Charged particle evaluation tools, inspection methods and images

Abstract

1. A multi-beam electron optics system for a charged particle characterization tool, comprising: an objective lens array assembly including a plurality of objective lenses each configured to project one of a plurality of charged particle beams onto a sample; a detector array associated with the objective lens array assembly and configured to detect charged particles emitted from the sample; and circuitry including an amplifier in data communication with the detector array, wherein the amplifier is configured to be adjustable to adjust amplification of a signal from the detector array.

Description

[Technical Field]

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims priority to European Patent Application Publication No. 20210844.5, filed December 1, 2020, which is incorporated herein by reference in its entirety.

[0002] FIELD OF THE INVENTION

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

[0003]

[0003] When manufacturing semiconductor integrated circuit (IC) chips, unwanted 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 unwanted 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 between the material structure at the probing spot and the landing electrons from the electron beam 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 structure of the sample. Scanning the primary electron beam as a probing spot across the sample surface can cause secondary electrons to 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 that represents the characteristics of the material structure of the surface of the sample.

[0005]

[0005] There is a general need to improve the quality of images that can be obtained by charged particle characterization tools, and in particular it is desirable to be able to improve the level of detail in the images. Summary of the Invention

[0006]

[0006] An object of the present disclosure is to provide embodiments that assist in improving the detail or other characteristics of images that can be obtained with charged particle evaluation tools.

[0007] According to a first aspect of the present invention, there is provided a multi-beam electron optics system for a charged particle characterization tool, comprising: an objective lens array assembly including a plurality of objective lenses each configured to project one of the plurality of charged particle beams onto the sample; a detector array associated with the objective lens array assembly and configured to detect charged particles emitted from the sample; a circuit including an amplifier in data communication with the detector array; A multi-beam electron optics system is provided in which the amplifier is configured to be adjustable to adjust the amplification of the signal from the detector array.

[0008] According to a second aspect of the present invention, there is provided a multi-beam electron optics system for a charged particle characterization tool, comprising: a current detector array configured to detect charged particles emitted from the sample by reference to their charge; a circuit including an amplifier in data communication with the detector array; A multi-beam electron optics system is provided in which the amplifier is configured to be adjustable to adjust the amplification of the signal from the detector array.

[0009] According to a third aspect of the present invention, there is provided a method for characterizing a surface of a sample using a plurality of sub-beams, comprising the steps of: projecting the sub-beams onto a surface of the sample using an objective lens array assembly; detecting charged particles emitted from the sample with a detector array associated with the objective lens array assembly; amplifying the signal from the detector array with an amplifier; A method is provided in which the amplifier is configured to be adjustable to adjust the amplification of the signal from the detector array.

[0010] According to a fourth aspect of the present invention, there is provided a method for characterizing a surface of a sample using a plurality of sub-beams, comprising the steps of: projecting the sub-beams onto a surface of a sample; detecting, with a detector array, current-charged particles emitted from the sample by reference to their charge; amplifying the signal from the detector array with an amplifier; A method is provided in which the amplifier is configured to be adjustable to adjust the amplification of the signal from the detector array.

[0011] According to a fifth aspect of the present invention, there is provided an image of a sample formed from data from a charged particle characterization tool, comprising: a plurality of image areas formed from data from respective detectors of the charged particle characterization tool, the data including a plurality of image areas indicative of a current of charged particles emitted from respective areas of the sample; The image area is provided with an image containing the same number of gray levels corresponding to different currents of charged particles emitted from the sample.

[0012]

[0012] 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]

[0013] [Figure 1] FIG. 1 is a schematic diagram illustrating an exemplary charged particle beam inspection apparatus. [Figure 2]

[0014] 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]

[0015] 1 is a schematic diagram of an exemplary multi-beam device according to one embodiment. [Figure 4]

[0016] 2 is a schematic cross-sectional view of an objective lens of an inspection apparatus according to an embodiment. [Figure 5]

[0017] 10 is a schematic cross-sectional view of an objective lens of an inspection apparatus according to an alternative embodiment. [Figure 6]

[0018] FIG. 6 is a bottom view of the objective lens of FIG. 4 or FIG. 5. [Figure 7]

[0019] FIG. 6 is a bottom view of a modification of the objective lens of FIG. 4 or FIG. 5. [Figure 8]

[0020] FIG. 6 is an enlarged schematic cross-sectional view of a detector incorporated in the objective lens of FIG. 4 or FIG. 5. [Figure 9]

[0021] 1 is a schematic diagram of an exemplary electron-optical system including a macro-collimator and a macro-scan deflector. [Figure 10]

[0022] FIG. 2 is a schematic diagram of an exemplary circuit incorporated into a multi-beam device according to one embodiment. [Figure 11]

[0023] FIG. 2 is a schematic diagram of a portion of an exemplary circuit incorporated into a multi-beam device according to one embodiment. [Figure 12]

[0024] 1 is a schematic diagram of an exemplary multi-beam device according to one embodiment. [Figure 13]

[0025] FIG. 13 is a schematic diagram of a portion of the multi-beam device of FIG. 12. [Figure 14]

[0026] 1 is a schematic diagram of an exemplary multi-beam device according to one embodiment. [Figure 15]

[0027] 1 is an exemplary image. [Figure 16]

[0028] 16 is a version of the image of FIG. 15 in which the signals in different quadrants are amplified by different factors. [Figure 17]

[0029] A version of the image in Figure 16 that has been post-processed to correct for brightness range. DETAILED DESCRIPTION OF THE INVENTION

[0014]

[0030] 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, unless otherwise indicated, identical numbers in different drawings represent identical or similar elements. 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.

[0015]

[0031] 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 ever-smaller structures. For example, an IC chip in a smartphone the size of a thumbnail and available before 2019 can contain over 2 billion transistors, each less than 1 / 1000 the size of a human hair. It is therefore 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 step 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 had a 95% yield, the overall process yield would be as low as 7%.

[0016]

[0032] In IC chip manufacturing facilities, while high process yields are desirable, 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.

[0017]

[0033] 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 one or more focused beams of primary electrons across a sample, such as a substrate. Together, at least the illumination system or illumination system and the projection system or projection system may be referred to as the electron-optical system or system. 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 may be referred to as subbeams or beamlets. A multibeam can simultaneously scan different portions of the sample. Therefore, multibeam inspection systems can inspect samples much faster than single-beam inspection systems.

[0018]

[0034] Known implementations of multi-beam inspection devices are described below.

[0019]

[0035] 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 specification, references to electrons can be considered to be references to charged particles more generally, and charged particles are not necessarily electrons.

[0020]

[0036] Reference is now made to Figure 1, which 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.

[0021]

[0037] 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 may receive, for example, substrate front-opening integrated 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) within the EFEM 30 transport the samples to the load lock chamber 20.

[0022]

[0038] 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 can 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 can include a multi-beam electron optical device.

[0023]

[0039] 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 the controller 50 is shown in FIG. 1 as being external to the structure including the main chamber 10, the load lock chamber 20, and the EFEM 30, it 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.

[0024]

[0040]

[0023] Referring now to Figure 2, Figure 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 Figure 1. The multi-beam electron beam tool 40 (also referred to herein as apparatus 40) 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 40 further includes a detector array 240 (e.g., an electron detection device).

[0025]

[0041] The electron source 201 may include a cathode (not shown) and an extractor or anode (not shown). In 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.

[0026]

[0042] 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 may be referred to as beamlets.

[0027]

[0043] 1, such as the electron emitter 201, the detector array 240, 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 the charged particle beam inspection system, including the charged particle multi-beam system.

[0028]

[0044] 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 within 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.

[0029]

[0045] Detector array 240 is configured to detect the secondary electrons and / or backscattered electrons and generate corresponding signals that are sent to a signal processing system (not shown), for example, to construct an image of a corresponding scanned area of ​​sample 208. Detector array 240 may be incorporated into projection apparatus 230. Alternatively, as shown in FIG. 14 , detector array 240 may be separate from projection apparatus 230, with a secondary optical column provided to direct the secondary electrons and / or backscattered electrons to an electron detection device.

[0030]

[0046] The signal processing system may include circuitry 60 (shown in FIG. 10 ) configured to process signals from the detector array 240 to form an image. The signal processing system may be incorporated into a component of a column, such as the detector array 240, or part of the projection device 230. Alternatively, the signal processing system may be incorporated into the controller 50, or additionally, part of the signal processing system may be incorporated into the controller 50. The image processing system may include an image acquirer (not shown) and a storage device (not shown). For example, the image processing system 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 detector array 240 via electrical conductors, fiber optic cables, portable storage media, IR, Bluetooth, the Internet, a wireless network, a wireless radio, or a combination thereof, among others, to enable signal communication. The image acquirer can receive signals from the detector array 240, process the data contained in the signals, and construct an image therefrom. Thus, the image acquirer can acquire an image of the sample 208. The image acquirer can also perform various post-processing functions, such as creating contours and superimposing indicators on the acquired image. The image acquirer can be configured to adjust the brightness and contrast of the acquired image, etc. The storage can be a storage medium, such as a hard disk, a flash drive, cloud storage, random access memory (RAM), or other type of computer-readable memory. The storage can be coupled to the image acquirer and can be used to store the raw scanned image data as the original image or to store post-processed images.

[0031]

[0047] The image acquirer can acquire one or more images of the sample based on imaging signals received from the detector array 240. The imaging signals 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 including features of the sample 208. Each imaging area can correspond to secondary electrons resulting from a respective sub-beam 211-213. 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 image processing system can be configured to perform image processing steps using multiple images of the same location of the sample 208.

[0032]

[0048] The image processing system 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.

[0033]

[0049] 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 speed, 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 50 may control the stage speed (including its direction) depending on the characteristics of the inspection step of the scanning process.

[0034]

[0050] FIG. 3 is a schematic diagram of the evaluation tool. An electron source 201 directs electrons toward an array of condenser lenses 231, which form part of a projection system 230. The electron source 201 is preferably a high-brightness thermal field emitter with a good compromise between brightness and total emission current. There may be tens, hundreds, or even thousands of condenser lenses 231. The condenser lenses 231 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 the electron beam into multiple sub-beams (the array providing one lens per sub-beam). The array of condenser lenses 231 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 positions of the sub-beams. At least two of the plates are maintained at different potentials during operation to achieve the desired lens effect. A voltage source is configured to apply a potential to each electrode. A further voltage source may be connected to the sample 208 to apply a potential, which may be defined relative to the sample 208 and / or the radiation source 201.

[0035]

[0051] In one configuration, the array of collecting lenses 231 is formed from a three-plate array in which charged particles have the same energy when they enter and exit each lens; this configuration can be called an Einzel lens. Dispersion therefore occurs only within the Einzel lens itself (between the entrance and exit electrodes of the lens), thereby limiting off-axis chromatic aberration. If the collecting lenses are thin, e.g., a few mm thick, the effect of such aberrations is small or negligible.

[0036]

[0052] Each condenser lens 231 in the array directs electrons into a respective sub-beam 211, 212, 213 that converges at a respective intermediate focus. The sub-beams diverge relative to one another. The sub-beam paths diverge down the condenser lens 231. In one embodiment, a deflector 235 is provided at the intermediate focus. The deflector 235 is positioned in the beamlet path at or at least around the position or focus point (i.e., convergence point) of the corresponding intermediate focus 233. The deflector is positioned in or near the beamlet path at an intermediate image plane of the associated sub-beam. The deflector 235 is configured to act on each sub-beam 211, 212, 213. The deflector 235 is configured to bend each beamlet 211, 212, 213 by an amount effective to ensure that the chief ray (which may also be referred to as the beam axis) is incident on the sample 208 substantially perpendicularly (i.e., at substantially 90° relative to the nominal surface of the sample). The deflector 235 may also be referred to as a collimator or a collimator-deflector. The deflector 235 effectively collimates the paths of the beamlets so that before the deflector, the paths of the beamlets diverge with respect to each other. Down the beam from the deflector, the beamlet paths are substantially parallel to each other, i.e., substantially collimated. A suitable collimator is the deflector disclosed in European Patent Application Publication No. 20156253.5, filed February 7, 2020, which is incorporated herein by reference with respect to the application of deflectors to multi-beam arrays.

[0037]

[0053] Below the deflector 235 (i.e., down the beam or further from the radiation source 201) is a control lens array 250 that includes a control lens for each of the sub-beams 211, 212, 213. The control lens array 250 may include a three-plate electrode array connected to a respective voltage source. The function of the control lens array 250 is to optimize the beam divergence angle with respect to the beam demagnification and / or to 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.

[0038]

[0054] For ease of illustration, lens arrays are generally depicted herein as arrays of ellipses. Each ellipse represents one of the lenses in the lens array. Ellipses are conventionally used to represent lenses by analogy with the biconvex shape often employed in optical lenses. However, it should be understood that in the context of charged particle mechanisms as discussed herein, lens arrays typically operate electrostatically and may not require physical elements employing a biconvex shape. Instead, lens arrays may include multiple plates having apertures.

[0039]

[0055] 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 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.

[0040]

[0056] A detector array 240 is provided to detect secondary and / or backscattered electrons emitted from the sample 208. In one embodiment, the detector array 240 is between the objective lens 234 and the sample 208. However, other locations are possible for the detector array 240, as shown, for example, in Figures 12 and 14. Exemplary configurations of the detector array 240 are described below.

[0041]

[0057] An exemplary embodiment of a detector array integrated with an objective lens array is shown in Figure 4, which shows a schematic cross-sectional view of a portion of a multi-beam objective lens array 240. In this embodiment, the detector array 240 is a plurality of detector elements 405 (e.g., sensor elements such as capture electrodes). In this embodiment, the detector array 240 is provided at the output side of the objective lens array 241. The output side is the output side of the objective lens array 241.

[0042]

[0058] The objective lens array 241 may be configured to demagnify the electron beam by a factor of more than 10, preferably in the range of 50-100 or more. The objective lens array 241 may include a central electrode, a lower electrode, and an upper electrode. The central electrode, the lower electrode, and the upper electrode each have an aperture through which each sub-beam propagates. The potential of the lower electrode may be similar to the potential of the sample 208. Thus, if the objective lens array has three electrodes, it may be an array of Einzel lenses.

[0043]

[0059] As shown in FIG. 5, in one embodiment related to the embodiment shown in FIG. 4, one of the electrodes may be omitted. An objective lens array 240 with only two electrodes may have smaller aberrations than an objective lens array 240 with more electrodes. A three-electrode objective lens allows for a larger potential difference between the electrodes, thereby enabling a more powerful lens. Additional electrodes (i.e., three or more electrodes) provide additional degrees of freedom in controlling the electron trajectory, for example, to focus secondary electrons in addition to the incident beam. An advantage of a two-electrode lens over an Einzel lens is that the energy of the incoming beam is not necessarily the same as the outgoing beam. The potential difference across such a two-electrode lens array advantageously allows it to function as a deceleration lens array.

[0044]

[0060] FIG. 6 is a bottom view of detector array 240, which includes a substrate 404 on which a plurality of detector elements 405 are provided, each surrounding a beam aperture 406. The beam apertures 406 may be formed by etching the substrate 404. In the configuration shown in FIG. 6, the beam apertures 406 are shown as a rectangular array. The beam apertures 406 may alternatively be arranged, for example, in a close-packed hexagonal array as shown in FIG. 7. The hexagonal beam configuration of FIG. 7 may be more densely packed than the square beam configuration shown in FIG. 6.

[0045]

[0061] FIG. 8 shows a cross-sectional view of a portion of the detector array 240 on a larger scale. The detector elements 405 form the bottom surface of the detector array 240, i.e., the surface closest to the sample 208. A logic layer 407 is provided between the detector elements 405 and the main body of the substrate 404. At least a portion of the image processing system may be integrated into the logic layer 407. The logic layer 407 may include at least a portion of the circuit 60 that embodies at least a portion of the image processing system. The logic layer 407 may include amplifiers, such as transimpedance amplifiers (TIAs), analog-to-digital converters, and readout logic. In one embodiment, there is one amplifier and one analog-to-digital converter per detector element 405. The logic layer 407 and the detector elements 405 may be fabricated using a CMOS process, with the detector elements 405 forming the final metallization layer.

[0046]

[0062] The wiring layer 408 is provided on the backside or inside the substrate 404 and is connected to the logic layer 407 by through-substrate vias 409. The number of through-substrate vias 409 does not need to be the same as the number of beam apertures 406. In particular, if the electrode signals are digitized in the logic layer 407, only a few through-silicon vias may be needed to provide a data bus. The wiring layer 408 may include control lines, data lines, and power lines. Note that despite the presence of the beam apertures 406, there is sufficient space for all necessary connections. The detection module 402 may also be fabricated using bipolar or other manufacturing techniques. A printed circuit board and / or other semiconductor chips may be provided on the backside of the detector array 240.

[0047]

[0063] The integrated detector array described above is particularly advantageous when used with tools having adjustable landing energies, since secondary electron capture can be optimized for a range of landing energies. The detector array can be integrated not only into the bottom electrode array, but also into other electrode arrays. Further details and alternative configurations of detector modules integrated into objective lenses can be found in EP 20184160.8, which is incorporated herein by reference.

[0048]

[0064] In one embodiment, each element in the objective lens array 240 is a microlens that manipulates a different beam or group of beams in the multi-beam. The objective lens array 240 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 group of 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.

[0049]

[0065] In some embodiments, the detector array 240 of the objective lens array assembly is in the downbeam of at least one electrode of the objective lens array 241. In one embodiment, at least a portion of the detector (e.g., a detector module) is adjacent to and / or integrated with the objective lens array 240. For example, the detector array can be implemented by integrating a CMOS chip detector into the bottom electrode of the objective lens array. Integrating the detector array into the objective lens array 240 or other components of the primary column replaces the secondary column. The CMOS chip is preferably oriented to face the sample (due to the short distance between the wafer and the bottom of the electron-optics system (e.g., 200 μm or less, 100 μm or less, or 50 μm or less)). In one embodiment, detector elements 405 for capturing secondary electrons are formed in a surface metal layer of the CMOS device. The detector elements 405 may be formed in other layers. CMOS power and control signals may be connected to the CMOS by through-silicon vias. For robustness, a passive silicon substrate with holes preferably shields the CMOS chip from high electric fields.

[0050]

[0066] To maximize detection efficiency, it is desirable to make the surface of the detector elements 405 as large as possible so that substantially all of the area of ​​the objective lens array 240 (excluding the aperture) is occupied by detector elements 405, with each detector element 405 having a diameter substantially equal to the array pitch. In one embodiment, the outer shape of the detector elements 405 is circular, but this could be made square to maximize the detection area. The diameter of the through-substrate vias 409 could also be minimized. A typical size of the electron beam is approximately 5-15 microns.

[0051]

[0067] In one embodiment, a single detector element 405 surrounds each beam aperture 406. In another embodiment, multiple detector elements 405 are provided around each beam aperture 406. Electrons captured by the detector elements 405 surrounding one beam aperture 406 may be combined into a single signal or used to generate independent signals. The detector elements 405 may be divided radially (i.e., to form multiple concentric rings), angularly (i.e., to form multiple sectors), both radially and angularly, or in any other convenient manner.

[0052]

[0068] However, increasing the surface of the detector element 405 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 detector element 405, especially if increasing the detector element 405 provides only a slight improvement in detection efficiency but a significant increase in capacitance. Circular (annular) detector elements 405 may offer a good compromise between collection efficiency and parasitic capacitance.

[0053]

[0069] Increasing the outer diameter of the detector element 405 can also result in increased crosstalk (sensitivity to signals from adjacent holes), which can be a reason to make the outer diameter of the detector element 405 smaller, especially if enlarging the detector element 405 only provides a slight improvement in detection efficiency but a large increase in crosstalk.

[0054]

[0070] The current of backscattered and / or secondary electrons collected by the detector elements 405 is amplified by an amplifier, such as a TIA.

[0055]

[0071] 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 one embodiment, each of at least a subset of the aberration correctors is located at or directly adjacent to a respective one of the intermediate foci (e.g., located at or adjacent to an intermediate image plane). The sub-beams have a smallest cross-sectional area at or near a focal plane, such as the mid-plane. This provides more space for the aberration correctors than would be available elsewhere, i.e., at the up-beam or down-beam of the mid-plane (or in an alternative configuration without an intermediate image plane).

[0056]

[0072] In one embodiment, an aberration corrector located 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.

[0057]

[0073] Aberration correctors can correct aberrations that prevent proper column alignment. Such aberrations can also lead to misalignment between the sub-beams and the correctors. Therefore, it may be desirable, additionally or alternatively, to locate the aberration correctors at or near the condenser lenses 231 (e.g., each such aberration corrector is integrated with or directly adjacent to one or more of the condenser lenses 231). This is desirable because the condenser lenses are close to perpendicular to or coincident with the beam aperture, so that aberrations at or near the condenser lenses 231 still do not cause shifts of the corresponding sub-beams. However, a challenge with locating the correctors at or near the condenser lenses is that the cross-sectional area of ​​each sub-beam is relatively large and the pitch is relatively small at this location compared to locations further downstream. 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.

[0058]

[0074] In some embodiments, at least a subset of the aberration correctors are each integrated with or directly adjacent to one or more of the objective lenses 234. In one embodiment, these aberration correctors reduce one or more of 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 234 for scanning the sub-beams 211, 212, 213 across the sample 208. In one embodiment, the scanning deflectors described in U.S. Patent Application Publication No. 2010 / 0276606 may be used, which is incorporated herein by reference in its entirety.

[0059]

[0075] 9 is a schematic diagram of an exemplary electron-optical system having an objective lens array assembly. The objective lens array assembly includes an objective lens array 241. The objective lens array 241 includes a plurality of objective lenses. For brevity, features of the objective lens array 241 already described above may not be repeated here.

[0060]

[0076] The objective lens array assembly may further include a control lens array 250. The control lens array 250 includes a plurality of control lenses. Each control lens includes at least two electrodes (e.g., two or three electrodes) connected to a respective potential source. The control lens array 250 may include two or more (e.g., three) plate electrode arrays connected to a respective potential source. The control lens array 250 is associated with the objective lens array 241 (e.g., the two arrays are located near each other and / or mechanically connected to each other and / or controlled together as a unit). The control lens array 250 is positioned in the up-beam of the objective lens array 241. 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 rate of the sub-beams. The control lens array 250 and the objective lens array 241 work together to provide a composite focal length. A compounding operation without intermediate foci may reduce the risk of aberrations.

[0061]

[0077] In one embodiment, the electron-optical system including the objective lens array assembly is configured to control the objective lens assembly (e.g., by controlling the potentials applied to the electrodes of the control lens array 250) so that the focal length of the control lens is greater than the separation distance between the control lens array 250 and the objective lens array 241. Thus, the control lens array 250 and the objective lens array 241 may be positioned relatively close to each other, in which case the focusing effect from the control lens array 250 is weak and no intermediate focus is formed between the control lens array 250 and the objective lens array 241. In other embodiments, the objective lens array assembly may be configured to form an intermediate focus between the control lens array 250 and the objective lens array 241.

[0062]

[0078] In one embodiment, the control lens array is a replaceable module, alone or in combination with other elements such as the objective lens array and / or detector array. The replaceable module may be field replaceable, i.e., the module can be replaced with a new module by a field engineer. In one embodiment, multiple replaceable modules are included within the tool and can be swapped between operational and non-operational positions without opening the tool.

[0063]

[0079] In one embodiment, the replaceable module includes an electron-optical component on a stage that allows actuation for positioning the electron-optical component. In one embodiment, the replaceable module includes a stage. In some configurations, the stage and the replaceable module can be an integral part of the electron-optical tool 40. In some configurations, the replaceable module is limited to the stage and the electron-optical device it supports. In some configurations, the stage is removable. In an alternative design, the replaceable module including the stage is removable. The portion of the electron-optical tool 40 for the replaceable module is separable, i.e., this portion of the electron-optical tool 40 is defined by valves on the up beam and down beam of the replaceable module. The valves can be operated to separate the environment between the valves from the vacuum of the up beam and down beam, respectively, allowing the replaceable module to be removed from the electron-optical tool 40 while maintaining the vacuum of the up beam and down beam of the portion of the column associated with the replaceable module. In one embodiment, the replaceable module includes a stage. The stage is configured to support the electron-optical device relative to the beam path. In one embodiment, the module includes one or more actuators. An actuator is associated with the stage and configured to move the electron-optical device relative to the beam path, such actuation can be used to align the electron-optical device and the beam path relative to one another.

[0064]

[0080] In one embodiment, the replaceable module is a microelectromechanical systems (MEMS) module. MEMS are miniature mechanical and electromechanical elements made using microfabrication techniques. In one embodiment, the replaceable module is configured to be replaceable within the electro-optical tool 40. In one embodiment, the replaceable module is configured to be field replaceable. Field replaceable is intended to mean that a module can be removed and replaced with the same or a different module while maintaining the vacuum in which the electro-optical tool 40 is located. Only the section of the column corresponding to the module is vented to remove and replace or replace the module.

[0065]

[0081] The control lens array 250 may be in the same module as the objective lens array 241, ie, forming an objective lens array assembly or objective lens arrangement, or it may be in a separate module.

[0066]

[0082] A power supply may be provided to apply respective potentials to electrodes of the control lenses of the control lens array 250 and the objective lenses of the objective lens array 241 .

[0067]

[0083] Providing the control lens array 250 in addition to the objective lens array 241 provides additional degrees of freedom for controlling the characteristics of the sub-beams. For example, this additional freedom is provided even when the control lens array 250 and the objective lens array 241 are disposed relatively close to each other so that no intermediate focus is formed between them. The control lens array 250 can be used to optimize the beam divergence angle with respect to the beam demagnification ratio and / or control the beam energy delivered to the objective lens array 241. The control lens may include two or more electrodes. When there are two electrodes, the demagnification ratio and landing energy are controlled together. When there are three or more electrodes, the demagnification ratio and landing energy can be controlled individually. Thus, the control lens may be configured to adjust the demagnification ratio and / or beam divergence angle of each sub-beam (e.g., by applying appropriate respective potentials to the electrodes of the control lens and the objective lens using a power supply). This optimization can be achieved without significantly negatively impacting the number of objective lenses and without excessively exacerbating the aberrations of the objective lenses (eg, without increasing the strength of the objective lenses).

[0068]

[0084] In another configuration (not shown), the macro-collimator may be partially or wholly replaced by a collimator element array provided in the down beam of the upper beam limiter. Each collimator element collimates a respective sub-beam. The collimator element array may be formed using MEMS fabrication techniques to be spatially compact. The collimator element array may be the first deflection or focusing electron optical array element in the beam path of the down beam of the radiation source 201. The collimator element array may be in the up beam of the control lens array 250. The collimator element array may be in the same module as the control lens array 250.

[0069]

[0085] In the embodiment of FIG. 9, the electron-optics system includes a radiation source 201. The radiation source 201 provides a beam of charged particles (e.g., electrons). Multiple beams that focus on the sample 208 are derived from the beam provided by the radiation source 201. Sub-beams may be derived from the beam using, for example, a beam limiter defining an array of beam-limiting apertures. The radiation source 201 is preferably a high-brightness thermal field emitter with a good compromise between brightness and total emission current. In the illustrated example, a collimator is provided in the up-beam of the objective lens array assembly. The collimator may include a macro-collimator 270. The macro-collimator 270 acts on the beam from the radiation source 201 before the beam is split into multiple beams. The macro-collimator 270 bends each portion of the beam by an amount effective to ensure that the beam axis of each of the sub-beams derived from the beam is incident on the sample 208 substantially perpendicularly (i.e., at substantially 90° relative to the nominal surface of the sample 208). The macro-collimator 270 applies macroscopic collimation to the beam. Thus, the macro-collimator 270 may act on the entire beam rather than including an array of collimator elements, each configured to act on a different individual portion of the beam. The macro-collimator 270 may include a magnetic lens or a magnetic lens configuration including multiple magnetic lens subunits (e.g., multiple electromagnets forming a multipole configuration). Alternatively or additionally, the macro-collimator may be implemented at least in part electrostatically. The macro-collimator may include an electrostatic lens or an electrostatic lens configuration including multiple electrostatic lens subunits. The macro-collimator 270 may use a combination of magnetic and electrostatic lenses.

[0070]

[0086] In the embodiment of FIG. 9, a macro-scan deflector 265 is provided to scan the sub-beams across the sample 208. The macro-scan deflector 265 deflects respective portions of the beam to cause the sub-beams to scan across the sample 208. In one embodiment, the macro-scan deflector 265 includes a macroscopic multi-pole deflector, e.g., having eight or more poles. The deflection is such that the sub-beams derived from the beam are scanned across the sample 208 in one direction (e.g., parallel to a single axis, such as the X axis) or two directions (e.g., relative to two non-parallel axes, such as the X and Y axes). The macro-scan deflector 265 acts macroscopically on the entire beam, rather than including an array of deflector elements each configured to act on a different individual portion of the beam. In the illustrated embodiment, the macro-scan deflector 265 is provided between the macro-collimator 270 and the control lens array 250.

[0071]

[0087] In another configuration (not shown), the macro scan deflector may be partially or entirely replaced by a scan deflector array. The scan deflector array 260 includes multiple scan deflectors. The scan deflector array 260 may be formed using MEMS fabrication techniques. Each scan deflector causes a respective sub-beam to scan across the sample 208. Thus, the scan deflector array 260 may include a scan deflector for each sub-beam. Each scan deflector may deflect a sub-beam in one direction (e.g., parallel to a single axis, such as the X axis) or two directions (e.g., relative to two non-parallel axes, such as the X axis and the Y axis). The deflection is such that the sub-beam is scanned across the sample 208 in one or two directions (i.e., one-dimensionally or two-dimensionally). The scan deflector array may be in the up beam of the objective lens array 241. The scan deflector array may be in the down beam of the control lens array 250. Although reference has been made to a single sub-beam associated with a scan deflector, multiple groups of sub-beams may be associated with one scan deflector. In one embodiment, the scan deflector described in EP 2425444 (which is incorporated herein by reference in its entirety, particularly with respect to scan deflectors) may be used to implement a scan deflector array. A scan deflector array (e.g., formed using MEMS fabrication techniques as described above) may be more spatially compact than a macro scan deflector. The scan deflector array may be in the same module as the objective lens array 241.

[0072]

[0088] In other embodiments, both a macro scan deflector 265 and a scan deflector array may be provided. In such a configuration, scanning of the sub-beams over the sample surface may be achieved by controlling the macro scan deflector and the scan deflector array 260 together, preferably synchronously.

[0073]

[0089] The objective lens array assembly may further include a collimator array and / or a scanning deflector array.

[0074]

[0090] Any of the objective lens array assemblies described herein may further include a detector array 240. The detector array 240 detects charged particles emitted from the sample 208. The detected charged particles may include any of the charged particles detected by an SEM, including secondary electrons and / or backscattered electrons emitted from the sample 208.

[0075]

[0091] In one embodiment, a multi-beam electron-optics system according to the configuration shown and described with reference to, for example, FIG. 3 or FIG. 9 includes a circuit 60. The circuit 60 is configured to perform at least a portion of the functions of an image processing system. FIG. 10 is a schematic diagram of a circuit according to one embodiment. FIG. 10 can be considered a diagrammatic representation of a data path, or at least a first portion of a data path, for signals from each detector element in a detector array. In one embodiment, the circuit 60 includes an amplifier 61. The amplifier 61 is in data communication with the detector array 240. In FIG. 10, data communication lines are shown as solid lines between components, with arrows indicating the direction of data flow. In one embodiment, the amplifier 61 is in data communication with one of the detector elements 405 of the detector array 240.

[0076]

[0092] In Figure 10, two amplifiers 61 are shown connected to each detector element 405. In one embodiment, an amplifier 61 is provided for each detector element 405. For example, there may be hundreds, thousands, or tens of thousands of detector elements 405 and associated amplifiers 61 associated with an electron optical column. For simplicity, only two are shown in Figure 10. The secondary electron measurements made by the detector elements 405 are transmitted as signals to the amplifiers 61. The amplifiers 61 are configured to apply an amplification factor to the signals.

[0077]

[0093] 10, the amplified signal is output by amplifier 61 to analog-to-digital converter (ADC) 62. ADC 62 is configured to convert the amplified signal to a digital signal. In one embodiment, ADC 62 is configured to output the converted digital signal to serializer 63. Signals from the plurality of detector elements 405 are provided to serializer 63. In one embodiment, serializer 63 is configured to serialize the converted digital signal. The serialized signal is used to form an image of sample 208, for example, by signal processing the signal.

[0078]

[0094] In one embodiment, amplifier 61 is configured to be adjustable to adjust the amplification of signals from detector array 240. The gain applied by amplifier 61 can be adjusted independently of the gain of other amplifiers 61. Note that the strength of signals from detector elements of a detector are not necessarily the same. Variations in detector element signal strength are to be expected.

[0079]

[0095] By adjusting amplifier 61, it is possible to control the amplification of the signal to increase the proportion of ADC 62's input range that is used. If the amplification factor is too low, part of ADC 62's potential input range remains unused. As a result, the range of different possible values ​​that can be output by ADC 62 to serializer 63 is less than its maximum value. This results in a loss of information in the image generated from the serialized signal. The image resolution is reduced in that the number of possible gray levels in the section of the image corresponding to amplifier 61 is less than its maximum value.

[0080]

[0096] If the gain is too large, the range of the signal output by the amplifier 61 will correspond to the upper limit of the input range of the ADC 62. This will result in information loss in the image. Higher value signals will be mapped to the same value in the serialized signal. Higher value signals will become indistinguishable from each other in the image.

[0081]

[0097] By providing that amplifier 61 is adjustable, loss of information can be reduced. In one embodiment of the present invention, it is expected that a higher resolution of the image of sample 208 can be achieved.

[0082]

[0098] In one embodiment, detector array 240 is configured to detect charged particles by reference to their charge, i.e., directly. Such detectors may be referred to as direct current detectors. In a different embodiment, detector array 240 may be configured to detect charged particles by reference to their energy, i.e., depending on their band gap.

[0083]

[0099] FIG. 15 illustrates an exemplary image 150. Image 150 preferably has high resolution. Each pixel in the image has the same number of possible grayscale levels. Note that each pixel may correspond to signals from a detector element or a group of detector elements. FIG. 16 illustrates an alternative version of image 150 shown in FIG. 15. Image 150 shown in FIG. 16 includes four different quadrants 151-154. The different quadrants 151-154 correspond to different gains. The upper left quadrant 151 represents data received using optimally adjusted gains. Each pixel in the upper left quadrant 151 has the maximum number of grayscale levels, similar to the image in FIG. 15. The other three quadrants 152-154 are based on data with too little gain. The upper right quadrant 152 corresponds to the lowest gain. The lower gains result in pixels appearing darker than in the optimal image. In addition, the pixels have a smaller number of possible grayscale shades. Shades at the white end of the scale are not possible. The image shown in Figure 16 can be viewed as a pictorial representation of a detector array with four detector elements, each with a different intensity.

[0084]

[0100] FIG. 17 is a modified version of image 150 shown in FIG. 16. The data used to form image 150 of FIG. 16 has been post-processed (i.e., downstream processing in the amplification and ADC data path) to improve the luminance range of quadrants 151-154. As a result, grayscale gradations at the white end of the grayscale are possible. However, the number of possible grayscale gradations in each of quadrants 152-154 in image 150 of FIG. 17 is the same as in image 150 of FIG. 16. Visually, the resulting image shown in FIG. 17 has poorer contrast compared to FIG. 15. FIG. 17 graphically illustrates that variations in signal intensity from detector elements in the data path following the amplifier and ADC are corrected at the expense of loss of signal resolution. Therefore, the resolution of the signal used to generate image 150 is not improved by post-processing. That is, the loss of signal, as indicated by the limited range of grayscale values, is not restored by post-processing. This is represented by the limited range of greyscale and the number of greyscale tones it has in the image of FIG. 17 compared to FIG.

[0085]

[0101] 15-17, if different amplifiers 61 have different gains (e.g., to account for variations in signal strength from the detector elements), image quality will be degraded (e.g., as shown in FIG. 16). Post-processing of the digital signal can be used to achieve an increased output signal range using an increased input range from ADC 62, but information will be lost and signal resolution will be limited (e.g., as shown in FIG. 17).

[0086]

[0102] In one embodiment, the ADC 62 is in data communication with the amplifier 61. The ADC 62 is configured to convert signals from the detector array 240 to a digital output. In one embodiment, the amplifier 61 is configured to be adjustable to adjust the amplification of the signals from the detector array 240 to increase the percentage of the input range of the ADC 62 that is used. According to one embodiment, by adjusting the amplifier 61, an embodiment of the present invention is expected to achieve an image of the sample 208 that has a greater amount of information.

[0087]

[0103] FIG. 11 is a schematic diagram of a portion of the circuit shown in FIG. 10 , according to one embodiment. In one embodiment, the circuit includes a calibrator 82. The calibrator 82 is configured to adjust the amplifier 61 to adjust the amplification of the signals from the detector array 240. In one embodiment, the calibrator 82 is configured to adjust the amplifier 61 to adjust the amplification of the signals from the detector array 240 to equalize the percentage of the input range of the ADC 62 used by the signals from the detector array 240. An embodiment of the present invention is expected to achieve an image in which each section of the image has the same number of possible gray levels. In one embodiment, the number of possible gray levels is optimized. In one embodiment, the circuit includes a switch 81 configured to control the calibrator 82. For example, the switch 82 may include a button that can be pressed to initiate the calibration process.

[0088]

[0104] 11, in one embodiment, amplifier 61 includes a feedback resistor 70 configured to determine the gain of amplifier 61. In one embodiment, feedback resistor 70 is variable. By adjusting the resistance value of feedback resistor 70, the gain applied by amplifier 61 can be controlled.

[0089]

[0105] The feedback resistor 70 may include multiple components. For example, in one embodiment, the feedback resistor 70 includes a fixed resistor 71 and a variable resistor 72. The fixed resistor 71 and the variable resistor 72 are connected in series. Adjusting the resistance of the variable resistor 72 controls the gain applied by the amplifier 61. The resistance of the fixed resistor 71 is not changed. Including the fixed resistor 72 as part of the feedback resistor 70 allows for more precise control of the gain. Including the fixed resistor 71 allows the variable resistor 72 to have a lower maximum resistance. As a result, proportional adjustments to the variable resistor 72 have less impact on the overall resistance of the feedback resistor 70. Adjusting the variable resistor 72 allows for more precise control of the resistance of the feedback resistor 70. However, in some alternative configurations, the fixed resistor 71 may not be included.

[0090]

[0106] In one embodiment, fixed resistor 71 has a higher resistance than variable resistor 72. For example, in one embodiment, fixed resistor 71 has a resistance that is at least twice, optionally at least four times, and optionally at least eight times the maximum resistance of variable resistor 72. An embodiment of the present invention is expected to improve the precision with which amplifier 61 can be controlled.

[0091]

[0107] In one embodiment, the resistance of feedback resistor 70 depends on an applied potential. This is a system control signal that is applied back to the feedback resistor. By applying a particular value of potential, the gain of amplifier 61 can be controlled. For example, a direct current can be applied to amplifier 61 to control its gain.

[0092]

[0108] Note that the calibration signal should be adjusted to optimize the signal-to-noise ratio. Higher resistance allows for higher amplification. When using a feedback (i.e., connecting the output to the input) system, the system can maintain its own stability, which is, in principle, how an amplifier works. In this way, the input current (e.g., the detector signal) is amplified by the resistor to generate a voltage (i.e., the output potential to the ADC). However, using larger resistors has implications in terms of noise contribution, i.e., signal-to-noise ratio. When using small currents, such as those provided by detector elements such as capture electrodes, there are consequences from the thermal noise contribution from the resistor, which has a significant impact considering the magnitude of the amplified signal. Naturally, the signal represents a current. Since the signal-to-noise relationship tends to be linear, while noise is proportional to the square root [of the measured current], amplification can improve the signal-to-noise ratio. Therefore, a larger resistor value is preferable to improve amplification. This allows input signals toward the upper end of the ADC's input range. However, there is a risk that the noise level will become too high relative to the signal. Thus, the present invention uses adjustable resistors to maximize the ADC range while taking into account the risk of introducing noise and therefore the trade-offs involved with the adjustment.

[0093]

[0109] In one embodiment, the feedback register 70 includes a sample and hold circuit 73 configured to hold an applied potential to maintain the resistance value of the feedback register 70. For example, a potential may be applied when calibrating an image processing system. In one embodiment, the potential is applied locally to the feedback register 70. Once the potential is set, the sample and hold circuit 73 holds the potential at that value. The applied potential may be held until a subsequent calibration process. In one embodiment, the sample and hold circuit 73 is configured to hold the value of the potential for at least one hour, optionally at least one day, and optionally at least one month. One embodiment of the present invention is expected to reduce the burden of calibration of an image processing system.

[0094]

[0110] In one embodiment, circuit 60 includes a potential applicator 83 configured to apply a potential to determine the resistance value of feedback resistor 70. In one embodiment, potential applicator 83 includes a digital-to-analog converter (DAC) configured to convert a digital calibration signal into an analog DC voltage. In one embodiment, calibrator 82 is configured to output the calibration signal to potential applicator 83.

[0095]

[0111] In one embodiment, circuit 60 includes a multiplexer 84 configured to sequentially control the application of potentials by potential applicators 83 to each of a plurality of amplifiers 61 for each detector element 405 of detector array 240. Multiplexer 84 is configured to distribute the voltages as needed to associated feedback resistors 70. Providing multiplexer 84 reduces the number of different power supplies required to apply independent voltages.

[0096]

[0112] In one embodiment, at least one element of circuit 60 is associated with detector array 240. For example, one or more of amplifier 61, ADC 62, calibrator 82, switch 81, multiplexer 84, and potential applicator 83 may be associated with detector array 240. In one embodiment, at least one element of circuit 60 is incorporated into logic layer 407. Additionally or alternatively, in one embodiment, at least one element of circuit 60 is associated with controller 50.

[0097]

[0113] In one embodiment, at least one element of the circuit 60 is structurally integrated into the detector array 240. A portion of the circuit may be associated with each detector element of the detector. In one embodiment, the detector array is part of an assembly of electro-optical components, such as an objective lens array assembly, as shown in and described with reference to, for example, FIGS. 3 and 9. In one embodiment, at least one element of the circuit 60 may be integrated into a detector arrangement that forms part of the objective lens array arrangement and / or a generic part of the objective lens array arrangement, i.e., a part not specifically assigned to a detector.

[0098]

[0114] By being associated with the electron optical column, elements of circuit 60 can reside within the column, avoiding the need for feedthroughs to the ambient atmosphere. Each additional connection through the wall of the vacuum chamber, and therefore the increased demand for feedthroughs, can potentially jeopardize vacuum integrity and / or increase design complexity. One embodiment of the present invention is expected to facilitate the manufacture and / or maintenance of electron beam tool 40.

[0099]

[0115] By defining the circuitry 60 in close proximity to the detector array 240, wiring routing is reduced. An embodiment of the present invention is expected to reduce the complexity of the electron beam tool 40, shortening the distance signals need to travel, resulting in a more efficient layout. Thus, the risk of such complexity may be related to data paths that may affect tool performance.

[0100]

[0116] In one embodiment, at least one of the elements of circuit 60 is integrated into the structural hardware associated with the objective lens array assembly. In one embodiment, at least one of the elements of circuit 60 is integrated into the logic layer 407 of detector array 240.

[0101]

[0117] Figure 12 shows a schematic diagram of an electron beam tool 40 according to one embodiment. Features that are the same as those described above are given the same reference numerals. For the sake of brevity, such features will not be described in detail with reference to Figure 12. For example, the radiation source 201, the condenser lens 231, the macro-collimator 270, the objective lens array 241 and the sample 208 may be as described above.

[0102]

[0118] As noted above, in one embodiment, the detector array 240 is between the objective lens array 241 and the sample 208. The detector array 240 may face the sample 208. Alternatively, as shown in Figure 12, in one embodiment, an objective lens array 241 including multiple objective lenses is between the detector array 240 and the sample 208. The detector elements of the detector array 240 are on the path of the multi-beam array, as shown in Figure 12. The detector elements are associated, for example, around and / or adjacent to the path of each primary sub-beam 211, 212, 213 in the multi-beam.

[0103]

[0119] In one embodiment, the deflector array 95 is between the detector array 240 and the objective lens array 241. In one embodiment, the deflector array 95 includes a Wien filter, so that the deflector array may be referred to as a beam separator. The deflector array 95 is configured to provide a magnetic field to separate charged particles projected onto the sample 208 and secondary electrons from the sample 208.

[0104]

[0120] In one embodiment, the detector array 240 is configured to detect charged particles by reference to their energy, i.e., by relying on the bandgap. Such a detector may be referred to as an indirect current detector. Secondary electrons emitted from the sample 208 gain energy from the electric field between the electrodes. When the secondary electrons reach the detector array 240, they have sufficient energy.

[0105]

[0121] Figure 13 is an enlarged view of a portion of the electron beam tool 40 shown in Figure 12. In one embodiment, the detector array 240 includes an electron-to-photon converter array 91. The electron-to-photon converter array 91 includes a plurality of fluorescent strips 92. Each fluorescent strip 92 is located in the plane of the electron-to-photon converter array 91. At least one fluorescent strip 92 is positioned between two adjacent charged particle beams projected toward the sample 208.

[0106]

[0122] In one embodiment, the phosphor strips 92 extend in a substantially horizontal direction. Alternatively, the electron-to-photon converter array 91 may include a plate of phosphor material having an aperture 93 for the projected charged particle beam.

[0107]

[0123] The projected charged particle beam, shown by the dashed line in FIG. 13, is projected through an aperture 93 between phosphor strips 92 and through the plane of electron-to-photon converter array 91 towards deflector array 95 .

[0108]

[0124] In one embodiment, the deflector array 95 includes a magnetic deflector 96 and an electrostatic deflector 97. The electrostatic deflector 97 is configured to cancel the deflection of the magnetic deflector 96 with respect to the projected charged particle beam transmitted towards the sample 208. Thus, the projected charged particle beam can be slightly shifted in the horizontal plane. The beams of the down beam of the deflector array 95 are substantially parallel to the beams of the up beam of the deflector array 95.

[0109]

[0125] In one embodiment, the objective lens array 241 includes multiple plates for directing secondary electrons generated at the sample 208 toward the deflector array 95. For secondary electrons traveling in the opposite direction relative to the projected charged particle beam, the electrostatic deflector 97 does not cancel the deflection of the magnetic deflector 96. Instead, the deflections of the secondary electrons by the electrostatic deflector 97 and the magnetic deflector 96 are additive. Thus, to transmit the secondary electrons onto the phosphor strips 92 of the detector array 240, the secondary electrons are deflected to travel at an angle to the optical axis.

[0110]

[0126] Photons are generated at the fluorescent strips 92 due to the incidence of secondary electrons. In one embodiment, the photons are transported from the fluorescent strips 92 to a photodetector (not shown) by a photon transport unit. In one embodiment, the photon transport unit includes an array of optical fibers 98. Each optical fiber 98 includes one end positioned adjacent to or attached to one of the fluorescent strips 92 to couple photons from the fluorescent strips 92 into the optical fiber 98, and another end positioned to project photons from the optical fiber 98 onto the photodetector.

[0111]

[0127] 14 schematically illustrates an electron beam tool 40 according to one embodiment. As noted above, in one embodiment, the detector array 240 is aligned with the primary electron optical axis of the electron beam tool 40. Alternatively, the detector array 240 may be aligned with a different axis, as shown in FIG.

[0112]

[0128] Features that are the same as those described above are given the same reference numerals. For the sake of brevity, such features will not be described in detail with reference to Figure 14. For example, the radiation source 201, primary electron beam 202, sub-beams 211, 212 and 213, projection device 230, collection lens 231, probe spots 221, 222, 223, controller 50, sample 208, sample holder 207, motorized stage 209 and detector array 240 may be as described above.

[0113]

[0129] The electron source 201, the gun aperture plate 271, the condenser lens 210, and the source conversion unit 220 are components of an illumination apparatus included by the electron beam tool 40. The gun aperture plate 271 is configured, in operation, to block peripheral electrons of the primary electron beam 202 to reduce the Coulomb effect. The gun aperture plate 271 may be referred to as a Coulomb aperture array. The Coulomb effect may increase the size of the probe spots 221, 222, and 223 of the primary sub-beams 211, 212, and 213, respectively, and thus degrade the inspection resolution. The gun aperture plate 271 may also include multiple apertures for generating primary sub-beams (not shown) even before the source conversion unit 220, and may be referred to as a Coulomb aperture array.

[0114]

[0130] The collecting lens 210 is configured to focus (or collimate) the primary electron beam 202. In one embodiment of the source conversion unit 220, 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, for example, be optional and may be present in embodiments where the collecting lens does not ensure substantially normal incidence of the sub-beams arising from the Coulomb aperture array on, for example, the beam-limiting aperture array, the image-forming element array, and / or the aberration compensator array.

[0115]

[0131] The electron beam tool 40 may include a secondary projection device 255 associated with the detector array 240. The primary projection device 230 may include an array of condenser lenses 231, which may be magnetic, that may function as an objective lens. The beam separator 233 and the deflection scanning unit 232 may be disposed within the primary projection device 230. The beam separator 233 may include a Wien filter. The detector array 240 may include a plurality of detector elements 405.

[0116]

[0132] The components used to generate the primary beam may be aligned with a primary electron optical axis 204 of the electron beam tool 40. These components may include the electron source 201, the gun aperture plate 271, the condenser lens 210, the source conversion unit 220, the beam separator 233, the deflection scanning unit 232, and the primary projection device 230. The secondary projection device 255 and its associated detector array 240 may be aligned with a secondary electron optical axis 251 of the electron beam tool 40.

[0117]

[0133] In this embodiment, the secondary electrons propagate in three secondary electron beams 261, 262, and 263. Secondary projection device 255 then focuses the paths of secondary electron beams 261, 262, and 263 onto multiple detector elements 405 of detector array 240.

[0118]

[0134] Detector elements 405 can detect secondary electron beams 261, 262, and 263. When a secondary electron beam is incident on detector element 405, the element can generate a corresponding intensity signal output (not shown). In one embodiment, the detector element can be a capture electrode. The output can be directed to an image processing system.

[0119]

[0135] An evaluation tool according to an embodiment of the present invention may be a tool that performs a qualitative evaluation of a sample (e.g., pass / fail), or a tool that performs a quantitative measurement of a sample (e.g., size of a feature), or a tool that generates an image of a map of the sample. Examples of evaluation tools are inspection tools (e.g., to identify defects), review tools (e.g., to classify defects), and metrology tools, or tools that can perform any combination of evaluation functions associated with inspection tools, review tools, or metrology tools (e.g., metrology inspection tools).

[0120]

[0136] The terms "sub-beam" and "beamlet" are used interchangeably herein and both are understood to encompass any radiation beam derived from a parent radiation beam by splitting or separating the parent radiation beam. The term "manipulator" is used to encompass any element that affects the path of a sub-beam or beamlet, such as a lens or deflector. References to an element being aligned along a beam path or sub-beam path shall be understood to mean that the respective element is located along the beam path or sub-beam path. References to optics shall be understood to mean electron optics.

[0121]

[0137] While the invention has been described in connection with various embodiments, other embodiments of the invention will be apparent to those skilled in the art from consideration of the specification and practice of the invention disclosed herein.

[0122]

[0138] For example, while the above description is directed to amplifying the current of secondary electrons using a TIA, those skilled in the art will know of other types of circuits that can provide adjustable amplification. Other topologies that include an op-amp and feedback resistor, such as variations of an integrator or a current-to-voltage converter, can provide adjustable amplification.

[0123]

[0139] The present invention is applicable to various types of detector arrays 240. For example, trapping electrodes, scintillators, or PIN elements for directly detecting electron charge may be used. The detector array 240 may be a direct current detector or an indirect current detector.

[0124]

[0140] The present invention can be applied to detector arrays 240 in various locations on electron beam tool 40. For example, detector array 240 can be associated with an objective lens array 241 at the bottom of a column, or can be above the bottom of a column, such as associated with an objective lens array 241 above the bottom of a column located elsewhere, such as in a primary column (e.g., as shown in FIG. 12) or a secondary column (e.g., as shown in FIG. 14).

[0125]

[0141] In one embodiment, the circuit 60, which embodies at least a portion of the image processing system, is part of the objective lens array assembly. The circuit 60 may be incorporated into the mechanical design of the objective lens array assembly. In one embodiment, the objective lens array assembly includes a control lens array 250, a pre-limiter array (which may be associated with the control lens array 250 as shown in FIG. 9 ), an objective lens array 241, a beam-forming array (which may be associated with the objective lens array 241 as shown in FIG. 9 ), and a detector array 240. Alternatively, the objective lens array assembly may include the control lens array 250, the objective lens array 241, and the detector array 240. The functions of the pre-limiter array and the beam-forming array (or final beam-limiting array) may be performed by an aperture array associated with the focusing lens 231 (see, for example, FIG. 3 ).

[0126]

[0142] The present invention is applicable to a variety of different tool architectures, for example, the electron beam tool 40 may be a single beam tool, may include multiple single beam columns, or may include multiple multi-beam columns.

[0127]

[0143] Any element or collection of elements may be replaceable within electron beam tool 40 or may be field replaceable. One or more electron optical components within electron beam tool 40, particularly those that act on or generate sub-beams, such as aperture arrays and manipulator arrays, may include one or more MEMS.

[0128]

[0144] The following provisions are provided:

[0129]

[0145] Clause 1. A multi-beam electron optics for a charged particle characterization tool, comprising: an objective lens array assembly including a plurality of objective lenses each configured to project one of a plurality of charged particle beams onto a sample; a detector array associated with the objective lens array assembly and configured to detect charged particles emitted from the sample; and circuitry including an amplifier in data communication with the detector array of detector elements, wherein the amplifier is configured to be adjustable to adjust amplification of signals from the detector array.

[0130]

[0146] Clause 2. A multi-beam electron optical system as described in clause 1, wherein the detector array is a current detector array configured to detect charged particles by reference to their charge.

[0131]

[0147] Clause 3. A multi-beam electron optics for a charged particle characterization tool, comprising: a current detector array configured to detect charged particles emitted from a sample by reference to their charge; and circuitry including an amplifier in data communication with the detector array of detector elements, the amplifier configured to be adjustable to adjust amplification of signals from the detector array.

[0132]

[0148] Clause 4. A multi-beam electron optical system as described in clause 3, including an objective lens array assembly including a plurality of objective lenses each configured to project one of a plurality of charged particle beams onto a sample, and preferably, a detector array is associated with the objective lens array assembly.

[0133]

[0149] Clause 5. A multi-beam electron optical system described in any one of clauses 1, 2 and 4, wherein the detector array preferably includes a plurality of detector elements, preferably each detector element being associated with a respective charged particle beam of the plurality of charged particle beams, the objective lens array assembly preferably includes a control lens array, each control lens being associated with an objective lens of the objective lens array, the detector array being between the plurality of objective lenses and the sample, or the plurality of objective lenses being between the detector array and the sample, preferably the detector array being within the objective lens array, preferably the detector elements of the detector array being in the path of the multi-beam array, preferably the detector elements being associated around and / or adjacent to the path of each charged particle beam of the multi-beam.

[0134]

[0150] Clause 6. The multi-beam electron optics of clause 5, wherein the detector array faces the sample.

[0135]

[0151] Clause 7. A multi-beam electron optical system according to any one of clauses 1, 2 and 4, wherein a plurality of objective lenses are located between the detector array and the sample.

[0136]

[0152] Clause 8. A multi-beam electron optical system according to any one of clauses 1 to 4 and 7, including a secondary projection device aligned with the secondary electron optical axis of the charged particle evaluation tool, wherein the detector array is associated with the secondary projection device.

[0137]

[0153] Clause 9. A multi-beam electron optical system as described in any one of the preceding clauses, wherein the circuitry includes an analog-to-digital converter in data communication with the amplifier for converting the signal from the detector array to a digital output, the amplifier being configured to be adjustable to adjust the amplification of the signal from the detector array to increase the proportion of the input range of the analog-to-digital converter used.

[0138]

[0154] Clause 10. A multi-beam electron optical system as described in any one of the preceding clauses, wherein the circuit includes a calibrator configured to adjust the amplifier to adjust the amplification of the signals from the detector array so as to equalize the proportion of the input range of the analog-to-digital converter used by the signals from the detector array.

[0139]

[0155] Clause 11. The multi-beam electron-optical system of clause 10, wherein the circuitry includes a switch configured to control the calibrator.

[0140]

[0156] Clause 12. A multi-beam electron-optical system according to any one of the preceding clauses, wherein the amplifier includes a feedback resistor configured to determine the gain of the amplifier.

[0141]

[0157] Clause 13. A multi-beam electron optical system according to clause 12, wherein the feedback register is variable.

[0142]

[0158] Clause 14. A multi-beam electron optical system according to clause 13, wherein the feedback register includes a fixed register and a variable register.

[0143]

[0159] Clause 15. A multi-beam electron optical system according to clause 14, wherein the fixed resistor has a higher resistance value than the variable resistor.

[0144]

[0160] Clause 16. A multi-beam electron optical system according to any one of clauses 13 to 15, wherein the resistance value of the feedback resistor depends on the applied potential.

[0145]

[0161] Clause 17. The multi-beam electron optical system of clause 16, wherein the feedback resistor includes a sample and hold circuit configured to hold an applied potential to maintain a resistance value of the feedback resistor.

[0146]

[0162] Clause 18. A multi-beam electron optical system according to clause 16 or 17, wherein the circuit includes a potential applicator configured to apply a potential to determine the resistance value of the feedback resistor.

[0147]

[0163] Clause 19. A multi-beam electron optical system according to clause 18, wherein the potential applicator includes a digital-to-analog converter configured to output the potential.

[0148]

[0164] Clause 20. A multi-beam electron optical system as described in clause 18 or 19, wherein the circuit includes a multiplexer configured to sequentially control the application of potentials by the potential applicators to each of a plurality of amplifiers for each detector element.

[0149]

[0165] Clause 21. A multi-beam electron optical system according to any one of the preceding clauses, wherein the detector array comprises a metal member configured to receive charged particles emitted from the sample.

[0150]

[0166] Clause 22. A multi-beam electron optical system according to any one of clauses 1 to 20, wherein the detector array comprises an array of scintillators or PIN elements.

[0151]

[0167] Clause 23. A multi-beam electron-optical system according to any one of the preceding clauses, wherein at least elements of the circuit are associated with a detector array.

[0152]

[0168] Clause 24. A multi-beam electron-optical system according to any one of the preceding clauses, wherein at least elements of the circuit are structurally integrated into the detector array.

[0153]

[0169] Clause 25. A method for evaluating a sample surface using a plurality of sub-beams, comprising: projecting the sub-beams onto the surface of the sample by using an objective lens array assembly; detecting charged particles emitted from the sample by a detector array associated with the objective lens array assembly; and amplifying signals from the detector array by an amplifier, wherein the amplifier is configured to be adjustable to adjust the amplification of the signals from the detector array, preferably the detector array comprises a plurality of detector elements, preferably each detector element is associated with a respective charged particle beam of the plurality of charged particle beams, the objective lens array assembly preferably comprises a control lens array, each control lens is associated with an objective lens of the objective lens array, the detector array is between the plurality of objective lenses and the sample, or the plurality of objective lenses are between the detector array and the sample, preferably the detector array is within the objective lens array, preferably the detector elements of the detector array are in the path of the multi-beam array, preferably the detector elements are associated around and / or adjacent to the path of each charged particle beam of the multi-beam.

[0154]

[0170] Clause 26. A method for evaluating a sample surface using a plurality of sub-beams, comprising: projecting the sub-beams onto the surface of the sample; detecting current-charged particles emitted from the sample by a detector array by reference to their charge; and amplifying signals from the detector array by an amplifier, wherein the amplifier is configured to be adjustable to adjust the amplification of the signals from the detector array.

[0155]

[0171] Clause 27. An image of a sample formed from data from a charged particle characterization tool, the image including a plurality of image areas formed from data from respective detectors of the charged particle characterization tool, the data being indicative of a current of charged particles emitted from respective areas of the sample, the image areas including the same number of gray levels corresponding to different currents of charged particles emitted from the sample.

[0156]

[0172] It is intended that the specification and examples be considered as exemplary only, with a true scope and spirit of the invention being indicated by the following claims and clauses presented herein.

Claims

1. 1. A multi-beam electron optics system for a charged particle characterization tool, comprising: an objective lens array assembly including a plurality of objective lenses each projecting one of the plurality of charged particle beams onto the sample; a detector array associated with the objective lens array assembly and configured to detect charged particles emitted from the sample; a circuit including an amplifier in data communication with the detector array of detector elements; the amplifier is adjustable to adjust the amplification of signals from the detector array; the amplifier includes a variable feedback resistor that determines the gain of the amplifier; the resistance of the feedback resistor is dependent on the applied potential; The circuit includes a potential applicator that applies the potential to determine the resistance value of the feedback resistor, and a multiplexer that sequentially controls the application of the potential by the potential applicator to each of a plurality of amplifiers for each detector element.

2. 2. The multi-beam electron optical system according to claim 1, wherein the detector array is a current detector array that detects the charged particles by referring to their electric charges.

3. the circuitry includes an analog-to-digital converter in data communication with the amplifier for converting signals from the detector array to a digital output; 3. A multi-beam electron-optical system according to claim 1, wherein the amplifier is adjustable to adjust the amplification of the signal from the detector array so as to increase the proportion of the input range of the analog-to-digital converter that is used.

4. 4. The multi-beam electron optical system of claim 1, wherein the circuit includes a calibrator that adjusts the amplifier to adjust the amplification of the signals from the detector array so as to equalize a proportion of the input range of the analog-to-digital converter used by the signals from the detector array.

5. The detector array a metal member that receives the charged particles emitted from the sample; or Scintillator or PIN element array 5. The multi-beam electron optical system according to claim 1, comprising:

6. A multi-beam electron-optical system according to any one of claims 1 to 5, wherein at least elements of said circuit are structurally integrated into said detector array.

7. the detector array is between the plurality of objective lenses and the sample; or The multi-beam electron optical system according to any one of claims 1 to 6, wherein the plurality of objective lenses are located between the detector array and the sample.

8. A multi-beam electron-optical system according to any one of the preceding claims, comprising a secondary projection arrangement aligned with a secondary electron optical axis of the charged particle characterization tool.

9. 1. A method for characterizing a sample surface using multiple sub-beams, comprising: projecting the sub-beams onto a surface of a sample using an objective lens array assembly; detecting charged particles emitted from the sample with a detector array associated with the objective lens array assembly; amplifying signals from the detector array with an amplifier; providing a circuit having the amplifier; the amplifier is adjustable to adjust the amplification of the signal from the detector array; the amplifier includes a variable feedback resistor that determines the gain of the amplifier; the resistance of the feedback resistor is dependent on the applied potential; the circuit includes a potential applicator that applies the potential to determine the resistance value of the feedback resistor, and a multiplexer that sequentially controls application of the potential by the potential applicator to each of a plurality of amplifiers for each detector element.

Images