Device for multiple charged particle beams

Abstract

Systems and methods for observing samples in a multi-beam device are disclosed. A charged particle optical system may include: a deflector configured to form a virtual image of a charged particle source; and a transfer lens configured to form a real image of the charged particle source on an image plane. The image plane may be formed at least near a beam splitter configured to separate primary charged particles generated by the source and secondary charged particles generated by the interaction of the primary charged particles with the sample. The image plane may be formed at a deflection plane of the beam splitter. The multi-beam device may include a charged particle dispersion compensator to compensate for the dispersion of the beam splitter. Between the transfer lens and the charged particle dispersion compensator, the image plane may be formed closer to the transfer lens than to the beam splitter.

Description

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims priority to U.S. Application No. 62 / 716,832 filed on August 9, 2018 and U.S. Application No. 62 / 827,765 filed on April 1, 2019, the entire contents of which are incorporated herein by reference. Technical Field

[0003] Embodiments provided herein disclose a multi-beam apparatus, such as an electron microscope apparatus utilizing one or more electron beams, and more particularly disclose a multi-beam electron microscope having reduced beam divergence, such as by reducing Coulomb interaction effects or by using transfer mirrors. Background Art

[0004] During the manufacture of integrated circuits (ICs), unfinished or completed circuit assemblies are inspected to ensure that they are manufactured according to design and are free of defects. Inspection systems utilizing optical microscopes or charged particle (e.g., electron) beam microscopes, such as scanning electron microscopes (SEMs), may be employed. As the physical dimensions of IC assemblies continue to shrink, the accuracy and yield of defect detection become increasingly important. Multiple charged particle beams may be used to increase inspection throughput; however, doing so compromises the imaging resolution of the device, rendering the inspection tool unsatisfactory for its intended purpose.

[0005] Charged particle (e.g., electron) beam microscopes with resolutions down to less than a nanometer, such as scanning electron microscopes (SEMs) or transmission electron microscopes (TEMs), are viable tools for inspecting IC components with feature sizes less than 100 nanometers. In an SEM tool, a primary electron beam with 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 primary electrons, secondary electrons will be generated from the surface. By scanning the probe spot over the sample surface and collecting the secondary electrons, a pattern inspection tool can acquire an image of the sample surface.

[0006] Optical components within a single-beam or multi-beam inspection tool (such as beam splitters, lenses, beam deflectors, etc.) may introduce dispersion in the beam used for inspection. For example, when a detector for collecting secondary electrons is placed off-axis, a primary electron beam can be generated along the optical axis. In an inspection system that includes multiple primary beams or multiple secondary beams, a beam splitter can be used to separate the secondary electron beam from the primary beam and direct the secondary beam to an off-axis detector. Because the beam splitter can include a magnetic deflector for deflecting electrons electromagnetically, the beam splitter can generate dispersion in the beam passing therethrough. Among other effects, dispersion may reduce the resolution of an image used to reconstruct the surface of the inspected sample. Summary of the invention

[0007] Embodiments of the present disclosure may provide a charged particle optical system, which may include a deflector configured to form a virtual image of a charged particle source; and a transfer lens configured to form a real image of the charged particle source on an image plane. The image plane may be formed at least near a beam splitter configured to separate primary charged particles generated by the charged particle source and secondary charged particles generated by the interaction of the primary charged particles with a sample. The image plane may be formed at a deflection plane of the beam splitter. The particle optical system may be used to reduce the dispersion effects of the beam splitter.

[0008] In some embodiments, a charged particle optical system may be provided, the charged particle optical system comprising a first deflector array configured to deflect multiple beam waves of a primary charged particle beam generated by a source, a first lens configured to focus the multiple beam waves to form multiple images of the source on an image plane, and an objective lens configured to project the multiple images onto a sample and form multiple detection points on the sample. The first deflector array may include an array of image forming elements. The first lens may include a transfer lens.

[0009] In some embodiments, a first aperture array may also be provided, the first aperture array being above the first deflector array and being configured to limit the current of the plurality of detection points. The first aperture array may comprise a beam limiting aperture array.

[0010] In some embodiments, a second lens may be provided between the charged particle source and the first aperture array and configured to focus the primary charged particle beam. The second lens may include a condenser lens. The second lens may include a movable lens or an anti-rotation lens.

[0011] In some embodiments, a compensator array configured to compensate for aberrations of a plurality of detection points may also be provided. The compensator array may include an aberration compensator array, an astigmatism compensator array, or a field curvature array.

[0012] In some embodiments, a main aperture may also be provided, which is above the second lens, close to the source, and is configured to cut off peripheral portions of the primary charged particle beam that are not used in the plurality of beam waves.

[0013] In some embodiments, a second aperture array may also be provided. The second aperture array may be between the main aperture and the first aperture array and configured to cut off portions of the primary charged particle beam that are not used in the plurality of beams. The second aperture array may include a pre-beamforming mechanism that may include a Coulomb aperture array.

[0014] In some embodiments, a second deflector array configured to deflect the plurality of beams to be perpendicularly incident on the first aperture array may also be provided. The second deflector array may include a beam bending front deflector array.

[0015] In some embodiments, a charged particle optical system may be provided, the charged particle optical system comprising: a first deflector configured to deflect a beam wave of a charged particle beam generated by a charged particle source; a first lens configured to focus the beam wave to form an image of the charged particle source on an image plane within a region of a beam splitter, the beam splitter configured to separate the beam wave and secondary charged particles generated from a sample in response to the charged particles of the beam wave interacting with the sample. The first deflector may be part of an array of image forming elements. The first lens may be a transfer lens.

[0016] In some embodiments, a method of forming a plurality of detection points on a sample may be provided, the method comprising: deflecting a plurality of beams of a light beam generated by a charged particle source; focusing the plurality of beams by a lens to form a plurality of images of the source on an image plane; and projecting the plurality of images onto the sample to form a plurality of detection points on the sample. The lens may be a transfer lens.

[0017] Some embodiments of the present disclosure may provide a multi-beam device, which may include a first lens, the first lens being configured to focus multiple beams to form multiple images of a charged particle source on an image plane formed closer to the first lens than a charged particle separator, the charged particle separator being configured to separate primary charged particles of the multiple beams and secondary charged particles emitted from a sample. The device may also include an objective lens configured to project the multiple images onto the sample and form multiple detection points thereon.

[0018] In some embodiments, the multi-beam device may include a first deflector array configured to deflect at least one of the multiple beam waves of the primary charged particle beam radially outward from the main optical axis and incident on a first lens, wherein an image plane is formed perpendicular to the main optical axis of the primary charged particle beam and between the first lens and the charged particle separator. The device may also include a second lens, which is disposed between the charged particle source and the first lens and is configured to focus the primary charged particle beam. The device may also include: a charged particle dispersion compensator, which is configured to compensate for the dispersion caused by the charged particle separator; and a first aperture array, which is disposed between the first deflector array and the charged particle source and is configured to limit the detection current of the multiple beam waves. In some embodiments, the second lens may be a movable lens disposed on a principal plane perpendicular to the main optical axis of the primary charged particle beam. The second lens may include a focusing lens. The multi-beam device may also include: an aperture plate, which is disposed between the charged particle source and the second lens and is configured to block the peripheral portion of the primary charged particle beam; and a second aperture array, which is disposed between the aperture plate and the second lens and is configured to generate multiple beam waves from the primary charged particle beam. In some embodiments, the first lens may include a transfer lens. The transfer lens may be an adjustable lens, which is configured to adjust the magnification of the multiple beam waves by adjusting the position of the formed image plane and form an image plane between the first lens and the charged particle separator.

[0019] Some embodiments of the present disclosure may provide a multi-beam device, which may include a first deflector array configured to deflect multiple beam waves of a primary charged particle beam, wherein the first deflector array is configured to collimate at least one of the multiple beam waves so that it is substantially parallel to the main optical axis of the primary charged particle beam. The multi-beam device may also include: a first lens, which is configured to focus the multiple beam waves to form multiple images of a charged particle source on an image plane formed closer to the first lens than a charged particle separator, the charged particle separator being configured to separate the primary charged particles of the multiple beam waves and the secondary charged particles emitted from the sample; and a second lens, which is configured to project the multiple images onto the sample and form multiple detection points thereon.

[0020] Some embodiments of the present disclosure may provide a method for observing a sample using a multi-beam device. The method may include: using a first lens, focusing a plurality of beams to form a plurality of images of a charged particle source on an image plane formed closer to the first lens than a charged particle separator, the charged particle separator being configured to separate primary charged particles of the plurality of beams and secondary charged particles emitted from the sample; and using an objective lens, projecting the plurality of images onto the sample and forming a plurality of detection points thereon.

[0021] Exemplary advantages and effects of the present invention will become apparent from the following description taken in conjunction with the accompanying drawings, in which certain embodiments of the present disclosure are set forth by way of illustration and example. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 is a schematic diagram illustrating an exemplary electron beam inspection (EBI) system according to an embodiment of the present disclosure.

[0023] Figure 2A It shows that it can be Figure 1 An exemplary electron beam tool that is a portion of an exemplary electron beam inspection system.

[0024] Figure 2B An exemplary configuration of a beam splitter is shown.

[0025] Figure 2C An exemplary configuration of a beam splitter is shown.

[0026] Figure 3 is a diagram illustrating an exemplary electron beam inspection tool according to an embodiment of the present disclosure.

[0027] Figure 4A , 4B 4C illustrate an exemplary electron beam inspection tool according to an embodiment of the present disclosure.

[0028] Figure 4D , 4E 4F and 4G illustrate exemplary electron beam inspection tools according to embodiments of the present disclosure.

[0029] Figure 5A , 5B 5C illustrate an exemplary electron beam inspection tool according to an embodiment of the present disclosure.

[0030] Fig. 6A and 6B Portions of an exemplary electron beam inspection tool are shown according to an embodiment of the present disclosure.

[0031] Figure 7 is a flow chart representing an exemplary method for forming a light beam according to an embodiment of the present disclosure.

[0032] Figure 8 is a flow chart representing an exemplary method of observing a sample using a multi-beam inspection tool according to an embodiment of the present disclosure. DETAILED DESCRIPTION

[0033] Reference will now be made in detail to exemplary embodiments, examples of which are shown in the accompanying drawings. The following description refers to the accompanying drawings, wherein, unless otherwise indicated, the same numbers in different drawings represent the same or similar elements. The implementations set forth in the following description of the exemplary embodiments do not represent all implementations consistent with the present invention. On the contrary, they are merely examples of systems, devices and methods consistent with aspects related to the present invention as described in the appended claims. For example, although some embodiments are described in the context of utilizing electron beams, the present disclosure is not limited thereto. Other types of charged particle beams may be applied similarly. In addition, other imaging systems such as optical imaging, light detection, x-ray detection, etc. may be used. For clarity, the relative sizes of the components in the figures may be exaggerated.

[0034] 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 greatly reduced so that more of them can be mounted on a substrate. For example, the IC chip in a smartphone can be as small as a thumbnail but can include over 2 billion transistors, each less than 1 / 1000 the size of a human hair.

[0035] Manufacturing 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 useless. Therefore, one goal of the manufacturing process is to avoid such defects in order to maximize the number of functional ICs manufactured in the process, i.e., to improve the overall yield of the process.

[0036] An integral part of improving yield is monitoring the chip manufacturing process to ensure that it is producing sufficient numbers 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 performed using a SEM. These very small structures can be imaged using an SEM, in effect taking a "photograph" of the structure. The image can be used to determine if the structure was formed correctly and in the correct location. If the structure is defective, the process can be adjusted to make the defect less likely to occur again.

[0037] In some inspection tools, a primary beam generated from a charged particle source can travel along an optical axis, hit a sample, and a secondary beam can be generated from the sample along the optical axis. A beam splitter can be provided on the optical axis to transfer the secondary beam to a detector. Thus, the primary beam can first pass through the beam splitter before reaching the sample. One of the several problems that may be encountered is that the primary beam may be dispersed when passing through the beam splitter, causing the resulting beam spot on the sample to deviate from the desired shape, such as by increasing the size. This may reduce the imaging resolution. In some embodiments of the present disclosure, the effects of such dispersion can be reduced or eliminated. For example, a transfer lens can be provided that is configured to form an image of the source on an image plane near the beam splitter. According to some embodiments, the beam can pass through the beam splitter without reducing the quality of the final image of the source on the sample, such as by increasing the size of the detection spot formed on the sample. Thus, the imaging resolution can be improved.

[0038] In addition to reducing beam dispersion, the transfer lens can also be used to further improve imaging resolution, for example, by reducing the magnification of the primary charged particle beam to generate a smaller detection spot on the sample. Although forming an intermediate image plane near the beam splitter can reduce beam dispersion, the magnification may not be small enough to achieve high resolution. Conversely, forming the intermediate image plane closer to the transfer lens than the beam splitter can reduce the magnification of the primary charged particle beam, but may result in increased beam dispersion. In order to improve imaging resolution by forming the image plane closer to the transfer lens than the charged particle separator, beam dispersion may deteriorate, resulting in a loss of imaging resolution. Therefore, a desired solution may be to reduce the magnification of the primary charged particle beam while reducing beam dispersion to achieve an overall improvement in imaging resolution.

[0039] In some embodiments of the present disclosure, a multi-beam device may include a lens configured to focus multiple beamlets to form multiple images of a charged particle source on an intermediate image plane. The intermediate image plane may be formed away from the charged particle separator, thereby reducing the magnification of the primary charged particle beam to generate a smaller detection point. The device may also include a charged particle dispersion compensator to compensate for the dispersion of the beamlet caused by forming the image plane away from the charged particle separator. Some embodiments of the present disclosure may enable the magnification of the primary beam to be reduced while reducing the beam dispersion to enhance the overall imaging resolution.

[0040] Without limiting the scope of the present disclosure, the description and drawings of the embodiments may be illustratively referred to as using an electron beam. However, these embodiments are not intended to limit the present invention to specific charged particles. For example, the systems and methods for beam forming may be applied to photons, x-rays, and ions, etc. In addition, the term "beam" may refer to a primary electron beam, a primary electron beam wave, a secondary electron beam, or a secondary electron beam wave, etc.

[0041] As used herein, unless expressly stated otherwise, the term "or" encompasses all possible combinations unless not feasible. For example, if it is stated that a component may include A or B, then unless expressly stated otherwise or not feasible, the component may include A or B, or A and B. As a second example, if it is stated that a component may include A, B, or C, then unless expressly stated otherwise or not feasible, 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.

[0042] Reference now Figure 1 , Figure 1 An exemplary electron beam inspection (EBI) system 10 is shown in accordance with an embodiment of the present disclosure. Figure 1 As shown, the EBI system 10 includes a main chamber 11, a load / lock chamber 20, an electron beam tool 100, and an equipment front end module (EFEM) 30. The electron beam tool 100 is located in the main chamber 11.

[0043] The EFEM 30 includes a first loading port 30a and a second loading port 30b. The EFEM 30 may include other loading ports. The first loading port 30a and the second loading port 30b may, for example, accommodate a wafer front opening box (FOUP) containing wafers (e.g., semiconductor wafers or wafers made of other materials) or samples (wafers and samples may be collectively referred to as "wafers" hereinafter) to be inspected. One or more robotic arms (not shown) in the EFEM 30 may transport the wafers to the load / lock chamber 20.

[0044] The load / lock chamber 20 is 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 robotic arms (not shown) can transfer the wafer from the load / lock chamber 20 to the main chamber 11. The main chamber 11 is connected to a main chamber vacuum pump system (not shown) that removes gas molecules in the main chamber 11 to reach a second pressure below the first pressure. After reaching the second pressure, the wafer is inspected by the electron beam tool 100. The electron beam tool 100 can be a single beam system or a multi-beam system. The controller 19 is electrically connected to the electron beam tool 100. Although the controller 19 is Figure 11 is shown as being external to the structure including the main chamber 11, the load / lock chamber 20 and the EFEM 30, but it is understood that the controller 19 may be part of the structure.

[0045] Although the present disclosure provides an example of a main chamber 11 housing an electron beam inspection system, it should be noted that the various aspects of the present disclosure in its broadest sense are not limited to a chamber housing an electron beam inspection system. Instead, it should be understood that the principles discussed herein can also be applied to other tools operating at a second pressure.

[0046] Figure 2A It shows that it can be Figure 1 An exemplary electron beam tool 100A that is part of an EBI system. The electron beam tool 100A (also referred to herein as "device 100A") includes an electron source 101, a gun hole plate 171, a condenser lens 110, a source conversion unit 120, a primary projection optical system 130, a secondary imaging system 150, and an electron detection device 140M. The primary projection optical system 130 may include an objective lens 131. A sample 1 having a sample surface 7 may be set on a movable stage (not shown). The electron detection device 140M may include a plurality of detection elements 140_1, 140_2, and 140_3. The beam splitter 160 and the deflection scanning unit 132 may be placed inside the primary projection optical system 130.

[0047] The electron source 101, the aperture plate 171, the condenser lens 110, the source conversion unit 120, the beam splitter 160, the deflection scanning unit 132 and the primary projection optical system 130 can be aligned with the main optical axis 100_1 of the device 100A. The secondary imaging system 150 and the electron detection device 140M can be aligned with the auxiliary optical axis 150_1 of the device 100A.

[0048] The electron source 101 may include a cathode (not shown) and an extractor or anode (not shown), wherein during operation, the electron source 101 is configured to emit primary electrons from the cathode, and the primary electrons are extracted or accelerated by the extractor or anode to form a primary electron beam 102, which forms a primary beam intersection (virtual or real) 101s. The primary electron beam 102 can be visualized as being emitted from the primary beam intersection 101s.

[0049] The source conversion unit 120 may include an image forming element array ( Figure 2A not shown) and the beam limiting aperture array ( Figure 2A1 , 102_2, 102_3 of the primary electron beam 102 and form a plurality of parallel images (virtual or real) of the primary beam intersection 101s, one for each of the primary beam waves 102_1, 102_2, 102_3. The beam limiting aperture array may be configured to limit the diameter of the individual primary beam waves 102_1, 102_2 and 102_3. Figure 2A As an example, three primary beams 102_1, 102_2, and 102_3 are shown, and it should be understood that the source conversion unit 120 can be configured to form any number of primary beams. For example, the source conversion unit 120 can be configured to form a 3×3 array of primary beams. The source conversion unit 120 may also include an aberration compensator array configured to compensate for the aberrations of the detection points 102_1S, 102_2S, and 102_3S. In some embodiments, the aberration compensator array may include a field curvature compensator array having microlenses, which are configured to compensate for the field curvature aberrations of the detection points 102_1S, 102_2S, and 102_3S, respectively. In some embodiments, the aberration compensator array may include an astigmatism compensator array having micro-diffusers, which are configured to compensate for the astigmatism aberrations of the detection points 102_1S, 102_2S, and 102_3S, respectively. In some embodiments, the image forming element array, the field curvature compensator array, and the astigmatism compensator array may include multiple layers of micro-deflectors, micro-lenses, and micro-astigmatism correctors, respectively. Examples of multiple layer arrays are further described in U.S. Patent Application No. 62 / 567,134, which is incorporated herein in its entirety.

[0050] The condenser lens 110 is configured to focus the primary electron beam 102. The condenser lens 110 can also be configured to adjust the current of the primary beam waves 102_1, 102_2 and 102_3 downstream of the source conversion unit 120 by changing the focusing ability of the condenser lens 110. Therefore, the beam waves 102_1, 102_2 and 102_3 can have a focusing state that can be changed by the condenser lens 110. Alternatively, the current can be changed by changing the radial size of the beam limiting apertures corresponding to the individual primary beam waves within the beam limiting aperture array. Therefore, the current of the beam wave can be different at different positions along the trajectory of the beam wave. The beam wave current can be adjusted so that the current of the beam wave on the sample surface (e.g., the detection point current) is set to a desired amount.

[0051] The focusing lens 110 can be a movable focusing lens, which can be configured so that the position of its first principal plane is movable. The movable focusing lens can be configured to be magnetic, or electrostatic or electromagnetic (e.g., composite). The movable focusing lens is further described in U.S. Patent No. 9,922,799 and U.S. Patent Application Publication No. 2017 / 0025243, the entire contents of which are incorporated herein by reference. In some embodiments, the focusing lens can be an anti-rotation lens, which can keep the rotation angle of the off-axis beam wave unchanged while changing the current of the beam wave. In some embodiments, the focusing lens 110 can be a movable anti-rotation focusing lens, which includes an anti-rotation lens having a movable first principal plane. The anti-rotation or movable anti-rotation focusing lens is further described in International Application No. PCT / EP2017 / 084429, the entire text of which is incorporated herein by reference.

[0052] The objective lens 131 may be configured to focus the beams 102_1, 102_2, and 102_3 onto the sample 1 for inspection, and in the current embodiment, three detection points 102_1S, 102_2S, and 102_3S may be formed on the surface 7. In operation, the aperture plate 171 is configured to block peripheral electrons of the primary electron beam 102 to reduce the Coulomb effect. The Coulomb effect may increase the size of each detection point 102_1S, 102_2S, and 102_3S of the primary beams 102_1, 102_2, 102_3, and thus reduce the inspection resolution.

[0053] The beam splitter 160 can be, for example, a Wien filter that includes an electrostatic deflector that generates an electrostatic dipole field E1 and a magnetic dipole field B1. The beam splitter 160 can use the Lorentz force to affect electrons passing therethrough. The beam splitter 160 can be activated to generate the electrostatic dipole field E1 and the magnetic dipole field B1. In operation, the beam splitter 160 can be configured to exert an electrostatic force on individual electrons of the primary beam waves 102_1, 102_2, and 102_3 through the electrostatic dipole field E1. The magnitude of the electrostatic force can be equal to the magnitude of the magnetic force exerted by the magnetic dipole field B1 of the beam splitter 160 on the individual electrons, but in the opposite direction. The primary beam waves 102_1, 102_2, and 102_3 can pass through the beam splitter 160 substantially straight.

[0054] In operation, the deflection scanning unit 132 is configured to deflect the primary beam waves 102_1, 102_2, and 102_3 to scan the detection points 102_1S, 102_2S, and 102_3S across the individual scanning areas in a portion of the surface 7. In response to the irradiation of the sample 1 by the primary beam waves 102_1, 102_2, and 102_3 at the detection points 102_1S, 102_2S, and 102_3S, secondary electrons are emitted from the sample 1 and form three secondary electron beams 102_1se, 102_2se, and 102_3se, which are emitted from the sample 1 in operation. Each of the secondary electron beams 102_1se, 102_2se, and 102_3se generally includes electrons with different energies, including secondary electrons (electron energy ≤ 50 eV) and backscattered electrons (having electron energies between 50 eV and the landing energies of the primary beams 102_1, 102_2, and 102_3). The beam splitter 160 is configured to deflect the secondary electron beams 102_1se, 102_2se, and 102_3se toward the secondary imaging system 150. The secondary imaging system 150 then focuses the secondary electron beams 102_1se, 102_2se, and 102_3se onto the detection elements 140_1, 140_2, and 140_3 of the electron detection device 140M. The detection elements 140_1 , 140_2 and 140_3 are arranged to detect the corresponding secondary electron beams 102_1se, 102_2se and 102_3se and to generate corresponding signals which may be sent to a signal processing unit (not shown) to, for example, construct an image of a corresponding scanned area of ​​the sample 1 .

[0055] As described above, the beam splitter 160 may be a deflection device including a magnetic deflector, such as a Wien filter. The deflection device may deflect electrons passing therethrough. The deflection direction and deflection angle of the electrons depend on the direction of movement and energy of the electrons (e.g., may be represented by velocity). Therefore, primary electrons moving in a direction different from secondary electrons or backscattered electrons may be distinguished from secondary electrons or backscattered electrons. Therefore, when the secondary electron beams 102_1se, 102_2se, and 102_3se are deflected away from the optical axis 100_1, the primary beam waves 102_1, 102_2, and 102_3 may be allowed to pass substantially straight through the beam splitter 160. However, the primary beam waves 102_1, 102_2, and 102_3 themselves may include electrons at different energy levels. Therefore, the electrons of the primary beam waves 102_1, 102_2, and 102_3 passing through the beam splitter 160 may not necessarily pass completely straight, but may be deflected at a deflection angle. Therefore, the deflection angle of the electrons in each beam may be different, thereby causing dispersion to be generated in each of the primary beams 102_1, 102_2 and 102_3. Figure 2AThe dispersion of each primary beamlet is shown with nominal energy V0 and energy spread ΔV. Each primary beamlet may undergo dispersion such that the beamlet is dispersed into a beamlet portion corresponding to energy V0, a ​​beamlet portion corresponding to energy V0+ΔV / 2, and a beamlet portion corresponding to energy V0-ΔV / 2.

[0056] The dispersion may affect the primary beams 102_1, 102_2, and 102_3 to form detection spots on the sample 1 that deviate from a desired shape, such as by causing the detection spots 102_1S, 102_2S, and 102_3S to be oriented in a direction related to the dispersion direction (e.g., Figure 2A The dispersion may result in, for example, an elliptical detection spot. The dispersion caused by the beam splitter 160 may reduce the imaging resolution.

[0057] Furthermore, the dispersion may affect the secondary electron beams 102_1se, 102_2se, and 102_3se to form larger spots on the electron detection device 140M. The dispersion may reduce the secondary electron collection efficiency and cause crosstalk.

[0058] Reference now Figure 2B , Figure 2B An exemplary configuration of a portion of a projection system according to an embodiment of the present disclosure is shown. Figure 2B The projection system may form part of the primary projection optical system 130 . Figure 2B Only the central beam 102_1 aligned with the main optical axis 100_1 is shown. The beam 102_1 can be focused onto the intermediate image plane 2. That is, the beam 102_1 having a focal point can be formed in the image plane 2. The image plane 2 is located above the deflection plane 160_2 of the beam splitter 160. The electrons of the beam 102_1 with different energies propagating along the main optical axis 100_1 can be dispersed after leaving the beam splitter 160. Therefore, the electrons can have a virtual radial displacement 3 on the image plane 2. That is, the electrons can be visualized as being emitted from a virtual position that is radially offset by 3 from the original position on the image plane 2. The radial direction is orthogonal to the main optical axis 100_1. Due to the radial offset 3, the focal point on the image plane 2 is visualized as being enlarged. Therefore, the beam spot 102S formed on the sample 1 can be widened. In addition, although Figure 2B Only the central beam wave is shown, but this effect may affect the off-axis beam waves even more strongly. The off-axis beam waves may pass through the beam splitter at an angle and thus may propagate a greater distance via the beam splitter and be more affected by the magnetic and electric fields, thus amplifying the dispersion.

[0059] When the image plane 2 approaches the deflection plane 160_2, the radial offset 3 can be reduced. If the image plane 2 coincides with the deflection plane 160_2, the radial offset 3 can become zero or close to or substantially zero, such as Figure 2C Thus, the beam spot 102S can be formed to be the same or nearly the same as when the beam splitter 160 is not present or activated.

[0060] The beam splitter 160 may be represented as having a deflection plane 160_2 at its center, but it should be understood that deflection may occur to electrons at locations other than directly at the deflection plane 160_2. For example, the Wiener filter may include electrodes and pole pieces arranged to extend a certain distance parallel to the main optical axis 100_1, thereby generating electric and magnetic fields over a specific area. Thus, the electrons may begin to experience deflection when they reach the beginning of the electric and magnetic fields, and may continue to experience deflection until they leave the electric field. In some embodiments, the deflection caused by the beam splitter may be approximated by a deflection plane that may be located at the center plane of the beam splitter. The deflection plane may intersect the beam splitter at a position corresponding to the center of distribution of the electric or magnetic field. In some embodiments, the deflection plane may be located at the geometric center of the structure forming the beam splitter.

[0061] like Figure 2B and Figure 2C As shown, beam 102_1 may be formed such that it can generate an image in image plane 2 by, for example, providing a lens above beam splitter 160. A lens or a lens array may be provided to focus the primary light beam or beam.

[0062] Figure 3 FIG. 2 shows an apparatus 200A that can be used to reduce dispersion according to an embodiment of the present disclosure. The apparatus 200A can be used as Figure 1 The electron beam tool 100. Figure 3 As shown, the electron source 101, the main opening of the aperture plate 171, the condenser lens 110, the source conversion unit 120 and the objective lens 131 are aligned with the main optical axis 200_1 of the device. The electron source 101 generates a primary electron beam 102 along the main optical axis 200_1 and having a source cross point (virtual or real) 101s.

[0063] The condenser lens 110 can focus the primary electron beam 102 to reduce divergence or become a parallel beam along the main optical axis 200_1. That is, in some embodiments, the condenser lens 110 can focus the primary electron beam 102 into a parallel beam. The condenser lens 110 can be configured to form a primary electron beam 102 that is perpendicularly incident on the source conversion unit 120. Examples of the source conversion unit 120 can be found in U.S. Patent No. 9,691,586; U.S. Patent Application Publication No. 2017 / 0025243; and International Application No. PCT / EP2017 / 084429, all of which are incorporated herein by reference in their entirety.

[0064] In the source conversion unit 120, a deflector may be provided so that the three beams 102_1, 102_2 and 102_3 of the primary electron beam 102 are deflected respectively. Therefore, the deflected beams may form a virtual image of the primary beam intersection 101s. The beams 102_1, 102_2 and 102_3 may be deflected, for example, toward, outward, or rotated around the main optical axis 200_1.

[0065] The primary projection system 130 includes a transfer lens 133 and an objective lens 131. The transfer lens 133 is aligned with the main optical axis 200_1 and may be a fixed lens in some embodiments and a movable lens in other embodiments. The transfer lens 133 is located between the source conversion unit 120 and the beam splitter 160. The transfer lens 133 projects a virtual image of the primary beam intersection 101s onto the image plane 2. The image plane 2 may be an intermediate real image plane. The transfer lens 133 may focus the beams 102_1, 102_2, and 102_3 to form a plurality of intermediate real images 102_1i, 102_2i, and 102_3i of the primary beam intersection 101s on the image plane 2. For example, the transfer lens 133 may be configured to focus each beam passing therethrough, thereby forming a focal point on the image plane 2.

[0066] The image plane 2 may be in the area of ​​the beam splitter 160. The transfer lens 133 and the beam splitter 160 may be arranged or adjusted so that the image plane 2 is appropriately positioned. For example, the beam splitter 160 may be arranged so that its deflection plane 160_2 is close to or coincides with the image plane 2. The transfer lens 133 may be arranged and its focusing power may be set so that the image plane 2 is close to or coincides with the deflection plane 160_2. The transfer lens 133 may also be configured so that the image plane 2 is at a specified distance from the transfer lens 133. The transfer lens 133 may be configured so that the image plane 2 intersects the beam splitter 160 vertically at its center (e.g., at the center point of the beam splitter 160 along the main optical axis 200_1).

[0067] The transfer lens 133 may be, for example, an electrostatic, magnetic, or electromagnetic composite lens. The magnetic field or electrostatic field generated by the lens may be changed by adjusting the electrical excitation of the lens (e.g., to change the focusing power of the lens). Thus, the lens may be configured to form an image plane at a specific distance from the lens by adjusting the excitation.

[0068] exist Figure 3 In the embodiment, the path of the beam wave in the primary projection optical system 130 may be only schematic. Figure 3 As shown, the diagram of the beam wave between the objective lens 131 and the transfer lens 133 represented by the dotted line can indicate the corresponding relationship between the beam wave entering and leaving the optical element (such as the primary projection optical system 130, etc.). That is, the trajectory of the beam wave can be related to Figure 3 The relative positions of the beams may vary depending on the configuration of the optical elements and the mode of operation.

[0069] The transfer lens 133 and the objective lens 131 of the primary projection optical system 130 can be configured to cooperate to form a beam spot on the sample 1. The objective lens 131 focuses the three deflected beam waves onto the surface 7 of the sample 1, and thus generates three images 102_1S, 102_2S and 102_3S of the primary beam intersection point 101s thereon to serve as detection points. Secondary electron beams 102_1se, 102_2se and 102_3se can be emitted from the sample 1 from the detection points 102_1S, 102_2S and 102_3S. The beam splitter 160 directs the secondary electron beams 102_1se, 102_2se and 102_3se to the secondary optical system 150.

[0070] Reference now Figure 4A , Figure 4A An exemplary multi-beam device 211A according to an embodiment of the present disclosure is shown. Figure 4A , the X-axis corresponds to the radial direction and the Z-axis corresponds to the direction along the main optical axis 211_1 of the device 211A. The device 211A can be used as Figure 1 The electron beam tool 100.

[0071] In the device 211A, the primary electron beam 102 emitted from the primary beam intersection 101s of the source 101 may be collimated by a condenser lens 110M and vertically incident on the source conversion unit 120. The source conversion unit 120 may be provided with a beam limiting aperture array 121 and an image forming element array 122. The beam limiting aperture array 121 may include beam limiting apertures 121_1, 121_2, and 121_3. The beam limiting apertures 121_1, 121_2, and 121_3 may limit the size of the beam waves 102_1, 102_2, and 102_3 of the primary electron beam 102. The image forming element array 122 may include image forming deflectors 122_1, 122_2, and 122_3. The deflectors 122_1, 122_2 and 122_3 can deflect the beams 102_1, 102_2 and 102_3 to form a virtual image of the primary beam intersection 101s. In some embodiments, the deflectors away from the main optical axis 211_1 can deflect the beams to a greater extent. In addition, the image forming element array 122 can include multiple layers, and the deflectors 122_1, 122_2 and 122_3 can be arranged in separate layers. The deflectors 122_1, 122_2 and 122_3 can be controlled individually and independently of each other. In some embodiments, the deflectors can be controlled to adjust the spacing of the detection points formed on the sample 1.

[0072] The condenser lens 110M can be configured to be movable to adjust the current of the beams 102_1, 102_2, and 102_3. The movable condenser lens 110M can have a main plane 110M_2 at a position P1 and can be moved along the main optical axis 211_1 of the device. For example, the main plane 110M_2 can be moved from the position P1 to a position P2 that is farther away from the electron source 101, and thus the current of the beams 102_1, 102_2, and 102_3 can be reduced. The main plane 110M_2 can be moved closer to the electron source 101 so that the current of the beams 102_1, 102_2, and 102_3 can be increased. In addition, the current of the beams 102_1, 102_2, and 102_3 can be changed by changing the size of the beam limiting apertures 121_1, 121_2, and 121_3. When the current of the beam is changed, the primary electron beam 102 can be maintained as a parallel beam.

[0073] The transfer lens 133 focuses the beams 102_1, 102_2, and 102_3 to project a virtual image of the primary beam intersection 101s onto the image plane 2 to form real images 102_1i, 102_2i, and 102_3i of the primary beam intersection 101s. The objective lens 131 projects the images 102_1i, 102_2i, and 102_3i onto the sample 1 to form detection points 102_1S, 102_2S, and 102_3S on the surface 7 of the sample 1. The deflectors 122_1, 122_2, and 122_3 may deflect the beams so that the detection points 102_1S, 102_2S, 102_3S, and 102_3S are spaced apart from each other by a predetermined amount.

[0074] The centrally located deflector of the image forming element array 122 can be aligned with the main optical axis 211_1 of the device 211A. Therefore, in some embodiments, the central deflector can be configured to maintain the trajectory of the beam wave 102_1 straight. In some embodiments, the central deflector can be omitted. However, in some embodiments, the primary electron source 101 may not be aligned with the center of the source conversion unit 120. In addition, it should be connected, although Figure 4A A side view of the device 211A is shown in which the beam 102_1 is on the main optical axis 211_1, but the beam 102_1 may be offset from the main optical axis 211_1 when viewed from a different side. That is, in some embodiments, all beams 102_1, 102_2, and 102_3 may be off-axis. The off-axis components may be offset relative to the main optical axis 211_1.

[0075] The deflection angle of the deflected beam can be set based on one or more criteria. Figure 4AAs shown, the deflectors 122_2 and 122_3 can deflect the off-axis beam waves radially outward or away from the main optical axis 211_1. In some embodiments, the deflectors 122_2 and 122_3 can deflect the off-axis beam waves radially inward or toward the main optical axis 211_1. The deflection angle of the beam waves can be set so that the beam waves 102_1, 102_2 and 102_3 land vertically on the sample 1. By adjusting the path of the beam waves through the lens, the off-axis aberration of the image caused by lenses such as the objective lens 131 can be reduced. Therefore, the deflection angles of the off-axis beam waves 102_2 and 102_3 generated by the deflectors 122_2 and 122_3 can be set so that the detection points 102_2S and 102_3S have smaller aberrations. The beam waves can be deflected to pass through or approach the front focus of the objective lens 131 to reduce the aberrations of the off-axis detection points 102_2S and 102_3S. In some embodiments, the deflector can be configured to make the beams 102_1, 102_2, and 102_3 land vertically on the sample 1, while the detection points 102_1S, 102_2S, and 102_3S have small aberrations. The arrangement of the transfer lens 133 and the objective lens 131 can be configured to focus the beams 102_1, 102_2, and 102_3, while the image forming element array 122 can be configured to deflect the beams 102_1, 102_2, and 102_3 at a deflection angle so that they pass through or approach the front focus of the objective lens 131.

[0076] A beam wave may include electrons at different energy levels. Since the image plane 2 is on the deflection plane 160_2 of the beam splitter 160, the electrons at different energy levels are deflected at different angles after leaving the beam splitter 160, but the radial displacement 3 on the image plane 2 (e.g. Figure 2B The deflected electrons can be refocused by the objective lens 131 to form a detection spot on the sample 1 without dispersion effects.

[0077] In response to the illumination of the primary beams 102_1 , 102_2 , and 102_3 at the detection points 102_1S, 102_2S, and 102_3S, secondary electrons SE emerge from the sample 1 and are deflected by the beam splitter 160 toward the secondary imaging system.

[0078] like Figure 4AAs shown, the transfer lens 133 can be configured so that the image plane 2 is at the deflection plane 160_2. However, in some embodiments, the image plane 2 does not have to be at the deflection plane 160_2 of the beam splitter 160. The image plane 2 can be located above or below the deflection plane 160_2. In some embodiments, due to the dispersion of the beam splitter 160 on the beam waves 102_1, 102_2, and 102_3, the transfer lens 133 can be configured to ensure that the size of the detection points 102_1S, 102_2S, and 102_3S increases relatively within 20%.

[0079] like Figure 2B As shown, as the distance between the image plane 2 and the deflection plane 160_2 increases, the radial offset 3 increases. Therefore, the size of the detection point 102S increases. In some embodiments, the distance between the image plane 2 and the deflection plane 160_2 is selected so that the size of the detection point increases by less than 20% compared to the non-dispersive size (for example, when the beam splitter 160 is closed). When the non-dispersive point size is 10nm, the size of the detection points 102_1S, 102_2S and 102_3S affected by dispersion can be limited to, for example, within 12nm. Therefore, the transfer lens 133 can be configured so that the image plane 2 is located in an area at or near the beam splitter 160. The image plane 2 formed by the transfer lens 133 can be located within the edge of the beam splitter 160 in the direction of the main optical axis 211_1 (Z direction), or it can be located outside the beam splitter 160.

[0080] In some semiconductor manufacturing processes, an increase in the beam spot size of less than 20% due to dispersion may be sufficient to image the smallest feature size of the pattern to be inspected. For example, when using 7nm node technology, an increase in the detection spot size of less than or equal to 20% may be sufficient to ensure sufficient resolution to image the smallest objects in the pattern. Other thresholds may be set appropriately for other processes, such as for 14nm, 10nm, and 5nm technologies.

[0081] The transfer lens configured to form an image of the charged particle source 101 on the image plane 2 at least near the deflection plane 160_2 of the beam splitter 160 may include a transfer lens 133, which is configured to form the image plane 2 at the deflection plane 160_2, or to form the image plane 2 by a certain amount offset from the deflection plane 160_2 of the beam splitter 160. The offset amount of the image plane 2 relative to the deflection plane 160_2 may correspond to an amount such that, for example, the increase in the size of the beam spot relative to the non-dispersive size is limited to 20%.

[0082] Reference now Figure 4B , Figure 4BAn exemplary multi-beam device 212A is shown according to an embodiment of the present disclosure. Figure 4A Compared to the embodiment of the device 211A shown, the device 212A also includes a pre-beanlet-forming mechanism 172 and an aberration compensator array 122-2. The pre-beamlet-forming mechanism 172 may include a Coulomb aperture array. The central aperture of the pre-beamlet-forming mechanism 172 and the central deflector of the aberration compensator array 122-2 may be aligned with the main optical axis 212_1 of the device 212A.

[0083] The pre-beam forming mechanism 172 may be provided with a plurality of trimmed pre-apertures (eg, a Coulomb aperture array). The pre-beam forming mechanism 172 may be provided above the movable condenser lens 110M and close to the electron source 101. Figure 4B , the three beams 102_1, 102_2, and 102_3 pass through the three pre-trim apertures, respectively, and most of the remaining parts of the primary electron beam 102 are cut off. That is, the pre-beamforming mechanism 172 can trim most or most of the electrons from the primary electron beam 102 that do not form the three beams 102_1, 102_2, and 102_3. Before the primary electron beam 102 enters the source conversion unit 120, the pre-beamforming mechanism 172 can cut off electrons that will not be used to form the detection points 102_1S, 102_2S, and 102_3S in the end. In this way, the Coulomb effect 121 above the beam limiting aperture array can be greatly reduced. The gun hole plate 171 can be set close to the electron source 101 to cut off the electrons at an early stage, and the pre-beamforming mechanism 172 can also be provided to further cut off the electrons around the multiple beams.

[0084] When the pre-beamforming mechanism 172 is placed in close proximity to the source 101, the size of the pre-trim aperture required to achieve the desired beam size or shape may be too small to be manufactured. In this case, the pre-beamforming mechanism 172 can be placed at a distance from the source 110, which is conducive to one or more manufacturable sizes of the pre-trim aperture, and the gun aperture plate 171 can be used and positioned above the pre-beamforming mechanism 172 to cut off electrons at an early stage to reduce the Coulomb effect. In order to more effectively cut off electrons that will not become part of the beam, the size of the pre-trim aperture is selected to facilitate setting the desired current of the detection points 102_1S, 102_2S and 102_3S. Smaller sizes are used for smaller currents and larger sizes are used for larger currents. The pre-beamforming mechanism 172 can be moved in a direction perpendicular to the main optical axis 212_1 so that the pre-trim aperture of the desired size can be moved to cut the primary electron beam 102 to obtain the desired current. For example, a motor may be coupled to the pre-beamforming mechanism 172 and configured to move in an XY plane (where the Y axis is in the Figure 4BIn the case where both the aperture plate 171 and the pre-beam forming mechanism 172 are provided, the aperture plate 171 above the pre-beam forming mechanism 172 can keep the electron emission of the source 101 stable when the pre-beam forming mechanism 172 moves.

[0085] In some embodiments, the pre-beamforming mechanism 172 can be placed below the movable condenser lens 110M. Placing the pre-beamforming mechanism 172 closer to the electron source 101 can more effectively reduce the Coulomb effect. In some embodiments, the aperture plate 171 can be omitted when the pre-beamforming mechanism 172 can be positioned close enough to the source 101 while still being manufacturable.

[0086] Image plane 2 is the object plane of objective lens 131, and the characteristics of objective lens 131 can remain constant. That is, in some embodiments, when the current of beams 102_1, 102_2, and 102_3 (and therefore detection points 102_1S, 102_2S, and 102_3S) changes, the characteristics of objective lens 131 do not need to change. For example, when changing the current of beams 102_1, 102_2, and 102_3, the objective lens excitation can be fixed.

[0087] The source conversion unit 120 may be provided with an image forming element array 122-1 and an aberration compensator array 122-2. The image forming element array 122-1 of the device 212A may be provided with an image forming element array 122-1 and an aberration compensator array 122-2. Figure 4A The beam limiting array 122 of the device 211A shown is the same. The image forming element array 122-1 may include an array of image forming micro deflectors 122_1d, 122_2d and 122_3d, and the array of image forming micro deflectors 122_1d, 122_2d and 122_3d may be arranged to make the beams 102_1, 102_2 and 102_3 land vertically on the sample 1 or make the aberration of the detection points 102_1S, 102_2S and 102_3S small. The aberration compensator array 122-2 may include an array of aberration compensators 122_1c, 122_2c and 122_3c configured to compensate for aberrations. For example, the aberration compensator array 122-2 may compensate for the field curvature aberration or the astigmatism aberration of the detection points 102_1S, 102_2S and 102_3S. The image forming micro deflector of the source conversion unit 120 may be configured to deflect the beam outward, inward, or even rotate around the main optical axis 212_1 .

[0088] Reference now Figure 4C , Figure 4C An exemplary multi-beam device 213A is shown according to an embodiment of the present disclosure. Figure 4BCompared to the embodiment of the device 212A shown, the device 213A includes a movable transfer lens 133M that can replace, for example, the transfer lens 133 in the embodiment of the device 212A. The movable transfer lens 133M can be aligned with the main optical axis 213_1 of the device 213A.

[0089] The movable transfer lens 133M may have a principal plane 133M_2 at a position M1 and may be movable along the principal optical axis 213_1 of the device. For example, the principal plane 133M_2 may be moved from the position M1 to a position M2 further away from the source conversion unit 120. Adjusting the position of the movable transfer lens 133M may affect the positions of the images 102_1i, 102_2i, and 102_3i formed in the image plane 2, thereby changing the spacing of the detection points 102_1S, 102_2S, and 102_3S on the sample 1. When the principal plane 133M_2 moves away from the source conversion unit 120, the spacing of the detection points 102_1S, 102_2S, and 102_3S becomes larger. The image forming micro deflectors 122_1d, 122_2d, and 122_3d may deflect the beams 102_1, 102_2, and 102_3 to cause the beams to land vertically on the sample 1 or have small aberration.

[0090] In some embodiments, the spacing of the detection points 102_1S, 102_2S, and 102_3S may be the same or may be different from each other. When the spacing is changed by adjusting the lens, and all beams pass through the lens, the spacing may be controlled together. For example, when the main plane of the lens (such as the main plane 133M_2) is moved, or when the image plane 2 is moved, the spacing of the detection points 102_1S, 102_2S, and 102_3S may be controlled together.

[0091] Reference now Figure 4D , Figure 4D An exemplary multi-beam device 214A is shown in accordance with an embodiment of the present disclosure. Figure 4D In FIG. 2 , the X-axis corresponds to the radial direction and the Z-axis corresponds to the direction along the main optical axis 214_1 of the multi-beam device 214A. The multi-beam device 214A can be used as Figure 1 The electron beam tool 100.

[0092] In the device 214A, the primary electron beam 102 emitted from the primary electron beam intersection 101s of the electron source 101 may be collimated by a condenser lens 110M to be vertically incident on the source conversion unit 120. The source conversion unit 120 may be provided with a beam limiting aperture array 121 and an image forming element array 122. The beam limiting aperture array 121 may include beam limiting apertures 121_1, 121_2, and 121_3. The beam limiting apertures 121_1, 121_2, and 121_3 may be configured to limit the size of the beam waves 102_1, 102_2, and 102_3 of the primary electron beam 102. The image forming element array 122 may include image forming deflectors 122_1, 122_2, and 122_3. The deflectors 122_1, 122_2, and 122_3 can deflect the beams 102_1, 102_2, and 102_3 to form a virtual image of the primary beam intersection 101s. In some embodiments, the deflectors away from the main optical axis 211_1 can deflect the beams to a greater extent. In addition, the image forming element array 122 may include multiple layers, and the deflectors 122_1, 122_2, and 122_3 may be arranged in a separate layer (not shown). The deflectors 122_1, 122_2, and 122_3 may be individually controlled independently of each other. In some embodiments, the deflectors may be controlled to adjust the spacing of the detection points formed on the sample 1.

[0093] like Figure 4D As shown, the multi-beam device 214A may include a gun aperture plate 171 configured to trim peripheral electrons of the primary electron beam 102. Due to the divergence of the primary electron beam 102, placing the gun aperture plate 171 too close to the electron source 101 may not effectively reduce the cross-section of the primary electron beam 102 incident on the condenser lens 110M. In addition, the deposition of debris or particles from the electron source 101 on the gun aperture plate 171 may undesirably reduce the aperture size. Placing the gun aperture plate 171 too far from the electron source 101 may result in a reduction in beam current by trimming a larger portion of the primary electron beam 102, which is also undesirable. Therefore, the gun aperture plate 171 may be placed at an optimal distance from the primary electron beam intersection 101s of the electron source 101.

[0094] In conjunction with the beam limiting aperture array 121, the condenser lens 110M may be configured to adjust the current of the beams 102_1, 102_2, and 102_3. In some embodiments, the adjustable condenser lens 110M may have a principal plane 110M_2 that may be moved along the principal optical axis 214_1 of the multi-beam device 214A. For example, the principal plane 110M_2 may be moved further away from the electron source 101 to reduce the current of the beams 102_1, 102_2, and 102_3, and the principal plane 110M_2 may be moved closer to the electron source 101 to increase the current of the beams 102_1, 102_2, and 102_3. In conjunction with adjusting the position of the principal plane 110M_2, changing the size of the aperture of the beam limiting aperture array 121 may change the current of the beams 102_1, 102_2, and 102_3. The current of the beam may be changed after the beam passes through the aperture of the beam limiting aperture array 121. When the current of the beam is changed, the primary electron beam 102 may be maintained as a parallel beam.

[0095] The transfer lens 133 may be configured to focus the beams 102_1, 102_2 and 102_3 to project a virtual image of the primary beam intersection 101s onto the intermediate image plane 2, thereby forming real images 102_1i, 102_2i and 102_3i of the primary beam intersection 101s. Figure 4D As shown, the transfer lens 133 can be configured so that the intermediate image plane 2 is formed closer to the transfer lens 133 than the deflection plane 160_2 of the beam splitter 160. The position of the intermediate image plane 2 can be adjusted along the main optical axis 214_1 to adjust the magnification of the primary electron beam 102 or the primary beam intersection 101s. In the context of the present disclosure, "closer" refers to the physical proximity of an object, whether real or virtual. For example, if the image plane 2 is closer to the transfer lens 133 than the beam splitter 160, it means that the vertical distance from the image plane 2 to the transfer lens 133 along the main optical axis 214_1 is less than the vertical distance from the image plane 2 to the beam splitter 160. The vertical distance between the image plane 2 and the transfer lens 133 can be measured as the distance between the image plane 2 and the central axis of the transfer lens 133 along the main optical axis 214_1. The vertical distance between the image plane 2 and the beam splitter 160 may be measured as the distance between the image plane 2 and the deflection plane 160_2 of the beam splitter 160 along the primary optical axis 214_1 .

[0096] In some embodiments, a small magnification of the primary beam intersection 101s may be desirable. For example, smaller detection spots (e.g., 102_1S, 102_2S, and 102_3S) generated from the primary beam intersection 101s may result in enhanced image resolution. The magnification may be determined based on a ratio of the size of the detection spot to the size of the primary beam intersection 101s.

[0097] In some embodiments, the magnification can be referred to as the ratio of the focal length of the objective lens 131 to the focal length of the condenser lens 110M. To obtain a smaller magnification, the focal length of the objective lens 131 may be shorter and the focal length of the condenser lens 110M may be longer to make the detection spot smaller, thereby improving the resolution.

[0098] In the multi-beam device 214A, the magnification can be determined based on the ratio of the distance between the objective lens 131 and the sample 1 and the distance between the intermediate image plane 2 and the objective lens 131. Increasing the distance between the intermediate image plane 2 and the objective lens 131 can further reduce the magnification of the primary beam intersection 101s.

[0099] The transfer lens 133 may be, for example, an electrostatic, magnetic or electromagnetic composite lens. The focal length or focusing power of the transfer lens 133 may be changed by changing the electrical excitation of the lens or by changing the physical position of the transfer lens 133 ( Figure 4D (not shown) or both. Figure 4D As shown, the transfer lens 133 can be configured to form the image plane 2 at a specific distance from the lens to change the magnification as desired.

[0100] The multi-beam device 214A may include a beam splitter 160 to separate primary charged particles incident on the sample 1 and secondary or backscattered electrons emitted from the sample 1 when interacting with the primary charged particles. In some embodiments, the beam splitter may be placed between the objective lens 131 and the transfer lens 133, so that the beam splitter 160 is closer to the objective lens 131 to allow sufficient space for placing the secondary imaging system 150.

[0101] Reference now Figure 4E , Figure 4E An exemplary multi-beam device 215A is shown according to an embodiment of the present disclosure. Figure 4D Compared to the illustrated embodiment of the multi-beam device 214A, the multi-beam device 215A includes a pre-beamforming mechanism 172. The pre-beamforming mechanism 172 may include a Coulomb aperture array.

[0102] In some embodiments, the pre-beam forming mechanism 172 may be provided with a plurality of trimmed pre-apertures (eg, a Coulomb aperture array). The pre-beam forming mechanism 172 may be provided above the movable condenser lens 110M and close to the electron source 101. Figure 4EIn the embodiment of the present invention, the primary electron beam 102 passes through three pre-trimming apertures, and most of the remaining portion of the primary electron beam 102 is trimmed. That is, the pre-beamforming mechanism 172 can trim most or most of the electrons from the primary electron beam 102 that do not form the three beams 102_1, 102_2, and 102_3 to reduce the Coulomb effect above the beam limiting aperture array 121. The shapes and sizes of the multiple pre-trimming apertures can be adjusted to maximize the reduction of the Coulomb effect.

[0103] In some embodiments, a gun aperture plate 171 may be provided close to the electron source 101 to cut off electrons at an early stage, and a pre-beam forming mechanism 172 may also be provided to further cut off electrons around multiple beams. In some embodiments, the pre-beam forming mechanism 172 may be used without a gun aperture plate 171. This may enable a simpler column design, lower maintenance costs, or reduced tool downtime.

[0104] Reference now Figure 4F , Figure 4F An exemplary multi-beam device 216A is shown in accordance with an embodiment of the present disclosure. Figure 4D In the illustrated embodiment of the multi-beam device 214A, the multi-beam device 216A further includes a beam dispersion compensator 161 .

[0105] The beam dispersion compensator 161 can be configured to compensate for the dispersion of the electron beam caused by the beam splitter 160 (as previously discussed in the present disclosure). The beam dispersion compensator 161 can be placed between the beam splitter 160 and the transfer lens 133. The beam dispersion compensator 161 can be represented as having a deflection plane 161_2 at its center. The beam dispersion compensator 161 can, for example, include a Wien filter. Examples of beam dispersion compensators 161 and exemplary methods of compensating beam dispersion can be found in U.S. Patent Application Publication No. 2019 / 0035595, which is incorporated herein by reference in its entirety.

[0106] The multi-beam device 216A can be configured to reduce magnification and compensate for beam dispersion to enhance imaging resolution. The position of the intermediate image plane 2 can be adjusted by changing the electrical excitation of the transfer lens 133. The change in the position of the image plane 2 can change the magnification. For example, the formation of the image plane 2 away from the beam splitter 160 but closer to the transfer lens 133 can result in a smaller magnification. However, in this configuration, the beam dispersion will be adversely affected. A beam dispersion compensator 161 can be used to alleviate the impact of the overall beam dispersion of the beam waves (102_1, 102_2 and 102_3). Therefore, the multi-beam device 216A (the multi-beam device 216A includes a beam dispersion compensator 161 combined with an image plane 2 formed away from the beam splitter) can be used to improve imaging resolution.

[0107] Reference now Figure 4G , Figure 4G An exemplary multi-beam device 217A is shown according to an embodiment of the present disclosure. Figure 4F Compared to the embodiment of the multi-beam device 216A shown in the figure, the multi-beam device 217A may further include a beam forming pre-mechanism 172. The beam forming pre-mechanism 172 may include a Coulomb aperture array, which is disposed above the movable condenser lens 110M and close to the electron source 101. Figure 4G In the embodiment of the present invention, the primary electron beam 102 passes through three pre-trimming apertures, and most of the remaining portion of the primary electron beam 102 is trimmed. That is, the pre-beamforming mechanism 172 can trim most of the electrons from the primary electron beam 102 that do not form the three beams 102_1, 102_2, and 102_3 to reduce the Coulomb effect above the beam limiting aperture array 121. The shapes and sizes of the multiple pre-trimming apertures can be adjusted to maximize the reduction of the Coulomb effect.

[0108] In addition to reducing the Coulomb effect by introducing the beam forming pre-mechanism 172, an embodiment of the multi-beam device 217A also includes a transfer lens 133, which is configured to form a real image of the primary beam intersection 101s on the intermediate image plane 2 representing the focal length of the transfer lens 133. The position of the intermediate image plane 2 can be adjusted by changing the electrical excitation of the transfer lens 133. The change in electrical excitation can cause a change in the focal length, thereby changing the magnification to improve the resolution. In addition, an embodiment of the multi-beam device 217A includes a beam dispersion compensator 161 configured to compensate for the dispersion of the beams 102_1, 102_2, and 102_3 caused by the beam splitter 160.

[0109] Reference now Figure 5A , Figure 5A An exemplary multi-beam device 221A according to an embodiment of the present disclosure is shown. The device 221A can be operated in a divergent mode, etc. (e.g., a convergent or parallel mode). In the divergent mode, instead of collimating the primary electron beam 102 into a parallel (or substantially parallel) beam, the condenser lens 110 is configured to focus the electron beam 102 only to a certain extent to form the electron beam 102 into a divergent beam. In the divergent mode, the current density of the primary electron beam 102 can be less than the density when operating in the parallel mode. Therefore, the current of the beam waves 102_1, 102_2, and 102_3 can be reduced.

[0110] The device 221A may be provided with a beam bending front deflector array 123 which may include pre-bending micro-deflectors. For example, the beam bending front deflector array 123 may include pre-bending micro-deflectors 123_1, 123_2, and 123_3. The beam bending front deflector array 123 may be provided to deflect the beams 102_1, 102_2, and 102_3 to be parallel to the main optical axis 221_1 and vertically incident on the beam limiting aperture array 121. The beam bending front deflector array 123 may deflect the beams to reduce electron scattering that may be caused by the beams entering the beam limiting apertures 121_1, 121_2, and 121_3 at a certain angle. The electron scattering in the beam may enlarge the corresponding detection spot size or cause background noise, thereby reducing the image resolution of the corresponding scanning area.

[0111] The condenser lens 110 may be configured to focus the electron beam 102 so that the beams 102_1, 102_2, and 102_3 have a desired current after passing through the beam limiting apertures 121_1, 121_2, and 121_3. The source conversion unit 120 may be provided with a beam limiting aperture array 121, an image forming element array 122, and a beam bending pre-deflector array 123. The beam limiting aperture array 121 may limit the size or current of the beams 102_1, 102_2, and 102_3 to a desired level. The image forming element array 122 may include image forming micro deflectors 122_1d, 122_2d, and 122_3d that may be configured to form a virtual image of the primary beam intersection 101s.

[0112] The transfer lens 133 can focus the beams 102_1, 102_2 and 102_3 and project the virtual image of the primary beam intersection point 101s onto the image plane 2 to form real images 102_1i, 102_2i and 102_3i. The objective lens 131 can project the images 102_1i, 102_2i and 102_3i onto the sample 1 to form detection points 102_1S, 102_2S and 102_3S on the surface 7.

[0113] The image forming micro deflectors 122_1 d , 122_2 d , and 122_3 d may be configured to deflect the beam waves 102_1 , 102_2 , and 102_3 such that the detection points 102_1S, 102_2S, and 102_3S are spaced apart from each other on the sample surface 7 .

[0114] In some embodiments, the image forming micro-deflectors 122_1d, 122_2d and 122_3d can be used to adjust the beams 102_1, 102_2, 102_3 to land vertically on the sample surface 7 or to reduce aberrations of the detection points 102_1S, 102_2S and 102_3S.

[0115] In the device 221A, the source conversion unit 120 can be configured so that the beams 102_1, 102_2, and 102_3 travel through the source conversion unit substantially parallel to the main optical axis 221_1. The beams 102_1, 102_2, and 102_3 can travel straight through the corresponding elements of the beam bending front deflector array 123, the beam limiting aperture array 121, and the image forming element array 122. The beam having a straight trajectory through the source conversion unit 120 can reduce the aberration of the beam limiting aperture array 121 and the image forming element array 122. In addition, the layers of the source conversion unit 120 can be made compact. In addition, the manufacture of the source conversion unit 120 can be made more efficient.

[0116] Reference now Figure 5B , Figure 5B An exemplary multi-beam device 222A is shown according to an embodiment of the present disclosure. Figure 5A Compared to the embodiment of the device 221A shown, the device 222A also includes a beam forming front mechanism 172 and an aberration compensator array 122-2. The beam forming front mechanism 172 may include a Coulomb aperture array. The central hole of the beam forming front mechanism and the central deflector of the aberration compensator array 122-2 may be aligned with the main optical axis 222_1 of the device 222A. In addition, the device 222A may be provided with an anti-rotation focusing lens 110AR.

[0117] Electrons from the primary electron beam 102 generated by the electron source 101 can be trimmed around the three beams 102_1, 102_2, and 102_3 by the beam forming aperture of the pre-beam forming mechanism 172. When the focusing power of the anti-rotation condenser lens 110AR is changed to change the current of the beams 102_1, 102_2, and 102_3, the rotation angles of the beams 102_1, 102_2, and 102_3 on the source conversion unit 120 can remain unchanged, so that the beams 102_1, 102_2, and 102_3 can pass through the pre-beam bending deflector array 123, the beam limiting aperture array 121, and the image forming element array 122.

[0118] The anti-rotation focusing lens 110AR can be an anti-rotation lens. The anti-rotation lens can have a focusing capability that can be changed without affecting the rotation angle of the electron beam passing therethrough. Examples of anti-rotation lenses are provided in International Application No. PCT / EP2017 / 084429, which is incorporated herein by reference in its entirety. The anti-rotation lens can be formed by two lenses. For example, the anti-rotation lens can be formed by two magnetic lenses, or by a magnetic lens and an electrostatic lens. By appropriately adjusting the excitation of the lens inside the anti-rotation lens, the focusing capability of the lens can be changed without affecting the rotation angle of the electron beam passing therethrough.

[0119] The anti-rotation focusing lens 110AR can be a movable anti-rotation lens (MARL). In the case of a MARL, the anti-rotation focusing lens 110AR can be formed by three lenses. An example of a movable anti-rotation lens is also provided in International Application No. PCT / EP2017 / 084429.

[0120] The pre-beam forming mechanism 172 may be provided with a plurality of trimmed pre-apertures that may help to form the beams 102_1 , 102_2 , and 102_3 . The anti-rotation focusing lens 110AR may help to ensure that the beams 102_1 , 102_2 , and 102_3 pass through the corresponding openings of the beam limiting mechanism 121 .

[0121] The source conversion unit 120 may be provided with an image forming element array 122-1 and an aberration compensator array 122-2. The image forming element array 122-1 of the device 222A may be provided with an image forming element array 122-1 and an aberration compensator array 122-2. Figure 5A The image forming element array 122 of the device 221A shown is the same. The image forming element array 122-1 may include an array of image forming micro deflectors 122_1d, 122_2d and 122_3d, and the array of image forming micro deflectors 122_1d, 122_2d and 122_3d may be set to make the beams 102_1, 102_2 and 102_3 land vertically on the sample 1 or make the aberration of the detection points 102_1S, 102_2S and 102_3S small. The aberration compensator array 122-2 may include an array of aberration compensators 122_1c, 122_2c and 122_3c that can compensate for the field curvature aberration or astigmatism aberration of the detection points 102_1S, 102_2S and 102_3S.

[0122] Reference now Figure 5C , Figure 5C An exemplary multi-beam device 223A is shown according to an embodiment of the present disclosure. Figure 5B Compared to the embodiment of the device 222A shown, the device 223A may include a movable transfer lens 133M that may replace, for example, the transfer lens 133 in the embodiment of the device 222A. The movable transfer lens 133M may be aligned with the primary optical axis 223_1 of the device 223A.

[0123] The movable transfer lens 133M may have a principal plane 110M_2 at a predetermined position and may be movable along the principal optical axis 223_1 of the device. For example, the principal plane 110M_2 may be moved closer to or farther from the source conversion unit 120. Adjusting the position of the movable transfer lens 133M may affect the positions of the images 102_1i, 102_2i, and 102_3i formed in the image plane 2, thereby changing the spacing of the detection points 102_1S, 102_2S, and 102_3S on the sample 1.

[0124] Fig. 6A and Figure 6B An exemplary deflection angle adjustment in the image forming element array 122 according to an embodiment of the present disclosure is shown. Fig. 6A and Figure 6B The arrangement may form part of the exemplary embodiments discussed herein. The deflector may be configured to deflect a light beam generated from an electron source. The deflector may be part of a deflector array, such as deflectors 122_1, 122_2, and 122_3 of the image forming element array 122. The deflectors 122_1, 122_2, and 122_3 may be configured to deflect the light beam symmetrically around the optical axis (Z axis). Fig. 6A In the side view of the embodiment of FIG. 1 , the deflector 122_1 can be configured to deflect the beam 102_1 in a direction outward from the paper.

[0125] Deflector 122_2 is an example of a deflector. Fig. 6A As shown, the deflector 122_2 deflects the beam 102_2 radially outward, and the deflection angle relative to the Z axis is θ. As the angle θ increases, the beam spacing can increase. Therefore, images 102_1i, 102_2i, and 102_3i can be formed at increasing separation distances on the image plane 2. Beam spots, such as detection spots 102_1S, 102_2S, and 102_3S, can be formed at increasing spacings.

[0126] The image forming element array 122 may include a 3×3 array of deflectors. The central deflector of the 3×3 deflector array may be aligned with the primary optical axis of the device and may therefore be configured to keep the trajectory of the center light beam straight. The central deflector may also be omitted. In some embodiments, more or fewer deflectors may be provided. For example, an 11×11 array of deflectors may be provided. All deflectors of the array may be configured to generate a desired deflection angle for a light beam passing therethrough. In some embodiments, some deflectors may be configured to deflect a light beam passing therethrough at different deflection angles. In embodiments where more deflectors are provided, for example, deflectors positioned radially outward may be configured to generate a larger deflection angle on the light beam.

[0127] like Figure 6B As shown, the beam wave can also be deflected radially inward toward the main optical axis. When the beam wave is deflected inward, a beam intersection point can be formed before the beam wave reaches the beam splitter 160. In addition, the inward deflection of the beam wave may cause the beam wave to have a larger beam separation after reaching the objective lens 103, so the beam wave may form a detection point with a larger aberration on the sample.

[0128] When a movable transfer lens is used, the deflector of the image forming element array 122 can be configured to deflect the beam wave at a deflection angle based on the displacement of the principal plane of the movable transfer lens relative to the reference position. The deflector can be configured to deflect the beam wave within a predetermined deflection angle range. The amount of deflection imparted by the deflector can be determined by a voltage applied to the deflector.

[0129] In some embodiments, the deflectors can be configured to generate small deflection angles. For example, multiple deflectors can be used to adjust a single beam so as to collectively deflect the beam at an angle greater than the individual small deflection angles. The benefit of such a small deflection angle is that the deflector array can be easier to manufacture and may require lower electrical excitation. In addition, such a configuration can be more energy efficient.

[0130] Figure 7 is a flow chart showing an exemplary method 700 for forming a light beam according to an embodiment of the present disclosure. For example, the method 700 may be performed as follows: Figure 1 The controller 19 of the illustrated EBI system 10 executes. The controller 19 may be programmed to implement one or more blocks of the method 700. For example, the controller 19 may instruct modules of a charged particle beam apparatus to generate a charged particle beam and perform other functions.

[0131] In step 710, a charged particle beam may be generated by a charged particle source. For example, the electron source 101 may be controlled to emit a primary electron beam 102 formed along a main optical axis. Step 710 may include generating a plurality of beam waves. The primary electron beam 102 may be trimmed by a gun aperture 171 or a beam wave forming pre-mechanism 172. Step 710 may include focusing the primary electron beam 102. The primary electron beam 102 may be focused by a condenser lens 110. Focusing the primary electron beam 102 may include generating an electric field or a magnetic field. The primary electron beam waves 102_1, 102_2, and 102_3 may be directed to a source conversion unit 120.

[0132] In step 720, the charged particle beam may be deflected by a deflector. For example, the primary electron beam 102 including beams 102_1, 102_2, and 102_3 may be deflected by a deflector of the beam bending front deflector array 123. The primary beam 102 may be deflected so that the beams 102_1, 102_2, and 102_3 are parallel to the main optical axis and vertically incident on the beam limiting array 121. A voltage may be provided to the deflector.

[0133] In step 730 , the size of the beams may be limited. For example, the sizes of the beams 102_1 , 102_2 , and 102_3 may be limited by passing the beams 102_1 , 102_2 , and 102_3 through corresponding openings of the beam limiting array 121 .

[0134] In step 740, the beams may be deflected by a deflector. For example, beams 102_1, 102_2, and 102_3 may be deflected by individual deflectors of the image forming element array 122. Individual deflectors of the image forming element array 122 (such as deflectors 122_1, 122_2, and 122_3) may be controlled to deflect beams 102_1, 102_2, and 102_3 at a deflection angle θ. A voltage may be provided to the deflectors. Deflecting the beams in step 740 may include deflecting the beams in a direction perpendicular to the main optical axis. The beams may be deflected radially outward. Step 740 may include forming a virtual image of the primary beam intersection 101s of the charged particle source 101. The deflection angle may be set so that beams 102_1, 102_2, and 102_3 land vertically on the sample 1. The deflection angle may be based on the characteristics of the transfer lens 133 and the objective lens 131 .

[0135] In step 750, the beams may be focused on an intermediate image plane. For example, the beams 102_1, 102_2, and 102_3 may be focused on the image plane 2 by the transfer lens 133. A plurality of intermediate real images 102_1i, 102_2i, and 102_3i of the primary beam intersection 101s may be formed on the image plane 2. The image plane 2 may be at least near the beam splitter 160, which may be configured to separate primary charged particles from secondary charged particles. The transfer lens 133 may be controlled to generate an electric field or a magnetic field. Step 750 may include controlling a movable lens to adjust the separation of the images formed in the image plane 2. For example, the movable transfer lens 133 may be moved to adjust the separation distance between the intermediate real images 102_1i, 102_2i, and 102_3i and adjust the spacing of the detection points 102_1S, 102_2S, and 102_3S.

[0136] In step 760, the beams may be focused onto a target. For example, the beams 102_1, 102_2, and 102_3 may be focused onto the sample 1 by the objective lens 131 for inspection, and may form detection points 102_1S, 102_2S, and 102_3S on the surface 7. Adjusting the spacing distance between the intermediate real images 102_1i, 102_2i, and 102_3i in step 750 may change the spacing between the detection points 102_1S, 102_2S, and 102_3S. Setting the deflection angle in step 740 may reduce the aberration of the detection points 102_1S, 102_2S, and 102_3S.

[0137] In step 770, the secondary electrons may be deflected to be directed toward the secondary imaging system. For example, in response to the irradiation of the primary beams 102_1, 102_2, and 102_3 at the detection points 102_1S, 102_2S, and 102_3S, the secondary electrons may be emitted from the sample 1 to form secondary electron beams 102_1se, 102_2se, and 102_3se that may be directed toward the secondary imaging system 150. The beam splitter 160 may be controlled to deflect the secondary electron beams 102_1se, 102_2se, and 102_3se toward the secondary imaging system 150. The secondary imaging system 150 may then focus the secondary electron beams 102_1se, 102_2se, and 102_3se onto the detection elements 140_1, 140_2, and 140_3 of the electron detection device 140M.

[0138] In step 780 , an image of the sample may be constructed. For example, the detection elements 140_1 , 140_2 , and 140_3 may detect the corresponding secondary electron beams 102_1se , 102_2se , and 102_3se and generate corresponding signals that may be sent to a signal processing unit to construct an image of the corresponding scanned area of ​​the sample 1 .

[0139] Figure 8 8 is a flow chart showing an exemplary method 800 for observing a sample using a multi-beam inspection tool according to an embodiment of the present disclosure. For example, the method 800 may be performed as follows: Figure 1 The controller 19 of the illustrated EBI system 10 performs the method 800. The controller 19 may be programmed to implement one or more blocks of the method 800. For example, the controller 19 may instruct modules of the charged particle beam apparatus to generate a charged particle beam and perform other functions.

[0140] In step 810, a charged particle source (e.g., Figure 2A The electron source 101) generates a charged particle beam (e.g., Figure 2A For example, the electron source 101 may be controlled to emit the primary electron beam 102 formed along the main optical axis. The primary electron beam may be passed through a gun aperture plate (e.g., Figure 2A of a gun aperture plate 171) or an aperture array (e.g., Figure 4B The beam wave forming front mechanism 172) or both are used for trimming.

[0141] In step 820, a plurality of beams (eg, beams 102_1, 102_2, and 102_3) may be generated after passing through the pre-beamforming mechanism. The number of beams generated may be based on the number of pre-trim apertures of the pre-beamforming mechanism. For illustration purposes, for example, Figure 4A Step 820 may include using a focusing lens (e.g., Figure 4A The focusing lens 110M) focuses the beam. Figure 4D In the embodiment of the multi-beam device 214A shown, for example, a condenser lens can focus the primary electron beam. Focusing the primary electron beam or multiple beams can include generating an electric field or a magnetic field. In some embodiments, the condenser lens can be configured to collimate the beam or primary electron beam. The beams 102_1, 102_2, and 102_3 can be directed to the source conversion unit 120.

[0142] In step 830, the size of the beam may be limited. For example, the beam may be passed through a beam limiting array (e.g., Figure 4A The size of the beams 102_1, 102_2 and 102_3 is limited by the corresponding openings of the beam limiting array 121. Although reducing the size of the beams can reduce the beam current, this can help to generate a smaller detection spot and a substantially uniform electron energy distribution within the cross section of the beams. This can, among other things, improve imaging resolution.

[0143] In step 840, the beam is deflected by a beam deflector (e.g., Figure 4A The image forming element array 122 may allow one or more beams to pass through a transfer lens (e.g., Figure 4D transfer lens 133). For example, beams 102_1, 102_2, and 102_3 may be deflected by individual deflectors of the image forming element array. It will be appreciated that on-axis beam 102_1 may not be deflected. Individual deflectors of the image forming element array (such as deflectors 122_1, 122_2, and 122_3) may be controlled by applying voltage signals to the deflectors to deflect beams 102_1, 102_2, and 102_3, respectively. For example, voltage signals may be applied to deflectors 122_2 and 122_3 to deflect beams 102_2 and 102_3, respectively, while no voltage signal may be applied to the deflectors to allow beam 102_1 to pass through without any deflection, for example, as Figure 4D shown.

[0144] Deflecting the beams in step 840 may include deflecting one or more beams radially outward to be incident on a transfer lens (e.g., Figure 4D on the transfer lens 133).

[0145] In step 850, the beam can be focused onto an intermediate image plane (e.g., image plane 2). For example, the beam can be focused onto the image plane by a transfer lens. A plurality of intermediate real images (e.g., primary beam intersection 101s) of the beam intersection (e.g., primary beam intersection 101s) can be formed. Figure 4DThe intermediate real images 102_1i, 102_2i, and 102_3i) of the image plane can be formed on the image plane. The image plane can be formed away from a beam splitter (e.g., beam splitter 160) configured to separate the primary charged particles and the secondary charged particles. The transfer lens can be controlled to generate an electric field or a magnetic field. Step 850 can include controlling a movable lens to adjust the separation of the image formed in the image plane. For example, the movable transfer lens (e.g., Figure 5C The movable transfer lens 133M) can be moved in a direction parallel to the main optical axis to adjust the horizontal separation distance between the intermediate real images and adjust the detection point (for example, Figure 4D The distance between the detection points 102_1S, 102_2S and 102_3S).

[0146] In some embodiments, the transfer lens is fixed, such as Figure 4D As shown. The focal length of the transfer lens can be adjusted by changing the electrical excitation. Changing the focal length of the transfer lens can change the position of the intermediate image plane, thereby changing the magnification of the beam wave and the size of the formed detection spot.

[0147] In step 860, a beam dispersion compensator (e.g., Figure 4F The beam dispersion compensator 161) can compensate for the dispersion of one or more beams based on the determined dispersion of the primary beams passing through the beam splitter. Forming the intermediate image plane away from the beam splitter may increase the beam dispersion, resulting in a decrease in image resolution. To alleviate this problem, the beam dispersion compensator can disperse the beams accordingly. The beam dispersion compensator can, for example, include a Wien filter.

[0148] In step 870, the Figure 4D The objective lens 131 of the embodiment of the present invention focuses the compensated beam onto a target (e.g., sample 1) for inspection, and the compensated beam can be applied to the surface of the sample (e.g., Figure 4D The detection points 102_1S, 102_2S and 102_3S are formed on the surface 7 of the image processing apparatus. The horizontal separation distance between the intermediate real images 102_1i, 102_2i and 102_3i can be adjusted in step 850 to change the spacing between the detection points. If the spacing between the detection points is too small, the crosstalk between adjacent beams may affect the size of the beams, thereby affecting the imaging resolution.

[0149] In step 880, the secondary electrons may be deflected by a beam splitter so as to be directed toward a secondary imaging system (e.g., Figure 2A The beam splitter can be controlled so that the secondary electron beam (e.g., Figure 2AThe secondary electron beams 102_1se, 102_2se, and 102_3se) are deflected toward the secondary imaging system. The secondary imaging system can then focus the secondary electron beams onto an electron detection device (e.g., Figure 2A The electronic detection device 140M) has a detection element (for example, Figure 2A on the detection elements 140_1, 140_2 and 140_3).

[0150] In step 890, an image of the detection area of ​​the sample may be constructed. For example, the detection elements 140_1, 140_2 and 140_3 may detect corresponding secondary electron beams and generate corresponding signals that may be sent to a signal processing unit to construct an image of a corresponding scanned area of ​​the sample.

[0151] The embodiments may be further described using the following terms:

[0152] 1. A charged particle optical system comprising:

[0153] a first deflector array configured to deflect a plurality of beam waves of a primary charged particle beam generated by a source;

[0154] a first lens configured to focus the plurality of beams to form a plurality of images of the source on an image plane; and

[0155] The objective lens is configured to project the multiple images onto the sample and form multiple detection points on the sample.

[0156] 2. The charged particle optical system according to clause 1, further comprising:

[0157] A beam splitter is configured to separate the plurality of beams and secondary charged particles emitted from the sample as a result of the illumination of the plurality of detection points.

[0158] 3. A charged particle optical system according to clause 2, wherein the image plane is at least near the beam splitter.

[0159] 4. A charged particle optical system according to clause 3, wherein the deflection angles of the multiple beams deflected by the first deflector array are set to obtain a predetermined spacing between the multiple detection points and reduce the aberrations of the multiple detection points.

[0160] 5. The charged particle optical system according to any one of clauses 1 to 4, further comprising a first aperture array, which is above the first deflector array and is configured to limit the current of the plurality of detection points.

[0161] 6. The charged particle optical system according to clause 5, further comprising a second lens, the second lens being between the charged particle source and the first aperture array and configured to focus the primary charged particle beam.

[0162] 7. A charged particle optical system according to clause 6, wherein the second lens is configured to focus the primary charged particle beam into a parallel beam.

[0163] 8. A charged particle optical system according to clause 7, wherein the second lens is a movable lens configured to change the current at the plurality of detection points.

[0164] 9. A charged particle optical system according to clause 7 or clause 8, further comprising a compensator array configured to compensate for aberrations of the plurality of detection points.

[0165] 10. A charged particle optical system according to any one of clauses 7 to 9, further comprising a main aperture, which is above the second lens, close to the source, and configured to cut off the peripheral portion of the primary charged particle beam that is not used in the multiple beam waves.

[0166] 11. The charged particle optical system according to clause 10, further comprising a second aperture array, the second aperture array being between the main aperture and the first aperture array and being configured to cut off a portion of the primary charged particle beam that is not used in the plurality of beam waves.

[0167] 12. A charged particle optical system according to clause 11, wherein the second aperture array is above the second lens and close to the source.

[0168] 13. The charged particle optical system according to clause 9 further comprises a second aperture array, which is above the second lens, close to the source, and configured to cut off the portion of the primary charged particle beam that is not used in the multiple beam waves.

[0169] 14. The charged particle optical system of clause 6, further comprising a second deflector array configured to deflect the plurality of beam waves to be perpendicularly incident on the first aperture array.

[0170] 15. The charged particle optical system according to clause 14, further comprising a compensator array configured to compensate for aberrations of the plurality of detection points.

[0171] 16. The charged particle optical system according to clause 15, further comprising a main aperture, which is above the second lens, close to the source, and configured to cut off a peripheral portion of the primary charged particle beam that is not used in the plurality of beam waves.

[0172] 17. The charged particle optical system according to clause 16, further comprising a second aperture array, the second aperture array being between the main aperture and the first aperture array and being configured to cut off a portion of the primary charged particle beam that is not used in the plurality of beam waves.

[0173] 18. A charged particle optical system according to clause 17, wherein the second aperture array is above the second lens and close to the source.

[0174] 19. A charged particle optical system according to clause 17, wherein the second aperture array is below the second lens.

[0175] 20. The charged particle optical system of clause 15, further comprising a second aperture array above the second lens, proximate to the source, and configured to cut off portions of the primary charged particle beam that are not used in the plurality of beam waves.

[0176] 21. A charged particle optical system according to any one of clauses 18 or 19, wherein the second lens is an anti-rotation lens, which is configured to change the current of the multiple beam waves below the first aperture array and keep the rotation angle of the multiple beam waves on the first aperture array unchanged.

[0177] 22. A charged particle optical system according to any one of clauses 12, 13 or 21, wherein the first lens is a movable lens configured to change the spacing of the plurality of detection points.

[0178] 23. A charged particle optical system according to any one of clauses 1, 12, 13 or 21, wherein the image plane is configured to ensure that the sizes of the multiple detection points increase relatively within 20% due to the dispersion of the beam splitter on the multiple beam waves.

[0179] 24. A charged particle optical system according to clause 23, wherein the image plane is at a deflection plane of the beam splitter.

[0180] 25. A charged particle optical system comprising:

[0181] A first deflector configured to deflect a beam wave of a charged particle beam generated by a charged particle source; and

[0182] A first lens is configured to focus the beam to form an image of a charged particle source on an image plane within a region of a beam splitter, wherein the beam splitter is configured to separate the beam and secondary charged particles generated from the sample in response to the charged particles of the beam interacting with the sample.

[0183] 26. A charged particle optical system according to clause 25, wherein

[0184] The first deflector is configured to deflect the beam toward an optical axis of the system.

[0185] 27. A charged particle optical system according to clause 25, wherein

[0186] The first deflector is configured to deflect the beam outwardly from an optical axis of the system.

[0187] 28. A method for forming a plurality of detection points on a sample, the method comprising:

[0188] deflecting a plurality of beams of a light beam generated by a charged particle source;

[0189] focusing the plurality of beams by a lens to form a plurality of images of the source on an image plane; and

[0190] The plurality of images are projected onto the sample to form a plurality of detection points on the sample.

[0191] 29. The method according to clause 28, further comprising:

[0192] The plurality of beams and secondary charged particles generated from the sample as a result of the illumination of the plurality of detection points are separated by a beam splitter.

[0193] 30. The method of clause 29, wherein the image plane is at or near a deflection plane of the beam splitter.

[0194] 31. The method according to clause 30, further comprising:

[0195] The current of the plurality of detection points is limited by the first aperture array.

[0196] 32. The method according to clause 31, further comprising:

[0197] The current is varied by changing the focus state of the light beam.

[0198] 33. The method according to clause 32, further comprising:

[0199] Portions of the light beam not used in the plurality of detection points are trimmed by a second aperture array above the first aperture array.

[0200] 34. A method according to clause 33, wherein the second aperture array is proximate to the source.

[0201] 35. The method according to clause 30, further comprising:

[0202] The intervals between the plurality of detection points are changed by changing the deflection angles of the plurality of beams.

[0203] 36. The method according to clause 30, further comprising:

[0204] The spacing between the plurality of detection points is changed by moving the main plane of the lens.

[0205] 37. The method according to clause 30, further comprising:

[0206] The spacing between the plurality of detection points is changed by moving the image plane.

[0207] 38. A charged particle optical system according to clause 4, wherein the spacings of the plurality of detection points are different from each other.

[0208] 39. A charged particle optical system according to clause 22, wherein the spacings of the plurality of detection points are different from each other.

[0209] 40. A charged particle optical system according to clause 4, wherein the plurality of detection points are equidistant from one another.

[0210] 41. A charged particle optical system according to clause 22, wherein the plurality of detection points are equidistant from one another.

[0211] 42. The method according to clause 35, wherein the spacings of the plurality of detection points are different from each other.

[0212] 43. A method according to clause 36 or clause 37, wherein the spacings of the plurality of detection points are different from each other.

[0213] 44. The method according to clause 34, wherein the plurality of detection points are spaced equally apart from one another.

[0214] 45. A method according to clause 36 or clause 37, wherein the plurality of detection points are spaced equally apart from one another.

[0215] 46. ​​A multi-beam device comprising:

[0216] a first lens configured to focus a plurality of beams to form a plurality of images of a charged particle source on an image plane formed closer to the first lens than a charged particle separator configured to separate primary charged particles of the plurality of beams and secondary charged particles emitted from a sample; and

[0217] An objective lens is configured to project the multiple images onto the sample and form multiple detection points on the sample.

[0218] 47. The apparatus according to clause 46 further comprises a first deflector array configured to deflect at least one of the plurality of beamlets of the primary charged particle beam radially outward from the main optical axis and incident on the first lens.

[0219] 48. The apparatus according to clause 47 further comprises a first aperture array, the first aperture array being disposed between the first deflector array and the charged particle source and configured to limit detection currents of the plurality of beam waves.

[0220] 49. An apparatus according to any of clauses 46 to 48, further comprising a charged particle dispersion compensator configured to compensate for dispersion caused by the charged particle separator.

[0221] 50. The apparatus of clause 49, wherein the charged particle dispersion compensator is disposed between the charged particle separator and the first lens.

[0222] 51. A device according to any of clauses 49 and 50, wherein the image plane is formed between the charged particle dispersion compensator and the first lens.

[0223] 52. An apparatus according to any one of clauses 46 to 51, wherein the first lens is an adjustable lens configured to adjust the magnification of the plurality of beams by adjusting the position of the formed image plane.

[0224] 53. The apparatus of clause 52, wherein the magnification is based on a ratio of a size of one of the plurality of detection points to a size of a corresponding beamlet in the plurality of beamlets.

[0225] 54. An apparatus according to any one of clauses 46 to 53, wherein the first lens is configured to form the image plane between the first lens and the charged particle separator.

[0226] 55. A device according to any of clauses 47 to 54, wherein the image plane is formed perpendicular to the main optical axis of the primary charged particle beam and between the first lens and the charged particle separator.

[0227] 56. The apparatus of any one of clauses 47 to 55, further comprising a second lens disposed between the charged particle source and the first lens and configured to focus the primary charged particle beam.

[0228] 57. A device according to clause 56, wherein the second lens is a movable lens, which is arranged on a main plane perpendicular to the main optical axis of the primary charged particle beam.

[0229] 58. The apparatus of clause 57, wherein a principal plane of the second lens is adjusted along the principal optical axis to adjust the detection currents of the plurality of beams.

[0230] 59. The apparatus of any one of clauses 56 to 58, further comprising an aperture plate disposed between the charged particle source and the second lens and configured to block a peripheral portion of the primary charged particle beam.

[0231] 60. The apparatus of any one of clauses 56 to 59, further comprising a second aperture array disposed between the aperture plate and the second lens and configured to generate the plurality of beam waves from the primary charged particle beam.

[0232] 61. A device according to any of clauses 56 to 60, wherein the first lens is arranged between the second lens and the charged particle separator.

[0233] 62. A multi-beam device comprising:

[0234] a first deflector array configured to deflect a plurality of beam waves of the primary charged particle beam;

[0235] a first lens configured to focus the plurality of beams to form a plurality of images of a charged particle source on an image plane formed closer to the first lens than a charged particle separator configured to separate primary charged particles of the plurality of beams and secondary charged particles emitted from a sample; and

[0236] An objective lens is configured to project the multiple images onto the sample and form multiple detection points on the sample.

[0237] 63. An apparatus according to clause 62, wherein the first deflector array is configured to collimate at least one of the plurality of beamlets to be substantially parallel to a principal optical axis of the primary charged particle beam.

[0238] 64. The device according to any one of clauses 62 and 63 further comprises an aperture plate disposed between the charged particle source and the first deflector array and configured to block a peripheral portion of the primary charged particle beam.

[0239] 65. A device according to any of clauses 63 and 64, wherein the image plane is formed perpendicular to the main optical axis of the primary charged particle beam and between the first lens and the charged particle separator.

[0240] 66. The device according to any one of clauses 63 to 65 further includes a second deflector array, which is arranged between the first deflector array and the first lens and is configured to deflect at least one of the multiple beam waves radially outward from the main optical axis and impinge on the first lens.

[0241] 67. An apparatus according to any one of clauses 62 to 66, wherein the first lens is configured to form the image plane between the first lens and the charged particle separator.

[0242] 68. The apparatus of any one of clauses 62 to 67, further comprising a first aperture array disposed between the first lens and the charged particle source and configured to limit detection currents of the plurality of beam waves.

[0243] 69. An apparatus according to any one of clauses 62 to 68, wherein the first lens is an adjustable lens configured to adjust the magnification of the multiple beams by adjusting the position of the formed image plane.

[0244] 70. The apparatus of clause 69, wherein the magnification is based on a ratio of a size of one of the plurality of detection points to a size of a corresponding beamlet of the plurality of beamlets.

[0245] 71. An apparatus according to any of clauses 62 to 70, further comprising a charged particle dispersion compensator configured to compensate for dispersion caused by the charged particle separator.

[0246] 72. An apparatus according to clause 71, wherein the charged particle dispersion compensator is disposed between the charged particle separator and the first lens.

[0247] 73. A device according to any of clauses 71 and 72, wherein the image plane is formed between the charged particle dispersion compensator and the first lens.

[0248] 74. The apparatus of any one of clauses 62 to 73, further comprising a second lens disposed between the charged particle source and the first lens and configured to focus the primary charged particle beam.

[0249] 75. A device according to clause 74, wherein the second lens is a movable lens arranged in a main plane perpendicular to the main optical axis of the primary charged particle beam.

[0250] 76. An apparatus according to clause 75, wherein the principal plane of the second lens is adjusted along the principal optical axis to adjust the detection current of the multiple beams.

[0251] 77. A device according to any of clauses 74 to 76, wherein the first lens is arranged between the second lens and the charged particle separator.

[0252] 78. The apparatus of any one of clauses 74 to 77, further comprising a second aperture array disposed between the aperture plate and the second lens and configured to generate the plurality of beam waves from the primary charged particle beam.

[0253] 79. A method of observing a sample using a multi-beam apparatus, the method comprising:

[0254] focusing the plurality of beams using a first lens to form a plurality of images of a charged particle source on an image plane formed closer to the first lens than to a charged particle separator; and

[0255] Using an objective mirror, the multiple images are projected onto the sample and multiple detection points are formed on the sample.

[0256] 80. The method of clause 79, further comprising deflecting at least one of the plurality of beamlets radially outward from a primary optical axis of the primary charged particle beam and incident on the first lens using a first deflector array.

[0257] 81. A method according to clause 80, wherein the image plane is formed perpendicular to the main optical axis of the primary charged particle beam and between the first lens and the charged particle separator.

[0258] 82. The method of any one of clauses 80 and 81, further comprising focusing the primary charged particle beam using a second lens disposed between the charged particle source and the first lens.

[0259] 83. The method of clause 82, further comprising adjusting a position of a principal plane of the second lens along the principal optical axis to adjust detection currents of the plurality of beams.

[0260] 84. The method according to any one of clauses 82 and 83, further comprising blocking a peripheral portion of the primary charged particle beam using an aperture plate disposed between the charged particle source and the second lens.

[0261] 85. The method of clause 84, further comprising forming the plurality of beam waves from the primary charged particle beam using a second aperture array disposed between the aperture plate and the second lens.

[0262] 86. The method of any one of clauses 79 to 85, further comprising compensating for dispersion caused by the charged particle separator using a charged particle dispersion compensator.

[0263] 87. A method according to any one of clauses 79 to 86, wherein the image plane is formed between the charged particle dispersion compensator and the first lens.

[0264] 88. The method according to any one of clauses 80 to 87 further comprises limiting the detection current of the plurality of beam waves using a first aperture array disposed between the first deflector array and the charged particle source.

[0265] 89. The method of any one of clauses 79 to 88, further comprising adjusting a magnification of the plurality of beams by adjusting the first lens.

[0266] 90. A method according to clause 89, wherein adjusting the first lens includes at least adjusting electrical excitation of the first lens to change the position of an image plane formed perpendicular to the primary optical axis.

[0267] 91. A method according to any of clauses 89 and 90, wherein the magnification is determined based on a ratio of a size of one of the plurality of detection points to a size of a corresponding beamlet in the plurality of beamlets.

[0268] 92. An apparatus according to clause 55, wherein a vertical distance between the image plane and the first lens is less than a vertical distance between the image plane and the charged particle separator.

[0269] 93. An apparatus according to clause 65, wherein a vertical distance between the image plane and the first lens is less than a vertical distance between the image plane and the charged particle separator.

[0270] In some embodiments, the controller can control the charged particle beam system. The controller can instruct the components of the charged particle beam system to perform various functions, such as controlling the charged particle source to generate a charged particle beam and controlling the deflector to scan the charged particle beam over the entire sample. The controller can also perform various post-processing functions, image acquisition, image segmentation, image processing, generating contours, superimposing indicators on the acquired images, etc. The controller may include a storage device, which is a storage medium, such as a hard disk, a cloud storage, a random access memory (RAM), other types of computer-readable memory, etc. The storage device can be used to save the scanned raw image data as a raw image, or to save a post-processed image. The controller can communicate with a cloud storage device. A non-transient computer-readable medium can be provided, which stores instructions for the processor of the controller 19 to perform beamforming or other functions and methods consistent with the present disclosure. Common forms of non-transitory media include, for example, floppy disks, flexible disks, hard disks, solid-state drives, magnetic tapes or any other magnetic data storage medium, CD-ROMs, any other optical data storage medium, any physical medium with a pattern of holes, RAM, PROM and EPROM, FLASH-EPROM or any other flash memory, NVRAM, cache, registers, any other memory chip or cartridge, and networked versions thereof.

[0271] The block diagrams in the accompanying drawings illustrate possible implementations of the architecture, functions, and operations of systems, methods, and computer hardware or software products according to various exemplary embodiments of the present disclosure. In this regard, each box in the schematic diagram may represent certain arithmetic or logic operations that can be implemented using hardware such as electronic circuits. The box may also represent a module, segment, or portion of a code that includes one or more executable instructions for implementing the specified logical functions. It should be understood that in some alternative implementations, the functions indicated in the box may not occur in the order indicated in the figure. For example, depending on the functions involved, two boxes shown in succession may be executed or implemented substantially simultaneously, or two boxes may sometimes be executed in the opposite order. Some boxes may also be omitted. For example, when the focusing lens is configured to form a parallel beam, it may not be necessary to deflect the beam before entering the beam limiting aperture array 121 as in step S720, so step S720 may be omitted. In addition, steps such as compensating for astigmatism or other steps may be added. It should also be understood that each box of the block diagram and the combination of these boxes may be implemented by a dedicated hardware-based system that performs the specified functions or actions, or may be implemented by a combination of dedicated hardware and computer instructions.

[0272] Although the present invention has been described with respect to some exemplary embodiments, it should be understood that other modifications and variations may be made without departing from the spirit and scope of the present invention as claimed below. For example, one or more lenses or other optical components may be added to the particular configuration of the exemplary particle optical systems discussed herein at various points. Optical components may be provided for purposes such as magnification, zooming, and image anti-rotation, etc.

Claims

1. A charged particle optical system comprising: a first deflector array configured to deflect a plurality of beam waves of a primary charged particle beam generated by a source; a first lens configured to focus the plurality of beams to form a plurality of images of the source on an image plane; an objective lens configured to project the plurality of images onto a sample and form a plurality of detection spots on the sample; as well as a beam splitter configured to separate the plurality of beamlets of the primary charged particle beam and secondary charged particles emitted from the sample as a result of the illumination of the plurality of detection points, Wherein the image plane is at least in the vicinity of the beam splitter.

2. A charged particle optical system according to claim 1, wherein the first deflector array is configured to deflect the multiple beam waves at a deflection angle, and the deflection angle is set to obtain a predetermined spacing between the multiple detection points and reduce the aberration of the multiple detection points.

3. The charged particle optical system according to claim 1 further comprises a first aperture array, which is above the first deflector array and is configured to limit the current of the plurality of detection points. 4 . The charged particle optical system of claim 3 , further comprising a second lens between the source and the first aperture array and configured to focus the primary charged particle beam. 5 . The charged particle optical system according to claim 4 , wherein the second lens is configured to focus the primary charged particle beam into a parallel beam.

6. The charged-particle optical system of claim 5, wherein the second lens is a movable lens configured to vary the current at the plurality of detection points.

7. The charged particle optical system of claim 5, further comprising a compensator array configured to compensate for aberrations of the plurality of detection points.

8. The charged particle optical system of claim 5, further comprising a main aperture above the second lens, close to the source, and configured to cut off a peripheral portion of the primary charged particle beam that is not used in the plurality of beam waves.

9. The charged particle optical system of claim 8, further comprising a second aperture array between the main aperture and the first aperture array and configured to cut off portions of the primary charged particle beam that are not used in the plurality of beam waves.

10. The charged particle optical system of claim 9, wherein the second aperture array is above the second lens and close to the source.

11. The charged particle optical system of claim 7, further comprising a second aperture array above the second lens, proximate the source, and configured to cut off portions of the primary charged particle beam that are not used in the plurality of beam waves.

12. The charged particle optical system of claim 4, further comprising a second deflector array configured to deflect the plurality of beam waves to be normally incident on the first aperture array.

13. A method for forming a plurality of detection points on a sample, the method comprising: deflecting a plurality of beams of a light beam generated by a charged particle source; focusing the plurality of beams by a lens to form a plurality of images of the source on an image plane; projecting the plurality of images onto a sample to form a plurality of detection points on the sample; as well as The lens is adjusted so that the image plane is at least in the vicinity of a beam splitter configured to separate the plurality of beamlets of the light beam and secondary electrons emitted from the sample as a result of illumination by the plurality of detection points.

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