System and method for alignment of secondary beams in a multi-beam inspection apparatus

Abstract

A multi-beam inspection apparatus including an adjustable beam splitter is disclosed. The adjustable beam splitter is configured to change the path of a secondary particle beam. The adjustable beam splitter includes a first Wien filter and a second Wien filter. Both Wien filters are aligned with a primary optical axis. The first Wien filter and the second Wien filter are independently controllable via a first excitation input and a second excitation input, respectively. The adjustable beam splitter is configured to move an effective bending point of the adjustable beam splitter along the primary optical axis based on the first excitation input and the second excitation input.

Description

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims the priority of U.S. Application No. 62 / 824,954, filed on March 27, 2019, which is incorporated herein by reference in its entirety. Technical Field

[0003] The embodiments provided herein generally relate to multi-beam inspection apparatuses, and more particularly, to multi-beam inspection apparatuses including adjustable beam splitters. Background Art

[0004] When manufacturing semiconductor integrated circuit (IC) chips, pattern defects or unwanted particles (residues) inevitably occur on wafers or masks during the fabrication process, thereby reducing the yield. For example, for patterns with small critical feature sizes, unwanted particles can be troublesome, and patterns with small critical feature sizes have been adopted to meet the increasingly advanced performance requirements of IC chips.

[0005] Pattern inspection tools using charged particle beams have been used to detect defects or unwanted particles. These tools typically employ scanning electron microscopes (SEM). In an SEM, a primary electron beam with a relatively high energy is decelerated so as to land on a sample with a relatively low landing energy and is focused to form a probe spot thereon. Due to this focused probe spot of the primary electrons, secondary electrons will be generated from the surface. The secondary electrons can include backscattered electrons, secondary electrons, or Auger electrons generated by the interaction of the primary electrons with the sample. By scanning the probe spot over the sample surface and collecting the secondary electrons, the pattern inspection tool can obtain an image of the sample surface. Summary of the Invention

[0006] The embodiments provided herein disclose a particle beam inspection apparatus, and more particularly, disclose a multi-beam inspection apparatus including an adjustable beam splitter.

[0007] In some embodiments, the adjustable beam splitter is configured to change the path of a secondary particle beam. The adjustable beam splitter includes a first Wien filter and a second Wien filter. Both Wien filters are aligned with the primary optical axis. The first Wien filter and the second Wien filter are independently controllable via a first excitation input and a second excitation input, respectively. The adjustable beam splitter is configured to move the effective bending point of the adjustable beam splitter along the primary optical axis based on the first excitation input and the second excitation input.

[0008] In some embodiments, a primary projection system with an adjustable beam splitter is disclosed. The primary projection system includes an objective lens configured to focus a primary electron beam onto a sample, wherein a secondary electron beam is emitted from the sample in response to the primary electron beam. The primary projection system also includes an adjustable beam splitter configured to change the path of the secondary electron beam toward the secondary projection system at an effective bending point. The adjustable beam splitter includes: a first Wien filter aligned with the primary optical axis, wherein the first Wien filter is independently controllable via a first excitation input; and a second Wien filter aligned with the primary optical axis, wherein the second Wien filter is independently controllable via a second excitation input. The adjustable beam splitter is configured to move the effective bending point of the adjustable beam splitter along the primary optical axis based on the first excitation input and the second excitation input.

[0009] Other advantages of the present invention will become apparent from the following description taken in conjunction with the accompanying drawings, in which certain embodiments of the invention are set forth by way of illustration and example. BRIEF DESCRIPTION OF THE DRAWINGS

[0010] The above and other aspects of the present disclosure will become more apparent from the description of exemplary embodiments with reference to the accompanying drawings.

[0011] Figure 1 is a schematic diagram illustrating an exemplary charged particle beam inspection system consistent with embodiments of the present disclosure.

[0012] Figure 2 It is a diagram of an embodiment consistent with the present disclosure. Figure 1 Schematic diagram of an exemplary multi-beam apparatus that is a portion of an exemplary charged particle beam inspection system.

[0013] Figure 3A , Figure 3B and Figure 3C are schematic diagrams of a multi-beam electron beam tool illustrating exemplary configurations of beam splitters for secondary particle beams.

[0014] Figure 4A , Figure 4B and Figure 4C is a schematic diagram of an adjustable beam splitter consistent with an embodiment of the present disclosure.

[0015] Figure 5A and Figure 5B It is consistent with the embodiments of the present disclosure. Figure 4A , Figure 4B and Figure 4C Schematic diagram of a multi-beam electron beam tool with an adjustable beam splitter.

[0016] Figure 6 is a schematic diagram of a multi-beam electron beam tool illustrating an exemplary configuration of a primary projection system with a conventional beam splitter.

[0017] Figure 7 is a schematic diagram of a multi-beam electron beam tool illustrating a primary projection system with an adjustable beam splitter consistent with an embodiment of the present disclosure.

[0018] Figure 8 is a flow chart illustrating an exemplary method of controlling an adjustable beam splitter consistent with an embodiment of the present disclosure. DETAILED DESCRIPTION

[0019] 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, wherein the same reference numerals in different drawings represent the same or similar elements unless otherwise indicated. The implementations set forth in the following description of the exemplary embodiments do not represent all implementations consistent with the present invention. Instead, they are merely examples of devices and methods consistent with aspects related to the present invention as set forth in the appended claims.

[0020] Electronic devices are made up of circuits formed on a silicon wafer called a substrate. Many circuits can be formed together on the same silicon wafer and are called an integrated circuit or IC. The size of these circuits has been reduced significantly so that more circuits can fit on a substrate. For example, an IC chip in a smartphone can be as small as a thumbnail and may also include over 2 billion transistors, each less than 1 / 1000 the size of a human hair.

[0021] Making these extremely small ICs is a complex, time-consuming and expensive process that typically involves hundreds of individual steps. An error in even one step can result in a defect in the finished IC, rendering it unusable. Therefore, one goal of the manufacturing process is to avoid such defects in order to maximize the number of functional ICs made in the process, that is, to improve the overall yield of the process.

[0022] An integral part of improving yield is monitoring the chip manufacturing process to ensure that it is producing a sufficient number of functional integrated circuits. One way to monitor the process is to inspect the chip circuit structures at various stages of their formation. Inspection can be done using a scanning electron microscope (SEM). The SEM can be used to image these extremely small structures, in effect taking a "picture" of the structure. The image can be used to determine if the structure was formed correctly and also if it was formed in the correct location. If the structure is defective, the process can be adjusted so the defect is less likely to occur again.

[0023] For high throughput inspection, some of the inspection systems use multiple focused beams of primary electrons. Since multiple focused beams can scan different parts of the wafer simultaneously, the multi-beam inspection system can inspect the wafer at a much higher speed than a single beam inspection system. However, due to alignment errors between different parts of the inspection system relative to the path traveled by the electron beam, conventional multi-beam inspection systems may suffer from low inspection accuracy. For example, in some cases, all optical components used for the secondary electron beam must be properly aligned with the optical components used for the primary electron beam within a deviation of about 100 μm, which is less than the thickness of a human hair; otherwise, the secondary electron beam may interfere with the detection of adjacent secondary electron beams, and the inspection image quality may suffer from aberrations and errors. One aspect of the present disclosure includes an improved secondary beam splitter that is adjustable and provides the ability to compensate for misalignment by adjusting the routing path of the secondary electron beam.

[0024] For the sake of clarity, the relative size of the parts in the accompanying drawings may be exaggerated. In the following description of the accompanying drawings, the same or similar reference numerals refer to the same or similar parts or entities, and only the difference about the individual embodiment is described. As used herein, unless otherwise clearly stated, the term "or" encompasses all possible combinations, except infeasible situations. For example, if the description component can include A or B, then unless otherwise clearly stated or infeasible, the component may include A, or B, or A and B. As a second example, if the description component can include A, B or C, then unless otherwise clearly stated or infeasible, the component may include A, or B, or C, or A and B, or A and C, or B and C, or A and B and C.

[0025] Now, refer to Figure 1 , Figure 1 is a schematic diagram illustrating an exemplary charged particle beam inspection system 100 consistent with an embodiment of the present disclosure. Figure 1 As shown, the charged particle beam inspection system 100 includes a main chamber 10, a load lock chamber 20, an electron beam tool 40, and an equipment front end module (EFEM) 30. The electron beam tool 40 is located within the main chamber 10. Although the description and drawings relate to electron beams, it should be appreciated that the embodiments are not intended to limit the present disclosure to specific charged particles.

[0026] 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. For example, the first load port 30a and the second load port 30b may receive a wafer front opening unified box (FOUP) containing wafers (e.g., semiconductor wafers or wafers made of (one or more) other materials) or samples to be inspected (wafers and samples are collectively referred to as "wafers" hereinafter). One or more robot arms (not shown) in the EFEM 30 transport the wafers to the load lock chamber 20.

[0027] The load lock chamber 20 may be connected to a load lock vacuum pump system (not shown) that removes gas molecules in the load lock chamber 20 to reach a first pressure below atmospheric pressure. After reaching the first pressure, one or more robot arms (not shown) transport the wafer from the load lock chamber 20 to the main chamber 10. The main chamber 10 is connected to a main chamber vacuum pump system (not shown) that removes gas molecules in the main chamber 10 to reach a second pressure below the first pressure. After reaching the second pressure, the wafer is inspected by the electron beam tool 40. In some embodiments, the electron beam tool 40 may include a single beam inspection tool. In other embodiments, the electron beam tool 40 may include a multi-beam inspection tool.

[0028] The controller 50 is electronically connected to the electron beam tool 40. The controller 50 may be a computer configured to perform various controls for the charged particle beam inspection system 100. The controller 50 may also include processing circuitry configured to perform various signal and image processing functions. Figure 1 Controller 50 is shown as being outside of the structure including main chamber 10, load lock chamber 20, and EFEM 30, but it should be appreciated that controller 50 may be part of the structure.

[0029] Although the present disclosure provides an example of a main chamber 10 housing an electron beam inspection tool, it should be noted that aspects of the present disclosure in its broadest sense are not limited to chambers housing electron beam inspection tools. Rather, it should be appreciated that the aforementioned principles may also be applied to other tools operating at a second pressure.

[0030] Now, refer to Figure 2 , Figure 2 is a schematic diagram illustrating an exemplary electron beam tool 40 consistent with an embodiment of the present disclosure, the exemplary electron beam tool 40 includes as Figure 1A multi-beam inspection tool that is part of an exemplary charged particle beam inspection system 100. The multi-beam electron beam tool 40 (also referred to herein as device 40) includes an electron source 201, a gun aperture plate 271, a bunching lens 210, a source conversion unit 220, a primary projection system 230, a motorized stage 209, and a sample holder 207. The sample holder 207 is supported by the motorized stage 209 to hold a sample 208 (e.g., a wafer or a photomask) to be inspected. The multi-beam electron beam tool 40 may further include a secondary projection system 250 and an electron detection device 240. The primary projection system 230 may include an objective lens 231. A beam splitter 233 and a deflection scanning unit 232 may be positioned inside the primary projection system 230. The electron detection device 240 may include a plurality of detection elements 241, 242, and 243.

[0031] The electron source 201, the gun aperture plate 271, the bunching lens 210, the source conversion unit 220, the beam splitter 233, the deflection scanning unit 232, and the primary projection system 230 may be aligned with a primary optical axis 204 of the device 40. The secondary projection system 250 and the electron detection device 240 may be aligned with a secondary optical axis 251 of the device 40.

[0032] The electron source 201 may include a cathode (not shown) and an extractor or anode (not shown). During operation, the electron source 201 is configured to emit primary electrons from the cathode, and the primary electrons are extracted or accelerated through the extractor and / or anode to form a primary electron beam 202. The primary electron beam 202 forms a primary beam crossover (virtual or real) 203. The primary electron beam 202 may be considered to be emitted from the primary beam crossover 203.

[0033] The source conversion unit 220 may include an image forming element array (not shown), an aberration compensator array (not shown), a beam limiting aperture array (not shown), and a pre-bent micro-deflector array (not shown). In some embodiments, the pre-bent micro-deflector array deflects the multiple primary sub-beams 211, 212, 213 of the primary electron beam 202 to enter the beam limiting aperture array, the image forming element array, and the aberration compensator array normally. In some embodiments, the condenser lens 210 is designed to focus the primary electron beam 202 to become a parallel beam and to be incident normally on the source conversion unit 220. The image forming element array may include a plurality of micro-deflectors or micro-lenses to affect the multiple primary sub-beams 211, 212, 213 of the primary electron beam 202 and form a plurality of parallel images (virtual or real) of the primary beam cross 203, one parallel image for each of the primary sub-beams 211, 212, and 213. In some embodiments, the aberration compensator array may include a field curvature compensator array (not shown) and an astigmatism compensator array (not shown). The field curvature compensator array may include a plurality of micro lenses to compensate for the field curvature aberration of the primary beamlets 211, 212, and 213. The astigmatism compensator array may include a plurality of micro stigmatizers to compensate for the astigmatism aberration of the primary beamlets 211, 212, and 213. The beam limiting aperture array may be configured to limit the diameter of the individual primary beamlets 211, 212, and 213. As an example, Figure 2 Three primary sub-beams 211, 212 and 213 are shown, and it should be appreciated that the source conversion unit 220 may be configured to form any number of primary sub-beams. The controller 50 may be connected to Figure 1 The controller 50 may be used to control various parts of the charged particle beam inspection system 100, such as the source conversion unit 220, the electronic detection device 240, the primary projection system 230, or the motorized stage 209. In some embodiments, as explained in further detail below, the controller 50 may perform various image and signal processing functions. The controller 50 may also generate various control signals to govern the operation of the charged particle beam inspection system.

[0034] The condenser lens 210 is configured to focus the primary electron beam 202. The condenser lens 210 may be further configured to adjust the current of the primary beamlets 211, 212, and 213 downstream of the source conversion unit 220 by varying the focusing power of the condenser lens 210. Alternatively, the current may be varied by changing the radial size of the beam limiting apertures within the beam limiting aperture array corresponding to the individual primary beamlets. The current may be varied by changing both the radial size of the beam limiting apertures and the focusing power of the condenser lens 210. The condenser lens 210 may be an adjustable condenser lens that may be configured such that the position of its first principal plane is movable. The adjustable condenser lens may be configured to be magnetic, which may cause the off-axis beamlets 212 and 213 to illuminate the source conversion unit 220 at a rotation angle. The rotation angle varies with the focusing power or the position of the first principal plane of the adjustable condenser lens. Accordingly, the condenser lens 210 may be an anti-rotation condenser lens that may be configured to maintain a rotation angle while the focusing power of the condenser lens 210 changes. In some embodiments, the condenser lens 210 may be an adjustable anti-rotation condenser lens, wherein the rotation angle remains unchanged while its focusing power and the position of its first principal plane change.

[0035] The objective lens 231 may be configured to focus the sub-beams 211, 212, and 213 onto the sample 208 for inspection, and in the current embodiment, three detection spots 221, 222, and 223 may be formed on the surface of the sample 208. The deflection scanning unit 232 is configured to deflect the primary sub-beams 211, 212, and 213 when in operation to scan the detection spots 221, 222, and 223 across individual scanning areas in a section of the surface of the sample 208. The gun aperture plate 271 is configured to block peripheral electrons of the primary electron beam 202 when in operation to reduce the Coulomb effect. The Coulomb effect may enlarge the size of each of the detection spots 221, 222, and 223 of the primary sub-beams 211, 212, 213, and thus degrade the inspection resolution.

[0036] In response to the incident of the primary beamlets 211, 212 and 213 or the detection spots 221, 222 and 223 on the sample 208, electrons come out of the sample 208 and generate three secondary electron beams 261, 262 and 263. Each of the secondary electron beams 261, 262 and 263 generally includes secondary electrons (having an electron energy of ≤50 eV) and backscattered electrons (having an electron energy between 50 eV and the landing energy of the primary beamlets 211, 212 and 213).

[0037] The beam splitter 233 can be a Wien filter that includes an electrostatic deflector that generates an electrostatic dipole field and a magnetic deflector that generates a magnetic dipole field (not shown). In operation, the beam splitter 233 can be configured to generate an electrostatic dipole field using the electrostatic deflector to exert an electrostatic force on individual electrons of the primary sub-beams 211, 212, and 213. The beam splitter 233 can also be configured to generate a magnetic dipole field to exert a magnetic force on the electrons. The electrostatic force is equal in magnitude to the magnetic force, but opposite in direction. Therefore, the primary sub-beams 211, 212, and 213 can pass through the beam splitter 233 at least substantially in a straight line and at a deflection angle that is at least substantially zero.

[0038] However, the secondary electron beams 261, 262 and 263 may be deflected toward the secondary projection system 250, which then focuses the secondary electron beams 261, 262 and 263 onto the detection elements 241, 242 and 243 of the electron detection device 240. The detection elements 241, 242 and 243 are arranged to detect the corresponding secondary electron beams 261, 262 and 263 and generate corresponding signals, which are sent to the controller 50 or a signal processing system (not shown), for example, to construct an image of the corresponding scan area of ​​the sample 208.

[0039] In some embodiments, the detection elements 241, 242, and 243 detect the corresponding secondary electron beams 261, 262, and 263, respectively, and generate corresponding intensity signal outputs (not shown) to an image processing system (e.g., controller 50). In some embodiments, each detection element 241, 242, and 243 may include one or more pixels. The intensity signal output of a detection element may be the sum of the signals generated by all pixels within the detection element.

[0040] In some embodiments, the controller 50 may include an image processing system including an image acquisition device (not shown) and a storage device (not shown). The image acquisition device may include one or more processors. For example, the image acquisition device may include a computer, a server, a mainframe, a terminal, a personal computer, any kind of mobile computing device, or the like, or a combination thereof. The image acquisition device may be coupled to the electronic detection device 240 of the device 40 through a medium such as an electrical conductor, an optical fiber cable, a portable storage medium, IR, Bluetooth, the Internet, a wireless network, a radio, or the like, or a combination thereof. In some embodiments, the image acquisition device may receive a signal from the electronic detection device 240 and may construct an image. Thus, the image acquisition device may acquire an image of the sample 208. The image acquisition device may also perform various post-processing functions, such as generating a contour, superimposing an indicator on the acquired image, or the like. The image acquisition device may be configured to perform adjustments to the brightness and contrast of the acquired image, or the like. In some embodiments, the storage device may be a storage medium such as a hard disk, a flash drive, a cloud storage device, a random access memory (RAM), other types of computer-readable memory, or the like. The storage device may be coupled to the image acquirer and may be used to save the scanned original image data as a raw image and save the post-processed image.

[0041] In some embodiments, the image acquirer can acquire one or more images of the sample based on the imaging signal received from the electronic detection device 240. The imaging signal can correspond to a scanning operation for performing charged particle imaging. The acquired image can be a single image including multiple imaging areas. The single image can be stored in a storage device. The single image can be an original image, and the original image can be divided into multiple areas. Each of the areas can include an imaging area, and the imaging area contains features of the sample 208. The acquired image can include multiple images of a single imaging area of ​​the sample 208 sampled multiple times over a time series. The multiple images can be stored in a storage device. In some embodiments, the controller 50 can be configured to perform an image processing step using multiple images of the same position of the sample 208.

[0042] In some embodiments, the controller 50 may include a measurement circuit device (e.g., an analog-to-digital converter) to obtain the distribution of the detected secondary electrons. The electron distribution data collected during the detection time window, combined with the corresponding scan path data of each of the primary beamlets 211, 212, and 213 incident on the wafer surface, can be used to reconstruct an image of the inspected wafer structure. The reconstructed image can be used to reveal various features of the internal or external structure of the sample 208, and thereby can be used to reveal any defects that may be present in the wafer.

[0043] In some embodiments, the controller 50 may control the motorized stage 209 to move the sample 208 during inspection of the sample 208. In some embodiments, the controller 50 may enable the motorized stage 209 to continuously move the sample 208 in one direction at a constant speed. In other embodiments, the controller 50 may enable the motorized stage 209 to change the movement speed of the sample 208 over time depending on the steps of the scanning process. In some embodiments, the controller 50 may adjust the configuration of the primary projection system 230 or the secondary projection system 250 based on the images of the secondary electron beams 261, 262, and 263.

[0044] although Figure 2 The electron beam tool 40 is shown using three primary electron beams, but it should be appreciated that the electron beam tool 40 may use two or more primary electron beams. The present disclosure does not limit the number of primary electron beams used in the apparatus 40.

[0045] Now, refer to Figure 3A , Figure 3A 3 is a schematic diagram of a multi-beam electron beam tool 300A, which illustrates an exemplary configuration of a beam splitter 333 for a secondary particle beam. The multi-beam electron beam tool 300A may be a multi-beam device such as Figure 1 The multi-beam device 100 is a part of the multi-beam electron beam tool. In the multi-beam electron beam tool, in response to the incidence of the primary electron beam (e.g., the primary electron beam 311), a plurality of secondary electron beams (e.g., the secondary electron beam 361) are generated from the sample 308. The secondary electron beams 361 are deflected toward the secondary projection system 350 by the beam splitter 333, which focuses the secondary electron beams 361 onto the electron detection device 340. The beam splitter 333 can be a part of the primary projection system 330.

[0046] In some embodiments, the beam splitter 333 can be a Wien filter including an electrostatic deflector generating an electrostatic dipole field and a magnetic deflector generating a magnetic dipole field (not shown). In operation, the beam splitter 333 can be configured to generate an electrostatic dipole field orthogonal to the magnetic dipole field, such that with respect to primary electrons, which travel in a downward direction along the primary optical axis 304, the electrostatic force induced by the electrostatic dipole field is equal in magnitude to the magnetic force induced by the magnetic dipole field, but opposite in direction. Thus, the primary electron beam 311 can pass through the beam splitter 333 at least substantially straight and with a deflection angle of at least substantially zero. On the other hand, with respect to secondary electrons, which travel in an upward direction along the primary optical axis 304, the electrostatic force and the magnetic force are applied in the same direction; as a result, the secondary beam 361 is deflected toward the secondary projection system 350 at the bending point 336.

[0047] In some embodiments, the secondary projection system 350 may include one or more lenses, such as a main zoom lens 352, a second zoom lens 353, and a projection lens 354, configured to focus the secondary electron beam 361 onto the electron detection device 340. The secondary projection system 350 may also include one or more deflectors 355, 356, and 357 to deflect the secondary electron beam 361. Figure 3A As shown, after being deflected by the beam splitter 333, the secondary electron beam 361 passes through the center of the main zoom lens 352. In some embodiments, the main zoom lens 352 can be the main lens in the secondary projection system and has a strong focusing ability; as a result, the main zoom lens 352 can dominate the optical performance of the secondary projection system 350. Accordingly, a well-aligned main zoom lens 352 provides better performance.

[0048] Although to simplify the diagram, Figure 3A Only one primary electron beam 311 and one secondary electron beam 361 are shown, but it should be appreciated that the multi-beam electron beam tool 300A may use any number of electron beams.

[0049] Now, refer to Figure 3B , Figure 3B 3 is a schematic diagram of a multi-beam electron beam tool 300B illustrating the effect of misalignment of the secondary projection system 350. The multi-beam electron beam tool 300B may be a multi-beam device such as Figure 1 The misalignment may be caused by manufacturing and processing errors of the various components of the primary projection system 330 and the secondary projection system 350. In addition, because so many components are integrated in the primary projection system 330 and the secondary projection system 350, even if each component is calibrated within the tolerance level after integration, the accumulated deviations may cause a large amount of misalignment between the primary projection system 330 and the secondary projection system 350.

[0050] If the secondary projection system 350 is not well aligned with the primary projection system 330, the lenses (e.g., the main zoom lens 352, the second zoom lens 353, and the projection lens 354) and the deflection modules (e.g., the deflectors 355, 356, and 357) in the secondary projection system 350 may introduce aberrations that may cause distortions in the shape, intensity, and layout of the secondary beam 361. Such distortions may result in reduced secondary electron collection efficiency and increased crosstalk levels, thereby degrading the quality of the information generated by the detection device 340.

[0051] For example, Figure 3BA multi-beam electron beam tool 300B is shown in which the main zoom lens 352 is not properly aligned, causing a mismatch between the actual bending point 337 (which is determined by the position of the beam splitter 333) and the desired bending point 338 (the point where the primary optical axis 304 intersects the secondary optical axis 351). In some embodiments, the desired bending point 338 can be determined by the overall alignment characteristics of the secondary projection system 350. In some embodiments, because the main zoom lens 352 (with its high focusing ability) can be the dominant factor in the optical performance of the secondary projection system 350, the desired bending point 338 can be determined by the alignment characteristics of the main zoom lens 352. Figure 3B 338 is lower than the actual bending point 337 because the secondary projection system 350 is not properly aligned with the center of the beam splitter 333. As explained above, this mismatch may introduce aberrations that may cause distortions in the shape, intensity and layout of the secondary beam 361, which in turn may degrade the quality of the information collected by the detection device 340.

[0052] Although to simplify the diagram, Figure 3B Only one primary electron beam 311 and one secondary electron beam 361 are shown, but it should be appreciated that the multi-beam electron beam tool 300B may use any number of electron beams.

[0053] Now, refer to Figure 3C , Figure 3C is a schematic diagram of a multi-beam electron beam tool 300C, in which a pre-lens deflector 390 is introduced to alleviate the above Figure 3B The multi-beam electron beam tool 300C may be a multi-beam device (such as Figure 1 The pre-lens deflector 390 may be a part of the multi-beam device 100 of the present invention. In some embodiments, a pre-lens deflector 390 may be added to the path of the secondary electron beam 361 to compensate for the effects of misalignment. For example, the pre-lens deflector 390 may be positioned between the beam splitter 333 and the main zoom lens 352 so that the pre-lens deflector 390 may bend the secondary electron beam 361 so that the secondary electron beam 361 can enter the main zoom lens 352 normally. However, adding the pre-lens deflector 390 before the main zoom lens 352 may require the main zoom lens 352 to be positioned farther from the sample 308. This increased distance between the sample 308 and the main zoom lens 352 may significantly deteriorate the overall optical performance of the secondary projection system 350. In a multi-beam device, as the distance between the sample 308 and the main zoom lens 352 increases, the aberrations and errors of the secondary electron beam increase nonlinearly (e.g., exponentially). Accordingly, it would be desirable to seek a different approach to addressing the misalignment problem without increasing the distance between the sample 308 and the main zoom lens 352 .

[0054] Although to simplify the diagram, Figure 3C Only one primary electron beam 311 and one secondary electron beam 361 are shown, but it should be appreciated that the multi-beam electron beam tool 300C may use any number of electron beams.

[0055] Now, refer to Figure 4A , Figure 4B and Figure 4C , Figure 4A , Figure 4B and Figure 4C 404. FIG. 4 is a schematic diagram illustrating the operation of an adjustable beam splitter 433 consistent with an embodiment of the present disclosure. In some embodiments, the beam splitter can be implemented using two or more Wien filters. By adjusting the deflection capability of each individual Wien filter, the effective bending point of the beam splitter can be moved up and down along the optical axis 404. The effective bending point is the point where the projection of the deflected secondary beam 451 coincides with the primary optical axis 404.

[0056] In some embodiments, the adjustable beam splitter 433 may include an upper Wien filter 433a and a lower Wien filter 433b, wherein both Wien filters 433a and 433b may receive separate excitation inputs. By independently adjusting the excitation inputs, the effective bending point of the adjustable beam splitter 433 may be moved up and down along the optical axis 404. Although for simplicity of illustration, Figure 4A , Figure 4B and Figure 4C Only one secondary electron beam 461 is shown, but it should be appreciated that the adjustable beam splitter 433 can operate with any number of secondary electron beams.

[0057] For example, Figure 4A As shown, if the desired bending point 437 is close to the center plane 436 of the adjustable beam splitter 433, the upper Wien filter 433a and the lower Wien filter 433b can be configured to deflect the secondary electron beam 461 by substantially the same amount so that the effective bending point of the adjustable beam splitter 433 matches the desired bending point 437.

[0058] like Figure 4B As shown, if the desired bending point 438 exists above the center plane 436, the adjustable beam splitter 433 can be configured so that the effective bending point can be moved upward toward the desired bending point 438. This can be achieved by configuring the upper Wien filter 433a to be deflected by a larger amount than the lower Wien filter 433b by relatively increasing the excitation input to the upper Wien filter 433a and relatively reducing the excitation input to the lower Wien filter 433b, so that the effective bending point of the adjustable beam splitter 433 matches the desired bending point 438.

[0059] On the other hand, Figure 4C As shown, if the desired bending point 439 exists below the center plane 436, the adjustable beam splitter 433 can be configured so that the effective bending point can be moved downward toward the desired bending point 439. This can be achieved by relatively reducing the excitation input to the upper Wien filter 433a and relatively increasing the excitation input to the lower Wien filter 433b to configure the upper Wien filter 433a to be deflected by a smaller amount than the lower Wien filter 433b, so that the effective bending point of the adjustable beam splitter 433 matches the desired bending point 439.

[0060] In some embodiments, the overall height of the adjustable beam splitter 433 (i.e., the sum of the height of the upper Wien filter 433a and the height of the lower Wien filter 433b) can be similar to that of a conventional beam splitter having a single Wien filter (such as Figure 3A As explained in the previous section, because the aberrations and error index of the secondary electron beam increase as the distance between the sample and the main zoom lens increases, it is desirable to maintain the sample (such as Figure 3A Sample 308) and a main zoom lens (such as Figure 3A The adjustable beam splitter 433 can be as powerful as a conventional beam splitter in deflecting electrons, while the adjustable beam splitter 433 additionally provides adjustability of the bending point. For example, while each Wien filter (e.g., upper Wien filter 433a and lower Wien filter 433b) is smaller and correspondingly capable of providing less deflection capability than a conventional one-piece Wien filter, the combined deflection capability of upper Wien filter 433a and lower Wien filter 433b can be substantially the same as the deflection capability of a conventional Wien filter. The adjustable beam splitter 433 can apply to the electron beam the same deflection capability as a conventional beam splitter (such as Figure 3A The beam splitter 333) has a similar force to that of the electron beam and deflects the electron beam by a comparable amount.

[0061] Now, refer to Figure 5A and Figure 5B , Figure 5A and Figure 5B It is consistent with the embodiments of the present disclosure. Figure 4A , Figure 4B and Figure 4C Schematic diagram of a multi-beam electron beam tool (e.g., 500A and 500B) with an adjustable beam splitter. The multi-beam electron beam tool 500A or 500B can be a multi-beam device (such as Figure 1 Part of a multi-beam device 100).

[0062] In some embodiments, the multi-beam electron beam tools 500A and 500B may include a primary projection system 530 and a secondary projection system 550. The primary projection system may include an adjustable beam splitter 533. The secondary projection system 550 may include one or more lenses, such as a primary zoom lens 552, a second zoom lens 553, and a projection lens 554, configured to focus the secondary electron beam 561 onto the electron detection device 540. The secondary projection system 550 may also include one or more deflectors 555, 556, and 557 to deflect the secondary electron beam 561.

[0063] Because the secondary projection system 550 is not properly aligned with the position of the adjustable beam splitter 533, Figure 5A The desired bending point 538 in is above the center plane 536 of the adjustable beam splitter 533. In such a case, as previously discussed with respect to Figure 4B As described, the adjustable beam splitter 533 can be configured such that: by configuring the upper Wien filter 533a to deflect more than the lower Wien filter 533b, the effective bending point can be moved upward (as illustrated by arrow 598) toward the desired bending point 538. This can be accomplished by relatively increasing the excitation input to the upper Wien filter 533a while relatively reducing the excitation input to the lower Wien filter 533b.

[0064] exist Figure 5B In contrast, due to the misalignment of the secondary projection system 550, the desired bending point 537 is below the center plane 536. In such a case, as previously discussed with respect to Figure 4C As described, the adjustable beam splitter 533 can be configured such that: by configuring the upper Wien filter 533a to deflect less than the lower Wien filter 533b, the effective bending point can be moved downward toward the desired bending point 537 (as illustrated by arrow 597). This can be accomplished by relatively reducing the excitation input to the upper Wien filter 533a and relatively increasing the excitation input to the lower Wien filter 533b.

[0065] In some embodiments, the upper Venn filter 533a and the lower Venn filter 533b may be controlled by a controller such as Figure 2 The controller 50) is independently controlled by the controller 50. For example, the controller can provide a first excitation control signal to the upper Wien filter 533a and a second excitation control signal to the lower Wien filter 533b. Based on the excitation control signal, each Wien filter can increase or decrease the deflection amount, so that the effective bending point of the adjustable beam splitter 533 can be moved up or down accordingly.

[0066] In some embodiments, the controller may receive one or more inputs related to adjustment of the effective bending point, wherein the controller may process the one or more inputs, detect the amount of misalignment, determine how much the bending point needs to be moved in which direction, and provide individual excitation control signals to the Wien filter. The one or more inputs may be related to the alignment characteristics of the secondary projection system 550 relative to the adjustable beam splitter 533. In some embodiments, the one or more inputs may be entered by an operator of the multi-beam electron beam tools 500A and 500B. In some embodiments, the one or more inputs may be generated by a secondary electron beam image viewer, which may be used to determine how well the electron optical elements (such as lenses, beam splitters, deflectors, and detectors) in the multi-beam device are aligned. An example of a secondary electron beam image viewer may be found in U.S. Application No. 62 / 748,251, which is incorporated by reference in its entirety.

[0067] In some embodiments, the adjustable beam splitter 533 can be manually controlled by an operator of the multi-beam electron beam tool. For example, via a control interface (e.g., a knob, switch, computer interface, etc.), the operator can gradually adjust the effective bending point up or down to find an optimal position. In some embodiments, the operator's control can be enhanced by a feedback mechanism. For example, while adjusting the position of the effective bending point to the optimal position, the operator can monitor the secondary beam image produced by the secondary electron beam image viewer.

[0068] In some embodiments, the adjustable beam splitter 533 can be controlled by a controller such as Figure 2 For example, information generated by the secondary electron beam image viewer can be provided to the controller, wherein the controller can process the information from the secondary electron beam image viewer, detect the amount of misalignment, determine how much and in which direction the bending point needs to be moved, and provide individual excitation control signals to the Wien filter.

[0069] Although to simplify the diagram, Figure 5A and Figure 5B Only one primary electron beam 511 and one secondary electron beam 561 are shown, but it should be appreciated that the multi-beam electron beam tools 500A and 500B may use any number of electron beams.

[0070] Now, refer to Figure 6 , Figure 6 6 is a schematic diagram of a multi-beam electron beam tool 600, which illustrates an exemplary configuration of a primary projection system 630 with a beam splitter 633. The multi-beam electron beam tool 600 may be a multi-beam device such as Figure 1The multi-beam device 100 of the present invention is a part of the multi-beam device 100. In some embodiments, the multi-beam electron beam tool 600 may include a primary projection system 630 and a secondary projection system 650. The secondary projection system 650 may include one or more lenses, such as a main zoom lens 652, a second zoom lens 653, and a projection lens 654, which are configured to focus the secondary electron beam 661 onto the electron detection device 640. The secondary projection system 650 may also include one or more deflectors 655, 656, and 657 to deflect the secondary electron beam 661. The primary projection system may include a beam splitter 633 and one or more deflectors (e.g., deflector No. 1 691 and a pre-objective lens deflector 692) that deflect the primary electron beam 611 to scan the surface of the sample 608.

[0071] Deflector No. 1 691 and pre-objective lens deflector 692 can generate an electrostatic field to deflect the primary electron beam 611 for scanning. Figure 3A As described, the beam splitter 633 may include a Wien filter including an electrostatic deflector (generating an electrostatic dipole field) and a magnetic lens (generating a magnetic dipole field orthogonal to the electrostatic dipole field). Therefore, the total force (including electrostatic force and magnetic force) exerted by the primary projection system 630 on the passing (primary or secondary) electrons can be expressed as the following equation (1):

[0072] F 总630 =F 扫描1号偏转器 +F 扫描前置物镜偏转器 +F 维恩过滤器静电 +F 维恩过滤器磁 (1)

[0073] As mentioned above Figure 3B As described above, because the aberrations and errors of the secondary electron beam 661 increase exponentially with increasing distance, it is desirable to reduce the distance between the sample 608 and the main zoom lens 652. However, one of the limiting factors in reducing the distance is the presence of the deflector No. 1 691, which is typically placed between the beam splitter 633 and the main zoom lens 652. In some embodiments, as Figure 7 As shown, an adjustable beam splitter (such as Figure 5A and Figure 5B Replacing beam splitter 633 with an adjustable beam splitter 533) may provide an opportunity to further reduce the distance between sample 608 and main zoom lens 652.

[0074] Now, refer to Figure 7 , Figure 77 is a schematic diagram of a multi-beam electron beam tool 700 consistent with an embodiment of the present disclosure, which illustrates a primary projection system 730 with an adjustable beam splitter 733. The multi-beam electron beam tool 700 may be a multi-beam device such as Figure 1 The multi-beam electron beam tool 700 may also include a primary projection system 730 and a Figure 6 The primary projection system 730 may include a secondary projection system 750 similar to the electron beam tool 600 of the present invention. However, in some embodiments, the primary projection system 730 may include an adjustable beam splitter 733 rather than a conventional one-piece beam splitter (such as Figure 6 beam splitter 633).

[0075] The use of an adjustable beam splitter 733 can provide advantages over conventional systems such as Figure 6 The adjustable beam splitter 733 provides several advantages over the electron beam tool 600 of the secondary projection system 750. First, as described in the previous section, by moving the effective bending point of the secondary electron beam 761 up or down along the primary optical axis 704, thereby enabling the secondary electron beam to travel substantially close to the center of the main zoom lens 752, the adjustable beam splitter 733 provides the ability to reduce aberrations caused by misalignment of the secondary projection system 750.

[0076] Second, in some embodiments, deflector No. 1 (such as Figure 6 The primary projection system 750 may further improve the optical performance of the secondary projection system 750 by placing the primary zoom lens 752 closer to the sample 708. In some embodiments, instead of the omitted deflector No. 1, the electrostatic deflector within the Wien filter (e.g., the upper Wien filter 733a or the lower Wien filter 733b) may also be used as the deflector No. 1 for scanning the primary electron beam. In such an embodiment, the scanning control input applied to the deflector No. 1 may be rewritten to the excitation input of the electrostatic deflector to the Wien filter.

[0077] Similar to equation (1) above, the total force exerted by the primary projection system on a passing (primary or secondary) electron can be expressed based on the following equation (2):

[0078] F 总730 =F 前置物镜偏转器 +F 维恩过滤器静电重写 +F 维恩过滤器磁 (2)

[0079] Because the electrostatic force generated by the electrostatic deflector within the Wien filter is the sum of the force of the original Wien filter function and the force of the rewrite scan function (as shown in equation (3) below), the total force (F) of the primary projection system 730 is 总730 ) and the total force (F 总630) are basically the same.

[0080] F 维恩过滤器静电重写 =F 维恩过滤器静电 +F 扫描1号偏转器 (3)

[0081] In some embodiments, more than one Wien filter (e.g., both the upper Wien filter 733a and the lower Wien filter 733b) can be rewritten to function as deflector No. 1 by assigning the scan control input to multiple Wien filters. Moreover, in order to further reduce the distance between the sample 708 and the main zoom lens 752, in some embodiments, the pre-objective lens deflector 792 can also be omitted. In such embodiments, similar to the rewriting of deflector No. 1, the scanning function of the omitted pre-objective lens deflector 792 can be rewritten to one or more of the Wien filters. For example, in some embodiments, the upper Wien filter 733a can be used as deflector No. 1 (such as Figure 6 1 deflector 691), and the lower Wien filter 733b can be used as a pre-objective lens deflector 792.

[0082] Now, refer to Figure 8 , Figure 8 is a flow chart illustrating an exemplary method of controlling an adjustable beam splitter consistent with an embodiment of the present disclosure.

[0083] In some embodiments, a multi-beam electron beam tool (such as Figure 5A The multi-beam electron beam tool 500A may include a primary projection system (such as Figure 5A A primary projection system 530) and a secondary projection system (such as Figure 5A The secondary projection system 550 may include one or more lenses, such as a primary zoom lens, a secondary zoom lens, and a projection lens (such as Figure 5A 552, 553 and 554), the one or more lenses are configured to direct the secondary electron beam (such as Figure 5A The secondary electron beam 561) is focused onto an electron detection device (such as Figure 5A The secondary projection system may also include one or more deflectors (such as Figure 5A The primary projection system may further include an adjustable beam splitter (such as a Figure 5A The adjustable beam splitter 533 may include a plurality of Wien filters, such as an upper Wien filter (such as Figure 5A 533a) and the lower Wien filter (such as Figure 5A 533b).

[0084] If the secondary projection system is not well aligned with the primary projection system, the optical components of the secondary projection system may introduce aberrations which may cause distortions in the shape, intensity and layout of the secondary beam image. Such distortions may lead to reduced secondary electron collection efficiency and increased levels of crosstalk, thereby degrading the quality of information generated by the electronic detection device. In such a situation, in order to reduce aberrations and errors, the adjustable beam splitter may be configured such that: the effective bending point of the beam splitter may be moved upward or downward towards a desired bending point so that the secondary electron beam may pass substantially close to the center of the main zoom lens of the secondary projection system, as previously described with respect to Figure 5A and Figure 5B As described.

[0085] In step 810, the multibeam electron beam tool identifies alignment characteristics of the secondary projection system relative to the primary projection system (specifically, relative to the beam splitter). In some embodiments, this information can be measured and provided by an operator of the multibeam electron beam tool. In some embodiments, the multibeam electron beam tool can include a secondary electron beam image viewer that can be used to determine the alignment characteristics.

[0086] In step 820, the multi-beam electron beam tool determines the location of the desired bend point based on the identified alignment characteristics of the secondary projection system.

[0087] In step 830, the multi-beam electron beam tool adjusts one or more control inputs of the adjustable beam splitter to move the effective bending point up or down toward the location of the desired bending point. In some embodiments, the Wien filters of the adjustable beam splitter can be independently controlled to move the effective bending point. For example, an upper Wien filter and a lower Wien filter (such as Figure 5A 533a and 533b) can be controlled by a controller (such as Figure 2 The controller 50 can be independently controlled by the controller 50. The controller can provide a first excitation control signal to the upper Wien filter and a second excitation control signal to the lower Wien filter. Based on the excitation control signal, each Wien filter can increase or decrease the deflection amount so that the effective bending point of the adjustable beam splitter can be moved up or down accordingly.

[0088] After performing the adjustment in step 830, in step 840, the multi-beam electron beam tool determines the difference between the location of the desired bending point and the location of the actual bending point. And then, in step 850, the multi-beam electron beam tool determines whether the adjusted effective bending point is substantially close to the location of the desired bending point. In some embodiments, the determination can be based on the characteristics of the detected secondary electrons. In some embodiments, the determination can be based on the characteristics of the sample image generated. If the answer is no, the multi-beam electron beam tool repeats steps 830 and 840 until the adjusted bending point matches the desired bending point. When the adjusted bending point becomes substantially close to the location of the desired bending point, the adjustment process is completed in step 860.

[0089] The embodiments can be further described using the following terms:

[0090] 1. An adjustable charged particle beam splitter, configured to change the path of a secondary particle beam, the adjustable charged particle beam splitter comprising:

[0091] a first Wien filter aligned with the primary optical axis, wherein the first Wien filter is independently controllable via a first excitation input; and

[0092] a second Wien filter aligned with the primary optical axis, wherein the second Wien filter is independently controllable via a second excitation input, and

[0093] The adjustable charged particle beam splitter is configured such that an effective bending point of the adjustable charged particle beam splitter is movable based on a first excitation input and a second excitation input.

[0094] 2. An adjustable charged particle beam splitter according to clause 1, wherein the adjustable charged particle beam splitter is configured such that the effective bending point can be moved along the primary optical axis.

[0095] 3. An adjustable charged particle beam splitter according to any one of clauses 1 and 2, wherein the adjustable charged particle beam splitter is configured so that when the first excitation input is higher than the second excitation input, the effective bending point can be positioned along the primary optical axis close to the first Wien filter and away from the second Wien filter.

[0096] 4. An adjustable charged particle beam splitter according to any one of clauses 1 and 2, wherein the adjustable charged particle beam splitter is configured to enable the effective bending point to be positioned along the primary optical axis close to the second Wien filter and away from the first Wien filter when the second excitation input is higher than the first excitation input.

[0097] 5. An adjustable charged particle beam splitter according to any one of clauses 1 to 4, wherein the adjustable charged particle beam splitter is configured to enable the effective bending point to move when the first excitation input and the second excitation input are adjusted.

[0098] 6. An adjustable charged particle beam splitter according to any one of clauses 1 to 5, wherein the adjustable charged particle beam splitter is configured to enable the effective bending point to move based on the alignment characteristics of the secondary projection system relative to the adjustable charged particle beam splitter to compensate for the alignment error of the secondary projection system.

[0099] 7. An adjustable charged particle beam splitter according to clause 6, wherein the alignment characteristics of the secondary projection system comprise alignment characteristics of a main zoom lens in the secondary projection system.

[0100] 8. An adjustable charged particle beam splitter according to any one of clauses 1 to 7, wherein the first Wien filter is further configured to deflect the primary particle beam to scan the sample.

[0101] 9. An adjustable charged particle beam separator according to claim 8, wherein the first Wien filter comprises a magnetic deflector and an electrostatic deflector, the electrostatic deflector generating an electrostatic field based on a third excitation input to deflect the primary particle beam to scan the sample.

[0102] 10. A primary projection system comprising:

[0103] an objective lens configured to focus the primary electron beam onto the sample, wherein a secondary electron beam is emitted from the sample in response to the primary electron beam; and

[0104] An adjustable beam splitter configured to change the path of the secondary electron beam, the adjustable beam splitter comprising:

[0105] a first Wien filter aligned with the primary optical axis, wherein the first Wien filter is independently controllable via a first excitation input; and

[0106] a second Wien filter aligned with the primary optical axis, wherein the second Wien filter is independently controllable via a second excitation input,

[0107] The adjustable beam splitter is configured such that an effective bending point of the adjustable beam splitter is movable based on a first excitation input and a second excitation input.

[0108] 11. The primary projection system of clause 10, wherein the adjustable beam splitter is configured such that the effective bending point can be moved along the primary optical axis.

[0109] 12. A primary projection system according to any of clauses 10 and 11, wherein the adjustable beam splitter is configured to enable the effective bending point to be positioned along the primary optical axis close to the first Wien filter and away from the second Wien filter when the first excitation input is higher than the second excitation input.

[0110] 13. A primary projection system according to any of clauses 10 and 11, wherein the adjustable beam splitter is configured to enable the effective bending point to be positioned along the primary optical axis close to the second Wien filter and away from the first Wien filter when the second excitation input is higher than the first excitation input.

[0111] 14. A primary projection system according to any of clauses 10 to 13, wherein the adjustable beam splitter is configured to enable the effective bending point to move when the first excitation input and the second excitation input are adjusted.

[0112] 15. The primary projection system of any of clauses 10 to 13, wherein the adjustable beam splitter is configured to enable the effective bending point to move based on an alignment characteristic of the secondary projection system relative to the adjustable beam splitter to compensate for alignment errors of the secondary projection system.

[0113] 16. The primary projection system of clause 15, wherein the alignment characteristics of the secondary projection system comprise alignment characteristics of a main zoom lens in the secondary projection system.

[0114] 17. A primary projection system according to any of clauses 10 to 16, wherein the first Wien filter is further configured to deflect the primary particle beam to scan the sample.

[0115] 18. A primary projection system according to clause 17, wherein the first Wien filter comprises a magnetic deflector and an electrostatic lens, the electrostatic deflector generating an electrostatic field based on a third excitation input to deflect the primary particle beam to scan the sample.

[0116] 19. A multi-beam device for inspecting a sample, comprising:

[0117] A primary projection system according to any of clauses 10 to 18;

[0118] a secondary projection system configured to focus the secondary electron beam onto an electron detection device; and

[0119] A controller includes circuit means for controlling the primary projection system.

[0120] 20. A multi-beam device according to claim 19, wherein the controller includes a circuit device for adjusting the first excitation input and the second excitation input based on the alignment characteristics of the secondary projection system relative to the adjustable beam splitter of the primary projection system to move the effective bending point to compensate for alignment errors of the secondary projection system.

[0121] 21. A multi-beam apparatus according to clause 20, wherein the controller comprises circuit means for adjusting the third excitation input to deflect the primary electron beam to scan the sample.

[0122] 22. The multi-beam apparatus of any of clauses 19 to 21, further comprising an image viewer configured to provide information to the controller for adjusting the first excitation input and the second excitation input.

[0123] 23. A method for inspecting a wafer using a multi-beam system having a secondary projection system to project a plurality of secondary electron beams onto an inspection surface, the method comprising:

[0124] determining a location of a desired bending point of the adjustable beam splitter based on an alignment characteristic of the secondary projection system; and

[0125] One or more control signals are sent to the adjustable beam splitter to cause the effective bending point of the adjustable beam splitter to move along the primary optical axis toward the location of a desired bending point.

[0126] 24. The method according to clause 23, further comprising:

[0127] After performing the effective inflection point adjustment, determining a difference between the position of the desired inflection point and the position of the effective inflection point; and

[0128] After determining the difference between the position of the desired inflection point and the position of the effective inflection point, the effective inflection point adjustment is repeated until the position of the effective inflection point becomes substantially close to the position of the desired inflection point.

[0129] 25. A method according to any of clauses 23 and 24, wherein the adjustable beam splitter comprises a first Wien filter and a second Wien filter, and wherein adjusting the one or more control signals comprises independently adjusting a first excitation input to the first Wien filter and a second excitation input to the second Wien filter.

[0130] 26. The method of clause 25, wherein adjusting the one or more control signals further comprises configuring the first excitation input to be higher than the second excitation input to enable moving the effective bending point toward the first Wien filter.

[0131] 27. The method of clause 25, wherein adjusting the one or more control signals further comprises configuring the second excitation input to be higher than the first excitation input to enable moving the effective bending point toward the second Wien filter.

[0132] 28. A method according to any of clauses 23 to 27, wherein alignment characteristics of the secondary projection system are identified based on one or more images of the plurality of secondary electron beams produced by a secondary electron beam image viewer.

[0133] A non-transitory computer readable medium storing instructions for a controller (eg, Figure 1 The processor of the controller 50) makes adjustments to the beam splitter (e.g., controls Figure 8 For example, common forms of non-transitory media include floppy disks, flexible disks, hard disks, solid-state drives, magnetic tape or any other magnetic data storage medium, compact disk read-only memory (CD-ROM), any other optical data storage medium, any physical medium with a pattern of holes, random access memory (RAM), programmable read-only memory (PROM) and erasable programmable read-only memory (EPROM), FLASH-EPROM or any other flash memory, non-volatile random access memory (NVRAM), cache, registers, any other memory chip or tape cartridge, and networked versions thereof.

[0134] It will be appreciated that the embodiments of the present disclosure are not limited to the exact constructions that have been described above and illustrated in the accompanying drawings, and that various modifications and changes may be made without departing from the scope thereof. The present disclosure has been described in conjunction with various embodiments, and other embodiments of the present invention will be apparent to those skilled in the art in view of the specification and practice of the invention disclosed herein. It is intended that the description and examples are to be considered exemplary only, with the true scope and spirit of the invention being indicated by the following claims.

[0135] The above description is intended to be illustrative, and not limiting. It will therefore be apparent to those skilled in the art that modifications may be made as described without departing from the scope of the claims set forth hereinafter.

Claims

1. An adjustable charged particle beam splitter, configured to change the path of a secondary particle beam at an effective bending point, the adjustable charged particle beam splitter include: a first Wien filter aligned with the primary optical axis, wherein the first Wien filter is independently controllable via a first excitation input; as well as a second Wien filter aligned with the primary optical axis, wherein the second Wien filter is independently controllable via a second excitation input, and The adjustable charged particle beam splitter is configured to enable the effective bending point to move by adjusting the first excitation input and the second excitation input based on an alignment characteristic of a secondary projection system relative to the adjustable charged particle beam splitter. 2 . The adjustable charged particle beam splitter according to claim 1 , wherein the adjustable charged particle beam splitter is configured such that the effective bending point is movable along the primary optical axis.

3. The adjustable charged particle beam splitter according to claim 1, wherein the adjustable charged particle beam splitter is configured such that when the first excitation input is higher than the second excitation input, the effective bending point can be positioned along the primary optical axis close to the first Wien filter and away from the second Wien filter.

4. The adjustable charged particle beam splitter according to claim 1, wherein the adjustable charged particle beam splitter is configured such that when the second excitation input is higher than the first excitation input, the effective bending point can be positioned along the primary optical axis close to the second Wien filter and away from the first Wien filter. 5 . The adjustable charged particle beam splitter according to claim 1 , wherein the adjustable charged particle beam splitter is configured to enable the effective bending point to move when the first excitation input and the second excitation input are adjusted.

6. The adjustable charged particle beam splitter according to claim 1, wherein the adjustable charged particle beam splitter is configured to compensate for alignment errors of the secondary projection system.

7. An adjustable charged particle beam splitter according to claim 6, wherein the alignment characteristics of the secondary projection system comprise alignment characteristics of a main zoom lens in the secondary projection system.

8. The adjustable charged particle beam splitter of claim 1, wherein the first Wien filter is further configured to deflect the primary particle beam to scan a sample.

9. An adjustable charged particle beam separator according to claim 8, wherein the first Wien filter comprises a magnetic deflector and an electrostatic deflector, the electrostatic deflector generating an electrostatic field based on a third excitation input to deflect the primary particle beam to scan the sample.

10. A method for inspecting a wafer using a multi-beam system having a secondary projection system for projecting a plurality of secondary electron beams onto an inspection surface, the method include: determining a position of a desired bending point of an adjustable beam splitter based on an alignment characteristic of the secondary projection system; as well as adjusting one or more control signals to the adjustable beam splitter to cause an effective bending point of the adjustable beam splitter to move along the primary optical axis toward the position of the desired bending point, the adjustable beam splitter being configured to change the path of the secondary electron beam at the effective bending point; wherein the adjustable beam splitter comprises a first Wien filter and a second Wien filter, and the one or more control signals comprise: a first excitation input to the first Wien filter and a second excitation input to the second Wien filter to independently control each of the first Wien filter and the second Wien filter.

11. The method according to claim 10, further comprising: include: After performing an effective bending point adjustment, determining a difference between the position of the desired bending point and the position of the effective bending point; as well as After determining the difference between the position of the desired inflection point and the position of the effective inflection point, the effective inflection point adjustment is repeated until the position of the effective inflection point becomes substantially close to the position of the desired inflection point.

12. The method of claim 10, wherein adjusting one or more control signals further comprises: include: The first excitation input is configured to be higher than the second excitation input to enable the effective bending point to be moved toward the first Wien filter.

13. The method of claim 10, wherein adjusting one or more control signals further comprises: include: The second excitation input is configured to be higher than the first excitation input to enable the effective bending point to be moved toward the second Venn filter.

14. The method of claim 10, wherein the alignment characteristic of the secondary projection system is identified based on one or more images of the plurality of secondary electron beams produced by a secondary electron beam image viewer.

Images