Simultaneous auto-focus and local alignment method

Abstract

Disclosed is a particle beam inspection apparatus, and more particularly, a method for simultaneous focusing and image alignment of an image-enhanced inspection image. The method for enhancing inspection images includes: acquiring a plurality of inspection images according to a plurality of focus conditions for a sample region including a pattern; determining whether an inspection image of the plurality of inspection images has a focus index within a first threshold range; and in response to determining that the examination image has a focus index within the first threshold range, performing image alignment using the examination image.

Description

[0001] Cross - Reference to Related Applications

[0002] This application claims the priority of U.S. Application No. 63 / 417,945, filed on October 20, 2022, the entire content of which is incorporated herein by reference. Technical Field

[0003] The embodiments provided herein relate to an inspection image enhancement technique, and more particularly, to enhancing inspection images by simultaneously performing a focusing sequence and local alignment. Background Art

[0004] During the manufacturing process of integrated circuits (ICs), it is necessary to inspect unfinished or finished circuit components to ensure that they are manufactured according to design requirements and are defect-free. Inspection systems using optical microscopes or charged particle (e.g., electron) beam microscopes such as scanning electron microscopes (SEM) can be employed. As the physical dimensions of IC components continue to shrink, the accuracy and throughput of defect detection become increasingly important. Inspection images such as SEM images can be used to identify or classify defects in manufactured ICs. To improve defect detection performance, an inspection image enhancement technique capable of increasing the throughput of the inspection system is desired. Summary of the Invention

[0005] The embodiments provided herein disclose a particle beam inspection apparatus, and more particularly, an inspection method for simultaneously focusing and image alignment of inspection images.

[0006] Some embodiments provide a method for enhancing an inspection image. The method includes: obtaining a plurality of inspection images for a sample region containing a pattern according to a plurality of focusing conditions; determining whether an inspection image among the plurality of inspection images has a focusing index within a first threshold range; and in response to determining that the inspection image has a focusing index within the first threshold range, using the inspection image for image alignment.

[0007] In some embodiments, the method includes: setting a plurality of focusing conditions for a region of a sample containing a pattern; obtaining a plurality of inspection images according to the plurality of focusing conditions; determining the focusing index of each inspection image among the plurality of inspection images; identifying an inspection image among the plurality of inspection images whose focusing index is determined to be within a first threshold range; estimating alignment parameters of the inspection image whose focusing index is determined to be within the first threshold range; identifying one or more inspection images among the plurality of inspection images whose focusing index is determined to be within a second threshold range; selecting a focusing condition associated with the inspection image having the largest focusing index among those determined to be within the second threshold range; and performing image alignment and focusing correction based on the estimated alignment parameters and the selected focusing condition.

[0008] In some embodiments, a device for enhancing inspection images is provided. The device includes: a memory storing an instruction set; and at least one processor configured to execute the instruction set to cause the device to perform: for a region of a sample containing a pattern, obtaining a plurality of inspection images according to a plurality of focusing conditions; determining whether an inspection image among the plurality of inspection images has a focusing index within a first threshold range; and in response to determining that the inspection image has a focusing index within the first threshold range, performing image alignment using the inspection image.

[0009] In some embodiments, the device includes a memory storing an instruction set, and at least one processor configured to execute the instruction set to cause the device to perform: setting a plurality of focusing conditions for a sample region containing a pattern; obtaining a plurality of inspection images according to the plurality of focusing conditions; determining a focusing index of each inspection image among the plurality of inspection images; identifying an inspection image among the plurality of inspection images whose focusing index is determined to be within a first threshold range; estimating alignment parameters of the inspection image whose focusing index is determined to be within the first threshold range; identifying one or more inspection images among the plurality of inspection images whose focusing index is determined to be within a second threshold range; selecting a focusing condition associated with the inspection image having the largest focusing index among those determined to be within the second threshold range; and performing image alignment and focusing correction based on the estimated alignment parameters and the selected focusing condition.

[0010] In some embodiments, a non-transitory computer-readable medium is provided, the non-transitory computer-readable medium including an instruction set executable by one or more processors of a computing device to cause the computing device to perform a method for enhancing inspection images. The method includes: for a sample region containing a pattern, obtaining a plurality of inspection images according to a plurality of focusing conditions; determining whether an inspection image among the plurality of inspection images has a focusing index within a first threshold range; and in response to determining that the inspection image has a focusing index within the first threshold range, performing image alignment using the inspection image.

[0011] In some embodiments, a non-transitory computer-readable medium includes a set of instructions executable by one or more processors of a computing device to cause the computing device to perform a method for enhancing inspection images, the method comprising: setting a plurality of focusing conditions for a region of a sample containing a pattern; acquiring a plurality of inspection images according to the plurality of focusing conditions; determining a focus index for each of the plurality of inspection images; identifying the inspection images among the plurality of inspection images for which the focus index is determined to be within a first threshold range; estimating alignment parameters for the inspection images for which the focus index is determined to be within the first threshold range; identifying one or more inspection images among the plurality of inspection images for which the focus index is determined to be within a second threshold range; selecting the focusing condition associated with the inspection image having the maximum focus index determined to be within the second threshold range; and performing image alignment and focus correction based on the estimated alignment parameters and the selected focusing condition.

[0012] Advantages of other embodiments of the present disclosure will become apparent from the following description in conjunction with the accompanying drawings, in which certain embodiments of the invention are illustrated by way of example and illustration. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] The above and other aspects of the present disclosure will become more apparent from the description of exemplary embodiments in conjunction with the accompanying drawings.

[0014] Figure 1 is a schematic diagram showing an example charged particle beam inspection system consistent with an embodiment of the present disclosure.

[0015] Figure 2 is a schematic diagram showing an example multi-beam tool consistent with an embodiment of the present disclosure, which example multi-beam tool may be Figure 1 part of an example charged particle beam inspection system.

[0016] Figure 3 is a block diagram of an example simultaneous autofocus and local alignment system consistent with an embodiment of the present disclosure.

[0017] Figure 4A shows an example inspection region consistent with an embodiment of the present disclosure.

[0018] Figure 4B shows an example collection of batches of inspection images according to various focusing conditions consistent with an embodiment of the present disclosure.

[0019] Figure 4C shows an example first focus index threshold range consistent with an embodiment of the present disclosure.

[0020] Figure 4D shows an example second focus index threshold range consistent with an embodiment of the present disclosure.

[0021] Figure 5 Shows an example process of partial alignment consistent with an embodiment of the present disclosure.

[0022] Figure 6 Shows an example alignment parameter estimation consistent with an embodiment of the present disclosure.

[0023] Figure 7 Is a flowchart representing an example simultaneous autofocus and partial alignment method consistent with an embodiment of the present disclosure. Detailed Description

[0024] Reference will now be made in detail to exemplary embodiments, which are illustrated in the accompanying drawings. The following description refers to the accompanying drawings, where like numbers in different drawings represent the same or similar elements unless otherwise noted. The implementations set forth in 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 (e.g., including protons, ions, muons, or any other charged particles) can be similarly applied. Additionally, other imaging systems can be used, including but not limited to optical imaging, photon detection, x-ray detection, ion detection, etc.

[0025] An electronic device is composed of circuits formed on a piece of semiconductor material (referred to as a substrate). The semiconductor material can include, for example, silicon, gallium arsenide, indium phosphide, silicon germanium, etc. Many circuits can be formed on the same piece of silicon, called an integrated circuit or IC. The sizes of these circuits have been significantly reduced, so more circuits can be installed on the substrate. For example, an IC chip in a smartphone can be as small as a thumbnail, but may contain more than 2 billion transistors, each transistor being less than one-thousandth the size of a human hair.

[0026] Manufacturing these integrated circuits with extremely small structures or components is a complex, time-consuming, and expensive process, typically involving hundreds of individual steps. Even an error in one step can cause defects in the finished IC, making it unusable. Therefore, one of the goals of the manufacturing process is to avoid such defects to maximize the number of functional ICs manufactured in the process, i.e., to increase the overall yield of the process.

[0027] One element in improving yield is to monitor the chip manufacturing process to ensure that it produces a sufficient number of functional integrated circuits. One way to monitor the process is to inspect the chip circuit structure at various stages of its formation. Inspection can be performed using inspection tools such as, for example, a Scanning Charged Particle Microscope (SCPM). For example, the SCPM can be a Scanning Electron Microscope (SEM). The SCPM inspection tool can be used to image these extremely small structures, effectively taking “pictures” of the wafer structure to generate inspection images. The inspection images can be used to determine whether the structures are correctly formed in the correct locations. If a structure is defective, the process can be adjusted, thereby reducing the likelihood of the defect recurring. The inspection images can also be used for autofocusing and local alignment of the IC structure.

[0028] As the physical dimensions of IC components continue to shrink, the accuracy and yield of defect detection become increasingly important. Inspection images such as SCPM images can be used to perform metrology measurements on the manufactured ICs (e.g., identify or classify (multiple) defects). Measurements (including but not limited to critical dimensions of inspection images) can be used to identify defects on the wafer. To perform metrology measurements more accurately, it is desirable to obtain inspection images that are accurately focused and correctly aligned. To obtain accurate inspection images, image enhancement techniques such as autofocusing and local alignment are typically performed. Autofocusing is a technique that automatically determines when an image is out of focus and immediately initiates a focusing operation to obtain a focused inspection image. During autofocusing, multiple inspection images with different focusing conditions can be acquired for a certain region of the sample, and the optimal focusing condition for that region can be determined based on the sharpness indices of the acquired multiple inspection images. Since defects can be identified or detected by comparing the inspection image with a corresponding reference image, it is desirable to obtain precise alignment between the inspection image and the reference image to improve defect detection performance. Local alignment is a technique that is applied to align the inspection image with the reference image. Current image enhancement applications (such as autofocusing and local alignment) are performed sequentially and independently. To obtain a clearer inspection image, autofocusing is typically performed at a larger magnification, so the field of view is smaller; while local alignment is performed with a larger field of view to enable comprehensive structural comparison. Both methods require a different set of images, thus increasing the time and effort associated with image enhancement. Therefore, this reduces the throughput of IC defect detection. Accordingly, a more efficient and faster image enhancement method is desired to enable more efficient and faster defect detection.

[0029] Embodiments of the present disclosure may provide a simultaneous autofocus and image alignment technique. According to some embodiments of the present disclosure, an accurate and fast simultaneous autofocus and image alignment technique with improved throughput may be provided. According to some embodiments of the present disclosure, the acquired inspection images may be used for the simultaneous autofocus and image alignment technique. According to some embodiments of the present disclosure, multiple acquired inspection images may be used for the simultaneous autofocus and image alignment technique.

[0030] For clarity, the relative dimensions of components in the drawings may be exaggerated. In the following description of the drawings, like or similar reference numerals refer to like or similar components or entities, and only the differences relevant to each embodiment are described. As used herein, the term "or" covers all possible combinations unless otherwise explicitly stated, unless infeasible. For example, if it is stated that a component may include A or B, then unless otherwise explicitly stated or infeasible, the component may include A, or B, or A and B. A second example is that if it is stated that a component may include A, B, or C, then unless otherwise explicitly stated 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.

[0031] Figure 1 An exemplary electron beam inspection (EBI) system 100 consistent with embodiments of the present disclosure is shown. The EBI system 100 may be used for imaging. As Figure 1 shown, the 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. The beam tool 104 is located within the main chamber 101. The EFEM 106 includes a first load port 106a and a second load port 106b. The EFEM 106 may include additional load ports. The first load port 106a and the second load port 106b receive front-opening unified pods (FOUPs) containing wafers (e.g., semiconductor wafers or wafers made of other (multiple) materials) or samples (wafers and samples may be used interchangeably) to be inspected. A "lot" refers to multiple wafers that can be loaded and processed as a batch.

[0032] One or more robotic arms (not shown) in the EFEM 106 can transport the wafer to the load / lock chamber 102. The load / lock chamber 102 is connected to a load / lock vacuum pump system (not shown), which can remove gas molecules in the load / lock chamber 102 to a first pressure below atmospheric pressure. After reaching the first pressure, one or more robotic arms (not shown) can transport the wafer from the load / lock chamber 102 to the main chamber 101. The main chamber 101 is connected to a main chamber vacuum pump system (not shown), which can remove gas molecules in the main chamber 101 to a second pressure below the first pressure. After reaching the second pressure, the wafer will be inspected by the beam tool 104. The beam tool 104 can be a single-beam system or a multi-beam system.

[0033] The controller 109 is electrically connected to the beam tool 104. The controller 109 can be a computer configured to perform various controls of the EBI system 100. The controller 109 can also include processing circuitry configured to perform various signal and image processing functions. Although Figure 1 the controller 109 is shown located outside the structure including the main chamber 101, the load / lock chamber 102, and the EFEM 106, it can be understood that the controller 109 can also be a part of the structure.

[0034] In some embodiments, the controller 109 can include one or more processors (not shown). The processor can be a general-purpose or special-purpose electronic device capable of manipulating or processing information. For example, the processor can include any combination of any number of the following: central processing unit (or "CPU"), graphics processing unit (or "GPU"), optical processor, programmable logic controller, microcontroller, microprocessor, digital signal processor, hardware accelerator, intellectual property (IP) core, programmable logic array (PLA), programmable array logic (PAL), generic array logic (GAL), complex programmable logic device (CPLD), field programmable gate array (FPGA), system on chip (SoC), application specific integrated circuit (ASIC), and any type of circuit capable of performing data processing. The processor can also be a virtual processor, which includes one or more processors distributed on multiple machines or devices coupled via a network.

[0035] In some embodiments, the controller 109 may further include one or more memories (not shown). The memory may be a general-purpose or special-purpose electronic device capable of storing code and data accessible to the processor (e.g., via a bus). For example, the memory may include any combination of any number of the following: random access memory (RAM), read-only memory (ROM), optical discs, magnetic disks, hard drives, solid-state drives, flash drives, secure digital (SD) cards, memory sticks, compact flash (CF) cards, or any type of storage device. The code and data may include an operating system (OS) and one or more applications (or “apps”) for specific tasks. The memory may also be virtual memory, which includes one or more memories distributed across multiple machines or devices coupled via a network.

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

[0037] The beam tool 104 includes a charged particle source 202, a gun aperture 204, a focusing lens 206, a primary charged particle beam 210 emitted from the charged particle source 202, a source conversion unit 212, multiple sub-beams 214, 216, and 218 of the 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. The primary projection optical system 220 may include a beam splitter 222, a deflection scanning unit 226, and an objective lens 228. The charged particle detection device 244 may include detection sub-regions 246, 248, and 250.

[0038] The charged particle source 202, the gun aperture 204, the focusing lens 206, the source conversion unit 212, the beam splitter 222, the deflection scanning unit 226, and the objective lens 228 may be aligned with a primary optical axis 260 of the apparatus 104. The secondary optical system 242 and the charged particle detection device 244 may be aligned with a secondary optical axis 252 of the apparatus 104.

[0039] The charged particle source 202 can emit one or more charged particles, such as electrons, protons, ions, muons, or any other charged particles. In some embodiments, the charged particle source 202 can be an electron source. For example, the charged particle 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 charged particle beam 210 (in this example, a primary electron beam) having an intersection point (virtual or real) 208. For ease of explanation and without causing ambiguity, electrons are used as examples in some descriptions herein. However, it should be noted that any charged particle can be used in any embodiment of the present disclosure, not limited to electrons. The primary charged particle beam 210 can appear to be emitted from the intersection point 208. The gun aperture 204 can block the peripheral charged particles of the primary charged particle beam 210 to reduce the Coulomb effect. The Coulomb effect may cause an increase in the size of the detection spot.

[0040] The source conversion unit 212 can include an imaging element array and a collimating aperture array. 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 intersection point 208 with multiple sub-beams 214, 216, and 218 of the primary charged particle beam 210. The collimating aperture array can collimate the multiple sub-beams 214, 216, and 218. Although Figure 2 three sub-beams 214, 216, and 218 are shown, the embodiments of the present disclosure are not limited thereto. For example, in some embodiments, the device 104 can be configured to generate a first number of sub-beams. In some embodiments, the first number of sub-beams can be in the range of 1 to 1000. In some embodiments, the first number of sub-beams can be in the range of 200 to 500. In an exemplary embodiment, the device 104 can produce 400 sub-beams.

[0041] The condenser lens 206 can focus the primary charged particle beam 210. By adjusting the optical power of the condenser lens 206 or changing the radial size of the corresponding collimating aperture in the collimating aperture array, the current of the sub-beams 214, 216, and 218 downstream of the source conversion unit 212 can be changed. The objective lens 228 can focus the sub-beams 214, 216, and 218 onto the wafer 230 for imaging and form multiple detection spots 270, 272, and 274 on the surface of the wafer 230.

[0042] The beam splitter 222 can be a beam splitter of the Wien filter type, generating an electrostatic dipole field and a magnetic dipole field. In some embodiments, if the electrostatic dipole field and the magnetic dipole field are applied, the force exerted on the charged particles (e.g., electrons) in the sub-beams 214, 216, and 218 by the electrostatic dipole field may be substantially equal in magnitude and opposite in direction to the force exerted on the charged particles 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 may also be non-zero. The beam splitter 222 can separate the secondary charged particle beams 236, 238, and 240 from the sub-beams 214, 216, and 218 and direct the secondary charged particle beams 236, 238, and 240 to the secondary optical system 242.

[0043] The deflection scanning unit 226 can deflect the sub-beams 214, 216, and 218 to scan the probe spots 270, 272, and 274 over 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, secondary charged particle beams 236, 238, and 240 can be emitted from the wafer 230. The secondary charged particle beams 236, 238, and 240 can include charged particles (e.g., electrons) having an energy distribution. For example, the secondary charged particle beams 236, 238, and 240 can be secondary electron beams, including secondary electrons (energy ≤ 50 eV) and backscattered electrons (energy between 50 eV and the landing energy of the sub-beams 214, 216, and 218). The secondary optical system 242 can focus the secondary charged particle beams 236, 238, and 240 onto the detection sub-regions 246, 248, and 250 of the charged particle detection device 244. The detection sub-regions 246, 248, and 250 can be configured to detect the corresponding secondary charged particle beams 236, 238, and 240 and generate corresponding signals (e.g., voltage or current) for reconstructing an SCPM image of the structure on or below the surface area of the wafer 230. The generated corresponding signals can also include a spectrum, where the low-frequency region contains information about the larger features of the wafer 230, while the high-frequency region contains information about the finer (i.e., clearer) features of the wafer 230.

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

[0045] The intensities of the secondary charged particle beams 236, 238, and 240 may vary according to the external or internal structure of the wafer 230, thereby indicating whether the wafer 230 includes defects. In addition, as described above, the sub-beams 214, 216, and 218 can be projected onto different positions on the top surface of the wafer 230 or different sides of the local structure of the wafer 230 to generate secondary charged particle beams 236, 238, and 240 with different intensities. Therefore, by mapping the intensities of the secondary charged particle beams 236, 238, and 240 to the regions of the wafer 230, the image processing system 290 can reconstruct an image reflecting the internal or external structural features of the wafer 230.

[0046] In some embodiments, the image processing system 290 may include an image acquirer 292, a memory 294, and a controller 296. The image acquirer 292 may include one or more processors. For example, the image acquirer 292 may include a computer, a server, a mainframe host, a terminal, a personal computer, or any other suitable mobile computing device. The image acquirer 292 may be communicatively coupled to the charged particle detection device 244 of the beam tool 104 through media such as electrical conductors, fiber optic cables, portable storage media, infrared, Bluetooth, the Internet, wireless networks, or radio. In some embodiments, the image acquirer 292 may receive signals from the charged particle detection device 244 and may construct an image. Thus, the image acquirer 292 may acquire SCPM images of the wafer 230. The image acquirer 292 may also perform various post-processing functions, including but not limited to generating contours and superimposing indicators on the acquired images. The image acquirer 292 may be configured to adjust the brightness and contrast of the acquired images. In some embodiments, the memory 294 may be a storage medium, including but not limited to a hard disk, a flash drive, cloud storage, random access memory (RAM), or other types of computer-readable memory. The memory 294 may be coupled to the image acquirer 292 and may be used to save the scanned raw image data as a raw image and store the post-processed images. The image acquirer 292 and the memory 294 may be connected to the controller 296. In some embodiments, the image acquirer 292, the memory 294, and the controller 296 may be integrated into one control unit.

[0047] In some embodiments, the image acquirer 292 may acquire one or more SCPM images of the wafer based on the imaging signals received from the charged particle detection device 244. The imaging signals may correspond to the scanning operations for performing charged particle imaging. The acquired images may be a single image including a plurality of imaging regions. The single image may be stored in the memory 294. The single image may be a raw image, and the raw image may be divided into a plurality of regions. Each region may include an imaging region containing features of the wafer 230. The acquired images may include a plurality of images of a single imaging region of the wafer 230, and the imaging region may be sampled multiple times in a time series. The plurality of images may be stored in the memory 294. In some embodiments, the image processing system 290 may include circuitry configured to perform image processing steps on the plurality of images of the same location of the wafer 230.

[0048] In some embodiments, the image processing system 290 may include measurement circuitry (e.g., an analog-to-digital converter) configured to acquire the distribution of detected secondary charged particles (e.g., secondary electrons). The charged particle distribution data collected during the detection time window, in combination with the corresponding scan path data of the sub-beams 214, 216, and 218 incident on the wafer surface, can be used to reconstruct an image of the wafer structure under inspection. The reconstructed image can be used to reveal various features of the internal or external structure of the wafer 230, and thus can be used to reveal any defects that may be present in the wafer.

[0049] In some embodiments, the charged particles may be electrons. When the electrons of the primary charged particle beam 210 are projected onto the surface of the wafer 230 (e.g., the probe spots 270, 272, and 274), the electrons of the primary charged particle beam 210 may penetrate a certain depth into the surface of the wafer 230 and interact with the particles of the wafer 230. Some of the electrons in the primary charged particle beam 210 may elastically interact with the material of the wafer 230 (e.g., in the form of elastic scattering or collisions) and may be reflected or bounced out of the surface of the wafer 230. Elastic interactions conserve the total kinetic energy of the interacting bodies (e.g., the electrons of the primary charged particle beam 210), where the kinetic energy of the interacting bodies is not converted into other forms of energy (e.g., thermal energy or electromagnetic energy). Such reflected electrons generated by elastic interactions may be referred to as backscattered electrons (BSEs). Some of the electrons in the primary charged particle beam 210 may inelastically interact with the material of the wafer 230 (e.g., in the form of inelastic scattering or collisions). Inelastic interactions do not conserve the total kinetic energy of the interacting bodies, where part or all of the kinetic energy of the interacting bodies is converted into other forms of energy. For example, through inelastic interactions, the kinetic energy of some electrons in the primary charged particle beam 210 may cause electron excitation and transition of the material atoms. Such inelastic interactions may also generate electrons emerging from the surface of the wafer 230, and these electrons may be referred to as secondary electrons (SEs). The yield or emission rate of BSEs and SEs may depend on factors such as the material under inspection and the landing energy of the electrons in the primary charged particle beam 210 landing on the material surface. The electron energy of the primary charged particle beam 210 is partially imparted by its acceleration voltage (e.g., Figure 2 the acceleration voltage between the anode and cathode of the charged particle source 202). The number of BSEs and SEs can be more than, less than (or even the same as) the number of incident electrons in the primary charged particle beam 210.

[0050] Images generated by SCPM can be used for defect inspection. For example, the generated image capturing the test device area of a wafer can be compared with a reference image capturing the same test device area. The reference image can be pre-determined (e.g., by simulation) and does not include known defects. If the difference between the generated image and the reference image exceeds the tolerance level, potential defects can be identified. As another example, SCPM can scan multiple areas of a wafer, each area including a test device area with the same design, and generate images capturing these test device areas during manufacturing. The multiple images can be compared with each other. If the difference between the multiple images exceeds the tolerance level, potential defects can be identified.

[0051] Figure 3 is a block diagram of an example simultaneous autofocus and image alignment system according to some embodiments of the present disclosure. In some embodiments, the simultaneous autofocus and alignment system 300 includes one or more processors and a memory. It should be understood that in various embodiments, the simultaneous autofocus and alignment system 300 can be part of a charged particle beam inspection system (e.g., Figure 1 the EBI system 100 in ) or can be separate from it. In some embodiments, the simultaneous autofocus and alignment system 300 can include one or more components (e.g., software modules or circuitry) that can be implemented in the controller 109 or system 290 described herein. In some embodiments, the simultaneous autofocus and alignment system 300 can include or be associated with a user interface (e.g., a display, keyboard, mouse, or controller) for receiving user input or presenting information to the user. As Figure 3 shown, the simultaneous autofocus and alignment system 300 can include an autofocus component 300A and an alignment component 300B. In some embodiments, the autofocus component 300A can include an inspection area processor 310, an inspection image acquirer 320, an evaluator 330, and a focus parameter selector 340. In some embodiments, the alignment component 300B can include a selected image acquirer 350, a reference image acquirer 360, and an alignment parameter estimator 370. The simultaneous autofocus and alignment system 300 can also include a parameter applicator 380.

[0052] According to some embodiments of the present disclosure, the inspection area processor 310 may be configured to set a plurality of focusing conditions for subsequent imaging of the inspection area. The inspection area processor 310 may utilize the set plurality of focusing conditions to determine the inspection area for subsequent imaging. In some embodiments, one or more factors may be considered to select the inspection area of the sample, and these factors include but are not limited to unique patterns, detected pattern edges, or fields of view. The unique patterns and detected pattern edges may provide a basis for comparison with the reference image pattern for local alignment. In some embodiments, the detected pattern edges may be distinguishable from the image background and indicate the boundaries of the pattern. In some embodiments, the field of view of the inspection area depends on the sample and pattern conditions. The field of view may provide an inspection area that includes unique patterns and pattern edges for comparison with the pattern of the reference image for local alignment. Figure 4A An example inspection area consistent with an embodiment of the present disclosure is shown. As Figure 4A shown, the inspection area 401 includes a unique pattern 401_1 that can be distinguished from the image background, and the inspection area 402 includes a unique pattern 402_1 that can be distinguished from the image background. In this example, the field of view of the inspection area 402 is larger than that of the inspection area 401.

[0053] In some embodiments, the focal plane or the focal point can be determined according to the set focusing conditions. In some embodiments, the focusing conditions can be set by adjusting the current of the objective lens 228, the current of the condenser lens 206, the bias voltage of the stage 280, or the vertical position of the stage 280, etc. In some embodiments, the current applied to the objective lens 228 can be controlled to adjust the acceleration voltage of the sub-beams 214, 216, and 218. Adjusting the acceleration voltage of the sub-beams 214, 216, 218 can change the vertical position of the intersection point of the sub-beams 214, 216, and 218, thereby changing the relative position of the focal points of the sub-beams 214, 216, and 218 with respect to the surface of the wafer 230. In some embodiments, the current applied to the condenser lens 206 can be controlled to adjust the beam size (i.e., diameter) of the primary charged particle beam 210. Adjusting the beam size of the primary charged particle beam 210 will adjust the number of electrons passing through the objective lens 228 in the primary charged particle beam 210. In some embodiments, the bias voltage applied to the stage 280 can be controlled to change the acceleration voltage of the sub-beams 214, 216, and 218 near the surface of the wafer 230, thereby changing the relative position of the focal points of the sub-beams 214, 216, and 218 with respect to the surface of the wafer 230. In some embodiments, adjusting the vertical position of the stage 280 will adjust the vertical position of the surface of the wafer 280 attached to the stage 280 with respect to the focal points of the sub-beams 214, 216, 218. In some embodiments, the focusing conditions can include different combinations of parameters related to the current of the objective lens 226, the current of the condenser lens 206, the bias voltage of the stage 280, or the vertical position of the stage 280, etc. It should be understood that the adjustment of the focusing conditions is not limited to the above description.

[0054] Figure 4B An exemplary set of sample focusing conditions for the sample inspection area is shown. In Figure 4B this, the sample surface 410 is irradiated by sub-beams (such as the first sub-beam 420, the second sub-beam 421, the third sub-beam 422, or the fourth sub-beam 423) with different focusing conditions. It should be noted that each sub-beam 420, 421, 422, and 423 is a separate illustrative example and does not occur simultaneously. Each sub-beam 420, 421, 422, and 423 has a corresponding focusing condition, through which the focal points 430, 431, 432, and 433 can be determined. It should be noted that the number of focusing conditions is for illustrative purposes only and is not limited to Figure 4BThe situation shown. Additionally, although each of the sub-beams 420, 421, 422, and 423 represents a different focusing condition, multiple sub-beams can be used for the focusing condition. Although the embodiments described herein are directed to a multi-beam environment, it can be understood that a single-beam environment can also be used to set the focusing condition. It can be understood that the sub-beams 420, 421, 422, and 423 can represent different focusing conditions applied sequentially to a single beam (e.g., such as a single beam in a single-beam environment or the central beam in a multi-beam environment). Additionally, although Figure 4B shows the relative positions between the sample surface 410 and the foci 430, 431, 432, and 433, it can also be understood that the vertical position of the sample surface 410 can be adjusted while keeping the positions of the foci 430, 431, 432, and 433 constant. In some embodiments, the inspection area processor 310 can be a component including circuitry for changing the current in the objective lens 228, the bias voltage of the stage 280, or the vertical position of the stage 280, etc.

[0055] Returning to Figure 3 , the inspection image acquirer 320 can acquire inspection images. In some embodiments, the inspection image can be an SCPM image of the sample or wafer. In some embodiments, the inspection image can be acquired from Figure 1 or Figure 2 devices. In some embodiments, the inspection image acquirer 320 can acquire the inspection image from a storage device, system, or database that stores the inspection image. In some embodiments, the inspection image acquirer 320 can acquire multiple inspection images of the inspection area according to multiple focusing conditions set by the inspection area processor 310. In some embodiments, the inspection image acquirer 320 can be connected to a computer-readable memory or storage device to store the focusing condition for each inspection image. The inspection image acquirer 320 can acquire Figure 4B multiple inspection images 430_1, 431_1, 432_1, and 433_1 in. It can be understood that the multiple inspection images can include more or fewer inspection images than Figure 4B shown. In some embodiments, the inspection image can include a pattern 440.

[0056] Returning to Figure 3, According to some embodiments, the evaluator 330 may be configured to determine a focus index of the acquired inspection image. In some embodiments, the evaluator 330 may be implemented as software that determines the focus index of the inspection image after the inspection image acquirer 320 acquires the inspection image. In some embodiments, the evaluator 330 may sequentially determine the focus index of each of the multiple inspection images in the order in which the inspection image acquirer 320 acquires them. In some embodiments, the evaluator 330 may determine the focus index of the inspection image based on image resolution or clarity. In some embodiments, the evaluator 330 may determine the focus index by determining the contrast between the background and the pattern (e.g., Figure 4B pattern 440) in the inspection image (e.g., inspection images 430_1, 431_1, 432_1, and 433_1). An inspection image containing a pattern more clearly defined relative to the background will, compared to a second inspection image having a more blurred defined pattern, enable insight into the focal plane setting with respect to the sample surface of each inspection image. In some embodiments, the focus index of each inspection image may be determined as a clarity index. In some embodiments, the clarity index may be determined by various mathematical operations, including but not limited to Fourier transform, contrast-gradient method, or derivative method. In an exemplary embodiment, the clarity index determined by the Fourier transform method may provide a comparison of the low-frequency and high-frequency signals generated by the detector sub-regions 246, 248, and 250 for each inspection image. According to this exemplary embodiment, a clearer and thus more focused inspection image will show a wider range of high-frequency signal amplitudes in the Fourier transform, thus showing a larger clarity index. An inspection image with a focus closer to the sample surface 410 has a higher frequency signal amplitude in the Fourier transform and thus a larger clarity index. Similarly, the focus of an inspection image with a more clearly defined pattern will be closer to the surface compared to an inspection image with a more blurred defined pattern. In this example, the focus 433 of the inspection image 433_1 is closest to the sample surface 410, and thus has the largest focus index. Similarly, the focus 430 of the inspection image 430_1 is farthest from the sample surface 410, and thus has the smallest focus index.

[0057] In some embodiments, the evaluator 330 may identify inspection images whose focus indices are within a first threshold range. In some embodiments, the focus index being within the first threshold range may indicate that the corresponding inspection image has a clarity or resolution level suitable for image alignment. Figure 4C An example focus index graph 450 is shown, where the x-axis represents the focus condition and the y-axis represents the focus index. In Figure 4C , each focus index is plotted according to the corresponding focus condition. Figure 4C The focus indices of the inspection images 430_1, 431_1, 432_1, and 433_1 are also shown.Figure 4C An example first focus index threshold range 460 is also shown. In some embodiments, the identified inspection images with the focus index within the first threshold range 460 may be forwarded to the selected image acquirer 350 for image alignment. In some embodiments, after identifying an inspection image with the focus index within the first threshold range 460, the evaluator 330 may not be able to determine whether the focus index of subsequent inspection images is within the first threshold range 460. As Figure 4C shown, inspection image 431_1 is the first identified inspection image with the focus index within the first threshold range 460. Then, the selected image acquirer 350 may use inspection image 431_1 for image alignment. In some embodiments, the evaluator 330 may not be able to identify whether the focus index value of any subsequent inspection images is within the first threshold range 460. For example, the evaluator 330 may not be able to determine whether the focus index of inspection image 432_1 is within the first threshold range 460.

[0058] In some embodiments, the evaluator 330 may identify inspection images with the focus index within a second threshold range. In some embodiments, the focus index within the second threshold range may indicate that the corresponding inspection image has a resolution or clarity that can be used for focus optimization. Figure 4D An example second focus index range 470 is shown, which is displayed on the same Figure 4C Figure 450. As Figure 4D shown, the second focus index range 470 may be narrower than the first focus index range 460. In some embodiments, the evaluator 330 may identify multiple inspection images with the focus index value within the second threshold range 470. In some embodiments, if the evaluator 330 cannot identify an inspection image with the focus index within the second threshold 470, the evaluator 330 may provide feedback to the inspection area processor 310 and the inspection image acquirer 320 to adjust the focus conditions and acquire more inspection images. In some embodiments, the identified inspection images with the focus index within the second threshold range 470 may be forwarded to the focus parameter selector 340. The evaluator 330 may identify inspection images 432_1 and 433_1 as having focus index values within the second threshold range 470. In some embodiments, the evaluator 330 does not identify whether inspection images 432_1 and 433_1 have focus index values within the first threshold range 460. In some embodiments, inspection images 432_1 and 433_1 may be forwarded to the focus parameter selector 340.

[0059] Returning to reference Figure 3, according to some embodiments of the present disclosure, the focus parameter selector 340 may select focus conditions for subsequent imaging. In some embodiments, the focus parameter selector 340 may identify inspection images whose focus indices are within the second threshold range 470 and select the focus conditions for capturing the identified inspection images. In some embodiments, the focus parameter selector 340 may be configured to communicate with the inspection image acquirer 320 to obtain the selected focus conditions. In some embodiments, the focus parameter selector 340 may be implemented as software or a component including circuitry that may obtain the selected focus conditions for inspection images with focus indices within the second threshold range 470 from the inspection image acquirer 320. In some embodiments, the focus parameter selector 340 may identify the maximum focus index value of inspection images from among a plurality of inspection images with focus index values within the second threshold range 470. In some embodiments, the focus parameter selector 340 may select the focus conditions for capturing the identified inspection images. In some embodiments, the focus parameter selector 340 may obtain from the inspection image acquirer 320 the focus conditions for the inspection image with the maximum focus index value from among a plurality of inspection images with focus index values located within the second threshold range 470. As Figure 4D shown, the inspection images 432_1 and 433_1 may be forwarded to the focus parameter selector 340. The focus parameter selector 340 may identify the inspection image 433_1 as having the maximum focus index and select the set of focus conditions for capturing the inspection image 433_1.

[0060] Returning to Figure 3 , according to some embodiments of the present disclosure, the selected image acquirer 350 may acquire inspection images determined to have focus index values within the first threshold range 460. In some embodiments, the selected image acquirer 350 may acquire inspection images from the evaluator 330 in parallel with or simultaneously with the autofocus sequence performed by the autofocus component 300A. In some embodiments, the selected image acquirer 350 may perform local image alignment using inspection images acquired during the autofocus process of the autofocus component 300A. For example, the selected image acquirer 350 may receive the inspection image 431_1 acquired by the inspection image acquirer 320 and determined to have a focus index within the first threshold range 460.

[0061] According to some embodiments, the reference image acquirer 360 may acquire a reference image corresponding to the inspection image acquired by the selected image acquirer 350. For example, the reference image acquirer 360 may acquire a reference image corresponding to the inspection image 431_1 and forward it to the selected image acquirer 350. In some embodiments, the reference image acquirer 360 may acquire the reference image in parallel with or simultaneously with the autofocus sequence performed by the autofocus component 300A. In some embodiments, the reference image may be a layout file of a wafer design corresponding to the inspection image. The layout file may be a golden image or in a format such as Graphic Database System (GDS), Graphic Database System II (GDS II), Open Artwork System Interchange Standard (OASIS), or Caltech Intermediate Format (CIF). The wafer design may include patterns or structures to be included on the wafer. These patterns or structures may be mask patterns for transferring features in a photolithography mask or reticle onto the wafer. In some embodiments, the layout in GDS or OASIS format (and other formats) may include feature information stored in a binary file format that represents planar geometries, text, and other information related to the wafer design. In some embodiments, the reference image may be an image rendered from the layout file. Figure 5 Shows a reference image 401 corresponding to the selected inspection image 431_1. As Figure 5 shown, the reference image 401 includes a pattern 401_1 corresponding to the pattern 440 of the selected inspection image 432_1.

[0062] Return reference Figure 3 , according to some embodiments of the present disclosure, the alignment parameter estimator 370 may estimate alignment parameters between the inspection image and the corresponding reference image. In some embodiments, the inspection image may be the inspection image acquired by the selected image acquirer 350, and the reference image may be the reference image acquired by the reference image acquirer 360. The alignment parameter estimator 370 may estimate the alignment parameters in parallel with or simultaneously with the autofocus sequence performed by the autofocus component 300A. In some embodiments, the alignment parameters may be pattern matching information between the inspection image and the reference image. Figure 5 Shows the inspection image 431_1 aligned with the reference image 401 such that the inspection image 431_1 is superimposed on the reference image 401, as shown in the composite image 510. According to some embodiments of the present disclosure, the alignment parameter estimator 370 may estimate the (multiple) alignment parameters to achieve local image alignment. In some embodiments, the alignment parameter estimator 370 may estimate displacement parameters in the XY plane in which the pattern position of the inspection image may be offset from the corresponding point of the corresponding pattern of the reference image. According to some embodiments of the present disclosure, the (multiple) alignment parameters may be determined such that the alignment between the inspection image and the reference image is as close as possible.Figure 6 An example alignment parameter 610 provided by the alignment parameter estimator 370 is shown such that the inspection image pattern 440 matches the corresponding pattern 401_1 of the reference image.

[0063] Return reference Figure 3 According to some embodiments of the present disclosure, the parameter applicator 380 may apply parameters obtained by the focus parameter selector 340 or the alignment parameter estimator 370. In some embodiments, the parameter applicator 380 may apply the selected focusing condition obtained from the focus parameter selector 340 when acquiring subsequent inspection images. In some embodiments, the parameter applicator 380 may apply the selected focusing condition obtained from the focus parameter selector 340 to the inspection area processor 310. In some embodiments, the parameter applicator 380 may apply a focusing condition to adjust the current of the objective lens 228, the bias voltage of the stage 280, or the vertical position of the stage 280, etc. In some embodiments, the parameter applicator 380 may apply the estimated alignment parameter 610 to subsequent inspection images. In some embodiments, the estimated alignment parameter 610 may be applied to inspection images taken according to the selected focusing condition. In some embodiments, the parameter applicator 380 may apply the estimated alignment parameter 610 to the inspection image acquirer 320. In some embodiments, the parameter applicator 380 may apply displacement parameters in the XY plane to move the inspection image such that the inspection image pattern matches the reference image pattern.

[0064] Figure 7 is a flowchart showing an example simultaneous autofocus and image alignment method consistent with embodiments of the present disclosure. The steps of method 700 may be performed by a system (e.g., Figure 1 system 300 in Figure 3 executing on or otherwise using the functionality of a controller 109 of a computing device (e.g.,

[0065] It can be understood that the shown method 700 may be altered to modify the order of steps and include additional steps.

[0066] In step S720, an inspection image can be obtained. Step S720 can be performed, for example, by the inspection image acquirer 320. In some embodiments, the inspection image can be an SCPM image of a sample or a wafer. In some embodiments, the inspection image can be obtained from Figure 1 or Figure 2 an apparatus. In some embodiments, the inspection image can be obtained from a storage device, system, or database that stores the inspection image. In some embodiments, multiple inspection images of the inspection area can be obtained according to multiple focusing conditions set by the inspection area processor 310.

[0067] In step S730, the focus index of the inspection image can be evaluated. Step S730 can be performed, for example, by the evaluator 330 or other image focusing processing software. In some embodiments, the focus index of each inspection image among the multiple inspection images can be evaluated one by one in the acquisition order of the inspection image acquirer 320. In some embodiments, the focus index of the inspection image can be determined as the image resolution or clarity. In some embodiments, the focus index of the inspection image can be determined by comparing the inspection image contrast between the background and the pattern (e.g., Figure 4B pattern 440 in) of the acquired inspection images (e.g., inspection images 430_1, 431_1, 432_1, and 433_1). In some embodiments, the focus index of each inspection image can be determined as a clarity index. In some embodiments, the clarity index can be determined by various mathematical operations, including but not limited to Fourier transform, contrast-gradient method, or derivative method. In some embodiments, the inspection images with the focus index within the first threshold range can be identified. In some embodiments, the inspection images with the identified focus index within the first threshold range 460 can be forwarded to the selected image acquirer 350 for local image alignment. In some embodiments, after the inspection images with the focus index within the first threshold range 460 are identified, subsequent inspection images are not identified within the first threshold range 460. In some embodiments, the inspection images with the focus index value within the second threshold range can be identified. In some embodiments, multiple inspection images with the focus index value within the second threshold range 470 can be identified. In some embodiments, if no inspection image with the focus index within the second threshold 470 can be identified, feedback can be provided to the inspection area processor 310 and the inspection image acquirer 320 to adjust the focal plane setting and obtain more inspection images. In some embodiments, the identified inspection images with the focus index value within the second threshold range 470 can be forwarded to the focus parameter selector 340.

[0068] In step S740, the focusing condition of the inspection image for subsequent imaging can be selected. Step S740 can be performed, for example, by the focusing parameter selector 340. In some embodiments, the inspection images with the focusing index within the second threshold range 470 can be identified. In some embodiments, the focusing condition of the identified inspection images can be obtained from a computer-readable memory or storage device connected to the inspection image acquirer 320. In some embodiments, the inspection image with the largest focusing index value within the second threshold range 470 can be identified from multiple inspection images. In some embodiments, the focusing condition of the inspection image with the largest focusing index value within the second threshold range 470 among multiple inspection images can be obtained from a computer-readable memory or storage device connected to the inspection image acquirer 320.

[0069] In step S750 (which can occur simultaneously or in parallel with step S740), the inspection image having a focusing index value within the first threshold range 460 can be acquired by the selected image acquirer 350, and the reference image can be acquired by the reference image acquirer 360. In some embodiments, the inspection image having a focusing index value within the first threshold range 460 from the evaluator 330 can be used. In some embodiments, the inspection image having a focusing index value within the first threshold range 460 from the inspection image acquirer 320 can be used.

[0070] In step S760, which can be performed simultaneously or in parallel with step S740, the alignment parameter between the inspection image and the corresponding reference image can be estimated. Step S760 can be performed, for example, by the alignment parameter estimator 370. In some embodiments, the inspection image can be acquired from the selected image acquirer 350, and the reference image can be acquired from the reference image acquirer 360. In some embodiments, the inspection image can be superimposed on the reference image. In some embodiments, the image alignment estimation can be the pattern matching information between the inspection image and the reference image. In some embodiments, the image alignment estimation can provide the displacement parameter in the X-Y plane, in which the pattern position of the inspection image may be offset from the corresponding point of the corresponding pattern of the reference image. In some embodiments, the (multiple) image alignment parameters can be determined such that the alignment between the inspection image and the reference image is as close as possible.

[0071] In step S770, the selected focusing conditions and the estimated alignment parameters can be applied to the inspection area processor 310 and the inspection image acquirer 320 for subsequent inspection image acquisition. Step S770 can be performed, for example, by the parameter applicator 380. In some embodiments, the selected focusing conditions applied to the inspection area processor 310 can include adjusting the current in the objective lens 228, adjusting the bias voltage of the stage 280, or adjusting the vertical position of the stage 280, etc., for subsequent inspection image acquisition. In some embodiments, the estimated (plural) image alignment parameters can be applied to the inspection image acquirer 320 for subsequent inspection image acquisition. In some embodiments, the displacement parameters in the X-Y plane can be applied to the inspection image acquirer 320 to move the inspection image so that the inspection image pattern matches the reference image pattern.

[0072] A non-transitory computer-readable medium can be provided, which can store instructions for a processor of a controller (e.g., the controller 109 in Figure 1 ), to perform inspection image area evaluation, inspection image acquisition, stage positioning, beam focusing, electric field regulation, objective lens regulation, starting a charged particle source, method 700, and other executable functions related to the simultaneous autofocus and image alignment method in the charged particle system. For example, common forms of non-transitory media include: floppy disks, flexible disks, hard disks, solid state drives, magnetic tapes, or any other magnetic data storage media, compact disc read-only memory (CD-ROM), any other optical data storage media, 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), caches, registers, any other storage chip or cartridge memory, and networked versions thereof.

[0073] The embodiments can be further described using the following clauses:

[0074] 1. A method for enhancing an inspection image, comprising:

[0075] Acquiring a plurality of inspection images for an area of a sample containing a pattern according to a plurality of focusing conditions;

[0076] Determining whether an inspection image among the plurality of inspection images has a focus index within a first threshold range; and

[0077] In response to determining that the inspection image has a focus index within the first threshold range, performing image alignment using the inspection image.

[0078] 2. The method according to Clause 1, wherein a first focusing condition and a second focusing condition among the plurality of focusing conditions respectively set a first focal point and a second focal point, and the first focal point and the second focal point have different relative positions with respect to the sample.

[0079] 3. The method according to Clause 1 or 2, wherein the plurality of focusing conditions include: a current value of an objective lens, a voltage bias applied to a stage, or a change in a vertical position of the stage.

[0080] 4. The method according to any one of Clauses 1 to 3, wherein performing image alignment using inspection images includes:

[0081] obtaining a reference image corresponding to the inspection image; and

[0082] estimating alignment parameters by comparing the inspection image with the reference image.

[0083] 5. The method according to any one of Clauses 1 to 4, further comprising:

[0084] determining a focus index for each of the plurality of inspection images;

[0085] identifying one or more inspection images among the plurality of inspection images having a focus index within a second threshold range;

[0086] selecting, from the identified one or more inspection images, an inspection image having the maximum focus index; and

[0087] selecting, among the plurality of focusing conditions, a focusing condition associated with the selected inspection image.

[0088] 6. The method according to Clause 5, wherein the second threshold range is narrower than the first threshold range, and the second threshold range is included within the first threshold range.

[0089] 7. The method according to any one of Clauses 1 - 6, wherein the region of the sample containing the pattern is selected to include a unique sample pattern, a distinguishable pattern edge, or a field of view.

[0090] 8. A method for enhancing inspection images, comprising:

[0091] setting a plurality of focusing conditions for a region of a sample containing a pattern;

[0092] acquiring a plurality of inspection images according to the plurality of focusing conditions;

[0093] determining a focus index for each of the plurality of inspection images;

[0094] Identify inspection images among the multiple inspection images whose focus indices are determined to be within a first threshold range;

[0095] Estimate alignment parameters of the inspection images whose focus indices are determined to be within the first threshold range;

[0096] Identify one or more inspection images among the multiple inspection images whose focus indices are determined to be within a second threshold range;

[0097] Select a focusing condition associated with the inspection image having the maximum focus index that is determined to be within the second threshold range; and

[0098] Perform image alignment and focus correction based on the estimated alignment parameters and the selected focusing condition.

[0099] 9. The method according to clause 8, wherein the following occur simultaneously or in parallel: estimating alignment parameters of the inspection images whose focus indices are determined to be within the first threshold range, identifying one or more inspection images among the multiple inspection images whose focus indices are determined to be within a second threshold range, and selecting a focusing condition associated with the inspection image having the maximum focus index that is determined to be within the second threshold range.

[0100] 10. The method according to clause 8 or 9, wherein a first focusing condition and a second focusing condition among the multiple focusing conditions respectively set a first focus and a second focus, and the first focus and the second focus have different relative positions with respect to the sample.

[0101] 11. The method according to any one of clauses 8 to 10, wherein the multiple focusing conditions include: a current value of an objective lens, a voltage bias applied to a stage, or a change in a vertical position of the stage.

[0102] 12. The method according to any one of clauses 8 to 11, wherein performing image alignment using the inspection image includes:

[0103] Obtain a reference image corresponding to the inspection image; and

[0104] Estimate alignment parameters by comparing the inspection image with the reference image.

[0105] 13. The method according to clause 8 or 9, wherein the second threshold range is narrower than the first threshold range, and the second threshold range is included within the first threshold range.

[0106] 14. The method according to any one of claims 8 to 12, wherein the region of the sample containing the pattern is selected to include a unique sample pattern, a distinguishable pattern edge, or a field of view.

[0107] 15. An apparatus for enhancing inspection images, comprising:

[0108] A memory for storing an instruction set; and

[0109] At least one processor configured to execute the instruction set so that the apparatus performs:

[0110] For a sample area containing a pattern, obtaining a plurality of inspection images according to a plurality of focusing conditions;

[0111] Determining whether an inspection image among the plurality of inspection images has a focusing index within a first threshold range; and

[0112] In response to determining that the inspection image has a focusing index within the first threshold range, performing image alignment using the inspection image.

[0113] 16. The apparatus according to clause 15, wherein a first focusing condition and a second focusing condition among the plurality of focusing conditions respectively set a first focus and a second focus, and the first focus and the second focus have different relative positions with respect to the sample.

[0114] 17. The apparatus according to clause 15 or 16, wherein the plurality of focusing conditions include: a current value of an objective lens, a voltage bias applied to a stage, or a change in a vertical position of the stage.

[0115] 18. The apparatus according to any one of clauses 15 to 17, wherein when performing image alignment using the inspection image, the at least one processor is configured to execute the instruction set so that the apparatus further performs:

[0116] Obtaining a reference image corresponding to the inspection image; and

[0117] Estimating alignment parameters by comparing the inspection image with the reference image.

[0118] 19. The apparatus according to any one of clauses 15 to 18, wherein the at least one processor is configured to execute the instruction set so that the apparatus further performs:

[0119] Determining the focusing index of each inspection image among the plurality of inspection images;

[0120] Identifying one or more inspection images among the plurality of inspection images having a focusing index within a second threshold range;

[0121] Selecting, from the identified one or more inspection images, an inspection image having the maximum focusing index; and

[0122] Select a focusing condition associated with the selected inspection image from among the plurality of focusing conditions.

[0123] 20. The apparatus according to clause 19, wherein the second threshold range is narrower than the first threshold range, and the second threshold range is included within the first threshold range.

[0124] 21. The apparatus according to any one of clauses 15 to 20, wherein the region of the sample containing the pattern is selected to include a unique sample pattern, a distinguishable pattern edge, or a field of view.

[0125] 22. An apparatus for enhancing an inspection image, comprising:

[0126] A memory storing an instruction set; and

[0127] At least one processor configured to execute the instruction set to cause the apparatus to perform:

[0128] Set a plurality of focusing conditions for a region of a sample containing a pattern;

[0129] Acquire a plurality of inspection images according to the plurality of focusing conditions;

[0130] Determine a focus index for each of the plurality of inspection images;

[0131] Identify the inspection images among the plurality of inspection images for which the focus index is determined to be within a first threshold range;

[0132] Estimate alignment parameters for the inspection images for which the focus index is determined to be within the first threshold range;

[0133] Identify one or more inspection images among the plurality of inspection images for which the focus index is determined to be within a second threshold range;

[0134] Select a focusing condition associated with the inspection image having the maximum focus index among those determined to be within the second threshold range; and

[0135] Perform image alignment and focus correction based on the estimated alignment parameters and the selected focusing condition.

[0136] 23. The apparatus according to clause 22, wherein the at least one processor is configured to execute the instruction set to cause the apparatus to also perform simultaneously or in parallel:

[0137] Estimate alignment parameters for the inspection images for which the focus index is determined to be within the first threshold range;

[0138] Identify one or more inspection images among the plurality of inspection images whose focus indices are determined to be within the second threshold range; and

[0139] Select a focusing condition associated with the inspection image having the maximum focus index determined to be within the second threshold range.

[0140] 24. The apparatus according to clause 22 or 23, wherein a first focusing condition and a second focusing condition among the plurality of focusing conditions respectively set a first focus and a second focus, and the first focus and the second focus have different relative positions with respect to the sample.

[0141] 25. The apparatus according to any one of clauses 22 to 24, wherein the plurality of focusing conditions include: a current value of an objective lens, a voltage bias applied to a stage, or a change in a vertical position of the stage.

[0142] 26. The apparatus according to any one of clauses 22 to 25, wherein when performing image alignment using the inspection image, the at least one processor is configured to execute the instruction set so that the apparatus further performs:

[0143] Obtain a reference image corresponding to the inspection image; and

[0144] Estimate alignment parameters by comparing the inspection image with the reference image.

[0145] 27. The apparatus according to clause 22 or 23, wherein the second threshold range is narrower than the first threshold range, and the second threshold range is included within the first threshold range.

[0146] 28. The apparatus according to any one of clauses 22 - 26, wherein the region of the sample containing the pattern is selected to include a unique sample pattern, a distinguishable pattern edge, or a field of view.

[0147] 29. A non - transitory computer - readable medium, including an instruction set that can be executed by one or more processors of a computing device to cause the computing device to execute a method for enhancing an inspection image, the method including:

[0148] For a sample region containing a pattern, obtain a plurality of inspection images according to a plurality of focusing conditions;

[0149] Determine whether an inspection image among the plurality of inspection images has a focus index within a first threshold range; and

[0150] In response to determining that the inspection image has a focus index within the first threshold range, perform image alignment using the inspection image.

[0151] 30. The non-transitory computer-readable medium according to clause 29, wherein a first focusing condition and a second focusing condition among the plurality of focusing conditions respectively set a first focal point and a second focal point, and the first focal point and the second focal point have different relative positions with respect to the sample.

[0152] 31. The non-transitory computer-readable medium according to clause 29 or 30, wherein the plurality of focusing conditions include: a current value of the objective lens, a voltage bias applied to the stage, or a change in the vertical position of the stage.

[0153] 32. The non-transitory computer-readable medium according to any one of clauses 29 to 31, wherein when performing image alignment using the inspection image, the instruction set executable by one or more processors of the computing device causes the computing device to further perform:

[0154] Obtain a reference image corresponding to the inspection image; and

[0155] Estimate alignment parameters by comparing the inspection image with the reference image.

[0156] 33. The non-transitory computer-readable medium according to any one of clauses 29 to 32, wherein the instruction set executable by one or more processors of the computing device causes the computing device to further perform:

[0157] Determine a focus index for each inspection image among the plurality of inspection images;

[0158] Identify one or more inspection images among the plurality of inspection images having a focus index within a second threshold range;

[0159] Select, among the identified one or more inspection images, the inspection image having the maximum focus index; and

[0160] Select, among the plurality of focusing conditions, the focusing condition associated with the selected inspection image.

[0161] 34. The non-transitory computer-readable medium according to clause 33, wherein the second threshold range is narrower than the first threshold range, and the second threshold range is included within the first threshold range.

[0162] 35. The non-transitory computer-readable medium according to clauses 29 - 34, wherein the region of the sample containing the pattern is selected to include a unique sample pattern, a distinguishable pattern edge, or a field of view.

[0163] 36. A non-transitory computer-readable medium includes an instruction set that can be executed by one or more processors of a computing device to cause the computing device to execute a method for enhancing an inspection image, the method including:

[0164] Setting a plurality of focusing conditions for an area of a sample containing a pattern;

[0165] Obtaining a plurality of inspection images according to the plurality of focusing conditions;

[0166] Determining a focusing index for each of the plurality of inspection images;

[0167] Identifying the inspection images among the plurality of inspection images whose focusing indices are determined to be within a first threshold range;

[0168] Estimating alignment parameters of the inspection images whose focusing indices are determined to be within the first threshold range;

[0169] Identifying one or more inspection images among the plurality of inspection images whose focusing indices are determined to be within a second threshold range;

[0170] Selecting the focusing condition associated with the inspection image having the maximum focusing index among those determined to be within the second threshold range; and

[0171] Performing image alignment and focusing correction based on the estimated alignment parameters and the selected focusing condition.

[0172] 37. The non-transitory computer-readable medium according to clause 36, wherein the instruction set that can be executed by one or more processors of the computing device causes the computing device to execute simultaneously or in parallel:

[0173] Estimating alignment parameters of the inspection images whose focusing indices are determined to be within the first threshold range;

[0174] Identifying one or more inspection images among the plurality of inspection images whose focusing indices are determined to be within a second threshold range; and

[0175] Selecting the focusing condition associated with the inspection image having the maximum focusing index among those determined to be within the second threshold range.

[0176] 38. The non-transitory computer-readable medium according to clause 36 or 37, wherein a first focusing condition and a second focusing condition among the plurality of focusing conditions set a first focal point and a second focal point respectively, and the first focal point and the second focal point have different relative positions with respect to the sample.

[0177] 39. The non-transitory computer-readable medium according to clauses 36 to 38, wherein the plurality of focusing conditions include: a current value of the objective lens, a voltage bias applied to the stage, or a change in the vertical position of the stage.

[0178] 40. The non-transitory computer-readable medium according to clauses 36 to 39, wherein, when performing image alignment using the inspection image, the instruction set executable by one or more processors of the computing device causes the computing device to perform:

[0179] Obtain a reference image corresponding to the inspection image; and

[0180] Estimate alignment parameters by comparing the inspection image with the reference image.

[0181] 41. The non-transitory computer-readable medium according to clause 36 or 37, wherein the second threshold range is narrower than the first threshold range, and the second threshold range is included within the first threshold range.

[0182] 42. The non-transitory computer-readable medium according to any one of clauses 36 - 40, wherein the region of the sample containing the pattern is selected to include a unique sample pattern, distinguishable pattern edges, or a field of view.

[0183] The block diagrams in the figures may illustrate the possible architectures, functions, and operations of systems, methods, and computer hardware or 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 (e.g., electronic circuits). The block may also represent a module, code segment, or portion of code containing one or more executable instructions for implementing the specified logical function. It should be understood that in certain alternative implementations, the functions indicated in the blocks may be different from the order shown in the figures. For example, two consecutively shown blocks may be executed or implemented substantially simultaneously, or the two blocks may sometimes be executed in the reverse order, depending on the functions involved. Certain blocks may also be omitted. It should also be understood that each block in the block diagram and their combinations may be implemented by a dedicated hardware system that performs the specified functions or actions, or by a combination of dedicated hardware and computer instructions.

[0184] It should be understood that the embodiments of the present disclosure are not limited to the specific structures described above and shown in the drawings, and 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 be able to understand other embodiments of the present invention by referring to the specification and practicing the invention disclosed herein. The specification and examples are for reference only, and the true scope and spirit of the present invention are indicated by the following claims.

Claims

1. An apparatus for enhancing inspection images, comprising: a memory storing an instruction set; and at least one processor configured to execute the instruction set such that the apparatus performs: acquiring a plurality of inspection images for a region of a sample containing a pattern according to a plurality of focusing conditions; determining whether an inspection image among the plurality of inspection images has a focusing index within a first threshold range; and in response to determining that the inspection image has a focusing index within the first threshold range, performing image alignment using the inspection image.

2. The apparatus according to claim 1, wherein a first focusing condition and a second focusing condition among the plurality of focusing conditions respectively set a first focal point and a second focal point, and the first focal point and the second focal point have different relative positions with respect to the sample.

3. The apparatus according to claim 1, wherein the plurality of focusing conditions comprise: a current value of an objective lens, a voltage bias applied to a stage, or a change in a vertical position of the stage.

4. The apparatus according to claim 1, wherein when performing the image alignment using the inspection image, the at least one processor is configured to execute the instruction set such that the apparatus further performs: acquiring a reference image corresponding to the inspection image; and estimating an alignment parameter by comparing the inspection image with the reference image.

5. The apparatus according to claim 1, wherein the at least one processor is configured to execute the instruction set such that the apparatus further performs: determining a focusing index of each inspection image among the plurality of inspection images; identifying one or more inspection images among the plurality of inspection images having a focusing index within a second threshold range; selecting, among the identified one or more inspection images, an inspection image having a maximum focusing index; and selecting, among the plurality of focusing conditions, a focusing condition associated with the selected inspection image.

6. The apparatus according to claim 5, wherein the second threshold range is narrower than the first threshold range, and the second threshold range is included within the first threshold range.

7. The apparatus according to claim 1, wherein the region of the sample containing the pattern is selected to include a unique sample pattern, a distinguishable pattern edge, or a field of view.

8. A non-transitory computer-readable medium comprising an instruction set that can be executed by one or more processors of a computing device to cause the computing device to perform a method for enhancing inspection images, the method comprising: acquiring a plurality of inspection images for a region of a sample containing a pattern according to a plurality of focusing conditions; determining whether an inspection image among the plurality of inspection images has a focusing index within a first threshold range; and in response to determining that the inspection image has a focusing index within the first threshold range, performing image alignment using the inspection image.

9. The non-transitory computer-readable medium according to claim 8, wherein a first focusing condition and a second focusing condition among the plurality of focusing conditions respectively set a first focal point and a second focal point, and the first focal point and the second focal point have different relative positions with respect to the sample.

10. The non-transitory computer-readable medium according to claim 8, wherein the plurality of focusing conditions comprise: a current value of the objective lens, a voltage bias applied to the stage, or a change in a vertical position of the stage.

11. The non-transitory computer-readable medium according to claim 8, wherein when performing image alignment using the inspection image, the instruction set executable by one or more processors of the computing device causes the computing device to further perform: obtaining a reference image corresponding to the inspection image; and estimating alignment parameters by comparing the inspection image with the reference image.

12. The non-transitory computer-readable medium according to claim 8, wherein the instruction set executable by one or more processors of the computing device causes the computing device to further perform: determining a focus index for each inspection image of the plurality of inspection images; identifying one or more inspection images of the plurality of inspection images having a focus index within a second threshold range; selecting, from the identified one or more inspection images, an inspection image having the maximum focus index; and selecting, from the plurality of focusing conditions, a focusing condition associated with the selected inspection image.

13. The non-transitory computer-readable medium according to claim 12, wherein the second threshold range is narrower than the first threshold range and the second threshold range is included within the first threshold range.

14. A method for enhancing an inspection image, comprising: acquiring a plurality of inspection images for a region of a sample containing a pattern according to a plurality of focusing conditions; determining whether an inspection image of the plurality of inspection images has a focus index within a first threshold range; and in response to determining that the inspection image has a focus index within the first threshold range, performing image alignment using the inspection image.

15. The method according to claim 14, wherein a first focusing condition and a second focusing condition among the plurality of focusing conditions respectively set a first focus and a second focus, and the first focus and the second focus have different relative positions with respect to the sample.

Images