Multiple charged particle beam devices

Abstract

An apparatus for multiple charged particle beams is disclosed. A secondary projection imaging system in a multiple beam apparatus is proposed, which enables secondary electron detection with high collection efficiency and low crosstalk. The system uses a zoom lens, a projection lens and an anti-scanning deflection unit. The zoom lens and the projection lens perform a zoom function and an anti-rotation function, respectively, to maintain a total imaging magnification and a total image rotation relative to the landing energy and / or current of multiple primary beamlets. The anti-scanning deflection unit performs an anti-scanning function to eliminate dynamic image shifts caused by deflection scanning of multiple primary beamlets.

Description

[0001] This application is a divisional application of the patent application with application number 201680069949.4 and invention name “Device for Multiple Charged Particle Beams”, which entered the Chinese national phase on May 30, 2018 (international application date is 2016-11-30, international application number is PCT / US2016 / 064195). Technical Field

[0002] The present invention relates to a charged particle device having multiple charged particle beams. More specifically, the present invention relates to a device that uses multiple charged particle beams to simultaneously acquire images of multiple scanned regions of an observation region on a surface of a sample. Thus, the device can be used to inspect and / or review defects on wafers / masks at high resolution and high throughput in the semiconductor manufacturing industry. Background Art

[0003] In order to manufacture semiconductor IC chips, pattern defects and / or unauthorized particles (residues) inevitably appear on the surface of the wafer / mask during the manufacturing process, which greatly reduces the yield. In order to meet the increasingly advanced requirements for IC chip performance, patterns with smaller and smaller critical feature sizes have been adopted. Therefore, traditional yield management tools with light beams have gradually become incompetent due to diffraction effects, and yield management tools with electron beams are increasingly being adopted. Compared with photon beams, electron beams have shorter wavelengths, which may provide excellent spatial resolution. At present, yield management tools with electron beams use the principle of single electron beam scanning electron microscope (SEM), so it can provide higher resolution, but cannot provide production volume that is competent for mass production. Although higher and higher beam currents can be used to increase production volume, the excellent spatial resolution will be fundamentally deteriorated by the Coulomb effect as the beam current increases.

[0004] In order to alleviate the limitation on production volume, instead of using a single electron beam with a large current, a promising solution is to use multiple electron beams with small currents. Multiple electron beams form multiple probe spots on a surface of a sample being inspected or observed. Multiple probe spots can scan multiple small scanning areas within a large observation area on the surface of the sample separately and simultaneously. The electrons of each probe spot generate secondary electrons from the surface of the sample where they land. Secondary electrons include secondary slow electrons (energy ≤ 50eV) and backscattered electrons (energy close to the electron landing energy). Secondary electrons from multiple small scanning areas can be collected separately and simultaneously by multiple electron detectors. Therefore, images of a large observation area can be obtained faster than scanning a large observation area with a single beam.

[0005] Multiple electron beams can come from multiple electron sources or from a single electron source. For the former, multiple electron beams are usually focused to multiple small scanning areas by multiple mirror cylinders and scan multiple small scanning areas respectively by multiple mirror cylinders, and the secondary electrons from each scanning area are detected by an electron detector in the corresponding mirror cylinder. Therefore, the device is usually called a multi-mirror cylinder device. Multiple mirror cylinders can be independent or shared multi-axis magnetic or electromagnetic composite mirrors (as shown in US 8,294,095). On the surface of the sample, the beam spacing or pitch between two adjacent beams is usually as large as 30 to 50 mm.

[0006] For the latter, the source conversion unit actually changes the single electron source into multiple sub-sources. The source conversion unit includes a beamlet forming (or beamlet limiting) device with multiple beam limiting openings and an imaging device with multiple electron optical elements. Multiple beam limiting openings divide the primary electron beam generated by a single electron source into multiple sub-beams or beamlets, and multiple electron optical elements (such as circular lenses of US 7,244,949 or deflectors such as those in the cross reference) affect multiple beamlets to form multiple parallel (virtual if deflectors are used, real if circular lenses are used) images of a single electron source. Each image can be regarded as a sub-source, which emits a corresponding beamlet. In order to make more beamlets available, the beamlet spacing is at the micron level. Naturally, a primary projection imaging system and a deflection scanning unit in a single barrel are used to project multiple parallel images onto multiple small scanning areas and scan them respectively. In the single barrel, multiple secondary electron beams generated by multiple small scanning areas are detected by multiple detection elements of an electronic detection device. The multiple detection elements can be multiple electron detectors (such as PMT, SDD) placed side by side or multiple pixels of one electron detector (such as e-CCD and SDD). Therefore, the device is usually called a multi-beam device.

[0007] FIG1 shows an embodiment of a multi-beam device (cross-referenced U.S. application No. 15 / 216,258). An electron source 101 generates a primary electron beam 102 along a main optical axis 100_1 and has a source electron cross 101s, whose peripheral electrons are intercepted by a main aperture plate 171. A movable condenser lens 110 collimates the primary electron beam 102, which is then vertically incident on a light source conversion unit 120. Three beamlets 102_1, 102_2, and 102_3 of the primary electron beam 102 pass through three beam limiting openings 121_1, 121_2, and 121_3 of a beamlet forming device 121, respectively, and are deflected to form three virtual images (located far away and difficult to show here) of the source electron cross 101s by three micro deflectors 122_1, 122_2, and 122_3 of an imaging device 122. The objective lens 131 focuses the three deflected beamlets 102_1, 102_2 and 102_3 onto the surface 7 of the sample 8, and thus generates three images 102_1S, 102_2S and 102_3S of the source electron cross 101s at equal intervals or pitches Ps thereon. Each image forms a probe spot on the surface 7, and these three images are also referred to as three probe spots 102_1S, 102_2S and 102_3S. The deflection scanning unit 132 deflects the three beamlets 102_1 to 102_3 together, and thus the three probe spots 102_1S to 102_3S respectively scan a scanning area of ​​the surface 7. The main plane 110_2 of the movable condenser lens 110 can be electrically moved along the main optical axis 100_1 within a desired range. By correctly changing the focusing power and the principal plane position of the movable condenser lens 110 simultaneously, the current density of the collimated primary electron beam 102 can be changed, and the currents of the three probe spots 102_1S to 102_3S will change accordingly.

[0008] In a multi-beam device, multiple detection elements are placed on an image plane on the surface of the sample, where each secondary electron beam from a small scanning area is focused onto a corresponding detection element. Since the emission of secondary electrons conforms to Lambert's law and has a large energy spread, all secondary electrons of each secondary electron beam cannot be completely focused into the corresponding detection element. The secondary electrons detected by one detection element can be divided into two parts, the first part includes a part from the corresponding secondary electron beam, and the second part includes the remaining part from the remaining secondary electron beams. These two parts respectively determine the collection efficiency of the secondary electrons from the corresponding small scanning area and the crosstalk level between multiple small scanning areas, and both affect the image resolution of the corresponding small scanning area.

[0009] The image plane can be an image plane formed by only the objective lens of a single projection imaging system (e.g., US6,943,349), or an image plane formed by a secondary projection imaging system (150 in FIG. 1 ) and an objective lens, such as US 9,035,249 and US application No. 15 / 065,342. In the first case, the position of the image plane and the imaging magnification thereon vary with the operating conditions of the objective lens, and the operating conditions vary with the landing energy and / or current of the multiple beamlets. Therefore, multiple detection elements can only provide high collection efficiency and low crosstalk levels for certain specific applications. In the second case, the secondary projection imaging system can maintain the position of the image plane and the imaging magnification thereon relative to the operating conditions of the objective lens, thereby being able to provide high collection efficiency and low crosstalk levels even when the landing energy and / or current vary over a wide range.

[0010] In FIG1 , each secondary electron beam generated by each probe spot (e.g., 102_1se due to the probe spot 102_1S) travels in the opposite direction of the main optical axis 100_1. After being focused by the objective lens 131 and deflected by the deflection scanning unit 132, the three secondary electron beams 102_1se, 102_2se, and 102_3se are intentionally turned by the beam splitter 160 (such as a Wien filter) to enter the secondary projection imaging system 150 along the secondary optical axis 150_1 of the secondary projection imaging system 150. The secondary projection imaging system 150 focuses the three secondary electron beams 102_1se to 102_3se onto the electronic detection device 140 having three detection elements with equal pitch Pd, that is, three secondary electron spots are formed inside the three detection elements, respectively. Therefore, the electronic detection device 140 can simultaneously generate images of three scanning areas scanned by the three probe spots 102_1S, 102_2S, and 102_3S, respectively.

[0011] As described above, a secondary projection imaging system is critical to providing high collection efficiency and low crosstalk levels even if the landing energies and / or currents of multiple beamlets vary over a wide range. High collection efficiency is particularly advantageous for achieving high detection throughput, and low crosstalk is particularly advantageous for achieving high detection resolution. Therefore, the performance of a secondary projection imaging system ultimately determines both detection resolution and detection throughput. The present invention will provide a secondary projection imaging system with advanced performance for multi-beam equipment, particularly for use as a yield management tool in the semiconductor manufacturing industry. Summary of the invention

[0012] The object of the present invention is to provide a re-projection imaging system for a multi-beam device, which can detect secondary electrons with high collection efficiency and low crosstalk level even when the landing energy and / or current of multiple beamlets vary over a wide range. As a yield management tool in the semiconductor manufacturing industry, the multi-beam device can therefore achieve high detection resolution and high detection throughput under many application conditions.

[0013] Therefore, the present invention provides a multi-beam device for observing the surface of a sample, which includes an electron source, a focusing lens located below the electron source, a source conversion unit located below the focusing lens, an objective lens located below the source conversion unit, a deflection scanning unit located below the source conversion unit, a sample stage located below the objective lens, a beam splitter located below the source conversion unit, and a detection unit located above the beam splitter, the detection unit having a secondary projection imaging system and an electronic detection device having multiple detection elements.

[0014] The electron source, the condenser lens, the source conversion unit, the objective lens, the deflection scanning unit and the beam splitter are aligned with the main optical axis of the multi-beam device. The sample stage supports the sample so that the surface faces the objective lens. The detection unit is aligned with the secondary optical axis of the multi-beam device, and the secondary optical axis is not parallel to the primary optical axis.

[0015] A plurality of detection elements are placed on a detection plane, and the secondary projection imaging system includes a zoom lens, an anti-scanning deflection unit and a projection lens.

[0016] The electron source generates a primary electron beam along the main optical axis. The condenser lens focuses the primary electron beam to a certain degree. The source conversion unit changes the primary electron beam into a plurality of beamlets (or sub-beams) and causes the plurality of beamlets to form a plurality of first images of the electron source. The objective lens focuses the plurality of beamlets to image the plurality of first images onto the surface, and thus forms a plurality of probe spots on the surface, respectively. The deflection scanning unit deflects the plurality of beamlets to scan the plurality of probe spots on a plurality of scanning areas within an observation area on the surface, respectively.

[0017] A plurality of secondary electron beams are generated from a plurality of scanning areas by a plurality of probe spots, respectively, and then incident on an objective lens. The objective lens focuses the plurality of secondary electron beams when the plurality of secondary electron beams pass therethrough. The beam splitter deflects the plurality of secondary electron beams to enter the secondary projection imaging system along the secondary optical axis. The zoom lens focuses the plurality of secondary electron beams onto a transmission plane. The transmission plane is located between the zoom lens and the projection lens. The plurality of secondary electron beams form a first intersection between the zoom lens and the transmission plane.

[0018] The projection lens then focuses the multiple secondary electron beams onto the detection plane. The multiple secondary electron beams form a second intersection between the projection lens and the detection plane, and form multiple secondary electron spots on the detection plane. The multiple secondary electron spots are respectively located inside the multiple detection elements. Therefore, a corresponding relationship between the multiple probe spots and the multiple detection elements is established. Therefore, each detection element generates an image signal of a corresponding scanning area.

[0019] The anti-scanning deflection unit deflects the plurality of secondary electron beams synchronously with the scanning of the plurality of probe spots on the plurality of scanning areas to maintain the positions of the plurality of secondary electron spots, thereby always maintaining the corresponding relationship.

[0020] The imaging magnification of the zoom lens is adjusted to maintain the correspondence when observing the surface under different conditions.

[0021] The device may further include a secondary beam limiting hole for cutting off peripheral electrons of a plurality of secondary electron beams. The device may further include a field lens placed at a transmission plane to reduce off-axis aberrations of the projection lens. The device may further include an astigmatism correction device for compensating for astigmatism aberrations of a plurality of secondary electron beams caused by a beam splitter. The device may further include an alignment deflector for compensating for deviations in the corresponding relationship caused by manufacturing and / or assembly errors of the detection unit. The anti-scanning deflection unit is located between the beam splitter and the zoom lens.

[0022] In one embodiment, the zoom lens includes a first zoom sub-lens and a second zoom sub-lens, and the second zoom sub-lens is located between the first zoom sub-lens and the transmission plane. The anti-scanning deflection unit is located between the first zoom sub-lens and the second zoom sub-lens. The anti-scanning deflection unit deflects multiple secondary electron beams incident on the second zoom sub-lens along the secondary optical axis. The secondary projection imaging system includes a field lens, which is placed at the transmission plane to reduce the radial offset and tilt angle of multiple secondary electron beams incident on the projection lens. The secondary projection imaging system includes a secondary beam limiting aperture plate having one opening or more openings, and one of the one or more openings is located at the position of the second intersection to cut off peripheral electrons of multiple secondary electron beams. The secondary projection imaging system includes a field lens, which is placed at the transmission plane to bend multiple secondary electron beams to maintain the position of the second intersection when observing the surface under different conditions.

[0023] In one embodiment, the secondary projection imaging system may include an astigmatism correction device placed at or near the first intersection to compensate for astigmatism aberrations of the multiple secondary electron spots caused by the beam splitter.

[0024] In one embodiment, the objective lens has a first magnetic lens. The field lens may have a second magnetic lens that eliminates rotational changes of multiple secondary electron spots when observing the surface under different conditions. The zoom lens may have a second magnetic lens that eliminates rotational changes of multiple secondary electron spots when observing the surface under different conditions. The projection lens may have a second magnetic lens that eliminates rotational changes of the multiple secondary electron spots when observing the surface under different conditions.

[0025] In one embodiment, the secondary projection imaging system includes an alignment deflector located between the secondary beam limiting aperture plate and the detection plane to compensate for the deviation of the corresponding relationship caused by the manufacturing and / or assembly errors of the detection unit. The multiple secondary electron beams are multiple secondary slow electron beams. The multiple secondary electron beams are multiple backscattered electron beams.

[0026] The present invention also provides a multi-beam device for observing the surface of a sample, which includes an electron source, a focusing lens located below the electron source, a source conversion unit located below the focusing lens, an objective lens located below the source conversion unit, a deflection scanning unit located below the source conversion unit, a sample stage located below the objective lens, a beam splitter located below the source conversion unit, and a detection unit located above the beam splitter, the detection unit including a secondary projection imaging system and an electronic detection device having multiple detection elements.

[0027] The electron source, the condenser lens, the source conversion unit, the objective lens, the deflection scanning unit and the beam splitter are aligned with the main optical axis of the multi-beam device. The sample stage supports the sample so that the surface faces the objective lens. The detection unit is aligned with the secondary optical axis of the multi-beam device, and the secondary optical axis is not parallel to the primary optical axis.

[0028] A plurality of detection elements are placed on the detection plane. The secondary projection imaging system includes a zoom lens, an anti-scanning deflection unit, a projection lens, a first field lens located at a first transmission plane, and a second field lens located at a second transmission plane. The first field lens and the second field lens are located between the zoom lens and the projection lens. The first field lens is located between the second field lens and the projection lens.

[0029] The electron source generates a primary electron beam along the main optical axis. The condenser lens focuses the primary electron beam to a certain degree. The source conversion unit changes the primary electron beam into a plurality of beamlets and causes the plurality of beamlets to form a plurality of first images of the electron source. The objective lens focuses the plurality of beamlets to image the plurality of first images onto the surface, and thus forms a plurality of probe spots on the surface, respectively. The deflection scanning unit deflects the plurality of beamlets to scan the plurality of probe spots on a plurality of scanning areas within an observation area on the surface, respectively.

[0030] A plurality of secondary slow electron beams and a plurality of backscattered electron beams are respectively generated from the plurality of scanning areas by a plurality of probe spots and then incident on an objective lens which focuses the plurality of secondary slow electron beams and the plurality of backscattered electron beams when the plurality of secondary slow electron beams and the plurality of backscattered electron beams pass therethrough.

[0031] When the beam splitter deflects the plurality of secondary slow electron beams and the plurality of backscattered electron beams respectively to enter the secondary projection imaging system along the secondary optical axis, the detection unit operates in the SSE mode and the BSE mode respectively.

[0032] In the SSE mode, the second field lens is turned off. The zoom lens focuses multiple secondary slow electron beams onto the first transmission plane. The first field lens bends the multiple secondary slow electron beams toward the secondary optical axis. The projection lens focuses the multiple secondary slow electron beams onto the detection plane. The multiple secondary slow electron beams then form an SSE intersection between the projection lens and the detection plane, and form multiple secondary slow electron spots on the detection plane. The multiple secondary slow electron spots are respectively located inside the multiple detection elements. Therefore, an SSE correspondence between the multiple probe spots and the multiple detection elements is established. Therefore, each detection element generates an SSE image signal of a corresponding scanning area.

[0033] In the BSE mode, the first field lens is turned off. The zoom lens focuses the multiple backscattered electron beams onto the second transmission plane. The second field lens bends the multiple backscattered electron beams toward the secondary optical axis. The projection lens focuses the multiple backscattered electron beams onto the detection plane. Then, the multiple backscattered electron beams form a BSE intersection between the projection lens and the detection plane, and form multiple backscattered electron spots on the detection plane. The multiple backscattered electron spots are respectively located inside the multiple detection elements. Therefore, a BSE correspondence between the multiple probe spots and the multiple detection elements is established. Therefore, each detection element generates a BSE image signal of a corresponding scanning area.

[0034] In the SSE mode, the anti-scanning deflection unit deflects the plurality of secondary slow electron beams in synchronization with the scanning of the plurality of probe spots on the plurality of scanning areas to maintain the positions of the plurality of secondary slow electron spots, thereby always maintaining the SSE corresponding relationship.

[0035] In the BSE mode, the anti-scanning deflection unit deflects the multiple backscattered electron beams synchronously with the scanning of the multiple probe spots on the multiple scanning areas to maintain the positions of the multiple backscattered electron spots, thereby always maintaining the corresponding relationship of BSE.

[0036] When observing the surface under different conditions, the imaging magnification of the zoom lens is adjusted to maintain the SSE correspondence and the BSE correspondence in the SSE mode and the BSE mode, respectively.

[0037] In one embodiment, the secondary projection imaging system includes a first secondary beam limiting hole, which is placed at the SSE intersection to cut off the peripheral electrons of multiple secondary slow electron beams in the SSE mode. The secondary projection imaging system includes a second secondary beam limiting hole, which is placed at the BSE intersection to cut off the peripheral electrons of multiple backscattered electron beams in the BSE mode. The secondary projection imaging system includes a first astigmatism correction device, which is used to compensate for the astigmatism aberrations of multiple secondary slow electron beams caused by the beam splitter in the SSE mode. The secondary projection imaging system includes a second astigmatism correction device, which is used to compensate for the astigmatism aberrations of multiple backscattered electron beams caused by the beam splitter in the BSE mode. The secondary projection imaging system includes an alignment deflector, and in the SSE mode and the BSE mode, the alignment deflector compensates for the deviations of the SSE correspondence and the BSE correspondence caused by the manufacturing and / or assembly errors of the detection unit, respectively. The anti-scanning deflection unit is located between the beam splitter and the zoom lens.

[0038] In one embodiment, the zoom lens includes a first zoom sub-lens and a second zoom sub-lens, and the second zoom sub-lens is located between the first zoom sub-lens and the second field lens. The anti-scanning deflection unit deflects multiple secondary slow electron beams in the SSE mode and multiple backscattered electron beams in the BSE mode incident on the second zoom sub-lens along the secondary optical axis. The secondary projection imaging system includes a first secondary beam limiting aperture plate and a second secondary beam limiting aperture plate, each of which has one or more openings. In the SSE mode, one opening of the first secondary beam limiting aperture plate is placed at the SSE intersection to cut off the peripheral electrons of the multiple secondary slow electron beams, and in the BSE mode, one opening of the second secondary beam limiting aperture is placed at the BSE intersection to cut off the peripheral electrons of the multiple backscattered electron beams. By adjusting the first field lens and the second field lens respectively, the SSE intersection and the BSE intersection are set at the same position. The secondary projection imaging system includes a third secondary beam limiting aperture plate having one opening or more openings, and in each of the SSE mode and the BSE mode, the one opening or one of the more openings is set at the same position. The secondary projection imaging system comprises an astigmatism correction device placed near the third secondary beam limiting aperture plate, which compensates for the astigmatism aberration of multiple secondary slow electron spots and multiple backscattered electron spots in SSE mode and BSE mode respectively caused by the beam splitter.

[0039] In one embodiment, the objective lens has a first magnetic lens. The first field lens may have a second magnetic lens, which eliminates the rotational changes of multiple secondary slow electron spots in the SSE mode when observing the surface under different conditions. The second field lens may have a third magnetic lens, which eliminates the rotational changes of multiple backscattered electron spots in the BSE mode when observing the surface under different conditions. The zoom lens may have a second magnetic lens, which eliminates the rotational changes of multiple secondary slow electron spots in the SSE mode and multiple backscattered electron spots in the BSE mode when observing the surface under different conditions. The projection lens may have a second magnetic lens, which eliminates the rotational changes of multiple secondary slow electron spots in the SSE mode and multiple backscattered electron spots in the BSE mode when observing the surface under different conditions.

[0040] In one embodiment, the secondary projection imaging system comprises an alignment deflector which compensates for deviations of the SSE correspondence and the BSE correspondence, respectively, caused by manufacturing and / or assembly errors of the detection unit.

[0041] The present invention also provides a method for configuring a detection system of a multi-beam device for observing the surface of a sample, the method comprising the following steps: using a beam splitter to deflect multiple secondary electron beams generated by multiple probe spots on the surface to travel along the secondary optical axis of the multi-beam device; using a zoom lens to focus the multiple secondary electron beams onto a transmission plane, wherein the zoom lens is aligned with the secondary optical axis; using a projection lens to focus the multiple secondary electron beams from the transmission plane to a detection plane and form multiple secondary electron spots on the detection plane, wherein the projection lens is aligned with the secondary optical axis; using an electronic detection device having multiple detection elements to respectively detect the multiple secondary electron spots, wherein the multiple detection elements are placed on the detection plane; using an anti-scanning deflection unit to deflect the multiple secondary electron beams synchronously with the scanning of the multiple probe spots on multiple scanning areas on the surface to always maintain the positions of the multiple secondary electron spots; and when observing the surface under different conditions, adjusting the zoom lens and the projection lens to eliminate radial changes and rotational changes in the positions of the multiple secondary electron spots.

[0042] The method may further include the step of using a secondary beam limiting aperture to cut off peripheral electrons in the plurality of secondary electron beams. The method may further include the step of using a field lens to reduce off-axis aberrations of the plurality of secondary electron spots. The method may further include the step of using an astigmatism correction device to compensate for astigmatism aberrations of the plurality of secondary electron spots caused by a beam splitter. The method may further include the step of using an alignment deflector to compensate for offsets between the plurality of secondary electron spots and the plurality of detection elements due to manufacturing and / or assembly errors of the detection unit.

[0043] The present invention also provides a method of configuring a detection system of a multi-beam device for observing a surface of a sample, the method comprising the steps of operating in an SSE mode and operating in a BSE mode. The steps of operating in the SSE mode include the following steps: using a beam splitter to deflect multiple secondary slow electron beams generated by multiple probe spots on the surface to travel along the secondary optical axis of the multi-beam device; using a zoom lens aligned with the secondary optical axis to focus the multiple secondary slow electron beams onto a first transmission plane; using a first field lens aligned with the secondary optical axis and placed at the first transmission plane to bend the multiple secondary slow electron beams; using a projection lens aligned with the secondary optical axis to focus the multiple secondary electron beams onto a detection plane and form an SSE intersection between the projection lens and the detection plane and form multiple secondary slow electron spots on the detection plane; using an electronic detection device with multiple detection elements to respectively detect the multiple secondary slow electron spots, wherein the multiple detection elements are placed on the detection plane; using an anti-scanning deflection unit to deflect the multiple secondary slow electron beams synchronously with the scanning of multiple probe spots on multiple scanning areas on the surface to always maintain the positions of the multiple secondary slow electron spots; and adjusting the zoom lens and the projection lens when observing the surface under different conditions to eliminate radial changes and rotational changes in the positions of the multiple secondary slow electron spots, respectively. The steps of operating in the BSE mode include the following steps: using a beam splitter to deflect multiple backscattered electron beams generated by multiple probe spots on the surface to travel along the secondary optical axis of the multi-beam device; using a zoom lens to focus the multiple backscattered electron beams onto a second transmission plane; using a second field lens aligned with the secondary optical axis and placed at the second transmission plane to bend the multiple backscattered electron beams; using a projection lens to focus the multiple backscattered electron beams onto a detection plane and form a BSE cross between the projection lens and the detection plane and form multiple backscattered electron spots on the detection plane; using multiple detection elements to respectively detect the multiple backscattered electron spots; using an anti-scanning deflection unit to deflect the multiple backscattered electron beams synchronously with the scanning of the multiple probe spots on the multiple scanning areas to always maintain the positions of the multiple backscattered electron spots; and adjusting the zoom lens and the projection lens when observing the surface under different conditions to eliminate radial changes and rotational changes in the positions of the multiple backscattered electron spots, respectively.

[0044] In one embodiment, the step of operating in SSE mode includes the sub-step of using a first secondary beam limiting aperture at an SSE intersection to cut off peripheral electrons of a plurality of secondary slow electron beams. The step of operating in BSE mode includes the sub-step of using a second secondary beam limiting aperture at a BSE intersection to cut off peripheral electrons of a plurality of backscattered electron beams. The SSE intersection and the BSE intersection are located at or near the same position. The step of operating in SSE mode includes the sub-step of using an astigmatism correction device placed near the same position to compensate for astigmatism aberrations of a plurality of secondary slow electron beams caused by a beam splitter. The step of operating in BSE mode includes the sub-step of using an astigmatism correction device to compensate for astigmatism aberrations of a plurality of backscattered electron spots caused by a beam splitter. The step of operating in SSE mode includes the sub-step of using an alignment deflector to compensate for offsets between a plurality of secondary slow electron spots and a plurality of detection elements due to manufacturing and / or assembly errors of the detection unit. The step of operating in BSE mode includes the sub-step of using an alignment deflector to compensate for offsets between a plurality of backscattered electron spots and a plurality of detection elements due to manufacturing and / or assembly errors of the detection unit.

[0045] The present invention also provides an imaging system for a detection device in a multi-beam device, which includes a device for focusing multiple charged particle beams emitted from the surface of a sample onto multiple detection elements of the detection device respectively and a device for eliminating the rotation of the multiple charged particle beams caused by a magnetic objective lens in the multi-beam device.

[0046] In one embodiment, the imaging system may further include a device for eliminating scanning of multiple charged particle beams caused by a deflection scanning unit in a multi-beam device on a detection device. The multiple charged particle beams include multiple secondary slow electron beams and multiple backscattered electron beams. The detection device is a semiconductor diode detector. The device for eliminating scanning is located near the entrance side of the imaging system. The device for eliminating scanning includes a first deflector and a second deflector sequentially along the optical axis of the imaging system. The focusing device includes a zoom lens and a projection lens sequentially along the optical axis.

[0047] In one embodiment, the magnetic objective lens and the zoom lens focus multiple charged particle beams into a transmission plane, and the projection lens focuses the multiple charged particle beams from the transmission plane into a detection plane on a detection device. The zoom lens includes a first electrostatic lens and a second electrostatic lens along the optical axis in sequence. The device for eliminating scanning is located between the first electrostatic lens and the second electrostatic lens. The zoom lens may include a magnetic lens as the device for eliminating rotation. The projection lens may include an electrostatic lens and a magnetic lens as the device for eliminating rotation.

[0048] In one embodiment, the imaging system may further include a field mirror at the transmission plane for reducing aberrations of the plurality of charged particle beams. The field mirror includes an electrostatic lens. The field mirror may include a magnetic lens as the means for eliminating rotation.

[0049] In one embodiment, the imaging system may further include a plate having at least one opening, one opening of the plate serving as a beam limiting aperture for reducing the size of the plurality of charged particle beams on the detection device. The plate includes a plurality of openings having different sizes that can be selected. The plate is located at the intersection of the plurality of charged particle beams between the projection lens and the detection device.

[0050] In one embodiment, the imaging system may further include an astigmatism correction device for reducing astigmatism of the plurality of charged particle beams. The astigmatism correction device is located at the intersection of the plurality of charged particle beams.

[0051] In one embodiment, the imaging system may further include an alignment deflector for respectively aligning the plurality of charged particle beams with the plurality of detection elements of the detection device. The alignment deflector is located between the detection device and the projection lens.

[0052] Other advantages of the present invention will become apparent from the following description taken in conjunction with the accompanying drawings, in which certain embodiments of the invention are illustrated and described by way of example. BRIEF DESCRIPTION OF THE DRAWINGS

[0053] The present invention will be readily understood by the following detailed description taken in conjunction with the accompanying drawings, in which like reference numerals denote like structural elements, and in which:

[0054] FIG. 1 is a schematic diagram of a conventional configuration of a multi-beam device.

[0055] Figure 2 is a schematic diagram of a secondary projection imaging system according to an embodiment of the present invention.

[0056] Figure 3A is a schematic diagram of a secondary projection imaging system according to another embodiment of the present invention.

[0057] Figure 3B According to the present invention Figure 3A Schematic diagram of the traveling secondary slow electrons in the secondary projection imaging system.

[0058] Figures 4A to 4C yes Figure 3B Schematic diagram of the secondary electron spot on the electron detection device in .

[0059] Figure 5 According to the present invention Figure 3A Schematic diagram of the anti-scan deflection unit operating in FIG.

[0060] Figures 6A to 6C According to the present invention Figure 3A Schematic diagram of three configurations of the electromagnetic compound projection lens.

[0061] Fig. 7A is a schematic diagram of a secondary projection imaging system according to another embodiment of the present invention.

[0062] Figure 7B According to the present invention Fig. 7A Schematic diagram of the traveling secondary slow electrons in the secondary projection imaging system.

[0063] Fig. 8A is a schematic diagram of a secondary projection imaging system according to another embodiment of the present invention.

[0064] Figure 8B According to the present invention Fig. 8A Schematic diagram of the traveling secondary slow electrons in the secondary projection imaging system.

[0065] Fig.9A is a schematic diagram of a secondary projection imaging system according to another embodiment of the present invention.

[0066] Fig. 9B According to the present invention Fig.9A Schematic diagram of the traveling secondary slow electrons in the secondary projection imaging system.

[0067] Fig. 9C According to the present invention Fig.9A Schematic diagram of backscattered electrons traveling in the reprojection imaging system.

[0068] Fig. 10A is a schematic diagram of a secondary projection imaging system according to another embodiment of the present invention.

[0069] Fig. 10B is a schematic diagram of a secondary projection imaging system according to another embodiment of the present invention.

[0070] Fig.11A is a schematic diagram of a secondary projection imaging system according to another embodiment of the present invention.

[0071] Fig. 11B According to the present invention Fig.11A Schematic diagram of the traveling secondary slow electrons in the secondary projection imaging system.

[0072] Fig.12 is a schematic diagram of a secondary projection imaging system according to another embodiment of the present invention.

[0073] Fig.13A and Fig. 13BSchematic diagram of two options for realizing the anti-rotation function in the secondary projection imaging system according to the present invention.

[0074] Fig.14 is a schematic diagram of a secondary projection imaging system according to another embodiment of the present invention.

[0075] Fig.15A is a schematic diagram of a configuration of a multi-beam device according to another embodiment of the present invention.

[0076] Fig. 15B is based on Fig.15A Schematic diagram of a detection system of an embodiment. DETAILED DESCRIPTION

[0077] Various exemplary embodiments of the present invention will now be described more fully with reference to the accompanying drawings, in which some exemplary embodiments of the present invention are shown. Without limiting the scope of the present invention, all descriptions and drawings of the embodiments will be exemplarily related to electron beams. However, these embodiments are not intended to limit the present invention to specific charged particles.

[0078] In the drawings, each component and the relative size therein may be exaggerated for clarity. In the following description of the drawings, the same or similar reference numerals refer to the same or similar components or entities, and only the differences with respect to the various embodiments are described.

[0079] Therefore, although the exemplary embodiments of the present invention can have various modifications and alternative forms, their embodiments are shown in the drawings by way of example and will be described in detail herein. However, it should be understood that it is not intended to limit the exemplary embodiments of the present invention to the specific forms disclosed, but on the contrary, the exemplary embodiments of the present invention will cover all modifications, equivalents and alternatives falling within the scope of the present invention.

[0080] In the present invention, "axial" means "in the direction of the optical axis of an electronic optical element (such as a circular lens or a multipole lens), an imaging system or a device", "radial" means "in the direction perpendicular to the optical axis", "on-axis" means "on the optical axis or aligned with the optical axis", and "off-axis" means "not on the optical axis or not aligned with the optical axis".

[0081] In the present invention, "the imaging system is aligned with the optical axis" means "all electron optical elements are aligned with the optical axis".

[0082] In the present invention, the X, Y and Z axes form a Cartesian coordinate system. The main optical axis of the primary projection imaging system is on the Z axis, and the primary electron beam travels along the Z axis.

[0083] In the present invention, "primary electrons" refer to "electrons emitted from an electron source and incident on a surface of a sample to be observed or inspected," and "secondary electrons" refer to electrons generated from the surface by "primary electrons."

[0084] In the present invention, "secondary electron beam intersection" means "a cross of secondary electron beams", "secondary beam limiting hole" means "an opening that limits a secondary electron beam", and "primary beam limiting opening" means "an opening that limits a primary beamlet".

[0085] The present invention proposes a secondary projection imaging system for a multi-beam device. In order to clearly describe how the secondary projection imaging system works in a multi-beam device, the embodiment 100A in FIG1 is taken as an example. For the sake of clarity, only three beamlets are shown, and the number of beamlets can be any number.

[0086] In FIG1 , three secondary electron beams 102_1se, 102_2se, and 102_3se generated by three probe spots 102_1S, 102_2S, and 102_3S respectively travel in the opposite direction to the main optical axis 100_1, and sequentially pass through the objective lens 131 and the deflection scanning unit 132. Then, the beam splitter 160 (Wien filter) deflects the three secondary electron beams to enter the secondary projection imaging system 150 along its secondary optical axis 150_1. The secondary projection imaging system 150 focuses the three secondary electron beams 102_1se to 102_3se onto three detection elements of the electronic detection device 140. Therefore, the three detection elements respectively and simultaneously generate image signals of the three scanning areas scanned by the three probe spots 102_1S to 102_3S. The electronic detection device 140 and the secondary projection imaging system 150 form a detection unit 180. The electron optical elements on the path of the secondary electron beam, namely the objective lens 131, the deflection scanning unit 132, the beam splitter 160, the secondary projection imaging system 150 and the electron detection device 140, form a detection system.

[0087] As is known to all, the emission of secondary electrons basically follows Lambert's law and has a large energy divergence. The energy of a secondary slow electron is as high as 50eV, and is mostly close to 1-5eV depending on the sample material, while the energy of a backscattered electron is as high as the landing energy of a primary electron, and is mostly close to the landing energy of a primary electron. Therefore, the secondary slow electrons and the backscattered electrons are very different in energy. Depending on the characteristics and materials of the sample, the landing energy range commonly used is 0.1keV-5keV, which is almost equal to the energy difference between the secondary slow electron beam and the backscattered electron beam. However, such a large energy difference brings two problems. First, since the focusing effect of the objective lens 131 on electrons increases as its energy decreases, the focusing ability or power of the secondary slow electron beam is stronger than that of the backscattered electron beam. Therefore, for each probe spot (e.g., 102_1S), the objective lens focuses the secondary slow electron beam and the backscattered electron beam into two different image planes with two different imaging magnifications. Secondly, since the deflection effect of the beam splitter 160 on electrons increases as their energy decreases, the deflection power of the secondary slow electron beam is stronger than the deflection power of the backscattered electron beam. Therefore, for each probe spot (such as 102_1S), the beam splitter 160 cannot simultaneously deflect the secondary slow electron beam and the backscattered electron beam to enter the secondary projection imaging system 150 along the secondary optical axis 150_1. Therefore, unlike a conventional SEM, for each scanning area scanned by one probe spot, the detection system cannot detect an image formed by the secondary slow electrons and the backscattered electrons together. Accordingly, the detection system will operate in a mode that detects images using secondary slow electrons or a mode that detects images using backscattered electrons (referred to as SSE mode and BSE mode, respectively). In the SSE mode and the BSE mode, the beam splitter 160 deflects the secondary slow electron beam and the backscattered electron beam to enter the secondary projection imaging system 150 along the secondary optical axis 150_1, and the secondary projection imaging system 150 focuses the secondary slow electron beam and the backscattered electron beam onto the detection elements of the electron detection device 140, respectively.

[0088] As described above, for different inspection applications, the landing energy of the beamlets 102_1 to 102_3 can be changed within the range of 0.1 keV to 5 keV. The landing energy can be changed by changing the potential of the single electron source 101 or the potential of the sample 8, or both of them. Therefore, it is necessary to adjust the excitation of the objective lens 131 to provide corresponding focusing capabilities for the three beamlets, and the focusing capabilities of the objective lens 131 on the secondary slow electron beam and the backscattered electron beam are changed accordingly. Therefore, the position and magnification of the images formed by the secondary slow electron beam and the backscattered electron beam, respectively, will change with the landing energy. In addition, the objective lens 131 is typically a magnetic lens or an electromagnetic compound lens due to its low aberration. In this case, the rotation of the images formed by the secondary slow electron beam and the backscattered electron beam, respectively, will also change with the landing energy. The above-mentioned image changes can move the position of the secondary electron spot formed by the secondary electron beam on the electronic detection device 140 to a degree where the secondary electron beam cannot be detected by the corresponding detection element. Therefore, the secondary projection imaging system 150 needs to include a zoom function to eliminate imaging magnification changes and an anti-rotation function to eliminate image rotation changes.

[0089] Since the position of the secondary electron spot will move as the three probe spots 102_1S to 102_3S scan the three scanning areas, when the corresponding probe spot moves to a position adjacent to an adjacent scanning area (that is, the size of each scanning area is close to the pitch Ps, or if the deflection scanning unit 132 has too strong an effect on the deflection of the secondary electrons), each secondary electron spot may partially enter an adjacent detection element. The secondary electrons detected by the adjacent detection elements will produce image overlaps of the three scanning areas. Such image overlaps will degrade the image resolution, so it is necessary to eliminate such image overlaps. Therefore, the secondary projection imaging system needs to have an anti-scanning function to always keep the three secondary electron spots within the corresponding detection elements.

[0090] Next, some embodiments of the secondary projection imaging system 150 will be shown and described together with the entire detection system. Following FIG. 1 , although the number of secondary electron beams can be any number, only three secondary electron beams about three probe spots are shown. Within the entire detection system, starting from the sample 8, the first part is along the main optical axis 100_1, and the second part is along the secondary optical axis 150_1. For clarity, the first part is rotated to be along the secondary optical axis 150_1, so that the entire detection system can be shown as being along a straight optical axis.

[0091] Figure 2An embodiment 150-1 of the secondary projection imaging system 150 in the detection system 100-1D is shown. The embodiment 150-1 includes a zoom lens 151, a projection lens 152 and an anti-scanning deflection unit 157, 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 are placed on the detection plane SP3. The zoom lens 151, the projection lens 152 and the objective lens 131 together project the surface 7 of the sample onto the detection plane SP3, that is, focus the secondary electron beams 102_1se~102_3se to form secondary electron spots on the detection elements 140_1, 140_2 and 140_3 respectively when the deflection scanning unit 132 is turned off. During the period when the deflection scanning unit 132 scans the fine beams 102_1~102_3 on the three scanning areas, the anti-scanning deflection unit 157 keeps the secondary electron spots within the corresponding detection elements.

[0092] The total imaging magnification M from the surface 7 of the sample to the detection plane SP3 is selected according to Pd and Ps, as shown in formula (1).

[0093]

[0094] In this way, each probe spot on the surface of the sample is imaged onto one detection element, thereby ensuring the correspondence between multiple probe spots and multiple detection elements. For different detection applications, the probe spot pitch Pd may be different, and the magnification M will always change accordingly.

[0095] The zoom lens 151 includes two electrostatic lenses 151_11 and 151_12. The image plane of the zoom lens 151 is always located at the transmission plane SP2. The position of the transmission plane SP2 in the SSE mode and the BSE mode is different and fixed. The projection lens 152 includes an electrostatic lens 152_11 and a magnetic lens 152_12, and its image plane is always at the detection plane SP3. The first imaging magnification M1 from the surface 7 of the sample to the transmission plane SP2 is achieved by the objective lens 131 and the zoom lens 151, the second imaging magnification M2 from the transmission plane SP2 to the detection plane SP3 is achieved by the projection lens 152, and the total imaging magnification M from the surface 7 of the sample to the detection plane SP3 is equal to M1*M2. In the SSE mode, the second imaging magnification M2 is preferably greater than the first imaging magnification M1.

[0096] The zoom lens 151 performs a zoom function. By adjusting the focusing capabilities of the two electrostatic lenses 151_11 and 151_12, the imaging magnification M1 can be changed to obtain the desired value of the total imaging magnification M. The projection lens 152 performs an anti-rotation function. By adjusting the magnetic field of the magnetic lens 152_12 and the focusing capability of the electrostatic lens 152_11, the total image rotation and the imaging magnification M2 on the detection plane SP3 can always remain the same. The anti-scanning deflection unit 157 performs an anti-scanning function. By synchronously deflecting the secondary electron beam with the deflection scanning unit 132, the displacement of the three secondary electron spots on the detection plane SP3 can be substantially eliminated. Therefore, the correspondence between multiple probe spots and multiple detection elements can always be maintained.

[0097] Basically, the anti-scanning deflection unit 157 can be placed at any position before the detection plane SP3. 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 anti-scanning deflection unit 157 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 as if the deflection scanning unit 132 is turned off. However, in this case, the zoom lens 151 must be placed away from the beam splitter 160, and thus a large initial aberration is generated. As the secondary projection imaging system 150 is Figure 3A As with the embodiment 150-2 in the detection system 100-2D, placing the anti-scanning deflection unit 157 between the electrostatic lenses 151_11 and 151_12 of the zoom lens 151 is a preferred balance for reducing both initial aberrations and additional aberrations.

[0098] Figure 3BShows how the detection system 100-2D works in SSE mode. First, the objective lens 131 focuses the three secondary slow electron beams 102_1sse, 102_2sse and 102_3sse from the three probe spots 102_1S, 102_2S and 102_3S, and forms a first secondary electron image of the three probe spots on the image plane SP1_sse. The image plane SP1_sse is located below the zoom lens 151 and moves as the operating state of the objective lens 131 changes. The beam splitter 160 deflects the three secondary slow electron beams 102_1sse~102_3sse to enter the secondary projection imaging system 150-2 along the secondary optical axis 150_1. The zoom lens 151 then focuses the three secondary slow electron beams 102_1sse~102_3sse and forms a second secondary electron image of the three probe spots on the transmission plane SP2. The projection lens 152 focuses the three secondary slow electron beams 102_1sse~102_3sse to form a third secondary electron image of three probe spots on the detection plane SP3, and the third secondary electron image then forms three secondary slow electron spots 102_1sseP, 102_2sseP and 102_3sseP respectively inside the three detection elements 140_1, 140_2 and 1403. In the BSE mode, the detection system 100-2D works in the same way, but the positions of the image plane SP1_sse and the transmission plane SP2 will be different from those in the SSE mode.

[0099] The anti-scanning deflection unit 157 compensates for the influence of the deflection scanning unit 132 on the three secondary slow electron beams 102_1sse~102_3sse. When the deflection scanning unit 132 deflects the three beamlets to scan the corresponding scanning area on the surface 7 of the sample, the three secondary slow electron beams 102_1sse~102_3sse are also deflected. On the detection plane SP3, the deflection moves the secondary slow electron spots 102_1sseP~102_3sseP from Figure 4A The original position shown is shifted to Figure 4B On the one hand, the collection efficiency of each secondary slow electron beam is reduced because part of its secondary slow electron spot is not inside the corresponding detection element. On the other hand, two secondary slow electron spots are simultaneously partially located inside one detection element, such as 102_1sseP and 102_2sseP inside 140_1. The image signal from one detection element includes information from more than one scanning area on the surface 7 of the sample, so crosstalk occurs.

[0100] In order to avoid crosstalk, the anti-scanning deflection unit 157 needs to deflect the three secondary slow electron beams to eliminate the offset of the secondary slow electron spot on the detection plane SP3. Figure 5An embodiment 157-1 of the anti-scanning deflection unit 157 is shown, which includes two (may be more) anti-scanning deflectors 157_11 and 157_12. Embodiment 157-1 works in the same way in both SSE mode and BSE mode, and the secondary slow electron beam 102_1sse is taken as an example here. When the deflection scanning unit 132 does not deflect the three beamlets, the secondary slow electron beam 102_1sse passes through the zoom lens 151 and the projection lens 152 along the secondary optical axis 1501 and hits the center of the detection element 140_1, and the path is shown by the thick line. When the deflection scanning unit 132 deflects the three beamlets to some positions away from the center of the corresponding scanning area on the surface 7 of the sample, when entering the electrostatic lens 151_11, the secondary slow electron beam 102_1sse is both offset from the secondary optical axis 150_1 and tilted toward the secondary optical axis 150_1, and the path is shown by the thin line. If the anti-scanning deflection unit 157 is not used, the secondary slow electron beam 102_1sse passes through the electrostatic lens 151_12 and the projection lens 152 along the dotted line path and partially hits the detection element 140_1. The off-axis aberration of the electrostatic lens 151_12 and the projection lens 152 increases, and the secondary slow electron spot 102_1sseP becomes larger as a result. The enlarged spot makes the crosstalk worse. If the anti-scanning deflection unit 157 is used, the first anti-scanning deflector 157_11 deflects the secondary slow electron beam 102_1sse to basically pass through the center of the second anti-scanning deflector 157_12, so the second anti-scanning deflector 157_12 can deflect the secondary slow electron beam 102_1sse back to travel along the secondary optical axis 150_1. In this way, the secondary slow electron beam 102_1sse will pass through the electrostatic lens 151_12 and the projection lens 152 along the same path as when the deflection scanning unit 132 does not deflect the three beamlets (ie, travel along a thick line and hit the center of the detection element 140_1).

[0101] The magnetic lens 152_12 of the projection lens 152 compensates for the effect of the objective lens 131 on the rotation of the three secondary slow electron beams 102_1sse~102_3sse. If the objective lens 131 includes a magnetic lens, the three secondary slow electron beams will rotate around the main optical axis 100_1 when passing through the magnetic lens, and the rotation angle will change with its magnetic field. Therefore, when the magnetic field changes due to some reasons (such as the change of the landing energy of the three beamlets 102_1~102_3), the three secondary slow electron spots 102_1sseP_102_3sseP will rotate around the secondary optical axis 150_1 from the primary optical axis 100_1 to the secondary optical axis 100_2. Figure 4A The original position in is rotated to something like Figure 4CTherefore, the collection efficiency of the three secondary slow electron beams 102_1sse~102_3sse is reduced, and crosstalk occurs if the beamlets are arranged in a two-dimensional array. In this case, the magnetic field of the magnetic lens 152_12 is adjusted to make the three secondary slow electron beams 102_1sse~102_3sse rotate in opposite directions to eliminate the rotation change of the three secondary slow electron spots 102_1sseP~102_3sseP caused by the change of the magnetic field of the objective lens 131.

[0102] Figures 6A to 6C 1 and 2 show a configuration of a projection lens 152 that can perform an anti-rotation function. Fig. 6A In the configuration 152-1, the electrostatic lens 152_11 is within the magnetic lens 152_12 and includes three electrodes 152_11_e1, 152_11_e2 and 152_11_e3. The electrostatic lens 152_11 can be used as a single lens. Since the electrostatic field of the electrostatic lens 152_11 and the magnetic field of the magnetic lens 152_12 are largely separated, the imaging magnification M2 will change with the change of the magnetic field of the magnetic lens 152_12. Therefore, when the magnetic lens 152_12 is adjusted to perform an anti-rotation function, the zoom lens 151 needs to compensate for the change in the imaging magnification M2. In order to avoid such a complicated procedure, the center of the electrostatic field of the electrostatic lens 152_11 and the center of the magnetic field of the magnetic lens 152_12 preferably coincide, such as Figure 6B If both electrodes 152_11_e3 and 152_11_e1 are grounded, they can be replaced by the upper and lower pole pieces of the magnetic lens 152_12, as shown in FIG. Figure 6C Embodiment 152-3 shown.

[0103] In order to obtain high collection efficiency and low crosstalk level, it is obviously better to make the secondary electron spot as small as possible, that is, to reduce the aberration of the zoom lens 151 and the projection lens 152 as much as possible. One solution is to use a field lens to reduce the aberration of the off-axis secondary electron spot. Figure 3B In the embodiment, two off-axis secondary slow electron beams 102_2sse and 102_3sse enter the projection lens 152 with large radial offset and tilt angles and therefore have large off-axis aberrations. Fig. 7A An embodiment 150-3 of the secondary projection imaging system 150 in the detection system 100-3D is shown. Fig. 7AIn the embodiment, the field (lens) 153 and the field (lens) 154 are respectively located on the transmission plane SP2_1 of the SSE mode and the transmission plane SP2_2 of the BSE mode, and both are aligned with the secondary optical axis 150_1. If the secondary projection imaging system 150 only needs to work in one of the SSE mode and the BSE mode, only the corresponding field lens is placed there. Figure 7B FIG. 1 shows how the field lens 153 operates in SSE mode. Figure 3B In contrast, the field lens 153 bends the secondary slow electron beams 102-2sse and 102-3sse toward the secondary optical axis 105_1 without affecting the on-axis secondary slow electron beam 102_1sse and the total imaging magnification M. Figure 7B In the embodiment, the secondary slow electron beams 102-2sse and 102-3sse are bent to pass through the center of the projection lens 152, that is, the radial offset is almost eliminated, but the tilt angle is large. In practice, the field lens 153 can be adjusted to balance the radial offset and the tilt angle, so that the secondary slow electron spots 102-2sseP and 102-3sseP are as small as possible.

[0104] Another solution is to use a beam-limit aperture to cut off peripheral electrons of a secondary electron beam, since peripheral electrons usually have large aberrations. Fig. 8A An embodiment 150-4 of the secondary projection imaging system 150 in the detection system 100-4D is shown, in which a second beam limiting aperture plate 155 having an opening 155_A is placed above the projection lens 152. The opening 155_A is aligned with the secondary optical axis 150_1 and is at or near the most recent or last crossing of the secondary electron beams 102_1se-102_3se. Figure 8B shows how the opening 155_A operates in SSE mode. Figure 3B In contrast, the opening 155_A is located at the last crossing CO3, so the peripheral electrons of the three secondary slow electron beams 102_1sse-102_3sse can be cut off together. Since the positions of the crossings in the SSE mode and the BSE mode are different and vary with the landing energy of the beamlets 102_1-102_3 and the operating conditions of the objective lens 131, if the opening 155_A is not moved to match the position of the corresponding crossing, it can only work well for certain application scenarios. Fig.9A An embodiment 150-5 of the secondary projection imaging system 150 in the detection system 100-5D is shown, in which the position of the last intersection in the SSE mode and the BSE mode is fixed at the same position and thus the opening 155_A of the beam limiting aperture plate 155 has good performance for all application cases.

[0105] Similar to Fig. 7A,exist Fig.9A In the embodiment, the field lens 153 and the field lens 154 are placed at the transmission plane SP2_1 of the SSE mode and the transmission plane SP2_2 of the BSE mode, respectively, and both are aligned with the secondary optical axis 150_1. If the secondary projection imaging system 150 only needs to work in one of the SSE mode and the BSE mode, only the corresponding field lens is placed there. In each of the SSE mode and the BSE mode, the corresponding field lens bends the off-axis secondary electron beam so that its last intersection is at or very close to the opening 155_A. In the embodiment of Fig. 9B In the SSE mode shown, the field lens 154 is turned off or does not exist, and the field lens 153 bends the secondary slow electron beams 102-2sse and 102-3sse toward the secondary optical axis 150_1 to pass through the opening 155_A. Fig. 9C In the BSE mode shown, the field lens 153 is closed or absent, and the field lens 154 bends the backscattered electron beams 102-2be and 102-3be toward the secondary optical axis 150_1 to pass through the opening 155_A. In the SSE mode and the BSE mode, the field lens 153 and the field lens 154 reduce the aberration of the projection lens 152 while maintaining the position of the last intersection.

[0106] The smaller the radial size of the opening 155_A used, the lower the collection efficiency of the image signals of the detection elements 140_1, 140_2 and 140_3 and the less crosstalk. Therefore, the radial size is selected by balancing the collection efficiency and the crosstalk level. The optimal radial size in the SSE mode and the BSE mode may be different. In order to enable each mode to work at its optimal radial size, the beam limiting aperture 155 may have two or more openings, such as Fig. 10A Embodiment 150-6-1 of the secondary projection imaging system 150 in the detection system 100-6-1D shown. Fig. 10A In the embodiment 150-6, the beam limiting aperture plate 155 has two openings 155_1 and 155_2 and can be moved perpendicular to the secondary optical axis 150_1. The opening 155_1 and the opening 155_2 have optimal radial sizes for the SSE mode and the BSE mode, respectively. When the embodiment 150-6 operates in the SSE mode, the beam limiting aperture plate 155 is moved to align the opening 155_1 with the secondary optical axis 150_1. When the embodiment 150-6 operates in the BSE mode, the beam limiting aperture plate 155 is moved to align the opening 155_2 with the secondary optical axis 150_1. If the beam limiting aperture plate 155 has two or more openings with different radial sizes for each mode, the collection efficiency and the crosstalk level can be balanced to different degrees.

[0107] For some applications, the optimal position of the last crossing of the secondary electron beams in SSE mode and BSE mode may be different. Therefore, two separate secondary beam limiting aperture plates can be used, which are placed at different positions above the projection lens 152 along the secondary optical axis 150_1, such as Fig. 10B Embodiment 150-6-2 of the secondary projection imaging system 150 in the detection system 100-6-2D shown. Fig. 10B In the embodiment, the first secondary beam limiting aperture plate 155 and the second secondary beam limiting aperture plate 156 are located at the optimal position of the last crossing of the secondary electron beams in the SSE mode and the BSE mode, respectively, and each may have one or more openings with different radial sizes for balancing the collection efficiency and the crosstalk level differently. In the SSE mode, the field lens 153 bends the secondary slow electron beams 102-2sse and 102-3sse (see Fig. 9B ) to form a primary intersection at an opening of the first secondary beam limiting aperture plate 155, wherein the opening is aligned with the secondary optical axis 150_1 and has a desired radial size, and thus the second secondary beam limiting aperture plate 156 can be moved away or a sufficiently large opening thereof is aligned with the secondary optical axis 150_1. In the BSE mode, the field lens 154 bends the backscattered electron beams 102-2be and 102-3be (refer to Fig. 9C ) to form a primary intersection at an opening of the second secondary beam limiting aperture plate 156, wherein the opening is aligned with the secondary optical axis 150_1 and has a desired radial dimension, and thus the first secondary beam limiting aperture plate 155 can be moved away or a sufficiently large opening thereof can be aligned with the secondary optical axis 150_1.

[0108] The beam splitter 160 generates astigmatism when deflecting the secondary electron beams 102_1se~102_3se to enter the secondary projection imaging system 150 along the secondary optical axis 150_1. The astigmatism enlarges the secondary electron spot on the detection plane SP3, thereby reducing the collection efficiency and increasing the crosstalk. An astigmatism correction device can be used to compensate for the astigmatism. In order to affect all secondary electron beams equally, it is best to place the astigmatism correction device at or near the intersection of the secondary electron beams. If the secondary projection imaging system 150 only needs to operate in one of the SSE mode and the BSE mode, the astigmatism correction device can be at or near the second to last intersection ( Figure 8B CO2 in) and the last crossover ( Figure 8B One of the CO3 in Fig.11A Embodiment 150-7 of the secondary projection imaging system 150 in the detection system 100-7D shown. Fig.11A In FIG. 1 , the astigmatism correction device 158 is placed at the penultimate intersection below the transmission plane SP2. Fig. 11BThe position of the astigmatism correction device 158 for the SSE mode is shown.

[0109] If the secondary projection imaging system 150 needs to operate in each of the SSE mode and the BSE mode, the astigmatism correction device is preferably located at or close to the last intersection. The positions of the penultimate intersections in the SSE mode and the BSE mode are obviously separate, and one astigmatism correction device cannot work for both of them at the same time. Therefore, the two astigmatism correction devices must be placed at or close to the penultimate intersections in the SSE mode and the BSE mode, respectively. Since the positions of the last intersections in the SSE mode and the BSE mode can be adjusted to the same position by their field lenses, the SSE mode and the BSE mode can simply share one astigmatism correction device, such as Fig.12 An embodiment 150 - 8 of the secondary projection imaging system 150 in the detection system 100 - 8D is shown.

[0110] Similar to Fig.9A ,exist Fig.12 In the embodiment, the field lens 153 and the field lens 154 are respectively placed at the transmission plane SP2_1 of the SSE mode and the transmission plane SP2_2 of the BSE mode, and both are aligned with the secondary optical axis 150_1. In each of the SSE mode and the BSE mode, a corresponding one of the field lenses 153 and 154 bends the secondary electron beam so that the last intersection thereof is at or very close to the opening 155_A of the secondary beam limiting aperture plate 155. The astigmatism correction device 158 is aligned with the secondary optical axis 150_1 and is close to (above or below) the secondary beam limiting aperture plate 155.

[0111] In the aforementioned embodiment of the secondary projection imaging system 150, the anti-rotation function is performed by the projection lens 152. In fact, the anti-rotation function can be performed by the zoom lens 151 or the corresponding field lens (153 or 154) or an additional magnetic lens. Fig.13A In the embodiment 150-9-1 of the secondary projection imaging system 150 of the detection system 100-9-1D shown in the figure, the field lens 153 includes an electrostatic lens 153_11 and a magnetic lens 153_12. The magnetic field of the magnetic lens 153_12 is adjusted to achieve the anti-rotation function, and the desired bending function of the field lens 153 is achieved by adjusting the focusing ability of the electrostatic lens 153_11 based on the magnetic field of the magnetic lens 153_12. Fig. 13BIn the embodiment 150-9-2 of the secondary projection imaging system 150 of the detection system 100-9-2D shown, a magnetic lens 151_13 is added to the electrostatic lens 151_12 of the zoom lens 151 to form an electromagnetic compound lens 151_12c. Similarly, the magnetic lens 151_13 can also be added to the electrostatic lens 151_11 to form an electromagnetic compound lens 151_11c or simply placed between the two electrostatic lenses 151_11 and 151_12. The magnetic field of the magnetic lens 151_13 is adjusted to achieve an anti-rotation function, and the desired zoom function of the zoom lens 151 is achieved by adjusting the focusing capabilities of the electrostatic lenses 151_11 and 151_12 based on the magnetic field of the magnetic lens 151_13. Fig.13A The field lens 153 and Fig. 13B The electromagnetic compound lens 151_12c or the electromagnetic compound lens 151_11c (not shown) in the embodiment can be respectively Figures 6A to 6C One of the configurations of projection lens 152 is shown.

[0112] In the aforementioned embodiment of the secondary projection imaging system 150, the zoom lens 151, the projection lens 152 and the central detection element (here 140_1) of the electron detection device 140 are aligned with the secondary optical axis 150_1. In practice, it is almost impossible to manufacture them all perfectly and assemble them all accurately in their correct positions, so the secondary electron spot on the detection plane SP3 may deviate from the corresponding detection element. In order to make the secondary electron spot coincide with the corresponding detection element, the electron detection device 140 can be moved or the secondary electron spot can be moved. In comparison, moving the secondary electron spot is simple and flexible. To this end, in the aforementioned embodiment of the secondary projection imaging system 150, an alignment deflector can be placed above the projection lens 152 to deflect the secondary electron beam, thereby moving the secondary electron spot relative to the actual position of the electron detection device 140. For example, an alignment deflector 159 is placed Fig.11A Above the projection lens 152 of the embodiment 150-7, as Fig.14 shown. Fig.14 The new embodiment in is named 150-10. Fig.14 It is further shown that if a secondary beam limiting aperture plate 155 is used, the alignment deflector 159 will be placed thereon. For embodiments of the secondary projection imaging system 150 that use an astigmatism correction device above the projection lens 152 (e.g. Fig.12 ), the astigmatism correction device can be designed to have a multi-pole structure, which can be used as an astigmatism correction device and an alignment deflector at the same time.

[0113] In FIG1 , the deflection scanning unit 132 is located below the beam splitter 160, thereby affecting the secondary electron beams 102_1se to 102_3se. Therefore, for the displacement of a secondary electron spot on the detection plane SP3, the first part comes from the displacement of the corresponding probe spot on the surface 7 of the sample and the total magnification M, and the second part is due to the deflection influence of the deflection scanning unit 132. If the deflection scanning unit 132 is located above the beam splitter 160, as shown in FIG1 , the deflection scanning unit 132 is located below the beam splitter 160, and the deflection scanning unit 132 is located below the beam splitter 160. Fig.15A In the embodiment 200A of the multi-beam device, the second part will not exist. In this case, the secondary projection imaging system 150 can adopt any of the aforementioned embodiments. Fig. 15B In one embodiment 200-1D of the corresponding detection system, Figure 3A The embodiment 151-2 shown, in which the anti-scan deflection unit 157 is only needed to eliminate the first part of the displacement of the secondary electron spot. In addition, if the size of each scanning area is small to a certain extent compared to the pitch Pd and compared to each adjacent probe spot, the anti-scan deflection unit 157 can even be removed.

[0114] In summary, the object of the present invention is to provide a secondary projection imaging system for a multi-beam device, which performs secondary electron detection with high collection efficiency and low crosstalk level, even if the landing energy and / or current of multiple beamlets vary over a wide range. As a yield management tool in the semiconductor manufacturing industry, the multi-beam device can therefore achieve high inspection resolution and high inspection throughput under many application conditions. The secondary projection imaging system basically adopts a zoom lens, a projection lens and an anti-scanning deflection unit. With respect to the changes in the landing energy of multiple beamlets and the corresponding operating conditions of the objective lens of the multi-beam device, the zoom lens and the projection lens respectively perform a zoom function and an anti-rotation function to maintain the total image rotation and the total imaging magnification from the surface of the sample to the detection plane, so that the multiple detection elements of the electronic detection device at the detection plane can respectively detect the multiple secondary electron beams generated by the multiple beamlets. When the deflection scanning unit scans the multiple beamlets on a small scanning area, the anti-scanning deflection unit performs an anti-scanning function, which synchronously deflects the secondary electron beams to maintain the landing positions of the multiple secondary electron beams on the detection plane. The secondary projection imaging system can further use a field lens and / or a secondary beam limiting aperture to reduce the size of multiple secondary electron beams on the detection plane, and thereby increase the collection efficiency of multiple secondary electron beams and reduce crosstalk between multiple secondary electron beams. The secondary projection imaging system can also use an alignment deflector to eliminate the mismatch of multiple secondary electron beams and multiple detection elements from manufacturing and / or assembly errors of the zoom lens, projection lens and electronic detection device. If a magnetic lens is used therein, the zoom lens or field lens can also perform an anti-rotation function.

[0115] Although the present invention has been described in conjunction with the preferred embodiments thereof, it should be understood that other modifications and variations may be made without departing from the spirit and scope of the invention as hereinafter claimed.

Claims

1. A multi-beam imaging system, comprising: a magnetic lens configured to adjust the rotation of the plurality of charged particle secondary beams of the multi-beam imaging system so as to enable the plurality of charged particle secondary beams to be detected by the corresponding plurality of detection elements, wherein the magnetic lens is configured to produce a second rotation that reduces a first rotation produced by another component of the multi-beam imaging system; and Wherein, the other component comprises an objective lens configured to focus the plurality of charged particle beamlets onto the sample surface.

2. The system according to claim 1, wherein: The magnetic lens is configured to minimize rotational variations of the plurality of charged particle secondary beams when observing a sample under different conditions.

3. The system according to claim 2, wherein: The magnetic lens is configured to adjust the rotation based on the focusing power of the objective lens.

4. The system according to claim 1, wherein: The further component comprises a beam splitter configured to separate a plurality of charged particle beamlets directed onto the sample surface from a plurality of charged particle secondary beams.

5. The system according to claim 1, wherein: The further component comprises a beam splitter configured to separate the plurality of charged particle beamlets from the plurality of charged particle secondary beams.

6. The system according to claim 1, further comprising: A secondary projection imaging system is configured to focus the plurality of charged particle secondary beams onto the plurality of detection elements, wherein the magnetic lens is included in the secondary projection imaging system.

7. The system according to claim 1, wherein: The magnetic lens is configured based on the focusing capability of the objective lens of the multi-beam imaging system.

8. The system according to claim 1, wherein: The multi-beam imaging system includes a multi-beam scanning electron microscope (SEM).

9. The system according to claim 1, wherein: The magnetic lens is included in the field lens.

10. The system according to claim 9, wherein: The field lens includes a plurality of lenses.

11. The system according to claim 9, wherein: The field mirror is arranged at a transmission plane of another component of a secondary projection imaging system, which is configured to focus the plurality of charged particle secondary beams onto the plurality of detection elements.

12. The system of claim 1, wherein: The magnetic lens includes a plurality of lenses.

13. The system of claim 1, further comprising: a zoom lens and a projection lens, which are configured to focus the plurality of charged particle secondary beams emitted from the sample surface onto a plurality of detection elements of a detection device, respectively; The zoom lens, the magnetic lens, and the projection lens are configured to respectively maintain a corresponding relationship between the plurality of charged particle secondary beams and the plurality of detection elements.

14. The system according to claim 13, wherein: The corresponding relationship includes imaging each probe spot on the sample surface onto one detection element among the plurality of detection elements, and The zoom lens, the magnetic lens, and the projection lens are configured to ensure the corresponding relationship.

15. The system of claim 13, wherein: The zoom lens and the projection lens are configured to eliminate imaging magnification changes caused by adjusting the focusing power of the objective lens, the objective lens is configured to focus multiple charged particle beamlets onto the sample surface, and the magnetic lens is configured to eliminate rotational changes of the multiple charged particle secondary beams when observing the sample under different conditions.

16. The system of claim 13, wherein: The zoom lens and the projection lens are configured to set an imaging magnification from the sample surface to a detection plane at the detection device, and The zoom lens and the projection lens are configured to adjust the imaging magnification based on a focusing capability of an objective lens.

17. The system of claim 13, further comprising: a beam splitter configured to separate the plurality of charged particle beamlets from the plurality of charged particle secondary beams, wherein The beam splitter is configured to switch between a secondary charged particle mode and a backscattered charged particle mode, and The zoom lens, the magnetic lens, and the projection lens are configured to maintain the corresponding relationship based on which mode of the secondary charged particle mode and the backscattered charged particle mode the beam splitter operates in.

18. The system of claim 13, wherein: The magnetic lens is included in the zoom lens or the projection lens.

19. An imaging system comprising: a zoom lens and a projection lens configured to focus the plurality of charged particle beams emitted from the sample surface as the plurality of charged particle secondary beams onto the plurality of detection elements of the detection device, respectively, wherein the zoom lens and the projection lens are configured to respectively maintain a corresponding relationship between the plurality of charged particle beams and the plurality of detection elements, Wherein, the imaging system further comprises: an objective lens configured to focus a plurality of charged particle beams onto the sample surface; and a field lens arranged at a transmission plane of the objective lens of the imaging system configured to focus the plurality of charged particle beams onto the plurality of detection elements, and Wherein, the magnetic lens is included in one of the objective lens, the zoom lens, and the projection lens, and is configured to adjust the rotation of the multiple charged particle beams by generating a second rotation that reduces the first rotation generated by the objective lens so as to enable the detection of the multiple charged particle beams by the multiple detection elements.

20. The imaging system of claim 19, wherein: The zoom lens and the projection lens are configured to set an imaging magnification from the sample surface to a detection plane at the detection device.

21. The imaging system of claim 19, wherein: The correspondence includes imaging each probe spot on the sample surface onto one detection element among the plurality of detection elements.

22. The imaging system of claim 19, wherein: The zoom lens and the projection lens are configured to eliminate imaging magnification changes caused by adjusting the focusing power of the objective lens.

23. The imaging system of claim 19, wherein: The zoom lens and the projection lens are configured to set an imaging magnification from the sample surface to a detection plane at the detection device, and The zoom lens and the projection lens are configured to adjust the imaging magnification based on a focusing capability of an objective lens.

24. The imaging system of claim 19, wherein: The zoom lens is configured to provide a first imaging magnification from the sample surface to a transmission plane, and the projection lens is configured to provide a second imaging magnification from the transmission plane to a detection plane located at the detection device.

25. The imaging system of claim 24, wherein: The second imaging magnification is greater than the first imaging magnification.

26. The imaging system of claim 24, wherein: The zoom lens and the projection lens are configured to set a total imaging magnification from the sample surface to a detection plane at the detection device, the total imaging magnification being equal to the first imaging magnification multiplied by the second imaging magnification.

27. The imaging system of claim 19, wherein: The zoom lens includes an electrostatic lens, and the zoom lens is configured to adjust a focusing capability of the electrostatic lens.

28. The imaging system of claim 27, wherein: The zoom lens includes two electrostatic lenses.

29. The imaging system of claim 19, further comprising: A magnetic lens is configured to eliminate rotation of the plurality of charged particle beams caused by the magnetic objective lens.

30. The imaging system of claim 29, wherein: The projection lens includes a magnetic lens configured to eliminate rotation of the plurality of charged particle beams.

31. The imaging system of claim 29, wherein: The zoom lens includes a magnetic lens configured to eliminate rotation of the plurality of charged particle beams.

32. The imaging system of claim 19, further comprising: An anti-scanning deflector configured to eliminate scanning of the plurality of charged particle beams on the detection device caused by a deflection scanning unit.

33. The imaging system of claim 32, wherein: The corresponding relationship includes maintaining the position of the image of each probe spot imaged onto one of the plurality of detection elements on the sample surface.

34. The imaging system of claim 19, further comprising: A beam splitter is configured to separate a plurality of charged particle beamlets and the plurality of charged particle beams.

35. The imaging system of claim 34, wherein The beam splitter is configured to switch between a secondary charged particle mode and a backscattered charged particle mode, and The zoom lens and the projection lens are configured to maintain the corresponding relationship based on which mode of the secondary charged particle mode and the backscattered charged particle mode the beam splitter operates in.

36. The imaging system of claim 19, wherein: The objective lens and the zoom lens are configured to focus the multiple charged particle beams into a transmission plane, and the projection lens is configured to focus the multiple charged particle beams from the transmission plane into a detection plane on the detection device.

37. The imaging system of claim 36, wherein: The field lens includes a magnetic lens configured to eliminate rotation of the plurality of charged particle beams caused by the magnetic lens of the objective lens.

38. A charged particle beam apparatus comprising: Charged particle sources; a focusing lens located below the charged particle source; a source conversion unit located below the condenser lens; an objective lens located below the source conversion unit; a deflection scanning unit located below the source conversion unit; a sample stage located below the objective lens; a beam splitter located below the source conversion unit; as well as a secondary projection imaging system located above the beam splitter, the secondary projection imaging system comprising the imaging system according to claim 19, wherein the charged particle source, the focusing lens, the source conversion unit, the objective lens, the deflection scanning unit, and the beam splitter are aligned with the main optical axis of the charged particle beam device, the sample stage is configured to hold the sample so that the sample surface faces the objective lens, the detection device is aligned with the secondary optical axis of the charged particle beam device, and the secondary optical axis is not parallel to the main optical axis, wherein the plurality of detection elements are placed on a detection plane located at the detection device, wherein the charged particle source is configured to generate a primary charged particle beam along the main optical axis, the condenser lens is configured to focus the primary charged particle beam, the source conversion unit is configured to change the primary charged particle beam into a plurality of beamlets, and to cause the plurality of beamlets to form a plurality of first images of the charged particle source, the objective lens is configured to focus the plurality of beamlets to image the plurality of first images onto the sample surface and thereby form a plurality of probe spots on the sample surface respectively, and the deflection scanning unit is configured to deflect the plurality of beamlets to scan the plurality of probe spots on a plurality of scanning areas within an observation area on the sample surface respectively, wherein the plurality of charged particle beams are configured to be generated by the plurality of probe spots from the plurality of scanning areas respectively and then incident on the objective lens, the objective lens is configured to focus the plurality of charged particle beams, and the beam splitter is configured to deflect the plurality of charged particle beams to enter the secondary projection imaging system along the secondary optical axis, wherein the zoom lens is configured to focus the plurality of charged particle beams onto a transmission plane, the transmission plane being located between the zoom lens and the projection lens, so that the plurality of charged particle beams form a first intersection between the zoom lens and the transmission plane, Wherein, the projection lens is configured to focus the multiple charged particle beams onto the detection plane, so that the multiple charged particle beams form a second intersection between the projection lens and the detection plane, and form multiple secondary charged particle spots on the detection plane, and the multiple secondary charged particle spots are respectively located inside the multiple detection elements, so that the corresponding relationship includes the relationship established between the multiple probe spots and the multiple detection elements, and accordingly, each detection element is configured to generate an image signal of a corresponding scanning area, wherein the anti-scanning deflection unit is configured to deflect the plurality of charged particle beams synchronously with the scanning of the plurality of probe spots on the plurality of scanning areas to maintain the positions of the plurality of secondary charged particle spots and thereby maintain the corresponding relationship, Wherein, the imaging magnification of the zoom lens is configured to be adjusted to maintain the corresponding relationship when observing the sample surface under different conditions.

Images