Distortion-optimized multi-beam scanning system

Abstract

A multi-beam charged particle inspection system and method of operating a multi-beam charged particle inspection system for high throughput, high resolution and reliable wafer inspection is provided, the method and the multi-beam charged particle inspection system comprising means for reducing and compensating for scanning induced aberrations, such as scanning distortions of a lumped multi-beam raster scanner for beamlets propagating at an angle relative to an optical axis of the multi-beam charged particle inspection system.

Description

[Technical Field]

[0001] The present invention relates to a multi-beam charged particle inspection system and a method for operating the same. More particularly, the present invention relates to a multi-beam charged particle inspection system for high-resolution wafer inspection provided by an optimized scanner system for scanning the deflection of multiple primary charged particle beamlets and a scanning corrector for inspection with minimal distortion and advanced stigma correction. The method and multi-beam charged particle inspection system enable high-precision wafer inspection over a large imaging field. [Background technology]

[0002] As miniaturization and high functionality of microstructures, such as semiconductor devices, continue to advance, further development and optimization of planar processing technologies and inspection systems for processing and inspecting the critical dimensions of microstructures is required. Semiconductor device development and processing require, for example, design verification of test wafers, and planar processing technologies involve process optimization for reliable, high-throughput processing. In recent years, analysis of semiconductor wafers has become necessary for reverse engineering and individual, customized configuration of semiconductor devices. Therefore, there is a need for high-throughput inspection tools that can accurately examine microstructures on wafers.

[0003] Typical silicon wafers used in semiconductor device manufacturing are up to 12 inches (300 mm) in diameter. Each wafer is divided into 30–60 repeating areas (“dies”), each measuring up to approximately 800 square mm. Semiconductor devices contain multiple semiconductor structures fabricated in layers on the surface of the wafer using planar integration techniques. Due to the fabrication processes involved, semiconductor wafers typically have flat surfaces. Feature sizes of integrated semiconductor structures have shrunk from a few microns to 5 nm critical dimensions (CDs), with further reductions expected in the near future, for example, to feature sizes or critical dimensions (CDs) of less than 3 nm (e.g., 2 nm) or even 1 nm. These small feature sizes necessitate identifying defects the size of the critical dimensions over very large areas in a short time. For some applications, the specification requirements for the accuracy of measurements provided by inspection equipment are even higher, for example, by a factor of two or an order of magnitude. For example, the width of semiconductor features must be measured with an accuracy of less than 1 nm (eg, 0.3 nm or less), and the relative positions of semiconductor structures must be determined with an overlay accuracy of less than 1 nm (eg, 0.3 nm or less).

[0004] It is therefore an object of the present invention to provide a charged particle system and a method for operating a charged particle system at high throughput that enables high precision measurements of semiconductor features with an accuracy of less than 1 nm, 0.3 nm or even less than 0.1 nm.

[0005] A recent development in the field of charged particle microscopy (CPM) is the multi-beam charged particle microscope (MSEM). Multi-beam scanning electron microscopes are disclosed, for example, in U.S. Pat. No. 7,244,949 and U.S. Patent Application Publication No. 2019 / 0355544. In a multi-beam electron microscope, a sample is illuminated by an array of electron beamlets, which may contain, for example, 4 to 10,000 electron beams as primary radiation, with each electron beam separated from adjacent electron beams by a distance of 1 to 200 micrometers. For example, a multi-beam charged particle microscope may have approximately 100 separated electron beams, or beamlets, arranged in a hexagonal array and separated by a distance of approximately 10 micrometers. The multiple primary charged particle beamlets are focused by a common objective lens onto the surface of the sample under investigation (e.g., a semiconductor wafer secured to a wafer chuck mounted on a movable stage). During irradiation of the wafer surface by the primary charged particle beamlets, interaction products (e.g., secondary electrons) are generated from multiple intersection points formed by the focal points of the primary charged particle beamlets, with the amount and energy of the interaction products depending on the material composition and topography of the wafer surface. The interaction products form multiple secondary charged particle beamlets, which are collected by a common objective lens and guided onto a detector arranged at a detector plane by a projection imaging system of the multi-beam inspection system. The detector includes multiple detection areas, each with multiple detection pixels, to detect the intensity distribution of each of the multiple secondary charged particle beamlets, resulting in an image patch of, for example, 100 μm × 100 μm. Prior art multi-beam charged particle microscopes include a series of electrostatic and magnetic elements. By adjusting at least some of the electrostatic and magnetic elements, the focal positions and stigmas of the multiple secondary charged particle beams can be adjusted. Prior art multi-beam charged particle microscopes include at least one crossover plane for the primary or secondary charged particles. Prior art multi-beam charged particle microscopes include a detection system that facilitates adjustment.Prior art multi-beam charged particle microscopes include at least one deflection scanner for obtaining image patches of a sample surface by collectively scanning a plurality of primary charged particle beamlets across an area of ​​the sample surface. Further details of multi-beam charged particle microscopes and methods for operating multi-beam charged particle microscopes are described in PCT / EP2021 / 061216, filed April 29, 2021, which is incorporated herein by reference.

[0006] However, in charged particle microscopes for wafer inspection, it is desirable to keep the imaging conditions stable so that reliable and reproducible imaging can be performed. The throughput is determined by several parameters (e.g., the speed of the stage and repositioning at a new measurement site) as well as the measurement area per acquisition time itself. The latter is determined by the dwell time, resolution, and number of beamlets. In addition, multi-beam charged particle microscopes require time-consuming image post-processing. For example, signals generated by the detection system of a multi-beam charged particle microscope need to be digitally corrected before stitching together image patches from multiple image sub-fields.

[0007] The multiple primary charged particle beamlets may deviate from their normal raster positions within a raster configuration (e.g., a hexagonal raster configuration). Also, the multiple primary charged particle beamlets may deviate from their normal raster positions for a raster scan motion within a planar area segment, and the resolution of the multi-beam charged particle inspection system may vary for and depend on the individual scan positions of the individual beamlets of the multiple primary charged particle beamlets. Scan-induced distortionThis difference has not been addressed previously. For multiple primary charged particle beamlets, each beamlet enters the intersection volume of the common scanning deflector at a different angle, is deflected to a different exit angle, and traverses the intersection volume of the common scanning deflector by a different path. Therefore, each beamlet experiences a different distortion pattern in the scanning motion. Prior art single-beam dynamic correctors can correct any of the multiple primary beamlets. Scan-induced distortion U.S. Patent Application Publication No. 2009 / 0001267 describes the calibration of the primary beam layout or static raster pattern configuration of a multi-beam charged particle system including five primary charged particle beamlets. Three causes of raster pattern anomalies are identified: rotation of the primary beam layout, scaling up or down of the primary beam layout, and shifting of the entire primary beam layout. Therefore, U.S. Patent Application Publication No. 2009 / 0001267 considers basic first-order distortions (rotation, magnification, global shift, or displacement) of the static primary beam raster pattern formed by the static focal points of multiple primary beamlets. U.S. Patent Application Publication No. 2009 / 0001267 also includes calibration of the first-order characteristics of the collective raster scanner (deflection width and deflection direction for collective raster scanning of multiple primary beamlets). While U.S. Patent Application Publication No. 2009 / 0001267 discusses means for compensating for these basic errors in the primary beam layout, it does not provide a solution for higher-order distortions (e.g., third-order distortions) of the static raster pattern. Even after calibration of the primary beam layout and, optionally, the secondary electron beam path, during the scan of each individual primary beamlet Scanning Distortion is introduced, which cannot be addressed by calibration of a static raster pattern of multiple primary beamlets.

[0008] US Patent Application Publication No. 2019 / 0088440 proposes a multi-aperture plate of a multi-beam generating unit including a plurality of apertures with a plurality of electrodes for controlling the spot size and shape of the focus of a plurality of primary beamlets. Scanning Distortion No dynamic means of controlling aberrations is provided.

[0009] Dynamic correctors for single-beam scanning systems are well known in the art. For example, methods are well known that can dynamically compensate for the field curvature or field-dependent astigmatism of a single scanning electron beam during scanning of a single charged particle beam. Scan-induced third-order distortions of a single beam can be compensated for by adding a third-order corrective field term to the linear scanning power of the scanning deflector. However, prior art methods correct dynamic aberrations for a single beam traversing the scanning deflector's intersection volume with a single beam path at a single angle of incidence and a single exit angle relative to the optical axis.

[0010] International Patent Application Publication No. WO2007 / 028596 describes multi-aperture plate configurations configured to perform a predetermined deflection of multiple primary charged particle beamlets. These configurations allow for simultaneous deflection of multiple beamlets, for example, enabling fast switching of operation modes. In one particular example, the number of primary beamlets is changed by deflecting multiple beamlets into a beam stop. In one example, the mechanical layout of a pair of consecutive multi-aperture plates and the application of an appropriate voltage difference between the two multi-aperture plates determines the individual deflection angle of each of the multiple primary beamlets. This allows, for example, predetermined decentering characteristics of the multiple beamlets to be achieved. However, International Patent Application Publication No. WO2007 / 028596: Scan-induced distortion WO 2007 / 028596 does not provide a solution for dealing with this. WO 2007 / 028596 refers to so-called blanking aperture arrays. Similar to the mode-switching operation of WO 2007 / 028596, the blanking aperture arrays are configured for fast binary switching of beamlets between on and off states and do not provide any means for highly accurate individual continuous-scan deflection of individual primary beamlets.

[0011] US Patent No. 6,897,458 shows a scanning deflector array for collective scanning deflection of multiple beamlets in a multi-column system. US Patent Application Publication No. 2010 / 0248166 shows a collective scanning deflector for collective scanning deflection of multiple primary beamlets in combination with a static deflector array for adjusting the position of each primary beamlet. The static deflector array serves the purpose of adjusting the static focus in a static raster configuration.

[0012] It is an object of the present invention to provide a multi-beam charged particle inspection system with means for enabling high-throughput, high-precision, and high-resolution image acquisition.It is an object of the present invention to provide a multi-beam charged particle inspection system that provides high-precision image acquisition of planar area segments with deviations from predetermined raster positions within the specification requirements of the measurement task.

[0013] The increasing demand for resolution and throughput is pushing conventional charged particle microscopes to their limits. Even in single-beam corrected charged particle microscopes, residual Scan-induced distortion The resolution and accuracy are reduced by scanning-induced aberrations such as scanning-induced astigmatism or spherical aberration. It is therefore an object of the present invention to provide a charged particle inspection system with means for enabling high-precision and high-resolution image acquisition with high throughput. Another object of the present invention is to provide a method for detecting the deflection of multiple primary beamlets during an image scanning operation by a collective deflection scanner of a multi-beam system. Scan-induced distortion It is another object of the present invention to compensate for distortion error variations in a collective deflection scanner or imaging optics for raster scanning and focusing of multiple primary beamlets on a wafer surface. Summary of the Invention

[0014] Embodiments of the present invention reduce scanning-induced aberrations in charged particle microscopes. The present invention provides improved multi-beam charged particle microscopes, improved methods of operating multi-beam charged particle microscopes, and improved methods of calibrating multi-beam charged particle microscopes. These improvements reduce scanning-induced aberrations induced during collective raster scanning of a plurality of J primary charged particle beamlets across the image field of the multi-beam charged particle microscope. Scan-induced distortion The improved multi-beam charged particle microscope comprises means for compensating for scan-induced aberrations. The means for compensating for scan-induced aberrations comprises at least one electrostatic correction element configured to, in use, affect at least a first primary charged particle beamlet of the plurality of J primary charged particle beamlets, and control means for operating the electrostatic correction element in synchronism with the collective raster scanning deflection of the plurality of J primary charged particle beamlets. The improved method of operation comprises: Scan-induced distortion The collective raster scanning deflector is configured and controlled to raster scan the J primary charged particle beamlets over the entire surface area of ​​an object, such as a wafer, across an image field including the J image sub-fields. Each of the J primary beamlets is raster scanned across a corresponding image sub-field. In each image sub-field having a lateral extension of about 8 μm to 12 μm (e.g., 10 μm), image information regarding the surface area is obtained by exposing a plurality of image pixel locations with a resolution of about 0.5 nm to 3 nm (e.g., 1 nm or 2 nm) by scanning deflection of the primary charged particle beamlets synchronously with the J primary charged particle beamlets. According to the invention, the resolution of each primary charged particle beamlet in the corresponding image sub-field is Scan-induced distortion can be suppressed. Scan-induced distortionmay be different for each primary charged particle beamlet in the corresponding image sub-field. Scan-induced distortion In one example, the improved calibration method reduces the difference between the image subfields by approximately 0.1 nm to 5 nm. Scan-induced distortion is determined, Scan-induced distortion Control parameters suitable for operating the improved multi-beam charged particle microscope with reduced noise are determined. When operating the improved multi-beam charged particle microscope, application of the control parameters reduces the number of J primary charged particle beamlets. Scan-induced distortion This reduces the number of J image subfields. Scan-induced distortion For example, in multiple image subfields Scan-induced distortion The improved calibration method is Scan-induced distortion and derive a control parameter for the control means. Scan-induced distortion The above-mentioned formula may be applied to scanning-induced aberrations such as, but not limited to, variations or differences in scanning-induced astigmatism, variations or differences in scanning-induced focal position changes, and variations or differences in scanning-induced spherical aberration of a plurality of J primary charged particle beamlets.

[0015] A multi-beam charged particle microscope (1) for wafer inspection according to some embodiments of the present invention comprises a charged-particle multi-beamlet generator (300) for generating a plurality of primary charged particle beamlets (3), an object irradiation unit (100) for illuminating an image patch (17.1) on a wafer surface (25) arranged in an object plane (101) with the plurality of J primary charged particle beamlets (3), thereby generating a plurality of J secondary electron beamlets (9) emitted from the wafer surface (25), in use, and a detection unit (200) comprising a projection system (205) and an image sensor (207) for imaging the plurality of J secondary electron beamlets (9) onto the image sensor (207) and for acquiring, in use, a digital image of the image patch (17.1) on the wafer surface (25). The image patch (17.1) is divided into a plurality of J image subfields (31), each subfield corresponding to a primary charged particle beamlet. The multi-beam charged particle microscope (1) further comprises a collective multi-beam raster scanner (110) comprising at least a first set of deflection electrodes and an intersection volume (189) traversed, in use, by the plurality of J primary charged particle beamlets (3), and a control unit (800) configured, in use, to apply at least a first scanning voltage difference VSp(t) to the first set of deflection electrodes for collective raster scanning of the plurality of J primary charged particle beamlets (3) in a first direction or p-direction. The multi-beam charged particle microscope (1) further comprises a collective multi-beam raster scanner (110) comprising at least a first set of deflection electrodes and an intersection volume (189) traversed, in use, by the plurality of J primary charged particle beamlets (3), and a control unit (800) configured, in use, to apply at least a first scanning voltage difference VSp(t) to the first set of deflection electrodes for collective raster scanning of the plurality of J primary charged particle beamlets (3) in a first direction or p-direction. Scan-induced distortionThe system further comprises means for individually compensating for the J primary charged particle beamlets. The plurality of J primary charged particle beamlets includes at least a first primary charged particle beamlet incident on the intersection volume (189) at a first tilt angle β1 and a second primary charged particle beamlet incident on the intersection volume (189) at a second tilt angle β2 different from β1. During image scanning, the first primary beamlet is raster scanned over a first image sub-field by the simultaneous multi-beam raster scanner (110), and the second primary beamlet is synchronously raster scanned over a second image sub-field by the simultaneous multi-beam raster scanner (110). The diameter of each image sub-field is approximately 5 μm to 12 μm (e.g., 8 μm or 10 μm). The residuals of at least the first primary charged particle beamlets are Scan-induced distortion between the first and second image subfields by means of compensating Scan-induced distortion As a result, in use, the focal points of both the first and second primary charged particle beamlets are raster scanned over each predetermined raster coordinate within the first and second subfields of view with a deviation below a predetermined threshold, for example, less than 1 nm, 0.3 nm, or even less than 0.1 nm. Scan-induced distortion The means for compensating for is configured to operate in synchronization with the scanning deflection of the plurality of primary charged particle beamlets by the simultaneous multi-beam raster scanner (110).

[0016] In one example, residual Scan-induced distortion The means for compensating for residuals of a plurality of primary beamlets including the first primary charged particle beamlet and the second primary charged particle beamlet Scan-induced distortion Individual compensation Scan-induced distortion A compensator array is provided.

[0017] In one example, residual Scan-induced distortion The means for compensating for the difference of the first and second primary charged particle beamlets incident on the intersection volume (189) at an inclination angle β2 deviating from β1 is Scan-induced distortionThe present invention provides a collective raster scanner (110) configured to generate a predetermined inhomogeneous scanning deflection field distribution in the intersection volume (189) for the reduction of the deflection field.

[0018] The multi-beam charged particle microscope includes a raster scanner for long-stroke scan deflection of at least one primary charged particle beamlet, which, in use, provides a scan deflection voltage difference VSp(t). The scan deflection voltage difference VSp(t) is a time-varying voltage difference (e.g., a voltage ramp) applied to the raster scanner electrodes for collective scan deflection of the multiple primary charged particle beamlets. The multi-beam charged particle microscope further includes at least a first scan correction element, which, in use, provides a first correction voltage difference VC1(t). The correction voltage difference VC1(t) is generated from the scan deflection voltage difference VSp(t) by a static voltage conversion unit, such that the scan deflection voltage difference VSp(t) is essentially at least one order of magnitude, preferably two or more orders of magnitude, smaller than the correction voltage difference VC1(t). The static voltage conversion unit may include a series or array of programmable resistors controlled by a plurality of control signals. As a result, the correction voltage difference VC1(t) becomes small and proportional to the scan deflection voltage difference VSp(t). This enables high-speed control of multiple scan correction elements in synchronization with the collective raster scanner. Typically, the time frequency of the scan deflection is about 80 MHz to 200 MHz (e.g., 100 MHz). The static voltage conversion unit according to the present invention can provide multiple synchronous correction voltage differences to multiple correction elements at the same time frequency of about 80 MHz to 200 MHz. The static voltage conversion unit according to the present invention reduces the scan deflection voltage difference VSp(t) for the long-stroke scan deflection (e.g., 10 μm) of each of the multiple primary charged particle beamlets to the correction voltage difference VC1(t) for the corrective short-stroke scan deflection (e.g., 5 nm) of each of the multiple primary charged particle beamlets, thereby reducing the individual correction voltages of the primary charged particle beamlets. Scan-induced distortionTherefore, according to the embodiment of the present invention, it is possible to generate a scanning deflection voltage difference VSp(t) of about −100 V to 100 V at a scanning frequency of, for example, about 100 MHz between scanning voltages in the case of long-stroke deflection, and to generate a plurality of correction voltage differences VCi(t) of up to about 100 mV at the same scanning frequency of, for example, 100 MHz in synchronization with the scanning deflection voltage difference VSp(t).

[0019] In one example, the first scanning deflection element is configured to perform a short-stroke deflection of at least the first primary charged particle beamlet in synchronization with the long-stroke deflection. In one example, a plurality of charged particle beamlets are raster scanned by a first long straw cluster scanner over a dimension of an image subfield D of, for example, ±5 μm, and a plurality of short straw cluster scanners constituting a scanning corrector array raster scan each of the plurality of primary beamlets in parallel and synchronized with the long straw cluster scanner. Scan-induced distortion is compensated, but this Scan-induced distortion is at most ±5 nm. Each short-stroke scanning deflection element, which suppresses the scanning-induced aberrations of the individual beamlets, is synchronized with the long-stroke scanning motion to achieve a scanning power that is approximately three orders of magnitude smaller. Each beamlet is focused by the objective lens of the multi-beam charged particle microscope to a predetermined scanning coordinate with an accuracy of more than three orders of magnitude greater than the scanning coordinate. For example, the predetermined maximum scanning coordinate at the maximum image height of a 5.0 μm image subfield is achieved with an accuracy of less than 3 nm, preferably less than 0.3 nm or even less than 0.1 nm.

[0020] The multi-beam charged particle microscope may include another scanning correction element to which another correction voltage difference VCi(t) is applied in use, synchronous and proportional to the scanning deflection voltage difference VSp(t). This suppresses scanning-induced aberrations, such as scanning-induced telecentricity aberrations or scanning-induced astigmatism, during image scanning. A second scanning deflection voltage difference VSq(t) may be applied to the long-stroke cluster scanner for long-stroke scanning deflection in a second direction or q direction perpendicular to the p direction, exceeding the scanning deflection voltage difference VSp(t) for long-stroke scanning deflection of the primary beamlets in the first direction or p direction. Another correction voltage difference VCj(t) is applied to the scanning correction element in use, synchronous and proportional to the second scanning deflection voltage difference VSq(t).

[0021] In a first embodiment, a multi-beam charged particle microscope includes a synchronous multi-beam raster scanner for long-stroke scan deflection of multiple primary charged particle beamlets. A first scan correction element is provided within the synchronous multi-beam raster scanner, and scan-induced aberrations of the synchronous multi-beam raster scanner are minimized by a modified raster scanner design. Typically, scan-induced aberrations increase with increasing propagation angle β of beamlets propagating through an intersection volume of the synchronous multi-beam raster scanner. The modified deflection scanner design generates an inhomogeneous variable electrostatic deflection field, thereby minimizing scan-induced aberrations for beamlets propagating through the intersection volume at angle β, particularly for beamlets propagating through the intersection volume at a large angle β. In one example, the synchronous multi-beam raster scanner includes a set of deflection electrodes and at least a first set of correction electrodes configured to generate a scan deflection field as well as a correction field during use. The inhomogeneous correction field is a scanning correction field generated by a scanning voltage difference applied to a set of correction electrodes in synchronization with a scanning voltage difference applied to a set of deflection electrodes. In one example, the predetermined inhomogeneous electrostatic deflection field minimizes additional scanning-induced aberrations induced in, for example, an objective lens of a multi-beam charged particle microscope. The set of correction electrodes and the scanning voltage difference applied to the set of correction electrodes are configured to generate the predetermined inhomogeneous electrostatic deflection field in synchronization with the scanning voltage difference applied to the set of deflection electrodes, thereby minimizing scanning-induced aberrations of the multi-beam charged particle microscope.

[0022] In a first embodiment, a multi-beam charged particle microscope (1) for wafer inspection comprises a charged particle multi-beamlet generator (300) for generating a plurality of primary charged particle beamlets (3), an object illumination unit (100) for irradiating an image patch (17.1) on a wafer surface (25) arranged in an object plane (101) with the plurality of primary charged particle beamlets (3) to generate a plurality of secondary electron beamlets (9) emitted from the wafer surface (25) in use, and a detection unit (200) comprising a projection system (205) and an image sensor (207) for imaging the plurality of secondary electron beamlets (9) onto the image sensor (207) and for acquiring a digital image of the image patch (17.1) on the wafer surface (25) in use. The multi-beam charged particle microscope (1) further comprises a collective multi-beam raster scanner (110) comprising at least a first set of deflection electrodes and an intersection volume (189) traversed, in use, by a plurality of primary charged particle beamlets (3), and a control unit (800) configured, in use, to apply at least a first scanning voltage difference Vsp(t) to the first set of deflection electrodes for collective raster scanning of the plurality of primary charged particle beamlets (3) in a first direction or p-direction. The collective multi-beam raster scanner (110) is configured to generate a predetermined inhomogeneous scanning deflection electric field distribution in the intersection volume (189) for reducing scan-induced aberrations of the primary charged particle beamlets incident on the intersection volume (189) at an inclination angle β deviating from the optical axis of the multi-beam charged particle microscope (1).

[0023] In one example, a deflection electrode of the first set of deflection electrodes consists of two spatially separated electrodes, and the control unit (800) is configured, in use, to apply first and second scanning voltage differences VSp1(t) and VSp2(t) to the two spatially separated electrodes, the first and second scanning voltage differences VSp1(t) and VSp2(t) being different.

[0024] In one example, the collective multi-beam raster scanner (110) of the multi-beam charged particle microscope (1) comprises a second set of deflection electrodes for generating, in use, a second predetermined inhomogeneous scanning deflection electric field distribution across the multiple primary charged particle beamlets (3) in the intersection volume (189) for scanning deflection of the multiple primary charged particle beamlets (3) in a second direction or q direction perpendicular to the first direction, and the control unit (800) is configured, in use, to apply at least a second scanning voltage difference VSq(t) to the second set of deflection electrodes.

[0025] In one example, the shape and configuration of at least the first or second set of deflection electrodes of the simultaneous multi-beam raster scanner (110) are adapted to the cross section of the intersection volume (189) of the multiple primary charged particle beamlets (3). In one example, the cross section of the intersection volume (189) is hexagonal, and the first or second set of deflection electrodes are arranged around an ellipse. In one example, the cross section of the intersection volume (189) is rectangular, and the first or second set of deflection electrodes are arranged around the rectangle. This allows for the generation of a predetermined electric field inhomogeneity in the inhomogeneous electrostatic field distribution.

[0026] In one example, in the average propagation direction of the plurality of primary charged particle beamlets (3), the first set of deflection electrodes and the second set of deflection electrodes have different lengths, which can generate a predetermined electric field inhomogeneity of the inhomogeneous electrostatic field distribution.

[0027] In one example, the collective multi-beam raster scanner (110) further comprises a first set of correction electrodes (185, 193) configured to generate, in use, a predetermined scan-correction electric field that contributes to a predetermined inhomogeneous electrostatic field distribution. In one example, certain electrodes (185.1, 185.2, 185.3, 185.4) of the first set of correction electrodes are positioned outside the intersection volume (189) in a space between certain electrodes of the first set of deflection electrodes and certain electrodes of the second set of deflection electrodes. In one example, the collective multi-beam raster scanner (110) further comprises a second set of correction electrodes (187, 195) configured to generate, in use, a second predetermined scan-correction electric field that contributes to a predetermined inhomogeneous electrostatic field distribution.

[0028] In one example, the collective multi-beam raster scanner (110) is configured to adjust a lateral position of a predetermined inhomogeneous scanning deflection electric field distribution relative to an intersection volume, and the control unit (800) is configured, in use, to apply a voltage offset to at least one of the first set of deflection electrodes or the second set of deflection electrodes, thereby adjusting the position of the predetermined inhomogeneous electrostatic field distribution and minimizing differences in scan-induced aberrations among the plurality of primary charged particle beamlets.

[0029] In one example, the multi-beam charged particle microscope (1) includes a first static deflection system (701) disposed between the charged particle multi-beamlet generator (300) and the collective multi-beam raster scanner (110), configured and set to adjust the lateral positions of the multiple primary charged particle beamlets (3) relative to the intersection volume (189), thereby adjusting the positions of the multiple primary charged particle beamlets relative to a predetermined inhomogeneous electrostatic field distribution and minimizing differences in scan-induced aberrations among the multiple primary charged particle beamlets.

[0030] In one example, the multi-beam charged particle microscope (1) further includes a second static deflection system (701) disposed between the charged particle multi-beamlet generator (300) and the collective multi-beam raster scanner (110) and configured and set to adjust the average incidence angle of the multiple primary charged particle beamlets (3) at the entrance side of the intersection volume (189), where the average incidence angle of the multiple primary charged particle beamlets (3) is the average of the multiple incidence angles of the individual primary beamlets, thereby minimizing scanning-induced aberrations between the multiple primary charged particle beamlets.

[0031] In a second embodiment, the object projection unit of the multi-beam charged particle microscope comprises a plurality of beam splitters for individually compensating for scan-induced aberrations of each primary beamlet during raster or image scanning. Scanning Distortion The apparatus includes a first multi-beam scanning corrector or multi-beam scanning correction system, such as a scanning distortion compensator array. The first multi-beam scanning correction system controls the positions of individual beamlets on the surface of the sample during simultaneous raster scanning by the long-stroke simultaneous multi-beam raster scanner. The simultaneous multi-beam raster scanner simultaneously deflects multiple primary charged particle beamlets across each image sub-field on the surface of the substrate, the image sub-field having an extension of approximately D=8 μm or 12 μm. The simultaneous multi-beam scanning deflector may be the optimized multi-beam scanning deflector according to the first embodiment. The first multi-beam scanning correction system is configured as an array element having multiple apertures with multiple deflection elements, and each of the multiple primary beamlets can be individually scan-deflected by a different amount of scan deflection in synchronization with the simultaneous raster scanning of the multiple primary beamlets by the simultaneous multi-beam raster scanner. Scanning Distortion Multi-beam scanning correction systems such as compensator arrays have residuals of approximately r = 1 nm to 5 nm. Scanning Distortion is dynamically corrected individually for each beamlet to a value of less than 0.3 nm, preferably less than 0.2 nm or less than 0.1 nm.

[0032] According to a second embodiment of the present invention, a multi-beam charged particle microscope (1) for wafer inspection comprises a charged particle multi-beamlet generator (300) for generating a plurality of primary charged particle beamlets (3), an object illumination unit (100) for illuminating an image patch (17.1) on a wafer surface (25) arranged in an object plane (101) with the plurality of primary charged particle beamlets (3) to generate a plurality of secondary electron beamlets (9) that, in use, are emitted from the wafer surface (25), a detection unit (200) comprising a projection system (205) and an image sensor (207) for imaging the plurality of secondary electron beamlets (9) onto the image sensor (207) and for, in use, acquiring a digital image of the image patch (17.1) on the wafer surface (25), and a simultaneous multi-beam raster scanner (110). The multi-beam charged particle microscope (1) is arranged in a propagation direction of the plurality of primary charged particles upstream of the simultaneous multi-beam raster scanner (110), and includes a plurality of apertures each configured to transmit a corresponding one of the plurality of primary charged particle beamlets when in use. Scanning Distortion a compensator array (601), wherein each of a plurality of apertures comprises a first deflection element for individually deflecting each corresponding primary charged particle beamlet in a first direction or p-direction, and a second deflection element for individually deflecting each corresponding primary charged particle beamlet in a second direction or q-direction perpendicular to the first direction, each of the plurality of deflection elements being disposed around each of the plurality of apertures; Scanning DistortionThe multi-beam scanning correction system further comprises a compensator array (601) and a control unit (800) configured, in use, to provide at least a first scanning voltage difference Vsp(t) to the collective multi-beam raster scanner (110) for scan deflection of the plurality of primary charged particle beamlets (3) in a first or p-direction. The scan deflection compensator array (601) further comprises a scanning array control unit (622) comprising a first static voltage conversion unit or array (611) configured to provide a plurality of first correction voltage differences to a plurality of first deflection elements, and a second static voltage conversion array (612) configured to provide a plurality of second correction voltage differences to a plurality of second deflection elements, to compensate for scan-induced aberrations during scan deflection of the plurality of primary charged particle beamlets (3) in the first direction. The first static voltage conversion array (611) and the second static voltage conversion array (612) are coupled to the control unit (800) and configured to apply at least a plurality of first voltage difference components to a plurality of first and second deflection elements, respectively, in synchronization with the first scanning voltage difference VSp(t).

[0033] In one example, the control unit (800) is configured, in use, to provide a second scan voltage difference Vsq(t) to the collective multi-beam raster scanner (110) for scan deflection of a plurality of primary charged particle beamlets (3) in a second direction, or q direction, perpendicular to the first direction. The first static voltage conversion array (611) and the second static voltage conversion array (612) are coupled to the control unit (800) and configured to provide at least a plurality of second voltage difference components to a plurality of first and second deflection elements, respectively, in synchronization with the second scan voltage difference Vsq(t). In one example, the first static voltage conversion array (611) is coupled to the control unit (800) and configured to provide a first voltage component and a second voltage component to a plurality of first deflection elements, respectively, in synchronization with the first scan voltage difference Vsp(t) and the second scan voltage difference Vsq(t).

[0034] In one example, the first or second static voltage conversion array (611, 612) is configured as a programmable resistor array.

[0035] Thereby, the scanning positions of the multiple focal points of the multiple primary charged particle beamlets on the object surface are adjusted in synchronization with the image scanning, and the scanning positions of the multiple primary charged particle beamlets are adjusted in synchronization with the image scanning. Scan-induced distortion The difference is minimized.

[0036] In a third embodiment, the object illumination unit includes a second multi-beam scanning correction system (e.g., a scanning compensator array (602)) for compensation of scan-induced decentering aberrations, the second multi-beam scanning correction system being arranged between the first multi-beam scanning correction system and the collective multi-beam raster scanner for individual control of the angles of incidence of individual beamlets at the surface of the sample. The second scanning compensator array (602) for compensation of scan-induced decentering aberrations is arranged near an intermediate image plane (321) of the multi-beam charged particle microscope (1) and includes a plurality of deflection elements arranged at a plurality of apertures to compensate for scan-induced decentering aberrations during image scanning of each primary charged particle beamlet (3), and a second scanning array control unit (622.2) including a second static voltage conversion array and configured to apply a plurality of second correction voltage differences to each of the plurality of deflection elements. Thereby, each of the multiple primary beamlets can be individually deflected by a different amount of deflection in synchronization with the collective deflection scanning of the multiple primary beamlets by the collective multi-beam deflection scanner, whereby the incidence angles of the multiple primary charged particle beamlets on the object surface are adjusted in synchronization with the image scanning, and the scan-induced decentering error of each of the multiple primary charged particle beamlets is minimized.

[0037] In one example, the multi-beam charged particle microscope (1) further comprises a multi-beam scanning correction system configured as a scanning astigmatism corrector array or a scanning lens array for compensating for scanning-induced aberrations, such as scanning-induced astigmatism or focus plane deviation, of each of the multiple primary beamlets (3) during raster scanning of the multiple primary charged particle beamlets (3), thereby adjusting imaging aberrations, such as astigmatism, of each of the multiple primary charged particle beamlets on the object surface in synchronization with the image scanning, thereby minimizing the scanning-induced imaging aberrations of each of the multiple primary charged particle beamlets.

[0038] In a fourth embodiment, a method for operating a multi-beam charged particle microscope is provided, the method including the step of calibrating the charged particle microscope by measuring scan-induced aberrations. In another step, a static control parameter or signal is derived to generate a reduction factor for generating a drive voltage difference V C(t) of a correction electrode or a first or second scan correction system. The static control parameter and the reduced drive voltage difference are then applied to the first or second scan correction system. During image scanning, the reduction factor reduces the scan deflection voltage difference V C(t) to at least one drive or correction voltage difference V C(t) and applies it to the correction electrode, thereby reducing scan-induced aberrations during operation of the charged particle microscope.

[0039] In a fifth embodiment, a multi-beam charged particle microscope (1) for wafer inspection comprises: a charged particle multi-beamlet generator (300) for generating a plurality of primary charged particle beamlets (3); an object illumination unit (100) for irradiating an image patch (17.1) on a wafer surface (25) arranged in an object plane (101) with the plurality of primary charged particle beamlets (3) to generate a plurality of secondary electron beamlets (9) emitted from the wafer surface (25) in use; a detection unit (200) comprising a projection system (205) and an image sensor (207) for imaging the plurality of secondary electron beamlets (9) onto the image sensor (207) and for acquiring a digital image of the image patch (17.1) on the wafer surface (25) in use; and a collective multi-beam raster scanner (110) comprising at least a first set of deflection electrodes and an intersection volume (189) traversed by the plurality of primary charged particle beamlets (3). The multi-beam charged particle microscope (1) further comprises a first static deflection system (701) disposed between the charged particle multi-beamlet generator (300) and the collective multi-beam raster scanner (110) and configured to adjust the lateral positions of the multiple primary charged particle beamlets (3) relative to the intersection volume (189). The control unit (800) is configured to apply at least a first scanning voltage difference VSp(t) to the collective multi-beam raster scanner (110) in use for scanning deflection of the multiple primary charged particle beamlets (3) in a first direction or p-direction. The collective multi-beam raster scanner of the multi-beam charged particle microscope defines an intersection volume through which the multiple primary charged particle beamlets propagate in use. According to a first embodiment, the collective multi-beam raster scanner is configured to generate an inhomogeneous scanning deflection electrostatic field in the intersection volume. Residual scanning-induced aberrations depend on the lateral transverse positions and incidence angles of the multiple primary beamlets in the intersection volume of the collective multi-beam deflection scanner. In a fifth embodiment, the multi-beam charged particle microscope comprises a first static deflector upstream of the collective multi-beam deflection scanner.The first static deflector adjusts the lateral transverse positions or incidence angles of the multiple primary charged particle beamlets at the intersection volume. In one example, the object illumination unit of the multi-beam charged particle microscope includes a second static deflector between the first static deflector and the collective multi-beam raster scanner for adjusting the lateral transverse positions and incidence angles of the multiple primary beamlets. In the operating method, the first static deflector adjusts the transverse positions at the intersection volume to a predetermined position, and the second static deflector adjusts the average incidence angle of the multiple primary beamlets on the intersection volume.

[0040] In one example, the multi-beam charged particle microscope (1) includes a second static deflection system (703) between the charged particle multi-beamlet generator (300) and the collective multi-beam raster scanner (110) that is configured and set to adjust the average incidence angle of the multiple primary charged particle beamlets (3) at the entrance side of the intersection volume (189).

[0041] This suppresses scanning-induced imaging aberrations, such as distortion or astigmatism, of each of the multiple primary charged particle beamlets on the object surface in synchronization with the image scanning, thereby minimizing scanning-induced imaging aberrations of each of the multiple primary charged particle beamlets.

[0042] In a sixth embodiment, an improved multi-beam charged particle microscope is provided that includes a long straw cluster scanner capable of lateral displacement or tilt. In one example, the lateral displacement or tilt is achieved by laterally displacing or tilting the deflection electrostatic field with respect to the intersection volume using additional correction electrodes, or by applying multiple predetermined voltage offsets to the deflection electrodes and correction electrodes of the first embodiment of the invention. In an alternative example, the long straw cluster scanner includes mechanical means, including guide elements or stages, for displacing the deflection electrostatic field with respect to the intersection volume, and at least one actuator for adjusting the lateral position or tilt angle of the deflection electrodes and optional correction electrodes.

[0043] This suppresses scanning-induced imaging aberrations, such as distortion or astigmatism, of each of the multiple primary charged particle beamlets on the object surface in synchronization with the image scanning, thereby minimizing scanning-induced imaging aberrations of each of the multiple primary charged particle beamlets.

[0044] In a seventh embodiment, an improved multi-beam charged particle microscope is provided that includes a combination of the fifth and sixth embodiments.

[0045] In one example, a method for operating a multi-beam charged particle microscope is provided. In a first step 1, the system is calibrated and actual control parameters are stored in a memory. In a second step 2, beam positions of multiple primary beamlets in an intersection volume of a simultaneous multi-beam raster scanner are adjusted. In an example according to a fifth embodiment, the adjustment is achieved by first and optional second static deflectors. In an example according to a sixth embodiment, a lateral displacement of an inhomogeneous deflection field is obtained by an offset signal applied to the simultaneous multi-beam deflection scanner. In a third step, a control signal is applied. In one example, a correction field is generated from the control signal using the actual control parameters stored in step 1, and a scanning correction field is generated by a correction electrode applied with a correction voltage difference synchronized with the scanning voltage difference. In one example, multiple correction voltage differences are generated from the static control signal, and each beamlet is individually deflected by a multi-beam scanning correction system. This suppresses scanning-induced imaging aberrations, such as distortion or astigmatism, of each of the multiple primary charged particle beamlets on the object surface in synchronization with the image scanning, thereby minimizing scanning-induced imaging aberrations of each of the multiple primary charged particle beamlets.

[0046] In the eighth embodiment, at least two of the measures of the first to seventh embodiments described above are combined to achieve further reduction in scanning-induced aberrations.

[0047] In a ninth embodiment of the present invention, there is provided a multi-beam charged particle microscope for wafer inspection, comprising: a beamlet generator for generating at least first primary charged particle beamlets; an object illumination unit for illuminating an image sub-field of a surface of a sample arranged in an object plane with the first primary charged particle beamlets; and a collective raster scanner. The multi-beam charged particle microscope further comprises a control unit configured to, in use, apply at least a first scan voltage difference Vsp(t) to the collective raster scanner for a scan deflection of the at least one first primary charged particle beamlet in a first or p direction across the image sub-field, the image sub-field having a lateral extension of at least 5 μm, preferably 8 μm or more; and at least a first scan corrector configured, in use, to generate a first scan correction field for influencing the first primary charged particle beamlets. The control unit is configured to provide a first scan voltage difference VSp(t) to the first scan corrector, where the first scan corrector is configured to suppress scan-induced aberrations of the first primary charged particle beamlets in synchronization with the collective scan deflection of the multiple primary charged particle beamlets. The first scan corrector comprises a static voltage conversion unit for converting the first scan voltage difference VSp(t) into at least a first scan correction voltage difference VCp(t), the static voltage conversion unit being configured to generate a first scan correction field in synchronization with the first scan voltage difference VSp(t). The static voltage conversion unit may comprise at least one programmable resistor array configured to be programmed by the multiple static control signals to generate the first scan correction voltage difference VCp(t) proportional to the first scan voltage difference VSp(t). The control unit may comprise a first delay line configured to synchronize the first scan correction field with the collective raster scanning of the multiple primary charged particle beamlets by the collective raster scanner. The first scan corrector, when in use, corrects at least about 0.5 nm to 5 nm of the first primary charged particle beamlet. Scan-induced distortionto a small amount of less than 0.3 nm, preferably less than 0.2 nm or less than 0.1 nm. Similarly, other scanning-induced aberrations of the multi-beam charged particle microscope (e.g., scanning-induced astigmatism) can also be reduced, but this typically increases with increasing image height of the image subfield of the first primary charged particle beamlet. In one example, the scanning-induced aberrations are Scan-induced distortion and the first deflection element, when in use, deflects the first primary charged particle beamlet in the first direction in synchronization with the scanning deflection of the plurality of primary charged particle beamlets by the collective raster scanner in the first direction. Scan-induced distortion The second deflection element is configured to individually compensate for the first primary charged particle beamlet in a second direction perpendicular to the first direction in synchronization with the scanning deflection of the plurality of primary charged particle beamlets by the collective raster scanner in the first direction. Scan-induced distortion In general, scanning-induced aberrations can be calculated as follows: Scan-induced distortion , scanning-induced astigmatism, scanning-induced decentering aberration, scanning-induced spherical aberration, or scanning-induced coma. In one example, the multi-beam charged particle microscope comprises a static correction system for correcting dispersion, field curvature, or static spherical aberration. In one example, the multi-beam charged particle microscope further comprises a second scan corrector configured to suppress a second scan-induced aberration upon raster scanning of the first primary charged particle beamlets by the collective raster scanner, the second scan-induced aberration being, for example, scanning-induced astigmatism, scanning-induced decentering aberration, scanning-induced spherical aberration, or scanning-induced coma.

[0048] In a fourth embodiment of the present invention, a charged particle multi-beamlet generator (300), an object irradiation unit (100), a detection unit (200), a simultaneous multi-beam raster scanner (110) for simultaneously raster scanning a plurality of primary charged particle beamlets (3), and a detection unit (200) disposed upstream of the simultaneous multi-beam raster scanner (110) in the propagation direction of the plurality of primary charged particle beamlets. Scanning DistortionA method for operating a multi-beam charged particle microscope (1) comprising a compensator array (601) and a control unit (800) is provided, the method comprising: providing at least a first scan voltage difference VSp(t) to a scan array control unit (622); generating a plurality of voltage difference components from at least a first voltage difference VSp(t) and a plurality of static control signals; Multiple voltage difference components Scanning Distortion By providing the plurality of deflection elements of the compensator array (601), each beamlet of the plurality of primary charged particle beamlets is individually scanned and deflected, thereby achieving a raster scan of the plurality of primary charged particle beamlets (3). Scan-induced distortion and compensating for Includes:

[0049] In one example, a method of operating a multi-beam charged particle microscope (1) includes: by raster scanning a plurality of primary charged particles across an image patch of a reference object; Scan-induced distortion determining a For each primary charged particle beamlet, Scan-induced distortion extracting a plurality of amplitudes of at least the linear portion of deriving a plurality of static control signals from each of the plurality of amplitudes; Multiple static control signals Scanning Distortion providing the scan array control unit (622) of the compensator array (601); Further includes:

[0050] According to an embodiment of the present invention, scanning-induced aberrations of individual primary beamlets are compensated in parallel and synchronously with the collective raster scanning of multiple primary beamlets. The scanning-induced aberrations of individual primary beamlets are compensated by a scan corrector (including a first scan corrector) that generates multiple individual voltage differences. The multiple individual voltage differences are generated from voltage differences VSp(t) generated for long straw cluster scanning in a first scan direction by the raster scanner. Therefore, according to one embodiment, a multi-beam charged particle microscope for wafer inspection includes a generator for generating multiple primary beamlets including at least a first individual beamlet; an object illumination unit for illuminating an image patch on a surface of a sample arranged in an object plane with the multiple primary beamlets to generate multiple secondary electron beamlets emitted from the surface in use; and a detection unit including a projection system and an image sensor, for imaging the multiple secondary electron beamlets onto the image sensor and for acquiring a digital image of the image patch on the surface of the sample in use. A multi-beam microscope for wafer inspection according to an embodiment further comprises a collective multi-beam raster scanner comprising at least a first set of deflection electrodes and an intersection volume traversed by a plurality of primary beamlets, at least a first scan corrector configured, in use, to generate a first scanning electrostatic field for influencing at least a first individual primary beamlet, and a control unit configured, in use, to provide at least a first scan voltage difference Vsp(t) to the first set of deflection electrodes for collective raster scanning of the plurality of primary beamlets in a first direction or p-direction, The control unit is further configured to provide the first scan voltage difference Vsp(t) to the first scan corrector, the first scan corrector being configured to counter scan-induced aberrations of at least the first individual beamlet. In one example, the first scan corrector of the multi-beam charged particle microscope comprises a first static voltage conversion unit for converting the first scan voltage difference VSp(t) into at least a first scan correction voltage difference VCp(t), the first static voltage conversion unit being configured to generate a first scan correction electric field in synchronization with the first scan voltage difference VSp(t).In one example, the first static voltage conversion unit is configured to generate a first scan correction voltage difference VCp(t) proportional to the first scan voltage difference VSp(t). In one example, the static voltage conversion unit comprises at least one programmable resistor array configured to be programmed by a plurality of static control signals. In one example, the control unit comprises a first delay line configured to synchronize the first scan correction field with the collective raster scanning of the plurality of primary beamlets by the collective multi-beam raster scanner.

[0051] In one example, the first scan corrector of the multi-beam charged particle microscope, when in use, for each of a plurality of primary beamlets: Scan-induced distortion For example, the plurality of deflection elements are configured to, in use, compensate for the deflection of a first individual primary beamlet in the first direction in synchronization with the scanning deflection of the plurality of primary beamlets by the collective multi-beam raster scanner in the first direction. Scan-induced distortion and a first deflection element configured to individually compensate for the first individual beamlets in a second direction perpendicular to the first direction in synchronization with the scanning deflection of the plurality of primary beamlets by the collective multi-beam raster scanner in the first direction, when in use. Scan-induced distortion and a second deflection element configured to individually compensate for the deflection of the second individual primary beamlets in the first direction in synchronization with the scanning deflection of the plurality of primary beamlets by the collective multi-beam raster scanner in the first direction, when in use. Scan-induced distortion The plurality of deflection elements, when in use, further includes a third deflection element configured to individually compensate for the respective deflection of the individual primary beamlets in the first direction. Scan-induced distortion and other deflection elements configured to individually compensate for the deflection of individual primary beamlets in a second direction in synchronization with the scanning deflection of the plurality of primary beamlets by the collective multi-beam raster scanner in a first direction, when used. Scan-induced distortionand other deflection elements configured to individually compensate for the first scanning voltage difference VSp(t). In one example, the static voltage conversion unit comprises a plurality of programmable resistor strings each electrically connected to a deflection element of the plurality of deflection elements, the plurality of programmable resistor strings being controlled by a plurality of static control signals to form a programmable resistor array configured, in use, to generate a plurality of scanning correction voltage differences VCAp(i,t) respectively in synchronization with the first scanning voltage difference VSp(t).

[0052] In one example, the first scan corrector comprises at least one correction electrode configured, in use, to contribute to an inhomogeneous electrostatic field distribution generated in the intersection volume of the collective multi-beam deflection system for reducing scan-induced aberrations of individual primary beamlets entering the intersection volume at an inclination angle β deviating from the optical axis of the multi-beam charged particle microscope.

[0053] According to one embodiment, a method for operating a multi-beam charged particle microscope includes generating a scan voltage difference Vsp(t) and applying the scan voltage difference Vsp(t) to a multi-beam raster scanner to deflect and scan a plurality of primary beamlets collectively in a first direction using the multi-beam raster scanner. The method further includes generating at least a first scan correction voltage difference Vcp(t) from the scan voltage difference Vsp(t) in synchronization with the scan voltage difference Vsp(t), and applying the first scan correction voltage difference Vcp(t) to deflection elements of a scan corrector to suppress scan-induced aberrations of at least one individual primary beamlet. To generate the first scan correction voltage difference Vcp(t), the method includes applying a plurality of static control signals to the scan corrector to generate the first scan correction voltage difference Vcp(t). For synchronizing the scanning deflection of the at least one primary beamlet and reducing the scanning-induced aberration of the at least one individual beamlet, the method further includes a step of generating a predetermined time delay between the first scanning correction voltage difference VCp(t) and the scanning voltage difference VSp(t).

[0054] The multi-beam charged particle microscope according to the first to ninth embodiments includes a static voltage conversion array configured to provide at least one scan correction voltage difference to at least one scan corrector or compensation element depending on a scan position (p, q) in an image field during an image or raster scan. The static voltage conversion array is configured to maintain the dependence of scan-induced aberrations on the scan position (p, q) in the image field during image scanning by providing the scan correction voltage difference from at least one common long-stroke scan voltage difference. In one example, the static voltage conversion array is programmable with a plurality of static control signals. The multi-beam charged particle microscope further includes a control unit configured to provide the plurality of static control signals to the static voltage conversion array. In one example, the control unit is configured to generate the plurality of static control signals through calibration measurements. In one example, the control unit is configured to generate the plurality of static control signals through monitoring a status of the charged particle microscope.

[0055] The control unit, in use, is configured to provide at least a first scan voltage difference VSp(t) to the first set of deflection electrodes for long-stroke scan deflection of single or multiple primary beamlets in a first or p-direction. The control unit is further configured to provide the first scan voltage difference VSp(t) to a first scan corrector, the first scan corrector configured to suppress scan-induced aberrations of at least the first individual primary beamlet. In one example, the first scan corrector of the multi-beam charged particle microscope comprises a first static voltage conversion unit for converting the first scan voltage difference VSp(t) into at least a first scan correction voltage difference VCp(t), the first static voltage conversion unit configured to generate a first scan electrostatic field in synchronization with the first scan voltage difference VSp(t). The first static voltage conversion unit is configured to generate the first scan correction voltage difference VCp(t) proportional to the first scan voltage difference VSp(t).

[0056] An example static voltage translation array is implemented as a programmable resistor array configured to be programmed by a plurality of static control signals. Scanning Distortion The dynamic signals required for compensation are limited to only two scan control voltage differences VCp(t) and VCq(t) obtained from the scan voltage differences VSp(t) and VSq(t) generated by the scan control unit for driving the collective multi-beam raster scanner. These two control voltage differences VCp(t) and VCq(t) allow, for example, Scan-induced distortion Compensation or correction of scan-induced aberrations is achieved for scan-induced decentering aberrations or scan-induced astigmatism. In one example, the control unit includes a first delay line configured to synchronize the first scan correction field with the simultaneous raster scanning of the multiple primary beamlets by the simultaneous multi-beam raster scanner. The compensation or correction is directly dependent on the scan voltage differences VSp(t) and VSq(t) due to the direct coupling via the delay line. Thus, the compensation or correction of scan-induced aberrations is synchronized with the scanning operation and proportional to the scan coordinates (p, q) of each image subfield. In one example, the linear portion of the scan-induced aberrations, which constitutes the majority of the scan-induced aberrations, is compensated for by making the control voltage differences VCp(t) and VCq(t) proportional to the scan voltage differences VSp(t) and VSq(t). For each of the multiple image subfields and corresponding beamlets, the amplitude of the linear portion of the scan-induced aberrations is different, and the required control signals are derived from a common control voltage difference VCp(t) and VCq(t), e.g., by a programmable resistor array, where corresponding proportional voltage differences are generated for each electrode from the common control voltage difference VCp(t) and VCq(t), e.g., Scanning DistortionThe individual voltage differences applied to the electrodes of the compensator array or the correction electrodes of the collective multi-beam raster scanner are directly coupled to the common control voltage differences VCp(t) and VCq(t) via the programmable resistor strings of the programmable resistor array. For example, the individual voltage differences applied to the electrodes for compensating for the scanning-induced aberrations of the individual beamlets are controlled by a plurality of predetermined static control signals to which each programmable resistor string is programmed. This makes the individual voltage differences proportional to the scanning voltage differences VSp(t) and VSq(t) and thus also to the scanning coordinates (p, q) of each image subfield. For example, the control voltage difference array includes at least one static voltage conversion array and conductive connection lines leading to the individual deflection electrodes. Scanning Distortion By proper engineering of the compensator array, propagation effects (i.e., time delays of different deflectors) are suppressed, enabling highly dynamic compensation of scan-induced aberrations in a dynamic range of 50 MHz or more (e.g., about 80 MHz or 100 MHz). Here, static delay lines are implemented to synchronize the scan-deflection of multiple primary charged particle beamlets by the simultaneous multi-beam deflection system with the compensation of scan-induced aberrations. Furthermore, the conductive connections for applying highly dynamic correction voltage differences to the electrodes can be configured as high-frequency connections and can be shielded, for example, by ground lines, to avoid crosstalk or radiation losses.

[0057] In one example, a scanning corrector for a multi-beam charged particle microscope, when in use, for each of a plurality of primary beamlets: Scan-induced distortion For example, the plurality of deflection elements are configured to compensate for the deflection of the first individual beamlets in the first direction in synchronization with the scanning deflection of the plurality of primary beamlets by the collective multi-beam raster scanner in the first direction. Scan-induced distortion and a first deflection element configured to individually compensate for the first individual beamlets in a second direction perpendicular to the first direction in synchronization with the scanning deflection of the plurality of primary beamlets by the collective multi-beam raster scanner in the first direction, when in use. Scan-induced distortionand a second deflection element configured to individually compensate for the deflection of the second individual beamlets in the first direction in synchronization with the scanning deflection of the plurality of primary beamlets by the collective multi-beam raster scanner in the first direction, when in use. Scan-induced distortion In one example, the static voltage conversion unit comprises a plurality of programmable resistor strings each connected to a deflection element of the plurality of deflection elements, the plurality of programmable resistor strings being controlled by a plurality of static control signals to form a programmable resistor array configured, in use, to generate a plurality of scan correction voltage differences VCAp(i,t) respectively in synchronization with the first scan voltage difference VSp(t).

[0058] In one example, the first scan corrector comprises at least one correction electrode configured, in use, to contribute to an inhomogeneous electrostatic field distribution generated in the intersection volume of the collective multi-beam deflection system for the reduction of scan-induced aberrations of individual primary beamlets propagating in at least one segment of the intersection volume at an angle deviating from the optical axis of the multi-beam particle microscope.

[0059] According to one embodiment, a method for operating a multi-beam charged particle microscope includes generating a scan voltage difference Vsp(t) and applying the scan voltage difference Vsp(t) to a multi-beam raster scanner to deflectively scan a plurality of primary beamlets in a first direction. The method further includes generating at least a first scan correction voltage difference Vcp(t) from the scan voltage difference Vsp(t) in synchronization with the scan voltage difference Vsp(t), and applying the first scan correction voltage difference Vcp(t) to deflection elements of a scan corrector to reduce scan-induced aberrations of at least one individual beamlet among the plurality of primary beamlets. To generate the first scan correction voltage difference Vcp(t), the method includes applying a plurality of static control signals to the scan corrector to generate the first scan correction voltage difference Vcp(t). To synchronize the collective raster scanning of multiple primary beamlets and reduce scan-induced aberrations of at least one individual beamlet, the method further includes a step of generating a predetermined time delay between the first scan correction voltage difference VCp(t) and the scan voltage difference VSp(t).

[0060] In some examples, scanning of the multiple primary charged particle beamlets on the wafer surface is achieved only in a first direction by a first collective multi-beam raster scanner (110), and the wafer is continuously moved in a second direction by a wafer stage. In this example, the scanning voltage difference Vsq(t) in the second direction is a constant voltage difference or zero.

[0061] The simultaneous multi-beam raster scanner for simultaneous deflection scanning of a plurality of primary charged particles according to the first embodiment reduces scan-induced aberrations during use. Furthermore, the scan-induced aberrations are reduced by an optimized design of the simultaneous multi-beam raster scanner for generating a predetermined non-uniform electric field distribution for deflection scanning. Since the propagation angles through the intersection volume of the simultaneous multi-beam raster scanner are different for each beamlet, the residual scan-induced aberrations are also different for each beamlet. In general, even if the nonlinear scan aberrations are minimized for, for example, a band of field points at similar distances to the optical axis, the residual scan-induced aberrations may be minimized for other field points corresponding to other beamlets. Scanning Distortion Therefore, the present invention is important for multi-beam systems involving two or more beams traversing a deflection scanner at different symmetrical positions and for the large field of view of, for example, a multi-beam scanning electron microscope. The angular spread of the beam angle at the scanning deflector corresponds to the field patch size divided by the focal length f of the objective lens. Because f cannot be very large and is limited by the practical limit of the objective lens diameter, the angular spread is much larger in a multi-SEM scanner compared to a single-beam scanner. The field patch size is, for example, 10 times larger than in a typical single-beam SEM. With an overlay or absolute position accuracy of 1 nm, the ratio provided by a simultaneous multi-beam raster scanner is 100,000:1. Therefore, 16-bit resolution is insufficient; at least 32 bits are required, corresponding to a 32-bit DAC conversion for generating the deflection voltage differences VSp(t) and VSq(t).

[0062] Typically, the objective lens includes a thick magnetic lens. The traversal paths of the primary charged particle beamlets are different for every field point and change during scanning. This causes residual aberrations and differences in aberrations between individual beamlets to be introduced by the objective lens during scanning. The modified design of the deflection electrodes allows the deflection of the beamlets in the image subfield during image scanning. Scan-induced distortionFor example, by separating the deflection electrodes into pairs, modifying the azimuthal or longitudinal extension of the deflection electrodes, or optimizing or adapting the deflection electrodes to the raster configuration of the multiple primary charged particle beamlets, the Scan-induced distortion In addition, by adding a correction electrode, Scanning Distortion In a preferred example, the performance of the deflection system is optimized together with the imaging aberrations induced by other optical elements, such as the objective lens (102), so that for each primary charged particle beamlet, Scan-induced distortion The additional degrees of freedom provided by the multiple deflection and correction electrodes allow for compensation of manufacturing tolerances or drifts in the deflection system by adjusting the voltages applied to the deflection and correction electrodes. The modified deflection system according to the first embodiment reduces residual drift by, for example, at least 15%, at least 20%, or even 30%. Scan-induced distortion This can reduce the uncorrected beam width caused by conventional deflection systems. Scanning Distortion (e.g., about 2 nm), compared with, according to the first embodiment, a residual of, for example, less than 1.5 nm. Scanning Distortion Further improvements are possible, but are susceptible to alignment errors, noise, and drift. Additional improvements in imaging performance are described in the second embodiment. This allows: Scanning Distortion is suppressed by at least 80%, with less than 0.3 nm remaining Scan-induced distortion By any of the means of the first to eighth embodiments, the scanning-induced aberrations caused by the simultaneous multi-beam raster scanner and other optical elements such as the objective lens are compensated for, and the scanning-induced aberrations are effectively minimized. By combining the embodiments as described in the eighth embodiment, the residual Scanning Distortion is suppressed by at least 90% (e.g., 95%), e.g., less than 0.2 nm, preferably less than 0.1 nm, or even smaller residues. Scan-induced distortion is realized.

[0063] According to an embodiment of the present invention, scan-induced aberrations of individual primary beamlets are compensated in parallel and synchronously with the collective raster scanning of multiple primary beamlets. The scan-induced aberrations of individual primary beamlets are compensated by a scan corrector (including a first scan corrector) that provides or generates multiple individual voltage differences. The multiple individual voltage differences for correcting or compensating for scan-induced aberrations are generated from voltage differences VSp(t) and VSq(t) that are generated for the collective raster scanning by the collective multi-beam raster scanner. The present invention relates to the compensation of scan-induced aberrations in a multi-beam charged particle microscope, particularly Scan-induced distortion The imaging performance of conventional multi-beam charged particle microscopes is as follows: Scanning Distortion It decreases with [dp,dq]. For example, Scan-induced distortion This causes overlay errors and variations in pixel spacing or pixel size across the digital image of the image patch on the wafer surface. For a system with a large number (J) of beamlets, Scan-induced distortion may become large and reach a value of 2 nm to 5 nm or more. Scanning Distortion In addition, other scanning-induced imaging aberrations, such as scanning astigmatism or scanning defocus, also degrade imaging performance. In one aspect of the present invention, the required scanning correction is achieved by a large data rate reduction corresponding to the scanning-induced aberrations, allowing for high-speed compensation of the scanning aberrations. The correction or compensation of the scanning-induced aberrations is achieved by: expanding the scanning-induced aberrations into a predetermined set of scanning-induced aberration vectors for each image subfield; determining multiple amplitudes of the normalized scanning-induced aberration vectors for each of the multiple image subfields; deriving multiple static correction or compensation control signals from the amplitudes for each image subfield; and obtaining, for each image subfield, control voltage differences for electrostatic compensation or correction elements that are proportional to the common scanning voltage differences VSp(t), VSq(t) in the first and second scanning directions (p, q), where such proportionality is achieved by a static voltage conversion array controlled by the static correction or compensation control signals. For example, a plurality of J line-shaped images in a plurality of J image subfields scanned in parallel by a simultaneous multi-beam raster scanner scanning a plurality of J primary charged particle beamlets. Scanning Distortion is compensated by at least one corrective electrostatic field for each beamlet and is generated by at least one electrostatic compensation or correction element, so that for each of the J beamlets, a correction voltage difference of the at least one electrostatic compensation or correction element is provided by the static voltage conversion array. The static voltage conversion array is implemented, for example, as a programmable resistor array having a plurality of programmable resistor rows, and two highly dynamic drive signals are proportional to the common scanning voltage differences VSp(t) and VSq(t) for parallel scanning of the plurality of J primary charged particle beamlets in first and second directions (p, q) by the simultaneous multi-beam raster scanner.

[0064] Additional details are provided in the example embodiments. Other embodiments include combinations or variations of the above examples and embodiments.

[0065] Further details are disclosed below with reference to the accompanying drawings. [Brief explanation of the drawings]

[0066] [Figure 1] FIG. 1 illustrates a multi-beam charged particle microscope system according to one embodiment. [Figure 2] FIG. 2 shows coordinates of a first test site and a second test site including first and second image patches. [Figure 3] FIG. 1 shows static distortion offsets for multiple primary charged particle beamlets (3). [Figure 4a] FIG. 10 illustrates scan deflection in a scan deflector for axial beamlets. [Figure 4b] FIG. 10 illustrates scan deflection in a scan deflector with scan-induced distortion of off-axis beamlets with propagation angle β. [Figure 5] FIG. 10 illustrates scan-induced decentering aberrations for off-axis beamlets with propagation angle β. [Figure 6]FIG. 1 shows typical scan-induced distortion of a single beamlet when scanning across an image subfield with image subfield coordinates (p,q) for a) scan distortion vectors dp, dq and b) scan distortion amplitude. [Figure 7] FIG. 10 is a diagram showing the maximum scanning distortion vector for each image sub-field, with the image sub-field center coordinates being xij and yij, for multiple primary charged particle beamlets. [Figure 8] 10A-10C show two examples of deflection and correction electrodes of a lumped multi-beam raster scanner for generating an inhomogeneous electrostatic deflection field inside the intersection volume of multiple primary charged particle beamlets. [Figure 9] FIG. 1 shows the voltage difference as a function of the scan angle α for scanning deflection for a) a single deflection electrode and b) a deflection electrode made up of two individual electrodes. [Figure 10] FIG. 10 shows deflection and correction electrodes of a collective multi-beam raster scanner arranged in the propagation direction to generate an inhomogeneous deflection electrostatic field inside the intersection volume of multiple primary charged particle beamlets. [Figure 11] FIG. 10 illustrates deflection electrodes of different lengths for generating a non-homogeneous electrostatic deflection field inside the intersection volume of multiple primary charged particle beamlets. [Figure 12] FIG. 1 illustrates multiple deflection elements arranged at multiple apertures of a multi-beam scanning distortion compensator array or scanning compensator array for decentering aberrations. [Figure 13] FIG. 1 illustrates a scanning array control unit in an example scanning distortion compensator array. [Figure 14] FIG. 1 illustrates a programmable resistor array as an example of a static voltage translation unit. [Figure 15] 10A and 10B are diagrams illustrating an example of a driving signal in an example of a scanning voltage difference. [Figure 16] FIG. 1 illustrates a method of operating a multi-beam charged particle microscope with reduced scanning-induced aberrations. [Figure 17-1]a) and b) show the usual field dependence of four linear distortion vectors SDV(i) on image patch coordinates (x, y) and their respective signatures in image subfields with subfield coordinates (p, q). [Figure 17-2] c) and d) show the usual field dependence of the four linear distortion vectors SDV(i) on the image patch coordinates (x, y) and their respective signatures in the image subfields with subfield coordinates (p, q). [Figure 17-3] e) and f) show the usual field dependence of the four linear distortion vectors SDV(i) on the image patch coordinates (x, y) and their respective signatures in the image subfields with subfield coordinates (p, q). [Figure 17-4] g) and h) show the usual field dependence of the four linear distortion vectors SDV(i) on the image patch coordinates (x, y) and their respective signatures in the image subfields with subfield coordinates (p, q). [Figure 18] FIG. 1 shows a multi-beam charged particle microscope with additional first and second static multi-beam deflection systems for adjustment. [Figure 19] FIG. 1 illustrates the typical field dependence of scan-induced distortion aberrations on image patch coordinates (x,y) for a system with misalignment. [Figure 20] FIG. 13 is a diagram showing a multi-beam charged particle microscope according to an eighth embodiment of the present invention. [Figure 21] FIG. 10 illustrates an example of scanning correction electrodes at an inclination angle relative to the optical axis to generate a non-homogeneous electrostatic deflection field inside the intersection volume of multiple primary charged particle beamlets. DETAILED DESCRIPTION OF THE INVENTION

[0067] In the exemplary embodiments described below, functionally and structurally similar components are denoted by similar or identical reference numerals whenever possible.

[0068] The schematic representation of FIG. 1 illustrates basic features and functionality of a multi-beam charged particle microscope system 1 according to some embodiments of the present invention. Note that the symbols used in the figure are chosen to symbolically represent the respective functions of the illustrated components, rather than to represent the physical configuration of the components. The system as shown is that of a multi-beam scanning electron microscope (MSEM or multi-SEM) that uses multiple primary electron beamlets 3 to generate multiple primary charged particle beam spots 5 on the surface of an object 7, such as a wafer, whose upper surface 25 is located in the object plane 101 of an objective lens 102. For simplicity, only five primary charged particle beamlets 3 and five primary charged particle beam spots 5 are shown. The features and functionality of the multi-beamlet charged particle microscope system 1 can be implemented using other types of primary charged particles, such as electrons or ions (particularly helium ions).

[0069] The microscope system 1 comprises an object illumination unit 100, a detection unit 200, and a beam splitter unit 400 for separating a secondary charged particle beam path 11 from a primary charged particle beam path 13. The object illumination unit 100 comprises a charged particle multi-beam generator 300 for generating a plurality of primary charged particle beamlets 3 and is configured to focus the plurality of primary charged particle beamlets 3 by a sample stage 500 onto an object plane 101 where a surface 25 of a wafer 7 is located.

[0070] The primary beam generator 300 generates a plurality of primary charged particle beamlet spots 311 in an intermediate image plane 321, which is typically a spherically curved surface to compensate for the field curvature of the object-illumination unit 100. The primary beamlet generator 300 comprises a primary charged particle (e.g., electron) source 301. The primary charged particle source 301 emits a diverging primary charged particle beam 309, which is collimated by at least one collimator lens 303 to form a parallel beam. The collimator lens 303 typically consists of one or more electrostatic or magnetic lenses, or a combination of electrostatic and magnetic lenses. The collimated primary charged particle beam enters a primary multi-beam formation unit 305. The multi-beam formation unit 305 essentially comprises a first multi-aperture plate 306.1, which is illuminated by the primary charged particle beam 309. The first multi-aperture plate 306.1 comprises a plurality of apertures in a raster arrangement for generating a plurality of primary charged particle beamlets 3 by transmission of the collimated primary charged particle beam 309. The multi-beamlet forming unit 305 comprises at least other multi-aperture plates 306.2 and 306.3 arranged downstream of the first multi-aperture plate 306.1 with respect to the electron travel direction of the beam 309. For example, the second multi-aperture plate 306.2 preferably has the function of a microlens array and is set to a defined potential so that the focal positions of the plurality of primary beamlets 3 at the intermediate image plane 321 are adjusted. The third multi-aperture active plate arrangement 306.3 (not shown) comprises an individual electrostatic element for each of the plurality of apertures, thereby individually influencing each of the plurality of beamlets. The multi-aperture active plate arrangement 306.3 consists of one or more multi-aperture plates with electrostatic elements such as circular electrodes, multi-pole electrodes or a series of multi-pole electrodes for microlenses constituting a static deflector array, a microlens array or an astigmatism corrector array. The multi-beamlet arrangement unit 305 comprises an adjacent first electrostatic field lens 307 which, together with a second field lens 308 and the second multi-aperture plate 306.2, focuses the multiple primary charged particle beamlets 3 onto or near an intermediate image plane 321.Downstream of the multi-beamlet configuration unit 305 is a second embodiment of the present invention. Scanning Distortion A compensator array 601 is arranged. Scanning Distortion Compensator array 601 is described in more detail below.

[0071] At or near the intermediate image plane 321, a static beam steering multi-aperture plate 390 is arranged, which includes multiple apertures with electrostatic elements (e.g., deflectors) that individually steer each of the multiple charged particle beamlets 3. The apertures of the beam steering multi-aperture plate 390 have a large diameter that allows the passage of the multiple primary charged particle beamlets 3 even when their focal spots are offset from the intermediate image plane or their respective designed lateral positions. Near the intermediate image plane, a scan compensator array 602 for compensating for scan-induced decentering errors according to a third embodiment of the present invention is arranged. The scan compensator array 602 for compensating for scan-induced decentering errors is described in more detail below. In one example, the beam steering multi-aperture plate 390 and the scan compensator array 602 can be configured as a single multi-aperture element.

[0072] The multiple focal points of the primary charged particle beamlets 3 passing through the intermediate image plane 321 are imaged by the field lens group 103 and the objective lens 102 at the object plane 101, where the investigation plane 25 of the object 7 is located. The object illumination system 100 further comprises, close to the first beam crossover 108, a simultaneous multi-beam raster scanner 110 capable of deflecting the multiple charged particle beamlets 3 in a direction perpendicular to the beam propagation direction or the optical axis 105 of the objective lens 102. In the example of Fig. 1, the optical axis 105 is parallel to the z-direction. The simultaneous multi-beam raster scanner 110 according to the first embodiment of the present invention is configured to detect the minimum deflection angle β when multiple primary charged particles pass through the simultaneous multi-beam raster scanner 110 at different propagation angles β. Scan-induced distortionThe simultaneous multi-beam raster scanner 110 according to the first embodiment is optimized for the above. Details of the simultaneous multi-beam raster scanner 110 will be described below. The objective lens 102 and the simultaneous multi-beam raster scanner 110 are centered on the optical axis 105 of the multi-beamlet charged particle microscope system 1, which is perpendicular to the wafer surface 25. The wafer surface 25, which is located on the image plane 101, is raster-scanned by the simultaneous multi-beam raster scanner 110. As a result, the multiple primary charged particle beamlets 3 constituting the multiple beam spots 5 arranged in a raster configuration are synchronously scanned over the wafer surface 101. In one example, the raster configuration of the focal spots 5 of the multiple primary charged particle beamlets 3 is a hexagonal raster of approximately 100 or more primary charged particle beamlets 3. The primary beam spots 5 have a distance of approximately 6 μm to 15 μm and a diameter of less than 5 nm (e.g., 3 nm, 2 nm, or less). In one example, the beam spot size is approximately 2 nm, and the distance between two adjacent beam spots is 8 μm. At each scanning position of each of the multiple primary beam spots 5, multiple secondary electrons are generated, forming multiple secondary electron beamlets 9 in the same raster configuration as the primary beam spots 5. The intensity of the secondary charged particle beamlets generated at each beam spot 5 depends on the intensity of the impinging primary charged particle beamlets 3 illuminating the corresponding spot and the material composition and topography of the object 7 under the beam spot 5. The secondary charged particle beamlets 9 are accelerated by an electrostatic field generated by the sample charging unit 503, collected by the objective lens 102, and guided by the beam splitter 400 to the detection unit 200. The detection unit 200 images the secondary electron beamlets 9 onto an image sensor 207 to form multiple secondary charged particle image spots 15. The detector includes multiple detector pixels or individual detectors. The intensity of each of the multiple secondary charged particle beam spots 15 is detected separately, and the material composition of the wafer surface 25 is detected with high resolution, achieving large image patches with high throughput.For example, a raster of 10×10 beamlets with an 8 μm pitch generates an image patch of approximately 88 μm×88 μm in a single image scan by the simultaneous multi-beam raster scanner 110, with an image resolution of, for example, 2 nm or less. For example, the image patch is sampled at half the beam spot size, resulting in 8000 pixels per image line for each beamlet, and a digital data set representing an image patch generated by 100 beamlets contains 6.4 billion pixels. Image data is collected by control unit 800. Details of image data collection and processing, for example using parallel processing, are described in German Patent Application No. 102019000470.1 and U.S. Patent No. 9,536,702, which are incorporated herein by reference.

[0073] The secondary electron beamlets 9 are scan-deflected as they pass through the first collective multi-beam raster scanner 110 and are guided by the beam splitter unit 400 to follow secondary beam paths 11 of the detection unit 200. The secondary electron beamlets 9 travel in the opposite direction to the primary charged particle beamlets 3, and the beam splitter unit 400 is configured to separate the secondary beam paths 11 from the primary beam path 13, typically by a magnetic field or a combination of a magnetic field and an electrostatic field. Optionally, additional magnetic correction elements 420 are also present in the primary or secondary beam paths. The projection system 205 further comprises at least a second collective raster scanner 222 connected to a projection system control unit 820. The control unit 800 is configured to compensate for residual errors in the positions of the focal points 15 of the secondary electron beamlets 9 so that the positions of the secondary electron focal spots 15 remain constant on the image sensor 207.

[0074] The projection system 205 of the detection unit 200 includes other electrostatic or magnetic lenses 208, 209, 210 and a second crossover 212 of the multiple secondary electron beamlets 9, at which an aperture 214 is arranged. In one example, the aperture 214 further includes a detector (not shown) connected to a projection system control unit 820. The projection system control unit 820 is further connected to at least one electrostatic lens 206 and a third deflection unit 218. The projection system 205 further includes at least a first multi-aperture corrector 220 having an aperture and an electrode that individually influences each of the multiple secondary electron beamlets 9, and optionally another active element 216 (e.g., a multipole element connected to the control unit 800).

[0075] The image sensor 207 is configured with an array of detection areas whose pattern matches the raster arrangement of the secondary electron beamlets 9 focused onto the image sensor 207 by the projection lens 205. This allows individual secondary electron beamlets 9 to be detected independently of the other secondary electron beamlets 9 incident on the image sensor 207. A plurality of electrical signals are generated, converted into digital image data, and processed in the control unit 800. During an image scan, the control unit 800 is configured to trigger the image sensor 207 to detect a plurality of time-resolved intensity signals from the plurality of secondary electron beamlets 9 over a predetermined time interval, and digital images of image patches from all scanning positions of the plurality of primary charged particle beamlets 3 are accumulated and stitched together.

[0076] The image sensor 207 shown in FIG. 1 can be an electron-sensitive detector array, such as a CMOS or CCD sensor. Such an electron-sensitive detector array can include an electron-to-photon conversion unit, such as a scintillator element or an array of scintillator elements. In one example, the image sensor 207 can be configured as an electron-to-photon conversion unit or scintillator plate located at the focal plane of the multiple secondary electron particle image spots 15. In this example, the image sensor 207 can further include relay optics that image and guide photons generated by the electron-to-photon conversion unit at the secondary charged particle image spots 15 onto dedicated photon detection elements, such as multiple photomultiplier tubes or avalanche photodiodes (not shown). Such an image sensor is disclosed in the above-cited U.S. Pat. No. 9,536,702. In one example, the relay optics further includes a beam splitter that splits and guides the light to a first slow photodetector and a second fast photodetector. The second high-speed photodetector is formed by a photodiode array, for example an avalanche photodiode, and is fast enough to resolve the image signals of the multiple secondary electron beamlets 9 according to the scanning speed of the multiple primary charged particle beamlets 3. The first low-speed photodetector is preferably a CMOS or CCD sensor, and provides high-resolution sensor data signals for monitoring the multiple secondary electron beamlets 9 or focal spots 15 and for controlling the operation of the multi-beam charged particle microscope.

[0077] In this example, the primary charged particle source is embodied in the form of an electron source 301 featuring an emitter tip and extraction electrodes. If primary charged particles other than electrons are used, such as helium ions, the configuration of the primary charged particle source 301 can differ from that shown. The primary charged particle source 301, the active multi-aperture active plate configurations 306.1...306.3, and the beam steering multi-aperture plate 390 are controlled by a primary beamlet control module 830, which is connected to the control unit 800.

[0078] Preferably, the stage 500 does not move during acquisition of an image patch by scanning the multiple primary charged particle beamlets 3, but moves after acquisition of an image patch to the next image patch to be acquired. In an alternative embodiment, the stage 500 moves continuously in a second direction while an image is acquired by scanning the multiple primary charged particle beamlets 3 in a first direction by the simultaneous multi-beam raster scanner 110. The stage movement and stage position are monitored and controlled by sensors known in the art, such as a laser interferometer, a grating interferometer, a confocal microlens array, etc.

[0079] The method of wafer inspection by image patch acquisition is explained in more detail in FIG. 2. The wafer is positioned with its wafer surface 25 in the focal plane of the plurality of primary charged particle beamlets 3, with the center 21.1 of the first image patch 17.1. Predetermined positions of the image patches 17.1...k correspond to inspection sites on the wafer for inspection of semiconductor features. The application is not limited to the wafer surface 25, but is also applicable to, for example, lithography masks used in semiconductor processing. The word "wafer" is therefore not limited to semiconductor wafers, but is intended to include general objects used or processed during semiconductor processing.

[0080] The predetermined positions of the first inspection site 33 and the second inspection site 35 are loaded from an inspection file in a standard file format. The predetermined first inspection site 33 is divided into multiple image patches (e.g., first image patch 17.1 and second image patch 17.2), and a first center position 21.1 of the first image patch 17.1 is aligned under the optical axis 105 of the multi-beam charged particle microscope system 1 for the first image acquisition step of the inspection task. The first center 21.1 of the first image patch is selected as the origin of a first local wafer coordinate system for the acquisition of the first image patch 17.1. Methods for aligning a wafer 7 such that the wafer surface 25 is positioned and a local coordinate system of wafer coordinates is generated are well known in the art.

[0081] The multiple primary beamlets 3 are distributed in a regular raster configuration in each image patch 17.1···k, and a digital image of the image patch is generated by scanning with a raster scanning mechanism. In this example, the multiple primary charged particle beamlets 3 are arranged in a rectangular raster configuration, with N primary beam spots 5.11, 5.12 to 5.1N present in a first line as N beam spots, and M lines containing beam spots 5.11 to 5.MN. For simplicity, M = 5 × N = 5 beam spots are shown, but the number of beam spots J = M × N can be larger (e.g., J = 61 beamlets or about 100 beamlets or more), and the multiple beam spots 5.11 to 5.MN can have various raster configurations, such as hexagonal or circular.

[0082] Each primary charged particle beamlet is scanned over the wafer surface 25. As shown, in the example of a primary charged particle beamlet including beam spots 5.11 and 5.MN, scan paths 27.11 and 27.MN are present. Scanning of each of the multiple primary charged particle beamlets is performed, for example, by moving back and forth along scan paths 27.11...27.MN, while each focal point 5.11...5.MN of each primary charged particle beamlet is moved by scanning the simultaneous multi-beam scanning deflection system 110 in the x-direction from the start position of the image subfield line, which is, for example, the leftmost image point of image subfield 31.MN in this example. Then, after each focal point 5.11...5.MN is scanned simultaneously by the simultaneous scanning of the primary charged particle beamlets 3 to the right position, the simultaneous multi-beam raster scanner 110 moves each of the multiple charged particle beamlets in parallel to the line start position of the next line in each subfield 31.11...31.MN. The return movement to the line start position of the subsequent scan line is called a flyback. Because the multiple primary charged particle beamlets 3 follow the scan paths 27.11-27.MN in parallel, multiple scan images of each subfield 31.11-31.MN are acquired in parallel. As described above, during image acquisition, multiple secondary electrons are emitted at the focal points 5.11-5.MN, generating multiple secondary electron beamlets 9. The multiple secondary electron beamlets 9 are collected by the objective lens 102, pass through the first simultaneous multi-beam raster scanner 110, guided to the detection unit 200, and detected by the image sensor 207. The continuous stream of data for each of the multiple secondary electron beamlets 9 is converted into multiple two-dimensional data sets in synchronization with the scan paths 27.11-27.MN, constituting digital image data for each image subfield. Finally, the multiple digital images of the multiple image subfields are stitched together by the image stitching unit to form a digital image of the first image patch 17.1. Each image subfield has a small overlap area with the adjacent image subfield, as shown by the overlap area 39 of subfield 31.mn and subfield 31.m(n+1).

[0083] Next, the requirements or specifications of the wafer inspection task are described. For high-throughput wafer inspection, the image acquisition time for each image patch 17.1···k must be fast, including the time required for image post-processing. Meanwhile, strict specifications for image quality, such as image resolution, image accuracy, and repeatability, must be maintained. For example, the image resolution requirement is typically 2 nm or less with high repeatability. Image accuracy is also referred to as image fidelity. For example, the edge position of a feature, typically the absolute position accuracy of a feature, is determined with high absolute accuracy. Typically, the position accuracy requirement is approximately 50% or less of the resolution requirement. For example, a measurement task requires absolute accuracy of the dimensions of semiconductor features with an accuracy of less than 1 nm, 0.3 nm, or even 0.1 nm. Therefore, the lateral position accuracy of each focal spot 5 of the multiple primary charged particle beamlets 3 must be less than 1 nm (e.g., less than 0.3 nm or less than 0.1 nm). High image repeatability means that repeated image acquisition of the same area produces first and second repeated digital images, with the difference between the first and second repeated digital images being below a predetermined threshold. For example, the difference in image distortion between the first and second repeated digital images should be less than 1 nm (e.g., less than 0.3 nm, or preferably less than 0.1 nm), and the difference in image contrast should be less than 10%. In this way, repeated imaging operations produce similar image results. This is important, for example, for acquiring and comparing images of similar semiconductor structures on different wafer dies, or for comparing acquired images to representative or reference images obtained from CAD-based image simulations or databases.

[0084] One of the requirements or specifications for a wafer inspection task is throughput. The measurement area per acquisition time is determined by the dwell time, resolution, and number of beamlets. Typical examples of dwell times are 20 ns to 80 ns. Therefore, the pixel rate in the high-speed image sensor 207 is in the range of 12 MHz to 50 MHz, and it is also possible to acquire approximately 15 to 20 image patches or frames per minute. For 100 beamlets, a typical example of throughput in high-resolution mode with a pixel size of 0.5 nm is approximately 0.045 mm 2 / min (millimeters per minute), and for an increased number of beamlets (e.g., 10,000 beamlets and a dwell time of 25 ns), a throughput of over 7 mm 2 / min is possible. However, in prior art systems, the requirements for digital image processing significantly limit the throughput. For example, in prior art Scanning Distortion Digital compensation of is undesirably time consuming. Embodiments of the present invention reduce image post-processing requirements and increase throughput for high precision metrology tasks. Embodiments of the present invention enable high throughput for wafer inspection tasks while maintaining image performance specifications well within the above requirements.

[0085] The imaging performance of the charged particle microscope 1 is limited by the design and higher-order aberrations of the electrostatic or magnetic elements of the object illumination unit 100, as well as by the manufacturing tolerances of the primary multi-beamlet configuration unit 305. The imaging performance is limited by aberrations such as distortion, focus aberration, decentering, and astigmatism of the multiple charged particle beamlets. FIG. 3 shows typical static distortion aberrations of multiple primary charged particle beamlets 3 at the image plane 101 as an example. The multiple primary charged particle beamlets 3 are focused at the image plane to form multiple primary charged particle beam spots 5 (three shown) in a raster configuration (a hexagonal raster in this example). In an ideal system, with the simultaneous multi-beam raster scanner 110 switched off, the beam spots 5 are each formed at a center position 29.mn (see FIG. 2) of the corresponding image subfield 31.mn (where m is the line number and n is the column number). However, in real systems, the beam spot 5 is formed at a position that deviates slightly from its ideal position on the ideal raster, as indicated by the static distortion vector in FIG. 3 . In the illustrated example of the primary beam spot 141, the deviation from the ideal position on the hexagonal raster is represented by the distortion vector 143. The distortion vector gives the lateral difference [dx, dy] from the ideal position, and the maximum absolute value of the distortion vector can be in the range of several nanometers (e.g., greater than 1 nm, 2 nm, or even 5 nm). Typically, the static distortion vector in real systems is measured and compensated for by an array of static deflection elements, such as one of the multi-aperture active plate configurations 306.2. Drift or dynamic changes in the static distortion are also taken into account and compensated for as described in German Patent Application No. 102020206739.2, filed May 28, 2020, which is incorporated herein by reference. Control and compensation of the aberrations is achieved by a monitoring or detection system and a control loop which may drive the compensator, for example multiple times during an image scan, thereby compensating for the aberrations of the multi-beam charged particle microscope 1 .

[0086] However, the imaging performance of a charged particle microscope is limited not only by design and drift aberrations of the electrostatic or magnetic elements of the object projection unit 100, but also, in particular, by the first collective multi-beam raster scanner 110. For single-beam microscopes, deflection scanning systems and their respective characteristics have been thoroughly investigated. However, for multi-beam microscopes, conventional deflection scanning systems for scanning deflection of multiple charged particle beamlets exhibit unique characteristics not disclosed in the prior art. These unique characteristics are shown in more detail in the beam path through the deflection scanner in FIG. 4.

[0087] FIG. 4a shows the beam path of a single primary charged particle beam through a prior art scanning deflector 110, including deflection electrodes 153.1 and 153.2 and a voltage source. For simplicity, only the deflection scanner electrodes for raster scan deflection in the first direction are shown. In use, a scanning deflection voltage difference VSp(t) is applied, creating an electrostatic field with equipotential lines 155 between electrodes 153.1 and 153.2. An axial charged particle beamlet 150a corresponding to image patch 31.c with image patch center 29.c is aligned with the optical axis 105 and deflected by the electrostatic field through intersection volume 189 between deflection electrodes 153.1 and 153.2 along real beam path 151f. The beam trajectory can be approximated by primary beam paths 150a and 150f with a single virtual deflection at pivot point 159. Charged particle beamlets traveling along path 150z are focused by objective lens 102 onto object plane 101 shown at the bottom of Figure 4a. Subfield coordinates are given in coordinates (p, q) relative to center point 29.c of subfield 31.c.

[0088] coordinate p f For maximum deflection to the maximum subfield point, the maximum voltage difference VSp max is applied and the distance p zIn the case of deflection of the incident beamlet 150a to a subfield point of p, a corresponding voltage VSp is applied and the incident beamlet 150a is deflected by a deflection angle α in the direction of the beam path 150z. The nonlinearity of the deflector is compensated by determining the functional dependence of the deflection angle α and the deflector voltage difference VSp. Calibration of the functional dependence VSp(sin(α)) realizes a nearly ideal scanner for a single charged particle beamlet, with a single common pivot point 159 for the deflection scanning of a single primary charged particle beamlet. Note that the lateral displacement (p,q) of the beam spot position in the image plane is proportional to the focal length f of the objective lens 102 multiplied by sin(α). In the example of a strip-shaped field point, p z =fsin(α z ) For small angles α, the function sin(α) is usually approximated by α. As explained in more detail below, for single-beam microscopes, Scan-induced distortion Despite the fact that the virtual pivot point 159 can be minimized, other scanning-induced aberrations such as astigmatism, defocus, coma, or spherical aberration can degrade the resolution of charged particle microscopes with large field sizes. Also, as the field size increases, deviations from the virtual pivot point 159 become increasingly significant.

[0089] In a multi-beam system, multiple charged particle beamlets are scanned in parallel by the same deflection scanner with the same voltage difference according to the functional dependence VSp(sin(α)). In FIG. 4b, the crossover 108 of multiple primary charged particle beamlets coincides with the virtual pivot point 159 of the axial primary beamlet 150a, and each charged particle beamlet passes through the electrostatic field at a different angle. A charged particle beamlet 157a at an incident angle β is shown along with the corresponding subfield 31.o with the image subfield center 29.o. The angle β is related to the distance X from the center coordinate 29.o to the optical axis 105 by sin(β)=X / f, using the focal length f of the objective lens 102. With the deflection scanner 110 switched off (VSp(t)=0V), the beamlet travels along the path 157a and is focused by the objective lens 102 to the center point 29.o of the subfield 31.o. However, despite the fact that the deflection scanner is nearly ideal for axial beamlets when a voltage difference is applied, as shown in Figure 4a, it is not ideal for field beamlets at incidence angles β. Due to the finite thickness of the deflection field, the path length through the electrostatic field is different for incident beamlets at different incidence angles β, and the actual beam paths 157z and 157f deviate from the ideal first-order beam paths 163z and 163f. This is referred to as the coordinate p z and p f The beam paths for the two sub-field points are shown as real beam paths 157z and 157f. The angles of the real beam paths 157z and 157f deviate from the angles of the ideal beam paths 163z and 163f, and each beam is virtually deflected at different virtual pivot points 161z and 161f that deviate from the beam crossover 108. For example, when a voltage Vsp(sin(α0)) is applied, the primary charged particle beamlet 157a is deflected by an angle α1 instead of an angle α0 and follows the beam path 157z that includes the virtual deflection point 161z. Therefore, the charged particle beam spot is distorted by a local distortion vector dpz.

[0090] The deviation of the deflection angle increases with the increase of the incident angle β, and the simultaneous multi-beam raster scanner 110 Scan-induced distortionIn a first embodiment of the present invention, modifications to the design and operation of the collective multi-beam raster scanner 110 result in: Scan-induced distortion In a second embodiment of the present invention, a first multi-beam scanning correction system 601 is provided to reduce residual Scan-induced distortion is further suppressed.

[0091] Depending on the difference in deflection angle α Scan-induced distortion, and the difference in the location of the virtual pivot point causes scan-induced decentering aberrations. Figure 5 shows a simplified system 171 preceding the scanning simultaneous multi-beam raster scanner 110, from which multiple primary charged particle beams enter the first simultaneous multi-beam raster scanner 110. Two beamlets, including axial charged particle beamlet 3.0 and off-axis beamlet 3.1, represent multiple charged particle beamlets that pass through an intersection volume 189 of the raster scanner 110 and are focused by the objective lens 102 to form multiple focal points, indicated by foci 5.0 and 5.1, on the surface 25 of the wafer 7. When the raster scanner 110 is off and no voltage difference VSp is applied to the electrode 153, the beam spots 5.0 and 5.1 are located at the center points 29.0 and 29.1 of each image subfield. When a voltage difference Vsp (sin(α0)) is applied, beamlet 3.0 deflects along ideal path 150 to strip field point Z0. In the linear representation of FIG. 5, beamlet 3.0 appears to be deflected at beam crossover 108, which corresponds to virtual pivot point 159 in FIG. 4a. Therefore, beamlet 3.0 irradiates wafer surface 25 at the same angle of incidence as at central position 29.0. Off-axis beamlet 3.1 deflects to a corresponding strip field point Z1 in the corresponding image subfield. Off-axis beamlet 3.1 appears to be deflected along representative beam path 157 at virtual deflection point 161, which deviates from beam crossover 108. Therefore, the decentering angle of beamlet 3.1 at its scan position relative to strip field point Z1 deviates from its decentering angle at central field 29.1, corresponding to the distortions described above as well as scan-induced decentering aberrations of beamlet 3.1. In a third embodiment of the present invention, a second multi-beam scanning correction system 602 reduces scan-induced decenter aberrations.

[0092] The deviation of the focal position at the scanning position of each of the plurality of charged particle beamlets 3 is, for each of the subfields 31.11 to 31.MN, Scanning Distortion The vector field is shown in Figure 6 for the example of image subfield 31.15. Scanning Distortion(See FIG. 7). Throughout this disclosure, image subfield coordinates (p, q) for each center of each image subfield 31.mn are used, Scanning Distortion is represented for each image subfield 31.mn by a vector [dp,dq] as a function of the image subfield coordinates (p,q). The center position (p,q)=(0,0) of each image subfield is represented by its (x,y) coordinate relative to the optical axis 105. Each image center coordinate can be distorted from a predetermined ideal raster configuration as a function of its (x,y) coordinate by a static offset (dx,dy), as shown in FIG. 3. The static distortion is usually compensated for by a static multi-aperture plate 306.2, Scanning Distortion [dp,dq] is not taken into account. Scanning Distortion Since is different for each image subfield 31.11···31.MN, in general, the local image subfield coordinates (p, q) and the discrete center coordinates of the image subfield (x ij ,y ij ) to get the fourth dimension Scanning Distortion Vector [dp,dq]=[dp,dq](p,q;x ij ,y ij )

[0093] Figure 6 shows the entire image subfield 31.15. Scanning Distortion The vector [dp, dq] is shown. In this example, the maximum Scanning Distortion is at the maximum image subfield coordinate p=q=6 μm, Scanning Distortion The vector [dp,dq] = [2.7nm,-1.6nm]. Scanning Distortion The vector length is 3.5 nm. Typical maximum in the image subfield Scanning Distortion The aberration ranges from 1 nm to 4 nm, but can exceed 5 nm.

[0094] Figure 7 shows the maximum image subfields of 31.11 to 31.MN for an example of a perfectly aligned conventional multibeam charged particle microscope containing multiple J = 61 primary charged particle beamlets in a hexagonal raster configuration. Scanning Distortion The maximum of each subfield of view is shown. Scanning Distortion The maximum image subfield of 31.55 on the optical axis of a multi-beam charged particle microscope is Scanning Distortion is small or nearly zero. Scanning Distortion increases with increasing distance of the image subfield to the optical axis, and at the image subfield 31.15 or 31.91 where the distance to the optical axis is greatest, all maximum Scanning Distortion and thus reaches a maximum propagation angle β with respect to the optical axis 105 at the beam crossover 108. The area of ​​the circle is Scanning Distortion , and the diameter of the circle increases linearly with the distance of the image subfield center from the optical axis, as shown by line 197. In this example, Scanning Distortion is dominated by a linear dependence on the subfield coordinates (p, q) and a quadratic dependence on the image subfield center position (x, y).

[0095] In the example of FIG. 7, the simultaneous multi-beam raster scanner 110 performs the following for the axial beamlets in the central subfield of view 31.55: Scan-induced distortion and the subfield of view corresponding to the primary beamlets with a large angle of incidence β relative to the intersection volume. Scan-induced distortion In one example of the present invention, the scanning deflection voltages VSp(t) and VSq(t) of the simultaneous multi-beam raster scanner 110 are configured to maximize the deflection of the axial beamlets. Scan-induced distortion at the expense of Scan-induced distortion It is configured to minimize the axial beamlets in the central subfield of view 31.55. Scan-induced distortion Although it shows that Scan-induced distortion becomes smaller, for example, from 5 nm to less than 3 nm.

[0096] In the first embodiment of the present invention, the multi-beam charged particle microscope 1 Scanning Distortion Scanning imaging aberrations, including (a) and (b), are reduced by an improved design of the simultaneous multi-beam raster scanner 110. The improved simultaneous multi-beam raster scanner 110 according to the first embodiment generates a laterally optimized deflection electrostatic field such that, in operation, primary beamlets entering and propagating through the electrostatic field at different angles β are deflected by a corrective deflection angle α and appear deflected at a common virtual pivot point corresponding to the beam crossover of the multiple primary charged particle beamlets 3. Scanning Distortion The modified collective multi-beam raster scanner 110 comprises a set of deflection electrodes with an optimized physical design and a set of correction electrodes for dynamically adjusting the deflection electrostatic field during the scanning deflection of a plurality of primary charged particle beamlets. In one example, the set of correction electrodes includes a correction electrode disposed between two deflection electrodes. In one example, the set of correction electrodes includes at least one correction electrode disposed upstream or downstream of at least one of the deflection electrodes in the propagation direction of the primary charged particle beamlets. In a first embodiment, the optimized multi-beam deflection scanner design enables the scanning deflection of a multi-beam charged particle microscope. Scanning Distortion , where the aberrations of the deflection system 110 and the additional scanning aberrations of the charged particle microscope (eg, the objective lens 102) are compensated for.

[0097] 8a shows a first example of the first embodiment. The set of scanning deflection electrodes includes first deflection electrodes 181.1 and 181.2 for scanning deflection of the plurality of primary charged particle beamlets in a first direction and a second set of deflection electrodes 183.1 and 183.2 for scanning deflection of the plurality of primary charged particle beamlets in a second direction. The design of a set of deflection electrodes optimized to generate a homogeneous deflection field, for example for a single electron beam system, is described in "DESIGN OF A NON-EQUISECTORED 20-ELECTRODE DEFLECTOR FOR E-BEAM LITHOGRAPHY USING A FIELD EMISSION ELECTRON BEAM" by E.R. Weidlich, Microelectronic Engineering Vol. 11, pp. 347-350 (1990), which is incorporated herein by reference. The multiple primary charged particle beamlets are arranged in a hexagonal raster configuration, with each beamlet propagating at a different propagation angle (β ) through the collective multi-beam raster scanner 110 corresponding to its position in the hexagonal raster. x ,β y) The cross section of the intersection volume 189 of the multiple primary charged particle beamlets is therefore approximately hexagonal. To compensate for the rotation of the multiple primary charged particle beamlets by the magnetic objective lens 102, the set of deflection electrodes 181 and 183 and the intersection volume 189 are rotated relative to the global xy coordinate system. Scanning Distortion The maximum area of ​​the deflection electrode is indicated by arrow 191. The modified deflection scanner design includes a set of deflection electrode configurations that deviate from a circular shape (dotted line). In this example, the deflection electrodes are arranged in an elliptical shape, with a maximum Scanning Distortion The shorter distance of the deflection electrodes to the intersection volume 189 in the direction of the area is indicated by arrow 191. In this example, the deflection electrodes have different azimuthal extensions: the azimuthal extension φ3 of the deflection electrodes 183.1 and 183.2 for the deflection scan in the second direction is different from the azimuthal extension φ1 of the deflection electrodes 181.1 and 181.2 for the deflection scan in the first direction.

[0098] Also disposed outside the intersection volume 189 is a set of correction electrodes 185, including electrodes 185.1, 185.2, 185.3, 185.4, arranged successively between the set of deflection electrodes. In use, a plurality of correction voltage differences VC(i=1...4,t) are applied to the correction electrodes in synchronization with the scanning voltage differences VSp(t) and VSq(t) across the set of deflection electrodes. In use, the correction electrodes 185 generate variable correction deflection fields that are added to the deflection fields generated by the set of deflection electrodes 181 and 183. The set of correction electrodes is configured to generate correction fields that, in use, specifically affect beamlets with the largest propagation angles at the corners of the hexagonal raster configuration during scanning. During scanning, for example as shown in FIG. 6, Scanning Distortion The correction voltage difference VC(i=1···4,t) changes depending on the Scanning Distortion can be suppressed.

[0099] 8b shows a second example of the first embodiment, where a modified simultaneous multi-beam raster scanner 110 is adapted for the symmetry of the raster configuration. In this example, multiple primary charged particle beamlets are oriented at corresponding angles βx , β y 8a, the deflection system 110 in FIG. 8b rotates relative to a global coordinate system (x, y) to pre-compensate for rotation by the objective lens 102 (see FIG. 1) located downstream of the collective multi-beam raster scanner 110. A set of deflection electrodes 181 and 183 for generating deflection fields for scanning deflection of the multiple primary charged particle beamlets are arranged in a rectangular shape and include deflection electrodes 181.11, 181.12, 181.21, and 181.22 for deflection or raster scanning in a first direction and deflection electrodes 183.11, 183.12, 183.21, and 183.22 for deflection or raster scanning in a second direction. The simultaneous multi-beam raster scanner 110 further comprises a first set of correction electrodes 185 including first correction electrodes 185.1 to 185.4 arranged in the vicinity of the beamlet with the maximum propagation angle. The first set of correction electrodes 185 is particularly adapted to correct the angle and thus the Scan-induced distortion The first set of correction electrodes 187.1-187.8 is configured to locally add an inhomogeneous correction field acting on the large primary charged particle beamlet. Next, the simultaneous multi-beam raster scanner 110 further includes a second set of correction electrodes 187.1-187.8 disposed between each pair of deflection electrodes 181 or 183 and the first correction electrode 185. The second set of correction electrodes adds a degree of freedom in generating the correction field, thereby controlling, for example, the range of the inhomogeneous correction field generated by the first set of correction electrodes.

[0100] In this example, each deflection electrode for generating a deflection field during image scanning is configured as a pair of deflection electrodes (e.g., a first pair of deflection electrodes 181.11 and 181.12 and a second pair of deflection electrodes 181.21 and 181.22 for scanning deflection in a first direction). Configuring the deflection electrodes as two or more pairs of electrodes provides additional flexibility. For example, during image scanning in the first direction using the deflection electrodes 181.11-181.22, a variable inhomogeneous scanning deflection field can be generated, which is homogeneous in the central area 190 of the intersection volume, but has a predetermined variable inhomogeneity for beamlets with large propagation angles β through the area 189. In addition, when the deflection electrodes 183.11 to 183.22 are used to scan the image in the second direction, the deflection electrodes 181.11 to 181.22 can generate a predetermined variable inhomogeneous scanning correction field in the first scanning direction in synchronization with the scanning deflection in the second direction, for example, for beamlets with larger propagation angles, in the form of image rotation. Scanning Distortion In addition, the increased degree of freedom allows for compensation for, for example, manufacturing tolerances of the actual collective multi-beam raster scanner 110.

[0101] FIG. 9 shows an embodiment of a modified deflection scanner according to FIG. 8b, in which the performance of the deflection scanner is optimized by the modified selection of voltage differences for pairs of deflection electrodes of the collective multi-beam raster scanner 110. In this example, the deflection electrodes 181 for a first direction of deflection scanning include a first pair of deflection electrodes 181.11 and 181.12 and a second pair of deflection electrodes 181.21 and 181.22. FIG. 9a shows the required voltage difference as a function of the deflection angle Vsp (sin α) for a deflection scanner with a pair of deflection electrodes. The graph shows the required voltage difference 175 applied to two pairs of deflection electrodes 181.1 and 181.2 for a first direction of deflection scanning. The deviation of the voltage difference 175 from the linear line 173 compensates for the nonlinear effects described above. The modified voltage difference for two pairs of deflection electrodes is shown in FIG. 9b. In use, a first voltage difference 177.1 of one sign is applied to one pair of opposing electrodes 181.11 and 181.21, respectively, and a second voltage difference 177.2 of the opposite sign is applied to the other pair of opposing electrodes 181.12 and 181.22, respectively. The average voltage difference applied to the pairs of electrodes is the same as voltage difference 175. Axial beamlets and beamlets close to the optical axis are transmitted through inner area 190 of FIG. 8b. In this area, the electrostatic field difference generated by voltage differences 177.1 and 177.2 has little effect. Residual rotation can also be compensated for by variable offset voltages 179.1 and 179.2 (not shown to scale) applied to pairs of electrodes 183.11-183.22 for scanning in the second direction. This results in beamlets transmitted through the outer zone of area 189 experiencing a slightly inhomogeneous deflection field. This results in: Scan-induced distortion can be suppressed.

[0102] FIG. 10 shows another example of the first embodiment. In this example, the set of correction electrodes includes electrodes arranged upstream or downstream of the deflection electrodes in the propagation direction of the primary charged particle beamlets 3. The first and second deflection electrodes 181.11, 181.12 are configured to face the first and second deflection electrodes 181.31, 181.32 for deflection scanning in a first direction X'. Due to their deflection, the primary charged particle beamlets pass through an intersection volume 189, which constitutes a beam tube including z-segments 189.1-189.3 with different lateral extensions. In this example, a set of first correction electrodes 195.1-195.4 is provided and configured to add correction fields during scanning deflection of the primary charged particle beamlets. The correction electrodes are arranged upstream and downstream of the deflection electrodes 181 in the propagation direction of the primary charged particle beamlets (z-direction in FIG. 10). At these z-positions, primary beamlets with larger propagation angles (e.g., beamlets 3.1 and 3.2) are located at a greater distance to the optical axis 105, and the effect of the inhomogeneous correction field generated by the correction electrodes increases with the beamlet's propagation angle. An additional second set of correction electrodes 193.1-193.4 provides an additional degree of freedom to optimize the modified inhomogeneous scanning deflection field in the intersection volume 189. The correction electrodes 193-195, shown in cross section in FIG. 10, are arranged in segments around the primary beamlets, thereby locally affecting multiple charged particle beamlets, similar to the correction electrodes shown in FIG. 8. In use, a variable correction voltage difference is applied to the correction electrodes, and a time-varying inhomogeneous correction field is added synchronously with the scanning deflection field during deflection scanning. For example, in the deflection field, the primary charged particle beamlet 3.1 is deflected to the right and propagates along a path 3.1f, passing through the correction field generated by the correction electrodes 193.2 and 195.2, while the primary charged particle beamlet 3.2, following a path 3.2f, is further away from the electrodes 193.2 and 195.2 and does not pass through the inhomogeneous correction field. This results in different localized regions in different image subfields. Scanning Distortion This makes it possible to correct fluctuations in the

[0103] 11 shows another embodiment of a modified deflection scanning system 110. By adjusting the length or longitudinal extension of the deflection electrodes in the z-direction by the length Z1 of the deflection electrodes 181.1 and 181.2 for scanning deflection in a first direction and the length Z3 of the deflection electrodes 183.1 and 183.2 for scanning deflection in a second direction, it is possible to achieve large deflection angles at the four corners, for example as indicated by arrows 191 in FIG. Scanning Distortion can be suppressed.

[0104] A modified design of the deflection electrodes provides a predetermined inhomogeneous electrostatic field inside the intersection volume 189 of the collective multi-beam raster scanner 110. The predetermined inhomogeneous electrostatic field is time-varying to achieve deflection scanning of the multiple primary charged particle beamlets, and the beamlets that transmit through the intersection volume at a large angle β to the optical axis. Scan-induced distortionScan-induced aberrations such as . . . are minimized. In a first example, the deflection electrodes are configured to generate a predetermined inhomogeneous scan deflection electrostatic field that increases the inhomogeneity for primary beamlets transmitting through the intersection volume 189 at large angles β. In a second example, additional correction electrodes are provided that variably increase the inhomogeneity for primary beamlets transmitting through the intersection volume 189 at large scan deflection angles α during image scanning. The shape and position of the scan electrodes and the shape and position of the correction electrodes are optimized during design and simulation of the multi-beam charged particle microscope 1. In one example, additional aberrations of other elements of the optical system are taken into account. The theoretical voltage differences VS(t) and VC(t) required to generate the scan deflection field and the scan correction field are calculated, and a control signal for generating the scan correction voltage difference VC(t) is stored in a memory of the control unit 800 of the multi-beam charged particle microscope 1. During adjustment and calibration of the multi-beam charged particle microscope 1, the voltage differences VS(t) and VC(t) required for the scan deflection and compensation fields are adjusted and calibrated, and control signals for generating the calibrated voltage difference VS(t) and the scan compensation voltage difference VC(t) are stored in the memory of the control unit 800 of the multi-beam charged particle microscope 1. During image scanning, the calibrated voltage differences VS(t) and VC(t) are generated. An example of generating the compensation voltage difference VC(t) synchronized with the scan voltage difference VS(t) will be described later. In one example, the inhomogeneity of the scan deflection field is generated by a compensation field having a parabolic or higher-order shape in the first or second scan direction. In one example, the inhomogeneity of the deflection field is generated by a compensation field having a saddle-point shape on the optical axis and exhibiting parabolic or higher-order inhomogeneities of opposite signs in the first and second directions.

[0105] 21 shows another example of a bulk raster scanner 110 with a predetermined inhomogeneous electric field distribution. In this example, additional electrodes 153.1a, 153.1c, 153.2a, and 153.2c are provided at angles to the optical axis of the charged particle microscope. This controls the tilt angle of the electric field at the entrance and exit sides of the intersection volume 189 for the charged particle beamlets. The correction electrodes at an angle to the optical axis allow the optimization of the effect of the scanning deflection field on multiple beamlets with different angles of incidence, including beamlet 3.0 parallel to the optical axis and beamlet 3.1 at a maximum angle β2 with respect to the optical axis.

[0106] According to the second embodiment of the present invention, the multi-beam charged particle microscope 1 is Scan-induced distortion is configured to compensate for Scanning Distortion A multi-beam scanning correction system such as a compensator array 601 is provided (see FIG. 1). Scanning Distortion The compensator array 601 affects each individual primary charged particle beamlet individually, resulting in a scanning deflection of a few nm of each primary beamlet, induced by the long-stroke collective multi-beam raster scanner 110. Scanning Distortion is compensated for for each individual image subfield. Scanning Distortion Compensator array 601 is shown. Scanning Distortion The compensator array 601 is configured as a multi-aperture array 620, comprising a plurality of apertures arranged in a raster configuration (in this example, a hexagonal raster configuration) of a plurality of primary charged particle beamlets 3. An embodiment of the multi-aperture array 620 is shown in FIG. 12. Three of the apertures are designated by reference numerals 685.1 to 685.3. A plurality of electrodes 681.1 to 681.8 are arranged around each of the plurality of apertures. In this example, there are eight electrodes per aperture 685, although other numbers, such as four or more, are possible. The electrodes 681 are electrically isolated from each other and from the carrier of the multi-aperture array 620. Each of the electrodes is connected to the high-speed array scanning control module by a conductive line 607.

[0107] Although, in principle, static multi-aperture array 620 designs are known for static compensation of static distortions as shown in FIG. 3 , conventional methods do not allow for scan correction or compensation of scan-induced aberrations. For scan correction, at least two highly dynamic scan correction voltage differences (e.g., eight scan correction voltage differences) per beamlet are generated in synchronization with the scan motion and applied to each of the J primary beamlets at the maximum scan speed in vacuum. A series of predetermined scan voltage differences VCA(t) are applied to each of electrodes 681 in synchronization with the image raster scan, resulting in scan deflection of each primary charged particle beamlet passing through one of apertures 685 in synchronization with the scan deflection by long-stroke collective multi-beam raster scanner 110. This results in residual aberrations of, for example, up to 3 nm due to the opposite deflection of individual beamlets corresponding to image subfields. Scan-induced distortion in the image subfield by the amount Scanning Distortion Since only electrostatic effects are involved, the charged particle beamlets transmitted through the corresponding apertures 685 can be rapidly and individually adjusted or changed in synchronization with the long straw cluster scan.

[0108] More details are provided in the example of aperture 685.3. A first set of electrodes 687.1 and 687.2 is provided for deflection scanning of the primary charged particle beamlets passing through aperture 685.3 in a first direction or p-direction. Also shown is a second set of electrodes 688.1 and 688.2 for deflection scanning of the primary charged particle beamlets passing through aperture 685.3 in a second direction or q-direction. Other electrodes, such as electrodes for correcting astigmatism, can also be provided for other manipulations of the charged particle beamlets passing through aperture 685.3.

[0109] The plurality of scan correction voltage differences VCA(t) applied to the first and second sets of deflection electrodes are synchronized with the raster scan voltage differences VSp(t) and VSq(t) applied to the collective multi-beam raster scanner 110 and are applied at a signal frequency of approximately 20 MHz to 50 MHz. Scanning DistortionThe compensator array 601 is shown to be capable of deflection scanning a plurality of J = M × N primary charged particle beamlets, where the number of charged particle beamlets J is greater than 10 beamlets, preferably J = 61 or greater (e.g., J > 100 or J > 1000 beamlets). Considering at least four deflection electrodes per beamlet, the number of drive signals or voltage difference VCAs (i = 1 · · 4J,t) for deflection scanning of the J beamlets is at least 4J, and each of the 4J signals or voltage difference VCAs (i = 1 · · 4J,t) has a signal frequency of approximately 20 MHz to 50 MHz or greater, corresponding to a dwell time of approximately 25 ns at each pixel. Therefore, data rates typically exceed 10 Gbit / s. Figures 13 and 14 show an example of achieving such a high data rate in the example of static voltage conversion arrays 611 and 612, which apply collective scanning voltages VSp(t) and VSq(t). Scanning DistortionThe compensator array 601 includes a multi-aperture plate 620 having a plurality of apertures 685 with deflection electrodes as shown in FIG. 12, and a scan array control unit 622. Each electrode for deflection scanning in the first direction is connected to the output of a first static voltage conversion array or unit 611 via a conductive line 607.1 and a first plurality of conductive lines 613. The first static voltage conversion array 611 is controlled by a first static control signal 615 provided by an operation control memory 626 of the scan array control unit 622. A first scan deflection voltage difference VCAp(t) for parallel deflection scanning of each of the plurality of primary charged particle beamlets in the first direction is provided by a scan voltage generator (not shown) via a first power line 609. The first scan deflection voltage difference VCAp(t) is proportional to the collective scan voltage VSp(t) generated for deflection scanning by the collective multi-beam scanning deflector 110. The first direction is the direction of the sub-field coordinate p and is parallel to the x-direction of the image plane. The scan array control unit 622 includes a memory 626 for storing a first plurality of control signals 615, including static control signals for each set of deflection electrodes (e.g., electrodes 687.1 and 687.2 in FIG. 12 ) for scan correction in the first direction. The first static voltage conversion array 611 generates, in synchronization with the first scan deflection voltage difference VCAp(t), a plurality of appropriate voltage differences VCAp (u=1 2J,t) for a set of u deflection electrodes for scan deflection of each charged particle beamlet in the first direction. Each voltage difference applied to the deflection electrodes (e.g., electrodes 687.1 and 687.2) for deflection in the first direction is proportional to the scan deflection voltage difference VCAp(t) and thus the global scan voltage difference VSp(t).

[0110] A second set of static control signals 616 is provided to a second static voltage conversion array 612 connected via conductive lines 614 and wiring 607.2 to each of the v second electrodes for deflection scanning in a second direction (e.g., including electrodes 688.1 and 688.2 of aperture 685.3 as shown in FIG. 12 ). The second static voltage conversion array 612 generates a plurality of second voltage differences VCAq(v=1 2J,t) for each of the v deflection electrodes for scan deflection of the beamlet in a second direction (here, the direction of the sub-field coordinate q, parallel to the y-direction of the image plane) by subtraction from the second scan deflection voltage difference VCAq(t) provided via second power line 610. Thus, each voltage difference applied to each of the deflection electrodes (eg, electrodes 688.1 and 688.2) for deflection in the second direction is proportional to the scan deflection voltage difference VCAq(t) and thus to the global scan voltage difference VSq(t).

[0111] As shown in Figure 6, Scanning Distortion The vector [dp,dq] generally has a first direction (here, the p coordinate) as well as a second direction (here, the q coordinate) Scanning Distortion 13, the first and second voltage conversion units 611 and 612 are connected by a signal line 618, and a plurality of voltage differences VCp(v,t) for scanning deflection in a second direction, which are proportional to the first scanning deflection voltage difference VCAp(t), are generated and applied to a plurality of electrodes for scanning in the second direction, and vice versa for VCAq(u,t). This allows the residual voltages in the first and second directions to be generated in synchronization with the collective scanning signals VSp(t) and VSp(t) applied to the collective multi-beam raster scanner 110. Scanning Distortion The vector components dp(p,q) and dq(p,q) are compensated. Scanning Distortion Since the amplitudes ||dp,dq|| of Scan-induced distortion The voltage difference required for individual compensation is very small, for example less than 100 mV, less than 10 mV, or even less.

[0112] An example of a static voltage conversion array or unit 611 or 612 is provided by a programmable resistor array that generates a plurality of output voltages proportional to a variable input voltage. Figure 14 shows an example of a static voltage conversion array 611. In this example, the static voltage conversion array 611 is Scan-induced distortion The static voltage conversion array 611 is configured as a programmable resistor array for individually reducing the variable drive voltages VCAp(t) and VCAq(t) to a plurality of voltage differences VCAp(u,t) and VCAp(v,t) for individual compensation of the (dp,dq). The static voltage conversion array 611 provides at least two components of a voltage difference, including a first voltage difference VCAp(u,t) synchronized with the drive voltage VCAp(t) and a second voltage difference VCAq(u,t) synchronized with the drive voltage VCAq(t), to each of the u=1···2J correction deflection electrodes. The first and second drive voltages VCAp(u,t) and VCAq(u,t) are summed by a voltage adder 641.u to generate a voltage difference VCAp(u,t) for each u-th electrode (e.g., VCAq(u,t) for each individual primary beamlet in the first direction). Scan-induced distortionA first series of resistors 633.j (e.g., a series of 1 Ω, 2 Ω, 4 Ω, 8 Ω resistors) is provided to the deflection electrode 687.1 for compensating for the voltage drop. For each of the j=1...4J deflection electrodes, a first series of resistors 633.j of increasing resistance (e.g., a series of 1 Ω, 2 Ω, 4 Ω, 8 Ω resistors) is arranged in series, and a series of transistors 639.n is arranged in parallel with each resistor. For example, in the case of the deflection electrode 687.1, a first series of resistors 633.11-633.14 is arranged in parallel with a first series of transistors 639.11-639.14 to reduce the drive voltage VCAp(t) provided by the power line 609, and the amount of voltage reduction is controlled by a plurality of static control signals 635.11-635.14 provided to the first series of transistors 639.11-639.14. For example, by switching a transistor 639.13 from an off state to an on state via a control signal 635.13 applied to the gate of resistor 639.13, the corresponding resistor 633.13 is bridged and no voltage is dropped across the resistor 633.13. When transistors 639.11-639.14 are in an off state, the corresponding resistor 633.11-633.14 reduces the drive voltage (e.g., scan deflection voltage difference VCAp(t)). When all transistors are switched to an off state, the drive voltage difference VCAp(t) is reduced to a minimum value, resulting in a minimum deflection of the corresponding beamlet. When all transistors are switched to an on state, a maximum scan deflection voltage difference VCAp(t) is applied to the corresponding electrode, resulting in a maximum deflection of the corresponding beamlet. This allows, for example, a maximum deflection of approximately 5 nm of the beamlet. Scanning Distortion The maximum value is compensated for. The four consecutive resistors can reduce the drive voltage difference VCAp(t) to 16 different voltage levels between the maximum and minimum voltage differences, thereby reducing the maximum residual distortion from approximately 5 nm to approximately 0.3 nm.

[0113] A plurality of static control signals 635 applied to a series of transistors 639 switch and hold the transistors in an on or off state to reduce the scan deflection voltage difference VCAp(t) in a predetermined manner for each of a plurality of electrodes of the multi-aperture array 620. The output voltage VCAp(u,t) 613.1 applied to a particular u-th electrode (e.g., electrode 687.1 in FIG. 12 ) includes a first correction voltage component VCAp(u,t) synchronous with the drive voltage VCAp(t), which is proportional to the first scan deflection voltage difference VCAp(t) for the long straw cluster scan of the primary charged particle beamlet in the first or p direction.

[0114] In one example, scan correction in a first direction (e.g., p-direction) depends on scan position in a second direction (e.g., q-direction). Accordingly, static voltage conversion array 611 further comprises voltage combiner 641.1 connected to a programmable resistor array including resistor 633.3 driven by a second scan deflection voltage difference VCAq(t) provided by power line 610. A set of drive signals 637.11-637.14 generates a second correction voltage component VCAq(u,t) synchronous with drive voltage VCAq(t) that is proportional to the second scan deflection voltage difference VCAq(t) and is added to a first correction voltage component proportional to and synchronous with the second scan deflection voltage difference VCAq(t) for long-straw cluster scanning in the second or q direction.

[0115] In one example, the scan correction in the second direction (here, the q direction) depends on the scan position in the first direction (here, the p direction). Accordingly, the static voltage conversion array 611 comprises another programmable resistor array driven by a first scan deflection voltage difference VCAp(t) provided by the power line 609. A set of drive signals (not shown) generates a second correction voltage component VCAp(v,t) synchronous with the drive voltage VCAp(t) and proportional to the first scan deflection voltage difference VSP(t), which is in turn proportional to the scan position in the second or q direction. Scanning Distortion For compensation, the vector components dq(p,q) are proportional to the scan position in the first direction.

[0116] Reduce the scanning deflection voltage difference to a predetermined voltage difference Scan-induced distortion The number L of resistors, transistors, and static control signals for compensating for the above is illustrated by way of example with L=4, but can be greater. Voltage combiner 641 can also be connected to additional voltage difference signals to provide, for example, individual predetermined voltage offsets to each of apertures 685, thereby compensating for static distortion offsets as shown in Figure 3. A programmable resistor array is an example of a quasi-static voltage converter, which can generate a large amount of data rate Scanning Distortion The 4J electrodes of the compensator array 601 can be provided. Equivalent implementations are also possible, such as an array of programmable source follower transistors that limits the drive voltage difference for each source follower transistor to an amount proportional to the static signal provided to each gate of each source follower transistor.

[0117] A plurality of static control signals (including control signals 635.11 to 635.14 and control signals 637.11 to 637.14) Scanning Distortion The static control signals are determined in a calibration step for at least every 4J electrodes of the compensator array 601 and stored in a memory 626 of the scanning array control unit 622. The static control signals stored in the memory 626 can be modified during operation of the multi-beam charged particle microscope (e.g., during image acquisition of the first and second image patches). Therefore, the scanning array control unit 622 is connected to the operation control unit 800 via a data connection 631 (see FIG. 13). In one example, the scanning array control unit 622 is connected to a clock line 624, thereby Scanning Distortion The operation of the compensator array 601 is synchronized with the collective multi-beam raster scanner 110. During image acquisition of an image patch, the plurality of static control signals 615 and 616 are constant and the Scanning Distortionis corrected by a plurality of 4J voltage differences applied to the 4J deflection electrodes, so that the 4J voltage differences include first and second components proportional to the first and second scanning deflection voltage differences VCAp(t) and VCAq(t), respectively, which are synchronized with the scanning deflection voltage differences VSp(t) and VSq(t) applied to the deflection scanner electrodes of the long-stroke simultaneous multi-beam raster scanner 110. Thus, according to the second embodiment, the Scanning Distortion teeth, Scanning Distortion Compensation is performed by the compensator array 601 .

[0118] In one example, the number J of primary charged particle beamlets in a raster configuration is J=100. For each beamlet, Scan-induced distortion Because correction of [dp,dq] requires at least four electrodes with correction voltage differences, 4J=400 correction voltage differences are generated by a programmable resistor array and applied to multiple electrodes. For each electrode, the voltage difference is a superposition of two components (a first component with a linear dependence on the first scanning direction and a second component with a linear dependence on the second scanning direction), and generating 8J=800 voltage difference components for 4J=400 electrodes requires an 8J=800 programmable resistor array. For example, with four consecutive resistors and four control signals for generating each of the voltage difference components, a residual voltage of more than 10 times (e.g., up to 16 times) can be generated. Scanning Distortion Also, a plurality of 32J=3200 static control signals can be predetermined and provided from the memory of the motion control unit 622.

[0119] Further reductions are possible by placing five or more programmable resistors in series (e.g., eight resistors), resulting in a factor of over 100 (e.g., up to 256). Scan-induced distortion This can achieve a reduction in Scanning Distortion is reduced by at least 10-fold, preferably by more than 100-fold.

[0120] Typical first and second scan deflection voltages VSp(t) and VSq(t) for the scan deflection of beamlets in the first and second directions are shown in Figure 15. For scan deflection in the first direction (p coordinate in each sub-field of view, parallel to the x coordinate) by the simultaneous multi-beam raster scanner 110, a series of fast voltage ramps VSp(t) are generated that deviate from linear ramps and compensate for the nonlinear effects of the deflection scanner, as described above. After a time interval tl(n) for line number n, the scan deflection voltage VSq(t) for deflection in the second direction (here, q direction at wafer level, parallel to the y coordinate) is changed to deflect the beamlets of the next line numbered (n+1), and the scan deflection voltage VSp(t) becomes VSp min The next voltage ramp in time interval tl(n+1) returns the end of the line to VSp max The beamlet of line (n+1) is scanned and deflected until it reaches the time interval tb, which is the flyback interval mentioned above. Both voltages are generated and applied in stages, for example, the first voltage ramp VSp(t) includes a series of constant voltages, which are applied for a dwell time t at each pixel before the voltage VSp(t) changes to the deflection voltage for deflecting the beam to the next pixel. d (See enlarged detail).

[0121] It should be noted that in a system with a scanning wafer stage, the charged particle beamlets are deflected in only one direction, while the position of the beamlets in the second direction remains constant. In this example, Vsq(t) is constant.

[0122] 15 are representative of the voltage differences VSp(t) and VSq(t) applied for the raster scanning deflection of multiple primary charged particle beamlets by the simultaneous multi-beam raster scanner 110. The voltage differences VSp(t) and VSq(t) are also representative of the voltage differences VSp(t) and VSq(t) applied for the raster scanning deflection of multiple primary charged particle beamlets by the simultaneous multi-beam raster scanner 110. Scanning Distortion are representative of the drive voltages VCAp(t) and VCAq(t) as applied to the power lines 609 and 610 of the compensator array 601, where VCAp min , VCApmax and VCAq min , VCAq max The maximum scanning voltage difference of the long-stroke batch multi-beam raster scanner 110 is typically VSp, depending on the number of primary charged particles J. max = approximately 10V or more. Scanning Distortion Maximum drive voltage difference VCAp for compensation max is the maximum Scanning Distortion For example, a maximum of less than about 5 nm (e.g., 2 nm or 1.5 nm) depending on Scanning Distortion Therefore, Scanning Distortion In the case of the compensator array 601, the maximum voltage VCAp of the voltage gradient according to FIG. max is typically in the range of 10 mV to 100 mV (for example, about 50 mV).

[0123] Typically, for a symmetric scanning system, the minimum value of the scanning voltage difference is symmetric with the maximum value of the scanning voltage difference. Scanning Distortion For the linear part of VCAp, the minimum voltage difference is min =-VCAp max , VCAq min =-VCAq max Manufacturing errors or thermal drift in the multi-beam charged particle microscope can induce additional static distortion offsets for each of the multiple primary charged particle beamlets, which can be compensated for by the static distortion compensator 306 as described above.

[0124] In one example, Scanning Distortion The drive voltages VCAp(t) and VCAq(t) applied to the compensator array 601 can be generated in synchronization with the scan voltage differences VSp(t) and VSq(t) by the same scan voltage generator as that used in the collective multi-beam raster scanner 110, or the maximum voltage VCAp required from the scan voltage differences VSp(t) and VSq(t) can be controlled by resistors. max and VCAq max This allows the programmable resistor array to be Scanning Distortion The compensator array 601 provides Scanning DistortionThe correction is directly coupled to the scanning deflection by the collective multi-beam raster scanner 110 .

[0125] FIG. 15 is a simplified representation showing the scan voltage differences VSp(t) and VSq(t) for only four lines, but the number of scan lines is greater than this, for example, M=5000 or more.

[0126] Furthermore, a similar embodiment of voltage conversion unit 611 or 612 for providing a plurality of correction voltage differences VCp(t) and VCq(t) proportional to the first and second scan correction voltage differences VSp(t) and VSq(t) can also be used for controlling a set of correction electrodes of collective multi-beam raster scanner 110 according to the first embodiment (for example, controlling a set of correction electrodes 185.1 to 185.4, 187.1 to 187.4, or 195.1 to 195.4). This allows the plurality of correction voltage differences to be provided to the correction electrodes in synchronization with the drive voltage differences VSp(t) and VSq(t) for deflection scanning by the deflection electrodes.

[0127] In one example, Scanning Distortion Compensator array 601 similarly compensates for other scanning-induced aberrations, such as scanning-induced astigmatism or focal plane changes. Scanning Distortion is typically associated with the dynamic spot shape aberrations that occur for perturbed and unperturbed systems. Scanning Distortion A scanning astigmatism corrector array similar to the compensator array is provided, with the correction voltage difference for each astigmatism corrector electrode generated by a programmable resistor array or network as described above. A plurality (e.g., two or three) of such multi-aperture plates are arranged in series with corresponding electrodes for compensation of aberrations such as astigmatism and defocus. The correction voltages are similarly provided by drive voltage differences VSp(t), VSq(t). For example, two voltage differences VCCp(t) and VCCq(t) are required for stigmation correction. Similarly, a scanning compensator array 620 for decentering aberrations can be configured and operated, as described in more detail below.

[0128] Figure 1 shows: Scanning Distortion 6 illustrates several aspects of a compensator array 601. In one example, Scanning Distortion The compensator array 601 is disposed after the primary multi-beamlet forming unit 305 (e.g., between the primary multi-beamlet forming unit 305 and the first field lens 307) in the propagation direction of the plurality of primary charged particle beamlets. Scanning Distortion The compensator array 601 is provided as an additional element of the active multi-aperture plate arrangement 306.1 or 306.2 to compensate for static aberrations, such as the static distortion offset shown in FIG. Scanning Distortion The compensator array 601 is an element of the primary multi-beamlet forming unit 305. Also, as mentioned above, Scanning Distortion Compensator array 601 can also be configured to compensate for static distortion offsets as shown in FIG. Scanning Distortion The compensator array 601 is used to synchronize the image or raster scan with the long straw cluster scan, and the compensation is performed by the simultaneous raster scanning of multiple primary charged particle beamlets by the simultaneous multi-beam raster scanner 110. Scan-induced distortion , the position of each charged particle beamlet focus 311 in the intermediate image plane 321 changes in the opposite direction.

[0129] In a third embodiment, the multi-beam charged particle microscope includes a second multi-beam scan correction system, such as a scan compensator array for compensating for scan decentering errors as described above. The scan compensator array 602 for compensating for scan-induced decentering errors is located near the intermediate image plane 321. The scan compensator array 602 for compensating for scan decentering errors includes: Scanning DistortionThe compensator array 602 is configured similarly to the compensator array 601 and provides a plurality of control signals for compensating for scan-induced decentering errors. The scan compensator array 602 for compensating for scan decentering errors can be arranged in addition to the static compensator 390 for compensating for static decentering errors, or can be configured to provide a plurality of additional offset voltages for compensating for static offsets of decentering errors. The scan compensator array 602 for compensating for scan decentering errors compensates for scan-induced decentering errors by adjusting the individual propagation angles of each beamlet near the intermediate image plane 311 so that, during an image scan, each of the multiple primary charged particle beamlets impinges on the wafer surface 25 at a 90° angle with a deviation of less than 3 mrad or less.

[0130] According to the fourth embodiment, Scanning Distortion Multi-beam charged particle microscope with reduced Scanning Distortion and a method for operating a multi-beam charged particle microscope with reduced deflection. Scanning Distortion For the derivation of the control signals of the compensator array 601, the Scanning Distortion [dp, dq] is expanded in a power series of the image subfield coordinates (p, q).

[0131]

number

[0132] Scanning Distortion The lowest order or linear part of at a+b=1 is described by:

number

number

number

[0133] Higher order distortions include those caused by pincushions. distortion Third-order distortions such as pincushion distortion. Usually linear per subfield. distortion Aberrations are Scan-induced distortion This contributes more than 80% of the total. Scanning Distortion The compensator array 601 provides a linear compensation by applying a plurality of voltage differences to the deflection electrodes proportional to the scanning voltage differences VSp(t) and VSq(t) proportional to the scanning position (p,q) in each image subfield. Scanning Distortion can be compensated for. Scanning Distortion The linear part of is described by four normalized linear distortion aberration vectors M, SQ, OR, and ROT for each image subfield with raster coordinates (n,m). This gives: Scanning Distortion The linear part of (dp,dq) is compensated.

[0134] In one example, the linear parts M, SQ, OR, and ROT are described by four normalized vectors SDV(i), where SDV(1) represents M, SDV(2) represents SQ, SDV(3) represents OR, and SDV(4) represents ROT. Scanning Distortion The linear part of Scanning Distortion It can be described by the vector amplitudes A(i;n,m) as follows: [dp,dq](p,q;n,m)=E·Σ i A(i;n,m) SDV(i;p,q)

[0135] In one example, normalization involves setting the maximum value of each linear distortion vector SDV(i) to 1 nm and setting the maximum sum of amplitudes to max{Σ iA(i;n,m)}=1. The scaling factor E is then Scan-induced distortion [dp,dq] is a multiplication coefficient that represents the maximum intensity of (p,q;n,m).

[0136] Figure 16 shows Scanning Distortion 1 shows a method for operating a multi-beam charged particle microscope with reduced scattering. Scanning Distortion In a first step S1 of the method for operating a multi-beam charged particle microscope 1 with suppressed residual Scanning Distortion The linear part of is determined. This determination can be done, for example, by Scanning Distortion The calibration sample may include a plurality of structures to be calibrated at a position to be calibrated and may be provided on a wafer stage. In one example, the calibration includes a plurality of repeating patterns in a raster configuration similar to the raster configuration of the plurality of charged particle beamlets, and a relative displacement of the calibration pattern by a length corresponding to at least one image subfield between the first and second measurements causes: Scanning Distortion The calibration measurement is repeated. The difference between the first and second measurements is derived to obtain Scanning Distortion The relative differences between the image subfields corresponding to the measured Scanning Distortion is analyzed, and Scanning Distortion The linear parts M (nm), SQ (nm), OR (nm), and ROT (nm) are calculated for each image subfield (n, m) by decomposition of the error vector [dp,dq]. Scanning Distortion A vector is determined, a scaling factor E is determined, and a plurality of amplitudes A(i;n,m) are determined.

[0137] In step S2, Scanning Distortion The correction voltage difference VCAp required for the compensator array 601 max , VCAq maxis determined from the scaling factor E, and first and second reduction factors F1 and F2 are determined. The reduction factors F1 and F2 are determined so as to realize correction voltage differences VCAp(t) and VCAq(t) for scanning correction of multiple primary charged particle beamlets from the scanning voltage differences VSp(t) and VSq(t) applied to the simultaneous multi-beam raster scanner 110.

[0138] In step S3, a plurality of control signals 635 and 637 for controlling the programmable resistor arrays 611 and 612 are derived according to the dependence of the plurality of amplitudes A(i;n,m) of the linear distortion vector SDV(i) on the image subfield coordinate (n,m) (see Figures 12 to 14 for reference numbers). For each beamlet or each image subfield coordinate (n,m), respectively: Scanning Distortion For each deflection electrode 687, 688 of each of the multiple apertures 685 of the compensator array 601, multiple (at least eight) control signals 635, 637 for controlling the programmable resistor arrays 611, 612 are derived from the multiple amplitudes A(i;n,m) and stored in the memory of the motion control unit 622. The control signals are expressed as the image subfield coordinates (n,m). Scan-induced distortion If the amplitude A(i;n,m) is scaled in arbitrary units to a maximum distortion of 1, the linear vector components correspond to matrix elements, and the corresponding control parameters of the programmable resistor array can be calculated by matrix multiplication and conversion to a binary number with a bit length depending on the number of consecutive resistors.

[0139] In step S4, during image scanning, a plurality of control signals 635 and 637 are applied to the programmable resistor arrays 611 and 612. The scanning voltage differences VSp(t) and VSq(t) are reduced by the reduction coefficients F1 and F2, and the reduced correction voltage differences VCAp(t) and VCAq(t) are applied to the power lines 609 and 610 of the programmable resistor array 611. As a result, during image scanning, a plurality of primary charged particle beamlets are scanned and deflected by the collective raster scanner 110, and residual Scanning Distortion The linear part of Scanning Distortion Compensation is performed by the compensator array 601 .

[0140] This will reduce residual Scanning Distortion is reduced by at least 80% (e.g., 10 times), e.g., less than 0.3 nm or less than 0.2 nm remaining Scan-induced distortion is realized.

[0141] FIG. 17 shows the linear distribution for multiple primary charged particle beamlets in an example of a multibeam charged particle microscope with J=61 beamlets in a hexagonal raster configuration. Scanning Distortion The figure shows the normal field dependence of the vector. Throughout images 17a, 17c, 17e, and 17g, positive numbers are represented by circles and negative numbers by squares, and the maximum or minimum value of the linear distortion vector is represented by the area of ​​the circle or square. Figure 17b shows the image subfield center coordinate (x nm ,y nm ), Fig. 17a shows the dependence of the linear scale SDV(l). Fig. 17d shows the normalized linear scale SDV(l)≈M for each of the J = 61 beamlets that make up the image patch with the image patch coordinates (x nm ,y nm ) in image subfield coordinates (p,q). Figure 17f shows the normalized orthogonality SDV(2)≈SQ distributed over the image patch coordinates (x,q) of the image subfields with the image patch dependence shown in Figure 17e. Figure 17g shows the normalized orthogonality SDV(3)≈OR in image subfield coordinates (x,q) for each of the J = 61 beamlets with the normalized rotation shown in Figure 17h. nm ,y nm ) shows the normalized rotation ROT=SDV(4).

[0142] In one example, linear distortion The field dependence of the vector SDV(i) is described by a polynomial expansion of the amplitude A(i;n,m) as follows:

number

number

[0143] Typically, the dominant part of the field dependence of the distortion amplitude is given by a small number of polynomials G (e.g., the parabolic term in the polynomial expansion G). Scanning Distortion is, for example, a 3x4 matrix

number

number

[0144] In the mixing element 641 as shown in FIG. 14, a correction voltage is provided that includes a first component proportional to the scan voltage difference VSp(t) for scanning in a first direction of the p coordinate in the image subfield and a second component proportional to the scan voltage difference VSq(t) for scanning in a second direction of the q coordinate in the image subfield. This compensates for the linear portion of the scan-induced aberration. The drive voltage differences VCAp(t) and VCAq(t) provided by the power lines 609 and 610 can be reduced from the scan voltage differences VSp(t) and VSq(t) depending on the maximum drive voltage difference required to drive the correction element. This compensates for the linear component of the linear image subfield dependence on the image subfield coordinates (p, q). The amplitude of the correction or compensation for each image subfield is provided by, for example, a static programmable resistor array 611, which includes a series of resistors for each compensator or correction electrode. High-order components of the scanning-induced aberrations, which have a high-order dependence on the image subfield coordinates (p,q), can be compensated for by adding another voltage difference component (e.g., a third component (e.g., the product of p and q)) that has a quadratic dependence on the image subfield coordinates (p,q). In one example, the static voltage conversion array further includes a nonlinear voltage reduction unit or nonlinear voltage amplifier that generates a third drive voltage difference VCAp(t) that is proportional to the product of the first and second drive voltage differences VCAp(t) and VCAq(t). An exemplary nonlinear voltage reduction unit includes a source follower transistor having the first drive voltage difference VCAp(t) at its gate and the second drive voltage difference VCAq(t) at its drain, and connected to a deflection electrode with a known capacitance. Another example of a nonlinear voltage conversion unit utilizes the nonlinear response of a Zener diode.

[0145] A similar setup allows for at least one series of resistors per image subfield to be used to determine the image patch coordinates (x ij ,y ij ) can be compensated for. This allows the image patch coordinates (x ij ,y ij ) is compensated for the quadratic or higher order dependence of the maximum image subfield distortion on

[0146] When using a multi-beam charged particle microscope, the scan compensator array 602 operates in a similar manner to compensate for scan decentering errors: the scan-induced decentering errors are similarly expanded in linear components, and the control signals for compensating for the scan-induced decentering errors are derived accordingly.

[0147] A similar method operates the scan compensator array to compensate for scan aberrations such as astigmatism or defocus when using the multi-beam charged particle microscope 1. The scan-induced aberrations are similarly expanded in linear components, and the control signals for the multi-beam astigmatism corrector array or multi-beam lens array to compensate for the scan-induced aberrations are derived accordingly.

[0148] In a similar manner, the correction voltage differences VCp(t) and VCq(t) calibrated for the multiple correction electrodes of the simultaneous multi-beam raster scanner 110 according to the first embodiment can be derived and applied to the multiple correction electrodes of the simultaneous multi-beam raster scanner 110. Scanning Distortion is suppressed by at least 10% (e.g., 20%), e.g., less than 1.5 nm of residual Scan-induced distortion can be realized.

[0149] In a similar manner, the correction voltage differences VCp(t) and VCq(t) calibrated for the plurality of correction electrodes of the collective multi-beam raster scanner 110 according to the first embodiment and the correction voltage differences VCp(t) and VCq(t) calibrated for the plurality of correction electrodes of the collective multi-beam raster scanner 110 according to the second embodiment are Scanning Distortion The deflection voltage differences VCAp(t) and VCAq(t) for the compensator array 601 are both derived, Scanning Distortion Residual Scanning Distortion is suppressed by at least 90% (e.g., 95%), e.g., less than 0.2 nm, preferably less than 0.1 nm. Scan-induced distortion can be realized.

[0150] According to the fifth embodiment, Scanning Distortion a multi-beam charged particle microscope improved to suppress Scanning DistortionThe improved multi-beam charged particle microscope includes a collective multi-beam raster scanner 110 according to the first embodiment, and is configured to perform a predetermined inhomogeneous scanning deflection electrostatic field to: Scanning Distortion The improved multi-beam charged particle microscope 1 further comprises at least a first static simultaneous multi-beam deflection system 701 for adjusting the positions of the plurality of primary charged particle beamlets in the simultaneous multi-beam raster scanner 110 according to the first embodiment. This reduces residual deflection due to misalignment of the simultaneous multi-beam raster scanner 110 with respect to the raster configuration of the plurality of primary charged particle beamlets. Scan-induced distortion FIG. 18 shows an improved multi-beam charged particle microscope 1 in one example. Here, the same reference numerals as in FIG. 1 are used. In addition to the elements shown in FIG. 1, the improved multi-beam charged particle microscope according to the fifth embodiment includes a first static collective deflection system 701 for adjusting the lateral position of the beam crossover 108 relative to the collective multi-beam raster scanner 110 by deflecting the multiple primary charged particle beamlets 3 in the lateral direction (x / y direction). This reduces the risk of light scattering due to lateral displacement of the collective multi-beam raster scanner 110 relative to the multiple primary charged particle beamlets passing through the collective multi-beam raster scanner 110. Scanning Distortion is further suppressed.

[0151] In one example, the improved multi-beam charged particle microscope 1 according to the fifth embodiment further includes a second static collective deflection system 703 for adjusting the average propagation angle of the multiple primary charged particle beamlets relative to the optical axis by deflecting the multiple primary charged particle beamlets in the lateral direction (x / y direction). This prevents the multiple primary charged particle beamlets passing through the collective multi-beam raster scanner 110 from being deflected by a lateral positional deviation of the collective multi-beam raster scanner 110. Scanning DistortionThe first static deflection system 701 and the second static deflection system 703 are connected to a static adjustment control unit 870, which provides a plurality of static voltage differences to adjust the positions and average propagation directions of the plurality of primary charged particle beamlets 3 through the intersection volume 189 of the collective multi-beam raster scanner 110.

[0152] Scanning Distortion is sensitive to the position and propagation angle at which the beamlets propagate through the scanning deflection electrostatic field in the intersection volume. In particular, the optimized simultaneous multi-beam raster scanner 110 according to the first embodiment of the present invention reduces residual Scan-induced distortion is susceptible to misalignment of the simultaneous multi-beam raster scanner 110 with respect to the lateral positions of the beam crossovers 108 of the multiple primary charged particle beamlets 3. Therefore, the lateral positions and propagation angles of the multiple primary charged particle beamlets are adjusted by the first static deflection system 701 and the second static deflection system 703.

[0153] In a method of operating an improved multi-beam charged particle microscope according to a fifth embodiment, residual Scan-induced distortion is measured as described in step 1 of the fourth embodiment. Scanning Distortion is analyzed and the positional deviation Scanning Distortion The static voltages are determined by the adjustment unit 870 and applied to the first static deflection system 701 and the second static deflection system 703, and the residual Scanning Distortion is measured again, and the residual Scanning Distortion is analyzed, and residual misalignment Scanning Distortion The components are determined again. This process eliminates residual misregistration. Scanning Distortion This adjustment method can be repeated during operation of the multi-beam charged particle microscope, for example to compensate for scanning-induced aberrations due to drift of the multi-beam charged particle microscope.

[0154] Due to misalignment Scanning Distortion The typical field of view dependence of is shown in Figure 19. Scanning Distortionis the residual of a perfectly aligned multi-beam charged particle microscope. Scanning Distortion In one example, Scanning Distortion It is possible to determine the sensitivity of the displacement of the element relative to its ideal position with respect to various field dependencies of Scanning Distortion Measurement and Scanning Distortion By determining the field dependence of , it is possible to derive the adjustments required to achieve a perfectly aligned multi-beam charged particle microscope.

[0155] In a sixth embodiment, an improved multi-beam charged particle microscope is provided that includes a collective multi-beam raster scanner 110 capable of lateral displacement or tilt. In one example, the lateral displacement or tilt is achieved by laterally displacing or tilting the deflection electrostatic field with respect to the intersection volume 189 using additional correction electrodes, or by applying multiple predetermined voltage offsets to the deflection electrodes and correction electrodes of the first embodiment of the present invention. In an alternative example, the collective multi-beam raster scanner 110 includes mechanical means, including guide elements or stages, for displacing the deflection electrostatic field with respect to the intersection volume 189, and at least one actuator for adjusting the lateral position or tilt angle of the deflection electrodes and optional correction electrodes.

[0156] Additional means provide lateral displacement and tilt of the inhomogeneous deflection field with respect to the intersection volume 189, thereby realizing adjustment of the inhomogeneous deflection field with respect to the lateral positions and average propagation angles of the multiple primary charged particle beamlets. For example, a method is provided in which a quadrupole or multipole field is generated in the intersection volume 189 in the collective deflection scanner 110. The quadrupole or multipole field can be generated by applying a predetermined voltage difference to the deflection electrodes (e.g., a first identical voltage difference applied to a first deflection electrode for deflection scanning in a first direction and a second identical voltage difference applied to a second deflection electrode for deflection scanning in a second direction). For example, the second voltage difference is given by multiplying the first voltage difference by −1. During alignment or adjustment, the first and second voltage differences for generating the quadrupole or multipole field are changed, and the central primary beamlet traveling along the optical axis 105 of the charged particle microscope 1 is monitored. Then, during the change of the quadrupole or multipole field by changing the first and second voltage difference, the lateral position or tilt angle of the quadrupole or multipole field is changed while the focal position of the central primary beamlet remains unchanged. If the quadrupole or multipole field is centered on the optical axis, the central primary beamlet does not move on the wafer even when the intensity of the quadrupole or multipole field changes. This allows for a residual Scanning Distortion is minimized.

[0157] In a seventh embodiment, an improved multi-beam charged particle microscope is provided, including a combination of the fifth and sixth embodiments, so that the inhomogeneous electrostatic deflection field inside the deflection scanner is adjusted relative to, for example, the objective lens of the multi-beam charged particle microscope by laterally displacing it relative to the intersection volume, for example, by predetermined offset voltages applied to multiple electrodes, thereby compensating for scanning aberrations due to misalignment of the raster scanner 110 and, for example, the objective lens 102, etc. Then, the multiple primary charged particle beamlets are adjusted laterally by the first and second static deflectors relative to the adjusted position of the inhomogeneous electrostatic deflection field distribution.

[0158] According to an embodiment of the present invention, there is provided an improved multi-beam charged particle microscope system 1 and a method for operating the multi-beam charged particle microscope system 1 to perform high precision and high throughput wafer inspection tasks. The improved multi-beam charged particle microscope system 1 for wafer inspection includes: Scanning Distortion The eighth embodiment has means for compensating or correcting scan-induced aberrations, such as scan decenter aberrations, scan induced astigmatism, or the like. In the eighth embodiment, the means of the above-mentioned embodiments are combined to achieve maximum reduction of scan-induced aberrations. A multi-beam charged particle microscope 1 for wafer inspection according to the eighth embodiment is shown in FIG. 20. In the example of the eighth embodiment, additional details of an improved multi-beam charged particle microscope system 1 and method of operation for each of the above-mentioned embodiments are described. The same reference numerals as those in the previous drawings are used, and therefore similar references shall be made to those drawings.

[0159] The multi-beam charged particle microscope 1 for wafer inspection comprises a charged particle multi-beamlet generator 300 for generating a plurality of primary charged particle beamlets 3. The multi-beam charged particle microscope 1 further comprises an object illumination unit 100 comprising a first collective multi-beam raster scanner 110 for scanning each of the plurality of primary charged particle beamlets 3 in each image sub-field across a wafer surface 25 arranged in an object plane 101 to generate a plurality of secondary electron beamlets 9 emitted from the wafer surface 25. The plurality of secondary electron beamlets 9 are imaged by a detection unit 200 and a second collective multi-beam raster scanner 222 for imaging the plurality of secondary electron beamlets 9 onto an image sensor 207 and, in use, for acquiring a digital image of a first image patch 17 of the wafer surface 25. The multi-beam charged particle microscope 1 further comprises a sample stage 500 for positioning and holding the wafer surface 25 in the object plane 101 during acquisition of the digital image of the first image patch 17.

[0160] The multi-beam charged particle microscope 1 comprises a control unit 800. The control unit 800 further comprises an image data acquisition unit 810. In use, the electron sensitive image sensor 207 receives a large image data stream of image sensor data of a plurality of secondary electron intensity values ​​and provides the image data to the image data acquisition unit 810 of the control unit 800. The image data acquisition unit 810 is configured to provide the sensor signal of the image sensor 207 to an image stitching unit 812. Suppression of scanning induced aberrations (e.g. Scan-induced distortion The suppression of the digital image processing enables high-speed image stitching without digital image processing, whereby the digital data from each image sub-field is stitched together to construct a digital image of the image patch at high speed and with low computational load, thereby increasing the throughput of wafer inspection tasks. With the image stitching unit 812 configured for high-speed image stitching without digital image processing, the final digital image is provided directly to the output unit 814 for analysis, for example, of defects or dimensions of semiconductor features.

[0161] The plurality of primary charged particle beamlets 3, in use, propagate through an intersection volume 189 of a first simultaneous multi-beam raster scanner 110 according to a first embodiment of the present invention. A first scanning electrode of the first simultaneous multi-beam raster scanner 110, in use, generates a first scanning deflection electric field distribution in the intersection volume 189 for long-stroke scanning deflection of the plurality of primary charged particle beamlets 3. A second scanning electrode of the first simultaneous multi-beam raster scanner 110, in use, generates a second scanning deflection electric field distribution in the intersection volume for long-stroke scanning deflection of the plurality of primary charged particle beamlets 3 in a second direction or q direction perpendicular to the first direction. The control unit 800 comprises a scanning deflection control module 860 configured to generate scanning deflection voltage differences VSp(t) and VSq(t) for scanning deflection of the plurality of primary charged particle beamlets 3 in the first direction or p direction and in the second direction or q direction. An example of the scanning deflection voltage differences VSp(t) and VSq(t) is shown in FIG.

[0162] The control unit 800 includes a delay line array 862. The scan deflection control module 860 is configured to provide the scan deflection voltage differences VSp(t) and VSq(t) to the delay line array 862, which is configured to generate multiple time-delayed copies of the scan deflection voltage differences VSp(t) and VSq(t). For example, a first copy of the scan deflection voltage difference VSp(t) with a first time delay t1 is provided to the first collective multi-beam raster scanner (110) for scan deflection of the multiple primary charged particle beamlets 3 in a first direction.

[0163] The first simultaneous multi-beam raster scanner 110 further includes a correction element 112 including a plurality of correction electrodes according to the first embodiment, for example, as the correction electrodes 185, 187, 193, or 195 shown in Figures 8 and 10. The correction element 112 corrects the beams of the plurality of primary charged particle beamlets 3 during scanning deflection. Scan-induced distortion 13 and 14. The first simultaneous multi-beam raster scanner 110 is configured to generate a variable inhomogeneity in the deflection electrostatic field distribution in the intersection volume to suppress the deflection. The first simultaneous multi-beam raster scanner 110 further includes a scan correction control module 120 including a static voltage conversion array connected to the scan deflection control module 860 via a delay line in a delay line array 862. The scan correction control module 120 is configured similarly to the scan array control unit 622 of the second embodiment. As mentioned above, the elements and features of the scan array control unit 622 of FIGS. 13 and 14 are similarly applicable to other scan correction elements, such as the correction element 112.

[0164] The delay line array 862 is configured to provide a second copy of the scan deflection voltage differences VSp(t) and VSq(t) having a second time delay t2 to the scan correction control module 120. The scan correction control module 120 further includes a static voltage reduction unit that reduces the second copy of the scan deflection voltage differences VSp(t) and VSq(t) to first correction voltage differences VC1p(t) and VC1q(t) required to produce a predetermined inhomogeneity in the electrostatic field distribution. The first correction voltage difference VC1p(t) is, for example, at least one order of magnitude smaller than the scan deflection voltage difference VSp(t) for scan deflection in the first or p-direction. A static voltage conversion array of the scan correction control module 120 generates multiple correction voltage differences from the first correction voltage differences VC1p(t) and VC1q(t). In one example, the static voltage conversion array is a programmable resistor array as shown in FIGS. 13 and 14. The plurality of correction voltage differences are applied to the plurality of correction electrodes of the correction element 112. The programmable resistor array of the scan correction control module 120 is controlled by a plurality of first static control signals stored in a memory of the scan correction control module 120. During the calibration step, the plurality of first static control signals can be changed by the primary beam path control module 830.

[0165] The delay line array 862 is further configured to provide a third copy of the scanning deflection voltage differences VSp(t) and VSq(t) having a third time delay t3 to the second collective multi-beam raster scanner 222 for scanning the multiple secondary electron beamlets 9. This keeps the beam spots of the secondary electron beamlets 9 constant at the image detector 207.

[0166] The multi-beam charged particle microscope 1 comprises a first scanning array control unit 622.1 according to a second embodiment of the present invention. Scanning DistortionThe first scanning array control unit 622.1 includes a compensator array 601. The first scanning array control unit 622.1 is connected to the scanning deflection control module 860 via a delay line array 862. The delay line array 862 is configured to provide a fourth copy of the scanning deflection voltage differences VSp(t) and VSq(t) having a fourth time delay t4 to the first scanning array control unit 622.1. The first scanning array control unit 622.1 provides the fourth copy of the scanning deflection voltage differences VSp(t) and VSq(t) with a fourth time delay t4. Scanning Distortion A static voltage reduction unit is provided to reduce the second correction voltage differences VC2p(t) and VC2q(t) required to produce a predetermined maximum deflection of the beamlets by the compensator array 601. The second correction voltage difference VC2p(t) is at least two orders of magnitude smaller than the scan deflection voltage difference VSp(t) for scan deflection in the first or p-direction, for example. In the above description, the symbol VCAp(t) is used for VC2p(t).

[0167] The multi-beam charged particle microscope 1 includes a scan compensator array 602 for compensating for scan-induced decentering errors according to a third embodiment of the present invention. The scan compensator array 602 includes a second scan array control unit 622.2. The second scan array control unit 622.2 is connected to a scan deflection control module 860 via a delay line array 862. The delay line array 862 is configured to provide a fifth copy of the scan deflection voltage differences VSp(t) and VSq(t) having a fifth time delay t5 to the second scan array control unit 622.2. The second scan array control unit 622.2 includes a static voltage reduction unit that reduces the fifth copy of the scan deflection voltage differences VSp(t) and VSq(t) to third correction voltage differences VC3p(t) and VC3q(t) required to produce a predetermined maximum correction of the beamlet propagation angle by the scan compensator array 602 for compensating for the scan-induced decentering errors. The third correction voltage difference VC3p(t) is, for example, at least two orders of magnitude smaller than the scan deflection voltage difference VSp(t) for scan deflection in the first or p-direction.

[0168] By providing multiple copies of the scanning deflection voltage differences VSp(t) and VSq(t) with multiple predetermined time delays, e.g. Scanning Distortion Compensator array 601 and decentration aberration scanning compensator array 602 Scan-induced distortion The compensation for the first to fifth time delays t1...t5 is synchronized with the scanning deflection of the multiple charged particle beamlets 3. The first to fifth time delays t1...t5 are determined, for example, during the design of the multi-beam charged particle microscope 1, adjusted in a setup or calibration step, and stored in the delay line array 862.

[0169] The eighth embodiment of the multi-beam charged particle microscope 1 further comprises a first static deflector 701 connected to the primary beam path control module 830 according to the fifth embodiment of the present invention. The static adjustment control unit 870 shown in FIG. 18 can be part of the primary beam path control module 830. In a calibration step, lateral positions of a plurality of primary charged particle beamlets in the first simultaneous multi-beam raster scanner 110 are determined. In use, the multi-beam charged particle microscope 1 is configured to adjust, by the first static deflector 701, the lateral positions of a plurality of primary charged particle beamlets in the intersection volume 189 of the first simultaneous multi-beam raster scanner 110. The multi-beam charged particle microscope 1 comprises a second static deflector 703 connected to the primary beam path control module 830. In a calibration step, the average angles of incidence of a plurality of primary charged particle beamlets in the intersection volume 189 of the first simultaneous multi-beam raster scanner 110 are determined. In use, the multi-beam charged particle microscope 1 is configured to adjust the average angle of incidence of multiple primary charged particle beamlets 3 in the intersection volume 189 of the first collective multi-beam raster scanner 110 by the second static deflector 703.

[0170] The scan correction control module 120 and the first and second scan array control units 622.1 and 622.2 are further connected to a primary beam path control module 830, which provides adjusted static control signals to the static voltage conversion units as described in the fourth embodiment of the present invention, by means of calibration results or other means. The primary beam path control module 830 is connected to a control operation processor 840, which can determine, for example, by means of calibration measurements according to the fourth embodiment, Scan-induced distortion The actual set of static control signals is derived from a calibration step that includes a measurement step of:

[0171] In one example, the image stitching unit 812 is coupled to the control action processor 840 and is configured to derive and provide a stitching quality parameter to the control action processor 840. If the stitching quality parameter is below a predetermined threshold, the control action processor 840: Scan-induced distortion 2. An example of a stitching quality parameter is the image contrast in the overlap area 39 of two adjacent image subfields, as shown in FIG. 2. With scan-induced aberrations kept below, for example, 0.3 nm, preferably below 0.1 nm, image stitching without digital image processing is possible, and image stitching by overlaying digital image data from the two image subfields in the overlap area 39 results in a high image contrast. The image contrast in the overlap area 39 can be affected by residual aberrations, for example due to drift or misalignment of the multi-beam charged particle microscope 1. Scan-induced distortion The image contrast in the overlap area 39 is an example of a stitching quality parameter, which can be used as an indicator of the quality of the compensation or correction of the scan-induced aberrations, and thus as an indicator of, for example, drift or misalignment of the multi-beam charged particle microscope 1. In a calibration step, the scan-induced aberrations are determined for each image sub-field. For example, the control operation processor 840 may, for example, by development as described in the fourth embodiment, Scan-induced distortion [dp,dq](p,q;x ij,y ij ), and a correction element 112 of the collective multi-beam raster scanner 110, Scanning Distortion The control operation processor 840 is configured to derive a plurality of actual static control signals for the compensator array 601, the decentering aberration scanning compensator array 602, the first static multi-beam deflection system 701, and the second static multi-beam deflection system 703. The control operation processor 840 is configured to provide the plurality of actual static control signals to the primary beam path control module 830, which is configured to provide the plurality of actual static control signals to individual compensators or correction elements 112, 601, 602, 701, or 702 of the multi-beam charged particle microscope 1.

[0172] The above-described embodiment is preferably applied to the primary beam path 13 or the plurality of primary charged particle beams 3 to compensate for scan-induced aberrations during scanning. However, an embodiment can also be applied to the secondary beam path 11 to correct, for example, scan-induced contrast variations. Referring now to FIG. 1 , the plurality of secondary electron beamlets are deflection-scanned by a combination of a first simultaneous multi-beam raster scanner 110 and a second simultaneous multi-beam raster scanner 222, and the image contrast is controlled, for example, by an aperture filter 214. Scan-induced aberrations in the secondary beam path 11, such as scan-induced decentering aberrations of the secondary electron beamlets 11, cause scan-induced contrast variations, which can be compensated for by a multi-beam scanning correction system arranged in the secondary beam path 11, for example, at the position of element 220, as in the second or third embodiment.

[0173] The multi-beam charged particle microscope and method of operating the multi-beam charged particle microscope allows, e.g. Scan-induced distortionis compensated for. The collective multi-beam raster scanner (110) defines an intersection volume (189) and is configured to perform collective raster scanning of a plurality of primary beamlets (3) to perform image scanning of an image patch (17). The plurality of primary beamlets includes a first primary beamlet (3.55) scanned across at least a first image subfield (31.55) of the image patch (17) and a second primary beamlet (3.15) synchronously scanned across a second image subfield (31.15). The first primary beamlet traverses the intersection volume (189) at a first angle β1, and the second primary beamlet traverses the intersection volume (189) at a second angle β2 different from the first angle β1. Thus, in conventional raster scanners and methods of operating conventional raster scanners, a time lag between the first and second beamlets is eliminated. Scan-induced distortion A first scanning corrector (601) connected to the control unit (800) determines the difference between the first primary beamlet (3.55) in the first image subfield (31.55) and the second primary beamlet (3.15) in the second image subfield (31.15). Scan-induced distortion The second scanning compensator array 602 for decentration aberrations suppresses the difference. Scan-induced distortion Similarly, the scan-induced decentering difference between the first primary beamlet (3.55) in the first image subfield (31.55) and the second primary beamlet (3.15) in the second image subfield (31.15) is compensated for.

[0174] The first collective raster scanner 110 is configured for a long straw cluster scan of each beamlet over the corresponding image subfield of view with dimensions of about 8 μm to 12 μm (e.g., D=10 μm) and a scan range of ±5 μm. The first scan corrector (601) constitutes a second short straw cluster scanner, which scans each beamlet over a smaller scan range, e.g., up to 5 nm. Scan-induced distortion are corrected individually. Scan-induced distortionis suppressed, and a raster scanning coordinate is realized with an accuracy of more than three orders of magnitude (0.5 nm, preferably 0.3 nm or less) for a scanning coordinate of, for example, 5.0 μm.

[0175] The present invention is of interest for multi-beam charged particle systems where multiple primary charged particle beamlets traverse an intersection volume at different angles. The multi-beam charged particle microscope comprises a multi-beamlet generator for generating multiple primary beamlets. In such a multi-beam charged particle microscope (1), the beamlet generator generates at least first and second primary charged particle beamlets (3.0, 3.1, 3.2), and the first scan corrector, when in use, corrects, for example, the second primary charged particle beamlet (3.1 or 3.2). Scan-induced distortion The multi-beam charged particle microscope further comprises a plurality of deflection elements configured to individually compensate for the primary beamlets. The multi-beam charged particle microscope further comprises an object illumination unit for illuminating a plurality of image sub-fields, which together form an image patch on a surface of a sample arranged in an object plane, with the primary beamlets to generate a plurality of secondary electron beamlets emitted from the surface in use, and a detection unit comprising a projection system and an image sensor for imaging the secondary electron beamlets onto the image sensor and for acquiring a digital image of the image patch on the surface of the sample in use. In one embodiment, the multi-beam microscope for wafer inspection further comprises a simultaneous multi-beam raster scanner. The simultaneous multi-beam raster scanner comprises at least a first set of deflection electrodes and an intersection volume traversed by the primary beamlets between the first set of deflection electrodes. The intersection volume is configured to transmit the primary beamlets incident on the intersection volume at different angles of incidence. The multi-beam charged particle microscope further comprises at least a first scan corrector or compensation element for correcting scan-induced aberrations. The first scanning corrector is configured, in use, to generate a first scanning electrostatic field for affecting at least a first individual beamlet.

[0176] A multi-beam charged particle microscope according to an embodiment of the present invention comprises a beamlet generator for generating a plurality of primary charged particle beamlets and an object illumination unit 100 for illuminating image sub-fields on a surface 25 of a sample 7 arranged in an object plane 101, thereby generating a plurality of secondary electron beamlets 9, which, in use, are emitted from focal points 5 of the primary beamlets 3 in each image sub-field. The sub-fields typically have a lateral extension of at least 5 μm, preferably 8 μm, 12 μm or more. The object illumination unit 100 further comprises first to third electrostatic or magnetic lenses and an objective lens 102. The multi-beam charged particle microscope 1 further comprises a detection unit 200 for acquiring, in use, a digital image of each image sub-field of the surface of the sample. The detection unit 200 comprises an electronic sensor 207 and, optionally, an electrostatic or electromagnetic deflection element 222. The multi-beam charged particle microscope 1 further comprises an electromagnetic beam splitter system 400 for guiding the primary beamlets 3 along the primary beam path 13 and for guiding the secondary beamlets 9 along the secondary beam path 11. The secondary beamlets 9 collected by the objective lens 102 are separated from the primary beamlets 3 by the magnetic beam splitter system 400 as they propagate counter-to-the primary beamlets 3.

[0177] The multi-beam charged particle microscope 1 for wafer inspection according to an embodiment further comprises a long-stroke collective raster scanner 110. The collective raster scanner 110 comprises at least a first set of deflection electrodes (181) and an intersection volume 189 traversed by a plurality of primary charged particle beamlets 3 between the first set of deflection electrodes (181). The charged particle microscope 1 for wafer inspection according to a ninth embodiment further comprises a control unit 800 configured to scan the primary beamlets, in use, over an image subfield of extension greater than 1 μm (e.g., about 8-10 μm), by applying at least a first scanning voltage difference Vsp(t) to the first set of deflection electrodes (181) for generation of a deflection electrostatic field in the intersection volume 189 for long-stroke scanning deflection of the plurality of first primary charged particle beamlets 3 in a first direction or p-direction.

[0178] The multi-beam charged particle microscope 1 further comprises at least a first scan corrector 112 for correcting scan-induced aberrations of the plurality of primary charged particle beamlets 3. The first scan corrector 112 is configured to generate, in use, a first scanning electrostatic field for influencing the plurality of primary beamlets 3, and the control unit 800 is further configured to provide a first scan voltage difference VSp(t) to the first scan corrector 112, the first scan corrector being configured to suppress scan-induced aberrations of at least the first primary charged particle beamlet 3.1. In one example, the first scan corrector 112 comprises a first static voltage conversion unit for converting the first scan voltage difference VSp(t) into at least a first scan correction voltage difference VCp(t), the static voltage conversion unit being configured to generate the first scan correction field by the scan correction electrode 185 in synchronization with the first scan voltage difference VSp(t). As described above, the static voltage conversion unit may include at least one programmable resistor array configured to be programmed by a plurality of static control signals to generate the scan correction voltage difference VCp(t). Accordingly, the first scan corrector 112 is connected to the primary beam path control module 830. In one example, the first static voltage conversion unit is configured to generate the first scan correction voltage difference VCp(t) that is proportional or linearly dependent on the first scan voltage difference VSp(t). To synchronize the correction of scan-induced aberrations, the control unit 800 further includes a delay line array 862 including at least a first delay line configured to synchronize the first scan correction electric field with the long straw cluster scan deflection of the plurality of primary charged particle beamlets 3 by the raster scanner (110). Due to the above-mentioned elements, the first scan corrector 112 comprising at least the first short-stroke deflection element 185 is configured, in use, to compensate for scan-induced aberrations (e.g., scan-induced astigmatism in the amount of about 0.5 nm to 3 nm) to a residual scan-induced astigmatism of less than 0.3 nm, preferably less than 0.2 nm or 0.1 nm.In one example, the first correction element 185 is configured, when in use, to individually compensate for scanning-induced astigmatism of the first primary charged particle beamlet 3.1 in synchronization with the scanning deflection of the first primary charged particle beamlet 1003 by the raster scanner 1110 in the first direction.

[0179] In another example, residual distortions are compensated for: while the long-stroke scanning deflector 110 scans the primary beamlet 3.1 over an image subfield with an extension of more than 1 μm, the first scanning corrector 112, in use, acts like a synchronous short-stroke deflector, Scan-induced distortion Synchronous short-stroke scanning deflection of primary beamlet 3.1 in opposite directions allows for up to approximately 5 nm Scan-induced distortion In one example, the first scan corrector 112, when in use, compensates for the scanning deflection of the first primary charged particle beamlet 3.1 by the collective raster scanner 110 in a first direction, in synchronization with the scanning deflection of the first primary charged particle beamlet 3.1 in a second direction perpendicular to the first direction. Scan-induced distortion and a second correction element 187 configured to individually compensate for

[0180] A multi-beam charged particle microscope 1 with reduced scan-induced aberrations according to a ninth embodiment comprises a long-stroke deflection system 110 for long-stroke deflection of a plurality of primary charged particle beamlets 3 by application of a deflection voltage difference Vsp(t), and a scan correction system for correcting scan-induced aberrations of individual beamlets of the plurality of primary beamlets, which, in use, provides a correction voltage difference Vc(t). The correction voltage difference Vc(t) is generated from the deflection voltage difference Vp(t) by a static voltage conversion unit (e.g., a programmable resistor string or array) controlled by a set of static control signals. This effectively reduces small scan-induced aberrations, e.g., 0.5 nm to 5 nm, to residual aberrations of less than 0.3 nm, preferably less than 0.2 nm or even less than 0.1 nm.

[0181] The present invention and some embodiments may be further described through the use of clauses, but the present invention is not intended to be limited to these clauses.

[0182] Clause 1: A multi-beam charged particle microscope (1) for wafer inspection, a charged particle multi-beamlet generator (300) for generating a plurality of primary charged particle beamlets (3); an object illumination unit (100) for illuminating an image patch (17.1) on a wafer surface (25) arranged in an object plane (101) with a plurality of primary charged particle beamlets (3) to generate, in use, a plurality of secondary electron beamlets (9) emitted from the wafer surface (25); a detection unit (200) comprising a projection system (205) and an image sensor (207) for imaging the plurality of secondary electron beamlets (9) onto the image sensor (207) and, in use, for acquiring a digital image of an image patch (17.1) on the wafer surface (25); a collective multi-beam raster scanner (110) comprising at least a first set of deflection electrodes and an intersection volume (189) traversed in use by a plurality of primary charged particle beamlets (3); a control unit (800) configured, in use, to apply at least a first scan voltage difference VSp(t) to a first set of deflection electrodes for scan deflection of a plurality of primary charged particle beamlets (3) in a first or p-direction; Equipped with A multi-beam charged particle microscope (1), wherein the collective multi-beam raster scanner (110) is configured to generate a predetermined inhomogeneous scanning deflection electric field distribution in the intersection volume (189) for reducing scanning-induced aberrations of a first primary charged particle beamlet entering the intersection volume (189) at an inclination angle β1 deviating from the optical axis of the multi-beam charged particle microscope (1).

[0183] Clause 2: A multi-beam charged particle microscope (1) as described in clause 1, wherein one of the first set of deflection electrodes is composed of two spatially separated electrodes, and the control unit (800) is configured, in use, to apply first and second scanning voltage differences VSp1(t) and VSp2(t) to the two spatially separated electrodes, and the first and second scanning voltage differences VSp1(t) and VSp2(t) are different.

[0184] Clause 3: A multi-beam charged particle microscope (1) as described in clause 1 or 2, wherein the collective multi-beam raster scanner (110) has, when in use, a second set of deflection electrodes for generating a second predetermined inhomogeneous scanning deflection electric field distribution traversed by the multiple primary charged particle beamlets (3) in the intersection volume (189) for scanning deflection of the multiple primary charged particle beamlets (3) in a second direction or q direction, and the control unit (800) is configured, when in use, to apply at least a second scanning voltage difference VSq(t) to the second set of deflection electrodes.

[0185] Clause 4: A multi-beam charged particle microscope (1) as described in Clause 4, wherein the shape and configuration of at least a first set or a second set of deflection electrodes of the collective multi-beam raster scanner (110) are adapted to a cross-section of the intersection volume (189) of the multiple primary charged particle beamlets (3).

[0186] Clause 5: A multi-beam charged particle microscope (1) according to clause 3 or 4, wherein the first set of deflection electrodes and the second set of deflection electrodes have different lengths in the average propagation direction of the plurality of primary charged particles (3).

[0187] Clause 6: A multi-beam charged particle microscope (1) described in any one of clauses 1 to 5, wherein the collective multi-beam raster scanner (110) further comprises a first set of correction electrodes (185, 193) configured to generate, in use, a predetermined scanning correction electric field that contributes to a predetermined inhomogeneous electrostatic field distribution.

[0188] Clause 7: A multi-beam charged particle microscope (1) as described in clause 6, wherein an electrode (185.1, 185.2, 185.3, 185.4) of the first set of correction electrodes is arranged outside the intersection volume (189) in the space between an electrode of the first set of deflection electrodes and an electrode of the second set of deflection electrodes.

[0189] Clause 8: A multi-beam charged particle microscope (1) as described in clause 6 or 7, wherein the collective multi-beam raster scanner (110) further comprises a second set of correction electrodes (187, 195) configured to generate, in use, a predetermined second scanning correction electric field that contributes to a predetermined inhomogeneous electrostatic field distribution.

[0190] Clause 9: A multi-beam charged particle microscope (1) described in any one of clauses 1 to 8, wherein the collective multi-beam raster scanner (110) is configured to adjust the lateral position of a predetermined inhomogeneous scanning deflection electric field distribution relative to the intersection volume, and the control unit (800) is configured, in use, to apply a voltage offset to at least one of the first set of deflection electrodes or the second set of deflection electrodes.

[0191] Clause 10: A multi-beam charged particle microscope (1) described in any one of clauses 1 to 9, further comprising a first static deflection system (701) arranged between the charged particle multi-beamlet generator (300) and the collective multi-beam raster scanner (110) and configured and set to adjust the lateral position of the multiple primary charged particle beamlets (3) relative to the intersection volume (189).

[0192] Clause 11: A multi-beam charged particle microscope (1) described in any one of clauses 1 to 10, further comprising a second static deflection system (701) between the charged particle multi-beamlet generator (300) and the collective multi-beam raster scanner (110), configured and set to adjust the average incidence angle of the multiple primary charged particle beamlets (3) at the entrance side of the intersection volume (189).

[0193] Clause 12: A first scanning array control unit (622.1) is provided with a plurality of deflection elements arranged at a plurality of apertures to compensate for scanning-induced aberrations during image scanning of each of the primary charged particle beamlets (3), and the first scanning array control unit (622.1) is provided with a first static voltage conversion array and configured to apply a plurality of first correction voltage differences to each of the plurality of deflection elements; Scanning Distortion 12. A multi-beam charged particle microscope (1) according to any one of clauses 1 to 11, further comprising a compensator array (601).

[0194] Clause 13: A multi-beam charged particle microscope (1) as described in Clause 12, wherein a first scanning array control unit (622.1) connects a plurality of first correction voltage differences to at least one of the scanning voltage differences VSp(t) or VSq(t) for scanning a plurality of primary charged particle beamlets (3) by the simultaneous multi-beam raster scanner (110).

[0195] Clause 14: A multi-beam charged particle microscope (1) described in any one of clauses 1 to 13, further comprising a scan compensator array (602) for compensating for scan-induced decentering aberrations, the scan compensator array (602) being arranged near the intermediate image plane (321) of the multi-beam charged particle microscope (1) and comprising a plurality of deflection elements arranged in a plurality of apertures to compensate for scan-induced decentering aberrations during image scanning of each primary charged particle beamlet (3), and a second scan array control unit (622.2) comprising a second static voltage conversion array and configured to apply a plurality of second correction voltage differences to each of the plurality of deflection elements.

[0196] Clause 15: A multi-beam charged particle microscope (1) as described in Clause 14, wherein for scanning of multiple primary charged particle beamlets (3) by a simultaneous multi-beam raster scanner (110), multiple second correction voltage differences each include a voltage difference connected to at least one of the scanning voltage differences VSp(t) or VSq(t).

[0197] Clause 16: A multi-beam charged particle microscope (1) for wafer inspection, comprising: a charged particle multi-beamlet generator (300) for generating a plurality of primary charged particle beamlets (3); an object illumination unit (100) for illuminating an image patch (17.1) on a wafer surface (25) arranged in an object plane (101) with a plurality of primary charged particle beamlets (3) to generate, in use, a plurality of secondary electron beamlets (9) emitted from the wafer surface (25); a detection unit (200) comprising a projection system (205) and an image sensor (207) for imaging the plurality of secondary electron beamlets (9) onto the image sensor (207) and, in use, for acquiring a digital image of an image patch (17.1) on the wafer surface (25); a batch multi-beam raster scanner (110); a plurality of apertures arranged in a propagation direction of the plurality of primary charged particle beamlets upstream of the simultaneous multi-beam raster scanner (110), each aperture being configured, in use, to transmit a corresponding one of the plurality of primary charged particle beamlets; Scanning Distortion a compensator array (601), wherein the plurality of apertures comprises a plurality of first deflection elements for individually deflecting each corresponding primary charged particle beamlet in a first direction or p-direction, and a plurality of second deflection elements for individually deflecting each corresponding primary charged particle beamlet in a second direction or q-direction perpendicular to the first direction, each of the plurality of deflection elements being disposed around a respective one of the plurality of apertures; Scanning Distortion a compensator array (601); a control unit (800) configured, in use, to provide at least a first scanning voltage difference VSp(t) to the collective multi-beam raster scanner (110) for scanning deflection of a plurality of primary charged particle beamlets (3) in a first direction or p-direction; Equipped with The multi-beam charged particle microscope (1) further comprises a scanning array control unit (622) including a first static voltage conversion array (611) configured to apply a plurality of first correction voltage differences to a plurality of first deflection elements, and a second static voltage conversion array (612) configured to apply a plurality of second correction voltage differences to a plurality of second deflection elements, in order to compensate for scan-induced aberrations during scan deflection of a plurality of primary charged particle beamlets (3) in a first direction.

[0198] Clause 17: A multi-beam charged particle microscope (1) for wafer inspection as described in Clause 16, wherein a first static voltage conversion array (611) is coupled to the control unit (800) and configured to apply at least a plurality of first voltage difference components to a plurality of first and second deflection elements, respectively, in synchronization with the first scanning voltage difference VSp(t).

[0199] Clause 18: A multi-beam charged particle microscope (1) as described in clause 16 or 17, wherein the control unit (800) is configured, in use, to apply a second scanning voltage difference VSq(t) to the collective multi-beam raster scanner (110) for scanning deflection of the plurality of primary charged particle beamlets (3) in a second direction or q direction.

[0200] Clause 19: A multi-beam charged particle microscope (1) for wafer inspection as described in Clause 18, wherein the first static voltage conversion array (611) and the second static voltage conversion array (612) are coupled to a control unit (800) and configured to apply at least a plurality of second voltage difference components to a plurality of first and second deflection elements, respectively, in synchronization with the second scanning voltage difference VSq(t).

[0201] Clause 20: A multi-beam charged particle microscope (1) for wafer inspection as described in Clause 18 or 19, wherein the first static voltage conversion array (611) is coupled to the control unit (800) and configured to provide at least a first voltage difference component synchronized with the first scanning voltage difference VSp(t) and a second voltage difference component synchronized with the second scanning voltage difference VSq(t) to each of the plurality of first deflection elements.

[0202] Clause 21: A multi-beam charged particle microscope (1) described in any one of clauses 16 to 20, wherein the first or second static voltage conversion array (611, 612) is configured as a programmable resistor array.

[0203] Clause 22: A multi-beam charged particle microscope (1) described in any one of clauses 16 to 21, wherein the collective multi-beam raster scanner (110) comprises at least a first set of deflection electrodes and an intersection volume (189) traversed by a plurality of primary charged particle beamlets (3), and the collective multi-beam raster scanner (110) is configured to generate a predetermined inhomogeneous scanning deflection electric field distribution in the intersection volume (189) for reducing scanning-induced aberrations of the primary charged particle beamlets entering the intersection volume (189) at an inclination angle β deviating from the optical axis of the multi-beam charged particle microscope (1).

[0204] Clause 23: A multi-beam charged particle microscope (1) as described in Clause 22, wherein one of the first set of deflection electrodes is composed of two spatially separated electrodes, and the control unit (800) is configured, in use, to apply first and second scanning voltage differences VSp1(t) and VSp2(t) to the two spatially separated electrodes, and the first and second scanning voltage differences VSp1(t) and VSp2(t) are different.

[0205] Clause 24: A multi-beam charged particle microscope (1) as described in clause 22 or 23, wherein the collective multi-beam raster scanner (110) comprises, when in use, a second set of deflection electrodes for generating a second predetermined inhomogeneous scanning deflection electric field distribution traversed by the multiple primary charged particle beamlets (3) in the intersection volume (189) for scanning deflection of the multiple primary charged particle beamlets (3) in a second direction or q direction.

[0206] Clause 25: A multi-beam charged particle microscope (1) as described in Clause 24, wherein the shape and configuration of at least a first set or a second set of deflection electrodes of the collective multi-beam raster scanner (110) are adapted to the cross section of the intersection volume (189) of the multiple primary charged particle beamlets (3).

[0207] Clause 26: A multi-beam charged particle microscope (1) described in clause 24 or 25, wherein the first set of deflection electrodes and the second set of deflection electrodes have different lengths in the average propagation direction of the multiple primary charged particles (3).

[0208] Clause 27: A multi-beam charged particle microscope (1) described in any one of clauses 16 to 26, wherein the collective multi-beam raster scanner (110) further comprises a first set of correction electrodes (185, 193) configured to generate, in use, a predetermined scanning correction electric field that contributes to a predetermined inhomogeneous electrostatic field distribution.

[0209] Clause 28: A multi-beam charged particle microscope (1) as described in clause 27, wherein an electrode (185.1, 185.2, 185.3, 185.4) of the first set of correction electrodes is arranged in a space between an electrode of the first set of deflection electrodes and an electrode of the second set of deflection electrodes.

[0210] Clause 29: A multi-beam charged particle microscope (1) as described in clause 27 or 28, wherein the collective multi-beam raster scanner (110) further comprises a second set of correction electrodes (187, 195) configured to generate, in use, a predetermined second scanning correction electric field that contributes to a predetermined inhomogeneous electrostatic field distribution.

[0211] Clause 30: A multi-beam charged particle microscope (1) described in any one of clauses 16 to 29, wherein the collective multi-beam raster scanner (110) is configured to adjust the lateral position of a predetermined inhomogeneous scanning deflection electric field distribution relative to the intersection volume, and the control unit (800) is configured, in use, to apply a voltage offset to at least one of the first set of deflection electrodes or the second set of deflection electrodes.

[0212] Clause 31: A multi-beam charged particle microscope (1) described in any one of clauses 16 to 30, further comprising a first static deflection system (701) arranged between the charged particle multi-beamlet generator (300) and the collective multi-beam raster scanner (110) and configured and set to adjust the lateral positions of the multiple primary charged particle beamlets (3) relative to the intersection volume (189).

[0213] Clause 32: A multi-beam charged particle microscope (1) described in any one of clauses 16 to 31, further comprising a second static deflection system (701) between the charged particle multi-beamlet generator (300) and the collective multi-beam raster scanner (110), configured and set to adjust the average incidence angle of the multiple primary charged particle beamlets (3) at the entrance side of the intersection volume (189).

[0214] Clause 33: A multi-beam charged particle microscope (1) described in any one of clauses 16 to 32, further comprising a scan compensator array (602) for compensating for scan-induced decentering aberrations, the scan compensator array (602) being arranged near the intermediate image plane (321) of the multi-beam charged particle microscope (1) and comprising a plurality of deflection elements arranged in a plurality of apertures to compensate for scan-induced decentering aberrations during image scanning of each primary charged particle beamlet (3), and a second scan array control unit (622.2) comprising a second static voltage conversion array and configured to apply a plurality of second correction voltage differences to each of the plurality of deflection elements.

[0215] Clause 34: A multi-beam charged particle microscope (1) described in any one of clauses 16 to 33, further comprising a separate scan compensator array for compensating for scan-induced aberrations, such as scan-induced astigmatism of the focal plane deviation of each beamlet of the plurality of primary charged particle beamlets (3).

[0216] Clause 35: A multi-beam charged particle microscope (1) for wafer inspection, comprising: a charged particle multi-beamlet generator (300) for generating a plurality of primary charged particle beamlets (3); an object illumination unit (100) for illuminating an image patch (17.1) on a wafer surface (25) arranged in an object plane (101) with a plurality of primary charged particle beamlets (3) to generate, in use, a plurality of secondary electron beamlets (9) emitted from the wafer surface (25); a detection unit (200) comprising a projection system (205) and an image sensor (207) for imaging the plurality of secondary electron beamlets (9) onto the image sensor (207) and, in use, for acquiring a digital image of an image patch (17.1) on the wafer surface (25); a collective multi-beam raster scanner (110) comprising at least a first set of deflection electrodes and an intersection volume (189) traversed in use by a plurality of primary charged particle beamlets (3); a control unit (800) configured, in use, to provide at least a first scanning voltage difference VSp(t) to the collective multi-beam raster scanner (110) for scanning deflection of a plurality of primary charged particle beamlets (3) in a first direction or p-direction; a first static deflection system (701) disposed between the charged particle multi-beamlet generator (300) and the collective multi-beam raster scanner (110), and configured to adjust the lateral positions of the plurality of primary charged particle beamlets (3) relative to the intersection volume (189); A multi-beam charged particle microscope (1) comprising:

[0217] Clause 36: A multi-beam charged particle microscope (1) as described in Clause 35, further comprising a second static deflection system (701) between the charged particle multi-beamlet generator (300) and the collective multi-beam raster scanner (110), configured and set to adjust the average incidence angle of the multiple primary charged particle beamlets (3) at the entrance side of the intersection volume (189).

[0218] Clause 37: A charged particle multi-beamlet generator (300), an object irradiation unit (100), a detection unit (200), a collective multi-beam raster scanner (110) for collective raster scanning of a plurality of primary charged particle beamlets (3), and a collective multi-beam raster scanner (110) arranged upstream of the collective multi-beam raster scanner (110) in the propagation direction of the plurality of primary charged particle beamlets. Scanning Distortion A method of operating a multi-beam charged particle microscope (1) comprising a compensator array (601) and a control unit (800), comprising: providing at least a first scan voltage difference VSp(t) to a scan array control unit (622); generating a plurality of voltage difference components from at least the first voltage difference VSp(t) and a plurality of control signals; Multiple voltage difference components Scanning Distortion By providing a plurality of deflection elements of the compensator array (601), each beamlet of the plurality of primary charged particle beamlets is individually scan-deflected, thereby obtaining a plurality of beamlets of the plurality of primary charged particle beamlets (3) during scan-deflection. Scan-induced distortion and compensating for A method for operating a multi-beam charged particle microscope (1), comprising:

[0219] Clause 38: By scanning a plurality of primary charged particles over the image patch of the reference object, a plurality of Scan-induced distortion determining a For each primary charged particle beamlet, multiple Scan-induced distortion extracting a plurality of amplitudes of at least the linear portion of each of the plurality of amplitudes; deriving a plurality of control signals from each of the plurality of amplitudes; Multiple control signals Scanning Distortion providing the scan array control unit of the compensator array (601); 38. A method of operating a multi-beam charged particle microscope (1) according to clause 37, further comprising:

[0220] Clause 39: A multi-beam microscope (1) for wafer inspection, a multi-beamlet generator (300) for generating a plurality of primary beamlets (3) including at least a first individual beamlet; an object illumination unit (100) for illuminating an image patch (17.1) on a surface (25) of a sample arranged in an object plane (101) with a plurality of primary beamlets (3), thereby generating, in use, a plurality of secondary electron beamlets (9) emitted from the surface (25); a detection unit (200) comprising a projection system (205) and an image sensor (207) for imaging the plurality of secondary electron beamlets (9) onto the image sensor (207) and for, in use, acquiring a digital image of an image patch (17.1) on the surface (25) of the sample; a collective multi-beam raster scanner (110) comprising at least a first set of deflection electrodes and an intersection volume (189) traversed by a plurality of primary beamlets (3); at least a first scanning corrector configured to generate, in use, a first electrostatic scanning field for affecting at least a first individual beamlet; a control unit (800) configured, in use, to apply at least a first scanning voltage difference VSp(t) to a first set of deflection electrodes for collective raster scanning of a plurality of primary beamlets (3) in a first or p direction; Equipped with A multi-beam microscope (1), wherein the control unit (800) is further configured to provide a first scan voltage difference VSp(t) to a first scan corrector, and the first scan corrector is configured to suppress scan-induced aberrations of at least a first individual beamlet.

[0221] Clause 40: A multi-beam charged particle microscope (1) as described in Clause 39, wherein the first scan corrector comprises a first static voltage conversion unit for converting the first scan voltage difference VSp(t) into at least a first scan correction voltage difference VCp(t), and configured to generate a first scanning electrostatic field in synchronization with the first scan voltage difference VSp(t).

[0222] Clause 41: A multi-beam charged particle microscope (1) as described in clause 40, wherein the static voltage conversion unit comprises at least one programmable resistor array configured to be programmed by a plurality of static control signals.

[0223] Clause 42: A multi-beam charged particle microscope (1) according to clause 40 or 41, wherein the first static voltage conversion unit is configured to generate a first scan correction voltage difference VCp(t) proportional to the first scan voltage difference VSp(t).

[0224] Clause 43: A multi-beam charged particle microscope (1) described in any one of clauses 39 to 42, wherein the control unit (800) further comprises a first delay line configured to synchronize the first scanning correction field with the collective raster scanning of multiple primary beamlets (3) by the collective multi-beam raster scanner (110).

[0225] Clause 44: The first scanning corrector, when in use, for each of the plurality of primary beamlets (3): Scan-induced distortion 44. A multi-beam charged particle microscope (1) according to any one of clauses 39 to 43, comprising a plurality of deflection elements configured to compensate for

[0226] Clause 45: A plurality of deflection elements, when in use, are adapted to deflect a plurality of primary beamlets (3) in a first direction in synchronization with the scanning deflection of the first individual beamlets (3) by the collective multi-beam raster scanner (110) in the first direction. Scan-induced distortion 45. A multi-beam charged particle microscope (1) according to clause 44, comprising a first deflection element configured to individually compensate for:

[0227] Clause 46: A plurality of deflection elements, when in use, are configured to deflect a plurality of primary beamlets (3) by a collective multi-beam raster scanner (110) in a first direction perpendicular to the second direction, in synchronization with the scanning deflection of the plurality of primary beamlets (3) by the collective multi-beam raster scanner (110) in a second direction perpendicular to the first direction. Scan-induced distortion 46. ​​The multi-beam charged particle microscope (1) according to clause 45, further comprising a second deflection element configured to individually compensate for

[0228] Clause 47: A plurality of deflection elements, when in use, are provided for scanning deflection of a plurality of primary beamlets (3) by a collective multi-beam raster scanner (110) in a perpendicular first direction, and for scanning deflection of a plurality of second individual beamlets in the first direction. Scan-induced distortion 47. The multi-beam charged particle microscope (1) according to clause 45 or 46, further comprising a third deflection element configured to individually compensate for:

[0229] Clause 48: A multi-beam charged particle microscope (1) described in any one of clauses 44 to 47, wherein the static voltage conversion unit comprises a plurality of programmable resistor arrays each connected to a deflection element among the plurality of deflection elements, the plurality of programmable resistor arrays being controlled by a plurality of static control signals and configured, in use, to generate a plurality of scan correction voltage differences VCAp(i,t), each synchronized with the first scan voltage difference VSp(t).

[0230] Clause 49: A multi-beam charged particle microscope (1) described in any one of clauses 39 to 43, wherein the first scan corrector comprises at least one correction electrode configured to contribute to an inhomogeneous electrostatic field distribution generated in the intersection volume (189) of the collective multi-beam deflection system (110) in use, in order to reduce scan-induced aberrations of individual primary beamlets entering the intersection volume (189) at an inclination angle β deviating from the optical axis of the multi-beam particle microscope (1).

[0231] Clause 50: A method of operating a multi-beam charged particle microscope (1), comprising: generating a scan voltage difference VSp(t); a step of simultaneously deflection scanning a plurality of primary beamlets (3) by the simultaneous multi-beam raster scanner (110) in a first direction by applying a scanning voltage difference VSp(t) to the simultaneous multi-beam raster scanner (110); generating at least a first scan correction voltage difference VCp(t) from the scan voltage difference VSp(t) in synchronization with the scan voltage difference VSp(t); - suppressing scan-induced aberrations of at least one individual beamlet of the plurality of primary beamlets (3) by applying a first scan-correction voltage difference VCp(t) to a deflection element of the scan corrector; A method for operating a multi-beam charged particle microscope (1), comprising:

[0232] Clause 51: A method of operating a multi-beam charged particle microscope (1) as described in clause 50, further comprising the step of generating a first scan correction voltage difference VCp(t) by providing a plurality of static control signals to the scan corrector.

[0233] Clause 52: A method for operating a multi-beam charged particle microscope (1) described in clause 50 or 51, further comprising the step of synchronizing the collective raster scanning of multiple primary beamlets (3) and suppressing scanning-induced aberrations of at least one individual beamlet by generating a predetermined time delay between the first scanning correction voltage difference VCp(t) and the scanning voltage difference VSp(t).

[0234] Clause 53: A multi-beam charged particle microscope (1, 1001) for wafer inspection, comprising: a beamlet generator for generating at least a first primary charged particle beamlet (3.0, 3.1, 3.2); an object illumination unit (100) for illuminating an image field of a surface (25) of a sample arranged in an object plane (101) by means of a first primary charged particle beamlet (3.0, 3.1, 3.2); a raster scanner (110) comprising at least a first set of deflection electrodes (153) and an intersection volume (189) traversed by a first primary charged particle beamlet (3.0, 3.1, 3.2); a control unit (800) configured, in use, to apply at least a first scanning voltage difference VSp(t) to a first set of deflection electrodes (153) for a scanning deflection of a first primary charged particle beamlet (3.0, 3.1, 3.2) in a first direction or p-direction across an image field, the image field having a lateral extension of at least 5 μm, preferably 8 μm or more; at least a first scan corrector (601, 185, 193) configured to generate a first scan correction field for influencing a first primary charged particle beamlet (3.0, 3.1, 3.2) in use; Equipped with A multi-beam charged particle microscope (1, 1001), wherein the control unit (800) is further configured to provide a first scan voltage difference VSp(t) to a first scan corrector (601, 185, 193), and the first scan corrector (601, 185, 193) is configured to suppress scan-induced aberrations of the first primary charged particle beamlets (3.0, 3.1, 3.2) in synchronization with scan deflection of the first primary charged particle beamlets (3.0, 3.1, 3.2).

[0235] Clause 54: A multi-beam charged particle microscope (1) as described in Clause 53, wherein the first scan corrector (601, 185, 193) is a static voltage conversion unit for converting the first scan voltage difference VSp(t) into at least a first scan correction voltage difference VCp(t), and is configured to generate a first scan correction electric field in synchronization with the first scan voltage difference VSp(t).

[0236] Clause 55: A multi-beam charged particle microscope (1) according to clause 54, wherein the static voltage conversion unit comprises at least one programmable resistor array configured to be programmed by a plurality of static control signals.

[0237] Clause 56: A multi-beam charged particle microscope (1) according to clause 54 or 55, wherein the static voltage conversion unit is configured to generate a first scan correction voltage difference VCp(t) proportional to the first scan voltage difference VSp(t).

[0238] Clause 57: A multi-beam charged particle microscope (1) described in any one of clauses 53 to 56, wherein the control unit (800) further comprises a first delay line configured to synchronize the raster scanning of the first primary charged particle beamlets (3.0, 3.1, 3.2) by the raster scanner (110) with the first scanning correction field.

[0239] Clause 58: A multi-beam charged particle microscope (1) according to any one of clauses 53 to 57, wherein the first scanning corrector (601, 185, 193) comprises at least a first deflection element configured, in use, to compensate for scanning-induced aberrations of approximately 0.5 nm to 5 nm of the first primary charged particle beamlet (3.0, 3.1, 3.2) to a small amount of less than 0.3 nm, preferably less than 0.2 nm or less than 0.1 nm.

[0240] Clause 59: Scan-induced aberrations are Scan-induced distortion 59. A multi-beam charged particle microscope (1) according to clause 58, wherein:

[0241] Clause 60: the first deflection element, when in use, synchronizes with the scanning deflection of the first primary charged particle beamlets (3.0, 3.1, 3.2) by the raster scanner (110) in the first direction, Scan-induced distortion 59. A multi-beam charged particle microscope (1) according to clause 58 or 59, configured to individually compensate for

[0242] Clause 61: In use, a raster scanner (110) scans and deflects the first primary charged particle beamlets (3.0, 3.1, 3.2) in a first direction, in synchronization with the scan deflection of the first primary charged particle beamlets (3.0, 3.1, 3.2) by the raster scanner (110) in a first direction, and a raster scanner (110) scans and deflects the first primary charged particle beamlets (3.0, 3.1, 3.2) in a second direction perpendicular to the first direction. Scan-induced distortion 61. The multi-beam charged particle microscope (1) of clause 60, further comprising a second deflection element configured to individually compensate for

[0243] Clause 62: A multi-beam charged particle microscope (1) according to clause 58, wherein the scanning-induced aberration is at least one of the group consisting of scanning-induced astigmatism, scanning-induced decentering aberration, scanning-induced spherical aberration, or scanning-induced coma.

[0244] Clause 63: A multi-beam charged particle microscope (1) described in any one of clauses 53 to 62, further comprising a beamlet generator for generating at least a second primary charged particle beamlet (3.1 or 3.2).

[0245] Clause 64: A multi-beam charged particle microscope (1) as described in Clause 63, wherein the first scanning corrector further comprises a third deflection element configured, in use, to individually compensate for scanning-induced aberrations of the second primary charged particle beamlet (3.1 or 3.2).

[0246] Clause 65: A multi-beam charged particle microscope (1) as described in Clause 64, wherein the static voltage conversion unit comprises at least a first programmable resistor array connected to the first deflection element, controlled by a plurality of static control signals, and configured, in use, to generate a scan correction voltage difference VCAp(t) in synchronization with the first scan voltage difference VSp(t).

[0247] Clause 66: A multi-beam charged particle microscope (1) described in any one of clauses 53 to 65, further comprising a second scan corrector (602, 187, 195) configured to suppress second scan-induced aberrations during raster scanning of at least the first primary charged particle beamlet (3.0, 3.1, 3.2) by the raster scanner (110).

[0248] Clause 67: A multi-beam charged particle microscope (1) for wafer inspection, comprising: a multi-beamlet generator (300) for generating a plurality of primary beamlets (3) including at least a first primary beamlet and a second primary beamlet; an object illumination unit (100) for illuminating an image patch (17) on a surface (25) of a wafer disposed in an object plane (101) to generate, in use, a plurality of secondary electron beamlets (9) emanating from the surface (25); a collective multi-beam raster scanner (110) that forms an intersection volume (189), and that is configured to perform a collective raster scan of a plurality of primary beamlets (3) including at least a first primary beamlet (3.55) that is scanned over a first image subfield (31.55) of the image patch (17) and a second primary beamlet (3.15) that is synchronously scanned over a second image subfield (31.15) of the image patch (17); a detection unit (200) comprising a projection system (205) and an image sensor (207), for imaging the plurality of secondary electron beamlets (9) onto the image sensor (207) and for acquiring a digital image during image scanning; A control unit (800) is connected to the control unit (800) and, during image scanning, the first primary beamlet (3.55) in the first image subfield (31.55) and the second primary beamlet (3.15) in the second image subfield (31.15) are connected to the control unit (800). Scan-induced distortion a first scan corrector (601) configured to reduce the difference; A multi-beam charged particle microscope (1) comprising:

[0249] Clause 68: A multi-beam charged particle microscope (1) as described in Clause 67, wherein the first scanning corrector (601), when in use, is configured to generate a plurality of scanning electrostatic fields for influencing a plurality of primary beamlets, including a first scanning electrostatic field for influencing a first primary beamlet (3.55) and a second scanning electrostatic field for individually influencing a second primary beamlet (3.55).

[0250] Clause 69: The first scanning corrector (601), when in use, corrects the first primary beamlet (3.55) Scan-induced distortion and the second of the second primary beamlet (3.15) Scan-induced distortiona plurality of primary beamlets (3) each of which includes a plurality of Scan-induced distortion 69. A multi-beam charged particle microscope (1) according to clause 68, comprising a plurality of deflection elements including a first deflection element and a second deflection element configured to compensate for

[0251] Clause 70: A multi-beam charged particle microscope (1) as described in clause 68 or 69, comprising a scanning array control unit (622) configured, in use, to apply a first scanning voltage difference VSp(t) to the collective multi-beam raster scanner (110), and a first scanning corrector (601) for converting the first scanning voltage difference VSp(t) into a plurality of scanning correction voltage differences VCAp(i,t), and configured, in use, to generate a plurality of electrostatic fields in synchronization with the first scanning voltage difference VSp(t).

[0252] Clause 71: A multi-beam charged particle microscope (1) as described in Clause 70, wherein the scanning array control unit (622) comprises a plurality of static voltage conversion units (611, 612) configured, in use, to generate a plurality of scanning correction voltage differences VCAp(i,t) from the first scanning voltage difference VSp(t).

[0253] Clause 72: A multi-beam charged particle microscope (1) as described in clause 71, wherein the plurality of static voltage conversion units (611, 612) are each configured as a programmable resistor array configured to be controlled by a plurality of static control signals.

[0254] Clause 73: A multi-beam charged particle microscope (1) described in any one of clauses 68 to 72, wherein the control unit (800) further comprises a first delay line configured to synchronize the collective raster scanning of the multiple primary beamlets (3) by the collective multi-beam raster scanner (110) with the multiple scanning electrostatic fields of the first scanning corrector (601).

[0255] Clause 74: The first deflection element, when in use, deflects a first primary beamlet (3.55) in a first direction in synchronism with the scanning deflection of the plurality of primary beamlets (3) by the collective multi-beam raster scanner (110) in the first direction. Scan-induced distortion 74. A multi-beam charged particle microscope (1) according to any one of clauses 69 to 73, configured to individually compensate for:

[0256] Clause 75: The first deflection element, when in use, deflects the first primary beamlet (3.55) in a second direction perpendicular to the first direction in synchronism with the scanning deflection of the plurality of primary beamlets (3) by the collective multi-beam raster scanner (110) in a first direction. Scan-induced distortion 75. The multi-beam charged particle microscope (1) of clause 74, further configured to individually compensate for:

[0257] Clause 76: The second deflection element, when in use, deflects a second primary beamlet in the first direction in synchronization with the scanning deflection of the plurality of primary beamlets (3) by the collective multi-beam raster scanner (110) in the first direction. Scan-induced distortion 76. A multi-beam charged particle microscope (1) according to clause 74 or 75, configured to individually compensate for:

[0258] Clause 77: A multi-beam charged particle microscope (1) described in any one of clauses 67 to 76, wherein, when in use, a first primary beamlet traverses the intersection volume (189) at a first angle β1 and a second primary beamlet traverses the intersection volume (189) at a second angle β2 different from the first angle β1.

[0259] Clause 78: A multi-beam charged particle microscope (1) described in any one of clauses 67 to 77, further comprising a second scan corrector (602) connected to the control unit (800) and configured to suppress, during image scanning, a scan-induced eccentricity difference between the first primary beamlet (3.55) in the first image subfield (31.55) and the second primary beamlet (3.15) in the second image subfield (31.15).

[0260] Clause 79: A method of operating a multi-beam charged particle microscope (1), comprising: generating a scan voltage difference VSp(t); a step of simultaneously deflection scanning a plurality of primary beamlets (3) by the simultaneous multi-beam raster scanner (110) in a first direction by applying a scanning voltage difference VSp(t) to the simultaneous multi-beam raster scanner (110); generating a plurality of scan-corrected voltage differences VCAp(i,t) from the scan voltage differences VSp(t) by a plurality of static voltage conversion units in synchronization with the scan voltage differences VSp(t); By applying a plurality of scan correction voltage differences VCAp(i,t) to a plurality of deflection elements of the scan corrector, the Scan-induced distortion and A method for operating a multi-beam charged particle microscope (1), comprising:

[0261] Clause 80: A method of operating a multi-beam charged particle microscope (1) according to clause 79, further comprising the step of generating a plurality of scan-corrected voltage differences VCAp(i,t) by providing a plurality of static control signals to a plurality of static voltage conversion units.

[0262] Clause 81: Synchronizing collective raster scanning of a plurality of primary beamlets (3) by generating a predetermined time delay between a plurality of scan correction voltage differences VCAp(i,t) and a scan voltage difference VSp(t); Scan-induced distortion 81. A method of operating a multi-beam charged particle microscope (1) according to clause 79 or 80, further comprising the step of suppressing

[0263] Clause 82: By scanning a plurality of primary charged particles over an image patch of a reference object, Scan-induced distortion determining a For each primary charged particle beamlet, Scan-induced distortion extracting a plurality of amplitudes of at least the linear portion of deriving a plurality of static control signals from each of the plurality of amplitudes; A method for operating the multi-beam charged particle microscope (1) according to clause 79, further comprising

[0264] Clause 83: A multi-beam charged particle microscope (1) for wafer inspection, A first long-stroke raster scanner (110) for performing a raster scan of a plurality of primary charged particle beamlets (3) including at least a first primary beamlet (3.0, 3.1, 3.2), configured to collectively scan and deflect each of the plurality of primary charged particle beamlets (3) over a scanning range corresponding to an extension D = 5 μm to 12 μm of an image sub-field (31) on a wafer surface (25), the first long-stroke raster scanner (110); A second short-stroke raster scanner (601) configured to individually correct the scan-induced aberration of each primary charged particle beamlet including the first primary beamlet (3.0, 3.1, 3.2), the scan-induced aberration being introduced during the collective scan deflection by the first long-stroke raster scanner (110), the second short-stroke raster scanner (601); A control unit (800) configured to synchronize the second short-stroke raster scanner (601) with the scan deflection of the first long-stroke raster scanner (110) for individual correction of the scan-induced aberrations; A multi-beam charged particle microscope (1) comprising

[0265] Clause 84: The scan-induced aberration is Scanning Distortion where the second short-stroke raster scanner (601) is configured to scan and deflect each primary beamlet over the entire scanning range corresponding to a maximum Scanning Distortion rm (|rm| < D / 1000), the multi-beam charged particle microscope (1) according to clause 83.

[0266] Clause 85: The charged particle microscope (1) described in Clause 83 or 84, wherein the charged particle microscope (1) comprises a third short straw cluster scanner (602) for performing scan correction of scan-induced decentering aberrations, the third short straw cluster scanner (602) being configured to correct scan-induced decentering aberrations introduced during scan deflection of the multiple primary beamlets (3) by the first long straw cluster scanner (110), and the control unit (800) is configured to synchronize the third short straw cluster scanner (602) with the scan deflection of the multiple primary beamlets by the first long straw cluster scanner (110) and the scan correction of scan-induced aberrations by the second short straw cluster scanner (601).

[0267] Clause 86: A multi-beam charged particle microscope (1) described in any one of clauses 83 to 85, further comprising at least one scanning array control unit (622) for converting the scanning voltage difference VSp(t) into a plurality of scanning correction voltage differences VCAp(i,t) to perform scanning correction of scanning-induced aberrations.

[0268] Clause 87: A multi-beam charged particle microscope (1) as described in clause 86, wherein the scanning array control unit (622) comprises a plurality of static voltage conversion units (611, 612) configured, in use, to generate a plurality of scanning correction voltage differences VCAp(i,t) from the first scanning voltage difference VSp(t).

[0269] Clause 88: A multi-beam charged particle microscope (1) as described in clause 87, wherein the plurality of static voltage conversion units (611, 612) are each configured as a programmable resistor array configured to be controlled by a plurality of static control signals.

[0270] Clause 89: A multi-beam charged particle microscope (1) described in any one of clauses 83 to 88, further comprising a beamlet generator (300) for generating a plurality of primary beamlets (3) and an object illumination unit (100) for irradiating a plurality of image patches (17) of a surface (25) of an object (7) arranged in the object plane (101) to generate a plurality of secondary electron beamlets (9) emitted from the surface (25) when in use.

[0271] Clause 90: A charged particle beam microscope (1) as described in Clause 89, wherein the beamlet generator (300) is configured to generate at least a second primary beamlet, the first long straw cluster scanner (110) is configured to collectively scan and deflect at least each of the first and second primary beamlets over an entire scanning range corresponding to the extension D of the image subfield on the wafer surface, and the second short straw cluster scanner (601) is configured to individually correct scanning-induced aberrations of the first and second primary beamlets.

[0272] Clause 91: A charged particle beam microscope (1) described in any one of clauses 83 to 90, comprising a projection system (205) and an image sensor (207), for imaging a plurality of secondary electron beamlets (9) onto the image sensor (207), and further comprising a detection unit (200) for acquiring a digital image during image scanning.

[0273] As will be apparent from the above description, combinations and various modifications of the above examples and embodiments are possible and are equally applicable to the above embodiments or examples. The charged particles of the primary beam can be, for example, electrons, but can also be other charged particles, such as He ions. Secondary electrons include secondary electrons in the strict sense as well as any other secondary charged particles generated by the interaction of the primary charged particle beamlet with the sample, such as backscattered electrons or second secondary electrons generated by backscattered electrons. In another example, secondary ions can be collected instead of secondary electrons. [Explanation of symbols]

[0274] 1. Multi-beam charged particle microscope system 3 Primary charged particle beamlets (composed of multiple primary charged particle beamlets) 5 Primary charged particle beam spot 7 Object 9 Secondary electron beamlets (composed of multiple secondary electron beamlets) 11 Secondary electron beam path 13 Primary beam path 15 Secondary charged particle image spot 17 Elephant Patch 19 Image patch overlap area 21 Image patch center position 25 Wafer surface 27 Primary beamlet scanning path 29 Center of image subfield 31 Image subfield 33 First Examination Site 35 Second Test Site 39 Superimposed area of ​​subfield 31 100 Object Irradiation Unit 101 Object or image plane 102 Objective Lens 103 Field of view lens group 105 Optical axis of multi-beam charged particle microscope system 108 First beam crossover 110 First multi-beam raster scanner 112 Correction element for multi-beam raster scanner 120 Scanning Correction Control Module 141 Example of primary beam spot position 143 Static displacement vector of the primary beam spot 150 central beamlets 151 Real beamlet trajectories 153 Deflection electrode 155 Equipotential lines of electrostatic potential 157 Off-axis or field of view beamlets 159 Virtual common pivot point 161 Virtual pivot point 163 Primary beam path 171 Scanner 110 Front-end System 173 Linear curve 175 Voltage difference as a function of deflection angle 177 Voltage difference as a function of deflection angle applied to deflection electrodes consisting of multiple pairs of electrodes 179 Offset voltage as a function of deflection angle applied to deflection electrodes consisting of multiple pairs of electrodes 181 deflection electrode for deflection in a first direction 183 Deflection electrodes for deflection in a second direction 185 first set of correction electrodes 187 Second set of correction electrodes 189 Intersection Volume of Transverse Beams 190 Inner area of ​​intersection volume 191 Asymmetric Direction 193 first set of correction electrodes 195 Second set of correction electrodes 197 Linear Dependence Lines 200 detection units 205 Projection system 206 Electrostatic Lens 207 Image Sensor 208 Imaging Lens 209 Imaging Lens 210 Imaging Lens 212 Second Crossover 214 Aperture Filter 216 Active Elements 218 Third deflection system 220 Multi-aperture corrector 222 Second deflection system 300 Charged Particle Multi-Beamlet Generator 301 Charged Particle Source 303 Collimator Lens 305 Primary Multibeamlet Configuration Unit 306 Active Multi-Aperture Plate 307 First Field Lens 308 Second Field Lens 309 Electron Beam 311 Primary electron beamlet spot 321 Intermediate image plane 390 Beam Steering Multi-Aperture Plate 400 Beam Splitter Unit 420 Magnetic Elements 500 sample stage 503 Sample Voltage Source 601 first scan corrector or Scanning Distortion Compensator Array 602 Second Scan Corrector or Decentering Aberration Scan Compensator Array 607 Conductive Line 609 First Power Line 610 Second Power Line 611 first voltage conversion unit 612 Second voltage conversion unit 613 first plurality of conductive lines 614 second plurality of conductive lines 615 first plurality of control signals 616 second plurality of control signals 618 Connection signal line 620 Multi-Aperture Plate 622 Scanning Array Control Unit 624 clock line 626 Operation Control Memory 631 Data or voltage connection line 633 resistor string 635 first set of control signals 637 Second Set of Control Signals 639 Transistor Array 641 Voltage Combiner 681 Electrode 685 One or more apertures 687 Electrode for deflection in the first direction 688 Electrode for deflection in second direction 701 First static multi-beam deflection system 703 Second static multi-beam deflection system 800 Control Unit 810 Image Data Acquisition Unit 812 Image Stitching Unit 814 Image data output 820 Projection System Control Module 830 Primary Beam Path Control Module 840 Control Action Processor 860 Scan Deflection Control Module 862 Delay Line Array 870 Static Adjustment Control Unit

Claims

1. A multi-beam charged particle microscope (1) for wafer inspection, comprising: a charged particle multi-beamlet generator (300) for generating a plurality of primary charged particle beamlets (3); an object illumination unit (100) for illuminating an image patch (17.1) on a surface (25) of an object (7) arranged in an object plane (101) with the plurality of primary charged particle beamlets (3), thereby generating, in use, a plurality of secondary electron beamlets (9) emitted from the surface (25); a detection unit (200) comprising a projection system (205) and an image sensor (207) for imaging the plurality of secondary electron beamlets (9) onto the image sensor (207) and, in use, for acquiring a digital image of the image patch (17.1) on the wafer surface (25); a collective multi-beam raster scanner (110) positioned near a crossover of the plurality of primary charged particle beamlets (3); a scanning distortion compensator array (601) arranged in a propagation direction of the plurality of primary charged particle beams upstream of the simultaneous multi-beam raster scanner (110), the scanning distortion compensator array (601) comprising a plurality of apertures, each of the plurality of apertures configured to transmit a corresponding primary charged particle beamlet (3.0, 3.1, 3.2) of the plurality of primary charged particle beamlets (3), in use, the plurality of apertures comprising a plurality of first deflection elements for individually deflecting each corresponding primary charged particle beamlet (3.0, 3.1, 3.2) in a first direction or p-direction, and a plurality of second deflection elements for individually deflecting each corresponding primary charged particle beamlet (3.0, 3.1, 3.2) in a second direction or q-direction perpendicular to the first direction, each of the plurality of deflection elements being arranged around a respective one of the plurality of apertures; a control unit (800) configured, in use, to provide at least a first scanning voltage difference Vsp(t) to the collective multi-beam raster scanner (110) for scanning deflection of the plurality of primary charged particle beamlets (3) in the first direction or p-direction; Equipped with the collective multi-beam raster scanner (110) comprises at least a first set of deflection electrodes for generating an electrostatic field and an intersection volume (189) traversed by the plurality of primary charged particle beamlets (3); the plurality of primary charged particle beamlets (3) are incident on the intersection volume (189) at different tilt angles β deviating from the optical axis of the multi-beam charged particle microscope (1); the electrostatic field has a finite thickness, and due to the finite thickness, path lengths through the electrostatic field are different for incident beamlets with different tilt angles β, and the different path lengths cause beam paths to deviate from an ideal primary beam path when deflected within the electrostatic field, and the different beam paths cause deflection angles to deviate from a deflection angle of the ideal beam path, thereby resulting in scan-induced distortions caused by the simultaneous multi-beam scanning scanner; the scan distortion compensator array (601) further comprises a scan array control unit (622) including: a first static voltage conversion array (611) configured to apply a plurality of first correction voltage differences to the plurality of first deflection elements; and a second static voltage conversion array (612) configured to apply a plurality of second correction voltage differences to the plurality of second deflection elements to compensate for the scan-induced distortion during the scan deflection of the plurality of primary charged particle beamlets (3) in the first direction; The first or second static voltage conversion array (611, 612) is configured as a programmable resistor array. Multibeam charged particle microscope (1).

2. 2. The multi-beam charged particle microscope (1) for wafer inspection according to claim 1, wherein the first static voltage conversion array (611) is coupled to the control unit (800) and configured to provide at least a plurality of first voltage difference components to each of the plurality of first and second deflection elements in synchronization with the first scanning voltage difference VSp(t).

3. 3. A multi-beam charged particle microscope (1) as described in claim 1 or 2, wherein the control unit (800) is configured, in use, to apply a second scanning voltage difference VSq(t) to the simultaneous multi-beam raster scanner (110) for scanning deflection of the plurality of primary charged particle beamlets (3) in a second direction or q direction.

4. 4. The multi-beam charged particle microscope (1) for wafer inspection according to claim 3, wherein the first static voltage conversion array (611) and the second static voltage conversion array (612) are coupled to the control unit (800) and configured to apply at least a plurality of second voltage difference components to the plurality of first and second deflection elements, respectively, in synchronization with the second scanning voltage difference VSq(t).

5. 5. A multi-beam charged particle microscope (1) for wafer inspection as described in claim 3 or 4, wherein the first static voltage conversion array (611) is coupled to the control unit (800) and is configured to provide at least a first voltage difference component synchronized with the first scanning voltage difference VSp(t) and a second voltage difference component synchronized with the second scanning voltage difference VSq(t) to each of the plurality of first deflection elements.

6. A multi-beam charged particle microscope (1) according to any one of claims 1 to 5, wherein the simultaneous multi-beam raster scanner (110) is configured to generate a predetermined inhomogeneous scanning deflection electric field distribution in the intersection volume (189) for reducing scanning-induced aberrations of primary charged particle beamlets entering the intersection volume (189) at an inclination angle β deviating from the optical axis of the multi-beam charged particle microscope (1).

7. 7. The multi-beam charged particle microscope (1) of claim 6, wherein a deflection electrode of the first set of deflection electrodes consists of two spatially separated electrodes, and wherein the control unit (800) is configured, in use, to apply first and second scanning voltage differences VSp1(t) and VSp2(t) to the two spatially separated electrodes, the first and second scanning voltage differences VSp1(t) and VSp2(t) being different.

8. 8. The multi-beam charged particle microscope (1) of claim 6 or 7, wherein the collective multi-beam raster scanner (110) comprises a second set of deflection electrodes for generating, in use, a second predetermined inhomogeneous scanning deflection electric field distribution traversed by the plurality of primary charged particle beamlets (3) in the intersection volume (189) for scanning deflection of the plurality of primary charged particle beamlets (3) in a second direction or q direction.

9. 9. The multi-beam charged particle microscope (1) of claim 8, wherein the shape and configuration of the at least first set or second set of deflection electrodes of the simultaneous multi-beam raster scanner (110) are adapted to the cross-section of the intersection volume (189) of the multiple primary charged particle beamlets (3).

10. 10. The multi-beam charged particle microscope (1) according to claim 8 or 9, wherein in the mean propagation direction of the plurality of primary charged particles (3), the first set of deflection electrodes and the second set of deflection electrodes have different lengths.

11. A multi-beam charged particle microscope (1) according to any one of claims 6 to 10, wherein the collective multi-beam raster scanner (110) further comprises a first set of correction electrodes (185, 193) configured to generate, in use, a predetermined scanning correction field that contributes to the predetermined inhomogeneous electrostatic field distribution.

12. 12. The multi-beam charged particle microscope (1) according to claim 11, wherein an electrode (185.1, 185.2, 185.3, 185.4) of the first set of correction electrodes is arranged in a space between an electrode of the first set of deflection electrodes and an electrode of the second set of deflection electrodes.

13. 12. The multi-beam charged particle microscope (1) of claim 10 or 11, wherein the collective multi-beam raster scanner (110) further comprises a second set of correction electrodes (187, 195) configured to generate, in use, a predetermined second scanning correction field that contributes to the predetermined inhomogeneous electrostatic field distribution.

14. 14. The multi-beam charged particle microscope (1) of any one of claims 1 to 13, wherein the collective multi-beam raster scanner (110) is configured to adjust the lateral position of the predetermined inhomogeneous scanning deflection electric field distribution relative to the intersection volume, and wherein the control unit (800) is configured, in use, to apply a voltage offset to at least one of the first set of deflection electrodes or the second set of deflection electrodes.

15. A multi-beam charged particle microscope (1) according to any one of claims 1 to 14, further comprising a first static deflection system (701) arranged between the charged particle multi-beamlet generator (300) and the simultaneous multi-beam raster scanner (110), configured and set to adjust the lateral positions of the plurality of primary charged particle beamlets (3) relative to the intersection volume (189).

16. A multi-beam charged particle microscope (1) according to any one of claims 1 to 15, further comprising a second static deflection system (701) arranged between the charged particle multi-beamlet generator (300) and the simultaneous multi-beam raster scanner (110), configured and set to adjust the average angle of incidence of the plurality of primary charged particle beamlets (3) at the entrance side of the intersection volume (189).

17. 17. The multi-beam charged particle microscope (1) according to claim 1, further comprising a scan compensator array (602) for compensating for scan-induced decentering aberrations, the scan compensator array (602) being arranged near an intermediate image plane (321) of the multi-beam charged particle microscope (1) and comprising: a plurality of deflection elements arranged at a plurality of apertures to compensate for scan-induced decentering aberrations during image scanning of each of the primary charged particle beamlets (3); and a second scan array control unit (622.2) comprising a second static voltage conversion array and configured to apply a plurality of second correction voltage differences to each of the plurality of deflection elements.

18. The multi-beam charged particle microscope (1) according to any one of claims 1 to 17, further comprising a further scan compensator array for compensation of scan-induced aberrations, such as scan-induced astigmatism or focal plane deviation, of each beamlet of the plurality of primary charged particle beamlets (3).

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