Systems and methods for signal electronic detection

Abstract

Some of the disclosed embodiments include an electronic detector, the electronic detector including: a first semiconductor layer having a first portion and a second portion; a second semiconductor layer; a third semiconductor layer; a PIN region formed by the first semiconductor layer, the second semiconductor layer, and the third semiconductor layer; a power supply configured to apply a reverse bias between the first semiconductor layer and the third semiconductor layer; and a depletion region formed within the PIN region by the reverse bias, and the depletion region is configured to generate a detector signal based on a first subset of a plurality of signal electrons captured within the depletion region, wherein the second portion of the first semiconductor layer is not depleted and is configured to provide an energy barrier to block a second subset of the plurality of signal electrons, and is configured to allow the first subset of the plurality of signal electrons to pass through to reach the depletion region.

Description

[0001] Cross - Reference to Related Applications

[0002] This application claims priority to U.S. Application No. 63 / 008,639, filed Apr. 10, 2020, the entire content of which is incorporated herein by reference. Technical Field

[0003] The embodiments provided herein disclose charged particle beam apparatuses and, more particularly, improved systems and methods for signal electron detection. Background Art

[0004] When manufacturing semiconductor integrated circuit (IC) chips, during the manufacturing process, as a result of, for example, optical effects and incidental particles, unwanted pattern defects inevitably occur on a substrate (i.e., a wafer) or a mask, thereby reducing the yield. Therefore, monitoring the degree of unwanted pattern defects is an important process in IC chip manufacturing. More generally, surface inspection or measurement of a substrate or other object / material is an important process during and after its manufacturing.

[0005] Pattern inspection tools with charged particle beams have been used to inspect objects, such as for detecting pattern defects. These tools typically use electron microscopy techniques, such as scanning electron microscopy (SEM). In SEM, a primary electron beam of electrons with relatively high energy is targeted at a final deceleration step so as to land on a sample with a relatively low landing energy. The electron beam is focused on the sample as a probe point. The interaction between the material structure at the probe point and the landing electrons from the electron beam causes electrons to be emitted from the surface, such as secondary electrons, backscattered electrons, or Auger electrons. The generated secondary electrons can be emitted from the material structure of the sample. By scanning the primary electron beam as a probe point over the sample surface, secondary electrons can be emitted across the sample surface. By collecting these emitted secondary electrons from the sample surface, the pattern inspection tool can obtain an image representing the characteristics of the material structure of the sample surface. Summary of the Invention

[0006] The embodiments provided herein disclose charged particle beam apparatuses and, more particularly, improved systems and methods for signal electron detection.

[0007] In some embodiments, an electron detector for detecting a plurality of signal electrons generated from a sample is provided. The detector includes: a first semiconductor layer having a first portion and a second portion; a second semiconductor layer adjacent to the first semiconductor layer; and a third semiconductor layer adjacent to the second semiconductor layer. The detector further includes: a PIN region formed by the first semiconductor layer, the second semiconductor layer, and the third semiconductor layer. The detector may further include: a power supply configured to apply a reverse bias between the first semiconductor layer and the third semiconductor layer. The detector further includes: a depletion region formed within the PIN region by the reverse bias, the depletion region including a portion of the second semiconductor layer, and the depletion region being configured to generate a detector signal based on a first subset of the plurality of signal electrons captured within the depletion region, wherein the second portion of the first semiconductor layer is undepleted and is configured to provide an energy barrier to block a second subset of the plurality of signal electrons and to allow the first subset of the plurality of signal electrons to pass through to reach the depletion region.

[0008] In some embodiments, an electron detector for detecting a plurality of signal electrons generated from a sample is provided. The detector includes: a first semiconductor layer having a first portion and a second portion; a second semiconductor layer adjacent to the first semiconductor layer. The detector further includes: a plurality of segments of a third semiconductor layer, each of the plurality of segments being adjacent to the second semiconductor layer. The detector further includes: a PIN region formed by the first semiconductor layer, the second semiconductor layer, and the third semiconductor layer, and a power supply configured to apply a reverse bias between the first semiconductor layer and the third semiconductor layer. The detector further includes: a depletion region formed within the PIN region by the reverse bias, the depletion region including a portion of the second semiconductor layer, and the depletion region being configured to generate a plurality of detector signals based on a first subset of the plurality of signal electrons captured within the depletion region, wherein the second portion of the first semiconductor layer is undepleted and the second portion of the first semiconductor layer is configured to provide an energy barrier to block a second subset of the plurality of signal electrons and the second portion of the first semiconductor layer is configured to allow the first subset of the plurality of signal electrons to pass through to reach the depletion region.

[0009] A method for manufacturing an electron detector having an energy barrier that filters electrons based on the energy of the electrons is provided. The method includes: providing a semiconductor substrate having a first portion, a second portion adjacent to the first portion, and a third portion adjacent to the second portion. The method further includes: forming a first semiconductor layer by doping the first portion of the substrate with a first type of dopant, forming a third semiconductor layer by doping the third portion of the substrate with a second type of dopant, and forming a second semiconductor layer within the second portion of the substrate. The doping concentration of the first type of dopant within the first semiconductor layer is determined to configure the energy barrier of the electron detector, and the thickness of the first semiconductor layer is determined to further configure the energy barrier of the electron detector.

[0010] In some embodiments, a charged particle beam apparatus for inspecting a sample is provided. The apparatus includes: a charged particle beam source configured to emit a charged particle beam along a main optical axis; an objective lens configured to focus the charged particle beam onto the sample; and an electron detector according to the above-described embodiments, the electron detector being configured to detect a plurality of signal electrons generated from the incidence of the charged particle beam onto the sample.

[0011] In some embodiments, a charged particle beam apparatus for inspecting a sample is provided. The apparatus includes a charged particle beam source configured to emit a charged particle beam along a main optical axis; an objective lens configured to focus the charged particle beam onto the sample; an electron detector configured to detect a plurality of signal electrons generated from the incidence of the charged particle beam onto the sample; and a passive energy filter between the electron detector and the sample.

[0012] In some embodiments, an electron detector for detecting a plurality of signal electrons generated from a sample is provided. The detector includes: a first semiconductor layer having a first portion and a second portion; a second semiconductor layer adjacent to the first semiconductor layer; and a third semiconductor layer adjacent to the second semiconductor layer. The detector further includes: a PIN region formed by the first semiconductor layer, the second semiconductor layer, and the third semiconductor layer. The detector further includes: a depletion region formed by a reverse bias applied to the PIN region, the depletion region including a portion of the second semiconductor layer, and the depletion region being configured to generate a detector signal based on a first subset of the plurality of signal electrons captured within the depletion region, wherein the second portion of the first semiconductor layer is not depleted and is configured to provide an energy barrier to block a second subset of the plurality of signal electrons, and to allow the first subset of the plurality of signal electrons to pass through to reach the depletion region.

[0013] In some embodiments, an electron detector for detecting a plurality of signal electrons generated from a sample is provided. The detector includes: a first semiconductor layer having a first portion and a second portion; a second semiconductor layer adjacent to the first semiconductor layer. The detector further includes: a plurality of segments of a third semiconductor layer, each of the plurality of segments being adjacent to the second semiconductor layer. The detector further includes a PIN region formed by the first semiconductor layer, the second semiconductor layer, and the third semiconductor layer. The detector further includes a depletion region formed by a reverse bias applied to the PIN region, the depletion region including a portion of the second semiconductor layer, and the depletion region being configured to generate a plurality of detector signals based on a first subset of the plurality of signal electrons captured within the depletion region, wherein the second portion of the first semiconductor layer is not depleted and is configured to provide an energy barrier to block a second subset of the plurality of signal electrons, and to allow the first subset of the plurality of signal electrons to pass through to reach the depletion region.

[0014] Other advantages of embodiments of the present disclosure will become apparent from the following description in conjunction with the accompanying drawings, in which certain embodiments of the present disclosure are illustrated by way of illustration and example. Description of the Drawings

[0015] Figure 1 is a schematic diagram illustrating a charged particle beam inspection system according to an embodiment of the present disclosure.

[0016] Figure 2 is a schematic diagram illustrating an exemplary configuration of an electron beam tool that can be Figure 1 a part of the charged particle beam inspection system according to an embodiment of the present disclosure.

[0017] Figure 3A is a schematic diagram illustrating a charged particle beam device including a plurality of signal electron detectors according to an embodiment of the present disclosure.

[0018] Figure 3B and Figure 3C is a schematic diagram of a charged particle beam device including a signal electron detector having an active energy filter.

[0019] Figure 4A is a schematic diagram of an exemplary signal electron detector according to an embodiment of the present disclosure.

[0020] Figure 4B and Figure 4C is a diagram illustrating an exemplary operation of a signal electron detector according to an embodiment of the present disclosure. Figure 4A thereof.

[0021] Figure 5A and Figure 5B is a schematic diagram of an exemplary signal electron detector having an external passive energy filter according to an embodiment of the present disclosure.

[0022] Figures 6A - 6F is an exemplary charged particle beam device according to an embodiment of the present disclosure including a signal electron detector and an external passive energy filter according to Figure 5A and Figure 5B described above.

[0023] Figure 7 Illustrates an exemplary method of forming a signal electron detector according to an embodiment of the present disclosure. Figure 4A thereof. Detailed Description

[0024] Reference will now be made in detail to the exemplary embodiments, examples of which are illustrated in the accompanying drawings. The following description refers to the accompanying drawings, where like reference numerals in different drawings indicate the same or similar elements unless otherwise noted. The implementations set forth in the following description of the exemplary embodiments do not represent all implementations. Rather, they are merely examples of devices and methods consistent with various aspects of the disclosed embodiments as recited in the appended claims. For example, although some embodiments are described in the context of using an electron beam, the present disclosure is not limited thereto. Other types of charged particle beams can be similarly applied. In addition, other imaging systems can be used, such as optical imaging, light detection, x-ray detection, etc.

[0025] An electronic device is composed of circuits formed on a silicon wafer called a substrate. Many circuits can be formed together on the same silicon wafer and are called integrated circuits or ICs. The size of these circuits has been significantly reduced so that many of them can be fitted on the substrate. For example, the IC chip in a smart phone can be as small as a thumb nail and can also include more than 2 billion transistors, each transistor being less than 1 / 1000 the size of a human hair.

[0026] Fabricating these extremely small ICs is a complex, time-consuming, and expensive process, typically involving hundreds of individual steps. Even an error in one step has the potential to cause defects in the finished IC, rendering it useless. Therefore, one goal of the manufacturing process is to avoid such defects in order to maximize the number of functional ICs manufactured in the process, i.e., to improve the overall yield of the process.

[0027] One component for improving yield is to monitor the chip manufacturing process to ensure that it produces a sufficient number of functional integrated circuits. One way to monitor the process is to inspect the chip circuit structure at various stages of its formation. The inspection can be performed using a scanning electron microscope (SEM). The SEM can be used to image these extremely small structures, effectively taking "photos" of these structures. The images can be used to determine whether the structure has been formed correctly and whether it has been formed in the correct location. If the structure is defective, the process can be adjusted so that the defect is less likely to occur again.

[0028] Using a SEM to examine the accuracy and reliability of high-density IC chips is particularly related to the imaging resolution of the system. One of several ways to obtain and maintain high imaging resolution is to maximize the collection efficiency of signal electrons such as secondary electrons (SE) and backscattered electrons (BSE). When a primary electron impacts the surface of a sample, it interacts with the volume of the sample particularly based on the landing energy, sample material, and spot size, and generates multiple signal electrons. SE, which is generated by the emission of valence electrons (e.g., outer shell electrons) of the constituent atoms of the sample, has an emission energy of ≤50 eV and originates from the surface or near-surface region of the sample. BSE, which is mainly generated by the elastic collision of the electrons in the electron beam with the atomic nuclei of the constituents, has a higher emission energy, for example, in the range of 50 eV to the landing energy of the primary electron on the sample (up to 1,000 to 10,000 eV or higher), and generally originates from a deeper region within the interaction volume of the sample, and thus can provide information related to the material composition and distribution of the sample. In some embodiments, it may be desirable to have a mechanism that only collects a specific type of signal electron such as BSE to enhance the quality of the obtained image. For example, it may be desirable to maximize the detection of backscattered electrons to obtain a high-resolution image of subsurface defects or structures from a deeper subsurface region of the sample.

[0029] In a conventional SEM, one method capable of selectively collecting a certain type of signal electron can include placing an active energy filter in the path of the signal electrons between the sample and the electron detector such that unwanted types of signal electrons can be filtered out before reaching the surface of the electron detector. For example, the active energy filter can include an electrode (negatively biased with respect to the sample when the charged particle beam is an electron beam), and the electrode generates an electric field to block SE while allowing BSE to pass through. However, in some embodiments, the electric field generated by the active energy filter may interfere with the primary electrons and increase the aberration of the objective lens, resulting in an increase in the size of the detection point on the sample and thus negatively affecting the imaging resolution. Therefore, it may be desirable to detect BSE only without using an active filter. Some embodiments of the present disclosure relate to charged particle beam devices and methods for forming images of a sample. The device can include an electron detector having a passive filter that provides the ability to selectively collect BSE without the need to generate an electric field.

[0030] For clarity, the relative dimensions of components in the drawings may be enlarged. In the following description of the drawings, like or similar reference numerals denote like or similar components or entities, and only the differences with respect to each embodiment are described. As used herein, unless otherwise specifically stated and unless infeasible, the term "or" encompasses all possible combinations. For example, if it is stated that a component may include A or B, then unless otherwise specifically stated or infeasible, the component may include A or B, or A and B. As a second example, if it is stated that a component may include A, B, or C, then unless specifically stated or infeasible, 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.

[0031] Now refer to Figure 1 , which illustrates an exemplary charged particle beam inspection system 100 in accordance with an embodiment of the present disclosure, such as an electron beam inspection (EBI) system. As Figure 1 shown, the charged particle beam inspection system 100 includes a main chamber 10, a load lock chamber 20, an electron beam tool 40, and an equipment front end module (EFEM) 30. The electron beam tool 40 is located within the main chamber 10. Although the description and drawings are directed to electron beams, it should be understood that these embodiments are not used to limit the present disclosure to a particular charged particle.

[0032] The EFEM 30 includes a first load port 30a and a second load port 30b. The EFEM 30 may include additional load ports. The first load port 30a and the second load port 30b receive front-opening unified pods (FOUPs) of wafers, which contain wafers (e.g., semiconductor wafers or wafers made of other materials) or samples to be inspected (wafers and samples are collectively referred to as "wafers" hereinafter). One or more robotic arms (not shown) in the EFEM 30 transport the wafers to the load lock chamber 20.

[0033] The load lock chamber 20 is connected to a load / lock vacuum pump system (not shown), which removes gas molecules from the load lock chamber 20 to achieve a first pressure below atmospheric pressure. After achieving the first pressure, one or more robotic arms (not shown) transport the wafers from the load lock chamber 20 to the main chamber 10. The main chamber 10 is connected to a main chamber vacuum pump system (not shown), which removes gas molecules from the main chamber 10 to achieve a second pressure below the first pressure. After achieving the second pressure, the wafers are inspected by the electron beam tool 40. In some embodiments, the electron beam tool 40 may include a single beam inspection tool.

[0034] The controller 50 may be electrically connected to the electron beam tool 40 and may be electrically connected to other components. The controller 50 may be a computer configured to perform various controls of the charged particle beam inspection system 100. The controller 50 may also include processing circuits configured to perform various signal and image processing functions. Although the controller 50 is Figure 1 Controller 50 is shown external to the structure including main chamber 10, load lock chamber 20 and EFEM 30, but it is understood that controller 50 may be part of the structure.

[0035] Although the present disclosure provides an example of a main chamber 10 housing an electron beam inspection system, it should be noted that aspects of the present disclosure in its broadest sense are not limited to a chamber housing an electron beam inspection system. Rather, it should be understood that the above principles may also be applied to other chambers.

[0036] Reference now Figure 2 , which illustrates that according to an embodiment of the present disclosure, it may be Figure 1 Schematic diagram of an exemplary configuration of an electron beam tool 40 as part of a charged particle beam inspection system 100. The electron beam tool 40 (also referred to herein as the device 40) may include an electron emitter, which may include a cathode 203, an anode 220, and a gun body aperture 222. The electron beam tool 40 may also include a Coulomb aperture array 224, a beam-condensing lens 226, a beam-limiting aperture array 235, an objective lens assembly 232, and an electron detector 244. The electron beam tool 40 may also include a sample holder 236 supported by a motorized stage 234 to support a sample 250 to be inspected. It should be understood that other related components may be added or omitted as needed.

[0037] In some embodiments, the electron emitter may include a cathode 203, an extractor anode 220, where primary electrons may be emitted from the cathode and extracted or accelerated to form a primary electron beam 204, which forms a primary beam intersection 202 (virtual or real). The primary electron beam 204 may be visualized as being emitted from the primary beam intersection 202.

[0038] In some embodiments, the electron emitter, condenser lens 226, objective lens assembly 232, beam limiting aperture array 235, and electron detector 244 can be aligned with the primary optical axis 201 of apparatus 40. In some embodiments, electron detector 244 can be positioned offset from primary optical axis 201 along a secondary optical axis (not shown).

[0039] In some embodiments, the objective lens assembly 232 may include a modified swing objective reduction immersion lens (SORIL), which includes pole pieces 232a, control electrodes 232b, deflectors 232c (or more than one deflector), and excitation coils 232d. During the overall imaging process, the primary electron beam 204 emitted from the tip of the cathode 203 is accelerated by the accelerating voltage applied to the anode 220. A portion of the primary electron beam 204 passes through the apertures of the gun body aperture 222 and the Coulomb aperture array 224, and is focused by the bunching lens 226 to pass through all or part of the apertures of the beam limiting aperture array 235. The electrons passing through the apertures of the beam limiting aperture array 235 can be focused by the modified SORIL lens to form a detection point on the surface of the sample 250, and are deflected by the deflector 232c to scan the surface of the sample 250. The secondary electrons emitted from the sample surface can be collected by the electron detector 244 to form an image of the scanned area of interest.

[0040] In the objective lens assembly 232, the excitation coils 232d and the pole pieces 232a can generate a magnetic field, which leaks out through the gap between the two ends of the pole pieces 232a and is distributed in the region around the optical axis 201. A portion of the sample 250 scanned by the primary electron beam 204 can be immersed in the magnetic field and can be charged, which in turn creates an electric field. The electric field can reduce the energy of the primary electron beam 204 hitting near and on the surface of the sample 250. The control electrodes 232b, which are electrically isolated from the pole pieces 232a, control the electric field on and above the sample 250 to reduce the aberration of the objective lens assembly 232 and control the focusing of the signal electron beam to obtain high detection efficiency. The deflector 232c can deflect the primary electron beam 204 to perform electron beam scanning on the wafer. For example, during the scanning process, the deflector 232c can be controlled to deflect the primary electron beam 204 to different positions on the top surface of the sample 250 at different time points to provide data for image reconstruction of different parts of the sample 250.

[0041] When the primary electron beam 204 is received, backscattered electrons (BSE) and secondary electrons (SE) can be emitted from portions of the sample 250. The electron detector 244 can capture the BSE and SE and generate an image of the sample based on information collected from the captured signal electrons. If the electron detector 244 is located outside the main optical axis 201, a beam splitter (not shown) can direct the BSE and SE to the sensor surface of the electron detector 244. The detected signal electron beam can form a corresponding secondary electron beam spot on the sensor surface of the electron detector 244. The electron detector 244 can generate a signal (e.g., voltage, current) representative of the intensity of the received signal electron beam spot and provide the signal to a processing system, such as the controller 50. The intensity of the secondary or backscattered electron beam and the resulting beam spot can vary according to the external or internal structure of the sample 250. Additionally, as described above, the primary electron beam 204 can be deflected to different positions on the top surface of the sample 250 to generate secondary or backscattered signal electron beams (and the resulting beam spots) of different intensities. Thus, by mapping the intensity of the signal electron beam spot to the position of the primary electron beam 204 on the sample 250, the processing system can reconstruct an image of the sample 250 that reflects the internal or external structure of the sample 250.

[0042] In some embodiments, the controller 50 can include an image processing system that includes an image acquirer (not shown) and a storage device (not shown). The image acquirer can include one or more processors. For example, the image acquirer can include a computer, server, mainframe, terminal, personal computer, any type of mobile computing device, etc. or a combination thereof. The image acquirer can be communicatively coupled to the electron detector 244 of the device 40 by means of media such as electrical conductors, fiber optic cables, portable storage media, IR, Bluetooth, the Internet, wireless networks, radio, etc. or a combination thereof. In some embodiments, the image acquirer can receive signals from the electron detector 244 and can construct an image. The image acquirer can thus acquire an image of an area of the sample 250. The image acquirer can also perform various post-processing functions, such as generating contours, overlaying indicators on the acquired image, etc. The image acquirer can be configured to perform adjustments such as brightness and contrast of the acquired image. In some embodiments, the storage device can be a storage medium such as a hard disk, flash drive device, cloud storage device, random access memory (RAM), other types of computer-readable memory, etc. The storage device can be coupled to the image acquirer and can be used to save the scanned raw image data as a raw image and save the post-processed image.

[0043] In some embodiments, the controller 50 may include a measurement circuit (e.g., an analog-to-digital converter) to obtain the detected distribution of secondary electrons. The electron distribution data collected during the detection time window combined with the corresponding scan path data of the primary beam 204 incident on the surface of the sample (e.g., a wafer) can be used to reconstruct an image of the wafer structure being inspected. The reconstructed image can be used to reveal various features of the internal or external structure of the sample 250 and can thus be used to reveal any defects that may be present in the sample 250, such as a wafer.

[0044] In some embodiments, the controller 50 may control the motorized stage 234 to move the sample 250 during inspection. In some embodiments, the controller 50 may cause the motorized stage 234 to continuously move the sample 250 in one direction at a constant speed. In other embodiments, the controller 50 may cause the motorized stage 234 to change the moving speed of the sample 250 over time according to the steps of the scanning process.

[0045] Now referring to Figure 3A , Figure 3A FIG. is a schematic diagram showing an embodiment of a charged particle beam apparatus 300A including a plurality of signal electron detectors according to an embodiment of the present disclosure. In some conventional SEMs, the apparatus 300A may include an electron source 302 configured to emit primary electrons from a cathode (e.g., Figure 2 cathode 203 of

[0046] ), and form a primary electron beam 304 that emanates from a primary electron beam crossover point 303 (virtual or real) along the main optical axis 301. The apparatus 300A may further include a bunching lens 321, a beam limiting aperture array 312, an in-lens electron detector 331, a backscattered electron detector 341, a scanning deflection unit 350, and an objective lens assembly 322. In the context of the present disclosure, the in-lens electron detector refers to a charged particle detector (e.g., an electron detector) located inside or above the objective lens assembly 322 and may be arranged rotationally symmetrically around the main optical axis (e.g., the main optical axis 301). In some embodiments, the in-lens electron detector may also be referred to as a lens-through detector, an immersion lens detector, or an upper detector. It should be understood that relevant components may be appropriately added, omitted, or rearranged. Figure 3A As shown in Figure 2 in currently existing SEMs, the primary electron beam 304 may be emitted from the electron source 302 and accelerated to a higher energy by an anode (e.g., Figure 2The gun body aperture 222) can limit the current of the primary electron beam 304 to a desired initial value and can work with the beam-limiting aperture array 312 to obtain the final beam current. The primary electron beam 304 can be focused by the bunching lens 321 and the objective lens assembly 322 to form a small detection point 306 on the surface of the sample 371. In some embodiments, the focusing ability of the bunching lens 321 and the opening size of the apertures of the beam-limiting aperture array 312 can be selected to obtain a desired detection current and make the detection point size as small as desired.

[0047] To obtain a small beam spot size over a wide range of detection currents, the beam-limiting aperture array 312 can include a plurality of apertures having various sizes. The beam-limiting aperture array 312 can be configured to move such that, based on the desired detection current or detection point size, one of the apertures of the aperture array 312 can be aligned with the principal optical axis 301. For example, as Figure 3A shown, one aperture of the aperture array 312 can be configured to generate a primary electron sub-beam 304-1 by blocking the peripheral electrons of the primary electron beam 304. In some embodiments, the scanning deflection unit 350 can include one or more deflectors configured to deflect the primary electron sub-beam 304-1 to scan a desired region on the surface of the sample 371.

[0048] As previously referenced Figure 2 described, the interaction of the electrons of the primary electron sub-beam 304-1 with the sample 371 can generate SEs and BSEs. As is well known in the art, the emission of SEs and BSEs follows Lambert's law and has a large energy spread, and electrons emerging from different depths of the sample 371 have different emission energies. For example, SEs originate from the surface or near-surface region of the sample 371 and have a lower emission energy (e.g., less than 50 eV). SEs can be used to provide information about surface or near-surface features and geometries. On the other hand, BSEs can be generated by elastic scattering events of incident electrons from deeper subsurface regions of the sample 371 and can have a higher emission energy compared to SEs, with an emission energy in the range from 50 eV to approximately the landing energy of the incident electrons. BSEs can provide compositional information of the material being examined. The number of BSEs generated can be related to factors such as the atomic number of the material in the sample or the landing energy of the primary electron beam.

[0049] In addition to focusing the primary electron beam 304 on the surface of the sample 371, the objective lens assembly 322 can also be configured to focus the signal electrons on the surface of the detector 331. As previously described with respect to Figure 2As described for sample 250, sample 371 can be immersed in the magnetic field of the objective lens assembly 322, and the magnetic field can focus the signal electrons with lower energy faster than the signal electrons with higher energy. For example, due to the low emission energy of SEs, the objective lens assembly 322 can strongly focus SEs (such as along electron paths 381 and 382), such that most of the SEs land on the detection layer of the in-lens detector 331. In contrast to SEs, the objective lens assembly 322 can only weakly focus BSEs due to their high emission energy. Thus, although some BSEs with small emission angles can travel along electron paths 391 and 392 and be detected by the in-lens electron detector 331, the BSEs with large emission angles (such as the electrons on path 393) may not be detected by the in-lens electron detector 331.

[0050] In some embodiments, an additional electron detector, such as the backscattered electron detector 341, can be used to detect those BSEs with large emission angles (e.g., the electrons traveling on path 393). In the context of the present disclosure, the emitter angle is referenced to be measured substantially perpendicular to the principal optical axis 301 of the sample 371. As Figure 3A shown, the emitter angle of the secondary electrons in path 382 is smaller than the emitter angles of the backscattered electrons in paths 391, 392, and 393. The backscattered electron detector 341 can be placed between the objective lens assembly 322 and the sample 371, and the in-lens electron detector 331 can be placed between the objective lens assembly 322 and the condenser lens 321, allowing the detection of both SEs and BSEs.

[0051] Based on differences such as emission energy or emission angle, SEs and BSEs can be detected separately using separate electron detectors, segmented electron detectors, energy filters, etc. For example, as Figure 3A shown, the in-lens electron detector 331 can be configured as a segmented detector (discussed later with reference to Figure 4C ), and the segmented detector includes detection segments arranged in a two-dimensional or three-dimensional arrangement. In some cases, the detection segments of the in-lens electron detector 331 can be arranged, for example, radially, circumferentially, or azimuthally around the principal optical axis 301.

[0052] Device 300A can include a condenser lens 321 configured to focus the primary electron beam 304 such that a portion 304-1 thereof can pass through the on-axis aperture of the aperture-limiting aperture array 312. The condenser lens 321 can be substantially similar to Figure 2 the condenser lens 226, and can perform a similar function. The condenser lens 321 can include an electrostatic, magnetic, or composite electromagnetic lens, etc. The condenser lens 321 can be associated with a controller (such as Figure 2electrically or communicatively coupled to the controller 50 shown. The controller 50 may apply an electrical excitation signal to the condenser lens 321 to adjust the focusing ability of the condenser lens 321 based on factors such as an operating mode, an application, a desired analysis, or a sample material being inspected.

[0053] The apparatus 300A may also include a scanning deflection unit 350 configured to dynamically deflect the primary electron beam 304 or the primary electron sub-beam 304-1 on the surface of the sample 371. The dynamic deflection of the primary electron sub-beam 304-1 may cause, for example, a desired area or a desired region of interest to be scanned in a raster scan pattern to generate SEs and BSEs for sample inspection. The scanning deflection unit 350 may include one or more deflectors (not shown) configured to deflect the primary electron sub-beam 304-1 along the X-axis or the Y-axis. As used herein, the X-axis and the Y-axis form a Cartesian coordinate, and the primary electron beam 304 propagates along the principal optical axis 301 aligned with the Z-axis. The X-axis refers to a horizontal axis or a transverse axis extending along the width of the paper, and the Y-axis refers to a vertical axis extending in and out of the plane of the paper.

[0054] Now referring to Figure 3B , which illustrates a schematic diagram of an embodiment of a charged particle beam apparatus 300B including a charged particle detector and an active energy filter. The apparatus 300B may include a magnetic objective lens assembly 322. In some embodiments, the objective lens assembly 322 may include a compound electromagnetic lens including a magnetic lens 322M formed by an inner pole piece 322A (similar to Figure 2 the pole piece 232a of Figure 2 ) and a control electrode 322B (similar to

[0055] One method of selectively detecting signal electrons (e.g., SEs versus BSEs) from the sample 371 is to use an active energy filter to filter specific types of electrons based on the emission energy of the electrons. As Figure 3B shown, in some embodiments, the control electrode 322B may be placed to form an energy filter between the sample 371 and the in-lens electron detector 331. In some embodiments, the control electrode 322B may be disposed between the sample 371 and the magnetic lens 322M of the objective lens assembly 322. When the power supply 375 biases the control electrode 322B to a voltage with reference to the sample 371, an electric field is generated between the control electrode 322B and the sample 371, resulting in an electrostatic potential barrier for the signal electrons. The electrostatic potential barrier blocks signal electrons having an emission energy lower than the threshold energy level of the barrier. It will be appreciated that an "active filter" refers to an electron filter that uses active components, such as an electrode that generates an "active" electric field, as opposed to a "passive filter" that uses only passive elements.

[0056] In one example, the control electrode 322B is negatively biased with respect to the sample 371 such that negatively charged signal electrons (e.g., SEs on path 381) are reflected back to the sample 371 because the SEs on path 381 do not have sufficient energy to cross the energy barrier. On the other hand, signal electrons having an emission energy higher than the threshold energy level of the barrier (e.g., BSEs on path 391) can overcome the energy barrier formed by the control electrode 322B and propagate toward the in-lens electron detector 331. Thus, the in-lens electron detector 331 can be configured as a backscattered electron detector. It should be understood that path 381 and path 391 respectively indicate the paths of exemplary SEs and BSEs generated from the sample 371.

[0057] Now referring Figure 3C , which illustrates a schematic diagram of an embodiment of a charged particle beam apparatus 300C including a charged particle detector and an active energy filter. Compared with the Figure 3B apparatus 300B, the apparatus 300C includes an energy filter disposed near the in-lens electron detector 331. As Figure 3C shown, the active energy filter can include a mesh electrode 331E configured to reflect signal electrons having a low emission energy (e.g., SEs on path 381) back to the sample 371 or the objective lens assembly 322 and allow signal electrons having a high emission energy (e.g., BSEs on path 391) to impinge on the detection layer of the in-lens electron detector 331. In some embodiments, the mesh electrode 331E can include a mesh structure made of a conductive material such as a metal, an alloy, a semiconductor, or a composite material. The mesh electrode 331E can be disposed between the objective lens assembly 322 and the in-lens electron detector 331. In some embodiments, the mesh electrode 331E can be disposed closer to the in-lens electron detector 331 than the objective lens assembly 322.

[0058] Detecting and inspecting some defects in semiconductor manufacturing processes, such as buried particles generated by lithography, metal deposition, dry etching, or wet etching, can benefit from inspecting the surface features of the sample as well as the compositional analysis of the features beneath the sample surface. Thus, a user can utilize the information obtained from an electron detector that can selectively detect SEs or BSEs to identify the defect(s), analyze the composition of the defect(s), and adjust process parameters based on the information obtained. In a charged particle beam apparatus (such as an SEM), the collection efficiency of BSEs can be improved by using an energy filter or an additional electron detector as discussed in reference Figures 3A - 3C . For example, as Figure 3B and Figure 3C shown, an active energy filter utilizing an electric field can be used to separate SEs from BSEs, thereby improving the respective collection efficiencies.

[0059] However, in some embodiments, the active energy filter may pose some drawbacks to the overall performance of the inspection system. For example, placing the negative bias energy filter closer to the sample (as Figure 3B shown) can increase the aberration of the objective lens assembly and increase the size of the detection point 306, thus adversely affecting the imaging resolution. As an alternative, the active energy filter can be placed closer to the in-lens electron detector (e.g., as Figure 3C shown, the mesh electrode 331E is placed near the detector 331) to minimize the impact on the aberration of the objective lens assembly. However, in such a configuration, the primary electron beam 304 may be directly affected by the energy filter, thereby enlarging the size of the detection point 306. To avoid the influence of the electric field on the primary electron beam, a shielding mesh or box (not shown) can be used to enclose the detector 331 and the electrode 331E. However, the shielding box may limit the detector shape (e.g., a large central hole of the detector 331 is required), which may hinder the detection of signal electrons with a small emission angle. In some configurations, to reduce the influence on the primary electron beam and improve the detection rate of signal electrons with a small emission angle, a beam splitter (not shown) can be used to deflect the signal electrons away from the main optical axis 301 and towards a detector placed on a secondary optical axis (not shown). However, even in this configuration, an active energy filter is still required for SE filtering, so a shielding mesh or box needs to be implemented. In addition, the beam splitter may add unwanted aberration to the incident primary electron beam, thereby negatively affecting the imaging resolution.

[0060] Now referring to Figure 4A , Figure 4A FIG. illustrates a schematic diagram of an exemplary structure of a signal electron detector 400 taken along a cross-section in the thickness direction of the signal electron detector according to an embodiment of the present disclosure. The signal electron detector 400 can be a part of a charged particle beam device (such as Figure 3A device 300A). The detector 400 can be aligned with the main optical axis 301 of the charged particle beam device. The primary electron beam 304 travels in the +Z direction (from Figure 4A the top to the bottom of Figure 4A ). The signal electrons 490 generated from the sample (not shown) travel in the -Z direction (from Figure 4A the bottom to the top of Figure 4A ) to enter the detector 400 from the first surface 401s of the detector 400.

[0061] In some embodiments, the signal electron detector 400 can be based on a PIN diode structure, which includes an intrinsic semiconductor layer between a p-type semiconductor layer and an n-type semiconductor layer, thereby creating a P-I-N structure. Figure 4AShows a five - layer PIN electron detector, which includes a first metal layer 410, a first semiconductor layer 420, a second semiconductor layer 430, a third semiconductor layer 440, and a second metal layer 450 along the thickness direction ( - Z direction) of the detector 400. The five layers (layer 410 - layer 450) have thicknesses 412, 422, 432, 442, and 452 respectively.

[0062] The first metal layer 410 and the second metal layer 450 at the bottom and top of the detector 400 can form electrodes configured to apply a bias voltage to the detector 400. For example, the first metal layer 410 can serve as the anode of the detector 400, and the second metal layer 450 can serve as the cathode of the detector 400. Additionally, the two metal layers can protect the internal semiconductor layers. Although Figure 4A An embodiment is illustrated where signal electrons enter from the anode side, but it can be understood that in different embodiments, signal electrons can enter from the cathode side.

[0063] The first metal layer 410 can be configured to receive signal electrons 490 incident on the surface 401s of the electron detector 400. The first metal layer 410 can be thin (e.g., in the range of 10 to 200 nm) and made of a light metal to reduce the scattering and energy loss of incoming electrons. For example, the material of the first metal layer 410 can be aluminum or other metals with high conductivity and easy penetration by signal electrons. The thickness 412 and material of the first metal layer 410 can be determined based on considerations of blocking particles other than incident electrons to reduce noise or filter them out based on the emission energy of some signal electrons (e.g., filtering out SE with very low emission energy).

[0064] The first semiconductor layer 420 is formed adjacent to the first metal layer 410. In some embodiments, the first semiconductor layer 420 can include a p - type semiconductor. For example, the first semiconductor layer 420 can be doped with trivalent impurities such as boron, aluminum, gallium, etc. to create free holes. The first semiconductor layer 420 can be a heavily doped region, such as a P + region. A portion of the first semiconductor layer 420 can form an energy barrier that selectively filters a certain type of incoming signal electrons. The doping concentration and thickness 422 of the first semiconductor layer 420 can be determined based on the desired characteristics of the energy filter, such as the threshold or cut - off energy level of the filter. Further details regarding the operation of the energy filter are provided below with reference to Figure 4B and Figure 4C The first metal layer 410 can be deposited on top of the first semiconductor layer 420. Thus, the first semiconductor layer 420 can be coated and protected by the first metal layer 410.

[0065] The second semiconductor layer 430 is formed adjacent to the first semiconductor layer 420. In some embodiments, the second semiconductor layer 430 may include an intrinsic semiconductor region. For example, the second semiconductor layer 430 may be an undoped pure semiconductor in the absence of any significant dopant species, or slightly n-doped or p-doped. The second semiconductor layer 430 may have a doping concentration lower than that of the other layers of the electron detector 400. The second semiconductor layer 430 may have a doping concentration that is set such that it has a high resistance due to being lightly doped. In some embodiments, the signal electron detector 400 may be formed from a silicon wafer, in which case the second semiconductor layer 430 may be an N-region. The thickness 432 of the second semiconductor layer 430 between the first semiconductor layer 420 and the third semiconductor layer 440 may be determined based on the range of the expected emission energy levels of the received signal electrons.

[0066] The third semiconductor layer 440 is formed adjacent to the second semiconductor layer 430. In some embodiments, the third semiconductor layer 440 may include an n-type semiconductor region. For example, the third semiconductor layer 440 may be doped with a pentavalent impurity such as phosphorus, antimony, arsenic, etc. to create free electrons. Similar to the first semiconductor layer 420, the third semiconductor layer 440 may be a heavily doped region such as an N+ region.

[0067] The second metal layer 450 may be deposited on the third semiconductor layer 440. The material of the second metal layer 450 may be a metal having high surface conductivity such as aluminum or copper. Different from the first metal layer 410, the second metal layer 450 may not need to be highly electron-penetrable because in some embodiments, signal electrons do not enter through the second metal layer 450.

[0068] Figure 4B and Figure 4C is a diagram showing an exemplary operation of a Figure 4A signal electron detector according to an embodiment of the present disclosure.

[0069] The first metal layer 410 and the second metal layer 450 can be connected to a power source 467. When the two metal layers 410 and 450 are directly formed on adjacent semiconductor layers (layer 420 and layer 440), an electrical connection can be formed by the metal layers between the three semiconductor layers (layer 420, layer 430, layer 440) and the power source 467. The power source 467 can be configured to provide a reverse bias to the PIN region formed by the first semiconductor layer, the second semiconductor layer, and the third semiconductor layer, connecting the negative terminal and the positive terminal of the power source 467 to the first metal layer 410 (anode) and the second metal layer 450 (cathode), respectively. The resulting potential difference between the first metal layer 410 and the second metal layer 450 can create an internal electric field across the PIN region. In some embodiments, the power source 467 can be directly connected to the first semiconductor layer 420 and the third semiconductor layer 440 because these semiconductor layers have low resistance due to high doping concentrations.

[0070] Under the reverse bias condition during normal operation, free charge carriers (e.g., free electrons and holes) are removed by the electric field, and thus a depletion region 437 can be formed within the volume of the detector body, particularly within the PIN region. As a result, under reverse bias, substantially no bias current flows through the detector (except for a very small leakage current). In some embodiments, the depletion region 437 can be almost entirely present within the second semiconductor layer 430 (intrinsic semiconductor region). In some embodiments, the depletion region 437 can extend beyond the second semiconductor layer 430, forming a depleted portion (420a) within the first semiconductor layer 420 and a depleted portion (440a) within the third semiconductor layer 440. The other portions (undepleted portions (420b)) of the first semiconductor layer 420 can remain with free holes. Similarly, the other portions (undepleted portions (440b)) of the third semiconductor layer 440 can remain with free electrons.

[0071] As previously mentioned, incoming signal electrons can have different emission energies. Since some signal electrons or charged particles may have very low emission energies (e.g., electron 495), they may be blocked or scattered by the first metal layer. Some signal electrons (e.g., electrons 496 and 497) can have higher emission energies to reach beyond the first metal layer 410.

[0072] When signal electrons (such as electrons 496 and 497) enter the detector body after passing through the first metal layer 410, the signal electrons can start to interact with the semiconductor material and generate electron-hole pairs (e.g., 496er - 496hr, 497er - 497hr, 497e - 497h). The signal electrons lose energy while interacting with the detector to form electron-hole pairs.

[0073] As Figure 4BAs shown, when electron-hole pairs (such as electron-hole pairs 496er - 496hr) are generated in the undepleted portion 420b of the first semiconductor region 420, some signal electrons (e.g., electron 496) may lose all of their energy and thus cannot reach the depletion region 437. In some embodiments, some of the generated electrons (e.g., electron 496er) themselves can contribute to the generation of other electron-hole pairs (not shown). These electron-hole pairs generated outside the depletion region 437 (e.g., pairs 496er - 496hr and other pairs generated by electron 496er) can drift slowly because the electric field outside the depletion region 437 is relatively weak. Therefore, the generated electrons and holes are likely to recombine with each other or with any other nearby free opposite carriers (e.g., as shown by arrow 496r). Due to this rapid recombination, the generated electron-hole pairs (e.g., pairs 496er - 496hr) may not contribute to the generation of a drift current, and as a result, the signal detection unit 468 does not generate a detector signal.

[0074] Only those incoming signal electrons with high enough emission energy (e.g., electron 497) can pass through and reach beyond the undepleted portion 420b of the first semiconductor layer 420. When passing through the undepleted portion 420b, the signal electron 497 may lose some energy (e.g., 497er - 497hr) used to generate electron-hole pairs. However, the initial emission energy of the signal electron 497 (before entering the detector body) can be high enough such that the electron can reach the depletion region 437 with some remaining energy to generate more electron-hole pairs 497e - 497h within the depletion region 437. In addition, some of the generated electrons (e.g., electron 497er) can have enough energy to pass through the undepleted portion 420b and reach the depletion region 437. These generated electrons can also contribute to the generation of other electron-hole pairs within the depletion region 437.

[0075] The electron-hole pairs 497e - 497h generated within the depletion region 437 can be separated by the electric field (formed by reverse biasing as described above) instead of recombining. For example, electron 497e can be directed towards the third semiconductor layer 440 (N+ region) as shown by arrow 497em, while hole 497h can be directed towards the first semiconductor layer 420 (P+ region) as shown by arrow 497hm. Therefore, these electrons 497e and holes 497h can eventually reach the electrodes at the top and bottom of the detector (e.g., cathode - second metal layer 450; anode - first metal layer 410) respectively and generate a current. In some embodiments, the signal detection unit 468 can measure this current and generate a corresponding detector signal. In some embodiments, the signal detection unit 468 can include a transimpedance amplifier (TIA) connected between the power supply 467 and the detector to process the current detector signal.

[0076] As described above, the combination of the metal layer 410 and the first semiconductor layer 420 provides an energy barrier that filters incoming signal electrons having an emission energy lower than the energy barrier (the initial energy required to reach the depletion region 437). In this way, incoming signal electrons having different energies can be separated and selectively detected without using an active energy filter as described in the previous reference Figure 3B and Figure 3C above.

[0077] In some embodiments, the energy barrier can increase as the thickness of the undepleted region 420b increases. For example, the energy barrier on a logarithmic scale can be proportional to the thickness of the undepleted region 420b on a logarithmic scale. In other words, when the thickness of the undepleted region 420b increases, the energy barrier can also increase such that signal electrons having a higher emission energy will be filtered out. The thickness of the undepleted region 420b can be determined based on a number of factors such as the bias voltage, the material used for the detector body (e.g., silicon), the doping profile of the semiconductor layer, or the thicknesses of the first, second, and third semiconductor layers (layers 420, 430, 440). For example, with the same bias voltage, the same device structure, and the same doping concentration, making the first semiconductor layer 420 thicker to some extent can result in a thicker undepleted region 420b. In some embodiments, the doping concentration of the first semiconductor layer 420 can be varied to configure the thickness of the undepleted region 420b.

[0078] In some embodiments, device simulations based on known detector structures can be performed to determine the appropriate thickness of the undepleted region 420b for a given desired level of the energy barrier. For example, in order to separate SE from BSE, it may be desirable for the detector to have an energy barrier approximately equal to the sum of 50 eV and the energy of the signal electrons obtained from the acceleration voltage in the column of the electron beam device. To configure the signal electron detector to have such an energy barrier, device simulations can be performed to determine various fabrication process knobs (such as doping profile, thickness of the semiconductor layer, bias voltage, etc.) that, when appropriately set, can provide an undepleted region 420b of an appropriate thickness corresponding to the desired level of the energy barrier.

[0079] Figure 4C is shown in the same manner as Figure 4BA segmented signal electron detector that operates in the same manner as the signal electron detector shown, except that the third semiconductor layer and the second metal layer are segmented to generate a plurality of detector signals based on the relative positions where incoming signal electrons are captured. In some embodiments, the electron detector may include a plurality of segments of the third semiconductor layer (e.g., segment 440-1, segment 440-2, segment 440-3). The material or doping profile of these segments 440-1, 440-2, 440-3 may be substantially similar to Figure 4B the third semiconductor layer 440. The electron detector may also include a plurality of segments of the second metal layer (e.g., segment 450-1, segment 450-2, segment 450-3), each second metal layer segment being formed directly on an adjacent segment of the third semiconductor layer (segment 440-1, 440-2, or 440-3). When the signal electron 498 reaches the depletion region 437, electron-hole pairs (e.g., pair 498e-498h) are generated, and most of these electrons 498e may move towards the nearest segment 440-2 of the third semiconductor layer. Accordingly, the detector signal corresponding to the electron 498 may be collected by the signal detection unit 468-2 electrically connected to the metal layer segment 450-2 and the semiconductor layer segment 440-2. Similarly, the detector signal generated by the incoming signal electron 497 may be collected by the signal detection unit 468-3.

[0080] Now referring to Figure 5A and Figure 5B , Figure 5A and Figure 5B are schematic diagrams of an exemplary signal electron detector 531 having an external passive energy filter 532 according to embodiments of the present disclosure. In some embodiments, the signal electron detector 531 may be a signal electron detector having a built-in passive energy filter as described in Figures 4A - 4C . In some embodiments, the signal electron detector 531 may be a conventional electron detector without a built-in passive energy filter.

[0081] As Figure 5A and Figure 5B shown, the signal electron detector 531 may include a PIN diode structure similar to the signal detector shown in Figures 4A - 4C . For example, the signal electron detector 531 may be reverse biased to create a depletion region 537. An internal energy barrier may be provided for the undepleted region (not shown) of the detector 531 to filter signal electrons having an energy lower than a predetermined threshold energy level.

[0082] In some embodiments, an external passive energy filter 532 may be used to provide an additional energy barrier in addition to the built-in energy barrier of the detector 531. The external passive energy filter 532 may be a plate made of a material capable of attenuating the energy of incoming signal electrons. For example, the external passive energy filter 532 may include a semiconductor material (such as silicon nitride) or a conductive material (such as an aluminum film), which provides the attenuation ability while also providing a certain level of conductivity to release any charge that may accumulate within the energy filter 532 due to the incidence of signal electrons. The external passive filter 532 may have a central opening aligned with the main optical axis of the inspection device so that the primary beam 304 can pass through. The energy barrier of the external passive energy filter 532 may be determined, for example, by adjusting the thickness or material of the plate.

[0083] In some embodiments, the external passive energy filter 532 may be in a first position in a high-filter mode (as Figure 5A shown) and a second position in a low-filter mode (as Figure 5B shown). When the inspection device is operating in the high-filter mode, the external passive energy filter 532 may be positioned in the first position between the sample (not shown) and the signal electron detector 531. In the high-filter mode, the external passive energy filter 532 may be configured to provide an additional energy barrier in addition to the built-in energy barrier of the detector 531. The effective total energy barrier of the incoming signal electrons may become the sum of the built-in energy barrier of the detector 531 and the additional energy barrier of the external passive energy filter 532. For example, Figure 5A and Figure 5B show three exemplary incoming signal electrons 595, electron 596, and electron 597. The emission energy of electron 595 may be lower than the additional energy barrier of the external passive energy filter 532. The emission energy of electron 596 may be higher than the additional energy barrier of the external passive energy filter 532 but lower than the effective total energy barrier. The emission energy of electron 597 may be higher than the effective total energy barrier. With the external passive energy filter 532 in the first position, the signal electrons 595 and electron 596 are filtered out because their energies are lower than the effective total energy barrier, and only the signal electron 597 can reach the depletion region 537 to be detected.

[0084] When the inspection device is operating in the low-filter mode, the external passive energy filter 532 may be in the second position away from the detector 531 such that the external passive energy filter 532 does not affect any incoming signal electrons. Thus, in the low-filter mode, the incoming signal electrons are filtered only by the built-in energy barrier of the detector 531. For example, as Figure 5BAs shown, when the external passive energy filter 532 is in the second position, only the signal electrons 595 can be filtered out, while the signal electrons 596 and the electrons 597 can reach the depletion region 537 to be detected.

[0085] Now refer to Figures 6A - 6F , Figures 6A - 6F which is a schematic diagram of an exemplary charged particle beam device including a signal electron detector and an external passive energy filter according to embodiments of the present disclosure in accordance with Figure 5A and Figure 5B the signal electron detector and the external passive energy filter described.

[0086] Figure 6A FIG. shows an exemplary charged particle beam device 600A according to some embodiments of the present disclosure, which is similar to Figure 3A the charged particle beam device 300A. A movable external passive energy filter 632 (similar to Figure 5A and Figure 5B the movable external passive energy filter 532 shown) can be used within the charged particle beam device 600A. The device 600A may include a signal electron detector 631, and the signal electron detector 631 may be a signal electron detector having a built-in passive energy filter as described in Figures 4A - 4C or a conventional electron detector without a built-in passive energy filter.

[0087] Similar to Figure 5A , when the device 600A is operating in a high filtration mode, the external passive energy filter 632 can be positioned in a first position between the sample 371 and the signal electron detector 631. In the high filtration mode, the external passive energy filter 632 can be configured to provide an additional energy barrier in addition to the built-in energy barrier of the detector 631. The effective total energy barrier for incoming signal electrons can become the sum of the two energy barriers of the detector 631 and the filter 632. For example, as Figure 6A shown, in the case where the external passive energy filter 632 is in the first position, the signal electrons 381 (e.g., electrons with low emission energy, such as SE) can be filtered out because their energy is lower than the effective total energy barrier, and only the signal electrons 391 (including electrons with emission energy higher than the effective total energy barrier, such as BSE) can reach the depletion region of the detector 631 to be detected.

[0088] When the device 600A is operating in a low filtration mode, the external passive energy filter 632 can be positioned in a second position away from the detector 631, such that the effective total energy barrier can be reduced, thereby allowing signal electrons with lower energy (e.g., SE on path 381) to also be detected by the detector 631.

[0089] Figure 6B Another example (600B) of a charged particle beam device with a movable passive energy filter according to some embodiments of the present disclosure is shown. Similar to Figure 6A the device 600A in Figures 4A - 4C , the device 600B may include a signal electron detector 631, which may be a signal electron detector with a built-in passive energy filter as Figure 6C described, or an electron detector without a built-in passive energy filter. In some embodiments, the movable external passive energy filter 632 may include a plurality of filtering zones (e.g., filtering zone 632a and filtering zone 632b). In some embodiments, as

[0090] shown, the movable external passive energy filter 632 may include a filter plate having a plurality of filtering zones, each filtering zone having a central hole allowing the primary beam 304 to pass through. Each filtering zone 632a or filtering zone 632b may provide a different level of energy barrier. As described above, the energy barriers of the external passive energy filtering zones 632a and 632b may be determined by adjusting the thickness or material of each filtering zone plate. Figure 6B and Figure 6C illustrate a filter 632 having two filtering zones 632a and 632b, it should be understood that any number of filtering zones may be implemented in the filter 632.

[0091] Figure 6D Another example of an external passive energy filter 632 with a plurality of filtering segments is shown. In some embodiments, the external passive energy filter 632 may include a central hole allowing the primary beam 304 to pass through and a plurality of filtering segments (e.g., filtering segment 632c, filtering segment 632d, and filtering segment 632e) positioned around the central hole. Each filtering segment 632c, filtering segment 632d, or filtering segment 632e may provide a different level of energy barrier. This enables an electron detector (such as Figure 6A and Figure 6BThe electron detector 631) in it can detect signal electrons having different energy levels (e.g., SE vs. BSE) in terms of their emission radial angles (emission angles relative to the surface normal), and is helpful for defect inspection of some types of samples.

[0092] As described above with respect to Figure 6A and Figure 6B stated, the external passive energy filter 632 can be used together with the signal electron detector 631, and the signal electron detector 631 can include an electron detector having a built-in passive energy filter as Figures 4A - 4C described, or an electron detector without a built-in passive energy filter.

[0093] As Figure 6E shown, in some embodiments, the movable passive energy filter 632 (e.g., the movable passive energy filter 632 used in the device 600B of Figure 6B ) can also include a plurality of filter segments in each of the filter zones 632a and 632b. This enables the detection of signal electrons according to various emission angles and emission energy levels. Although Figure 6E illustrates a filter 632 having two filter zones 632a and 632b, it should be understood that any number of filter zones can be implemented in the filter 632. Similarly, although Figure 6E illustrates three segments in the filter zone 632a and two segments in the filter zone 632b, it should be understood that any number of segments can be implemented in each filter zone.

[0094] Figure 6F Another example (600F) of a charged particle beam device having a movable passive energy filter 632 according to some embodiments of the present disclosure is shown. The movable passive energy filter 632 can have the configuration as Figures 6C - 6E shown. As previously referred to Figure 3A stated, some BSEs (e.g., electrons on path 393) can have large emission angles such that the objective lens assembly 322 cannot focus the BSE 393 onto the electron detector 631. In some embodiments, the device 600F can include an additional electron detector 641 to detect those BSEs having large emission angles (e.g., electrons traveling on path 393). Although Figure 6F illustrates a device having a movable passive energy filter, the passive energy filter 632 can be implemented as a fixed filter (similar to the passive energy filter 632 as Figure 6A shown).

[0095] Now referring to Figure 7 , which illustrates an exemplary method of forming a signal electron detector according to an embodiment of the present disclosure. Figures 4A - 4C of

[0096] In step A1, a substrate 700 is provided. The substrate 700 can be a part of a semiconductor wafer having a first surface 701s and a second surface 702s. The substrate 700 can be made of silicon, germanium, or other suitable semiconductor materials. Although Figure 7 an example process using a lightly doped N-silicon wafer as the substrate 700 is shown, it should be understood that different materials, such as P-doped semiconductors, can be used.

[0097] In step A2, a first semiconductor layer 720 is formed in a portion of the substrate 700 having the first surface 701s. In some embodiments, the first semiconductor layer 720 can include a p-type semiconductor. For example, to create the first semiconductor layer 720, the substrate 700 can be doped with a trivalent impurity, such as boron, aluminum, gallium, etc., to create free holes. The doping impurity (e.g., boron) can be implanted from the first surface 701s of the substrate 700. In some embodiments, the first semiconductor layer 720 can be heavily doped, such as Figure 7 the P+ region shown.

[0098] As previously referenced Figures 4A - 4C and described, when the detector is in normal operation, the undepleted region of the first semiconductor layer 720 (such as Figure 4B the undepleted region 420b) can form an energy barrier that selectively filters certain types of incoming signal electrons based on their emission energy. The energy barrier can increase as the thickness of the undepleted region increases, and thus the energy barrier can be changed by varying the thickness of the undepleted region. Among them, the thickness of the undepleted region can be related to the doping concentration or thickness of the first semiconductor layer 720. Therefore, a plurality of manufacturing knobs including the doping concentration and thickness of the first semiconductor layer 720 can be determined based on the desired characteristics of the energy filter (such as the level of the energy barrier) before step A2.

[0099] In step A3, a second semiconductor layer 730 and a third semiconductor layer 740 are formed within the body of the substrate 700. The third semiconductor layer 740 is formed in a portion of the substrate 700 having the second surface 702s. In some embodiments, the third semiconductor layer 740 can include an n-type semiconductor region. For example, to create the third semiconductor layer 740, the substrate 700 can be doped with a pentavalent impurity, such as phosphorus, antimony, arsenic, etc., to create free electrons. The doping impurity (e.g., phosphorus) can be implanted from the second surface 702s of the substrate 700. Similar to the first semiconductor layer 720, the third semiconductor layer 740 can be a heavily doped region, such as Figure 7 the N+ region shown.

[0100] After the first semiconductor layer and the third semiconductor layer (layer 720, layer 740) are formed, the remaining portion between these two layers can become the second semiconductor layer 730. Since the second semiconductor layer 730 remains undoped or slightly n-doped or p-doped without any significant dopant substances, this layer is referred to as an intrinsic semiconductor region. Together with the adjacent P+ region (the first semiconductor layer 720) and N+ region (the third semiconductor layer 740), the intrinsic semiconductor region (the second semiconductor layer 730) forms a PIN region.

[0101] When a reverse bias is applied to the detector, a depletion region (such as Figure 4B the depletion region 437) can be formed within the PIN region. In some embodiments, the depletion region can be almost entirely present within the second semiconductor layer 730. Therefore, the thickness of the second semiconductor layer 730, which is one of the factors controlling the thickness of the depletion region, can be determined based on the characteristics of the incoming signal electrons (e.g., the range of the emission energy of the incoming electrons) before steps A1 and A2.

[0102] In step A4, the first metal layer 710 is formed on the first surface 701 of the substrate 700 and is adjacent to the first semiconductor layer 720. For example, after doping impurities are introduced into the substrate 700, the first metal layer 710 can be deposited on top of the first semiconductor layer 720 (P+ region).

[0103] The first metal layer 710 can be configured to receive signal electrons (not shown). Therefore, the first metal layer 710 can be thin and made of a light metal to reduce the scattering and energy loss of the incoming electrons. For example, the material of the first metal layer 710 can be aluminum or other metals with high conductivity and easy penetration by signal electrons. The thickness and material of the first metal layer 710 can be determined based on the consideration of blocking particles other than incident electrons to reduce noise or filtering some signal electrons based on the emission energy of some signal electrons (e.g., filtering SE with very low emission energy).

[0104] In step A5, the second metal layer 750 is formed on the second surface 702s of the substrate 700 and is adjacent to the third semiconductor layer 740. For example, after doping impurities are introduced into the substrate 700, the second metal layer 750 can be deposited on top of the second semiconductor layer 740 (N+ region). The material of the second metal layer 750 can be a metal with high surface conductivity, such as aluminum or copper. Different from the first metal layer 710, in some embodiments, the second metal layer 750 may not need to be highly penetrable by electrons.

[0105] Although Figure 7Illustrated is a method depicting an exemplary sequence of a manufacturing process for forming an electron detector, but it should be understood that some steps may be reordered. For example, the third semiconductor layer 740 may be formed before the first semiconductor layer 720. The first metal layer 710 may be formed before the second metal layer 750.

[0106] Aspects of the present disclosure are set forth in the following numbered clauses:

[0107] 1. An electron detector for detecting a plurality of signal electrons generated from a sample, comprising:

[0108] A first semiconductor layer having a first portion and a second portion;

[0109] A second semiconductor layer adjacent to the first semiconductor layer;

[0110] A third semiconductor layer adjacent to the second semiconductor layer;

[0111] A PIN region formed by the first semiconductor layer, the second semiconductor layer, and the third semiconductor layer;

[0112] A power supply configured to apply a reverse bias between the first semiconductor layer and the third semiconductor layer; and

[0113] A depletion region formed within the PIN region by the reverse bias, the depletion region including a portion of the second semiconductor layer, and the depletion region being configured to generate a detector signal based on a first subset of the plurality of signal electrons captured within the depletion region,

[0114] Wherein the second portion of the first semiconductor layer is not depleted and is configured to provide an energy barrier to block a second subset of the plurality of signal electrons, and is configured to allow the first subset of the plurality of signal electrons to pass through to reach the depletion region.

[0115] 2. The detector according to clause 1, wherein the depletion region further includes a first portion of the first semiconductor layer.

[0116] 3. The detector according to any one of clauses 1 and 2, wherein the depletion region further includes a portion of the third semiconductor layer.

[0117] 4. The detector according to any one of clauses 1-3, wherein the portion of the second semiconductor layer includes the entirety of the second semiconductor layer.

[0118] 5. The detector according to any one of clauses 1-4, wherein the first subset of the plurality of signal electrons includes electrons having a high enough energy to pass through the energy barrier.

[0119] 6. The detector according to any one of clauses 1-5, wherein the second subset of the plurality of signal electrons includes electrons having an energy insufficient to pass through the energy barrier.

[0120] 7. The detector according to any one of clauses 1 - 6, wherein the detector signal is further affected by a first set of internal electrons generated by the interaction between a plurality of signal electrons and a second portion of the first semiconductor layer.

[0121] 8. The detector according to clause 7, wherein the first set of internal electrons includes electrons having high enough energy to cross an energy barrier.

[0122] 9. The detector according to any one of clauses 7 and 8, wherein the second portion of the first semiconductor layer is further configured to prevent a second set of internal electrons from reaching the depletion region, wherein the second set of internal electrons is generated by the interaction between a plurality of signal electrons and the second portion of the first semiconductor layer and has energy insufficient to cross the energy barrier.

[0123] 10. The detector according to any one of clauses 1 - 9, wherein the first semiconductor layer is doped with a dopant, and the cut-off energy level of the energy barrier of the first semiconductor layer is determined by the doping concentration in the first semiconductor layer, the thickness of the first semiconductor layer, or the reverse bias voltage applied by a power supply.

[0124] 11. The detector according to any one of clauses 1 - 10, wherein the detector signal is generated based on electron-hole pairs generated in the depletion region by a first subset of a plurality of signal electrons or a first set of internal electrons.

[0125] 12. The detector according to any one of clauses 1 - 11, wherein the first semiconductor layer is doped with a p-type dopant, and the second and third semiconductor layers are doped with an n-type dopant.

[0126] 13. The detector according to clause 12, wherein the electric potential near the first semiconductor layer is lower than the electric potential near the third semiconductor layer.

[0127] 14. The detector according to any one of clauses 1 - 11, wherein the first semiconductor layer is doped with an n-type dopant, and the second semiconductor layer and the third semiconductor layer are doped with a p-type dopant.

[0128] 15. The detector according to clause 14, wherein the electric potential near the first semiconductor layer is higher than the electric potential near the third semiconductor layer.

[0129] 16. The detector according to any one of clauses 1 - 15, further comprising:

[0130] A first electrode adjacent to the first semiconductor layer and coupled to a first terminal of a power supply; and

[0131] A second electrode, which is adjacent to the third semiconductor layer and is coupled to a second terminal of a power supply.

[0132] 17. The detector according to clause 16, wherein the first electrode is part of a first metal layer adjacent to the first semiconductor layer.

[0133] 18. The detector according to any one of clauses 16 and 17, wherein the second electrode is part of a second metal layer adjacent to the third semiconductor layer.

[0134] 19. An electronic detector for detecting a plurality of signal electrons generated from a sample, comprising:

[0135] A first semiconductor layer having a first part and a second part;

[0136] A second semiconductor layer adjacent to the first semiconductor layer;

[0137] A plurality of segments of a third semiconductor layer, each of the plurality of segments being adjacent to the second semiconductor layer,

[0138] A PIN region formed by the first semiconductor layer, the second semiconductor layer, and the third semiconductor layer;

[0139] A power supply configured to apply a reverse bias between the first semiconductor layer and the third semiconductor layer; and

[0140] A depletion region formed within the PIN region by the reverse bias, the depletion region including a part of the second semiconductor layer, and the depletion region being configured to generate a plurality of detector signals based on a first subset of the plurality of signal electrons captured within the depletion region,

[0141] wherein the second part of the first semiconductor layer is not depleted and is configured to provide an energy barrier to block a second subset of the plurality of signal electrons, and is configured to allow the first subset of the plurality of signal electrons to pass through to reach the depletion region.

[0142] 20. The detector according to clause 19, wherein the depletion region further includes a first part of the first semiconductor layer.

[0143] 21. The detector according to any one of clauses 19 and 20, wherein the depletion region further includes a part of the third semiconductor layer.

[0144] 22. The detector according to any one of clauses 19 - 21, wherein the part of the second semiconductor layer includes the entirety of the second semiconductor layer.

[0145] 23. The detector according to any one of clauses 19 - 22, wherein the first subset of the plurality of signal electrons includes electrons having high enough energy to pass through the energy barrier.

[0146] 24. The detector according to any one of clauses 19 - 23, wherein the second subset of the plurality of signal electrons includes electrons having energy insufficient to cross the energy barrier.

[0147] 25. The detector according to any one of clauses 19 - 24, wherein the plurality of detector signals are further affected by a first set of internal electrons generated by the interaction between the plurality of signal electrons and a second portion of the first semiconductor layer.

[0148] 26. The detector according to clause 25, wherein the first set of internal electrons includes electrons having energy high enough to cross the energy barrier.

[0149] 27. The detector according to any one of clauses 25 and 26, wherein the second portion of the first semiconductor layer is further configured to prevent a second set of internal electrons from reaching the depletion region, wherein the second set of internal electrons is generated by the interaction between the plurality of signal electrons and the second portion of the first semiconductor layer and has energy insufficient to cross the energy barrier.

[0150] 28. The detector according to any one of clauses 19 - 27, wherein the first semiconductor layer is doped with a dopant, and the cut-off energy level of the energy barrier of the first semiconductor layer is determined by the doping concentration in the first semiconductor layer, the thickness of the first semiconductor layer, or the reverse bias voltage applied by a power supply.

[0151] 29. The detector according to any one of clauses 19 - 28, wherein the plurality of detector signals are generated based on electron-hole pairs generated in the depletion region by a first subset of the plurality of signal electrons or a first set of internal electrons.

[0152] 30. The detector according to clause 29, wherein one of the plurality of detector signals is generated based on a subset of electron-hole pairs captured by a corresponding segment among the plurality of segments of the third semiconductor layer.

[0153] 31. The detector according to clause 30, wherein the corresponding segment is the segment closest to the position where the subset of electron-hole pairs is generated.

[0154] 32. The detector according to clause 30, wherein the corresponding segment is determined by the electric field generated by the reverse bias in the PIN region.

[0155] 33. The detector according to any one of clauses 19 - 32, wherein the first semiconductor layer is doped with a p-type dopant, and the plurality of segments of the second semiconductor layer and the third semiconductor layer are doped with an n-type dopant.

[0156] 34. The detector according to clause 33, wherein the electric potential near the first semiconductor layer is lower than the electric potential near the plurality of segments of the third semiconductor layer.

[0157] 35. The detector according to any one of clauses 19 - 32, wherein the first semiconductor layer is doped with an n - type dopant, and the plurality of segments of the second semiconductor layer and the third semiconductor layer are doped with a p - type dopant.

[0158] 36. The detector according to clause 35, wherein the electric potential near the first semiconductor layer is higher than the electric potential near the plurality of segments of the third semiconductor layer.

[0159] 37. The detector according to any one of clauses 19 - 36, further comprising:

[0160] A first electrode, which is adjacent to the first semiconductor layer and is coupled to the first terminal of a power supply;

[0161] A second electrode, which is adjacent to one of the plurality of segments of the third semiconductor layer and is coupled to the second terminal of the power supply; and

[0162] A third electrode, which is adjacent to another one of the plurality of segments of the third semiconductor layer and is coupled to the second terminal of the power supply.

[0163] 38. The detector according to clause 37, wherein the first electrode comprises a part of a first metal layer adjacent to the first semiconductor layer.

[0164] 39. The detector according to any one of clauses 37 and 38, wherein the second electrode and the third electrode are parts of a second metal layer adjacent to the third semiconductor layer.

[0165] 40. A method for manufacturing an electron detector having an energy barrier, the energy barrier filtering electrons based on the energy of the electrons, the method comprising:

[0166] Providing a semiconductor substrate having:

[0167] A first part;

[0168] A second part adjacent to the first part; and

[0169] A third part adjacent to the second part;

[0170] Forming a first semiconductor layer by doping the first part of the substrate with a first type of dopant;

[0171] Forming a third semiconductor layer by doping the third part of the substrate with a second type of dopant; and

[0172] Forming a second semiconductor layer in the second part of the substrate,

[0173] wherein a doping concentration of a first type of dopant in the first semiconductor layer is determined to configure an energy barrier of the electron detector, and

[0174] a thickness of the first semiconductor layer is determined to further configure the energy barrier of the electron detector.

[0175] 41. The method according to clause 40, wherein after the first and third portions of the substrate are doped, a second semiconductor layer is formed in the second portion of the substrate.

[0176] 42. The method according to any one of clauses 40 and 41, wherein the third semiconductor layer has a higher doping concentration than the doping concentration in the second semiconductor layer.

[0177] 43. The method according to any one of clauses 40 - 42, further comprising forming a first metal layer adjacent to the first semiconductor layer.

[0178] 44. The method according to clause 43, wherein the first metal layer is configured to receive a connection from a first terminal of a power supply.

[0179] 45. The method according to clause 44, further comprising forming a second metal layer adjacent to the third semiconductor layer.

[0180] 46. The method according to clause 45, wherein the second metal layer is configured to receive a connection from a second terminal of a power supply.

[0181] 47. The method according to any one of clauses 43 - 46, wherein the first metal layer includes a first electrode configured to function as an anode or a cathode.

[0182] 48. The method according to any one of clauses 43 - 47, wherein the second metal layer includes a second electrode configured to function as a cathode or an anode.

[0183] 49. A charged particle beam apparatus for inspecting a sample, comprising:

[0184] a charged particle beam source configured to emit a charged particle beam along a main optical axis;

[0185] an objective lens configured to focus the charged particle beam onto the sample; and

[0186] an electron detector according to any one of clauses 1 - 39, configured to detect a plurality of signal electrons generated from the charged particle beam incident on the sample.

[0187] 50. The apparatus according to clause 49, further comprising a passive energy filter between the electron detector and the sample.

[0188] 51. The device according to clause 49 further includes a passive energy filter movable between a first position and a second position, wherein:

[0189] When the device operates in a high filtration mode, the passive energy filter is positioned at a first position between the sample and the electron detector and is configured to filter a first subset of a plurality of signal electrons, and

[0190] When the device operates in a low filtration mode, the passive energy filter is positioned at a second position away from the electron detector and is configured to allow a second subset of the plurality of signal electrons to pass through to reach the electron detector, wherein the second subset of the plurality of signal electrons includes electrons having energy levels similar to those of the first subset of the plurality of signal electrons.

[0191] 52. The device according to clause 51, wherein the passive energy filter is configured to provide a first external energy barrier in addition to the energy barrier of the electron detector to filter a subset of the plurality of signal electrons.

[0192] 53. The device according to clause 52, wherein when the device operates in the high filtration mode, it is configured to filter a subset of the plurality of signal electrons that has an energy lower than the sum of the energy barrier of the electron detector and the first external energy barrier of the passive energy filter.

[0193] 54. The device according to clause 49 further includes a passive energy filter movable between a first position, a second position, and a third position, the passive energy filter including a first filtration region having a first external energy barrier and a second filtration region having a second external energy barrier.

[0194] 55. The device according to clause 54, wherein:

[0195] When the device operates in a first filtration mode, the passive energy filter is positioned at the first position such that the first filtration region is positioned between the sample and the electron detector and is configured to provide a first external energy barrier in addition to the energy barrier of the electron detector,

[0196] When the device operates in a second filtration mode, the passive energy filter is positioned at the second position such that the second filtration region is positioned between the sample and the electron detector and is configured to provide a second external energy barrier in addition to the energy barrier of the electron detector, and

[0197] When the device operates in a third filtration mode, the passive energy filter is positioned at the third position away from the electron detector.

[0198] 56. The device according to any one of clauses 54 and 55, the first external energy barrier being higher than the second external energy barrier.

[0199] 57. The device according to any one of clauses 50 - 56, wherein the passive energy filter comprises any material capable of attenuating the energy of a plurality of signal electrons.

[0200] 58. The device according to any one of clauses 50 - 57, wherein the passive energy filter comprises a semiconductor material or a conductor material.

[0201] 59. The device according to clause 49, further comprising a passive energy filter, the passive energy filter comprising a plurality of filter segments, each segment of the plurality of filter segments being configured to provide a different level of energy barrier.

[0202] 60. The device according to clause 59, wherein the passive energy filter is movable.

[0203] 61. A charged particle beam device for inspecting a sample, comprising:

[0204] A charged particle beam source configured to emit a charged particle beam along a main optical axis;

[0205] An objective lens configured to focus the charged particle beam onto the sample;

[0206] An electron detector configured to detect a plurality of signal electrons generated from the incidence of the charged particle beam on the sample; and

[0207] A passive energy filter between the electron detector and the sample.

[0208] 62. The device according to clause 61, wherein the passive energy filter is movable between a first position and a second position, wherein:

[0209] When the device is operating in a high - filter mode, the passive energy filter is positioned at a first position between the sample and the electron detector and is configured to filter a subset of the plurality of signal electrons, and

[0210] When the device is operating in a low - filter mode, the passive energy filter is positioned at a second position away from the electron detector and is configured to allow a subset of the plurality of signal electrons to pass through to reach the electron detector.

[0211] 63. The device according to any one of clauses 61 and 62, wherein the electron detector comprises the electron detector according to any one of clauses 1 - 39.

[0212] 64. The device according to any one of clauses 61 - 63, wherein the passive energy filter is configured to provide a first external energy barrier to filter a subset of the plurality of signal electrons.

[0213] 65. The device according to clause 64, wherein when the device operates in a high filtration mode, it is configured to filter a subset of a plurality of signal electrons having an energy lower than the first external energy barrier of the passive energy filter.

[0214] 66. The device according to any one of clauses 61 - 65, wherein the passive energy filter includes a plurality of filtering segments, and each of the plurality of filtering segments is configured to provide a different level of energy barrier.

[0215] 67. The device according to any one of clauses 61 - 66, wherein the passive energy filter includes a material capable of attenuating the energy of a plurality of signal electrons.

[0216] 68. The device according to any one of clauses 61 - 67, wherein the passive energy filter includes a semiconductor material or a conductor material.

[0217] 69. An electron detector for detecting a plurality of signal electrons generated from a sample, comprising:

[0218] A first semiconductor layer having a first part and a second part;

[0219] A second semiconductor layer adjacent to the first semiconductor layer;

[0220] A third semiconductor layer adjacent to the second semiconductor layer;

[0221] A PIN region formed by the first semiconductor layer, the second semiconductor layer, and the third semiconductor layer; and

[0222] A depletion region formed by applying a reverse bias to the PIN region, the depletion region includes a part of the second semiconductor layer, and the depletion region is configured to generate a detector signal based on a first subset of a plurality of signal electrons captured in the depletion region,

[0223] wherein the second part of the first semiconductor layer is not depleted, and is configured to provide an energy barrier to block a second subset of a plurality of signal electrons, and is configured to allow a first subset of a plurality of signal electrons to pass through to reach the depletion region.

[0224] 70. The detector according to clause 69, wherein the depletion region further includes a first part of the first semiconductor layer.

[0225] 71. The detector according to any one of clauses 69 and 70, wherein the depletion region further includes a part of the third semiconductor layer.

[0226] 72. The detector according to any one of clauses 69 - 71, wherein the part of the second semiconductor layer includes the whole of the second semiconductor layer.

[0227] 73. The detector according to any one of clauses 69 - 72, wherein the first subset of the plurality of signal electrons includes electrons having sufficient energy to pass through the energy barrier.

[0228] 74. The detector according to any one of clauses 69 - 73, wherein the second subset of the plurality of signal electrons includes electrons having insufficient energy to pass through the energy barrier.

[0229] 75. The detector according to any one of clauses 69 - 74, wherein the detector signal is generated based on a first set of internal electrons generated by the interaction between the plurality of signal electrons and the second part of the first semiconductor layer.

[0230] 76. The detector according to clause 75, wherein the first set of internal electrons includes electrons having sufficient energy to pass through the energy barrier.

[0231] 77. The detector according to any one of clauses 75 and 76, wherein the second part of the first semiconductor layer is further configured to prevent a second set of internal electrons from reaching the depletion region, wherein the second set of internal electrons is generated by the interaction between the plurality of signal electrons and the second part of the first semiconductor layer and has insufficient energy to pass through the energy barrier.

[0232] 78. The detector according to any one of clauses 69 - 77, wherein the first semiconductor layer is doped with a dopant, and the cut-off energy level of the energy barrier of the first semiconductor layer is determined by the doping concentration in the first semiconductor layer or the thickness of the first semiconductor layer.

[0233] 79. The detector according to any one of clauses 69 - 78, wherein the detector signal is generated based on electron-hole pairs generated by the first subset of the plurality of signal electrons in the depletion region.

[0234] 80. An electron detector for detecting a plurality of signal electrons generated from a sample, comprising:

[0235] A first semiconductor layer having a first part and a second part;

[0236] A second semiconductor layer adjacent to the first semiconductor layer;

[0237] A plurality of segments of a third semiconductor layer, each of the plurality of segments being adjacent to the second semiconductor layer,

[0238] A PIN region formed by the first semiconductor layer, the second semiconductor layer, and the third semiconductor layer; and

[0239] A depletion region formed by a reverse bias applied to the PIN region, the depletion region including a portion of the second semiconductor layer, and the depletion region being configured to generate a plurality of detector signals based on a first subset of a plurality of signal electrons captured within the depletion region.

[0240] Wherein a second portion of the first semiconductor layer is not depleted and is configured to provide an energy barrier to block a second subset of the plurality of signal electrons and is configured to allow the first subset of the plurality of signal electrons to pass through to reach the depletion region.

[0241] 81. The detector according to clause 80, wherein the depletion region further includes a first portion of the first semiconductor layer.

[0242] 82. The detector according to any one of clauses 80 and 81, wherein the depletion region further includes a portion of the third semiconductor layer.

[0243] 83. The detector according to any one of clauses 80-82, wherein the portion of the second semiconductor layer includes the entirety of the second semiconductor layer.

[0244] 84. The detector according to any one of clauses 80-83, wherein the first subset of the plurality of signal electrons includes electrons having a high enough energy to pass through the energy barrier.

[0245] 85. The detector according to any one of clauses 80-84, wherein the second subset of the plurality of signal electrons includes electrons having an energy insufficient to pass through the energy barrier.

[0246] 86. The detector according to any one of clauses 80-85, wherein the plurality of detector signals are generated based on a first set of internal electrons generated by an interaction between the plurality of signal electrons and the second portion of the first semiconductor layer.

[0247] 87. The detector according to clause 86, wherein the first set of internal electrons includes electrons having a high enough energy to pass through the energy barrier.

[0248] 88. The detector according to any one of clauses 86 and 87, wherein the second portion of the first semiconductor layer is further configured to prevent a second set of internal electrons from reaching the depletion region, wherein the second set of internal electrons is generated by an interaction between the plurality of signal electrons and the second portion of the first semiconductor layer and has an energy insufficient to pass through the energy barrier.

[0249] 89. The detector according to any one of clauses 80-88, wherein the first semiconductor layer is doped with a dopant, and the cut-off energy level of the energy barrier of the first semiconductor layer is determined by the doping concentration in the first semiconductor layer or the thickness of the first semiconductor layer.

[0250] 90. The detector according to any one of clauses 80 - 89, wherein the plurality of detector signals are generated based on electron - hole pairs generated by a first subset of a plurality of signal electrons within the depletion region.

[0251] 91. The detector according to clause 90, wherein one of the plurality of detector signals is generated based on a subset of electron - hole pairs captured by a corresponding segment among a plurality of segments of a third semiconductor layer.

[0252] 92. The detector according to clause 91, wherein the corresponding segment is the segment closest to the position where the subset of electron - hole pairs is generated.

[0253] 93. The detector according to clause 91, wherein the corresponding segment is determined by an electric field generated by reverse biasing within the PIN region.

[0254] A non - transitory computer - readable medium can be provided to store instructions for a processor of a controller (e.g., Figure 1 controller 50) to perform charged particle beam detection, image processing, adjusting bias voltage, switching between various filtering modes, moving an external passive energy filter (e.g., Figures 6A - 6E filter 632) 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 drive devices, magnetic tapes or any other magnetic data - storage media, compact disc read - only memory (CD - ROM), any other optical data - storage media, any physical medium with a hole pattern, random access memory (RAM), programmable read - only memory (PROM), and erasable programmable read - only memory (EPROM), FLASH - EPROM or any other flash memory, non - volatile random access memory (NVRAM), cache, registers, any other memory chip or cartridge, and their networked versions.

[0255] It should be understood that the embodiments of the present disclosure are not limited to the exact configurations described above and illustrated in the drawings, and various modifications and changes can be made without departing from the scope of the present disclosure. The present disclosure has been described in connection with various embodiments, and other embodiments of the present invention will be apparent to those skilled in the art in view of the specification and practice of the invention disclosed herein. The specification and embodiments are to be considered as exemplary only, and the true scope and spirit of the invention are indicated by the appended claims.

[0256] The above description is intended to be illustrative and not restrictive. Thus, it will be apparent to those skilled in the art that modifications can be made as described without departing from the scope of the claims set forth below.

Claims

1. An electronic detector for detecting a plurality of signal electrons generated from a sample, comprising: a first semiconductor layer having a first part and a second part; a second semiconductor layer adjacent to the first semiconductor layer; a third semiconductor layer adjacent to the second semiconductor layer; a PIN region formed by the first semiconductor layer, the second semiconductor layer, and the third semiconductor layer; a power supply configured to apply a reverse bias between the first semiconductor layer and the third semiconductor layer; and a depletion region formed within the PIN region by the reverse bias, the depletion region including a part of the second semiconductor layer, and the depletion region being configured to generate a detector signal based on a first subset of the plurality of signal electrons captured within the depletion region, wherein the second part of the first semiconductor layer is not depleted, and the second part is configured to provide an energy barrier to block a second subset of the plurality of signal electrons, and the second part is configured to allow the first subset of the plurality of signal electrons to pass through to reach the depletion region.

2. The detector according to claim 1, wherein the depletion region further includes the first part of the first semiconductor layer.

3. The detector according to claim 1, wherein the depletion region further includes a part of the third semiconductor layer.

4. The detector according to claim 1, wherein the part of the second semiconductor layer includes the entirety of the second semiconductor layer.

5. The detector according to claim 1, wherein the first subset of the plurality of signal electrons includes electrons having high enough energy to pass through the energy barrier.

6. The detector according to claim 1, wherein the second subset of the plurality of signal electrons includes electrons having insufficient energy to pass through the energy barrier.

7. The detector according to claim 1, wherein the detector signal is further affected by a first set of internal electrons generated by an interaction between the plurality of signal electrons and the second part of the first semiconductor layer.

8. The detector according to claim 7, wherein the first set of internal electrons includes electrons having high enough energy to pass through the energy barrier.

9. The detector according to claim 7, wherein the second part of the first semiconductor layer is further configured to prevent a second set of internal electrons from reaching the depletion region, wherein the second set of internal electrons is generated by an interaction between the plurality of signal electrons and the second part of the first semiconductor layer, and the second set of internal electrons has insufficient energy to pass through the energy barrier.

10. The detector according to claim 1, wherein the first semiconductor layer is doped with a dopant, and a cut-off energy level of the energy barrier of the first semiconductor layer is determined by a doping concentration in the first semiconductor layer, a thickness of the first semiconductor layer, or a reverse bias voltage applied by the power supply.

11. The detector according to claim 7, wherein the detector signal is generated based on electron-hole pairs generated by the first subset of the plurality of signal electrons or the first set of internal electrons within the depletion region.

12. The detector according to claim 1, wherein the first semiconductor layer is doped with a p-type dopant, and the second and third semiconductor layers are doped with an n-type dopant.

13. The detector according to claim 12, wherein the electric potential near the first semiconductor layer is lower than the electric potential near the third semiconductor layer.

14. The detector according to claim 1, wherein the first semiconductor layer is doped with an n-type dopant, and the second and third semiconductor layers are doped with a p-type dopant.

15. A method for manufacturing an electron detector having an energy barrier that filters electrons based on the energy of the electrons, the method comprising: providing a semiconductor substrate having: a first portion; a second portion adjacent to the first portion; and a third portion adjacent to the second portion; forming a first semiconductor layer by doping the first portion of the substrate with a first type of dopant; forming a third semiconductor layer by doping the third portion of the substrate with a second type of dopant; and forming a second semiconductor layer in the second portion of the substrate, wherein the doping concentration of the first type of dopant in the first semiconductor layer is determined to configure the energy barrier of the electron detector, and the thickness of the first semiconductor layer is determined to further configure the energy barrier of the electron detector.

16. A charged particle beam apparatus for inspecting a sample, comprising: a charged particle beam source configured to emit a charged particle beam along a main optical axis; an objective lens configured to focus the charged particle beam onto the sample; and the electron detector according to claim 1, configured to detect a plurality of signal electrons generated from the charged particle beam incident on the sample.

17. The apparatus according to claim 16, further comprising a passive energy filter between the electron detector and the sample.

18. The apparatus according to claim 16, further comprising a passive energy filter movable between a first position and a second position, wherein: when the apparatus operates in a high filtering mode, the passive energy filter is positioned at the first position between the sample and the electron detector, and the passive energy filter is configured to filter a first subset of the plurality of signal electrons, and when the apparatus operates in a low filtering mode, the passive energy filter is positioned at the second position away from the electron detector, and the passive energy filter is configured to allow a second subset of the plurality of signal electrons to pass through to reach the electron detector, wherein the second subset of the plurality of signal electrons includes electrons having energy levels similar to those of the first subset of the plurality of signal electrons.

19. The apparatus according to claim 18, wherein the passive energy filter is configured to provide a first external energy barrier in addition to the energy barrier of the electron detector to filter the first subset of the plurality of signal electrons in the high filtering mode.

20. The apparatus according to claim 19, wherein when the apparatus operates in the high filtering mode, it is configured to filter the first subset of the plurality of signal electrons: the first subset has an energy lower than the sum of the energy barrier of the electron detector and the first external energy barrier of the passive energy filter.

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