Charged particle detectors for microscopy

Abstract

1. A charged particle detector comprising: an array of sensing elements arranged in a column configured to generate an electrical signal in response to a charged particle; an array of optical modulators each connected to a respective one of the sensing elements, the optical modulators configured to modulate a sensing light beam in response to the electrical signal; a plurality of waveguides configured to direct each of a plurality of sensing light beams through the column of optical modulators; a beam combiner configured to combine the plurality of sensing light beams that have passed through each column of optical modulators into a combined beam; and a readout unit configured to measure the modulation of the combined beam to detect charged particles incident on the sensing elements.

Description

[Technical Field]

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims priority to European Application No. 22186172.7, filed July 21, 2022, which is incorporated herein by reference in its entirety. [Background technology]

[0002] FIELD OF THE INVENTION

[0002] The description herein relates to charged particle detection, and more particularly to systems and methods applicable to charged particle beam detection.

[0003]

[0003] Detectors can be used to detect physically observable phenomena. For example, a charged particle beam tool such as an electron microscope may 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 under inspection and can be used to reveal, for example, defects in the sample. Detection of defects in samples is becoming increasingly important in the manufacture of semiconductor devices, which may include many densely packed miniature integrated circuit (IC) components. Dedicated inspection tools can be provided for this purpose.

[0004]

[0004] 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 or secondary electrons generated from the sample. In related art, the electron detection system of an SEM tool can include a detector configured to detect electrons coming from the sample. Existing detectors in SEM tools can only detect the intensity of the beam. The sensitivity of conventional detection systems can be limited by a low signal-to-noise ratio (SNR), especially when the beam current is reduced, for example, to the picoampere range. Some detection methods can use large-area semiconductor detectors, or a group of small-area semiconductor detectors with areas equal to, smaller than, or larger than the area of the beam spot. A current induced by the incoming electron beam can be generated in the detector and then amplified by an amplifier following the detector.

[0005]

[0005] With the continued miniaturization of semiconductor devices, detection systems may use increasingly lower electron beam currents. As the beam current decreases, maintaining SNR becomes more difficult. For example, if the probe current is reduced to 200 pA or less, the SNR can decrease dramatically. A low SNR may require taking measures such as image averaging or extending the signal integration time corresponding to each pixel in the image of the sample, which increases the electron dose on the sample surface and can result in surface charging artifacts or other deleterious effects. Such measures may also reduce the overall throughput of the inspection system.

[0006]

[0006] In the related art, particle counting can 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). ETDs can exhibit good SNR in probe current ranges, such as 8 pA to 100 pA, for some applications. However, they have a limited lifetime because the light yield of the scintillator can deteriorate with electron dose accumulation. Scintillator aging can cause system-level performance drift and lead to non-uniform images. Therefore, ETDs may not be suitable for use in inspection tools, especially when used in semiconductor manufacturing facilities that may need to operate 24 hours a day, 7 days a week.

[0007] There is a need for a charged particle detector that can achieve a high SNR and can be used at low probe currents, such as less than 200 pA, while the detector must ensure stable quantum efficiency and long lifetime with low performance drift, even when used in continuous operation, for example, at probe currents of 1 nA or more.

[0008]

[0008] Detection systems employing related art methods may face limitations in detection sensitivity and SNR, especially at low electron doses. To improve the SNR, the related art has proposed so-called pixelated electron counting detectors, in which the detector is subdivided into multiple detection elements whose outputs are combined to generate a detection signal. However, the process of combining the outputs of the individual detection elements can be slow and / or require complex electronic circuitry. For this reason, improved detection systems and methods are desirable. Summary of the Invention

[0009]

[0009] An embodiment of the present disclosure provides a radiation detector comprising a set of sensing elements configured to generate an electrical signal in response to radiation, a set of optical modulators connected to each of the sensing elements and configured to modulate a sensing light beam in response to the electrical signal, and a sensing optical system configured to direct the sensing light beam through each of the optical modulators.

[0010]

[0010] An embodiment of the present disclosure provides a charged particle detection system comprising a set of sensing elements configured to generate an electrical signal in response to radiation, a set of optical modulators connected to each of the sensing elements and configured to modulate a sensing light beam in response to the electrical signal, and a sensing optical system configured to direct the sensing light beam through each of the optical modulators.

[0011]

[0011] An embodiment of the present disclosure provides a method for detecting radiation, the method including directing radiation to a plurality of sensing elements configured to generate an electrical signal in response to the radiation, modulating a sensing light beam in response to the electrical signal, and measuring the modulation of the sensing light beam to detect the radiation.

[0012]

[0012] An embodiment of the present disclosure provides a charged particle detector comprising: an array of sensing elements arranged in a row, the sensing elements configured to generate an electrical signal in response to a charged particle; an array of optical modulators each connected to a respective one of the sensing elements, the optical modulators configured to modulate a sensing light beam in response to the electrical signal; a plurality of waveguides configured to guide a plurality of sensing light beams through the row of optical modulators; a beam combiner configured to combine the plurality of sensing light beams that have passed through each row of optical modulators into a combined beam; and a readout unit configured to measure the modulation of the combined beam to detect charged particles incident on the sensing elements.

[0013]

[0013] An embodiment of the present disclosure provides a non-transitory computer-readable medium including 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 including directing radiation to a plurality of sensing elements, the plurality of sensing elements generating electrical signals in response to the radiation and being part of a detection component, the detection component being configured to modulate a detection light beam in response to the electrical signals and measure the modulation of the detection light beam to detect the radiation, and causing the detection component to output a signal indicative of the measured modulation.

[0014]

[0014] 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 embodiments of the disclosure as may be claimed. [Brief explanation of the drawings]

[0015]

[0015] The above and other aspects of the present disclosure will become apparent from the description of exemplary embodiments read in conjunction with the accompanying drawings. [Figure 1]

[0016] FIG. 1 is a schematic diagram illustrating an exemplary electron beam inspection (EBI) system, according to an embodiment of the present disclosure. [Figures 2A-2B-2C]

[0017] FIG. 2 is a schematic diagram illustrating an example electron beam tool according to an embodiment of the present disclosure that may be part of the example electron beam inspection system of FIG. 1. [Figure 3]

[0018] FIG. 1 is a schematic diagram of an embodiment of a radiation detector. [Figure 4]

[0019] FIG. 4 is a schematic cross-sectional view of the radiation detector of FIG. 3. [Figure 5]

[0020] FIG. 4 is a timing diagram for the radiation detector of FIG. 3. [Figure 6]

[0021] FIG. 2 is a schematic diagram of another embodiment of a radiation detector. DETAILED DESCRIPTION OF THE INVENTION

[0016]

[0022] Reference will now be made in detail to the exemplary embodiments, examples of which are illustrated in the drawings. The following description refers to the accompanying drawings, in which, unless otherwise indicated, identical numbers represent identical or similar elements in the various figures. The implementations set forth in the following description of exemplary embodiments do not represent all implementations in accordance with the present invention. Instead, they are merely examples of devices, systems, and methods in accordance with aspects related to the subject matter that may be recited in the appended claims.

[0017]

[0023] Aspects of the present application relate to systems and methods for charged particle beam detection. The systems and methods can utilize counting of charged particles, such as electrons, and can be useful in inspection tools such as scanning electron microscopes (SEMs). The inspection tools can be used in the manufacturing process of integrated circuit (IC) components. To achieve the increased computing power of today's electronic devices, the packing density of circuit components, such as transistors, capacitors, and diodes, on IC chips can be significantly increased while the physical size of the devices is reduced. For example, in a smartphone, an IC chip (which may be the size of a thumbnail) can contain over two billion transistors, each less than one-thousandth the size of a human hair. Not surprisingly, semiconductor IC manufacturing is a complex process involving hundreds of individual steps. An error in even one step can dramatically affect the functionality of the final product. The goal of the manufacturing process is to improve the overall yield of the process. For example, for a process with 50 steps to achieve a 75% yield, each individual step must have a yield greater than 99.4%, and if the individual step yield is 95%, the overall process yield drops to 7%.

[0018]

[0024] Ensuring the ability to detect defects 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 throughput can be affected by the presence of defects, especially when operator intervention is involved. Therefore, the detection and identification of micro- and nano-sized defects by inspection tools (e.g., SEM) is critical to maintaining high yields and low costs.

[0019]

[0025] In some inspection tools, samples can be inspected by scanning a high-energy electron beam across the sample surface, where interactions can generate secondary or backscattered electrons from the sample, which can then be detected by a detector.

[0020]

[0026] Related art detectors may have limitations, such as slow readout speeds or requirements 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 electron detector) having a set of sensing elements, a set of optical modulators coupled to the set of sensing elements, and a detection optical system that directs a light beam through the optical modulators to enable readout of the detection of radiation by the sensing elements. This optical readout may enable faster readout and / or allow simpler and smaller components to be implemented on-chip compared to, for example, electronic readout circuits. Optical readout may have lower power consumption than electronic readout circuits, leading to lower heat dissipation in the vacuum chamber and reduced cooling requirements. While the present disclosure discusses some exemplary embodiments in the context of electrons, it will be understood that the present disclosure is applicable to other types of charged particles, such as ions.

[0021]

[0027] In some embodiments of the present disclosure, the sensing elements of the array can be sized so that the area of each sensing element receives no more than a certain number of charged particles per sampling period. The certain 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. Thus, each sensing element can be configured to receive fewer charged particles than the total number of charged particles incident on the detector. According to various criteria, aspects of the detector, such as the size, sampling rate, and other characteristics of the sensing element, can be configured to enable charged particle counting.

[0022]

[0028] Without limiting the scope of the present disclosure, some embodiments may be described in the context of providing detectors and methods of detection in systems utilizing electron beams. However, the disclosure is not so limited. Other types of charged particle beams may be similarly applicable. Furthermore, the systems and methods for detection may be used in other imaging systems, such as optical imaging, photon detection, x-ray detection, ion detection, etc.

[0023]

[0029] As used herein, unless otherwise indicated, the term "or" includes all possible combinations unless impracticable. For example, if a component is described as including A or B, the component may include A or B, or A and B, unless otherwise indicated or impracticable. As a second example, if a component is described as including A, B, or C, the component may include A or B or C, or A and B, or A and C, or B and C, or A, B, and C, unless otherwise indicated or impracticable.

[0024]

[0030] Furthermore, the term "detector element" can include or encompass "sensing element," "sensor element," "detector cell," or "detector segment," etc. A sensing element can be a diode configured with a depleted region, and in some embodiments discussed herein, the term "sensing element" may exclude an avalanche diode operating in Geiger mode. A detector element can include the diode, interconnections, and circuitry, which may include, for example, front-end electronics. Furthermore, the term "frame" can include or encompass "sampling period," "SEM image pixel period," or "pixel period," etc. An SEM image frame can refer to a frame of pixels that may be updated frame-by-frame, while a data frame can refer to a group of data acquired by a detection system within a specified time period.

[0025]

[0031] 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. This method may be applied to an 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 an incoming electron beam may be determined. The term "incoming electrons" may include or encompass incident electrons, such as electrons that strike a detector surface. According to some embodiments, noise from the charged particle detection process may be reduced. However, improving the SNR alone may not be enough to meet the ever-increasing needs of various SEM applications.

[0026]

[0032] Electron counting can involve determining individual electron arrival events occurring at a detector. For example, electrons can be detected one by one as they arrive at the detector. In some embodiments, electrons incident on the detector can generate an electrical signal that is sent to an electro-optic modulator, which selectively modulates the light beam by changing a parameter of the light beam, such as its phase, amplitude, or polarization. Signal processing circuitry detects the modulation of the light beam and then reads it out to an interface, such as a digital controller. The detector can be configured to resolve the signal generated by the incident electrons and identify individual electrons with discrete count values.

[0027]

[0033] In some embodiments, electron counting can be applied to situations where the beam current is very low. For example, the electron beam can be set to irradiate the sample at a low dose. A low current can be used to prevent oversaturation of the electron counting detector due to a large current. For example, a large current can have a nonlinear effect on the detection results. On the other hand, for detectors that can be used in industrial environments, the detector must also be able to handle large beam current situations.

[0028]

[0034] Some embodiments can address the above-mentioned problems. For example, some embodiments can provide multiple relatively small sensing elements that can be used to detect an electron beam. Separation between adjacent sensing elements can be provided to reduce the probability that an incoming electron will travel from one sensing element to its neighboring sensing element. In this way, crosstalk between adjacent sensing elements can be reduced.

[0029]

[0035] In some embodiments, detectors can be constructed using digital circuits and optical electronic elements rather than implementations requiring extensive analog or digital electronic circuitry, thus improving various aspects of the detector implementation, such as speed of operation.

[0030]

[0036] Reference is now made to FIG. 1 , which illustrates an exemplary electron beam inspection (EBI) system 10 that may include a detector according to an embodiment of the present disclosure. The EBI system 10 may be used for imaging. As shown in FIG. 1 , 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 disposed within the main chamber 11. The EFEM 30 includes a first loading port 30 a and a second loading port 30 b. The EFEM 30 may include additional loading ports. The first loading port 30 a and the second loading port 30 b receive a wafer front-opening integrated pod (FOUP) containing wafers (e.g., semiconductor wafers or wafers made of other materials) or samples to be inspected (wafers and samples may be collectively referred to herein as “wafers”).

[0031]

[0037] One or more robot arms (not shown) within the EFEM 30 can transfer wafers to the load / lock chamber 20. The load / lock chamber 20 is connected to a load / lock vacuum pumping system (not shown), which removes gas molecules from the load / lock chamber 20 to achieve a first pressure below atmospheric pressure. After the first pressure is reached, one or more robot arms (not shown) can transfer the wafers from the load / lock chamber 20 to the main chamber 11. The main chamber 11 is connected to a main chamber vacuum pumping system (not shown), which removes gas molecules from the main chamber 11 to achieve a second pressure below the first pressure. After the second pressure is reached, the wafers are inspected by the electron beam tool 100. The electron beam tool 100 can be a single-beam system or a multi-beam system. A controller 109 is electronically connected to the electron beam tool 100 and can also be electronically connected to other components. The controller 109 can be a computer configured to perform various controls of the EBI system 10. Although the controller 109 is shown in FIG. 1 outside the structure including the main chamber 11, the load / lock chamber 20, and the EFEM 30, it will be understood that the controller 109 can be part of this structure.

[0032]

[0038] FIG. 2A illustrates a charged particle beam device in which the inspection system may include a multi-beam inspection tool that uses multiple primary electron beamlets to simultaneously scan multiple locations on a sample.

[0033]

[0039] As shown in FIG. 2A , the electron beam tool 100A (also referred to herein as apparatus 100A) may include an electron source 202, a gun aperture 204, a condenser lens 206, a primary electron beam 210 emitted from the electron source 202, a source conversion unit 212, multiple beamlets 214, 216, and 218 of the primary electron beam 210, a primary projection optical system 220, a wafer stage (not shown in FIG. 2A ), multiple 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 in the primary electron beam 210. A controller, an image processing system, or the like may be coupled to the electron detection device 244. The primary projection optical system 220 may include a beam separator 222, a deflection scanning unit 226, and an objective lens 228. The electronic detection device 244 may include detection sub-regions 246 , 248 , and 250 .

[0034]

[0040] Electron source 202, gun aperture 204, condenser lens 206, source conversion unit 212, beam separator 222, deflection scanning unit 226, and objective lens 228 can be aligned with a primary optical axis 260 of apparatus 100A. Secondary optical system 242 and electron detection device 244 can be aligned with a secondary optical axis 252 of apparatus 100A.

[0035]

[0041] The electron source 202 may include a cathode, extractor, or anode, and primary electrons may be emitted from the cathode and extracted or accelerated to form a primary electron beam 210 with a crossover (virtual or real) 208. The primary electron beam 210 may be visualized as being emitted from the crossover 208. The gun aperture 204 may block peripheral electrons of the primary electron beam 210 to reduce the size of the probe spots 270, 272, and 274.

[0036]

[0042] The source conversion unit 212 may include an array of image-forming elements (not shown in FIG. 2A ) and an array of beam-limiting apertures (not shown in FIG. 2A ). An example of the source conversion unit 212 can be found in U.S. Pat. No. 9,691,586, U.S. Publication No. 2017 / 0025243, and International Application No. PCT / EP2017 / 084429, all of which are incorporated by reference in their entirety. The array of image-forming elements may include an array of micro-deflectors or micro-lenses. The array of image-forming elements may form multiple parallel images (virtual or real) of the crossover 208 using multiple beamlets 214, 216, and 218 of the primary electron beam 210. The array of beam-limiting apertures may limit the multiple beamlets 214, 216, and 218.

[0037]

[0043] The condenser lens 206 can focus the primary electron beam 210. The current of the beamlets 214, 216, and 218 downstream of the source conversion unit 212 can be varied by adjusting the focusing power of the condenser lens 206 or by changing the radial size of the corresponding beam-limiting aperture in the beam-limiting aperture array. The condenser lens 206 can be a movable condenser lens that can be configured with a movable first principal plane position. The movable condenser lens can be configured as a magnetic type with a rotation angle to allow the off-axis beamlets 216 and 218 to enter the beamlet-limiting aperture. The rotation angle varies with the focusing power and the position of the first principal plane of the movable condenser lens. In some embodiments, the movable condenser lens can be a movable, non-rotating condenser lens, including a non-rotating lens with a movable first principal plane. Movable condenser lenses are further described in U.S. Publication No. 2017 / 0025241, which is incorporated by reference in its entirety.

[0038]

[0044] The objective lens 228 can focus the beamlets 214 , 216 , and 218 onto the wafer 230 for inspection, and can form multiple probe spots 270 , 272 , and 274 on the surface of the wafer 230 .

[0039]

[0045] Beam separator 222 may be a Wien filter-type beam separator that generates electrostatic and magnetic dipole fields. In some embodiments, when applied, the force exerted by the electrostatic dipole field on the electrons of beamlets 214, 216, and 218 may be equal in magnitude but opposite in direction to the force exerted by the magnetic dipole field on the electrons. Thus, beamlets 214, 216, and 218 may pass straight through beam separator 222 with a zero deflection angle. However, the total dispersion of beamlets 214, 216, and 218 generated by beam separator 222 may be non-zero. Beam separator 222 may separate secondary electron beams 236, 238, and 240 from beamlets 214, 216, and 218 and direct secondary electron beams 236, 238, and 240 toward secondary optical system 242.

[0040]

[0046] The deflection scanning unit 226 can deflect the beamlets 214, 216, and 218 to scan the probe spots 270, 272, and 274 over the surface area of the wafer 230. In response to the beamlets 214, 216, and 218 impinging on 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 can 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 detection subregions 246, 248, and 250 of the electron detection device 244. The detection subregions 246, 248, and 250 can be configured to detect the corresponding secondary electron beams 236, 238, and 240 and generate corresponding signals used to reconstruct an image of the surface area of the wafer 230.

[0041]

[0047] 2A shows an example of electron beam tool 100 as a multi-beam tool using multiple beamlets, embodiments of the present disclosure are not so limited. For example, electron beam tool 100 may be a single-beam tool that uses only one primary electron beam to scan one location on the wafer at a time.

[0042]

[0048] As shown in FIG. 2B , electron beam tool 100B (also referred to herein as apparatus 100B) can be a single-beam inspection tool used in EBI system 10. Apparatus 100B includes a wafer holder 136 supported by a motorized stage 134 for holding a wafer 150 to be inspected. Electron beam tool 100B includes an electron emitter, which can include a cathode 103, an anode 121, and a gun aperture 122. Electron beam tool 100B further includes a beam-limiting aperture 125, a condenser lens 126, a column aperture 135, an objective lens assembly 132, and a detector 144. Objective lens assembly 132 can be a modified SORIL lens in some embodiments, which includes a pole piece 132a, a control electrode 132b, a deflector 132c, and an excitation coil 132d. In the imaging process, electron beam 161 generated from the tip of cathode 103 is accelerated by the voltage on anode 121, passes through gun aperture 122, beam-limiting aperture 125, condenser lens 126, and is focused by a modified SORIL lens to a probe spot 170, which can impinge on the surface of wafer 150. A deflector, such as deflector 132c or another deflector in a SORIL lens, can scan probe spot 170 over the surface of wafer 150. Secondary particles or scattered primary particles, such as secondary electrons or scattered primary electrons, generated from the wafer surface are collected by detector 144, allowing the beam intensity to be determined and an image of the region of interest on wafer 150 to be reconstructed.

[0043]

[0049] An image processing system 199 may also be provided, including the image acquirer 120, the storage 130, and the controller 109. The image acquirer 120 may include one or more processors. For example, the image acquirer 120 may include a computer, a server, a mainframe host, a terminal, a personal computer, any type of mobile computing device, etc., or a combination thereof. The image acquirer 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, wireless radio, or a combination thereof. The image acquirer 120 may receive signals from the detector 144 and construct an image. Thus, the image acquirer 120 may acquire an image of the wafer 150. The image acquirer 120 may also perform various post-processing functions, such as contour generation and overlaying indicators on the acquired image. The image acquirer 120 may be configured to adjust the brightness, contrast, etc., of the acquired image. The storage 130 may be a storage medium such as a hard disk, random access memory (RAM), cloud storage, other types of computer-readable memory, etc. The storage 130 may be coupled to the image acquirer 120 and may be used to store raw scanned image data as original images and post-processed images. The image acquirer 120 and the storage 130 may be connected to the controller 109. In some embodiments, the image acquirer 120, the storage 130, and the controller 109 may be integrated into one electronic control unit.

[0044]

[0050] In some embodiments, the image acquirer 120 can acquire one or more images of the sample based on an imaging signal received from the detector 144. The imaging signal can correspond to a scanning motion to perform charged particle imaging. The acquired image can be a single image that includes multiple imaging areas that can include various features of the wafer 150. The single image can be stored in the storage 130. The imaging can be based on imaging frames.

[0045]

[0051] The condenser and illumination optics of the electron beam tool can include or be supplemented by electromagnetic quadrupole electron lenses. For example, as shown in FIG. 2B , electron beam tool 100B can 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, first quadrupole lens 148 can be controlled to adjust the beam current, and second quadrupole lens 158 can be controlled to adjust the beam spot size and beam shape.

[0046]

[0052] FIG. 2B illustrates a charged particle beam device in which an inspection system can use a single primary beam that can be configured to generate secondary electrons by interacting with a wafer 150. As in the embodiment shown in FIG. 2B, a detector 144 can be positioned along the optical axis 105. The primary electron beam can be configured to travel along the optical axis 105. Accordingly, the detector 144 can include a hole in the center to allow the primary electron beam to pass through and reach the wafer 150. However, some embodiments can use a detector 224 that is positioned off-axis with respect to the optical axis along which the primary electron beam travels. For example, as in the embodiment shown in FIG. 2A, a beam separator 222 can be provided to direct the secondary electron beam toward the off-axis detector. The beam separator 222 can be configured to deflect the secondary electron beam by an angle α.

[0047]

[0053] Another example of a charged particle beam device will now be discussed with reference to Figure 2C. Electron beam tool 100C (also referred to herein as device 100C) is an example of an electron beam tool 100 and may be similar to electron beam tool 100A shown in Figure 2A.

[0048]

[0054] 2C, beam separator 222 may be a Wien filter-type beam separator that generates electrostatic and magnetic dipole fields. In some embodiments, when applied, the force exerted by the electrostatic dipole field on the electrons of beamlets 214, 216, and 218 may be equal in magnitude but opposite in direction to the force exerted by the magnetic dipole field on the electrons. Thus, beamlets 214, 216, and 218 may pass straight through beam separator 222 with a zero deflection angle. However, the total dispersion of beamlets 214, 216, and 218 generated by beam separator 222 may be non-zero. 2C shows that beamlet 214, having a nominal energy V and an energy distribution ΔV, disperses into beamlet portion 262 corresponding to energy V, beamlet 264 corresponding to energy V+ΔV / 2, and beamlet portion 266 corresponding to energy V−ΔV / 2. The total force exerted by beam separator 222 on the electrons in secondary electron beams 236, 238, and 240 can be non-zero. Beam separator 222 can separate secondary electron beams 236, 238, and 240 from beamlets 214, 216, and 218 and direct secondary electron beams 236, 238, and 240 toward secondary optical system 242.

[0049]

[0055] A semiconductor electron detector (often referred to as a "PIN detector") can be used in the device 100 of 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 illuminate the surface of a sample or penetrate the sample. The EBI system 10 can be used to image surface or subsurface structures of the sample for purposes such as analyzing layer alignment. In some embodiments, the EBI system 10 can detect and report process defects associated with the fabrication of semiconductor wafers, for example, by comparing an SEM image to a device layout pattern or to an SEM image of the same pattern at another location on the wafer under inspection. 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 incoming electrons generate a relatively large, well-defined detection signal. In some embodiments, the PIN detector can be configured so that incoming electrons can generate several electron-hole pairs, while photons can generate only one electron-hole pair. As discussed below, PIN detectors used for electron counting can have many differences compared to photodiodes used for photon detection.

[0050]

[0056] Reference is now made to Figure 3A, which shows a schematic diagram of an exemplary structure of a detector 300. The detector 300 may be provided as the detector 144 or the electronic detection device 244, with reference to Figures 2A, 2B and 2C.

[0051]

[0057] Briefly, detector 300 includes sensing elements 311, 312, 313 for generating an electrical signal 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 modulators, a light source 340 for generating the light beam, and readout circuitry 330 for providing an electron count output signal to a data processor 500. There may be a large number of sensing elements (e.g., 1000 or more, preferably 5000 or more, and more preferably 10000 or more). These components are described in more detail below.

[0052]

[0058] Detector 300 may include an array of detector elements, including detector elements 311, 312, and 313. The detector elements may be arranged in a planar, two-dimensional array, with the array plane being substantially perpendicular to the direction of incidence of the incoming charged particles. In some embodiments, detector 300 may be arranged at an angle to the direction of incidence. The array may include 10 or more rows, preferably 50 or more rows, and more preferably 100 or more rows, with each row including 10 or more detector elements, preferably 50 or more rows, and more preferably 100 or more detector elements. While one array is shown in FIG. 3, it will be appreciated that detector 300 may include multiple arrays, such as one array for each secondary electron beam.

[0053]

[0059] The detector 300 may include a substrate 310. The substrate 310 may be a semiconductor substrate that may include sensing elements. The sensing elements may be diodes. The sensing elements may be diode-like elements capable of converting incident energy into a measurable signal. The sensing elements may include, for example, PIN diodes, avalanche diodes, electron multiplier tubes (EMTs), etc., or combinations thereof. Areas 325 may be provided between adjacent sensing elements. The areas 325 may be isolation areas that isolate sides or corners of neighboring sensing elements from each other. The areas 325 may include an insulating material that is a different material from other areas of the sensing surface of the detector 300. The areas 325 may be provided as cross-shaped areas, as seen in the plan view of FIG. 3 . The areas 325 may be provided as squares. In some embodiments, the areas 325 may not be provided between adjacent sides of the sensing elements. For example, in some embodiments, no isolation areas may be provided on the sensing surface of the detector.

[0054]

[0060] The sensing element can generate an electrical signal in response to charged particles received at the active area of the sensing element. For example, the sensing element can generate a current signal in response to the energy of the received electrons. A pre-processing circuit can convert the generated current signal into a voltage that can represent the intensity of the electron beam spot or a portion thereof. The pre-processing circuit can include, for example, a pre-amplifier circuit. The pre-amplifier circuit can include, for example, a charge transfer amplifier (CTA), a transimpedance amplifier (TIA), an impedance conversion circuit coupled with a CTA or TIA, or a three-transistor amplifier. In some embodiments, a signal processing circuit can be provided that provides an output signal in any unit in a time series. One or more substrates, such as dies, can be provided, which can form circuit layers for processing the output of the sensing element. The dies can be stacked across the thickness of the detector. Other circuits can also be provided for other functions. For example, a switch actuation circuit can be provided that can control switching elements for connecting the sensing elements to each other.

[0055]

[0061] Although the drawings may show the sensing elements 311, 312, and 313 as discrete units, such division may not exist in practice. For example, the sensing elements of the detector may be formed by semiconductor devices that constitute a PIN diode device. The PIN diode device may be fabricated as a substrate having 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 cross-section. However, in some embodiments, physical separation may be provided between the sensing elements. In addition to the sensor layer, further layers may be provided, such as a circuit layer and a readout layer.

[0056]

[0062] As an example of additional layers, the detector 300 can include one or more circuit layers adjacent to the sensor layer. The one or more circuit layers can include line wires, interconnects, and various electronic circuit components. The one or more circuit layers can include a processing system. The one or more circuit layers can include signal processing circuitry. The one or more circuit layers can be configured to receive detected output current from the sensing elements in the sensor layer. The one or more circuit layers and the sensor layer can be provided on the same die or on separate dies, for example.

[0057]

[0063] Further details of the operation of detection elements, such as diodes, for the detection of electrons can be found in U.S. Application No. 2019 / 0378682A1, which is incorporated herein by reference in its entirety. As an alternative to PIN diodes, embodiments can use low-gain avalanche diodes (LGADs).

[0058]

[0064] Each of the sensing elements 311, 312, and 313 outputs an electrical signal, which may be referred to herein as a detection signal, in response to incident charged particles (particularly electrons). The detection signal may be, for example, a signal in amperes, volts, or any unit depending on the energy of the electrons received at the respective sensing element. In some embodiments, the detection signal may represent the number of charged particles incident on a sensing element of the detector within a period of time (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 identified as an integer.

[0059]

[0065] The radiation receiver of the sensing element (e.g., a PIN diode) may emit a short pulse of current when struck by a charged particle. The sensing element may therefore be set to an "ON" state by the pulse of current, or may include a persistence element such as an accumulator or sample-and-hold circuit that accumulates charge in response to the pulse of current until reset by a reset circuit at the end of the sample period or frame. The sample period or frame rate may be preset or may be automatically determined based on operating conditions.

[0060]

[0066] As shown in FIGS. 3 and 4 , each sensing element 311, 312, 313 is connected to a respective one of optical modulators 351, 352, 353, which may also be referred to as electro-optical devices. Note 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 its respective sensing element, each optical modulator applies a modulation to the light beam passing therethrough. The optical modulation may be a change in a parameter of the beam, such as phase, amplitude, or polarization, or a combination thereof. The change may be binary (i.e., modulation is applied if the electrical signal output by the sensing element indicates that one or more charged particles have been detected, and not otherwise, or vice versa), multi-level, or analog.

[0061]

[0067] The parameter changes are preferably cumulative and linearly additive. For example, if an optical modulator selectively applies a phase delay of δ, then a light beam passing through n active optical modulators is delayed by an amount equal to nδ. The phase delay δ is preferably selected so that the sum of the delays 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 when divided by the total number of optical modulators. The phase delay imparted by an optical modulator is determined by the design of the optical path length of the optical modulator and / or the voltage applied to the optical modulator. Details of suitable optical modulators are described in Abdul Rahim, Artur Hermans, Benjamin Wohlfeil, Despoina Petousi, Bart Kuyken, Dries Van Thourhout, and Roel G. Baets, "Taking silicon photonics modulators a higher performance level: state-of-the-art and a review of new technologies," Advanced Photonics 3(2), 024003 (April 29, 2021), https: / / doi.org / 10.1117 / 1.AP.3.2.024003. Desirably, all of the optical modulators may be constructed using silicon photonics technology on a single substrate 350 as a single integrated circuit device. Alternatively, separate devices may be used.

[0062]

[0068] In configurations where the modulation is linearly additive, the total modulation of the measurement beam represents the sum of the incident radiation on all sensing elements with which the measurement beam is associated. In some embodiments, a weighted sum may be desired, which is achieved by introducing a weighting factor for each sensing element. The weighting factor may, for example, vary between 0 and 1. The weighting factor can be implemented in several different ways. For example, the weighting factor may be applied to the gain of an electronic amplifier associated with each sensing element. The weighting factor may be applied at the modulator, for example, by varying the voltage of a phase modulator. The weighting factor for each sensing element may be fixed at the time of manufacture or calibration, or may be variable during use of the device.

[0063]

[0069] The modulated light beam, which may be referred to as the sensing light beam, may be generated by a light source 340 located on the same substrate 350 as the optical modulators 351, 352, and 353, or may be generated remotely using fiber optics used to deliver light to the optical modulators. Having the light source on the substrate 350 allows for a more compact device. Having a remote light source reduces heat dissipation in the detector. The wavelength of the light output by the light source 340 is not particularly limited and is preferably selected to be compatible with the optical modulator used. Wavelengths in the infrared, visible, or ultraviolet ranges are likely to be suitable. Preferably, the light source 340 outputs substantially monochromatic light, for example, when a phase modulator is used. Light sources emitting multiple wavelengths may be used in some embodiments. When amplitude modulation is used, a broadband light source may be suitable. The light source 340 may be, for example, a laser diode emitting in the infrared range (e.g., 1550 nm).

[0064]

[0070] Light source 340 is coupled (either directly or via optical fiber) to input waveguide 320. Beam splitter 341 splits the input light beam to multiple sensing waveguides (which are examples of sensing optical systems), thereby forming multiple sensing beams. Each of sensing waveguides 321 directs a respective sensing beam through a set of optical modulators 351, 352, 353. For example, as shown in FIG. 3, each set of optical modulators forms one row of an array of optical modulators, and the sensing light beam follows a straight beam path through the optical modulators, although other arrangements are possible, as described below.

[0065]

[0071] After the sensing beams pass through the optical modulators, a beam combiner 342 combines the sensing beams into a measurement beam, which is passed to the readout unit 330. After combining the sensing beams, the modulation of the measurement beam can be the average of the modulations of the sensing beams. For example, in a configuration with 100 sensing elements and 100 rows of optical modulators, if only one optical modulator is active and applies a phase delay of δ, the phase delay of the measurement beam will be δ / 100. If 50 optical modulators are active, the phase delay of the measurement beam will be δ / 2. (As an example of a reference optical system, a reference waveguide 322 may be provided to pass the reference beam directly to the readout unit 330 without passing it through any of the optical modulators.) The reference waveguide may have substantially the same optical path length as the sensing waveguide and may be configured to provide the same effect (e.g., attenuation) as that provided by the beam path of the sensing light beam when no optical modulators are active. As an alternative to combining all of the beams measured by a single readout unit, multiple readout units can be provided, each measuring one sensing beam or a combination of a subset of the sensing beams.

[0066]

[0072] The structure of the readout unit 330 depends on the parameter being measured. If the modulated parameter is phase, the readout unit may include an interferometer. If the modulated parameter is amplitude, the readout unit may include a power sensor. If the modulated parameter is polarization, the readout unit may include a polarization analyzer. The readout unit 330 can measure the modulated parameter by comparing a measurement beam derived from a separate sensing beam that has passed through an optical modulator with a reference beam that is also derived from the light source 340 but is directed to the readout unit by the reference waveguide 322 without passing through any optical modulators. If a reference beam is used, the readout unit is preferably configured with a balanced detection setup (with optical detectors 331 and 332 for the measurement and reference beams, respectively, and a comparator 333, as shown in FIG. 3) to suppress common-mode fluctuations (e.g., laser intensity noise). If amplitude modulation is used, the reference beam may be omitted. Alternatively, the reference beam can be used with a static phase delay to cause destructive interference with the measurement beam. If a charged particle is detected, the measurement beam is attenuated and the destructive interference is not complete, so that light is detected in the readout unit, which can be easier than making an absolute measurement of the beam intensity.

[0067]

[0073] The readout unit 330 is configured to measure the modulation of the measurement beam and output a signal to the data processor 550 representative of the charged particles (preferably the number of charged particles) incident during a measurement period or frame. The readout unit 300 may include other signal processing elements (e.g., a digital-to-analog converter) that process the measurement of the modulation of the measurement beam to generate an output signal representative of the charged particles incident on the sensing element. The signal processor 500 may also include, among other things, a digital switch, a digital control unit, or a controller configured to perform image processing. Additional circuitry may be provided within the architecture, such as a signal processing path configured to provide gain and offset control.

[0068]

[0074] As shown in FIG. 4 , the sensing elements 311, 312, and 313 can be formed on a first substrate 310, and the optical modulators 351, 352, and 353 can be formed on a second substrate 350. The first substrate 310 and the second substrate 350 are arranged back-to-back and bonded together. Connections between the sensing elements 311, 312, and 313 and the optical modulators 351, 352, and 353 can be made through through-silicon vias 361 and 362. Arranging the first and second substrates back-to-back in this manner minimizes the signal path length between the sensing elements and their corresponding optical modulators, thereby maximizing the operating speed of the detector. This configuration is feasible because the optical modulators can provide a detectable phase shift even when they are smaller than the sensing elements. The sensing elements 311, 312, and 313 and the optical modulators 351, 352, and 353, along with any other associated elements such as amplifiers, can be collectively referred to as the detection component.

[0069]

[0075] The SEM system can scan the primary electron beam across the sample in a pattern, such as a raster pattern. The pixels generated in the image can be related to the location of the sample surface being scanned. The pixels can be correlated to a specific scan time. Data from the detector can be correlated to the scan time. A scaler can be used to correlate the data received from the detector to a specific scan time. The scaler can be configured to correlate the detector data with the scan time (and therefore with the pixel) based on a delay time. For example, the scaler can record the time when data related to an electron arrival event is received and apply a correction based on the delay from a trigger. The trigger can correspond to an electron in the primary electron beam striking the sample. The delay can take into account the travel time of the electron (e.g., a secondary electron) from the sample to the detector or the time to generate and output a signal pulse at the sensing element. Additionally, the time Δt required for the optical beam to propagate through the sensing waveguide and optical modulator can be significant in some cases. 5, the sampling window Win of the readout unit 330 is desirably offset from the pixel clock clk that defines the pixel boundaries by the time Δt it takes for the light beam to propagate through the sensing waveguide and optical modulator. In general, Δt is the period t of the pixel clock clk. p is much smaller than

[0070]

[0076] As mentioned above, other configurations of the sensing waveguide are possible. Figure 6 shows one such configuration, in which a single sensing waveguide 323 guides the sensing beam along a serpentine path that passes through all of the optical modulators 351, 352, and 353. It will be appreciated that the longer the optical path traversed by the sensing beam, the longer it takes, reducing the maximum sampling rate. The choice of optical path is therefore a trade-off between device simplicity (by reducing the number of beam splitters and combiners) and the desired sampling rate. For example, rather than each sensing beam passing through one row of optical modulators (as in Figure 3), each sensing beam can pass through a portion of a row (to increase the sampling rate) or through more than one row (if a lower sampling rate is sufficient). When there are multiple optical paths for the sensing beams that are then combined and interfere with the reference beam, it is desirable for the optical path length to be equal to the coherence length of the light source. In some embodiments, high-speed sampling can be achieved. The readout unit may therefore be configured to operate at speeds of 100 MHz or greater, preferably 200 MHz or greater, and more preferably 400 MHz or greater.

[0071]

[0077] In some embodiments, the beam spot on the detector surface may be larger than the beam spot on the sample surface. Therefore, the overall size of the detector's detection surface may be configured to be large enough to accommodate the wide beam spot. The beam spot on the detector surface may be on the scale of several millimeters in diameter. However, increasing the size of the detector may lead to 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 resulting from components (e.g., amplifiers) coupled to the detector, may be capacitance-related.

[0072]

[0078] In some embodiments, the area of the sensing element can be reduced by configuring the sensing element to be smaller than the geometric distribution of secondary electrons incident on the entire detection surface. The signal and capacitance of the detector sensing element can be proportional to the area of the sensing element when the sensing element is completely covered by the beam spot. In some cases, the sensing element may be only partially covered by the beam spot. The reduction in SNR due to capacitance can be mitigated by reducing the area of the sensing element when the sensing element is not completely covered by the beam spot.

[0073]

[0079] In some embodiments, the area ratio, which is the ratio of the area of an individual sensing element to the area of the entire detector surface, can be varied. The area ratio can have a correspondence relationship with the SNR. For example, in some embodiments, reducing the size of the sensing element to 1 / 1000 of the detector area can correspond to a 1000-fold increase in SNR.

[0074]

[0080] In some embodiments, the detector may include an array of sensing elements. The array may include a plurality of sensing elements, each having dimensions, for example, Dx and Dy or less. For example, each sensing element may have a radiation receiving area having a size of 500 μm×500 μm or less, preferably 200 μm×200 μm or less, and more preferably 150 μm×150 μm or less. In some embodiments, the radiation detector may include 1,000 or more sensing elements, preferably 5,000 or more sensing elements, and more preferably 10,000 or more sensing elements. The sensing elements may be arranged in a planar, two-dimensional array, with the array plane being substantially perpendicular to the direction of incidence of the incoming charged particles. In some embodiments, the detector may be arranged at an angle to the direction of incidence.

[0075]

[0081] In some embodiments, the sensing element may be capable of distinguishing between incident electrons having different energies, for example, to distinguish between backscattered and secondary electrons. Such sensors may output multiple independent signals, each indicating the number or intensity of received electrons of a particular type or range of energies. In such cases, a variety of different techniques may be used to separately read out the independent signals. For example, multiple independent modulators may be provided per sensing element, one for each independent signal. Multiple independent modulators may be applied to modulate different parameters of a single beam, to modulate separate beams traveling on separate optical paths, to modulate beams of different wavelengths traveling on the same optical path, or some combination of these techniques.

[0076]

[0082] Based on the same set of acquired raw data sets, a wide variety of results can be obtained according to specific application requirements. The results can be used for post-processing rather than pre-processing. In some embodiments, pre-processing can include grouping of sensing elements. The data can be further adapted to optimize specific objectives. For example, there may be a trade-off 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 loss of information. This allows more flexibility at the application layer and reduces the risk of having to re-run certain operations just to acquire data with different detection parameter settings.

[0077]

[0083] In some embodiments, the detector can communicate with a controller that controls the charged particle beam system. The controller can instruct components of the charged particle beam system to perform various functions, such as controlling the charged particle source to generate the charged particle beam and controlling the deflector to scan the charged particle beam. The controller can also perform various other functions, such as adjusting the sampling rate of the detector, resetting the sensing elements, or performing image processing. The controller can include storage, which can be a storage medium such as a hard disk, random access memory (RAM), or other type of computer-readable memory. The storage can be used to store raw scanned image data as original images and post-processed images. A processor in the controller 109 can provide a non-transitory computer-readable medium that stores instructions for performing 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, flexible disks, hard disks, solid state drives, magnetic tape or any other magnetic data storage media, CD-ROMs, any other optical data storage media, any physical media with a pattern of holes, ROMs, PROMs, and EPROMs, FLASH-EPROMs or any other flash memory, NVRAMs, caches, registers, any other memory chips or cartridges, and networked versions of these.

[0078]

[0084] The block diagrams in the figures may illustrate the architecture, functionality, and operation of possible implementations of systems, methods, and computer hardware / software products according to various exemplary embodiments of the present disclosure. In this regard, each block in the schematic diagrams may represent a specific mathematical or logical operation that can be implemented using hardware, such as electronic circuits. A block may also represent a module, segment, or portion of code, including one or more executable instructions for implementing the specified logical function(s). It should be understood that in some alternative embodiments, the functions shown in the blocks may occur out of the order shown in the figures. For example, two blocks shown in succession may be executed or implemented substantially simultaneously, or the two blocks may often be executed in the reverse order, depending on the functionality involved. Some blocks may also be omitted. It should also be understood that each block of the block diagrams, and combinations of blocks, may be implemented by a special-purpose hardware-based system that performs the specified function or operation, or by a combination of special-purpose hardware and computer instructions.

[0079]

[0085] Exemplary embodiments of the present invention are presented in the following numbered clauses. 1. A set of sensing elements configured to generate an electrical signal in response to radiation; a set of optical modulators connected to respective ones of the sensing elements, the set of optical modulators configured to modulate the sensing light beam in response to an electrical signal; a detection optical system configured to direct a detection light beam through each of the optical modulators. 2. A radiation detector as described in clause 1, wherein the optical modulator is arranged along a straight line and the detection optical system directs the detection light beam through the optical modulator along a straight beam path. 3. A radiation detector as described in clause 1, wherein the optical modulators are arranged in a two-dimensional array and the detection optical system directs the detection light beam through the optical modulators along a serpentine beam path. 4. A radiation detector according to any one 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. 5. A radiation detector as described in clause 4, further comprising a beam splitter configured to split the input light beam into a plurality of detection light beams and direct the detection light beams to each of the detection optical system and the further detection optical system. 6. A radiation detector according to clause 4 or 5, further comprising a beam combiner configured to combine multiple detection light beams that have passed through the detection optical system or the further detection optical system into a measurement beam. 7. A radiation detector according to any one of clauses 1 to 6, wherein the optical modulator is configured to modulate a property of the light beam selected from the group consisting of phase, amplitude, and polarization. 8. A radiation detector as described in any one of clauses 1 to 7, wherein the optical modulator is configured to cumulatively modulate the characteristics of the light beam such that the cumulative modulation of the characteristics of the light beam is indicative of the electrical signal output by all of the sensing elements. 9. A radiation detector according to clause 8, wherein the modulation of the light beam represents a sum of electrical signals, preferably a weighted sum of electrical signals. 10. A radiation detector according to any one of clauses 1 to 9, further comprising a readout unit configured to measure the modulation of the light beam. 11. A radiation detector according to clause 10, further comprising a reference optical system configured to provide a reference light beam to the readout unit. 12. A radiation detector according to clause 10 or 11, wherein the readout unit is configured to operate at a speed of 100 MHz or higher, preferably 200 MHz or higher, more preferably 400 MHz or higher. 13. A radiation detector according to any one of clauses 1 to 12, wherein the detection optical system and the further detection optical system comprise waveguides. 14. A radiation detector as described in any one of clauses 1 to 13, 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. 15. The radiation detector of clause 14, further comprising a light source on the second substrate. 16. A radiation detector according to any one of clauses 1 to 15, wherein the set of sensing elements comprises CMOS devices. 17. A radiation detector according to any one of clauses 1 to 16, wherein the set of sensing elements includes a PIN diode. 18. A radiation detector according to any one of clauses 1 to 17, wherein the set of optical modulators is formed on a silicon substrate. 19. A radiation detector according to any one of clauses 1 to 18, wherein each of the sensing elements has a radiation receiving area having a size of 500 μm x 500 μm or less, preferably 200 μm x 200 μm or less, more preferably 150 μm x 150 μm or less. 20. A radiation detector according to any one of clauses 1 to 19, comprising 1000 or more sensing elements, preferably 5000 or more sensing elements, more preferably 10000 or more sensing elements. 21. A radiation detector according to any one of clauses 1 to 20, wherein each sensing element is configured to generate an electrical signal in response to incident electrons as radiation, preferably a single incident electron. 22. A radiation detector according to any one of clauses 1 to 21, wherein each optical modulator is connected to a respective one of the sensing elements. 23. A radiation detector according to any one of clauses 1 to 22, wherein each optical modulator is connected to a plurality of the sensing elements. 24. A charged particle detection system comprising a radiation detector according to any one of clauses 1 to 23. 25. A charged particle detection system according to clause 24, further comprising a secondary optical system configured to direct electrons emitted from the sample to the radiation detector. 26. A set of sensing elements configured to generate an electrical signal in response to radiation; a set of optical modulators connected to respective ones of the sensing elements, the set of optical modulators configured to modulate the sensing light beam in response to an electrical signal; a detection optical system configured to direct a detection light beam through each of the optical modulators. 27. A charged particle detection system as described in clause 26, wherein the optical modulators are arranged along a straight line and the detection optical system directs the detection light beam through the optical modulators along a straight beam path. 28. A charged particle detection system as described in clause 26, wherein the optical modulators are arranged in a two-dimensional array and the detection optical system directs the detection light beam through the optical modulators along a serpentine beam path. 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 to generate an output signal representative of the total amount of radiation received by the set of sensing elements in a sampling period, preferably a weighted sum of the total amount of radiation received by the set of sensing elements in a sampling period. 30. A charged particle detection system according to any one of clauses 26 to 28, further comprising at least one further set of sensing elements, at least one further set of optical modulators, and at least one further detection optical system. 31. A charged particle detection system according to clause 30, further comprising a readout unit configured to measure the modulation of the light beam and to generate an output signal representative of the total amount of radiation received by all sets of sensing elements in a sampling period, preferably a weighted sum of the total amount of radiation received by all sets of sensing elements in a sampling period. 32. A charged particle detection system according to clause 30, further comprising a readout unit configured to measure the modulation of the light beam and to generate a plurality of output signals, each representing a total amount of radiation received by one of the set of sensing elements in a sampling period, preferably a weighted sum of the total amount of radiation received by one of the set of sensing elements in a sampling period. 33. A charged particle detection system according to any one of clauses 29, 31 or 32, further comprising a reference optical system configured to provide a reference light beam to the readout unit. 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 speed of 100 MHz or more, preferably 200 MHz or more, more preferably 400 MHz or more. 35. A charged particle detection system according to any one of clauses 26 to 34, wherein the optical modulator is configured to modulate a property of the light beam selected from the group consisting of phase, amplitude, and polarization. 36. A charged particle detection system according to any one of clauses 26 to 35, wherein the detection optical system and the further detection optical system comprise waveguides. 37. A charged particle detection system described in any one 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, and the second substrate is bonded to the first substrate. 38. A charged particle detection system according to any one of clauses 26 to 37, wherein each of the sensing elements has a radiation receiving area having a size of 500 μm x 500 μm or less, preferably 200 μm x 200 μm or less, more preferably 150 μm x 150 μm or less. 39. A charged particle detection system according to any one of clauses 26 to 38, comprising 1000 or more sensing elements, preferably 5000 or more sensing elements, more preferably 10000 or more sensing elements. 40. A charged particle detection system according to any one of clauses 26 to 39, wherein each optical modulator is connected to a respective one of the sensing elements. 41. A charged particle detection system according to any one of clauses 26 to 39, wherein each optical modulator is connected to a plurality of sensing elements. 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 the sample to the set of sensing elements. 43. A method for detecting radiation, comprising: directing radiation to a plurality of sensing elements configured to generate electrical signals in response to the radiation; modulating a sensing light beam in response to an electrical signal; and detecting the radiation by measuring modulation of the sensing light beam. 44. The method of clause 43, wherein the modulation comprises directing the sensing light beam along a linear beam path through a set of optical modulators connected to the set of sensing elements. 45. The method of clause 43, wherein the modulation includes directing the sensing light beam along a serpentine beam path through optical modulators arranged in a two-dimensional array. 46. The method of any one of clauses 43 to 45, wherein the modulation comprises directing a plurality of sensing light beams along beam paths through respective sets of optical modulators. 47. The method of clause 46, further comprising splitting the input light beam into multiple sensing light beams. 48. The method of clause 46 or 47, further comprising combining the multiple sensing light beams into a measurement beam after modulation. 49. The method of any one of clauses 43 to 48, wherein the modulation comprises modulating a property of the light beam selected from the group consisting of phase, amplitude, and polarization. 50. A method according to any one of clauses 43 to 49, wherein the modulation comprises cumulatively modulating a characteristic of the light beam such that the modulation of the light beam is indicative of the electrical signal output by all of the sensing elements. 51. A method according to clause 50, wherein the modulation of the light beam represents a sum of electrical signals, preferably a weighted sum of the total amount of radiation received by the sensing element in a sampling period. 52. The method of any one of clauses 43 to 50, further comprising measuring the modulation of the light beam. 53. The method of clause 52, wherein the measuring includes measuring modulation relative to a reference light beam. 54. A method according to clause 52 or 53, wherein the measurements include measuring modulation at a rate of 100 MHz or more, preferably 200 MHz or more, more preferably 400 MHz or more. 55. A method according to any one of clauses 43 to 54, wherein each sensing element is configured to generate an electrical signal in response to incident electrons as radiation, preferably a single incident electron. 56. An array of sensing elements configured to generate an electrical signal in response to charged particles, the array of sensing elements being arranged in columns; an array of optical modulators each connected to a respective one of the sensing elements, the array of optical modulators configured to modulate the sensing light beam in response to an electrical signal; a plurality of waveguides configured to direct each of a plurality of sensing light beams through the array of light modulators; a beam combiner configured to combine the plurality of sensing light beams that have passed through the respective rows of optical modulators into a combined beam; a readout unit configured to measure modulation of the combined beam to detect charged particles incident on the sensing element. 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: directing radiation to a plurality of sensing elements, the plurality of sensing elements generating electrical signals in response to the radiation and being part of a detection component configured to modulate a detection light beam in response to the electrical signals and to measure the modulation of the detection light beam to detect the radiation; and causing the detection component to output a signal indicative of the measured modulation. 58. The non-transitory computer-readable medium of clause 57, wherein the set of instructions executable by one or more processors of the controller further causes the controller to generate an image 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, the cumulative modulation of the characteristic of the light beam being indicative of an electrical signal output by all of the sensing elements, and the signal indicative of the measured modulation being indicative of the cumulative modulation of the characteristic of the light beam.

[0080]

[0086] It will be understood that the present invention is not strictly limited to the configurations described above and illustrated in the accompanying drawings, and that various modifications and variations can be made without departing from the scope thereof. For example, while PIN diodes have been discussed with reference to certain exemplary embodiments, other types of diodes, such as NIP diodes, may be used as well. Furthermore, other types of devices capable of generating a measurable signal in response to receiving incident energy may also be used in the detector.

[0081]

[0087] It will be understood that elements shown in different figures may be combined.

[0082]

[0088] Furthermore, although scanning electron microscopes are discussed with reference to some embodiments, other types of systems are also applicable, for example, the detectors can be used in transmission electron microscopes (TEM), scanning transmission electron microscopes (STEM), or structured illumination microscopes (SIM).

Claims

1. 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, the set of optical modulators configured to modulate sensing light beams in response to the electrical signal; a detection optical system configured to direct the detection light beam through each of the optical modulators.

2. 10. The radiation detector of claim 1, wherein the optical modulator is disposed along a straight line, and the detection optical system directs the detection light beam through the optical modulator along a straight beam path.

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

4. 10. The radiation detector of claim 1, 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.

5. 5. The radiation detector of claim 4, further comprising a beam splitter configured to split the input light beam into a plurality of detection light beams and direct the detection light beams to each of the detection optical system and the further detection optical system.

6. 5. The radiation detector of claim 4, further comprising a beam combiner configured to combine the plurality of detection light beams that have passed through the detection optical system or the further detection optical system into a measurement beam.

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

8. 2. The radiation detector of claim 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. 9. A radiation detector according to claim 8, wherein the modulation of the light beam is indicative of a sum of the electrical signals, preferably 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 light beam to the readout unit.

12. The radiation detector of claim 1 , wherein the detection optical system and the further detection optical system comprise waveguides.

13. 10. 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. 2. The radiation detector of claim 1, wherein each optical modulator is connected to a respective one of the sensing elements.

15. 1. 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: directing radiation to a plurality of sensing elements, the plurality of sensing elements generating electrical signals in response to the radiation and being part of a detection component configured to modulate a detection light beam in response to the electrical signals and to measure the modulation of the detection light beam to detect the radiation; causing the detection component to output a signal indicative of the measured modulation.

Images