How to process samples with a charged particle characterization system

Abstract

A method for processing a sample and a charged particle characterization system are disclosed. In one arrangement, the sample is processed using multiple beams of sub-beams of charged particles. At least a portion of a sub-beam addressable area is processed with each sub-beam. The sub-beam addressable area includes an array of sections having rows of sections and columns of sections. Each row of sections defines an elongated region that is substantially equal to or less than the pitch at the sample surface of the sub-beams in the multiple beams. A plurality of sections are processed.

Description

[Technical field]

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims priority to European Patent Application Publication No. 21216074.1, filed on December 20, 2021, and incorporated by reference in its entirety into this specification.

[0002] FIELD OF THE DISCLOSURE

[0002] Embodiments disclosed herein relate to processing of samples using multiple beams of charged particles, particularly in connection with inspecting the samples to, for example, identify defects. [Background technology]

[0003]

[0003] When manufacturing semiconductor integrated circuit (IC) chips, undesirable pattern defects inevitably occur on a substrate (i.e., wafer) or mask during the fabrication process, e.g., as a result of optical effects and accidental particles, thereby reducing yield. Therefore, monitoring the extent of undesirable pattern defects is an important process in the manufacture of IC chips. More generally, inspection and / or measurement of the surface of a substrate or other object / material during and / or after its manufacture is an important process.

[0004]

[0004] Charged particle beam pattern inspection devices are used to inspect objects, which may be referred to as samples, for example to detect pattern defects. These devices typically use electron microscopy techniques, such as scanning electron microscopes (SEMs). In an SEM, a primary electron beam of relatively high energy electrons is targeted with a final deceleration step to land on the sample with a relatively low landing energy. The electron beam is focused as a probing spot on the sample. Interaction of the landing electrons from the electron beam with material structures at the probing spot causes signal electrons, such as secondary electrons, backscattered electrons or Auger electrons, to be emitted from the surface. The signal electrons may be emitted from the material structures of the sample. By scanning the primary electron beam as a probing spot across the sample surface, signal electrons may be emitted across the surface of the sample. By collecting these emitted signal electrons from the sample surface, the pattern inspection device may obtain an image that is representative of the material structure of the surface of the sample.

[0005]

[0005] Exposure of a sample to an electron beam can apply a thermal load to the sample. Such thermal load can cause distortions in the sample and lead to position errors. There is a general need to mitigate such thermal loads and at least maintain, if not improve, the throughput, position accuracy and other properties of charged particle tools and methods. Summary of the Invention

[0006]

[0006] It is an object of the present disclosure to provide embodiments that assist in improving the throughput or other characteristics of a charged particle tool.

[0007]

[0007] According to one aspect of the present invention, there is provided a method for processing a sample using a multiple beam of sub-beams of charged particles using a charged particle device for projecting the multiple beam onto a sample surface, the method sequentially comprising: (a) using the charged particle device to move the sample in a direction parallel to a first direction and to repeatedly move the multiple beams relative to the sample surface in a direction parallel to a second direction, thereby repeatedly scanning each sub-beam in a direction parallel to the first direction and in a direction parallel to the second direction to process a section of a plurality of elongated regions on the sample surface with the sub-beams, wherein the distance of movement of the sample in (a) is half the pitch of the sub-beams in the multiple beams at the sample surface in the first direction. (b) displacing the sample in a direction oblique or perpendicular to the first direction; (c) repeating step (a) to process further sections of the plurality of elongated regions with each sub-beam; (d) repeating steps (b) and (c) multiple times to process further respective sections of the plurality of elongated regions with each sub-beam; and (e) repeating steps (a)-(d) for each sub-beam for a set of unprocessed sections of the elongated region, the set of unprocessed sections being adjacent in a direction parallel to the movement in step (a) to a corresponding set of sections of the respective elongated region previously processed by the sub-beam.

[0008]

[0008] According to one aspect of the present invention, there is provided a method of processing a sample using a multi-beam of sub-beams of charged particles using a charged particle device for projecting the multi-beam onto the sample surface, the method comprising processing at least a portion of a sub-beam-processable area with each sub-beam, the sub-beam-processable area comprising an array of sections having rows of sections and columns of sections, each row of sections defining an elongated region that is substantially less than or equal to the pitch of the sub-beams in the multi-beam at the sample surface, and the processing comprises processing a plurality of sections.

[0009]

[0009] According to one aspect of the present invention, there is provided a charged particle characterization system comprising a sample support configured to support a sample, a charged particle device configured to project a plurality of sub-beams of charged particles in a multi-beam configuration onto a portion of a sample surface, and the following steps: (a) using the charged particle device, moving the sample in a direction parallel to a first direction and repeatedly moving the multi-beams relative to the sample surface in a direction parallel to a second direction, thereby scanning each sub-beam repeatedly in a direction parallel to the first direction and in a direction parallel to the second direction to process a section of a plurality of elongated regions on the sample surface with the sub-beams, wherein the distance of movement of the sample in (a) is less than or equal to half the pitch of the sub-beams in the multi-beam at the sample surface in the first direction. (b) displacing the sample in a direction oblique or perpendicular to the first direction; (c) repeating step (a) to process further sections of the plurality of elongated regions with each sub-beam; (d) repeating steps (b) and (c) multiple times to process further respective sections of the plurality of elongated regions with each sub-beam; and (e) repeating steps (a)-(d) for each sub-beam for a set of unprocessed sections of the elongated region, the set of unprocessed sections being adjacent in a direction parallel to the movement in step (a) to a corresponding set of sections of each elongated region previously processed by a sub-beam.

[0010]

[0010] According to one aspect of the present invention, there is provided a charged particle characterization system comprising a sample support configured to support a sample; a charged particle device configured to project a plurality of sub-beams of charged particles onto a portion of a sample surface in a multi-beam configuration; and a charging device configured to: a) process at least a portion of a sub-beam addressable area with each sub-beam, the sub-beam addressable area comprising an array of sections having rows of sections and columns of sections, each row of sections defining an elongated region that is substantially equal to or less than the pitch of the sub-beams in the multi-beam at the sample surface, the processing comprising processing the plurality of sections; and b) exposing at least a portion of the sub-beam scannable area to each sub-beam, the sub-beam scannable area comprising an array of sections having rows of sections and columns of sections. and / or c) exposing at least a portion of the sub-beam scannable area to each sub-beam, the sub-beam scannable area comprising an array of sections having rows of sections and columns of sections, each row of sections defining an elongated region that is substantially equal to or less than the pitch of the sub-beams in the multi-beam at the sample surface, the sample support and charged particle device being configured to be controlled to expose a plurality of sections; and / or b) exposing at least a portion of the sub-beam scannable area to each sub-beam, the sub-beam scannable area comprising an array of sections having rows of sections and columns of sections, each row of sections defining an elongated region that is substantially equal to or less than the pitch of the sub-beams in the multi-beam at the sample surface, and a controller configured to control the sample support and charged particle device to perform sample alignment operations between scanning of different sections in the array of sections.

[0011]

[0011] According to one aspect of the invention there is provided a rendering of an image derived from scanning a sample, the image comprising a plurality of processing areas arranged in a grid, each processing area corresponding to a portion of the sample surface scanned by a sub-beam of the multi-beam arrangement, the grid having a dimension corresponding to the pitch of the sub-beams of the multi-beam arrangement, each processing area comprising an array of sections arranged in section rows and section columns, a row of processed sections in a processing area corresponding to an elongated region having a longitudinal dimension of the width of the processing area, preferably each processing area having sections arranged in the same grid, preferably the sections in the elongated region having similar dimensions in the longitudinal dimension.

[0012]

[0012] According to one aspect of the invention there is provided a method of processing a sample using a multiple beam of sub-beams of charged particles using a charged particle device for projecting the multiple beam onto a sample surface, the method comprising: using the charged particle device to project a plurality of sub-beams of charged particles in a multi-beam arrangement onto a portion of the sample surface, a portion corresponding to a field of view of the multi-beam arrangement, each sub-beam corresponding to a sub-portion of a portion, each sub-portion corresponding to a field of view of a corresponding sub-beam of the multi-beam arrangement, the sub-portions including a plurality of elongated regions extending across the field of view in a first direction and together having an area which includes an area of ​​the sample surface of the sub-portion, each elongated region being arranged and controlling the sample support and charged particle device such that sub-beams of the multi-beam configuration scan sections within each sub-portion, wherein scanning the sections comprises moving the sample in a direction parallel to the first direction and moving the multi-beams relative to the sample surface in a direction parallel to a second direction, preferably oblique to the first direction, to scan the sections; and using the same movements to scan a next section adjacent to the previously scanned section.

[0013]

[0013] According to one aspect of the present invention, there is provided a charged particle characterization system comprising a sample support configured to support a sample; and a charged particle device configured to project a plurality of sub-beams of charged particles onto a portion of a sample surface in a multi-beam configuration, a portion corresponding to a field of view of the multi-beam configuration, each sub-beam being assigned to a sub-portion of a portion, each sub-portion corresponding to a field of view of a corresponding sub-beam of the multi-beam configuration, the sub-portions including a plurality of elongated regions extending across the field of view in a first direction and together having an area that includes an area of ​​the sample surface of the sub-portion, each elongated region including a plurality of sections arranged within the elongated region. the elongated region optionally having similar dimensions in a direction oblique or perpendicular to the first direction, and a controller configured to control the sample support and the charged particle device such that the sample moves in a direction parallel to the first direction and the multi-beam moves relative to the sample surface in a direction parallel to a second direction, preferably oblique to the first direction, and sub-beams of the multi-beam are controlled to scan sections within each sub-portion such that after each section is scanned, it becomes the previously scanned section and a next section adjacent to the previously scanned section is scanned using the same movement.

[0014]

[0014] According to one aspect of the present invention, there is provided a charged particle characterization system comprising a sample support for supporting a sample having a sample surface, and a charged particle device configured to direct a multi-beam of sub-beams of charged particles towards the sample surface, wherein a portion of the sample surface corresponding to a multi-beam output area of ​​the charged particle device faces the sample surface, the system is configured to control the sample support and the charged particle device such that a portion is scanned by the sub-beams of the multi-beam, a sub-portion of the portion being assigned to each sub-beam, and the system displaces the sample in successive steps in a direction oblique or perpendicular to a first direction, and at each step The system is configured to control the sample support to move the sample in a direction parallel to a first direction in each step such that each sub-beam scans across a section of a corresponding sub-portion in a direction parallel to the first direction, the corresponding sub-portion in a direction parallel to the first direction including a plurality of sections, the system is configured to control the charged particle device to repeatedly scan the multi-beam across the sample surface in a direction parallel to the second direction during movement of the sample in the direction parallel to the first direction, and the system is configured to scan further sections, either multiple sections or subsequent successive steps along the sub-portion in the direction parallel to the first direction.

[0015]

[0015] The above and other aspects of the present disclosure will become more apparent from the following description of exemplary embodiments taken in conjunction with the accompanying drawings. [Brief description of the drawings]

[0016] [Figure 1] FIG. 1 is a schematic diagram illustrating an example charged particle beam inspection system. [Diagram 2]

[0017] 2 is a schematic diagram illustrating an example multi-beam charged particle characterization apparatus that is part of the example charged particle beam inspection system of FIG. 1. [Diagram 3]

[0018] 1 is a schematic diagram of an exemplary electron optical column including a focusing lens array. [Figure 4]

[0019] 1 is a schematic diagram of an exemplary electron optical column including a macro-collimator and a macro-scanning deflector. [Diagram 5]

[0020] 1 is a schematic diagram of an exemplary electron optical column including a beam separator. [Figure 6]

[0021] 1 is a schematic cross-sectional view of an objective lens array of a charged particle characterization system according to an embodiment. [Figure 7]

[0022] FIG. 8 is a bottom view of a modified version of the objective lens array of FIG. [Figure 8]

[0023] 2 is a schematic diagram of a data path including a data processing device according to one embodiment. [Figure 9]

[0024] 1 is a flow diagram of a method according to one embodiment. [Figure 10]

[0025] The processing of regions on the sample corresponding to sub-beam processing areas is shown. [Figure 11]

[0026] 1 shows the positioning of sub-beams in a hexagonal grid. [Figure 12]

[0027] 12 shows sub-beam treatment areas corresponding to the sub-beams arranged as shown in FIG. [Figure 13]

[0028] 1 shows an array of sections. [Figure 14]

[0029] 14 shows a sequence of steps for scanning the array of FIG. [Figure 15]

[0030] 13 shows an example of a large displacement movement of the sample between the formation of different groups of sub-beam treatment areas. [Figure 16]

[0031] 1 illustrates alternating scanning of sub-beams within an elongated region. [Figure 17]

[0032] 13 shows an example of a short stroke movement of a sample during processing of a sub-beam processing area. [Figure 18]

[0033] FIG. 1 is a diagram showing a step-and-scan sequence. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0017]

[0034] These schematic diagrams show the components described below, however, the components depicted in the figures are not drawn to scale.

[0018]

[0035] Reference will now be made in detail to the exemplary embodiments, examples of which are illustrated in the accompanying drawings. The following description refers to the accompanying drawings, in which the same numbers in different drawings represent the same or similar elements unless otherwise indicated. The implementations set forth in the following description of the exemplary embodiments do not represent all implementations consistent with the present invention. Instead, the implementations are merely examples of apparatus and methods consistent with related aspects of the present invention, as described in the appended claims.

[0019]

[0036] Increased computing power of electronic devices, which reduces the physical size of the device, can be achieved by greatly increasing the packing density of circuit components such as transistors, capacitors, and diodes on an IC chip. This is made possible by increased resolution. For example, in an IC chip for a smartphone, which may be the size of a thumb and contain over 2 billion transistors, the size of each transistor may need to be less than 1 / 1000 of a human hair. To achieve increased resolution, the fabrication of semiconductor ICs becomes a complex and time-consuming process, with hundreds of individual steps. An error in even one of the steps can affect the functionality of the final product. The goal of the manufacturing process is to increase the overall yield of the process. For example, to obtain a 75% yield for a process with 50 steps (where a step may refer to the number of layers formed on a wafer), each individual step must have a yield of greater than 99.4%. If each individual step had a yield of 95%, the overall process yield would be as low as 7%.

[0020]

[0037] In IC chip manufacturing facilities, while high process yields are desirable, it is also essential to maintain high substrate (i.e., wafer) throughput, defined as the number of substrates processed per hour. High process yields and high substrate throughput can be affected by the presence of defects. This is especially true when operator intervention is required to investigate the defects. Thus, high throughput detection and identification of micro- and nano-scale defects by inspection devices, such as scanning electron microscopes ("SEMs"), is essential to maintain high yields and low costs.

[0021]

[0038] The SEM includes a scanning device and a detector device. The scanning device includes an illumination device, which includes an electron source for generating primary electrons, and a projection device for scanning a sample, such as a substrate, with one or more focused beams of primary electrons. Together, at least the illumination device or illumination system and the projection device or projection system may be referred to as an electron optical system or device. The primary electrons interact with the sample and generate secondary electrons. The detector device captures the secondary electrons from the sample as it is scanned so that the SEM can generate an image of the scanned area of ​​the sample. For high throughput inspection, some inspection devices use multiple focused beams of primary electrons, i.e., multibeams. The component beams of a multibeam may be referred to as sub-beams or beamlets. The multibeams may scan different parts of the sample simultaneously. Thus, multibeam inspection devices can inspect samples much faster than single-beam inspection devices.

[0022]

[0039] Known implementations of multi-beam inspection devices are described below.

[0023]

[0040] Although the description and drawings are directed to electron-optical systems, it is understood that the embodiments are not used to limit the disclosure to specific charged particles, and thus, throughout this specification, references to electrons can be considered to be references to charged particles more generally, and charged particles are not necessarily electrons.

[0024]

[0041] Reference is now made to Figure 1, which is a schematic diagram illustrating an exemplary charged particle beam inspection system 100, which may also be referred to as a charged particle beam evaluation system or simply an evaluation system. The charged particle beam inspection system 100 of Figure 1 includes a main chamber 10, a load lock chamber 20, an electron beam system 40, a front end equipment module (EFEM) 30, and a controller 50. The electron beam system 40 is located within the main chamber 10.

[0025]

[0042] The EFEM 30 includes a first load port 30a and a second load port 30b. The EFEM 30 may include one or more additional load ports. The first load port 30a and the second load port 30b may receive, for example, a substrate front-opening integrated pod (FOUP) that contains a substrate (e.g., a semiconductor substrate or a substrate made of other material) or a sample to be inspected (hereinafter, substrates, wafers and samples are collectively referred to as "samples"). One or more robotic arms (not shown) in the EFEM 30 transport the sample to the load lock chamber 20.

[0026]

[0043] The load lock chamber 20 is used to remove gas from around the sample. This creates a vacuum, which is a local gas pressure lower than the pressure of the surrounding environment. The load lock chamber 20 may be connected to a load lock vacuum pumping system (not shown), which removes gas particles in the load lock chamber 20. Operation of the load lock vacuum pumping system allows the load lock chamber to reach a first pressure below atmospheric pressure. After the first pressure is reached, one or more robotic arms (not shown) transport the sample from the load lock chamber 20 to the main chamber 10. The main chamber 10 is connected to a main chamber vacuum pumping system (not shown). The main chamber vacuum pumping system removes gas particles in the main chamber 10 such that the pressure around the sample reaches a second pressure below the first pressure. After the second pressure is reached, the sample is transported to the electron beam system 40, where the sample can be inspected by the electron beam system 40. The electron beam system 40 may include a multi-beam electron optical device.

[0027]

[0044] The controller 50 is electronically connected to the electron beam system 40. The controller 50 may be a processor (such as a computer) configured to control the charged particle beam inspection apparatus 100. The controller 50 may also include processing circuitry configured to perform various signal and image processing functions. Although in FIG. 1 the controller 50 is shown as being external to the structure including the main chamber 10, the load lock chamber 20 and the EFEM 30, it is understood that the controller 50 may be part of the structure. The controller 50 may be located within one of the component elements of the charged particle beam inspection apparatus, or the controller 50 may be distributed among at least two of the component elements. While the present disclosure provides an example of a main chamber 10 housing an electron beam system, it is noted that aspects of the present disclosure are not limited in the broad sense to a chamber housing an electron beam system. Rather, it is understood that the principles described above may be applied to other devices and other arrangements of the apparatus operating under a second pressure.

[0028]

[0045] Reference is now made to FIG. 2, which is a schematic diagram illustrating an exemplary electron beam system 40 including a multi-beam electron optical system 41, which is part of the exemplary charged particle beam inspection system 100 of FIG. 1. The electron beam system 40 includes an electron source 201 and a projection device 230. The electron beam system 40 further includes a motorized stage 209 and a sample holder 207. The electron source 201 and the projection device 230 are collectively referred to as an electron optical system 41 or an electron optical column. The sample holder 207 is supported by the motorized stage 209 to hold a sample 208 (e.g., a substrate or a mask) for inspection. The multi-beam electron optical system 41 further includes a detector 240 (e.g., an electron detection device).

[0029]

[0046] The electron source 201 may include a cathode (not shown) and an extractor or anode (not shown). In operation, the electron source 201 is configured to emit electrons from the cathode as primary electrons. The primary electrons are extracted or accelerated by the extractor and / or anode to form a primary electron beam 202.

[0030]

[0047] The projection device 230 is configured to convert the primary electron beam 202 into multiple sub-beams 211, 212, 213 and direct each sub-beam onto the sample 208. Although three sub-beams are shown for simplicity, there may be tens, hundreds, thousands or hundreds of thousands of sub-beams. The sub-beams may be referred to as beamlets.

[0031]

[0048] 1, such as the electron emitter 201, the detector 240, the projection device 230, and the motorized stage 209. The controller 50 may perform various image and signal processing functions. The controller 50 may also generate various control signals for controlling the operation of the charged particle beam inspection device, including the charged particle multi-beam device.

[0032]

[0049] The projection device 230 may be configured to focus the sub-beams 211, 212, and 213 onto the sample 208 for inspection, forming three probe spots 221, 222, and 223 on the surface of the sample 208. The projection device 230 may be configured to deflect the primary sub-beams 211, 212, and 213 to scan the probe spots 221, 222, and 223 over respective scan areas within a section of the surface of the sample 208. In response to the incidence of the primary sub-beams 211, 212, and 213 on the probe spots 221, 222, and 223 on the sample 208, electrons are generated from the sample 208, including secondary electrons and backscattered electrons, which may be referred to as signal particles. Secondary electrons typically have electron energies of 50 eV or less. Actual secondary electrons may have energies less than 5 eV, but any energy less than 50 eV is typically treated as secondary electrons. Backscattered electrons typically have electron energies between 0 eV and the landing energy of the primary sub-beams 211, 212, 213. Detected electrons with energies less than 50 eV are typically treated as secondary electrons, so that a certain percentage of the actual backscattered electrons are counted as secondary electrons.

[0033]

[0050] The detector 240 is configured to detect signal particles, such as secondary electrons and / or backscattered electrons, and generate corresponding signals, which are sent to a signal processing system 280, for example, to construct an image of a corresponding scanned area of ​​the sample 208. The detector 240 may be integrated into the projection device 230.

[0034]

[0051] The signal processing system 280 may include circuitry (not shown) configured to process signals from the detector 240 to form an image. The signal processing system 280 may alternatively be referred to as an image processing system. The signal processing system may be incorporated within a component of the electron beam system 40, such as the detector 240 (as shown in FIG. 2). However, the signal processing system 280 may be incorporated within any number of components of the inspection apparatus 100 or the electron beam system 40, such as as part of the projection apparatus 230 or the controller 50. The signal processing system 280 may include an image acquirer (not shown) and a storage device (not shown). For example, the signal processing system may include a processor, a computer, a server, a mainframe host, a terminal, a personal computer, any type of mobile computing device, etc., or a combination thereof. The image acquirer may include at least a portion of the processing functionality of the controller. Thus, the image acquirer may include at least one or more processors. The image acquirer may be communicatively coupled to the detector 240 that allows for signal communication, such as electrical conductors, fiber optic cables, portable storage media, IR, Bluetooth, Internet, wireless networks, wireless radios, or combinations thereof, among others. The image acquirer may receive signals from the detector 240, process the data contained in the signals, and construct an image therefrom. Thus, the image acquirer may acquire an image of the sample 208. The image acquirer may also perform various post-processing functions, such as generating contours and superimposing indicators on the acquired image. The image acquirer may be configured to make adjustments, such as brightness and contrast, of the acquired image. The storage may be a storage medium, such as a hard disk, a flash drive, cloud storage, random access memory (RAM), or other types of computer readable memory. The storage may be coupled to the image acquirer and may be used to store the raw scanned image data as an original image or to store a post-processed image.

[0035]

[0052] The signal processing system 280 may include measurement circuitry (e.g., analog-to-digital converter) to obtain a distribution of detected secondary electrons. The electron distribution data collected during the detection time window, in combination with the corresponding scan path data of each of the primary sub-beams 211, 212 and 213 incident on the sample surface, may be used to reconstruct an image of the sample structure under inspection. The reconstructed image may be used to reveal various features of the internal or external structure of the sample 208. Thus, the reconstructed image may be used to reveal any defects that may be present in the sample. The above functions of the signal processing system 280 may be performed within the controller 50 or may be shared between the signal processing system 280 and the controller 50 as convenient.

[0036]

[0053] The controller 50 may control the motorized stage 209 to move the sample 208 during inspection of the sample 208. The controller 50 may cause the motorized stage 209 to move the sample 208 continuously or intermittently in one or more selected directions. In some configurations, the movement may be performed at a constant speed. The movement of the sample 208 may be referred to as a scan. Thus, the scan may be continuous or intermittent. The controller 50 may control the movement of the motorized stage 209 such that the motorized stage 209 varies the speed of the movement of the sample 208 depending on various parameters. For example, the controller 50 may control the stage speed (and / or direction) depending on the characteristics of the inspection step of the scanning process and / or the scan of the scanning process, at least as far as the combined step / scan strategy of the stage is concerned, for example as disclosed in European Patent Application Publication No. A21171877.0, filed May 3, 2021, which is incorporated herein by reference.

[0037]

[0054] Known multi-beam systems, such as the electron beam system 40 and charged particle beam inspection apparatus 100 described above, are disclosed in U.S. Patent Application Publication No. 2020118784, U.S. Patent Application Publication No. 20200203116, U.S. Patent Application Publication No. 2019 / 0259570, and U.S. Patent Application Publication No. 2019 / 0259564, which are incorporated by reference herein.

[0038]

[0055] The electron beam system 40 may include a projection assembly for illuminating the sample 208 and thereby regulating charge build-up on the sample.

[0039]

[0056] FIG. 3 is a schematic diagram of an exemplary electron optical column 41 used in the evaluation system. For ease of illustration, the lens array is generally depicted herein by an array of ellipses. Each elliptical shape represents one of the lenses in the lens array. An elliptical shape is conventionally used to represent a lens by analogy with the biconvex shape often adopted by optical lenses. However, it should be understood that in the context of the charged particle arrangement as discussed herein, the lens array does not require any physical element to adopt a biconvex shape, since it usually operates electrostatically. As described below, the lens array may instead include multiple plates having apertures. Each plate having an aperture may be referred to as an electrode. The electrodes may be provided in series along the sub-beam paths of the sub-beams of the multi-beam.

[0040]

[0057] The electron source 201 directs electrons towards an array of collecting lenses 231 (otherwise referred to as a collecting lens array). The electron source 201 is preferably a high-brightness thermal field emitter with a good compromise between brightness and total emission current. There may be tens, hundreds or thousands of collecting lenses 231. The collecting lenses 231 may include multi-electrode lenses and may have a structure based on EP 1 602 121 A1, which is incorporated herein by reference, in particular for its disclosure of a lens array for splitting an electron beam into a number of sub-beams, the array providing one lens per sub-beam. The array of collecting lenses 231 may take the form of at least two, preferably three, plates acting as electrodes, the apertures of each plate being aligned with each other and corresponding to the position of a sub-beam. At least two of the plates are maintained at different potentials during operation to achieve the desired lens effect. Between the plates of the focusing lens array are electrically insulating plates, made of insulating material such as ceramic or glass, with one or more apertures for each sub-beam. One or more alternative arrangements of the plates may feature apertures, each with its own electrode, each with an array of electrodes around its periphery, or arranged as a group of apertures with a common electrode.

[0041]

[0058] In one configuration, the array of collecting lenses 231 is formed from a three-plate array in which a charged particle has the same energy when it enters each lens as when it leaves each lens, and this configuration can be called an Einzel lens. Dispersion therefore occurs only within the Einzel lens itself (between the entrance and exit electrodes of the lens), thereby limiting off-axis chromatic aberration. If the thickness of the collecting lens is small, for example a few mm, the effect of such aberrations is small or negligible.

[0042]

[0059] Each collecting lens in the array directs electrons into a respective sub-beam 211, 212, 213 that is focused at a respective intermediate focus 233. A collimator or an array of collimators may be positioned to operate on each intermediate focus 233. The collimator may take the form of a deflector 235 provided at the intermediate focus 233. The deflector 235 is configured to bend each beamlet 211, 212, 213 by an effective amount to ensure that the chief ray (which may also be referred to as the beam axis) is incident on the sample 208 approximately normal (i.e. at approximately 90° to the nominal surface of the sample).

[0043]

[0060] Below the deflector 235 (i.e. on the down-beam side of or further from the electron source 201) there is a control lens array 250 which includes a control lens 251 for each sub-beam 211, 212, 213. The control lens array 250 may for example include two or more, preferably at least three, plate electrode arrays in contact with respective potential sources between the electrodes, preferably with insulating plates in contact with the electrodes. Each of the plate electrode arrays may be referred to as a control electrode. The function of the control lens array 250 is to optimize the beam opening angle with respect to the beam reduction ratio and / or to control the beam energy delivered to the objective lenses 234, each of which directs the respective sub-beam 211, 212, 213 onto the sample 208.

[0044]

[0061] Optionally, an array of scan deflectors 260 is provided between the control lens array 250 and the array of objective lenses 234 (objective lens array). The array of scan deflectors 260 includes one scan deflector 261 for each sub-beam 211, 212, 213. Each scan deflector is configured to deflect a respective sub-beam 211, 212, 213 in one or two directions to scan the sub-beam in one or two directions across the sample 208.

[0045]

[0062] A detector module 240 of the detector is provided between the objective lens 234 and the sample 208 to detect signal electrons / particles emitted from the sample 208. An exemplary configuration of such a detector module 240 is described below. It should be noted that the detector may additionally or alternatively have detector elements on the up-beam side along the primary beam path of the objective lens array or even the control lens array.

[0046]

[0063] 4 is a schematic diagram of an exemplary electron beam system having an alternative electron optical column 41'. The electron optical column 41' includes an objective lens array 241. The objective lens array 241 includes a plurality of objective lenses. The objective lens array 241 may be an interchangeable module. For the sake of brevity, features of the electron beam system already described above may not be repeated here.

[0047]

[0064] As shown in FIG. 4, the electron optical column 41′ includes an electron source 201. The electron source 201 provides a beam of charged particles (e.g., electrons). A multibeam that is focused on a sample 208 is derived from the beam provided by the electron source 201. Sub-beams may be derived from the beam, for example, by using a beam limiter that defines an array of beam-limiting apertures. The beam may be separated into sub-beams upon hitting the control lens array 250. The sub-beams are approximately parallel upon incidence on the control lens array 250. The sub-beams of the multibeam may be arranged in a pattern that may be referred to as a multi-beam arrangement. The pattern may form a grid. The grid may be hexagonal, linear, diamond or square. In the example shown, a collimator is provided on the up-beam side of the objective lens array assembly.

[0048]

[0065] The collimator may include a macro collimator 270, which acts on the beam from the electron source 201 before the beam is split into multiple beams. The macro collimator 270 bends each portion of the beam by an effective amount to ensure that the beam axis of each sub-beam derived from the beam is incident on the sample 208 approximately normal (i.e., approximately 90° to the nominal surface of the sample 208). The macro collimator 270 includes a magnetic lens and / or an electrostatic lens. In an alternative configuration (not shown), the macro collimator may be partially or wholly replaced by a collimator element array provided on the down beam side of the upper beam restrictor.

[0049]

[0066] In the electron optical column 41' of FIG. 4, a macro scan deflector 265 is provided to cause the sub-beams to scan across the sample 208. The macro scan deflector 265 deflects the respective portions of the beam to cause the sub-beams to scan across the sample 208. In one embodiment, the macro scan deflector 265 includes a macro multi-pole deflector, for example having eight poles or more. The deflection is such that the sub-beams derived from the beam are deflected across the sample 208 in one direction (for example parallel to a single axis, such as the X axis) or two directions (for example with respect to two non-parallel axes, such as the X axis and the Y axis). The macro scan deflector 265 does not include an array of deflector elements, each configured to act on a different individual portion of the beam, but acts macroscopically on all of the beam. In the embodiment shown, the macro scan deflector 265 is provided between the macro collimator 270 and the control lens array 250. In another configuration (not shown), the macro scan deflector 265 may be partially or completely replaced by a scan deflector array, for example as each sub-beam scan deflector 267. In other embodiments, both the macro scan deflector 265 and the scan deflector array may be provided and may operate synchronously.

[0050]

[0067] In some embodiments, the electron optical system 41 further includes an upper beam limiter 252. The upper beam limiter 252 defines an array of beam limiting apertures. The upper beam limiter 252 may be referred to as an upper beam limiting aperture array or an up-beam side beam limiting aperture array. The upper beam limiter 252 may include a plate having a plurality of apertures. The upper beam limiter 252 forms sub-beams from the beam of charged particles emitted by the electron source 201. Portions of the beam other than those that contribute to the formation of the sub-beams may be blocked (e.g., absorbed) by the upper beam limiter 252 so as not to interfere with the down-beam side sub-beams. The upper beam limiter 252 may be referred to as a sub-beam defining aperture array.

[0051]

[0068] In some embodiments, as illustrated in FIG. 4, the objective lens array assembly (which is a unit including the objective lens array 241) further includes a beam-shaping limiter 262. The beam-shaping limiter 262 defines an array of beam-limiting apertures. The beam-shaping limiter 262 may be referred to as a lower beam limiter, a lower beam-limiting aperture array, or a final beam-limiting aperture array. The beam-shaping limiter 262 may include a plate having a plurality of apertures. The beam-shaping limiter 262 may be down-beam from at least one electrode (optionally all electrodes) of the control lens array 250. In some embodiments, the beam-shaping limiter 262 is down-beam from at least one electrode (optionally all electrodes) of the objective lens array 241. In one arrangement, the beam-shaping limiter 262 may be structurally integrated with the electrodes of the objective lens array 241. Desirably, the beam shaping restrictor 262 is positioned in a region of low electrostatic field strength. The beam limiting apertures are aligned with the objective lens array such that a portion of the sub-beams from a corresponding objective lens can pass through the beam limiting aperture and impinge on the sample 208, such that only a selected portion of the sub-beams incident on the beam shaping restrictor 262 pass through the beam limiting aperture.

[0052]

[0069] Any of the objective lens array assemblies described herein may further include a detector 240. The detector detects electrons emitted from the sample 208. The detected electrons may include any of the electrons detected by the SEM, including signal particles such as secondary electrons and / or backscattered electrons emitted from the sample 208. An exemplary structure of the detector 240 is described in more detail below with reference to Figures 6 and 7.

[0053]

[0070] FIG. 5 illustrates diagrammatically an electron beam system 40 including an electron optical column 41″ according to one embodiment. Features that are the same as those described above are labeled with the same reference numerals. For brevity, such features will not be described in detail with reference to FIG. 5. For example, the electron source 201, the collection lens 231, the macro-collimator 270, the objective lens array 241 and the sample 208 may be as described above.

[0054]

[0071] As explained above, in one embodiment, the detector 240 is between the objective lens array 241 and the sample 208. The detector 240 may face the sample 208. Alternatively, as shown in FIG. 5, in one embodiment, the objective lens array 241 including multiple objective lenses is between the detector 240 and the sample 208.

[0055]

[0072] In one embodiment, the deflector array 95 is between the detector 240 and the objective lens array 241. In one embodiment, the deflector array 95 may be referred to as a beam separator since it includes a Wien filter array. The deflector array 95 is configured to provide a magnetic field to separate the charged particles projected onto the sample 208 and the secondary electrons from the sample 208 towards the detector 240. The deflector array 95 may function as a scanning deflector. Such a scanning deflector may scan the sub-beams relative to the sample surface during evaluation of the sample 208.

[0056]

[0073] In one embodiment, the detector 240 is configured to detect signal particles by reference to the energy of the charged particles, i.e. depending on the band gap. Such a detector 240 may be called an indirect current detector. Secondary electrons emitted from the sample 208 gain energy from the electric field between the electrodes. When the secondary electrons reach the detector 240, they have sufficient energy. In a different arrangement, the detector 240 may be a scintillator array, e.g. a fluorescent strip between the beams, positioned on the up-beam side along the primary beam path relative to the Wien filter. The primary beam passing through the Wien filter array (of magnetic and electrostatic strips perpendicular to the primary beam path) has a path on the approximately parallel up-beam and down-beam sides of the Wien filter array, while the signal electrons from the sample are guided by the Wien filter array towards the scintillator array. The generated photons are guided via a photon transport unit (e.g. an array of optical fibers) to a remote photodetector that generates a detection signal in response to the detection of the photons.

[0057]

[0074] The objective lens array 241 of any embodiment may include at least two electrodes in which an aperture array is defined. In other words, the objective lens array includes at least two electrodes having a plurality of holes or apertures. FIG. 5 shows electrodes 242, 243 that are part of an exemplary objective lens array 241 with respective aperture arrays 245, 246. The position of each aperture in an electrode corresponds to the position of a corresponding aperture in another electrode. The corresponding apertures, in use, act on the same beam, sub-beam or group of beams in the multi-beam. In other words, the corresponding apertures in the at least two electrodes are aligned with and disposed along one of the sub-beam paths, i.e., the sub-beam paths 220. Thus, the electrodes each include an aperture through which the respective sub-beam 211, 212, 213 propagates.

[0058]

[0075] The objective lens array 241 may include two or three electrodes as shown in FIG. 6, or may have more electrodes (not shown). An objective lens array 241 with only two electrodes may have less aberration than an objective lens array 241 with more electrodes. A three-electrode objective lens allows for a stronger lens because the potential difference between the electrodes can be larger. Additional electrodes (i.e., more than two electrodes) provide additional degrees of freedom in controlling the electron trajectory, for example to focus secondary electrons in addition to the incident beam. The advantage of a two-electrode lens over an Einzel lens is that the energy of the incoming beam is not necessarily the same as the outgoing beam. The potential difference on such a two-electrode lens array advantageously allows it to function as either an acceleration or deceleration lens array.

[0059]

[0076] Adjacent electrodes of the objective lens array 241 are spaced apart from one another along the sub-beam paths such that the distance between adjacent electrodes is greater than the objective lenses of the objective lens array, and insulating structures may be arranged as described below.

[0060]

[0077] Preferably, each of the electrodes provided in the objective lens array 241 is a plate. The electrodes may alternatively be described as flat sheets. Preferably, each of the electrodes is flat. In other words, each of the electrodes is preferably provided as a thin flat plate in the form of a plate. Of course, the electrodes do not have to be flat. For example, the electrodes may bend due to forces resulting from high electrostatic fields. It is preferred to provide flat electrodes, as this makes the electrodes easier to manufacture, since known fabrication methods may be used. Flat electrodes may also be preferred, as they may provide a more accurate alignment of the apertures between the various electrodes.

[0061]

[0078] The objective lens array 241 may be configured to demagnify the charged particle beam by a factor of more than 10, preferably in the range of 50-100 or more.

[0062]

[0079] The detector 240 is provided for detecting signal particles, i.e. secondary charged particles and / or backscattered charged particles, emitted from the sample 208. The detector 240 is positioned between the objective lens 234 and the sample 208. Depending on the direction of the signal particles, the detector generates a detection signal. The detector 240 may alternatively be referred to as a detector array or a sensor array, and the terms "detector" and "sensor" are used interchangeably throughout this application.

[0063]

[0080] An electron optical device of the electron optical system 41 may be provided. The electron optical device is configured to project the electron beam towards the sample 208. The electron optical device may include an objective lens array 241. The electron optical device may include a detector 240. The array of objective lenses (i.e., objective lens array 241) may correspond to an array of detectors (i.e., detector 240) and / or may correspond to any of the beams (i.e., sub-beams).

[0064]

[0081] An exemplary detector 240 is described below. However, any reference to detector 240 may be a single detector (i.e., at least one detector) or multiple detectors, as appropriate. Detector 240 may include detector elements 405 (e.g., sensor elements such as capture electrodes). Detector 240 may include any suitable type of detector. For example, capture electrodes, scintillators, or PIN elements for, e.g., directly detecting electronic charges may be used. Detector 240 may be a direct current detector or an indirect current detector. Detector 240 may be a detector as described below with respect to FIG. 7.

[0065]

[0082] The detector 240 may be positioned between the objective lens array 241 and the sample 208. The detector 240 is configured to be close to the sample 208. The detector 240 may be very close to the sample 208. Alternatively, there may be a large gap from the detector 240 to the sample 208. The detector 240 may be positioned within the device such that it faces the sample 208. Alternatively, the detector 240 may be positioned elsewhere in the electron-optical system 41 such that a part of the electron-optical device that is not the detector faces the sample 208.

[0066]

[0083] FIG. 7 is a bottom view of a detector 240 including a substrate 404 on which a number of detector elements 405 are provided, each surrounding a beam aperture 406. The beam apertures 406 may be formed by etching the substrate 404. In the arrangement shown in FIG. 7, the beam apertures 406 are arranged in a hexagonal close-packed array. The beam apertures 406 may also be arranged differently, for example in a rectangular or diamond array. The beam arrangement of the hexagonal arrangement of FIG. 7 may be more densely packed than a square beam arrangement. The detector elements 405 may be arranged in a rectangular array or a hexagonal array. The beam apertures may correspond to a multi-beam arrangement of sub-beams directed to the substrate 404.

[0067]

[0084] The capture electrode 405 forms the bottom, i.e. the surface closest to the sample, of the detector module 240. Between the capture electrode 405 and the body of the silicon substrate 404, a logic layer is provided. The logic layer may include amplifiers, e.g. transimpedance amplifiers, analogue to digital converters and readout logic. In one embodiment, there is one amplifier and one analogue to digital converter per capture electrode 405. Circuits featuring these elements may be contained within unit areas called cells associated with apertures. The detector model 240 may have several cells, each associated with an aperture. Within or on the substrate, there is a wiring layer connected to the logic layer, which connects the logic layer of each cell to the outside world, e.g. via power, control and data lines. The integrated detector module 240 described above is particularly advantageous when used with systems having adjustable landing energies, since secondary electron capture can be optimized for a range of landing energies. The detector module in the form of an array may be integrated into other electrode arrays as well as the bottom electrode array. Such a detector module may, for example, feature a detector that is a scintillator or semiconductor detector, such as a PIN detector, above the most down-beam surface of the objective lens. Such a detector module may feature a circuit architecture similar to that of a detector module that includes a current detector. Further details and alternative arrangements of detector modules integrated into the objective lens, at least as far as the details of the detector module are concerned, may be found in European Patent Application Publication Nos. 20184160.8 and 20217152.6, which are incorporated herein by reference.

[0068]

[0085] The detector may comprise multiple parts, specifically multiple detection parts. A detector including multiple parts may be associated with one of the sub-beams 211, 212, 213. Thus, multiple parts of one detector 240 may be configured to detect signal particles emitted from the sample 208 in association with one of the primary beams (which may otherwise be referred to as sub-beams 211, 212, 213). In other words, a detector including multiple parts may be associated with one of the apertures in at least one electrode of the electrodes of the objective lens assembly. More specifically, a detector 405 including multiple parts may be arranged around a single aperture 406, which provides an example of such a detector. As mentioned, the detection signal from the detector module is used to generate an image. With multiple detection parts, the detection signal includes components from various detection signals that may be processed as a data set or in a detection image.

[0069]

[0086] In one embodiment, the objective lens array 241 is either a replaceable module by itself or in combination with other elements such as a control lens array and / or a detector array. The replaceable modules may be field replaceable, i.e., replaced with a new module by a field engineer. In one embodiment, multiple replaceable modules are included within the system and thus may be swapped between operative and inoperative positions without opening the electron beam system.

[0070]

[0087] In some embodiments, one or more aberration correctors are provided to reduce one or more aberrations in the sub-beams. The aberration correctors, positioned at or directly adjacent to the intermediate focus (or intermediate image plane), may include deflectors that correct the electron source 201 so that it appears to be in different positions for different beams. The correctors may be used to correct macro-aberrations due to the radiation source that prevent good alignment between each sub-beam and the corresponding objective lens. The aberration correctors may correct aberrations that prevent proper column alignment. The aberration correctors may be CMOS-based individual programmable deflectors as disclosed in EP 2702595 A1 or an array of multiple deflectors as disclosed in EP 2715768 A2, the description of the beamlet manipulator in both patent documents being incorporated herein by reference. The aberration correctors may reduce one or more of field curvature, focus error and astigmatism.

[0071]

[0088] An image (which may be represented by an image data set) output from a charged particle evaluation system, such as the electron beam system 40, may be automatically processed to detect defects in the sample 208 under evaluation. The image data set (sometimes called an image) may include data points. The data points may also be called pixels. A region of pixels is an image that may be called a clip. A region of pixels may surround a pixel or group of pixels that have been identified as a potential defect. An example data processing device 500 for detecting defects in an image generated by a charged particle evaluation system is shown in FIG. 8. The data processing device 500 may be part of the controller 50, may be part of another computer in an assembly plant, or may be integrated elsewhere in the charged particle evaluation device. It should be noted that the configuration of components of the data processing device 500 shown and described with reference to FIG. 8 is exemplary and is provided to aid in the description of the functionality of the data processor operating on images generated by the charged particle evaluation system. Any feasible configuration conceived by one skilled in the art of data processors that is capable of achieving the functionality of the data processing device 500 described herein may be used.

[0072]

[0089] In some embodiments, the data processing device 500 includes a filter module 501 that receives and filters a sample image from the charged particle evaluation system 40, a reference image generator 503 that generates a reference image based on the source image, a comparator 502 that compares the filtered sample image with the reference image, and an output module 504 that processes and outputs the results of the comparison.

[0073]

[0090] The filter module 501 applies a filter of a predefined size, for example a uniform filter, to the sample image. Applying the uniform filter involves convolving the sample image with a uniform kernel. The size of the uniform kernel is determined, for example by a user, for the inspection of a given sample based on, for example, the size of the features on the sample, the size of the defects to be detected, the resolution of the charged particle evaluation device, the amount of noise in the image, and the desired compromise between sensitivity and selectivity. Deviations from a mathematical uniform filter are acceptable. For example, corner filters may have values ​​that would slightly over-weight those pixels, but not excessively. A non-uniform filter, for example a Gaussian filter, may be conveniently implemented by convolution with a suitable kernel. The filter module 501, especially when configured to apply a uniform filter of a predefined size, is conveniently implemented by dedicated hardware, for example an FPGA or an ASIC.

[0074]

[0091] The reference image generator 503 may be operable in one or more modes, each mode representing a different approach to the generation of a reference image.

[0075]

[0092] In library mode, the reference image generator 503 averages multiple source images acquired from previous scans of a pattern nominally the same as the one currently being evaluated. Such images may be generated previously within the same batch of samples or from samples in a previous batch. Library images may be derived from test samples or production samples. Before averaging, the images are desirably aligned with each other. Averaging the source images to generate the reference image has the effect of reducing noise. Averaging the source images in this manner averages out any defects that may be visible in the source images.

[0076]

[0093] If the pattern being inspected is a repeating pattern, it is possible to generate a reference image by averaging multiple shifted versions of the source image. If either or both dimensions of the unit cell are not equal to an integer number of pixels, the shift amount can be rounded to the nearest pixel, or a fractional pixel shift can be implemented by interpolation, e.g., 3-dimensional interpolation such as linear or bicubic interpolation, or any other known interpolation technique. Another possibility is to shift by a multiple of the pitch of the repeating pattern such that the multiple is an integer number of pixels. In effect, multiple instances of the unit cell are extracted from the source image and averaged. This approach can be referred to as an example of providing a reference image for the array mode, and more specifically for the array mode.

[0077]

[0094] In die-to-die mode, three columns of the multi-column charged particle evaluation device may be used to generate a sample image and two reference images. An image aligner may be provided to align the images, if necessary, before they are fed to the reference image generator 503 and the filter module 501. This arrangement is particularly efficient when the spacing between the columns is equal to the die size of the sample under inspection, since the columns then automatically scan corresponding pattern features simultaneously. If there is a difference between the column spacing and the die size, a buffer may be employed to correct the timing of the image input to the data processing device.

[0078]

[0095] In an alternative variant of the die-to-die mode, the same beam (of the same row in case of a multi-column system) is used to generate the sample image and the two reference images. This has the advantage that row-to-row and beam-to-beam corrections are not required (e.g., correction of the relative position of the beam with respect to the ideal beam position for that or each beam) and data routing may be simplified. Using the same beam avoids calibration, e.g., evaluation of offsets, between the beams of the different scans to be compared. Using the same beam means that although the beams may have offsets with respect to the ideal beam position, there is no position offset for correction when the comparison data is retrieved from the scans. However, the need for data buffering may be increased, e.g., in terms of frequency if not the amount of data buffered before the start of the comparison of data from different dies.

[0079]

[0096] For example, an alternative version of the array mode using a single column of a single-column system provides a sample image that is compared against a reference image derived from two shifted versions of itself as a source image. A buffer may be used to provide the shifted image.

[0080]

[0097] It should be noted that it is also possible to apply a uniform filter to the source images and / or the reference images, especially when the reference images are derived from a small number of source images acquired simultaneously with the source images.

[0081]

[0098] 8, the comparator 502 can be any logic circuit capable of comparing two values, such as an XOR gate, a subtractor. The comparator 502 is also suitable for implementation by dedicated hardware, such as an FPGA, an ASIC. Preferably, the comparator 502 is implemented on the same dedicated hardware as the filter module 501.

[0082]

[0099] In some cases, the reference image generator 503 may also be implemented in dedicated hardware, especially if the reference image generator operates only in a mode where the reference image is generated from a small number of source images, e.g. two. In this case, it is preferable for the reference image generator to be implemented in the same dedicated hardware as the comparator and / or filter module. The mathematical operations of averaging the pixels of the source images and comparing them with the pixels of the sample image may in preferred cases be combined into a single logic circuit.

[0083]

[0100] The output module 504 receives the results output by the comparator 502 and produces an output to a user or other factory system. The output can be in any of several different forms. In the simplest option, the output can simply be an indication that the sample does or does not have a defect. However, since nearly all samples have at least one potential defect, more detailed information is desirable. The output can include, for example, a map of defect locations, a difference image, and / or information regarding the severity of the potential defects as represented by the magnitude of the difference between the sample image and the reference image. The output module 504 can also filter the potential defects, for example, by outputting only defect locations where the magnitude of the difference between the sample image and the reference image is greater than a threshold value, or where the density of pixels showing the difference is greater than a threshold value. Another possibility is to output only a predetermined number of the most severe defect sites as indicated by the magnitude of the difference. This can be done by storing the defect sites in a buffer 510 and, when the buffer is full, overwriting the least severe defects if a larger magnitude defect is detected.

[0084]

[0101] Any suitable format for outputting the defect information as a data set may be used, for example a list or a map. Desirably, the output module 504 may output a clip. A clip is an image of a portion of the sample surface or an image of a region of pixels that represents a potential defect. This allows the potential defect to be further examined to determine whether the clip represents a defect, i.e., the defect is not in fact an inconvenience signal. Processing of the clip may determine whether the defect is formed or may be formed on the sample, or is significant enough to affect the operation of a device structure that exists or may exist. The remainder of the source image, i.e., the portion not saved as a clip, may be discarded to avoid data storage and data transfer requirements.

[0085]

[0102] FIG. 9 shows a framework (or process flow) of a method for processing a sample 208 using multiple beams of sub-beams of charged particles. The method can be implemented using a charged particle characterization system. In this context, "processing a sample" is intended to mean a relative scanning of the charged particle beam and the surface of the sample 208, typically a scanning of the charged particle beam across the sample surface. Scanning can be, for example, an electro-optical actuation of the charged particle beam, for example by a deflector, and / or a relative movement of the sample with respect to the path of the charged particle beam, for example by an actuable stage. In the characterization system, processing can include detecting signal electrons from the sample. The signal electrons are generated in response to the relative scanning of the sample and the charged particle beam.

[0086]

[0103] The charged particle characterization system may include a sample support. The sample support supports a sample 208. The sample 208 has a sample surface. The sample support may include or consist of a stage 209. The stage 209 may take any of the forms described above with reference to Figures 1 to 7. The stage 209 may support the sample 208 via, for example, a sample holder 207. The sample support may be configured to provide relative movement between the sample 208 and a column. The sample support may include, for example, a motorized stage 209.

[0087]

[0104] The charged particle characterization system may include a charged particle device. The charged particle device may include or consist of an electron optical column or even multiple columns, e.g. multi-column. The charged particle device projects multiple beams onto the sample surface. The multiple beams may be referred to as a multi-beam configuration. The charged particle device may take any suitable form of an electron optical column, such as those described above with reference to Figures 1 to 7. In a configuration with multiple columns, the column may include an electron optical system 41 as described in any of the above embodiments or aspects. As a multiple column (or multi-column system), the devices may be arranged in an array, which may have from 2 to 100 or more rows.

[0088]

[0105] The method includes sequentially performing steps S1-S5 of FIG. 9. The method also includes sequentially performing steps S6 and S7 of FIG. 9. In some embodiments, the charged particle characterization system includes a controller 50 that causes the system to perform the steps. The controller 50 may take any of the forms described above with reference to FIGS. 1 and 2 or other forms. The controller 50 may be configured to control at least the sample support and the charged particle device (e.g., a column) to perform the method. The controller 50 may take the form of a distributed sub-controller. For example, the controller 50 may include any suitable combination of data processing hardware, firmware, software and / or computer controlled actuators, sensors, etc. necessary to provide the desired functionality.

[0089]

[0106] In step S1, as illustrated in FIG. 10 for an example of a single sub-beam of the multi-beam, the sample support is used to move the sample 208 in a direction parallel to a first direction (e.g., along one of the horizontal paths 721 shown in FIG. 10). The movement of the sample 208 can be considered as a movement relative to the path of the multi-beam (e.g., the overall path of the multi-beam, ignoring variations in the paths of the sub-beams due to electrostatic deflection). During this movement, a charged particle device is used to repeatedly move the multi-beam relative to the sample surface in a direction parallel to a second direction different from the first direction (e.g., along the vertical path 722 shown in FIG. 10). Such scanning of the sample surface, e.g., processing, scans an elongated region 724. The scanning of the elongated region 724 of the surface of the sample 208 by the sub-beam is continuous. The charged particle device may, for example, include an electrostatic deflector configured to perform the movement of the multi-beam relative to the sample surface in step S1. The deflector may take any of the forms described above with reference to FIGS. 3 to 7. The deflector may be implemented as an array of scanning deflectors 260, 267 as illustrated in FIG. 3, a macro scanning deflector 265 as illustrated in FIG. 4, or a deflector array 95 as illustrated in FIG. 5. The component of the movement of the multi-beam relative to the sample surface provided by the charged particle device may be referred to as electrostatic scanning of the multi-beam and / or sub-beam. In some embodiments, the deflectors (e.g., deflectors 260, 265, 267, and 95) are located relatively close to the sample 208. As a result, the leverage (or length of the beam path) with which the deflectors operate is small compared to the scale of the sample 208. Other designs of scanning deflectors are also known in which the scanning deflector is at a longer distance from the sample and therefore has a larger leverage. The smaller the leverage, the shorter the scan distance on the sample 208 over which the sub-beams can be scanned without introducing aberrations above an acceptable threshold. For a scan distance of 0.5 μm or 2.0 μm, the unacceptable threshold may be about 10 percent or greater.

[0090]

[0107] The combination of the movement of the sample 208 by the sample support and electrostatic scanning (movement of the multi-beam relative to the sample surface by the eddy particle device) scans each sub-beam repeatedly in a direction parallel to the first direction and in a direction parallel to the second direction, respectively, to process an elongated region 724 on the sample surface. Each sub-beam may simultaneously process each of the different elongated regions 724. Each of the different elongated regions 724 is of a different portion of the sample assigned to a different sub-beam of the multi-beam configuration, which may be referred to as a processing area 740. Thus, the multi-beam may simultaneously process multiple elongated regions 724 corresponding to multiple sub-beams in the multi-beam. The processing may include emitting charged particles from the sample 208. The emitted charged particles may be detected and used to determine information about the sample surface in each elongated region 724. The emitted charged particles may be used, for example, to obtain an image of the processed elongated region 724. The image may be represented by an image data set. Nominally identical patterns in different images may be compared to each other to detect defects.

[0091]

[0108] The paths 721 and 722 and the elongated regions 724 are shown in FIG. 10 diagrammatically as they are visible in the figure. In practice, the spacing of the paths 721 and 722 is denser and much more, for example 20-1000, elongated regions 724 will be processed. The width of the elongated region 724, which may be defined by the available range of the electrostatic deflector, may typically be in the range of 0.2-5.0 μm, for example in the range of 0.5-2.0 μm. The length of the region 724, which may be defined by the pitch of the sub-beams in the multi-beam, may typically be in the range of 50-500 μm. The different elongated regions 724 of the surface of the sample scanned by the sub-beams together define a treatment region 740. The scanning, and therefore the treatment, of the treatment area 740 by the sub-beams is therefore discontinuous.

[0092]

[0109] In the example of Fig. 10, the first and second directions are horizontal and vertical (in the plane of the page). Thus, the first and second directions are perpendicular to each other in this example. Thus, the movement of the sample surface relative to the multibeam, which may be continuous (e.g., along path 721), may be in a direction orthogonal to the relative movement between the multibeam and the sample provided by the charged particle device (e.g., in the direction of electrostatic scanning of the sub-beams). In other embodiments, the first and second directions are oblique to each other.

[0093]

[0110] It should be noted that the movement is continuous along the length of the path 721. The length of the path 721 corresponds to (i.e. is the same as) the length of the elongated region 724. The length of the path 721 is the pitch between the sub-beams in the long direction of the elongated region 724. Beyond or beyond the length of the path, which is longer than the sub-beam pitch in the direction of the path 721 of the elongated region 724, the movement is discontinuous. This is because the area of ​​the sample scanned at one end of the elongated region 724 (if the sub-beam defines a side of a multi-beam configuration) or at both ends (if the sub-beam is between two other sub-beams in a multi-beam configuration) is scanned by each of the adjacent sub-beams respectively.

[0094]

[0111] Over time, the properties of the sub-beams and the electronic optical components acting on them vary. This variation can be referred to as drift. Thus, variations in the properties of the sub-beams and the intensities of the electronic optical components, such as the deflectors of the deflector array, can occur. Drifts in the electronic optical properties of the sub-beams and the intensities of the deflectors of the deflector array (which can be referred to as sub-beam deflectors, since each deflector can act on a different sub-beam) can lead to variations in the position on the surface of the sample where each sub-beam is incident. Charged particles, such as electrons, impart heat to the surface upon impact. Thus, the sub-beams impart a thermal load to the surface of the sample 208. Such an imparted thermal load can cause distortions, such as thermal expansion, of the surface of the sample. Thus, the application of heat increases the uncertainty of the location of the incidence of the sub-beams on the sample surface. The thermal load imparted to the sample surface can contribute to a drift over time of the relative positions of the sample and the sub-beams. In view of the localized heating of the sample surface by the multi-beam configuration (or the footprint of the sample surface on which the multi-beams impinge) and the localization of each sub-beam to an elongated region at any given moment, the applied heat load is non-uniform. The expansion of the sample surface is not common to all sub-beams of the multi-beam. The effect of drift from one or more of the different sources on the positional accuracy of each sub-beam with respect to each elongated region is too large for each sub-beam to reliably scan the elongated region of the sample surface.

[0095]

[0112] In embodiments of the present disclosure, various strategies are proposed to mitigate the effects of drift on the positional accuracy of the sub-beams with respect to the sample surface, allowing improved scanning and processing of the processing area by each sub-beam in a multi-beam configuration.

[0096]

[0113] In one embodiment, a combination of movement of the sample 208 by the sample support and electrostatic scanning (movement of multiple beams relative to the sample surface by a charged particle device) scans each sub-beam repeatedly in a direction parallel to a first direction and in a direction parallel to a second direction, respectively, to process only a section 730 of the elongated region 724 on the sample surface, rather than the entire elongated region 724.

[0097]

[0114] For example, a charged particle characterization system may be provided having a sample support and a charged particle device. The charged particle device directs a multi-beam of sub-beams of charged particles onto a sample surface. A portion of the sample surface corresponds to a multi-beam output area of ​​the charged particle device facing the sample surface. The system controls the sample support and the charged particle device such that a portion is scanned by the sub-beams of the multi-beam. A sub-portion is assigned to each sub-beam. The sample support displaces the sample 208 in successive steps in a direction oblique or perpendicular to a first direction. In each step, the sample 208 moves in a direction parallel to the first direction, such that in each step, each sub-beam scans a section 730 of a corresponding sub-portion (e.g., a section 730 of an elongated region 724) in a direction parallel to the first direction. The corresponding sub-portion includes a plurality of sections 730 in a direction parallel to the first direction. The plurality of sections 730 form the elongated region 724. The charged particle device repeatedly scans the multi-beam across the sample surface in a direction parallel to the second direction during the movement of the sample 208 in a direction parallel to the first direction. Then, a further section 730 is scanned. The further section 730 can be a plurality of sections 730 along the subsection in a direction parallel to the first direction (e.g., in the same row of sections 730) or can be of subsequent successive steps (e.g., in different rows of sections 730).

[0098]

[0115] Such scanning of a reduced area (i.e., section 730, rather than the entire elongated region 724) can reduce the effects of drift, for example, as described below. The layout of the sections 730 is described in more detail below with reference to FIG. 13. Each sub-beam can process a section 730 of a different elongated region 724. Thus, a multiple beam can simultaneously process multiple sections 730 of the elongated region 724 corresponding to multiple sub-beams in the multiple beams. The processing can include emitting charged particles from the sample 208. The emitted charged particles can be detected and used to determine information about the sample surface in each section 730. The emitted charged particles can be used, for example, to obtain an image of the section 730. The image can be represented by an image dataset. Nominally identical patterns in different images can be compared to each other to detect defects.

[0099]

[0116] Considering the elongated region 724 in Fig. 10 as section 730 in an adjacent configuration, adjacent sections 730 of the elongated region 724 in a direction perpendicular to the longitudinal direction can be shown in Fig. 10. The same comments apply, for example, that the paths 721 and 722 and the elongated region 724 (corresponding to section 730 in this respect) are shown diagrammatically in Fig. 10 as they are visible in the figure, that the spacing of the paths 721 and 722 is closer so that much more sections 730, for example 20 to 1000, are processed, that the width of the section 730, which may be defined by the available range of the electrostatic deflector, may typically be in the range of 0.2 to 5.0 μm, for example 0.5 to 2.0 μm, and that the length of the section 730, which may be defined by the pitch of the sub-beams in the multi-beam, may typically be in the range of 50 to 500 μm. The different sections 730 of the surface of the sample scanned by the sub-beams together define an elongated region 724 in the direction of the path 721, a column 737 in the direction of relative movement between the sections 730 within the column 737 (see also FIG. 13 ), and the scanning, and thus the processing, of all sections 730 of all elongated regions 724 defines a processing area 740. The scanning of the sections 730 in the column and in the elongated region 724 by the sub-beams is therefore discontinuous.

[0100]

[0117] Where the method processes sections 730 arranged in an array of rows of sections 730 and columns of sections 730, as shown in Figures 13 and 14 discussed below, each section 730 may be processed by repeatedly moving the multibeam relative to the sample surface in a direction diagonal or perpendicular to the rows while using a charged particle device, moving the sample in a direction parallel to the rows. Desirably, the diagonal or perpendicular direction to the rows is a direction parallel to the columns of the array of sections 730.

[0101]

[0118] Each sub-beam scans a section 730 of each elongated region 724. Each elongated region 724 may have a length substantially equal to the pitch of the sub-beams in the multi-beam at the sample surface in a first direction. Each elongated region 724 may include at least two of the sections 730. In one configuration, the two sections 730 are similarly sized, alternatively, the sections 730 are differently sized. For example, one section 730 may be a factor larger than another of the sections 730. The sections 730 may be sized to be greater than half the pitch of the sub-beams at the sample surface.

[0102]

[0119] Thus, for example, if sections 730 are of similar length, the distance of movement of sample 208 in step S1 may be substantially less than or equal to half the pitch of the sub-beams in the multi-beam at the sample surface in the first direction. The limited movement in step S1 ensures that even after step S1 is performed multiple times according to steps S1-S5 or S1-S7, each sub-beam primarily or exclusively processes the sample surface in its own assigned area on the sample surface. As described below, each assigned area may be referred to as a sub-beam processing area 740, a sub-beam processable area, or a sub-portion of the portion of the sample surface that corresponds to the field of view of the multi-beam (multi-beam configuration) (assigned to a sub-beam). The area assigned to a sub-beam may also be referred to as the field of view of the sub-beam. The sub-beam processing area 740 may include a plurality of elongated regions 724, each elongated region 724 extending across the sub-beam processing area 740 in the first direction. The elongated regions 724 may together have an area that includes or consists of an area of ​​the sample surface of the sub-beam processing area 740. The elongated regions 724 may be of similar dimensions in a direction oblique or perpendicular to the first direction.

[0103]

[0120] The combination of sub-beam processing areas 740 may be referred to, for example, as the footprint of the charged particle device on the sample surface, the field of view of the charged particle device, or the field of view of the multi-beam or multi-beam configuration. The scanning of the sub-beams over the footprint on the sample surface defines the limit of continuous scanning by all sub-beams of the multi-beam configuration, with each sub-beam scanning each sub-beam processing area of ​​the sample surface within the footprint. To further scan the sample surface, discontinuous scanning is required. The sample is moved relative to the path of the multi-beam configuration so that the sub-beams can scan each sub-beam processing area within the new footprint of the sample surface. The new footprint of the sample surface may be adjacent to the previous footprint of the sample surface, thereby allowing a continuous surface to be scanned and thus processed by discontinuous scanning.

[0104]

[0121] A section 730 or elongated region 724 processed by one sub-beam does not overlap at all or excessively with any section 730 or elongated region 724 processed by a neighboring sub-beam. In some embodiments, the distance of movement of the sample in step S1 is substantially equal to the pitch of the sub-beams in the multi-beam at the sample surface in the first direction divided by an integer, optionally 3, optionally 4, optionally 5, optionally 6, optionally 8, optionally 10 or more. The entire elongated region 724 may be processed by repeatedly performing step S1 to process as many sections 730 as necessary to fill the elongated region 724. Example geometries of the sections 730 and elongated regions 724 are described in further detail below with reference to Figures 13 and 14.

[0105]

[0122] 11 and 12 show an example of the relationship between the geometry of the grid of sub-beams in a multi-beam (defined by the grid positions 702 of the sub-beams) and the geometry of the sub-beam processing areas 740 obtained by performing steps S1-S5 of the method of FIG. 9. Each sub-beam processing area 740 may be formed by an array of sections 730 including rows of sections 730 and columns of sections 730. The array is typically rectangular or square. The array may have other forms such as parallelograms or diamonds. The sub-beam processing areas 740 are scanned together by different sub-beams and thus define discontinuously scanned regions of the surface of the sample 208. The footprint of the surface of the sample 208 may be considered to be the discontinuously scanned portions of the surface of the sample 208.

[0106]

[0123] The examples of Figures 11 and 12 demonstrate that the symmetry of the grid of sub-beams does not have to be the same as the symmetry of the sub-beam processing area 740. In the illustrated example, the sub-beams are provided on a hexagonal grid (i.e. a grid with hexagonal symmetry), while the sub-beam processing area 740 is rectangular. Continuous coverage of the sample surface parallel to a first direction (horizontal in the illustrated orientation) is achieved by configuring the length of the elongated region 724 to be substantially equal to the pitch 711 of the grid of sub-beams in the first direction (i.e. the width of the tessellated hexagon centered on the grid position 702). Continuous coverage of the sample surface parallel to a second direction (vertical in the illustrated orientation) may be achieved by configuring the sum of the widths of the sections 730 (and thus the elongated regions 724) in each column 737 of the sections 730 to be substantially equal to the pitch 712 of the grid of sub-beams in the second direction. However, the scanning of the sub-beams may be discontinuous such that continuous coverage is achieved through continuous coverage by the discontinuous scanning section 730. In practice, it may be necessary for the elongated regions 724 along the columns to overlap slightly, in which case the sum of the widths of the elongated regions 724 in each row 737 may need to be correspondingly longer. Less than 100% coverage may be acceptable. For example, in some cases a threshold gap, e.g., gaps down to 100 nm, may be acceptable. In such cases, it may be possible for the sum of the widths of the elongated regions 724 in each row 737 to be slightly smaller than the pitch 712.

[0107]

[0124] In the particular case where the sub-beams are provided in a hexagonal array with a 70 μm pitch (for simplicity, ignoring possible overlaps or gaps between sections 730), each sub-beam is scanned over a rectangular area of ​​70 μm×60.6 μm (defining the sub-beam processing area 740) to scan a continuous area (60.6, resulting from 0.5×√3×70=60.6). In the case where the field of view of the objective lens (defining the maximum range of relative movement between the multi-beam and the sample surface that the charged particle device can provide at a fixed position of the sample relative to the charged particle device) is about 1 μm, 60 scans of 1.01 μm wide sections 730 in each row 737 of sections 730 are required to cover one area of ​​70 μm×60.6 μm. The length of each section 730 multiplied by the number of rows of sections 730 equals 70 μm. It should be noted that in different configurations, the sub-beams may be provided in an array having a grid of different shapes, e.g., parallelograms, diamonds, rectangles, or squares. In each shaped beam configuration, the sub-beam processing area 740 may be rectangular.

[0108]

[0125] FIG. 13 shows diagrammatically how sections 730 of elongated region 724 can fill a single sub-beam processing area 740. Although sections 730 are shown as contiguous (touching with no overlap or gap), in practice, as discussed above, sections 730 may be processed such that there is a small overlap and / or gap between them. The overlap or gap may be controlled by controlling the width of sections 730 (e.g., changing the distance over which electrostatic scanning is performed) and / or by controlling the positioning of sections 730 (e.g., positioning sections 730 closer together to increase overlap or positioning sections 730 further apart to reduce overlap or provide gaps between sections 730). Sections 730 are provided in a rectangular array with seven rows and three columns. Each row of three sections 730 fills a single elongated region 724. The single elongated region 724 may correspond to the sub-beam pitch.

[0109]

[0126] To ensure that the length of the elongated regions 724 is pitched, scanning of the elongated regions 724 may be accomplished with overlap between the sections 730 in at least the long direction of the sections 730. The elongated regions 724 together define a sub-beam processing area 740. Thus, the sub-beam processing area 740 is made up of multiple rows of sections 730. The overlap between the sections 730 may be configured to be the same for all elongated regions 724 that are scanned simultaneously by different sub-beams of a multi-beam configuration. An example elongated region 724 is shown in bold and labeled 724. As discussed above, the degree to which the sections 730 overlap along a column (or whether they overlap at all) may be controlled by controlling the width and / or position of the sections 730 along the column.

[0110]

[0127] FIG. 14 shows diagrammatically how steps S1-S5 can be used to process a sub-beam processing area 740 such as that shown in FIG. 13 with each sub-beam.

[0111]

[0128] Each sub-beam processing area 740 may be processed in whole or only in part. For example, during processing of a sub-beam processing area 740, a sub-beam of the multi-beam may be stopped or switched to process a different area of ​​the sample. A sub-beam may be blank (which may be referred to as "switched off") during a portion of the scan of FIG. 14. Thus, the method of the present disclosure may be configured to process at least a portion of the sub-beam processing area 740 with each sub-beam. Each sub-beam processing area 740 may include an array of sections 730 having rows of sections 730 and columns of sections 730. Each row of sections 730 may define an elongated region 724 as described above (the elongated region 724 may be substantially equal to or smaller than the pitch of the sub-beams in the multi-beam at the sample surface). Processing at least a portion of the sub-beam processing area 740 includes processing a plurality of sections 730.

[0112]

[0129] As mentioned above, in step S1, one section 730 is processed for each sub-beam. This step S1 processing is illustrated in Figure 14 for one sub-beam (the sub-beam corresponding to the sub-beam processing area 740 shown in Figures 13 and 14) by the solid horizontal arrow labeled S1 pointing right at the section 730 located in the upper left corner of the array of sections 730.

[0113]

[0130] In step S2, the sample 208 is displaced in a direction oblique or perpendicular to the first direction. The displacement of the sample 208 can be considered relative to the path of the multibeam. In the example of FIG. 14, the displacement of the sample 208 moves the center of the objective's field of view relative to the sample 208, as shown by the dashed line marked S2. In the examples of FIGS. 10 and 14, the objective's field of view is displaced in S2 in a direction perpendicular to the first direction (e.g., vertically downward in the plane of the page). The corresponding displacement of the sample 208 can be referred to as a step. The sample support (e.g., stage 209) can thus be configured to step the sample 208. The direction of the displacement can be referred to as the step direction. The movement of the sample surface relative to the multibeam along the path 721 can thus be in a direction perpendicular to the stepping of the stage 209. The distance of displacement of the sample in step S2 after each repetition of step S1 may be such that the multiple processed sections 730 in each row 737 partially overlap (as illustrated in FIG. 10), are contiguous, or are close enough to provide acceptable coverage of the sample surface, taking imperfections into account, with less than a coverage gap, such as 20 nm, 50 nm, 100 nm, or 200 nm. Such overlap may be referred to as stripe overscanning. Such overscanning may be achieved by scanning the sections 730 wider or by positioning the sections 730 closer together. Stripe overscanning may mean that additional sections 730 may need to be scanned in each row to process the entirety of the sub-beam processing area 740. Scanning more sections 730 in each row is undesirable, as it reduces throughput.

[0114]

[0131] Therefore, the distance of successive step displacement of the sample 208 by the sample support (e.g., stage 209) in a direction oblique or perpendicular to the first direction may be close to (and typically slightly narrower than) the maximum range of movement of the multi-beam by the charged particle device relative to the sample surface in a direction parallel to the second direction (e.g., the maximum range of electrostatic deflection) in step S1.

[0115]

[0132] The term overscanning refers to scanning a larger area than would nominally be necessary to achieve proper processing (e.g., scanning of the sample surface by the sub-beams) in the absence of scanning imperfections. Overscanning can be performed for a variety of different reasons: for example, to allow data from adjacent scans to be combined together (e.g., stitched together) to form an image of a larger area, to account for alignment errors (location of the region of interest not precisely known) or for a combination of multiple reasons, some of which may be disclosed herein. For example, with respect to a method of the type described above with reference to FIG. 9, stripe overscanning may be necessary to account for drift in the properties of the sub-beams or intensity variations of the sub-beam deflectors. Stripe overscanning may be such that the sections 730 are arranged to overlap each other along a row 737 of sections 730. The overlap may, for example, be in the range of 5% to 10% of the width of the sections 730. For a typical deflection range of 1.0 μm, this would correspond to an overlap in the range of 10 to 250 nm, e.g., 50 nm to 100 nm. In embodiments where small gaps between sections 730 are tolerable (e.g., up to a threshold gap, such as up to about 100 nm), sections 730 may be arranged to have an average spacing closer to a nominally tolerable gap size to compensate for imperfections in the scanning process. Thus, sections 730 are scanned more closely than nominally required to compensate for imperfections.

[0116]

[0133] In step S3, step S1 is repeated to process a section 730 with each sub-beam. A section can be considered as a portion of a further elongated region 724 that may be adjacent to the elongated region 724 of the section 730 previously scanned during step S1. In the example of FIG. 14, the repetition of step S1 processes the second section down in the first column 737 of the array (e.g., the left-most column as shown). The second section 730 down in the column 737, e.g., the second section 730 down, is part of the second row. The second row forms the further elongated region 724. The distance of the sample displacement in step S2 can be such as to include a stripe overscan, as described above. Thus, after scanning a section 730 in step S1, the next section 730 adjacent to the previously scanned section 730 is scanned (in step S3) using the same movement as that used to scan the previously scanned section 730 (because both sections 730 are scanned using the movement defined in step S1).

[0117]

[0134] In step S4, steps S2 and S3 are repeated multiple times to process each section 730 of the further elongated regions 724 in each sub-beam, each elongated region 724 corresponding to a different row in the array. In the example of FIG. 14, the repetition of S2 and S3 processes the third through seventh sections 730 in the first column 737 of the array, thereby completing the processing of one column 737 in the array. Note that in a variant, step S2 moves the sample relative to the path of the sub-beam such that the relative movement of the sample and the sub-beam in step S3 is the same as in step S1, whereby S3 is an alternative label for S1. That is, instead of moving the sample 208 along column 737 to an adjacent section 730 relative to the path of the sub-beam, the sample moves in the reverse direction of movement in S1, such that the scanning movement of the sample relative to the beam path is the same in steps S1 and S3. Similarly, step S4 comprises a repeat of steps S1 and S2) according to steps S1 to S3 (or alternatively, an alternative embodiment, since S3 comprises the same movement as S1).

[0118]

[0135] A step or pitch area overscan (or column area overscan if applied to columns) may be applied in step S4 when scanning the sections 730 forming a column. Pitch area overscan refers to configuring the overall size of the sub-beam processing area 740 to be larger than would nominally be necessary in the absence of imperfections. For example, the size of the sub-beam processing area 740 may be slightly larger than the pitch of the multi-beam configuration in a direction parallel to the columns of sections 730 and / or in a direction parallel to the rows of sections 730. Pitch area overscan may be achieved by arranging the sections 730 at the edges of the sub-beam processing area 740 to extend beyond the nominal boundaries of the sub-beam processing area 740. This may be achieved by controlling the width, length and / or position of these sections 730 and / or adding additional sections 730 to the rows and / or columns. Pitch area overscan may account for beam or sample drift during the overall scan of the sub-beam processing area 740 and / or imperfections in the sub-beam grid. It may be useful for stitching sub-beam processing areas 740 together.

[0119]

[0136] In step S5, steps S1-S4 are repeated to process a series of sections 730 of the elongated region 724 with each sub-beam. The series of sections to be processed may be referred to as the unprocessed region before processing. Each repetition of steps S1-S4 processes a row 737 of sections 730. Thus, each unprocessed section 730 of the series may correspond to one row 737 of sections 730. In the example of FIG. 14, the series of unprocessed sections consists of sections 730 in a central row 737 of the array. The series of unprocessed sections is adjacent in a direction parallel to the movement in step S1 to a corresponding series of sections 730 of the respective elongated region 724 previously processed by a sub-beam. In the example of FIG. 13, the previously processed sections are sections 730 in a left row 737 of the array. Thus, the section 730 in the central row may be adjacent in a horizontal direction to the section 730 in the left row, as shown.

[0120]

[0137] Step S5 may be performed one or more times. For example, step S5 may be repeated one to nine times or a sufficient number of times that the sections 730 of the sample surface of each elongated region 724 are processed. In some embodiments, S5 is performed a sufficient number of times that the generated plurality of processed sections 730 cover the plurality of elongated regions 724. The processed plurality of elongated regions 724 then cover and / or define the sub-beam processing areas 740 of each sub-beam. Typically, the number of times step S5 is repeated is equal to the number of sections 730 in the elongated region 724 minus one or the division that the elongated region 724 undergoes to define its constituent sections 730. For example, if there are ten sections 730 per elongated region 724, then step S5 is repeated nine times. This corresponds to the number of divisions made to the elongated region 724 to define the ten sections 730. 14, each elongated region 724 includes three sections 730, so step S5 is performed twice. The first performance of S5 processes a center row 737 of sections 730. The second performance of S5 processes a right row 737 of sections 730. The direction of processing the sections 730 in each row 737 may be the same as step S2, e.g., down the row 737, or may be a different direction, e.g., up the row 737. The direction of processing the sections 730 in a row 737 may be the same, or the direction of scanning the sections 730 in different rows may be reversed, e.g., for every other or adjacent row 737.

[0121]

[0138] Thus, the method of steps S1-S5 may be used to process columns of sections 730 in sequence, with all sections 730 in each column 737 processed before processing subsequent columns 737. Thus, in other embodiments in which an array of sections 730 is processed, rows of sections 730 may be processed in alternating sequence, optionally with all sections 730 in each row processed before processing subsequent rows.

[0122]

[0139] As mentioned above, overscanning can be used to compensate for imperfections including factors that drift over time such as variations in deflector performance and thermal effects from heating caused by sub-beams. Overscanning reduces throughput by increasing the total amount of scanning required. The amount of overscanning required depends on the magnitude of the imperfections that need to be compensated for by overscanning. The magnitude of the imperfections therefore depends on the delay between processing one section 730 and processing the next section 730. This delay is reduced by making the sections 730 smaller than the elongated regions 724 compared to processing each elongated region 724 in its entirety before moving on to the next elongated region 724. Making the sections 730 smaller means that they can be scanned faster for the same dose. The smaller the sections, the more sections there are per elongated region 724 or across the processing area 740. A processing area with smaller sections has more columns 737. Reducing the delay between scanning different sections 730 reduces the effect of drift in the positioning accuracy of the sample relative to the path of the multi-beam between scanning different sections 730. The resulting improved positioning accuracy means that less overscan is required to ensure adequate coverage of the sample surface. For example, less overlap may be required between neighboring sections 730 within a row of sections 730. Reducing overscan improves throughput by reducing the total amount of scanning that is performed. For example, the portion of each sub-beam processing area 740 that is scanned twice is reduced. If overscanning results in additional sections 730 being required within a row of an array of sections 730, the number of such additional sections 730 is reduced. Thus, processing sub-beam processing areas 740 in an array of sections having multiple rows (rather than a single row) contributes to improved throughput.

[0123]

[0140] The embodiments of the present disclosure are particularly applicable when the electrostatic deflection range () in step S1 is substantially equal to or less than half (50%), optionally less than 10%, optionally less than 5%, optionally less than 2%, optionally less than 1%, optionally less than 0.5% of the minimum pitch of the sub-beams in the multi-beam at the sample surface. As described above with reference to FIG. 11, the sub-beams in the multi-beam may be provided in a grid defined by grid positions 702. The pitch of the sub-beams may refer to the pitch of the grid positions 702. The sub-beams are thus arranged to scan within the pitch. The pitch along different major axes of the grid may be different. The minimum pitch may be the pitch of the major axis having the minimum pitch. The embodiments are therefore particularly applicable when the hardware is not capable of scanning the sub-beams over a distance large enough to cover more than half the pitch without movement of the sample 208 relative to the charged particle device 41, 41', 41''. Thus, the techniques can be effectively applied to embodiments having an objective lens array assembly, such as the objective lens array assemblies described above with reference to Figures 3 to 7. As noted, such devices may have scanning deflectors relatively close to the sample, limiting the electrostatic scanning range of the deflectors.

[0124]

[0141] In some embodiments, the method further comprises steps S6 and S7, in sequence (S6 followed by S7). In step S6, the sample support is used to displace the sample 208 by a distance equal to at least twice the pitch of the sub-beams in the multi-beam at the sample surface. This displacement may be referred to as leap displacement. The displacement distance may be much larger than twice the pitch, optionally many times longer, for example 10-100 times the pitch, optionally as large as the overall size of the footprint of the multi-beam on the sample surface.

[0125]

[0142] In step S7, steps S1-S5, optionally steps S1-S6, are repeated from a new location of the sample 208 after the displacement of step S6. Thus, the scanning of the multi-beam in successive steps (e.g. steps S1-S5) is performed multiple times to process a corresponding number of sub-beam processing areas 740 with each sub-beam, and the stage 209 may optionally perform a leap displacement (e.g. step S6) after each performance of the successive steps. Thus, the sample 208 is moved each time so that a new area of ​​the sample surface is located under the multi-beam output area of ​​the charged particle device. The method may be used to process a multi-beam sized area in each performance of steps S1-S5. The multi-beam sized areas may be scanned adjacent to each other to scan a large continuous area, i.e. a continuous area of ​​the sample that is discontinuously scanned by the sub-beams of the multi-beam configuration. Alternatively, multi-beam sized areas spaced apart from each other may be processed. The movement of the sample 208 in S6 may be in a first direction or in a second direction. However, movement can be in any direction to any area of ​​the sample surface.

[0126]

[0143] In some embodiments, each sub-beam processes a respective sub-beam processing area 740, and the resulting multiple sub-beam processing areas 740 overlap and / or are contiguous with respect to each other. Thus, a contiguous area larger than any individual sub-beam processing area 740 is processed between each leap displacement. The multiple sub-beam processing areas 740 forming the contiguous area may define a footprint of the charged particle device 41, 41', 41''. As illustrated in FIG. 15, the footprint 732 of the charged particle device may be defined as a minimum bounding box on the sample surface that encloses all of the sub-beam processing areas 740. Thus, the footprint 732 has a contour or boundary that corresponds to (e.g., the same as) the contour of the minimum bounding box on the sample surface that encloses all of the sub-beam processing areas 740. The sub-beam processing area 740 enclosed by the minimum bounding box is the sub-beam processing area 740 that is formed with a small position range (corresponding to the movement of the sample 208 required to perform steps S1-S5) between leap displacements (performing step S6). The size and shape of the footprint of the charged particle device may be defined by the size and shape of the multi-beam output surface of the charged particle device (e.g., the portion of the objective lens example closest to the sample 208). In some embodiments, the distance of the displacement of the sample 208 in step S6 (schematically shown by the arrow 734 leading from the center 731 of one footprint 732 to the center 731 of another footprint 732) is substantially equal to or greater than the dimension 735 of the footprint parallel to the direction of displacement. The direction of the displacement of the sample 208 in step S6 may be parallel to the first direction (corresponding to the direction of movement of the sample 208 in step S1) or may be in a different direction. The displacement in step S6 may be configured such that the sub-beam processing areas 740 filling the footprint between the leap displacements fit together, as illustrated in FIG. 15. Thus, one performance of steps S1-S5 may define a first group of sub-beam processing areas 740 (e.g., within the bottom left footprint 732 in FIG. 15).Step S7 may continue by forming a second group of sub-beam processing areas 740 that overlaps and / or is contiguous with the first group of sub-beam processing areas 740 (eg, within the top right footprint 732 in FIG. 15).

[0127]

[0144] In the embodiment described above, the sections 730 in the array of sections 730 are processed column by column. In other embodiments, the sections 730 are processed in a different order. For example, in some embodiments, the sections 730 are processed row by row (i.e., the processing of each row is completed before the processing of the next row begins). For example, the processing of all of the sections 730 in the top row of the example configuration of FIG. 13 may be followed by the processing of all of the sections 730 in the next row down. The processing continues until all of the sub-beam processing areas 740 have been processed. In some embodiments, different subsets of the sections 730 are processed using different directions of sample displacement in steps S1 and S3. This is illustrated in FIG. 14, where half of the sections 730 are processed with the samples moving to the right with S1 and S3, and half of the sections 730 are processed with the samples moving to the left with S1 and S3. Various other configurations are possible. For example, samples may move in the same direction for all sections 730 in a column and in the opposite direction for all sections 730 in another column. Furthermore, it is not necessary to move downward (as shown in FIG. 13 ) from one section 730 in a column 737 to the next section 730 in the column 737. The sections 730 within each column 737 may instead be processed from bottom to top. Alternatively, different columns 737 may be processed in different directions. The sections 730 in a column 737 may be processed from top to bottom, and the sections 730 in an adjacent column 737 may be processed from bottom to top. In some embodiments, the sections 730 in an array may be processed such that multiple, but not all, sections 730 in one row are processed, followed by processing of multiple, but not all, sections 730 in a different row, such as an adjacent row. In some embodiments, a first row of sections 730 is processed, and a second row of sections 730 is processed immediately after the first row of sections 730, and the first row of sections 730 and the second row of sections 730 are not immediately adjacent to one another. Thus, a third row of sections 730 may be provided between the first and second rows and processed at a later time.Similarly, in some embodiments, the first row of section 730 is processed, the second row of section 730 is processed immediately after the first row of section 730, and the first row of section 730 and the second row of section 730 are not immediately adjacent to one another. Thus, the third row of section 730 may be provided between the first and second rows and processed at a later time.

[0128]

[0145] In some embodiments, the paths 722 of movement of the multi-beams with the charged particle device over the sample 208 in step S1 are all in the same direction, as illustrated in FIG. 10. This approach may promote uniformity of the scanning process from one scan to the next and / or allow errors to be corrected more easily. For example, if the scanning with the charged particle device in step S1 is all performed in the same direction (i.e., stepped), mis-synchronization between the deflector and the detector may lead to shifting of the pattern. Such shifting may be corrected in downstream processing of the image. However, if the scanning with the charged particle device in step S1 is performed in alternating directions, mis-synchronization between the deflector and the detector may lead to blurring of the pattern (as alternating pixel rows of the image are shifted up or down). This blurring is more difficult to correct. In other embodiments, as illustrated in FIG. 16, the scanning of the multi-beams with the charged particle device over the sample 209 in step S1 is performed in alternating directions (e.g., in the order up-down-up-down-up in the orientation shown in FIG. 16). This allows the scan path to be more contiguous. Arranging the scan path 722 to be more contiguous may reduce bandwidth requirements compared to the approach of FIG.

[0129]

[0146] In some embodiments, as illustrated in FIG. 10 and FIG. 14, during repeated performances of step S1, the movements of the sample 208 in step S1 are performed in alternating directions (e.g., such that the path 721 follows a right-left-right-left order in the orientation shown in FIG. 10). In such a configuration, the direction of the sequential path 721 can be referred to as continuous and serpentine. This approach minimizes the overall distance traveled by the sample 208. In other embodiments, as illustrated in FIG. 17, during repeated performances of step S1, the movements of the sample 208 in step S1 are all in the same direction. In such a configuration, the direction of the sequential path 721 can be referred to as stepping.

[0130]

[0147] As previously mentioned, processing with the sub-beams may cause charged particles to be ejected from the sample 208. The ejected charged particles may be detected and used to determine information about the sample 208. In some embodiments, the method includes generating image data sets by detecting the ejected charged particles from the sample 208 during processing of the multiple sections 730. In one embodiment, each image data set represents information about a portion of the sample surface corresponding to a different one of the sections 730. In some embodiments, the sample 208 has nominally identical pattern repeat portions at different locations on the sample surface. The method may include detecting defects in the sample by comparing image data sets of sections 730 where the sample has nominally identical patterns. For example, if the nominally identical pattern repeat portions extend across a large portion of the sample surface, the image data sets may be compared to sections 730 located at corresponding locations in different nominally identical pattern repeat portions. Corresponding locations are such that the patterns in the sections 730 are identical if the nominally identical pattern repeat locations are completely identical. For example, the section 730 may be located at the same location relative to the boundaries of each of the nominally identical pattern repeat portions. For example, the section 730 at the geometric center of one of the nominally identical pattern repeat portions may be compared to the section 730 at the geometric center of another of the nominally identical pattern repeat portions. The comparison may be performed using any of the techniques described above with reference to FIG. 8. The comparison may be performed by a data processing device 500 such as that described above with reference to FIG. 8. The comparison may include using a first subset of the image data set to generate a reference image (e.g., using the reference image generator 503) and comparing a second subset of the image data to the reference image to detect defects. The different image data sets may be acquired simultaneously or at different times. The image data sets may be of different locations on the sample. The image data sets may include each sub-beam processing area 740 at different locations.

[0131]

[0148] In some embodiments, each sub-beam processes a sub-beam processing area 740 in multiple different processing regions on the sample surface. The different processing regions can be different regions in the same die (e.g., array mode) or different dies (e.g., die-to-die mode). The different processing regions can correspond to different footprints on the surface of the sample 208 that can be spaced apart. FIG. 18 shows an example of a step and scan sequence in an example embodiment where a rectangular grid of pattern repeat regions 760 exists on the sample surface. In this case, the different processing regions can be within or overlap different individual pattern repeat regions 760 or combinations of pattern repeat regions 760. Thus, the sub-beams can process a sub-beam processing area 740 with the charged particle device primarily facing one of the pattern repeat regions 760, and then move the sample 208 to a position where the charged particle device primarily faces a different one of the pattern repeat regions 760. This can be referred to as a step and scan sequence. In the illustrated example, the sub-beam processing areas 740 corresponding to each scan phase are within a hexagonal footprint 732 (e.g., corresponding to an example multi-beam geometry as described above with reference to FIG. 15). An example step and scan sequence moves footprint 732 in sequence from a starting footprint location 821 through footprint locations 822-823 via steps 802. A larger step 803 can then move footprint 732 back to either a different starting footprint location 824 (as shown in FIG. 18) or the same starting footprint location (not shown) and the sequence can be repeated.

[0132]

[0149] In some embodiments, all sections 730 in each sub-beam processing area 740 are processed at each footprint location 821-823. In this case, it may be appropriate to bring the footprint 732 to a different starting footprint location by a larger step 803, as illustrated in Figure 18, before the sequence is repeated.

[0133]

[0150] In some embodiments, only a subgroup (less than all) of the sections 730 of the sub-beam processing area 740, e.g., at least one section 730, is processed in each visit to footprint locations 821-823. The sections 730 may be processed in groups, for example, for each sub-beam. Each group includes one or more subgroups of sections 730 (e.g., two or more different nominally identical pattern repeat portions 760 that may or may not be located on different dies) in each of two or more different processing regions on the sample 208. Thus, in the example of FIG. 18, one group of sub-beams may include a first subgroup of sections 730 (including one or more sections) in footprint 732 at footprint location 821, a second subgroup of sections 732 (including one or more sections) in footprint 732 at footprint location 822, a third subgroup of sections 732 (including one or more sections) in footprint 732 at footprint location 823. The subgroups of a group may be processed in order, followed by subsequent groups. The image data sets derived from the processing of sections 730 in each group can be compared to each other to detect defects in the sample 208. In such embodiments where only a subgroup of sections 730 are processed at each visit to a footprint 821-823, it may be appropriate to return footprint 732 to the same starting footprint location 824 by a larger step 803. The step and scan sequence may then be repeated, with a different subgroup of sections 730 being processed at each footprint location 821-823.

[0134]

[0151] Any sections 730 or groups of sections 730 located at corresponding positions in different nominally identical pattern repeats can be compared to each other to detect defects in the sample 208.

[0135]

[0152] Processing only a subgroup of sections 730 (rather than all of sections 730) at each visit to footprint locations 821-823 may advantageously reduce the delay between processing of sections 730 in different processing regions that are to be compared to each other to detect defects. Reducing the delay may reduce the likelihood that the properties of the sub-beams change between measurements of each section 730, thereby improving accuracy. Reducing the delay may also reduce buffering requirements in the data processing device 500. Buffering may be reduced to account for movement between at least two footprints. Such movement may occur after processing of sections 730 instead of the entirety of the elongated region 724. Moving the footprint 732 more frequently between footprint locations 821-823 may also reduce adverse effects from heating caused by the multi-beam. More frequent movement of the footprint 732 spreads the heating more evenly across the sample 208. Non-uniform heating causes expansion that is not common to all sub-beams of the multi-beam. Effects that are not common to all sub-beams cannot be completely corrected by realignment of the sample 208. It is therefore particularly desirable to minimize non-uniform heating of the sample 208.

[0136]

[0153] Processing only a subgroup of sections 730, e.g., only a single section 730, at each visit to a footprint 821-823 may increase the delay between processing of sections 730 in the same row 737 of sections of a sub-beam processing area 740. For example, if processing of a section 730 takes 30 seconds, the delay between the start of processing of the section 730 and the start of processing of the section 730 below the section 730 in the same row 737 would be approximately 30 seconds if the sections 730 in the row 737 are processed directly sequentially, but would be 90 seconds (three times longer) if processing is performed according to a scheme such as that shown in FIG. 18. The method described above with reference to FIGS. 9-17, including processing of sections 730 shorter than the elongated region 724 being scanned, e.g., shorter than the length of the sub-beam processing area 740, is particularly advantageous in controlling the effects of drift, thereby reducing the need for increased throughput degradation in stripe overscan. Section 730 may be any fraction of the length, such as a portion of the length or 1 / 3 of the length, of sub-beam treatment area 740, for example, as illustrated in Figures 13-14).

[0137]

[0154] Sample alignment operations may be performed periodically to compensate for effects such as thermal expansion induced by heating of the sample 208 during processing by the multi-beam. Thus, in some embodiments, the method of the present disclosure includes performing one or more sample alignment operations. In some embodiments, the method includes performing a sample alignment operation between processing of different sections 730 in an array of sections 730, such as those shown in Figures 13 and 14. Performing a sample alignment operation between processing of different sections 730 may reduce the delay between sample alignment operations compared to an alternative approach in which an alignment operation is performed only after the entire array of sections 730 of a sub-beam processing area has been processed. As discussed above, reducing the delay may reduce the effects of drift and may reduce stripe overscan requirements. Each sample alignment operation takes a certain period of time (e.g., 2 seconds) to perform. Increased overscan requirements (e.g., stripe overscan requirements for each section and step overscan requirements for columns and processing areas 740) also increase the amount of time required to process the entirety of the sub-beam processing areas 740 by increasing the number of sections 730 that need to be processed. Although the sample alignment operation may appear to add time to complete the alignment, the total time is less than the time required for the same process without the sample alignment operation, taking into account the time required for additional overscan due to drift, etc. The inclusion of the sample alignment operation helps to reduce the total time for sample processing from the time required to account for overscan requirements due to drift, etc., without the sample alignment operation. For example, in one example implementation, it was found that the column 737 of the section 730 needed to include 76 sections without the interleaved sample alignment operation, while only 64 sections per column were needed when the interleaved sample alignment operation was used (due to the reduced stripe overscan requirement).In one example implementation, the interleaved sample alignment operations can reduce the stripe overscan requirement from about 20-25% overlap between sections 730 to about 10-15% overlap between sections 730. Thus, a balance can be found that improves throughput. In one class of embodiments, an optimal balance is found when sample alignment operations are performed every 10-50 seconds, optionally every 20-40 seconds, optionally about every 30 seconds.

[0138]

[0155] The sample alignment operation may be performed using any of a variety of known techniques for aligning the sample 208 with respect to a reference. For example, the sample alignment operation may include detecting a reference marker on the sample 208 or a reference pattern on the sample 208 and aligning the sample 208 to align the reference marker or reference pattern to the charged particle device.

[0139]

[0156] In some embodiments, sample alignment operations are interleaved between the processing of sections 730 such that each of at least a subset of sections 730 has a sample alignment operation performed immediately before and after the processing of a section 730. Thus, the number of sample alignment operations may be substantially equal to the number of sections 730.

[0140]

[0157] In other embodiments, sample alignment operations are interleaved between processing of two or more groups of sections 730. The sections 730 may be in the same sub-beam processing area 740 or in different sub-beam processing areas 740. The groups may consist of different portions of columns 737 of sections 730 in the array. The groups may consist of different entire columns of sections 730 in the array. The groups may consist of different portions of rows of sections 730 in the array, for example different sections 730 in the same elongated region 724 of the processing area 740. The groups may consist of different entire rows of sections 730 in the array. The two or more groups of sections 730 may each include the same number of sections 730. The groups may optionally include at least 3, at least 5, at least 10, at least 20 or at least 50 sections 730. In one configuration, at least one alignment operation may be performed with a scan of the sections 730 of the processing area 740. In one configuration, an alignment operation may be performed by the controller if overscan of a section (i.e. stripe overscan) exceeds a threshold or if overscan of a column or entire processing area of ​​a section (i.e. step overscan or pitch area overscan) exceeds an overscan threshold and / or pitch area threshold.

[0141]

[0158] The method comprising steps S1-S5 may be used to perform sample alignment operations interleaved between processing of single sections (groups of sections) in different sub-beam processing areas 740 to perform various different embodiments described herein. In one such embodiment, step S1 may be configured to include stepping the sample 208 from a position where a first processing region of the sample faces the output of a charged particle device to a position where a further processing region faces the output of a charged particle device or to each of a plurality of positions where each further processing region faces the output of a charged particle device. The position where the first processing region of the sample faces the output of the charged particle device may correspond to the footprint 732 of the charged particle device at footprint position 821 in FIG. 18. The position where the further processing region faces the output of the charged particle device may correspond to the footprint 732 of the charged particle device at footprint position 822, for example. For example, the positions where each further processing region faces the output of the charged particle device may correspond in sequence, e.g. sequentially or alternately, to the footprints 732 at the footprint positions 822 and 823, respectively. The method repeats at each position the movement of the sample 208 in a direction parallel to the first direction and the movement of the multi-beams relative to the sample surface in a direction parallel to the second direction while using the charged particle device. Thereby, one section 730 of the multiple elongated regions on the sample surface is processed with each sub-beam in each of the one or more further processing regions. The sample alignment operation may be performed, for example, between different executions of step S3 within step S4. Thus, the following sequence may be performed. To start, a single section 730 (e.g. having a length less than the size of the corresponding sub-beam processing area) is processed at the footprint position 821. Then, a sample alignment operation is performed. Then, a single section 730 is processed at the footprint position 822. Then, a sample alignment operation is performed. A single section 730 is then processed at footprint location 823. The sample then moves footprint 732 back to footprint location 821.

[0142]

[0159] In some embodiments, an image rendering is derived from a scan of the sample 208. The image includes a number of processing areas 740 arranged in a grid. Each processing area 740 corresponds to a portion of the sample surface scanned by a sub-beam of the multi-beam configuration. The grid has a dimension corresponding to the pitch of the sub-beams of the multi-beam configuration. Each processing area 740 includes an array of sections 730 arranged in rows of sections 730 and columns of sections 730. A row of processed sections in a processing area 740 corresponds to an elongated region 724 having a long dimension of the width of the processing area 740. Each processing area may have sections 730 arranged in the same grid. The sections 730 in an elongated region may be of similar dimensions in the long dimension.

[0143]

[0160] References to top and bottom, up and down, above and below should be understood as referring to directions parallel to the (typically, but not always perpendicular) up-beam and down-beam directions of the electron beam or multi-beam impinging on the sample 208. Thus, up-beam and down-beam references are intended to refer to directions relative to the beam path, independent of any prevailing gravitational fields.

[0144]

[0161] The embodiments described herein may take the form of a series of aperture arrays or electron optical elements arranged in an array along the beam path or multi-beam path. Such electron optical elements may be electrostatic. In one embodiment, for example, all the electron optical elements from the beam limiting aperture array to the final electron optical element in the sub-beam path before the sample may be electrostatic and / or in the form of aperture arrays or plate arrays. In some configurations, one or more of the electron optical elements are fabricated as microelectromechanical systems (MEMS) (i.e., by using MEMS fabrication techniques). The electron optical elements may have magnetic and electrostatic elements. For example, a compound array lens may feature a macro magnetic lens disposed along the multi-beam path, containing the multi-beam path by upper and lower pole plates within the magnetic lens. Within the pole plates there may be an array of apertures for the beam paths of the multi-beam. Electrodes may be above, below or between the pole plates to control and optimize the electromagnetic field of the compound lens array.

[0145]

[0162] Evaluation tools or systems according to the present disclosure may include devices that perform qualitative evaluations (e.g., pass / fail) of a sample, devices that perform quantitative (e.g., size of features) measurements of a sample, or devices that generate images of maps of a sample. Examples of evaluation tools or systems are inspection tools (e.g., to identify defects), review tools (e.g., to classify defects), and metrology tools or tools that can perform any combination of evaluation functions associated with an inspection tool, review tool, or metrology tool (e.g., metro inspection tool).

[0146]

[0163] Reference to a component or a system of components or elements that is controllable to manipulate a charged particle beam in a certain manner includes configuring a controller, or control system, or control unit to control the components to manipulate the charged particle beam in the manner described above, and optionally using other controllers or devices (e.g., voltage sources) to control the components to manipulate the charged particle beam in this manner. For example, a voltage source may be electrically connected to electrodes of one or more components, such as the control lens array 250 and the objective lens array 241, to apply a potential to the components under the control of the controller, or control system, or control unit. An activatable component, such as a stage, may be controllable to be activated and thus moved relative to another component, such as the beam path, by using one or more controllers, control systems, or control units to control the activation of the component.

[0147]

[0164] The functions provided by the controller, or control system, or control unit may be computer-implemented. Any suitable combination of elements may be used to provide the required functionality, including, for example, CPU, RAM, SSD, motherboard, network connections, firmware, software and / or other elements known in the art that allow the required computing operations to be performed. The required computing operations may be defined by one or more computer programs. The one or more computer programs may be provided in the form of a medium, optionally a non-transitory medium, that stores computer-readable instructions. When the computer-readable instructions are read by the computer, the computer performs the required method steps. The computer may be comprised of a distributed computing system having multiple different computers connected to each other in a self-contained unit or via a network.

[0148]

[0165] The terms "sub-beam" and "beamlet" are used interchangeably herein and are both understood to encompass any radiation beam derived from a parent radiation beam by splitting or separating the parent radiation beam. The term "manipulator" is used to encompass any element that affects the path of a sub-beam or beamlet, such as a lens or deflector. References to elements aligned along a beam path or sub-beam path are understood to mean that the respective element is positioned along the beam path or sub-beam path. References to an optical system are understood to mean an electron-optical system.

[0149]

[0166] The method of the present invention may be performed by a computer system including one or more computers. The computer used to implement the present invention may include one or more processors including a general purpose CPU, a graphic processing unit (GPU), a field programmable gate array (FPGA), an application specific integrated circuit (ASIC) or other dedicated processor. As discussed above, in some cases, a particular type of processor may provide advantages in terms of reduced cost and / or increased processing speed, and the method of the present invention may be adapted for use with a particular processor type. Some steps of the method of the present invention involve parallel processing that is amenable to implementation on a processor with parallel processing capabilities, such as a GPU.

[0150]

[0167] The term "image" as used herein is intended to refer to any array of values, where each value relates to a sample at a location, and the arrangement of values ​​in the array corresponds to the spatial arrangement of the sampled locations. An image may include a single layer or multiple layers. In the case of a multiple layer image, each layer, which may also be called a channel, represents a different sample at some location. The term "pixel" is intended to refer to a single value of the array, or a group of values ​​corresponding to a single location in the case of a multiple layer image.

[0151]

[0168] The computer used to implement the present invention may be physical or virtual. The computer used to implement the present invention may be a server, client or workstation. Multiple computers used to implement the present invention may be distributed and interconnected via a local area network (LAN) or a wide area network (WAN). The results of the method of the present invention may be displayed to a user or may be stored in any suitable storage medium. The present invention may be embodied in a non-transitory computer-readable storage medium that stores instructions for performing the method of the present invention. The present invention may be embodied in a computer system including one or more processors and a memory or storage that stores instructions for performing the method of the present invention.

[0152]

[0169] Aspects of the invention are set forth in the following numbered clauses.

[0153]

[0170] Clause 1: A method of processing a sample using multiple sub-beams of charged particles using a charged particle device for projecting the multiple beams onto a sample surface, comprising the steps of: (a) moving the sample in a direction parallel to a first direction while using the charged particle device, and repeatedly moving the multiple beams relative to the sample surface in a direction parallel to a second direction, thereby scanning each sub-beam repeatedly in a direction parallel to the first direction and in a direction parallel to the second direction to process a section of a plurality of elongated regions on the sample surface with the sub-beams, wherein a distance of movement of the sample in (a) is less than or equal to half a pitch of the sub-beams in the multiple beams at the sample surface in the first direction. (b) displacing the sample in a direction oblique or perpendicular to the first direction; (c) repeating step (a) to process further sections of the plurality of elongated regions with each sub-beam; (d) repeating steps (b) and (c) a plurality of times to process further respective sections of the plurality of elongated regions with each sub-beam; and (e) repeating steps (a)-(d) for each sub-beam for a set of unprocessed sections of the elongated region, the set of unprocessed sections being adjacent in a direction parallel to the movement in step (a) to a corresponding set of sections of the respective elongated region previously processed by the sub-beam.

[0154]

[0171] Clause 2: The method of clause 1, wherein in (a), the maximum range of movement of the multi-beam relative to the sample surface by the charged particle device in a direction parallel to the second direction is substantially less than half the minimum pitch of the sub-beams in the multi-beam at the sample surface.

[0155]

[0172] Clause 3: A method according to clause 1 or 2, wherein the distance of movement of the sample in (a) is substantially equal to an integer division of the pitch of the sub-beams in the multi-beam on the sample surface in the first direction.

[0156]

[0173] Clause 4: A method according to any of clauses 1 to 3, wherein step (e) is performed one or more times and the resulting plurality of processed sections cover a plurality of elongated regions, the plurality of processed elongated regions defining a sub-beam processing area for each sub-beam.

[0157]

[0174] The method of claim 4, wherein the distance of the sample displacement in clause 5:(b) is such that the elongated regions in each sub-beam processing area partially overlap each other, are contiguous with each other, or are spaced apart from each other by less than a threshold gap, for example less than 100 nm.

[0158]

[0175] Clause 6: The method of clause 4 or 5, wherein each sub-beam treats a respective sub-beam treatment area, and the resulting sub-beam treatment areas are overlapping and / or contiguous with respect to each other.

[0159]

[0176] Clause 7: A method according to any of clauses 4 to 6, further comprising, after steps (a) to (e), sequentially performing steps (f) of displacing the sample by a distance equal to at least twice the pitch of the sub-beams in the multi-beam on the sample surface, and (g) of repeating steps (a) to (e).

[0160]

[0177] Clause 8: The method of clause 7, wherein performing steps (a) to (e) once defines a first group of sub-beam processing areas, and step (g) forms a second group of sub-beam processing areas overlapping and / or contiguous with the first group of sub-beam processing areas.

[0161]

[0178] Clause 9: A method as described in clause 7 or 8, wherein the footprint of the charged particle device is defined as the smallest bounding box on the sample surface that encloses all of the sub-beam processing areas from the implementation of (a) to (e), and the distance of the sample displacement in (f) is substantially greater than or equal to the dimension of the footprint parallel to the direction of movement.

[0162]

[0179] Clause 10: The method of any one of clauses 4 to 9, wherein step (e) is repeated 1 to 9 times.

[0163]

[0180] Clause 11: A method according to any of clauses 1 to 10, wherein step (a) further comprises stepping the sample from a position where a first processing region of the sample faces the output of the charged particle device to a position where a further processing region faces the output of the charged particle device to each of a plurality of positions where the or each further processing region faces the output of the charged particle device, and repeating the movement of the sample in a direction parallel to the first direction while using the charged particle device at each position to repeatedly move the multi-beam relative to the sample surface in a direction parallel to the second direction, thereby processing a section of a plurality of elongated regions on the sample surface with each sub-beam at the or each further processing region, and step (b) comprises displacing the sample and positioning it back to a position where the first processing region faces the output of the charged particle device.

[0164]

[0181] Clause 12: The method of any of clauses 4 to 11, further comprising performing a sample alignment operation between processing of different sections of the sample surface.

[0165]

[0182] Clause 13: The method described in clause 12, wherein a sample alignment operation is performed between processing of different sections in the same sub-beam processing area.

[0166]

[0183] Clause 14: A method as described in clause 12 or 13, wherein the sample alignment operation includes detecting a reference marker on the sample or a reference pattern on the sample, and aligning the sample to align the reference marker or reference pattern with respect to the charged particle device.

[0167]

[0184] Clause 15: The method according to any of clauses 12 to 14, wherein a sample alignment operation is performed between different performances of step (c) within step (d).

[0168]

[0185] Clause 16: A method for processing a sample using multiple sub-beams of charged particles using a charged particle device for projecting the multiple beams onto a sample surface, comprising processing at least a portion of a sub-beam processable area with each sub-beam, wherein the sub-beam processable area comprises an array of sections having rows of sections and columns of sections, each row of sections defining an elongated region that is substantially less than or equal to the pitch of the sub-beams in the multiple beams at the sample surface, and wherein the processing comprises processing a plurality of sections.

[0169]

[0186] Clause 17: The method of clause 16, further comprising performing a sample alignment operation between processing of different sections in the array of sections.

[0170]

[0187] Clause 18: The method of clause 17, wherein the sample alignment operation includes detecting a reference marker on the sample or a reference pattern on the sample, and aligning the sample to align the reference marker or reference pattern with respect to the charged particle device.

[0171]

[0188] Clause 19: A method according to clause 17 or 18, wherein the sample alignment operations are interleaved between the processing of the sections such that each of at least a subset of the sections has a sample alignment operation performed immediately before and after the processing of the section.

[0172]

[0189] Clause 20: A method as described in clause 17 or 18, wherein sample alignment operations are interleaved between processing of two or more groups of sections, optionally between groups consisting of different portions of columns of sections in the array, optionally between groups consisting of different whole columns of sections in the array, optionally between groups consisting of different portions of rows of sections in the array, optionally between groups consisting of different whole rows of sections in the array.

[0173]

[0190] Clause 21: A method according to any of clauses 16 to 20, wherein each section is processed using a charged particle device by moving the sample in a direction parallel to the rows whilst moving the multi-beam relative to the sample surface in a direction diagonal or perpendicular to the rows, preferably the direction diagonal or perpendicular to the rows being a direction parallel to the columns of the array of sections.

[0174]

[0191] Clause 22: A method according to any of clauses 16 to 21, wherein during processing of each section, the maximum range of movement of the multi-beam relative to the sample by the charged particle device is less than half the minimum pitch of the sub-beams in the multi-beam at the sample surface, and preferably the maximum range is substantially equal to the minimum pitch divided by an integer.

[0175]

[0192] Clause 23: The method of any of clauses 16 to 22, wherein the string of sections is processed in order, and all sections of each string are processed before processing the subsequent string.

[0176]

[0193] Clause 24: A method according to any of clauses 16 to 23, wherein the lines of the sections are processed in order and all sections of each line are processed before processing subsequent lines.

[0177]

[0194] Clause 25: A method according to any of clauses 16 to 24, wherein the array of sections is a rectangular, square or parallelogram array.

[0178]

[0195] Clause 26: A method according to any of clauses 16 to 25, wherein each sub-beam processes a sub-beam processable area in a plurality of different processing regions on the sample surface to define a corresponding plurality of sub-beam processing areas for each sub-beam.

[0179]

[0196] Clause 27: The method of clause 26, wherein the sections are processed in groups for each sub-beam, each group including one or more sub-groups of sections in each of two different processing regions, and the sub-groups of a group are processed in sequence before a subsequent group is processed.

[0180]

[0197] Clause 28: The method of clause 27, wherein the plurality of different processing regions correspond to nominally identical pattern repeats.

[0181]

[0198] Clause 29: A method according to any of clauses 16 to 28, wherein the method comprises generating an image dataset by detecting charged particles emitted from the sample during processing of the plurality of sections.

[0182]

[0199] Clause 30: The method of clause 29, further comprising detecting defects in the sample by comparing image datasets of sections having nominally identical patterns.

[0183]

[0200] Clause 31: The method of clause 30, wherein the different image data sets are acquired simultaneously.

[0184]

[0201] Clause 32: A method as described in clause 30 or 31, wherein the image data sets are of different locations on the sample and sequentially include each sub-beam processable area at the different locations.

[0185]

[0202] Clause 33: A charged particle characterization system comprising a sample support configured to support a sample, and a charged particle device configured to project a plurality of sub-beams of charged particles in a multi-beam configuration onto a portion of a sample surface, the system comprising the steps of: (a) moving the sample in a direction parallel to a first direction while using the charged particle device, and repeatedly moving the multi-beams relative to the sample surface in a direction parallel to a second direction, thereby scanning each sub-beam repeatedly in a direction parallel to the first direction and in a direction parallel to the second direction to process a section of a plurality of elongated regions on the sample surface with the sub-beams, wherein a distance of movement of the sample in (a) is less than or equal to half a pitch of the sub-beams in the multi-beam at the sample surface in the first direction; (b) moving the sample in the first direction while using the charged particle device, (c) repeating step (a) to process further sections of the elongated regions with each sub-beam; (d) repeating steps (b) and (c) multiple times to process further respective sections of the elongated regions with each sub-beam; and (e) repeating steps (a)-(d) for each sub-beam for a set of unprocessed sections of the elongated region, the set of unprocessed sections being adjacent in a direction parallel to the movement in step (a) to a corresponding set of sections of each elongated region previously processed by a sub-beam.

[0186]

[0203] Clause 34: A charged particle characterization system, comprising: a sample support configured to support a sample; and a charged particle device configured to project a plurality of sub-beams of charged particles onto a portion of a sample surface in a multi-beam configuration; the charged particle device comprising: a) processing at least a portion of a sub-beam addressable area with each sub-beam, the sub-beam addressable area comprising an array of sections having rows of sections and columns of sections, each row of sections defining an elongated region that is substantially equal to or less than a pitch of the sub-beams in the multi-beam at the sample surface, the processing comprising processing the plurality of sections; b) exposing at least a portion of a sub-beam scannable area to each sub-beam, the sub-beam scannable area comprising an array of sections having rows of sections and columns of sections, the processing comprising processing the plurality of sections; a) exposing a plurality of sections to each sub-beam; and / or b) exposing at least a portion of the sub-beam scannable area to each sub-beam, the sub-beam scannable area including an array of sections having rows of sections and columns of sections, each row of sections defining an elongated region that is substantially equal to or less than the pitch of the sub-beams in the multi-beam at the sample surface; and a controller configured to control the sample support and charged particle device to do the exposing and perform a sample alignment operation between scanning of different sections in the array of sections.

[0187]

[0204] Clause 35: Rendering of an image derived from a scan of a sample, the image comprising a plurality of processing areas arranged in a grid, each processing area corresponding to a portion of the sample surface scanned by a sub-beam of a multi-beam arrangement, the grid having a dimension corresponding to the pitch of the sub-beams of the multi-beam arrangement, each processing area comprising an array of sections arranged in section rows and section columns, a row of processed sections in a processing area corresponding to an elongated region having a major dimension of the width of the processing area, preferably each processing area having sections arranged in the same grid, preferably the sections in the elongated region having similar dimensions in the major dimension.

[0188]

[0205] Clause 36: A method of processing a sample using a multiple beam of sub-beams of charged particles using a charged particle device for projecting the multiple beams onto a sample surface, comprising: using the charged particle device to project a plurality of sub-beams of charged particles onto a portion of the sample surface in a multi-beam configuration, the portion corresponding to a field of view of the multi-beam configuration, each sub-beam corresponding to a sub-portion of the portion, each sub-portion corresponding to a field of view of a corresponding sub-beam of the multi-beam configuration, the sub-portions including a plurality of elongated regions having together an area extending across the field of view in a first direction and including an area of ​​the sample surface of the sub-portion, each elongated region including a plurality of elongated regions arranged within the elongated region; a first direction, the elongated region optionally having similar dimensions in a direction oblique or perpendicular to the first direction; controlling the sample support and charged particle device so that sub-beams of the multi-beam configuration scan the section within each sub-portion, wherein scanning the section includes moving the sample in a direction parallel to the first direction and moving the multi-beams relative to the sample surface in a direction parallel to a second direction, preferably oblique to the first direction, to scan the section; and using the same movement to scan a next section adjacent to the previously scanned section.

[0189]

[0206] Clause 37: A charged particle characterization system, comprising: a sample support configured to support a sample; and a charged particle device configured to project a plurality of sub-beams of charged particles onto a portion of a sample surface in a multi-beam configuration, the portion corresponding to a field of view of the multi-beam configuration, each sub-beam being assigned to a sub-portion of the portion, each sub-portion corresponding to a field of view of a corresponding sub-beam of the multi-beam configuration, the sub-portions including a plurality of elongated regions extending across the field of view in a first direction and together having an area including an area of ​​the sample surface of the sub-portion, each elongated region including a plurality of sections arranged within the elongated region, the elongated regions including an optional a charged particle device having similar dimensions in a direction oblique or perpendicular to the first direction, and a controller configured to control the sample support and the charged particle device such that the sample moves in a direction parallel to the first direction and the multi-beam moves relative to the sample surface in a direction parallel to a second direction, preferably inclined to the first direction, and sub-beams of the multi-beam are controlled to scan sections within each sub-portion such that after each section is scanned, it becomes the previously scanned section and a next section adjacent to the previously scanned section is scanned using the same movement.

[0190]

[0207] Clause 38: A charged particle characterization system, comprising: a sample support for supporting a sample having a sample surface; and a charged particle device configured to direct a multi-beam of sub-beams of charged particles to the sample surface, a part of the sample surface corresponding to a multi-beam output area of ​​the charged particle device facing the sample surface, the charged particle device being configured to control the sample support and the charged particle device such that a part is scanned by the sub-beams of the multi-beam, a sub-part of the part being assigned to each sub-beam, the system displacing the sample in successive steps in a direction oblique or perpendicular to a first direction, in each step each sub-beam being parallel to the first direction. a charged particle evaluation system configured to control the sample support to move the sample in a direction parallel to a first direction in each step to scan across a section of a corresponding sub-portion in the row direction, the corresponding sub-portion in the direction parallel to the first direction including a plurality of sections, the system configured to control the charged particle device to repeatedly scan the multi-beam across the sample surface in a direction parallel to a second direction during movement of the sample in the direction parallel to the first direction, the system configured to scan further sections, which are either a plurality of sections or subsequent successive steps along the sub-portion in the direction parallel to the first direction.

[0191]

[0208] While the invention has been described in connection with various embodiments, other embodiments of the invention will be apparent to those skilled in the art from consideration of the specification and practice of the invention disclosed herein. It is intended that the uses and examples be considered as exemplary only, with a true scope and spirit of the invention being indicated by the following claims.

Claims

1. 1. A method for processing a sample using a multiple beam of sub-beams of charged particles using a charged particle device for projecting said multiple beams onto a sample surface, comprising the steps of: (a) using the charged particle device, moving the sample in a direction parallel to a first direction and repeatedly moving the multiple beams relative to the sample surface in a direction parallel to a second direction, thereby scanning each sub-beam repeatedly in the direction parallel to the first direction and in the direction parallel to the second direction to process a section of a plurality of elongated regions on the sample surface with the sub-beams, wherein a distance of movement of the sample in (a) is less than or equal to half a pitch of the sub-beams in the multiple beams on the sample surface in the first direction; (b) displacing the sample in a direction oblique or perpendicular to the first direction; (c) repeating step (a) to process sections of further elongated regions of the plurality of elongated regions with each sub-beam; and (d) repeating steps (b) and (c) a plurality of times to process sections of further respective elongated regions of the plurality of elongated regions with each sub-beam; (e) repeating steps (a)-(d) for each sub-beam for a series of unprocessed sections of the elongated region, the series of unprocessed sections being adjacent in a direction parallel to the movement in step (a) to a corresponding series of sections of the respective elongated region previously processed by the sub-beam; The method includes:

2. 2. The method of claim 1 , wherein in (a), the maximum range of movement of the multiple beams relative to the sample surface by the charged particle device in the direction parallel to the second direction is substantially less than or equal to half the minimum pitch of the sub-beams in the multiple beams at the sample surface.

3. 3. The method of claim 1 or 2, wherein the distance of movement of the sample in (a) is substantially equal to an integer division of the pitch of the sub-beams in the multi-beam at the sample surface in the first direction.

4. 4. The method of claim 1, wherein step (e) is performed one or more times and the resulting processed sections cover the elongated regions, the processed elongated regions defining sub-beam processing areas for each sub-beam.

5. 5. The method of claim 4, wherein the distance of the sample displacement in (b) is such that the elongated regions in each sub-beam processing area overlap one another, are contiguous with one another, or are spaced apart from one another by less than a threshold gap.

6. 6. The method of claim 4 or 5, wherein each sub-beam treats a respective sub-beam treatment area, and the resulting sub-beam treatment areas are overlapping and / or contiguous with respect to each other.

7. After steps (a) to (e), in order: (f) displacing the sample a distance equal to at least twice the pitch of the sub-beams in the multi-beam at the sample surface; (g) repeating (a) to (e); The method of any one of claims 4 to 6, further comprising carrying out:

8. 8. The method of claim 7, wherein a single performance of (a)-(e) defines a first group of sub-beam processing areas, and step (g) forms a second group of sub-beam processing areas overlapping and / or contiguous with the first group of sub-beam processing areas.

9. the footprint of the charged particle device is defined as the smallest bounding box on the sample surface that encloses all of the sub-beam processing areas from implementations (a)-(e); 9. The method of claim 7 or 8, wherein the distance of displacement of the sample in (f) is substantially greater than or equal to a dimension of the footprint parallel to the direction of movement.

10. 10. The method of any one of claims 4 to 9, wherein step (e) is repeated 1 to 9 times.

11. step (a) further comprises: stepping the sample from a position where a first processing region of the sample faces an output of the charged particle device to each of a plurality of positions where a further processing region faces the output of the charged particle device and, while using the charged particle device, repeating the movement of the sample in a direction parallel to the first direction at each position and repeatedly moving the multi-beams relative to the sample surface in the direction parallel to the second direction, thereby processing a section of a plurality of elongated regions on the sample surface with each sub-beam in the or each further processing region; 11. The method of claim 1, wherein step (b) comprises displacing the sample and positioning it back to the position where the first processing region faces the output of the charged particle device.

12. The method according to any one of claims 4 to 11, further comprising performing a sample alignment operation between processing of different sections of the sample surface.

13. The method of claim 12 , wherein the sample alignment operation is performed between processing of different sections in the same sub-beam processing area.

14. 14. The method of claim 12 or 13, wherein the sample alignment operation comprises detecting a reference marker on the sample or a reference pattern on the sample, and aligning the sample to align the reference marker or reference pattern with respect to the charged particle device.

15. The method according to any one of claims 12 to 14, wherein the sample alignment operation is performed within step (d) between different executions of step (c).

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