Charged particle detecting device, detecting method and scanning electron microscope

Abstract

The application discloses a charged particle detection device, a detection method and a scanning electron microscope. The charged particle detection device comprises a scintillator unit, a light guide tube unit and a photomultiplier tube unit. The scintillator unit is used for collecting received charged particles and converting the charged particles into optical signals. The light guide tube unit is used for transmitting the optical signals. The light guide tube unit comprises a front end and a rear end. The front end comprises a concave part and a plane part. The plane part is connected with the scintillator unit. The rear end is connected with the photomultiplier tube unit. The photomultiplier tube unit is used for receiving the optical signals. In the application, the front end of the light guide tube unit comprises the concave part. The structure of the concave part enables more optical signals, especially the optical signals with an incident angle less than the critical angle of the rear end of the light guide tube unit, to be reflected to the rear end of the light guide tube unit through the front end of the light guide tube unit and to reach the photomultiplier tube unit, thereby achieving the effect that the brightness of the image of the sample surface is more uniform.

Description

Technical Field

[0001] This application generally relates to the field of scanning electron microscopy. More specifically, this application relates to a charged particle detection device, detection method, and scanning electron microscope. Background Technology

[0002] A scanning electron microscope (SEM) is a precision analytical instrument that uses an electron beam to scan the surface of a sample, thereby obtaining information about the sample's microstructure and structure. In an SEM, an electron beam emitted by an electron source is focused into an ultrafine probe that scans the sample surface line by line. The signal electrons emitted by the sample, including secondary electrons and backscattered electrons, are collected by a charged particle detector. The signal intensity of the signal electrons is converted into a grayscale image, thus forming an image of the sample surface.

[0003] Currently, common charged particle detection devices are detectors that combine scintillators, light guides, and photomultiplier tubes. Signal electrons released from the sample surface strike the front surface of the scintillator, which excites a light signal. The light signal is reflected from the front end of the light guide to the rear end of the light guide, and then transmitted to the photomultiplier tube through total internal reflection at the rear end of the light guide.

[0004] However, the front end of a light guide is typically a planar or convex structure. A portion of the light signal bypasses reflection at the front end and directly enters the rear end. Since the incident angle is less than the critical angle at the rear end, the light signal exits the light guide and fails to reach the photomultiplier tube, resulting in uneven brightness in the image of the sample surface. Therefore, reducing the amount of light exiting the light guide to achieve more uniform brightness in the image of the sample surface has become a pressing problem. Summary of the Invention

[0005] In order to at least solve one or more of the technical problems mentioned above, this application proposes a charged particle detection device, detection method and scanning electron microscope in several aspects.

[0006] In a first aspect, this application provides a charged particle detection device, comprising: a scintillator unit, a light guide unit, and a photomultiplier tube unit; the scintillator unit is used to collect received charged particles and convert the charged particles into optical signals; the light guide unit is used to transmit the optical signals, the light guide unit includes a front end and a rear end, the front end includes a concave portion and a planar portion, the planar portion is connected to the scintillator unit, and the rear end is connected to the photomultiplier tube unit; the photomultiplier tube unit is used to receive the optical signals.

[0007] In some embodiments, the concave portion includes a left curved portion and a right curved portion along a first direction, wherein the slope of the left curved portion is smaller than the slope of the right curved portion.

[0008] In some embodiments, the angle between the left curved surface portion and the flat surface portion is 15 to 40 degrees, and the angle between the right curved surface portion and the rear end is 100 to 140 degrees.

[0009] In some embodiments, the concave portion is coated with a reflective coating.

[0010] In some embodiments, the projected length of the concave portion onto the planar portion is related to the material of the light guide unit.

[0011] In some embodiments, the charged particle detection device further includes a metal tube, the scintillator unit has a central hole, the light guide unit has a through hole, and the central hole, the through hole, and the metal tube are collinear.

[0012] In some embodiments, the rear end includes a prism structure and a rotating body structure. The prism structure is connected to the front end. The first end of the rotating body structure is the inscribed circle of the prism structure, and the second end is a circle equal to the incident surface of the photomultiplier tube. The second end is connected to the photomultiplier tube unit.

[0013] The rear end is a rotating structure, and the rear end and the planar part are smoothly connected by a circular arc transition surface.

[0014] In a second aspect, this application provides a charged particle detection method applied to the charged particle detection device of the first aspect. The charged particle detection method includes: emitting an electron beam, focusing the electron beam onto the surface of a sample, and exciting the sample to generate charged particles; converting the charged particles into optical signals through a scintillator unit; transmitting the optical signals through a light guide unit, wherein the optical signals enter the light guide unit through a planar portion, are reflected by a concave portion of the light guide unit, and are transmitted to the rear end of the light guide unit; and receiving the optical signals through a photomultiplier tube unit.

[0015] In some embodiments, emitting an electron beam specifically includes emitting an electron beam such that the electron beam passes through a metal tube to reach the surface of the sample, wherein the metal tube is collinear with the center hole of the scintillator unit and the center of the through hole of the light guide unit.

[0016] In a third aspect, this application provides a scanning electron microscope, which includes the charged particle detection device of the first aspect.

[0017] According to the charged particle detection device, detection method, and scanning electron microscope provided above, the front end of the light guide unit in this embodiment of the application is a concave part and a planar part. The planar part is connected to the scintillator unit. The light signal from the scintillator unit enters the planar part and reaches the concave part. The concave structure enables more light signals, especially light signals from the right side of the scintillator unit with an incident angle smaller than the critical angle at the rear end of the light guide unit, to enter the rear end of the light guide unit after reflection by the concave surface, thereby reaching the photomultiplier tube unit. This improves the light signal collection efficiency of the light guide, especially the collection efficiency of light signals from the right side of the scintillator unit. It solves the problem of "bright left and dark right" image of the sample surface in the prior art and achieves a more uniform brightness effect in the image of the sample surface.

[0018] Furthermore, in some embodiments, the rear end of the light guide unit includes a prism structure and a rotating body structure. The prism structure is connected to the front end, and the first end of the rotating body structure is the inscribed circle of the prism structure, and the second end is a circle equal to the incident surface of the photomultiplier tube. The second end is connected to the photomultiplier tube unit, which can better connect the light guide unit and the photomultiplier tube unit.

[0019] Furthermore, in some embodiments, the rear end of the light guide unit is a rotating structure, and the rear end is smoothly connected to the planar part through an arc transition surface. This can reduce the energy loss of some light signals due to multiple reflections caused by the prism structure when the light signal is transmitted in the light guide unit, thereby improving the transmission efficiency of the light signal in the light guide unit and achieving a brighter image of the sample surface. Attached Figure Description

[0020] The above and other objects, features, and advantages of exemplary embodiments of this application will become readily understood by reading the following detailed description with reference to the accompanying drawings. In the drawings, several embodiments of this application are illustrated by way of example and not limitation, and the same or corresponding reference numerals denote the same or corresponding parts, wherein:

[0021] Figure 1 Exemplary application scenarios of embodiments of this application are shown; Figure 2 An exemplary process for the transmission of optical signals in a light guide unit in the prior art is illustrated; Figure 3 Schematic diagrams of charged particle detection devices according to some embodiments of this application are shown; Figure 4 A schematic diagram illustrating the transmission of optical signals in a light guide unit according to some embodiments of this application is shown; Figure 5 Examples of projected views of concave portions of some embodiments of this application are shown; Figure 6This diagram illustrates the image simulation effect of the sample surface based on existing technology. Figure 7 The diagram shows a simulated image of a sample surface based on some embodiments of this application. Figure 8 Schematic diagrams of the optical guide unit in some embodiments of this application are shown; Figure 9 Simulation diagrams of the optical signal transmission effect in the optical guide unit in some embodiments of this application are shown; Figure 10 A schematic diagram of another optical guide unit in some embodiments of this application is shown; Figure 11 A cross-sectional schematic diagram of another optical guide unit in some embodiments of this application is shown; Figure 12 The following are schematic diagrams illustrating simulation results of optical signal transmission efficiency based on existing structures in some embodiments of this application; Figure 13 The following are schematic diagrams illustrating simulation results of optical signal transmission efficiency based on a rotating body structure in some embodiments of this application; Figure 14 A flowchart of a charged particle detection method provided by some embodiments of this application is shown. Detailed Implementation

[0022] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of this application. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0023] It should be understood that the terms "comprising" and "including" used in the specification and claims of this application indicate the presence of the described features, integrals, steps, operations, elements and / or components, but do not exclude the presence or addition of one or more other features, integrals, steps, operations, elements, components and / or collections thereof.

[0024] It should also be understood that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the application. As used in this specification and claims, the singular forms “a,” “an,” and “the” are intended to include the plural forms unless the context clearly indicates otherwise. It should also be understood that the term “and / or” as used in this specification and claims refers to any combination and all possible combinations of one or more of the associated listed items, and includes such combinations.

[0025] As used in this specification and claims, the term "if" may be interpreted, depending on the context, as "when," "once," "in response to determination," or "in response to detection." Similarly, the phrase "if determined" or "if [described condition or event] is detected" may be interpreted, depending on the context, as "once determined," "in response to determination," "once [described condition or event] is detected," or "in response to detection of [described condition or event]."

[0026] The specific embodiments of this application will now be described in detail with reference to the accompanying drawings.

[0027] Exemplary application scenarios A scanning electron microscope (SEM) is a precision analytical instrument that uses an electron beam to scan the surface of a sample, thereby obtaining information about the sample's microstructure and morphology. In an SEM, an electron beam emitted by an electron source is focused into an ultrafine probe, which scans the sample surface line by line using a deflector. The signal electrons emitted by the sample are collected by a charged particle detector. These signal electrons include secondary electrons (SE) and backscattered electrons (BSE). The signal intensity of the signal electrons can be converted into the grayscale value of the image pixels at the probe's position on the sample surface, thus obtaining a grayscale image formed by the electron probe scanning, which forms an image of the sample surface.

[0028] Charged particle detection devices are an indispensable part of SEM, including in-lens detectors and side-mounted secondary electron detectors (Everhart-Thornley detectors, or ET detectors for short). Among them, the in-lens detector is a high-energy charged particle detector built into the objective lens optical path in SEM. Its core advantage is ultra-high resolution surface imaging, especially suitable for the high-resolution and low-voltage scenarios of field emission SEM.

[0029] Currently, common in-lens detectors combine a scintillator, a light guide, and a photomultiplier tube (PMT). The front end of the light guide is connected to the scintillator, and the rear end is coupled to the photomultiplier tube. Signal electrons released from the sample surface strike the scintillator, pass through the scintillator's incident surface, and generate a light signal. The light signal is reflected from the front end of the light guide to the rear end, where it undergoes total internal reflection and is transmitted to the photomultiplier tube.

[0030] Figure 1 Exemplary application scenarios of embodiments of this application are shown.

[0031] Figure 1 This demonstrates a typical SEM system, in Figure 1 In the middle, above the objective lens 12 is the charged particle detection device 10, and below it is the sample 13. The charged particle detection device 10 includes a scintillator unit 14, a light guide unit 15, a photomultiplier tube unit 17, and a through hole 16 located in the scintillator unit 14 and the light guide unit 15.

[0032] When the SEM system is working, the electron source 11 emits an electron beam 18, which moves along the optical axis and impacts the surface of the sample 13 through the through-hole 16 to generate charged particles 19. The charged particles 19 include secondary electrons and backscattered electrons. The charged particles 19 impact the incident surface of the scintillator unit 14 and excite photons to generate light signals. The light signals are reflected by the light guide unit 15 and enter the photomultiplier tube unit 17. In the photomultiplier tube unit 17, they are converted into electrical signals. After processing the electrical signals, an image of the surface of the sample 13 can be obtained.

[0033] Figure 2 An exemplary process for transmitting optical signals in a light guide unit in the prior art is shown.

[0034] In the charged particle detection device 10, charged particles 19 collide with the scintillator unit 14, exciting photons and generating optical signals. The transmission of the optical signals in the optical guide unit 15 is as follows: Figure 2 As shown.

[0035] Optical signal 21 is a photon emitted from the left side of scintillator unit 14 in a certain direction. It is reflected by the first plane 151 at the front end of the light guide unit 15 and enters the rear end of the light guide unit 15. After total internal reflection by the third plane 152 and the fourth plane 153 at the rear end, it is transmitted to the photomultiplier tube unit 17. Optical signal 22 is a photon emitted from the right side of scintillator unit 14 in the same direction (parallel) to optical signal 21. Due to the angle, when optical signal 22 reaches the light guide unit 15, it is not reflected by the first plane 151, but is directly refracted by the third plane 152. This is because the incident angle of optical signal 22 is less than the critical angle of the light guide unit 15, and optical signal 22 cannot be transmitted by total internal reflection in the light guide unit 15. In other words, optical signal 22 represents a portion of the optical signal. Due to the angle, this portion of the optical signal cannot be reflected by the first plane 151. Furthermore, because the incident angle is less than the critical angle of the third plane 152 of the light guide unit 15, total internal reflection cannot occur at the third plane 152 or the fourth plane 153. Instead, it is directly refracted at the third plane 152 and thus exits directly outside the light guide unit 15, failing to reach the photomultiplier tube unit 17. The first plane 151 is generally a plane or a convex surface. Regardless of whether it is a plane or a convex surface, this portion of the optical signal, represented by optical signal 22, has the problem of exiting outside the light guide unit 15.

[0036] Therefore, the light signal represented by light signal 21 on the left side of the scintillator unit 14 can be reflected by the first plane 151 and totally reflected by the third plane 152 and the fourth plane 153, thus being transmitted to the photomultiplier tube unit 17. However, a portion of the light signal represented by light signal 22 on the right side of the scintillator unit 14 exits the light guide unit 15 due to the angle, resulting in a loss of light energy. This leads to uneven energy distribution of the light signals transmitted to the photomultiplier tube unit 17 from the left and right sides of the scintillator unit 14. The image generated by the electron beam 18 scanning the left side of the scintillator is brighter than the image generated by scanning the right side, resulting in an overall left-bright-right dark image of the sample 13 surface. Therefore, reducing the amount of light emitted outside the light guide to achieve more uniform brightness in the sample surface image is a problem that urgently needs to be solved.

[0037] Exemplary charged particle detection device In view of this, this application provides a charged particle detection device, including a scintillator unit, a light guide unit, and a photomultiplier tube unit. The scintillator unit collects received charged particles and converts them into light signals. The light guide unit transmits the light signals and includes a front end and a rear end. The front end includes a concave portion and a planar portion. The planar portion is connected to the scintillator unit, and the rear end is connected to the photomultiplier tube unit. The photomultiplier tube unit receives the light signals. This application modifies the front-end planar portion into a concave portion and a planar portion, so that light signals from the left side of the scintillator unit are reflected in the concave portion, and light signals from the right side of the scintillator unit are also reflected in the concave portion. This allows light signals from both the left and right sides of the scintillator unit to enter the light guide unit for transmission, resulting in a more uniform brightness of the sample surface image.

[0038] Figure 3 A schematic diagram of a charged particle detection device according to some embodiments of this application is shown.

[0039] exist Figure 3 In the process, the electron source 11 emits an electron beam 18, which moves along the optical axis and impacts the surface of the sample 13 through the through hole 16 to generate charged particles 19. The charged particles 19 impact the incident surface of the scintillator unit 14 to excite photons and generate light signals. The light signals enter the light guide unit 15 through the second plane 155 at the front end of the light guide unit 15. After reflection by the concave surface 154 at the front end and total internal reflection by the third plane 152 and the fourth plane 153, they enter the photomultiplier tube unit 17.

[0040] In some embodiments of this application, the scintillator unit 14 is a quartz sheet coated with crystalline material or fluorescent powder, capable of accepting charged particles 19 to excite photons. The choice of material is related to the wavelength of the excited photons, photon yield, decay time, refractive index, etc. The scintillator unit 14 needs to be fully polished according to optical processing requirements to improve light transmission efficiency and reduce diffuse stray light caused by surface roughness. To prevent stray light caused by corners, the scintillator unit 14 can be made into a thin frustum shape. A central hole can be provided at the center of the scintillator unit 14 to allow the electron beam 18 to pass through.

[0041] In this application, the incident surface and side surface of the scintillator unit 14 may be coated with a coating, wherein the incident surface may be coated with a conductive coating.

[0042] Specifically, regarding the incident surface, since charged particles 19 reach the scintillator unit 14 via the incident surface, the coating on the incident surface must be conductive. It can generally be a metal coating or a metal alloy coating, or other coatings with conductive properties. Therefore, the coating on the incident surface in this application must have good conductivity; the material used for the coating is not specified. Furthermore, since the light signal may be reflected at the incident surface during reflection from the scintillator unit 14, the coating on the incident surface also has the function of reflecting the light signal, thereby improving the transmission efficiency of the light signal. In addition, regarding the thickness of the coating on the incident surface, a moderate thickness is sufficient. Too thin a coating will cause charge accumulation, while too thick a coating will affect the arrival of charged particles 19 at the scintillator unit 14. This application does not impose specific requirements on this. For example, the coating on the incident surface can be a film, such as an aluminum film deposited on the incident surface, with a thickness between 50-100 nm.

[0043] Regarding the side surface, in this application, the scintillator unit 14 can be cylindrical or truncated conical. When the scintillator unit 14 is truncated conical, some charged particles 19 may collide with the side surface and enter the scintillator unit 14 through the side. Therefore, in some embodiments of this application, the coating on the side surface can be consistent with the coating on the incident surface, allowing charged particles 19 to pass through while also reflecting the light signal. In other embodiments of this application, the side surface may only need to reflect the light signal; therefore, the coating on the side surface only needs to reflect the light signal.

[0044] In this application, the coating can be applied using existing technical means, and this application does not impose any restrictions on this method.

[0045] In some embodiments of this application, the light guide unit 15 is made of glass. When selecting the glass material, the wavelength of the light signal excited by the scintillator unit 14 can be considered. The selected glass material can transmit the light signal of that wavelength with very high transmittance. Each surface of the light guide unit 15 also needs to be finely polished to improve light transmission efficiency. When the light guide unit 15 is connected to the scintillator unit 14, the second plane 155 at the front end of the light guide unit 15 can be connected to the emission surface of the scintillator unit 14. For example, optical glass adhesive can be used for fixing and bonding. Other connection methods can also be used in this application.

[0046] In some embodiments of this application, the second plane 155 and the fourth plane 153 at the front end of the light guide unit 15 are on the same plane. In other embodiments of this application, the second plane 155 and the fourth plane 153 at the front end of the light guide unit 15 may be a single plane.

[0047] In some embodiments of this application, the scintillator unit 14 has a central hole, the light guide unit 15 has a through hole, the through hole of the light guide unit 15 passes through the concave surface 154 and the second plane 155 at the front end of the light guide, the emission surface of the scintillator unit 14 is connected to the second plane 155 at the front end of the light guide unit 15, and the central hole of the scintillator unit 14 and the through hole of the light guide unit 15 form a through hole 16.

[0048] In some embodiments of this application, the charged particle detection device 10 further includes a metal tube ( Figure 3 (Not shown in the image), the center hole, the through hole, and the center of the metal tube are collinear. That is, the metal tube is located in the through hole 16. The metal tube is made of non-magnetic metal material, and its diameter matches the through hole 16. It can be installed and fixed in the through hole 16, for example, by adhesive bonding. Other existing methods can also be used for fixing. The metal tube provides a channel for the electron beam 18 to pass through the charged particle detection device 10, thus avoiding stray electromagnetic field interference. The lower end of the metal tube protrudes from the incident surface of the scintillator unit 14 to avoid interference from charged particles 19 flying towards the scintillator unit 14.

[0049] In some other embodiments of this application, the charged particle detection device 10 can be placed at a position where no electron beam 18 passes through, that is, the charged particle detection device 10 is far away from the optical axis, and the electron beam 18 does not need to pass through the through hole 16. Therefore, the through hole 16 can be eliminated, so the scintillator unit 14 does not need to be provided with a central hole, and the light guide unit 15 does not need to be provided with a through hole.

[0050] In some embodiments of this application, the photomultiplier tube unit 17 is a vacuum glass tube, consisting of an entrance window, a photocathode surface, a multiplication system, and an anode. After passing through the entrance window, the light signal reaches the photocathode surface. Due to the photoelectric effect, the light signal is converted into an electrical signal. This electrical signal is then multiplied by the multiplication system, and finally, a current signal is output from the anode so that an image of the surface of the sample 13 can be obtained subsequently based on the current signal.

[0051] Based on Figure 3 The description, Figure 4 A schematic diagram of optical signal transmission in a light guide unit according to some embodiments of this application is shown.

[0052] exist Figure 4 In the image, the angle between the concave surface 154 at the front end of the light guide unit 15 and the second plane 155 is angle A, and the angle between the concave surface 154 and the third plane 152 is angle B. For example... Figure 4 As shown by the solid arrow, the light signal 21 from the left side of the scintillator unit 14 enters the light guide unit 15 through the second plane 155 at the front end of the light guide unit 15, is reflected at the concave surface 154, undergoes total internal reflection at the second plane 155 and the third plane 152, and then enters the photomultiplier tube unit 17. Figure 4As shown by the dashed arrow, the light signal 22 from the right side of the scintillator unit 14 enters the light guide unit 15 through the second plane 155 at the front end of the light guide unit 15, and enters the photomultiplier tube unit 17 after being reflected by the concave surface 154.

[0053] Therefore, by changing the front end of the light guide unit 15 from the first plane 151 to the concave surface 154, this application enables the light signal 22 from the right side of the scintillator unit 14 to be reflected on the concave surface 154 (a portion of the light signal can undergo total internal reflection on the third plane 152 and the fourth plane 153 of the light guide unit). Figure 4 (Only a portion of the optical signal transmission is shown; the transmission of other optical signals is not shown.) The light signal reaches the photomultiplier tube unit 17, allowing the optical signal from the scintillator unit 14 to enter the photomultiplier tube unit 17 uniformly, thereby achieving a more uniform image brightness on the surface of the sample 13.

[0054] In this application, the concave surface 154 includes a left curved surface portion and a right curved surface portion along the first direction, and the slope of the left curved surface portion is smaller than the slope of the right curved surface portion. The concave surface 154 can be a sphere, a parabola, a hyperboloid, an ellipsoid, a surface composed of multiple broken lines, etc. This application does not make specific requirements in this regard, as long as the slope of the left curved surface portion is smaller than the slope of the right curved surface portion.

[0055] Specifically, the first direction can be the transmission direction of the optical signal in the light guide unit 15. In this application, the concave surface 154 can be divided into a left curved surface portion and a right curved surface portion along the first direction. The angle between the left curved surface portion and the second plane 155 is angle A, and the angle between the right curved surface portion and the third plane 152 is angle B. Among them, angle A is an acute angle and angle B is an obtuse angle. In this application, the concave surface 154 is designed to reduce the angles of angle A and angle B, that is, the slope of the left curved surface portion is smaller than the slope of the right curved surface portion, so as to enable the light guide unit 15 to collect more optical signals from the scintillator unit 14 and transmit them to the photomultiplier tube unit 17.

[0056] By appropriately reducing the angle A, the slope of the left curved surface portion of the concave surface 154 can be reduced. The light signal from the left side of the scintillator unit 14 can be transmitted to the photomultiplier tube unit 17 after reflection from the concave surface 154. Figure 4 The diagram illustrates the transmission of optical signal 21. By appropriately reducing angle B, the slope of the right curved portion of the concave surface 154 can be increased, allowing the optical signal from the right side of the scintillator unit 14 to be reflected by the concave surface 154 as much as possible. This results in more optical signal from the right side of the scintillator unit 14 being transmitted to the photomultiplier tube unit 17, such as... Figure 4The transmission of light signal 22 shown in the figure achieves the beneficial effect that the light signals on the left and right sides of the scintillator unit 14 enter the photomultiplier tube unit 17 more evenly, thereby making the brightness of the image on the surface of the sample 13 more uniform.

[0057] Furthermore, simulations show that the angle between the left curved surface and the second plane 155 can be between 15 and 40 degrees, with a better effect when the angle between the left curved surface and the plane is between 20 and 30 degrees. That is, the value of angle A is between 15 and 40 degrees, preferably between 20 and 30 degrees. The angle between the right curved surface and the third plane 152 is between 100 and 140 degrees, meaning the value of angle B is between 100 and 140 degrees.

[0058] Specifically, the setting of angle A is related to the diameter of scintillator unit 14 and the diameter of photomultiplier tube unit 17. The larger the diameter of photomultiplier tube unit 17, the larger the angle A will be, provided that the diameter of scintillator unit 14 remains unchanged.

[0059] Table 1 shows some simulation results of the relationship between diagonal A and optical signal transmission efficiency in this application.

[0060]

[0061] Analysis of Table 1 shows that an angle A greater than 20 degrees has a better effect. In some embodiments of this application, the angle A can be set to 20 to 30 degrees.

[0062] In some embodiments of this application, a reflective coating may be applied to the concave surface 154 to improve the reflectivity of the optical signal. In this application, the reflective coating can be a film, for example, an aluminum film, typically with a thickness between 50-100 nm. This application does not limit the film thickness. Similarly, this application does not limit the material of the reflective coating, as long as it can improve the reflectivity of the optical signal. Alternatively, this application may also employ other existing methods to apply the reflective coating.

[0063] In some embodiments of this application, the projected length a of the concave surface 154 on the second plane 155 is related to the material of the light guide unit 15.

[0064] Specifically, such as Figure 5 As shown, Figure 5 Example projection diagrams of concave portions of some embodiments of this application are shown.

[0065] exist Figure 5In the process, another portion of the light signal, represented by the light signal 23 on the right side of the scintillator unit 14, can undergo total internal reflection on the third plane 152 of the light guide unit 15 after entering the light guide unit 15 from the scintillator unit 14, because the incident angle is greater than the critical angle of the light guide unit 15, and thus enter the photomultiplier tube unit 17. That is, the light signals excited by the scintillator unit 14 are divided into the following types: light signal 21 on the left side of the scintillator unit 14, light signal 22 on the right side, and light signal 23. Among them, the light signal represented by light signal 21 can be reflected by the concave surface 154, transmitted through the light guide unit 15, and enter the photomultiplier tube unit 17. The light signal represented by light signal 22 can also be reflected by the concave surface 154, transmitted through the light guide unit 15, and enter the photomultiplier tube unit 17. However, the light signal represented by light signal 23, because the incident angle is greater than the critical angle of the light guide unit 15, undergoes total internal reflection on the third plane 152 of the light guide unit 15 and thus enters the photomultiplier tube unit 17.

[0066] Therefore, the length of the concave surface 154 can be set in this application so that light signals with angles smaller than the critical angle, represented by light signal 22 on the right side of the scintillator unit 14, can be reflected by the concave surface 154. Obviously, the length of the concave surface 154 is related to the size of the scintillator unit 14 and the critical angle of the light guide unit 15. Since the scintillator unit 14 is connected to the second plane 155, the minimum value of the projection length a of the length of the concave surface 154 onto the second plane 155 cannot be less than the size of the exit surface of the scintillator unit 14 (i.e., the diameter of the exit surface). The maximum value of the projection length a is related to the critical angle of the light guide unit 15. Based on the principle of total internal reflection, the critical angle of the light guide unit 15 is related to the material of the light guide unit. Furthermore, the critical angle of the light guide unit 15 is related to the materials of the light guide unit 15 and the scintillator unit 14, that is, the projection length a is related to the materials of the light guide unit 15 and the scintillator unit 14.

[0067] When selecting the material for the light guide unit 15, the higher the glass refractive index, the better, provided that the selected material can transmit photons of a specific wavelength excited by the scintillator unit 14 with high transmittance. According to the total internal reflection formula, the critical angle of total internal reflection is inversely proportional to the refractive index of the optically dense medium (here, the glass material of the light guide unit 15). The higher the refractive index, the smaller the critical angle of total internal reflection, the more light can undergo total internal reflection, and the more energy is ultimately transmitted to the photomultiplier tube unit 17.

[0068] In addition, since the front end of the light guide unit 15 is a concave structure (i.e., concave surface 154), this concave structure not only satisfies the requirement that the light signal represented by the light signal 22 on the right side of the scintillator unit 14 be reflected into the light guide unit 15, but also effectively reduces the height h of the light guide unit 15. Thus, compared with the existing technical solutions, the concave structure can more effectively reduce the structural size of the light guide unit 15.

[0069] Based on the above description, this application also performed simulation calculations, see [link to relevant documentation]. Figure 6 and Figure 7 . Figure 6 This diagram illustrates the image simulation effect of the sample surface based on existing technology. Figure 7 A schematic diagram illustrating the image simulation effect of a sample surface based on some embodiments of this application is shown.

[0070] exist Figure 6 In the image, it is clearly visible that the image on the left side of the sample surface is brighter than the image on the right side, and the overall brightness distribution is uneven. Figure 7 Based on the above description, this application modifies the front end of the light guide unit to a concave structure and obtains the sample surface image through simulation calculation of the light signal. Comparative analysis of the simulation results shows that the contrast between the left and right images of the sample surface decreases, while the uniformity of brightness between the left and right images improves.

[0071] In some embodiments of this application, the rear end of the light guide unit 15 includes a prism structure and a rotating body structure. The prism structure is connected to the front end. The first end of the rotating body structure is the inscribed circle of the prism structure, and the second end is a circle equal to the incident surface of the photomultiplier tube. The second end is connected to the photomultiplier tube unit.

[0072] Figure 8 Schematic diagrams of the optical guide unit in some embodiments of this application are shown. For example... Figure 8 As shown, the rear end of the light guide unit 15 includes a prism structure 156 and a rotating body structure (hereinafter referred to as the first rotating body 157). The prism structure 156 is a square prism, such as a cuboid; the first rotating body 157 can be a cylinder or a frustum of a cone, depending on the area of ​​its two ends. One end of the prism structure 156 is connected to the front end of the light guide unit 15, with angles A and B between it and the front end, respectively, and the other end is connected to the first rotating body 157. Along the direction of light signal transmission, the first end of the first rotating body 157 is the inscribed circle of the prism structure 156, and the second end is connected to the photomultiplier tube unit 17. In this application, to better couple the first rotating body 157 with the photomultiplier tube unit 17 and facilitate installation, the second end is designed as a circle equal to the incident surface of the photomultiplier tube unit 17. In this application, through... Figure 8The structure of the light guide unit 15 shown allows for better coupling with the photomultiplier tube unit 17, making installation more convenient and advantageous.

[0073] against Figure 8 The structural diagram of the optical guide unit 15 shown is presented. Simulation results were performed in this application, and the simulation results are as follows: Figure 9 As shown, Figure 9 Simulation diagrams of the optical signal transmission effect in the optical guide unit in some embodiments of this application are shown.

[0074] Depend on Figure 9 It is known that when the rear end of the light guide unit 15 is a prism structure 156, such as a cuboid composed of four planes, the corners at the connections between the planes can easily trap the light signal. This means the light signal undergoes continuous reflection at the corners, resulting in energy attenuation, or it may exit the light guide unit 15 directly during one of the reflections, thus causing a loss of light energy. Furthermore, the discontinuity between the prism structure 156 and the first rotating body 157 also leads to a loss of some light signal energy. This loss of light signal energy reduces the transmission efficiency of the light guide unit 15, which, in turn, reduces the image brightness of the sample surface.

[0075] Therefore, in some embodiments of this application, in order to improve the transmission efficiency of optical signals in the optical guide unit and enhance the image brightness of the sample surface, the structure of the optical guide unit has been improved. Specifically, the rear end of the optical guide unit is entirely replaced with another rotating body structure, which is smoothly connected to the front planar portion via a circular arc transition surface. For example... Figure 10 , Figure 11 As shown, Figure 10 A schematic diagram of another optical guide unit in some embodiments of this application is shown. Figure 11 A cross-sectional schematic diagram of another light guide unit in some embodiments of this application is shown.

[0076] exist Figure 10 as well as Figure 11In this design, the rotating body structure (hereinafter referred to as the second rotating body 158) is the rear end of the light guide unit 15. Along the direction of light signal transmission, the first end of the second rotating body 158 is connected to the concave surface 154 and to the second plane 155 through the arc transition surface 159. The second end is connected to the photomultiplier tube unit 17. The angle between the arc transition surface 159 and the rear end of the light guide unit 15 is greater than 90 degrees. The second rotating body 158 can be a cylindrical or frustum structure depending on the area of ​​its two ends. The size of the first end is related to the length of the concave surface 154 of the light guide unit 15, the projected length a of the second plane 155, and the height h of the light guide unit 15. In this application, to facilitate better coupling between the second rotating body 158 and the photomultiplier tube unit 17 and to make installation easier, the second end is designed as a circle equal to the incident surface of the photomultiplier tube unit 17.

[0077] In this application, the arc transition surface 159 can be a smooth transition between the first end of the second rotating body 158 and the second plane 155, which is beneficial to suppress stray light. At the same time, in actual production and use, it can reduce the occurrence of light guide unit breakage due to material, structure and other reasons, and maintain the stability of light guide unit 15.

[0078] This application was passed Figure 10 , Figure 11 The rear end of the light guide unit 15 shown is changed to a rotating structure. On the one hand, it can be better coupled with the photomultiplier tube unit 17, making installation more convenient and advantageous. On the other hand, it can reduce the situation where light signals are easily reflected multiple times and directly emitted at the corners of the light guide unit 15, resulting in energy loss, thereby improving the transmission efficiency of light signals and enhancing the image brightness of the sample surface.

[0079] Based on the above description, this application has undergone simulation. Figure 12 The following are schematic diagrams illustrating simulation results of optical signal transmission efficiency based on existing structures in some embodiments of this application; Figure 13 The diagram illustrates simulation results of optical signal transmission efficiency based on a rotating body structure in some embodiments of this application. The simulation results are as follows: Figure 12 and Figure 13 As shown, both the transmission efficiency and uniformity of the optical signal have been improved.

[0080] Based on the above description of the charged particle detection device, this application also provides a charged particle detection method, such as... Figure 14 As shown, Figure 14 A flowchart of a charged particle detection method provided by some embodiments of this application is shown.

[0081] This application provides a charged particle detection method, applied to the aforementioned charged particle detection device, comprising: S310: emitting an electron beam and focusing the electron beam onto the surface of a sample to excite the sample to generate charged particles; S320: converting the charged particles into optical signals through a scintillator unit; S330: transmitting the optical signals through a light guide unit, wherein the optical signals enter the light guide unit through the planar portion of the light guide unit, are reflected by the concave portion of the light guide unit, and are transmitted to the rear end of the light guide unit; S340: receiving the optical signals through a photomultiplier tube unit.

[0082] Specifically, the light guide unit in this application includes a front end and a rear end. The front end includes a concave portion and a planar portion. The planar portion is connected to the scintillator unit, and the rear end is connected to the photomultiplier tube unit. An electron beam can be emitted by an electron source, causing the electron beam to move along the optical axis and impact the sample surface through a through-hole to generate charged particles. The charged particles impact the incident surface of the scintillator unit, exciting photons and generating an optical signal. The optical signal enters the light guide unit through the planar portion at the front end. After reflection by the concave portion at the front end and total internal reflection by the planar portion at the rear end, it enters the photomultiplier tube unit, where it is converted into an electrical signal. After processing the electrical signal, an image of the sample surface can be obtained. The scintillator unit has a central hole, and the light guide unit has a through hole. The through hole of the light guide unit passes through the concave and planar portions at the front end of the light guide unit. The exit surface of the scintillator unit is connected to the planar portion at the front end of the light guide unit. The central hole of the scintillator unit and the through hole of the light guide unit form a through hole. The charged particle detection device also includes a metal tube, with the central hole, through hole, and metal tube centered collinear. The concave portion includes a left curved portion and a right curved portion along the first direction, and the slope of the left curved portion is smaller than the slope of the right curved portion.

[0083] Furthermore, by appropriately reducing the slope of the left curved surface portion of the concave section, the light signal from the left side of the scintillator unit can be transmitted to the photomultiplier tube unit after reflection through the concave section. By appropriately increasing the slope of the right curved surface portion of the concave section, the light signal from the right side of the scintillator unit can be reflected through the concave section as much as possible, thereby transmitting more light signal from the right side of the scintillator unit to the photomultiplier tube unit. This achieves a more uniform light signal transmission from both the left and right sides of the scintillator unit into the photomultiplier tube unit, resulting in a more uniform brightness of the image on the sample surface. Moreover, compared with existing solutions, the concave structure design allows for a lower height of the light guide unit when the light signal on the right side of the scintillator unit reaches the critical angle of total internal reflection, reducing the size of the light guide unit while ensuring the light signal transmission energy.

[0084] Furthermore, this application modifies the rear end of the light guide unit into a rotating body structure. The first end of the rotating body structure better connects the concave part and the planar part connected to the scintillator unit, and the second end better connects to the photomultiplier tube unit. The frustum or cylindrical shape better transmits light signals, reducing the light signal energy loss caused by multiple reflections easily generated by the square prism, and effectively improving the light transmission efficiency.

[0085] In some embodiments of this application, a scanning electron microscope (SEM) is also provided, which includes the aforementioned charged particle detection device. The charged particle detection device is mounted within the SEM. Specifically, integrating the charged particle detection device into the SEM makes the light signal converted and transmitted by the charged particles more uniform, thereby achieving a more uniform image brightness on the sample surface. Simultaneously, it reduces energy loss during light signal transmission, improves light signal transmission efficiency, and makes the image brightness of the sample surface brighter. Further details regarding the charged particle detection device can be found in the above description, and will not be repeated here.

[0086] While numerous embodiments of this application have been shown and described herein, it will be apparent to those skilled in the art that such embodiments are provided by way of example only. Many modifications, alterations, and alternatives will arise for those skilled in the art without departing from the spirit and intent of this application. It should be understood that various alternatives to the embodiments of this application described herein may be employed in the practice of this application. The appended claims are intended to define the scope of protection of this application and therefore cover equivalents or alternatives within the scope of these claims.

Claims

1. A charged particle detection device, characterized in that, The charged particle detection device includes: a scintillator unit, a light guide unit, and a photomultiplier tube unit; The scintillator unit is used to collect the received charged particles and convert the charged particles into light signals; The light guide unit is used to transmit the optical signal. The light guide unit includes a front end and a rear end. The front end includes a concave portion and a planar portion. The planar portion is connected to the scintillator unit, and the rear end is connected to the photomultiplier tube unit. The photomultiplier tube unit is used to receive the optical signal.

2. The charged particle detection device according to claim 1, characterized in that, The concave portion includes a left curved portion and a right curved portion along the first direction, wherein the slope of the left curved portion is smaller than the slope of the right curved portion.

3. The charged particle detection device according to claim 2, characterized in that, The angle between the left curved surface portion and the flat surface portion is 15 to 40 degrees, and the angle between the right curved surface portion and the rear end portion is 100 to 140 degrees.

4. The charged particle detection device according to claim 1, characterized in that, The concave portion is coated with a reflective coating.

5. The charged particle detection device according to claim 1, characterized in that, The projection length of the concave portion onto the planar portion is related to the material of the light guide unit.

6. The charged particle detection device according to claim 1, characterized in that, The charged particle detection device further includes a metal tube, the scintillator unit has a central hole, the optical guide unit has a through hole, and the central hole, the through hole, and the metal tube are collinear.

7. The charged particle detection device according to claim 1, characterized in that, The rear end includes a prism structure and a rotating body structure. The prism structure is connected to the front end. The first end of the rotating body structure is the inscribed circle of the prism structure, and the second end is a circle equal to the incident surface of the photomultiplier tube. The second end is connected to the photomultiplier tube unit.

8. The charged particle detection device according to claim 1, characterized in that, The rear end is a rotating structure, and the rear end and the planar part are smoothly connected by a circular arc transition surface.

9. A method for detecting charged particles, applied to the charged particle detection device according to any one of claims 1-8, characterized in that, The charged particle detection method includes: An electron beam is emitted and focused onto the surface of the sample, exciting the sample to generate charged particles; The charged particles are converted into optical signals by a scintillator unit; The optical signal is transmitted through the optical guide unit, wherein the optical signal enters the optical guide unit through the planar portion of the optical guide unit, is reflected by the concave portion of the optical guide unit, and is transmitted to the rear end of the optical guide unit; The optical signal is received by a photomultiplier tube unit.

10. The charged particle detection method according to claim 9, characterized in that, The emission of an electron beam specifically includes: An electron beam is emitted so that it passes through a metal tube to reach the surface of the sample, wherein the metal tube is collinear with the center hole of the scintillator unit and the center of the through hole of the light guide unit.

11. A scanning electron microscope, characterized in that, The scanning electron microscope includes the charged particle detection device according to any one of claims 1-8.

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