Isolator, charged particle gun and particle beam device

Abstract

An object of the disclosure is to provide an insulator capable of shortening conditioning time and reducing withstand voltage failure when a voltage difference between electrodes is approximately several tens of kV. The insulator according to the disclosure includes an insulating material portion and a glass layer, and a boundary between the insulating material portion and an end portion of a cathode on a side facing an anode is covered with the glass layer.

Description

Technical area

[0001] The present disclosure relates to an insulator disposed between electrodes in a vacuum chamber. State of the art

[0002] An electron beam or ion beam, such as that used in an electron beam accelerator or the like provided in an electron microscope, an ion beam processing device, an irradiation system, or the like, is emitted from a slightly tapered tip of an electron or ion source by concentrating an electric field at the tapered tip in a vacuum. To realize this, a plurality of electrodes with different voltages are attached near the electron and ion source via insulators. The voltage difference between the electrodes is often several hundred V to several tens of kV. To maintain such a voltage difference stably and without discharge, a conditioning process is required when an electron or ion gun is started.

[0003] During the conditioning process, a surface arc discharge is generated by concentrating an electric field at the tip end of a tiny protrusion formed on the surface of the electrode. Accordingly, the protrusion is repeatedly removed by Joule heating. Accordingly, the number of protrusions where the electric field is concentrated is reduced, so that the voltage that can be applied between the electrodes can be increased without causing surface arc discharge.

[0004] Since the conditioning process leads to an increase in the labor and time required for the start-up process of the electron or ion gun, shortening the process time is a challenge. Furthermore, there is also the problem that the conditioning process may not complete normally, a predetermined withstand voltage may not be achieved, the product may be rejected as defective, and the yield may be reduced.

[0005] Document 1 (PTL 1) discloses a method for preventing surface flashover discharges by applying vanadium-containing glass, a metallic glass with semiconductivity, to the entire surface of an insulator. It is also described that the surface of the vanadium-containing glass has a vacuum evacuation function for gas adsorption. Cited publicationsPatent applications

[0006] PTL 1: US 2018 / 0019096 A1 Summary of the inventionTechnical problem

[0007] A specific resistance of the vanadium-containing glass described in Reference 1 is 106 to 1013 Ω cm. This specific resistance correlates with a layer thickness and corresponds approximately to several tens of μm to 1 nm. For example, to maintain a voltage difference between electrodes of several tens of kV, the layer thickness of the metallic glass must be thinner than at least 1 μm. However, since the height of the asperities of a cathode edge is in the micrometer range, an uneven shape remains as such when the metallic glass layer thickness is 1 μm or less. Then, even if the conditioning process is performed, there is a problem that the electric field is inevitably concentrated on the protrusion portion of the electrode surface, causing surface flashover discharge.

[0008] The disclosure has been made in view of the above-mentioned problems, and an object of the disclosure is to provide an insulator capable of shortening a conditioning time and reducing a withstand voltage failure when a voltage difference between electrodes is about several tens of kV. Solution to the problem

[0009] The insulator according to the disclosure includes an insulating material portion and a glass layer, and a boundary between the insulating material portion and an end portion of a cathode on a side facing an anode is covered with the glass layer. Advantageous effects of the invention

[0010] According to an insulator of the disclosure, when a voltage difference between electrodes is about several tens of kV, a conditioning time can be significantly shortened and a breakdown of withstand voltage can be reduced. Short description of the drawings [ Fig. 1] Fig. Figure 1 shows a schematic view illustrating a physical phenomenon in a conditioning process of an insulator. [ Fig. 2] Fig. 2 is a side view illustrating a structure of the insulator according to Embodiment 1. [ Fig. 3] Fig. 3 shows a model for the numerical calculation of an electric field strength distribution when a voltage of -10 kV is applied to a cathode 2 with the Fig. 2 shown structure is created. [ Fig. 4] Fig. 4 shows a calculation result using the model of Fig. 3. [ Fig. 5] Fig. Figure 5 shows an enlarged schematic view of an actual electrode surface. [ Fig. 6] Fig. 6 shows an enlarged schematic view of the insulator according to Embodiment 1. [ Fig. 7] Fig. 7 shows an enlarged schematic view of the insulator described in document 1. [ Fig. 8] Fig. 8 shows a configuration example in which an alumina insulator 1 according to Embodiment 1 is applied to a power introduction terminal of an electron gun. [ Fig. 9] Fig. 9 shows a component in which the cylindrical aluminum oxide insulator 1 and an annular metal part 10 are connected and fixed by a metallization layer 8. [ Fig. 10] Fig. 10 shows a configuration example in which the alumina insulator 1 according to Embodiment 1 is applied to a scanning electron microscope (SEM). Description of the embodiments< Conditioning process >

[0011] Fig. Figure 1 shows a schematic view illustrating a physical phenomenon in a conditioning process of an insulator. To facilitate understanding of the disclosure, an overview of the conditioning process is given with reference to Fig. 1 before describing an embodiment of the disclosure.

[0012] A discharge in a portion where a cathode 2 and an anode 5 are fixed with an alumina insulator 1 between them is called a surface flashover discharge. In a general design, a distance is ensured between the cathode and the anode to reduce an electric field strength so that a surface flashover discharge does not occur. However, on an actual cathode end surface (an end portion surface on a side where the cathode 2 faces the anode 5), unevennesses of the micrometer order are formed, and their shape also varies. In this state, when a negative voltage is gradually applied to the cathode 2, an electric field concentrates on the sharpest protrusion portion to generate field emission electrons, resulting in a surface flashover discharge (I). At this time, the sharpened end is melted by Joule heat and eliminated (II).When the cathode 2 is energized again and the voltage is gradually increased, the electric field concentrates on the tapered protrusion portion, and a surface flashover discharge (III) occurs. If this process is repeated, as the voltage applied to the cathode 2 increases, this process continues until the voltage is equal to or higher than a predetermined voltage. The above processing is called conditioning. <Ausführungsform 1>

[0013] Fig. 2 shows a side view illustrating a structure of an insulator according to Embodiment 1 of the disclosure. The insulator according to the embodiment is to be arranged between the cathode 2 and the anode 5 in a vacuum chamber and is formed of the alumina insulator 1 and a low-melting metallic glass 3. When a negative voltage is applied to the cathode 2 formed on a surface of the alumina insulator 1 (insulating material portion) placed in the vacuum, an electric field concentrates at a triple point 4, which is an edge of the cathode 2, and field emission electrons are emitted, resulting in a surface flashover discharge. In the structure of Fig. 2, the electric field concentration exerted on the triple point 4 is mitigated by covering the triple point 4 with the low-melting metallic glass 3. An example in which vanadium-containing glass is used as the low-melting metallic glass 3 is described below.

[0014] Aluminium oxide is often used as an insulating material section (insulator body, which is indicated by the reference numeral 1 in Fig. 2). The surface roughness of the aluminum oxide insulator 1 is about 20 µm. Many of the cathodes 2 are formed by plating a metallization layer of molybdenum or manganese with nickel. The low-melting metallic glass 3 extends along a depth direction in Fig. 2 (a longitudinal direction in Fig. 1).

[0015] The low-melting-point metallic glass 3 covers the triple point 4 and its vicinity. The triple point 4 is a boundary between the alumina insulator 1 and an end portion of the cathode 2 on a side facing the anode 5. Therefore, the low-melting-point metallic glass 3 covers a range from (a) an upper surface of the cathode 2 to (c) a position of a region between the cathode 2 and the anode 5 via (b) the boundary (triple point 4) between the end portion surface of the cathode 2 and the alumina insulator 1. However, the low-melting-point metallic glass 3 is arranged so as not to electrically connect the cathode 2 and the anode 5 (that is, the low-melting-point metallic glass 3 does not extend to the anode 5).

[0016] Fig. 3 shows a model for the numerical calculation of an electric field strength distribution when a voltage of -10 kV is applied to the cathode 2 with the Fig. 2 is applied. A relative permittivity of the alumina insulator 1 is 10, and a relative permittivity of the vanadium-containing glass is 15. The vanadium-containing glass (low-melting metallic glass 3) has a width of 400 µm to cover the cathode 2 and the alumina insulator (alumina insulator 1), and has a layer thickness of 20 µm.

[0017] Fig. 4 shows a calculation result using the model of Fig. 3. As in the upper part of Fig. As shown in Figure 4, when no vanadium-containing glass is present, an electric field concentrates at a cathode edge, generating a strong electric field of 1.7 × 103 MV / m. In contrast, when the vanadium-containing glass is applied, the electric field at the cathode edge is reduced to 4.8 × 102 MV / m.

[0018] The lower part of Fig. Figure 4 illustrates the calculation result considering the wettability of the vanadium-containing glass at the end section. The boundary (a peak near x = 0.2 in the lower part of Fig. 4) Between the alumina insulator 1 and the end portion of the vanadium-containing glass (low-melting metallic glass 3) on the anode 5 side, there tends to be a secondary triple point where the electric field is concentrated. However, it can be seen that the electric field is significantly smaller than the electric field at the cathode edge (x = 0) when no vanadium-containing glass is present.

[0019] An arrow on the right side in the lower part of Fig. Figure 4 shows an electric field at an edge portion (near x = 0.2) of the low-melting metallic glass 3 when the wettability of the low-melting metallic glass 3 is good. As shown in the diagram, it can be seen that when the wettability of the low-melting metallic glass is good, the electric field near the edge portion can be further reduced.

[0020] The result of Fig. 4 can be understood as follows. A surface shape of the low-melting metallic glass 3 on the side facing the anode 5 is smoother than a surface shape of the cathode 2. That is, a radius of curvature of a surface shape of the low-melting metallic glass 3 is larger than a radius of curvature of a protrusion portion formed on the surface of the cathode 2. Accordingly, the electric field is less likely to concentrate on a surface of the end portion of the low-melting metallic glass 3 on the anode 5 side, resulting in the Fig. 4. Furthermore, when the wettability of the low-melting metallic glass 3 is good, the surface shape becomes smoother, so that the electric field is less likely to be further concentrated, and a result indicated by two arrows in the lower part of Fig. 4. The wettability may be such that at least one contact angle of the low-melting metallic glass 3 with respect to the alumina insulator 1 is less than 90°.

[0021] Fig. Figure 5 shows an enlarged schematic view of an actual electrode surface. The electrode surface shown in Fig. 3 and Fig. The calculation results described in Figure 4 are a numerical estimate based on a simplified form. However, the unevenness, as shown in Fig. 5, formed on an actual cathode end face. The asperities are an uneven shape corresponding to a surface roughness of aluminum oxide and a grain size of cathode metal. Since a size of the asperities varies randomly, it is difficult to specify a local position where an electric field concentrates when a voltage is applied to the cathode 2 before discharge. Therefore, field emission electrons are emitted from a location where the electric field concentration is strongest, resulting in a surface flashover discharge. Therefore, a conditioning process is performed at the time of startup in the manufacturing of an electron gun to ensure a withstand voltage characteristic.

[0022] Fig. Fig. 6 shows an enlarged schematic view of the insulator according to Embodiment 1. In the embodiment, as shown in Fig. As shown in Figure 6, the low-melting-point metallic glass 3 is formed to have a thickness of approximately 20 μm along the periphery of the cathode 2. With such a layer thickness, the entire vicinity of the triple point can be covered without being affected by the unevenness of the surface of the cathode 2 and the unevenness of the surface of the alumina insulator 1. When heated to a softening temperature, the vanadium-containing glass, which is a metallic glass, softens in an amorphous state, and therefore, the vanadium-containing glass adsorbs by following the uneven shape and exhibiting a smooth surface. When returned to room temperature, the vanadium-containing glass solidifies in an amorphous state. Since a resistivity of the vanadium-containing glass with a layer thickness of 20 μm is approximately 106 Ω cm, the voltage of the low-melting-point metallic glass 3 is substantially the same as the voltage of the cathode 2.Accordingly, the electric field concentration at the cathode edge can be eliminated, a smooth edge of the vanadium-containing glass can be obtained, and the overall electric field concentration can be mitigated. Therefore, it is possible to achieve an effect of reducing the work and time of the conditioning process.

[0023] The thickness of the low-melting-point metallic glass 3 is preferably at least greater than a maximum height of the protrusion portion formed on the surface of the cathode 2 (a maximum peak height on the surface of the cathode 2 on the side facing the anode 5). More desirably, when a portion of the low-melting-point metallic glass 3 covering the cathode 2 is thicker than a maximum thickness of a portion of the cathode 2 covered with the low-melting-point metallic glass 3, the protrusion portion on the surface of the cathode 2 can be completely covered. When a standard layer thickness of the cathode 2 is about 20 μm, the layer thickness of the low-melting-point metallic glass 3 may also be 20 μm.

[0024] Fig. 7 shows an enlarged schematic view of the insulator described in Reference 1. The metallic glass 7 (vanadium-containing glass) in the prior art is formed to cover the entire section between the cathode 2 and the anode 5. Since a voltage of minus several tens of kV or more is applied to the cathode 2, the actual layer thickness is 1 μm or less because the resistivity must be approximately 10 10 Ω cm. Accordingly, the charge buildup of the alumina insulator 1 can be eliminated, but it is difficult to eliminate the unevenness of the alumina insulator 1 of 20 μm or more. Then, when a defect is generated in the layer of the metallic glass 7 in the prior art, there is a problem that the electric field concentrates thereon and field emission electrons are generated.Furthermore, it is difficult to reduce field emission electrons because tiny protrusions of about several µm, formed on the cathode 2 with a film thickness of about 20 µm, are exposed. According to the embodiment, such field emission electrons can also be reduced. <Ausführungsform 1: Zusammenfassung>

[0025] The insulator according to Embodiment 1 comprises the alumina insulator 1 and the low-melting metallic glass 3. The low-melting metallic glass 3 covers the boundary (triple point 4) between the alumina insulator 1 and the end portion of the cathode 2 on the side facing the anode 5. Accordingly, it is possible to prevent the concentration of the electric field on the protrusion portion formed on the end portion surface of the cathode 2 and shorten the conditioning process. <Ausführungsform 2>

[0026] Fig. 8 shows a configuration example in which the alumina insulator 1 according to Embodiment 1 is applied to a power introduction terminal of an electron gun. A pin 9 is used to supply a voltage or current from the atmosphere side into the vacuum. For vacuum sealing, the alumina insulator 1 and the pin 9 are connected and fixed by a metallization layer 8. Since the metallization layer 8 is a conductive metal, there is a risk of surface flashover discharge when multiple pins 9 are present. Therefore, a low-melting metallic glass 6 (vanadium-containing glass) of the disclosure is applied to cover the vicinity of an end portion of the metallization layer 8. Although in Fig. 8, a voltage difference of several kV exists between the pins 9, the risk of surface flashover discharge is significantly reduced by adopting such a structure. Therefore, the conditioning process time can be shortened.

[0027] Fig. Figure 9 shows a component in which the cylindrical aluminum oxide insulator 1 and a ring-shaped metal part 10 are connected and fixed by the metallization layer 8. This component can be applied to a part with a larger dimension than that shown in Fig. 8 described pin 9 can be used. <Ausführungsform 3>

[0028] Fig.10 shows a configuration example in which the alumina insulator 1 according to Embodiment 1 is applied to a scanning electron microscope (SEM). An electron source 14 is arranged on top of a jig, and a voltage is applied from a power supply 19 through a via 20. The pin 9 described in Embodiment 2 is used for the via 20, and the low-melting metallic glass 3 is applied to cover the metallization layer 8 and the alumina insulator 1. An extraction electrode 15 for extracting electrons is provided near the electron source 14. The extraction electrode 15 is fixed to a column 21 through the alumina insulator 1. Since the column 21 is grounded, the extraction electrode 15 serves as a cathode, and the column 21 serves as an anode.Therefore, the low-melting metallic glass 3 is applied to cover an edge of the extraction electrode 15 and the metallization layer for connecting and fixing the extraction electrode 15 to the alumina insulator 1. A component from the power supply 19 to the extraction electrode 15 functions as the electron gun 11.

[0029] An electron beam 22 extracted from the electron source 14 is focused by a condenser lens 12 and an objective lens 13 to irradiate a sample 18. Secondary electrons 23, which are generated when the electron beam 22 is deflected by a deflector 16 on the sample 18 to perform raster scanning, are detected by a secondary electron detector 17. Accordingly, a magnified image of the sample 18 can be obtained. <Bezüglich der Abwandlung der Offenbarung>

[0030] In the above embodiments, the insulator according to the disclosure is arranged between the cathode 2 and the anode 5. When the insulator according to the disclosure is used, the cathode 2 may have a lower voltage than that of the anode 5 and does not necessarily have to have a negative voltage.

[0031] In the above embodiments, an example in which the insulator according to the disclosure is applied to the electron gun or the scanning electron microscope has been described, and the insulator according to the disclosure can also be applied to other charged particle guns or particle beam devices.

[0032] In the above embodiments, vanadium-containing glass is given as an example of the low-melting metallic glass 3. The vanadium-containing glass is an example of a semiconductive glass or a semiconductive low-melting metallic glass and is made of a metal oxide (including vanadium, tungsten, and the like), but other chalcogenide glasses (including arsenic, antimony, bismuth, and the like) can also be used as the low-melting metallic glass 3. List of reference symbols 1 aluminum oxide insulator 2 Cathode 3 low-melting metallic glass 4 Triple Point 5 Anode 7 metallic glass 8 Metallization layer 9 pin 10 metal part 11 Electron gun 12 Condenser lens 13 Objective lens 14 Electron source 15 Extraction electrode 16 Deflector 17 Secondary electron detector 18 Sample 19 Power supply 20 Implementation 21 Pillar 22 Electron beam 23 secondary electrons QUOTES CONTAINED IN THE DESCRIPTION

[0000] This list of documents submitted by the applicant was generated automatically and is included solely for the convenience of the reader. This list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions. Cited patent literature

[0000] US 2018 / 0019096 A1

[0006]

Claims

[1] An insulator disposed between a cathode and an anode with respect to the cathode in a vacuum chamber, the insulator comprising: an insulating material portion disposed beneath both the cathode and the anode; and a glass layer arranged to cover a boundary between the insulating material portion and an end portion of the cathode on a side facing the anode, wherein the glass layer is made of a material containing at least one of semiconductive glass or semiconductive low-melting metallic glass, and an area not covered with the glass layer is arranged between the cathode and the anode. [2] The insulator according to claim 1, wherein the glass layer is arranged to cover a triple point generated at the end portion. [3] The insulator of claim 1, wherein the glass layer covers the boundary and is arranged so as not to electrically connect the anode and the cathode. [4] The insulator according to claim 1, wherein the glass layer is arranged to cover a region from a surface of the cathode not in contact with the insulating material portion to a position between the cathode and the anode in the insulating material portion across the end portion. [5] The insulator of claim 1, wherein a thickness of the glass layer is greater than a maximum tip height of the cathode. [6] The insulator according to claim 1, wherein a thickness of a part of the glass layer covering the cathode is greater than a maximum thickness of a part of the cathode covered with the glass layer. [7] The insulator according to claim 1, wherein a radius of curvature of a shape of the glass layer at the end portion is larger than a radius of curvature of a protrusion portion formed by surface roughness of the cathode at the end portion. [8] The insulator according to claim 1, wherein a thickness of the glass layer at the end portion is 20 µm or more. [9] The insulator according to claim 1, wherein a contact angle of the glass layer is less than 90°. [10] An insulator according to claim 1, wherein the glass layer is vanadium-containing glass. [11] The insulator according to claim 1, wherein the insulating material portion is made of alumina. [12] Charged particle gun, comprising: the insulator according to claim 1. [13] Particle beam device comprising: the insulator according to claim 1.

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