Multiple charged particle beam device with low crosstalk

Abstract

Disclosed are systems and methods for enhancing imaging resolution by reducing crosstalk between detection elements of a secondary charged particle detector in a multi-beam device. The multi-beam device includes an electro-optical system for projecting multiple secondary charged particle beams from a sample onto a charged particle detector (140). The electro-optical system includes a first pre-limiting aperture plate (155P) and a beam limiting aperture array (155), wherein the first pre-limiting aperture plate (155P) includes a first aperture configured to block peripheral charged particles of the multiple secondary charged particle beams; and the beam limiting aperture array (155) includes a second aperture configured to trim the multiple secondary charged particle beams. The charged particle detector may include multiple detection elements (140_1, 140_2, 140_3), wherein one of the multiple detection elements is associated with a corresponding trimmed beam of the multiple secondary charged particle beams.

Description

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims priority to U.S. Application No. 62 / 853,677, filed May 28, 2019, and which is incorporated herein by reference in its entirety. Technical Field

[0003] Embodiments provided herein disclose a multi-beam apparatus, and more particularly disclose a multi-beam charged particle microscope with enhanced imaging signal fidelity using a combination of aperture arrays configured to reduce crosstalk. 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 size of IC assemblies continues to shrink, the accuracy and yield of defect detection become more important. Although multiple electron beams may be used to increase throughput, limitations in the fidelity of the imaging signals received by charged particle detectors may limit the imaging resolution desired for reliable defect detection and analysis, rendering the inspection tool inadequate for its intended purpose. Summary of the invention

[0005] In some embodiments of the present disclosure, an electro-optical system of a multiple charged particle beam device is disclosed. The electro-optical system may include a first pre-limiting aperture plate and a beam limiting aperture array, the first pre-limiting aperture plate including a first aperture configured to block peripheral charged particles of multiple secondary charged particle beams from a sample; the beam limiting aperture array including a second aperture configured to trim the multiple secondary charged particle beams. The electro-optical system may also include a charged particle detector, the charged particle detector including a plurality of detection elements, wherein a detection element in the plurality of detection elements is associated with a corresponding trimmed beam in the plurality of secondary charged particle beams.

[0006] The distance between the first pre-limiting aperture plate and the beam limiting aperture array may be 5 mm or less. The first pre-limiting aperture plate may be positioned upstream or downstream of the beam limiting aperture array. The electro-optical system may include a second pre-limiting aperture plate. The first pre-limiting aperture plate may be positioned upstream of the beam limiting aperture array and the second pre-limiting aperture plate may be positioned downstream of the beam limiting aperture array. The beam limiting aperture array may include a plurality of apertures of different sizes. At least two of the plurality of apertures may have similar sizes. The plurality of apertures may be arranged in a rectangular, circular or spiral pattern.

[0007] The multiple secondary charged particle beams may include at least one of the following: secondary electrons or backscattered electrons from the sample generated in response to the interaction between the multiple primary charged particle beams and the sample. The multiple secondary charged particle beams may overlap to create an intersection region on an intersection plane perpendicular to the secondary optical axis of the electro-optical system. The beam limiting aperture array may be placed at the position of the intersection plane or within the range of the position of the intersection plane and be placed perpendicular to the secondary optical axis. The range of the position of the intersection plane may be determined based on the landing energy of the multiple primary charged particle beams on the sample. The beam limiting aperture array may be moved along the secondary optical axis based on the range of the position of the intersection plane.

[0008] The second aperture may be centered at the intersection region. The centers of the first aperture and the second aperture may be aligned with the secondary optical axis. The beam limiting aperture array may be movable to align an aperture of the plurality of apertures with the intersection region. The plane of the first pre-limiting aperture plate may be outside the range of the position of the intersection plane, and the planes of the beam limiting aperture array and the first pre-limiting aperture plate may be within the range of the position of the intersection plane.

[0009] In another embodiment of the present disclosure, a multi-charged particle beam device is disclosed. The multi-charged particle beam device may include an electro-optical system for projecting multiple secondary charged particle beams from a sample onto a charged particle detector. The electro-optical system may include a first pre-limiting aperture plate and a beam limiting aperture array, the first pre-limiting aperture plate including a first aperture configured to block peripheral charged particles of the multiple secondary charged particle beams; the beam limiting aperture array including a second aperture configured to trim the multiple secondary charged particle beams. The charged particle detector may include a plurality of detection elements, and a detection element of the plurality of detection elements may be associated with a corresponding trimmed beam of the multiple secondary charged particle beams.

[0010] In some embodiments of the present disclosure, a method performed by a secondary imaging system to form an image of a sample may be disclosed. The method may include generating multiple secondary charged particle beams from the sample, using a predetermined aperture plate to block peripheral charged particles of the multiple secondary charged particle beams, using the aperture of a beam limiting aperture array to trim the multiple secondary charged particle beams; and projecting the trimmed multiple secondary charged particle beams onto corresponding detection elements of a charged particle detector.

[0011] Other advantages of the disclosed embodiments will become apparent from the following description taken in conjunction with the accompanying drawings, in which certain embodiments of the invention are set forth by way of illustration and example. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] Figure 1is a schematic diagram illustrating an exemplary electron beam inspection (EBI) system consistent with embodiments of the present disclosure.

[0013] Figure 2 is a schematic diagram illustrating an exemplary electron beam tool consistent with embodiments of the present disclosure, which may be Figure 1 A portion of an exemplary electron beam inspection system.

[0014] Figure 3 is a schematic diagram illustrating an exemplary configuration of a secondary imaging system in a multi-beam device consistent with an embodiment of the present disclosure.

[0015] Figure 4 It is a diagram consistent with the embodiment of the present disclosure Figure 3 Schematic diagram of an exemplary arrangement of apertures on an aperture array of a secondary imaging system.

[0016] Figure 5 is a schematic diagram illustrating an exemplary configuration of a secondary imaging system in a multi-beam device consistent with an embodiment of the present disclosure.

[0017] FIG. 6A to FIG. 6D It is a diagram consistent with the embodiment of the present disclosure Figure 5 Schematic diagram of an exemplary arrangement of apertures of an aperture array of a secondary imaging system.

[0018] Figure 7 is a schematic diagram illustrating an exemplary configuration of a secondary imaging system in a multi-beam device consistent with an embodiment of the present disclosure.

[0019] Figure 8 is a schematic diagram illustrating an exemplary configuration of a secondary imaging system in a multi-beam device consistent with an embodiment of the present disclosure.

[0020] Fig. 9 It indicates the use consistent with the embodiments of the present disclosure. Figure 5 A process flow chart of an exemplary method for detecting secondary charged particles from a sample using a secondary imaging system. DETAILED DESCRIPTION

[0021] Reference will now be made in detail to exemplary embodiments, examples of which are illustrated in the accompanying drawings. The following descriptions all refer to the accompanying drawings, and unless otherwise specified, the same reference numerals 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. Instead, they are merely examples of devices and methods consistent with the various aspects related to the disclosed embodiments as recorded 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 can be similarly applied. In addition, other imaging systems such as optical imaging, light detection, X-ray detection, etc. can be used.

[0022] Electronic devices consist of circuits formed on a silicon chip called a substrate. Many circuits can be formed together on the same silicon chip and are called an integrated circuit or IC. The size of these circuits has been greatly reduced so that more circuits can be assembled on a substrate. For example, the IC chip in a smartphone may be as small as a thumbnail, but may include more than 2 billion transistors, each less than 1 / 1000 the size of a human hair.

[0023] 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 unusable. Therefore, one goal of the manufacturing process is to avoid such defects in order to maximize the number of functional ICs made in the process, i.e., to increase the overall yield of the process.

[0024] 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 scanning electron microscope (SEM). The SEM can be used to image these extremely small structures, in effect taking a "photo" of the structure. The image can be used to determine if the structure was formed correctly and if it was formed in the correct location. If the structure is defective, then the process can be adjusted to make the defect less likely to occur again.

[0025] Although multi-beam charged particle imaging systems such as multi-beam SEMs can be used to increase wafer inspection throughput, the imaging resolution of multi-beam SEMs may be limited by the quality of the imaging signal received and detected by the secondary electron detection system. Secondary charged particle beams such as electron beams are generated by the interaction of primary beamlets on the sample surface and may contain secondary electrons with a large energy spread of ~50eV and a large emission angle range of ~90° relative to the normal of the sample surface. Such defocused electron beams may have a large incident spot on the secondary electron detector. In a conventional multi-beam SEM, the defocused electron beam may be incident on multiple detection elements of the secondary electron detector. In other words, each of the multiple detection elements may receive secondary electrons from the corresponding secondary electron beam and other adjacent beams. Therefore, the imaging signal of one detection element may include a main component originating from the corresponding secondary electron beam and a crosstalk component originating from an adjacent electron beam. Among other things, the crosstalk component may deteriorate the fidelity of the imaging signal. Therefore, it is desirable to minimize the crosstalk between multiple detection elements to improve the imaging resolution.

[0026] In order to reduce the occurrence of crosstalk, an aperture mechanism can be used in the secondary imaging system to block peripheral secondary electrons. However, if the radius of the secondary electron beam is larger than the distance between the two apertures of the aperture mechanism, some electrons of the secondary electron beam may escape through adjacent apertures, thereby causing crosstalk between the detection elements of the secondary electron detector.

[0027] To accommodate the large radius of the secondary electron beam, the aperture can be placed farther away and the aperture mechanism can be moved in the x-axis and y-axis relative to the optical axis (z-axis) of the secondary imaging system. However, due to space limitations within the secondary imaging system, the movement of the aperture mechanism in the x- and y-axes may be limited, and therefore the number of apertures within the aperture array may be limited. One of the several problems that may be encountered is that the aperture mechanism may not be able to mitigate crosstalk while allowing the maximum number of secondary electrons to pass through to enhance imaging resolution.

[0028] In some embodiments of the present disclosure, a multi-beam device may include an electro-optical system for projecting multiple secondary electrons from a sample onto a charged particle detector. The electro-optical system may include a pre-limiting aperture plate configured to block peripheral secondary electrons, and a beam-limiting aperture array configured to trim the aperture of the multiple secondary electrons. The pre-limiting aperture plate may be positioned upstream of the beam-limiting aperture array, and may prevent the peripheral secondary electrons from irradiating unintended apertures of the beam-limiting aperture array, and the beam-limiting aperture array may further prevent the peripheral secondary electrons from irradiating detection elements of the detection electron detector. The combination of the pre-limiting aperture plate and the beam-limiting aperture array may mitigate crosstalk between detection elements, thereby enhancing imaging resolution.

[0029] For clarity, the relative sizes of the components in the drawings may be exaggerated. In the following description of the drawings, the same or similar reference numerals refer to the same or similar components or entities, and only describe the differences related to each embodiment. As used herein, unless otherwise specifically stated, the term "or" covers all possible combinations unless not feasible. For example, if a component is stated to include A or B, then unless otherwise clearly stated or not feasible, the component may include A, or B, or A and B. As a second example, if a component is stated to include A, B, or C, then unless otherwise clearly stated 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.

[0030] Now to Figure 1 Reference is made to , which illustrates an exemplary electron beam inspection (EBI) system 100 consistent with embodiments of the present disclosure. Figure 1 As shown in FIG, a charged particle beam detection system 100 includes a main chamber 10, a load lock chamber 20, an electron beam tool 40, and an equipment front end module (EFEM) 30. The electron beam tool 40 is positioned within the main chamber 10. Although the description and drawings are directed to electron beams, it should be understood that the embodiments are not intended to limit the present disclosure to specific charged particles.

[0031] The EFEM 30 includes a first loading port 30a and a second loading port 30b. The EFEM 30 may include additional (one or more) loading ports. The first loading port 30a and the second loading port 30b receive wafer front opening unified containers (FOUPs) containing wafers (e.g., semiconductor wafers or wafers made of (one or more) other materials) or samples to be inspected (wafers and samples are collectively referred to as "wafers" hereinafter). One or more robotic arms (not shown) in the EFEM 30 transfer the wafers to the load lock chamber 20.

[0032] The 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) transfer the wafer from the load lock chamber 20 to the main chamber 10. The main chamber 10 is connected to a main chamber vacuum pump system (not shown) that removes gas molecules in the main chamber 10 to reach a second pressure below the first pressure. After reaching the second pressure, the wafer is subjected to inspection by an electron beam tool 40. In some embodiments, the electron beam tool 40 may include a single beam inspection tool. In other embodiments, the electron beam tool 40 may include a multi-beam inspection tool.

[0033] The controller 50 may be electrically connected to the electron beam tool 40 and may also be electrically connected to other components. The controller 50 may be a computer configured to perform various controls of the charged particle beam inspection system 100. The controller 50 may also include processing circuits configured to perform various signal and image processing functions. Figure 1 Controller 50 is shown outside the structure including main chamber 10, load lock chamber 20 and EFEM 30, but it should be understood that controller 50 may be part of the structure.

[0034] Although the present disclosure provides an example of a main chamber 10 housing an electron beam inspection system, it should be noted that aspects of the present disclosure in its broadest sense are not limited to chambers housing electron beam inspection systems. Rather, it should be understood that the aforementioned principles may also be applied to other chambers.

[0035] Now to Figure 2 Reference is made to a schematic diagram consistent with an embodiment of the present disclosure, which illustrates an exemplary electron beam tool 40, which may be Figure 1 The electron beam tool 40 (also referred to herein as the device 40) includes an electron source 101, a gun aperture plate 171 having a gun aperture 103, a pre-beamlet forming mechanism 172, a condenser lens 110, a source conversion unit 120, a primary projection optical system 130, a sample stage ( Figure 2 ), a secondary imaging system 150 and an electronic detection device 140. The primary projection optical system 130 may include an objective lens 131. The electronic detection device 140 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 main projection optical system 130. It can be appreciated that other known components of the device 40 may be appropriately added / omitted.

[0036] The electron source 101, the gun 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 may be aligned with the primary optical axis 100_1 of the device 100. The secondary imaging system 150 and the electron detection device 140 may be aligned with the secondary optical axis 150_1 of the device 40.

[0037] The electron source 101 may include a cathode, an extractor or an anode, wherein primary electrons may be emitted from the cathode and extracted or accelerated to form a primary electron beam 102, which forms a crossbar (virtual or real) 101s. The primary electron beam 102 may be visualized as emitted from the crossbar 101s.

[0038] The source conversion unit 120 may include an imaging element array ( Figure 2 ), an aberration compensator array (not shown), a beam limiting aperture array (not shown) and a pre-bent micro-deflector array (not shown). The imaging element array may include a plurality of micro-deflectors or micro-lenses to form a plurality of parallel images (virtual or real) of the cross 101s with the beamlets of the plurality of primary electron beams 102. Figure 2 While three beamlets 102_1 , 102_2 , and 102_3 are shown as an example, it will be appreciated that the source conversion unit 120 may process any number of beamlets.

[0039] In some embodiments, the source conversion unit 120 may be provided with a beam limiting aperture array and an imaging element array (neither of which is shown). The beam limiting aperture array may include a beam limiting aperture. It should be understood that any number of apertures may be used appropriately. The beam limiting aperture may be configured to limit the size of the beamlets 102_1, 102_2, and 102_3 of the primary electron beam 102. The imaging element array may include an imaging deflector (not shown) configured to deflect the beamlets 102_1, 102_2, and 102_3 by changing the angle toward the main optical axis 100_1. In some embodiments, a deflector farther from the main optical axis 100_1 may deflect the beamlets to a greater extent. In addition, the imaging element array may include multiple layers (not shown), and the deflectors may be provided in separate layers. The deflectors may be configured to be individually controlled independently of each other. In some embodiments, the deflector can be controlled to adjust the spacing of the detection spots (e.g., 102_1S, 102_2S, and 102_3S) formed on the surface of the sample 1. As referred to herein, the spacing of the detection spots can be defined as the distance between two directly adjacent detection spots on the surface of the sample 1.

[0040] The centrally positioned deflector of the imaging element array may be aligned with the primary optical axis 100_1 of the electron beam tool 40. Thus, in some embodiments, the central deflector may be configured to keep the trajectory of the beamlet 102_1 straight. In some embodiments, the central deflector may be omitted. However, in some embodiments, the primary electron source 101 may not necessarily be aligned with the center of the source conversion unit 120. Furthermore, it should be understood that although Figure 2 A side view of the device 40 is shown, where the beamlet 102_1 is on the primary optical axis 100_1, which may deviate from the primary optical axis 100_1 when viewed from different sides. That is, in some embodiments, all beamlets 102_1, 102_2 and 102_3 may be off-axis. The off-axis component may be offset relative to the primary optical axis 100_1.

[0041] The deflection angle of the deflected beamlet can be set based on one or more criteria. In some embodiments, the deflector can deflect the off-axis beamlet radially outward or away from (not shown) the main optical axis 100_1. In some embodiments, the deflector can be configured to deflect the off-axis beamlet radially inward or toward the main optical axis 100_1. The deflection angle of the beamlet can be set so that the beamlets 102_1, 102_2 and 102_3 fall vertically on the sample 1. The off-axis aberration caused by the lens can be reduced by adjusting the path of the beamlet through the lens (such as the objective lens 131). Therefore, the deflection angle of the off-axis beamlets 102_2 and 102_3 can be set so that the detection spots 102_2S and 102_3S have small aberrations. The beamlets can be deflected so as to pass through or approach the front focus of the objective lens 131 to reduce the aberrations of the off-axis detection spots 102_2S and 102_3S. In some embodiments, the deflector may be arranged to make the beamlets 102_1 , 102_2 and 102_3 fall perpendicularly on the sample 1 , while the detection spots 102_1S, 102_2S and 102_3S have small aberrations.

[0042] The condenser lens 110 is configured to focus the primary electron beam 102. The current of the beamlets 102_1, 102_2 and 102_3 downstream of the source conversion unit 120 can be changed by adjusting the focusing power of the condenser lens 110 or by changing the radial size of the corresponding beam limiting apertures within the beam limiting aperture array. The current can be changed by changing both the radial size of the beam limiting aperture and the focusing power of the condenser lens 110. The condenser lens 110 can be an adjustable condenser lens, which can be configured so that the position of its first principal plane is movable. The adjustable condenser lens can be configured magnetically, which can cause the off-axis beamlets 102_2 and 102_3 to illuminate the source conversion unit 120 at a rotation angle. The rotation angle can change with the focusing power or the position of the first principal plane of the adjustable condenser lens. Therefore, the condenser lens 110 can be an anti-rotation condenser lens, which can be configured to keep the rotation angle unchanged when the focusing power of the condenser lens 110 changes. In some embodiments, the condenser lens 110 may be an adjustable anti-rotation condenser lens, wherein the rotation angle does not change when the focusing power and the position of the first principal plane of the condenser lens 110 are changed.

[0043] The electron beam tool 40 may include a pre-beamlet forming mechanism 172. In some embodiments, the electron source 101 may be configured to emit primary electrons and form a primary electron beam 102. In some embodiments, the gun aperture plate 171 may be configured to block peripheral electrons of the primary electron beam 102 to reduce the Coulomb effect. In some embodiments, the pre-beamlet forming mechanism 172 further cuts peripheral electrons of the primary electron beam 102 to further reduce the Coulomb effect. The primary electron beam 102 may be trimmed into three primary electron beamlets 102_1, 102_2, and 102_3 (or any other number of beamlets) after passing through the pre-beamlet forming mechanism 172. The electron source 101, the gun aperture plate 171, the pre-beamlet forming mechanism 172, and the condenser lens 110 may be aligned with the main optical axis 100_1 of the electron beam tool 40.

[0044] The pre-beamlet forming mechanism 172 may include a Coulomb aperture array. The central aperture (also referred to herein as the on-axis aperture) of the pre-beamlet forming mechanism 172 and the central deflector of the source conversion unit 120 may be aligned with the main optical axis 100_1 of the electron beam tool 40. The pre-beamlet forming mechanism 172 may be provided with a plurality of pre-trimmed apertures (e.g., a Coulomb aperture array). Figure 2 In the embodiment, three beamlets 102_1, 102_2 and 102_3 are generated when the primary electron beam 102 passes through the three pre-trimmed apertures, and most of the remaining parts of the primary electron beam 102 are cut off. That is, the pre-beamlet forming mechanism 172 can trim most or most of the electrons from the primary electron beam 102 that do not form the three beamlets 102_1, 102_2 and 102_3. The pre-beamlet forming mechanism 172 can cut off the electrons that will not be used to form the detection spots 102_1S, 102_2S and 102_3S in the end before the primary electron beam 102 enters the source conversion unit 120. In some embodiments, a gun hole plate 171 can be provided close to the electron source 101 to cut off the electrons at an early stage, and a pre-beamlet forming mechanism 172 can also be provided to further cut off the electrons around the multiple beamlets. Although Figure 2 Three apertures of the pre-beamlet forming mechanism 172 are shown, but it will be appreciated that any number of apertures may be suitable.

[0045] In some embodiments, the pre-beamlet forming mechanism 172 may be placed below the condenser lens 110. Placing the pre-beamlet forming mechanism 172 closer to the electron source 101 may more effectively reduce the Coulomb effect. In some embodiments, the gun aperture plate 171 may be omitted when the pre-beamlet forming mechanism 172 can be positioned close enough to the source 101 while still being manufacturable.

[0046] The objective lens 131 may be configured to focus the beamlets 102_1, 102_2, and 102_3 onto the sample 1 for inspection and may form three detection spots 102_1s, 102_2s, and 102_3s on the surface of the sample 1. The gun aperture plate 171 may block peripheral electrons of the primary electron beam 102 from being used to reduce the Coulomb interaction effect. The Coulomb interaction effect may enlarge the size of each of the detection spots 102_1s, 102_2s, and 102_3s and thus deteriorate the inspection resolution.

[0047] The beam splitter 160 may be a Wien filter type beam splitter that includes generating an electrostatic dipole field E1 and a magnetic dipole field B1 (both of which are not Figure 2 1 and 102_3). If they are applied, the force exerted by the electrostatic dipole field E1 on the electrons of the beamlets 102_1, 102_2 and 102_3 is equal in magnitude and opposite in direction to the force exerted by the magnetic dipole field B1 on the electrons. The beamlets 102_1, 102_2 and 102_3 can therefore pass directly through the beam splitter 160 at a zero deflection angle.

[0048] The deflection scanning unit 132 may deflect the beamlets 102_1, 102_2, and 102_3 to scan the detection spots 102_1s, 102_2s, and 102_3s over three small scanning areas in a portion of the surface of the sample 1. In response to the incidence of the beamlets 102_1, 102_2, and 102_3 at the detection spots 102_1s, 102_2s, and 102_3s, three secondary electron beams 102_1se, 102_2se, and 102_3se may be emitted from the sample 1. Each of the secondary electron beams 102_1se, 102_2s, and 102_3s may include electrons having an energy distribution including secondary electrons (energy <50 eV) and backscattered electrons (the energy sum between 50 eV and the landing energy of the beamlets 102_1, 102_2, and 102_3). The beam splitter 160 can direct the secondary electron beams 102_1se, 102_2se, and 102_3se toward the secondary imaging system 150. The secondary imaging system 150 can 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 140. The detection elements 140_1, 140_2, and 140_3 can detect the corresponding secondary electron beams 102_1se, 102_2se, and 102_3se and generate corresponding signals used to construct an image of the corresponding scanning area of ​​the sample 1.

[0049] exist Figure 2, three secondary electron beams 102_1se, 102_2se and 102_3se generated by three detection spots 102_1S, 102_2S and 102_3S, respectively, travel upward toward the electron source 101 along the main optical axis 100_1, and continuously pass through the objective lens deflection lens 11 and the deflection scanning unit 132. The three secondary electron beams 102_1se, 102_2se and 102_3se are turned by a beam splitter 160 (such as a Wien filter) to enter the secondary imaging system 150 along the secondary optical axis 150_1 of the secondary imaging system 150. The secondary imaging system 150 focuses the three secondary electron beams 102_1se to 102_3se onto an electron detection device 140 including three detection elements 140_1, 140_2 and 140_3. Therefore, the electronic detection device 140 can simultaneously generate images of three scanning areas scanned by the three detection spots 102_1S, 102_2S and 102_3S respectively. In some embodiments, the electronic detection device 140 and the secondary imaging system 150 form a detection unit (not shown). In some embodiments, the electron optical elements on the secondary electron beam path such as but not limited to the objective lens 131, the deflection scanning unit 132, the beam splitter 160, the secondary imaging system 150 and the electronic detection device 140 can form a detection system.

[0050] In some embodiments, the controller 50 may include an image processing system including an image collector (not shown) and a storage device (not shown). The image collector may include one or more processors. For example, the image collector may include a computer, a server, a mainframe, a terminal, a personal computer, any kind of mobile computing device, or the like, or a combination thereof. The image collector may be communicatively coupled to the electronic detection device 140 of the device 40 through a medium such as an electrical conductor, a fiber optic cable, a portable storage medium, IR, Bluetooth, the Internet, a wireless network, radio, or the like, or a combination thereof. In some embodiments, the image collector may receive a signal from the electronic detection device 140 and may construct an image. The image collector may thus collect an image of the sample 1. The image collector may also perform various post-processing functions, such as generating contours, superimposing indicators on the collected image, and the like. The image collector may be configured to perform adjustments such as brightness and contrast on the collected image. In some embodiments, the storage device may be a storage medium such as a hard disk, a flash drive, a cloud storage device, a random access memory (RAM), other types of computer-readable memory, and the like. The storage device may be coupled to the image collector and may be used to save scanned raw image data (as a raw image) and post-processed images.

[0051] In some embodiments, the image collector can acquire one or more images of the sample based on the imaging signal received from the electronic detection device 140. The imaging signal can correspond to a scanning operation for implementing charged particle imaging. The acquired image can be a single image including multiple imaging areas. The single image can be stored in a storage device. The single image can be an original image that can be divided into multiple areas. Each area can include an imaging area that contains features of sample 1. The acquired image can include multiple images of a single imaging area of ​​sample 1 sampled multiple times in a time series. Multiple images can be stored in a storage device. In some embodiments, the controller 50 can be configured to perform an image processing step on multiple images of the same position of sample 1.

[0052] In some embodiments, the controller 50 may include a measurement circuit (e.g., an analog-to-digital converter) to obtain the distribution of the detected secondary electrons. The electron distribution data collected during the detection time window, combined with the corresponding scan path data of each primary beamlet 102_1, 102_2, and 102_3 incident on the wafer surface, can be used to reconstruct an image of the wafer structure to be inspected. The reconstructed image can be used to reveal various features of the internal or external structure of the sample 1, and thus can be used to reveal any defects that may exist in the wafer.

[0053] In some embodiments, the controller 50 may control a motorized stage (not shown) to move the sample 1 during inspection. In some embodiments, the controller 50 may enable the motorized stage to continuously move the sample 1 in one direction at a constant speed. In other embodiments, the controller 50 may enable the motorized stage to change the movement speed of the sample 1 over time depending on the steps of the scanning process. In some embodiments, the controller 50 may adjust the configuration of the primary projection optical system 130 or the secondary imaging system 150 based on the images of the secondary electron beams 102_1se, 102_2se, and 102_3se.

[0054] Although Figure 2 The electron beam tool 40 is shown using three primary electron beams, but it should be understood that the electron beam tool 40 may use two or more primary electron beams. The present disclosure does not limit the number of primary electron beams used in the apparatus 40.

[0055] Now to Figure 3 Reference is made to , which is a schematic diagram of an exemplary configuration of a secondary imaging system in a multi-beam device consistent with an embodiment of the present disclosure. It should be understood that the secondary imaging system 150 can be a charged particle beam inspection system (e.g., Figure 1 Part of an electron beam inspection system 100).

[0056] In some embodiments, the secondary imaging system 150 will be shown and described together with the entire detection system. Figure 3 As shown in the figure. Figure 3 , only three secondary electron beams associated with three detection spots are shown, but there may be any number of secondary electron beams. In the entire detection system, starting from sample 1, the first part is along the main optical axis 100_1, and the second part is along the secondary optical axis 150_1. For illustration purposes only and not similar to the actual configuration, the first part is rotated to rotate along the secondary optical axis 150_1 so that the entire detection system can be shown along a straight optical axis.

[0057] In some embodiments, Figure 3 As shown in FIG. 1 , the secondary imaging system 150 may include a zoom lens 151, a projection lens 152, a secondary beam limiting aperture array 155, and an anti-scanning deflection unit (not shown), all of which are aligned with the secondary optical axis 150_1. The detection elements 140_1, 140_2, and 140_3 of the electronic detection device 140 may be placed on a detection plane SP3, perpendicular to the secondary optical axis 150_1. When the deflection scanning unit 132 is turned off, the zoom lens 151, the projection lens 152, and the objective lens 131 jointly project the surface of the sample 1 onto the detection plane SP3, i.e., focus the secondary electron beams 102_1se to 102_3se to form secondary electron spots on the detection elements 140_1, 140_2, and 140_3, respectively.

[0058] In some embodiments, the zoom lens 151 may include two electrostatic lenses 151_11 and 151_12. The image plane of the zoom lens 151 may be at the transmission plane SP2, such as Figure 3 As shown in FIG. The projection lens 152 may include an electrostatic lens and a magnetic lens (neither of which is shown), and its image plane may be at the detection plane SP3. The first imaging magnification M1 from the surface of the sample 1 to the transmission plane SP2 may be achieved by the objective lens 131 and the zoom lens 151, while the second imaging magnification M2 from the transmission plane SP2 to the detection plane SP3 may be achieved by the projection lens 152, and the total imaging magnification M from the surface of the sample 1 to the detection plane SP3 may be determined based on M1 and M2. Specifically, the total imaging magnification M may be based on M1*M2.

[0059] In some embodiments, the zoom lens 151 can be configured to perform a zoom function. By adjusting the focusing power of the two electrostatic lenses 151_11 and 151_12, the first imaging magnification M1 can be changed to achieve the desired value of the total imaging magnification M. The projection lens 152 can be configured to perform an anti-rotation function. By adjusting the magnetic field of the magnetic lens and the focusing power of the electrostatic lens, the total image rotation and the second imaging magnification M2 on the detection plane SP3 can remain unchanged. The reverse scanning deflection unit (not shown) can be configured to perform a reverse scanning function. By synchronously deflecting the secondary electron beam using the deflection scanning unit 132, the displacement of the three secondary electron spots on the detection plane SP3 can be substantially offset. Therefore, the correspondence between multiple detection spots and multiple detection elements can always be maintained. In order to reduce the additional aberration of the zoom lens 151 and the projection lens 152 caused by the deflection of the secondary electron beam generated by the deflection scanning unit 132, the reverse scanning deflection unit is preferably placed before the zoom lens 151, and thus, the secondary electron beam will pass through the zoom lens 151 and the projection lens 152 in a manner that the deflection scanning unit 132 is closed. However, in this case, the zoom lens 151 may be placed far away from the beam splitter 160, and thus a large initial aberration may be generated.

[0060] As is well known in the art, the emission of secondary electrons follows Lambert's law and has a large energy spread. Although the energy of secondary electrons may be as high as 50 eV, most have an energy of about 5 eV, depending on the sample material, etc. The landing energy of the primary electron beamlet, such as the energy of the beamlet 102_1 when it falls on the sample, can be in the range of 0.1 keV to 5 keV. The landing energy can be adjusted by changing either or both of the bias of the primary electron source 101 or the bias of the sample 1. Therefore, the excitation of the objective lens 131 can be adjusted to provide corresponding focusing powers for the three beamlets. In addition, in order to reduce aberrations, the objective lens 131 can be a magnetic or electromagnetic compound lens that is configured to rotate the beamlet and affect the landing energy. Since the size, position or magnification of the secondary electron spots formed by the secondary electron beams 102_lse, 102_2se and 102_3se on the detection elements 140_1, 140_2 and 140_3 may be different, the secondary electron spots may partially enter the detection elements adjacent to the corresponding detection elements. The secondary electrons detected by the adjacent detection elements may generate image overlap, for example, causing a deterioration in image resolution. The image signal from one detection element may include information from more than one scan area of ​​the sample 1, resulting in a loss of resolution due to crosstalk.

[0061] For example, crosstalk in a multi-beam SEM such as the EBI system 100 can be mitigated by using the secondary beam limiting aperture array 155 to cut off peripheral secondary electrons of a secondary electron beam such as 102_1se. The secondary beam limiting aperture array 155 may include multiple apertures. Figure 3 Only two apertures 155_1 and 155_2 are shown, but any number of apertures may be used as appropriate. Figure 4 The secondary beam-limiting aperture array 155 illustrated in FIG. 1 (described later) includes six apertures, 155_1 , 155_2 , 155_3 , 155_4 , 155_5 , and 155_6 .

[0062] Generally speaking, when the aperture of the secondary beam-limiting aperture 155 (e.g., Figure 3 When the size of the aperture 155_1) of the secondary electron detector increases, the total collection efficiency of the secondary electron detector can be increased. However, the difference in the collection efficiency of each detection element of the detector may also increase, and the crosstalk between the detection elements 140_1, 140_2 and 140_3 may also increase. Although the increase in the overall collection efficiency of the electronic detection device 140 increases the throughput, the difference in the collection efficiency of each detection element 140_1, 140_2 and 140_3 may cause the grayscale levels of the image formed by the secondary electron beams 102_lse-102_3se to be more different. One or more additional processes may be performed to eliminate inspection errors caused by grayscale level differences, thereby reducing the inspection throughput and deteriorating the resolution of the MBI device. When the crosstalk between the secondary electron beams 102_lse-102_3se increases, the image formed by the secondary electron beams 102_lse-102_3se may deteriorate. That is, large crosstalk deteriorates the inspection resolution of the MBI device.

[0063] In some embodiments, each aperture of the secondary beam limiting aperture array 155 may have a uniform or non-uniform size, shape or cross-section. The smaller the radial size of the aperture, the lower the collection efficiency and crosstalk of the imaging signals of the detection elements 140_1, 140_2 and 140_3 will generally be. Therefore, the radial size of the aperture may depend on the application or the desired result.

[0064] In some embodiments where the objective lens 131 functions in a non-magnetic immersion mode, the angular velocity of the secondary electrons appearing on the sample surface can be zero. In such embodiments, the primary rays of the off-axis secondary electron beams 102_2se and 102_3se can still be meridian after leaving the objective lens 131 and can be able to pass through the secondary optical axis 150_1 of the secondary imaging system 150. In addition, the primary rays can pass through the secondary optical axis 150_1 at the same position in the secondary imaging system 150 (if aberrations are not considered). In this way, the secondary electron beams 102_lse-102_3se can be configured to overlap at a common intersection area and thereby form a relatively sharp secondary beam intersection. The plane where the common area of ​​intersection or secondary beam intersection is located is called the intersection plane or secondary beam intersection plane.

[0065] Although Figure 3 An exemplary relatively sharp secondary electron beam intersection plane is illustrated, which is formed by secondary electron beams 102_lse_102_3se that completely overlap on one intersection plane, but it should be understood that one or more of the secondary electron beams may be offset from other secondary electron beams on the intersection plane and the secondary beam intersection may not be so sharp, forming a series of secondary beam intersection planes along the secondary optical axis 150_1. The position of the secondary beam intersection plane may depend on the landing energy of the primary beamlet or the excitation of the objective lens 131, etc. In some embodiments, the secondary beam limiting aperture array 155 can be positioned on the secondary beam intersection plane, or in other words, the plane of the secondary beam limiting aperture array 155 can coincide with the secondary beam intersection plane. In some embodiments, the plane of the secondary beam limiting aperture array 155 can be within a moving range of the position of the secondary beam intersection plane. The secondary beam limiting aperture array 155 can be moved along the secondary beam intersection plane so that the desired aperture or aperture size can be used to block peripheral secondary electrons directed toward the electron detection device 140. In some embodiments, the secondary beam-limiting aperture array 155 may be placed at an optimal position within a range of secondary beam intersection plane locations.

[0066] Now to Figure 4 Reference is made to , which illustrates a schematic diagram of an exemplary arrangement of apertures on a secondary beam-limiting aperture array 155 consistent with an embodiment of the present disclosure. Figure 4 The middle figure shows that the beam-limiting aperture array 155 includes six apertures of different sizes, but any number of apertures may be used.

[0067] like Figure 4As shown in , the cross section 102se represents the cross section of the overlapping secondary electron beams 102_1se-102_3se incident on the secondary beam limiting aperture array 155. In some embodiments, the secondary electron beams 102_1se-102_3se may not overlap at the same intersection plane to form a sharp secondary beam intersection, but may be offset along the secondary optical axis 150_1 so that they form a series of intersection planes. In this case, the cross section 102se of the overlapping secondary electron beams 102_1se-102_3se may not be sharp.

[0068] In some embodiments, in order to minimize the occurrence of crosstalk, the distance between two adjacent apertures such as 155_2 and 155_3 may be greater than the sum of the radius R of the overlapping secondary electron beam 102se and the radius of the larger of the two apertures. In some embodiments, the secondary beam limiting aperture array 155 may include at least two apertures of the same size, and in this case, the distance between two adjacent apertures such as 155_2 and 155_3 may be greater than the sum of the radius R of the cross section 102se of the overlapping secondary electron beams 102_1se-102_3se and the radius of either of the two apertures.

[0069] In some embodiments, the radius R of the cross section 102se of the overlapping secondary electron beams 102_1se-102_3se may depend on the landing energy of the primary beamlets or the excitation of the objective lens 131. Therefore, in order to accommodate the wide radius range of the overlapping secondary electron beams 102_1se-102_3se (given by Figure 4 As represented by cross section 102se), the distance between two adjacent apertures can be determined based on the maximum value of the radius R.

[0070] Now to Figure 5 Reference is made to , which illustrates an exemplary configuration of a secondary imaging system 150 in an electron beam tool 500 of a multi-beam apparatus consistent with an embodiment of the present disclosure. Figure 3 Compared to the secondary imaging system 150 of the electron beam tool 40 , the secondary imaging system 150 of the electron beam tool 500 may include a pre-limiting aperture plate 155P.

[0071] like Figure 5As illustrated in , the pre-limiting aperture plate 155P may include a plate having an aperture configured to block peripheral electrons while allowing axial electrons of the secondary electron beams 102_1se-102_3se. In some embodiments, the pre-limiting aperture plate 155P may be aligned with the secondary beam limiting aperture array 155 and the secondary optical axis 150_1 so that it blocks most of the peripheral electrons of the off-axis secondary electron beams 102_2se and 102_3se. In some embodiments, the pre-limiting aperture plate 155P may be configured to prevent secondary electrons from irradiating unintended apertures of the secondary beam limiting aperture array 155.

[0072] In some embodiments, the pre-limiting aperture plate 155P may be positioned upstream of the secondary beam-limiting aperture array 155, such as Figure 5 In the context of the present disclosure, “upstream” refers to the position of the pre-limiting aperture plate 155P so that one or more secondary electron beams 102_1se-102_3se can be incident on the pre-limiting aperture plate 155P before irradiating the secondary beam limiting aperture array 155.

[0073] The pre-limiting aperture plate 155P may be placed before the secondary beam-limiting aperture array 155 so that the aperture of the pre-limiting aperture plate 155P is aligned with the desired aperture of the secondary beam-limiting aperture array 155. In this case, the number of peripheral secondary electrons incident on the secondary beam-limiting aperture array 155 may be reduced or minimized. In some embodiments, the pre-limiting aperture plate 155P may be configured to block peripheral secondary electrons from being incident on other unintended apertures of the secondary beam-limiting aperture array 155, thereby reducing crosstalk. This configuration may also enable the apertures of the secondary beam-limiting aperture array 155 to be positioned closer to each other, thereby allowing more apertures to be placed in a smaller area on the aperture array 155 while mitigating the occurrence of crosstalk.

[0074] The size and shape of the apertures of the secondary beam-limiting aperture array 155 may vary over time based on duration of use, materials, inspection parameters, etc. For example, exposure to secondary electrons may result in contamination and debris formation at the edges of the apertures, thereby reducing the effective size and shape of the apertures through which the secondary electrons may pass. In some embodiments, placing a pre-limiting aperture plate 155P in front of the secondary beam-limiting aperture array 155 may reduce or minimize variations in the size and shape of the apertures of the secondary beam-limiting aperture array 155 by reducing the number of incident peripheral secondary electrons.

[0075] In some embodiments, Figure 4As illustrated in , the apertures 155_1 and 155_2 of the secondary beam-limiting aperture array 155 may be separated from each other so that the secondary electrons passing through the pre-limiting aperture plate 155P may pass through only one intended aperture of the secondary beam-limiting aperture array 155. In some embodiments, the pre-limiting aperture plate 155P may be configured to block peripheral electrons so that they do not pass through apertures adjacent to the intended apertures of the secondary beam-limiting aperture array 155, so that the apertures of the secondary beam-limiting aperture array 155 can be positioned closer to each other. This may allow an aperture array including more aperture sizes to be designed in a smaller area on the aperture array 155 while mitigating the occurrence of crosstalk.

[0076] In some embodiments, the pre-limiting aperture plate 155P may be positioned downstream of the secondary beam limiting aperture array 155 (this embodiment is not shown), for example, between the secondary beam limiting aperture array 155 and the electron detection device 140. In the context of the present disclosure, “downstream” refers to the position of the pre-limiting aperture plate 155P so that one or more secondary electron beams 102_1se-102_3se may be incident on the pre-limiting aperture plate 155P after irradiating the secondary beam limiting aperture array 155. The limiting aperture plate 155P may be closer to the secondary beam limiting aperture array 155 than the electron detection device 140.

[0077] Despite Figure 5 155P_1, but in some embodiments, the secondary imaging system 150 may include more than one pre-limiting aperture plate 155P. For example, the primary pre-limiting aperture plate 155P_1 (not shown) may be positioned upstream of the secondary beam-limiting aperture array 155, and the secondary pre-limiting aperture plate 155P_2 (not shown) may be positioned downstream of the secondary beam-limiting aperture array 155. In such a configuration, the primary pre-limiting aperture plate 155P_1 may be configured to block most of the peripheral secondary electrons from irradiating the unintended apertures of the secondary beam-limiting aperture array 155, and the secondary pre-limiting aperture plate 155P_2 may be configured to block any stray peripheral secondary electrons that may not be blocked by the primary pre-limiting aperture plate 155, thereby mitigating the occurrence of crosstalk. It should be appreciated that other combinations of the number of pre-limiting aperture plates and their arrangements are also possible.

[0078] like Figure 5, the pre-limiting aperture plate 155P and the secondary beam-limiting aperture array 155 may be separated by an optimal distance 155G. While it may be desirable to minimize the distance 155G between the pre-limiting aperture plate 155P and the secondary beam-limiting aperture array 155 to reduce the likelihood of peripheral secondary electrons escaping and irradiating other apertures of the secondary beam-limiting aperture array 155, the distance 155G may be optimized to allow unrestricted movement of the pre-limiting aperture plate 155P and the secondary beam-limiting aperture array 155. In some embodiments, the distance between the pre-limiting aperture plate 155P and the secondary beam-limiting aperture array 155 may be 5 mm. In some embodiments, the distance 155G may be determined based on mechanical design considerations, available space, manufacturability, and cost efficiency, among other things. For example, some techniques may be used to reliably and repeatably achieve a distance of 3 mm to 5 mm between the pre-limiting aperture plate 155P and the secondary beam-limiting aperture array 155. In some embodiments, distance 155G may be greater than 5 mm, such as 10 mm, based on factors including but not limited to space availability, design constraints, cost efficiency, materials, and intended application.

[0079] Now to FIG. 6A to FIG. 6D For reference, they are consistent with the embodiments of the present invention Figure 5 Schematic diagram of the aperture arrangement of the secondary beam limiting aperture array 155 in the secondary imaging system 150 of the electron beam tool 500 is shown in FIG. It will be appreciated that the size of the apertures, the size of the secondary beam limiting aperture array 155, the size of the secondary electron beam before the pre-limiting aperture plate 155P, and the size of the secondary electron beam incident on the secondary beam limiting aperture array 155 after passing through the pre-limiting aperture plate 155P are for illustration purposes only and are not drawn to scale.

[0080] like FIG. 6A to FIG. 6D As shown in FIG. 1 , section 102se represents the cross-section 102e after interacting with the sample at detection spots 102_1S, 102_2S and 102_3S, respectively, by primary beamlets (eg, Figure 2 The profile of the secondary electron beam generated by the primary beamlets 102_1, 102_2 and 102_3).

[0081] Fig. 6AThe figure shows a secondary beam limiting aperture array 155A including three apertures 155_1, 155_2 and 155_3, which are placed in a direction so that the geometric centers of all the apertures are aligned along an axis (e.g., the x-axis). Although only three apertures are shown, any number of apertures may be used. In some embodiments, based on the physical space available in the secondary imaging system 150, the number of apertures in this configuration may be limited by the allowable size of the secondary beam limiting aperture array 155A. One of the several advantages of using a pre-limiting aperture plate 155P is that it allows the separation distance between two adjacent apertures to be reduced by blocking all peripheral secondary electrons from irradiating the apertures of the secondary beam limiting aperture array 155A that are not used for detection. In addition, the use of a pre-limiting aperture plate 155P can allow crosstalk to be reduced.

[0082] Fig. 6A , the reduced separation distance between two adjacent apertures is shown in . In this context, the separation distance between two apertures can be referred to as the linear distance between the geometric centers of the two adjacent apertures. In some embodiments, the separation distance between two apertures across the array can be uniform. For example, the separation distance between apertures 155_1 and 155_2 can be similar to the separation distance between apertures 155_2 and 155_3. In some embodiments, the separation distance can be non-uniform.

[0083] In some embodiments, the secondary beam-limiting aperture array 155A may be configured to move along a single axis, such as the x-axis, to adjust the size of the apertures through which overlapping secondary electron beams may pass.

[0084] like Fig. 6A As shown in , the secondary beam-limiting aperture array 155A may include apertures of different sizes. In some embodiments, the apertures 155_1, 155_2, and 155_3 of the secondary beam-limiting aperture array 155A may be uniform in size, shape, cross-section, and spacing. In some embodiments, the radius of the aperture of the pre-limiting aperture plate 155P may be slightly larger than the radius of the maximum aperture of the secondary beam-limiting aperture array 155. The pre-limiting aperture plate 155P and the secondary beam-limiting aperture array 155 may be aligned so that the geometric centers of the apertures of the pre-limiting aperture plate 155P and the secondary beam-limiting aperture array 155 are aligned with the secondary optical axis 150_1.

[0085] Figure 6BA secondary beam limiting aperture array 155B is illustrated that includes six apertures 155_1-155_6 placed in a rectangular matrix along the x-axis and the y-axis. In some embodiments, the secondary beam limiting aperture array 155B may include apertures of different sizes. In some embodiments, the secondary beam limiting aperture array 155B may include at least two apertures of similar size. Section 102se_155P represents the profile of the secondary electron beam (represented by section 102se) generated by the primary beamlets 102_1, 102_2 and 102_3 and passing through the predetermined aperture plate 155P. It should be understood that sections 102se and 102se_155P represent the profile of the secondary electron beam at different planes along the secondary optical axis 150_1.

[0086] In some embodiments, the secondary beam limiting aperture array 155B may be configured to move along both the x-axis and the y-axis to adjust the size of the apertures through which the overlapping secondary electron beams may pass. Fig. 6A and Figure 6B Rectangular secondary beam-limiting aperture arrays (e.g., 155A and 155B) are illustrated, but other shapes may be used including, but not limited to, circular, triangular, elliptical, etc. It will be appreciated that the size and shape of the secondary beam-limiting aperture array may be determined based on available physical space, mechanical design considerations, cost efficiency, etc.

[0087] Now to Figure 6C For reference, a circular secondary beam limiting aperture array 155C including seven apertures 155_1-155_7 is illustrated. In some embodiments, the secondary beam limiting aperture array 155C may include a central aperture 155_1 and six eccentric apertures 155_2-155_7 radially arranged around the central aperture 155_1. Figure 6C As shown in FIG. 1 , the eccentric apertures may be positioned along a virtual circle 155R such that the separation distance between the center of the central aperture 155_1 and the center of each of the eccentric apertures 155_2-155_7 may be uniform. In other words, the separation distance between the center of the central aperture 155_1 and the center of each of the eccentric apertures 155_2-155_7 may be similar or substantially similar to the radius of 155R. In such an embodiment, the separation distance may be similar to the radius of the cross section 102se_155P and the maximum aperture of the secondary beam limiting aperture array 155C (e.g., Figure 6C The separation distance or radius of the virtual circle 155R is determined by the radius of the aperture 155_6 of the cross section 102se_155P. In some embodiments, the separation distance may be greater than the sum of the radius of the cross section 102se_155P and the radius of the maximum aperture 155_6 of the secondary beam limiting aperture array 155C, for example.

[0088] like Figure 6CAs shown in FIG. 1 , the secondary beam-limiting aperture array 155C may include apertures of different sizes. The size of the central aperture 155_1 may be different compared to the eccentric apertures 155_2-155_7. In some embodiments, each eccentric aperture may have a different size, randomly arranged in size along the circumference of the virtual circle 155R.

[0089] In some embodiments, the secondary beam limiting aperture array 155C can be configured to move along both the x-axis and the y-axis to adjust the size of the apertures through which the overlapping secondary electron beams can pass. One of the several advantages of the circular arrangement of apertures in the secondary beam limiting aperture array 155C is that various aperture sizes can be moved in and out with limited movement in both the x-axis and the y-axis.

[0090] Fig.6D A circular secondary beam-limiting aperture array 155D comprising seven apertures 155_1-155_7 is shown. Figure 6C In contrast, two or more apertures of secondary beam-limiting aperture array 155D may be similar or substantially similar in size. For example, eccentric apertures 155_3 and 155_7 are similar in size. Fig.6D Two eccentric apertures 155_3 and 155_7 are illustrated as having similar dimensions, but it should be understood that any two or more apertures may have similar dimensions.

[0091] In some embodiments, the aperture may become contaminated after extended use, for example due to particles, debris, and gases generated by secondary electrons incident on the secondary beam limiting aperture array 155D. The contamination may change the effective size or shape of the aperture, affecting the detection elements of the electron detection device 140 (e.g., Figure 3 140_1, 140_2, and 140_3), and therefore affects the overall throughput and resolution of the image. Contamination issues may be amplified in smaller apertures, such as 155_3, in part because the small aperture blocks a larger portion of the secondary electrons incident on the array than larger apertures. In addition, smaller apertures have smaller circumferences, and therefore, for the same exposure duration to secondary electrons, the percentage reduction in the effective size of the aperture may be greater than for larger apertures. One of the several advantages of having two or more similarly sized apertures is that it can reduce tool downtime due to maintenance. For example, if one of the apertures is contaminated, a second aperture of similar size can be used, allowing uninterrupted use of the tool and thereby improving the overall throughput of wafer inspection.

[0092] Now to Figure 7Reference is made to , which illustrates an exemplary configuration 700 of a secondary imaging system 150 in a multi-beam device consistent with an embodiment of the present disclosure. It should be appreciated that the secondary imaging system 150 may be a charged particle beam inspection system (e.g., Figure 1 Part of an electron beam inspection system 100).

[0093] like Figure 7 As shown in , the secondary imaging system 150 may include a movable secondary beam limiting aperture array 155 configured to move in three directions along the x, y, and z axes. In some embodiments, the secondary beam limiting aperture array 155 may be moved along the x and y axes to select a desired aperture size, and moved along the z axis to match the position of the secondary beam intersection plane, while the pre-limiting aperture plate 155P is fixed in its position. The x and y axes may be perpendicular to the secondary optical axis 150_1 and the z axis may be parallel to the secondary optical axis 150_1.

[0094] In some embodiments, the position of the secondary beam intersection plane along the secondary optical axis 150_1 may be determined based at least on factors including, but not limited to, the landing energy of the primary beamlets and the excitation of the objective lens 131. In some embodiments, the corresponding position of the secondary beam intersection plane for a range of landing energies of the primary beamlets may be determined based on simulation and data modeling algorithms.

[0095] Based on the landing energy of the primary beamlet, the secondary electron beam can overlap at different planes perpendicular to the secondary optical axis 150_1, thereby forming a range of secondary beam intersection plane positions for a corresponding range of landing energies. In some embodiments, the intersection plane position can be determined based on a simulation of the landing energy, and therefore, the range of secondary beam intersection plane positions can be determined based on the range of landing energies used in the system. For example, a user or a system can theoretically determine the coordinates of the secondary beam intersection plane for a given value of the landing energy of the primary beamlet based on a simulation such as an algorithm.

[0096] In some embodiments, if the position of the secondary beam limiting aperture array 155 is adjusted along the z-axis to align with the position of the secondary beam intersection plane, the position of the pre-limiting aperture plate 155P may deviate from the range of the position of the secondary beam intersection plane. This may increase the secondary electron beam incident on the secondary beam limiting aperture array 155 (e.g., Figures 6A-6D Although a large beam size incident on the secondary beam limiting aperture array 155 can increase the number of secondary electrons incident on the detection element of the electron detection device, it may also increase the possibility of crosstalk occurring.

[0097] Now to Figure 8Reference is made to , which illustrates an exemplary configuration 800 of a secondary imaging system 150 in a multi-beam device consistent with an embodiment of the present disclosure. It should be appreciated that the secondary imaging system 150 may be a charged particle beam inspection system (e.g., Figure 1 Part of an electron beam inspection system 100).

[0098] like Figure 8 As shown in FIG. 1 , the secondary imaging system 150 may include a movable pre-limiting aperture plate 155P and a movable secondary beam limiting aperture array 155. The movable pre-limiting aperture plate 155P may be configured to move independently in three directions along the x, y, and z axes. In some embodiments, the movable pre-limiting aperture plate 155P may be configured to move together with the movable secondary beam limiting aperture array 155 so as to maintain the distance 155G.

[0099] In some embodiments, the movable pre-limiting aperture plate 155P and the secondary beam limiting aperture array 155 can be moved together so that the position of the secondary beam limiting aperture array 155 is aligned with the position of the secondary beam intersection plane. In such a scenario, based on the distance 155G and the range of intersection positions, both the pre-limiting aperture plate 155P and the secondary beam limiting aperture array 155 can be placed within the range of intersection positions. In some embodiments, it may be desirable to have the pre-limiting aperture plate 155P and the secondary beam limiting aperture array 155 within the range of intersection positions along the secondary optical axis 150_1 to effectively block peripheral electrons and reduce the possibility of crosstalk.

[0100] Now to Fig. 9 Reference is made to a diagram illustrating a secondary imaging system (eg, Figure 3 100) to form an image of a sample. The method 900 may be performed by the controller 50 of the EBI system 100, for example, as Figure 1 The controller 50 may be programmed to implement one or more steps of the method 900. For example, the controller 50 may instruct a module of the charged particle beam device to activate a charged particle source to generate a charged particle beam, which may generate a secondary charged particle beam when interacting with the sample.

[0101] In step 910, a primary beamlet (eg, Figure 2 102_1, 102_2 and 102_3) and the detection spots of the sample (e.g., Figure 2 After the interaction of 102_1S, 102_2S and 102_3S) from the sample (e.g., Figure 2 of a sample 1) with multiple secondary electron beams (e.g., Figure 3In some embodiments, the number of secondary electron beams generated may be equal to the number of primary beamlets incident on the sample. The three secondary electron beams 102_1se, 102_2se, and 102_3se may be separated by a beam splitter such as a Wien filter (e.g., Figure 2 The beam splitter 160) is turned to enter the secondary imaging system 150 along the secondary optical axis 150_1 of the secondary imaging system 150.

[0102] Step 910 may also include directing the secondary electron beams 102_1se-102_3se so that they overlap at a common intersection region along the secondary optical axis and thereby form a secondary beam intersection (e.g., such as a relatively sharp secondary beam intersection). The plane where the common region of the intersection or secondary beam intersection lies is called the intersection plane or secondary beam intersection plane. The beam limiting aperture array (e.g., Figure 3 The secondary beam limiting aperture array 155 of the embodiment of the present invention can be positioned at or near the secondary beam intersection plane. In some embodiments, the pre-limiting aperture plate (e.g., Figure 3 A pre-limiting aperture plate 155P) can be placed before the secondary beam-limiting aperture array.

[0103] In step 920, a pre-limiting aperture plate may be used to block peripheral secondary electrons of the secondary electron beam prior to irradiating the secondary electron beam limiting aperture array. The pre-limiting aperture plate may include a plate having an aperture configured to block peripheral electrons while allowing axial electrons of the secondary electron beam. In some embodiments, the pre-limiting aperture plate may be aligned with the secondary beam limiting aperture array and the secondary optical axis so that it blocks most of the peripheral electrons of the off-axis secondary electron beam.

[0104] In some embodiments, the pre-limiting aperture plate and the secondary beam-limiting aperture array may be separated by an optimal distance (e.g., Figure 5155G). Although it may be desirable to minimize the distance between the pre-limiting aperture plate and the secondary beam limiting aperture array to reduce the possibility of peripheral secondary electrons escaping and irradiating other unintended apertures of the secondary beam limiting aperture array, it can be optimized to allow unrestricted movement of the pre-limiting aperture plate and the secondary beam limiting aperture array. In some embodiments, the distance between the pre-limiting aperture plate and the secondary beam limiting aperture array can be 5 mm. In some embodiments, the distance can be determined based on mechanical design considerations, available space, manufacturability, and cost effectiveness, among others. For example, some techniques can be used to reliably and repeatably achieve a distance of 3 mm to 5 mm between the pre-limiting aperture plate 155P and the secondary beam limiting aperture array 155. In some embodiments, the distance can be greater than 5 mm, such as 10 mm, based on factors including but not limited to space availability, design constraints, cost effectiveness, materials, and intended applications.

[0105] In step 930, a beam limiting aperture array may be used to further shape the secondary electron beam. The secondary beam limiting aperture array may be placed at or within a moving range of the position of the secondary beam intersection plane. The secondary beam limiting aperture array may be moved along the secondary beam intersection plane so that a desired aperture or aperture size may be used to block electrons directed toward a charged particle detection element (e.g., Figure 3 The position of the secondary beam intersection plane may depend on the landing energy of the primary beamlet or the objective lens (e.g., Figure 2 The secondary beam limiting aperture array may be placed at an optimal position within the movement range of the secondary beam intersection plane.

[0106] In some embodiments, the order of steps 920 and 930 can be interchanged. For example, the pre-limiting aperture plate can be placed upstream or downstream of the secondary beam-limiting aperture array so that the secondary electron beams 102_1se-102_3se can be incident thereon before or after irradiating the secondary beam-limiting aperture array, respectively. In some embodiments, a pre-limiting aperture plate (e.g., primary pre-limiting aperture plate 155P_1 (not shown)) can be placed upstream of the secondary beam-limiting aperture array, and another pre-limiting aperture plate (e.g., pre-limiting aperture plate 155P_2 (not shown)) can be placed downstream of the secondary beam-limiting aperture array 155. In such a configuration, one pre-limiting aperture plate (e.g., 155P_1) can be configured to block most of the peripheral secondary electrons from irradiating the unintended apertures of the secondary beam limiting aperture array 155, and another pre-limiting aperture plate (e.g., 155P_2) can be configured to block any stray peripheral secondary electrons that may not be blocked by the first pre-limiting aperture plate, thereby reducing the possibility of crosstalk. It should be understood that other combinations of the number of pre-limiting aperture plates and their arrangements can be used as desired.

[0107] In step 940, the trimmed secondary electron beam may be projected onto a detection element of an electron detection device (e.g., Figure 3 140_1, 140_2 and 140_3) to create an image of the detection area of ​​the sample.

[0108] The embodiments may be further described using the following terms:

[0109] 1. An electro-optical system comprising:

[0110] a first pre-limiting aperture plate comprising a first aperture configured to block peripheral charged particles of the plurality of secondary charged particle beams from the sample; and

[0111] A beam-limiting aperture array includes a second aperture configured to shape the plurality of secondary charged particle beams.

[0112] 2. The system according to clause 1, further comprising: a charged particle detector comprising a plurality of detection elements, wherein a detection element of the plurality of detection elements is associated with a corresponding trimmed beam of the plurality of secondary charged particle beams.

[0113] 3. A system according to any of clauses 1 and 2, wherein the distance between the first pre-limiting aperture plate and the beam-limiting aperture array is 5 mm or less.

[0114] 4. The system according to any of clauses 1-3, wherein the first pre-limiting aperture plate is positioned upstream of the beam limiting aperture array.

[0115] 5. The system according to any of clauses 2-4, wherein the first pre-limiting aperture plate is positioned downstream of the beam limiting aperture array.

[0116] 6. The system according to any of clauses 1 and 2, further comprising a second pre-limiting aperture plate.

[0117] 7. The system of clause 6, wherein the first pre-limiting aperture plate is positioned upstream of the beam-limiting aperture array and the second pre-limiting aperture plate is positioned downstream of the beam-limiting aperture array.

[0118] 8. A system according to any of clauses 1-7, wherein the plurality of secondary charged particle beams comprises at least one of: secondary electrons or backscattered electrons from the sample generated in response to interactions between the plurality of primary charged particle beams and the sample.

[0119] 9. A system according to any of clauses 1-8, wherein the beam-limiting aperture array comprises a plurality of apertures of different sizes.

[0120] 10. The system of clause 9, wherein at least two of the plurality of apertures have similar sizes.

[0121] 11. The system according to any of clauses 9-10, wherein the plurality of apertures are arranged in a rectangular, circular or spiral pattern.

[0122] 12. A system according to any of clauses 1-11, wherein a plurality of secondary charged particle beams overlap to create an intersection region in an intersection plane perpendicular to a secondary optical axis of the electro-optical system.

[0123] 13. A system according to clause 12, wherein the beam limiting aperture array is placed at or within the position of the intersection plane and is placed perpendicular to the secondary optical axis.

[0124] 14. A system according to any of clauses 12 and 13, wherein the range of positions of the intersection plane is determined based on landing energies of multiple primary charged particle beams on the sample.

[0125] 15. A system according to any of clauses 12-14, wherein the second aperture is centred on the intersection region.

[0126] 16. A system according to any of clauses 12-15, wherein the centres of the first aperture and the second aperture are aligned with the secondary optical axis.

[0127] 17. A system according to any of clauses 12-16, wherein the beam-limiting aperture array is movable to align an aperture of the plurality of apertures with the intersection region.

[0128] 18. A system according to any of clauses 14-17, wherein the beam-limiting aperture array is movable along the secondary optical axis based on a range of positions of the intersection plane.

[0129] 19. A system according to any of clauses 12-18, wherein the plane of the first pre-limiting aperture plate is outside the range of the position of the intersection plane.

[0130] 20. The system of clause 19, wherein the planes of the beam limiting aperture array and the first pre-limiting aperture plate are within the range of the position of the intersection plane.

[0131] 21. A multi-charged particle beam device comprising:

[0132] An electro-optical system for projecting a plurality of secondary charged particle beams from a sample onto a charged particle detector, the electro-optical system comprising:

[0133] a first pre-limiting aperture plate comprising a first aperture configured to block peripheral charged particles of the plurality of secondary charged particle beams from the sample; and

[0134] a beam-limiting aperture array comprising a second aperture configured to shape the plurality of secondary charged particle beams,

[0135] Wherein the charged particle detector comprises a plurality of detection elements, and wherein a detection element of the plurality of detection elements is associated with a corresponding trimmed beam of the plurality of secondary charged particle beams.

[0136] 22. Apparatus according to clause 21, wherein the distance between the first pre-limiting aperture plate and the beam-limiting aperture array is 5 mm or less.

[0137] 23. Apparatus according to any of clauses 21 and 22, wherein the first pre-limiting aperture plate is positioned upstream of the beam limiting aperture array.

[0138] 24. Apparatus according to any of clauses 21-23, wherein the first pre-limiting aperture plate is positioned downstream of the beam limiting aperture array.

[0139] 25. The apparatus of clause 21, further comprising a second pre-limiting aperture plate.

[0140] 26. Apparatus according to clause 25, wherein a first pre-limiting aperture plate is positioned upstream of the beam-limiting aperture array and the second pre-limiting aperture plate is positioned downstream of the beam-limiting aperture array.

[0141] 27. Apparatus according to any of clauses 21-26, wherein the plurality of secondary charged particle beams comprises at least one of: secondary electrons or backscattered electrons from the sample generated in response to interactions between the plurality of primary charged particles and the sample.

[0142] 28. Apparatus according to any of clauses 21-27, wherein the beam-limiting aperture array comprises a plurality of apertures of different sizes.

[0143] 29. The apparatus of clause 28, wherein at least two apertures of the plurality of apertures have similar sizes.

[0144] 30. Apparatus according to any of clauses 28 and 29, wherein the plurality of apertures are arranged in a rectangular, circular or spiral pattern.

[0145] 31. Apparatus according to any of clauses 21-30, wherein a plurality of secondary charged particle beams overlap to create an intersection region in an intersection plane perpendicular to a secondary optical axis of the electro-optical system.

[0146] 32. Apparatus according to clause 31, wherein the array of beam-limiting apertures is positioned at or within the position of the intersection plane and is positioned perpendicular to the secondary optical axis.

[0147] 33. An apparatus according to any of clauses 31 and 32, wherein the range of positions of the intersection plane is determined based on the landing energies of multiple primary charged particle beams on the sample.

[0148] 34. Apparatus according to any of clauses 31-33, wherein the second aperture is centred on the intersection region.

[0149] 35. Apparatus according to any of clauses 31-34, wherein centres of the first aperture and the second aperture are aligned with the secondary optical axis.

[0150] 36. Apparatus according to any of clauses 31-35, wherein the beam-limiting aperture array is movable to align an aperture of the plurality of apertures with the intersection region.

[0151] 37. Apparatus according to any of clauses 33-36, wherein the beam-limiting aperture array is movable along the secondary optical axis based on a range of positions of the intersection plane.

[0152] 38. Apparatus according to any of clauses 31 to 37, wherein the plane of the first pre-limiting aperture plate is outside the range of the position of the intersection plane.

[0153] 39. Apparatus according to clause 38, wherein the planes of the beam limiting aperture array and the first pre-limiting aperture plate are within the range of the position of the intersection plane.

[0154] 40. A method performed by a secondary imaging system to form an image of a sample, the method comprising:

[0155] generating a plurality of secondary charged particle beams from the sample;

[0156] Using a pre-limiting aperture plate to block peripheral charged particles of the plurality of secondary charged particle beams;

[0157] shaping the plurality of secondary charged particle beams using apertures of a beam limiting aperture array; and

[0158] The trimmed plurality of secondary charged particle beams are projected onto corresponding detection elements of the charged particle detector.

[0159] A non-transitory computer-readable medium storing instructions for a controller (e.g., Figure 1 A processor of the controller 50) performs image inspection, image acquisition, condenser adjustment, activation of charged particle sources, beam deflection, positioning of a beam limiting aperture array (e.g., secondary beam limiting aperture array 155), positioning of a pre-limiting aperture plate (e.g., pre-limiting aperture plate 155P), etc. 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 media, compact disk read-only memory (CD-ROM), any other optical data storage media, any physical media with a pattern of holes, random access memory (RAM), programmable read-only memory (PROM) and erasable programmable read-only memory (EPROM), FLASH-EPROM or any other flash memory, non-volatile random access memory (NVRAM), cache, registers, any other memory chip or cartridge, and network versions thereof.

[0160] It should be understood that the embodiments of the present disclosure are not limited to the exact constructions that have been described above and illustrated in the accompanying drawings, and that various modifications and changes may be made without departing from the scope thereof. The present disclosure has been described in conjunction with various embodiments, and other embodiments of the present invention will be apparent to those skilled in the art in view of the specification and practice of the invention disclosed herein. The description and embodiments are intended to be considered as exemplary only, with the true scope and spirit of the present invention being indicated by the following claims.

[0161] The above description is intended to be illustrative rather than limiting. It will therefore be apparent to one skilled in the art that modifications described may be made without departing from the scope of the claims set forth below.

Claims

1. An electro-optical system comprising: a first pre-limiting aperture plate comprising a first aperture configured to block peripheral charged particles of the plurality of secondary charged particle beams from the sample; as well as a beam-limiting aperture array comprising a plurality of apertures, wherein a second aperture of the plurality of apertures is configured to shape the plurality of secondary charged particle beams, and Wherein the beam-limiting aperture array is configured to be movable along an x-axis and / or a y-axis direction such that each aperture of the plurality of apertures can be selected for the secondary charged particle beam.

2. The system of claim 1 , further comprising a charged particle detector comprising a plurality of detection elements, wherein a detection element of the plurality of detection elements is associated with a corresponding trimmed beam of the plurality of secondary charged particle beams.

3. The system of claim 1, wherein a distance between the first pre-limiting aperture plate and the beam-limiting aperture array is 5 mm or less.

4. The system of claim 1, wherein the first pre-limiting aperture plate is positioned upstream of the beam-limiting aperture array.

5. The system of claim 2, wherein the first pre-limiting aperture plate is positioned downstream of the beam-limiting aperture array.

6. The system of claim 1, further comprising a second pre-limiting aperture plate.

7. The system of claim 6, wherein the first pre-limiting aperture plate is positioned upstream of the beam-limiting aperture array and the second pre-limiting aperture plate is positioned downstream of the beam-limiting aperture array.

8. The system of claim 1, wherein the plurality of secondary charged particle beams comprises at least one of: secondary electrons or backscattered electrons from the sample generated in response to interactions between the plurality of primary charged particle beams and the sample.

9. The system of claim 1, wherein the beam-limiting aperture array comprises a plurality of apertures of different sizes.

10. The system of claim 9, wherein at least two apertures of the plurality of apertures have similar sizes.

11. The system of claim 9, wherein the plurality of apertures are arranged in a rectangular, circular, or spiral pattern.

12. The system of claim 11, wherein the plurality of secondary charged particle beams overlap to create an intersection region in an intersection plane perpendicular to a secondary optical axis of the electro-optical system.

13. The system of claim 12, wherein the beam-limiting aperture array is placed at or within the location of the intersection plane and is placed perpendicular to the secondary optical axis.

14. The system of claim 13, wherein the range of positions of the intersection plane is determined based on landing energies of multiple primary charged particle beams on the sample.

15. A method performed by a secondary imaging system to form an image of a sample, the method comprising: generating a plurality of secondary charged particle beams from the sample; using a pre-limiting aperture plate to block peripheral charged particles of the plurality of secondary charged particle beams; shaping the plurality of secondary charged particle beams using apertures of a beam limiting aperture array; and projecting the trimmed multiple secondary charged particle beams onto corresponding detection elements of the charged particle detector, wherein the beam limiting aperture array comprises a plurality of apertures, and The beam-limiting aperture array is configured to be movable along an x-axis and / or a y-axis direction such that each aperture of the plurality of apertures can be selected for the secondary charged particle beam.

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