Method and system for overlay measurement using a charged particle inspection apparatus

Abstract

A system and method for measuring an overlay of a sample under a scan performed by a charged particle beam inspection apparatus includes obtaining a first detector signal in response to a first scan of a first target of the sample, and obtaining a second detector signal in response to a second scan of a second target of the sample, determining a first conversion signal and a second conversion signal by performing a Fourier transform on the first detector signal and the second detector signal, and determining an overlay value of the sample based on the first conversion signal and the second conversion signal.

Description

Technical Field

[0001] Cross - reference to related applications

[0001] This application claims the priority of European Patent No. 22172200.2, filed on May 6, 2022, which is incorporated herein by reference in its entirety.

[0002]

[0002] This specification relates to the field of image inspection apparatuses, and more particularly, to overlay measurement using a charged particle inspection apparatus.

Background Art

[0003]

[0003] An image inspection apparatus (e.g., a charged particle beam apparatus or an optical beam apparatus) can generate a two - dimensional (2D) image of a wafer substrate by detecting particles (e.g., photons, secondary electrons, backscattered electrons, mirror electrons, or other types of electrons) from the surface of the wafer substrate upon collision of a beam (e.g., a charged particle beam or an optical beam) generated by a radiation source associated with the inspection apparatus. In the semiconductor industry, various image inspection apparatuses are used on semiconductor wafers for various purposes such as wafer processing (e.g., e - beam direct write lithography systems), process monitoring (e.g., critical dimension scanning electron microscopes (CD - SEM)), wafer inspection (e.g., e - beam inspection systems), or defect analysis (e.g., defect review SEM, or e.g., DR - SEM and focused ion beam systems, or e.g., FIB).

[0004]

[0004] In semiconductor manufacturing, integrated circuits can be fabricated on a wafer as one or more stacked layers of materials (e.g., silicon, silicon dioxide, metal, or the like). Each layer of material can include a designed pattern (referred to herein as a "pattern layer") for forming components of the integrated circuit (e.g., transistors, contacts, or the like). The manufacture of each layer includes transferring a pattern from a mask to the wafer surface through a lithography process. The relative position of each pattern layer with respect to the previous pattern layer (referred to herein as "alignment") can affect the characteristics or quality of the integrated circuit being manufactured.

[0005]

[0005] Overlay refers to a shift, displacement, or misalignment of a planar vector of a pattern layer with respect to an adjacent pattern layer. For example, for two patterns of two adjacent pattern layers, two in-pattern reference points (e.g., center points) can be selected respectively, and the overlay between two adjacent pattern layers can refer to the displacement of the planar vector between the two in-pattern reference points. If the overlay is large, problems or obstacles can occur in the manufactured integrated circuit. Therefore, high-precision overlay measurement plays an important role in reducing overlay.

Summary of the Invention

[0006]

[0006] Embodiments of the present disclosure provide a system and method for measuring an overlay of a sample under a scan performed by a charged particle beam inspection apparatus. In some embodiments, the system may include a charged particle beam inspection apparatus configured to scan a sample and a controller including a circuit. The controller is configured to obtain a first detector signal in response to a first scan of a first target of the sample, and obtain a second detector signal in response to a second scan of a second target of the sample, and determine a first conversion signal and a second conversion signal by performing a Fourier transform on the first detector signal and the second detector signal, and determine an overlay value of the sample based on the first conversion signal and the second conversion signal.

[0007]

[0007] In some embodiments, a non-transitory computer-readable medium can store a set of instructions executable by at least one processor of the apparatus to cause the apparatus to perform a method. The method can include obtaining a first detector signal in response to a first scan of a first target of the sample, and obtaining a second detector signal in response to a second scan of a second target of the sample, and determining a first conversion signal and a second conversion signal by performing a Fourier transform on the first detector signal and the second detector signal, and determining an overlay value of the sample based on the first conversion signal and the second conversion signal.

[0008]

[0008] In some embodiments, a method for measuring an overlay of a sample under a scan performed by a charged particle beam inspection apparatus includes obtaining a first detector signal in response to a first scan of a first target of the sample, and obtaining a second detector signal in response to a second scan of a second target of the sample, and determining a first conversion signal and a second conversion signal by performing a Fourier transform on the first detector signal and the second detector signal, and determining an overlay value of the sample based on the first conversion signal and the second conversion signal.

[0009]

[0009] In some embodiments, the system may include a charged particle beam inspection device configured to scan a sample, and a controller including a circuit. The controller is configured to obtain a detector signal in response to scanning a target of the sample, determine a first conversion signal by performing a Fourier transform on the detector signal, and determine a second conversion signal by converting the first conversion signal, and determine an overlay value of the sample based on the first conversion signal, the second conversion signal, a first predetermined amplitude value, and a second predetermined amplitude value.

[0010]

[0010] In some embodiments, a non-transitory computer-readable medium can store a set of instructions executable by at least one processor of the device to cause the device to perform a method. The method may include obtaining a detector signal in response to scanning a target of a sample scanned by a charged particle beam inspection device, determining a first conversion signal by performing a Fourier transform on the detector signal, and determining a second conversion signal by converting the first conversion signal, and determining an overlay value of the sample based on the first conversion signal, the second conversion signal, a first predetermined amplitude value, and a second predetermined amplitude value.

[0011]

[0011] In some embodiments, a method of measuring an overlay of a sample under a scan performed by a charged particle beam inspection device may include obtaining a detector signal in response to scanning a target of the sample scanned by the charged particle beam inspection device, determining a first conversion signal by performing a Fourier transform on the detector signal, and determining a second conversion signal by converting the first conversion signal, and determining an overlay value of the sample based on the first conversion signal, the second conversion signal, a first predetermined amplitude value, and a second predetermined amplitude value.

Brief Description of the Drawings

[0012]

Figure 1

Figure 2

[0013] FIG. 2 is a schematic diagram showing an exemplary charged particle beam tool in accordance with some embodiments of the present disclosure, which may be part of the exemplary charged particle beam inspection system of FIG. 1.

Figure 3

[0014] FIG. 3 is a schematic diagram showing an example of a measurement process of a surface structure and a subsurface structure using a charged particle beam tool in accordance with some embodiments of the present disclosure.

Figure 4

[0015] FIG. 4 is a schematic diagram showing examples of a first target and a second target manufactured on a sample in accordance with some embodiments of the present disclosure.

Figure 5

[0016] FIG. 5 is a graph showing an exemplary visualization of a first detector signal and a second detector signal in accordance with some embodiments of the present disclosure.

Figure 6

[0017] FIG. 6 is a schematic diagram showing an example of a target manufactured on a sample in accordance with some embodiments of the present disclosure.

Figure 7

[0018] FIG. 7 is a schematic diagram showing an example of an arrangement of targets manufactured on a sample in accordance with some embodiments of the present disclosure.

Figure 8

[0019] FIG. 8 is a flowchart showing an exemplary method of overlay measurement in accordance with some embodiments of the present disclosure.

Figure 9

[0020] FIG. 9 is a flowchart showing another exemplary method of overlay measurement in accordance with some embodiments of the present disclosure. DETAILED DESCRIPTION OF THE INVENTION

[0013]

[0021] Next, reference is made in detail to exemplary embodiments shown in the accompanying drawings. The following description refers to the accompanying drawings, and unless otherwise specified, the same numbers in different drawings represent the same or similar elements in the accompanying drawings. The implementations described in the following description of the exemplary embodiments do not represent all implementations consistent with the present disclosure. Rather, they are merely examples of apparatuses and methods consistent with aspects related to the content listed in the appended claims. Without limiting the scope of the present disclosure, some embodiments may be described in the context of providing a detection system and a detection method in a system that utilizes an electron beam ("e-beam"). However, the present disclosure is not limited thereto. Other types of charged particle beams (including, for example, protons, ions, muons, or any other particle carrying a charge) may be similarly irradiated. Further, the systems and methods for detection may be used within other imaging systems such as optical imaging, light detection, x-ray detection, ion detection, and the like.

[0014]

[0022] An electronic device is composed of circuits formed on a piece of semiconductor material called a substrate. The semiconductor material may include, for example, silicon, gallium arsenide, indium phosphide, or silicon germanium. A number of circuits can be formed together on the same silicon piece and are called integrated circuits or ICs. The dimensions of these circuits have been dramatically reduced so that a larger number of more circuits can be accommodated on the substrate. For example, an IC chip in a smartphone can be as small as a fingernail, but can contain more than two billion transistors, and the dimensions of each transistor are smaller than 1 / 1000 of the dimension of a human hair.

[0015]

[0023] Manufacturing an IC with these extremely small structures or components is a complex, time-consuming, and expensive process, often involving hundreds of individual steps. An error in just one step can result in a defect in the completed IC, rendering the IC useless. Thus, one of the goals of the manufacturing process is to avoid such defects and maximize the number of functional ICs produced in the process, i.e., to improve the overall yield of the process.

[0016]

[0024] One component for improving yield is to monitor the chip fabrication process to confirm that a sufficient number of functional integrated circuits are being manufactured. One way to monitor the process is to inspect the chip circuit structure at various stages of forming the chip circuit structure. The inspection can be performed using a scanning charged particle microscope (“SCPM”). For example, the scanning charged particle microscope can be a scanning electron microscope (SEM). The scanning charged particle microscope can actually take “pictures” of the structure of the wafer and can be used to image those extremely small structures. This image can be used to determine whether the structures are properly formed in the proper locations. If there are defects in the structure, the process can be adjusted so that the defects are less likely to recur.

[0017]

[0025] The operating principle of a scanning charged particle microscope (e.g., SEM) is similar to that of a camera. A camera takes a photograph by receiving and recording the intensity of light reflected or emitted from a person or object. A scanning charged particle microscope takes a "photograph" by receiving and recording the energy or quantity of charged particles (e.g., electrons) reflected or emitted from the structure of a wafer. Typically, the structure is fabricated on a substrate (e.g., a silicon substrate) placed on a platform called a stage for imaging. Before taking such a "photograph", a charged particle beam can be projected onto the structure, and when the charged particles are reflected or emitted ( "emitted") from the structure (e.g., from the wafer surface, from a structure under the wafer surface, or from both), the detector of the scanning charged particle microscope can receive and record the energy or quantity of those charged particles to generate an inspection image. To take such a "photograph", the charged particle beam can scan the wafer (e.g., line by line or in a zigzag pattern), and the detector can receive the emitted charged particles coming from the area under the projection of the charged particle beam (referred to as the "beam spot"). The detector can receive and record the emitted charged particles from each beam spot one by one, and combine the information recorded for all the beam spots to generate an inspection image. Some scanning charged particle microscopes use one charged particle beam to take one "image" for generating an inspection image (referred to as a "single beam scanning charged particle microscope" such as a single beam SEM), while some scanning charged particle microscopes take a plurality of "sub - pictures" of the wafer in parallel and use a plurality of charged particle beams to stitch them together to generate an inspection image (referred to as a "multi - beam scanning charged particle microscope" such as a multi - beam SEM). By using a plurality of charged particle beams, the SEM can direct more charged particle beams at the structure to obtain these plurality of "sub - pictures", and as a result, more charged particles are emitted from the structure. Therefore, the detector can receive more emitted charged particles simultaneously and generate an inspection image of the wafer structure with higher efficiency and at a faster speed.

[0018]

[0026] To control the quality of the manufactured semiconductor structure, various overlay measurement techniques can be used. Typically, the overlay can be measured using an optical tool. For example, a broadband light beam can be applied to the surface of the sample. The surface may include a specially designed and manufactured structure (also referred to herein as a "target"). The target may include a first layer (e.g., the top layer) and a second layer (e.g., the bottom layer) below the first patterned layer. To measure the reflection or diffraction of the broadband light reflected by the target, an optical scatterometry tool can be used. The reflection or diffraction may have various characteristics such as different wavelengths, polarizations, incident angles, phases, or other optical properties, from which unknown properties of the sample (e.g., the overlay) can be determined.

[0019]

[0027] As an example, the overlay of the target can be determined based on the phase difference between the diffractions of the first layer (e.g., the top layer) and the second layer (e.g., the layer immediately below the first layer), and each of the first layer and the second layer includes a specific structure (e.g., a diffraction grating). The overlay determined using such a target may be referred to as a diffraction-based overlay ("DBO"). To measure the diffraction-based overlay, the structures of the first player and the second player (e.g., the diffraction gratings) can be manufactured using a programmed shift. The programmed shift between two layers herein may refer to the displacement of a designed (known) vector on a plane between the two layers. The programmed shift can be used to remove or reduce the incompleteness in the optical scatterometry measurement.

[0020]

[0028] There are several technical challenges in optical-based overlay measurement techniques. The first challenge is that as the pitch of the target (e.g., the pitch of a diffraction grating) decreases and the separation between adjacent pattern layers increases, the reflection or diffraction signal becomes weaker. In the present disclosure, "pitch" refers to the minimum center-to-center distance between interconnect lines in a manufactured integrated circuit and can be used as an indicator of the integration level of the integrated circuit. The second challenge is that selecting the wavelength of a broadband optical beam for optical-based overlay measurement techniques can be complex because different measurement results may be obtained for each wavelength. The third challenge is that the measurement results of optical-based overlay measurement techniques can be sensitive to subtle tilts in the area between the lines of the target (e.g., the lines of a diffraction grating). These challenges can increase the uncertainty and inaccuracy in overlay measurement.

[0021]

[0029] Embodiments of the present disclosure can provide methods, apparatuses, and systems for non-optical overlay measurement. In some disclosed embodiments, a scanning charged particle microscope (e.g., SEM) can be used for overlay measurement using one or more targets. The scanning charged particle microscope can inject a charged particle beam (e.g., an electron beam) onto the surface of one or more targets, and each target includes a first layer (e.g., the top layer) and a second layer (e.g., below the first layer). Each of the first layer and the second layer can include a similar pattern (e.g., a diffraction grating having the same pitch and a programmed shift). The incident charged particle beam may interact with the pattern of the first layer and the pattern of the second layer to generate secondary electrons and backscattered electrons. The emitted secondary electrons and backscattered electrons are detected by a detector to generate a signal. By analyzing the signal, the overlay between the first layer and the second layer can be determined. Compared with optical-based overlay measurement techniques, non-optical overlay measurement can reduce or eliminate the above-mentioned challenges and significantly improve the accuracy of overlay measurement.

[0022]

[0030] The relative dimensions of the components in the drawings may be exaggerated for ease of understanding. In the following description of the drawings, the same or similar reference numerals refer to the same or similar components or entities, and only the differences with respect to individual embodiments are described.

[0023]

[0031] As used herein, unless otherwise specified, the term "or" includes all possible combinations except when the combination is infeasible. For example, if it is described that a component can include A or B, then unless otherwise specified or infeasible, the component can include A, or B, or A and B. As a second example, if it is described that a component can include A, B, or C, then unless otherwise specified or infeasible, the component can include A, or B, or C, or A and B, or A and C, or B and C, or A and B and C.

[0024]

[0032] FIG. 1 shows an exemplary charged particle beam inspection (CPBI) system 100 that conforms to some embodiments of the present disclosure. The CPBI system 100 can be used for imaging. For example, the CPBI system 100 can use an electron beam for imaging. As shown in FIG. 1, the CPBI system 100 includes a main chamber 101, a load / lock chamber 102, a beam tool 104, and an equipment front-end module (EFEM) 106. The beam tool 104 is disposed inside the main chamber 101. The EFEM 106 includes a first loading port 106a and a second loading port 106b. The EFEM 106 can include additional loading ports. The first loading port 106a and the second loading port 106b receive a wafer front opening unified pod (FOUP) that houses a wafer to be inspected (e.g., a semiconductor wafer or a wafer made of other materials) or a sample (the wafer and the sample can be used interchangeably). A "lot" is a plurality of wafers that can be loaded for processing as a batch.

[0025]

[0033] One or more robot arms (not shown) within the EFEM 106 can carry wafers to the load / lock chamber 102. The load / lock chamber 102 is connected to a load / lock vacuum pump system (not shown), and this pump system removes gas molecules within the load / lock chamber 102 so as to reach a first pressure lower than atmospheric pressure. After reaching the first pressure, one or more robot arms (not shown) can carry wafers from the load / lock chamber 102 to the main chamber 101. The main chamber 101 is connected to a main chamber vacuum pump system (not shown), and this pump system removes gas molecules within the main chamber 101 so as to reach a second pressure lower than the first pressure. After reaching the second pressure, the wafers are subjected to inspection by the beam tool 104. The beam tool 104 can be a single beam system or a multi-beam system.

[0026]

[0034] The controller 109 is electronically connected to the beam tool 104. The controller 109 can be a computer capable of performing various controls of the CPBI system 100. Although the controller 109 is illustrated outside the structure including the main chamber 101, the load / lock chamber 102, and the EFEM 106 in FIG. 1, it will be understood that the controller 109 can be part of the structure.

[0027]

[0035] In some embodiments, the controller 109 can include one or more processors (not shown). A processor can be a general-purpose or specific electronic device capable of manipulating or processing information. For example, the processor can include any combination of any number of central processing units (i.e., "CPUs"), graphics processing units (i.e., "GPUs"), optical processors, programmable logic controllers, microcontrollers, microprocessors, digital signal processors, IP (intellectual property) cores, programmable logic arrays (PLAs), programmable array logic (PALs), generic array logic (GALs), complex programmable logic devices (CPLDs), field programmable gate arrays (FPGAs), system-on-chips (SoCs), application specific integrated circuits (ASICs), and any type of circuit capable of data processing. The processor can also be a virtual processor including one or more processors distributed across a plurality of machines or devices coupled via a network.

[0028]

[0036] In some embodiments, the controller 109 can further include one or more memories (not shown). A memory can be a general-purpose or specific electronic device capable of storing code and data accessible by the processor (e.g., via a bus). For example, the memory can include any combination of any number of random access memories (RAMs), read-only memories (ROMs), optical disks, magnetic disks, hard drives, solid state drives, flash drives, security digital (SD) cards, memory sticks, compact flash (CF) cards, or any type of storage device. The code can include an operating system (OS) and one or more application programs (i.e., "apps") for specific tasks. The memory can also be a virtual memory including one or more memories distributed across a plurality of machines or devices coupled via a network.

[0029]

[0037] Figure 2 shows an exemplary imaging system 200 that conforms to an embodiment of the present disclosure. The beam tool 104 of FIG. 2 can be configured for use in the CPBI system 100. The beam tool 104 can be a single beam device or a multi-beam device. As shown in FIG. 2, the beam tool 104 includes an electric sample stage 201 and a wafer holder 202 supported by the electric sample stage 201 for holding the wafer 203 to be inspected. The beam tool 104 further includes an objective lens assembly 204, a charged particle detector 206 (including charged particle sensor surfaces 206a and 206b), an objective aperture 208, a condenser lens 210, a beam limiting aperture 212, a gun aperture 214, an anode 216, and a cathode 218. In some embodiments, the objective lens assembly 204 can include a modified swing objective retarding immersion lens (SORIL) including magnetic pole pieces 204a, control electrodes 204b, deflectors 204c, and excitation coils 204d. The beam tool 104 can further include an energy dispersive X-ray spectrometer (EDS) detector (not shown) for characterizing materials on the wafer 203.

[0030]

[0038] A primary charged particle beam 220 such as an electron beam (or simply "primary beam 220") is emitted from a cathode 218 by applying an accelerating voltage between an anode 216 and the cathode 218. The primary beam 220 passes through a gun aperture 214 and a beam limiting aperture 212, which can determine the size of the charged particle beam entering the condenser lens 210, both of which are under the beam limiting aperture 212. The condenser lens 210 focuses the primary beam 220 before the beam enters the objective aperture 208 to set the size of the charged particle beam before it enters the objective lens assembly 204. The deflector 204c deflects the primary beam 220 to facilitate beam scanning on the wafer. For example, in a scanning process, the deflector 204c can be controlled to sequentially deflect the primary beam 220 to different positions on the upper surface of the wafer 203 at different times to provide data for reconstructing images of different parts of the wafer 203. Further, the deflector 204c can also be controlled to deflect the primary beam 220 to different side surfaces of the wafer 203 at a specific position at different times to provide data for reconstructing a three-dimensional image of the wafer structure at that position. Further, in some embodiments, the anode 216 and the cathode 218 can generate a plurality of primary beams 220, and the beam tool 104 can include a plurality of deflectors 204c for simultaneously projecting the plurality of primary beams 220 to different parts / sides of the wafer to provide data for reconstructing images of different parts of the wafer 203.

[0031]

[0039] The excitation coil 204d and the pole piece 204a generate a magnetic field that starts at one end of the pole piece 204a and ends at the other end of the pole piece 204a. A portion of the wafer 203 being scanned by the primary beam 220 can enter the magnetic field, become charged, and thereby generate an electric field. The electric field reduces the energy of the impinging primary beam 220 near the surface of the wafer 203 before the primary beam 220 collides with the wafer 203. The control electrode 204b, which is electrically insulated from the pole piece 204a, controls the electric field on the wafer 203 to prevent micro-arching of the wafer 203 and to ensure an appropriate beam focus.

[0032]

[0040] After receiving the primary beam 220, a secondary charged particle beam 222, such as a secondary electron beam (or "secondary beam 222"), can be emitted from a portion of the wafer 203. The secondary beam 222 can form beam spots on the sensor surfaces 206a and 206b of the charged particle detector 206. The charged particle detector 206 can generate a signal (e.g., voltage, current, etc.) representative of the intensity of the beam spot and provide that signal to the image processing system 250. The intensity of the secondary beam 222 and the resulting beam spots can vary depending on the external or internal structure of the wafer 203. Further, as discussed above, the primary beam 220 can be projected onto different positions on the upper surface of the wafer or onto different side surfaces of the wafer at specific locations in order to generate secondary beams 222 of different intensities (and the resulting beam spots). Thus, by mapping the position of the wafer 203 and the intensity of the beam spots, the processing system can reconstruct an image that reflects the internal or surface structure of the wafer 203.

[0033]

[0041] The imaging system 200 can be used to inspect the wafer 203 on the electric sample stage 201 and includes the beam tool 104 as discussed above. The imaging system 200 may also include an image processing system 250 including an image acquirer 260, a storage 270, and a controller 109. The image acquirer 260 can include one or more processors. For example, the image acquirer 260 can include a computer, a server, a mainframe host, a terminal, a personal computer, any kind of mobile computing device, etc., or a combination thereof. The image acquirer 260 can be connected to the detector 206 of the beam tool 104 via a medium such as a conductor, an optical fiber cable, a portable storage medium, IR, Bluetooth, the Internet, a wireless network, wireless radio, or a combination thereof. The image acquirer 260 can receive signals from the detector 206 and can construct an image. In this way, the image acquirer 260 can acquire an image of the wafer 203. The image acquirer 260 can also perform various post-processing functions such as generating a contour and superimposing an indicator on the acquired image. The image acquirer 260 can adjust the brightness and contrast of the acquired image. The storage 270 can be a storage medium such as a hard disk, cloud storage, random access memory (RAM), or other types of computer-readable memory. The storage 270 can be coupled to the image acquirer 260 and can be used to store the scanned raw image data as the original image, the post-processed image, or other images to assist in processing. The image acquirer 260 and the storage 270 may be connected to the controller 109. In some embodiments, the image acquirer 260, the storage 270, and the controller 109 can be integrated as one control unit.

[0034]

[0042] In some embodiments, the image acquirer 260 can acquire one or more images of the sample based on the imaging signal received from the detector 206. The imaging signal can correspond to a scanning operation for performing charged particle imaging. The acquired image can be a single image including a plurality of imaging areas. The single image can be stored in the storage 270. The single image can be an original image that can be divided into a plurality of regions. Each of these regions can include one imaging area including features of the wafer 203.

[0035]

[0043] FIG. 3 is a schematic diagram showing an example of a measurement process of a surface structure and a subsurface structure using a charged particle beam tool (e.g., a scanning charged particle microscope) in accordance with some embodiments of the present disclosure. A scanning charged particle microscope (hereinafter, referred to as "SCPM") generates a primary charged particle beam for inspection (e.g., the primary charged particle beam 220 in FIG. 2). For example, the primary charged particle beam can be a primary electron beam. In FIG. 3, electrons of the primary electron beam 302 are projected onto the surface of the sample 304. The sample 304 can be any material, such as a non-conductive resist, a silicon dioxide layer, a metal layer, or any laminated combination of any dielectric material or conductive material.

[0036]

[0044] The electrons of the primary electron beam 302 penetrate the surface of the sample 304 to a certain depth (for example, from several nanometers to several micrometers) and can interact with the particles of the sample 304 within the interaction volume 306. Some of the electrons of the primary electron beam 302 interact elastically with the particles within the interaction volume 306 (for example, in the form of elastic scattering or collisions) and can be reflected or recoiled from the surface of the sample 304. Elastic interactions conserve the total kinetic energy of the interacting bodies (for example, the electrons of the primary electron beam 302 and the particles of the sample 304), and the kinetic energy of the interacting bodies is not converted into other forms of energy (for example, heat, electromagnetic energy, etc.). Such reflected electrons generated from elastic interactions are sometimes called backscattered electrons (BSE) like the BSE 308 in FIG. 3. Some of the electrons of the primary electron beam 302 can interact inelastically with the particles within the interaction volume 306 (for example, in the form of inelastic scattering or collisions). Inelastic interactions do not conserve the total kinetic energy of the interacting bodies, and part or all of the kinetic energy of the interacting bodies can be converted into other forms of energy. For example, through inelastic interactions, the kinetic energy of some of the electrons of the primary electron beam 302 can cause electron excitation and generate electrons emerging from the surface of the sample 304 called secondary electrons (SE) like the SE 310 in FIG. 3. As shown in FIG. 3, some of the SE 310 (for example, SE with sufficient energy) finally emerge from the surface of the sample 304 and reach a detector (not shown in FIG. 3), and some of the SE 310 (for example, SE with insufficient energy) can finally emerge from the surface of the sample 304 and re-enter (for example, when the surface of the sample 304 is positively charged). The yield or emission rate of BSE and SE can depend on, for example, among several factors, particularly the energy of the electrons of the primary electron beam 302 and the material of the inspection target. The energy of the electrons of the primary electron beam 302 can be partially imparted by its acceleration voltage (for example, the acceleration voltage between the anode 216 and the cathode 218 in FIG. 2). The quantity of BSE and SE can be at least as good as (or the same as) the injected electrons of the primary electron beam 302 at most.

[0037]

[0045] As an example, sample 304 may include a first layer (e.g., a resist layer on the wafer surface, not shown in FIG. 3) and a second layer (e.g., a pattern layer directly below the wafer surface, not shown in FIG. 3). Each of the first layer and the second layer may include a designed pattern (e.g., a target) such as a line, slot, corner, edge, hole, etc. Those features may have different heights. The primary electron beam 302 may interact with the particles of the first layer to generate SE 310, and the SE 310 generated at different locations of the target of the first layer may reflect the geometric information of the target of the first layer. Also, the primary electron beam 302 may penetrate the first layer and reach the second layer, and may interact with the particles of the second layer to generate BSE 308. The BSE 308 generated at different positions of the target of the second layer may reflect the geometric information of the target of the second layer.

[0038]

[0046] In accordance with some embodiments of the present disclosure, a computer-implemented method for measuring an overlay of a sample under a scan performed by a charged particle beam inspection apparatus may include obtaining a first detector signal in response to a first scan of a first target of the sample and obtaining a second detector signal in response to a second scan of a second target of the sample. As used herein, obtaining may refer to receiving, capturing, putting in, acquiring, obtaining, retrieving, receiving, reading, accessing, collecting, or any operation for inputting data. In some embodiments, the charged particle beam inspection apparatus may include a scanning electron microscope. The sample may include a wafer.

[0039]

[0047] As an example, the charged particle beam inspection apparatus can be an imaging system (e.g., the imaging system 200 of FIG. 2). The sample can be a wafer (e.g., the wafer 203 of FIG. 2) having a structure (e.g., a circuit) fabricated on its surface. In some embodiments, the first target and the second target can be two specially designed and fabricated structures. For example, the first target and the second target may be independent of the fabricated circuits on the wafer and may not have a functional relationship. In some embodiments, the first target and the second target can be fabricated in one or more empty spaces on the wafer not occupied by the fabricated circuits. In some embodiments, the first target and the second target may be adjacent to each other. In some other embodiments, the first target and the second target may be separated from each other by other fabricated structures on the sample. In some embodiments, the first target and the second target can be fabricated on a specific wafer.

[0040]

[0048] The first detector signal and the second detector signal can each be a signal output by a detector (e.g., the detector 206 of FIG. 2) of the charged particle inspection apparatus in response to the first scan and the second scan. In some embodiments, the first scan and the second scan can be the same scan. For example, the first target and the second target can be scanned by a single charged particle beam (e.g., of a single beam inspection apparatus) or a single charged particle beamlet (e.g., of a multi-beam inspection apparatus) in the same field of view. In some embodiments, the first scan and the second scan can be different scans. As an example, when the charged particle inspection apparatus is a single beam inspection apparatus (e.g., a single beam SEM), the first target may be scanned before the second target. As another example, when the charged particle inspection apparatus is a multi-beam inspection apparatus (e.g., a multi-beam SEM), the first target and the second target may be scanned simultaneously by two different beamlets.

[0041]

[0049] During the scanning of the sample, after charged particles (e.g., electrons) of the primary beam (e.g., the primary beam 220 in FIG. 2) hit the surface of the sample, at least one of the secondary charged particles (e.g., the SE 310 shown in FIG. 3) and the backscattered charged particles (e.g., the BSE 308 in FIG. 3) is emitted from the surface of the sample and can be induced to the detector (e.g., the detector 206 in FIG. 2). In some embodiments, at least one of the secondary electrons and the backscattered electrons is emitted from the first target, induced to the detector, and a first detector signal can be generated. At least one of the secondary electrons and the backscattered electrons is also emitted from the second target, induced to the detector, and a second detector signal can be generated.

[0042]

[0050] In some embodiments, the first detector signal and the second detector signal can each be a value representing the sum or count of the electrons emitted from and detected by the first target and the second target, respectively. In some embodiments, the first detector signal and the second detector signal can each be a value representing the sum of the charges of the electrons emitted from and detected by the first target and the second target, respectively. In some embodiments, the first detector signal and the second detector signal can be visualized.

[0043]

[0051] In some embodiments, the first target can include a first pattern layer and a second pattern layer below the first pattern layer. The second target can include a third pattern layer and a fourth pattern layer below the third pattern layer. The pitch values of the first pattern layer and the second pattern layer can be equal to the first pitch value of the first target. Also, the pitch values of the third pattern layer and the fourth pattern layer can be equal to the second pitch value of the second target. In some embodiments, each of the first pattern layer, the second pattern layer, the third pattern layer, and the fourth pattern layer can include a diffraction grating.

[0044]

[0052] As an example, FIG. 4 is a schematic diagram showing an example of a first target 402 and a second target 404 fabricated on a sample 400 that conforms to some embodiments of the present disclosure. The sample 400 can be a silicon wafer substrate (represented by the shaded area in FIG. 4). In some embodiments, the first target 402 and the second target 404 can be diffraction-based overlay targets. As shown in FIG. 4, the first target 402 includes a first pattern layer 406 (represented by the hatched area within the dashed box of the first target 402) and a second pattern layer 408 below the first pattern layer 406 (represented by the dotted area within the dashed box of the first target 402), and the second target 404 includes a third pattern layer 410 (represented by the hatched area within the dashed box of the second target 404) and a fourth pattern layer 412 below the third pattern layer 410 (represented by the dotted area within the dashed box of the second target 404). In FIG. 4, the first pattern layer 406, the second pattern layer 408, the third pattern layer 410, and the fourth pattern layer 412 can be a type of diffraction grating (e.g., a line diffraction grating).

[0045]

[0053] In some embodiments, the first pattern layer 406 and the third pattern layer 410 can be a polymethyl methacrylate (PMMA) material. For example, as shown in FIG. 4, the first pattern layer 406 and the third pattern layer 410 can be fabricated (e.g., via coating, lithography, and etching processes) on a PMMA layer 414 (represented by the hatched region below the first pattern layer 406 and the third pattern layer 410). In some embodiments, the second pattern layer 408 and the fourth pattern layer 412 can be a copper material. For example, as shown in FIG. 4, the second pattern layer 408 and the fourth pattern layer 412 can be fabricated (e.g., via coating, lithography, and etching processes) on the sample 400. In some embodiments, a silicon dioxide layer 416 (represented by the white region) may separate the PMMA layer 414 from the second pattern layer 408 and also separate the PMMA layer 414 from the fourth pattern layer 412. As shown in FIG. 4, the first pattern layer 406 and the second pattern layer 408 are separated by a separation distance d, and the third pattern layer 410 and the fourth pattern layer 412 are also separated by the separation distance d.

[0046]

[0054] In FIG. 4, each of the first pattern layer 406, the second pattern layer 408, the third pattern layer 410, and the fourth pattern layer 412 can have a pitch. For example, when the first pattern layer 406, the second pattern layer 408, the third pattern layer 410, and the fourth pattern layer 412 are a type of diffraction grating, the pitch of any of the first pattern layer 406, the second pattern layer 408, the third pattern layer 410, and the fourth pattern layer 412 can be represented by the distance between the centers of two adjacent lines of the diffraction grating (referred to herein as the "pitch value").

[0047]

[0055] In some embodiments, the pitch values of the first pattern layer 406 and the second pattern layer 408 can be equal to the first pitch value of the first target 402. Also, the pitch values of the third pattern layer 410 and the fourth pattern layer 412 can be equal to the second pitch value of the second target 404. In some embodiments, the first pitch value can be equal to the second pitch value. In some embodiments, the first pitch value does not have to be equal to the second pitch value. As an example, as shown in FIG. 4, each of the first pattern layer 406 and the second pattern layer 408 can have a first pitch value 418, and each of the third pattern layer 410 and the fourth pattern layer 412 can have a second pitch value 420. In some embodiments, the first pitch value 418 can be equal to the second pitch value 420.

[0048]

[0056] In some embodiments, the first pattern layer can have a first shift relative to the second pattern layer, in which case the first shift can have a magnitude equal to the overlay value (e.g., the size of the overlay of the sample) minus a predetermined shift value. The third pattern layer can have a second shift relative to the fourth pattern layer, in which case the second shift can have a magnitude equal to the overlay value plus a predetermined shift value. As used herein, the shift between two pattern layers refers to the horizontal distance between two corresponding structural portions on two adjacent pattern layers. For example, if the two corresponding structural portions are two corresponding diffraction grating lines, the shift between them can be the distance between the centers of the corresponding lines along the horizontal direction. In some embodiments, the shift can be represented as a displacement of a vector having a magnitude and a direction.

[0049]

[0057] As an example, as shown in FIG. 4, the first pattern layer 406 may have a first shift 422 (represented by the left arrow between the centers of two corresponding diffraction grating lines) with respect to the second pattern layer 408. The third pattern layer 410 may have a second shift 424 (represented by the right arrow between the centers of two corresponding diffraction grating lines) with respect to the fourth pattern layer 412. The first shift 422 and the second shift 424 can be represented as displacements of vectors having magnitude and direction. As shown in FIG. 4, the first shift 422 and the second shift 424 may have opposite directions. Assuming that the rightward horizontal direction in FIG. 4 represents the positive direction, the first shift 422 may be a negative vector, and the second shift 320 may be a positive vector.

[0050]

[0058] Each of the first shift 422 and the second shift 424 in FIG. 4 can be determined based on two components. For example, assume that the sample 400 has an overlay (not shown in FIG. 4) representing a misalignment in the horizontal direction of the vector between the first pattern layer 406 and the second pattern layer 408 (or between the third pattern layer 410 and the fourth pattern layer 412) due to manufacturing errors or inaccuracies. The overlay of the sample 400 can be represented as a vector having magnitude (i.e., overlay value) and direction. As shown in FIG. 4, assuming that the overlay is a positive vector (i.e., rightward), the first shift 422 may have a magnitude equal to the value obtained by subtracting a predetermined shift value (e.g., a positive value) from the overlay value, and the second shift 424 may have a magnitude equal to the value obtained by adding the predetermined shift value to the overlay value. The predetermined shift value may be a designed or programmed shift value. In an ideal case, when there are no manufacturing errors or inaccuracies, the overlay may be zero, and in this case, the first shift 422 and the second shift 424 may have the same magnitude (i.e., the predetermined shift value) and opposite directions.

[0051]

[0059] FIG. 4 shows the first shift 422 and the second shift 424 using the first pattern layer 406 and the third pattern layer 410 as static reference points, but it should be noted that the present disclosure is not so limited in preparing the first target 402 and the second target 404. For example, in preparing the first target 402 and the second target 404, the second pattern layer 408 and the fourth pattern layer 412 may be used as static reference points. In this case, the first pattern layer 406 can be fabricated as being shifted by a predetermined shift value in a first direction with respect to the second pattern layer 408, and the third pattern layer 410 can be fabricated as being shifted by a predetermined shift value in a second direction opposite to the first direction with respect to the fourth pattern layer 412.

[0052]

[0060] FIG. 5 is a graph 500 showing an exemplary visualization of a first detector signal and a second detector signal in accordance with some embodiments of the present disclosure. For example, the first detector signal of FIG. 5 can be obtained in response to the first scan of the first target 402 of FIG. 4, and the second detector signal of FIG. 5 can be obtained in response to the second scan of the second target 404 of FIG. 4. In graph 500, the horizontal axis represents distance (e.g., in pixels or nanometers), and the vertical axis can represent the magnitudes of the first detector signal and the second detector signal. The first detector signal includes information (e.g., amplitude and phase information) corresponding to electrons emitted from the first pattern layer 406 and information (e.g., amplitude and phase information) corresponding to electrons emitted from the second pattern layer 408. The second detector signal includes information (e.g., amplitude and phase information) corresponding to electrons emitted from the third pattern layer 410 and information (e.g., amplitude and phase information) corresponding to electrons emitted from the fourth pattern layer 412. In some embodiments, based on the shapes of the first detector signal and the second detector signal, an analysis can be performed to determine the overlay value described herein, which will be described below.

[0053]

[0061] In accordance with some embodiments of the present disclosure, a computer-implemented method of measuring an overlay may also include determining a first conversion signal and a second conversion signal by performing a Fourier transform on a first detector signal and a second detector signal. In some embodiments, a first period of the first conversion signal (e.g., a first sine series or a first cosine series) may correspond to a first pitch value of a first target. A second period of the second conversion signal (e.g., a second sine series or a second cosine series) may correspond to a second pitch value of a second target. By way of example, referring to FIG. 4, the first pitch value of the first target may be the first pitch value 418, and the second pitch value of the second target may be the second pitch value 420.

[0054]

[0062] In accordance with some embodiments of the present disclosure, a computer-implemented method of measuring an overlay may further include determining an overlay value of a sample based on the first conversion signal and the second conversion signal.

[0055]

[0063] By way of example, a Fourier transform may be performed on the first detector signal and the second detector signal (e.g., the first detector signal and the second detector signal of FIG. 5) to determine the first conversion signal and the second conversion signal. When the first pitch value (e.g., the first pitch value 418) is equal to the second pitch value (e.g., the second pitch value 420), the first conversion signal S - and the second conversion signal S + may be represented by Equations (1) and (2), respectively. S - =a·sin(kx + θ a ) + b·sin(kx + θ b- ) Equation (1) S + =a·sin(kx + θ a ) + b·sin(kx + θ b+ ) Equation (2)

[0056]

[0064] In Equation (1), a·sin(kx + θ a) represents the sine series of the first signal corresponding to the electrons emitted from the first pattern layer 406, a represents the amplitude of the first signal,

Number

Number

[0057]

[0065] The phase terms θ b- and θ b+ are respectively represented by Equations (3) and (4). θ b- = θ a + φ - ψ Equation (3) θ b+ = θ a + φ + ψ Equation (4)

[0058]

[0066] In Equations (3) and (4), ψ represents the phase term contributed by the predetermined shift value described in this specification, and φ represents the phase term contributed by the overlay value. The phase value φ is the first conversion signal S - and the second conversion signal S +It can represent the partial phase difference between them. Since the predetermined shift value is known, the value of ψ can be inferred in equations (3) and (4).

[0059]

[0067] S in equation (1) - and S in equation (2) + Assuming that, as represented by equations (5) and (6), they are equivalent to two signals in the complex space, the differential signal S ± can be determined as a differential signal (for example, by subtraction) as represented by equation (7).

Number

Number

[0060]

[0068] In equations (5) to (10), C - , C + and C Δ are respectively called the first amplitude, the second amplitude and the third amplitude. C - and C + are related to the amplitudes of the first detector signal and the second detector signal (for example, the first detector signal and the second detector signal in FIG. 5) by Fourier transform, and since the amplitudes of the first detector signal and the second detector signal are measurable, C - can be determined based on the measured amplitude of the first detector signal according to equation (5), and C + can be determined based on the measured amplitude of the second detector signal according to equation (6).

[0061]

[0069] C Δ can be determined in different ways. For example, after determining C - and C + , S ± can be analytically determined using equation (7), and based on this, C ΔIt can also be determined analytically. As another example, first, a differential detector signal can be determined based on the difference between a first detector signal and a second detector signal (e.g., the first detector signal and the second detector signal in FIG. 5) (e.g., by subtraction), and then a Fourier transform can be applied to the differential detector signal. In such a case, C Δ can be determined as the norm of the Fourier-transformed differential detector signal.

[0062]

[0070] Based on Equations (5) to (10), Equations (1) to (4) can be converted into a quadratic function of tan φ, as represented by Equation (11), where φ is the only unknown variable.

Number

Number

[0063]

[0071] In some embodiments, to determine the overlay value, the computer-implemented method may include determining a first amplitude value of the first conversion signal, a second amplitude value of the second conversion signal, and a third amplitude value associated with the difference between the first conversion signal and the second conversion signal. Then, a phase value representing the partial phase difference between the first conversion signal and the second conversion signal can be determined. Thereafter, based on the phase value and the first pitch value (i.e., equal to the second pitch value), the overlay value of the sample can be determined.

[0064]

[0072] As an example, the first conversion signal and the second conversion signal may be S - and S + respectively, as described in connection with Equations (1) and (2). The first amplitude value, the second amplitude value, and the third amplitude value are C - , C + and C ΔIt can be. The phase value can be the value of φ determined by solving Equation (11). When the first pitch value (e.g., the first pitch value 418) and the second pitch value (e.g., the second pitch value 420) are equal and known (e.g., equal to the value of P), the overlay value is [Number] can be determined as follows.

[0065]

[0073] The exemplary method described in connection with FIGS. 4, 5 and Equations (1)-(12) may have a first target and a second target manufactured in one or more empty spaces on the wafer not occupied by the manufactured circuit. If there is not enough space on the wafer to manufacture two targets, a single target can also be used to measure the overlay of the sample, which will be described below.

[0066]

[0074] In accordance with some embodiments of the present disclosure, another computer-implemented method of measuring the overlay of a sample under a scan performed by a charged particle beam inspection device may include obtaining a detector signal in response to scanning a target of the sample. In some embodiments, the charged particle beam inspection device may include a scanning electron microscope. The sample may include a wafer.

[0067]

[0075] As an example, the charged particle beam inspection device can be an imaging system (e.g., the imaging system 200 in FIG. 2). The sample can be a wafer (e.g., the wafer 203 in FIG. 2) having a structure (e.g., a circuit) manufactured on its surface. In some embodiments, the target can be a specially designed and manufactured structure. For example, the target may be independent of the manufactured circuit on the wafer and may have no functional relationship. In some embodiments, the target can be manufactured in an empty space on the wafer not occupied by the manufactured circuit.

[0068]

[0076] The detector signal can be a signal output by a detector (e.g., detector 206 in FIG. 2) of a charged particle inspection apparatus in response to scanning. In some embodiments, the target can be scanned by a charged particle beam (e.g., of a single beam inspection apparatus) or a charged particle beamlet (e.g., of a multi-beam inspection apparatus). During the scanning of the sample, after charged particles (e.g., electrons) of the primary beam (e.g., primary beam 220 in FIG. 2) hit the surface of the sample, at least one of secondary charged particles (e.g., SE 310 shown in FIG. 3) and backscattered charged particles (e.g., BSE 308 in FIG. 3) is emitted from the surface of the sample and can be induced to the detector (e.g., detector 206 in FIG. 2). In some embodiments, at least one of secondary electrons and backscattered electrons can be emitted from the target, induced to the detector, and a detector signal can be generated.

[0069]

[0077] In some embodiments, the detector signal can be a value representing the sum or count of electrons emitted from and detected by the target. In some embodiments, the detector signal can be a value representing the sum of the charges of electrons emitted from and detected by the target. In some embodiments, the detector signal can be visualized.

[0070]

[0078] In some embodiments, the target can include a first pattern layer and a second pattern layer below the first pattern layer. The pitch values of the first pattern layer and the second pattern layer can be relative to the pitch value of the target. The first pattern layer may not have a predetermined shift relative to the second pattern layer. In some embodiments, each of the first pattern layer and the second pattern layer can include a diffraction grating.

[0071]

[0079] As an example, FIG. 6 is a schematic diagram showing an exemplary target 602 fabricated on a sample 600 that conforms to some embodiments of the present disclosure. The sample 600 can be a silicon wafer substrate (represented by the shaded area in FIG. 6). In some embodiments, the target 602 can be a diffraction-based overlay target. As shown in FIG. 6, the target 602 includes a first pattern layer 606 (represented by the hatched area within the dashed box of the target 602) and a second pattern layer 608 (represented by the dotted area within the dashed box of the target 602) below the first pattern layer 606. In FIG. 6, the first pattern layer 606 and the second pattern layer 608 can be a type of diffraction grating (e.g., a line diffraction grating). In some embodiments, the first pattern layer 606 can be a polymethyl methacrylate (PMMA) material. For example, as shown in FIG. 6, the first pattern layer 606 can be fabricated (e.g., via coating, lithography, and etching processes) on a PMMA layer 614 (represented by the hatched area below the first pattern layer 606 and the third pattern layer 610). In some embodiments, the second pattern layer 608 can be a copper material. For example, as shown in FIG. 6, the second pattern layer 608 can be fabricated (e.g., via coating, lithography, and etching processes) on the sample 600. In some embodiments, a silicon dioxide layer 616 (represented by the white area) may separate the PMMA layer 614 and the second pattern layer 608. As shown in FIG. 6, the first pattern layer 606 and the second pattern layer 608 are separated by a separation distance d.

[0072]

[0080] In FIG. 6, each of the first pattern layer 606 and the second pattern layer 608 may have a pitch. For example, when the first pattern layer 606 and the second pattern layer 608 are a kind of diffraction grating, the pitch of either the first pattern layer 606 or the second pattern layer 608 can be represented by the distance between the centers of two adjacent lines of the diffraction grating (referred to as the "pitch value" in this specification). In some embodiments, the pitch values of the first pattern layer 606 and the second pattern layer 608 can be equal to the pitch value of the target. As an example, as shown in FIG. 6, each of the first pattern layer 606 and the second pattern layer 608 may have a pitch value 618.

[0073]

[0081] In some embodiments, the first pattern layer may have a shift relative to the second pattern layer, in which case the shift can have a magnitude equal to an overlay value (e.g., the size of the overlay of the sample) or an overlay value plus or minus a predetermined shift value. In some embodiments, the shift can be represented as a displacement of a vector having a magnitude and a direction.

[0074]

[0082] As an example, as shown in FIG. 6, the first pattern layer 606 may have a shift 622 (the scales are different in FIG. 6 and are represented by the left arrow between the centers of two corresponding diffraction grating lines) with respect to the second pattern layer 608. The shift 622 can be represented as a displacement of a vector having a magnitude and a direction. Assuming that the rightward horizontal direction in FIG. 6 represents the positive direction, the shift 622 can be a negative vector. Assume that the sample 600 has an overlay (not shown in FIG. 6) representing a misalignment in the horizontal direction of the vector between the first pattern layer 606 and the second pattern layer 608 due to manufacturing errors or inaccuracies. The overlay of the sample 600 can be represented as a vector having a magnitude (i.e., an overlay value) and a direction. As shown in FIG. 6, assuming that the overlay is a positive vector (i.e., rightward), the shift 622 can have a magnitude equal to the overlay value or a value obtained by adding or subtracting a predetermined shift value (e.g., a positive value) from the overlay value. The predetermined shift value can be a designed or programmed shift value. In an ideal case, when there are no manufacturing errors or inaccuracies, the overlay can be zero, and in this case, the shift 622 can have a magnitude equal to the predetermined shift value. In FIG. 6, the predetermined shift value is zero, and the shift 622 represents the overlay of the sample.

[0075]

[0083] In accordance with some embodiments of the present disclosure, a computer-implemented method for measuring an overlay may include determining a first conversion signal by performing a Fourier transform on a detector signal, and determining a second conversion signal by converting the first conversion signal. In some embodiments, the period of the first conversion signal (e.g., the first sine series or the first cosine series) and the period of the second conversion signal (e.g., the second sine series or the second cosine series) may correspond to a pitch value of a target. As an example, referring to FIG. 6, the pitch value of the target may be the pitch value 618.

[0076]

[0084] In accordance with some embodiments of the present disclosure, a computer-implemented method for measuring an overlay may further include determining an overlay value of a sample based on a first conversion signal, a second conversion signal, a first predetermined amplitude value, and a second predetermined amplitude value. In some embodiments, the first predetermined amplitude value and the second predetermined amplitude value can be associated with two targets adjacent to the target.

[0077]

[0085] As an example, a Fourier transform can be performed on the detector signal to determine a first conversion signal S represented by the following equation (13). 1 can be determined. S 1 =a·sin(x + θ a ) + b·sin(x + θ b ) Equation (13)

[0078]

[0086] In Equation (13), a·sin(x + θ a ) represents a sine series of a first signal corresponding to electrons emitted from the first pattern layer 606, has a period corresponding to a pitch value (e.g., pitch value 618), a represents the amplitude of the first signal, and θ a represents the phase term of the first signal. Also, in Equation (13), b·sin(x + θ b ) represents a sine series of a second signal corresponding to electrons emitted from the second pattern layer 608, has a period corresponding to a pitch value (e.g., pitch value 618), b represents the amplitude of the second signal, and θ b represents the phase term of the second signal.

[0079]

[0087] As an example, the first conversion signal S represented by Equation (13) 1 is converted (e.g., by obtaining the sum of a·sin(x + θ a ) and b·sin(x + θ b )) to generate a second conversion signal S represented by Equation (14). 2 can be generated. S 2 =c·sin(x + φ) Equation (14)

[0080]

[0088] In Equation (14), c represents the third amplitude value (e.g., representing the amplitude of the sum signal), and φ represents the phase term contributed by the sum of two waves of a·sin(x + θ a ) and b·sin(x + θ b ). The overlay value is related to the phase difference (θ a - θ b ). By making S 1 equal to S 2 , the following relationship can be inferred. [Number]

[0081]

[0089] In some embodiments, the value of tanφ can be determined based on the measured value of the detector signal, and its Fourier transform is the first conversion signal S 1 . Note that the first amplitude value a and the second amplitude value b cannot be solved by Equations (13) to (17) themselves. In some embodiments, a and b in Equations (16) to (17) can be replaced with a first predetermined amplitude value a' and a second predetermined amplitude value b', and both a' and b' can be solved based on Equations (1) to (12).

[0082]

[0090] As an example, FIG. 7 is a schematic diagram showing an example of the arrangement 700 of targets manufactured on a sample, which conforms to some embodiments of the present disclosure. As shown in FIG. 7, the large white box represents a device (e.g., an integrated circuit) manufactured on a sample (e.g., the sample 500 in FIG. 5 or the sample 600 in FIG. 6). In the present disclosure, the space between two adjacent large white boxes may sometimes be referred to as a scribe lane. As an example, the arrangement 700 shows one horizontal scribe lane and two vertical scribe lanes. Pairs of a first target and a second target can be manufactured in the scribe lanes. In FIG. 7, as an example, the first target can be manufactured in the same manner as the first target 402 in FIG. 4 (having the first shift 422), and the second target can be manufactured in the same manner as the second target 404 in FIG. 4 (having the second shift 424). As shown by the legend in FIG. 7, the first target of the arrangement 700 can be represented by a small white box, and the second target of the arrangement 700 can be represented by a small black box.

[0083]

[0091] To determine the overlay value of the manufactured device shown in the arrangement 700, a third target (or referred to as "intra-device target") can be manufactured within the device, which is represented by a hatched box in FIG. 7. The third target can be manufactured in the same manner as the target 602 in FIG. 6 (having the shift 622) without having a programmed shift. The overlay value of the device (e.g., represented by the shift 622) can be determined using the exemplary method described in association with equations (13) to (17), where in this case, the values of a, b, and (θ a - θ b ) are unknown. In such a case, using the exemplary method described in association with equations (1) to (12), a first predetermined amplitude value a' and a second predetermined amplitude value b' can be generated for the pair of the first target and the second target adjacent to the third target.

[0084]

[0092] For example, referring to FIG. 7, an exemplary method described in connection with equations (13)-(17) can be applied to a third target 702 to generate a value of tan φ represented by equation (17). In this case, however, the values of a, b, and (θ a -θ b ) associated with the third target 702 are unknown. However, the exemplary method described in connection with equations (1)-(12) can be applied to a pair of a first target 704 and a second target 706. In this case, a first predetermined amplitude value a' (corresponding to the value of a in equations (1)-(12)) and a second predetermined amplitude value b' (corresponding to the value of b in equations (1)-(12)) can be determined (e.g., C - C + C Δ , ψ, and known values of φ are used to infer from equations (8) and (9)).

[0085]

[0093] The first predetermined amplitude value a' and the second predetermined amplitude value b' can each be used to determine the unknown values of a and b associated with the third target 702. For example, the unknown values of a and b associated with the third target 702 can be determined by interpolating the first predetermined amplitude value a' and the second predetermined amplitude value b' of a plurality of pairs of the first target and the second target (including the pair of the first target 704 and the second target 706). As another example, the unknown values of a and b associated with the third target 702 can be determined as the first predetermined amplitude value a' and the second predetermined amplitude value b' determined from the pair of the first target 704 and the second target 706).

[0086]

[0094] Further, based on the amplitude of the detector signal corresponding to the third target 702, the amplitude of the Fourier transform signal of the detector signal (e.g., corresponding to S 2 in equation (14)) (e.g., corresponding to c in equation (14)) can be determined. Referring to equation (16), for the third target 702, c is determined, and a and b are determined based on a' and b' as described herein. Therefore, (θ a-θ b ) values can also be determined. The overlay value of target 702 (which represents the overlay value of the manufactured device where target 702 is located) is

Number

[0087]

[0095] As an alternative, after determining the values of a, b, and c (e.g., in the manner described in connection with FIG. 7) to determine the overlay value of target 702, equation (16) is used to determine the value of (θ a -θ b ). Next, based on the secondary electron signal corresponding to target 702, the value of θ a can be determined (e.g., using an edge detection technique), and the secondary electron signal represents secondary electrons emitted from the first pattern layer of target 702 (similar to the first pattern layer 606 in FIG. 6) and may have a significant peak. After determining the values of θ a and tan φ, the value of θ b can also be determined from equation (17) (since θ b is the only remaining unknown parameter). Then, the overlay value of target 702 (which represents the overlay value of the manufactured device where target 702 is located) is

Number

[0088]

[0096] As an example, FIG. 8 is a flowchart showing an exemplary method 800 for overlay measurement that conforms to some embodiments of the present disclosure. Method 800 can be executed by a controller that can be coupled to a charged particle beam inspection apparatus (e.g., charged particle beam inspection system 100). For example, the controller can be controller 109 of FIG. 2. The controller can be programmed to implement method 800.

[0089]

[0097] In step 802, the controller can obtain a first detector signal (e.g., the first detector signal visualized in FIG. 5) in response to a first scan (e.g., by a single beam inspection apparatus or a multi-beam inspection apparatus) of a first target (e.g., the first target 402 of FIG. 4) of a sample (e.g., the sample 400 of FIG. 4), and can obtain a second detector signal (e.g., the second detector signal visualized in FIG. 5) in response to a second scan (e.g., by a single beam inspection apparatus or a multi-beam inspection apparatus) of a second target (e.g., the second target 404 of FIG. 4) of the sample. In some embodiments, the charged particle beam inspection apparatus can include a scanning electron microscope. As an example, the sample can include a wafer.

[0090]

[0098] In some embodiments, the first target may include a first pattern layer (e.g., the first pattern layer 406 in FIG. 4) and a second pattern layer below the first pattern layer (e.g., the second pattern layer 408 in FIG. 4). The second target may include a third pattern layer (e.g., the third pattern layer 410 in FIG. 4) and a fourth pattern layer below the third pattern layer (e.g., the fourth pattern layer 412 in FIG. 4). The pitch values of the first pattern layer and the second pattern layer may be equal to the first pitch value of the first target (e.g., the first pitch value 418 in FIG. 4). Also, the pitch values of the third pattern layer and the fourth pattern layer may be equal to the second pitch value of the second target (e.g., the second pitch value 420 in FIG. 4). In some embodiments, each of the first pattern layer, the second pattern layer, the third pattern layer, and the fourth pattern layer may include a diffraction grating (e.g., a line diffraction grating).

[0091]

[0099] In some embodiments, the first pattern layer may have a first shift (e.g., the first shift 422 in FIG. 4) relative to the second pattern layer, where the first shift may have a magnitude equal to a value obtained by subtracting a predetermined shift value from an overlay value (e.g., the magnitude of the overlay of the sample). The third pattern layer may have a second shift (e.g., the second shift 424 in FIG. 4) relative to the fourth pattern layer, where the second shift may have a magnitude equal to a value obtained by adding the predetermined shift value to the overlay value.

[0092]

[0100] In step 804, the controller can determine a first conversion signal (e.g., S described in connection with Equation (1)) and a second conversion signal (e.g., S described in connection with Equation (2)) by performing a Fourier transform on the first detector signal and the second detector signal. In some embodiments, the first period of the first conversion signal (e.g., described in connection with Equation (1)) - ) and the second conversion signal (e.g., S described in connection with Equation (2)) + ) can be determined. In some embodiments, the first period of the first conversion signal (e.g., described in connection with Equation (1))

Number

Number

[0093]

[0101] In step 806, the controller can determine the overlay value of the samples based on the first conversion signal and the second conversion signal (e.g., based on tanφ as described in connection with Equations (3)-(12)). In some embodiments, when the first pitch value is equal to the second pitch value (e.g., both pitch values are P), in order to determine the overlay value in step 806, the controller uses the first amplitude value of the first conversion signal (e.g., C as described in connection with Equations (5)-(12)) - ), the second amplitude value of the second conversion signal (e.g., C as described in connection with Equations (5)-(12)) + ), and the difference between the first conversion signal and the second conversion signal (e.g., S as described in connection with Equations (5)-(12)) ± ) to determine a third amplitude value (e.g., C as described in connection with Equations (5)-(12)). Then, the controller can determine a phase value (e.g., φ as described in connection with Equations (1)-(12)) representing the partial phase difference between the first conversion signal and the second conversion signal. Thereafter, the controller can determine the overlay value of the samples (e.g., Δ ) based on the first amplitude value and the first pitch value.

Number

[0094]

[0102] Figure 9 is a flowchart showing another exemplary method 900 for overlay measurement that conforms to some embodiments of the present disclosure. Method 900 can be executed by a controller that can be coupled to a charged particle beam inspection apparatus (e.g., charged particle beam inspection system 100). For example, the controller can be controller 109 of FIG. 2. The controller can be programmed to implement method 900.

[0095]

[0103] In step 902, the controller can obtain a detector signal in response to scanning (e.g., by a single beam inspection apparatus or a multi-beam inspection apparatus) of a target (e.g., target 602 of FIG. 6) of a sample (e.g., sample 600 of FIG. 6). In some embodiments, the charged particle beam inspection apparatus can include a scanning electron microscope. By way of example, the sample can include a wafer.

[0096]

[0104] In some embodiments, the first target can include a first pattern layer (e.g., first pattern layer 606 of FIG. 6) and a second pattern layer (e.g., second pattern layer 608 of FIG. 6) below the first pattern layer. The pitch values of the first pattern layer and the second pattern layer can be equal to the pitch value of the target (e.g., pitch value 618 of FIG. 6). The first pattern layer may not have a predetermined shift with respect to the second pattern layer. In some embodiments, each of the first pattern layer and the second pattern layer can include a diffraction grating (e.g., a line diffraction grating).

[0097]

[0105] In step 904, the controller can determine a first conversion signal (e.g., S 1 ) associated with Equation (13) by performing a Fourier transform on the first detector signal, and a second conversion signal (e.g., S 2It is possible to determine ( ). In some embodiments, the period of the first conversion signal and the period of the second conversion signal may correspond to a target pitch value (e.g., the pitch value 618 in FIG. 6).

[0098]

[0106] In step 906, the controller can determine an overlay value of the sample (e.g., the overlay value corresponding to tan φ described in connection with equations (17)-(20)) based on the first conversion signal, the second conversion signal, the first predetermined amplitude value, and the second predetermined amplitude value. In some embodiments, the first predetermined amplitude value (e.g., a' determined using equations (1)-(9)) and the second predetermined amplitude value (e.g., b' determined using equations (1)-(9)) can be associated with two targets adjacent to the target. For example, a target (e.g., the target 602 described in connection with FIG. 6) can be located in a first space (e.g., a die) sufficient to create a single target, and two targets (e.g., the first target 402 and the second target 404 described in connection with FIG. 4) can be adjacent to the first space and located in a second space (e.g., a scribe line) sufficient to create two targets. Both the first space and the second space are on the same sample.

[0099]

[0107] A non-transitory computer-readable medium can be provided in which a processor (e.g., the processor of the controller 109 in FIG. 1) stores instructions for performing operations such as overlay measurement, data processing, database management, graphical display, operation of an image inspection apparatus or another imaging device, detection of defects on a sample, etc., such as the method 800 in FIG. 8 or the method 900 in FIG. 9. General forms of non-transitory media include, for example, floppy disks, flexible disks, hard disks, solid state drives, magnetic tapes or any other magnetic data recording media, CD-ROMs, any other optical data recording media, any physical media having a punched pattern, RAM, PROM and EPROM, FLASH-EPROM or any other flash memory, NVRAM, caches, registers, any other memory chips or cartridges, and networked versions of these.

[0100]

[0108] Embodiments can be further described using the following clauses. 1. A charged particle beam inspection apparatus configured to scan a sample, A controller including circuitry, A system comprising: the controller is configured to Obtain a first detector signal in response to a first scan of a first target of the sample and a second detector signal in response to a second scan of a second target of the sample; and Determine a first conversion signal and a second conversion signal by performing a Fourier transform on the first detector signal and the second detector signal; and Determine an overlay value of the sample based on the first conversion signal and the second conversion signal. A system configured to perform the above. 2. The system according to clause 1, wherein a first period of the first conversion signal corresponds to a first pitch value of the first target, and a second period of the second conversion signal corresponds to a second pitch value of the second target. 3. The system according to clause 1 or 2, wherein the charged particle beam inspection apparatus includes a scanning electron microscope and the sample includes a wafer. 4. The first target includes a first pattern layer and a second pattern layer below the first pattern layer. The second target includes a third pattern layer and a fourth pattern layer below the third pattern layer. The pitch values of the first pattern layer and the second pattern layer are equal to the first pitch value of the first target. The system according to any one of clauses 1 to 3, wherein the pitch values of the third pattern layer and the fourth pattern layer are equal to the second pitch value of the second target. 5. The system according to clause 4, wherein each of the first pattern layer, the second pattern layer, the third pattern layer, and the fourth pattern layer includes a diffraction grating. 6. The first pattern layer has a first shift with respect to the second pattern layer, and the first shift has a magnitude equal to that obtained by subtracting a predetermined shift value from the overlay value. The system according to clause 4 or 5, wherein the third pattern layer has a second shift with respect to the fourth pattern layer, and the second shift has a magnitude equal to that obtained by adding a predetermined shift value to the overlay value. 7. The system according to clause 4 or 5, wherein the first pitch value is equal to the second pitch value. 8. The controller determines a first amplitude value of the first conversion signal, a second amplitude value of the second conversion signal, and a third amplitude value associated with the difference between the first conversion signal and the second conversion signal; determines a phase value representing a partial phase difference between the first conversion signal and the second conversion signal; determines an overlay value of the sample based on the phase value and the first pitch value; and is further configured to perform the operations. The system according to clause 7. 9. A non-transitory computer-readable medium storing a set of instructions executable by at least one processor of the device to cause the device to execute a method, the method comprising Obtaining a first detector signal in response to a first scan of a first target of a sample scanned by a charged particle beam inspection apparatus, and obtaining a second detector signal in response to a second scan of a second target of the sample; Determining a first conversion signal and a second conversion signal by performing a Fourier transform on the first detector signal and the second detector signal; Determining an overlay value of the sample based on the first conversion signal and the second conversion signal; A non-transitory computer-readable medium comprising: 10. The non-transitory computer-readable medium according to clause 9, wherein a first period of the first conversion signal corresponds to a first pitch value of the first target, and a second period of the second conversion signal corresponds to a second pitch value of the second target. 11. The non-transitory computer-readable medium according to clause 9 or 10, wherein the charged particle beam inspection apparatus includes a scanning electron microscope, and the sample includes a wafer. 12. The first target includes a first pattern layer and a second pattern layer below the first pattern layer; The second target includes a third pattern layer and a fourth pattern layer below the third pattern layer; Pitch values of the first pattern layer and the second pattern layer are equal to a first pitch value of the first target; The non-transitory computer-readable medium according to any one of clauses 9 to 11, wherein pitch values of the third pattern layer and the fourth pattern layer are equal to a second pitch value of the second target. 13. The non-transitory computer-readable medium according to clause 12, wherein each of the first pattern layer, the second pattern layer, the third pattern layer, and the fourth pattern layer includes a diffraction grating. 14. The first pattern layer has a first shift with respect to the second pattern layer, and the first shift has a magnitude equal to that obtained by subtracting a predetermined shift value from the overlay value. The non - transitory computer - readable medium according to clause 12 or 13, wherein the third pattern layer has a second shift with respect to the fourth pattern layer, and the second shift has a magnitude equal to the overlay value plus a predetermined shift value. 15. The non - transitory computer - readable medium according to any one of clauses 12 to 14, wherein the first pitch value is equal to the second pitch value. 16. Determining an overlay value of a sample based on a first conversion signal and a second conversion signal includes: determining a first amplitude value of the first conversion signal, a second amplitude value of the second conversion signal, and a third amplitude value associated with a difference between the first conversion signal and the second conversion signal; determining a phase value representing a fractional phase difference between the first conversion signal and the second conversion signal; determining the overlay value of the sample based on the phase value and the first pitch value. The non - transitory computer - readable medium according to clause 15. 17. A computer - implemented method for measuring an overlay of a sample under a scan performed by a charged - particle beam inspection apparatus, the method including: obtaining a first detector signal in response to a first scan of a first target of the sample and obtaining a second detector signal in response to a second scan of a second target of the sample; determining a first conversion signal and a second conversion signal by performing a Fourier transform on the first detector signal and the second detector signal; determining an overlay value of the sample based on the first conversion signal and the second conversion signal. The computer - implemented method. 18. The computer - implemented method according to clause 17, wherein a first period of the first conversion signal corresponds to a first pitch value of the first target, and a second period of the second conversion signal corresponds to a second pitch value of the second target. 19. The computer - implemented method according to clause 17 or 18, wherein the charged - particle beam inspection apparatus includes a scanning electron microscope and the sample includes a wafer. 20. The first target includes a first pattern layer and a second pattern layer below the first pattern layer. The second target includes a third pattern layer and a fourth pattern layer below the third pattern layer. The pitch values of the first pattern layer and the second pattern layer are equal to the first pitch value of the first target. The pitch values of the third pattern layer and the fourth pattern layer are equal to the second pitch value of the second target. The computer-implemented method according to any one of clauses 17 to 19. 21. The computer-implemented method according to clause 20, wherein each of the first pattern layer, the second pattern layer, the third pattern layer, and the fourth pattern layer includes a diffraction grating. 22. The first pattern layer has a first shift with respect to the second pattern layer, and the first shift has a magnitude equal to that obtained by subtracting a predetermined shift value from the overlay value. The third pattern layer has a second shift with respect to the fourth pattern layer, and the second shift has a magnitude equal to that obtained by adding a predetermined shift value to the overlay value. The computer-implemented method according to clause 20 or 21. 23. The computer-implemented method according to any one of clauses 20 to 22, wherein the first pitch value is equal to the second pitch value. 24. Determining an overlay value of a sample based on the first conversion signal and the second conversion signal includes: Determining a first amplitude value of the first conversion signal, a second amplitude value of the second conversion signal, and a third amplitude value associated with the difference between the first conversion signal and the second conversion signal; Determining a phase value representing a partial phase difference between the first conversion signal and the second conversion signal; Determining an overlay value of the sample based on the phase value and the first pitch value. The computer-implemented method according to clause 23. 25. A charged particle beam inspection apparatus configured to scan a sample, A controller including a circuit, A system including, wherein the controller Obtaining a detector signal in response to scanning of a target of a sample, Determining a first conversion signal by performing a Fourier transform on the detector signal, and determining a second conversion signal by converting the first conversion signal, Determining an overlay value of the sample based on the first conversion signal, the second conversion signal, a first predetermined amplitude value, and a second predetermined amplitude value, A system configured to perform. 26. The system according to clause 25, wherein the first predetermined amplitude value and the second predetermined amplitude value are associated with two targets adjacent to the target. 27. The system according to clause 25 or 26, wherein the period of the first conversion signal and the period of the second conversion signal correspond to a pitch value of the target. 28. The system according to any one of clauses 25 to 27, wherein the charged particle beam inspection device includes a scanning electron microscope, and the sample includes a wafer. 29. The target includes a first pattern layer and a second pattern layer below the first pattern layer, The pitch values of the first pattern layer and the second pattern layer are equal to the pitch value of the target, The system according to any one of clauses 25 to 28, wherein the first pattern layer has no predetermined shift with respect to the second pattern layer. 30. The system according to clause 29, wherein each of the first pattern layer and the second pattern layer includes a diffraction grating. 31. A non-transitory computer-readable medium storing a set of instructions executable by at least one processor of a device to cause the device to execute a method, the method being Obtaining a detector signal in response to scanning of a target of a sample scanned by a charged particle beam inspection device, Determining a first conversion signal by performing a Fourier transform on the detector signal, and determining a second conversion signal by converting the first conversion signal, Determining an overlay value of a sample based on a first conversion signal, a second conversion signal, a first predetermined amplitude value, and a second predetermined amplitude value; A non-transitory computer-readable medium including 32. The non-transitory computer-readable medium according to clause 31, wherein the first predetermined amplitude value and the second predetermined amplitude value can be associated with two targets adjacent to the target. 33. The non-transitory computer-readable medium according to clause 31 or 32, wherein the period of the first conversion signal and the period of the second conversion signal correspond to the pitch value of the target. 34. The non-transitory computer-readable medium according to any one of clauses 31 to 33, wherein the charged particle beam inspection apparatus includes a scanning electron microscope and the sample includes a wafer. 35. The target includes a first pattern layer and a second pattern layer below the first pattern layer, the pitch values of the first pattern layer and the second pattern layer are equal to the pitch value of the target, and the first pattern layer has no predetermined shift with respect to the second pattern layer. The non-transitory computer-readable medium according to any one of clauses 31 to 34. 36. The non-transitory computer-readable medium according to any one of clauses 31 to 35, wherein each of the first pattern layer and the second pattern layer includes a diffraction grating. 37. A computer-implemented method for measuring an overlay of a sample under a scan performed by a charged particle beam inspection apparatus, obtaining a detector signal in response to scanning of a target of the sample; determining a first conversion signal by performing a Fourier transform on the detector signal, and determining a second conversion signal by converting the first conversion signal; determining an overlay value of the sample based on the first conversion signal, the second conversion signal, the first predetermined amplitude value, and the second predetermined amplitude value; A computer-implemented method including. 38. The computer-implemented method according to clause 37, wherein a first predetermined amplitude value and a second predetermined amplitude value are associated with two targets adjacent to the target. 39. The computer-implemented method according to clause 37 or 38, wherein the period of the first conversion signal and the period of the second conversion signal correspond to the pitch value of the target. 40. The computer-implemented method according to any one of clauses 37 to 39, wherein the charged particle beam inspection apparatus includes a scanning electron microscope and the sample includes a wafer. 41. The target includes a first pattern layer and a second pattern layer below the first pattern layer, the pitch values of the first pattern layer and the second pattern layer are equal to the pitch value of the target, the computer-implemented method according to any one of clauses 37 to 40, wherein the first pattern layer has no predetermined shift with respect to the second pattern layer. 42. The computer-implemented method according to clause 41, wherein each of the first pattern layer and the second pattern layer includes a diffraction grating.

[0101]

[0109] The block diagrams in the figures illustrate the architecture, functionality, and operation of possible implementations of systems, methods, and computer hardware or software products according to various exemplary embodiments of the present disclosure. In this regard, each block in the flowchart or block diagram may represent a module, segment, or portion of code that includes one or more executable instructions for implementing the specified logical function. It should be understood that in some alternative implementations, the functions shown within the blocks may occur in a different order than shown in the drawings. For example, depending on the functions involved, two consecutive blocks shown may be executed or implemented substantially simultaneously, or the two blocks may be executed in reverse order. Some blocks may also be omitted. It should also be understood that each block in the block diagram and combinations of blocks may be implemented by a dedicated hardware-based system for performing the specified function or act, or by a combination of dedicated hardware and computer instructions.

[0102]

[0110] It should be understood that the embodiments of the present disclosure are not limited to the configurations as described above and illustrated in the accompanying drawings, and various modifications and changes can be made without departing from the scope of the present invention.

Claims

1. A charged particle beam inspection apparatus configured to scan a sample, a controller including a circuit, and a system including: wherein the controller is configured to obtain a first detector signal in response to a first scan of a first target of the sample and obtain a second detector signal in response to a second scan of a second target of the sample; determine a first conversion signal and a second conversion signal by performing a Fourier transform on the first detector signal and the second detector signal; determine an overlay value of the sample based on the first conversion signal and the second conversion signal; A system configured to perform the above.

2. wherein a first period of the first conversion signal corresponds to a first pitch value of the first target, and a second period of the second conversion signal corresponds to a second pitch value of the second target. The system according to claim 1.

3. wherein the charged particle beam inspection apparatus includes a scanning electron microscope, and the sample includes a wafer. The system according to claim 1.

4. wherein the first target includes a first pattern layer and a second pattern layer below the first pattern layer, the second target includes a third pattern layer and a fourth pattern layer below the third pattern layer, a pitch value of the first pattern layer and the second pattern layer is equal to a first pitch value of the first target, and a pitch value of the third pattern layer and the fourth pattern layer is equal to a second pitch value of the second target. The system according to claim 1.

5. wherein each of the first pattern layer, the second pattern layer, the third pattern layer, and the fourth pattern layer includes a diffraction grating. The system according to claim 4.

6. wherein the first pattern layer has a first shift with respect to the second pattern layer, the first shift has a magnitude equal to that obtained by subtracting a predetermined shift value from the overlay value, the third pattern layer has a second shift with respect to the fourth pattern layer, and the second shift has a magnitude equal to that obtained by adding the predetermined shift value to the overlay value. The system according to claim 4.

7. wherein the first pitch value is equal to the second pitch value. The system according to claim 4.

8. wherein the controller is configured to Determining a first amplitude value of the first conversion signal, a second amplitude value of the second conversion signal, and a third amplitude value associated with a difference between the first conversion signal and the second conversion signal; Determining a phase value representing a partial phase difference between the first conversion signal and the second conversion signal; Determining the overlay value of the sample based on the phase value and the first pitch value; The system according to claim 7, further configured to perform the above.

9. A non-transitory computer-readable medium storing a set of instructions executable by at least one processor of the device to cause the device to execute a method, the method comprising: Obtaining a first detector signal in response to a first scan of a first target of a sample scanned by a charged particle beam inspection device, and obtaining a second detector signal in response to a second scan of a second target of the sample; Determining a first conversion signal and a second conversion signal by performing a Fourier transform on the first detector signal and the second detector signal; Determining an overlay value of the sample based on the first conversion signal and the second conversion signal; A non-transitory computer-readable medium including the above.

10. A first period of the first conversion signal corresponds to a first pitch value of the first target; The non-transitory computer-readable medium according to claim 9, wherein a second period of the second conversion signal corresponds to a second pitch value of the second target.

11. The charged particle beam inspection device includes a scanning electron microscope; The non-transitory computer-readable medium according to claim 9, wherein the sample includes a wafer.

12. The first target includes a first pattern layer and a second pattern layer below the first pattern layer; The second target includes a third pattern layer and a fourth pattern layer below the third pattern layer; Pitch values of the first pattern layer and the second pattern layer are equal to a first pitch value of the first target; The non-transitory computer-readable medium according to claim 9, wherein pitch values of the third pattern layer and the fourth pattern layer are equal to a second pitch value of the second target.

13. The non - transitory computer - readable medium according to claim 12, wherein each of the first pattern layer, the second pattern layer, the third pattern layer, and the fourth pattern layer includes a diffraction grating.

14. The first pattern layer has a first shift with respect to the second pattern layer, The first shift has a magnitude equal to that obtained by subtracting a predetermined shift value from the overlay value, The third pattern layer has a second shift with respect to the fourth pattern layer, The non - transitory computer - readable medium according to claim 12, wherein the second shift has a magnitude equal to that obtained by adding the predetermined shift value to the overlay value.

15. The non - transitory computer - readable medium according to claim 12, wherein the first pitch value is equal to the second pitch value.

Images