Charged particle detector for microscopy

Abstract

A charged particle detector includes: an array of sensing elements configured to generate electrical signals in response to charged particles and arranged in rows; an array of optical modulators, each connected to a respective one of the sensing elements and configured to modulate the sensing beam in response to an electrical signal; a plurality of waveguides configured to guide each of the plurality of sensing beams through the row of optical modulators; a beam combiner configured to combine the plurality of sensing beams having passed through the respective rows of the optical modulator into a combined beam; and a readout unit configured to measure modulation of the combined beam to detect charged particles incident on the sensing element.

Description

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims the benefit of European patent application 22186172.7 filed on July 21, 2022, which is incorporated herein by reference in its entirety. Technical Field

[0003] The description herein relates to charged particle detection, and more particularly, to systems and methods that may be applicable to charged particle beam detection. Background Art

[0004] Detectors can be used to sense physically observable phenomena. For example, a charged particle beam tool (such as an electron microscope) can include a detector that receives charged particles projected from a sample and outputs a detection signal. The detection signal can be used to reconstruct an image of the sample structure being inspected, and can be used, for example, to expose defects in the sample. In the manufacture of semiconductor devices, it becomes increasingly important to detect defects in the sample, which can include a large number of densely packed miniaturized integrated circuit (IC) components. For this purpose, a dedicated inspection tool can be provided.

[0005] In some applications in the field of inspection, such as microscopy using a scanning electron microscope (SEM), an electron beam can be scanned across a sample to derive information from backscattered electrons or secondary electrons generated by the sample. In the related art, an electron detection system in a SEM tool may include a detector configured to detect electrons from a sample. Existing detectors in SEM tools can only detect the intensity of the beam. The sensitivity of conventional detection systems may be limited by a poor signal-to-noise ratio (SNR), especially when the beam current is reduced to, for example, the picoampere range. In some detection methods, a large area semiconductor detector or a group of small area semiconductor detectors having an area equal to, less than, or greater than the beam spot area can be used. The current induced by the incoming electron beam can be generated within the detector and then amplified by an amplifier behind the detector.

[0006] As semiconductor devices continue to miniaturize, inspection systems can use lower and lower electron beam currents. As beam current decreases, maintaining SNR becomes more difficult. For example, when the probe current is reduced to 200pA or below, the SNR can drop dramatically. Poor SNR can require measures such as image averaging or extending the integration time of the signal corresponding to each pixel in the image of the sample, which can increase the electron dose on the sample surface, resulting in surface charging artifacts or other deleterious effects. Such measures can also reduce the overall throughput of the inspection system.

[0007] In the related art, particle counting may be useful in low current applications. Particle counting can be used in detectors such as Everhart-Thornley detectors (ETDs), which can use scintillators and photomultiplier tubes (PMTs). In the probe current range of some applications (such as 8pA to 100pA), ETD can exhibit good SNR. However, the light output of the scintillator may decrease with the accumulated electron dose, and therefore has a limited service life. The aging of the scintillator can also cause system-level performance drift and can cause the generation of uneven images. Therefore, ETD may not be suitable for use in inspection tools, especially when used in semiconductor manufacturing facilities, where it may need to run 24 hours a day, 7 days a week.

[0008] There is a need for a charged particle detector that can achieve high SNR and can be used with low probe currents, such as low probe currents below 200 pA. At the same time, the detector should ensure stable quantum efficiency and long lifetime with low performance drift, for example even when used with probe currents of 1 nA or more in continuous operation.

[0009] Detection systems using related art methods may face limitations in detection sensitivity and SNR, especially at low electron doses. In order to improve the SNR, the related art has proposed so-called pixelated electron counting detectors, in which the detector is subdivided into a large number of sensing elements, and the outputs of these sensing elements are combined to generate a detection signal. However, the process of combining the outputs of individual sensing elements may be slow and / or require complex electronic circuit devices. Therefore, improvements to detection systems and methods are needed. Summary of the invention

[0010] An embodiment of the present disclosure provides a radiation detector, comprising:

[0011] a set of sensing elements configured to generate an electrical signal in response to the radiation;

[0012] a set of optical modulators connected to respective ones of the sensing elements and configured to modulate the sensing light beam in response to the electrical signal; and

[0013] The sensing optical system is configured to direct a sensing light beam through each of the optical modulators.

[0014] An embodiment of the present disclosure provides a charged particle detection system, comprising:

[0015] a set of sensing elements configured to generate an electrical signal in response to the radiation;

[0016] a set of optical modulators connected to respective ones of the sensing elements and configured to modulate the sensing light beam in response to the electrical signal; and

[0017] The sensing optical system is configured to direct a sensing light beam through each of the optical modulators.

[0018] An embodiment of the present disclosure provides a method for detecting radiation, comprising:

[0019] directing radiation to a plurality of sensing elements configured to generate electrical signals in response to the radiation;

[0020] modulating a sensing light beam in response to the electrical signal; and

[0021] The modulation of the sensing beam is measured to detect the radiation.

[0022] An embodiment of the present disclosure provides a charged particle detector, comprising:

[0023] an array of sensing elements configured to generate electrical signals in response to charged particles and arranged in rows;

[0024] an array of optical modulators, each connected to a corresponding one of the sensing elements and configured to modulate the sensing light beam in response to the electrical signal;

[0025] a plurality of waveguides configured to direct each of the plurality of sensing beams through the row of optical modulators;

[0026] a beam combiner configured to combine the plurality of sensing light beams that have passed through corresponding rows of the optical modulator into a combined beam; and

[0027] A readout unit is configured to measure the modulation of the combined beam to detect charged particles incident on the sensing element.

[0028] Embodiments of the present disclosure provide a non-transitory computer-readable medium including an instruction set executable by one or more processors of a controller to cause the controller to perform a method for controlling a deflector of a charged particle inspection system, the method comprising:

[0029] causing radiation to be directed to a plurality of sensing elements that generate electrical signals in response to the radiation and are part of a detection component configured to modulate a sensing beam in response to the electrical signals and to measure the modulation of the sensing beam to detect the radiation; and

[0030] The detection component is caused to output a signal indicative of the measured modulation.

[0031] 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 may be claimed. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] The above and other aspects of the present disclosure will become more apparent from the description of exemplary embodiments taken in conjunction with the accompanying drawings, in which:

[0033] Figure 1 is a schematic diagram illustrating an exemplary electron beam inspection (EBI) system according to an embodiment of the present disclosure.

[0034] Figure 2A , Figure 2B and Figure 2C is a schematic diagram illustrating an exemplary electron beam tool according to an embodiment of the present disclosure, which may be Figure 1 A portion of an exemplary electron beam inspection system.

[0035] Figure 3 is a schematic diagram of a radiation detector of an embodiment.

[0036] Figure 4 yes Figure 3 Schematic cross section of a radiation detector.

[0037] Figure 5 yes Figure 3 Timing diagram of a radiation detector.

[0038] Figure 6 is a schematic diagram of a radiation detector according to another embodiment. DETAILED DESCRIPTION

[0039] Reference will now be made in detail to exemplary embodiments, examples of which are illustrated in the accompanying drawings. The following description refers to the accompanying drawings, in which, unless otherwise specified, 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 embodiments according to the present invention. Instead, they are merely examples of devices, systems, and methods according to aspects related to the subject matter that may be recited in the appended claims.

[0040] Aspects of the present application relate to systems and methods for charged particle beam detection. Systems and methods may employ counting of charged particles (such as electrons) and may be useful in inspection tools (such as scanning electron microscopes (SEMs)). Inspection tools may be used in the manufacturing process of integrated circuit (IC) components. In order to achieve the enhanced computing power of modern electronic devices, the physical size of the device may be reduced, while the packaging density of circuit components (such as transistors, capacitors, diodes, etc.) is significantly increased on the IC chip. For example, in a smart phone, an IC chip (which may be thumbnail size) may include more than 2 billion transistors, each of which is less than 1 / 1,000 the size of a human hair. Not surprisingly, semiconductor IC manufacturing is a complex process with hundreds of individual steps. Even an error in one step is likely to greatly affect the functionality of the final product. The goal of the manufacturing process is to increase the overall yield of the process. For example, for a 50-step process to obtain a 75% yield, each individual step must have a yield greater than 99.4%, and if the individual step yield is 95%, then the overall process yield drops to 7%.

[0041] The ability to ensure defects are detected with high accuracy and resolution while maintaining high throughput (e.g., defined as the number of wafers processed per hour) is becoming increasingly important. High process yields and high wafer throughputs can be impacted by the presence of defects, especially when operator intervention is involved. Therefore, the detection and identification of micron and nanometer sized defects by inspection tools (such as SEMs) is important to maintain high yields and low costs.

[0042] In some inspection tools, a sample can be inspected by scanning a high energy electron beam over the sample surface. Due to the interaction at the sample surface, secondary or backscattered electrons can be generated from the sample, which can then be detected by a detector.

[0043] Related art detectors may have limitations, such as low readout rates or the need for complex electronic circuitry. Aspects of the present disclosure may address some of these limitations by providing: a radiation detector (e.g., a charged particle detector or, more specifically, an electronic detector) having a set of sensing elements; a set of optical modulators coupled to the sensing elements; and a sensing optical system for directing a light beam through the optical modulator to enable detection of radiation to be read out by the sensing elements. Such optical readout may enable faster readout and / or simpler and smaller components to be packaged on a chip relative to, for example, an electronic readout circuitry. Optical readout may have lower power consumption than electronic readout circuitry, resulting in lower heat dissipation and reduced cooling requirements in a vacuum chamber. Although the present disclosure discusses some exemplary embodiments in the context of electronics, it should be understood that the present disclosure may be applicable to other types of charged particles, such as ions.

[0044] In some embodiments of the present disclosure, the size of the sensing elements of the array can be set so that no more than a specific number of charged particles are received in the area of ​​an individual sensing element per sampling period. The specific number can be one. The size of the sensing element can be smaller than the geometric spread of the charged particles incident on the detector. Therefore, an individual sensing element can be configured to receive fewer charged particles than the total number of charged particles incident on the detector. Aspects of the detector can be set according to various criteria to achieve charged particle counting, such as the size of the sensing element, the sampling rate, and other characteristics.

[0045] Without limiting the scope of the present disclosure, some embodiments may be described in the context of providing detectors and detection methods in systems utilizing electron beams. However, the present disclosure is not limited thereto. Other types of charged particle beams may be similarly applied. In addition, the systems and methods for detection may be used in other imaging systems, such as optical imaging, photon detection, x-ray detection, ion detection, and the like.

[0046] As used herein, unless expressly stated otherwise, the term "or" includes all possible combinations unless not feasible. For example, if a component is specified to include A or B, then unless expressly stated otherwise or not feasible, the component may include A, or B, or A and B. As a second example, if a component is specified to include A, B, or C, then unless expressly stated otherwise or not feasible, the component may include A, or B, or C, or A and B, or A and C, or B and C, or A and B and C.

[0047] In addition, the term "detector element" may include or cover "sensing element", "sensor element", "detection unit" or "detector segment", etc. A sensing element may be a diode configured to have a depletion region, and in some embodiments discussed herein, the term "sensing element" may not include an avalanche diode operating in Geiger mode. Detector elements may include diodes, interconnects, and circuits, which may include, for example, front-end electronics. In addition, the term "frame" may include or cover "sampling period", "SEM image pixel period" or "pixel period", etc. A SEM image frame may refer to a pixel frame that can be refreshed on a frame-by-frame basis, while a data frame may refer to a set of data acquired by a detection system over a specified time period.

[0048] Embodiments of the present disclosure may provide a detection method. The detection method may include charged particle counting. For example, in some embodiments, a charged particle detection method may be provided for electron microscopy. The method may be applied to a SEM detection system. The charged particle detection method may be based on electron counting. By counting the number of electrons received during a predefined period, the intensity of the incoming electron beam may be determined. The term "incoming electrons" may include or encompass incident electrons, such as electrons that collide with the surface of the detector. According to some embodiments, noise from the charged particle detection process may be reduced. However, simply improving the SNR may not meet the growing demands of various SEM applications.

[0049] Electron counting can involve determining individual electron arrival events that occur at a detector. For example, as electrons arrive at the detector, the electrons can be detected individually. In some embodiments, electrons incident on the detector can generate an electrical signal that is routed to an electro-optic modulator that selectively modulates the beam by changing a parameter of the beam, such as phase, amplitude, or polarization. Signal processing circuitry detects the modulation of the beam and then reads out to an interface, such as a digital controller. The detector can be configured to parse the signal generated by the incident electrons and distinguish individual electrons from discrete counts.

[0050] In some embodiments, electron counting can be applied in situations where the beam current is very small. For example, the electron beam can be set to irradiate the sample at a low dose. Low current can be used to prevent the electron counting detector from being oversaturated by large currents. For example, large currents can have the effect of introducing nonlinearities into the detection results. At the same time, for the detector to be useful in an industrial setting, the detector should also be able to handle situations with large beam currents.

[0051] Some embodiments can address the above issues. For example, some embodiments can provide a plurality of relatively small sensing elements that can be used to detect electron beams. Isolation can be provided between adjacent sensing elements so that the probability of an incoming electron from one sensing element traveling to its adjacent sensing element can be reduced. In this way, crosstalk between adjacent sensing elements can be reduced.

[0052] In some embodiments, the detector can be constructed using digital circuitry and optoelectronic elements, rather than implementations that require extensive analog or digital electronic circuitry. As a result, various aspects of the detector's implementation, such as operating speed, can be improved.

[0053] Reference now Figure 1 , which illustrates an exemplary electron beam inspection (EBI) system 10 that may include a detector consistent with embodiments of the present disclosure. The EBI system 10 may be used for imaging. Figure 1As shown, the EBI system 10 includes a main chamber 11, a load / lock chamber 20, an electron beam tool 100, and an equipment front end module (EFEM) 30. The electron beam tool 100 is located in the main chamber 11. The EFEM 30 includes a first load port 30a and a second load port 30b. The EFEM 30 may include (multiple) additional load ports. The first load port 30a and the second load port 30b receive a front-opening wafer transport box (FOUP), which contains wafers to be inspected (e.g., semiconductor wafers or wafers made of (multiple) other materials) or samples (wafers and samples may be collectively referred to as "wafers" in this article).

[0054] One or more robotic arms (not shown) in the EFEM 30 can transport the wafer to the load / lock chamber 20. The load / lock chamber 20 is connected to a load / lock vacuum pump system (not shown) that removes gas molecules in the load / lock chamber 20 to reach a first pressure below atmospheric pressure. After reaching the first pressure, one or more robotic arms (not shown) can transport the wafer from the load / lock chamber 20 to the main chamber 11. The main chamber 11 is connected to a main chamber vacuum pump system (not shown) that removes gas molecules in the main chamber 11 to reach a second pressure below the first pressure. After reaching the second pressure, the wafer undergoes inspection by the electron beam tool 100. The electron beam tool 100 can be a single beam system or a multi-beam system. The controller 109 is electrically connected to the electron beam tool 100 and can also be electrically connected to other components. The controller 109 can be a computer configured to execute various controls of the EBI system 10. Although the controller 109 is Figure 1 1. The controller 109 is shown as being located outside of the structure including the main chamber 11, the load / lock chamber 20, and the EFEM 30, but it should be understood that the controller 109 may be part of the structure.

[0055] Figure 2A A charged particle beam apparatus is illustrated, wherein the inspection system may include a multi-beam inspection tool that uses multiple primary electron beam waves to simultaneously scan multiple locations on the sample.

[0056] like Figure 2A As shown, the electron beam tool 100A (also referred to herein as the apparatus 100A) may include an electron source 202, a gun body aperture 204, a focusing 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 primary projection optical system 220, a wafer stage ( Figure 2A), a plurality of secondary electron beams 236, 238 and 240, a secondary optical system 242 and an electron detection device 244. The electron source 202 may generate primary particles, such as electrons of the primary electron beam 210. A controller, an image processing system, etc. may be coupled to the electron detection device 244. The primary projection optical system 220 may include a beam splitter 222, a deflection scanning unit 226 and an objective lens 228. The electron detection device 244 may include detection sub-areas 246, 248 and 250.

[0057] Electron source 202, gun aperture 204, focusing lens 206, source conversion unit 212, beam splitter 222, deflection scanning unit 226 and objective lens 228 can be aligned with the primary optical axis 260 of apparatus 100A. Secondary optical system 242 and electron detection device 244 can be aligned with the secondary optical axis 252 of apparatus 100A.

[0058] The electron source 202 may include a cathode, an extractor, or an anode, wherein primary electrons can be emitted from the cathode and extracted or accelerated to form a primary electron beam 210 having a (virtual or real) intersection point 208. The primary electron beam 210 can be viewed as being emitted from the intersection point 208. The gun body aperture 204 can block peripheral electrons of the primary electron beam 210 to reduce the size of the probe spots 270, 272, and 274.

[0059] The source conversion unit 212 may include an imaging element array ( Figure 2A ) and the beam-limiting aperture array ( Figure 2A 214 , 216 , and 218 ). Examples of source conversion units 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 imaging element array may include a microdeflector or a microlens array. The imaging element array may form multiple (virtual or real) parallel images of the intersection 208 with multiple beams 214, 216, and 218 of the primary electron beam 210. The beam limiting aperture array may limit the multiple beams 214, 216, and 218.

[0060] The converging lens 206 can focus the primary electron beam 210. The current of the beams 214, 216 and 218 downstream of the source conversion unit 212 can be changed by adjusting the focusing ability of the converging lens 206 or by changing the radial size of the corresponding beam limiting apertures in the beam limiting aperture array. The converging lens 206 can be a movable converging lens, which can be configured so that the position of its first principal plane is movable. The movable converging lens can be configured to be magnetic, which can cause the off-axis beams 216 and 218 to land on the beam limiting aperture at a rotation angle. The rotation angle changes with the focusing ability of the movable converging lens and the position of the first principal plane of the movable converging lens. In some embodiments, the movable converging lens can be a movable anti-rotation converging lens, which involves an anti-rotation lens having a movable first principal plane. The movable converging lens is also described in U.S. Publication No. 2017 / 0025241, which is incorporated herein by reference in its entirety.

[0061] The objective lens 228 may focus the beams 214 , 216 , and 218 onto the wafer 230 for inspection, and may form a plurality of probe spots 270 , 272 , and 274 on the surface of the wafer 230 .

[0062] 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 the electrostatic dipole field and the magnetic dipole field are applied, the force exerted by the electrostatic dipole field on the electrons of the beam waves 214, 216, and 218 and the force exerted by the magnetic dipole field on the electrons can be equal in magnitude but opposite in direction. The beam waves 214, 216, and 218 can therefore pass directly through the beam splitter 222 at 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. The beam splitter 222 can separate the secondary electron beams 236, 238, and 240 from the beam waves 214, 216, and 218, and guide the secondary electron beams 236, 238, and 240 toward the secondary optical system 242.

[0063] The deflection scanning unit 226 can deflect the beams 214, 216, and 218 to scan the probe 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 probe 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-areas 246, 248, and 250 of the electron detection device 244. The detection sub-areas 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.

[0064] although Figure 2A The example of the electron beam tool 100 is shown as a multi-beam tool using multiple beam waves, but the embodiments of the present disclosure are not limited thereto. For example, the electron beam tool 100 can also be a single beam tool that scans one location on the wafer at a time using only one primary electron beam.

[0065] like Figure 2B As shown, the electron beam tool 100B (also referred to herein as the apparatus 100B) can be a single beam inspection tool for use in the EBI system 10. The apparatus 100B includes a wafer holder 136 supported by a motorized stage 134 to hold a wafer 150 to be inspected. The electron beam tool 100B includes an electron emitter, which may include a cathode 103, an anode 121, and a gun body aperture 122. The electron beam tool 100B also includes a beam limiting aperture 125, a converging lens 126, a column aperture 135, an objective lens assembly 132, and a detector 144. In some embodiments, the objective lens assembly 132 can be a modified SORIL lens, 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 121 voltage, pass through the gun aperture 122, the beam limiting aperture 125, the converging lens 126, and be focused by the modified SORIL lens into a probe spot 170, and impinge on the surface of the wafer 150. The probe spot 170 may be scanned across the surface of the wafer 150 by a deflector (such as deflector 132c or other deflectors in the SORIL lens). Secondary particles or scattered primary particles (such as secondary electrons or scattered primary electrons) emitted from the wafer surface may be collected by a detector 144 to determine the intensity of the beam and enable an image of an area of ​​interest on the wafer 150 to be reconstructed.

[0066] An image processing system 199 including an image acquisition device 120, a storage device 130 and a controller 109 may also be provided. The image acquisition device 120 may include one or more processors. For example, the image acquisition device 120 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 acquisition device 120 may be connected to the detector 144 of the electron beam tool 100B 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 120 may receive a signal from the detector 144 and may construct an image. The image acquisition device 120 may thus acquire an image of the wafer 150. The image acquisition device 120 may also perform various post-processing functions, such as generating a contour, superimposing an indicator on the acquired image, etc. The image acquisition device 120 may be configured to adjust 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, etc. The storage device 130 may be coupled to the image acquirer 120 and may be used to save the scanned raw image data as an original image and save a post-processed image. The image acquirer 120 and the storage device 130 may be connected to the controller 109. In some embodiments, the image acquirer 120, the storage device 130 and the controller 109 may be integrated together as an electronic control unit.

[0067] In some embodiments, the image acquirer 120 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 performed on an imaging frame basis.

[0068] The electron beam tool's convergence and illumination optics may include or be supplemented by an electromagnetic quadrupole electron lens. Figure 2B As shown, the electron beam tool 100B 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 can be controlled to adjust the beam current, and the second quadrupole lens 158 can be controlled to adjust the beam spot size and beam shape.

[0069] Figure 2BA charged particle beam arrangement is illustrated, where the inspection system may use a single primary beam that may be configured to generate secondary electrons by interacting with the wafer 150. The detector 144 may be positioned along the optical axis 105, such as at Figure 2B In the embodiment shown. The primary electron beam can be configured to travel along the optical axis 105. Therefore, the detector 144 can include a hole in its center so that the primary electron beam can pass through to reach the wafer 150. However, some embodiments may use a detector that is placed off-axis relative to the optical axis along which the primary electron beam travels. For example, as in Figure 2A In the embodiment shown, a beam splitter 222 may be provided to direct the secondary electron beam towards an off-axis positioned detector. The beam splitter 222 may be configured to steer the secondary electron beam at an angle α.

[0070] Now refer to Figure 2C Another example of a charged particle beam apparatus is discussed. An electron beam tool 100C (also referred to herein as apparatus 100C) may be an example of an electron beam tool 100 and may be similar to Figure 2A An electron beam tool 100A is shown.

[0071] like Figure 2C As shown, 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 the electrostatic dipole field and the magnetic dipole field are applied, the force exerted by the electrostatic dipole field on the electrons of the beam waves 214, 216, and 218 and the force exerted by the magnetic dipole field on the electrons can be equal in magnitude but opposite in direction. The beam waves 214, 216, and 218 can therefore pass directly 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. For the dispersion plane 224 of the beam splitter 222, Figure 2C A beam 214 having a nominal energy V0 and an energy spread ΔV is shown being dispersed into a beam portion 262 corresponding to energy V0, a ​​beam portion 264 corresponding to energy V0+ΔV / 2, and a beam portion 266 corresponding to energy V0-ΔV / 2. The resultant force exerted by the beam splitter 222 on the electrons of the secondary electron beams 236, 238, and 240 can be non-zero. The beam splitter 222 can separate the secondary electron beams 236, 238, and 240 from the beams 214, 216, and 218 and direct the secondary electron beams 236, 238, and 240 toward the secondary optical system 242.

[0072] Semiconductor electron detectors (sometimes referred to as "PIN detectors") can be used in the device 100 in the EBI system 10. The EBI system 10 can be a high-speed wafer imaging SEM including an image processor. The electron beam generated by the EBI system 10 can irradiate the surface of the sample or can penetrate the sample. The EBI system 10 can be used to image the surface of the sample or the structure below the surface, such as for analyzing layer alignment. In some embodiments, the EBI system 10 can detect and report process defects related to the manufacture of semiconductor wafers, for example, by the following steps: comparing the SEM image with the device layout pattern or the SEM image of the same pattern at other locations on the wafer being inspected. The PIN detector can include a silicon PIN diode that can be operated with a negative bias. The PIN detector can be configured so that the incoming electrons generate relatively large and different detection signals. In some embodiments, the PIN detector can be configured so that the incoming electrons can generate multiple electron-hole pairs, while the photons can only generate one electron-hole pair. Compared with photodiodes for photon detection, PIN detectors for electron counting can have many differences, as will be discussed below.

[0073] Reference now Figure 3 and Figure 4 , which illustrate schematic diagrams of exemplary structures of the detector 300. Figure 2A , Figure 2B and Figure 2C , the detector 300 may be provided as the detector 144 or the electronic detection device 244 .

[0074] Briefly, the detector 300 includes: sensing elements 311, 312, 313 for generating electrical signals in response to radiation; optical modulators 351, 352, 353 for modulating a light beam in response to the electrical signal; optical systems 320, 321, 322 for directing the light beam to the optical modulator; a light source 340 for generating the light beam; and a readout circuit 330 for providing an electron count output signal to the data processor 500. There may be a large number of sensing elements, such as 1,000 or more, desirably 5,000 or more, and more desirably 10,000 or more. These components will be described in more detail below.

[0075] The detector 300 may include an array of sensing elements, including sensing elements 311, 312, and 313. The sensing elements may be arranged in a planar two-dimensional array, the plane of the array being substantially perpendicular to the incident direction of the incoming charged particles. In some embodiments, the detector 300 may be arranged to be tilted relative to the incident direction. The array may include 10 or more rows, desirably 50 or more rows, and more desirably 100 or more rows, wherein each row includes 10 or more sensing elements, desirably 50 or more sensing elements, and more desirably 100 or more transmitting elements. Although Figure 3 One array is shown in FIG. 3 , but it should be understood that the detector 300 may include multiple arrays, such as one array for each secondary electron beam.

[0076] The detector 300 may include a substrate 310. The substrate 310 may be a semiconductor substrate that may include a sensing element. The sensing element may be a diode. The sensing element may also be an element similar to a diode that is capable of converting incident energy into a measurable signal. The sensing element may include, for example, a PIN diode, an avalanche diode, an electron multiplier tube (EMT), etc., or a combination thereof. Region 325 may be disposed between adjacent sensing elements. Region 325 may be an isolation region to isolate sides or corners of adjacent sensing elements from each other. Region 325 may include an insulating material that is a material different from the material of other regions of the detection surface of the detector 300. Region 325 may be provided as a cross-shaped region, such as Figure 3 Region 325 may be provided as a square. In some embodiments, region 325 may not be provided between adjacent sides of the sensing element. For example, in some embodiments, there may be no isolation region provided on the detection surface of the detector.

[0077] The sensing element may generate an electrical signal equivalent to the charged particles received in the active region of the sensing element. For example, the sensing element may generate a current signal equivalent to the energy of the received electrons. The preprocessing circuit may convert the generated current signal into a voltage, which may represent the intensity of the electron beam spot or a portion thereof. The preprocessing circuit device may include, for example, a preamplifier circuit device. The preamplifier circuit device may include, for example, a charge transfer amplifier (CTA), a transimpedance amplifier (TIA), an impedance conversion circuit coupled to a CTA or TIA, or a three-transistor amplifier. In some embodiments, a signal processing circuit device may be provided, which provides an output signal in arbitrary units on a time basis. One or more substrates, such as a bare die, may be provided, which may form a circuit layer for processing the output of the sensing element. The bare die may be stacked together in the thickness direction of the detector. Other circuit devices may also be provided for other functions. For example, a switch actuation circuit device may be provided, which may control a switch element for connecting the sensing elements to each other.

[0078] Although the figure may show sensing elements 311, 312, and 313 as discrete units, such divisions may not actually exist. For example, the sensing elements of the detector may be formed by semiconductor devices that constitute PIN diode devices. The PIN diode device may be manufactured as a substrate having multiple layers, the multiple layers including a p-type region, an intrinsic region, and an n-type region. One or more of such layers may be continuous in a cross-sectional view. However, in some embodiments, the sensing elements may be provided with physical separation therebetween. For example, in addition to the sensor layer, other layers such as a circuit layer and a readout layer may also be provided.

[0079] As an example of another layer, the detector 300 can be provided with one or more circuit layers adjacent to the sensor layer. One or more circuit layers can include line conductors, interconnects, and various electronic circuit components. One or more circuit layers can include a processing system. One or more circuit layers can include a signal processing circuit device. One or more circuit layers can be configured to receive an output current detected from a sensing element in the sensor layer. For example, one or more circuit layers and the sensor layer can be provided in the same or separate die.

[0080] Further details of the operation of a detection element (such as a diode) for detecting electrons can be found in US2019 / 0378682A1, which is incorporated herein by reference in its entirety. As an alternative to a PIN diode, an embodiment may employ a low gain avalanche diode (LGAD).

[0081] In response to incident charged particles, in particular electrons, each of the sensing elements 311, 312, 313 outputs an electrical signal, which may be referred to as a detection signal. The detection signal may be, for example, a signal expressed in amperes, volts, or any unit equivalent to the energy of the electrons received at the corresponding sensing element. In some embodiments, the detection signal may represent the number of charged particles incident on the sensing element of the detector within a time period (e.g., a frame). The detection signal may indicate that a discrete number of charged particles have reached the sensing element. The number of charged particles may be viewed as an integer.

[0082] When a charged particle is incident, the radiation receiving portion of the sensing element (e.g., a PIN diode) may emit a brief current pulse. Thus, the sensing element may include a persistent element, such as an accumulator or a sample-and-hold circuit, which is set to an "on" state by the current pulse or accumulates charge in response to the current pulse until reset by a reset circuit at the end of a sampling period or frame. The sampling period or frame rate may be pre-set or automatically determined based on operating conditions.

[0083] like Figure 3 and Figure 4 As depicted, each sensing element 311, 312, 313 is connected to a corresponding optical modulator in optical modulators 351, 352, 353 (which may also be referred to as electro-optical devices). It should be noted that a one-to-one relationship between sensing elements and optical modulators is not required; in embodiments, there may be a one-to-two relationship, a one-to-many relationship, a two-to-one relationship, a many-to-one relationship, etc. In response to the output from the corresponding sensing element(s), each optical modulator modulates the light beam passing therethrough. The optical modulation may be a change in a beam parameter such as phase, amplitude, or polarization, or a combination thereof. The change may be binary (i.e., if the electrical signal output by the sensing element indicates that one or more charged particles have been detected, then modulation is applied, otherwise modulation is not applied, and vice versa), multi-valued, or analog.

[0084] The parameter change is desirably cumulative and linearly additive. For example, if an optical modulator selectively applies a phase delay of δ, then a light beam that has passed through n active optical modulators will be delayed by an amount equal to nδ. The phase delay δ is desirably selected so that the total delay imparted when the maximum expected number of charged particles is detected is less than 2π. However, the phase delay δ need not be less than 2π divided by the total number of optical modulators. The phase delay imparted by an optical modulator can be determined by designing the optical path length of the optical modulator and / or the voltage applied to the optical modulator. Details of suitable optical modulators are given in "Taking silicon photonics modulators to a higher performance level: state-of-the-art and a review of new technologies" by Abdul Rahim, Artur Hermans, Benjamin Wohlfeil, Despoina Petousi, Bart Kuyken, Dries Van Thourhout and Roel G. Baets, Advanced Photonics 3(2), 024003 (April 29, 2021). https: / / doi.org / 10.1117 / 1.AP.3.2.024003. Desirably, all of the optical modulators in the optical modulator can be constructed as a single integrated circuit device on a single substrate 350 using silicon photonics technology. Alternatively, separate devices can be used.

[0085] In an arrangement where the modulation is linearly additive, the total modulation of the measurement beam represents the sum of the incident radiation on all sensing elements associated with the measurement beam. In some embodiments, a weighted sum can be desired and is achieved by introducing a weighting factor for each sensing element. The weighting factor can vary, for example, between 0 and 1. The weighting factor can be implemented in several different ways. For example, the weighting factor can be applied to the gain of an electronic amplifier associated with each sensing element. The weighting factor can be applied in the modulator, for example, by changing the voltage of the phase modulator. The weighting factor for each sensing element can be fixed at the time of manufacture or calibration, or can be changed during the use of the device.

[0086] The modulated light beam (which may be referred to as a sensing beam) may be generated by a light source 340 mounted on the same substrate 350 as the optical modulators 351, 352, 353 or away from the optical fiber used to bring the light to the optical modulator. Mounting the light source on the substrate 350 may make the device more compact. Having a remote light source may reduce heat dissipation in the detector. The wavelength of the light output by the light source 340 is not particularly limited and is preferably selected for compatibility with the optical modulator to be used. Wavelengths in the infrared, visible or ultraviolet range may be suitable. Desirably, for example, if phase modulation is to be used, the light source 340 outputs substantially monochromatic light. In some embodiments, a light source emitting multiple wavelengths may be available. If amplitude modulation is used, a broadband source may be suitable. The light source 340 may be, for example, a laser diode emitting in the infrared range (e.g., at 1550nm).

[0087] A light source 340 is coupled to the input waveguide 320 (directly or via an optical fiber). A beam splitter 341 divides the input light beam into a plurality of sensing waveguides 321 (which is an example of a sensing optical system), thereby forming a plurality of sensing beams. Each sensing waveguide in the sensing waveguides 321 guides a corresponding sensing beam through a set of optical modulators 351, 352, 353. For example, Figure 3 As depicted, each set of optical modulators forms a row of the optical modulator array, and the sensing light beam follows a straight beam path through the optical modulators, but other arrangements are possible as discussed below.

[0088] After the sensing beams have passed through the optical modulators, the beam combiner 342 combines the sensing beams into a measurement beam, which is passed to the readout unit 330. After the sensing beams are combined, the modulation of the measurement beam can be the average of the modulation of the sensing beams. For example, in an arrangement with 100 rows of 100 sensing elements and optical modulators, if only one optical modulator is active and applies a phase delay of δ, then the phase delay of the measurement beam will be δ / 100. If 50 optical modulators are active, then the phase delay of the measurement beam will be δ / 2. A reference waveguide 322 (as an example of a reference optical system) can be provided to pass the reference beam directly to the readout unit 330 without passing through any optical modulator. The reference waveguide can be configured to have substantially the same optical path length as the sensing waveguide and impart the same effect, such as attenuation, as imparted by the beam path of the (multiple) sensing beams when no optical modulator is active. As an alternative to combining all of the beams to be measured by a single readout unit, a plurality of readout units may be provided, each measuring one sensing beam or a combination of subsets of sensing beams.

[0089] The structure of the readout unit 330 depends on the parameter to be measured. If the modulation parameter is phase, the readout unit may include an interferometer. If the modulation parameter is amplitude, the readout unit may include a power sensor. If the modulation parameter is polarization, the readout unit may include a polarization analyzer. The readout unit 330 may measure the modulation parameter by comparing a measurement beam, which has been derived from a separate sensing beam through an optical modulator, with a reference beam, which also originates from the source 340 but is guided to the readout unit 330 by a reference waveguide 322 without passing through any optical modulator. In case a reference beam is used, the readout unit is desirably configured in a balanced detection setup (having optical detectors 331, 332 and a comparator 333 for the measurement beam and the reference beam, respectively, as shown in FIG. 2 ). Figure 3 The reference beam is preferably a phase-modulated beam (as shown) such that common mode fluctuations (e.g. laser intensity noise) are suppressed. If amplitude modulation is used, then the reference beam can be omitted. Alternatively, the reference beam can be used with a static phase delay so that destructive interference occurs with the measurement beam. When a charged particle is detected, the measurement beam is attenuated and the destructive interference is no longer complete, so light is detected at the readout unit. This may be easier than making an absolute measurement of the beam intensity.

[0090] The readout unit 330 is configured to measure the modulation of the measurement beam and output a signal to the data processor 500, which is representative of the charged particles incident during the measurement period or frame, desirably the number of charged particles. The readout unit 330 may include other signal processing elements, such as an analog-to-digital converter, which processes the result of measuring the modulation of the measurement beam to generate an output signal representing the charged particles incident on the sensing element. Among other things, the signal processor 500 may also include a digital switch, a digital control unit, or a controller configured to perform image processing. For example, other circuit devices may be provided in the architecture, such as a signal processing path configured to provide gain and offset control.

[0091] like Figure 4As depicted, sensing elements 311, 312, 313 may be formed on a first substrate 310, and optical modulators 351, 352, 353 may be formed on a second substrate 350. The first substrate 310 and the second substrate 350 are placed back to back and combined. The connection between the sensing elements 311, 312, 313 and the optical modulators 351, 352, 353 can be realized by through-silicon vias 361, 362. Mounting the first substrate and the second substrate back to back in this manner minimizes the length of the signal path between the sensing element and the corresponding optical modulator, thereby maximizing the operating speed of the detector. This arrangement is feasible because the optical modulator can be smaller than the sensing element and still impart a detectable phase shift. The sensing elements 311, 312, 313 and the optical modulators 351, 352, 353 together with any other related elements (such as amplifiers) can be collectively referred to as detection components.

[0092] The SEM system can scan a primary electron beam across a sample in a pattern such as a raster pattern. The pixels to be generated in the image can be associated with the location of the sample surface being scanned. The pixels can be associated with a specific scan time. The data from the detector can be associated with the scan time. A calibrator can be used to associate the data received from the detector to a specific scan time. The calibrator can be configured to associate the detector data with the scan time (and therefore, the pixel) based on a delay time. For example, the calibrator can record the time when data associated with an electron arrival event is received and apply a correction based on a delay from a trigger. The trigger can correspond to an electron of the primary electron beam impinging on the sample. The delay can take into account the travel time of the electron (e.g., secondary electron) from the sample to the detector, or the time for signal pulse generation and output in the sensing element. In addition, the time Δt taken for the (multiple) beams to propagate through the sensing waveguide and the optical modulator can be non-negligible in some cases. Therefore, as Figure 5 As depicted, the sampling window Win of the readout unit 330 is desirably offset by a time Δt from the pixel clock clk defining the pixel boundary to allow the (multiple) light beams to propagate through the sensing waveguide and the optical modulator. Generally speaking, Δt is much smaller than the period t of the pixel clock clk. p .

[0093] As mentioned previously, other arrangements of sensing waveguides are possible. Figure 6 One such arrangement is depicted in which a single sensing waveguide 323 guides the sensing beam along a tortuous path that passes through all of the optical modulators 351, 352, 353. It will be appreciated that if the optical path traversed by the sensing beam is longer, then the time taken is also longer and the maximum sampling rate is reduced. The choice of optical path is therefore a compromise between device simplicity (via a reduced number of beam splitters and combiners) and the desired sampling rate. For example, rather than (as in Figure 3 Instead of each sensing beam passing through a row of optical modulators (in the example of FIG. 1 ), each sensing beam may pass through a fraction of a row (to increase the sampling rate) or more than one row (where a lower sampling rate is sufficient). Where there are multiple optical paths for the sensing beams (which are then combined and interfered with the reference beam), it is desirable that the optical path length is equal to the coherence length of the light source. In some embodiments, it is possible to achieve high sampling rates. Thus, the readout unit may be configured to operate at a rate of not less than 100 MHz, desirably at a rate of not less than 200 MHz, and more desirably at a rate of not less than 400 MHz.

[0094] In some embodiments, the beam spot on the detector surface can be larger than the beam spot on the sample surface. Therefore, the total size of the detection surface of the detector can be configured to be large enough to accommodate the wide beam spot. The beam spot on the detector surface can be on the order of a few millimeters in diameter. However, increasing the size of the detector may result in noise effects. For example, the capacitance of the detector may be proportional to the area of ​​the detector surface. Some noise sources, such as those due to components coupled to the detector (e.g., amplifiers), may be related to capacitance.

[0095] In some embodiments, the area of ​​the sensing element can be reduced by configuring the sensing element to be smaller than the geometric spread of secondary electrons incident on the entire detector surface. In the case where the sensing element is completely covered by the beam spot, the signal and capacitance of the detector sensing element can be proportional to the area of ​​the sensing element. In some cases, the sensing element may be only partially covered by the beam spot. When the sensing element is not completely covered by the beam spot, the SNR reduction due to capacitance can be mitigated by reducing the sensing element area.

[0096] In some embodiments, the area ratio may be varied, which may be the ratio of the area of ​​a single sensing element to the area of ​​the entire surface of the detector. The area ratio may have a corresponding relationship with the SNR. For example, in some embodiments, reducing the size of the sensing element to 1 / 1000 of the area of ​​the detector may correspond to a 1000-fold increase in the SNR.

[0097] In some embodiments, the detector may include an array of sensing elements. The array may include a plurality of sensing elements, each of which has a size of, for example, Dx and Dy or less. For example, each of the sensing elements may have a radiation receiving area of ​​no more than 500 μm×500 μm, desirably no more than 200 μm×200 μm, and more desirably no more than 150 μm×150 μm. In some embodiments, the radiation detector may include no less than 1,000 sensing elements, desirably no less than 5,000 sensing elements, and more desirably no less than 10,000 sensing elements. The sensing elements may be arranged in a planar two-dimensional array, the plane of the array being substantially perpendicular to the incident direction of the incoming charged particles. In some embodiments, the detector may be arranged to be tilted relative to the incident direction.

[0098] In some embodiments, the sensing element may be able to distinguish incident electrons with different energies, for example to distinguish backscattered electrons from secondary electrons. Such a sensor can output multiple independent signals, each of which indicates the number or intensity of received electrons of a specific type or energy range. In this case, a variety of different approaches can be used to read out the independent signals separately. For example, multiple independent modulators can be provided per sensing element, with one independent modulator for each of the independent signals. Multiple independent modulators can be applied to modulate different parameters of a single beam, to modulate separate beams traveling on separate optical paths, or to modulate beams of different wavelengths traveling on the same optical path, or some combination of these approaches.

[0099] Based on the same set of acquired raw data, various results can be obtained according to specific application requirements. The results can be used for post-processing instead of pre-processing. In some embodiments, pre-processing can include grouping of sensing elements. Data can also be customized to optimize specific purposes. For example, there can be a trade-off relationship between optimizing detection parameters (such as crosstalk and secondary charged particle collection efficiency). However, when post-processing is used to adjust the data, the trade-off can be adjusted without losing information. This can provide greater flexibility for the application layer and reduce the risk of having to redo a specific operation just to obtain data with different detection parameter settings.

[0100] In some embodiments, the detector can communicate with a controller that controls the charged particle beam system. The controller can instruct the components of the charged particle beam system to perform various functions, such as controlling a charged particle source to generate a charged particle beam and controlling a deflector to scan a charged particle beam. The controller can also perform various other functions, such as adjusting the sampling rate of the detector, resetting a sensing element, or performing image processing. The controller can include a storage device, which is a storage medium, such as a hard disk, a random access memory (RAM), other types of computer-readable memory, etc. The storage device can be used to save the scanned raw image data as an original image and save a post-processing image. A non-transitory computer-readable medium can be provided, which stores instructions for causing the processor of the controller 109 to perform charged particle beam detection, sampling period determination, image processing, or other functions and methods according to the present disclosure. Common forms of non-transitory media include, for example, floppy disks, diskettes, hard disks, solid-state drives, magnetic tapes or any other magnetic data storage medium, CD-ROMs, any other optical data storage medium, any physical medium with a pattern of holes, ROMs, PROMs and EPROMs, FLASH-EPROMs or any other flash memory, NVRAM, caches, registers, any other memory chip or cassette and networked versions thereof.

[0101] The block diagram in the figure can illustrate the architecture, functionality and operation of the possible implementation of the system, method and computer hardware / software product according to various exemplary embodiments of the present disclosure. In this regard, each frame in the schematic diagram can represent a specific arithmetic or logic operation process that can be implemented using hardware (such as an electronic circuit). The frame can also represent a module, a code segment or a code portion, which includes one or more executable instructions for implementing a specified logical function. It should be understood that in some alternative embodiments, the function indicated in the frame may not occur in the order mentioned in the figure. For example, the two frames shown in succession can be performed or implemented substantially at the same time, or the two frames can sometimes be performed in reverse order, depending on the functionality involved. Some frames can also be omitted. It should also be understood that each frame of the block diagram and the combination of these frames can be implemented by a system based on special-purpose hardware that performs a specified function or action or by a combination of special-purpose hardware and computer instructions.

[0102] Exemplary embodiments of the invention are set forth in the following numbered clauses:

[0103] 1. A radiation detector, comprising:

[0104] a set of sensing elements configured to generate an electrical signal in response to the radiation;

[0105] a set of optical modulators connected to respective ones of the sensing elements and configured to modulate a sensing light beam in response to the electrical signal; and

[0106] A sensing optical system is configured to direct the sensing light beam through each of the optical modulators.

[0107] 2. The radiation detector according to clause 1, wherein the optical modulator is arranged along a straight line, and the sensing optical system guides the sensing light beam along a straight beam path through the optical modulator.

[0108] 3. The radiation detector of clause 1, wherein the optical modulators are arranged in a two-dimensional array, and the sensing optical system directs the sensing light beam along a tortuous beam path through the optical modulators.

[0109] 4. The radiation detector according to any of clauses 1 to 3, further comprising at least one further set of sensing elements, at least one further set of optical modulators and at least one further sensing optical system.

[0110] 5. The radiation detector according to clause 4, further comprising a beam splitter configured to split an input light beam into a plurality of sensing light beams and to direct the sensing light beams into the sensing optical system and each additional sensing optical system.

[0111] 6. The radiation detector according to clause 4 or 5, further comprising a beam combiner configured to combine the plurality of sensing light beams that have passed through the sensing optical system or another sensing optical system into a measurement beam.

[0112] 7. The radiation detector of any of clauses 1 to 6, wherein the optical modulator is configured to modulate a property of the light beam, the property being selected from the group consisting of: phase, amplitude and polarization.

[0113] 8. A radiation detector according to any one of clauses 1 to 7, wherein the optical modulator is configured to cumulatively modulate the characteristics of the light beam so that the cumulative modulation of the characteristics of the light beam is indicative of the electrical signals output by all of the sensing elements.

[0114] 9. The radiation detector of clause 8, wherein the modulation of the light beam is indicative of a sum of electrical signals, desirably a weighted sum of the electrical signals.

[0115] 10. The radiation detector according to any preceding clause, further comprising a readout unit configured to measure the modulation of the light beam.

[0116] 11. The radiation detector according to clause 10, further comprising a reference optical system configured to provide a reference beam to the readout unit.

[0117] 12. The radiation detector of clause 10 or 11, wherein the readout unit is configured to operate at a rate of not less than 100 MHz, desirably not less than 200 MHz, more desirably not less than 400 MHz.

[0118] 13. A radiation detector according to any preceding clause, wherein the sensing optics and any further sensing optics comprise a waveguide.

[0119] 14. A radiation detector according to any preceding clause, wherein the set of sensing elements is formed on a first substrate and the set of optical modulators is formed on a second substrate; the second substrate being bonded to the first substrate.

[0120] 15. The radiation detector of clause 14, further comprising a light source on the second substrate.

[0121] 16. A radiation detector according to any preceding clause, wherein the set of sensing elements comprises CMOS devices.

[0122] 17. A radiation detector according to any preceding clause, wherein the set of sensing elements comprises PIN diodes.

[0123] 18. A radiation detector according to any preceding clause, wherein the set of optical modulators is formed on a silicon substrate.

[0124] 19. A radiation detector according to any preceding clause, wherein each of the sensing elements has a radiation receiving area having a size not exceeding 500 μm×500 μm, desirably not exceeding 200 μm×200 μm, more desirably not exceeding 150 μm×150 μm.

[0125] 20. A radiation detector according to any preceding clause, comprising no less than 1,000 sensing elements, desirably no less than 5,000 sensing elements, more desirably no less than 10,000 sensing elements.

[0126] 21. A radiation detector according to any preceding clause, wherein each sensing element is configured to generate an electrical signal in response to an incident electron as radiation, the incident electron desirably being a single incident electron.

[0127] 22. A radiation detector according to any preceding clause, wherein each optical modulator is connected to a respective one of the sensing elements.

[0128] 23. A radiation detector according to any preceding clause, wherein each optical modulator is connected to a plurality of said sensing elements.

[0129] 24. A charged particle detection system comprising a radiation detector according to any preceding clause.

[0130] 25. The charged particle detection system of clause 24, further comprising a secondary optical system configured to direct electrons emitted from a sample to the radiation detector.

[0131] 26. A charged particle detection system comprising:

[0132] a set of sensing elements configured to generate an electrical signal in response to the radiation;

[0133] a set of optical modulators connected to respective ones of the sensing elements and configured to modulate a sensing light beam in response to the electrical signal; and

[0134] A sensing optical system is configured to direct the sensing light beam through each of the optical modulators.

[0135] 27. A charged particle detection system according to clause 26, wherein the optical modulator is arranged along a straight line and the sensing optical system guides the sensing light beam along a straight beam path through the optical modulator.

[0136] 28. A charged particle detection system according to clause 26, wherein the optical modulators are arranged in a two-dimensional array and the sensing optical system directs the sensing light beam along a tortuous beam path through the optical modulators.

[0137] 29. A charged particle detection system according to any one of clauses 26 to 28, further comprising a readout unit configured to measure the modulation of the light beam and generate an output signal, the output signal representing the total amount of radiation received by the set of sensing elements during a sampling period, desirably representing a weighted sum of the total amount of radiation received by the set of sensing elements during a sampling period.

[0138] 30. A charged particle detection system according to any of clauses 26 to 28, further comprising at least a further set of sensing elements, at least a further set of optical modulators and at least a further sensing optical system.

[0139] 31. The charged particle detection system according to clause 30 further includes a readout unit, which is configured to measure the modulation of the light beam and generate an output signal, wherein the output signal represents the total amount of radiation received by all sets of sensing elements during a sampling period, and desirably represents the weighted sum of the total amount of radiation received by all sets of sensing elements during a sampling period.

[0140] 32. The charged particle detection system according to clause 30 further includes a readout unit configured to measure the modulation of the light beam and generate a plurality of output signals, each of the plurality of output signals representing a total amount of radiation received by a sensing element in the set of sensing elements during a sampling period, desirably a weighted sum of the total amount of radiation received by a sensing element in the set of sensing elements during a sampling period.

[0141] 33. A charged particle detection system according to any of clauses 29, 31 or 32, further comprising a reference optical system configured to provide a reference beam to the readout unit.

[0142] 34. A charged particle detection system according to any one of clauses 29 or 31 to 33, wherein the readout unit is configured to operate at a rate of not less than 100 MHz, desirably at a rate of not less than 200 MHz, and more desirably at a rate of not less than 400 MHz.

[0143] 35. A charged particle detection system according to any of clauses 26 to 34, wherein the optical modulator is configured to modulate a property of the light beam, the property being selected from the group consisting of: phase, amplitude and polarization.

[0144] 36. A charged particle detection system according to any of clauses 26 to 35, wherein the sensing optics and any further sensing optics comprise a waveguide.

[0145] 37. A charged particle detection system according to any of clauses 26 to 36, wherein the set of sensing elements is formed on a first substrate and the set of optical modulators is formed on a second substrate; the second substrate being bonded to the first substrate.

[0146] 38. A charged particle detection system according to any of clauses 26 to 37, wherein each of the sensing elements has a radiation receiving area having a size not exceeding 500 μm x 500 μm, desirably not exceeding 200 μm x 200 μm, more desirably not exceeding 150 μm x 150 μm.

[0147] 39. A charged particle detection system according to any of clauses 26 to 38, comprising no less than 1,000 sensing elements, desirably no less than 5,000 sensing elements, more desirably no less than 10,000 sensing elements.

[0148] 40. A charged particle detection system according to any of clauses 26 to 39, wherein each optical modulator is connected to a respective one of the sensing elements.

[0149] 41. A charged particle detection system according to any of clauses 26 to 39, wherein each optical modulator is connected to a plurality of said sensing elements.

[0150] 42. A charged particle detection system according to any one of clauses 26 to 41, further comprising a secondary optical system configured to direct electrons emitted from a sample to the set(s) of sensing elements.

[0151] 43. A method of detecting radiation, comprising:

[0152] directing radiation to a plurality of sensing elements configured to generate electrical signals in response to the radiation;

[0153] modulating a sensing light beam in response to the electrical signal; and

[0154] The modulation of the sensing beam is measured to detect radiation.

[0155] 44. The method of clause 43, wherein the modulating comprises directing the sensing light beam along a straight beam path through the set of optical modulators connected to the set of sensing elements.

[0156] 45. The method of clause 43, wherein the modulating comprises directing the sensing beam along a tortuous beam path through optical modulators arranged in a two-dimensional array.

[0157] 46. ​​A method according to any of clauses 43 to 45, said modulating comprising directing a plurality of sensing light beams along beam paths through a respective set of said optical modulators.

[0158] 47. The method of clause 46, further comprising: splitting the input beam into a plurality of sensing beams.

[0159] 48. The method of clause 46 or 47, further comprising combining the plurality of sensing light beams into a measurement beam after the modulating.

[0160] 49. A method according to any of clauses 43 to 48, wherein the modulating comprises modulating a property of the light beam, the property being selected from the group consisting of: phase, amplitude and polarization.

[0161] 50. A method according to any of clauses 43 to 49, wherein the modulating comprises cumulatively modulating a characteristic of the light beam such that the modulation of the light beam is indicative of electrical signals output by all of the sensing elements.

[0162] 51. A method according to clause 50, wherein the modulation of the light beam is indicative of a sum of the electrical signals, desirably indicative of a weighted sum of the total amount of radiation received by the sensing element in a sampling period.

[0163] 52. The method of any of clauses 43 to 50, further comprising measuring the modulation of the light beam.

[0164] 53. A method according to clause 52, wherein measuring comprises: measuring the modulation relative to a reference beam.

[0165] 54. A method according to clause 52 or 53, wherein measuring comprises measuring the modulation at a rate of not less than 100 MHz, desirably measuring the modulation at a rate of not less than 200 MHz, and more desirably measuring the modulation at a rate of not less than 400 MHz.

[0166] 55. A method according to any of clauses 43 to 54, wherein each sensing element is configured to generate an electrical signal in response to an incident electron as radiation, the incident electron desirably being a single incident electron.

[0167] 56. A charged particle detector comprising:

[0168] an array of sensing elements configured to generate electrical signals in response to charged particles and arranged in rows;

[0169] an array of optical modulators, each connected to a corresponding one of the sensing elements and configured to modulate a sensing light beam in response to the electrical signal;

[0170] a plurality of waveguides configured to direct each of a plurality of sensing beams through the row of optical modulators;

[0171] a beam combiner configured to combine the plurality of sensing light beams that have passed through corresponding rows of the optical modulator into a combined beam; and

[0172] A readout unit is configured to measure the modulation of the combined beam to detect charged particles incident on the sensing element.

[0173] 57. A non-transitory computer readable medium comprising a set of instructions executable by one or more processors of a controller to cause the controller to perform a method for controlling a deflector of a charged particle inspection system, the method comprising:

[0174] causing radiation to be directed to a plurality of sensing elements that generate electrical signals in response to the radiation and are part of a detection component configured to modulate the sensing beam in response to the electrical signals and measure the modulation of the sensing beam to detect the radiation; and

[0175] The detection component is caused to output a signal indicative of the measured modulation.

[0176] 58. The non-transitory computer-readable medium of clause 57, wherein the set of instructions is executable by one or more processors of a controller to cause the controller to further:

[0177] An image is generated based on the signal indicative of the measured modulation, wherein the detection component includes an optical modulator configured to cumulatively modulate a characteristic of the light beam, wherein the cumulative modulation of the characteristic of the light beam is indicative of the electrical signals output by all of the sensing elements, and wherein the signal indicative of the measured modulation is indicative of the cumulative modulation of the characteristic of the light beam.

[0178] It should be understood that the present invention is not limited to the exact configurations that have been described above and illustrated in the accompanying drawings, and that various modifications and changes can be made without departing from the scope of the present invention. For example, although PIN diodes have been discussed with reference to certain exemplary embodiments, other types of diodes, such as NIP diodes, may be similarly applied. In addition, other types of devices that can generate a measurable signal in response to receiving incident energy may be applied to the detector.

[0179] It is to be understood that elements shown in separate figures may be combined.

[0180] Furthermore, although scanning electron microscopy has been discussed with reference to some embodiments, other types of systems may also be applicable. For example, the detector may be used in a transmission electron microscopy (TEM), scanning transmission electron microscopy (STEM), or structured illumination microscopy (SIM) system.

Claims

1. A radiation detector comprising: a set of sensing elements configured to generate an electrical signal in response to the radiation; a set of optical modulators connected to respective ones of the sensing elements and configured to modulate a sensing light beam in response to the electrical signal; as well as A sensing optical system is configured to direct the sensing light beam through each of the optical modulators. 2 . The radiation detector according to claim 1 , wherein the optical modulator is arranged along a straight line, and the sensing optical system guides the sensing light beam to pass through the optical modulator along a straight beam path.

3. The radiation detector of claim 1, wherein the optical modulators are arranged in a two-dimensional array, and the sensing optical system guides the sensing light beam through the optical modulators along a tortuous beam path.

4. The radiation detector of claim 1, further comprising at least one additional set of sensing elements, at least one additional set of optical modulators, and at least one additional sensing optical system. 5 . The radiation detector according to claim 4 , further comprising a beam splitter configured to split the input beam into a plurality of sensing beams and to guide the sensing beams into the sensing optical system and each of the additional sensing optical systems. 6 . The radiation detector according to claim 4 , further comprising a beam combiner configured to combine the plurality of sensing light beams that have passed through the sensing optical system or another sensing optical system into a measuring beam.

7. The radiation detector of any one of claims 1, wherein the optical modulator is configured to modulate a property of the light beam, the property selected from the group consisting of: phase, amplitude, and polarization.

8. The radiation detector of any one of claims 1, wherein the optical modulator is configured to cumulatively modulate a characteristic of the light beam such that the cumulative modulation of the characteristic of the light beam is indicative of the electrical signal output by all of the sensing elements.

9. The radiation detector of claim 8, wherein the modulation of the light beam is indicative of a sum of the electrical signals, desirably a weighted sum of the electrical signals.

10. The radiation detector of claim 1, further comprising a readout unit configured to measure the modulation of the light beam. 11 . The radiation detector of claim 10 , further comprising a reference optical system configured to provide a reference beam to the readout unit.

12. The radiation detector of claim 1, wherein the sensing optics and any further sensing optics comprise a waveguide.

13. The radiation detector of claim 1, wherein the set of sensing elements is formed on a first substrate and the set of optical modulators is formed on a second substrate; the second substrate being bonded to the first substrate.

14. The radiation detector of claim 1, wherein each optical modulator is connected to a corresponding one of the sensing elements.

15. A non-transitory computer readable medium comprising a set of instructions executable by one or more processors of a controller to cause the controller to perform a method for controlling a deflector of a charged particle inspection system, the method comprising: causing radiation to be directed to a plurality of sensing elements that generate electrical signals in response to the radiation and are part of a detection component configured to modulate a sensing beam in response to the electrical signals and to measure the modulation of the sensing beam to detect the radiation; as well as The detection component is caused to output a signal indicative of the measured modulation.

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