures 4-7.

[0103]

[0119] In some embodiments, a single sensor unit (e.g., a PIN detector) surrounds each aperture. The single sensor unit may have a circular perimeter and / or outer diameter. The sensor unit may have an area extending between the aperture and the perimeter of the sensor unit. The sensor units 503 may be arranged in a rectangular array or a hexagonal array. In another embodiment, multiple sensor elements (e.g., smaller PIN detectors) are provided around each aperture. The multiple sensor elements may together have a circular perimeter and / or diameter. The multiple sensor elements may together have an area extending between the aperture and the perimeter of the multiple sensor elements. The multiple sensor elements may be arranged in a rectangular array or a hexagonal array. Signals generated from electrons captured by multiple sensor elements surrounding an aperture may be combined into a single signal or used to generate independent signals. The sensor elements may be divided radially. The sensor elements may form multiple concentric annuli or rings. The sensor elements may be divided angularly. The sensor elements may form multiple sector-like pieces or segments. The segments may be of similar angular size and / or similar area. The sensor elements may be divided radially and angularly, or in any other convenient manner. The surfaces of the sensor units, and optionally their sensor elements, may substantially fill the surface of the substrate supporting the sensor units.

[0104]

[0120] Figure 15 is a schematic diagram of an assessment tool. Parts in common with the previous embodiment are indicated by the same reference numerals and will not be described further below. Differences will be described.

[0105]

[0121] Each focusing lens of the array 1231 directs the electrons into a respective sub-beam 211, 212, 213, which is focused at a respective intermediate focus 1233. A deflector 235 is provided at the intermediate focus 1233.

[0106]

[0122] Below the deflector 235 (i.e., down the beam or further from the source 201), there is a control lens array 250 including a control lens 251 for each of the sub-beams 211, 212, 213. The control lens array 250 may include at least two, e.g., three, plate electrode arrays connected to respective potential sources. The function of the control lens array 250 is to optimize the beam aperture angle relative to the beam demagnification and / or control the beam energy delivered to the objective lenses 234, each of which directs a respective sub-beam 211, 212, 213 onto the sample 208. The control lenses prefocus the sub-beams (e.g., apply a focusing action to the sub-beams before they reach the objective lens array 241). Prefocusing can reduce the divergence of the sub-beams or increase the convergence of the sub-beams. The control lens array and the objective lens array together operate to provide a compound focal length. Compound operation without the use of intermediate foci can reduce the risk of aberrations. Note that references to demagnification and aperture angle are intended to refer to variations of the same parameter. In an ideal arrangement, the product of the demagnification and the corresponding aperture angle is constant over a range of values. However, the aperture angle can be affected by the use of apertures. (Note that in the arrangement shown in FIG. 15, adjustments to the magnification result in a similar adjustment of the aperture angle, since the beam current remains consistent along the beam path.)

[0107]

[0123] Providing a control lens array 250 in addition to the objective lens array 241 provides additional freedom for controlling the characteristics of the sub-beams, as described in European Patent Application No. 20196716.3, filed September 17, 2020, the portions of which refer to the use and control of control lenses, are incorporated herein by reference. Additional freedom is provided even when the control lens array 250 and the objective lens array 241 are located relatively close to each other, for example, such that no intermediate focal point is formed between the control lens array 250 and the objective lens array 241. When two electrodes are present, the demagnification ratio and landing energy are controlled together. When three or more electrodes are present, the demagnification ratio and landing energy can be controlled individually. Thus, the control lens can be configured to adjust the demagnification ratio and / or beam aperture angle of each sub-beam (e.g., using a power source to apply appropriate respective potentials to the electrodes of the control lens and the objective lens). This optimization can be achieved without having an excessively adverse effect on the number of objective lenses and without excessively exacerbating the aberrations of the objective lenses (eg, without increasing the strength of the objective lenses).

[0108]

[0124] Optionally, an array of scan deflectors 260 is provided between the control lens array 250 and the array of objective lenses 234. The array of scan deflectors 260 includes one scan deflector 261 for each sub-beam 211, 212, 213. Each scan deflector is configured to deflect a respective sub-beam 211, 212, 213 in one or two directions to scan the sub-beam in one or two directions across the sample 208.

[0109]

[0125] An electron detection device 1240 is provided between the objective lens 234 and the sample 208 to detect secondary and / or backscattered electrons emitted from the sample 208. An exemplary structure of the electron detection system is described below.

[0110]

[0126] The system of FIG. 15 is configured to control the landing energy of electrons on a sample by varying the potentials applied to electrodes of the control lens and the objective lens. The control lens and objective lens, working together, are sometimes referred to as an objective lens assembly. The landing energy can be selected to enhance secondary electron emission and detection depending on the nature of the sample being evaluated. The controller can be configured to control the landing energy to any desired value within a predetermined range or to a desired one of multiple predetermined values. In one embodiment, the landing energy can be controlled to a desired value within a range of 1000 eV to 5000 eV.

[0111]

[0127] Desirably, the landing energy is varied primarily by controlling the energy of the electrons exiting the control lens. The potential difference within the objective lens is preferably kept constant during this variation so that the electric field within the objective lens remains as high as possible. In addition, the potential applied to the control lens can be used to optimize the beam aperture angle and reduction ratio. The control lens can also be referred to as a refocusing lens, as it can function to correct the focal position to account for changes in landing energy. The use of a control lens array allows the objective lens array to operate at its optimal electric field strength.

[0112]

[0128] In some embodiments, the charged particle evaluation tool further includes one or more aberration correctors that reduce one or more aberrations in the sub-beams, as described above.

[0113]

[0129] In certain embodiments, the aberration corrector is positioned at or immediately adjacent to the intermediate focus (or intermediate image plane), as described above.

[0114]

[0130] In some embodiments, the detector 1240 of the objective lens assembly includes a detector array in the downbeam of at least one electrode of the objective lens array 241. In certain embodiments, the detector 1240 is adjacent to and / or integrated with the objective lens array 241. For example, the detector array may be implemented by incorporating a CMOS chip detector into the bottom electrode of the objective lens array.

[0115]

[0131] In one variation on the embodiment of Figure 15, the condenser lens array 1231 and collimator 235 are omitted, as disclosed in European Patent Application No. 20196714.8, filed September 17, 2020, which is incorporated by reference at least solely for its disclosure of such an electron-optical architecture. Such an arrangement may include a source 201, a collimator (which may be a macro-collimator lens or a collimator lens array), a scanning deflector (which may be a macro-scanning deflector or a scanning deflector array), a control lens, an objective lens array, and a detector array. This arrangement may include a beam-shaping limiter (or beam-shaping limiting array) and an upper beam limiter. The source 201 emits electrons toward the upper beam limiter, which defines an array of beam-limiting apertures. The upper beam limiter may be referred to as an upper beam-limiting aperture array or an upper beam-limiting aperture array. The upper beam limiter may include a plate (which may be a slab) with multiple apertures. The upper beam limiter forms sub-beams from the charged particle beam emitted by the source 201. The upper beam limiter may be associated with a control lens array and may form the up-beam electrode of the control lens array. Portions of the beam other than those contributing to the formation of the sub-beams may be blocked (e.g., absorbed) by the upper beam limiter, e.g., to prevent interference with the down-beam sub-beams. A collimator array (e.g., formed using MEMS fabrication techniques) may collimate the individual sub-beams and direct them to the control lenses. In this variation, optionally, the upper beam limiter, collimator element array, control lens 250, scanning deflector array 260, objective lens 234, beam shaping limiter, and detector module 1240 may all be formed using MEMS fabrication techniques.

[0116]

[0132] The beam shaping limiter is associated with the objective lens and shapes the sub-beams in the down beam of the control lens. The scanning deflector scans the sub-beams defined in the up beam of the beam shaping limiter over the beam shaping limiter. The beam shaping limiter shapes the accidental sub-beams on the sample surface. The use of the beam shaping limiter can reduce, if not minimize, the aberrations imparted by the control lens. Because the beam shaping limiter is in the down beam of the control lens array, the aperture of the beam shaping limiter adjusts the beam current along the beam path. Therefore, the control of the magnification by the control lens acts differently on the aperture angle. That is, the aperture of the beam shaping limiter breaks the direct correspondence between the variation of the magnification and the aperture angle.

[0117]

[0133] In tools with variable landing energy (such as those described above with reference to Figure 15), the Z position of the focal spot (i.e., its position along the beam path) varies with landing energy. The primary reason for this is that the focal length of the objective lens is approximately equal to four times the landing energy divided by the electrostatic field of the objective lens. To improve the objective lens's aberration level, it is desirable to maintain the electrostatic field as high as possible. As a result, the focal length varies proportionally with the landing energy. If the Z position of the focal spot is too close to the objective lens, it is possible to reduce the electrostatic field of the objective lens, but this results in a loss of resolution. Traditionally, the sample is moved in the Z direction to ensure that the primary beam is accurately focused on the wafer. In some configurations, the Z position of the focal spot can vary by up to 1 mm with a landing energy change of 500 V to 5 kV, resulting in significant fluctuations in the measurement signal, which depends on the distance between the sample and the detector. The relationship between changes in landing energy and changes in the Z position of the focal spot depends in part on the lens strength of the objective lens, and therefore, in other configurations, the range of variation in the Z position of the focal spot may be greater or less than 1 mm. There may be a linear relationship between landing energy and focal length. Within the above range of landing energy, resolution can be substantially maintained.

[0118]

[0134] According to certain embodiments, it is proposed to maintain the position of the detector relative to the sample even if the sample moves relative to the objective lens, for example, due to a change in focal position as a result of a change in landing energy. For example, the distance between the sample and the detector is maintained within a range of approximately 50 to 100 μm. In certain embodiments, the distance between the objective lens and the sample may be approximately 250 μm or greater. However, there is a lower limit to how close the objective lens can be positioned relative to the sample, and therefore the proximity of the focal points of the sub-beams to the objective lens. In such situations, there is a risk that the objective lens electrodes may need to be too thin to be easily manufactured. Detectors used in such arrangements may need to be too thin to be easily manufactured. The desired distance between the sample and the detector may depend on the size of the detector (e.g., electrode diameter) and / or the detector pitch. Other things being equal, larger detectors and / or larger detector pitches may allow for a greater distance between the sample and the detector. Thus, certain embodiments of the present invention can maintain high secondary electron detection at a given beam pitch and detector diameter.

[0119]

[0135] Two approaches are proposed for maintaining a constant distance between the sample and the detector. As shown in FIG. 16, the detector module 240 is connected to an actuator system 245, which is configured to position the detector module 245 in a direction parallel to the propagation direction of the electron beam (i.e., perpendicular to the surface of the sample). In FIG. 16, A, B, and C show configurations with the detector at different vertical positions. The actuator system 245 can be connected to the overall control system 50 to maintain the detector module 245 at a constant distance from the sample. This is true even when the sample is moved, for example, to position the surface at a focal position that changes due to changes in the landing energy of the electron beam. Maintaining a precise constant distance between the detector module 240 and the sample 208 may not be necessary. Rather, it may be sufficient to reduce the variation in distance to an acceptable level. The actuator system 245 can include a variety of different types of actuators, such as piezoelectric actuators and Lorentz actuators. One actuator may be sufficient to position all sensor units of a detector module, or multiple actuators may be used, each actuator positioning a group of sensor units. It is also possible to have one or multiple actuators per sensor unit. Because there may be multiple detectors in an array on a substrate, the actuator arrangement may actuate the substrate. Desirably, the actuators can reposition the detector modules in a few seconds or less.

[0120]

[0136] In addition to positioning the detector in Z, the actuator system 245 may be configured to position the detector in other degrees of freedom, such as Rx and Ry. However, providing actuation in additional degrees of freedom may undesirably increase complexity.

[0121]

[0137] In another approach, the detectors are interchangeable. In one embodiment, shown in FIG. 17, two or more (e.g., three, four, or five) detector modules are interchangeable. Each interchangeable detector module 240a, 240b, 240c is configured to have the charged particle receiving surface of its sensor unit at a different vertical position relative to the objective lens 401. For example, each detector module 240a, 240b, 240c may be formed on a substrate of different dimensions (e.g., thickness). Alternatively or additionally, spacers of different thicknesses may be provided. Such spacers may be used to space the detectors relative to the objective lens array. Detector modules may be interchangeable alone or in combination with other elements, such as the objective lens assembly, objective lens array, beam shaping restrictor, upper restrictor array, collimator array, scanning deflector array, and / or control lens array. Different electronic optical components may have their own designated modules. They may be configured with other electron-optical components in the same module so that there are fewer modules than the number of replaceable electron-optical components. Alternatively, all replaceable electron-optical components (preferably MEMS elements), for example, of an objective lens assembly, may be in a replaceable module. In some arrangements, the module may include an actuator for actuating, for example, the detector array relative to other electron-optical components in the module. Spacers used to space electron-optical components may be replaceable. Spacers may be incorporated between electron-optical components in modules with multiple electronic components.

[0122]

[0138] Desirably, an automatic exchange mechanism is provided so that modules, such as detector modules, can be swapped between operational and non-operational positions, for example, between evaluations of successive samples or groups of samples, without opening the tool. Alternatively, modules, such as detector modules, may be manually exchangeable (e.g., field exchangeable). As described in U.S. patent application Ser. No. 63 / 037,481, filed June 10, 2020, a field exchangeable module can be removed and replaced with the same or a different module while maintaining the vacuum within which the electro-optical tool 40 is located, which U.S. patent application is incorporated herein by reference, at least insofar as the features enabling the exchangeable modules are incorporated by reference. To allow a module to be removed and replaced or replaced, holes are drilled only in the section of the column corresponding to the module being replaced. This is less desirable than an automatic exchange mechanism because opening the tool increases downtime, but may still be beneficial when measurements are made over an extended period of time with the same beam settings. If an automatic exchange device is provided, replacing a module may take on the order of minutes, whereas manual exchange may take on the order of hours. Activating an electro-optical component such as a detector may be quicker than automatic or manual exchange of a module, taking a few seconds. The vertical position of the detector module may also be controlled by the use of an exchangeable spacer, which may be exchangeable by an automatic or manual operation arrangement as described for the electro-optical module. The exchangeable spacer may be incorporated into the exchangeable module.

[0123]

[0139] An evaluation tool according to an embodiment of the present invention may be a tool that makes a qualitative evaluation of a sample (e.g., pass / fail), a tool that makes a qualitative measurement of a sample (e.g., size of a feature), or a tool that generates an image of a map of a sample. Examples of evaluation tools are inspection tools and metrology tools.

[0124]

[0140] The following clauses are exemplary embodiments of the present invention.

[0125]

[0141] Clause 1: A charged particle evaluation tool comprising: an objective lens configured to project a plurality of charged particle beams onto a sample, the objective lens having a sample-facing surface defining a plurality of beam apertures through which each charged particle beam of the charged particle beams is emitted toward the sample; and a plurality of capture electrodes adjacent to each of the beam apertures and configured to capture charged particles emitted from the sample.

[0126]

[0142] Clause 2: The tool of clause 1, wherein each capture electrode is configured to substantially surround a respective beam aperture.

[0127]

[0143] Clause 3: The tool of clause 1 or 2, wherein the capture electrode is configured to substantially fill the sample-facing surface.

[0128]

[0144] Clause 4: The tool of clause 1 or 2, wherein the capture electrode has a circular perimeter.

[0129]

[0145] Clause 5: The tool of any one of clauses 1 to 4, further comprising a substrate mounted on the sample-facing surface of the objective lens, the substrate having a capture electrode formed thereon.

[0130]

[0146] Clause 6: The tool of clause 5, further comprising control circuitry formed on the substrate.

[0131]

[0147] Clause 7: The tool of clause 6, wherein the control circuitry includes one or more of an amplifier, e.g., a transimpedance amplifier, an analog-to-digital converter, a data multiplexer, and a readout gate.

[0132]

[0148] Clause 8: The tool of clause 7, wherein the control circuitry includes one amplifier per capture electrode.

[0133]

[0149] Clause 9: The tool of any one of clauses 5 to 8, further comprising a conductive trace to a capture electrode on the opposite side of the substrate.

[0134]

[0150] Clause 10: The tool of any one of clauses 5 to 9, further comprising a via through the substrate.

[0135]

[0151] Clause 11: The tool of any one of clauses 5 to 10, wherein the substrate is formed from silicon.

[0136]

[0152] Clause 12: A tool according to any one of clauses 1 to 11, wherein the capture electrode is formed by a CMOS process.

[0137]

[0153] Clause 13: A tool according to any one of clauses 1 to 12, wherein each capture electrode comprises a plurality of electrode elements.

[0138]

[0154] Clause 14: A method for manufacturing an evaluation tool, comprising forming a plurality of capture electrodes on a substrate and forming a plurality of apertures in the substrate, and attaching the substrate to an objective lens configured to project the plurality of charged particle beams onto a sample so that the plurality of charged particle beams can be emitted through the apertures.

[0139]

[0155] Clause 15: The method of clause 14, wherein the aperture is formed by etching through the substrate.

[0140]

[0156] Clause 16: An inspection method comprising emitting a plurality of charged particle beams onto a sample through a plurality of beam apertures, and capturing charged particles emitted by the sample in response to the charged particle beams using a plurality of capture electrodes provided adjacent to each of the beam apertures.

[0141]

[0157] Clause 17: A multi-beam electron optical system including a last electron optical element in a multi-beam path of the multi-beam electron optical system, the last electron optical element including: a multi-manipulator array, each array element configured to manipulate at least one electron beam in the multi-beam path; and a detector configured and oriented to detect electrons emitted from a sample positioned in the multi-beam beam path, the detector including a plurality of electrodes incorporated within the multi-manipulator array, at least one electrode associated with each array element.

[0142]

[0158] Clause 18: A final electron optical element of a multi-charged beam projection system configured to project a plurality of charged particle beams onto a sample, the final electron optical element comprising: an objective lens having a sample-facing surface defining a plurality of beam apertures through which each charged particle beam of the charged particle beams is emitted towards the sample; and a plurality of capture electrodes adjacent to each of the beam apertures and configured to capture charged particles emitted from the sample.

[0143]

[0159] Clause 19: A charged particle evaluation tool comprising: an objective lens configured to project a plurality of charged particle beams onto a sample, the objective lens defining a plurality of beam apertures through which each charged particle beam of the charged particle beams can propagate towards the sample; and a plurality of sensor units adjacent to each beam aperture of the beam apertures and configured to capture charged particles emitted from the sample.

[0144]

[0160] Clause 20: A tool as described in clause 19, wherein each sensor unit is configured to substantially surround a respective beam aperture.

[0145]

[0161] Clause 21: The tool of clause 19 or 20, wherein the sensor unit has a circular perimeter.

[0146]

[0162] Clause 22: The tool according to any one of clauses 19 to 21, further comprising a substrate provided on a surface of the objective lens facing the down beam, the sensor unit being formed on the substrate.

[0147]

[0163] Clause 23: The tool of clause 22, wherein the sensor unit is configured to substantially fill the sample-facing surface.

[0148]

[0164] Clause 24: A tool according to clause 22 or 23, wherein the sensor unit is a capture electrode.

[0149]

[0165] Clause 25: A tool described in any one of clauses 19 to 24, further comprising a substrate provided on the up-beam facing surface of the objective lens, on which a sensor unit is formed, preferably the sensor unit being configured to face the down-beam.

[0150]

[0166] Clause 26: The tool of clause 25, wherein the sensor unit is selected from the group consisting of a PIN detector and a scintillator.

[0151]

[0167] Clause 27: The tool of any one of clauses 22 to 26, further comprising control circuitry formed on the substrate.

[0152]

[0168] Clause 28: The tool of clause 27, wherein the control circuitry includes one or more of an amplifier, e.g., a transimpedance amplifier, an analog-to-digital converter, a data multiplexer, and a readout gate.

[0153]

[0169] Clause 29: The tool of clause 28, wherein the control circuit includes one amplifier per sensor unit.

[0154]

[0170] Clause 30: A tool according to any one of clauses 22 to 29, further comprising conductive traces to the sensor unit on the opposite side of the substrate.

[0155]

[0171] Clause 31: The tool of any one of clauses 22 to 30, further comprising a via through the substrate.

[0156]

[0172] Clause 32: The tool of any one of clauses 22 to 31, wherein the substrate is formed from silicon.

[0157]

[0173] Clause 33: A tool according to any one of clauses 19 to 32, wherein the sensor unit is formed by a CMOS process.

[0158]

[0174] Clause 34: A tool according to any one of clauses 19 to 33, wherein each sensor unit comprises a plurality of sensor elements.

[0159]

[0175] Clause 35: A tool according to any one of clauses 19 to 34, wherein the objective lens is an electrostatic lens.

[0160]

[0176] Clause 36: A tool described in any one of clauses 19 to 35, further comprising an actuation system configured to adjust the position of the sensor unit in a direction parallel to the direction of propagation of the electron beam.

[0161]

[0177] Clause 37: A tool described in any one of clauses 19 to 36, comprising a first sensor unit array, a second sensor unit array, and an exchange mechanism configured to selectively position one of the first sensor unit array and the second sensor unit array on the down beam facing surface of the objective lens, wherein the first sensor unit array and the second sensor unit array are configured such that when each array is positioned on the down beam facing surface, the sensor units of the first sensor unit array are positioned at a different distance from the objective lens than the sensor units of the second sensor unit array.

[0162]

[0178] Clause 38: A charged particle evaluation tool comprising: an objective lens configured to project a plurality of charged particle beams onto a sample through a plurality of beam apertures defined in the objective lens; and a sensor array comprising a plurality of sensor units adjacent to each beam aperture and configured to capture charged particles emitted from the sample, wherein the sensor array is configured to be adjustable between positions along the beam path of the charged particle beam.

[0163]

[0179] Clause 39: A tool as described in clause 38, wherein the sensor array is configured to be adjustable by actuating the sensor array along the beam path.

[0164]

[0180] Clause 40: The tool of clause 39, further comprising an actuator configured to actuate the sensor array along the beam path.

[0165]

[0181] Clause 41: A charged particle evaluation tool comprising: an objective lens configured to project a plurality of charged particle beams onto a sample through a plurality of beam apertures defined in the objective lens; and a sensor array comprising a plurality of sensor units adjacent to each beam aperture and configured to capture charged particles emitted from the sample, wherein the sensor array is configured to be operable along the beam path of the charged particle beams.

[0166]

[0182] Clause 42: A tool described in any one of clauses 36 to 41, further comprising a beam energy control system configured to control the landing energy of the electron beam on the sample.

[0167]

[0183] Clause 43: A tool according to any one of clauses 36 to 42, further comprising a control lens array in the up-beam of the objective lens array.

[0168]

[0184] Clause 44: A tool as described in Clause 43, wherein the objective lens array and the control lens array include at least a plurality of electrodes configured such that, when operated, the objective lens focuses the charged particle beam onto the sample and the control lens adjusts the beam aperture angle and / or reduction ratio.

[0169]

[0185] Clause 45: A multi-beam charged particle optical column configured to direct multiple beams towards a sample, the multiple beams being generated down beam from a source, the column including a detector configured to capture charged particles emitted from the sample, the detector being operable along the beam path.

[0170]

[0186] Clause 46: A multi-beam charged particle optical column according to clause 45, wherein the detector comprises a sensor array, each sensor being assigned to a respective sub-beam of the multi-beam.

[0171]

[0187] Clause 47: A multi-beam charged particle optical column according to clause 45 or 46, wherein the column comprises a beam-limiting aperture array configured to generate multiple beams arising from the source beam.

[0172]

[0188] Clause 48: A multi-beam charged particle optical column according to clause 47, wherein the detector is in the down beam of the beam limiting aperture array.

[0173]

[0189] Clause 49: A multi-beam charged particle optical column according to any one of clauses 45 to 48, wherein the detector is incorporated within an objective lens assembly including the objective lens.

[0174]

[0190] Clause 50: A method for manufacturing an evaluation tool, comprising forming a plurality of sensor units on a substrate and forming a plurality of apertures in the substrate, and attaching the substrate to an objective lens configured to project the plurality of charged particle beams onto a sample so that the charged particle beams can be emitted through the apertures.

[0175]

[0191] Clause 51: The method of clause 50, wherein the aperture is formed by etching through the substrate.

[0176]

[0192] Clause 52: An inspection method comprising: emitting a plurality of charged particle beams onto a sample through a plurality of beam apertures; and capturing charged particles emitted by the sample in response to the charged particle beams using a plurality of sensor units provided adjacent to respective beam apertures of the beam apertures.

[0177]

[0193] Clause 53: The method of clause 52, further comprising changing the position of the sensor unit along the path of the charged particle beam.

[0178]

[0194] Clause 54: A multi-beam electron optical system comprising a last electron optical element in a multi-beam path of the multi-beam electron optical system, the last electron optical element comprising: a multi-manipulator array, each array element configured to manipulate at least one electron beam in the multi-beam path; and a detector configured and oriented to detect electrons emitted from a sample positioned in the multi-beam beam path, the detector comprising a plurality of sensor units incorporated within the multi-manipulator array, at least one sensor unit associated with each array element.

[0179]

[0195] Clause 55: A final electron optical element of a multi-charged beam projection system configured to project a plurality of charged particle beams onto a sample, the final electron optical element comprising: an objective lens having a sample-facing surface defining a plurality of beam apertures through which each charged particle beam of the charged particle beams can propagate towards the sample; and a plurality of sensor units adjacent to each of the beam apertures and configured to capture charged particles emitted from the sample.

[0180]

[0196] The above description is intended to be illustrative rather than limiting. Thus, it will be apparent to one skilled in the art that modifications can be made as described without departing from the scope of the claims set out below.

Claims

1. an objective lens for projecting a plurality of charged particle beams onto a sample, the objective lens defining a plurality of beam apertures through which each of the charged particle beams can propagate toward the sample; a plurality of sensor units substantially surrounding each of the beam apertures and configured to capture charged particles emitted from the sample; Charged particle evaluation tools, including:

2. The tool of claim 1 , wherein the sensor unit has a circular perimeter.

3. The tool according to claim 1 or 2, further comprising a substrate provided on a down-beam-facing surface of the objective lens, the sensor unit being formed on the substrate.

4. The tool of claim 3 , wherein the sensor unit substantially fills the sample-facing surface.

5. The tool according to claim 3 or 4, wherein the sensor unit is a capture electrode.

6. A tool described in any one of claims 1 to 5, further comprising a substrate provided on an up-beam facing surface of the objective lens, the sensor unit being formed on the substrate, and preferably configured so that the sensor unit faces the down-beam.

7. The tool according to any one of claims 1 to 6, wherein the plurality of sensor units are integrated into the objective lens.

8. A tool according to any one of claims 3 to 7, further comprising control circuitry formed on the substrate.

9. The control circuit an amplifier, e.g., a transimpedance amplifier; analog-to-digital converter, a data multiplexer, and Readout gate, The tool of claim 8 , comprising one or more of:

10. The tool of any one of claims 3 to 9, further comprising a via through the substrate.

11. A tool according to any one of claims 1 to 10, wherein each sensor unit comprises a plurality of sensor elements.

12. The tool of claim 11 , wherein the plurality of sensor elements radially divide each sensor unit.

13. 13. The tool of claim 11 or 12, wherein the plurality of sensor elements angularly separate each sensor unit.

14. A tool according to any one of the preceding claims, wherein the beam apertures can be arranged in a hexagonal array.

15. directing a plurality of charged particle beams toward a sample through a plurality of beam apertures; capturing charged particles emitted by the sample in response to the charged particle beam using a plurality of sensor units disposed around each of the beam apertures; 12. A testing method comprising:

Images