Image enhancement based on charge accumulation reduction in charged particle beam inspection

Abstract

An improved method and apparatus for enhancing an inspection image in a charged particle beam inspection system. An improved method for enhancing an inspection image includes: acquiring a plurality of test images of a sample obtained at different landing energies; determining a level of distortion of the plurality of test images; based on the level of distortion, determining a landing energy level at which the sample is enabled to be in a neutral charge condition during an inspection; and based on the determined landing energy level, acquiring the inspection image.

Description

[0001] Cross-reference to related applications

[0002] This application claims priority to U.S. Application 63 / 005,074, filed April 3, 2020, the entire contents of which are incorporated herein by reference. Technical Field

[0003] The embodiments provided herein relate to image enhancement techniques, and more specifically to inspection image enhancement based on the reduction of charge accumulation on a wafer in charged particle beam inspection. Background Technology

[0004] In the manufacturing process of integrated circuits (ICs), incomplete or finished circuit components are inspected to ensure they are manufactured according to the design and free of defects. Inspection systems utilizing 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 yield of defect detection become increasingly important.

[0005] Pattern / structure displacement and dimensional deviations from the design can be measured from SEM images with sub-nanometer (nm) precision. These measurements help identify defects in the manufactured ICs and control the manufacturing process. Charge buildup on the wafer during inspection can cause distortion, defocusing, and abnormal gray levels in SEM images, thereby introducing errors in measuring critical dimensions and overlays, as well as in detecting defects from SEM images. Summary of the Invention

[0006] The embodiments provided herein disclose a particle beam inspection apparatus, and more specifically, an inspection apparatus using a charged particle beam.

[0007] In some embodiments, a method is provided for enhancing inspection images in a charged particle beam inspection system. The method includes: acquiring multiple test images of a sample obtained at different landing energies; determining distortion levels in the multiple test images; determining, based on the distortion levels, a landing energy level that enables the sample to be in a neutral charge condition during inspection; and acquiring inspection images based on the determined landing energy level.

[0008] In some embodiments, an image enhancement device includes a memory and at least one processor, the memory storing an instruction set, the at least one processor being configured to execute the instruction set to cause the device to perform: acquiring multiple test images of a sample obtained at different landing energies; determining a distortion level of the multiple test images; determining, based on the distortion level, a landing energy level that enables the sample to be in a neutral charge condition during inspection; and acquiring an inspection image based on the determined landing energy level.

[0009] In some embodiments, a non-transient computer-readable medium is provided that stores a set of instructions executable by at least one processor of a computing device to perform a method for enhancing an image. The method includes: acquiring a plurality of test images of a sample obtained at different landing energies; determining distortion levels of the plurality of test images; determining, based on the distortion levels, a landing energy level that enables the sample to be under neutral charge conditions during inspection; and acquiring an inspection image based on the determined landing energy level.

[0010] In some embodiments, a method is provided for identifying the optimal landing energy in a charged particle beam inspection system. The method includes: acquiring multiple test images of a sample obtained at different landing energies; determining the distortion level of the multiple test images, wherein determining the distortion level includes: comparing the first test image with a first reference image corresponding to the first test image based on the location of features in the first test image and the first reference image; and determining, based on the distortion level, a landing energy level that enables the sample to be under neutral charge conditions during inspection.

[0011] In some embodiments, a method for enhancing an inspection image in a charged particle beam inspection system is provided. The method includes: acquiring a first test image and a second test image of a sample, wherein the first test image and the second test image are acquired at different landing energies; determining a first distortion level of the first test image and a second distortion level of the second test image; determining a landing energy level that makes the distortion level substantially zero when inspecting the sample, the determination of the landing energy level being based on the first distortion level, the second distortion level, and the different landing energies; and acquiring the inspection image based on the determined landing energy level.

[0012] Other advantages of the embodiments of this disclosure will become apparent from the following description taken in conjunction with the accompanying drawings, in which certain embodiments of the invention are illustrated by way of example. Attached Figure Description

[0013] Figure 1 This is a schematic diagram illustrating an example electron beam inspection (EBI) system according to an embodiment of the present disclosure.

[0014] Figure 2 The illustration shows embodiments that can be implemented according to this disclosure. Figure 1 A schematic diagram of an example electron beam tool, which is part of an electron beam inspection system.

[0015] Figure 3A This is an example comparison of feature locations in an examination image obtained under neutral charge conditions with reference feature locations.

[0016] Figure 3BThis is an example comparison of feature locations in an inspection image obtained under negative charge conditions with reference feature locations.

[0017] Figure 3C This is an example comparison of feature locations in an inspection image obtained under positive charge conditions with reference feature locations.

[0018] Figure 4 This is a block diagram of an example image enhancement device according to an embodiment of the present disclosure.

[0019] Figure 5 This is an example test area on a sample according to an embodiment of this disclosure.

[0020] Figure 6 An example method for measuring distortion according to an embodiment of the present disclosure is illustrated.

[0021] Figure 7 This is an example graph used to identify the landing energy corresponding to a neutral charge condition, according to embodiments of the present disclosure.

[0022] Figure 8 This is a processing flowchart illustrating an example method for enhancing images in a multi-beam inspection system according to embodiments of the present disclosure. Detailed Implementation

[0023] Exemplary embodiments will now be described in detail, examples of which are illustrated in the accompanying drawings. The following description refers to the accompanying drawings, wherein, unless otherwise indicated, the same numerals in the different drawings denote the same or similar elements. The implementations set forth in the following description of the exemplary embodiments do not represent all implementations. Rather, they are merely examples of apparatuses and methods consistent with aspects recounted in the appended claims and relevant to the disclosed embodiments. For example, although some embodiments are described in the context of the use of electron beams, this disclosure is not limited thereto. Other types of charged particle beams can be applied similarly. Furthermore, other imaging systems can be used, such as optical imaging, photoelectric detection, X-ray detection, etc.

[0024] Electronic devices consist of circuits formed on a silicon wafer called a substrate. Many circuits can be formed together on the same silicon wafer and are called integrated circuits or ICs. The size of these circuits has been reduced significantly, allowing more circuits to be mounted on the substrate. For example, the IC chip in a smartphone can be as small as a thumbnail but may contain more than 2 billion transistors, each less than 1 / 1000th the size of a human hair.

[0025] Manufacturing these tiny ICs is a complex, time-consuming, and expensive process, typically involving hundreds of individual steps. Even an error in one step can lead to a defect in the finished IC, rendering it unusable. Therefore, one goal of the manufacturing process is to avoid such defects in order to maximize the number of functional ICs manufactured in the process, i.e., to improve the overall yield of the process.

[0026] A component of improving yield is monitoring the chip manufacturing process to ensure it produces a sufficient number of functional integrated circuits. One way to monitor the process is to inspect the chip's circuit structure at various stages of its formation. This inspection can be performed using a scanning electron microscope (SEM). SEM can be used to image these extremely small structures, essentially taking "pictures" of them. This image can be used to determine if the structure is formed correctly and in the correct location. If a defect is found in the structure, the process can be adjusted to make it less likely to recur.

[0027] When identifying defects in manufactured ICs, critical dimensions of the pattern / structure measured from SEM images can be used. For example, shifts or edge arrangement variations between patterns determined by measured critical dimensions can help identify defects and control the manufacturing process. Charge can accumulate on the wafer during inspection when there is an imbalance between incoming primary electrons and outgoing secondary electrons. This charge accumulation can cause significant distortion, defocusing, and abnormal gray levels in the SEM images, leading to errors in the measurement of critical dimensions based on the SEM images.

[0028] Some embodiments of this disclosure provide a technique for identifying energy levels that can balance the charge on a sample during inspection. Inspecting the sample based on the identified energy level can help provide more accurate SEM images and thus enable the detection of defects in the sample with greater accuracy and efficiency. In this disclosure, identifying neutral energy levels and inspecting the sample based on the identified neutral energy levels can be automated.

[0029] For clarity, the relative sizes of components in the accompanying drawings may be exaggerated. Throughout the following description of the drawings, the same or similar reference numerals refer to the same or similar components or entities, and differences are described only with respect to individual embodiments. As used herein, unless otherwise specifically stated, the term "or" covers all possible combinations except where impractical. For example, if an illustrated component may include A or B, then unless otherwise specifically stated or impractical, the component may include A or B or A and B. As a second example, if an illustrated component may include A, B, or C, then unless otherwise specifically stated or impractical, 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.

[0030] Now for reference Figure 1 , Figure 1 An example electron beam inspection (EBI) system 100 according to an embodiment of the present disclosure is illustrated. Figure 1 As shown, the charged particle beam inspection system 100 includes a main chamber 10, a loading-locking chamber 20, an electron beam tool 40, and an equipment front-end module (EFEM) 30. The electron beam tool 40 is located within the main chamber 10. Although the description and figures relate to electron beams, it should be understood that the embodiments are not intended to limit this disclosure to specific charged particles.

[0031] EFEM 30 includes a first loading port 30a and a second loading port 30b. EFEM 30 may include multiple additional loading ports. The first loading port 30a and the second loading port 30b receive front-opening unified pods (FOUPs) containing wafers to be inspected (e.g., one or more semiconductor wafers made of (multiple) other materials) or samples (wafers and samples are collectively referred to as “wafers” hereinafter). One or more robotic arms (not shown) in EFEM 30 transfer the wafers to the loading-locking chamber 20.

[0032] Load-lock chamber 20 is connected to a load / lock vacuum pump system (not shown) that removes gas molecules from the load-lock chamber 20 to achieve a first pressure below atmospheric pressure. After reaching the first pressure, one or more robotic arms (not shown) transfer the wafer from the load-lock chamber 20 to the main chamber 10. The main chamber 10 is connected to a main chamber vacuum pump system (not shown) that removes gas molecules from the main chamber 10 to achieve a second pressure below the first pressure. After reaching the second pressure, the wafer is inspected by an electron beam tool 40. In some embodiments, the electron beam tool 40 may include a single-beam inspection tool. In other embodiments, the electron beam tool 40 may include a multi-beam inspection tool.

[0033] The controller 50 can be electrically connected to the electron beam tool 40 and can also be electrically connected to other components. The controller 50 can be a computer configured to perform various controls on the charged particle beam inspection system 100. The controller 50 may also include a processing circuitry system configured to perform various signal and image processing functions. Although the controller 50 is... Figure 1 The controller 50 is shown outside the structure comprising the main chamber 10, the loading-locking chamber 20, and the EFEM 30, but it should be understood that the controller 50 may be part of the structure.

[0034] While this disclosure provides an example of a main chamber 10 for housing an electron beam inspection system, it should be noted that aspects of this disclosure are not limited, in their broadest sense, to the chamber housing the electron beam inspection system. Rather, it should be understood that the above principles can also be applied to other chambers.

[0035] Now for reference Figure 2 , Figure 2 The illustration shows a schematic diagram according to an embodiment of the present disclosure, illustrating that it may be... Figure 1 Example electron beam tool 40 is a part of the example charged particle beam inspection system 100. Electron beam tool 40 (also referred to herein as the apparatus) includes an electron source 101, a bore plate 171 with a bore diameter 103, a pre-beam forming mechanism 172, a focusing lens 110, a source conversion unit 120, a primary projection optics system 130, and a sample stage (not shown in the original text). Figure 2 (Shown in the diagram) Secondary imaging system 150 and electronic detection device 140. Primary projection optics system 130 may include objective lens 131. Electronic detection device 140 may include multiple detection elements 140_1, 140_2, and 140_3. Beam splitter 160 and deflection scanning unit 132 may be housed within primary projection optics system 130. It is understood that other known components of electron beam tool 40 may be appropriately added or omitted.

[0036] The electron source 101, the aperture plate 171, the focusing lens 110, the source conversion unit 120, the beam splitter 160, the deflection scanning unit 132, and the primary projection optics system 130 can be aligned with the primary optical axis 100_1 of the charged particle beam inspection system 100. The secondary imaging system 150 and the electronic detection device 140 can be aligned with the secondary optical axis 150_1 of the electron beam tool 40.

[0037] The electron source 101 may include a cathode, an extractor, or an anode, wherein primary electrons may be emitted from the cathode and extracted or accelerated to form a primary electron beam 102, which forms crosses (virtual or real) 101s. The primary electron beam 102 may be visualized as being emitted from the crosses 101s.

[0038] Source conversion unit 120 may include an image forming element array (not in) Figure 2 The image forming element array may include multiple micropolarizers or microlenses to form multiple parallel images (virtual or real) with multiple sub-beams of the primary electron beam 102 crossing 101s. Figure 2 Three sub-bundles 102_1, 102_2 and 102_3 are shown as examples, and it should be understood that the source conversion unit 120 can handle any number of sub-bundles.

[0039] In some embodiments, the source conversion unit 120 may be provided with a beam-limiting aperture array and an image-forming element array (both not shown). The beam-limiting aperture array may include a beam-limiting aperture. It should be understood that any number of apertures may be used appropriately. The beam-limiting aperture may be configured to limit the size of sub-beams 102_1, 102_2, and 102_3 of the primary electron beam 102. The image-forming element array 122 may include an image-forming deflector (not shown) configured to deflect sub-beams 102_1, 102_2, and 102_3 by changing the angle toward the primary optical axis 100_1. In some embodiments, a deflector further away from the primary optical axis 100_1 may deflect the sub-beams to a greater extent. Furthermore, the image-forming element array 122 may include multiple layers (not shown), and deflectors may be disposed in separate layers. The deflectors may be configured to be controlled individually and independently of each other. In some embodiments, the deflector can be controlled to adjust the spacing of the probe spots (e.g., 102_1S, 102_2S, and 102_3S) formed on the surface of sample 1. As mentioned herein, the spacing of the probe spots can be defined as the distance between two adjacent probe spots on the surface of sample 1.

[0040] The centrally located deflector of the image forming element array can be aligned with the primary optical axis 100_1 of the electron beam tool 40. Therefore, in some embodiments, the central deflector can be configured to maintain the trajectory of the sub-beam 102_1 as straight. In some embodiments, the central deflector can be omitted. However, in some embodiments, the primary electron source 101 may not need to be aligned with the center of the source conversion unit 120. Furthermore, it should be understood that although... Figure 2 A side view of the electron beam tool 40 is shown, wherein sub-beam 102_1 is on the primary optical axis 100_1, and sub-beam 102_1 may deviate from the primary optical axis 100_1 when viewed from different sides. That is, in some embodiments, all sub-beams 102_1, 102_2, and 102_3 may be off-axis. The off-axis component may be offset relative to the primary optical axis 100_1.

[0041] The deflection angle of the deflected sub-beams can be set based on one or more criteria. In some embodiments, the deflector can deflect the off-axis sub-beams radially outward or away from (not shown) the primary optical axis 100_1. In some embodiments, the deflector can be configured to deflect the off-axis sub-beams radially inward or toward the primary optical axis 100_1. The deflection angle of the sub-beams can be set such that sub-beams 102_1, 102_2, and 102_3 fall perpendicularly onto sample 1. Off-axis aberrations in the image caused by lenses (such as objective lens 131) can be reduced by adjusting the path of the sub-beams passing through the lenses. Therefore, the deflection angles of off-axis sub-beams 102_2 and 102_3 can be set such that probe spots 102_2S and 102_3S have small aberrations. The sub-beams can be deflected to pass through or near the front focal point of objective lens 131 to reduce the aberrations of off-axis probe spots 102_2S and 102_3S. In some embodiments, the deflector can be configured to make the sub-beams 102_1, 102_2 and 102_3 fall vertically onto sample 1, while the probe spots 102_1S, 102_2S and 102_3S have small aberrations.

[0042] A focusing lens 110 is configured to focus the primary electron beam 102. The currents of the sub-beams 102_1, 102_2, and 102_3 downstream of the source conversion unit 120 can be varied by adjusting the focusing capability of the focusing lens 110 or by changing the radial size of the corresponding beam-limiting aperture within the beam-limiting aperture array. The currents can be changed by altering the radial size of the beam-limiting aperture and the focusing capability of the focusing lens 110. The focusing lens 110 can be an adjustable focusing lens, which can be configured such that the position of its first principal plane is movable. The adjustable focusing lens can be configured to be magnetic, which may cause the off-axis sub-beams 102_2 and 102_3 to illuminate the source conversion unit 120 at a rotational angle. The rotational angle can be changed with the focusing capability or position of the first principal plane of the adjustable focusing lens. Therefore, the focusing lens 110 can be an anti-rotation focusing lens, which can be configured to maintain a constant rotational angle while the focusing capability of the focusing lens 110 is changed. In some embodiments, the focusing lens 110 may be an adjustable anti-rotation focusing lens, wherein the rotation angle does not change when the focusing capability of the focusing lens 110 and the position of the first principal plane change.

[0043] The electron beam tool 40 may include a pre-beam forming mechanism 172. In some embodiments, the electron source 101 may be configured to emit primary electrons and form a primary electron beam 102. In some embodiments, the aperture plate 171 may be configured to block peripheral electrons in the primary electron beam 102 to reduce the Coulomb effect. In some embodiments, the pre-beam forming mechanism 172 further cuts off peripheral electrons in the primary electron beam 102 to further reduce the Coulomb effect. The primary electron beam 102 may be trimmed into three primary electron sub-beams 102_1, 102_2, and 102_3 (or any other number of sub-beams) after passing through the pre-beam forming mechanism 172. The electron source 101, aperture plate 171, pre-beam forming mechanism 172, and focusing lens 110 may be aligned with the primary optical axis 100_1 of the electron beam tool 40.

[0044] The pre-beam forming mechanism 172 may include a coulomb aperture array. The center aperture of the pre-beam forming mechanism 172 (also referred to herein as an on-axis aperture) and the center deflector of the source conversion unit 120 can be aligned with the primary optical axis 100_1 of the electron beam tool 40. The pre-beam forming mechanism 172 may be provided with multiple pre-trimmed apertures (e.g., a coulomb aperture array). Figure 2 In this process, three sub-beams 102_1, 102_2, and 102_3 are generated as the primary electron beam 102 passes through three pre-trimmed apertures, and many of the remaining portions of the primary electron beam 102 are cut off. That is, the pre-beam forming mechanism 172 can trim many or most of the electrons from the primary electron beam 102 that do not form the three sub-beams 102_1, 102_2, and 102_3. The pre-beam forming mechanism 172 can cut off electrons that will ultimately not be used to form probe spots 102_1S, 102_2S, and 102_3S before the primary electron beam 102 enters the source conversion unit 120. In some embodiments, the gun aperture plate 171 can be positioned near the electron source 101 to cut off electrons in an early stage, while the pre-beam forming mechanism 172 can also be configured to further cut off electrons around multiple sub-beams. Although Figure 2 Three apertures of the pre-bundle forming mechanism 172 are shown, but it should be understood that any number of apertures may exist as appropriate.

[0045] In some embodiments, the pre-beam forming mechanism 172 may be positioned below the focusing lens 110. Placing the pre-beam forming mechanism 172 closer to the electron source 101 can more effectively reduce the Coulomb effect. In some embodiments, the gun aperture plate 171 may be omitted when the pre-beam forming mechanism 172 can be manufactured close enough to the source 101.

[0046] Objective lens 131 can be configured to focus sub-beams 102_1, 102_2, and 102_3 onto sample 1 for inspection, and can form three probe spots 102_1s, 102_2s, and 102_3s on the surface of sample 1. A gun aperture plate 171 can block unused peripheral electrons in the primary electron beam 102 to reduce Coulomb interaction effects. Coulomb interaction effects can increase the size of each of the probe spots 102_1s, 102_2s, and 102_3s, thus degrading the inspection resolution.

[0047] Beam splitter 160 can be a Wien filter type beam splitter, including generating an electrostatic dipole field E1 and a magnetic dipole field B1 (neither of which is in the...) Figure 2 The electrostatic deflectors (shown in the diagram) are used. If they are applied, the force exerted on the electrons of sub-bundles 102_1, 102_2, and 102_3 by the electrostatic dipole field E1 is equal in amplitude and opposite in direction to the force exerted on the electrons by the magnetic dipole field B1. Therefore, sub-bundles 102_1, 102_2, and 102_3 can pass directly through the beam splitter 160 with zero deflection angle.

[0048] The deflection scanning unit 132 can deflect sub-beams 102_1, 102_2, and 102_3 to scan probe spots 102_1s, 102_2s, and 102_3s over three small scanning regions in a segment of the surface of sample 1. In response to the incident sub-beams 102_1, 102_2, and 102_3 at probe spots 102_1s, 102_2s, and 102_3s, three secondary electron beams 102_1se, 102_2se, and 102_3se can be emitted from sample 1. Each of the secondary electron beams 102_1se, 102_2se, and 102_3se can include electrons with an energy distribution comprising secondary electrons (energy ≤ 50 eV) and backscattered electrons (energys between 50 eV and the landing energies of sub-beams 102_1, 102_2, and 102_3). Beam splitter 160 can guide secondary electron beams 102_1se, 102_2se, and 102_3se to secondary imaging system 150. Secondary imaging system 150 can focus secondary electron beams 102_1se, 102_2se, and 102_3se onto detection elements 140_1, 140_2, and 140_3 of electron detection device 140. Detection elements 140_1, 140_2, and 140_3 can detect the corresponding secondary electron beams 102_1se, 102_2se, and 102_3se, and generate corresponding signals for constructing images of the corresponding scan areas of sample 1.

[0049] exist Figure 2In the secondary imaging system 150, three secondary electron beams 102_1se, 102_2se, and 102_3se, generated by three detector spots 102_1S, 102_2S, and 102_3S respectively, travel upwards along the primary optical axis 100_1 toward the electron source 101, passing successively through the objective lens 131 and the deflection scanning unit 132. The three secondary electron beams 102_1se, 102_2se, and 102_3se are deflected by a beam splitter 160 (such as a Wien filter) to enter the secondary imaging system 150 along the secondary optical axis 150_1. The secondary imaging system 150 focuses the three secondary electron beams 102_1se to 102_3se onto an electron detection device 140 comprising three detection elements 140_1, 140_2, and 140_3. Therefore, the electronic detection device 140 can simultaneously generate images of three scanning areas scanned by three detector spots 102_1S, 102_2S, and 102_3S, respectively. In some embodiments, the electronic detection device 140 and the secondary imaging system 150 form a detection unit (not shown). In some embodiments, the electron optical components (such as, but not limited to, objective lens 131, deflection scanning unit 132, beam splitter 160, secondary imaging system 150, and electronic detection device 140) along the secondary electron beam path can form a detection system.

[0050] In some embodiments, controller 50 ( Figure 1 The controller 50 may include an image processing system comprising an image acquirer (not shown) and a storage device (not shown). The image acquirer may include one or more processors. For example, the image acquirer may include a computer, server, mainframe, terminal, personal computer, any kind of mobile computing device, or combinations thereof. The image acquirer may be communicatively coupled to the electronic detection device 140 of the electron beam tool 40 via a medium such as an electrical conductor, fiber optic cable, portable storage medium, IR, Bluetooth, Internet, wireless network, radio, or combinations thereof. In some embodiments, the image acquirer may receive signals from the electronic detection device 140 and may construct an image. The image acquirer can thus acquire an image of sample 1. The image acquirer may also perform various post-processing functions, such as generating contours, overlaying indicators on the acquired image, etc. The image acquirer may be configured to perform adjustments to the brightness and contrast, etc., of the acquired image. In some embodiments, the storage device may be a storage medium such as a hard disk, flash drive, cloud storage, random access memory (RAM), other types of computer-readable storage, etc. The storage device can be coupled to the image acquirer and can be used to save scanned raw image data as an initial image and to save post-processed images.

[0051] In some embodiments, the image acquirer may acquire one or more images of the sample based on one or more imaging signals received from the electronic detection device 140. The imaging signals may correspond to a scanning operation for imaging charged particles. The acquired image may be a single image comprising multiple imaging regions or may involve multiple images. The single image may be stored in a storage device. The single image may be an initial image that can be divided into multiple regions. Each of these regions may include an imaging region containing features of sample 1. The acquired images may include multiple images sampled multiple times over a time series of a single imaging region of sample 1, or multiple images that may include different imaging regions of sample 1. Multiple images may be stored in a storage device. In some embodiments, the controller 50 may be configured to perform image processing steps on multiple images of the same location of sample 1.

[0052] In some embodiments, the controller 50 may include a measurement circuitry (e.g., an analog-to-digital converter) to obtain the distribution of detected secondary electrons. The electron distribution data collected during the detection time window, combined with the corresponding scan path data of each of the primary sub-beams 102_1, 102_2, and 102_3 incident on the wafer surface, can be used to reconstruct an image of the inspected wafer structure. The reconstructed image can be used to reveal various features of the internal or external structure of sample 1, and thus can be used to reveal any defects that may exist in the wafer.

[0053] In some embodiments, controller 50 may control a motorized stage (not shown) to move sample 1 during examination. In some embodiments, controller 50 may enable the motorized stage to continuously move sample 1 in a certain direction at a constant speed. In other embodiments, controller 50 may enable the motorized stage to change the speed of sample 1 over time depending on the steps of the scanning process. In some embodiments, controller 50 may adjust the configuration of primary projection optics system 130 or secondary imaging system 150 based on images from secondary electron beams 102_1se, 102_2se, and 102_3se.

[0054] although Figure 2 The electron beam tool 40 is shown using three primary electron beams; however, it should be understood that the electron beam tool 40 may use two or more primary electron beams. This disclosure does not limit the number of primary electron beams used in the electron beam tool 40.

[0055] Now for reference Figure 3A , Figure 3AThis is an example comparison of feature locations in an inspection image obtained under neutral charge conditions with reference feature locations. In this disclosure, a neutral charge condition can refer to a sample state during inspection in which primary electrons incident on the sample are balanced with secondary electrons emitted from the sample, thus preventing charge accumulation on the sample. A feature can refer to a pattern or structure formed on the sample. Figure 3A In this context, a charged particle beam inspection system (e.g., Figure 1 An electron beam inspection system 100 obtains a first inspection image 300. For example, the first inspection image 300 may be an electron beam image generated based on an electron detection signal from an electron detection device 140. The first inspection image 300 may be an inspection image of the sample including multiple features. Figure 3A In the first inspected image 300, the location 301 of the feature is represented by a circle. It should be understood that, for simplification purposes, in... Figure 3A The first inspection image 300 does not show a pattern indicating features.

[0056] Figure 3A Reference locations 302 (e.g., represented as squares) of features superimposed on the inspection image 300 are also shown. According to embodiments of this disclosure, reference locations 302 of features on a sample can be obtained from a reference image corresponding to the sample. In some embodiments, the reference image may be a ground truth image of the sample. The ground truth image may include an original image of a wafer or die containing a corresponding pattern, or may include a ground truth wafer image measured from a wafer or die containing a corresponding pattern. In some embodiments, the reference image may include a wafer design layout corresponding to the sample, such as in Graphical Database System (GDS) format, Graphical Database System II (GDSII) format, Open Artwork System Interchange Standard (OASIS) format, Caltech Intermediate Format (CIF), etc. The wafer design layout may be based on a pattern layout used to construct the wafer. In some embodiments, the reference image, etc., may include feature information (representing planar geometry, text, and other information related to the wafer design layout) stored in a binary file format. Figure 3A As shown, when the sample is inspected under neutral charge conditions, the position 301 of the feature on the first inspection image 300 matches the reference position 302 of the feature in the reference image.

[0057] However, when examining samples under charge accumulation conditions such as negative or positive charge conditions, the examination images may be distorted. In this disclosure, a negative charge condition can refer to a sample state during examination in which the amount of primary electrons incident on the sample is greater than the amount of secondary electrons emitted from the sample, thus accumulating negative charge on the sample. Similarly, a positive charge condition can refer to a sample state during examination in which the amount of primary electrons incident on the sample is less than the amount of secondary electrons emitted from the sample, thus accumulating positive charge on the sample.

[0058] like Figure 3B As shown, Figure 3B An example comparison of feature locations in an inspection image under negative charge conditions with reference feature locations is shown, and the second inspection image 310 obtained under negative charge conditions can be extended. Figure 3B In the second inspected image 310, the distance between two locations (e.g., d1) of a feature at location 311 is greater than the reference distance (e.g., d2) between two reference locations 302 of the corresponding feature. Figure 3C As shown, Figure 3C An example comparison of feature locations in an inspection image under positive charge conditions with reference feature locations is shown. The third inspection image 320 obtained under positive charge conditions can be scaled down. For example... Figure 3C As shown, the distance between two locations (e.g., d1) of the feature positions 321 on the third inspection image 320 is less than the reference distance (e.g., d2) between two reference locations 302 of the corresponding feature. Although image expansion and image contraction are discussed in this disclosure as types of distortion that occur due to charge accumulation on the sample (e.g., as... Figure 3B , Figure 3C and Figure 6 (as shown), but it should be understood that different types of distortion can also occur due to charge accumulation, such as defocusing, pattern shape distortion (e.g., pincushion or asymmetric trapezoidal distortion), etc.

[0059] Such as about Figures 3A to 3C As explained, charge accumulation on the sample can be used to bend the electron beam scanning the sample, leading to significant distortion of feature locations or displacements in the inspection image. This distortion can cause errors in detecting critical dimensions, edge displacements, etc., from the inspection image. Embodiments of this disclosure can provide techniques for determining a landing energy that enables the balancing of charges on the sample, thereby providing more accurate SEM images.

[0060] Figure 4 This is a block diagram of an example image enhancement device 400 according to an embodiment of the present disclosure. It should be understood that, in various embodiments, the image enhancement device 400 may be a charged particle beam inspection system (e.g., Figure 1The image enhancement device 400 may be part of the electron beam inspection system 100 or may be separate from the charged particle beam inspection system. In some embodiments, the image enhancement device 400 may be part of the controller 50 and may include an image acquisition unit, a measurement circuit system, or a storage device, etc. In some embodiments, the image enhancement device 400 may include an image processing system and may include an image acquisition unit, a storage device, etc.

[0061] like Figure 4 As shown, the image enhancement device 400 may include a test image acquirer 410, a test image analyzer 420, an inspection condition controller 430, and an inspection image acquirer.

[0062] According to embodiments of this disclosure, a test image acquirer 410 is configured to receive multiple test images. The test images may be inspection images of a sample region. Multiple test images may be acquired at different landing energies. In some embodiments, multiple test images may be acquired for different test regions of the sample. For example, multiple test regions may be selected for testing, and a corresponding test image may be acquired for each test region. In some embodiments, multiple test images for different test regions of the sample may be acquired simultaneously (e.g., via multi-beam SEM). In this case, the test regions for multiple test images may be spaced apart, such that one test region is not affected by the electron beams used for other test regions during testing. In some other embodiments, multiple test images may be acquired sequentially for a region of the sample. In some embodiments, the test image acquirer 410 may generate test images based on detection signals from the electron detection device 140 of the electron beam tool 40. In some embodiments, the test image acquirer 410 may be part of an image acquirer included in the controller 50 or may be detached from the image acquirer. In some embodiments, the test image acquirer 410 may acquire test images generated by an image acquirer included in the controller 50. In some embodiments, the test image acquirer 410 may obtain test images from a storage device or system storing test images. In some embodiments, to reduce processing time and resources, test images may be obtained for a small portion of the sample.

[0063] According to embodiments of this disclosure, a test area on a sample can be selected such that image distortion, such as image expansion or image contraction, can be measured from the corresponding test image. Figure 5 An example of a test area 501 on a sample 500 according to an embodiment of the present disclosure is shown. Figure 5 As shown, the test area 501 may include multiple features 502, and the center 503 of the test area 501 is also indicated for illustrative purposes. Although Figure 5Features 502 arranged in a regular pattern are shown; however, it should be understood that features 502 included in the test area 501 may not be arranged in a regular pattern. Similarly, features 502 included in the test area 501 may have different shapes, even if... Figure 5 Features 502 with the same shape are shown. In some embodiments, the area of ​​the test region 501 may correspond to the field of view of the primary electron beam (e.g., sub-beams 102_1, 102_2, or 102_3). Selecting a region having multiple features 502 as the test region 501 is one of several ways to measure image distortion (e.g., image expansion or image extraction) of the test image based on feature displacement. In some embodiments, the sample may include a region designed or designated as the test region and comprising multiple features 502, which is advantageous in determining the distortion level of the test image from it.

[0064] When multiple test images are obtained for different test regions of sample 500, multiple test regions on different portions of sample 500 can be selected for the multiple test images. Similarly, each test region among the multiple test regions may have multiple features (e.g., 502). In some embodiments, selecting multiple test regions with similar patterns or features may be advantageous in comparing displacement measurements (e.g., distortion levels) of multiple test images corresponding to the multiple test regions. In some embodiments, the sample may include multiple regions designed or designated as test regions and including multiple features 502 having the same shape as each other, which is advantageous in comparing distortion levels of test images from these regions. In some embodiments, the multiple regions may include features at the same relative position in each region. In some embodiments, the distance between two adjacent test regions may be large enough that one test region is not affected by the primary electron beam used for the other test region during testing.

[0065] Return to reference Figure 4The test image analyzer 420 is configured to determine whether the test image 501 is distorted and to measure the amount of distortion. According to embodiments of this disclosure, the test image analyzer 420 can analyze the test image by referring to a reference image corresponding to the test image. According to embodiments of this disclosure, the information file 440 may contain a reference image corresponding to the test image. The information file 440 can be any means of storing information, such as a file, file set, database, database set, etc. The information file 440 may, for example, include a reference image of a test area for the test image. In some embodiments, the reference image included in the information file 440 may be a ground truth image of the corresponding test area. The ground truth image may include an original image of a wafer or die containing a corresponding pattern, or may include a ground truth wafer image measured from a wafer or die containing a corresponding pattern, etc. In some embodiments, the reference image included in the information file 440 may be in Graphics Database System (GDS) format, Graphics Database System II (GDS II) format, Open Art System Interchange Standard (OASIS) format, Caltech Intermediate Format (CIF), etc. In some embodiments, the reference image included in the information file 440 may include a wafer design layout of the corresponding test area. Wafer design layout can be based on a pattern layout used to construct the wafer. The wafer design layout can correspond to one or more photomasks or stencils used to transfer features from a photomask or stencil to the wafer. In some embodiments, a reference image such as GDS or OASIS may include feature information stored in a binary file format, representing planar geometry, text, and other information related to the wafer design layout.

[0066] For the purposes of explanation and simplification, Figures 3A to 3C The inspection images 300, 310, and 320 are used to explain the operation of the test image analyzer 420 under the assumption that they are test images. Regarding Figure 3A Assume that position 301 is a feature position on the first inspected image 300, and reference position 302 is a corresponding feature position on a first reference image corresponding to the first inspected image 300. Figure 3A As shown, the position 301 of a feature on the first inspection image 300 matches the corresponding reference position 302 of the feature. In this example, the test image analyzer 420 can determine that the first inspection image 300 is not distorted.

[0067] about Figure 3B Assume that position 311 is a feature position on the second test image 310, and reference position 302 is a corresponding feature position on a second reference image corresponding to the second test image 310. Figure 3BAs shown, the position 311 of the feature on the second test image 310 does not match the corresponding reference position 302 of the feature, therefore the test image analyzer 420 can determine that the second test image 310 is distorted. In some embodiments, based on a comparison of feature distances on the second test image 310 and the second reference image, the test image analyzer 420 can determine whether the second test image 310 has been expanded or reduced. For example, the test image analyzer 420 can compare a first distance d1 between two feature positions 311 on the second test image 310 with a second distance d2 between two reference feature positions 302 corresponding to the two feature positions 311 on the second reference image. In this example, since the first distance d1 is greater than the second distance d2, the test image analyzer 420 can determine that the second test image 310 has been expanded.

[0068] In some embodiments, the test image analyzer 420 can determine the amount of distortion based on the distance between a feature location 311 on the second test image 310 and a reference feature location 302 corresponding to that feature. For example... Figure 3B As shown, the amount of distortion can be determined based on a third distance d3 between the center of feature location 311 on the second test image 310 and the corresponding reference feature location 302. In some embodiments, because the absolute distortion can be as follows: Figure 3B The distortion amount (e.g., d3) of feature position 321 at a standard position (e.g., a distance from the center) of the second test image 310, varying according to feature position 311 on the second test image 310, can be used as the distortion amount. In some embodiments, if no feature exists at the standard position, the distortion amount can be estimated based on the measured distortion amount of feature position 311 in the second test image 310. Thus, a sufficient comparison between the distortion amounts of multiple test images can be obtained. In some embodiments, the distortion amount for the second test image 310 can be determined based on the average of the displacement amounts (e.g., a third distance d3) for multiple features in the second test image 310. In this example, the test image analyzer 420 can determine that the second test image 310 is distorted (e.g., expanded) and the distortion amount corresponds to the third distance d3 or the average of the displacement amounts for features in the second test image 310.

[0069] about Figure 3C Assume that position 321 is a feature position on the third inspection image 320, and reference position 302 is the corresponding feature position on the third reference image corresponding to the third inspection image 320. Figure 3CAs shown, the position 321 of the feature on the third inspection image 320 does not match the corresponding reference position 302 of the feature, therefore the test image analyzer 420 can determine that the third inspection image 320 is distorted. In some embodiments, based on a comparison of feature distances on the third inspection image 320 and the third reference image, the test image analyzer 420 can determine whether the third inspection image 320 has been expanded or shrunk. For example, the test image analyzer 420 can compare a first distance d1 between two feature positions 321 on the third inspection image 320 with a second distance d2 between two reference feature positions 302 on the third reference image corresponding to the two feature positions 321. In this example, since the first distance d1 is less than the second distance d2, the test image analyzer 420 can determine that the third inspection image 320 has been shrunk.

[0070] In some embodiments, the test image analyzer 420 can determine the amount of distortion based on the distance between a feature location 321 on the third inspection image 320 and a reference feature location 302 corresponding to that feature. For example... Figure 3C As shown, the amount of distortion can be determined based on a third distance d3 between the center of feature position 321 on the third inspection image 320 and the corresponding reference feature position 302. In some embodiments, because the absolute distortion can be as follows: Figure 3C The distortion amount (e.g., d3) of the feature position 321 at a standard position (e.g., a distance from the center) of the third inspection image 320, varying according to the feature position 321 on the third inspection image 320, can be used as the distortion amount. In some embodiments, if no feature is present at the standard position, the distortion amount can be estimated based on the measured distortion amount of the feature position 321 in the third inspection image 320. Therefore, a sufficient comparison between the distortion amounts of multiple test images can be obtained. In some embodiments, the distortion amount for the third inspection image 320 can be determined based on the average of the displacement amounts (e.g., third distance d3) for multiple features in the third inspection image 320. In this example, the test image analyzer 420 can determine that the third inspection image 320 is distorted (e.g., shrunken) and the distortion amount corresponds to the third distance d3 or the average of the displacement amounts for features in the third inspection image 320.

[0071] Although the determination of the test image has been explained by aligning the test image with the reference image so that the centers of the test image and the reference image match (e.g., Figures 3A to 3C The distortion level is 300, 310, or 320, but it should be understood that any method used to determine the distortion level can be applied to embodiments of this disclosure. Figure 6 An example method for measuring distortion levels according to embodiments of this disclosure is shown. Figure 6As shown, the amount of distortion can be analyzed and determined by aligning the test image 610 and the corresponding reference image so that the feature position 611 at a corner (e.g., the upper left corner) of the test image 610 matches the corresponding feature position 302 on the reference image. In this example, the distortion can be analyzed and determined based on another corner (e.g., the corner diagonally opposite to the first corner) of the test image 610. Figure 6 The third distance d3 between the center of feature position 611 (lower right corner) and the center of the corresponding reference feature position 302 is used to determine the amount of distortion. Although Figure 6 An example method for measuring the distortion level of a test image 610 obtained under negative charge conditions is shown; however, it should be noted that the same method can be applied to measure the distortion level of test images obtained under positive charge conditions or neutral charge conditions.

[0072] As described above, the test image analyzer 420 is configured to analyze a plurality of test images acquired by the test image acquirer 410. According to embodiments of the present disclosure, based on a determined distortion trend (e.g., expansion or contraction) and a distortion amount (e.g., displacement), the test image analyzer 420 is configured to determine the landing energy that enables the sample to be in a neutral charge condition during inspection. Figure 7 This is an example graph 700, according to embodiments of the present disclosure, used to identify landing energies corresponding to neutral charge conditions. Figure 7 In this context, the landing energy is represented by the voltage V applied to the primary electron beam, for example, to accelerate or decelerate the electron beam during testing. Because electrons have a constant charge value, the voltage applied to the electrons can be an indication of the electron energy when the electrons land on the sample.

[0073] like Figure 7 As shown, test results T1 to T7 are illustrated in graph 700. In this example, test results T1 to T7 can be obtained by test image analyzer 420 from seven test images (e.g., Figure 3B or Figure 3C The amount of distortion determined by the test image (310 or 320). For example, the first, second, third, and seventh test results T1, T2, T3, and T7 can be obtained from the test image (310 or 320). Figure 3B The second test image 310 is similar to four other test images, where test results T1, T2, T3, and T7 indicate image expansion. Similarly, the fourth, fifth, and sixth test results T4, T5, and T6 can be obtained from the image expansion. Figure 3C The third inspection image 320 is obtained from three similar test images, where test results T4, T5, and T6 indicate image shrinkage. For example... Figure 7As shown, each test result T1 to T7 is located in graph 700 according to its corresponding landing energy and distortion. For example, the first test result T1 represents the distortion of the test image obtained with a landing energy of 300V. Similarly, the second to seventh test results T2 to T7 are shown in graph 700. In some embodiments, when test results T1 to T7 are obtained from test images for different test areas, the distortion for each test result T1 to T7 on graph 700 can be a normalized value or distortion at a standard location to allow for fair comparison between test results T1 to T7. Although Figure 7 Seven test results are shown, but it should be understood that any number of test results can be applied to the embodiments of this disclosure.

[0074] It may be impossible to obtain undistorted test images (e.g., Figure 3A The first inspection image 300). According to embodiments of the present disclosure, the test image analyzer 420 is configured to determine, based on test results (e.g., T1 to T7), the landing energy (also referred to as the neutral landing energy in this disclosure) that enables the sample to be in a neutral charge condition during inspection. In some embodiments, the test image analyzer 420 can estimate the neutral landing energy by interpolating the curves of the test results (e.g., T1 to T7) on a graph 700. For example, the interpolation line L1 connecting the test results T1 to T7 can be as follows: Figure 7 The definition is shown, and the neutral landing energy E1 or E2 can be obtained at the intersection of the interpolation line L1 and the neutral charge condition line L2, which is a horizontal line indicating zero displacement. In this example, the two landing energies E1 and E2 are estimated as the neutral landing energies for the sample.

[0075] Return to reference Figure 4 According to embodiments of the present disclosure, the inspection condition controller 430 is configured to set inspection conditions for inspecting a sample based on determinations made by the test image analyzer 420. According to embodiments of the present disclosure, the inspection conditions may include the landing energy of the primary electron beam used to inspect the sample. The neutral landing energy (e.g., E1 or E2) may be a material or property-specific parameter, so a neutral landing energy determined from a portion of the sample (e.g., the test area) can be used to inspect the entire sample. In some embodiments, the neutral landing energy determined for a sample having a certain material can also be used to inspect another sample having the same material. In some embodiments, the inspection condition controller 430 may set the landing energy for inspecting the sample to a neutral landing energy E1 or E2 determined by the test image analyzer 420, which makes it possible to avoid charge accumulation on the sample.

[0076] In some embodiments, such as due to inspection requirements, constraints, etc., the landing energy may not be allowed to be set to a neutral landing energy E1 or E2. For example, the landing energy may not be set above a certain level because the sample may be damaged starting from an electron beam with a higher energy level. The landing energy may not be set below a certain level because the secondary electron beam may not be emitted sufficiently at a lower energy level. Alternatively, to obtain an inspection image with the desired resolution, the landing energy may not be set below a certain level. Therefore, in some embodiments, the landing energy used to inspect the sample may be set close to a neutral landing energy E1 or E2. In addition to controlling the landing energy of the primary electron beam, the inspection condition controller 430 may also perform inspection tool calibration to suppress or compensate for charging on the sample during inspection. For example, other inspection conditions, such as the primary beam dose on the sample, may also be adjusted.

[0077] According to embodiments of this disclosure, the inspection image acquirer 450 can acquire inspection images of a sample. Inspection images can be acquired using a landing energy set by the inspection condition controller 430. In some embodiments, the inspection image acquirer 450 can generate inspection images of the sample based on a detection signal from the electron detection device 140 of the electron beam tool 40. In some embodiments, the inspection image acquirer 450 may be part of an image acquirer included in the controller 50 or may be detached from that image acquirer. In some embodiments, the inspection image acquirer 450 can acquire inspection images generated by an image acquirer included in the controller 50. In some embodiments, the inspection image acquirer 450 may obtain inspection images from a storage device or system storing inspection images.

[0078] As mentioned above, due to inspection requirements, constraints, etc., it may not be permissible to set the landing energy to a neutral landing energy E1 or E2, or the estimated neutral landing energy E1 or E2 may be inaccurate. Therefore, during inspection with a landing energy set by the inspection condition controller 430, charge may still accumulate on the sample, and the inspection image obtained from it may still be distorted.

[0079] According to embodiments of this disclosure, the image enhancement device 400 may further include, for example, Figure 4 The image corrector 460 is shown. The image corrector 460 can be configured to perform image correction to compensate for charge accumulation effects. In some embodiments, the image corrector 460 can correct the examination image by referring to a reference image corresponding to the examination image of the sample. For example, the image corrector 460 can compare the reference image included in the information file 440 with the examination image acquired by the examination image acquirer 450 and correct errors in the examination image. In some embodiments, the reference image can be an image of the entire sample.

[0080] In some other embodiments, the image corrector 460 can correct the inspection image by applying a predetermined offset to the inspection image. The predetermined offset can be obtained from multiple experiments. In some embodiments, multiple experimental inspection images can be obtained using the landing energy set by the inspection condition controller 430, and the amount of error (e.g., distortion or displacement) for each experimental inspection image can be determined, for example, by comparison with a reference image. The offset can be determined based on the average of the amount of error for multiple experimental inspections. In some embodiments, to reduce processing time and resources, each experimental inspection image can be obtained for a small portion of the sample. In some embodiments, multiple experimental inspection images can be obtained simultaneously, similar to test images. In some embodiments, multiple test regions used for testing can also be used for multiple experimental inspection images.

[0081] According to embodiments of the present disclosure, the operation of the image enhancement device 400 can be automated. According to embodiments of the present disclosure, for example, when image processing time and resources for test image analysis or experimental inspection image analysis are sufficiently limited, identifying the neutral landing energy for a sample, inspecting the sample using landing energy based on the neutral landing energy, and correcting the inspection image obtained therefrom can be performed in real time.

[0082] Figure 8 This is a processing flowchart illustrating an example method for enhancing images in a multi-beam inspection system according to embodiments of the present disclosure. For illustrative purposes, reference will be made to... Figure 4 The image enhancement device 400 describes a method for enhancing images.

[0083] In step S810, multiple test images can be obtained (e.g., Figures 3A to 3C (e.g., 300, 310, or 320). Step S810 can be performed by, for example, a test image acquirer 410. The test image can be an inspection image of a region of the sample. Multiple test images can be acquired at different landing energies. In some embodiments, multiple test images can be acquired simultaneously for different test regions of the sample (e.g., via multi-beam SEM). In this case, the test regions for multiple test images can be spaced apart so that one test region is not affected by the electron beams used for other test regions during testing. In some other embodiments, multiple test images can be acquired sequentially for a region of the sample at different times. In some embodiments, to reduce processing time and resources, test images can be acquired for a small portion of the sample.

[0084] According to embodiments of this disclosure, a test area on a sample can be selected such that image distortion (e.g., image expansion or image contraction) is measured from its corresponding test image. Figure 5An example of a test area 501 on a sample 500 according to an embodiment of the present disclosure is shown. Figure 5 As shown, the test area 501 may include multiple features 502, and the center 503 of the test area 501 is also indicated for illustrative purposes. Although Figure 5 Features 502 arranged in a regular pattern are shown; however, it should be understood that features 502 included in the test area 501 may not be arranged in a regular pattern. Similarly, features 502 included in the test area 501 may have different shapes, even if... Figure 5 Features 502 with the same shape are shown. In some embodiments, the area of ​​the test region 501 may correspond to the field of view of the primary electron beam (e.g., sub-beams 102_1, 102_2, or 102_3). Selecting a region having multiple features 502 as the test region 501 is one of several ways to measure image distortion (e.g., image expansion or image extraction) of the test image based on feature displacement. In some embodiments, the sample may include a region designed or designated as the test region and comprising multiple features 502, which is advantageous in determining the distortion level of the test image from it.

[0085] When multiple test images are obtained for different test areas of sample 500, multiple test areas on different portions of sample 500 can be selected for the multiple test images. Similarly, each of the multiple test areas can have multiple features (e.g., 502). In some embodiments, the sample may include multiple areas designed as test areas and including multiple features 502 having the same shape as each other, which is advantageous in comparing the distortion levels of test images from these areas. In some embodiments, the multiple areas may include features at the same relative position in each area. In some embodiments, selecting multiple test areas with similar patterns or features can be advantageous in comparing displacement measurements from multiple test images corresponding to the multiple test areas.

[0086] In step S820, the acquired test image is analyzed. Step S820 can be performed by, for example, a test image analyzer 420. In step S820, the distortion level (e.g., distortion trend, distortion amount, etc.) can be determined. According to embodiments of this disclosure, the test image can be analyzed by referring to a reference image corresponding to the test image. In some embodiments, the reference image can be a ground truth image of the corresponding test area. The ground truth image can include an original image of a wafer or die containing the corresponding pattern, or it can include a ground truth wafer image measured from a wafer or die containing the corresponding pattern, etc. In some embodiments, the reference image can be in Graphics Database System (GDS) format, Graphics Database System II (GDS II) format, Open Art System Interchange Standard (OASIS) format, Caltech Intermediate Format (CIF), etc. In some embodiments, the reference image can include a wafer design layout of the corresponding test area. The wafer design layout can be based on a pattern layout used to construct the wafer. The wafer design layout can correspond to one or more photomasks or stencils used to transfer features from a photomask or stencil to the wafer. In some embodiments, a reference image such as GDS or OASIS may include feature information stored in a binary file format, which represents planar geometry, text, and other information related to the wafer design layout.

[0087] For the purposes of explanation and simplification, Figures 3A to 3C The inspection images 300, 310, and 320 are interpreted under the assumption that they are test images in step S820. For example... Figure 3A As shown, the position 301 of the feature on the first inspection image 300 corresponds to the reference position 302 of the feature. In this example, it will be determined that the first inspection image 300 is not distorted.

[0088] like Figure 3B As shown, the position 311 of a feature on the second inspection image 310 does not match the corresponding reference position 302 of the feature, therefore the second inspection image 310 is determined to be distorted. In some embodiments, it is determined whether the second inspection image 310 has been expanded or shrunk based on a comparison of feature distances on the second inspection image 310 and the second reference image. For example, a first distance d1 between two feature positions 311 on the second inspection image 310 can be compared with a second distance d2 between two reference feature positions 302 corresponding to the two feature positions 311 on the second reference image. In this example, since the first distance d1 is greater than the second distance d2, it is determined that the second inspection image 310 has been expanded.

[0089] In some embodiments, the amount of distortion can be determined based on the distance between a feature location 311 on the second inspected image 310 and a reference feature location 302 corresponding to that feature. For example... Figure 3BAs shown, the amount of distortion can be determined based on a third distance d3 between the center of feature position 311 on the second inspection image 310 and the corresponding reference feature position 302. In some embodiments, because the absolute amount of distortion can be as follows: Figure 3B The distortion amount (e.g., d3) of feature position 321 at a standard position (e.g., a distance from the center) of the second inspection image 310, varying according to feature position 311 on the second inspection image 310, can be used as the distortion amount. In some embodiments, if no feature is present at the standard position, the distortion amount can be estimated based on the measured distortion amount of feature position 311 in the second inspection image 310. Therefore, a sufficient comparison between the distortion amounts of multiple test images can be obtained. In some embodiments, the distortion amount for the second inspection image 310 can be determined based on the average of the displacement amounts (e.g., a third distance d3) for multiple features in the second inspection image 310. In this example, the distortion (e.g., expansion) of the second inspection image 310 will be determined, and the distortion amount corresponds to the third distance d3 or the average of the displacement amounts for features in the second inspection image 310.

[0090] like Figure 3C As shown, the position 321 of a feature on the third inspection image 320 does not match the corresponding reference position 302 of the feature, therefore the third inspection image 320 is determined to be distorted. In some embodiments, it is determined whether the third inspection image 320 has been expanded or shrunk based on a comparison of feature distances on the third inspection image 320 and the third reference image. For example, a first distance d1 between two feature positions 321 on the third inspection image 320 can be compared with a second distance d2 between two reference feature positions 302 on the third reference image corresponding to the two feature positions 321. In this example, since the first distance d1 is less than the second distance d2, it is determined that the third inspection image 320 has been shrunk.

[0091] In some embodiments, the amount of distortion can be determined based on the distance between a feature location 321 on the third inspected image 320 and a reference feature location 302 corresponding to that feature. For example... Figure 3C As shown, the amount of distortion can be determined based on a third distance d3 between the center of feature position 321 on the third inspection image 320 and the corresponding reference feature position 302. In some embodiments, because the absolute distortion can be as follows: Figure 3CThe distortion amount (e.g., d3) of the feature position 321 at a standard position (e.g., a distance from the center) in the third inspection image 320, varying according to the feature position 321 on the third inspection image 320, can be used as the distortion amount. In some embodiments, if no feature is present at the standard position, the distortion amount can be estimated based on the measured distortion amount of the feature position 321 in the third inspection image 320. Therefore, a sufficient comparison between the distortion amounts of multiple test images can be obtained. In some embodiments, the distortion amount for the third inspection image 320 can be determined based on the average of the displacement amounts (e.g., a third distance d3) for multiple features in the second inspection image 320. In this example, the distortion (e.g., shrinkage) of the third inspection image 320 will be determined, and the distortion amount corresponds to the third distance d3 or the average of the displacement amounts for features in the third inspection image 320.

[0092] Although the determination of the test image has been explained by aligning the test image with the reference image so that the centers of the test image and the reference image match (e.g., Figures 3A to 3C The distortion levels (300, 310, and 320) are specified, but it should be understood that any method used to determine the distortion levels can be applied to embodiments of this disclosure. Figure 6 An example method for measuring distortion levels according to embodiments of this disclosure is shown. Figure 6 As shown, the amount of distortion can be analyzed and determined by aligning the test image 610 and the corresponding reference image so that the feature position 611 at a corner (e.g., the upper left corner) of the test image 610 matches the corresponding feature position 302 on the reference image. In this example, the distortion can be analyzed and determined based on another corner (e.g., the corner diagonally opposite to the first corner) of the test image 610. Figure 6 The third distance d3 between the center of feature position 611 (lower right corner) and the center of the corresponding reference feature position 302 is used to determine the amount of distortion. Although Figure 6 An example method for measuring the distortion level of a test image 610 obtained under negative charge conditions is shown; however, it should be noted that the same method can be applied to measure the distortion level of test images obtained under positive charge conditions or neutral charge conditions.

[0093] Figure 7 This is an example graph 700 illustrating the landing energy corresponding to a neutral charge condition, according to embodiments of the present disclosure. Figure 7 In this method, the landing energy is represented by the voltage V applied to the primary electron beam, for example, to accelerate or decelerate the electron beam during testing. Because electrons have a constant charge value, the voltage applied to the electrons can be an indication of the electron energy when the electrons land on the sample.

[0094] like Figure 7As shown, the test results T1 to T7 are illustrated in graph 700. In this example, the test results T1 to T7 can be distortion values. Figure 7 As shown, each test result T1 to T7 is located in graph 700 according to its corresponding landing energy and distortion. In some embodiments, when test results T1 to T7 are obtained from test images for different test areas, the distortion for each test result T1 to T7 on graph 700 can be a normalized value or distortion at a standard location to allow for fair comparison between test results T1 to T7. According to embodiments of this disclosure, in step S820, the landing energy (also referred to as the neutral landing energy in this disclosure) that enables the sample to be in a neutral charge condition during inspection can be determined based on the test results (e.g., T1 to T7). In some embodiments, the neutral landing energy can be estimated by interpolating the curves of the test results (e.g., T1 to T7) on graph 700. For example, the interpolation line L1 connecting test results T1 to T7 can be as follows: Figure 7 The definition is shown, and the neutral landing energy E1 or E2 can be obtained at the intersection of the interpolation line L1 and the neutral charge condition line L2, which is a horizontal line indicating zero displacement. In this example, the two landing energies E1 and E2 are estimated as the neutral landing energies for the sample.

[0095] Return to reference Figure 8 In step S830, the inspection conditions for examining the sample can be controlled based on the analysis in step S820. Step S830 can be performed by, for example, an inspection condition controller 430. According to embodiments of this disclosure, the inspection conditions may include the landing energy of the primary electron beam used to examine the sample. The neutral landing energies (e.g., E1 and E2) may be material or property-specific parameters, and therefore the neutral landing energies determined from some portions of the sample (e.g., the test area) can be used to examine the entire sample. In some embodiments, the neutral landing energies determined for a sample having a certain material can also be used to examine another sample having the same material. In some embodiments, the landing energy used to examine the sample can be set to the neutral landing energy E1 or E2 determined in step S820, which makes it possible to avoid charge accumulation on the sample.

[0096] In some embodiments, such as due to inspection requirements, constraints, etc., setting the landing energy to a neutral landing energy E1 or E2 may not be permitted. Therefore, in some embodiments, the landing energy used to inspect the sample may be set to be close to a neutral landing energy E1 or E2. Furthermore, in addition to controlling the landing energy of the primary electron beam, inspection tool calibration may be performed to suppress or compensate for charging on the sample during inspection. For example, other inspection conditions, such as the primary beam dose on the sample, may also be adjusted.

[0097] In step S840, an inspection image of the sample can be acquired. Step S8740 can be performed by, for example, an inspection image acquisition device 450. The inspection image can be acquired using the landing energy set in step S830.

[0098] As mentioned above, due to inspection requirements, constraints, etc., it may not be permissible to set the landing energy to a neutral landing energy E1 or E2, or the estimated neutral landing energy E1 or E2 may be inaccurate. Therefore, during inspection with the landing energy set in step S830, charge may still accumulate on the sample, and the inspection image obtained from it may still be distorted.

[0099] According to embodiments of this disclosure, the method may further include step S850. In step S850, image correction may be performed to compensate for charge accumulation effects. In some embodiments, the examination image may be corrected by referring to a reference image corresponding to the examination image of the sample. For example, the reference image may be compared with the examination image obtained in step S840, and errors on the examination image may be corrected based on this comparison. Here, the reference image may be an image of the entire sample.

[0100] In some embodiments, the examination image can be corrected by applying a predetermined offset to the examination image. The predetermined offset can be obtained from multiple experiments. In some embodiments, multiple experimental examination images can be obtained using the landing energy set in step S830, and the amount of error (e.g., distortion or displacement) for each experimental examination image can be determined, for example, by comparing it with a reference image. The offset can be determined based on the average of the error amounts for multiple experimental examinations. In some embodiments, to reduce processing time and resources, each experimental examination image can be obtained for a small subset of the sample.

[0101] The aspects of this disclosure are set forth in the following numbered clauses:

[0102] 1. A method for enhancing an inspection image in a charged particle beam inspection system, the method comprising:

[0103] Acquire multiple test images of samples obtained at different landing energies;

[0104] Determine the distortion level of multiple test images;

[0105] Based on the distortion level, determine the landing energy level that allows the sample to be under neutral charge conditions during the inspection; and

[0106] Based on the determined landing energy level, acquire inspection images.

[0107] 2. The method according to Clause 1 also includes:

[0108] The inspection image is corrected based on a reference image corresponding to the inspection image.

[0109] 3. The method according to Clause 1 or 2, wherein each of the plurality of test images of the acquired sample corresponds to a test area among the plurality of test regions of the sample.

[0110] 4. The method according to any one of clauses 1 to 3, wherein determining the distortion level of the plurality of test images comprises: determining a first distortion level of the first test image based on a first reference image corresponding to a first test image among the plurality of test images.

[0111] 5. The method according to Clause 4, wherein the first distortion level includes information indicating whether the first test image is expanded or shrunken.

[0112] 6. The method according to Clause 4, wherein the first distortion level includes a first distortion amount based on the displacement between a feature on the first test image and a corresponding feature on the first reference image.

[0113] 7. The method according to any one of clauses 1 to 6, wherein determining the landing energy level that enables the sample to be in a neutral charge condition includes: estimating the landing energy level that enables the amount of distortion to be zero based on the level of distortion.

[0114] 8. The method according to Clause 4, wherein the determination of the first distortion level is based on a comparison between a first distance between two features on the first test image and a second distance between corresponding two features on the first reference image.

[0115] 9. The method according to Clause 3, wherein each of the multiple test regions includes multiple features.

[0116] 10. The method according to Clause 1 further includes: correcting the inspection image by applying a predetermined offset to the inspection image.

[0117] 11. The method according to Clause 10, wherein the predetermined offset is determined based on the amount of error of an experimentally examined image obtained based on a determined landing energy level corresponding to a portion of the sample.

[0118] 12. An image enhancement device, comprising:

[0119] Memory, storing instruction sets; and

[0120] At least one processor is configured to execute a set of instructions to cause the device to perform:

[0121] Acquire multiple test images of samples obtained at different landing energies;

[0122] Determine the distortion level of multiple test images;

[0123] Based on the distortion level, determine the landing energy level that allows the sample to be under neutral charge conditions during the inspection; and

[0124] Based on the determined landing energy level, acquire inspection images.

[0125] 13. A device according to Clause 12, wherein at least one processor is configured to execute a set of instructions to cause the device to perform further actions:

[0126] The inspection image is corrected based on a reference image corresponding to the inspection image.

[0127] 14. The device according to Clause 12 or 13, wherein each of the plurality of test images of the acquired sample corresponds to a test area among the plurality of test areas of the sample.

[0128] 15. The device according to any one of clauses 12 to 14, wherein determining the distortion level of a plurality of test images comprises: determining a first distortion level of the first test image based on a first reference image corresponding to a first test image among the plurality of test images.

[0129] 16. The device according to Clause 15, wherein the first distortion level includes information indicating whether the first test image is expanded or contracted.

[0130] 17. The device according to Clause 15, wherein the first distortion level includes a first distortion amount based on the displacement between a feature on a first test image and a corresponding feature on a first reference image.

[0131] 18. The apparatus according to any one of clauses 13 to 17, wherein determining the landing energy level that enables the sample to be in a neutral charge condition includes: estimating the landing energy level that enables the amount of distortion to be zero based on the level of distortion.

[0132] 19. A non-transient computer-readable medium storing an instruction set executable by at least one processor of a computing device to perform a method for enhancing an image, the method comprising:

[0133] Acquire multiple test images of samples obtained at different landing energies;

[0134] Determine the distortion level of multiple test images;

[0135] Based on the distortion level, determine the landing energy level that allows the sample to be under neutral charge conditions during the inspection; and

[0136] Based on the determined landing energy level, acquire inspection images.

[0137] 20. A computer-readable medium pursuant to Clause 19, wherein the instruction set is executable by at least one processor of a computing device to further perform:

[0138] The inspection image is corrected based on a reference image corresponding to the inspection image.

[0139] 21. A computer-readable medium pursuant to Clause 19 or 20, wherein each of a plurality of test images of the obtained sample corresponds to a test area among a plurality of test areas of the sample.

[0140] 22. A computer-readable medium according to any one of clauses 19 to 21, wherein determining the distortion level of a plurality of test images comprises: determining a first distortion level of the first test image based on a first reference image corresponding to a first test image among the plurality of test images.

[0141] 23. The computer-readable medium pursuant to Clause 22, wherein the first distortion level includes information indicating whether the first test image is expanded or contracted.

[0142] 24. The computer-readable medium pursuant to Clause 22, wherein the first distortion level includes a first distortion amount based on the displacement between a feature on a first test image and a corresponding feature on a first reference image.

[0143] 25. A computer-readable medium according to any one of clauses 19 to 24, wherein determining the landing energy level that enables the sample to be in a neutral charge condition includes: estimating the landing energy level that enables the amount of distortion to be zero based on the level of distortion.

[0144] 26. A method for identifying the optimal landing energy in a charged particle beam inspection system, the method comprising:

[0145] Acquire multiple test images of samples obtained at different landing energies;

[0146] Determining the distortion level of multiple test images, wherein determining the distortion level includes: comparing the first test image with a first reference image corresponding to the first test image based on the location of features in the first test image and the first reference image; and

[0147] Based on the distortion level, determine the landing energy level that allows the sample to be in a neutral charge condition during the inspection.

[0148] 27. The method pursuant to Clause 26 also includes:

[0149] The inspection image is corrected based on a reference image corresponding to the inspection image, which is based on the determined landing energy level.

[0150] 28. The method according to Clause 26 further includes: correcting the inspection image by applying a predetermined offset to the inspection image.

[0151] 29. The method according to any one of clauses 26 to 28, wherein each of the plurality of test images of the acquired sample corresponds to a test area among the plurality of test areas of the sample.

[0152] 30. A method for enhancing an inspection image in a charged particle beam inspection system, the method comprising:

[0153] Acquire a first test image and a second test image of the sample, wherein the first test image and the second test image are obtained at different landing energies;

[0154] Determine the first distortion level of the first test image and the second distortion level of the second test image;

[0155] Determine the landing energy level that will result in substantially zero distortion when inspecting the sample. This determination of the landing energy level is based on a first distortion level, a second distortion level, and different landing energies; and

[0156] Based on the determined landing energy level, acquire inspection images.

[0157] 31. The method according to Clause 30, wherein the determination of the landing energy level includes: performing interpolation based on a first distortion level, a second distortion level, and different landing energies.

[0158] 32. The methods pursuant to Clause 30 or 31 also include:

[0159] The inspection image is corrected based on a reference image corresponding to the inspection image.

[0160] 33. The method according to Clause 30 or 31 further includes: correcting the inspection image by applying a predetermined offset to the inspection image.

[0161] A non-transient computer-readable medium may be provided that stores information for a controller (e.g., Figure 1The processor of the controller 50) executes the following instructions: image inspection, image acquisition, stage positioning, beam focusing, electric field adjustment, beam bending, focusing lens adjustment, activation of charged particle sources, beam deflection, and method 800, etc. Common forms of non-transient media include, for example, floppy disks, flexible disks, hard disks, solid-state drives, magnetic tape or any other magnetic data storage media, optical disc read-only memory (CD-ROM), any other optical data storage media, any physical media with a perforated pattern, random access memory (RAM), programmable read-only memory (PROM), and erasable programmable read-only memory (EPROM), FLASH-EPROM or any other flash memory, non-volatile random access memory (NVRAM), cache, registers, any other memory chips or cartridges, and their networked versions.

[0162] It should be understood that the embodiments of this disclosure are not limited to the exact constructions described above and shown in the accompanying drawings, and various modifications and changes can be made without departing from its scope. This disclosure has been described in conjunction with various embodiments, and other embodiments of the invention will be apparent to those skilled in the art in light of the specification and practice of the invention disclosed herein. The specification and examples are to be considered exemplary only, and the true scope and spirit of the invention are indicated by the following claims.

[0163] The above description is intended to be illustrative and not restrictive. Therefore, it will be apparent to those skilled in the art that modifications can be made to the description without departing from the scope of the claims set forth below.

Claims

1. A method for enhancing an inspection image in a charged particle beam inspection system, the method comprising: Acquire multiple test images of samples obtained at different landing energies; Determine the distortion level of the plurality of test images; Based on the distortion level, determine the landing energy level that enables the sample to be under neutral charge conditions during the inspection. as well as Based on the determined landing energy level, an inspection image is acquired.

2. The method according to claim 1, further comprising: The inspection image is corrected based on a reference image corresponding to the inspection image.

3. The method of claim 1, wherein each of the plurality of test images of the acquired sample corresponds to a test region among the plurality of test regions of the sample.

4. The method of claim 1, wherein determining the distortion level of the plurality of test images comprises: A first distortion level of the first test image is determined based on a first reference image corresponding to the first test image among the plurality of test images.

5. The method of claim 4, wherein the first distortion level includes information indicating whether the first test image is expanded or shrunken.

6. The method of claim 4, wherein the first distortion level includes a first distortion amount, the first distortion amount being based on the displacement between a feature on the first test image and a corresponding feature on the first reference image.

7. The method of claim 1, wherein determining the landing energy level that enables the sample to be in a neutral charge condition comprises: Based on the aforementioned distortion level, estimate the landing energy level that would allow the distortion to be zero.

8. The method of claim 4, wherein the determination of the first distortion level is based on a comparison between a first distance between two features on the first test image and a second distance between corresponding two features on the first reference image.

9. The method of claim 3, wherein each of the plurality of test regions comprises a plurality of features.

10. The method according to claim 1, further comprising: The inspection image is corrected by applying a predetermined offset to it.

11. The method of claim 10, wherein the predetermined offset is determined based on the amount of error of an experimental examination image corresponding to a portion of the sample, the experimental examination image being acquired based on the determined landing energy level.

12. An image enhancement device, comprising: Memory stores instruction sets; as well as At least one processor is configured to execute the instruction set to cause the device to perform: Acquire multiple test images of samples obtained at different landing energies; Determine the distortion level of the plurality of test images; Based on the distortion level, determine the landing energy level that enables the sample to be under neutral charge conditions during the inspection. as well as Based on the determined landing energy level, an inspection image is acquired.

13. The device of claim 12, wherein the at least one processor is configured to execute the instruction set to cause the device to further perform: The inspection image is corrected based on a reference image corresponding to the inspection image.

14. The apparatus of claim 12, wherein each of the plurality of test images of the acquired sample corresponds to a test area among a plurality of test regions of the sample.

15. The apparatus of claim 12, wherein determining the distortion level of the plurality of test images comprises: A first distortion level of the first test image is determined based on a first reference image corresponding to the first test image among the plurality of test images.

16. The device of claim 15, wherein the first distortion level includes information indicating whether the first test image is expanded or contracted.

17. The apparatus of claim 15, wherein the first distortion level includes a first distortion amount, the first distortion amount being based on the displacement between a feature on the first test image and a corresponding feature on the first reference image.

18. The apparatus of claim 13, wherein determining the landing energy level that enables the sample to be in a neutral charge condition comprises: Based on the aforementioned distortion level, estimate the landing energy level that would allow the distortion to be zero.

19. A non-transient computer-readable medium storing an instruction set executable by at least one processor of a computing device to perform a method for enhancing an image, the method comprising: Acquire multiple test images of samples obtained at different landing energies; Determine the distortion level of the plurality of test images; Based on the distortion level, determine the landing energy level that enables the sample to be under neutral charge conditions during the inspection. as well as Based on the determined landing energy level, an inspection image is acquired.

20. The computer-readable medium of claim 19, wherein the instruction set is executable by at least one processor of the computing device to further perform: The inspection image is corrected based on a reference image corresponding to the inspection image.

21. The computer-readable medium of claim 19, wherein each of the plurality of test images of the acquired sample corresponds to a test region among a plurality of test regions of the sample.

22. The computer-readable medium of claim 19, wherein determining the distortion level of the plurality of test images comprises: A first distortion level of the first test image is determined based on a first reference image corresponding to the first test image among the plurality of test images.

23. The computer-readable medium of claim 22, wherein the first distortion level includes information indicating whether the first test image is expanded or shrunk.

24. The computer-readable medium of claim 22, wherein the first distortion level includes a first distortion amount based on the displacement between a feature on the first test image and a corresponding feature on the first reference image.

25. The computer-readable medium of claim 19, wherein determining the landing energy level that enables the sample to be in a neutral charge condition comprises: Based on the aforementioned distortion level, estimate the landing energy level that would allow the distortion to be zero.

26. A method for identifying the optimal landing energy in a charged particle beam inspection system, the method comprising: Acquire multiple test images of samples obtained at different landing energies; Determine the distortion level of the plurality of test images, wherein determining the distortion level includes: comparing the first test image with a first reference image corresponding to the first test image based on the location of features in the first test image and the first reference image; as well as Based on the distortion level, a landing energy level is determined that enables the sample to be in a neutral charge condition during the inspection.

27. The method of claim 26, further comprising: The inspection image, obtained based on the determined landing energy level, is corrected based on a reference image corresponding to the inspection image.

28. The method of claim 27, further comprising: The inspection image is corrected by applying a predetermined offset to it.

29. The method of claim 26, wherein each of the plurality of test images of the acquired sample corresponds to a test region among a plurality of test regions of the sample.

30. A method for enhancing an inspection image in a charged particle beam inspection system, the method comprising: Acquire a first test image and a second test image of the sample, wherein the first test image and the second test image are obtained at different landing energies; Determine the first distortion level of the first test image and the second distortion level of the second test image; Determine the landing energy level that enables the distortion level to be substantially zero when examining the sample, the determination of the landing energy level being based on the first distortion level, the second distortion level, and the different landing energies; as well as Based on the determined landing energy level, an inspection image is acquired.

31. The method of claim 30, wherein determining the landing energy level comprises: Interpolation is performed based on the first distortion level, the second distortion level, and the different landing energies.

32. The method of claim 30, further comprising: The inspection image is corrected based on a reference image corresponding to the inspection image.

33. The method of claim 30, further comprising: The inspection image is corrected by applying a predetermined offset to it.

Images