Charged particle inspection tool, inspection method

Abstract

A charged particle evaluation tool comprises a condensing lens array, a collimator, a plurality of objective lenses, and an electric power source. The condensing lens array is configured to split a beam of charged particles into a plurality of sub-beams and to focus each of the sub-beams at a respective intermediate focus. The collimator is located at each intermediate focus and is configured to deflect each sub-beam so as to be incident substantially perpendicularly to the sample. Each of the plurality of objective lenses is configured to project one of the plurality of charged particle beams onto the sample. Each objective lens includes a first electrode; and a second electrode located between the first electrode and the sample. The electric power source is configured to apply a first and a second potential to the first and second electrodes, respectively, so that each charged particle beam is decelerated and incident on the sample with a desired landing energy.

Description

Technology Field

[0001] Cross-reference regarding related applications

[0002] The present application claims priority to EP application 20158804.3 filed on February 21, 2020 and EP application 20206984.5 filed on November 11, 2020, which are incorporated herein by reference in their entirety.

[0003] The embodiments provided herein generally relate to a charged particle evaluation tool and inspection method, in particular to a charged particle evaluation tool and inspection method utilizing multiple sub-beams of charged particles. Background Technology

[0004] When manufacturing semiconductor integrated circuit (IC) chips, unwanted pattern defects inevitably occur on the substrate (i.e., wafer) or mask during the manufacturing process as a result of factors such as optical effects and incidental particles, thereby reducing yield. Therefore, monitoring the extent of unwanted pattern defects is a critical process in IC chip manufacturing. More generally, inspection and / or measurement of the substrate surface or other objects / materials are critical processes during and / or after manufacturing.

[0005] Pattern inspection tools equipped with a beam of charged particles have been used to inspect objects, for example, to detect pattern defects. These tools typically utilize electron microscopy techniques such as scanning electron microscopes (SEM). In SEM, a primary electron beam of electrons at a relatively high energy targets a final deceleration phase to land on the sample at a relatively low landing energy. The electron beam is focused as a probing spot on the sample. The 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. By scanning the primary electron beam as a probing spot on the sample surface, secondary electrons can be emitted across the surface of the sample. By collecting these emitted secondary electrons from the sample surface, the pattern inspection tool can acquire an image representing the characteristics of the material structure on the sample surface.

[0006] In general, there is a need to improve the throughput and other characteristics of charged particle inspection devices. means of solving the problem

[0007] The embodiments provided in this specification disclose a charged particle beam inspection device.

[0008] According to a first aspect of the present invention, a charged particle evaluation tool is provided, and the charged particle evaluation tool is:

[0009] A focusing lens array configured to divide a beam of charged particles into multiple sub-beams and to focus each of the sub-beams at a respective intermediate focal point;

[0010] A collimator located at each intermediate focus and configured to deflect each sub-beam so as to be incident substantially perpendicularly to the sample;

[0011] Multiple objective lenses, each configured to project one of multiple charged particle beams onto a sample

[0012] - Each objective lens,

[0013] First electrode; and

[0014] Includes a second electrode located between the first electrode and the sample; and

[0015] It includes an electric power source configured to apply a first and second potential to the first and second electrodes, respectively, so that each charged particle beam is decelerated and incident on the sample with a desired landing energy.

[0016] According to a second aspect of the present invention, an inspection method is provided, wherein the inspection method is:

[0017] Dividing a beam of charged particles into multiple sub-beams;

[0018] Focusing each of the sub-beams at their respective intermediate focal points;

[0019] Using a collimator at each intermediate focal point to deflect each sub-beam so that each sub-beam is incident substantially perpendicularly to the sample;

[0020] Using a plurality of objective lenses to project a plurality of charged particle beams onto a sample—each objective lens comprising a first electrode and a second electrode located between the first electrode and the sample—and

[0021] It includes controlling the potential applied to the first and second electrodes of each objective lens so that each charged particle beam is decelerated and incident on the sample with a desired landing energy.

[0022] According to a third aspect of the present invention, a multi-beam charged particle optical system is provided, wherein the multi-beam charged particle optical system comprises:

[0023] A focusing lens array configured to divide a beam of charged particles into multiple sub-beams and to focus each of the sub-beams at a respective intermediate focal point;

[0024] A collimator located at each intermediate focus and configured to deflect each sub-beam so as to be incident substantially perpendicularly to the sample;

[0025] Multiple objective lenses, each configured to project one of multiple charged particle beams onto a sample

[0026] - Each objective lens,

[0027] First electrode; and

[0028] Includes a second electrode located between the first electrode and the sample; and

[0029] It includes an electric power source configured to apply a first and second potential to the first and second electrodes, respectively, so that each charged particle beam is decelerated and incident on the sample with a desired landing energy.

[0030] According to a fourth aspect of the present invention, a final charged particle optical element for a multi-beam projection system configured to project a plurality of charged particle beams onto a sample is provided, wherein the final charged particle optical element is:

[0031] Multiple objective lenses, each configured to project one of multiple charged particle beams onto a sample

[0032] Here, each objective lens is,

[0033] First electrode; and

[0034] Includes a second electrode located between the first electrode and the sample; and

[0035] It includes an electric power source configured to apply a first and second potential to the first and second electrodes, respectively, so that each charged particle beam is decelerated and incident on the sample with a desired landing energy. Brief explanation of the drawing

[0036] The above and other aspects of the present invention will become more apparent from the description of exemplary embodiments taken together with the accompanying drawings. FIG. 1 is a schematic diagram illustrating an exemplary charged particle beam inspection device. FIG. 2 is a schematic diagram illustrating an exemplary multi-beam device that is part of the exemplary charged particle beam inspection device of FIG. 1. FIG. 3 is a schematic diagram of an exemplary multi-beam device according to an embodiment. FIG. 4 is a schematic diagram of another exemplary multi-beam device according to an embodiment. Figure 5 is a graph of landing energy versus spot size. FIG. 6 is an enlarged view of the objective lens of an embodiment of the present invention. FIG. 7 is a schematic cross-sectional view of the objective lens of an inspection device according to an embodiment. Fig. 8 is a bottom view of the objective lens of Fig. 7. Fig. 9 is a bottom view of a modified example of the objective lens of Fig. 7. Figure 10 is an enlarged schematic cross-sectional view of the detector included in the objective lens of Figure 7. Specific details for implementing the invention

[0037] Reference to exemplary embodiments will now be made in detail, and examples thereof are illustrated in the accompanying drawings. Unless otherwise indicated, the following description refers to the accompanying drawings, where the same number in other drawings represents the same or similar elements. The embodiments presented in the following description of exemplary embodiments do not represent all embodiments consistent with the present invention. Rather, they are merely examples of apparatuses and methods consistent with aspects related to the present invention as cited in the appended claims.

[0038] The enhanced computational capabilities of electronic devices, which reduce the physical size of the device, can be achieved by significantly increasing the packing density of circuit components such as transistors, capacitors, and diodes within IC chips. This has been made possible by increased resolution, which enables the creation of smaller structures. For example, an IC chip in a smartphone the size of a thumbnail, available since 2019 or earlier, may contain over 2 billion transistors, each smaller than 1 / 1,000th the size of a human hair. Therefore, it is not surprising that semiconductor IC manufacturing is a complex and time-consuming process involving hundreds of individual steps. Even an error in a single step has the potential to dramatically affect the functionality of the final product. A single "killer defect" can cause device failure. The goal of the manufacturing process is to improve the overall yield. For example, to achieve a 75% yield for a 50-step process (where a step can represent the number of layers formed on a wafer), each individual step must have a yield greater than 99.4%. If each individual step has a yield of 95%, the overall process yield will be 7% lower.

[0039] In IC chip manufacturing facilities, while high process yield is desirable, maintaining high substrate (i.e., wafer) throughput, defined by the number of substrates processed per hour, is also essential. Both high process yield and high substrate throughput can be affected by the presence of defects. This is especially true if operator intervention is required to inspect for defects. Therefore, high-throughput detection and identification of micro- and nano-sized defects using inspection tools (such as scanning electron microscopes ("SEM")) is essential for maintaining high yield and low costs.

[0040] A SEM includes a scanning device and a detector device. The scanning device includes an illumination device comprising an electron source for generating primary electrons and a projection device for scanning a sample, such as a substrate, with one or more focused beams of primary electrons. At least the illumination device, or illumination system, and the projection device or projection system may be collectively referred to as an electro-optical system or device. Primary electrons interact with the sample and generate secondary electrons. The detector device captures the secondary electrons from the sample as it is scanned so that the SEM can generate an image of the scanned area of ​​the sample. For high-throughput inspection, some inspection devices use multiple focused beams of primary electrons, i.e., multiple beams. The component beams of a multiple beam may be referred to as sub-beams or beamlets. A multiple beam can scan different parts of a sample simultaneously. Therefore, a multiple beam inspection device can inspect samples at a much higher speed than a single beam inspection device.

[0041] The implementation form of the announced multi-beam inspection device is described below.

[0042] The drawings are schematic. Accordingly, the relative dimensions of the components in the drawings are exaggerated for clarity. Within the following description of the drawings, identical or similar reference numbers refer to identical or similar components or objects, and only differences regarding individual embodiments are described. It is recognized that while the description and drawings relate to electron-optical devices, the embodiments are not intended to limit the invention to specific charged particles. Accordingly, throughout this specification, references to electrons may be considered more generally as references to charged particles, and the charged particles are not necessarily electrons.

[0043] Now, reference is made to FIG. 1, which is a schematic diagram illustrating an exemplary charged particle beam inspection device (100). The charged particle beam inspection device (100) of FIG. 1 includes a main chamber (10), a load lock chamber (20), an electron beam tool (40), an equipment front end module (EFEM) (30), and a controller (50). The electron beam tool (40) is located within the main chamber (10).

[0044] The EFEM (30) includes a first loading port (30a) and a second loading port (30b). The EFEM (30) may include additional loading port(s). The first loading port (30a) and the second loading port (30b) may accommodate, for example, a substrate front opening unified pod (FOUP), which contains a substrate (e.g., a semiconductor substrate or a substrate made of other material(s)) or a sample to be inspected (substrate, wafer, and sample are collectively referred to as “sample” below). One or more robotic arms (not visible) within the EFEM (30) transfer the sample to a load lock chamber (20).

[0045] A load lock chamber (20) is used to remove gas around a sample. This creates a vacuum, which is a local gas pressure lower than the pressure of the surrounding environment. The load lock chamber (20) may be connected to a load lock vacuum pump system (not visible), which removes gas particles within the load lock chamber (20). Operation of the load lock vacuum pump system enables the load lock chamber to reach a first pressure lower than atmospheric pressure. After reaching the first pressure, one or more robotic arms (not visible) transfer the sample from the load lock chamber (20) to the main chamber (10). The main chamber (10) is connected to a main chamber vacuum pump system (not visible). The main chamber vacuum pump system removes gas particles within the main chamber (10) so that the pressure around the sample reaches a second pressure lower than the first pressure. After reaching the second pressure, the sample is transferred to an electron beam tool, and the sample can be inspected by the electron beam tool. The electron beam tool (40) may include a multi-beam electron-optical device.

[0046] The controller (50) is electronically connected to the electron beam tool (40). The controller (50) may be a processor (such as a computer) configured to control the charged particle beam inspection device (100). The controller (50) may also include processing circuits configured to perform various signal and image processing functions. Although the controller (50) is shown in FIG. 1 as being outside a structure comprising the main chamber (10), the load lock chamber (20), and the EFEM (30), it is recognized that the controller (50) may be part of this structure. The controller (50) may be located in one of the components of the charged particle beam inspection device or may be distributed across at least two of the components. It should be noted that while the present invention provides an example of a main chamber (10) that accommodates the electron beam inspection tool, the aspects of the present invention in its broadest sense are not limited to a chamber that accommodates the electron beam inspection tool. Rather, it is recognized that the aforementioned principles may also be applied to other arrangements of other tools and devices operating under a second pressure.

[0047] Now, reference is made to FIG. 2, which 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 device (100) of FIG. 1. The multi-beam electron beam tool (40) (also referred to herein as the device (40)) includes an electron source (201), a projection device (230), an electric stage (209), and a sample holder (207). The electron source (201) and the projection device (230) together may be referred to as an illumination device. The sample holder (207) is supported by the electric stage (209) to hold a sample (208) (e.g., a substrate or a mask) for inspection. The multi-beam electron beam tool (40) may further include an electron detection device (240).

[0048] The electron source (201) may include a cathode (not visible) and an extractor or an anode (not visible). During operation, the electron source (201) is configured to emit electrons as primary electrons from the cathode. The primary electrons are extracted or accelerated by the extractor and / or anode to form a primary electron beam (202).

[0049] The projection device (230) is configured to convert a primary electron beam (202) into a plurality of sub-beams (211, 212, 213) and to direct each sub-beam onto a sample (208). For simplicity, three sub-beams are shown, but there may be tens, hundreds, or thousands of sub-beams. Sub-beams may be referred to as beamlets.

[0050] The controller (50) can be connected to various parts of the charged particle beam inspection device (100) of FIG. 1, such as an electronic source (201), an electronic detection device (240), a projection device (230), and an electric stage (209). The controller (50) can perform various image and signal processing functions. The controller (50) can also generate various control signals to control the operation of the charged particle beam inspection device, including a charged particle multi-beam device.

[0051] The projection device (230) may be configured to focus sub-beams (211, 212, and 213) onto a sample (208) for inspection and to form 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) across individual scanning regions within a portion 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 electron beam typically has an electron energy of less than 50 eV, and the backscattered electrons have an electron energy between 50 eV and the landing energy of the primary sub-beam (211, 212, and 213).

[0052] The electronic detection device (1240) is configured to detect secondary electrons and / or backscattered electrons and to generate a corresponding signal transmitted to a controller or signal processing system (not visible) to form an image of a corresponding scan area of, for example, a sample (208). The electronic detection device may be integrated into a projection device or may be separate from the projection device, and a secondary optical column is provided to direct the secondary electrons and / or backscattered electrons toward the electronic detection device.

[0053] The controller (50) may include an image processing system comprising an image acquirer (not visible) and a storage device (not visible). For example, the controller may include a processor, a computer, a server, a mainframe host, a terminal, a personal computer, any type of mobile computing device, or a combination thereof. The image acquirer may include at least some of the processing functions of the controller. Thus, the image acquirer may include at least one processor. The image acquirer may be connected to communicate with an electronic detection device (240) of a device (40) that allows signal communication, such as an electrical conductor, a fiber optic cable, a portable storage medium, IR, Bluetooth, the Internet, a wireless network, a wireless radio, or a combination thereof. The image acquirer may receive a signal from the electronic detection device (240), process data contained in the signal, and also construct an image therefrom. Thus, the image acquirer may acquire an image of the sample (208). The image acquirer may also perform various post-processing functions, such as generating contours or superimposing markers on the acquired image. The image acquirer may be configured to perform adjustments such as brightness and contrast of the acquired image. The storage unit may be a storage medium such as a hard disk, flash drive, cloud storage, random access memory (RAM), or other types of computer-readable memory. The storage unit may be combined with the image acquirer and may be used to store scanned raw image data as the original image and post-processed images.

[0054] The image acquisition device can acquire one or more images of a sample based on an imaging signal received from an electronic detection device (240). The imaging signal may correspond to a scanning operation for performing imaging of charged particles. The acquired image may be a single image containing multiple imaging zones. The single image may be stored in a storage unit. The single image may be an original image that can be divided into multiple zones. Each of the zones may include a single imaging zone containing a feature of the sample (208). The acquired image may include multiple images of a single imaging zone of the sample (208) that has been sampled multiple times over a certain period. Multiple images may be stored in a storage unit. The controller (50) may be configured to perform an image processing step with multiple images of the same location of the sample (208).

[0055] The controller (50) may include a measurement circuit (e.g., an analog-to-digital converter) to acquire the distribution of detected secondary electrons. The electron distribution data collected during the detection time window may be used in combination with the respective corresponding scan path data of the primary sub-beams (211, 212 and 213) incident on the sample surface to reconstruct an image of the sample structure being inspected. The reconstructed image may be used to reveal various features of the internal or external structure of the sample (208). Accordingly, the reconstructed image may be used to reveal any defects that may be present in the sample.

[0056] The controller (50) can control the motorized stage (209) to move the sample (208) during the inspection of the sample (208). The controller (50) can enable the motorized stage (209) to move the sample (208) in one direction, preferably continuously, for example, at a constant speed, at least during the sample inspection. The controller (50) can control the movement of the motorized stage (209) to change the movement speed of the sample (208) according to various parameters. For example, the controller can control the stage speed (including its direction) according to the characteristics of the inspection step of the scanning process.

[0057] FIG. 3 is a schematic diagram of an evaluation tool. An electron source (201) directs electrons to an array of condensing lenses (231) that form part of a projection system (230). FIG. 3 is a schematic diagram of an inspection tool according to an embodiment of the present invention. An electron source (201) directs electrodes to an array of condensing lenses (231) that form part of a projection system (230). The electron source is preferably a high-intensity thermoelectric field emitter having a good compromise between brightness and total emission current. There may be tens, hundreds, or thousands of condensing lenses (231). The condensing lenses may include multi-electrode lenses and may also have a configuration based on EP1602121A1, which is incorporated herein by reference to the disclosure of a lens array for splitting an e-beam into a plurality of beams—the array provides a lens for each sub-beam. The lens array may take the form of at least two plates. The lens array may include a beam-limiting aperture array which may be one of at least two plates. At least two plates act as electrodes, and the apertures of each plate are aligned with each other and correspond to the position of the sub-beam. To achieve the desired lens effect, at least two plates are maintained at different potentials during operation.

[0058] In an array, the condensing lens array can be formed with three plate arrays having the same energy as when charged particles enter and exit each lens, and the plate array can be referred to as an Einzel lens. Therefore, dispersion occurs only within the Einzel lens itself (between the incident and exit electrodes of the lens), thereby limiting out-of-axis chromatic aberration. When the thickness of the condensing lens is small, for example, a few millimeters, this aberration has a small or negligible effect.

[0059] Each condensing lens in the array directs electrons toward each sub-beam (211, 212, 213) focused at each intermediate focus (233). The sub-beams diverge from one another. Down-beams of the intermediate focus (233) are a plurality of objective lenses (234), each of which directs each sub-beam (211, 212, 213) toward a sample (208). The objective lenses (234) may be Einsel lenses. At least the chromatic aberrations generated in the beam by the condensing lenses and the corresponding down-beam objective lenses can be mutually canceled out.

[0060] An electronic detection device (240) is provided between the objective lens (234) and the sample (208) to detect secondary and / or backscattered electrons emitted from the sample (208). An exemplary configuration of the electronic detection system is described below.

[0061] In the system of FIG. 3, beamlets (211, 212, 213) propagate along straight paths from the condensing lens (231) to the sample (208). The beamlet paths branch downstream of the condensing lens (231). A modified configuration identical to the system of FIG. 3 is shown in FIG. 4, except that a deflector (235) is provided at the intermediate focus (233). The deflector (235) is located in the beamlet path at or at least around the location of the corresponding intermediate focus (233) or the point of convergence (i.e., the point of convergence). The deflector is located in the beamlet path at the intermediate image plane of the associated beamlet, i.e., at its focal point or point of convergence. The deflector (235) is configured to operate at each beamlet (211, 212, 213). The deflector (235) is configured to deflect each beamlet (211, 212, 213) by an amount effective to ensure that the main ray (which may also be referred to as the beam axis) is incident substantially perpendicular to the sample (208) (i.e., 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) collimates the beamlet paths so that the beamlet paths diverge from each other prior to the deflector. Downstream of the deflector, the beamlet paths are substantially parallel to each other, i.e., substantially collimated. Thus, each beamlet path may be in a straight line between the array of condensing lenses (231) and the array of collimators, e.g., deflectors (235). Each beamlet path may be in a straight line between the array of deflectors (235) and the array of objective lenses (234) and optionally the sample (208). A suitable collimator is the deflector disclosed in EP application 20156253.5 filed on February 7, 2020, which is incorporated herein by reference in relation to the application of a deflector to a multi-beam array.

[0062] The system of FIG. 4 can be configured to control the landing energy of electrons on a sample. The landing energy can be selected to increase the emission and detection of secondary electrons depending on the characteristics of the sample being evaluated. A controller provided to control the objective lens (234) can be configured to control the landing energy to any desired value within a predetermined range or to a desired value among a plurality of predetermined values. In an embodiment, the landing energy can be controlled to a desired value within the range of 1,000 eV to 5,000 eV. The landing energy of electrons can be controlled more easily in the system of FIG. 4 because any out-of-axis aberration generated in the beamlet path is generated at the condensing lens (231) or at least primarily at the condensing lens (231). The objective lens (234) of the system shown in FIG. 4 does not need to be an Einzel lens. This is because out-of-axis aberration will not occur at the objective lens if the beam is collimated. Out-of-axis aberration can be controlled better at the condensing lens than at the objective lens (234). By making the condensing lens (231) substantially thinner, the contribution of the condensing lens to off-axis aberrations, particularly chromatic off-axis aberrations, can be minimized. The thickness of the condensing lens (231) can be changed to adjust the chromatic off-axis contribution to balance the other contribution of chromatic aberration in each beamlet path. Thus, the objective lens (234) may have two or more electrodes. The beam energy entering the objective lens may be different from its energy leaving the objective lens.

[0063] FIG. 6 is an enlarged schematic diagram of one objective lens (300) of an array of objective lenses. The objective lens (300) may be configured to reduce the electron beam by a factor greater than 10, preferably within the range of 50 to 100 or more. The objective lens comprises a middle or first electrode (301), a lower or second electrode (302), and a top or third electrode (303). Voltage sources (V1, V2, V3) are configured to apply potentials to the first, second, and third electrodes, respectively. An additional voltage source (V4) is connected to the sample to apply a fourth potential that can be grounded. The potential may be defined for the sample (208). Each of the first, second, and third electrodes has an aperture, and each sub-beam propagates through this aperture. The second potential may be similar to the potential of the sample, for example, within the range of +50V to +200V. Alternatively, the second potential may be within the range of approximately +500V to approximately +1,500V. A higher potential is useful when the detector is higher in the optical column than the lowest electrode. The first and / or second potentials may vary for each aperture and affect focus correction.

[0064] Preferably, in the embodiment, the third electrode is omitted. An objective lens having only two electrodes can have lower aberrations than an objective lens having more electrodes. A three-electrode objective lens can have a larger potential difference between the electrodes and thus enables a stronger lens. Additional electrodes (i.e., more than two electrodes) provide additional degrees of freedom to control electron trajectories, for example, focusing not only the incident beam but also the secondary electrodes.

[0065] In order to provide a deceleration function to the objective lens (300) so that the landing energy can be determined, it is desirable to change the potential of the lowest electrode and the sample. To decelerate the electrons, the lower (second) electrode is made more negative than the central electrode. The highest electrostatic field strength occurs when the lowest landing energy is selected. The distance between the second electrode and the middle electrode, the lowest landing energy, and the maximum potential difference between the second electrode and the middle electrode are selected so that the resulting electric field strength is acceptable. For higher landing energies, the electrostatic field becomes lower (less deceleration for the same length).

[0066] Since the electron optical system configuration between the electron source and the beam limit aperture (immediately above the condensing lens) remains the same, the beam current remains unchanged with respect to changes in landing energy. Changing the landing energy affects the resolution, which can be improved or reduced. Figure 5 is a graph showing landing energy versus spot size in two cases. The dashed line with non-empty circles represents the effect of changing only the landing energy, i.e., the condensing lens voltage remains the same. The solid line with empty circles represents the effect when the landing energy is changed and the condensing lens voltage (optimization of magnification versus opening angle) is re-optimized.

[0067] If the condensing lens voltage changes, the collimator will not be in the accurate mid-image plane for all landing energies. Therefore, it is desirable to correct the astigmatism induced by the collimator.

[0068] In some embodiments, the charged particle evaluation tool further includes one or more aberration correctors that reduce one or more aberrations within the sub-beam. In the embodiments, each of at least a subset of aberration correctors is located within or immediately adjacent to each of the intermediate foci (e.g., within or adjacent to the intermediate image plane). The sub-beam has the smallest cross-sectional area within or near the same focal plane as the intermediate plane. This provides more space for the aberration correctors than is available elsewhere, i.e., upbeam or downbeam of the intermediate plane (or than is available in an alternative array that does not have an intermediate image plane).

[0069] In an embodiment, an aberration corrector located within or immediately adjacent to intermediate focals (or intermediate image plane or focusing point) includes a deflector for correcting a source (201) that appears to be in a different position for a different beam. The corrector may be used to correct macroscopic aberrations originating from the source that prevent good alignment between each sub-beam and the corresponding objective lens.

[0070] An aberration corrector can correct aberrations that prevent proper column alignment. Such aberrations can also lead to misalignment between the sub-beam and the corrector. For this reason, it may be desirable to position the aberration corrector additionally or alternatively at or near the condensing lens (231) (e.g., each of these aberration correctors is integrated with or directly adjacent to one or more of the condensing lenses (231)). This is desirable in that, since the condensing lens (231) is perpendicular to or aligned with the beam aperture, the aberrations at or near the condensing lens (231) will not yet cause a shift in the corresponding sub-beam. However, the problem with positioning the corrector at or near the condensing lens (231) is that each of the sub-beams has a relatively wide cross-sectional area and a relatively small pitch at this position compared to a more downstream position.

[0071] In some embodiments, each of at least a subset of aberration correctors is integrated with or immediately adjacent to one or more of the objective lenses (234). In an embodiment, this aberration corrector reduces 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 immediately adjacent to one or more of the objective lenses (234) to scan the sub-beams (211, 212, 214) over the sample (208). In an embodiment, the scanning deflector may be used as described in US2010 / 0276606, which is incorporated herein by reference in its entirety.

[0072] The aberration corrector may be a CMOS-based individual programmable deflector as disclosed in EP2702595A1 or an array of multipole deflectors as disclosed in EP2715768A2, and the description of the beamlet manipulator in both of these documents is incorporated into this specification by reference.

[0073] In the example, the objective lens mentioned in the previous example is an array objective lens. Each element of the array is a microlens that operates a different beam or group of beams in a multi-beam system. The electrostatic array objective lens has at least two plates, each having a plurality of holes or apertures. The position of each hole in a plate corresponds to the position of a corresponding hole in another plate. The corresponding holes operate on the same beam or group of beams in the multi-beam system during use. A suitable example of a lens type for each element of the array is a two-electrode deceleration lens. The bottom electrode of the objective lens is a detector, for example, a CMOS chip. The detector can be integrated into a multi-beam manipulator array, such as the objective lens. The integration of the detector array into the objective lens replaces the secondary column. (Because of the small distance (e.g., 100 μm) between the wafer and the bottom of the electro-optical system, the detector array, for example, the CMOS chip, is preferably oriented toward the sample. In the example, an electrode for capturing a secondary electronic signal is formed on the top metal layer of the CMOS device. The electrode can be formed on a different layer. Power and control signals of the CMOS can be connected to the CMOS via silicon-through vias. For robustness, the bottom electrode preferably consists of two elements: a CMOS chip and a passive Si plate having holes. The plate shields the CMOS from high electric fields.

[0074] To maximize detection efficiency, it is desirable to make the electrode surface as large as possible, so that substantially all of the array objective lens area (excluding the aperture) is occupied by the electrodes, and each electrode has a diameter substantially equal to the array pitch. In the examples, the external shape of the electrode is circular, but it can be made square to maximize the detection area. Additionally, the diameter of the substrate through-hole can be minimized. The typical size of the electron beam is about 5 to 15 microns.

[0075] In an embodiment, a single electrode surrounds each aperture. In another embodiment, multiple electrode elements are provided around each aperture. Electrons captured by the electrode elements surrounding a single aperture can be combined into a single signal or used to generate independent signals. The electrode elements can be divided radially (i.e., to form multiple concentric rings), angularly (i.e., to form multiple fan-shaped pieces), radially and angularly, or in any other convenient manner.

[0076] However, a larger electrode surface leads to greater parasitic capacitance, which consequently lowers the bandwidth. For this reason, it may be desirable to limit the outer diameter of the electrode. This is especially true when a larger electrode provides slightly higher detection efficiency but offers significantly larger capacitance. Circular (annular) electrodes can provide a good trade-off between collection efficiency and parasitic capacitance.

[0077] A larger outer diameter of the electrode can also lead to greater crosstalk (sensitivity to signals from neighboring holes). This may also be a reason to make the electrode outer diameter smaller. This is especially true in cases where a larger electrode provides slightly higher detection efficiency but offers significantly greater crosstalk.

[0078] The backscattered and / or secondary electron current collected by the electrode is amplified by a trans-impedance amplifier.

[0079] In FIG. 7, which illustrates a multi-beam objective lens (401) in a schematic cross-section, an exemplary embodiment of a detector integrated into an objective lens array is shown. A detector module (402) is provided on the output side of the objective lens (401), i.e., the side facing the sample (403). FIG. 8 is a bottom view of the detector module (402) comprising a substrate (404) provided with a plurality of capture electrodes (405) each surrounding a beam aperture (406). The beam aperture (406) may be formed by etching through the substrate (404). In the array shown in FIG. 8, the beam apertures (406) are shown as a rectangular array. The beam apertures (406) may also be arranged differently, for example, as a hexagonal close-packed array as shown in FIG. 9.

[0080] FIG. 10 illustrates a portion of the detector module (402) in a cross-sectional view on a larger scale. The capture electrode (405) forms the bottom part of the detector module (402), that is, the surface closest to the sample. A logic layer (407) is provided between the capture electrode (405) and the body of the silicon substrate (404). The logic layer (407) may include an amplifier, for example, a transimpedance amplifier, an analog-to-digital converter, and read logic. In an embodiment, there is one amplifier and one analog-to-digital converter per capture electrode (405). The logic layer (407) and the capture electrode (405) may be manufactured using a CMOS process, and the capture electrode (405) forms a final metallization layer.

[0081] A wiring layer (408) is provided on the back of the substrate (404) and connected to the logic layer (407) by silicon-through vias (409). The number of silicon-through vias (409) does not need to be equal to the number of beam apertures (406). In particular, if the electrode signal is digitized in the logic layer (407), only a small number of silicon-through vias may be required to provide the data bus. The wiring layer (408) may include control lines, data lines, and power lines. It will be noted that there is sufficient space for all necessary connections despite the beam apertures (406). The detection module (402) may also be manufactured using bipolar or other manufacturing techniques. A printed circuit board and / or other semiconductor chip may be provided on the back of the detector module (402).

[0082] The integrated detector array described above is particularly advantageous when used with tools having adjustable landing energy, as secondary electron capture can be optimized over a range of landing energies. The detector array can be integrated not only into the lowest electrode array but also into other electrode arrays.

[0083] 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), performs a quantitative measurement of a sample (e.g., size of features), or generates an image of a map of a sample. Examples of evaluation tools are an inspection tool (e.g., for identifying defects), a review tool (e.g., for classifying defects), and a measurement tool.

[0084] The terms “sub-beam” and “beamlet” are used interchangeably herein and are both understood to include any radiation beam derived from a parent radiation beam by splitting or dividing the parent radiation beam. The term “manipulator” is used to include any element that influences the path of the sub-beam or beamlet, such as a lens or a deflector. The embodiments described herein may take the form of a series of aperture arrays or electro-optical elements arranged in an array along a beam or multi-beam path. These electro-optical elements may be electrostatic. In the embodiments, for example, all electro-optical elements from a beam-limiting aperture array to the last electro-optical element within the sub-beam path prior to the sample may be electrostatic and / or may take the form of an aperture array or a plate array. In the array, one or more of the electro-optical elements may be manufactured as a microelectromechanical system (MEMS).

[0085] The term "adjacent" may include meaning "abut."

[0086] Embodiments of the present invention are provided by the following provisions:

[0087] Clause 1: A charged particle evaluation tool comprises: a condensing lens array configured to divide a beam of charged particles into a plurality of sub-beams and to focus each of the sub-beams at a respective intermediate focus; a collimator configured to deflect each sub-beam at each intermediate focus and incident substantially perpendicularly to a sample; a plurality of objective lenses each configured to project one of the plurality of charged particle beams onto a sample—wherein each objective lens comprises a first electrode; and a second electrode located between the first electrode and the sample—; and an electric power source configured to apply a first and a second potential to the first and second electrodes, respectively, so that each charged particle beam is decelerated and incident on the sample with a desired landing energy.

[0088] Clause 2: In the tool according to Clause 1, the first potential is a more positive value than the second potential.

[0089] Clause 3: In the tool according to Clause 1 or 2, the second potential is a positive value for the sample, preferably within the range of +50V to +200V for the sample.

[0090] Clause 4: In the tool according to Clause 1 or 2, the second potential is a positive value for the sample, preferably within the range of +500 to +1,500 V for the sample.

[0091] Clause 5: In a tool according to Clause 1, 2, 3 or 4, each objective lens further comprises a third electrode—the third electrode is located between the first electrode and the charged particle beam source—and an electric power source is configured to apply a third potential to the third electrode, preferably the electric power source is configured to apply a different potential to at least some of the first and second electrodes.

[0092] Clause 6: A tool according to any one of Clauses 1 through 5 further comprises a detector configured to detect charged particles emitted from a sample—the detector is located between a plurality of objective lenses and the sample.

[0093] Clause 7: In a tool according to any one of Clauses 1 through 6, the electric power source is configured to apply the same first potential to all first electrodes and to apply the same second potential to all second electrodes.

[0094] Clause 8: A tool according to any one of Clauses 1 through 7 further comprises one or more aberration correctors configured to reduce one or more aberrations within a sub-beam—preferably each of at least a subset of aberration correctors is located within or immediately adjacent to each of the intermediate foci of intermediate foci.

[0095] Clause 9: A tool according to any one of Clauses 1 through 8 further comprises one or more scanning deflectors for scanning a sub-beam over a sample.

[0096] Clause 10: In the tool according to Clause 11, one or more scanning deflectors are integrated with or immediately adjacent to one or more of the objective lenses.

[0097] Clause 11: In a tool according to any one of Clauses 1 through 10, the collimator is one or more collimator deflectors.

[0098] Clause 12: In the tool according to Clause 13, one or more collimator deflectors are configured to deflect each beamlet by an amount effective to ensure that the main ray of the sub-beam is incident substantially perpendicularly to the sample.

[0099] Clause 13: In a tool according to any one of Clauses 1 through 12, the collimator at each intermediate focal point comprises a collimator positioned in the divergence path of the sub-beam substantially at the location of the corresponding focusing point of the sub-beam path.

[0100] Clause 14: In a tool according to any one of Clauses 1 through 13, the collimator is configured to operate at each diverging sub-beam so that the downstream of the collimator collimates the sub-beams relative to each other.

[0101] Clause 15: The inspection method comprises: dividing a beam of charged particles into a plurality of sub-beams; focusing each of the sub-beams at a respective intermediate focus; using a collimator at each intermediate focus to deflect each sub-beam so that each sub-beam is incident substantially perpendicularly to the sample; using a plurality of objective lenses—each objective lens comprising a first electrode and a second electrode located between the first electrode and the sample—to project the plurality of charged particle beams onto the sample; and controlling the potential applied to the first and second electrodes of each objective lens so that each charged particle beam is decelerated and incident on the sample with a desired landing energy.

[0102] Although the present invention has been described in relation to various embodiments, other embodiments of the present invention will be apparent to those skilled in the art from considering the specifications and practices of the present invention disclosed herein. The specifications and embodiments are to be regarded merely as illustrative, and it is intended that the true scope and spirit of the present invention is indicated by the following claims.

Claims

Claim 1 A charged particle evaluation tool comprises: a condensing lens array configured to divide a beam of charged particles into a plurality of sub-beams and to focus each of the sub-beams at a respective intermediate focus, wherein the plurality of sub-beams diverge from one another; a collimator configured to deflect each sub-beam at each intermediate focus and positioned in the divergence path of the sub-beams and incident substantially perpendicularly to a sample; a plurality of objective lenses each configured to project one of the plurality of charged particle beams onto the sample, wherein each objective lens comprises a first electrode; and a second electrode positioned between the first electrode and the sample; and one or more aberration correctors configured to reduce one or more aberrations within the sub-beams, wherein each of at least a subset of the aberration correctors is located within one or more of the respective intermediate focus of the intermediate focuses and / or objective lenses, or is immediately adjacent thereto. Claim 2 A tool comprising: an electric power source configured to apply first and second potentials to the first and second electrodes, respectively, so that each of the charged particle beams is decelerated and incident on the sample with a desired landing energy; and a controller configured to control the landing energy by controlling the objective lens. Claim 3 In paragraph 2, the tool in which the first potential is a more positive value than the second potential. Claim 4 In paragraph 2 or 3, the tool in which the second potential is a positive value for the sample. Claim 5 In claim 2 or 3, each objective lens further comprises a third electrode—the third electrode is located between the first electrode and the charged particle beam source—and the electric power source is configured to apply a third potential to the third electrode. Claim 6 A tool according to claim 1 or 2 further comprising a detector configured to detect charged particles emitted from the sample—the detector being located between the plurality of objective lenses and the sample. Claim 7 In paragraph 2 or 3, the electric power source is a tool configured to apply the same first potential to all first electrodes and the same second potential to all second electrodes. Claim 8 A tool according to claim 1 or 2, further comprising one or more scanning deflectors for scanning the sub-beam above the sample. Claim 9 In claim 8, the one or more scanning deflectors are integrated with one or more of the objective lenses or are a tool immediately adjacent thereto. Claim 10 A tool according to claim 1 or 2, further comprising a source configured to emit a beam of charged particles along a divergence path, wherein the focusing lens array is configured to divide the beam of charged particles into a plurality of sub-beams along the divergence path. Claim 11 In claim 1 or 2, the collimator is a tool that is one or more collimator deflectors. Claim 12 In paragraph 11, the above one or more collimator deflectors are tools configured to deflect each beamlet by an effective amount to ensure that the main ray of the sub-beam is incident substantially perpendicularly to the sample. Claim 13 A tool comprising, in accordance with claim 1 or 2, a collimator at each intermediate focal point substantially located in the divergence path of the sub-beam at the location of the corresponding focusing point of the sub-beam path. Claim 14 In claim 1 or 2, the collimator is a tool configured to operate at each diverging sub-beam so that the downstream of the collimator collimates the sub-beams relative to each other. Claim 15 A method of inspection comprising: dividing a beam of charged particles into a plurality of sub-beams, wherein the plurality of sub-beams diverge from one another; focusing each of the sub-beams at a respective intermediate focal point; using a collimator at each intermediate focal point to deflect each sub-beam so that each sub-beam is incident substantially perpendicularly to a sample, wherein the collimator is positioned in the divergence path of the sub-beams; using a plurality of objective lenses to project the plurality of charged particle beams onto the sample, wherein each objective lens comprises a first electrode and a second electrode located between the first electrode and the sample; and applying a correction to the sub-beams to reduce one or more aberrations within the sub-beams using one or more aberration correctors, wherein the one or more aberration correctors are located within or immediately adjacent to one or more of the respective intermediate focal points and / or objective lenses.

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