Astigmatism manipulation for charged-particle beam tool

Abstract

A method comprises scanning one or more features on a sample using a charged-particle beam having a first beam profile to obtain a first signal, and scanning the one or more features on the sample using a charged-particle beam having a second beam profile to obtain a second signal. The first and second signals are compared and one or more parameters of the one or more features are determined based on the comparison.

Description

ASTIGMATISM MANIPULATION FOR CHARGED-PARTICLE BEAM TOOLCROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims priority of EP application 24207346.8 which was filed on October 17, 2024 and which is incorporated herein in its entirety by reference.TECHNICAL FIELD

[0002] The embodiments provided herein generally relate to metrology improvement, and more particularly, to a metrology improvement technique by manipulating the astigmatism of a charged- particle beam.BACKGROUND

[0003] In manufacturing processes of integrated circuits (ICs), unfinished or finished circuit components are inspected to ensure that they are manufactured according to design and are free of defects. Charged particle beam based systems such as charged particle (e.g., electron) beam microscopes, such as a scanning electron microscope (SEM) can be employed. Metrology, in the context of a charged particle beam system, refers to the science and technology of measurement of micro and nanoscale structures using the system. As the physical sizes of IC components continue to shrink, accuracy and repeatability in metrology and defect detection becomes more and more important. Metrology and defect inspection involves measurements of semiconductor device structures using inspection images during the device fabrication processes, and then the measurements are further processed to identify possible defects on the wafer.SUMMARY

[0004] In some embodiments, an apparatus is disclosed. The apparatus comprises a memory storing a set of instructions and at least one processor configured to execute the set of instructions to cause the apparatus to perform operations. The operations may comprise scanning one or more features on a sample using a charged-particle beam having a first beam profile to obtain a first signal and scanning the one or more features on the sample using a charged-particle beam having a second beam profile to obtain a second signal. The operations may also include comparing the first signal and the second signal, and determining a first set of parameters of the one or more features based on the comparison.

[0005] In some embodiments, a non-transitory computer readable medium that stores a set of instructions that is executable by at least on processor of a computing device to cause the computing device to perform operations is disclosed. The operations may comprise scanning one or more features on a sample using a charged-particle beam having a first beam profile to obtain a first signal, and scanning the one or more features on the sample using a charged-particle beam having a secondbeam profile to obtain a second signal. The operations may also include comparing the first signal and the second signal, and determining a first set of parameters of the one or more features based on the comparison.

[0006] In some embodiments, a method is disclosed. The method may include scanning one or more features on a sample using a charged-particle beam having a first beam profile to obtain a first signal, and scanning the one or more features on the sample using a charged-particle beam having a second beam profile to obtain a second signal. The method may also include comparing the first signal and the second signal, and determining a first set of parameters of the one or more features based on the comparison.

[0007] In some embodiments, a non-transitory computer readable medium that stores a set of instructions that is executable by at least on processor of a computing device to cause the computing device to perform operations is disclosed. The operations may comprise adjusting an astigmatism of a charged-particle beam to a first astigmatism to generate a first elongated beam profile, and scanning one or more features on a sample using the charged-particle beam having the first elongated beam profile to obtain a first signal. The operations may also include adjusting an astigmatism of a charged- particle beam to a second astigmatism to generate a second elongated beam profile different from the first elongated beam profile and scanning the one or more features on the sample using the charged- particle beam having the second elongated beam profile to obtain a second signal. The operations may further include determining a first set of parameters of the one or more features based on the first signal and second signal.

[0008] Other advantages of the embodiments of the present disclosure will become apparent from the following description taken in conjunction with the accompanying drawings wherein are set forth, by way of illustration and example, certain embodiments of the present invention.BRIEF DESCRIPTION OF FIGURES

[0009] The above and other aspects of the present disclosure will become more apparent from the description of exemplary embodiments, taken in conjunction with the accompanying drawings.

[0010] Fig. 1 is a schematic diagram illustrating an example charged-particle beam system, consistent with embodiments of the present disclosure.

[0011] Fig. 2A is a schematic diagram illustrating an example multi-beam tool, consistent with embodiments of the present disclosure that can be a part of the example charged-particle beam system of Fig. 1.

[0012] Fig. 2B is a schematic diagram illustrating an example single-beam tool, consistent with embodiments of the present disclosure that can be a part of the example charged-particle beam system of Fig. 1.

[0013] Figs. 3A-3C are schematic diagrams illustrating an exemplary technique to determine characteristics of a feature, consistent with embodiments of the present disclosure.

[0014] Figs. 4A-4D are schematic diagrams illustrating exemplary embodiments of determining characteristics of a feature, consistent with embodiments of the present disclosure.

[0015] Figs. 5A-5B are schematic diagrams comparing different exemplary embodiments of determining characteristics of a feature, consistent with some embodiments of the present disclosure.

[0016] Figs. 6A-6B are schematic diagrams illustrating an exemplary technique to determine characteristics of a feature, consistent with embodiments of the present disclosure.

[0017] Figs. 7A-7C are schematic diagrams illustrating an exemplary technique to determine characteristics of a feature, consistent with embodiments of the present disclosure.

[0018] Fig. 8 is a flow chart of an exemplary method of determining characteristics of a feature, consistent with embodiments of the current disclosure.DETAILED DESCRIPTION

[0019] Reference will now be made in detail to 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 represented. The implementations set forth in the following description of exemplary embodiments do not represent all implementations. Instead, they are merely examples of apparatuses and methods consistent with aspects related to the disclosed embodiments as recited in the appended claims. For example, although some embodiments are described in the context of utilizing electron beams, the disclosure is not so limited. Other types of charged particle beams (e.g., including protons, ions, muons, or any other particle carrying electric charges) may be similarly applied. Furthermore, other imaging systems may be used, such as optical imaging, photon detection, x-ray detection, ion detection, etc.

[0020] Electronic devices are constructed of circuits formed on a piece of semiconductor material called a substrate. The semiconductor material may include, for example, silicon, gallium arsenide, indium phosphide, or silicon germanium, or the like. Many circuits may be formed together on the same piece of silicon and are called integrated circuits or ICs. The size of these circuits has decreased dramatically so that many more of them can be fit on the substrate. For example, an IC chip in a smartphone can be as small as a thumbnail and yet may include over 2 billion transistors, the size of each transistor being less than 1 / 1000th the size of a human hair.

[0021] Making these ICs with extremely small structures or components is a complex, timeconsuming, and expensive process, often involving hundreds of individual steps. Errors in even one step have the potential to result in defects in the finished IC, rendering it useless. Thus, one goal of the manufacturing process is to avoid such defects to maximize the number of functional ICs made in the process; that is, to improve the overall yield of the process.

[0022] One component of improving yield is monitoring the chip-making process to ensure that it is producing a sufficient number of functional integrated circuits. One way to monitor the process is toinspect the chip circuit structures at various stages of their formation. Inspection can be carried out using a scanning charged-particle microscope (“SCPM”). For example, an SCPM may be a scanning electron microscope (SEM). A SCPM can be used to image these extremely small structures, in effect, taking a “picture” of the structures of the wafer. The image can be used to determine if the structure was formed properly in the proper location. If the structure is defective, then the process can be adjusted, so the defect is less likely to recur.

[0023] As the physical sizes of IC components continue to shrink, accuracy and yield in defect detection becomes more and more important. Defect inspection involves measurements of device structures using inspection images during wafer fabrication processes, and then the measurements are further processed to identify possible defects on the wafer. Critical dimensions (CDs) of patterns / structures measured from a SEM image can be used for identifying defects of manufactured ICs. The term critical dimensions refer to any geometric parameters or features (e.g., line width, space width, thickness, aspect ratio, overlay accuracy, etc.) of the device structure that, for example, may affect the functionality and performance of the device. The term parameters refer to various measurable characteristics of features on a substrate that may, for example, be useful for evaluating their performance and functionality in applications like semiconductor manufacturing, materials science, and nanotechnology. A feature refers to any defined structure or pattern that is intentionally created on, for example, a semiconductor wafer during the fabrication process. These features can encompass a wide range of geometrical shapes and sizes, including traces, vias, contact holes, and active regions. For example, shifts between patterns or edge placement variations, which are determined from measured critical dimensions, can be helpful in identifying defects. Without accurate metrology of critical dimensions of device structures, accurate defect identification is hardly possible. Therefore, accuracy and yield in defect detection is fundamentally based on accurate measurements of critical dimensions of device structures. However, measurement accuracy and repeatability of the measurement is limited by metrology tool error (e.g., calibration ruler error), process variations (e.g., leading to line-width roughness or trench-width roughness), measurement error (e.g., alignment variation), a measurement tool noise (e.g., a limited number of electrons when inspecting a line / edge), limitations of the metrology, etc.

[0024] In conventional systems, noise reduction of SCPM type metrology is achieved by averaging over multiple measurements. For example, a line width as a critical dimension can be determined by averaging multiple measurements measured from a section of a line or from multiple lines. In such systems, critical dimension measurement precision can be improved by increasing the number of measurements to be averaged. Currently, measurement of a critical dimension (CD) is based on locating edges of a structure or a pattern (e.g., a trace) from a gray level value (GLV) profile obtained from an electron-beam (e-beam) image. Gray level value profile represents the variation of pixel intensity values along a line in the image. Pixels with intensity values above a default threshold are considered part of the pattern, while pixels below this threshold are considered background.

[0025] According to some embodiments of the present disclosure, a critical dimension measurement technique is provided where a threshold value that is relatively insensitive to expected variations in the performance of the tool is selected and used. Precision and repeatability of critical dimension measurements may be improved by using a threshold value that is determined to be insensitive to tool performance.

[0026] Relative dimensions of components in drawings may be exaggerated for clarity. Within the following description of drawings, the same or like reference numbers refer to the same or like components or entities, and only the differences with respect to the individual embodiments are described. Other objects and advantages of the disclosure may be realized by the elements and combinations as set forth in the embodiments discussed herein. However, embodiments of the present disclosure are not necessarily required to achieve such exemplary objects or advantages, and some embodiments may not achieve any of the stated objects or advantages.

[0027] Without limiting the scope of the present disclosure, some embodiments may be described in the context of providing scanning deflection systems and scanning deflection methods in systems utilizing electron beams (“e-beams”). Some scanning deflection systems may use electric fields to influence a charged particle beam. However, the disclosure is not so limited. Other types of charged particle beams may be similarly applied. For example, systems and methods may be applicable with optics, photons, x-rays, and ions, etc. Deflection may be used to scan a beam over a surface in, for example, cathode ray tubes (CRTs), lithography machines, scanning charged-particle microscopes (SCPMs), or other analytical instruments. While some embodiments are discussed with reference to deflection systems that use electric field to influence a beam, deflection may also be achieved with magnetic fields, for example.

[0028] As used herein, unless specifically stated otherwise, the term “or” encompasses all possible combinations, except where infeasible. For example, if it is stated that a component includes A or B, then, unless specifically stated otherwise or infeasible, the component may include A, or B, or A and B. As a second example, if it is stated that a component includes A, B, or C, then, unless specifically stated otherwise or infeasible, the component may include A, or B, or C, or A and B, or A and C, or B and C, or A and B and C. Expressions such as “at least one of’ do not necessarily modify an entirety of a following list and do not necessarily modify each member of the list, such that “at least one of A, B, and C” should be understood as including only one of A, only one of B, only one of C, or any combination of A, B, and C. The phrase “one of A and B” or “any one of A and B” shall be interpreted in the broadest sense to include one of A, or one of B.

[0029] Fig. 1 illustrates an example electron beam inspection (EBI) system 100 consistent with embodiments of the present disclosure. EBI system 100 may be used for imaging. As shown in Fig. 1, EBI system 100 includes a main chamber 101, a load / lock chamber 102, a beam tool 104, and an equipment front end module (EFEM) 106. Beam tool 104 is located within main chamber 101. EFEM 106 includes a first loading port 106a and a second loading port 106b. EFEM 106 may includeadditional loading port(s). First loading port 106a and second loading port 106b receive wafer front opening unified pods (FOUPs) that contain wafers (e.g., semiconductor wafers or wafers made of other material(s)) or samples to be inspected (wafers and samples may be used interchangeably). A “lot” is a plurality of wafers that may be loaded for processing as a batch.

[0030] One or more robotic arms (not shown) in EFEM 106 may transport the wafers to load / lock chamber 102. Load / lock chamber 102 is connected to a load / lock vacuum pump system (not shown) which removes gas molecules in load / lock chamber 102 to reach a first pressure below the atmospheric pressure. After reaching the first pressure, one or more robotic arms (not shown) may transport the wafer from load / lock chamber 102 to main chamber 101. Main chamber 101 is connected to a main chamber vacuum pump system (not shown) which removes gas molecules in main chamber 101 to reach a second pressure below the first pressure. After reaching the second pressure, the wafer is subject to inspection by beam tool 104. Beam tool 104 may be a single-beam system or a multi-beam system.

[0031] A controller 109 (or control unit) is electronically connected to beam tool 104. In the context of a charged particle beam apparatus, the controller may be responsible for managing and regulating various aspects of the beam generation, manipulation, and delivery processes of EBI system 100. Controller 109 may include circuits (or circuitry) that enables various functionalities. Some exemplary circuits and their related functionalities will be described. For example, in some embodiments, controller 109 may include circuitry that enables it to control one or more of the intensity, focus, energy, and direction of the charged particle beam in beam tool 104. The controller may adjust these parameters according to the requirements of the specific application. Alternatively, or additionally, the controller may also include circuitry that enables it to manage mechanisms for steering and deflecting the charged particle beam. These steering or deflecting circuits may activate electromagnetic fields or use other techniques to manipulate the trajectory of the beam. For example, these circuits may include power supplies, electromagnetic coils, electrostatic lenses, or other mechanisms for controlling the trajectory and direction of the beam.

[0032] In some embodiments, controller 109 may additionally or alternatively include circuits that enable it to continuously monitors the stability of the beam and adjust parameters to maintain suitable performance of beam tool 104. These circuits may include sensors, detectors, and feedback loops to measure parameters such as beam current, position, energy, intensity, etc. in real-time. These circuits may incorporate feedback systems to detect deviations from desired beam characteristics and make real-time corrections. For example, the feedback system may compare measured beam parameters with desired setpoints and adjust control signals to minimize deviations and ensure consistent beam quality. In some embodiments, controller 109 may also include circuits that enable data acquisition and analysis, allowing users to collect and analyze data generated by the charged particle beam interactions with the sample.

[0033] It should be noted that it is not a requirement that controller 109 include circuits corresponding to all, or any, of the above-described exemplary functionalities. In other words, controller 109 include circuitry that enables it to control some aspects of EBI system 100. In some embodiments, controller 109 may be a computer configured to execute various controls of EBI system 100. While controller 109 is shown in Fig. 1 as being outside of the structure that includes main chamber 101, load / lock chamber 102, and EFEM 106, it is appreciated that controller 109 may be a part of the structure.

[0034] In some embodiments, controller 109 may include one or more processors (not shown). A processor may be an electronic device capable of manipulating or processing information. For example, the processor may include any combination of any number of a central processing unit (or “CPU”), a graphics processing unit (or “GPU”), an optical processor, a programmable logic controllers, a microcontroller, a microprocessor, a digital signal processor, an intellectual property (IP) core, a Programmable Logic Array (PLA), a Programmable Array Logic (PAL), a Generic Array Logic (GAL), a Complex Programmable Logic Device (CPLD), a Field-Programmable Gate Array (FPGA), a System On Chip (SoC), an Application-Specific Integrated Circuit (ASIC), a neural processing unit (NPU), and any other type of circuit capable of data processing. The processor may also be a virtual processor that includes one or more processors distributed across multiple machines or devices coupled via a network.

[0035] In some embodiments, controller 109 may further include one or more memories (not shown). A memory may be an electronic device capable of storing codes and data accessible by the processor (e.g., via a bus). For example, the memory may include any combination of any number of a randomaccess memory (RAM), a read-only memory (ROM), an optical disc, a magnetic disk, a hard drive, a solid-state drive, a flash drive, a security digital (SD) card, a memory stick, a compact flash (CF) card, or any type of storage device. The codes and data may include an operating system (OS) and one or more application programs (or “apps”) for specific tasks. The memory may also be a virtual memory that includes one or more memories distributed across multiple machines or devices coupled via a network.

[0036] Fig. 2A illustrates a schematic diagram of an example multi-beam beam tool 104A (also referred to herein as apparatus 104A) and an image processing system 290 that may be configured for use in EBI system 100 (Fig. 1), consistent with embodiments of the present disclosure.

[0037] Beam tool 104 A comprises a charged-particle source 202, a gun aperture 204, a condenser lens 206, a primary charged-particle beam 210 emitted from charged-particle source 202, a source conversion unit 212, a plurality of beamlets 214, 216, and 218 of primary charged-particle beam 210, a primary projection optical system 220, a motorized wafer stage 280, a wafer holder 282, multiple secondary charged-particle beams 236, 238, and 240, a secondary optical system 242, and a charged- particle detection device 244. Primary projection optical system 220 can comprise a beam separator222, a deflection scanning unit 226, and an objective lens 228. Charged-particle detection device 244 can comprise detection sub-regions 246, 248, and 250.

[0038] Charged-particle source 202, gun aperture 204, condenser lens 206, source conversion unit 212, beam separator 222, deflection scanning unit 226, and objective lens 228 can be aligned with a primary optical axis 260 of apparatus 104A. Secondary optical system 242 and charged-particle detection device 244 can be aligned with a secondary optical axis 252 of apparatus 104A.

[0039] Charged-particle source 202 can emit one or more charged particles, such as electrons, protons, ions, muons, or any other particle carrying electric charges. In some embodiments, charged- particle source 202 may be an electron source. For example, charged-particle source 202 may include a cathode, an extractor, or an anode, wherein primary electrons can be emitted from the cathode and extracted or accelerated to form primary charged-particle beam 210 (in this case, a primary electron beam) with a crossover (virtual or real) 208. For ease of explanation without causing ambiguity, electrons are used as examples in some of the descriptions herein. However, it should be noted that any charged-particle beam may be used in any of the examples described in this disclosure, not limited to electrons. Primary charged-particle beam 210 can be visualized as being emitted from crossover 208. Gun aperture 204 can block off peripheral charged particles of primary charged- particle beam 210 to reduce Coulomb effect. The Coulomb effect may cause an increase in size of probe spots.

[0040] Source conversion unit 212 can comprise an array of image-forming elements and an array of beam-limit apertures. The array of image-forming elements can comprise an array of micro-deflectors or micro-lenses. The array of image-forming elements can form a plurality of parallel images (virtual or real) of crossover 208 with a plurality of beamlets 214, 216, and 218 of primary charged-particle beam 210. The array of beam-limit apertures can limit the plurality of beamlets 214, 216, and 218. While three beamlets 214, 216, and 218 are shown in Fig. 2A, embodiments of the present disclosure are not so limited. For example, in some embodiments, the apparatus 104A may be configured to generate a first number of beamlets. In some embodiments, the first number of beamlets may be in a range from 1 to 1000. In some embodiments, the first number of beamlets may be in a range from 200-500. In some embodiments, an apparatus 104A may generate 400 beamlets.

[0041] Condenser lens 206 can focus primary charged-particle beam 210. The electric currents of beamlets 214, 216, and 218 downstream of source conversion unit 212 can be varied by adjusting the focusing power of condenser lens 206 or by changing the radial sizes of the corresponding beam-limit apertures within the array of beam-limit apertures. Objective lens 228 can focus beamlets 214, 216, and 218 onto a wafer 230 for imaging, and can form a plurality of probe spots 270, 272, and 274 on a surface of wafer 230.

[0042] Beam separator 222 can be a beam separator of Wien filter type generating an electrostatic dipole field and a magnetic dipole field. In some embodiments, if they are applied, the force exerted by the electrostatic dipole field on a charged particle (e.g., an electron) of beamlets 214, 216, and 218can be substantially equal in magnitude and opposite in a direction to the force exerted on the charged particle by magnetic dipole field. Beamlets 214, 216, and 218 can, therefore, pass straight through beam separator 222 with zero deflection angle. However, the total dispersion of beamlets 214, 216, and 218 generated by beam separator 222 can also be non-zero. Beam separator 222 can separate secondary charged-particle beams 236, 238, and 240 from beamlets 214, 216, and 218 and direct secondary charged-particle beams 236, 238, and 240 towards secondary optical system 242.

[0043] Deflection scanning unit 226 can deflect beamlets 214, 216, and 218 to scan probe spots 270, 272, and 274 over a surface area of wafer 230. In response to the incidence of beamlets 214, 216, and 218 at probe spots 270, 272, and 274, secondary charged-particle beams 236, 238, and 240 may be emitted from wafer 230. Secondary charged-particle beams 236, 238, and 240 may comprise charged particles (e.g., electrons) with a distribution of energies. For example, secondary charged-particle beams 236, 238, and 240 may be secondary electron beams including secondary electrons (energies < 50 eV) and backscattered electrons (energies between 50 eV and landing energies of beamlets 214, 216, and 218). Secondary optical system 242 can focus secondary charged-particle beams 236, 238, and 240 onto detection sub-regions 246, 248, and 250 of charged-particle detection device 244. Detection sub-regions 246, 248, and 250 may be configured to detect corresponding secondary charged-particle beams 236, 238, and 240 and generate corresponding signals (e.g., voltage, current, or the like) used to reconstruct an inspection image of structures on or underneath the surface area of wafer 230.

[0044] The generated signals may represent intensities of secondary charged-particle beams 236, 238, and 240 and may be provided to image processing system 290 that is in communication with charged-particle detection device 244, primary projection optical system 220, and motorized wafer stage 280. The movement speed of motorized wafer stage 280 may be synchronized and coordinated with the beam deflections controlled by deflection scanning unit 226, such that the movement of the scan probe spots (e.g., scan probe spots 270, 272, and 274) may orderly cover regions of interest on the wafer 230. The parameters of such synchronization and coordination may be adjusted to adapt to different materials of wafer 230. For example, different materials of wafer 230 may have different resistance-capacitance characteristics that may cause different signal sensitivities to the movement of the scan probe spots.

[0045] The intensity of secondary charged-particle beams 236, 238, and 240 may vary according to the external or internal structure of wafer 230, and thus may indicate whether wafer 230 includes defects. Moreover, as discussed above, beamlets 214, 216, and 218 may be projected onto different locations of the top surface of wafer 230, or different sides of local structures of wafer 230, to generate secondary charged-particle beams 236, 238, and 240 that may have different intensities. Therefore, by mapping the intensity of secondary charged-particle beams 236, 238, and 240 with the areas of wafer 230, image processing system 290 may reconstruct an image that reflects the characteristics of internal or external structures of wafer 230.

[0046] In some embodiments, image processing system 290 may include an image acquirer 292, a storage 294, and a controller 296. Image acquirer 292 may comprise one or more processors. For example, image acquirer 292 may comprise a computer, server, mainframe host, terminals, personal computer, any kind of mobile computing devices, or the like, or a combination thereof. Image acquirer 292 may be communicatively coupled to charged-particle detection device 244 of beam tool 104A through a medium such as an electric conductor, optical fiber cable, portable storage media, IR, Bluetooth, internet, wireless network, wireless radio, or a combination thereof. In some embodiments, image acquirer 292 may receive a signal from charged-particle detection device 244 and may construct an image. Image acquirer 292 may thus acquire inspection images of wafer 230. Image acquirer 292 may also perform various post-processing functions, such as generating contours, superimposing indicators on an acquired image, or the like. Image acquirer 292 may be configured to perform adjustments of brightness and contrast of acquired images. In some embodiments, storage 294 may be a storage medium such as a hard disk, flash drive, cloud storage, random access memory (RAM), other types of computer-readable memory, or the like. Storage 294 may be coupled with image acquirer 292 and may be used for saving scanned raw image data as original images, and postprocessed images. Image acquirer 292 and storage 294 may be connected to controller 296. In some embodiments, image acquirer 292, storage 294, and controller 296 may be integrated together as one control unit.

[0047] In some embodiments, image acquirer 292 may acquire one or more inspection images of a wafer based on an imaging signal received from charged-particle detection device 244. An imaging signal may correspond to a scanning operation for conducting charged particle imaging. An acquired image may be a single image comprising a plurality of imaging areas. The single image may be stored in storage 294. The single image may be an original image that may be divided into a plurality of regions. Each of the regions may comprise one imaging area containing a feature of wafer 230. The acquired images may comprise multiple images of a single imaging area of wafer 230 sampled multiple times over a time sequence. The multiple images may be stored in storage 294. In some embodiments, image processing system 290 may be configured to perform image processing steps with the multiple images of the same location of wafer 230.

[0048] In some embodiments, image processing system 290 may include measurement circuits (e.g., analog-to-digital converters) to obtain a distribution of the detected secondary charged particles (e.g., secondary electrons). The charged-particle distribution data collected during a detection time window, in combination with corresponding scan path data of beamlets 214, 216, and 218 incident on the wafer surface, can be used to reconstruct images of the wafer structures under inspection. The reconstructed images can be used to reveal various features of the internal or external structures of wafer 230, and thereby can be used to reveal any defects that may exist in the wafer.

[0049] In some embodiments, the charged particles may be electrons. When electrons of primary charged-particle beam 210 are projected onto a surface of wafer 230 (e.g., probe spots 270, 272, and274), the electrons of primary charged-particle beam 210 may penetrate the surface of wafer 230 for a certain depth, interacting with particles of wafer 230. Some electrons of primary charged-particle beam 210 may elastically interact with (e.g., in the form of elastic scattering or collision) the materials of wafer 230 and may be reflected or recoiled out of the surface of wafer 230. An elastic interaction conserves the total kinetic energies of the bodies (e.g., electrons of primary charged-particle beam 210) of the interaction, in which the kinetic energy of the interacting bodies does not convert to other forms of energy (e.g., heat, electromagnetic energy, or the like). Such reflected electrons generated from elastic interaction may be referred to as backscattered electrons (BSEs). Some electrons of primary charged-particle beam 210 may inelastically interact with (e.g., in the form of inelastic scattering or collision) the materials of wafer 230. An inelastic interaction does not conserve the total kinetic energies of the bodies of the interaction, in which some or all of the kinetic energy of the interacting bodies convert to other forms of energy. For example, through the inelastic interaction, the kinetic energy of some electrons of primary charged-particle beam 210 may cause electron excitation and transition of atoms of the materials. Such inelastic interaction may also generate electrons exiting the surface of wafer 230, which may be referred to as secondary electrons (SEs). Yield or emission rates of BSEs and SEs depend on, e.g., the material under inspection and the landing energy of the electrons of primary charged-particle beam 210 landing on the surface of the material, among others. The energy of the electrons of primary charged-particle beam 210 may be imparted in part by its acceleration voltage (e.g., the acceleration voltage between the anode and cathode of charged-particle source 202 in Fig. 2A). The quantity of BSEs and SEs may be more or fewer (or even the same) than the injected electrons of primary charged-particle beam 210.

[0050] Another example of a charged particle beam apparatus will now be discussed with reference to Fig. 2B. Beam tool 104B (also referred to herein as apparatus 104B) may be an example of beam tool 104 and may be similar to beam tool 104A shown in Fig. 2A. However, different from apparatus 104A, apparatus 104B may be a single -beam tool that uses only one primary electron beam to scan one location on the wafer at a time.

[0051] As shown in Fig. 2B, apparatus 104B includes a wafer holder 136 supported by motorized stage 134 to hold a wafer 150 to be inspected. Beam tool 104B includes an electron emitter, which may comprise a cathode 103, an anode 121, and a gun aperture 122. Beam tool 104B further includes a beam limit aperture 125, a condenser lens 126, a column aperture 135, an objective lens assembly 132, and a detector 144. Objective lens assembly 132, in some embodiments, may be a modified SORIL lens, which includes a pole piece 132a, a control electrode 132b, a deflector unit 132c, and an exciting coil 132d. In a detection or imaging process, an electron beam 161 emanating from the tip of cathode 103 may be accelerated by anode 121 voltage, pass through gun aperture 122, beam limit aperture 125, condenser lens 126, and be focused into a probe spot 170 by the modified SORIL lens and impinge onto the surface of wafer 150. Probe spot 170 may be scanned across the surface of wafer 150 by a deflector, such as deflector unit 132c or other deflectors in the SORIL lens. Secondaryor scattered particles, such as secondary electrons or scattered primary electrons emanated from the wafer surface may be collected by detector 144 to determine intensity of the beam and so that an image of an area of interest on wafer 150 may be reconstructed.

[0052] There may also be provided an image processing system 199 that includes an image acquirer 120, a storage 130, and controller 109. Image acquirer 120 may comprise one or more processors. For example, image acquirer 120 may comprise a computer, server, mainframe host, terminals, personal computer, any kind of mobile computing devices, and the like, or a combination thereof. Image acquirer 120 may connect with detector 144 of beam tool 104B through a medium such as an electrical conductor, optical fiber cable, portable storage media, IR, Bluetooth, internet, wireless network, wireless radio, or a combination thereof. Image acquirer 120 may receive a signal from detector 144 and may construct an image. Image acquirer 120 may thus acquire images of wafer 150. Image acquirer 120 may also perform various post-processing functions, such as image averaging, generating contours, superimposing indicators on an acquired image, and the like. Image acquirer 120 may be configured to perform adjustments of brightness and contrast, etc. of acquired images. Storage 130 may be a storage medium such as a hard disk, random access memory (RAM), cloud storage, other types of computer readable memory, and the like. Storage 130 may be coupled with image acquirer 120 and may be used for saving scanned raw image data as original images, and postprocessed images. Image acquirer 120 and storage 130 may be connected to controller 109. In some embodiments, image acquirer 120, storage 130, and controller 109 may be integrated together as one electronic control unit.

[0053] In some embodiments, image acquirer 120 may acquire one or more images of a sample based on an imaging signal received from detector 144. An imaging signal may correspond to a scanning operation for conducting charged particle imaging. An acquired image may be a single image comprising a plurality of imaging areas that may contain various features of wafer 150. The single image may be stored in storage 130. Imaging may be performed on the basis of imaging frames.

[0054] The condenser and illumination optics of the electron beam tool may comprise or be supplemented by electromagnetic quadrupole electron lenses. For example, as shown in Fig. 2B, electron beam tool 104B may comprise a first quadrupole lens 148 and a second quadrupole lens 158. In some embodiments, the quadrupole lenses may be used for controlling the electron beam. For example, first quadrupole lens 148 may be controlled to adjust the beam current and second quadrupole lens 158 may be controlled to adjust the beam spot size and beam shape.

[0055] Fig. 2B illustrates a charged particle beam apparatus that may use a single primary beam configured to generate secondary electrons by interacting with wafer 150. Detector 144 may be placed along optical axis 105, as in the example shown in Fig. 2B. The primary electron beam may be configured to travel along optical axis 105. Accordingly, detector 144 may include a hole at its center so that the primary electron beam may pass through to reach wafer 150. Fig. 2B shows an example ofdetector 144 having an opening at its center. However, some embodiments may use a detector placed off-axis relative to the optical axis along which the primary electron beam travels. For example, as in the example shown in Fig. 2B, discussed above, a beam separator 222 may be provided to direct secondary electron beams toward a detector placed off-axis. Beam separator 222 may be configured to divert secondary electron beams toward an electron detection device 244, as shown in Fig. 2A.

[0056] The images generated by SCPM may be used for defect inspection on a sample being imaged. For example, a generated image capturing a test device region of a wafer may be compared with a reference image capturing the same test device region. The reference image may be predetermined (e.g., by simulation) and include no known defect. If a difference between the generated image and the reference image exceeds a tolerance level, a potential defect may be identified. For another example, the SCPM may scan multiple regions of the wafer, each region including a test device region designed as the same and generate multiple images capturing those test device regions as manufactured. The multiple images may be compared with each other. If a difference between the multiple images exceeds a tolerance level, a potential defect may be identified.

[0057] In some embodiments, the images generated by SCPM may be used for metrology, such as, for example, determining feature sizes of structures (e.g., circuits, etc.) on the sample being imaged. For example, to measure a critical dimension or CD (e.g., width, pitch, thickness, spacing, etc.) of structures on the sample surface. To measure a critical dimension of a pattern such as a circuit line or a trace on the sample surface, a pattern edge gray level value (GLV) profile of the captured image may be used. Pattern edge gray level value (GLV) profile refers to the variation in grayscale intensity (or gray scale values) along the edge of a pattern within the captured image. In an exemplary application, the SEM image of the trace or pattern on the sample surface is captured. Then, suitable algorithms (e.g., edge detection algorithms) may be applied to identify the boundary or edge of the trace. The grayscale intensity values of the pixels along the detected edge are then analyzed.Grayscale intensity typically corresponds to the contrast or brightness of the pixels in the image and may be represented on a scale from 0 (black) to 255 (white) in an 8-bit grayscale image. A curve or profile may then be generated by plotting the grayscale intensity values along a line across the width of the trace. This profile represents the variation in grayscale intensity (or gray scale values (GLVs)) across the width of the trace. By analyzing the gray level value profile, measurements such as the distance between specific intensity thresholds may be used to determine a critical dimension (CD) (e.g., the width) of the trace.

[0058] Figs. 3A-3C are schematic representations demonstrating the measurement of a critical dimension (such as width) of a feature (for example, trace 300) using an electron beam 310, consistent with some embodiments of the current disclosure. An electron beam 310, typically from a scanning electron microscope (SEM), scans the trace 300 along a designated line 320 in a specified scan direction (e.g., along the x-axis). As the electron beam 310 moves across the surface of the trace 300, it interacts with the material, causing the emission of signal electrons, including secondary electrons,backscattered electrons, etc. These emitted electrons are then detected and translated into images or field of views (FOVs) 330A-330E, which contain gray level values that indicate the intensity of the signal captured at each pixel. The width 340A of the trace 300 along line 320 is derived from these FOVs 330A-330E, for example, utilizing a two pattern-edges metrology or another suitable approach. To improve measurement accuracy, after performing the first scan of the electron beam 310 at the initial Y-axis location (Y i), the beam is moved along the y-axis to various locations Y-axis locations (e.g., Yz, Y3, etc.) to conduct additional scans, determining the widths 340B and 340C of the trace 300 at these adjacent Y-axis positions. The critical dimension 350 of the trace 300 is then calculated based on (e.g., by averaging, smoothing, etc.) the measured widths 340A, 340B, and 340C.

[0059] Averaging measurements over multiple FOVs can effectively mitigate the impact of stochastic effects, leading to more meaningful and accurate critical dimension measurements. Stochastic effects refer to random variations that can arise due to factors such as electron beam noise, surface irregularities, material inconsistencies, detection channel noise, etc. By collecting data from multiple FOVs, these random fluctuations can be smoothed out, resulting in a more reliable estimate of the critical dimension. Statistical analysis (e.g. 3 sigma analysis) may also be performed using the multiple FOVs to quantify high-frequency physics such as, for example, line width roughness, line edge roughness, etc. Such statistical analyses can provide deeper insights into high-frequency variations in features like line width roughness (LWR) and line edge roughness (LER), which indicates the spread or dispersion of the measured data and the degree of variability around the determined critical dimension.

[0060] Traditional approaches to measuring critical dimensions of features on a substrate employ an electron beam 310 that is optimized to minimize astigmatism, resulting in a circular (or a nearly circular) beam shape or beam profile on the surface of the substrate (as illustrated in Fig. 3 A). Beam profile refers to the spatial distribution of intensity or energy that a beam, such as an electron beam (or a charged-particle beam), projects onto the surface of the substrate when it is directed at the substrate. A circular beam profile (or a beam with a circular shape) is suitable for lithographic features of various geometries and angular orientations, such as linear traces at different angles relative to the scanning direction, circular contact pads, etc. A circular beam profile is characterized by a uniform intensity distribution in a circular shape and provides consistent interaction across the surface of the substrate. However, insisting on a circular beam profile may impose unnecessary limitations for some applications. In some embodiments of the present application, the astigmatism of the beam is adjusted based on the characteristics of the measured feature to vary the beam profile (or beam shape).

[0061] For example, in some applications, as illustrated in Fig. 4A, the astigmatism of an electron beam 410A is adjusted to create a narrower beam profile in the scan direction (e.g., the X-axis direction). As described in Figs. 3A-3C, to ensure accuracy in critical dimension measurements of a feature (e.g., trace 400), multiple fields of view (FOVs) are averaged across the Y-axis to mitigate variations caused by stochastic effects. For such a scenario, an elongated beam profile along the Y-axis — such as an elongated or elliptical beam 410A with its major axis oriented along the Y-axis and minor axis oriented along the X-axis — can be advantageous because it allows for greater interaction with the length of trace 300. Consequently, as shown in Fig. 4A, the signal obtained from scanning trace 400 with electron beam 410A may effectively replicate the result of averaging signals from multiple scans conducted with a traditional circular beam 310.

[0062] It is recognized that reducing the beam spot size, or the diameter of a circular beam profile, by 50% can lead to an improvement in measurement accuracy of approximately 40%. However, making hardware modifications to achieve this reduction can be costly and time-consuming. Scanning a feature (e.g., trace 400) using beam 410A that is narrowed along the scan direction by adjusting the astigmatism provides an alternative approach that can effectively simulate the benefits of a smaller beam spot size without incurring the associated costs.

[0063] In some applications, as illustrated in Fig. 4B, the astigmatism of an electron beam 410B is adjusted to create a narrower profile in a direction orthogonal to the scan direction. For example, for measuring characteristics like line width roughness, line edge roughness, 3-sigma values, and other high-frequency parameters (e.g., characteristics, properties, etc.) of trace 400, a beam profile that is reduced in width a direction orthogonal to the scan direction (or reduced in width along the principal direction of the trace 400 — such as an elongated or elliptical beam 410B with its major axis aligned along the X-axis and minor axis along the Y -axis — could be more suitable. For example, the length of the trace 400 that the beam 410B interacts with as it moves across the trace 400 will be reduced (as compared to the traditional circular beam 310), thereby resulting in more accurate line width and line edge roughness measurements.

[0064] As the size of beam 410B in the direction perpendicular to the scan is smaller than that of a conventional circular beam 310, it allows for more scans to be conducted and averaged, facilitating the measurement of parameters along the same length of trace 400 more accurately. Additionally, beam 410B can effectively replicate the advantages of using a smaller beam spot size, particularly when measuring parameters related to the edges of trace 400.

[0065] It should be noted that the beam shapes described in Figs. 4A and 4B are only examples. In general, the astigmatism of the electron beam can be adjusted to achieve any desired beam profile. For instance, when trace 400 extends along an inclined axis A (e.g., the principal direction of the trace is inclined with respect to the scan direction or the X-axis), the astigmatism of the beam can be adjusted so that the beam 410C is elongated or widened along axis A as illustrated in Fig. 4C, or narrowed along axis A as shown in beam 410D of Fig. 4D.

[0066] Although the terms “major axis” and “minor axis” commonly refer to the long and short axes of an ellipse, in the current disclosure there terms are used to refer to the long and short axes of elongated shapes that are not necessarily elliptical. In other words, the terms major and minor axes refer to the long and short axes, respectively, of an elongated beam profile regardless of its specific shape. Moreover, the term “principal direction” refers to the dominant orientation along which theshape extends or exhibits its largest dimensions. For example, for an elongated shape like an ellipse, the principal direction corresponds to its major axis, which is the longest diameter. And for a trace (such as trace 400 of Figs. 4A-4B), the principal direction is the direction along which the trace extends.

[0067] The astigmatism of the electron beam may be adjusted to obtain a desired beam profile in any manner. For example, in some embodiments, an off-axis beam may be used to change the beam profile. As another example, a stigmator, an aberration controller, or another suitable apparatus may be used to adjust the astigmatism of the beam. Astigmatism arises when an electron beam does not focus uniformly, leading to a beam profile that appears elongated or distorted instead of circular. To adjust or manipulate astigmatism and change the beam profile, a stigmator or aberration controller may be utilized. These devices typically work by applying small electrical fields to the beam, which alters its trajectory as it travels through the instrument's column. For instance, one or more coils can generate a magnetic field that modifies the beam path in specific directions to achieve the desired profile. By varying the currents flowing through these coils, both the magnetic field and the beam's trajectory can be adjusted, resulting in changes to the beam profile. Furthermore, temporal variations in the beam profile — such as rotation or periodic alterations — can also be accomplished through similar means. For example, by adjusting the current directed to the magnetic coils, the resulting beam profile can be made to fluctuate over time in the desired manner and frequency. This capability allows for enhanced control and optimization of the electron beam during the scanning processes.

[0068] In some embodiments, a quadrupole lens (of a stigmator) is utilized to intentionally adjust the beam focus in two dimensions (e.g., X and Y directions), resulting in the creation of two focal planes (meridional and sagittal). This adjustment generates different forces on the beam, leading to various beam profile shapes. By varying the voltage applied to the electrodes of the quadrupole lens (or other lens having more than 4 electrodes), these forces can be fine-tuned to achieve the desired beam spot shape. Moreover, the voltages applied to the electrodes can be varied over time to provide a rotation effect.

[0069] Figs. 5A and 5B illustrate a comparison of signals obtained from scanning a specific feature, trace 500, using elongated electron beams 410A and 410B, alongside a conventional circular beam 310 and a hypothetical beam 510 with a reduced spot size. As shown in Fig. 5B, the signals S310, S410A, and S510 reveal that when the astigmatism of the beam is adjusted to create beam 410A, resulting in an elongated profile in the direction perpendicular (the Y-direction) to the scan direction (X-direction), the slope of the signal S410A at the edge of the trace is steeper than that of signal S310 from the conventional beam. This slope approaches that of signal S510, associated with the hypothetical beam 510 with a smaller spot size. The steeper slope enhances the accuracy of measurements related to the edges of trace 500, such as line width roughness and line edge roughness.

[0070] Although the beam 410A interacts with the trace 500 over a greater distance in the Y- direction compared to beam 310, measurements of edge parameters typically employ a dynamicaverage of the profile intensity across a selected range in the Y-direction. This dynamic average functions as a single data point for analysis, effectively simulating the benefits of using the elongated beam 410A.

[0071] When the astigmatism is adjusted to form beam 410B, which is elongated in the scan direction (X-direction) and narrowed in the perpendicular direction (Y-direction), the slope of signal S410B is less steep compared to signal S310 from the conventional beam. While this beam may not be ideal for measuring line width roughness and line edge roughness in a single scan, its smaller size in the Y-direction allows for a greater number of scans to be performed over the same length. This capability facilitates averaging, thereby enhancing the accuracy of measurements for parameters along the same length of trace 500.

[0072] In some applications, the shape or orientation of a feature may not be known in advance. For instance, a contact hole intended to be round may exhibit ellipticity, or an array of lines that should be vertically aligned may be inclined. In such situations, it becomes challenging to select an appropriate beam profile based on the feature’ s shape or orientation prior to measurement. Therefore, in some embodiments of the current disclosure, a feature may be scanned multiple times using electron beams with varying beam profiles achieved by adjusting the astigmatism. The signals collected from these multiple scans may then be analyzed and compared to ascertain the parameters of the feature, such as its shape or orientation. Additionally, the astigmatism of the electron beam may be modified based on the determined parameters, allowing for follow-up scans to be conducted with electron beams that have a more suitable profile for measuring other characteristics, such as critical dimensions and edge roughness. This adaptive approach can enhance efficiency and measurement accuracy and provide a more comprehensive understanding of the feature characteristics, which is especially beneficial in semiconductor manufacturing and materials science.

[0073] In one illustrative application, as depicted in Fig. 6A, an array of features, such as contact holes 600 on a semiconductor wafer, can be scanned multiple times using electron beams with varying astigmatisms resulting in different beam profiles. For instance, the array may be scanned with an electron beam 610A exhibiting a first astigmatism (ast 1) and another beam 610B with a second astigmatism (ast 2). The signals obtained from these scans provide insights into the orientation or ellipticity of the contact holes 600. By comparing the signals from the multiple scans, the orientation or ellipticity of the contact holes 600 can be ascertained. If the contact holes are perfectly circular, the signals from the different scans should be substantially or nearly the same with minimal variation. Although the signals will nearly be same, small practical variations often occur in real-world applications due to factors such as, for example, changes in beam current, focus, sample misalignment, and environmental influences like temperature fluctuations and vibrations. Based on the orientation or ellipticity inferred from the signal comparisons, the astigmatism of electron beam 610 may be adjusted to refine the beam profile for the specific parameters being measured. Forexample, as shown in Fig. 6B, the astigmatism of beam 610 may be adjusted to elongate or narrow the beam profile along a desired axis, such as the major or minor axis of an elliptical hole.

[0074] In some embodiments, the astigmatism and beam profile of an electron beam used to scan an array of features (such as the array of contact holes depicted in Fig. 6A) may be changed dynamically over time. For instance, as illustrated in Fig. 7 A, the beam profile of an electron beam 710A can alternate its orientation at a specific frequency (any known frequency) as it moves in the scan direction. This means that the beam profile can take on an elongated or elliptical shape, with its major axis shifting between different angles at predetermined time intervals. For example, the major axis of the elliptical beam 710A may be inclined at 45 degrees relative to the scan direction at a first time (e.g., at time ti), then rotate to 135 degrees after a predetermined time period. Subsequently, the beam profile could return to its initial orientation (e.g., inclined at 45 degrees) after this predetermined time period and continue this alternating pattern as it moves in the scan direction. The predetermined time period may depend on the application and may, in general, vary between (e.g., tens of) nanoseconds to seconds. For example, in some applications, the predetermined time period may depend on the image averaging mode (e.g., dot average, line average, frame average, etc.) applied in an application. The predetermined time period for dynamic astigmatism used for these modes may be in the order of tens of nanoseconds, milliseconds, and 0.1 to a few seconds, respectively. In general, the beam profile of the electron beam 710A can alternate between multiple angular orientations at any predetermined frequency. For instance, at time ti, the major axis of the elongated beam profile may be inclined at first angle relative to the scan direction. After a designated time period, such as 10 seconds, the major axis inclination could shift to a second angle. This pattern continues, with the beam inclined at a third angle after 20 seconds, a fourth angle after 30 seconds, etc., eventually reverting back to the first angle to continue the cycle.

[0075] When using a beam 710A with an alternating beam profile to scan an array of features, such as traces 700 illustrated in Fig. 7B, the cyclical adjustments in astigmatism and beam profile occur as the beam 710A moves over the features along the scan direction. This results in differently oriented beams interacting with different traces 700 within the array. Given that the frequency of the beam orientation changes and the scan speed are known, the signals generated from scanning the array reflect the interactions of traces 700 with these differently oriented beams 710A. Since the geometry and other characteristics of individual traces 700 in the array are expected to be quite similar, comparing the signals associated with the different traces 700 enables the determination of their orientations. Subsequently, the astigmatism of the beam 710A can be adjusted to create a beam profile that is optimal for the specific orientation of the traces 700 and the parameters being measured, thereby enhancing measurement accuracy.

[0076] While the process of scanning an array of features with an electron beam that has an alternating beam profile is described with reference to Figs. 7A-7B, this serves merely as an example. In some embodiments, as depicted in Fig. 7C, the beam profile may continuously rotate over time as itprogresses in the scan direction. For instance, an electron beam 710B could possess an elongated profile, with its major axis rotating at a predetermined frequency (such as 10° per second or 20° per second) while scanning. This rotating beam 710B can be employed to scan an array of features, like traces 700 shown in Fig. 7B, allowing for the determination of the orientation or other characteristics of these features. Based on the identified orientation or other parameters, the astigmatism of the beam can then be adjusted to create a beam profile that is better suited for the application, thereby enhancing measurement accuracy and efficiency.

[0077] While some embodiments have been described using a features in the form of traces and contact holes, it will be appreciated that the present disclosure can be applied to any type of individual or an array of features including vias, pillars, contact pads, lines with reduced length, staggered lines, lines or trenches with various widths, overlay patterns, etc.

[0078] Fig. 8 is a flow chart of an exemplary method 800 for metrology measurement using an electron beam. The method 800 can be executed using systems and devices described with reference to Figs. 1-2B applying the techniques described with reference to Figs. 3A-7C. In step 810, one or more features (e.g., traces 300, 400, 500, 700, contact hole 600, etc.) on sample (e.g., a semiconductor wafer) are scanned using a first electron beam (e.g., electron beam 410A, 410B, 410C, 410D, 610A, 710A, 710B, etc.) having a first astigmatism to obtain a first signal (e.g., signal S410A, S410B, etc.). In step 820, one or more features on the sample are scanned using a second electron beam having a second astigmatism to generate a second signal.

[0079] In some embodiments, a single feature (e.g., a trace, contact hole, etc.) or multiple features (e.g., multiple features of an array of features) may be scanned in step 810 using the first electron beam to generate the first signal, and the same features(s) (single or multiple features) may be scanned in step 820 using the second electron beam to generate the second signal. In other words, a first scan of the first electron beam over one or more features generates the first signal, and a second scan of the second electron beam over the same one or more features generates the second signal.

[0080] Alternatively, in some embodiments, the first and second signals of steps 810 and 820 may be generated during a single scan of an electron beam over an array of features. For example, as described with reference to Fig. 7A-7C, the astigmatism of an electron beam may change over time as its scans over an array of features resulting in an electron beam with an alternating or rotating beam profile during the single scan. The first signal may be generated as the electron beam (having one astigmatism) scans over one feature of the array and the second signal may be generated when the electron beam (now with a different astigmatism) scans over another feature of the array.

[0081] In step 830, the first and second signals may be compared to determine parameters or characteristics (e.g., orientation, ellipticity, etc.) of the scanned one or more features. For example, in some embodiments, the orientation or the features (e.g., traces) or configuration of the features (e.g., ellipticity of contact holes, etc.) may be determined based on the comparison of signals of step 830. In some embodiments, ascertaining these characteristics may be the objective and method 800 may endwith this step. In some embodiments, method 800 may include additional steps. For example, in step 840, based on the comparison of the signals in step 830 (or the characteristics determined in this step), the astigmatism of the electron beam may be tuned to generate a beam profile suitable to measure parameters of interest of the one or more features, and the tuned electron beam may be used to scan the one or more features and determine the parameters of interest.

[0082] It is noted that the sequence of steps shown in the flow chart of method 800 is merely illustrative. The steps can be carried out in any order and some of the steps may be combined. For instance, in different embodiments, steps 810 or 820 may be combined, step 820 may be performed before step 810, etc. Additionally, some steps may be omitted and others may be added. In some cases, the steps of method 800 may be integrated into, and a part of, another method.

[0083] In some embodiments of the current disclosure, a non-transitory computer readable medium may be provided that stores instructions for a processor of a controller (e.g., controller 109 of Fig. 1) to carry out, among other things, operations associated with the methods described herein (including the operations associated with method 800 of Fig. 8). Common forms of non-transitory media include, for example, a floppy disk, a flexible disk, hard disk, solid state drive, magnetic tape, or any other magnetic data storage medium, a Compact Disc Read Only Memory (CD-ROM), any other optical data storage medium, any physical medium with patterns of holes, a Random Access Memory (RAM), a Programmable Read Only Memory (PROM), and Erasable Programmable Read Only Memory (EPROM), a FLASH-EPROM or any other flash memory, Non-Volatile Random Access Memory (NVRAM), a cache, a register, any other memory chip or cartridge, and networked versions of the same.

[0084] The embodiments may further be described using the following clauses:1. An apparatus, the apparatus comprising: a memory storing a set of instructions; and at least one processor configured to execute the set of instructions to cause the apparatus to perform operations comprising: scanning one or more features on a sample using a charged-particle beam having a first beam profile to obtain a first signal; scanning the one or more features on the sample using a charged-particle beam having a second beam profile to obtain a second signal; comparing the first signal and the second signal; and determining a first set of parameters of the one or more features based on the comparison.2. The apparatus of clause 1, wherein the operations further comprise scanning the one or more features using a charged-particle beam having a third beam profile to determine a second set of parameters of the one or more features, and wherein the third beam profile is selected based on the comparison of the first signal and the second signal.3. The apparatus of clause 2, wherein the first set of parameters include one or more of a shape or a directionality of the one or more features and the second set of parameters includes one or more of a dimension or an edge roughness of the one or more features.4. The apparatus of any of clauses 1 to 3, wherein the operations further comprise adjusting an astigmatism of the charged-particle beam having the first beam profile to a first astigmatism to generate the first beam profile.5. The apparatus of clause 4, wherein the operations further comprise adjusting the astigmatism of the charged-particle beam having the second beam profile to a second astigmatism to generate the second beam profile.6. The apparatus of any of clauses 1 to 3, wherein the first beam profile is an elongated beam profile with a major axis extending along a scan direction of the charged-particle beam.7. The apparatus of clause 6, wherein the second beam profile is an elongated beam profile with the major axis extending orthogonal to the scan direction.8. The apparatus of any of clauses 1 to 3, wherein scanning the one or more features with the first beam profile includes scanning multiple features of an array of features with the first beam profile, and scanning the one or more features with the second beam profile includes scanning the multiple features with the second beam profile.9. The apparatus of any of clauses 1 to 3, wherein each feature of the one or more features includes at least one of a trace, a contact hole, a via, or a contact pad.10. The apparatus of any of clauses 1 to 3, wherein each charged-particle beam is an electron beam.11. A non-transitory computer readable medium that stores a set of instructions that is executable by at least on processor of a computing device to cause the computing device to perform operations, the operations comprising: scanning one or more features on a sample using a charged-particle beam having a first beam profile to obtain a first signal; scanning the one or more features on the sample using a charged-particle beam having a second beam profile to obtain a second signal; comparing the first signal and the second signal; and determining a first set of parameters of the one or more features based on the comparison.12. The non-transitory computer readable medium of clause 11, wherein the operations further comprises, selecting a third beam profile based on the comparison of the first signal and the second signal, and scanning the one or more features on the sample using a charged-particle beam having the third beam profile to determine a second set of parameters of the one or more features.13. The non-transitory computer readable medium of clause 12, wherein the first set of parameters includes one or more of a shape or a directionality of the one or more features, and the second set of parameters includes one or more a dimension or an edge roughness of the one or more features.14. The non-transitory computer readable medium of any of clauses 11 to 13, wherein the operations further comprise adjusting an astigmatism of the charged-particle beam having the first beam profile to a first astigmatism to generate the first beam profile.15. The non-transitory computer readable medium of clause 14, wherein the operations further comprise adjusting the astigmatism of the charged-particle beam having the second beam profile to a second astigmatism to generate the second beam profile.16. The non-transitory computer readable medium of any of clauses 11 to 13, wherein the first beam profile is an elongated beam profile with a major axis extending along a scan direction of the charged-particle beam.17. The non-transitory computer readable medium of clause 16, wherein the second beam profile is an elongated beam profile with the major axis extending orthogonal to the scan direction.18. The non-transitory computer readable medium of any of clauses 11 to 13, wherein scanning one or more features with the first beam profile includes scanning multiple features of an array of features with the first beam profile, and scanning one or more features with the second beam profile includes scanning the multiple features with the second beam profile.19. The non-transitory computer readable medium of any of clauses 11 to 13, wherein each feature of the one or more features includes a trace, a contact hole, a via, or a contact pad.20. The non-transitory computer readable medium of any of clauses 11 to 13, wherein each charged-particle beam includes an electron beam.21. A method, comprising: scanning one or more features on a sample using a charged-particle beam having a first beam profile to obtain a first signal; scanning the one or more features on the sample using a charged-particle beam having a second beam profile to obtain a second signal; comparing the first signal and the second signal; and determining a first set of parameters of the one or more features based on the comparison.22. The method of clause 21, wherein the method further comprises, selecting a third beam profile based on the comparison of the first signal and the second signal, and scanning the one or more features on the sample using a charged-particle beam having the third beam profile to determine a second set of parameters of the one or more features.23. The method of clause 22, wherein the first set of parameters includes one or more of a shape or a directionality of the one or more features, and the second set of parameters includes one or more a dimension or an edge roughness of the one or more features.24. The method of any of clauses 21 to 23, wherein the method further comprises adjusting an astigmatism of the charged-particle beam having the first beam profile to a first astigmatism to generate the first beam profile.25. The method of clause 24, wherein the method further comprises adjusting the astigmatism of the charged-particle beam having the second beam profile to a second astigmatism to generate the second beam profile.26. The method of any of clauses 21 to 23, wherein the first beam profile is an elongated beam profile with a major axis extending along a scan direction of the charged-particle beam.27. The method of clause 26, wherein the second beam profile is an elongated beam profile with the major axis extending orthogonal to the scan direction.28. The method of any of clauses 21 to 23, wherein scanning one or more features with the first beam profile includes scanning multiple features of an array of features with the first beam profile, and scanning one or more features with the second beam profile includes scanning the multiple features with the second beam profile.29. The method of any of clauses 21 to 23, wherein each feature of the one or more features includes a trace, a contact hole, a via, or a contact pad.30. The method of any of clauses 21 to 23, wherein each charged-particle beam includes an electron beam.31. A non-transitory computer readable medium that stores a set of instructions that is executable by at least on processor of a computing device to cause the computing device to perform operations, the operations comprising: adjusting an astigmatism of a charged-particle beam to a first astigmatism to generate a first elongated beam profile; scanning one or more features on a sample using the charged-particle beam having the first elongated beam profile to obtain a first signal; adjusting an astigmatism of a charged-particle beam to a second astigmatism to generate a second elongated beam profile different from the first elongated beam profile; scanning the one or more features on the sample using the charged-particle beam having the second elongated beam profile to obtain a second signal; and determining a first set of parameters of the one or more features based on the first signal and second signal.32. The non-transitory computer readable medium of clause 31, wherein the operations further comprise:adjusting an astigmatism of a charged-particle beam to a third astigmatism to generate a third elongated beam profile, wherein the third astigmatism is selected based on the first set of parameters, and scanning the one or more features on the sample using a charged-particle beam having the third elongated beam profile to determine a second set of parameters of the one or more features.33. The non-transitory computer readable medium of clause 32, wherein the first set of parameters includes one or more of a shape or a directionality of the one or more features, and the second set of parameters includes one or more a dimension or an edge roughness of the one or more features.34. The non-transitory computer readable medium of any of clauses 31 to 33, wherein the first elongated beam profile is an elongated beam profile with a major axis extending along a scan direction of the charged-particle beam.35. The non-transitory computer readable medium of clause 34, wherein the second beam profile is an elongated beam profile with the major axis extending orthogonal to the scan direction.36. The non-transitory computer readable medium of any of clauses 31 to 33, wherein scanning one or more features with the first elongated beam profile includes scanning multiple features of an array of features with the first elongated beam profile, and scanning one or more features with the second elongated beam profile includes scanning the multiple features with the second elongated beam profile.37. The non-transitory computer readable medium of any of clauses 31 to 33, wherein each feature of the one or more features includes a trace, a contact hole, a via, or a contact pad.38. The non-transitory computer readable medium of any of clauses 31 to 33, wherein each charged-particle beam includes an electron beam.

[0085] Block diagrams in the figures may illustrate the architecture, functionality, and operation of possible implementations of systems, methods, and computer hardware or software products according to various exemplary embodiments of the present disclosure. In this regard, each block may represent one or multiple arithmetical or logical operation processing that may be implemented using hardware such as an electronic circuit. Blocks may also represent modules, segments, or portions of code that comprises one or more executable instructions for implementing the specified logical functions. It should be understood that in some alternative implementations, functions indicated in a block may occur out of the order noted in the figures. For example, two blocks shown in succession may be executed or implemented substantially concurrently, or two blocks may sometimes be executed in reverse order, depending upon the functionality involved. Some blocks may also be omitted. It should also be understood that each block of the block diagrams, and combination of theblocks, may be implemented by special purpose hardware-based systems that perform the specified functions or acts, or by combinations of special purpose hardware and computer instructions.

[0086] Although embodiments have been described with reference to an electron beam, this is merely exemplary. In general, any charged-particle beam may be used in embodiments of the current disclosure. Moreover, it should be appreciated that the embodiments of the present disclosure are not limited to the exact construction that has been described above and illustrated in the accompanying drawings, and that various modifications and changes may be made without departing from the scope thereof. The present disclosure 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 specification and examples be considered as exemplary only, with a true scope and spirit of the invention being indicated by the following claims.

Claims

CLAIMS1. An apparatus, the apparatus comprising: a memory storing a set of instructions; and at least one processor configured to execute the set of instructions to cause the apparatus to perform operations comprising: scanning one or more features on a sample using a charged-particle beam having a first beam profile to obtain a first signal; scanning the one or more features on the sample using a charged-particle beam having a second beam profile to obtain a second signal; comparing the first signal and the second signal; and determining a first set of parameters of the one or more features based on the comparison.

2. The apparatus of claim 1, wherein the operations further comprise scanning the one or more features using a charged-particle beam having a third beam profile to determine a second set of parameters of the one or more features, and wherein the third beam profile is selected based on the comparison of the first signal and the second signal.

3. The apparatus of claim 2, wherein the first set of parameters include one or more of a shape or a directionality of the one or more features and the second set of parameters includes one or more of a dimension or an edge roughness of the one or more features.

4. The apparatus of claim 1, wherein the operations further comprise adjusting an astigmatism of the charged-particle beam having the first beam profile to a first astigmatism to generate the first beam profile.

5. The apparatus of claim 4, wherein the operations further comprise adjusting the astigmatism of the charged-particle beam having the second beam profile to a second astigmatism to generate the second beam profile.

6. The apparatus of claim 1, wherein the first beam profile is an elongated beam profile with a major axis extending along a scan direction of the charged-particle beam.

7. The apparatus of claim 6, wherein the second beam profile is an elongated beam profile with the major axis extending orthogonal to the scan direction.

8. The apparatus of claim 1, wherein scanning the one or more features with the first beam profile includes scanning multiple features of an array of features with the first beam profile, and scanning the one or more features with the second beam profile includes scanning the multiple features with the second beam profile.

9. The apparatus of claim 1, wherein each feature of the one or more features includes at least one of a trace, a contact hole, a via, or a contact pad.

10. The apparatus of claim 1, wherein each charged-particle beam is an electron beam.

11. A non-transitory computer readable medium that stores a set of instructions that is executable by at least on processor of a computing device to cause the computing device to perform operations, the operations comprising: scanning one or more features on a sample using a charged-particle beam having a first beam profile to obtain a first signal; scanning the one or more features on the sample using a charged-particle beam having a second beam profile to obtain a second signal; comparing the first signal and the second signal; and determining a first set of parameters of the one or more features based on the comparison.

12. The non-transitory computer readable medium of claim 11, wherein the operations further comprises, selecting a third beam profile based on the comparison of the first signal and the second signal, and scanning the one or more features on the sample using a charged-particle beam having the third beam profile to determine a second set of parameters of the one or more features.

13. The non-transitory computer readable medium of claim 12, wherein the first set of parameters includes one or more of a shape or a directionality of the one or more features, and the second set of parameters includes one or more a dimension or an edge roughness of the one or more features.

14. The non-transitory computer readable medium of claim 11, wherein the operations further comprise adjusting an astigmatism of the charged-particle beam having the first beam profile to a first astigmatism to generate the first beam profile.

15. The non-transitory computer readable medium of claim 14, wherein the operations further comprise adjusting the astigmatism of the charged-particle beam having the second beam profile to a second astigmatism to generate the second beam profile.

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