JPH10283978A - Electron detector - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electron detector on which a sample for observation can be placed directly. SOLUTION: An electron-to-light conversion member 12 comprising a phosphor plate 12a coated with a metallic thin film 12b is mounted in an opening 2a in a bottomed cylinder 2, and a microchannel plate MCP and an anode 10 are placed in the bottomed cylinder 2 via insulative annular spacers 4, 6, 8. When the metallic thin film 12b, the microchannel plate MCP, and the anode 10 are biased to predetermined potential and a sample OBJ is directly placed on the metallic thin film 12b and scanned by an electron beam EB from above, ultraviolet rays excited by secondary electrons and transmitted charged particles emitted from the metallic thin film 12b are released from the phosphor plate 12a, the microchannel plate MCP detects the ultraviolet rays and performs secondary electron multiplication, and a detection signal is produced in the anode 10.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electronic detector for detecting charged particles, converting the detected particles into electric signals, and outputting the electric signals.

[0002]

2. Description of the Related Art Conventionally, an electron multiplier (EMT) has been known as such an electron detector. When charged particles enter a dynode in a vacuum, the electron multiplier emits photoelectrons and secondary electrons and multiplies the secondary electrons. The secondary electrons multiplied by the dynode are collected by the anode and electricity is generated. It has the function of converting it to a signal and outputting it. It is a powerful means mainly for detecting weak charged particles. For example, a scanning electron microscope (SEM) or a transmission scanning electron microscope (ST)
EM) to obtain image information necessary for observing the shape of the sample by detecting secondary electrons and transmitted electrons emitted from the sample when scanning the sample with an electron beam. Has become an effective means.

[0003]

SUMMARY OF THE INVENTION A conventional electron multiplier is S
To obtain information for reconstructing a clear sample image by applying it to EM, STEM, etc., the first-stage dynode is placed as close to the sample as possible, and the secondary electrons and transmitted electrons emitted from the sample are efficiently used. It is desirable to detect well. However, S
It is necessary to place the sample on a sample mounting table provided in advance in EM or STEM, and to place the first-stage dynode facing the sample mounting table with a relatively large gap (interval). It was difficult to make them close enough.

In an electron multiplier (MCP-EMT) in which a microchannel plate is used as a dynode, the input end of the microchannel plate is flat, and the sample is placed directly on this input end. Although it is conceivable to adopt a technique of bringing the dynode and the dynode closest, this causes a problem that the electron multiplier itself must be frequently replaced because the input end is contaminated with the sample.

[0005] The present invention has been made in view of such problems of the prior art, and has as its object to provide an electronic detector provided with means for directly mounting a sample in advance.

[0006]

The electronic detector of the present invention comprises:
A two-layer structure of a metal thin film that transmits the incident charged particles or emits electrons according to the incident intensity of the incident charged particles, and a fluorescent plate that generates fluorescence when excited by the transmitted charged particles or the emitted electrons. And a photoelectric conversion element that is disposed in close proximity to the fluorescent plate of the electron-light conversion member and that photoelectrically converts the fluorescence.

Further, the electro-optical conversion member is configured to be detachably supported on the photoelectric conversion element.

[0008]

When charged particles enter the metal thin film of the electron-light conversion member, the incident charged particles pass through the metal thin film or emit electrons from the metal thin film. Fluorescence is emitted from the fluorescent plate by the transmitted charged particles or emitted electrons, detected by the photoelectric conversion element, and output as a detection signal. The sample can be directly mounted on the metal thin film of the electron-light conversion member. Further, the electron-light conversion member is detachable, and can be replaced with a new electron-light conversion member.

[0009]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a partially cutaway perspective view showing the structure of an electron detector according to an embodiment, and FIG. 2 is an enlarged longitudinal sectional view showing a main part cross-sectional structure of the electron detector.

1 and 2, an insulating layer ISO made of a rubber material or an insulating paint is coated on the entire inner wall of a bottomed cylindrical body 2 having a circular opening 2a at one end and made of a conductive material. In addition, the inside of the bottomed cylindrical body 2 is
Thin annular insulating spacers 4, 6, 8 having a uniform thickness within a range of about 5 to 1.0 mm are provided.
6, a micro-channel plate MCP is interposed, and between the insulating spacers 6, 8, a disk-shaped anode electrode 10 facing the output end of the micro-channel plate MCP is interposed. The electron-light converting member 12 facing the input end of the microchannel plate MCP is fixed to the opening 2a so as not to be loosened.

The electron-to-light conversion member 12 is formed of Ca ₃ (PO ₄ ) facing the input end of the micro channel plate MCP.
₂ : A metal thin film 12b having a thickness of about several hundred nm on which charged particles EB are incident on a fluorescent plate 12a formed of a Tl material.
Has a two-layer structure coated by vapor deposition or the like.

An electron-light conversion member 1 is provided on a side wall of the bottomed cylinder 2.
2 metal thin film 12b and micro channel plate MC
A voltage supply line 14 comprising a plurality of wire bundles for applying a predetermined bias voltage to each of the P and anode electrodes 10;
A signal extraction line 16 for extracting a detection signal generated at the anode electrode 10 to the outside is provided.

In the electron detector having such a structure,
As shown in FIG. 2, the metal thin film 12
b is the lowest potential, the anode electrode 10 is at the highest potential, and the predetermined external voltages V _b1 , V _b2 (V
_Operate in vacuum by applying _b1 < _Vb2 ). When the charged particles EB enter from the surface side of the metal thin film 12b in a vacuum, the charged particles EB are transmitted (passed) through the metal thin film 12b according to the incident energy of the charged particles EB, or secondary electrons are emitted from the metal thin film 12b to the fluorescent screen 12a. The ultraviolet rays having a peak at a wavelength of 326 nm are excited from the phosphor plate 12a by the emitted charged particles and secondary electrons. Then, the micro-channel plate MCP detects the ultraviolet rays and multiplies the secondary electrons, and the secondary electrons multiplied by the micro-channel plate MCP are collected by the anode electrode 10 and the current proportional to the secondary electrons is increased. The change is output as a detection signal.

Here, since the ultraviolet rays are generated in almost all directions in the fluorescent plate 12a, they are not only directly incident on the input end of the microchannel plate MCP but also are generated on the back side of the metal thin film 12b. Ultraviolet rays generated on the back side of the metal thin film 12b
Since the light is reflected by the back surface of the metal thin film 12b in contact with the microchannel plate MCP and is incident on the input end of the microchannel plate MCP, ultraviolet rays generated for the incident charged particles EB are incident on the microchannel plate MCP extremely efficiently. I have.

Further, since the fluorescent plate 12a can be made relatively thick, the mechanical strength can be maintained even when the sample OBJ such as a living cell piece is directly placed on the surface of the metal thin film 12b. As a result, the sample OBJ is scanned by the electron beam (charged particles) EB, and the metal thin film 12b or the sample OBJ is scanned.
The secondary electrons and transmitted charged particles emitted from J
is converted to ultraviolet light by the micro channel plate MC
By multiplying secondary electrons by P and outputting a detection signal from the anode electrode 10, application to a scanning electron microscope or a transmission scanning electron microscope for observing the shape or the like of the sample OBJ is possible.

In other words, the electron detector is provided with the electron-light conversion member 12 so that the function as a mounting means for directly mounting the sample OBJ and the incident charged particles EB can be obtained.
The microchannel plate MCP has a structure capable of skillfully exhibiting two functions, namely, a function as conversion means for generating ultraviolet light having sensitivity. Further, as described above, the metal thin film 12b not only effectively reflects the ultraviolet light generated by the fluorescent screen 12a to the input end side of the microchannel plate MCP, but also reflects the electron-light conversion member 12 and the input end of the microchannel plate MCP. Is very narrow, so that ultraviolet light generated by the fluorescent plate 12a can be efficiently incident on the microchannel plate MCP. Furthermore, since the metal thin film 12b has a function of covering the fluorescent plate 12a and protecting it from damage or the like, an excellent synergistic effect is exhibited between the metal thin film 12b and the fluorescent plate 12a.

Furthermore, although the space between the electron-light conversion member 12 and the input end of the microchannel plate MCP is extremely small, there is a gap between the two, so that ultraviolet light propagates in this gap and the microchannel plate Since the light enters the input end of the MCP, the incident charged particles EB can be reliably detected.

The effect will be described in more detail. The micro channel plate MCP has a plate-like structure in which a number of extremely thin glass pipes each having an inner wall as a resistor and a secondary electron emitter are bundled, and each glass pipe (channel) is formed. Has an independent secondary electron multiplying function, but portions other than the inner wall of each glass pipe (that is, glass portions) have no secondary electron multiplying function and are insensitive areas. Therefore,
As described in the section of “Problems to be solved by the present invention”,
If the sample OBJ is placed directly on the input end of the microchannel plate MCP and scanned by the electron beam EB, secondary electrons and the like emitted from the sample OBJ directly enter the input end of the microchannel plate MCP without flying. And the glass part (dead area)
Are not multiplied by secondary electrons, and as a result, the spatial resolution is limited.

However, in the electron multiplier according to the present embodiment, as shown in FIG. 2, a small gap is provided between the electron-light conversion member 12 and the input end of the microchannel plate MCP. Is scanned by the electron beam EB, the ultraviolet light emitted from the fluorescent plate 12a propagates in various directions in this gap and is incident with high probability on the inner wall of any one of the glass pipes. Is done.
Therefore, the electron detector has a structure capable of obtaining a substantially higher spatial resolution than directly mounting the sample OBJ on the input end of the microchannel plate MCP.

As described above, the electron detector has a structure in which the electron-light conversion member 12 is disposed with a small gap from the input end of the microchannel plate MCP, so that the sample OBJ is directly mounted. And effectively improves the spatial resolution.

The electron-light conversion member 12 is connected to a fluorescent plate 12a.
Although the case of forming a two-layer structure of a thin film and a metal thin film 12b has been described, the present invention is not limited to this, and the fluorescent plate 12a is bonded on a thin transparent support plate made of quartz or glass material, and The fluorescent plate 12a may have a three-layer structure in which the metal thin film 12b is coated by vapor deposition or the like. When such a transparent support plate is provided, an electron-light conversion member having higher mechanical strength can be realized, and the function for mounting the sample OBJ can be improved. However, it is desirable that the transparent support plate be made of a material that efficiently transmits ultraviolet light generated by the fluorescent plate 12a.

The fluorescent plate 12a is made of Ca ₃ (PO ₄ )
₂ : Although the case of forming with Tl was described, (CaZn)
₃ (PO ₄ ) ₂ : formed of Tl material or HfP ₂ O
₇ or LaPO ₄ : Ce material.

As shown in FIG. 2, by covering the inner wall of the bottomed cylinder 2 with an insulating layer ISO, the space between the microchannel plate MCP, the anode electrode 10 and the conductive bottomed cylinder 2 is formed. Although the structure in which the electric short circuit is prevented has been described, the present invention is not limited to such a structure. A structure may be provided in which an electrical short is prevented by providing a gap between them and further sandwiching them by insulating spacers 4, 6, and 8. In this case, the insulating layer ISO can be omitted.

Next, an application example in which the electron detector is applied to a scanning electron microscope (SEM) so that the shape and the like of a sample can be more clearly observed will be described with reference to the structural explanatory view of FIG. 3 and the timing chart of FIG. It is explained together with.

Referring to FIG. 3, this scanning electron microscope
An electron gun 20 for emitting a thin electron beam EB, a horizontal deflection coil 22 and a vertical deflection coil 24 for horizontally and vertically deflecting the electron beam EB, an XY stage 26, and an XY stage 26 are provided in the vacuum chamber 18. A directed secondary electron detector 28 is provided. The electronic detector 30 is
The electron-light conversion member 12 is attached to one end of the XY stage 26 so as to face the electron gun 20, and the sample OBJ to be observed is directly mounted on the surface of the metal thin film 12 b of the electron-light conversion member 12.

Then, the horizontal synchronizing signal HD and the vertical synchronizing signal VD are supplied from the synchronizing signal generating circuit 32 to the deflection power supply 34, and the horizontal power supply 34 supplies the horizontal synchronization signal HD and the vertical deflection coil 24 to the horizontal deflection coil 22 and the vertical deflection coil 24. Signal VD
Supplies the horizontal deflection current HI and the vertical deflection current VI synchronized with the electron beam EB, and horizontally and vertically deflects the electron beam EB emitted from the electron gun 20, thereby scanning the electron beam conversion member 12 and the sample OBJ with the electron beam EB. Let it.

As shown in the timing chart of FIG.
The electron detector 30 includes secondary electrons and transmission charged particles emitted from the metal thin film 12b by scanning of the electron beam EB,
Alternatively, ultraviolet rays are generated from the fluorescent screen 12a by secondary electrons or transmitted charged particles emitted from the metal thin film 12b by the electron beam EB transmitted through the sample OBJ, and the ultraviolet rays enter the microchannel plate MCP, Secondary electron multiplication by MCP,
The detection signal A is converted from the anode electrode 10 to a binarization circuit 36.
Output to Binarizing circuit 36, a logic "H" when the detection signal A is larger amplitude than a predetermined threshold value V _TH, small amplitude background is converted into a binary signal A _HL becomes the logic "L" when the Transfer to the removal circuit 38. On the other hand, a secondary electron detector 28 disposed obliquely above the XY stage 26 detects secondary electrons emitted to the electron-light conversion member 12 and the surface side of the sample OBJ by scanning of the electron beam EB, and detects the secondary electrons. Detection signal B
To the background removal circuit 38 directly.

The background removing circuit 38 receives a detection signal B when the binary signal _AHL is at logic "L", and switches off the input when the binary signal _AHL is at logic "H". And a video signal forming circuit (not shown) for forming a composite signal C having image information of the sample OBJ by superimposing the horizontal synchronizing signal HD and the vertical synchronizing signal VD on the detection signal B input via the CPU. . Then, by supplying the composite signal C to a monitor device 40 such as a CRT (cathode ray tube), the shape and the like of the sample OBJ are reproduced and displayed, thereby enabling real-time observation.

According to this scanning electron microscope, the background removal circuit 38 detects only image information during a period in which the sample OBJ is scanned by the electron beam EB (a period during which the binary signal _AHL is at logic "L"). Since it is extracted from the signal B and background information other than the sample OBJ is removed and supplied to the monitor device 40, the outline of the sample OBJ can be clearly reproduced and displayed.

As described above, the electron detector 30 is connected to the sample O
Since the electron-light conversion member 12 on which the BJ can be directly mounted is provided in advance, it can be applied to a scanning electron microscope for precisely photographing the shape and the like of the sample OBJ. Further, the present invention can be applied not only to a scanning electron microscope but also to a transmission scanning electron microscope.

However, this application example is merely an example, and the electronic detector 30 has versatility suitable for various other applications. That is, in addition to the same use as a conventional electron multiplier that detects and multiplies weak charged particles, the sample OBJ is directly mounted on the electron-light conversion member 12 to perform precise observation of the sample. It can be used for various uses.

In this embodiment, the microchannel plate MCP is applied to the dynode, and the anode electrode 10 is connected to the output end of the microchannel plate MCP.
Although the case where a photoelectric conversion element configured by disposing is used has been described,
The electron detector of the present invention is not limited to such a photoelectric conversion element.

For example, a photomultiplier (PMT) is provided instead of the microchannel plate MCP and the anode electrode 10 shown in FIG.
Alternatively, the photomultiplier may be made to emit light in the visible region where the photomultiplier tube has sensitivity by being formed of a material such as ZnS: Ag and Cd ₂ O ₂ S: Tb. Furthermore, instead of the micro-channel plate MCP and the anode electrode 10 shown in FIG. 1, a semiconductor light-receiving element such as a semiconductor photodiode PD or an avalanche photodiode APD is provided, the fluorescent screen 12a LiAlO _2: by forming in Fe ^3+, visible Light or near-infrared rays may be generated.

Further, the electronic light conversion member 12 may be detachably fitted to the opening 2a of the bottomed cylindrical body 2 so that a new electron conversion member can be appropriately replaced.

Further, the combination relationship between the material (composition) of the fluorescent plate 12a and the photoelectric conversion elements such as the photomultiplier tube (PMT) and the semiconductor light receiving element is described in the following. Indicates a suitable combination of fluorescence that can be detected with high sensitivity. Therefore, as long as these photoelectric conversion elements emit fluorescent light having sensitivity, the present invention is not limited to this embodiment, and other fluorescent materials can be used.

[0036]

As described above, according to the electron detector of the present invention, an electron-light conversion member on which a sample can be directly mounted is provided, so that the electron detector exhibits an excellent effect for close observation. I do. In addition, since the electron-light conversion member is detachable, there can be obtained an effect that the electron-light conversion member can be replaced with a new electron-light conversion member to always ensure the use in an optimal state.

Further, in spite of a novel structure including an electron-light conversion member on which a sample can be directly mounted, the same application as that of a conventional electron multiplier is possible.
Therefore, it can be said that the electronic detector of the present invention has general versatility in which various applications for electron detection can be performed, and enables development to various applications that were not previously considered. .

[Brief description of the drawings]

FIG. 1 is a partially cutaway perspective view showing a structure of an electron detector according to an embodiment.

FIG. 2 is an enlarged longitudinal sectional view showing a main structure of the electron detector shown in FIG.

FIG. 3 is an explanatory diagram illustrating a configuration of a scanning electron microscope to which the electron detector according to the embodiment is applied.

FIG. 4 is a timing chart representatively showing an operation of one horizontal scanning feedback of an electron beam for explaining an operation of the scanning electron microscope shown in FIG. 3;

[Explanation of symbols]

2 ... bottomed cylinder, 2a ... opening, 4,6,8 ... spacer,
10: anode electrode, 12: electron-light conversion member, 12a ...
Fluorescent plate, 12b: metal thin film, 14: voltage supply line, 16
… Signal extraction line, MCP… Micro channel plate.

Claims (9)

[Claims] 1. A metal thin film that transmits an incident charged particle or emits electrons according to the incident intensity of the incident charged particle, and a fluorescent plate that generates fluorescence when excited by the transmitted charged particle or the emitted electron. An electron detector comprising: an electron-to-light conversion member having a two-layer structure; and a photoelectric conversion element, which is disposed to face and close to the fluorescent plate of the electron-to-light conversion member and photoelectrically converts the fluorescence. 2. The electron detector according to claim 1, wherein the electron-light conversion member is detachably supported on the photoelectric conversion element. 3. The electron detector according to claim 1, wherein the photoelectric conversion element includes a microchannel plate and an anode electrode disposed on a back surface of the microchannel plate. 4. The electron detector according to claim 1, wherein the photoelectric conversion element includes a microchannel plate and an anode electrode disposed on a back surface of the microchannel plate. 5. The electron detector according to claim 1, wherein the photoelectric conversion element is a photomultiplier tube. 6. The phosphor screen is composed of (CaZn) ₃ (PO ₄ )
₂ : Tl, Ca ₃ (PO ₄ ) ₂ : Tl, HfP ₂ O ₇ , LaP
O _4: formed of any material of Ce, the photoelectric conversion element according to claim 1, characterized in that an anode electrode disposed on the back surface with a micro-channel plate
An electronic detector according to claim 1. 7. The fluorescent screen according to claim 1, wherein the fluorescent screen comprises CsI / Na, ZnS:
Ag, Gd ₂ O ₂ S: formed of any material of Tb,
The electron detector according to claim 1, wherein the photoelectric conversion element is a photomultiplier tube. 8. The electron detector according to claim 1, wherein the fluorescent plate is formed of LiAlO ₂ : Fe ³⁺ , and the photoelectric conversion element is a semiconductor light receiving element. 9. The electron detector according to claim 1, wherein the fluorescent plate is formed on a support plate made of a material transparent to the fluorescent light.