Patent Publication Number: US-2023133404-A1

Title: Method of inspecting a sample, and multi-electron beam inspection system

Description:
FIELD 
     The present disclosure relates to a method and a system for inspecting a sample with charged particle beams. More specifically, embodiments described herein relate to the inspection of a sample with a plurality of electron beams in parallel. Particularly, embodiments relate to methods of inspecting a sample with a multi-electron beam inspection system, and to multi-electron beam inspection systems for the fast inspection of samples with a high resolution, e.g. for inspecting semiconductor wafers or other substrates. 
     BACKGROUND 
     Charged particle beam devices, particularly electron microscopes, have many functions in a plurality of industrial fields, including, but not limited to, critical dimensioning of semiconductor devices during manufacturing, defect review of semiconductor devices, inspection and imaging of semiconductor devices, exposure systems for lithography, detecting devices and testing systems, such as electron beam inspection systems. Thus, there is a high demand for structuring, testing, and inspecting samples within the micrometer and nanometer scale. 
     Micrometer and nanometer scale process control, inspection or structuring is often done with charged particle beams, particularly with electron beams, which are generated and focused in charged particle beam devices, such as electron microscopes. Charged particle beams offer superior spatial resolution compared to, e.g., photon beams, due to the short wavelengths. 
     In many applications, a sample is inspected to monitor the quality of the sample. For example, wafers or glass substrates on which layers of coating material and/or electronic devices are deposited are manufactured for the display market or for producing electronic chips or integrated die packages. Since defects may occur during the processing of the samples, e.g. during the coating, an inspection of the samples for reviewing the defects and for monitoring the quality may be beneficial. Additionally, the size, shape and relative location of structures created by any patterning process needs to be monitored and controlled. 
     Inspecting samples with a high resolution within the nanometer range, e.g. with a scanning electron microscope, is time consuming. In order to increase the sample throughput, only selected areas of the sample may be inspected, e.g. areas that on average include more defects than others. Alternatively, only random sub-portions of samples may be inspected for increasing the throughput. 
     Another approach for increasing the throughput is the parallel inspection of a sample with several electron beams at the same time. For example, a multi-electron beam inspection system may include several inspection columns for inspecting a sample at a higher speed, though typically with a reduced resolution. 
     Samples are typically inspected by scanning one or more electron beams of a scanning electron microscope (SEM) system over a sample surface with scan deflectors, followed by a movement of the sample to position another part of the sample in the field of view of the SEM. However, SEMs with scan deflectors are complex, large and expensive devices. 
     In view of the above, it would be highly beneficial to provide electron beam inspection methods and systems for quickly and reliably inspecting samples with a high resolution, such as wafers or large-area substrates. 
     SUMMARY 
     In light of the above, a method of inspecting a sample with a multi-electron beam inspection system, and multi-electron beam inspection systems are provided. Further aspects, advantages and features of the present disclosure are apparent from the description and the accompanying drawings. 
     According to one aspect, a method of inspecting a sample is provided. The method includes: placing the sample on a movable stage extending in an X-Y-plane; generating a plurality of electron beams propagating toward the sample; focusing the plurality of electron beams on the sample at a plurality of probe positions arranged in a two-dimensional array; scanning the sample by moving the movable stage in a predetermined scanning pattern while maintaining the plurality of electron beams stationary; and detecting signal electrons emitted from the sample during the scanning for inspecting the sample. In some embodiments, the plurality of electron beams may propagate essentially parallel to each other toward the sample. 
     According to another aspect, a multi-electron beam inspection system is provided. The multi-electron beam inspection system is configured to carry out the sample inspection methods described herein. In particular, the multi-electron beam inspection system may include a movable stage extending in an X-Y-plane for placing the sample thereon, and a plurality of inspection columns for generating a plurality of electron beams and configured to focus the plurality of electron beams on the sample at a plurality of probe positions arranged in a two-dimensional array. The plurality of inspection columns respectively include a beam emitter, a focusing lens, and a detector for detecting signal electrons. The multi-electron beam inspection system further includes a stage controller configured to move the movable stage in a predetermined scanning pattern during an inspection of the sample while maintaining the plurality of electron beams stationary. In some embodiments, the plurality of inspection columns may be configured for generating the plurality of electron beams such that the electron beams propagate essentially parallel to each other toward the sample. 
     The plurality of inspection columns may be static electron beam microcolumns without scan deflectors, configured to provide static electron beams while the movable stage is moved in a scanning pattern for scanning the sample. 
     According to another aspect, a multi-electron beam inspection system is provided. The system includes a plurality of inspection columns without scan deflectors, being arranged in a two-dimensional array in X- and Y-directions and facing toward a movable stage for placing the sample thereon, and a stage controller configured to move the movable stage in a predetermined scanning pattern in an X-Y-plane. 
     Embodiments are also directed at assemblies for carrying out the disclosed methods and include assembly parts for performing each described method aspect. These method aspects may be performed by way of hardware components, a computer programmed by appropriate software, and any combination of the two or in any other manner. Furthermore, embodiments according to the disclosure are also directed at methods for operating the described assemblies and methods of manufacturing the described systems. The methods for operating the described assembly include method aspects for carrying out every function of the assembly. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       So that the manner in which the above recited feature of the present disclosure can be understood in detail, a more particular description of the disclosure, briefly summarized above, may be had by reference to embodiments, some of which are illustrated in the appended drawings. It is to be noted, however, that the appended drawings illustrate only exemplary embodiments and are therefore not to be considered as limiting. A full and enabling disclosure to one of ordinary skill in the art is set forth more particularly in the remainder of the specification including reference to the accompanying drawings wherein: 
         FIG.  1    is a schematic sectional view of a multi-electron beam inspection system according to embodiments described herein; 
         FIG.  2 A  is a schematic top view of a multi-electron beam inspection system according to embodiments described herein; 
         FIG.  2 B  shows a sample to be inspected for illustrating an inspection method described herein; 
         FIG.  3    shows a schematic sectional view of an inspection column of a multi-electron beam inspection system according to embodiments described herein; and 
         FIG.  4    shows a flow chart illustrating a method of inspecting a sample with a multi-electron beam inspection system according to embodiments described herein. 
     
    
    
     DETAILED DESCRIPTION 
     Reference will now be made in detail to the various exemplary embodiments, one or more examples of which are illustrated in each figure. Each example is provided by way of explanation and is not meant as a limitation. For example, features illustrated or described as part of one embodiment can be used on or in conjunction with other embodiments to yield yet further embodiments. The intention is that the present disclosure includes such modifications and variations. 
     Within the following description of the drawings, the same reference numbers refer to the same components. Only the differences with respect to the individual embodiments are described. The structures shown in the drawings are not necessarily depicted true to scale but rather serve the better understanding of the embodiments. 
     Embodiments described herein relate to multi-electron beam inspection systems for inspecting a sample with a plurality of electron beams in parallel. In multi-electron beam inspection systems, a plurality of primary electron beams or beamlets is generated and focused on the sample that is to be inspected. Signal electrons are emitted from the sample when the primary electron beams hit the sample surface. The signal electrons are detected with one or more detectors for obtaining spatial information about the sample. The sample can be imaged or otherwise inspected. 
     Signal electron detection may encompass the detection of secondary electrons (SE), i.e. signal electrons generated at the sample when being hit by the primary electrons (PE), and/or the detection of backscattered electrons (BSE), i.e. primary electrons backscattered from the sample at various scattering angles. Whereas secondary electrons may typically be low-energy electrons in an energy range of several eV up to a few tens of eV, backscattered electrons may have particle energies of several keV, e.g. between 1 keV and 30 keV or more. 
     In typical multi-electron beam inspection systems, the primary electron beams are scanned over the sample surface with scan deflectors arranged in respective inspection columns. However, a multi-electron beam inspection system with a plurality of scanning electron microscopes is typically complex and expensive, and the individual scanning electron microscopes are space-consuming. For this reason, such systems typically include only a limited number of inspection columns, which in turn limits the increase of inspection speed. 
     In modern electron beam inspection systems, it is becoming increasingly important to inspect samples, e.g. semiconductor wafers, very fast, accurately and with a high resolution. These objectives can be achieved with a multi-electron beam inspection system according to embodiments described herein. 
       FIG.  1    shows a schematic sectional view of a multi-electron beam inspection system  100  for inspecting a sample  10  (hereinafter referred to as “system  100 ”) according to embodiments described herein. The system  100  includes a movable stage  110  for placing the sample  10  thereon and a plurality of inspection columns  130 . A sample support surface of the movable stage  110  extends in an X-Y-plane. Accordingly, if a flat sample, e.g., a wafer or a glass substrate, is placed on the movable stage  110 , a main surface of the sample  10  extends in the X-Y-plane, and the plurality of inspection columns  130  face toward the sample. The movable stage  110  is movable in the X-Y-plane in two transverse directions, e.g. in an X-direction (exemplarily illustrated as a horizontal direction in  FIG.  1   ) and in a Y-direction (exemplarily illustrated as a direction perpendicular to the paper plane of  FIG.  1   ) perpendicular to the X-direction. Alternatively or additionally, the movable stage  110  may be rotatable, such that the sample can be rotated around an axis (θ-movement). 
     The movable stage  110  may additionally also be movable in a Z-direction, i.e. toward and away from the plurality of inspection columns  130 , e.g. in order to place the sample surface in a focal plane of the plurality of inspection columns  130  or in order to adapt the working distance of the system. 
     The plurality of inspection columns  130  are configured to generate a plurality of electron beams  105 . As is schematically depicted in  FIG.  1   , the plurality of electron beams  105  propagate essentially parallel to each other toward the sample  10  that is placed on the movable stage  110 . Each of the plurality of inspection columns  130  defines an optical axis  138  along which a respective one of the plurality of electron beams propagates toward the sample  10 . The system  100  is configured for focusing the plurality of electron beams on the sample at a plurality of probe positions  106 , the probe position  106  being arranged in a two-dimensional array. 
     In the sectional view of  FIG.  1   , only probe positions arranged next to each other in the X-direction are shown. However, it is to be understood that the two-dimensional array that is formed by the plurality of probe positions  106  on the sample extends in two transverse directions in the X-Y-plane, as is schematically depicted in  FIG.  2 A . 
     In particular, the plurality of inspection columns  130  may be arranged in a two-dimensional array extending in two transverse directions, as is schematically shown in  FIG.  2 A  showing the system in a top view. A “two-dimensional array” as used herein may be understood as an array of inspection columns in which the inspection columns, in sectional planes perpendicular to the optical axis  138 , are not only arranged next to each other along one single line (“one-dimension array”), but along two or more adjacent lines or in another two-dimensional pattern of inspection columns. Accordingly, the plurality of probe positions  106  where the electron beams generated in the plurality of inspection columns  130  impinge on the sample form a two-dimensional pattern of beam spots on the sample surface in the X-Y-plane (see  FIG.  2 A ). 
     Returning back to  FIG.  1   , each inspection column of the plurality of inspection columns  130  may include a beam emitter  131  for providing an electron beam, a focusing lens  132  for focusing the electron beam on the sample at a probe position, and a detector  133  for detecting signal electrons emitted by the sample when the electron beam impinges on the sample. 
     In typical embodiments, the plurality of inspection columns  130  do not include any scan deflectors for scanning the electron beams over the sample surface during the sample inspection. Inspection columns  130  described herein can therefore also be referred to as “static electron beam microcolumns”, which is different from conventionally used scanning electron beam columns. A static electron beam microcolumn can be understood as an electron beam inspection column configured for a sample inspection with a stationary electron beam, i.e. without a beam scanning with a scan deflector, namely by moving the sample in a scanning pattern relative to the static electron beam. 
     The system  100  further includes a stage controller  180  configured to move the movable stage  110  in a predetermined scanning pattern during the inspection of the sample while maintaining the plurality of electron beams stationary. Accordingly, the sample  10  is inspected by exclusively moving the movable stage  110  relative to static electron beams in the predetermined scanning pattern. The stage movement causes a scanning of the stationary electron beams over the sample surface in the predetermined scanning pattern. The electron beams may remain static during the entire inspection of the sample. 
     As a result, the plurality of inspection columns  130  can be built very small and comparatively inexpensively. A large number of inspection columns  130  can be provided in an array, e.g. ten or more inspection columns, particularly 50 or more inspection columns, more particularly 100 or more inspection columns, or even 150 or more inspection columns. The number of inspection columns may depend on the size of the sample that is to be inspected. For example, a system configured to inspect wafers with a diameter of 300 mm may include 100 or more and 200 or less inspection columns. A system configured to inspect wafers with a diameter of 450 mm may include even more inspection columns. 
     In some embodiments, each inspection column includes the beam emitter  131 , the focusing lens  132 , and optionally a beam corrector (shown in  FIG.  3   ), e.g. a stigmator. In some implementations, no further beam influencing elements for influencing the primary electron beams are provided in the inspection columns. In other embodiments, a beam deflector unit (not shown) may optionally be provided in the inspection columns for tuning and/or alignment purposes of the electron beam. However, the inspection columns do typically not include a scan deflector for scanning the electron beam over the sample for inspecting the sample. 
     In some embodiments, the focusing lens may be an electrostatic lens, e.g. an electrostatic multipole lens, such as an octupole lens. Electrostatic lenses are small and easy to implement, such that many inspection columns can be provided next to each other at close distances. 
     The beam emitter may include an electron source, e.g. a cold field emitter, a thermionic emitter, a Schottky-type emitter, or another emitter configured to provide an electron beam. For example, the beam emitter may include a tip for emitting electrons and an extraction electrode. 
     The plurality of inspection columns include detectors for detecting signal electrons released from the sample. The detector  133  may be configured to detect any of secondary electrons (SE) and backscattered electrons (BSEs), and/or may include any one or more of a scintillator, a PIN diode, a multichannel plate, and an Everhard-Thornley detector. In some implementations, each inspection column may be provided with a respective detector for detecting secondary electrons and/or backscattered electrons generated by the respective electron beam. In some embodiments, the detector has a detector surface that surrounds the optical axis  138  of the inspection columns and has an opening for the primary electron beam to propagate therethrough. A distance between the movable stage  110  and the detector  133  may be 1 mm or more and 1 cm or less in some embodiments. 
     Each inspection column of the plurality of inspection columns  130  may include a respective vacuum chamber (also referred to herein as a “microscope chamber  102 ”), such that an interior space of each of the inspection columns can be evacuated. The microscope chamber  102  may house the beam-optical elements of the respective inspection column, particularly the beam emitter  131  and the focusing lens  132 . The interior of the microscope chamber  102  can be pumped down to an ultra-high vacuum during the operation of the inspection column, e.g. to a pressure of 1×10 −8  mbar or less. Alternatively, two or more inspection columns of the plurality of inspection columns  130 , particularly all the inspection columns, may include a single microscope chamber (not shown) that houses several beam emitters and focusing lenses. By evacuating the single microscope chamber, an interior of several inspection columns can be evacuated and be provided at an ultra-high vacuum during the inspection. 
     In some embodiments, the movable stage  110  for positioning the sample thereon may be provided in a sample chamber  101 . The sample chamber  101  can be pumped down to a high vacuum during the operation of the system, e.g. to a pressure of 1×10 −2  mbar or less. The one or more microscope chambers  102  may protrude into the sample chamber  101 , such that respective front ends of the plurality of inspection columns  130  are directed toward the movable stage  110 . A “working distance WD” of the system as used herein may be understood as a distance between the front ends of the microscope chambers  102  (or the lowest mechanical column surface) and the sample  10  during the inspection. The sample inspection according to embodiments described herein may be carried out at a working distance of 1 mm or more and 5 mm or less. 
     The plurality of inspection columns  130  may be configured to inspect the sample with a resolution of 20 nm or less, particularly 10 nm or less, or even 5 nm or less. In particular, the plurality of inspection columns  130  may be configured to focus the plurality of electron beams such that electron beam probes with diameters of 20 nm or less, particularly 10 nm or less, are provided on the sample surface at the plurality of probe positions  106 . 
     In some implementations, the plurality of inspection columns  130  are arranged in a two-dimensional array of inspection columns, the two-dimensional array including an array of A×B inspection columns extending in two transverse directions, wherein A and B are integers of 5 or more, particularly 10 or more. For example, 10x10 inspection columns may be provided in a closely packed array next to each other. In particular, essentially the whole surface of the movable stage may be “covered” with inspection columns in a top view, as is schematically depicted in  FIG.  2 A . The optical axes of adjacent inspection columns of the array may be arranged close to each other, e.g. at distances  135  of 5 cm or less. 
     The sample  10  may be inspected with the multi-electron beam inspection system  100  of  FIG.  1    in the following way: 
     First, the sample  10  may be placed on the movable stage  110 . For example, the sample  10  may be a wafer, such as a semiconductor wafer that is to be inspected. In other embodiments, the sample  10  may include a die package including two or more interconnected dies. Specifically, the sample may include an interconnection between two or more packaged dies that may be connected by advanced packaging. In yet further embodiments, the sample  10  may be a substrate, e.g. a large-area glass substrate including one or more layers deposited thereon that are to be inspected, e.g. a substrate for display manufacturing. The large-area substrate may have a surface area of 1 m 2  or more. A sample surface may extend in the X-Y-plane that is defined by the movable stage  110 . 
     A plurality of electron beams  105  are generated that propagate essentially parallel to each other toward the sample  10 . The plurality of electron beams  105  are focused on the sample at the plurality of probe positions  106 , the plurality of probe positions  106  being arranged in a two-dimensional array in the X-Y-plane. 
     The movable stage  110  is moved in a predetermined scanning pattern for scanning the sample, while the plurality of electron beams are maintained static. Signal electrons emitted from the sample are detected during the stage scanning for inspecting the sample. 
     The movable stage  110  may be controlled by a stage controller  180 , wherein the stage controller may be configured to determine a stage position with an accuracy of 20 nm or less, particularly 10 nm or less, or even 5 nm or less, and to position the stage accordingly, particularly with the assistance of an interferometer that is configured to determine a stage position in an X-direction and/or in a Y-direction (i.e., and X/Y-interferometer). Hence, the movable stage can be moved in the predetermined scanning pattern with a high accuracy. In some implementations, the stage may be interferometer-controlled. In particular, a laser interferometer may be provided for monitoring the stage position with an accuracy of 10 nm or less, particularly 5 nm or less, particularly in X— and Y&#39; directions. The current stage position may be forwarded to an inspection controller that receives and evaluates the signals of one detector  133  or of all the detectors of the plurality of inspection columns. The secondary electron signal vs the current coordinates of the movable stage as determined by the stage controller  180  may be recorded to generate an image of the sample and/or to detect sample defects with a high resolution. By transmitting the signals of all the detectors to one inspection controller, an image of the whole sample can be composed of the individual detector signals, if desired. 
     Accordingly, the resulting image resolution provided by the inspection system is based on both the primary beam resolution (spot size, Upe), here typically a spot size of 20 nm or less, and the stage position accuracy reading by the interferometer, here typically 10 nm or less, resulting in an image resolution of 10 nm or less. 
     If the plurality of electron beams  105  provide beam probes having probe diameters of 20 nm or less (or 10 nm or less) on the sample, and the stage position is monitored and transmitted to the inspection controller with an accuracy of 10 nm or less (or 5 nm or less), it is possible to inspect the sample with a resolution of 10 nm or less (or 5 nm or less). Even better resolutions are possible. 
     In some embodiments, a plurality of ten or more electron beams are generated and focused on the sample, particularly 50 or more electron beams, or even 100 or more electron beams. Accordingly, the inspection speed can be increased by a factor of 50 or 100 as compared to a one-beam inspection system, and at the same time a high-resolution inspection of the sample surface within a nm-scale is possible. To give an example: In a one-beam inspection system, the inspection of a surface area of 1 cm 2  with a resolution of 10 nm may typically take several hours, such that the inspection of a surface area of several hundred cm 2  (e.g., the inspection of a typical wafer) is impossible in practice. Using the system described herein that uses 100 or more electron beams in parallel, it becomes possible to inspect entire wafer surfaces (e.g., hundreds of cm 2 ) on a reasonable timescale, e.g. in several hours of scanning. 
       FIG.  2 A  is a schematic top view of a multi-electron beam inspection system  100  according to embodiments described herein. The system  100  includes a plurality of inspection columns  130  arranged in a two-dimensional array, the array extending in X- and Y-directions above the movable stage  110  on which a sample  10  is placed in the X-Y-plane. The sample is exemplarily illustrated as a round wafer. 
       FIG.  2 B  shows a top view of the sample  10  of  FIG.  2 A  without the plurality of columns  130 , for explaining a scanning pattern used according to method described herein. 
     The plurality of inspection columns  130 , e.g. inspection column  140 , are schematically illustrated as circles in the top view of  FIG.  2 A . The inspection columns may be configured in accordance with the plurality of inspection columns  130  of the system  100  of  FIG.  1   , such that reference can be made to the above explanations, which are not repeated here. 
     The two-dimensional array that is defined by the plurality of inspection columns  130  may be arranged in “lines” and “columns”. At least some of the lines of the array may include five, ten or more inspection columns, and at least some of the columns of the array may include five, ten or more inspection columns. Specifically, the two-dimensional array may include a (sub-)array of A×B inspection columns arranged in lines and columns, A and B being integers of five, ten, or more. A 10×10 (sub-)array of the two-dimensional array is illustrated in  FIG.  2 A  by dashed line  201 . 
     In some embodiments, adjacent inspection columns of the plurality of inspection columns  130  are arranged at close distances next to each other. In particular, optical axes of two adjacent columns of the plurality of inspection columns  130  may be spaced from each other at distances of 5 cm or less, particularly 3 cm or less, more particularly about 2 cm, respectively. As is schematically depicted in  FIG.  2 A , distances  135  between two adjacent inspection columns in the rows of the array may be 5 cm or less, respectively, and/or distances  135  between two adjacent inspection columns in the columns of the array may be 5 cm or less, respectively (the distances  135  are measured between the optical axes of the inspection columns). Accordingly, an array of closely packed inspection columns is provided. In some implementations, essentially the entire sample support surface of the movable stage  110  may be covered with inspection columns, each inspection column having a maximum dimension of 5 cm in a sectional plane extending in X-Y-directions. 
     In some embodiments, which can be combined with other embodiments described herein, the plurality of inspection columns  130  are small static electron beam microcolumns. A microcolumn may have a maximum dimension in a plane perpendicular to the optical axis of 5 cm or less, particularly 3 cm or less. Providing very many small microcolumns in a closely packed array allows for a considerable increase of the inspection speed of a sample. 
     During the inspection, the plurality of static electron beams form, in sectional planes parallel to the X-Y-plane, a two-dimensional beam array. Likewise, the plurality of probe positions  106  are arranged in a two-dimensional array on the sample. Electron beams arranged adjacent to each other in a first direction (e.g., in the X-direction) and/or electron beams arranged adjacent to each other in a second direction (e.g., in the Y-direction) transverse to the first direction may be spaced from each other at the distances  135  of 5 cm or less, particularly 3 cm or less, more particularly about 2 cm, respectively. 
     Referring now to  FIG.  2 B , each inspection column may be arranged above a respective sub-area of the sample  10  for inspecting the respective sub-area with a high resolution. The sample  10  may include a plurality of sub-areas  142  of essentially corresponding shape (e.g. rectangular or quadratic sub-areas), and in each of the plurality of sub-areas  142  an associated one of the plurality of electron beams may be focused at a respective probe position. The scanning may include moving the movable stage  110  in the predetermined scanning pattern, such that the plurality of sub-areas  142  are simultaneously inspected by the plurality of electron beams, until 90% or more of the surface area of the plurality of sub-areas  142  is inspected, particularly with a resolution of 20 nm or less. In particular, essentially the whole surface area of the plurality of sub-areas may be inspected with a high resolution (e.g., 20 nm or 10 nm or less) with static electron beams by moving the movable stage in the predetermined scanning pattern. 
     In some implementations, 10, 50, 100 or more sub-areas of the sample are inspected in parallel with a plurality of static electron beams at a high resolution. 
     The plurality of sub-areas  141  may be essentially rectangularly shaped and/or may have a respective surface area of 3 cm 2  or more and 10 cm 2  or less, particularly about 4 cm 2 . Specifically, the sub-areas may be rectangles having a width between 1.5 cm and 3 cm and a length between 1.5 cm and 3 cm, e.g. rectangles having a width of about 2 cm and a length of about 2 cm, i.e. a surface area of about 4 cm 2 . Optionally, further sub-areas that include an edge region of the sample may have the shape of cut rectangles. The rectangles may be synchronously inspected with the static electron beams via the stage movement. 
     The plurality of sub-areas may be raster-scanned by moving the movable stage in a raster-scanning pattern. The line length of the raster-scanning pattern may essentially correspond to a width of the plurality of sub-areas  141 . Moving the movable stage in a raster-scanning pattern may cause the static electron beams to move over the sub-areas until essentially the entire sub-area surface is inspected with a high resolution. In some embodiments, the scanning pattern may include stage movements in scan lines in an X-direction and Y-shifts to the respective next line in a Y-direction in an alternating manner. In order to save time, the inspection may take place both during a forward and a back movement in the X-direction, i.e. lines may alternatively be scanned during back- and forward movements of the movable stage in the X-direction, as is schematically depicted for the enlarged sub-area  141  in  FIG.  2 B . 
     In some implementations, 90% or more of the surface area of the sample, particularly essentially the entire surface of the sample is inspected with the plurality of electron beams with a high resolution, particularly with a resolution of 10 nm or less. For example, the sample may be a wafer with a surface area of 400 cm 2  or more, and 360 cm 2  or more of said surface area, or the whole surface area, may be inspected with said high resolution with static electron beams. Specifically, each electron beam of 100 or more electron beams may inspect a sub-area of the sample with a surface area of 3 cm 2  or more and 10 cm 2  or less. 
     Example: The plurality of inspection columns  130  may be configured to read secondary electron (SE) signals with a frequency of 100 MHz. The sub-area  141  of the sample that is to be inspected with one inspection column  140  may be a 2 cm×2 cm rectangle. In order to obtain a resolution of 10 nm,  2   e - 6  secondary electron signals need to be read out during the stage movement along a 2 cm scan line, and a total of 2e-6 lines are to be scanned. Considering the inspection frequency of 100 MHz, the inspection of one scan line with a resolution of 10 nm takes 20 msec, and the inspection of the total of 2e-6 lines takes about 11 hours. 
     Accordingly, a sample with a surface area of 400 cm 2  can be inspected with a system as described herein, including 100 or more inspection columns, with a 10-nm resolution in 11 hours or less, as compared to 11x100 hours (1.5 months) in a one-beam system. 
       FIG.  3    shows a schematic sectional view of an inspection column  140  of a multi-electron beam inspection system  100  according to embodiments described herein. A plurality of such inspection columns may be arranged adjacent to each other at close distances, as is depicted in  FIG.  1   . 
     The inspection column  140  may be a static electron beam microcolumn as previously described. The inspection column  140  may be configured to direct a static electron beam on a sample  10 . The inspection column  140  includes a beam emitter  131  for generating an electron beam that propagates along an optical axis  138  of the inspection column toward a sample  10 . The inspection column  140  further includes a focusing lens  132 , and optionally a beam corrector  134 , e.g. a stigmator, arranged in a microscope chamber  102  that can be evacuated. The focusing lens  132  is configured to focus the electron beam on the sample  10  at a probe position  106 . 
     Further, the inspection column  140  includes a detector  133  for detecting signal electrons  107 . The signal of the detector  133  may be forwarded to an inspection controller  137  that receives the current stage position of the movable stage from the stage controller  180  with a high accuracy, e.g. in the range of 10 nm or less. By recording the electron signal vs stage position during the movement of the movable stage in the predetermined scanning pattern, a high-resolution image of the sample can be generated, and/or the sample can be inspected with a high accuracy. Sample defects can be reliably detected. 
     The inspection column  140  may not include any scan deflector for scanning the electron beam over the sample for inspection purposes. Optionally, a beam deflector (not shown) for alignment or tuning purposes may be provided. 
     The electron beam may have a probe diameter of 20 nm or less at the probe position  106 , such that an inspection with a sub-10-nm resolution is possible. 
     Accordingly, a comparatively simple and small inspection column  140  is provided that is nevertheless suitable for a high-resolution inspection of sample surfaces. Accordingly, very many inspection columns can be arranged close to each other in a two-dimensional array of inspection columns, allowing an increased inspection speed due to the parallel inspection with many electron beams. 
       FIG.  4    shows a flow chart illustrating a method of inspecting a sample with a multi-electron beam inspection system according to embodiments described herein. 
     In box  510 , a sample is placed on the movable stage, such that a main surface of the sample extends essentially in the X-Y-plane. The sample may be any of a semiconductor wafer, a die package, or a coated substrate. 
     In box  520 , a plurality of electron beams is generated that propagate essentially parallel to each other toward the sample. The plurality of electron beams are focused on the sample at a plurality of probe positions. 
     In box  530 , the sample is scanned by moving the movable stage in a predetermined scanning pattern while maintaining the plurality of electron beams stationary. The movable stage may be moved such that each of the plurality of electron beams inspects a predetermined sub-area of the sample with a high resolution, e.g. by moving the movable stage in a raster-scanning pattern. The scanning pattern of the movable stage causes a synchronous movement of the plurality of electron beams relative to the respective sub-area exactly in the same manner. No synchronous control of a plurality of scan deflectors is required. This is because all the electron beams remain immovable, and the relative movement is exclusively due to the stage movement. Signal acquisition accuracy can be improved and the complexity of the signal evaluation can be decreased. This allows the inspection speed to be increased further. 
     In box  530 , signal electrons emitted from the sample are detected by respective detectors of the plurality of inspection columns during the scanning movement of the movable stage. The detector signals may be transmitted to an inspection controller that records and/or evaluates the signal in dependence of the current stage position. A high-resolution image of the sample can be generated and/or the sample can be inspected with a high accuracy. 
     The scanning and detecting in box  530  may continue until a large portion of the sample is inspected with a high resolution, e.g. 50% or more of the sample surface, particularly 90% or more of the sample surface, or even essentially the whole sample surface. Optionally, an image of the whole sample can be generated by combining the measurements of the plurality of inspection columns. 
     Methods and systems described herein are beneficial and provide the following advantages: The inspection speed is increased due to the parallel signal acquisition from very many inspection columns. The sample can be inspected with a high resolution that is determined by the accuracy of the stage coordinates, i.e. is limited by the interferometer resolution of the stage controller. A better and stronger signal is obtained, as the detector and the inspection column design is simpler and more efficient than for scanning electron beam columns. 
     Summarizing the above, the present disclosure specifically provides the following embodiments: 
     Embodiment 1: A method of inspecting a sample with a multi-electron beam inspection system, including: placing the sample on a movable stage extending in an X-Y-plane; generating a plurality of electron beams propagating essentially parallel to each other toward the sample; focusing the plurality of electron beams on the sample at a plurality of probe positions  106  arranged in a two-dimensional array; scanning the sample by moving the movable stage in a predetermined scanning pattern while maintaining the plurality of electron beams stationary; and detecting signal electrons emitted from the sample during the moving of the movable stage for inspecting the sample. 
     Embodiment 2: The method of embodiment 1, wherein the plurality of electron beams includes ten or more electron beams, particularly 50 or more electron beams, more particularly 100 or more electron beams. 
     Embodiment 3: The method of embodiment 1 or 2, wherein the plurality of electron beams form, in sectional planes parallel to the X-Y-plane, a two-dimensional beam array, wherein electron beams arranged adjacent to each other in a first direction (X) and/or electron beams arranged adjacent to each other in a second direction (Y) transverse to the first direction are spaced from each other at distances of 5 cm or less, particularly of 3 cm or less, respectively. In particular, the distances between adjacent electron beams are from 1 cm to 3 cm, e.g. about 2 cm. 
     Embodiment 4: The method of any one of embodiments 1 to 3, wherein the sample is inspected with a resolution of 20 nm or less, particularly 10 nm or less, and/or wherein the plurality of electron beams have probe diameters at the plurality of probe positions of 40 nm or less, particularly of 20 nm or less, more particularly of 10 nm or less, or even 5 nm or less. 
     Embodiment 5: the method of any one of embodiments 1 to 4, wherein 90% or more of a surface area of the sample is inspected with the plurality of electron beams, in particular wherein the entire sample surface is inspected with the plurality of electron beams. The plurality of electron beams may be maintained stationary during the entire inspection, while the stage is moved relative to the plurality of electron beams in a predetermined scanning pattern. Specifically, the electron beams are not scanned with a scan deflector. The inspection resolution may be 20 nm or less, particularly 10 nm or less. 
     Embodiment 6: The method of any one of embodiments 1 to 5, wherein the sample includes a plurality of sub-areas of essentially the same shape, and in each of the plurality of sub-areas an associated one of the plurality of electron beams is focused at a probe position. The scanning includes moving the movable stage in the predetermined scanning pattern such that the plurality of sub-areas are simultaneously inspected with the plurality of electron beams, until 90% or more of the surface area of the plurality of sub-areas is inspected, specifically until essentially the entire surface area of the plurality of sub-areas is inspected. 
     Embodiment 7: The method of embodiment 6, wherein the plurality of sub-areas are essentially rectangularly shaped, and the movable stage is moved in the predetermined scanning pattern, e.g. in a raster-scan pattern, until essentially the entire surface area of the plurality of sub-areas is inspected, particularly at a resolution of 20 nm or less. For example, the scanning pattern may include stage movements in scan lines in an X-direction and Y-shifts in a Y-direction in an alternating manner. 
     Embodiment 8: The method of embodiment 6 or 7, wherein the sub-areas of the plurality of sub-areas have a respective surface area of 3 cm 2  or more and 10 cm 2  or less, particularly 4 cm 2  or more and 6 cm 2  or less. In particular the sub-areas may be rectangles of about 2 cm×2 cm. 
     Embodiment 9: The method of any one of embodiments 1 to 8, wherein the plurality of electron beams includes 100 or more electron beams, the sample has a surface area of 400 cm 2  or more, and the movement of the movable stage in the predetermined scan pattern causes each of the plurality of electron beams to move over a surface area of 3 cm 2  or more and 10 cm 2  or less of a sub-area of the sample while providing an inspection resolution of 20 nm or less. 
     Embodiment 10: The method of any one of embodiments 1 to 9, wherein the movable stage is interferometer-controlled, and a stage controller is configured to determine a stage position with a resolution of 20 nm or less, particularly 10 nm or less, or even 5 nm or less. 
     Embodiment 11: The method of any one of claims  1  to  10 , wherein the sample is at least one of a wafer and a die package including two or more connected dies. 
     Embodiment 12: The method of any one of claims  1  to  11 , wherein the sample is inspected with a working distance WD of 2 mm or more and 5 mm or less. 
     Embodiment 13: A multi-electron beam inspection system, particularly for inspecting a sample in accordance with any of the above methods, including: a movable stage extending in an X-Y-plane for placing the sample thereon, and a plurality of inspection columns for generating a plurality of electron beams propagating essentially parallel to each other and configured to focus the plurality of electron beams on the sample at a plurality of probe positions arranged in a two-dimensional array. The plurality of inspection columns respectively include a beam emitter, a focusing lens, and a detector for detecting signal electrons. The multi-electron beam inspection system further includes a stage controller configured to move the movable stage in a predetermined scanning pattern during a sample inspection while maintaining the plurality of electron beams stationary. 
     Embodiment 14: The system of embodiment 13, wherein the plurality of inspection columns do not include any scan deflectors. The focusing lens may be an electrostatic lens, e.g. including an electrostatic octupole. 
     Embodiment 15: The system of embodiment 13 or 14, wherein the plurality of inspection columns further include a beam corrector, particularly a stigmator, respectively. 
     Embodiment 16: The system of any of embodiments 13 to 15, wherein the plurality of inspection columns are configured to provide beam probes having probe diameters of 20 nm or less on the sample, particularly 10 nm or less, for obtaining an inspection resolution of 10 nm or less. 
     Embodiment 17: The system of any of embodiments 13 to 16, wherein the plurality of inspection columns are arranged in a closely packed array of A×B columns in X- and Y-directions, A and B being respective integers of 5 or more, particularly of 10 or more. 
     Embodiment 18: A multi-electron beam inspection system, including a plurality of inspection columns arranged in a two-dimensional array in X- and Y-directions and facing toward a movable stage for placing the sample thereon, and a stage controller configured to move the movable stage in a predetermined scanning pattern in an X-Y-plane. The plurality of inspection columns are static electron beam microcolumns without scan deflectors. 
     Embodiment 19: The system of embodiment 18, wherein the plurality of inspection columns are configured for a parallel sample inspection with a resolution of 20 nm or less, particularly 10 nm or less. 
     Embodiment 20: The system of embodiment 18 or 19, wherein the two-dimensional array comprises an array of A×B columns in X- and Y-directions, A and B being respective integers of 5 or more, particularly 10 or more. Optical axes of two adjacent columns of the array may be spaced from each other at distances of 5 cm or less, particularly 3 cm or less, respectively. 
     While the foregoing is directed to some embodiments, other and further embodiments may be devised without departing from the basic scope thereof, and the scope thereof is determined by the claims that follow.