A conductive ultrathin film installed in an atmospheric pressure electron microscope is used as a secondary electron detector.

Abstract

We provide a secondary electron detector for atmospheric pressure electron microscopes. [Solution] The secondary electron detector 100 provided in an atmospheric pressure electron microscope is characterized in that secondary electrons generated when a high-energy electron beam is irradiated onto a sample are collected in a graphene ultrathin film, and when a voltage is applied between the graphene ultrathin film and the sample, ionization of the air or injected gas between the graphene ultrathin film and the sample occurs, which is greatly amplified by the avalanche effect, and the ion current is displayed as an image on a monitor through the amplifier.

Description

[Technical Field]

[0001] The present invention relates to a secondary electron detector using a conductive ultrathin film provided in an atmospheric pressure electron microscope, and more specifically, to a secondary electron detector for an atmospheric pressure electron microscope in which secondary electrons generated when an electron beam is irradiated onto a sample are collected in a graphene ultrathin film, an avalanche effect occurs in the air or gas layer due to a voltage applied between the graphene ultrathin film and the sample, an avalanche effect is generated, and a current is amplified between the graphene ultrathin film and the sample, and this current is displayed as an image on a monitor through the amplifier. [Background technology]

[0002] An atmospheric scanning electron microscope (A-SEM) is an electron microscope that observes samples under atmospheric pressure or low vacuum conditions, rather than high vacuum. Atmospheric electron microscopes have higher resolution and a deeper depth of field than optical microscopes, allowing for clearer observation of living biological samples.

[0003] An atmospheric pressure electron microscope includes a column having a high-vacuum internal space, a thin film provided at the lower end of the column to separate the internal space from the outside, and a sample stage provided below the thin film.

[0004] The mean-free path (MFP) over which electrons can move freely in the atmosphere without colliding with molecules is tens of micrometers to hundreds of micrometers. The longer the MFP (Multi-Function Picture), the less electron scattering occurs, resulting in a stronger signal, less noise, a higher signal-to-noise ratio, and the acquisition of high-quality images.

[0005] Since the length of an MFP (Multi-Functional Process) is greatly influenced by the number of molecules present in the electron pathway, the higher the vacuum level, the longer the MFP. Therefore, the inside of the microscope tube, which occupies most of the electron path, must be kept at a high vacuum, while only the area near the sample must be kept at a low vacuum or atmospheric pressure to minimize electron scattering. Therefore, high vacuum and low vacuum (or atmospheric pressure) are separated from each other by a thin film near the sample.

[0006] Thin films allow small electrons to pass through easily, but block atoms that are much larger than electrons.

[0007] Electrons generated by the electron gun pass through the internal space of the microscope tube without scattering, and are scattered by the thin film and the air surrounding the sample before irradiating the sample.

[0008] Furthermore, electrons irradiated onto a sample generate backscattered electrons (BSE), secondary electrons (SE), and X-rays, among which secondary electrons are detected by a secondary electron detector (SED). Secondary electrons (SEs) have low energy due to inelastic scattering, but because they are generated on the surface of the sample, the difference between the angle of incidence and the angle of reflection is large.

[0009] As a result, the secondary electron detector (SED) is usually located to the side of the lower end of the microscope tube.

[0010] However, with atmospheric pressure electron microscopes, the gap between the lower end of the microscope tube and the sample is very narrow, resulting in insufficient space to mount a secondary electron detector. Even if a secondary electron detector is mounted, it is difficult to effectively collect secondary electrons. [Overview of the project] [Problems that the invention aims to solve]

[0011] The present invention was proposed to solve the above-mentioned problems and aims to provide a secondary electron detector for atmospheric pressure electron microscopes in which secondary electrons generated when an electron beam is irradiated onto a sample are collected in a graphene ultrathin film, an avalanche effect occurs in the air or gas layer due to a voltage applied between the graphene ultrathin film and the sample, the current between the graphene ultrathin film and the sample is amplified, and the current is displayed as an image on a monitor through the amplifier. [Means for solving the problem]

[0012] To solve the above problems, a preferred embodiment of the present invention provides a secondary electron detector 100, 100a, 100b, 100c, 100d for an atmospheric pressure electron microscope, comprising: an electrically conductive substrate 101 provided at the lower end of a microscope tube 10, with a through-hole 102 formed in the center through which a high-energy electron beam passes; and a first thin film 110 provided on the substrate 101 to hermetically seal the through-hole 102, the first thin film 110 having a thickness of several nanometers or less and being electrically conductive, while blocking air to maintain a high vacuum inside the microscope tube 10, and allowing the high-energy electron beam to pass through and collecting low-energy secondary electrons. A voltage V is applied between the first thin film 110 and the sample S. b As a result, a positive voltage is connected to the first thin film 110 and a negative voltage is connected to the sample S. Low-energy secondary electrons generated when the electron beam irradiates the sample S are collected in the first thin film 110, and an ionic charge is generated between the first thin film 110 and the sample S by the avalanche effect, which is amplified and generates a large current flow, which can be displayed as an image of the sample S on the display unit. A second thin film 120 is attached to the front surface of the substrate 101 so as to cover the through-hole 102, and a plurality of through-holes 121 may be formed in at least the portion of the second thin film 120 corresponding to the through-hole 102. The first thin film 110 covers the second thin film 120 so as to airtightly seal the through-holes 121. The first thin film 110 is an ultrathin film made of graphene or a 2D material, and the second thin film 120 is a thin film having a thickness of 20 nm to 1 μm, which may have a thickness greater than that of the first thin film 110. The second thin film 120 supports the first thin film 110. The distance d between the upper surface of the sample S and the first thin film 110 is preferably 50 μm to 500 μm. An electrical insulating board or an electrical insulating PCB 130 is provided on the back surface of the substrate 101, and a metal pattern is formed on the front or back surface of the insulating board or the insulating PCB 130 so as to be partially electrically connected to the amplifier. An adapter 140 for fastening the substrate 101 to the lower end of the lens barrel may be attached to the back surface of the substrate 101. A groove 141 is formed on the surface of the adapter 140 facing the substrate 101 of both surfaces of the adapter 140, and a predetermined conductive adhesive 142 is filled in the groove 141 to facilitate the electrical connection between the adapter 140 and the substrate 101. The first thin film 110 may be manufactured by depositing graphene on the second thin film 120.

Advantages of the Invention

[0013] In the secondary electron detector for an atmospheric pressure electron microscope according to one aspect of the present invention, since the graphene ultrathin film (first thin film) is located directly above the sample and serves as a positive electrode, secondary electrons can be effectively collected. That is, secondary electrons generated by irradiating the sample with an electron beam are collected by the graphene ultrathin film (first thin film), and an avalanche effect occurs due to the voltage acting between the graphene thin film and the sample, resulting in a large current flowing between the graphene thin film and the sample. The current can be more clearly displayed as an image on a monitor through an amplifier.

Brief Description of the Drawings

[0014] [Figure 1] It is a diagram showing the main configuration of an atmospheric pressure electron microscope provided with a secondary electron detector according to the first embodiment of the present invention. [Figure 2]It is a cross-sectional view showing the configuration of the secondary electron detector of FIG. 1. [Figure 3] It is a cross-sectional view showing the secondary electron detector according to the second embodiment of the present invention. [Figure 4] It is a cross-sectional view showing the secondary electron detector according to the third embodiment of the present invention. [Figure 5] It is a cross-sectional view showing the secondary electron detector according to the fourth embodiment of the present invention. [Figure 6] It is a plan view showing the secondary electron detector of FIG. 5. [Figure 7] It is a front view showing the secondary electron detector of FIG. 5. [Figure 8] It is a cross-sectional view showing the secondary electron detector according to the fifth embodiment of the present invention.

Embodiments for Carrying Out the Invention

[0015] Hereinafter, the present invention will be described in detail with reference to the accompanying drawings. Prior to this, the terms and words used in this specification and the claims are not to be construed as being limited to their general and dictionary meanings, but rather are to be construed in accordance with the meaning and concept corresponding to the technical idea of the present invention in accordance with the principle that the inventor himself can appropriately define the concept of the terms in order to explain the invention in the best way. Therefore, it should be understood that the embodiments described in this specification and the configurations shown in the drawings are merely the most preferred embodiments of the present invention and do not represent all of the technical ideas of the present invention, and thus there may be various equivalents and modifications that can replace them at the time of this application. In the drawings, the same reference numerals indicate the same or substantially the same components.

[0016] [First Embodiment] FIG. 1 is a diagram showing the main configuration of an atmospheric pressure electron microscope provided with a secondary electron detector according to the first embodiment of the present invention, and FIG. 2 is a cross-sectional view showing the secondary electron detector of FIG. 1.

[0017] In Figure 1, the dotted lines indicate the paths through which various electrical control signals, data, and images are transmitted, while the dashed lines indicate the paths through which high-energy electrons (electron beams) generated by the electron gun travel to the sample. Furthermore, in the diagrams, the distance between the sample and the graphene ultrathin film, as well as the width and thickness of the film, are exaggerated compared to reality to aid understanding.

[0018] As shown in the diagram, the atmospheric pressure electron microscope may include a microscope tube 10, a secondary electron detector 100 including a conductive ultrathin film, a sample stage 60, a central processing unit, and a display unit.

[0019] The lens barrel 10 has a high-vacuum space 11 inside. Inside the lens barrel 10, an electron optics system 30 including an electron gun 20 for generating electrons, a focusing lens, an objective lens, and a deflector, and a BSD (Back Scattered Electron Detector) 40 may be provided. Since the configuration of the electron gun 20 is publicly known, its explanation will be omitted.

[0020] The electron optical system 30 can change the electron movement path by control signals transmitted from the control unit of the central processing unit (CPU), and preferably these control signals can be linked to the movement of the sample stage 60. For example, a deflector (or scanner) inside the electron optical system 30 can adjust the path of the electron beam, allowing electrons to pass through to a specific point in the graphene ultrathin film 120 (first thin film).

[0021] The BSD40 may be located below the electron optical system 30. The BSD40 senses backscattered electrons and transmits the signal to a central processing unit, where the calculation unit processes the transmitted signal, generates an image of the sample, and outputs it to the display unit.

[0022] The secondary electron detector 100 consists of a substrate 101 provided at the lower end of the microscope tube 10, a first thin film 110 and a second thin film 120 provided on the substrate 101, and a voltage V applied between the first thin film 110 and the sample S. b Includes. In the drawing, the voltage V b The positive electrode is connected to the substrate 101, but it may also be connected to the first thin film 110. Furthermore, in the diagram, the voltage V b The negative electrode is connected to sample S, but it may be grounded.

[0023] The substrate 101 is manufactured from an electrically conductive material. The electrically conductive material may, but is not limited to, a wafer made from silicon (Si). A through-hole 102 is formed in the center of the substrate 101, and an electrical insulating plate 103 may be attached to the periphery of the substrate 101. The through-hole 102 is a hole that penetrates the substrate 101 and can have various shapes such as square or circular. Furthermore, the electrical insulating plate 103 is a circular ring attached to the back surface of the substrate 101, which blocks the current from the substrate 101 from flowing to the lens barrel 10.

[0024] The first thin film 110 and the second thin film 120 are attached or glued so as to cover the front surface of the substrate 101 and hermetically seal the through-hole 102. The drawing shows that the thin film consists of a first thin film 110 and a second thin film 120, but it may also consist of only the first thin film 110.

[0025] The second thin film 120 includes a grid 122 and through holes 121 formed at least in the portion corresponding to the through portion 102. The second thin film 120 is provided on the front surface of the substrate 101 so as to cover the through portion 102 and its surroundings, but it is preferable that a part of the front surface of the substrate 101, such as the periphery of the front surface, is not covered. This is to electrically connect the first thin film 110 to the conductive substrate 101 by ensuring that at least a portion of the first thin film 110 is in direct contact with the substrate 101.

[0026] The through-holes 121 are holes formed to penetrate the second thin film 120, and the grid 122 is the part between the through-holes 121, playing a role in supporting the first thin film 110 (acting as a kind of frame). The through-holes 121 are holes through which electrons pass, but at the location of the lattice 122, electrons can hardly pass through and simply serve to support the first thin film 110. Similar morphologies of through-holes 121 can be repeatedly formed and patterned. The through-holes 121 can be patterned using photolithography and reactive ion etching.

[0027] Preferably, the second thin film 120 is SiN x A thick thin film manufactured from (for example, Si3N4) having a thickness of 20 nm to 1 μm, which is thicker than the first thin film 110 (ultrathin film).

[0028] The second thin film 120 (thick thin film) may have an area of ​​3 mm in width and 3 mm in height, and can be formed on the substrate 101 by vapor deposition.

[0029] The first thin film 110 is provided on the substrate 101 and the second thin film 120 so as to hermetically seal the through hole 121. The first thin film 110 blocks air so as to maintain a high vacuum inside the lens barrel 10, but allows the high-energy electron beam (electrons) to pass through. Furthermore, the first thin film 110 can collect low-energy secondary electrons.

[0030] The first thin film 110 is an ultrathin film thinner than the second thin film 120 and can be manufactured from graphene or a two-dimensional material (2D material) with high electron transmittance. However, a thickness of 1 nm to 10 nm is preferred, usually in integer multiples of a single layer of graphene or other 2D material, taking into consideration resolution and signal strength. If the thickness range is less than 1 nm, the first thin film 110 is easily damaged, and if the thickness range exceeds 10 nm, there is a problem in that the image is not clear.

[0031] Conventional atmospheric pressure electron microscopes used Si3N4 thin films without through-pores 121, but it was difficult to manufacture Si3N4 thin films that were thin and uniform to a few nanometers. Therefore, conventional atmospheric pressure electron microscopes had no choice but to use thin films thicker than 20 nm due to their intensity, which limited the resolution and clarity of the images.

[0032] Graphene has a single layer thickness of 0.2 nm, and can be uniformly manufactured to a thickness of several nanometers by stacking multiple layers. Graphene has traditionally been used to encase samples when observing them in a vacuum, but recent research has shown that thin films made from graphene provide an electron transparent window with only a 2% reduction in contrast. Therefore, by forming (depositing) a graphene ultrathin film 110 (first thin film) on a second thin film 120 (Si3N4 thin film) with through-holes 121 and using it as an electron transmission window for an atmospheric pressure electron microscope, the signal-to-noise ratio is improved by five times compared to using a Si3N4 thin film, thereby enabling high contrast in backscattering, transmission electron microscopy, and surface imaging modes of general electron microscopes (SEM). Furthermore, the thin graphene ultrathin film (first thin film 110) has good electron permeability, resulting in significantly reduced degradation and contamination by electron beams compared to the Si3N4 thin film, and also exhibiting superior mechanical durability.

[0033] On the other hand, a secondary electron detector 100 according to one aspect of the present invention is characterized in that the first thin film 110 (graphene ultrathin film) is used not only to separate the high vacuum inside the microscope tube from the external atmospheric space, but also to collect secondary electrons. That is, since the graphene ultra-thin film 110 of the present invention has excellent electrical conductivity, the graphene ultra-thin film 110 is used as an electrode. This will be described in detail below.

[0034] The electron beam generated by the electron gun 20 irradiates the sample S to generate secondary electrons. At this time, a predetermined voltage V b acts between the first thin film 110 and the sample S. If a positive voltage is connected to the first thin film 110 and a negative voltage is connected to the sample S, the air or the injected gas (for example, He) between the sample S and the first thin film 110 is ionized by the avalanche effect, and the ionization is accelerated by the chain action, and a large current I SE flows between the first thin film 110 and the sample S. This current I SE is amplified by a current amplifier and can be clearly displayed as an image of the sample S on a display unit (such as a monitor).

[0035] In FIG. 2, V out represents the voltage amplified by the current amplifier. V out can be calculated by the following formula 1.

[0036] [Formula 1] V out =R f ×I SE Also, if the voltage V b acts at a distance d, an electric field E d as shown in the following formula 2 is generated between the first thin film 110 and the sample S.

[0037] [Formula 2] E d =V b / d The voltage V b can be several tens of volts to several hundreds of volts, and the distance d between the upper surface of the sample S and the first thin film 110 can be 50 μm to 500 μm. Furthermore, an electrical insulating plate 61 made of a highly insulating material may be provided between the sample S and the sample stage 60 to prevent leakage current. The electrical insulating board 61 is preferably cleaned periodically to minimize leakage current.

[0038] [Second to Fifth Embodiments] Figure 3 is a cross-sectional view showing a secondary electron detector according to a second embodiment of the present invention. The secondary electron detector 100a has an insulating PCB 130 on the back (top) surface of the substrate 101, and a copper pattern (Cu pattern) 132 is formed only on the bottom surface of the insulating PCB 130. The copper pattern on the bottom surface of the PCB 130 and the back (top) surface of the silicon substrate 101 are electrically connected by a direct conductive epoxy or indium thin film, and the copper pattern 132 is electrically connected to the current amplifier. The insulating PCB 130 is made of a material with high insulating properties in order to prevent leakage current between the substrate 101 and the lens barrel 10.

[0039] Figure 4 is a cross-sectional view showing a secondary electron detector according to a third embodiment of the present invention. The secondary electron detector 100b has an insulating PCB 130 on the back surface of the substrate 101, and current I is transmitted through via holes 131 that penetrate the insulating PCB 130. SE The current flows into the current amplifier.

[0040] Copper patterns 132 are formed on both sides of the insulating PCB 130, and the top and bottom surfaces are electrically connected through via holes 131. Therefore, current I SE The current passes sequentially through the first thin film 110, the substrate 101, the copper pattern 132, the copper in the via hole 131, and the copper pattern 132 before flowing to the current amplifier. This method has the advantage of facilitating the connection of wires between a secondary electron detector and a current amplifier, which are located very close to the sample. In other words, in the secondary electron detector 100a shown in Figure 3, the wire connected to the copper pattern 132 is located very close to the sample S (not shown in Figure 3), and there is a risk of interference with the sample S. The secondary electron detector 100b shown in Figure 4 solves this problem.

[0041] On the other hand, although not shown in Figure 4, an electrical insulating plate (reference numeral 103 in Figure 2) or insulating epoxy for fixing may be provided on the copper pattern 132 of the insulating PCB 130. The electrical insulating board 103 or insulating epoxy is subjected to current I SE This blocks the flow of current into the telescope tube 10 or blocks the leakage current.

[0042] Figure 5 is a cross-sectional view showing a secondary electron detector according to the fourth embodiment of the present invention, Figure 6 is a plan view of Figure 5, and Figure 7 is a front view of Figure 5.

[0043] The secondary electron detector 100c differs in that it has through-silicon vias (TSVs) 104 formed through the substrate 101, the vias 104 are filled with copper, and a copper pattern 132 is formed at the upper end of the vias 104. The copper pattern 132 is electrically connected to the copper of the via hole 104. Therefore, current I SE The material flows sequentially through the first thin film 110, the copper of the via hole 104, and the copper pattern 132. As shown in Figure 4, the secondary electron detector 100b has current I SE Rather than when current I flows through the high-resistance silicon substrate 101, the secondary electron detector 100c receives current I through the low-resistance Cu via. SE This has the advantage of minimizing noise or leakage current by allowing the current to flow freely.

[0044] Figure 8 is a cross-sectional view showing a secondary electron detector according to a fifth embodiment of the present invention. The secondary electron detector 100d has a ring-shaped adapter 140 attached to the back surface (top surface) of the substrate 101, and a groove 141 is formed on the front surface of the adapter 140 (the surface of the adapter facing the substrate), and adhesive 142 is filled into the groove 141 to maintain airtightness. The groove 141 may be formed in a ring shape on the front surface (bottom surface) of the adapter 140.

[0045] The adapter 140 is a device that makes the circuit board 101 detachable from the telescope tube 10 and makes the inside of the telescope tube airtight. Its configuration is well known, so a detailed explanation is omitted. The adapter 140 may be composed of an insulator.

[0046] When indium is used as the adhesive 142, a ring-shaped copper pattern 132 is formed locally on the insulator on the front (bottom) surface of the adapter 140, thereby maintaining airtightness and preventing short circuits between the secondary electron detector and the microscope column. In this case, current I SE The material flows sequentially through the first thin film 110, the copper of the via hole 104, and the copper pattern 132.

[0047] On the other hand, if insulating epoxy is used instead of indium, an insulating plate and a copper pattern 132 on the insulating plate are not required for insulation. [Explanation of symbols]

[0048] 1: Atmospheric pressure space (or low vacuum space) 10: Telescope tube 11: Internal space (high vacuum space) 20: Electron gun 30: Electron optics (including scanners) 40: BSD 60: Sample Stage 61: Electrical insulating board 100, 100a, 100b, 100c, 100d: Secondary electron detectors 101: Circuit board 102: Penetration 103: Electrical insulating board 104: Beer Hall 105: Hall 110: First thin film (graphene ultrathin film) 120: Second thin film (Si3N4 thin film) 121:Through hole 122: Lattice 130: Insulated PCB 131: Beer Hall 132: Copper pattern 140: Adapter 141: Groove 142: Adhesive S: Sample

Claims

1. A secondary electron detector for an atmospheric pressure electron microscope, for detecting secondary electrons generated in a sample S of the atmospheric pressure electron microscope, A substrate 101 is provided at the lower end of the microscope tube 10 of the atmospheric pressure electron microscope, with a through-hole 102 formed in the center through which a high-energy electron beam passes, A second thin film 120 is attached to the front surface of the substrate 101 so as to cover the through-hole 102, and has a plurality of through-holes 121 formed therein. The first thin film 110 is provided in the second thin film 120 to hermetically seal the through hole 121, blocking air so as to maintain a high vacuum inside the lens barrel 10, while allowing a high-energy electron beam to pass through and collecting low-energy secondary electrons, and is electrically conductive and thinner than the second thin film 120. A voltage V is applied between the first thin film 110 and the sample S. ｂ This is applied, and a positive voltage is connected to the first thin film 110. Secondary electron detector of an atmospheric pressure electron microscope, wherein secondary electrons generated when the electron beam is irradiated onto a sample S are collected on a first thin film 110, and an ionic charge is generated between the first thin film 110 and the sample S by the avalanche effect, which is amplified to generate a large current flow, and the current is displayed on the display unit as an image of the sample S.

2. The first thin film 110 is an ultrathin film made from graphene or a 2D material, and has a thickness of 1 nm to 10 nm. The secondary electron detector of the atmospheric pressure electron microscope according to claim 1, wherein the second thin film 120 is a thin film having a thickness of 20 nm to 1 μm and supports the first thin film 110.

3. The secondary electron detector of the atmospheric pressure electron microscope according to claim 1, wherein the distance d between the upper surface of the sample S and the first thin film 110 is 50 μm to 500 μm.

4. A secondary electron detector for an atmospheric pressure electron microscope according to any one of claims 1 to 3, wherein an electrical insulating board or an electrical insulating PCB 130 is provided on the back surface of the substrate 101, and a partially metal pattern is formed on the front or back surface of the electrical insulating board or electrical insulating PCB 130 so as to be electrically connected to an amplifier.

5. An adapter 140 for fastening the circuit board 101 to the lower end of the lens barrel is attached to the back surface of the circuit board 101. A secondary electron detector for an atmospheric pressure electron microscope according to any one of claims 1 to 3, wherein a groove 141 is formed on one of the two sides of the adapter 140 that faces the substrate 101, and a predetermined adhesive 142 is filled into the groove 141.

6. The secondary electron detector of an atmospheric pressure electron microscope according to claim 1, wherein the first thin film 110 is manufactured by depositing graphene onto the second thin film 120.

7. An atmospheric pressure electron microscope comprising a secondary electron detector according to any one of claims 1 to 3.

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