Method and apparatus for monitoring beam profile and power

Abstract

A system and method for monitoring a beam (322) in an inspection system is provided. The system comprises: an image sensor (360) configured to collect a sequence of images of a beam spot of a beam formed on a surface (340), each image in the sequence of images having been collected at a different exposure time of the image sensor; and a controller (380) configured to combine the sequence of images to derive a beam profile of the beam.

Description

[0001] Description of the case

[0002] This application is a divisional application of the Chinese national phase patent application of the PCT application with international application number PCT / EP2019 / 072678, Chinese national application number 201980059911.2, and invention name “Method and device for monitoring beam profile and power”. Technical Field

[0003] The present disclosure relates generally to the field of charged particle beam systems, and more particularly to methods and apparatus for monitoring beam profile and beam power of a laser beam used in a charged particle beam system. Background Art

[0004] During the manufacturing process of integrated circuits (ICs), unfinished or completed circuit components are inspected to ensure that they are manufactured according to the design and are free of defects. Inspection systems using optical microscopes typically have a resolution of up to several hundred nanometers; and the resolution is limited by the wavelength of light. As the physical size of IC components continues to decrease to below 100 nanometers or even below 10 nanometers, inspection systems with higher resolution than those using optical microscopes are needed.

[0005] Charged particle (e.g., electron) beam microscopes (such as scanning electron microscopes (SEMs) or transmission electron microscopes (TEMs)) with sub-nanometer resolution are useful tools for inspecting IC components with feature sizes less than 100 nanometers. Using an SEM, electrons from a single primary electron beam or electrons from multiple primary electron beams can be focused on a location of interest on a wafer during inspection. The primary electrons interact with the wafer and may be backscattered or may cause the wafer to emit secondary electrons. The intensity of the electron beam, including the backscattered electrons and the secondary electrons, may vary based on the properties of the internal and external structures of the wafer, and may thereby indicate whether the wafer has a defect. Summary of the invention

[0006] Embodiments consistent with the present disclosure include systems, methods, and non-transitory computer readable media for monitoring a beam in an inspection system. The system includes an image sensor that collects a sequence of images of a beam spot of a beam formed on a surface. Each image in the sequence of images has been collected at a different exposure time of the image sensor. The system also includes a controller configured to combine the sequence of images to derive a beam profile of the beam.

[0007] Embodiments consistent with the present disclosure include systems, methods, and non-transitory computer readable media for monitoring a beam in an inspection system. The system includes: an image sensor configured to collect an image of a beam spot of the beam formed on a surface; and a controller configured to transform coordinates of the image based on a position of the beam and the image sensor relative to the beam spot and a magnification factor of an optical system disposed between the image sensor and the surface.

[0008] Embodiments consistent with the present disclosure include systems, methods, and non-transitory computer readable media for monitoring a beam in an inspection system. The system includes: an image sensor configured to collect multiple images of a beam spot of a beam formed at different locations on a surface; and a controller configured to generate an average image based on the multiple images.

[0009] Embodiments consistent with the present disclosure include systems, methods, and non-transitory computer readable media for monitoring a beam in an inspection system. The system includes: an image sensor configured to collect an image of a beam spot of a beam formed on a surface; and a controller configured to derive a beam profile of the beam based on the image, derive a total grayscale of the beam spot based on the beam profile, and determine a power based on a predetermined relationship between the total grayscale and the power of the beam.

[0010] Other purposes and advantages of the disclosed embodiments will be partially set forth in the following description, and in part will be clear from the description, or may be learned through the implementation of the embodiments. The purposes and advantages of the disclosed embodiments may be realized and obtained through the elements and combinations set forth in the claims.

[0011] It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the disclosed embodiments, as claimed. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] Figure 1 An exemplary electron beam inspection (EBI) system 100 consistent with embodiments of the present disclosure is shown.

[0013] Figure 2A and Figure 2B It is shown that the embodiment consistent with the present disclosure may be Figure 1 A schematic diagram of an exemplary electron beam tool that is a portion of an exemplary electron beam inspection system.

[0014] Figure 3A is a side view of an inspection system consistent with an embodiment of the present disclosure.

[0015] Figure 3B is consistent with the embodiments of the present disclosure Figure 3A Top view of the inspection system.

[0016] Figure 4 is an exemplary flow chart of a process for transforming an image of a beam spot by using a coordinate transformation method consistent with an embodiment of the present disclosure.

[0017] Figure 5A is an exemplary image of a beam spot captured by an image sensor consistent with an embodiment of the present disclosure.

[0018] Figure 5B is an exemplary image of a top view of a beam spot formed on a sample surface consistent with an embodiment of the present disclosure.

[0019] Figure 6 is a graph of a 3D beam profile derived based on an image of a beam spot formed on a relatively rough sample surface consistent with an embodiment of the present disclosure.

[0020] Figure 7 is an exemplary flow chart of a process for deriving an average beam spot image consistent with an embodiment of the present disclosure.

[0021] Fig. 8A are examples of different locations where beam spot images may be captured consistent with embodiments of the present disclosure.

[0022] Figure 8B is a diagram of a 3D beam profile derived based on an average beam spot image consistent with an embodiment of the present disclosure.

[0023] Fig. 9 is an exemplary flow chart of a process for deriving a beam profile using a dynamic range extension method consistent with an embodiment of the present disclosure.

[0024] Figures 10A-10C is an example of beam spot images obtained at different exposure times consistent with an embodiment of the present disclosure.

[0025] Figures 10D-10F is consistent with the embodiments of the present disclosure. Figures 10A-10C Example of a partial beam profile derived from the beam spot image.

[0026] Figure 10G It is consistent with the embodiments of the present disclosure based on Figures 10A-10C The complete beam profile is obtained by using the beam spot image.

[0027] Fig.11 A-11G illustrates an exemplary method of determining a grayscale amplification factor consistent with an embodiment of the present disclosure.

[0028] Fig.12 is an exemplary flow chart of a process for determining beam power using a power calibration method consistent with embodiments of the present disclosure.

[0029] Fig.13Ais an example of a 3D beam profile consistent with embodiments of the present disclosure.

[0030] Fig. 13B A method of measuring beam power by a power meter consistent with an embodiment of the present disclosure is schematically illustrated.

[0031] Fig. 13C is a graph of an exemplary relationship between beam power and overall grayscale of a beam spot consistent with some embodiments of the present disclosure. DETAILED DESCRIPTION

[0032] Reference will now be made in detail to exemplary embodiments, examples of which are shown in the accompanying drawings. The following description refers to the accompanying drawings, wherein, unless otherwise indicated, the same numbers in different drawings represent the same or similar elements. The implementations set forth in the following description of the exemplary embodiments do not represent all implementations consistent with the present invention. Instead, they are merely examples of devices and methods consistent with various aspects of the present invention as described in the appended claims.

[0033] The enhanced computing power of electronic devices can be achieved by significantly increasing the packaging density of circuit components such as transistors, capacitors, diodes, etc. on IC chips while reducing the physical size of the devices. For example, in a smart phone, an IC chip (i.e., the size of a thumb) can include more than 2 billion transistors, each of which is less than 1 / 1000 the size of a human hair. Not surprisingly, semiconductor IC manufacturing is a complex process that requires hundreds of individual steps. Even if one step goes wrong, it is likely to greatly affect the functionality of the final product. Even a "fatal defect" can cause device failure. The goal of the manufacturing process is to increase the overall yield of the process. For example, to obtain a 75% yield for a 50-step process, the yield of each individual step must be greater than 99.4%, and if the yield of a single step is 95%, the yield of the entire process will drop to 7%.

[0034] Defects may occur at various stages of semiconductor processing. For the reasons stated above, it is important to detect defects as early as possible, accurately and efficiently. A charged particle (e.g., electron) beam microscope (such as a scanning electron microscope (SEM)) is a useful tool for inspecting the surface of a semiconductor wafer to detect defects. During operation, a charged particle beam microscope scans a primary charged particle beam such as an electron beam (e-beam) on a semiconductor wafer fixed on a stage, and generates an image of the wafer surface by detecting a secondary charged particle beam reflected from the wafer surface. When the charged particle beam scans the wafer, charge may accumulate on the wafer due to the large beam current, which may have a negative impact on image quality. In order to regulate the accumulated charge on the wafer, an advanced charge controller (ACC) module is used to irradiate a light beam, such as a laser beam, on the wafer to control the accumulated charge generated due to photoconductivity and / or the photoelectric effect. Therefore, it is important to monitor the power and quality of the beam in order to effectively control the accumulated charge.

[0035] Conventionally, the power and quality of the beam are monitored by a power meter and a beam profiler. However, during the operation of a charged particle beam microscope, the microscope, the ACC module that irradiates the beam, and the stage that holds the semiconductor wafer are arranged in a vacuum chamber. Due to the limited space in the vacuum chamber, the power meter and the beam profiler cannot be arranged in the vacuum chamber. As a result, during the operation of the charged particle beam microscope, the power meter and the beam profiler cannot be used to monitor the power and quality of the beam.

[0036] To monitor the beam in the confined space of the vacuum chamber, the disclosed system uses an image sensor that has been included in a charged particle beam microscope used for other purposes (e.g., observing the wafer surface, etc.) to monitor the power and profile of the beam emitted from the ACC module.

[0037] Due to the high intensity of a light beam (e.g., a laser beam), the dynamic range of an image sensor may not be sufficient to capture a complete beam profile of the light beam. To address this problem, the disclosed system may configure the image sensor to collect an image sequence of a beam spot formed on a semiconductor wafer at different exposure times, thereby obtaining a set of images that capture a complete beam profile. As a result, even if the dynamic range of the image sensor is not large enough to capture the complete beam profile of the light beam, the controller can still obtain the complete beam profile based on a partial beam file obtained from the image sequence.

[0038] Due to the limited space inside the vacuum chamber of the microscope, the image sensor may not be able to collect images from the top side of the semiconductor wafer. Therefore, the shape of the beam spot in the image acquired by the image sensor may not be the true beam projection on the wafer. To solve this problem, the disclosed system can transform the coordinates of the image based on the position of the light and image sensor relative to the beam spot and the magnification factor of the optical system arranged between the image sensor and the wafer surface. As a result, the projection of the beam on the surface can be acquired, and the interaction between the beam and the surface can be accurately evaluated.

[0039] In some cases, the ACC module, the beam spot, and the image sensor may not be in the same plane. Therefore, the light beam cannot be directly reflected into the image sensor. To solve this problem, the disclosed system may emit the light beam onto a relatively rough surface, such as a corner of a wafer stage, and the image sensor may be configured to collect light scattered or diffracted from the rough surface. In this case, since the surface is rough, the beam profile acquired from the captured image is also rough. To solve this problem, the disclosed system may configure the image sensor to capture multiple images of the beam spot formed at different locations on the surface. Using these images, the disclosed system may generate an average image based on the multiple images, and use the average image as the collected image within at least one exposure time. As a result, even if the surface on which the beam spot is formed is relatively rough, the beam profile acquired based on the average image can be smooth.

[0040] In some cases, the disclosed system can emit a beam onto a relatively smooth and mirror-like surface, and the beam can be directly reflected into an image sensor. In this case, a single beam spot image captured by the image sensor can be used to obtain the beam profile, and it is not necessary to generate an average image based on multiple images of the beam spot formed at different locations on the surface.

[0041] In addition, the disclosed system can obtain the total grayscale of the beam spot and determine the power based on a predetermined relationship between the total grayscale and the power of the beam. The disclosed system can control the power of the ACC module based on the determined power of the beam to obtain the desired power of the beam.

[0042] Figure 1 An exemplary electron beam inspection (EBI) system 100 consistent with embodiments of the present disclosure is shown. Although this example and other examples make reference to an electron beam system, it should be understood that the techniques disclosed herein are applicable to systems other than electron beam systems, such as ellipsometers, velocimeters, CO2 lasers (e.g., for machining), non-electron beam systems (where monitoring of the laser is desired but space is limited), etc. Figure 1As shown, the EBI system 100 includes a main chamber 101, a load / lock chamber 102, an electron beam tool 104, and an equipment front end module (EFEM) 106. The electron beam tool 104 is located in the main chamber 101. The EFEM 106 includes a first load port 106a and a second load port 106b. The EFEM 106 may include a plurality of additional load ports. The first load port 106a and the second load port 106b accommodate a wafer front opening unified pod (FOUP), which accommodates wafers (e.g., semiconductor wafers or wafers made of other materials) or samples to be inspected (wafers and samples may be collectively referred to as "wafers" herein).

[0043] One or more robots (not shown) in the EFEM 106 can transport the wafer to the load / lock chamber 102. The load / lock chamber 102 is connected to a load / lock vacuum pump system (not shown) that removes gas molecules in the load / lock chamber 102 to reach a first pressure below atmospheric pressure. After reaching the first pressure, one or more robots (not shown) can transport the wafer from the load / lock chamber 102 to the main chamber 101. The main chamber 101 is connected to a main chamber vacuum pump system (not shown) that removes gas molecules in the main chamber 101 to reach a second pressure below the first pressure. After reaching the second pressure, the wafer is inspected by the electron beam tool 104. The electron beam tool 104 can be a single beam system or a multi-beam system. The controller 109 is electrically connected to the electron beam tool 104. The controller 109 can be a computer configured to perform various controls of the EBI system 100. Although the controller 109 is Figure 1 106 , but it should be understood that the controller 109 may be part of the structure.

[0044] Figure 2A A charged particle beam arrangement is shown, wherein the inspection system may include a single primary beam that may be configured to generate a secondary beam. Figure 2A In the embodiment shown, the detectors may be placed along the optical axis 105. In some embodiments, the detectors may be placed off-axis.

[0045] like Figure 2AAs shown, the electron beam tool 104 may include a wafer holder 136 supported by a motorized stage 134 to hold a wafer 150 to be inspected. The electron beam tool 104 includes an electron emitter, which may include a cathode 103, an anode 120, and a gun hole 122. The electron beam tool 104 also includes a beam limiting hole 125, a condenser lens 126, a column hole 135, an objective lens assembly 132, and an electron detector 144. In some embodiments, the objective lens assembly 132 may be a modified swinging objective delayed immersion lens (SORIL), which includes a pole piece 132a, a control electrode 132b, a deflector 132c, and an excitation coil 132d. During imaging, an electron beam 161 emitted from the tip of the cathode 103 may be accelerated by the anode 120 voltage, pass through the gun hole 122, the beam limiting hole 125, the condenser lens 126, and is focused into a detection spot by the modified SORIL lens, and then incident on the surface of the wafer 150. The detection spot can be scanned over the surface of the wafer 150 by a deflector (such as the deflector 132c in the SORIL lens or other deflectors). Secondary electrons emitted from the wafer surface can be collected by the detector 144 to form an image of the region of interest on the wafer 150.

[0046] An image processing system 199 may also be provided, which includes an image acquisition device 200, a storage device 130, and a controller 109. The image acquisition device 200 may include one or more processors. For example, the image acquisition device 200 may include a computer, a server, a mainframe, a terminal, a personal computer, any kind of mobile computing device, etc., or a combination thereof. The image collector 200 may be connected to the detector 144 of the electron beam tool 104 through a medium such as an electrical conductor, a fiber optic cable, a portable storage medium, IR, Bluetooth, the Internet, a wireless network, radio, or a combination thereof. The image acquisition device 200 may receive a signal from the detector 144 and may construct an image. The image acquisition device 200 may thus acquire an image of the wafer 150. The image acquisition device 200 may also perform various post-processing functions, such as generating a contour, superimposing an indicator on the acquired image, and the like. The image acquisition device 200 may be configured to perform adjustments to the brightness and contrast of the acquired image, etc. The storage device 130 may be a storage medium such as a hard disk, a random access memory (RAM), a cloud storage device, other types of computer-readable memory, and the like. The storage device 130 may be coupled to the image acquirer 200 and may be used to save the scanned raw image data as a raw image and save a post-processed image. The image acquirer 200 and the storage device 130 may be connected to the controller 109. In some embodiments, the image acquirer 200, the storage device 130 and the controller 109 may be integrated together as a control unit.

[0047] In some embodiments, the image acquirer 200 may acquire one or more images of the sample based on the imaging signal received from the detector 144. The imaging signal may correspond to a scanning operation for performing charged particle imaging. The acquired image may be a single image including a plurality of imaging regions, which may include various features of the wafer 150. The single image may be stored in the storage device 130. Imaging may be implemented based on imaging frames.

[0048] The light collector and illumination optics of an electron beam tool may include or be supplemented by an electromagnetic quadrupole electron lens. Figure 2A As shown, the electron beam tool 104 may include a first quadrupole lens 148 and a second quadrupole lens 158. In some embodiments, the quadrupole lenses are used to control the electron beam. For example, the first quadrupole lens 148 may be controlled to adjust the beam current, and the second quadrupole lens 158 may be controlled to adjust the beam spot size and beam shape.

[0049] although Figure 2A The electron beam tool 104 is shown as a single beam inspection tool that can use only one primary electron beam to scan one position of the wafer 150 at a time, but the embodiments of the present disclosure are not limited thereto. For example, the electron beam tool 104 can also be a multi-beam inspection tool that uses multiple primary electron beams to scan multiple positions on the wafer 150 simultaneously.

[0050] For example, now refer to Figure 2B , Figure 2B Another embodiment of the electron beam tool 104 is shown. The electron beam tool 104 (also referred to herein as the device 104) may include an electron source 202, a gun hole 204, a condenser lens 206, a primary electron beam 210 emitted from the electron source 202, a source conversion unit 212, a plurality of beams 214, 216 and 218 of the primary electron beam 210, a main projection optical system 220, a wafer stage ( Figure 2B ), a plurality of secondary electron beams 236, 238 and 240, a secondary optical system 242 and an electronic detection device 244. A controller, an image processing system, etc. may be coupled to the electronic detection device 244. The main projection optical system 220 may include a beam splitter 222, a deflection scanning unit 226 and an objective lens 228. The electronic detection device 244 may include detection sub-areas 246, 248 and 250.

[0051] Electron source 202, gun aperture 204, condenser lens 206, source conversion unit 212, beam splitter 222, deflection scanning unit 226, and objective lens 228 may be aligned with primary optical axis 260 of apparatus 104. Secondary optical system 242 and electron detection device 244 may be aligned with secondary optical axis 252 of apparatus 104.

[0052] The electron source 202 may include a cathode, an extractor, or an anode, where primary electrons may be emitted from the cathode and extracted or accelerated to form a primary electron beam 210 having a cross (virtual or real) 208. The primary electron beam 210 may be visualized as being emitted from the cross 208. The gun aperture 204 may block peripheral electrons of the primary electron beam 210 to reduce the size of the detection spots 270, 272, and 274.

[0053] The source conversion unit 212 may include an array of image forming elements ( Figure 2B ) and an array of beam limiting apertures ( Figure 2B 201 ). Examples of source conversion unit 212 can be found in: U.S. Patent No. 9,691,586; U.S. Publication No. 2017 / 0025243; and International Application No. PCT / EP2017 / 084429, all of which are incorporated herein by reference in their entirety. The array of image forming elements may include an array of microdeflectors or microlenses. The array of image forming elements may form multiple parallel images (virtual or real) of intersection 208 with multiple beamlets 214, 216, and 218 of primary electron beam 210. The array of beam limiting apertures may limit the multiple beamlets 214, 216, and 218.

[0054] The condenser lens 206 can focus the primary electron beam 210. The current of the beam waves 214, 216 and 218 downstream of the source conversion unit 212 can be changed by adjusting the focal length of the condenser lens 206 or by changing the radial size of the corresponding beam limiting holes in the array of beam limiting holes. The condenser lens 206 can be a movable condenser lens, which can be configured so that the position of its first principal plane is movable. The movable condenser lens can be configured to be magnetic, which can cause the off-axis beam waves 216 and 218 to fall on the beam limiting holes at a rotation angle. The rotation angle varies with the focal length and position of the first principal plane of the movable condenser lens. In some embodiments, the movable condenser lens can be a movable anti-rotation condenser lens, which involves an anti-rotation lens having a movable first principal plane. The movable condenser lens is further described in U.S. Publication No. 2017 / 0025241 (which is incorporated herein by reference in its entirety).

[0055] The objective lens 228 may focus the beams 214 , 216 , and 218 onto the wafer 230 for inspection, and may form a plurality of detection spots 270 , 272 , and 274 on the surface of the wafer 230 .

[0056] The beam splitter 222 can be a Wien filter type beam splitter that generates an electrostatic dipole field and a magnetic dipole field. In some embodiments, if they are applied, when the electrons of the beam travel at a specific speed, the magnitude of the force exerted by the electrostatic dipole field on the electrons of the beam waves 214, 216 and 218 can be equal and opposite in direction to the force applied to the electrons by the magnetic dipole field. Therefore, the beam waves 214, 216 and 218 can pass straight through the beam splitter 222 with a zero deflection angle. However, the total dispersion of the beam waves 214, 216 and 218 generated by the beam splitter 222 can also be non-zero, such as when the electrons of the beam travel at a speed different from the specific speed. The beam splitter 222 can separate the secondary electron beams 236, 238 and 240 from the beam waves 214, 216 and 218, and direct the secondary electron beams 236, 238 and 240 to the secondary optical system 242.

[0057] The deflection scanning unit 226 can deflect the beams 214, 216, and 218 to scan the detection spots 270, 272, and 274 on the surface area of ​​the wafer 230. In response to the incidence of the beams 214, 216, and 218 at the detection spots 270, 272, and 274, secondary electron beams 236, 238, and 240 can be emitted from the wafer 230. The secondary electron beams 236, 238, and 240 may include electrons having an energy distribution including secondary electrons and backscattered electrons. The secondary optical system 242 can focus the secondary electron beams 236, 238, and 240 onto the detection sub-regions 246, 248, and 250 of the electron detection device 244. The detection sub-regions 246, 248, and 250 can be configured to detect the corresponding secondary electron beams 236, 238, and 240, and generate corresponding signals for reconstructing an image of the surface area of ​​the wafer 230.

[0058] Figure 3A is a side view of an inspection system 300 consistent with an embodiment of the present disclosure. Figure 3AAs shown, the inspection system 300 includes an electron beam tool 310, an advanced charge controller (ACC) module 320, a stage 330 on which a sample to be inspected (e.g., a wafer 340) is set, and a beam monitoring system 350. The electron beam tool 310 can emit a primary electron beam 312 to an area of ​​interest on the wafer 340, and collect secondary electrons emitted from the wafer surface to form an image of the area of ​​interest on the wafer 340. The ACC module 320 may include an ACC emitter that emits a light beam 322 (e.g., a laser beam) onto the wafer 340 and forms a beam spot of the light beam 322 on the wafer surface. When the primary electron beam 312 irradiates the area of ​​interest on the wafer 340, charges may be accumulated due to the large beam current. The light beam 322 emitted from the ACC module 320 may be configured to adjust the accumulated charge caused by photoconductivity or photoelectric effect or a combination of photoconductivity and photoelectric effect. It is important to monitor the power and quality of the light beam 322 emitted from the ACC module 320 to effectively adjust the accumulated charge by the light beam 322.

[0059] Conventionally, the power and quality of the beam are monitored by a power meter and a beam profiler. However, the inspection system 300 may not be provided with a power meter or a beam profiler. As a result, the power and quality of the beam may not be monitored in situ (ie, during operation of the monitoring system 300).

[0060] According to an embodiment of the present disclosure, a beam monitoring system 350 may be included in the inspection system 300 to monitor the power and profile of the light beam 322 emitted from the ACC module 320. The beam monitoring system 350 may include an image sensor 360, an optical system 370 disposed between the wafer 340 and the image sensor 360, and a controller 380. The optical system 370 may include one or more optical lenses configured to focus the secondary beam 324 onto the image sensor 360. The secondary beam 324 may include a light beam scattered from the wafer surface, or a light beam diffracted from the wafer surface, or a combination of a light beam scattered from the wafer surface and a light beam diffracted from the wafer surface. The image sensor 360 may be a charge coupled device (CCD) camera or a complementary metal oxide semiconductor (CMOS) sensor that detects the secondary beam 324 to form an image of the secondary beam 324. The controller 380 may be a computer configured to receive an image of the secondary beam 324 from the image sensor 360 and acquire a beam profile and a beam power of the light beam 322 emitted from the ACC module 320 based on the image of the secondary beam 324. In addition, the controller 380 may be configured to control the ACC module 320 based on the beam profile and beam power of the light beam 322. For example, based on the beam power of the light beam 322, the controller 380 may automatically adjust the operating current of the ACC emitter included in the ACC module 320 to keep the output power of the ACC emitter at the target power or to maintain stability. At the same time, based on the beam profile of the light beam 322, the controller 380 may adjust the beam shaper included in the ACC module 320 to obtain the desired shape of the beam profile or the desired power distribution. Moreover, based on the beam power of the light beam 322, the controller 380 may be configured to monitor the position of the beam spot formed by the light beam 322 on the wafer surface. In the event of misalignment, the controller 380 may be configured to realign the beam spot to the field of view of the electron beam tool 310. That is, the controller 380 may control the ACC emitter to emit the light beam 322 to the position on the wafer 340 irradiated by the primary electron beam 312.

[0061] Figure 3B FIG. 3 is a top view of an inspection system 300 during operation of a beam monitoring system 350 consistent with an embodiment of the present disclosure. To simplify the illustration, the electron beam tool 310 and the controller 380 are shown from the top. Figure 3B is omitted. Figure 3BAs shown, in the inspection system 300, the light beam 322 from the ACC module 320 can be aligned with the field of view of the electron beam tool 310. At the same time, the field of view of the image sensor 360 can also be aligned with the field of view of the electron beam tool 310. At the beginning of the electron beam monitoring process, the field of view of the electron beam tool 310 can be moved to the corner portion of the stage 330 where the wafer 340 is not provided. This corner portion of the stage 330 can have a relatively rough surface, and the secondary beam 324 can be scattered or diffracted from the rough surface. In this way, the image sensor 360 can capture an image of the beam spot formed on the corner portion of the stage 330. In some alternative embodiments, a specially designed sample surface can be used to collect the beam signal emitted from the ACC module 320. In addition, alternatively, a wafer surface or a smooth surface can also be used to collect the beam signal emitted from the ACC module 320.

[0062] In some embodiments (such as Figure 3A In the embodiment shown in FIG. 3 , the ACC module 320 and the image sensor 360 are disposed outside the vacuum chamber 390, in which the electron beam tool 310 and the wafer 340 are disposed. During operation of the inspection system 300, the light beam 322 and the secondary beam 324 may pass through one or more windows formed in the vacuum chamber 390. In some alternative embodiments, at least one of the ACC module 320 and the image sensor 360 may be disposed inside the vacuum chamber 390.

[0063] In some embodiments (such as Figure 3A and 3B In the embodiment shown in the figure), the image sensor 360 is not directly disposed above the beam spot formed by the light beam 322 emitted from the ACC module 320, and thus the image sensor 360 may not capture an image of the beam spot from the top side of the beam spot. As a result, the shape of the beam spot in the image captured by the image sensor 360 may be different from the projection of the light beam 322 on the surface. Nevertheless, the projection of the light beam 322 on the sample surface (“top view”) enables the interaction between the light beam 322 and the sample (e.g., the wafer 340) to be evaluated. Therefore, according to an embodiment of the present disclosure, the controller 380 may be configured to transform the image of the beam spot acquired by the image sensor 360 (hereinafter referred to as the “beam spot image”) to obtain the projection of the light beam 322 on the sample surface. The method performed by the controller 380 is referred to as a coordinate transformation method.

[0064] Figure 4 is an exemplary flow chart of a process 400 for transforming a beam spot image by using a coordinate transformation method consistent with an embodiment of the present disclosure. The process 400 may be performed by, for example, Figure 3A The controller 380 shown is executed by a controller such as the controller.

[0065] like Figure 4 As shown, in step 410, the controller may acquire a sample formed on the sample surface and imaged by an image sensor (eg, Figure 3A The beam spot image is captured by the image sensor 360). Figure 5A is set in Figure 3B An exemplary beam spot image captured by the image sensor 360 at the position shown. Figure 5A As shown, the shape of the beam spot at the center of the image is distorted.

[0066] In step 420, the controller may transform the coordinates of the beam spot image to obtain a top view of the beam spot formed on the sample surface. The coordinate transformation may be performed based on the position and layout of the optical system 370, the ACC module 320, and the image sensor 360. For example, the controller 380 may transform the coordinates of at least one pixel in the beam spot image based on the following equation:

[0067]

[0068] Where x' and y' are Cartesian coordinates on the wafer, x and y are coordinates in the beam spot image captured by the image sensor 360, m is the magnification of the optical system 370, and θ is the angle of the image sensor 360 relative to the sample surface, as Figure 3A shown. Figure 5B is a top view of the beam spot formed on the sample surface that can be obtained by using the coordinate transformation method. Figure 5B As shown, after the coordinate transformation, the shape of the beam spot becomes less distorted.

[0069] As previously mentioned, in some embodiments, the image is on a relatively rough surface (such as Figure 3B Due to the rough surface, light from the beam 322 may be scattered or diffracted into the image sensor 360. However, the scattering rate is not uniform across the beam spot, resulting in a distorted beam profile acquired by the controller 380 based on the beam spot image captured by the image sensor 360. Figure 6 is a diagram of an exemplary 3D beam profile acquired based on a beam spot image formed on a relatively rough sample surface. Figure 6 In the figure, the horizontal axis represents the position on the sample surface, and the vertical axis represents the light intensity (eg, gray scale) of the beam spot at different positions. Figure 6 As shown, the intensity of the beam spot formed on the relatively rough sample surface is not smoothly distributed.

[0070] In order to minimize or eliminate the influence of the rough surface on the beam profile, according to an embodiment of the present disclosure, the image sensor 360 can be configured to capture multiple beam spot images at different positions on the sample surface, and the controller 380 can obtain an average image based on the multiple images. This method is called a position average method.

[0071] Figure 7 FIG. 7 is an exemplary flow chart of a process 700 for acquiring an average beam spot image consistent with an embodiment of the present disclosure. The process 700 may be performed by, for example, Figure 3A The controller 380 shown is executed by a controller such as the controller.

[0072] like Figure 7 As shown, the controller may acquire multiple images of beam spots formed at different positions on the sample surface at step 710. The positions selected for performing the position averaging method may be, but are not limited to, a 4×4 or 5×5 matrix. Fig. 8A is an example of a 4×4 matrix of positions 1 to 16 where the beam spot image can be captured using the position averaging method. Fig. 8A In the 4×4 matrix shown, the controller may first place the stage (e.g., Figure 3A The stage 330 of the embodiment of the present invention is moved to position 1 so that the carrier from the ACC module (e.g., Figure 3A ACC module 320) bundle (e.g., Figure 3A The light beam 322) forms a beam spot at position 1, and an image sensor (e.g., Figure 3A The image sensor 360 of the ACC module can capture an image of the beam spot formed at position 1. Then, the controller can move the stage to position 2 while keeping the positions of the ACC module and the image sensor unchanged, so that the light beam from the ACC module forms a beam spot at position 2, and the image sensor can capture an image of the beam spot formed at position 2. This process continues for positions 3 to 16 until the image sensor captures an image of the beam spot formed at position 16. As a result, the controller can acquire sixteen (16) beam spot images formed at positions 1 to 16, respectively.

[0073] Reference again Figure 7 At step 720, the controller may generate an average image based on the plurality of images. Fig. 8A In the example of the 4×4 matrix shown, the controller may generate an average image based on sixteen (16) beam spot images acquired at positions 1 to 16. In some embodiments, the beam spot images may be grayscale images, each grayscale image including a plurality of pixels, and each pixel having a grayscale level. The controller may calculate an average grayscale level for at least one pixel based on the grayscale levels of all corresponding pixels in the plurality of images. For example, in Fig. 8AIn the example of the 4×4 matrix shown, for a pixel at position (x, y), the controller may sum the grayscale levels of all pixels at position (x, y) in all sixteen (16) images, and divide the obtained grayscale levels by 16 to obtain the average grayscale level of the pixel. Figure 8B is a graph of an exemplary 3D beam profile acquired based on an average image generated based on sixteen (16) beam spot images captured at positions 1 to 16. Figure 8B As shown, the intensity of the beam spot in the average image is smoothly distributed.

[0074] Typically, image sensors have a dynamic range of 8, 10, or 16 bits. Because a light beam (e.g., a laser beam) may have a high intensity, or the beam intensity may vary greatly from the center to the edge of the light beam, it may be difficult to obtain the entire beam profile (i.e., the entire intensity distribution) of the light beam through the image sensor due to the limited dynamic range of the image sensor. According to some embodiments of the present disclosure, in order to overcome the limited dynamic range of the image sensor and avoid using overexposed pixel information, the complete beam profile can be restored by using images of the beam spot acquired at different exposure times. As used herein, exposure time refers to the length of time when a film or digital sensor in an image sensor is exposed to light. This method may be referred to as a dynamic range extension method.

[0075] Fig. 9 FIG. 9 is a flow chart of a process 900 for obtaining a beam profile using a dynamic range extension method consistent with an embodiment of the present disclosure. The process 900 may be performed by, for example, Figure 3A The controller 380 shown is executed by a controller such as the controller.

[0076] like Fig. 9 As shown, in step 910, the controller may first obtain Figure 3A The image sensor 360 and the like are used to capture a sequence of images of a beam spot at different exposure times of an image sensor. That is, each image in the sequence of images is captured by the image sensor at a different exposure time of the image sensor. The exposure time can range from a shortened exposure time available for the image sensor to an exposure time long enough to capture the edge of the beam spot. Different exposure times can be selected to ensure that the partial beam profiles acquired from the sequence of images overlap each other. Figures 10A-10C is an example of images of beam spots captured at exposure times t1, t2, and t3. Figures 10D-10F They are respectively from Figures 10A-10C Example of a partial beam profile obtained in an image of . The exposure time t1 is the shortest of t1, t2, and t3. Fig. 10D As shown, the exposure time t1 can produce a first partial beam profile of high level. Then, by increasing the exposure time to t2, the following can be obtained: Fig. 10ENext, the exposure time is increased to t3, which can produce a low-level third partial beam profile, as shown in FIG. Fig.10F shown. Figures 10D-10F Some of the beam contours in partially overlap each other.

[0077] In step 920, the controller may adjust at least one beam spot image by using a grayscale magnification factor of the at least one beam spot image. Here, in order to overcome the limited dynamic range of the image sensor, the controller may first select useful pixel information by selecting pixels that are within the dynamic range or do not have a dynamic range (also referred to as "pixels containing useful information") from all pixels in the image. Pixels without useful information (also referred to as "useless pixels") may be discarded or ignored by the controller. In other words, in some embodiments, only pixels with useful information are used in the processing. The controller may adjust the beam spot image by, for example, multiplying the grayscale of each pixel containing useful information in the beam spot image by the grayscale magnification factor of the image.

[0078] In some embodiments, the controller may determine the grayscale magnification factor of the beam spot image based on the exposure time for capturing the beam spot image. The grayscale magnification factor may be inversely proportional to the exposure time. The longer the exposure time, the lower the grayscale magnification factor; and vice versa. For example, the grayscale magnification factor of the first selected beam spot image may be calculated by dividing the first exposure time for capturing the first selected beam spot image by the second exposure time for capturing the second selected beam spot image.

[0079] In some other embodiments, the controller may determine the grayscale magnification factor based on the grayscale of the same pixel at different exposure times. For example, the controller may determine the grayscale magnification factor associated with the beam spot image by comparing the grayscale of the pixel in the beam spot image with the grayscale of the pixel in other beam spot images. Fig.11 A-11G illustrates an exemplary method of determining a grayscale amplification factor according to these embodiments.

[0080] Specifically, Fig.11 A is a first exemplary beam spot image collected at exposure time t1. Fig.11 B is a second exemplary beam spot image collected at exposure time t2. Fig.11 C is when observing along the x-axis on the sample surface where the beam spot is formed, Fig.11 A and 11B are graphs of the grayscale levels of pixels (i.e., useful pixels) in the first and second beam spot images. Fig.11 In the graph of C, the values ​​on the horizontal axis represent the positions along the x-axis, and the values ​​on the vertical axis represent the grayscale levels. Fig.11 D is Fig.11 A and 11B are top views of the grayscale levels of useful pixels in the first and second beam spot images. Fig.11 In the graph of FIG. 3D, the value on the horizontal axis represents the position along the x-axis, and the value on the vertical axis represents the position along the y-axis perpendicular to the x-axis. The controller 380 can compare the grayscales of the first and second beam spot images to obtain a plurality of overlapping pixel pairs. The pixels in each overlapping pixel pair have the same position in the corresponding beam spot image. Fig.11 E is a graph of gray levels of a plurality of overlapping pixel pairs when viewed along the x-axis on the sample surface where the beam spot is formed. Fig.11 F is a top view of the grayscale of the plurality of overlapping pixel pairs. The controller may determine the grayscale amplification factor associated with the first beam spot image based on the grayscale of the overlapping pixel pairs by using at least one of the two exemplary methods described below.

[0081] In a first exemplary method, the controller may determine a single grayscale magnification factor for each overlapping pixel pair based on a ratio of grayscales of the overlapping pixel pairs. For example, for an overlapping pixel pair consisting of a first pixel from a first beam spot image and a second pixel from a second beam spot image, the controller may determine a single grayscale magnification factor by, for example, dividing the grayscale of the second pixel by the grayscale of the first pixel. The controller may then determine a grayscale magnification factor associated with the first beam spot image, for example, by averaging the single grayscale magnification factors of all multiple overlapping pixel pairs.

[0082] In a second exemplary method, assuming that the plurality of overlapping pixel pairs include a first group of pixels from the first beam spot image and a second group of pixels from the second beam spot image, the controller may obtain a first total grayscale by adding the grayscales of the first group of pixels, and obtain a second total grayscale by adding the grayscales of the second group of pixels. The controller may then determine a grayscale amplification factor associated with the first beam spot image by dividing the first total grayscale by the second total grayscale.

[0083] After determining the grayscale magnification factor associated with the first beam spot image, the controller can adjust the first beam spot image by, for example, multiplying the grayscale of each pixel containing useful information in the first beam spot image by the grayscale magnification factor. The controller can then combine the grayscale in the adjusted first beam spot image with the grayscale in the second beam spot image to derive a beam profile. Fig.11 G is a graph of gray levels in the beam profile acquired by the controller 380 .

[0084] Reference again Fig. 9 At step 930, the controller may combine the image sequence to obtain a beam profile. For example, the controller may align the image obtained from the beam spot image. Figures 10D-10F Combine the partial bundle contours in Figures 10A-10C The beam spot image in Figure 10GThe complete beam profile is shown. The complete beam profile can be used to monitor beam quality.

[0085] exist Figures 10A-10G In the example shown, three (3) beam spot images are used to acquire a complete beam profile. The present disclosure is not limited thereto, and fewer or more images acquired at different exposure times may be used to acquire a complete beam profile. Typically, 5 to 13 beam spot images may be used. In some cases where the dynamic range of the image sensor is large enough, a single beam spot image may be sufficient to generate a complete beam profile.

[0086] According to some embodiments of the present disclosure, the power of the light beam ("beam power") may also be determined based on the beam spot image captured by the image sensor. This method is called a power calibration method. Fig.12 FIG. 1 is a flow chart of a process 1200 for determining beam power using a power calibration method consistent with such an embodiment. Process 1200 may be performed by, for example, Figure 3A The controller 380 and other controllers are executed.

[0087] like Fig.12 As shown, in step 1210, the controller may obtain a Figure 3A In step 1220, the controller may obtain a beam profile of the light beam based on the beam spot image. For example, the controller may use a reference Fig. 9 In step 1230, the controller may obtain the total grayscale of the beam spot by, for example, summing the grayscales of all pixels in the beam profile. In step 1240, the controller may determine the power of the light beam based on the relationship between the beam power and the total grayscale.

[0088] The total gray level GL can be written as:

[0089] GL=Power*β*η

[0090] Where Power is the power of the beam spot from the diffraction surface, which can be measured by a power meter, β is the energy diffraction efficiency to the image sensor, and η is the conversion ratio of power to grayscale. β*η represents the relationship between power and total grayscale GL. β*η can be calibrated before the operation of the inspection system (e.g., the inspection system 100) and can be stored in a memory.

[0091] For example, to calibrate β*n, the controller may first acquire the image signal received by an image sensor such as Figure 3A The controller may capture an image of a sample beam spot of the sample beam (hereinafter referred to as a “sample beam spot image”) by an image sensor 360 of the vacuum chamber. The beam spot image may be captured inside or outside the vacuum chamber. The controller may derive a beam profile of the sample beam based on the beam spot image. Fig.13Ais an example of a 3D beam profile that can be derived by the controller. After the beam profile of the sample beam is derived, the controller can derive the total gray level of the sample beam spot by, for example, summing the gray levels of the pixels in the beam profile of the sample beam. The controller can then derive the power of the sample beam measured by the power meter. Fig. 13B A method for measuring beam power by a power meter consistent with some embodiments of the present disclosure is schematically shown. Fig. 13B As shown, the ACC module 1300 can be configured to emit a beam 1310 directly into a power meter 1320, and the power meter 1320 can measure the beam power of the beam 1310. After the controller derives the beam power of the sample beam, the controller can determine β* η , which represents the relationship between the total grayscale of the sample beam spot and the power of the sample beam. Fig. 13C is a graph of an exemplary relationship between beam power and total grayscale level of a sample beam. Fig. 13C In the figure, the horizontal axis represents beam power and the vertical axis represents the total grayscale of the beam spot. By doing so, the total grayscale of the beam spot can be related to the beam power. The beam power of the ACC module can then be monitored using the total grayscale count of the beam spot image captured in situ by the image sensor.

[0092] According to the embodiments disclosed above, a beam monitoring system for monitoring a light beam emitted from an ACC module in an inspection system may include an image sensor configured to collect an image sequence of a beam spot formed by the beam at different exposure times of the image sensor, and a controller configured to combine the image sequence to obtain a beam profile of the beam. As a result, even if the dynamic range of the image sensor is not sufficient to capture the complete beam profile of the beam, the controller can still derive the complete beam profile based on the partial beam file derived from the image sequence.

[0093] In addition, the controller can be configured to transform the coordinates of the image for at least one image in the image sequence based on the position of the light and image sensor relative to the beam spot and the magnification factor of the optical system arranged between the image sensor and the surface. As a result, the projection of the beam on the surface can be derived and the interaction between the light beam and the surface can be accurately evaluated.

[0094] In addition, the image sensor may be configured to collect a plurality of images of the beam spot formed at different positions on the surface at at least one exposure time, and the controller may be configured to generate an average image based on the plurality of images, and use the average image as the collected image at at least one exposure time. As a result, even if the surface on which the beam spot is formed is relatively rough, the beam profile derived based on the average image may be smooth.

[0095] Furthermore, the controller can be configured to derive a total grayscale level of the beam spot by summing the grayscale levels of all pixels in the beam profile, and determine the power based on a predetermined relationship between the total grayscale level and the power of the beam. As a result, the beam power can be derived in situ while the inspection system is running, without the need for a power meter.

[0096] The embodiments may be further described using the following terms:

[0097] 1. A system for monitoring a beam in an inspection system, comprising:

[0098] an image sensor comprising circuitry to collect a sequence of images of a beam spot of the beam formed on a surface, each image in the sequence of images having been collected at a different exposure time of the image sensor; and

[0099] A controller having one or more processors and memory is configured to combine the sequence of images to derive a beam profile for the beam.

[0100] 2. The system of clause 1, wherein the controller is further configured to adjust an image in the sequence of images by using a grayscale magnification factor associated with the image.

[0101] 3. A system according to clause 2, wherein the controller is further configured to adjust the image by multiplying the grayscale level of each pixel in the image containing useful information by the grayscale amplification factor associated with the image.

[0102] 4. A system according to any one of clauses 2 and 3, wherein the controller is configured to determine the grayscale amplification factor associated with the image based on an exposure time for collecting the image.

[0103] 5. A system according to any one of clauses 2 and 3, wherein the controller is configured to determine the grayscale amplification factor associated with the image based on a comparison of grayscale of pixels in the sequence of images.

[0104] 6. The system of clause 5, wherein the image is a first selected image in the sequence of images, and the controller is configured to determine the grayscale magnification factor associated with the first selected image based on:

[0105] comparing the first selected image to a second selected image of the plurality of images to derive a plurality of overlapping pixel pairs; and

[0106] The grayscale amplification factor associated with the first selected image is determined based on grayscales of pixels in the plurality of overlapping pixel pairs.

[0107] 7. A system according to any one of clauses 1 to 6, wherein the controller is further configured to transform the coordinates of a specific image in the image sequence based on the position of the beam and the image sensor relative to the beam spot and a magnification factor of an optical system arranged between the image sensor and the surface.

[0108] 8. A system according to any one of clauses 1 to 7, wherein

[0109] The image sensor includes circuitry to collect multiple images of the beam spot formed at different locations on the surface during an exposure time, and

[0110] The controller is configured to:

[0111] generating an average image based on the plurality of images; and

[0112] The average image is used as the image collected at the exposure time.

[0113] 9. The system of clause 8, wherein the controller is configured to generate the average image by:

[0114] For a pixel, an average gray level is determined based on the gray levels of the pixel in the plurality of images.

[0115] 10. The system according to any one of clauses 1 to 9, wherein the controller is further configured to:

[0116] deriving a total gray level of the beam spot by summing the gray levels of all pixels in the beam profile; and

[0117] The power is determined based on a relationship between the total grey scale and the power of the beam.

[0118] 11. The system of clause 10, wherein the controller is configured to determine the relationship between the total grayscale and the power by:

[0119] deriving the power of the sample beam measured by the power meter;

[0120] obtaining an image of a sample beam spot formed by the sample beam;

[0121] deriving a beam profile of the sample beam based on the image of the sample beam;

[0122] deriving a total gray level of the sample beam spot by summing the gray levels of the pixels in the beam profile of the sample beam;

[0123] determining a relationship between the total grayscale level of the sample beam spot and the power of the sample beam; and

[0124] The relationship between the total gray level and the power is determined based on the relationship between the total gray level of the sample beam spot and the power of the sample beam.

[0125] 12. A system according to any one of clauses 10 and 11, wherein

[0126] The inspection system also includes a transmitter including circuitry to transmit the beam, and

[0127] The controller is also configured to adjust an output power of the transmitter based on the determined power of the beam.

[0128] 13. A system according to any one of clauses 1 to 12, wherein

[0129] The inspection system also includes a transmitter including circuitry to transmit the beam, and the transmitter includes a beam shaper, and

[0130] The controller is further configured to control the beam shaper based on the beam profile of the beam.

[0131] 14. The system of any of clauses 1 to 13, wherein the inspection system further comprises a charged particle beam tool comprising circuitry to emit a charged particle beam onto the surface.

[0132] 15. The system of clause 14, wherein the controller is further configured to align the beam spot of the beam to a field of view of the charged particle beam tool.

[0133] 16. The system of clause 14, wherein the inspection system further comprises an advanced charge control module comprising circuitry to emit the beam.

[0134] 17. The system of clause 16, wherein the charged particle beam tool, the advanced charge control module, and the image detector are disposed outside a vacuum chamber.

[0135] 18. A method of monitoring a beam in an inspection system, comprising:

[0136] deriving a sequence of images of a beam spot of the beam formed on a surface, each image in said sequence of images having been collected by an image sensor at a different exposure time of said image sensor; and

[0137] The sequence of images is combined to derive a bundle profile of the bundle.

[0138] 19. The method of clause 18, further comprising adjusting an image in the sequence of images by using a grayscale magnification factor associated with the image.

[0139] 20. The method of clause 19, wherein adjusting the image in the sequence of images comprises:

[0140] The grayscale level of each pixel in the image containing useful information is multiplied by the grayscale amplification factor associated with the image.

[0141] 21. The method of any of clauses 19 and 20, further comprising determining the grayscale amplification factor associated with the image based on an exposure time over which the image was collected.

[0142] 22. The method of any of clauses 19 and 20, further comprising determining the grayscale amplification factor associated with the image based on a comparison of grayscale of pixels in the sequence of images.

[0143] 23. A method according to clause 22, wherein the image is a first selected image in the sequence of images, and the method further comprises:

[0144] comparing the first selected image to a second selected image of the plurality of images to derive a plurality of overlapping pixel pairs; and

[0145] The grayscale amplification factor associated with the first selected image is determined based on grayscales of pixels in the plurality of overlapping pixel pairs.

[0146] 24. The method according to any one of clauses 18 to 23 further comprises: for a specific image in the image sequence, transforming the coordinates of the specific image based on the position of the beam and the image sensor relative to the beam spot and the magnification factor of the optical system arranged between the image sensor and the surface.

[0147] 25. The method according to any one of clauses 18 to 24, further comprising:

[0148] deriving a plurality of images of the beam spot formed at different locations on the surface; and

[0149] An average image is generated based on the plurality of images.

[0150] 26. The method of clause 25, wherein said generating said average image comprises:

[0151] For a pixel, an average gray level is determined based on the gray levels of the pixel in the plurality of images.

[0152] 27. The method according to any one of clauses 18 to 26, further comprising:

[0153] deriving a total gray level of the beam spot by summing the gray levels of all the pixels in the beam profile; and

[0154] The power is determined based on a predetermined relationship between the overall grey scale and the power of the beam.

[0155] 28. The method according to clause 27, further comprising determining the relationship between the total grayscale and the power by:

[0156] deriving the power of the sample beam measured by the power meter;

[0157] obtaining an image of a sample beam spot formed by the sample beam;

[0158] deriving a beam profile of the sample beam based on the image of the sample beam;

[0159] deriving a total gray level of the sample beam spot by summing the gray levels of the pixels in the beam profile of the sample beam;

[0160] determining a relationship between the total grayscale level of the sample beam spot and the power of the sample beam; and

[0161] The relationship between the total gray level and the power is determined based on the relationship between the total gray level of the sample beam spot and the power of the sample beam.

[0162] 29. A method according to any one of clauses 27 and 28, wherein

[0163] The inspection system also includes a transmitter that transmits the beam, and

[0164] The method also includes adjusting an output power of the transmitter based on the determined power of the beam.

[0165] 30. A method according to any one of clauses 18 to 29, wherein

[0166] The inspection system further comprises a transmitter that transmits the beam, and the transmitter comprises a beam shaper, and

[0167] The method further comprises controlling the beam shaper based on the beam profile of the beam.

[0168] 31. A method according to any one of clauses 18 to 30, wherein

[0169] The inspection system further comprises an emitter for emitting the beam and a charged particle beam tool for emitting the charged particle beam onto the surface,

[0170] The method also includes aligning the beam spot of the beam with a field of view of the charged particle beam tool.

[0171] 32. A non-transitory computer readable medium storing a set of instructions executable by a processor of a system for monitoring a beam in an inspection system to cause the system to perform a method comprising:

[0172] deriving a sequence of images of a beam spot of the beam formed on a surface, each image in said sequence of images having been collected by an image sensor at a different exposure time of said image sensor; and

[0173] The sequence of images is combined to derive a bundle profile of the bundle.

[0174] 33. The medium of clause 32, wherein the set of instructions executable by the processor of the system further causes the system to perform:

[0175] An image in the sequence of images is adjusted using a grayscale magnification factor associated with the image.

[0176] 34. The medium of clause 33, wherein adjusting the image in the sequence of images comprises:

[0177] The grayscale level of each pixel in the image containing useful information is multiplied by the grayscale amplification factor associated with the image.

[0178] 35. A medium according to any of clauses 33 and 34, wherein the set of instructions executable by the processor of the system further causes the system to perform:

[0179] The grayscale amplification factor associated with the image is determined based on an exposure time over which the image was collected.

[0180] 36. A medium according to any of clauses 33 and 34, wherein the set of instructions executable by the processor of the system further causes the system to perform:

[0181] The grayscale amplification factor associated with the image is determined based on a comparison of grayscale of pixels in the sequence of images.

[0182] 37. The medium of clause 36, wherein the image is a first selected image in the sequence of images, and the set of instructions executable by the processor of the system further causes the system to perform:

[0183] comparing the first selected image to a second selected image of the plurality of images to derive a plurality of overlapping pixel pairs; and

[0184] The grayscale amplification factor associated with the first selected image is determined based on grayscales of pixels in the plurality of overlapping pixel pairs.

[0185] 38. A medium according to any of clauses 18 to 23, wherein the set of instructions executable by the processor of the system further causes the system to perform:

[0186] For a specific image in the sequence of images, coordinates of the specific image are transformed based on the positions of the beam and the image sensor relative to the beam spot and a magnification factor of an optical system arranged between the image sensor and the surface.

[0187] 39. A medium according to any of clauses 32 to 38, wherein the set of instructions executable by the processor of the system further causes the system to perform:

[0188] deriving a plurality of images of the beam spot formed at different locations on the surface; and

[0189] An average image is generated based on the plurality of images.

[0190] 40. The medium of clause 39, wherein generating the average image comprises:

[0191] For a pixel, an average gray level is determined based on the gray levels of the pixel in the plurality of images.

[0192] 41. A medium according to any of clauses 32 to 40, wherein the set of instructions executable by the processor of the system further causes the system to perform:

[0193] deriving a total gray level of the beam spot by summing the gray levels of all the pixels in the beam profile; and

[0194] The power is determined based on a predetermined relationship between the overall grey scale and the power of the beam.

[0195] 42. The medium of clause 41, wherein the set of instructions executable by the processor of the system further causes the system to perform determining a relationship between the total grayscale and the power by:

[0196] deriving the power of the sample beam measured by the power meter;

[0197] obtaining an image of a sample beam spot formed by the sample beam;

[0198] deriving a beam profile of the sample beam based on the image of the sample beam;

[0199] deriving a total gray level of the sample beam spot by summing the gray levels of the pixels in the beam profile of the sample beam;

[0200] determining a relationship between the total grayscale level of the sample beam spot and the power of the sample beam; and

[0201] The relationship between the total gray level and the power is determined based on the relationship between the total gray level of the sample beam spot and the power of the sample beam.

[0202] 43. A medium according to any of clauses 41 and 42, wherein the inspection system further comprises an emitter that emits the beam, and the set of instructions executable by the processor of the system further causes the system to perform:

[0203] An output power of the transmitter is adjusted based on the determined power of the beam.

[0204] 44. A medium according to any of clauses 32 to 43, wherein the inspection system further comprises a transmitter that transmits the beam, and the transmitter comprises a beam shaper, and the set of instructions executable by the processor of the system further causes the system to perform:

[0205] The beam shaper is controlled based on the beam profile of the beam.

[0206] 45. A medium according to any of clauses 18 to 30, wherein the inspection system further comprises an emitter that emits the beam and a charged particle beam tool that emits the charged particle beam onto the surface, the set of instructions executable by the processor of the system further causing the system to perform:

[0207] The beam spot of the beam is aligned with the field of view of the charged particle beam tool.

[0208] 46. ​​A system for monitoring a beam in an inspection system, comprising:

[0209] an image sensor including circuitry to collect an image of a beam spot of the beam formed on a surface; and

[0210] A controller having one or more processors and a memory is configured to transform coordinates of the image based on a position of the beam and the image sensor relative to the beam spot and a magnification factor of an optical system disposed between the image sensor and the surface.

[0211] 47. A method of monitoring a beam in an inspection system, comprising:

[0212] collecting an image of a beam spot of the beam formed on the surface by an image sensor; and

[0213] The coordinates of the image are transformed based on the positions of the beam and the image sensor relative to the beam spot and a magnification factor of an optical system arranged between the image sensor and the surface.

[0214] 48. A non-transitory computer readable medium storing a set of instructions executable by a processor of a system for monitoring a beam in an inspection system to cause the system to perform a method comprising:

[0215] receiving an image of a beam spot of the beam formed on the surface and collected by an image sensor; and

[0216] The coordinates of the image are transformed based on the position of the beam and the image sensor relative to the beam spot and a magnification factor of an optical system arranged between the image sensor and the surface

[0217] 49. A system for monitoring a beam in an inspection system, comprising:

[0218] an image sensor including circuitry to collect a plurality of images of a beam spot of the beam, each of the plurality of images being formed at a different location on a surface; and

[0219] A controller having one or more processors and a memory is configured to generate an average image based on the plurality of images.

[0220] 50. The system of clause 49, wherein the controller is configured to generate the average image by:

[0221] For a pixel, an average gray level is determined based on the gray levels of the pixel in the plurality of images.

[0222] 51. A method of monitoring a beam in an inspection system, comprising:

[0223] collecting a plurality of images of a beam spot of the beam, each of the plurality of images being formed at a different location on the surface; and

[0224] An average image is generated based on the plurality of images.

[0225] 52. The method of clause 51, wherein said generating said average image comprises:

[0226] For a pixel, an average gray level is determined based on the gray levels of the pixel in the plurality of images.

[0227] 53. A non-transitory computer readable medium storing a set of instructions executable by a processor of a system for monitoring a beam in an inspection system to cause the system to perform a method comprising:

[0228] receiving a plurality of images of a beam spot of the beam, each of the plurality of images being formed at a different location on the surface; and

[0229] An average image is generated based on the plurality of images.

[0230] 54. The medium of clause 53, wherein said generating said average image comprises:

[0231] For a pixel, an average gray level is determined based on the gray levels of the pixel in the plurality of images.

[0232] 55. A system for monitoring a beam in an inspection system, comprising:

[0233] an image sensor including circuitry to collect an image of a beam spot of the beam formed on a surface; and

[0234] A controller having one or more processors and a memory, the controller being configured to:

[0235] deriving a beam profile of the beam based on the image;

[0236] deriving a total grayscale level of the beam spot based on the beam profile; and

[0237] The power is determined based on a predetermined relationship between the overall grey scale and the power of the beam.

[0238] 56. The system of clause 55, wherein the controller is configured to determine the predetermined relationship between the total grayscale and the power by:

[0239] deriving the power of the sample beam measured by the power meter;

[0240] obtaining an image of a sample beam spot formed by the sample beam;

[0241] deriving a beam profile of the sample beam based on the image of the sample beam;

[0242] deriving a total gray level of the sample beam spot by summing the gray levels of the pixels in the beam profile of the sample beam;

[0243] determining a relationship between the total grayscale level of the sample beam spot and the power of the sample beam; and

[0244] The relationship between the total gray level and the power is determined based on the relationship between the total gray level of the sample beam spot and the power of the sample beam.

[0245] 57. A system according to any one of clauses 55 and 56, wherein

[0246] The inspection system also includes a transmitter including circuitry to transmit the beam, and

[0247] The controller is also configured to adjust an output power of the transmitter based on the determined power of the beam.

[0248] 58. The system of any of clauses 55 to 57, wherein the inspection system further comprises a charged particle beam tool comprising circuitry to emit a charged particle beam onto the surface.

[0249] 59. The system of clause 58, wherein the inspection system further comprises an advanced charge control module comprising circuitry to emit the beam.

[0250] 60. The system of clause 59, wherein the charged particle beam tool, the advanced charge control module, and the image detector are disposed outside a vacuum chamber.

[0251] 61. A method of monitoring a beam in an inspection system, comprising:

[0252] collecting an image of a beam spot of the beam formed on the surface;

[0253] deriving a beam profile of the beam based on the image;

[0254] deriving a total grayscale level of the beam spot based on the beam profile; and

[0255] The power is determined based on a predetermined relationship between the overall grey scale and the power of the beam.

[0256] 62. The method of clause 61, further comprising determining the predetermined relationship between the total grayscale and the power by:

[0257] deriving the power of the sample beam measured by the power meter;

[0258] obtaining an image of a sample beam spot formed by the sample beam;

[0259] deriving a beam profile of the sample beam based on the image of the sample beam;

[0260] deriving a total gray level of the sample beam spot by summing the gray levels of the pixels in the beam profile of the sample beam;

[0261] determining a relationship between the total grayscale level of the sample beam spot and the power of the sample beam; and

[0262] The relationship between the total gray level and the power is determined based on the relationship between the total gray level of the sample beam spot and the power of the sample beam.

[0263] 63. A non-transitory computer readable medium storing a set of instructions executable by a processor of a system for monitoring a beam in an inspection system to cause the system to perform a method comprising:

[0264] receiving an image of a beam spot of the beam formed on the surface;

[0265] deriving a beam profile of the beam based on the image;

[0266] deriving a total grayscale level of the beam spot based on the beam profile; and

[0267] The power is determined based on a predetermined relationship between the overall grey scale and the power of the beam.

[0268] 64. The non-transitory computer-readable medium of clause 63, wherein the set of instructions executable by the processor of the system further causes the system to perform determining the predetermined relationship between the total grayscale and the power by:

[0269] receiving a power of the sample beam measured by a power meter;

[0270] receiving an image of a sample beam spot formed by the sample beam;

[0271] deriving a beam profile of the sample beam based on the image of the sample beam;

[0272] deriving a total gray level of the sample beam spot by summing the gray levels of the pixels in the beam profile of the sample beam;

[0273] determining a relationship between the total grayscale level of the sample beam spot and the power of the sample beam; and

[0274] The relationship between the total gray level and the power is determined based on the relationship between the total gray level of the sample beam spot and the power of the sample beam.

[0275] It should be understood that the present invention is not limited to the exact constructions that have been described above and shown in the accompanying drawings, and that various modifications and changes may be made without departing from the scope of the present invention. It is intended that the scope of the present invention shall be limited only by the appended claims.

Claims

1. A system for monitoring a beam in an inspection system, comprising: an image sensor including circuitry to collect an image of a beam spot of the beam formed on a surface; as well as A controller having one or more processors and a memory is configured to transform coordinates of the image based on a position of the beam and the image sensor relative to the beam spot and a magnification factor of an optical system disposed between the image sensor and the surface.

2. A method for monitoring a beam in an inspection system, comprising: collecting, by an image sensor, an image of a beam spot of the beam formed on the surface; as well as The coordinates of the image are transformed based on the positions of the beam and the image sensor relative to the beam spot and a magnification factor of an optical system arranged between the image sensor and the surface.

3. A non-transitory computer readable medium storing a set of instructions executable by a processor of a system for monitoring a beam in an inspection system to cause the system to perform a method comprising: receiving an image of a beam spot of the beam formed on the surface and collected by an image sensor; as well as The coordinates of the image are transformed based on the positions of the beam and the image sensor relative to the beam spot and a magnification factor of an optical system arranged between the image sensor and the surface.

4. A system for monitoring a beam in an inspection system, comprising: an image sensor including circuitry to collect a plurality of images of a beam spot of the beam, each of the plurality of images being formed at a different location on a surface; as well as A controller having one or more processors and a memory is configured to generate an average image based on the plurality of images.

5. The system of claim 4, wherein the controller is configured to generate the average image by: For a pixel, an average gray level is determined based on the gray levels of the pixel in the plurality of images.

6. A method of monitoring a beam in an inspection system, comprising: collecting a plurality of images of a beam spot of the beam, each of the plurality of images being formed at a different location on the surface; as well as An average image is generated based on the plurality of images.

7. The method of claim 6, wherein said generating said average image comprises: For a pixel, an average gray level is determined based on the gray levels of the pixel in the plurality of images.

8. A non-transitory computer readable medium storing a set of instructions executable by a processor of a system for monitoring a beam in an inspection system to cause the system to perform a method comprising: receiving a plurality of images of a beam spot of the beam, each of the plurality of images being formed at a different location on the surface; as well as An average image is generated based on the plurality of images.

9. A system for monitoring a beam in an inspection system, comprising: an image sensor including circuitry to collect an image of a beam spot of the beam formed on a surface; as well as A controller having one or more processors and a memory, the controller being configured to: deriving a beam profile of the beam based on the image; deriving a total grayscale level of the beam spot based on the beam profile; as well as The power is determined based on a predetermined relationship between the overall grey scale and the power of the beam.

10. A method of monitoring a beam in an inspection system, comprising: collecting an image of a beam spot of the beam formed on the surface; deriving a beam profile of the beam based on the image; deriving a total grayscale level of the beam spot based on the beam profile; as well as The power is determined based on a predetermined relationship between the overall grey scale and the power of the beam.

Images