Method of operating multi-beam charged particle beam system, multi-beam charged particle beam system and method of inspection of finfet by operating multi-beam charged particle imaging system

Abstract

This invention provides a multi-beam charged particle system with reduced charge effects and a method for operating the multi-beam charged particle system. For charge compensation during a second scan operation in mirror mode, surface charges appearing on the sample surface are compensated, for example, those generated during a first image scan operation.

Description

Multibeam charged particle microscopy is used to examine reduced charging effects. This invention relates to a multi-beam charged particle microscope that reduces the charge effect of samples and a method for operating the multi-beam charged particle microscope to examine semiconductor features with reduced charge effect. Patent document WO 2005 / 024881 A2 discloses an electron microscope system that operates by utilizing a plurality of electron microbeams to perform parallel scanning of an object to be examined using a cluster of electron microbeams. Clustered primary charged particle microbeams are generated by guiding a primary charged particle beam to a multi-beam forming unit, which includes at least one porous plate having multiple openings. A portion of the electron beam is incident on the porous plate and absorbed, while another portion passes through the openings of the porous plate, thereby forming an electron microbeam in a beam path downstream of each opening, the profile of which is defined by the profile of the corresponding opening. The plurality of primary charged particle beams are focused by an objective lens onto the surface of a sample, triggering secondary electrons or backscattered electrons to be emitted from the sample as secondary electron microbeams. The plurality of secondary electron microbeams are then clustered and imaged onto a detector. Each of a plurality of secondary electron beams is incident on a separate detector element or a group of detector elements, such that the intensity of the secondary electrons detected by the beams provides information about the sample surface at the location where the corresponding primary electron beam was incident on the sample. The primary electron beams are systematically scanned on the sample surface, producing an electron microscope image of the sample. Generally, the imaging contrast of a scanning electron microscope largely depends on the signal generated by secondary electrons, which in turn depends on the secondary electron (SE) emission coefficient of each primary electron and the geometric focusing efficiency of the electron microscope. The SE emission coefficient depends on material properties and the kinetic energy of the primary electrons. However, the SE emission coefficient is affected by the charging effect on the sample surface. This charging effect occurs at local capacitances or insulators, where accumulated charge produces a degraded electric field on the small beams of primary and secondary electrons. Different methods have been proposed to mitigate the charging effect. Fluid guns are widely used to pre-charge a sample surface. An example of a multi-beam charged particle system is given in US 11,239,053 BB. However, in some cases, the application of this method has proven to severely interfere with accurate imaging. In German patent application DE 10 2022 211 883.9, filed November 10, 2022, a selected primary electron beam energy is used at a point where the secondary electron emission and incident primary electron current are in equilibrium. This reduces the charging effect. However, to reduce the charging effect, different material compositions present on a wafer surface require different specific kinetic energies of primary electrons, and the kinetic energy of a small primary beam cannot be individually adjusted during an image scan. Therefore, it remains necessary to mitigate the charging effect or avoid sample charging during wafer inspection. Therefore, an object of the present invention is to provide an improved multi-beam charged imaging system and an improved method for operating a multi-beam charged particle system configured to reduce the charging effect during semiconductor sample inspection. Document US 6,563,114 B1 provides background information on this patent application. Document DE 10 2021 105 201 A1 and its patent family document WO 002022069073 A1 provide background information on this patent application. This patent application claims priority to German Patent Application No. 10 2023 211 031.8, filed on 7 November 2023, the disclosure of which is incorporated herein by reference in its entirety. This invention discloses a multi-beam charged particle imaging system and an improved method for operating the system, by which surface charge generated, for example, during scanning image acquisition using a plurality of primary charged particle beams is compensated or balanced. According to these improvements, surface charge is at least partially removed, allowing a subsequent second image acquisition to be performed with high precision and at least with reduced deteriorating effects of surface charge. The method includes a scanning operation step for charge compensation. This charge-compensated scanning operation step includes setting a negative voltage difference VD2 on a sample mounted on a sample stage, causing the primary charged particle beams to reverse their propagation direction before reaching uncharged regions on the sample surface. This operation mode is also called a mirror mode. The second negative voltage difference VD2 can be adjusted so that the primary charged particles only reach the surface of the sample in regions where positive surface charge exists. Surface charge can be generated, for example, during a first pre-image acquisition, or even before the first image acquisition, on the surface of a sample. This removes the positive surface charge and at least partially compensates for the charge. A method of operating a multi-beam charged particle system according to a first embodiment includes a first or image scanning operation step A and a second scanning operation step B for charge compensation. The method includes acquiring an image of a surface segment of a wafer surface during the first or image scanning operation step A, and at least partially compensating for surface charge on the surface segment during the second scanning operation step B for charge compensation. The method includes setting a first positive voltage difference VD1 during the first or image scanning operation step A. The first positive voltage difference VD1 is selected and adjusted such that a primary charged particle microbeam reaches the sample surface with an impact energy LE within an impact energy range, wherein the secondary and backscattered electron emission coefficients generated by individual primary charged particle microbeams exceed an incident beam current of the primary charged particle microbeam. Within the impact energy range, at least a positive surface charge is generated at a region on the sample surface during the image scanning operation. The method further includes setting a second negative voltage difference VD2 during the second scanning operation step B for charge compensation. The second negative voltage difference VD2 is selected such that the primary charged particle beam reverses its propagation direction before reaching the uncharged region of the sample surface and reaches the sample surface at a region with positive surface charge, for example, generated during the first or imaging scanning operation step A. In the region with surface charge, the primary charged particles collide with the surface and compensate for the positive surface charge. For example, during the first or image scanning operation step A, a positive surface charge is established on a surface. For example, when electrons are primary charged particles, secondary and backscattered electrons exceed the incident current of the primary electrons during the first or image scanning operation step A, resulting in a positive surface charge. During the second scan operation step B for charge compensation, primary electrons bombard the surface region with the positive surface charge and at least partially compensate for the positive surface charge. During the second scan operation step B for charge compensation, the kinetic energy of the primary electrons is insufficient to reach the surface region without the positive surface charge, and no additional charge is generated at the surface region without the positive surface charge. In one example, the absolute value of the second negative voltage difference VD2 is less than 100 V, for example 50 V, for example 10 V, or 5 V, for example 1 V. Thus, for example, a low threshold value for the primary electrons is set such that the primary electrons bombard the region with even a low positive surface charge. In one example, a second scan operation step B for charge compensation is performed before or before a first or image scan operation step A, and the second scan operation step B for charge compensation reduces or removes the charge present on the sample surface before image capture. In one example, the method includes iteratively repeating the first or image scanning operation step A and the second scanning operation step B for charge compensation. In one example, the first or image scanning operation step A and the second scanning operation step B for charge compensation are iteratively repeated for each sequence of scan lines, wherein the sequence of scan lines includes 1, 2, 10, or more scan lines. In one example, during the first or image scanning operation step A, the second scanning operation step B for charge compensation is performed during each retracement of a single charged particle beam. In one example, the second scanning operation step B for charge compensation is performed at the first inspection position before a wafer is moved to a second inspection position adjacent to a first inspection position. This reduces the effect of surface charge on a pre-exposed surface segment adjacent to the second inspection position. This reduces the charge on a surface segment before performing a subsequent scanning image acquisition step on an adjacent surface segment. In one example, the second scanning operation step B for charge compensation is limited to a scanning range at a boundary or edge of a surface segment. This reduces the charge on the boundary or edge of a surface segment before performing subsequent scanning image acquisition steps on an adjacent surface segment. In one example, the method further includes a setting adjustment step S. The setting adjustment step S includes adjusting the inspection position of a wafer surface in the object plane of the multi-beam charged particle system; and selecting an image setting, including selecting the first positive voltage difference VD1 and the second negative voltage difference VD2. In one example, the first positive voltage difference VD1 and the second negative voltage difference VD2 are selected based on a material composition present on the surface of a sample. A material composition can be prior information received, for example, from a CAD file of the semiconductor structure within the processed wafer. In one example, the method further includes an adjustment step M. During adjustment step M, settings for the second scan operation B for charge compensation are restricted. This restriction is, for example, based on image data obtained in a preceding first or second image scan operation step A. In one example, the first voltage difference VD1 = VS1 - VK1 is set between the first sample voltage VS1 applied to the sample and the voltage VK1 of the primary charged particle emitter, within a voltage range of approximately 1 kV, for example, VD1 = 800 V or less, 1 kV, 1.2 kV, or 2 kV. In one example, the second voltage difference VD2 is set or limited by setting or limiting at least one of a sample voltage VS, the voltage VK of the primary charged particle emitter, and a voltage VE supplied to the electrodes within the multi-beam charged particle system. The method further includes an image acquisition step I for receiving and storing image data acquired during a first image scanning operation step A. In one example, the method further includes a clustering step C for receiving, analyzing, and storing information acquired during a second scan operation step B for charge compensation. This information can be, for example, a cluster of secondary electrons received from a region with a positive surface charge, wherein primary charged particles collide with the surface during the second scan operation step B for charge compensation. This allows, for example, the recording of regions with positive surface charges during the second scan operation. This information can be used for inspection tasks such as at similar inspection locations, or combined with image data received during the first image scanning operation step A. According to a second embodiment, a multi-beam charged particle system includes an emitter of primary charged particles connected to an emitter voltage source to provide an emitter voltage VK to the emitter. The multi-beam charged particle system further includes a sample voltage source for providing a sample voltage VS to a wafer mounted on a sample stage of the multi-beam charged particle system during use. The multi-beam charged particle system further includes a control unit configured to adjust at least one of the emitter voltage VK or the sample voltage VS. The control unit further includes a memory for storing a plurality of software instructions and an operation processor for executing the software instructions, which, when executed, cause the multi-beam charged particle system to perform any of the plurality of method steps according to the first embodiment. This invention can be used for wafer inspection. In one example, the task of wafer inspection is to investigate defects or dimensions in structured photoresist. Photoresist is an insulator and exhibits a strong electrical charge effect. Using an apparatus and method according to a specific embodiment, the electrical charge effect of the structured photoresist can be reduced. In one example of a wafer inspection task, the structure to be investigated is configured at the boundary or edge of a die. For example, a dedicated process control monitor (PCM) can be configured close to the edge of a die. According to another specific embodiment, a method for inspecting a FinFET using a multi-beam charged particle imaging system is provided. The method includes a first or image scanning operation step A, which includes setting a first positive voltage difference VD1 such that a primary charged particle beam reaches the surface of the FinFET with an impact energy LE within an impact energy range, wherein the secondary and backscattered electron emission coefficients exceed an incident beam current of the primary charged particles, thereby generating image data and generating at least a positive surface charge in a region of the FinFET's insulator. The method further includes a second scan operation step B for charge compensation, which includes setting a second negative voltage difference VD2 such that the primary charged particle beam is reversed in its propagation direction before reaching an uncharged region on the surface of the FinFET (e.g., a gate structure). However, during the second scan operation step B for charge compensation, the primary charged particles reach the insulator, where a positive surface charge was generated during the first or image scanning operation step A, and a positive surface charge is compensated or balanced. The method further includes repeatedly performing the first or image scanning operation step A and the second scanning operation step B for charge compensation, and calculating the image of the surface by image processing of the plurality of images generated during the repeated performance of the first or image scanning operation step A. In the exemplary embodiments of the invention described below, components with similar functions and structures are shown using similar or identical reference numerals whenever possible. Some array elements (e.g., a plurality of primary charged particle beams) are identified by a single reference numeral. According to this document, the same reference numeral may also identify individual elements within the array. Each primary charged particle beam (3.1, 3.2, 3.3) is one of a plurality of primary charged particle beams (3). picture Figure 1 is a schematic diagram of a multi-beam charged imaging system 1 (hereinafter referred to as multi-beam system 1) according to a specific embodiment. Multi-beam system 1 uses a plurality of charged particle beams to form an image of an object 7. Multi-beam system 1 generates a plurality of J primary particle beams 3 to strike the object 7 to be examined, generating interaction products from the object 7, such as secondary electrons, which are subsequently detected. Multi-beam system 1 is a scanning electron microscope (SEM) type that uses a plurality of primary electron beams 3 incident on the surface of the object 7 at a plurality of locations, generating a plurality of spatially separated primary electron beam focal spots 5 thereon. The object 7 to be examined can be of any desired type, such as a semiconductor wafer or semiconductor mask, and can contain a configuration of miniaturized components. The surface 25 of the object 7 is disposed in the object plane 101 of the objective lens 102 of an object illumination unit 100. The object 7 can be a wafer or a semiconductor mask. The diameter of the smallest beam spot or focal spot 5 shaped in the object plane 101 can be very small. An exemplary value for this diameter is less than four nanometers, for example, three nanometers or less. The focusing of the primary charged particle beam 3 used to shape the focal spot 5 is performed by the objective lens system 102. In this case, the objective lens system 102 may include a magnetically immersed lens. Other examples of focusing components are described in German Patent DE 10 2020 125534 B3, the entire contents of which are incorporated herein by reference. A plurality of focal spots 5 of a primary beam 3 are formed in a regular grating configuration of incident positions in the object plane 101. The number J of the primary beams can be 5, 25, or more. In practice, the number of beams J, and therefore the number of incident positions or focal spots 5, can be chosen to be significantly larger, such as, for example, J = 10 × 10, J = 20 × 30, or J = 100 × 100. An exemplary value for the spacing P between the incident positions is 1 micrometer, 10 micrometers, or greater, such as 40 micrometers. For simplicity, only three primary beams 3.1, 3.2, and 3.3 with corresponding focal points 5.1, 5.2, and 5.3 are shown in Figure 1. The primary particle 3 impacting object 7 produces interaction products generated from the surface of object 7, such as secondary electrons, backscattered electrons, or primary particles that have undergone reverse motion for other reasons. The interaction products generated from the surface of object 7 are shaped by objective lens 102 to form a secondary electron beam 9. For simplicity, in this invention, all interaction products are collectively referred to as secondary electrons, forming the secondary electron beam 9. The multi-beam system 1 provides a detection beam path 13 for guiding a plurality of secondary particle beams 9 to a secondary electron imaging system or detection unit 200. The secondary electron imaging system 200 includes several electron optical lenses 205.1 to 205.5 for guiding the secondary particle beams 9 toward a spatially resolving particle detector 600. The spatially resolving particle detector 600 is disposed in an image plane 225. The detector 600 includes a plurality of detection elements. These detection elements may be, for example, diodes such as PMDs or CMOS detection elements, having electron-to-light conversion elements, or may be configured as direct electron detection elements. In one example, detector 600 includes an electron-to-light conversion element (such as a scintillator) that converts secondary electrons into light and a plurality of photodetector elements. The combination of the electron-to-light conversion element and the plurality of photodetector elements thereby forms a plurality of electron detection elements. Detector or image sensor 600 may further include a relay optics system for imaging a secondary charged particle image spot 15 on a dedicated photon detection element (such as a plurality of photomultiplier tubes or avalanche photodiodes (not shown)) and guiding photons generated by the electron-to-light conversion unit. This image sensor is disclosed in US 9,536,702, which is incorporated herein by reference. The imaging system of the secondary electron imaging system 200 is strongly magnified, so that the grating spacing of the primary beam and the size and shape of the focal spot of the primary small beam 3 on the wafer surface are imaged in a magnified manner. For example, the magnification is between 100x and 300x, so that a 1 nm field on the wafer surface is magnified to between 100 nm and 300 nm. In one example, the image field of a multi-beam system with a diameter of, for example, 100 μm is magnified to about 30 mm. A primary particle beam 3 is generated in a beam generating apparatus 300, which includes at least one charged particle emitter 301, at least one collimating lens 303, a porous configuration 305, and a first field lens 331 and a second field lens 333. The charged particle emitter 301 is connected to a voltage source to provide an emitter voltage VK to the emitter 301 and generate at least one diverging charged particle beam 309, which is at least substantially collimated by at least one collimating lens 303 and irradiates the porous configuration 305. The porous configuration 305 includes at least one first porous or filter plate 304 having a plurality of J openings formed therein in a first grating configuration. Particles illuminating the particle beam 309 pass through the J holes or openings of the porous plate 304, forming a plurality of J primary small beams 3. The particles of the illumination beam 309 impacting the first aperture plate 304 are absorbed by the first aperture plate and do not contribute to the formation of the primary small beam 3. The aperture configuration 305 typically has at least one additional aperture plate 306, such as a lens array, an astigmatism array, or a deflection element array. In this example, the particle beam 309 is perfectly collimated by the collimating lens 303. However, the aperture configuration 305 can also be designed to diverge or converge the incident particle beam 309. Together with field lens 331 and second field lens 333, the aperture configuration 305 focuses each of the plurality of primary small beams 3 by forming a focal point in the intermediate image surface 321. Alternatively, the beam focal point and the intermediate image surface 321 may be virtual. The intermediate image surface 321 may be bent and tilted to pre-compensate for the field curvature and image plane tilt of the charged particle imaging system disposed downstream of the intermediate image surface 321. At least one field lens 103 and objective lens 102 provide a first imaging particle optics unit for imaging the surface 321 forming the beam focal point onto the object plane 101, such that a second grating configuration is formed at the focal point 5 of a primary beam at that location. Typically, the surface 25 of the object 7 is disposed in the object plane 101, and the focal point 5 is correspondingly formed on the object surface 25. A plurality of primary beams 3 form an intersection point 108, near which a first scanning deflector 110 is disposed. The first scanning deflector 110 is used to deflect the plurality of primary beams 3 entirely and synchronously, such that the plurality of focal points 5 move simultaneously on the surface 25 of the object 7. The first scanning deflector 110 is driven by a scanning control unit 860, such that in the inspection operation mode, a plurality of two-dimensional image data of the surface are acquired. Additionally, the multi-beam system 1 may also include additional static deflectors and multipole elements 112 configured to adjust the positioning and beam shape of the plurality of primary beams 3. Objective lens 102 and projection lens 205 provide a secondary electronic imaging system 200 for imaging object plane 101 onto detection plane 225. Thus, objective lens 102 is a lens or lens system that is part of both the first and second example optical units, while field lenses 103, 331, and 333 belong only to the first particle optical unit 100, and projection lens 205 belongs only to the secondary electronic imaging system 200. A beam splitter 400 is disposed in the beam path of the first particle optical unit 100 between the field lens 103 and the objective lens system 102. The beam splitter 400 is also part of a second optical unit in the beam path between the objective lens system 102 and the projection lens 205. The first deflector 110 is configured in either a primary electron beam path or a combined electron beam path. In the example shown in FIG1, the secondary electron beam 9 is emitted in the opposite direction during use by the first deflector 110, partially compensating for the scanning motion of the secondary electron beam 9. Secondary electrons typically have a different kinetic energy than primary electrons. Therefore, only the scanning motion of the illumination positioning is partially compensated. The secondary electron imaging system 200 thus includes a second beam deflector 222, configured near a cross plane or pupil plane 21a of the secondary electron beam 9. The second beam deflector 222 operates synchronously with the first beam deflector 110 and compensates for the beam deflection of the secondary electron beam 9 during use, such that the focal point 15 of the secondary electron beam 9 remains at a constant position on the detection plane 225. In this way, each focal point 15 of each individual secondary electron beam 9 remains within the region of a set of detection elements assigned to the individual secondary electron beam 9. Along with objective lens 102, lens 205 is used to focus the secondary beam 9 onto spatial resolution detector 600 and, during processing, compensate for the imaging scaling and distortion of the plurality of secondary electron beams 9 caused by a magnetic lens, so that the third grating configuration of the focal point 15 of the plurality of secondary electron beams 9 remains constant on the detection plane 225. Electro-optical lenses 205.1 to 205.5 are shown as magneto-optical elements, but are not limited to magneto-optical elements, and may also include multiple electrostatic lens elements or astigmatisms. The secondary electron imaging system 200 further includes an interchangeable contrast aperture 284a, 284b, which is mounted on an exchange mechanism 214 at the pupil plane 21 of the secondary electron imaging system 200. Using an exchange mechanism 215, different aperture stops 284a or 284b can be positioned on the second pupil plane 21b and aligned with respect to the optical axis 2105 of the secondary electron imaging system 200. Further information regarding such multi-beam particle systems and the components used therein, such as particle sources, perforated plates, and lenses, is available from international patent applications WO 2005 / 024881, WO 2007 / 028595, WO 2007 / 028596, WO 2011 / 124352 and WO 2007 / 060017 and German patent applications DE 10 2013 016 113 A1 and DE 10 2013 014 976 A1, the disclosures of which are incorporated herein by reference in their entirety. The multi-beam charged particle imaging system 1 further includes a control system 800 configured to control individual particle optics components of the multi-beam system and to evaluate and analyze signals acquired by the detector 600. In this case, the control or controller system 800 can be composed of a plurality of individual computers or electronic components. For example, the control unit 800 includes a control operation processor 880; a control module 840 for controlling the electro-optics of the secondary electro-optic system 200; and a control module 830 for controlling the electro-optics of the primary small beam generating unit 100. The control unit 800 further includes a stage control module 850 for positioning the sample surface 25 or the sample 7 within the object plane 101 by means of the stage 500. The control unit 800 further includes a control module for adjusting a sample voltage VS, which is connected to a module 503 for providing a sample voltage VS to the sample 7, also known as the extraction voltage. Thereby, during use, an extraction field is generated between the objective lens 102 and the surface 25 of the object 7. During use, the lead-in field decelerates the charged particles of the primary beam 3 before reaching the sample surface 25 and produces an additional focusing effect on the plurality of primary beams 3. Simultaneously, the lead-in field is used during use to accelerate secondary particles away from the surface 25 of the object 7. Furthermore, the control unit 800 includes a scanning control module 860. During an inspection operation mode, a plurality of focal spots 15 of the secondary electron microbeams are formed in the detection plane 225, and a plurality of signals are recorded during the scanning operation of the primary microbeam 3 over the surface 25 of the sample 7. The detector 600 includes a plurality of sets of detection elements, one set of detection elements for each secondary electron microbeam 9. During use, each set of detection elements is configured to record the intensity signal of the assigned secondary electron microbeam 9. The plurality of intensity signals of the plurality of secondary electron microbeams 9 are transmitted to the image data acquisition unit 810, where the image data is processed and stored in the memory 890. The settings of the secondary electron optical imaging system 200, the detector 600, and the allocation of the focal spots 15 of the secondary electron microbeams 9 by the multiple sets of detection elements are initially determined and stored in the memory 890 of the control unit 800 of the multi-beam charged imaging system 1. According to the example in Figure 1, the multi-beam charged imaging system 1 further includes a retractable monitoring system 230, which can be inserted into the secondary electron beam path in front of the detection plane 225. The monitoring system 230 further includes multiple imaging elements and a high-resolution detector. The monitoring system 230 is connected to a monitoring control unit 820. picture 2. Schematic illustration of further details of a multi-beam charged particle system 1 according to a specific embodiment. The same reference numerals are used in FIG1, and also with reference to the description of FIG1. ​​A porous configuration 305 generates a plurality of primary charged particle beams 3 according to a collimated electron beam 309. For simplicity, only three beams 3.1 to 3.3 are shown again. A beam tube 151 is disposed downstream of the porous configuration 305 and is connected to a voltage supply having a first or tube voltage VT. From the inlet of the beam tube 151, the plurality of primary charged particle beams 3 are at a constant kinetic energy ET until the outlet opening 153 of the beam tube 151 (see the energy diagram on the right side of FIG2). The kinetic energy ET of the primary charged particle beams 3 is, for example, 20 keV, 30 keV, or greater. A plurality of primary charged particle beams 3 are imaged, and focal spots 5.1 to 5.3 are formed in image plane 101 through field lenses 333 and 103 and objective lens 102. Objective lens 102 is a type of magnetic lens with coil 161 and pole shoe 163 with lower pole shoe section 165 to form a magnetic field axial gap. During use, a current I is supplied to coil 161 to generate a focusing magnetic field (not shown). Other types of magnetic lenses may also be used, such as radial gap lenses for generating an immersion lens field, or magnetic lenses with several coils and pole shoes. A beam splitter 400 is disposed upstream of or partially integrated into objective lens 102, which is configured to separate secondary electrons along secondary electron beam path 13 to detector unit 200. Below lower pole shoe section 165, an electrode 133 is provided, which is connected to a voltage supply to provide a second voltage VE to the electrode. In the example shown, electrode 133 is configured as an individual electrode. After exiting the beam tube 151, the plurality of primary charged particle beams 3 decelerate from a kinetic energy ET to a second kinetic energy EE. The voltage difference between VT and VE generates a first electric field 135, as shown by the equipotential energy lines of the first electric field 135 in Figure 2. The first electric field vector is almost parallel to the propagation direction of the primary charged particle beams 3 and exerts a decelerating force on the primary charged particles. The first voltage VE is typically adjusted so that the second kinetic energy EE is below 5 keV, below 3 keV, or even below 2 keV. A third sample voltage VS is provided to a sample mounting platform 505 via a sample voltage source 503 for holding and contacting a wafer 7 during use. At the surface 25 of the wafer 7, a first material composition 67 is disposed below a first group of primary charged particle beams 3.1 and 3.2, and a second material composition 69 is disposed below a second group of primary charged particle beams containing a primary charged particle beam 3.3. Based on the voltage difference between VS and VE, a second electric field 137 is generated. This second electric field is almost parallel to the propagation direction of the primary charged particle beam 3 and exerts a decelerating force on the primary charged particles. For example, the third or sample voltage VS is adjusted so that the third kinetic energy LE is adjusted to a kinetic impact energy in the range of less than 800 eV, less than 300 eV, or even less than 100 eV. The first electric field 135 also forms an accelerating field on the secondary electrons extracted from the wafer 7. The second electric field 137 forms an extraction field for extracting and accelerating secondary electrons from the wafer 7. Therefore, the second field 137 is also called the extraction field 137. Figure 4 further illustrates the image forming and extraction mechanism according to a first embodiment. The primary charged particle beam 3.i is focused to a focal point 5.i during an image scanning operation step and impacts the surface 25 of the wafer 7, forming an interaction volume 141.i within the wafer 7. For example, during low-energy operation below 1 keV, the interaction volume 141.i has a small extension of less than 5 nm. During use, a parallel extraction field 137 is generated, where the electric field vector 139 is perpendicular to the wafer surface 25. The extraction field 137 (illustrated by equipotential lines) extracts and accelerates the secondary electrons generated in the interaction volume 141.i along electron trajectories (some examples of electron trajectories 191.1 to 191.3 are shown) in a propagation direction opposite to the primary electron beam direction. After sufficient secondary electrons are gathered during a residence time of approximately 50 ns, a small primary beam 3.i is moved to the next image pixel position along the scanning direction 143 by a scanning deflector (not shown). In this way, image data of the surface of a sample is obtained. The example shown in Figure 2 illustrates a multi-beam charged particle system 1 with two-stage deceleration fields 135 and 137 and an additional electrode 133. In another example, a single deceleration or extraction field 137 is generated only between the exit orifice 153 of the beam tube 151 and a sample 7 mounted on the sample platform 505. In this case, the exit orifice 153 of the beam tube 151 serves as the electrode 133 for extracting the field 137. During the acquisition of an image patch by scanning a plurality of primary charged particle beams 3, it is preferable not to move the stage 500, and after acquiring an image patch, move the stage 500 to the next image patch to be acquired. In an alternative embodiment, the stage 500 moves continuously along a second direction while acquiring an image by scanning a plurality of primary charged particle beams 3 along a first direction using a clustered multi-beam grating scanner 110. The stage movement and stage positioning are monitored and controlled by sensors known in the art, such as laser interferometers, grating interferometers, confocal microlens arrays, etc. During an image scan, the control unit 800 is configured to trigger the image sensor 600 to detect intensity signals from a plurality of secondary electron microbeams 9 at predetermined time intervals, and the digital image of an image patch is accumulated and stitched together from all scan positions of a plurality of primary charged particle microbeams 3. picture Figure 3 illustrates the scanning operation of a plurality of primary charged particle beams 3 during image acquisition. A scanning operation control module 860 is configured to provide a scanning signal to a scanning deflector 110 during use. Here, each primary charged particle beam 3 is deflected by a clustered multi-beam scanner 110, such that the corresponding focal spot 5.i is scanned on an image patch 245.i of a single beam (Figure 3a). Each image patch 245.i has a diameter AP, for example, 8 μm to 10 μm. The scanning operation involves scanning a plurality of parallel image scan lines 241 along a scanning direction 143.1 to acquire an image. At the end of each image scan line 241, each beam 3 moves to the starting position of the next scan line; this is also referred to as "retrace" 243. During image acquisition along the image scan lines 241, the scanning operation is controlled to achieve a dwell time of approximately 50 ns at each image point, for example, 8000 image points per image scan line 241. The scan time 243 can be very short, for example, a total of 20 ns. Figure 3b shows the parallel operation of a plurality of primary charged particle small beams 3 to obtain an image of a surface segment 251 on the wafer surface, which is composed of a plurality of image patches 245. Figure 3c shows two adjacent surface segments 251.1 and 251.2, each surface segment containing a plurality of patches corresponding to a plurality of primary charged particle small beams 3. The backscattering and secondary electron emission coefficient SEY is a function of the primary beam energy. picture 5. Two examples illustrating the residual charge curves of different material compositions in relation to the primary charged particle energy are shown. The residual charge of a first material composition is indicated by reference numeral 61. Residual charge curve 61 shows the region where a sample is positively charged between the two kinetic energies ELT1 and EHT1, i.e., more secondary and backscattered electrons leave the sample compared to the deposited charge. Residual charge curve 61 also shows the region where the sample is negatively charged at energies below ELT1 and above EHT1, i.e., fewer secondary or backscattered electrons leave the sample compared to the deposited charge, resulting in an accumulation of negative charge in the sample. The residual charge of a second material composition is indicated by reference numeral 62, having two kinetic energies ELT2 and EHT2. For each material composition, the sample charge is reduced at the transition energies ELT and EHT, respectively. A first minimum sample charge is achieved at a low kinetic energy ELT, corresponding to a low-energy transition point ELT with no sample charge. A low-energy transition point (ELT) depends on the material composition, typically below 800 eV, below 500 eV, or even lower. For example, for semiconductor wafers containing materials such as Cu, W, Al, Si, and SiO... 2 or SiN For typical materials of class 2, the low-energy transition point (ELT) is between 80 eV and 250 eV. A second minimum sample charge is achieved at a higher kinetic energy EHT, corresponding to a high-energy EHT with no sample charge. The high-energy EHT depends on the material composition and is typically above 1 keV. For example, the high-energy EHT for copper (Cu) or tungsten (W) is above 2 keV, at which point high-resolution imaging is no longer possible. A low-energy EHT is sometimes referred to as an unstable neutral point 63. A high-energy EHT is sometimes referred to as a stable neutral point 65. However, the backscattering and secondary electron emission coefficients SEY, as well as the transition points ELT and EHT, further depend on layout effects. By appropriately adjusting the extraction field generated by the voltage source 503, the residual charge of the selected material composition can be reduced. According to the first embodiment, the impact energy LE of the primary charged particles is selected and adjusted such that for each primary charged particle beam, the secondary and backscattered electron emission coefficients exceed the beam current of the primary charged particle beam, thereby achieving a high image contrast and low noise level. Furthermore, through the selected impact energy between the ELT and EHT of the majority of materials present on surface 25 at the test location of sample 7, positive surface charge is generated at least in some areas of surface 25 of sample 7. picture Figure 6a illustrates the reversal of the primary electron beam 3.i during the second scan operation step for charge compensation. In Figure 6a, the extraction intensity 139.2 of an extraction field 137.2 is increased by the sample voltage VS2 provided by the voltage supply unit 503. Therefore, the primary electrons do not have sufficient kinetic energy to reach the sample surface 25 and are reflected in the opposite direction. This operating mode is also called mirror mode. During mirror mode operation, the wafer surface is uncharged. In an example illustrated in Figure 6b, the beam impact energy LE is defined by the difference between the emitter voltage VK and the sample voltage source VS. In the example of Figure 6b, the tube voltage VT is set to ground potential. The impact energy or operation in mirror mode can be adjusted by changing the emitter voltage VK or the sample voltage VS. If the absolute value of the sample voltage VS2 exceeds the emitter voltage VK2 by several volts, electrons may not reach the surface 25 of a wafer 7. For example, for a dynamic beam energy of 30 keV, the emitter voltage VK2 is set to -30 kV, and the sample voltage is set to VS2 = -30005 V, where the voltage difference is only 5 V. Thus, electrons from the small electron beam 3.1 may not reach the sample surface 25. For example, for a dynamic beam energy of 29995 eV, the emitter voltage VK2 is set to -29995 kV, and the sample voltage is set to VS2 = -30 kV, where the voltage difference is only 5 V. Therefore, the electrons from the small electron beam 3.1 may not reach the sample surface 25. According to a first specific embodiment, the kinetic energy or field strength of the introduced field is adjusted such that, in the presence of charged regions on the wafer surface, a primary discharge or reversal of electrons is achieved. This compensates for the charge distribution of different material compositions on the wafer surface. picture An example is shown in Figure 7. Figure 7a illustrates a first step of image acquisition along a scan line 143.1 from different regions 67.1 to 67.3 and a first sample voltage VS1. In this example, the kinetic energy of the primary electron beam 3 is adjusted between low and high energy transition points, thereby achieving positive surface charging in some material compositions. The primary beam 3.i is first scanned above a scan position 3.i1 at the first material composition 67.1 with a low secondary electron emission or emission coefficient SEY1, and no charge is accumulated in the first material composition 67.1. Then, the primary beam 3.i is scanned above a scan position 3.i2 at the second material composition 67.2 with a moderate secondary electron emission or emission coefficient SEY2, and a moderate positive surface charge 71.2 is accumulated on the surface of the second material composition 67.2. Then, a small beam 3.i is scanned once at the scanning position 3.i3 of the third material composition 67.3 with a high secondary electron emission or emission coefficient SEY3, and a large positive surface charge 71.3 is accumulated at the surface of the second material composition 67.3 (see Figure 7b). In the second scan 143.2 shown in Figure 7c, the kinetic energy system of the primary electrons is adjusted to operate in mirror mode using the sample voltage VS2. Therefore, at the first scan position 3.i1 where there is no positive surface charge, the primary beam 3.i is reversed. However, at the second and third positions 3.i2 and 3.i3, the primary beam arrives at the sample with low kinetic energy and absorbs primary electrons, compensating for the positive local surface or volume charges 71.2 and 71.3 accumulated by the second and third material compositions 67.2 and 67.3. After charge balance, the primary beam 3.i is reversed at all positions on the surface of wafer 7, including scan positions 3.i2 and 3.i3 at material compositions 67.2 and 67.3 (Figure 7d). Image acquisition then continues using the next scan line. This repeatedly removes the charge, for example, before each next scan line or after each 10th scan line, and obtains a high-precision image without any degradation caused by the charging effect. Using the method according to the first embodiment shown in FIG7, a positively charged sample is compensated or balanced by operation of a multi-beam charged particle microscope in mirror mode. In a first scan operation, a first impact energy of a primary charged particle is adjusted such that a positive surface charge 71 is generated under a specific material composition. During the first scan operation, secondary electrons are generated and bundled by the detection unit 200, and image lines are recorded by the imaging control module 810. In a second scan operation, a second energy of the primary charged particle is adjusted such that a small primary beam is reflected at an uncharged portion or sample surface 25. For example, the second energy is adjusted in such a way that the positive charge 71 accumulated at surface 27 provides sufficient additional acceleration to the sample surface 25 via the sample voltage VS, such that the primary charged particle arrives at the sample surface with, for example, low kinetic energy (e.g., below ELT), resulting in the absorption of most of the primary charged particles without generating many secondary electrons. As a result, positive surface charges 71.2 and 71.3 are removed during the second scan operation. The first and second scan operations can be repeated repeatedly. In one example, the first and second scan operations are repeated repeatedly for each scan line 241 (see Figure 3). In another example, the second scan operation is performed either during the retrace operation 243. In one example, after capturing an image segment 251.1, a second scan operation is performed at a second energy level for charged particles. This removes residual charge before acquiring an image of the adjacent image segment 251.2. In one example, during a second scan operation, in addition to the second energy change via VS2, other properties of the primary charged particle beam 3 are also altered. For example, a focal position is changed such that the focal point 5 of the primary charged particle beam 3 does not form on the surface 25 of the sample 7. This allows for coarse sampling with large distances between scan lines and enables the second scan operation to be performed within a shortened time interval. For example, the location of surface segments with charged material compositions is determined based on an image or prior information, and the second scan operation is limited to the region with positive surface charge 71.2 or 71.3. This increases throughput. picture 8 further describes the method according to the first specific embodiment. In setting adjustments step In step S, an inspection position on the surface 25 of a wafer 7 is adjusted in the object plane 101 of the multi-beam charged particle system 1, and an image setting is selected. For example, for at least some material compositions present at the inspection position on the sample surface, a primary electron impact energy LE is selected for a large secondary electron emission coefficient SEY. This achieves a large image contrast with low image noise. Typically, an impact energy LE is selected between a low-energy transition energy ELT and a high-energy transition energy EHT (see Figure 5). For example, for insulating material compositions such as silicon dioxide with a high dielectric constant, an impact energy LE is selected to achieve a large secondary electron emission coefficient SEY, where charge has accumulated. The image setting includes setting a first positive voltage difference VD1 such that a small beam of primary charged particles reaches the sample surface (25) at an impact energy LE within the impact energy range, where the secondary and backscattered electron emission coefficients exceed the incident beam current of the primary charged particles. Selectively, for example, prior information about the material composition of the surface 25 of the wafer 7 at the inspection position is loaded from a CAD file. exist First or image scanning operation steps In step A, a first or image scan operation is performed. During the first or image scan operation A(1), a first image setting is adjusted. In a part of the first image setting, the impact energy LE of the primary electrons is adjusted to the selected impact energy selected in step S via voltages VK1, VE1, and VS1 to achieve a large SEY (see Figure 5). For example, VS1 is set to VS1 = (ET-LE) / e. For example, when the primary electrons in the beam tube 151 are at ET = 30 keV and VS1 = -29 kV, an impact energy LE = 1 keV is adjusted, at which point a large secondary electron emission coefficient can be obtained (see Figure 5). For example, when the emitter potential VK1 = -30 kV and VS1 = -29 kV, an impact energy of 1 keV is adjusted, at which point a large secondary electron emission coefficient can be obtained. Generally, with a positive first voltage difference VD1 = VS1-VK1, electrons reach the surface 25 of the sample 7 with an impact energy LE = e*VD. In one example, the first scan operation includes a first set of image scan lines 241, each set of image scan lines 241 including, for example, 1, 2, 10 or more scan lines 241 for each image patch 245 of each primary charged particle small beam. In selectivity Adjustment steps In M, the limitation settings for a subsequent second scan operation B for charge compensation are adjusted. In one example, the adjustment includes an evaluation of image information obtained during the previous image scan operation A(i); and a separate adjustment of the first-line scan operation for charge compensation B(i) based on the previous image scan operation A(i). In response to charge compensation Second scanning operation steps In step B, a second scan operation for charge compensation is performed. The settings of the multi-beam charged particle system 1 are adjusted to a compensation setting. During the compensation setting, at least one of the emitter potential VK2, electrode voltage VE2, or sample voltage VS2 is adjusted such that primary particles are reversed at uncharged segments or segments with negative surface charge on surface 25 (see Figure 6). For example, when primary electrons in beam tube 151 are at a kinetic energy of ET = 30 keV and VS2 = -30.001 kV, the primary electrons are reversed in the propagation direction and do not reach the sample. A negative second voltage difference VD2 = VS2 - ET / e, where VD2 = -1V, defines the minimum required charge threshold at surface 25 of sample 7. For example, when the emitter potential VK1 = -30 kV and VS2 = -30003 V, a mirror mode is adjusted using a negative second voltage difference VD2 = VS2 - VK1 = -3 V. For example, when the emitter potential VK2 = -29995 V and VS2 = -30000 V, a mirror mode would use a second voltage difference VD2 = VS2 - VK2 = -5 V to adjust. Using this second voltage difference VD2, a minimum required charge threshold is defined at surface 25 of sample 7, such that primary electrons only reach the surface region that generates a positive surface charge and the local voltage U = Q / C exceeds the voltage difference VD2. The absolute value of VD2, |VD2|, can be 100 V, 50 V, 10 V, or even smaller, such as 5 V or 1 V. In one example, the second scan operation includes a second set of scan lines 241, such as 1, 2, 10, or more scan lines 241 for each image patch 245 of each primary charged particle small beam. In one example, the second scan operation is performed during a retrace 243 of each primary charged particle small beam 3. This compensates for the charge during image acquisition. In one example, an inspection task includes several adjacent surface segments 251.1, 251.2 (see Figure 3c). After image capture of the first surface segment 251.1, a surface charge may be generated at the first surface segment 251.1. This may degrade a second image capture of the adjacent surface segment 251.2. According to the method, before the wafer stage 500 moves a wafer to the second surface segment 251.2 adjacent to surface segment 251.1, a second scan operation step B for charge compensation is performed at the first surface segment 251.1. This reduces the influence of surface charge on a second or subsequent surface segment from an adjacent pre-exposed surface segment. This reduces the charge on a surface segment before performing a subsequent scan image capture step for an adjacent surface segment. In one example, the second scan operation is limited to a scan range at a boundary or edge of surface segment 251.1 (see Figure 3). This compensates for or reduces the charge in subsequent image captures of an adjacent surface segment 251.2. During mirror mode, reflected primary electrons provide a constant detection signal at the image sensor of the detection unit. In one example, the second scan operation is repeated until the secondary electron signal is minimal and the signal changes from a secondary electron signal to a mirrored primary electron signal. Secondary electrons are emitted only from positively charged surface regions, where primary electrons may strike the sample surface and generate secondary electrons. In mirror mode, there are no positively charged surface regions, no secondary electrons are excited, and a constant detection signal is received. The first or image scanning operation step A(i), the second scanning operation step B(i) for charge compensation, and the selective adjustment step M(i) are repeated a predetermined N times, for example, for each scan line (e.g., N = 8000), for each group of 10 scan lines (N = 800), or for each frame of the image of a surface segment 251 (N = 1). Each image data string generated during each first or image scanning operation step A(i) is received and stored in image capturing step I. Image capturing step I includes a selection of image processing operations from a set of operations that include image stitching, image filtering, object detection, and defect detection. In selectivity Bundling steps In C, data is collected and analyzed for charge compensation. Second scanning operation steps Image information acquired during step B. For example, image information acquired during the second scan operation step B in mirror mode is used to identify regions with strong charged characteristics. In one example, this information from the clustering step C is used for charge compensation at subsequent inspection locations. Surface charge can be generated during a first image capture, or it may even be present on the surface of a sample before the first image capture. However, the method is not limited to surface charge generated during the first image capture step A. In one example, a second scan operation step B for charge compensation is performed before or after the first or image scan operation step A, and reduces or removes the charge present on the surface of a sample before an image capture. The method typically includes a scan operation step B for charge compensation. The scan operation step B for charge compensation includes setting a negative voltage difference VD2 on a sample mounted to a sample stage, such that the primary charged particle beam is reversed in its propagation direction before reaching the uncharged region of the sample surface. This operation mode is also called a mirror mode. The second negative voltage difference VD2 can be adjusted so that the primary charged particles only reach the surface of the sample in the region where a positive surface charge exists. Thereby, the positive surface charge is removed, and the charge is at least partially compensated. In one example, a wafer surface contains a surface region where negative charges accumulate during imaging. This negative charge cannot be compensated by a second scan operation for charge compensation. In this example, a further scan operation can be added, wherein an impact energy LE is adjusted to a material composition such that, also at the negatively charged surface region, the secondary and backscattered electron emission coefficients exceed the incident current of the electron beam, thereby compensating for the negative charge in the negatively charged surface region and, for example, achieving a positively charged surface. This third scan operation can be inserted before each of the second scan operations B(i) for charge compensation for positive charges. A multi-beam charged particle beam system 1 according to a second embodiment includes a control operation processor 880 and software code installed in a memory 890. When the control operation processor 880 executes the software code, it controls the multi-beam charged particle beam system 1 to perform a method according to a first embodiment. Using a multi-beam charged particle system 1 according to a second embodiment and a method according to a first embodiment, distributed surface charge generated during a first image scanning operation is compensated for by a second scan operation for charge compensation. In some instances, the charging effect appears in specific structures or features on a limited region of the surface of a sample, such as a wafer. For example, a wafer typically contains multiple repeating structures (grains) separated by small gaps. The charging effect typically accumulates at the gaps or boundaries of the grains. Using the method according to the first embodiment, the charging effect at the boundaries or edges of the grains generated during the first image scanning is compensated for by a second scan operation in mirror mode. This invention can be used for wafer inspection. In one example, a wafer inspection task is to investigate defects or dimensions of structured photoresist. Photoresist is an insulator and exhibits a strong charging effect. Using an apparatus and method according to one of several specific embodiments, the charging effect of the structured photoresist can be reduced. In one example of a wafer inspection task, it is necessary to measure the structural dimensions of a FinFET. picture 9 illustrates an example of a FinFET. A wafer 7 containing a FinFET 701 includes a surface layout having: a first surface 25.1 containing a polysilicon gate structure 707, a second surface 25.2 containing a silicon dioxide insulating layer 705, and a third surface 25.3 containing a source 709 and a drain 711 (made of bulk silicon material 703 of wafer 7). The source 709 and drain 711 are isolated from the gate 707 by a high-k dielectric coating 713 (e.g., made of tantalum pentoxide, hafnium silicate, zirconium silicate, hafnium dioxide, or zirconium dioxide). The polysilicon gate 707, the insulating layer 705, and the high-k dielectric coating 713 can accumulate charge during imaging, which may result in the source 709 and drain 711 being barely visible during electron beam imaging. According to one of the various embodiments of the apparatus and method, the charging effect of FinFETs can be mitigated, and for example, the dimensions of a FinFET structure containing a source 709 and a drain 711 can be measured with high precision. In one example of a wafer inspection task, the structure to be studied is configured at the boundary or edge of the die. For example, a dedicated process control monitor (PCM) can be configured close to the edge of the die. Using the apparatus and method according to one of the various embodiments, charging of gap surfaces between dies or at die edges can be avoided, and the charging effect can be prevented. The present invention is further described by the following examples: Example 1: A method of operating a multi-beam charged particle system (1) comprising: - a first or image scanning operation step A comprising setting a first positive voltage difference VD1 such that a primary charged particle beam reaches the sample surface (25) with an impact energy LE within the impact energy range, wherein the secondary and backscattered electron emission coefficients exceed an incident beam current of the primary charged particles, thereby generating image data and generating a positive surface charge at least in a region of the surface (25) of the sample (7); - a second scan operation step B for charge compensation comprising setting a second negative voltage difference VD2 such that a primary charged particle beam (3) reverses its propagation direction before reaching an uncharged region of the surface (25) of the sample (7) and reaches the region of the surface (25) of the sample (7), wherein the positive surface charge is generated during the first or image scanning operation step A. Example 2: According to the method described in Example 1, the absolute value of the second negative voltage difference VD2 is less than 100V, for example 50V, for example 10V or 5V, for example 1V. Example 3: The method described in Example 1 or 2 further includes repeatedly performing the first or image scanning operation step A and the second scanning operation step B to perform charge compensation. Example 4: According to the method described in Example 3, the first or image scanning operation step A and the second scanning operation step B for charge compensation are repeated repeatedly for each sequence of scan lines (241), wherein the sequence of scan lines (241) includes one, two, ten or more scan lines (241). Example 5: According to the method described in Example 3 or 4, the second scan operation step B for charge compensation is performed during the retrace (243) of each charged particle small beam (3). Example 6: According to any one of Examples 1 to 4, the method includes capturing an image of a surface segment (251) of a wafer surface (25) during the first or image scanning operation step A, and at least partially compensating a surface charge at the surface segment (251) during the second scan operation step B for charge compensation. Example 7: According to the method described in Example 6, the second scan operation step B for charge compensation is limited to the scan range at the boundary or edge of a surface segment (251). Example 8: The method according to any one of Examples 1 to 7 further includes a setting adjustment step S, which includes adjusting the inspection position of the surface (25) of the wafer (7) in the object plane (101) of the multi-beam charged particle beam system (1); and selecting an image setting, which includes selecting the first positive voltage difference VD1 and the second negative voltage difference VD2. Example 9: According to the method described in Example 8, the first positive voltage difference VD1 and the second negative voltage difference VD2 are selected based on the material composition present at the surface (25) of the sample (7). Example 10: The method according to any one of Examples 1 to 9 further includes an adjustment step M for limiting the setting of a second scan operation B for charge compensation. Example 11: The method according to any one of Examples 1 to 10 further includes setting the first voltage difference VD1 = VS1-VK1 between a first sample voltage VS1 applied to the sample (7) and a voltage VK1 of a primary charged particle emitter (301) in a voltage range of about 1kV. Example 12: The method according to any one of Examples 1 to 11 further includes setting or limiting the second voltage difference VD2 by setting or limiting at least one of a sample voltage VS, a voltage VK of a primary charged particle emitter (301) and a voltage VE supplied to the electrode (133). Example 13: The method according to any one of Examples 1 to 12 further includes an image acquisition step I for receiving and storing image data acquired during a first image scanning operation step A. Example 14: The method according to any one of Examples 1 to 13 further includes a clustering step C for receiving, analyzing and storing information obtained during a second scan operation step B for charge compensation. Example 15: A multi-beam charged particle beam system (1) comprising: - a primary charged particle emitter (301) connected to an emitter voltage source to provide an emitter voltage VK to the emitter (301); - a sample voltage source (503) for providing a sample voltage VS to a sample (7) mounted on a sample stage (500) of the multi-beam charged particle beam system (1) during use; - a control unit (800) configured to adjust at least one of the emitter voltage VK or the sample voltage VS; the control unit (800) further comprising a memory (890) for storing a plurality of software instructions and an operation processor (880) for executing the software instructions, which, when executed, cause the multi-beam charged particle beam system (1) to perform any of the plurality of method steps described in Examples 1 to 14. Example 16: A method for inspecting a FinFET (701) using a multi-beam charged particle imaging system (1), comprising: - a first or image scanning operation step A comprising setting a first positive voltage difference VD1 such that a primary charged particle beam reaches the surface (25.1, 25.2, 25.3) of the FinFET (701) with an impact energy LE within the impact energy range, wherein the secondary and backscattered electron emission coefficients exceed an incident beam current of the primary charged particles, thereby generating image data and generating a positive surface charge at least in the region of the insulator (705) of the FinFET (701); - a second scan operation step B for charge compensation comprising setting a second negative voltage difference VD2 such that a primary charged particle beam (3) reverses its propagation direction before reaching the uncharged region of the surface (25.1, 25.3) of the insulator (705) and reaches the insulator (705), wherein the positive surface charge is generated during the first or image scanning operation step A. Example 17: The method according to Example 16 further includes repeatedly repeating the first or image scanning operation step A and the second scanning operation step B to perform charge compensation, and calculating the image of the surface (25.1, 25.2, 25.3) by image processing of the plurality of images generated during the repeated repetition of the first or image scanning operation step A. However, the present invention is not limited to the foregoing specific embodiments or examples, and changes and modifications are also possible. 1: Multi-beam charged particle beam system; 3: Primary charged particle beam; 5: Primary charged particle beam spot; 7: Object; 9: Secondary electron beam; 11: Primary beam path; 13: Secondary electron beam path; 15: Secondary charged particle image spot; 21: Common pupil plane; 25: Object surface; 61: SE yield curve of the first material composition; 62: SE yield curve of the second material composition; 63: Low-energy transition point; 65: High-energy transition point; 67: First material composition; 69: Second material composition; 71: Surface charging; 100: Object irradiation unit; 101: Object plane; 102: Objective lens. 103: Field lens; 108: Beam crossover; 110: First scanning deflector; 112: Electrostatic lens; 133: Electrode; 135: First electron field; 137: Isotropic lines of the drawn field; 139: Electric field vector; 141: Interaction volume; 143: Scanning direction; 149: Pre-exposure surface area; 151: Beam tube section; 153: Beam tube section exit opening; 161: Lens coil; 163: Pole shoe; 165: Lower pole shoe section; 191: Secondary electron trajectory; 200: Detection unit; 205: Electro-optical lens; 214: Aperture filter module; 215: Moving mechanism; 222: Second deflector. 25: Detection or image plane; 230: Monitoring system; 241: Scan line; 243: Retracing; 245: Single-beam image patch; 251: Surface fragment image; 284: Aperture filter; 300: Charged particle majority beam generator; 301: Charged particle emitter; 303: Collimating lens; 304: Filter plate; 305: Porous configuration; 306: Porous plate; 309: Primary electron beam; 321: Intermediate image surface; 331: First field lens; 333: Second field lens; 400: Beam splitter; 500: Sample stage; 503: Sample voltage supply; 505: Sample platform, such as wafer chuck; 60 0: Image sensor or detector; 701: FinFET structure; 703: Silicon wafer; 705: Silicon dioxide insulator; 707: Polycrystalline silicon gate; 709: Source; 711: Drain; 713: High dielectric constant dielectric material; 800: Control unit; 810: Imaging control module; 820: Monitoring and control unit; 830: Primary beam path control module; 840: Secondary beam path control module; 850: Stage control module; 860: Scanning operation control unit; 880: Control operation processor; 890: Memory; 2105: Optical axis of the detection unit; SEY: Secondary electron emission coefficient. Several specific embodiments of the present invention will be explained in more detail with reference to the accompanying drawings, wherein: Figure 1 is a schematic cross-sectional view of a multi-beam charged particle system according to a specific embodiment. Figure 2 is a further schematic cross-sectional view of a multi-beam charged particle system according to a specific embodiment. Figures 3a and 3c illustrate an example of scanning image capture of a surface segment of a wafer. Figure 4 illustrates an example of imaging settings during step A of a first image scanning operation. Figure 5 illustrates the relationship between the emission coefficients of secondary electrons and backscattered electrons and the impact energy LE or primary charged particles. Figures 6a and 6b illustrate several examples of imaging settings during a second scan operation step B in mirror mode. Figure 7 illustrates an example of the method according to the first specific embodiment. Figure 8 illustrates an example of the method according to the first specific embodiment. Figure 9 illustrates a FinFET structure. 3: A single charged particle beam 7:Object 25: Object surface 67: First material composition 71: Surface charged 143: Scanning direction SEY: Secondary electron emission coefficient

Claims

1. A method for operating a multi-beam charged particle beam system (1), comprising: - A first or image scanning operation step A includes setting a first positive voltage difference VD1 such that a primary charged particle beam reaches the sample surface (25) with an impact energy LE within the impact energy range, wherein secondary and backscattered electrons generate an incident beam current exceeding that of the primary charged particles, thereby generating image data and generating a positive surface charge at least in a region of the surface (25) of the sample (7); - A second scanning operation step B for charge compensation includes setting a second negative voltage difference VD2 such that a primary charged particle beam (3) reverses its propagation direction before reaching an uncharged region of the surface (25) of the sample (7) and reaches a region of the surface (25) of the sample (7), wherein the positive surface charge is generated during the first or image scanning operation step A.

2. The method as described in claim 1, wherein the absolute value of the second negative voltage difference VD2 is less than 100V, for example 50V, for example 10V or 5V, for example 1V.

3. The method as described in claim 1 or 2 further includes repeatedly performing the first or image scanning operation step A and the second scanning operation step B to perform charge compensation.

4. The method as described in claim 3, wherein the first or image scanning operation step A and the second scanning operation step B for charge compensation are repeated iteratively for each scan line (241) sequence, wherein the sequence of scan lines (241) comprises one, two, ten or more scan lines (241).

5. The method as described in claim 3, wherein the second scan operation step B for charge compensation is performed during the retrace (243) of each primary charged particle beam (3).

6. The method as described in claim 1 or 2 further includes capturing an image of a surface segment (251) of the wafer surface (25) during the first or image scanning operation step A, and at least partially compensating a surface charge at the surface segment (251) during the second scanning operation step B for charge compensation.

7. The method as described in claim 6, wherein the second scan operation step B for charge compensation is limited to a scan range at the boundary or edge of a surface segment (251).

8. The method as described in claim 1 or 2 further includes a setting adjustment step S, comprising adjusting the inspection position of the surface (25) of the wafer (7) in the object plane (101) of the multi-beam charged particle system (1); and selecting an image setting, comprising selecting the first positive voltage difference VD1 and the second negative voltage difference VD2.

9. The method as claimed in claim 8, wherein the first positive voltage difference VD1 and the second negative voltage difference VD2 are selected based on the material composition present at the surface (25) of a sample (7).

10. The method as described in claim 1 or 2 further includes an adjustment step M for limiting the setting of a second scan operation B for charge compensation.

11. The method as described in claim 1 or 2 further includes setting the first voltage difference VD1 = VS1-VK1 between a first sample voltage VS1 applied to the sample (7) and a voltage VK1 of a primary charged particle emitter (301) in a voltage range of about 1 kV.

12. The method as described in claim 1 or 2 further includes setting or limiting the second voltage difference VD2 by setting or limiting at least one of a sample voltage VS, a voltage VK of an emitter (301) of a primary charged particle, and a voltage VE supplied to an electrode (133).

13. The method as described in claim 1 or 2 further includes an image capturing step I for receiving and storing image data captured during a first image scanning operation step A.

14. The method as described in claim 1 or 2 further includes a clustering step C for receiving, analyzing, and storing information acquired during a second scan operation step B for charge compensation.

15. A method for verifying FinFET (701) by operating a multi-beam charged particle imaging system (1), comprising: - A first or image scanning operation step A includes setting a first positive voltage difference VD1 such that a primary charged particle beam reaches the surface (25.1, 25.2, 25.3) of the FinFET (701) with an impact energy LE within the impact energy range, wherein the secondary and backscattered electron emission coefficients exceed an incident beam current of the primary charged particles, thereby generating image data and generating a positive surface charge at least in the region of the insulator (705) of the FinFET (701); - A second scanning operation step B for charge compensation includes setting a second negative voltage difference VD2 such that a primary charged particle beam (3) reverses its propagation direction before reaching the uncharged region of the surface (25.1, 25.3) of the insulator (705) and reaches the insulator (705), wherein the positive surface charge is generated during the first or image scanning operation step A.

16. The method as described in claim 15 further includes repeatedly performing the first or image scanning operation step A and the second scanning operation step B to perform charge compensation, and calculating an image of the surface (25.1, 25.2, 25.3) by image processing of a plurality of images generated during the repeated performance of the first or image scanning operation step A.

17. A multi-beam charged particle beam system (1), comprising: - A primary charged particle emitter (301) connected to an emitter voltage source to provide an emitter voltage VK to the emitter (301); - A sample voltage source (503) for providing a sample voltage VS to a sample (7) mounted on a sample stage (500) of the multi-beam charged particle system (1) during use; - A control unit (800) configured to adjust at least one of the emitter voltage VK or the sample voltage VS; The control unit (800) further includes a memory (890) for storing a plurality of software instructions and an operation processor (880) for executing the software instructions, which, when executed, cause the multi-beam charged particle system (1) to perform a plurality of method steps as described in claims 1, 2, 15 or 16.

Images