Correcting scan data

Abstract

A method for correcting scan data generated by scanning a sample with charged particles and detecting signal charged particles emitted from the sample, the method comprising: selecting at least one scan profile (50) for scanning the sample; and correcting (74) scan data generated by scanning of the sample based on at least one known distortion function f (x, y) associated with the selected at least one scan profile.

Description

[0001] Cross - Reference to Related Applications

[0002] This application claims priority to European Application No. 22206511.2, filed on Nov. 9, 2022, the entire content of which is incorporated herein by reference. Technical Field

[0003] Embodiments provided herein disclose a method for correcting scanned data, a charged particle optical device, and a non-transitory computer-readable medium. Background Art

[0004] In the manufacturing process of integrated circuits (ICs), uncompleted or completed circuit components are evaluated to ensure that they are manufactured according to design and are free of defects. Evaluation (e.g., metrology or inspection) systems can be employed that utilize an optical microscope or a charged particle (e.g., electron) beam microscope such as a scanning electron microscope (SEM). As the physical dimensions of IC components continue to shrink and their structures become increasingly complex, the accuracy and throughput of evaluation (e.g., metrology or defect detection and inspection) become more important. The overall image quality depends on a combination such as high secondary electron and backscattered electron signal detection efficiency. Backscattered electrons have a higher emission energy to escape from deeper layers of the sample, and thus, their detection can be ideal for imaging complex structures such as buried layers, nodes, high aspect ratio trenches, or holes in 3D NAND devices. For applications such as critical dimension, periodicity, and placement error metrology, it may be desirable to simultaneously obtain high-quality imaging and efficient surface information collection from secondary electrons and buried layer information from backscattered electrons, which highlights the necessity of using multiple electron detectors in an SEM. Although multiple electron detectors with various structural arrangements can be used to maximize the individual collection and detection efficiency of secondary and backscattered electrons, the combined detection efficiency is still low, and thus, the acquired image quality may not be sufficient for high-precision and high-throughput evaluation of two-dimensional and three-dimensional structures. Summary of the Invention

[0005] An embodiment of the present disclosure provides a method for correcting scanned data generated by scanning a sample with charged particles and detecting charged particles of signals emitted from the sample, the method including: selecting at least one scan profile for scanning the sample based on at least one known distortion function, the at least one known distortion function being associated with the selected at least one scan profile and indicating distortion of the scanned data; and correcting the scanned data generated by scanning the sample based on the at least one known distortion function associated with the selected at least one scan profile.

[0006] One embodiment of the present disclosure provides a charged particle optical device that scans a sample with charged particles and detects signal charged particles emitted from the sample. The charged particle optical device includes: a charged particle optical apparatus configured to direct a charged particle beam onto a sample according to at least one selected scanning profile, the at least one selected scanning profile being selected based on at least one known distortion function that indicates distortion of scanning data and is associated with the at least one selected scanning profile; a detector configured to detect signal charged particles emitted from the sample to generate scanning data; and a controller configured to correct the scanning data based on the at least one known distortion function associated with the at least one selected scanning profile.

[0007] Other advantages of the embodiments of the present disclosure will become apparent from the following description taken in conjunction with the accompanying drawings, in which certain embodiments of the invention are illustrated by way of example. BRIEF DESCRIPTION OF THE DRAWINGS

[0008] The foregoing 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, in which:

[0009] Figure 1 is a schematic diagram showing an exemplary electron beam evaluation system consistent with an embodiment of the present disclosure.

[0010] Figure 2A 、 Figure 2B and Figure 2C is a schematic diagram showing an exemplary electron beam tool consistent with an embodiment of the present disclosure, which may be part of the exemplary electron beam evaluation system of Figure 1

[0011] Figure 3 is a diagram of a candidate scanning profile.

[0012] Figure 4 is a diagram of the selection of a scanning profile.

[0013] Figure 5 is a diagram of the correction of scanning data. DETAILED DESCRIPTION

[0014] Reference will now be made in detail to exemplary embodiments, which are illustrated in the accompanying drawings. The following description refers to the drawings, where the same numbers in different drawings represent the same or similar elements, unless otherwise noted. The implementations set forth in the description of the following exemplary embodiments do not represent all implementations. Instead, they are merely examples of devices and methods consistent with aspects of the disclosed embodiments described in the appended claims. For example, although some embodiments are described in the context of using an electron beam, the present disclosure is not limited thereto. Other types of charged particle beams can be similarly applied.

[0015] One component of increasing throughput is monitoring the chip manufacturing process to ensure that it produces a sufficient number of functional integrated circuits. One way to monitor the process is to evaluate the chip circuit structure at various stages during its formation. The evaluation can be performed using SEM. SEM can be used to image these extremely small structures, effectively "taking a picture" of the structure. This image can be used to determine whether the structure has been correctly formed and whether it has been formed in the correct location. If the structure is defective, the process can be adjusted so that the defect is less likely to occur again. It may be desirable for the defect detection and evaluation process to have a higher throughput to meet the requirements of IC manufacturers.

[0016] One of the main challenges in ensuring the quality of functional integrated circuits is accurately measuring the relative positions of structures / features. Due to errors in the lithography process, this position may be different from the desired design, which can lead to distortion of the printed pattern and structure. Measuring this (true) distortion or placement error (PE) is one of the main objectives of metrology. This task is complicated because other artifacts and sources of distortion may affect the acquired image. These distortions may be caused by the measurement process itself, such as due to hardware problems in the SEM tool, or sample charging (i.e., charging of the sample surface by the SEM affects the trajectory of the incident primary electrons). This charging-induced distortion typically depends on the way the SEM scans the structure. These distortions are not real, i.e., they do not exist on the sample, and should be decoupled from the true distortion of the structure that one wants to measure on the sample. The SEM can scan the structure in different ways, such as different scan modes. Some scan modes may cause distortions that are more easily separable from the useful structural information about the structure itself (i.e., distortions or placement errors that can be expected on the sample and may be caused by the manufacturing process of the structure). By selecting a scan mode that causes distortions that are more easily separable from the structural information of the structure itself, the distortions caused by the way the SEM scans the structure can be better corrected in the SEM image.

[0017] For clarity, the relative sizes of components in the figures may be exaggerated. In the following description of the figures, like or similar reference numerals refer to like or similar components or entities, and only the differences from individual embodiments are described. As used herein, unless otherwise specifically stated, the term "or" includes all possible combinations, unless infeasible. For example, if it is specified that a component can include A or B, then, unless otherwise specifically stated or infeasible, the component can include A or B or A and B. As a second example, if it is specified that a component can include A, B, or C, then, unless otherwise specifically stated or infeasible, the component can include A, or B, or C, or A and B, or A and C, or B and C, or A and B and C.

[0018] Now refer toFigure 1 , which shows an exemplary electron beam evaluation system 10 consistent with embodiments of the present disclosure. The system may include a detector. The evaluation system 10 may be used for imaging. As Figure 1 shown, the evaluation system 10 includes a main chamber 11, a load / lock chamber 20, an electron beam tool 100, and an equipment front end module (EFEM) 30. The electron beam tool 100 is located within the main chamber 11. The EFEM 30 includes a first load port 30a and a second load port 30b. The EFEM 30 may include additional load ports. The first load port 30a and the second load port 30b receive wafer front opening unified pods (FOUPs), which accommodate wafers to be evaluated (e.g., semiconductor wafers or wafers made of other materials) or samples (wafers and samples may be collectively referred to as "samples" herein).

[0019] One or more robotic arms (not shown) in the EFEM 30 may transport the wafer to the load / lock chamber 20. The load / lock chamber 20 is connected to a load / lock vacuum pump system (not shown), which removes gas molecules within the load / lock chamber to reach a first pressure below atmospheric pressure. After reaching the first pressure, one or more robotic arms (not shown) may transport the wafer from the load / lock chamber 20 to the main chamber 11. The main chamber 11 is connected to a main chamber vacuum pump system (not shown), which removes gas molecules within the main chamber 11 to reach a second pressure below the first pressure. After reaching the second pressure, the wafer is evaluated by the electron beam tool 100. The electron beam tool 100 may be a single beam system or a multi-beam system. The controller 109 is electrically connected to the electron beam tool 100 and may also be electrically connected to other components. The controller 109 may be a computer configured to perform various controls of the evaluation system 10. Although Figure 1 the shown controller 109 is located outside the structure including the main chamber 11, the load / lock chamber 20, and the EFEM 30, it can be understood that the controller 109 may be a part of this structure.

[0020] Figure 2A shows a charged particle beam apparatus, wherein the evaluation system may include a multi-beam evaluation tool that uses multiple primary electron sub-beams to simultaneously scan multiple positions on a sample.

[0021] As Figure 2A shown, the electron beam tool 100A (also referred to herein as the electron beam apparatus 100A or the electron optical device) may include an electron source 202, a gun aperture 204, a condenser lens 206, a primary electron beam 210 emitted from the electron source 202, a source conversion unit 212, multiple sub-beams 214, 216, and 218 of the primary electron beam 210, a main projection optical system 220, a wafer stage ( Figure 2A(not shown in the figure), multiple secondary electron beams 236, 238, and 240, an auxiliary optical system 242, and an electron detection device 244. The electron source 202 can generate primary particles, such as electrons of the primary electron beam 210. A controller, an image processing system, etc. can be coupled to the electron detection device 244. The main projection optical system 220 can include a beam splitter 222, a deflection scanning unit 226, and an objective lens 228. The electron detection device 244 can include detection sub-regions 246, 248, and 250.

[0022] The electron source 202, the gun hole 204, the condenser lens 206, the source conversion unit 212, the beam splitter 222, the deflection scanning unit 226, and the objective lens 228 can be aligned with the main optical axis 260 of the electron beam apparatus 100A. The auxiliary optical system 242 and the electron detection device 244 can be aligned with the secondary optical axis 252 of the electron beam apparatus 100A.

[0023] The electron source 202 can include a cathode, an extractor, or an anode, where primary electrons can be emitted from the cathode and extracted or accelerated to form a primary electron beam 210 having a crossover (virtual or real) 208. The primary electron beam 210 can be visualized as being emitted from the crossover 208. The gun hole 204 can block the peripheral electrons of the primary electron beam 210 to reduce the sizes of the detection spots 270, 272, and 274.

[0024] The source conversion unit 212 can include an imaging element array ( Figure 2A (not shown in the figure) and a beam limiting hole array ( Figure 2A (not shown in the figure). Examples of the source conversion unit 212 can be found in U.S. Patent No. 9,691,586; U.S. Publication No. 2017 / 0025243; and International Application No. PCT / EP2017 / 084429, the entire contents of all of which are incorporated herein by reference. The imaging element array can include a microdeflector or a microlens array. The imaging element array can form multiple parallel images (virtual or real) of the crossover 208 using multiple sub-beams 214, 216, and 218 of the primary electron beam 210. The beam limiting hole array can limit the multiple sub-beams 214, 216, and 218.

[0025] The condenser lens 206 can focus the primary electron beam 210. The currents of the sub-beams 214, 216, and 218 downstream of the source conversion unit 212 can be changed by adjusting the focusing ability of the condenser lens 206 or by changing the radial dimensions of the corresponding beam-limiting holes within the beam-limiting hole array. The condenser lens 206 can be a movable condenser lens that can be configured such that the position of its first principal plane is movable. The movable condenser lens can be configured to be magnetic, which may cause the off-axis sub-beams 216 and 218 to land on the sub-beam limiting holes at a rotational angle. The rotational angle varies with the focusing ability of the movable condenser lens and the position of the first principal plane. In some embodiments, the movable condenser lens can be a movable anti-rotation condenser lens, which involves an anti-rotation lens having a movable first principal plane. The movable condenser lens is further described in U.S. Publication No. 2017 / 0025241, the entire disclosure of which is incorporated herein by reference.

[0026] The objective lens 228 can focus the sub-beams 214, 216, and 218 onto the wafer 230 (i.e., the sample) for evaluation and can form a plurality of probe spots 270, 272, and 274 on the surface of the wafer 230.

[0027] The beam separator 222 can be a Wien filter type beam separator that generates an electrostatic dipole field and a magnetic dipole field. In some embodiments, if the electrostatic dipole field is applied, the magnitude of the force exerted on the electrons of the sub-beams 214, 216, and 218 by the electrostatic dipole field can be equal to and opposite in direction to the magnitude of the force exerted on the electrons by the magnetic dipole field. Thus, the sub-beams 214, 216, and 218 can pass directly through the beam separator 222 with a zero deflection angle. However, the total dispersion of the sub-beams 214, 216, and 218 generated by the beam separator 222 can also be non-zero. The beam separator 222 can separate the secondary electron beams 236, 238, and 240 from the sub-beams 214, 216, and 218 and direct the secondary electron beams 236, 238, and 240 to the auxiliary optical system 242.

[0028] The deflection scanning unit 226 can deflect the sub-beams 214, 216, and 218 to scan the probe spots 270, 272, and 274 on the surface area of the wafer 230. In response to the incidence of the sub-beams 214, 216, and 218 at the probe spots 270, 272, and 274, the secondary electron beams 236, 238, and 240 can be emitted from the wafer 230. The secondary electron beams 236, 238, and 240 can include electrons having an energy distribution that includes secondary electrons and backscattered electrons. The auxiliary optical system 242 can focus the secondary electron beams 236, 238, and 240 onto the detection sub-regions 246, 248, and 250 of the electron detection device 244. The detection sub-regions 246, 248, and 250 can be configured to detect the corresponding secondary electron beams 236, 238, and 240 and generate corresponding signals for reconstructing an image of the surface area of the wafer 230.

[0029] Although Figure 2A the electron beam tool 100 is shown as an example of a multi-beam tool using multiple sub-beams, embodiments of the present disclosure are not limited thereto. For example, the electron beam tool 100 can also be a single-beam tool that scans only one position on the wafer using only one primary electron beam at a time.

[0030] As Figure 2B shown, the electron beam tool 100B (also referred to herein as the electron beam device 100B) can be a single-beam evaluation tool used in the evaluation system 10. The electron beam device 100B includes electron optics and a wafer holder 136, the electron optics being configured to project electrons towards a sample position (i.e., the position where the wafer is located), and the wafer holder being supported by a motorized stage 134 to hold the wafer 150 (i.e., the sample) to be evaluated. The electron beam tool 100B includes an electron emitter, which can include a cathode 103, an anode 121, and a gun aperture 122. The electron beam tool 100B also includes a beam limiting aperture 125, a condenser lens 126, a column aperture 135, an objective lens assembly 132, and a detector 144. In some embodiments, the objective lens assembly 132 can be a modified SORIL lens, which includes pole pieces 132a, a control electrode 132b, a deflector 132c, and an excitation coil 132d. During imaging, the electron beam 161 emitted from the tip of the cathode 103 can be accelerated by the anode 121 voltage, pass through the gun aperture 122, the beam limiting aperture 125, the condenser lens 126, and be focused by the modified SORIL lens into the probe spot 170 and impinge on the surface of the wafer 150. The probe spot 170 can be scanned on the surface of the wafer 150 by a deflector (such as the deflector 132c or other deflectors in the SORIL lens). Secondary or scattered primary particles (such as secondary electrons or scattered primary electrons emitted from the wafer surface) can be collected by the detector 144 to determine the intensity of the beam and enable an image of the region of interest on the wafer 150 to be reconstructed.

[0031] An image processing system 199 can also be provided, which includes an image acquirer 120, a storage device 130, and a controller 109. The image acquirer 120 can include one or more processors. For example, the image acquirer 120 can include a computer, a server, a mainframe, a terminal, a personal computer, any type of mobile computing device, etc., or a combination thereof. The image acquirer 120 can be connected to the detector 144 of the electron beam tool 100B through media such as electrical conductors, fiber optic cables, portable storage media, IR, Bluetooth, the Internet, wireless networks, wireless radio, or a combination thereof. The image acquirer 120 can receive signals from the detector 144 and can construct an image. Thus, the image acquirer 120 can acquire an image of the wafer 150. The image acquirer 120 can also perform various post-processing functions, such as generating contours, superimposing indicators on the acquired image, and so on. The image acquirer 120 can be configured to adjust the brightness, contrast, etc. of the acquired image. The storage device 130 can be a storage medium such as a hard disk, a random access memory (RAM), a cloud storage device, or other types of computer-readable memories. The storage device 130 can be coupled to the image acquirer 120 and can be used to save the scanned raw image data as a raw image and save the post-processed image. The image acquirer 120 and the storage device 130 can be connected to the controller 109. In some embodiments, the image acquirer 120, the storage device 130, and the controller 109 can be integrated together as an electronic control unit.

[0032] In some embodiments, the image acquirer 120 can acquire one or more images of a sample based on the imaging signals received from the detector 144. The imaging signals can correspond to scanning operations for performing charged particle imaging. The acquired images can be a single image including multiple imaging regions, and these imaging regions can contain various features of the wafer 150. The single image can be stored in the storage device 130. The imaging can be performed based on imaging frames.

[0033] The condenser and irradiation optics of the electron beam tool can include or be supplemented by an electromagnetic quadrupole electron lens. For example, as Figure 2B shown, the electron beam tool 100B can include a first quadrupole lens 148 and a second quadrupole lens 158. In some embodiments, the quadrupole lenses are used to control the electron beam. For example, the first quadrupole lens 148 can be controlled to adjust the beam current, and the second quadrupole lens 158 can be controlled to adjust the beam spot size and beam shape.

[0034] Figure 2Bshows a charged particle beam apparatus, in which an evaluation system can use a single primary beam that can be configured to generate secondary electrons by interacting with a wafer 150. A detector 144 can be placed along the optical axis 105, as Figure 2B shown in the illustrated embodiment. The primary electron beam can be configured to travel along the optical axis 105. Thus, the detector 144 can include a hole at its center such that the primary electron beam can pass through to reach the wafer 150. However, some embodiments can use a detector placed off-axis with respect to the optical axis along which the primary electron beam travels. For example, as Figure 2A shown in the illustrated embodiment, a beam splitter 222 can be provided to direct the secondary electron beam to a detector placed off-axis. The beam splitter 222 can be configured to deflect the secondary electron beam by an angle α.

[0035] Now another example of a charged particle beam apparatus will be referred to Figure 2C for discussion. An electron beam tool 100C (also referred to herein as electron beam apparatus 100C or electron optical device) can be an example of an electron beam tool 100 and can be similar to Figure 2A the electron beam tool 100A shown.

[0036] As Figure 2C shown, the beam splitter 222 can be a Wien filter type beam splitter that generates an electrostatic dipole field and a magnetic dipole field. In some embodiments, if an electrostatic dipole field is applied, the magnitude of the force exerted on the electrons of the sub-beams 214, 216, and 218 by the electrostatic dipole field can be equal in magnitude and opposite in direction to the force exerted on the electrons by the magnetic dipole field. Thus, the sub-beams 214, 216, and 218 can pass directly through the beam splitter 222 with a zero deflection angle. However, the total dispersion of the sub-beams 214, 216, and 218 generated by the beam splitter 222 can also be non-zero. For the dispersion plane 224 of the beam splitter 222, Figure 2C shows that a sub-beam 214 with a nominal energy V0 and an energy spread ΔV is dispersed into a sub-beam portion 262 corresponding to the energy V0, a sub-beam portion 264 corresponding to the energy V0 + ΔV / 2, and a sub-beam portion 266 corresponding to the energy V0 - ΔV / 2. The total force exerted on the electrons of the secondary electron beams 236, 238, and 240 by the beam splitter 222 can be non-zero. The beam splitter 222 can separate the secondary electron beams 236, 238, and 240 from the sub-beams 214, 216, and 218 and direct the secondary electron beams 236, 238, and 240 to the auxiliary optical system 242.

[0037] A semiconductor electron detector (sometimes referred to as a "PIN detector") can be used in the device 100 in the evaluation system 10. The evaluation system 10 can be a high-speed wafer imaging SEM including an image processor. The electron beam generated by the evaluation system 10 can irradiate the surface of the sample or can penetrate the sample. The evaluation system 10 can be used to image the surface or subsurface structures of the sample, such as for analyzing layer alignment. In some embodiments, the evaluation system 10 can detect and report process defects related to semiconductor wafer manufacturing by, for example, comparing the SEM image with the device layout pattern or the SEM image of the same pattern at other locations on the wafer being evaluated. The PIN detector can include a silicon PIN diode that can operate under a negative bias. The PIN detector can be configured such that incident electrons generate relatively large and different detection signals. In some embodiments, the PIN detector can be configured such that incident electrons can generate multiple electron-hole pairs, while photons can only generate one electron-hole pair. There are many differences between the PIN detector for electron counting and the photodiode for photon detection, as described below.

[0038] In one embodiment, the detector (e.g., Figure 2A or Figure 2C the electron detection device 244 shown, or Figure 2B the detector 144 shown) includes a plurality of detector elements (e.g., detection sub-regions 246, 248, and 250). The detector elements can be connected to one or more circuit layers. The circuit layers of the detector can include circuitry having amplification and / or digitization functions, e.g., it can include an amplification circuit. The circuit layers can include one or more transimpedance amplifiers (TIAs) and one or more ADCs. The detector elements and associated feedback resistors can be connected to the TIAs and ADCs. One or more digital signal lines can be connected from the ADC for transmitting digital signals, e.g., connected to Figure 2B the image acquirer 120 shown.

[0039] In some embodiments, the detector can communicate with a controller that controls a charged particle beam system. The controller can instruct components of the charged particle beam system to perform various functions, such as controlling a charged particle source to generate a charged particle beam and controlling a deflector to scan the charged particle beam. The controller can also perform various other functions, such as adjusting the sampling rate of the detector, resetting sensing elements, or performing image processing. In one embodiment, the controller is configured to control the settings of an ADC. The controller can include a storage device, which is a storage medium such as a hard disk, random access memory (RAM), other types of computer-readable memory, etc. The storage device can be used to save the original image data of the scan as the original image and the post-processed image. A non-transitory computer-readable medium can be provided, which stores instructions for a processor of the controller 109 to perform charged particle beam detection, sampling period determination, image processing, or other functions and methods consistent with the present disclosure. Common forms of the non-transitory medium include, for example, floppy disks, flexible disks, hard disks, solid state drives, magnetic tapes, or any other magnetic data storage medium, CD-ROMs, any other optical data storage medium, any physical medium with a hole pattern, ROMs, PROMs, and EPROMs, FLASH-EPROMs, or any other flash memory, NVRAM, caches, registers, any other storage chip or cartridge, and their network versions.

[0040] The block diagrams in the figures may illustrate the possible architectures, functions, and operations of systems, methods, and computer hardware / software products according to various exemplary embodiments of the present disclosure. In this regard, each block in the schematic diagram may represent certain arithmetic or logical operation processing that can be implemented using hardware such as electronic circuits. The block may also represent a module, segment, or portion of code that includes one or more executable instructions for implementing the specified logical function. It should be understood that in some alternative implementations, the functions indicated in the blocks may not occur in the order shown in the figures. For example, depending on the functions involved, two consecutively shown blocks may be executed or implemented substantially concurrently, or the two blocks may sometimes be executed in the reverse order. Some blocks may also be omitted. It should also be understood that each block of the block diagram, and combinations of blocks, can be implemented by a system based on dedicated hardware that performs the specified functions or actions, or by a combination of dedicated hardware and computer instructions.

[0041] The electron beam device 100 (such as Figure 2A , Figure 2B or Figure 2CAs shown, a sample can be scanned with one or more electron beams. The electron beam device 100 is configured to detect signal electrons emitted from the sample to generate scan data. The scan data can be image data. An image can be generated from the scan data. The scan data can be data of the current of signal electrons emitted from different positions of the sample. The electron beam device 100 can be embodied as an SEM. The scan data can be SEM image data.

[0042] In one embodiment, there is a method for correcting scan data. The scan data is generated by scanning a sample with charged particles (e.g., electrons) and detecting signal charged particles (e.g., electrons) emitted from the sample. It may be desirable to correct for distortions in the scan data. An image (e.g., an SEM image) that can be generated from the scan data may include distortions. By correcting the scan data, unwanted distortions can be reduced or eliminated.

[0043] In one embodiment, the method includes selecting at least one scan profile 51 to scan the sample. The scan profile determines the way the electron beam device 100 scans the sample. For example, in one embodiment, the scan profile determines the scan path 52 that the electron beam follows on the sample. The scan path 52 can be a meandering path. Additionally or alternatively, the scan profile can determine one or more other parameters of the sample scan. For example, the scan profile can determine the electron current directed at the sample, the focus of the electron beam on the sample, and / or the landing energy of the electrons at the sample surface.

[0044] In one embodiment, the controller 109 is configured to control the scanning of the sample according to the selected scan profile 51. For example, the controller 109 can control the voltage applied to the electron optical elements (e.g., electron optical lenses and / or deflectors) of the electron beam device 100 according to the selected scan profile 51.

[0045] In one embodiment, the method includes correcting the scan data based on at least one known distortion function associated with the selected at least one scan profile 51. There can be multiple different scan profiles according to which the electron beam device 100 can scan the sample. Each scan profile can be associated with a corresponding distortion function. The distortion function associated with a scan profile (which can also be referred to as a distortion fingerprint) indicates the distortion of the scan data caused by the scan profile. When the distortion function associated with the selected scan profile 51 is known, unwanted distortions caused by the way the sample is scanned can be compensated for.

[0046] Figure 3A plurality of scan profiles 50 and their associated distortion functions are schematically shown. Different beam scan settings can be considered, such as but not limited to the settings shown. Each beam scan setting can generate a specific charging (i.e., distortion) fingerprint. By correcting the scan data based on the known distortion function associated with the selected scan profile 51, the distortion of the scan data can be reduced. Embodiments of the present disclosure are expected to reduce the undesired distortion of the scan data.

[0047] The selected scan profile 51 can be selected to take into account the characteristics of the sample and the expected impact on the scan data caused by the structure of the sample itself. The expected impact caused by the structure of the sample itself can be desired structural information. It is not desired to remove information about the sample structure from the scan data. There is a risk that some useful structural information will also be removed from the scan data when compensating for the undesired distortion.

[0048] In one embodiment, the selected scan profile can be selected to increase the degree of separation between the distortion caused by the scan profile and the structural information in the scan data caused by the substrate structure. By correcting based on the known distortion function associated with the selected scan profile, the distortion specific to the selected scan profile can be corrected.

[0049] In one embodiment, the scan data generated by scanning a sample includes distortion and structural information. The distortion is associated with (e.g., caused by) at least one selected scan profile 51. This distortion is undesired. Each scan profile 50 can be associated with a distortion (i.e., the distortion of the scan data generated from the scan). For example, the distortion of the scan data can depend on the scan path 52 and / or one or more other parameters of the scan. For example, during sample scanning, the electron beam can charge one or more portions of the sample surface. The charging can depend on the degree to which the sample structure provides a channel for charge transfer into or through the sample. The charging of portions of the sample surface affects the current of electrons emitted from the sample. The charging caused by the electron beam device 100 results in an undesired distortion of the scan data. This distortion can depend on the scan profile.

[0050] In addition to the distortion, the scan data can also include structural information. The structural information is associated with the sample. The sample can include a plurality of structures, such as transistor and / or DRAM structures. The type and arrangement of the sample structure affect the electron current emitted from the sample surface. It may be desirable to detect the structural information of the scan data. The structural information can provide useful information about the sample structure.

[0051] In one embodiment, the correction of the scan data is used to compensate for the distortion associated with at least one selected scan profile 51. The distortion caused by a particular scan profile used during scanning can be reduced or eliminated. Meanwhile, the structural information indicating the sample structure can desirably be retained in the scan data.

[0052] In one embodiment, the selected scan profile 51 is selected based on the degree of separability between the distortion associated with the candidate scan profile 50 and the predicted structural information of the predicted scan data. A particular scan profile or a set of scan profiles can be selected (and used for scanning). The selected scan profile (or scan profiles) can be selected to take into account the characteristics of the sample and the expected structural information. In particular, the scan profile can be selected so that the distortion (which is undesirable) can be optimally separated from the structural information (which can be desirable). The structural information can include the wafer fingerprint of the distortion caused by the structural features of the sample. For example, the structural information can include pitch-walk and stress. "Pitch-walk" is a piecewise increase or decrease in the distance between adjacent structures. This effect may be caused by errors in the production and lithography processes. Here, the pitch of the repeating pattern varies across the wafer. "Stress" on the wafer or stack causes displacement of the structures. This typically occurs in processing steps (such as deposition, etching, and polishing) after the lithography step. These are examples of inaccuracies (sometimes referred to as distortions) of the structure itself. These inaccuracies are undesirable in the structure, but it is desirable to measure these inaccuracies. This effect on the sample structure may be due to errors in the production process. Of course, metrology distortion caused by the SEM measurement itself also appears in the acquired image. Metrology distortion is an artifact (not real) and should desirably be reduced. These artifacts may come from sample charging or from the SEM tool hardware.

[0053] Embodiments of the present disclosure are expected to improve the correction of scan data. By selecting a particular scan profile based on the distortion and the predicted structural information, the distortion can be compensated to a greater extent without over-removing the true content of the structural information.

[0054] An alternative method of correcting scan data is to use a simple model (such as a simple polynomial model) to compensate for the distortion. However, using such a simple model runs the risk of overcorrecting the scan data and thus removing the true content (i.e., the desired information about the sample structure). An embodiment of the present disclosure provides an improved method for correcting scan data that reduces the risk of undesirable overcorrection (i.e., removing useful structural information).

[0055] One embodiment of the present disclosure is expected to improve the correction of distortions that may be caused by the electron beam device 100. In particular, at a scale of dozens of nanometers, using a simple polynomial model may not be able to properly correct the distortions that may be caused by the SEM. By using a specific scan profile or a set of scan profiles that take into account the sample characteristics and the expected structural information, the scan distortions can be better corrected, especially at small scales.

[0056] Figure 3 A calibration step is shown, in which the distortion fingerprints caused by each scan strategy are evaluated. As Figure 3 shown, in one embodiment, a plurality of candidate scan profiles 50 are identified. As Figure 3 shown, each candidate scan profile 50 can be associated with different scan parameters, such as different scan routes 52 on the sample surface. Figure 3 N different scan profiles 50_1, 50_2, 50_3 to 50_N are shown. Figure 3 N candidate scan profiles 50 are shown. Each candidate scan profile 50 can be associated with a known distortion function. The distortion function is as Figure 3 shown on the right. The distortion function represents the distortion of the scan data caused by a specific scan profile 50. The distortion function can indicate the distortion of the scan data at different positions on the sample surface (indicated by the x and y variables). The superscript of each distortion function corresponds to the scan profile 50 with which it is associated. For example, the distortion function with superscript "1" is associated with the scan profile 50_1.

[0057] In one embodiment, the method includes generating a database 40 of candidate scan profiles 50 associated with the distortion functions. Each distortion function indicates the expected distortion effect caused by its associated candidate profile 50. Such a database 40 can be generated during the calibration phase of the method. Alternatively, the database 40 can have been pre-generated. The method can utilize such a previously generated database 40 to perform.

[0058] In one embodiment, the database 40 is generated by using a physical model to predict the expected distortion effect. The parameters of the scan can be input into a mathematical model to predict the distortion of the scan data caused by the scan profile 50. The generation of the distortion function is indicated by the arrow 71 in Figure 3 .

[0059] Additionally or alternatively, the database 40 can be generated by using empirical training to predict the expected distortion effect. For example, the scan profile 50 can be used to scan one or more samples. The distortion caused by the scan profile can be measured and used to help determine the distortion function associated with the scan profile 50.

[0060] Figure 4 The setup for selecting a scan profile is schematically shown.Figure 4 It is a conceptual flowchart for selecting the best scanning strategy (or combination of scanning strategies) for a specific application, that is, a scanning strategy that can well separate the image distortion from the (non-SEM-related) distortion to be measured on the sample 208. To determine the best scanning profile, a multi-scanning profile database 40 can be used in the setup phase, and then a self-reference algorithm 41 can be used to decide which or which scanning profiles 51 can perform the best post-correction. Figure 4 It shows a database 40 of candidate scanning profiles 50 associated with a distortion function. The selection of one of the candidate scanning profiles 50 as the selected scanning profile 51 is indicated by an arrow 72. Although Figure 4 It shows one selected scanning profile 51, but in an alternative embodiment, multiple scanning profiles are selected. In one embodiment, the selected scanning profile 51 is a scanning profile that can perform the best post-correction (i.e., correction / compensation after generating scanning data by performing a scan).

[0061] For example, in one embodiment, at least one selected scanning profile 51 is selected based on the degree of separability between the distortion associated with the candidate scanning profile 50 and the predicted structural information. The predicted structural information is used to predict the structural information of the scanning data.

[0062] For example, in one embodiment, at least one selected scanning profile 51 is selected based on the degree of orthogonality of the distortion associated with the candidate scanning profile 50 relative to the predicted structural information. For example, a pair of two adjacent through-holes aligned with each other in the x direction along any coordinate system are expected to have a pattern placement error in the x direction. In this case, it is best to scan the SEM along the orthogonal y direction. Then, the measurement artifacts will be more dominant in the y direction, and they can be more easily separated from the pattern placement error. The predicted structural information can be predicted based on the known design of the structure expected to be formed on the sample and optionally based on the lithography steps involved in manufacturing.

[0063] For a given structural design on the sample, the relationship between the predicted structural information and the distortion of different scanning profiles 50 can be evaluated. When the distortions are more orthogonal to each other, they can be more easily separated. When the distortions are more orthogonal to each other, the distortions can be compensated while reducing the impact on the structural information.

[0064] As described above, in one embodiment, a plurality of scan profiles are selected to scan a sample. In one embodiment, the plurality of selected scan profiles are selected based on the degree of orthogonality of the distortions associated with the candidate scan profiles relative to each other. For example, a set of scan profiles can be selected in which the distortions are expected to be more orthogonal to each other. When using a set of scan profiles, the data from the scans can be combined. For example, the selected scan profiles can be used for independent acquisitions. The scan data can be corrected with its associated distortion function. Two sets of scan data can be scaled with corresponding scaling factors. For example, by adjusting the scaling factors, the two sets of corrected scan data can be forced to be the same. This can reduce overcorrection.

[0065] In one embodiment, the distortion function associated with the candidate scan profile 50 is based on the expected design of the sample structure. In one embodiment, the candidate scan profile 50 can be associated with a plurality of distortion functions corresponding to the respective designs of the sample structure. A set of scan profiles can be selected in which, for a particular pattern (i.e., a particular design of the sample structure), the distortions are expected to be more orthogonal to each other. When the distortions are more orthogonal to each other, their effects can be more easily separated from each other and compensated for independently.

[0066] As Figure 4 shown, in one embodiment, the method includes using a self-reference algorithm 41 to select one or more candidate scan profiles 50 as the selected scan profiles 51. The self-reference algorithm 41 can consider the above criteria, such as the degree to which the distortion effects can be separated from each other and / or the degree to which the expected distortions are orthogonal to each other. The self-reference algorithm 41 can be configured to select the scan profiles that can be optimally post-corrected.

[0067] Figure 5 A distortion correction process using the scan profile database 40 is schematically shown. Figure 5 An example of a distortion correction process using the scan profile database 40 is shown. Figure 5 A database 40 of candidate scan profiles 50 is shown. At least one of the candidate scan profiles 50 is selected. The electron beam device 100 is configured to scan the sample according to the selected scan profile 51. The scanning of the sample is represented by Figure 5 the arrow 73 in. The scanning of the sample generates scan data. The scan data includes a complex distortion fingerprint 61. The complex distortion fingerprint 61 can be a high-order distortion fingerprint.

[0068] The complex distortion fingerprint 61 can include the distortion associated with the selected scan profile 51 and the structural information providing information about the structure on the sample. In one embodiment, the scan data is corrected using a known distortion function associated with the at least one selected scan profile 51. This correction is performed by Figure 5The arrow 74 in [Figure] indicates. The corrected scan data includes sample distortion 62. A suitable scan profile 51 is used for measurements in production mode. Then, post-correction is performed on the induced distortion fingerprint 61 using early knowledge of the physical modeling fingerprint from the scan profile database 40.

[0069] Of course, the correction of the distortion may not be perfect. In addition, structural information may be undesirably removed to some extent by the correction. However, it is expected that the corrected scan data better represents the structural information caused by the actual structure of the sample.

[0070] In one embodiment, a non-transitory computer-readable medium stores instructions for a processor of a controller (e.g., controller 109) to perform the above method.

[0071] Exemplary embodiments of the present disclosure are listed in the following numbered clauses:

[0072] 1. A method for correcting scan data, the scan data being generated by scanning a sample with charged particles and detecting signal charged particles emitted from the sample, the method comprising:

[0073] Selecting at least one scan profile for scanning the sample based on at least one known distortion function, the at least one known distortion function being associated with the selected at least one scan profile and indicating distortion of the scan data; and

[0074] Correcting the scan data generated by the scanning of the sample based on the at least one known distortion function associated with the selected at least one scan profile.

[0075] 2. The method according to clause 1, wherein the scan data generated by the scanning of the sample includes: distortion associated with the selected at least one scan profile, and structural information associated with the sample, wherein the correction is for compensating the distortion associated with the selected at least one scan profile.

[0076] 3. The method according to clause 2, wherein the selected at least one scan profile is selected based on the degree of separability of the distortion associated with a candidate scan profile from the predicted structural information of the scan data.

[0077] 4. The method according to clause 2 or 3, wherein the selected at least one scan profile is selected based on the degree of orthogonality of the distortion associated with a candidate scan profile with respect to the predicted structural information of the scan data.

[0078] 5. The method according to any one of the preceding clauses, wherein the plurality of selected scan profiles are selected based on the degree of orthogonality of the distortions associated with the candidate scan profiles relative to each other.

[0079] 6. The method according to clause 5, wherein the plurality of selected scan profiles are selected based on the degree of orthogonality of the distortions associated with the candidate scan profiles for the sample relative to each other.

[0080] 7. The method according to any one of the preceding clauses, comprising:

[0081] Generating a database of candidate scan profiles associated with a distortion function that indicates the expected distortion caused by the respective candidate scan profiles.

[0082] 8. The method according to clause 7, wherein the database is generated by using a physical model to predict the expected distortion.

[0083] 9. The method according to clause 7 or 8, wherein the database is generated by using empirical training to predict the expected distortion.

[0084] 10. The method according to any one of the preceding clauses, comprising:

[0085] Scanning the sample using the selected at least one scan profile.

[0086] 11. The method according to any one of the preceding clauses, wherein the scan profile determines the scan path followed by the charged particle beam on the sample.

[0087] 12. A charged particle optical device that uses charged particles to scan a sample and detect signal charged particles emitted from the sample, the charged particle optical device comprising:

[0088] A charged particle optical device configured to direct a charged particle beam onto the sample according to at least one selected scan profile, the at least one selected scan profile being selected based on at least one known distortion function that indicates the distortion of scan data and is associated with the at least one selected scan profile;

[0089] A detector configured to detect signal charged particles emitted from the sample to generate scan data; and

[0090] A controller configured to correct the scan data based on the at least one known distortion function associated with the at least one selected scan profile.

[0091] 13. The charged particle optical device according to clause 12, wherein the scan data generated by the scan of the sample includes: distortion associated with the selected at least one scan profile, and structural information associated with the sample, wherein the correction is for compensating the distortion associated with the selected at least one scan profile.

[0092] 14. The charged particle optical device according to clause 13, wherein the controller is configured to: select the selected at least one scan profile based on the degree of separability between the distortion associated with a candidate scan profile and the predicted structural information of the scan data.

[0093] 15. The charged particle optical device according to clause 13 or 14, wherein the controller is configured to: select the selected at least one scan profile based on the degree of orthogonality of the distortion associated with a candidate scan profile with respect to the predicted structural information of the scan data.

[0094] 16. The charged particle optical device according to any one of clauses 12 to 15, wherein the controller is configured to: select the selected plurality of scan profiles based on the degree of orthogonality of the distortions associated with candidate scan profiles with respect to each other.

[0095] 17. The charged particle optical device according to clause 16, wherein the controller is configured to: select the selected plurality of scan profiles based on the degree of orthogonality of the distortions associated with candidate scan profiles with respect to the sample.

[0096] 18. The charged particle optical device according to any one of clauses 12 to 17, wherein the controller is configured to: generate a database of candidate scan profiles, the candidate scan profiles being associated with a distortion function that indicates the expected distortion caused by the respective candidate scan profiles.

[0097] 19. The charged particle optical device according to clause 18, wherein the controller is configured to: generate the database by predicting the expected distortion using a physical model.

[0098] 20. The charged particle optical device according to clause 18 or 19, wherein the controller is configured to: generate the database by predicting the expected distortion using empirical training.

[0099] 21. The charged particle optical device according to any one of clauses 12 to 20, wherein the controller is configured to: scan the sample by guiding the charged particle beam along a scan path on the sample defined by the selected at least one scan profile.

[0100] 22. A non-transitory computer-readable medium storing instructions for a processor of a controller to execute a method for correcting scanned data, the scanned data being generated by scanning a sample with charged particles and detecting signal charged particles emitted from the sample, the method comprising:

[0101] selecting, based on at least one known distortion function, at least one scan profile for scanning the sample, the at least one known distortion function being associated with the selected at least one scan profile and indicating distortion of the scanned data; and

[0102] correcting the scanned data generated by the scanning of the sample based on the at least one known distortion function associated with the selected at least one scan profile.

[0103] 23. A method for processing scanning electron microscope (SEM) image data of a sample, the method comprising:

[0104] determining, for each of a plurality of scan profiles, a distortion function that indicates distortion of the SEM image data of the sample;

[0105] selecting a scan profile based on the determined distortion function, the sample having a known design being scanned according to the scan profile;

[0106] acquiring SEM image data by scanning the sample according to the selected scan profile; and

[0107] applying the distortion function to the SEM image data to reduce the distortion of the SEM image data.

[0108] 24. The method according to clause 23, wherein the distortion is caused by charging of the sample during scanning according to the scan profile.

[0109] 25. A scanning electron microscope (SEM) for scanning a sample with electrons and detecting signal electrons emitted from the sample, the SEM comprising:

[0110] an electron optical device configured to direct an electron beam onto the sample according to a selected scan profile, the selected scan profile being selected based on a distortion function that indicates distortion of the SEM image data of a candidate scan profile;

[0111] a detector configured to detect signal electrons emitted from the sample to generate SEM image data; and

[0112] A controller configured to apply the distortion function of the selected scan profile to the SEM image data to reduce the distortion of the SEM image data.

[0113] 26. A non-transitory computer-readable medium storing instructions for a processor of a controller to execute a method for processing scanning electron microscope (SEM) image data, the image data being acquired by electronically scanning a sample and detecting signal electrons emitted from the sample, the method comprising:

[0114] Determining a distortion function for each of a plurality of scan profiles, the distortion function indicating the distortion of the SEM image data of the sample;

[0115] Selecting a scan profile based on the determined distortion function, the sample with a known design will be scanned according to the scan profile;

[0116] Controlling to acquire SEM image data by scanning the sample according to the selected scan profile; and

[0117] Applying the distortion function to the SEM image data to reduce the distortion of the SEM image data.

[0118] A non-transitory computer-readable medium may be provided that stores instructions for a processor of a controller (e.g., Figure 1 controller 109) to perform image evaluation (e.g., metrology or inspection), image acquisition, activation of a charged particle source, adjustment of the electrical excitation of an astigmatizer, adjustment of the landing energy of electrons, adjustment of the objective lens excitation, adjustment of the position and orientation of a secondary electron detector, stage motion control, beam separator excitation, application of a scan deflection voltage to a beam deflector, receiving and processing data related to signal information from an electron detector, configuring electrostatic elements, detecting signal electrons, adjusting the potential of a control electrode, adjusting the voltages applied to an electron source, an extractor electrode, and a sample, etc. Common forms of non-transitory media include, for example, floppy disks, flexible disks, hard disks, solid state drives, magnetic tapes, or any other magnetic data storage medium, compact disc read-only memory (CD-ROM), any other optical data storage medium, any physical medium with a hole pattern, random access memory (RAM), programmable read-only memory (PROM), and erasable programmable read-only memory (EPROM), FLASH-EPROM, or any other flash memory, non-volatile random access memory (NVRAM), cache, registers, any other memory chip or cartridge, and their network versions.

[0119] It should be understood that the embodiments of the present disclosure are not limited to the exact configurations described above and shown in the drawings, but various modifications and changes can be made without departing from its scope. The present disclosure has been described in connection with various embodiments, and those skilled in the art will appreciate other embodiments of the present invention by considering the specification and practice of the invention disclosed herein. It is intended that the specification and examples be considered exemplary only, and the true scope and spirit of the present invention be indicated by the following claims.

[0120] The foregoing description is intended to be illustrative and not restrictive. Accordingly, those skilled in the art will appreciate that modifications can be made as described above without departing from the scope of the claims listed below.

Claims

1. A method for correcting scanned data, wherein the scanned data is generated by scanning a sample with charged particles and detecting signal charged particles emitted from the sample, the method comprising: selecting at least one scan profile for scanning the sample based on at least one known distortion function, the at least one known distortion function being associated with the selected at least one scan profile and indicating distortion of the scanned data; and correcting the scanned data generated by the scanning of the sample based on the at least one known distortion function associated with the selected at least one scan profile.

2. The method according to claim 1, wherein the scan data generated by the scan of the sample includes: the distortion associated with the selected at least one scan profile and the structural information associated with the sample, wherein the correction is for compensating the distortion associated with the selected at least one scan profile.

3. The method according to claim 2, wherein the selected at least one scan profile is selected based on the degree of separability of the distortion associated with the candidate scan profile and the predicted structural information of the scanned data.

4. The method according to claim 2, wherein the selected at least one scan profile is selected based on the degree of orthogonality of the distortion associated with the candidate scan profile with respect to the predicted structural information of the scanned data.

5. The method according to claim 1, wherein the selected plurality of scan profiles are selected based on the degree of orthogonality of the distortions associated with the candidate scan profiles with respect to each other.

6. The method according to claim 5, wherein the selected plurality of scan profiles are selected based on the degree of orthogonality of the distortions associated with the candidate scan profiles with respect to each other for the sample.

7. The method according to claim 1, comprising: generating a database of candidate scan profiles, the candidate scan profiles being associated with distortion functions that indicate the expected distortion caused by the respective candidate scan profiles.

8. The method according to claim 7, wherein the database is generated by using a physical model to predict the expected distortion.

9. The method according to claim 7, wherein the database is generated by using empirical training to predict the expected distortion.

10. The method according to claim 1, comprising: scanning the sample using the selected at least one scan profile.

11. The method according to claim 1, wherein the scan profile determines the scan path followed by the charged particle beam on the sample.

12. A charged particle optical device that scans a sample with charged particles and detects signal charged particles emitted from the sample, the charged particle optical device comprising: a charged particle optical device configured to direct a charged particle beam onto the sample according to at least one selected scan profile, the at least one selected scan profile being selected based on at least one known distortion function that indicates distortion of the scanned data and is associated with the at least one selected scan profile; a detector configured to detect signal charged particles emitted from the sample to generate scanned data; and A controller configured to correct the scan data based on the at least one known distortion function associated with the at least one selected scan profile.

13. The charged particle optical device according to claim 12, wherein the scan data generated by the scan of the sample includes: Distortion associated with the at least one selected scan profile and structural information associated with the sample, wherein the correction is for compensating the distortion associated with the at least one selected scan profile.

14. The charged particle optical device according to claim 13, wherein the controller is configured to: select the at least one selected scan profile based on a degree of separability between the distortion associated with a candidate scan profile and predicted structural information of the scan data.

15. The charged particle optical device according to claim 13, wherein the controller is configured to: select the at least one selected scan profile based on a degree of orthogonality of the distortion associated with a candidate scan profile with respect to predicted structural information of the scan data.

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