Charged particle detector and scanning electron microscope

Abstract

To provide a charged particle detector capable of achieving reduction in thickness and improvement in assembly accuracy.SOLUTION: A charged particle detector 30 includes: MCPs 51 and 52; an anode electrode 55 that collects electrons output from the MCPs 51 and 52; a first plate part 61 and a second plate part 63 that sandwich the MCPs 51 and 52 and the anode electrode 55 between each other in a direction D; and a spacer 64 disposed between the first plate part 61 and the second plate part 63 so as to overlap the MCPs 51 and 52 when viewed from a direction perpendicular to the direction D. A first screw hole 64a and a second screw hole 64b are formed in the spacer 64, and the first plate part 61 is fixed to the spacer 64 by screwing a first screw 65 penetrating the first plate part 61 into the first screw hole 64a, and the second plate part 63 is fixed to the spacer 64 by screwing a second screw 66 penetrating the second plate part 63 into the second screw hole 64b.SELECTED DRAWING: Figure 4

Description

[Technical Field]

[0001] The present invention relates to a charged particle detector and a scanning electron microscope. [Background technology]

[0002] As a charged particle detector, there is one that detects electrons multiplied in a microchannel plate by an anode electrode (see, for example, Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent No. 3561018 Summary of the Invention [Problem to be solved by the invention]

[0004] The above-described charged particle detector may be used to detect electrons in, for example, a scanning electron microscope, and in this case, the charged particle detector is required to be thin in order to increase the resolution of the scanning electron microscope. Also, the charged particle detector may be required to have improved assembly precision.

[0005] An object of the present invention is to provide a charged particle detector that can be made thinner and has improved assembly accuracy, and a scanning electron microscope equipped with such a charged particle detector. [Means for solving the problem]

[0006] The charged particle detector of the present invention is [1] "a charged particle detector comprising: a microchannel plate that generates electrons in response to incident charged particles and multiplies and outputs the generated electrons; an electron collector that collects the electrons output from the microchannel plate; a first plate and a second plate that sandwich the microchannel plate and the electron collector between them in a predetermined direction; and a spacer that is arranged between the first plate and the second plate so as to overlap with the microchannel plate when viewed from a direction perpendicular to the predetermined direction, wherein a first screw hole and a second screw hole are formed in the spacer, and the first plate is fixed to the spacer by a first screw that passes through the first plate and threading into the first screw hole, and the second plate is fixed to the spacer by a second screw that passes through the second plate and threading into the second screw hole."

[0007] In this charged particle detector, a spacer is disposed between a first plate and a second plate so as to overlap the microchannel plate when viewed perpendicular to a predetermined direction. A first screw passing through the first plate is threaded into the first screw hole, thereby securing the first plate to the spacer. A second screw passing through the second plate is threaded into the second screw hole, thereby securing the second plate to the spacer. This configuration allows the overall thickness of the first plate, the second plate, and the spacer to be thinner than a configuration in which, for example, a screw hole is formed in the first plate and a screw passing through the second plate and the spacer is threaded into the screw hole in the first plate to secure the first and second plates to the spacer. Furthermore, while this configuration may result in assembly errors due to gaps between the spacer and the screws, in this charged particle detector, the first screw threads into the first screw hole and the second screw threads into the second screw hole, thereby reducing the occurrence of such assembly errors. Therefore, this charged particle detector can be made thinner and its assembly accuracy can be improved.

[0008] The charged particle detector of the present invention may be [2] "the charged particle detector according to [1], wherein the first screw hole is positioned so as not to overlap with the second screw hole when viewed from the predetermined direction." In this case, the first screw and the second screw can be positioned so as not to interfere with each other, and the lengths of the first screw and the second screw (the first screw hole and the second screw hole) can be ensured to be sufficient. This makes it possible to increase the degree of engagement between the first screw and the first screw hole and the degree of engagement between the second screw and the second screw hole, thereby ensuring sufficient fixing strength of the first plate portion and the second plate portion to the spacer.

[0009] The charged particle detector of the present invention may be [3] "the charged particle detector according to [1] or [2], wherein each of the first screw hole and the second screw hole penetrates the spacer along the predetermined direction." In this case, it is possible to ensure sufficient lengths of the first screw and the second screw (the first screw hole and the second screw hole). This makes it possible to increase the degree of engagement between the first screw and the first screw hole and the degree of engagement between the second screw and the second screw hole, thereby ensuring sufficient fixing strength of the first plate portion and the second plate portion to the spacer.

[0010] The charged particle detector of the present invention may be the charged particle detector according to [4] "the charged particle detector according to [3], wherein a first recess is formed in the surface of the first plate portion facing the spacer, and a second recess is formed in the surface of the second plate portion facing the spacer, the first recess being positioned so as to overlap with the second screw hole when viewed from the predetermined direction and having a larger shape than the second screw when viewed from the predetermined direction, and the second recess being positioned so as to overlap with the first screw hole when viewed from the predetermined direction and having a larger shape than the first screw when viewed from the predetermined direction." In this case, even if the length of the first screw is increased to such an extent that the first screw is exposed on the second plate portion side from the spacer, the second recess can prevent the first screw from interfering with the second plate portion. Furthermore, even if the length of the second screw is increased to such an extent that the second screw is exposed on the first plate portion side from the spacer, the first recess can prevent the second screw from interfering with the first plate portion.

[0011] The charged particle detector of the present invention may be [5] "the charged particle detector according to any one of [1] to [4], wherein the first screw and the second screw extend so as to overlap each other when viewed from a direction perpendicular to the predetermined direction." In this case, the first screw and the second screw can be ensured to have a sufficient length, and the first plate portion and the second plate portion can be sufficiently fixed to the spacer with sufficient strength.

[0012] The charged particle detector of the present invention may be [6] "the charged particle detector according to any one of [1] to [5], wherein the first screw extends so as to overlap the microchannel plate when viewed from a direction perpendicular to the predetermined direction, and the second screw extends so as to overlap the microchannel plate when viewed from a direction perpendicular to the predetermined direction." In this case, the lengths of the first screw and the second screw can be ensured sufficiently, and the fixing strength of the first plate portion and the second plate portion to the spacer can be ensured sufficiently.

[0013] The charged particle detector of the present invention may be [7] "the charged particle detector according to any one of [1] to [6], wherein the first screw extends so as to overlap substantially the entire spacer when viewed from a direction perpendicular to the predetermined direction, and the second screw extends so as to overlap substantially the entire spacer when viewed from a direction perpendicular to the predetermined direction." In this case, the lengths of the first screw and the second screw can be ensured sufficiently, and the fixing strength of the first plate portion and the second plate portion to the spacer can be ensured sufficiently.

[0014] The charged particle detector of the present invention may be [8] "the charged particle detector according to any one of [1] to [7], wherein the first plate portion and the second plate portion are formed of a conductive material and the spacer is formed of an insulating material, and the first plate portion and the second plate portion are electrically insulated from each other." In this case, since the first plate portion and the second plate portion are electrically insulated from each other, different potentials can be applied to the first plate portion and the second plate portion.

[0015] The charged particle detector of the present invention may be [9] "the charged particle detector according to [8], further comprising a conductive mesh member, wherein the second plate portion has a charged particle passage opening through which the charged particles pass, the mesh member being fixed to the second plate portion so as to cover the charged particle passage opening and electrically connected to the second plate portion." In this case, for example, the mesh member can be made to function as a filter for charged particles by applying a predetermined potential to the mesh member.

[0016] The scanning electron microscope of the present invention is

[10] "a scanning electron microscope comprising an electron beam source that outputs an electron beam, an objective lens that focuses the electron beam onto a sample, and a charged particle detector according to any one of [1] to [9] that detects electrons generated in the sample by irradiation with the electron beam." In this scanning electron microscope, the charged particle detector is made thin for the reasons described above, and therefore high resolution can be achieved. [Effects of the Invention]

[0017] According to the present invention, it is possible to provide a charged particle detector that can be made thinner and has improved assembly accuracy, and a scanning electron microscope equipped with such a charged particle detector. [Brief explanation of the drawings]

[0018] [Figure 1] FIG. 1 is a configuration diagram of a scanning electron microscope according to an embodiment. [Figure 2] FIG. 2 is a plan view of a charged particle detector. [Figure 3] FIG. 2 is a bottom view of the charged particle detector. [Figure 4] FIG. 4 is a cross-sectional view taken along line IV-IV in FIG. 2. [Figure 5] FIG. 10 is a cross-sectional view of a charged particle detector according to a comparative example. DETAILED DESCRIPTION OF THE INVENTION

[0019] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. In the following description, the same or equivalent elements are designated by the same reference numerals, and redundant description will be omitted.

[0020] As shown in FIG. 1 , a scanning electron microscope 1 according to an embodiment includes an electron beam source 10, an objective lens 20, a charged particle detector 30, and a sample stage 40. During observation, a sample S to be observed is placed on the sample stage 40. The electron beam source 10 outputs an electron beam EB along a direction D (a predetermined direction). The objective lens 20 is disposed between the electron beam source 10 and the sample stage 40 in the direction D and focuses the electron beam EB output from the electron beam source 10 toward the sample S. Irradiation of the electron beam EB generates reflected electrons and secondary electrons in the sample S. The reflected electrons are electrons that are incident on the sample S and are backscattered inside the sample S, while the secondary electrons are low-energy electrons generated near the surface of the sample S. For example, the energy of the reflected electrons is 50 eV or more, and the energy of the secondary electrons is 50 eV or less. The charged particle detector 30 is disposed between the sample stage 40 and the objective lens 20 in the direction D and detects the reflected electrons generated in the sample S. The scanning electron microscope 1 further includes a detector (for example, a detector composed of a scintillator and a photomultiplier tube) (not shown) for detecting secondary electrons generated in the sample S. In the scanning electron microscope 1, the electron beam EB is scanned over the surface of the sample S, and the electrons generated in the sample S are detected by a detector such as the charged particle detector 30, thereby making it possible to observe the morphology and microstructure of the surface of the sample S.

[0021] As shown in FIGS. 2 to 4 , the charged particle detector 30 includes two microchannel plates 51 and 52, an input electrode 53, an output electrode 54, an anode electrode (electron collector) 55, multiple (three in this example) insulating members 56, 57, and 58, multiple (four in this example) terminals 59, and a terminal holder 60. The microchannel plates 51 and 52, the input electrode 53, the output electrode 54, the anode electrode 55, and the insulating members 56 to 58 are held by being sandwiched in direction D between a first plate 61 and a second plate 63 (described later). The terminal holder 60 is fixed to the first plate 61 so that the multiple terminals 59 face the same side. This allows wiring and the like to be easily connected to the multiple terminals 59. The charged particle detector 30 also includes a power supply (not shown) for applying a predetermined potential to each component via the terminals 59. Hereinafter, the microchannel plates 51 and 52 are also referred to as MCPs (microchannel plates) 51 and 52. Note that the actual shape of the charged particle detector 30 is much flatter than the shape of the charged particle detector 30 shown in Fig. 4, but in Fig. 4 the shape of the charged particle detector 30 is enlarged in direction D for ease of understanding.

[0022] Each of the MCPs 51 and 52 is, for example, a disk-shaped member having a central axis CL parallel to the direction D. Each of the MCPs 51 and 52 is formed of an insulating material such as glass. Each of the MCPs 51 and 52 has a plurality of through-holes (channels CH) formed therethrough along the direction D. The channels CH extend at a predetermined angle with respect to the direction D. When electrons E generated in the sample S collide with the inner walls of the channels CH, a plurality of secondary electrons are emitted. The MCPs 51 and 52 are stacked along the direction D such that the MCP 51 is disposed on the second plate 63 side (the lower side in FIG. 4 ). The MCP 51 has an incident surface 51 a facing the second plate 63, and the MCP 52 has an output surface 52 a facing away from the second plate 63. When electrons E are incident on the incident surface 51 a, electrons multiplied by the MCPs 51 and 52 are output from the output surface 52 a.

[0023] The MCPs 51 and 52 are disposed between an input electrode 53 disposed on the incident surface 51 a and an output electrode 54 disposed on the output surface 52 a. The input electrode 53 and the output electrode 54 are, for example, annular members each having a central axis coinciding with the central axis CL of the MCP 51. The input electrode 53 and the output electrode 54 are disposed on the outer edge of each of the MCPs 51 and 52. A terminal 59 is connected to the input electrode 53, and a predetermined potential is applied to the input electrode 53 from a power supply via the terminal 59. Similarly, a terminal 59 is connected to the output electrode 54, and a predetermined potential is applied to the output electrode 54 from a power supply via the terminal 59. This applies a predetermined potential to the incident surface 51 a of the MCP 51 and the output surface 52 a of the MCP 52.

[0024] In the charged particle detector 30, the potential of the output surface 52a is set higher than the potential of the incident surface 51a. As an example, the incident surface 51a is connected to ground, and a positive potential is applied to the output surface 52a. In this state, when electrons E incident from the incident surface 51a collide with the inner wall of the channel CH, multiple secondary electrons emitted from the inner wall of the channel CH are accelerated toward the output surface 52a. When these secondary electrons collide with the inner wall of the channel CH, secondary electrons are emitted again. In this way, the electrons collide with the inner wall of the channel CH multiple times and proceed toward the output surface 52a, resulting in multiplied electrons being output from the output surface 52a.

[0025] The anode electrode 55 is, for example, a disk-shaped member, and has a central axis that coincides with the central axis CL of each of the MCPs 51 and 52. The anode electrode 55 is disposed on the output surface 52a of the MCP 52 so that the surface 55a of the anode electrode 55 faces the output surface 52a. The anode electrode 55 collects (detects) electrons output from the output surface 52a and outputs an output signal corresponding to the amount of collected electrons to the outside. A terminal 59 is connected to the anode electrode 55, and a predetermined potential is applied to the anode electrode 55 from a power supply via the terminal 59. For example, a potential greater than the positive potential applied to the output surface 52a is applied to the anode electrode 55. As a result, the electrons output from the output surface 52a are accelerated toward the surface 55a of the anode electrode 55.

[0026] Openings 51b and 52b are formed in the MCPs 51 and 52, respectively. An opening 55b is formed in the anode electrode 55. The openings 51b, 52b, and 55b have central axes that coincide with the central axis CL of the MCP 51.

[0027] Each of the insulating members 56 to 58 is, for example, an annular member and has a central axis that coincides with the central axis CL of the MCP 51. Each of the insulating members 56 to 58 is formed of an insulating material such as ceramic. The insulating member 56 is disposed between the output electrode 54 and the anode electrode 55 and electrically insulates the output electrode 54 from the anode electrode 55. The insulating member 56 is disposed on the surface 55a of the anode electrode 55 and is disposed at the outer edge of the anode electrode 55. The insulating member 57 is disposed between the anode electrode 55 and the first plate portion 61 and electrically insulates the anode electrode 55 from the first plate portion 61. The insulating member 57 is disposed on the opposite side of the anode electrode 55 from the insulating member 56 and is disposed at the outer edge of the anode electrode 55. The insulating member 58 is disposed between the input electrode 53 and the second plate portion 63 and electrically insulates the input electrode 53 from the second plate portion 63. That is, these components are arranged between the first plate portion 61 and the second plate portion 63 in the following order from the first plate portion 61 side: insulating member 57, anode electrode 55, insulating member 56, output side electrode 54, MCP 52, MCP 51, input side electrode 53, and insulating member 58.

[0028] The charged particle detector 30 further includes a first plate portion 61, a cylindrical portion 62, a second plate portion 63, a spacer 64, a plurality of (four in this example) first screws 65, a plurality of (three in this example) second screws 66, and a mesh member 67. The charged particle detector 30 is disposed so that the second plate portion 63 faces the sample stage 40 (sample S). The first plate portion 61 and the cylindrical portion 62 are integrally formed to constitute a single member 71. Note that the mesh member 67 is not shown in FIG. 2.

[0029] The first plate portion 61 and the second plate portion 63 sandwich the MCPs 51 and 52, the input electrode 53, the output electrode 54, the anode electrode 55, and the insulating members 56 to 58 between them in the direction D. The first plate portion 61 is formed in a substantially circular plate shape with the direction D as its thickness direction. The first plate portion 61 is formed of a conductive material such as a metal material. The first plate portion 61 is disposed to face the anode electrode 55 with the insulating member 57 interposed therebetween, and has a surface 61a in contact with the insulating member 57. The tubular portion 62 is formed in a cylindrical shape, for example, and has a central axis that coincides with the central axis CL of the MCP 51. The tubular portion 62 is formed of a conductive material such as a metal material. The tubular portion 62 extends from the surface 61a toward the second plate portion 63 along the direction D. The cylindrical portion 62 is inserted into the openings 51b, 52b of the MCPs 51, 52 and the opening 55b of the anode electrode 55, and protrudes toward the second plate portion 63 with respect to the MCPs 51, 52. The tip of the cylindrical portion 62 faces the sample S (sample stage 40). The inside of the cylindrical portion 62 communicates with the through-hole 61b formed in the first plate portion 61. The electron beam EB transmitted through the objective lens 20 passes through the through-hole 61b and the inside of the cylindrical portion 62 and is irradiated onto the sample S.

[0030] The second plate portion 63 is formed in a substantially circular plate shape with direction D as its thickness direction. The second plate portion 63 is formed of a conductive material such as a metal material. The second plate portion 63 is disposed to face the input electrode 53 via the insulating member 58, and has a surface 63a that contacts the insulating member 58. The second plate portion 63 is formed with an electron passing opening 63b (charged particle passing opening) through which electrons E (charged particles) generated in the sample S pass. The electron passing opening 63b is formed in a circular shape when viewed from direction D, and has a central axis that coincides with the central axis CL of the MCP 51.

[0031] A plurality of (four in this example) through holes 61d are formed in the first plate portion 61. Shanks 65a of four first screws 65, which will be described later, are inserted into these four through holes 61d, respectively. A plurality of (three in this example) through holes 63d are formed in the second plate portion 63. Shanks 66a of three second screws 66, which will be described later, are inserted into these three through holes 63d, respectively.

[0032] The spacer 64 is, for example, an annular member having a central axis that coincides with the central axis CL of the MCP 51. The spacer 64 is formed of an insulating material such as ceramic. The spacer 64 is disposed between the first plate portion 61 and the second plate portion 63, thereby forming a gap between the first plate portion 61 and the second plate portion 63 for disposing the MCPs 51 and 52, the input electrode 53, the output electrode 54, the anode electrode 55, and the insulating members 56 to 58. The spacer 64 is disposed between the first plate portion 61 and the second plate portion 63 so as to overlap with the MCPs 51 and 52, the input electrode 53, the output electrode 54, the anode electrode 55, and the insulating members 56 to 58 when viewed from a direction perpendicular to the direction D. The spacer 64 electrically insulates the first plate portion 61 and the second plate portion 63. The MCPs 51 and 52, the input electrode 53, the output electrode 54, the anode electrode 55, and the insulating members 56 to 58 are disposed inside a spacer 64 when viewed from direction D. The inner diameter of the spacer 64 is set to be approximately the same as the outer diameters of the MCPs 51 and 52, the input electrode 53, the output electrode 54, the anode electrode 55, and the insulating members 56 to 58, for example.

[0033] The spacer 64 is formed with a plurality of (four in this example) first screw holes 64a and a plurality of (three in this example) second screw holes 64b. The first screw holes 64a and the second screw holes 64b penetrate the spacer 64 along direction D. Four first screws 65 are screwed into the four first screw holes 64a, respectively, and three second screws 66 are screwed into the three second screw holes 64b, respectively. The four through holes 61d of the first plate portion 61 described above are arranged at positions corresponding to the four first screw holes 64a (positions overlapping with the first screw holes 64a when viewed from direction D). The three through holes 63d of the second plate portion 63 described above are arranged at positions corresponding to the three second screw holes 64b (positions overlapping with the second screw holes 64b when viewed from direction D). No screw grooves are formed on the inner surfaces of the through holes 61d and 63d, and no screw holes are formed in the first plate portion 61 and the second plate portion 63.

[0034] Each first screw 65 has a shaft portion 65a with a thread formed thereon to screw into the first screw hole 64a, and a head portion 65b formed at the end of the shaft portion 65a. Each second screw 66 has a shaft portion 66a with a thread formed thereon to screw into the second screw hole 64b, and a head portion 66b formed at the end of the shaft portion 66a. The first screws 65 and the second screws 66 are formed, for example, from a metal material. The four first screws 65 (first screw holes 64a) are aligned at regular intervals along the circumferential direction when viewed from the direction D. The three second screws 66 (second screw holes 64b) are aligned at regular intervals along the circumferential direction when viewed from the direction D. The first screws 65 and the second screws 66 are positioned at offset positions from each other in the circumferential direction when viewed from the direction D. In other words, the first screws 65 and the second screws 66 are not aligned in the radial direction when viewed from the direction D. In this way, the first screws 65 are arranged in positions that do not overlap with the second screws 66 when viewed from direction D. Similarly, the first screw holes 64a are arranged in positions that do not overlap with the second screw holes 64b when viewed from direction D. In the example of FIG. 3, the four first screws 65 are arranged at 90-degree intervals in the circumferential direction around the central axis CL of the MCP 51 when viewed from direction D. In the example of FIG. 2, the three second screws 66 are arranged at 120-degree intervals in the circumferential direction around the central axis CL of the MCP 51 when viewed from direction D.

[0035] The shaft 65a of the first screw 65 is inserted into the through-hole 61d to pass through the first plate portion 61 and is screwed into the first screw hole 64a, thereby fixing the first plate portion 61 (member 71) to the spacer 64. At this time, the head 65b of the first screw 65 is located outside the first plate portion 61 in direction D. The shaft 66a of the second screw 66 is inserted into the through-hole 63d to pass through the second plate portion 63 and is screwed into the second screw hole 64b, thereby fixing the second plate portion 63 to the spacer 64. At this time, the head 66b of the second screw 66 is located outside the second plate portion 63 in direction D. That is, the first plate portion 61 is fixed to the spacer 64 by the first screw 65 from one side of the spacer 64 in the direction D (the side opposite to the second plate portion 63), and the second plate portion 63 is fixed to the spacer 64 by the second screw 66 from the other side of the spacer 64 in the direction D (the side opposite to the first plate portion 61). At this time, the shank 65a of the first screw 65 is in close contact with the inner surface of the first screw hole 64a, and the shank 66a of the second screw 66 is in close contact with the inner surface of the second screw hole 64b. By fixing the first plate portion 61 and the second plate portion 63 to the spacer 64 from both sides of the spacer 64 in the direction D, the MCPs 51 and 52, the input electrode 53, the output electrode 54, the anode electrode 55, and the insulating members 56 to 58 can be firmly sandwiched between the first plate portion 61 and the second plate portion 63 in the direction D. Furthermore, using the first screw 65 and the second screw 66 made of a metal material, the first plate portion 61 and the second plate portion 63 can be firmly fixed to the spacer 64 while different potentials can be applied to the first plate portion 61 and the second plate portion 63.

[0036] The first screw 65 extends so as to overlap substantially the entire spacer 64 when viewed perpendicular to the direction D and in a direction in which the first screw 65 and the central axis CL of the MCP 51 (the central axis of the spacer 64) are aligned. The second screw 66 extends so as to overlap substantially the entire spacer 64 when viewed perpendicular to the direction D and in a direction in which the second screw 66 and the central axis CL of the MCP 51 (the central axis of the spacer 64) are aligned. "Substantially the entire spacer 64" refers to, for example, 95% to 100% of the spacer 64 when the entire spacer 64 in the direction D is taken as 100%. In the example of FIG. 4, the first screw 65 and the second screw 66 overlap the entire spacer 64 in the direction D. That is, the tip surface of the shaft portion 65a of the first screw 65 is located on the same plane as the surface of the spacer 64. Furthermore, the tip surface of the shaft portion 66a of the second screw 66 is located on the same plane as the surface of the spacer 64. Note that, due to manufacturing tolerances, assembly errors, etc., the tip surface of the shaft portion 65a may be located inside or outside the direction D with respect to the surface of the spacer 64. Similarly, the tip surface of the shaft portion 66a may be located inside or outside the direction D with respect to the surface of the spacer 64.

[0037] When viewed perpendicular to direction D and in a direction in which the first screw 65 and the central axis CL of the MCP 51 (the central axis of the spacer 64) are aligned, the first screw 65 overlaps with the MCPs 51 and 52, the input electrode 53, the output electrode 54, the anode electrode 55, and the insulating members 56 to 58. When viewed perpendicular to direction D and in a direction in which the second screw 66 and the central axis CL of the MCP 51 (the central axis of the spacer 64) are aligned, the second screw 66 overlaps with the MCPs 51 and 52, the input electrode 53, the output electrode 54, the anode electrode 55, and the insulating members 56 to 58.

[0038] As described above, the first screw 65 overlaps with 50% or more of the spacer 64 (100% in the example of FIG. 4), and the second screw 66 overlaps with 50% or more of the spacer 64 (100% in the example of FIG. 4). Therefore, the first screw 65 and the second screw 66 overlap with each other when viewed perpendicular to direction D and in a direction in which the first screw 65 and the second screw 66 are aligned.

[0039] A plurality of (three in this example) first recesses 61c are formed in the surface 61a of the first plate portion 61 facing the spacer 64. The three first recesses 61c are arranged at positions that overlap with the three second screw holes 64b (second screws 66) when viewed from the direction D. That is, like the second screws 66, the three first recesses 61c are arranged at 120-degree intervals in the circumferential direction around the central axis CL of the MCP 51 (the central axis of the spacer 64) when viewed from the direction D. The first recesses 61c are formed in a circular shape when viewed from the direction D, and penetrate the first plate portion 61 along the direction D.

[0040] The first recess 61c has a shape larger than the second screw 66 when viewed from the direction D. In other words, the first recess 61c has a size and shape that surrounds the second screw 66 when viewed from the direction D. The first recess 61c is formed so that the second screw 66 does not come into contact with the first plate portion 61 even if the length of the second screw 66 is increased to such an extent that the second screw 66 is exposed on the side of the first plate portion 61 from the spacer 64 (for example, even if the shank 66a of the second screw 66 protrudes from the spacer 64). In the example of FIG. 4, the diameter of the first recess 61c is formed larger than the diameter of the shank 66a of the second screw 66. When the shank 66a of the second screw 66 is placed in the first recess 61c so that their central axes coincide, the shank 66a does not come into contact with the inner surface of the first recess 61c. In other words, the second screw 66 is prevented from coming into contact with not only the first recess 61c but also the first plate portion 61.

[0041] A plurality of (four in this example) second recesses 63c are formed in the surface 63a of the second plate portion 63 facing the spacer 64. The four second recesses 63c are arranged at positions overlapping with the four first screw holes 64a (first screws 65) when viewed from the direction D. That is, like the first screws 65, the four second recesses 63c are arranged at 90-degree intervals in the circumferential direction around the central axis CL of the MCP 51 (the central axis of the spacer 64) when viewed from the direction D. The second recesses 63c are formed in a circular shape when viewed from the direction D, and penetrate the second plate portion 63 along the direction D.

[0042] The second recess 63c has a shape larger than the first screw 65 when viewed from the direction D. That is, the second recess 63c has a size and shape that surrounds the first screw 65 when viewed from the direction D. The second recess 63c is formed so that the first screw 65 does not come into contact with the second plate portion 63 even if the length of the first screw 65 is increased to such an extent that the first screw 65 is exposed on the side of the second plate portion 63 from the spacer 64 (for example, even if the shank 65a of the first screw 65 protrudes from the spacer 64). In the example of FIG. 4, the diameter of the second recess 63c is formed larger than the diameter of the shank 65a of the first screw 65. When the shank 65a of the first screw 65 is placed in the second recess 63c so that their central axes coincide, the shank 65a does not come into contact with the inner surface of the first recess 61c. That is, the first screw 65 is prevented from coming into contact with not only the second recess 63c but also the second plate portion 63.

[0043] The mesh member 67 is a thin, mesh-like member having numerous openings for allowing electrons E generated in the sample S to pass through. The mesh member 67 is formed of a conductive material such as a metal material. In this example, the mesh member 67 is sandwiched and held in direction D between the insulating member 58 and the second plate portion 63. As a result, the mesh member 67 covers the electron passage openings 63b of the second plate portion 63 from the surface 63a side of the second plate portion 63 and is electrically connected to the second plate portion 63. A terminal 59 is connected to the mesh member 67, and a predetermined potential is applied to the mesh member 67 from the power supply via the terminal 59. As a result, the second plate portion 63 and the mesh member 67 are set to the same potential. By applying a potential to the second plate portion 63 via the mesh member 67 in this manner, the number of terminals for directly applying a potential to the second plate portion 63 can be reduced, thereby reducing the number of terminals 59. As an example, a negative potential is applied to the mesh member 67. An opening 67a is formed in the mesh member 67, and the cylindrical portion 62 is inserted into the opening 67a.

[0044] In the charged particle detector 30 configured as described above, a predetermined potential is applied to each component of the charged particle detector 30 from the power supply unit via each terminal 59. As an example, the incident surface 51a is connected to ground, a positive potential is applied to the output surface 52a, and a potential greater than the positive potential applied to the output surface 52a is applied to the anode electrode 55. Furthermore, the first plate portion 61 and the cylindrical portion 62 are connected to ground, and a negative potential is applied to the second plate portion 63 and the mesh member 67. In this state, an electron beam EB is output from the electron beam source 10, and the electron beam EB that has passed through the cylindrical portion 62 is irradiated onto the sample S. Electrons E generated in the sample S pass through the electron passing opening 63b and are incident on the incident surface 51a of the MCP 51. At this time, low-energy electrons E (e.g., secondary electrons) are blocked by the mesh member 67, and high-energy electrons E (e.g., reflected electrons) pass through the openings of the mesh member 67 and are incident on the incident surface 51a of the MCP 51. Electrons are generated in the MCP 51 in response to the incidence of electrons E, and the electrons multiplied in the MCPs 51 and 52 are output from the output surface 52a. The electrons output from the output surface 52a are collected (detected) by the anode electrode 55, and an output signal corresponding to the amount of the collected electrons is output to the outside. [Action and effect]

[0045] As described above, in the charged particle detector 30, the first screw hole 64a and the second screw hole 64b are formed in the spacer 64 disposed between the first plate portion 61 and the second plate portion 63 so as to overlap the MCPs 51, 52 when viewed from a direction perpendicular to the direction D. The first screw 65 passing through the first plate portion 61 is threaded into the first screw hole 64a, thereby fixing the first plate portion 61 to the spacer 64, and the second screw 66 passing through the second plate portion 63 is threaded into the second screw hole 64b, thereby fixing the second plate portion 63 to the spacer 64. This makes it possible to reduce the overall thickness of the first plate portion 61, the second plate portion 63, and the spacer 64, compared to a configuration in which, for example, screw holes are formed in the first plate portion 61 and screws passing through the second plate portion 63 and the spacer 64 are threaded into the screw holes of the second plate portion 63 to fix the first plate portion 61 and the second plate portion 63 to the spacer 64. Furthermore, while this configuration may cause assembly errors due to gaps between the spacers 64 and the screws, the first screws 65 are threaded into the first screw holes 64a and the second screws 66 are threaded into the second screw holes 64b in the charged particle detector 30, thereby preventing such assembly errors from occurring. Therefore, the charged particle detector 30 can be made thinner and have improved assembly accuracy.

[0046] This point will be further explained with reference to FIG. 5. FIG. 5 is a cross-sectional view of a charged particle detector 300 according to a comparative example. The charged particle detector 300 differs from the charged particle detector 30 mainly in that the first screw 65 is not provided and that the spacer 64 does not have a first screw hole 64a and a second screw hole 64b. In the charged particle detector 300, a screw hole 61s into which the second screw 66 is screwed is formed in the first plate portion 61. A through hole 64s is formed in the spacer 64, penetrating the spacer 64 along direction D. In the charged particle detector 300, a shaft portion 66a of the second screw 66 penetrates the second plate portion 63 and is inserted into the through hole 64s. The shaft portion 66a of the second screw 66 is screwed into the screw hole 61s, thereby fixing the first plate portion 61 (member 71), the spacer 64, and the second plate portion 63 to one another.

[0047] In contrast, in the charged particle detector 30, no screw holes are formed in the first plate portion 61, and a first screw hole 64a and a second screw hole 64b are formed in the spacer 64. The first plate portion 61 and the second plate portion 63 are fixed to the spacer 64 from both sides of the spacer 64 in the direction D. Unlike the charged particle detector 300 according to the comparative example, in the charged particle detector 30, the first plate portion 61 does not need to have a thickness necessary to screw the second screw 66 into the first plate portion 61. In other words, in the charged particle detector 30, the thickness of the first plate portion 61 can be made thinner.

[0048] While the thickness of the charged particle detector 300 according to the comparative example is approximately 4 mm, the thickness of the charged particle detector 30 according to the embodiment is approximately 3 mm, which is approximately 75% of the thickness of the charged particle detector 300. As described above, in the charged particle detector 30, the first screw hole 64a and the second screw hole 64b are formed in the spacer 64, so that the thickness of the first plate portion 61 can be made thinner than that of the charged particle detector 300 according to the comparative example, and as a result, the charged particle detector 30 can be made thinner.

[0049] 5, the second screw 66 is not threaded into the spacer 64, resulting in a gap between the shank 66a of the second screw and the inner surface of the through-hole 64s. In other words, in this case, the through-hole 64s needs to be larger than the shank 66a to allow for insertion of the shank 66a. In the charged particle detector 300, this gap may result in assembly errors (e.g., misalignment of the central axes of components such as the MCP 51). In contrast, in the charged particle detector 30, the first screw 65 is threaded into the first screw hole 64a and the second screw 66 is threaded into the second screw hole 64b, resulting in less gaps between the first screw 65 and the spacer 64 and between the second screw 66 and the spacer 64. This reduces the occurrence of assembly errors in the charged particle detector 30.

[0050] In the charged particle detector 30, the first screw hole 64a is disposed at a position where it does not overlap with the second screw hole 64b when viewed from direction D. In this case, the first screw 65 and the second screw 66 can be disposed so as not to interfere with each other, and the lengths of the first screw 65 and the second screw 66 (the first screw hole 64a and the second screw hole 64b) can be ensured to be sufficient. This makes it possible to increase the degree of engagement between the first screw 65 and the first screw hole 64a and the degree of engagement between the second screw 66 and the second screw hole 64b, and as a result, it becomes possible to ensure sufficient fixing strength of the first plate portion 61 and the second plate portion 63 to the spacer 64.

[0051] In the charged particle detector 30, each of the first screw hole 64a and the second screw hole 64b penetrates the spacer 64 along the direction D. In this case, it is possible to ensure a sufficient length for the first screw 65 and the second screw 66 (the first screw hole 64a and the second screw hole 64b). This makes it possible to increase the degree of engagement between the first screw 65 and the first screw hole 64a and the degree of engagement between the second screw 66 and the second screw hole 64b, thereby ensuring a sufficient fixing strength of the first plate portion 61 and the second plate portion 63 to the spacer 64. Furthermore, in the charged particle detector 30, it is possible to prevent gas from accumulating inside each of the first screw hole 64a and the second screw hole 64b. This makes it possible to prevent loosening of the first screw 65 and the second screw 66 due to gas pressure.

[0052] In the charged particle detector 30, a first recess 61c is formed in a surface 61a of the first plate portion 61 facing the spacer 64, and a second recess 63c is formed in a surface 63a of the second plate portion 63 facing the spacer 64. The first recess 61c is disposed at a position overlapping with the second screw hole 64b when viewed from the direction D, and has a larger shape than the second screw 66 when viewed from the direction D. The second recess 63c is disposed at a position overlapping with the first screw hole 64a when viewed from the direction D, and has a larger shape than the first screw 65 when viewed from the direction D. In this case, even if the length of the first screw 65 is increased to such an extent that the first screw 65 is exposed on the side of the second plate portion 63 from the spacer 64 (for example, even if the shaft portion 65a of the first screw 65 protrudes from the spacer 64), the second recess 63c can prevent the first screw 65 from interfering with the second plate portion 63. Furthermore, even if the length of the second screw 66 is increased to the extent that the second screw 66 is exposed from the spacer 64 to the side of the first plate portion 61 (for example, even if the shaft portion 66a of the second screw 66 protrudes from the spacer 64), the first recess 61c can prevent the second screw 66 from interfering with the first plate portion 61.

[0053] A further explanation on this point is provided. In the charged particle detector 30, the first screw 65 is made of a metal material, and therefore the first screw 65 has the same potential as the first plate portion 61. Furthermore, the second screw 66 is made of a metal material, and therefore the second screw 66 has the same potential as the second plate portion 63. In this case, if the first screw 65 interferes with the second plate portion 63, the first screw 65 may affect the potential of the second plate portion 63. Furthermore, if the second screw 66 interferes with the first plate portion 61, the second screw 66 may affect the potential of the first plate portion 61. As described above, in the charged particle detector 30, the second recess 63c can prevent the first screw 65 from interfering with the second plate portion 63, and the first recess 61c can prevent the second screw 66 from interfering with the first plate portion 61. Therefore, the first screw 65 and the second screw 66 can be prevented from affecting the potentials of the second plate portion 63 and the first plate portion 61.

[0054] In the charged particle detector 30, the first screw 65 and the second screw 66 extend so as to overlap each other when viewed from the direction in which the first screw 65 and the second screw 66 are aligned (a direction perpendicular to direction D). In this case, the lengths of the first screw 65 and the second screw 66 can be ensured sufficiently, and the fixing strength of the first plate portion 61 and the second plate portion 63 to the spacer 64 can be ensured sufficiently.

[0055] In the charged particle detector 30, the first screw 65 extends so as to overlap the MCPs 51 and 52 when viewed from the direction in which the first screw 65 and the central axis CL of the MCP 51 (the central axis of the spacer 64) are aligned (the direction perpendicular to direction D). Moreover, the second screw 66 extends so as to overlap the MCPs 51 and 52 when viewed from the direction in which the second screw 66 and the central axis CL of the MCP 51 (the central axis of the spacer 64) are aligned (the direction perpendicular to direction D). In this case, the lengths of the first screw 65 and the second screw 66 can be sufficiently ensured, and the fixing strength of the first plate portion 61 and the second plate portion 63 to the spacer 64 can be sufficiently ensured.

[0056] In the charged particle detector 30, the first screw 65 extends so as to overlap substantially the entire spacer 64 when viewed from a direction (a direction perpendicular to direction D) in which the first screw 65 and the central axis CL of the MCP 51 (the central axis of the spacer 64) are aligned. Moreover, the second screw 66 extends so as to overlap substantially the entire spacer 64 when viewed from a direction perpendicular to direction D and in which the second screw 66 and the central axis CL of the MCP 51 (the central axis of the spacer 64) are aligned. In this case, the lengths of the first screw 65 and the second screw 66 can be sufficiently ensured, and it is possible to sufficiently ensure the fixing strength of the first plate portion 61 and the second plate portion 63 to the spacer 64.

[0057] In the charged particle detector 30, the first plate portion 61 and the second plate portion 63 are formed from a conductive material, and the spacer 64 is formed from an insulating material, so that the first plate portion 61 and the second plate portion 63 are electrically insulated from each other. In this case, since the first plate portion 61 and the second plate portion 63 are electrically insulated from each other, different potentials can be applied to the first plate portion 61 and the second plate portion 63. In this example, the first plate portion 61 is connected to ground, and an arbitrary positive or negative potential is applied to the second plate portion 63.

[0058] The charged particle detector 30 includes a conductive mesh member 67, and the second plate portion 63 has an electron passing opening 63b formed therein, through which electrons E pass. The mesh member 67 is fixed to the second plate portion 63 so as to cover the electron passing opening 63b, and is electrically connected to the second plate portion 63. In this case, for example, by applying a predetermined potential to the mesh member 67, the mesh member 67 can be made to function as a filter for electrons. In this example, a negative potential is applied to the mesh member 67, and low-energy electrons E (e.g., secondary electrons) are blocked by the mesh member 67.

[0059] The scanning electron microscope 1 includes an electron beam source 10 that outputs an electron beam EB, an objective lens 20 that focuses the electron beam EB toward a sample S, and a charged particle detector 30 that detects electrons E generated in the sample S by irradiation with the electron beam EB. In the scanning electron microscope 1, the charged particle detector 30 is made thin for the reasons described above, and therefore high resolution can be achieved.

[0060] This point will be further explained with reference to Figure 1. The charged particle detector 30 is disposed between the objective lens 20 and the specimen stage 40 on which the specimen S is placed. If the charged particle detector 30 is made thinner for the reasons described above, the distance (working distance) between the specimen S and the objective lens 20 can be shortened. This allows the scanning electron microscope 1 to have higher resolution.

[0061] In the scanning electron microscope 1, the charged particle detector 30 detects backscattered electrons generated in the sample S by irradiation with the electron beam EB. The energy of the backscattered electrons is, for example, 50 eV or more. The MCPs 51 and 52 of the charged particle detector 30 have high sensitivity to most of the above energy range. This allows the scanning electron microscope 1 to detect backscattered electrons with high accuracy. Furthermore, compared to the case where a silicon photodiode is used, for example, it is possible to detect electrons in a wider energy range. [Variations]

[0062] The present invention is not limited to the above-described embodiment. For example, the materials and shapes of the components are not limited to those described above, and various materials and shapes can be used.

[0063] In the above embodiment, the first recess 61c penetrates the first plate portion 61 along the direction D, and the second recess 63c penetrates the second plate portion 63 along the direction D, but the first recess 61c does not have to penetrate the first plate portion 61, and the second recess 63c does not have to penetrate the second plate portion 63. For example, the first recess 61c may not penetrate the first plate portion 61 and open only to the surface 61a of the first plate portion 61, and the second recess 63c may not penetrate the second plate portion 63 and open only to the surface 63a of the second plate portion 63.

[0064] The charged particle detector 30 may be applied to an application other than a scanning electron microscope, in which case the charged particle detector 30 does not need to have the cylindrical portion 62 through which the electron beam EB passes.

[0065] In the above embodiment, the first plate portion 61 and the second plate portion 63 were formed from a conductive material, but the first plate portion 61 and the second plate portion 63 may also be formed from a material other than a conductive material (for example, an insulating material).

[0066] In the above embodiment, the charged particle detector 30 detects electrons, but the charged particle detector 30 may detect charged particles other than electrons (for example, ions). In this case, the electron passing opening 63b functions as a charged particle passing opening through which charged particles pass, and the mesh member 67 functions as a filter for the charged particles.

[0067] In the above embodiment, the first screw hole 64a and the second screw hole 64b penetrate the spacer 64 along the direction D, but the first screw hole 64a and the second screw hole 64b do not have to penetrate the spacer 64 along the direction D. In other words, the first screw hole 64a and the second screw hole 64b may be holes with a bottom.

[0068] In the above embodiment, the first screw 65 and the second screw 66 extend so as to overlap substantially the entire spacer 64 when viewed from a direction perpendicular to the direction D. However, the first screw 65 and the second screw 66 may extend so as to overlap only a portion of the spacer 64 when viewed from a direction perpendicular to the direction D. In this case, the first screw 65 and the second screw 66 may not overlap the MCPs 51, 52 when viewed from a direction perpendicular to the direction D. Furthermore, the first screw 65 and the second screw 66 may not overlap each other when viewed from a direction perpendicular to the direction D. In other words, the length of the first screw 65 and the second screw 66 in the direction D may be smaller than half the thickness of the spacer 64 in the direction D.

[0069] In the above embodiment, the first screw 65 (first screw hole 64a) and the second screw 66 (second screw hole 64b) are arranged at positions offset from each other in the circumferential direction when viewed from direction D. However, the first screw 65 and the second screw 66 may be arranged at positions offset from each other in the radial direction when viewed from direction D. Alternatively, the first screw 65 and the second screw 66 may be arranged at the same position when viewed from direction D.

[0070] In the above embodiment, the number of first screws 65 is four and the number of second screws 66 is three, but the number of first screws 65 and second screws 66 may be any number equal to or greater than one. The first recess 61c may not be formed in the first plate portion 61, and the second recess 63c may not be formed in the second plate portion 63. The mesh member 67 may be omitted.

[0071] In the above embodiment, the anode electrode 55 is used as an electron collector that collects electrons output from the microchannel plates 51 and 52, but an electron detection element such as a semiconductor element may also be used as the electron collector. [Explanation of symbols]

[0072] 1...scanning electron microscope, 10...electron beam source, 20...objective lens, 30...charged particle detector, 51, 52...microchannel plate, 55...anode electrode (electron collecting portion), 61...first plate portion, 61a...surface, 61c...first recess, 63...second plate portion, 63a...surface, 63b...electron passage opening (charged particle passage opening), 63c...second recess, 64...spacer, 64a...first screw hole, 64b...second screw hole, 65...first screw, 66...second screw, 67...mesh member, E...electrons, EB...electron beam, S...sample.

Claims

1. a microchannel plate that generates electrons in response to incident charged particles, multiplies the generated electrons, and outputs them; an electron collector that collects electrons output from the microchannel plate; a first plate portion and a second plate portion sandwiching the microchannel plate and the electron collector portion therebetween in a predetermined direction; a spacer disposed between the first plate portion and the second plate portion so as to overlap the microchannel plate when viewed from a direction perpendicular to the predetermined direction; The spacer has a first screw hole and a second screw hole formed therein, a first screw passing through the first plate portion and threading into the first screw hole, thereby fixing the first plate portion to the spacer, and a second screw passing through the second plate portion and threading into the second screw hole, thereby fixing the second plate portion to the spacer.

2. The charged particle detector according to claim 1 , wherein the first screw hole is disposed at a position that does not overlap with the second screw hole when viewed from the predetermined direction.

3. The charged particle detector according to claim 1 , wherein each of the first screw hole and the second screw hole penetrates the spacer along the predetermined direction.

4. a first recess is formed in a surface of the first plate portion facing the spacer, a second recess is formed in a surface of the second plate portion facing the spacer, the first recess is disposed at a position overlapping the second screw hole when viewed from the predetermined direction, and has a shape larger than the second screw when viewed from the predetermined direction; 4. The charged particle detector according to claim 3, wherein the second recess is positioned so as to overlap with the first screw hole when viewed from the predetermined direction, and has a shape larger than that of the first screw when viewed from the predetermined direction.

5. 3. The charged particle detector according to claim 1, wherein the first screw and the second screw extend so as to overlap each other when viewed from a direction perpendicular to the predetermined direction.

6. the first screw extends so as to overlap the microchannel plate when viewed from a direction perpendicular to the predetermined direction; 3. The charged particle detector according to claim 1, wherein the second screw extends so as to overlap the microchannel plate when viewed from a direction perpendicular to the predetermined direction.

7. the first screw extends so as to overlap substantially the entire spacer when viewed from a direction perpendicular to the predetermined direction, 3. The charged particle detector according to claim 1, wherein the second screw extends so as to overlap substantially the entire spacer when viewed from a direction perpendicular to the predetermined direction.

8. 3. The charged particle detector according to claim 1, wherein the first plate portion and the second plate portion are formed of a conductive material and the spacer is formed of an insulating material, so that the first plate portion and the second plate portion are electrically insulated from each other.

9. Further provided with a conductive mesh member, a charged particle passage opening through which the charged particles pass is formed in the second plate portion; The charged particle detector according to claim 8 , wherein the mesh member is fixed to the second plate portion so as to cover the charged particle passage opening and is electrically connected to the second plate portion.

10. an electron beam source that outputs an electron beam; an objective lens that focuses the electron beam toward a sample; 3. A scanning electron microscope comprising: the charged particle detector according to claim 1, which detects electrons generated in the sample by irradiation with the electron beam.

Images